This is python.info, produced by makeinfo version 6.5 from python.texi.

     Python 3.9.10, January 14, 2022

     unknown

     Copyright © 2001-2022, Python Software Foundation

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Python
******

     Python 3.9.10, January 14, 2022

     unknown

     Copyright © 2001-2022, Python Software Foundation

* Menu:

* What’s New in Python::
* The Python Tutorial::
* Python Setup and Usage::
* The Python Language Reference::
* The Python Standard Library::
* Extending and Embedding the Python Interpreter::
* Python/C API Reference Manual::
* Distributing Python Modules::
* Installing Python Modules::
* Python HOWTOs::
* Python Frequently Asked Questions::
* Glossary::
* About these documents::
* Dealing with Bugs::
* Copyright::
* History and License::
* Distributing Python Modules (Legacy version): Distributing Python Modules Legacy version.
* Installing Python Modules (Legacy version): Installing Python Modules Legacy version.
* Python Module Index::
* Index::

 — The Detailed Node Listing —

What’s New in Python

* What’s New In Python 3.9: What’s New In Python 3 9.
* What’s New In Python 3.8: What’s New In Python 3 8.
* What’s New In Python 3.7: What’s New In Python 3 7.
* What’s New In Python 3.6: What’s New In Python 3 6.
* What’s New In Python 3.5: What’s New In Python 3 5.
* What’s New In Python 3.4: What’s New In Python 3 4.
* What’s New In Python 3.3: What’s New In Python 3 3.
* What’s New In Python 3.2: What’s New In Python 3 2.
* What’s New In Python 3.1: What’s New In Python 3 1.
* What’s New In Python 3.0: What’s New In Python 3 0.
* What’s New in Python 2.7: What’s New in Python 2 7.
* What’s New in Python 2.6: What’s New in Python 2 6.
* What’s New in Python 2.5: What’s New in Python 2 5.
* What’s New in Python 2.4: What’s New in Python 2 4.
* What’s New in Python 2.3: What’s New in Python 2 3.
* What’s New in Python 2.2: What’s New in Python 2 2.
* What’s New in Python 2.1: What’s New in Python 2 1.
* What’s New in Python 2.0: What’s New in Python 2 0.
* Changelog::

What’s New In Python 3.9

* Summary – Release highlights::
* You should check for DeprecationWarning in your code::
* New Features::
* Other Language Changes::
* New Modules::
* Improved Modules::
* Optimizations::
* Deprecated::
* Removed::
* Porting to Python 3.9: Porting to Python 3 9.
* Build Changes::
* C API Changes::
* Notable changes in Python 3.9.1: Notable changes in Python 3 9 1.
* Notable changes in Python 3.9.2: Notable changes in Python 3 9 2.
* Notable changes in Python 3.9.3: Notable changes in Python 3 9 3.
* Notable changes in Python 3.9.5: Notable changes in Python 3 9 5.

New Features

* Dictionary Merge & Update Operators::
* New String Methods to Remove Prefixes and Suffixes::
* Type Hinting Generics in Standard Collections::
* New Parser::

New Modules

* zoneinfo::
* graphlib::

Improved Modules

* ast::
* asyncio::
* compileall::
* concurrent.futures: concurrent futures.
* curses::
* datetime::
* distutils::
* fcntl::
* ftplib::
* gc::
* hashlib::
* http::
* IDLE and idlelib::
* imaplib::
* importlib::
* inspect::
* ipaddress::
* math::
* multiprocessing::
* nntplib::
* os::
* pathlib::
* pdb::
* poplib::
* pprint::
* pydoc::
* random::
* signal::
* smtplib::
* socket::
* time::
* sys::
* tracemalloc::
* typing::
* unicodedata::
* venv::
* xml::

Porting to Python 3.9

* Changes in the Python API::
* Changes in the C API::
* CPython bytecode changes::

C API Changes

* New Features: New Features<2>.
* Porting to Python 3.9: Porting to Python 3 9<2>.
* Removed: Removed<2>.

Notable changes in Python 3.9.1

* typing: typing<2>.
* macOS 11.0 (Big Sur) and Apple Silicon Mac support: macOS 11 0 Big Sur and Apple Silicon Mac support.

Notable changes in Python 3.9.2

* collections.abc: collections abc.
* urllib.parse: urllib parse.

Notable changes in Python 3.9.5

* urllib.parse: urllib parse<2>.

What’s New In Python 3.8

* Summary – Release highlights: Summary – Release highlights<2>.
* New Features: New Features<3>.
* Other Language Changes: Other Language Changes<2>.
* New Modules: New Modules<2>.
* Improved Modules: Improved Modules<2>.
* Optimizations: Optimizations<2>.
* Build and C API Changes::
* Deprecated: Deprecated<2>.
* API and Feature Removals::
* Porting to Python 3.8: Porting to Python 3 8.
* Notable changes in Python 3.8.1: Notable changes in Python 3 8 1.
* Notable changes in Python 3.8.8: Notable changes in Python 3 8 8.
* Notable changes in Python 3.8.12: Notable changes in Python 3 8 12.

New Features

* Assignment expressions::
* Positional-only parameters::
* Parallel filesystem cache for compiled bytecode files::
* Debug build uses the same ABI as release build::
* f-strings support = for self-documenting expressions and debugging::
* PEP 578; Python Runtime Audit Hooks: PEP 578 Python Runtime Audit Hooks.
* PEP 587; Python Initialization Configuration: PEP 587 Python Initialization Configuration.
* PEP 590; Vectorcall; a fast calling protocol for CPython: PEP 590 Vectorcall a fast calling protocol for CPython.
* Pickle protocol 5 with out-of-band data buffers::

Improved Modules

* ast: ast<2>.
* asyncio: asyncio<2>.
* builtins::
* collections::
* cProfile::
* csv::
* curses: curses<2>.
* ctypes::
* datetime: datetime<2>.
* functools::
* gc: gc<2>.
* gettext::
* gzip::
* IDLE and idlelib: IDLE and idlelib<2>.
* inspect: inspect<2>.
* io::
* itertools::
* json.tool: json tool.
* logging::
* math: math<2>.
* mmap::
* multiprocessing: multiprocessing<2>.
* os: os<2>.
* os.path: os path.
* pathlib: pathlib<2>.
* pickle::
* plistlib::
* pprint: pprint<2>.
* py_compile::
* shlex::
* shutil::
* socket: socket<2>.
* ssl::
* statistics::
* sys: sys<2>.
* tarfile::
* threading::
* tokenize::
* tkinter::
* time: time<2>.
* typing: typing<3>.
* unicodedata: unicodedata<2>.
* unittest::
* venv: venv<2>.
* weakref::
* xml: xml<2>.
* xmlrpc::

Porting to Python 3.8

* Changes in Python behavior::
* Changes in the Python API: Changes in the Python API<2>.
* Changes in the C API: Changes in the C API<2>.
* CPython bytecode changes: CPython bytecode changes<2>.
* Demos and Tools::

What’s New In Python 3.7

* Summary – Release Highlights::
* New Features: New Features<4>.
* Other Language Changes: Other Language Changes<3>.
* New Modules: New Modules<3>.
* Improved Modules: Improved Modules<3>.
* C API Changes: C API Changes<2>.
* Build Changes: Build Changes<2>.
* Optimizations: Optimizations<3>.
* Other CPython Implementation Changes::
* Deprecated Python Behavior::
* Deprecated Python modules, functions and methods: Deprecated Python modules functions and methods.
* Deprecated functions and types of the C API::
* Platform Support Removals::
* API and Feature Removals: API and Feature Removals<2>.
* Module Removals::
* Windows-only Changes::
* Porting to Python 3.7: Porting to Python 3 7.
* Notable changes in Python 3.7.1: Notable changes in Python 3 7 1.
* Notable changes in Python 3.7.2: Notable changes in Python 3 7 2.
* Notable changes in Python 3.7.6: Notable changes in Python 3 7 6.
* Notable changes in Python 3.7.10: Notable changes in Python 3 7 10.

New Features

* PEP 563; Postponed Evaluation of Annotations: PEP 563 Postponed Evaluation of Annotations.
* PEP 538; Legacy C Locale Coercion: PEP 538 Legacy C Locale Coercion.
* PEP 540; Forced UTF-8 Runtime Mode: PEP 540 Forced UTF-8 Runtime Mode.
* PEP 553; Built-in breakpoint(): PEP 553 Built-in breakpoint.
* PEP 539; New C API for Thread-Local Storage: PEP 539 New C API for Thread-Local Storage.
* PEP 562; Customization of Access to Module Attributes: PEP 562 Customization of Access to Module Attributes.
* PEP 564; New Time Functions With Nanosecond Resolution: PEP 564 New Time Functions With Nanosecond Resolution.
* PEP 565; Show DeprecationWarning in __main__: PEP 565 Show DeprecationWarning in __main__.
* PEP 560; Core Support for typing module and Generic Types: PEP 560 Core Support for typing module and Generic Types.
* PEP 552; Hash-based .pyc Files: PEP 552 Hash-based pyc Files.
* PEP 545; Python Documentation Translations: PEP 545 Python Documentation Translations.
* Python Development Mode (-X dev): Python Development Mode -X dev.

New Modules

* contextvars::
* dataclasses::
* importlib.resources: importlib resources.

Improved Modules

* argparse::
* asyncio: asyncio<3>.
* binascii::
* calendar::
* collections: collections<2>.
* compileall: compileall<2>.
* concurrent.futures: concurrent futures<2>.
* contextlib::
* cProfile: cProfile<2>.
* crypt::
* datetime: datetime<3>.
* dbm::
* decimal::
* dis::
* distutils: distutils<2>.
* enum::
* functools: functools<2>.
* gc: gc<3>.
* hmac::
* http.client: http client.
* http.server: http server.
* idlelib and IDLE::
* importlib: importlib<2>.
* io: io<2>.
* ipaddress: ipaddress<2>.
* itertools: itertools<2>.
* locale::
* logging: logging<2>.
* math: math<3>.
* mimetypes::
* msilib::
* multiprocessing: multiprocessing<3>.
* os: os<3>.
* pathlib: pathlib<3>.
* pdb: pdb<2>.
* py_compile: py_compile<2>.
* pydoc: pydoc<2>.
* queue::
* re::
* signal: signal<2>.
* socket: socket<3>.
* socketserver::
* sqlite3::
* ssl: ssl<2>.
* string::
* subprocess::
* sys: sys<3>.
* time: time<3>.
* tkinter: tkinter<2>.
* tracemalloc: tracemalloc<2>.
* types::
* unicodedata: unicodedata<3>.
* unittest: unittest<2>.
* unittest.mock: unittest mock.
* urllib.parse: urllib parse<3>.
* uu::
* uuid::
* warnings::
* xml.etree: xml etree.
* xmlrpc.server: xmlrpc server.
* zipapp::
* zipfile::

Deprecated Python modules, functions and methods

* aifc::
* asyncio: asyncio<4>.
* collections: collections<3>.
* dbm: dbm<2>.
* enum: enum<2>.
* gettext: gettext<2>.
* importlib: importlib<3>.
* locale: locale<2>.
* macpath::
* threading: threading<2>.
* socket: socket<4>.
* ssl: ssl<3>.
* sunau::
* sys: sys<4>.
* wave::

Porting to Python 3.7

* Changes in Python Behavior::
* Changes in the Python API: Changes in the Python API<3>.
* Changes in the C API: Changes in the C API<3>.
* CPython bytecode changes: CPython bytecode changes<3>.
* Windows-only Changes: Windows-only Changes<2>.
* Other CPython implementation changes::

What’s New In Python 3.6

* Summary – Release highlights: Summary – Release highlights<3>.
* New Features: New Features<5>.
* Other Language Changes: Other Language Changes<4>.
* New Modules: New Modules<4>.
* Improved Modules: Improved Modules<4>.
* Optimizations: Optimizations<4>.
* Build and C API Changes: Build and C API Changes<2>.
* Other Improvements::
* Deprecated: Deprecated<3>.
* Removed: Removed<3>.
* Porting to Python 3.6: Porting to Python 3 6.
* Notable changes in Python 3.6.2: Notable changes in Python 3 6 2.
* Notable changes in Python 3.6.4: Notable changes in Python 3 6 4.
* Notable changes in Python 3.6.5: Notable changes in Python 3 6 5.
* Notable changes in Python 3.6.7: Notable changes in Python 3 6 7.
* Notable changes in Python 3.6.10: Notable changes in Python 3 6 10.
* Notable changes in Python 3.6.13: Notable changes in Python 3 6 13.

New Features

* PEP 498; Formatted string literals: PEP 498 Formatted string literals.
* PEP 526; Syntax for variable annotations: PEP 526 Syntax for variable annotations.
* PEP 515; Underscores in Numeric Literals: PEP 515 Underscores in Numeric Literals.
* PEP 525; Asynchronous Generators: PEP 525 Asynchronous Generators.
* PEP 530; Asynchronous Comprehensions: PEP 530 Asynchronous Comprehensions.
* PEP 487; Simpler customization of class creation: PEP 487 Simpler customization of class creation.
* PEP 487; Descriptor Protocol Enhancements: PEP 487 Descriptor Protocol Enhancements.
* PEP 519; Adding a file system path protocol: PEP 519 Adding a file system path protocol.
* PEP 495; Local Time Disambiguation: PEP 495 Local Time Disambiguation.
* PEP 529; Change Windows filesystem encoding to UTF-8: PEP 529 Change Windows filesystem encoding to UTF-8.
* PEP 528; Change Windows console encoding to UTF-8: PEP 528 Change Windows console encoding to UTF-8.
* PEP 520; Preserving Class Attribute Definition Order: PEP 520 Preserving Class Attribute Definition Order.
* PEP 468; Preserving Keyword Argument Order: PEP 468 Preserving Keyword Argument Order.
* New dict implementation::
* PEP 523; Adding a frame evaluation API to CPython: PEP 523 Adding a frame evaluation API to CPython.
* PYTHONMALLOC environment variable::
* DTrace and SystemTap probing support::

New Modules

* secrets::

Improved Modules

* array::
* ast: ast<3>.
* asyncio: asyncio<5>.
* binascii: binascii<2>.
* cmath::
* collections: collections<4>.
* concurrent.futures: concurrent futures<3>.
* contextlib: contextlib<2>.
* datetime: datetime<4>.
* decimal: decimal<2>.
* distutils: distutils<3>.
* email::
* encodings::
* enum: enum<3>.
* faulthandler::
* fileinput::
* hashlib: hashlib<2>.
* http.client: http client<2>.
* idlelib and IDLE: idlelib and IDLE<2>.
* importlib: importlib<4>.
* inspect: inspect<3>.
* json::
* logging: logging<3>.
* math: math<4>.
* multiprocessing: multiprocessing<4>.
* os: os<4>.
* pathlib: pathlib<4>.
* pdb: pdb<3>.
* pickle: pickle<2>.
* pickletools::
* pydoc: pydoc<3>.
* random: random<2>.
* re: re<2>.
* readline::
* rlcompleter::
* shlex: shlex<2>.
* site::
* sqlite3: sqlite3<2>.
* socket: socket<5>.
* socketserver: socketserver<2>.
* ssl: ssl<4>.
* statistics: statistics<2>.
* struct::
* subprocess: subprocess<2>.
* sys: sys<5>.
* telnetlib::
* time: time<4>.
* timeit::
* tkinter: tkinter<3>.
* traceback::
* tracemalloc: tracemalloc<3>.
* typing: typing<4>.
* unicodedata: unicodedata<4>.
* unittest.mock: unittest mock<2>.
* urllib.request: urllib request.
* urllib.robotparser: urllib robotparser.
* venv: venv<3>.
* warnings: warnings<2>.
* winreg::
* winsound::
* xmlrpc.client: xmlrpc client.
* zipfile: zipfile<2>.
* zlib::

Deprecated

* New Keywords::
* Deprecated Python behavior::
* Deprecated Python modules, functions and methods: Deprecated Python modules functions and methods<2>.
* Deprecated functions and types of the C API: Deprecated functions and types of the C API<2>.
* Deprecated Build Options::

Deprecated Python modules, functions and methods

* asynchat::
* asyncore::
* dbm: dbm<3>.
* distutils: distutils<4>.
* grp::
* importlib: importlib<5>.
* os: os<5>.
* re: re<3>.
* ssl: ssl<5>.
* tkinter: tkinter<4>.
* venv: venv<4>.

Removed

* API and Feature Removals: API and Feature Removals<3>.

Porting to Python 3.6

* Changes in ‘python’ Command Behavior::
* Changes in the Python API: Changes in the Python API<4>.
* Changes in the C API: Changes in the C API<4>.
* CPython bytecode changes: CPython bytecode changes<4>.

Notable changes in Python 3.6.2

* New make regen-all build target::
* Removal of make touch build target::

What’s New In Python 3.5

* Summary – Release highlights: Summary – Release highlights<4>.
* New Features: New Features<6>.
* Other Language Changes: Other Language Changes<5>.
* New Modules: New Modules<5>.
* Improved Modules: Improved Modules<5>.
* Other module-level changes::
* Optimizations: Optimizations<5>.
* Build and C API Changes: Build and C API Changes<3>.
* Deprecated: Deprecated<4>.
* Removed: Removed<4>.
* Porting to Python 3.5: Porting to Python 3 5.
* Notable changes in Python 3.5.4: Notable changes in Python 3 5 4.

New Features

* PEP 492 - Coroutines with async and await syntax::
* PEP 465 - A dedicated infix operator for matrix multiplication::
* PEP 448 - Additional Unpacking Generalizations::
* PEP 461 - percent formatting support for bytes and bytearray::
* PEP 484 - Type Hints::
* PEP 471 - os.scandir() function – a better and faster directory iterator: PEP 471 - os scandir function – a better and faster directory iterator.
* PEP 475; Retry system calls failing with EINTR: PEP 475 Retry system calls failing with EINTR.
* PEP 479; Change StopIteration handling inside generators: PEP 479 Change StopIteration handling inside generators.
* PEP 485; A function for testing approximate equality: PEP 485 A function for testing approximate equality.
* PEP 486; Make the Python Launcher aware of virtual environments: PEP 486 Make the Python Launcher aware of virtual environments.
* PEP 488; Elimination of PYO files: PEP 488 Elimination of PYO files.
* PEP 489; Multi-phase extension module initialization: PEP 489 Multi-phase extension module initialization.

New Modules

* typing: typing<5>.
* zipapp: zipapp<2>.

Improved Modules

* argparse: argparse<2>.
* asyncio: asyncio<6>.
* bz2::
* cgi::
* cmath: cmath<2>.
* code::
* collections: collections<5>.
* collections.abc: collections abc<2>.
* compileall: compileall<3>.
* concurrent.futures: concurrent futures<4>.
* configparser::
* contextlib: contextlib<3>.
* csv: csv<2>.
* curses: curses<3>.
* dbm: dbm<4>.
* difflib::
* distutils: distutils<5>.
* doctest::
* email: email<2>.
* enum: enum<4>.
* faulthandler: faulthandler<2>.
* functools: functools<3>.
* glob::
* gzip: gzip<2>.
* heapq::
* http: http<2>.
* http.client: http client<3>.
* idlelib and IDLE: idlelib and IDLE<3>.
* imaplib: imaplib<2>.
* imghdr::
* importlib: importlib<6>.
* inspect: inspect<4>.
* io: io<3>.
* ipaddress: ipaddress<3>.
* json: json<2>.
* linecache::
* locale: locale<3>.
* logging: logging<4>.
* lzma::
* math: math<5>.
* multiprocessing: multiprocessing<5>.
* operator::
* os: os<6>.
* pathlib: pathlib<5>.
* pickle: pickle<3>.
* poplib: poplib<2>.
* re: re<4>.
* readline: readline<2>.
* selectors::
* shutil: shutil<2>.
* signal: signal<3>.
* smtpd::
* smtplib: smtplib<2>.
* sndhdr::
* socket: socket<6>.
* ssl: ssl<6>.
* sqlite3: sqlite3<3>.
* subprocess: subprocess<3>.
* sys: sys<6>.
* sysconfig::
* tarfile: tarfile<2>.
* threading: threading<3>.
* time: time<5>.
* timeit: timeit<2>.
* tkinter: tkinter<5>.
* traceback: traceback<2>.
* types: types<2>.
* unicodedata: unicodedata<5>.
* unittest: unittest<3>.
* unittest.mock: unittest mock<3>.
* urllib::
* wsgiref::
* xmlrpc: xmlrpc<2>.
* xml.sax: xml sax.
* zipfile: zipfile<3>.

ssl

* Memory BIO Support::
* Application-Layer Protocol Negotiation Support::
* Other Changes::

Deprecated

* New Keywords: New Keywords<2>.
* Deprecated Python Behavior: Deprecated Python Behavior<2>.
* Unsupported Operating Systems::
* Deprecated Python modules, functions and methods: Deprecated Python modules functions and methods<3>.

Removed

* API and Feature Removals: API and Feature Removals<4>.

Porting to Python 3.5

* Changes in Python behavior: Changes in Python behavior<2>.
* Changes in the Python API: Changes in the Python API<5>.
* Changes in the C API: Changes in the C API<5>.

Notable changes in Python 3.5.4

* New make regen-all build target: New make regen-all build target<2>.
* Removal of make touch build target: Removal of make touch build target<2>.

What’s New In Python 3.4

* Summary – Release Highlights: Summary – Release Highlights<2>.
* New Features: New Features<7>.
* New Modules: New Modules<6>.
* Improved Modules: Improved Modules<6>.
* CPython Implementation Changes::
* Deprecated: Deprecated<5>.
* Removed: Removed<5>.
* Porting to Python 3.4: Porting to Python 3 4.
* Changed in 3.4.3: Changed in 3 4 3.

New Features

* PEP 453; Explicit Bootstrapping of PIP in Python Installations: PEP 453 Explicit Bootstrapping of PIP in Python Installations.
* PEP 446; Newly Created File Descriptors Are Non-Inheritable: PEP 446 Newly Created File Descriptors Are Non-Inheritable.
* Improvements to Codec Handling::
* PEP 451; A ModuleSpec Type for the Import System: PEP 451 A ModuleSpec Type for the Import System.
* Other Language Changes: Other Language Changes<6>.

PEP 453: Explicit Bootstrapping of PIP in Python Installations

* Bootstrapping pip By Default::
* Documentation Changes::

New Modules

* asyncio: asyncio<7>.
* ensurepip::
* enum: enum<5>.
* pathlib: pathlib<6>.
* selectors: selectors<2>.
* statistics: statistics<3>.
* tracemalloc: tracemalloc<4>.

Improved Modules

* abc::
* aifc: aifc<2>.
* argparse: argparse<3>.
* audioop::
* base64::
* collections: collections<6>.
* colorsys::
* contextlib: contextlib<4>.
* dbm: dbm<5>.
* dis: dis<2>.
* doctest: doctest<2>.
* email: email<3>.
* filecmp::
* functools: functools<4>.
* gc: gc<4>.
* glob: glob<2>.
* hashlib: hashlib<3>.
* hmac: hmac<2>.
* html::
* http: http<3>.
* idlelib and IDLE: idlelib and IDLE<4>.
* importlib: importlib<7>.
* inspect: inspect<5>.
* ipaddress: ipaddress<4>.
* logging: logging<5>.
* marshal::
* mmap: mmap<2>.
* multiprocessing: multiprocessing<6>.
* operator: operator<2>.
* os: os<7>.
* pdb: pdb<4>.
* pickle: pickle<4>.
* plistlib: plistlib<2>.
* poplib: poplib<3>.
* pprint: pprint<3>.
* pty::
* pydoc: pydoc<4>.
* re: re<5>.
* resource::
* select::
* shelve::
* shutil: shutil<3>.
* smtpd: smtpd<2>.
* smtplib: smtplib<3>.
* socket: socket<7>.
* sqlite3: sqlite3<4>.
* ssl: ssl<7>.
* stat::
* struct: struct<2>.
* subprocess: subprocess<4>.
* sunau: sunau<2>.
* sys: sys<7>.
* tarfile: tarfile<3>.
* textwrap::
* threading: threading<4>.
* traceback: traceback<3>.
* types: types<3>.
* urllib: urllib<2>.
* unittest: unittest<4>.
* venv: venv<5>.
* wave: wave<2>.
* weakref: weakref<2>.
* xml.etree: xml etree<2>.
* zipfile: zipfile<4>.

CPython Implementation Changes

* PEP 445; Customization of CPython Memory Allocators: PEP 445 Customization of CPython Memory Allocators.
* PEP 442; Safe Object Finalization: PEP 442 Safe Object Finalization.
* PEP 456; Secure and Interchangeable Hash Algorithm: PEP 456 Secure and Interchangeable Hash Algorithm.
* PEP 436; Argument Clinic: PEP 436 Argument Clinic.
* Other Build and C API Changes::
* Other Improvements: Other Improvements<2>.
* Significant Optimizations::

Deprecated

* Deprecations in the Python API::
* Deprecated Features::

Removed

* Operating Systems No Longer Supported::
* API and Feature Removals: API and Feature Removals<5>.
* Code Cleanups::

Porting to Python 3.4

* Changes in ‘python’ Command Behavior: Changes in ‘python’ Command Behavior<2>.
* Changes in the Python API: Changes in the Python API<6>.
* Changes in the C API: Changes in the C API<6>.

Changed in 3.4.3

* PEP 476; Enabling certificate verification by default for stdlib http clients: PEP 476 Enabling certificate verification by default for stdlib http clients.

What’s New In Python 3.3

* Summary – Release highlights: Summary – Release highlights<5>.
* PEP 405; Virtual Environments: PEP 405 Virtual Environments.
* PEP 420; Implicit Namespace Packages: PEP 420 Implicit Namespace Packages.
* PEP 3118; New memoryview implementation and buffer protocol documentation: PEP 3118 New memoryview implementation and buffer protocol documentation.
* PEP 393; Flexible String Representation: PEP 393 Flexible String Representation.
* PEP 397; Python Launcher for Windows: PEP 397 Python Launcher for Windows.
* PEP 3151; Reworking the OS and IO exception hierarchy: PEP 3151 Reworking the OS and IO exception hierarchy.
* PEP 380; Syntax for Delegating to a Subgenerator: PEP 380 Syntax for Delegating to a Subgenerator.
* PEP 409; Suppressing exception context: PEP 409 Suppressing exception context.
* PEP 414; Explicit Unicode literals: PEP 414 Explicit Unicode literals.
* PEP 3155; Qualified name for classes and functions: PEP 3155 Qualified name for classes and functions.
* PEP 412; Key-Sharing Dictionary: PEP 412 Key-Sharing Dictionary.
* PEP 362; Function Signature Object: PEP 362 Function Signature Object.
* PEP 421; Adding sys.implementation: PEP 421 Adding sys implementation.
* Using importlib as the Implementation of Import::
* Other Language Changes: Other Language Changes<7>.
* A Finer-Grained Import Lock::
* Builtin functions and types::
* New Modules: New Modules<7>.
* Improved Modules: Improved Modules<7>.
* Optimizations: Optimizations<6>.
* Build and C API Changes: Build and C API Changes<4>.
* Deprecated: Deprecated<6>.
* Porting to Python 3.3: Porting to Python 3 3.

PEP 3118: New memoryview implementation and buffer protocol documentation

* Features::
* API changes::

PEP 393: Flexible String Representation

* Functionality::
* Performance and resource usage::

PEP 421: Adding sys.implementation

* SimpleNamespace::

Using importlib as the Implementation of Import

* New APIs::
* Visible Changes::

New Modules

* faulthandler: faulthandler<3>.
* ipaddress: ipaddress<5>.
* lzma: lzma<2>.

Improved Modules

* abc: abc<2>.
* array: array<2>.
* base64: base64<2>.
* binascii: binascii<3>.
* bz2: bz2<2>.
* codecs::
* collections: collections<7>.
* contextlib: contextlib<5>.
* crypt: crypt<2>.
* curses: curses<4>.
* datetime: datetime<5>.
* decimal: decimal<3>.
* email: email<4>.
* ftplib: ftplib<2>.
* functools: functools<5>.
* gc: gc<5>.
* hmac: hmac<3>.
* http: http<4>.
* html: html<2>.
* imaplib: imaplib<3>.
* inspect: inspect<6>.
* io: io<4>.
* itertools: itertools<3>.
* logging: logging<6>.
* math: math<6>.
* mmap: mmap<3>.
* multiprocessing: multiprocessing<7>.
* nntplib: nntplib<2>.
* os: os<8>.
* pdb: pdb<5>.
* pickle: pickle<5>.
* pydoc: pydoc<5>.
* re: re<6>.
* sched::
* select: select<2>.
* shlex: shlex<3>.
* shutil: shutil<4>.
* signal: signal<4>.
* smtpd: smtpd<3>.
* smtplib: smtplib<4>.
* socket: socket<8>.
* socketserver: socketserver<3>.
* sqlite3: sqlite3<5>.
* ssl: ssl<8>.
* stat: stat<2>.
* struct: struct<3>.
* subprocess: subprocess<5>.
* sys: sys<8>.
* tarfile: tarfile<4>.
* tempfile::
* textwrap: textwrap<2>.
* threading: threading<5>.
* time: time<6>.
* types: types<4>.
* unittest: unittest<5>.
* urllib: urllib<3>.
* webbrowser::
* xml.etree.ElementTree: xml etree ElementTree.
* zlib: zlib<2>.

decimal

* Features: Features<2>.
* API changes: API changes<2>.

email

* Policy Framework::
* Provisional Policy with New Header API::
* Other API Changes::

Deprecated

* Unsupported Operating Systems: Unsupported Operating Systems<2>.
* Deprecated Python modules, functions and methods: Deprecated Python modules functions and methods<4>.
* Deprecated functions and types of the C API: Deprecated functions and types of the C API<3>.
* Deprecated features::

Porting to Python 3.3

* Porting Python code::
* Porting C code::
* Building C extensions::
* Command Line Switch Changes::

What’s New In Python 3.2

* PEP 384; Defining a Stable ABI: PEP 384 Defining a Stable ABI.
* PEP 389; Argparse Command Line Parsing Module: PEP 389 Argparse Command Line Parsing Module.
* PEP 391; Dictionary Based Configuration for Logging: PEP 391 Dictionary Based Configuration for Logging.
* PEP 3148; The concurrent.futures module: PEP 3148 The concurrent futures module.
* PEP 3147; PYC Repository Directories: PEP 3147 PYC Repository Directories.
* PEP 3149; ABI Version Tagged .so Files: PEP 3149 ABI Version Tagged so Files.
* PEP 3333; Python Web Server Gateway Interface v1.0.1: PEP 3333 Python Web Server Gateway Interface v1 0 1.
* Other Language Changes: Other Language Changes<8>.
* New, Improved, and Deprecated Modules: New Improved and Deprecated Modules.
* Multi-threading::
* Optimizations: Optimizations<7>.
* Unicode::
* Codecs::
* Documentation::
* IDLE::
* Code Repository::
* Build and C API Changes: Build and C API Changes<5>.
* Porting to Python 3.2: Porting to Python 3 2.

New, Improved, and Deprecated Modules

* email: email<5>.
* elementtree::
* functools: functools<6>.
* itertools: itertools<4>.
* collections: collections<8>.
* threading: threading<6>.
* datetime and time::
* math: math<7>.
* abc: abc<3>.
* io: io<5>.
* reprlib::
* logging: logging<7>.
* csv: csv<3>.
* contextlib: contextlib<6>.
* decimal and fractions::
* ftp::
* popen::
* select: select<3>.
* gzip and zipfile::
* tarfile: tarfile<5>.
* hashlib: hashlib<4>.
* ast: ast<4>.
* os: os<9>.
* shutil: shutil<5>.
* sqlite3: sqlite3<6>.
* html: html<3>.
* socket: socket<9>.
* ssl: ssl<9>.
* nntp::
* certificates::
* imaplib: imaplib<4>.
* http.client: http client<4>.
* unittest: unittest<6>.
* random: random<3>.
* poplib: poplib<4>.
* asyncore: asyncore<2>.
* tempfile: tempfile<2>.
* inspect: inspect<7>.
* pydoc: pydoc<6>.
* dis: dis<3>.
* dbm: dbm<6>.
* ctypes: ctypes<2>.
* site: site<2>.
* sysconfig: sysconfig<2>.
* pdb: pdb<6>.
* configparser: configparser<2>.
* urllib.parse: urllib parse<4>.
* mailbox::
* turtledemo::

What’s New In Python 3.1

* PEP 372; Ordered Dictionaries: PEP 372 Ordered Dictionaries.
* PEP 378; Format Specifier for Thousands Separator: PEP 378 Format Specifier for Thousands Separator.
* Other Language Changes: Other Language Changes<9>.
* New, Improved, and Deprecated Modules: New Improved and Deprecated Modules<2>.
* Optimizations: Optimizations<8>.
* IDLE: IDLE<2>.
* Build and C API Changes: Build and C API Changes<6>.
* Porting to Python 3.1: Porting to Python 3 1.

What’s New In Python 3.0

* Common Stumbling Blocks::
* Overview Of Syntax Changes::
* Changes Already Present In Python 2.6: Changes Already Present In Python 2 6.
* Library Changes::
* PEP 3101; A New Approach To String Formatting: PEP 3101 A New Approach To String Formatting.
* Changes To Exceptions::
* Miscellaneous Other Changes::
* Build and C API Changes: Build and C API Changes<7>.
* Performance::
* Porting To Python 3.0: Porting To Python 3 0.

Common Stumbling Blocks

* Print Is A Function::
* Views And Iterators Instead Of Lists::
* Ordering Comparisons::
* Integers::
* Text Vs. Data Instead Of Unicode Vs. 8-bit: Text Vs Data Instead Of Unicode Vs 8-bit.

Overview Of Syntax Changes

* New Syntax::
* Changed Syntax::
* Removed Syntax::

Miscellaneous Other Changes

* Operators And Special Methods::
* Builtins::

What’s New in Python 2.7

* The Future for Python 2.x: The Future for Python 2 x.
* Changes to the Handling of Deprecation Warnings::
* Python 3.1 Features: Python 3 1 Features.
* PEP 372; Adding an Ordered Dictionary to collections: PEP 372 Adding an Ordered Dictionary to collections.
* PEP 378; Format Specifier for Thousands Separator: PEP 378 Format Specifier for Thousands Separator<2>.
* PEP 389; The argparse Module for Parsing Command Lines: PEP 389 The argparse Module for Parsing Command Lines.
* PEP 391; Dictionary-Based Configuration For Logging: PEP 391 Dictionary-Based Configuration For Logging.
* PEP 3106; Dictionary Views: PEP 3106 Dictionary Views.
* PEP 3137; The memoryview Object: PEP 3137 The memoryview Object.
* Other Language Changes: Other Language Changes<10>.
* New and Improved Modules::
* Build and C API Changes: Build and C API Changes<8>.
* Other Changes and Fixes::
* Porting to Python 2.7: Porting to Python 2 7.
* New Features Added to Python 2.7 Maintenance Releases: New Features Added to Python 2 7 Maintenance Releases.
* Acknowledgements::

Other Language Changes

* Interpreter Changes::
* Optimizations: Optimizations<9>.

New and Improved Modules

* New module; importlib: New module importlib.
* New module; sysconfig: New module sysconfig.
* ttk; Themed Widgets for Tk: ttk Themed Widgets for Tk.
* Updated module; unittest: Updated module unittest.
* Updated module; ElementTree 1.3: Updated module ElementTree 1 3.

Build and C API Changes

* Capsules::
* Port-Specific Changes; Windows: Port-Specific Changes Windows.
* Port-Specific Changes; Mac OS X: Port-Specific Changes Mac OS X.
* Port-Specific Changes; FreeBSD: Port-Specific Changes FreeBSD.

New Features Added to Python 2.7 Maintenance Releases

* Two new environment variables for debug mode::
* PEP 434; IDLE Enhancement Exception for All Branches: PEP 434 IDLE Enhancement Exception for All Branches.
* PEP 466; Network Security Enhancements for Python 2.7: PEP 466 Network Security Enhancements for Python 2 7.
* PEP 477; Backport ensurepip (PEP 453) to Python 2.7: PEP 477 Backport ensurepip PEP 453 to Python 2 7.
* PEP 476; Enabling certificate verification by default for stdlib http clients: PEP 476 Enabling certificate verification by default for stdlib http clients<2>.
* PEP 493; HTTPS verification migration tools for Python 2.7: PEP 493 HTTPS verification migration tools for Python 2 7.
* New make regen-all build target: New make regen-all build target<3>.
* Removal of make touch build target: Removal of make touch build target<3>.

PEP 477: Backport ensurepip (PEP 453) to Python 2.7

* Bootstrapping pip By Default: Bootstrapping pip By Default<2>.
* Documentation Changes: Documentation Changes<2>.

What’s New in Python 2.6

* Python 3.0: Python 3 0.
* Changes to the Development Process::
* PEP 343; The ‘with’ statement: PEP 343 The ‘with’ statement.
* PEP 366; Explicit Relative Imports From a Main Module: PEP 366 Explicit Relative Imports From a Main Module.
* PEP 370; Per-user site-packages Directory: PEP 370 Per-user site-packages Directory.
* PEP 371; The multiprocessing Package: PEP 371 The multiprocessing Package.
* PEP 3101; Advanced String Formatting: PEP 3101 Advanced String Formatting.
* PEP 3105; print As a Function: PEP 3105 print As a Function.
* PEP 3110; Exception-Handling Changes: PEP 3110 Exception-Handling Changes.
* PEP 3112; Byte Literals: PEP 3112 Byte Literals.
* PEP 3116; New I/O Library: PEP 3116 New I/O Library.
* PEP 3118; Revised Buffer Protocol: PEP 3118 Revised Buffer Protocol.
* PEP 3119; Abstract Base Classes: PEP 3119 Abstract Base Classes.
* PEP 3127; Integer Literal Support and Syntax: PEP 3127 Integer Literal Support and Syntax.
* PEP 3129; Class Decorators: PEP 3129 Class Decorators.
* PEP 3141; A Type Hierarchy for Numbers: PEP 3141 A Type Hierarchy for Numbers.
* Other Language Changes: Other Language Changes<11>.
* New and Improved Modules: New and Improved Modules<2>.
* Deprecations and Removals::
* Build and C API Changes: Build and C API Changes<9>.
* Porting to Python 2.6: Porting to Python 2 6.
* Acknowledgements: Acknowledgements<2>.

Changes to the Development Process

* New Issue Tracker; Roundup: New Issue Tracker Roundup.
* New Documentation Format; reStructuredText Using Sphinx: New Documentation Format reStructuredText Using Sphinx.

PEP 343: The ‘with’ statement

* Writing Context Managers::
* The contextlib module::

PEP 3141: A Type Hierarchy for Numbers

* The fractions Module::

Other Language Changes

* Optimizations: Optimizations<10>.
* Interpreter Changes: Interpreter Changes<2>.

New and Improved Modules

* The ast module::
* The future_builtins module::
* The json module; JavaScript Object Notation: The json module JavaScript Object Notation.
* The plistlib module; A Property-List Parser: The plistlib module A Property-List Parser.
* ctypes Enhancements::
* Improved SSL Support::

Build and C API Changes

* Port-Specific Changes; Windows: Port-Specific Changes Windows<2>.
* Port-Specific Changes; Mac OS X: Port-Specific Changes Mac OS X<2>.
* Port-Specific Changes; IRIX: Port-Specific Changes IRIX.

What’s New in Python 2.5

* PEP 308; Conditional Expressions: PEP 308 Conditional Expressions.
* PEP 309; Partial Function Application: PEP 309 Partial Function Application.
* PEP 314; Metadata for Python Software Packages v1.1: PEP 314 Metadata for Python Software Packages v1 1.
* PEP 328; Absolute and Relative Imports: PEP 328 Absolute and Relative Imports.
* PEP 338; Executing Modules as Scripts: PEP 338 Executing Modules as Scripts.
* PEP 341; Unified try/except/finally: PEP 341 Unified try/except/finally.
* PEP 342; New Generator Features: PEP 342 New Generator Features.
* PEP 343; The ‘with’ statement: PEP 343 The ‘with’ statement<2>.
* PEP 352; Exceptions as New-Style Classes: PEP 352 Exceptions as New-Style Classes.
* PEP 353; Using ssize_t as the index type: PEP 353 Using ssize_t as the index type.
* PEP 357; The ‘__index__’ method: PEP 357 The ‘__index__’ method.
* Other Language Changes: Other Language Changes<12>.
* New, Improved, and Removed Modules: New Improved and Removed Modules.
* Build and C API Changes: Build and C API Changes<10>.
* Porting to Python 2.5: Porting to Python 2 5.
* Acknowledgements: Acknowledgements<3>.

PEP 343: The ‘with’ statement

* Writing Context Managers: Writing Context Managers<2>.
* The contextlib module: The contextlib module<2>.

Other Language Changes

* Interactive Interpreter Changes::
* Optimizations: Optimizations<11>.

New, Improved, and Removed Modules

* The ctypes package::
* The ElementTree package::
* The hashlib package::
* The sqlite3 package::
* The wsgiref package::

Build and C API Changes

* Port-Specific Changes::

What’s New in Python 2.4

* PEP 218; Built-In Set Objects: PEP 218 Built-In Set Objects.
* PEP 237; Unifying Long Integers and Integers: PEP 237 Unifying Long Integers and Integers.
* PEP 289; Generator Expressions: PEP 289 Generator Expressions.
* PEP 292; Simpler String Substitutions: PEP 292 Simpler String Substitutions.
* PEP 318; Decorators for Functions and Methods: PEP 318 Decorators for Functions and Methods.
* PEP 322; Reverse Iteration: PEP 322 Reverse Iteration.
* PEP 324; New subprocess Module: PEP 324 New subprocess Module.
* PEP 327; Decimal Data Type: PEP 327 Decimal Data Type.
* PEP 328; Multi-line Imports: PEP 328 Multi-line Imports.
* PEP 331; Locale-Independent Float/String Conversions: PEP 331 Locale-Independent Float/String Conversions.
* Other Language Changes: Other Language Changes<13>.
* New, Improved, and Deprecated Modules: New Improved and Deprecated Modules<3>.
* Build and C API Changes: Build and C API Changes<11>.
* Porting to Python 2.4: Porting to Python 2 4.
* Acknowledgements: Acknowledgements<4>.

PEP 327: Decimal Data Type

* Why is Decimal needed?::
* The Decimal type::
* The Context type::

Other Language Changes

* Optimizations: Optimizations<12>.

New, Improved, and Deprecated Modules

* cookielib::
* doctest: doctest<3>.

Build and C API Changes

* Port-Specific Changes: Port-Specific Changes<2>.

What’s New in Python 2.3

* PEP 218; A Standard Set Datatype: PEP 218 A Standard Set Datatype.
* PEP 255; Simple Generators: PEP 255 Simple Generators.
* PEP 263; Source Code Encodings: PEP 263 Source Code Encodings.
* PEP 273; Importing Modules from ZIP Archives: PEP 273 Importing Modules from ZIP Archives.
* PEP 277; Unicode file name support for Windows NT: PEP 277 Unicode file name support for Windows NT.
* PEP 278; Universal Newline Support: PEP 278 Universal Newline Support.
* PEP 279; enumerate(): PEP 279 enumerate.
* PEP 282; The logging Package: PEP 282 The logging Package.
* PEP 285; A Boolean Type: PEP 285 A Boolean Type.
* PEP 293; Codec Error Handling Callbacks: PEP 293 Codec Error Handling Callbacks.
* PEP 301; Package Index and Metadata for Distutils: PEP 301 Package Index and Metadata for Distutils.
* PEP 302; New Import Hooks: PEP 302 New Import Hooks.
* PEP 305; Comma-separated Files: PEP 305 Comma-separated Files.
* PEP 307; Pickle Enhancements: PEP 307 Pickle Enhancements.
* Extended Slices::
* Other Language Changes: Other Language Changes<14>.
* New, Improved, and Deprecated Modules: New Improved and Deprecated Modules<4>.
* Pymalloc; A Specialized Object Allocator: Pymalloc A Specialized Object Allocator.
* Build and C API Changes: Build and C API Changes<12>.
* Other Changes and Fixes: Other Changes and Fixes<2>.
* Porting to Python 2.3: Porting to Python 2 3.
* Acknowledgements: Acknowledgements<5>.

Other Language Changes

* String Changes::
* Optimizations: Optimizations<13>.

New, Improved, and Deprecated Modules

* Date/Time Type::
* The optparse Module::

Build and C API Changes

* Port-Specific Changes: Port-Specific Changes<3>.

What’s New in Python 2.2

* Introduction::
* PEPs 252 and 253; Type and Class Changes: PEPs 252 and 253 Type and Class Changes.
* PEP 234; Iterators: PEP 234 Iterators.
* PEP 255; Simple Generators: PEP 255 Simple Generators<2>.
* PEP 237; Unifying Long Integers and Integers: PEP 237 Unifying Long Integers and Integers<2>.
* PEP 238; Changing the Division Operator: PEP 238 Changing the Division Operator.
* Unicode Changes::
* PEP 227; Nested Scopes: PEP 227 Nested Scopes.
* New and Improved Modules: New and Improved Modules<3>.
* Interpreter Changes and Fixes::
* Other Changes and Fixes: Other Changes and Fixes<3>.
* Acknowledgements: Acknowledgements<6>.

PEPs 252 and 253: Type and Class Changes

* Old and New Classes::
* Descriptors::
* Multiple Inheritance; The Diamond Rule: Multiple Inheritance The Diamond Rule.
* Attribute Access::
* Related Links::

What’s New in Python 2.1

* Introduction: Introduction<2>.
* PEP 227; Nested Scopes: PEP 227 Nested Scopes<2>.
* PEP 236; __future__ Directives: PEP 236 __future__ Directives.
* PEP 207; Rich Comparisons: PEP 207 Rich Comparisons.
* PEP 230; Warning Framework: PEP 230 Warning Framework.
* PEP 229; New Build System: PEP 229 New Build System.
* PEP 205; Weak References: PEP 205 Weak References.
* PEP 232; Function Attributes: PEP 232 Function Attributes.
* PEP 235; Importing Modules on Case-Insensitive Platforms: PEP 235 Importing Modules on Case-Insensitive Platforms.
* PEP 217; Interactive Display Hook: PEP 217 Interactive Display Hook.
* PEP 208; New Coercion Model: PEP 208 New Coercion Model.
* PEP 241; Metadata in Python Packages: PEP 241 Metadata in Python Packages.
* New and Improved Modules: New and Improved Modules<4>.
* Other Changes and Fixes: Other Changes and Fixes<4>.
* Acknowledgements: Acknowledgements<7>.

What’s New in Python 2.0

* Introduction: Introduction<3>.
* What About Python 1.6?: What About Python 1 6?.
* New Development Process::
* Unicode: Unicode<2>.
* List Comprehensions::
* Augmented Assignment::
* String Methods::
* Garbage Collection of Cycles::
* Other Core Changes::
* Porting to 2.0: Porting to 2 0.
* Extending/Embedding Changes::
* Distutils; Making Modules Easy to Install: Distutils Making Modules Easy to Install.
* XML Modules::
* Module changes::
* New modules::
* IDLE Improvements::
* Deleted and Deprecated Modules::
* Acknowledgements: Acknowledgements<8>.

Other Core Changes

* Minor Language Changes::
* Changes to Built-in Functions::

XML Modules

* SAX2 Support::
* DOM Support::
* Relationship to PyXML::

Changelog

* Python 3.9.10 final: Python 3 9 10 final.
* Python 3.9.9 final: Python 3 9 9 final.
* Python 3.9.8 final: Python 3 9 8 final.
* Python 3.9.7 final: Python 3 9 7 final.
* Python 3.9.6 final: Python 3 9 6 final.
* Python 3.9.5 final: Python 3 9 5 final.
* Python 3.9.4 final: Python 3 9 4 final.
* Python 3.9.3 final: Python 3 9 3 final.
* Python 3.9.2 final: Python 3 9 2 final.
* Python 3.9.2 release candidate 1: Python 3 9 2 release candidate 1.
* Python 3.9.1 final: Python 3 9 1 final.
* Python 3.9.1 release candidate 1: Python 3 9 1 release candidate 1.
* Python 3.9.0 final: Python 3 9 0 final.
* Python 3.9.0 release candidate 2: Python 3 9 0 release candidate 2.
* Python 3.9.0 release candidate 1: Python 3 9 0 release candidate 1.
* Python 3.9.0 beta 5: Python 3 9 0 beta 5.
* Python 3.9.0 beta 4: Python 3 9 0 beta 4.
* Python 3.9.0 beta 3: Python 3 9 0 beta 3.
* Python 3.9.0 beta 2: Python 3 9 0 beta 2.
* Python 3.9.0 beta 1: Python 3 9 0 beta 1.
* Python 3.9.0 alpha 6: Python 3 9 0 alpha 6.
* Python 3.9.0 alpha 5: Python 3 9 0 alpha 5.
* Python 3.9.0 alpha 4: Python 3 9 0 alpha 4.
* Python 3.9.0 alpha 3: Python 3 9 0 alpha 3.
* Python 3.9.0 alpha 2: Python 3 9 0 alpha 2.
* Python 3.9.0 alpha 1: Python 3 9 0 alpha 1.
* Python 3.8.0 beta 1: Python 3 8 0 beta 1.
* Python 3.8.0 alpha 4: Python 3 8 0 alpha 4.
* Python 3.8.0 alpha 3: Python 3 8 0 alpha 3.
* Python 3.8.0 alpha 2: Python 3 8 0 alpha 2.
* Python 3.8.0 alpha 1: Python 3 8 0 alpha 1.
* Python 3.7.0 final: Python 3 7 0 final.
* Python 3.7.0 release candidate 1: Python 3 7 0 release candidate 1.
* Python 3.7.0 beta 5: Python 3 7 0 beta 5.
* Python 3.7.0 beta 4: Python 3 7 0 beta 4.
* Python 3.7.0 beta 3: Python 3 7 0 beta 3.
* Python 3.7.0 beta 2: Python 3 7 0 beta 2.
* Python 3.7.0 beta 1: Python 3 7 0 beta 1.
* Python 3.7.0 alpha 4: Python 3 7 0 alpha 4.
* Python 3.7.0 alpha 3: Python 3 7 0 alpha 3.
* Python 3.7.0 alpha 2: Python 3 7 0 alpha 2.
* Python 3.7.0 alpha 1: Python 3 7 0 alpha 1.
* Python 3.6.6 final: Python 3 6 6 final.
* Python 3.6.6 release candidate 1: Python 3 6 6 release candidate 1.
* Python 3.6.5 final: Python 3 6 5 final.
* Python 3.6.5 release candidate 1: Python 3 6 5 release candidate 1.
* Python 3.6.4 final: Python 3 6 4 final.
* Python 3.6.4 release candidate 1: Python 3 6 4 release candidate 1.
* Python 3.6.3 final: Python 3 6 3 final.
* Python 3.6.3 release candidate 1: Python 3 6 3 release candidate 1.
* Python 3.6.2 final: Python 3 6 2 final.
* Python 3.6.2 release candidate 2: Python 3 6 2 release candidate 2.
* Python 3.6.2 release candidate 1: Python 3 6 2 release candidate 1.
* Python 3.6.1 final: Python 3 6 1 final.
* Python 3.6.1 release candidate 1: Python 3 6 1 release candidate 1.
* Python 3.6.0 final: Python 3 6 0 final.
* Python 3.6.0 release candidate 2: Python 3 6 0 release candidate 2.
* Python 3.6.0 release candidate 1: Python 3 6 0 release candidate 1.
* Python 3.6.0 beta 4: Python 3 6 0 beta 4.
* Python 3.6.0 beta 3: Python 3 6 0 beta 3.
* Python 3.6.0 beta 2: Python 3 6 0 beta 2.
* Python 3.6.0 beta 1: Python 3 6 0 beta 1.
* Python 3.6.0 alpha 4: Python 3 6 0 alpha 4.
* Python 3.6.0 alpha 3: Python 3 6 0 alpha 3.
* Python 3.6.0 alpha 2: Python 3 6 0 alpha 2.
* Python 3.6.0 alpha 1: Python 3 6 0 alpha 1.
* Python 3.5.5 final: Python 3 5 5 final.
* Python 3.5.5 release candidate 1: Python 3 5 5 release candidate 1.
* Python 3.5.4 final: Python 3 5 4 final.
* Python 3.5.4 release candidate 1: Python 3 5 4 release candidate 1.
* Python 3.5.3 final: Python 3 5 3 final.
* Python 3.5.3 release candidate 1: Python 3 5 3 release candidate 1.
* Python 3.5.2 final: Python 3 5 2 final.
* Python 3.5.2 release candidate 1: Python 3 5 2 release candidate 1.
* Python 3.5.1 final: Python 3 5 1 final.
* Python 3.5.1 release candidate 1: Python 3 5 1 release candidate 1.
* Python 3.5.0 final: Python 3 5 0 final.
* Python 3.5.0 release candidate 4: Python 3 5 0 release candidate 4.
* Python 3.5.0 release candidate 3: Python 3 5 0 release candidate 3.
* Python 3.5.0 release candidate 2: Python 3 5 0 release candidate 2.
* Python 3.5.0 release candidate 1: Python 3 5 0 release candidate 1.
* Python 3.5.0 beta 4: Python 3 5 0 beta 4.
* Python 3.5.0 beta 3: Python 3 5 0 beta 3.
* Python 3.5.0 beta 2: Python 3 5 0 beta 2.
* Python 3.5.0 beta 1: Python 3 5 0 beta 1.
* Python 3.5.0 alpha 4: Python 3 5 0 alpha 4.
* Python 3.5.0 alpha 3: Python 3 5 0 alpha 3.
* Python 3.5.0 alpha 2: Python 3 5 0 alpha 2.
* Python 3.5.0 alpha 1: Python 3 5 0 alpha 1.

Python 3.9.10 final

* Core and Builtins::
* Library::
* Documentation: Documentation<2>.
* Tests::
* Build::
* Windows::
* macOS::
* Tools/Demos::
* C API::

Python 3.9.9 final

* Core and Builtins: Core and Builtins<2>.
* Library: Library<2>.
* Documentation: Documentation<3>.
* Windows: Windows<2>.

Python 3.9.8 final

* Core and Builtins: Core and Builtins<3>.
* Library: Library<3>.
* Documentation: Documentation<4>.
* Tests: Tests<2>.
* Build: Build<2>.
* Windows: Windows<3>.
* macOS: macOS<2>.
* IDLE: IDLE<3>.
* C API: C API<2>.

Python 3.9.7 final

* Security::
* Core and Builtins: Core and Builtins<4>.
* Library: Library<4>.
* Documentation: Documentation<5>.
* Tests: Tests<3>.
* Build: Build<3>.
* Windows: Windows<4>.
* macOS: macOS<3>.

Python 3.9.6 final

* Security: Security<2>.
* Core and Builtins: Core and Builtins<5>.
* Library: Library<5>.
* Documentation: Documentation<6>.
* Tests: Tests<4>.
* Build: Build<4>.
* Windows: Windows<5>.
* macOS: macOS<4>.
* IDLE: IDLE<4>.
* Tools/Demos: Tools/Demos<2>.
* C API: C API<3>.

Python 3.9.5 final

* Security: Security<3>.
* Core and Builtins: Core and Builtins<6>.
* Library: Library<6>.
* Documentation: Documentation<7>.
* Tests: Tests<5>.
* Windows: Windows<6>.
* macOS: macOS<5>.
* IDLE: IDLE<5>.

Python 3.9.4 final

* Core and Builtins: Core and Builtins<7>.
* Library: Library<7>.

Python 3.9.3 final

* Security: Security<4>.
* Core and Builtins: Core and Builtins<8>.
* Library: Library<8>.
* Documentation: Documentation<8>.
* Tests: Tests<6>.
* Build: Build<5>.
* macOS: macOS<6>.
* IDLE: IDLE<6>.

Python 3.9.2 final

* Windows: Windows<7>.

Python 3.9.2 release candidate 1

* Security: Security<5>.
* Core and Builtins: Core and Builtins<9>.
* Library: Library<9>.
* Documentation: Documentation<9>.
* Tests: Tests<7>.
* Build: Build<6>.
* Windows: Windows<8>.
* macOS: macOS<7>.
* IDLE: IDLE<7>.
* Tools/Demos: Tools/Demos<3>.
* C API: C API<4>.

Python 3.9.1 final

* Core and Builtins: Core and Builtins<10>.
* Library: Library<10>.
* Tests: Tests<8>.
* macOS: macOS<8>.
* IDLE: IDLE<8>.

Python 3.9.1 release candidate 1

* Security: Security<6>.
* Core and Builtins: Core and Builtins<11>.
* Library: Library<11>.
* Documentation: Documentation<10>.
* Tests: Tests<9>.
* Build: Build<7>.
* Windows: Windows<9>.
* macOS: macOS<9>.
* IDLE: IDLE<9>.
* C API: C API<5>.

Python 3.9.0 final

* Library: Library<12>.
* Tests: Tests<10>.
* Build: Build<8>.

Python 3.9.0 release candidate 2

* Core and Builtins: Core and Builtins<12>.
* Library: Library<13>.
* Documentation: Documentation<11>.
* Tests: Tests<11>.
* Build: Build<9>.
* Windows: Windows<10>.
* C API: C API<6>.

Python 3.9.0 release candidate 1

* Core and Builtins: Core and Builtins<13>.
* Library: Library<14>.
* Documentation: Documentation<12>.
* Windows: Windows<11>.
* IDLE: IDLE<10>.

Python 3.9.0 beta 5

* Security: Security<7>.
* Core and Builtins: Core and Builtins<14>.
* Library: Library<15>.
* Documentation: Documentation<13>.
* macOS: macOS<10>.
* IDLE: IDLE<11>.
* C API: C API<7>.

Python 3.9.0 beta 4

* Security: Security<8>.
* Core and Builtins: Core and Builtins<15>.
* Library: Library<16>.
* Tests: Tests<12>.
* Build: Build<10>.
* Windows: Windows<12>.
* macOS: macOS<11>.
* IDLE: IDLE<12>.
* C API: C API<8>.

Python 3.9.0 beta 3

* Library: Library<17>.
* Build: Build<11>.

Python 3.9.0 beta 2

* Core and Builtins: Core and Builtins<16>.
* Library: Library<18>.
* Tests: Tests<13>.
* Build: Build<12>.
* Windows: Windows<13>.
* macOS: macOS<12>.
* IDLE: IDLE<13>.
* C API: C API<9>.

Python 3.9.0 beta 1

* Security: Security<9>.
* Core and Builtins: Core and Builtins<17>.
* Library: Library<19>.
* Documentation: Documentation<14>.
* Tests: Tests<14>.
* Build: Build<13>.
* Windows: Windows<14>.
* macOS: macOS<13>.
* Tools/Demos: Tools/Demos<4>.
* C API: C API<10>.

Python 3.9.0 alpha 6

* Security: Security<10>.
* Core and Builtins: Core and Builtins<18>.
* Library: Library<20>.
* Documentation: Documentation<15>.
* Tests: Tests<15>.
* Build: Build<14>.
* Windows: Windows<15>.
* macOS: macOS<14>.
* IDLE: IDLE<14>.
* Tools/Demos: Tools/Demos<5>.
* C API: C API<11>.

Python 3.9.0 alpha 5

* Security: Security<11>.
* Core and Builtins: Core and Builtins<19>.
* Library: Library<21>.
* Documentation: Documentation<16>.
* Tests: Tests<16>.
* Build: Build<15>.
* Windows: Windows<16>.
* macOS: macOS<15>.
* IDLE: IDLE<15>.
* Tools/Demos: Tools/Demos<6>.
* C API: C API<12>.

Python 3.9.0 alpha 4

* Security: Security<12>.
* Core and Builtins: Core and Builtins<20>.
* Library: Library<22>.
* Documentation: Documentation<17>.
* Tests: Tests<17>.
* Build: Build<16>.
* Windows: Windows<17>.
* IDLE: IDLE<16>.
* C API: C API<13>.

Python 3.9.0 alpha 3

* Core and Builtins: Core and Builtins<21>.
* Library: Library<23>.
* Documentation: Documentation<18>.
* Build: Build<17>.
* IDLE: IDLE<17>.
* C API: C API<14>.

Python 3.9.0 alpha 2

* Security: Security<13>.
* Core and Builtins: Core and Builtins<22>.
* Library: Library<24>.
* Documentation: Documentation<19>.
* Tests: Tests<18>.
* Build: Build<18>.
* Windows: Windows<18>.
* macOS: macOS<16>.
* IDLE: IDLE<18>.
* C API: C API<15>.

Python 3.9.0 alpha 1

* Security: Security<14>.
* Core and Builtins: Core and Builtins<23>.
* Library: Library<25>.
* Documentation: Documentation<20>.
* Tests: Tests<19>.
* Build: Build<19>.
* Windows: Windows<19>.
* macOS: macOS<17>.
* IDLE: IDLE<19>.
* Tools/Demos: Tools/Demos<7>.
* C API: C API<16>.

Python 3.8.0 beta 1

* Security: Security<15>.
* Core and Builtins: Core and Builtins<24>.
* Library: Library<26>.
* Documentation: Documentation<21>.
* Tests: Tests<20>.
* Build: Build<20>.
* Windows: Windows<20>.
* macOS: macOS<18>.
* IDLE: IDLE<20>.
* Tools/Demos: Tools/Demos<8>.
* C API: C API<17>.

Python 3.8.0 alpha 4

* Security: Security<16>.
* Core and Builtins: Core and Builtins<25>.
* Library: Library<27>.
* Documentation: Documentation<22>.
* Tests: Tests<21>.
* Build: Build<21>.
* Windows: Windows<21>.
* macOS: macOS<19>.
* IDLE: IDLE<21>.
* Tools/Demos: Tools/Demos<9>.
* C API: C API<18>.

Python 3.8.0 alpha 3

* Security: Security<17>.
* Core and Builtins: Core and Builtins<26>.
* Library: Library<28>.
* Documentation: Documentation<23>.
* Tests: Tests<22>.
* Build: Build<22>.
* Windows: Windows<22>.
* IDLE: IDLE<22>.
* Tools/Demos: Tools/Demos<10>.
* C API: C API<19>.

Python 3.8.0 alpha 2

* Core and Builtins: Core and Builtins<27>.
* Library: Library<29>.
* Documentation: Documentation<24>.
* Tests: Tests<23>.
* Windows: Windows<23>.
* IDLE: IDLE<23>.

Python 3.8.0 alpha 1

* Security: Security<18>.
* Core and Builtins: Core and Builtins<28>.
* Library: Library<30>.
* Documentation: Documentation<25>.
* Tests: Tests<24>.
* Build: Build<23>.
* Windows: Windows<24>.
* macOS: macOS<20>.
* IDLE: IDLE<24>.
* Tools/Demos: Tools/Demos<11>.
* C API: C API<20>.

Python 3.7.0 final

* Library: Library<31>.
* C API: C API<21>.

Python 3.7.0 release candidate 1

* Core and Builtins: Core and Builtins<29>.
* Library: Library<32>.
* Documentation: Documentation<26>.
* Build: Build<24>.
* Windows: Windows<25>.
* IDLE: IDLE<25>.

Python 3.7.0 beta 5

* Core and Builtins: Core and Builtins<30>.
* Library: Library<33>.
* Documentation: Documentation<27>.
* Tests: Tests<25>.
* Build: Build<25>.
* macOS: macOS<21>.
* IDLE: IDLE<26>.

Python 3.7.0 beta 4

* Core and Builtins: Core and Builtins<31>.
* Library: Library<34>.
* Documentation: Documentation<28>.
* Tests: Tests<26>.
* Build: Build<26>.
* Windows: Windows<26>.
* macOS: macOS<22>.
* IDLE: IDLE<27>.
* Tools/Demos: Tools/Demos<12>.

Python 3.7.0 beta 3

* Security: Security<19>.
* Core and Builtins: Core and Builtins<32>.
* Library: Library<35>.
* Documentation: Documentation<29>.
* Tests: Tests<27>.
* Build: Build<27>.
* Windows: Windows<27>.
* macOS: macOS<23>.
* IDLE: IDLE<28>.
* Tools/Demos: Tools/Demos<13>.
* C API: C API<22>.

Python 3.7.0 beta 2

* Security: Security<20>.
* Core and Builtins: Core and Builtins<33>.
* Library: Library<36>.
* Documentation: Documentation<30>.
* Tests: Tests<28>.
* Build: Build<28>.
* Windows: Windows<28>.
* macOS: macOS<24>.
* IDLE: IDLE<29>.
* Tools/Demos: Tools/Demos<14>.

Python 3.7.0 beta 1

* Core and Builtins: Core and Builtins<34>.
* Library: Library<37>.
* Documentation: Documentation<31>.
* Tests: Tests<29>.
* Build: Build<29>.
* Windows: Windows<29>.
* macOS: macOS<25>.
* C API: C API<23>.

Python 3.7.0 alpha 4

* Core and Builtins: Core and Builtins<35>.
* Library: Library<38>.
* Documentation: Documentation<32>.
* Tests: Tests<30>.
* Windows: Windows<30>.
* Tools/Demos: Tools/Demos<15>.
* C API: C API<24>.

Python 3.7.0 alpha 3

* Core and Builtins: Core and Builtins<36>.
* Library: Library<39>.
* Documentation: Documentation<33>.
* Tests: Tests<31>.
* Build: Build<30>.
* Windows: Windows<31>.
* macOS: macOS<26>.
* IDLE: IDLE<30>.
* Tools/Demos: Tools/Demos<16>.
* C API: C API<25>.

Python 3.7.0 alpha 2

* Core and Builtins: Core and Builtins<37>.
* Library: Library<40>.
* Documentation: Documentation<34>.
* Build: Build<31>.
* IDLE: IDLE<31>.
* C API: C API<26>.

Python 3.7.0 alpha 1

* Security: Security<21>.
* Core and Builtins: Core and Builtins<38>.
* Library: Library<41>.
* Documentation: Documentation<35>.
* Tests: Tests<32>.
* Build: Build<32>.
* Windows: Windows<32>.
* IDLE: IDLE<32>.
* Tools/Demos: Tools/Demos<17>.
* C API: C API<27>.

Python 3.6.6 release candidate 1

* Core and Builtins: Core and Builtins<39>.
* Library: Library<42>.
* Documentation: Documentation<36>.
* Tests: Tests<33>.
* Build: Build<33>.
* Windows: Windows<33>.
* macOS: macOS<27>.
* IDLE: IDLE<33>.
* Tools/Demos: Tools/Demos<18>.
* C API: C API<28>.

Python 3.6.5 final

* Tests: Tests<34>.
* Build: Build<34>.

Python 3.6.5 release candidate 1

* Security: Security<22>.
* Core and Builtins: Core and Builtins<40>.
* Library: Library<43>.
* Documentation: Documentation<37>.
* Tests: Tests<35>.
* Build: Build<35>.
* Windows: Windows<34>.
* macOS: macOS<28>.
* IDLE: IDLE<34>.
* Tools/Demos: Tools/Demos<19>.
* C API: C API<29>.

Python 3.6.4 release candidate 1

* Core and Builtins: Core and Builtins<41>.
* Library: Library<44>.
* Documentation: Documentation<38>.
* Tests: Tests<36>.
* Build: Build<36>.
* Windows: Windows<35>.
* macOS: macOS<29>.
* IDLE: IDLE<35>.
* Tools/Demos: Tools/Demos<20>.
* C API: C API<30>.

Python 3.6.3 final

* Library: Library<45>.
* Build: Build<37>.

Python 3.6.3 release candidate 1

* Security: Security<23>.
* Core and Builtins: Core and Builtins<42>.
* Library: Library<46>.
* Documentation: Documentation<39>.
* Tests: Tests<37>.
* Build: Build<38>.
* Windows: Windows<36>.
* IDLE: IDLE<36>.
* Tools/Demos: Tools/Demos<21>.

Python 3.6.2 release candidate 2

* Security: Security<24>.

Python 3.6.2 release candidate 1

* Core and Builtins: Core and Builtins<43>.
* Library: Library<47>.
* Security: Security<25>.
* Library: Library<48>.
* IDLE: IDLE<37>.
* C API: C API<31>.
* Build: Build<39>.
* Documentation: Documentation<40>.
* Tools/Demos: Tools/Demos<22>.
* Tests: Tests<38>.
* Windows: Windows<37>.

Python 3.6.1 final

* Core and Builtins: Core and Builtins<44>.
* Build: Build<40>.

Python 3.6.1 release candidate 1

* Core and Builtins: Core and Builtins<45>.
* Library: Library<49>.
* IDLE: IDLE<38>.
* Windows: Windows<38>.
* C API: C API<32>.
* Documentation: Documentation<41>.
* Tests: Tests<39>.
* Build: Build<41>.

Python 3.6.0 release candidate 2

* Core and Builtins: Core and Builtins<46>.
* Tools/Demos: Tools/Demos<23>.
* Windows: Windows<39>.
* Build: Build<42>.

Python 3.6.0 release candidate 1

* Core and Builtins: Core and Builtins<47>.
* Library: Library<50>.
* C API: C API<33>.
* Documentation: Documentation<42>.
* Tools/Demos: Tools/Demos<24>.

Python 3.6.0 beta 4

* Core and Builtins: Core and Builtins<48>.
* Library: Library<51>.
* Documentation: Documentation<43>.
* Tests: Tests<40>.
* Build: Build<43>.

Python 3.6.0 beta 3

* Core and Builtins: Core and Builtins<49>.
* Library: Library<52>.
* Windows: Windows<40>.
* Build: Build<44>.
* Tests: Tests<41>.

Python 3.6.0 beta 2

* Core and Builtins: Core and Builtins<50>.
* Library: Library<53>.
* Windows: Windows<41>.
* C API: C API<34>.
* Build: Build<45>.
* Tests: Tests<42>.

Python 3.6.0 beta 1

* Core and Builtins: Core and Builtins<51>.
* Library: Library<54>.
* IDLE: IDLE<39>.
* C API: C API<35>.
* Tests: Tests<43>.
* Build: Build<46>.
* Tools/Demos: Tools/Demos<25>.
* Windows: Windows<42>.

Python 3.6.0 alpha 4

* Core and Builtins: Core and Builtins<52>.
* Library: Library<55>.
* IDLE: IDLE<40>.
* Tests: Tests<44>.
* Windows: Windows<43>.
* Build: Build<47>.

Python 3.6.0 alpha 3

* Core and Builtins: Core and Builtins<53>.
* Library: Library<56>.
* Security: Security<26>.
* Library: Library<57>.
* Security: Security<27>.
* Library: Library<58>.
* IDLE: IDLE<41>.
* C API: C API<36>.
* Build: Build<48>.
* Tools/Demos: Tools/Demos<26>.
* Documentation: Documentation<44>.
* Tests: Tests<45>.

Python 3.6.0 alpha 2

* Core and Builtins: Core and Builtins<54>.
* Library: Library<59>.
* Security: Security<28>.
* Library: Library<60>.
* Security: Security<29>.
* Library: Library<61>.
* IDLE: IDLE<42>.
* Documentation: Documentation<45>.
* Tests: Tests<46>.
* Windows: Windows<44>.
* Build: Build<49>.
* Windows: Windows<45>.
* C API: C API<37>.
* Tools/Demos: Tools/Demos<27>.

Python 3.6.0 alpha 1

* Core and Builtins: Core and Builtins<55>.
* Library: Library<62>.
* Security: Security<30>.
* Library: Library<63>.
* Security: Security<31>.
* Library: Library<64>.
* Security: Security<32>.
* Library: Library<65>.
* IDLE: IDLE<43>.
* Documentation: Documentation<46>.
* Tests: Tests<47>.
* Build: Build<50>.
* Windows: Windows<46>.
* Tools/Demos: Tools/Demos<28>.
* C API: C API<38>.

Python 3.5.5 release candidate 1

* Security: Security<33>.
* Core and Builtins: Core and Builtins<56>.
* Library: Library<66>.

Python 3.5.4 final

* Library: Library<67>.

Python 3.5.4 release candidate 1

* Security: Security<34>.
* Core and Builtins: Core and Builtins<57>.
* Library: Library<68>.
* Documentation: Documentation<47>.
* Tests: Tests<48>.
* Build: Build<51>.
* Windows: Windows<47>.
* C API: C API<39>.

Python 3.5.3 release candidate 1

* Core and Builtins: Core and Builtins<58>.
* Library: Library<69>.
* Security: Security<35>.
* Library: Library<70>.
* Security: Security<36>.
* Library: Library<71>.
* IDLE: IDLE<44>.
* C API: C API<40>.
* Documentation: Documentation<48>.
* Tests: Tests<49>.
* Tools/Demos: Tools/Demos<29>.
* Windows: Windows<48>.
* Build: Build<52>.

Python 3.5.2 final

* Core and Builtins: Core and Builtins<59>.
* Tests: Tests<50>.
* IDLE: IDLE<45>.

Python 3.5.2 release candidate 1

* Core and Builtins: Core and Builtins<60>.
* Security: Security<37>.
* Library: Library<72>.
* Security: Security<38>.
* Library: Library<73>.
* Security: Security<39>.
* Library: Library<74>.
* Security: Security<40>.
* Library: Library<75>.
* Security: Security<41>.
* Library: Library<76>.
* IDLE: IDLE<46>.
* Documentation: Documentation<49>.
* Tests: Tests<51>.
* Build: Build<53>.
* Windows: Windows<49>.
* Tools/Demos: Tools/Demos<30>.
* Windows: Windows<50>.

Python 3.5.1 final

* Core and Builtins: Core and Builtins<61>.
* Windows: Windows<51>.

Python 3.5.1 release candidate 1

* Core and Builtins: Core and Builtins<62>.
* Library: Library<77>.
* IDLE: IDLE<47>.
* Documentation: Documentation<50>.
* Tests: Tests<52>.
* Build: Build<54>.
* Windows: Windows<52>.
* Tools/Demos: Tools/Demos<31>.

Python 3.5.0 final

* Build: Build<55>.

Python 3.5.0 release candidate 4

* Library: Library<78>.
* Build: Build<56>.

Python 3.5.0 release candidate 3

* Core and Builtins: Core and Builtins<63>.
* Library: Library<79>.

Python 3.5.0 release candidate 2

* Core and Builtins: Core and Builtins<64>.
* Library: Library<80>.

Python 3.5.0 release candidate 1

* Core and Builtins: Core and Builtins<65>.
* Library: Library<81>.
* IDLE: IDLE<48>.
* Documentation: Documentation<51>.
* Tests: Tests<53>.

Python 3.5.0 beta 4

* Core and Builtins: Core and Builtins<66>.
* Library: Library<82>.
* Build: Build<57>.

Python 3.5.0 beta 3

* Core and Builtins: Core and Builtins<67>.
* Library: Library<83>.
* Tests: Tests<54>.
* Documentation: Documentation<52>.
* Build: Build<58>.

Python 3.5.0 beta 2

* Core and Builtins: Core and Builtins<68>.
* Library: Library<84>.

Python 3.5.0 beta 1

* Core and Builtins: Core and Builtins<69>.
* Library: Library<85>.
* IDLE: IDLE<49>.
* Tests: Tests<55>.
* Documentation: Documentation<53>.
* Tools/Demos: Tools/Demos<32>.

Python 3.5.0 alpha 4

* Core and Builtins: Core and Builtins<70>.
* Library: Library<86>.
* Build: Build<59>.
* Tests: Tests<56>.
* Tools/Demos: Tools/Demos<33>.
* C API: C API<41>.

Python 3.5.0 alpha 3

* Core and Builtins: Core and Builtins<71>.
* Library: Library<87>.
* Build: Build<60>.
* Tests: Tests<57>.
* Tools/Demos: Tools/Demos<34>.

Python 3.5.0 alpha 2

* Core and Builtins: Core and Builtins<72>.
* Library: Library<88>.
* Build: Build<61>.
* C API: C API<42>.
* Windows: Windows<53>.

Python 3.5.0 alpha 1

* Core and Builtins: Core and Builtins<73>.
* Library: Library<89>.
* IDLE: IDLE<50>.
* Build: Build<62>.
* C API: C API<43>.
* Documentation: Documentation<54>.
* Tests: Tests<58>.
* Tools/Demos: Tools/Demos<35>.
* Windows: Windows<54>.

The Python Tutorial

* Whetting Your Appetite::
* Using the Python Interpreter::
* An Informal Introduction to Python::
* More Control Flow Tools::
* Data Structures::
* Modules::
* Input and Output::
* Errors and Exceptions::
* Classes::
* Brief Tour of the Standard Library::
* Brief Tour of the Standard Library — Part II::
* Virtual Environments and Packages::
* What Now?::
* Interactive Input Editing and History Substitution::
* Floating Point Arithmetic; Issues and Limitations: Floating Point Arithmetic Issues and Limitations.
* Appendix::

Using the Python Interpreter

* Invoking the Interpreter::
* The Interpreter and Its Environment::

Invoking the Interpreter

* Argument Passing::
* Interactive Mode::

The Interpreter and Its Environment

* Source Code Encoding::

An Informal Introduction to Python

* Using Python as a Calculator::
* First Steps Towards Programming::

Using Python as a Calculator

* Numbers::
* Strings::
* Lists::

More Control Flow Tools

* if Statements::
* for Statements::
* The range() Function: The range Function.
* break and continue Statements, and else Clauses on Loops: break and continue Statements and else Clauses on Loops.
* pass Statements::
* Defining Functions::
* More on Defining Functions::
* Intermezzo; Coding Style: Intermezzo Coding Style.

More on Defining Functions

* Default Argument Values::
* Keyword Arguments::
* Special parameters::
* Arbitrary Argument Lists::
* Unpacking Argument Lists::
* Lambda Expressions::
* Documentation Strings::
* Function Annotations::

Special parameters

* Positional-or-Keyword Arguments::
* Positional-Only Parameters::
* Keyword-Only Arguments::
* Function Examples::
* Recap::

Data Structures

* More on Lists::
* The del statement::
* Tuples and Sequences::
* Sets::
* Dictionaries::
* Looping Techniques::
* More on Conditions::
* Comparing Sequences and Other Types::

More on Lists

* Using Lists as Stacks::
* Using Lists as Queues::
* List Comprehensions: List Comprehensions<2>.
* Nested List Comprehensions::

Modules

* More on Modules::
* Standard Modules::
* The dir() Function: The dir Function.
* Packages::

More on Modules

* Executing modules as scripts::
* The Module Search Path::
* “Compiled” Python files::

Packages

* Importing * From a Package::
* Intra-package References::
* Packages in Multiple Directories::

Input and Output

* Fancier Output Formatting::
* Reading and Writing Files::

Fancier Output Formatting

* Formatted String Literals::
* The String format() Method: The String format Method.
* Manual String Formatting::
* Old string formatting::

Reading and Writing Files

* Methods of File Objects::
* Saving structured data with json::

Errors and Exceptions

* Syntax Errors::
* Exceptions::
* Handling Exceptions::
* Raising Exceptions::
* Exception Chaining::
* User-defined Exceptions::
* Defining Clean-up Actions::
* Predefined Clean-up Actions::

Classes

* A Word About Names and Objects::
* Python Scopes and Namespaces::
* A First Look at Classes::
* Random Remarks::
* Inheritance::
* Private Variables::
* Odds and Ends::
* Iterators::
* Generators::
* Generator Expressions::

Python Scopes and Namespaces

* Scopes and Namespaces Example::

A First Look at Classes

* Class Definition Syntax::
* Class Objects::
* Instance Objects::
* Method Objects::
* Class and Instance Variables::

Inheritance

* Multiple Inheritance::

Brief Tour of the Standard Library

* Operating System Interface::
* File Wildcards::
* Command Line Arguments::
* Error Output Redirection and Program Termination::
* String Pattern Matching::
* Mathematics::
* Internet Access::
* Dates and Times::
* Data Compression::
* Performance Measurement::
* Quality Control::
* Batteries Included::

Brief Tour of the Standard Library — Part II

* Output Formatting::
* Templating::
* Working with Binary Data Record Layouts::
* Multi-threading: Multi-threading<2>.
* Logging::
* Weak References::
* Tools for Working with Lists::
* Decimal Floating Point Arithmetic::

Virtual Environments and Packages

* Introduction: Introduction<4>.
* Creating Virtual Environments::
* Managing Packages with pip::

Interactive Input Editing and History Substitution

* Tab Completion and History Editing::
* Alternatives to the Interactive Interpreter::

Floating Point Arithmetic:  Issues and Limitations

* Representation Error::

Appendix

* Interactive Mode: Interactive Mode<2>.

Interactive Mode

* Error Handling::
* Executable Python Scripts::
* The Interactive Startup File::
* The Customization Modules::

Python Setup and Usage

* Command line and environment::
* Using Python on Unix platforms::
* Using Python on Windows::
* Using Python on a Mac::
* Editors and IDEs::

Command line and environment

* Command line::
* Environment variables::

Command line

* Interface options::
* Generic options::
* Miscellaneous options::
* Options you shouldn’t use::

Environment variables

* Debug-mode variables::

Using Python on Unix platforms

* Getting and installing the latest version of Python::
* Building Python::
* Python-related paths and files::
* Miscellaneous::

Getting and installing the latest version of Python

* On Linux::
* On FreeBSD and OpenBSD::
* On OpenSolaris::

Using Python on Windows

* The full installer::
* The Microsoft Store package::
* The nuget.org packages: The nuget org packages.
* The embeddable package::
* Alternative bundles::
* Configuring Python::
* UTF-8 mode::
* Python Launcher for Windows::
* Finding modules::
* Additional modules::
* Compiling Python on Windows::
* Other Platforms::

The full installer

* Installation steps::
* Removing the MAX_PATH Limitation::
* Installing Without UI::
* Installing Without Downloading::
* Modifying an install::

The Microsoft Store package

* Known Issues::

The embeddable package

* Python Application::
* Embedding Python::

Configuring Python

* Excursus; Setting environment variables: Excursus Setting environment variables.
* Finding the Python executable::

Python Launcher for Windows

* Getting started::
* Shebang Lines::
* Arguments in shebang lines::
* Customization::
* Diagnostics::

Getting started

* From the command-line::
* Virtual environments::
* From a script::
* From file associations::

Customization

* Customization via INI files::
* Customizing default Python versions::

Additional modules

* PyWin32::
* cx_Freeze::
* WConio::

Using Python on a Mac

* Getting and Installing MacPython::
* The IDE::
* Installing Additional Python Packages::
* GUI Programming on the Mac::
* Distributing Python Applications on the Mac::
* Other Resources::

Getting and Installing MacPython

* How to run a Python script::
* Running scripts with a GUI::
* Configuration::

The Python Language Reference

* Introduction: Introduction<5>.
* Lexical analysis::
* Data model::
* Execution model::
* The import system::
* Expressions::
* Simple statements::
* Compound statements::
* Top-level components::
* Full Grammar specification::

Introduction

* Alternate Implementations::
* Notation::

Lexical analysis

* Line structure::
* Other tokens::
* Identifiers and keywords::
* Literals::
* Operators::
* Delimiters::

Line structure

* Logical lines::
* Physical lines::
* Comments::
* Encoding declarations::
* Explicit line joining::
* Implicit line joining::
* Blank lines::
* Indentation::
* Whitespace between tokens::

Identifiers and keywords

* Keywords::
* Reserved classes of identifiers::

Literals

* String and Bytes literals::
* String literal concatenation::
* Formatted string literals::
* Numeric literals::
* Integer literals::
* Floating point literals::
* Imaginary literals::

Data model

* Objects, values and types: Objects values and types.
* The standard type hierarchy::
* Special method names::
* Coroutines::

Special method names

* Basic customization::
* Customizing attribute access::
* Customizing class creation::
* Customizing instance and subclass checks::
* Emulating generic types::
* Emulating callable objects::
* Emulating container types::
* Emulating numeric types::
* With Statement Context Managers::
* Special method lookup::

Customizing attribute access

* Customizing module attribute access::
* Implementing Descriptors::
* Invoking Descriptors::
* __slots__::

__slots__

* Notes on using __slots__::

Customizing class creation

* Metaclasses::
* Resolving MRO entries::
* Determining the appropriate metaclass::
* Preparing the class namespace::
* Executing the class body::
* Creating the class object::
* Uses for metaclasses::

Emulating generic types

* The purpose of __class_getitem__::
* __class_getitem__ versus __getitem__::

Coroutines

* Awaitable Objects::
* Coroutine Objects::
* Asynchronous Iterators::
* Asynchronous Context Managers::

Execution model

* Structure of a program::
* Naming and binding::
* Exceptions: Exceptions<2>.

Naming and binding

* Binding of names::
* Resolution of names::
* Builtins and restricted execution::
* Interaction with dynamic features::

The import system

* importlib: importlib<8>.
* Packages: Packages<2>.
* Searching::
* Loading::
* The Path Based Finder::
* Replacing the standard import system::
* Package Relative Imports::
* Special considerations for __main__::
* Open issues::
* References::

Packages

* Regular packages::
* Namespace packages::

Searching

* The module cache::
* Finders and loaders::
* Import hooks::
* The meta path::

Loading

* Loaders::
* Submodules::
* Module spec::
* Import-related module attributes::
* module.__path__: module __path__.
* Module reprs::
* Cached bytecode invalidation::

The Path Based Finder

* Path entry finders::
* Path entry finder protocol::

Special considerations for __main__

* __main__.__spec__: __main__ __spec__.

Expressions

* Arithmetic conversions::
* Atoms::
* Primaries::
* Await expression::
* The power operator::
* Unary arithmetic and bitwise operations::
* Binary arithmetic operations::
* Shifting operations::
* Binary bitwise operations::
* Comparisons::
* Boolean operations::
* Assignment expressions: Assignment expressions<2>.
* Conditional expressions::
* Lambdas::
* Expression lists::
* Evaluation order::
* Operator precedence::

Atoms

* Identifiers (Names): Identifiers Names.
* Literals: Literals<2>.
* Parenthesized forms::
* Displays for lists, sets and dictionaries: Displays for lists sets and dictionaries.
* List displays::
* Set displays::
* Dictionary displays::
* Generator expressions::
* Yield expressions::

Yield expressions

* Generator-iterator methods::
* Examples::
* Asynchronous generator functions::
* Asynchronous generator-iterator methods::

Primaries

* Attribute references::
* Subscriptions::
* Slicings::
* Calls::

Comparisons

* Value comparisons::
* Membership test operations::
* Identity comparisons::

Simple statements

* Expression statements::
* Assignment statements::
* The assert statement::
* The pass statement::
* The del statement: The del statement<2>.
* The return statement::
* The yield statement::
* The raise statement::
* The break statement::
* The continue statement::
* The import statement::
* The global statement::
* The nonlocal statement::

Assignment statements

* Augmented assignment statements::
* Annotated assignment statements::

The import statement

* Future statements::

Compound statements

* The if statement::
* The while statement::
* The for statement::
* The try statement::
* The with statement::
* Function definitions::
* Class definitions::
* Coroutines: Coroutines<2>.

Coroutines

* Coroutine function definition::
* The async for statement::
* The async with statement::

Top-level components

* Complete Python programs::
* File input::
* Interactive input::
* Expression input::

The Python Standard Library

* Introduction: Introduction<6>.
* Built-in Functions::
* Built-in Constants::
* Built-in Types::
* Built-in Exceptions::
* Text Processing Services::
* Binary Data Services::
* Data Types::
* Numeric and Mathematical Modules::
* Functional Programming Modules::
* File and Directory Access::
* Data Persistence::
* Data Compression and Archiving::
* File Formats::
* Cryptographic Services::
* Generic Operating System Services::
* Concurrent Execution::
* Networking and Interprocess Communication::
* Internet Data Handling::
* Structured Markup Processing Tools::
* Internet Protocols and Support::
* Multimedia Services::
* Internationalization::
* Program Frameworks::
* Graphical User Interfaces with Tk::
* Development Tools::
* Debugging and Profiling::
* Software Packaging and Distribution::
* Python Runtime Services::
* Custom Python Interpreters::
* Importing Modules::
* Python Language Services::
* Miscellaneous Services::
* MS Windows Specific Services::
* Unix Specific Services::
* Superseded Modules::
* Undocumented Modules::
* Security Considerations: Security Considerations<2>.

Introduction

* Notes on availability::

Built-in Constants

* Constants added by the site module::

Built-in Types

* Truth Value Testing::
* Boolean Operations — and, or, not: Boolean Operations — and or not.
* Comparisons: Comparisons<2>.
* Numeric Types — int, float, complex: Numeric Types — int float complex.
* Iterator Types::
* Sequence Types — list, tuple, range: Sequence Types — list tuple range.
* Text Sequence Type — str::
* Binary Sequence Types — bytes, bytearray, memoryview: Binary Sequence Types — bytes bytearray memoryview.
* Set Types — set, frozenset: Set Types — set frozenset.
* Mapping Types — dict::
* Context Manager Types::
* Generic Alias Type::
* Other Built-in Types::
* Special Attributes::

Numeric Types — int, float, complex

* Bitwise Operations on Integer Types::
* Additional Methods on Integer Types::
* Additional Methods on Float::
* Hashing of numeric types::

Iterator Types

* Generator Types::

Sequence Types — list, tuple, range

* Common Sequence Operations::
* Immutable Sequence Types::
* Mutable Sequence Types::
* Lists: Lists<2>.
* Tuples::
* Ranges::

Text Sequence Type — str

* String Methods: String Methods<2>.
* printf-style String Formatting::

Binary Sequence Types — bytes, bytearray, memoryview

* Bytes Objects::
* Bytearray Objects::
* Bytes and Bytearray Operations::
* printf-style Bytes Formatting::
* Memory Views::

Mapping Types — dict

* Dictionary view objects::

Generic Alias Type

* Standard Generic Collections::
* Special Attributes of Generic Alias::

Other Built-in Types

* Modules: Modules<2>.
* Classes and Class Instances::
* Functions::
* Methods::
* Code Objects::
* Type Objects::
* The Null Object::
* The Ellipsis Object::
* The NotImplemented Object::
* Boolean Values::
* Internal Objects::

Built-in Exceptions

* Exception context::
* Inheriting from built-in exceptions::
* Base classes::
* Concrete exceptions::
* Warnings::
* Exception hierarchy::

Concrete exceptions

* OS exceptions::

Text Processing Services

* string — Common string operations::
* re — Regular expression operations::
* difflib — Helpers for computing deltas::
* textwrap — Text wrapping and filling::
* unicodedata — Unicode Database::
* stringprep — Internet String Preparation::
* readline — GNU readline interface::
* rlcompleter — Completion function for GNU readline::

string — Common string operations

* String constants::
* Custom String Formatting::
* Format String Syntax::
* Template strings::
* Helper functions::

Format String Syntax

* Format Specification Mini-Language::
* Format examples::

re — Regular expression operations

* Regular Expression Syntax::
* Module Contents::
* Regular Expression Objects::
* Match Objects::
* Regular Expression Examples::

Regular Expression Examples

* Checking for a Pair::
* Simulating scanf(): Simulating scanf.
* search() vs. match(): search vs match.
* Making a Phonebook::
* Text Munging::
* Finding all Adverbs::
* Finding all Adverbs and their Positions::
* Raw String Notation::
* Writing a Tokenizer::

difflib — Helpers for computing deltas

* SequenceMatcher Objects::
* SequenceMatcher Examples::
* Differ Objects::
* Differ Example::
* A command-line interface to difflib::

readline — GNU readline interface

* Init file::
* Line buffer::
* History file::
* History list::
* Startup hooks::
* Completion::
* Example::

rlcompleter — Completion function for GNU readline

* Completer Objects::

Binary Data Services

* struct — Interpret bytes as packed binary data::
* codecs — Codec registry and base classes::

struct — Interpret bytes as packed binary data

* Functions and Exceptions::
* Format Strings::
* Classes: Classes<2>.

Format Strings

* Byte Order, Size, and Alignment: Byte Order Size and Alignment.
* Format Characters::
* Examples: Examples<2>.

codecs — Codec registry and base classes

* Codec Base Classes::
* Encodings and Unicode::
* Standard Encodings::
* Python Specific Encodings::
* encodings.idna — Internationalized Domain Names in Applications: encodings idna — Internationalized Domain Names in Applications.
* encodings.mbcs — Windows ANSI codepage: encodings mbcs — Windows ANSI codepage.
* encodings.utf_8_sig — UTF-8 codec with BOM signature: encodings utf_8_sig — UTF-8 codec with BOM signature.

Codec Base Classes

* Error Handlers::
* Stateless Encoding and Decoding::
* Incremental Encoding and Decoding::
* Stream Encoding and Decoding::

Incremental Encoding and Decoding

* IncrementalEncoder Objects::
* IncrementalDecoder Objects::

Stream Encoding and Decoding

* StreamWriter Objects::
* StreamReader Objects::
* StreamReaderWriter Objects::
* StreamRecoder Objects::

Python Specific Encodings

* Text Encodings::
* Binary Transforms::
* Text Transforms::

Data Types

* datetime — Basic date and time types::
* zoneinfo — IANA time zone support::
* calendar — General calendar-related functions::
* collections — Container datatypes::
* collections.abc — Abstract Base Classes for Containers: collections abc — Abstract Base Classes for Containers.
* heapq — Heap queue algorithm::
* bisect — Array bisection algorithm::
* array — Efficient arrays of numeric values::
* weakref — Weak references::
* types — Dynamic type creation and names for built-in types::
* copy — Shallow and deep copy operations::
* pprint — Data pretty printer::
* reprlib — Alternate repr() implementation: reprlib — Alternate repr implementation.
* enum — Support for enumerations::
* graphlib — Functionality to operate with graph-like structures::

datetime — Basic date and time types

* Aware and Naive Objects::
* Constants::
* Available Types::
* timedelta Objects::
* date Objects::
* datetime Objects::
* time Objects::
* tzinfo Objects::
* timezone Objects::
* strftime() and strptime() Behavior: strftime and strptime Behavior.

Available Types

* Common Properties::
* Determining if an Object is Aware or Naive::

timedelta Objects

* Examples of usage; timedelta: Examples of usage timedelta.

date Objects

* Examples of Usage; date: Examples of Usage date.

datetime Objects

* Examples of Usage; datetime: Examples of Usage datetime.

time Objects

* Examples of Usage; time: Examples of Usage time.

strftime() and strptime() Behavior

* strftime() and strptime() Format Codes: strftime and strptime Format Codes.
* Technical Detail::

zoneinfo — IANA time zone support

* Using ZoneInfo::
* Data sources::
* The ZoneInfo class::
* Functions: Functions<2>.
* Globals::
* Exceptions and warnings::

Data sources

* Configuring the data sources::

Configuring the data sources

* Compile-time configuration::
* Environment configuration::
* Runtime configuration::

The ZoneInfo class

* String representations::
* Pickle serialization::

collections — Container datatypes

* ChainMap objects::
* Counter objects::
* deque objects::
* defaultdict objects::
* namedtuple() Factory Function for Tuples with Named Fields: namedtuple Factory Function for Tuples with Named Fields.
* OrderedDict objects::
* UserDict objects::
* UserList objects::
* UserString objects::

ChainMap objects

* ChainMap Examples and Recipes::

deque objects

* deque Recipes::

defaultdict objects

* defaultdict Examples::

OrderedDict objects

* OrderedDict Examples and Recipes::

collections.abc — Abstract Base Classes for Containers

* Collections Abstract Base Classes::

heapq — Heap queue algorithm

* Basic Examples::
* Priority Queue Implementation Notes::
* Theory::

bisect — Array bisection algorithm

* Searching Sorted Lists::
* Other Examples::

weakref — Weak references

* Weak Reference Objects::
* Example: Example<2>.
* Finalizer Objects::
* Comparing finalizers with __del__() methods: Comparing finalizers with __del__ methods.

types — Dynamic type creation and names for built-in types

* Dynamic Type Creation::
* Standard Interpreter Types::
* Additional Utility Classes and Functions::
* Coroutine Utility Functions::

pprint — Data pretty printer

* PrettyPrinter Objects::
* Example: Example<3>.

reprlib — Alternate repr() implementation

* Repr Objects::
* Subclassing Repr Objects::

enum — Support for enumerations

* Module Contents: Module Contents<2>.
* Creating an Enum::
* Programmatic access to enumeration members and their attributes::
* Duplicating enum members and values::
* Ensuring unique enumeration values::
* Using automatic values::
* Iteration::
* Comparisons: Comparisons<3>.
* Allowed members and attributes of enumerations::
* Restricted Enum subclassing::
* Pickling::
* Functional API::
* Derived Enumerations::
* When to use __new__() vs. __init__(): When to use __new__ vs __init__.
* Interesting examples::
* How are Enums different?::

Derived Enumerations

* IntEnum::
* IntFlag::
* Flag::
* Others::

Interesting examples

* Omitting values::
* OrderedEnum::
* DuplicateFreeEnum::
* Planet::
* TimePeriod::

Omitting values

* Using auto::
* Using object::
* Using a descriptive string::
* Using a custom __new__(): Using a custom __new__.

How are Enums different?

* Enum Classes::
* Enum Members (aka instances): Enum Members aka instances.
* Finer Points::

Finer Points

* Supported __dunder__ names::
* Supported _sunder_ names::
* _Private__names::
* Enum member type::
* Boolean value of Enum classes and members::
* Enum classes with methods::
* Combining members of Flag::

graphlib — Functionality to operate with graph-like structures

* Exceptions: Exceptions<3>.

Numeric and Mathematical Modules

* numbers — Numeric abstract base classes::
* math — Mathematical functions::
* cmath — Mathematical functions for complex numbers::
* decimal — Decimal fixed point and floating point arithmetic::
* fractions — Rational numbers::
* random — Generate pseudo-random numbers::
* statistics — Mathematical statistics functions::

numbers — Numeric abstract base classes

* The numeric tower::
* Notes for type implementors::

Notes for type implementors

* Adding More Numeric ABCs::
* Implementing the arithmetic operations::

math — Mathematical functions

* Number-theoretic and representation functions::
* Power and logarithmic functions::
* Trigonometric functions::
* Angular conversion::
* Hyperbolic functions::
* Special functions::
* Constants: Constants<2>.

cmath — Mathematical functions for complex numbers

* Conversions to and from polar coordinates::
* Power and logarithmic functions: Power and logarithmic functions<2>.
* Trigonometric functions: Trigonometric functions<2>.
* Hyperbolic functions: Hyperbolic functions<2>.
* Classification functions::
* Constants: Constants<3>.

decimal — Decimal fixed point and floating point arithmetic

* Quick-start Tutorial::
* Decimal objects::
* Context objects::
* Constants: Constants<4>.
* Rounding modes::
* Signals::
* Floating Point Notes::
* Working with threads::
* Recipes::
* Decimal FAQ::

Decimal objects

* Logical operands::

Floating Point Notes

* Mitigating round-off error with increased precision::
* Special values::

random — Generate pseudo-random numbers

* Bookkeeping functions::
* Functions for bytes::
* Functions for integers::
* Functions for sequences::
* Real-valued distributions::
* Alternative Generator::
* Notes on Reproducibility::
* Examples: Examples<3>.
* Recipes: Recipes<2>.

statistics — Mathematical statistics functions

* Averages and measures of central location::
* Measures of spread::
* Function details::
* Exceptions: Exceptions<4>.
* NormalDist objects::

NormalDist objects

* NormalDist Examples and Recipes::

Functional Programming Modules

* itertools — Functions creating iterators for efficient looping::
* functools — Higher-order functions and operations on callable objects::
* operator — Standard operators as functions::

itertools — Functions creating iterators for efficient looping

* Itertool functions::
* Itertools Recipes::

functools — Higher-order functions and operations on callable objects

* partial Objects::

operator — Standard operators as functions

* Mapping Operators to Functions::
* In-place Operators::

File and Directory Access

* pathlib — Object-oriented filesystem paths::
* os.path — Common pathname manipulations: os path — Common pathname manipulations.
* fileinput — Iterate over lines from multiple input streams::
* stat — Interpreting stat() results: stat — Interpreting stat results.
* filecmp — File and Directory Comparisons::
* tempfile — Generate temporary files and directories::
* glob — Unix style pathname pattern expansion::
* fnmatch — Unix filename pattern matching::
* linecache — Random access to text lines::
* shutil — High-level file operations::

pathlib — Object-oriented filesystem paths

* Basic use::
* Pure paths::
* Concrete paths::
* Correspondence to tools in the os module::

Pure paths

* General properties::
* Operators: Operators<2>.
* Accessing individual parts::
* Methods and properties::

Concrete paths

* Methods: Methods<2>.

filecmp — File and Directory Comparisons

* The dircmp class::

tempfile — Generate temporary files and directories

* Examples: Examples<4>.
* Deprecated functions and variables::

shutil — High-level file operations

* Directory and files operations::
* Archiving operations::
* Querying the size of the output terminal::

Directory and files operations

* Platform-dependent efficient copy operations::
* copytree example::
* rmtree example::

Archiving operations

* Archiving example::
* Archiving example with base_dir::

Data Persistence

* pickle — Python object serialization::
* copyreg — Register pickle support functions::
* shelve — Python object persistence::
* marshal — Internal Python object serialization::
* dbm — Interfaces to Unix “databases”::
* sqlite3 — DB-API 2.0 interface for SQLite databases: sqlite3 — DB-API 2 0 interface for SQLite databases.

pickle — Python object serialization

* Relationship to other Python modules::
* Data stream format::
* Module Interface::
* What can be pickled and unpickled?::
* Pickling Class Instances::
* Custom Reduction for Types, Functions, and Other Objects: Custom Reduction for Types Functions and Other Objects.
* Out-of-band Buffers::
* Restricting Globals::
* Performance: Performance<2>.
* Examples: Examples<5>.

Relationship to other Python modules

* Comparison with marshal::
* Comparison with json::

Pickling Class Instances

* Persistence of External Objects::
* Dispatch Tables::
* Handling Stateful Objects::

Out-of-band Buffers

* Provider API::
* Consumer API::
* Example: Example<4>.

copyreg — Register pickle support functions

* Example: Example<5>.

shelve — Python object persistence

* Restrictions::
* Example: Example<6>.

dbm — Interfaces to Unix “databases”

* dbm.gnu — GNU’s reinterpretation of dbm: dbm gnu — GNU’s reinterpretation of dbm.
* dbm.ndbm — Interface based on ndbm: dbm ndbm — Interface based on ndbm.
* dbm.dumb — Portable DBM implementation: dbm dumb — Portable DBM implementation.

sqlite3 — DB-API 2.0 interface for SQLite databases

* Module functions and constants::
* Connection Objects::
* Cursor Objects::
* Row Objects::
* Exceptions: Exceptions<5>.
* SQLite and Python types::
* Controlling Transactions::
* Using sqlite3 efficiently::

SQLite and Python types

* Introduction: Introduction<7>.
* Using adapters to store additional Python types in SQLite databases::
* Converting SQLite values to custom Python types::
* Default adapters and converters::

Using adapters to store additional Python types in SQLite databases

* Letting your object adapt itself::
* Registering an adapter callable::

Using sqlite3 efficiently

* Using shortcut methods::
* Accessing columns by name instead of by index::
* Using the connection as a context manager::

Data Compression and Archiving

* zlib — Compression compatible with gzip::
* gzip — Support for gzip files::
* bz2 — Support for bzip2 compression::
* lzma — Compression using the LZMA algorithm::
* zipfile — Work with ZIP archives::
* tarfile — Read and write tar archive files::

gzip — Support for gzip files

* Examples of usage::
* Command Line Interface::

Command Line Interface

* Command line options::

bz2 — Support for bzip2 compression

* (De)compression of files: De compression of files.
* Incremental (de)compression: Incremental de compression.
* One-shot (de)compression: One-shot de compression.
* Examples of usage: Examples of usage<2>.

lzma — Compression using the LZMA algorithm

* Reading and writing compressed files::
* Compressing and decompressing data in memory::
* Miscellaneous: Miscellaneous<2>.
* Specifying custom filter chains::
* Examples: Examples<6>.

zipfile — Work with ZIP archives

* ZipFile Objects::
* Path Objects::
* PyZipFile Objects::
* ZipInfo Objects::
* Command-Line Interface::
* Decompression pitfalls::

Command-Line Interface

* Command-line options::

Decompression pitfalls

* From file itself::
* File System limitations::
* Resources limitations::
* Interruption::
* Default behaviors of extraction::

tarfile — Read and write tar archive files

* TarFile Objects::
* TarInfo Objects::
* Command-Line Interface: Command-Line Interface<2>.
* Examples: Examples<7>.
* Supported tar formats::
* Unicode issues::

Command-Line Interface

* Command-line options: Command-line options<2>.

File Formats

* csv — CSV File Reading and Writing::
* configparser — Configuration file parser::
* netrc — netrc file processing::
* xdrlib — Encode and decode XDR data::
* plistlib — Generate and parse Apple .plist files: plistlib — Generate and parse Apple plist files.

csv — CSV File Reading and Writing

* Module Contents: Module Contents<3>.
* Dialects and Formatting Parameters::
* Reader Objects::
* Writer Objects::
* Examples: Examples<8>.

configparser — Configuration file parser

* Quick Start::
* Supported Datatypes::
* Fallback Values::
* Supported INI File Structure::
* Interpolation of values::
* Mapping Protocol Access::
* Customizing Parser Behaviour::
* Legacy API Examples::
* ConfigParser Objects::
* RawConfigParser Objects::
* Exceptions: Exceptions<6>.

netrc — netrc file processing

* netrc Objects::

xdrlib — Encode and decode XDR data

* Packer Objects::
* Unpacker Objects::
* Exceptions: Exceptions<7>.

plistlib — Generate and parse Apple .plist files

* Examples: Examples<9>.

Cryptographic Services

* hashlib — Secure hashes and message digests::
* hmac — Keyed-Hashing for Message Authentication::
* secrets — Generate secure random numbers for managing secrets::

hashlib — Secure hashes and message digests

* Hash algorithms::
* SHAKE variable length digests::
* Key derivation::
* BLAKE2::

BLAKE2

* Creating hash objects::
* Constants: Constants<5>.
* Examples: Examples<10>.
* Credits::

Examples

* Simple hashing::
* Using different digest sizes::
* Keyed hashing::
* Randomized hashing::
* Personalization::
* Tree mode::

secrets — Generate secure random numbers for managing secrets

* Random numbers::
* Generating tokens::
* Other functions::
* Recipes and best practices::

Generating tokens

* How many bytes should tokens use?::

Generic Operating System Services

* os — Miscellaneous operating system interfaces::
* io — Core tools for working with streams::
* time — Time access and conversions::
* argparse — Parser for command-line options, arguments and sub-commands: argparse — Parser for command-line options arguments and sub-commands.
* getopt — C-style parser for command line options::
* logging — Logging facility for Python::
* logging.config — Logging configuration: logging config — Logging configuration.
* logging.handlers — Logging handlers: logging handlers — Logging handlers.
* getpass — Portable password input::
* curses — Terminal handling for character-cell displays::
* curses.textpad — Text input widget for curses programs: curses textpad — Text input widget for curses programs.
* curses.ascii — Utilities for ASCII characters: curses ascii — Utilities for ASCII characters.
* curses.panel — A panel stack extension for curses: curses panel — A panel stack extension for curses.
* platform — Access to underlying platform’s identifying data::
* errno — Standard errno system symbols::
* ctypes — A foreign function library for Python::

os — Miscellaneous operating system interfaces

* File Names, Command Line Arguments, and Environment Variables: File Names Command Line Arguments and Environment Variables.
* Process Parameters::
* File Object Creation::
* File Descriptor Operations::
* Files and Directories::
* Process Management::
* Interface to the scheduler::
* Miscellaneous System Information::
* Random numbers: Random numbers<2>.

File Descriptor Operations

* Querying the size of a terminal::
* Inheritance of File Descriptors::

Files and Directories

* Linux extended attributes::

io — Core tools for working with streams

* Overview::
* High-level Module Interface::
* Class hierarchy::
* Performance: Performance<3>.

Overview

* Text I/O::
* Binary I/O::
* Raw I/O::

Class hierarchy

* I/O Base Classes::
* Raw File I/O::
* Buffered Streams::
* Text I/O: Text I/O<2>.

Performance

* Binary I/O: Binary I/O<2>.
* Text I/O: Text I/O<3>.
* Multi-threading: Multi-threading<3>.
* Reentrancy::

time — Time access and conversions

* Functions: Functions<3>.
* Clock ID Constants::
* Timezone Constants::

argparse — Parser for command-line options, arguments and sub-commands

* Example: Example<7>.
* ArgumentParser objects::
* The add_argument() method: The add_argument method.
* The parse_args() method: The parse_args method.
* Other utilities::
* Upgrading optparse code::

Example

* Creating a parser::
* Adding arguments::
* Parsing arguments::

ArgumentParser objects

* prog::
* usage::
* description::
* epilog::
* parents::
* formatter_class::
* prefix_chars::
* fromfile_prefix_chars::
* argument_default::
* allow_abbrev::
* conflict_handler::
* add_help::
* exit_on_error::

The add_argument() method

* name or flags::
* action::
* nargs::
* const::
* default::
* type::
* choices::
* required::
* help::
* metavar::
* dest::
* Action classes::

The parse_args() method

* Option value syntax::
* Invalid arguments::
* Arguments containing -::
* Argument abbreviations (prefix matching): Argument abbreviations prefix matching.
* Beyond sys.argv: Beyond sys argv.
* The Namespace object::

Other utilities

* Sub-commands::
* FileType objects::
* Argument groups::
* Mutual exclusion::
* Parser defaults::
* Printing help::
* Partial parsing::
* Customizing file parsing::
* Exiting methods::
* Intermixed parsing::

logging — Logging facility for Python

* Logger Objects::
* Logging Levels::
* Handler Objects::
* Formatter Objects::
* Filter Objects::
* LogRecord Objects::
* LogRecord attributes::
* LoggerAdapter Objects::
* Thread Safety::
* Module-Level Functions::
* Module-Level Attributes::
* Integration with the warnings module::

logging.config — Logging configuration

* Configuration functions::
* Security considerations::
* Configuration dictionary schema::
* Configuration file format::

Configuration dictionary schema

* Dictionary Schema Details::
* Incremental Configuration::
* Object connections::
* User-defined objects::
* Access to external objects::
* Access to internal objects::
* Import resolution and custom importers::

logging.handlers — Logging handlers

* StreamHandler::
* FileHandler::
* NullHandler::
* WatchedFileHandler::
* BaseRotatingHandler::
* RotatingFileHandler::
* TimedRotatingFileHandler::
* SocketHandler::
* DatagramHandler::
* SysLogHandler::
* NTEventLogHandler::
* SMTPHandler::
* MemoryHandler::
* HTTPHandler::
* QueueHandler::
* QueueListener::

curses — Terminal handling for character-cell displays

* Functions: Functions<4>.
* Window Objects::
* Constants: Constants<6>.

curses.textpad — Text input widget for curses programs

* Textbox objects::

curses.panel — A panel stack extension for curses

* Functions: Functions<5>.
* Panel Objects::

platform —  Access to underlying platform’s identifying data

* Cross Platform::
* Java Platform::
* Windows Platform::
* macOS Platform::
* Unix Platforms::

ctypes — A foreign function library for Python

* ctypes tutorial::
* ctypes reference::

ctypes tutorial

* Loading dynamic link libraries::
* Accessing functions from loaded dlls::
* Calling functions::
* Fundamental data types::
* Calling functions, continued: Calling functions continued.
* Calling functions with your own custom data types::
* Specifying the required argument types (function prototypes): Specifying the required argument types function prototypes.
* Return types::
* Passing pointers (or; passing parameters by reference): Passing pointers or passing parameters by reference.
* Structures and unions::
* Structure/union alignment and byte order::
* Bit fields in structures and unions::
* Arrays::
* Pointers::
* Type conversions::
* Incomplete Types::
* Callback functions::
* Accessing values exported from dlls::
* Surprises::
* Variable-sized data types::

ctypes reference

* Finding shared libraries::
* Loading shared libraries::
* Foreign functions::
* Function prototypes::
* Utility functions::
* Data types::
* Fundamental data types: Fundamental data types<2>.
* Structured data types::
* Arrays and pointers::

Concurrent Execution

* threading — Thread-based parallelism::
* multiprocessing — Process-based parallelism::
* multiprocessing.shared_memory — Provides shared memory for direct access across processes: multiprocessing shared_memory — Provides shared memory for direct access across processes.
* The concurrent package::
* concurrent.futures — Launching parallel tasks: concurrent futures — Launching parallel tasks.
* subprocess — Subprocess management::
* sched — Event scheduler::
* queue — A synchronized queue class::
* contextvars — Context Variables::
* _thread — Low-level threading API::

threading — Thread-based parallelism

* Thread-Local Data::
* Thread Objects::
* Lock Objects::
* RLock Objects::
* Condition Objects::
* Semaphore Objects::
* Event Objects::
* Timer Objects::
* Barrier Objects::
* Using locks, conditions, and semaphores in the with statement: Using locks conditions and semaphores in the with statement.

Semaphore Objects

* Semaphore Example::

multiprocessing — Process-based parallelism

* Introduction: Introduction<8>.
* Reference::
* Programming guidelines::
* Examples: Examples<11>.

Introduction

* The Process class::
* Contexts and start methods::
* Exchanging objects between processes::
* Synchronization between processes::
* Sharing state between processes::
* Using a pool of workers::

Reference

* Process and exceptions::
* Pipes and Queues::
* Miscellaneous: Miscellaneous<3>.
* Connection Objects: Connection Objects<2>.
* Synchronization primitives::
* Shared ctypes Objects::
* Managers::
* Proxy Objects::
* Process Pools::
* Listeners and Clients::
* Authentication keys::
* Logging: Logging<2>.
* The multiprocessing.dummy module: The multiprocessing dummy module.

Shared ctypes Objects

* The multiprocessing.sharedctypes module: The multiprocessing sharedctypes module.

Managers

* Customized managers::
* Using a remote manager::

Proxy Objects

* Cleanup::

Listeners and Clients

* Address Formats::

Programming guidelines

* All start methods::
* The spawn and forkserver start methods::

concurrent.futures — Launching parallel tasks

* Executor Objects::
* ThreadPoolExecutor::
* ProcessPoolExecutor::
* Future Objects::
* Module Functions::
* Exception classes::

ThreadPoolExecutor

* ThreadPoolExecutor Example::

ProcessPoolExecutor

* ProcessPoolExecutor Example::

subprocess — Subprocess management

* Using the subprocess Module::
* Security Considerations::
* Popen Objects::
* Windows Popen Helpers::
* Older high-level API::
* Replacing Older Functions with the subprocess Module::
* Legacy Shell Invocation Functions::
* Notes::

Using the subprocess Module

* Frequently Used Arguments::
* Popen Constructor::
* Exceptions: Exceptions<8>.

Windows Popen Helpers

* Windows Constants::

Replacing Older Functions with the subprocess Module

* Replacing /bin/sh shell command substitution::
* Replacing shell pipeline::
* Replacing os.system(): Replacing os system.
* Replacing the os.spawn family: Replacing the os spawn family.
* Replacing os.popen(), os.popen2(), os.popen3(): Replacing os popen os popen2 os popen3.
* Replacing functions from the popen2 module::

Notes

* Converting an argument sequence to a string on Windows::

sched — Event scheduler

* Scheduler Objects::

queue — A synchronized queue class

* Queue Objects::
* SimpleQueue Objects::

contextvars — Context Variables

* Context Variables::
* Manual Context Management::
* asyncio support::

Networking and Interprocess Communication

* asyncio — Asynchronous I/O::
* socket — Low-level networking interface::
* ssl — TLS/SSL wrapper for socket objects::
* select — Waiting for I/O completion::
* selectors — High-level I/O multiplexing::
* asyncore — Asynchronous socket handler::
* asynchat — Asynchronous socket command/response handler::
* signal — Set handlers for asynchronous events::
* mmap — Memory-mapped file support::

asyncio — Asynchronous I/O

* Coroutines and Tasks::
* Streams::
* Synchronization Primitives::
* Subprocesses::
* Queues::
* Exceptions: Exceptions<10>.
* Event Loop::
* Futures::
* Transports and Protocols::
* Policies::
* Platform Support::
* High-level API Index::
* Low-level API Index::
* Developing with asyncio::

Coroutines and Tasks

* Coroutines: Coroutines<3>.
* Awaitables::
* Running an asyncio Program::
* Creating Tasks::
* Sleeping::
* Running Tasks Concurrently::
* Shielding From Cancellation::
* Timeouts::
* Waiting Primitives::
* Running in Threads::
* Scheduling From Other Threads::
* Introspection::
* Task Object::
* Generator-based Coroutines::

Streams

* StreamReader::
* StreamWriter::
* Examples: Examples<12>.

Examples

* TCP echo client using streams::
* TCP echo server using streams::
* Get HTTP headers::
* Register an open socket to wait for data using streams::

Synchronization Primitives

* Lock::
* Event::
* Condition::
* Semaphore::
* BoundedSemaphore::

Subprocesses

* Creating Subprocesses::
* Constants: Constants<7>.
* Interacting with Subprocesses::

Interacting with Subprocesses

* Subprocess and Threads::
* Examples: Examples<13>.

Queues

* Queue::
* Priority Queue::
* LIFO Queue::
* Exceptions: Exceptions<9>.
* Examples: Examples<14>.

Event Loop

* Event Loop Methods::
* Callback Handles::
* Server Objects::
* Event Loop Implementations::
* Examples: Examples<15>.

Event Loop Methods

* Running and stopping the loop::
* Scheduling callbacks::
* Scheduling delayed callbacks::
* Creating Futures and Tasks::
* Opening network connections::
* Creating network servers::
* Transferring files::
* TLS Upgrade::
* Watching file descriptors::
* Working with socket objects directly::
* DNS::
* Working with pipes::
* Unix signals::
* Executing code in thread or process pools::
* Error Handling API::
* Enabling debug mode::
* Running Subprocesses::

Examples

* Hello World with call_soon(): Hello World with call_soon.
* Display the current date with call_later(): Display the current date with call_later.
* Watch a file descriptor for read events::
* Set signal handlers for SIGINT and SIGTERM::

Futures

* Future Functions::
* Future Object::

Transports and Protocols

* Transports::
* Protocols::
* Examples: Examples<16>.

Transports

* Transports Hierarchy::
* Base Transport::
* Read-only Transports::
* Write-only Transports::
* Datagram Transports::
* Subprocess Transports::

Protocols

* Base Protocols::
* Base Protocol::
* Streaming Protocols::
* Buffered Streaming Protocols::
* Datagram Protocols::
* Subprocess Protocols::

Examples

* TCP Echo Server::
* TCP Echo Client::
* UDP Echo Server::
* UDP Echo Client::
* Connecting Existing Sockets::
* loop.subprocess_exec() and SubprocessProtocol: loop subprocess_exec and SubprocessProtocol.

Policies

* Getting and Setting the Policy::
* Policy Objects::
* Process Watchers::
* Custom Policies::

Platform Support

* All Platforms::
* Windows: Windows<55>.
* macOS: macOS<30>.

Windows

* Subprocess Support on Windows::

High-level API Index

* Tasks::
* Queues: Queues<2>.
* Subprocesses: Subprocesses<2>.
* Streams: Streams<2>.
* Synchronization::
* Exceptions: Exceptions<11>.

Low-level API Index

* Obtaining the Event Loop::
* Event Loop Methods: Event Loop Methods<2>.
* Transports: Transports<2>.
* Protocols: Protocols<2>.
* Event Loop Policies::

Developing with asyncio

* Debug Mode::
* Concurrency and Multithreading::
* Running Blocking Code::
* Logging: Logging<3>.
* Detect never-awaited coroutines::
* Detect never-retrieved exceptions::

socket — Low-level networking interface

* Socket families::
* Module contents::
* Socket Objects::
* Notes on socket timeouts::
* Example: Example<8>.

Module contents

* Exceptions: Exceptions<12>.
* Constants: Constants<8>.
* Functions: Functions<6>.

Functions

* Creating sockets::
* Other functions: Other functions<2>.

Notes on socket timeouts

* Timeouts and the connect method::
* Timeouts and the accept method::

ssl — TLS/SSL wrapper for socket objects

* Functions, Constants, and Exceptions: Functions Constants and Exceptions.
* SSL Sockets::
* SSL Contexts::
* Certificates::
* Examples: Examples<17>.
* Notes on non-blocking sockets::
* Memory BIO Support: Memory BIO Support<2>.
* SSL session::
* Security considerations: Security considerations<2>.
* TLS 1.3: TLS 1 3.
* LibreSSL support::

Functions, Constants, and Exceptions

* Socket creation::
* Context creation::
* Exceptions: Exceptions<13>.
* Random generation::
* Certificate handling::
* Constants: Constants<9>.

Certificates

* Certificate chains::
* CA certificates::
* Combined key and certificate::
* Self-signed certificates::

Examples

* Testing for SSL support::
* Client-side operation::
* Server-side operation::

Security considerations

* Best defaults::
* Manual settings::
* Multi-processing::

Manual settings

* Verifying certificates::
* Protocol versions::
* Cipher selection::

select — Waiting for I/O completion

* /dev/poll Polling Objects::
* Edge and Level Trigger Polling (epoll) Objects: Edge and Level Trigger Polling epoll Objects.
* Polling Objects::
* Kqueue Objects::
* Kevent Objects::

selectors — High-level I/O multiplexing

* Introduction: Introduction<9>.
* Classes: Classes<3>.
* Examples: Examples<18>.

asyncore — Asynchronous socket handler

* asyncore Example basic HTTP client::
* asyncore Example basic echo server::

asynchat — Asynchronous socket command/response handler

* asynchat Example::

signal — Set handlers for asynchronous events

* General rules::
* Module contents: Module contents<2>.
* Example: Example<9>.
* Note on SIGPIPE::

General rules

* Execution of Python signal handlers::
* Signals and threads::

mmap — Memory-mapped file support

* MADV_* Constants::

Internet Data Handling

* email — An email and MIME handling package::
* json — JSON encoder and decoder::
* mailcap — Mailcap file handling::
* mailbox — Manipulate mailboxes in various formats::
* mimetypes — Map filenames to MIME types::
* base64 — Base16, Base32, Base64, Base85 Data Encodings: base64 — Base16 Base32 Base64 Base85 Data Encodings.
* binhex — Encode and decode binhex4 files::
* binascii — Convert between binary and ASCII::
* quopri — Encode and decode MIME quoted-printable data::
* uu — Encode and decode uuencode files::

email — An email and MIME handling package

* email.message; Representing an email message: email message Representing an email message.
* email.parser; Parsing email messages: email parser Parsing email messages.
* email.generator; Generating MIME documents: email generator Generating MIME documents.
* email.policy; Policy Objects: email policy Policy Objects.
* email.errors; Exception and Defect classes: email errors Exception and Defect classes.
* email.headerregistry; Custom Header Objects: email headerregistry Custom Header Objects.
* email.contentmanager; Managing MIME Content: email contentmanager Managing MIME Content.
* email; Examples: email Examples.
* email.message.Message; Representing an email message using the compat32 API: email message Message Representing an email message using the compat32 API.
* email.mime; Creating email and MIME objects from scratch: email mime Creating email and MIME objects from scratch.
* email.header; Internationalized headers: email header Internationalized headers.
* email.charset; Representing character sets: email charset Representing character sets.
* email.encoders; Encoders: email encoders Encoders.
* email.utils; Miscellaneous utilities: email utils Miscellaneous utilities.
* email.iterators; Iterators: email iterators Iterators.

email.parser: Parsing email messages

* FeedParser API::
* Parser API::
* Additional notes::

email.contentmanager: Managing MIME Content

* Content Manager Instances::

json — JSON encoder and decoder

* Basic Usage::
* Encoders and Decoders::
* Exceptions: Exceptions<14>.
* Standard Compliance and Interoperability::
* Command Line Interface: Command Line Interface<2>.

Standard Compliance and Interoperability

* Character Encodings::
* Infinite and NaN Number Values::
* Repeated Names Within an Object::
* Top-level Non-Object, Non-Array Values: Top-level Non-Object Non-Array Values.
* Implementation Limitations::

Command Line Interface

* Command line options: Command line options<2>.

mailbox — Manipulate mailboxes in various formats

* Mailbox objects::
* Message objects::
* Exceptions: Exceptions<15>.
* Examples: Examples<19>.

Mailbox objects

* Maildir::
* mbox::
* MH::
* Babyl::
* MMDF::

Message objects

* MaildirMessage::
* mboxMessage::
* MHMessage::
* BabylMessage::
* MMDFMessage::

mimetypes — Map filenames to MIME types

* MimeTypes Objects::

binhex — Encode and decode binhex4 files

* Notes: Notes<2>.

Structured Markup Processing Tools

* html — HyperText Markup Language support::
* html.parser — Simple HTML and XHTML parser: html parser — Simple HTML and XHTML parser.
* html.entities — Definitions of HTML general entities: html entities — Definitions of HTML general entities.
* XML Processing Modules::
* xml.etree.ElementTree — The ElementTree XML API: xml etree ElementTree — The ElementTree XML API.
* xml.dom — The Document Object Model API: xml dom — The Document Object Model API.
* xml.dom.minidom — Minimal DOM implementation: xml dom minidom — Minimal DOM implementation.
* xml.dom.pulldom — Support for building partial DOM trees: xml dom pulldom — Support for building partial DOM trees.
* xml.sax — Support for SAX2 parsers: xml sax — Support for SAX2 parsers.
* xml.sax.handler — Base classes for SAX handlers: xml sax handler — Base classes for SAX handlers.
* xml.sax.saxutils — SAX Utilities: xml sax saxutils — SAX Utilities.
* xml.sax.xmlreader — Interface for XML parsers: xml sax xmlreader — Interface for XML parsers.
* xml.parsers.expat — Fast XML parsing using Expat: xml parsers expat — Fast XML parsing using Expat.

html.parser — Simple HTML and XHTML parser

* Example HTML Parser Application::
* HTMLParser Methods::
* Examples: Examples<20>.

XML Processing Modules

* XML vulnerabilities::
* The defusedxml Package::

xml.etree.ElementTree — The ElementTree XML API

* Tutorial::
* XPath support::
* Reference: Reference<2>.
* XInclude support::
* Reference: Reference<3>.

Tutorial

* XML tree and elements::
* Parsing XML::
* Pull API for non-blocking parsing::
* Finding interesting elements::
* Modifying an XML File::
* Building XML documents::
* Parsing XML with Namespaces::
* Additional resources::

XPath support

* Example: Example<10>.
* Supported XPath syntax::

Reference

* Functions: Functions<7>.

XInclude support

* Example: Example<11>.

Reference

* Functions: Functions<8>.
* Element Objects::
* ElementTree Objects::
* QName Objects::
* TreeBuilder Objects::
* XMLParser Objects::
* XMLPullParser Objects::
* Exceptions: Exceptions<16>.

xml.dom — The Document Object Model API

* Module Contents: Module Contents<4>.
* Objects in the DOM::
* Conformance::

Objects in the DOM

* DOMImplementation Objects::
* Node Objects::
* NodeList Objects::
* DocumentType Objects::
* Document Objects::
* Element Objects: Element Objects<2>.
* Attr Objects::
* NamedNodeMap Objects::
* Comment Objects::
* Text and CDATASection Objects::
* ProcessingInstruction Objects::
* Exceptions: Exceptions<17>.

Conformance

* Type Mapping::
* Accessor Methods::

xml.dom.minidom — Minimal DOM implementation

* DOM Objects::
* DOM Example::
* minidom and the DOM standard::

xml.dom.pulldom — Support for building partial DOM trees

* DOMEventStream Objects::

xml.sax — Support for SAX2 parsers

* SAXException Objects::

xml.sax.handler — Base classes for SAX handlers

* ContentHandler Objects::
* DTDHandler Objects::
* EntityResolver Objects::
* ErrorHandler Objects::

xml.sax.xmlreader — Interface for XML parsers

* XMLReader Objects::
* IncrementalParser Objects::
* Locator Objects::
* InputSource Objects::
* The Attributes Interface::
* The AttributesNS Interface::

xml.parsers.expat — Fast XML parsing using Expat

* XMLParser Objects: XMLParser Objects<2>.
* ExpatError Exceptions::
* Example: Example<12>.
* Content Model Descriptions::
* Expat error constants::

Internet Protocols and Support

* webbrowser — Convenient Web-browser controller::
* cgi — Common Gateway Interface support::
* cgitb — Traceback manager for CGI scripts::
* wsgiref — WSGI Utilities and Reference Implementation::
* urllib — URL handling modules::
* urllib.request — Extensible library for opening URLs: urllib request — Extensible library for opening URLs.
* urllib.response — Response classes used by urllib: urllib response — Response classes used by urllib.
* urllib.parse — Parse URLs into components: urllib parse — Parse URLs into components.
* urllib.error — Exception classes raised by urllib.request: urllib error — Exception classes raised by urllib request.
* urllib.robotparser — Parser for robots.txt: urllib robotparser — Parser for robots txt.
* http — HTTP modules::
* http.client — HTTP protocol client: http client — HTTP protocol client.
* ftplib — FTP protocol client::
* poplib — POP3 protocol client::
* imaplib — IMAP4 protocol client::
* nntplib — NNTP protocol client::
* smtplib — SMTP protocol client::
* smtpd — SMTP Server::
* telnetlib — Telnet client::
* uuid — UUID objects according to RFC 4122::
* socketserver — A framework for network servers::
* http.server — HTTP servers: http server — HTTP servers.
* http.cookies — HTTP state management: http cookies — HTTP state management.
* http.cookiejar — Cookie handling for HTTP clients: http cookiejar — Cookie handling for HTTP clients.
* xmlrpc — XMLRPC server and client modules::
* xmlrpc.client — XML-RPC client access: xmlrpc client — XML-RPC client access.
* xmlrpc.server — Basic XML-RPC servers: xmlrpc server — Basic XML-RPC servers.
* ipaddress — IPv4/IPv6 manipulation library::

webbrowser — Convenient Web-browser controller

* Browser Controller Objects::

cgi — Common Gateway Interface support

* Introduction: Introduction<10>.
* Using the cgi module::
* Higher Level Interface::
* Functions: Functions<9>.
* Caring about security::
* Installing your CGI script on a Unix system::
* Testing your CGI script::
* Debugging CGI scripts::
* Common problems and solutions::

wsgiref — WSGI Utilities and Reference Implementation

* wsgiref.util – WSGI environment utilities: wsgiref util – WSGI environment utilities.
* wsgiref.headers – WSGI response header tools: wsgiref headers – WSGI response header tools.
* wsgiref.simple_server – a simple WSGI HTTP server: wsgiref simple_server – a simple WSGI HTTP server.
* wsgiref.validate — WSGI conformance checker: wsgiref validate — WSGI conformance checker.
* wsgiref.handlers – server/gateway base classes: wsgiref handlers – server/gateway base classes.
* Examples: Examples<21>.

urllib.request — Extensible library for opening URLs

* Request Objects::
* OpenerDirector Objects::
* BaseHandler Objects::
* HTTPRedirectHandler Objects::
* HTTPCookieProcessor Objects::
* ProxyHandler Objects::
* HTTPPasswordMgr Objects::
* HTTPPasswordMgrWithPriorAuth Objects::
* AbstractBasicAuthHandler Objects::
* HTTPBasicAuthHandler Objects::
* ProxyBasicAuthHandler Objects::
* AbstractDigestAuthHandler Objects::
* HTTPDigestAuthHandler Objects::
* ProxyDigestAuthHandler Objects::
* HTTPHandler Objects::
* HTTPSHandler Objects::
* FileHandler Objects::
* DataHandler Objects::
* FTPHandler Objects::
* CacheFTPHandler Objects::
* UnknownHandler Objects::
* HTTPErrorProcessor Objects::
* Examples: Examples<22>.
* Legacy interface::
* urllib.request Restrictions: urllib request Restrictions.

urllib.parse — Parse URLs into components

* URL Parsing::
* Parsing ASCII Encoded Bytes::
* Structured Parse Results::
* URL Quoting::

http — HTTP modules

* HTTP status codes::

http.client — HTTP protocol client

* HTTPConnection Objects::
* HTTPResponse Objects::
* Examples: Examples<23>.
* HTTPMessage Objects::

ftplib — FTP protocol client

* FTP Objects::
* FTP_TLS Objects::

poplib — POP3 protocol client

* POP3 Objects::
* POP3 Example::

imaplib — IMAP4 protocol client

* IMAP4 Objects::
* IMAP4 Example::

nntplib — NNTP protocol client

* NNTP Objects::
* Utility functions: Utility functions<2>.

NNTP Objects

* Attributes::
* Methods: Methods<3>.

smtplib — SMTP protocol client

* SMTP Objects::
* SMTP Example::

smtpd — SMTP Server

* SMTPServer Objects::
* DebuggingServer Objects::
* PureProxy Objects::
* MailmanProxy Objects::
* SMTPChannel Objects::

telnetlib — Telnet client

* Telnet Objects::
* Telnet Example::

uuid — UUID objects according to RFC 4122

* Example: Example<13>.

socketserver — A framework for network servers

* Server Creation Notes::
* Server Objects: Server Objects<2>.
* Request Handler Objects::
* Examples: Examples<24>.

Examples

* socketserver.TCPServer Example: socketserver TCPServer Example.
* socketserver.UDPServer Example: socketserver UDPServer Example.
* Asynchronous Mixins::

http.cookies — HTTP state management

* Cookie Objects::
* Morsel Objects::
* Example: Example<14>.

http.cookiejar — Cookie handling for HTTP clients

* CookieJar and FileCookieJar Objects::
* FileCookieJar subclasses and co-operation with web browsers::
* CookiePolicy Objects::
* DefaultCookiePolicy Objects::
* Cookie Objects: Cookie Objects<2>.
* Examples: Examples<25>.

xmlrpc.client — XML-RPC client access

* ServerProxy Objects::
* DateTime Objects::
* Binary Objects::
* Fault Objects::
* ProtocolError Objects::
* MultiCall Objects::
* Convenience Functions::
* Example of Client Usage::
* Example of Client and Server Usage::

xmlrpc.server — Basic XML-RPC servers

* SimpleXMLRPCServer Objects::
* CGIXMLRPCRequestHandler::
* Documenting XMLRPC server::
* DocXMLRPCServer Objects::
* DocCGIXMLRPCRequestHandler::

SimpleXMLRPCServer Objects

* SimpleXMLRPCServer Example::

ipaddress — IPv4/IPv6 manipulation library

* Convenience factory functions::
* IP Addresses::
* IP Network definitions::
* Interface objects::
* Other Module Level Functions::
* Custom Exceptions::

IP Addresses

* Address objects::
* Conversion to Strings and Integers::
* Operators: Operators<3>.

Operators

* Comparison operators::
* Arithmetic operators::

IP Network definitions

* Prefix, net mask and host mask: Prefix net mask and host mask.
* Network objects::
* Operators: Operators<4>.

Operators

* Logical operators::
* Iteration: Iteration<2>.
* Networks as containers of addresses::

Interface objects

* Operators: Operators<5>.

Operators

* Logical operators: Logical operators<2>.

Multimedia Services

* audioop — Manipulate raw audio data::
* aifc — Read and write AIFF and AIFC files::
* sunau — Read and write Sun AU files::
* wave — Read and write WAV files::
* chunk — Read IFF chunked data::
* colorsys — Conversions between color systems::
* imghdr — Determine the type of an image::
* sndhdr — Determine type of sound file::
* ossaudiodev — Access to OSS-compatible audio devices::

sunau — Read and write Sun AU files

* AU_read Objects::
* AU_write Objects::

wave — Read and write WAV files

* Wave_read Objects::
* Wave_write Objects::

ossaudiodev — Access to OSS-compatible audio devices

* Audio Device Objects::
* Mixer Device Objects::

Internationalization

* gettext — Multilingual internationalization services::
* locale — Internationalization services::

gettext — Multilingual internationalization services

* GNU gettext API::
* Class-based API::
* Internationalizing your programs and modules::
* Acknowledgements: Acknowledgements<9>.

Class-based API

* The NullTranslations class::
* The GNUTranslations class::
* Solaris message catalog support::
* The Catalog constructor::

Internationalizing your programs and modules

* Localizing your module::
* Localizing your application::
* Changing languages on the fly::
* Deferred translations::

locale — Internationalization services

* Background, details, hints, tips and caveats: Background details hints tips and caveats.
* For extension writers and programs that embed Python::
* Access to message catalogs::

Program Frameworks

* turtle — Turtle graphics::
* cmd — Support for line-oriented command interpreters::
* shlex — Simple lexical analysis::

turtle — Turtle graphics

* Introduction: Introduction<11>.
* Overview of available Turtle and Screen methods::
* Methods of RawTurtle/Turtle and corresponding functions::
* Methods of TurtleScreen/Screen and corresponding functions::
* Public classes::
* Help and configuration::
* turtledemo — Demo scripts::
* Changes since Python 2.6: Changes since Python 2 6.
* Changes since Python 3.0: Changes since Python 3 0.

Overview of available Turtle and Screen methods

* Turtle methods::
* Methods of TurtleScreen/Screen::

Methods of RawTurtle/Turtle and corresponding functions

* Turtle motion::
* Tell Turtle’s state::
* Settings for measurement::
* Pen control::
* Turtle state::
* Using events::
* Special Turtle methods::
* Compound shapes::

Pen control

* Drawing state::
* Color control::
* Filling::
* More drawing control::

Turtle state

* Visibility::
* Appearance::

Methods of TurtleScreen/Screen and corresponding functions

* Window control::
* Animation control::
* Using screen events::
* Input methods::
* Settings and special methods::
* Methods specific to Screen, not inherited from TurtleScreen: Methods specific to Screen not inherited from TurtleScreen.

Help and configuration

* How to use help::
* Translation of docstrings into different languages::
* How to configure Screen and Turtles::

cmd — Support for line-oriented command interpreters

* Cmd Objects::
* Cmd Example::

shlex — Simple lexical analysis

* shlex Objects::
* Parsing Rules::
* Improved Compatibility with Shells::

Graphical User Interfaces with Tk

* tkinter — Python interface to Tcl/Tk::
* tkinter.colorchooser — Color choosing dialog: tkinter colorchooser — Color choosing dialog.
* tkinter.font — Tkinter font wrapper: tkinter font — Tkinter font wrapper.
* Tkinter Dialogs::
* tkinter.messagebox — Tkinter message prompts: tkinter messagebox — Tkinter message prompts.
* tkinter.scrolledtext — Scrolled Text Widget: tkinter scrolledtext — Scrolled Text Widget.
* tkinter.dnd — Drag and drop support: tkinter dnd — Drag and drop support.
* tkinter.ttk — Tk themed widgets: tkinter ttk — Tk themed widgets.
* tkinter.tix — Extension widgets for Tk: tkinter tix — Extension widgets for Tk.
* IDLE: IDLE<51>.

tkinter — Python interface to Tcl/Tk

* Tkinter Modules::
* Tkinter Life Preserver::
* A (Very) Quick Look at Tcl/Tk: A Very Quick Look at Tcl/Tk.
* Mapping Basic Tk into Tkinter::
* How Tk and Tkinter are Related::
* Handy Reference::
* File Handlers::

Tkinter Life Preserver

* How To Use This Section::
* A Simple Hello World Program::

Handy Reference

* Setting Options::
* The Packer::
* Packer Options::
* Coupling Widget Variables::
* The Window Manager::
* Tk Option Data Types::
* Bindings and Events::
* The index Parameter::
* Images::

Tkinter Dialogs

* tkinter.simpledialog — Standard Tkinter input dialogs: tkinter simpledialog — Standard Tkinter input dialogs.
* tkinter.filedialog — File selection dialogs: tkinter filedialog — File selection dialogs.
* tkinter.commondialog — Dialog window templates: tkinter commondialog — Dialog window templates.

tkinter.filedialog — File selection dialogs

* Native Load/Save Dialogs::

tkinter.ttk — Tk themed widgets

* Using Ttk::
* Ttk Widgets::
* Widget::
* Combobox::
* Spinbox::
* Notebook::
* Progressbar::
* Separator::
* Sizegrip::
* Treeview::
* Ttk Styling::

Widget

* Standard Options::
* Scrollable Widget Options::
* Label Options::
* Compatibility Options::
* Widget States::
* ttk.Widget: ttk Widget.

Combobox

* Options::
* Virtual events::
* ttk.Combobox: ttk Combobox.

Spinbox

* Options: Options<2>.
* Virtual events: Virtual events<2>.
* ttk.Spinbox: ttk Spinbox.

Notebook

* Options: Options<3>.
* Tab Options::
* Tab Identifiers::
* Virtual Events::
* ttk.Notebook: ttk Notebook.

Progressbar

* Options: Options<4>.
* ttk.Progressbar: ttk Progressbar.

Separator

* Options: Options<5>.

Sizegrip

* Platform-specific notes::
* Bugs::

Treeview

* Options: Options<6>.
* Item Options::
* Tag Options::
* Column Identifiers::
* Virtual Events: Virtual Events<2>.
* ttk.Treeview: ttk Treeview.

Ttk Styling

* Layouts::

tkinter.tix — Extension widgets for Tk

* Using Tix::
* Tix Widgets::
* Tix Commands::

Tix Widgets

* Basic Widgets::
* File Selectors::
* Hierarchical ListBox::
* Tabular ListBox::
* Manager Widgets::
* Image Types::
* Miscellaneous Widgets::
* Form Geometry Manager::

IDLE

* Menus::
* Editing and navigation::
* Startup and code execution::
* Help and preferences::

Menus

* File menu (Shell and Editor): File menu Shell and Editor.
* Edit menu (Shell and Editor): Edit menu Shell and Editor.
* Format menu (Editor window only): Format menu Editor window only.
* Run menu (Editor window only): Run menu Editor window only.
* Shell menu (Shell window only): Shell menu Shell window only.
* Debug menu (Shell window only): Debug menu Shell window only.
* Options menu (Shell and Editor): Options menu Shell and Editor.
* Window menu (Shell and Editor): Window menu Shell and Editor.
* Help menu (Shell and Editor): Help menu Shell and Editor.
* Context Menus::

Editing and navigation

* Editor windows::
* Key bindings::
* Automatic indentation::
* Completions::
* Calltips::
* Code Context::
* Python Shell window::
* Text colors::

Startup and code execution

* Command line usage::
* Startup failure::
* Running user code::
* User output in Shell::
* Developing tkinter applications::
* Running without a subprocess::

Help and preferences

* Help sources::
* Setting preferences::
* IDLE on macOS::
* Extensions::

Development Tools

* typing — Support for type hints::
* pydoc — Documentation generator and online help system::
* Python Development Mode::
* Effects of the Python Development Mode::
* ResourceWarning Example::
* Bad file descriptor error example::
* doctest — Test interactive Python examples::
* unittest — Unit testing framework::
* unittest.mock — mock object library: unittest mock — mock object library.
* unittest.mock — getting started: unittest mock — getting started.
* 2to3 - Automated Python 2 to 3 code translation::
* test — Regression tests package for Python::
* test.support — Utilities for the Python test suite: test support — Utilities for the Python test suite.
* test.support.socket_helper — Utilities for socket tests: test support socket_helper — Utilities for socket tests.
* test.support.script_helper — Utilities for the Python execution tests: test support script_helper — Utilities for the Python execution tests.
* test.support.bytecode_helper — Support tools for testing correct bytecode generation: test support bytecode_helper — Support tools for testing correct bytecode generation.

typing — Support for type hints

* Relevant PEPs::
* Type aliases::
* NewType::
* Callable::
* Generics::
* User-defined generic types::
* The Any type::
* Nominal vs structural subtyping::
* Module contents: Module contents<3>.

Module contents

* Special typing primitives::
* Generic concrete collections::
* Abstract Base Classes::
* Protocols: Protocols<3>.
* Functions and decorators::
* Introspection helpers::
* Constant::

Special typing primitives

* Special types::
* Special forms::
* Building generic types::
* Other special directives::

Generic concrete collections

* Corresponding to built-in types::
* Corresponding to types in collections::
* Other concrete types::

Abstract Base Classes

* Corresponding to collections in collections.abc: Corresponding to collections in collections abc.
* Corresponding to other types in collections.abc: Corresponding to other types in collections abc.
* Asynchronous programming::
* Context manager types::

doctest — Test interactive Python examples

* Simple Usage; Checking Examples in Docstrings: Simple Usage Checking Examples in Docstrings.
* Simple Usage; Checking Examples in a Text File: Simple Usage Checking Examples in a Text File.
* How It Works::
* Basic API::
* Unittest API::
* Advanced API::
* Debugging::
* Soapbox::

How It Works

* Which Docstrings Are Examined?::
* How are Docstring Examples Recognized?::
* What’s the Execution Context?::
* What About Exceptions?::
* Option Flags::
* Directives::
* Warnings: Warnings<2>.

Advanced API

* DocTest Objects::
* Example Objects::
* DocTestFinder objects::
* DocTestParser objects::
* DocTestRunner objects::
* OutputChecker objects::

unittest — Unit testing framework

* Basic example::
* Command-Line Interface: Command-Line Interface<3>.
* Test Discovery::
* Organizing test code::
* Re-using old test code::
* Skipping tests and expected failures::
* Distinguishing test iterations using subtests::
* Classes and functions::
* Class and Module Fixtures::
* Signal Handling::

Command-Line Interface

* Command-line options: Command-line options<3>.

Classes and functions

* Test cases::
* Grouping tests::
* Loading and running tests::

Test cases

* Deprecated aliases::

Loading and running tests

* load_tests Protocol::

Class and Module Fixtures

* setUpClass and tearDownClass::
* setUpModule and tearDownModule::

unittest.mock — mock object library

* Quick Guide::
* The Mock Class::
* The patchers::
* MagicMock and magic method support::
* Helpers::

The Mock Class

* Calling::
* Deleting Attributes::
* Mock names and the name attribute::
* Attaching Mocks as Attributes::

The patchers

* patch::
* patch.object: patch object.
* patch.dict: patch dict.
* patch.multiple: patch multiple.
* patch methods; start and stop: patch methods start and stop.
* patch builtins::
* TEST_PREFIX::
* Nesting Patch Decorators::
* Where to patch::
* Patching Descriptors and Proxy Objects::

MagicMock and magic method support

* Mocking Magic Methods::
* Magic Mock::

Helpers

* sentinel::
* DEFAULT::
* call::
* create_autospec::
* ANY::
* FILTER_DIR::
* mock_open::
* Autospeccing::
* Sealing mocks::

unittest.mock — getting started

* Using Mock::
* Patch Decorators::
* Further Examples::

Using Mock

* Mock Patching Methods::
* Mock for Method Calls on an Object::
* Mocking Classes::
* Naming your mocks::
* Tracking all Calls::
* Setting Return Values and Attributes::
* Raising exceptions with mocks::
* Side effect functions and iterables::
* Mocking asynchronous iterators::
* Mocking asynchronous context manager::
* Creating a Mock from an Existing Object::

Further Examples

* Mocking chained calls::
* Partial mocking::
* Mocking a Generator Method::
* Applying the same patch to every test method::
* Mocking Unbound Methods::
* Checking multiple calls with mock::
* Coping with mutable arguments::
* Nesting Patches::
* Mocking a dictionary with MagicMock::
* Mock subclasses and their attributes::
* Mocking imports with patch.dict: Mocking imports with patch dict.
* Tracking order of calls and less verbose call assertions::
* More complex argument matching::

2to3 - Automated Python 2 to 3 code translation

* Using 2to3::
* Fixers::
* lib2to3 - 2to3’s library::

test — Regression tests package for Python

* Writing Unit Tests for the test package::
* Running tests using the command-line interface::

Debugging and Profiling

* Audit events table::
* bdb — Debugger framework::
* faulthandler — Dump the Python traceback::
* pdb — The Python Debugger::
* The Python Profilers::
* timeit — Measure execution time of small code snippets::
* trace — Trace or track Python statement execution::
* tracemalloc — Trace memory allocations::

faulthandler — Dump the Python traceback

* Dumping the traceback::
* Fault handler state::
* Dumping the tracebacks after a timeout::
* Dumping the traceback on a user signal::
* Issue with file descriptors::
* Example: Example<15>.

pdb — The Python Debugger

* Debugger Commands::

The Python Profilers

* Introduction to the profilers::
* Instant User’s Manual::
* profile and cProfile Module Reference::
* The Stats Class::
* What Is Deterministic Profiling?::
* Limitations::
* Calibration::
* Using a custom timer::

timeit — Measure execution time of small code snippets

* Basic Examples: Basic Examples<2>.
* Python Interface::
* Command-Line Interface: Command-Line Interface<4>.
* Examples: Examples<26>.

trace — Trace or track Python statement execution

* Command-Line Usage::
* Programmatic Interface::

Command-Line Usage

* Main options::
* Modifiers::
* Filters::

tracemalloc — Trace memory allocations

* Examples: Examples<27>.
* API::

Examples

* Display the top 10::
* Compute differences::
* Get the traceback of a memory block::
* Pretty top::

Pretty top

* Record the current and peak size of all traced memory blocks::

API

* Functions: Functions<10>.
* DomainFilter::
* Filter::
* Frame::
* Snapshot::
* Statistic::
* StatisticDiff::
* Trace::
* Traceback::

Software Packaging and Distribution

* distutils — Building and installing Python modules::
* ensurepip — Bootstrapping the pip installer::
* venv — Creation of virtual environments::
* zipapp — Manage executable Python zip archives::

ensurepip — Bootstrapping the pip installer

* Command line interface::
* Module API::

venv — Creation of virtual environments

* Creating virtual environments::
* API: API<2>.
* An example of extending EnvBuilder::

zipapp — Manage executable Python zip archives

* Basic Example::
* Command-Line Interface: Command-Line Interface<5>.
* Python API::
* Examples: Examples<28>.
* Specifying the Interpreter::
* Creating Standalone Applications with zipapp::
* The Python Zip Application Archive Format::

Creating Standalone Applications with zipapp

* Making a Windows executable::
* Caveats::

Python Runtime Services

* sys — System-specific parameters and functions::
* sysconfig — Provide access to Python’s configuration information::
* builtins — Built-in objects::
* __main__ — Top-level script environment::
* warnings — Warning control::
* dataclasses — Data Classes::
* contextlib — Utilities for with-statement contexts::
* abc — Abstract Base Classes::
* atexit — Exit handlers::
* traceback — Print or retrieve a stack traceback::
* __future__ — Future statement definitions::
* gc — Garbage Collector interface::
* inspect — Inspect live objects::
* site — Site-specific configuration hook::

sysconfig — Provide access to Python’s configuration information

* Configuration variables::
* Installation paths::
* Other functions: Other functions<3>.
* Using sysconfig as a script::

warnings — Warning control

* Warning Categories::
* The Warnings Filter::
* Temporarily Suppressing Warnings::
* Testing Warnings::
* Updating Code For New Versions of Dependencies::
* Available Functions::
* Available Context Managers::

The Warnings Filter

* Describing Warning Filters::
* Default Warning Filter::
* Overriding the default filter::

dataclasses — Data Classes

* Module-level decorators, classes, and functions: Module-level decorators classes and functions.
* Post-init processing::
* Class variables::
* Init-only variables::
* Frozen instances::
* Inheritance: Inheritance<2>.
* Default factory functions::
* Mutable default values::
* Exceptions: Exceptions<18>.

contextlib — Utilities for with-statement contexts

* Utilities::
* Examples and Recipes::
* Single use, reusable and reentrant context managers: Single use reusable and reentrant context managers.

Examples and Recipes

* Supporting a variable number of context managers::
* Catching exceptions from __enter__ methods::
* Cleaning up in an __enter__ implementation::
* Replacing any use of try-finally and flag variables::
* Using a context manager as a function decorator::

Single use, reusable and reentrant context managers

* Reentrant context managers::
* Reusable context managers::

atexit — Exit handlers

* atexit Example::

traceback — Print or retrieve a stack traceback

* TracebackException Objects::
* StackSummary Objects::
* FrameSummary Objects::
* Traceback Examples::

inspect — Inspect live objects

* Types and members::
* Retrieving source code::
* Introspecting callables with the Signature object::
* Classes and functions: Classes and functions<2>.
* The interpreter stack::
* Fetching attributes statically::
* Current State of Generators and Coroutines::
* Code Objects Bit Flags::
* Command Line Interface: Command Line Interface<3>.

site — Site-specific configuration hook

* Readline configuration::
* Module contents: Module contents<4>.
* Command Line Interface: Command Line Interface<4>.

Custom Python Interpreters

* code — Interpreter base classes::
* codeop — Compile Python code::

code — Interpreter base classes

* Interactive Interpreter Objects::
* Interactive Console Objects::

Importing Modules

* zipimport — Import modules from Zip archives::
* pkgutil — Package extension utility::
* modulefinder — Find modules used by a script::
* runpy — Locating and executing Python modules::
* importlib — The implementation of import::
* Using importlib.metadata: Using importlib metadata.

zipimport — Import modules from Zip archives

* zipimporter Objects::
* Examples: Examples<29>.

modulefinder — Find modules used by a script

* Example usage of ModuleFinder::

importlib — The implementation of import

* Introduction: Introduction<12>.
* Functions: Functions<11>.
* importlib.abc – Abstract base classes related to import: importlib abc – Abstract base classes related to import.
* importlib.resources – Resources: importlib resources – Resources.
* importlib.machinery – Importers and path hooks: importlib machinery – Importers and path hooks.
* importlib.util – Utility code for importers: importlib util – Utility code for importers.
* Examples: Examples<30>.

Examples

* Importing programmatically::
* Checking if a module can be imported::
* Importing a source file directly::
* Setting up an importer::
* Approximating importlib.import_module(): Approximating importlib import_module.

Using importlib.metadata

* Overview: Overview<2>.
* Functional API: Functional API<2>.
* Distributions::
* Extending the search algorithm::

Functional API

* Entry points::
* Distribution metadata::
* Distribution versions::
* Distribution files::
* Distribution requirements::

Python Language Services

* parser — Access Python parse trees::
* ast — Abstract Syntax Trees::
* symtable — Access to the compiler’s symbol tables::
* symbol — Constants used with Python parse trees::
* token — Constants used with Python parse trees::
* keyword — Testing for Python keywords::
* tokenize — Tokenizer for Python source::
* tabnanny — Detection of ambiguous indentation::
* pyclbr — Python module browser support::
* py_compile — Compile Python source files::
* compileall — Byte-compile Python libraries::
* dis — Disassembler for Python bytecode::
* pickletools — Tools for pickle developers::

parser — Access Python parse trees

* Creating ST Objects::
* Converting ST Objects::
* Queries on ST Objects::
* Exceptions and Error Handling::
* ST Objects::
* Example; Emulation of compile(): Example Emulation of compile.

ast — Abstract Syntax Trees

* Abstract Grammar::
* Node classes::
* ast Helpers::
* Compiler Flags::
* Command-Line Usage: Command-Line Usage<2>.

Node classes

* Literals: Literals<3>.
* Variables::
* Expressions: Expressions<2>.
* Statements::
* Control flow::
* Function and class definitions::
* Async and await::

Expressions

* Subscripting::
* Comprehensions::

Statements

* Imports::

symtable — Access to the compiler’s symbol tables

* Generating Symbol Tables::
* Examining Symbol Tables::

tokenize — Tokenizer for Python source

* Tokenizing Input::
* Command-Line Usage: Command-Line Usage<3>.
* Examples: Examples<31>.

pyclbr — Python module browser support

* Function Objects::
* Class Objects: Class Objects<2>.

compileall — Byte-compile Python libraries

* Command-line use::
* Public functions::

dis — Disassembler for Python bytecode

* Bytecode analysis::
* Analysis functions::
* Python Bytecode Instructions::
* Opcode collections::

pickletools — Tools for pickle developers

* Command line usage: Command line usage<2>.
* Programmatic Interface: Programmatic Interface<2>.

Command line usage

* Command line options: Command line options<3>.

Miscellaneous Services

* formatter — Generic output formatting::

formatter — Generic output formatting

* The Formatter Interface::
* Formatter Implementations::
* The Writer Interface::
* Writer Implementations::

MS Windows Specific Services

* msilib — Read and write Microsoft Installer files::
* msvcrt — Useful routines from the MS VC++ runtime::
* winreg — Windows registry access::
* winsound — Sound-playing interface for Windows::

msilib — Read and write Microsoft Installer files

* Database Objects::
* View Objects::
* Summary Information Objects::
* Record Objects::
* Errors::
* CAB Objects::
* Directory Objects::
* Features: Features<3>.
* GUI classes::
* Precomputed tables::

msvcrt — Useful routines from the MS VC++ runtime

* File Operations::
* Console I/O::
* Other Functions::

winreg — Windows registry access

* Functions: Functions<12>.
* Constants: Constants<10>.
* Registry Handle Objects::

Constants

* HKEY_* Constants::
* Access Rights::
* Value Types::

Access Rights

* 64-bit Specific::

Unix Specific Services

* posix — The most common POSIX system calls::
* pwd — The password database::
* spwd — The shadow password database::
* grp — The group database::
* crypt — Function to check Unix passwords::
* termios — POSIX style tty control::
* tty — Terminal control functions::
* pty — Pseudo-terminal utilities::
* fcntl — The fcntl and ioctl system calls::
* pipes — Interface to shell pipelines::
* resource — Resource usage information::
* nis — Interface to Sun’s NIS (Yellow Pages): nis — Interface to Sun’s NIS Yellow Pages.
* syslog — Unix syslog library routines::

posix — The most common POSIX system calls

* Large File Support::
* Notable Module Contents::

crypt — Function to check Unix passwords

* Hashing Methods::
* Module Attributes::
* Module Functions: Module Functions<2>.
* Examples: Examples<32>.

termios — POSIX style tty control

* Example: Example<16>.

pty — Pseudo-terminal utilities

* Example: Example<17>.

pipes — Interface to shell pipelines

* Template Objects::

resource — Resource usage information

* Resource Limits::
* Resource Usage::

syslog — Unix syslog library routines

* Examples: Examples<33>.

Examples

* Simple example::

Superseded Modules

* optparse — Parser for command line options::
* imp — Access the import internals::

optparse — Parser for command line options

* Background::
* Tutorial: Tutorial<2>.
* Reference Guide::
* Option Callbacks::
* Extending optparse::

Background

* Terminology::
* What are options for?::
* What are positional arguments for?::

Tutorial

* Understanding option actions::
* The store action::
* Handling boolean (flag) options: Handling boolean flag options.
* Other actions::
* Default values::
* Generating help::
* Printing a version string::
* How optparse handles errors::
* Putting it all together::

Generating help

* Grouping Options::

Reference Guide

* Creating the parser::
* Populating the parser::
* Defining options::
* Option attributes::
* Standard option actions::
* Standard option types::
* Parsing arguments: Parsing arguments<2>.
* Querying and manipulating your option parser::
* Conflicts between options::
* Cleanup: Cleanup<2>.
* Other methods::

Option Callbacks

* Defining a callback option::
* How callbacks are called::
* Raising errors in a callback::
* Callback example 1; trivial callback: Callback example 1 trivial callback.
* Callback example 2; check option order: Callback example 2 check option order.
* Callback example 3; check option order (generalized): Callback example 3 check option order generalized.
* Callback example 4; check arbitrary condition: Callback example 4 check arbitrary condition.
* Callback example 5; fixed arguments: Callback example 5 fixed arguments.
* Callback example 6; variable arguments: Callback example 6 variable arguments.

Extending optparse

* Adding new types::
* Adding new actions::

imp — Access the import internals

* Examples: Examples<34>.

Undocumented Modules

* Platform specific modules::

Extending and Embedding the Python Interpreter

* Recommended third party tools::
* Creating extensions without third party tools::
* Embedding the CPython runtime in a larger application::

Creating extensions without third party tools

* Extending Python with C or C++::
* Defining Extension Types; Tutorial: Defining Extension Types Tutorial.
* Defining Extension Types; Assorted Topics: Defining Extension Types Assorted Topics.
* Building C and C++ Extensions::
* Building C and C++ Extensions on Windows::

Extending Python with C or C++

* A Simple Example::
* Intermezzo; Errors and Exceptions: Intermezzo Errors and Exceptions.
* Back to the Example::
* The Module’s Method Table and Initialization Function::
* Compilation and Linkage::
* Calling Python Functions from C::
* Extracting Parameters in Extension Functions::
* Keyword Parameters for Extension Functions::
* Building Arbitrary Values::
* Reference Counts::
* Writing Extensions in C++::
* Providing a C API for an Extension Module::

Reference Counts

* Reference Counting in Python::
* Ownership Rules::
* Thin Ice::
* NULL Pointers::

Defining Extension Types: Tutorial

* The Basics::
* Adding data and methods to the Basic example::
* Providing finer control over data attributes::
* Supporting cyclic garbage collection::
* Subclassing other types::

Defining Extension Types: Assorted Topics

* Finalization and De-allocation::
* Object Presentation::
* Attribute Management::
* Object Comparison::
* Abstract Protocol Support::
* Weak Reference Support::
* More Suggestions::

Attribute Management

* Generic Attribute Management::
* Type-specific Attribute Management::

Building C and C++ Extensions

* Building C and C++ Extensions with distutils::
* Distributing your extension modules::

Building C and C++ Extensions on Windows

* A Cookbook Approach::
* Differences Between Unix and Windows::
* Using DLLs in Practice::

Embedding the CPython runtime in a larger application

* Embedding Python in Another Application::

Embedding Python in Another Application

* Very High Level Embedding::
* Beyond Very High Level Embedding; An overview: Beyond Very High Level Embedding An overview.
* Pure Embedding::
* Extending Embedded Python::
* Embedding Python in C++::
* Compiling and Linking under Unix-like systems::

Python/C API Reference Manual

* Introduction: Introduction<13>.
* Stable Application Binary Interface::
* The Very High Level Layer::
* Reference Counting::
* Exception Handling::
* Utilities: Utilities<2>.
* Abstract Objects Layer::
* Concrete Objects Layer::
* Initialization, Finalization, and Threads: Initialization Finalization and Threads.
* Python Initialization Configuration::
* Memory Management::
* Object Implementation Support::
* API and ABI Versioning::

Introduction

* Coding standards::
* Include Files::
* Useful macros::
* Objects, Types and Reference Counts: Objects Types and Reference Counts.
* Exceptions: Exceptions<19>.
* Embedding Python: Embedding Python<2>.
* Debugging Builds::

Objects, Types and Reference Counts

* Reference Counts: Reference Counts<2>.
* Types::

Reference Counts

* Reference Count Details::

Exception Handling

* Printing and clearing::
* Raising exceptions::
* Issuing warnings::
* Querying the error indicator::
* Signal Handling: Signal Handling<2>.
* Exception Classes::
* Exception Objects::
* Unicode Exception Objects::
* Recursion Control::
* Standard Exceptions::
* Standard Warning Categories::

Utilities

* Operating System Utilities::
* System Functions::
* Process Control::
* Importing Modules: Importing Modules<2>.
* Data marshalling support::
* Parsing arguments and building values::
* String conversion and formatting::
* Reflection::
* Codec registry and support functions::

Parsing arguments and building values

* Parsing arguments: Parsing arguments<3>.
* Building values::

Parsing arguments

* Strings and buffers::
* Numbers: Numbers<2>.
* Other objects::
* API Functions::

Codec registry and support functions

* Codec lookup API::
* Registry API for Unicode encoding error handlers::

Abstract Objects Layer

* Object Protocol::
* Call Protocol::
* Number Protocol::
* Sequence Protocol::
* Mapping Protocol::
* Iterator Protocol::
* Buffer Protocol::
* Old Buffer Protocol::

Call Protocol

* The tp_call Protocol::
* The Vectorcall Protocol::
* Object Calling API::
* Call Support API::

The Vectorcall Protocol

* Recursion Control: Recursion Control<2>.
* Vectorcall Support API::

Buffer Protocol

* Buffer structure::
* Buffer request types::
* Complex arrays::
* Buffer-related functions::

Buffer request types

* request-independent fields::
* readonly, format: readonly format.
* shape, strides, suboffsets: shape strides suboffsets.
* contiguity requests::
* compound requests::

Complex arrays

* NumPy-style; shape and strides: NumPy-style shape and strides.
* PIL-style; shape, strides and suboffsets: PIL-style shape strides and suboffsets.

Concrete Objects Layer

* Fundamental Objects::
* Numeric Objects::
* Sequence Objects::
* Container Objects::
* Function Objects: Function Objects<2>.
* Other Objects::

Fundamental Objects

* Type Objects: Type Objects<2>.
* The None Object::

Type Objects

* Creating Heap-Allocated Types::

Numeric Objects

* Integer Objects::
* Boolean Objects::
* Floating Point Objects::
* Complex Number Objects::

Complex Number Objects

* Complex Numbers as C Structures::
* Complex Numbers as Python Objects::

Sequence Objects

* Bytes Objects: Bytes Objects<2>.
* Byte Array Objects::
* Unicode Objects and Codecs::
* Tuple Objects::
* Struct Sequence Objects::
* List Objects::

Byte Array Objects

* Type check macros::
* Direct API functions::
* Macros::

Unicode Objects and Codecs

* Unicode Objects::
* Built-in Codecs::
* Methods and Slot Functions::

Unicode Objects

* Unicode Type::
* Unicode Character Properties::
* Creating and accessing Unicode strings::
* Deprecated Py_UNICODE APIs::
* Locale Encoding::
* File System Encoding::
* wchar_t Support::

Built-in Codecs

* Generic Codecs::
* UTF-8 Codecs::
* UTF-32 Codecs::
* UTF-16 Codecs::
* UTF-7 Codecs::
* Unicode-Escape Codecs::
* Raw-Unicode-Escape Codecs::
* Latin-1 Codecs::
* ASCII Codecs::
* Character Map Codecs::
* MBCS codecs for Windows::
* Methods & Slots::

Container Objects

* Dictionary Objects::
* Set Objects::

Function Objects

* Function Objects: Function Objects<3>.
* Instance Method Objects::
* Method Objects: Method Objects<2>.
* Cell Objects::
* Code Objects: Code Objects<2>.

Other Objects

* File Objects::
* Module Objects::
* Iterator Objects::
* Descriptor Objects::
* Slice Objects::
* Ellipsis Object::
* MemoryView objects::
* Weak Reference Objects: Weak Reference Objects<2>.
* Capsules: Capsules<2>.
* Generator Objects::
* Coroutine Objects: Coroutine Objects<2>.
* Context Variables Objects::
* DateTime Objects: DateTime Objects<2>.
* Objects for Type Hinting::

Module Objects

* Initializing C modules::
* Module lookup::

Initializing C modules

* Single-phase initialization::
* Multi-phase initialization::
* Low-level module creation functions::
* Support functions::

Initialization, Finalization, and Threads

* Before Python Initialization::
* Global configuration variables::
* Initializing and finalizing the interpreter::
* Process-wide parameters::
* Thread State and the Global Interpreter Lock::
* Sub-interpreter support::
* Asynchronous Notifications::
* Profiling and Tracing::
* Advanced Debugger Support::
* Thread Local Storage Support::

Thread State and the Global Interpreter Lock

* Releasing the GIL from extension code::
* Non-Python created threads::
* Cautions about fork(): Cautions about fork.
* High-level API::
* Low-level API::

Sub-interpreter support

* Bugs and caveats::

Thread Local Storage Support

* Thread Specific Storage (TSS) API: Thread Specific Storage TSS API.
* Thread Local Storage (TLS) API: Thread Local Storage TLS API.

Thread Specific Storage (TSS) API

* Dynamic Allocation::
* Methods: Methods<4>.

Python Initialization Configuration

* PyWideStringList::
* PyStatus::
* PyPreConfig::
* Preinitialization with PyPreConfig::
* PyConfig::
* Initialization with PyConfig::
* Isolated Configuration::
* Python Configuration::
* Path Configuration::
* Py_RunMain(): Py_RunMain.
* Py_GetArgcArgv(): Py_GetArgcArgv.
* Multi-Phase Initialization Private Provisional API::

Memory Management

* Overview: Overview<3>.
* Raw Memory Interface::
* Memory Interface::
* Object allocators::
* Default Memory Allocators::
* Customize Memory Allocators::
* The pymalloc allocator::
* tracemalloc C API::
* Examples: Examples<35>.

The pymalloc allocator

* Customize pymalloc Arena Allocator::

Object Implementation Support

* Allocating Objects on the Heap::
* Common Object Structures::
* Type Objects: Type Objects<3>.
* Number Object Structures::
* Mapping Object Structures::
* Sequence Object Structures::
* Buffer Object Structures::
* Async Object Structures::
* Slot Type typedefs::
* Examples: Examples<36>.
* Supporting Cyclic Garbage Collection::

Common Object Structures

* Base object types and macros::
* Implementing functions and methods::
* Accessing attributes of extension types::

Type Objects

* Quick Reference::
* PyTypeObject Definition::
* PyObject Slots::
* PyVarObject Slots::
* PyTypeObject Slots::
* Heap Types::

Quick Reference

* “tp slots”::
* sub-slots::
* slot typedefs::

Distributing Python Modules

* Key terms::
* Open source licensing and collaboration::
* Installing the tools::
* Reading the Python Packaging User Guide::
* How do I…?::

How do I…?

* … choose a name for my project?::
* … create and distribute binary extensions?::

Installing Python Modules

* Key terms: Key terms<2>.
* Basic usage::
* How do I …?::
* Common installation issues::

How do I …?

* … install pip in versions of Python prior to Python 3.4?: … install pip in versions of Python prior to Python 3 4?.
* … install packages just for the current user?::
* … install scientific Python packages?::
* … work with multiple versions of Python installed in parallel?::

Common installation issues

* Installing into the system Python on Linux::
* Pip not installed::
* Installing binary extensions::

Python HOWTOs

* Porting Python 2 Code to Python 3::
* Porting Extension Modules to Python 3::
* Curses Programming with Python::
* Descriptor HowTo Guide::
* Functional Programming HOWTO::
* Logging HOWTO::
* Logging Cookbook::
* Regular Expression HOWTO::
* Socket Programming HOWTO::
* Sorting HOW TO::
* Unicode HOWTO::
* HOWTO Fetch Internet Resources Using The urllib Package::
* Argparse Tutorial::
* An introduction to the ipaddress module::
* Argument Clinic How-To::
* Instrumenting CPython with DTrace and SystemTap::

Porting Python 2 Code to Python 3

* The Short Explanation::
* Details::

Details

* Drop support for Python 2.6 and older: Drop support for Python 2 6 and older.
* Make sure you specify the proper version support in your setup.py file: Make sure you specify the proper version support in your setup py file.
* Have good test coverage::
* Learn the differences between Python 2 & 3::
* Update your code::
* Prevent compatibility regressions::
* Check which dependencies block your transition::
* Update your setup.py file to denote Python 3 compatibility: Update your setup py file to denote Python 3 compatibility.
* Use continuous integration to stay compatible::
* Consider using optional static type checking::

Update your code

* Division::
* Text versus binary data::
* Use feature detection instead of version detection::

Curses Programming with Python

* What is curses?::
* Starting and ending a curses application::
* Windows and Pads::
* Displaying Text::
* User Input::
* For More Information::

What is curses?

* The Python curses module::

Displaying Text

* Attributes and Color::

Descriptor HowTo Guide

* Primer::
* Complete Practical Example::
* Technical Tutorial::
* Pure Python Equivalents::

Primer

* Simple example; A descriptor that returns a constant: Simple example A descriptor that returns a constant.
* Dynamic lookups::
* Managed attributes::
* Customized names::
* Closing thoughts::

Complete Practical Example

* Validator class::
* Custom validators::
* Practical application::

Technical Tutorial

* Abstract::
* Definition and introduction::
* Descriptor protocol::
* Overview of descriptor invocation::
* Invocation from an instance::
* Invocation from a class::
* Invocation from super::
* Summary of invocation logic::
* Automatic name notification::
* ORM example::

Pure Python Equivalents

* Properties::
* Functions and methods::
* Kinds of methods::
* Static methods::
* Class methods::
* Member objects and __slots__::

Functional Programming HOWTO

* Introduction: Introduction<14>.
* Iterators: Iterators<2>.
* Generator expressions and list comprehensions::
* Generators: Generators<2>.
* Built-in functions::
* The itertools module::
* The functools module::
* Small functions and the lambda expression::
* Revision History and Acknowledgements::
* References: References<2>.

Introduction

* Formal provability::
* Modularity::
* Ease of debugging and testing::
* Composability::

Iterators

* Data Types That Support Iterators::

Generators

* Passing values into a generator::

The itertools module

* Creating new iterators::
* Calling functions on elements::
* Selecting elements::
* Combinatoric functions::
* Grouping elements::

The functools module

* The operator module::

References

* General::
* Python-specific::
* Python documentation::

Logging HOWTO

* Basic Logging Tutorial::
* Advanced Logging Tutorial::
* Logging Levels: Logging Levels<2>.
* Useful Handlers::
* Exceptions raised during logging::
* Using arbitrary objects as messages::
* Optimization::

Basic Logging Tutorial

* When to use logging::
* A simple example::
* Logging to a file::
* Logging from multiple modules::
* Logging variable data::
* Changing the format of displayed messages::
* Displaying the date/time in messages::
* Next Steps::

Advanced Logging Tutorial

* Logging Flow::
* Loggers::
* Handlers::
* Formatters::
* Configuring Logging::
* What happens if no configuration is provided::
* Configuring Logging for a Library::

Logging Levels

* Custom Levels::

Logging Cookbook

* Using logging in multiple modules::
* Logging from multiple threads::
* Multiple handlers and formatters::
* Logging to multiple destinations::
* Configuration server example::
* Dealing with handlers that block::
* Sending and receiving logging events across a network::
* Adding contextual information to your logging output::
* Logging to a single file from multiple processes::
* Using file rotation::
* Use of alternative formatting styles::
* Customizing LogRecord::
* Subclassing QueueHandler - a ZeroMQ example::
* Subclassing QueueListener - a ZeroMQ example::
* An example dictionary-based configuration::
* Using a rotator and namer to customize log rotation processing::
* A more elaborate multiprocessing example::
* Inserting a BOM into messages sent to a SysLogHandler::
* Implementing structured logging::
* Customizing handlers with dictConfig(): Customizing handlers with dictConfig.
* Using particular formatting styles throughout your application::
* Configuring filters with dictConfig(): Configuring filters with dictConfig.
* Customized exception formatting::
* Speaking logging messages::
* Buffering logging messages and outputting them conditionally::
* Formatting times using UTC (GMT) via configuration: Formatting times using UTC GMT via configuration.
* Using a context manager for selective logging::
* A CLI application starter template::
* A Qt GUI for logging::
* Patterns to avoid::

Sending and receiving logging events across a network

* Running a logging socket listener in production::

Adding contextual information to your logging output

* Using LoggerAdapters to impart contextual information::
* Using Filters to impart contextual information::

Using LoggerAdapters to impart contextual information

* Using objects other than dicts to pass contextual information::

Logging to a single file from multiple processes

* Using concurrent.futures.ProcessPoolExecutor: Using concurrent futures ProcessPoolExecutor.
* Deploying Web applications using Gunicorn and uWSGI::

Using particular formatting styles throughout your application

* Using LogRecord factories::
* Using custom message objects::

Patterns to avoid

* Opening the same log file multiple times::
* Using loggers as attributes in a class or passing them as parameters::
* Adding handlers other than NullHandler to a logger in a library::
* Creating a lot of loggers::

Regular Expression HOWTO

* Introduction: Introduction<15>.
* Simple Patterns::
* Using Regular Expressions::
* More Pattern Power::
* Modifying Strings::
* Common Problems::
* Feedback::

Simple Patterns

* Matching Characters::
* Repeating Things::

Using Regular Expressions

* Compiling Regular Expressions::
* The Backslash Plague::
* Performing Matches::
* Module-Level Functions: Module-Level Functions<2>.
* Compilation Flags::

More Pattern Power

* More Metacharacters::
* Grouping::
* Non-capturing and Named Groups::
* Lookahead Assertions::

Modifying Strings

* Splitting Strings::
* Search and Replace::

Common Problems

* Use String Methods::
* match() versus search(): match versus search.
* Greedy versus Non-Greedy::
* Using re.VERBOSE: Using re VERBOSE.

Socket Programming HOWTO

* Sockets::
* Creating a Socket::
* Using a Socket::
* Disconnecting::
* Non-blocking Sockets::

Sockets

* History::

Creating a Socket

* IPC::

Using a Socket

* Binary Data::

Disconnecting

* When Sockets Die::

Sorting HOW TO

* Sorting Basics::
* Key Functions::
* Operator Module Functions::
* Ascending and Descending::
* Sort Stability and Complex Sorts::
* The Old Way Using Decorate-Sort-Undecorate::
* The Old Way Using the cmp Parameter::
* Odd and Ends::

Unicode HOWTO

* Introduction to Unicode::
* Python’s Unicode Support::
* Reading and Writing Unicode Data::
* Acknowledgements: Acknowledgements<10>.

Introduction to Unicode

* Definitions::
* Encodings::
* References: References<3>.

Python’s Unicode Support

* The String Type::
* Converting to Bytes::
* Unicode Literals in Python Source Code::
* Unicode Properties::
* Comparing Strings::
* Unicode Regular Expressions::
* References: References<4>.

Reading and Writing Unicode Data

* Unicode filenames::
* Tips for Writing Unicode-aware Programs::
* References: References<5>.

Tips for Writing Unicode-aware Programs

* Converting Between File Encodings::
* Files in an Unknown Encoding::

HOWTO Fetch Internet Resources Using The urllib Package

* Introduction: Introduction<16>.
* Fetching URLs::
* Handling Exceptions: Handling Exceptions<2>.
* info and geturl::
* Openers and Handlers::
* Basic Authentication::
* Proxies::
* Sockets and Layers::
* Footnotes::

Fetching URLs

* Data::
* Headers::

Handling Exceptions

* URLError::
* HTTPError::
* Wrapping it Up::

HTTPError

* Error Codes::

Wrapping it Up

* Number 1::
* Number 2::

Argparse Tutorial

* Concepts::
* The basics::
* Introducing Positional arguments::
* Introducing Optional arguments::
* Combining Positional and Optional arguments::
* Getting a little more advanced::
* Conclusion::

Introducing Optional arguments

* Short options::

Getting a little more advanced

* Conflicting options::

An introduction to the ipaddress module

* Creating Address/Network/Interface objects::
* Inspecting Address/Network/Interface Objects::
* Networks as lists of Addresses::
* Comparisons: Comparisons<4>.
* Using IP Addresses with other modules::
* Getting more detail when instance creation fails::

Creating Address/Network/Interface objects

* A Note on IP Versions::
* IP Host Addresses::
* Defining Networks::
* Host Interfaces::

Argument Clinic How-To

* The Goals Of Argument Clinic::
* Basic Concepts And Usage::
* Converting Your First Function::
* Advanced Topics::

Advanced Topics

* Symbolic default values::
* Renaming the C functions and variables generated by Argument Clinic::
* Converting functions using PyArg_UnpackTuple::
* Optional Groups::
* Using real Argument Clinic converters, instead of “legacy converters”: Using real Argument Clinic converters instead of “legacy converters”.
* Py_buffer::
* Advanced converters::
* Parameter default values::
* The NULL default value::
* Expressions specified as default values::
* Using a return converter::
* Cloning existing functions::
* Calling Python code::
* Using a “self converter”::
* Writing a custom converter::
* Writing a custom return converter::
* METH_O and METH_NOARGS::
* tp_new and tp_init functions::
* Changing and redirecting Clinic’s output::
* The #ifdef trick::
* Using Argument Clinic in Python files::

Instrumenting CPython with DTrace and SystemTap

* Enabling the static markers::
* Static DTrace probes::
* Static SystemTap markers::
* Available static markers::
* SystemTap Tapsets::
* Examples: Examples<37>.

Python Frequently Asked Questions

* General Python FAQ::
* Programming FAQ::
* Design and History FAQ::
* Library and Extension FAQ::
* Extending/Embedding FAQ::
* Python on Windows FAQ::
* Graphic User Interface FAQ::
* “Why is Python Installed on my Computer?” FAQ::

General Python FAQ

* General Information::
* Python in the real world::

General Information

* What is Python?::
* What is the Python Software Foundation?::
* Are there copyright restrictions on the use of Python?::
* Why was Python created in the first place?::
* What is Python good for?::
* How does the Python version numbering scheme work?::
* How do I obtain a copy of the Python source?::
* How do I get documentation on Python?::
* I’ve never programmed before. Is there a Python tutorial?: I’ve never programmed before Is there a Python tutorial?.
* Is there a newsgroup or mailing list devoted to Python?::
* How do I get a beta test version of Python?::
* How do I submit bug reports and patches for Python?::
* Are there any published articles about Python that I can reference?::
* Are there any books on Python?::
* Where in the world is www.python.org located?: Where in the world is www python org located?.
* Why is it called Python?::
* Do I have to like “Monty Python’s Flying Circus”?::

Python in the real world

* How stable is Python?::
* How many people are using Python?::
* Have any significant projects been done in Python?::
* What new developments are expected for Python in the future?::
* Is it reasonable to propose incompatible changes to Python?::
* Is Python a good language for beginning programmers?::

Programming FAQ

* General Questions::
* Core Language::
* Numbers and strings::
* Performance: Performance<4>.
* Sequences (Tuples/Lists): Sequences Tuples/Lists.
* Objects::
* Modules: Modules<3>.

General Questions

* Is there a source code level debugger with breakpoints, single-stepping, etc.?: Is there a source code level debugger with breakpoints single-stepping etc ?.
* Are there tools to help find bugs or perform static analysis?::
* How can I create a stand-alone binary from a Python script?::
* Are there coding standards or a style guide for Python programs?::

Core Language

* Why am I getting an UnboundLocalError when the variable has a value?::
* What are the rules for local and global variables in Python?::
* Why do lambdas defined in a loop with different values all return the same result?::
* How do I share global variables across modules?::
* What are the “best practices” for using import in a module?::
* Why are default values shared between objects?::
* How can I pass optional or keyword parameters from one function to another?::
* What is the difference between arguments and parameters?::
* Why did changing list ‘y’ also change list ‘x’?::
* How do I write a function with output parameters (call by reference)?: How do I write a function with output parameters call by reference ?.
* How do you make a higher order function in Python?::
* How do I copy an object in Python?::
* How can I find the methods or attributes of an object?::
* How can my code discover the name of an object?::
* What’s up with the comma operator’s precedence?::
* Is there an equivalent of C’s “?;” ternary operator?: Is there an equivalent of C’s “? ” ternary operator?.
* Is it possible to write obfuscated one-liners in Python?::
* What does the slash(/) in the parameter list of a function mean?: What does the slash / in the parameter list of a function mean?.

Numbers and strings

* How do I specify hexadecimal and octal integers?::
* Why does -22 // 10 return -3?::
* How do I get int literal attribute instead of SyntaxError?::
* How do I convert a string to a number?::
* How do I convert a number to a string?::
* How do I modify a string in place?::
* How do I use strings to call functions/methods?::
* Is there an equivalent to Perl’s chomp() for removing trailing newlines from strings?: Is there an equivalent to Perl’s chomp for removing trailing newlines from strings?.
* Is there a scanf() or sscanf() equivalent?: Is there a scanf or sscanf equivalent?.
* What does ‘UnicodeDecodeError’ or ‘UnicodeEncodeError’ error mean?::

Performance

* My program is too slow. How do I speed it up?: My program is too slow How do I speed it up?.
* What is the most efficient way to concatenate many strings together?::

Sequences (Tuples/Lists)

* How do I convert between tuples and lists?::
* What’s a negative index?::
* How do I iterate over a sequence in reverse order?::
* How do you remove duplicates from a list?::
* How do you remove multiple items from a list::
* How do you make an array in Python?::
* How do I create a multidimensional list?::
* How do I apply a method to a sequence of objects?::
* Why does a_tuple[i] += [‘item’] raise an exception when the addition works?::
* I want to do a complicated sort; can you do a Schwartzian Transform in Python?: I want to do a complicated sort can you do a Schwartzian Transform in Python?.
* How can I sort one list by values from another list?::

Objects

* What is a class?::
* What is a method?::
* What is self?::
* How do I check if an object is an instance of a given class or of a subclass of it?::
* What is delegation?::
* How do I call a method defined in a base class from a derived class that overrides it?::
* How can I organize my code to make it easier to change the base class?::
* How do I create static class data and static class methods?::
* How can I overload constructors (or methods) in Python?: How can I overload constructors or methods in Python?.
* I try to use __spam and I get an error about _SomeClassName__spam.: I try to use __spam and I get an error about _SomeClassName__spam.
* My class defines __del__ but it is not called when I delete the object.: My class defines __del__ but it is not called when I delete the object.
* How do I get a list of all instances of a given class?::
* Why does the result of id() appear to be not unique?: Why does the result of id appear to be not unique?.
* When can I rely on identity tests with the is operator?::
* How can a subclass control what data is stored in an immutable instance?::

Modules

* How do I create a .pyc file?: How do I create a pyc file?.
* How do I find the current module name?::
* How can I have modules that mutually import each other?::
* __import__(‘x.y.z’) returns <module ‘x’>; how do I get z?: __import__ ‘x y z’ returns <module ‘x’>; how do I get z?.
* When I edit an imported module and reimport it, the changes don’t show up. Why does this happen?: When I edit an imported module and reimport it the changes don’t show up Why does this happen?.

Design and History FAQ

* Why does Python use indentation for grouping of statements?::
* Why am I getting strange results with simple arithmetic operations?::
* Why are floating-point calculations so inaccurate?::
* Why are Python strings immutable?::
* Why must ‘self’ be used explicitly in method definitions and calls?::
* Why can’t I use an assignment in an expression?::
* Why does Python use methods for some functionality (e.g. list.index()) but functions for other (e.g. len(list))?: Why does Python use methods for some functionality e g list index but functions for other e g len list ?.
* Why is join() a string method instead of a list or tuple method?: Why is join a string method instead of a list or tuple method?.
* How fast are exceptions?::
* Why isn’t there a switch or case statement in Python?::
* Can’t you emulate threads in the interpreter instead of relying on an OS-specific thread implementation?::
* Why can’t lambda expressions contain statements?::
* Can Python be compiled to machine code, C or some other language?: Can Python be compiled to machine code C or some other language?.
* How does Python manage memory?::
* Why doesn’t CPython use a more traditional garbage collection scheme?::
* Why isn’t all memory freed when CPython exits?::
* Why are there separate tuple and list data types?::
* How are lists implemented in CPython?::
* How are dictionaries implemented in CPython?::
* Why must dictionary keys be immutable?::
* Why doesn’t list.sort() return the sorted list?: Why doesn’t list sort return the sorted list?.
* How do you specify and enforce an interface spec in Python?::
* Why is there no goto?::
* Why can’t raw strings (r-strings) end with a backslash?: Why can’t raw strings r-strings end with a backslash?.
* Why doesn’t Python have a “with” statement for attribute assignments?::
* Why don’t generators support the with statement?::
* Why are colons required for the if/while/def/class statements?::
* Why does Python allow commas at the end of lists and tuples?::

Library and Extension FAQ

* General Library Questions::
* Common tasks::
* Threads::
* Input and Output: Input and Output<2>.
* Network/Internet Programming::
* Databases::
* Mathematics and Numerics::

General Library Questions

* How do I find a module or application to perform task X?::
* Where is the math.py (socket.py, regex.py, etc.) source file?: Where is the math py socket py regex py etc source file?.
* How do I make a Python script executable on Unix?::
* Is there a curses/termcap package for Python?::
* Is there an equivalent to C’s onexit() in Python?: Is there an equivalent to C’s onexit in Python?.
* Why don’t my signal handlers work?::

Common tasks

* How do I test a Python program or component?::
* How do I create documentation from doc strings?::
* How do I get a single keypress at a time?::

Threads

* How do I program using threads?::
* None of my threads seem to run; why?: None of my threads seem to run why?.
* How do I parcel out work among a bunch of worker threads?::
* What kinds of global value mutation are thread-safe?::
* Can’t we get rid of the Global Interpreter Lock?::

Input and Output

* How do I delete a file? (And other file questions…): How do I delete a file? And other file questions….
* How do I copy a file?::
* How do I read (or write) binary data?: How do I read or write binary data?.
* I can’t seem to use os.read() on a pipe created with os.popen(); why?: I can’t seem to use os read on a pipe created with os popen ; why?.
* How do I access the serial (RS232) port?: How do I access the serial RS232 port?.
* Why doesn’t closing sys.stdout (stdin, stderr) really close it?: Why doesn’t closing sys stdout stdin stderr really close it?.

Network/Internet Programming

* What WWW tools are there for Python?::
* How can I mimic CGI form submission (METHOD=POST)?: How can I mimic CGI form submission METHOD=POST ?.
* What module should I use to help with generating HTML?::
* How do I send mail from a Python script?::
* How do I avoid blocking in the connect() method of a socket?: How do I avoid blocking in the connect method of a socket?.

Databases

* Are there any interfaces to database packages in Python?::
* How do you implement persistent objects in Python?::

Mathematics and Numerics

* How do I generate random numbers in Python?::

Extending/Embedding FAQ

* Can I create my own functions in C?::
* Can I create my own functions in C++?::
* Writing C is hard; are there any alternatives?::
* How can I execute arbitrary Python statements from C?::
* How can I evaluate an arbitrary Python expression from C?::
* How do I extract C values from a Python object?::
* How do I use Py_BuildValue() to create a tuple of arbitrary length?: How do I use Py_BuildValue to create a tuple of arbitrary length?.
* How do I call an object’s method from C?::
* How do I catch the output from PyErr_Print() (or anything that prints to stdout/stderr)?: How do I catch the output from PyErr_Print or anything that prints to stdout/stderr ?.
* How do I access a module written in Python from C?::
* How do I interface to C++ objects from Python?::
* I added a module using the Setup file and the make fails; why?::
* How do I debug an extension?::
* I want to compile a Python module on my Linux system, but some files are missing. Why?: I want to compile a Python module on my Linux system but some files are missing Why?.
* How do I tell “incomplete input” from “invalid input”?::
* How do I find undefined g++ symbols __builtin_new or __pure_virtual?::
* Can I create an object class with some methods implemented in C and others in Python (e.g. through inheritance)?: Can I create an object class with some methods implemented in C and others in Python e g through inheritance ?.

Python on Windows FAQ

* How do I run a Python program under Windows?::
* How do I make Python scripts executable?::
* Why does Python sometimes take so long to start?::
* How do I make an executable from a Python script?::
* Is a *.pyd file the same as a DLL?: Is a * pyd file the same as a DLL?.
* How can I embed Python into a Windows application?::
* How do I keep editors from inserting tabs into my Python source?::
* How do I check for a keypress without blocking?::

Graphic User Interface FAQ

* General GUI Questions::
* What GUI toolkits exist for Python?::
* Tkinter questions::

Tkinter questions

* How do I freeze Tkinter applications?::
* Can I have Tk events handled while waiting for I/O?::
* I can’t get key bindings to work in Tkinter; why?: I can’t get key bindings to work in Tkinter why?.

“Why is Python Installed on my Computer?” FAQ

* What is Python?: What is Python?<2>.
* Why is Python installed on my machine?::
* Can I delete Python?::

About these documents

* Contributors to the Python Documentation::

Dealing with Bugs

* Documentation bugs::
* Using the Python issue tracker::
* Getting started contributing to Python yourself::

History and License

* History of the software::
* Terms and conditions for accessing or otherwise using Python::
* Licenses and Acknowledgements for Incorporated Software::

Terms and conditions for accessing or otherwise using Python

* PSF LICENSE AGREEMENT FOR PYTHON 3.9.10: PSF LICENSE AGREEMENT FOR PYTHON 3 9 10.
* BEOPEN.COM LICENSE AGREEMENT FOR PYTHON 2.0: BEOPEN COM LICENSE AGREEMENT FOR PYTHON 2 0.
* CNRI LICENSE AGREEMENT FOR PYTHON 1.6.1: CNRI LICENSE AGREEMENT FOR PYTHON 1 6 1.
* CWI LICENSE AGREEMENT FOR PYTHON 0.9.0 THROUGH 1.2: CWI LICENSE AGREEMENT FOR PYTHON 0 9 0 THROUGH 1 2.
* ZERO-CLAUSE BSD LICENSE FOR CODE IN THE PYTHON 3.9.10 DOCUMENTATION: ZERO-CLAUSE BSD LICENSE FOR CODE IN THE PYTHON 3 9 10 DOCUMENTATION.

Licenses and Acknowledgements for Incorporated Software

* Mersenne Twister::
* Sockets: Sockets<2>.
* Asynchronous socket services::
* Cookie management::
* Execution tracing::
* UUencode and UUdecode functions::
* XML Remote Procedure Calls::
* test_epoll::
* Select kqueue::
* SipHash24::
* strtod and dtoa::
* OpenSSL::
* expat::
* libffi::
* zlib: zlib<3>.
* cfuhash::
* libmpdec::
* W3C C14N test suite::

Distributing Python Modules (Legacy version)

* An Introduction to Distutils::
* Writing the Setup Script::
* Writing the Setup Configuration File::
* Creating a Source Distribution::
* Creating Built Distributions::
* Distutils Examples::
* Extending Distutils::
* Command Reference::
* API Reference::

An Introduction to Distutils

* Concepts & Terminology::
* A Simple Example: A Simple Example<2>.
* General Python terminology::
* Distutils-specific terminology::

Writing the Setup Script

* Listing whole packages::
* Listing individual modules::
* Describing extension modules::
* Relationships between Distributions and Packages::
* Installing Scripts::
* Installing Package Data::
* Installing Additional Files::
* Additional meta-data::
* Debugging the setup script::

Describing extension modules

* Extension names and packages::
* Extension source files::
* Preprocessor options::
* Library options::
* Other options::

Creating a Source Distribution

* Specifying the files to distribute::
* Manifest-related options::

Creating Built Distributions

* Creating RPM packages::
* Creating Windows Installers::
* Cross-compiling on Windows::
* Vista User Access Control (UAC): Vista User Access Control UAC.

Cross-compiling on Windows

* The Postinstallation script::

Distutils Examples

* Pure Python distribution (by module): Pure Python distribution by module.
* Pure Python distribution (by package): Pure Python distribution by package.
* Single extension module::
* Checking a package::
* Reading the metadata::

Extending Distutils

* Integrating new commands::
* Adding new distribution types::

Command Reference

* Installing modules; the install command family: Installing modules the install command family.
* Creating a source distribution; the sdist command: Creating a source distribution the sdist command.

Installing modules: the install command family

* install_data::
* install_scripts::

API Reference

* distutils.core — Core Distutils functionality: distutils core — Core Distutils functionality.
* distutils.ccompiler — CCompiler base class: distutils ccompiler — CCompiler base class.
* distutils.unixccompiler — Unix C Compiler: distutils unixccompiler — Unix C Compiler.
* distutils.msvccompiler — Microsoft Compiler: distutils msvccompiler — Microsoft Compiler.
* distutils.bcppcompiler — Borland Compiler: distutils bcppcompiler — Borland Compiler.
* distutils.cygwincompiler — Cygwin Compiler: distutils cygwincompiler — Cygwin Compiler.
* distutils.archive_util — Archiving utilities: distutils archive_util — Archiving utilities.
* distutils.dep_util — Dependency checking: distutils dep_util — Dependency checking.
* distutils.dir_util — Directory tree operations: distutils dir_util — Directory tree operations.
* distutils.file_util — Single file operations: distutils file_util — Single file operations.
* distutils.util — Miscellaneous other utility functions: distutils util — Miscellaneous other utility functions.
* distutils.dist — The Distribution class: distutils dist — The Distribution class.
* distutils.extension — The Extension class: distutils extension — The Extension class.
* distutils.debug — Distutils debug mode: distutils debug — Distutils debug mode.
* distutils.errors — Distutils exceptions: distutils errors — Distutils exceptions.
* distutils.fancy_getopt — Wrapper around the standard getopt module: distutils fancy_getopt — Wrapper around the standard getopt module.
* distutils.filelist — The FileList class: distutils filelist — The FileList class.
* distutils.log — Simple PEP 282-style logging: distutils log — Simple PEP 282-style logging.
* distutils.spawn — Spawn a sub-process: distutils spawn — Spawn a sub-process.
* distutils.sysconfig — System configuration information: distutils sysconfig — System configuration information.
* distutils.text_file — The TextFile class: distutils text_file — The TextFile class.
* distutils.version — Version number classes: distutils version — Version number classes.
* distutils.cmd — Abstract base class for Distutils commands: distutils cmd — Abstract base class for Distutils commands.
* Creating a new Distutils command::
* distutils.command — Individual Distutils commands: distutils command — Individual Distutils commands.
* distutils.command.bdist — Build a binary installer: distutils command bdist — Build a binary installer.
* distutils.command.bdist_packager — Abstract base class for packagers: distutils command bdist_packager — Abstract base class for packagers.
* distutils.command.bdist_dumb — Build a “dumb” installer: distutils command bdist_dumb — Build a “dumb” installer.
* distutils.command.bdist_msi — Build a Microsoft Installer binary package: distutils command bdist_msi — Build a Microsoft Installer binary package.
* distutils.command.bdist_rpm — Build a binary distribution as a Redhat RPM and SRPM: distutils command bdist_rpm — Build a binary distribution as a Redhat RPM and SRPM.
* distutils.command.bdist_wininst — Build a Windows installer: distutils command bdist_wininst — Build a Windows installer.
* distutils.command.sdist — Build a source distribution: distutils command sdist — Build a source distribution.
* distutils.command.build — Build all files of a package: distutils command build — Build all files of a package.
* distutils.command.build_clib — Build any C libraries in a package: distutils command build_clib — Build any C libraries in a package.
* distutils.command.build_ext — Build any extensions in a package: distutils command build_ext — Build any extensions in a package.
* distutils.command.build_py — Build the .py/.pyc files of a package: distutils command build_py — Build the py/ pyc files of a package.
* distutils.command.build_scripts — Build the scripts of a package: distutils command build_scripts — Build the scripts of a package.
* distutils.command.clean — Clean a package build area: distutils command clean — Clean a package build area.
* distutils.command.config — Perform package configuration: distutils command config — Perform package configuration.
* distutils.command.install — Install a package: distutils command install — Install a package.
* distutils.command.install_data — Install data files from a package: distutils command install_data — Install data files from a package.
* distutils.command.install_headers — Install C/C++ header files from a package: distutils command install_headers — Install C/C++ header files from a package.
* distutils.command.install_lib — Install library files from a package: distutils command install_lib — Install library files from a package.
* distutils.command.install_scripts — Install script files from a package: distutils command install_scripts — Install script files from a package.
* distutils.command.register — Register a module with the Python Package Index: distutils command register — Register a module with the Python Package Index.
* distutils.command.check — Check the meta-data of a package: distutils command check — Check the meta-data of a package.

Installing Python Modules (Legacy version)

* Introduction: Introduction<17>.
* Standard Build and Install::
* Alternate Installation::
* Custom Installation::
* Distutils Configuration Files::
* Building Extensions; Tips and Tricks: Building Extensions Tips and Tricks.

Introduction

* Distutils based source distributions::

Standard Build and Install

* Platform variations::
* Splitting the job up::
* How building works::
* How installation works::

Alternate Installation

* Alternate installation; the user scheme: Alternate installation the user scheme.
* Alternate installation; the home scheme: Alternate installation the home scheme.
* Alternate installation; Unix (the prefix scheme): Alternate installation Unix the prefix scheme.
* Alternate installation; Windows (the prefix scheme): Alternate installation Windows the prefix scheme.

Custom Installation

* Modifying Python’s Search Path::

Distutils Configuration Files

* Location and names of config files::
* Syntax of config files::

Building Extensions: Tips and Tricks

* Tweaking compiler/linker flags::
* Using non-Microsoft compilers on Windows::

Using non-Microsoft compilers on Windows

* Borland/CodeGear C++::
* GNU C / Cygwin / MinGW::

GNU C / Cygwin / MinGW

* Older Versions of Python and MinGW::



File: python.info,  Node: What’s New in Python,  Next: The Python Tutorial,  Prev: Top,  Up: Top

1 What’s New in Python
**********************

The “What’s New in Python” series of essays takes tours through the most
important changes between major Python versions.  They are a “must read”
for anyone wishing to stay up-to-date after a new release.

* Menu:

* What’s New In Python 3.9: What’s New In Python 3 9.
* What’s New In Python 3.8: What’s New In Python 3 8.
* What’s New In Python 3.7: What’s New In Python 3 7.
* What’s New In Python 3.6: What’s New In Python 3 6.
* What’s New In Python 3.5: What’s New In Python 3 5.
* What’s New In Python 3.4: What’s New In Python 3 4.
* What’s New In Python 3.3: What’s New In Python 3 3.
* What’s New In Python 3.2: What’s New In Python 3 2.
* What’s New In Python 3.1: What’s New In Python 3 1.
* What’s New In Python 3.0: What’s New In Python 3 0.
* What’s New in Python 2.7: What’s New in Python 2 7.
* What’s New in Python 2.6: What’s New in Python 2 6.
* What’s New in Python 2.5: What’s New in Python 2 5.
* What’s New in Python 2.4: What’s New in Python 2 4.
* What’s New in Python 2.3: What’s New in Python 2 3.
* What’s New in Python 2.2: What’s New in Python 2 2.
* What’s New in Python 2.1: What’s New in Python 2 1.
* What’s New in Python 2.0: What’s New in Python 2 0.
* Changelog::


File: python.info,  Node: What’s New In Python 3 9,  Next: What’s New In Python 3 8,  Up: What’s New in Python

1.1 What’s New In Python 3.9
============================


Release: 3.9.10


Date: January 14, 2022


Editor: Łukasz Langa

This article explains the new features in Python 3.9, compared to 3.8.
Python 3.9 was released on October 5th, 2020.

For full details, see the *note changelog: 156.

See also
........

PEP 596(1) - Python 3.9 Release Schedule

* Menu:

* Summary – Release highlights::
* You should check for DeprecationWarning in your code::
* New Features::
* Other Language Changes::
* New Modules::
* Improved Modules::
* Optimizations::
* Deprecated::
* Removed::
* Porting to Python 3.9: Porting to Python 3 9.
* Build Changes::
* C API Changes::
* Notable changes in Python 3.9.1: Notable changes in Python 3 9 1.
* Notable changes in Python 3.9.2: Notable changes in Python 3 9 2.
* Notable changes in Python 3.9.3: Notable changes in Python 3 9 3.
* Notable changes in Python 3.9.5: Notable changes in Python 3 9 5.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0596


File: python.info,  Node: Summary – Release highlights,  Next: You should check for DeprecationWarning in your code,  Up: What’s New In Python 3 9

1.1.1 Summary – Release highlights
----------------------------------

New syntax features:

   * PEP 584(1), union operators added to ‘dict’;

   * PEP 585(2), type hinting generics in standard collections;

   * PEP 614(3), relaxed grammar restrictions on decorators.

New built-in features:

   * PEP 616(4), string methods to remove prefixes and suffixes.

New features in the standard library:

   * PEP 593(5), flexible function and variable annotations;

   * *note os.pidfd_open(): 158. added that allows process management
     without races and signals.

Interpreter improvements:

   * PEP 573(6), fast access to module state from methods of C extension
     types;

   * PEP 617(7), CPython now uses a new parser based on PEG;

   * a number of Python builtins (range, tuple, set, frozenset, list,
     dict) are now sped up using PEP 590(8) vectorcall;

   * garbage collection does not block on resurrected objects;

   * a number of Python modules (‘_abc’, *note audioop: c, ‘_bz2’,
     ‘_codecs’, ‘_contextvars’, ‘_crypt’, ‘_functools’, ‘_json’,
     ‘_locale’, *note math: b1, *note operator: c2, *note resource: e0,
     *note time: 10c, ‘_weakref’) now use multiphase initialization as
     defined by PEP 489;

   * a number of standard library modules (*note audioop: c, *note ast:
     7, *note grp: 8a, ‘_hashlib’, *note pwd: d6, ‘_posixsubprocess’,
     *note random: dc, *note select: e5, *note struct: f8, *note
     termios: 104, *note zlib: 14d.) are now using the stable ABI
     defined by PEP 384.

New library modules:

   * PEP 615(9), the IANA Time Zone Database is now present in the
     standard library in the *note zoneinfo: 14e. module;

   * an implementation of a topological sort of a graph is now provided
     in the new *note graphlib: 89. module.

Release process changes:

   * PEP 602(10), CPython adopts an annual release cycle.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0584

   (2) https://www.python.org/dev/peps/pep-0585

   (3) https://www.python.org/dev/peps/pep-0614

   (4) https://www.python.org/dev/peps/pep-0616

   (5) https://www.python.org/dev/peps/pep-0593

   (6) https://www.python.org/dev/peps/pep-0573

   (7) https://www.python.org/dev/peps/pep-0617

   (8) https://www.python.org/dev/peps/pep-0590

   (9) https://www.python.org/dev/peps/pep-0615

   (10) https://www.python.org/dev/peps/pep-0602


File: python.info,  Node: You should check for DeprecationWarning in your code,  Next: New Features,  Prev: Summary – Release highlights,  Up: What’s New In Python 3 9

1.1.2 You should check for DeprecationWarning in your code
----------------------------------------------------------

When Python 2.7 was still supported, a lot of functionality in Python 3
was kept for backward compatibility with Python 2.7.  With the end of
Python 2 support, these backward compatibility layers have been removed,
or will be removed soon.  Most of them emitted a *note
DeprecationWarning: 15a. warning for several years.  For example, using
‘collections.Mapping’ instead of ‘collections.abc.Mapping’ emits a *note
DeprecationWarning: 15a. since Python 3.3, released in 2012.

Test your application with the *note -W: 15b. ‘default’ command-line
option to see *note DeprecationWarning: 15a. and *note
PendingDeprecationWarning: 15c, or even with *note -W: 15b. ‘error’ to
treat them as errors.  *note Warnings Filter: 15d. can be used to ignore
warnings from third-party code.

Python 3.9 is the last version providing those Python 2 backward
compatibility layers, to give more time to Python projects maintainers
to organize the removal of the Python 2 support and add support for
Python 3.9.

Aliases to *note Abstract Base Classes: 15e. in the *note collections:
1d. module, like ‘collections.Mapping’ alias to *note
collections.abc.Mapping: 15f, are kept for one last release for backward
compatibility.  They will be removed from Python 3.10.

More generally, try to run your tests in the *note Python Development
Mode: 160. which helps to prepare your code to make it compatible with
the next Python version.

Note: a number of pre-existing deprecations were removed in this version
of Python as well.  Consult the *note Removed: 161. section.


File: python.info,  Node: New Features,  Next: Other Language Changes,  Prev: You should check for DeprecationWarning in your code,  Up: What’s New In Python 3 9

1.1.3 New Features
------------------

* Menu:

* Dictionary Merge & Update Operators::
* New String Methods to Remove Prefixes and Suffixes::
* Type Hinting Generics in Standard Collections::
* New Parser::


File: python.info,  Node: Dictionary Merge & Update Operators,  Next: New String Methods to Remove Prefixes and Suffixes,  Up: New Features

1.1.3.1 Dictionary Merge & Update Operators
...........................................

Merge (‘|’) and update (‘|=’) operators have been added to the built-in
*note dict: 164. class.  Those complement the existing ‘dict.update’ and
‘{**d1, **d2}’ methods of merging dictionaries.

Example:

     >>> x = {"key1": "value1 from x", "key2": "value2 from x"}
     >>> y = {"key2": "value2 from y", "key3": "value3 from y"}
     >>> x | y
     {'key1': 'value1 from x', 'key2': 'value2 from y', 'key3': 'value3 from y'}
     >>> y | x
     {'key2': 'value2 from x', 'key3': 'value3 from y', 'key1': 'value1 from x'}

See PEP 584(1) for a full description.  (Contributed by Brandt Bucher in
bpo-36144(2).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0584

   (2) https://bugs.python.org/issue36144


File: python.info,  Node: New String Methods to Remove Prefixes and Suffixes,  Next: Type Hinting Generics in Standard Collections,  Prev: Dictionary Merge & Update Operators,  Up: New Features

1.1.3.2 New String Methods to Remove Prefixes and Suffixes
..........................................................

*note str.removeprefix(prefix): 166. and *note str.removesuffix(suffix):
167. have been added to easily remove an unneeded prefix or a suffix
from a string.  Corresponding ‘bytes’, ‘bytearray’, and
‘collections.UserString’ methods have also been added.  See PEP 616(1)
for a full description.  (Contributed by Dennis Sweeney in
bpo-39939(2).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0616

   (2) https://bugs.python.org/issue39939


File: python.info,  Node: Type Hinting Generics in Standard Collections,  Next: New Parser,  Prev: New String Methods to Remove Prefixes and Suffixes,  Up: New Features

1.1.3.3 Type Hinting Generics in Standard Collections
.....................................................

In type annotations you can now use built-in collection types such as
‘list’ and ‘dict’ as generic types instead of importing the
corresponding capitalized types (e.g.  ‘List’ or ‘Dict’) from ‘typing’.
Some other types in the standard library are also now generic, for
example ‘queue.Queue’.

Example:

     def greet_all(names: list[str]) -> None:
         for name in names:
             print("Hello", name)

See PEP 585(1) for more details.  (Contributed by Guido van Rossum,
Ethan Smith, and Batuhan Taşkaya in bpo-39481(2).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0585

   (2) https://bugs.python.org/issue39481


File: python.info,  Node: New Parser,  Prev: Type Hinting Generics in Standard Collections,  Up: New Features

1.1.3.4 New Parser
..................

Python 3.9 uses a new parser, based on PEG(1) instead of LL(1)(2).  The
new parser’s performance is roughly comparable to that of the old
parser, but the PEG formalism is more flexible than LL(1) when it comes
to designing new language features.  We’ll start using this flexibility
in Python 3.10 and later.

The *note ast: 7. module uses the new parser and produces the same AST
as the old parser.

In Python 3.10, the old parser will be deleted and so will all
functionality that depends on it (primarily the *note parser: c7.
module, which has long been deprecated).  In Python 3.9 `only', you can
switch back to the LL(1) parser using a command line switch (‘-X
oldparser’) or an environment variable (‘PYTHONOLDPARSER=1’).

See PEP 617(3) for more details.  (Contributed by Guido van Rossum,
Pablo Galindo and Lysandros Nikolaou in bpo-40334(4).)

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Parsing_expression_grammar

   (2) https://en.wikipedia.org/wiki/LL_parser

   (3) https://www.python.org/dev/peps/pep-0617

   (4) https://bugs.python.org/issue40334


File: python.info,  Node: Other Language Changes,  Next: New Modules,  Prev: New Features,  Up: What’s New In Python 3 9

1.1.4 Other Language Changes
----------------------------

   * *note __import__(): 16b. now raises *note ImportError: 16c. instead
     of *note ValueError: 16d, which used to occur when a relative
     import went past its top-level package.  (Contributed by Ngalim
     Siregar in bpo-37444(1).)

   * Python now gets the absolute path of the script filename specified
     on the command line (ex: ‘python3 script.py’): the ‘__file__’
     attribute of the *note __main__: 1. module became an absolute path,
     rather than a relative path.  These paths now remain valid after
     the current directory is changed by *note os.chdir(): 16e.  As a
     side effect, the traceback also displays the absolute path for
     *note __main__: 1. module frames in this case.  (Contributed by
     Victor Stinner in bpo-20443(2).)

   * In the *note Python Development Mode: 160. and in debug build, the
     `encoding' and `errors' arguments are now checked for string
     encoding and decoding operations.  Examples: *note open(): 16f,
     *note str.encode(): 170. and *note bytes.decode(): 171.

     By default, for best performance, the `errors' argument is only
     checked at the first encoding/decoding error and the `encoding'
     argument is sometimes ignored for empty strings.  (Contributed by
     Victor Stinner in bpo-37388(3).)

   * ‘"".replace("", s, n)’ now returns ‘s’ instead of an empty string
     for all non-zero ‘n’.  It is now consistent with ‘"".replace("",
     s)’.  There are similar changes for *note bytes: 172. and *note
     bytearray: 173. objects.  (Contributed by Serhiy Storchaka in
     bpo-28029(4).)

   * Any valid expression can now be used as a *note decorator: 174.
     Previously, the grammar was much more restrictive.  See PEP 614(5)
     for details.  (Contributed by Brandt Bucher in bpo-39702(6).)

   * Improved help for the *note typing: 122. module.  Docstrings are
     now shown for all special forms and special generic aliases (like
     ‘Union’ and ‘List’).  Using *note help(): 175. with generic alias
     like ‘List[int]’ will show the help for the correspondent concrete
     type (‘list’ in this case).  (Contributed by Serhiy Storchaka in
     bpo-40257(7).)

   * Parallel running of *note aclose(): 176. / *note asend(): 177. /
     *note athrow(): 178. is now prohibited, and ‘ag_running’ now
     reflects the actual running status of the async generator.
     (Contributed by Yury Selivanov in bpo-30773(8).)

   * Unexpected errors in calling the ‘__iter__’ method are no longer
     masked by ‘TypeError’ in the *note in: 179. operator and functions
     *note contains(): 17a, *note indexOf(): 17b. and *note countOf():
     17c. of the *note operator: c2. module.  (Contributed by Serhiy
     Storchaka in bpo-40824(9).)

   * Unparenthesized lambda expressions can no longer be the expression
     part in an ‘if’ clause in comprehensions and generator expressions.
     See bpo-41848(10) and bpo-43755(11) for details.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37444

   (2) https://bugs.python.org/issue20443

   (3) https://bugs.python.org/issue37388

   (4) https://bugs.python.org/issue28029

   (5) https://www.python.org/dev/peps/pep-0614

   (6) https://bugs.python.org/issue39702

   (7) https://bugs.python.org/issue40257

   (8) https://bugs.python.org/issue30773

   (9) https://bugs.python.org/issue40824

   (10) https://bugs.python.org/issue41848

   (11) https://bugs.python.org/issue43755


File: python.info,  Node: New Modules,  Next: Improved Modules,  Prev: Other Language Changes,  Up: What’s New In Python 3 9

1.1.5 New Modules
-----------------

* Menu:

* zoneinfo::
* graphlib::


File: python.info,  Node: zoneinfo,  Next: graphlib,  Up: New Modules

1.1.5.1 zoneinfo
................

The *note zoneinfo: 14e. module brings support for the IANA time zone
database to the standard library.  It adds *note zoneinfo.ZoneInfo: 17f,
a concrete *note datetime.tzinfo: 180. implementation backed by the
system’s time zone data.

Example:

     >>> from zoneinfo import ZoneInfo
     >>> from datetime import datetime, timedelta

     >>> # Daylight saving time
     >>> dt = datetime(2020, 10, 31, 12, tzinfo=ZoneInfo("America/Los_Angeles"))
     >>> print(dt)
     2020-10-31 12:00:00-07:00
     >>> dt.tzname()
     'PDT'

     >>> # Standard time
     >>> dt += timedelta(days=7)
     >>> print(dt)
     2020-11-07 12:00:00-08:00
     >>> print(dt.tzname())
     PST

As a fall-back source of data for platforms that don’t ship the IANA
database, the tzdata(1) module was released as a first-party package –
distributed via PyPI and maintained by the CPython core team.

See also
........

PEP 615(2) – Support for the IANA Time Zone Database in the Standard Library

     PEP written and implemented by Paul Ganssle

   ---------- Footnotes ----------

   (1) https://pypi.org/project/tzdata/

   (2) https://www.python.org/dev/peps/pep-0615


File: python.info,  Node: graphlib,  Prev: zoneinfo,  Up: New Modules

1.1.5.2 graphlib
................

A new module, *note graphlib: 89, was added that contains the *note
graphlib.TopologicalSorter: 182. class to offer functionality to perform
topological sorting of graphs.  (Contributed by Pablo Galindo, Tim
Peters and Larry Hastings in bpo-17005(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17005


File: python.info,  Node: Improved Modules,  Next: Optimizations,  Prev: New Modules,  Up: What’s New In Python 3 9

1.1.6 Improved Modules
----------------------

* Menu:

* ast::
* asyncio::
* compileall::
* concurrent.futures: concurrent futures.
* curses::
* datetime::
* distutils::
* fcntl::
* ftplib::
* gc::
* hashlib::
* http::
* IDLE and idlelib::
* imaplib::
* importlib::
* inspect::
* ipaddress::
* math::
* multiprocessing::
* nntplib::
* os::
* pathlib::
* pdb::
* poplib::
* pprint::
* pydoc::
* random::
* signal::
* smtplib::
* socket::
* time::
* sys::
* tracemalloc::
* typing::
* unicodedata::
* venv::
* xml::


File: python.info,  Node: ast,  Next: asyncio,  Up: Improved Modules

1.1.6.1 ast
...........

Added the `indent' option to *note dump(): 185. which allows it to
produce a multiline indented output.  (Contributed by Serhiy Storchaka
in bpo-37995(1).)

Added *note ast.unparse(): 186. as a function in the *note ast: 7.
module that can be used to unparse an *note ast.AST: 187. object and
produce a string with code that would produce an equivalent *note
ast.AST: 187. object when parsed.  (Contributed by Pablo Galindo and
Batuhan Taskaya in bpo-38870(2).)

Added docstrings to AST nodes that contains the ASDL signature used to
construct that node.  (Contributed by Batuhan Taskaya in bpo-39638(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37995

   (2) https://bugs.python.org/issue38870

   (3) https://bugs.python.org/issue39638


File: python.info,  Node: asyncio,  Next: compileall,  Prev: ast,  Up: Improved Modules

1.1.6.2 asyncio
...............

Due to significant security concerns, the `reuse_address' parameter of
*note asyncio.loop.create_datagram_endpoint(): 189. is no longer
supported.  This is because of the behavior of the socket option
‘SO_REUSEADDR’ in UDP. For more details, see the documentation for
‘loop.create_datagram_endpoint()’.  (Contributed by Kyle Stanley,
Antoine Pitrou, and Yury Selivanov in bpo-37228(1).)

Added a new *note coroutine: 18a. *note shutdown_default_executor():
18b. that schedules a shutdown for the default executor that waits on
the *note ThreadPoolExecutor: 18c. to finish closing.  Also, *note
asyncio.run(): 18d. has been updated to use the new *note coroutine:
18a.  (Contributed by Kyle Stanley in bpo-34037(2).)

Added *note asyncio.PidfdChildWatcher: 18e, a Linux-specific child
watcher implementation that polls process file descriptors.
(bpo-38692(3))

Added a new *note coroutine: 18a. *note asyncio.to_thread(): 18f.  It is
mainly used for running IO-bound functions in a separate thread to avoid
blocking the event loop, and essentially works as a high-level version
of *note run_in_executor(): 190. that can directly take keyword
arguments.  (Contributed by Kyle Stanley and Yury Selivanov in
bpo-32309(4).)

When cancelling the task due to a timeout, *note asyncio.wait_for():
191. will now wait until the cancellation is complete also in the case
when `timeout' is <= 0, like it does with positive timeouts.
(Contributed by Elvis Pranskevichus in bpo-32751(5).)

*note asyncio: 9. now raises ‘TyperError’ when calling incompatible
methods with an *note ssl.SSLSocket: 192. socket.  (Contributed by Ido
Michael in bpo-37404(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37228

   (2) https://bugs.python.org/issue34037

   (3) https://bugs.python.org/issue38692

   (4) https://bugs.python.org/issue32309

   (5) https://bugs.python.org/issue32751

   (6) https://bugs.python.org/issue37404


File: python.info,  Node: compileall,  Next: concurrent futures,  Prev: asyncio,  Up: Improved Modules

1.1.6.3 compileall
..................

Added new possibility to use hardlinks for duplicated ‘.pyc’ files:
`hardlink_dupes' parameter and –hardlink-dupes command line option.
(Contributed by Lumír ‘Frenzy’ Balhar in bpo-40495(1).)

Added new options for path manipulation in resulting ‘.pyc’ files:
`stripdir', `prependdir', `limit_sl_dest' parameters and -s, -p, -e
command line options.  Added the possibility to specify the option for
an optimization level multiple times.  (Contributed by Lumír ‘Frenzy’
Balhar in bpo-38112(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40495

   (2) https://bugs.python.org/issue38112


File: python.info,  Node: concurrent futures,  Next: curses,  Prev: compileall,  Up: Improved Modules

1.1.6.4 concurrent.futures
..........................

Added a new `cancel_futures' parameter to *note
concurrent.futures.Executor.shutdown(): 195. that cancels all pending
futures which have not started running, instead of waiting for them to
complete before shutting down the executor.  (Contributed by Kyle
Stanley in bpo-39349(1).)

Removed daemon threads from *note ThreadPoolExecutor: 18c. and *note
ProcessPoolExecutor: 196.  This improves compatibility with
subinterpreters and predictability in their shutdown processes.
(Contributed by Kyle Stanley in bpo-39812(2).)

Workers in *note ProcessPoolExecutor: 196. are now spawned on demand,
only when there are no available idle workers to reuse.  This optimizes
startup overhead and reduces the amount of lost CPU time to idle
workers.  (Contributed by Kyle Stanley in bpo-39207(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39349

   (2) https://bugs.python.org/issue39812

   (3) https://bugs.python.org/issue39207


File: python.info,  Node: curses,  Next: datetime,  Prev: concurrent futures,  Up: Improved Modules

1.1.6.5 curses
..............

Added *note curses.get_escdelay(): 198, *note curses.set_escdelay():
199, *note curses.get_tabsize(): 19a, and *note curses.set_tabsize():
19b. functions.  (Contributed by Anthony Sottile in bpo-38312(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38312


File: python.info,  Node: datetime,  Next: distutils,  Prev: curses,  Up: Improved Modules

1.1.6.6 datetime
................

The *note isocalendar(): 19d. of *note datetime.date: 19e. and *note
isocalendar(): 19f. of *note datetime.datetime: 1a0. methods now returns
a *note namedtuple(): 1a1. instead of a *note tuple: 1a2.  (Contributed
by Dong-hee Na in bpo-24416(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24416


File: python.info,  Node: distutils,  Next: fcntl,  Prev: datetime,  Up: Improved Modules

1.1.6.7 distutils
.................

The ‘upload’ command now creates SHA2-256 and Blake2b-256 hash digests.
It skips MD5 on platforms that block MD5 digest.  (Contributed by
Christian Heimes in bpo-40698(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40698


File: python.info,  Node: fcntl,  Next: ftplib,  Prev: distutils,  Up: Improved Modules

1.1.6.8 fcntl
.............

Added constants ‘F_OFD_GETLK’, ‘F_OFD_SETLK’ and ‘F_OFD_SETLKW’.
(Contributed by Dong-hee Na in bpo-38602(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38602


File: python.info,  Node: ftplib,  Next: gc,  Prev: fcntl,  Up: Improved Modules

1.1.6.9 ftplib
..............

*note FTP: 1a6. and *note FTP_TLS: 1a7. now raise a *note ValueError:
16d. if the given timeout for their constructor is zero to prevent the
creation of a non-blocking socket.  (Contributed by Dong-hee Na in
bpo-39259(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39259


File: python.info,  Node: gc,  Next: hashlib,  Prev: ftplib,  Up: Improved Modules

1.1.6.10 gc
...........

When the garbage collector makes a collection in which some objects
resurrect (they are reachable from outside the isolated cycles after the
finalizers have been executed), do not block the collection of all
objects that are still unreachable.  (Contributed by Pablo Galindo and
Tim Peters in bpo-38379(1).)

Added a new function *note gc.is_finalized(): 1a9. to check if an object
has been finalized by the garbage collector.  (Contributed by Pablo
Galindo in bpo-39322(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38379

   (2) https://bugs.python.org/issue39322


File: python.info,  Node: hashlib,  Next: http,  Prev: gc,  Up: Improved Modules

1.1.6.11 hashlib
................

The *note hashlib: 8c. module can now use SHA3 hashes and SHAKE XOF from
OpenSSL when available.  (Contributed by Christian Heimes in
bpo-37630(1).)

Builtin hash modules can now be disabled with ‘./configure
--without-builtin-hashlib-hashes’ or selectively enabled with e.g.
‘./configure --with-builtin-hashlib-hashes=sha3,blake2’ to force use of
OpenSSL based implementation.  (Contributed by Christian Heimes in
bpo-40479(2))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37630

   (2) https://bugs.python.org/issue40479


File: python.info,  Node: http,  Next: IDLE and idlelib,  Prev: hashlib,  Up: Improved Modules

1.1.6.12 http
.............

HTTP status codes ‘103 EARLY_HINTS’, ‘418 IM_A_TEAPOT’ and ‘425
TOO_EARLY’ are added to *note http.HTTPStatus: 1ac.  (Contributed by
Dong-hee Na in bpo-39509(1) and Ross Rhodes in bpo-39507(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39509

   (2) https://bugs.python.org/issue39507


File: python.info,  Node: IDLE and idlelib,  Next: imaplib,  Prev: http,  Up: Improved Modules

1.1.6.13 IDLE and idlelib
.........................

Added option to toggle cursor blink off.  (Contributed by Zackery Spytz
in bpo-4603(1).)

Escape key now closes IDLE completion windows.  (Contributed by Johnny
Najera in bpo-38944(2).)

Added keywords to module name completion list.  (Contributed by Terry J.
Reedy in bpo-37765(3).)

The changes above have been backported to 3.8 maintenance releases.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4603

   (2) https://bugs.python.org/issue38944

   (3) https://bugs.python.org/issue37765


File: python.info,  Node: imaplib,  Next: importlib,  Prev: IDLE and idlelib,  Up: Improved Modules

1.1.6.14 imaplib
................

*note IMAP4: 1af. and *note IMAP4_SSL: 1b0. now have an optional
`timeout' parameter for their constructors.  Also, the *note open():
1b1. method now has an optional `timeout' parameter with this change.
The overridden methods of *note IMAP4_SSL: 1b0. and *note IMAP4_stream:
1b2. were applied to this change.  (Contributed by Dong-hee Na in
bpo-38615(1).)

*note imaplib.IMAP4.unselect(): 1b3. is added.  *note
imaplib.IMAP4.unselect(): 1b3. frees server’s resources associated with
the selected mailbox and returns the server to the authenticated state.
This command performs the same actions as *note imaplib.IMAP4.close():
1b4, except that no messages are permanently removed from the currently
selected mailbox.  (Contributed by Dong-hee Na in bpo-40375(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38615

   (2) https://bugs.python.org/issue40375


File: python.info,  Node: importlib,  Next: inspect,  Prev: imaplib,  Up: Improved Modules

1.1.6.15 importlib
..................

To improve consistency with import statements, *note
importlib.util.resolve_name(): 1b6. now raises *note ImportError: 16c.
instead of *note ValueError: 16d. for invalid relative import attempts.
(Contributed by Ngalim Siregar in bpo-37444(1).)

Import loaders which publish immutable module objects can now publish
immutable packages in addition to individual modules.  (Contributed by
Dino Viehland in bpo-39336(2).)

Added *note importlib.resources.files(): 1b7. function with support for
subdirectories in package data, matching backport in
‘importlib_resources’ version 1.5.  (Contributed by Jason R. Coombs in
bpo-39791(3).)

Refreshed ‘importlib.metadata’ from ‘importlib_metadata’ version 1.6.1.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37444

   (2) https://bugs.python.org/issue39336

   (3) https://bugs.python.org/issue39791


File: python.info,  Node: inspect,  Next: ipaddress,  Prev: importlib,  Up: Improved Modules

1.1.6.16 inspect
................

*note inspect.BoundArguments.arguments: 1b9. is changed from
‘OrderedDict’ to regular dict.  (Contributed by Inada Naoki in
bpo-36350(1) and bpo-39775(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36350

   (2) https://bugs.python.org/issue39775


File: python.info,  Node: ipaddress,  Next: math,  Prev: inspect,  Up: Improved Modules

1.1.6.17 ipaddress
..................

*note ipaddress: a2. now supports IPv6 Scoped Addresses (IPv6 address
with suffix ‘%<scope_id>’).

Scoped IPv6 addresses can be parsed using *note ipaddress.IPv6Address:
1bb.  If present, scope zone ID is available through the *note scope_id:
1bc. attribute.  (Contributed by Oleksandr Pavliuk in bpo-34788(1).)

Starting with Python 3.9.5 the *note ipaddress: a2. module no longer
accepts any leading zeros in IPv4 address strings.  (Contributed by
Christian Heimes in bpo-36384(2)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34788

   (2) https://bugs.python.org/issue36384


File: python.info,  Node: math,  Next: multiprocessing,  Prev: ipaddress,  Up: Improved Modules

1.1.6.18 math
.............

Expanded the *note math.gcd(): 1be. function to handle multiple
arguments.  Formerly, it only supported two arguments.  (Contributed by
Serhiy Storchaka in bpo-39648(1).)

Added *note math.lcm(): 1bf.: return the least common multiple of
specified arguments.  (Contributed by Mark Dickinson, Ananthakrishnan
and Serhiy Storchaka in bpo-39479(2) and bpo-39648(3).)

Added *note math.nextafter(): 1c0.: return the next floating-point value
after `x' towards `y'.  (Contributed by Victor Stinner in bpo-39288(4).)

Added *note math.ulp(): 1c1.: return the value of the least significant
bit of a float.  (Contributed by Victor Stinner in bpo-39310(5).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39648

   (2) https://bugs.python.org/issue39479

   (3) https://bugs.python.org/issue39648

   (4) https://bugs.python.org/issue39288

   (5) https://bugs.python.org/issue39310


File: python.info,  Node: multiprocessing,  Next: nntplib,  Prev: math,  Up: Improved Modules

1.1.6.19 multiprocessing
........................

The *note multiprocessing.SimpleQueue: 1c3. class has a new *note
close(): 1c4. method to explicitly close the queue.  (Contributed by
Victor Stinner in bpo-30966(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30966


File: python.info,  Node: nntplib,  Next: os,  Prev: multiprocessing,  Up: Improved Modules

1.1.6.20 nntplib
................

*note NNTP: 1c6. and *note NNTP_SSL: 1c7. now raise a *note ValueError:
16d. if the given timeout for their constructor is zero to prevent the
creation of a non-blocking socket.  (Contributed by Dong-hee Na in
bpo-39259(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39259


File: python.info,  Node: os,  Next: pathlib,  Prev: nntplib,  Up: Improved Modules

1.1.6.21 os
...........

Added *note CLD_KILLED: 1c9. and *note CLD_STOPPED: 1ca. for ‘si_code’.
(Contributed by Dong-hee Na in bpo-38493(1).)

Exposed the Linux-specific *note os.pidfd_open(): 158. (bpo-38692(2))
and *note os.P_PIDFD: 1cb. (bpo-38713(3)) for process management with
file descriptors.

The *note os.unsetenv(): 1cc. function is now also available on Windows.
(Contributed by Victor Stinner in bpo-39413(4).)

The *note os.putenv(): 1cd. and *note os.unsetenv(): 1cc. functions are
now always available.  (Contributed by Victor Stinner in bpo-39395(5).)

Added *note os.waitstatus_to_exitcode(): 1ce. function: convert a wait
status to an exit code.  (Contributed by Victor Stinner in
bpo-40094(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38493

   (2) https://bugs.python.org/issue38692

   (3) https://bugs.python.org/issue38713

   (4) https://bugs.python.org/issue39413

   (5) https://bugs.python.org/issue39395

   (6) https://bugs.python.org/issue40094


File: python.info,  Node: pathlib,  Next: pdb,  Prev: os,  Up: Improved Modules

1.1.6.22 pathlib
................

Added *note pathlib.Path.readlink(): 1d0. which acts similarly to *note
os.readlink(): 1d1.  (Contributed by Girts Folkmanis in bpo-30618(1))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30618


File: python.info,  Node: pdb,  Next: poplib,  Prev: pathlib,  Up: Improved Modules

1.1.6.23 pdb
............

On Windows now *note Pdb: 1d3. supports ‘~/.pdbrc’.  (Contributed by Tim
Hopper and Dan Lidral-Porter in bpo-20523(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20523


File: python.info,  Node: poplib,  Next: pprint,  Prev: pdb,  Up: Improved Modules

1.1.6.24 poplib
...............

*note POP3: 1d5. and *note POP3_SSL: 1d6. now raise a *note ValueError:
16d. if the given timeout for their constructor is zero to prevent the
creation of a non-blocking socket.  (Contributed by Dong-hee Na in
bpo-39259(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39259


File: python.info,  Node: pprint,  Next: pydoc,  Prev: poplib,  Up: Improved Modules

1.1.6.25 pprint
...............

*note pprint: d2. can now pretty-print *note types.SimpleNamespace: 1d8.
(Contributed by Carl Bordum Hansen in bpo-37376(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37376


File: python.info,  Node: pydoc,  Next: random,  Prev: pprint,  Up: Improved Modules

1.1.6.26 pydoc
..............

The documentation string is now shown not only for class, function,
method etc, but for any object that has its own ‘__doc__’ attribute.
(Contributed by Serhiy Storchaka in bpo-40257(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40257


File: python.info,  Node: random,  Next: signal,  Prev: pydoc,  Up: Improved Modules

1.1.6.27 random
...............

Added a new ‘random.Random.randbytes’ method: generate random bytes.
(Contributed by Victor Stinner in bpo-40286(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40286


File: python.info,  Node: signal,  Next: smtplib,  Prev: random,  Up: Improved Modules

1.1.6.28 signal
...............

Exposed the Linux-specific *note signal.pidfd_send_signal(): 1dc. for
sending to signals to a process using a file descriptor instead of a
pid.  (bpo-38712(1))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38712


File: python.info,  Node: smtplib,  Next: socket,  Prev: signal,  Up: Improved Modules

1.1.6.29 smtplib
................

*note SMTP: 1de. and *note SMTP_SSL: 1df. now raise a *note ValueError:
16d. if the given timeout for their constructor is zero to prevent the
creation of a non-blocking socket.  (Contributed by Dong-hee Na in
bpo-39259(1).)

*note LMTP: 1e0. constructor now has an optional `timeout' parameter.
(Contributed by Dong-hee Na in bpo-39329(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39259

   (2) https://bugs.python.org/issue39329


File: python.info,  Node: socket,  Next: time,  Prev: smtplib,  Up: Improved Modules

1.1.6.30 socket
...............

The *note socket: ef. module now exports the *note CAN_RAW_JOIN_FILTERS:
1e2. constant on Linux 4.1 and greater.  (Contributed by Stefan
Tatschner and Zackery Spytz in bpo-25780(1).)

The socket module now supports the *note CAN_J1939: 1e3. protocol on
platforms that support it.  (Contributed by Karl Ding in bpo-40291(2).)

The socket module now has the *note socket.send_fds(): 1e4. and *note
socket.recv_fds(): 1e5. functions.  (Contributed by Joannah Nanjekye,
Shinya Okano and Victor Stinner in bpo-28724(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25780

   (2) https://bugs.python.org/issue40291

   (3) https://bugs.python.org/issue28724


File: python.info,  Node: time,  Next: sys,  Prev: socket,  Up: Improved Modules

1.1.6.31 time
.............

On AIX, *note thread_time(): 1e7. is now implemented with
‘thread_cputime()’ which has nanosecond resolution, rather than
‘clock_gettime(CLOCK_THREAD_CPUTIME_ID)’ which has a resolution of 10
ms.  (Contributed by Batuhan Taskaya in bpo-40192(1))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40192


File: python.info,  Node: sys,  Next: tracemalloc,  Prev: time,  Up: Improved Modules

1.1.6.32 sys
............

Added a new *note sys.platlibdir: 1e9. attribute: name of the
platform-specific library directory.  It is used to build the path of
standard library and the paths of installed extension modules.  It is
equal to ‘"lib"’ on most platforms.  On Fedora and SuSE, it is equal to
‘"lib64"’ on 64-bit platforms.  (Contributed by Jan Matějek, Matěj Cepl,
Charalampos Stratakis and Victor Stinner in bpo-1294959(1).)

Previously, *note sys.stderr: 1ea. was block-buffered when
non-interactive.  Now ‘stderr’ defaults to always being line-buffered.
(Contributed by Jendrik Seipp in bpo-13601(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1294959

   (2) https://bugs.python.org/issue13601


File: python.info,  Node: tracemalloc,  Next: typing,  Prev: sys,  Up: Improved Modules

1.1.6.33 tracemalloc
....................

Added *note tracemalloc.reset_peak(): 1ec. to set the peak size of
traced memory blocks to the current size, to measure the peak of
specific pieces of code.  (Contributed by Huon Wilson in bpo-40630(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40630


File: python.info,  Node: typing,  Next: unicodedata,  Prev: tracemalloc,  Up: Improved Modules

1.1.6.34 typing
...............

PEP 593(1) introduced an *note typing.Annotated: 1ee. type to decorate
existing types with context-specific metadata and new ‘include_extras’
parameter to *note typing.get_type_hints(): 1ef. to access the metadata
at runtime.  (Contributed by Till Varoquaux and Konstantin Kashin.)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0593


File: python.info,  Node: unicodedata,  Next: venv,  Prev: typing,  Up: Improved Modules

1.1.6.35 unicodedata
....................

The Unicode database has been updated to version 13.0.0.
(bpo-39926(1)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39926


File: python.info,  Node: venv,  Next: xml,  Prev: unicodedata,  Up: Improved Modules

1.1.6.36 venv
.............

The activation scripts provided by *note venv: 12e. now all specify
their prompt customization consistently by always using the value
specified by ‘__VENV_PROMPT__’.  Previously some scripts unconditionally
used ‘__VENV_PROMPT__’, others only if it happened to be set (which was
the default case), and one used ‘__VENV_NAME__’ instead.  (Contributed
by Brett Cannon in bpo-37663(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37663


File: python.info,  Node: xml,  Prev: venv,  Up: Improved Modules

1.1.6.37 xml
............

White space characters within attributes are now preserved when
serializing *note xml.etree.ElementTree: 140. to XML file.  EOLNs are no
longer normalized to “n”.  This is the result of discussion about how to
interpret section 2.11 of XML spec.  (Contributed by Mefistotelis in
bpo-39011(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39011


File: python.info,  Node: Optimizations,  Next: Deprecated,  Prev: Improved Modules,  Up: What’s New In Python 3 9

1.1.7 Optimizations
-------------------

   * Optimized the idiom for assignment a temporary variable in
     comprehensions.  Now ‘for y in [expr]’ in comprehensions is as fast
     as a simple assignment ‘y = expr’.  For example:

          sums = [s for s in [0] for x in data for s in [s + x]]

     Unlike the ‘:=’ operator this idiom does not leak a variable to the
     outer scope.

     (Contributed by Serhiy Storchaka in bpo-32856(1).)

   * Optimized signal handling in multithreaded applications.  If a
     thread different than the main thread gets a signal, the bytecode
     evaluation loop is no longer interrupted at each bytecode
     instruction to check for pending signals which cannot be handled.
     Only the main thread of the main interpreter can handle signals.

     Previously, the bytecode evaluation loop was interrupted at each
     instruction until the main thread handles signals.  (Contributed by
     Victor Stinner in bpo-40010(2).)

   * Optimized the *note subprocess: f9. module on FreeBSD using
     ‘closefrom()’.  (Contributed by Ed Maste, Conrad Meyer, Kyle Evans,
     Kubilay Kocak and Victor Stinner in bpo-38061(3).)

   * *note PyLong_FromDouble(): 1f4. is now up to 1.87x faster for
     values that fit into ‘long’.  (Contributed by Sergey Fedoseev in
     bpo-37986(4).)

   * A number of Python builtins (*note range: 1f5, *note tuple: 1a2,
     *note set: 1f6, *note frozenset: 1f7, *note list: 1f8, *note dict:
     164.) are now sped up by using PEP 590(5) vectorcall protocol.
     (Contributed by Dong-hee Na, Mark Shannon, Jeroen Demeyer and Petr
     Viktorin in bpo-37207(6).)

   * Optimized ‘difference_update()’ for the case when the other set is
     much larger than the base set.  (Suggested by Evgeny Kapun with
     code contributed by Michele Orrù in bpo-8425(7).)

   * Python’s small object allocator (‘obmalloc.c’) now allows (no more
     than) one empty arena to remain available for immediate reuse,
     without returning it to the OS. This prevents thrashing in simple
     loops where an arena could be created and destroyed anew on each
     iteration.  (Contributed by Tim Peters in bpo-37257(8).)

   * *note floor division: 1f9. of float operation now has a better
     performance.  Also the message of *note ZeroDivisionError: 1fa. for
     this operation is updated.  (Contributed by Dong-hee Na in
     bpo-39434(9).)

   * Decoding short ASCII strings with UTF-8 and ascii codecs is now
     about 15% faster.  (Contributed by Inada Naoki in bpo-37348(10).)

Here’s a summary of performance improvements from Python 3.4 through
Python 3.9:

     Python version                       3.4     3.5     3.6     3.7     3.8    3.9
     --------------                       ---     ---     ---     ---     ---    ---

     Variable and attribute read access:
         read_local                       7.1     7.1     5.4     5.1     3.9    3.9
         read_nonlocal                    7.1     8.1     5.8     5.4     4.4    4.5
         read_global                     15.5    19.0    14.3    13.6     7.6    7.8
         read_builtin                    21.1    21.6    18.5    19.0     7.5    7.8
         read_classvar_from_class        25.6    26.5    20.7    19.5    18.4   17.9
         read_classvar_from_instance     22.8    23.5    18.8    17.1    16.4   16.9
         read_instancevar                32.4    33.1    28.0    26.3    25.4   25.3
         read_instancevar_slots          27.8    31.3    20.8    20.8    20.2   20.5
         read_namedtuple                 73.8    57.5    45.0    46.8    18.4   18.7
         read_boundmethod                37.6    37.9    29.6    26.9    27.7   41.1

     Variable and attribute write access:
         write_local                      8.7     9.3     5.5     5.3     4.3    4.3
         write_nonlocal                  10.5    11.1     5.6     5.5     4.7    4.8
         write_global                    19.7    21.2    18.0    18.0    15.8   16.7
         write_classvar                  92.9    96.0   104.6   102.1    39.2   39.8
         write_instancevar               44.6    45.8    40.0    38.9    35.5   37.4
         write_instancevar_slots         35.6    36.1    27.3    26.6    25.7   25.8

     Data structure read access:
         read_list                       24.2    24.5    20.8    20.8    19.0   19.5
         read_deque                      24.7    25.5    20.2    20.6    19.8   20.2
         read_dict                       24.3    25.7    22.3    23.0    21.0   22.4
         read_strdict                    22.6    24.3    19.5    21.2    18.9   21.5

     Data structure write access:
         write_list                      27.1    28.5    22.5    21.6    20.0   20.0
         write_deque                     28.7    30.1    22.7    21.8    23.5   21.7
         write_dict                      31.4    33.3    29.3    29.2    24.7   25.4
         write_strdict                   28.4    29.9    27.5    25.2    23.1   24.5

     Stack (or queue) operations:
         list_append_pop                 93.4   112.7    75.4    74.2    50.8   50.6
         deque_append_pop                43.5    57.0    49.4    49.2    42.5   44.2
         deque_append_popleft            43.7    57.3    49.7    49.7    42.8   46.4

     Timing loop:
         loop_overhead                    0.5     0.6     0.4     0.3     0.3    0.3

These results were generated from the variable access benchmark script
at: ‘Tools/scripts/var_access_benchmark.py’.  The benchmark script
displays timings in nanoseconds.  The benchmarks were measured on an
Intel® Core™ i7-4960HQ processor(11) running the macOS 64-bit builds
found at python.org(12).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32856

   (2) https://bugs.python.org/issue40010

   (3) https://bugs.python.org/issue38061

   (4) https://bugs.python.org/issue37986

   (5) https://www.python.org/dev/peps/pep-0590

   (6) https://bugs.python.org/issue37207

   (7) https://bugs.python.org/issue8425

   (8) https://bugs.python.org/issue37257

   (9) https://bugs.python.org/issue39434

   (10) https://bugs.python.org/issue37348

   (11) 
https://ark.intel.com/content/www/us/en/ark/products/76088/intel-core-i7-4960hq-processor-6m-cache-up-to-3-80-ghz.html

   (12) https://www.python.org/downloads/mac-osx/


File: python.info,  Node: Deprecated,  Next: Removed,  Prev: Optimizations,  Up: What’s New In Python 3 9

1.1.8 Deprecated
----------------

   * The distutils ‘bdist_msi’ command is now deprecated, use
     ‘bdist_wheel’ (wheel packages) instead.  (Contributed by Hugo van
     Kemenade in bpo-39586(1).)

   * Currently *note math.factorial(): 1fc. accepts *note float: 1fd.
     instances with non-negative integer values (like ‘5.0’).  It raises
     a *note ValueError: 16d. for non-integral and negative floats.  It
     is now deprecated.  In future Python versions it will raise a *note
     TypeError: 1fe. for all floats.  (Contributed by Serhiy Storchaka
     in bpo-37315(2).)

   * The *note parser: c7. and *note symbol: fb. modules are deprecated
     and will be removed in future versions of Python.  For the majority
     of use cases, users can leverage the Abstract Syntax Tree (AST)
     generation and compilation stage, using the *note ast: 7. module.

   * The Public C API functions *note PyParser_SimpleParseStringFlags():
     1ff, *note PyParser_SimpleParseStringFlagsFilename(): 200, *note
     PyParser_SimpleParseFileFlags(): 201. and ‘PyNode_Compile()’ are
     deprecated and will be removed in Python 3.10 together with the old
     parser.

   * Using *note NotImplemented: 202. in a boolean context has been
     deprecated, as it is almost exclusively the result of incorrect
     rich comparator implementations.  It will be made a *note
     TypeError: 1fe. in a future version of Python.  (Contributed by
     Josh Rosenberg in bpo-35712(3).)

   * The *note random: dc. module currently accepts any hashable type as
     a possible seed value.  Unfortunately, some of those types are not
     guaranteed to have a deterministic hash value.  After Python 3.9,
     the module will restrict its seeds to *note None: 203, *note int:
     204, *note float: 1fd, *note str: 205, *note bytes: 172, and *note
     bytearray: 173.

   * Opening the *note GzipFile: 206. file for writing without
     specifying the `mode' argument is deprecated.  In future Python
     versions it will always be opened for reading by default.  Specify
     the `mode' argument for opening it for writing and silencing a
     warning.  (Contributed by Serhiy Storchaka in bpo-28286(4).)

   * Deprecated the ‘split()’ method of ‘_tkinter.TkappType’ in favour
     of the ‘splitlist()’ method which has more consistent and
     predicable behavior.  (Contributed by Serhiy Storchaka in
     bpo-38371(5).)

   * The explicit passing of coroutine objects to *note asyncio.wait():
     207. has been deprecated and will be removed in version 3.11.
     (Contributed by Yury Selivanov and Kyle Stanley in bpo-34790(6).)

   * binhex4 and hexbin4 standards are now deprecated.  The *note
     binhex: 10. module and the following *note binascii: f. functions
     are now deprecated:

        * *note b2a_hqx(): 208, *note a2b_hqx(): 209.

        * *note rlecode_hqx(): 20a, *note rledecode_hqx(): 20b.

     (Contributed by Victor Stinner in bpo-39353(7).)

   * *note ast: 7. classes ‘slice’, ‘Index’ and ‘ExtSlice’ are
     considered deprecated and will be removed in future Python
     versions.  ‘value’ itself should be used instead of ‘Index(value)’.
     ‘Tuple(slices, Load())’ should be used instead of
     ‘ExtSlice(slices)’.  (Contributed by Serhiy Storchaka in
     bpo-34822(8).)

   * *note ast: 7. classes ‘Suite’, ‘Param’, ‘AugLoad’ and ‘AugStore’
     are considered deprecated and will be removed in future Python
     versions.  They were not generated by the parser and not accepted
     by the code generator in Python 3.  (Contributed by Batuhan Taskaya
     in bpo-39639(9) and bpo-39969(10) and Serhiy Storchaka in
     bpo-39988(11).)

   * The *note PyEval_InitThreads(): 20c. and *note
     PyEval_ThreadsInitialized(): 20d. functions are now deprecated and
     will be removed in Python 3.11.  Calling *note
     PyEval_InitThreads(): 20c. now does nothing.  The *note GIL: 20e.
     is initialized by *note Py_Initialize(): 20f. since Python 3.7.
     (Contributed by Victor Stinner in bpo-39877(12).)

   * Passing ‘None’ as the first argument to the *note shlex.split():
     210. function has been deprecated.  (Contributed by Zackery Spytz
     in bpo-33262(13).)

   * *note smtpd.MailmanProxy(): 211. is now deprecated as it is
     unusable without an external module, ‘mailman’.  (Contributed by
     Samuel Colvin in bpo-35800(14).)

   * The *note lib2to3: a7. module now emits a *note
     PendingDeprecationWarning: 15c.  Python 3.9 switched to a PEG
     parser (see PEP 617(15)), and Python 3.10 may include new language
     syntax that is not parsable by lib2to3’s LL(1) parser.  The
     ‘lib2to3’ module may be removed from the standard library in a
     future Python version.  Consider third-party alternatives such as
     LibCST(16) or parso(17).  (Contributed by Carl Meyer in
     bpo-40360(18).)

   * The `random' parameter of *note random.shuffle(): 212. has been
     deprecated.  (Contributed by Raymond Hettinger in bpo-40465(19))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39586

   (2) https://bugs.python.org/issue37315

   (3) https://bugs.python.org/issue35712

   (4) https://bugs.python.org/issue28286

   (5) https://bugs.python.org/issue38371

   (6) https://bugs.python.org/issue34790

   (7) https://bugs.python.org/issue39353

   (8) https://bugs.python.org/issue34822

   (9) https://bugs.python.org/issue39639

   (10) https://bugs.python.org/issue39969

   (11) https://bugs.python.org/issue39988

   (12) https://bugs.python.org/issue39877

   (13) https://bugs.python.org/issue33262

   (14) https://bugs.python.org/issue35800

   (15) https://www.python.org/dev/peps/pep-0617

   (16) https://libcst.readthedocs.io/

   (17) https://parso.readthedocs.io/

   (18) https://bugs.python.org/issue40360

   (19) https://bugs.python.org/issue40465


File: python.info,  Node: Removed,  Next: Porting to Python 3 9,  Prev: Deprecated,  Up: What’s New In Python 3 9

1.1.9 Removed
-------------

   * The erroneous version at ‘unittest.mock.__version__’ has been
     removed.

   * *note nntplib.NNTP: 1c6.: ‘xpath()’ and ‘xgtitle()’ methods have
     been removed.  These methods are deprecated since Python 3.3.
     Generally, these extensions are not supported or not enabled by
     NNTP server administrators.  For ‘xgtitle()’, please use *note
     nntplib.NNTP.descriptions(): 214. or *note
     nntplib.NNTP.description(): 215. instead.  (Contributed by Dong-hee
     Na in bpo-39366(1).)

   * *note array.array: 216.: ‘tostring()’ and ‘fromstring()’ methods
     have been removed.  They were aliases to ‘tobytes()’ and
     ‘frombytes()’, deprecated since Python 3.2.  (Contributed by Victor
     Stinner in bpo-38916(2).)

   * The undocumented ‘sys.callstats()’ function has been removed.
     Since Python 3.7, it was deprecated and always returned *note None:
     203.  It required a special build option ‘CALL_PROFILE’ which was
     already removed in Python 3.7.  (Contributed by Victor Stinner in
     bpo-37414(3).)

   * The ‘sys.getcheckinterval()’ and ‘sys.setcheckinterval()’ functions
     have been removed.  They were deprecated since Python 3.2.  Use
     *note sys.getswitchinterval(): 217. and *note
     sys.setswitchinterval(): 218. instead.  (Contributed by Victor
     Stinner in bpo-37392(4).)

   * The C function ‘PyImport_Cleanup()’ has been removed.  It was
     documented as: “Empty the module table.  For internal use only.”
     (Contributed by Victor Stinner in bpo-36710(5).)

   * ‘_dummy_thread’ and ‘dummy_threading’ modules have been removed.
     These modules were deprecated since Python 3.7 which requires
     threading support.  (Contributed by Victor Stinner in
     bpo-37312(6).)

   * ‘aifc.openfp()’ alias to ‘aifc.open()’, ‘sunau.openfp()’ alias to
     ‘sunau.open()’, and ‘wave.openfp()’ alias to *note wave.open():
     219. have been removed.  They were deprecated since Python 3.7.
     (Contributed by Victor Stinner in bpo-37320(7).)

   * The ‘isAlive()’ method of *note threading.Thread: 21a. has been
     removed.  It was deprecated since Python 3.8.  Use *note
     is_alive(): 21b. instead.  (Contributed by Dong-hee Na in
     bpo-37804(8).)

   * Methods ‘getchildren()’ and ‘getiterator()’ of classes *note
     ElementTree: 21c. and *note Element: 21d. in the *note ElementTree:
     140. module have been removed.  They were deprecated in Python 3.2.
     Use ‘iter(x)’ or ‘list(x)’ instead of ‘x.getchildren()’ and
     ‘x.iter()’ or ‘list(x.iter())’ instead of ‘x.getiterator()’.
     (Contributed by Serhiy Storchaka in bpo-36543(9).)

   * The old *note plistlib: cf. API has been removed, it was deprecated
     since Python 3.4.  Use the *note load(): 21e, *note loads(): 21f,
     *note dump(): 220, and *note dumps(): 221. functions.
     Additionally, the `use_builtin_types' parameter was removed,
     standard *note bytes: 172. objects are always used instead.
     (Contributed by Jon Janzen in bpo-36409(10).)

   * The C function ‘PyGen_NeedsFinalizing’ has been removed.  It was
     not documented, tested, or used anywhere within CPython after the
     implementation of PEP 442(11).  Patch by Joannah Nanjekye.
     (Contributed by Joannah Nanjekye in bpo-15088(12))

   * ‘base64.encodestring()’ and ‘base64.decodestring()’, aliases
     deprecated since Python 3.1, have been removed: use *note
     base64.encodebytes(): 222. and *note base64.decodebytes(): 223.
     instead.  (Contributed by Victor Stinner in bpo-39351(13).)

   * ‘fractions.gcd()’ function has been removed, it was deprecated
     since Python 3.5 (bpo-22486(14)): use *note math.gcd(): 1be.
     instead.  (Contributed by Victor Stinner in bpo-39350(15).)

   * The `buffering' parameter of *note bz2.BZ2File: 224. has been
     removed.  Since Python 3.0, it was ignored and using it emitted a
     *note DeprecationWarning: 15a.  Pass an open file object to control
     how the file is opened.  (Contributed by Victor Stinner in
     bpo-39357(16).)

   * The `encoding' parameter of *note json.loads(): 225. has been
     removed.  As of Python 3.1, it was deprecated and ignored; using it
     has emitted a *note DeprecationWarning: 15a. since Python 3.8.
     (Contributed by Inada Naoki in bpo-39377(17))

   * ‘with (await asyncio.lock):’ and ‘with (yield from asyncio.lock):’
     statements are not longer supported, use ‘async with lock’ instead.
     The same is correct for ‘asyncio.Condition’ and
     ‘asyncio.Semaphore’.  (Contributed by Andrew Svetlov in
     bpo-34793(18).)

   * The ‘sys.getcounts()’ function, the ‘-X showalloccount’ command
     line option and the ‘show_alloc_count’ field of the C structure
     *note PyConfig: 226. have been removed.  They required a special
     Python build by defining ‘COUNT_ALLOCS’ macro.  (Contributed by
     Victor Stinner in bpo-39489(19).)

   * The ‘_field_types’ attribute of the *note typing.NamedTuple: 227.
     class has been removed.  It was deprecated since Python 3.8.  Use
     the ‘__annotations__’ attribute instead.  (Contributed by Serhiy
     Storchaka in bpo-40182(20).)

   * The ‘symtable.SymbolTable.has_exec()’ method has been removed.  It
     was deprecated since 2006, and only returning ‘False’ when it’s
     called.  (Contributed by Batuhan Taskaya in bpo-40208(21))

   * The ‘asyncio.Task.current_task()’ and ‘asyncio.Task.all_tasks()’
     have been removed.  They were deprecated since Python 3.7 and you
     can use *note asyncio.current_task(): 228. and *note
     asyncio.all_tasks(): 229. instead.  (Contributed by Rémi Lapeyre in
     bpo-40967(22))

   * The ‘unescape()’ method in the *note html.parser.HTMLParser: 22a.
     class has been removed (it was deprecated since Python 3.4).  *note
     html.unescape(): 22b. should be used for converting character
     references to the corresponding unicode characters.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39366

   (2) https://bugs.python.org/issue38916

   (3) https://bugs.python.org/issue37414

   (4) https://bugs.python.org/issue37392

   (5) https://bugs.python.org/issue36710

   (6) https://bugs.python.org/issue37312

   (7) https://bugs.python.org/issue37320

   (8) https://bugs.python.org/issue37804

   (9) https://bugs.python.org/issue36543

   (10) https://bugs.python.org/issue36409

   (11) https://www.python.org/dev/peps/pep-0442

   (12) https://bugs.python.org/issue15088

   (13) https://bugs.python.org/issue39351

   (14) https://bugs.python.org/issue22486

   (15) https://bugs.python.org/issue39350

   (16) https://bugs.python.org/issue39357

   (17) https://bugs.python.org/issue39377

   (18) https://bugs.python.org/issue34793

   (19) https://bugs.python.org/issue39489

   (20) https://bugs.python.org/issue40182

   (21) https://bugs.python.org/issue40208

   (22) https://bugs.python.org/issue40967


File: python.info,  Node: Porting to Python 3 9,  Next: Build Changes,  Prev: Removed,  Up: What’s New In Python 3 9

1.1.10 Porting to Python 3.9
----------------------------

This section lists previously described changes and other bugfixes that
may require changes to your code.

* Menu:

* Changes in the Python API::
* Changes in the C API::
* CPython bytecode changes::


File: python.info,  Node: Changes in the Python API,  Next: Changes in the C API,  Up: Porting to Python 3 9

1.1.10.1 Changes in the Python API
..................................

   * *note __import__(): 16b. and *note importlib.util.resolve_name():
     1b6. now raise *note ImportError: 16c. where it previously raised
     *note ValueError: 16d.  Callers catching the specific exception
     type and supporting both Python 3.9 and earlier versions will need
     to catch both using ‘except (ImportError, ValueError):’.

   * The *note venv: 12e. activation scripts no longer special-case when
     ‘__VENV_PROMPT__’ is set to ‘""’.

   * The *note select.epoll.unregister(): 22e. method no longer ignores
     the *note EBADF: 22f. error.  (Contributed by Victor Stinner in
     bpo-39239(1).)

   * The `compresslevel' parameter of *note bz2.BZ2File: 224. became
     keyword-only, since the `buffering' parameter has been removed.
     (Contributed by Victor Stinner in bpo-39357(2).)

   * Simplified AST for subscription.  Simple indices will be
     represented by their value, extended slices will be represented as
     tuples.  ‘Index(value)’ will return a ‘value’ itself,
     ‘ExtSlice(slices)’ will return ‘Tuple(slices, Load())’.
     (Contributed by Serhiy Storchaka in bpo-34822(3).)

   * The *note importlib: 9a. module now ignores the *note PYTHONCASEOK:
     230. environment variable when the *note -E: 231. or *note -I: 232.
     command line options are being used.

   * The `encoding' parameter has been added to the classes *note
     ftplib.FTP: 1a6. and *note ftplib.FTP_TLS: 1a7. as a keyword-only
     parameter, and the default encoding is changed from Latin-1 to
     UTF-8 to follow RFC 2640(4).

   * *note asyncio.loop.shutdown_default_executor(): 18b. has been added
     to *note AbstractEventLoop: 233, meaning alternative event loops
     that inherit from it should have this method defined.  (Contributed
     by Kyle Stanley in bpo-34037(5).)

   * The constant values of future flags in the *note __future__: 0.
     module is updated in order to prevent collision with compiler
     flags.  Previously ‘PyCF_ALLOW_TOP_LEVEL_AWAIT’ was clashing with
     ‘CO_FUTURE_DIVISION’.  (Contributed by Batuhan Taskaya in
     bpo-39562(6))

   * ‘array('u')’ now uses ‘wchar_t’ as C type instead of ‘Py_UNICODE’.
     This change doesn’t affect to its behavior because ‘Py_UNICODE’ is
     alias of ‘wchar_t’ since Python 3.3.  (Contributed by Inada Naoki
     in bpo-34538(7).)

   * The *note logging.getLogger(): 234. API now returns the root logger
     when passed the name ‘'root'’, whereas previously it returned a
     non-root logger named ‘'root'’.  This could affect cases where user
     code explicitly wants a non-root logger named ‘'root'’, or
     instantiates a logger using ‘logging.getLogger(__name__)’ in some
     top-level module called ‘'root.py'’.  (Contributed by Vinay Sajip
     in bpo-37742(8).)

   * Division handling of *note PurePath: 235. now returns
     ‘NotImplemented’ instead of raising a *note TypeError: 1fe. when
     passed something other than an instance of ‘str’ or *note PurePath:
     235.  This allows creating compatible classes that don’t inherit
     from those mentioned types.  (Contributed by Roger Aiudi in
     bpo-34775(9)).

   * Starting with Python 3.9.5 the *note ipaddress: a2. module no
     longer accepts any leading zeros in IPv4 address strings.  Leading
     zeros are ambiguous and interpreted as octal notation by some
     libraries.  For example the legacy function *note
     socket.inet_aton(): 236. treats leading zeros as octal notatation.
     glibc implementation of modern *note inet_pton(): 237. does not
     accept any leading zeros.  (Contributed by Christian Heimes in
     bpo-36384(10)).

   * *note codecs.lookup(): 238. now normalizes the encoding name the
     same way as ‘encodings.normalize_encoding()’, except that *note
     codecs.lookup(): 238. also converts the name to lower case.  For
     example, ‘"latex+latin1"’ encoding name is now normalized to
     ‘"latex_latin1"’.  (Contributed by Jordon Xu in bpo-37751(11).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39239

   (2) https://bugs.python.org/issue39357

   (3) https://bugs.python.org/issue34822

   (4) https://tools.ietf.org/html/rfc2640.html

   (5) https://bugs.python.org/issue34037

   (6) https://bugs.python.org/issue39562

   (7) https://bugs.python.org/issue34538

   (8) https://bugs.python.org/issue37742

   (9) https://bugs.python.org/issue34775

   (10) https://bugs.python.org/issue36384

   (11) https://bugs.python.org/issue37751


File: python.info,  Node: Changes in the C API,  Next: CPython bytecode changes,  Prev: Changes in the Python API,  Up: Porting to Python 3 9

1.1.10.2 Changes in the C API
.............................

   * Instances of heap-allocated types (such as those created with *note
     PyType_FromSpec(): 23a. and similar APIs) hold a reference to their
     type object since Python 3.8.  As indicated in the “Changes in the
     C API” of Python 3.8, for the vast majority of cases, there should
     be no side effect but for types that have a custom *note
     tp_traverse: 23b. function, ensure that all custom ‘tp_traverse’
     functions of heap-allocated types visit the object’s type.

          Example:

               int
               foo_traverse(foo_struct *self, visitproc visit, void *arg) {
               // Rest of the traverse function
               #if PY_VERSION_HEX >= 0x03090000
                   // This was not needed before Python 3.9 (Python issue 35810 and 40217)
                   Py_VISIT(Py_TYPE(self));
               #endif
               }

     If your traverse function delegates to ‘tp_traverse’ of its base
     class (or another type), ensure that ‘Py_TYPE(self)’ is visited
     only once.  Note that only heap types are expected to visit the
     type in ‘tp_traverse’.

          For example, if your ‘tp_traverse’ function includes:

               base->tp_traverse(self, visit, arg)

          then add:

               #if PY_VERSION_HEX >= 0x03090000
                   // This was not needed before Python 3.9 (Python issue 35810 and 40217)
                   if (base->tp_flags & Py_TPFLAGS_HEAPTYPE) {
                       // a heap type's tp_traverse already visited Py_TYPE(self)
                   } else {
                       Py_VISIT(Py_TYPE(self));
                   }
               #else

     (See bpo-35810(1) and bpo-40217(2) for more information.)

   * The functions ‘PyEval_CallObject’, ‘PyEval_CallFunction’,
     ‘PyEval_CallMethod’ and ‘PyEval_CallObjectWithKeywords’ are
     deprecated.  Use *note PyObject_Call(): 23c. and its variants
     instead.  (See more details in bpo-29548(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35810

   (2) https://bugs.python.org/issue40217

   (3) https://bugs.python.org/issue29548


File: python.info,  Node: CPython bytecode changes,  Prev: Changes in the C API,  Up: Porting to Python 3 9

1.1.10.3 CPython bytecode changes
.................................

   * The *note LOAD_ASSERTION_ERROR: 23e. opcode was added for handling
     the *note assert: 23f. statement.  Previously, the assert statement
     would not work correctly if the *note AssertionError: 240.
     exception was being shadowed.  (Contributed by Zackery Spytz in
     bpo-34880(1).)

   * The *note COMPARE_OP: 241. opcode was split into four distinct
     instructions:

        * ‘COMPARE_OP’ for rich comparisons

        * ‘IS_OP’ for ‘is’ and ‘is not’ tests

        * ‘CONTAINS_OP’ for ‘in’ and ‘not in’ tests

        * ‘JUMP_IF_NOT_EXC_MATCH’ for checking exceptions in
          ‘try-except’ statements.

     (Contributed by Mark Shannon in bpo-39156(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34880

   (2) https://bugs.python.org/issue39156


File: python.info,  Node: Build Changes,  Next: C API Changes,  Prev: Porting to Python 3 9,  Up: What’s New In Python 3 9

1.1.11 Build Changes
--------------------

   * Added ‘--with-platlibdir’ option to the ‘configure’ script: name of
     the platform-specific library directory, stored in the new *note
     sys.platlibdir: 1e9. attribute.  See *note sys.platlibdir: 1e9.
     attribute for more information.  (Contributed by Jan Matějek, Matěj
     Cepl, Charalampos Stratakis and Victor Stinner in bpo-1294959(1).)

   * The ‘COUNT_ALLOCS’ special build macro has been removed.
     (Contributed by Victor Stinner in bpo-39489(2).)

   * On non-Windows platforms, the ‘setenv()’ and ‘unsetenv()’ functions
     are now required to build Python.  (Contributed by Victor Stinner
     in bpo-39395(3).)

   * On non-Windows platforms, creating ‘bdist_wininst’ installers is
     now officially unsupported.  (See bpo-10945(4) for more details.)

   * When building Python on macOS from source, ‘_tkinter’ now links
     with non-system Tcl and Tk frameworks if they are installed in
     ‘/Library/Frameworks’, as had been the case on older releases of
     macOS. If a macOS SDK is explicitly configured, by using
     ‘--enable-universalsdk=’ or ‘-isysroot’, only the SDK itself is
     searched.  The default behavior can still be overridden with
     ‘--with-tcltk-includes’ and ‘--with-tcltk-libs’.  (Contributed by
     Ned Deily in bpo-34956(5).)

   * Python can now be built for Windows 10 ARM64.  (Contributed by
     Steve Dower in bpo-33125(6).)

   * Some individual tests are now skipped when ‘--pgo’ is used.  The
     tests in question increased the PGO task time significantly and
     likely didn’t help improve optimization of the final executable.
     This speeds up the task by a factor of about 15x.  Running the full
     unit test suite is slow.  This change may result in a slightly less
     optimized build since not as many code branches will be executed.
     If you are willing to wait for the much slower build, the old
     behavior can be restored using ‘./configure [..] PROFILE_TASK="-m
     test --pgo-extended"’.  We make no guarantees as to which PGO task
     set produces a faster build.  Users who care should run their own
     relevant benchmarks as results can depend on the environment,
     workload, and compiler tool chain.  (See bpo-36044(7) and
     bpo-37707(8) for more details.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1294959

   (2) https://bugs.python.org/issue39489

   (3) https://bugs.python.org/issue39395

   (4) https://bugs.python.org/issue10945

   (5) https://bugs.python.org/issue34956

   (6) https://bugs.python.org/issue33125

   (7) https://bugs.python.org/issue36044

   (8) https://bugs.python.org/issue37707


File: python.info,  Node: C API Changes,  Next: Notable changes in Python 3 9 1,  Prev: Build Changes,  Up: What’s New In Python 3 9

1.1.12 C API Changes
--------------------

* Menu:

* New Features: New Features<2>.
* Porting to Python 3.9: Porting to Python 3 9<2>.
* Removed: Removed<2>.


File: python.info,  Node: New Features<2>,  Next: Porting to Python 3 9<2>,  Up: C API Changes

1.1.12.1 New Features
.....................

   * PEP 573(1): Added *note PyType_FromModuleAndSpec(): 245. to
     associate a module with a class; *note PyType_GetModule(): 246. and
     *note PyType_GetModuleState(): 247. to retrieve the module and its
     state; and *note PyCMethod: 248. and ‘METH_METHOD’ to allow a
     method to access the class it was defined in.  (Contributed by
     Marcel Plch and Petr Viktorin in bpo-38787(2).)

   * Added *note PyFrame_GetCode(): 249. function: get a frame code.
     Added *note PyFrame_GetBack(): 24a. function: get the frame next
     outer frame.  (Contributed by Victor Stinner in bpo-40421(3).)

   * Added *note PyFrame_GetLineNumber(): 24b. to the limited C API.
     (Contributed by Victor Stinner in bpo-40421(4).)

   * Added *note PyThreadState_GetInterpreter(): 24c. and *note
     PyInterpreterState_Get(): 24d. functions to get the interpreter.
     Added *note PyThreadState_GetFrame(): 24e. function to get the
     current frame of a Python thread state.  Added *note
     PyThreadState_GetID(): 24f. function: get the unique identifier of
     a Python thread state.  (Contributed by Victor Stinner in
     bpo-39947(5).)

   * Added a new public *note PyObject_CallNoArgs(): 250. function to
     the C API, which calls a callable Python object without any
     arguments.  It is the most efficient way to call a callable Python
     object without any argument.  (Contributed by Victor Stinner in
     bpo-37194(6).)

   * Changes in the limited C API (if ‘Py_LIMITED_API’ macro is
     defined):

        * Provide *note Py_EnterRecursiveCall(): 251. and *note
          Py_LeaveRecursiveCall(): 252. as regular functions for the
          limited API. Previously, there were defined as macros, but
          these macros didn’t compile with the limited C API which
          cannot access ‘PyThreadState.recursion_depth’ field (the
          structure is opaque in the limited C API).

        * ‘PyObject_INIT()’ and ‘PyObject_INIT_VAR()’ become regular
          “opaque” function to hide implementation details.

     (Contributed by Victor Stinner in bpo-38644(7) and bpo-39542(8).)

   * The *note PyModule_AddType(): 253. function is added to help adding
     a type to a module.  (Contributed by Dong-hee Na in bpo-40024(9).)

   * Added the functions *note PyObject_GC_IsTracked(): 254. and *note
     PyObject_GC_IsFinalized(): 255. to the public API to allow to query
     if Python objects are being currently tracked or have been already
     finalized by the garbage collector respectively.  (Contributed by
     Pablo Galindo Salgado in bpo-40241(10).)

   * Added ‘_PyObject_FunctionStr()’ to get a user-friendly string
     representation of a function-like object.  (Patch by Jeroen Demeyer
     in bpo-37645(11).)

   * Added *note PyObject_CallOneArg(): 256. for calling an object with
     one positional argument (Patch by Jeroen Demeyer in bpo-37483(12).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0573

   (2) https://bugs.python.org/issue38787

   (3) https://bugs.python.org/issue40421

   (4) https://bugs.python.org/issue40421

   (5) https://bugs.python.org/issue39947

   (6) https://bugs.python.org/issue37194

   (7) https://bugs.python.org/issue38644

   (8) https://bugs.python.org/issue39542

   (9) https://bugs.python.org/issue40024

   (10) https://bugs.python.org/issue40241

   (11) https://bugs.python.org/issue37645

   (12) https://bugs.python.org/issue37483


File: python.info,  Node: Porting to Python 3 9<2>,  Next: Removed<2>,  Prev: New Features<2>,  Up: C API Changes

1.1.12.2 Porting to Python 3.9
..............................

   * ‘PyInterpreterState.eval_frame’ ( PEP 523(1)) now requires a new
     mandatory `tstate' parameter (‘PyThreadState*’).  (Contributed by
     Victor Stinner in bpo-38500(2).)

   * Extension modules: *note m_traverse: 258, *note m_clear: 259. and
     *note m_free: 25a. functions of *note PyModuleDef: 25b. are no
     longer called if the module state was requested but is not
     allocated yet.  This is the case immediately after the module is
     created and before the module is executed (*note Py_mod_exec: 25c.
     function).  More precisely, these functions are not called if *note
     m_size: 25d. is greater than 0 and the module state (as returned by
     *note PyModule_GetState(): 25e.) is ‘NULL’.

     Extension modules without module state (‘m_size <= 0’) are not
     affected.

   * If *note Py_AddPendingCall(): 25f. is called in a subinterpreter,
     the function is now scheduled to be called from the subinterpreter,
     rather than being called from the main interpreter.  Each
     subinterpreter now has its own list of scheduled calls.
     (Contributed by Victor Stinner in bpo-39984(3).)

   * The Windows registry is no longer used to initialize *note
     sys.path: 260. when the ‘-E’ option is used (if *note
     PyConfig.use_environment: 261. is set to ‘0’).  This is significant
     when embedding Python on Windows.  (Contributed by Zackery Spytz in
     bpo-8901(4).)

   * The global variable *note PyStructSequence_UnnamedField: 262. is
     now a constant and refers to a constant string.  (Contributed by
     Serhiy Storchaka in bpo-38650(5).)

   * The ‘PyGC_Head’ structure is now opaque.  It is only defined in the
     internal C API (‘pycore_gc.h’).  (Contributed by Victor Stinner in
     bpo-40241(6).)

   * The ‘Py_UNICODE_COPY’, ‘Py_UNICODE_FILL’, ‘PyUnicode_WSTR_LENGTH’,
     *note PyUnicode_FromUnicode(): 263, *note PyUnicode_AsUnicode():
     264, ‘_PyUnicode_AsUnicode’, and *note
     PyUnicode_AsUnicodeAndSize(): 265. are marked as deprecated in C.
     They have been deprecated by PEP 393(7) since Python 3.3.
     (Contributed by Inada Naoki in bpo-36346(8).)

   * The *note Py_FatalError(): 266. function is replaced with a macro
     which logs automatically the name of the current function, unless
     the ‘Py_LIMITED_API’ macro is defined.  (Contributed by Victor
     Stinner in bpo-39882(9).)

   * The vectorcall protocol now requires that the caller passes only
     strings as keyword names.  (See bpo-37540(10) for more
     information.)

   * Implementation details of a number of macros and functions are now
     hidden:

        * *note PyObject_IS_GC(): 267. macro was converted to a
          function.

        * The ‘PyObject_NEW()’ macro becomes an alias to the *note
          PyObject_New(): 268. macro, and the ‘PyObject_NEW_VAR()’ macro
          becomes an alias to the *note PyObject_NewVar(): 269. macro.
          They no longer access directly the *note
          PyTypeObject.tp_basicsize: 26a. member.

        * ‘PyObject_GET_WEAKREFS_LISTPTR()’ macro was converted to a
          function: the macro accessed directly the *note
          PyTypeObject.tp_weaklistoffset: 26b. member.

        * *note PyObject_CheckBuffer(): 26c. macro was converted to a
          function: the macro accessed directly the *note
          PyTypeObject.tp_as_buffer: 26d. member.

        * *note PyIndex_Check(): 26e. is now always declared as an
          opaque function to hide implementation details: removed the
          ‘PyIndex_Check()’ macro.  The macro accessed directly the
          *note PyTypeObject.tp_as_number: 26f. member.

     (See bpo-40170(11) for more details.)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0523

   (2) https://bugs.python.org/issue38500

   (3) https://bugs.python.org/issue39984

   (4) https://bugs.python.org/issue8901

   (5) https://bugs.python.org/issue38650

   (6) https://bugs.python.org/issue40241

   (7) https://www.python.org/dev/peps/pep-0393

   (8) https://bugs.python.org/issue36346

   (9) https://bugs.python.org/issue39882

   (10) https://bugs.python.org/issue37540

   (11) https://bugs.python.org/issue40170


File: python.info,  Node: Removed<2>,  Prev: Porting to Python 3 9<2>,  Up: C API Changes

1.1.12.3 Removed
................

   * Excluded ‘PyFPE_START_PROTECT()’ and ‘PyFPE_END_PROTECT()’ macros
     of ‘pyfpe.h’ from the limited C API. (Contributed by Victor Stinner
     in bpo-38835(1).)

   * The ‘tp_print’ slot of *note PyTypeObject: 271. has been removed.
     It was used for printing objects to files in Python 2.7 and before.
     Since Python 3.0, it has been ignored and unused.  (Contributed by
     Jeroen Demeyer in bpo-36974(2).)

   * Changes in the limited C API (if ‘Py_LIMITED_API’ macro is
     defined):

        * Excluded the following functions from the limited C API:

             * ‘PyThreadState_DeleteCurrent()’ (Contributed by Joannah
               Nanjekye in bpo-37878(3).)

             * ‘_Py_CheckRecursionLimit’

             * ‘_Py_NewReference()’

             * ‘_Py_ForgetReference()’

             * ‘_PyTraceMalloc_NewReference()’

             * ‘_Py_GetRefTotal()’

             * The trashcan mechanism which never worked in the limited
               C API.

             * ‘PyTrash_UNWIND_LEVEL’

             * ‘Py_TRASHCAN_BEGIN_CONDITION’

             * ‘Py_TRASHCAN_BEGIN’

             * ‘Py_TRASHCAN_END’

             * ‘Py_TRASHCAN_SAFE_BEGIN’

             * ‘Py_TRASHCAN_SAFE_END’

        * Moved following functions and definitions to the internal C
          API:

             * ‘_PyDebug_PrintTotalRefs()’

             * ‘_Py_PrintReferences()’

             * ‘_Py_PrintReferenceAddresses()’

             * ‘_Py_tracemalloc_config’

             * ‘_Py_AddToAllObjects()’ (specific to ‘Py_TRACE_REFS’
               build)

     (Contributed by Victor Stinner in bpo-38644(4) and bpo-39542(5).)

   * Removed ‘_PyRuntime.getframe’ hook and removed
     ‘_PyThreadState_GetFrame’ macro which was an alias to
     ‘_PyRuntime.getframe’.  They were only exposed by the internal C
     API. Removed also ‘PyThreadFrameGetter’ type.  (Contributed by
     Victor Stinner in bpo-39946(6).)

   * Removed the following functions from the C API. Call
     ‘PyGC_Collect()’ explicitly to clear all free lists.  (Contributed
     by Inada Naoki and Victor Stinner in bpo-37340(7), bpo-38896(8) and
     bpo-40428(9).)

        * ‘PyAsyncGen_ClearFreeLists()’

        * ‘PyContext_ClearFreeList()’

        * ‘PyDict_ClearFreeList()’

        * ‘PyFloat_ClearFreeList()’

        * ‘PyFrame_ClearFreeList()’

        * ‘PyList_ClearFreeList()’

        * ‘PyMethod_ClearFreeList()’ and ‘PyCFunction_ClearFreeList()’:
          the free lists of bound method objects have been removed.

        * ‘PySet_ClearFreeList()’: the set free list has been removed in
          Python 3.4.

        * ‘PyTuple_ClearFreeList()’

        * ‘PyUnicode_ClearFreeList()’: the Unicode free list has been
          removed in Python 3.3.

   * Removed ‘_PyUnicode_ClearStaticStrings()’ function.  (Contributed
     by Victor Stinner in bpo-39465(10).)

   * Removed ‘Py_UNICODE_MATCH’.  It has been deprecated by PEP 393(11),
     and broken since Python 3.3.  The *note PyUnicode_Tailmatch(): 272.
     function can be used instead.  (Contributed by Inada Naoki in
     bpo-36346(12).)

   * Cleaned header files of interfaces defined but with no
     implementation.  The public API symbols being removed are:
     ‘_PyBytes_InsertThousandsGroupingLocale’,
     ‘_PyBytes_InsertThousandsGrouping’, ‘_Py_InitializeFromArgs’,
     ‘_Py_InitializeFromWideArgs’, ‘_PyFloat_Repr’, ‘_PyFloat_Digits’,
     ‘_PyFloat_DigitsInit’, ‘PyFrame_ExtendStack’,
     ‘_PyAIterWrapper_Type’, ‘PyNullImporter_Type’, ‘PyCmpWrapper_Type’,
     ‘PySortWrapper_Type’, ‘PyNoArgsFunction’.  (Contributed by Pablo
     Galindo Salgado in bpo-39372(13).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38835

   (2) https://bugs.python.org/issue36974

   (3) https://bugs.python.org/issue37878

   (4) https://bugs.python.org/issue38644

   (5) https://bugs.python.org/issue39542

   (6) https://bugs.python.org/issue39946

   (7) https://bugs.python.org/issue37340

   (8) https://bugs.python.org/issue38896

   (9) https://bugs.python.org/issue40428

   (10) https://bugs.python.org/issue39465

   (11) https://www.python.org/dev/peps/pep-0393

   (12) https://bugs.python.org/issue36346

   (13) https://bugs.python.org/issue39372


File: python.info,  Node: Notable changes in Python 3 9 1,  Next: Notable changes in Python 3 9 2,  Prev: C API Changes,  Up: What’s New In Python 3 9

1.1.13 Notable changes in Python 3.9.1
--------------------------------------

* Menu:

* typing: typing<2>.
* macOS 11.0 (Big Sur) and Apple Silicon Mac support: macOS 11 0 Big Sur and Apple Silicon Mac support.


File: python.info,  Node: typing<2>,  Next: macOS 11 0 Big Sur and Apple Silicon Mac support,  Up: Notable changes in Python 3 9 1

1.1.13.1 typing
...............

The behavior of *note typing.Literal: 275. was changed to conform with
PEP 586(1) and to match the behavior of static type checkers specified
in the PEP.

  1. ‘Literal’ now de-duplicates parameters.

  2. Equality comparisons between ‘Literal’ objects are now order
     independent.

  3. ‘Literal’ comparisons now respect types.  For example, ‘Literal[0]
     == Literal[False]’ previously evaluated to ‘True’.  It is now
     ‘False’.  To support this change, the internally used type cache
     now supports differentiating types.

  4. ‘Literal’ objects will now raise a *note TypeError: 1fe. exception
     during equality comparisons if any of their parameters are not
     *note hashable: 276.  Note that declaring ‘Literal’ with mutable
     parameters will not throw an error:

          >>> from typing import Literal
          >>> Literal[{0}]
          >>> Literal[{0}] == Literal[{False}]
          Traceback (most recent call last):
            File "<stdin>", line 1, in <module>
          TypeError: unhashable type: 'set'

(Contributed by Yurii Karabas in bpo-42345(2).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0586

   (2) https://bugs.python.org/issue42345


File: python.info,  Node: macOS 11 0 Big Sur and Apple Silicon Mac support,  Prev: typing<2>,  Up: Notable changes in Python 3 9 1

1.1.13.2 macOS 11.0 (Big Sur) and Apple Silicon Mac support
...........................................................

As of 3.9.1, Python now fully supports building and running on macOS
11.0 (Big Sur) and on Apple Silicon Macs (based on the ‘ARM64’
architecture).  A new universal build variant, ‘universal2’, is now
available to natively support both ‘ARM64’ and ‘Intel 64’ in one set of
executables.  Binaries can also now be built on current versions of
macOS to be deployed on a range of older macOS versions (tested to 10.9)
while making some newer OS functions and options conditionally available
based on the operating system version in use at runtime (“weaklinking”).

(Contributed by Ronald Oussoren and Lawrence D’Anna in bpo-41100(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41100


File: python.info,  Node: Notable changes in Python 3 9 2,  Next: Notable changes in Python 3 9 3,  Prev: Notable changes in Python 3 9 1,  Up: What’s New In Python 3 9

1.1.14 Notable changes in Python 3.9.2
--------------------------------------

* Menu:

* collections.abc: collections abc.
* urllib.parse: urllib parse.


File: python.info,  Node: collections abc,  Next: urllib parse,  Up: Notable changes in Python 3 9 2

1.1.14.1 collections.abc
........................

*note collections.abc.Callable: 27a. generic now flattens type
parameters, similar to what *note typing.Callable: 27b. currently does.
This means that ‘collections.abc.Callable[[int, str], str]’ will have
‘__args__’ of ‘(int, str, str)’; previously this was ‘([int, str],
str)’.  To allow this change, *note types.GenericAlias: 27c. can now be
subclassed, and a subclass will be returned when subscripting the *note
collections.abc.Callable: 27a. type.  Code which accesses the arguments
via *note typing.get_args(): 27d. or ‘__args__’ need to account for this
change.  A *note DeprecationWarning: 15a. may be emitted for invalid
forms of parameterizing *note collections.abc.Callable: 27a. which may
have passed silently in Python 3.9.1.  This *note DeprecationWarning:
15a. will become a *note TypeError: 1fe. in Python 3.10.  (Contributed
by Ken Jin in bpo-42195(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42195


File: python.info,  Node: urllib parse,  Prev: collections abc,  Up: Notable changes in Python 3 9 2

1.1.14.2 urllib.parse
.....................

Earlier Python versions allowed using both ‘;’ and ‘&’ as query
parameter separators in *note urllib.parse.parse_qs(): 27f. and *note
urllib.parse.parse_qsl(): 280.  Due to security concerns, and to conform
with newer W3C recommendations, this has been changed to allow only a
single separator key, with ‘&’ as the default.  This change also affects
*note cgi.parse(): 281. and *note cgi.parse_multipart(): 282. as they
use the affected functions internally.  For more details, please see
their respective documentation.  (Contributed by Adam Goldschmidt,
Senthil Kumaran and Ken Jin in bpo-42967(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42967


File: python.info,  Node: Notable changes in Python 3 9 3,  Next: Notable changes in Python 3 9 5,  Prev: Notable changes in Python 3 9 2,  Up: What’s New In Python 3 9

1.1.15 Notable changes in Python 3.9.3
--------------------------------------

A security fix alters the *note ftplib.FTP: 1a6. behavior to not trust
the IPv4 address sent from the remote server when setting up a passive
data channel.  We reuse the ftp server IP address instead.  For unusual
code requiring the old behavior, set a ‘trust_server_pasv_ipv4_address’
attribute on your FTP instance to ‘True’.  (See bpo-43285(1))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43285


File: python.info,  Node: Notable changes in Python 3 9 5,  Prev: Notable changes in Python 3 9 3,  Up: What’s New In Python 3 9

1.1.16 Notable changes in Python 3.9.5
--------------------------------------

* Menu:

* urllib.parse: urllib parse<2>.


File: python.info,  Node: urllib parse<2>,  Up: Notable changes in Python 3 9 5

1.1.16.1 urllib.parse
.....................

The presence of newline or tab characters in parts of a URL allows for
some forms of attacks.  Following the WHATWG specification that updates
RFC 3986(1), ASCII newline ‘\n’, ‘\r’ and tab ‘\t’ characters are
stripped from the URL by the parser in *note urllib.parse: 128.
preventing such attacks.  The removal characters are controlled by a new
module level variable ‘urllib.parse._UNSAFE_URL_BYTES_TO_REMOVE’.  (See
bpo-43882(2))

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3986.html

   (2) https://bugs.python.org/issue43882


File: python.info,  Node: What’s New In Python 3 8,  Next: What’s New In Python 3 7,  Prev: What’s New In Python 3 9,  Up: What’s New in Python

1.2 What’s New In Python 3.8
============================


Editor: Raymond Hettinger

This article explains the new features in Python 3.8, compared to 3.7.
For full details, see the *note changelog: 156.

* Menu:

* Summary – Release highlights: Summary – Release highlights<2>.
* New Features: New Features<3>.
* Other Language Changes: Other Language Changes<2>.
* New Modules: New Modules<2>.
* Improved Modules: Improved Modules<2>.
* Optimizations: Optimizations<2>.
* Build and C API Changes::
* Deprecated: Deprecated<2>.
* API and Feature Removals::
* Porting to Python 3.8: Porting to Python 3 8.
* Notable changes in Python 3.8.1: Notable changes in Python 3 8 1.
* Notable changes in Python 3.8.8: Notable changes in Python 3 8 8.
* Notable changes in Python 3.8.12: Notable changes in Python 3 8 12.


File: python.info,  Node: Summary – Release highlights<2>,  Next: New Features<3>,  Up: What’s New In Python 3 8

1.2.1 Summary – Release highlights
----------------------------------


File: python.info,  Node: New Features<3>,  Next: Other Language Changes<2>,  Prev: Summary – Release highlights<2>,  Up: What’s New In Python 3 8

1.2.2 New Features
------------------

* Menu:

* Assignment expressions::
* Positional-only parameters::
* Parallel filesystem cache for compiled bytecode files::
* Debug build uses the same ABI as release build::
* f-strings support = for self-documenting expressions and debugging::
* PEP 578; Python Runtime Audit Hooks: PEP 578 Python Runtime Audit Hooks.
* PEP 587; Python Initialization Configuration: PEP 587 Python Initialization Configuration.
* PEP 590; Vectorcall; a fast calling protocol for CPython: PEP 590 Vectorcall a fast calling protocol for CPython.
* Pickle protocol 5 with out-of-band data buffers::


File: python.info,  Node: Assignment expressions,  Next: Positional-only parameters,  Up: New Features<3>

1.2.2.1 Assignment expressions
..............................

There is new syntax ‘:=’ that assigns values to variables as part of a
larger expression.  It is affectionately known as “the walrus operator”
due to its resemblance to the eyes and tusks of a walrus(1).

In this example, the assignment expression helps avoid calling *note
len(): 28b. twice:

     if (n := len(a)) > 10:
         print(f"List is too long ({n} elements, expected <= 10)")

A similar benefit arises during regular expression matching where match
objects are needed twice, once to test whether a match occurred and
another to extract a subgroup:

     discount = 0.0
     if (mo := re.search(r'(\d+)% discount', advertisement)):
         discount = float(mo.group(1)) / 100.0

The operator is also useful with while-loops that compute a value to
test loop termination and then need that same value again in the body of
the loop:

     # Loop over fixed length blocks
     while (block := f.read(256)) != '':
         process(block)

Another motivating use case arises in list comprehensions where a value
computed in a filtering condition is also needed in the expression body:

     [clean_name.title() for name in names
      if (clean_name := normalize('NFC', name)) in allowed_names]

Try to limit use of the walrus operator to clean cases that reduce
complexity and improve readability.

See PEP 572(2) for a full description.

(Contributed by Emily Morehouse in bpo-35224(3).)

   ---------- Footnotes ----------

   (1) 
https://en.wikipedia.org/wiki/Walrus#/media/File:Pacific_Walrus_-_Bull_(8247646168).jpg

   (2) https://www.python.org/dev/peps/pep-0572

   (3) https://bugs.python.org/issue35224


File: python.info,  Node: Positional-only parameters,  Next: Parallel filesystem cache for compiled bytecode files,  Prev: Assignment expressions,  Up: New Features<3>

1.2.2.2 Positional-only parameters
..................................

There is a new function parameter syntax ‘/’ to indicate that some
function parameters must be specified positionally and cannot be used as
keyword arguments.  This is the same notation shown by ‘help()’ for C
functions annotated with Larry Hastings’ Argument Clinic(1) tool.

In the following example, parameters `a' and `b' are positional-only,
while `c' or `d' can be positional or keyword, and `e' or `f' are
required to be keywords:

     def f(a, b, /, c, d, *, e, f):
         print(a, b, c, d, e, f)

The following is a valid call:

     f(10, 20, 30, d=40, e=50, f=60)

However, these are invalid calls:

     f(10, b=20, c=30, d=40, e=50, f=60)   # b cannot be a keyword argument
     f(10, 20, 30, 40, 50, f=60)           # e must be a keyword argument

One use case for this notation is that it allows pure Python functions
to fully emulate behaviors of existing C coded functions.  For example,
the built-in *note divmod(): 28d. function does not accept keyword
arguments:

     def divmod(a, b, /):
         "Emulate the built in divmod() function"
         return (a // b, a % b)

Another use case is to preclude keyword arguments when the parameter
name is not helpful.  For example, the builtin *note len(): 28b.
function has the signature ‘len(obj, /)’.  This precludes awkward calls
such as:

     len(obj='hello')  # The "obj" keyword argument impairs readability

A further benefit of marking a parameter as positional-only is that it
allows the parameter name to be changed in the future without risk of
breaking client code.  For example, in the *note statistics: f5. module,
the parameter name `dist' may be changed in the future.  This was made
possible with the following function specification:

     def quantiles(dist, /, *, n=4, method='exclusive')
         ...

Since the parameters to the left of ‘/’ are not exposed as possible
keywords, the parameters names remain available for use in ‘**kwargs’:

     >>> def f(a, b, /, **kwargs):
     ...     print(a, b, kwargs)
     ...
     >>> f(10, 20, a=1, b=2, c=3)         # a and b are used in two ways
     10 20 {'a': 1, 'b': 2, 'c': 3}

This greatly simplifies the implementation of functions and methods that
need to accept arbitrary keyword arguments.  For example, here is an
excerpt from code in the *note collections: 1d. module:

     class Counter(dict):

         def __init__(self, iterable=None, /, **kwds):
             # Note "iterable" is a possible keyword argument

See PEP 570(2) for a full description.

(Contributed by Pablo Galindo in bpo-36540(3).)

   ---------- Footnotes ----------

   (1) https://docs.python.org/3/howto/clinic.html

   (2) https://www.python.org/dev/peps/pep-0570

   (3) https://bugs.python.org/issue36540


File: python.info,  Node: Parallel filesystem cache for compiled bytecode files,  Next: Debug build uses the same ABI as release build,  Prev: Positional-only parameters,  Up: New Features<3>

1.2.2.3 Parallel filesystem cache for compiled bytecode files
.............................................................

The new *note PYTHONPYCACHEPREFIX: 28f. setting (also available as *note
-X: 290. ‘pycache_prefix’) configures the implicit bytecode cache to use
a separate parallel filesystem tree, rather than the default
‘__pycache__’ subdirectories within each source directory.

The location of the cache is reported in *note sys.pycache_prefix: 291.
(*note None: 203. indicates the default location in ‘__pycache__’
subdirectories).

(Contributed by Carl Meyer in bpo-33499(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33499


File: python.info,  Node: Debug build uses the same ABI as release build,  Next: f-strings support = for self-documenting expressions and debugging,  Prev: Parallel filesystem cache for compiled bytecode files,  Up: New Features<3>

1.2.2.4 Debug build uses the same ABI as release build
......................................................

Python now uses the same ABI whether it’s built in release or debug
mode.  On Unix, when Python is built in debug mode, it is now possible
to load C extensions built in release mode and C extensions built using
the stable ABI.

Release builds and debug builds are now ABI compatible: defining the
‘Py_DEBUG’ macro no longer implies the ‘Py_TRACE_REFS’ macro, which
introduces the only ABI incompatibility.  The ‘Py_TRACE_REFS’ macro,
which adds the ‘sys.getobjects()’ function and the *note PYTHONDUMPREFS:
293. environment variable, can be set using the new ‘./configure
--with-trace-refs’ build option.  (Contributed by Victor Stinner in
bpo-36465(1).)

On Unix, C extensions are no longer linked to libpython except on
Android and Cygwin.  It is now possible for a statically linked Python
to load a C extension built using a shared library Python.  (Contributed
by Victor Stinner in bpo-21536(2).)

On Unix, when Python is built in debug mode, import now also looks for C
extensions compiled in release mode and for C extensions compiled with
the stable ABI. (Contributed by Victor Stinner in bpo-36722(3).)

To embed Python into an application, a new ‘--embed’ option must be
passed to ‘python3-config --libs --embed’ to get ‘-lpython3.8’ (link the
application to libpython).  To support both 3.8 and older, try
‘python3-config --libs --embed’ first and fallback to ‘python3-config
--libs’ (without ‘--embed’) if the previous command fails.

Add a pkg-config ‘python-3.8-embed’ module to embed Python into an
application: ‘pkg-config python-3.8-embed --libs’ includes
‘-lpython3.8’.  To support both 3.8 and older, try ‘pkg-config
python-X.Y-embed --libs’ first and fallback to ‘pkg-config python-X.Y
--libs’ (without ‘--embed’) if the previous command fails (replace ‘X.Y’
with the Python version).

On the other hand, ‘pkg-config python3.8 --libs’ no longer contains
‘-lpython3.8’.  C extensions must not be linked to libpython (except on
Android and Cygwin, whose cases are handled by the script); this change
is backward incompatible on purpose.  (Contributed by Victor Stinner in
bpo-36721(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36465

   (2) https://bugs.python.org/issue21536

   (3) https://bugs.python.org/issue36722

   (4) https://bugs.python.org/issue36721


File: python.info,  Node: f-strings support = for self-documenting expressions and debugging,  Next: PEP 578 Python Runtime Audit Hooks,  Prev: Debug build uses the same ABI as release build,  Up: New Features<3>

1.2.2.5 f-strings support ‘=’ for self-documenting expressions and debugging
............................................................................

Added an ‘=’ specifier to *note f-string: 295.s.  An f-string such as
‘f'{expr=}'’ will expand to the text of the expression, an equal sign,
then the representation of the evaluated expression.  For example:

     >>> user = 'eric_idle'
     >>> member_since = date(1975, 7, 31)
     >>> f'{user=} {member_since=}'
     "user='eric_idle' member_since=datetime.date(1975, 7, 31)"

The usual *note f-string format specifiers: 296. allow more control over
how the result of the expression is displayed:

     >>> delta = date.today() - member_since
     >>> f'{user=!s}  {delta.days=:,d}'
     'user=eric_idle  delta.days=16,075'

The ‘=’ specifier will display the whole expression so that calculations
can be shown:

     >>> print(f'{theta=}  {cos(radians(theta))=:.3f}')
     theta=30  cos(radians(theta))=0.866

(Contributed by Eric V. Smith and Larry Hastings in bpo-36817(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36817


File: python.info,  Node: PEP 578 Python Runtime Audit Hooks,  Next: PEP 587 Python Initialization Configuration,  Prev: f-strings support = for self-documenting expressions and debugging,  Up: New Features<3>

1.2.2.6 PEP 578: Python Runtime Audit Hooks
...........................................

The PEP adds an Audit Hook and Verified Open Hook.  Both are available
from Python and native code, allowing applications and frameworks
written in pure Python code to take advantage of extra notifications,
while also allowing embedders or system administrators to deploy builds
of Python where auditing is always enabled.

See PEP 578(1) for full details.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0578


File: python.info,  Node: PEP 587 Python Initialization Configuration,  Next: PEP 590 Vectorcall a fast calling protocol for CPython,  Prev: PEP 578 Python Runtime Audit Hooks,  Up: New Features<3>

1.2.2.7 PEP 587: Python Initialization Configuration
....................................................

The PEP 587(1) adds a new C API to configure the Python Initialization
providing finer control on the whole configuration and better error
reporting.

New structures:

   * *note PyConfig: 226.

   * *note PyPreConfig: 299.

   * *note PyStatus: 29a.

   * *note PyWideStringList: 29b.

New functions:

   * *note PyConfig_Clear(): 29c.

   * *note PyConfig_InitIsolatedConfig(): 29d.

   * *note PyConfig_InitPythonConfig(): 29e.

   * *note PyConfig_Read(): 29f.

   * *note PyConfig_SetArgv(): 2a0.

   * *note PyConfig_SetBytesArgv(): 2a1.

   * *note PyConfig_SetBytesString(): 2a2.

   * *note PyConfig_SetString(): 2a3.

   * *note PyPreConfig_InitIsolatedConfig(): 2a4.

   * *note PyPreConfig_InitPythonConfig(): 2a5.

   * *note PyStatus_Error(): 2a6.

   * *note PyStatus_Exception(): 2a7.

   * *note PyStatus_Exit(): 2a8.

   * *note PyStatus_IsError(): 2a9.

   * *note PyStatus_IsExit(): 2aa.

   * *note PyStatus_NoMemory(): 2ab.

   * *note PyStatus_Ok(): 2ac.

   * *note PyWideStringList_Append(): 2ad.

   * *note PyWideStringList_Insert(): 2ae.

   * *note Py_BytesMain(): 2af.

   * *note Py_ExitStatusException(): 2b0.

   * *note Py_InitializeFromConfig(): 2b1.

   * *note Py_PreInitialize(): 2b2.

   * *note Py_PreInitializeFromArgs(): 2b3.

   * *note Py_PreInitializeFromBytesArgs(): 2b4.

   * *note Py_RunMain(): 2b5.

This PEP also adds ‘_PyRuntimeState.preconfig’ (*note PyPreConfig: 299.
type) and ‘PyInterpreterState.config’ (*note PyConfig: 226. type) fields
to these internal structures.  ‘PyInterpreterState.config’ becomes the
new reference configuration, replacing global configuration variables
and other private variables.

See *note Python Initialization Configuration: 2b6. for the
documentation.

See PEP 587(2) for a full description.

(Contributed by Victor Stinner in bpo-36763(3).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0587

   (2) https://www.python.org/dev/peps/pep-0587

   (3) https://bugs.python.org/issue36763


File: python.info,  Node: PEP 590 Vectorcall a fast calling protocol for CPython,  Next: Pickle protocol 5 with out-of-band data buffers,  Prev: PEP 587 Python Initialization Configuration,  Up: New Features<3>

1.2.2.8 PEP 590: Vectorcall: a fast calling protocol for CPython
................................................................

*note The Vectorcall Protocol: 2b8. is added to the Python/C API. It is
meant to formalize existing optimizations which were already done for
various classes.  Any static type implementing a callable can use this
protocol.

This is currently provisional.  The aim is to make it fully public in
Python 3.9.

See PEP 590(1) for a full description.

(Contributed by Jeroen Demeyer, Mark Shannon and Petr Viktorin in
bpo-36974(2).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0590

   (2) https://bugs.python.org/issue36974


File: python.info,  Node: Pickle protocol 5 with out-of-band data buffers,  Prev: PEP 590 Vectorcall a fast calling protocol for CPython,  Up: New Features<3>

1.2.2.9 Pickle protocol 5 with out-of-band data buffers
.......................................................

When *note pickle: ca. is used to transfer large data between Python
processes in order to take advantage of multi-core or multi-machine
processing, it is important to optimize the transfer by reducing memory
copies, and possibly by applying custom techniques such as
data-dependent compression.

The *note pickle: ca. protocol 5 introduces support for out-of-band
buffers where PEP 3118(1)-compatible data can be transmitted separately
from the main pickle stream, at the discretion of the communication
layer.

See PEP 574(2) for a full description.

(Contributed by Antoine Pitrou in bpo-36785(3).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3118

   (2) https://www.python.org/dev/peps/pep-0574

   (3) https://bugs.python.org/issue36785


File: python.info,  Node: Other Language Changes<2>,  Next: New Modules<2>,  Prev: New Features<3>,  Up: What’s New In Python 3 8

1.2.3 Other Language Changes
----------------------------

   * A *note continue: 2bb. statement was illegal in the *note finally:
     2bc. clause due to a problem with the implementation.  In Python
     3.8 this restriction was lifted.  (Contributed by Serhiy Storchaka
     in bpo-32489(1).)

   * The *note bool: 2bd, *note int: 204, and *note fractions.Fraction:
     2be. types now have an *note as_integer_ratio(): 2bf. method like
     that found in *note float: 1fd. and *note decimal.Decimal: 2c0.
     This minor API extension makes it possible to write ‘numerator,
     denominator = x.as_integer_ratio()’ and have it work across
     multiple numeric types.  (Contributed by Lisa Roach in bpo-33073(2)
     and Raymond Hettinger in bpo-37819(3).)

   * Constructors of *note int: 204, *note float: 1fd. and *note
     complex: 2c1. will now use the *note __index__(): 2c2. special
     method, if available and the corresponding method *note __int__():
     2c3, *note __float__(): 2c4. or *note __complex__(): 2c5. is not
     available.  (Contributed by Serhiy Storchaka in bpo-20092(4).)

   * Added support of ‘\N{name}’ escapes in *note regular expressions:
     dd.:

          >>> notice = 'Copyright © 2019'
          >>> copyright_year_pattern = re.compile(r'\N{copyright sign}\s*(\d{4})')
          >>> int(copyright_year_pattern.search(notice).group(1))
          2019

     (Contributed by Jonathan Eunice and Serhiy Storchaka in
     bpo-30688(5).)

   * Dict and dictviews are now iterable in reversed insertion order
     using *note reversed(): 2c6.  (Contributed by Rémi Lapeyre in
     bpo-33462(6).)

   * The syntax allowed for keyword names in function calls was further
     restricted.  In particular, ‘f((keyword)=arg)’ is no longer
     allowed.  It was never intended to permit more than a bare name on
     the left-hand side of a keyword argument assignment term.
     (Contributed by Benjamin Peterson in bpo-34641(7).)

   * Generalized iterable unpacking in *note yield: 2c7. and *note
     return: 2c8. statements no longer requires enclosing parentheses.
     This brings the `yield' and `return' syntax into better agreement
     with normal assignment syntax:

          >>> def parse(family):
                  lastname, *members = family.split()
                  return lastname.upper(), *members

          >>> parse('simpsons homer marge bart lisa maggie')
          ('SIMPSONS', 'homer', 'marge', 'bart', 'lisa', 'maggie')

     (Contributed by David Cuthbert and Jordan Chapman in bpo-32117(8).)

   * When a comma is missed in code such as ‘[(10, 20) (30, 40)]’, the
     compiler displays a *note SyntaxWarning: 2c9. with a helpful
     suggestion.  This improves on just having a *note TypeError: 1fe.
     indicating that the first tuple was not callable.  (Contributed by
     Serhiy Storchaka in bpo-15248(9).)

   * Arithmetic operations between subclasses of *note datetime.date:
     19e. or *note datetime.datetime: 1a0. and *note datetime.timedelta:
     2ca. objects now return an instance of the subclass, rather than
     the base class.  This also affects the return type of operations
     whose implementation (directly or indirectly) uses *note
     datetime.timedelta: 2ca. arithmetic, such as *note astimezone():
     2cb.  (Contributed by Paul Ganssle in bpo-32417(10).)

   * When the Python interpreter is interrupted by Ctrl-C (SIGINT) and
     the resulting *note KeyboardInterrupt: 2cc. exception is not
     caught, the Python process now exits via a SIGINT signal or with
     the correct exit code such that the calling process can detect that
     it died due to a Ctrl-C. Shells on POSIX and Windows use this to
     properly terminate scripts in interactive sessions.  (Contributed
     by Google via Gregory P. Smith in bpo-1054041(11).)

   * Some advanced styles of programming require updating the *note
     types.CodeType: 2cd. object for an existing function.  Since code
     objects are immutable, a new code object needs to be created, one
     that is modeled on the existing code object.  With 19 parameters,
     this was somewhat tedious.  Now, the new ‘replace()’ method makes
     it possible to create a clone with a few altered parameters.

     Here’s an example that alters the *note statistics.mean(): 2ce.
     function to prevent the `data' parameter from being used as a
     keyword argument:

          >>> from statistics import mean
          >>> mean(data=[10, 20, 90])
          40
          >>> mean.__code__ = mean.__code__.replace(co_posonlyargcount=1)
          >>> mean(data=[10, 20, 90])
          Traceback (most recent call last):
            ...
          TypeError: mean() got some positional-only arguments passed as keyword arguments: 'data'

     (Contributed by Victor Stinner in bpo-37032(12).)

   * For integers, the three-argument form of the *note pow(): 2cf.
     function now permits the exponent to be negative in the case where
     the base is relatively prime to the modulus.  It then computes a
     modular inverse to the base when the exponent is ‘-1’, and a
     suitable power of that inverse for other negative exponents.  For
     example, to compute the modular multiplicative inverse(13) of 38
     modulo 137, write:

          >>> pow(38, -1, 137)
          119
          >>> 119 * 38 % 137
          1

     Modular inverses arise in the solution of linear Diophantine
     equations(14).  For example, to find integer solutions for ‘4258𝑥 +
     147𝑦 = 369’, first rewrite as ‘4258𝑥 ≡ 369 (mod 147)’ then solve:

          >>> x = 369 * pow(4258, -1, 147) % 147
          >>> y = (4258 * x - 369) // -147
          >>> 4258 * x + 147 * y
          369

     (Contributed by Mark Dickinson in bpo-36027(15).)

   * Dict comprehensions have been synced-up with dict literals so that
     the key is computed first and the value second:

          >>> # Dict comprehension
          >>> cast = {input('role? '): input('actor? ') for i in range(2)}
          role? King Arthur
          actor? Chapman
          role? Black Knight
          actor? Cleese

          >>> # Dict literal
          >>> cast = {input('role? '): input('actor? ')}
          role? Sir Robin
          actor? Eric Idle

     The guaranteed execution order is helpful with assignment
     expressions because variables assigned in the key expression will
     be available in the value expression:

          >>> names = ['Martin von Löwis', 'Łukasz Langa', 'Walter Dörwald']
          >>> {(n := normalize('NFC', name)).casefold() : n for name in names}
          {'martin von löwis': 'Martin von Löwis',
           'łukasz langa': 'Łukasz Langa',
           'walter dörwald': 'Walter Dörwald'}

     (Contributed by Jörn Heissler in bpo-35224(16).)

   * The *note object.__reduce__(): 2d0. method can now return a tuple
     from two to six elements long.  Formerly, five was the limit.  The
     new, optional sixth element is a callable with a ‘(obj, state)’
     signature.  This allows the direct control over the state-updating
     behavior of a specific object.  If not `None', this callable will
     have priority over the object’s *note __setstate__(): 2d1. method.
     (Contributed by Pierre Glaser and Olivier Grisel in bpo-35900(17).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32489

   (2) https://bugs.python.org/issue33073

   (3) https://bugs.python.org/issue37819

   (4) https://bugs.python.org/issue20092

   (5) https://bugs.python.org/issue30688

   (6) https://bugs.python.org/issue33462

   (7) https://bugs.python.org/issue34641

   (8) https://bugs.python.org/issue32117

   (9) https://bugs.python.org/issue15248

   (10) https://bugs.python.org/issue32417

   (11) https://bugs.python.org/issue1054041

   (12) https://bugs.python.org/issue37032

   (13) https://en.wikipedia.org/wiki/Modular_multiplicative_inverse

   (14) https://en.wikipedia.org/wiki/Diophantine_equation

   (15) https://bugs.python.org/issue36027

   (16) https://bugs.python.org/issue35224

   (17) https://bugs.python.org/issue35900


File: python.info,  Node: New Modules<2>,  Next: Improved Modules<2>,  Prev: Other Language Changes<2>,  Up: What’s New In Python 3 8

1.2.4 New Modules
-----------------

   * The new *note importlib.metadata: 9d. module provides (provisional)
     support for reading metadata from third-party packages.  For
     example, it can extract an installed package’s version number, list
     of entry points, and more:

          >>> # Note following example requires that the popular "requests"
          >>> # package has been installed.
          >>>
          >>> from importlib.metadata import version, requires, files
          >>> version('requests')
          '2.22.0'
          >>> list(requires('requests'))
          ['chardet (<3.1.0,>=3.0.2)']
          >>> list(files('requests'))[:5]
          [PackagePath('requests-2.22.0.dist-info/INSTALLER'),
           PackagePath('requests-2.22.0.dist-info/LICENSE'),
           PackagePath('requests-2.22.0.dist-info/METADATA'),
           PackagePath('requests-2.22.0.dist-info/RECORD'),
           PackagePath('requests-2.22.0.dist-info/WHEEL')]

     (Contributed by Barry Warsaw and Jason R. Coombs in bpo-34632(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34632


File: python.info,  Node: Improved Modules<2>,  Next: Optimizations<2>,  Prev: New Modules<2>,  Up: What’s New In Python 3 8

1.2.5 Improved Modules
----------------------

* Menu:

* ast: ast<2>.
* asyncio: asyncio<2>.
* builtins::
* collections::
* cProfile::
* csv::
* curses: curses<2>.
* ctypes::
* datetime: datetime<2>.
* functools::
* gc: gc<2>.
* gettext::
* gzip::
* IDLE and idlelib: IDLE and idlelib<2>.
* inspect: inspect<2>.
* io::
* itertools::
* json.tool: json tool.
* logging::
* math: math<2>.
* mmap::
* multiprocessing: multiprocessing<2>.
* os: os<2>.
* os.path: os path.
* pathlib: pathlib<2>.
* pickle::
* plistlib::
* pprint: pprint<2>.
* py_compile::
* shlex::
* shutil::
* socket: socket<2>.
* ssl::
* statistics::
* sys: sys<2>.
* tarfile::
* threading::
* tokenize::
* tkinter::
* time: time<2>.
* typing: typing<3>.
* unicodedata: unicodedata<2>.
* unittest::
* venv: venv<2>.
* weakref::
* xml: xml<2>.
* xmlrpc::


File: python.info,  Node: ast<2>,  Next: asyncio<2>,  Up: Improved Modules<2>

1.2.5.1 ast
...........

AST nodes now have ‘end_lineno’ and ‘end_col_offset’ attributes, which
give the precise location of the end of the node.  (This only applies to
nodes that have ‘lineno’ and ‘col_offset’ attributes.)

New function *note ast.get_source_segment(): 2d5. returns the source
code for a specific AST node.

(Contributed by Ivan Levkivskyi in bpo-33416(1).)

The *note ast.parse(): 2d6. function has some new flags:

   * ‘type_comments=True’ causes it to return the text of PEP 484(2) and
     PEP 526(3) type comments associated with certain AST nodes;

   * ‘mode='func_type'’ can be used to parse PEP 484(4) “signature type
     comments” (returned for function definition AST nodes);

   * ‘feature_version=(3, N)’ allows specifying an earlier Python 3
     version.  For example, ‘feature_version=(3, 4)’ will treat *note
     async: 2d7. and *note await: 2d8. as non-reserved words.

(Contributed by Guido van Rossum in bpo-35766(5).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33416

   (2) https://www.python.org/dev/peps/pep-0484

   (3) https://www.python.org/dev/peps/pep-0526

   (4) https://www.python.org/dev/peps/pep-0484

   (5) https://bugs.python.org/issue35766


File: python.info,  Node: asyncio<2>,  Next: builtins,  Prev: ast<2>,  Up: Improved Modules<2>

1.2.5.2 asyncio
...............

*note asyncio.run(): 18d. has graduated from the provisional to stable
API. This function can be used to execute a *note coroutine: 18a. and
return the result while automatically managing the event loop.  For
example:

     import asyncio

     async def main():
         await asyncio.sleep(0)
         return 42

     asyncio.run(main())

This is `roughly' equivalent to:

     import asyncio

     async def main():
         await asyncio.sleep(0)
         return 42

     loop = asyncio.new_event_loop()
     asyncio.set_event_loop(loop)
     try:
         loop.run_until_complete(main())
     finally:
         asyncio.set_event_loop(None)
         loop.close()

The actual implementation is significantly more complex.  Thus, *note
asyncio.run(): 18d. should be the preferred way of running asyncio
programs.

(Contributed by Yury Selivanov in bpo-32314(1).)

Running ‘python -m asyncio’ launches a natively async REPL. This allows
rapid experimentation with code that has a top-level *note await: 2d8.
There is no longer a need to directly call ‘asyncio.run()’ which would
spawn a new event loop on every invocation:

     $ python -m asyncio
     asyncio REPL 3.8.0
     Use "await" directly instead of "asyncio.run()".
     Type "help", "copyright", "credits" or "license" for more information.
     >>> import asyncio
     >>> await asyncio.sleep(10, result='hello')
     hello

(Contributed by Yury Selivanov in bpo-37028(2).)

The exception *note asyncio.CancelledError: 2da. now inherits from *note
BaseException: 2db. rather than *note Exception: 2dc. and no longer
inherits from *note concurrent.futures.CancelledError: 2dd.
(Contributed by Yury Selivanov in bpo-32528(3).)

On Windows, the default event loop is now *note ProactorEventLoop: 2de.
(Contributed by Victor Stinner in bpo-34687(4).)

*note ProactorEventLoop: 2de. now also supports UDP. (Contributed by
Adam Meily and Andrew Svetlov in bpo-29883(5).)

*note ProactorEventLoop: 2de. can now be interrupted by *note
KeyboardInterrupt: 2cc. (“CTRL+C”).  (Contributed by Vladimir Matveev in
bpo-23057(6).)

Added *note asyncio.Task.get_coro(): 2df. for getting the wrapped
coroutine within an *note asyncio.Task: 2e0.  (Contributed by Alex
Grönholm in bpo-36999(7).)

Asyncio tasks can now be named, either by passing the ‘name’ keyword
argument to *note asyncio.create_task(): 2e1. or the *note
create_task(): 2e2. event loop method, or by calling the *note
set_name(): 2e3. method on the task object.  The task name is visible in
the ‘repr()’ output of *note asyncio.Task: 2e0. and can also be
retrieved using the *note get_name(): 2e4. method.  (Contributed by Alex
Grönholm in bpo-34270(8).)

Added support for Happy Eyeballs(9) to *note
asyncio.loop.create_connection(): 2e5.  To specify the behavior, two new
parameters have been added: `happy_eyeballs_delay' and `interleave'.
The Happy Eyeballs algorithm improves responsiveness in applications
that support IPv4 and IPv6 by attempting to simultaneously connect using
both.  (Contributed by twisteroid ambassador in bpo-33530(10).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32314

   (2) https://bugs.python.org/issue37028

   (3) https://bugs.python.org/issue32528

   (4) https://bugs.python.org/issue34687

   (5) https://bugs.python.org/issue29883

   (6) https://bugs.python.org/issue23057

   (7) https://bugs.python.org/issue36999

   (8) https://bugs.python.org/issue34270

   (9) https://en.wikipedia.org/wiki/Happy_Eyeballs

   (10) https://bugs.python.org/issue33530


File: python.info,  Node: builtins,  Next: collections,  Prev: asyncio<2>,  Up: Improved Modules<2>

1.2.5.3 builtins
................

The *note compile(): 2e7. built-in has been improved to accept the
‘ast.PyCF_ALLOW_TOP_LEVEL_AWAIT’ flag.  With this new flag passed, *note
compile(): 2e7. will allow top-level ‘await’, ‘async for’ and ‘async
with’ constructs that are usually considered invalid syntax.
Asynchronous code object marked with the ‘CO_COROUTINE’ flag may then be
returned.  (Contributed by Matthias Bussonnier in bpo-34616(1))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34616


File: python.info,  Node: collections,  Next: cProfile,  Prev: builtins,  Up: Improved Modules<2>

1.2.5.4 collections
...................

The *note _asdict(): 2e9. method for *note collections.namedtuple():
1a1. now returns a *note dict: 164. instead of a *note
collections.OrderedDict: 2ea.  This works because regular dicts have
guaranteed ordering since Python 3.7.  If the extra features of
‘OrderedDict’ are required, the suggested remediation is to cast the
result to the desired type: ‘OrderedDict(nt._asdict())’.  (Contributed
by Raymond Hettinger in bpo-35864(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35864


File: python.info,  Node: cProfile,  Next: csv,  Prev: collections,  Up: Improved Modules<2>

1.2.5.5 cProfile
................

The *note cProfile.Profile: 2ec. class can now be used as a context
manager.  Profile a block of code by running:

     import cProfile

     with cProfile.Profile() as profiler:
           # code to be profiled
           ...

(Contributed by Scott Sanderson in bpo-29235(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29235


File: python.info,  Node: csv,  Next: curses<2>,  Prev: cProfile,  Up: Improved Modules<2>

1.2.5.6 csv
...........

The *note csv.DictReader: 2ee. now returns instances of *note dict: 164.
instead of a *note collections.OrderedDict: 2ea.  The tool is now faster
and uses less memory while still preserving the field order.
(Contributed by Michael Selik in bpo-34003(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34003


File: python.info,  Node: curses<2>,  Next: ctypes,  Prev: csv,  Up: Improved Modules<2>

1.2.5.7 curses
..............

Added a new variable holding structured version information for the
underlying ncurses library: *note ncurses_version: 2f0.  (Contributed by
Serhiy Storchaka in bpo-31680(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31680


File: python.info,  Node: ctypes,  Next: datetime<2>,  Prev: curses<2>,  Up: Improved Modules<2>

1.2.5.8 ctypes
..............

On Windows, *note CDLL: 2f2. and subclasses now accept a `winmode'
parameter to specify flags for the underlying ‘LoadLibraryEx’ call.  The
default flags are set to only load DLL dependencies from trusted
locations, including the path where the DLL is stored (if a full or
partial path is used to load the initial DLL) and paths added by *note
add_dll_directory(): 2f3.  (Contributed by Steve Dower in bpo-36085(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36085


File: python.info,  Node: datetime<2>,  Next: functools,  Prev: ctypes,  Up: Improved Modules<2>

1.2.5.9 datetime
................

Added new alternate constructors *note datetime.date.fromisocalendar():
2f5. and *note datetime.datetime.fromisocalendar(): 2f6, which construct
‘date’ and *note datetime: 30. objects respectively from ISO year, week
number, and weekday; these are the inverse of each class’s ‘isocalendar’
method.  (Contributed by Paul Ganssle in bpo-36004(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36004


File: python.info,  Node: functools,  Next: gc<2>,  Prev: datetime<2>,  Up: Improved Modules<2>

1.2.5.10 functools
..................

*note functools.lru_cache(): 2f8. can now be used as a straight
decorator rather than as a function returning a decorator.  So both of
these are now supported:

     @lru_cache
     def f(x):
         ...

     @lru_cache(maxsize=256)
     def f(x):
         ...

(Contributed by Raymond Hettinger in bpo-36772(1).)

Added a new *note functools.cached_property(): 2f9. decorator, for
computed properties cached for the life of the instance.

     import functools
     import statistics

     class Dataset:
        def __init__(self, sequence_of_numbers):
           self.data = sequence_of_numbers

        @functools.cached_property
        def variance(self):
           return statistics.variance(self.data)

(Contributed by Carl Meyer in bpo-21145(2))

Added a new *note functools.singledispatchmethod(): 2fa. decorator that
converts methods into *note generic functions: 2fb. using *note single
dispatch: 2fc.:

     from functools import singledispatchmethod
     from contextlib import suppress

     class TaskManager:

         def __init__(self, tasks):
             self.tasks = list(tasks)

         @singledispatchmethod
         def discard(self, value):
             with suppress(ValueError):
                 self.tasks.remove(value)

         @discard.register(list)
         def _(self, tasks):
             targets = set(tasks)
             self.tasks = [x for x in self.tasks if x not in targets]

(Contributed by Ethan Smith in bpo-32380(3))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36772

   (2) https://bugs.python.org/issue21145

   (3) https://bugs.python.org/issue32380


File: python.info,  Node: gc<2>,  Next: gettext,  Prev: functools,  Up: Improved Modules<2>

1.2.5.11 gc
...........

*note get_objects(): 2fe. can now receive an optional `generation'
parameter indicating a generation to get objects from.  (Contributed by
Pablo Galindo in bpo-36016(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36016


File: python.info,  Node: gettext,  Next: gzip,  Prev: gc<2>,  Up: Improved Modules<2>

1.2.5.12 gettext
................

Added *note pgettext(): 300. and its variants.  (Contributed by Franz
Glasner, Éric Araujo, and Cheryl Sabella in bpo-2504(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue2504


File: python.info,  Node: gzip,  Next: IDLE and idlelib<2>,  Prev: gettext,  Up: Improved Modules<2>

1.2.5.13 gzip
.............

Added the `mtime' parameter to *note gzip.compress(): 302. for
reproducible output.  (Contributed by Guo Ci Teo in bpo-34898(1).)

A *note BadGzipFile: 303. exception is now raised instead of *note
OSError: 304. for certain types of invalid or corrupt gzip files.
(Contributed by Filip Gruszczyński, Michele Orrù, and Zackery Spytz in
bpo-6584(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34898

   (2) https://bugs.python.org/issue6584


File: python.info,  Node: IDLE and idlelib<2>,  Next: inspect<2>,  Prev: gzip,  Up: Improved Modules<2>

1.2.5.14 IDLE and idlelib
.........................

Output over N lines (50 by default) is squeezed down to a button.  N can
be changed in the PyShell section of the General page of the Settings
dialog.  Fewer, but possibly extra long, lines can be squeezed by right
clicking on the output.  Squeezed output can be expanded in place by
double-clicking the button or into the clipboard or a separate window by
right-clicking the button.  (Contributed by Tal Einat in
bpo-1529353(1).)

Add “Run Customized” to the Run menu to run a module with customized
settings.  Any command line arguments entered are added to sys.argv.
They also re-appear in the box for the next customized run.  One can
also suppress the normal Shell main module restart.  (Contributed by
Cheryl Sabella, Terry Jan Reedy, and others in bpo-5680(2) and
bpo-37627(3).)

Added optional line numbers for IDLE editor windows.  Windows open
without line numbers unless set otherwise in the General tab of the
configuration dialog.  Line numbers for an existing window are shown and
hidden in the Options menu.  (Contributed by Tal Einat and Saimadhav
Heblikar in bpo-17535(4).)

OS native encoding is now used for converting between Python strings and
Tcl objects.  This allows IDLE to work with emoji and other non-BMP
characters.  These characters can be displayed or copied and pasted to
or from the clipboard.  Converting strings from Tcl to Python and back
now never fails.  (Many people worked on this for eight years but the
problem was finally solved by Serhiy Storchaka in bpo-13153(5).)

New in 3.8.1:

Add option to toggle cursor blink off.  (Contributed by Zackery Spytz in
bpo-4603(6).)

Escape key now closes IDLE completion windows.  (Contributed by Johnny
Najera in bpo-38944(7).)

The changes above have been backported to 3.7 maintenance releases.

Add keywords to module name completion list.  (Contributed by Terry J.
Reedy in bpo-37765(8).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1529353

   (2) https://bugs.python.org/issue5680

   (3) https://bugs.python.org/issue37627

   (4) https://bugs.python.org/issue17535

   (5) https://bugs.python.org/issue13153

   (6) https://bugs.python.org/issue4603

   (7) https://bugs.python.org/issue38944

   (8) https://bugs.python.org/issue37765


File: python.info,  Node: inspect<2>,  Next: io,  Prev: IDLE and idlelib<2>,  Up: Improved Modules<2>

1.2.5.15 inspect
................

The *note inspect.getdoc(): 307. function can now find docstrings for
‘__slots__’ if that attribute is a *note dict: 164. where the values are
docstrings.  This provides documentation options similar to what we
already have for *note property(): 308, *note classmethod(): 309, and
*note staticmethod(): 30a.:

     class AudioClip:
         __slots__ = {'bit_rate': 'expressed in kilohertz to one decimal place',
                      'duration': 'in seconds, rounded up to an integer'}
         def __init__(self, bit_rate, duration):
             self.bit_rate = round(bit_rate / 1000.0, 1)
             self.duration = ceil(duration)

(Contributed by Raymond Hettinger in bpo-36326(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36326


File: python.info,  Node: io,  Next: itertools,  Prev: inspect<2>,  Up: Improved Modules<2>

1.2.5.16 io
...........

In development mode (*note -X: 290. ‘env’) and in debug build, the *note
io.IOBase: 30c. finalizer now logs the exception if the ‘close()’ method
fails.  The exception is ignored silently by default in release build.
(Contributed by Victor Stinner in bpo-18748(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18748


File: python.info,  Node: itertools,  Next: json tool,  Prev: io,  Up: Improved Modules<2>

1.2.5.17 itertools
..................

The *note itertools.accumulate(): 30e. function added an option
`initial' keyword argument to specify an initial value:

     >>> from itertools import accumulate
     >>> list(accumulate([10, 5, 30, 15], initial=1000))
     [1000, 1010, 1015, 1045, 1060]

(Contributed by Lisa Roach in bpo-34659(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34659


File: python.info,  Node: json tool,  Next: logging,  Prev: itertools,  Up: Improved Modules<2>

1.2.5.18 json.tool
..................

Add option ‘--json-lines’ to parse every input line as a separate JSON
object.  (Contributed by Weipeng Hong in bpo-31553(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31553


File: python.info,  Node: logging,  Next: math<2>,  Prev: json tool,  Up: Improved Modules<2>

1.2.5.19 logging
................

Added a `force' keyword argument to *note logging.basicConfig(): 311.
When set to true, any existing handlers attached to the root logger are
removed and closed before carrying out the configuration specified by
the other arguments.

This solves a long-standing problem.  Once a logger or `basicConfig()'
had been called, subsequent calls to `basicConfig()' were silently
ignored.  This made it difficult to update, experiment with, or teach
the various logging configuration options using the interactive prompt
or a Jupyter notebook.

(Suggested by Raymond Hettinger, implemented by Dong-hee Na, and
reviewed by Vinay Sajip in bpo-33897(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33897


File: python.info,  Node: math<2>,  Next: mmap,  Prev: logging,  Up: Improved Modules<2>

1.2.5.20 math
.............

Added new function *note math.dist(): 313. for computing Euclidean
distance between two points.  (Contributed by Raymond Hettinger in
bpo-33089(1).)

Expanded the *note math.hypot(): 314. function to handle multiple
dimensions.  Formerly, it only supported the 2-D case.  (Contributed by
Raymond Hettinger in bpo-33089(2).)

Added new function, *note math.prod(): 315, as analogous function to
*note sum(): 316. that returns the product of a ‘start’ value (default:
1) times an iterable of numbers:

     >>> prior = 0.8
     >>> likelihoods = [0.625, 0.84, 0.30]
     >>> math.prod(likelihoods, start=prior)
     0.126

(Contributed by Pablo Galindo in bpo-35606(3).)

Added two new combinatoric functions *note math.perm(): 317. and *note
math.comb(): 318.:

     >>> math.perm(10, 3)    # Permutations of 10 things taken 3 at a time
     720
     >>> math.comb(10, 3)    # Combinations of 10 things taken 3 at a time
     120

(Contributed by Yash Aggarwal, Keller Fuchs, Serhiy Storchaka, and
Raymond Hettinger in bpo-37128(4), bpo-37178(5), and bpo-35431(6).)

Added a new function *note math.isqrt(): 319. for computing accurate
integer square roots without conversion to floating point.  The new
function supports arbitrarily large integers.  It is faster than
‘floor(sqrt(n))’ but slower than *note math.sqrt(): 31a.:

     >>> r = 650320427
     >>> s = r ** 2
     >>> isqrt(s - 1)         # correct
     650320426
     >>> floor(sqrt(s - 1))   # incorrect
     650320427

(Contributed by Mark Dickinson in bpo-36887(7).)

The function *note math.factorial(): 1fc. no longer accepts arguments
that are not int-like.  (Contributed by Pablo Galindo in bpo-33083(8).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33089

   (2) https://bugs.python.org/issue33089

   (3) https://bugs.python.org/issue35606

   (4) https://bugs.python.org/issue37128

   (5) https://bugs.python.org/issue37178

   (6) https://bugs.python.org/issue35431

   (7) https://bugs.python.org/issue36887

   (8) https://bugs.python.org/issue33083


File: python.info,  Node: mmap,  Next: multiprocessing<2>,  Prev: math<2>,  Up: Improved Modules<2>

1.2.5.21 mmap
.............

The *note mmap.mmap: 31c. class now has an *note madvise(): 31d. method
to access the ‘madvise()’ system call.  (Contributed by Zackery Spytz in
bpo-32941(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32941


File: python.info,  Node: multiprocessing<2>,  Next: os<2>,  Prev: mmap,  Up: Improved Modules<2>

1.2.5.22 multiprocessing
........................

Added new *note multiprocessing.shared_memory: bc. module.  (Contributed
by Davin Potts in bpo-35813(1).)

On macOS, the `spawn' start method is now used by default.  (Contributed
by Victor Stinner in bpo-33725(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35813

   (2) https://bugs.python.org/issue33725


File: python.info,  Node: os<2>,  Next: os path,  Prev: multiprocessing<2>,  Up: Improved Modules<2>

1.2.5.23 os
...........

Added new function *note add_dll_directory(): 2f3. on Windows for
providing additional search paths for native dependencies when importing
extension modules or loading DLLs using *note ctypes: 2a.  (Contributed
by Steve Dower in bpo-36085(1).)

A new *note os.memfd_create(): 320. function was added to wrap the
‘memfd_create()’ syscall.  (Contributed by Zackery Spytz and Christian
Heimes in bpo-26836(2).)

On Windows, much of the manual logic for handling reparse points
(including symlinks and directory junctions) has been delegated to the
operating system.  Specifically, *note os.stat(): 321. will now traverse
anything supported by the operating system, while *note os.lstat(): 322.
will only open reparse points that identify as “name surrogates” while
others are opened as for *note os.stat(): 321.  In all cases,
‘stat_result.st_mode’ will only have ‘S_IFLNK’ set for symbolic links
and not other kinds of reparse points.  To identify other kinds of
reparse point, check the new ‘stat_result.st_reparse_tag’ attribute.

On Windows, *note os.readlink(): 1d1. is now able to read directory
junctions.  Note that *note islink(): 323. will return ‘False’ for
directory junctions, and so code that checks ‘islink’ first will
continue to treat junctions as directories, while code that handles
errors from *note os.readlink(): 1d1. may now treat junctions as links.

(Contributed by Steve Dower in bpo-37834(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36085

   (2) https://bugs.python.org/issue26836

   (3) https://bugs.python.org/issue37834


File: python.info,  Node: os path,  Next: pathlib<2>,  Prev: os<2>,  Up: Improved Modules<2>

1.2.5.24 os.path
................

*note os.path: c5. functions that return a boolean result like *note
exists(): 325, *note lexists(): 326, *note isdir(): 327, *note isfile():
328, *note islink(): 323, and *note ismount(): 329. now return ‘False’
instead of raising *note ValueError: 16d. or its subclasses *note
UnicodeEncodeError: 32a. and *note UnicodeDecodeError: 32b. for paths
that contain characters or bytes unrepresentable at the OS level.
(Contributed by Serhiy Storchaka in bpo-33721(1).)

*note expanduser(): 32c. on Windows now prefers the ‘USERPROFILE’
environment variable and does not use ‘HOME’, which is not normally set
for regular user accounts.  (Contributed by Anthony Sottile in
bpo-36264(2).)

*note isdir(): 327. on Windows no longer returns ‘True’ for a link to a
non-existent directory.

*note realpath(): 32d. on Windows now resolves reparse points, including
symlinks and directory junctions.

(Contributed by Steve Dower in bpo-37834(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33721

   (2) https://bugs.python.org/issue36264

   (3) https://bugs.python.org/issue37834


File: python.info,  Node: pathlib<2>,  Next: pickle,  Prev: os path,  Up: Improved Modules<2>

1.2.5.25 pathlib
................

*note pathlib.Path: 32f. methods that return a boolean result like *note
exists(): 330, *note is_dir(): 331, *note is_file(): 332, *note
is_mount(): 333, *note is_symlink(): 334, *note is_block_device(): 335,
*note is_char_device(): 336, *note is_fifo(): 337, *note is_socket():
338. now return ‘False’ instead of raising *note ValueError: 16d. or its
subclass *note UnicodeEncodeError: 32a. for paths that contain
characters unrepresentable at the OS level.  (Contributed by Serhiy
Storchaka in bpo-33721(1).)

Added *note pathlib.Path.link_to(): 339. which creates a hard link
pointing to a path.  (Contributed by Joannah Nanjekye in bpo-26978(2))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33721

   (2) https://bugs.python.org/issue26978


File: python.info,  Node: pickle,  Next: plistlib,  Prev: pathlib<2>,  Up: Improved Modules<2>

1.2.5.26 pickle
...............

*note pickle: ca. extensions subclassing the C-optimized *note Pickler:
33b. can now override the pickling logic of functions and classes by
defining the special *note reducer_override(): 33c. method.
(Contributed by Pierre Glaser and Olivier Grisel in bpo-35900(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35900


File: python.info,  Node: plistlib,  Next: pprint<2>,  Prev: pickle,  Up: Improved Modules<2>

1.2.5.27 plistlib
.................

Added new *note plistlib.UID: 33e. and enabled support for reading and
writing NSKeyedArchiver-encoded binary plists.  (Contributed by Jon
Janzen in bpo-26707(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26707


File: python.info,  Node: pprint<2>,  Next: py_compile,  Prev: plistlib,  Up: Improved Modules<2>

1.2.5.28 pprint
...............

The *note pprint: d2. module added a `sort_dicts' parameter to several
functions.  By default, those functions continue to sort dictionaries
before rendering or printing.  However, if `sort_dicts' is set to false,
the dictionaries retain the order that keys were inserted.  This can be
useful for comparison to JSON inputs during debugging.

In addition, there is a convenience new function, *note pprint.pp():
340. that is like *note pprint.pprint(): 341. but with `sort_dicts'
defaulting to ‘False’:

     >>> from pprint import pprint, pp
     >>> d = dict(source='input.txt', operation='filter', destination='output.txt')
     >>> pp(d, width=40)                  # Original order
     {'source': 'input.txt',
      'operation': 'filter',
      'destination': 'output.txt'}
     >>> pprint(d, width=40)              # Keys sorted alphabetically
     {'destination': 'output.txt',
      'operation': 'filter',
      'source': 'input.txt'}

(Contributed by Rémi Lapeyre in bpo-30670(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30670


File: python.info,  Node: py_compile,  Next: shlex,  Prev: pprint<2>,  Up: Improved Modules<2>

1.2.5.29 py_compile
...................

*note py_compile.compile(): 343. now supports silent mode.  (Contributed
by Joannah Nanjekye in bpo-22640(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22640


File: python.info,  Node: shlex,  Next: shutil,  Prev: py_compile,  Up: Improved Modules<2>

1.2.5.30 shlex
..............

The new *note shlex.join(): 345. function acts as the inverse of *note
shlex.split(): 210.  (Contributed by Bo Bayles in bpo-32102(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32102


File: python.info,  Node: shutil,  Next: socket<2>,  Prev: shlex,  Up: Improved Modules<2>

1.2.5.31 shutil
...............

*note shutil.copytree(): 347. now accepts a new ‘dirs_exist_ok’ keyword
argument.  (Contributed by Josh Bronson in bpo-20849(1).)

*note shutil.make_archive(): 348. now defaults to the modern pax
(POSIX.1-2001) format for new archives to improve portability and
standards conformance, inherited from the corresponding change to the
*note tarfile: 101. module.  (Contributed by C.A.M. Gerlach in
bpo-30661(2).)

*note shutil.rmtree(): 349. on Windows now removes directory junctions
without recursively removing their contents first.  (Contributed by
Steve Dower in bpo-37834(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20849

   (2) https://bugs.python.org/issue30661

   (3) https://bugs.python.org/issue37834


File: python.info,  Node: socket<2>,  Next: ssl,  Prev: shutil,  Up: Improved Modules<2>

1.2.5.32 socket
...............

Added *note create_server(): 34b. and *note has_dualstack_ipv6(): 34c.
convenience functions to automate the necessary tasks usually involved
when creating a server socket, including accepting both IPv4 and IPv6
connections on the same socket.  (Contributed by Giampaolo Rodolà in
bpo-17561(1).)

The *note socket.if_nameindex(): 34d, *note socket.if_nametoindex():
34e, and *note socket.if_indextoname(): 34f. functions have been
implemented on Windows.  (Contributed by Zackery Spytz in bpo-37007(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17561

   (2) https://bugs.python.org/issue37007


File: python.info,  Node: ssl,  Next: statistics,  Prev: socket<2>,  Up: Improved Modules<2>

1.2.5.33 ssl
............

Added *note post_handshake_auth: 351. to enable and *note
verify_client_post_handshake(): 352. to initiate TLS 1.3 post-handshake
authentication.  (Contributed by Christian Heimes in bpo-34670(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34670


File: python.info,  Node: statistics,  Next: sys<2>,  Prev: ssl,  Up: Improved Modules<2>

1.2.5.34 statistics
...................

Added *note statistics.fmean(): 354. as a faster, floating point variant
of *note statistics.mean(): 2ce.  (Contributed by Raymond Hettinger and
Steven D’Aprano in bpo-35904(1).)

Added *note statistics.geometric_mean(): 355. (Contributed by Raymond
Hettinger in bpo-27181(2).)

Added *note statistics.multimode(): 356. that returns a list of the most
common values.  (Contributed by Raymond Hettinger in bpo-35892(3).)

Added *note statistics.quantiles(): 357. that divides data or a
distribution in to equiprobable intervals (e.g.  quartiles, deciles, or
percentiles).  (Contributed by Raymond Hettinger in bpo-36546(4).)

Added *note statistics.NormalDist: 358, a tool for creating and
manipulating normal distributions of a random variable.  (Contributed by
Raymond Hettinger in bpo-36018(5).)

     >>> temperature_feb = NormalDist.from_samples([4, 12, -3, 2, 7, 14])
     >>> temperature_feb.mean
     6.0
     >>> temperature_feb.stdev
     6.356099432828281

     >>> temperature_feb.cdf(3)            # Chance of being under 3 degrees
     0.3184678262814532
     >>> # Relative chance of being 7 degrees versus 10 degrees
     >>> temperature_feb.pdf(7) / temperature_feb.pdf(10)
     1.2039930378537762

     >>> el_niño = NormalDist(4, 2.5)
     >>> temperature_feb += el_niño        # Add in a climate effect
     >>> temperature_feb
     NormalDist(mu=10.0, sigma=6.830080526611674)

     >>> temperature_feb * (9/5) + 32      # Convert to Fahrenheit
     NormalDist(mu=50.0, sigma=12.294144947901014)
     >>> temperature_feb.samples(3)        # Generate random samples
     [7.672102882379219, 12.000027119750287, 4.647488369766392]

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35904

   (2) https://bugs.python.org/issue27181

   (3) https://bugs.python.org/issue35892

   (4) https://bugs.python.org/issue36546

   (5) https://bugs.python.org/issue36018


File: python.info,  Node: sys<2>,  Next: tarfile,  Prev: statistics,  Up: Improved Modules<2>

1.2.5.35 sys
............

Add new *note sys.unraisablehook(): 35a. function which can be
overridden to control how “unraisable exceptions” are handled.  It is
called when an exception has occurred but there is no way for Python to
handle it.  For example, when a destructor raises an exception or during
garbage collection (*note gc.collect(): 35b.).  (Contributed by Victor
Stinner in bpo-36829(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36829


File: python.info,  Node: tarfile,  Next: threading,  Prev: sys<2>,  Up: Improved Modules<2>

1.2.5.36 tarfile
................

The *note tarfile: 101. module now defaults to the modern pax
(POSIX.1-2001) format for new archives, instead of the previous
GNU-specific one.  This improves cross-platform portability with a
consistent encoding (UTF-8) in a standardized and extensible format, and
offers several other benefits.  (Contributed by C.A.M. Gerlach in
bpo-36268(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36268


File: python.info,  Node: threading,  Next: tokenize,  Prev: tarfile,  Up: Improved Modules<2>

1.2.5.37 threading
..................

Add a new *note threading.excepthook(): 35e. function which handles
uncaught *note threading.Thread.run(): 35f. exception.  It can be
overridden to control how uncaught *note threading.Thread.run(): 35f.
exceptions are handled.  (Contributed by Victor Stinner in
bpo-1230540(1).)

Add a new *note threading.get_native_id(): 360. function and a *note
native_id: 361. attribute to the *note threading.Thread: 21a. class.
These return the native integral Thread ID of the current thread
assigned by the kernel.  This feature is only available on certain
platforms, see *note get_native_id: 360. for more information.
(Contributed by Jake Tesler in bpo-36084(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1230540

   (2) https://bugs.python.org/issue36084


File: python.info,  Node: tokenize,  Next: tkinter,  Prev: threading,  Up: Improved Modules<2>

1.2.5.38 tokenize
.................

The *note tokenize: 11a. module now implicitly emits a ‘NEWLINE’ token
when provided with input that does not have a trailing new line.  This
behavior now matches what the C tokenizer does internally.  (Contributed
by Ammar Askar in bpo-33899(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33899


File: python.info,  Node: tkinter,  Next: time<2>,  Prev: tokenize,  Up: Improved Modules<2>

1.2.5.39 tkinter
................

Added methods ‘selection_from()’, ‘selection_present()’,
‘selection_range()’ and ‘selection_to()’ in the ‘tkinter.Spinbox’ class.
(Contributed by Juliette Monsel in bpo-34829(1).)

Added method ‘moveto()’ in the ‘tkinter.Canvas’ class.  (Contributed by
Juliette Monsel in bpo-23831(2).)

The ‘tkinter.PhotoImage’ class now has ‘transparency_get()’ and
‘transparency_set()’ methods.  (Contributed by Zackery Spytz in
bpo-25451(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34829

   (2) https://bugs.python.org/issue23831

   (3) https://bugs.python.org/issue25451


File: python.info,  Node: time<2>,  Next: typing<3>,  Prev: tkinter,  Up: Improved Modules<2>

1.2.5.40 time
.............

Added new clock *note CLOCK_UPTIME_RAW: 365. for macOS 10.12.
(Contributed by Joannah Nanjekye in bpo-35702(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35702


File: python.info,  Node: typing<3>,  Next: unicodedata<2>,  Prev: time<2>,  Up: Improved Modules<2>

1.2.5.41 typing
...............

The *note typing: 122. module incorporates several new features:

   * A dictionary type with per-key types.  See PEP 589(1) and *note
     typing.TypedDict: 367.  TypedDict uses only string keys.  By
     default, every key is required to be present.  Specify
     “total=False” to allow keys to be optional:

          class Location(TypedDict, total=False):
              lat_long: tuple
              grid_square: str
              xy_coordinate: tuple

   * Literal types.  See PEP 586(2) and *note typing.Literal: 275.
     Literal types indicate that a parameter or return value is
     constrained to one or more specific literal values:

          def get_status(port: int) -> Literal['connected', 'disconnected']:
              ...

   * “Final” variables, functions, methods and classes.  See PEP 591(3),
     *note typing.Final: 368. and *note typing.final(): 369.  The final
     qualifier instructs a static type checker to restrict subclassing,
     overriding, or reassignment:

          pi: Final[float] = 3.1415926536

   * Protocol definitions.  See PEP 544(4), *note typing.Protocol: 36a.
     and *note typing.runtime_checkable(): 36b.  Simple ABCs like *note
     typing.SupportsInt: 36c. are now ‘Protocol’ subclasses.

   * New protocol class *note typing.SupportsIndex: 36d.

   * New functions *note typing.get_origin(): 36e. and *note
     typing.get_args(): 27d.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0589

   (2) https://www.python.org/dev/peps/pep-0586

   (3) https://www.python.org/dev/peps/pep-0591

   (4) https://www.python.org/dev/peps/pep-0544


File: python.info,  Node: unicodedata<2>,  Next: unittest,  Prev: typing<3>,  Up: Improved Modules<2>

1.2.5.42 unicodedata
....................

The *note unicodedata: 123. module has been upgraded to use the Unicode
12.1.0(1) release.

New function *note is_normalized(): 370. can be used to verify a string
is in a specific normal form, often much faster than by actually
normalizing the string.  (Contributed by Max Belanger, David Euresti,
and Greg Price in bpo-32285(2) and bpo-37966(3)).

   ---------- Footnotes ----------

   (1) http://blog.unicode.org/2019/05/unicode-12-1-en.html

   (2) https://bugs.python.org/issue32285

   (3) https://bugs.python.org/issue37966


File: python.info,  Node: unittest,  Next: venv<2>,  Prev: unicodedata<2>,  Up: Improved Modules<2>

1.2.5.43 unittest
.................

Added *note AsyncMock: 372. to support an asynchronous version of *note
Mock: 373.  Appropriate new assert functions for testing have been added
as well.  (Contributed by Lisa Roach in bpo-26467(1)).

Added *note addModuleCleanup(): 374. and *note addClassCleanup(): 375.
to unittest to support cleanups for ‘setUpModule()’ and *note
setUpClass(): 376.  (Contributed by Lisa Roach in bpo-24412(2).)

Several mock assert functions now also print a list of actual calls upon
failure.  (Contributed by Petter Strandmark in bpo-35047(3).)

*note unittest: 124. module gained support for coroutines to be used as
test cases with *note unittest.IsolatedAsyncioTestCase: 377.
(Contributed by Andrew Svetlov in bpo-32972(4).)

Example:

     import unittest


     class TestRequest(unittest.IsolatedAsyncioTestCase):

         async def asyncSetUp(self):
             self.connection = await AsyncConnection()

         async def test_get(self):
             response = await self.connection.get("https://example.com")
             self.assertEqual(response.status_code, 200)

         async def asyncTearDown(self):
             await self.connection.close()


     if __name__ == "__main__":
         unittest.main()

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26467

   (2) https://bugs.python.org/issue24412

   (3) https://bugs.python.org/issue35047

   (4) https://bugs.python.org/issue32972


File: python.info,  Node: venv<2>,  Next: weakref,  Prev: unittest,  Up: Improved Modules<2>

1.2.5.44 venv
.............

*note venv: 12e. now includes an ‘Activate.ps1’ script on all platforms
for activating virtual environments under PowerShell Core 6.1.
(Contributed by Brett Cannon in bpo-32718(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32718


File: python.info,  Node: weakref,  Next: xml<2>,  Prev: venv<2>,  Up: Improved Modules<2>

1.2.5.45 weakref
................

The proxy objects returned by *note weakref.proxy(): 37a. now support
the matrix multiplication operators ‘@’ and ‘@=’ in addition to the
other numeric operators.  (Contributed by Mark Dickinson in
bpo-36669(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36669


File: python.info,  Node: xml<2>,  Next: xmlrpc,  Prev: weakref,  Up: Improved Modules<2>

1.2.5.46 xml
............

As mitigation against DTD and external entity retrieval, the *note
xml.dom.minidom: 13e. and *note xml.sax: 144. modules no longer process
external entities by default.  (Contributed by Christian Heimes in
bpo-17239(1).)

The ‘.find*()’ methods in the *note xml.etree.ElementTree: 140. module
support wildcard searches like ‘{*}tag’ which ignores the namespace and
‘{namespace}*’ which returns all tags in the given namespace.
(Contributed by Stefan Behnel in bpo-28238(2).)

The *note xml.etree.ElementTree: 140. module provides a new function
‘–xml.etree.ElementTree.canonicalize()’ that implements C14N 2.0.
(Contributed by Stefan Behnel in bpo-13611(3).)

The target object of *note xml.etree.ElementTree.XMLParser: 37c. can
receive namespace declaration events through the new callback methods
‘start_ns()’ and ‘end_ns()’.  Additionally, the *note
xml.etree.ElementTree.TreeBuilder: 37d. target can be configured to
process events about comments and processing instructions to include
them in the generated tree.  (Contributed by Stefan Behnel in
bpo-36676(4) and bpo-36673(5).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17239

   (2) https://bugs.python.org/issue28238

   (3) https://bugs.python.org/issue13611

   (4) https://bugs.python.org/issue36676

   (5) https://bugs.python.org/issue36673


File: python.info,  Node: xmlrpc,  Prev: xml<2>,  Up: Improved Modules<2>

1.2.5.47 xmlrpc
...............

*note xmlrpc.client.ServerProxy: 37f. now supports an optional `headers'
keyword argument for a sequence of HTTP headers to be sent with each
request.  Among other things, this makes it possible to upgrade from
default basic authentication to faster session authentication.
(Contributed by Cédric Krier in bpo-35153(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35153


File: python.info,  Node: Optimizations<2>,  Next: Build and C API Changes,  Prev: Improved Modules<2>,  Up: What’s New In Python 3 8

1.2.6 Optimizations
-------------------

   * The *note subprocess: f9. module can now use the *note
     os.posix_spawn(): 381. function in some cases for better
     performance.  Currently, it is only used on macOS and Linux (using
     glibc 2.24 or newer) if all these conditions are met:

        * `close_fds' is false;

        * `preexec_fn', `pass_fds', `cwd' and `start_new_session'
          parameters are not set;

        * the `executable' path contains a directory.

     (Contributed by Joannah Nanjekye and Victor Stinner in
     bpo-35537(1).)

   * *note shutil.copyfile(): 382, *note shutil.copy(): 383, *note
     shutil.copy2(): 384, *note shutil.copytree(): 347. and *note
     shutil.move(): 385. use platform-specific “fast-copy” syscalls on
     Linux and macOS in order to copy the file more efficiently.
     “fast-copy” means that the copying operation occurs within the
     kernel, avoiding the use of userspace buffers in Python as in
     “‘outfd.write(infd.read())’”.  On Windows *note shutil.copyfile():
     382. uses a bigger default buffer size (1 MiB instead of 16 KiB)
     and a *note memoryview(): 386.-based variant of *note
     shutil.copyfileobj(): 387. is used.  The speedup for copying a 512
     MiB file within the same partition is about +26% on Linux, +50% on
     macOS and +40% on Windows.  Also, much less CPU cycles are
     consumed.  See *note Platform-dependent efficient copy operations:
     388. section.  (Contributed by Giampaolo Rodolà in bpo-33671(2).)

   * *note shutil.copytree(): 347. uses *note os.scandir(): 389.
     function and all copy functions depending from it use cached *note
     os.stat(): 321. values.  The speedup for copying a directory with
     8000 files is around +9% on Linux, +20% on Windows and +30% on a
     Windows SMB share.  Also the number of *note os.stat(): 321.
     syscalls is reduced by 38% making *note shutil.copytree(): 347.
     especially faster on network filesystems.  (Contributed by
     Giampaolo Rodolà in bpo-33695(3).)

   * The default protocol in the *note pickle: ca. module is now
     Protocol 4, first introduced in Python 3.4.  It offers better
     performance and smaller size compared to Protocol 3 available since
     Python 3.0.

   * Removed one ‘Py_ssize_t’ member from ‘PyGC_Head’.  All GC tracked
     objects (e.g.  tuple, list, dict) size is reduced 4 or 8 bytes.
     (Contributed by Inada Naoki in bpo-33597(4).)

   * *note uuid.UUID: 38a. now uses ‘__slots__’ to reduce its memory
     footprint.  (Contributed by Wouter Bolsterlee and Tal Einat in
     bpo-30977(5))

   * Improved performance of *note operator.itemgetter(): 38b. by 33%.
     Optimized argument handling and added a fast path for the common
     case of a single non-negative integer index into a tuple (which is
     the typical use case in the standard library).  (Contributed by
     Raymond Hettinger in bpo-35664(6).)

   * Sped-up field lookups in *note collections.namedtuple(): 1a1.  They
     are now more than two times faster, making them the fastest form of
     instance variable lookup in Python.  (Contributed by Raymond
     Hettinger, Pablo Galindo, and Joe Jevnik, Serhiy Storchaka in
     bpo-32492(7).)

   * The *note list: 1f8. constructor does not overallocate the internal
     item buffer if the input iterable has a known length (the input
     implements ‘__len__’).  This makes the created list 12% smaller on
     average.  (Contributed by Raymond Hettinger and Pablo Galindo in
     bpo-33234(8).)

   * Doubled the speed of class variable writes.  When a non-dunder
     attribute was updated, there was an unnecessary call to update
     slots.  (Contributed by Stefan Behnel, Pablo Galindo Salgado,
     Raymond Hettinger, Neil Schemenauer, and Serhiy Storchaka in
     bpo-36012(9).)

   * Reduced an overhead of converting arguments passed to many builtin
     functions and methods.  This sped up calling some simple builtin
     functions and methods up to 20–50%.  (Contributed by Serhiy
     Storchaka in bpo-23867(10), bpo-35582(11) and bpo-36127(12).)

   * ‘LOAD_GLOBAL’ instruction now uses new “per opcode cache”
     mechanism.  It is about 40% faster now.  (Contributed by Yury
     Selivanov and Inada Naoki in bpo-26219(13).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35537

   (2) https://bugs.python.org/issue33671

   (3) https://bugs.python.org/issue33695

   (4) https://bugs.python.org/issue33597

   (5) https://bugs.python.org/issue30977

   (6) https://bugs.python.org/issue35664

   (7) https://bugs.python.org/issue32492

   (8) https://bugs.python.org/issue33234

   (9) https://bugs.python.org/issue36012

   (10) https://bugs.python.org/issue23867

   (11) https://bugs.python.org/issue35582

   (12) https://bugs.python.org/issue36127

   (13) https://bugs.python.org/issue26219


File: python.info,  Node: Build and C API Changes,  Next: Deprecated<2>,  Prev: Optimizations<2>,  Up: What’s New In Python 3 8

1.2.7 Build and C API Changes
-----------------------------

   * Default *note sys.abiflags: 38d. became an empty string: the ‘m’
     flag for pymalloc became useless (builds with and without pymalloc
     are ABI compatible) and so has been removed.  (Contributed by
     Victor Stinner in bpo-36707(1).)

     Example of changes:

        * Only ‘python3.8’ program is installed, ‘python3.8m’ program is
          gone.

        * Only ‘python3.8-config’ script is installed,
          ‘python3.8m-config’ script is gone.

        * The ‘m’ flag has been removed from the suffix of dynamic
          library filenames: extension modules in the standard library
          as well as those produced and installed by third-party
          packages, like those downloaded from PyPI. On Linux, for
          example, the Python 3.7 suffix
          ‘.cpython-37m-x86_64-linux-gnu.so’ became
          ‘.cpython-38-x86_64-linux-gnu.so’ in Python 3.8.

   * The header files have been reorganized to better separate the
     different kinds of APIs:

        * ‘Include/*.h’ should be the portable public stable C API.

        * ‘Include/cpython/*.h’ should be the unstable C API specific to
          CPython; public API, with some private API prefixed by ‘_Py’
          or ‘_PY’.

        * ‘Include/internal/*.h’ is the private internal C API very
          specific to CPython.  This API comes with no backward
          compatibility warranty and should not be used outside CPython.
          It is only exposed for very specific needs like debuggers and
          profiles which has to access to CPython internals without
          calling functions.  This API is now installed by ‘make
          install’.

     (Contributed by Victor Stinner in bpo-35134(2) and bpo-35081(3),
     work initiated by Eric Snow in Python 3.7.)

   * Some macros have been converted to static inline functions:
     parameter types and return type are well defined, they don’t have
     issues specific to macros, variables have a local scopes.
     Examples:

        * *note Py_INCREF(): 38e, *note Py_DECREF(): 38f.

        * *note Py_XINCREF(): 390, *note Py_XDECREF(): 391.

        * ‘PyObject_INIT()’, ‘PyObject_INIT_VAR()’

        * Private functions: ‘_PyObject_GC_TRACK()’,
          ‘_PyObject_GC_UNTRACK()’, ‘_Py_Dealloc()’

     (Contributed by Victor Stinner in bpo-35059(4).)

   * The ‘PyByteArray_Init()’ and ‘PyByteArray_Fini()’ functions have
     been removed.  They did nothing since Python 2.7.4 and Python
     3.2.0, were excluded from the limited API (stable ABI), and were
     not documented.  (Contributed by Victor Stinner in bpo-35713(5).)

   * The result of ‘PyExceptionClass_Name()’ is now of type ‘const char
     *’ rather of ‘char *’.  (Contributed by Serhiy Storchaka in
     bpo-33818(6).)

   * The duality of ‘Modules/Setup.dist’ and ‘Modules/Setup’ has been
     removed.  Previously, when updating the CPython source tree, one
     had to manually copy ‘Modules/Setup.dist’ (inside the source tree)
     to ‘Modules/Setup’ (inside the build tree) in order to reflect any
     changes upstream.  This was of a small benefit to packagers at the
     expense of a frequent annoyance to developers following CPython
     development, as forgetting to copy the file could produce build
     failures.

     Now the build system always reads from ‘Modules/Setup’ inside the
     source tree.  People who want to customize that file are encouraged
     to maintain their changes in a git fork of CPython or as patch
     files, as they would do for any other change to the source tree.

     (Contributed by Antoine Pitrou in bpo-32430(7).)

   * Functions that convert Python number to C integer like *note
     PyLong_AsLong(): 392. and argument parsing functions like *note
     PyArg_ParseTuple(): 393. with integer converting format units like
     ‘'i'’ will now use the *note __index__(): 2c2. special method
     instead of *note __int__(): 2c3, if available.  The deprecation
     warning will be emitted for objects with the ‘__int__()’ method but
     without the ‘__index__()’ method (like *note Decimal: 2c0. and
     *note Fraction: 2be.).  *note PyNumber_Check(): 394. will now
     return ‘1’ for objects implementing ‘__index__()’.  *note
     PyNumber_Long(): 395, *note PyNumber_Float(): 396. and *note
     PyFloat_AsDouble(): 397. also now use the ‘__index__()’ method if
     available.  (Contributed by Serhiy Storchaka in bpo-36048(8) and
     bpo-20092(9).)

   * Heap-allocated type objects will now increase their reference count
     in *note PyObject_Init(): 398. (and its parallel macro
     ‘PyObject_INIT’) instead of in *note PyType_GenericAlloc(): 399.
     Types that modify instance allocation or deallocation may need to
     be adjusted.  (Contributed by Eddie Elizondo in bpo-35810(10).)

   * The new function *note PyCode_NewWithPosOnlyArgs(): 39a. allows to
     create code objects like *note PyCode_New(): 39b, but with an extra
     `posonlyargcount' parameter for indicating the number of
     positional-only arguments.  (Contributed by Pablo Galindo in
     bpo-37221(11).)

   * *note Py_SetPath(): 39c. now sets *note sys.executable: 39d. to the
     program full path (*note Py_GetProgramFullPath(): 39e.) rather than
     to the program name (*note Py_GetProgramName(): 39f.).
     (Contributed by Victor Stinner in bpo-38234(12).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36707

   (2) https://bugs.python.org/issue35134

   (3) https://bugs.python.org/issue35081

   (4) https://bugs.python.org/issue35059

   (5) https://bugs.python.org/issue35713

   (6) https://bugs.python.org/issue33818

   (7) https://bugs.python.org/issue32430

   (8) https://bugs.python.org/issue36048

   (9) https://bugs.python.org/issue20092

   (10) https://bugs.python.org/issue35810

   (11) https://bugs.python.org/issue37221

   (12) https://bugs.python.org/issue38234


File: python.info,  Node: Deprecated<2>,  Next: API and Feature Removals,  Prev: Build and C API Changes,  Up: What’s New In Python 3 8

1.2.8 Deprecated
----------------

   * The distutils ‘bdist_wininst’ command is now deprecated, use
     ‘bdist_wheel’ (wheel packages) instead.  (Contributed by Victor
     Stinner in bpo-37481(1).)

   * Deprecated methods ‘getchildren()’ and ‘getiterator()’ in the *note
     ElementTree: 140. module now emit a *note DeprecationWarning: 15a.
     instead of *note PendingDeprecationWarning: 15c.  They will be
     removed in Python 3.9.  (Contributed by Serhiy Storchaka in
     bpo-29209(2).)

   * Passing an object that is not an instance of *note
     concurrent.futures.ThreadPoolExecutor: 18c. to *note
     loop.set_default_executor(): 3a1. is deprecated and will be
     prohibited in Python 3.9.  (Contributed by Elvis Pranskevichus in
     bpo-34075(3).)

   * The *note __getitem__(): 3a2. methods of *note
     xml.dom.pulldom.DOMEventStream: 3a3, *note
     wsgiref.util.FileWrapper: 3a4. and *note fileinput.FileInput: 3a5.
     have been deprecated.

     Implementations of these methods have been ignoring their `index'
     parameter, and returning the next item instead.  (Contributed by
     Berker Peksag in bpo-9372(4).)

   * The *note typing.NamedTuple: 227. class has deprecated the
     ‘_field_types’ attribute in favor of the ‘__annotations__’
     attribute which has the same information.  (Contributed by Raymond
     Hettinger in bpo-36320(5).)

   * *note ast: 7. classes ‘Num’, ‘Str’, ‘Bytes’, ‘NameConstant’ and
     ‘Ellipsis’ are considered deprecated and will be removed in future
     Python versions.  *note Constant: 3a6. should be used instead.
     (Contributed by Serhiy Storchaka in bpo-32892(6).)

   * *note ast.NodeVisitor: 3a7. methods ‘visit_Num()’, ‘visit_Str()’,
     ‘visit_Bytes()’, ‘visit_NameConstant()’ and ‘visit_Ellipsis()’ are
     deprecated now and will not be called in future Python versions.
     Add the ‘visit_Constant()’ method to handle all constant nodes.
     (Contributed by Serhiy Storchaka in bpo-36917(7).)

   * The *note asyncio.coroutine(): 3a8. *note decorator: 174. is
     deprecated and will be removed in version 3.10.  Instead of
     ‘@asyncio.coroutine’, use *note async def: 3a9. instead.
     (Contributed by Andrew Svetlov in bpo-36921(8).)

   * In *note asyncio: 9, the explicit passing of a `loop' argument has
     been deprecated and will be removed in version 3.10 for the
     following: *note asyncio.sleep(): 3aa, *note asyncio.gather(): 3ab,
     *note asyncio.shield(): 3ac, *note asyncio.wait_for(): 191, *note
     asyncio.wait(): 207, *note asyncio.as_completed(): 3ad, *note
     asyncio.Task: 2e0, *note asyncio.Lock: 3ae, *note asyncio.Event:
     3af, *note asyncio.Condition: 3b0, *note asyncio.Semaphore: 3b1,
     *note asyncio.BoundedSemaphore: 3b2, *note asyncio.Queue: 3b3,
     *note asyncio.create_subprocess_exec(): 3b4, and *note
     asyncio.create_subprocess_shell(): 3b5.

   * The explicit passing of coroutine objects to *note asyncio.wait():
     207. has been deprecated and will be removed in version 3.11.
     (Contributed by Yury Selivanov in bpo-34790(9).)

   * The following functions and methods are deprecated in the *note
     gettext: 87. module: *note lgettext(): 3b6, *note ldgettext(): 3b7,
     *note lngettext(): 3b8. and *note ldngettext(): 3b9.  They return
     encoded bytes, and it’s possible that you will get unexpected
     Unicode-related exceptions if there are encoding problems with the
     translated strings.  It’s much better to use alternatives which
     return Unicode strings in Python 3.  These functions have been
     broken for a long time.

     Function *note bind_textdomain_codeset(): 3ba, methods *note
     output_charset(): 3bb. and *note set_output_charset(): 3bc, and the
     `codeset' parameter of functions *note translation(): 3bd. and
     *note install(): 3be. are also deprecated, since they are only used
     for the ‘l*gettext()’ functions.  (Contributed by Serhiy Storchaka
     in bpo-33710(10).)

   * The ‘isAlive()’ method of *note threading.Thread: 21a. has been
     deprecated.  (Contributed by Dong-hee Na in bpo-35283(11).)

   * Many builtin and extension functions that take integer arguments
     will now emit a deprecation warning for *note Decimal: 2c0.s, *note
     Fraction: 2be.s and any other objects that can be converted to
     integers only with a loss (e.g.  that have the *note __int__():
     2c3. method but do not have the *note __index__(): 2c2. method).
     In future version they will be errors.  (Contributed by Serhiy
     Storchaka in bpo-36048(12).)

   * Deprecated passing the following arguments as keyword arguments:

        - `func' in *note functools.partialmethod(): 3bf, *note
          weakref.finalize(): 3c0, *note profile.Profile.runcall(): 3c1,
          ‘cProfile.Profile.runcall()’, *note bdb.Bdb.runcall(): 3c2,
          *note trace.Trace.runfunc(): 3c3. and *note curses.wrapper():
          3c4.

        - `function' in *note unittest.TestCase.addCleanup(): 3c5.

        - `fn' in the *note submit(): 3c6. method of *note
          concurrent.futures.ThreadPoolExecutor: 18c. and *note
          concurrent.futures.ProcessPoolExecutor: 196.

        - `callback' in *note contextlib.ExitStack.callback(): 3c7,
          ‘contextlib.AsyncExitStack.callback()’ and *note
          contextlib.AsyncExitStack.push_async_callback(): 3c8.

        - `c' and `typeid' in the ‘create()’ method of
          ‘multiprocessing.managers.Server’ and
          ‘multiprocessing.managers.SharedMemoryServer’.

        - `obj' in *note weakref.finalize(): 3c0.

     In future releases of Python, they will be *note positional-only:
     3c9.  (Contributed by Serhiy Storchaka in bpo-36492(13).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37481

   (2) https://bugs.python.org/issue29209

   (3) https://bugs.python.org/issue34075

   (4) https://bugs.python.org/issue9372

   (5) https://bugs.python.org/issue36320

   (6) https://bugs.python.org/issue32892

   (7) https://bugs.python.org/issue36917

   (8) https://bugs.python.org/issue36921

   (9) https://bugs.python.org/issue34790

   (10) https://bugs.python.org/issue33710

   (11) https://bugs.python.org/issue35283

   (12) https://bugs.python.org/issue36048

   (13) https://bugs.python.org/issue36492


File: python.info,  Node: API and Feature Removals,  Next: Porting to Python 3 8,  Prev: Deprecated<2>,  Up: What’s New In Python 3 8

1.2.9 API and Feature Removals
------------------------------

The following features and APIs have been removed from Python 3.8:

   * Starting with Python 3.3, importing ABCs from *note collections:
     1d. was deprecated, and importing should be done from *note
     collections.abc: 1e.  Being able to import from collections was
     marked for removal in 3.8, but has been delayed to 3.9.  (See
     bpo-36952(1).)

   * The ‘macpath’ module, deprecated in Python 3.7, has been removed.
     (Contributed by Victor Stinner in bpo-35471(2).)

   * The function ‘platform.popen()’ has been removed, after having been
     deprecated since Python 3.3: use *note os.popen(): 3cb. instead.
     (Contributed by Victor Stinner in bpo-35345(3).)

   * The function ‘time.clock()’ has been removed, after having been
     deprecated since Python 3.3: use *note time.perf_counter(): 3cc. or
     *note time.process_time(): 3cd. instead, depending on your
     requirements, to have well-defined behavior.  (Contributed by
     Matthias Bussonnier in bpo-36895(4).)

   * The ‘pyvenv’ script has been removed in favor of ‘python3.8 -m
     venv’ to help eliminate confusion as to what Python interpreter the
     ‘pyvenv’ script is tied to.  (Contributed by Brett Cannon in
     bpo-25427(5).)

   * ‘parse_qs’, ‘parse_qsl’, and ‘escape’ are removed from the *note
     cgi: 15. module.  They are deprecated in Python 3.2 or older.  They
     should be imported from the ‘urllib.parse’ and ‘html’ modules
     instead.

   * ‘filemode’ function is removed from the *note tarfile: 101. module.
     It is not documented and deprecated since Python 3.3.

   * The *note XMLParser: 37c. constructor no longer accepts the `html'
     argument.  It never had an effect and was deprecated in Python 3.4.
     All other parameters are now *note keyword-only: 3ce.  (Contributed
     by Serhiy Storchaka in bpo-29209(6).)

   * Removed the ‘doctype()’ method of *note XMLParser: 37c.
     (Contributed by Serhiy Storchaka in bpo-29209(7).)

   * “unicode_internal” codec is removed.  (Contributed by Inada Naoki
     in bpo-36297(8).)

   * The ‘Cache’ and ‘Statement’ objects of the *note sqlite3: f2.
     module are not exposed to the user.  (Contributed by Aviv Palivoda
     in bpo-30262(9).)

   * The ‘bufsize’ keyword argument of *note fileinput.input(): 3cf. and
     *note fileinput.FileInput(): 3a5. which was ignored and deprecated
     since Python 3.6 has been removed.  bpo-36952(10) (Contributed by
     Matthias Bussonnier.)

   * The functions ‘sys.set_coroutine_wrapper()’ and
     ‘sys.get_coroutine_wrapper()’ deprecated in Python 3.7 have been
     removed; bpo-36933(11) (Contributed by Matthias Bussonnier.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36952

   (2) https://bugs.python.org/issue35471

   (3) https://bugs.python.org/issue35345

   (4) https://bugs.python.org/issue36895

   (5) https://bugs.python.org/issue25427

   (6) https://bugs.python.org/issue29209

   (7) https://bugs.python.org/issue29209

   (8) https://bugs.python.org/issue36297

   (9) https://bugs.python.org/issue30262

   (10) https://bugs.python.org/issue36952

   (11) https://bugs.python.org/issue36933


File: python.info,  Node: Porting to Python 3 8,  Next: Notable changes in Python 3 8 1,  Prev: API and Feature Removals,  Up: What’s New In Python 3 8

1.2.10 Porting to Python 3.8
----------------------------

This section lists previously described changes and other bugfixes that
may require changes to your code.

* Menu:

* Changes in Python behavior::
* Changes in the Python API: Changes in the Python API<2>.
* Changes in the C API: Changes in the C API<2>.
* CPython bytecode changes: CPython bytecode changes<2>.
* Demos and Tools::


File: python.info,  Node: Changes in Python behavior,  Next: Changes in the Python API<2>,  Up: Porting to Python 3 8

1.2.10.1 Changes in Python behavior
...................................

   * Yield expressions (both ‘yield’ and ‘yield from’ clauses) are now
     disallowed in comprehensions and generator expressions (aside from
     the iterable expression in the leftmost ‘for’ clause).
     (Contributed by Serhiy Storchaka in bpo-10544(1).)

   * The compiler now produces a *note SyntaxWarning: 2c9. when identity
     checks (‘is’ and ‘is not’) are used with certain types of literals
     (e.g.  strings, numbers).  These can often work by accident in
     CPython, but are not guaranteed by the language spec.  The warning
     advises users to use equality tests (‘==’ and ‘!=’) instead.
     (Contributed by Serhiy Storchaka in bpo-34850(2).)

   * The CPython interpreter can swallow exceptions in some
     circumstances.  In Python 3.8 this happens in fewer cases.  In
     particular, exceptions raised when getting the attribute from the
     type dictionary are no longer ignored.  (Contributed by Serhiy
     Storchaka in bpo-35459(3).)

   * Removed ‘__str__’ implementations from builtin types *note bool:
     2bd, *note int: 204, *note float: 1fd, *note complex: 2c1. and few
     classes from the standard library.  They now inherit ‘__str__()’
     from *note object: 3d2.  As result, defining the ‘__repr__()’
     method in the subclass of these classes will affect their string
     representation.  (Contributed by Serhiy Storchaka in bpo-36793(4).)

   * On AIX, *note sys.platform: 3d3. doesn’t contain the major version
     anymore.  It is always ‘'aix'’, instead of ‘'aix3'’ ..  ‘'aix7'’.
     Since older Python versions include the version number, so it is
     recommended to always use ‘sys.platform.startswith('aix')’.
     (Contributed by M. Felt in bpo-36588(5).)

   * *note PyEval_AcquireLock(): 3d4. and *note PyEval_AcquireThread():
     3d5. now terminate the current thread if called while the
     interpreter is finalizing, making them consistent with *note
     PyEval_RestoreThread(): 3d6, *note Py_END_ALLOW_THREADS(): 3d7, and
     *note PyGILState_Ensure(): 3d8.  If this behavior is not desired,
     guard the call by checking ‘_Py_IsFinalizing()’ or
     ‘sys.is_finalizing()’.  (Contributed by Joannah Nanjekye in
     bpo-36475(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10544

   (2) https://bugs.python.org/issue34850

   (3) https://bugs.python.org/issue35459

   (4) https://bugs.python.org/issue36793

   (5) https://bugs.python.org/issue36588

   (6) https://bugs.python.org/issue36475


File: python.info,  Node: Changes in the Python API<2>,  Next: Changes in the C API<2>,  Prev: Changes in Python behavior,  Up: Porting to Python 3 8

1.2.10.2 Changes in the Python API
..................................

   * The *note os.getcwdb(): 3da. function now uses the UTF-8 encoding
     on Windows, rather than the ANSI code page: see PEP 529(1) for the
     rationale.  The function is no longer deprecated on Windows.
     (Contributed by Victor Stinner in bpo-37412(2).)

   * *note subprocess.Popen: 3db. can now use *note os.posix_spawn():
     381. in some cases for better performance.  On Windows Subsystem
     for Linux and QEMU User Emulation, the ‘Popen’ constructor using
     *note os.posix_spawn(): 381. no longer raises an exception on
     errors like “missing program”.  Instead the child process fails
     with a non-zero ‘returncode’.  (Contributed by Joannah Nanjekye and
     Victor Stinner in bpo-35537(3).)

   * The `preexec_fn' argument of * *note subprocess.Popen: 3db. is no
     longer compatible with subinterpreters.  The use of the parameter
     in a subinterpreter now raises *note RuntimeError: 3dc.
     (Contributed by Eric Snow in bpo-34651(4), modified by Christian
     Heimes in bpo-37951(5).)

   * The ‘imap.IMAP4.logout()’ method no longer silently ignores
     arbitrary exceptions.  (Contributed by Victor Stinner in
     bpo-36348(6).)

   * The function ‘platform.popen()’ has been removed, after having been
     deprecated since Python 3.3: use *note os.popen(): 3cb. instead.
     (Contributed by Victor Stinner in bpo-35345(7).)

   * The *note statistics.mode(): 3dd. function no longer raises an
     exception when given multimodal data.  Instead, it returns the
     first mode encountered in the input data.  (Contributed by Raymond
     Hettinger in bpo-35892(8).)

   * The *note selection(): 3de. method of the *note
     tkinter.ttk.Treeview: 3df. class no longer takes arguments.  Using
     it with arguments for changing the selection was deprecated in
     Python 3.6.  Use specialized methods like *note selection_set():
     3e0. for changing the selection.  (Contributed by Serhiy Storchaka
     in bpo-31508(9).)

   * The ‘writexml()’, ‘toxml()’ and ‘toprettyxml()’ methods of *note
     xml.dom.minidom: 13e, and the ‘write()’ method of ‘xml.etree’, now
     preserve the attribute order specified by the user.  (Contributed
     by Diego Rojas and Raymond Hettinger in bpo-34160(10).)

   * A *note dbm.dumb: 32. database opened with flags ‘'r'’ is now
     read-only.  *note dbm.dumb.open(): 3e1. with flags ‘'r'’ and ‘'w'’
     no longer creates a database if it does not exist.  (Contributed by
     Serhiy Storchaka in bpo-32749(11).)

   * The ‘doctype()’ method defined in a subclass of *note XMLParser:
     37c. will no longer be called and will emit a *note RuntimeWarning:
     3e2. instead of a *note DeprecationWarning: 15a.  Define the *note
     doctype(): 3e3. method on a target for handling an XML doctype
     declaration.  (Contributed by Serhiy Storchaka in bpo-29209(12).)

   * A *note RuntimeError: 3dc. is now raised when the custom metaclass
     doesn’t provide the ‘__classcell__’ entry in the namespace passed
     to ‘type.__new__’.  A *note DeprecationWarning: 15a. was emitted in
     Python 3.6–3.7.  (Contributed by Serhiy Storchaka in
     bpo-23722(13).)

   * The ‘cProfile.Profile’ class can now be used as a context manager.
     (Contributed by Scott Sanderson in bpo-29235(14).)

   * *note shutil.copyfile(): 382, *note shutil.copy(): 383, *note
     shutil.copy2(): 384, *note shutil.copytree(): 347. and *note
     shutil.move(): 385. use platform-specific “fast-copy” syscalls (see
     *note Platform-dependent efficient copy operations: 388. section).

   * *note shutil.copyfile(): 382. default buffer size on Windows was
     changed from 16 KiB to 1 MiB.

   * The ‘PyGC_Head’ struct has changed completely.  All code that
     touched the struct member should be rewritten.  (See
     bpo-33597(15).)

   * The *note PyInterpreterState: 3e4. struct has been moved into the
     “internal” header files (specifically
     Include/internal/pycore_pystate.h).  An opaque ‘PyInterpreterState’
     is still available as part of the public API (and stable ABI). The
     docs indicate that none of the struct’s fields are public, so we
     hope no one has been using them.  However, if you do rely on one or
     more of those private fields and have no alternative then please
     open a BPO issue.  We’ll work on helping you adjust (possibly
     including adding accessor functions to the public API). (See
     bpo-35886(16).)

   * The *note mmap.flush(): 3e5. method now returns ‘None’ on success
     and raises an exception on error under all platforms.  Previously,
     its behavior was platform-dependent: a nonzero value was returned
     on success; zero was returned on error under Windows.  A zero value
     was returned on success; an exception was raised on error under
     Unix.  (Contributed by Berker Peksag in bpo-2122(17).)

   * *note xml.dom.minidom: 13e. and *note xml.sax: 144. modules no
     longer process external entities by default.  (Contributed by
     Christian Heimes in bpo-17239(18).)

   * Deleting a key from a read-only *note dbm: 31. database (*note
     dbm.dumb: 32, *note dbm.gnu: 33. or *note dbm.ndbm: 34.) raises
     ‘error’ (*note dbm.dumb.error: 3e6, *note dbm.gnu.error: 3e7. or
     *note dbm.ndbm.error: 3e8.) instead of *note KeyError: 3e9.
     (Contributed by Xiang Zhang in bpo-33106(19).)

   * Simplified AST for literals.  All constants will be represented as
     *note ast.Constant: 3a6. instances.  Instantiating old classes
     ‘Num’, ‘Str’, ‘Bytes’, ‘NameConstant’ and ‘Ellipsis’ will return an
     instance of ‘Constant’.  (Contributed by Serhiy Storchaka in
     bpo-32892(20).)

   * *note expanduser(): 32c. on Windows now prefers the ‘USERPROFILE’
     environment variable and does not use ‘HOME’, which is not normally
     set for regular user accounts.  (Contributed by Anthony Sottile in
     bpo-36264(21).)

   * The exception *note asyncio.CancelledError: 2da. now inherits from
     *note BaseException: 2db. rather than *note Exception: 2dc. and no
     longer inherits from *note concurrent.futures.CancelledError: 2dd.
     (Contributed by Yury Selivanov in bpo-32528(22).)

   * The function *note asyncio.wait_for(): 191. now correctly waits for
     cancellation when using an instance of *note asyncio.Task: 2e0.
     Previously, upon reaching `timeout', it was cancelled and
     immediately returned.  (Contributed by Elvis Pranskevichus in
     bpo-32751(23).)

   * The function *note asyncio.BaseTransport.get_extra_info(): 3ea. now
     returns a safe to use socket object when ‘socket’ is passed to the
     `name' parameter.  (Contributed by Yury Selivanov in
     bpo-37027(24).)

   * *note asyncio.BufferedProtocol: 3eb. has graduated to the stable
     API.

   * DLL dependencies for extension modules and DLLs loaded with *note
     ctypes: 2a. on Windows are now resolved more securely.  Only the
     system paths, the directory containing the DLL or PYD file, and
     directories added with *note add_dll_directory(): 2f3. are searched
     for load-time dependencies.  Specifically, ‘PATH’ and the current
     working directory are no longer used, and modifications to these
     will no longer have any effect on normal DLL resolution.  If your
     application relies on these mechanisms, you should check for *note
     add_dll_directory(): 2f3. and if it exists, use it to add your DLLs
     directory while loading your library.  Note that Windows 7 users
     will need to ensure that Windows Update KB2533623 has been
     installed (this is also verified by the installer).  (Contributed
     by Steve Dower in bpo-36085(25).)

   * The header files and functions related to pgen have been removed
     after its replacement by a pure Python implementation.
     (Contributed by Pablo Galindo in bpo-36623(26).)

   * *note types.CodeType: 2cd. has a new parameter in the second
     position of the constructor (`posonlyargcount') to support
     positional-only arguments defined in PEP 570(27).  The first
     argument (`argcount') now represents the total number of positional
     arguments (including positional-only arguments).  The new
     ‘replace()’ method of *note types.CodeType: 2cd. can be used to
     make the code future-proof.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0529

   (2) https://bugs.python.org/issue37412

   (3) https://bugs.python.org/issue35537

   (4) https://bugs.python.org/issue34651

   (5) https://bugs.python.org/issue37951

   (6) https://bugs.python.org/issue36348

   (7) https://bugs.python.org/issue35345

   (8) https://bugs.python.org/issue35892

   (9) https://bugs.python.org/issue31508

   (10) https://bugs.python.org/issue34160

   (11) https://bugs.python.org/issue32749

   (12) https://bugs.python.org/issue29209

   (13) https://bugs.python.org/issue23722

   (14) https://bugs.python.org/issue29235

   (15) https://bugs.python.org/issue33597

   (16) https://bugs.python.org/issue35886

   (17) https://bugs.python.org/issue2122

   (18) https://bugs.python.org/issue17239

   (19) https://bugs.python.org/issue33106

   (20) https://bugs.python.org/issue32892

   (21) https://bugs.python.org/issue36264

   (22) https://bugs.python.org/issue32528

   (23) https://bugs.python.org/issue32751

   (24) https://bugs.python.org/issue37027

   (25) https://bugs.python.org/issue36085

   (26) https://bugs.python.org/issue36623

   (27) https://www.python.org/dev/peps/pep-0570


File: python.info,  Node: Changes in the C API<2>,  Next: CPython bytecode changes<2>,  Prev: Changes in the Python API<2>,  Up: Porting to Python 3 8

1.2.10.3 Changes in the C API
.............................

   * The *note PyCompilerFlags: 3ee. structure got a new
     `cf_feature_version' field.  It should be initialized to
     ‘PY_MINOR_VERSION’.  The field is ignored by default, and is used
     if and only if ‘PyCF_ONLY_AST’ flag is set in `cf_flags'.
     (Contributed by Guido van Rossum in bpo-35766(1).)

   * The ‘PyEval_ReInitThreads()’ function has been removed from the C
     API. It should not be called explicitly: use *note
     PyOS_AfterFork_Child(): 3ef. instead.  (Contributed by Victor
     Stinner in bpo-36728(2).)

   * On Unix, C extensions are no longer linked to libpython except on
     Android and Cygwin.  When Python is embedded, ‘libpython’ must not
     be loaded with ‘RTLD_LOCAL’, but ‘RTLD_GLOBAL’ instead.
     Previously, using ‘RTLD_LOCAL’, it was already not possible to load
     C extensions which were not linked to ‘libpython’, like C
     extensions of the standard library built by the ‘*shared*’ section
     of ‘Modules/Setup’.  (Contributed by Victor Stinner in
     bpo-21536(3).)

   * Use of ‘#’ variants of formats in parsing or building value (e.g.
     *note PyArg_ParseTuple(): 393, *note Py_BuildValue(): 3f0, *note
     PyObject_CallFunction(): 3f1, etc.)  without ‘PY_SSIZE_T_CLEAN’
     defined raises ‘DeprecationWarning’ now.  It will be removed in
     3.10 or 4.0.  Read *note Parsing arguments and building values:
     3f2. for detail.  (Contributed by Inada Naoki in bpo-36381(4).)

   * Instances of heap-allocated types (such as those created with *note
     PyType_FromSpec(): 23a.) hold a reference to their type object.
     Increasing the reference count of these type objects has been moved
     from *note PyType_GenericAlloc(): 399. to the more low-level
     functions, *note PyObject_Init(): 398. and ‘PyObject_INIT()’.  This
     makes types created through *note PyType_FromSpec(): 23a. behave
     like other classes in managed code.

     Statically allocated types are not affected.

     For the vast majority of cases, there should be no side effect.
     However, types that manually increase the reference count after
     allocating an instance (perhaps to work around the bug) may now
     become immortal.  To avoid this, these classes need to call
     Py_DECREF on the type object during instance deallocation.

     To correctly port these types into 3.8, please apply the following
     changes:

        * Remove *note Py_INCREF: 38e. on the type object after
          allocating an instance - if any.  This may happen after
          calling *note PyObject_New(): 268, *note PyObject_NewVar():
          269, *note PyObject_GC_New(): 3f3, *note PyObject_GC_NewVar():
          3f4, or any other custom allocator that uses *note
          PyObject_Init(): 398. or ‘PyObject_INIT()’.

          Example:

               static foo_struct *
               foo_new(PyObject *type) {
                   foo_struct *foo = PyObject_GC_New(foo_struct, (PyTypeObject *) type);
                   if (foo == NULL)
                       return NULL;
               #if PY_VERSION_HEX < 0x03080000
                   // Workaround for Python issue 35810; no longer necessary in Python 3.8
                   PY_INCREF(type)
               #endif
                   return foo;
               }

        * Ensure that all custom ‘tp_dealloc’ functions of
          heap-allocated types decrease the type’s reference count.

          Example:

               static void
               foo_dealloc(foo_struct *instance) {
                   PyObject *type = Py_TYPE(instance);
                   PyObject_GC_Del(instance);
               #if PY_VERSION_HEX >= 0x03080000
                   // This was not needed before Python 3.8 (Python issue 35810)
                   Py_DECREF(type);
               #endif
               }

     (Contributed by Eddie Elizondo in bpo-35810(5).)

   * The ‘Py_DEPRECATED()’ macro has been implemented for MSVC. The
     macro now must be placed before the symbol name.

     Example:

          Py_DEPRECATED(3.8) PyAPI_FUNC(int) Py_OldFunction(void);

     (Contributed by Zackery Spytz in bpo-33407(6).)

   * The interpreter does not pretend to support binary compatibility of
     extension types across feature releases, anymore.  A *note
     PyTypeObject: 3f5. exported by a third-party extension module is
     supposed to have all the slots expected in the current Python
     version, including *note tp_finalize: 3f6. (*note
     Py_TPFLAGS_HAVE_FINALIZE: 3f7. is not checked anymore before
     reading *note tp_finalize: 3f6.).

     (Contributed by Antoine Pitrou in bpo-32388(7).)

   * The functions ‘PyNode_AddChild()’ and ‘PyParser_AddToken()’ now
     accept two additional ‘int’ arguments `end_lineno' and
     `end_col_offset'.

   * The ‘libpython38.a’ file to allow MinGW tools to link directly
     against ‘python38.dll’ is no longer included in the regular Windows
     distribution.  If you require this file, it may be generated with
     the ‘gendef’ and ‘dlltool’ tools, which are part of the MinGW
     binutils package:

          gendef - python38.dll > tmp.def
          dlltool --dllname python38.dll --def tmp.def --output-lib libpython38.a

     The location of an installed ‘pythonXY.dll’ will depend on the
     installation options and the version and language of Windows.  See
     *note Using Python on Windows: 3f8. for more information.  The
     resulting library should be placed in the same directory as
     ‘pythonXY.lib’, which is generally the ‘libs’ directory under your
     Python installation.

     (Contributed by Steve Dower in bpo-37351(8).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35766

   (2) https://bugs.python.org/issue36728

   (3) https://bugs.python.org/issue21536

   (4) https://bugs.python.org/issue36381

   (5) https://bugs.python.org/issue35810

   (6) https://bugs.python.org/issue33407

   (7) https://bugs.python.org/issue32388

   (8) https://bugs.python.org/issue37351


File: python.info,  Node: CPython bytecode changes<2>,  Next: Demos and Tools,  Prev: Changes in the C API<2>,  Up: Porting to Python 3 8

1.2.10.4 CPython bytecode changes
.................................

   * The interpreter loop has been simplified by moving the logic of
     unrolling the stack of blocks into the compiler.  The compiler
     emits now explicit instructions for adjusting the stack of values
     and calling the cleaning-up code for *note break: 3fa, *note
     continue: 2bb. and *note return: 2c8.

     Removed opcodes ‘BREAK_LOOP’, ‘CONTINUE_LOOP’, ‘SETUP_LOOP’ and
     ‘SETUP_EXCEPT’.  Added new opcodes *note ROT_FOUR: 3fb,
     ‘BEGIN_FINALLY’, ‘CALL_FINALLY’ and ‘POP_FINALLY’.  Changed the
     behavior of ‘END_FINALLY’ and ‘WITH_CLEANUP_START’.

     (Contributed by Mark Shannon, Antoine Pitrou and Serhiy Storchaka
     in bpo-17611(1).)

   * Added new opcode *note END_ASYNC_FOR: 3fc. for handling exceptions
     raised when awaiting a next item in an *note async for: 3fd. loop.
     (Contributed by Serhiy Storchaka in bpo-33041(2).)

   * The *note MAP_ADD: 3fe. now expects the value as the first element
     in the stack and the key as the second element.  This change was
     made so the key is always evaluated before the value in dictionary
     comprehensions, as proposed by PEP 572(3).  (Contributed by Jörn
     Heissler in bpo-35224(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17611

   (2) https://bugs.python.org/issue33041

   (3) https://www.python.org/dev/peps/pep-0572

   (4) https://bugs.python.org/issue35224


File: python.info,  Node: Demos and Tools,  Prev: CPython bytecode changes<2>,  Up: Porting to Python 3 8

1.2.10.5 Demos and Tools
........................

Added a benchmark script for timing various ways to access variables:
‘Tools/scripts/var_access_benchmark.py’.  (Contributed by Raymond
Hettinger in bpo-35884(1).)

Here’s a summary of performance improvements since Python 3.3:

     Python version                       3.3     3.4     3.5     3.6     3.7     3.8
     --------------                       ---     ---     ---     ---     ---     ---

     Variable and attribute read access:
         read_local                       4.0     7.1     7.1     5.4     5.1     3.9
         read_nonlocal                    5.3     7.1     8.1     5.8     5.4     4.4
         read_global                     13.3    15.5    19.0    14.3    13.6     7.6
         read_builtin                    20.0    21.1    21.6    18.5    19.0     7.5
         read_classvar_from_class        20.5    25.6    26.5    20.7    19.5    18.4
         read_classvar_from_instance     18.5    22.8    23.5    18.8    17.1    16.4
         read_instancevar                26.8    32.4    33.1    28.0    26.3    25.4
         read_instancevar_slots          23.7    27.8    31.3    20.8    20.8    20.2
         read_namedtuple                 68.5    73.8    57.5    45.0    46.8    18.4
         read_boundmethod                29.8    37.6    37.9    29.6    26.9    27.7

     Variable and attribute write access:
         write_local                      4.6     8.7     9.3     5.5     5.3     4.3
         write_nonlocal                   7.3    10.5    11.1     5.6     5.5     4.7
         write_global                    15.9    19.7    21.2    18.0    18.0    15.8
         write_classvar                  81.9    92.9    96.0   104.6   102.1    39.2
         write_instancevar               36.4    44.6    45.8    40.0    38.9    35.5
         write_instancevar_slots         28.7    35.6    36.1    27.3    26.6    25.7

     Data structure read access:
         read_list                       19.2    24.2    24.5    20.8    20.8    19.0
         read_deque                      19.9    24.7    25.5    20.2    20.6    19.8
         read_dict                       19.7    24.3    25.7    22.3    23.0    21.0
         read_strdict                    17.9    22.6    24.3    19.5    21.2    18.9

     Data structure write access:
         write_list                      21.2    27.1    28.5    22.5    21.6    20.0
         write_deque                     23.8    28.7    30.1    22.7    21.8    23.5
         write_dict                      25.9    31.4    33.3    29.3    29.2    24.7
         write_strdict                   22.9    28.4    29.9    27.5    25.2    23.1

     Stack (or queue) operations:
         list_append_pop                144.2    93.4   112.7    75.4    74.2    50.8
         deque_append_pop                30.4    43.5    57.0    49.4    49.2    42.5
         deque_append_popleft            30.8    43.7    57.3    49.7    49.7    42.8

     Timing loop:
         loop_overhead                    0.3     0.5     0.6     0.4     0.3     0.3

The benchmarks were measured on an Intel® Core™ i7-4960HQ processor(2)
running the macOS 64-bit builds found at python.org(3).  The benchmark
script displays timings in nanoseconds.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35884

   (2) 
https://ark.intel.com/content/www/us/en/ark/products/76088/intel-core-i7-4960hq-processor-6m-cache-up-to-3-80-ghz.html

   (3) https://www.python.org/downloads/mac-osx/


File: python.info,  Node: Notable changes in Python 3 8 1,  Next: Notable changes in Python 3 8 8,  Prev: Porting to Python 3 8,  Up: What’s New In Python 3 8

1.2.11 Notable changes in Python 3.8.1
--------------------------------------

Due to significant security concerns, the `reuse_address' parameter of
*note asyncio.loop.create_datagram_endpoint(): 189. is no longer
supported.  This is because of the behavior of the socket option
‘SO_REUSEADDR’ in UDP. For more details, see the documentation for
‘loop.create_datagram_endpoint()’.  (Contributed by Kyle Stanley,
Antoine Pitrou, and Yury Selivanov in bpo-37228(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37228


File: python.info,  Node: Notable changes in Python 3 8 8,  Next: Notable changes in Python 3 8 12,  Prev: Notable changes in Python 3 8 1,  Up: What’s New In Python 3 8

1.2.12 Notable changes in Python 3.8.8
--------------------------------------

Earlier Python versions allowed using both ‘;’ and ‘&’ as query
parameter separators in *note urllib.parse.parse_qs(): 27f. and *note
urllib.parse.parse_qsl(): 280.  Due to security concerns, and to conform
with newer W3C recommendations, this has been changed to allow only a
single separator key, with ‘&’ as the default.  This change also affects
*note cgi.parse(): 281. and *note cgi.parse_multipart(): 282. as they
use the affected functions internally.  For more details, please see
their respective documentation.  (Contributed by Adam Goldschmidt,
Senthil Kumaran and Ken Jin in bpo-42967(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42967


File: python.info,  Node: Notable changes in Python 3 8 12,  Prev: Notable changes in Python 3 8 8,  Up: What’s New In Python 3 8

1.2.13 Notable changes in Python 3.8.12
---------------------------------------

Starting with Python 3.8.12 the *note ipaddress: a2. module no longer
accepts any leading zeros in IPv4 address strings.  Leading zeros are
ambiguous and interpreted as octal notation by some libraries.  For
example the legacy function *note socket.inet_aton(): 236. treats
leading zeros as octal notation.  glibc implementation of modern *note
inet_pton(): 237. does not accept any leading zeros.

(Originally contributed by Christian Heimes in bpo-36384(1), and
backported to 3.8 by Achraf Merzouki.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36384


File: python.info,  Node: What’s New In Python 3 7,  Next: What’s New In Python 3 6,  Prev: What’s New In Python 3 8,  Up: What’s New in Python

1.3 What’s New In Python 3.7
============================


Editor: Elvis Pranskevichus <<elvis@magic.io>>

This article explains the new features in Python 3.7, compared to 3.6.
Python 3.7 was released on June 27, 2018.  For full details, see the
*note changelog: 156.

* Menu:

* Summary – Release Highlights::
* New Features: New Features<4>.
* Other Language Changes: Other Language Changes<3>.
* New Modules: New Modules<3>.
* Improved Modules: Improved Modules<3>.
* C API Changes: C API Changes<2>.
* Build Changes: Build Changes<2>.
* Optimizations: Optimizations<3>.
* Other CPython Implementation Changes::
* Deprecated Python Behavior::
* Deprecated Python modules, functions and methods: Deprecated Python modules functions and methods.
* Deprecated functions and types of the C API::
* Platform Support Removals::
* API and Feature Removals: API and Feature Removals<2>.
* Module Removals::
* Windows-only Changes::
* Porting to Python 3.7: Porting to Python 3 7.
* Notable changes in Python 3.7.1: Notable changes in Python 3 7 1.
* Notable changes in Python 3.7.2: Notable changes in Python 3 7 2.
* Notable changes in Python 3.7.6: Notable changes in Python 3 7 6.
* Notable changes in Python 3.7.10: Notable changes in Python 3 7 10.


File: python.info,  Node: Summary – Release Highlights,  Next: New Features<4>,  Up: What’s New In Python 3 7

1.3.1 Summary – Release Highlights
----------------------------------

New syntax features:

   * *note PEP 563: 406, postponed evaluation of type annotations.

Backwards incompatible syntax changes:

   * *note async: 2d7. and *note await: 2d8. are now reserved keywords.

New library modules:

   * *note contextvars: 24.: *note PEP 567 – Context Variables: 407.

   * *note dataclasses: 2f.: *note PEP 557 – Data Classes: 408.

   * *note importlib.resources: 409.

New built-in features:

   * *note PEP 553: 40a, the new *note breakpoint(): 40b. function.

Python data model improvements:

   * *note PEP 562: 40c, customization of access to module attributes.

   * *note PEP 560: 40d, core support for typing module and generic
     types.

   * the insertion-order preservation nature of *note dict: 40e. objects
     has been declared(1) to be an official part of the Python language
     spec.

Significant improvements in the standard library:

   * The *note asyncio: 9. module has received new features, significant
     *note usability and performance improvements: 40f.

   * The *note time: 10c. module gained support for *note functions with
     nanosecond resolution: 410.

CPython implementation improvements:

   * Avoiding the use of ASCII as a default text encoding:

        * *note PEP 538: 411, legacy C locale coercion

        * *note PEP 540: 412, forced UTF-8 runtime mode

   * *note PEP 552: 413, deterministic .pycs

   * *note New Python Development Mode: 414.

   * *note PEP 565: 415, improved *note DeprecationWarning: 15a.
     handling

C API improvements:

   * *note PEP 539: 416, new C API for thread-local storage

Documentation improvements:

   * *note PEP 545: 417, Python documentation translations

   * New documentation translations: Japanese(2), French(3), and
     Korean(4).

This release features notable performance improvements in many areas.
The *note Optimizations: 418. section lists them in detail.

For a list of changes that may affect compatibility with previous Python
releases please refer to the *note Porting to Python 3.7: 419. section.

   ---------- Footnotes ----------

   (1) 
https://mail.python.org/pipermail/python-dev/2017-December/151283.html

   (2) https://docs.python.org/ja/

   (3) https://docs.python.org/fr/

   (4) https://docs.python.org/ko/


File: python.info,  Node: New Features<4>,  Next: Other Language Changes<3>,  Prev: Summary – Release Highlights,  Up: What’s New In Python 3 7

1.3.2 New Features
------------------

* Menu:

* PEP 563; Postponed Evaluation of Annotations: PEP 563 Postponed Evaluation of Annotations.
* PEP 538; Legacy C Locale Coercion: PEP 538 Legacy C Locale Coercion.
* PEP 540; Forced UTF-8 Runtime Mode: PEP 540 Forced UTF-8 Runtime Mode.
* PEP 553; Built-in breakpoint(): PEP 553 Built-in breakpoint.
* PEP 539; New C API for Thread-Local Storage: PEP 539 New C API for Thread-Local Storage.
* PEP 562; Customization of Access to Module Attributes: PEP 562 Customization of Access to Module Attributes.
* PEP 564; New Time Functions With Nanosecond Resolution: PEP 564 New Time Functions With Nanosecond Resolution.
* PEP 565; Show DeprecationWarning in __main__: PEP 565 Show DeprecationWarning in __main__.
* PEP 560; Core Support for typing module and Generic Types: PEP 560 Core Support for typing module and Generic Types.
* PEP 552; Hash-based .pyc Files: PEP 552 Hash-based pyc Files.
* PEP 545; Python Documentation Translations: PEP 545 Python Documentation Translations.
* Python Development Mode (-X dev): Python Development Mode -X dev.


File: python.info,  Node: PEP 563 Postponed Evaluation of Annotations,  Next: PEP 538 Legacy C Locale Coercion,  Up: New Features<4>

1.3.2.1 PEP 563: Postponed Evaluation of Annotations
....................................................

The advent of type hints in Python uncovered two glaring usability
issues with the functionality of annotations added in PEP 3107(1) and
refined further in PEP 526(2):

   * annotations could only use names which were already available in
     the current scope, in other words they didn’t support forward
     references of any kind; and

   * annotating source code had adverse effects on startup time of
     Python programs.

Both of these issues are fixed by postponing the evaluation of
annotations.  Instead of compiling code which executes expressions in
annotations at their definition time, the compiler stores the annotation
in a string form equivalent to the AST of the expression in question.
If needed, annotations can be resolved at runtime using *note
typing.get_type_hints(): 1ef.  In the common case where this is not
required, the annotations are cheaper to store (since short strings are
interned by the interpreter) and make startup time faster.

Usability-wise, annotations now support forward references, making the
following syntax valid:

     class C:
         @classmethod
         def from_string(cls, source: str) -> C:
             ...

         def validate_b(self, obj: B) -> bool:
             ...

     class B:
         ...

Since this change breaks compatibility, the new behavior needs to be
enabled on a per-module basis in Python 3.7 using a *note __future__: 0.
import:

     from __future__ import annotations

It will become the default in Python 3.10.

See also
........

PEP 563(3) – Postponed evaluation of annotations

     PEP written and implemented by Łukasz Langa.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3107

   (2) https://www.python.org/dev/peps/pep-0526

   (3) https://www.python.org/dev/peps/pep-0563


File: python.info,  Node: PEP 538 Legacy C Locale Coercion,  Next: PEP 540 Forced UTF-8 Runtime Mode,  Prev: PEP 563 Postponed Evaluation of Annotations,  Up: New Features<4>

1.3.2.2 PEP 538: Legacy C Locale Coercion
.........................................

An ongoing challenge within the Python 3 series has been determining a
sensible default strategy for handling the “7-bit ASCII” text encoding
assumption currently implied by the use of the default C or POSIX locale
on non-Windows platforms.

PEP 538(1) updates the default interpreter command line interface to
automatically coerce that locale to an available UTF-8 based locale as
described in the documentation of the new *note PYTHONCOERCECLOCALE:
41d. environment variable.  Automatically setting ‘LC_CTYPE’ this way
means that both the core interpreter and locale-aware C extensions (such
as *note readline: de.) will assume the use of UTF-8 as the default text
encoding, rather than ASCII.

The platform support definition in PEP 11(2) has also been updated to
limit full text handling support to suitably configured non-ASCII based
locales.

As part of this change, the default error handler for *note stdin: 41e.
and *note stdout: 41f. is now ‘surrogateescape’ (rather than ‘strict’)
when using any of the defined coercion target locales (currently
‘C.UTF-8’, ‘C.utf8’, and ‘UTF-8’).  The default error handler for *note
stderr: 1ea. continues to be ‘backslashreplace’, regardless of locale.

Locale coercion is silent by default, but to assist in debugging
potentially locale related integration problems, explicit warnings
(emitted directly on *note stderr: 1ea.) can be requested by setting
‘PYTHONCOERCECLOCALE=warn’.  This setting will also cause the Python
runtime to emit a warning if the legacy C locale remains active when the
core interpreter is initialized.

While PEP 538(3)’s locale coercion has the benefit of also affecting
extension modules (such as GNU ‘readline’), as well as child processes
(including those running non-Python applications and older versions of
Python), it has the downside of requiring that a suitable target locale
be present on the running system.  To better handle the case where no
suitable target locale is available (as occurs on RHEL/CentOS 7, for
example), Python 3.7 also implements *note PEP 540; Forced UTF-8 Runtime
Mode: 412.

See also
........

PEP 538(4) – Coercing the legacy C locale to a UTF-8 based locale

     PEP written and implemented by Nick Coghlan.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0538

   (2) https://www.python.org/dev/peps/pep-0011

   (3) https://www.python.org/dev/peps/pep-0538

   (4) https://www.python.org/dev/peps/pep-0538


File: python.info,  Node: PEP 540 Forced UTF-8 Runtime Mode,  Next: PEP 553 Built-in breakpoint,  Prev: PEP 538 Legacy C Locale Coercion,  Up: New Features<4>

1.3.2.3 PEP 540: Forced UTF-8 Runtime Mode
..........................................

The new *note -X: 290. ‘utf8’ command line option and *note PYTHONUTF8:
421. environment variable can be used to enable the CPython `UTF-8
mode'.

When in UTF-8 mode, CPython ignores the locale settings, and uses the
UTF-8 encoding by default.  The error handlers for *note sys.stdin: 41e.
and *note sys.stdout: 41f. streams are set to ‘surrogateescape’.

The forced UTF-8 mode can be used to change the text handling behavior
in an embedded Python interpreter without changing the locale settings
of an embedding application.

While PEP 540(1)’s UTF-8 mode has the benefit of working regardless of
which locales are available on the running system, it has the downside
of having no effect on extension modules (such as GNU ‘readline’), child
processes running non-Python applications, and child processes running
older versions of Python.  To reduce the risk of corrupting text data
when communicating with such components, Python 3.7 also implements
*note PEP 540; Forced UTF-8 Runtime Mode: 412.).

The UTF-8 mode is enabled by default when the locale is ‘C’ or ‘POSIX’,
and the PEP 538(2) locale coercion feature fails to change it to a UTF-8
based alternative (whether that failure is due to
‘PYTHONCOERCECLOCALE=0’ being set, ‘LC_ALL’ being set, or the lack of a
suitable target locale).

See also
........

PEP 540(3) – Add a new UTF-8 mode

     PEP written and implemented by Victor Stinner

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0540

   (2) https://www.python.org/dev/peps/pep-0538

   (3) https://www.python.org/dev/peps/pep-0540


File: python.info,  Node: PEP 553 Built-in breakpoint,  Next: PEP 539 New C API for Thread-Local Storage,  Prev: PEP 540 Forced UTF-8 Runtime Mode,  Up: New Features<4>

1.3.2.4 PEP 553: Built-in ‘breakpoint()’
........................................

Python 3.7 includes the new built-in *note breakpoint(): 40b. function
as an easy and consistent way to enter the Python debugger.

Built-in ‘breakpoint()’ calls *note sys.breakpointhook(): 423.  By
default, the latter imports *note pdb: c9. and then calls
‘pdb.set_trace()’, but by binding ‘sys.breakpointhook()’ to the function
of your choosing, ‘breakpoint()’ can enter any debugger.  Additionally,
the environment variable *note PYTHONBREAKPOINT: 424. can be set to the
callable of your debugger of choice.  Set ‘PYTHONBREAKPOINT=0’ to
completely disable built-in ‘breakpoint()’.

See also
........

PEP 553(1) – Built-in breakpoint()

     PEP written and implemented by Barry Warsaw

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0553


File: python.info,  Node: PEP 539 New C API for Thread-Local Storage,  Next: PEP 562 Customization of Access to Module Attributes,  Prev: PEP 553 Built-in breakpoint,  Up: New Features<4>

1.3.2.5 PEP 539: New C API for Thread-Local Storage
...................................................

While Python provides a C API for thread-local storage support; the
existing *note Thread Local Storage (TLS) API: 426. has used ‘int’ to
represent TLS keys across all platforms.  This has not generally been a
problem for officially-support platforms, but that is neither
POSIX-compliant, nor portable in any practical sense.

PEP 539(1) changes this by providing a new *note Thread Specific Storage
(TSS) API: 427. to CPython which supersedes use of the existing TLS API
within the CPython interpreter, while deprecating the existing API. The
TSS API uses a new type *note Py_tss_t: 428. instead of ‘int’ to
represent TSS keys–an opaque type the definition of which may depend on
the underlying TLS implementation.  Therefore, this will allow to build
CPython on platforms where the native TLS key is defined in a way that
cannot be safely cast to ‘int’.

Note that on platforms where the native TLS key is defined in a way that
cannot be safely cast to ‘int’, all functions of the existing TLS API
will be no-op and immediately return failure.  This indicates clearly
that the old API is not supported on platforms where it cannot be used
reliably, and that no effort will be made to add such support.

See also
........

PEP 539(2) – A New C-API for Thread-Local Storage in CPython

     PEP written by Erik M. Bray; implementation by Masayuki Yamamoto.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0539

   (2) https://www.python.org/dev/peps/pep-0539


File: python.info,  Node: PEP 562 Customization of Access to Module Attributes,  Next: PEP 564 New Time Functions With Nanosecond Resolution,  Prev: PEP 539 New C API for Thread-Local Storage,  Up: New Features<4>

1.3.2.6 PEP 562: Customization of Access to Module Attributes
.............................................................

Python 3.7 allows defining *note __getattr__(): 42a. on modules and will
call it whenever a module attribute is otherwise not found.  Defining
*note __dir__(): 42b. on modules is now also allowed.

A typical example of where this may be useful is module attribute
deprecation and lazy loading.

See also
........

PEP 562(1) – Module ‘__getattr__’ and ‘__dir__’

     PEP written and implemented by Ivan Levkivskyi

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0562


File: python.info,  Node: PEP 564 New Time Functions With Nanosecond Resolution,  Next: PEP 565 Show DeprecationWarning in __main__,  Prev: PEP 562 Customization of Access to Module Attributes,  Up: New Features<4>

1.3.2.7 PEP 564: New Time Functions With Nanosecond Resolution
..............................................................

The resolution of clocks in modern systems can exceed the limited
precision of a floating point number returned by the *note time.time():
42d. function and its variants.  To avoid loss of precision, PEP 564(1)
adds six new “nanosecond” variants of the existing timer functions to
the *note time: 10c. module:

   * *note time.clock_gettime_ns(): 42e.

   * *note time.clock_settime_ns(): 42f.

   * *note time.monotonic_ns(): 430.

   * *note time.perf_counter_ns(): 431.

   * *note time.process_time_ns(): 432.

   * *note time.time_ns(): 433.

The new functions return the number of nanoseconds as an integer value.

Measurements(2) show that on Linux and Windows the resolution of *note
time.time_ns(): 433. is approximately 3 times better than that of *note
time.time(): 42d.

See also
........

PEP 564(3) – Add new time functions with nanosecond resolution

     PEP written and implemented by Victor Stinner

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0564

   (2) 
https://www.python.org/dev/peps/pep-0564/#annex-clocks-resolution-in-python

   (3) https://www.python.org/dev/peps/pep-0564


File: python.info,  Node: PEP 565 Show DeprecationWarning in __main__,  Next: PEP 560 Core Support for typing module and Generic Types,  Prev: PEP 564 New Time Functions With Nanosecond Resolution,  Up: New Features<4>

1.3.2.8 PEP 565: Show DeprecationWarning in ‘__main__’
......................................................

The default handling of *note DeprecationWarning: 15a. has been changed
such that these warnings are once more shown by default, but only when
the code triggering them is running directly in the *note __main__: 1.
module.  As a result, developers of single file scripts and those using
Python interactively should once again start seeing deprecation warnings
for the APIs they use, but deprecation warnings triggered by imported
application, library and framework modules will continue to be hidden by
default.

As a result of this change, the standard library now allows developers
to choose between three different deprecation warning behaviours:

   * *note FutureWarning: 435.: always displayed by default, recommended
     for warnings intended to be seen by application end users (e.g.
     for deprecated application configuration settings).

   * *note DeprecationWarning: 15a.: displayed by default only in *note
     __main__: 1. and when running tests, recommended for warnings
     intended to be seen by other Python developers where a version
     upgrade may result in changed behaviour or an error.

   * *note PendingDeprecationWarning: 15c.: displayed by default only
     when running tests, intended for cases where a future version
     upgrade will change the warning category to *note
     DeprecationWarning: 15a. or *note FutureWarning: 435.

Previously both *note DeprecationWarning: 15a. and *note
PendingDeprecationWarning: 15c. were only visible when running tests,
which meant that developers primarily writing single file scripts or
using Python interactively could be surprised by breaking changes in the
APIs they used.

See also
........

PEP 565(1) – Show DeprecationWarning in ‘__main__’

     PEP written and implemented by Nick Coghlan

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0565


File: python.info,  Node: PEP 560 Core Support for typing module and Generic Types,  Next: PEP 552 Hash-based pyc Files,  Prev: PEP 565 Show DeprecationWarning in __main__,  Up: New Features<4>

1.3.2.9 PEP 560: Core Support for ‘typing’ module and Generic Types
...................................................................

Initially PEP 484(1) was designed in such way that it would not
introduce `any' changes to the core CPython interpreter.  Now type hints
and the *note typing: 122. module are extensively used by the community,
so this restriction is removed.  The PEP introduces two special methods
*note __class_getitem__(): 437. and ‘__mro_entries__’, these methods are
now used by most classes and special constructs in *note typing: 122.
As a result, the speed of various operations with types increased up to
7 times, the generic types can be used without metaclass conflicts, and
several long standing bugs in *note typing: 122. module are fixed.

See also
........

PEP 560(2) – Core support for typing module and generic types

     PEP written and implemented by Ivan Levkivskyi

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0484

   (2) https://www.python.org/dev/peps/pep-0560


File: python.info,  Node: PEP 552 Hash-based pyc Files,  Next: PEP 545 Python Documentation Translations,  Prev: PEP 560 Core Support for typing module and Generic Types,  Up: New Features<4>

1.3.2.10 PEP 552: Hash-based .pyc Files
.......................................

Python has traditionally checked the up-to-dateness of bytecode cache
files (i.e., ‘.pyc’ files) by comparing the source metadata
(last-modified timestamp and size) with source metadata saved in the
cache file header when it was generated.  While effective, this
invalidation method has its drawbacks.  When filesystem timestamps are
too coarse, Python can miss source updates, leading to user confusion.
Additionally, having a timestamp in the cache file is problematic for
build reproducibility(1) and content-based build systems.

PEP 552(2) extends the pyc format to allow the hash of the source file
to be used for invalidation instead of the source timestamp.  Such
‘.pyc’ files are called “hash-based”.  By default, Python still uses
timestamp-based invalidation and does not generate hash-based ‘.pyc’
files at runtime.  Hash-based ‘.pyc’ files may be generated with *note
py_compile: d7. or *note compileall: 20.

Hash-based ‘.pyc’ files come in two variants: checked and unchecked.
Python validates checked hash-based ‘.pyc’ files against the
corresponding source files at runtime but doesn’t do so for unchecked
hash-based pycs.  Unchecked hash-based ‘.pyc’ files are a useful
performance optimization for environments where a system external to
Python (e.g., the build system) is responsible for keeping ‘.pyc’ files
up-to-date.

See *note Cached bytecode invalidation: 439. for more information.

See also
........

PEP 552(3) – Deterministic pycs

     PEP written and implemented by Benjamin Peterson

   ---------- Footnotes ----------

   (1) https://reproducible-builds.org/

   (2) https://www.python.org/dev/peps/pep-0552

   (3) https://www.python.org/dev/peps/pep-0552


File: python.info,  Node: PEP 545 Python Documentation Translations,  Next: Python Development Mode -X dev,  Prev: PEP 552 Hash-based pyc Files,  Up: New Features<4>

1.3.2.11 PEP 545: Python Documentation Translations
...................................................

PEP 545(1) describes the process of creating and maintaining Python
documentation translations.

Three new translations have been added:

   - Japanese: ‘https://docs.python.org/ja/’

   - French: ‘https://docs.python.org/fr/’

   - Korean: ‘https://docs.python.org/ko/’

See also
........

PEP 545(2) – Python Documentation Translations

     PEP written and implemented by Julien Palard, Inada Naoki, and
     Victor Stinner.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0545

   (2) https://www.python.org/dev/peps/pep-0545


File: python.info,  Node: Python Development Mode -X dev,  Prev: PEP 545 Python Documentation Translations,  Up: New Features<4>

1.3.2.12 Python Development Mode (-X dev)
.........................................

The new *note -X: 290. ‘dev’ command line option or the new *note
PYTHONDEVMODE: 43c. environment variable can be used to enable *note
Python Development Mode: 160.  When in development mode, Python performs
additional runtime checks that are too expensive to be enabled by
default.  See *note Python Development Mode: 160. documentation for the
full description.


File: python.info,  Node: Other Language Changes<3>,  Next: New Modules<3>,  Prev: New Features<4>,  Up: What’s New In Python 3 7

1.3.3 Other Language Changes
----------------------------

   * An *note await: 2d8. expression and comprehensions containing an
     *note async for: 3fd. clause were illegal in the expressions in
     *note formatted string literals: 296. due to a problem with the
     implementation.  In Python 3.7 this restriction was lifted.

   * More than 255 arguments can now be passed to a function, and a
     function can now have more than 255 parameters.  (Contributed by
     Serhiy Storchaka in bpo-12844(1) and bpo-18896(2).)

   * *note bytes.fromhex(): 43e. and *note bytearray.fromhex(): 43f. now
     ignore all ASCII whitespace, not only spaces.  (Contributed by
     Robert Xiao in bpo-28927(3).)

   * *note str: 205, *note bytes: 172, and *note bytearray: 173. gained
     support for the new *note isascii(): 440. method, which can be used
     to test if a string or bytes contain only the ASCII characters.
     (Contributed by INADA Naoki in bpo-32677(4).)

   * *note ImportError: 16c. now displays module name and module
     ‘__file__’ path when ‘from ... import ...’ fails.  (Contributed by
     Matthias Bussonnier in bpo-29546(5).)

   * Circular imports involving absolute imports with binding a
     submodule to a name are now supported.  (Contributed by Serhiy
     Storchaka in bpo-30024(6).)

   * ‘object.__format__(x, '')’ is now equivalent to ‘str(x)’ rather
     than ‘format(str(self), '')’.  (Contributed by Serhiy Storchaka in
     bpo-28974(7).)

   * In order to better support dynamic creation of stack traces, *note
     types.TracebackType: 441. can now be instantiated from Python code,
     and the ‘tb_next’ attribute on *note tracebacks: 442. is now
     writable.  (Contributed by Nathaniel J. Smith in bpo-30579(8).)

   * When using the *note -m: 443. switch, ‘sys.path[0]’ is now eagerly
     expanded to the full starting directory path, rather than being
     left as the empty directory (which allows imports from the
     `current' working directory at the time when an import occurs)
     (Contributed by Nick Coghlan in bpo-33053(9).)

   * The new *note -X: 290. ‘importtime’ option or the *note
     PYTHONPROFILEIMPORTTIME: 444. environment variable can be used to
     show the timing of each module import.  (Contributed by Victor
     Stinner in bpo-31415(10).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12844

   (2) https://bugs.python.org/issue18896

   (3) https://bugs.python.org/issue28927

   (4) https://bugs.python.org/issue32677

   (5) https://bugs.python.org/issue29546

   (6) https://bugs.python.org/issue30024

   (7) https://bugs.python.org/issue28974

   (8) https://bugs.python.org/issue30579

   (9) https://bugs.python.org/issue33053

   (10) https://bugs.python.org/issue31415


File: python.info,  Node: New Modules<3>,  Next: Improved Modules<3>,  Prev: Other Language Changes<3>,  Up: What’s New In Python 3 7

1.3.4 New Modules
-----------------

* Menu:

* contextvars::
* dataclasses::
* importlib.resources: importlib resources.


File: python.info,  Node: contextvars,  Next: dataclasses,  Up: New Modules<3>

1.3.4.1 contextvars
...................

The new *note contextvars: 24. module and a set of *note new C APIs:
447. introduce support for `context variables'.  Context variables are
conceptually similar to thread-local variables.  Unlike TLS, context
variables support asynchronous code correctly.

The *note asyncio: 9. and *note decimal: 35. modules have been updated
to use and support context variables out of the box.  Particularly the
active decimal context is now stored in a context variable, which allows
decimal operations to work with the correct context in asynchronous
code.

See also
........

PEP 567(1) – Context Variables

     PEP written and implemented by Yury Selivanov

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0567


File: python.info,  Node: dataclasses,  Next: importlib resources,  Prev: contextvars,  Up: New Modules<3>

1.3.4.2 dataclasses
...................

The new *note dataclass(): 449. decorator provides a way to declare
`data classes'.  A data class describes its attributes using class
variable annotations.  Its constructor and other magic methods, such as
*note __repr__(): 44a, *note __eq__(): 44b, and *note __hash__(): 44c.
are generated automatically.

Example:

     @dataclass
     class Point:
         x: float
         y: float
         z: float = 0.0

     p = Point(1.5, 2.5)
     print(p)   # produces "Point(x=1.5, y=2.5, z=0.0)"

See also
........

PEP 557(1) – Data Classes

     PEP written and implemented by Eric V. Smith

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0557


File: python.info,  Node: importlib resources,  Prev: dataclasses,  Up: New Modules<3>

1.3.4.3 importlib.resources
...........................

The new *note importlib.resources: 9e. module provides several new APIs
and one new ABC for access to, opening, and reading `resources' inside
packages.  Resources are roughly similar to files inside packages, but
they needn’t be actual files on the physical file system.  Module
loaders can provide a ‘get_resource_reader()’ function which returns a
*note importlib.abc.ResourceReader: 44e. instance to support this new
API. Built-in file path loaders and zip file loaders both support this.

Contributed by Barry Warsaw and Brett Cannon in bpo-32248(1).

See also
........

importlib_resources(2) – a PyPI backport for earlier Python versions.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32248

   (2) http://importlib-resources.readthedocs.io/en/latest/


File: python.info,  Node: Improved Modules<3>,  Next: C API Changes<2>,  Prev: New Modules<3>,  Up: What’s New In Python 3 7

1.3.5 Improved Modules
----------------------

* Menu:

* argparse::
* asyncio: asyncio<3>.
* binascii::
* calendar::
* collections: collections<2>.
* compileall: compileall<2>.
* concurrent.futures: concurrent futures<2>.
* contextlib::
* cProfile: cProfile<2>.
* crypt::
* datetime: datetime<3>.
* dbm::
* decimal::
* dis::
* distutils: distutils<2>.
* enum::
* functools: functools<2>.
* gc: gc<3>.
* hmac::
* http.client: http client.
* http.server: http server.
* idlelib and IDLE::
* importlib: importlib<2>.
* io: io<2>.
* ipaddress: ipaddress<2>.
* itertools: itertools<2>.
* locale::
* logging: logging<2>.
* math: math<3>.
* mimetypes::
* msilib::
* multiprocessing: multiprocessing<3>.
* os: os<3>.
* pathlib: pathlib<3>.
* pdb: pdb<2>.
* py_compile: py_compile<2>.
* pydoc: pydoc<2>.
* queue::
* re::
* signal: signal<2>.
* socket: socket<3>.
* socketserver::
* sqlite3::
* ssl: ssl<2>.
* string::
* subprocess::
* sys: sys<3>.
* time: time<3>.
* tkinter: tkinter<2>.
* tracemalloc: tracemalloc<2>.
* types::
* unicodedata: unicodedata<3>.
* unittest: unittest<2>.
* unittest.mock: unittest mock.
* urllib.parse: urllib parse<3>.
* uu::
* uuid::
* warnings::
* xml.etree: xml etree.
* xmlrpc.server: xmlrpc server.
* zipapp::
* zipfile::


File: python.info,  Node: argparse,  Next: asyncio<3>,  Up: Improved Modules<3>

1.3.5.1 argparse
................

The new *note ArgumentParser.parse_intermixed_args(): 451. method allows
intermixing options and positional arguments.  (Contributed by paul.j3
in bpo-14191(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14191


File: python.info,  Node: asyncio<3>,  Next: binascii,  Prev: argparse,  Up: Improved Modules<3>

1.3.5.2 asyncio
...............

The *note asyncio: 9. module has received many new features, usability
and *note performance improvements: 453.  Notable changes include:

   * The new *note provisional: 454. *note asyncio.run(): 18d. function
     can be used to run a coroutine from synchronous code by
     automatically creating and destroying the event loop.  (Contributed
     by Yury Selivanov in bpo-32314(1).)

   * asyncio gained support for *note contextvars: 24.  *note
     loop.call_soon(): 455, *note loop.call_soon_threadsafe(): 456,
     *note loop.call_later(): 457, *note loop.call_at(): 458, and *note
     Future.add_done_callback(): 459. have a new optional keyword-only
     `context' parameter.  *note Tasks: 2e0. now track their context
     automatically.  See PEP 567(2) for more details.  (Contributed by
     Yury Selivanov in bpo-32436(3).)

   * The new *note asyncio.create_task(): 2e1. function has been added
     as a shortcut to ‘asyncio.get_event_loop().create_task()’.
     (Contributed by Andrew Svetlov in bpo-32311(4).)

   * The new *note loop.start_tls(): 45a. method can be used to upgrade
     an existing connection to TLS. (Contributed by Yury Selivanov in
     bpo-23749(5).)

   * The new *note loop.sock_recv_into(): 45b. method allows reading
     data from a socket directly into a provided buffer making it
     possible to reduce data copies.  (Contributed by Antoine Pitrou in
     bpo-31819(6).)

   * The new *note asyncio.current_task(): 228. function returns the
     currently running *note Task: 2e0. instance, and the new *note
     asyncio.all_tasks(): 229. function returns a set of all existing
     ‘Task’ instances in a given loop.  The ‘Task.current_task()’ and
     ‘Task.all_tasks()’ methods have been deprecated.  (Contributed by
     Andrew Svetlov in bpo-32250(7).)

   * The new `provisional' *note BufferedProtocol: 3eb. class allows
     implementing streaming protocols with manual control over the
     receive buffer.  (Contributed by Yury Selivanov in bpo-32251(8).)

   * The new *note asyncio.get_running_loop(): 45c. function returns the
     currently running loop, and raises a *note RuntimeError: 3dc. if no
     loop is running.  This is in contrast with *note
     asyncio.get_event_loop(): 45d, which will `create' a new event loop
     if none is running.  (Contributed by Yury Selivanov in
     bpo-32269(9).)

   * The new *note StreamWriter.wait_closed(): 45e. coroutine method
     allows waiting until the stream writer is closed.  The new *note
     StreamWriter.is_closing(): 45f. method can be used to determine if
     the writer is closing.  (Contributed by Andrew Svetlov in
     bpo-32391(10).)

   * The new *note loop.sock_sendfile(): 460. coroutine method allows
     sending files using *note os.sendfile: 461. when possible.
     (Contributed by Andrew Svetlov in bpo-32410(11).)

   * The new *note Future.get_loop(): 462. and ‘Task.get_loop()’ methods
     return the instance of the loop on which a task or a future were
     created.  *note Server.get_loop(): 463. allows doing the same for
     *note asyncio.Server: 464. objects.  (Contributed by Yury Selivanov
     in bpo-32415(12) and Srinivas Reddy Thatiparthy in bpo-32418(13).)

   * It is now possible to control how instances of *note
     asyncio.Server: 464. begin serving.  Previously, the server would
     start serving immediately when created.  The new `start_serving'
     keyword argument to *note loop.create_server(): 465. and *note
     loop.create_unix_server(): 466, as well as *note
     Server.start_serving(): 467, and *note Server.serve_forever(): 468.
     can be used to decouple server instantiation and serving.  The new
     *note Server.is_serving(): 469. method returns ‘True’ if the server
     is serving.  *note Server: 464. objects are now asynchronous
     context managers:

          srv = await loop.create_server(...)

          async with srv:
              # some code

          # At this point, srv is closed and no longer accepts new connections.

     (Contributed by Yury Selivanov in bpo-32662(14).)

   * Callback objects returned by *note loop.call_later(): 457. gained
     the new *note when(): 46a. method which returns an absolute
     scheduled callback timestamp.  (Contributed by Andrew Svetlov in
     bpo-32741(15).)

   * The *note loop.create_datagram_endpoint(): 189. method gained
     support for Unix sockets.  (Contributed by Quentin Dawans in
     bpo-31245(16).)

   * The *note asyncio.open_connection(): 46b, *note
     asyncio.start_server(): 46c. functions, *note
     loop.create_connection(): 2e5, *note loop.create_server(): 465,
     *note loop.create_accepted_socket(): 46d. methods and their
     corresponding UNIX socket variants now accept the
     `ssl_handshake_timeout' keyword argument.  (Contributed by Neil
     Aspinall in bpo-29970(17).)

   * The new *note Handle.cancelled(): 46e. method returns ‘True’ if the
     callback was cancelled.  (Contributed by Marat Sharafutdinov in
     bpo-31943(18).)

   * The asyncio source has been converted to use the *note async:
     2d7./*note await: 2d8. syntax.  (Contributed by Andrew Svetlov in
     bpo-32193(19).)

   * The new *note ReadTransport.is_reading(): 46f. method can be used
     to determine the reading state of the transport.  Additionally,
     calls to *note ReadTransport.resume_reading(): 470. and *note
     ReadTransport.pause_reading(): 471. are now idempotent.
     (Contributed by Yury Selivanov in bpo-32356(20).)

   * Loop methods which accept socket paths now support passing *note
     path-like objects: 472.  (Contributed by Yury Selivanov in
     bpo-32066(21).)

   * In *note asyncio: 9. TCP sockets on Linux are now created with
     ‘TCP_NODELAY’ flag set by default.  (Contributed by Yury Selivanov
     and Victor Stinner in bpo-27456(22).)

   * Exceptions occurring in cancelled tasks are no longer logged.
     (Contributed by Yury Selivanov in bpo-30508(23).)

   * New ‘WindowsSelectorEventLoopPolicy’ and
     ‘WindowsProactorEventLoopPolicy’ classes.  (Contributed by Yury
     Selivanov in bpo-33792(24).)

Several ‘asyncio’ APIs have been *note deprecated: 473.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32314

   (2) https://www.python.org/dev/peps/pep-0567

   (3) https://bugs.python.org/issue32436

   (4) https://bugs.python.org/issue32311

   (5) https://bugs.python.org/issue23749

   (6) https://bugs.python.org/issue31819

   (7) https://bugs.python.org/issue32250

   (8) https://bugs.python.org/issue32251

   (9) https://bugs.python.org/issue32269

   (10) https://bugs.python.org/issue32391

   (11) https://bugs.python.org/issue32410

   (12) https://bugs.python.org/issue32415

   (13) https://bugs.python.org/issue32418

   (14) https://bugs.python.org/issue32662

   (15) https://bugs.python.org/issue32741

   (16) https://bugs.python.org/issue31245

   (17) https://bugs.python.org/issue29970

   (18) https://bugs.python.org/issue31943

   (19) https://bugs.python.org/issue32193

   (20) https://bugs.python.org/issue32356

   (21) https://bugs.python.org/issue32066

   (22) https://bugs.python.org/issue27456

   (23) https://bugs.python.org/issue30508

   (24) https://bugs.python.org/issue33792


File: python.info,  Node: binascii,  Next: calendar,  Prev: asyncio<3>,  Up: Improved Modules<3>

1.3.5.3 binascii
................

The *note b2a_uu(): 475. function now accepts an optional `backtick'
keyword argument.  When it’s true, zeros are represented by ‘'`'’
instead of spaces.  (Contributed by Xiang Zhang in bpo-30103(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30103


File: python.info,  Node: calendar,  Next: collections<2>,  Prev: binascii,  Up: Improved Modules<3>

1.3.5.4 calendar
................

The *note HTMLCalendar: 477. class has new class attributes which ease
the customization of CSS classes in the produced HTML calendar.
(Contributed by Oz Tiram in bpo-30095(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30095


File: python.info,  Node: collections<2>,  Next: compileall<2>,  Prev: calendar,  Up: Improved Modules<3>

1.3.5.5 collections
...................

‘collections.namedtuple()’ now supports default values.  (Contributed by
Raymond Hettinger in bpo-32320(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32320


File: python.info,  Node: compileall<2>,  Next: concurrent futures<2>,  Prev: collections<2>,  Up: Improved Modules<3>

1.3.5.6 compileall
..................

*note compileall.compile_dir(): 47a. learned the new `invalidation_mode'
parameter, which can be used to enable *note hash-based .pyc
invalidation: 413.  The invalidation mode can also be specified on the
command line using the new ‘--invalidation-mode’ argument.  (Contributed
by Benjamin Peterson in bpo-31650(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31650


File: python.info,  Node: concurrent futures<2>,  Next: contextlib,  Prev: compileall<2>,  Up: Improved Modules<3>

1.3.5.7 concurrent.futures
..........................

*note ProcessPoolExecutor: 196. and *note ThreadPoolExecutor: 18c. now
support the new `initializer' and `initargs' constructor arguments.
(Contributed by Antoine Pitrou in bpo-21423(1).)

The *note ProcessPoolExecutor: 196. can now take the multiprocessing
context via the new `mp_context' argument.  (Contributed by Thomas
Moreau in bpo-31540(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21423

   (2) https://bugs.python.org/issue31540


File: python.info,  Node: contextlib,  Next: cProfile<2>,  Prev: concurrent futures<2>,  Up: Improved Modules<3>

1.3.5.8 contextlib
..................

The new *note nullcontext(): 47d. is a simpler and faster no-op context
manager than *note ExitStack: 47e.  (Contributed by Jesse-Bakker in
bpo-10049(1).)

The new *note asynccontextmanager(): 47f, *note
AbstractAsyncContextManager: 480, and *note AsyncExitStack: 481. have
been added to complement their synchronous counterparts.  (Contributed
by Jelle Zijlstra in bpo-29679(2) and bpo-30241(3), and by Alexander
Mohr and Ilya Kulakov in bpo-29302(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10049

   (2) https://bugs.python.org/issue29679

   (3) https://bugs.python.org/issue30241

   (4) https://bugs.python.org/issue29302


File: python.info,  Node: cProfile<2>,  Next: crypt,  Prev: contextlib,  Up: Improved Modules<3>

1.3.5.9 cProfile
................

The *note cProfile: 27. command line now accepts ‘-m module_name’ as an
alternative to script path.  (Contributed by Sanyam Khurana in
bpo-21862(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21862


File: python.info,  Node: crypt,  Next: datetime<3>,  Prev: cProfile<2>,  Up: Improved Modules<3>

1.3.5.10 crypt
..............

The *note crypt: 28. module now supports the Blowfish hashing method.
(Contributed by Serhiy Storchaka in bpo-31664(1).)

The *note mksalt(): 484. function now allows specifying the number of
rounds for hashing.  (Contributed by Serhiy Storchaka in bpo-31702(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31664

   (2) https://bugs.python.org/issue31702


File: python.info,  Node: datetime<3>,  Next: dbm,  Prev: crypt,  Up: Improved Modules<3>

1.3.5.11 datetime
.................

The new *note datetime.fromisoformat(): 486. method constructs a *note
datetime: 1a0. object from a string in one of the formats output by
*note datetime.isoformat(): 487.  (Contributed by Paul Ganssle in
bpo-15873(1).)

The *note tzinfo: 180. class now supports sub-minute offsets.
(Contributed by Alexander Belopolsky in bpo-5288(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15873

   (2) https://bugs.python.org/issue5288


File: python.info,  Node: dbm,  Next: decimal,  Prev: datetime<3>,  Up: Improved Modules<3>

1.3.5.12 dbm
............

*note dbm.dumb: 32. now supports reading read-only files and no longer
writes the index file when it is not changed.


File: python.info,  Node: decimal,  Next: dis,  Prev: dbm,  Up: Improved Modules<3>

1.3.5.13 decimal
................

The *note decimal: 35. module now uses *note context variables: 407. to
store the decimal context.  (Contributed by Yury Selivanov in
bpo-32630(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32630


File: python.info,  Node: dis,  Next: distutils<2>,  Prev: decimal,  Up: Improved Modules<3>

1.3.5.14 dis
............

The *note dis(): 48b. function is now able to disassemble nested code
objects (the code of comprehensions, generator expressions and nested
functions, and the code used for building nested classes).  The maximum
depth of disassembly recursion is controlled by the new `depth'
parameter.  (Contributed by Serhiy Storchaka in bpo-11822(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11822


File: python.info,  Node: distutils<2>,  Next: enum,  Prev: dis,  Up: Improved Modules<3>

1.3.5.15 distutils
..................

‘README.rst’ is now included in the list of distutils standard READMEs
and therefore included in source distributions.  (Contributed by Ryan
Gonzalez in bpo-11913(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11913


File: python.info,  Node: enum,  Next: functools<2>,  Prev: distutils<2>,  Up: Improved Modules<3>

1.3.5.16 enum
.............

The *note Enum: 48e. learned the new ‘_ignore_’ class property, which
allows listing the names of properties which should not become enum
members.  (Contributed by Ethan Furman in bpo-31801(1).)

In Python 3.8, attempting to check for non-Enum objects in ‘Enum’
classes will raise a *note TypeError: 1fe. (e.g.  ‘1 in Color’);
similarly, attempting to check for non-Flag objects in a ‘Flag’ member
will raise *note TypeError: 1fe. (e.g.  ‘1 in Perm.RW’); currently, both
operations return *note False: 48f. instead and are deprecated.
(Contributed by Ethan Furman in bpo-33217(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31801

   (2) https://bugs.python.org/issue33217


File: python.info,  Node: functools<2>,  Next: gc<3>,  Prev: enum,  Up: Improved Modules<3>

1.3.5.17 functools
..................

*note functools.singledispatch(): 491. now supports registering
implementations using type annotations.  (Contributed by Łukasz Langa in
bpo-32227(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32227


File: python.info,  Node: gc<3>,  Next: hmac,  Prev: functools<2>,  Up: Improved Modules<3>

1.3.5.18 gc
...........

The new *note gc.freeze(): 493. function allows freezing all objects
tracked by the garbage collector and excluding them from future
collections.  This can be used before a POSIX ‘fork()’ call to make the
GC copy-on-write friendly or to speed up collection.  The new *note
gc.unfreeze(): 494. functions reverses this operation.  Additionally,
*note gc.get_freeze_count(): 495. can be used to obtain the number of
frozen objects.  (Contributed by Li Zekun in bpo-31558(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31558


File: python.info,  Node: hmac,  Next: http client,  Prev: gc<3>,  Up: Improved Modules<3>

1.3.5.19 hmac
.............

The *note hmac: 8e. module now has an optimized one-shot *note digest():
497. function, which is up to three times faster than ‘HMAC()’.
(Contributed by Christian Heimes in bpo-32433(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32433


File: python.info,  Node: http client,  Next: http server,  Prev: hmac,  Up: Improved Modules<3>

1.3.5.20 http.client
....................

*note HTTPConnection: 499. and *note HTTPSConnection: 49a. now support
the new `blocksize' argument for improved upload throughput.
(Contributed by Nir Soffer in bpo-31945(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31945


File: python.info,  Node: http server,  Next: idlelib and IDLE,  Prev: http client,  Up: Improved Modules<3>

1.3.5.21 http.server
....................

*note SimpleHTTPRequestHandler: 49c. now supports the HTTP
‘If-Modified-Since’ header.  The server returns the 304 response status
if the target file was not modified after the time specified in the
header.  (Contributed by Pierre Quentel in bpo-29654(1).)

*note SimpleHTTPRequestHandler: 49c. accepts the new `directory'
argument, in addition to the new ‘--directory’ command line argument.
With this parameter, the server serves the specified directory, by
default it uses the current working directory.  (Contributed by Stéphane
Wirtel and Julien Palard in bpo-28707(2).)

The new *note ThreadingHTTPServer: 49d. class uses threads to handle
requests using ‘ThreadingMixin’.  It is used when ‘http.server’ is run
with ‘-m’.  (Contributed by Julien Palard in bpo-31639(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29654

   (2) https://bugs.python.org/issue28707

   (3) https://bugs.python.org/issue31639


File: python.info,  Node: idlelib and IDLE,  Next: importlib<2>,  Prev: http server,  Up: Improved Modules<3>

1.3.5.22 idlelib and IDLE
.........................

Multiple fixes for autocompletion.  (Contributed by Louie Lu in
bpo-15786(1).)

Module Browser (on the File menu, formerly called Class Browser), now
displays nested functions and classes in addition to top-level functions
and classes.  (Contributed by Guilherme Polo, Cheryl Sabella, and Terry
Jan Reedy in bpo-1612262(2).)

The Settings dialog (Options, Configure IDLE) has been partly rewritten
to improve both appearance and function.  (Contributed by Cheryl Sabella
and Terry Jan Reedy in multiple issues.)

The font sample now includes a selection of non-Latin characters so that
users can better see the effect of selecting a particular font.
(Contributed by Terry Jan Reedy in bpo-13802(3).)  The sample can be
edited to include other characters.  (Contributed by Serhiy Storchaka in
bpo-31860(4).)

The IDLE features formerly implemented as extensions have been
reimplemented as normal features.  Their settings have been moved from
the Extensions tab to other dialog tabs.  (Contributed by Charles
Wohlganger and Terry Jan Reedy in bpo-27099(5).)

Editor code context option revised.  Box displays all context lines up
to maxlines.  Clicking on a context line jumps the editor to that line.
Context colors for custom themes is added to Highlights tab of Settings
dialog.  (Contributed by Cheryl Sabella and Terry Jan Reedy in
bpo-33642(6), bpo-33768(7), and bpo-33679(8).)

On Windows, a new API call tells Windows that tk scales for DPI. On
Windows 8.1+ or 10, with DPI compatibility properties of the Python
binary unchanged, and a monitor resolution greater than 96 DPI, this
should make text and lines sharper.  It should otherwise have no effect.
(Contributed by Terry Jan Reedy in bpo-33656(9).)

New in 3.7.1:

Output over N lines (50 by default) is squeezed down to a button.  N can
be changed in the PyShell section of the General page of the Settings
dialog.  Fewer, but possibly extra long, lines can be squeezed by right
clicking on the output.  Squeezed output can be expanded in place by
double-clicking the button or into the clipboard or a separate window by
right-clicking the button.  (Contributed by Tal Einat in
bpo-1529353(10).)

The changes above have been backported to 3.6 maintenance releases.

NEW in 3.7.4:

Add “Run Customized” to the Run menu to run a module with customized
settings.  Any command line arguments entered are added to sys.argv.
They re-appear in the box for the next customized run.  One can also
suppress the normal Shell main module restart.  (Contributed by Cheryl
Sabella, Terry Jan Reedy, and others in bpo-5680(11) and bpo-37627(12).)

New in 3.7.5:

Add optional line numbers for IDLE editor windows.  Windows open without
line numbers unless set otherwise in the General tab of the
configuration dialog.  Line numbers for an existing window are shown and
hidden in the Options menu.  (Contributed by Tal Einat and Saimadhav
Heblikar in bpo-17535(13).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15786

   (2) https://bugs.python.org/issue1612262

   (3) https://bugs.python.org/issue13802

   (4) https://bugs.python.org/issue31860

   (5) https://bugs.python.org/issue27099

   (6) https://bugs.python.org/issue33642

   (7) https://bugs.python.org/issue33768

   (8) https://bugs.python.org/issue33679

   (9) https://bugs.python.org/issue33656

   (10) https://bugs.python.org/issue1529353

   (11) https://bugs.python.org/issue5680

   (12) https://bugs.python.org/issue37627

   (13) https://bugs.python.org/issue17535


File: python.info,  Node: importlib<2>,  Next: io<2>,  Prev: idlelib and IDLE,  Up: Improved Modules<3>

1.3.5.23 importlib
..................

The *note importlib.abc.ResourceReader: 44e. ABC was introduced to
support the loading of resources from packages.  See also *note
importlib.resources: 409.  (Contributed by Barry Warsaw, Brett Cannon in
bpo-32248(1).)

*note importlib.reload(): 4a0. now raises *note ModuleNotFoundError:
4a1. if the module lacks a spec.  (Contributed by Garvit Khatri in
bpo-29851(2).)

‘importlib.find_spec()’ now raises *note ModuleNotFoundError: 4a1.
instead of *note AttributeError: 4a2. if the specified parent module is
not a package (i.e.  lacks a ‘__path__’ attribute).  (Contributed by
Milan Oberkirch in bpo-30436(3).)

The new ‘importlib.source_hash()’ can be used to compute the hash of the
passed source.  A *note hash-based .pyc file: 413. embeds the value
returned by this function.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32248

   (2) https://bugs.python.org/issue29851

   (3) https://bugs.python.org/issue30436


File: python.info,  Node: io<2>,  Next: ipaddress<2>,  Prev: importlib<2>,  Up: Improved Modules<3>

1.3.5.24 io
...........

The new *note TextIOWrapper.reconfigure(): 4a4. method can be used to
reconfigure the text stream with the new settings.  (Contributed by
Antoine Pitrou in bpo-30526(1) and INADA Naoki in bpo-15216(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30526

   (2) https://bugs.python.org/issue15216


File: python.info,  Node: ipaddress<2>,  Next: itertools<2>,  Prev: io<2>,  Up: Improved Modules<3>

1.3.5.25 ipaddress
..................

The new ‘subnet_of()’ and ‘supernet_of()’ methods of *note
ipaddress.IPv6Network: 4a6. and *note ipaddress.IPv4Network: 4a7. can be
used for network containment tests.  (Contributed by Michel Albert and
Cheryl Sabella in bpo-20825(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20825


File: python.info,  Node: itertools<2>,  Next: locale,  Prev: ipaddress<2>,  Up: Improved Modules<3>

1.3.5.26 itertools
..................

*note itertools.islice(): 4a9. now accepts *note integer-like objects:
2c2. as start, stop, and slice arguments.  (Contributed by Will Roberts
in bpo-30537(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30537


File: python.info,  Node: locale,  Next: logging<2>,  Prev: itertools<2>,  Up: Improved Modules<3>

1.3.5.27 locale
...............

The new `monetary' argument to *note locale.format_string(): 4ab. can be
used to make the conversion use monetary thousands separators and
grouping strings.  (Contributed by Garvit in bpo-10379(1).)

The *note locale.getpreferredencoding(): 4ac. function now always
returns ‘'UTF-8'’ on Android or when in the *note forced UTF-8 mode:
412.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10379


File: python.info,  Node: logging<2>,  Next: math<3>,  Prev: locale,  Up: Improved Modules<3>

1.3.5.28 logging
................

*note Logger: 4ae. instances can now be pickled.  (Contributed by Vinay
Sajip in bpo-30520(1).)

The new *note StreamHandler.setStream(): 4af. method can be used to
replace the logger stream after handler creation.  (Contributed by Vinay
Sajip in bpo-30522(2).)

It is now possible to specify keyword arguments to handler constructors
in configuration passed to *note logging.config.fileConfig(): 4b0.
(Contributed by Preston Landers in bpo-31080(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30520

   (2) https://bugs.python.org/issue30522

   (3) https://bugs.python.org/issue31080


File: python.info,  Node: math<3>,  Next: mimetypes,  Prev: logging<2>,  Up: Improved Modules<3>

1.3.5.29 math
.............

The new *note math.remainder(): 4b2. function implements the IEEE
754-style remainder operation.  (Contributed by Mark Dickinson in
bpo-29962(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29962


File: python.info,  Node: mimetypes,  Next: msilib,  Prev: math<3>,  Up: Improved Modules<3>

1.3.5.30 mimetypes
..................

The MIME type of .bmp has been changed from ‘'image/x-ms-bmp'’ to
‘'image/bmp'’.  (Contributed by Nitish Chandra in bpo-22589(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22589


File: python.info,  Node: msilib,  Next: multiprocessing<3>,  Prev: mimetypes,  Up: Improved Modules<3>

1.3.5.31 msilib
...............

The new *note Database.Close(): 4b5. method can be used to close the MSI
database.  (Contributed by Berker Peksag in bpo-20486(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20486


File: python.info,  Node: multiprocessing<3>,  Next: os<3>,  Prev: msilib,  Up: Improved Modules<3>

1.3.5.32 multiprocessing
........................

The new *note Process.close(): 4b7. method explicitly closes the process
object and releases all resources associated with it.  *note ValueError:
16d. is raised if the underlying process is still running.  (Contributed
by Antoine Pitrou in bpo-30596(1).)

The new *note Process.kill(): 4b8. method can be used to terminate the
process using the ‘SIGKILL’ signal on Unix.  (Contributed by Vitor
Pereira in bpo-30794(2).)

Non-daemonic threads created by *note Process: 4b9. are now joined on
process exit.  (Contributed by Antoine Pitrou in bpo-18966(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30596

   (2) https://bugs.python.org/issue30794

   (3) https://bugs.python.org/issue18966


File: python.info,  Node: os<3>,  Next: pathlib<3>,  Prev: multiprocessing<3>,  Up: Improved Modules<3>

1.3.5.33 os
...........

*note os.fwalk(): 4bb. now accepts the `path' argument as *note bytes:
172.  (Contributed by Serhiy Storchaka in bpo-28682(1).)

*note os.scandir(): 389. gained support for *note file descriptors: 4bc.
(Contributed by Serhiy Storchaka in bpo-25996(2).)

The new *note register_at_fork(): 4bd. function allows registering
Python callbacks to be executed at process fork.  (Contributed by
Antoine Pitrou in bpo-16500(3).)

Added *note os.preadv(): 4be. (combine the functionality of *note
os.readv(): 4bf. and *note os.pread(): 4c0.) and *note os.pwritev():
4c1. functions (combine the functionality of *note os.writev(): 4c2. and
*note os.pwrite(): 4c3.).  (Contributed by Pablo Galindo in
bpo-31368(4).)

The mode argument of *note os.makedirs(): 4c4. no longer affects the
file permission bits of newly-created intermediate-level directories.
(Contributed by Serhiy Storchaka in bpo-19930(5).)

*note os.dup2(): 4c5. now returns the new file descriptor.  Previously,
‘None’ was always returned.  (Contributed by Benjamin Peterson in
bpo-32441(6).)

The structure returned by *note os.stat(): 321. now contains the *note
st_fstype: 4c6. attribute on Solaris and its derivatives.  (Contributed
by Jesús Cea Avión in bpo-32659(7).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28682

   (2) https://bugs.python.org/issue25996

   (3) https://bugs.python.org/issue16500

   (4) https://bugs.python.org/issue31368

   (5) https://bugs.python.org/issue19930

   (6) https://bugs.python.org/issue32441

   (7) https://bugs.python.org/issue32659


File: python.info,  Node: pathlib<3>,  Next: pdb<2>,  Prev: os<3>,  Up: Improved Modules<3>

1.3.5.34 pathlib
................

The new *note Path.is_mount(): 333. method is now available on POSIX
systems and can be used to determine whether a path is a mount point.
(Contributed by Cooper Ry Lees in bpo-30897(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30897


File: python.info,  Node: pdb<2>,  Next: py_compile<2>,  Prev: pathlib<3>,  Up: Improved Modules<3>

1.3.5.35 pdb
............

*note pdb.set_trace(): 4c9. now takes an optional `header' keyword-only
argument.  If given, it is printed to the console just before debugging
begins.  (Contributed by Barry Warsaw in bpo-31389(1).)

*note pdb: c9. command line now accepts ‘-m module_name’ as an
alternative to script file.  (Contributed by Mario Corchero in
bpo-32206(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31389

   (2) https://bugs.python.org/issue32206


File: python.info,  Node: py_compile<2>,  Next: pydoc<2>,  Prev: pdb<2>,  Up: Improved Modules<3>

1.3.5.36 py_compile
...................

*note py_compile.compile(): 343. – and by extension, *note compileall:
20. – now respects the ‘SOURCE_DATE_EPOCH’ environment variable by
unconditionally creating ‘.pyc’ files for hash-based validation.  This
allows for guaranteeing reproducible builds(1) of ‘.pyc’ files when they
are created eagerly.  (Contributed by Bernhard M. Wiedemann in
bpo-29708(2).)

   ---------- Footnotes ----------

   (1) https://reproducible-builds.org/

   (2) https://bugs.python.org/issue29708


File: python.info,  Node: pydoc<2>,  Next: queue,  Prev: py_compile<2>,  Up: Improved Modules<3>

1.3.5.37 pydoc
..............

The pydoc server can now bind to an arbitrary hostname specified by the
new ‘-n’ command-line argument.  (Contributed by Feanil Patel in
bpo-31128(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31128


File: python.info,  Node: queue,  Next: re,  Prev: pydoc<2>,  Up: Improved Modules<3>

1.3.5.38 queue
..............

The new *note SimpleQueue: 4cd. class is an unbounded FIFO queue.
(Contributed by Antoine Pitrou in bpo-14976(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14976


File: python.info,  Node: re,  Next: signal<2>,  Prev: queue,  Up: Improved Modules<3>

1.3.5.39 re
...........

The flags *note re.ASCII: 4cf, *note re.LOCALE: 4d0. and ‘re.UNICODE’
can be set within the scope of a group.  (Contributed by Serhiy
Storchaka in bpo-31690(1).)

*note re.split(): 4d1. now supports splitting on a pattern like ‘r'\b'’,
‘'^$'’ or ‘(?=-)’ that matches an empty string.  (Contributed by Serhiy
Storchaka in bpo-25054(2).)

Regular expressions compiled with the *note re.LOCALE: 4d0. flag no
longer depend on the locale at compile time.  Locale settings are
applied only when the compiled regular expression is used.  (Contributed
by Serhiy Storchaka in bpo-30215(3).)

*note FutureWarning: 435. is now emitted if a regular expression
contains character set constructs that will change semantically in the
future, such as nested sets and set operations.  (Contributed by Serhiy
Storchaka in bpo-30349(4).)

Compiled regular expression and match objects can now be copied using
*note copy.copy(): 4d2. and *note copy.deepcopy(): 4d3.  (Contributed by
Serhiy Storchaka in bpo-10076(5).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31690

   (2) https://bugs.python.org/issue25054

   (3) https://bugs.python.org/issue30215

   (4) https://bugs.python.org/issue30349

   (5) https://bugs.python.org/issue10076


File: python.info,  Node: signal<2>,  Next: socket<3>,  Prev: re,  Up: Improved Modules<3>

1.3.5.40 signal
...............

The new `warn_on_full_buffer' argument to the *note
signal.set_wakeup_fd(): 4d5. function makes it possible to specify
whether Python prints a warning on stderr when the wakeup buffer
overflows.  (Contributed by Nathaniel J. Smith in bpo-30050(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30050


File: python.info,  Node: socket<3>,  Next: socketserver,  Prev: signal<2>,  Up: Improved Modules<3>

1.3.5.41 socket
...............

The new *note socket.getblocking(): 4d7. method returns ‘True’ if the
socket is in blocking mode and ‘False’ otherwise.  (Contributed by Yury
Selivanov in bpo-32373(1).)

The new *note socket.close(): 4d8. function closes the passed socket
file descriptor.  This function should be used instead of *note
os.close(): 4d9. for better compatibility across platforms.
(Contributed by Christian Heimes in bpo-32454(2).)

The *note socket: ef. module now exposes the ‘socket.TCP_CONGESTION’
(Linux 2.6.13), ‘socket.TCP_USER_TIMEOUT’ (Linux 2.6.37), and
‘socket.TCP_NOTSENT_LOWAT’ (Linux 3.12) constants.  (Contributed by Omar
Sandoval in bpo-26273(3) and Nathaniel J. Smith in bpo-29728(4).)

Support for *note socket.AF_VSOCK: 4da. sockets has been added to allow
communication between virtual machines and their hosts.  (Contributed by
Cathy Avery in bpo-27584(5).)

Sockets now auto-detect family, type and protocol from file descriptor
by default.  (Contributed by Christian Heimes in bpo-28134(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32373

   (2) https://bugs.python.org/issue32454

   (3) https://bugs.python.org/issue26273

   (4) https://bugs.python.org/issue29728

   (5) https://bugs.python.org/issue27584

   (6) https://bugs.python.org/issue28134


File: python.info,  Node: socketserver,  Next: sqlite3,  Prev: socket<3>,  Up: Improved Modules<3>

1.3.5.42 socketserver
.....................

‘socketserver.ThreadingMixIn.server_close()’ now waits until all
non-daemon threads complete.  ‘socketserver.ForkingMixIn.server_close()’
now waits until all child processes complete.

Add a new ‘socketserver.ForkingMixIn.block_on_close’ class attribute to
*note socketserver.ForkingMixIn: 4dc. and *note
socketserver.ThreadingMixIn: 4dd. classes.  Set the class attribute to
‘False’ to get the pre-3.7 behaviour.


File: python.info,  Node: sqlite3,  Next: ssl<2>,  Prev: socketserver,  Up: Improved Modules<3>

1.3.5.43 sqlite3
................

*note sqlite3.Connection: 4df. now exposes the *note backup(): 4e0.
method when the underlying SQLite library is at version 3.6.11 or
higher.  (Contributed by Lele Gaifax in bpo-27645(1).)

The `database' argument of *note sqlite3.connect(): 4e1. now accepts any
*note path-like object: 472, instead of just a string.  (Contributed by
Anders Lorentsen in bpo-31843(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27645

   (2) https://bugs.python.org/issue31843


File: python.info,  Node: ssl<2>,  Next: string,  Prev: sqlite3,  Up: Improved Modules<3>

1.3.5.44 ssl
............

The *note ssl: f3. module now uses OpenSSL’s builtin API instead of
*note match_hostname(): 4e3. to check a host name or an IP address.
Values are validated during TLS handshake.  Any certificate validation
error including failing the host name check now raises *note
SSLCertVerificationError: 4e4. and aborts the handshake with a proper
TLS Alert message.  The new exception contains additional information.
Host name validation can be customized with *note
SSLContext.hostname_checks_common_name: 4e5.  (Contributed by Christian
Heimes in bpo-31399(1).)

     Note: The improved host name check requires a `libssl'
     implementation compatible with OpenSSL 1.0.2 or 1.1.  Consequently,
     OpenSSL 0.9.8 and 1.0.1 are no longer supported (see *note Platform
     Support Removals: 4e6. for more details).  The ssl module is mostly
     compatible with LibreSSL 2.7.2 and newer.

The ‘ssl’ module no longer sends IP addresses in SNI TLS extension.
(Contributed by Christian Heimes in bpo-32185(2).)

*note match_hostname(): 4e3. no longer supports partial wildcards like
‘www*.example.org’.  (Contributed by Mandeep Singh in bpo-23033(3) and
Christian Heimes in bpo-31399(4).)

The default cipher suite selection of the ‘ssl’ module now uses a
blacklist approach rather than a hard-coded whitelist.  Python no longer
re-enables ciphers that have been blocked by OpenSSL security updates.
Default cipher suite selection can be configured at compile time.
(Contributed by Christian Heimes in bpo-31429(5).)

Validation of server certificates containing internationalized domain
names (IDNs) is now supported.  As part of this change, the *note
SSLSocket.server_hostname: 4e7. attribute now stores the expected
hostname in A-label form (‘"xn--pythn-mua.org"’), rather than the
U-label form (‘"pythön.org"’).  (Contributed by Nathaniel J. Smith and
Christian Heimes in bpo-28414(6).)

The ‘ssl’ module has preliminary and experimental support for TLS 1.3
and OpenSSL 1.1.1.  At the time of Python 3.7.0 release, OpenSSL 1.1.1
is still under development and TLS 1.3 hasn’t been finalized yet.  The
TLS 1.3 handshake and protocol behaves slightly differently than TLS 1.2
and earlier, see *note TLS 1.3: 4e8.  (Contributed by Christian Heimes
in bpo-32947(7), bpo-20995(8), bpo-29136(9), bpo-30622(10) and
bpo-33618(11))

*note SSLSocket: 192. and *note SSLObject: 4e9. no longer have a public
constructor.  Direct instantiation was never a documented and supported
feature.  Instances must be created with *note SSLContext: 4ea. methods
*note wrap_socket(): 4eb. and *note wrap_bio(): 4ec.  (Contributed by
Christian Heimes in bpo-32951(12))

OpenSSL 1.1 APIs for setting the minimum and maximum TLS protocol
version are available as *note SSLContext.minimum_version: 4ed. and
*note SSLContext.maximum_version: 4ee.  Supported protocols are
indicated by several new flags, such as *note HAS_TLSv1_1: 4ef.
(Contributed by Christian Heimes in bpo-32609(13).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31399

   (2) https://bugs.python.org/issue32185

   (3) https://bugs.python.org/issue23033

   (4) https://bugs.python.org/issue31399

   (5) https://bugs.python.org/issue31429

   (6) https://bugs.python.org/issue28414

   (7) https://bugs.python.org/issue32947

   (8) https://bugs.python.org/issue20995

   (9) https://bugs.python.org/issue29136

   (10) https://bugs.python.org/issue30622

   (11) https://bugs.python.org/issue33618

   (12) https://bugs.python.org/issue32951

   (13) https://bugs.python.org/issue32609


File: python.info,  Node: string,  Next: subprocess,  Prev: ssl<2>,  Up: Improved Modules<3>

1.3.5.45 string
...............

*note string.Template: 4f1. now lets you to optionally modify the
regular expression pattern for braced placeholders and non-braced
placeholders separately.  (Contributed by Barry Warsaw in
bpo-1198569(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1198569


File: python.info,  Node: subprocess,  Next: sys<3>,  Prev: string,  Up: Improved Modules<3>

1.3.5.46 subprocess
...................

The *note subprocess.run(): 4f3. function accepts the new
`capture_output' keyword argument.  When true, stdout and stderr will be
captured.  This is equivalent to passing *note subprocess.PIPE: 4f4. as
`stdout' and `stderr' arguments.  (Contributed by Bo Bayles in
bpo-32102(1).)

The ‘subprocess.run’ function and the *note subprocess.Popen: 3db.
constructor now accept the `text' keyword argument as an alias to
`universal_newlines'.  (Contributed by Andrew Clegg in bpo-31756(2).)

On Windows the default for `close_fds' was changed from ‘False’ to
‘True’ when redirecting the standard handles.  It’s now possible to set
`close_fds' to true when redirecting the standard handles.  See *note
subprocess.Popen: 3db.  This means that `close_fds' now defaults to
‘True’ on all supported platforms.  (Contributed by Segev Finer in
bpo-19764(3).)

The subprocess module is now more graceful when handling *note
KeyboardInterrupt: 2cc. during *note subprocess.call(): 4f5, *note
subprocess.run(): 4f3, or in a *note Popen: 3db. context manager.  It
now waits a short amount of time for the child to exit, before
continuing the handling of the ‘KeyboardInterrupt’ exception.
(Contributed by Gregory P. Smith in bpo-25942(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32102

   (2) https://bugs.python.org/issue31756

   (3) https://bugs.python.org/issue19764

   (4) https://bugs.python.org/issue25942


File: python.info,  Node: sys<3>,  Next: time<3>,  Prev: subprocess,  Up: Improved Modules<3>

1.3.5.47 sys
............

The new *note sys.breakpointhook(): 423. hook function is called by the
built-in *note breakpoint(): 40b.  (Contributed by Barry Warsaw in
bpo-31353(1).)

On Android, the new *note sys.getandroidapilevel(): 4f7. returns the
build-time Android API version.  (Contributed by Victor Stinner in
bpo-28740(2).)

The new *note sys.get_coroutine_origin_tracking_depth(): 4f8. function
returns the current coroutine origin tracking depth, as set by the new
*note sys.set_coroutine_origin_tracking_depth(): 4f9.  *note asyncio: 9.
has been converted to use this new API instead of the deprecated
‘sys.set_coroutine_wrapper()’.  (Contributed by Nathaniel J. Smith in
bpo-32591(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31353

   (2) https://bugs.python.org/issue28740

   (3) https://bugs.python.org/issue32591


File: python.info,  Node: time<3>,  Next: tkinter<2>,  Prev: sys<3>,  Up: Improved Modules<3>

1.3.5.48 time
.............

PEP 564(1) adds six new functions with nanosecond resolution to the
*note time: 10c. module:

   * *note time.clock_gettime_ns(): 42e.

   * *note time.clock_settime_ns(): 42f.

   * *note time.monotonic_ns(): 430.

   * *note time.perf_counter_ns(): 431.

   * *note time.process_time_ns(): 432.

   * *note time.time_ns(): 433.

New clock identifiers have been added:

   * *note time.CLOCK_BOOTTIME: 4fb. (Linux): Identical to *note
     time.CLOCK_MONOTONIC: 4fc, except it also includes any time that
     the system is suspended.

   * *note time.CLOCK_PROF: 4fd. (FreeBSD, NetBSD and OpenBSD):
     High-resolution per-process CPU timer.

   * *note time.CLOCK_UPTIME: 4fe. (FreeBSD, OpenBSD): Time whose
     absolute value is the time the system has been running and not
     suspended, providing accurate uptime measurement.

The new *note time.thread_time(): 1e7. and *note time.thread_time_ns():
4ff. functions can be used to get per-thread CPU time measurements.
(Contributed by Antoine Pitrou in bpo-32025(2).)

The new *note time.pthread_getcpuclockid(): 500. function returns the
clock ID of the thread-specific CPU-time clock.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0564

   (2) https://bugs.python.org/issue32025


File: python.info,  Node: tkinter<2>,  Next: tracemalloc<2>,  Prev: time<3>,  Up: Improved Modules<3>

1.3.5.49 tkinter
................

The new *note tkinter.ttk.Spinbox: 502. class is now available.
(Contributed by Alan Moore in bpo-32585(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32585


File: python.info,  Node: tracemalloc<2>,  Next: types,  Prev: tkinter<2>,  Up: Improved Modules<3>

1.3.5.50 tracemalloc
....................

*note tracemalloc.Traceback: 504. behaves more like regular tracebacks,
sorting the frames from oldest to most recent.  *note
Traceback.format(): 505. now accepts negative `limit', truncating the
result to the ‘abs(limit)’ oldest frames.  To get the old behaviour, use
the new `most_recent_first' argument to ‘Traceback.format()’.
(Contributed by Jesse Bakker in bpo-32121(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32121


File: python.info,  Node: types,  Next: unicodedata<3>,  Prev: tracemalloc<2>,  Up: Improved Modules<3>

1.3.5.51 types
..............

The new *note WrapperDescriptorType: 507, *note MethodWrapperType: 508,
*note MethodDescriptorType: 509, and *note ClassMethodDescriptorType:
50a. classes are now available.  (Contributed by Manuel Krebber and
Guido van Rossum in bpo-29377(1), and Serhiy Storchaka in bpo-32265(2).)

The new *note types.resolve_bases(): 50b. function resolves MRO entries
dynamically as specified by PEP 560(3).  (Contributed by Ivan Levkivskyi
in bpo-32717(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29377

   (2) https://bugs.python.org/issue32265

   (3) https://www.python.org/dev/peps/pep-0560

   (4) https://bugs.python.org/issue32717


File: python.info,  Node: unicodedata<3>,  Next: unittest<2>,  Prev: types,  Up: Improved Modules<3>

1.3.5.52 unicodedata
....................

The internal *note unicodedata: 123. database has been upgraded to use
Unicode 11(1).  (Contributed by Benjamin Peterson.)

   ---------- Footnotes ----------

   (1) http://www.unicode.org/versions/Unicode11.0.0/


File: python.info,  Node: unittest<2>,  Next: unittest mock,  Prev: unicodedata<3>,  Up: Improved Modules<3>

1.3.5.53 unittest
.................

The new ‘-k’ command-line option allows filtering tests by a name
substring or a Unix shell-like pattern.  For example, ‘python -m
unittest -k foo’ runs ‘foo_tests.SomeTest.test_something’,
‘bar_tests.SomeTest.test_foo’, but not
‘bar_tests.FooTest.test_something’.  (Contributed by Jonas Haag in
bpo-32071(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32071


File: python.info,  Node: unittest mock,  Next: urllib parse<3>,  Prev: unittest<2>,  Up: Improved Modules<3>

1.3.5.54 unittest.mock
......................

The *note sentinel: 50f. attributes now preserve their identity when
they are *note copied: 25. or *note pickled: ca.  (Contributed by Serhiy
Storchaka in bpo-20804(1).)

The new *note seal(): 510. function allows sealing *note Mock: 373.
instances, which will disallow further creation of attribute mocks.  The
seal is applied recursively to all attributes that are themselves mocks.
(Contributed by Mario Corchero in bpo-30541(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20804

   (2) https://bugs.python.org/issue30541


File: python.info,  Node: urllib parse<3>,  Next: uu,  Prev: unittest mock,  Up: Improved Modules<3>

1.3.5.55 urllib.parse
.....................

*note urllib.parse.quote(): 512. has been updated from RFC 2396(1) to
RFC 3986(2), adding ‘~’ to the set of characters that are never quoted
by default.  (Contributed by Christian Theune and Ratnadeep Debnath in
bpo-16285(3).)

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2396.html

   (2) https://tools.ietf.org/html/rfc3986.html

   (3) https://bugs.python.org/issue16285


File: python.info,  Node: uu,  Next: uuid,  Prev: urllib parse<3>,  Up: Improved Modules<3>

1.3.5.56 uu
...........

The *note uu.encode(): 514. function now accepts an optional `backtick'
keyword argument.  When it’s true, zeros are represented by ‘'`'’
instead of spaces.  (Contributed by Xiang Zhang in bpo-30103(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30103


File: python.info,  Node: uuid,  Next: warnings,  Prev: uu,  Up: Improved Modules<3>

1.3.5.57 uuid
.............

The new *note UUID.is_safe: 516. attribute relays information from the
platform about whether generated UUIDs are generated with a
multiprocessing-safe method.  (Contributed by Barry Warsaw in
bpo-22807(1).)

*note uuid.getnode(): 517. now prefers universally administered MAC
addresses over locally administered MAC addresses.  This makes a better
guarantee for global uniqueness of UUIDs returned from *note
uuid.uuid1(): 518.  If only locally administered MAC addresses are
available, the first such one found is returned.  (Contributed by Barry
Warsaw in bpo-32107(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22807

   (2) https://bugs.python.org/issue32107


File: python.info,  Node: warnings,  Next: xml etree,  Prev: uuid,  Up: Improved Modules<3>

1.3.5.58 warnings
.................

The initialization of the default warnings filters has changed as
follows:

   * warnings enabled via command line options (including those for
     *note -b: 51a. and the new CPython-specific *note -X: 290. ‘dev’
     option) are always passed to the warnings machinery via the *note
     sys.warnoptions: 51b. attribute.

   * warnings filters enabled via the command line or the environment
     now have the following order of precedence:

             * the ‘BytesWarning’ filter for *note -b: 51a. (or ‘-bb’)

             * any filters specified with the *note -W: 15b. option

             * any filters specified with the *note PYTHONWARNINGS: 51c.
               environment variable

             * any other CPython specific filters (e.g.  the ‘default’
               filter added for the new ‘-X dev’ mode)

             * any implicit filters defined directly by the warnings
               machinery

   * in CPython debug builds, all warnings are now displayed by default
     (the implicit filter list is empty)

(Contributed by Nick Coghlan and Victor Stinner in bpo-20361(1),
bpo-32043(2), and bpo-32230(3).)

Deprecation warnings are once again shown by default in single-file
scripts and at the interactive prompt.  See *note PEP 565; Show
DeprecationWarning in __main__: 415. for details.  (Contributed by Nick
Coghlan in bpo-31975(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20361

   (2) https://bugs.python.org/issue32043

   (3) https://bugs.python.org/issue32230

   (4) https://bugs.python.org/issue31975


File: python.info,  Node: xml etree,  Next: xmlrpc server,  Prev: warnings,  Up: Improved Modules<3>

1.3.5.59 xml.etree
..................

*note ElementPath: 51e. predicates in the ‘find()’ methods can now
compare text of the current node with ‘[. = "text"]’, not only text in
children.  Predicates also allow adding spaces for better readability.
(Contributed by Stefan Behnel in bpo-31648(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31648


File: python.info,  Node: xmlrpc server,  Next: zipapp,  Prev: xml etree,  Up: Improved Modules<3>

1.3.5.60 xmlrpc.server
......................

‘SimpleXMLRPCDispatcher.register_function’ can now be used as a
decorator.  (Contributed by Xiang Zhang in bpo-7769(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue7769


File: python.info,  Node: zipapp,  Next: zipfile,  Prev: xmlrpc server,  Up: Improved Modules<3>

1.3.5.61 zipapp
...............

Function *note create_archive(): 521. now accepts an optional `filter'
argument to allow the user to select which files should be included in
the archive.  (Contributed by Irmen de Jong in bpo-31072(1).)

Function *note create_archive(): 521. now accepts an optional
`compressed' argument to generate a compressed archive.  A command line
option ‘--compress’ has also been added to support compression.
(Contributed by Zhiming Wang in bpo-31638(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31072

   (2) https://bugs.python.org/issue31638


File: python.info,  Node: zipfile,  Prev: zipapp,  Up: Improved Modules<3>

1.3.5.62 zipfile
................

*note ZipFile: 523. now accepts the new `compresslevel' parameter to
control the compression level.  (Contributed by Bo Bayles in
bpo-21417(1).)

Subdirectories in archives created by ‘ZipFile’ are now stored in
alphabetical order.  (Contributed by Bernhard M. Wiedemann in
bpo-30693(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21417

   (2) https://bugs.python.org/issue30693


File: python.info,  Node: C API Changes<2>,  Next: Build Changes<2>,  Prev: Improved Modules<3>,  Up: What’s New In Python 3 7

1.3.6 C API Changes
-------------------

A new API for thread-local storage has been implemented.  See *note PEP
539; New C API for Thread-Local Storage: 416. for an overview and *note
Thread Specific Storage (TSS) API: 427. for a complete reference.
(Contributed by Masayuki Yamamoto in bpo-25658(1).)

The new *note context variables: 407. functionality exposes a number of
*note new C APIs: 447.

The new *note PyImport_GetModule(): 525. function returns the previously
imported module with the given name.  (Contributed by Eric Snow in
bpo-28411(2).)

The new *note Py_RETURN_RICHCOMPARE: 526. macro eases writing rich
comparison functions.  (Contributed by Petr Victorin in bpo-23699(3).)

The new *note Py_UNREACHABLE: 527. macro can be used to mark unreachable
code paths.  (Contributed by Barry Warsaw in bpo-31338(4).)

The *note tracemalloc: 11d. now exposes a C API through the new *note
PyTraceMalloc_Track(): 528. and *note PyTraceMalloc_Untrack(): 529.
functions.  (Contributed by Victor Stinner in bpo-30054(5).)

The new ‘import__find__load__start()’ and ‘import__find__load__done()’
static markers can be used to trace module imports.  (Contributed by
Christian Heimes in bpo-31574(6).)

The fields ‘name’ and ‘doc’ of structures *note PyMemberDef: 52a, *note
PyGetSetDef: 52b, *note PyStructSequence_Field: 52c, *note
PyStructSequence_Desc: 52d, and ‘wrapperbase’ are now of type ‘const
char *’ rather of ‘char *’.  (Contributed by Serhiy Storchaka in
bpo-28761(7).)

The result of *note PyUnicode_AsUTF8AndSize(): 52e. and *note
PyUnicode_AsUTF8(): 52f. is now of type ‘const char *’ rather of ‘char
*’.  (Contributed by Serhiy Storchaka in bpo-28769(8).)

The result of *note PyMapping_Keys(): 530, *note PyMapping_Values():
531. and *note PyMapping_Items(): 532. is now always a list, rather than
a list or a tuple.  (Contributed by Oren Milman in bpo-28280(9).)

Added functions *note PySlice_Unpack(): 533. and *note
PySlice_AdjustIndices(): 534.  (Contributed by Serhiy Storchaka in
bpo-27867(10).)

*note PyOS_AfterFork(): 535. is deprecated in favour of the new
functions *note PyOS_BeforeFork(): 536, *note PyOS_AfterFork_Parent():
537. and *note PyOS_AfterFork_Child(): 3ef.  (Contributed by Antoine
Pitrou in bpo-16500(11).)

The ‘PyExc_RecursionErrorInst’ singleton that was part of the public API
has been removed as its members being never cleared may cause a segfault
during finalization of the interpreter.  Contributed by Xavier de Gaye
in bpo-22898(12) and bpo-30697(13).

Added C API support for timezones with timezone constructors *note
PyTimeZone_FromOffset(): 538. and *note PyTimeZone_FromOffsetAndName():
539, and access to the UTC singleton with *note PyDateTime_TimeZone_UTC:
53a.  Contributed by Paul Ganssle in bpo-10381(14).

The type of results of ‘PyThread_start_new_thread()’ and
‘PyThread_get_thread_ident()’, and the `id' parameter of *note
PyThreadState_SetAsyncExc(): 53b. changed from ‘long’ to ‘unsigned
long’.  (Contributed by Serhiy Storchaka in bpo-6532(15).)

*note PyUnicode_AsWideCharString(): 53c. now raises a *note ValueError:
16d. if the second argument is ‘NULL’ and the ‘wchar_t*’ string contains
null characters.  (Contributed by Serhiy Storchaka in bpo-30708(16).)

Changes to the startup sequence and the management of dynamic memory
allocators mean that the long documented requirement to call *note
Py_Initialize(): 20f. before calling most C API functions is now relied
on more heavily, and failing to abide by it may lead to segfaults in
embedding applications.  See the *note Porting to Python 3.7: 419.
section in this document and the *note Before Python Initialization:
53d. section in the C API documentation for more details.

The new *note PyInterpreterState_GetID(): 53e. returns the unique ID for
a given interpreter.  (Contributed by Eric Snow in bpo-29102(17).)

*note Py_DecodeLocale(): 53f, *note Py_EncodeLocale(): 540. now use the
UTF-8 encoding when the *note UTF-8 mode: 412. is enabled.  (Contributed
by Victor Stinner in bpo-29240(18).)

*note PyUnicode_DecodeLocaleAndSize(): 541. and *note
PyUnicode_EncodeLocale(): 542. now use the current locale encoding for
‘surrogateescape’ error handler.  (Contributed by Victor Stinner in
bpo-29240(19).)

The `start' and `end' parameters of *note PyUnicode_FindChar(): 543. are
now adjusted to behave like string slices.  (Contributed by Xiang Zhang
in bpo-28822(20).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25658

   (2) https://bugs.python.org/issue28411

   (3) https://bugs.python.org/issue23699

   (4) https://bugs.python.org/issue31338

   (5) https://bugs.python.org/issue30054

   (6) https://bugs.python.org/issue31574

   (7) https://bugs.python.org/issue28761

   (8) https://bugs.python.org/issue28769

   (9) https://bugs.python.org/issue28280

   (10) https://bugs.python.org/issue27867

   (11) https://bugs.python.org/issue16500

   (12) https://bugs.python.org/issue22898

   (13) https://bugs.python.org/issue30697

   (14) https://bugs.python.org/issue10381

   (15) https://bugs.python.org/issue6532

   (16) https://bugs.python.org/issue30708

   (17) https://bugs.python.org/issue29102

   (18) https://bugs.python.org/issue29240

   (19) https://bugs.python.org/issue29240

   (20) https://bugs.python.org/issue28822


File: python.info,  Node: Build Changes<2>,  Next: Optimizations<3>,  Prev: C API Changes<2>,  Up: What’s New In Python 3 7

1.3.7 Build Changes
-------------------

Support for building ‘--without-threads’ has been removed.  The *note
threading: 10b. module is now always available.  (Contributed by Antoine
Pitrou in bpo-31370(1).).

A full copy of libffi is no longer bundled for use when building the
*note _ctypes: 2a. module on non-OSX UNIX platforms.  An installed copy
of libffi is now required when building ‘_ctypes’ on such platforms.
(Contributed by Zachary Ware in bpo-27979(2).)

The Windows build process no longer depends on Subversion to pull in
external sources, a Python script is used to download zipfiles from
GitHub instead.  If Python 3.6 is not found on the system (via ‘py
-3.6’), NuGet is used to download a copy of 32-bit Python for this
purpose.  (Contributed by Zachary Ware in bpo-30450(3).)

The *note ssl: f3. module requires OpenSSL 1.0.2 or 1.1 compatible
libssl.  OpenSSL 1.0.1 has reached end of lifetime on 2016-12-31 and is
no longer supported.  LibreSSL is temporarily not supported as well.
LibreSSL releases up to version 2.6.4 are missing required OpenSSL 1.0.2
APIs.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31370

   (2) https://bugs.python.org/issue27979

   (3) https://bugs.python.org/issue30450


File: python.info,  Node: Optimizations<3>,  Next: Other CPython Implementation Changes,  Prev: Build Changes<2>,  Up: What’s New In Python 3 7

1.3.8 Optimizations
-------------------

The overhead of calling many methods of various standard library classes
implemented in C has been significantly reduced by porting more code to
use the ‘METH_FASTCALL’ convention.  (Contributed by Victor Stinner in
bpo-29300(1), bpo-29507(2), bpo-29452(3), and bpo-29286(4).)

Various optimizations have reduced Python startup time by 10% on Linux
and up to 30% on macOS. (Contributed by Victor Stinner, INADA Naoki in
bpo-29585(5), and Ivan Levkivskyi in bpo-31333(6).)

Method calls are now up to 20% faster due to the bytecode changes which
avoid creating bound method instances.  (Contributed by Yury Selivanov
and INADA Naoki in bpo-26110(7).)  The *note asyncio: 9. module received
a number of notable optimizations for commonly used functions:

   * The *note asyncio.get_event_loop(): 45d. function has been
     reimplemented in C to make it up to 15 times faster.  (Contributed
     by Yury Selivanov in bpo-32296(8).)

   * *note asyncio.Future: 546. callback management has been optimized.
     (Contributed by Yury Selivanov in bpo-32348(9).)

   * *note asyncio.gather(): 3ab. is now up to 15% faster.  (Contributed
     by Yury Selivanov in bpo-32355(10).)

   * *note asyncio.sleep(): 3aa. is now up to 2 times faster when the
     `delay' argument is zero or negative.  (Contributed by Andrew
     Svetlov in bpo-32351(11).)

   * The performance overhead of asyncio debug mode has been reduced.
     (Contributed by Antoine Pitrou in bpo-31970(12).)

As a result of *note PEP 560 work: 40d, the import time of *note typing:
122. has been reduced by a factor of 7, and many typing operations are
now faster.  (Contributed by Ivan Levkivskyi in bpo-32226(13).)

*note sorted(): 547. and *note list.sort(): 548. have been optimized for
common cases to be up to 40-75% faster.  (Contributed by Elliot
Gorokhovsky in bpo-28685(14).)

*note dict.copy(): 549. is now up to 5.5 times faster.  (Contributed by
Yury Selivanov in bpo-31179(15).)

*note hasattr(): 54a. and *note getattr(): 54b. are now about 4 times
faster when `name' is not found and `obj' does not override *note
object.__getattr__(): 42a. or *note object.__getattribute__(): 54c.
(Contributed by INADA Naoki in bpo-32544(16).)

Searching for certain Unicode characters (like Ukrainian capital “Є”) in
a string was up to 25 times slower than searching for other characters.
It is now only 3 times slower in the worst case.  (Contributed by Serhiy
Storchaka in bpo-24821(17).)

The *note collections.namedtuple(): 1a1. factory has been reimplemented
to make the creation of named tuples 4 to 6 times faster.  (Contributed
by Jelle Zijlstra with further improvements by INADA Naoki, Serhiy
Storchaka, and Raymond Hettinger in bpo-28638(18).)

‘date.fromordinal()’ and ‘date.fromtimestamp()’ are now up to 30% faster
in the common case.  (Contributed by Paul Ganssle in bpo-32403(19).)

The *note os.fwalk(): 4bb. function is now up to 2 times faster thanks
to the use of *note os.scandir(): 389.  (Contributed by Serhiy Storchaka
in bpo-25996(20).)

The speed of the *note shutil.rmtree(): 349. function has been improved
by 20–40% thanks to the use of the *note os.scandir(): 389. function.
(Contributed by Serhiy Storchaka in bpo-28564(21).)

Optimized case-insensitive matching and searching of *note regular
expressions: dd.  Searching some patterns can now be up to 20 times
faster.  (Contributed by Serhiy Storchaka in bpo-30285(22).)

*note re.compile(): 54d. now converts ‘flags’ parameter to int object if
it is ‘RegexFlag’.  It is now as fast as Python 3.5, and faster than
Python 3.6 by about 10% depending on the pattern.  (Contributed by INADA
Naoki in bpo-31671(23).)

The *note modify(): 54e. methods of classes *note
selectors.EpollSelector: 54f, *note selectors.PollSelector: 550. and
*note selectors.DevpollSelector: 551. may be around 10% faster under
heavy loads.  (Contributed by Giampaolo Rodola’ in bpo-30014(24))

Constant folding has been moved from the peephole optimizer to the new
AST optimizer, which is able perform optimizations more consistently.
(Contributed by Eugene Toder and INADA Naoki in bpo-29469(25) and
bpo-11549(26).)

Most functions and methods in *note abc: 3. have been rewritten in C.
This makes creation of abstract base classes, and calling *note
isinstance(): 552. and *note issubclass(): 553. on them 1.5x faster.
This also reduces Python start-up time by up to 10%.  (Contributed by
Ivan Levkivskyi and INADA Naoki in bpo-31333(27))

Significant speed improvements to alternate constructors for *note
datetime.date: 19e. and *note datetime.datetime: 1a0. by using fast-path
constructors when not constructing subclasses.  (Contributed by Paul
Ganssle in bpo-32403(28))

The speed of comparison of *note array.array: 216. instances has been
improved considerably in certain cases.  It is now from 10x to 70x
faster when comparing arrays holding values of the same integer type.
(Contributed by Adrian Wielgosik in bpo-24700(29).)

The *note math.erf(): 554. and *note math.erfc(): 555. functions now use
the (faster) C library implementation on most platforms.  (Contributed
by Serhiy Storchaka in bpo-26121(30).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29300

   (2) https://bugs.python.org/issue29507

   (3) https://bugs.python.org/issue29452

   (4) https://bugs.python.org/issue29286

   (5) https://bugs.python.org/issue29585

   (6) https://bugs.python.org/issue31333

   (7) https://bugs.python.org/issue26110

   (8) https://bugs.python.org/issue32296

   (9) https://bugs.python.org/issue32348

   (10) https://bugs.python.org/issue32355

   (11) https://bugs.python.org/issue32351

   (12) https://bugs.python.org/issue31970

   (13) https://bugs.python.org/issue32226

   (14) https://bugs.python.org/issue28685

   (15) https://bugs.python.org/issue31179

   (16) https://bugs.python.org/issue32544

   (17) https://bugs.python.org/issue24821

   (18) https://bugs.python.org/issue28638

   (19) https://bugs.python.org/issue32403

   (20) https://bugs.python.org/issue25996

   (21) https://bugs.python.org/issue28564

   (22) https://bugs.python.org/issue30285

   (23) https://bugs.python.org/issue31671

   (24) https://bugs.python.org/issue30014

   (25) https://bugs.python.org/issue29469

   (26) https://bugs.python.org/issue11549

   (27) https://bugs.python.org/issue31333

   (28) https://bugs.python.org/issue32403

   (29) https://bugs.python.org/issue24700

   (30) https://bugs.python.org/issue26121


File: python.info,  Node: Other CPython Implementation Changes,  Next: Deprecated Python Behavior,  Prev: Optimizations<3>,  Up: What’s New In Python 3 7

1.3.9 Other CPython Implementation Changes
------------------------------------------

   * Trace hooks may now opt out of receiving the ‘line’ and opt into
     receiving the ‘opcode’ events from the interpreter by setting the
     corresponding new ‘f_trace_lines’ and ‘f_trace_opcodes’ attributes
     on the frame being traced.  (Contributed by Nick Coghlan in
     bpo-31344(1).)

   * Fixed some consistency problems with namespace package module
     attributes.  Namespace module objects now have an ‘__file__’ that
     is set to ‘None’ (previously unset), and their ‘__spec__.origin’ is
     also set to ‘None’ (previously the string ‘"namespace"’).  See
     bpo-32305(2).  Also, the namespace module object’s
     ‘__spec__.loader’ is set to the same value as ‘__loader__’
     (previously, the former was set to ‘None’).  See bpo-32303(3).

   * The *note locals(): 557. dictionary now displays in the lexical
     order that variables were defined.  Previously, the order was
     undefined.  (Contributed by Raymond Hettinger in bpo-32690(4).)

   * The *note distutils: 38. ‘upload’ command no longer tries to change
     CR end-of-line characters to CRLF. This fixes a corruption issue
     with sdists that ended with a byte equivalent to CR. (Contributed
     by Bo Bayles in bpo-32304(5).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31344

   (2) https://bugs.python.org/issue32305

   (3) https://bugs.python.org/issue32303

   (4) https://bugs.python.org/issue32690

   (5) https://bugs.python.org/issue32304


File: python.info,  Node: Deprecated Python Behavior,  Next: Deprecated Python modules functions and methods,  Prev: Other CPython Implementation Changes,  Up: What’s New In Python 3 7

1.3.10 Deprecated Python Behavior
---------------------------------

Yield expressions (both ‘yield’ and ‘yield from’ clauses) are now
deprecated in comprehensions and generator expressions (aside from the
iterable expression in the leftmost ‘for’ clause).  This ensures that
comprehensions always immediately return a container of the appropriate
type (rather than potentially returning a *note generator iterator: 559.
object), while generator expressions won’t attempt to interleave their
implicit output with the output from any explicit yield expressions.  In
Python 3.7, such expressions emit *note DeprecationWarning: 15a. when
compiled, in Python 3.8 this will be a *note SyntaxError: 55a.
(Contributed by Serhiy Storchaka in bpo-10544(1).)

Returning a subclass of *note complex: 2c1. from *note
object.__complex__(): 2c5. is deprecated and will be an error in future
Python versions.  This makes ‘__complex__()’ consistent with *note
object.__int__(): 2c3. and *note object.__float__(): 2c4.  (Contributed
by Serhiy Storchaka in bpo-28894(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10544

   (2) https://bugs.python.org/issue28894


File: python.info,  Node: Deprecated Python modules functions and methods,  Next: Deprecated functions and types of the C API,  Prev: Deprecated Python Behavior,  Up: What’s New In Python 3 7

1.3.11 Deprecated Python modules, functions and methods
-------------------------------------------------------

* Menu:

* aifc::
* asyncio: asyncio<4>.
* collections: collections<3>.
* dbm: dbm<2>.
* enum: enum<2>.
* gettext: gettext<2>.
* importlib: importlib<3>.
* locale: locale<2>.
* macpath::
* threading: threading<2>.
* socket: socket<4>.
* ssl: ssl<3>.
* sunau::
* sys: sys<4>.
* wave::


File: python.info,  Node: aifc,  Next: asyncio<4>,  Up: Deprecated Python modules functions and methods

1.3.11.1 aifc
.............

‘aifc.openfp()’ has been deprecated and will be removed in Python 3.9.
Use *note aifc.open(): 55d. instead.  (Contributed by Brian Curtin in
bpo-31985(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31985


File: python.info,  Node: asyncio<4>,  Next: collections<3>,  Prev: aifc,  Up: Deprecated Python modules functions and methods

1.3.11.2 asyncio
................

Support for directly ‘await’-ing instances of *note asyncio.Lock: 3ae.
and other asyncio synchronization primitives has been deprecated.  An
asynchronous context manager must be used in order to acquire and
release the synchronization resource.  (Contributed by Andrew Svetlov in
bpo-32253(1).)

The ‘asyncio.Task.current_task()’ and ‘asyncio.Task.all_tasks()’ methods
have been deprecated.  (Contributed by Andrew Svetlov in bpo-32250(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32253

   (2) https://bugs.python.org/issue32250


File: python.info,  Node: collections<3>,  Next: dbm<2>,  Prev: asyncio<4>,  Up: Deprecated Python modules functions and methods

1.3.11.3 collections
....................

In Python 3.8, the abstract base classes in *note collections.abc: 1e.
will no longer be exposed in the regular *note collections: 1d. module.
This will help create a clearer distinction between the concrete classes
and the abstract base classes.  (Contributed by Serhiy Storchaka in
bpo-25988(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25988


File: python.info,  Node: dbm<2>,  Next: enum<2>,  Prev: collections<3>,  Up: Deprecated Python modules functions and methods

1.3.11.4 dbm
............

*note dbm.dumb: 32. now supports reading read-only files and no longer
writes the index file when it is not changed.  A deprecation warning is
now emitted if the index file is missing and recreated in the ‘'r'’ and
‘'w'’ modes (this will be an error in future Python releases).
(Contributed by Serhiy Storchaka in bpo-28847(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28847


File: python.info,  Node: enum<2>,  Next: gettext<2>,  Prev: dbm<2>,  Up: Deprecated Python modules functions and methods

1.3.11.5 enum
.............

In Python 3.8, attempting to check for non-Enum objects in ‘Enum’
classes will raise a *note TypeError: 1fe. (e.g.  ‘1 in Color’);
similarly, attempting to check for non-Flag objects in a ‘Flag’ member
will raise *note TypeError: 1fe. (e.g.  ‘1 in Perm.RW’); currently, both
operations return *note False: 48f. instead.  (Contributed by Ethan
Furman in bpo-33217(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33217


File: python.info,  Node: gettext<2>,  Next: importlib<3>,  Prev: enum<2>,  Up: Deprecated Python modules functions and methods

1.3.11.6 gettext
................

Using non-integer value for selecting a plural form in *note gettext:
87. is now deprecated.  It never correctly worked.  (Contributed by
Serhiy Storchaka in bpo-28692(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28692


File: python.info,  Node: importlib<3>,  Next: locale<2>,  Prev: gettext<2>,  Up: Deprecated Python modules functions and methods

1.3.11.7 importlib
..................

Methods *note MetaPathFinder.find_module(): 564. (replaced by *note
MetaPathFinder.find_spec(): 565.) and *note
PathEntryFinder.find_loader(): 566. (replaced by *note
PathEntryFinder.find_spec(): 567.) both deprecated in Python 3.4 now
emit *note DeprecationWarning: 15a.  (Contributed by Matthias Bussonnier
in bpo-29576(1))

The *note importlib.abc.ResourceLoader: 568. ABC has been deprecated in
favour of *note importlib.abc.ResourceReader: 44e.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29576


File: python.info,  Node: locale<2>,  Next: macpath,  Prev: importlib<3>,  Up: Deprecated Python modules functions and methods

1.3.11.8 locale
...............

*note locale.format(): 56a. has been deprecated, use *note
locale.format_string(): 4ab. instead.  (Contributed by Garvit in
bpo-10379(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10379


File: python.info,  Node: macpath,  Next: threading<2>,  Prev: locale<2>,  Up: Deprecated Python modules functions and methods

1.3.11.9 macpath
................

The ‘macpath’ is now deprecated and will be removed in Python 3.8.
(Contributed by Chi Hsuan Yen in bpo-9850(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9850


File: python.info,  Node: threading<2>,  Next: socket<4>,  Prev: macpath,  Up: Deprecated Python modules functions and methods

1.3.11.10 threading
...................

‘dummy_threading’ and ‘_dummy_thread’ have been deprecated.  It is no
longer possible to build Python with threading disabled.  Use *note
threading: 10b. instead.  (Contributed by Antoine Pitrou in
bpo-31370(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31370


File: python.info,  Node: socket<4>,  Next: ssl<3>,  Prev: threading<2>,  Up: Deprecated Python modules functions and methods

1.3.11.11 socket
................

The silent argument value truncation in *note socket.htons(): 56e. and
*note socket.ntohs(): 56f. has been deprecated.  In future versions of
Python, if the passed argument is larger than 16 bits, an exception will
be raised.  (Contributed by Oren Milman in bpo-28332(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28332


File: python.info,  Node: ssl<3>,  Next: sunau,  Prev: socket<4>,  Up: Deprecated Python modules functions and methods

1.3.11.12 ssl
.............

*note ssl.wrap_socket(): 571. is deprecated.  Use *note
ssl.SSLContext.wrap_socket(): 4eb. instead.  (Contributed by Christian
Heimes in bpo-28124(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28124


File: python.info,  Node: sunau,  Next: sys<4>,  Prev: ssl<3>,  Up: Deprecated Python modules functions and methods

1.3.11.13 sunau
...............

‘sunau.openfp()’ has been deprecated and will be removed in Python 3.9.
Use *note sunau.open(): 573. instead.  (Contributed by Brian Curtin in
bpo-31985(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31985


File: python.info,  Node: sys<4>,  Next: wave,  Prev: sunau,  Up: Deprecated Python modules functions and methods

1.3.11.14 sys
.............

Deprecated ‘sys.set_coroutine_wrapper()’ and
‘sys.get_coroutine_wrapper()’.

The undocumented ‘sys.callstats()’ function has been deprecated and will
be removed in a future Python version.  (Contributed by Victor Stinner
in bpo-28799(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28799


File: python.info,  Node: wave,  Prev: sys<4>,  Up: Deprecated Python modules functions and methods

1.3.11.15 wave
..............

‘wave.openfp()’ has been deprecated and will be removed in Python 3.9.
Use *note wave.open(): 219. instead.  (Contributed by Brian Curtin in
bpo-31985(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31985


File: python.info,  Node: Deprecated functions and types of the C API,  Next: Platform Support Removals,  Prev: Deprecated Python modules functions and methods,  Up: What’s New In Python 3 7

1.3.12 Deprecated functions and types of the C API
--------------------------------------------------

Function *note PySlice_GetIndicesEx(): 577. is deprecated and replaced
with a macro if ‘Py_LIMITED_API’ is not set or set to a value in the
range between ‘0x03050400’ and ‘0x03060000’ (not inclusive), or is
‘0x03060100’ or higher.  (Contributed by Serhiy Storchaka in
bpo-27867(1).)

*note PyOS_AfterFork(): 535. has been deprecated.  Use *note
PyOS_BeforeFork(): 536, *note PyOS_AfterFork_Parent(): 537. or *note
PyOS_AfterFork_Child(): 3ef. instead.  (Contributed by Antoine Pitrou in
bpo-16500(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27867

   (2) https://bugs.python.org/issue16500


File: python.info,  Node: Platform Support Removals,  Next: API and Feature Removals<2>,  Prev: Deprecated functions and types of the C API,  Up: What’s New In Python 3 7

1.3.13 Platform Support Removals
--------------------------------

   * FreeBSD 9 and older are no longer officially supported.

   * For full Unicode support, including within extension modules, *nix
     platforms are now expected to provide at least one of ‘C.UTF-8’
     (full locale), ‘C.utf8’ (full locale) or ‘UTF-8’ (‘LC_CTYPE’-only
     locale) as an alternative to the legacy ‘ASCII’-based ‘C’ locale.

   * OpenSSL 0.9.8 and 1.0.1 are no longer supported, which means
     building CPython 3.7 with SSL/TLS support on older platforms still
     using these versions requires custom build options that link to a
     more recent version of OpenSSL.

     Notably, this issue affects the Debian 8 (aka “jessie”) and Ubuntu
     14.04 (aka “Trusty”) LTS Linux distributions, as they still use
     OpenSSL 1.0.1 by default.

     Debian 9 (“stretch”) and Ubuntu 16.04 (“xenial”), as well as recent
     releases of other LTS Linux releases (e.g.  RHEL/CentOS 7.5, SLES
     12-SP3), use OpenSSL 1.0.2 or later, and remain supported in the
     default build configuration.

     CPython’s own CI configuration file(1) provides an example of using
     the SSL compatibility testing infrastructure(2) in CPython’s test
     suite to build and link against OpenSSL 1.1.0 rather than an
     outdated system provided OpenSSL.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/.travis.yml

   (2) 
https://github.com/python/cpython/tree/3.9/Tools/ssl/multissltests.py


File: python.info,  Node: API and Feature Removals<2>,  Next: Module Removals,  Prev: Platform Support Removals,  Up: What’s New In Python 3 7

1.3.14 API and Feature Removals
-------------------------------

The following features and APIs have been removed from Python 3.7:

   * The ‘os.stat_float_times()’ function has been removed.  It was
     introduced in Python 2.3 for backward compatibility with Python
     2.2, and was deprecated since Python 3.1.

   * Unknown escapes consisting of ‘'\'’ and an ASCII letter in
     replacement templates for *note re.sub(): 57a. were deprecated in
     Python 3.5, and will now cause an error.

   * Removed support of the `exclude' argument in *note
     tarfile.TarFile.add(): 57b.  It was deprecated in Python 2.7 and
     3.2.  Use the `filter' argument instead.

   * The ‘splitunc()’ function in the ‘ntpath’ module was deprecated in
     Python 3.1, and has now been removed.  Use the *note splitdrive():
     57c. function instead.

   * *note collections.namedtuple(): 1a1. no longer supports the
     `verbose' parameter or ‘_source’ attribute which showed the
     generated source code for the named tuple class.  This was part of
     an optimization designed to speed-up class creation.  (Contributed
     by Jelle Zijlstra with further improvements by INADA Naoki, Serhiy
     Storchaka, and Raymond Hettinger in bpo-28638(1).)

   * Functions *note bool(): 2bd, *note float(): 1fd, *note list(): 1f8.
     and *note tuple(): 1a2. no longer take keyword arguments.  The
     first argument of *note int(): 204. can now be passed only as
     positional argument.

   * Removed previously deprecated in Python 2.4 classes ‘Plist’, ‘Dict’
     and ‘_InternalDict’ in the *note plistlib: cf. module.  Dict values
     in the result of functions ‘readPlist()’ and ‘readPlistFromBytes()’
     are now normal dicts.  You no longer can use attribute access to
     access items of these dictionaries.

   * The ‘asyncio.windows_utils.socketpair()’ function has been removed.
     Use the *note socket.socketpair(): 57d. function instead, it is
     available on all platforms since Python 3.5.
     ‘asyncio.windows_utils.socketpair’ was just an alias to
     ‘socket.socketpair’ on Python 3.5 and newer.

   * *note asyncio: 9. no longer exports the *note selectors: e6. and
     ‘_overlapped’ modules as ‘asyncio.selectors’ and
     ‘asyncio._overlapped’.  Replace ‘from asyncio import selectors’
     with ‘import selectors’.

   * Direct instantiation of *note ssl.SSLSocket: 192. and *note
     ssl.SSLObject: 4e9. objects is now prohibited.  The constructors
     were never documented, tested, or designed as public constructors.
     Users were supposed to use *note ssl.wrap_socket(): 571. or *note
     ssl.SSLContext: 4ea.  (Contributed by Christian Heimes in
     bpo-32951(2).)

   * The unused *note distutils: 38. ‘install_misc’ command has been
     removed.  (Contributed by Eric N. Vander Weele in bpo-29218(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28638

   (2) https://bugs.python.org/issue32951

   (3) https://bugs.python.org/issue29218


File: python.info,  Node: Module Removals,  Next: Windows-only Changes,  Prev: API and Feature Removals<2>,  Up: What’s New In Python 3 7

1.3.15 Module Removals
----------------------

The ‘fpectl’ module has been removed.  It was never enabled by default,
never worked correctly on x86-64, and it changed the Python ABI in ways
that caused unexpected breakage of C extensions.  (Contributed by
Nathaniel J. Smith in bpo-29137(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29137


File: python.info,  Node: Windows-only Changes,  Next: Porting to Python 3 7,  Prev: Module Removals,  Up: What’s New In Python 3 7

1.3.16 Windows-only Changes
---------------------------

The python launcher, (py.exe), can accept 32 & 64 bit specifiers
`without' having to specify a minor version as well.  So ‘py -3-32’ and
‘py -3-64’ become valid as well as ‘py -3.7-32’, also the -`m'-64 and
-`m.n'-64 forms are now accepted to force 64 bit python even if 32 bit
would have otherwise been used.  If the specified version is not
available py.exe will error exit.  (Contributed by Steve Barnes in
bpo-30291(1).)

The launcher can be run as ‘py -0’ to produce a list of the installed
pythons, `with default marked with an asterisk'.  Running ‘py -0p’ will
include the paths.  If py is run with a version specifier that cannot be
matched it will also print the `short form' list of available
specifiers.  (Contributed by Steve Barnes in bpo-30362(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30291

   (2) https://bugs.python.org/issue30362


File: python.info,  Node: Porting to Python 3 7,  Next: Notable changes in Python 3 7 1,  Prev: Windows-only Changes,  Up: What’s New In Python 3 7

1.3.17 Porting to Python 3.7
----------------------------

This section lists previously described changes and other bugfixes that
may require changes to your code.

* Menu:

* Changes in Python Behavior::
* Changes in the Python API: Changes in the Python API<3>.
* Changes in the C API: Changes in the C API<3>.
* CPython bytecode changes: CPython bytecode changes<3>.
* Windows-only Changes: Windows-only Changes<2>.
* Other CPython implementation changes::


File: python.info,  Node: Changes in Python Behavior,  Next: Changes in the Python API<3>,  Up: Porting to Python 3 7

1.3.17.1 Changes in Python Behavior
...................................

   * *note async: 2d7. and *note await: 2d8. names are now reserved
     keywords.  Code using these names as identifiers will now raise a
     *note SyntaxError: 55a.  (Contributed by Jelle Zijlstra in
     bpo-30406(1).)

   * PEP 479(2) is enabled for all code in Python 3.7, meaning that
     *note StopIteration: 582. exceptions raised directly or indirectly
     in coroutines and generators are transformed into *note
     RuntimeError: 3dc. exceptions.  (Contributed by Yury Selivanov in
     bpo-32670(3).)

   * *note object.__aiter__(): 583. methods can no longer be declared as
     asynchronous.  (Contributed by Yury Selivanov in bpo-31709(4).)

   * Due to an oversight, earlier Python versions erroneously accepted
     the following syntax:

          f(1 for x in [1],)

          class C(1 for x in [1]):
              pass

     Python 3.7 now correctly raises a *note SyntaxError: 55a, as a
     generator expression always needs to be directly inside a set of
     parentheses and cannot have a comma on either side, and the
     duplication of the parentheses can be omitted only on calls.
     (Contributed by Serhiy Storchaka in bpo-32012(5) and bpo-32023(6).)

   * When using the *note -m: 443. switch, the initial working directory
     is now added to *note sys.path: 260, rather than an empty string
     (which dynamically denoted the current working directory at the
     time of each import).  Any programs that are checking for the empty
     string, or otherwise relying on the previous behaviour, will need
     to be updated accordingly (e.g.  by also checking for ‘os.getcwd()’
     or ‘os.path.dirname(__main__.__file__)’, depending on why the code
     was checking for the empty string in the first place).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30406

   (2) https://www.python.org/dev/peps/pep-0479

   (3) https://bugs.python.org/issue32670

   (4) https://bugs.python.org/issue31709

   (5) https://bugs.python.org/issue32012

   (6) https://bugs.python.org/issue32023


File: python.info,  Node: Changes in the Python API<3>,  Next: Changes in the C API<3>,  Prev: Changes in Python Behavior,  Up: Porting to Python 3 7

1.3.17.2 Changes in the Python API
..................................

   * ‘socketserver.ThreadingMixIn.server_close()’ now waits until all
     non-daemon threads complete.  Set the new
     ‘socketserver.ThreadingMixIn.block_on_close’ class attribute to
     ‘False’ to get the pre-3.7 behaviour.  (Contributed by Victor
     Stinner in bpo-31233(1) and bpo-33540(2).)

   * ‘socketserver.ForkingMixIn.server_close()’ now waits until all
     child processes complete.  Set the new
     ‘socketserver.ForkingMixIn.block_on_close’ class attribute to
     ‘False’ to get the pre-3.7 behaviour.  (Contributed by Victor
     Stinner in bpo-31151(3) and bpo-33540(4).)

   * The *note locale.localeconv(): 585. function now temporarily sets
     the ‘LC_CTYPE’ locale to the value of ‘LC_NUMERIC’ in some cases.
     (Contributed by Victor Stinner in bpo-31900(5).)

   * *note pkgutil.walk_packages(): 586. now raises a *note ValueError:
     16d. if `path' is a string.  Previously an empty list was returned.
     (Contributed by Sanyam Khurana in bpo-24744(6).)

   * A format string argument for *note string.Formatter.format(): 587.
     is now *note positional-only: 3c9.  Passing it as a keyword
     argument was deprecated in Python 3.5.  (Contributed by Serhiy
     Storchaka in bpo-29193(7).)

   * Attributes *note key: 588, *note value: 589. and *note coded_value:
     58a. of class *note http.cookies.Morsel: 58b. are now read-only.
     Assigning to them was deprecated in Python 3.5.  Use the *note
     set(): 58c. method for setting them.  (Contributed by Serhiy
     Storchaka in bpo-29192(8).)

   * The `mode' argument of *note os.makedirs(): 4c4. no longer affects
     the file permission bits of newly-created intermediate-level
     directories.  To set their file permission bits you can set the
     umask before invoking ‘makedirs()’.  (Contributed by Serhiy
     Storchaka in bpo-19930(9).)

   * The *note struct.Struct.format: 58d. type is now *note str: 205.
     instead of *note bytes: 172.  (Contributed by Victor Stinner in
     bpo-21071(10).)

   * *note parse_multipart(): 282. now accepts the `encoding' and
     `errors' arguments and returns the same results as ‘FieldStorage’:
     for non-file fields, the value associated to a key is a list of
     strings, not bytes.  (Contributed by Pierre Quentel in
     bpo-29979(11).)

   * Due to internal changes in *note socket: ef, calling *note
     socket.fromshare(): 58e. on a socket created by *note socket.share:
     58f. in older Python versions is not supported.

   * ‘repr’ for *note BaseException: 2db. has changed to not include the
     trailing comma.  Most exceptions are affected by this change.
     (Contributed by Serhiy Storchaka in bpo-30399(12).)

   * ‘repr’ for *note datetime.timedelta: 2ca. has changed to include
     the keyword arguments in the output.  (Contributed by Utkarsh
     Upadhyay in bpo-30302(13).)

   * Because *note shutil.rmtree(): 349. is now implemented using the
     *note os.scandir(): 389. function, the user specified handler
     `onerror' is now called with the first argument ‘os.scandir’
     instead of ‘os.listdir’ when listing the directory is failed.

   * Support for nested sets and set operations in regular expressions
     as in Unicode Technical Standard #18(14) might be added in the
     future.  This would change the syntax.  To facilitate this future
     change a *note FutureWarning: 435. will be raised in ambiguous
     cases for the time being.  That include sets starting with a
     literal ‘'['’ or containing literal character sequences ‘'--'’,
     ‘'&&'’, ‘'~~'’, and ‘'||'’.  To avoid a warning, escape them with a
     backslash.  (Contributed by Serhiy Storchaka in bpo-30349(15).)

   * The result of splitting a string on a *note regular expression: dd.
     that could match an empty string has been changed.  For example
     splitting on ‘r'\s*'’ will now split not only on whitespaces as it
     did previously, but also on empty strings before all non-whitespace
     characters and just before the end of the string.  The previous
     behavior can be restored by changing the pattern to ‘r'\s+'’.  A
     *note FutureWarning: 435. was emitted for such patterns since
     Python 3.5.

     For patterns that match both empty and non-empty strings, the
     result of searching for all matches may also be changed in other
     cases.  For example in the string ‘'a\n\n'’, the pattern
     ‘r'(?m)^\s*?$'’ will not only match empty strings at positions 2
     and 3, but also the string ‘'\n'’ at positions 2–3.  To match only
     blank lines, the pattern should be rewritten as
     ‘r'(?m)^[^\S\n]*$'’.

     *note re.sub(): 57a. now replaces empty matches adjacent to a
     previous non-empty match.  For example ‘re.sub('x*', '-', 'abxd')’
     returns now ‘'-a-b--d-'’ instead of ‘'-a-b-d-'’ (the first minus
     between ‘b’ and ‘d’ replaces ‘x’, and the second minus replaces an
     empty string between ‘x’ and ‘d’).

     (Contributed by Serhiy Storchaka in bpo-25054(16) and
     bpo-32308(17).)

   * Change *note re.escape(): 590. to only escape regex special
     characters instead of escaping all characters other than ASCII
     letters, numbers, and ‘'_'’.  (Contributed by Serhiy Storchaka in
     bpo-29995(18).)

   * *note tracemalloc.Traceback: 504. frames are now sorted from oldest
     to most recent to be more consistent with *note traceback: 11c.
     (Contributed by Jesse Bakker in bpo-32121(19).)

   * On OSes that support *note socket.SOCK_NONBLOCK: 591. or *note
     socket.SOCK_CLOEXEC: 592. bit flags, the *note socket.type: 593. no
     longer has them applied.  Therefore, checks like ‘if sock.type ==
     socket.SOCK_STREAM’ work as expected on all platforms.
     (Contributed by Yury Selivanov in bpo-32331(20).)

   * On Windows the default for the `close_fds' argument of *note
     subprocess.Popen: 3db. was changed from *note False: 48f. to *note
     True: 594. when redirecting the standard handles.  If you
     previously depended on handles being inherited when using *note
     subprocess.Popen: 3db. with standard io redirection, you will have
     to pass ‘close_fds=False’ to preserve the previous behaviour, or
     use *note STARTUPINFO.lpAttributeList: 595.

   * *note importlib.machinery.PathFinder.invalidate_caches(): 596. –
     which implicitly affects *note importlib.invalidate_caches(): 597.
     – now deletes entries in *note sys.path_importer_cache: 598. which
     are set to ‘None’.  (Contributed by Brett Cannon in bpo-33169(21).)

   * In *note asyncio: 9, *note loop.sock_recv(): 599, *note
     loop.sock_sendall(): 59a, *note loop.sock_accept(): 59b, *note
     loop.getaddrinfo(): 59c, *note loop.getnameinfo(): 59d. have been
     changed to be proper coroutine methods to match their
     documentation.  Previously, these methods returned *note
     asyncio.Future: 546. instances.  (Contributed by Yury Selivanov in
     bpo-32327(22).)

   * *note asyncio.Server.sockets: 59e. now returns a copy of the
     internal list of server sockets, instead of returning it directly.
     (Contributed by Yury Selivanov in bpo-32662(23).)

   * *note Struct.format: 58d. is now a *note str: 205. instance instead
     of a *note bytes: 172. instance.  (Contributed by Victor Stinner in
     bpo-21071(24).)

   * *note argparse: 5. subparsers can now be made mandatory by passing
     ‘required=True’ to *note ArgumentParser.add_subparsers(): 59f.
     (Contributed by Anthony Sottile in bpo-26510(25).)

   * *note ast.literal_eval(): 5a0. is now stricter.  Addition and
     subtraction of arbitrary numbers are no longer allowed.
     (Contributed by Serhiy Storchaka in bpo-31778(26).)

   * *note Calendar.itermonthdates: 5a1. will now consistently raise an
     exception when a date falls outside of the ‘0001-01-01’ through
     ‘9999-12-31’ range.  To support applications that cannot tolerate
     such exceptions, the new *note Calendar.itermonthdays3: 5a2. and
     *note Calendar.itermonthdays4: 5a3. can be used.  The new methods
     return tuples and are not restricted by the range supported by
     *note datetime.date: 19e.  (Contributed by Alexander Belopolsky in
     bpo-28292(27).)

   * *note collections.ChainMap: 5a4. now preserves the order of the
     underlying mappings.  (Contributed by Raymond Hettinger in
     bpo-32792(28).)

   * The ‘submit()’ method of *note
     concurrent.futures.ThreadPoolExecutor: 18c. and *note
     concurrent.futures.ProcessPoolExecutor: 196. now raises a *note
     RuntimeError: 3dc. if called during interpreter shutdown.
     (Contributed by Mark Nemec in bpo-33097(29).)

   * The *note configparser.ConfigParser: 5a5. constructor now uses
     ‘read_dict()’ to process the default values, making its behavior
     consistent with the rest of the parser.  Non-string keys and values
     in the defaults dictionary are now being implicitly converted to
     strings.  (Contributed by James Tocknell in bpo-23835(30).)

   * Several undocumented internal imports were removed.  One example is
     that ‘os.errno’ is no longer available; use ‘import errno’ directly
     instead.  Note that such undocumented internal imports may be
     removed any time without notice, even in micro version releases.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31233

   (2) https://bugs.python.org/issue33540

   (3) https://bugs.python.org/issue31151

   (4) https://bugs.python.org/issue33540

   (5) https://bugs.python.org/issue31900

   (6) https://bugs.python.org/issue24744

   (7) https://bugs.python.org/issue29193

   (8) https://bugs.python.org/issue29192

   (9) https://bugs.python.org/issue19930

   (10) https://bugs.python.org/issue21071

   (11) https://bugs.python.org/issue29979

   (12) https://bugs.python.org/issue30399

   (13) https://bugs.python.org/issue30302

   (14) https://unicode.org/reports/tr18/

   (15) https://bugs.python.org/issue30349

   (16) https://bugs.python.org/issue25054

   (17) https://bugs.python.org/issue32308

   (18) https://bugs.python.org/issue29995

   (19) https://bugs.python.org/issue32121

   (20) https://bugs.python.org/issue32331

   (21) https://bugs.python.org/issue33169

   (22) https://bugs.python.org/issue32327

   (23) https://bugs.python.org/issue32662

   (24) https://bugs.python.org/issue21071

   (25) https://bugs.python.org/issue26510

   (26) https://bugs.python.org/issue31778

   (27) https://bugs.python.org/issue28292

   (28) https://bugs.python.org/issue32792

   (29) https://bugs.python.org/issue33097

   (30) https://bugs.python.org/issue23835


File: python.info,  Node: Changes in the C API<3>,  Next: CPython bytecode changes<3>,  Prev: Changes in the Python API<3>,  Up: Porting to Python 3 7

1.3.17.3 Changes in the C API
.............................

The function *note PySlice_GetIndicesEx(): 577. is considered unsafe for
resizable sequences.  If the slice indices are not instances of *note
int: 204, but objects that implement the ‘__index__()’ method, the
sequence can be resized after passing its length to
‘PySlice_GetIndicesEx()’.  This can lead to returning indices out of the
length of the sequence.  For avoiding possible problems use new
functions *note PySlice_Unpack(): 533. and *note
PySlice_AdjustIndices(): 534.  (Contributed by Serhiy Storchaka in
bpo-27867(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27867


File: python.info,  Node: CPython bytecode changes<3>,  Next: Windows-only Changes<2>,  Prev: Changes in the C API<3>,  Up: Porting to Python 3 7

1.3.17.4 CPython bytecode changes
.................................

There are two new opcodes: *note LOAD_METHOD: 5a8. and *note
CALL_METHOD: 5a9.  (Contributed by Yury Selivanov and INADA Naoki in
bpo-26110(1).)

The ‘STORE_ANNOTATION’ opcode has been removed.  (Contributed by Mark
Shannon in bpo-32550(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26110

   (2) https://bugs.python.org/issue32550


File: python.info,  Node: Windows-only Changes<2>,  Next: Other CPython implementation changes,  Prev: CPython bytecode changes<3>,  Up: Porting to Python 3 7

1.3.17.5 Windows-only Changes
.............................

The file used to override *note sys.path: 260. is now called
‘<python-executable>._pth’ instead of ‘'sys.path'’.  See *note Finding
modules: 5ab. for more information.  (Contributed by Steve Dower in
bpo-28137(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28137


File: python.info,  Node: Other CPython implementation changes,  Prev: Windows-only Changes<2>,  Up: Porting to Python 3 7

1.3.17.6 Other CPython implementation changes
.............................................

In preparation for potential future changes to the public CPython
runtime initialization API (see PEP 432(1) for an initial, but somewhat
outdated, draft), CPython’s internal startup and configuration
management logic has been significantly refactored.  While these updates
are intended to be entirely transparent to both embedding applications
and users of the regular CPython CLI, they’re being mentioned here as
the refactoring changes the internal order of various operations during
interpreter startup, and hence may uncover previously latent defects,
either in embedding applications, or in CPython itself.  (Initially
contributed by Nick Coghlan and Eric Snow as part of bpo-22257(2), and
further updated by Nick, Eric, and Victor Stinner in a number of other
issues).  Some known details affected:

   * *note PySys_AddWarnOptionUnicode(): 5ad. is not currently usable by
     embedding applications due to the requirement to create a Unicode
     object prior to calling ‘Py_Initialize’.  Use *note
     PySys_AddWarnOption(): 5ae. instead.

   * warnings filters added by an embedding application with *note
     PySys_AddWarnOption(): 5ae. should now more consistently take
     precedence over the default filters set by the interpreter

Due to changes in the way the default warnings filters are configured,
setting *note Py_BytesWarningFlag: 5af. to a value greater than one is
no longer sufficient to both emit *note BytesWarning: 5b0. messages and
have them converted to exceptions.  Instead, the flag must be set (to
cause the warnings to be emitted in the first place), and an explicit
‘error::BytesWarning’ warnings filter added to convert them to
exceptions.

Due to a change in the way docstrings are handled by the compiler, the
implicit ‘return None’ in a function body consisting solely of a
docstring is now marked as occurring on the same line as the docstring,
not on the function’s header line.

The current exception state has been moved from the frame object to the
co-routine.  This simplified the interpreter and fixed a couple of
obscure bugs caused by having swap exception state when entering or
exiting a generator.  (Contributed by Mark Shannon in bpo-25612(3).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0432

   (2) https://bugs.python.org/issue22257

   (3) https://bugs.python.org/issue25612


File: python.info,  Node: Notable changes in Python 3 7 1,  Next: Notable changes in Python 3 7 2,  Prev: Porting to Python 3 7,  Up: What’s New In Python 3 7

1.3.18 Notable changes in Python 3.7.1
--------------------------------------

Starting in 3.7.1, *note Py_Initialize(): 20f. now consistently reads
and respects all of the same environment settings as *note Py_Main():
5b2. (in earlier Python versions, it respected an ill-defined subset of
those environment variables, while in Python 3.7.0 it didn’t read any of
them due to bpo-34247(1)).  If this behavior is unwanted, set *note
Py_IgnoreEnvironmentFlag: 5b3. to 1 before calling *note
Py_Initialize(): 20f.

In 3.7.1 the C API for Context Variables *note was updated: 5b4. to use
*note PyObject: 5b5. pointers.  See also bpo-34762(2).

In 3.7.1 the *note tokenize: 11a. module now implicitly emits a
‘NEWLINE’ token when provided with input that does not have a trailing
new line.  This behavior now matches what the C tokenizer does
internally.  (Contributed by Ammar Askar in bpo-33899(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34247

   (2) https://bugs.python.org/issue34762

   (3) https://bugs.python.org/issue33899


File: python.info,  Node: Notable changes in Python 3 7 2,  Next: Notable changes in Python 3 7 6,  Prev: Notable changes in Python 3 7 1,  Up: What’s New In Python 3 7

1.3.19 Notable changes in Python 3.7.2
--------------------------------------

In 3.7.2, *note venv: 12e. on Windows no longer copies the original
binaries, but creates redirector scripts named ‘python.exe’ and
‘pythonw.exe’ instead.  This resolves a long standing issue where all
virtual environments would have to be upgraded or recreated with each
Python update.  However, note that this release will still require
recreation of virtual environments in order to get the new scripts.


File: python.info,  Node: Notable changes in Python 3 7 6,  Next: Notable changes in Python 3 7 10,  Prev: Notable changes in Python 3 7 2,  Up: What’s New In Python 3 7

1.3.20 Notable changes in Python 3.7.6
--------------------------------------

Due to significant security concerns, the `reuse_address' parameter of
*note asyncio.loop.create_datagram_endpoint(): 189. is no longer
supported.  This is because of the behavior of the socket option
‘SO_REUSEADDR’ in UDP. For more details, see the documentation for
‘loop.create_datagram_endpoint()’.  (Contributed by Kyle Stanley,
Antoine Pitrou, and Yury Selivanov in bpo-37228(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37228


File: python.info,  Node: Notable changes in Python 3 7 10,  Prev: Notable changes in Python 3 7 6,  Up: What’s New In Python 3 7

1.3.21 Notable changes in Python 3.7.10
---------------------------------------

Earlier Python versions allowed using both ‘;’ and ‘&’ as query
parameter separators in *note urllib.parse.parse_qs(): 27f. and *note
urllib.parse.parse_qsl(): 280.  Due to security concerns, and to conform
with newer W3C recommendations, this has been changed to allow only a
single separator key, with ‘&’ as the default.  This change also affects
*note cgi.parse(): 281. and *note cgi.parse_multipart(): 282. as they
use the affected functions internally.  For more details, please see
their respective documentation.  (Contributed by Adam Goldschmidt,
Senthil Kumaran and Ken Jin in bpo-42967(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42967


File: python.info,  Node: What’s New In Python 3 6,  Next: What’s New In Python 3 5,  Prev: What’s New In Python 3 7,  Up: What’s New in Python

1.4 What’s New In Python 3.6
============================


Editors: Elvis Pranskevichus <<elvis@magic.io>>, Yury Selivanov
<<yury@magic.io>>

This article explains the new features in Python 3.6, compared to 3.5.
Python 3.6 was released on December 23, 2016.   See the changelog(1) for
a full list of changes.

See also
........

PEP 494(2) - Python 3.6 Release Schedule

* Menu:

* Summary – Release highlights: Summary – Release highlights<3>.
* New Features: New Features<5>.
* Other Language Changes: Other Language Changes<4>.
* New Modules: New Modules<4>.
* Improved Modules: Improved Modules<4>.
* Optimizations: Optimizations<4>.
* Build and C API Changes: Build and C API Changes<2>.
* Other Improvements::
* Deprecated: Deprecated<3>.
* Removed: Removed<3>.
* Porting to Python 3.6: Porting to Python 3 6.
* Notable changes in Python 3.6.2: Notable changes in Python 3 6 2.
* Notable changes in Python 3.6.4: Notable changes in Python 3 6 4.
* Notable changes in Python 3.6.5: Notable changes in Python 3 6 5.
* Notable changes in Python 3.6.7: Notable changes in Python 3 6 7.
* Notable changes in Python 3.6.10: Notable changes in Python 3 6 10.
* Notable changes in Python 3.6.13: Notable changes in Python 3 6 13.

   ---------- Footnotes ----------

   (1) https://docs.python.org/3.6/whatsnew/changelog.html

   (2) https://www.python.org/dev/peps/pep-0494


File: python.info,  Node: Summary – Release highlights<3>,  Next: New Features<5>,  Up: What’s New In Python 3 6

1.4.1 Summary – Release highlights
----------------------------------

New syntax features:

   * *note PEP 498: 5bc, formatted string literals.

   * *note PEP 515: 5bd, underscores in numeric literals.

   * *note PEP 526: 5be, syntax for variable annotations.

   * *note PEP 525: 5bf, asynchronous generators.

   * *note PEP 530: 5c0.: asynchronous comprehensions.

New library modules:

   * *note secrets: e4.: *note PEP 506 – Adding A Secrets Module To The
     Standard Library: 5c1.

CPython implementation improvements:

   * The *note dict: 40e. type has been reimplemented to use a *note
     more compact representation: 5c2. based on a proposal by Raymond
     Hettinger(1) and similar to the PyPy dict implementation(2).  This
     resulted in dictionaries using 20% to 25% less memory when compared
     to Python 3.5.

   * Customization of class creation has been simplified with the *note
     new protocol: 5c3.

   * The class attribute definition order is *note now preserved: 5c4.

   * The order of elements in ‘**kwargs’ now *note corresponds to the
     order: 5c5. in which keyword arguments were passed to the function.

   * DTrace and SystemTap *note probing support: 5c6. has been added.

   * The new *note PYTHONMALLOC: 5c7. environment variable can now be
     used to debug the interpreter memory allocation and access errors.

Significant improvements in the standard library:

   * The *note asyncio: 9. module has received new features, significant
     usability and performance improvements, and a fair amount of bug
     fixes.  Starting with Python 3.6 the ‘asyncio’ module is no longer
     provisional and its API is considered stable.

   * A new *note file system path protocol: 5c8. has been implemented to
     support *note path-like objects: 472.  All standard library
     functions operating on paths have been updated to work with the new
     protocol.

   * The *note datetime: 30. module has gained support for *note Local
     Time Disambiguation: 5c9.

   * The *note typing: 122. module received a number of *note
     improvements: 5ca.

   * The *note tracemalloc: 11d. module has been significantly reworked
     and is now used to provide better output for *note ResourceWarning:
     5cb. as well as provide better diagnostics for memory allocation
     errors.  See the *note PYTHONMALLOC section: 5c7. for more
     information.

Security improvements:

   * The new *note secrets: e4. module has been added to simplify the
     generation of cryptographically strong pseudo-random numbers
     suitable for managing secrets such as account authentication,
     tokens, and similar.

   * On Linux, *note os.urandom(): 5cc. now blocks until the system
     urandom entropy pool is initialized to increase the security.  See
     the PEP 524(3) for the rationale.

   * The *note hashlib: 8c. and *note ssl: f3. modules now support
     OpenSSL 1.1.0.

   * The default settings and feature set of the *note ssl: f3. module
     have been improved.

   * The *note hashlib: 8c. module received support for the BLAKE2,
     SHA-3 and SHAKE hash algorithms and the *note scrypt(): 5cd. key
     derivation function.

Windows improvements:

   * *note PEP 528: 5ce. and *note PEP 529: 5cf, Windows filesystem and
     console encoding changed to UTF-8.

   * The ‘py.exe’ launcher, when used interactively, no longer prefers
     Python 2 over Python 3 when the user doesn’t specify a version (via
     command line arguments or a config file).  Handling of shebang
     lines remains unchanged - “python” refers to Python 2 in that case.

   * ‘python.exe’ and ‘pythonw.exe’ have been marked as long-path aware,
     which means that the 260 character path limit may no longer apply.
     See *note removing the MAX_PATH limitation: 5d0. for details.

   * A ‘._pth’ file can be added to force isolated mode and fully
     specify all search paths to avoid registry and environment lookup.
     See *note the documentation: 5ab. for more information.

   * A ‘python36.zip’ file now works as a landmark to infer *note
     PYTHONHOME: 5d1.  See *note the documentation: 5ab. for more
     information.

   ---------- Footnotes ----------

   (1) 
https://mail.python.org/pipermail/python-dev/2012-December/123028.html

   (2) 
https://morepypy.blogspot.com/2015/01/faster-more-memory-efficient-and-more.html

   (3) https://www.python.org/dev/peps/pep-0524


File: python.info,  Node: New Features<5>,  Next: Other Language Changes<4>,  Prev: Summary – Release highlights<3>,  Up: What’s New In Python 3 6

1.4.2 New Features
------------------

* Menu:

* PEP 498; Formatted string literals: PEP 498 Formatted string literals.
* PEP 526; Syntax for variable annotations: PEP 526 Syntax for variable annotations.
* PEP 515; Underscores in Numeric Literals: PEP 515 Underscores in Numeric Literals.
* PEP 525; Asynchronous Generators: PEP 525 Asynchronous Generators.
* PEP 530; Asynchronous Comprehensions: PEP 530 Asynchronous Comprehensions.
* PEP 487; Simpler customization of class creation: PEP 487 Simpler customization of class creation.
* PEP 487; Descriptor Protocol Enhancements: PEP 487 Descriptor Protocol Enhancements.
* PEP 519; Adding a file system path protocol: PEP 519 Adding a file system path protocol.
* PEP 495; Local Time Disambiguation: PEP 495 Local Time Disambiguation.
* PEP 529; Change Windows filesystem encoding to UTF-8: PEP 529 Change Windows filesystem encoding to UTF-8.
* PEP 528; Change Windows console encoding to UTF-8: PEP 528 Change Windows console encoding to UTF-8.
* PEP 520; Preserving Class Attribute Definition Order: PEP 520 Preserving Class Attribute Definition Order.
* PEP 468; Preserving Keyword Argument Order: PEP 468 Preserving Keyword Argument Order.
* New dict implementation::
* PEP 523; Adding a frame evaluation API to CPython: PEP 523 Adding a frame evaluation API to CPython.
* PYTHONMALLOC environment variable::
* DTrace and SystemTap probing support::


File: python.info,  Node: PEP 498 Formatted string literals,  Next: PEP 526 Syntax for variable annotations,  Up: New Features<5>

1.4.2.1 PEP 498: Formatted string literals
..........................................

PEP 498(1) introduces a new kind of string literals: `f-strings', or
*note formatted string literals: 296.

Formatted string literals are prefixed with ‘'f'’ and are similar to the
format strings accepted by *note str.format(): 5d5.  They contain
replacement fields surrounded by curly braces.  The replacement fields
are expressions, which are evaluated at run time, and then formatted
using the *note format(): 5d6. protocol:

     >>> name = "Fred"
     >>> f"He said his name is {name}."
     'He said his name is Fred.'
     >>> width = 10
     >>> precision = 4
     >>> value = decimal.Decimal("12.34567")
     >>> f"result: {value:{width}.{precision}}"  # nested fields
     'result:      12.35'

See also
........

PEP 498(2) – Literal String Interpolation.

     PEP written and implemented by Eric V. Smith.

*note Feature documentation: 296.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0498

   (2) https://www.python.org/dev/peps/pep-0498


File: python.info,  Node: PEP 526 Syntax for variable annotations,  Next: PEP 515 Underscores in Numeric Literals,  Prev: PEP 498 Formatted string literals,  Up: New Features<5>

1.4.2.2 PEP 526: Syntax for variable annotations
................................................

PEP 484(1) introduced the standard for type annotations of function
parameters, a.k.a.  type hints.  This PEP adds syntax to Python for
annotating the types of variables including class variables and instance
variables:

     primes: List[int] = []

     captain: str  # Note: no initial value!

     class Starship:
         stats: Dict[str, int] = {}

Just as for function annotations, the Python interpreter does not attach
any particular meaning to variable annotations and only stores them in
the ‘__annotations__’ attribute of a class or module.

In contrast to variable declarations in statically typed languages, the
goal of annotation syntax is to provide an easy way to specify
structured type metadata for third party tools and libraries via the
abstract syntax tree and the ‘__annotations__’ attribute.

See also
........

PEP 526(2) – Syntax for variable annotations.

     PEP written by Ryan Gonzalez, Philip House, Ivan Levkivskyi, Lisa
     Roach, and Guido van Rossum.  Implemented by Ivan Levkivskyi.

Tools that use or will use the new syntax: mypy(3), pytype(4), PyCharm,
etc.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0484

   (2) https://www.python.org/dev/peps/pep-0526

   (3) http://www.mypy-lang.org/

   (4) https://github.com/google/pytype


File: python.info,  Node: PEP 515 Underscores in Numeric Literals,  Next: PEP 525 Asynchronous Generators,  Prev: PEP 526 Syntax for variable annotations,  Up: New Features<5>

1.4.2.3 PEP 515: Underscores in Numeric Literals
................................................

PEP 515(1) adds the ability to use underscores in numeric literals for
improved readability.  For example:

     >>> 1_000_000_000_000_000
     1000000000000000
     >>> 0x_FF_FF_FF_FF
     4294967295

Single underscores are allowed between digits and after any base
specifier.  Leading, trailing, or multiple underscores in a row are not
allowed.

The *note string formatting: 5d9. language also now has support for the
‘'_'’ option to signal the use of an underscore for a thousands
separator for floating point presentation types and for integer
presentation type ‘'d'’.  For integer presentation types ‘'b'’, ‘'o'’,
‘'x'’, and ‘'X'’, underscores will be inserted every 4 digits:

     >>> '{:_}'.format(1000000)
     '1_000_000'
     >>> '{:_x}'.format(0xFFFFFFFF)
     'ffff_ffff'

See also
........

PEP 515(2) – Underscores in Numeric Literals

     PEP written by Georg Brandl and Serhiy Storchaka.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0515

   (2) https://www.python.org/dev/peps/pep-0515


File: python.info,  Node: PEP 525 Asynchronous Generators,  Next: PEP 530 Asynchronous Comprehensions,  Prev: PEP 515 Underscores in Numeric Literals,  Up: New Features<5>

1.4.2.4 PEP 525: Asynchronous Generators
........................................

PEP 492(1) introduced support for native coroutines and ‘async’ /
‘await’ syntax to Python 3.5.  A notable limitation of the Python 3.5
implementation is that it was not possible to use ‘await’ and ‘yield’ in
the same function body.  In Python 3.6 this restriction has been lifted,
making it possible to define `asynchronous generators':

     async def ticker(delay, to):
         """Yield numbers from 0 to *to* every *delay* seconds."""
         for i in range(to):
             yield i
             await asyncio.sleep(delay)

The new syntax allows for faster and more concise code.

See also
........

PEP 525(2) – Asynchronous Generators

     PEP written and implemented by Yury Selivanov.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0492

   (2) https://www.python.org/dev/peps/pep-0525


File: python.info,  Node: PEP 530 Asynchronous Comprehensions,  Next: PEP 487 Simpler customization of class creation,  Prev: PEP 525 Asynchronous Generators,  Up: New Features<5>

1.4.2.5 PEP 530: Asynchronous Comprehensions
............................................

PEP 530(1) adds support for using ‘async for’ in list, set, dict
comprehensions and generator expressions:

     result = [i async for i in aiter() if i % 2]

Additionally, ‘await’ expressions are supported in all kinds of
comprehensions:

     result = [await fun() for fun in funcs if await condition()]

See also
........

PEP 530(2) – Asynchronous Comprehensions

     PEP written and implemented by Yury Selivanov.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0530

   (2) https://www.python.org/dev/peps/pep-0530


File: python.info,  Node: PEP 487 Simpler customization of class creation,  Next: PEP 487 Descriptor Protocol Enhancements,  Prev: PEP 530 Asynchronous Comprehensions,  Up: New Features<5>

1.4.2.6 PEP 487: Simpler customization of class creation
........................................................

It is now possible to customize subclass creation without using a
metaclass.  The new ‘__init_subclass__’ classmethod will be called on
the base class whenever a new subclass is created:

     class PluginBase:
         subclasses = []

         def __init_subclass__(cls, **kwargs):
             super().__init_subclass__(**kwargs)
             cls.subclasses.append(cls)

     class Plugin1(PluginBase):
         pass

     class Plugin2(PluginBase):
         pass

In order to allow zero-argument *note super(): 5dd. calls to work
correctly from *note __init_subclass__(): 5de. implementations, custom
metaclasses must ensure that the new ‘__classcell__’ namespace entry is
propagated to ‘type.__new__’ (as described in *note Creating the class
object: 5df.).

See also
........

PEP 487(1) – Simpler customization of class creation

     PEP written and implemented by Martin Teichmann.

*note Feature documentation: 5e0.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0487


File: python.info,  Node: PEP 487 Descriptor Protocol Enhancements,  Next: PEP 519 Adding a file system path protocol,  Prev: PEP 487 Simpler customization of class creation,  Up: New Features<5>

1.4.2.7 PEP 487: Descriptor Protocol Enhancements
.................................................

PEP 487(1) extends the descriptor protocol to include the new optional
*note __set_name__(): 5e3. method.  Whenever a new class is defined, the
new method will be called on all descriptors included in the definition,
providing them with a reference to the class being defined and the name
given to the descriptor within the class namespace.  In other words,
instances of descriptors can now know the attribute name of the
descriptor in the owner class:

     class IntField:
         def __get__(self, instance, owner):
             return instance.__dict__[self.name]

         def __set__(self, instance, value):
             if not isinstance(value, int):
                 raise ValueError(f'expecting integer in {self.name}')
             instance.__dict__[self.name] = value

         # this is the new initializer:
         def __set_name__(self, owner, name):
             self.name = name

     class Model:
         int_field = IntField()

See also
........

PEP 487(2) – Simpler customization of class creation

     PEP written and implemented by Martin Teichmann.

*note Feature documentation: 5e4.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0487

   (2) https://www.python.org/dev/peps/pep-0487


File: python.info,  Node: PEP 519 Adding a file system path protocol,  Next: PEP 495 Local Time Disambiguation,  Prev: PEP 487 Descriptor Protocol Enhancements,  Up: New Features<5>

1.4.2.8 PEP 519: Adding a file system path protocol
...................................................

File system paths have historically been represented as *note str: 205.
or *note bytes: 172. objects.  This has led to people who write code
which operate on file system paths to assume that such objects are only
one of those two types (an *note int: 204. representing a file
descriptor does not count as that is not a file path).  Unfortunately
that assumption prevents alternative object representations of file
system paths like *note pathlib: c8. from working with pre-existing
code, including Python’s standard library.

To fix this situation, a new interface represented by *note os.PathLike:
5e6. has been defined.  By implementing the *note __fspath__(): 5e7.
method, an object signals that it represents a path.  An object can then
provide a low-level representation of a file system path as a *note str:
205. or *note bytes: 172. object.  This means an object is considered
*note path-like: 472. if it implements *note os.PathLike: 5e6. or is a
*note str: 205. or *note bytes: 172. object which represents a file
system path.  Code can use *note os.fspath(): 5e8, *note os.fsdecode():
5e9, or *note os.fsencode(): 5ea. to explicitly get a *note str: 205.
and/or *note bytes: 172. representation of a path-like object.

The built-in *note open(): 16f. function has been updated to accept
*note os.PathLike: 5e6. objects, as have all relevant functions in the
*note os: c4. and *note os.path: c5. modules, and most other functions
and classes in the standard library.  The *note os.DirEntry: 5eb. class
and relevant classes in *note pathlib: c8. have also been updated to
implement *note os.PathLike: 5e6.

The hope is that updating the fundamental functions for operating on
file system paths will lead to third-party code to implicitly support
all *note path-like objects: 472. without any code changes, or at least
very minimal ones (e.g.  calling *note os.fspath(): 5e8. at the
beginning of code before operating on a path-like object).

Here are some examples of how the new interface allows for *note
pathlib.Path: 32f. to be used more easily and transparently with
pre-existing code:

     >>> import pathlib
     >>> with open(pathlib.Path("README")) as f:
     ...     contents = f.read()
     ...
     >>> import os.path
     >>> os.path.splitext(pathlib.Path("some_file.txt"))
     ('some_file', '.txt')
     >>> os.path.join("/a/b", pathlib.Path("c"))
     '/a/b/c'
     >>> import os
     >>> os.fspath(pathlib.Path("some_file.txt"))
     'some_file.txt'

(Implemented by Brett Cannon, Ethan Furman, Dusty Phillips, and Jelle
Zijlstra.)

See also
........

PEP 519(1) – Adding a file system path protocol

     PEP written by Brett Cannon and Koos Zevenhoven.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0519


File: python.info,  Node: PEP 495 Local Time Disambiguation,  Next: PEP 529 Change Windows filesystem encoding to UTF-8,  Prev: PEP 519 Adding a file system path protocol,  Up: New Features<5>

1.4.2.9 PEP 495: Local Time Disambiguation
..........................................

In most world locations, there have been and will be times when local
clocks are moved back.  In those times, intervals are introduced in
which local clocks show the same time twice in the same day.  In these
situations, the information displayed on a local clock (or stored in a
Python datetime instance) is insufficient to identify a particular
moment in time.

PEP 495(1) adds the new `fold' attribute to instances of *note
datetime.datetime: 1a0. and *note datetime.time: 5ed. classes to
differentiate between two moments in time for which local times are the
same:

     >>> u0 = datetime(2016, 11, 6, 4, tzinfo=timezone.utc)
     >>> for i in range(4):
     ...     u = u0 + i*HOUR
     ...     t = u.astimezone(Eastern)
     ...     print(u.time(), 'UTC =', t.time(), t.tzname(), t.fold)
     ...
     04:00:00 UTC = 00:00:00 EDT 0
     05:00:00 UTC = 01:00:00 EDT 0
     06:00:00 UTC = 01:00:00 EST 1
     07:00:00 UTC = 02:00:00 EST 0

The values of the *note fold: 5ee. attribute have the value ‘0’ for all
instances except those that represent the second (chronologically)
moment in time in an ambiguous case.

See also
........

PEP 495(2) – Local Time Disambiguation

     PEP written by Alexander Belopolsky and Tim Peters, implementation
     by Alexander Belopolsky.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0495

   (2) https://www.python.org/dev/peps/pep-0495


File: python.info,  Node: PEP 529 Change Windows filesystem encoding to UTF-8,  Next: PEP 528 Change Windows console encoding to UTF-8,  Prev: PEP 495 Local Time Disambiguation,  Up: New Features<5>

1.4.2.10 PEP 529: Change Windows filesystem encoding to UTF-8
.............................................................

Representing filesystem paths is best performed with str (Unicode)
rather than bytes.  However, there are some situations where using bytes
is sufficient and correct.

Prior to Python 3.6, data loss could result when using bytes paths on
Windows.  With this change, using bytes to represent paths is now
supported on Windows, provided those bytes are encoded with the encoding
returned by *note sys.getfilesystemencoding(): 5f0, which now defaults
to ‘'utf-8'’.

Applications that do not use str to represent paths should use *note
os.fsencode(): 5ea. and *note os.fsdecode(): 5e9. to ensure their bytes
are correctly encoded.  To revert to the previous behaviour, set *note
PYTHONLEGACYWINDOWSFSENCODING: 5f1. or call *note
sys._enablelegacywindowsfsencoding(): 5f2.

See PEP 529(1) for more information and discussion of code modifications
that may be required.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0529


File: python.info,  Node: PEP 528 Change Windows console encoding to UTF-8,  Next: PEP 520 Preserving Class Attribute Definition Order,  Prev: PEP 529 Change Windows filesystem encoding to UTF-8,  Up: New Features<5>

1.4.2.11 PEP 528: Change Windows console encoding to UTF-8
..........................................................

The default console on Windows will now accept all Unicode characters
and provide correctly read str objects to Python code.  ‘sys.stdin’,
‘sys.stdout’ and ‘sys.stderr’ now default to utf-8 encoding.

This change only applies when using an interactive console, and not when
redirecting files or pipes.  To revert to the previous behaviour for
interactive console use, set *note PYTHONLEGACYWINDOWSSTDIO: 5f4.

See also
........

PEP 528(1) – Change Windows console encoding to UTF-8

     PEP written and implemented by Steve Dower.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0528


File: python.info,  Node: PEP 520 Preserving Class Attribute Definition Order,  Next: PEP 468 Preserving Keyword Argument Order,  Prev: PEP 528 Change Windows console encoding to UTF-8,  Up: New Features<5>

1.4.2.12 PEP 520: Preserving Class Attribute Definition Order
.............................................................

Attributes in a class definition body have a natural ordering: the same
order in which the names appear in the source.  This order is now
preserved in the new class’s *note __dict__: 5f6. attribute.

Also, the effective default class `execution' namespace (returned from
*note type.__prepare__(): 5f7.) is now an insertion-order-preserving
mapping.

See also
........

PEP 520(1) – Preserving Class Attribute Definition Order

     PEP written and implemented by Eric Snow.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0520


File: python.info,  Node: PEP 468 Preserving Keyword Argument Order,  Next: New dict implementation,  Prev: PEP 520 Preserving Class Attribute Definition Order,  Up: New Features<5>

1.4.2.13 PEP 468: Preserving Keyword Argument Order
...................................................

‘**kwargs’ in a function signature is now guaranteed to be an
insertion-order-preserving mapping.

See also
........

PEP 468(1) – Preserving Keyword Argument Order

     PEP written and implemented by Eric Snow.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0468


File: python.info,  Node: New dict implementation,  Next: PEP 523 Adding a frame evaluation API to CPython,  Prev: PEP 468 Preserving Keyword Argument Order,  Up: New Features<5>

1.4.2.14 New dict implementation
................................

The *note dict: 40e. type now uses a “compact” representation based on a
proposal by Raymond Hettinger(1) which was first implemented by PyPy(2).
The memory usage of the new *note dict(): 164. is between 20% and 25%
smaller compared to Python 3.5.

The order-preserving aspect of this new implementation is considered an
implementation detail and should not be relied upon (this may change in
the future, but it is desired to have this new dict implementation in
the language for a few releases before changing the language spec to
mandate order-preserving semantics for all current and future Python
implementations; this also helps preserve backwards-compatibility with
older versions of the language where random iteration order is still in
effect, e.g.  Python 3.5).

(Contributed by INADA Naoki in bpo-27350(3).  Idea originally suggested
by Raymond Hettinger(4).)

   ---------- Footnotes ----------

   (1) 
https://mail.python.org/pipermail/python-dev/2012-December/123028.html

   (2) 
https://morepypy.blogspot.com/2015/01/faster-more-memory-efficient-and-more.html

   (3) https://bugs.python.org/issue27350

   (4) 
https://mail.python.org/pipermail/python-dev/2012-December/123028.html


File: python.info,  Node: PEP 523 Adding a frame evaluation API to CPython,  Next: PYTHONMALLOC environment variable,  Prev: New dict implementation,  Up: New Features<5>

1.4.2.15 PEP 523: Adding a frame evaluation API to CPython
..........................................................

While Python provides extensive support to customize how code executes,
one place it has not done so is in the evaluation of frame objects.  If
you wanted some way to intercept frame evaluation in Python there really
wasn’t any way without directly manipulating function pointers for
defined functions.

PEP 523(1) changes this by providing an API to make frame evaluation
pluggable at the C level.  This will allow for tools such as debuggers
and JITs to intercept frame evaluation before the execution of Python
code begins.  This enables the use of alternative evaluation
implementations for Python code, tracking frame evaluation, etc.

This API is not part of the limited C API and is marked as private to
signal that usage of this API is expected to be limited and only
applicable to very select, low-level use-cases.  Semantics of the API
will change with Python as necessary.

See also
........

PEP 523(2) – Adding a frame evaluation API to CPython

     PEP written by Brett Cannon and Dino Viehland.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0523

   (2) https://www.python.org/dev/peps/pep-0523


File: python.info,  Node: PYTHONMALLOC environment variable,  Next: DTrace and SystemTap probing support,  Prev: PEP 523 Adding a frame evaluation API to CPython,  Up: New Features<5>

1.4.2.16 PYTHONMALLOC environment variable
..........................................

The new *note PYTHONMALLOC: 5fd. environment variable allows setting the
Python memory allocators and installing debug hooks.

It is now possible to install debug hooks on Python memory allocators on
Python compiled in release mode using ‘PYTHONMALLOC=debug’.  Effects of
debug hooks:

   * Newly allocated memory is filled with the byte ‘0xCB’

   * Freed memory is filled with the byte ‘0xDB’

   * Detect violations of the Python memory allocator API. For example,
     *note PyObject_Free(): 5fe. called on a memory block allocated by
     *note PyMem_Malloc(): 5ff.

   * Detect writes before the start of a buffer (buffer underflows)

   * Detect writes after the end of a buffer (buffer overflows)

   * Check that the *note GIL: 600. is held when allocator functions of
     *note PYMEM_DOMAIN_OBJ: 601. (ex: *note PyObject_Malloc(): 602.)
     and *note PYMEM_DOMAIN_MEM: 603. (ex: *note PyMem_Malloc(): 5ff.)
     domains are called.

Checking if the GIL is held is also a new feature of Python 3.6.

See the *note PyMem_SetupDebugHooks(): 604. function for debug hooks on
Python memory allocators.

It is now also possible to force the usage of the ‘malloc()’ allocator
of the C library for all Python memory allocations using
‘PYTHONMALLOC=malloc’.  This is helpful when using external memory
debuggers like Valgrind on a Python compiled in release mode.

On error, the debug hooks on Python memory allocators now use the *note
tracemalloc: 11d. module to get the traceback where a memory block was
allocated.

Example of fatal error on buffer overflow using ‘python3.6 -X
tracemalloc=5’ (store 5 frames in traces):

     Debug memory block at address p=0x7fbcd41666f8: API 'o'
         4 bytes originally requested
         The 7 pad bytes at p-7 are FORBIDDENBYTE, as expected.
         The 8 pad bytes at tail=0x7fbcd41666fc are not all FORBIDDENBYTE (0xfb):
             at tail+0: 0x02 *** OUCH
             at tail+1: 0xfb
             at tail+2: 0xfb
             at tail+3: 0xfb
             at tail+4: 0xfb
             at tail+5: 0xfb
             at tail+6: 0xfb
             at tail+7: 0xfb
         The block was made by call #1233329 to debug malloc/realloc.
         Data at p: 1a 2b 30 00

     Memory block allocated at (most recent call first):
       File "test/test_bytes.py", line 323
       File "unittest/case.py", line 600
       File "unittest/case.py", line 648
       File "unittest/suite.py", line 122
       File "unittest/suite.py", line 84

     Fatal Python error: bad trailing pad byte

     Current thread 0x00007fbcdbd32700 (most recent call first):
       File "test/test_bytes.py", line 323 in test_hex
       File "unittest/case.py", line 600 in run
       File "unittest/case.py", line 648 in __call__
       File "unittest/suite.py", line 122 in run
       File "unittest/suite.py", line 84 in __call__
       File "unittest/suite.py", line 122 in run
       File "unittest/suite.py", line 84 in __call__
       ...

(Contributed by Victor Stinner in bpo-26516(1) and bpo-26564(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26516

   (2) https://bugs.python.org/issue26564


File: python.info,  Node: DTrace and SystemTap probing support,  Prev: PYTHONMALLOC environment variable,  Up: New Features<5>

1.4.2.17 DTrace and SystemTap probing support
.............................................

Python can now be built ‘--with-dtrace’ which enables static markers for
the following events in the interpreter:

   * function call/return

   * garbage collection started/finished

   * line of code executed.

This can be used to instrument running interpreters in production,
without the need to recompile specific debug builds or providing
application-specific profiling/debugging code.

More details in *note Instrumenting CPython with DTrace and SystemTap:
606.

The current implementation is tested on Linux and macOS. Additional
markers may be added in the future.

(Contributed by Łukasz Langa in bpo-21590(1), based on patches by Jesús
Cea Avión, David Malcolm, and Nikhil Benesch.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21590


File: python.info,  Node: Other Language Changes<4>,  Next: New Modules<4>,  Prev: New Features<5>,  Up: What’s New In Python 3 6

1.4.3 Other Language Changes
----------------------------

Some smaller changes made to the core Python language are:

   * A ‘global’ or ‘nonlocal’ statement must now textually appear before
     the first use of the affected name in the same scope.  Previously
     this was a *note SyntaxWarning: 2c9.

   * It is now possible to set a *note special method: 608. to ‘None’ to
     indicate that the corresponding operation is not available.  For
     example, if a class sets *note __iter__(): 609. to ‘None’, the
     class is not iterable.  (Contributed by Andrew Barnert and Ivan
     Levkivskyi in bpo-25958(1).)

   * Long sequences of repeated traceback lines are now abbreviated as
     ‘"[Previous line repeated {count} more times]"’ (see *note
     traceback: 60a. for an example).  (Contributed by Emanuel Barry in
     bpo-26823(2).)

   * Import now raises the new exception *note ModuleNotFoundError: 4a1.
     (subclass of *note ImportError: 16c.) when it cannot find a module.
     Code that currently checks for ImportError (in try-except) will
     still work.  (Contributed by Eric Snow in bpo-15767(3).)

   * Class methods relying on zero-argument ‘super()’ will now work
     correctly when called from metaclass methods during class creation.
     (Contributed by Martin Teichmann in bpo-23722(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25958

   (2) https://bugs.python.org/issue26823

   (3) https://bugs.python.org/issue15767

   (4) https://bugs.python.org/issue23722


File: python.info,  Node: New Modules<4>,  Next: Improved Modules<4>,  Prev: Other Language Changes<4>,  Up: What’s New In Python 3 6

1.4.4 New Modules
-----------------

* Menu:

* secrets::


File: python.info,  Node: secrets,  Up: New Modules<4>

1.4.4.1 secrets
...............

The main purpose of the new *note secrets: e4. module is to provide an
obvious way to reliably generate cryptographically strong pseudo-random
values suitable for managing secrets, such as account authentication,
tokens, and similar.

     Warning: Note that the pseudo-random generators in the *note
     random: dc. module should `NOT' be used for security purposes.  Use
     *note secrets: e4. on Python 3.6+ and *note os.urandom(): 5cc. on
     Python 3.5 and earlier.

See also
........

PEP 506(1) – Adding A Secrets Module To The Standard Library

     PEP written and implemented by Steven D’Aprano.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0506


File: python.info,  Node: Improved Modules<4>,  Next: Optimizations<4>,  Prev: New Modules<4>,  Up: What’s New In Python 3 6

1.4.5 Improved Modules
----------------------

* Menu:

* array::
* ast: ast<3>.
* asyncio: asyncio<5>.
* binascii: binascii<2>.
* cmath::
* collections: collections<4>.
* concurrent.futures: concurrent futures<3>.
* contextlib: contextlib<2>.
* datetime: datetime<4>.
* decimal: decimal<2>.
* distutils: distutils<3>.
* email::
* encodings::
* enum: enum<3>.
* faulthandler::
* fileinput::
* hashlib: hashlib<2>.
* http.client: http client<2>.
* idlelib and IDLE: idlelib and IDLE<2>.
* importlib: importlib<4>.
* inspect: inspect<3>.
* json::
* logging: logging<3>.
* math: math<4>.
* multiprocessing: multiprocessing<4>.
* os: os<4>.
* pathlib: pathlib<4>.
* pdb: pdb<3>.
* pickle: pickle<2>.
* pickletools::
* pydoc: pydoc<3>.
* random: random<2>.
* re: re<2>.
* readline::
* rlcompleter::
* shlex: shlex<2>.
* site::
* sqlite3: sqlite3<2>.
* socket: socket<5>.
* socketserver: socketserver<2>.
* ssl: ssl<4>.
* statistics: statistics<2>.
* struct::
* subprocess: subprocess<2>.
* sys: sys<5>.
* telnetlib::
* time: time<4>.
* timeit::
* tkinter: tkinter<3>.
* traceback::
* tracemalloc: tracemalloc<3>.
* typing: typing<4>.
* unicodedata: unicodedata<4>.
* unittest.mock: unittest mock<2>.
* urllib.request: urllib request.
* urllib.robotparser: urllib robotparser.
* venv: venv<3>.
* warnings: warnings<2>.
* winreg::
* winsound::
* xmlrpc.client: xmlrpc client.
* zipfile: zipfile<2>.
* zlib::


File: python.info,  Node: array,  Next: ast<3>,  Up: Improved Modules<4>

1.4.5.1 array
.............

Exhausted iterators of *note array.array: 216. will now stay exhausted
even if the iterated array is extended.  This is consistent with the
behavior of other mutable sequences.

Contributed by Serhiy Storchaka in bpo-26492(1).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26492


File: python.info,  Node: ast<3>,  Next: asyncio<5>,  Prev: array,  Up: Improved Modules<4>

1.4.5.2 ast
...........

The new *note ast.Constant: 3a6. AST node has been added.  It can be
used by external AST optimizers for the purposes of constant folding.

Contributed by Victor Stinner in bpo-26146(1).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26146


File: python.info,  Node: asyncio<5>,  Next: binascii<2>,  Prev: ast<3>,  Up: Improved Modules<4>

1.4.5.3 asyncio
...............

Starting with Python 3.6 the ‘asyncio’ module is no longer provisional
and its API is considered stable.

Notable changes in the *note asyncio: 9. module since Python 3.5.0 (all
backported to 3.5.x due to the provisional status):

   * The *note get_event_loop(): 45d. function has been changed to
     always return the currently running loop when called from
     coroutines and callbacks.  (Contributed by Yury Selivanov in
     bpo-28613(1).)

   * The *note ensure_future(): 611. function and all functions that use
     it, such as *note loop.run_until_complete(): 612, now accept all
     kinds of *note awaitable objects: 613.  (Contributed by Yury
     Selivanov.)

   * New *note run_coroutine_threadsafe(): 614. function to submit
     coroutines to event loops from other threads.  (Contributed by
     Vincent Michel.)

   * New *note Transport.is_closing(): 615. method to check if the
     transport is closing or closed.  (Contributed by Yury Selivanov.)

   * The *note loop.create_server(): 465. method can now accept a list
     of hosts.  (Contributed by Yann Sionneau.)

   * New *note loop.create_future(): 616. method to create Future
     objects.  This allows alternative event loop implementations, such
     as uvloop(2), to provide a faster *note asyncio.Future: 546.
     implementation.  (Contributed by Yury Selivanov in bpo-27041(3).)

   * New *note loop.get_exception_handler(): 617. method to get the
     current exception handler.  (Contributed by Yury Selivanov in
     bpo-27040(4).)

   * New *note StreamReader.readuntil(): 618. method to read data from
     the stream until a separator bytes sequence appears.  (Contributed
     by Mark Korenberg.)

   * The performance of *note StreamReader.readexactly(): 619. has been
     improved.  (Contributed by Mark Korenberg in bpo-28370(5).)

   * The *note loop.getaddrinfo(): 59c. method is optimized to avoid
     calling the system ‘getaddrinfo’ function if the address is already
     resolved.  (Contributed by A. Jesse Jiryu Davis.)

   * The *note loop.stop(): 61a. method has been changed to stop the
     loop immediately after the current iteration.  Any new callbacks
     scheduled as a result of the last iteration will be discarded.
     (Contributed by Guido van Rossum in bpo-25593(6).)

   * ‘Future.set_exception’ will now raise *note TypeError: 1fe. when
     passed an instance of the *note StopIteration: 582. exception.
     (Contributed by Chris Angelico in bpo-26221(7).)

   * New *note loop.connect_accepted_socket(): 46d. method to be used by
     servers that accept connections outside of asyncio, but that use
     asyncio to handle them.  (Contributed by Jim Fulton in
     bpo-27392(8).)

   * ‘TCP_NODELAY’ flag is now set for all TCP transports by default.
     (Contributed by Yury Selivanov in bpo-27456(9).)

   * New *note loop.shutdown_asyncgens(): 61b. to properly close pending
     asynchronous generators before closing the loop.  (Contributed by
     Yury Selivanov in bpo-28003(10).)

   * *note Future: 546. and *note Task: 2e0. classes now have an
     optimized C implementation which makes asyncio code up to 30%
     faster.  (Contributed by Yury Selivanov and INADA Naoki in
     bpo-26081(11) and bpo-28544(12).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28613

   (2) https://github.com/MagicStack/uvloop

   (3) https://bugs.python.org/issue27041

   (4) https://bugs.python.org/issue27040

   (5) https://bugs.python.org/issue28370

   (6) https://bugs.python.org/issue25593

   (7) https://bugs.python.org/issue26221

   (8) https://bugs.python.org/issue27392

   (9) https://bugs.python.org/issue27456

   (10) https://bugs.python.org/issue28003

   (11) https://bugs.python.org/issue26081

   (12) https://bugs.python.org/issue28544


File: python.info,  Node: binascii<2>,  Next: cmath,  Prev: asyncio<5>,  Up: Improved Modules<4>

1.4.5.4 binascii
................

The *note b2a_base64(): 61d. function now accepts an optional `newline'
keyword argument to control whether the newline character is appended to
the return value.  (Contributed by Victor Stinner in bpo-25357(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25357


File: python.info,  Node: cmath,  Next: collections<4>,  Prev: binascii<2>,  Up: Improved Modules<4>

1.4.5.5 cmath
.............

The new *note cmath.tau: 61f. (`τ') constant has been added.
(Contributed by Lisa Roach in bpo-12345(1), see PEP 628(2) for details.)

New constants: *note cmath.inf: 620. and *note cmath.nan: 621. to match
*note math.inf: 622. and *note math.nan: 623, and also *note cmath.infj:
624. and *note cmath.nanj: 625. to match the format used by complex
repr.  (Contributed by Mark Dickinson in bpo-23229(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12345

   (2) https://www.python.org/dev/peps/pep-0628

   (3) https://bugs.python.org/issue23229


File: python.info,  Node: collections<4>,  Next: concurrent futures<3>,  Prev: cmath,  Up: Improved Modules<4>

1.4.5.6 collections
...................

The new *note Collection: 627. abstract base class has been added to
represent sized iterable container classes.  (Contributed by Ivan
Levkivskyi, docs by Neil Girdhar in bpo-27598(1).)

The new *note Reversible: 628. abstract base class represents iterable
classes that also provide the *note __reversed__(): 629. method.
(Contributed by Ivan Levkivskyi in bpo-25987(2).)

The new *note AsyncGenerator: 62a. abstract base class represents
asynchronous generators.  (Contributed by Yury Selivanov in
bpo-28720(3).)

The *note namedtuple(): 1a1. function now accepts an optional keyword
argument `module', which, when specified, is used for the ‘__module__’
attribute of the returned named tuple class.  (Contributed by Raymond
Hettinger in bpo-17941(4).)

The `verbose' and `rename' arguments for *note namedtuple(): 1a1. are
now keyword-only.  (Contributed by Raymond Hettinger in bpo-25628(5).)

Recursive *note collections.deque: 62b. instances can now be pickled.
(Contributed by Serhiy Storchaka in bpo-26482(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27598

   (2) https://bugs.python.org/issue25987

   (3) https://bugs.python.org/issue28720

   (4) https://bugs.python.org/issue17941

   (5) https://bugs.python.org/issue25628

   (6) https://bugs.python.org/issue26482


File: python.info,  Node: concurrent futures<3>,  Next: contextlib<2>,  Prev: collections<4>,  Up: Improved Modules<4>

1.4.5.7 concurrent.futures
..........................

The *note ThreadPoolExecutor: 18c. class constructor now accepts an
optional `thread_name_prefix' argument to make it possible to customize
the names of the threads created by the pool.  (Contributed by Gregory
P. Smith in bpo-27664(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27664


File: python.info,  Node: contextlib<2>,  Next: datetime<4>,  Prev: concurrent futures<3>,  Up: Improved Modules<4>

1.4.5.8 contextlib
..................

The *note contextlib.AbstractContextManager: 62e. class has been added
to provide an abstract base class for context managers.  It provides a
sensible default implementation for ‘__enter__()’ which returns ‘self’
and leaves ‘__exit__()’ an abstract method.  A matching class has been
added to the *note typing: 122. module as *note typing.ContextManager:
62f.  (Contributed by Brett Cannon in bpo-25609(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25609


File: python.info,  Node: datetime<4>,  Next: decimal<2>,  Prev: contextlib<2>,  Up: Improved Modules<4>

1.4.5.9 datetime
................

The *note datetime: 1a0. and *note time: 5ed. classes have the new
‘fold’ attribute used to disambiguate local time when necessary.  Many
functions in the *note datetime: 30. have been updated to support local
time disambiguation.  See *note Local Time Disambiguation: 5c9. section
for more information.  (Contributed by Alexander Belopolsky in
bpo-24773(1).)

The *note datetime.strftime(): 631. and *note date.strftime(): 632.
methods now support ISO 8601 date directives ‘%G’, ‘%u’ and ‘%V’.
(Contributed by Ashley Anderson in bpo-12006(2).)

The *note datetime.isoformat(): 487. function now accepts an optional
`timespec' argument that specifies the number of additional components
of the time value to include.  (Contributed by Alessandro Cucci and
Alexander Belopolsky in bpo-19475(3).)

The *note datetime.combine(): 633. now accepts an optional `tzinfo'
argument.  (Contributed by Alexander Belopolsky in bpo-27661(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24773

   (2) https://bugs.python.org/issue12006

   (3) https://bugs.python.org/issue19475

   (4) https://bugs.python.org/issue27661


File: python.info,  Node: decimal<2>,  Next: distutils<3>,  Prev: datetime<4>,  Up: Improved Modules<4>

1.4.5.10 decimal
................

New *note Decimal.as_integer_ratio(): 635. method that returns a pair
‘(n, d)’ of integers that represent the given *note Decimal: 2c0.
instance as a fraction, in lowest terms and with a positive denominator:

     >>> Decimal('-3.14').as_integer_ratio()
     (-157, 50)

(Contributed by Stefan Krah amd Mark Dickinson in bpo-25928(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25928


File: python.info,  Node: distutils<3>,  Next: email,  Prev: decimal<2>,  Up: Improved Modules<4>

1.4.5.11 distutils
..................

The ‘default_format’ attribute has been removed from
‘distutils.command.sdist.sdist’ and the ‘formats’ attribute defaults to
‘['gztar']’.  Although not anticipated, any code relying on the presence
of ‘default_format’ may need to be adapted.  See bpo-27819(1) for more
details.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27819


File: python.info,  Node: email,  Next: encodings,  Prev: distutils<3>,  Up: Improved Modules<4>

1.4.5.12 email
..............

The new email API, enabled via the `policy' keyword to various
constructors, is no longer provisional.  The *note email: 67.
documentation has been reorganized and rewritten to focus on the new
API, while retaining the old documentation for the legacy API.
(Contributed by R. David Murray in bpo-24277(1).)

The *note email.mime: 71. classes now all accept an optional `policy'
keyword.  (Contributed by Berker Peksag in bpo-27331(2).)

The *note DecodedGenerator: 638. now supports the `policy' keyword.

There is a new *note policy: 73. attribute, *note message_factory: 639,
that controls what class is used by default when the parser creates new
message objects.  For the *note email.policy.compat32: 63a. policy this
is *note Message: 63b, for the new policies it is *note EmailMessage:
63c.  (Contributed by R. David Murray in bpo-20476(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24277

   (2) https://bugs.python.org/issue27331

   (3) https://bugs.python.org/issue20476


File: python.info,  Node: encodings,  Next: enum<3>,  Prev: email,  Up: Improved Modules<4>

1.4.5.13 encodings
..................

On Windows, added the ‘'oem'’ encoding to use ‘CP_OEMCP’, and the
‘'ansi'’ alias for the existing ‘'mbcs'’ encoding, which uses the
‘CP_ACP’ code page.  (Contributed by Steve Dower in bpo-27959(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27959


File: python.info,  Node: enum<3>,  Next: faulthandler,  Prev: encodings,  Up: Improved Modules<4>

1.4.5.14 enum
.............

Two new enumeration base classes have been added to the *note enum: 79.
module: *note Flag: 63f. and ‘IntFlags’.  Both are used to define
constants that can be combined using the bitwise operators.
(Contributed by Ethan Furman in bpo-23591(1).)

Many standard library modules have been updated to use the ‘IntFlags’
class for their constants.

The new *note enum.auto: 640. value can be used to assign values to enum
members automatically:

     >>> from enum import Enum, auto
     >>> class Color(Enum):
     ...     red = auto()
     ...     blue = auto()
     ...     green = auto()
     ...
     >>> list(Color)
     [<Color.red: 1>, <Color.blue: 2>, <Color.green: 3>]

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23591


File: python.info,  Node: faulthandler,  Next: fileinput,  Prev: enum<3>,  Up: Improved Modules<4>

1.4.5.15 faulthandler
.....................

On Windows, the *note faulthandler: 7b. module now installs a handler
for Windows exceptions: see *note faulthandler.enable(): 642.
(Contributed by Victor Stinner in bpo-23848(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23848


File: python.info,  Node: fileinput,  Next: hashlib<2>,  Prev: faulthandler,  Up: Improved Modules<4>

1.4.5.16 fileinput
..................

*note hook_encoded(): 644. now supports the `errors' argument.
(Contributed by Joseph Hackman in bpo-25788(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25788


File: python.info,  Node: hashlib<2>,  Next: http client<2>,  Prev: fileinput,  Up: Improved Modules<4>

1.4.5.17 hashlib
................

*note hashlib: 8c. supports OpenSSL 1.1.0.  The minimum recommend
version is 1.0.2.  (Contributed by Christian Heimes in bpo-26470(1).)

BLAKE2 hash functions were added to the module.  *note blake2b(): 646.
and *note blake2s(): 647. are always available and support the full
feature set of BLAKE2.  (Contributed by Christian Heimes in bpo-26798(2)
based on code by Dmitry Chestnykh and Samuel Neves.  Documentation
written by Dmitry Chestnykh.)

The SHA-3 hash functions ‘sha3_224()’, ‘sha3_256()’, ‘sha3_384()’,
‘sha3_512()’, and SHAKE hash functions ‘shake_128()’ and ‘shake_256()’
were added.  (Contributed by Christian Heimes in bpo-16113(3).  Keccak
Code Package by Guido Bertoni, Joan Daemen, Michaël Peeters, Gilles Van
Assche, and Ronny Van Keer.)

The password-based key derivation function *note scrypt(): 5cd. is now
available with OpenSSL 1.1.0 and newer.  (Contributed by Christian
Heimes in bpo-27928(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26470

   (2) https://bugs.python.org/issue26798

   (3) https://bugs.python.org/issue16113

   (4) https://bugs.python.org/issue27928


File: python.info,  Node: http client<2>,  Next: idlelib and IDLE<2>,  Prev: hashlib<2>,  Up: Improved Modules<4>

1.4.5.18 http.client
....................

*note HTTPConnection.request(): 649. and *note endheaders(): 64a. both
now support chunked encoding request bodies.  (Contributed by Demian
Brecht and Rolf Krahl in bpo-12319(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12319


File: python.info,  Node: idlelib and IDLE<2>,  Next: importlib<4>,  Prev: http client<2>,  Up: Improved Modules<4>

1.4.5.19 idlelib and IDLE
.........................

The idlelib package is being modernized and refactored to make IDLE look
and work better and to make the code easier to understand, test, and
improve.  Part of making IDLE look better, especially on Linux and Mac,
is using ttk widgets, mostly in the dialogs.  As a result, IDLE no
longer runs with tcl/tk 8.4.  It now requires tcl/tk 8.5 or 8.6.  We
recommend running the latest release of either.

‘Modernizing’ includes renaming and consolidation of idlelib modules.
The renaming of files with partial uppercase names is similar to the
renaming of, for instance, Tkinter and TkFont to tkinter and
tkinter.font in 3.0.  As a result, imports of idlelib files that worked
in 3.5 will usually not work in 3.6.  At least a module name change will
be needed (see idlelib/README.txt), sometimes more.  (Name changes
contributed by Al Swiegart and Terry Reedy in bpo-24225(1).  Most
idlelib patches since have been and will be part of the process.)

In compensation, the eventual result with be that some idlelib classes
will be easier to use, with better APIs and docstrings explaining them.
Additional useful information will be added to idlelib when available.

New in 3.6.2:

Multiple fixes for autocompletion.  (Contributed by Louie Lu in
bpo-15786(2).)

New in 3.6.3:

Module Browser (on the File menu, formerly called Class Browser), now
displays nested functions and classes in addition to top-level functions
and classes.  (Contributed by Guilherme Polo, Cheryl Sabella, and Terry
Jan Reedy in bpo-1612262(3).)

The IDLE features formerly implemented as extensions have been
reimplemented as normal features.  Their settings have been moved from
the Extensions tab to other dialog tabs.  (Contributed by Charles
Wohlganger and Terry Jan Reedy in bpo-27099(4).)

The Settings dialog (Options, Configure IDLE) has been partly rewritten
to improve both appearance and function.  (Contributed by Cheryl Sabella
and Terry Jan Reedy in multiple issues.)

New in 3.6.4:

The font sample now includes a selection of non-Latin characters so that
users can better see the effect of selecting a particular font.
(Contributed by Terry Jan Reedy in bpo-13802(5).)  The sample can be
edited to include other characters.  (Contributed by Serhiy Storchaka in
bpo-31860(6).)

New in 3.6.6:

Editor code context option revised.  Box displays all context lines up
to maxlines.  Clicking on a context line jumps the editor to that line.
Context colors for custom themes is added to Highlights tab of Settings
dialog.  (Contributed by Cheryl Sabella and Terry Jan Reedy in
bpo-33642(7), bpo-33768(8), and bpo-33679(9).)

On Windows, a new API call tells Windows that tk scales for DPI. On
Windows 8.1+ or 10, with DPI compatibility properties of the Python
binary unchanged, and a monitor resolution greater than 96 DPI, this
should make text and lines sharper.  It should otherwise have no effect.
(Contributed by Terry Jan Reedy in bpo-33656(10).)

New in 3.6.7:

Output over N lines (50 by default) is squeezed down to a button.  N can
be changed in the PyShell section of the General page of the Settings
dialog.  Fewer, but possibly extra long, lines can be squeezed by right
clicking on the output.  Squeezed output can be expanded in place by
double-clicking the button or into the clipboard or a separate window by
right-clicking the button.  (Contributed by Tal Einat in
bpo-1529353(11).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24225

   (2) https://bugs.python.org/issue15786

   (3) https://bugs.python.org/issue1612262

   (4) https://bugs.python.org/issue27099

   (5) https://bugs.python.org/issue13802

   (6) https://bugs.python.org/issue31860

   (7) https://bugs.python.org/issue33642

   (8) https://bugs.python.org/issue33768

   (9) https://bugs.python.org/issue33679

   (10) https://bugs.python.org/issue33656

   (11) https://bugs.python.org/issue1529353


File: python.info,  Node: importlib<4>,  Next: inspect<3>,  Prev: idlelib and IDLE<2>,  Up: Improved Modules<4>

1.4.5.20 importlib
..................

Import now raises the new exception *note ModuleNotFoundError: 4a1.
(subclass of *note ImportError: 16c.) when it cannot find a module.
Code that current checks for ‘ImportError’ (in try-except) will still
work.  (Contributed by Eric Snow in bpo-15767(1).)

*note importlib.util.LazyLoader: 64d. now calls *note create_module():
64e. on the wrapped loader, removing the restriction that *note
importlib.machinery.BuiltinImporter: 64f. and *note
importlib.machinery.ExtensionFileLoader: 650. couldn’t be used with
*note importlib.util.LazyLoader: 64d.

*note importlib.util.cache_from_source(): 651, *note
importlib.util.source_from_cache(): 652, and *note
importlib.util.spec_from_file_location(): 653. now accept a *note
path-like object: 472.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15767


File: python.info,  Node: inspect<3>,  Next: json,  Prev: importlib<4>,  Up: Improved Modules<4>

1.4.5.21 inspect
................

The *note inspect.signature(): 655. function now reports the implicit
‘.0’ parameters generated by the compiler for comprehension and
generator expression scopes as if they were positional-only parameters
called ‘implicit0’.  (Contributed by Jelle Zijlstra in bpo-19611(1).)

To reduce code churn when upgrading from Python 2.7 and the legacy *note
inspect.getargspec(): 656. API, the previously documented deprecation of
*note inspect.getfullargspec(): 657. has been reversed.  While this
function is convenient for single/source Python 2/3 code bases, the
richer *note inspect.signature(): 655. interface remains the recommended
approach for new code.  (Contributed by Nick Coghlan in bpo-27172(2))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19611

   (2) https://bugs.python.org/issue27172


File: python.info,  Node: json,  Next: logging<3>,  Prev: inspect<3>,  Up: Improved Modules<4>

1.4.5.22 json
.............

*note json.load(): 659. and *note json.loads(): 225. now support binary
input.  Encoded JSON should be represented using either UTF-8, UTF-16,
or UTF-32.  (Contributed by Serhiy Storchaka in bpo-17909(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17909


File: python.info,  Node: logging<3>,  Next: math<4>,  Prev: json,  Up: Improved Modules<4>

1.4.5.23 logging
................

The new *note WatchedFileHandler.reopenIfNeeded(): 65b. method has been
added to add the ability to check if the log file needs to be reopened.
(Contributed by Marian Horban in bpo-24884(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24884


File: python.info,  Node: math<4>,  Next: multiprocessing<4>,  Prev: logging<3>,  Up: Improved Modules<4>

1.4.5.24 math
.............

The tau (`τ') constant has been added to the *note math: b1. and *note
cmath: 18. modules.  (Contributed by Lisa Roach in bpo-12345(1), see PEP
628(2) for details.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12345

   (2) https://www.python.org/dev/peps/pep-0628


File: python.info,  Node: multiprocessing<4>,  Next: os<4>,  Prev: math<4>,  Up: Improved Modules<4>

1.4.5.25 multiprocessing
........................

*note Proxy Objects: 65e. returned by ‘multiprocessing.Manager()’ can
now be nested.  (Contributed by Davin Potts in bpo-6766(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue6766


File: python.info,  Node: os<4>,  Next: pathlib<4>,  Prev: multiprocessing<4>,  Up: Improved Modules<4>

1.4.5.26 os
...........

See the summary of *note PEP 519: 5c8. for details on how the *note os:
c4. and *note os.path: c5. modules now support *note path-like objects:
472.

*note scandir(): 389. now supports *note bytes: 172. paths on Windows.

A new *note close(): 660. method allows explicitly closing a *note
scandir(): 389. iterator.  The *note scandir(): 389. iterator now
supports the *note context manager: 661. protocol.  If a ‘scandir()’
iterator is neither exhausted nor explicitly closed a *note
ResourceWarning: 5cb. will be emitted in its destructor.  (Contributed
by Serhiy Storchaka in bpo-25994(1).)

On Linux, *note os.urandom(): 5cc. now blocks until the system urandom
entropy pool is initialized to increase the security.  See the PEP
524(2) for the rationale.

The Linux ‘getrandom()’ syscall (get random bytes) is now exposed as the
new *note os.getrandom(): 662. function.  (Contributed by Victor
Stinner, part of the PEP 524(3))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25994

   (2) https://www.python.org/dev/peps/pep-0524

   (3) https://www.python.org/dev/peps/pep-0524


File: python.info,  Node: pathlib<4>,  Next: pdb<3>,  Prev: os<4>,  Up: Improved Modules<4>

1.4.5.27 pathlib
................

*note pathlib: c8. now supports *note path-like objects: 472.
(Contributed by Brett Cannon in bpo-27186(1).)

See the summary of *note PEP 519: 5c8. for details.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27186


File: python.info,  Node: pdb<3>,  Next: pickle<2>,  Prev: pathlib<4>,  Up: Improved Modules<4>

1.4.5.28 pdb
............

The *note Pdb: 1d3. class constructor has a new optional `readrc'
argument to control whether ‘.pdbrc’ files should be read.


File: python.info,  Node: pickle<2>,  Next: pickletools,  Prev: pdb<3>,  Up: Improved Modules<4>

1.4.5.29 pickle
...............

Objects that need ‘__new__’ called with keyword arguments can now be
pickled using *note pickle protocols: 666. older than protocol version
4.  Protocol version 4 already supports this case.  (Contributed by
Serhiy Storchaka in bpo-24164(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24164


File: python.info,  Node: pickletools,  Next: pydoc<3>,  Prev: pickle<2>,  Up: Improved Modules<4>

1.4.5.30 pickletools
....................

*note pickletools.dis(): 668. now outputs the implicit memo index for
the ‘MEMOIZE’ opcode.  (Contributed by Serhiy Storchaka in
bpo-25382(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25382


File: python.info,  Node: pydoc<3>,  Next: random<2>,  Prev: pickletools,  Up: Improved Modules<4>

1.4.5.31 pydoc
..............

The *note pydoc: d9. module has learned to respect the ‘MANPAGER’
environment variable.  (Contributed by Matthias Klose in bpo-8637(1).)

*note help(): 175. and *note pydoc: d9. can now list named tuple fields
in the order they were defined rather than alphabetically.  (Contributed
by Raymond Hettinger in bpo-24879(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8637

   (2) https://bugs.python.org/issue24879


File: python.info,  Node: random<2>,  Next: re<2>,  Prev: pydoc<3>,  Up: Improved Modules<4>

1.4.5.32 random
...............

The new *note choices(): 66b. function returns a list of elements of
specified size from the given population with optional weights.
(Contributed by Raymond Hettinger in bpo-18844(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18844


File: python.info,  Node: re<2>,  Next: readline,  Prev: random<2>,  Up: Improved Modules<4>

1.4.5.33 re
...........

Added support of modifier spans in regular expressions.  Examples:
‘'(?i:p)ython'’ matches ‘'python'’ and ‘'Python'’, but not ‘'PYTHON'’;
‘'(?i)g(?-i:v)r'’ matches ‘'GvR'’ and ‘'gvr'’, but not ‘'GVR'’.
(Contributed by Serhiy Storchaka in bpo-433028(1).)

Match object groups can be accessed by ‘__getitem__’, which is
equivalent to ‘group()’.  So ‘mo['name']’ is now equivalent to
‘mo.group('name')’.  (Contributed by Eric Smith in bpo-24454(2).)

‘Match’ objects now support *note index-like objects: 2c2. as group
indices.  (Contributed by Jeroen Demeyer and Xiang Zhang in
bpo-27177(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue433028

   (2) https://bugs.python.org/issue24454

   (3) https://bugs.python.org/issue27177


File: python.info,  Node: readline,  Next: rlcompleter,  Prev: re<2>,  Up: Improved Modules<4>

1.4.5.34 readline
.................

Added *note set_auto_history(): 66e. to enable or disable automatic
addition of input to the history list.  (Contributed by Tyler Crompton
in bpo-26870(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26870


File: python.info,  Node: rlcompleter,  Next: shlex<2>,  Prev: readline,  Up: Improved Modules<4>

1.4.5.35 rlcompleter
....................

Private and special attribute names now are omitted unless the prefix
starts with underscores.  A space or a colon is added after some
completed keywords.  (Contributed by Serhiy Storchaka in bpo-25011(1)
and bpo-25209(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25011

   (2) https://bugs.python.org/issue25209


File: python.info,  Node: shlex<2>,  Next: site,  Prev: rlcompleter,  Up: Improved Modules<4>

1.4.5.36 shlex
..............

The *note shlex: 671. has much *note improved shell compatibility: 672.
through the new `punctuation_chars' argument to control which characters
are treated as punctuation.  (Contributed by Vinay Sajip in
bpo-1521950(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1521950


File: python.info,  Node: site,  Next: sqlite3<2>,  Prev: shlex<2>,  Up: Improved Modules<4>

1.4.5.37 site
.............

When specifying paths to add to *note sys.path: 260. in a ‘.pth’ file,
you may now specify file paths on top of directories (e.g.  zip files).
(Contributed by Wolfgang Langner in bpo-26587(1)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26587


File: python.info,  Node: sqlite3<2>,  Next: socket<5>,  Prev: site,  Up: Improved Modules<4>

1.4.5.38 sqlite3
................

*note sqlite3.Cursor.lastrowid: 675. now supports the ‘REPLACE’
statement.  (Contributed by Alex LordThorsen in bpo-16864(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16864


File: python.info,  Node: socket<5>,  Next: socketserver<2>,  Prev: sqlite3<2>,  Up: Improved Modules<4>

1.4.5.39 socket
...............

The *note ioctl(): 677. function now supports the *note
SIO_LOOPBACK_FAST_PATH: 678. control code.  (Contributed by Daniel
Stokes in bpo-26536(1).)

The *note getsockopt(): 679. constants ‘SO_DOMAIN’, ‘SO_PROTOCOL’,
‘SO_PEERSEC’, and ‘SO_PASSSEC’ are now supported.  (Contributed by
Christian Heimes in bpo-26907(2).)

The *note setsockopt(): 67a. now supports the ‘setsockopt(level,
optname, None, optlen: int)’ form.  (Contributed by Christian Heimes in
bpo-27744(3).)

The socket module now supports the address family *note AF_ALG: 67b. to
interface with Linux Kernel crypto API. ‘ALG_*’, ‘SOL_ALG’ and *note
sendmsg_afalg(): 67c. were added.  (Contributed by Christian Heimes in
bpo-27744(4) with support from Victor Stinner.)

New Linux constants ‘TCP_USER_TIMEOUT’ and ‘TCP_CONGESTION’ were added.
(Contributed by Omar Sandoval, issue:‘26273’).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26536

   (2) https://bugs.python.org/issue26907

   (3) https://bugs.python.org/issue27744

   (4) https://bugs.python.org/issue27744


File: python.info,  Node: socketserver<2>,  Next: ssl<4>,  Prev: socket<5>,  Up: Improved Modules<4>

1.4.5.40 socketserver
.....................

Servers based on the *note socketserver: f0. module, including those
defined in *note http.server: 96, *note xmlrpc.server: 149. and *note
wsgiref.simple_server: 138, now support the *note context manager: 661.
protocol.  (Contributed by Aviv Palivoda in bpo-26404(1).)

The ‘wfile’ attribute of *note StreamRequestHandler: 67e. classes now
implements the *note io.BufferedIOBase: 67f. writable interface.  In
particular, calling *note write(): 680. is now guaranteed to send the
data in full.  (Contributed by Martin Panter in bpo-26721(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26404

   (2) https://bugs.python.org/issue26721


File: python.info,  Node: ssl<4>,  Next: statistics<2>,  Prev: socketserver<2>,  Up: Improved Modules<4>

1.4.5.41 ssl
............

*note ssl: f3. supports OpenSSL 1.1.0.  The minimum recommend version is
1.0.2.  (Contributed by Christian Heimes in bpo-26470(1).)

3DES has been removed from the default cipher suites and ChaCha20
Poly1305 cipher suites have been added.  (Contributed by Christian
Heimes in bpo-27850(2) and bpo-27766(3).)

*note SSLContext: 4ea. has better default configuration for options and
ciphers.  (Contributed by Christian Heimes in bpo-28043(4).)

SSL session can be copied from one client-side connection to another
with the new *note SSLSession: 682. class.  TLS session resumption can
speed up the initial handshake, reduce latency and improve performance
(Contributed by Christian Heimes in bpo-19500(5) based on a draft by
Alex Warhawk.)

The new *note get_ciphers(): 683. method can be used to get a list of
enabled ciphers in order of cipher priority.

All constants and flags have been converted to *note IntEnum: 684. and
‘IntFlags’.  (Contributed by Christian Heimes in bpo-28025(6).)

Server and client-side specific TLS protocols for *note SSLContext: 4ea.
were added.  (Contributed by Christian Heimes in bpo-28085(7).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26470

   (2) https://bugs.python.org/issue27850

   (3) https://bugs.python.org/issue27766

   (4) https://bugs.python.org/issue28043

   (5) https://bugs.python.org/issue19500

   (6) https://bugs.python.org/issue28025

   (7) https://bugs.python.org/issue28085


File: python.info,  Node: statistics<2>,  Next: struct,  Prev: ssl<4>,  Up: Improved Modules<4>

1.4.5.42 statistics
...................

A new *note harmonic_mean(): 686. function has been added.  (Contributed
by Steven D’Aprano in bpo-27181(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27181


File: python.info,  Node: struct,  Next: subprocess<2>,  Prev: statistics<2>,  Up: Improved Modules<4>

1.4.5.43 struct
...............

*note struct: f8. now supports IEEE 754 half-precision floats via the
‘'e'’ format specifier.  (Contributed by Eli Stevens, Mark Dickinson in
bpo-11734(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11734


File: python.info,  Node: subprocess<2>,  Next: sys<5>,  Prev: struct,  Up: Improved Modules<4>

1.4.5.44 subprocess
...................

*note subprocess.Popen: 3db. destructor now emits a *note
ResourceWarning: 5cb. warning if the child process is still running.
Use the context manager protocol (‘with proc: ...’) or explicitly call
the *note wait(): 689. method to read the exit status of the child
process.  (Contributed by Victor Stinner in bpo-26741(1).)

The *note subprocess.Popen: 3db. constructor and all functions that pass
arguments through to it now accept `encoding' and `errors' arguments.
Specifying either of these will enable text mode for the `stdin',
`stdout' and `stderr' streams.  (Contributed by Steve Dower in
bpo-6135(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26741

   (2) https://bugs.python.org/issue6135


File: python.info,  Node: sys<5>,  Next: telnetlib,  Prev: subprocess<2>,  Up: Improved Modules<4>

1.4.5.45 sys
............

The new *note getfilesystemencodeerrors(): 68b. function returns the
name of the error mode used to convert between Unicode filenames and
bytes filenames.  (Contributed by Steve Dower in bpo-27781(1).)

On Windows the return value of the *note getwindowsversion(): 68c.
function now includes the `platform_version' field which contains the
accurate major version, minor version and build number of the current
operating system, rather than the version that is being emulated for the
process (Contributed by Steve Dower in bpo-27932(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27781

   (2) https://bugs.python.org/issue27932


File: python.info,  Node: telnetlib,  Next: time<4>,  Prev: sys<5>,  Up: Improved Modules<4>

1.4.5.46 telnetlib
..................

*note Telnet: 68e. is now a context manager (contributed by Stéphane
Wirtel in bpo-25485(1)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25485


File: python.info,  Node: time<4>,  Next: timeit,  Prev: telnetlib,  Up: Improved Modules<4>

1.4.5.47 time
.............

The *note struct_time: 690. attributes ‘tm_gmtoff’ and ‘tm_zone’ are now
available on all platforms.


File: python.info,  Node: timeit,  Next: tkinter<3>,  Prev: time<4>,  Up: Improved Modules<4>

1.4.5.48 timeit
...............

The new *note Timer.autorange(): 692. convenience method has been added
to call *note Timer.timeit(): 693. repeatedly so that the total run time
is greater or equal to 200 milliseconds.  (Contributed by Steven
D’Aprano in bpo-6422(1).)

*note timeit: 10d. now warns when there is substantial (4x) variance
between best and worst times.  (Contributed by Serhiy Storchaka in
bpo-23552(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue6422

   (2) https://bugs.python.org/issue23552


File: python.info,  Node: tkinter<3>,  Next: traceback,  Prev: timeit,  Up: Improved Modules<4>

1.4.5.49 tkinter
................

Added methods ‘trace_add()’, ‘trace_remove()’ and ‘trace_info()’ in the
‘tkinter.Variable’ class.  They replace old methods ‘trace_variable()’,
‘trace()’, ‘trace_vdelete()’ and ‘trace_vinfo()’ that use obsolete Tcl
commands and might not work in future versions of Tcl.  (Contributed by
Serhiy Storchaka in bpo-22115(1)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22115


File: python.info,  Node: traceback,  Next: tracemalloc<3>,  Prev: tkinter<3>,  Up: Improved Modules<4>

1.4.5.50 traceback
..................

Both the traceback module and the interpreter’s builtin exception
display now abbreviate long sequences of repeated lines in tracebacks as
shown in the following example:

     >>> def f(): f()
     ...
     >>> f()
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
       File "<stdin>", line 1, in f
       File "<stdin>", line 1, in f
       File "<stdin>", line 1, in f
       [Previous line repeated 995 more times]
     RecursionError: maximum recursion depth exceeded

(Contributed by Emanuel Barry in bpo-26823(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26823


File: python.info,  Node: tracemalloc<3>,  Next: typing<4>,  Prev: traceback,  Up: Improved Modules<4>

1.4.5.51 tracemalloc
....................

The *note tracemalloc: 11d. module now supports tracing memory
allocations in multiple different address spaces.

The new *note DomainFilter: 697. filter class has been added to filter
block traces by their address space (domain).

(Contributed by Victor Stinner in bpo-26588(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26588


File: python.info,  Node: typing<4>,  Next: unicodedata<4>,  Prev: tracemalloc<3>,  Up: Improved Modules<4>

1.4.5.52 typing
...............

Since the *note typing: 122. module is *note provisional: 454, all
changes introduced in Python 3.6 have also been backported to Python
3.5.x.

The *note typing: 122. module has a much improved support for generic
type aliases.  For example ‘Dict[str, Tuple[S, T]]’ is now a valid type
annotation.  (Contributed by Guido van Rossum in Github #195(1).)

The *note typing.ContextManager: 62f. class has been added for
representing *note contextlib.AbstractContextManager: 62e.  (Contributed
by Brett Cannon in bpo-25609(2).)

The *note typing.Collection: 699. class has been added for representing
*note collections.abc.Collection: 627.  (Contributed by Ivan Levkivskyi
in bpo-27598(3).)

The *note typing.ClassVar: 69a. type construct has been added to mark
class variables.  As introduced in PEP 526(4), a variable annotation
wrapped in ClassVar indicates that a given attribute is intended to be
used as a class variable and should not be set on instances of that
class.  (Contributed by Ivan Levkivskyi in Github #280(5).)

A new *note TYPE_CHECKING: 69b. constant that is assumed to be ‘True’ by
the static type checkers, but is ‘False’ at runtime.  (Contributed by
Guido van Rossum in Github #230(6).)

A new *note NewType(): 69c. helper function has been added to create
lightweight distinct types for annotations:

     from typing import NewType

     UserId = NewType('UserId', int)
     some_id = UserId(524313)

The static type checker will treat the new type as if it were a subclass
of the original type.  (Contributed by Ivan Levkivskyi in Github
#189(7).)

   ---------- Footnotes ----------

   (1) https://github.com/python/typing/pull/195

   (2) https://bugs.python.org/issue25609

   (3) https://bugs.python.org/issue27598

   (4) https://www.python.org/dev/peps/pep-0526

   (5) https://github.com/python/typing/pull/280

   (6) https://github.com/python/typing/issues/230

   (7) https://github.com/python/typing/issues/189


File: python.info,  Node: unicodedata<4>,  Next: unittest mock<2>,  Prev: typing<4>,  Up: Improved Modules<4>

1.4.5.53 unicodedata
....................

The *note unicodedata: 123. module now uses data from Unicode 9.0.0(1).
(Contributed by Benjamin Peterson.)

   ---------- Footnotes ----------

   (1) http://unicode.org/versions/Unicode9.0.0/


File: python.info,  Node: unittest mock<2>,  Next: urllib request,  Prev: unicodedata<4>,  Up: Improved Modules<4>

1.4.5.54 unittest.mock
......................

The *note Mock: 373. class has the following improvements:

   * Two new methods, *note Mock.assert_called(): 69f. and *note
     Mock.assert_called_once(): 6a0. to check if the mock object was
     called.  (Contributed by Amit Saha in bpo-26323(1).)

   * The *note Mock.reset_mock(): 6a1. method now has two optional
     keyword only arguments: `return_value' and `side_effect'.
     (Contributed by Kushal Das in bpo-21271(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26323

   (2) https://bugs.python.org/issue21271


File: python.info,  Node: urllib request,  Next: urllib robotparser,  Prev: unittest mock<2>,  Up: Improved Modules<4>

1.4.5.55 urllib.request
.......................

If a HTTP request has a file or iterable body (other than a bytes
object) but no ‘Content-Length’ header, rather than throwing an error,
‘AbstractHTTPHandler’ now falls back to use chunked transfer encoding.
(Contributed by Demian Brecht and Rolf Krahl in bpo-12319(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12319


File: python.info,  Node: urllib robotparser,  Next: venv<3>,  Prev: urllib request,  Up: Improved Modules<4>

1.4.5.56 urllib.robotparser
...........................

*note RobotFileParser: 6a4. now supports the ‘Crawl-delay’ and
‘Request-rate’ extensions.  (Contributed by Nikolay Bogoychev in
bpo-16099(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16099


File: python.info,  Node: venv<3>,  Next: warnings<2>,  Prev: urllib robotparser,  Up: Improved Modules<4>

1.4.5.57 venv
.............

*note venv: 12e. accepts a new parameter ‘--prompt’.  This parameter
provides an alternative prefix for the virtual environment.  (Proposed
by Łukasz Balcerzak and ported to 3.6 by Stéphane Wirtel in
bpo-22829(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22829


File: python.info,  Node: warnings<2>,  Next: winreg,  Prev: venv<3>,  Up: Improved Modules<4>

1.4.5.58 warnings
.................

A new optional `source' parameter has been added to the *note
warnings.warn_explicit(): 6a7. function: the destroyed object which
emitted a *note ResourceWarning: 5cb.  A `source' attribute has also
been added to ‘warnings.WarningMessage’ (contributed by Victor Stinner
in bpo-26568(1) and bpo-26567(2)).

When a *note ResourceWarning: 5cb. warning is logged, the *note
tracemalloc: 11d. module is now used to try to retrieve the traceback
where the destroyed object was allocated.

Example with the script ‘example.py’:

     import warnings

     def func():
         return open(__file__)

     f = func()
     f = None

Output of the command ‘python3.6 -Wd -X tracemalloc=5 example.py’:

     example.py:7: ResourceWarning: unclosed file <_io.TextIOWrapper name='example.py' mode='r' encoding='UTF-8'>
       f = None
     Object allocated at (most recent call first):
       File "example.py", lineno 4
         return open(__file__)
       File "example.py", lineno 6
         f = func()

The “Object allocated at” traceback is new and is only displayed if
*note tracemalloc: 11d. is tracing Python memory allocations and if the
*note warnings: 12f. module was already imported.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26568

   (2) https://bugs.python.org/issue26567


File: python.info,  Node: winreg,  Next: winsound,  Prev: warnings<2>,  Up: Improved Modules<4>

1.4.5.59 winreg
...............

Added the 64-bit integer type *note REG_QWORD: 6a9.  (Contributed by
Clement Rouault in bpo-23026(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23026


File: python.info,  Node: winsound,  Next: xmlrpc client,  Prev: winreg,  Up: Improved Modules<4>

1.4.5.60 winsound
.................

Allowed keyword arguments to be passed to *note Beep: 6ab, *note
MessageBeep: 6ac, and *note PlaySound: 6ad. (bpo-27982(1)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27982


File: python.info,  Node: xmlrpc client,  Next: zipfile<2>,  Prev: winsound,  Up: Improved Modules<4>

1.4.5.61 xmlrpc.client
......................

The *note xmlrpc.client: 148. module now supports unmarshalling
additional data types used by the Apache XML-RPC implementation for
numerics and ‘None’.  (Contributed by Serhiy Storchaka in bpo-26885(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26885


File: python.info,  Node: zipfile<2>,  Next: zlib,  Prev: xmlrpc client,  Up: Improved Modules<4>

1.4.5.62 zipfile
................

A new *note ZipInfo.from_file(): 6b0. class method allows making a *note
ZipInfo: 6b1. instance from a filesystem file.  A new *note
ZipInfo.is_dir(): 6b2. method can be used to check if the *note ZipInfo:
6b1. instance represents a directory.  (Contributed by Thomas Kluyver in
bpo-26039(1).)

The *note ZipFile.open(): 6b3. method can now be used to write data into
a ZIP file, as well as for extracting data.  (Contributed by Thomas
Kluyver in bpo-26039(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26039

   (2) https://bugs.python.org/issue26039


File: python.info,  Node: zlib,  Prev: zipfile<2>,  Up: Improved Modules<4>

1.4.5.63 zlib
.............

The *note compress(): 6b5. and *note decompress(): 6b6. functions now
accept keyword arguments.  (Contributed by Aviv Palivoda in bpo-26243(1)
and Xiang Zhang in bpo-16764(2) respectively.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26243

   (2) https://bugs.python.org/issue16764


File: python.info,  Node: Optimizations<4>,  Next: Build and C API Changes<2>,  Prev: Improved Modules<4>,  Up: What’s New In Python 3 6

1.4.6 Optimizations
-------------------

   * The Python interpreter now uses a 16-bit wordcode instead of
     bytecode which made a number of opcode optimizations possible.
     (Contributed by Demur Rumed with input and reviews from Serhiy
     Storchaka and Victor Stinner in bpo-26647(1) and bpo-28050(2).)

   * The *note asyncio.Future: 546. class now has an optimized C
     implementation.  (Contributed by Yury Selivanov and INADA Naoki in
     bpo-26081(3).)

   * The *note asyncio.Task: 2e0. class now has an optimized C
     implementation.  (Contributed by Yury Selivanov in bpo-28544(4).)

   * Various implementation improvements in the *note typing: 122.
     module (such as caching of generic types) allow up to 30 times
     performance improvements and reduced memory footprint.

   * The ASCII decoder is now up to 60 times as fast for error handlers
     ‘surrogateescape’, ‘ignore’ and ‘replace’ (Contributed by Victor
     Stinner in bpo-24870(5)).

   * The ASCII and the Latin1 encoders are now up to 3 times as fast for
     the error handler ‘surrogateescape’ (Contributed by Victor Stinner
     in bpo-25227(6)).

   * The UTF-8 encoder is now up to 75 times as fast for error handlers
     ‘ignore’, ‘replace’, ‘surrogateescape’, ‘surrogatepass’
     (Contributed by Victor Stinner in bpo-25267(7)).

   * The UTF-8 decoder is now up to 15 times as fast for error handlers
     ‘ignore’, ‘replace’ and ‘surrogateescape’ (Contributed by Victor
     Stinner in bpo-25301(8)).

   * ‘bytes % args’ is now up to 2 times faster.  (Contributed by Victor
     Stinner in bpo-25349(9)).

   * ‘bytearray % args’ is now between 2.5 and 5 times faster.
     (Contributed by Victor Stinner in bpo-25399(10)).

   * Optimize *note bytes.fromhex(): 43e. and *note bytearray.fromhex():
     43f.: they are now between 2x and 3.5x faster.  (Contributed by
     Victor Stinner in bpo-25401(11)).

   * Optimize ‘bytes.replace(b'', b'.')’ and ‘bytearray.replace(b'',
     b'.')’: up to 80% faster.  (Contributed by Josh Snider in
     bpo-26574(12)).

   * Allocator functions of the *note PyMem_Malloc(): 5ff. domain (*note
     PYMEM_DOMAIN_MEM: 603.) now use the *note pymalloc memory
     allocator: 6b8. instead of ‘malloc()’ function of the C library.
     The pymalloc allocator is optimized for objects smaller or equal to
     512 bytes with a short lifetime, and use ‘malloc()’ for larger
     memory blocks.  (Contributed by Victor Stinner in bpo-26249(13)).

   * *note pickle.load(): 6b9. and *note pickle.loads(): 6ba. are now up
     to 10% faster when deserializing many small objects (Contributed by
     Victor Stinner in bpo-27056(14)).

   * Passing *note keyword arguments: 6bb. to a function has an overhead
     in comparison with passing *note positional arguments: 6bc.  Now in
     extension functions implemented with using Argument Clinic this
     overhead is significantly decreased.  (Contributed by Serhiy
     Storchaka in bpo-27574(15)).

   * Optimized *note glob(): 6bd. and *note iglob(): 6be. functions in
     the *note glob: 88. module; they are now about 3–6 times faster.
     (Contributed by Serhiy Storchaka in bpo-25596(16)).

   * Optimized globbing in *note pathlib: c8. by using *note
     os.scandir(): 389.; it is now about 1.5–4 times faster.
     (Contributed by Serhiy Storchaka in bpo-26032(17)).

   * *note xml.etree.ElementTree: 140. parsing, iteration and deepcopy
     performance has been significantly improved.  (Contributed by
     Serhiy Storchaka in bpo-25638(18), bpo-25873(19), and
     bpo-25869(20).)

   * Creation of *note fractions.Fraction: 2be. instances from floats
     and decimals is now 2 to 3 times faster.  (Contributed by Serhiy
     Storchaka in bpo-25971(21).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26647

   (2) https://bugs.python.org/issue28050

   (3) https://bugs.python.org/issue26081

   (4) https://bugs.python.org/issue28544

   (5) https://bugs.python.org/issue24870

   (6) https://bugs.python.org/issue25227

   (7) https://bugs.python.org/issue25267

   (8) https://bugs.python.org/issue25301

   (9) https://bugs.python.org/issue25349

   (10) https://bugs.python.org/issue25399

   (11) https://bugs.python.org/issue25401

   (12) https://bugs.python.org/issue26574

   (13) https://bugs.python.org/issue26249

   (14) https://bugs.python.org/issue27056

   (15) https://bugs.python.org/issue27574

   (16) https://bugs.python.org/issue25596

   (17) https://bugs.python.org/issue26032

   (18) https://bugs.python.org/issue25638

   (19) https://bugs.python.org/issue25873

   (20) https://bugs.python.org/issue25869

   (21) https://bugs.python.org/issue25971


File: python.info,  Node: Build and C API Changes<2>,  Next: Other Improvements,  Prev: Optimizations<4>,  Up: What’s New In Python 3 6

1.4.7 Build and C API Changes
-----------------------------

   * Python now requires some C99 support in the toolchain to build.
     Most notably, Python now uses standard integer types and macros in
     place of custom macros like ‘PY_LONG_LONG’.  For more information,
     see PEP 7(1) and bpo-17884(2).

   * Cross-compiling CPython with the Android NDK and the Android API
     level set to 21 (Android 5.0 Lollipop) or greater runs
     successfully.  While Android is not yet a supported platform, the
     Python test suite runs on the Android emulator with only about 16
     tests failures.  See the Android meta-issue bpo-26865(3).

   * The ‘--enable-optimizations’ configure flag has been added.
     Turning it on will activate expensive optimizations like PGO.
     (Original patch by Alecsandru Patrascu of Intel in bpo-26359(4).)

   * The *note GIL: 600. must now be held when allocator functions of
     *note PYMEM_DOMAIN_OBJ: 601. (ex: *note PyObject_Malloc(): 602.)
     and *note PYMEM_DOMAIN_MEM: 603. (ex: *note PyMem_Malloc(): 5ff.)
     domains are called.

   * New *note Py_FinalizeEx(): 6c0. API which indicates if flushing
     buffered data failed.  (Contributed by Martin Panter in
     bpo-5319(5).)

   * *note PyArg_ParseTupleAndKeywords(): 6c1. now supports *note
     positional-only parameters: 3c9.  Positional-only parameters are
     defined by empty names.  (Contributed by Serhiy Storchaka in
     bpo-26282(6)).

   * ‘PyTraceback_Print’ method now abbreviates long sequences of
     repeated lines as ‘"[Previous line repeated {count} more times]"’.
     (Contributed by Emanuel Barry in bpo-26823(7).)

   * The new *note PyErr_SetImportErrorSubclass(): 6c2. function allows
     for specifying a subclass of *note ImportError: 16c. to raise.
     (Contributed by Eric Snow in bpo-15767(8).)

   * The new *note PyErr_ResourceWarning(): 6c3. function can be used to
     generate a *note ResourceWarning: 5cb. providing the source of the
     resource allocation.  (Contributed by Victor Stinner in
     bpo-26567(9).)

   * The new *note PyOS_FSPath(): 6c4. function returns the file system
     representation of a *note path-like object: 472.  (Contributed by
     Brett Cannon in bpo-27186(10).)

   * The *note PyUnicode_FSConverter(): 6c5. and *note
     PyUnicode_FSDecoder(): 6c6. functions will now accept *note
     path-like objects: 472.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0007

   (2) https://bugs.python.org/issue17884

   (3) https://bugs.python.org/issue26865

   (4) https://bugs.python.org/issue26359

   (5) https://bugs.python.org/issue5319

   (6) https://bugs.python.org/issue26282

   (7) https://bugs.python.org/issue26823

   (8) https://bugs.python.org/issue15767

   (9) https://bugs.python.org/issue26567

   (10) https://bugs.python.org/issue27186


File: python.info,  Node: Other Improvements,  Next: Deprecated<3>,  Prev: Build and C API Changes<2>,  Up: What’s New In Python 3 6

1.4.8 Other Improvements
------------------------

   * When *note –version: 6c8. (short form: *note -V: 6c9.) is supplied
     twice, Python prints *note sys.version: 6ca. for detailed
     information.

          $ ./python -VV
          Python 3.6.0b4+ (3.6:223967b49e49+, Nov 21 2016, 20:55:04)
          [GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.42.1)]


File: python.info,  Node: Deprecated<3>,  Next: Removed<3>,  Prev: Other Improvements,  Up: What’s New In Python 3 6

1.4.9 Deprecated
----------------

* Menu:

* New Keywords::
* Deprecated Python behavior::
* Deprecated Python modules, functions and methods: Deprecated Python modules functions and methods<2>.
* Deprecated functions and types of the C API: Deprecated functions and types of the C API<2>.
* Deprecated Build Options::


File: python.info,  Node: New Keywords,  Next: Deprecated Python behavior,  Up: Deprecated<3>

1.4.9.1 New Keywords
....................

‘async’ and ‘await’ are not recommended to be used as variable, class,
function or module names.  Introduced by PEP 492(1) in Python 3.5, they
will become proper keywords in Python 3.7.  Starting in Python 3.6, the
use of ‘async’ or ‘await’ as names will generate a *note
DeprecationWarning: 15a.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0492


File: python.info,  Node: Deprecated Python behavior,  Next: Deprecated Python modules functions and methods<2>,  Prev: New Keywords,  Up: Deprecated<3>

1.4.9.2 Deprecated Python behavior
..................................

Raising the *note StopIteration: 582. exception inside a generator will
now generate a *note DeprecationWarning: 15a, and will trigger a *note
RuntimeError: 3dc. in Python 3.7.  See *note PEP 479; Change
StopIteration handling inside generators: 6ce. for details.

The *note __aiter__(): 583. method is now expected to return an
asynchronous iterator directly instead of returning an awaitable as
previously.  Doing the former will trigger a *note DeprecationWarning:
15a.  Backward compatibility will be removed in Python 3.7.
(Contributed by Yury Selivanov in bpo-27243(1).)

A backslash-character pair that is not a valid escape sequence now
generates a *note DeprecationWarning: 15a.  Although this will
eventually become a *note SyntaxError: 55a, that will not be for several
Python releases.  (Contributed by Emanuel Barry in bpo-27364(2).)

When performing a relative import, falling back on ‘__name__’ and
‘__path__’ from the calling module when ‘__spec__’ or ‘__package__’ are
not defined now raises an *note ImportWarning: 6cf.  (Contributed by
Rose Ames in bpo-25791(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27243

   (2) https://bugs.python.org/issue27364

   (3) https://bugs.python.org/issue25791


File: python.info,  Node: Deprecated Python modules functions and methods<2>,  Next: Deprecated functions and types of the C API<2>,  Prev: Deprecated Python behavior,  Up: Deprecated<3>

1.4.9.3 Deprecated Python modules, functions and methods
........................................................

* Menu:

* asynchat::
* asyncore::
* dbm: dbm<3>.
* distutils: distutils<4>.
* grp::
* importlib: importlib<5>.
* os: os<5>.
* re: re<3>.
* ssl: ssl<5>.
* tkinter: tkinter<4>.
* venv: venv<4>.


File: python.info,  Node: asynchat,  Next: asyncore,  Up: Deprecated Python modules functions and methods<2>

1.4.9.4 asynchat
................

The *note asynchat: 8. has been deprecated in favor of *note asyncio: 9.
(Contributed by Mariatta in bpo-25002(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25002


File: python.info,  Node: asyncore,  Next: dbm<3>,  Prev: asynchat,  Up: Deprecated Python modules functions and methods<2>

1.4.9.5 asyncore
................

The *note asyncore: a. has been deprecated in favor of *note asyncio: 9.
(Contributed by Mariatta in bpo-25002(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25002


File: python.info,  Node: dbm<3>,  Next: distutils<4>,  Prev: asyncore,  Up: Deprecated Python modules functions and methods<2>

1.4.9.6 dbm
...........

Unlike other *note dbm: 31. implementations, the *note dbm.dumb: 32.
module creates databases with the ‘'rw'’ mode and allows modifying the
database opened with the ‘'r'’ mode.  This behavior is now deprecated
and will be removed in 3.8.  (Contributed by Serhiy Storchaka in
bpo-21708(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21708


File: python.info,  Node: distutils<4>,  Next: grp,  Prev: dbm<3>,  Up: Deprecated Python modules functions and methods<2>

1.4.9.7 distutils
.................

The undocumented ‘extra_path’ argument to the ‘Distribution’ constructor
is now considered deprecated and will raise a warning if set.  Support
for this parameter will be removed in a future Python release.  See
bpo-27919(1) for details.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27919


File: python.info,  Node: grp,  Next: importlib<5>,  Prev: distutils<4>,  Up: Deprecated Python modules functions and methods<2>

1.4.9.8 grp
...........

The support of non-integer arguments in *note getgrgid(): 6d6. has been
deprecated.  (Contributed by Serhiy Storchaka in bpo-26129(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26129


File: python.info,  Node: importlib<5>,  Next: os<5>,  Prev: grp,  Up: Deprecated Python modules functions and methods<2>

1.4.9.9 importlib
.................

The *note importlib.machinery.SourceFileLoader.load_module(): 6d8. and
*note importlib.machinery.SourcelessFileLoader.load_module(): 6d9.
methods are now deprecated.  They were the only remaining
implementations of *note importlib.abc.Loader.load_module(): 6da. in
*note importlib: 9a. that had not been deprecated in previous versions
of Python in favour of *note importlib.abc.Loader.exec_module(): 6db.

The *note importlib.machinery.WindowsRegistryFinder: 6dc. class is now
deprecated.  As of 3.6.0, it is still added to *note sys.meta_path: 6dd.
by default (on Windows), but this may change in future releases.


File: python.info,  Node: os<5>,  Next: re<3>,  Prev: importlib<5>,  Up: Deprecated Python modules functions and methods<2>

1.4.9.10 os
...........

Undocumented support of general *note bytes-like objects: 6df. as paths
in *note os: c4. functions, *note compile(): 2e7. and similar functions
is now deprecated.  (Contributed by Serhiy Storchaka in bpo-25791(1) and
bpo-26754(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25791

   (2) https://bugs.python.org/issue26754


File: python.info,  Node: re<3>,  Next: ssl<5>,  Prev: os<5>,  Up: Deprecated Python modules functions and methods<2>

1.4.9.11 re
...........

Support for inline flags ‘(?letters)’ in the middle of the regular
expression has been deprecated and will be removed in a future Python
version.  Flags at the start of a regular expression are still allowed.
(Contributed by Serhiy Storchaka in bpo-22493(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22493


File: python.info,  Node: ssl<5>,  Next: tkinter<4>,  Prev: re<3>,  Up: Deprecated Python modules functions and methods<2>

1.4.9.12 ssl
............

OpenSSL 0.9.8, 1.0.0 and 1.0.1 are deprecated and no longer supported.
In the future the *note ssl: f3. module will require at least OpenSSL
1.0.2 or 1.1.0.

SSL-related arguments like ‘certfile’, ‘keyfile’ and ‘check_hostname’ in
*note ftplib: 82, *note http.client: 93, *note imaplib: 97, *note
poplib: d0, and *note smtplib: ed. have been deprecated in favor of
‘context’.  (Contributed by Christian Heimes in bpo-28022(1).)

A couple of protocols and functions of the *note ssl: f3. module are now
deprecated.  Some features will no longer be available in future
versions of OpenSSL. Other features are deprecated in favor of a
different API. (Contributed by Christian Heimes in bpo-28022(2) and
bpo-26470(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28022

   (2) https://bugs.python.org/issue28022

   (3) https://bugs.python.org/issue26470


File: python.info,  Node: tkinter<4>,  Next: venv<4>,  Prev: ssl<5>,  Up: Deprecated Python modules functions and methods<2>

1.4.9.13 tkinter
................

The *note tkinter.tix: 117. module is now deprecated.  *note tkinter:
10e. users should use *note tkinter.ttk: 118. instead.


File: python.info,  Node: venv<4>,  Prev: tkinter<4>,  Up: Deprecated Python modules functions and methods<2>

1.4.9.14 venv
.............

The ‘pyvenv’ script has been deprecated in favour of ‘python3 -m venv’.
This prevents confusion as to what Python interpreter ‘pyvenv’ is
connected to and thus what Python interpreter will be used by the
virtual environment.  (Contributed by Brett Cannon in bpo-25154(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25154


File: python.info,  Node: Deprecated functions and types of the C API<2>,  Next: Deprecated Build Options,  Prev: Deprecated Python modules functions and methods<2>,  Up: Deprecated<3>

1.4.9.15 Deprecated functions and types of the C API
....................................................

Undocumented functions ‘PyUnicode_AsEncodedObject()’,
‘PyUnicode_AsDecodedObject()’, ‘PyUnicode_AsEncodedUnicode()’ and
‘PyUnicode_AsDecodedUnicode()’ are deprecated now.  Use the *note
generic codec based API: 6e5. instead.


File: python.info,  Node: Deprecated Build Options,  Prev: Deprecated functions and types of the C API<2>,  Up: Deprecated<3>

1.4.9.16 Deprecated Build Options
.................................

The ‘--with-system-ffi’ configure flag is now on by default on non-macOS
UNIX platforms.  It may be disabled by using ‘--without-system-ffi’, but
using the flag is deprecated and will not be accepted in Python 3.7.
macOS is unaffected by this change.  Note that many OS distributors
already use the ‘--with-system-ffi’ flag when building their system
Python.


File: python.info,  Node: Removed<3>,  Next: Porting to Python 3 6,  Prev: Deprecated<3>,  Up: What’s New In Python 3 6

1.4.10 Removed
--------------

* Menu:

* API and Feature Removals: API and Feature Removals<3>.


File: python.info,  Node: API and Feature Removals<3>,  Up: Removed<3>

1.4.10.1 API and Feature Removals
.................................

   * Unknown escapes consisting of ‘'\'’ and an ASCII letter in regular
     expressions will now cause an error.  In replacement templates for
     *note re.sub(): 57a. they are still allowed, but deprecated.  The
     *note re.LOCALE: 4d0. flag can now only be used with binary
     patterns.

   * ‘inspect.getmoduleinfo()’ was removed (was deprecated since CPython
     3.3).  *note inspect.getmodulename(): 6e9. should be used for
     obtaining the module name for a given path.  (Contributed by Yury
     Selivanov in bpo-13248(1).)

   * ‘traceback.Ignore’ class and ‘traceback.usage’,
     ‘traceback.modname’, ‘traceback.fullmodname’,
     ‘traceback.find_lines_from_code’, ‘traceback.find_lines’,
     ‘traceback.find_strings’, ‘traceback.find_executable_lines’ methods
     were removed from the *note traceback: 11c. module.  They were
     undocumented methods deprecated since Python 3.2 and equivalent
     functionality is available from private methods.

   * The ‘tk_menuBar()’ and ‘tk_bindForTraversal()’ dummy methods in
     *note tkinter: 10e. widget classes were removed (corresponding Tk
     commands were obsolete since Tk 4.0).

   * The *note open(): 6b3. method of the *note zipfile.ZipFile: 523.
     class no longer supports the ‘'U'’ mode (was deprecated since
     Python 3.4).  Use *note io.TextIOWrapper: 6ea. for reading
     compressed text files in *note universal newlines: 6eb. mode.

   * The undocumented ‘IN’, ‘CDROM’, ‘DLFCN’, ‘TYPES’, ‘CDIO’, and
     ‘STROPTS’ modules have been removed.  They had been available in
     the platform specific ‘Lib/plat-*/’ directories, but were
     chronically out of date, inconsistently available across platforms,
     and unmaintained.  The script that created these modules is still
     available in the source distribution at Tools/scripts/h2py.py(2).

   * The deprecated ‘asynchat.fifo’ class has been removed.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13248

   (2) https://github.com/python/cpython/tree/3.9/Tools/scripts/h2py.py


File: python.info,  Node: Porting to Python 3 6,  Next: Notable changes in Python 3 6 2,  Prev: Removed<3>,  Up: What’s New In Python 3 6

1.4.11 Porting to Python 3.6
----------------------------

This section lists previously described changes and other bugfixes that
may require changes to your code.

* Menu:

* Changes in ‘python’ Command Behavior::
* Changes in the Python API: Changes in the Python API<4>.
* Changes in the C API: Changes in the C API<4>.
* CPython bytecode changes: CPython bytecode changes<4>.


File: python.info,  Node: Changes in ‘python’ Command Behavior,  Next: Changes in the Python API<4>,  Up: Porting to Python 3 6

1.4.11.1 Changes in ‘python’ Command Behavior
.............................................

   * The output of a special Python build with defined ‘COUNT_ALLOCS’,
     ‘SHOW_ALLOC_COUNT’ or ‘SHOW_TRACK_COUNT’ macros is now off by
     default.  It can be re-enabled using the ‘-X showalloccount’
     option.  It now outputs to ‘stderr’ instead of ‘stdout’.
     (Contributed by Serhiy Storchaka in bpo-23034(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23034


File: python.info,  Node: Changes in the Python API<4>,  Next: Changes in the C API<4>,  Prev: Changes in ‘python’ Command Behavior,  Up: Porting to Python 3 6

1.4.11.2 Changes in the Python API
..................................

   * *note open(): 16f. will no longer allow combining the ‘'U'’ mode
     flag with ‘'+'’.  (Contributed by Jeff Balogh and John O’Connor in
     bpo-2091(1).)

   * *note sqlite3: f2. no longer implicitly commits an open transaction
     before DDL statements.

   * On Linux, *note os.urandom(): 5cc. now blocks until the system
     urandom entropy pool is initialized to increase the security.

   * When *note importlib.abc.Loader.exec_module(): 6db. is defined,
     *note importlib.abc.Loader.create_module(): 64e. must also be
     defined.

   * *note PyErr_SetImportError(): 6ef. now sets *note TypeError: 1fe.
     when its `msg' argument is not set.  Previously only ‘NULL’ was
     returned.

   * The format of the ‘co_lnotab’ attribute of code objects changed to
     support a negative line number delta.  By default, Python does not
     emit bytecode with a negative line number delta.  Functions using
     ‘frame.f_lineno’, ‘PyFrame_GetLineNumber()’ or ‘PyCode_Addr2Line()’
     are not affected.  Functions directly decoding ‘co_lnotab’ should
     be updated to use a signed 8-bit integer type for the line number
     delta, but this is only required to support applications using a
     negative line number delta.  See ‘Objects/lnotab_notes.txt’ for the
     ‘co_lnotab’ format and how to decode it, and see the PEP 511(2) for
     the rationale.

   * The functions in the *note compileall: 20. module now return
     booleans instead of ‘1’ or ‘0’ to represent success or failure,
     respectively.  Thanks to booleans being a subclass of integers,
     this should only be an issue if you were doing identity checks for
     ‘1’ or ‘0’.  See bpo-25768(3).

   * Reading the ‘port’ attribute of *note urllib.parse.urlsplit(): 6f0.
     and *note urlparse(): 6f1. results now raises *note ValueError:
     16d. for out-of-range values, rather than returning *note None:
     203.  See bpo-20059(4).

   * The *note imp: 99. module now raises a *note DeprecationWarning:
     15a. instead of *note PendingDeprecationWarning: 15c.

   * The following modules have had missing APIs added to their
     ‘__all__’ attributes to match the documented APIs: *note calendar:
     14, *note cgi: 15, *note csv: 29, *note ElementTree: 140, *note
     enum: 79, *note fileinput: 7e, *note ftplib: 82, *note logging: aa,
     *note mailbox: ae, *note mimetypes: b2, *note optparse: c3, *note
     plistlib: cf, *note smtpd: ec, *note subprocess: f9, *note tarfile:
     101, *note threading: 10b. and *note wave: 130.  This means they
     will export new symbols when ‘import *’ is used.  (Contributed by
     Joel Taddei and Jacek Kołodziej in bpo-23883(5).)

   * When performing a relative import, if ‘__package__’ does not
     compare equal to ‘__spec__.parent’ then *note ImportWarning: 6cf.
     is raised.  (Contributed by Brett Cannon in bpo-25791(6).)

   * When a relative import is performed and no parent package is known,
     then *note ImportError: 16c. will be raised.  Previously, *note
     SystemError: 6f2. could be raised.  (Contributed by Brett Cannon in
     bpo-18018(7).)

   * Servers based on the *note socketserver: f0. module, including
     those defined in *note http.server: 96, *note xmlrpc.server: 149.
     and *note wsgiref.simple_server: 138, now only catch exceptions
     derived from *note Exception: 2dc.  Therefore if a request handler
     raises an exception like *note SystemExit: 6f3. or *note
     KeyboardInterrupt: 2cc, *note handle_error(): 6f4. is no longer
     called, and the exception will stop a single-threaded server.
     (Contributed by Martin Panter in bpo-23430(8).)

   * *note spwd.getspnam(): 6f5. now raises a *note PermissionError:
     6f6. instead of *note KeyError: 3e9. if the user doesn’t have
     privileges.

   * The *note socket.socket.close(): 6f7. method now raises an
     exception if an error (e.g.  ‘EBADF’) was reported by the
     underlying system call.  (Contributed by Martin Panter in
     bpo-26685(9).)

   * The `decode_data' argument for the *note smtpd.SMTPChannel: 6f8.
     and *note smtpd.SMTPServer: 6f9. constructors is now ‘False’ by
     default.  This means that the argument passed to *note
     process_message(): 6fa. is now a bytes object by default, and
     ‘process_message()’ will be passed keyword arguments.  Code that
     has already been updated in accordance with the deprecation warning
     generated by 3.5 will not be affected.

   * All optional arguments of the *note dump(): 6fb, *note dumps():
     6fc, *note load(): 659. and *note loads(): 225. functions and *note
     JSONEncoder: 6fd. and *note JSONDecoder: 6fe. class constructors in
     the *note json: a4. module are now *note keyword-only: 3ce.
     (Contributed by Serhiy Storchaka in bpo-18726(10).)

   * Subclasses of *note type: 6ff. which don’t override ‘type.__new__’
     may no longer use the one-argument form to get the type of an
     object.

   * As part of PEP 487(11), the handling of keyword arguments passed to
     *note type: 6ff. (other than the metaclass hint, ‘metaclass’) is
     now consistently delegated to *note object.__init_subclass__():
     5de.  This means that ‘type.__new__()’ and ‘type.__init__()’ both
     now accept arbitrary keyword arguments, but *note
     object.__init_subclass__(): 5de. (which is called from
     ‘type.__new__()’) will reject them by default.  Custom metaclasses
     accepting additional keyword arguments will need to adjust their
     calls to ‘type.__new__()’ (whether direct or via *note super: 5dd.)
     accordingly.

   * In ‘distutils.command.sdist.sdist’, the ‘default_format’ attribute
     has been removed and is no longer honored.  Instead, the gzipped
     tarfile format is the default on all platforms and no
     platform-specific selection is made.  In environments where
     distributions are built on Windows and zip distributions are
     required, configure the project with a ‘setup.cfg’ file containing
     the following:

          [sdist]
          formats=zip

     This behavior has also been backported to earlier Python versions
     by Setuptools 26.0.0.

   * In the *note urllib.request: 129. module and the *note
     http.client.HTTPConnection.request(): 649. method, if no
     Content-Length header field has been specified and the request body
     is a file object, it is now sent with HTTP 1.1 chunked encoding.
     If a file object has to be sent to a HTTP 1.0 server, the
     Content-Length value now has to be specified by the caller.
     (Contributed by Demian Brecht and Rolf Krahl with tweaks from
     Martin Panter in bpo-12319(12).)

   * The *note DictReader: 2ee. now returns rows of type *note
     OrderedDict: 2ea.  (Contributed by Steve Holden in bpo-27842(13).)

   * The *note crypt.METHOD_CRYPT: 700. will no longer be added to
     ‘crypt.methods’ if unsupported by the platform.  (Contributed by
     Victor Stinner in bpo-25287(14).)

   * The `verbose' and `rename' arguments for *note namedtuple(): 1a1.
     are now keyword-only.  (Contributed by Raymond Hettinger in
     bpo-25628(15).)

   * On Linux, *note ctypes.util.find_library(): 701. now looks in
     ‘LD_LIBRARY_PATH’ for shared libraries.  (Contributed by Vinay
     Sajip in bpo-9998(16).)

   * The *note imaplib.IMAP4: 1af. class now handles flags containing
     the ‘']'’ character in messages sent from the server to improve
     real-world compatibility.  (Contributed by Lita Cho in
     bpo-21815(17).)

   * The ‘mmap.write()’ function now returns the number of bytes written
     like other write methods.  (Contributed by Jakub Stasiak in
     bpo-26335(18).)

   * The *note pkgutil.iter_modules(): 702. and *note
     pkgutil.walk_packages(): 586. functions now return *note
     ModuleInfo: 703. named tuples.  (Contributed by Ramchandra Apte in
     bpo-17211(19).)

   * *note re.sub(): 57a. now raises an error for invalid numerical
     group references in replacement templates even if the pattern is
     not found in the string.  The error message for invalid group
     references now includes the group index and the position of the
     reference.  (Contributed by SilentGhost, Serhiy Storchaka in
     bpo-25953(20).)

   * *note zipfile.ZipFile: 523. will now raise *note
     NotImplementedError: 704. for unrecognized compression values.
     Previously a plain *note RuntimeError: 3dc. was raised.
     Additionally, calling *note ZipFile: 523. methods on a closed
     ZipFile or calling the *note write(): 705. method on a ZipFile
     created with mode ‘'r'’ will raise a *note ValueError: 16d.
     Previously, a *note RuntimeError: 3dc. was raised in those
     scenarios.

   * when custom metaclasses are combined with zero-argument *note
     super(): 5dd. or direct references from methods to the implicit
     ‘__class__’ closure variable, the implicit ‘__classcell__’
     namespace entry must now be passed up to ‘type.__new__’ for
     initialisation.  Failing to do so will result in a *note
     DeprecationWarning: 15a. in Python 3.6 and a *note RuntimeError:
     3dc. in Python 3.8.

   * With the introduction of *note ModuleNotFoundError: 4a1, import
     system consumers may start expecting import system replacements to
     raise that more specific exception when appropriate, rather than
     the less-specific *note ImportError: 16c.  To provide future
     compatibility with such consumers, implementors of alternative
     import systems that completely replace *note __import__(): 16b.
     will need to update their implementations to raise the new subclass
     when a module can’t be found at all.  Implementors of compliant
     plugins to the default import system shouldn’t need to make any
     changes, as the default import system will raise the new subclass
     when appropriate.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue2091

   (2) https://www.python.org/dev/peps/pep-0511

   (3) https://bugs.python.org/issue25768

   (4) https://bugs.python.org/issue20059

   (5) https://bugs.python.org/issue23883

   (6) https://bugs.python.org/issue25791

   (7) https://bugs.python.org/issue18018

   (8) https://bugs.python.org/issue23430

   (9) https://bugs.python.org/issue26685

   (10) https://bugs.python.org/issue18726

   (11) https://www.python.org/dev/peps/pep-0487

   (12) https://bugs.python.org/issue12319

   (13) https://bugs.python.org/issue27842

   (14) https://bugs.python.org/issue25287

   (15) https://bugs.python.org/issue25628

   (16) https://bugs.python.org/issue9998

   (17) https://bugs.python.org/issue21815

   (18) https://bugs.python.org/issue26335

   (19) https://bugs.python.org/issue17211

   (20) https://bugs.python.org/issue25953


File: python.info,  Node: Changes in the C API<4>,  Next: CPython bytecode changes<4>,  Prev: Changes in the Python API<4>,  Up: Porting to Python 3 6

1.4.11.3 Changes in the C API
.............................

   * The *note PyMem_Malloc(): 5ff. allocator family now uses the *note
     pymalloc allocator: 6b8. rather than the system ‘malloc()’.
     Applications calling *note PyMem_Malloc(): 5ff. without holding the
     GIL can now crash.  Set the *note PYTHONMALLOC: 5fd. environment
     variable to ‘debug’ to validate the usage of memory allocators in
     your application.  See bpo-26249(1).

   * *note Py_Exit(): 707. (and the main interpreter) now override the
     exit status with 120 if flushing buffered data failed.  See
     bpo-5319(2).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26249

   (2) https://bugs.python.org/issue5319


File: python.info,  Node: CPython bytecode changes<4>,  Prev: Changes in the C API<4>,  Up: Porting to Python 3 6

1.4.11.4 CPython bytecode changes
.................................

There have been several major changes to the *note bytecode: 709. in
Python 3.6.

   * The Python interpreter now uses a 16-bit wordcode instead of
     bytecode.  (Contributed by Demur Rumed with input and reviews from
     Serhiy Storchaka and Victor Stinner in bpo-26647(1) and
     bpo-28050(2).)

   * The new *note FORMAT_VALUE: 70a. and *note BUILD_STRING: 70b.
     opcodes as part of the *note formatted string literal: 5bc.
     implementation.  (Contributed by Eric Smith in bpo-25483(3) and
     Serhiy Storchaka in bpo-27078(4).)

   * The new *note BUILD_CONST_KEY_MAP: 70c. opcode to optimize the
     creation of dictionaries with constant keys.  (Contributed by
     Serhiy Storchaka in bpo-27140(5).)

   * The function call opcodes have been heavily reworked for better
     performance and simpler implementation.  The *note MAKE_FUNCTION:
     70d, *note CALL_FUNCTION: 70e, *note CALL_FUNCTION_KW: 70f. and
     ‘BUILD_MAP_UNPACK_WITH_CALL’ opcodes have been modified, the new
     *note CALL_FUNCTION_EX: 710. and ‘BUILD_TUPLE_UNPACK_WITH_CALL’
     have been added, and ‘CALL_FUNCTION_VAR’, ‘CALL_FUNCTION_VAR_KW’
     and ‘MAKE_CLOSURE’ opcodes have been removed.  (Contributed by
     Demur Rumed in bpo-27095(6), and Serhiy Storchaka in bpo-27213(7),
     bpo-28257(8).)

   * The new *note SETUP_ANNOTATIONS: 711. and ‘STORE_ANNOTATION’
     opcodes have been added to support the new *note variable
     annotation: 712. syntax.  (Contributed by Ivan Levkivskyi in
     bpo-27985(9).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26647

   (2) https://bugs.python.org/issue28050

   (3) https://bugs.python.org/issue25483

   (4) https://bugs.python.org/issue27078

   (5) https://bugs.python.org/issue27140

   (6) https://bugs.python.org/issue27095

   (7) https://bugs.python.org/issue27213

   (8) https://bugs.python.org/issue28257

   (9) https://bugs.python.org/issue27985


File: python.info,  Node: Notable changes in Python 3 6 2,  Next: Notable changes in Python 3 6 4,  Prev: Porting to Python 3 6,  Up: What’s New In Python 3 6

1.4.12 Notable changes in Python 3.6.2
--------------------------------------

* Menu:

* New make regen-all build target::
* Removal of make touch build target::


File: python.info,  Node: New make regen-all build target,  Next: Removal of make touch build target,  Up: Notable changes in Python 3 6 2

1.4.12.1 New ‘make regen-all’ build target
..........................................

To simplify cross-compilation, and to ensure that CPython can reliably
be compiled without requiring an existing version of Python to already
be available, the autotools-based build system no longer attempts to
implicitly recompile generated files based on file modification times.

Instead, a new ‘make regen-all’ command has been added to force
regeneration of these files when desired (e.g.  after an initial version
of Python has already been built based on the pregenerated versions).

More selective regeneration targets are also defined - see
Makefile.pre.in(1) for details.

(Contributed by Victor Stinner in bpo-23404(2).)

New in version 3.6.2.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Makefile.pre.in

   (2) https://bugs.python.org/issue23404


File: python.info,  Node: Removal of make touch build target,  Prev: New make regen-all build target,  Up: Notable changes in Python 3 6 2

1.4.12.2 Removal of ‘make touch’ build target
.............................................

The ‘make touch’ build target previously used to request implicit
regeneration of generated files by updating their modification times has
been removed.

It has been replaced by the new ‘make regen-all’ target.

(Contributed by Victor Stinner in bpo-23404(1).)

Changed in version 3.6.2.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23404


File: python.info,  Node: Notable changes in Python 3 6 4,  Next: Notable changes in Python 3 6 5,  Prev: Notable changes in Python 3 6 2,  Up: What’s New In Python 3 6

1.4.13 Notable changes in Python 3.6.4
--------------------------------------

The ‘PyExc_RecursionErrorInst’ singleton that was part of the public API
has been removed as its members being never cleared may cause a segfault
during finalization of the interpreter.  (Contributed by Xavier de Gaye
in bpo-22898(1) and bpo-30697(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22898

   (2) https://bugs.python.org/issue30697


File: python.info,  Node: Notable changes in Python 3 6 5,  Next: Notable changes in Python 3 6 7,  Prev: Notable changes in Python 3 6 4,  Up: What’s New In Python 3 6

1.4.14 Notable changes in Python 3.6.5
--------------------------------------

The *note locale.localeconv(): 585. function now sets temporarily the
‘LC_CTYPE’ locale to the ‘LC_NUMERIC’ locale in some cases.
(Contributed by Victor Stinner in bpo-31900(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31900


File: python.info,  Node: Notable changes in Python 3 6 7,  Next: Notable changes in Python 3 6 10,  Prev: Notable changes in Python 3 6 5,  Up: What’s New In Python 3 6

1.4.15 Notable changes in Python 3.6.7
--------------------------------------

In 3.6.7 the *note tokenize: 11a. module now implicitly emits a
‘NEWLINE’ token when provided with input that does not have a trailing
new line.  This behavior now matches what the C tokenizer does
internally.  (Contributed by Ammar Askar in bpo-33899(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33899


File: python.info,  Node: Notable changes in Python 3 6 10,  Next: Notable changes in Python 3 6 13,  Prev: Notable changes in Python 3 6 7,  Up: What’s New In Python 3 6

1.4.16 Notable changes in Python 3.6.10
---------------------------------------

Due to significant security concerns, the `reuse_address' parameter of
*note asyncio.loop.create_datagram_endpoint(): 189. is no longer
supported.  This is because of the behavior of the socket option
‘SO_REUSEADDR’ in UDP. For more details, see the documentation for
‘loop.create_datagram_endpoint()’.  (Contributed by Kyle Stanley,
Antoine Pitrou, and Yury Selivanov in bpo-37228(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37228


File: python.info,  Node: Notable changes in Python 3 6 13,  Prev: Notable changes in Python 3 6 10,  Up: What’s New In Python 3 6

1.4.17 Notable changes in Python 3.6.13
---------------------------------------

Earlier Python versions allowed using both ‘;’ and ‘&’ as query
parameter separators in *note urllib.parse.parse_qs(): 27f. and *note
urllib.parse.parse_qsl(): 280.  Due to security concerns, and to conform
with newer W3C recommendations, this has been changed to allow only a
single separator key, with ‘&’ as the default.  This change also affects
*note cgi.parse(): 281. and *note cgi.parse_multipart(): 282. as they
use the affected functions internally.  For more details, please see
their respective documentation.  (Contributed by Adam Goldschmidt,
Senthil Kumaran and Ken Jin in bpo-42967(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42967


File: python.info,  Node: What’s New In Python 3 5,  Next: What’s New In Python 3 4,  Prev: What’s New In Python 3 6,  Up: What’s New in Python

1.5 What’s New In Python 3.5
============================


Editors: Elvis Pranskevichus <<elvis@magic.io>>, Yury Selivanov
<<yury@magic.io>>

This article explains the new features in Python 3.5, compared to 3.4.
Python 3.5 was released on September 13, 2015.   See the changelog(1)
for a full list of changes.

See also
........

PEP 478(2) - Python 3.5 Release Schedule

* Menu:

* Summary – Release highlights: Summary – Release highlights<4>.
* New Features: New Features<6>.
* Other Language Changes: Other Language Changes<5>.
* New Modules: New Modules<5>.
* Improved Modules: Improved Modules<5>.
* Other module-level changes::
* Optimizations: Optimizations<5>.
* Build and C API Changes: Build and C API Changes<3>.
* Deprecated: Deprecated<4>.
* Removed: Removed<4>.
* Porting to Python 3.5: Porting to Python 3 5.
* Notable changes in Python 3.5.4: Notable changes in Python 3 5 4.

   ---------- Footnotes ----------

   (1) https://docs.python.org/3.5/whatsnew/changelog.html

   (2) https://www.python.org/dev/peps/pep-0478


File: python.info,  Node: Summary – Release highlights<4>,  Next: New Features<6>,  Up: What’s New In Python 3 5

1.5.1 Summary – Release highlights
----------------------------------

New syntax features:

   * *note PEP 492: 71e, coroutines with async and await syntax.

   * *note PEP 465: 71f, a new matrix multiplication operator: ‘a @ b’.

   * *note PEP 448: 720, additional unpacking generalizations.

New library modules:

   * *note typing: 122.: *note PEP 484 – Type Hints: 721.

   * *note zipapp: 14a.: *note PEP 441 Improving Python ZIP Application
     Support: 722.

New built-in features:

   * ‘bytes % args’, ‘bytearray % args’: *note PEP 461: 723. – Adding
     ‘%’ formatting to bytes and bytearray.

   * New *note bytes.hex(): 724, *note bytearray.hex(): 725. and *note
     memoryview.hex(): 726. methods.  (Contributed by Arnon Yaari in
     bpo-9951(1).)

   * *note memoryview: 386. now supports tuple indexing (including
     multi-dimensional).  (Contributed by Antoine Pitrou in
     bpo-23632(2).)

   * Generators have a new ‘gi_yieldfrom’ attribute, which returns the
     object being iterated by ‘yield from’ expressions.  (Contributed by
     Benno Leslie and Yury Selivanov in bpo-24450(3).)

   * A new *note RecursionError: 727. exception is now raised when
     maximum recursion depth is reached.  (Contributed by Georg Brandl
     in bpo-19235(4).)

CPython implementation improvements:

   * When the ‘LC_TYPE’ locale is the POSIX locale (‘C’ locale), *note
     sys.stdin: 41e. and *note sys.stdout: 41f. now use the
     ‘surrogateescape’ error handler, instead of the ‘strict’ error
     handler.  (Contributed by Victor Stinner in bpo-19977(5).)

   * ‘.pyo’ files are no longer used and have been replaced by a more
     flexible scheme that includes the optimization level explicitly in
     ‘.pyc’ name.  (See *note PEP 488 overview: 728.)

   * Builtin and extension modules are now initialized in a multi-phase
     process, which is similar to how Python modules are loaded.  (See
     *note PEP 489 overview: 729.)

Significant improvements in the standard library:

   * *note collections.OrderedDict: 2ea. is now *note implemented in C:
     72a, which makes it 4 to 100 times faster.

   * The *note ssl: f3. module gained *note support for Memory BIO: 72b,
     which decouples SSL protocol handling from network IO.

   * The new *note os.scandir(): 389. function provides a *note better
     and significantly faster way: 72c. of directory traversal.

   * *note functools.lru_cache(): 2f8. has been mostly *note
     reimplemented in C: 72d, yielding much better performance.

   * The new *note subprocess.run(): 4f3. function provides a *note
     streamlined way to run subprocesses: 72e.

   * The *note traceback: 11c. module has been significantly *note
     enhanced: 72f. for improved performance and developer convenience.

Security improvements:

   * SSLv3 is now disabled throughout the standard library.  It can
     still be enabled by instantiating a *note ssl.SSLContext: 4ea.
     manually.  (See bpo-22638(6) for more details; this change was
     backported to CPython 3.4 and 2.7.)

   * HTTP cookie parsing is now stricter, in order to protect against
     potential injection attacks.  (Contributed by Antoine Pitrou in
     bpo-22796(7).)

Windows improvements:

   * A new installer for Windows has replaced the old MSI. See *note
     Using Python on Windows: 3f8. for more information.

   * Windows builds now use Microsoft Visual C++ 14.0, and extension
     modules should use the same.

Please read on for a comprehensive list of user-facing changes,
including many other smaller improvements, CPython optimizations,
deprecations, and potential porting issues.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9951

   (2) https://bugs.python.org/issue23632

   (3) https://bugs.python.org/issue24450

   (4) https://bugs.python.org/issue19235

   (5) https://bugs.python.org/issue19977

   (6) https://bugs.python.org/issue22638

   (7) https://bugs.python.org/issue22796


File: python.info,  Node: New Features<6>,  Next: Other Language Changes<5>,  Prev: Summary – Release highlights<4>,  Up: What’s New In Python 3 5

1.5.2 New Features
------------------

* Menu:

* PEP 492 - Coroutines with async and await syntax::
* PEP 465 - A dedicated infix operator for matrix multiplication::
* PEP 448 - Additional Unpacking Generalizations::
* PEP 461 - percent formatting support for bytes and bytearray::
* PEP 484 - Type Hints::
* PEP 471 - os.scandir() function – a better and faster directory iterator: PEP 471 - os scandir function – a better and faster directory iterator.
* PEP 475; Retry system calls failing with EINTR: PEP 475 Retry system calls failing with EINTR.
* PEP 479; Change StopIteration handling inside generators: PEP 479 Change StopIteration handling inside generators.
* PEP 485; A function for testing approximate equality: PEP 485 A function for testing approximate equality.
* PEP 486; Make the Python Launcher aware of virtual environments: PEP 486 Make the Python Launcher aware of virtual environments.
* PEP 488; Elimination of PYO files: PEP 488 Elimination of PYO files.
* PEP 489; Multi-phase extension module initialization: PEP 489 Multi-phase extension module initialization.


File: python.info,  Node: PEP 492 - Coroutines with async and await syntax,  Next: PEP 465 - A dedicated infix operator for matrix multiplication,  Up: New Features<6>

1.5.2.1 PEP 492 - Coroutines with async and await syntax
........................................................

PEP 492(1) greatly improves support for asynchronous programming in
Python by adding *note awaitable objects: 613, *note coroutine
functions: 732, *note asynchronous iteration: 733, and *note
asynchronous context managers: 734.

Coroutine functions are declared using the new *note async def: 3a9.
syntax:

     >>> async def coro():
     ...     return 'spam'

Inside a coroutine function, the new *note await: 2d8. expression can be
used to suspend coroutine execution until the result is available.  Any
object can be `awaited', as long as it implements the *note awaitable:
613. protocol by defining the *note __await__(): 735. method.

PEP 492 also adds *note async for: 3fd. statement for convenient
iteration over asynchronous iterables.

An example of a rudimentary HTTP client written using the new syntax:

     import asyncio

     async def http_get(domain):
         reader, writer = await asyncio.open_connection(domain, 80)

         writer.write(b'\r\n'.join([
             b'GET / HTTP/1.1',
             b'Host: %b' % domain.encode('latin-1'),
             b'Connection: close',
             b'', b''
         ]))

         async for line in reader:
             print('>>>', line)

         writer.close()

     loop = asyncio.get_event_loop()
     try:
         loop.run_until_complete(http_get('example.com'))
     finally:
         loop.close()

Similarly to asynchronous iteration, there is a new syntax for
asynchronous context managers.  The following script:

     import asyncio

     async def coro(name, lock):
         print('coro {}: waiting for lock'.format(name))
         async with lock:
             print('coro {}: holding the lock'.format(name))
             await asyncio.sleep(1)
             print('coro {}: releasing the lock'.format(name))

     loop = asyncio.get_event_loop()
     lock = asyncio.Lock()
     coros = asyncio.gather(coro(1, lock), coro(2, lock))
     try:
         loop.run_until_complete(coros)
     finally:
         loop.close()

will output:

     coro 2: waiting for lock
     coro 2: holding the lock
     coro 1: waiting for lock
     coro 2: releasing the lock
     coro 1: holding the lock
     coro 1: releasing the lock

Note that both *note async for: 3fd. and *note async with: 736. can only
be used inside a coroutine function declared with *note async def: 3a9.

Coroutine functions are intended to be run inside a compatible event
loop, such as the *note asyncio loop: 737.

     Note: 
     Changed in version 3.5.2: Starting with CPython 3.5.2, ‘__aiter__’
     can directly return *note asynchronous iterators: 738.  Returning
     an *note awaitable: 613. object will result in a *note
     PendingDeprecationWarning: 15c.

     See more details in the *note Asynchronous Iterators: 739.
     documentation section.

See also
........

PEP 492(2) – Coroutines with async and await syntax

     PEP written and implemented by Yury Selivanov.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0492

   (2) https://www.python.org/dev/peps/pep-0492


File: python.info,  Node: PEP 465 - A dedicated infix operator for matrix multiplication,  Next: PEP 448 - Additional Unpacking Generalizations,  Prev: PEP 492 - Coroutines with async and await syntax,  Up: New Features<6>

1.5.2.2 PEP 465 - A dedicated infix operator for matrix multiplication
......................................................................

PEP 465(1) adds the ‘@’ infix operator for matrix multiplication.
Currently, no builtin Python types implement the new operator, however,
it can be implemented by defining *note __matmul__(): 73b, *note
__rmatmul__(): 73c, and *note __imatmul__(): 73d. for regular,
reflected, and in-place matrix multiplication.  The semantics of these
methods is similar to that of methods defining other infix arithmetic
operators.

Matrix multiplication is a notably common operation in many fields of
mathematics, science, engineering, and the addition of ‘@’ allows
writing cleaner code:

     S = (H @ beta - r).T @ inv(H @ V @ H.T) @ (H @ beta - r)

instead of:

     S = dot((dot(H, beta) - r).T,
             dot(inv(dot(dot(H, V), H.T)), dot(H, beta) - r))

NumPy 1.10 has support for the new operator:

     >>> import numpy

     >>> x = numpy.ones(3)
     >>> x
     array([ 1., 1., 1.])

     >>> m = numpy.eye(3)
     >>> m
     array([[ 1., 0., 0.],
            [ 0., 1., 0.],
            [ 0., 0., 1.]])

     >>> x @ m
     array([ 1., 1., 1.])

See also
........

PEP 465(2) – A dedicated infix operator for matrix multiplication

     PEP written by Nathaniel J. Smith; implemented by Benjamin
     Peterson.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0465

   (2) https://www.python.org/dev/peps/pep-0465


File: python.info,  Node: PEP 448 - Additional Unpacking Generalizations,  Next: PEP 461 - percent formatting support for bytes and bytearray,  Prev: PEP 465 - A dedicated infix operator for matrix multiplication,  Up: New Features<6>

1.5.2.3 PEP 448 - Additional Unpacking Generalizations
......................................................

PEP 448(1) extends the allowed uses of the ‘*’ iterable unpacking
operator and ‘**’ dictionary unpacking operator.  It is now possible to
use an arbitrary number of unpackings in *note function calls: 73f.:

     >>> print(*[1], *[2], 3, *[4, 5])
     1 2 3 4 5

     >>> def fn(a, b, c, d):
     ...     print(a, b, c, d)
     ...

     >>> fn(**{'a': 1, 'c': 3}, **{'b': 2, 'd': 4})
     1 2 3 4

Similarly, tuple, list, set, and dictionary displays allow multiple
unpackings (see *note Expression lists: 740. and *note Dictionary
displays: 741.):

     >>> *range(4), 4
     (0, 1, 2, 3, 4)

     >>> [*range(4), 4]
     [0, 1, 2, 3, 4]

     >>> {*range(4), 4, *(5, 6, 7)}
     {0, 1, 2, 3, 4, 5, 6, 7}

     >>> {'x': 1, **{'y': 2}}
     {'x': 1, 'y': 2}

See also
........

PEP 448(2) – Additional Unpacking Generalizations

     PEP written by Joshua Landau; implemented by Neil Girdhar, Thomas
     Wouters, and Joshua Landau.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0448

   (2) https://www.python.org/dev/peps/pep-0448


File: python.info,  Node: PEP 461 - percent formatting support for bytes and bytearray,  Next: PEP 484 - Type Hints,  Prev: PEP 448 - Additional Unpacking Generalizations,  Up: New Features<6>

1.5.2.4 PEP 461 - percent formatting support for bytes and bytearray
....................................................................

PEP 461(1) adds support for the ‘%’ *note interpolation operator: 743.
to *note bytes: 172. and *note bytearray: 173.

While interpolation is usually thought of as a string operation, there
are cases where interpolation on ‘bytes’ or ‘bytearrays’ makes sense,
and the work needed to make up for this missing functionality detracts
from the overall readability of the code.  This issue is particularly
important when dealing with wire format protocols, which are often a
mixture of binary and ASCII compatible text.

Examples:

     >>> b'Hello %b!' % b'World'
     b'Hello World!'

     >>> b'x=%i y=%f' % (1, 2.5)
     b'x=1 y=2.500000'

Unicode is not allowed for ‘%b’, but it is accepted by ‘%a’ (equivalent
of ‘repr(obj).encode('ascii', 'backslashreplace')’):

     >>> b'Hello %b!' % 'World'
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: %b requires bytes, or an object that implements __bytes__, not 'str'

     >>> b'price: %a' % '10€'
     b"price: '10\\u20ac'"

Note that ‘%s’ and ‘%r’ conversion types, although supported, should
only be used in codebases that need compatibility with Python 2.

See also
........

PEP 461(2) – Adding % formatting to bytes and bytearray

     PEP written by Ethan Furman; implemented by Neil Schemenauer and
     Ethan Furman.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0461

   (2) https://www.python.org/dev/peps/pep-0461


File: python.info,  Node: PEP 484 - Type Hints,  Next: PEP 471 - os scandir function – a better and faster directory iterator,  Prev: PEP 461 - percent formatting support for bytes and bytearray,  Up: New Features<6>

1.5.2.5 PEP 484 - Type Hints
............................

Function annotation syntax has been a Python feature since version 3.0 (
PEP 3107(1)), however the semantics of annotations has been left
undefined.

Experience has shown that the majority of function annotation uses were
to provide type hints to function parameters and return values.  It
became evident that it would be beneficial for Python users, if the
standard library included the base definitions and tools for type
annotations.

PEP 484(2) introduces a *note provisional module: 454. to provide these
standard definitions and tools, along with some conventions for
situations where annotations are not available.

For example, here is a simple function whose argument and return type
are declared in the annotations:

     def greeting(name: str) -> str:
         return 'Hello ' + name

While these annotations are available at runtime through the usual
‘__annotations__’ attribute, `no automatic type checking happens at
runtime'.  Instead, it is assumed that a separate off-line type checker
(e.g.  mypy(3)) will be used for on-demand source code analysis.

The type system supports unions, generic types, and a special type named
*note Any: 745. which is consistent with (i.e.  assignable to and from)
all types.

See also
........

   * *note typing: 122. module documentation

   * 
     PEP 484(4) – Type Hints

          PEP written by Guido van Rossum, Jukka Lehtosalo, and Łukasz
          Langa; implemented by Guido van Rossum.

   * 
     PEP 483(5) – The Theory of Type Hints

          PEP written by Guido van Rossum

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3107

   (2) https://www.python.org/dev/peps/pep-0484

   (3) http://mypy-lang.org

   (4) https://www.python.org/dev/peps/pep-0484

   (5) https://www.python.org/dev/peps/pep-0483


File: python.info,  Node: PEP 471 - os scandir function – a better and faster directory iterator,  Next: PEP 475 Retry system calls failing with EINTR,  Prev: PEP 484 - Type Hints,  Up: New Features<6>

1.5.2.6 PEP 471 - os.scandir() function – a better and faster directory iterator
................................................................................

PEP 471(1) adds a new directory iteration function, *note os.scandir():
389, to the standard library.  Additionally, *note os.walk(): 747. is
now implemented using ‘scandir’, which makes it 3 to 5 times faster on
POSIX systems and 7 to 20 times faster on Windows systems.  This is
largely achieved by greatly reducing the number of calls to *note
os.stat(): 321. required to walk a directory tree.

Additionally, ‘scandir’ returns an iterator, as opposed to returning a
list of file names, which improves memory efficiency when iterating over
very large directories.

The following example shows a simple use of *note os.scandir(): 389. to
display all the files (excluding directories) in the given `path' that
don’t start with ‘'.'’.  The *note entry.is_file(): 748. call will
generally not make an additional system call:

     for entry in os.scandir(path):
         if not entry.name.startswith('.') and entry.is_file():
             print(entry.name)

See also
........

PEP 471(2) – os.scandir() function – a better and faster directory iterator

     PEP written and implemented by Ben Hoyt with the help of Victor
     Stinner.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0471

   (2) https://www.python.org/dev/peps/pep-0471


File: python.info,  Node: PEP 475 Retry system calls failing with EINTR,  Next: PEP 479 Change StopIteration handling inside generators,  Prev: PEP 471 - os scandir function – a better and faster directory iterator,  Up: New Features<6>

1.5.2.7 PEP 475: Retry system calls failing with EINTR
......................................................

An *note errno.EINTR: 74b. error code is returned whenever a system
call, that is waiting for I/O, is interrupted by a signal.  Previously,
Python would raise *note InterruptedError: 74c. in such cases.  This
meant that, when writing a Python application, the developer had two
choices:

  1. Ignore the ‘InterruptedError’.

  2. Handle the ‘InterruptedError’ and attempt to restart the
     interrupted system call at every call site.

The first option makes an application fail intermittently.  The second
option adds a large amount of boilerplate that makes the code nearly
unreadable.  Compare:

     print("Hello World")

and:

     while True:
         try:
             print("Hello World")
             break
         except InterruptedError:
             continue

PEP 475(1) implements automatic retry of system calls on ‘EINTR’.  This
removes the burden of dealing with ‘EINTR’ or *note InterruptedError:
74c. in user code in most situations and makes Python programs,
including the standard library, more robust.  Note that the system call
is only retried if the signal handler does not raise an exception.

Below is a list of functions which are now retried when interrupted by a
signal:

   * *note open(): 16f. and *note io.open(): 74d.;

   * functions of the *note faulthandler: 7b. module;

   * *note os: c4. functions: *note fchdir(): 74e, *note fchmod(): 74f,
     *note fchown(): 750, *note fdatasync(): 751, *note fstat(): 752,
     *note fstatvfs(): 753, *note fsync(): 754, *note ftruncate(): 755,
     *note mkfifo(): 756, *note mknod(): 757, *note open(): 758, *note
     posix_fadvise(): 759, *note posix_fallocate(): 75a, *note pread():
     4c0, *note pwrite(): 4c3, *note read(): 75b, *note readv(): 4bf,
     *note sendfile(): 461, *note wait3(): 75c, *note wait4(): 75d,
     *note wait(): 75e, *note waitid(): 75f, *note waitpid(): 760, *note
     write(): 761, *note writev(): 4c2.;

   * special cases: *note os.close(): 4d9. and *note os.dup2(): 4c5. now
     ignore *note EINTR: 74b. errors; the syscall is not retried (see
     the PEP for the rationale);

   * *note select: e5. functions: *note devpoll.poll(): 762, *note
     epoll.poll(): 763, *note kqueue.control(): 764, *note poll.poll():
     765, *note select(): 766.;

   * methods of the *note socket: 767. class: *note accept(): 768, *note
     connect(): 769. (except for non-blocking sockets), *note recv():
     76a, *note recvfrom(): 76b, *note recvmsg(): 76c, *note send():
     76d, *note sendall(): 76e, *note sendmsg(): 76f, *note sendto():
     770.;

   * *note signal.sigtimedwait(): 771. and *note signal.sigwaitinfo():
     772.;

   * *note time.sleep(): 773.

See also
........

PEP 475(2) – Retry system calls failing with EINTR

     PEP and implementation written by Charles-François Natali and
     Victor Stinner, with the help of Antoine Pitrou (the French
     connection).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0475

   (2) https://www.python.org/dev/peps/pep-0475


File: python.info,  Node: PEP 479 Change StopIteration handling inside generators,  Next: PEP 485 A function for testing approximate equality,  Prev: PEP 475 Retry system calls failing with EINTR,  Up: New Features<6>

1.5.2.8 PEP 479: Change StopIteration handling inside generators
................................................................

The interaction of generators and *note StopIteration: 582. in Python
3.4 and earlier was sometimes surprising, and could conceal obscure
bugs.  Previously, ‘StopIteration’ raised accidentally inside a
generator function was interpreted as the end of the iteration by the
loop construct driving the generator.

PEP 479(1) changes the behavior of generators: when a ‘StopIteration’
exception is raised inside a generator, it is replaced with a *note
RuntimeError: 3dc. before it exits the generator frame.  The main goal
of this change is to ease debugging in the situation where an unguarded
*note next(): 775. call raises ‘StopIteration’ and causes the iteration
controlled by the generator to terminate silently.  This is particularly
pernicious in combination with the ‘yield from’ construct.

This is a backwards incompatible change, so to enable the new behavior,
a *note __future__: 776. import is necessary:

     >>> from __future__ import generator_stop

     >>> def gen():
     ...     next(iter([]))
     ...     yield
     ...
     >>> next(gen())
     Traceback (most recent call last):
       File "<stdin>", line 2, in gen
     StopIteration

     The above exception was the direct cause of the following exception:

     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     RuntimeError: generator raised StopIteration

Without a ‘__future__’ import, a *note PendingDeprecationWarning: 15c.
will be raised whenever a *note StopIteration: 582. exception is raised
inside a generator.

See also
........

PEP 479(2) – Change StopIteration handling inside generators

     PEP written by Chris Angelico and Guido van Rossum.  Implemented by
     Chris Angelico, Yury Selivanov and Nick Coghlan.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0479

   (2) https://www.python.org/dev/peps/pep-0479


File: python.info,  Node: PEP 485 A function for testing approximate equality,  Next: PEP 486 Make the Python Launcher aware of virtual environments,  Prev: PEP 479 Change StopIteration handling inside generators,  Up: New Features<6>

1.5.2.9 PEP 485: A function for testing approximate equality
............................................................

PEP 485(1) adds the *note math.isclose(): 779. and *note
cmath.isclose(): 77a. functions which tell whether two values are
approximately equal or “close” to each other.  Whether or not two values
are considered close is determined according to given absolute and
relative tolerances.  Relative tolerance is the maximum allowed
difference between ‘isclose’ arguments, relative to the larger absolute
value:

     >>> import math
     >>> a = 5.0
     >>> b = 4.99998
     >>> math.isclose(a, b, rel_tol=1e-5)
     True
     >>> math.isclose(a, b, rel_tol=1e-6)
     False

It is also possible to compare two values using absolute tolerance,
which must be a non-negative value:

     >>> import math
     >>> a = 5.0
     >>> b = 4.99998
     >>> math.isclose(a, b, abs_tol=0.00003)
     True
     >>> math.isclose(a, b, abs_tol=0.00001)
     False

See also
........

PEP 485(2) – A function for testing approximate equality

     PEP written by Christopher Barker; implemented by Chris Barker and
     Tal Einat.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0485

   (2) https://www.python.org/dev/peps/pep-0485


File: python.info,  Node: PEP 486 Make the Python Launcher aware of virtual environments,  Next: PEP 488 Elimination of PYO files,  Prev: PEP 485 A function for testing approximate equality,  Up: New Features<6>

1.5.2.10 PEP 486: Make the Python Launcher aware of virtual environments
........................................................................

PEP 486(1) makes the Windows launcher (see PEP 397(2)) aware of an
active virtual environment.  When the default interpreter would be used
and the ‘VIRTUAL_ENV’ environment variable is set, the interpreter in
the virtual environment will be used.

See also
........

PEP 486(3) – Make the Python Launcher aware of virtual environments

     PEP written and implemented by Paul Moore.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0486

   (2) https://www.python.org/dev/peps/pep-0397

   (3) https://www.python.org/dev/peps/pep-0486


File: python.info,  Node: PEP 488 Elimination of PYO files,  Next: PEP 489 Multi-phase extension module initialization,  Prev: PEP 486 Make the Python Launcher aware of virtual environments,  Up: New Features<6>

1.5.2.11 PEP 488: Elimination of PYO files
..........................................

PEP 488(1) does away with the concept of ‘.pyo’ files.  This means that
‘.pyc’ files represent both unoptimized and optimized bytecode.  To
prevent the need to constantly regenerate bytecode files, ‘.pyc’ files
now have an optional ‘opt-’ tag in their name when the bytecode is
optimized.  This has the side-effect of no more bytecode file name
clashes when running under either *note -O: 77e. or *note -OO: 77f.
Consequently, bytecode files generated from *note -O: 77e, and *note
-OO: 77f. may now exist simultaneously.  *note
importlib.util.cache_from_source(): 651. has an updated API to help with
this change.

See also
........

PEP 488(2) – Elimination of PYO files

     PEP written and implemented by Brett Cannon.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0488

   (2) https://www.python.org/dev/peps/pep-0488


File: python.info,  Node: PEP 489 Multi-phase extension module initialization,  Prev: PEP 488 Elimination of PYO files,  Up: New Features<6>

1.5.2.12 PEP 489: Multi-phase extension module initialization
.............................................................

PEP 489(1) updates extension module initialization to take advantage of
the two step module loading mechanism introduced by PEP 451(2) in Python
3.4.

This change brings the import semantics of extension modules that opt-in
to using the new mechanism much closer to those of Python source and
bytecode modules, including the ability to use any valid identifier as a
module name, rather than being restricted to ASCII.

See also
........

PEP 489(3) – Multi-phase extension module initialization

     PEP written by Petr Viktorin, Stefan Behnel, and Nick Coghlan;
     implemented by Petr Viktorin.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0489

   (2) https://www.python.org/dev/peps/pep-0451

   (3) https://www.python.org/dev/peps/pep-0489


File: python.info,  Node: Other Language Changes<5>,  Next: New Modules<5>,  Prev: New Features<6>,  Up: What’s New In Python 3 5

1.5.3 Other Language Changes
----------------------------

Some smaller changes made to the core Python language are:

   * Added the ‘"namereplace"’ error handlers.  The ‘"backslashreplace"’
     error handlers now work with decoding and translating.
     (Contributed by Serhiy Storchaka in bpo-19676(1) and bpo-22286(2).)

   * The *note -b: 51a. option now affects comparisons of *note bytes:
     172. with *note int: 204.  (Contributed by Serhiy Storchaka in
     bpo-23681(3).)

   * New Kazakh ‘kz1048’ and Tajik ‘koi8_t’ *note codecs: 782.
     (Contributed by Serhiy Storchaka in bpo-22682(4) and bpo-22681(5).)

   * Property docstrings are now writable.  This is especially useful
     for *note collections.namedtuple(): 1a1. docstrings.  (Contributed
     by Berker Peksag in bpo-24064(6).)

   * Circular imports involving relative imports are now supported.
     (Contributed by Brett Cannon and Antoine Pitrou in bpo-17636(7).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19676

   (2) https://bugs.python.org/issue22286

   (3) https://bugs.python.org/issue23681

   (4) https://bugs.python.org/issue22682

   (5) https://bugs.python.org/issue22681

   (6) https://bugs.python.org/issue24064

   (7) https://bugs.python.org/issue17636


File: python.info,  Node: New Modules<5>,  Next: Improved Modules<5>,  Prev: Other Language Changes<5>,  Up: What’s New In Python 3 5

1.5.4 New Modules
-----------------

* Menu:

* typing: typing<5>.
* zipapp: zipapp<2>.


File: python.info,  Node: typing<5>,  Next: zipapp<2>,  Up: New Modules<5>

1.5.4.1 typing
..............

The new *note typing: 122. *note provisional: 454. module provides
standard definitions and tools for function type annotations.  See *note
Type Hints: 721. for more information.


File: python.info,  Node: zipapp<2>,  Prev: typing<5>,  Up: New Modules<5>

1.5.4.2 zipapp
..............

The new *note zipapp: 14a. module (specified in PEP 441(1)) provides an
API and command line tool for creating executable Python Zip
Applications, which were introduced in Python 2.6 in bpo-1739468(2), but
which were not well publicized, either at the time or since.

With the new module, bundling your application is as simple as putting
all the files, including a ‘__main__.py’ file, into a directory ‘myapp’
and running:

     $ python -m zipapp myapp
     $ python myapp.pyz

The module implementation has been contributed by Paul Moore in
bpo-23491(3).

See also
........

PEP 441(4) – Improving Python ZIP Application Support

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0441

   (2) https://bugs.python.org/issue1739468

   (3) https://bugs.python.org/issue23491

   (4) https://www.python.org/dev/peps/pep-0441


File: python.info,  Node: Improved Modules<5>,  Next: Other module-level changes,  Prev: New Modules<5>,  Up: What’s New In Python 3 5

1.5.5 Improved Modules
----------------------

* Menu:

* argparse: argparse<2>.
* asyncio: asyncio<6>.
* bz2::
* cgi::
* cmath: cmath<2>.
* code::
* collections: collections<5>.
* collections.abc: collections abc<2>.
* compileall: compileall<3>.
* concurrent.futures: concurrent futures<4>.
* configparser::
* contextlib: contextlib<3>.
* csv: csv<2>.
* curses: curses<3>.
* dbm: dbm<4>.
* difflib::
* distutils: distutils<5>.
* doctest::
* email: email<2>.
* enum: enum<4>.
* faulthandler: faulthandler<2>.
* functools: functools<3>.
* glob::
* gzip: gzip<2>.
* heapq::
* http: http<2>.
* http.client: http client<3>.
* idlelib and IDLE: idlelib and IDLE<3>.
* imaplib: imaplib<2>.
* imghdr::
* importlib: importlib<6>.
* inspect: inspect<4>.
* io: io<3>.
* ipaddress: ipaddress<3>.
* json: json<2>.
* linecache::
* locale: locale<3>.
* logging: logging<4>.
* lzma::
* math: math<5>.
* multiprocessing: multiprocessing<5>.
* operator::
* os: os<6>.
* pathlib: pathlib<5>.
* pickle: pickle<3>.
* poplib: poplib<2>.
* re: re<4>.
* readline: readline<2>.
* selectors::
* shutil: shutil<2>.
* signal: signal<3>.
* smtpd::
* smtplib: smtplib<2>.
* sndhdr::
* socket: socket<6>.
* ssl: ssl<6>.
* sqlite3: sqlite3<3>.
* subprocess: subprocess<3>.
* sys: sys<6>.
* sysconfig::
* tarfile: tarfile<2>.
* threading: threading<3>.
* time: time<5>.
* timeit: timeit<2>.
* tkinter: tkinter<5>.
* traceback: traceback<2>.
* types: types<2>.
* unicodedata: unicodedata<5>.
* unittest: unittest<3>.
* unittest.mock: unittest mock<3>.
* urllib::
* wsgiref::
* xmlrpc: xmlrpc<2>.
* xml.sax: xml sax.
* zipfile: zipfile<3>.


File: python.info,  Node: argparse<2>,  Next: asyncio<6>,  Up: Improved Modules<5>

1.5.5.1 argparse
................

The *note ArgumentParser: 788. class now allows disabling *note
abbreviated usage: 789. of long options by setting *note allow_abbrev:
78a. to ‘False’.  (Contributed by Jonathan Paugh, Steven Bethard, paul
j3 and Daniel Eriksson in bpo-14910(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14910


File: python.info,  Node: asyncio<6>,  Next: bz2,  Prev: argparse<2>,  Up: Improved Modules<5>

1.5.5.2 asyncio
...............

Since the *note asyncio: 9. module is *note provisional: 454, all
changes introduced in Python 3.5 have also been backported to Python
3.4.x.

Notable changes in the *note asyncio: 9. module since Python 3.4.0:

   * New debugging APIs: *note loop.set_debug(): 78c. and *note
     loop.get_debug(): 78d. methods.  (Contributed by Victor Stinner.)

   * The proactor event loop now supports SSL. (Contributed by Antoine
     Pitrou and Victor Stinner in bpo-22560(1).)

   * A new *note loop.is_closed(): 78e. method to check if the event
     loop is closed.  (Contributed by Victor Stinner in bpo-21326(2).)

   * A new *note loop.create_task(): 2e2. to conveniently create and
     schedule a new *note Task: 2e0. for a coroutine.  The ‘create_task’
     method is also used by all asyncio functions that wrap coroutines
     into tasks, such as *note asyncio.wait(): 207, *note
     asyncio.gather(): 3ab, etc.  (Contributed by Victor Stinner.)

   * A new *note transport.get_write_buffer_limits(): 78f. method to
     inquire for `high-' and `low-' water limits of the flow control.
     (Contributed by Victor Stinner.)

   * The ‘async()’ function is deprecated in favor of *note
     ensure_future(): 611.  (Contributed by Yury Selivanov.)

   * New *note loop.set_task_factory(): 790. and *note
     loop.get_task_factory(): 791. methods to customize the task factory
     that *note loop.create_task(): 2e2. method uses.  (Contributed by
     Yury Selivanov.)

   * New *note Queue.join(): 792. and *note Queue.task_done(): 793.
     queue methods.  (Contributed by Victor Stinner.)

   * The ‘JoinableQueue’ class was removed, in favor of the *note
     asyncio.Queue: 3b3. class.  (Contributed by Victor Stinner.)

Updates in 3.5.1:

   * The *note ensure_future(): 611. function and all functions that use
     it, such as *note loop.run_until_complete(): 612, now accept all
     kinds of *note awaitable objects: 613.  (Contributed by Yury
     Selivanov.)

   * New *note run_coroutine_threadsafe(): 614. function to submit
     coroutines to event loops from other threads.  (Contributed by
     Vincent Michel.)

   * New *note Transport.is_closing(): 615. method to check if the
     transport is closing or closed.  (Contributed by Yury Selivanov.)

   * The *note loop.create_server(): 465. method can now accept a list
     of hosts.  (Contributed by Yann Sionneau.)

Updates in 3.5.2:

   * New *note loop.create_future(): 616. method to create Future
     objects.  This allows alternative event loop implementations, such
     as uvloop(3), to provide a faster *note asyncio.Future: 546.
     implementation.  (Contributed by Yury Selivanov.)

   * New *note loop.get_exception_handler(): 617. method to get the
     current exception handler.  (Contributed by Yury Selivanov.)

   * New *note StreamReader.readuntil(): 618. method to read data from
     the stream until a separator bytes sequence appears.  (Contributed
     by Mark Korenberg.)

   * The *note loop.create_connection(): 2e5. and *note
     loop.create_server(): 465. methods are optimized to avoid calling
     the system ‘getaddrinfo’ function if the address is already
     resolved.  (Contributed by A. Jesse Jiryu Davis.)

   * The *note loop.sock_connect(sock, address): 794. no longer requires
     the `address' to be resolved prior to the call.  (Contributed by A.
     Jesse Jiryu Davis.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22560

   (2) https://bugs.python.org/issue21326

   (3) https://github.com/MagicStack/uvloop


File: python.info,  Node: bz2,  Next: cgi,  Prev: asyncio<6>,  Up: Improved Modules<5>

1.5.5.3 bz2
...........

The *note BZ2Decompressor.decompress: 796. method now accepts an
optional `max_length' argument to limit the maximum size of decompressed
data.  (Contributed by Nikolaus Rath in bpo-15955(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15955


File: python.info,  Node: cgi,  Next: cmath<2>,  Prev: bz2,  Up: Improved Modules<5>

1.5.5.4 cgi
...........

The ‘FieldStorage’ class now supports the *note context manager: 661.
protocol.  (Contributed by Berker Peksag in bpo-20289(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20289


File: python.info,  Node: cmath<2>,  Next: code,  Prev: cgi,  Up: Improved Modules<5>

1.5.5.5 cmath
.............

A new function *note isclose(): 77a. provides a way to test for
approximate equality.  (Contributed by Chris Barker and Tal Einat in
bpo-24270(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24270


File: python.info,  Node: code,  Next: collections<5>,  Prev: cmath<2>,  Up: Improved Modules<5>

1.5.5.6 code
............

The *note InteractiveInterpreter.showtraceback(): 79a. method now prints
the full chained traceback, just like the interactive interpreter.
(Contributed by Claudiu Popa in bpo-17442(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17442


File: python.info,  Node: collections<5>,  Next: collections abc<2>,  Prev: code,  Up: Improved Modules<5>

1.5.5.7 collections
...................

The *note OrderedDict: 2ea. class is now implemented in C, which makes
it 4 to 100 times faster.  (Contributed by Eric Snow in bpo-16991(1).)

‘OrderedDict.items()’, ‘OrderedDict.keys()’, ‘OrderedDict.values()’
views now support *note reversed(): 2c6. iteration.  (Contributed by
Serhiy Storchaka in bpo-19505(2).)

The *note deque: 62b. class now defines *note index(): 79c, *note
insert(): 79d, and *note copy(): 79e, and supports the ‘+’ and ‘*’
operators.  This allows deques to be recognized as a *note
MutableSequence: 79f. and improves their substitutability for lists.
(Contributed by Raymond Hettinger in bpo-23704(3).)

Docstrings produced by *note namedtuple(): 1a1. can now be updated:

     Point = namedtuple('Point', ['x', 'y'])
     Point.__doc__ += ': Cartesian coodinate'
     Point.x.__doc__ = 'abscissa'
     Point.y.__doc__ = 'ordinate'

(Contributed by Berker Peksag in bpo-24064(4).)

The *note UserString: 7a0. class now implements the *note
__getnewargs__(): 7a1, *note __rmod__(): 7a2, *note casefold(): 7a3,
*note format_map(): 7a4, *note isprintable(): 7a5, and *note
maketrans(): 7a6. methods to match the corresponding methods of *note
str: 205.  (Contributed by Joe Jevnik in bpo-22189(5).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16991

   (2) https://bugs.python.org/issue19505

   (3) https://bugs.python.org/issue23704

   (4) https://bugs.python.org/issue24064

   (5) https://bugs.python.org/issue22189


File: python.info,  Node: collections abc<2>,  Next: compileall<3>,  Prev: collections<5>,  Up: Improved Modules<5>

1.5.5.8 collections.abc
.......................

The ‘Sequence.index()’ method now accepts `start' and `stop' arguments
to match the corresponding methods of *note tuple: 1a2, *note list: 1f8,
etc.  (Contributed by Devin Jeanpierre in bpo-23086(1).)

A new *note Generator: 7a8. abstract base class.  (Contributed by Stefan
Behnel in bpo-24018(2).)

New *note Awaitable: 7a9, *note Coroutine: 7aa, *note AsyncIterator:
7ab, and *note AsyncIterable: 7ac. abstract base classes.  (Contributed
by Yury Selivanov in bpo-24184(3).)

For earlier Python versions, a backport of the new ABCs is available in
an external PyPI package(4).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23086

   (2) https://bugs.python.org/issue24018

   (3) https://bugs.python.org/issue24184

   (4) https://pypi.org/project/backports_abc


File: python.info,  Node: compileall<3>,  Next: concurrent futures<4>,  Prev: collections abc<2>,  Up: Improved Modules<5>

1.5.5.9 compileall
..................

A new *note compileall: 20. option, ‘-j `N'’, allows running `N' workers
simultaneously to perform parallel bytecode compilation.  The *note
compile_dir(): 47a. function has a corresponding ‘workers’ parameter.
(Contributed by Claudiu Popa in bpo-16104(1).)

Another new option, ‘-r’, allows controlling the maximum recursion level
for subdirectories.  (Contributed by Claudiu Popa in bpo-19628(2).)

The ‘-q’ command line option can now be specified more than once, in
which case all output, including errors, will be suppressed.  The
corresponding ‘quiet’ parameter in *note compile_dir(): 47a, *note
compile_file(): 7ae, and *note compile_path(): 7af. can now accept an
integer value indicating the level of output suppression.  (Contributed
by Thomas Kluyver in bpo-21338(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16104

   (2) https://bugs.python.org/issue19628

   (3) https://bugs.python.org/issue21338


File: python.info,  Node: concurrent futures<4>,  Next: configparser,  Prev: compileall<3>,  Up: Improved Modules<5>

1.5.5.10 concurrent.futures
...........................

The *note Executor.map(): 7b1. method now accepts a `chunksize' argument
to allow batching of tasks to improve performance when *note
ProcessPoolExecutor(): 196. is used.  (Contributed by Dan O’Reilly in
bpo-11271(1).)

The number of workers in the *note ThreadPoolExecutor: 18c. constructor
is optional now.  The default value is 5 times the number of CPUs.
(Contributed by Claudiu Popa in bpo-21527(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11271

   (2) https://bugs.python.org/issue21527


File: python.info,  Node: configparser,  Next: contextlib<3>,  Prev: concurrent futures<4>,  Up: Improved Modules<5>

1.5.5.11 configparser
.....................

*note configparser: 22. now provides a way to customize the conversion
of values by specifying a dictionary of converters in the *note
ConfigParser: 5a5. constructor, or by defining them as methods in
‘ConfigParser’ subclasses.  Converters defined in a parser instance are
inherited by its section proxies.

Example:

     >>> import configparser
     >>> conv = {}
     >>> conv['list'] = lambda v: [e.strip() for e in v.split() if e.strip()]
     >>> cfg = configparser.ConfigParser(converters=conv)
     >>> cfg.read_string("""
     ... [s]
     ... list = a b c d e f g
     ... """)
     >>> cfg.get('s', 'list')
     'a b c d e f g'
     >>> cfg.getlist('s', 'list')
     ['a', 'b', 'c', 'd', 'e', 'f', 'g']
     >>> section = cfg['s']
     >>> section.getlist('list')
     ['a', 'b', 'c', 'd', 'e', 'f', 'g']

(Contributed by Łukasz Langa in bpo-18159(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18159


File: python.info,  Node: contextlib<3>,  Next: csv<2>,  Prev: configparser,  Up: Improved Modules<5>

1.5.5.12 contextlib
...................

The new *note redirect_stderr(): 7b4. *note context manager: 661.
(similar to *note redirect_stdout(): 7b5.) makes it easier for utility
scripts to handle inflexible APIs that write their output to *note
sys.stderr: 1ea. and don’t provide any options to redirect it:

     >>> import contextlib, io, logging
     >>> f = io.StringIO()
     >>> with contextlib.redirect_stderr(f):
     ...     logging.warning('warning')
     ...
     >>> f.getvalue()
     'WARNING:root:warning\n'

(Contributed by Berker Peksag in bpo-22389(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22389


File: python.info,  Node: csv<2>,  Next: curses<3>,  Prev: contextlib<3>,  Up: Improved Modules<5>

1.5.5.13 csv
............

The *note writerow(): 7b7. method now supports arbitrary iterables, not
just sequences.  (Contributed by Serhiy Storchaka in bpo-23171(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23171


File: python.info,  Node: curses<3>,  Next: dbm<4>,  Prev: csv<2>,  Up: Improved Modules<5>

1.5.5.14 curses
...............

The new *note update_lines_cols(): 7b9. function updates the ‘LINES’ and
‘COLS’ environment variables.  This is useful for detecting manual
screen resizing.  (Contributed by Arnon Yaari in bpo-4254(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4254


File: python.info,  Node: dbm<4>,  Next: difflib,  Prev: curses<3>,  Up: Improved Modules<5>

1.5.5.15 dbm
............

*note dumb.open: 3e1. always creates a new database when the flag has
the value ‘"n"’.  (Contributed by Claudiu Popa in bpo-18039(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18039


File: python.info,  Node: difflib,  Next: distutils<5>,  Prev: dbm<4>,  Up: Improved Modules<5>

1.5.5.16 difflib
................

The charset of HTML documents generated by *note HtmlDiff.make_file():
7bc. can now be customized by using a new `charset' keyword-only
argument.  The default charset of HTML document changed from
‘"ISO-8859-1"’ to ‘"utf-8"’.  (Contributed by Berker Peksag in
bpo-2052(1).)

The *note diff_bytes(): 7bd. function can now compare lists of byte
strings.  This fixes a regression from Python 2.  (Contributed by Terry
J. Reedy and Greg Ward in bpo-17445(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue2052

   (2) https://bugs.python.org/issue17445


File: python.info,  Node: distutils<5>,  Next: doctest,  Prev: difflib,  Up: Improved Modules<5>

1.5.5.17 distutils
..................

Both the ‘build’ and ‘build_ext’ commands now accept a ‘-j’ option to
enable parallel building of extension modules.  (Contributed by Antoine
Pitrou in bpo-5309(1).)

The *note distutils: 38. module now supports ‘xz’ compression, and can
be enabled by passing ‘xztar’ as an argument to ‘bdist --format’.
(Contributed by Serhiy Storchaka in bpo-16314(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5309

   (2) https://bugs.python.org/issue16314


File: python.info,  Node: doctest,  Next: email<2>,  Prev: distutils<5>,  Up: Improved Modules<5>

1.5.5.18 doctest
................

The *note DocTestSuite(): 7c0. function returns an empty *note
unittest.TestSuite: 7c1. if `module' contains no docstrings, instead of
raising *note ValueError: 16d.  (Contributed by Glenn Jones in
bpo-15916(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15916


File: python.info,  Node: email<2>,  Next: enum<4>,  Prev: doctest,  Up: Improved Modules<5>

1.5.5.19 email
..............

A new policy option *note Policy.mangle_from_: 7c3. controls whether or
not lines that start with ‘"From "’ in email bodies are prefixed with a
‘">"’ character by generators.  The default is ‘True’ for *note
compat32: 63a. and ‘False’ for all other policies.  (Contributed by
Milan Oberkirch in bpo-20098(1).)

A new *note Message.get_content_disposition(): 7c4. method provides easy
access to a canonical value for the ‘Content-Disposition’ header.
(Contributed by Abhilash Raj in bpo-21083(2).)

A new policy option *note EmailPolicy.utf8: 7c5. can be set to ‘True’ to
encode email headers using the UTF-8 charset instead of using encoded
words.  This allows ‘Messages’ to be formatted according to RFC 6532(3)
and used with an SMTP server that supports the RFC 6531(4) ‘SMTPUTF8’
extension.  (Contributed by R. David Murray in bpo-24211(5).)

The *note mime.text.MIMEText: 7c6. constructor now accepts a *note
charset.Charset: 7c7. instance.  (Contributed by Claude Paroz and Berker
Peksag in bpo-16324(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20098

   (2) https://bugs.python.org/issue21083

   (3) https://tools.ietf.org/html/rfc6532.html

   (4) https://tools.ietf.org/html/rfc6531.html

   (5) https://bugs.python.org/issue24211

   (6) https://bugs.python.org/issue16324


File: python.info,  Node: enum<4>,  Next: faulthandler<2>,  Prev: email<2>,  Up: Improved Modules<5>

1.5.5.20 enum
.............

The *note Enum: 48e. callable has a new parameter `start' to specify the
initial number of enum values if only `names' are provided:

     >>> Animal = enum.Enum('Animal', 'cat dog', start=10)
     >>> Animal.cat
     <Animal.cat: 10>
     >>> Animal.dog
     <Animal.dog: 11>

(Contributed by Ethan Furman in bpo-21706(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21706


File: python.info,  Node: faulthandler<2>,  Next: functools<3>,  Prev: enum<4>,  Up: Improved Modules<5>

1.5.5.21 faulthandler
.....................

The *note enable(): 642, *note register(): 7ca, *note dump_traceback():
7cb. and *note dump_traceback_later(): 7cc. functions now accept file
descriptors in addition to file-like objects.  (Contributed by Wei Wu in
bpo-23566(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23566


File: python.info,  Node: functools<3>,  Next: glob,  Prev: faulthandler<2>,  Up: Improved Modules<5>

1.5.5.22 functools
..................

Most of the *note lru_cache(): 2f8. machinery is now implemented in C,
making it significantly faster.  (Contributed by Matt Joiner, Alexey
Kachayev, and Serhiy Storchaka in bpo-14373(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14373


File: python.info,  Node: glob,  Next: gzip<2>,  Prev: functools<3>,  Up: Improved Modules<5>

1.5.5.23 glob
.............

The *note iglob(): 6be. and *note glob(): 6bd. functions now support
recursive search in subdirectories, using the ‘"**"’ pattern.
(Contributed by Serhiy Storchaka in bpo-13968(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13968


File: python.info,  Node: gzip<2>,  Next: heapq,  Prev: glob,  Up: Improved Modules<5>

1.5.5.24 gzip
.............

The `mode' argument of the *note GzipFile: 206. constructor now accepts
‘"x"’ to request exclusive creation.  (Contributed by Tim Heaney in
bpo-19222(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19222


File: python.info,  Node: heapq,  Next: http<2>,  Prev: gzip<2>,  Up: Improved Modules<5>

1.5.5.25 heapq
..............

Element comparison in *note merge(): 7d1. can now be customized by
passing a *note key function: 7d2. in a new optional `key' keyword
argument, and a new optional `reverse' keyword argument can be used to
reverse element comparison:

     >>> import heapq
     >>> a = ['9', '777', '55555']
     >>> b = ['88', '6666']
     >>> list(heapq.merge(a, b, key=len))
     ['9', '88', '777', '6666', '55555']
     >>> list(heapq.merge(reversed(a), reversed(b), key=len, reverse=True))
     ['55555', '6666', '777', '88', '9']

(Contributed by Raymond Hettinger in bpo-13742(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13742


File: python.info,  Node: http<2>,  Next: http client<3>,  Prev: heapq,  Up: Improved Modules<5>

1.5.5.26 http
.............

A new *note HTTPStatus: 1ac. enum that defines a set of HTTP status
codes, reason phrases and long descriptions written in English.
(Contributed by Demian Brecht in bpo-21793(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21793


File: python.info,  Node: http client<3>,  Next: idlelib and IDLE<3>,  Prev: http<2>,  Up: Improved Modules<5>

1.5.5.27 http.client
....................

*note HTTPConnection.getresponse(): 7d5. now raises a *note
RemoteDisconnected: 7d6. exception when a remote server connection is
closed unexpectedly.  Additionally, if a *note ConnectionError: 7d7. (of
which ‘RemoteDisconnected’ is a subclass) is raised, the client socket
is now closed automatically, and will reconnect on the next request:

     import http.client
     conn = http.client.HTTPConnection('www.python.org')
     for retries in range(3):
         try:
             conn.request('GET', '/')
             resp = conn.getresponse()
         except http.client.RemoteDisconnected:
             pass

(Contributed by Martin Panter in bpo-3566(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue3566


File: python.info,  Node: idlelib and IDLE<3>,  Next: imaplib<2>,  Prev: http client<3>,  Up: Improved Modules<5>

1.5.5.28 idlelib and IDLE
.........................

Since idlelib implements the IDLE shell and editor and is not intended
for import by other programs, it gets improvements with every release.
See ‘Lib/idlelib/NEWS.txt’ for a cumulative list of changes since 3.4.0,
as well as changes made in future 3.5.x releases.  This file is also
available from the IDLE Help ‣ About IDLE dialog.


File: python.info,  Node: imaplib<2>,  Next: imghdr,  Prev: idlelib and IDLE<3>,  Up: Improved Modules<5>

1.5.5.29 imaplib
................

The *note IMAP4: 1af. class now supports the *note context manager: 661.
protocol.  When used in a *note with: 7da. statement, the IMAP4 ‘LOGOUT’
command will be called automatically at the end of the block.
(Contributed by Tarek Ziadé and Serhiy Storchaka in bpo-4972(1).)

The *note imaplib: 97. module now supports RFC 5161(2) (ENABLE
Extension) and RFC 6855(3) (UTF-8 Support) via the *note IMAP4.enable():
7db. method.  A new *note IMAP4.utf8_enabled: 7dc. attribute tracks
whether or not RFC 6855(4) support is enabled.  (Contributed by Milan
Oberkirch, R. David Murray, and Maciej Szulik in bpo-21800(5).)

The *note imaplib: 97. module now automatically encodes non-ASCII string
usernames and passwords using UTF-8, as recommended by the RFCs.
(Contributed by Milan Oberkirch in bpo-21800(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4972

   (2) https://tools.ietf.org/html/rfc5161.html

   (3) https://tools.ietf.org/html/rfc6855.html

   (4) https://tools.ietf.org/html/rfc6855.html

   (5) https://bugs.python.org/issue21800

   (6) https://bugs.python.org/issue21800


File: python.info,  Node: imghdr,  Next: importlib<6>,  Prev: imaplib<2>,  Up: Improved Modules<5>

1.5.5.30 imghdr
...............

The *note what(): 7de. function now recognizes the OpenEXR(1) format
(contributed by Martin Vignali and Claudiu Popa in bpo-20295(2)), and
the WebP(3) format (contributed by Fabrice Aneche and Claudiu Popa in
bpo-20197(4).)

   ---------- Footnotes ----------

   (1) http://www.openexr.com

   (2) https://bugs.python.org/issue20295

   (3) https://en.wikipedia.org/wiki/WebP

   (4) https://bugs.python.org/issue20197


File: python.info,  Node: importlib<6>,  Next: inspect<4>,  Prev: imghdr,  Up: Improved Modules<5>

1.5.5.31 importlib
..................

The *note util.LazyLoader: 64d. class allows for lazy loading of modules
in applications where startup time is important.  (Contributed by Brett
Cannon in bpo-17621(1).)

The *note abc.InspectLoader.source_to_code(): 7e0. method is now a
static method.  This makes it easier to initialize a module object with
code compiled from a string by running ‘exec(code, module.__dict__)’.
(Contributed by Brett Cannon in bpo-21156(2).)

The new *note util.module_from_spec(): 7e1. function is now the
preferred way to create a new module.  As opposed to creating a *note
types.ModuleType: 7e2. instance directly, this new function will set the
various import-controlled attributes based on the passed-in spec object.
(Contributed by Brett Cannon in bpo-20383(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17621

   (2) https://bugs.python.org/issue21156

   (3) https://bugs.python.org/issue20383


File: python.info,  Node: inspect<4>,  Next: io<3>,  Prev: importlib<6>,  Up: Improved Modules<5>

1.5.5.32 inspect
................

Both the *note Signature: 7e4. and *note Parameter: 7e5. classes are now
picklable and hashable.  (Contributed by Yury Selivanov in bpo-20726(1)
and bpo-20334(2).)

A new *note BoundArguments.apply_defaults(): 7e6. method provides a way
to set default values for missing arguments:

     >>> def foo(a, b='ham', *args): pass
     >>> ba = inspect.signature(foo).bind('spam')
     >>> ba.apply_defaults()
     >>> ba.arguments
     OrderedDict([('a', 'spam'), ('b', 'ham'), ('args', ())])

(Contributed by Yury Selivanov in bpo-24190(3).)

A new class method *note Signature.from_callable(): 7e7. makes
subclassing of *note Signature: 7e4. easier.  (Contributed by Yury
Selivanov and Eric Snow in bpo-17373(4).)

The *note signature(): 655. function now accepts a `follow_wrapped'
optional keyword argument, which, when set to ‘False’, disables
automatic following of ‘__wrapped__’ links.  (Contributed by Yury
Selivanov in bpo-20691(5).)

A set of new functions to inspect *note coroutine functions: 732. and
*note coroutine objects: 18a. has been added: *note iscoroutine(): 7e8,
*note iscoroutinefunction(): 7e9, *note isawaitable(): 7ea, *note
getcoroutinelocals(): 7eb, and *note getcoroutinestate(): 7ec.
(Contributed by Yury Selivanov in bpo-24017(6) and bpo-24400(7).)

The *note stack(): 7ed, *note trace(): 7ee, *note getouterframes(): 7ef,
and *note getinnerframes(): 7f0. functions now return a list of named
tuples.  (Contributed by Daniel Shahaf in bpo-16808(8).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20726

   (2) https://bugs.python.org/issue20334

   (3) https://bugs.python.org/issue24190

   (4) https://bugs.python.org/issue17373

   (5) https://bugs.python.org/issue20691

   (6) https://bugs.python.org/issue24017

   (7) https://bugs.python.org/issue24400

   (8) https://bugs.python.org/issue16808


File: python.info,  Node: io<3>,  Next: ipaddress<3>,  Prev: inspect<4>,  Up: Improved Modules<5>

1.5.5.33 io
...........

A new *note BufferedIOBase.readinto1(): 7f2. method, that uses at most
one call to the underlying raw stream’s *note RawIOBase.read(): 7f3. or
*note RawIOBase.readinto(): 7f4. methods.  (Contributed by Nikolaus Rath
in bpo-20578(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20578


File: python.info,  Node: ipaddress<3>,  Next: json<2>,  Prev: io<3>,  Up: Improved Modules<5>

1.5.5.34 ipaddress
..................

Both the *note IPv4Network: 4a7. and *note IPv6Network: 4a6. classes now
accept an ‘(address, netmask)’ tuple argument, so as to easily construct
network objects from existing addresses:

     >>> import ipaddress
     >>> ipaddress.IPv4Network(('127.0.0.0', 8))
     IPv4Network('127.0.0.0/8')
     >>> ipaddress.IPv4Network(('127.0.0.0', '255.0.0.0'))
     IPv4Network('127.0.0.0/8')

(Contributed by Peter Moody and Antoine Pitrou in bpo-16531(1).)

A new ‘reverse_pointer’ attribute for the *note IPv4Network: 4a7. and
*note IPv6Network: 4a6. classes returns the name of the reverse DNS PTR
record:

     >>> import ipaddress
     >>> addr = ipaddress.IPv4Address('127.0.0.1')
     >>> addr.reverse_pointer
     '1.0.0.127.in-addr.arpa'
     >>> addr6 = ipaddress.IPv6Address('::1')
     >>> addr6.reverse_pointer
     '1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa'

(Contributed by Leon Weber in bpo-20480(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16531

   (2) https://bugs.python.org/issue20480


File: python.info,  Node: json<2>,  Next: linecache,  Prev: ipaddress<3>,  Up: Improved Modules<5>

1.5.5.35 json
.............

The *note json.tool: a5. command line interface now preserves the order
of keys in JSON objects passed in input.  The new ‘--sort-keys’ option
can be used to sort the keys alphabetically.  (Contributed by Berker
Peksag in bpo-21650(1).)

JSON decoder now raises *note JSONDecodeError: 7f7. instead of *note
ValueError: 16d. to provide better context information about the error.
(Contributed by Serhiy Storchaka in bpo-19361(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21650

   (2) https://bugs.python.org/issue19361


File: python.info,  Node: linecache,  Next: locale<3>,  Prev: json<2>,  Up: Improved Modules<5>

1.5.5.36 linecache
..................

A new *note lazycache(): 7f9. function can be used to capture
information about a non-file-based module to permit getting its lines
later via *note getline(): 7fa.  This avoids doing I/O until a line is
actually needed, without having to carry the module globals around
indefinitely.  (Contributed by Robert Collins in bpo-17911(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17911


File: python.info,  Node: locale<3>,  Next: logging<4>,  Prev: linecache,  Up: Improved Modules<5>

1.5.5.37 locale
...............

A new *note delocalize(): 7fc. function can be used to convert a string
into a normalized number string, taking the ‘LC_NUMERIC’ settings into
account:

     >>> import locale
     >>> locale.setlocale(locale.LC_NUMERIC, 'de_DE.UTF-8')
     'de_DE.UTF-8'
     >>> locale.delocalize('1.234,56')
     '1234.56'
     >>> locale.setlocale(locale.LC_NUMERIC, 'en_US.UTF-8')
     'en_US.UTF-8'
     >>> locale.delocalize('1,234.56')
     '1234.56'

(Contributed by Cédric Krier in bpo-13918(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13918


File: python.info,  Node: logging<4>,  Next: lzma,  Prev: locale<3>,  Up: Improved Modules<5>

1.5.5.38 logging
................

All logging methods (*note Logger: 4ae. *note log(): 7fe, *note
exception(): 7ff, *note critical(): 800, *note debug(): 801, etc.), now
accept exception instances as an `exc_info' argument, in addition to
boolean values and exception tuples:

     >>> import logging
     >>> try:
     ...     1/0
     ... except ZeroDivisionError as ex:
     ...     logging.error('exception', exc_info=ex)
     ERROR:root:exception

(Contributed by Yury Selivanov in bpo-20537(1).)

The *note handlers.HTTPHandler: 802. class now accepts an optional *note
ssl.SSLContext: 4ea. instance to configure SSL settings used in an HTTP
connection.  (Contributed by Alex Gaynor in bpo-22788(2).)

The *note handlers.QueueListener: 803. class now takes a
`respect_handler_level' keyword argument which, if set to ‘True’, will
pass messages to handlers taking handler levels into account.
(Contributed by Vinay Sajip.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20537

   (2) https://bugs.python.org/issue22788


File: python.info,  Node: lzma,  Next: math<5>,  Prev: logging<4>,  Up: Improved Modules<5>

1.5.5.39 lzma
.............

The *note LZMADecompressor.decompress(): 805. method now accepts an
optional `max_length' argument to limit the maximum size of decompressed
data.  (Contributed by Martin Panter in bpo-15955(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15955


File: python.info,  Node: math<5>,  Next: multiprocessing<5>,  Prev: lzma,  Up: Improved Modules<5>

1.5.5.40 math
.............

Two new constants have been added to the *note math: b1. module: *note
inf: 622. and *note nan: 623.  (Contributed by Mark Dickinson in
bpo-23185(1).)

A new function *note isclose(): 779. provides a way to test for
approximate equality.  (Contributed by Chris Barker and Tal Einat in
bpo-24270(2).)

A new *note gcd(): 1be. function has been added.  The ‘fractions.gcd()’
function is now deprecated.  (Contributed by Mark Dickinson and Serhiy
Storchaka in bpo-22486(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23185

   (2) https://bugs.python.org/issue24270

   (3) https://bugs.python.org/issue22486


File: python.info,  Node: multiprocessing<5>,  Next: operator,  Prev: math<5>,  Up: Improved Modules<5>

1.5.5.41 multiprocessing
........................

*note sharedctypes.synchronized(): 808. objects now support the *note
context manager: 661. protocol.  (Contributed by Charles-François Natali
in bpo-21565(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21565


File: python.info,  Node: operator,  Next: os<6>,  Prev: multiprocessing<5>,  Up: Improved Modules<5>

1.5.5.42 operator
.................

*note attrgetter(): 80a, *note itemgetter(): 38b, and *note
methodcaller(): 80b. objects now support pickling.  (Contributed by Josh
Rosenberg and Serhiy Storchaka in bpo-22955(1).)

New *note matmul(): 80c. and *note imatmul(): 80d. functions to perform
matrix multiplication.  (Contributed by Benjamin Peterson in
bpo-21176(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22955

   (2) https://bugs.python.org/issue21176


File: python.info,  Node: os<6>,  Next: pathlib<5>,  Prev: operator,  Up: Improved Modules<5>

1.5.5.43 os
...........

The new *note scandir(): 389. function returning an iterator of *note
DirEntry: 5eb. objects has been added.  If possible, *note scandir():
389. extracts file attributes while scanning a directory, removing the
need to perform subsequent system calls to determine file type or
attributes, which may significantly improve performance.  (Contributed
by Ben Hoyt with the help of Victor Stinner in bpo-22524(1).)

On Windows, a new *note stat_result.st_file_attributes: 80f. attribute
is now available.  It corresponds to the ‘dwFileAttributes’ member of
the ‘BY_HANDLE_FILE_INFORMATION’ structure returned by
‘GetFileInformationByHandle()’.  (Contributed by Ben Hoyt in
bpo-21719(2).)

The *note urandom(): 5cc. function now uses the ‘getrandom()’ syscall on
Linux 3.17 or newer, and ‘getentropy()’ on OpenBSD 5.6 and newer,
removing the need to use ‘/dev/urandom’ and avoiding failures due to
potential file descriptor exhaustion.  (Contributed by Victor Stinner in
bpo-22181(3).)

New *note get_blocking(): 810. and *note set_blocking(): 811. functions
allow getting and setting a file descriptor’s blocking mode (*note
O_NONBLOCK: 812.)  (Contributed by Victor Stinner in bpo-22054(4).)

The *note truncate(): 813. and *note ftruncate(): 755. functions are now
supported on Windows.  (Contributed by Steve Dower in bpo-23668(5).)

There is a new *note os.path.commonpath(): 814. function returning the
longest common sub-path of each passed pathname.  Unlike the *note
os.path.commonprefix(): 815. function, it always returns a valid path:

     >>> os.path.commonprefix(['/usr/lib', '/usr/local/lib'])
     '/usr/l'

     >>> os.path.commonpath(['/usr/lib', '/usr/local/lib'])
     '/usr'

(Contributed by Rafik Draoui and Serhiy Storchaka in bpo-10395(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22524

   (2) https://bugs.python.org/issue21719

   (3) https://bugs.python.org/issue22181

   (4) https://bugs.python.org/issue22054

   (5) https://bugs.python.org/issue23668

   (6) https://bugs.python.org/issue10395


File: python.info,  Node: pathlib<5>,  Next: pickle<3>,  Prev: os<6>,  Up: Improved Modules<5>

1.5.5.44 pathlib
................

The new *note Path.samefile(): 817. method can be used to check whether
the path points to the same file as another path, which can be either
another *note Path: 32f. object, or a string:

     >>> import pathlib
     >>> p1 = pathlib.Path('/etc/hosts')
     >>> p2 = pathlib.Path('/etc/../etc/hosts')
     >>> p1.samefile(p2)
     True

(Contributed by Vajrasky Kok and Antoine Pitrou in bpo-19775(1).)

The *note Path.mkdir(): 818. method now accepts a new optional
`exist_ok' argument to match ‘mkdir -p’ and *note os.makedirs(): 4c4.
functionality.  (Contributed by Berker Peksag in bpo-21539(2).)

There is a new *note Path.expanduser(): 819. method to expand ‘~’ and
‘~user’ prefixes.  (Contributed by Serhiy Storchaka and Claudiu Popa in
bpo-19776(3).)

A new *note Path.home(): 81a. class method can be used to get a *note
Path: 32f. instance representing the user’s home directory.
(Contributed by Victor Salgado and Mayank Tripathi in bpo-19777(4).)

New *note Path.write_text(): 81b, *note Path.read_text(): 81c, *note
Path.write_bytes(): 81d, *note Path.read_bytes(): 81e. methods to
simplify read/write operations on files.

The following code snippet will create or rewrite existing file
‘~/spam42’:

     >>> import pathlib
     >>> p = pathlib.Path('~/spam42')
     >>> p.expanduser().write_text('ham')
     3

(Contributed by Christopher Welborn in bpo-20218(5).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19775

   (2) https://bugs.python.org/issue21539

   (3) https://bugs.python.org/issue19776

   (4) https://bugs.python.org/issue19777

   (5) https://bugs.python.org/issue20218


File: python.info,  Node: pickle<3>,  Next: poplib<2>,  Prev: pathlib<5>,  Up: Improved Modules<5>

1.5.5.45 pickle
...............

Nested objects, such as unbound methods or nested classes, can now be
pickled using *note pickle protocols: 666. older than protocol version
4.  Protocol version 4 already supports these cases.  (Contributed by
Serhiy Storchaka in bpo-23611(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23611


File: python.info,  Node: poplib<2>,  Next: re<4>,  Prev: pickle<3>,  Up: Improved Modules<5>

1.5.5.46 poplib
...............

A new *note POP3.utf8(): 821. command enables RFC 6856(1)
(Internationalized Email) support, if a POP server supports it.
(Contributed by Milan OberKirch in bpo-21804(2).)

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc6856.html

   (2) https://bugs.python.org/issue21804


File: python.info,  Node: re<4>,  Next: readline<2>,  Prev: poplib<2>,  Up: Improved Modules<5>

1.5.5.47 re
...........

References and conditional references to groups with fixed length are
now allowed in lookbehind assertions:

     >>> import re
     >>> pat = re.compile(r'(a|b).(?<=\1)c')
     >>> pat.match('aac')
     <_sre.SRE_Match object; span=(0, 3), match='aac'>
     >>> pat.match('bbc')
     <_sre.SRE_Match object; span=(0, 3), match='bbc'>

(Contributed by Serhiy Storchaka in bpo-9179(1).)

The number of capturing groups in regular expressions is no longer
limited to 100.  (Contributed by Serhiy Storchaka in bpo-22437(2).)

The *note sub(): 57a. and *note subn(): 823. functions now replace
unmatched groups with empty strings instead of raising an exception.
(Contributed by Serhiy Storchaka in bpo-1519638(3).)

The *note re.error: 824. exceptions have new attributes, *note msg: 825,
*note pattern: 826, *note pos: 827, *note lineno: 828, and *note colno:
829, that provide better context information about the error:

     >>> re.compile("""
     ...     (?x)
     ...     .++
     ... """)
     Traceback (most recent call last):
        ...
     sre_constants.error: multiple repeat at position 16 (line 3, column 7)

(Contributed by Serhiy Storchaka in bpo-22578(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9179

   (2) https://bugs.python.org/issue22437

   (3) https://bugs.python.org/issue1519638

   (4) https://bugs.python.org/issue22578


File: python.info,  Node: readline<2>,  Next: selectors,  Prev: re<4>,  Up: Improved Modules<5>

1.5.5.48 readline
.................

A new *note append_history_file(): 82b. function can be used to append
the specified number of trailing elements in history to the given file.
(Contributed by Bruno Cauet in bpo-22940(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22940


File: python.info,  Node: selectors,  Next: shutil<2>,  Prev: readline<2>,  Up: Improved Modules<5>

1.5.5.49 selectors
..................

The new *note DevpollSelector: 551. supports efficient ‘/dev/poll’
polling on Solaris.  (Contributed by Giampaolo Rodola’ in bpo-18931(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18931


File: python.info,  Node: shutil<2>,  Next: signal<3>,  Prev: selectors,  Up: Improved Modules<5>

1.5.5.50 shutil
...............

The *note move(): 385. function now accepts a `copy_function' argument,
allowing, for example, the *note copy(): 383. function to be used
instead of the default *note copy2(): 384. if there is a need to ignore
file metadata when moving.  (Contributed by Claudiu Popa in
bpo-19840(1).)

The *note make_archive(): 348. function now supports the `xztar' format.
(Contributed by Serhiy Storchaka in bpo-5411(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19840

   (2) https://bugs.python.org/issue5411


File: python.info,  Node: signal<3>,  Next: smtpd,  Prev: shutil<2>,  Up: Improved Modules<5>

1.5.5.51 signal
...............

On Windows, the *note set_wakeup_fd(): 4d5. function now also supports
socket handles.  (Contributed by Victor Stinner in bpo-22018(1).)

Various ‘SIG*’ constants in the *note signal: ea. module have been
converted into *note Enums: 79.  This allows meaningful names to be
printed during debugging, instead of integer “magic numbers”.
(Contributed by Giampaolo Rodola’ in bpo-21076(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22018

   (2) https://bugs.python.org/issue21076


File: python.info,  Node: smtpd,  Next: smtplib<2>,  Prev: signal<3>,  Up: Improved Modules<5>

1.5.5.52 smtpd
..............

Both the *note SMTPServer: 6f9. and *note SMTPChannel: 6f8. classes now
accept a `decode_data' keyword argument to determine if the ‘DATA’
portion of the SMTP transaction is decoded using the ‘"utf-8"’ codec or
is instead provided to the *note SMTPServer.process_message(): 6fa.
method as a byte string.  The default is ‘True’ for backward
compatibility reasons, but will change to ‘False’ in Python 3.6.  If
`decode_data' is set to ‘False’, the ‘process_message’ method must be
prepared to accept keyword arguments.  (Contributed by Maciej Szulik in
bpo-19662(1).)

The *note SMTPServer: 6f9. class now advertises the ‘8BITMIME’ extension
( RFC 6152(2)) if `decode_data' has been set ‘True’.  If the client
specifies ‘BODY=8BITMIME’ on the ‘MAIL’ command, it is passed to *note
SMTPServer.process_message(): 6fa. via the `mail_options' keyword.
(Contributed by Milan Oberkirch and R. David Murray in bpo-21795(3).)

The *note SMTPServer: 6f9. class now also supports the ‘SMTPUTF8’
extension ( RFC 6531(4): Internationalized Email).  If the client
specified ‘SMTPUTF8 BODY=8BITMIME’ on the ‘MAIL’ command, they are
passed to *note SMTPServer.process_message(): 6fa. via the
`mail_options' keyword.  It is the responsibility of the
‘process_message’ method to correctly handle the ‘SMTPUTF8’ data.
(Contributed by Milan Oberkirch in bpo-21725(5).)

It is now possible to provide, directly or via name resolution, IPv6
addresses in the *note SMTPServer: 6f9. constructor, and have it
successfully connect.  (Contributed by Milan Oberkirch in bpo-14758(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19662

   (2) https://tools.ietf.org/html/rfc6152.html

   (3) https://bugs.python.org/issue21795

   (4) https://tools.ietf.org/html/rfc6531.html

   (5) https://bugs.python.org/issue21725

   (6) https://bugs.python.org/issue14758


File: python.info,  Node: smtplib<2>,  Next: sndhdr,  Prev: smtpd,  Up: Improved Modules<5>

1.5.5.53 smtplib
................

A new *note SMTP.auth(): 831. method provides a convenient way to
implement custom authentication mechanisms.  (Contributed by Milan
Oberkirch in bpo-15014(1).)

The *note SMTP.set_debuglevel(): 832. method now accepts an additional
debuglevel (2), which enables timestamps in debug messages.
(Contributed by Gavin Chappell and Maciej Szulik in bpo-16914(2).)

Both the *note SMTP.sendmail(): 833. and *note SMTP.send_message(): 834.
methods now support RFC 6531(3) (SMTPUTF8).  (Contributed by Milan
Oberkirch and R. David Murray in bpo-22027(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15014

   (2) https://bugs.python.org/issue16914

   (3) https://tools.ietf.org/html/rfc6531.html

   (4) https://bugs.python.org/issue22027


File: python.info,  Node: sndhdr,  Next: socket<6>,  Prev: smtplib<2>,  Up: Improved Modules<5>

1.5.5.54 sndhdr
...............

The *note what(): 836. and *note whathdr(): 837. functions now return a
*note namedtuple(): 1a1.  (Contributed by Claudiu Popa in bpo-18615(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18615


File: python.info,  Node: socket<6>,  Next: ssl<6>,  Prev: sndhdr,  Up: Improved Modules<5>

1.5.5.55 socket
...............

Functions with timeouts now use a monotonic clock, instead of a system
clock.  (Contributed by Victor Stinner in bpo-22043(1).)

A new *note socket.sendfile(): 839. method allows sending a file over a
socket by using the high-performance *note os.sendfile(): 461. function
on UNIX, resulting in uploads being from 2 to 3 times faster than when
using plain *note socket.send(): 76d.  (Contributed by Giampaolo Rodola’
in bpo-17552(2).)

The *note socket.sendall(): 76e. method no longer resets the socket
timeout every time bytes are received or sent.  The socket timeout is
now the maximum total duration to send all data.  (Contributed by Victor
Stinner in bpo-23853(3).)

The `backlog' argument of the *note socket.listen(): 83a. method is now
optional.  By default it is set to *note SOMAXCONN: 83b. or to ‘128’,
whichever is less.  (Contributed by Charles-François Natali in
bpo-21455(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22043

   (2) https://bugs.python.org/issue17552

   (3) https://bugs.python.org/issue23853

   (4) https://bugs.python.org/issue21455


File: python.info,  Node: ssl<6>,  Next: sqlite3<3>,  Prev: socket<6>,  Up: Improved Modules<5>

1.5.5.56 ssl
............

* Menu:

* Memory BIO Support::
* Application-Layer Protocol Negotiation Support::
* Other Changes::


File: python.info,  Node: Memory BIO Support,  Next: Application-Layer Protocol Negotiation Support,  Up: ssl<6>

1.5.5.57 Memory BIO Support
...........................

(Contributed by Geert Jansen in bpo-21965(1).)

The new *note SSLObject: 4e9. class has been added to provide SSL
protocol support for cases when the network I/O capabilities of *note
SSLSocket: 192. are not necessary or are suboptimal.  ‘SSLObject’
represents an SSL protocol instance, but does not implement any network
I/O methods, and instead provides a memory buffer interface.  The new
*note MemoryBIO: 83e. class can be used to pass data between Python and
an SSL protocol instance.

The memory BIO SSL support is primarily intended to be used in
frameworks implementing asynchronous I/O for which *note SSLSocket:
192.’s readiness model (“select/poll”) is inefficient.

A new *note SSLContext.wrap_bio(): 4ec. method can be used to create a
new ‘SSLObject’ instance.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21965


File: python.info,  Node: Application-Layer Protocol Negotiation Support,  Next: Other Changes,  Prev: Memory BIO Support,  Up: ssl<6>

1.5.5.58 Application-Layer Protocol Negotiation Support
.......................................................

(Contributed by Benjamin Peterson in bpo-20188(1).)

Where OpenSSL support is present, the *note ssl: f3. module now
implements the `Application-Layer Protocol Negotiation' TLS extension as
described in RFC 7301(2).

The new *note SSLContext.set_alpn_protocols(): 840. can be used to
specify which protocols a socket should advertise during the TLS
handshake.

The new *note SSLSocket.selected_alpn_protocol(): 841. returns the
protocol that was selected during the TLS handshake.  The *note
HAS_ALPN: 842. flag indicates whether ALPN support is present.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20188

   (2) https://tools.ietf.org/html/rfc7301.html


File: python.info,  Node: Other Changes,  Prev: Application-Layer Protocol Negotiation Support,  Up: ssl<6>

1.5.5.59 Other Changes
......................

There is a new *note SSLSocket.version(): 844. method to query the
actual protocol version in use.  (Contributed by Antoine Pitrou in
bpo-20421(1).)

The *note SSLSocket: 192. class now implements a ‘SSLSocket.sendfile()’
method.  (Contributed by Giampaolo Rodola’ in bpo-17552(2).)

The ‘SSLSocket.send()’ method now raises either the *note
ssl.SSLWantReadError: 845. or *note ssl.SSLWantWriteError: 846.
exception on a non-blocking socket if the operation would block.
Previously, it would return ‘0’.  (Contributed by Nikolaus Rath in
bpo-20951(3).)

The *note cert_time_to_seconds(): 847. function now interprets the input
time as UTC and not as local time, per RFC 5280(4).  Additionally, the
return value is always an *note int: 204.  (Contributed by Akira Li in
bpo-19940(5).)

New ‘SSLObject.shared_ciphers()’ and *note SSLSocket.shared_ciphers():
848. methods return the list of ciphers sent by the client during the
handshake.  (Contributed by Benjamin Peterson in bpo-23186(6).)

The *note SSLSocket.do_handshake(): 849, *note SSLSocket.read(): 84a,
‘SSLSocket.shutdown()’, and *note SSLSocket.write(): 84b. methods of the
*note SSLSocket: 192. class no longer reset the socket timeout every
time bytes are received or sent.  The socket timeout is now the maximum
total duration of the method.  (Contributed by Victor Stinner in
bpo-23853(7).)

The *note match_hostname(): 4e3. function now supports matching of IP
addresses.  (Contributed by Antoine Pitrou in bpo-23239(8).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20421

   (2) https://bugs.python.org/issue17552

   (3) https://bugs.python.org/issue20951

   (4) https://tools.ietf.org/html/rfc5280.html

   (5) https://bugs.python.org/issue19940

   (6) https://bugs.python.org/issue23186

   (7) https://bugs.python.org/issue23853

   (8) https://bugs.python.org/issue23239


File: python.info,  Node: sqlite3<3>,  Next: subprocess<3>,  Prev: ssl<6>,  Up: Improved Modules<5>

1.5.5.60 sqlite3
................

The *note Row: 84d. class now fully supports the sequence protocol, in
particular *note reversed(): 2c6. iteration and slice indexing.
(Contributed by Claudiu Popa in bpo-10203(1); by Lucas Sinclair, Jessica
McKellar, and Serhiy Storchaka in bpo-13583(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10203

   (2) https://bugs.python.org/issue13583


File: python.info,  Node: subprocess<3>,  Next: sys<6>,  Prev: sqlite3<3>,  Up: Improved Modules<5>

1.5.5.61 subprocess
...................

The new *note run(): 4f3. function has been added.  It runs the
specified command and returns a *note CompletedProcess: 84f. object,
which describes a finished process.  The new API is more consistent and
is the recommended approach to invoking subprocesses in Python code that
does not need to maintain compatibility with earlier Python versions.
(Contributed by Thomas Kluyver in bpo-23342(1).)

Examples:

     >>> subprocess.run(["ls", "-l"])  # doesn't capture output
     CompletedProcess(args=['ls', '-l'], returncode=0)

     >>> subprocess.run("exit 1", shell=True, check=True)
     Traceback (most recent call last):
       ...
     subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1

     >>> subprocess.run(["ls", "-l", "/dev/null"], stdout=subprocess.PIPE)
     CompletedProcess(args=['ls', '-l', '/dev/null'], returncode=0,
     stdout=b'crw-rw-rw- 1 root root 1, 3 Jan 23 16:23 /dev/null\n')

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23342


File: python.info,  Node: sys<6>,  Next: sysconfig,  Prev: subprocess<3>,  Up: Improved Modules<5>

1.5.5.62 sys
............

A new ‘set_coroutine_wrapper()’ function allows setting a global hook
that will be called whenever a *note coroutine object: 18a. is created
by an *note async def: 3a9. function.  A corresponding
‘get_coroutine_wrapper()’ can be used to obtain a currently set wrapper.
Both functions are *note provisional: 454, and are intended for
debugging purposes only.  (Contributed by Yury Selivanov in
bpo-24017(1).)

A new *note is_finalizing(): 851. function can be used to check if the
Python interpreter is *note shutting down: 852.  (Contributed by Antoine
Pitrou in bpo-22696(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24017

   (2) https://bugs.python.org/issue22696


File: python.info,  Node: sysconfig,  Next: tarfile<2>,  Prev: sys<6>,  Up: Improved Modules<5>

1.5.5.63 sysconfig
..................

The name of the user scripts directory on Windows now includes the first
two components of the Python version.  (Contributed by Paul Moore in
bpo-23437(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23437


File: python.info,  Node: tarfile<2>,  Next: threading<3>,  Prev: sysconfig,  Up: Improved Modules<5>

1.5.5.64 tarfile
................

The `mode' argument of the *note open(): 855. function now accepts ‘"x"’
to request exclusive creation.  (Contributed by Berker Peksag in
bpo-21717(1).)

The *note TarFile.extractall(): 856. and *note TarFile.extract(): 857.
methods now take a keyword argument `numeric_owner'.  If set to ‘True’,
the extracted files and directories will be owned by the numeric ‘uid’
and ‘gid’ from the tarfile.  If set to ‘False’ (the default, and the
behavior in versions prior to 3.5), they will be owned by the named user
and group in the tarfile.  (Contributed by Michael Vogt and Eric Smith
in bpo-23193(2).)

The *note TarFile.list(): 858. now accepts an optional `members' keyword
argument that can be set to a subset of the list returned by *note
TarFile.getmembers(): 859.  (Contributed by Serhiy Storchaka in
bpo-21549(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21717

   (2) https://bugs.python.org/issue23193

   (3) https://bugs.python.org/issue21549


File: python.info,  Node: threading<3>,  Next: time<5>,  Prev: tarfile<2>,  Up: Improved Modules<5>

1.5.5.65 threading
..................

Both the *note Lock.acquire(): 85b. and *note RLock.acquire(): 85c.
methods now use a monotonic clock for timeout management.  (Contributed
by Victor Stinner in bpo-22043(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22043


File: python.info,  Node: time<5>,  Next: timeit<2>,  Prev: threading<3>,  Up: Improved Modules<5>

1.5.5.66 time
.............

The *note monotonic(): 85e. function is now always available.
(Contributed by Victor Stinner in bpo-22043(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22043


File: python.info,  Node: timeit<2>,  Next: tkinter<5>,  Prev: time<5>,  Up: Improved Modules<5>

1.5.5.67 timeit
...............

A new command line option ‘-u’ or ‘--unit=`U'’ can be used to specify
the time unit for the timer output.  Supported options are ‘usec’,
‘msec’, or ‘sec’.  (Contributed by Julian Gindi in bpo-18983(1).)

The *note timeit(): 860. function has a new `globals' parameter for
specifying the namespace in which the code will be running.
(Contributed by Ben Roberts in bpo-2527(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18983

   (2) https://bugs.python.org/issue2527


File: python.info,  Node: tkinter<5>,  Next: traceback<2>,  Prev: timeit<2>,  Up: Improved Modules<5>

1.5.5.68 tkinter
................

The ‘tkinter._fix’ module used for setting up the Tcl/Tk environment on
Windows has been replaced by a private function in the ‘_tkinter’ module
which makes no permanent changes to environment variables.  (Contributed
by Zachary Ware in bpo-20035(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20035


File: python.info,  Node: traceback<2>,  Next: types<2>,  Prev: tkinter<5>,  Up: Improved Modules<5>

1.5.5.69 traceback
..................

New *note walk_stack(): 863. and *note walk_tb(): 864. functions to
conveniently traverse frame and traceback objects.  (Contributed by
Robert Collins in bpo-17911(1).)

New lightweight classes: *note TracebackException: 865, *note
StackSummary: 866, and *note FrameSummary: 867.  (Contributed by Robert
Collins in bpo-17911(2).)

Both the *note print_tb(): 868. and *note print_stack(): 869. functions
now support negative values for the `limit' argument.  (Contributed by
Dmitry Kazakov in bpo-22619(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17911

   (2) https://bugs.python.org/issue17911

   (3) https://bugs.python.org/issue22619


File: python.info,  Node: types<2>,  Next: unicodedata<5>,  Prev: traceback<2>,  Up: Improved Modules<5>

1.5.5.70 types
..............

A new *note coroutine(): 86b. function to transform *note generator:
559. and *note generator-like: 7a8. objects into *note awaitables: 613.
(Contributed by Yury Selivanov in bpo-24017(1).)

A new type called *note CoroutineType: 86c, which is used for *note
coroutine: 18a. objects created by *note async def: 3a9. functions.
(Contributed by Yury Selivanov in bpo-24400(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24017

   (2) https://bugs.python.org/issue24400


File: python.info,  Node: unicodedata<5>,  Next: unittest<3>,  Prev: types<2>,  Up: Improved Modules<5>

1.5.5.71 unicodedata
....................

The *note unicodedata: 123. module now uses data from Unicode 8.0.0(1).

   ---------- Footnotes ----------

   (1) http://unicode.org/versions/Unicode8.0.0/


File: python.info,  Node: unittest<3>,  Next: unittest mock<3>,  Prev: unicodedata<5>,  Up: Improved Modules<5>

1.5.5.72 unittest
.................

The *note TestLoader.loadTestsFromModule(): 86f. method now accepts a
keyword-only argument `pattern' which is passed to ‘load_tests’ as the
third argument.  Found packages are now checked for ‘load_tests’
regardless of whether their path matches `pattern', because it is
impossible for a package name to match the default pattern.
(Contributed by Robert Collins and Barry A. Warsaw in bpo-16662(1).)

Unittest discovery errors now are exposed in the *note
TestLoader.errors: 870. attribute of the *note TestLoader: 871.
instance.  (Contributed by Robert Collins in bpo-19746(2).)

A new command line option ‘--locals’ to show local variables in
tracebacks.  (Contributed by Robert Collins in bpo-22936(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16662

   (2) https://bugs.python.org/issue19746

   (3) https://bugs.python.org/issue22936


File: python.info,  Node: unittest mock<3>,  Next: urllib,  Prev: unittest<3>,  Up: Improved Modules<5>

1.5.5.73 unittest.mock
......................

The *note Mock: 373. class has the following improvements:

   * The class constructor has a new `unsafe' parameter, which causes
     mock objects to raise *note AttributeError: 4a2. on attribute names
     starting with ‘"assert"’.  (Contributed by Kushal Das in
     bpo-21238(1).)

   * A new *note Mock.assert_not_called(): 873. method to check if the
     mock object was called.  (Contributed by Kushal Das in
     bpo-21262(2).)

The *note MagicMock: 874. class now supports *note __truediv__(): 875,
*note __divmod__(): 876. and *note __matmul__(): 73b. operators.
(Contributed by Johannes Baiter in bpo-20968(3), and Håkan Lövdahl in
bpo-23581(4) and bpo-23568(5).)

It is no longer necessary to explicitly pass ‘create=True’ to the *note
patch(): 877. function when patching builtin names.  (Contributed by
Kushal Das in bpo-17660(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21238

   (2) https://bugs.python.org/issue21262

   (3) https://bugs.python.org/issue20968

   (4) https://bugs.python.org/issue23581

   (5) https://bugs.python.org/issue23568

   (6) https://bugs.python.org/issue17660


File: python.info,  Node: urllib,  Next: wsgiref,  Prev: unittest mock<3>,  Up: Improved Modules<5>

1.5.5.74 urllib
...............

A new *note request.HTTPPasswordMgrWithPriorAuth: 879. class allows HTTP
Basic Authentication credentials to be managed so as to eliminate
unnecessary ‘401’ response handling, or to unconditionally send
credentials on the first request in order to communicate with servers
that return a ‘404’ response instead of a ‘401’ if the ‘Authorization’
header is not sent.  (Contributed by Matej Cepl in bpo-19494(1) and
Akshit Khurana in bpo-7159(2).)

A new `quote_via' argument for the *note parse.urlencode(): 87a.
function provides a way to control the encoding of query parts if
needed.  (Contributed by Samwyse and Arnon Yaari in bpo-13866(3).)

The *note request.urlopen(): 87b. function accepts an *note
ssl.SSLContext: 4ea. object as a `context' argument, which will be used
for the HTTPS connection.  (Contributed by Alex Gaynor in bpo-22366(4).)

The *note parse.urljoin(): 87c. was updated to use the RFC 3986(5)
semantics for the resolution of relative URLs, rather than RFC 1808(6)
and RFC 2396(7).  (Contributed by Demian Brecht and Senthil Kumaran in
bpo-22118(8).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19494

   (2) https://bugs.python.org/issue7159

   (3) https://bugs.python.org/issue13866

   (4) https://bugs.python.org/issue22366

   (5) https://tools.ietf.org/html/rfc3986.html

   (6) https://tools.ietf.org/html/rfc1808.html

   (7) https://tools.ietf.org/html/rfc2396.html

   (8) https://bugs.python.org/issue22118


File: python.info,  Node: wsgiref,  Next: xmlrpc<2>,  Prev: urllib,  Up: Improved Modules<5>

1.5.5.75 wsgiref
................

The `headers' argument of the *note headers.Headers: 87e. class
constructor is now optional.  (Contributed by Pablo Torres Navarrete and
SilentGhost in bpo-5800(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5800


File: python.info,  Node: xmlrpc<2>,  Next: xml sax,  Prev: wsgiref,  Up: Improved Modules<5>

1.5.5.76 xmlrpc
...............

The *note client.ServerProxy: 37f. class now supports the *note context
manager: 661. protocol.  (Contributed by Claudiu Popa in bpo-20627(1).)

The *note client.ServerProxy: 37f. constructor now accepts an optional
*note ssl.SSLContext: 4ea. instance.  (Contributed by Alex Gaynor in
bpo-22960(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20627

   (2) https://bugs.python.org/issue22960


File: python.info,  Node: xml sax,  Next: zipfile<3>,  Prev: xmlrpc<2>,  Up: Improved Modules<5>

1.5.5.77 xml.sax
................

SAX parsers now support a character stream of the *note
xmlreader.InputSource: 881. object.  (Contributed by Serhiy Storchaka in
bpo-2175(1).)

*note parseString(): 882. now accepts a *note str: 205. instance.
(Contributed by Serhiy Storchaka in bpo-10590(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue2175

   (2) https://bugs.python.org/issue10590


File: python.info,  Node: zipfile<3>,  Prev: xml sax,  Up: Improved Modules<5>

1.5.5.78 zipfile
................

ZIP output can now be written to unseekable streams.  (Contributed by
Serhiy Storchaka in bpo-23252(1).)

The `mode' argument of *note ZipFile.open(): 6b3. method now accepts
‘"x"’ to request exclusive creation.  (Contributed by Serhiy Storchaka
in bpo-21717(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23252

   (2) https://bugs.python.org/issue21717


File: python.info,  Node: Other module-level changes,  Next: Optimizations<5>,  Prev: Improved Modules<5>,  Up: What’s New In Python 3 5

1.5.6 Other module-level changes
--------------------------------

Many functions in the *note mmap: b3, *note ossaudiodev: c6, *note
socket: ef, *note ssl: f3, and *note codecs: 1b. modules now accept
writable *note bytes-like objects: 6df.  (Contributed by Serhiy
Storchaka in bpo-23001(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23001


File: python.info,  Node: Optimizations<5>,  Next: Build and C API Changes<3>,  Prev: Other module-level changes,  Up: What’s New In Python 3 5

1.5.7 Optimizations
-------------------

The *note os.walk(): 747. function has been sped up by 3 to 5 times on
POSIX systems, and by 7 to 20 times on Windows.  This was done using the
new *note os.scandir(): 389. function, which exposes file information
from the underlying ‘readdir’ or ‘FindFirstFile’/‘FindNextFile’ system
calls.  (Contributed by Ben Hoyt with help from Victor Stinner in
bpo-23605(1).)

Construction of ‘bytes(int)’ (filled by zero bytes) is faster and uses
less memory for large objects.  ‘calloc()’ is used instead of ‘malloc()’
to allocate memory for these objects.  (Contributed by Victor Stinner in
bpo-21233(2).)

Some operations on *note ipaddress: a2. *note IPv4Network: 4a7. and
*note IPv6Network: 4a6. have been massively sped up, such as *note
subnets(): 886, *note supernet(): 887, *note summarize_address_range():
888, *note collapse_addresses(): 889.  The speed up can range from 3 to
15 times.  (Contributed by Antoine Pitrou, Michel Albert, and Markus in
bpo-21486(3), bpo-21487(4), bpo-20826(5), bpo-23266(6).)

Pickling of *note ipaddress: a2. objects was optimized to produce
significantly smaller output.  (Contributed by Serhiy Storchaka in
bpo-23133(7).)

Many operations on *note io.BytesIO: 88a. are now 50% to 100% faster.
(Contributed by Serhiy Storchaka in bpo-15381(8) and David Wilson in
bpo-22003(9).)

The *note marshal.dumps(): 88b. function is now faster: 65–85% with
versions 3 and 4, 20–25% with versions 0 to 2 on typical data, and up to
5 times in best cases.  (Contributed by Serhiy Storchaka in
bpo-20416(10) and bpo-23344(11).)

The UTF-32 encoder is now 3 to 7 times faster.  (Contributed by Serhiy
Storchaka in bpo-15027(12).)

Regular expressions are now parsed up to 10% faster.  (Contributed by
Serhiy Storchaka in bpo-19380(13).)

The *note json.dumps(): 6fc. function was optimized to run with
‘ensure_ascii=False’ as fast as with ‘ensure_ascii=True’.  (Contributed
by Naoki Inada in bpo-23206(14).)

The *note PyObject_IsInstance(): 88c. and *note PyObject_IsSubclass():
88d. functions have been sped up in the common case that the second
argument has *note type: 6ff. as its metaclass.  (Contributed Georg
Brandl by in bpo-22540(15).)

Method caching was slightly improved, yielding up to 5% performance
improvement in some benchmarks.  (Contributed by Antoine Pitrou in
bpo-22847(16).)

Objects from the *note random: dc. module now use 50% less memory on
64-bit builds.  (Contributed by Serhiy Storchaka in bpo-23488(17).)

The *note property(): 308. getter calls are up to 25% faster.
(Contributed by Joe Jevnik in bpo-23910(18).)

Instantiation of *note fractions.Fraction: 2be. is now up to 30% faster.
(Contributed by Stefan Behnel in bpo-22464(19).)

String methods *note find(): 88e, *note rfind(): 88f, *note split():
890, *note partition(): 891. and the *note in: 179. string operator are
now significantly faster for searching 1-character substrings.
(Contributed by Serhiy Storchaka in bpo-23573(20).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23605

   (2) https://bugs.python.org/issue21233

   (3) https://bugs.python.org/issue21486

   (4) https://bugs.python.org/issue21487

   (5) https://bugs.python.org/issue20826

   (6) https://bugs.python.org/issue23266

   (7) https://bugs.python.org/issue23133

   (8) https://bugs.python.org/issue15381

   (9) https://bugs.python.org/issue22003

   (10) https://bugs.python.org/issue20416

   (11) https://bugs.python.org/issue23344

   (12) https://bugs.python.org/issue15027

   (13) https://bugs.python.org/issue19380

   (14) https://bugs.python.org/issue23206

   (15) https://bugs.python.org/issue22540

   (16) https://bugs.python.org/issue22847

   (17) https://bugs.python.org/issue23488

   (18) https://bugs.python.org/issue23910

   (19) https://bugs.python.org/issue22464

   (20) https://bugs.python.org/issue23573


File: python.info,  Node: Build and C API Changes<3>,  Next: Deprecated<4>,  Prev: Optimizations<5>,  Up: What’s New In Python 3 5

1.5.8 Build and C API Changes
-----------------------------

New ‘calloc’ functions were added:

   * *note PyMem_RawCalloc(): 893,

   * *note PyMem_Calloc(): 894,

   * *note PyObject_Calloc(): 895.

(Contributed by Victor Stinner in bpo-21233(1).)

New encoding/decoding helper functions:

   * *note Py_DecodeLocale(): 53f. (replaced ‘_Py_char2wchar()’),

   * *note Py_EncodeLocale(): 540. (replaced ‘_Py_wchar2char()’).

(Contributed by Victor Stinner in bpo-18395(2).)

A new *note PyCodec_NameReplaceErrors(): 896. function to replace the
unicode encode error with ‘\N{...}’ escapes.  (Contributed by Serhiy
Storchaka in bpo-19676(3).)

A new *note PyErr_FormatV(): 897. function similar to *note
PyErr_Format(): 898, but accepts a ‘va_list’ argument.  (Contributed by
Antoine Pitrou in bpo-18711(4).)

A new ‘PyExc_RecursionError’ exception.  (Contributed by Georg Brandl in
bpo-19235(5).)

New *note PyModule_FromDefAndSpec(): 899, *note
PyModule_FromDefAndSpec2(): 89a, and *note PyModule_ExecDef(): 89b.
functions introduced by PEP 489(6) – multi-phase extension module
initialization.  (Contributed by Petr Viktorin in bpo-24268(7).)

New *note PyNumber_MatrixMultiply(): 89c. and *note
PyNumber_InPlaceMatrixMultiply(): 89d. functions to perform matrix
multiplication.  (Contributed by Benjamin Peterson in bpo-21176(8).  See
also PEP 465(9) for details.)

The *note PyTypeObject.tp_finalize: 3f6. slot is now part of the stable
ABI.

Windows builds now require Microsoft Visual C++ 14.0, which is available
as part of Visual Studio 2015(10).

Extension modules now include a platform information tag in their
filename on some platforms (the tag is optional, and CPython will import
extensions without it, although if the tag is present and mismatched,
the extension won’t be loaded):

   * On Linux, extension module filenames end with
     ‘.cpython-<major><minor>m-<architecture>-<os>.pyd’:

        * ‘<major>’ is the major number of the Python version; for
          Python 3.5 this is ‘3’.

        * ‘<minor>’ is the minor number of the Python version; for
          Python 3.5 this is ‘5’.

        * ‘<architecture>’ is the hardware architecture the extension
          module was built to run on.  It’s most commonly either ‘i386’
          for 32-bit Intel platforms or ‘x86_64’ for 64-bit Intel (and
          AMD) platforms.

        * ‘<os>’ is always ‘linux-gnu’, except for extensions built to
          talk to the 32-bit ABI on 64-bit platforms, in which case it
          is ‘linux-gnu32’ (and ‘<architecture>’ will be ‘x86_64’).

   * On Windows, extension module filenames end with
     ‘<debug>.cp<major><minor>-<platform>.pyd’:

        * ‘<major>’ is the major number of the Python version; for
          Python 3.5 this is ‘3’.

        * ‘<minor>’ is the minor number of the Python version; for
          Python 3.5 this is ‘5’.

        * ‘<platform>’ is the platform the extension module was built
          for, either ‘win32’ for Win32, ‘win_amd64’ for Win64,
          ‘win_ia64’ for Windows Itanium 64, and ‘win_arm’ for Windows
          on ARM.

        * If built in debug mode, ‘<debug>’ will be ‘_d’, otherwise it
          will be blank.

   * On OS X platforms, extension module filenames now end with
     ‘-darwin.so’.

   * On all other platforms, extension module filenames are the same as
     they were with Python 3.4.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21233

   (2) https://bugs.python.org/issue18395

   (3) https://bugs.python.org/issue19676

   (4) https://bugs.python.org/issue18711

   (5) https://bugs.python.org/issue19235

   (6) https://www.python.org/dev/peps/pep-0489

   (7) https://bugs.python.org/issue24268

   (8) https://bugs.python.org/issue21176

   (9) https://www.python.org/dev/peps/pep-0465

   (10) https://www.visualstudio.com/


File: python.info,  Node: Deprecated<4>,  Next: Removed<4>,  Prev: Build and C API Changes<3>,  Up: What’s New In Python 3 5

1.5.9 Deprecated
----------------

* Menu:

* New Keywords: New Keywords<2>.
* Deprecated Python Behavior: Deprecated Python Behavior<2>.
* Unsupported Operating Systems::
* Deprecated Python modules, functions and methods: Deprecated Python modules functions and methods<3>.


File: python.info,  Node: New Keywords<2>,  Next: Deprecated Python Behavior<2>,  Up: Deprecated<4>

1.5.9.1 New Keywords
....................

‘async’ and ‘await’ are not recommended to be used as variable, class,
function or module names.  Introduced by PEP 492(1) in Python 3.5, they
will become proper keywords in Python 3.7.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0492


File: python.info,  Node: Deprecated Python Behavior<2>,  Next: Unsupported Operating Systems,  Prev: New Keywords<2>,  Up: Deprecated<4>

1.5.9.2 Deprecated Python Behavior
..................................

Raising the *note StopIteration: 582. exception inside a generator will
now generate a silent *note PendingDeprecationWarning: 15c, which will
become a non-silent deprecation warning in Python 3.6 and will trigger a
*note RuntimeError: 3dc. in Python 3.7.  See *note PEP 479; Change
StopIteration handling inside generators: 6ce. for details.


File: python.info,  Node: Unsupported Operating Systems,  Next: Deprecated Python modules functions and methods<3>,  Prev: Deprecated Python Behavior<2>,  Up: Deprecated<4>

1.5.9.3 Unsupported Operating Systems
.....................................

Windows XP is no longer supported by Microsoft, thus, per PEP 11(1),
CPython 3.5 is no longer officially supported on this OS.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0011


File: python.info,  Node: Deprecated Python modules functions and methods<3>,  Prev: Unsupported Operating Systems,  Up: Deprecated<4>

1.5.9.4 Deprecated Python modules, functions and methods
........................................................

The *note formatter: 80. module has now graduated to full deprecation
and is still slated for removal in Python 3.6.

The ‘asyncio.async()’ function is deprecated in favor of *note
ensure_future(): 611.

The *note smtpd: ec. module has in the past always decoded the DATA
portion of email messages using the ‘utf-8’ codec.  This can now be
controlled by the new `decode_data' keyword to *note SMTPServer: 6f9.
The default value is ‘True’, but this default is deprecated.  Specify
the `decode_data' keyword with an appropriate value to avoid the
deprecation warning.

Directly assigning values to the *note key: 588, *note value: 589. and
*note coded_value: 58a. of *note http.cookies.Morsel: 58b. objects is
deprecated.  Use the *note set(): 58c. method instead.  In addition, the
undocumented `LegalChars' parameter of *note set(): 58c. is deprecated,
and is now ignored.

Passing a format string as keyword argument `format_string' to the *note
format(): 587. method of the *note string.Formatter: 8a3. class has been
deprecated.  (Contributed by Serhiy Storchaka in bpo-23671(1).)

The ‘platform.dist()’ and ‘platform.linux_distribution()’ functions are
now deprecated.  Linux distributions use too many different ways of
describing themselves, so the functionality is left to a package.
(Contributed by Vajrasky Kok and Berker Peksag in bpo-1322(2).)

The previously undocumented ‘from_function’ and ‘from_builtin’ methods
of *note inspect.Signature: 7e4. are deprecated.  Use the new *note
Signature.from_callable(): 7e7. method instead.  (Contributed by Yury
Selivanov in bpo-24248(3).)

The *note inspect.getargspec(): 656. function is deprecated and
scheduled to be removed in Python 3.6.  (See bpo-20438(4) for details.)

The *note inspect: a0. *note getfullargspec(): 657, *note getcallargs():
8a4, and *note formatargspec(): 8a5. functions are deprecated in favor
of the *note inspect.signature(): 655. API. (Contributed by Yury
Selivanov in bpo-20438(5).)

*note getargvalues(): 8a6. and *note formatargvalues(): 8a7. functions
were inadvertently marked as deprecated with the release of Python
3.5.0.

Use of *note re.LOCALE: 4d0. flag with str patterns or *note re.ASCII:
4cf. is now deprecated.  (Contributed by Serhiy Storchaka in
bpo-22407(6).)

Use of unrecognized special sequences consisting of ‘'\'’ and an ASCII
letter in regular expression patterns and replacement patterns now
raises a deprecation warning and will be forbidden in Python 3.6.
(Contributed by Serhiy Storchaka in bpo-23622(7).)

The undocumented and unofficial `use_load_tests' default argument of the
*note unittest.TestLoader.loadTestsFromModule(): 86f. method now is
deprecated and ignored.  (Contributed by Robert Collins and Barry A.
Warsaw in bpo-16662(8).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23671

   (2) https://bugs.python.org/issue1322

   (3) https://bugs.python.org/issue24248

   (4) https://bugs.python.org/issue20438

   (5) https://bugs.python.org/issue20438

   (6) https://bugs.python.org/issue22407

   (7) https://bugs.python.org/issue23622

   (8) https://bugs.python.org/issue16662


File: python.info,  Node: Removed<4>,  Next: Porting to Python 3 5,  Prev: Deprecated<4>,  Up: What’s New In Python 3 5

1.5.10 Removed
--------------

* Menu:

* API and Feature Removals: API and Feature Removals<4>.


File: python.info,  Node: API and Feature Removals<4>,  Up: Removed<4>

1.5.10.1 API and Feature Removals
.................................

The following obsolete and previously deprecated APIs and features have
been removed:

   * The ‘__version__’ attribute has been dropped from the email
     package.  The email code hasn’t been shipped separately from the
     stdlib for a long time, and the ‘__version__’ string was not
     updated in the last few releases.

   * The internal ‘Netrc’ class in the *note ftplib: 82. module was
     deprecated in 3.4, and has now been removed.  (Contributed by Matt
     Chaput in bpo-6623(1).)

   * The concept of ‘.pyo’ files has been removed.

   * The JoinableQueue class in the provisional *note asyncio: 9. module
     was deprecated in 3.4.4 and is now removed.  (Contributed by A.
     Jesse Jiryu Davis in bpo-23464(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue6623

   (2) https://bugs.python.org/issue23464


File: python.info,  Node: Porting to Python 3 5,  Next: Notable changes in Python 3 5 4,  Prev: Removed<4>,  Up: What’s New In Python 3 5

1.5.11 Porting to Python 3.5
----------------------------

This section lists previously described changes and other bugfixes that
may require changes to your code.

* Menu:

* Changes in Python behavior: Changes in Python behavior<2>.
* Changes in the Python API: Changes in the Python API<5>.
* Changes in the C API: Changes in the C API<5>.


File: python.info,  Node: Changes in Python behavior<2>,  Next: Changes in the Python API<5>,  Up: Porting to Python 3 5

1.5.11.1 Changes in Python behavior
...................................

   * Due to an oversight, earlier Python versions erroneously accepted
     the following syntax:

          f(1 for x in [1], *args)
          f(1 for x in [1], **kwargs)

     Python 3.5 now correctly raises a *note SyntaxError: 55a, as
     generator expressions must be put in parentheses if not a sole
     argument to a function.


File: python.info,  Node: Changes in the Python API<5>,  Next: Changes in the C API<5>,  Prev: Changes in Python behavior<2>,  Up: Porting to Python 3 5

1.5.11.2 Changes in the Python API
..................................

   * PEP 475(1): System calls are now retried when interrupted by a
     signal instead of raising *note InterruptedError: 74c. if the
     Python signal handler does not raise an exception.

   * Before Python 3.5, a *note datetime.time: 5ed. object was
     considered to be false if it represented midnight in UTC. This
     behavior was considered obscure and error-prone and has been
     removed in Python 3.5.  See bpo-13936(2) for full details.

   * The ‘ssl.SSLSocket.send()’ method now raises either *note
     ssl.SSLWantReadError: 845. or *note ssl.SSLWantWriteError: 846. on
     a non-blocking socket if the operation would block.  Previously, it
     would return ‘0’.  (Contributed by Nikolaus Rath in bpo-20951(3).)

   * The ‘__name__’ attribute of generators is now set from the function
     name, instead of being set from the code name.  Use
     ‘gen.gi_code.co_name’ to retrieve the code name.  Generators also
     have a new ‘__qualname__’ attribute, the qualified name, which is
     now used for the representation of a generator (‘repr(gen)’).
     (Contributed by Victor Stinner in bpo-21205(4).)

   * The deprecated “strict” mode and argument of *note HTMLParser: 22a,
     ‘HTMLParser.error()’, and the ‘HTMLParserError’ exception have been
     removed.  (Contributed by Ezio Melotti in bpo-15114(5).)  The
     `convert_charrefs' argument of *note HTMLParser: 22a. is now ‘True’
     by default.  (Contributed by Berker Peksag in bpo-21047(6).)

   * Although it is not formally part of the API, it is worth noting for
     porting purposes (ie: fixing tests) that error messages that were
     previously of the form “‘sometype’ does not support the buffer
     protocol” are now of the form “a *note bytes-like object: 6df. is
     required, not ‘sometype’”.  (Contributed by Ezio Melotti in
     bpo-16518(7).)

   * If the current directory is set to a directory that no longer
     exists then *note FileNotFoundError: 8ad. will no longer be raised
     and instead *note find_spec(): 8ae. will return ‘None’ `without'
     caching ‘None’ in *note sys.path_importer_cache: 598, which is
     different than the typical case (bpo-22834(8)).

   * HTTP status code and messages from *note http.client: 93. and *note
     http.server: 96. were refactored into a common *note HTTPStatus:
     1ac. enum.  The values in *note http.client: 93. and *note
     http.server: 96. remain available for backwards compatibility.
     (Contributed by Demian Brecht in bpo-21793(9).)

   * When an import loader defines
     ‘importlib.machinery.Loader.exec_module()’ it is now expected to
     also define ‘create_module()’ (raises a *note DeprecationWarning:
     15a. now, will be an error in Python 3.6).  If the loader inherits
     from *note importlib.abc.Loader: 8af. then there is nothing to do,
     else simply define ‘create_module()’ to return ‘None’.
     (Contributed by Brett Cannon in bpo-23014(10).)

   * The *note re.split(): 4d1. function always ignored empty pattern
     matches, so the ‘"x*"’ pattern worked the same as ‘"x+"’, and the
     ‘"\b"’ pattern never worked.  Now *note re.split(): 4d1. raises a
     warning if the pattern could match an empty string.  For
     compatibility, use patterns that never match an empty string (e.g.
     ‘"x+"’ instead of ‘"x*"’).  Patterns that could only match an empty
     string (such as ‘"\b"’) now raise an error.  (Contributed by Serhiy
     Storchaka in bpo-22818(11).)

   * The *note http.cookies.Morsel: 58b. dict-like interface has been
     made self consistent: morsel comparison now takes the *note key:
     588. and *note value: 589. into account, *note copy(): 8b0. now
     results in a *note Morsel: 58b. instance rather than a *note dict:
     164, and *note update(): 8b1. will now raise an exception if any of
     the keys in the update dictionary are invalid.  In addition, the
     undocumented `LegalChars' parameter of *note set(): 58c. is
     deprecated and is now ignored.  (Contributed by Demian Brecht in
     bpo-2211(12).)

   * PEP 488(13) has removed ‘.pyo’ files from Python and introduced the
     optional ‘opt-’ tag in ‘.pyc’ file names.  The *note
     importlib.util.cache_from_source(): 651. has gained an
     `optimization' parameter to help control the ‘opt-’ tag.  Because
     of this, the `debug_override' parameter of the function is now
     deprecated.  ‘.pyo’ files are also no longer supported as a file
     argument to the Python interpreter and thus serve no purpose when
     distributed on their own (i.e.  sourceless code distribution).  Due
     to the fact that the magic number for bytecode has changed in
     Python 3.5, all old ‘.pyo’ files from previous versions of Python
     are invalid regardless of this PEP.

   * The *note socket: ef. module now exports the *note
     CAN_RAW_FD_FRAMES: 8b2. constant on linux 3.6 and greater.

   * The *note ssl.cert_time_to_seconds(): 847. function now interprets
     the input time as UTC and not as local time, per RFC 5280(14).
     Additionally, the return value is always an *note int: 204.
     (Contributed by Akira Li in bpo-19940(15).)

   * The ‘pygettext.py’ Tool now uses the standard +NNNN format for
     timezones in the POT-Creation-Date header.

   * The *note smtplib: ed. module now uses *note sys.stderr: 1ea.
     instead of the previous module-level ‘stderr’ variable for debug
     output.  If your (test) program depends on patching the
     module-level variable to capture the debug output, you will need to
     update it to capture sys.stderr instead.

   * The *note str.startswith(): 8b3. and *note str.endswith(): 8b4.
     methods no longer return ‘True’ when finding the empty string and
     the indexes are completely out of range.  (Contributed by Serhiy
     Storchaka in bpo-24284(16).)

   * The *note inspect.getdoc(): 307. function now returns documentation
     strings inherited from base classes.  Documentation strings no
     longer need to be duplicated if the inherited documentation is
     appropriate.  To suppress an inherited string, an empty string must
     be specified (or the documentation may be filled in).  This change
     affects the output of the *note pydoc: d9. module and the *note
     help(): 175. function.  (Contributed by Serhiy Storchaka in
     bpo-15582(17).)

   * Nested *note functools.partial(): 8b5. calls are now flattened.  If
     you were relying on the previous behavior, you can now either add
     an attribute to a *note functools.partial(): 8b5. object or you can
     create a subclass of *note functools.partial(): 8b5.  (Contributed
     by Alexander Belopolsky in bpo-7830(18).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0475

   (2) https://bugs.python.org/issue13936

   (3) https://bugs.python.org/issue20951

   (4) https://bugs.python.org/issue21205

   (5) https://bugs.python.org/issue15114

   (6) https://bugs.python.org/issue21047

   (7) https://bugs.python.org/issue16518

   (8) https://bugs.python.org/issue22834

   (9) https://bugs.python.org/issue21793

   (10) https://bugs.python.org/issue23014

   (11) https://bugs.python.org/issue22818

   (12) https://bugs.python.org/issue2211

   (13) https://www.python.org/dev/peps/pep-0488

   (14) https://tools.ietf.org/html/rfc5280.html

   (15) https://bugs.python.org/issue19940

   (16) https://bugs.python.org/issue24284

   (17) https://bugs.python.org/issue15582

   (18) https://bugs.python.org/issue7830


File: python.info,  Node: Changes in the C API<5>,  Prev: Changes in the Python API<5>,  Up: Porting to Python 3 5

1.5.11.3 Changes in the C API
.............................

   * The undocumented ‘format’ member of the (non-public)
     ‘PyMemoryViewObject’ structure has been removed.  All extensions
     relying on the relevant parts in ‘memoryobject.h’ must be rebuilt.

   * The ‘PyMemAllocator’ structure was renamed to *note
     PyMemAllocatorEx: 8b7. and a new ‘calloc’ field was added.

   * Removed non-documented macro ‘PyObject_REPR’ which leaked
     references.  Use format character ‘%R’ in *note
     PyUnicode_FromFormat(): 8b8.-like functions to format the *note
     repr(): 8b9. of the object.  (Contributed by Serhiy Storchaka in
     bpo-22453(1).)

   * Because the lack of the ‘__module__’ attribute breaks pickling and
     introspection, a deprecation warning is now raised for builtin
     types without the ‘__module__’ attribute.  This would be an
     AttributeError in the future.  (Contributed by Serhiy Storchaka in
     bpo-20204(2).)

   * As part of the PEP 492(3) implementation, the ‘tp_reserved’ slot of
     *note PyTypeObject: 3f5. was replaced with a ‘tp_as_async’ slot.
     Refer to *note Coroutine Objects: 8ba. for new types, structures
     and functions.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22453

   (2) https://bugs.python.org/issue20204

   (3) https://www.python.org/dev/peps/pep-0492


File: python.info,  Node: Notable changes in Python 3 5 4,  Prev: Porting to Python 3 5,  Up: What’s New In Python 3 5

1.5.12 Notable changes in Python 3.5.4
--------------------------------------

* Menu:

* New make regen-all build target: New make regen-all build target<2>.
* Removal of make touch build target: Removal of make touch build target<2>.


File: python.info,  Node: New make regen-all build target<2>,  Next: Removal of make touch build target<2>,  Up: Notable changes in Python 3 5 4

1.5.12.1 New ‘make regen-all’ build target
..........................................

To simplify cross-compilation, and to ensure that CPython can reliably
be compiled without requiring an existing version of Python to already
be available, the autotools-based build system no longer attempts to
implicitly recompile generated files based on file modification times.

Instead, a new ‘make regen-all’ command has been added to force
regeneration of these files when desired (e.g.  after an initial version
of Python has already been built based on the pregenerated versions).

More selective regeneration targets are also defined - see
Makefile.pre.in(1) for details.

(Contributed by Victor Stinner in bpo-23404(2).)

New in version 3.5.4.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Makefile.pre.in

   (2) https://bugs.python.org/issue23404


File: python.info,  Node: Removal of make touch build target<2>,  Prev: New make regen-all build target<2>,  Up: Notable changes in Python 3 5 4

1.5.12.2 Removal of ‘make touch’ build target
.............................................

The ‘make touch’ build target previously used to request implicit
regeneration of generated files by updating their modification times has
been removed.

It has been replaced by the new ‘make regen-all’ target.

(Contributed by Victor Stinner in bpo-23404(1).)

Changed in version 3.5.4.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23404


File: python.info,  Node: What’s New In Python 3 4,  Next: What’s New In Python 3 3,  Prev: What’s New In Python 3 5,  Up: What’s New in Python

1.6 What’s New In Python 3.4
============================


Author: R. David Murray <<rdmurray@bitdance.com>> (Editor)

This article explains the new features in Python 3.4, compared to 3.3.
Python 3.4 was released on March 16, 2014.  For full details, see the
changelog(1).

See also
........

PEP 429(2) – Python 3.4 Release Schedule

* Menu:

* Summary – Release Highlights: Summary – Release Highlights<2>.
* New Features: New Features<7>.
* New Modules: New Modules<6>.
* Improved Modules: Improved Modules<6>.
* CPython Implementation Changes::
* Deprecated: Deprecated<5>.
* Removed: Removed<5>.
* Porting to Python 3.4: Porting to Python 3 4.
* Changed in 3.4.3: Changed in 3 4 3.

   ---------- Footnotes ----------

   (1) https://docs.python.org/3.4/whatsnew/changelog.html

   (2) https://www.python.org/dev/peps/pep-0429


File: python.info,  Node: Summary – Release Highlights<2>,  Next: New Features<7>,  Up: What’s New In Python 3 4

1.6.1 Summary – Release Highlights
----------------------------------

New syntax features:

   * No new syntax features were added in Python 3.4.

Other new features:

   * *note pip should always be available: 8c1. ( PEP 453(1)).

   * *note Newly created file descriptors are non-inheritable: 8c2. (
     PEP 446(2)).

   * command line option for *note isolated mode: 8c3. (bpo-16499(3)).

   * *note improvements in the handling of codecs: 8c4. that are not
     text encodings (multiple issues).

   * *note A ModuleSpec Type: 8c5. for the Import System ( PEP 451(4)).
     (Affects importer authors.)

   * The *note marshal: b0. format has been made *note more compact and
     efficient: 8c6. (bpo-16475(5)).

New library modules:

   * *note asyncio: 9.: *note New provisional API for asynchronous IO:
     8c7. ( PEP 3156(6)).

   * *note ensurepip: 78.: *note Bootstrapping the pip installer: 8c8. (
     PEP 453(7)).

   * *note enum: 79.: *note Support for enumeration types: 8c9. ( PEP
     435(8)).

   * *note pathlib: c8.: *note Object-oriented filesystem paths: 8ca. (
     PEP 428(9)).

   * *note selectors: e6.: *note High-level and efficient I/O
     multiplexing: 8cb, built upon the *note select: e5. module
     primitives (part of PEP 3156(10)).

   * *note statistics: f5.: A basic *note numerically stable statistics
     library: 8cc. ( PEP 450(11)).

   * *note tracemalloc: 11d.: *note Trace Python memory allocations:
     8cd. ( PEP 454(12)).

Significantly improved library modules:

   * *note Single-dispatch generic functions: 8ce. in *note functools:
     83. ( PEP 443(13)).

   * New *note pickle: ca. *note protocol 4: 8cf. ( PEP 3154(14)).

   * *note multiprocessing: b7. now has *note an option to avoid using
     os.fork on Unix: 8d0. (bpo-8713(15)).

   * *note email: 67. has a new submodule, *note contentmanager: 69, and
     a new *note Message: 63b. subclass (‘EmailMessage’) that *note
     simplify MIME handling: 8d1. (bpo-18891(16)).

   * The *note inspect: a0. and *note pydoc: d9. modules are now capable
     of correct introspection of a much wider variety of callable
     objects, which improves the output of the Python *note help(): 175.
     system.

   * The *note ipaddress: a2. module API has been declared stable

Security improvements:

   * *note Secure and interchangeable hash algorithm: 8d2. ( PEP
     456(17)).

   * *note Make newly created file descriptors non-inheritable: 8c2. (
     PEP 446(18)) to avoid leaking file descriptors to child processes.

   * New command line option for *note isolated mode: 8c3,
     (bpo-16499(19)).

   * *note multiprocessing: b7. now has *note an option to avoid using
     os.fork on Unix: 8d0.  `spawn' and `forkserver' are more secure
     because they avoid sharing data with child processes.

   * *note multiprocessing: b7. child processes on Windows no longer
     inherit all of the parent’s inheritable handles, only the necessary
     ones.

   * A new *note hashlib.pbkdf2_hmac(): 8d3. function provides the
     PKCS#5 password-based key derivation function 2(20).

   * *note TLSv1.1 and TLSv1.2 support: 8d4. for *note ssl: f3.

   * *note Retrieving certificates from the Windows system cert store
     support: 8d5. for *note ssl: f3.

   * *note Server-side SNI (Server Name Indication) support: 8d6. for
     *note ssl: f3.

   * The *note ssl.SSLContext: 4ea. class has a *note lot of
     improvements: 8d7.

   * All modules in the standard library that support SSL now support
     server certificate verification, including hostname matching (*note
     ssl.match_hostname(): 4e3.) and CRLs (Certificate Revocation lists,
     see *note ssl.SSLContext.load_verify_locations(): 8d8.).

CPython implementation improvements:

   * *note Safe object finalization: 8d9. ( PEP 442(21)).

   * Leveraging PEP 442(22), in most cases *note module globals are no
     longer set to None during finalization: 8d9. (bpo-18214(23)).

   * *note Configurable memory allocators: 8da. ( PEP 445(24)).

   * *note Argument Clinic: 8db. ( PEP 436(25)).

Please read on for a comprehensive list of user-facing changes,
including many other smaller improvements, CPython optimizations,
deprecations, and potential porting issues.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0453

   (2) https://www.python.org/dev/peps/pep-0446

   (3) https://bugs.python.org/issue16499

   (4) https://www.python.org/dev/peps/pep-0451

   (5) https://bugs.python.org/issue16475

   (6) https://www.python.org/dev/peps/pep-3156

   (7) https://www.python.org/dev/peps/pep-0453

   (8) https://www.python.org/dev/peps/pep-0435

   (9) https://www.python.org/dev/peps/pep-0428

   (10) https://www.python.org/dev/peps/pep-3156

   (11) https://www.python.org/dev/peps/pep-0450

   (12) https://www.python.org/dev/peps/pep-0454

   (13) https://www.python.org/dev/peps/pep-0443

   (14) https://www.python.org/dev/peps/pep-3154

   (15) https://bugs.python.org/issue8713

   (16) https://bugs.python.org/issue18891

   (17) https://www.python.org/dev/peps/pep-0456

   (18) https://www.python.org/dev/peps/pep-0446

   (19) https://bugs.python.org/issue16499

   (20) https://en.wikipedia.org/wiki/PBKDF2

   (21) https://www.python.org/dev/peps/pep-0442

   (22) https://www.python.org/dev/peps/pep-0442

   (23) https://bugs.python.org/issue18214

   (24) https://www.python.org/dev/peps/pep-0445

   (25) https://www.python.org/dev/peps/pep-0436


File: python.info,  Node: New Features<7>,  Next: New Modules<6>,  Prev: Summary – Release Highlights<2>,  Up: What’s New In Python 3 4

1.6.2 New Features
------------------

* Menu:

* PEP 453; Explicit Bootstrapping of PIP in Python Installations: PEP 453 Explicit Bootstrapping of PIP in Python Installations.
* PEP 446; Newly Created File Descriptors Are Non-Inheritable: PEP 446 Newly Created File Descriptors Are Non-Inheritable.
* Improvements to Codec Handling::
* PEP 451; A ModuleSpec Type for the Import System: PEP 451 A ModuleSpec Type for the Import System.
* Other Language Changes: Other Language Changes<6>.


File: python.info,  Node: PEP 453 Explicit Bootstrapping of PIP in Python Installations,  Next: PEP 446 Newly Created File Descriptors Are Non-Inheritable,  Up: New Features<7>

1.6.2.1 PEP 453: Explicit Bootstrapping of PIP in Python Installations
......................................................................

* Menu:

* Bootstrapping pip By Default::
* Documentation Changes::


File: python.info,  Node: Bootstrapping pip By Default,  Next: Documentation Changes,  Up: PEP 453 Explicit Bootstrapping of PIP in Python Installations

1.6.2.2 Bootstrapping pip By Default
....................................

The new *note ensurepip: 78. module (defined in PEP 453(1)) provides a
standard cross-platform mechanism to bootstrap the pip installer into
Python installations and virtual environments.  The version of ‘pip’
included with Python 3.4.0 is ‘pip’ 1.5.4, and future 3.4.x maintenance
releases will update the bundled version to the latest version of ‘pip’
that is available at the time of creating the release candidate.

By default, the commands ‘pipX’ and ‘pipX.Y’ will be installed on all
platforms (where X.Y stands for the version of the Python installation),
along with the ‘pip’ Python package and its dependencies.  On Windows
and in virtual environments on all platforms, the unversioned ‘pip’
command will also be installed.  On other platforms, the system wide
unversioned ‘pip’ command typically refers to the separately installed
Python 2 version.

The ‘pyvenv’ command line utility and the *note venv: 12e. module make
use of the *note ensurepip: 78. module to make ‘pip’ readily available
in virtual environments.  When using the command line utility, ‘pip’ is
installed by default, while when using the *note venv: 12e. module *note
API: 8df. installation of ‘pip’ must be requested explicitly.

For CPython *note source builds on POSIX systems: 8e0, the ‘make
install’ and ‘make altinstall’ commands bootstrap ‘pip’ by default.
This behaviour can be controlled through configure options, and
overridden through Makefile options.

On Windows and Mac OS X, the CPython installers now default to
installing ‘pip’ along with CPython itself (users may opt out of
installing it during the installation process).  Window users will need
to opt in to the automatic ‘PATH’ modifications to have ‘pip’ available
from the command line by default, otherwise it can still be accessed
through the Python launcher for Windows as ‘py -m pip’.

As discussed in the PEP(2), platform packagers may choose not to install
these commands by default, as long as, when invoked, they provide clear
and simple directions on how to install them on that platform (usually
using the system package manager).

     Note: To avoid conflicts between parallel Python 2 and Python 3
     installations, only the versioned ‘pip3’ and ‘pip3.4’ commands are
     bootstrapped by default when ‘ensurepip’ is invoked directly - the
     ‘--default-pip’ option is needed to also request the unversioned
     ‘pip’ command.  ‘pyvenv’ and the Windows installer ensure that the
     unqualified ‘pip’ command is made available in those environments,
     and ‘pip’ can always be invoked via the ‘-m’ switch rather than
     directly to avoid ambiguity on systems with multiple Python
     installations.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0453

   (2) 
https://www.python.org/dev/peps/pep-0453/#recommendations-for-downstream-distributors


File: python.info,  Node: Documentation Changes,  Prev: Bootstrapping pip By Default,  Up: PEP 453 Explicit Bootstrapping of PIP in Python Installations

1.6.2.3 Documentation Changes
.............................

As part of this change, the *note Installing Python Modules: 8e2. and
*note Distributing Python Modules: 8e3. sections of the documentation
have been completely redesigned as short getting started and FAQ
documents.  Most packaging documentation has now been moved out to the
Python Packaging Authority maintained Python Packaging User Guide(1) and
the documentation of the individual projects.

However, as this migration is currently still incomplete, the legacy
versions of those guides remaining available as *note Installing Python
Modules (Legacy version): 8e4. and *note Distributing Python Modules
(Legacy version): 8e5.

See also
........

PEP 453(2) – Explicit bootstrapping of pip in Python installations

     PEP written by Donald Stufft and Nick Coghlan, implemented by
     Donald Stufft, Nick Coghlan, Martin von Löwis and Ned Deily.

   ---------- Footnotes ----------

   (1) https://packaging.python.org

   (2) https://www.python.org/dev/peps/pep-0453


File: python.info,  Node: PEP 446 Newly Created File Descriptors Are Non-Inheritable,  Next: Improvements to Codec Handling,  Prev: PEP 453 Explicit Bootstrapping of PIP in Python Installations,  Up: New Features<7>

1.6.2.4 PEP 446: Newly Created File Descriptors Are Non-Inheritable
...................................................................

PEP 446(1) makes newly created file descriptors *note non-inheritable:
8e7.  In general, this is the behavior an application will want: when
launching a new process, having currently open files also open in the
new process can lead to all sorts of hard to find bugs, and potentially
to security issues.

However, there are occasions when inheritance is desired.  To support
these cases, the following new functions and methods are available:

   * *note os.get_inheritable(): 8e8, *note os.set_inheritable(): 8e9.

   * *note os.get_handle_inheritable(): 8ea, *note
     os.set_handle_inheritable(): 8eb.

   * *note socket.socket.get_inheritable(): 8ec, *note
     socket.socket.set_inheritable(): 8ed.

See also
........

PEP 446(2) – Make newly created file descriptors non-inheritable

     PEP written and implemented by Victor Stinner.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0446

   (2) https://www.python.org/dev/peps/pep-0446


File: python.info,  Node: Improvements to Codec Handling,  Next: PEP 451 A ModuleSpec Type for the Import System,  Prev: PEP 446 Newly Created File Descriptors Are Non-Inheritable,  Up: New Features<7>

1.6.2.5 Improvements to Codec Handling
......................................

Since it was first introduced, the *note codecs: 1b. module has always
been intended to operate as a type-neutral dynamic encoding and decoding
system.  However, its close coupling with the Python text model,
especially the type restricted convenience methods on the builtin *note
str: 205, *note bytes: 172. and *note bytearray: 173. types, has
historically obscured that fact.

As a key step in clarifying the situation, the *note codecs.encode():
8ef. and *note codecs.decode(): 8f0. convenience functions are now
properly documented in Python 2.7, 3.3 and 3.4.  These functions have
existed in the *note codecs: 1b. module (and have been covered by the
regression test suite) since Python 2.4, but were previously only
discoverable through runtime introspection.

Unlike the convenience methods on *note str: 205, *note bytes: 172. and
*note bytearray: 173, the *note codecs: 1b. convenience functions
support arbitrary codecs in both Python 2 and Python 3, rather than
being limited to Unicode text encodings (in Python 3) or ‘basestring’
<-> ‘basestring’ conversions (in Python 2).

In Python 3.4, the interpreter is able to identify the known non-text
encodings provided in the standard library and direct users towards
these general purpose convenience functions when appropriate:

     >>> b"abcdef".decode("hex")
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     LookupError: 'hex' is not a text encoding; use codecs.decode() to handle arbitrary codecs

     >>> "hello".encode("rot13")
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     LookupError: 'rot13' is not a text encoding; use codecs.encode() to handle arbitrary codecs

     >>> open("foo.txt", encoding="hex")
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     LookupError: 'hex' is not a text encoding; use codecs.open() to handle arbitrary codecs

In a related change, whenever it is feasible without breaking backwards
compatibility, exceptions raised during encoding and decoding operations
are wrapped in a chained exception of the same type that mentions the
name of the codec responsible for producing the error:

     >>> import codecs

     >>> codecs.decode(b"abcdefgh", "hex")
     Traceback (most recent call last):
       File "/usr/lib/python3.4/encodings/hex_codec.py", line 20, in hex_decode
         return (binascii.a2b_hex(input), len(input))
     binascii.Error: Non-hexadecimal digit found

     The above exception was the direct cause of the following exception:

     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     binascii.Error: decoding with 'hex' codec failed (Error: Non-hexadecimal digit found)

     >>> codecs.encode("hello", "bz2")
     Traceback (most recent call last):
       File "/usr/lib/python3.4/encodings/bz2_codec.py", line 17, in bz2_encode
         return (bz2.compress(input), len(input))
       File "/usr/lib/python3.4/bz2.py", line 498, in compress
         return comp.compress(data) + comp.flush()
     TypeError: 'str' does not support the buffer interface

     The above exception was the direct cause of the following exception:

     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: encoding with 'bz2' codec failed (TypeError: 'str' does not support the buffer interface)

Finally, as the examples above show, these improvements have permitted
the restoration of the convenience aliases for the non-Unicode codecs
that were themselves restored in Python 3.2.  This means that encoding
binary data to and from its hexadecimal representation (for example) can
now be written as:

     >>> from codecs import encode, decode
     >>> encode(b"hello", "hex")
     b'68656c6c6f'
     >>> decode(b"68656c6c6f", "hex")
     b'hello'

The binary and text transforms provided in the standard library are
detailed in *note Binary Transforms: 8f1. and *note Text Transforms:
8f2.

(Contributed by Nick Coghlan in bpo-7475(1), bpo-17827(2), bpo-17828(3)
and bpo-19619(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue7475

   (2) https://bugs.python.org/issue17827

   (3) https://bugs.python.org/issue17828

   (4) https://bugs.python.org/issue19619


File: python.info,  Node: PEP 451 A ModuleSpec Type for the Import System,  Next: Other Language Changes<6>,  Prev: Improvements to Codec Handling,  Up: New Features<7>

1.6.2.6 PEP 451: A ModuleSpec Type for the Import System
........................................................

PEP 451(1) provides an encapsulation of the information about a module
that the import machinery will use to load it (that is, a module
specification).  This helps simplify both the import implementation and
several import-related APIs.  The change is also a stepping stone for
several future import-related improvements(2).

The public-facing changes from the PEP are entirely backward-compatible.
Furthermore, they should be transparent to everyone but importer
authors.  Key finder and loader methods have been deprecated, but they
will continue working.  New importers should use the new methods
described in the PEP. Existing importers should be updated to implement
the new methods.  See the *note Deprecated: 8f4. section for a list of
methods that should be replaced and their replacements.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0451

   (2) 
https://mail.python.org/pipermail/python-dev/2013-November/130111.html


File: python.info,  Node: Other Language Changes<6>,  Prev: PEP 451 A ModuleSpec Type for the Import System,  Up: New Features<7>

1.6.2.7 Other Language Changes
..............................

Some smaller changes made to the core Python language are:

   * Unicode database updated to UCD version 6.3.

   * *note min(): 8f6. and *note max(): 8f7. now accept a `default'
     keyword-only argument that can be used to specify the value they
     return if the iterable they are evaluating has no elements.
     (Contributed by Julian Berman in bpo-18111(1).)

   * Module objects are now *note weakref: 131.’able.

   * Module ‘__file__’ attributes (and related values) should now always
     contain absolute paths by default, with the sole exception of
     ‘__main__.__file__’ when a script has been executed directly using
     a relative path.  (Contributed by Brett Cannon in bpo-18416(2).)

   * All the UTF-* codecs (except UTF-7) now reject surrogates during
     both encoding and decoding unless the ‘surrogatepass’ error handler
     is used, with the exception of the UTF-16 decoder (which accepts
     valid surrogate pairs) and the UTF-16 encoder (which produces them
     while encoding non-BMP characters).  (Contributed by Victor
     Stinner, Kang-Hao (Kenny) Lu and Serhiy Storchaka in bpo-12892(3).)

   * New German EBCDIC *note codec: 782. ‘cp273’.  (Contributed by
     Michael Bierenfeld and Andrew Kuchling in bpo-1097797(4).)

   * New Ukrainian *note codec: 782. ‘cp1125’.  (Contributed by Serhiy
     Storchaka in bpo-19668(5).)

   * *note bytes: 172.join() and *note bytearray: 173.join() now accept
     arbitrary buffer objects as arguments.  (Contributed by Antoine
     Pitrou in bpo-15958(6).)

   * The *note int: 204. constructor now accepts any object that has an
     ‘__index__’ method for its `base' argument.  (Contributed by Mark
     Dickinson in bpo-16772(7).)

   * Frame objects now have a *note clear(): 8f8. method that clears all
     references to local variables from the frame.  (Contributed by
     Antoine Pitrou in bpo-17934(8).)

   * *note memoryview: 386. is now registered as a *note Sequence: 1e,
     and supports the *note reversed(): 2c6. builtin.  (Contributed by
     Nick Coghlan and Claudiu Popa in bpo-18690(9) and bpo-19078(10).)

   * Signatures reported by *note help(): 175. have been modified and
     improved in several cases as a result of the introduction of
     Argument Clinic and other changes to the *note inspect: a0. and
     *note pydoc: d9. modules.

   * *note __length_hint__(): 8f9. is now part of the formal language
     specification (see PEP 424(11)).  (Contributed by Armin Ronacher in
     bpo-16148(12).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18111

   (2) https://bugs.python.org/issue18416

   (3) https://bugs.python.org/issue12892

   (4) https://bugs.python.org/issue1097797

   (5) https://bugs.python.org/issue19668

   (6) https://bugs.python.org/issue15958

   (7) https://bugs.python.org/issue16772

   (8) https://bugs.python.org/issue17934

   (9) https://bugs.python.org/issue18690

   (10) https://bugs.python.org/issue19078

   (11) https://www.python.org/dev/peps/pep-0424

   (12) https://bugs.python.org/issue16148


File: python.info,  Node: New Modules<6>,  Next: Improved Modules<6>,  Prev: New Features<7>,  Up: What’s New In Python 3 4

1.6.3 New Modules
-----------------

* Menu:

* asyncio: asyncio<7>.
* ensurepip::
* enum: enum<5>.
* pathlib: pathlib<6>.
* selectors: selectors<2>.
* statistics: statistics<3>.
* tracemalloc: tracemalloc<4>.


File: python.info,  Node: asyncio<7>,  Next: ensurepip,  Up: New Modules<6>

1.6.3.1 asyncio
...............

The new *note asyncio: 9. module (defined in PEP 3156(1)) provides a
standard pluggable event loop model for Python, providing solid
asynchronous IO support in the standard library, and making it easier
for other event loop implementations to interoperate with the standard
library and each other.

For Python 3.4, this module is considered a *note provisional API: 454.

See also
........

PEP 3156(2) – Asynchronous IO Support Rebooted: the “asyncio” Module

     PEP written and implementation led by Guido van Rossum.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3156

   (2) https://www.python.org/dev/peps/pep-3156


File: python.info,  Node: ensurepip,  Next: enum<5>,  Prev: asyncio<7>,  Up: New Modules<6>

1.6.3.2 ensurepip
.................

The new *note ensurepip: 78. module is the primary infrastructure for
the PEP 453(1) implementation.  In the normal course of events end users
will not need to interact with this module, but it can be used to
manually bootstrap ‘pip’ if the automated bootstrapping into an
installation or virtual environment was declined.

*note ensurepip: 78. includes a bundled copy of ‘pip’, up-to-date as of
the first release candidate of the release of CPython with which it
ships (this applies to both maintenance releases and feature releases).
‘ensurepip’ does not access the internet.  If the installation has
Internet access, after ‘ensurepip’ is run the bundled ‘pip’ can be used
to upgrade ‘pip’ to a more recent release than the bundled one.  (Note
that such an upgraded version of ‘pip’ is considered to be a separately
installed package and will not be removed if Python is uninstalled.)

The module is named `ensure'pip because if called when ‘pip’ is already
installed, it does nothing.  It also has an ‘--upgrade’ option that will
cause it to install the bundled copy of ‘pip’ if the existing installed
version of ‘pip’ is older than the bundled copy.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0453


File: python.info,  Node: enum<5>,  Next: pathlib<6>,  Prev: ensurepip,  Up: New Modules<6>

1.6.3.3 enum
............

The new *note enum: 79. module (defined in PEP 435(1)) provides a
standard implementation of enumeration types, allowing other modules
(such as *note socket: ef.) to provide more informative error messages
and better debugging support by replacing opaque integer constants with
backwards compatible enumeration values.

See also
........

PEP 435(2) – Adding an Enum type to the Python standard library

     PEP written by Barry Warsaw, Eli Bendersky and Ethan Furman,
     implemented by Ethan Furman.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0435

   (2) https://www.python.org/dev/peps/pep-0435


File: python.info,  Node: pathlib<6>,  Next: selectors<2>,  Prev: enum<5>,  Up: New Modules<6>

1.6.3.4 pathlib
...............

The new *note pathlib: c8. module offers classes representing filesystem
paths with semantics appropriate for different operating systems.  Path
classes are divided between `pure paths', which provide purely
computational operations without I/O, and `concrete paths', which
inherit from pure paths but also provide I/O operations.

For Python 3.4, this module is considered a *note provisional API: 454.

See also
........

PEP 428(1) – The pathlib module – object-oriented filesystem paths

     PEP written and implemented by Antoine Pitrou.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0428


File: python.info,  Node: selectors<2>,  Next: statistics<3>,  Prev: pathlib<6>,  Up: New Modules<6>

1.6.3.5 selectors
.................

The new *note selectors: e6. module (created as part of implementing PEP
3156(1)) allows high-level and efficient I/O multiplexing, built upon
the *note select: e5. module primitives.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3156


File: python.info,  Node: statistics<3>,  Next: tracemalloc<4>,  Prev: selectors<2>,  Up: New Modules<6>

1.6.3.6 statistics
..................

The new *note statistics: f5. module (defined in PEP 450(1)) offers some
core statistics functionality directly in the standard library.  This
module supports calculation of the mean, median, mode, variance and
standard deviation of a data series.

See also
........

PEP 450(2) – Adding A Statistics Module To The Standard Library

     PEP written and implemented by Steven D’Aprano

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0450

   (2) https://www.python.org/dev/peps/pep-0450


File: python.info,  Node: tracemalloc<4>,  Prev: statistics<3>,  Up: New Modules<6>

1.6.3.7 tracemalloc
...................

The new *note tracemalloc: 11d. module (defined in PEP 454(1)) is a
debug tool to trace memory blocks allocated by Python.  It provides the
following information:

   * Trace where an object was allocated

   * Statistics on allocated memory blocks per filename and per line
     number: total size, number and average size of allocated memory
     blocks

   * Compute the differences between two snapshots to detect memory
     leaks

See also
........

PEP 454(2) – Add a new tracemalloc module to trace Python memory allocations

     PEP written and implemented by Victor Stinner

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0454

   (2) https://www.python.org/dev/peps/pep-0454


File: python.info,  Node: Improved Modules<6>,  Next: CPython Implementation Changes,  Prev: New Modules<6>,  Up: What’s New In Python 3 4

1.6.4 Improved Modules
----------------------

* Menu:

* abc::
* aifc: aifc<2>.
* argparse: argparse<3>.
* audioop::
* base64::
* collections: collections<6>.
* colorsys::
* contextlib: contextlib<4>.
* dbm: dbm<5>.
* dis: dis<2>.
* doctest: doctest<2>.
* email: email<3>.
* filecmp::
* functools: functools<4>.
* gc: gc<4>.
* glob: glob<2>.
* hashlib: hashlib<3>.
* hmac: hmac<2>.
* html::
* http: http<3>.
* idlelib and IDLE: idlelib and IDLE<4>.
* importlib: importlib<7>.
* inspect: inspect<5>.
* ipaddress: ipaddress<4>.
* logging: logging<5>.
* marshal::
* mmap: mmap<2>.
* multiprocessing: multiprocessing<6>.
* operator: operator<2>.
* os: os<7>.
* pdb: pdb<4>.
* pickle: pickle<4>.
* plistlib: plistlib<2>.
* poplib: poplib<3>.
* pprint: pprint<3>.
* pty::
* pydoc: pydoc<4>.
* re: re<5>.
* resource::
* select::
* shelve::
* shutil: shutil<3>.
* smtpd: smtpd<2>.
* smtplib: smtplib<3>.
* socket: socket<7>.
* sqlite3: sqlite3<4>.
* ssl: ssl<7>.
* stat::
* struct: struct<2>.
* subprocess: subprocess<4>.
* sunau: sunau<2>.
* sys: sys<7>.
* tarfile: tarfile<3>.
* textwrap::
* threading: threading<4>.
* traceback: traceback<3>.
* types: types<3>.
* urllib: urllib<2>.
* unittest: unittest<4>.
* venv: venv<5>.
* wave: wave<2>.
* weakref: weakref<2>.
* xml.etree: xml etree<2>.
* zipfile: zipfile<4>.


File: python.info,  Node: abc,  Next: aifc<2>,  Up: Improved Modules<6>

1.6.4.1 abc
...........

New function *note abc.get_cache_token(): 904. can be used to know when
to invalidate caches that are affected by changes in the object graph.
(Contributed by Łukasz Langa in bpo-16832(1).)

New class *note ABC: 905. has *note ABCMeta: 906. as its meta class.
Using ‘ABC’ as a base class has essentially the same effect as
specifying ‘metaclass=abc.ABCMeta’, but is simpler to type and easier to
read.  (Contributed by Bruno Dupuis in bpo-16049(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16832

   (2) https://bugs.python.org/issue16049


File: python.info,  Node: aifc<2>,  Next: argparse<3>,  Prev: abc,  Up: Improved Modules<6>

1.6.4.2 aifc
............

The *note getparams(): 908. method now returns a namedtuple rather than
a plain tuple.  (Contributed by Claudiu Popa in bpo-17818(1).)

*note aifc.open(): 55d. now supports the context management protocol:
when used in a *note with: 7da. block, the *note close(): 909. method of
the returned object will be called automatically at the end of the
block.  (Contributed by Serhiy Storchacha in bpo-16486(2).)

The *note writeframesraw(): 90a. and *note writeframes(): 90b. methods
now accept any *note bytes-like object: 6df.  (Contributed by Serhiy
Storchaka in bpo-8311(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17818

   (2) https://bugs.python.org/issue16486

   (3) https://bugs.python.org/issue8311


File: python.info,  Node: argparse<3>,  Next: audioop,  Prev: aifc<2>,  Up: Improved Modules<6>

1.6.4.3 argparse
................

The *note FileType: 90d. class now accepts `encoding' and `errors'
arguments, which are passed through to *note open(): 16f.  (Contributed
by Lucas Maystre in bpo-11175(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11175


File: python.info,  Node: audioop,  Next: base64,  Prev: argparse<3>,  Up: Improved Modules<6>

1.6.4.4 audioop
...............

*note audioop: c. now supports 24-bit samples.  (Contributed by Serhiy
Storchaka in bpo-12866(1).)

New *note byteswap(): 90f. function converts big-endian samples to
little-endian and vice versa.  (Contributed by Serhiy Storchaka in
bpo-19641(2).)

All *note audioop: c. functions now accept any *note bytes-like object:
6df.  Strings are not accepted: they didn’t work before, now they raise
an error right away.  (Contributed by Serhiy Storchaka in bpo-16685(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12866

   (2) https://bugs.python.org/issue19641

   (3) https://bugs.python.org/issue16685


File: python.info,  Node: base64,  Next: collections<6>,  Prev: audioop,  Up: Improved Modules<6>

1.6.4.5 base64
..............

The encoding and decoding functions in *note base64: d. now accept any
*note bytes-like object: 6df. in cases where it previously required a
*note bytes: 172. or *note bytearray: 173. instance.  (Contributed by
Nick Coghlan in bpo-17839(1).)

New functions *note a85encode(): 911, *note a85decode(): 912, *note
b85encode(): 913, and *note b85decode(): 914. provide the ability to
encode and decode binary data from and to ‘Ascii85’ and the
git/mercurial ‘Base85’ formats, respectively.  The ‘a85’ functions have
options that can be used to make them compatible with the variants of
the ‘Ascii85’ encoding, including the Adobe variant.  (Contributed by
Martin Morrison, the Mercurial project, Serhiy Storchaka, and Antoine
Pitrou in bpo-17618(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17839

   (2) https://bugs.python.org/issue17618


File: python.info,  Node: collections<6>,  Next: colorsys,  Prev: base64,  Up: Improved Modules<6>

1.6.4.6 collections
...................

The *note ChainMap.new_child(): 916. method now accepts an `m' argument
specifying the child map to add to the chain.  This allows an existing
mapping and/or a custom mapping type to be used for the child.
(Contributed by Vinay Sajip in bpo-16613(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16613


File: python.info,  Node: colorsys,  Next: contextlib<4>,  Prev: collections<6>,  Up: Improved Modules<6>

1.6.4.7 colorsys
................

The number of digits in the coefficients for the RGB — YIQ conversions
have been expanded so that they match the FCC NTSC versions.  The change
in results should be less than 1% and may better match results found
elsewhere.  (Contributed by Brian Landers and Serhiy Storchaka in
bpo-14323(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14323


File: python.info,  Node: contextlib<4>,  Next: dbm<5>,  Prev: colorsys,  Up: Improved Modules<6>

1.6.4.8 contextlib
..................

The new *note contextlib.suppress: 919. context manager helps to clarify
the intent of code that deliberately suppresses exceptions from a single
statement.  (Contributed by Raymond Hettinger in bpo-15806(1) and Zero
Piraeus in bpo-19266(2).)

The new *note contextlib.redirect_stdout(): 7b5. context manager makes
it easier for utility scripts to handle inflexible APIs that write their
output to *note sys.stdout: 41f. and don’t provide any options to
redirect it.  Using the context manager, the *note sys.stdout: 41f.
output can be redirected to any other stream or, in conjunction with
*note io.StringIO: 91a, to a string.  The latter can be especially
useful, for example, to capture output from a function that was written
to implement a command line interface.  It is recommended only for
utility scripts because it affects the global state of *note sys.stdout:
41f.  (Contributed by Raymond Hettinger in bpo-15805(3).)

The *note contextlib: 23. documentation has also been updated to include
a *note discussion: 91b. of the differences between single use, reusable
and reentrant context managers.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15806

   (2) https://bugs.python.org/issue19266

   (3) https://bugs.python.org/issue15805


File: python.info,  Node: dbm<5>,  Next: dis<2>,  Prev: contextlib<4>,  Up: Improved Modules<6>

1.6.4.9 dbm
...........

*note dbm.open(): 91d. objects now support the context management
protocol.  When used in a *note with: 7da. statement, the ‘close’ method
of the database object will be called automatically at the end of the
block.  (Contributed by Claudiu Popa and Nick Coghlan in bpo-19282(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19282


File: python.info,  Node: dis<2>,  Next: doctest<2>,  Prev: dbm<5>,  Up: Improved Modules<6>

1.6.4.10 dis
............

Functions *note show_code(): 91f, *note dis(): 48b, *note distb(): 920,
and *note disassemble(): 921. now accept a keyword-only `file' argument
that controls where they write their output.

The *note dis: 37. module is now built around an *note Instruction: 922.
class that provides object oriented access to the details of each
individual bytecode operation.

A new method, *note get_instructions(): 923, provides an iterator that
emits the Instruction stream for a given piece of Python code.  Thus it
is now possible to write a program that inspects and manipulates a
bytecode object in ways different from those provided by the *note dis:
37. module itself.  For example:

     >>> import dis
     >>> for instr in dis.get_instructions(lambda x: x + 1):
     ...     print(instr.opname)
     LOAD_FAST
     LOAD_CONST
     BINARY_ADD
     RETURN_VALUE

The various display tools in the *note dis: 37. module have been
rewritten to use these new components.

In addition, a new application-friendly class *note Bytecode: 924.
provides an object-oriented API for inspecting bytecode in both in
human-readable form and for iterating over instructions.  The *note
Bytecode: 924. constructor takes the same arguments that
‘get_instruction()’ does (plus an optional `current_offset'), and the
resulting object can be iterated to produce *note Instruction: 922.
objects.  But it also has a *note dis: 925. method, equivalent to
calling *note dis: 48b. on the constructor argument, but returned as a
multi-line string:

     >>> bytecode = dis.Bytecode(lambda x: x + 1, current_offset=3)
     >>> for instr in bytecode:
     ...     print('{} ({})'.format(instr.opname, instr.opcode))
     LOAD_FAST (124)
     LOAD_CONST (100)
     BINARY_ADD (23)
     RETURN_VALUE (83)
     >>> bytecode.dis().splitlines()
     ['  1           0 LOAD_FAST                0 (x)',
      '      -->     3 LOAD_CONST               1 (1)',
      '              6 BINARY_ADD',
      '              7 RETURN_VALUE']

*note Bytecode: 924. also has a class method, *note from_traceback():
926, that provides the ability to manipulate a traceback (that is,
‘print(Bytecode.from_traceback(tb).dis())’ is equivalent to
‘distb(tb)’).

(Contributed by Nick Coghlan, Ryan Kelly and Thomas Kluyver in
bpo-11816(1) and Claudiu Popa in bpo-17916(2).)

New function *note stack_effect(): 927. computes the effect on the
Python stack of a given opcode and argument, information that is not
otherwise available.  (Contributed by Larry Hastings in bpo-19722(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11816

   (2) https://bugs.python.org/issue17916

   (3) https://bugs.python.org/issue19722


File: python.info,  Node: doctest<2>,  Next: email<3>,  Prev: dis<2>,  Up: Improved Modules<6>

1.6.4.11 doctest
................

A new *note option flag: 929, *note FAIL_FAST: 92a, halts test running
as soon as the first failure is detected.  (Contributed by R. David
Murray and Daniel Urban in bpo-16522(1).)

The *note doctest: 66. command line interface now uses *note argparse:
5, and has two new options, ‘-o’ and ‘-f’.  ‘-o’ allows *note doctest
options: 929. to be specified on the command line, and ‘-f’ is a
shorthand for ‘-o FAIL_FAST’ (to parallel the similar option supported
by the *note unittest: 124. CLI). (Contributed by R. David Murray in
bpo-11390(2).)

*note doctest: 66. will now find doctests in extension module ‘__doc__’
strings.  (Contributed by Zachary Ware in bpo-3158(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16522

   (2) https://bugs.python.org/issue11390

   (3) https://bugs.python.org/issue3158


File: python.info,  Node: email<3>,  Next: filecmp,  Prev: doctest<2>,  Up: Improved Modules<6>

1.6.4.12 email
..............

*note as_string(): 92c. now accepts a `policy' argument to override the
default policy of the message when generating a string representation of
it.  This means that ‘as_string’ can now be used in more circumstances,
instead of having to create and use a *note generator: 6c. in order to
pass formatting parameters to its ‘flatten’ method.  (Contributed by R.
David Murray in bpo-18600(1).)

New method *note as_bytes(): 92d. added to produce a bytes
representation of the message in a fashion similar to how ‘as_string’
produces a string representation.  It does not accept the `maxheaderlen'
argument, but does accept the `unixfrom' and `policy' arguments.  The
*note Message: 63b. *note __bytes__(): 92e. method calls it, meaning
that ‘bytes(mymsg)’ will now produce the intuitive result: a bytes
object containing the fully formatted message.  (Contributed by R. David
Murray in bpo-18600(2).)

The *note Message.set_param(): 92f. message now accepts a `replace'
keyword argument.  When specified, the associated header will be updated
without changing its location in the list of headers.  For backward
compatibility, the default is ‘False’.  (Contributed by R. David Murray
in bpo-18891(3).)  A pair of new subclasses of *note Message: 63b. have
been added (*note EmailMessage: 63c. and *note MIMEPart: 930.), along
with a new sub-module, *note contentmanager: 69. and a new *note policy:
73. attribute *note content_manager: 931.  All documentation is
currently in the new module, which is being added as part of email’s new
*note provisional API: 454.  These classes provide a number of new
methods that make extracting content from and inserting content into
email messages much easier.  For details, see the *note contentmanager:
69. documentation and the *note email; Examples: 932.  These API
additions complete the bulk of the work that was planned as part of the
email6 project.  The currently provisional API is scheduled to become
final in Python 3.5 (possibly with a few minor additions in the area of
error handling).  (Contributed by R. David Murray in bpo-18891(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18600

   (2) https://bugs.python.org/issue18600

   (3) https://bugs.python.org/issue18891

   (4) https://bugs.python.org/issue18891


File: python.info,  Node: filecmp,  Next: functools<4>,  Prev: email<3>,  Up: Improved Modules<6>

1.6.4.13 filecmp
................

A new *note clear_cache(): 934. function provides the ability to clear
the *note filecmp: 7d. comparison cache, which uses *note os.stat():
321. information to determine if the file has changed since the last
compare.  This can be used, for example, if the file might have been
changed and re-checked in less time than the resolution of a particular
filesystem’s file modification time field.  (Contributed by Mark Levitt
in bpo-18149(1).)

New module attribute *note DEFAULT_IGNORES: 935. provides the list of
directories that are used as the default value for the `ignore'
parameter of the *note dircmp(): 936. function.  (Contributed by Eli
Bendersky in bpo-15442(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18149

   (2) https://bugs.python.org/issue15442


File: python.info,  Node: functools<4>,  Next: gc<4>,  Prev: filecmp,  Up: Improved Modules<6>

1.6.4.14 functools
..................

The new *note partialmethod(): 3bf. descriptor brings partial argument
application to descriptors, just as *note partial(): 8b5. provides for
normal callables.  The new descriptor also makes it easier to get
arbitrary callables (including *note partial(): 8b5. instances) to
behave like normal instance methods when included in a class definition.
(Contributed by Alon Horev and Nick Coghlan in bpo-4331(1).)  The new
*note singledispatch(): 491. decorator brings support for
single-dispatch generic functions to the Python standard library.  Where
object oriented programming focuses on grouping multiple operations on a
common set of data into a class, a generic function focuses on grouping
multiple implementations of an operation that allows it to work with
`different' kinds of data.

See also
........

PEP 443(2) – Single-dispatch generic functions

     PEP written and implemented by Łukasz Langa.

*note total_ordering(): 938. now supports a return value of *note
NotImplemented: 202. from the underlying comparison function.
(Contributed by Katie Miller in bpo-10042(3).)

A pure-python version of the *note partial(): 8b5. function is now in
the stdlib; in CPython it is overridden by the C accelerated version,
but it is available for other implementations to use.  (Contributed by
Brian Thorne in bpo-12428(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4331

   (2) https://www.python.org/dev/peps/pep-0443

   (3) https://bugs.python.org/issue10042

   (4) https://bugs.python.org/issue12428


File: python.info,  Node: gc<4>,  Next: glob<2>,  Prev: functools<4>,  Up: Improved Modules<6>

1.6.4.15 gc
...........

New function *note get_stats(): 93a. returns a list of three
per-generation dictionaries containing the collections statistics since
interpreter startup.  (Contributed by Antoine Pitrou in bpo-16351(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16351


File: python.info,  Node: glob<2>,  Next: hashlib<3>,  Prev: gc<4>,  Up: Improved Modules<6>

1.6.4.16 glob
.............

A new function *note escape(): 93c. provides a way to escape special
characters in a filename so that they do not become part of the globbing
expansion but are instead matched literally.  (Contributed by Serhiy
Storchaka in bpo-8402(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8402


File: python.info,  Node: hashlib<3>,  Next: hmac<2>,  Prev: glob<2>,  Up: Improved Modules<6>

1.6.4.17 hashlib
................

A new *note hashlib.pbkdf2_hmac(): 8d3. function provides the PKCS#5
password-based key derivation function 2(1).  (Contributed by Christian
Heimes in bpo-18582(2).)

The *note name: 93e. attribute of *note hashlib: 8c. hash objects is now
a formally supported interface.  It has always existed in CPython’s
*note hashlib: 8c. (although it did not return lower case names for all
supported hashes), but it was not a public interface and so some other
Python implementations have not previously supported it.  (Contributed
by Jason R. Coombs in bpo-18532(3).)

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/PBKDF2

   (2) https://bugs.python.org/issue18582

   (3) https://bugs.python.org/issue18532


File: python.info,  Node: hmac<2>,  Next: html,  Prev: hashlib<3>,  Up: Improved Modules<6>

1.6.4.18 hmac
.............

*note hmac: 8e. now accepts ‘bytearray’ as well as ‘bytes’ for the `key'
argument to the *note new(): 940. function, and the `msg' parameter to
both the *note new(): 940. function and the *note update(): 941. method
now accepts any type supported by the *note hashlib: 8c. module.
(Contributed by Jonas Borgström in bpo-18240(1).)

The `digestmod' argument to the *note hmac.new(): 940. function may now
be any hash digest name recognized by *note hashlib: 8c.  In addition,
the current behavior in which the value of `digestmod' defaults to ‘MD5’
is deprecated: in a future version of Python there will be no default
value.  (Contributed by Christian Heimes in bpo-17276(2).)

With the addition of *note block_size: 942. and *note name: 943.
attributes (and the formal documentation of the *note digest_size: 944.
attribute), the *note hmac: 8e. module now conforms fully to the PEP
247(3) API. (Contributed by Christian Heimes in bpo-18775(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18240

   (2) https://bugs.python.org/issue17276

   (3) https://www.python.org/dev/peps/pep-0247

   (4) https://bugs.python.org/issue18775


File: python.info,  Node: html,  Next: http<3>,  Prev: hmac<2>,  Up: Improved Modules<6>

1.6.4.19 html
.............

New function *note unescape(): 22b. function converts HTML5 character
references to the corresponding Unicode characters.  (Contributed by
Ezio Melotti in bpo-2927(1).)

*note HTMLParser: 22a. accepts a new keyword argument `convert_charrefs'
that, when ‘True’, automatically converts all character references.  For
backward-compatibility, its value defaults to ‘False’, but it will
change to ‘True’ in a future version of Python, so you are invited to
set it explicitly and update your code to use this new feature.
(Contributed by Ezio Melotti in bpo-13633(2).)

The `strict' argument of *note HTMLParser: 22a. is now deprecated.
(Contributed by Ezio Melotti in bpo-15114(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue2927

   (2) https://bugs.python.org/issue13633

   (3) https://bugs.python.org/issue15114


File: python.info,  Node: http<3>,  Next: idlelib and IDLE<4>,  Prev: html,  Up: Improved Modules<6>

1.6.4.20 http
.............

*note send_error(): 947. now accepts an optional additional `explain'
parameter which can be used to provide an extended error description,
overriding the hardcoded default if there is one.  This extended error
description will be formatted using the ‘error_message_format’ attribute
and sent as the body of the error response.  (Contributed by Karl Cow in
bpo-12921(1).)

The *note http.server: 96. *note command line interface: 948. now has a
‘-b/--bind’ option that causes the server to listen on a specific
address.  (Contributed by Malte Swart in bpo-17764(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12921

   (2) https://bugs.python.org/issue17764


File: python.info,  Node: idlelib and IDLE<4>,  Next: importlib<7>,  Prev: http<3>,  Up: Improved Modules<6>

1.6.4.21 idlelib and IDLE
.........................

Since idlelib implements the IDLE shell and editor and is not intended
for import by other programs, it gets improvements with every release.
See ‘Lib/idlelib/NEWS.txt’ for a cumulative list of changes since 3.3.0,
as well as changes made in future 3.4.x releases.  This file is also
available from the IDLE Help ‣ About IDLE dialog.


File: python.info,  Node: importlib<7>,  Next: inspect<5>,  Prev: idlelib and IDLE<4>,  Up: Improved Modules<6>

1.6.4.22 importlib
..................

The *note InspectLoader: 94b. ABC defines a new method, *note
source_to_code(): 7e0. that accepts source data and a path and returns a
code object.  The default implementation is equivalent to ‘compile(data,
path, 'exec', dont_inherit=True)’.  (Contributed by Eric Snow and Brett
Cannon in bpo-15627(1).)

*note InspectLoader: 94b. also now has a default implementation for the
*note get_code(): 94c. method.  However, it will normally be desirable
to override the default implementation for performance reasons.
(Contributed by Brett Cannon in bpo-18072(2).)

The *note reload(): 4a0. function has been moved from *note imp: 99. to
*note importlib: 9a. as part of the *note imp: 99. module deprecation.
(Contributed by Berker Peksag in bpo-18193(3).)

*note importlib.util: 9f. now has a *note MAGIC_NUMBER: 94d. attribute
providing access to the bytecode version number.  This replaces the
*note get_magic(): 94e. function in the deprecated *note imp: 99.
module.  (Contributed by Brett Cannon in bpo-18192(4).)

New *note importlib.util: 9f. functions *note cache_from_source(): 651.
and *note source_from_cache(): 652. replace the same-named functions in
the deprecated *note imp: 99. module.  (Contributed by Brett Cannon in
bpo-18194(5).)

The *note importlib: 9a. bootstrap ‘NamespaceLoader’ now conforms to the
*note InspectLoader: 94b. ABC, which means that ‘runpy’ and ‘python -m’
can now be used with namespace packages.  (Contributed by Brett Cannon
in bpo-18058(6).)

*note importlib.util: 9f. has a new function *note decode_source(): 94f.
that decodes source from bytes using universal newline processing.  This
is useful for implementing *note InspectLoader.get_source(): 950.
methods.

*note importlib.machinery.ExtensionFileLoader: 650. now has a *note
get_filename(): 951. method.  This was inadvertently omitted in the
original implementation.  (Contributed by Eric Snow in bpo-19152(7).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15627

   (2) https://bugs.python.org/issue18072

   (3) https://bugs.python.org/issue18193

   (4) https://bugs.python.org/issue18192

   (5) https://bugs.python.org/issue18194

   (6) https://bugs.python.org/issue18058

   (7) https://bugs.python.org/issue19152


File: python.info,  Node: inspect<5>,  Next: ipaddress<4>,  Prev: importlib<7>,  Up: Improved Modules<6>

1.6.4.23 inspect
................

The *note inspect: a0. module now offers a basic *note command line
interface: 953. to quickly display source code and other information for
modules, classes and functions.  (Contributed by Claudiu Popa and Nick
Coghlan in bpo-18626(1).)

*note unwrap(): 954. makes it easy to unravel wrapper function chains
created by *note functools.wraps(): 955. (and any other API that sets
the ‘__wrapped__’ attribute on a wrapper function).  (Contributed by
Daniel Urban, Aaron Iles and Nick Coghlan in bpo-13266(2).)

As part of the implementation of the new *note enum: 79. module, the
*note inspect: a0. module now has substantially better support for
custom ‘__dir__’ methods and dynamic class attributes provided through
metaclasses.  (Contributed by Ethan Furman in bpo-18929(3) and
bpo-19030(4).)

*note getfullargspec(): 657. and *note getargspec(): 656. now use the
*note signature(): 655. API. This allows them to support a much broader
range of callables, including those with ‘__signature__’ attributes,
those with metadata provided by argument clinic, *note
functools.partial(): 8b5. objects and more.  Note that, unlike *note
signature(): 655, these functions still ignore ‘__wrapped__’ attributes,
and report the already bound first argument for bound methods, so it is
still necessary to update your code to use *note signature(): 655.
directly if those features are desired.  (Contributed by Yury Selivanov
in bpo-17481(5).)

*note signature(): 655. now supports duck types of CPython functions,
which adds support for functions compiled with Cython.  (Contributed by
Stefan Behnel and Yury Selivanov in bpo-17159(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18626

   (2) https://bugs.python.org/issue13266

   (3) https://bugs.python.org/issue18929

   (4) https://bugs.python.org/issue19030

   (5) https://bugs.python.org/issue17481

   (6) https://bugs.python.org/issue17159


File: python.info,  Node: ipaddress<4>,  Next: logging<5>,  Prev: inspect<5>,  Up: Improved Modules<6>

1.6.4.24 ipaddress
..................

*note ipaddress: a2. was added to the standard library in Python 3.3 as
a *note provisional API: 454.  With the release of Python 3.4, this
qualification has been removed: *note ipaddress: a2. is now considered a
stable API, covered by the normal standard library requirements to
maintain backwards compatibility.

A new *note is_global: 957. property is ‘True’ if an address is globally
routeable.  (Contributed by Peter Moody in bpo-17400(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17400


File: python.info,  Node: logging<5>,  Next: marshal,  Prev: ipaddress<4>,  Up: Improved Modules<6>

1.6.4.25 logging
................

The *note TimedRotatingFileHandler: 959. has a new `atTime' parameter
that can be used to specify the time of day when rollover should happen.
(Contributed by Ronald Oussoren in bpo-9556(1).)

*note SocketHandler: 95a. and *note DatagramHandler: 95b. now support
Unix domain sockets (by setting `port' to ‘None’).  (Contributed by
Vinay Sajip in commit ce46195b56a9.)

*note fileConfig(): 4b0. now accepts a *note
configparser.RawConfigParser: 95c. subclass instance for the `fname'
parameter.  This facilitates using a configuration file when logging
configuration is just a part of the overall application configuration,
or where the application modifies the configuration before passing it to
*note fileConfig(): 4b0.  (Contributed by Vinay Sajip in bpo-16110(2).)

Logging configuration data received from a socket via the *note
logging.config.listen(): 95d. function can now be validated before being
processed by supplying a verification function as the argument to the
new `verify' keyword argument.  (Contributed by Vinay Sajip in
bpo-15452(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9556

   (2) https://bugs.python.org/issue16110

   (3) https://bugs.python.org/issue15452


File: python.info,  Node: marshal,  Next: mmap<2>,  Prev: logging<5>,  Up: Improved Modules<6>

1.6.4.26 marshal
................

The default *note marshal: b0. version has been bumped to 3.  The code
implementing the new version restores the Python2 behavior of recording
only one copy of interned strings and preserving the interning on
deserialization, and extends this “one copy” ability to any object type
(including handling recursive references).  This reduces both the size
of ‘.pyc’ files and the amount of memory a module occupies in memory
when it is loaded from a ‘.pyc’ (or ‘.pyo’) file.  (Contributed by
Kristján Valur Jónsson in bpo-16475(1), with additional speedups by
Antoine Pitrou in bpo-19219(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16475

   (2) https://bugs.python.org/issue19219


File: python.info,  Node: mmap<2>,  Next: multiprocessing<6>,  Prev: marshal,  Up: Improved Modules<6>

1.6.4.27 mmap
.............

mmap objects can now be *note weakref: 131.ed.  (Contributed by Valerie
Lambert in bpo-4885(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4885


File: python.info,  Node: multiprocessing<6>,  Next: operator<2>,  Prev: mmap<2>,  Up: Improved Modules<6>

1.6.4.28 multiprocessing
........................

On Unix two new *note start methods: 961, ‘spawn’ and ‘forkserver’, have
been added for starting processes using *note multiprocessing: b7.
These make the mixing of processes with threads more robust, and the
‘spawn’ method matches the semantics that multiprocessing has always
used on Windows.  New function *note get_all_start_methods(): 962.
reports all start methods available on the platform, *note
get_start_method(): 963. reports the current start method, and *note
set_start_method(): 964. sets the start method.  (Contributed by Richard
Oudkerk in bpo-8713(1).)

*note multiprocessing: b7. also now has the concept of a ‘context’,
which determines how child processes are created.  New function *note
get_context(): 965. returns a context that uses a specified start
method.  It has the same API as the *note multiprocessing: b7. module
itself, so you can use it to create *note Pool: 966.s and other objects
that will operate within that context.  This allows a framework and an
application or different parts of the same application to use
multiprocessing without interfering with each other.  (Contributed by
Richard Oudkerk in bpo-18999(2).)

Except when using the old `fork' start method, child processes no longer
inherit unneeded handles/file descriptors from their parents (part of
bpo-8713(3)).

*note multiprocessing: b7. now relies on *note runpy: e2. (which
implements the ‘-m’ switch) to initialise ‘__main__’ appropriately in
child processes when using the ‘spawn’ or ‘forkserver’ start methods.
This resolves some edge cases where combining multiprocessing, the ‘-m’
command line switch, and explicit relative imports could cause obscure
failures in child processes.  (Contributed by Nick Coghlan in
bpo-19946(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8713

   (2) https://bugs.python.org/issue18999

   (3) https://bugs.python.org/issue8713

   (4) https://bugs.python.org/issue19946


File: python.info,  Node: operator<2>,  Next: os<7>,  Prev: multiprocessing<6>,  Up: Improved Modules<6>

1.6.4.29 operator
.................

New function *note length_hint(): 968. provides an implementation of the
specification for how the *note __length_hint__(): 8f9. special method
should be used, as part of the PEP 424(1) formal specification of this
language feature.  (Contributed by Armin Ronacher in bpo-16148(2).)

There is now a pure-python version of the *note operator: c2. module
available for reference and for use by alternate implementations of
Python.  (Contributed by Zachary Ware in bpo-16694(3).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0424

   (2) https://bugs.python.org/issue16148

   (3) https://bugs.python.org/issue16694


File: python.info,  Node: os<7>,  Next: pdb<4>,  Prev: operator<2>,  Up: Improved Modules<6>

1.6.4.30 os
...........

There are new functions to get and set the *note inheritable flag: 8e7.
of a file descriptor (*note os.get_inheritable(): 8e8, *note
os.set_inheritable(): 8e9.) or a Windows handle (*note
os.get_handle_inheritable(): 8ea, *note os.set_handle_inheritable():
8eb.).

New function *note cpu_count(): 96a. reports the number of CPUs
available on the platform on which Python is running (or ‘None’ if the
count can’t be determined).  The *note multiprocessing.cpu_count(): 96b.
function is now implemented in terms of this function).  (Contributed by
Trent Nelson, Yogesh Chaudhari, Victor Stinner, and Charles-François
Natali in bpo-17914(1).)

*note os.path.samestat(): 96c. is now available on the Windows platform
(and the *note os.path.samefile(): 96d. implementation is now shared
between Unix and Windows).  (Contributed by Brian Curtin in
bpo-11939(2).)

*note os.path.ismount(): 329. now recognizes volumes mounted below a
drive root on Windows.  (Contributed by Tim Golden in bpo-9035(3).)

*note os.open(): 758. supports two new flags on platforms that provide
them, *note O_PATH: 96e. (un-opened file descriptor), and *note
O_TMPFILE: 96f. (unnamed temporary file; as of 3.4.0 release available
only on Linux systems with a kernel version of 3.11 or newer that have
uapi headers).  (Contributed by Christian Heimes in bpo-18673(4) and
Benjamin Peterson, respectively.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17914

   (2) https://bugs.python.org/issue11939

   (3) https://bugs.python.org/issue9035

   (4) https://bugs.python.org/issue18673


File: python.info,  Node: pdb<4>,  Next: pickle<4>,  Prev: os<7>,  Up: Improved Modules<6>

1.6.4.31 pdb
............

*note pdb: c9. has been enhanced to handle generators, *note yield: 2c7,
and ‘yield from’ in a more useful fashion.  This is especially helpful
when debugging *note asyncio: 9. based programs.  (Contributed by Andrew
Svetlov and Xavier de Gaye in bpo-16596(1).)

The ‘print’ command has been removed from *note pdb: c9, restoring
access to the Python *note print(): 971. function from the pdb command
line.  Python2’s ‘pdb’ did not have a ‘print’ command; instead, entering
‘print’ executed the ‘print’ statement.  In Python3 ‘print’ was
mistakenly made an alias for the pdb *note p: 972. command.  ‘p’,
however, prints the ‘repr’ of its argument, not the ‘str’ like the
Python2 ‘print’ command did.  Worse, the Python3 ‘pdb print’ command
shadowed the Python3 ‘print’ function, making it inaccessible at the
‘pdb’ prompt.  (Contributed by Connor Osborn in bpo-18764(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16596

   (2) https://bugs.python.org/issue18764


File: python.info,  Node: pickle<4>,  Next: plistlib<2>,  Prev: pdb<4>,  Up: Improved Modules<6>

1.6.4.32 pickle
...............

*note pickle: ca. now supports (but does not use by default) a new
pickle protocol, protocol 4.  This new protocol addresses a number of
issues that were present in previous protocols, such as the
serialization of nested classes, very large strings and containers, and
classes whose *note __new__(): 974. method takes keyword-only arguments.
It also provides some efficiency improvements.

See also
........

PEP 3154(1) – Pickle protocol 4

     PEP written by Antoine Pitrou and implemented by Alexandre
     Vassalotti.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3154


File: python.info,  Node: plistlib<2>,  Next: poplib<3>,  Prev: pickle<4>,  Up: Improved Modules<6>

1.6.4.33 plistlib
.................

*note plistlib: cf. now has an API that is similar to the standard
pattern for stdlib serialization protocols, with new *note load(): 21e,
*note dump(): 220, *note loads(): 21f, and *note dumps(): 221.
functions.  (The older API is now deprecated.)  In addition to the
already supported XML plist format (*note FMT_XML: 976.), it also now
supports the binary plist format (*note FMT_BINARY: 977.).  (Contributed
by Ronald Oussoren and others in bpo-14455(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14455


File: python.info,  Node: poplib<3>,  Next: pprint<3>,  Prev: plistlib<2>,  Up: Improved Modules<6>

1.6.4.34 poplib
...............

Two new methods have been added to *note poplib: d0.: *note capa(): 979,
which returns the list of capabilities advertised by the POP server, and
*note stls(): 97a, which switches a clear-text POP3 session into an
encrypted POP3 session if the POP server supports it.  (Contributed by
Lorenzo Catucci in bpo-4473(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4473


File: python.info,  Node: pprint<3>,  Next: pty,  Prev: poplib<3>,  Up: Improved Modules<6>

1.6.4.35 pprint
...............

The *note pprint: d2. module’s *note PrettyPrinter: 97c. class and its
*note pformat(): 97d, and *note pprint(): 341. functions have a new
option, `compact', that controls how the output is formatted.  Currently
setting `compact' to ‘True’ means that sequences will be printed with as
many sequence elements as will fit within `width' on each (indented)
line.  (Contributed by Serhiy Storchaka in bpo-19132(1).)

Long strings are now wrapped using Python’s normal line continuation
syntax.  (Contributed by Antoine Pitrou in bpo-17150(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19132

   (2) https://bugs.python.org/issue17150


File: python.info,  Node: pty,  Next: pydoc<4>,  Prev: pprint<3>,  Up: Improved Modules<6>

1.6.4.36 pty
............

*note pty.spawn(): 97f. now returns the status value from *note
os.waitpid(): 760. on the child process, instead of ‘None’.
(Contributed by Gregory P. Smith.)


File: python.info,  Node: pydoc<4>,  Next: re<5>,  Prev: pty,  Up: Improved Modules<6>

1.6.4.37 pydoc
..............

The *note pydoc: d9. module is now based directly on the *note
inspect.signature(): 655. introspection API, allowing it to provide
signature information for a wider variety of callable objects.  This
change also means that ‘__wrapped__’ attributes are now taken into
account when displaying help information.  (Contributed by Larry
Hastings in bpo-19674(1).)

The *note pydoc: d9. module no longer displays the ‘self’ parameter for
already bound methods.  Instead, it aims to always display the exact
current signature of the supplied callable.  (Contributed by Larry
Hastings in bpo-20710(2).)

In addition to the changes that have been made to *note pydoc: d9.
directly, its handling of custom ‘__dir__’ methods and various
descriptor behaviours has also been improved substantially by the
underlying changes in the *note inspect: a0. module.

As the *note help(): 175. builtin is based on *note pydoc: d9, the above
changes also affect the behaviour of *note help(): 175.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19674

   (2) https://bugs.python.org/issue20710


File: python.info,  Node: re<5>,  Next: resource,  Prev: pydoc<4>,  Up: Improved Modules<6>

1.6.4.38 re
...........

New *note fullmatch(): 982. function and ‘regex.fullmatch()’ method
anchor the pattern at both ends of the string to match.  This provides a
way to be explicit about the goal of the match, which avoids a class of
subtle bugs where ‘$’ characters get lost during code changes or the
addition of alternatives to an existing regular expression.
(Contributed by Matthew Barnett in bpo-16203(1).)

The repr of *note regex objects: 983. now includes the pattern and the
flags; the repr of *note match objects: 984. now includes the start,
end, and the part of the string that matched.  (Contributed by Hugo
Lopes Tavares and Serhiy Storchaka in bpo-13592(2) and bpo-17087(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16203

   (2) https://bugs.python.org/issue13592

   (3) https://bugs.python.org/issue17087


File: python.info,  Node: resource,  Next: select,  Prev: re<5>,  Up: Improved Modules<6>

1.6.4.39 resource
.................

New *note prlimit(): 986. function, available on Linux platforms with a
kernel version of 2.6.36 or later and glibc of 2.13 or later, provides
the ability to query or set the resource limits for processes other than
the one making the call.  (Contributed by Christian Heimes in
bpo-16595(1).)

On Linux kernel version 2.6.36 or later, there are also some new Linux
specific constants: *note RLIMIT_MSGQUEUE: 987, *note RLIMIT_NICE: 988,
*note RLIMIT_RTPRIO: 989, *note RLIMIT_RTTIME: 98a, and *note
RLIMIT_SIGPENDING: 98b.  (Contributed by Christian Heimes in
bpo-19324(2).)

On FreeBSD version 9 and later, there some new FreeBSD specific
constants: *note RLIMIT_SBSIZE: 98c, *note RLIMIT_SWAP: 98d, and *note
RLIMIT_NPTS: 98e.  (Contributed by Claudiu Popa in bpo-19343(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16595

   (2) https://bugs.python.org/issue19324

   (3) https://bugs.python.org/issue19343


File: python.info,  Node: select,  Next: shelve,  Prev: resource,  Up: Improved Modules<6>

1.6.4.40 select
...............

*note epoll: 990. objects now support the context management protocol.
When used in a *note with: 7da. statement, the *note close(): 991.
method will be called automatically at the end of the block.
(Contributed by Serhiy Storchaka in bpo-16488(1).)

*note devpoll: 992. objects now have *note fileno(): 993. and *note
close(): 994. methods, as well as a new attribute *note closed: 995.
(Contributed by Victor Stinner in bpo-18794(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16488

   (2) https://bugs.python.org/issue18794


File: python.info,  Node: shelve,  Next: shutil<3>,  Prev: select,  Up: Improved Modules<6>

1.6.4.41 shelve
...............

*note Shelf: 997. instances may now be used in *note with: 7da.
statements, and will be automatically closed at the end of the ‘with’
block.  (Contributed by Filip Gruszczyński in bpo-13896(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13896


File: python.info,  Node: shutil<3>,  Next: smtpd<2>,  Prev: shelve,  Up: Improved Modules<6>

1.6.4.42 shutil
...............

*note copyfile(): 382. now raises a specific *note Error: 999. subclass,
*note SameFileError: 99a, when the source and destination are the same
file, which allows an application to take appropriate action on this
specific error.  (Contributed by Atsuo Ishimoto and Hynek Schlawack in
bpo-1492704(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1492704


File: python.info,  Node: smtpd<2>,  Next: smtplib<3>,  Prev: shutil<3>,  Up: Improved Modules<6>

1.6.4.43 smtpd
..............

The *note SMTPServer: 6f9. and *note SMTPChannel: 6f8. classes now
accept a `map' keyword argument which, if specified, is passed in to
*note asynchat.async_chat: 99c. as its `map' argument.  This allows an
application to avoid affecting the global socket map.  (Contributed by
Vinay Sajip in bpo-11959(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11959


File: python.info,  Node: smtplib<3>,  Next: socket<7>,  Prev: smtpd<2>,  Up: Improved Modules<6>

1.6.4.44 smtplib
................

*note SMTPException: 99e. is now a subclass of *note OSError: 304, which
allows both socket level errors and SMTP protocol level errors to be
caught in one try/except statement by code that only cares whether or
not an error occurred.  (Contributed by Ned Jackson Lovely in
bpo-2118(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue2118


File: python.info,  Node: socket<7>,  Next: sqlite3<4>,  Prev: smtplib<3>,  Up: Improved Modules<6>

1.6.4.45 socket
...............

The socket module now supports the *note CAN_BCM: 9a0. protocol on
platforms that support it.  (Contributed by Brian Thorne in
bpo-15359(1).)

Socket objects have new methods to get or set their *note inheritable
flag: 8e7, *note get_inheritable(): 8ec. and *note set_inheritable():
8ed.

The ‘socket.AF_*’ and ‘socket.SOCK_*’ constants are now enumeration
values using the new *note enum: 79. module.  This allows meaningful
names to be printed during debugging, instead of integer “magic
numbers”.

The *note AF_LINK: 9a1. constant is now available on BSD and OSX.

*note inet_pton(): 237. and *note inet_ntop(): 9a2. are now supported on
Windows.  (Contributed by Atsuo Ishimoto in bpo-7171(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15359

   (2) https://bugs.python.org/issue7171


File: python.info,  Node: sqlite3<4>,  Next: ssl<7>,  Prev: socket<7>,  Up: Improved Modules<6>

1.6.4.46 sqlite3
................

A new boolean parameter to the *note connect(): 4e1. function, `uri',
can be used to indicate that the `database' parameter is a ‘uri’ (see
the SQLite URI documentation(1)).  (Contributed by poq in bpo-13773(2).)

   ---------- Footnotes ----------

   (1) https://www.sqlite.org/uri.html

   (2) https://bugs.python.org/issue13773


File: python.info,  Node: ssl<7>,  Next: stat,  Prev: sqlite3<4>,  Up: Improved Modules<6>

1.6.4.47 ssl
............

*note PROTOCOL_TLSv1_1: 9a5. and *note PROTOCOL_TLSv1_2: 9a6. (TLSv1.1
and TLSv1.2 support) have been added; support for these protocols is
only available if Python is linked with OpenSSL 1.0.1 or later.
(Contributed by Michele Orrù and Antoine Pitrou in bpo-16692(1).)  New
function *note create_default_context(): 9a7. provides a standard way to
obtain an *note SSLContext: 4ea. whose settings are intended to be a
reasonable balance between compatibility and security.  These settings
are more stringent than the defaults provided by the *note SSLContext:
4ea. constructor, and may be adjusted in the future, without prior
deprecation, if best-practice security requirements change.  The new
recommended best practice for using stdlib libraries that support SSL is
to use *note create_default_context(): 9a7. to obtain an *note
SSLContext: 4ea. object, modify it if needed, and then pass it as the
`context' argument of the appropriate stdlib API. (Contributed by
Christian Heimes in bpo-19689(2).)

*note SSLContext: 4ea. method *note load_verify_locations(): 8d8.
accepts a new optional argument `cadata', which can be used to provide
PEM or DER encoded certificates directly via strings or bytes,
respectively.  (Contributed by Christian Heimes in bpo-18138(3).)

New function *note get_default_verify_paths(): 9a8. returns a named
tuple of the paths and environment variables that the *note
set_default_verify_paths(): 9a9. method uses to set OpenSSL’s default
‘cafile’ and ‘capath’.  This can be an aid in debugging default
verification issues.  (Contributed by Christian Heimes in bpo-18143(4).)

*note SSLContext: 4ea. has a new method, *note cert_store_stats(): 9aa,
that reports the number of loaded ‘X.509’ certs, ‘X.509 CA’ certs, and
certificate revocation lists (‘crl’s), as well as a *note
get_ca_certs(): 9ab. method that returns a list of the loaded ‘CA’
certificates.  (Contributed by Christian Heimes in bpo-18147(5).)

If OpenSSL 0.9.8 or later is available, *note SSLContext: 4ea. has a new
attribute *note verify_flags: 9ac. that can be used to control the
certificate verification process by setting it to some combination of
the new constants *note VERIFY_DEFAULT: 9ad, *note
VERIFY_CRL_CHECK_LEAF: 9ae, *note VERIFY_CRL_CHECK_CHAIN: 9af, or *note
VERIFY_X509_STRICT: 9b0.  OpenSSL does not do any CRL verification by
default.  (Contributed by Christien Heimes in bpo-8813(6).)

New *note SSLContext: 4ea. method *note load_default_certs(): 9b1. loads
a set of default “certificate authority” (CA) certificates from default
locations, which vary according to the platform.  It can be used to load
both TLS web server authentication certificates (‘purpose=’*note
SERVER_AUTH: 9b2.) for a client to use to verify a server, and
certificates for a server to use in verifying client certificates
(‘purpose=’*note CLIENT_AUTH: 9b3.).  (Contributed by Christian Heimes
in bpo-19292(7).)  Two new windows-only functions, *note
enum_certificates(): 9b4. and *note enum_crls(): 9b5. provide the
ability to retrieve certificates, certificate information, and CRLs from
the Windows cert store.  (Contributed by Christian Heimes in
bpo-17134(8).)  Support for server-side SNI (Server Name Indication)
using the new *note ssl.SSLContext.set_servername_callback(): 9b6.
method.  (Contributed by Daniel Black in bpo-8109(9).)

The dictionary returned by *note SSLSocket.getpeercert(): 9b7. contains
additional ‘X509v3’ extension items: ‘crlDistributionPoints’,
‘calIssuers’, and ‘OCSP’ URIs.  (Contributed by Christian Heimes in
bpo-18379(10).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16692

   (2) https://bugs.python.org/issue19689

   (3) https://bugs.python.org/issue18138

   (4) https://bugs.python.org/issue18143

   (5) https://bugs.python.org/issue18147

   (6) https://bugs.python.org/issue8813

   (7) https://bugs.python.org/issue19292

   (8) https://bugs.python.org/issue17134

   (9) https://bugs.python.org/issue8109

   (10) https://bugs.python.org/issue18379


File: python.info,  Node: stat,  Next: struct<2>,  Prev: ssl<7>,  Up: Improved Modules<6>

1.6.4.48 stat
.............

The *note stat: f4. module is now backed by a C implementation in
‘_stat’.  A C implementation is required as most of the values aren’t
standardized and are platform-dependent.  (Contributed by Christian
Heimes in bpo-11016(1).)

The module supports new *note ST_MODE: 9b9. flags, *note S_IFDOOR: 9ba,
*note S_IFPORT: 9bb, and *note S_IFWHT: 9bc.  (Contributed by Christian
Hiemes in bpo-11016(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11016

   (2) https://bugs.python.org/issue11016


File: python.info,  Node: struct<2>,  Next: subprocess<4>,  Prev: stat,  Up: Improved Modules<6>

1.6.4.49 struct
...............

New function *note iter_unpack: 9be. and a new *note
struct.Struct.iter_unpack(): 9bf. method on compiled formats provide
streamed unpacking of a buffer containing repeated instances of a given
format of data.  (Contributed by Antoine Pitrou in bpo-17804(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17804


File: python.info,  Node: subprocess<4>,  Next: sunau<2>,  Prev: struct<2>,  Up: Improved Modules<6>

1.6.4.50 subprocess
...................

*note check_output(): 9c1. now accepts an `input' argument that can be
used to provide the contents of ‘stdin’ for the command that is run.
(Contributed by Zack Weinberg in bpo-16624(1).)

‘getstatus()’ and *note getstatusoutput(): 9c2. now work on Windows.
This change was actually inadvertently made in 3.3.4.  (Contributed by
Tim Golden in bpo-10197(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16624

   (2) https://bugs.python.org/issue10197


File: python.info,  Node: sunau<2>,  Next: sys<7>,  Prev: subprocess<4>,  Up: Improved Modules<6>

1.6.4.51 sunau
..............

The ‘getparams()’ method now returns a namedtuple rather than a plain
tuple.  (Contributed by Claudiu Popa in bpo-18901(1).)

*note sunau.open(): 573. now supports the context management protocol:
when used in a *note with: 7da. block, the ‘close’ method of the
returned object will be called automatically at the end of the block.
(Contributed by Serhiy Storchaka in bpo-18878(2).)

*note AU_write.setsampwidth(): 9c4. now supports 24 bit samples, thus
adding support for writing 24 sample using the module.  (Contributed by
Serhiy Storchaka in bpo-19261(3).)

The *note writeframesraw(): 9c5. and *note writeframes(): 9c6. methods
now accept any *note bytes-like object: 6df.  (Contributed by Serhiy
Storchaka in bpo-8311(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18901

   (2) https://bugs.python.org/issue18878

   (3) https://bugs.python.org/issue19261

   (4) https://bugs.python.org/issue8311


File: python.info,  Node: sys<7>,  Next: tarfile<3>,  Prev: sunau<2>,  Up: Improved Modules<6>

1.6.4.52 sys
............

New function *note sys.getallocatedblocks(): 9c8. returns the current
number of blocks allocated by the interpreter.  (In CPython with the
default ‘--with-pymalloc’ setting, this is allocations made through the
*note PyObject_Malloc(): 602. API.) This can be useful for tracking
memory leaks, especially if automated via a test suite.  (Contributed by
Antoine Pitrou in bpo-13390(1).)

When the Python interpreter starts in *note interactive mode: 9c9, it
checks for an *note __interactivehook__: 9ca. attribute on the *note
sys: fd. module.  If the attribute exists, its value is called with no
arguments just before interactive mode is started.  The check is made
after the *note PYTHONSTARTUP: 9cb. file is read, so it can be set
there.  The *note site: eb. module *note sets it: 9cc. to a function
that enables tab completion and history saving (in ‘~/.python-history’)
if the platform supports *note readline: de.  If you do not want this
(new) behavior, you can override it in *note PYTHONSTARTUP: 9cb,
‘sitecustomize’, or ‘usercustomize’ by deleting this attribute from
*note sys: fd. (or setting it to some other callable).  (Contributed by
Éric Araujo and Antoine Pitrou in bpo-5845(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13390

   (2) https://bugs.python.org/issue5845


File: python.info,  Node: tarfile<3>,  Next: textwrap,  Prev: sys<7>,  Up: Improved Modules<6>

1.6.4.53 tarfile
................

The *note tarfile: 101. module now supports a simple *note Command-Line
Interface: 9ce. when called as a script directly or via ‘-m’.  This can
be used to create and extract tarfile archives.  (Contributed by Berker
Peksag in bpo-13477(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13477


File: python.info,  Node: textwrap,  Next: threading<4>,  Prev: tarfile<3>,  Up: Improved Modules<6>

1.6.4.54 textwrap
.................

The *note TextWrapper: 9d0. class has two new attributes/constructor
arguments: *note max_lines: 9d1, which limits the number of lines in the
output, and *note placeholder: 9d2, which is a string that will appear
at the end of the output if it has been truncated because of
`max_lines'.  Building on these capabilities, a new convenience function
*note shorten(): 9d3. collapses all of the whitespace in the input to
single spaces and produces a single line of a given `width' that ends
with the `placeholder' (by default, ‘[...]’).  (Contributed by Antoine
Pitrou and Serhiy Storchaka in bpo-18585(1) and bpo-18725(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18585

   (2) https://bugs.python.org/issue18725


File: python.info,  Node: threading<4>,  Next: traceback<3>,  Prev: textwrap,  Up: Improved Modules<6>

1.6.4.55 threading
..................

The *note Thread: 21a. object representing the main thread can be
obtained from the new *note main_thread(): 9d5. function.  In normal
conditions this will be the thread from which the Python interpreter was
started.  (Contributed by Andrew Svetlov in bpo-18882(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18882


File: python.info,  Node: traceback<3>,  Next: types<3>,  Prev: threading<4>,  Up: Improved Modules<6>

1.6.4.56 traceback
..................

A new *note traceback.clear_frames(): 9d7. function takes a traceback
object and clears the local variables in all of the frames it
references, reducing the amount of memory consumed.  (Contributed by
Andrew Kuchling in bpo-1565525(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1565525


File: python.info,  Node: types<3>,  Next: urllib<2>,  Prev: traceback<3>,  Up: Improved Modules<6>

1.6.4.57 types
..............

A new *note DynamicClassAttribute(): 9d9. descriptor provides a way to
define an attribute that acts normally when looked up through an
instance object, but which is routed to the `class' ‘__getattr__’ when
looked up through the class.  This allows one to have properties active
on a class, and have virtual attributes on the class with the same name
(see ‘Enum’ for an example).  (Contributed by Ethan Furman in
bpo-19030(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19030


File: python.info,  Node: urllib<2>,  Next: unittest<4>,  Prev: types<3>,  Up: Improved Modules<6>

1.6.4.58 urllib
...............

*note urllib.request: 129. now supports ‘data:’ URLs via the *note
DataHandler: 9db. class.  (Contributed by Mathias Panzenböck in
bpo-16423(1).)

The http method that will be used by a *note Request: 9dc. class can now
be specified by setting a *note method: 9dd. class attribute on the
subclass.  (Contributed by Jason R Coombs in bpo-18978(2).)

*note Request: 9dc. objects are now reusable: if the *note full_url:
9de. or *note data: 9df. attributes are modified, all relevant internal
properties are updated.  This means, for example, that it is now
possible to use the same *note Request: 9dc. object in more than one
*note OpenerDirector.open(): 9e0. call with different `data' arguments,
or to modify a *note Request: 9dc.’s ‘url’ rather than recomputing it
from scratch.  There is also a new *note remove_header(): 9e1. method
that can be used to remove headers from a *note Request: 9dc.
(Contributed by Alexey Kachayev in bpo-16464(3), Daniel Wozniak in
bpo-17485(4), and Damien Brecht and Senthil Kumaran in bpo-17272(5).)

*note HTTPError: 9e2. objects now have a *note headers: 9e3. attribute
that provides access to the HTTP response headers associated with the
error.  (Contributed by Berker Peksag in bpo-15701(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16423

   (2) https://bugs.python.org/issue18978

   (3) https://bugs.python.org/issue16464

   (4) https://bugs.python.org/issue17485

   (5) https://bugs.python.org/issue17272

   (6) https://bugs.python.org/issue15701


File: python.info,  Node: unittest<4>,  Next: venv<5>,  Prev: urllib<2>,  Up: Improved Modules<6>

1.6.4.59 unittest
.................

The *note TestCase: 9e5. class has a new method, *note subTest(): 9e6,
that produces a context manager whose *note with: 7da. block becomes a
“sub-test”.  This context manager allows a test method to dynamically
generate subtests by, say, calling the ‘subTest’ context manager inside
a loop.  A single test method can thereby produce an indefinite number
of separately-identified and separately-counted tests, all of which will
run even if one or more of them fail.  For example:

     class NumbersTest(unittest.TestCase):
         def test_even(self):
             for i in range(6):
                 with self.subTest(i=i):
                     self.assertEqual(i % 2, 0)

will result in six subtests, each identified in the unittest verbose
output with a label consisting of the variable name ‘i’ and a particular
value for that variable (‘i=0’, ‘i=1’, etc).  See *note Distinguishing
test iterations using subtests: 9e7. for the full version of this
example.  (Contributed by Antoine Pitrou in bpo-16997(1).)

*note unittest.main(): 9e8. now accepts an iterable of test names for
`defaultTest', where previously it only accepted a single test name as a
string.  (Contributed by Jyrki Pulliainen in bpo-15132(2).)

If *note SkipTest: 9e9. is raised during test discovery (that is, at the
module level in the test file), it is now reported as a skip instead of
an error.  (Contributed by Zach Ware in bpo-16935(3).)

*note discover(): 9ea. now sorts the discovered files to provide
consistent test ordering.  (Contributed by Martin Melin and Jeff Ramnani
in bpo-16709(4).)

*note TestSuite: 7c1. now drops references to tests as soon as the test
has been run, if the test is successful.  On Python interpreters that do
garbage collection, this allows the tests to be garbage collected if
nothing else is holding a reference to the test.  It is possible to
override this behavior by creating a *note TestSuite: 7c1. subclass that
defines a custom ‘_removeTestAtIndex’ method.  (Contributed by Tom
Wardill, Matt McClure, and Andrew Svetlov in bpo-11798(5).)

A new test assertion context-manager, *note assertLogs(): 9eb, will
ensure that a given block of code emits a log message using the *note
logging: aa. module.  By default the message can come from any logger
and have a priority of ‘INFO’ or higher, but both the logger name and an
alternative minimum logging level may be specified.  The object returned
by the context manager can be queried for the *note LogRecord: 9ec.s
and/or formatted messages that were logged.  (Contributed by Antoine
Pitrou in bpo-18937(6).)

Test discovery now works with namespace packages (Contributed by Claudiu
Popa in bpo-17457(7).)

*note unittest.mock: 125. objects now inspect their specification
signatures when matching calls, which means an argument can now be
matched by either position or name, instead of only by position.
(Contributed by Antoine Pitrou in bpo-17015(8).)

‘mock_open()’ objects now have ‘readline’ and ‘readlines’ methods.
(Contributed by Toshio Kuratomi in bpo-17467(9).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16997

   (2) https://bugs.python.org/issue15132

   (3) https://bugs.python.org/issue16935

   (4) https://bugs.python.org/issue16709

   (5) https://bugs.python.org/issue11798

   (6) https://bugs.python.org/issue18937

   (7) https://bugs.python.org/issue17457

   (8) https://bugs.python.org/issue17015

   (9) https://bugs.python.org/issue17467


File: python.info,  Node: venv<5>,  Next: wave<2>,  Prev: unittest<4>,  Up: Improved Modules<6>

1.6.4.60 venv
.............

*note venv: 12e. now includes activation scripts for the ‘csh’ and
‘fish’ shells.  (Contributed by Andrew Svetlov in bpo-15417(1).)

*note EnvBuilder: 9ee. and the *note create(): 9ef. convenience function
take a new keyword argument `with_pip', which defaults to ‘False’, that
controls whether or not *note EnvBuilder: 9ee. ensures that ‘pip’ is
installed in the virtual environment.  (Contributed by Nick Coghlan in
bpo-19552(2) as part of the PEP 453(3) implementation.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15417

   (2) https://bugs.python.org/issue19552

   (3) https://www.python.org/dev/peps/pep-0453


File: python.info,  Node: wave<2>,  Next: weakref<2>,  Prev: venv<5>,  Up: Improved Modules<6>

1.6.4.61 wave
.............

The ‘getparams()’ method now returns a namedtuple rather than a plain
tuple.  (Contributed by Claudiu Popa in bpo-17487(1).)

*note wave.open(): 219. now supports the context management protocol.
(Contributed by Claudiu Popa in bpo-17616(2).)

*note wave: 130. can now *note write output to unseekable files: 9f1.
(Contributed by David Jones, Guilherme Polo, and Serhiy Storchaka in
bpo-5202(3).)

The *note writeframesraw(): 9f2. and *note writeframes(): 9f3. methods
now accept any *note bytes-like object: 6df.  (Contributed by Serhiy
Storchaka in bpo-8311(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17487

   (2) https://bugs.python.org/issue17616

   (3) https://bugs.python.org/issue5202

   (4) https://bugs.python.org/issue8311


File: python.info,  Node: weakref<2>,  Next: xml etree<2>,  Prev: wave<2>,  Up: Improved Modules<6>

1.6.4.62 weakref
................

New *note WeakMethod: 9f5. class simulates weak references to bound
methods.  (Contributed by Antoine Pitrou in bpo-14631(1).)

New *note finalize: 3c0. class makes it possible to register a callback
to be invoked when an object is garbage collected, without needing to
carefully manage the lifecycle of the weak reference itself.
(Contributed by Richard Oudkerk in bpo-15528(2).)

The callback, if any, associated with a *note ref: 9f6. is now exposed
via the *note __callback__: 9f7. attribute.  (Contributed by Mark
Dickinson in bpo-17643(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14631

   (2) https://bugs.python.org/issue15528

   (3) https://bugs.python.org/issue17643


File: python.info,  Node: xml etree<2>,  Next: zipfile<4>,  Prev: weakref<2>,  Up: Improved Modules<6>

1.6.4.63 xml.etree
..................

A new parser, *note XMLPullParser: 9f9, allows a non-blocking
applications to parse XML documents.  An example can be seen at *note
Pull API for non-blocking parsing: 9fa.  (Contributed by Antoine Pitrou
in bpo-17741(1).)

The *note xml.etree.ElementTree: 140. *note tostring(): 9fb. and *note
tostringlist(): 9fc. functions, and the *note ElementTree: 21c. *note
write(): 9fd. method, now have a `short_empty_elements' *note
keyword-only parameter: 3ce. providing control over whether elements
with no content are written in abbreviated (‘<tag />’) or expanded
(‘<tag></tag>’) form.  (Contributed by Ariel Poliak and Serhiy Storchaka
in bpo-14377(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17741

   (2) https://bugs.python.org/issue14377


File: python.info,  Node: zipfile<4>,  Prev: xml etree<2>,  Up: Improved Modules<6>

1.6.4.64 zipfile
................

The *note writepy(): 9ff. method of the *note PyZipFile: a00. class has
a new `filterfunc' option that can be used to control which directories
and files are added to the archive.  For example, this could be used to
exclude test files from the archive.  (Contributed by Christian Tismer
in bpo-19274(1).)

The `allowZip64' parameter to *note ZipFile: 523. and ‘PyZipfile’ is now
‘True’ by default.  (Contributed by William Mallard in bpo-17201(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19274

   (2) https://bugs.python.org/issue17201


File: python.info,  Node: CPython Implementation Changes,  Next: Deprecated<5>,  Prev: Improved Modules<6>,  Up: What’s New In Python 3 4

1.6.5 CPython Implementation Changes
------------------------------------

* Menu:

* PEP 445; Customization of CPython Memory Allocators: PEP 445 Customization of CPython Memory Allocators.
* PEP 442; Safe Object Finalization: PEP 442 Safe Object Finalization.
* PEP 456; Secure and Interchangeable Hash Algorithm: PEP 456 Secure and Interchangeable Hash Algorithm.
* PEP 436; Argument Clinic: PEP 436 Argument Clinic.
* Other Build and C API Changes::
* Other Improvements: Other Improvements<2>.
* Significant Optimizations::


File: python.info,  Node: PEP 445 Customization of CPython Memory Allocators,  Next: PEP 442 Safe Object Finalization,  Up: CPython Implementation Changes

1.6.5.1 PEP 445: Customization of CPython Memory Allocators
...........................................................

PEP 445(1) adds new C level interfaces to customize memory allocation in
the CPython interpreter.

See also
........

PEP 445(2) – Add new APIs to customize Python memory allocators

     PEP written and implemented by Victor Stinner.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0445

   (2) https://www.python.org/dev/peps/pep-0445


File: python.info,  Node: PEP 442 Safe Object Finalization,  Next: PEP 456 Secure and Interchangeable Hash Algorithm,  Prev: PEP 445 Customization of CPython Memory Allocators,  Up: CPython Implementation Changes

1.6.5.2 PEP 442: Safe Object Finalization
.........................................

PEP 442(1) removes the current limitations and quirks of object
finalization in CPython.  With it, objects with *note __del__(): a04.
methods, as well as generators with *note finally: 2bc. clauses, can be
finalized when they are part of a reference cycle.

As part of this change, module globals are no longer forcibly set to
*note None: 203. during interpreter shutdown in most cases, instead
relying on the normal operation of the cyclic garbage collector.  This
avoids a whole class of interpreter-shutdown-time errors, usually
involving ‘__del__’ methods, that have plagued Python since the cyclic
GC was first introduced.

See also
........

PEP 442(2) – Safe object finalization

     PEP written and implemented by Antoine Pitrou.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0442

   (2) https://www.python.org/dev/peps/pep-0442


File: python.info,  Node: PEP 456 Secure and Interchangeable Hash Algorithm,  Next: PEP 436 Argument Clinic,  Prev: PEP 442 Safe Object Finalization,  Up: CPython Implementation Changes

1.6.5.3 PEP 456: Secure and Interchangeable Hash Algorithm
..........................................................

PEP 456(1) follows up on earlier security fix work done on Python’s hash
algorithm to address certain DOS attacks to which public facing APIs
backed by dictionary lookups may be subject.  (See bpo-14621(2) for the
start of the current round of improvements.)  The PEP unifies CPython’s
hash code to make it easier for a packager to substitute a different
hash algorithm, and switches Python’s default implementation to a
SipHash implementation on platforms that have a 64 bit data type.  Any
performance differences in comparison with the older FNV algorithm are
trivial.

The PEP adds additional fields to the *note sys.hash_info: a06. named
tuple to describe the hash algorithm in use by the currently executing
binary.  Otherwise, the PEP does not alter any existing CPython APIs.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0456

   (2) https://bugs.python.org/issue14621


File: python.info,  Node: PEP 436 Argument Clinic,  Next: Other Build and C API Changes,  Prev: PEP 456 Secure and Interchangeable Hash Algorithm,  Up: CPython Implementation Changes

1.6.5.4 PEP 436: Argument Clinic
................................

“Argument Clinic” ( PEP 436(1)) is now part of the CPython build process
and can be used to simplify the process of defining and maintaining
accurate signatures for builtins and standard library extension modules
implemented in C.

Some standard library extension modules have been converted to use
Argument Clinic in Python 3.4, and *note pydoc: d9. and *note inspect:
a0. have been updated accordingly.

It is expected that signature metadata for programmatic introspection
will be added to additional callables implemented in C as part of Python
3.4 maintenance releases.

     Note: The Argument Clinic PEP is not fully up to date with the
     state of the implementation.  This has been deemed acceptable by
     the release manager and core development team in this case, as
     Argument Clinic will not be made available as a public API for
     third party use in Python 3.4.

See also
........

PEP 436(2) – The Argument Clinic DSL

     PEP written and implemented by Larry Hastings.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0436

   (2) https://www.python.org/dev/peps/pep-0436


File: python.info,  Node: Other Build and C API Changes,  Next: Other Improvements<2>,  Prev: PEP 436 Argument Clinic,  Up: CPython Implementation Changes

1.6.5.5 Other Build and C API Changes
.....................................

   * The new *note PyType_GetSlot(): a09. function has been added to the
     stable ABI, allowing retrieval of function pointers from named type
     slots when using the limited API. (Contributed by Martin von Löwis
     in bpo-17162(1).)

   * The new *note Py_SetStandardStreamEncoding(): a0a.
     pre-initialization API allows applications embedding the CPython
     interpreter to reliably force a particular encoding and error
     handler for the standard streams.  (Contributed by Bastien Montagne
     and Nick Coghlan in bpo-16129(2).)

   * Most Python C APIs that don’t mutate string arguments are now
     correctly marked as accepting ‘const char *’ rather than ‘char *’.
     (Contributed by Serhiy Storchaka in bpo-1772673(3).)

   * A new shell version of ‘python-config’ can be used even when a
     python interpreter is not available (for example, in cross
     compilation scenarios).

   * *note PyUnicode_FromFormat(): 8b8. now supports width and precision
     specifications for ‘%s’, ‘%A’, ‘%U’, ‘%V’, ‘%S’, and ‘%R’.
     (Contributed by Ysj Ray and Victor Stinner in bpo-7330(4).)

   * New function *note PyStructSequence_InitType2(): a0b. supplements
     the existing *note PyStructSequence_InitType(): a0c. function.  The
     difference is that it returns ‘0’ on success and ‘-1’ on failure.

   * The CPython source can now be compiled using the address sanity
     checking features of recent versions of GCC and clang: the false
     alarms in the small object allocator have been silenced.
     (Contributed by Dhiru Kholia in bpo-18596(5).)

   * The Windows build now uses Address Space Layout Randomization(6)
     and Data Execution Prevention(7).  (Contributed by Christian Heimes
     in bpo-16632(8).)

   * New function *note PyObject_LengthHint(): a0d. is the C API
     equivalent of *note operator.length_hint(): 968.  (Contributed by
     Armin Ronacher in bpo-16148(9).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17162

   (2) https://bugs.python.org/issue16129

   (3) https://bugs.python.org/issue1772673

   (4) https://bugs.python.org/issue7330

   (5) https://bugs.python.org/issue18596

   (6) https://en.wikipedia.org/wiki/Address_space_layout_randomization

   (7) https://en.wikipedia.org/wiki/Data_Execution_Prevention

   (8) https://bugs.python.org/issue16632

   (9) https://bugs.python.org/issue16148


File: python.info,  Node: Other Improvements<2>,  Next: Significant Optimizations,  Prev: Other Build and C API Changes,  Up: CPython Implementation Changes

1.6.5.6 Other Improvements
..........................

   * The *note python: a10. command has a new *note option: a11, ‘-I’,
     which causes it to run in “isolated mode”, which means that *note
     sys.path: 260. contains neither the script’s directory nor the
     user’s ‘site-packages’ directory, and all ‘PYTHON*’ environment
     variables are ignored (it implies both ‘-s’ and ‘-E’).  Other
     restrictions may also be applied in the future, with the goal being
     to isolate the execution of a script from the user’s environment.
     This is appropriate, for example, when Python is used to run a
     system script.  On most POSIX systems it can and should be used in
     the ‘#!’ line of system scripts.  (Contributed by Christian Heimes
     in bpo-16499(1).)

   * Tab-completion is now enabled by default in the interactive
     interpreter on systems that support *note readline: de.  History is
     also enabled by default, and is written to (and read from) the file
     ‘~/.python-history’.  (Contributed by Antoine Pitrou and Éric
     Araujo in bpo-5845(2).)

   * Invoking the Python interpreter with ‘--version’ now outputs the
     version to standard output instead of standard error
     (bpo-18338(3)).  Similar changes were made to *note argparse: 5.
     (bpo-18920(4)) and other modules that have script-like invocation
     capabilities (bpo-18922(5)).

   * The CPython Windows installer now adds ‘.py’ to the ‘PATHEXT’
     variable when extensions are registered, allowing users to run a
     python script at the windows command prompt by just typing its name
     without the ‘.py’ extension.  (Contributed by Paul Moore in
     bpo-18569(6).)

   * A new ‘make’ target coverage-report(7) will build python, run the
     test suite, and generate an HTML coverage report for the C codebase
     using ‘gcov’ and lcov(8).

   * The ‘-R’ option to the *note python regression test suite: a12. now
     also checks for memory allocation leaks, using *note
     sys.getallocatedblocks(): 9c8.  (Contributed by Antoine Pitrou in
     bpo-13390(9).)

   * ‘python -m’ now works with namespace packages.

   * The *note stat: f4. module is now implemented in C, which means it
     gets the values for its constants from the C header files, instead
     of having the values hard-coded in the python module as was
     previously the case.

   * Loading multiple python modules from a single OS module (‘.so’,
     ‘.dll’) now works correctly (previously it silently returned the
     first python module in the file).  (Contributed by Václav Šmilauer
     in bpo-16421(10).)

   * A new opcode, *note LOAD_CLASSDEREF: a13, has been added to fix a
     bug in the loading of free variables in class bodies that could be
     triggered by certain uses of *note __prepare__: 5f7.  (Contributed
     by Benjamin Peterson in bpo-17853(11).)

   * A number of MemoryError-related crashes were identified and fixed
     by Victor Stinner using his PEP 445(12)-based ‘pyfailmalloc’ tool
     (bpo-18408(13), bpo-18520(14)).

   * The ‘pyvenv’ command now accepts a ‘--copies’ option to use copies
     rather than symlinks even on systems where symlinks are the
     default.  (Contributed by Vinay Sajip in bpo-18807(15).)

   * The ‘pyvenv’ command also accepts a ‘--without-pip’ option to
     suppress the otherwise-automatic bootstrapping of pip into the
     virtual environment.  (Contributed by Nick Coghlan in bpo-19552(16)
     as part of the PEP 453(17) implementation.)

   * The encoding name is now optional in the value set for the *note
     PYTHONIOENCODING: a14. environment variable.  This makes it
     possible to set just the error handler, without changing the
     default encoding.  (Contributed by Serhiy Storchaka in
     bpo-18818(18).)

   * The *note bz2: 13, *note lzma: ad, and *note gzip: 8b. module
     ‘open’ functions now support ‘x’ (exclusive creation) mode.
     (Contributed by Tim Heaney and Vajrasky Kok in bpo-19201(19),
     bpo-19222(20), and bpo-19223(21).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16499

   (2) https://bugs.python.org/issue5845

   (3) https://bugs.python.org/issue18338

   (4) https://bugs.python.org/issue18920

   (5) https://bugs.python.org/issue18922

   (6) https://bugs.python.org/issue18569

   (7) 
https://devguide.python.org/coverage/#measuring-coverage-of-c-code-with-gcov-and-lcov

   (8) http://ltp.sourceforge.net/coverage/lcov.php

   (9) https://bugs.python.org/issue13390

   (10) https://bugs.python.org/issue16421

   (11) https://bugs.python.org/issue17853

   (12) https://www.python.org/dev/peps/pep-0445

   (13) https://bugs.python.org/issue18408

   (14) https://bugs.python.org/issue18520

   (15) https://bugs.python.org/issue18807

   (16) https://bugs.python.org/issue19552

   (17) https://www.python.org/dev/peps/pep-0453

   (18) https://bugs.python.org/issue18818

   (19) https://bugs.python.org/issue19201

   (20) https://bugs.python.org/issue19222

   (21) https://bugs.python.org/issue19223


File: python.info,  Node: Significant Optimizations,  Prev: Other Improvements<2>,  Up: CPython Implementation Changes

1.6.5.7 Significant Optimizations
.................................

   * The UTF-32 decoder is now 3x to 4x faster.  (Contributed by Serhiy
     Storchaka in bpo-14625(1).)

   * The cost of hash collisions for sets is now reduced.  Each hash
     table probe now checks a series of consecutive, adjacent key/hash
     pairs before continuing to make random probes through the hash
     table.  This exploits cache locality to make collision resolution
     less expensive.  The collision resolution scheme can be described
     as a hybrid of linear probing and open addressing.  The number of
     additional linear probes defaults to nine.  This can be changed at
     compile-time by defining LINEAR_PROBES to be any value.  Set
     LINEAR_PROBES=0 to turn-off linear probing entirely.  (Contributed
     by Raymond Hettinger in bpo-18771(2).)

   * The interpreter starts about 30% faster.  A couple of measures lead
     to the speedup.  The interpreter loads fewer modules on startup,
     e.g.  the *note re: dd, *note collections: 1d. and *note locale:
     a9. modules and their dependencies are no longer imported by
     default.  The marshal module has been improved to load compiled
     Python code faster.  (Contributed by Antoine Pitrou, Christian
     Heimes and Victor Stinner in bpo-19219(3), bpo-19218(4),
     bpo-19209(5), bpo-19205(6) and bpo-9548(7).)

   * *note bz2.BZ2File: 224. is now as fast or faster than the Python2
     version for most cases.  *note lzma.LZMAFile: a16. has also been
     optimized.  (Contributed by Serhiy Storchaka and Nadeem Vawda in
     bpo-16034(8).)

   * *note random.getrandbits(): a17. is 20%-40% faster for small
     integers (the most common use case).  (Contributed by Serhiy
     Storchaka in bpo-16674(9).)

   * By taking advantage of the new storage format for strings, pickling
     of strings is now significantly faster.  (Contributed by Victor
     Stinner and Antoine Pitrou in bpo-15596(10).)

   * A performance issue in ‘io.FileIO.readall()’ has been solved.  This
     particularly affects Windows, and significantly speeds up the case
     of piping significant amounts of data through *note subprocess: f9.
     (Contributed by Richard Oudkerk in bpo-15758(11).)

   * *note html.escape(): a18. is now 10x faster.  (Contributed by Matt
     Bryant in bpo-18020(12).)

   * On Windows, the native ‘VirtualAlloc’ is now used instead of the
     CRT ‘malloc’ in ‘obmalloc’.  Artificial benchmarks show about a 3%
     memory savings.

   * *note os.urandom(): 5cc. now uses a lazily-opened persistent file
     descriptor so as to avoid using many file descriptors when run in
     parallel from multiple threads.  (Contributed by Antoine Pitrou in
     bpo-18756(13).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14625

   (2) https://bugs.python.org/issue18771

   (3) https://bugs.python.org/issue19219

   (4) https://bugs.python.org/issue19218

   (5) https://bugs.python.org/issue19209

   (6) https://bugs.python.org/issue19205

   (7) https://bugs.python.org/issue9548

   (8) https://bugs.python.org/issue16034

   (9) https://bugs.python.org/issue16674

   (10) https://bugs.python.org/issue15596

   (11) https://bugs.python.org/issue15758

   (12) https://bugs.python.org/issue18020

   (13) https://bugs.python.org/issue18756


File: python.info,  Node: Deprecated<5>,  Next: Removed<5>,  Prev: CPython Implementation Changes,  Up: What’s New In Python 3 4

1.6.6 Deprecated
----------------

This section covers various APIs and other features that have been
deprecated in Python 3.4, and will be removed in Python 3.5 or later.
In most (but not all) cases, using the deprecated APIs will produce a
*note DeprecationWarning: 15a. when the interpreter is run with
deprecation warnings enabled (for example, by using ‘-Wd’).

* Menu:

* Deprecations in the Python API::
* Deprecated Features::


File: python.info,  Node: Deprecations in the Python API,  Next: Deprecated Features,  Up: Deprecated<5>

1.6.6.1 Deprecations in the Python API
......................................

   * As mentioned in *note PEP 451; A ModuleSpec Type for the Import
     System: 8c5, a number of *note importlib: 9a. methods and functions
     are deprecated: *note importlib.find_loader(): a1b. is replaced by
     *note importlib.util.find_spec(): a1c.; *note
     importlib.machinery.PathFinder.find_module(): a1d. is replaced by
     *note importlib.machinery.PathFinder.find_spec(): a1e.; *note
     importlib.abc.MetaPathFinder.find_module(): 564. is replaced by
     *note importlib.abc.MetaPathFinder.find_spec(): 565.; *note
     importlib.abc.PathEntryFinder.find_loader(): 566. and *note
     find_module(): a1f. are replaced by *note
     importlib.abc.PathEntryFinder.find_spec(): 567.; all of the
     ‘xxxLoader’ ABC ‘load_module’ methods (*note
     importlib.abc.Loader.load_module(): 6da, *note
     importlib.abc.InspectLoader.load_module(): a20, *note
     importlib.abc.FileLoader.load_module(): a21, *note
     importlib.abc.SourceLoader.load_module(): a22.) should no longer be
     implemented, instead loaders should implement an ‘exec_module’
     method (*note importlib.abc.Loader.exec_module(): 6db, *note
     importlib.abc.InspectLoader.exec_module(): a23. *note
     importlib.abc.SourceLoader.exec_module(): a24.) and let the import
     system take care of the rest; and *note
     importlib.abc.Loader.module_repr(): a25, *note
     importlib.util.module_for_loader(): a26, *note
     importlib.util.set_loader(): a27, and *note
     importlib.util.set_package(): a28. are no longer needed because
     their functions are now handled automatically by the import system.

   * The *note imp: 99. module is pending deprecation.  To keep
     compatibility with Python 2/3 code bases, the module’s removal is
     currently not scheduled.

   * The *note formatter: 80. module is pending deprecation and is
     slated for removal in Python 3.6.

   * ‘MD5’ as the default `digestmod' for the *note hmac.new(): 940.
     function is deprecated.  Python 3.6 will require an explicit digest
     name or constructor as `digestmod' argument.

   * The internal ‘Netrc’ class in the *note ftplib: 82. module has been
     documented as deprecated in its docstring for quite some time.  It
     now emits a *note DeprecationWarning: 15a. and will be removed
     completely in Python 3.5.

   * The undocumented `endtime' argument to *note
     subprocess.Popen.wait(): 689. should not have been exposed and is
     hopefully not in use; it is deprecated and will mostly likely be
     removed in Python 3.5.

   * The `strict' argument of *note HTMLParser: 22a. is deprecated.

   * The *note plistlib: cf. ‘readPlist()’, ‘writePlist()’,
     ‘readPlistFromBytes()’, and ‘writePlistToBytes()’ functions are
     deprecated in favor of the corresponding new functions *note
     load(): 21e, *note dump(): 220, *note loads(): 21f, and *note
     dumps(): 221.  ‘Data()’ is deprecated in favor of just using the
     *note bytes: 172. constructor.

   * The *note sysconfig: fe. key ‘SO’ is deprecated, it has been
     replaced by ‘EXT_SUFFIX’.

   * The ‘U’ mode accepted by various ‘open’ functions is deprecated.
     In Python3 it does not do anything useful, and should be replaced
     by appropriate uses of *note io.TextIOWrapper: 6ea. (if needed) and
     its `newline' argument.

   * The `parser' argument of *note xml.etree.ElementTree.iterparse():
     a29. has been deprecated, as has the `html' argument of *note
     XMLParser(): 37c.  To prepare for the removal of the latter, all
     arguments to ‘XMLParser’ should be passed by keyword.


File: python.info,  Node: Deprecated Features,  Prev: Deprecations in the Python API,  Up: Deprecated<5>

1.6.6.2 Deprecated Features
...........................

   * Running *note IDLE: a2b. with the ‘-n’ flag (no subprocess) is
     deprecated.  However, the feature will not be removed until
     bpo-18823(1) is resolved.

   * The site module adding a “site-python” directory to sys.path, if it
     exists, is deprecated (bpo-19375(2)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18823

   (2) https://bugs.python.org/issue19375


File: python.info,  Node: Removed<5>,  Next: Porting to Python 3 4,  Prev: Deprecated<5>,  Up: What’s New In Python 3 4

1.6.7 Removed
-------------

* Menu:

* Operating Systems No Longer Supported::
* API and Feature Removals: API and Feature Removals<5>.
* Code Cleanups::


File: python.info,  Node: Operating Systems No Longer Supported,  Next: API and Feature Removals<5>,  Up: Removed<5>

1.6.7.1 Operating Systems No Longer Supported
.............................................

Support for the following operating systems has been removed from the
source and build tools:

   * OS/2 (bpo-16135(1)).

   * Windows 2000 (changeset e52df05b496a).

   * Windows systems where ‘COMSPEC’ points to ‘command.com’
     (bpo-14470(2)).

   * VMS (bpo-16136(3)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16135

   (2) https://bugs.python.org/issue14470

   (3) https://bugs.python.org/issue16136


File: python.info,  Node: API and Feature Removals<5>,  Next: Code Cleanups,  Prev: Operating Systems No Longer Supported,  Up: Removed<5>

1.6.7.2 API and Feature Removals
................................

The following obsolete and previously deprecated APIs and features have
been removed:

   * The unmaintained ‘Misc/TextMate’ and ‘Misc/vim’ directories have
     been removed (see the devguide(1) for suggestions on what to use
     instead).

   * The ‘SO’ makefile macro is removed (it was replaced by the
     ‘SHLIB_SUFFIX’ and ‘EXT_SUFFIX’ macros) (bpo-16754(2)).

   * The ‘PyThreadState.tick_counter’ field has been removed; its value
     has been meaningless since Python 3.2, when the “new GIL” was
     introduced (bpo-19199(3)).

   * ‘PyLoader’ and ‘PyPycLoader’ have been removed from *note
     importlib: 9a.  (Contributed by Taras Lyapun in bpo-15641(4).)

   * The `strict' argument to *note HTTPConnection: 499. and *note
     HTTPSConnection: 49a. has been removed.  HTTP 0.9-style “Simple
     Responses” are no longer supported.

   * The deprecated *note urllib.request.Request: 9dc. getter and setter
     methods ‘add_data’, ‘has_data’, ‘get_data’, ‘get_type’, ‘get_host’,
     ‘get_selector’, ‘set_proxy’, ‘get_origin_req_host’, and
     ‘is_unverifiable’ have been removed (use direct attribute access
     instead).

   * Support for loading the deprecated ‘TYPE_INT64’ has been removed
     from *note marshal: b0.  (Contributed by Dan Riti in bpo-15480(5).)

   * *note inspect.Signature: 7e4.: positional-only parameters are now
     required to have a valid name.

   * *note object.__format__(): a2f. no longer accepts non-empty format
     strings, it now raises a *note TypeError: 1fe. instead.  Using a
     non-empty string has been deprecated since Python 3.2.  This change
     has been made to prevent a situation where previously working (but
     incorrect) code would start failing if an object gained a
     __format__ method, which means that your code may now raise a *note
     TypeError: 1fe. if you are using an ‘'s'’ format code with objects
     that do not have a __format__ method that handles it.  See
     bpo-7994(6) for background.

   * ‘difflib.SequenceMatcher.isbjunk()’ and
     ‘difflib.SequenceMatcher.isbpopular()’ were deprecated in 3.2, and
     have now been removed: use ‘x in sm.bjunk’ and ‘x in sm.bpopular’,
     where `sm' is a *note SequenceMatcher: a30. object (bpo-13248(7)).

   ---------- Footnotes ----------

   (1) https://devguide.python.org

   (2) https://bugs.python.org/issue16754

   (3) https://bugs.python.org/issue19199

   (4) https://bugs.python.org/issue15641

   (5) https://bugs.python.org/issue15480

   (6) https://bugs.python.org/issue7994

   (7) https://bugs.python.org/issue13248


File: python.info,  Node: Code Cleanups,  Prev: API and Feature Removals<5>,  Up: Removed<5>

1.6.7.3 Code Cleanups
.....................

   * The unused and undocumented internal ‘Scanner’ class has been
     removed from the *note pydoc: d9. module.

   * The private and effectively unused ‘_gestalt’ module has been
     removed, along with the private *note platform: ce. functions
     ‘_mac_ver_lookup’, ‘_mac_ver_gstalt’, and ‘_bcd2str’, which would
     only have ever been called on badly broken OSX systems (see
     bpo-18393(1)).

   * The hardcoded copies of certain *note stat: f4. constants that were
     included in the *note tarfile: 101. module namespace have been
     removed.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18393


File: python.info,  Node: Porting to Python 3 4,  Next: Changed in 3 4 3,  Prev: Removed<5>,  Up: What’s New In Python 3 4

1.6.8 Porting to Python 3.4
---------------------------

This section lists previously described changes and other bugfixes that
may require changes to your code.

* Menu:

* Changes in ‘python’ Command Behavior: Changes in ‘python’ Command Behavior<2>.
* Changes in the Python API: Changes in the Python API<6>.
* Changes in the C API: Changes in the C API<6>.


File: python.info,  Node: Changes in ‘python’ Command Behavior<2>,  Next: Changes in the Python API<6>,  Up: Porting to Python 3 4

1.6.8.1 Changes in ‘python’ Command Behavior
............................................

   * In a posix shell, setting the ‘PATH’ environment variable to an
     empty value is equivalent to not setting it at all.  However,
     setting *note PYTHONPATH: a34. to an empty value was `not'
     equivalent to not setting it at all: setting *note PYTHONPATH: a34.
     to an empty value was equivalent to setting it to ‘.’, which leads
     to confusion when reasoning by analogy to how ‘PATH’ works.  The
     behavior now conforms to the posix convention for ‘PATH’.

   * The [X refs, Y blocks] output of a debug (‘--with-pydebug’) build
     of the CPython interpreter is now off by default.  It can be
     re-enabled using the ‘-X showrefcount’ option.  (Contributed by
     Ezio Melotti in bpo-17323(1).)

   * The python command and most stdlib scripts (as well as *note
     argparse: 5.) now output ‘--version’ information to ‘stdout’
     instead of ‘stderr’ (for issue list see *note Other Improvements:
     a0f. above).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17323


File: python.info,  Node: Changes in the Python API<6>,  Next: Changes in the C API<6>,  Prev: Changes in ‘python’ Command Behavior<2>,  Up: Porting to Python 3 4

1.6.8.2 Changes in the Python API
.................................

   * The ABCs defined in *note importlib.abc: 9b. now either raise the
     appropriate exception or return a default value instead of raising
     *note NotImplementedError: 704. blindly.  This will only affect
     code calling *note super(): 5dd. and falling through all the way to
     the ABCs.  For compatibility, catch both *note NotImplementedError:
     704. or the appropriate exception as needed.

   * The module type now initializes the *note __package__: a36. and
     *note __loader__: a37. attributes to ‘None’ by default.  To
     determine if these attributes were set in a backwards-compatible
     fashion, use e.g.  ‘getattr(module, '__loader__', None) is not
     None’.  (bpo-17115(1).)

   * *note importlib.util.module_for_loader(): a26. now sets
     ‘__loader__’ and ‘__package__’ unconditionally to properly support
     reloading.  If this is not desired then you will need to set these
     attributes manually.  You can use ‘importlib.util.module_to_load()’
     for module management.

   * Import now resets relevant attributes (e.g.  ‘__name__’,
     ‘__loader__’, ‘__package__’, ‘__file__’, ‘__cached__’)
     unconditionally when reloading.  Note that this restores a pre-3.3
     behavior in that it means a module is re-found when re-loaded
     (bpo-19413(2)).

   * Frozen packages no longer set ‘__path__’ to a list containing the
     package name, they now set it to an empty list.  The previous
     behavior could cause the import system to do the wrong thing on
     submodule imports if there was also a directory with the same name
     as the frozen package.  The correct way to determine if a module is
     a package or not is to use ‘hasattr(module, '__path__')’
     (bpo-18065(3)).

   * Frozen modules no longer define a ‘__file__’ attribute.  It’s
     semantically incorrect for frozen modules to set the attribute as
     they are not loaded from any explicit location.  If you must know
     that a module comes from frozen code then you can see if the
     module’s ‘__spec__.location’ is set to ‘'frozen'’, check if the
     loader is a subclass of *note importlib.machinery.FrozenImporter:
     a38, or if Python 2 compatibility is necessary you can use
     ‘imp.is_frozen()’.

   * *note py_compile.compile(): 343. now raises *note FileExistsError:
     a39. if the file path it would write to is a symlink or a
     non-regular file.  This is to act as a warning that import will
     overwrite those files with a regular file regardless of what type
     of file path they were originally.

   * *note importlib.abc.SourceLoader.get_source(): a3a. no longer
     raises *note ImportError: 16c. when the source code being loaded
     triggers a *note SyntaxError: 55a. or *note UnicodeDecodeError:
     32b.  As *note ImportError: 16c. is meant to be raised only when
     source code cannot be found but it should, it was felt to be
     over-reaching/overloading of that meaning when the source code is
     found but improperly structured.  If you were catching ImportError
     before and wish to continue to ignore syntax or decoding issues,
     catch all three exceptions now.

   * *note functools.update_wrapper(): a3b. and *note functools.wraps():
     955. now correctly set the ‘__wrapped__’ attribute to the function
     being wrapped, even if that function also had its ‘__wrapped__’
     attribute set.  This means ‘__wrapped__’ attributes now correctly
     link a stack of decorated functions rather than every ‘__wrapped__’
     attribute in the chain referring to the innermost function.
     Introspection libraries that assumed the previous behaviour was
     intentional can use *note inspect.unwrap(): 954. to access the
     first function in the chain that has no ‘__wrapped__’ attribute.

   * *note inspect.getfullargspec(): 657. has been reimplemented on top
     of *note inspect.signature(): 655. and hence handles a much wider
     variety of callable objects than it did in the past.  It is
     expected that additional builtin and extension module callables
     will gain signature metadata over the course of the Python 3.4
     series.  Code that assumes that *note inspect.getfullargspec():
     657. will fail on non-Python callables may need to be adjusted
     accordingly.

   * *note importlib.machinery.PathFinder: a3c. now passes on the
     current working directory to objects in *note sys.path_hooks: a3d.
     for the empty string.  This results in *note
     sys.path_importer_cache: 598. never containing ‘''’, thus iterating
     through *note sys.path_importer_cache: 598. based on *note
     sys.path: 260. will not find all keys.  A module’s ‘__file__’ when
     imported in the current working directory will also now have an
     absolute path, including when using ‘-m’ with the interpreter
     (except for ‘__main__.__file__’ when a script has been executed
     directly using a relative path) (Contributed by Brett Cannon in
     bpo-18416(4)).  is specified on the command-line) (bpo-18416(5)).

   * The removal of the `strict' argument to *note HTTPConnection: 499.
     and *note HTTPSConnection: 49a. changes the meaning of the
     remaining arguments if you are specifying them positionally rather
     than by keyword.  If you’ve been paying attention to deprecation
     warnings your code should already be specifying any additional
     arguments via keywords.

   * Strings between ‘from __future__ import ...’ statements now
     `always' raise a *note SyntaxError: 55a.  Previously if there was
     no leading docstring, an interstitial string would sometimes be
     ignored.  This brings CPython into compliance with the language
     spec; Jython and PyPy already were.  (bpo-17434(6)).

   * *note ssl.SSLSocket.getpeercert(): 9b7. and *note
     ssl.SSLSocket.do_handshake(): 849. now raise an *note OSError: 304.
     with ‘ENOTCONN’ when the ‘SSLSocket’ is not connected, instead of
     the previous behavior of raising an *note AttributeError: 4a2.  In
     addition, *note getpeercert(): 9b7. will raise a *note ValueError:
     16d. if the handshake has not yet been done.

   * *note base64.b32decode(): a3e. now raises a *note binascii.Error:
     a3f. when the input string contains non-b32-alphabet characters,
     instead of a *note TypeError: 1fe.  This particular *note
     TypeError: 1fe. was missed when the other *note TypeError: 1fe.s
     were converted.  (Contributed by Serhiy Storchaka in bpo-18011(7).)
     Note: this change was also inadvertently applied in Python 3.3.3.

   * The ‘file’ attribute is now automatically closed when the creating
     ‘cgi.FieldStorage’ instance is garbage collected.  If you were
     pulling the file object out separately from the ‘cgi.FieldStorage’
     instance and not keeping the instance alive, then you should either
     store the entire ‘cgi.FieldStorage’ instance or read the contents
     of the file before the ‘cgi.FieldStorage’ instance is garbage
     collected.

   * Calling ‘read’ or ‘write’ on a closed SSL socket now raises an
     informative *note ValueError: 16d. rather than the previous more
     mysterious *note AttributeError: 4a2. (bpo-9177(8)).

   * *note slice.indices(): a40. no longer produces an *note
     OverflowError: a41. for huge values.  As a consequence of this fix,
     *note slice.indices(): a40. now raises a *note ValueError: 16d. if
     given a negative length; previously it returned nonsense values
     (bpo-14794(9)).

   * The *note complex: 2c1. constructor, unlike the *note cmath: 18.
     functions, was incorrectly accepting *note float: 1fd. values if an
     object’s ‘__complex__’ special method returned one.  This now
     raises a *note TypeError: 1fe.  (bpo-16290(10).)

   * The *note int: 204. constructor in 3.2 and 3.3 erroneously accepts
     *note float: 1fd. values for the `base' parameter.  It is unlikely
     anyone was doing this, but if so, it will now raise a *note
     TypeError: 1fe. (bpo-16772(11)).

   * Defaults for keyword-only arguments are now evaluated `after'
     defaults for regular keyword arguments, instead of before.
     Hopefully no one wrote any code that depends on the previous buggy
     behavior (bpo-16967(12)).

   * Stale thread states are now cleared after *note fork(): a42.  This
     may cause some system resources to be released that previously were
     incorrectly kept perpetually alive (for example, database
     connections kept in thread-local storage).  (bpo-17094(13).)

   * Parameter names in ‘__annotations__’ dicts are now mangled
     properly, similarly to ‘__kwdefaults__’.  (Contributed by Yury
     Selivanov in bpo-20625(14).)

   * *note hashlib.hash.name: 93e. now always returns the identifier in
     lower case.  Previously some builtin hashes had uppercase names,
     but now that it is a formal public interface the naming has been
     made consistent (bpo-18532(15)).

   * Because *note unittest.TestSuite: 7c1. now drops references to
     tests after they are run, test harnesses that re-use a *note
     TestSuite: 7c1. to re-run a set of tests may fail.  Test suites
     should not be re-used in this fashion since it means state is
     retained between test runs, breaking the test isolation that *note
     unittest: 124. is designed to provide.  However, if the lack of
     isolation is considered acceptable, the old behavior can be
     restored by creating a *note TestSuite: 7c1. subclass that defines
     a ‘_removeTestAtIndex’ method that does nothing (see *note
     TestSuite.__iter__(): a43.) (bpo-11798(16)).

   * *note unittest: 124. now uses *note argparse: 5. for command line
     parsing.  There are certain invalid command forms that used to work
     that are no longer allowed; in theory this should not cause
     backward compatibility issues since the disallowed command forms
     didn’t make any sense and are unlikely to be in use.

   * The *note re.split(): 4d1, *note re.findall(): a44, and *note
     re.sub(): 57a. functions, and the ‘group()’ and ‘groups()’ methods
     of ‘match’ objects now always return a `bytes' object when the
     string to be matched is a *note bytes-like object: 6df.  Previously
     the return type matched the input type, so if your code was
     depending on the return value being, say, a ‘bytearray’, you will
     need to change your code.

   * *note audioop: c. functions now raise an error immediately if
     passed string input, instead of failing randomly later on
     (bpo-16685(17)).

   * The new `convert_charrefs' argument to *note HTMLParser: 22a.
     currently defaults to ‘False’ for backward compatibility, but will
     eventually be changed to default to ‘True’.  It is recommended that
     you add this keyword, with the appropriate value, to any *note
     HTMLParser: 22a. calls in your code (bpo-13633(18)).

   * Since the `digestmod' argument to the *note hmac.new(): 940.
     function will in the future have no default, all calls to *note
     hmac.new(): 940. should be changed to explicitly specify a
     `digestmod' (bpo-17276(19)).

   * Calling *note sysconfig.get_config_var(): a45. with the ‘SO’ key,
     or looking ‘SO’ up in the results of a call to *note
     sysconfig.get_config_vars(): a46. is deprecated.  This key should
     be replaced by ‘EXT_SUFFIX’ or ‘SHLIB_SUFFIX’, depending on the
     context (bpo-19555(20)).

   * Any calls to ‘open’ functions that specify ‘U’ should be modified.
     ‘U’ is ineffective in Python3 and will eventually raise an error if
     used.  Depending on the function, the equivalent of its old Python2
     behavior can be achieved using either a `newline' argument, or if
     necessary by wrapping the stream in *note TextIOWrapper: 6ea. to
     use its `newline' argument (bpo-15204(21)).

   * If you use ‘pyvenv’ in a script and desire that pip `not' be
     installed, you must add ‘--without-pip’ to your command invocation.

   * The default behavior of *note json.dump(): 6fb. and *note
     json.dumps(): 6fc. when an indent is specified has changed: it no
     longer produces trailing spaces after the item separating commas at
     the ends of lines.  This will matter only if you have tests that
     are doing white-space-sensitive comparisons of such output
     (bpo-16333(22)).

   * *note doctest: 66. now looks for doctests in extension module
     ‘__doc__’ strings, so if your doctest test discovery includes
     extension modules that have things that look like doctests in them
     you may see test failures you’ve never seen before when running
     your tests (bpo-3158(23)).

   * The *note collections.abc: 1e. module has been slightly refactored
     as part of the Python startup improvements.  As a consequence of
     this, it is no longer the case that importing *note collections:
     1d. automatically imports *note collections.abc: 1e.  If your
     program depended on the (undocumented) implicit import, you will
     need to add an explicit ‘import collections.abc’ (bpo-20784(24)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17115

   (2) https://bugs.python.org/issue19413

   (3) https://bugs.python.org/issue18065

   (4) https://bugs.python.org/issue18416

   (5) https://bugs.python.org/issue18416

   (6) https://bugs.python.org/issue17434

   (7) https://bugs.python.org/issue18011

   (8) https://bugs.python.org/issue9177

   (9) https://bugs.python.org/issue14794

   (10) https://bugs.python.org/issue16290

   (11) https://bugs.python.org/issue16772

   (12) https://bugs.python.org/issue16967

   (13) https://bugs.python.org/issue17094

   (14) https://bugs.python.org/issue20625

   (15) https://bugs.python.org/issue18532

   (16) https://bugs.python.org/issue11798

   (17) https://bugs.python.org/issue16685

   (18) https://bugs.python.org/issue13633

   (19) https://bugs.python.org/issue17276

   (20) https://bugs.python.org/issue19555

   (21) https://bugs.python.org/issue15204

   (22) https://bugs.python.org/issue16333

   (23) https://bugs.python.org/issue3158

   (24) https://bugs.python.org/issue20784


File: python.info,  Node: Changes in the C API<6>,  Prev: Changes in the Python API<6>,  Up: Porting to Python 3 4

1.6.8.3 Changes in the C API
............................

   * *note PyEval_EvalFrameEx(): a48, *note PyObject_Repr(): a49, and
     *note PyObject_Str(): a4a, along with some other internal C APIs,
     now include a debugging assertion that ensures they are not used in
     situations where they may silently discard a currently active
     exception.  In cases where discarding the active exception is
     expected and desired (for example, because it has already been
     saved locally with *note PyErr_Fetch(): a4b. or is being
     deliberately replaced with a different exception), an explicit
     *note PyErr_Clear(): a4c. call will be needed to avoid triggering
     the assertion when invoking these operations (directly or
     indirectly) and running against a version of Python that is
     compiled with assertions enabled.

   * *note PyErr_SetImportError(): 6ef. now sets *note TypeError: 1fe.
     when its `msg' argument is not set.  Previously only ‘NULL’ was
     returned with no exception set.

   * The result of the *note PyOS_ReadlineFunctionPointer: a4d. callback
     must now be a string allocated by *note PyMem_RawMalloc(): a4e. or
     *note PyMem_RawRealloc(): a4f, or ‘NULL’ if an error occurred,
     instead of a string allocated by *note PyMem_Malloc(): 5ff. or
     *note PyMem_Realloc(): a50. (bpo-16742(1))

   * *note PyThread_set_key_value(): a51. now always set the value.  In
     Python 3.3, the function did nothing if the key already exists (if
     the current value is a non-‘NULL’ pointer).

   * The ‘f_tstate’ (thread state) field of the *note PyFrameObject:
     a52. structure has been removed to fix a bug: see bpo-14432(2) for
     the rationale.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16742

   (2) https://bugs.python.org/issue14432


File: python.info,  Node: Changed in 3 4 3,  Prev: Porting to Python 3 4,  Up: What’s New In Python 3 4

1.6.9 Changed in 3.4.3
----------------------

* Menu:

* PEP 476; Enabling certificate verification by default for stdlib http clients: PEP 476 Enabling certificate verification by default for stdlib http clients.


File: python.info,  Node: PEP 476 Enabling certificate verification by default for stdlib http clients,  Up: Changed in 3 4 3

1.6.9.1 PEP 476: Enabling certificate verification by default for stdlib http clients
.....................................................................................

*note http.client: 93. and modules which use it, such as *note
urllib.request: 129. and *note xmlrpc.client: 148, will now verify that
the server presents a certificate which is signed by a CA in the
platform trust store and whose hostname matches the hostname being
requested by default, significantly improving security for many
applications.

For applications which require the old previous behavior, they can pass
an alternate context:

     import urllib.request
     import ssl

     # This disables all verification
     context = ssl._create_unverified_context()

     # This allows using a specific certificate for the host, which doesn't need
     # to be in the trust store
     context = ssl.create_default_context(cafile="/path/to/file.crt")

     urllib.request.urlopen("https://invalid-cert", context=context)


File: python.info,  Node: What’s New In Python 3 3,  Next: What’s New In Python 3 2,  Prev: What’s New In Python 3 4,  Up: What’s New in Python

1.7 What’s New In Python 3.3
============================

This article explains the new features in Python 3.3, compared to 3.2.
Python 3.3 was released on September 29, 2012.  For full details, see
the changelog(1).

See also
........

PEP 398(2) - Python 3.3 Release Schedule

* Menu:

* Summary – Release highlights: Summary – Release highlights<5>.
* PEP 405; Virtual Environments: PEP 405 Virtual Environments.
* PEP 420; Implicit Namespace Packages: PEP 420 Implicit Namespace Packages.
* PEP 3118; New memoryview implementation and buffer protocol documentation: PEP 3118 New memoryview implementation and buffer protocol documentation.
* PEP 393; Flexible String Representation: PEP 393 Flexible String Representation.
* PEP 397; Python Launcher for Windows: PEP 397 Python Launcher for Windows.
* PEP 3151; Reworking the OS and IO exception hierarchy: PEP 3151 Reworking the OS and IO exception hierarchy.
* PEP 380; Syntax for Delegating to a Subgenerator: PEP 380 Syntax for Delegating to a Subgenerator.
* PEP 409; Suppressing exception context: PEP 409 Suppressing exception context.
* PEP 414; Explicit Unicode literals: PEP 414 Explicit Unicode literals.
* PEP 3155; Qualified name for classes and functions: PEP 3155 Qualified name for classes and functions.
* PEP 412; Key-Sharing Dictionary: PEP 412 Key-Sharing Dictionary.
* PEP 362; Function Signature Object: PEP 362 Function Signature Object.
* PEP 421; Adding sys.implementation: PEP 421 Adding sys implementation.
* Using importlib as the Implementation of Import::
* Other Language Changes: Other Language Changes<7>.
* A Finer-Grained Import Lock::
* Builtin functions and types::
* New Modules: New Modules<7>.
* Improved Modules: Improved Modules<7>.
* Optimizations: Optimizations<6>.
* Build and C API Changes: Build and C API Changes<4>.
* Deprecated: Deprecated<6>.
* Porting to Python 3.3: Porting to Python 3 3.

   ---------- Footnotes ----------

   (1) https://docs.python.org/3.3/whatsnew/changelog.html

   (2) https://www.python.org/dev/peps/pep-0398


File: python.info,  Node: Summary – Release highlights<5>,  Next: PEP 405 Virtual Environments,  Up: What’s New In Python 3 3

1.7.1 Summary – Release highlights
----------------------------------

New syntax features:

   * New ‘yield from’ expression for *note generator delegation: a59.

   * The ‘u'unicode'’ syntax is accepted again for *note str: 205.
     objects.

New library modules:

   * *note faulthandler: 7b. (helps debugging low-level crashes)

   * *note ipaddress: a2. (high-level objects representing IP addresses
     and masks)

   * *note lzma: ad. (compress data using the XZ / LZMA algorithm)

   * *note unittest.mock: 125. (replace parts of your system under test
     with mock objects)

   * *note venv: 12e. (Python *note virtual environments: a5a, as in the
     popular ‘virtualenv’ package)

New built-in features:

   * Reworked *note I/O exception hierarchy: a5b.

Implementation improvements:

   * Rewritten *note import machinery: a5c. based on *note importlib:
     9a.

   * More compact *note unicode strings: a5d.

   * More compact *note attribute dictionaries: a5e.

Significantly Improved Library Modules:

   * C Accelerator for the *note decimal: a5f. module.

   * Better unicode handling in the *note email: a60. module (*note
     provisional: a61.).

Security improvements:

   * Hash randomization is switched on by default.

Please read on for a comprehensive list of user-facing changes.


File: python.info,  Node: PEP 405 Virtual Environments,  Next: PEP 420 Implicit Namespace Packages,  Prev: Summary – Release highlights<5>,  Up: What’s New In Python 3 3

1.7.2 PEP 405: Virtual Environments
-----------------------------------

Virtual environments help create separate Python setups while sharing a
system-wide base install, for ease of maintenance.  Virtual environments
have their own set of private site packages (i.e.  locally-installed
libraries), and are optionally segregated from the system-wide site
packages.  Their concept and implementation are inspired by the popular
‘virtualenv’ third-party package, but benefit from tighter integration
with the interpreter core.

This PEP adds the *note venv: 12e. module for programmatic access, and
the ‘pyvenv’ script for command-line access and administration.  The
Python interpreter checks for a ‘pyvenv.cfg’, file whose existence
signals the base of a virtual environment’s directory tree.

See also
........

PEP 405(1) - Python Virtual Environments

     PEP written by Carl Meyer; implementation by Carl Meyer and Vinay
     Sajip

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0405


File: python.info,  Node: PEP 420 Implicit Namespace Packages,  Next: PEP 3118 New memoryview implementation and buffer protocol documentation,  Prev: PEP 405 Virtual Environments,  Up: What’s New In Python 3 3

1.7.3 PEP 420: Implicit Namespace Packages
------------------------------------------

Native support for package directories that don’t require ‘__init__.py’
marker files and can automatically span multiple path segments (inspired
by various third party approaches to namespace packages, as described in
PEP 420(1))

See also
........

PEP 420(2) - Implicit Namespace Packages

     PEP written by Eric V. Smith; implementation by Eric V. Smith and
     Barry Warsaw

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0420

   (2) https://www.python.org/dev/peps/pep-0420


File: python.info,  Node: PEP 3118 New memoryview implementation and buffer protocol documentation,  Next: PEP 393 Flexible String Representation,  Prev: PEP 420 Implicit Namespace Packages,  Up: What’s New In Python 3 3

1.7.4 PEP 3118: New memoryview implementation and buffer protocol documentation
-------------------------------------------------------------------------------

The implementation of PEP 3118(1) has been significantly improved.

The new memoryview implementation comprehensively fixes all ownership
and lifetime issues of dynamically allocated fields in the Py_buffer
struct that led to multiple crash reports.  Additionally, several
functions that crashed or returned incorrect results for non-contiguous
or multi-dimensional input have been fixed.

The memoryview object now has a PEP-3118 compliant getbufferproc() that
checks the consumer’s request type.  Many new features have been added,
most of them work in full generality for non-contiguous arrays and
arrays with suboffsets.

The documentation has been updated, clearly spelling out
responsibilities for both exporters and consumers.  Buffer request flags
are grouped into basic and compound flags.  The memory layout of
non-contiguous and multi-dimensional NumPy-style arrays is explained.

* Menu:

* Features::
* API changes::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3118


File: python.info,  Node: Features,  Next: API changes,  Up: PEP 3118 New memoryview implementation and buffer protocol documentation

1.7.4.1 Features
................

   * All native single character format specifiers in struct module
     syntax (optionally prefixed with ‘@’) are now supported.

   * With some restrictions, the cast() method allows changing of format
     and shape of C-contiguous arrays.

   * Multi-dimensional list representations are supported for any array
     type.

   * Multi-dimensional comparisons are supported for any array type.

   * One-dimensional memoryviews of hashable (read-only) types with
     formats B, b or c are now hashable.  (Contributed by Antoine Pitrou
     in bpo-13411(1).)

   * Arbitrary slicing of any 1-D arrays type is supported.  For
     example, it is now possible to reverse a memoryview in O(1) by
     using a negative step.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13411


File: python.info,  Node: API changes,  Prev: Features,  Up: PEP 3118 New memoryview implementation and buffer protocol documentation

1.7.4.2 API changes
...................

   * The maximum number of dimensions is officially limited to 64.

   * The representation of empty shape, strides and suboffsets is now an
     empty tuple instead of ‘None’.

   * Accessing a memoryview element with format ‘B’ (unsigned bytes) now
     returns an integer (in accordance with the struct module syntax).
     For returning a bytes object the view must be cast to ‘c’ first.

   * memoryview comparisons now use the logical structure of the
     operands and compare all array elements by value.  All format
     strings in struct module syntax are supported.  Views with
     unrecognised format strings are still permitted, but will always
     compare as unequal, regardless of view contents.

   * For further changes see *note Build and C API Changes: a68. and
     *note Porting C code: a69.

(Contributed by Stefan Krah in bpo-10181(1).)

See also
........

PEP 3118(2) - Revising the Buffer Protocol

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10181

   (2) https://www.python.org/dev/peps/pep-3118


File: python.info,  Node: PEP 393 Flexible String Representation,  Next: PEP 397 Python Launcher for Windows,  Prev: PEP 3118 New memoryview implementation and buffer protocol documentation,  Up: What’s New In Python 3 3

1.7.5 PEP 393: Flexible String Representation
---------------------------------------------

The Unicode string type is changed to support multiple internal
representations, depending on the character with the largest Unicode
ordinal (1, 2, or 4 bytes) in the represented string.  This allows a
space-efficient representation in common cases, but gives access to full
UCS-4 on all systems.  For compatibility with existing APIs, several
representations may exist in parallel; over time, this compatibility
should be phased out.

On the Python side, there should be no downside to this change.

On the C API side, PEP 393(1) is fully backward compatible.  The legacy
API should remain available at least five years.  Applications using the
legacy API will not fully benefit of the memory reduction, or - worse -
may use a bit more memory, because Python may have to maintain two
versions of each string (in the legacy format and in the new efficient
storage).

* Menu:

* Functionality::
* Performance and resource usage::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0393


File: python.info,  Node: Functionality,  Next: Performance and resource usage,  Up: PEP 393 Flexible String Representation

1.7.5.1 Functionality
.....................

Changes introduced by PEP 393(1) are the following:

   * Python now always supports the full range of Unicode code points,
     including non-BMP ones (i.e.  from ‘U+0000’ to ‘U+10FFFF’).  The
     distinction between narrow and wide builds no longer exists and
     Python now behaves like a wide build, even under Windows.

   * With the death of narrow builds, the problems specific to narrow
     builds have also been fixed, for example:

        * *note len(): 28b. now always returns 1 for non-BMP characters,
          so ‘len('\U0010FFFF') == 1’;

        * surrogate pairs are not recombined in string literals, so
          ‘'\uDBFF\uDFFF' != '\U0010FFFF'’;

        * indexing or slicing non-BMP characters returns the expected
          value, so ‘'\U0010FFFF'[0]’ now returns ‘'\U0010FFFF'’ and not
          ‘'\uDBFF'’;

        * all other functions in the standard library now correctly
          handle non-BMP code points.

   * The value of *note sys.maxunicode: a6c. is now always ‘1114111’
     (‘0x10FFFF’ in hexadecimal).  The ‘PyUnicode_GetMax()’ function
     still returns either ‘0xFFFF’ or ‘0x10FFFF’ for backward
     compatibility, and it should not be used with the new Unicode API
     (see bpo-13054(2)).

   * The ‘./configure’ flag ‘--with-wide-unicode’ has been removed.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0393

   (2) https://bugs.python.org/issue13054


File: python.info,  Node: Performance and resource usage,  Prev: Functionality,  Up: PEP 393 Flexible String Representation

1.7.5.2 Performance and resource usage
......................................

The storage of Unicode strings now depends on the highest code point in
the string:

   * pure ASCII and Latin1 strings (‘U+0000-U+00FF’) use 1 byte per code
     point;

   * BMP strings (‘U+0000-U+FFFF’) use 2 bytes per code point;

   * non-BMP strings (‘U+10000-U+10FFFF’) use 4 bytes per code point.

The net effect is that for most applications, memory usage of string
storage should decrease significantly - especially compared to former
wide unicode builds - as, in many cases, strings will be pure ASCII even
in international contexts (because many strings store non-human language
data, such as XML fragments, HTTP headers, JSON-encoded data, etc.).  We
also hope that it will, for the same reasons, increase CPU cache
efficiency on non-trivial applications.  The memory usage of Python 3.3
is two to three times smaller than Python 3.2, and a little bit better
than Python 2.7, on a Django benchmark (see the PEP for details).

See also
........

PEP 393(1) - Flexible String Representation

     PEP written by Martin von Löwis; implementation by Torsten Becker
     and Martin von Löwis.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0393


File: python.info,  Node: PEP 397 Python Launcher for Windows,  Next: PEP 3151 Reworking the OS and IO exception hierarchy,  Prev: PEP 393 Flexible String Representation,  Up: What’s New In Python 3 3

1.7.6 PEP 397: Python Launcher for Windows
------------------------------------------

The Python 3.3 Windows installer now includes a ‘py’ launcher
application that can be used to launch Python applications in a version
independent fashion.

This launcher is invoked implicitly when double-clicking ‘*.py’ files.
If only a single Python version is installed on the system, that version
will be used to run the file.  If multiple versions are installed, the
most recent version is used by default, but this can be overridden by
including a Unix-style “shebang line” in the Python script.

The launcher can also be used explicitly from the command line as the
‘py’ application.  Running ‘py’ follows the same version selection rules
as implicitly launching scripts, but a more specific version can be
selected by passing appropriate arguments (such as ‘-3’ to request
Python 3 when Python 2 is also installed, or ‘-2.6’ to specifically
request an earlier Python version when a more recent version is
installed).

In addition to the launcher, the Windows installer now includes an
option to add the newly installed Python to the system PATH.
(Contributed by Brian Curtin in bpo-3561(1).)

See also
........

PEP 397(2) - Python Launcher for Windows

     PEP written by Mark Hammond and Martin v.  Löwis; implementation by
     Vinay Sajip.

Launcher documentation: *note Python Launcher for Windows: a70.

Installer PATH modification: *note Finding the Python executable: a71.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue3561

   (2) https://www.python.org/dev/peps/pep-0397


File: python.info,  Node: PEP 3151 Reworking the OS and IO exception hierarchy,  Next: PEP 380 Syntax for Delegating to a Subgenerator,  Prev: PEP 397 Python Launcher for Windows,  Up: What’s New In Python 3 3

1.7.7 PEP 3151: Reworking the OS and IO exception hierarchy
-----------------------------------------------------------

The hierarchy of exceptions raised by operating system errors is now
both simplified and finer-grained.

You don’t have to worry anymore about choosing the appropriate exception
type between *note OSError: 304, *note IOError: a73, *note
EnvironmentError: a74, *note WindowsError: a75, ‘mmap.error’, *note
socket.error: a76. or *note select.error: a77.  All these exception
types are now only one: *note OSError: 304.  The other names are kept as
aliases for compatibility reasons.

Also, it is now easier to catch a specific error condition.  Instead of
inspecting the ‘errno’ attribute (or ‘args[0]’) for a particular
constant from the *note errno: 7a. module, you can catch the adequate
*note OSError: 304. subclass.  The available subclasses are the
following:

   * *note BlockingIOError: a78.

   * *note ChildProcessError: a79.

   * *note ConnectionError: 7d7.

   * *note FileExistsError: a39.

   * *note FileNotFoundError: 8ad.

   * *note InterruptedError: 74c.

   * *note IsADirectoryError: a7a.

   * *note NotADirectoryError: a7b.

   * *note PermissionError: 6f6.

   * *note ProcessLookupError: a7c.

   * *note TimeoutError: a7d.

And the *note ConnectionError: 7d7. itself has finer-grained subclasses:

   * *note BrokenPipeError: a7e.

   * *note ConnectionAbortedError: a7f.

   * *note ConnectionRefusedError: a80.

   * *note ConnectionResetError: a81.

Thanks to the new exceptions, common usages of the *note errno: 7a. can
now be avoided.  For example, the following code written for Python 3.2:

     from errno import ENOENT, EACCES, EPERM

     try:
         with open("document.txt") as f:
             content = f.read()
     except IOError as err:
         if err.errno == ENOENT:
             print("document.txt file is missing")
         elif err.errno in (EACCES, EPERM):
             print("You are not allowed to read document.txt")
         else:
             raise

can now be written without the *note errno: 7a. import and without
manual inspection of exception attributes:

     try:
         with open("document.txt") as f:
             content = f.read()
     except FileNotFoundError:
         print("document.txt file is missing")
     except PermissionError:
         print("You are not allowed to read document.txt")

See also
........

PEP 3151(1) - Reworking the OS and IO Exception Hierarchy

     PEP written and implemented by Antoine Pitrou

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3151


File: python.info,  Node: PEP 380 Syntax for Delegating to a Subgenerator,  Next: PEP 409 Suppressing exception context,  Prev: PEP 3151 Reworking the OS and IO exception hierarchy,  Up: What’s New In Python 3 3

1.7.8 PEP 380: Syntax for Delegating to a Subgenerator
------------------------------------------------------

PEP 380 adds the ‘yield from’ expression, allowing a *note generator:
a83. to delegate part of its operations to another generator.  This
allows a section of code containing *note yield: 2c7. to be factored out
and placed in another generator.  Additionally, the subgenerator is
allowed to return with a value, and the value is made available to the
delegating generator.

While designed primarily for use in delegating to a subgenerator, the
‘yield from’ expression actually allows delegation to arbitrary
subiterators.

For simple iterators, ‘yield from iterable’ is essentially just a
shortened form of ‘for item in iterable: yield item’:

     >>> def g(x):
     ...     yield from range(x, 0, -1)
     ...     yield from range(x)
     ...
     >>> list(g(5))
     [5, 4, 3, 2, 1, 0, 1, 2, 3, 4]

However, unlike an ordinary loop, ‘yield from’ allows subgenerators to
receive sent and thrown values directly from the calling scope, and
return a final value to the outer generator:

     >>> def accumulate():
     ...     tally = 0
     ...     while 1:
     ...         next = yield
     ...         if next is None:
     ...             return tally
     ...         tally += next
     ...
     >>> def gather_tallies(tallies):
     ...     while 1:
     ...         tally = yield from accumulate()
     ...         tallies.append(tally)
     ...
     >>> tallies = []
     >>> acc = gather_tallies(tallies)
     >>> next(acc)  # Ensure the accumulator is ready to accept values
     >>> for i in range(4):
     ...     acc.send(i)
     ...
     >>> acc.send(None)  # Finish the first tally
     >>> for i in range(5):
     ...     acc.send(i)
     ...
     >>> acc.send(None)  # Finish the second tally
     >>> tallies
     [6, 10]

The main principle driving this change is to allow even generators that
are designed to be used with the ‘send’ and ‘throw’ methods to be split
into multiple subgenerators as easily as a single large function can be
split into multiple subfunctions.

See also
........

PEP 380(1) - Syntax for Delegating to a Subgenerator

     PEP written by Greg Ewing; implementation by Greg Ewing, integrated
     into 3.3 by Renaud Blanch, Ryan Kelly and Nick Coghlan;
     documentation by Zbigniew Jędrzejewski-Szmek and Nick Coghlan

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0380


File: python.info,  Node: PEP 409 Suppressing exception context,  Next: PEP 414 Explicit Unicode literals,  Prev: PEP 380 Syntax for Delegating to a Subgenerator,  Up: What’s New In Python 3 3

1.7.9 PEP 409: Suppressing exception context
--------------------------------------------

PEP 409 introduces new syntax that allows the display of the chained
exception context to be disabled.  This allows cleaner error messages in
applications that convert between exception types:

     >>> class D:
     ...     def __init__(self, extra):
     ...         self._extra_attributes = extra
     ...     def __getattr__(self, attr):
     ...         try:
     ...             return self._extra_attributes[attr]
     ...         except KeyError:
     ...             raise AttributeError(attr) from None
     ...
     >>> D({}).x
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
       File "<stdin>", line 8, in __getattr__
     AttributeError: x

Without the ‘from None’ suffix to suppress the cause, the original
exception would be displayed by default:

     >>> class C:
     ...     def __init__(self, extra):
     ...         self._extra_attributes = extra
     ...     def __getattr__(self, attr):
     ...         try:
     ...             return self._extra_attributes[attr]
     ...         except KeyError:
     ...             raise AttributeError(attr)
     ...
     >>> C({}).x
     Traceback (most recent call last):
       File "<stdin>", line 6, in __getattr__
     KeyError: 'x'

     During handling of the above exception, another exception occurred:

     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
       File "<stdin>", line 8, in __getattr__
     AttributeError: x

No debugging capability is lost, as the original exception context
remains available if needed (for example, if an intervening library has
incorrectly suppressed valuable underlying details):

     >>> try:
     ...     D({}).x
     ... except AttributeError as exc:
     ...     print(repr(exc.__context__))
     ...
     KeyError('x',)

See also
........

PEP 409(1) - Suppressing exception context

     PEP written by Ethan Furman; implemented by Ethan Furman and Nick
     Coghlan.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0409


File: python.info,  Node: PEP 414 Explicit Unicode literals,  Next: PEP 3155 Qualified name for classes and functions,  Prev: PEP 409 Suppressing exception context,  Up: What’s New In Python 3 3

1.7.10 PEP 414: Explicit Unicode literals
-----------------------------------------

To ease the transition from Python 2 for Unicode aware Python
applications that make heavy use of Unicode literals, Python 3.3 once
again supports the “‘u’” prefix for string literals.  This prefix has no
semantic significance in Python 3, it is provided solely to reduce the
number of purely mechanical changes in migrating to Python 3, making it
easier for developers to focus on the more significant semantic changes
(such as the stricter default separation of binary and text data).

See also
........

PEP 414(1) - Explicit Unicode literals

     PEP written by Armin Ronacher.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0414


File: python.info,  Node: PEP 3155 Qualified name for classes and functions,  Next: PEP 412 Key-Sharing Dictionary,  Prev: PEP 414 Explicit Unicode literals,  Up: What’s New In Python 3 3

1.7.11 PEP 3155: Qualified name for classes and functions
---------------------------------------------------------

Functions and class objects have a new ‘__qualname__’ attribute
representing the “path” from the module top-level to their definition.
For global functions and classes, this is the same as ‘__name__’.  For
other functions and classes, it provides better information about where
they were actually defined, and how they might be accessible from the
global scope.

Example with (non-bound) methods:

     >>> class C:
     ...     def meth(self):
     ...         pass
     >>> C.meth.__name__
     'meth'
     >>> C.meth.__qualname__
     'C.meth'

Example with nested classes:

     >>> class C:
     ...     class D:
     ...         def meth(self):
     ...             pass
     ...
     >>> C.D.__name__
     'D'
     >>> C.D.__qualname__
     'C.D'
     >>> C.D.meth.__name__
     'meth'
     >>> C.D.meth.__qualname__
     'C.D.meth'

Example with nested functions:

     >>> def outer():
     ...     def inner():
     ...         pass
     ...     return inner
     ...
     >>> outer().__name__
     'inner'
     >>> outer().__qualname__
     'outer.<locals>.inner'

The string representation of those objects is also changed to include
the new, more precise information:

     >>> str(C.D)
     "<class '__main__.C.D'>"
     >>> str(C.D.meth)
     '<function C.D.meth at 0x7f46b9fe31e0>'

See also
........

PEP 3155(1) - Qualified name for classes and functions

     PEP written and implemented by Antoine Pitrou.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3155


File: python.info,  Node: PEP 412 Key-Sharing Dictionary,  Next: PEP 362 Function Signature Object,  Prev: PEP 3155 Qualified name for classes and functions,  Up: What’s New In Python 3 3

1.7.12 PEP 412: Key-Sharing Dictionary
--------------------------------------

Dictionaries used for the storage of objects’ attributes are now able to
share part of their internal storage between each other (namely, the
part which stores the keys and their respective hashes).  This reduces
the memory consumption of programs creating many instances of
non-builtin types.

See also
........

PEP 412(1) - Key-Sharing Dictionary

     PEP written and implemented by Mark Shannon.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0412


File: python.info,  Node: PEP 362 Function Signature Object,  Next: PEP 421 Adding sys implementation,  Prev: PEP 412 Key-Sharing Dictionary,  Up: What’s New In Python 3 3

1.7.13 PEP 362: Function Signature Object
-----------------------------------------

A new function *note inspect.signature(): 655. makes introspection of
python callables easy and straightforward.  A broad range of callables
is supported: python functions, decorated or not, classes, and *note
functools.partial(): 8b5. objects.  New classes *note inspect.Signature:
7e4, *note inspect.Parameter: 7e5. and *note inspect.BoundArguments:
a89. hold information about the call signatures, such as, annotations,
default values, parameters kinds, and bound arguments, which
considerably simplifies writing decorators and any code that validates
or amends calling signatures or arguments.

See also
........

PEP 362(1): - Function Signature Object

     PEP written by Brett Cannon, Yury Selivanov, Larry Hastings, Jiwon
     Seo; implemented by Yury Selivanov.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0362


File: python.info,  Node: PEP 421 Adding sys implementation,  Next: Using importlib as the Implementation of Import,  Prev: PEP 362 Function Signature Object,  Up: What’s New In Python 3 3

1.7.14 PEP 421: Adding sys.implementation
-----------------------------------------

A new attribute on the *note sys: fd. module exposes details specific to
the implementation of the currently running interpreter.  The initial
set of attributes on *note sys.implementation: a8b. are ‘name’,
‘version’, ‘hexversion’, and ‘cache_tag’.

The intention of ‘sys.implementation’ is to consolidate into one
namespace the implementation-specific data used by the standard library.
This allows different Python implementations to share a single standard
library code base much more easily.  In its initial state,
‘sys.implementation’ holds only a small portion of the
implementation-specific data.  Over time that ratio will shift in order
to make the standard library more portable.

One example of improved standard library portability is ‘cache_tag’.  As
of Python 3.3, ‘sys.implementation.cache_tag’ is used by *note
importlib: 9a. to support PEP 3147(1) compliance.  Any Python
implementation that uses ‘importlib’ for its built-in import system may
use ‘cache_tag’ to control the caching behavior for modules.

* Menu:

* SimpleNamespace::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3147


File: python.info,  Node: SimpleNamespace,  Up: PEP 421 Adding sys implementation

1.7.14.1 SimpleNamespace
........................

The implementation of ‘sys.implementation’ also introduces a new type to
Python: *note types.SimpleNamespace: 1d8.  In contrast to a
mapping-based namespace, like *note dict: 164, ‘SimpleNamespace’ is
attribute-based, like *note object: 3d2.  However, unlike ‘object’,
‘SimpleNamespace’ instances are writable.  This means that you can add,
remove, and modify the namespace through normal attribute access.

See also
........

PEP 421(1) - Adding sys.implementation

     PEP written and implemented by Eric Snow.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0421


File: python.info,  Node: Using importlib as the Implementation of Import,  Next: Other Language Changes<7>,  Prev: PEP 421 Adding sys implementation,  Up: What’s New In Python 3 3

1.7.15 Using importlib as the Implementation of Import
------------------------------------------------------

bpo-2377(1) - Replace __import__ w/ importlib.__import__ bpo-13959(2) -
Re-implement parts of *note imp: 99. in pure Python bpo-14605(3) - Make
import machinery explicit bpo-14646(4) - Require loaders set __loader__
and __package__

The *note __import__(): 16b. function is now powered by *note
importlib.__import__(): a8e.  This work leads to the completion of
“phase 2” of PEP 302(5).  There are multiple benefits to this change.
First, it has allowed for more of the machinery powering import to be
exposed instead of being implicit and hidden within the C code.  It also
provides a single implementation for all Python VMs supporting Python
3.3 to use, helping to end any VM-specific deviations in import
semantics.  And finally it eases the maintenance of import, allowing for
future growth to occur.

For the common user, there should be no visible change in semantics.
For those whose code currently manipulates import or calls import
programmatically, the code changes that might possibly be required are
covered in the *note Porting Python code: a8f. section of this document.

* Menu:

* New APIs::
* Visible Changes::

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue2377

   (2) https://bugs.python.org/issue13959

   (3) https://bugs.python.org/issue14605

   (4) https://bugs.python.org/issue14646

   (5) https://www.python.org/dev/peps/pep-0302


File: python.info,  Node: New APIs,  Next: Visible Changes,  Up: Using importlib as the Implementation of Import

1.7.15.1 New APIs
.................

One of the large benefits of this work is the exposure of what goes into
making the import statement work.  That means the various importers that
were once implicit are now fully exposed as part of the *note importlib:
9a. package.

The abstract base classes defined in *note importlib.abc: 9b. have been
expanded to properly delineate between *note meta path finders: a91. and
*note path entry finders: a92. by introducing *note
importlib.abc.MetaPathFinder: a93. and *note
importlib.abc.PathEntryFinder: a94, respectively.  The old ABC of *note
importlib.abc.Finder: a95. is now only provided for
backwards-compatibility and does not enforce any method requirements.

In terms of finders, *note importlib.machinery.FileFinder: a96. exposes
the mechanism used to search for source and bytecode files of a module.
Previously this class was an implicit member of *note sys.path_hooks:
a3d.

For loaders, the new abstract base class *note importlib.abc.FileLoader:
a97. helps write a loader that uses the file system as the storage
mechanism for a module’s code.  The loader for source files (*note
importlib.machinery.SourceFileLoader: a98.), sourceless bytecode files
(*note importlib.machinery.SourcelessFileLoader: a99.), and extension
modules (*note importlib.machinery.ExtensionFileLoader: 650.) are now
available for direct use.

*note ImportError: 16c. now has ‘name’ and ‘path’ attributes which are
set when there is relevant data to provide.  The message for failed
imports will also provide the full name of the module now instead of
just the tail end of the module’s name.

The *note importlib.invalidate_caches(): 597. function will now call the
method with the same name on all finders cached in *note
sys.path_importer_cache: 598. to help clean up any stored state as
necessary.


File: python.info,  Node: Visible Changes,  Prev: New APIs,  Up: Using importlib as the Implementation of Import

1.7.15.2 Visible Changes
........................

For potential required changes to code, see the *note Porting Python
code: a8f. section.

Beyond the expanse of what *note importlib: 9a. now exposes, there are
other visible changes to import.  The biggest is that *note
sys.meta_path: 6dd. and *note sys.path_hooks: a3d. now store all of the
meta path finders and path entry hooks used by import.  Previously the
finders were implicit and hidden within the C code of import instead of
being directly exposed.  This means that one can now easily remove or
change the order of the various finders to fit one’s needs.

Another change is that all modules have a ‘__loader__’ attribute,
storing the loader used to create the module.  PEP 302(1) has been
updated to make this attribute mandatory for loaders to implement, so in
the future once 3rd-party loaders have been updated people will be able
to rely on the existence of the attribute.  Until such time, though,
import is setting the module post-load.

Loaders are also now expected to set the ‘__package__’ attribute from
PEP 366(2).  Once again, import itself is already setting this on all
loaders from *note importlib: 9a. and import itself is setting the
attribute post-load.

‘None’ is now inserted into *note sys.path_importer_cache: 598. when no
finder can be found on *note sys.path_hooks: a3d.  Since *note
imp.NullImporter: a9b. is not directly exposed on *note sys.path_hooks:
a3d. it could no longer be relied upon to always be available to use as
a value representing no finder found.

All other changes relate to semantic changes which should be taken into
consideration when updating code for Python 3.3, and thus should be read
about in the *note Porting Python code: a8f. section of this document.

(Implementation by Brett Cannon)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0302

   (2) https://www.python.org/dev/peps/pep-0366


File: python.info,  Node: Other Language Changes<7>,  Next: A Finer-Grained Import Lock,  Prev: Using importlib as the Implementation of Import,  Up: What’s New In Python 3 3

1.7.16 Other Language Changes
-----------------------------

Some smaller changes made to the core Python language are:

   * Added support for Unicode name aliases and named sequences.  Both
     *note unicodedata.lookup(): a9d. and ‘'\N{...}'’ now resolve name
     aliases, and *note unicodedata.lookup(): a9d. resolves named
     sequences too.

     (Contributed by Ezio Melotti in bpo-12753(1).)

   * Unicode database updated to UCD version 6.1.0

   * Equality comparisons on *note range(): 1f5. objects now return a
     result reflecting the equality of the underlying sequences
     generated by those range objects.  (bpo-13201(2))

   * The ‘count()’, ‘find()’, ‘rfind()’, ‘index()’ and ‘rindex()’
     methods of *note bytes: 172. and *note bytearray: 173. objects now
     accept an integer between 0 and 255 as their first argument.

     (Contributed by Petri Lehtinen in bpo-12170(3).)

   * The ‘rjust()’, ‘ljust()’, and ‘center()’ methods of *note bytes:
     172. and *note bytearray: 173. now accept a *note bytearray: 173.
     for the ‘fill’ argument.  (Contributed by Petri Lehtinen in
     bpo-12380(4).)

   * New methods have been added to *note list: 1f8. and *note
     bytearray: 173.: ‘copy()’ and ‘clear()’ (bpo-10516(5)).
     Consequently, *note MutableSequence: 79f. now also defines a
     ‘clear()’ method (bpo-11388(6)).

   * Raw bytes literals can now be written ‘rb"..."’ as well as
     ‘br"..."’.

     (Contributed by Antoine Pitrou in bpo-13748(7).)

   * *note dict.setdefault(): a9e. now does only one lookup for the
     given key, making it atomic when used with built-in types.

     (Contributed by Filip Gruszczyński in bpo-13521(8).)

   * The error messages produced when a function call does not match the
     function signature have been significantly improved.

     (Contributed by Benjamin Peterson.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12753

   (2) https://bugs.python.org/issue13201

   (3) https://bugs.python.org/issue12170

   (4) https://bugs.python.org/issue12380

   (5) https://bugs.python.org/issue10516

   (6) https://bugs.python.org/issue11388

   (7) https://bugs.python.org/issue13748

   (8) https://bugs.python.org/issue13521


File: python.info,  Node: A Finer-Grained Import Lock,  Next: Builtin functions and types,  Prev: Other Language Changes<7>,  Up: What’s New In Python 3 3

1.7.17 A Finer-Grained Import Lock
----------------------------------

Previous versions of CPython have always relied on a global import lock.
This led to unexpected annoyances, such as deadlocks when importing a
module would trigger code execution in a different thread as a
side-effect.  Clumsy workarounds were sometimes employed, such as the
*note PyImport_ImportModuleNoBlock(): aa0. C API function.

In Python 3.3, importing a module takes a per-module lock.  This
correctly serializes importation of a given module from multiple threads
(preventing the exposure of incompletely initialized modules), while
eliminating the aforementioned annoyances.

(Contributed by Antoine Pitrou in bpo-9260(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9260


File: python.info,  Node: Builtin functions and types,  Next: New Modules<7>,  Prev: A Finer-Grained Import Lock,  Up: What’s New In Python 3 3

1.7.18 Builtin functions and types
----------------------------------

   * *note open(): 16f. gets a new `opener' parameter: the underlying
     file descriptor for the file object is then obtained by calling
     `opener' with (`file', `flags').  It can be used to use custom
     flags like *note os.O_CLOEXEC: aa2. for example.  The ‘'x'’ mode
     was added: open for exclusive creation, failing if the file already
     exists.

   * *note print(): 971.: added the `flush' keyword argument.  If the
     `flush' keyword argument is true, the stream is forcibly flushed.

   * *note hash(): aa3.: hash randomization is enabled by default, see
     *note object.__hash__(): 44c. and *note PYTHONHASHSEED: aa4.

   * The *note str: 205. type gets a new *note casefold(): 7a3. method:
     return a casefolded copy of the string, casefolded strings may be
     used for caseless matching.  For example, ‘'ß'.casefold()’ returns
     ‘'ss'’.

   * The sequence documentation has been substantially rewritten to
     better explain the binary/text sequence distinction and to provide
     specific documentation sections for the individual builtin sequence
     types (bpo-4966(1)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4966


File: python.info,  Node: New Modules<7>,  Next: Improved Modules<7>,  Prev: Builtin functions and types,  Up: What’s New In Python 3 3

1.7.19 New Modules
------------------

* Menu:

* faulthandler: faulthandler<3>.
* ipaddress: ipaddress<5>.
* lzma: lzma<2>.


File: python.info,  Node: faulthandler<3>,  Next: ipaddress<5>,  Up: New Modules<7>

1.7.19.1 faulthandler
.....................

This new debug module *note faulthandler: 7b. contains functions to dump
Python tracebacks explicitly, on a fault (a crash like a segmentation
fault), after a timeout, or on a user signal.  Call *note
faulthandler.enable(): 642. to install fault handlers for the ‘SIGSEGV’,
‘SIGFPE’, ‘SIGABRT’, ‘SIGBUS’, and ‘SIGILL’ signals.  You can also
enable them at startup by setting the *note PYTHONFAULTHANDLER: aa7.
environment variable or by using *note -X: 290. ‘faulthandler’ command
line option.

Example of a segmentation fault on Linux:

     $ python -q -X faulthandler
     >>> import ctypes
     >>> ctypes.string_at(0)
     Fatal Python error: Segmentation fault

     Current thread 0x00007fb899f39700:
       File "/home/python/cpython/Lib/ctypes/__init__.py", line 486 in string_at
       File "<stdin>", line 1 in <module>
     Segmentation fault


File: python.info,  Node: ipaddress<5>,  Next: lzma<2>,  Prev: faulthandler<3>,  Up: New Modules<7>

1.7.19.2 ipaddress
..................

The new *note ipaddress: a2. module provides tools for creating and
manipulating objects representing IPv4 and IPv6 addresses, networks and
interfaces (i.e.  an IP address associated with a specific IP subnet).

(Contributed by Google and Peter Moody in PEP 3144(1).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3144


File: python.info,  Node: lzma<2>,  Prev: ipaddress<5>,  Up: New Modules<7>

1.7.19.3 lzma
.............

The newly-added *note lzma: ad. module provides data compression and
decompression using the LZMA algorithm, including support for the ‘.xz’
and ‘.lzma’ file formats.

(Contributed by Nadeem Vawda and Per Øyvind Karlsen in bpo-6715(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue6715


File: python.info,  Node: Improved Modules<7>,  Next: Optimizations<6>,  Prev: New Modules<7>,  Up: What’s New In Python 3 3

1.7.20 Improved Modules
-----------------------

* Menu:

* abc: abc<2>.
* array: array<2>.
* base64: base64<2>.
* binascii: binascii<3>.
* bz2: bz2<2>.
* codecs::
* collections: collections<7>.
* contextlib: contextlib<5>.
* crypt: crypt<2>.
* curses: curses<4>.
* datetime: datetime<5>.
* decimal: decimal<3>.
* email: email<4>.
* ftplib: ftplib<2>.
* functools: functools<5>.
* gc: gc<5>.
* hmac: hmac<3>.
* http: http<4>.
* html: html<2>.
* imaplib: imaplib<3>.
* inspect: inspect<6>.
* io: io<4>.
* itertools: itertools<3>.
* logging: logging<6>.
* math: math<6>.
* mmap: mmap<3>.
* multiprocessing: multiprocessing<7>.
* nntplib: nntplib<2>.
* os: os<8>.
* pdb: pdb<5>.
* pickle: pickle<5>.
* pydoc: pydoc<5>.
* re: re<6>.
* sched::
* select: select<2>.
* shlex: shlex<3>.
* shutil: shutil<4>.
* signal: signal<4>.
* smtpd: smtpd<3>.
* smtplib: smtplib<4>.
* socket: socket<8>.
* socketserver: socketserver<3>.
* sqlite3: sqlite3<5>.
* ssl: ssl<8>.
* stat: stat<2>.
* struct: struct<3>.
* subprocess: subprocess<5>.
* sys: sys<8>.
* tarfile: tarfile<4>.
* tempfile::
* textwrap: textwrap<2>.
* threading: threading<5>.
* time: time<6>.
* types: types<4>.
* unittest: unittest<5>.
* urllib: urllib<3>.
* webbrowser::
* xml.etree.ElementTree: xml etree ElementTree.
* zlib: zlib<2>.


File: python.info,  Node: abc<2>,  Next: array<2>,  Up: Improved Modules<7>

1.7.20.1 abc
............

Improved support for abstract base classes containing descriptors
composed with abstract methods.  The recommended approach to declaring
abstract descriptors is now to provide ‘__isabstractmethod__’ as a
dynamically updated property.  The built-in descriptors have been
updated accordingly.

        * *note abc.abstractproperty: aac. has been deprecated, use
          *note property: 308. with *note abc.abstractmethod(): aad.
          instead.

        * *note abc.abstractclassmethod: aae. has been deprecated, use
          *note classmethod: 309. with *note abc.abstractmethod(): aad.
          instead.

        * *note abc.abstractstaticmethod: aaf. has been deprecated, use
          *note staticmethod: 30a. with *note abc.abstractmethod(): aad.
          instead.

(Contributed by Darren Dale in bpo-11610(1).)

*note abc.ABCMeta.register(): ab0. now returns the registered subclass,
which means it can now be used as a class decorator (bpo-10868(2)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11610

   (2) https://bugs.python.org/issue10868


File: python.info,  Node: array<2>,  Next: base64<2>,  Prev: abc<2>,  Up: Improved Modules<7>

1.7.20.2 array
..............

The *note array: 6. module supports the ‘long long’ type using ‘q’ and
‘Q’ type codes.

(Contributed by Oren Tirosh and Hirokazu Yamamoto in bpo-1172711(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1172711


File: python.info,  Node: base64<2>,  Next: binascii<3>,  Prev: array<2>,  Up: Improved Modules<7>

1.7.20.3 base64
...............

ASCII-only Unicode strings are now accepted by the decoding functions of
the *note base64: d. modern interface.  For example,
‘base64.b64decode('YWJj')’ returns ‘b'abc'’.  (Contributed by Catalin
Iacob in bpo-13641(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13641


File: python.info,  Node: binascii<3>,  Next: bz2<2>,  Prev: base64<2>,  Up: Improved Modules<7>

1.7.20.4 binascii
.................

In addition to the binary objects they normally accept, the ‘a2b_’
functions now all also accept ASCII-only strings as input.  (Contributed
by Antoine Pitrou in bpo-13637(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13637


File: python.info,  Node: bz2<2>,  Next: codecs,  Prev: binascii<3>,  Up: Improved Modules<7>

1.7.20.5 bz2
............

The *note bz2: 13. module has been rewritten from scratch.  In the
process, several new features have been added:

   * New *note bz2.open(): ab5. function: open a bzip2-compressed file
     in binary or text mode.

   * *note bz2.BZ2File: 224. can now read from and write to arbitrary
     file-like objects, by means of its constructor’s `fileobj'
     argument.

     (Contributed by Nadeem Vawda in bpo-5863(1).)

   * *note bz2.BZ2File: 224. and *note bz2.decompress(): ab6. can now
     decompress multi-stream inputs (such as those produced by the
     ‘pbzip2’ tool).  *note bz2.BZ2File: 224. can now also be used to
     create this type of file, using the ‘'a'’ (append) mode.

     (Contributed by Nir Aides in bpo-1625(2).)

   * *note bz2.BZ2File: 224. now implements all of the *note
     io.BufferedIOBase: 67f. API, except for the ‘detach()’ and
     ‘truncate()’ methods.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5863

   (2) https://bugs.python.org/issue1625


File: python.info,  Node: codecs,  Next: collections<7>,  Prev: bz2<2>,  Up: Improved Modules<7>

1.7.20.6 codecs
...............

The *note mbcs: 76. codec has been rewritten to handle correctly
‘replace’ and ‘ignore’ error handlers on all Windows versions.  The
*note mbcs: 76. codec now supports all error handlers, instead of only
‘replace’ to encode and ‘ignore’ to decode.

A new Windows-only codec has been added: ‘cp65001’ (bpo-13216(1)).  It
is the Windows code page 65001 (Windows UTF-8, ‘CP_UTF8’).  For example,
it is used by ‘sys.stdout’ if the console output code page is set to
cp65001 (e.g., using ‘chcp 65001’ command).

Multibyte CJK decoders now resynchronize faster.  They only ignore the
first byte of an invalid byte sequence.  For example,
‘b'\xff\n'.decode('gb2312', 'replace')’ now returns a ‘\n’ after the
replacement character.

(bpo-12016(2))

Incremental CJK codec encoders are no longer reset at each call to their
encode() methods.  For example:

     >>> import codecs
     >>> encoder = codecs.getincrementalencoder('hz')('strict')
     >>> b''.join(encoder.encode(x) for x in '\u52ff\u65bd\u65bc\u4eba\u3002 Bye.')
     b'~{NpJ)l6HK!#~} Bye.'

This example gives ‘b'~{Np~}~{J)~}~{l6~}~{HK~}~{!#~} Bye.'’ with older
Python versions.

(bpo-12100(3))

The ‘unicode_internal’ codec has been deprecated.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13216

   (2) https://bugs.python.org/issue12016

   (3) https://bugs.python.org/issue12100


File: python.info,  Node: collections<7>,  Next: contextlib<5>,  Prev: codecs,  Up: Improved Modules<7>

1.7.20.7 collections
....................

Addition of a new *note ChainMap: 5a4. class to allow treating a number
of mappings as a single unit.  (Written by Raymond Hettinger for
bpo-11089(1), made public in bpo-11297(2).)

The abstract base classes have been moved in a new *note
collections.abc: 1e. module, to better differentiate between the
abstract and the concrete collections classes.  Aliases for ABCs are
still present in the *note collections: 1d. module to preserve existing
imports.  (bpo-11085(3))

The *note Counter: ab9. class now supports the unary ‘+’ and ‘-’
operators, as well as the in-place operators ‘+=’, ‘-=’, ‘|=’, and ‘&=’.
(Contributed by Raymond Hettinger in bpo-13121(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11089

   (2) https://bugs.python.org/issue11297

   (3) https://bugs.python.org/issue11085

   (4) https://bugs.python.org/issue13121


File: python.info,  Node: contextlib<5>,  Next: crypt<2>,  Prev: collections<7>,  Up: Improved Modules<7>

1.7.20.8 contextlib
...................

*note ExitStack: 47e. now provides a solid foundation for programmatic
manipulation of context managers and similar cleanup functionality.
Unlike the previous ‘contextlib.nested’ API (which was deprecated and
removed), the new API is designed to work correctly regardless of
whether context managers acquire their resources in their ‘__init__’
method (for example, file objects) or in their ‘__enter__’ method (for
example, synchronisation objects from the *note threading: 10b. module).

(bpo-13585(1))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13585


File: python.info,  Node: crypt<2>,  Next: curses<4>,  Prev: contextlib<5>,  Up: Improved Modules<7>

1.7.20.9 crypt
..............

Addition of salt and modular crypt format (hashing method) and the *note
mksalt(): 484. function to the *note crypt: 28. module.

(bpo-10924(1))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10924


File: python.info,  Node: curses<4>,  Next: datetime<5>,  Prev: crypt<2>,  Up: Improved Modules<7>

1.7.20.10 curses
................

        * If the *note curses: 2b. module is linked to the ncursesw
          library, use Unicode functions when Unicode strings or
          characters are passed (e.g.  ‘waddwstr()’), and bytes
          functions otherwise (e.g.  ‘waddstr()’).

        * Use the locale encoding instead of ‘utf-8’ to encode Unicode
          strings.

        * ‘curses.window’ has a new *note curses.window.encoding: abd.
          attribute.

        * The ‘curses.window’ class has a new *note get_wch(): abe.
          method to get a wide character

        * The *note curses: 2b. module has a new *note unget_wch(): abf.
          function to push a wide character so the next *note get_wch():
          abe. will return it

(Contributed by Iñigo Serna in bpo-6755(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue6755


File: python.info,  Node: datetime<5>,  Next: decimal<3>,  Prev: curses<4>,  Up: Improved Modules<7>

1.7.20.11 datetime
..................

        * Equality comparisons between naive and aware *note datetime:
          1a0. instances now return *note False: 48f. instead of raising
          *note TypeError: 1fe. (bpo-15006(1)).

        * New *note datetime.datetime.timestamp(): ac1. method: Return
          POSIX timestamp corresponding to the *note datetime: 1a0.
          instance.

        * The *note datetime.datetime.strftime(): 631. method supports
          formatting years older than 1000.

        * The *note datetime.datetime.astimezone(): 2cb. method can now
          be called without arguments to convert datetime instance to
          the system timezone.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15006


File: python.info,  Node: decimal<3>,  Next: email<4>,  Prev: datetime<5>,  Up: Improved Modules<7>

1.7.20.12 decimal
.................

bpo-7652(1) - integrate fast native decimal arithmetic.

     C-module and libmpdec written by Stefan Krah.

The new C version of the decimal module integrates the high speed
libmpdec library for arbitrary precision correctly-rounded decimal
floating point arithmetic.  libmpdec conforms to IBM’s General Decimal
Arithmetic Specification.

Performance gains range from 10x for database applications to 100x for
numerically intensive applications.  These numbers are expected gains
for standard precisions used in decimal floating point arithmetic.
Since the precision is user configurable, the exact figures may vary.
For example, in integer bignum arithmetic the differences can be
significantly higher.

The following table is meant as an illustration.  Benchmarks are
available at ‘http://www.bytereef.org/mpdecimal/quickstart.html’.

                   decimal.py        _decimal           speedup
                                                        
     ---------------------------------------------------------------------
                                                        
     pi            42.02s            0.345s             120x
                                                        
                                                        
     telco         172.19s           5.68s              30x
                                                        
                                                        
     psycopg       3.57s             0.29s              12x
                                                        

* Menu:

* Features: Features<2>.
* API changes: API changes<2>.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue7652


File: python.info,  Node: Features<2>,  Next: API changes<2>,  Up: decimal<3>

1.7.20.13 Features
..................

   * The *note FloatOperation: ac4. signal optionally enables stricter
     semantics for mixing floats and Decimals.

   * If Python is compiled without threads, the C version automatically
     disables the expensive thread local context machinery.  In this
     case, the variable *note HAVE_THREADS: ac5. is set to ‘False’.


File: python.info,  Node: API changes<2>,  Prev: Features<2>,  Up: decimal<3>

1.7.20.14 API changes
.....................

   * The C module has the following context limits, depending on the
     machine architecture:

                                  32-bit                    64-bit
                                                            
          -------------------------------------------------------------------------------------
                                                            
          ‘MAX_PREC’              ‘425000000’               ‘999999999999999999’
                                                            
                                                            
          ‘MAX_EMAX’              ‘425000000’               ‘999999999999999999’
                                                            
                                                            
          ‘MIN_EMIN’              ‘-425000000’              ‘-999999999999999999’
                                                            

   * In the context templates (*note DefaultContext: ac7, *note
     BasicContext: ac8. and *note ExtendedContext: ac9.) the magnitude
     of ‘Emax’ and ‘Emin’ has changed to ‘999999’.

   * The *note Decimal: 2c0. constructor in decimal.py does not observe
     the context limits and converts values with arbitrary exponents or
     precision exactly.  Since the C version has internal limits, the
     following scheme is used: If possible, values are converted
     exactly, otherwise *note InvalidOperation: aca. is raised and the
     result is NaN. In the latter case it is always possible to use
     *note create_decimal(): acb. in order to obtain a rounded or
     inexact value.

   * The power function in decimal.py is always correctly-rounded.  In
     the C version, it is defined in terms of the correctly-rounded
     *note exp(): acc. and *note ln(): acd. functions, but the final
     result is only “almost always correctly rounded”.

   * In the C version, the context dictionary containing the signals is
     a *note MutableMapping: ace.  For speed reasons, ‘flags’ and
     ‘traps’ always refer to the same *note MutableMapping: ace. that
     the context was initialized with.  If a new signal dictionary is
     assigned, ‘flags’ and ‘traps’ are updated with the new values, but
     they do not reference the RHS dictionary.

   * Pickling a *note Context: acf. produces a different output in order
     to have a common interchange format for the Python and C versions.

   * The order of arguments in the *note Context: acf. constructor has
     been changed to match the order displayed by *note repr(): 8b9.

   * The ‘watchexp’ parameter in the *note quantize(): ad0. method is
     deprecated.


File: python.info,  Node: email<4>,  Next: ftplib<2>,  Prev: decimal<3>,  Up: Improved Modules<7>

1.7.20.15 email
...............

* Menu:

* Policy Framework::
* Provisional Policy with New Header API::
* Other API Changes::


File: python.info,  Node: Policy Framework,  Next: Provisional Policy with New Header API,  Up: email<4>

1.7.20.16 Policy Framework
..........................

The email package now has a *note policy: 73. framework.  A *note
Policy: ad3. is an object with several methods and properties that
control how the email package behaves.  The primary policy for Python
3.3 is the *note Compat32: ad4. policy, which provides backward
compatibility with the email package in Python 3.2.  A ‘policy’ can be
specified when an email message is parsed by a *note parser: 72, or when
a *note Message: 63b. object is created, or when an email is serialized
using a *note generator: 6c.  Unless overridden, a policy passed to a
‘parser’ is inherited by all the ‘Message’ object and sub-objects
created by the ‘parser’.  By default a ‘generator’ will use the policy
of the ‘Message’ object it is serializing.  The default policy is *note
compat32: 63a.

The minimum set of controls implemented by all ‘policy’ objects are:

     max_line_length     The maximum length, excluding the linesep character(s),
                         individual lines may have when a ‘Message’ is serialized.
                         Defaults to 78.
                         
                         
     linesep             The character used to separate individual lines when a
                         ‘Message’ is serialized.  Defaults to ‘\n’.
                         
                         
     cte_type            ‘7bit’ or ‘8bit’.  ‘8bit’ applies only to a ‘Bytes’
                         ‘generator’, and means that non-ASCII may be used where
                         allowed by the protocol (or where it exists in the
                         original input).
                         
                         
     raise_on_defect     Causes a ‘parser’ to raise error when defects are
                         encountered instead of adding them to the ‘Message’
                         object’s ‘defects’ list.
                         

A new policy instance, with new settings, is created using the *note
clone(): ad5. method of policy objects.  ‘clone’ takes any of the above
controls as keyword arguments.  Any control not specified in the call
retains its default value.  Thus you can create a policy that uses
‘\r\n’ linesep characters like this:

     mypolicy = compat32.clone(linesep='\r\n')

Policies can be used to make the generation of messages in the format
needed by your application simpler.  Instead of having to remember to
specify ‘linesep='\r\n'’ in all the places you call a ‘generator’, you
can specify it once, when you set the policy used by the ‘parser’ or the
‘Message’, whichever your program uses to create ‘Message’ objects.  On
the other hand, if you need to generate messages in multiple forms, you
can still specify the parameters in the appropriate ‘generator’ call.
Or you can have custom policy instances for your different cases, and
pass those in when you create the ‘generator’.


File: python.info,  Node: Provisional Policy with New Header API,  Next: Other API Changes,  Prev: Policy Framework,  Up: email<4>

1.7.20.17 Provisional Policy with New Header API
................................................

While the policy framework is worthwhile all by itself, the main
motivation for introducing it is to allow the creation of new policies
that implement new features for the email package in a way that
maintains backward compatibility for those who do not use the new
policies.  Because the new policies introduce a new API, we are
releasing them in Python 3.3 as a *note provisional policy: a61.
Backwards incompatible changes (up to and including removal of the code)
may occur if deemed necessary by the core developers.

The new policies are instances of *note EmailPolicy: ad7, and add the
following additional controls:

     refold_source       Controls whether or not headers parsed by a
                         *note parser: 72. are refolded by the
                         *note generator: 6c.  It can be ‘none’, ‘long’, or ‘all’.
                         The default is ‘long’, which means that source headers
                         with a line longer than ‘max_line_length’ get refolded.
                         ‘none’ means no line get refolded, and ‘all’ means that
                         all lines get refolded.
                         
                         
     header_factory      A callable that take a ‘name’ and ‘value’ and produces a
                         custom header object.
                         

The ‘header_factory’ is the key to the new features provided by the new
policies.  When one of the new policies is used, any header retrieved
from a ‘Message’ object is an object produced by the ‘header_factory’,
and any time you set a header on a ‘Message’ it becomes an object
produced by ‘header_factory’.  All such header objects have a ‘name’
attribute equal to the header name.  Address and Date headers have
additional attributes that give you access to the parsed data of the
header.  This means you can now do things like this:

     >>> m = Message(policy=SMTP)
     >>> m['To'] = 'Éric <foo@example.com>'
     >>> m['to']
     'Éric <foo@example.com>'
     >>> m['to'].addresses
     (Address(display_name='Éric', username='foo', domain='example.com'),)
     >>> m['to'].addresses[0].username
     'foo'
     >>> m['to'].addresses[0].display_name
     'Éric'
     >>> m['Date'] = email.utils.localtime()
     >>> m['Date'].datetime
     datetime.datetime(2012, 5, 25, 21, 39, 24, 465484, tzinfo=datetime.timezone(datetime.timedelta(-1, 72000), 'EDT'))
     >>> m['Date']
     'Fri, 25 May 2012 21:44:27 -0400'
     >>> print(m)
     To: =?utf-8?q?=C3=89ric?= <foo@example.com>
     Date: Fri, 25 May 2012 21:44:27 -0400

You will note that the unicode display name is automatically encoded as
‘utf-8’ when the message is serialized, but that when the header is
accessed directly, you get the unicode version.  This eliminates any
need to deal with the *note email.header: 6d. *note decode_header():
ad8. or *note make_header(): ad9. functions.

You can also create addresses from parts:

     >>> m['cc'] = [Group('pals', [Address('Bob', 'bob', 'example.com'),
     ...                           Address('Sally', 'sally', 'example.com')]),
     ...            Address('Bonzo', addr_spec='bonz@laugh.com')]
     >>> print(m)
     To: =?utf-8?q?=C3=89ric?= <foo@example.com>
     Date: Fri, 25 May 2012 21:44:27 -0400
     cc: pals: Bob <bob@example.com>, Sally <sally@example.com>;, Bonzo <bonz@laugh.com>

Decoding to unicode is done automatically:

     >>> m2 = message_from_string(str(m))
     >>> m2['to']
     'Éric <foo@example.com>'

When you parse a message, you can use the ‘addresses’ and ‘groups’
attributes of the header objects to access the groups and individual
addresses:

     >>> m2['cc'].addresses
     (Address(display_name='Bob', username='bob', domain='example.com'), Address(display_name='Sally', username='sally', domain='example.com'), Address(display_name='Bonzo', username='bonz', domain='laugh.com'))
     >>> m2['cc'].groups
     (Group(display_name='pals', addresses=(Address(display_name='Bob', username='bob', domain='example.com'), Address(display_name='Sally', username='sally', domain='example.com')), Group(display_name=None, addresses=(Address(display_name='Bonzo', username='bonz', domain='laugh.com'),))

In summary, if you use one of the new policies, header manipulation
works the way it ought to: your application works with unicode strings,
and the email package transparently encodes and decodes the unicode to
and from the RFC standard Content Transfer Encodings.


File: python.info,  Node: Other API Changes,  Prev: Provisional Policy with New Header API,  Up: email<4>

1.7.20.18 Other API Changes
...........................

New *note BytesHeaderParser: adb, added to the *note parser: 72. module
to complement *note HeaderParser: adc. and complete the Bytes API.

New utility functions:

        * *note format_datetime(): add.: given a *note datetime: 1a0,
          produce a string formatted for use in an email header.

        * *note parsedate_to_datetime(): ade.: given a date string from
          an email header, convert it into an aware *note datetime: 1a0,
          or a naive *note datetime: 1a0. if the offset is ‘-0000’.

        * *note localtime(): adf.: With no argument, returns the current
          local time as an aware *note datetime: 1a0. using the local
          *note timezone: ae0.  Given an aware *note datetime: 1a0,
          converts it into an aware *note datetime: 1a0. using the local
          *note timezone: ae0.


File: python.info,  Node: ftplib<2>,  Next: functools<5>,  Prev: email<4>,  Up: Improved Modules<7>

1.7.20.19 ftplib
................

   * *note ftplib.FTP: 1a6. now accepts a ‘source_address’ keyword
     argument to specify the ‘(host, port)’ to use as the source address
     in the bind call when creating the outgoing socket.  (Contributed
     by Giampaolo Rodolà in bpo-8594(1).)

   * The *note FTP_TLS: 1a7. class now provides a new *note ccc(): ae2.
     function to revert control channel back to plaintext.  This can be
     useful to take advantage of firewalls that know how to handle NAT
     with non-secure FTP without opening fixed ports.  (Contributed by
     Giampaolo Rodolà in bpo-12139(2).)

   * Added *note ftplib.FTP.mlsd(): ae3. method which provides a
     parsable directory listing format and deprecates *note
     ftplib.FTP.nlst(): ae4. and *note ftplib.FTP.dir(): ae5.
     (Contributed by Giampaolo Rodolà in bpo-11072(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8594

   (2) https://bugs.python.org/issue12139

   (3) https://bugs.python.org/issue11072


File: python.info,  Node: functools<5>,  Next: gc<5>,  Prev: ftplib<2>,  Up: Improved Modules<7>

1.7.20.20 functools
...................

The *note functools.lru_cache(): 2f8. decorator now accepts a ‘typed’
keyword argument (that defaults to ‘False’ to ensure that it caches
values of different types that compare equal in separate cache slots.
(Contributed by Raymond Hettinger in bpo-13227(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13227


File: python.info,  Node: gc<5>,  Next: hmac<3>,  Prev: functools<5>,  Up: Improved Modules<7>

1.7.20.21 gc
............

It is now possible to register callbacks invoked by the garbage
collector before and after collection using the new *note callbacks:
ae8. list.


File: python.info,  Node: hmac<3>,  Next: http<4>,  Prev: gc<5>,  Up: Improved Modules<7>

1.7.20.22 hmac
..............

A new *note compare_digest(): aea. function has been added to prevent
side channel attacks on digests through timing analysis.  (Contributed
by Nick Coghlan and Christian Heimes in bpo-15061(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15061


File: python.info,  Node: http<4>,  Next: html<2>,  Prev: hmac<3>,  Up: Improved Modules<7>

1.7.20.23 http
..............

*note http.server.BaseHTTPRequestHandler: aec. now buffers the headers
and writes them all at once when *note end_headers(): aed. is called.  A
new method *note flush_headers(): aee. can be used to directly manage
when the accumulated headers are sent.  (Contributed by Andrew Schaaf in
bpo-3709(1).)

*note http.server: 96. now produces valid ‘HTML 4.01 strict’ output.
(Contributed by Ezio Melotti in bpo-13295(2).)

*note http.client.HTTPResponse: aef. now has a *note readinto(): af0.
method, which means it can be used as an *note io.RawIOBase: af1. class.
(Contributed by John Kuhn in bpo-13464(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue3709

   (2) https://bugs.python.org/issue13295

   (3) https://bugs.python.org/issue13464


File: python.info,  Node: html<2>,  Next: imaplib<3>,  Prev: http<4>,  Up: Improved Modules<7>

1.7.20.24 html
..............

*note html.parser.HTMLParser: 22a. is now able to parse broken markup
without raising errors, therefore the `strict' argument of the
constructor and the ‘HTMLParseError’ exception are now deprecated.  The
ability to parse broken markup is the result of a number of bug fixes
that are also available on the latest bug fix releases of Python
2.7/3.2.  (Contributed by Ezio Melotti in bpo-15114(1), and
bpo-14538(2), bpo-13993(3), bpo-13960(4), bpo-13358(5), bpo-1745761(6),
bpo-755670(7), bpo-13357(8), bpo-12629(9), bpo-1200313(10),
bpo-670664(11), bpo-13273(12), bpo-12888(13), bpo-7311(14).)

A new *note html5: af3. dictionary that maps HTML5 named character
references to the equivalent Unicode character(s) (e.g.  ‘html5['gt;']
== '>'’) has been added to the *note html.entities: 90. module.  The
dictionary is now also used by *note HTMLParser: 22a.  (Contributed by
Ezio Melotti in bpo-11113(15) and bpo-15156(16).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15114

   (2) https://bugs.python.org/issue14538

   (3) https://bugs.python.org/issue13993

   (4) https://bugs.python.org/issue13960

   (5) https://bugs.python.org/issue13358

   (6) https://bugs.python.org/issue1745761

   (7) https://bugs.python.org/issue755670

   (8) https://bugs.python.org/issue13357

   (9) https://bugs.python.org/issue12629

   (10) https://bugs.python.org/issue1200313

   (11) https://bugs.python.org/issue670664

   (12) https://bugs.python.org/issue13273

   (13) https://bugs.python.org/issue12888

   (14) https://bugs.python.org/issue7311

   (15) https://bugs.python.org/issue11113

   (16) https://bugs.python.org/issue15156


File: python.info,  Node: imaplib<3>,  Next: inspect<6>,  Prev: html<2>,  Up: Improved Modules<7>

1.7.20.25 imaplib
.................

The *note IMAP4_SSL: 1b0. constructor now accepts an SSLContext
parameter to control parameters of the secure channel.

(Contributed by Sijin Joseph in bpo-8808(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8808


File: python.info,  Node: inspect<6>,  Next: io<4>,  Prev: imaplib<3>,  Up: Improved Modules<7>

1.7.20.26 inspect
.................

A new *note getclosurevars(): af6. function has been added.  This
function reports the current binding of all names referenced from the
function body and where those names were resolved, making it easier to
verify correct internal state when testing code that relies on stateful
closures.

(Contributed by Meador Inge and Nick Coghlan in bpo-13062(1).)

A new *note getgeneratorlocals(): af7. function has been added.  This
function reports the current binding of local variables in the
generator’s stack frame, making it easier to verify correct internal
state when testing generators.

(Contributed by Meador Inge in bpo-15153(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13062

   (2) https://bugs.python.org/issue15153


File: python.info,  Node: io<4>,  Next: itertools<3>,  Prev: inspect<6>,  Up: Improved Modules<7>

1.7.20.27 io
............

The *note open(): 74d. function has a new ‘'x'’ mode that can be used to
exclusively create a new file, and raise a *note FileExistsError: a39.
if the file already exists.  It is based on the C11 ‘x’ mode to fopen().

(Contributed by David Townshend in bpo-12760(1).)

The constructor of the *note TextIOWrapper: 6ea. class has a new
`write_through' optional argument.  If `write_through' is ‘True’, calls
to ‘write()’ are guaranteed not to be buffered: any data written on the
*note TextIOWrapper: 6ea. object is immediately handled to its
underlying binary buffer.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12760


File: python.info,  Node: itertools<3>,  Next: logging<6>,  Prev: io<4>,  Up: Improved Modules<7>

1.7.20.28 itertools
...................

*note accumulate(): 30e. now takes an optional ‘func’ argument for
providing a user-supplied binary function.


File: python.info,  Node: logging<6>,  Next: math<6>,  Prev: itertools<3>,  Up: Improved Modules<7>

1.7.20.29 logging
.................

The *note basicConfig(): 311. function now supports an optional
‘handlers’ argument taking an iterable of handlers to be added to the
root logger.

A class level attribute ‘append_nul’ has been added to *note
SysLogHandler: afb. to allow control of the appending of the ‘NUL’
(‘\000’) byte to syslog records, since for some daemons it is required
while for others it is passed through to the log.


File: python.info,  Node: math<6>,  Next: mmap<3>,  Prev: logging<6>,  Up: Improved Modules<7>

1.7.20.30 math
..............

The *note math: b1. module has a new function, *note log2(): afd, which
returns the base-2 logarithm of `x'.

(Written by Mark Dickinson in bpo-11888(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11888


File: python.info,  Node: mmap<3>,  Next: multiprocessing<7>,  Prev: math<6>,  Up: Improved Modules<7>

1.7.20.31 mmap
..............

The *note read(): aff. method is now more compatible with other
file-like objects: if the argument is omitted or specified as ‘None’, it
returns the bytes from the current file position to the end of the
mapping.  (Contributed by Petri Lehtinen in bpo-12021(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12021


File: python.info,  Node: multiprocessing<7>,  Next: nntplib<2>,  Prev: mmap<3>,  Up: Improved Modules<7>

1.7.20.32 multiprocessing
.........................

The new *note multiprocessing.connection.wait(): b01. function allows
polling multiple objects (such as connections, sockets and pipes) with a
timeout.  (Contributed by Richard Oudkerk in bpo-12328(1).)

‘multiprocessing.Connection’ objects can now be transferred over
multiprocessing connections.  (Contributed by Richard Oudkerk in
bpo-4892(2).)

*note multiprocessing.Process: 4b9. now accepts a ‘daemon’ keyword
argument to override the default behavior of inheriting the ‘daemon’
flag from the parent process (bpo-6064(3)).

New attribute *note multiprocessing.Process.sentinel: b02. allows a
program to wait on multiple *note Process: 4b9. objects at one time
using the appropriate OS primitives (for example, *note select: e5. on
posix systems).

New methods *note multiprocessing.pool.Pool.starmap(): b03. and *note
starmap_async(): b04. provide *note itertools.starmap(): b05.
equivalents to the existing *note multiprocessing.pool.Pool.map(): b06.
and *note map_async(): b07. functions.  (Contributed by Hynek Schlawack
in bpo-12708(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12328

   (2) https://bugs.python.org/issue4892

   (3) https://bugs.python.org/issue6064

   (4) https://bugs.python.org/issue12708


File: python.info,  Node: nntplib<2>,  Next: os<8>,  Prev: multiprocessing<7>,  Up: Improved Modules<7>

1.7.20.33 nntplib
.................

The *note nntplib.NNTP: 1c6. class now supports the context management
protocol to unconditionally consume *note socket.error: a76. exceptions
and to close the NNTP connection when done:

     >>> from nntplib import NNTP
     >>> with NNTP('news.gmane.org') as n:
     ...     n.group('gmane.comp.python.committers')
     ...
     ('211 1755 1 1755 gmane.comp.python.committers', 1755, 1, 1755, 'gmane.comp.python.committers')
     >>>

(Contributed by Giampaolo Rodolà in bpo-9795(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9795


File: python.info,  Node: os<8>,  Next: pdb<5>,  Prev: nntplib<2>,  Up: Improved Modules<7>

1.7.20.34 os
............

   * The *note os: c4. module has a new *note pipe2(): b0a. function
     that makes it possible to create a pipe with *note O_CLOEXEC: aa2.
     or *note O_NONBLOCK: 812. flags set atomically.  This is especially
     useful to avoid race conditions in multi-threaded programs.

   * The *note os: c4. module has a new *note sendfile(): 461. function
     which provides an efficient “zero-copy” way for copying data from
     one file (or socket) descriptor to another.  The phrase “zero-copy”
     refers to the fact that all of the copying of data between the two
     descriptors is done entirely by the kernel, with no copying of data
     into userspace buffers.  *note sendfile(): 461. can be used to
     efficiently copy data from a file on disk to a network socket, e.g.
     for downloading a file.

     (Patch submitted by Ross Lagerwall and Giampaolo Rodolà in
     bpo-10882(1).)

   * To avoid race conditions like symlink attacks and issues with
     temporary files and directories, it is more reliable (and also
     faster) to manipulate file descriptors instead of file names.
     Python 3.3 enhances existing functions and introduces new functions
     to work on file descriptors (bpo-4761(2), bpo-10755(3) and
     bpo-14626(4)).

        - The *note os: c4. module has a new *note fwalk(): 4bb.
          function similar to *note walk(): 747. except that it also
          yields file descriptors referring to the directories visited.
          This is especially useful to avoid symlink races.

        - The following functions get new optional `dir_fd' (*note paths
          relative to directory descriptors: b0b.) and/or
          `follow_symlinks' (*note not following symlinks: b0c.): *note
          access(): b0d, *note chflags(): b0e, *note chmod(): b0f, *note
          chown(): b10, *note link(): b11, *note lstat(): 322, *note
          mkdir(): b12, *note mkfifo(): 756, *note mknod(): 757, *note
          open(): 758, *note readlink(): 1d1, *note remove(): b13, *note
          rename(): b14, *note replace(): b15, *note rmdir(): b16, *note
          stat(): 321, *note symlink(): b17, *note unlink(): b18, *note
          utime(): b19.  Platform support for using these parameters can
          be checked via the sets *note os.supports_dir_fd: b1a. and
          ‘os.supports_follows_symlinks’.

        - The following functions now support a file descriptor for
          their path argument: *note chdir(): 16e, *note chmod(): b0f,
          *note chown(): b10, *note execve(): b1b, *note listdir(): b1c,
          *note pathconf(): b1d, *note exists(): 325, *note stat(): 321,
          *note statvfs(): b1e, *note utime(): b19.  Platform support
          for this can be checked via the *note os.supports_fd: b1f.
          set.

   * *note access(): b0d. accepts an ‘effective_ids’ keyword argument to
     turn on using the effective uid/gid rather than the real uid/gid in
     the access check.  Platform support for this can be checked via the
     *note supports_effective_ids: b20. set.

   * The *note os: c4. module has two new functions: *note
     getpriority(): b21. and *note setpriority(): b22.  They can be used
     to get or set process niceness/priority in a fashion similar to
     *note os.nice(): b23. but extended to all processes instead of just
     the current one.

     (Patch submitted by Giampaolo Rodolà in bpo-10784(5).)

   * The new *note os.replace(): b15. function allows cross-platform
     renaming of a file with overwriting the destination.  With *note
     os.rename(): b14, an existing destination file is overwritten under
     POSIX, but raises an error under Windows.  (Contributed by Antoine
     Pitrou in bpo-8828(6).)

   * The stat family of functions (*note stat(): 321, *note fstat():
     752, and *note lstat(): 322.) now support reading a file’s
     timestamps with nanosecond precision.  Symmetrically, *note
     utime(): b19. can now write file timestamps with nanosecond
     precision.  (Contributed by Larry Hastings in bpo-14127(7).)

   * The new *note os.get_terminal_size(): b24. function queries the
     size of the terminal attached to a file descriptor.  See also *note
     shutil.get_terminal_size(): b25.  (Contributed by Zbigniew
     Jędrzejewski-Szmek in bpo-13609(8).)

   * New functions to support Linux extended attributes (bpo-12720(9)):
     *note getxattr(): b26, *note listxattr(): b27, *note removexattr():
     b28, *note setxattr(): b29.

   * New interface to the scheduler.  These functions control how a
     process is allocated CPU time by the operating system.  New
     functions: *note sched_get_priority_max(): b2a, *note
     sched_get_priority_min(): b2b, *note sched_getaffinity(): b2c,
     *note sched_getparam(): b2d, *note sched_getscheduler(): b2e, *note
     sched_rr_get_interval(): b2f, *note sched_setaffinity(): b30, *note
     sched_setparam(): b31, *note sched_setscheduler(): b32, *note
     sched_yield(): b33,

   * New functions to control the file system:

        * *note posix_fadvise(): 759.: Announces an intention to access
          data in a specific pattern thus allowing the kernel to make
          optimizations.

        * *note posix_fallocate(): 75a.: Ensures that enough disk space
          is allocated for a file.

        * *note sync(): b34.: Force write of everything to disk.

   * Additional new posix functions:

        * *note lockf(): b35.: Apply, test or remove a POSIX lock on an
          open file descriptor.

        * *note pread(): 4c0.: Read from a file descriptor at an offset,
          the file offset remains unchanged.

        * *note pwrite(): 4c3.: Write to a file descriptor from an
          offset, leaving the file offset unchanged.

        * *note readv(): 4bf.: Read from a file descriptor into a number
          of writable buffers.

        * *note truncate(): 813.: Truncate the file corresponding to
          `path', so that it is at most `length' bytes in size.

        * *note waitid(): 75f.: Wait for the completion of one or more
          child processes.

        * *note writev(): 4c2.: Write the contents of `buffers' to a
          file descriptor, where `buffers' is an arbitrary sequence of
          buffers.

        * *note getgrouplist(): b36. (bpo-9344(10)): Return list of
          group ids that specified user belongs to.

   * *note times(): b37. and *note uname(): b38.: Return type changed
     from a tuple to a tuple-like object with named attributes.

   * Some platforms now support additional constants for the *note
     lseek(): b39. function, such as ‘os.SEEK_HOLE’ and ‘os.SEEK_DATA’.

   * New constants *note RTLD_LAZY: b3a, *note RTLD_NOW: b3b, *note
     RTLD_GLOBAL: b3c, *note RTLD_LOCAL: b3d, *note RTLD_NODELETE: b3e,
     *note RTLD_NOLOAD: b3f, and *note RTLD_DEEPBIND: b40. are available
     on platforms that support them.  These are for use with the *note
     sys.setdlopenflags(): b41. function, and supersede the similar
     constants defined in *note ctypes: 2a. and ‘DLFCN’.  (Contributed
     by Victor Stinner in bpo-13226(11).)

   * *note os.symlink(): b17. now accepts (and ignores) the
     ‘target_is_directory’ keyword argument on non-Windows platforms, to
     ease cross-platform support.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10882

   (2) https://bugs.python.org/issue4761

   (3) https://bugs.python.org/issue10755

   (4) https://bugs.python.org/issue14626

   (5) https://bugs.python.org/issue10784

   (6) https://bugs.python.org/issue8828

   (7) https://bugs.python.org/issue14127

   (8) https://bugs.python.org/issue13609

   (9) https://bugs.python.org/issue12720

   (10) https://bugs.python.org/issue9344

   (11) https://bugs.python.org/issue13226


File: python.info,  Node: pdb<5>,  Next: pickle<5>,  Prev: os<8>,  Up: Improved Modules<7>

1.7.20.35 pdb
.............

Tab-completion is now available not only for command names, but also
their arguments.  For example, for the ‘break’ command, function and
file names are completed.

(Contributed by Georg Brandl in bpo-14210(1))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14210


File: python.info,  Node: pickle<5>,  Next: pydoc<5>,  Prev: pdb<5>,  Up: Improved Modules<7>

1.7.20.36 pickle
................

*note pickle.Pickler: 33b. objects now have an optional *note
dispatch_table: b44. attribute allowing per-pickler reduction functions
to be set.

(Contributed by Richard Oudkerk in bpo-14166(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14166


File: python.info,  Node: pydoc<5>,  Next: re<6>,  Prev: pickle<5>,  Up: Improved Modules<7>

1.7.20.37 pydoc
...............

The Tk GUI and the ‘serve()’ function have been removed from the *note
pydoc: d9. module: ‘pydoc -g’ and ‘serve()’ have been deprecated in
Python 3.2.


File: python.info,  Node: re<6>,  Next: sched,  Prev: pydoc<5>,  Up: Improved Modules<7>

1.7.20.38 re
............

*note str: 205. regular expressions now support ‘\u’ and ‘\U’ escapes.

(Contributed by Serhiy Storchaka in bpo-3665(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue3665


File: python.info,  Node: sched,  Next: select<2>,  Prev: re<6>,  Up: Improved Modules<7>

1.7.20.39 sched
...............

   * *note run(): b48. now accepts a `blocking' parameter which when set
     to false makes the method execute the scheduled events due to
     expire soonest (if any) and then return immediately.  This is
     useful in case you want to use the *note scheduler: b49. in
     non-blocking applications.  (Contributed by Giampaolo Rodolà in
     bpo-13449(1).)

   * *note scheduler: b49. class can now be safely used in
     multi-threaded environments.  (Contributed by Josiah Carlson and
     Giampaolo Rodolà in bpo-8684(2).)

   * `timefunc' and `delayfunct' parameters of *note scheduler: b49.
     class constructor are now optional and defaults to *note
     time.time(): 42d. and *note time.sleep(): 773. respectively.
     (Contributed by Chris Clark in bpo-13245(3).)

   * *note enter(): b4a. and *note enterabs(): b4b. `argument' parameter
     is now optional.  (Contributed by Chris Clark in bpo-13245(4).)

   * *note enter(): b4a. and *note enterabs(): b4b. now accept a
     `kwargs' parameter.  (Contributed by Chris Clark in bpo-13245(5).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13449

   (2) https://bugs.python.org/issue8684

   (3) https://bugs.python.org/issue13245

   (4) https://bugs.python.org/issue13245

   (5) https://bugs.python.org/issue13245


File: python.info,  Node: select<2>,  Next: shlex<3>,  Prev: sched,  Up: Improved Modules<7>

1.7.20.40 select
................

Solaris and derivative platforms have a new class *note select.devpoll:
992. for high performance asynchronous sockets via ‘/dev/poll’.
(Contributed by Jesús Cea Avión in bpo-6397(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue6397


File: python.info,  Node: shlex<3>,  Next: shutil<4>,  Prev: select<2>,  Up: Improved Modules<7>

1.7.20.41 shlex
...............

The previously undocumented helper function ‘quote’ from the *note
pipes: cc. modules has been moved to the *note shlex: e8. module and
documented.  *note quote(): b4e. properly escapes all characters in a
string that might be otherwise given special meaning by the shell.


File: python.info,  Node: shutil<4>,  Next: signal<4>,  Prev: shlex<3>,  Up: Improved Modules<7>

1.7.20.42 shutil
................

   * New functions:

        * *note disk_usage(): b50.: provides total, used and free disk
          space statistics.  (Contributed by Giampaolo Rodolà in
          bpo-12442(1).)

        * *note chown(): b51.: allows one to change user and/or group of
          the given path also specifying the user/group names and not
          only their numeric ids.  (Contributed by Sandro Tosi in
          bpo-12191(2).)

        * *note shutil.get_terminal_size(): b25.: returns the size of
          the terminal window to which the interpreter is attached.
          (Contributed by Zbigniew Jędrzejewski-Szmek in bpo-13609(3).)

   * *note copy2(): 384. and *note copystat(): b52. now preserve file
     timestamps with nanosecond precision on platforms that support it.
     They also preserve file “extended attributes” on Linux.
     (Contributed by Larry Hastings in bpo-14127(4) and bpo-15238(5).)

   * Several functions now take an optional ‘symlinks’ argument: when
     that parameter is true, symlinks aren’t dereferenced and the
     operation instead acts on the symlink itself (or creates one, if
     relevant).  (Contributed by Hynek Schlawack in bpo-12715(6).)

   * When copying files to a different file system, *note move(): 385.
     now handles symlinks the way the posix ‘mv’ command does,
     recreating the symlink rather than copying the target file
     contents.  (Contributed by Jonathan Niehof in bpo-9993(7).)  *note
     move(): 385. now also returns the ‘dst’ argument as its result.

   * *note rmtree(): 349. is now resistant to symlink attacks on
     platforms which support the new ‘dir_fd’ parameter in *note
     os.open(): 758. and *note os.unlink(): b18.  (Contributed by Martin
     von Löwis and Hynek Schlawack in bpo-4489(8).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12442

   (2) https://bugs.python.org/issue12191

   (3) https://bugs.python.org/issue13609

   (4) https://bugs.python.org/issue14127

   (5) https://bugs.python.org/issue15238

   (6) https://bugs.python.org/issue12715

   (7) https://bugs.python.org/issue9993

   (8) https://bugs.python.org/issue4489


File: python.info,  Node: signal<4>,  Next: smtpd<3>,  Prev: shutil<4>,  Up: Improved Modules<7>

1.7.20.43 signal
................

   * The *note signal: ea. module has new functions:

        * *note pthread_sigmask(): b54.: fetch and/or change the signal
          mask of the calling thread (Contributed by Jean-Paul Calderone
          in bpo-8407(1));

        * *note pthread_kill(): b55.: send a signal to a thread;

        * *note sigpending(): b56.: examine pending functions;

        * *note sigwait(): b57.: wait a signal;

        * *note sigwaitinfo(): 772.: wait for a signal, returning
          detailed information about it;

        * *note sigtimedwait(): 771.: like *note sigwaitinfo(): 772. but
          with a timeout.

   * The signal handler writes the signal number as a single byte
     instead of a nul byte into the wakeup file descriptor.  So it is
     possible to wait more than one signal and know which signals were
     raised.

   * *note signal.signal(): b58. and *note signal.siginterrupt(): b59.
     raise an OSError, instead of a RuntimeError: OSError has an errno
     attribute.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8407


File: python.info,  Node: smtpd<3>,  Next: smtplib<4>,  Prev: signal<4>,  Up: Improved Modules<7>

1.7.20.44 smtpd
...............

The *note smtpd: ec. module now supports RFC 5321(1) (extended SMTP) and
RFC 1870(2) (size extension).  Per the standard, these extensions are
enabled if and only if the client initiates the session with an ‘EHLO’
command.

(Initial ‘ELHO’ support by Alberto Trevino.  Size extension by Juhana
Jauhiainen.  Substantial additional work on the patch contributed by
Michele Orrù and Dan Boswell.  bpo-8739(3))

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc5321.html

   (2) https://tools.ietf.org/html/rfc1870.html

   (3) https://bugs.python.org/issue8739


File: python.info,  Node: smtplib<4>,  Next: socket<8>,  Prev: smtpd<3>,  Up: Improved Modules<7>

1.7.20.45 smtplib
.................

The *note SMTP: 1de, *note SMTP_SSL: 1df, and *note LMTP: 1e0. classes
now accept a ‘source_address’ keyword argument to specify the ‘(host,
port)’ to use as the source address in the bind call when creating the
outgoing socket.  (Contributed by Paulo Scardine in bpo-11281(1).)

*note SMTP: 1de. now supports the context management protocol, allowing
an ‘SMTP’ instance to be used in a ‘with’ statement.  (Contributed by
Giampaolo Rodolà in bpo-11289(2).)

The *note SMTP_SSL: 1df. constructor and the *note starttls(): b5c.
method now accept an SSLContext parameter to control parameters of the
secure channel.  (Contributed by Kasun Herath in bpo-8809(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11281

   (2) https://bugs.python.org/issue11289

   (3) https://bugs.python.org/issue8809


File: python.info,  Node: socket<8>,  Next: socketserver<3>,  Prev: smtplib<4>,  Up: Improved Modules<7>

1.7.20.46 socket
................

   * The *note socket: 767. class now exposes additional methods to
     process ancillary data when supported by the underlying platform:

        * *note sendmsg(): 76f.

        * *note recvmsg(): 76c.

        * *note recvmsg_into(): b5e.

     (Contributed by David Watson in bpo-6560(1), based on an earlier
     patch by Heiko Wundram)

   * The *note socket: 767. class now supports the PF_CAN protocol
     family (‘https://en.wikipedia.org/wiki/Socketcan’), on Linux
     (‘https://lwn.net/Articles/253425’).

     (Contributed by Matthias Fuchs, updated by Tiago Gonçalves in
     bpo-10141(2).)

   * The *note socket: 767. class now supports the PF_RDS protocol
     family (‘https://en.wikipedia.org/wiki/Reliable_Datagram_Sockets’
     and ‘https://oss.oracle.com/projects/rds/’).

   * The *note socket: 767. class now supports the ‘PF_SYSTEM’ protocol
     family on OS X. (Contributed by Michael Goderbauer in
     bpo-13777(3).)

   * New function *note sethostname(): b5f. allows the hostname to be
     set on unix systems if the calling process has sufficient
     privileges.  (Contributed by Ross Lagerwall in bpo-10866(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue6560

   (2) https://bugs.python.org/issue10141

   (3) https://bugs.python.org/issue13777

   (4) https://bugs.python.org/issue10866


File: python.info,  Node: socketserver<3>,  Next: sqlite3<5>,  Prev: socket<8>,  Up: Improved Modules<7>

1.7.20.47 socketserver
......................

*note BaseServer: b61. now has an overridable method *note
service_actions(): b62. that is called by the *note serve_forever():
b63. method in the service loop.  *note ForkingMixIn: 4dc. now uses this
to clean up zombie child processes.  (Contributed by Justin Warkentin in
bpo-11109(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11109


File: python.info,  Node: sqlite3<5>,  Next: ssl<8>,  Prev: socketserver<3>,  Up: Improved Modules<7>

1.7.20.48 sqlite3
.................

New *note sqlite3.Connection: 4df. method *note set_trace_callback():
b65. can be used to capture a trace of all sql commands processed by
sqlite.  (Contributed by Torsten Landschoff in bpo-11688(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11688


File: python.info,  Node: ssl<8>,  Next: stat<2>,  Prev: sqlite3<5>,  Up: Improved Modules<7>

1.7.20.49 ssl
.............

   * The *note ssl: f3. module has two new random generation functions:

        * *note RAND_bytes(): b67.: generate cryptographically strong
          pseudo-random bytes.

        * *note RAND_pseudo_bytes(): b68.: generate pseudo-random bytes.

     (Contributed by Victor Stinner in bpo-12049(1).)

   * The *note ssl: f3. module now exposes a finer-grained exception
     hierarchy in order to make it easier to inspect the various kinds
     of errors.  (Contributed by Antoine Pitrou in bpo-11183(2).)

   * *note load_cert_chain(): b69. now accepts a `password' argument to
     be used if the private key is encrypted.  (Contributed by Adam
     Simpkins in bpo-12803(3).)

   * Diffie-Hellman key exchange, both regular and Elliptic Curve-based,
     is now supported through the *note load_dh_params(): b6a. and *note
     set_ecdh_curve(): b6b. methods.  (Contributed by Antoine Pitrou in
     bpo-13626(4) and bpo-13627(5).)

   * SSL sockets have a new *note get_channel_binding(): b6c. method
     allowing the implementation of certain authentication mechanisms
     such as SCRAM-SHA-1-PLUS. (Contributed by Jacek Konieczny in
     bpo-12551(6).)

   * You can query the SSL compression algorithm used by an SSL socket,
     thanks to its new *note compression(): b6d. method.  The new
     attribute *note OP_NO_COMPRESSION: b6e. can be used to disable
     compression.  (Contributed by Antoine Pitrou in bpo-13634(7).)

   * Support has been added for the Next Protocol Negotiation extension
     using the *note ssl.SSLContext.set_npn_protocols(): b6f. method.
     (Contributed by Colin Marc in bpo-14204(8).)

   * SSL errors can now be introspected more easily thanks to *note
     library: b70. and *note reason: b71. attributes.  (Contributed by
     Antoine Pitrou in bpo-14837(9).)

   * The *note get_server_certificate(): b72. function now supports
     IPv6.  (Contributed by Charles-François Natali in bpo-11811(10).)

   * New attribute *note OP_CIPHER_SERVER_PREFERENCE: b73. allows
     setting SSLv3 server sockets to use the server’s cipher ordering
     preference rather than the client’s (bpo-13635(11)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12049

   (2) https://bugs.python.org/issue11183

   (3) https://bugs.python.org/issue12803

   (4) https://bugs.python.org/issue13626

   (5) https://bugs.python.org/issue13627

   (6) https://bugs.python.org/issue12551

   (7) https://bugs.python.org/issue13634

   (8) https://bugs.python.org/issue14204

   (9) https://bugs.python.org/issue14837

   (10) https://bugs.python.org/issue11811

   (11) https://bugs.python.org/issue13635


File: python.info,  Node: stat<2>,  Next: struct<3>,  Prev: ssl<8>,  Up: Improved Modules<7>

1.7.20.50 stat
..............

The undocumented tarfile.filemode function has been moved to *note
stat.filemode(): b75.  It can be used to convert a file’s mode to a
string of the form ‘-rwxrwxrwx’.

(Contributed by Giampaolo Rodolà in bpo-14807(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14807


File: python.info,  Node: struct<3>,  Next: subprocess<5>,  Prev: stat<2>,  Up: Improved Modules<7>

1.7.20.51 struct
................

The *note struct: f8. module now supports ‘ssize_t’ and ‘size_t’ via the
new codes ‘n’ and ‘N’, respectively.  (Contributed by Antoine Pitrou in
bpo-3163(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue3163


File: python.info,  Node: subprocess<5>,  Next: sys<8>,  Prev: struct<3>,  Up: Improved Modules<7>

1.7.20.52 subprocess
....................

Command strings can now be bytes objects on posix platforms.
(Contributed by Victor Stinner in bpo-8513(1).)

A new constant *note DEVNULL: b78. allows suppressing output in a
platform-independent fashion.  (Contributed by Ross Lagerwall in
bpo-5870(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8513

   (2) https://bugs.python.org/issue5870


File: python.info,  Node: sys<8>,  Next: tarfile<4>,  Prev: subprocess<5>,  Up: Improved Modules<7>

1.7.20.53 sys
.............

The *note sys: fd. module has a new *note thread_info: b7a. *note named
tuple: b7b. holding information about the thread implementation
(bpo-11223(1)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue11223


File: python.info,  Node: tarfile<4>,  Next: tempfile,  Prev: sys<8>,  Up: Improved Modules<7>

1.7.20.54 tarfile
.................

*note tarfile: 101. now supports ‘lzma’ encoding via the *note lzma: ad.
module.  (Contributed by Lars Gustäbel in bpo-5689(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5689


File: python.info,  Node: tempfile,  Next: textwrap<2>,  Prev: tarfile<4>,  Up: Improved Modules<7>

1.7.20.55 tempfile
..................

*note tempfile.SpooledTemporaryFile: b7e.’s ‘truncate()’ method now
accepts a ‘size’ parameter.  (Contributed by Ryan Kelly in bpo-9957(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9957


File: python.info,  Node: textwrap<2>,  Next: threading<5>,  Prev: tempfile,  Up: Improved Modules<7>

1.7.20.56 textwrap
..................

The *note textwrap: 10a. module has a new *note indent(): b80. that
makes it straightforward to add a common prefix to selected lines in a
block of text (bpo-13857(1)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13857


File: python.info,  Node: threading<5>,  Next: time<6>,  Prev: textwrap<2>,  Up: Improved Modules<7>

1.7.20.57 threading
...................

*note threading.Condition: b82, *note threading.Semaphore: b83, *note
threading.BoundedSemaphore: b84, *note threading.Event: b85, and *note
threading.Timer: b86, all of which used to be factory functions
returning a class instance, are now classes and may be subclassed.
(Contributed by Éric Araujo in bpo-10968(1).)

The *note threading.Thread: 21a. constructor now accepts a ‘daemon’
keyword argument to override the default behavior of inheriting the
‘daemon’ flag value from the parent thread (bpo-6064(2)).

The formerly private function ‘_thread.get_ident’ is now available as
the public function *note threading.get_ident(): b87.  This eliminates
several cases of direct access to the ‘_thread’ module in the stdlib.
Third party code that used ‘_thread.get_ident’ should likewise be
changed to use the new public interface.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10968

   (2) https://bugs.python.org/issue6064


File: python.info,  Node: time<6>,  Next: types<4>,  Prev: threading<5>,  Up: Improved Modules<7>

1.7.20.58 time
..............

The PEP 418(1) added new functions to the *note time: 10c. module:

   * *note get_clock_info(): b89.: Get information on a clock.

   * *note monotonic(): 85e.: Monotonic clock (cannot go backward), not
     affected by system clock updates.

   * *note perf_counter(): 3cc.: Performance counter with the highest
     available resolution to measure a short duration.

   * *note process_time(): 3cd.: Sum of the system and user CPU time of
     the current process.

Other new functions:

   * *note clock_getres(): b8a, *note clock_gettime(): b8b. and *note
     clock_settime(): b8c. functions with ‘CLOCK_xxx’ constants.
     (Contributed by Victor Stinner in bpo-10278(2).)

To improve cross platform consistency, *note sleep(): 773. now raises a
*note ValueError: 16d. when passed a negative sleep value.  Previously
this was an error on posix, but produced an infinite sleep on Windows.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0418

   (2) https://bugs.python.org/issue10278


File: python.info,  Node: types<4>,  Next: unittest<5>,  Prev: time<6>,  Up: Improved Modules<7>

1.7.20.59 types
...............

Add a new *note types.MappingProxyType: b8e. class: Read-only proxy of a
mapping.  (bpo-14386(1))

The new functions *note types.new_class(): b8f. and *note
types.prepare_class(): b90. provide support for PEP 3115(2) compliant
dynamic type creation.  (bpo-14588(3))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14386

   (2) https://www.python.org/dev/peps/pep-3115

   (3) https://bugs.python.org/issue14588


File: python.info,  Node: unittest<5>,  Next: urllib<3>,  Prev: types<4>,  Up: Improved Modules<7>

1.7.20.60 unittest
..................

*note assertRaises(): b92, *note assertRaisesRegex(): b93, *note
assertWarns(): b94, and *note assertWarnsRegex(): b95. now accept a
keyword argument `msg' when used as context managers.  (Contributed by
Ezio Melotti and Winston Ewert in bpo-10775(1).)

*note unittest.TestCase.run(): b96. now returns the *note TestResult:
b97. object.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10775


File: python.info,  Node: urllib<3>,  Next: webbrowser,  Prev: unittest<5>,  Up: Improved Modules<7>

1.7.20.61 urllib
................

The *note Request: 9dc. class, now accepts a `method' argument used by
*note get_method(): b99. to determine what HTTP method should be used.
For example, this will send a ‘'HEAD'’ request:

     >>> urlopen(Request('https://www.python.org', method='HEAD'))

(bpo-1673007(1))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1673007


File: python.info,  Node: webbrowser,  Next: xml etree ElementTree,  Prev: urllib<3>,  Up: Improved Modules<7>

1.7.20.62 webbrowser
....................

The *note webbrowser: 132. module supports more “browsers”: Google
Chrome (named ‘chrome’, ‘chromium’, ‘chrome-browser’ or
‘chromium-browser’ depending on the version and operating system), and
the generic launchers ‘xdg-open’, from the FreeDesktop.org project, and
‘gvfs-open’, which is the default URI handler for GNOME 3.  (The former
contributed by Arnaud Calmettes in bpo-13620(1), the latter by Matthias
Klose in bpo-14493(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13620

   (2) https://bugs.python.org/issue14493


File: python.info,  Node: xml etree ElementTree,  Next: zlib<2>,  Prev: webbrowser,  Up: Improved Modules<7>

1.7.20.63 xml.etree.ElementTree
...............................

The *note xml.etree.ElementTree: 140. module now imports its C
accelerator by default; there is no longer a need to explicitly import
‘xml.etree.cElementTree’ (this module stays for backwards compatibility,
but is now deprecated).  In addition, the ‘iter’ family of methods of
*note Element: 21d. has been optimized (rewritten in C). The module’s
documentation has also been greatly improved with added examples and a
more detailed reference.


File: python.info,  Node: zlib<2>,  Prev: xml etree ElementTree,  Up: Improved Modules<7>

1.7.20.64 zlib
..............

New attribute *note zlib.Decompress.eof: b9d. makes it possible to
distinguish between a properly-formed compressed stream and an
incomplete or truncated one.  (Contributed by Nadeem Vawda in
bpo-12646(1).)

New attribute *note zlib.ZLIB_RUNTIME_VERSION: b9e. reports the version
string of the underlying ‘zlib’ library that is loaded at runtime.
(Contributed by Torsten Landschoff in bpo-12306(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12646

   (2) https://bugs.python.org/issue12306


File: python.info,  Node: Optimizations<6>,  Next: Build and C API Changes<4>,  Prev: Improved Modules<7>,  Up: What’s New In Python 3 3

1.7.21 Optimizations
--------------------

Major performance enhancements have been added:

   * Thanks to PEP 393(1), some operations on Unicode strings have been
     optimized:

        * the memory footprint is divided by 2 to 4 depending on the
          text

        * encode an ASCII string to UTF-8 doesn’t need to encode
          characters anymore, the UTF-8 representation is shared with
          the ASCII representation

        * the UTF-8 encoder has been optimized

        * repeating a single ASCII letter and getting a substring of an
          ASCII string is 4 times faster

   * UTF-8 is now 2x to 4x faster.  UTF-16 encoding is now up to 10x
     faster.

     (Contributed by Serhiy Storchaka, bpo-14624(2), bpo-14738(3) and
     bpo-15026(4).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0393

   (2) https://bugs.python.org/issue14624

   (3) https://bugs.python.org/issue14738

   (4) https://bugs.python.org/issue15026


File: python.info,  Node: Build and C API Changes<4>,  Next: Deprecated<6>,  Prev: Optimizations<6>,  Up: What’s New In Python 3 3

1.7.22 Build and C API Changes
------------------------------

Changes to Python’s build process and to the C API include:

   * New PEP 3118(1) related function:

        * *note PyMemoryView_FromMemory(): ba0.

   * PEP 393(2) added new Unicode types, macros and functions:

        * High-level API:

             * *note PyUnicode_CopyCharacters(): ba1.

             * *note PyUnicode_FindChar(): 543.

             * *note PyUnicode_GetLength(): ba2, *note
               PyUnicode_GET_LENGTH: ba3.

             * *note PyUnicode_New(): ba4.

             * *note PyUnicode_Substring(): ba5.

             * *note PyUnicode_ReadChar(): ba6, *note
               PyUnicode_WriteChar(): ba7.

        * Low-level API:

             * *note Py_UCS1: ba8, *note Py_UCS2: ba9, *note Py_UCS4:
               baa. types

             * *note PyASCIIObject: bab. and *note
               PyCompactUnicodeObject: bac. structures

             * *note PyUnicode_READY: bad.

             * *note PyUnicode_FromKindAndData(): bae.

             * *note PyUnicode_AsUCS4(): baf, *note
               PyUnicode_AsUCS4Copy(): bb0.

             * *note PyUnicode_DATA: bb1, *note PyUnicode_1BYTE_DATA:
               bb2, *note PyUnicode_2BYTE_DATA: bb3, *note
               PyUnicode_4BYTE_DATA: bb4.

             * *note PyUnicode_KIND: bb5. with ‘PyUnicode_Kind’ enum:
               *note PyUnicode_WCHAR_KIND: bb6, *note
               PyUnicode_1BYTE_KIND: bb7, *note PyUnicode_2BYTE_KIND:
               bb8, *note PyUnicode_4BYTE_KIND: bb9.

             * *note PyUnicode_READ: bba, *note PyUnicode_READ_CHAR:
               bbb, *note PyUnicode_WRITE: bbc.

             * *note PyUnicode_MAX_CHAR_VALUE: bbd.

   * *note PyArg_ParseTuple: 393. now accepts a *note bytearray: 173.
     for the ‘c’ format (bpo-12380(3)).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3118

   (2) https://www.python.org/dev/peps/pep-0393

   (3) https://bugs.python.org/issue12380


File: python.info,  Node: Deprecated<6>,  Next: Porting to Python 3 3,  Prev: Build and C API Changes<4>,  Up: What’s New In Python 3 3

1.7.23 Deprecated
-----------------

* Menu:

* Unsupported Operating Systems: Unsupported Operating Systems<2>.
* Deprecated Python modules, functions and methods: Deprecated Python modules functions and methods<4>.
* Deprecated functions and types of the C API: Deprecated functions and types of the C API<3>.
* Deprecated features::


File: python.info,  Node: Unsupported Operating Systems<2>,  Next: Deprecated Python modules functions and methods<4>,  Up: Deprecated<6>

1.7.23.1 Unsupported Operating Systems
......................................

OS/2 and VMS are no longer supported due to the lack of a maintainer.

Windows 2000 and Windows platforms which set ‘COMSPEC’ to ‘command.com’
are no longer supported due to maintenance burden.

OSF support, which was deprecated in 3.2, has been completely removed.


File: python.info,  Node: Deprecated Python modules functions and methods<4>,  Next: Deprecated functions and types of the C API<3>,  Prev: Unsupported Operating Systems<2>,  Up: Deprecated<6>

1.7.23.2 Deprecated Python modules, functions and methods
.........................................................

   * Passing a non-empty string to ‘object.__format__()’ is deprecated,
     and will produce a *note TypeError: 1fe. in Python 3.4
     (bpo-9856(1)).

   * The ‘unicode_internal’ codec has been deprecated because of the PEP
     393(2), use UTF-8, UTF-16 (‘utf-16-le’ or ‘utf-16-be’), or UTF-32
     (‘utf-32-le’ or ‘utf-32-be’)

   * *note ftplib.FTP.nlst(): ae4. and *note ftplib.FTP.dir(): ae5.: use
     *note ftplib.FTP.mlsd(): ae3.

   * ‘platform.popen()’: use the *note subprocess: f9. module.  Check
     especially the *note Replacing Older Functions with the subprocess
     Module: bc1. section (bpo-11377(3)).

   * bpo-13374(4): The Windows bytes API has been deprecated in the
     *note os: c4. module.  Use Unicode filenames, instead of bytes
     filenames, to not depend on the ANSI code page anymore and to
     support any filename.

   * bpo-13988(5): The ‘xml.etree.cElementTree’ module is deprecated.
     The accelerator is used automatically whenever available.

   * The behaviour of ‘time.clock()’ depends on the platform: use the
     new *note time.perf_counter(): 3cc. or *note time.process_time():
     3cd. function instead, depending on your requirements, to have a
     well defined behaviour.

   * The ‘os.stat_float_times()’ function is deprecated.

   * *note abc: 3. module:

        * *note abc.abstractproperty: aac. has been deprecated, use
          *note property: 308. with *note abc.abstractmethod(): aad.
          instead.

        * *note abc.abstractclassmethod: aae. has been deprecated, use
          *note classmethod: 309. with *note abc.abstractmethod(): aad.
          instead.

        * *note abc.abstractstaticmethod: aaf. has been deprecated, use
          *note staticmethod: 30a. with *note abc.abstractmethod(): aad.
          instead.

   * *note importlib: 9a. package:

        * *note importlib.abc.SourceLoader.path_mtime(): bc2. is now
          deprecated in favour of *note
          importlib.abc.SourceLoader.path_stats(): bc3. as bytecode
          files now store both the modification time and size of the
          source file the bytecode file was compiled from.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9856

   (2) https://www.python.org/dev/peps/pep-0393

   (3) https://bugs.python.org/issue11377

   (4) https://bugs.python.org/issue13374

   (5) https://bugs.python.org/issue13988


File: python.info,  Node: Deprecated functions and types of the C API<3>,  Next: Deprecated features,  Prev: Deprecated Python modules functions and methods<4>,  Up: Deprecated<6>

1.7.23.3 Deprecated functions and types of the C API
....................................................

The *note Py_UNICODE: bc5. has been deprecated by PEP 393(1) and will be
removed in Python 4.  All functions using this type are deprecated:

Unicode functions and methods using *note Py_UNICODE: bc5. and *note
Py_UNICODE*: bc5. types:

   * *note PyUnicode_FromUnicode: 263.: use *note
     PyUnicode_FromWideChar(): bc6. or *note
     PyUnicode_FromKindAndData(): bae.

   * *note PyUnicode_AS_UNICODE: bc7, *note PyUnicode_AsUnicode(): 264,
     *note PyUnicode_AsUnicodeAndSize(): 265.: use *note
     PyUnicode_AsWideCharString(): 53c.

   * *note PyUnicode_AS_DATA: bc8.: use *note PyUnicode_DATA: bb1. with
     *note PyUnicode_READ: bba. and *note PyUnicode_WRITE: bbc.

   * *note PyUnicode_GET_SIZE: bc9, *note PyUnicode_GetSize(): bca.: use
     *note PyUnicode_GET_LENGTH: ba3. or *note PyUnicode_GetLength():
     ba2.

   * *note PyUnicode_GET_DATA_SIZE: bcb.: use ‘PyUnicode_GET_LENGTH(str)
     * PyUnicode_KIND(str)’ (only work on ready strings)

   * *note PyUnicode_AsUnicodeCopy(): bcc.: use *note
     PyUnicode_AsUCS4Copy(): bb0. or *note PyUnicode_AsWideCharString():
     53c.

   * ‘PyUnicode_GetMax()’

Functions and macros manipulating Py_UNICODE* strings:

   * ‘Py_UNICODE_strlen’: use *note PyUnicode_GetLength(): ba2. or *note
     PyUnicode_GET_LENGTH: ba3.

   * ‘Py_UNICODE_strcat’: use *note PyUnicode_CopyCharacters(): ba1. or
     *note PyUnicode_FromFormat(): 8b8.

   * ‘Py_UNICODE_strcpy’, ‘Py_UNICODE_strncpy’, ‘Py_UNICODE_COPY’: use
     *note PyUnicode_CopyCharacters(): ba1. or *note
     PyUnicode_Substring(): ba5.

   * ‘Py_UNICODE_strcmp’: use *note PyUnicode_Compare(): bcd.

   * ‘Py_UNICODE_strncmp’: use *note PyUnicode_Tailmatch(): 272.

   * ‘Py_UNICODE_strchr’, ‘Py_UNICODE_strrchr’: use *note
     PyUnicode_FindChar(): 543.

   * ‘Py_UNICODE_FILL’: use *note PyUnicode_Fill(): bce.

   * ‘Py_UNICODE_MATCH’

Encoders:

   * *note PyUnicode_Encode(): bcf.: use ‘PyUnicode_AsEncodedObject()’

   * *note PyUnicode_EncodeUTF7(): bd0.

   * *note PyUnicode_EncodeUTF8(): bd1.: use *note PyUnicode_AsUTF8():
     52f. or *note PyUnicode_AsUTF8String(): bd2.

   * *note PyUnicode_EncodeUTF32(): bd3.

   * *note PyUnicode_EncodeUTF16(): bd4.

   * *note PyUnicode_EncodeUnicodeEscape(): bd5. use *note
     PyUnicode_AsUnicodeEscapeString(): bd6.

   * *note PyUnicode_EncodeRawUnicodeEscape(): bd7. use *note
     PyUnicode_AsRawUnicodeEscapeString(): bd8.

   * *note PyUnicode_EncodeLatin1(): bd9.: use *note
     PyUnicode_AsLatin1String(): bda.

   * *note PyUnicode_EncodeASCII(): bdb.: use *note
     PyUnicode_AsASCIIString(): bdc.

   * *note PyUnicode_EncodeCharmap(): bdd.

   * *note PyUnicode_TranslateCharmap(): bde.

   * *note PyUnicode_EncodeMBCS(): bdf.: use *note
     PyUnicode_AsMBCSString(): be0. or *note PyUnicode_EncodeCodePage():
     be1. (with ‘CP_ACP’ code_page)

   * ‘PyUnicode_EncodeDecimal()’, *note
     PyUnicode_TransformDecimalToASCII(): be2.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0393


File: python.info,  Node: Deprecated features,  Prev: Deprecated functions and types of the C API<3>,  Up: Deprecated<6>

1.7.23.4 Deprecated features
............................

The *note array: 6. module’s ‘'u'’ format code is now deprecated and
will be removed in Python 4 together with the rest of the (*note
Py_UNICODE: bc5.) API.


File: python.info,  Node: Porting to Python 3 3,  Prev: Deprecated<6>,  Up: What’s New In Python 3 3

1.7.24 Porting to Python 3.3
----------------------------

This section lists previously described changes and other bugfixes that
may require changes to your code.

* Menu:

* Porting Python code::
* Porting C code::
* Building C extensions::
* Command Line Switch Changes::


File: python.info,  Node: Porting Python code,  Next: Porting C code,  Up: Porting to Python 3 3

1.7.24.1 Porting Python code
............................

   * Hash randomization is enabled by default.  Set the *note
     PYTHONHASHSEED: aa4. environment variable to ‘0’ to disable hash
     randomization.  See also the *note object.__hash__(): 44c. method.

   * bpo-12326(1): On Linux, sys.platform doesn’t contain the major
     version anymore.  It is now always ‘linux’, instead of ‘linux2’ or
     ‘linux3’ depending on the Linux version used to build Python.
     Replace sys.platform == ‘linux2’ with
     sys.platform.startswith(‘linux’), or directly sys.platform ==
     ‘linux’ if you don’t need to support older Python versions.

   * bpo-13847(2), bpo-14180(3): *note time: 10c. and *note datetime:
     30.: *note OverflowError: a41. is now raised instead of *note
     ValueError: 16d. if a timestamp is out of range.  *note OSError:
     304. is now raised if C functions ‘gmtime()’ or ‘localtime()’
     failed.

   * The default finders used by import now utilize a cache of what is
     contained within a specific directory.  If you create a Python
     source file or sourceless bytecode file, make sure to call *note
     importlib.invalidate_caches(): 597. to clear out the cache for the
     finders to notice the new file.

   * *note ImportError: 16c. now uses the full name of the module that
     was attempted to be imported.  Doctests that check ImportErrors’
     message will need to be updated to use the full name of the module
     instead of just the tail of the name.

   * The `index' argument to *note __import__(): 16b. now defaults to 0
     instead of -1 and no longer support negative values.  It was an
     oversight when PEP 328(4) was implemented that the default value
     remained -1.  If you need to continue to perform a relative import
     followed by an absolute import, then perform the relative import
     using an index of 1, followed by another import using an index of
     0.  It is preferred, though, that you use *note
     importlib.import_module(): be6. rather than call *note
     __import__(): 16b. directly.

   * *note __import__(): 16b. no longer allows one to use an index value
     other than 0 for top-level modules.  E.g.  ‘__import__('sys',
     level=1)’ is now an error.

   * Because *note sys.meta_path: 6dd. and *note sys.path_hooks: a3d.
     now have finders on them by default, you will most likely want to
     use ‘list.insert()’ instead of ‘list.append()’ to add to those
     lists.

   * Because ‘None’ is now inserted into *note sys.path_importer_cache:
     598, if you are clearing out entries in the dictionary of paths
     that do not have a finder, you will need to remove keys paired with
     values of ‘None’ `and' *note imp.NullImporter: a9b. to be
     backwards-compatible.  This will lead to extra overhead on older
     versions of Python that re-insert ‘None’ into *note
     sys.path_importer_cache: 598. where it represents the use of
     implicit finders, but semantically it should not change anything.

   * *note importlib.abc.Finder: a95. no longer specifies a
     ‘find_module()’ abstract method that must be implemented.  If you
     were relying on subclasses to implement that method, make sure to
     check for the method’s existence first.  You will probably want to
     check for ‘find_loader()’ first, though, in the case of working
     with *note path entry finders: a92.

   * *note pkgutil: cd. has been converted to use *note importlib: 9a.
     internally.  This eliminates many edge cases where the old
     behaviour of the PEP 302(5) import emulation failed to match the
     behaviour of the real import system.  The import emulation itself
     is still present, but is now deprecated.  The *note
     pkgutil.iter_importers(): be7. and *note pkgutil.walk_packages():
     586. functions special case the standard import hooks so they are
     still supported even though they do not provide the non-standard
     ‘iter_modules()’ method.

   * A longstanding RFC-compliance bug (bpo-1079(6)) in the parsing done
     by *note email.header.decode_header(): ad8. has been fixed.  Code
     that uses the standard idiom to convert encoded headers into
     unicode (‘str(make_header(decode_header(h))’) will see no change,
     but code that looks at the individual tuples returned by
     decode_header will see that whitespace that precedes or follows
     ‘ASCII’ sections is now included in the ‘ASCII’ section.  Code that
     builds headers using ‘make_header’ should also continue to work
     without change, since ‘make_header’ continues to add whitespace
     between ‘ASCII’ and non-‘ASCII’ sections if it is not already
     present in the input strings.

   * *note email.utils.formataddr(): be8. now does the correct content
     transfer encoding when passed non-‘ASCII’ display names.  Any code
     that depended on the previous buggy behavior that preserved the
     non-‘ASCII’ unicode in the formatted output string will need to be
     changed (bpo-1690608(7)).

   * *note poplib.POP3.quit(): be9. may now raise protocol errors like
     all other ‘poplib’ methods.  Code that assumes ‘quit’ does not
     raise *note poplib.error_proto: bea. errors may need to be changed
     if errors on ‘quit’ are encountered by a particular application
     (bpo-11291(8)).

   * The ‘strict’ argument to *note email.parser.Parser: beb, deprecated
     since Python 2.4, has finally been removed.

   * The deprecated method ‘unittest.TestCase.assertSameElements’ has
     been removed.

   * The deprecated variable ‘time.accept2dyear’ has been removed.

   * The deprecated ‘Context._clamp’ attribute has been removed from the
     *note decimal: 35. module.  It was previously replaced by the
     public attribute ‘clamp’.  (See bpo-8540(9).)

   * The undocumented internal helper class ‘SSLFakeFile’ has been
     removed from *note smtplib: ed, since its functionality has long
     been provided directly by *note socket.socket.makefile(): bec.

   * Passing a negative value to *note time.sleep(): 773. on Windows now
     raises an error instead of sleeping forever.  It has always raised
     an error on posix.

   * The ‘ast.__version__’ constant has been removed.  If you need to
     make decisions affected by the AST version, use *note
     sys.version_info: bed. to make the decision.

   * Code that used to work around the fact that the *note threading:
     10b. module used factory functions by subclassing the private
     classes will need to change to subclass the now-public classes.

   * The undocumented debugging machinery in the threading module has
     been removed, simplifying the code.  This should have no effect on
     production code, but is mentioned here in case any application
     debug frameworks were interacting with it (bpo-13550(10)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12326

   (2) https://bugs.python.org/issue13847

   (3) https://bugs.python.org/issue14180

   (4) https://www.python.org/dev/peps/pep-0328

   (5) https://www.python.org/dev/peps/pep-0302

   (6) https://bugs.python.org/issue1079

   (7) https://bugs.python.org/issue1690608

   (8) https://bugs.python.org/issue11291

   (9) https://bugs.python.org/issue8540

   (10) https://bugs.python.org/issue13550


File: python.info,  Node: Porting C code,  Next: Building C extensions,  Prev: Porting Python code,  Up: Porting to Python 3 3

1.7.24.2 Porting C code
.......................

   * In the course of changes to the buffer API the undocumented
     ‘smalltable’ member of the *note Py_buffer: bee. structure has been
     removed and the layout of the ‘PyMemoryViewObject’ has changed.

     All extensions relying on the relevant parts in ‘memoryobject.h’ or
     ‘object.h’ must be rebuilt.

   * Due to *note PEP 393: a5d, the *note Py_UNICODE: bc5. type and all
     functions using this type are deprecated (but will stay available
     for at least five years).  If you were using low-level Unicode APIs
     to construct and access unicode objects and you want to benefit of
     the memory footprint reduction provided by PEP 393(1), you have to
     convert your code to the new *note Unicode API: bef.

     However, if you only have been using high-level functions such as
     *note PyUnicode_Concat(): bf0, *note PyUnicode_Join(): bf1. or
     *note PyUnicode_FromFormat(): 8b8, your code will automatically
     take advantage of the new unicode representations.

   * *note PyImport_GetMagicNumber(): bf2. now returns ‘-1’ upon
     failure.

   * As a negative value for the `level' argument to *note __import__():
     16b. is no longer valid, the same now holds for *note
     PyImport_ImportModuleLevel(): bf3.  This also means that the value
     of `level' used by *note PyImport_ImportModuleEx(): bf4. is now ‘0’
     instead of ‘-1’.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0393


File: python.info,  Node: Building C extensions,  Next: Command Line Switch Changes,  Prev: Porting C code,  Up: Porting to Python 3 3

1.7.24.3 Building C extensions
..............................

   * The range of possible file names for C extensions has been
     narrowed.  Very rarely used spellings have been suppressed: under
     POSIX, files named ‘xxxmodule.so’, ‘xxxmodule.abi3.so’ and
     ‘xxxmodule.cpython-*.so’ are no longer recognized as implementing
     the ‘xxx’ module.  If you had been generating such files, you have
     to switch to the other spellings (i.e., remove the ‘module’ string
     from the file names).

     (implemented in bpo-14040(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14040


File: python.info,  Node: Command Line Switch Changes,  Prev: Building C extensions,  Up: Porting to Python 3 3

1.7.24.4 Command Line Switch Changes
....................................

   * The -Q command-line flag and related artifacts have been removed.
     Code checking sys.flags.division_warning will need updating.

     (bpo-10998(1), contributed by Éric Araujo.)

   * When ‘python’ is started with *note -S: bf7, ‘import site’ will no
     longer add site-specific paths to the module search paths.  In
     previous versions, it did.

     (bpo-11591(2), contributed by Carl Meyer with editions by Éric
     Araujo.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10998

   (2) https://bugs.python.org/issue11591


File: python.info,  Node: What’s New In Python 3 2,  Next: What’s New In Python 3 1,  Prev: What’s New In Python 3 3,  Up: What’s New in Python

1.8 What’s New In Python 3.2
============================


Author: Raymond Hettinger

This article explains the new features in Python 3.2 as compared to 3.1.
It focuses on a few highlights and gives a few examples.  For full
details, see the Misc/NEWS(1) file.

See also
........

PEP 392(2) - Python 3.2 Release Schedule

* Menu:

* PEP 384; Defining a Stable ABI: PEP 384 Defining a Stable ABI.
* PEP 389; Argparse Command Line Parsing Module: PEP 389 Argparse Command Line Parsing Module.
* PEP 391; Dictionary Based Configuration for Logging: PEP 391 Dictionary Based Configuration for Logging.
* PEP 3148; The concurrent.futures module: PEP 3148 The concurrent futures module.
* PEP 3147; PYC Repository Directories: PEP 3147 PYC Repository Directories.
* PEP 3149; ABI Version Tagged .so Files: PEP 3149 ABI Version Tagged so Files.
* PEP 3333; Python Web Server Gateway Interface v1.0.1: PEP 3333 Python Web Server Gateway Interface v1 0 1.
* Other Language Changes: Other Language Changes<8>.
* New, Improved, and Deprecated Modules: New Improved and Deprecated Modules.
* Multi-threading::
* Optimizations: Optimizations<7>.
* Unicode::
* Codecs::
* Documentation::
* IDLE::
* Code Repository::
* Build and C API Changes: Build and C API Changes<5>.
* Porting to Python 3.2: Porting to Python 3 2.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/blob/076ca6c3c8df3030307e548d9be792ce3c1c6eea/Misc/NEWS

   (2) https://www.python.org/dev/peps/pep-0392


File: python.info,  Node: PEP 384 Defining a Stable ABI,  Next: PEP 389 Argparse Command Line Parsing Module,  Up: What’s New In Python 3 2

1.8.1 PEP 384: Defining a Stable ABI
------------------------------------

In the past, extension modules built for one Python version were often
not usable with other Python versions.  Particularly on Windows, every
feature release of Python required rebuilding all extension modules that
one wanted to use.  This requirement was the result of the free access
to Python interpreter internals that extension modules could use.

With Python 3.2, an alternative approach becomes available: extension
modules which restrict themselves to a limited API (by defining
Py_LIMITED_API) cannot use many of the internals, but are constrained to
a set of API functions that are promised to be stable for several
releases.  As a consequence, extension modules built for 3.2 in that
mode will also work with 3.3, 3.4, and so on.  Extension modules that
make use of details of memory structures can still be built, but will
need to be recompiled for every feature release.

See also
........

PEP 384(1) - Defining a Stable ABI

     PEP written by Martin von Löwis.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0384


File: python.info,  Node: PEP 389 Argparse Command Line Parsing Module,  Next: PEP 391 Dictionary Based Configuration for Logging,  Prev: PEP 384 Defining a Stable ABI,  Up: What’s New In Python 3 2

1.8.2 PEP 389: Argparse Command Line Parsing Module
---------------------------------------------------

A new module for command line parsing, *note argparse: 5, was introduced
to overcome the limitations of *note optparse: c3. which did not provide
support for positional arguments (not just options), subcommands,
required options and other common patterns of specifying and validating
options.

This module has already had widespread success in the community as a
third-party module.  Being more fully featured than its predecessor, the
*note argparse: 5. module is now the preferred module for command-line
processing.  The older module is still being kept available because of
the substantial amount of legacy code that depends on it.

Here’s an annotated example parser showing features like limiting
results to a set of choices, specifying a `metavar' in the help screen,
validating that one or more positional arguments is present, and making
a required option:

     import argparse
     parser = argparse.ArgumentParser(
                 description = 'Manage servers',         # main description for help
                 epilog = 'Tested on Solaris and Linux') # displayed after help
     parser.add_argument('action',                       # argument name
                 choices = ['deploy', 'start', 'stop'],  # three allowed values
                 help = 'action on each target')         # help msg
     parser.add_argument('targets',
                 metavar = 'HOSTNAME',                   # var name used in help msg
                 nargs = '+',                            # require one or more targets
                 help = 'url for target machines')       # help msg explanation
     parser.add_argument('-u', '--user',                 # -u or --user option
                 required = True,                        # make it a required argument
                 help = 'login as user')

Example of calling the parser on a command string:

     >>> cmd = 'deploy sneezy.example.com sleepy.example.com -u skycaptain'
     >>> result = parser.parse_args(cmd.split())
     >>> result.action
     'deploy'
     >>> result.targets
     ['sneezy.example.com', 'sleepy.example.com']
     >>> result.user
     'skycaptain'

Example of the parser’s automatically generated help:

     >>> parser.parse_args('-h'.split())

     usage: manage_cloud.py [-h] -u USER
                            {deploy,start,stop} HOSTNAME [HOSTNAME ...]

     Manage servers

     positional arguments:
       {deploy,start,stop}   action on each target
       HOSTNAME              url for target machines

     optional arguments:
       -h, --help            show this help message and exit
       -u USER, --user USER  login as user

     Tested on Solaris and Linux

An especially nice *note argparse: 5. feature is the ability to define
subparsers, each with their own argument patterns and help displays:

     import argparse
     parser = argparse.ArgumentParser(prog='HELM')
     subparsers = parser.add_subparsers()

     parser_l = subparsers.add_parser('launch', help='Launch Control')   # first subgroup
     parser_l.add_argument('-m', '--missiles', action='store_true')
     parser_l.add_argument('-t', '--torpedos', action='store_true')

     parser_m = subparsers.add_parser('move', help='Move Vessel',        # second subgroup
                                      aliases=('steer', 'turn'))         # equivalent names
     parser_m.add_argument('-c', '--course', type=int, required=True)
     parser_m.add_argument('-s', '--speed', type=int, default=0)

     $ ./helm.py --help                         # top level help (launch and move)
     $ ./helm.py launch --help                  # help for launch options
     $ ./helm.py launch --missiles              # set missiles=True and torpedos=False
     $ ./helm.py steer --course 180 --speed 5   # set movement parameters

See also
........

PEP 389(1) - New Command Line Parsing Module

     PEP written by Steven Bethard.

*note Upgrading optparse code: bfc. for details on the differences from
*note optparse: c3.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0389


File: python.info,  Node: PEP 391 Dictionary Based Configuration for Logging,  Next: PEP 3148 The concurrent futures module,  Prev: PEP 389 Argparse Command Line Parsing Module,  Up: What’s New In Python 3 2

1.8.3 PEP 391: Dictionary Based Configuration for Logging
---------------------------------------------------------

The *note logging: aa. module provided two kinds of configuration, one
style with function calls for each option or another style driven by an
external file saved in a ‘ConfigParser’ format.  Those options did not
provide the flexibility to create configurations from JSON or YAML
files, nor did they support incremental configuration, which is needed
for specifying logger options from a command line.

To support a more flexible style, the module now offers *note
logging.config.dictConfig(): bfe. for specifying logging configuration
with plain Python dictionaries.  The configuration options include
formatters, handlers, filters, and loggers.  Here’s a working example of
a configuration dictionary:

     {"version": 1,
      "formatters": {"brief": {"format": "%(levelname)-8s: %(name)-15s: %(message)s"},
                     "full": {"format": "%(asctime)s %(name)-15s %(levelname)-8s %(message)s"}
                     },
      "handlers": {"console": {
                        "class": "logging.StreamHandler",
                        "formatter": "brief",
                        "level": "INFO",
                        "stream": "ext://sys.stdout"},
                   "console_priority": {
                        "class": "logging.StreamHandler",
                        "formatter": "full",
                        "level": "ERROR",
                        "stream": "ext://sys.stderr"}
                   },
      "root": {"level": "DEBUG", "handlers": ["console", "console_priority"]}}

If that dictionary is stored in a file called ‘conf.json’, it can be
loaded and called with code like this:

     >>> import json, logging.config
     >>> with open('conf.json') as f:
     ...     conf = json.load(f)
     ...
     >>> logging.config.dictConfig(conf)
     >>> logging.info("Transaction completed normally")
     INFO    : root           : Transaction completed normally
     >>> logging.critical("Abnormal termination")
     2011-02-17 11:14:36,694 root            CRITICAL Abnormal termination

See also
........

PEP 391(1) - Dictionary Based Configuration for Logging

     PEP written by Vinay Sajip.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0391


File: python.info,  Node: PEP 3148 The concurrent futures module,  Next: PEP 3147 PYC Repository Directories,  Prev: PEP 391 Dictionary Based Configuration for Logging,  Up: What’s New In Python 3 2

1.8.4 PEP 3148: The ‘concurrent.futures’ module
-----------------------------------------------

Code for creating and managing concurrency is being collected in a new
top-level namespace, `concurrent'.  Its first member is a `futures'
package which provides a uniform high-level interface for managing
threads and processes.

The design for *note concurrent.futures: 21. was inspired by the
`java.util.concurrent' package.  In that model, a running call and its
result are represented by a *note Future: c00. object that abstracts
features common to threads, processes, and remote procedure calls.  That
object supports status checks (running or done), timeouts,
cancellations, adding callbacks, and access to results or exceptions.

The primary offering of the new module is a pair of executor classes for
launching and managing calls.  The goal of the executors is to make it
easier to use existing tools for making parallel calls.  They save the
effort needed to setup a pool of resources, launch the calls, create a
results queue, add time-out handling, and limit the total number of
threads, processes, or remote procedure calls.

Ideally, each application should share a single executor across multiple
components so that process and thread limits can be centrally managed.
This solves the design challenge that arises when each component has its
own competing strategy for resource management.

Both classes share a common interface with three methods: *note
submit(): 3c6. for scheduling a callable and returning a *note Future:
c00. object; *note map(): 7b1. for scheduling many asynchronous calls at
a time, and *note shutdown(): 195. for freeing resources.  The class is
a *note context manager: 661. and can be used in a *note with: 7da.
statement to assure that resources are automatically released when
currently pending futures are done executing.

A simple of example of *note ThreadPoolExecutor: 18c. is a launch of
four parallel threads for copying files:

     import concurrent.futures, shutil
     with concurrent.futures.ThreadPoolExecutor(max_workers=4) as e:
         e.submit(shutil.copy, 'src1.txt', 'dest1.txt')
         e.submit(shutil.copy, 'src2.txt', 'dest2.txt')
         e.submit(shutil.copy, 'src3.txt', 'dest3.txt')
         e.submit(shutil.copy, 'src3.txt', 'dest4.txt')

See also
........

PEP 3148(1) - Futures – Execute Computations Asynchronously

     PEP written by Brian Quinlan.

*note Code for Threaded Parallel URL reads: c01, an example using
threads to fetch multiple web pages in parallel.

*note Code for computing prime numbers in parallel: c02, an example
demonstrating *note ProcessPoolExecutor: 196.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3148


File: python.info,  Node: PEP 3147 PYC Repository Directories,  Next: PEP 3149 ABI Version Tagged so Files,  Prev: PEP 3148 The concurrent futures module,  Up: What’s New In Python 3 2

1.8.5 PEP 3147: PYC Repository Directories
------------------------------------------

Python’s scheme for caching bytecode in `.pyc' files did not work well
in environments with multiple Python interpreters.  If one interpreter
encountered a cached file created by another interpreter, it would
recompile the source and overwrite the cached file, thus losing the
benefits of caching.

The issue of “pyc fights” has become more pronounced as it has become
commonplace for Linux distributions to ship with multiple versions of
Python.  These conflicts also arise with CPython alternatives such as
Unladen Swallow.

To solve this problem, Python’s import machinery has been extended to
use distinct filenames for each interpreter.  Instead of Python 3.2 and
Python 3.3 and Unladen Swallow each competing for a file called
“mymodule.pyc”, they will now look for “mymodule.cpython-32.pyc”,
“mymodule.cpython-33.pyc”, and “mymodule.unladen10.pyc”.  And to prevent
all of these new files from cluttering source directories, the `pyc'
files are now collected in a “__pycache__” directory stored under the
package directory.

Aside from the filenames and target directories, the new scheme has a
few aspects that are visible to the programmer:

   * Imported modules now have a *note __cached__: c04. attribute which
     stores the name of the actual file that was imported:

          >>> import collections
          >>> collections.__cached__
          'c:/py32/lib/__pycache__/collections.cpython-32.pyc'

   * The tag that is unique to each interpreter is accessible from the
     *note imp: 99. module:

          >>> import imp
          >>> imp.get_tag()
          'cpython-32'

   * Scripts that try to deduce source filename from the imported file
     now need to be smarter.  It is no longer sufficient to simply strip
     the “c” from a “.pyc” filename.  Instead, use the new functions in
     the *note imp: 99. module:

          >>> imp.source_from_cache('c:/py32/lib/__pycache__/collections.cpython-32.pyc')
          'c:/py32/lib/collections.py'
          >>> imp.cache_from_source('c:/py32/lib/collections.py')
          'c:/py32/lib/__pycache__/collections.cpython-32.pyc'

   * The *note py_compile: d7. and *note compileall: 20. modules have
     been updated to reflect the new naming convention and target
     directory.  The command-line invocation of `compileall' has new
     options: ‘-i’ for specifying a list of files and directories to
     compile and ‘-b’ which causes bytecode files to be written to their
     legacy location rather than `__pycache__'.

   * The *note importlib.abc: 9b. module has been updated with new *note
     abstract base classes: c05. for loading bytecode files.  The
     obsolete ABCs, ‘PyLoader’ and ‘PyPycLoader’, have been deprecated
     (instructions on how to stay Python 3.1 compatible are included
     with the documentation).

See also
........

PEP 3147(1) - PYC Repository Directories

     PEP written by Barry Warsaw.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3147


File: python.info,  Node: PEP 3149 ABI Version Tagged so Files,  Next: PEP 3333 Python Web Server Gateway Interface v1 0 1,  Prev: PEP 3147 PYC Repository Directories,  Up: What’s New In Python 3 2

1.8.6 PEP 3149: ABI Version Tagged .so Files
--------------------------------------------

The PYC repository directory allows multiple bytecode cache files to be
co-located.  This PEP implements a similar mechanism for shared object
files by giving them a common directory and distinct names for each
version.

The common directory is “pyshared” and the file names are made distinct
by identifying the Python implementation (such as CPython, PyPy, Jython,
etc.), the major and minor version numbers, and optional build flags
(such as “d” for debug, “m” for pymalloc, “u” for wide-unicode).  For an
arbitrary package “foo”, you may see these files when the distribution
package is installed:

     /usr/share/pyshared/foo.cpython-32m.so
     /usr/share/pyshared/foo.cpython-33md.so

In Python itself, the tags are accessible from functions in the *note
sysconfig: fe. module:

     >>> import sysconfig
     >>> sysconfig.get_config_var('SOABI')       # find the version tag
     'cpython-32mu'
     >>> sysconfig.get_config_var('EXT_SUFFIX')  # find the full filename extension
     '.cpython-32mu.so'

See also
........

PEP 3149(1) - ABI Version Tagged .so Files

     PEP written by Barry Warsaw.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3149


File: python.info,  Node: PEP 3333 Python Web Server Gateway Interface v1 0 1,  Next: Other Language Changes<8>,  Prev: PEP 3149 ABI Version Tagged so Files,  Up: What’s New In Python 3 2

1.8.7 PEP 3333: Python Web Server Gateway Interface v1.0.1
----------------------------------------------------------

This informational PEP clarifies how bytes/text issues are to be handled
by the WSGI protocol.  The challenge is that string handling in Python 3
is most conveniently handled with the *note str: 205. type even though
the HTTP protocol is itself bytes oriented.

The PEP differentiates so-called `native strings' that are used for
request/response headers and metadata versus `byte strings' which are
used for the bodies of requests and responses.

The `native strings' are always of type *note str: 205. but are
restricted to code points between `U+0000' through `U+00FF' which are
translatable to bytes using `Latin-1' encoding.  These strings are used
for the keys and values in the environment dictionary and for response
headers and statuses in the ‘start_response()’ function.  They must
follow RFC 2616(1) with respect to encoding.  That is, they must either
be `ISO-8859-1' characters or use RFC 2047(2) MIME encoding.

For developers porting WSGI applications from Python 2, here are the
salient points:

   * If the app already used strings for headers in Python 2, no change
     is needed.

   * If instead, the app encoded output headers or decoded input
     headers, then the headers will need to be re-encoded to Latin-1.
     For example, an output header encoded in utf-8 was using
     ‘h.encode('utf-8')’ now needs to convert from bytes to native
     strings using ‘h.encode('utf-8').decode('latin-1')’.

   * Values yielded by an application or sent using the ‘write()’ method
     must be byte strings.  The ‘start_response()’ function and environ
     must use native strings.  The two cannot be mixed.

For server implementers writing CGI-to-WSGI pathways or other CGI-style
protocols, the users must to be able access the environment using native
strings even though the underlying platform may have a different
convention.  To bridge this gap, the *note wsgiref: 135. module has a
new function, *note wsgiref.handlers.read_environ(): c08. for
transcoding CGI variables from *note os.environ: c09. into native
strings and returning a new dictionary.

See also
........

PEP 3333(3) - Python Web Server Gateway Interface v1.0.1

     PEP written by Phillip Eby.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2616.html

   (2) https://tools.ietf.org/html/rfc2047.html

   (3) https://www.python.org/dev/peps/pep-3333


File: python.info,  Node: Other Language Changes<8>,  Next: New Improved and Deprecated Modules,  Prev: PEP 3333 Python Web Server Gateway Interface v1 0 1,  Up: What’s New In Python 3 2

1.8.8 Other Language Changes
----------------------------

Some smaller changes made to the core Python language are:

   * String formatting for *note format(): 5d6. and *note str.format():
     5d5. gained new capabilities for the format character `#'.
     Previously, for integers in binary, octal, or hexadecimal, it
     caused the output to be prefixed with ‘0b’, ‘0o’, or ‘0x’
     respectively.  Now it can also handle floats, complex, and Decimal,
     causing the output to always have a decimal point even when no
     digits follow it.

          >>> format(20, '#o')
          '0o24'
          >>> format(12.34, '#5.0f')
          '  12.'

     (Suggested by Mark Dickinson and implemented by Eric Smith in
     bpo-7094(1).)

   * There is also a new *note str.format_map(): 7a4. method that
     extends the capabilities of the existing *note str.format(): 5d5.
     method by accepting arbitrary *note mapping: c0b. objects.  This
     new method makes it possible to use string formatting with any of
     Python’s many dictionary-like objects such as *note defaultdict:
     c0c, *note Shelf: 997, *note ConfigParser: 5a5, or *note dbm: 31.
     It is also useful with custom *note dict: 164. subclasses that
     normalize keys before look-up or that supply a *note __missing__():
     c0d. method for unknown keys:

          >>> import shelve
          >>> d = shelve.open('tmp.shl')
          >>> 'The {project_name} status is {status} as of {date}'.format_map(d)
          'The testing project status is green as of February 15, 2011'

          >>> class LowerCasedDict(dict):
          ...     def __getitem__(self, key):
          ...         return dict.__getitem__(self, key.lower())
          >>> lcd = LowerCasedDict(part='widgets', quantity=10)
          >>> 'There are {QUANTITY} {Part} in stock'.format_map(lcd)
          'There are 10 widgets in stock'

          >>> class PlaceholderDict(dict):
          ...     def __missing__(self, key):
          ...         return '<{}>'.format(key)
          >>> 'Hello {name}, welcome to {location}'.format_map(PlaceholderDict())
          'Hello <name>, welcome to <location>'

     (Suggested by Raymond Hettinger and implemented by Eric Smith in
     bpo-6081(2).)

   * The interpreter can now be started with a quiet option, ‘-q’, to
     prevent the copyright and version information from being displayed
     in the interactive mode.  The option can be introspected using the
     *note sys.flags: c0e. attribute:

          $ python -q
          >>> sys.flags
          sys.flags(debug=0, division_warning=0, inspect=0, interactive=0,
          optimize=0, dont_write_bytecode=0, no_user_site=0, no_site=0,
          ignore_environment=0, verbose=0, bytes_warning=0, quiet=1)

     (Contributed by Marcin Wojdyr in bpo-1772833(3)).

   * The *note hasattr(): 54a. function works by calling *note
     getattr(): 54b. and detecting whether an exception is raised.  This
     technique allows it to detect methods created dynamically by *note
     __getattr__(): 42a. or *note __getattribute__(): 54c. which would
     otherwise be absent from the class dictionary.  Formerly, `hasattr'
     would catch any exception, possibly masking genuine errors.  Now,
     `hasattr' has been tightened to only catch *note AttributeError:
     4a2. and let other exceptions pass through:

          >>> class A:
          ...     @property
          ...     def f(self):
          ...         return 1 // 0
          ...
          >>> a = A()
          >>> hasattr(a, 'f')
          Traceback (most recent call last):
            ...
          ZeroDivisionError: integer division or modulo by zero

     (Discovered by Yury Selivanov and fixed by Benjamin Peterson;
     bpo-9666(4).)

   * The *note str(): 205. of a float or complex number is now the same
     as its *note repr(): 8b9.  Previously, the *note str(): 205. form
     was shorter but that just caused confusion and is no longer needed
     now that the shortest possible *note repr(): 8b9. is displayed by
     default:

          >>> import math
          >>> repr(math.pi)
          '3.141592653589793'
          >>> str(math.pi)
          '3.141592653589793'

     (Proposed and implemented by Mark Dickinson; bpo-9337(5).)

   * *note memoryview: 386. objects now have a *note release(): c0f.
     method and they also now support the context management protocol.
     This allows timely release of any resources that were acquired when
     requesting a buffer from the original object.

          >>> with memoryview(b'abcdefgh') as v:
          ...     print(v.tolist())
          [97, 98, 99, 100, 101, 102, 103, 104]

     (Added by Antoine Pitrou; bpo-9757(6).)

   * Previously it was illegal to delete a name from the local namespace
     if it occurs as a free variable in a nested block:

          def outer(x):
              def inner():
                  return x
              inner()
              del x

     This is now allowed.  Remember that the target of an *note except:
     c10. clause is cleared, so this code which used to work with Python
     2.6, raised a *note SyntaxError: 55a. with Python 3.1 and now works
     again:

          def f():
              def print_error():
                  print(e)
              try:
                  something
              except Exception as e:
                  print_error()
                  # implicit "del e" here

     (See bpo-4617(7).)

   * The internal ‘structsequence’ tool now creates subclasses of tuple.
     This means that C structures like those returned by *note
     os.stat(): 321, *note time.gmtime(): c11, and *note
     sys.version_info: bed. now work like a *note named tuple: b7b. and
     now work with functions and methods that expect a tuple as an
     argument.  This is a big step forward in making the C structures as
     flexible as their pure Python counterparts:

          >>> import sys
          >>> isinstance(sys.version_info, tuple)
          True
          >>> 'Version %d.%d.%d %s(%d)' % sys.version_info
          'Version 3.2.0 final(0)'

     (Suggested by Arfrever Frehtes Taifersar Arahesis and implemented
     by Benjamin Peterson in bpo-8413(8).)

   * Warnings are now easier to control using the *note PYTHONWARNINGS:
     51c. environment variable as an alternative to using ‘-W’ at the
     command line:

          $ export PYTHONWARNINGS='ignore::RuntimeWarning::,once::UnicodeWarning::'

     (Suggested by Barry Warsaw and implemented by Philip Jenvey in
     bpo-7301(9).)

   * A new warning category, *note ResourceWarning: 5cb, has been added.
     It is emitted when potential issues with resource consumption or
     cleanup are detected.  It is silenced by default in normal release
     builds but can be enabled through the means provided by the *note
     warnings: 12f. module, or on the command line.

     A *note ResourceWarning: 5cb. is issued at interpreter shutdown if
     the *note gc.garbage: c12. list isn’t empty, and if *note
     gc.DEBUG_UNCOLLECTABLE: c13. is set, all uncollectable objects are
     printed.  This is meant to make the programmer aware that their
     code contains object finalization issues.

     A *note ResourceWarning: 5cb. is also issued when a *note file
     object: c14. is destroyed without having been explicitly closed.
     While the deallocator for such object ensures it closes the
     underlying operating system resource (usually, a file descriptor),
     the delay in deallocating the object could produce various issues,
     especially under Windows.  Here is an example of enabling the
     warning from the command line:

          $ python -q -Wdefault
          >>> f = open("foo", "wb")
          >>> del f
          __main__:1: ResourceWarning: unclosed file <_io.BufferedWriter name='foo'>

     (Added by Antoine Pitrou and Georg Brandl in bpo-10093(10) and
     bpo-477863(11).)

   * *note range: 1f5. objects now support `index' and `count' methods.
     This is part of an effort to make more objects fully implement the
     ‘collections.Sequence’ *note abstract base class: c05.  As a
     result, the language will have a more uniform API. In addition,
     *note range: 1f5. objects now support slicing and negative indices,
     even with values larger than *note sys.maxsize: c15.  This makes
     `range' more interoperable with lists:

          >>> range(0, 100, 2).count(10)
          1
          >>> range(0, 100, 2).index(10)
          5
          >>> range(0, 100, 2)[5]
          10
          >>> range(0, 100, 2)[0:5]
          range(0, 10, 2)

     (Contributed by Daniel Stutzbach in bpo-9213(12), by Alexander
     Belopolsky in bpo-2690(13), and by Nick Coghlan in bpo-10889(14).)

   * The *note callable(): c16. builtin function from Py2.x was
     resurrected.  It provides a concise, readable alternative to using
     an *note abstract base class: c05. in an expression like
     ‘isinstance(x, collections.Callable)’:

          >>> callable(max)
          True
          >>> callable(20)
          False

     (See bpo-10518(15).)

   * Python’s import mechanism can now load modules installed in
     directories with non-ASCII characters in the path name.  This
     solved an aggravating problem with home directories for users with
     non-ASCII characters in their usernames.

     (Required extensive work by Victor Stinner in bpo-9425(16).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue7094

   (2) https://bugs.python.org/issue6081

   (3) https://bugs.python.org/issue1772833

   (4) https://bugs.python.org/issue9666

   (5) https://bugs.python.org/issue9337

   (6) https://bugs.python.org/issue9757

   (7) https://bugs.python.org/issue4617

   (8) https://bugs.python.org/issue8413

   (9) https://bugs.python.org/issue7301

   (10) https://bugs.python.org/issue10093

   (11) https://bugs.python.org/issue477863

   (12) https://bugs.python.org/issue9213

   (13) https://bugs.python.org/issue2690

   (14) https://bugs.python.org/issue10889

   (15) https://bugs.python.org/issue10518

   (16) https://bugs.python.org/issue9425


File: python.info,  Node: New Improved and Deprecated Modules,  Next: Multi-threading,  Prev: Other Language Changes<8>,  Up: What’s New In Python 3 2

1.8.9 New, Improved, and Deprecated Modules
-------------------------------------------

Python’s standard library has undergone significant maintenance efforts
and quality improvements.

The biggest news for Python 3.2 is that the *note email: 67. package,
*note mailbox: ae. module, and *note nntplib: c0. modules now work
correctly with the bytes/text model in Python 3.  For the first time,
there is correct handling of messages with mixed encodings.

Throughout the standard library, there has been more careful attention
to encodings and text versus bytes issues.  In particular, interactions
with the operating system are now better able to exchange non-ASCII data
using the Windows MBCS encoding, locale-aware encodings, or UTF-8.

Another significant win is the addition of substantially better support
for `SSL' connections and security certificates.

In addition, more classes now implement a *note context manager: 661. to
support convenient and reliable resource clean-up using a *note with:
7da. statement.

* Menu:

* email: email<5>.
* elementtree::
* functools: functools<6>.
* itertools: itertools<4>.
* collections: collections<8>.
* threading: threading<6>.
* datetime and time::
* math: math<7>.
* abc: abc<3>.
* io: io<5>.
* reprlib::
* logging: logging<7>.
* csv: csv<3>.
* contextlib: contextlib<6>.
* decimal and fractions::
* ftp::
* popen::
* select: select<3>.
* gzip and zipfile::
* tarfile: tarfile<5>.
* hashlib: hashlib<4>.
* ast: ast<4>.
* os: os<9>.
* shutil: shutil<5>.
* sqlite3: sqlite3<6>.
* html: html<3>.
* socket: socket<9>.
* ssl: ssl<9>.
* nntp::
* certificates::
* imaplib: imaplib<4>.
* http.client: http client<4>.
* unittest: unittest<6>.
* random: random<3>.
* poplib: poplib<4>.
* asyncore: asyncore<2>.
* tempfile: tempfile<2>.
* inspect: inspect<7>.
* pydoc: pydoc<6>.
* dis: dis<3>.
* dbm: dbm<6>.
* ctypes: ctypes<2>.
* site: site<2>.
* sysconfig: sysconfig<2>.
* pdb: pdb<6>.
* configparser: configparser<2>.
* urllib.parse: urllib parse<4>.
* mailbox::
* turtledemo::


File: python.info,  Node: email<5>,  Next: elementtree,  Up: New Improved and Deprecated Modules

1.8.9.1 email
.............

The usability of the *note email: 67. package in Python 3 has been
mostly fixed by the extensive efforts of R. David Murray.  The problem
was that emails are typically read and stored in the form of *note
bytes: 172. rather than *note str: 205. text, and they may contain
multiple encodings within a single email.  So, the email package had to
be extended to parse and generate email messages in bytes format.

   * New functions *note message_from_bytes(): c19. and *note
     message_from_binary_file(): c1a, and new classes *note
     BytesFeedParser: c1b. and *note BytesParser: c1c. allow binary
     message data to be parsed into model objects.

   * Given bytes input to the model, *note get_payload(): c1d. will by
     default decode a message body that has a
     ‘Content-Transfer-Encoding’ of `8bit' using the charset specified
     in the MIME headers and return the resulting string.

   * Given bytes input to the model, *note Generator: c1e. will convert
     message bodies that have a ‘Content-Transfer-Encoding’ of `8bit' to
     instead have a `7bit' ‘Content-Transfer-Encoding’.

     Headers with unencoded non-ASCII bytes are deemed to be RFC
     2047(1)-encoded using the `unknown-8bit' character set.

   * A new class *note BytesGenerator: c1f. produces bytes as output,
     preserving any unchanged non-ASCII data that was present in the
     input used to build the model, including message bodies with a
     ‘Content-Transfer-Encoding’ of `8bit'.

   * The *note smtplib: ed. *note SMTP: 1de. class now accepts a byte
     string for the `msg' argument to the *note sendmail(): 833. method,
     and a new method, *note send_message(): 834. accepts a *note
     Message: 63b. object and can optionally obtain the `from_addr' and
     `to_addrs' addresses directly from the object.

(Proposed and implemented by R. David Murray, bpo-4661(2) and
bpo-10321(3).)

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2047.html

   (2) https://bugs.python.org/issue4661

   (3) https://bugs.python.org/issue10321


File: python.info,  Node: elementtree,  Next: functools<6>,  Prev: email<5>,  Up: New Improved and Deprecated Modules

1.8.9.2 elementtree
...................

The *note xml.etree.ElementTree: 140. package and its
‘xml.etree.cElementTree’ counterpart have been updated to version 1.3.

Several new and useful functions and methods have been added:

   * *note xml.etree.ElementTree.fromstringlist(): c21. which builds an
     XML document from a sequence of fragments

   * *note xml.etree.ElementTree.register_namespace(): c22. for
     registering a global namespace prefix

   * *note xml.etree.ElementTree.tostringlist(): 9fc. for string
     representation including all sublists

   * *note xml.etree.ElementTree.Element.extend(): c23. for appending a
     sequence of zero or more elements

   * *note xml.etree.ElementTree.Element.iterfind(): c24. searches an
     element and subelements

   * *note xml.etree.ElementTree.Element.itertext(): c25. creates a text
     iterator over an element and its subelements

   * *note xml.etree.ElementTree.TreeBuilder.end(): c26. closes the
     current element

   * *note xml.etree.ElementTree.TreeBuilder.doctype(): 3e3. handles a
     doctype declaration

Two methods have been deprecated:

   * ‘xml.etree.ElementTree.getchildren()’ use ‘list(elem)’ instead.

   * ‘xml.etree.ElementTree.getiterator()’ use ‘Element.iter’ instead.

For details of the update, see Introducing ElementTree(1) on Fredrik
Lundh’s website.

(Contributed by Florent Xicluna and Fredrik Lundh, bpo-6472(2).)

   ---------- Footnotes ----------

   (1) http://effbot.org/zone/elementtree-13-intro.htm

   (2) https://bugs.python.org/issue6472


File: python.info,  Node: functools<6>,  Next: itertools<4>,  Prev: elementtree,  Up: New Improved and Deprecated Modules

1.8.9.3 functools
.................

   * The *note functools: 83. module includes a new decorator for
     caching function calls.  *note functools.lru_cache(): 2f8. can save
     repeated queries to an external resource whenever the results are
     expected to be the same.

     For example, adding a caching decorator to a database query
     function can save database accesses for popular searches:

          >>> import functools
          >>> @functools.lru_cache(maxsize=300)
          ... def get_phone_number(name):
          ...     c = conn.cursor()
          ...     c.execute('SELECT phonenumber FROM phonelist WHERE name=?', (name,))
          ...     return c.fetchone()[0]

          >>> for name in user_requests:
          ...     get_phone_number(name)        # cached lookup

     To help with choosing an effective cache size, the wrapped function
     is instrumented for tracking cache statistics:

          >>> get_phone_number.cache_info()
          CacheInfo(hits=4805, misses=980, maxsize=300, currsize=300)

     If the phonelist table gets updated, the outdated contents of the
     cache can be cleared with:

          >>> get_phone_number.cache_clear()

     (Contributed by Raymond Hettinger and incorporating design ideas
     from Jim Baker, Miki Tebeka, and Nick Coghlan; see recipe
     498245(1), recipe 577479(2), bpo-10586(3), and bpo-10593(4).)

   * The *note functools.wraps(): 955. decorator now adds a
     ‘__wrapped__’ attribute pointing to the original callable function.
     This allows wrapped functions to be introspected.  It also copies
     ‘__annotations__’ if defined.  And now it also gracefully skips
     over missing attributes such as ‘__doc__’ which might not be
     defined for the wrapped callable.

     In the above example, the cache can be removed by recovering the
     original function:

          >>> get_phone_number = get_phone_number.__wrapped__    # uncached function

     (By Nick Coghlan and Terrence Cole; bpo-9567(5), bpo-3445(6), and
     bpo-8814(7).)

   * To help write classes with rich comparison methods, a new decorator
     *note functools.total_ordering(): 938. will use existing equality
     and inequality methods to fill in the remaining methods.

     For example, supplying `__eq__' and `__lt__' will enable *note
     total_ordering(): 938. to fill-in `__le__', `__gt__' and `__ge__':

          @total_ordering
          class Student:
              def __eq__(self, other):
                  return ((self.lastname.lower(), self.firstname.lower()) ==
                          (other.lastname.lower(), other.firstname.lower()))

              def __lt__(self, other):
                  return ((self.lastname.lower(), self.firstname.lower()) <
                          (other.lastname.lower(), other.firstname.lower()))

     With the `total_ordering' decorator, the remaining comparison
     methods are filled in automatically.

     (Contributed by Raymond Hettinger.)

   * To aid in porting programs from Python 2, the *note
     functools.cmp_to_key(): c28. function converts an old-style
     comparison function to modern *note key function: 7d2.:

          >>> # locale-aware sort order
          >>> sorted(iterable, key=cmp_to_key(locale.strcoll))

     For sorting examples and a brief sorting tutorial, see the Sorting
     HowTo(8) tutorial.

     (Contributed by Raymond Hettinger.)

   ---------- Footnotes ----------

   (1) https://code.activestate.com/recipes/498245

   (2) https://code.activestate.com/recipes/577479

   (3) https://bugs.python.org/issue10586

   (4) https://bugs.python.org/issue10593

   (5) https://bugs.python.org/issue9567

   (6) https://bugs.python.org/issue3445

   (7) https://bugs.python.org/issue8814

   (8) https://wiki.python.org/moin/HowTo/Sorting/


File: python.info,  Node: itertools<4>,  Next: collections<8>,  Prev: functools<6>,  Up: New Improved and Deprecated Modules

1.8.9.4 itertools
.................

   * The *note itertools: a3. module has a new *note accumulate(): 30e.
     function modeled on APL’s `scan' operator and Numpy’s `accumulate'
     function:

          >>> from itertools import accumulate
          >>> list(accumulate([8, 2, 50]))
          [8, 10, 60]

          >>> prob_dist = [0.1, 0.4, 0.2, 0.3]
          >>> list(accumulate(prob_dist))      # cumulative probability distribution
          [0.1, 0.5, 0.7, 1.0]

     For an example using *note accumulate(): 30e, see the *note
     examples for the random module: c2a.

     (Contributed by Raymond Hettinger and incorporating design
     suggestions from Mark Dickinson.)


File: python.info,  Node: collections<8>,  Next: threading<6>,  Prev: itertools<4>,  Up: New Improved and Deprecated Modules

1.8.9.5 collections
...................

   * The *note collections.Counter: ab9. class now has two forms of
     in-place subtraction, the existing `-=' operator for saturating
     subtraction(1) and the new *note subtract(): c2c. method for
     regular subtraction.  The former is suitable for multisets(2) which
     only have positive counts, and the latter is more suitable for use
     cases that allow negative counts:

          >>> from collections import Counter
          >>> tally = Counter(dogs=5, cats=3)
          >>> tally -= Counter(dogs=2, cats=8)    # saturating subtraction
          >>> tally
          Counter({'dogs': 3})

          >>> tally = Counter(dogs=5, cats=3)
          >>> tally.subtract(dogs=2, cats=8)      # regular subtraction
          >>> tally
          Counter({'dogs': 3, 'cats': -5})

     (Contributed by Raymond Hettinger.)

   * The *note collections.OrderedDict: 2ea. class has a new method
     *note move_to_end(): c2d. which takes an existing key and moves it
     to either the first or last position in the ordered sequence.

     The default is to move an item to the last position.  This is
     equivalent of renewing an entry with ‘od[k] = od.pop(k)’.

     A fast move-to-end operation is useful for resequencing entries.
     For example, an ordered dictionary can be used to track order of
     access by aging entries from the oldest to the most recently
     accessed.

          >>> from collections import OrderedDict
          >>> d = OrderedDict.fromkeys(['a', 'b', 'X', 'd', 'e'])
          >>> list(d)
          ['a', 'b', 'X', 'd', 'e']
          >>> d.move_to_end('X')
          >>> list(d)
          ['a', 'b', 'd', 'e', 'X']

     (Contributed by Raymond Hettinger.)

   * The *note collections.deque: 62b. class grew two new methods *note
     count(): c2e. and *note reverse(): c2f. that make them more
     substitutable for *note list: 1f8. objects:

          >>> from collections import deque
          >>> d = deque('simsalabim')
          >>> d.count('s')
          2
          >>> d.reverse()
          >>> d
          deque(['m', 'i', 'b', 'a', 'l', 'a', 's', 'm', 'i', 's'])

     (Contributed by Raymond Hettinger.)

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Saturation_arithmetic

   (2) https://en.wikipedia.org/wiki/Multiset


File: python.info,  Node: threading<6>,  Next: datetime and time,  Prev: collections<8>,  Up: New Improved and Deprecated Modules

1.8.9.6 threading
.................

The *note threading: 10b. module has a new *note Barrier: c31.
synchronization class for making multiple threads wait until all of them
have reached a common barrier point.  Barriers are useful for making
sure that a task with multiple preconditions does not run until all of
the predecessor tasks are complete.

Barriers can work with an arbitrary number of threads.  This is a
generalization of a Rendezvous(1) which is defined for only two threads.

Implemented as a two-phase cyclic barrier, *note Barrier: c31. objects
are suitable for use in loops.  The separate `filling' and `draining'
phases assure that all threads get released (drained) before any one of
them can loop back and re-enter the barrier.  The barrier fully resets
after each cycle.

Example of using barriers:

     from threading import Barrier, Thread

     def get_votes(site):
         ballots = conduct_election(site)
         all_polls_closed.wait()        # do not count until all polls are closed
         totals = summarize(ballots)
         publish(site, totals)

     all_polls_closed = Barrier(len(sites))
     for site in sites:
         Thread(target=get_votes, args=(site,)).start()

In this example, the barrier enforces a rule that votes cannot be
counted at any polling site until all polls are closed.  Notice how a
solution with a barrier is similar to one with *note
threading.Thread.join(): c32, but the threads stay alive and continue to
do work (summarizing ballots) after the barrier point is crossed.

If any of the predecessor tasks can hang or be delayed, a barrier can be
created with an optional `timeout' parameter.  Then if the timeout
period elapses before all the predecessor tasks reach the barrier point,
all waiting threads are released and a *note BrokenBarrierError: c33.
exception is raised:

     def get_votes(site):
         ballots = conduct_election(site)
         try:
             all_polls_closed.wait(timeout=midnight - time.now())
         except BrokenBarrierError:
             lockbox = seal_ballots(ballots)
             queue.put(lockbox)
         else:
             totals = summarize(ballots)
             publish(site, totals)

In this example, the barrier enforces a more robust rule.  If some
election sites do not finish before midnight, the barrier times-out and
the ballots are sealed and deposited in a queue for later handling.

See Barrier Synchronization Patterns(2) for more examples of how
barriers can be used in parallel computing.  Also, there is a simple but
thorough explanation of barriers in The Little Book of Semaphores(3),
`section 3.6'.

(Contributed by Kristján Valur Jónsson with an API review by Jeffrey
Yasskin in bpo-8777(4).)

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Synchronous_rendezvous

   (2) 
http://osl.cs.illinois.edu/media/papers/karmani-2009-barrier_synchronization_pattern.pdf

   (3) https://greenteapress.com/semaphores/LittleBookOfSemaphores.pdf

   (4) https://bugs.python.org/issue8777


File: python.info,  Node: datetime and time,  Next: math<7>,  Prev: threading<6>,  Up: New Improved and Deprecated Modules

1.8.9.7 datetime and time
.........................

   * The *note datetime: 30. module has a new type *note timezone: ae0.
     that implements the *note tzinfo: 180. interface by returning a
     fixed UTC offset and timezone name.  This makes it easier to create
     timezone-aware datetime objects:

          >>> from datetime import datetime, timezone

          >>> datetime.now(timezone.utc)
          datetime.datetime(2010, 12, 8, 21, 4, 2, 923754, tzinfo=datetime.timezone.utc)

          >>> datetime.strptime("01/01/2000 12:00 +0000", "%m/%d/%Y %H:%M %z")
          datetime.datetime(2000, 1, 1, 12, 0, tzinfo=datetime.timezone.utc)

   * Also, *note timedelta: 2ca. objects can now be multiplied by *note
     float: 1fd. and divided by *note float: 1fd. and *note int: 204.
     objects.  And *note timedelta: 2ca. objects can now divide one
     another.

   * The *note datetime.date.strftime(): 632. method is no longer
     restricted to years after 1900.  The new supported year range is
     from 1000 to 9999 inclusive.

   * Whenever a two-digit year is used in a time tuple, the
     interpretation has been governed by ‘time.accept2dyear’.  The
     default is ‘True’ which means that for a two-digit year, the
     century is guessed according to the POSIX rules governing the ‘%y’
     strptime format.

     Starting with Py3.2, use of the century guessing heuristic will
     emit a *note DeprecationWarning: 15a.  Instead, it is recommended
     that ‘time.accept2dyear’ be set to ‘False’ so that large date
     ranges can be used without guesswork:

          >>> import time, warnings
          >>> warnings.resetwarnings()      # remove the default warning filters

          >>> time.accept2dyear = True      # guess whether 11 means 11 or 2011
          >>> time.asctime((11, 1, 1, 12, 34, 56, 4, 1, 0))
          Warning (from warnings module):
            ...
          DeprecationWarning: Century info guessed for a 2-digit year.
          'Fri Jan  1 12:34:56 2011'

          >>> time.accept2dyear = False     # use the full range of allowable dates
          >>> time.asctime((11, 1, 1, 12, 34, 56, 4, 1, 0))
          'Fri Jan  1 12:34:56 11'

     Several functions now have significantly expanded date ranges.
     When ‘time.accept2dyear’ is false, the *note time.asctime(): c35.
     function will accept any year that fits in a C int, while the *note
     time.mktime(): c36. and *note time.strftime(): c37. functions will
     accept the full range supported by the corresponding operating
     system functions.

(Contributed by Alexander Belopolsky and Victor Stinner in
bpo-1289118(1), bpo-5094(2), bpo-6641(3), bpo-2706(4), bpo-1777412(5),
bpo-8013(6), and bpo-10827(7).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1289118

   (2) https://bugs.python.org/issue5094

   (3) https://bugs.python.org/issue6641

   (4) https://bugs.python.org/issue2706

   (5) https://bugs.python.org/issue1777412

   (6) https://bugs.python.org/issue8013

   (7) https://bugs.python.org/issue10827


File: python.info,  Node: math<7>,  Next: abc<3>,  Prev: datetime and time,  Up: New Improved and Deprecated Modules

1.8.9.8 math
............

The *note math: b1. module has been updated with six new functions
inspired by the C99 standard.

The *note isfinite(): c39. function provides a reliable and fast way to
detect special values.  It returns ‘True’ for regular numbers and
‘False’ for `Nan' or `Infinity':

     >>> from math import isfinite
     >>> [isfinite(x) for x in (123, 4.56, float('Nan'), float('Inf'))]
     [True, True, False, False]

The *note expm1(): c3a. function computes ‘e**x-1’ for small values of
`x' without incurring the loss of precision that usually accompanies the
subtraction of nearly equal quantities:

     >>> from math import expm1
     >>> expm1(0.013671875)   # more accurate way to compute e**x-1 for a small x
     0.013765762467652909

The *note erf(): 554. function computes a probability integral or
Gaussian error function(1).  The complementary error function, *note
erfc(): 555, is ‘1 - erf(x)’:

     >>> from math import erf, erfc, sqrt
     >>> erf(1.0/sqrt(2.0))   # portion of normal distribution within 1 standard deviation
     0.682689492137086
     >>> erfc(1.0/sqrt(2.0))  # portion of normal distribution outside 1 standard deviation
     0.31731050786291404
     >>> erf(1.0/sqrt(2.0)) + erfc(1.0/sqrt(2.0))
     1.0

The *note gamma(): c3b. function is a continuous extension of the
factorial function.  See ‘https://en.wikipedia.org/wiki/Gamma_function’
for details.  Because the function is related to factorials, it grows
large even for small values of `x', so there is also a *note lgamma():
c3c. function for computing the natural logarithm of the gamma function:

     >>> from math import gamma, lgamma
     >>> gamma(7.0)           # six factorial
     720.0
     >>> lgamma(801.0)        # log(800 factorial)
     4551.950730698041

(Contributed by Mark Dickinson.)

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Error_function


File: python.info,  Node: abc<3>,  Next: io<5>,  Prev: math<7>,  Up: New Improved and Deprecated Modules

1.8.9.9 abc
...........

The *note abc: 3. module now supports *note abstractclassmethod(): aae.
and *note abstractstaticmethod(): aaf.

These tools make it possible to define an *note abstract base class:
c05. that requires a particular *note classmethod(): 309. or *note
staticmethod(): 30a. to be implemented:

     class Temperature(metaclass=abc.ABCMeta):
         @abc.abstractclassmethod
         def from_fahrenheit(cls, t):
             ...
         @abc.abstractclassmethod
         def from_celsius(cls, t):
             ...

(Patch submitted by Daniel Urban; bpo-5867(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5867


File: python.info,  Node: io<5>,  Next: reprlib,  Prev: abc<3>,  Up: New Improved and Deprecated Modules

1.8.9.10 io
...........

The *note io.BytesIO: 88a. has a new method, *note getbuffer(): c3f,
which provides functionality similar to *note memoryview(): 386.  It
creates an editable view of the data without making a copy.  The
buffer’s random access and support for slice notation are well-suited to
in-place editing:

     >>> REC_LEN, LOC_START, LOC_LEN = 34, 7, 11

     >>> def change_location(buffer, record_number, location):
     ...     start = record_number * REC_LEN + LOC_START
     ...     buffer[start: start+LOC_LEN] = location

     >>> import io

     >>> byte_stream = io.BytesIO(
     ...     b'G3805  storeroom  Main chassis    '
     ...     b'X7899  shipping   Reserve cog     '
     ...     b'L6988  receiving  Primary sprocket'
     ... )
     >>> buffer = byte_stream.getbuffer()
     >>> change_location(buffer, 1, b'warehouse  ')
     >>> change_location(buffer, 0, b'showroom   ')
     >>> print(byte_stream.getvalue())
     b'G3805  showroom   Main chassis    '
     b'X7899  warehouse  Reserve cog     '
     b'L6988  receiving  Primary sprocket'

(Contributed by Antoine Pitrou in bpo-5506(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5506


File: python.info,  Node: reprlib,  Next: logging<7>,  Prev: io<5>,  Up: New Improved and Deprecated Modules

1.8.9.11 reprlib
................

When writing a *note __repr__(): 44a. method for a custom container, it
is easy to forget to handle the case where a member refers back to the
container itself.  Python’s builtin objects such as *note list: 1f8. and
*note set: 1f6. handle self-reference by displaying “…” in the recursive
part of the representation string.

To help write such *note __repr__(): 44a. methods, the *note reprlib:
df. module has a new decorator, *note recursive_repr(): c41, for
detecting recursive calls to *note __repr__(): 44a. and substituting a
placeholder string instead:

     >>> class MyList(list):
     ...     @recursive_repr()
     ...     def __repr__(self):
     ...         return '<' + '|'.join(map(repr, self)) + '>'
     ...
     >>> m = MyList('abc')
     >>> m.append(m)
     >>> m.append('x')
     >>> print(m)
     <'a'|'b'|'c'|...|'x'>

(Contributed by Raymond Hettinger in bpo-9826(1) and bpo-9840(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9826

   (2) https://bugs.python.org/issue9840


File: python.info,  Node: logging<7>,  Next: csv<3>,  Prev: reprlib,  Up: New Improved and Deprecated Modules

1.8.9.12 logging
................

In addition to dictionary-based configuration described above, the *note
logging: aa. package has many other improvements.

The logging documentation has been augmented by a *note basic tutorial:
c43, an *note advanced tutorial: c44, and a *note cookbook: c45. of
logging recipes.  These documents are the fastest way to learn about
logging.

The *note logging.basicConfig(): 311. set-up function gained a `style'
argument to support three different types of string formatting.  It
defaults to “%” for traditional %-formatting, can be set to “{” for the
new *note str.format(): 5d5. style, or can be set to “$” for the
shell-style formatting provided by *note string.Template: 4f1.  The
following three configurations are equivalent:

     >>> from logging import basicConfig
     >>> basicConfig(style='%', format="%(name)s -> %(levelname)s: %(message)s")
     >>> basicConfig(style='{', format="{name} -> {levelname} {message}")
     >>> basicConfig(style='$', format="$name -> $levelname: $message")

If no configuration is set-up before a logging event occurs, there is
now a default configuration using a *note StreamHandler: c46. directed
to *note sys.stderr: 1ea. for events of ‘WARNING’ level or higher.
Formerly, an event occurring before a configuration was set-up would
either raise an exception or silently drop the event depending on the
value of ‘logging.raiseExceptions’.  The new default handler is stored
in *note logging.lastResort: c47.

The use of filters has been simplified.  Instead of creating a *note
Filter: c48. object, the predicate can be any Python callable that
returns ‘True’ or ‘False’.

There were a number of other improvements that add flexibility and
simplify configuration.  See the module documentation for a full listing
of changes in Python 3.2.


File: python.info,  Node: csv<3>,  Next: contextlib<6>,  Prev: logging<7>,  Up: New Improved and Deprecated Modules

1.8.9.13 csv
............

The *note csv: 29. module now supports a new dialect, *note
unix_dialect: c4a, which applies quoting for all fields and a
traditional Unix style with ‘'\n'’ as the line terminator.  The
registered dialect name is ‘unix’.

The *note csv.DictWriter: c4b. has a new method, *note writeheader():
c4c. for writing-out an initial row to document the field names:

     >>> import csv, sys
     >>> w = csv.DictWriter(sys.stdout, ['name', 'dept'], dialect='unix')
     >>> w.writeheader()
     "name","dept"
     >>> w.writerows([
     ...     {'name': 'tom', 'dept': 'accounting'},
     ...     {'name': 'susan', 'dept': 'Salesl'}])
     "tom","accounting"
     "susan","sales"

(New dialect suggested by Jay Talbot in bpo-5975(1), and the new method
suggested by Ed Abraham in bpo-1537721(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5975

   (2) https://bugs.python.org/issue1537721


File: python.info,  Node: contextlib<6>,  Next: decimal and fractions,  Prev: csv<3>,  Up: New Improved and Deprecated Modules

1.8.9.14 contextlib
...................

There is a new and slightly mind-blowing tool *note ContextDecorator:
c4e. that is helpful for creating a *note context manager: 661. that
does double duty as a function decorator.

As a convenience, this new functionality is used by *note
contextmanager(): c4f. so that no extra effort is needed to support both
roles.

The basic idea is that both context managers and function decorators can
be used for pre-action and post-action wrappers.  Context managers wrap
a group of statements using a *note with: 7da. statement, and function
decorators wrap a group of statements enclosed in a function.  So,
occasionally there is a need to write a pre-action or post-action
wrapper that can be used in either role.

For example, it is sometimes useful to wrap functions or groups of
statements with a logger that can track the time of entry and time of
exit.  Rather than writing both a function decorator and a context
manager for the task, the *note contextmanager(): c4f. provides both
capabilities in a single definition:

     from contextlib import contextmanager
     import logging

     logging.basicConfig(level=logging.INFO)

     @contextmanager
     def track_entry_and_exit(name):
         logging.info('Entering: %s', name)
         yield
         logging.info('Exiting: %s', name)

Formerly, this would have only been usable as a context manager:

     with track_entry_and_exit('widget loader'):
         print('Some time consuming activity goes here')
         load_widget()

Now, it can be used as a decorator as well:

     @track_entry_and_exit('widget loader')
     def activity():
         print('Some time consuming activity goes here')
         load_widget()

Trying to fulfill two roles at once places some limitations on the
technique.  Context managers normally have the flexibility to return an
argument usable by a *note with: 7da. statement, but there is no
parallel for function decorators.

In the above example, there is not a clean way for the
`track_entry_and_exit' context manager to return a logging instance for
use in the body of enclosed statements.

(Contributed by Michael Foord in bpo-9110(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9110


File: python.info,  Node: decimal and fractions,  Next: ftp,  Prev: contextlib<6>,  Up: New Improved and Deprecated Modules

1.8.9.15 decimal and fractions
..............................

Mark Dickinson crafted an elegant and efficient scheme for assuring that
different numeric datatypes will have the same hash value whenever their
actual values are equal (bpo-8188(1)):

     assert hash(Fraction(3, 2)) == hash(1.5) == \
            hash(Decimal("1.5")) == hash(complex(1.5, 0))

Some of the hashing details are exposed through a new attribute, *note
sys.hash_info: a06, which describes the bit width of the hash value, the
prime modulus, the hash values for `infinity' and `nan', and the
multiplier used for the imaginary part of a number:

     >>> sys.hash_info
     sys.hash_info(width=64, modulus=2305843009213693951, inf=314159, nan=0, imag=1000003)

An early decision to limit the inter-operability of various numeric
types has been relaxed.  It is still unsupported (and ill-advised) to
have implicit mixing in arithmetic expressions such as ‘Decimal('1.1') +
float('1.1')’ because the latter loses information in the process of
constructing the binary float.  However, since existing floating point
value can be converted losslessly to either a decimal or rational
representation, it makes sense to add them to the constructor and to
support mixed-type comparisons.

   * The *note decimal.Decimal: 2c0. constructor now accepts *note
     float: 1fd. objects directly so there in no longer a need to use
     the *note from_float(): c51. method (bpo-8257(2)).

   * Mixed type comparisons are now fully supported so that *note
     Decimal: 2c0. objects can be directly compared with *note float:
     1fd. and *note fractions.Fraction: 2be. (bpo-2531(3) and
     bpo-8188(4)).

Similar changes were made to *note fractions.Fraction: 2be. so that the
*note from_float(): c52. and *note from_decimal(): c53. methods are no
longer needed (bpo-8294(5)):

     >>> from decimal import Decimal
     >>> from fractions import Fraction
     >>> Decimal(1.1)
     Decimal('1.100000000000000088817841970012523233890533447265625')
     >>> Fraction(1.1)
     Fraction(2476979795053773, 2251799813685248)

Another useful change for the *note decimal: 35. module is that the
‘Context.clamp’ attribute is now public.  This is useful in creating
contexts that correspond to the decimal interchange formats specified in
IEEE 754 (see bpo-8540(6)).

(Contributed by Mark Dickinson and Raymond Hettinger.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8188

   (2) https://bugs.python.org/issue8257

   (3) https://bugs.python.org/issue2531

   (4) https://bugs.python.org/issue8188

   (5) https://bugs.python.org/issue8294

   (6) https://bugs.python.org/issue8540


File: python.info,  Node: ftp,  Next: popen,  Prev: decimal and fractions,  Up: New Improved and Deprecated Modules

1.8.9.16 ftp
............

The *note ftplib.FTP: 1a6. class now supports the context management
protocol to unconditionally consume *note socket.error: a76. exceptions
and to close the FTP connection when done:

     >>> from ftplib import FTP
     >>> with FTP("ftp1.at.proftpd.org") as ftp:
             ftp.login()
             ftp.dir()

     '230 Anonymous login ok, restrictions apply.'
     dr-xr-xr-x   9 ftp      ftp           154 May  6 10:43 .
     dr-xr-xr-x   9 ftp      ftp           154 May  6 10:43 ..
     dr-xr-xr-x   5 ftp      ftp          4096 May  6 10:43 CentOS
     dr-xr-xr-x   3 ftp      ftp            18 Jul 10  2008 Fedora

Other file-like objects such as *note mmap.mmap: 31c. and *note
fileinput.input(): 3cf. also grew auto-closing context managers:

     with fileinput.input(files=('log1.txt', 'log2.txt')) as f:
         for line in f:
             process(line)

(Contributed by Tarek Ziadé and Giampaolo Rodolà in bpo-4972(1), and by
Georg Brandl in bpo-8046(2) and bpo-1286(3).)

The *note FTP_TLS: 1a7. class now accepts a `context' parameter, which
is a *note ssl.SSLContext: 4ea. object allowing bundling SSL
configuration options, certificates and private keys into a single
(potentially long-lived) structure.

(Contributed by Giampaolo Rodolà; bpo-8806(4).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4972

   (2) https://bugs.python.org/issue8046

   (3) https://bugs.python.org/issue1286

   (4) https://bugs.python.org/issue8806


File: python.info,  Node: popen,  Next: select<3>,  Prev: ftp,  Up: New Improved and Deprecated Modules

1.8.9.17 popen
..............

The *note os.popen(): 3cb. and *note subprocess.Popen(): 3db. functions
now support *note with: 7da. statements for auto-closing of the file
descriptors.

(Contributed by Antoine Pitrou and Brian Curtin in bpo-7461(1) and
bpo-10554(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue7461

   (2) https://bugs.python.org/issue10554


File: python.info,  Node: select<3>,  Next: gzip and zipfile,  Prev: popen,  Up: New Improved and Deprecated Modules

1.8.9.18 select
...............

The *note select: e5. module now exposes a new, constant attribute,
*note PIPE_BUF: c57, which gives the minimum number of bytes which are
guaranteed not to block when *note select.select(): 766. says a pipe is
ready for writing.

     >>> import select
     >>> select.PIPE_BUF
     512

(Available on Unix systems.  Patch by Sébastien Sablé in bpo-9862(1))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9862


File: python.info,  Node: gzip and zipfile,  Next: tarfile<5>,  Prev: select<3>,  Up: New Improved and Deprecated Modules

1.8.9.19 gzip and zipfile
.........................

*note gzip.GzipFile: 206. now implements the *note io.BufferedIOBase:
67f. *note abstract base class: c05. (except for ‘truncate()’).  It also
has a *note peek(): c59. method and supports unseekable as well as
zero-padded file objects.

The *note gzip: 8b. module also gains the *note compress(): 302. and
*note decompress(): c5a. functions for easier in-memory compression and
decompression.  Keep in mind that text needs to be encoded as *note
bytes: 172. before compressing and decompressing:

     >>> import gzip
     >>> s = 'Three shall be the number thou shalt count, '
     >>> s += 'and the number of the counting shall be three'
     >>> b = s.encode()                        # convert to utf-8
     >>> len(b)
     89
     >>> c = gzip.compress(b)
     >>> len(c)
     77
     >>> gzip.decompress(c).decode()[:42]      # decompress and convert to text
     'Three shall be the number thou shalt count'

(Contributed by Anand B. Pillai in bpo-3488(1); and by Antoine Pitrou,
Nir Aides and Brian Curtin in bpo-9962(2), bpo-1675951(3), bpo-7471(4)
and bpo-2846(5).)

Also, the ‘zipfile.ZipExtFile’ class was reworked internally to
represent files stored inside an archive.  The new implementation is
significantly faster and can be wrapped in an *note io.BufferedReader:
c5b. object for more speedups.  It also solves an issue where
interleaved calls to `read' and `readline' gave the wrong results.

(Patch submitted by Nir Aides in bpo-7610(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue3488

   (2) https://bugs.python.org/issue9962

   (3) https://bugs.python.org/issue1675951

   (4) https://bugs.python.org/issue7471

   (5) https://bugs.python.org/issue2846

   (6) https://bugs.python.org/issue7610


File: python.info,  Node: tarfile<5>,  Next: hashlib<4>,  Prev: gzip and zipfile,  Up: New Improved and Deprecated Modules

1.8.9.20 tarfile
................

The *note TarFile: c5d. class can now be used as a context manager.  In
addition, its *note add(): 57b. method has a new option, `filter', that
controls which files are added to the archive and allows the file
metadata to be edited.

The new `filter' option replaces the older, less flexible `exclude'
parameter which is now deprecated.  If specified, the optional `filter'
parameter needs to be a *note keyword argument: 6bb.  The user-supplied
filter function accepts a *note TarInfo: c5e. object and returns an
updated *note TarInfo: c5e. object, or if it wants the file to be
excluded, the function can return ‘None’:

     >>> import tarfile, glob

     >>> def myfilter(tarinfo):
     ...     if tarinfo.isfile():             # only save real files
     ...         tarinfo.uname = 'monty'      # redact the user name
     ...         return tarinfo

     >>> with tarfile.open(name='myarchive.tar.gz', mode='w:gz') as tf:
     ...     for filename in glob.glob('*.txt'):
     ...         tf.add(filename, filter=myfilter)
     ...     tf.list()
     -rw-r--r-- monty/501        902 2011-01-26 17:59:11 annotations.txt
     -rw-r--r-- monty/501        123 2011-01-26 17:59:11 general_questions.txt
     -rw-r--r-- monty/501       3514 2011-01-26 17:59:11 prion.txt
     -rw-r--r-- monty/501        124 2011-01-26 17:59:11 py_todo.txt
     -rw-r--r-- monty/501       1399 2011-01-26 17:59:11 semaphore_notes.txt

(Proposed by Tarek Ziadé and implemented by Lars Gustäbel in
bpo-6856(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue6856


File: python.info,  Node: hashlib<4>,  Next: ast<4>,  Prev: tarfile<5>,  Up: New Improved and Deprecated Modules

1.8.9.21 hashlib
................

The *note hashlib: 8c. module has two new constant attributes listing
the hashing algorithms guaranteed to be present in all implementations
and those available on the current implementation:

     >>> import hashlib

     >>> hashlib.algorithms_guaranteed
     {'sha1', 'sha224', 'sha384', 'sha256', 'sha512', 'md5'}

     >>> hashlib.algorithms_available
     {'md2', 'SHA256', 'SHA512', 'dsaWithSHA', 'mdc2', 'SHA224', 'MD4', 'sha256',
     'sha512', 'ripemd160', 'SHA1', 'MDC2', 'SHA', 'SHA384', 'MD2',
     'ecdsa-with-SHA1','md4', 'md5', 'sha1', 'DSA-SHA', 'sha224',
     'dsaEncryption', 'DSA', 'RIPEMD160', 'sha', 'MD5', 'sha384'}

(Suggested by Carl Chenet in bpo-7418(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue7418


File: python.info,  Node: ast<4>,  Next: os<9>,  Prev: hashlib<4>,  Up: New Improved and Deprecated Modules

1.8.9.22 ast
............

The *note ast: 7. module has a wonderful a general-purpose tool for
safely evaluating expression strings using the Python literal syntax.
The *note ast.literal_eval(): 5a0. function serves as a secure
alternative to the builtin *note eval(): c61. function which is easily
abused.  Python 3.2 adds *note bytes: 172. and *note set: 1f6. literals
to the list of supported types: strings, bytes, numbers, tuples, lists,
dicts, sets, booleans, and ‘None’.

     >>> from ast import literal_eval

     >>> request = "{'req': 3, 'func': 'pow', 'args': (2, 0.5)}"
     >>> literal_eval(request)
     {'args': (2, 0.5), 'req': 3, 'func': 'pow'}

     >>> request = "os.system('do something harmful')"
     >>> literal_eval(request)
     Traceback (most recent call last):
       ...
     ValueError: malformed node or string: <_ast.Call object at 0x101739a10>

(Implemented by Benjamin Peterson and Georg Brandl.)


File: python.info,  Node: os<9>,  Next: shutil<5>,  Prev: ast<4>,  Up: New Improved and Deprecated Modules

1.8.9.23 os
...........

Different operating systems use various encodings for filenames and
environment variables.  The *note os: c4. module provides two new
functions, *note fsencode(): 5ea. and *note fsdecode(): 5e9, for
encoding and decoding filenames:

     >>> import os
     >>> filename = 'Sehenswürdigkeiten'
     >>> os.fsencode(filename)
     b'Sehensw\xc3\xbcrdigkeiten'

Some operating systems allow direct access to encoded bytes in the
environment.  If so, the *note os.supports_bytes_environ: c63. constant
will be true.

For direct access to encoded environment variables (if available), use
the new *note os.getenvb(): c64. function or use *note os.environb: c65.
which is a bytes version of *note os.environ: c09.

(Contributed by Victor Stinner.)


File: python.info,  Node: shutil<5>,  Next: sqlite3<6>,  Prev: os<9>,  Up: New Improved and Deprecated Modules

1.8.9.24 shutil
...............

The *note shutil.copytree(): 347. function has two new options:

   * `ignore_dangling_symlinks': when ‘symlinks=False’ so that the
     function copies a file pointed to by a symlink, not the symlink
     itself.  This option will silence the error raised if the file
     doesn’t exist.

   * `copy_function': is a callable that will be used to copy files.
     *note shutil.copy2(): 384. is used by default.

(Contributed by Tarek Ziadé.)

In addition, the *note shutil: e9. module now supports *note archiving
operations: c67. for zipfiles, uncompressed tarfiles, gzipped tarfiles,
and bzipped tarfiles.  And there are functions for registering
additional archiving file formats (such as xz compressed tarfiles or
custom formats).

The principal functions are *note make_archive(): 348. and *note
unpack_archive(): c68.  By default, both operate on the current
directory (which can be set by *note os.chdir(): 16e.) and on any
sub-directories.  The archive filename needs to be specified with a full
pathname.  The archiving step is non-destructive (the original files are
left unchanged).

     >>> import shutil, pprint

     >>> os.chdir('mydata')  # change to the source directory
     >>> f = shutil.make_archive('/var/backup/mydata',
     ...                         'zip')      # archive the current directory
     >>> f                                   # show the name of archive
     '/var/backup/mydata.zip'
     >>> os.chdir('tmp')                     # change to an unpacking
     >>> shutil.unpack_archive('/var/backup/mydata.zip')  # recover the data

     >>> pprint.pprint(shutil.get_archive_formats())  # display known formats
     [('bztar', "bzip2'ed tar-file"),
      ('gztar', "gzip'ed tar-file"),
      ('tar', 'uncompressed tar file'),
      ('zip', 'ZIP file')]

     >>> shutil.register_archive_format(     # register a new archive format
     ...     name='xz',
     ...     function=xz.compress,           # callable archiving function
     ...     extra_args=[('level', 8)],      # arguments to the function
     ...     description='xz compression'
     ... )

(Contributed by Tarek Ziadé.)


File: python.info,  Node: sqlite3<6>,  Next: html<3>,  Prev: shutil<5>,  Up: New Improved and Deprecated Modules

1.8.9.25 sqlite3
................

The *note sqlite3: f2. module was updated to pysqlite version 2.6.0.  It
has two new capabilities.

   * The ‘sqlite3.Connection.in_transit’ attribute is true if there is
     an active transaction for uncommitted changes.

   * The *note sqlite3.Connection.enable_load_extension(): c6a. and
     *note sqlite3.Connection.load_extension(): c6b. methods allows you
     to load SQLite extensions from “.so” files.  One well-known
     extension is the fulltext-search extension distributed with SQLite.

(Contributed by R. David Murray and Shashwat Anand; bpo-8845(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8845


File: python.info,  Node: html<3>,  Next: socket<9>,  Prev: sqlite3<6>,  Up: New Improved and Deprecated Modules

1.8.9.26 html
.............

A new *note html: 8f. module was introduced with only a single function,
*note escape(): a18, which is used for escaping reserved characters from
HTML markup:

     >>> import html
     >>> html.escape('x > 2 && x < 7')
     'x &gt; 2 &amp;&amp; x &lt; 7'


File: python.info,  Node: socket<9>,  Next: ssl<9>,  Prev: html<3>,  Up: New Improved and Deprecated Modules

1.8.9.27 socket
...............

The *note socket: ef. module has two new improvements.

   * Socket objects now have a *note detach(): c6e. method which puts
     the socket into closed state without actually closing the
     underlying file descriptor.  The latter can then be reused for
     other purposes.  (Added by Antoine Pitrou; bpo-8524(1).)

   * *note socket.create_connection(): c6f. now supports the context
     management protocol to unconditionally consume *note socket.error:
     a76. exceptions and to close the socket when done.  (Contributed by
     Giampaolo Rodolà; bpo-9794(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8524

   (2) https://bugs.python.org/issue9794


File: python.info,  Node: ssl<9>,  Next: nntp,  Prev: socket<9>,  Up: New Improved and Deprecated Modules

1.8.9.28 ssl
............

The *note ssl: f3. module added a number of features to satisfy common
requirements for secure (encrypted, authenticated) internet connections:

   * A new class, *note SSLContext: 4ea, serves as a container for
     persistent SSL data, such as protocol settings, certificates,
     private keys, and various other options.  It includes a *note
     wrap_socket(): 4eb. for creating an SSL socket from an SSL context.

   * A new function, *note ssl.match_hostname(): 4e3, supports server
     identity verification for higher-level protocols by implementing
     the rules of HTTPS (from RFC 2818(1)) which are also suitable for
     other protocols.

   * The *note ssl.wrap_socket(): 571. constructor function now takes a
     `ciphers' argument.  The `ciphers' string lists the allowed
     encryption algorithms using the format described in the OpenSSL
     documentation(2).

   * When linked against recent versions of OpenSSL, the *note ssl: f3.
     module now supports the Server Name Indication extension to the TLS
     protocol, allowing multiple “virtual hosts” using different
     certificates on a single IP port.  This extension is only supported
     in client mode, and is activated by passing the `server_hostname'
     argument to *note ssl.SSLContext.wrap_socket(): 4eb.

   * Various options have been added to the *note ssl: f3. module, such
     as *note OP_NO_SSLv2: c71. which disables the insecure and obsolete
     SSLv2 protocol.

   * The extension now loads all the OpenSSL ciphers and digest
     algorithms.  If some SSL certificates cannot be verified, they are
     reported as an “unknown algorithm” error.

   * The version of OpenSSL being used is now accessible using the
     module attributes *note ssl.OPENSSL_VERSION: c72. (a string), *note
     ssl.OPENSSL_VERSION_INFO: c73. (a 5-tuple), and *note
     ssl.OPENSSL_VERSION_NUMBER: c74. (an integer).

(Contributed by Antoine Pitrou in bpo-8850(3), bpo-1589(4), bpo-8322(5),
bpo-5639(6), bpo-4870(7), bpo-8484(8), and bpo-8321(9).)

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2818.html

   (2) 
https://www.openssl.org/docs/manmaster/man1/ciphers.html#CIPHER-LIST-FORMAT

   (3) https://bugs.python.org/issue8850

   (4) https://bugs.python.org/issue1589

   (5) https://bugs.python.org/issue8322

   (6) https://bugs.python.org/issue5639

   (7) https://bugs.python.org/issue4870

   (8) https://bugs.python.org/issue8484

   (9) https://bugs.python.org/issue8321


File: python.info,  Node: nntp,  Next: certificates,  Prev: ssl<9>,  Up: New Improved and Deprecated Modules

1.8.9.29 nntp
.............

The *note nntplib: c0. module has a revamped implementation with better
bytes and text semantics as well as more practical APIs.  These
improvements break compatibility with the nntplib version in Python 3.1,
which was partly dysfunctional in itself.

Support for secure connections through both implicit (using *note
nntplib.NNTP_SSL: 1c7.) and explicit (using *note
nntplib.NNTP.starttls(): c76.) TLS has also been added.

(Contributed by Antoine Pitrou in bpo-9360(1) and Andrew Vant in
bpo-1926(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9360

   (2) https://bugs.python.org/issue1926


File: python.info,  Node: certificates,  Next: imaplib<4>,  Prev: nntp,  Up: New Improved and Deprecated Modules

1.8.9.30 certificates
.....................

*note http.client.HTTPSConnection: 49a, *note
urllib.request.HTTPSHandler: c78. and *note urllib.request.urlopen():
87b. now take optional arguments to allow for server certificate
checking against a set of Certificate Authorities, as recommended in
public uses of HTTPS.

(Added by Antoine Pitrou, bpo-9003(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9003


File: python.info,  Node: imaplib<4>,  Next: http client<4>,  Prev: certificates,  Up: New Improved and Deprecated Modules

1.8.9.31 imaplib
................

Support for explicit TLS on standard IMAP4 connections has been added
through the new *note imaplib.IMAP4.starttls: c7a. method.

(Contributed by Lorenzo M. Catucci and Antoine Pitrou, bpo-4471(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4471


File: python.info,  Node: http client<4>,  Next: unittest<6>,  Prev: imaplib<4>,  Up: New Improved and Deprecated Modules

1.8.9.32 http.client
....................

There were a number of small API improvements in the *note http.client:
93. module.  The old-style HTTP 0.9 simple responses are no longer
supported and the `strict' parameter is deprecated in all classes.

The *note HTTPConnection: 499. and *note HTTPSConnection: 49a. classes
now have a `source_address' parameter for a (host, port) tuple
indicating where the HTTP connection is made from.

Support for certificate checking and HTTPS virtual hosts were added to
*note HTTPSConnection: 49a.

The *note request(): 649. method on connection objects allowed an
optional `body' argument so that a *note file object: c14. could be used
to supply the content of the request.  Conveniently, the `body' argument
now also accepts an *note iterable: c7c. object so long as it includes
an explicit ‘Content-Length’ header.  This extended interface is much
more flexible than before.

To establish an HTTPS connection through a proxy server, there is a new
*note set_tunnel(): c7d. method that sets the host and port for HTTP
Connect tunneling.

To match the behavior of *note http.server: 96, the HTTP client library
now also encodes headers with ISO-8859-1 (Latin-1) encoding.  It was
already doing that for incoming headers, so now the behavior is
consistent for both incoming and outgoing traffic.  (See work by Armin
Ronacher in bpo-10980(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10980


File: python.info,  Node: unittest<6>,  Next: random<3>,  Prev: http client<4>,  Up: New Improved and Deprecated Modules

1.8.9.33 unittest
.................

The unittest module has a number of improvements supporting test
discovery for packages, easier experimentation at the interactive
prompt, new testcase methods, improved diagnostic messages for test
failures, and better method names.

   * The command-line call ‘python -m unittest’ can now accept file
     paths instead of module names for running specific tests
     (bpo-10620(1)).  The new test discovery can find tests within
     packages, locating any test importable from the top-level
     directory.  The top-level directory can be specified with the ‘-t’
     option, a pattern for matching files with ‘-p’, and a directory to
     start discovery with ‘-s’:

          $ python -m unittest discover -s my_proj_dir -p _test.py

     (Contributed by Michael Foord.)

   * Experimentation at the interactive prompt is now easier because the
     ‘unittest.case.TestCase’ class can now be instantiated without
     arguments:

          >>> from unittest import TestCase
          >>> TestCase().assertEqual(pow(2, 3), 8)

     (Contributed by Michael Foord.)

   * The *note unittest: 124. module has two new methods, *note
     assertWarns(): b94. and *note assertWarnsRegex(): b95. to verify
     that a given warning type is triggered by the code under test:

          with self.assertWarns(DeprecationWarning):
              legacy_function('XYZ')

     (Contributed by Antoine Pitrou, bpo-9754(2).)

     Another new method, *note assertCountEqual(): c7f. is used to
     compare two iterables to determine if their element counts are
     equal (whether the same elements are present with the same number
     of occurrences regardless of order):

          def test_anagram(self):
              self.assertCountEqual('algorithm', 'logarithm')

     (Contributed by Raymond Hettinger.)

   * A principal feature of the unittest module is an effort to produce
     meaningful diagnostics when a test fails.  When possible, the
     failure is recorded along with a diff of the output.  This is
     especially helpful for analyzing log files of failed test runs.
     However, since diffs can sometime be voluminous, there is a new
     *note maxDiff: c80. attribute that sets maximum length of diffs
     displayed.

   * In addition, the method names in the module have undergone a number
     of clean-ups.

     For example, *note assertRegex(): c81. is the new name for
     ‘assertRegexpMatches()’ which was misnamed because the test uses
     *note re.search(): c82, not *note re.match(): c83.  Other methods
     using regular expressions are now named using short form “Regex” in
     preference to “Regexp” – this matches the names used in other
     unittest implementations, matches Python’s old name for the *note
     re: dd. module, and it has unambiguous camel-casing.

     (Contributed by Raymond Hettinger and implemented by Ezio Melotti.)

   * To improve consistency, some long-standing method aliases are being
     deprecated in favor of the preferred names:

          Old Name                            Preferred Name
                                              
          -----------------------------------------------------------------------
                                              
          ‘assert_()’                         *note assertTrue(): c84.
                                              
                                              
          ‘assertEquals()’                    *note assertEqual(): c85.
                                              
                                              
          ‘assertNotEquals()’                 *note assertNotEqual(): c86.
                                              
                                              
          ‘assertAlmostEquals()’              *note assertAlmostEqual(): c87.
                                              
                                              
          ‘assertNotAlmostEquals()’           *note assertNotAlmostEqual(): c88.
                                              

     Likewise, the ‘TestCase.fail*’ methods deprecated in Python 3.1 are
     expected to be removed in Python 3.3.  Also see the *note
     Deprecated aliases: c89. section in the *note unittest: 124.
     documentation.

     (Contributed by Ezio Melotti; bpo-9424(3).)

   * The ‘assertDictContainsSubset()’ method was deprecated because it
     was misimplemented with the arguments in the wrong order.  This
     created hard-to-debug optical illusions where tests like
     ‘TestCase().assertDictContainsSubset({'a':1, 'b':2}, {'a':1})’
     would fail.

     (Contributed by Raymond Hettinger.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10620

   (2) https://bugs.python.org/issue9754

   (3) https://bugs.python.org/issue9424


File: python.info,  Node: random<3>,  Next: poplib<4>,  Prev: unittest<6>,  Up: New Improved and Deprecated Modules

1.8.9.34 random
...............

The integer methods in the *note random: dc. module now do a better job
of producing uniform distributions.  Previously, they computed
selections with ‘int(n*random())’ which had a slight bias whenever `n'
was not a power of two.  Now, multiple selections are made from a range
up to the next power of two and a selection is kept only when it falls
within the range ‘0 <= x < n’.  The functions and methods affected are
*note randrange(): c8b, *note randint(): c8c, *note choice(): c8d, *note
shuffle(): 212. and *note sample(): c8e.

(Contributed by Raymond Hettinger; bpo-9025(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9025


File: python.info,  Node: poplib<4>,  Next: asyncore<2>,  Prev: random<3>,  Up: New Improved and Deprecated Modules

1.8.9.35 poplib
...............

*note POP3_SSL: 1d6. class now accepts a `context' parameter, which is a
*note ssl.SSLContext: 4ea. object allowing bundling SSL configuration
options, certificates and private keys into a single (potentially
long-lived) structure.

(Contributed by Giampaolo Rodolà; bpo-8807(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8807


File: python.info,  Node: asyncore<2>,  Next: tempfile<2>,  Prev: poplib<4>,  Up: New Improved and Deprecated Modules

1.8.9.36 asyncore
.................

*note asyncore.dispatcher: c91. now provides a *note handle_accepted():
c92. method returning a ‘(sock, addr)’ pair which is called when a
connection has actually been established with a new remote endpoint.
This is supposed to be used as a replacement for old *note
handle_accept(): c93. and avoids the user to call *note accept(): c94.
directly.

(Contributed by Giampaolo Rodolà; bpo-6706(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue6706


File: python.info,  Node: tempfile<2>,  Next: inspect<7>,  Prev: asyncore<2>,  Up: New Improved and Deprecated Modules

1.8.9.37 tempfile
.................

The *note tempfile: 103. module has a new context manager, *note
TemporaryDirectory: c96. which provides easy deterministic cleanup of
temporary directories:

     with tempfile.TemporaryDirectory() as tmpdirname:
         print('created temporary dir:', tmpdirname)

(Contributed by Neil Schemenauer and Nick Coghlan; bpo-5178(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5178


File: python.info,  Node: inspect<7>,  Next: pydoc<6>,  Prev: tempfile<2>,  Up: New Improved and Deprecated Modules

1.8.9.38 inspect
................

   * The *note inspect: a0. module has a new function *note
     getgeneratorstate(): c98. to easily identify the current state of a
     generator-iterator:

          >>> from inspect import getgeneratorstate
          >>> def gen():
          ...     yield 'demo'
          >>> g = gen()
          >>> getgeneratorstate(g)
          'GEN_CREATED'
          >>> next(g)
          'demo'
          >>> getgeneratorstate(g)
          'GEN_SUSPENDED'
          >>> next(g, None)
          >>> getgeneratorstate(g)
          'GEN_CLOSED'

     (Contributed by Rodolpho Eckhardt and Nick Coghlan, bpo-10220(1).)

   * To support lookups without the possibility of activating a dynamic
     attribute, the *note inspect: a0. module has a new function, *note
     getattr_static(): c99.  Unlike *note hasattr(): 54a, this is a true
     read-only search, guaranteed not to change state while it is
     searching:

          >>> class A:
          ...     @property
          ...     def f(self):
          ...         print('Running')
          ...         return 10
          ...
          >>> a = A()
          >>> getattr(a, 'f')
          Running
          10
          >>> inspect.getattr_static(a, 'f')
          <property object at 0x1022bd788>

     (Contributed by Michael Foord.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10220


File: python.info,  Node: pydoc<6>,  Next: dis<3>,  Prev: inspect<7>,  Up: New Improved and Deprecated Modules

1.8.9.39 pydoc
..............

The *note pydoc: d9. module now provides a much-improved Web server
interface, as well as a new command-line option ‘-b’ to automatically
open a browser window to display that server:

     $ pydoc3.2 -b

(Contributed by Ron Adam; bpo-2001(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue2001


File: python.info,  Node: dis<3>,  Next: dbm<6>,  Prev: pydoc<6>,  Up: New Improved and Deprecated Modules

1.8.9.40 dis
............

The *note dis: 37. module gained two new functions for inspecting code,
*note code_info(): c9c. and *note show_code(): 91f.  Both provide
detailed code object information for the supplied function, method,
source code string or code object.  The former returns a string and the
latter prints it:

     >>> import dis, random
     >>> dis.show_code(random.choice)
     Name:              choice
     Filename:          /Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/random.py
     Argument count:    2
     Kw-only arguments: 0
     Number of locals:  3
     Stack size:        11
     Flags:             OPTIMIZED, NEWLOCALS, NOFREE
     Constants:
        0: 'Choose a random element from a non-empty sequence.'
        1: 'Cannot choose from an empty sequence'
     Names:
        0: _randbelow
        1: len
        2: ValueError
        3: IndexError
     Variable names:
        0: self
        1: seq
        2: i

In addition, the *note dis(): 48b. function now accepts string arguments
so that the common idiom ‘dis(compile(s, '', 'eval'))’ can be shortened
to ‘dis(s)’:

     >>> dis('3*x+1 if x%2==1 else x//2')
       1           0 LOAD_NAME                0 (x)
                   3 LOAD_CONST               0 (2)
                   6 BINARY_MODULO
                   7 LOAD_CONST               1 (1)
                  10 COMPARE_OP               2 (==)
                  13 POP_JUMP_IF_FALSE       28
                  16 LOAD_CONST               2 (3)
                  19 LOAD_NAME                0 (x)
                  22 BINARY_MULTIPLY
                  23 LOAD_CONST               1 (1)
                  26 BINARY_ADD
                  27 RETURN_VALUE
             >>   28 LOAD_NAME                0 (x)
                  31 LOAD_CONST               0 (2)
                  34 BINARY_FLOOR_DIVIDE
                  35 RETURN_VALUE

Taken together, these improvements make it easier to explore how CPython
is implemented and to see for yourself what the language syntax does
under-the-hood.

(Contributed by Nick Coghlan in bpo-9147(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9147


File: python.info,  Node: dbm<6>,  Next: ctypes<2>,  Prev: dis<3>,  Up: New Improved and Deprecated Modules

1.8.9.41 dbm
............

All database modules now support the ‘get()’ and ‘setdefault()’ methods.

(Suggested by Ray Allen in bpo-9523(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9523


File: python.info,  Node: ctypes<2>,  Next: site<2>,  Prev: dbm<6>,  Up: New Improved and Deprecated Modules

1.8.9.42 ctypes
...............

A new type, *note ctypes.c_ssize_t: c9f. represents the C ‘ssize_t’
datatype.


File: python.info,  Node: site<2>,  Next: sysconfig<2>,  Prev: ctypes<2>,  Up: New Improved and Deprecated Modules

1.8.9.43 site
.............

The *note site: eb. module has three new functions useful for reporting
on the details of a given Python installation.

   * *note getsitepackages(): ca1. lists all global site-packages
     directories.

   * *note getuserbase(): ca2. reports on the user’s base directory
     where data can be stored.

   * *note getusersitepackages(): ca3. reveals the user-specific
     site-packages directory path.

     >>> import site
     >>> site.getsitepackages()
     ['/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/site-packages',
      '/Library/Frameworks/Python.framework/Versions/3.2/lib/site-python',
      '/Library/Python/3.2/site-packages']
     >>> site.getuserbase()
     '/Users/raymondhettinger/Library/Python/3.2'
     >>> site.getusersitepackages()
     '/Users/raymondhettinger/Library/Python/3.2/lib/python/site-packages'

Conveniently, some of site’s functionality is accessible directly from
the command-line:

     $ python -m site --user-base
     /Users/raymondhettinger/.local
     $ python -m site --user-site
     /Users/raymondhettinger/.local/lib/python3.2/site-packages

(Contributed by Tarek Ziadé in bpo-6693(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue6693


File: python.info,  Node: sysconfig<2>,  Next: pdb<6>,  Prev: site<2>,  Up: New Improved and Deprecated Modules

1.8.9.44 sysconfig
..................

The new *note sysconfig: fe. module makes it straightforward to discover
installation paths and configuration variables that vary across
platforms and installations.

The module offers access simple access functions for platform and
version information:

   * *note get_platform(): ca5. returning values like `linux-i586' or
     `macosx-10.6-ppc'.

   * *note get_python_version(): ca6. returns a Python version string
     such as “3.2”.

It also provides access to the paths and variables corresponding to one
of seven named schemes used by *note distutils: 38.  Those include
`posix_prefix', `posix_home', `posix_user', `nt', `nt_user', `os2',
`os2_home':

   * *note get_paths(): ca7. makes a dictionary containing installation
     paths for the current installation scheme.

   * *note get_config_vars(): a46. returns a dictionary of platform
     specific variables.

There is also a convenient command-line interface:

     C:\Python32>python -m sysconfig
     Platform: "win32"
     Python version: "3.2"
     Current installation scheme: "nt"

     Paths:
             data = "C:\Python32"
             include = "C:\Python32\Include"
             platinclude = "C:\Python32\Include"
             platlib = "C:\Python32\Lib\site-packages"
             platstdlib = "C:\Python32\Lib"
             purelib = "C:\Python32\Lib\site-packages"
             scripts = "C:\Python32\Scripts"
             stdlib = "C:\Python32\Lib"

     Variables:
             BINDIR = "C:\Python32"
             BINLIBDEST = "C:\Python32\Lib"
             EXE = ".exe"
             INCLUDEPY = "C:\Python32\Include"
             LIBDEST = "C:\Python32\Lib"
             SO = ".pyd"
             VERSION = "32"
             abiflags = ""
             base = "C:\Python32"
             exec_prefix = "C:\Python32"
             platbase = "C:\Python32"
             prefix = "C:\Python32"
             projectbase = "C:\Python32"
             py_version = "3.2"
             py_version_nodot = "32"
             py_version_short = "3.2"
             srcdir = "C:\Python32"
             userbase = "C:\Documents and Settings\Raymond\Application Data\Python"

(Moved out of Distutils by Tarek Ziadé.)


File: python.info,  Node: pdb<6>,  Next: configparser<2>,  Prev: sysconfig<2>,  Up: New Improved and Deprecated Modules

1.8.9.45 pdb
............

The *note pdb: c9. debugger module gained a number of usability
improvements:

   * ‘pdb.py’ now has a ‘-c’ option that executes commands as given in a
     ‘.pdbrc’ script file.

   * A ‘.pdbrc’ script file can contain ‘continue’ and ‘next’ commands
     that continue debugging.

   * The ‘Pdb’ class constructor now accepts a `nosigint' argument.

   * New commands: ‘l(list)’, ‘ll(long list)’ and ‘source’ for listing
     source code.

   * New commands: ‘display’ and ‘undisplay’ for showing or hiding the
     value of an expression if it has changed.

   * New command: ‘interact’ for starting an interactive interpreter
     containing the global and local names found in the current scope.

   * Breakpoints can be cleared by breakpoint number.

(Contributed by Georg Brandl, Antonio Cuni and Ilya Sandler.)


File: python.info,  Node: configparser<2>,  Next: urllib parse<4>,  Prev: pdb<6>,  Up: New Improved and Deprecated Modules

1.8.9.46 configparser
.....................

The *note configparser: 22. module was modified to improve usability and
predictability of the default parser and its supported INI syntax.  The
old ‘ConfigParser’ class was removed in favor of ‘SafeConfigParser’
which has in turn been renamed to *note ConfigParser: 5a5.  Support for
inline comments is now turned off by default and section or option
duplicates are not allowed in a single configuration source.

Config parsers gained a new API based on the mapping protocol:

     >>> parser = ConfigParser()
     >>> parser.read_string("""
     ... [DEFAULT]
     ... location = upper left
     ... visible = yes
     ... editable = no
     ... color = blue
     ...
     ... [main]
     ... title = Main Menu
     ... color = green
     ...
     ... [options]
     ... title = Options
     ... """)
     >>> parser['main']['color']
     'green'
     >>> parser['main']['editable']
     'no'
     >>> section = parser['options']
     >>> section['title']
     'Options'
     >>> section['title'] = 'Options (editable: %(editable)s)'
     >>> section['title']
     'Options (editable: no)'

The new API is implemented on top of the classical API, so custom parser
subclasses should be able to use it without modifications.

The INI file structure accepted by config parsers can now be customized.
Users can specify alternative option/value delimiters and comment
prefixes, change the name of the `DEFAULT' section or switch the
interpolation syntax.

There is support for pluggable interpolation including an additional
interpolation handler *note ExtendedInterpolation: caa.:

     >>> parser = ConfigParser(interpolation=ExtendedInterpolation())
     >>> parser.read_dict({'buildout': {'directory': '/home/ambv/zope9'},
     ...                   'custom': {'prefix': '/usr/local'}})
     >>> parser.read_string("""
     ... [buildout]
     ... parts =
     ...   zope9
     ...   instance
     ... find-links =
     ...   ${buildout:directory}/downloads/dist
     ...
     ... [zope9]
     ... recipe = plone.recipe.zope9install
     ... location = /opt/zope
     ...
     ... [instance]
     ... recipe = plone.recipe.zope9instance
     ... zope9-location = ${zope9:location}
     ... zope-conf = ${custom:prefix}/etc/zope.conf
     ... """)
     >>> parser['buildout']['find-links']
     '\n/home/ambv/zope9/downloads/dist'
     >>> parser['instance']['zope-conf']
     '/usr/local/etc/zope.conf'
     >>> instance = parser['instance']
     >>> instance['zope-conf']
     '/usr/local/etc/zope.conf'
     >>> instance['zope9-location']
     '/opt/zope'

A number of smaller features were also introduced, like support for
specifying encoding in read operations, specifying fallback values for
get-functions, or reading directly from dictionaries and strings.

(All changes contributed by Łukasz Langa.)


File: python.info,  Node: urllib parse<4>,  Next: mailbox,  Prev: configparser<2>,  Up: New Improved and Deprecated Modules

1.8.9.47 urllib.parse
.....................

A number of usability improvements were made for the *note urllib.parse:
128. module.

The *note urlparse(): 6f1. function now supports IPv6(1) addresses as
described in RFC 2732(2):

     >>> import urllib.parse
     >>> urllib.parse.urlparse('http://[dead:beef:cafe:5417:affe:8FA3:deaf:feed]/foo/')
     ParseResult(scheme='http',
                 netloc='[dead:beef:cafe:5417:affe:8FA3:deaf:feed]',
                 path='/foo/',
                 params='',
                 query='',
                 fragment='')

The *note urldefrag(): cac. function now returns a *note named tuple:
b7b.:

     >>> r = urllib.parse.urldefrag('http://python.org/about/#target')
     >>> r
     DefragResult(url='http://python.org/about/', fragment='target')
     >>> r[0]
     'http://python.org/about/'
     >>> r.fragment
     'target'

And, the *note urlencode(): 87a. function is now much more flexible,
accepting either a string or bytes type for the `query' argument.  If it
is a string, then the `safe', `encoding', and `error' parameters are
sent to *note quote_plus(): cad. for encoding:

     >>> urllib.parse.urlencode([
     ...      ('type', 'telenovela'),
     ...      ('name', '¿Dónde Está Elisa?')],
     ...      encoding='latin-1')
     'type=telenovela&name=%BFD%F3nde+Est%E1+Elisa%3F'

As detailed in *note Parsing ASCII Encoded Bytes: cae, all the *note
urllib.parse: 128. functions now accept ASCII-encoded byte strings as
input, so long as they are not mixed with regular strings.  If
ASCII-encoded byte strings are given as parameters, the return types
will also be an ASCII-encoded byte strings:

     >>> urllib.parse.urlparse(b'http://www.python.org:80/about/')
     ParseResultBytes(scheme=b'http', netloc=b'www.python.org:80',
                      path=b'/about/', params=b'', query=b'', fragment=b'')

(Work by Nick Coghlan, Dan Mahn, and Senthil Kumaran in bpo-2987(3),
bpo-5468(4), and bpo-9873(5).)

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/IPv6

   (2) https://tools.ietf.org/html/rfc2732.html

   (3) https://bugs.python.org/issue2987

   (4) https://bugs.python.org/issue5468

   (5) https://bugs.python.org/issue9873


File: python.info,  Node: mailbox,  Next: turtledemo,  Prev: urllib parse<4>,  Up: New Improved and Deprecated Modules

1.8.9.48 mailbox
................

Thanks to a concerted effort by R. David Murray, the *note mailbox: ae.
module has been fixed for Python 3.2.  The challenge was that mailbox
had been originally designed with a text interface, but email messages
are best represented with *note bytes: 172. because various parts of a
message may have different encodings.

The solution harnessed the *note email: 67. package’s binary support for
parsing arbitrary email messages.  In addition, the solution required a
number of API changes.

As expected, the *note add(): cb0. method for *note mailbox.Mailbox:
cb1. objects now accepts binary input.

*note StringIO: 91a. and text file input are deprecated.  Also, string
input will fail early if non-ASCII characters are used.  Previously it
would fail when the email was processed in a later step.

There is also support for binary output.  The *note get_file(): cb2.
method now returns a file in the binary mode (where it used to
incorrectly set the file to text-mode).  There is also a new *note
get_bytes(): cb3. method that returns a *note bytes: 172. representation
of a message corresponding to a given `key'.

It is still possible to get non-binary output using the old API’s *note
get_string(): cb4. method, but that approach is not very useful.
Instead, it is best to extract messages from a *note Message: cb5.
object or to load them from binary input.

(Contributed by R. David Murray, with efforts from Steffen Daode
Nurpmeso and an initial patch by Victor Stinner in bpo-9124(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue9124


File: python.info,  Node: turtledemo,  Prev: mailbox,  Up: New Improved and Deprecated Modules

1.8.9.49 turtledemo
...................

The demonstration code for the *note turtle: 11f. module was moved from
the `Demo' directory to main library.  It includes over a dozen sample
scripts with lively displays.  Being on *note sys.path: 260, it can now
be run directly from the command-line:

     $ python -m turtledemo

(Moved from the Demo directory by Alexander Belopolsky in bpo-10199(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10199


File: python.info,  Node: Multi-threading,  Next: Optimizations<7>,  Prev: New Improved and Deprecated Modules,  Up: What’s New In Python 3 2

1.8.10 Multi-threading
----------------------

   * The mechanism for serializing execution of concurrently running
     Python threads (generally known as the *note GIL: 20e. or Global
     Interpreter Lock) has been rewritten.  Among the objectives were
     more predictable switching intervals and reduced overhead due to
     lock contention and the number of ensuing system calls.  The notion
     of a “check interval” to allow thread switches has been abandoned
     and replaced by an absolute duration expressed in seconds.  This
     parameter is tunable through *note sys.setswitchinterval(): 218.
     It currently defaults to 5 milliseconds.

     Additional details about the implementation can be read from a
     python-dev mailing-list message(1) (however, “priority requests” as
     exposed in this message have not been kept for inclusion).

     (Contributed by Antoine Pitrou.)

   * Regular and recursive locks now accept an optional `timeout'
     argument to their *note acquire(): 85b. method.  (Contributed by
     Antoine Pitrou; bpo-7316(2).)

   * Similarly, *note threading.Semaphore.acquire(): cb8. also gained a
     `timeout' argument.  (Contributed by Torsten Landschoff;
     bpo-850728(3).)

   * Regular and recursive lock acquisitions can now be interrupted by
     signals on platforms using Pthreads.  This means that Python
     programs that deadlock while acquiring locks can be successfully
     killed by repeatedly sending SIGINT to the process (by pressing
     ‘Ctrl+C’ in most shells).  (Contributed by Reid Kleckner;
     bpo-8844(4).)

   ---------- Footnotes ----------

   (1) 
https://mail.python.org/pipermail/python-dev/2009-October/093321.html

   (2) https://bugs.python.org/issue7316

   (3) https://bugs.python.org/issue850728

   (4) https://bugs.python.org/issue8844


File: python.info,  Node: Optimizations<7>,  Next: Unicode,  Prev: Multi-threading,  Up: What’s New In Python 3 2

1.8.11 Optimizations
--------------------

A number of small performance enhancements have been added:

   * Python’s peephole optimizer now recognizes patterns such ‘x in {1,
     2, 3}’ as being a test for membership in a set of constants.  The
     optimizer recasts the *note set: 1f6. as a *note frozenset: 1f7.
     and stores the pre-built constant.

     Now that the speed penalty is gone, it is practical to start
     writing membership tests using set-notation.  This style is both
     semantically clear and operationally fast:

          extension = name.rpartition('.')[2]
          if extension in {'xml', 'html', 'xhtml', 'css'}:
              handle(name)

     (Patch and additional tests contributed by Dave Malcolm;
     bpo-6690(1)).

   * Serializing and unserializing data using the *note pickle: ca.
     module is now several times faster.

     (Contributed by Alexandre Vassalotti, Antoine Pitrou and the
     Unladen Swallow team in bpo-9410(2) and bpo-3873(3).)

   * The Timsort algorithm(4) used in *note list.sort(): 548. and *note
     sorted(): 547. now runs faster and uses less memory when called
     with a *note key function: 7d2.  Previously, every element of a
     list was wrapped with a temporary object that remembered the key
     value associated with each element.  Now, two arrays of keys and
     values are sorted in parallel.  This saves the memory consumed by
     the sort wrappers, and it saves time lost to delegating
     comparisons.

     (Patch by Daniel Stutzbach in bpo-9915(5).)

   * JSON decoding performance is improved and memory consumption is
     reduced whenever the same string is repeated for multiple keys.
     Also, JSON encoding now uses the C speedups when the ‘sort_keys’
     argument is true.

     (Contributed by Antoine Pitrou in bpo-7451(6) and by Raymond
     Hettinger and Antoine Pitrou in bpo-10314(7).)

   * Recursive locks (created with the *note threading.RLock(): cba.
     API) now benefit from a C implementation which makes them as fast
     as regular locks, and between 10x and 15x faster than their
     previous pure Python implementation.

     (Contributed by Antoine Pitrou; bpo-3001(8).)

   * The fast-search algorithm in stringlib is now used by the
     ‘split()’, ‘rsplit()’, ‘splitlines()’ and ‘replace()’ methods on
     *note bytes: 172, *note bytearray: 173. and *note str: 205.
     objects.  Likewise, the algorithm is also used by ‘rfind()’,
     ‘rindex()’, ‘rsplit()’ and ‘rpartition()’.

     (Patch by Florent Xicluna in bpo-7622(9) and bpo-7462(10).)

   * Integer to string conversions now work two “digits” at a time,
     reducing the number of division and modulo operations.

     (bpo-6713(11) by Gawain Bolton, Mark Dickinson, and Victor
     Stinner.)

There were several other minor optimizations.  Set differencing now runs
faster when one operand is much larger than the other (patch by Andress
Bennetts in bpo-8685(12)).  The ‘array.repeat()’ method has a faster
implementation (bpo-1569291(13) by Alexander Belopolsky).  The
‘BaseHTTPRequestHandler’ has more efficient buffering (bpo-3709(14) by
Andrew Schaaf).  The *note operator.attrgetter(): 80a. function has been
sped-up (bpo-10160(15) by Christos Georgiou).  And ‘ConfigParser’ loads
multi-line arguments a bit faster (bpo-7113(16) by Łukasz Langa).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue6690

   (2) https://bugs.python.org/issue9410

   (3) https://bugs.python.org/issue3873

   (4) https://en.wikipedia.org/wiki/Timsort

   (5) https://bugs.python.org/issue9915

   (6) https://bugs.python.org/issue7451

   (7) https://bugs.python.org/issue10314

   (8) https://bugs.python.org/issue3001

   (9) https://bugs.python.org/issue7622

   (10) https://bugs.python.org/issue7462

   (11) https://bugs.python.org/issue6713

   (12) https://bugs.python.org/issue8685

   (13) https://bugs.python.org/issue1569291

   (14) https://bugs.python.org/issue3709

   (15) https://bugs.python.org/issue10160

   (16) https://bugs.python.org/issue7113


File: python.info,  Node: Unicode,  Next: Codecs,  Prev: Optimizations<7>,  Up: What’s New In Python 3 2

1.8.12 Unicode
--------------

Python has been updated to Unicode 6.0.0(1).  The update to the standard
adds over 2,000 new characters including emoji(2) symbols which are
important for mobile phones.

In addition, the updated standard has altered the character properties
for two Kannada characters (U+0CF1, U+0CF2) and one New Tai Lue numeric
character (U+19DA), making the former eligible for use in identifiers
while disqualifying the latter.  For more information, see Unicode
Character Database Changes(3).

   ---------- Footnotes ----------

   (1) http://unicode.org/versions/Unicode6.0.0/

   (2) https://en.wikipedia.org/wiki/Emoji

   (3) http://www.unicode.org/versions/Unicode6.0.0/#Database_Changes


File: python.info,  Node: Codecs,  Next: Documentation,  Prev: Unicode,  Up: What’s New In Python 3 2

1.8.13 Codecs
-------------

Support was added for `cp720' Arabic DOS encoding (bpo-1616979(1)).

MBCS encoding no longer ignores the error handler argument.  In the
default strict mode, it raises an *note UnicodeDecodeError: 32b. when it
encounters an undecodable byte sequence and an *note UnicodeEncodeError:
32a. for an unencodable character.

The MBCS codec supports ‘'strict'’ and ‘'ignore'’ error handlers for
decoding, and ‘'strict'’ and ‘'replace'’ for encoding.

To emulate Python3.1 MBCS encoding, select the ‘'ignore'’ handler for
decoding and the ‘'replace'’ handler for encoding.

On Mac OS X, Python decodes command line arguments with ‘'utf-8'’ rather
than the locale encoding.

By default, *note tarfile: 101. uses ‘'utf-8'’ encoding on Windows
(instead of ‘'mbcs'’) and the ‘'surrogateescape'’ error handler on all
operating systems.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1616979


File: python.info,  Node: Documentation,  Next: IDLE,  Prev: Codecs,  Up: What’s New In Python 3 2

1.8.14 Documentation
--------------------

The documentation continues to be improved.

   * A table of quick links has been added to the top of lengthy
     sections such as *note Built-in Functions: cbe.  In the case of
     *note itertools: a3, the links are accompanied by tables of
     cheatsheet-style summaries to provide an overview and memory jog
     without having to read all of the docs.

   * In some cases, the pure Python source code can be a helpful adjunct
     to the documentation, so now many modules now feature quick links
     to the latest version of the source code.  For example, the *note
     functools: 83. module documentation has a quick link at the top
     labeled:

          `Source code' Lib/functools.py(1).

     (Contributed by Raymond Hettinger; see rationale(2).)

   * The docs now contain more examples and recipes.  In particular,
     *note re: dd. module has an extensive section, *note Regular
     Expression Examples: cbf.  Likewise, the *note itertools: a3.
     module continues to be updated with new *note Itertools Recipes:
     cc0.

   * The *note datetime: 30. module now has an auxiliary implementation
     in pure Python.  No functionality was changed.  This just provides
     an easier-to-read alternate implementation.

     (Contributed by Alexander Belopolsky in bpo-9528(3).)

   * The unmaintained ‘Demo’ directory has been removed.  Some demos
     were integrated into the documentation, some were moved to the
     ‘Tools/demo’ directory, and others were removed altogether.

     (Contributed by Georg Brandl in bpo-7962(4).)

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/functools.py

   (2) 
https://rhettinger.wordpress.com/2011/01/28/open-your-source-more/

   (3) https://bugs.python.org/issue9528

   (4) https://bugs.python.org/issue7962


File: python.info,  Node: IDLE,  Next: Code Repository,  Prev: Documentation,  Up: What’s New In Python 3 2

1.8.15 IDLE
-----------

   * The format menu now has an option to clean source files by
     stripping trailing whitespace.

     (Contributed by Raymond Hettinger; bpo-5150(1).)

   * IDLE on Mac OS X now works with both Carbon AquaTk and Cocoa
     AquaTk.

     (Contributed by Kevin Walzer, Ned Deily, and Ronald Oussoren;
     bpo-6075(2).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5150

   (2) https://bugs.python.org/issue6075


File: python.info,  Node: Code Repository,  Next: Build and C API Changes<5>,  Prev: IDLE,  Up: What’s New In Python 3 2

1.8.16 Code Repository
----------------------

In addition to the existing Subversion code repository at
‘http://svn.python.org’ there is now a Mercurial(1) repository at
‘https://hg.python.org/’.

After the 3.2 release, there are plans to switch to Mercurial as the
primary repository.  This distributed version control system should make
it easier for members of the community to create and share external
changesets.  See PEP 385(2) for details.

To learn to use the new version control system, see the Quick Start(3)
or the Guide to Mercurial Workflows(4).

   ---------- Footnotes ----------

   (1) https://www.mercurial-scm.org/

   (2) https://www.python.org/dev/peps/pep-0385

   (3) https://www.mercurial-scm.org/wiki/QuickStart

   (4) https://www.mercurial-scm.org/guide


File: python.info,  Node: Build and C API Changes<5>,  Next: Porting to Python 3 2,  Prev: Code Repository,  Up: What’s New In Python 3 2

1.8.17 Build and C API Changes
------------------------------

Changes to Python’s build process and to the C API include:

   * The `idle', `pydoc' and `2to3' scripts are now installed with a
     version-specific suffix on ‘make altinstall’ (bpo-10679(1)).

   * The C functions that access the Unicode Database now accept and
     return characters from the full Unicode range, even on narrow
     unicode builds (Py_UNICODE_TOLOWER, Py_UNICODE_ISDECIMAL, and
     others).  A visible difference in Python is that *note
     unicodedata.numeric(): cc4. now returns the correct value for large
     code points, and *note repr(): 8b9. may consider more characters as
     printable.

     (Reported by Bupjoe Lee and fixed by Amaury Forgeot D’Arc;
     bpo-5127(2).)

   * Computed gotos are now enabled by default on supported compilers
     (which are detected by the configure script).  They can still be
     disabled selectively by specifying ‘--without-computed-gotos’.

     (Contributed by Antoine Pitrou; bpo-9203(3).)

   * The option ‘--with-wctype-functions’ was removed.  The built-in
     unicode database is now used for all functions.

     (Contributed by Amaury Forgeot D’Arc; bpo-9210(4).)

   * Hash values are now values of a new type, ‘Py_hash_t’, which is
     defined to be the same size as a pointer.  Previously they were of
     type long, which on some 64-bit operating systems is still only 32
     bits long.  As a result of this fix, *note set: 1f6. and *note
     dict: 164. can now hold more than ‘2**32’ entries on builds with
     64-bit pointers (previously, they could grow to that size but their
     performance degraded catastrophically).

     (Suggested by Raymond Hettinger and implemented by Benjamin
     Peterson; bpo-9778(5).)

   * A new macro ‘Py_VA_COPY’ copies the state of the variable argument
     list.  It is equivalent to C99 `va_copy' but available on all
     Python platforms (bpo-2443(6)).

   * A new C API function *note PySys_SetArgvEx(): cc5. allows an
     embedded interpreter to set *note sys.argv: cc6. without also
     modifying *note sys.path: 260. (bpo-5753(7)).

   * ‘PyEval_CallObject’ is now only available in macro form.  The
     function declaration, which was kept for backwards compatibility
     reasons, is now removed – the macro was introduced in 1997
     (bpo-8276(8)).

   * There is a new function *note PyLong_AsLongLongAndOverflow(): cc7.
     which is analogous to *note PyLong_AsLongAndOverflow(): cc8.  They
     both serve to convert Python *note int: 204. into a native
     fixed-width type while providing detection of cases where the
     conversion won’t fit (bpo-7767(9)).

   * The *note PyUnicode_CompareWithASCIIString(): cc9. function now
     returns `not equal' if the Python string is `NUL' terminated.

   * There is a new function *note PyErr_NewExceptionWithDoc(): cca.
     that is like *note PyErr_NewException(): ccb. but allows a
     docstring to be specified.  This lets C exceptions have the same
     self-documenting capabilities as their pure Python counterparts
     (bpo-7033(10)).

   * When compiled with the ‘--with-valgrind’ option, the pymalloc
     allocator will be automatically disabled when running under
     Valgrind.  This gives improved memory leak detection when running
     under Valgrind, while taking advantage of pymalloc at other times
     (bpo-2422(11)).

   * Removed the ‘O?’ format from the `PyArg_Parse' functions.  The
     format is no longer used and it had never been documented
     (bpo-8837(12)).

There were a number of other small changes to the C-API. See the
Misc/NEWS(13) file for a complete list.

Also, there were a number of updates to the Mac OS X build, see
Mac/BuildScript/README.txt(14) for details.  For users running a
32/64-bit build, there is a known problem with the default Tcl/Tk on Mac
OS X 10.6.  Accordingly, we recommend installing an updated alternative
such as ActiveState Tcl/Tk 8.5.9(15).  See
‘https://www.python.org/download/mac/tcltk/’ for additional details.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10679

   (2) https://bugs.python.org/issue5127

   (3) https://bugs.python.org/issue9203

   (4) https://bugs.python.org/issue9210

   (5) https://bugs.python.org/issue9778

   (6) https://bugs.python.org/issue2443

   (7) https://bugs.python.org/issue5753

   (8) https://bugs.python.org/issue8276

   (9) https://bugs.python.org/issue7767

   (10) https://bugs.python.org/issue7033

   (11) https://bugs.python.org/issue2422

   (12) https://bugs.python.org/issue8837

   (13) https://github.com/python/cpython/tree/3.9/Misc/NEWS

   (14) 
https://github.com/python/cpython/tree/3.9/Mac/BuildScript/README.txt

   (15) https://www.activestate.com/activetcl/downloads


File: python.info,  Node: Porting to Python 3 2,  Prev: Build and C API Changes<5>,  Up: What’s New In Python 3 2

1.8.18 Porting to Python 3.2
----------------------------

This section lists previously described changes and other bugfixes that
may require changes to your code:

   * The *note configparser: 22. module has a number of clean-ups.  The
     major change is to replace the old ‘ConfigParser’ class with
     long-standing preferred alternative ‘SafeConfigParser’.  In
     addition there are a number of smaller incompatibilities:

        * The interpolation syntax is now validated on *note get(): ccd.
          and *note set(): cce. operations.  In the default
          interpolation scheme, only two tokens with percent signs are
          valid: ‘%(name)s’ and ‘%%’, the latter being an escaped
          percent sign.

        * The *note set(): cce. and *note add_section(): ccf. methods
          now verify that values are actual strings.  Formerly,
          unsupported types could be introduced unintentionally.

        * Duplicate sections or options from a single source now raise
          either *note DuplicateSectionError: cd0. or *note
          DuplicateOptionError: cd1.  Formerly, duplicates would
          silently overwrite a previous entry.

        * Inline comments are now disabled by default so now the `;'
          character can be safely used in values.

        * Comments now can be indented.  Consequently, for `;' or `#' to
          appear at the start of a line in multiline values, it has to
          be interpolated.  This keeps comment prefix characters in
          values from being mistaken as comments.

        * ‘""’ is now a valid value and is no longer automatically
          converted to an empty string.  For empty strings, use ‘"option
          ="’ in a line.

   * The *note nntplib: c0. module was reworked extensively, meaning
     that its APIs are often incompatible with the 3.1 APIs.

   * *note bytearray: 173. objects can no longer be used as filenames;
     instead, they should be converted to *note bytes: 172.

   * The ‘array.tostring()’ and ‘array.fromstring()’ have been renamed
     to ‘array.tobytes()’ and ‘array.frombytes()’ for clarity.  The old
     names have been deprecated.  (See bpo-8990(1).)

   * ‘PyArg_Parse*()’ functions:

        * “t#” format has been removed: use “s#” or “s*” instead

        * “w” and “w#” formats has been removed: use “w*” instead

   * The ‘PyCObject’ type, deprecated in 3.1, has been removed.  To wrap
     opaque C pointers in Python objects, the *note PyCapsule: cd2. API
     should be used instead; the new type has a well-defined interface
     for passing typing safety information and a less complicated
     signature for calling a destructor.

   * The ‘sys.setfilesystemencoding()’ function was removed because it
     had a flawed design.

   * The *note random.seed(): cd3. function and method now salt string
     seeds with an sha512 hash function.  To access the previous version
     of `seed' in order to reproduce Python 3.1 sequences, set the
     `version' argument to `1', ‘random.seed(s, version=1)’.

   * The previously deprecated ‘string.maketrans()’ function has been
     removed in favor of the static methods *note bytes.maketrans():
     cd4. and *note bytearray.maketrans(): cd5.  This change solves the
     confusion around which types were supported by the *note string:
     f6. module.  Now, *note str: 205, *note bytes: 172, and *note
     bytearray: 173. each have their own `maketrans' and `translate'
     methods with intermediate translation tables of the appropriate
     type.

     (Contributed by Georg Brandl; bpo-5675(2).)

   * The previously deprecated ‘contextlib.nested()’ function has been
     removed in favor of a plain *note with: 7da. statement which can
     accept multiple context managers.  The latter technique is faster
     (because it is built-in), and it does a better job finalizing
     multiple context managers when one of them raises an exception:

          with open('mylog.txt') as infile, open('a.out', 'w') as outfile:
              for line in infile:
                  if '<critical>' in line:
                      outfile.write(line)

     (Contributed by Georg Brandl and Mattias Brändström; appspot issue
     53094(3).)

   * *note struct.pack(): cd6. now only allows bytes for the ‘s’ string
     pack code.  Formerly, it would accept text arguments and implicitly
     encode them to bytes using UTF-8.  This was problematic because it
     made assumptions about the correct encoding and because a
     variable-length encoding can fail when writing to fixed length
     segment of a structure.

     Code such as ‘struct.pack('<6sHHBBB', 'GIF87a', x, y)’ should be
     rewritten with to use bytes instead of text,
     ‘struct.pack('<6sHHBBB', b'GIF87a', x, y)’.

     (Discovered by David Beazley and fixed by Victor Stinner;
     bpo-10783(4).)

   * The *note xml.etree.ElementTree: 140. class now raises an *note
     xml.etree.ElementTree.ParseError: cd7. when a parse fails.
     Previously it raised an *note xml.parsers.expat.ExpatError: cd8.

   * The new, longer *note str(): 205. value on floats may break
     doctests which rely on the old output format.

   * In *note subprocess.Popen: 3db, the default value for `close_fds'
     is now ‘True’ under Unix; under Windows, it is ‘True’ if the three
     standard streams are set to ‘None’, ‘False’ otherwise.  Previously,
     `close_fds' was always ‘False’ by default, which produced difficult
     to solve bugs or race conditions when open file descriptors would
     leak into the child process.

   * Support for legacy HTTP 0.9 has been removed from *note
     urllib.request: 129. and *note http.client: 93.  Such support is
     still present on the server side (in *note http.server: 96.).

     (Contributed by Antoine Pitrou, bpo-10711(5).)

   * SSL sockets in timeout mode now raise *note socket.timeout: cd9.
     when a timeout occurs, rather than a generic *note SSLError: cda.

     (Contributed by Antoine Pitrou, bpo-10272(6).)

   * The misleading functions *note PyEval_AcquireLock(): 3d4. and *note
     PyEval_ReleaseLock(): cdb. have been officially deprecated.  The
     thread-state aware APIs (such as *note PyEval_SaveThread(): cdc.
     and *note PyEval_RestoreThread(): 3d6.) should be used instead.

   * Due to security risks, ‘asyncore.handle_accept()’ has been
     deprecated, and a new function, ‘asyncore.handle_accepted()’, was
     added to replace it.

     (Contributed by Giampaolo Rodola in bpo-6706(7).)

   * Due to the new *note GIL: 20e. implementation, *note
     PyEval_InitThreads(): 20c. cannot be called before *note
     Py_Initialize(): 20f. anymore.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8990

   (2) https://bugs.python.org/issue5675

   (3) https://codereview.appspot.com/53094

   (4) https://bugs.python.org/issue10783

   (5) https://bugs.python.org/issue10711

   (6) https://bugs.python.org/issue10272

   (7) https://bugs.python.org/issue6706


File: python.info,  Node: What’s New In Python 3 1,  Next: What’s New In Python 3 0,  Prev: What’s New In Python 3 2,  Up: What’s New in Python

1.9 What’s New In Python 3.1
============================


Author: Raymond Hettinger

This article explains the new features in Python 3.1, compared to 3.0.

* Menu:

* PEP 372; Ordered Dictionaries: PEP 372 Ordered Dictionaries.
* PEP 378; Format Specifier for Thousands Separator: PEP 378 Format Specifier for Thousands Separator.
* Other Language Changes: Other Language Changes<9>.
* New, Improved, and Deprecated Modules: New Improved and Deprecated Modules<2>.
* Optimizations: Optimizations<8>.
* IDLE: IDLE<2>.
* Build and C API Changes: Build and C API Changes<6>.
* Porting to Python 3.1: Porting to Python 3 1.


File: python.info,  Node: PEP 372 Ordered Dictionaries,  Next: PEP 378 Format Specifier for Thousands Separator,  Up: What’s New In Python 3 1

1.9.1 PEP 372: Ordered Dictionaries
-----------------------------------

Regular Python dictionaries iterate over key/value pairs in arbitrary
order.  Over the years, a number of authors have written alternative
implementations that remember the order that the keys were originally
inserted.  Based on the experiences from those implementations, a new
*note collections.OrderedDict: 2ea. class has been introduced.

The OrderedDict API is substantially the same as regular dictionaries
but will iterate over keys and values in a guaranteed order depending on
when a key was first inserted.  If a new entry overwrites an existing
entry, the original insertion position is left unchanged.  Deleting an
entry and reinserting it will move it to the end.

The standard library now supports use of ordered dictionaries in several
modules.  The *note configparser: 22. module uses them by default.  This
lets configuration files be read, modified, and then written back in
their original order.  The `_asdict()' method for *note
collections.namedtuple(): 1a1. now returns an ordered dictionary with
the values appearing in the same order as the underlying tuple indices.
The *note json: a4. module is being built-out with an
`object_pairs_hook' to allow OrderedDicts to be built by the decoder.
Support was also added for third-party tools like PyYAML(1).

See also
........

PEP 372(2) - Ordered Dictionaries

     PEP written by Armin Ronacher and Raymond Hettinger.
     Implementation written by Raymond Hettinger.

   ---------- Footnotes ----------

   (1) http://pyyaml.org/

   (2) https://www.python.org/dev/peps/pep-0372


File: python.info,  Node: PEP 378 Format Specifier for Thousands Separator,  Next: Other Language Changes<9>,  Prev: PEP 372 Ordered Dictionaries,  Up: What’s New In Python 3 1

1.9.2 PEP 378: Format Specifier for Thousands Separator
-------------------------------------------------------

The built-in *note format(): 5d6. function and the *note str.format():
5d5. method use a mini-language that now includes a simple, non-locale
aware way to format a number with a thousands separator.  That provides
a way to humanize a program’s output, improving its professional
appearance and readability:

     >>> format(1234567, ',d')
     '1,234,567'
     >>> format(1234567.89, ',.2f')
     '1,234,567.89'
     >>> format(12345.6 + 8901234.12j, ',f')
     '12,345.600000+8,901,234.120000j'
     >>> format(Decimal('1234567.89'), ',f')
     '1,234,567.89'

The supported types are *note int: 204, *note float: 1fd, *note complex:
2c1. and *note decimal.Decimal: 2c0.

Discussions are underway about how to specify alternative separators
like dots, spaces, apostrophes, or underscores.  Locale-aware
applications should use the existing `n' format specifier which already
has some support for thousands separators.

See also
........

PEP 378(1) - Format Specifier for Thousands Separator

     PEP written by Raymond Hettinger and implemented by Eric Smith and
     Mark Dickinson.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0378


File: python.info,  Node: Other Language Changes<9>,  Next: New Improved and Deprecated Modules<2>,  Prev: PEP 378 Format Specifier for Thousands Separator,  Up: What’s New In Python 3 1

1.9.3 Other Language Changes
----------------------------

Some smaller changes made to the core Python language are:

   * Directories and zip archives containing a ‘__main__.py’ file can
     now be executed directly by passing their name to the interpreter.
     The directory/zipfile is automatically inserted as the first entry
     in sys.path.  (Suggestion and initial patch by Andy Chu; revised
     patch by Phillip J. Eby and Nick Coghlan; bpo-1739468(1).)

   * The *note int(): 204. type gained a ‘bit_length’ method that
     returns the number of bits necessary to represent its argument in
     binary:

          >>> n = 37
          >>> bin(37)
          '0b100101'
          >>> n.bit_length()
          6
          >>> n = 2**123-1
          >>> n.bit_length()
          123
          >>> (n+1).bit_length()
          124

     (Contributed by Fredrik Johansson, Victor Stinner, Raymond
     Hettinger, and Mark Dickinson; bpo-3439(2).)

   * The fields in *note format(): 5d6. strings can now be automatically
     numbered:

          >>> 'Sir {} of {}'.format('Gallahad', 'Camelot')
          'Sir Gallahad of Camelot'

     Formerly, the string would have required numbered fields such as:
     ‘'Sir {0} of {1}'’.

     (Contributed by Eric Smith; bpo-5237(3).)

   * The ‘string.maketrans()’ function is deprecated and is replaced by
     new static methods, *note bytes.maketrans(): cd4. and *note
     bytearray.maketrans(): cd5.  This change solves the confusion
     around which types were supported by the *note string: f6. module.
     Now, *note str: 205, *note bytes: 172, and *note bytearray: 173.
     each have their own `maketrans' and `translate' methods with
     intermediate translation tables of the appropriate type.

     (Contributed by Georg Brandl; bpo-5675(4).)

   * The syntax of the *note with: 7da. statement now allows multiple
     context managers in a single statement:

          >>> with open('mylog.txt') as infile, open('a.out', 'w') as outfile:
          ...     for line in infile:
          ...         if '<critical>' in line:
          ...             outfile.write(line)

     With the new syntax, the ‘contextlib.nested()’ function is no
     longer needed and is now deprecated.

     (Contributed by Georg Brandl and Mattias Brändström; appspot issue
     53094(5).)

   * ‘round(x, n)’ now returns an integer if `x' is an integer.
     Previously it returned a float:

          >>> round(1123, -2)
          1100

     (Contributed by Mark Dickinson; bpo-4707(6).)

   * Python now uses David Gay’s algorithm for finding the shortest
     floating point representation that doesn’t change its value.  This
     should help mitigate some of the confusion surrounding binary
     floating point numbers.

     The significance is easily seen with a number like ‘1.1’ which does
     not have an exact equivalent in binary floating point.  Since there
     is no exact equivalent, an expression like ‘float('1.1')’ evaluates
     to the nearest representable value which is ‘0x1.199999999999ap+0’
     in hex or ‘1.100000000000000088817841970012523233890533447265625’
     in decimal.  That nearest value was and still is used in subsequent
     floating point calculations.

     What is new is how the number gets displayed.  Formerly, Python
     used a simple approach.  The value of ‘repr(1.1)’ was computed as
     ‘format(1.1, '.17g')’ which evaluated to ‘'1.1000000000000001'’.
     The advantage of using 17 digits was that it relied on IEEE-754
     guarantees to assure that ‘eval(repr(1.1))’ would round-trip
     exactly to its original value.  The disadvantage is that many
     people found the output to be confusing (mistaking intrinsic
     limitations of binary floating point representation as being a
     problem with Python itself).

     The new algorithm for ‘repr(1.1)’ is smarter and returns ‘'1.1'’.
     Effectively, it searches all equivalent string representations
     (ones that get stored with the same underlying float value) and
     returns the shortest representation.

     The new algorithm tends to emit cleaner representations when
     possible, but it does not change the underlying values.  So, it is
     still the case that ‘1.1 + 2.2 != 3.3’ even though the
     representations may suggest otherwise.

     The new algorithm depends on certain features in the underlying
     floating point implementation.  If the required features are not
     found, the old algorithm will continue to be used.  Also, the text
     pickle protocols assure cross-platform portability by using the old
     algorithm.

     (Contributed by Eric Smith and Mark Dickinson; bpo-1580(7))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1739468

   (2) https://bugs.python.org/issue3439

   (3) https://bugs.python.org/issue5237

   (4) https://bugs.python.org/issue5675

   (5) https://codereview.appspot.com/53094

   (6) https://bugs.python.org/issue4707

   (7) https://bugs.python.org/issue1580


File: python.info,  Node: New Improved and Deprecated Modules<2>,  Next: Optimizations<8>,  Prev: Other Language Changes<9>,  Up: What’s New In Python 3 1

1.9.4 New, Improved, and Deprecated Modules
-------------------------------------------

   * Added a *note collections.Counter: ab9. class to support convenient
     counting of unique items in a sequence or iterable:

          >>> Counter(['red', 'blue', 'red', 'green', 'blue', 'blue'])
          Counter({'blue': 3, 'red': 2, 'green': 1})

     (Contributed by Raymond Hettinger; bpo-1696199(1).)

   * Added a new module, *note tkinter.ttk: 118. for access to the Tk
     themed widget set.  The basic idea of ttk is to separate, to the
     extent possible, the code implementing a widget’s behavior from the
     code implementing its appearance.

     (Contributed by Guilherme Polo; bpo-2983(2).)

   * The *note gzip.GzipFile: 206. and *note bz2.BZ2File: 224. classes
     now support the context management protocol:

          >>> # Automatically close file after writing
          >>> with gzip.GzipFile(filename, "wb") as f:
          ...     f.write(b"xxx")

     (Contributed by Antoine Pitrou.)

   * The *note decimal: 35. module now supports methods for creating a
     decimal object from a binary *note float: 1fd.  The conversion is
     exact but can sometimes be surprising:

          >>> Decimal.from_float(1.1)
          Decimal('1.100000000000000088817841970012523233890533447265625')

     The long decimal result shows the actual binary fraction being
     stored for `1.1'.  The fraction has many digits because `1.1'
     cannot be exactly represented in binary.

     (Contributed by Raymond Hettinger and Mark Dickinson.)

   * The *note itertools: a3. module grew two new functions.  The *note
     itertools.combinations_with_replacement(): ce3. function is one of
     four for generating combinatorics including permutations and
     Cartesian products.  The *note itertools.compress(): ce4. function
     mimics its namesake from APL. Also, the existing *note
     itertools.count(): ce5. function now has an optional `step'
     argument and can accept any type of counting sequence including
     *note fractions.Fraction: 2be. and *note decimal.Decimal: 2c0.:

          >>> [p+q for p,q in combinations_with_replacement('LOVE', 2)]
          ['LL', 'LO', 'LV', 'LE', 'OO', 'OV', 'OE', 'VV', 'VE', 'EE']

          >>> list(compress(data=range(10), selectors=[0,0,1,1,0,1,0,1,0,0]))
          [2, 3, 5, 7]

          >>> c = count(start=Fraction(1,2), step=Fraction(1,6))
          >>> [next(c), next(c), next(c), next(c)]
          [Fraction(1, 2), Fraction(2, 3), Fraction(5, 6), Fraction(1, 1)]

     (Contributed by Raymond Hettinger.)

   * *note collections.namedtuple(): 1a1. now supports a keyword
     argument `rename' which lets invalid fieldnames be automatically
     converted to positional names in the form _0, _1, etc.  This is
     useful when the field names are being created by an external source
     such as a CSV header, SQL field list, or user input:

          >>> query = input()
          SELECT region, dept, count(*) FROM main GROUPBY region, dept

          >>> cursor.execute(query)
          >>> query_fields = [desc[0] for desc in cursor.description]
          >>> UserQuery = namedtuple('UserQuery', query_fields, rename=True)
          >>> pprint.pprint([UserQuery(*row) for row in cursor])
          [UserQuery(region='South', dept='Shipping', _2=185),
           UserQuery(region='North', dept='Accounting', _2=37),
           UserQuery(region='West', dept='Sales', _2=419)]

     (Contributed by Raymond Hettinger; bpo-1818(3).)

   * The *note re.sub(): 57a, *note re.subn(): 823. and *note
     re.split(): 4d1. functions now accept a flags parameter.

     (Contributed by Gregory Smith.)

   * The *note logging: aa. module now implements a simple *note
     logging.NullHandler: ce6. class for applications that are not using
     logging but are calling library code that does.  Setting-up a null
     handler will suppress spurious warnings such as “No handlers could
     be found for logger foo”:

          >>> h = logging.NullHandler()
          >>> logging.getLogger("foo").addHandler(h)

     (Contributed by Vinay Sajip; bpo-4384(4)).

   * The *note runpy: e2. module which supports the ‘-m’ command line
     switch now supports the execution of packages by looking for and
     executing a ‘__main__’ submodule when a package name is supplied.

     (Contributed by Andi Vajda; bpo-4195(5).)

   * The *note pdb: c9. module can now access and display source code
     loaded via *note zipimport: 14c. (or any other conformant PEP
     302(6) loader).

     (Contributed by Alexander Belopolsky; bpo-4201(7).)

   * *note functools.partial: 8b5. objects can now be pickled.

     (Suggested by Antoine Pitrou and Jesse Noller.  Implemented by Jack
     Diederich; bpo-5228(8).)

   * Add *note pydoc: d9. help topics for symbols so that ‘help('@')’
     works as expected in the interactive environment.

     (Contributed by David Laban; bpo-4739(9).)

   * The *note unittest: 124. module now supports skipping individual
     tests or classes of tests.  And it supports marking a test as an
     expected failure, a test that is known to be broken, but shouldn’t
     be counted as a failure on a TestResult:

          class TestGizmo(unittest.TestCase):

              @unittest.skipUnless(sys.platform.startswith("win"), "requires Windows")
              def test_gizmo_on_windows(self):
                  ...

              @unittest.expectedFailure
              def test_gimzo_without_required_library(self):
                  ...

     Also, tests for exceptions have been builtout to work with context
     managers using the *note with: 7da. statement:

          def test_division_by_zero(self):
              with self.assertRaises(ZeroDivisionError):
                  x / 0

     In addition, several new assertion methods were added including
     ‘assertSetEqual()’, ‘assertDictEqual()’,
     ‘assertDictContainsSubset()’, ‘assertListEqual()’,
     ‘assertTupleEqual()’, ‘assertSequenceEqual()’,
     ‘assertRaisesRegexp()’, ‘assertIsNone()’, and ‘assertIsNotNone()’.

     (Contributed by Benjamin Peterson and Antoine Pitrou.)

   * The *note io: a1. module has three new constants for the ‘seek()’
     method ‘SEEK_SET’, ‘SEEK_CUR’, and ‘SEEK_END’.

   * The *note sys.version_info: bed. tuple is now a named tuple:

          >>> sys.version_info
          sys.version_info(major=3, minor=1, micro=0, releaselevel='alpha', serial=2)

     (Contributed by Ross Light; bpo-4285(10).)

   * The *note nntplib: c0. and *note imaplib: 97. modules now support
     IPv6.

     (Contributed by Derek Morr; bpo-1655(11) and bpo-1664(12).)

   * The *note pickle: ca. module has been adapted for better
     interoperability with Python 2.x when used with protocol 2 or
     lower.  The reorganization of the standard library changed the
     formal reference for many objects.  For example, ‘__builtin__.set’
     in Python 2 is called ‘builtins.set’ in Python 3.  This change
     confounded efforts to share data between different versions of
     Python.  But now when protocol 2 or lower is selected, the pickler
     will automatically use the old Python 2 names for both loading and
     dumping.  This remapping is turned-on by default but can be
     disabled with the `fix_imports' option:

          >>> s = {1, 2, 3}
          >>> pickle.dumps(s, protocol=0)
          b'c__builtin__\nset\np0\n((lp1\nL1L\naL2L\naL3L\natp2\nRp3\n.'
          >>> pickle.dumps(s, protocol=0, fix_imports=False)
          b'cbuiltins\nset\np0\n((lp1\nL1L\naL2L\naL3L\natp2\nRp3\n.'

     An unfortunate but unavoidable side-effect of this change is that
     protocol 2 pickles produced by Python 3.1 won’t be readable with
     Python 3.0.  The latest pickle protocol, protocol 3, should be used
     when migrating data between Python 3.x implementations, as it
     doesn’t attempt to remain compatible with Python 2.x.

     (Contributed by Alexandre Vassalotti and Antoine Pitrou,
     bpo-6137(13).)

   * A new module, *note importlib: 9a. was added.  It provides a
     complete, portable, pure Python reference implementation of the
     *note import: ce7. statement and its counterpart, the *note
     __import__(): 16b. function.  It represents a substantial step
     forward in documenting and defining the actions that take place
     during imports.

     (Contributed by Brett Cannon.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1696199

   (2) https://bugs.python.org/issue2983

   (3) https://bugs.python.org/issue1818

   (4) https://bugs.python.org/issue4384

   (5) https://bugs.python.org/issue4195

   (6) https://www.python.org/dev/peps/pep-0302

   (7) https://bugs.python.org/issue4201

   (8) https://bugs.python.org/issue5228

   (9) https://bugs.python.org/issue4739

   (10) https://bugs.python.org/issue4285

   (11) https://bugs.python.org/issue1655

   (12) https://bugs.python.org/issue1664

   (13) https://bugs.python.org/issue6137


File: python.info,  Node: Optimizations<8>,  Next: IDLE<2>,  Prev: New Improved and Deprecated Modules<2>,  Up: What’s New In Python 3 1

1.9.5 Optimizations
-------------------

Major performance enhancements have been added:

   * The new I/O library (as defined in PEP 3116(1)) was mostly written
     in Python and quickly proved to be a problematic bottleneck in
     Python 3.0.  In Python 3.1, the I/O library has been entirely
     rewritten in C and is 2 to 20 times faster depending on the task at
     hand.  The pure Python version is still available for
     experimentation purposes through the ‘_pyio’ module.

     (Contributed by Amaury Forgeot d’Arc and Antoine Pitrou.)

   * Added a heuristic so that tuples and dicts containing only
     untrackable objects are not tracked by the garbage collector.  This
     can reduce the size of collections and therefore the garbage
     collection overhead on long-running programs, depending on their
     particular use of datatypes.

     (Contributed by Antoine Pitrou, bpo-4688(2).)

   * Enabling a configure option named ‘--with-computed-gotos’ on
     compilers that support it (notably: gcc, SunPro, icc), the bytecode
     evaluation loop is compiled with a new dispatch mechanism which
     gives speedups of up to 20%, depending on the system, the compiler,
     and the benchmark.

     (Contributed by Antoine Pitrou along with a number of other
     participants, bpo-4753(3)).

   * The decoding of UTF-8, UTF-16 and LATIN-1 is now two to four times
     faster.

     (Contributed by Antoine Pitrou and Amaury Forgeot d’Arc,
     bpo-4868(4).)

   * The *note json: a4. module now has a C extension to substantially
     improve its performance.  In addition, the API was modified so that
     json works only with *note str: 205, not with *note bytes: 172.
     That change makes the module closely match the JSON
     specification(5) which is defined in terms of Unicode.

     (Contributed by Bob Ippolito and converted to Py3.1 by Antoine
     Pitrou and Benjamin Peterson; bpo-4136(6).)

   * Unpickling now interns the attribute names of pickled objects.
     This saves memory and allows pickles to be smaller.

     (Contributed by Jake McGuire and Antoine Pitrou; bpo-5084(7).)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3116

   (2) https://bugs.python.org/issue4688

   (3) https://bugs.python.org/issue4753

   (4) https://bugs.python.org/issue4868

   (5) http://json.org/

   (6) https://bugs.python.org/issue4136

   (7) https://bugs.python.org/issue5084


File: python.info,  Node: IDLE<2>,  Next: Build and C API Changes<6>,  Prev: Optimizations<8>,  Up: What’s New In Python 3 1

1.9.6 IDLE
----------

   * IDLE’s format menu now provides an option to strip trailing
     whitespace from a source file.

     (Contributed by Roger D. Serwy; bpo-5150(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5150


File: python.info,  Node: Build and C API Changes<6>,  Next: Porting to Python 3 1,  Prev: IDLE<2>,  Up: What’s New In Python 3 1

1.9.7 Build and C API Changes
-----------------------------

Changes to Python’s build process and to the C API include:

   * Integers are now stored internally either in base ‘2**15’ or in
     base ‘2**30’, the base being determined at build time.  Previously,
     they were always stored in base ‘2**15’.  Using base ‘2**30’ gives
     significant performance improvements on 64-bit machines, but
     benchmark results on 32-bit machines have been mixed.  Therefore,
     the default is to use base ‘2**30’ on 64-bit machines and base
     ‘2**15’ on 32-bit machines; on Unix, there’s a new configure option
     ‘--enable-big-digits’ that can be used to override this default.

     Apart from the performance improvements this change should be
     invisible to end users, with one exception: for testing and
     debugging purposes there’s a new *note sys.int_info: ceb. that
     provides information about the internal format, giving the number
     of bits per digit and the size in bytes of the C type used to store
     each digit:

          >>> import sys
          >>> sys.int_info
          sys.int_info(bits_per_digit=30, sizeof_digit=4)

     (Contributed by Mark Dickinson; bpo-4258(1).)

   * The *note PyLong_AsUnsignedLongLong(): cec. function now handles a
     negative `pylong' by raising *note OverflowError: a41. instead of
     *note TypeError: 1fe.

     (Contributed by Mark Dickinson and Lisandro Dalcrin; bpo-5175(2).)

   * Deprecated ‘PyNumber_Int()’.  Use *note PyNumber_Long(): 395.
     instead.

     (Contributed by Mark Dickinson; bpo-4910(3).)

   * Added a new *note PyOS_string_to_double(): ced. function to replace
     the deprecated functions ‘PyOS_ascii_strtod()’ and
     ‘PyOS_ascii_atof()’.

     (Contributed by Mark Dickinson; bpo-5914(4).)

   * Added *note PyCapsule: cd2. as a replacement for the ‘PyCObject’
     API. The principal difference is that the new type has a well
     defined interface for passing typing safety information and a less
     complicated signature for calling a destructor.  The old type had a
     problematic API and is now deprecated.

     (Contributed by Larry Hastings; bpo-5630(5).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4258

   (2) https://bugs.python.org/issue5175

   (3) https://bugs.python.org/issue4910

   (4) https://bugs.python.org/issue5914

   (5) https://bugs.python.org/issue5630


File: python.info,  Node: Porting to Python 3 1,  Prev: Build and C API Changes<6>,  Up: What’s New In Python 3 1

1.9.8 Porting to Python 3.1
---------------------------

This section lists previously described changes and other bugfixes that
may require changes to your code:

   * The new floating point string representations can break existing
     doctests.  For example:

          def e():
              '''Compute the base of natural logarithms.

              >>> e()
              2.7182818284590451

              '''
              return sum(1/math.factorial(x) for x in reversed(range(30)))

          doctest.testmod()

          **********************************************************************
          Failed example:
              e()
          Expected:
              2.7182818284590451
          Got:
              2.718281828459045
          **********************************************************************

   * The automatic name remapping in the pickle module for protocol 2 or
     lower can make Python 3.1 pickles unreadable in Python 3.0.  One
     solution is to use protocol 3.  Another solution is to set the
     `fix_imports' option to ‘False’.  See the discussion above for more
     details.


File: python.info,  Node: What’s New In Python 3 0,  Next: What’s New in Python 2 7,  Prev: What’s New In Python 3 1,  Up: What’s New in Python

1.10 What’s New In Python 3.0
=============================


Author: Guido van Rossum

This article explains the new features in Python 3.0, compared to 2.6.
Python 3.0, also known as “Python 3000” or “Py3K”, is the first ever
`intentionally backwards incompatible' Python release.  There are more
changes than in a typical release, and more that are important for all
Python users.  Nevertheless, after digesting the changes, you’ll find
that Python really hasn’t changed all that much – by and large, we’re
mostly fixing well-known annoyances and warts, and removing a lot of old
cruft.

This article doesn’t attempt to provide a complete specification of all
new features, but instead tries to give a convenient overview.  For full
details, you should refer to the documentation for Python 3.0, and/or
the many PEPs referenced in the text.  If you want to understand the
complete implementation and design rationale for a particular feature,
PEPs usually have more details than the regular documentation; but note
that PEPs usually are not kept up-to-date once a feature has been fully
implemented.

Due to time constraints this document is not as complete as it should
have been.  As always for a new release, the ‘Misc/NEWS’ file in the
source distribution contains a wealth of detailed information about
every small thing that was changed.

* Menu:

* Common Stumbling Blocks::
* Overview Of Syntax Changes::
* Changes Already Present In Python 2.6: Changes Already Present In Python 2 6.
* Library Changes::
* PEP 3101; A New Approach To String Formatting: PEP 3101 A New Approach To String Formatting.
* Changes To Exceptions::
* Miscellaneous Other Changes::
* Build and C API Changes: Build and C API Changes<7>.
* Performance::
* Porting To Python 3.0: Porting To Python 3 0.


File: python.info,  Node: Common Stumbling Blocks,  Next: Overview Of Syntax Changes,  Up: What’s New In Python 3 0

1.10.1 Common Stumbling Blocks
------------------------------

This section lists those few changes that are most likely to trip you up
if you’re used to Python 2.5.

* Menu:

* Print Is A Function::
* Views And Iterators Instead Of Lists::
* Ordering Comparisons::
* Integers::
* Text Vs. Data Instead Of Unicode Vs. 8-bit: Text Vs Data Instead Of Unicode Vs 8-bit.


File: python.info,  Node: Print Is A Function,  Next: Views And Iterators Instead Of Lists,  Up: Common Stumbling Blocks

1.10.1.1 Print Is A Function
............................

The ‘print’ statement has been replaced with a *note print(): 971.
function, with keyword arguments to replace most of the special syntax
of the old ‘print’ statement ( PEP 3105(1)).  Examples:

     Old: print "The answer is", 2*2
     New: print("The answer is", 2*2)

     Old: print x,           # Trailing comma suppresses newline
     New: print(x, end=" ")  # Appends a space instead of a newline

     Old: print              # Prints a newline
     New: print()            # You must call the function!

     Old: print >>sys.stderr, "fatal error"
     New: print("fatal error", file=sys.stderr)

     Old: print (x, y)       # prints repr((x, y))
     New: print((x, y))      # Not the same as print(x, y)!

You can also customize the separator between items, e.g.:

     print("There are <", 2**32, "> possibilities!", sep="")

which produces:

     There are <4294967296> possibilities!

Note:

   * The *note print(): 971. function doesn’t support the “softspace”
     feature of the old ‘print’ statement.  For example, in Python 2.x,
     ‘print "A\n", "B"’ would write ‘"A\nB\n"’; but in Python 3.0,
     ‘print("A\n", "B")’ writes ‘"A\n B\n"’.

   * Initially, you’ll be finding yourself typing the old ‘print x’ a
     lot in interactive mode.  Time to retrain your fingers to type
     ‘print(x)’ instead!

   * When using the ‘2to3’ source-to-source conversion tool, all ‘print’
     statements are automatically converted to *note print(): 971.
     function calls, so this is mostly a non-issue for larger projects.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3105


File: python.info,  Node: Views And Iterators Instead Of Lists,  Next: Ordering Comparisons,  Prev: Print Is A Function,  Up: Common Stumbling Blocks

1.10.1.2 Views And Iterators Instead Of Lists
.............................................

Some well-known APIs no longer return lists:

   * *note dict: 164. methods *note dict.keys(): cf4, *note
     dict.items(): cf5. and *note dict.values(): cf6. return “views”
     instead of lists.  For example, this no longer works: ‘k =
     d.keys(); k.sort()’.  Use ‘k = sorted(d)’ instead (this works in
     Python 2.5 too and is just as efficient).

   * Also, the ‘dict.iterkeys()’, ‘dict.iteritems()’ and
     ‘dict.itervalues()’ methods are no longer supported.

   * *note map(): cf7. and *note filter(): cf8. return iterators.  If
     you really need a list and the input sequences are all of equal
     length, a quick fix is to wrap *note map(): cf7. in *note list():
     1f8, e.g.  ‘list(map(...))’, but a better fix is often to use a
     list comprehension (especially when the original code uses *note
     lambda: cf9.), or rewriting the code so it doesn’t need a list at
     all.  Particularly tricky is *note map(): cf7. invoked for the side
     effects of the function; the correct transformation is to use a
     regular *note for: cfa. loop (since creating a list would just be
     wasteful).

     If the input sequences are not of equal length, *note map(): cf7.
     will stop at the termination of the shortest of the sequences.  For
     full compatibility with *note map(): cf7. from Python 2.x, also
     wrap the sequences in *note itertools.zip_longest(): cfb, e.g.
     ‘map(func, *sequences)’ becomes ‘list(map(func,
     itertools.zip_longest(*sequences)))’.

   * *note range(): 1f5. now behaves like ‘xrange()’ used to behave,
     except it works with values of arbitrary size.  The latter no
     longer exists.

   * *note zip(): cfc. now returns an iterator.


File: python.info,  Node: Ordering Comparisons,  Next: Integers,  Prev: Views And Iterators Instead Of Lists,  Up: Common Stumbling Blocks

1.10.1.3 Ordering Comparisons
.............................

Python 3.0 has simplified the rules for ordering comparisons:

   * The ordering comparison operators (‘<’, ‘<=’, ‘>=’, ‘>’) raise a
     TypeError exception when the operands don’t have a meaningful
     natural ordering.  Thus, expressions like ‘1 < ''’, ‘0 > None’ or
     ‘len <= len’ are no longer valid, and e.g.  ‘None < None’ raises
     *note TypeError: 1fe. instead of returning ‘False’.  A corollary is
     that sorting a heterogeneous list no longer makes sense – all the
     elements must be comparable to each other.  Note that this does not
     apply to the ‘==’ and ‘!=’ operators: objects of different
     incomparable types always compare unequal to each other.

   * ‘builtin.sorted()’ and *note list.sort(): 548. no longer accept the
     `cmp' argument providing a comparison function.  Use the `key'
     argument instead.  N.B. the `key' and `reverse' arguments are now
     “keyword-only”.

   * The ‘cmp()’ function should be treated as gone, and the ‘__cmp__()’
     special method is no longer supported.  Use *note __lt__(): cfe.
     for sorting, *note __eq__(): 44b. with *note __hash__(): 44c, and
     other rich comparisons as needed.  (If you really need the ‘cmp()’
     functionality, you could use the expression ‘(a > b) - (a < b)’ as
     the equivalent for ‘cmp(a, b)’.)


File: python.info,  Node: Integers,  Next: Text Vs Data Instead Of Unicode Vs 8-bit,  Prev: Ordering Comparisons,  Up: Common Stumbling Blocks

1.10.1.4 Integers
.................

   * PEP 237(1): Essentially, ‘long’ renamed to *note int: 204.  That
     is, there is only one built-in integral type, named *note int:
     204.; but it behaves mostly like the old ‘long’ type.

   * PEP 238(2): An expression like ‘1/2’ returns a float.  Use ‘1//2’
     to get the truncating behavior.  (The latter syntax has existed for
     years, at least since Python 2.2.)

   * The ‘sys.maxint’ constant was removed, since there is no longer a
     limit to the value of integers.  However, *note sys.maxsize: c15.
     can be used as an integer larger than any practical list or string
     index.  It conforms to the implementation’s “natural” integer size
     and is typically the same as ‘sys.maxint’ in previous releases on
     the same platform (assuming the same build options).

   * The *note repr(): 8b9. of a long integer doesn’t include the
     trailing ‘L’ anymore, so code that unconditionally strips that
     character will chop off the last digit instead.  (Use *note str():
     205. instead.)

   * Octal literals are no longer of the form ‘0720’; use ‘0o720’
     instead.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0237

   (2) https://www.python.org/dev/peps/pep-0238


File: python.info,  Node: Text Vs Data Instead Of Unicode Vs 8-bit,  Prev: Integers,  Up: Common Stumbling Blocks

1.10.1.5 Text Vs. Data Instead Of Unicode Vs. 8-bit
...................................................

Everything you thought you knew about binary data and Unicode has
changed.

   * Python 3.0 uses the concepts of `text' and (binary) `data' instead
     of Unicode strings and 8-bit strings.  All text is Unicode; however
     `encoded' Unicode is represented as binary data.  The type used to
     hold text is *note str: 205, the type used to hold data is *note
     bytes: 172.  The biggest difference with the 2.x situation is that
     any attempt to mix text and data in Python 3.0 raises *note
     TypeError: 1fe, whereas if you were to mix Unicode and 8-bit
     strings in Python 2.x, it would work if the 8-bit string happened
     to contain only 7-bit (ASCII) bytes, but you would get *note
     UnicodeDecodeError: 32b. if it contained non-ASCII values.  This
     value-specific behavior has caused numerous sad faces over the
     years.

   * As a consequence of this change in philosophy, pretty much all code
     that uses Unicode, encodings or binary data most likely has to
     change.  The change is for the better, as in the 2.x world there
     were numerous bugs having to do with mixing encoded and unencoded
     text.  To be prepared in Python 2.x, start using ‘unicode’ for all
     unencoded text, and *note str: 205. for binary or encoded data
     only.  Then the ‘2to3’ tool will do most of the work for you.

   * You can no longer use ‘u"..."’ literals for Unicode text.  However,
     you must use ‘b"..."’ literals for binary data.

   * As the *note str: 205. and *note bytes: 172. types cannot be mixed,
     you must always explicitly convert between them.  Use *note
     str.encode(): 170. to go from *note str: 205. to *note bytes: 172,
     and *note bytes.decode(): 171. to go from *note bytes: 172. to
     *note str: 205.  You can also use ‘bytes(s, encoding=...)’ and
     ‘str(b, encoding=...)’, respectively.

   * Like *note str: 205, the *note bytes: 172. type is immutable.
     There is a separate `mutable' type to hold buffered binary data,
     *note bytearray: 173.  Nearly all APIs that accept *note bytes:
     172. also accept *note bytearray: 173.  The mutable API is based on
     ‘collections.MutableSequence’.

   * All backslashes in raw string literals are interpreted literally.
     This means that ‘'\U'’ and ‘'\u'’ escapes in raw strings are not
     treated specially.  For example, ‘r'\u20ac'’ is a string of 6
     characters in Python 3.0, whereas in 2.6, ‘ur'\u20ac'’ was the
     single “euro” character.  (Of course, this change only affects raw
     string literals; the euro character is ‘'\u20ac'’ in Python 3.0.)

   * The built-in ‘basestring’ abstract type was removed.  Use *note
     str: 205. instead.  The *note str: 205. and *note bytes: 172. types
     don’t have functionality enough in common to warrant a shared base
     class.  The ‘2to3’ tool (see below) replaces every occurrence of
     ‘basestring’ with *note str: 205.

   * Files opened as text files (still the default mode for *note
     open(): 16f.) always use an encoding to map between strings (in
     memory) and bytes (on disk).  Binary files (opened with a ‘b’ in
     the mode argument) always use bytes in memory.  This means that if
     a file is opened using an incorrect mode or encoding, I/O will
     likely fail loudly, instead of silently producing incorrect data.
     It also means that even Unix users will have to specify the correct
     mode (text or binary) when opening a file.  There is a
     platform-dependent default encoding, which on Unixy platforms can
     be set with the ‘LANG’ environment variable (and sometimes also
     with some other platform-specific locale-related environment
     variables).  In many cases, but not all, the system default is
     UTF-8; you should never count on this default.  Any application
     reading or writing more than pure ASCII text should probably have a
     way to override the encoding.  There is no longer any need for
     using the encoding-aware streams in the *note codecs: 1b. module.

   * The initial values of *note sys.stdin: 41e, *note sys.stdout: 41f.
     and *note sys.stderr: 1ea. are now unicode-only text files (i.e.,
     they are instances of *note io.TextIOBase: d01.).  To read and
     write bytes data with these streams, you need to use their *note
     io.TextIOBase.buffer: d02. attribute.

   * Filenames are passed to and returned from APIs as (Unicode)
     strings.  This can present platform-specific problems because on
     some platforms filenames are arbitrary byte strings.  (On the other
     hand, on Windows filenames are natively stored as Unicode.)  As a
     work-around, most APIs (e.g.  *note open(): 16f. and many functions
     in the *note os: c4. module) that take filenames accept *note
     bytes: 172. objects as well as strings, and a few APIs have a way
     to ask for a *note bytes: 172. return value.  Thus, *note
     os.listdir(): b1c. returns a list of *note bytes: 172. instances if
     the argument is a *note bytes: 172. instance, and *note
     os.getcwdb(): 3da. returns the current working directory as a *note
     bytes: 172. instance.  Note that when *note os.listdir(): b1c.
     returns a list of strings, filenames that cannot be decoded
     properly are omitted rather than raising *note UnicodeError: d03.

   * Some system APIs like *note os.environ: c09. and *note sys.argv:
     cc6. can also present problems when the bytes made available by the
     system is not interpretable using the default encoding.  Setting
     the ‘LANG’ variable and rerunning the program is probably the best
     approach.

   * PEP 3138(1): The *note repr(): 8b9. of a string no longer escapes
     non-ASCII characters.  It still escapes control characters and code
     points with non-printable status in the Unicode standard, however.

   * PEP 3120(2): The default source encoding is now UTF-8.

   * PEP 3131(3): Non-ASCII letters are now allowed in identifiers.
     (However, the standard library remains ASCII-only with the
     exception of contributor names in comments.)

   * The ‘StringIO’ and ‘cStringIO’ modules are gone.  Instead, import
     the *note io: a1. module and use *note io.StringIO: 91a. or *note
     io.BytesIO: 88a. for text and data respectively.

   * See also the *note Unicode HOWTO: d04, which was updated for Python
     3.0.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3138

   (2) https://www.python.org/dev/peps/pep-3120

   (3) https://www.python.org/dev/peps/pep-3131


File: python.info,  Node: Overview Of Syntax Changes,  Next: Changes Already Present In Python 2 6,  Prev: Common Stumbling Blocks,  Up: What’s New In Python 3 0

1.10.2 Overview Of Syntax Changes
---------------------------------

This section gives a brief overview of every `syntactic' change in
Python 3.0.

* Menu:

* New Syntax::
* Changed Syntax::
* Removed Syntax::


File: python.info,  Node: New Syntax,  Next: Changed Syntax,  Up: Overview Of Syntax Changes

1.10.2.1 New Syntax
...................

   * PEP 3107(1): Function argument and return value annotations.  This
     provides a standardized way of annotating a function’s parameters
     and return value.  There are no semantics attached to such
     annotations except that they can be introspected at runtime using
     the ‘__annotations__’ attribute.  The intent is to encourage
     experimentation through metaclasses, decorators or frameworks.

   * PEP 3102(2): Keyword-only arguments.  Named parameters occurring
     after ‘*args’ in the parameter list `must' be specified using
     keyword syntax in the call.  You can also use a bare ‘*’ in the
     parameter list to indicate that you don’t accept a variable-length
     argument list, but you do have keyword-only arguments.

   * Keyword arguments are allowed after the list of base classes in a
     class definition.  This is used by the new convention for
     specifying a metaclass (see next section), but can be used for
     other purposes as well, as long as the metaclass supports it.

   * PEP 3104(3): *note nonlocal: d07. statement.  Using ‘nonlocal x’
     you can now assign directly to a variable in an outer (but
     non-global) scope.  ‘nonlocal’ is a new reserved word.

   * PEP 3132(4): Extended Iterable Unpacking.  You can now write things
     like ‘a, b, *rest = some_sequence’.  And even ‘*rest, a = stuff’.
     The ‘rest’ object is always a (possibly empty) list; the right-hand
     side may be any iterable.  Example:

          (a, *rest, b) = range(5)

     This sets `a' to ‘0’, `b' to ‘4’, and `rest' to ‘[1, 2, 3]’.

   * Dictionary comprehensions: ‘{k: v for k, v in stuff}’ means the
     same thing as ‘dict(stuff)’ but is more flexible.  (This is PEP
     274(5) vindicated.  :-)

   * Set literals, e.g.  ‘{1, 2}’.  Note that ‘{}’ is an empty
     dictionary; use ‘set()’ for an empty set.  Set comprehensions are
     also supported; e.g., ‘{x for x in stuff}’ means the same thing as
     ‘set(stuff)’ but is more flexible.

   * New octal literals, e.g.  ‘0o720’ (already in 2.6).  The old octal
     literals (‘0720’) are gone.

   * New binary literals, e.g.  ‘0b1010’ (already in 2.6), and there is
     a new corresponding built-in function, *note bin(): d08.

   * Bytes literals are introduced with a leading ‘b’ or ‘B’, and there
     is a new corresponding built-in function, *note bytes(): 172.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3107

   (2) https://www.python.org/dev/peps/pep-3102

   (3) https://www.python.org/dev/peps/pep-3104

   (4) https://www.python.org/dev/peps/pep-3132

   (5) https://www.python.org/dev/peps/pep-0274


File: python.info,  Node: Changed Syntax,  Next: Removed Syntax,  Prev: New Syntax,  Up: Overview Of Syntax Changes

1.10.2.2 Changed Syntax
.......................

   * PEP 3109(1) and PEP 3134(2): new *note raise: d0a. statement
     syntax: ‘raise [`expr' [from `expr']]’.  See below.

   * ‘as’ and *note with: 7da. are now reserved words.  (Since 2.6,
     actually.)

   * ‘True’, ‘False’, and ‘None’ are reserved words.  (2.6 partially
     enforced the restrictions on ‘None’ already.)

   * Change from *note except: c10. `exc', `var' to ‘except’ `exc' ‘as’
     `var'.  See PEP 3110(3).

   * PEP 3115(4): New Metaclass Syntax.  Instead of:

          class C:
              __metaclass__ = M
              ...

     you must now use:

          class C(metaclass=M):
              ...

     The module-global ‘__metaclass__’ variable is no longer supported.
     (It was a crutch to make it easier to default to new-style classes
     without deriving every class from *note object: 3d2.)

   * List comprehensions no longer support the syntactic form ‘[... for
     `var' in `item1', `item2', ...]’.  Use ‘[... for `var' in (`item1',
     `item2', ...)]’ instead.  Also note that list comprehensions have
     different semantics: they are closer to syntactic sugar for a
     generator expression inside a *note list(): 1f8. constructor, and
     in particular the loop control variables are no longer leaked into
     the surrounding scope.

   * The `ellipsis' (‘...’) can be used as an atomic expression
     anywhere.  (Previously it was only allowed in slices.)  Also, it
     `must' now be spelled as ‘...’.  (Previously it could also be
     spelled as ‘. . .’, by a mere accident of the grammar.)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3109

   (2) https://www.python.org/dev/peps/pep-3134

   (3) https://www.python.org/dev/peps/pep-3110

   (4) https://www.python.org/dev/peps/pep-3115


File: python.info,  Node: Removed Syntax,  Prev: Changed Syntax,  Up: Overview Of Syntax Changes

1.10.2.3 Removed Syntax
.......................

   * PEP 3113(1): Tuple parameter unpacking removed.  You can no longer
     write ‘def foo(a, (b, c)): ...’.  Use ‘def foo(a, b_c): b, c = b_c’
     instead.

   * Removed backticks (use *note repr(): 8b9. instead).

   * Removed ‘<>’ (use ‘!=’ instead).

   * Removed keyword: *note exec(): d0c. is no longer a keyword; it
     remains as a function.  (Fortunately the function syntax was also
     accepted in 2.x.)  Also note that *note exec(): d0c. no longer
     takes a stream argument; instead of ‘exec(f)’ you can use
     ‘exec(f.read())’.

   * Integer literals no longer support a trailing ‘l’ or ‘L’.

   * String literals no longer support a leading ‘u’ or ‘U’.

   * The *note from: d0d. `module' *note import: ce7. ‘*’ syntax is only
     allowed at the module level, no longer inside functions.

   * The only acceptable syntax for relative imports is ‘from
     .[`module'] import `name'’.  All *note import: ce7. forms not
     starting with ‘.’ are interpreted as absolute imports.  ( PEP
     328(2))

   * Classic classes are gone.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3113

   (2) https://www.python.org/dev/peps/pep-0328


File: python.info,  Node: Changes Already Present In Python 2 6,  Next: Library Changes,  Prev: Overview Of Syntax Changes,  Up: What’s New In Python 3 0

1.10.3 Changes Already Present In Python 2.6
--------------------------------------------

Since many users presumably make the jump straight from Python 2.5 to
Python 3.0, this section reminds the reader of new features that were
originally designed for Python 3.0 but that were back-ported to Python
2.6.  The corresponding sections in *note What’s New in Python 2.6: d0f.
should be consulted for longer descriptions.

   * *note PEP 343; The ‘with’ statement: d10.  The *note with: 7da.
     statement is now a standard feature and no longer needs to be
     imported from the *note __future__: 0.  Also check out *note
     Writing Context Managers: d11. and *note The contextlib module:
     d12.

   * *note PEP 366; Explicit Relative Imports From a Main Module: d13.
     This enhances the usefulness of the *note -m: 443. option when the
     referenced module lives in a package.

   * *note PEP 370; Per-user site-packages Directory: d14.

   * *note PEP 371; The multiprocessing Package: d15.

   * *note PEP 3101; Advanced String Formatting: d16.  Note: the 2.6
     description mentions the *note format(): 5d6. method for both 8-bit
     and Unicode strings.  In 3.0, only the *note str: 205. type (text
     strings with Unicode support) supports this method; the *note
     bytes: 172. type does not.  The plan is to eventually make this the
     only API for string formatting, and to start deprecating the ‘%’
     operator in Python 3.1.

   * *note PEP 3105; print As a Function: d17.  This is now a standard
     feature and no longer needs to be imported from *note __future__:
     0.  More details were given above.

   * *note PEP 3110; Exception-Handling Changes: d18.  The *note except:
     c10. `exc' ‘as’ `var' syntax is now standard and ‘except’ `exc',
     `var' is no longer supported.  (Of course, the ‘as’ `var' part is
     still optional.)

   * *note PEP 3112; Byte Literals: d19.  The ‘b"..."’ string literal
     notation (and its variants like ‘b'...'’, ‘b"""..."""’, and
     ‘br"..."’) now produces a literal of type *note bytes: 172.

   * *note PEP 3116; New I/O Library: d1a.  The *note io: a1. module is
     now the standard way of doing file I/O. The built-in *note open():
     16f. function is now an alias for *note io.open(): 74d. and has
     additional keyword arguments `encoding', `errors', `newline' and
     `closefd'.  Also note that an invalid `mode' argument now raises
     *note ValueError: 16d, not *note IOError: a73.  The binary file
     object underlying a text file object can be accessed as ‘f.buffer’
     (but beware that the text object maintains a buffer of itself in
     order to speed up the encoding and decoding operations).

   * *note PEP 3118; Revised Buffer Protocol: d1b.  The old builtin
     ‘buffer()’ is now really gone; the new builtin *note memoryview():
     386. provides (mostly) similar functionality.

   * *note PEP 3119; Abstract Base Classes: d1c.  The *note abc: 3.
     module and the ABCs defined in the *note collections: 1d. module
     plays a somewhat more prominent role in the language now, and
     built-in collection types like *note dict: 164. and *note list:
     1f8. conform to the ‘collections.MutableMapping’ and
     ‘collections.MutableSequence’ ABCs, respectively.

   * *note PEP 3127; Integer Literal Support and Syntax: d1d.  As
     mentioned above, the new octal literal notation is the only one
     supported, and binary literals have been added.

   * *note PEP 3129; Class Decorators: d1e.

   * *note PEP 3141; A Type Hierarchy for Numbers: d1f.  The *note
     numbers: c1. module is another new use of ABCs, defining Python’s
     “numeric tower”.  Also note the new *note fractions: 81. module
     which implements *note numbers.Rational: d20.


File: python.info,  Node: Library Changes,  Next: PEP 3101 A New Approach To String Formatting,  Prev: Changes Already Present In Python 2 6,  Up: What’s New In Python 3 0

1.10.4 Library Changes
----------------------

Due to time constraints, this document does not exhaustively cover the
very extensive changes to the standard library.  PEP 3108(1) is the
reference for the major changes to the library.  Here’s a capsule
review:

   * Many old modules were removed.  Some, like ‘gopherlib’ (no longer
     used) and ‘md5’ (replaced by *note hashlib: 8c.), were already
     deprecated by PEP 4(2).  Others were removed as a result of the
     removal of support for various platforms such as Irix, BeOS and Mac
     OS 9 (see PEP 11(3)).  Some modules were also selected for removal
     in Python 3.0 due to lack of use or because a better replacement
     exists.  See PEP 3108(4) for an exhaustive list.

   * The ‘bsddb3’ package was removed because its presence in the core
     standard library has proved over time to be a particular burden for
     the core developers due to testing instability and Berkeley DB’s
     release schedule.  However, the package is alive and well,
     externally maintained at
     ‘https://www.jcea.es/programacion/pybsddb.htm’.

   * Some modules were renamed because their old name disobeyed PEP
     8(5), or for various other reasons.  Here’s the list:

     Old Name                    New Name
                                 
     --------------------------------------------------------
                                 
     _winreg                     winreg
                                 
                                 
     ConfigParser                configparser
                                 
                                 
     copy_reg                    copyreg
                                 
                                 
     Queue                       queue
                                 
                                 
     SocketServer                socketserver
                                 
                                 
     markupbase                  _markupbase
                                 
                                 
     repr                        reprlib
                                 
                                 
     test.test_support           test.support
                                 

   * A common pattern in Python 2.x is to have one version of a module
     implemented in pure Python, with an optional accelerated version
     implemented as a C extension; for example, *note pickle: ca. and
     ‘cPickle’.  This places the burden of importing the accelerated
     version and falling back on the pure Python version on each user of
     these modules.  In Python 3.0, the accelerated versions are
     considered implementation details of the pure Python versions.
     Users should always import the standard version, which attempts to
     import the accelerated version and falls back to the pure Python
     version.  The *note pickle: ca. / ‘cPickle’ pair received this
     treatment.  The *note profile: d3. module is on the list for 3.1.
     The ‘StringIO’ module has been turned into a class in the *note io:
     a1. module.

   * Some related modules have been grouped into packages, and usually
     the submodule names have been simplified.  The resulting new
     packages are:

        * *note dbm: 31. (‘anydbm’, ‘dbhash’, *note dbm: 31, ‘dumbdbm’,
          ‘gdbm’, ‘whichdb’).

        * *note html: 8f. (‘HTMLParser’, ‘htmlentitydefs’).

        * *note http: 92. (‘httplib’, ‘BaseHTTPServer’, ‘CGIHTTPServer’,
          ‘SimpleHTTPServer’, ‘Cookie’, ‘cookielib’).

        * *note tkinter: 10e. (all ‘Tkinter’-related modules except
          *note turtle: 11f.).  The target audience of *note turtle:
          11f. doesn’t really care about *note tkinter: 10e.  Also note
          that as of Python 2.6, the functionality of *note turtle: 11f.
          has been greatly enhanced.

        * *note urllib: 126. (*note urllib: 126, ‘urllib2’, ‘urlparse’,
          ‘robotparse’).

        * ‘xmlrpc’ (‘xmlrpclib’, ‘DocXMLRPCServer’,
          ‘SimpleXMLRPCServer’).

Some other changes to standard library modules, not covered by PEP
3108(6):

   * Killed ‘sets’.  Use the built-in *note set(): 1f6. class.

   * Cleanup of the *note sys: fd. module: removed ‘sys.exitfunc()’,
     ‘sys.exc_clear()’, ‘sys.exc_type’, ‘sys.exc_value’,
     ‘sys.exc_traceback’.  (Note that *note sys.last_type: d22. etc.
     remain.)

   * Cleanup of the *note array.array: 216. type: the ‘read()’ and
     ‘write()’ methods are gone; use ‘fromfile()’ and ‘tofile()’
     instead.  Also, the ‘'c'’ typecode for array is gone – use either
     ‘'b'’ for bytes or ‘'u'’ for Unicode characters.

   * Cleanup of the *note operator: c2. module: removed
     ‘sequenceIncludes()’ and ‘isCallable()’.

   * Cleanup of the ‘thread’ module: ‘acquire_lock()’ and
     ‘release_lock()’ are gone; use ‘acquire()’ and ‘release()’ instead.

   * Cleanup of the *note random: dc. module: removed the ‘jumpahead()’
     API.

   * The ‘new’ module is gone.

   * The functions ‘os.tmpnam()’, ‘os.tempnam()’ and ‘os.tmpfile()’ have
     been removed in favor of the *note tempfile: 103. module.

   * The *note tokenize: 11a. module has been changed to work with
     bytes.  The main entry point is now *note tokenize.tokenize(): d23,
     instead of generate_tokens.

   * ‘string.letters’ and its friends (‘string.lowercase’ and
     ‘string.uppercase’) are gone.  Use *note string.ascii_letters: d24.
     etc.  instead.  (The reason for the removal is that
     ‘string.letters’ and friends had locale-specific behavior, which is
     a bad idea for such attractively-named global “constants”.)

   * Renamed module ‘__builtin__’ to *note builtins: 12. (removing the
     underscores, adding an ‘s’).  The ‘__builtins__’ variable found in
     most global namespaces is unchanged.  To modify a builtin, you
     should use *note builtins: 12, not ‘__builtins__’!

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3108

   (2) https://www.python.org/dev/peps/pep-0004

   (3) https://www.python.org/dev/peps/pep-0011

   (4) https://www.python.org/dev/peps/pep-3108

   (5) https://www.python.org/dev/peps/pep-0008

   (6) https://www.python.org/dev/peps/pep-3108


File: python.info,  Node: PEP 3101 A New Approach To String Formatting,  Next: Changes To Exceptions,  Prev: Library Changes,  Up: What’s New In Python 3 0

1.10.5 `PEP 3101': A New Approach To String Formatting
------------------------------------------------------

   * A new system for built-in string formatting operations replaces the
     ‘%’ string formatting operator.  (However, the ‘%’ operator is
     still supported; it will be deprecated in Python 3.1 and removed
     from the language at some later time.)  Read PEP 3101(1) for the
     full scoop.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3101


File: python.info,  Node: Changes To Exceptions,  Next: Miscellaneous Other Changes,  Prev: PEP 3101 A New Approach To String Formatting,  Up: What’s New In Python 3 0

1.10.6 Changes To Exceptions
----------------------------

The APIs for raising and catching exception have been cleaned up and new
powerful features added:

   * PEP 352(1): All exceptions must be derived (directly or indirectly)
     from *note BaseException: 2db.  This is the root of the exception
     hierarchy.  This is not new as a recommendation, but the
     `requirement' to inherit from *note BaseException: 2db. is new.
     (Python 2.6 still allowed classic classes to be raised, and placed
     no restriction on what you can catch.)  As a consequence, string
     exceptions are finally truly and utterly dead.

   * Almost all exceptions should actually derive from *note Exception:
     2dc.; *note BaseException: 2db. should only be used as a base class
     for exceptions that should only be handled at the top level, such
     as *note SystemExit: 6f3. or *note KeyboardInterrupt: 2cc.  The
     recommended idiom for handling all exceptions except for this
     latter category is to use *note except: c10. *note Exception: 2dc.

   * ‘StandardError’ was removed.

   * Exceptions no longer behave as sequences.  Use the ‘args’ attribute
     instead.

   * PEP 3109(2): Raising exceptions.  You must now use ‘raise
     `Exception'(`args')’ instead of ‘raise `Exception', `args'’.
     Additionally, you can no longer explicitly specify a traceback;
     instead, if you `have' to do this, you can assign directly to the
     ‘__traceback__’ attribute (see below).

   * PEP 3110(3): Catching exceptions.  You must now use ‘except
     `SomeException' as `variable'’ instead of ‘except `SomeException',
     `variable'’.  Moreover, the `variable' is explicitly deleted when
     the *note except: c10. block is left.

   * PEP 3134(4): Exception chaining.  There are two cases: implicit
     chaining and explicit chaining.  Implicit chaining happens when an
     exception is raised in an *note except: c10. or *note finally: 2bc.
     handler block.  This usually happens due to a bug in the handler
     block; we call this a `secondary' exception.  In this case, the
     original exception (that was being handled) is saved as the
     ‘__context__’ attribute of the secondary exception.  Explicit
     chaining is invoked with this syntax:

          raise SecondaryException() from primary_exception

     (where `primary_exception' is any expression that produces an
     exception object, probably an exception that was previously
     caught).  In this case, the primary exception is stored on the
     ‘__cause__’ attribute of the secondary exception.  The traceback
     printed when an unhandled exception occurs walks the chain of
     ‘__cause__’ and ‘__context__’ attributes and prints a separate
     traceback for each component of the chain, with the primary
     exception at the top.  (Java users may recognize this behavior.)

   * PEP 3134(5): Exception objects now store their traceback as the
     ‘__traceback__’ attribute.  This means that an exception object now
     contains all the information pertaining to an exception, and there
     are fewer reasons to use *note sys.exc_info(): d27. (though the
     latter is not removed).

   * A few exception messages are improved when Windows fails to load an
     extension module.  For example, ‘error code 193’ is now ‘%1 is not
     a valid Win32 application’.  Strings now deal with non-English
     locales.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0352

   (2) https://www.python.org/dev/peps/pep-3109

   (3) https://www.python.org/dev/peps/pep-3110

   (4) https://www.python.org/dev/peps/pep-3134

   (5) https://www.python.org/dev/peps/pep-3134


File: python.info,  Node: Miscellaneous Other Changes,  Next: Build and C API Changes<7>,  Prev: Changes To Exceptions,  Up: What’s New In Python 3 0

1.10.7 Miscellaneous Other Changes
----------------------------------

* Menu:

* Operators And Special Methods::
* Builtins::


File: python.info,  Node: Operators And Special Methods,  Next: Builtins,  Up: Miscellaneous Other Changes

1.10.7.1 Operators And Special Methods
......................................

   * ‘!=’ now returns the opposite of ‘==’, unless ‘==’ returns *note
     NotImplemented: 202.

   * The concept of “unbound methods” has been removed from the
     language.  When referencing a method as a class attribute, you now
     get a plain function object.

   * ‘__getslice__()’, ‘__setslice__()’ and ‘__delslice__()’ were
     killed.  The syntax ‘a[i:j]’ now translates to
     ‘a.__getitem__(slice(i, j))’ (or *note __setitem__(): d2a. or *note
     __delitem__(): d2b, when used as an assignment or deletion target,
     respectively).

   * PEP 3114(1): the standard *note next(): 775. method has been
     renamed to *note __next__(): d2c.

   * The ‘__oct__()’ and ‘__hex__()’ special methods are removed – *note
     oct(): d2d. and *note hex(): d2e. use *note __index__(): 2c2. now
     to convert the argument to an integer.

   * Removed support for ‘__members__’ and ‘__methods__’.

   * The function attributes named ‘func_X’ have been renamed to use the
     ‘__X__’ form, freeing up these names in the function attribute
     namespace for user-defined attributes.  To wit, ‘func_closure’,
     ‘func_code’, ‘func_defaults’, ‘func_dict’, ‘func_doc’,
     ‘func_globals’, ‘func_name’ were renamed to ‘__closure__’,
     ‘__code__’, ‘__defaults__’, *note __dict__: 5f6, ‘__doc__’,
     ‘__globals__’, *note __name__: d2f, respectively.

   * ‘__nonzero__()’ is now *note __bool__(): d30.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3114


File: python.info,  Node: Builtins,  Prev: Operators And Special Methods,  Up: Miscellaneous Other Changes

1.10.7.2 Builtins
.................

   * PEP 3135(1): New *note super(): 5dd.  You can now invoke *note
     super(): 5dd. without arguments and (assuming this is in a regular
     instance method defined inside a *note class: d32. statement) the
     right class and instance will automatically be chosen.  With
     arguments, the behavior of *note super(): 5dd. is unchanged.

   * PEP 3111(2): ‘raw_input()’ was renamed to *note input(): d33.  That
     is, the new *note input(): d33. function reads a line from *note
     sys.stdin: 41e. and returns it with the trailing newline stripped.
     It raises *note EOFError: d34. if the input is terminated
     prematurely.  To get the old behavior of *note input(): d33, use
     ‘eval(input())’.

   * A new built-in function *note next(): 775. was added to call the
     *note __next__(): d2c. method on an object.

   * The *note round(): d35. function rounding strategy and return type
     have changed.  Exact halfway cases are now rounded to the nearest
     even result instead of away from zero.  (For example, ‘round(2.5)’
     now returns ‘2’ rather than ‘3’.)  ‘round(x[, n])’ now delegates to
     ‘x.__round__([n])’ instead of always returning a float.  It
     generally returns an integer when called with a single argument and
     a value of the same type as ‘x’ when called with two arguments.

   * Moved ‘intern()’ to *note sys.intern(): d36.

   * Removed: ‘apply()’.  Instead of ‘apply(f, args)’ use ‘f(*args)’.

   * Removed *note callable(): c16.  Instead of ‘callable(f)’ you can
     use ‘isinstance(f, collections.Callable)’.  The
     ‘operator.isCallable()’ function is also gone.

   * Removed ‘coerce()’.  This function no longer serves a purpose now
     that classic classes are gone.

   * Removed ‘execfile()’.  Instead of ‘execfile(fn)’ use
     ‘exec(open(fn).read())’.

   * Removed the ‘file’ type.  Use *note open(): 16f.  There are now
     several different kinds of streams that open can return in the
     *note io: a1. module.

   * Removed ‘reduce()’.  Use *note functools.reduce(): d37. if you
     really need it; however, 99 percent of the time an explicit *note
     for: cfa. loop is more readable.

   * Removed ‘reload()’.  Use *note imp.reload(): d38.

   * Removed.  ‘dict.has_key()’ – use the *note in: 179. operator
     instead.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3135

   (2) https://www.python.org/dev/peps/pep-3111


File: python.info,  Node: Build and C API Changes<7>,  Next: Performance,  Prev: Miscellaneous Other Changes,  Up: What’s New In Python 3 0

1.10.8 Build and C API Changes
------------------------------

Due to time constraints, here is a `very' incomplete list of changes to
the C API.

   * Support for several platforms was dropped, including but not
     limited to Mac OS 9, BeOS, RISCOS, Irix, and Tru64.

   * PEP 3118(1): New Buffer API.

   * PEP 3121(2): Extension Module Initialization & Finalization.

   * PEP 3123(3): Making *note PyObject_HEAD: d3a. conform to standard
     C.

   * No more C API support for restricted execution.

   * ‘PyNumber_Coerce()’, ‘PyNumber_CoerceEx()’, ‘PyMember_Get()’, and
     ‘PyMember_Set()’ C APIs are removed.

   * New C API *note PyImport_ImportModuleNoBlock(): aa0, works like
     *note PyImport_ImportModule(): d3b. but won’t block on the import
     lock (returning an error instead).

   * Renamed the boolean conversion C-level slot and method:
     ‘nb_nonzero’ is now ‘nb_bool’.

   * Removed ‘METH_OLDARGS’ and ‘WITH_CYCLE_GC’ from the C API.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3118

   (2) https://www.python.org/dev/peps/pep-3121

   (3) https://www.python.org/dev/peps/pep-3123


File: python.info,  Node: Performance,  Next: Porting To Python 3 0,  Prev: Build and C API Changes<7>,  Up: What’s New In Python 3 0

1.10.9 Performance
------------------

The net result of the 3.0 generalizations is that Python 3.0 runs the
pystone benchmark around 10% slower than Python 2.5.  Most likely the
biggest cause is the removal of special-casing for small integers.
There’s room for improvement, but it will happen after 3.0 is released!


File: python.info,  Node: Porting To Python 3 0,  Prev: Performance,  Up: What’s New In Python 3 0

1.10.10 Porting To Python 3.0
-----------------------------

For porting existing Python 2.5 or 2.6 source code to Python 3.0, the
best strategy is the following:

  0. (Prerequisite:) Start with excellent test coverage.

  1. Port to Python 2.6.  This should be no more work than the average
     port from Python 2.x to Python 2.(x+1).  Make sure all your tests
     pass.

  2. (Still using 2.6:) Turn on the ‘-3’ command line switch.  This
     enables warnings about features that will be removed (or change) in
     3.0.  Run your test suite again, and fix code that you get warnings
     about until there are no warnings left, and all your tests still
     pass.

  3. Run the ‘2to3’ source-to-source translator over your source code
     tree.  (See *note 2to3 - Automated Python 2 to 3 code translation:
     d3e. for more on this tool.)  Run the result of the translation
     under Python 3.0.  Manually fix up any remaining issues, fixing
     problems until all tests pass again.

It is not recommended to try to write source code that runs unchanged
under both Python 2.6 and 3.0; you’d have to use a very contorted coding
style, e.g.  avoiding ‘print’ statements, metaclasses, and much more.
If you are maintaining a library that needs to support both Python 2.6
and Python 3.0, the best approach is to modify step 3 above by editing
the 2.6 version of the source code and running the ‘2to3’ translator
again, rather than editing the 3.0 version of the source code.

For porting C extensions to Python 3.0, please see *note Porting
Extension Modules to Python 3: d3f.


File: python.info,  Node: What’s New in Python 2 7,  Next: What’s New in Python 2 6,  Prev: What’s New In Python 3 0,  Up: What’s New in Python

1.11 What’s New in Python 2.7
=============================


Author: A.M. Kuchling (amk at amk.ca)

This article explains the new features in Python 2.7.  Python 2.7 was
released on July 3, 2010.

Numeric handling has been improved in many ways, for both floating-point
numbers and for the *note Decimal: 2c0. class.  There are some useful
additions to the standard library, such as a greatly enhanced *note
unittest: 124. module, the *note argparse: 5. module for parsing
command-line options, convenient *note OrderedDict: 2ea. and *note
Counter: ab9. classes in the *note collections: 1d. module, and many
other improvements.

Python 2.7 is planned to be the last of the 2.x releases, so we worked
on making it a good release for the long term.  To help with porting to
Python 3, several new features from the Python 3.x series have been
included in 2.7.

This article doesn’t attempt to provide a complete specification of the
new features, but instead provides a convenient overview.  For full
details, you should refer to the documentation for Python 2.7 at
‘https://docs.python.org’.  If you want to understand the rationale for
the design and implementation, refer to the PEP for a particular new
feature or the issue on ‘https://bugs.python.org’ in which a change was
discussed.  Whenever possible, “What’s New in Python” links to the
bug/patch item for each change.

* Menu:

* The Future for Python 2.x: The Future for Python 2 x.
* Changes to the Handling of Deprecation Warnings::
* Python 3.1 Features: Python 3 1 Features.
* PEP 372; Adding an Ordered Dictionary to collections: PEP 372 Adding an Ordered Dictionary to collections.
* PEP 378; Format Specifier for Thousands Separator: PEP 378 Format Specifier for Thousands Separator<2>.
* PEP 389; The argparse Module for Parsing Command Lines: PEP 389 The argparse Module for Parsing Command Lines.
* PEP 391; Dictionary-Based Configuration For Logging: PEP 391 Dictionary-Based Configuration For Logging.
* PEP 3106; Dictionary Views: PEP 3106 Dictionary Views.
* PEP 3137; The memoryview Object: PEP 3137 The memoryview Object.
* Other Language Changes: Other Language Changes<10>.
* New and Improved Modules::
* Build and C API Changes: Build and C API Changes<8>.
* Other Changes and Fixes::
* Porting to Python 2.7: Porting to Python 2 7.
* New Features Added to Python 2.7 Maintenance Releases: New Features Added to Python 2 7 Maintenance Releases.
* Acknowledgements::


File: python.info,  Node: The Future for Python 2 x,  Next: Changes to the Handling of Deprecation Warnings,  Up: What’s New in Python 2 7

1.11.1 The Future for Python 2.x
--------------------------------

Python 2.7 is the last major release in the 2.x series, as the Python
maintainers have shifted the focus of their new feature development
efforts to the Python 3.x series.  This means that while Python 2
continues to receive bug fixes, and to be updated to build correctly on
new hardware and versions of supported operated systems, there will be
no new full feature releases for the language or standard library.

However, while there is a large common subset between Python 2.7 and
Python 3, and many of the changes involved in migrating to that common
subset, or directly to Python 3, can be safely automated, some other
changes (notably those associated with Unicode handling) may require
careful consideration, and preferably robust automated regression test
suites, to migrate effectively.

This means that Python 2.7 will remain in place for a long time,
providing a stable and supported base platform for production systems
that have not yet been ported to Python 3.  The full expected lifecycle
of the Python 2.7 series is detailed in PEP 373(1).

Some key consequences of the long-term significance of 2.7 are:

   * As noted above, the 2.7 release has a much longer period of
     maintenance when compared to earlier 2.x versions.  Python 2.7 is
     currently expected to remain supported by the core development team
     (receiving security updates and other bug fixes) until at least
     2020 (10 years after its initial release, compared to the more
     typical support period of 18–24 months).

   * As the Python 2.7 standard library ages, making effective use of
     the Python Package Index (either directly or via a redistributor)
     becomes more important for Python 2 users.  In addition to a wide
     variety of third party packages for various tasks, the available
     packages include backports of new modules and features from the
     Python 3 standard library that are compatible with Python 2, as
     well as various tools and libraries that can make it easier to
     migrate to Python 3.  The Python Packaging User Guide(2) provides
     guidance on downloading and installing software from the Python
     Package Index.

   * While the preferred approach to enhancing Python 2 is now the
     publication of new packages on the Python Package Index, this
     approach doesn’t necessarily work in all cases, especially those
     related to network security.  In exceptional cases that cannot be
     handled adequately by publishing new or updated packages on PyPI,
     the Python Enhancement Proposal process may be used to make the
     case for adding new features directly to the Python 2 standard
     library.  Any such additions, and the maintenance releases where
     they were added, will be noted in the *note New Features Added to
     Python 2.7 Maintenance Releases: d44. section below.

For projects wishing to migrate from Python 2 to Python 3, or for
library and framework developers wishing to support users on both Python
2 and Python 3, there are a variety of tools and guides available to
help decide on a suitable approach and manage some of the technical
details involved.  The recommended starting point is the *note Porting
Python 2 Code to Python 3: d45. HOWTO guide.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0373

   (2) https://packaging.python.org


File: python.info,  Node: Changes to the Handling of Deprecation Warnings,  Next: Python 3 1 Features,  Prev: The Future for Python 2 x,  Up: What’s New in Python 2 7

1.11.2 Changes to the Handling of Deprecation Warnings
------------------------------------------------------

For Python 2.7, a policy decision was made to silence warnings only of
interest to developers by default.  *note DeprecationWarning: 15a. and
its descendants are now ignored unless otherwise requested, preventing
users from seeing warnings triggered by an application.  This change was
also made in the branch that became Python 3.2.  (Discussed on
stdlib-sig and carried out in bpo-7319(1).)

In previous releases, *note DeprecationWarning: 15a. messages were
enabled by default, providing Python developers with a clear indication
of where their code may break in a future major version of Python.

However, there are increasingly many users of Python-based applications
who are not directly involved in the development of those applications.
*note DeprecationWarning: 15a. messages are irrelevant to such users,
making them worry about an application that’s actually working correctly
and burdening application developers with responding to these concerns.

You can re-enable display of *note DeprecationWarning: 15a. messages by
running Python with the *note -Wdefault: 15b. (short form: *note -Wd:
15b.) switch, or by setting the *note PYTHONWARNINGS: 51c. environment
variable to ‘"default"’ (or ‘"d"’) before running Python.  Python code
can also re-enable them by calling ‘warnings.simplefilter('default')’.

The ‘unittest’ module also automatically reenables deprecation warnings
when running tests.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue7319


File: python.info,  Node: Python 3 1 Features,  Next: PEP 372 Adding an Ordered Dictionary to collections,  Prev: Changes to the Handling of Deprecation Warnings,  Up: What’s New in Python 2 7

1.11.3 Python 3.1 Features
--------------------------

Much as Python 2.6 incorporated features from Python 3.0, version 2.7
incorporates some of the new features in Python 3.1.  The 2.x series
continues to provide tools for migrating to the 3.x series.

A partial list of 3.1 features that were backported to 2.7:

   * The syntax for set literals (‘{1,2,3}’ is a mutable set).

   * Dictionary and set comprehensions (‘{i: i*2 for i in range(3)}’).

   * Multiple context managers in a single *note with: 7da. statement.

   * A new version of the *note io: a1. library, rewritten in C for
     performance.

   * The ordered-dictionary type described in *note PEP 372; Adding an
     Ordered Dictionary to collections: d48.

   * The new ‘","’ format specifier described in *note PEP 378; Format
     Specifier for Thousands Separator: d49.

   * The *note memoryview: 386. object.

   * A small subset of the *note importlib: 9a. module, *note described
     below: d4a.

   * The *note repr(): 8b9. of a float ‘x’ is shorter in many cases:
     it’s now based on the shortest decimal string that’s guaranteed to
     round back to ‘x’.  As in previous versions of Python, it’s
     guaranteed that ‘float(repr(x))’ recovers ‘x’.

   * Float-to-string and string-to-float conversions are correctly
     rounded.  The *note round(): d35. function is also now correctly
     rounded.

   * The *note PyCapsule: cd2. type, used to provide a C API for
     extension modules.

   * The *note PyLong_AsLongAndOverflow(): cc8. C API function.

Other new Python3-mode warnings include:

   * ‘operator.isCallable()’ and ‘operator.sequenceIncludes()’, which
     are not supported in 3.x, now trigger warnings.

   * The ‘-3’ switch now automatically enables the ‘-Qwarn’ switch that
     causes warnings about using classic division with integers and long
     integers.


File: python.info,  Node: PEP 372 Adding an Ordered Dictionary to collections,  Next: PEP 378 Format Specifier for Thousands Separator<2>,  Prev: Python 3 1 Features,  Up: What’s New in Python 2 7

1.11.4 PEP 372: Adding an Ordered Dictionary to collections
-----------------------------------------------------------

Regular Python dictionaries iterate over key/value pairs in arbitrary
order.  Over the years, a number of authors have written alternative
implementations that remember the order that the keys were originally
inserted.  Based on the experiences from those implementations, 2.7
introduces a new *note OrderedDict: 2ea. class in the *note collections:
1d. module.

The *note OrderedDict: 2ea. API provides the same interface as regular
dictionaries but iterates over keys and values in a guaranteed order
depending on when a key was first inserted:

     >>> from collections import OrderedDict
     >>> d = OrderedDict([('first', 1),
     ...                  ('second', 2),
     ...                  ('third', 3)])
     >>> d.items()
     [('first', 1), ('second', 2), ('third', 3)]

If a new entry overwrites an existing entry, the original insertion
position is left unchanged:

     >>> d['second'] = 4
     >>> d.items()
     [('first', 1), ('second', 4), ('third', 3)]

Deleting an entry and reinserting it will move it to the end:

     >>> del d['second']
     >>> d['second'] = 5
     >>> d.items()
     [('first', 1), ('third', 3), ('second', 5)]

The *note popitem(): d4c. method has an optional `last' argument that
defaults to ‘True’.  If `last' is true, the most recently added key is
returned and removed; if it’s false, the oldest key is selected:

     >>> od = OrderedDict([(x,0) for x in range(20)])
     >>> od.popitem()
     (19, 0)
     >>> od.popitem()
     (18, 0)
     >>> od.popitem(last=False)
     (0, 0)
     >>> od.popitem(last=False)
     (1, 0)

Comparing two ordered dictionaries checks both the keys and values, and
requires that the insertion order was the same:

     >>> od1 = OrderedDict([('first', 1),
     ...                    ('second', 2),
     ...                    ('third', 3)])
     >>> od2 = OrderedDict([('third', 3),
     ...                    ('first', 1),
     ...                    ('second', 2)])
     >>> od1 == od2
     False
     >>> # Move 'third' key to the end
     >>> del od2['third']; od2['third'] = 3
     >>> od1 == od2
     True

Comparing an *note OrderedDict: 2ea. with a regular dictionary ignores
the insertion order and just compares the keys and values.

How does the *note OrderedDict: 2ea. work?  It maintains a doubly-linked
list of keys, appending new keys to the list as they’re inserted.  A
secondary dictionary maps keys to their corresponding list node, so
deletion doesn’t have to traverse the entire linked list and therefore
remains O(1).

The standard library now supports use of ordered dictionaries in several
modules.

   * The ‘ConfigParser’ module uses them by default, meaning that
     configuration files can now be read, modified, and then written
     back in their original order.

   * The *note _asdict(): 2e9. method for *note
     collections.namedtuple(): 1a1. now returns an ordered dictionary
     with the values appearing in the same order as the underlying tuple
     indices.

   * The *note json: a4. module’s *note JSONDecoder: 6fe. class
     constructor was extended with an `object_pairs_hook' parameter to
     allow ‘OrderedDict’ instances to be built by the decoder.  Support
     was also added for third-party tools like PyYAML(1).

See also
........

PEP 372(2) - Adding an ordered dictionary to collections

     PEP written by Armin Ronacher and Raymond Hettinger; implemented by
     Raymond Hettinger.

   ---------- Footnotes ----------

   (1) http://pyyaml.org/

   (2) https://www.python.org/dev/peps/pep-0372


File: python.info,  Node: PEP 378 Format Specifier for Thousands Separator<2>,  Next: PEP 389 The argparse Module for Parsing Command Lines,  Prev: PEP 372 Adding an Ordered Dictionary to collections,  Up: What’s New in Python 2 7

1.11.5 PEP 378: Format Specifier for Thousands Separator
--------------------------------------------------------

To make program output more readable, it can be useful to add separators
to large numbers, rendering them as 18,446,744,073,709,551,616 instead
of 18446744073709551616.

The fully general solution for doing this is the *note locale: a9.
module, which can use different separators (“,” in North America, “.” in
Europe) and different grouping sizes, but *note locale: a9. is
complicated to use and unsuitable for multi-threaded applications where
different threads are producing output for different locales.

Therefore, a simple comma-grouping mechanism has been added to the
mini-language used by the *note str.format(): 5d5. method.  When
formatting a floating-point number, simply include a comma between the
width and the precision:

     >>> '{:20,.2f}'.format(18446744073709551616.0)
     '18,446,744,073,709,551,616.00'

When formatting an integer, include the comma after the width:

     >>> '{:20,d}'.format(18446744073709551616)
     '18,446,744,073,709,551,616'

This mechanism is not adaptable at all; commas are always used as the
separator and the grouping is always into three-digit groups.  The
comma-formatting mechanism isn’t as general as the *note locale: a9.
module, but it’s easier to use.

See also
........

PEP 378(1) - Format Specifier for Thousands Separator

     PEP written by Raymond Hettinger; implemented by Eric Smith.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0378


File: python.info,  Node: PEP 389 The argparse Module for Parsing Command Lines,  Next: PEP 391 Dictionary-Based Configuration For Logging,  Prev: PEP 378 Format Specifier for Thousands Separator<2>,  Up: What’s New in Python 2 7

1.11.6 PEP 389: The argparse Module for Parsing Command Lines
-------------------------------------------------------------

The *note argparse: 5. module for parsing command-line arguments was
added as a more powerful replacement for the *note optparse: c3. module.

This means Python now supports three different modules for parsing
command-line arguments: *note getopt: 85, *note optparse: c3, and *note
argparse: 5.  The *note getopt: 85. module closely resembles the C
library’s ‘getopt()’ function, so it remains useful if you’re writing a
Python prototype that will eventually be rewritten in C. *note optparse:
c3. becomes redundant, but there are no plans to remove it because there
are many scripts still using it, and there’s no automated way to update
these scripts.  (Making the *note argparse: 5. API consistent with *note
optparse: c3.’s interface was discussed but rejected as too messy and
difficult.)

In short, if you’re writing a new script and don’t need to worry about
compatibility with earlier versions of Python, use *note argparse: 5.
instead of *note optparse: c3.

Here’s an example:

     import argparse

     parser = argparse.ArgumentParser(description='Command-line example.')

     # Add optional switches
     parser.add_argument('-v', action='store_true', dest='is_verbose',
                         help='produce verbose output')
     parser.add_argument('-o', action='store', dest='output',
                         metavar='FILE',
                         help='direct output to FILE instead of stdout')
     parser.add_argument('-C', action='store', type=int, dest='context',
                         metavar='NUM', default=0,
                         help='display NUM lines of added context')

     # Allow any number of additional arguments.
     parser.add_argument(nargs='*', action='store', dest='inputs',
                         help='input filenames (default is stdin)')

     args = parser.parse_args()
     print args.__dict__

Unless you override it, ‘-h’ and ‘--help’ switches are automatically
added, and produce neatly formatted output:

     -> ./python.exe argparse-example.py --help
     usage: argparse-example.py [-h] [-v] [-o FILE] [-C NUM] [inputs [inputs ...]]

     Command-line example.

     positional arguments:
       inputs      input filenames (default is stdin)

     optional arguments:
       -h, --help  show this help message and exit
       -v          produce verbose output
       -o FILE     direct output to FILE instead of stdout
       -C NUM      display NUM lines of added context

As with *note optparse: c3, the command-line switches and arguments are
returned as an object with attributes named by the `dest' parameters:

     -> ./python.exe argparse-example.py -v
     {'output': None,
      'is_verbose': True,
      'context': 0,
      'inputs': []}

     -> ./python.exe argparse-example.py -v -o /tmp/output -C 4 file1 file2
     {'output': '/tmp/output',
      'is_verbose': True,
      'context': 4,
      'inputs': ['file1', 'file2']}

*note argparse: 5. has much fancier validation than *note optparse: c3.;
you can specify an exact number of arguments as an integer, 0 or more
arguments by passing ‘'*'’, 1 or more by passing ‘'+'’, or an optional
argument with ‘'?'’.  A top-level parser can contain sub-parsers to
define subcommands that have different sets of switches, as in ‘svn
commit’, ‘svn checkout’, etc.  You can specify an argument’s type as
*note FileType: 90d, which will automatically open files for you and
understands that ‘'-'’ means standard input or output.

See also
........

*note argparse: 5. documentation

     The documentation page of the argparse module.

*note Upgrading optparse code: bfc.

     Part of the Python documentation, describing how to convert code
     that uses *note optparse: c3.

PEP 389(1) - argparse - New Command Line Parsing Module

     PEP written and implemented by Steven Bethard.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0389


File: python.info,  Node: PEP 391 Dictionary-Based Configuration For Logging,  Next: PEP 3106 Dictionary Views,  Prev: PEP 389 The argparse Module for Parsing Command Lines,  Up: What’s New in Python 2 7

1.11.7 PEP 391: Dictionary-Based Configuration For Logging
----------------------------------------------------------

The *note logging: aa. module is very flexible; applications can define
a tree of logging subsystems, and each logger in this tree can filter
out certain messages, format them differently, and direct messages to a
varying number of handlers.

All this flexibility can require a lot of configuration.  You can write
Python statements to create objects and set their properties, but a
complex set-up requires verbose but boring code.  *note logging: aa.
also supports a ‘fileConfig()’ function that parses a file, but the file
format doesn’t support configuring filters, and it’s messier to generate
programmatically.

Python 2.7 adds a ‘dictConfig()’ function that uses a dictionary to
configure logging.  There are many ways to produce a dictionary from
different sources: construct one with code; parse a file containing
JSON; or use a YAML parsing library if one is installed.  For more
information see *note Configuration functions: d50.

The following example configures two loggers, the root logger and a
logger named “network”.  Messages sent to the root logger will be sent
to the system log using the syslog protocol, and messages to the
“network” logger will be written to a ‘network.log’ file that will be
rotated once the log reaches 1MB.

     import logging
     import logging.config

     configdict = {
      'version': 1,    # Configuration schema in use; must be 1 for now
      'formatters': {
          'standard': {
              'format': ('%(asctime)s %(name)-15s '
                         '%(levelname)-8s %(message)s')}},

      'handlers': {'netlog': {'backupCount': 10,
                          'class': 'logging.handlers.RotatingFileHandler',
                          'filename': '/logs/network.log',
                          'formatter': 'standard',
                          'level': 'INFO',
                          'maxBytes': 1000000},
                   'syslog': {'class': 'logging.handlers.SysLogHandler',
                              'formatter': 'standard',
                              'level': 'ERROR'}},

      # Specify all the subordinate loggers
      'loggers': {
                  'network': {
                              'handlers': ['netlog']
                  }
      },
      # Specify properties of the root logger
      'root': {
               'handlers': ['syslog']
      },
     }

     # Set up configuration
     logging.config.dictConfig(configdict)

     # As an example, log two error messages
     logger = logging.getLogger('/')
     logger.error('Database not found')

     netlogger = logging.getLogger('network')
     netlogger.error('Connection failed')

Three smaller enhancements to the *note logging: aa. module, all
implemented by Vinay Sajip, are:

   * The *note SysLogHandler: afb. class now supports syslogging over
     TCP. The constructor has a `socktype' parameter giving the type of
     socket to use, either *note socket.SOCK_DGRAM: d51. for UDP or
     *note socket.SOCK_STREAM: d52. for TCP. The default protocol
     remains UDP.

   * *note Logger: 4ae. instances gained a *note getChild(): d53. method
     that retrieves a descendant logger using a relative path.  For
     example, once you retrieve a logger by doing ‘log =
     getLogger('app')’, calling ‘log.getChild('network.listen')’ is
     equivalent to ‘getLogger('app.network.listen')’.

   * The *note LoggerAdapter: d54. class gained an ‘isEnabledFor()’
     method that takes a `level' and returns whether the underlying
     logger would process a message of that level of importance.

See also
........

PEP 391(1) - Dictionary-Based Configuration For Logging

     PEP written and implemented by Vinay Sajip.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0391


File: python.info,  Node: PEP 3106 Dictionary Views,  Next: PEP 3137 The memoryview Object,  Prev: PEP 391 Dictionary-Based Configuration For Logging,  Up: What’s New in Python 2 7

1.11.8 PEP 3106: Dictionary Views
---------------------------------

The dictionary methods *note keys(): cf4, *note values(): cf6, and *note
items(): cf5. are different in Python 3.x.  They return an object called
a `view' instead of a fully materialized list.

It’s not possible to change the return values of *note keys(): cf4,
*note values(): cf6, and *note items(): cf5. in Python 2.7 because too
much code would break.  Instead the 3.x versions were added under the
new names ‘viewkeys()’, ‘viewvalues()’, and ‘viewitems()’.

     >>> d = dict((i*10, chr(65+i)) for i in range(26))
     >>> d
     {0: 'A', 130: 'N', 10: 'B', 140: 'O', 20: ..., 250: 'Z'}
     >>> d.viewkeys()
     dict_keys([0, 130, 10, 140, 20, 150, 30, ..., 250])

Views can be iterated over, but the key and item views also behave like
sets.  The ‘&’ operator performs intersection, and ‘|’ performs a union:

     >>> d1 = dict((i*10, chr(65+i)) for i in range(26))
     >>> d2 = dict((i**.5, i) for i in range(1000))
     >>> d1.viewkeys() & d2.viewkeys()
     set([0.0, 10.0, 20.0, 30.0])
     >>> d1.viewkeys() | range(0, 30)
     set([0, 1, 130, 3, 4, 5, 6, ..., 120, 250])

The view keeps track of the dictionary and its contents change as the
dictionary is modified:

     >>> vk = d.viewkeys()
     >>> vk
     dict_keys([0, 130, 10, ..., 250])
     >>> d[260] = '&'
     >>> vk
     dict_keys([0, 130, 260, 10, ..., 250])

However, note that you can’t add or remove keys while you’re iterating
over the view:

     >>> for k in vk:
     ...     d[k*2] = k
     ...
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     RuntimeError: dictionary changed size during iteration

You can use the view methods in Python 2.x code, and the 2to3 converter
will change them to the standard *note keys(): cf4, *note values(): cf6,
and *note items(): cf5. methods.

See also
........

PEP 3106(1) - Revamping dict.keys(), .values() and .items()

     PEP written by Guido van Rossum.  Backported to 2.7 by Alexandre
     Vassalotti; bpo-1967(2).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3106

   (2) https://bugs.python.org/issue1967


File: python.info,  Node: PEP 3137 The memoryview Object,  Next: Other Language Changes<10>,  Prev: PEP 3106 Dictionary Views,  Up: What’s New in Python 2 7

1.11.9 PEP 3137: The memoryview Object
--------------------------------------

The *note memoryview: 386. object provides a view of another object’s
memory content that matches the *note bytes: 172. type’s interface.

     >>> import string
     >>> m = memoryview(string.letters)
     >>> m
     <memory at 0x37f850>
     >>> len(m)           # Returns length of underlying object
     52
     >>> m[0], m[25], m[26]   # Indexing returns one byte
     ('a', 'z', 'A')
     >>> m2 = m[0:26]         # Slicing returns another memoryview
     >>> m2
     <memory at 0x37f080>

The content of the view can be converted to a string of bytes or a list
of integers:

     >>> m2.tobytes()
     'abcdefghijklmnopqrstuvwxyz'
     >>> m2.tolist()
     [97, 98, 99, 100, 101, 102, 103, ... 121, 122]
     >>>

*note memoryview: 386. objects allow modifying the underlying object if
it’s a mutable object.

     >>> m2[0] = 75
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: cannot modify read-only memory
     >>> b = bytearray(string.letters)  # Creating a mutable object
     >>> b
     bytearray(b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
     >>> mb = memoryview(b)
     >>> mb[0] = '*'         # Assign to view, changing the bytearray.
     >>> b[0:5]              # The bytearray has been changed.
     bytearray(b'*bcde')
     >>>

See also
........

PEP 3137(1) - Immutable Bytes and Mutable Buffer

     PEP written by Guido van Rossum.  Implemented by Travis Oliphant,
     Antoine Pitrou and others.  Backported to 2.7 by Antoine Pitrou;
     bpo-2396(2).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3137

   (2) https://bugs.python.org/issue2396


File: python.info,  Node: Other Language Changes<10>,  Next: New and Improved Modules,  Prev: PEP 3137 The memoryview Object,  Up: What’s New in Python 2 7

1.11.10 Other Language Changes
------------------------------

Some smaller changes made to the core Python language are:

   * The syntax for set literals has been backported from Python 3.x.
     Curly brackets are used to surround the contents of the resulting
     mutable set; set literals are distinguished from dictionaries by
     not containing colons and values.  ‘{}’ continues to represent an
     empty dictionary; use ‘set()’ for an empty set.

          >>> {1, 2, 3, 4, 5}
          set([1, 2, 3, 4, 5])
          >>> set() # empty set
          set([])
          >>> {}    # empty dict
          {}

     Backported by Alexandre Vassalotti; bpo-2335(1).

   * Dictionary and set comprehensions are another feature backported
     from 3.x, generalizing list/generator comprehensions to use the
     literal syntax for sets and dictionaries.

          >>> {x: x*x for x in range(6)}
          {0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
          >>> {('a'*x) for x in range(6)}
          set(['', 'a', 'aa', 'aaa', 'aaaa', 'aaaaa'])

     Backported by Alexandre Vassalotti; bpo-2333(2).

   * The *note with: 7da. statement can now use multiple context
     managers in one statement.  Context managers are processed from
     left to right and each one is treated as beginning a new ‘with’
     statement.  This means that:

          with A() as a, B() as b:
              ... suite of statements ...

     is equivalent to:

          with A() as a:
              with B() as b:
                  ... suite of statements ...

     The ‘contextlib.nested()’ function provides a very similar
     function, so it’s no longer necessary and has been deprecated.

     (Proposed in ‘https://codereview.appspot.com/53094’; implemented by
     Georg Brandl.)

   * Conversions between floating-point numbers and strings are now
     correctly rounded on most platforms.  These conversions occur in
     many different places: *note str(): 205. on floats and complex
     numbers; the *note float: 1fd. and *note complex: 2c1.
     constructors; numeric formatting; serializing and deserializing
     floats and complex numbers using the *note marshal: b0, *note
     pickle: ca. and *note json: a4. modules; parsing of float and
     imaginary literals in Python code; and *note Decimal: 2c0.-to-float
     conversion.

     Related to this, the *note repr(): 8b9. of a floating-point number
     `x' now returns a result based on the shortest decimal string
     that’s guaranteed to round back to `x' under correct rounding (with
     round-half-to-even rounding mode).  Previously it gave a string
     based on rounding x to 17 decimal digits.

     The rounding library responsible for this improvement works on
     Windows and on Unix platforms using the gcc, icc, or suncc
     compilers.  There may be a small number of platforms where correct
     operation of this code cannot be guaranteed, so the code is not
     used on such systems.  You can find out which code is being used by
     checking *note sys.float_repr_style: d58, which will be ‘short’ if
     the new code is in use and ‘legacy’ if it isn’t.

     Implemented by Eric Smith and Mark Dickinson, using David Gay’s
     ‘dtoa.c’ library; bpo-7117(3).

   * Conversions from long integers and regular integers to floating
     point now round differently, returning the floating-point number
     closest to the number.  This doesn’t matter for small integers that
     can be converted exactly, but for large numbers that will
     unavoidably lose precision, Python 2.7 now approximates more
     closely.  For example, Python 2.6 computed the following:

          >>> n = 295147905179352891391
          >>> float(n)
          2.9514790517935283e+20
          >>> n - long(float(n))
          65535L

     Python 2.7’s floating-point result is larger, but much closer to
     the true value:

          >>> n = 295147905179352891391
          >>> float(n)
          2.9514790517935289e+20
          >>> n - long(float(n))
          -1L

     (Implemented by Mark Dickinson; bpo-3166(4).)

     Integer division is also more accurate in its rounding behaviours.
     (Also implemented by Mark Dickinson; bpo-1811(5).)

   * Implicit coercion for complex numbers has been removed; the
     interpreter will no longer ever attempt to call a ‘__coerce__()’
     method on complex objects.  (Removed by Meador Inge and Mark
     Dickinson; bpo-5211(6).)

   * The *note str.format(): 5d5. method now supports automatic
     numbering of the replacement fields.  This makes using *note
     str.format(): 5d5. more closely resemble using ‘%s’ formatting:

          >>> '{}:{}:{}'.format(2009, 04, 'Sunday')
          '2009:4:Sunday'
          >>> '{}:{}:{day}'.format(2009, 4, day='Sunday')
          '2009:4:Sunday'

     The auto-numbering takes the fields from left to right, so the
     first ‘{...}’ specifier will use the first argument to *note
     str.format(): 5d5, the next specifier will use the next argument,
     and so on.  You can’t mix auto-numbering and explicit numbering –
     either number all of your specifier fields or none of them – but
     you can mix auto-numbering and named fields, as in the second
     example above.  (Contributed by Eric Smith; bpo-5237(7).)

     Complex numbers now correctly support usage with *note format():
     5d6, and default to being right-aligned.  Specifying a precision or
     comma-separation applies to both the real and imaginary parts of
     the number, but a specified field width and alignment is applied to
     the whole of the resulting ‘1.5+3j’ output.  (Contributed by Eric
     Smith; bpo-1588(8) and bpo-7988(9).)

     The ‘F’ format code now always formats its output using uppercase
     characters, so it will now produce ‘INF’ and ‘NAN’.  (Contributed
     by Eric Smith; bpo-3382(10).)

     A low-level change: the *note object.__format__(): a2f. method now
     triggers a *note PendingDeprecationWarning: 15c. if it’s passed a
     format string, because the *note __format__(): a2f. method for
     *note object: 3d2. converts the object to a string representation
     and formats that.  Previously the method silently applied the
     format string to the string representation, but that could hide
     mistakes in Python code.  If you’re supplying formatting
     information such as an alignment or precision, presumably you’re
     expecting the formatting to be applied in some object-specific way.
     (Fixed by Eric Smith; bpo-7994(11).)

   * The *note int(): 204. and ‘long()’ types gained a ‘bit_length’
     method that returns the number of bits necessary to represent its
     argument in binary:

          >>> n = 37
          >>> bin(n)
          '0b100101'
          >>> n.bit_length()
          6
          >>> n = 2**123-1
          >>> n.bit_length()
          123
          >>> (n+1).bit_length()
          124

     (Contributed by Fredrik Johansson and Victor Stinner;
     bpo-3439(12).)

   * The *note import: ce7. statement will no longer try an absolute
     import if a relative import (e.g.  ‘from .os import sep’) fails.
     This fixes a bug, but could possibly break certain ‘import’
     statements that were only working by accident.  (Fixed by Meador
     Inge; bpo-7902(13).)

   * It’s now possible for a subclass of the built-in ‘unicode’ type to
     override the ‘__unicode__()’ method.  (Implemented by Victor
     Stinner; bpo-1583863(14).)

   * The *note bytearray: 173. type’s *note translate(): d59. method now
     accepts ‘None’ as its first argument.  (Fixed by Georg Brandl;
     bpo-4759(15).)

   * When using ‘@classmethod’ and ‘@staticmethod’ to wrap methods as
     class or static methods, the wrapper object now exposes the wrapped
     function as their ‘__func__’ attribute.  (Contributed by Amaury
     Forgeot d’Arc, after a suggestion by George Sakkis; bpo-5982(16).)

   * When a restricted set of attributes were set using ‘__slots__’,
     deleting an unset attribute would not raise *note AttributeError:
     4a2. as you would expect.  Fixed by Benjamin Peterson;
     bpo-7604(17).)

   * Two new encodings are now supported: “cp720”, used primarily for
     Arabic text; and “cp858”, a variant of CP 850 that adds the euro
     symbol.  (CP720 contributed by Alexander Belchenko and Amaury
     Forgeot d’Arc in bpo-1616979(18); CP858 contributed by Tim Hatch in
     bpo-8016(19).)

   * The ‘file’ object will now set the ‘filename’ attribute on the
     *note IOError: a73. exception when trying to open a directory on
     POSIX platforms (noted by Jan Kaliszewski; bpo-4764(20)), and now
     explicitly checks for and forbids writing to read-only file objects
     instead of trusting the C library to catch and report the error
     (fixed by Stefan Krah; bpo-5677(21)).

   * The Python tokenizer now translates line endings itself, so the
     *note compile(): 2e7. built-in function now accepts code using any
     line-ending convention.  Additionally, it no longer requires that
     the code end in a newline.

   * Extra parentheses in function definitions are illegal in Python
     3.x, meaning that you get a syntax error from ‘def f((x)): pass’.
     In Python3-warning mode, Python 2.7 will now warn about this odd
     usage.  (Noted by James Lingard; bpo-7362(22).)

   * It’s now possible to create weak references to old-style class
     objects.  New-style classes were always weak-referenceable.  (Fixed
     by Antoine Pitrou; bpo-8268(23).)

   * When a module object is garbage-collected, the module’s dictionary
     is now only cleared if no one else is holding a reference to the
     dictionary (bpo-7140(24)).

* Menu:

* Interpreter Changes::
* Optimizations: Optimizations<9>.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue2335

   (2) https://bugs.python.org/issue2333

   (3) https://bugs.python.org/issue7117

   (4) https://bugs.python.org/issue3166

   (5) https://bugs.python.org/issue1811

   (6) https://bugs.python.org/issue5211

   (7) https://bugs.python.org/issue5237

   (8) https://bugs.python.org/issue1588

   (9) https://bugs.python.org/issue7988

   (10) https://bugs.python.org/issue3382

   (11) https://bugs.python.org/issue7994

   (12) https://bugs.python.org/issue3439

   (13) https://bugs.python.org/issue7902

   (14) https://bugs.python.org/issue1583863

   (15) https://bugs.python.org/issue4759

   (16) https://bugs.python.org/issue5982

   (17) https://bugs.python.org/issue7604

   (18) https://bugs.python.org/issue1616979

   (19) https://bugs.python.org/issue8016

   (20) https://bugs.python.org/issue4764

   (21) https://bugs.python.org/issue5677

   (22) https://bugs.python.org/issue7362

   (23) https://bugs.python.org/issue8268

   (24) https://bugs.python.org/issue7140


File: python.info,  Node: Interpreter Changes,  Next: Optimizations<9>,  Up: Other Language Changes<10>

1.11.10.1 Interpreter Changes
.............................

A new environment variable, *note PYTHONWARNINGS: 51c, allows
controlling warnings.  It should be set to a string containing warning
settings, equivalent to those used with the *note -W: 15b. switch,
separated by commas.  (Contributed by Brian Curtin; bpo-7301(1).)

For example, the following setting will print warnings every time they
occur, but turn warnings from the ‘Cookie’ module into an error.  (The
exact syntax for setting an environment variable varies across operating
systems and shells.)

     export PYTHONWARNINGS=all,error:::Cookie:0

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue7301


File: python.info,  Node: Optimizations<9>,  Prev: Interpreter Changes,  Up: Other Language Changes<10>

1.11.10.2 Optimizations
.......................

Several performance enhancements have been added:

   * A new opcode was added to perform the initial setup for *note with:
     7da. statements, looking up the *note __enter__(): d5d. and *note
     __exit__(): d5e. methods.  (Contributed by Benjamin Peterson.)

   * The garbage collector now performs better for one common usage
     pattern: when many objects are being allocated without deallocating
     any of them.  This would previously take quadratic time for garbage
     collection, but now the number of full garbage collections is
     reduced as the number of objects on the heap grows.  The new logic
     only performs a full garbage collection pass when the middle
     generation has been collected 10 times and when the number of
     survivor objects from the middle generation exceeds 10% of the
     number of objects in the oldest generation.  (Suggested by Martin
     von Löwis and implemented by Antoine Pitrou; bpo-4074(1).)

   * The garbage collector tries to avoid tracking simple containers
     which can’t be part of a cycle.  In Python 2.7, this is now true
     for tuples and dicts containing atomic types (such as ints,
     strings, etc.).  Transitively, a dict containing tuples of atomic
     types won’t be tracked either.  This helps reduce the cost of each
     garbage collection by decreasing the number of objects to be
     considered and traversed by the collector.  (Contributed by Antoine
     Pitrou; bpo-4688(2).)

   * Long integers are now stored internally either in base ‘2**15’ or
     in base ‘2**30’, the base being determined at build time.
     Previously, they were always stored in base ‘2**15’.  Using base
     ‘2**30’ gives significant performance improvements on 64-bit
     machines, but benchmark results on 32-bit machines have been mixed.
     Therefore, the default is to use base ‘2**30’ on 64-bit machines
     and base ‘2**15’ on 32-bit machines; on Unix, there’s a new
     configure option ‘--enable-big-digits’ that can be used to override
     this default.

     Apart from the performance improvements this change should be
     invisible to end users, with one exception: for testing and
     debugging purposes there’s a new structseq ‘sys.long_info’ that
     provides information about the internal format, giving the number
     of bits per digit and the size in bytes of the C type used to store
     each digit:

          >>> import sys
          >>> sys.long_info
          sys.long_info(bits_per_digit=30, sizeof_digit=4)

     (Contributed by Mark Dickinson; bpo-4258(3).)

     Another set of changes made long objects a few bytes smaller: 2
     bytes smaller on 32-bit systems and 6 bytes on 64-bit.
     (Contributed by Mark Dickinson; bpo-5260(4).)

   * The division algorithm for long integers has been made faster by
     tightening the inner loop, doing shifts instead of multiplications,
     and fixing an unnecessary extra iteration.  Various benchmarks show
     speedups of between 50% and 150% for long integer divisions and
     modulo operations.  (Contributed by Mark Dickinson; bpo-5512(5).)
     Bitwise operations are also significantly faster (initial patch by
     Gregory Smith; bpo-1087418(6)).

   * The implementation of ‘%’ checks for the left-side operand being a
     Python string and special-cases it; this results in a 1–3%
     performance increase for applications that frequently use ‘%’ with
     strings, such as templating libraries.  (Implemented by Collin
     Winter; bpo-5176(7).)

   * List comprehensions with an ‘if’ condition are compiled into faster
     bytecode.  (Patch by Antoine Pitrou, back-ported to 2.7 by Jeffrey
     Yasskin; bpo-4715(8).)

   * Converting an integer or long integer to a decimal string was made
     faster by special-casing base 10 instead of using a generalized
     conversion function that supports arbitrary bases.  (Patch by
     Gawain Bolton; bpo-6713(9).)

   * The ‘split()’, ‘replace()’, ‘rindex()’, ‘rpartition()’, and
     ‘rsplit()’ methods of string-like types (strings, Unicode strings,
     and *note bytearray: 173. objects) now use a fast reverse-search
     algorithm instead of a character-by-character scan.  This is
     sometimes faster by a factor of 10.  (Added by Florent Xicluna;
     bpo-7462(10) and bpo-7622(11).)

   * The *note pickle: ca. and ‘cPickle’ modules now automatically
     intern the strings used for attribute names, reducing memory usage
     of the objects resulting from unpickling.  (Contributed by Jake
     McGuire; bpo-5084(12).)

   * The ‘cPickle’ module now special-cases dictionaries, nearly halving
     the time required to pickle them.  (Contributed by Collin Winter;
     bpo-5670(13).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4074

   (2) https://bugs.python.org/issue4688

   (3) https://bugs.python.org/issue4258

   (4) https://bugs.python.org/issue5260

   (5) https://bugs.python.org/issue5512

   (6) https://bugs.python.org/issue1087418

   (7) https://bugs.python.org/issue5176

   (8) https://bugs.python.org/issue4715

   (9) https://bugs.python.org/issue6713

   (10) https://bugs.python.org/issue7462

   (11) https://bugs.python.org/issue7622

   (12) https://bugs.python.org/issue5084

   (13) https://bugs.python.org/issue5670


File: python.info,  Node: New and Improved Modules,  Next: Build and C API Changes<8>,  Prev: Other Language Changes<10>,  Up: What’s New in Python 2 7

1.11.11 New and Improved Modules
--------------------------------

As in every release, Python’s standard library received a number of
enhancements and bug fixes.  Here’s a partial list of the most notable
changes, sorted alphabetically by module name.  Consult the ‘Misc/NEWS’
file in the source tree for a more complete list of changes, or look
through the Subversion logs for all the details.

   * The *note bdb: e. module’s base debugging class *note Bdb: d60.
     gained a feature for skipping modules.  The constructor now takes
     an iterable containing glob-style patterns such as ‘django.*’; the
     debugger will not step into stack frames from a module that matches
     one of these patterns.  (Contributed by Maru Newby after a
     suggestion by Senthil Kumaran; bpo-5142(1).)

   * The *note binascii: f. module now supports the buffer API, so it
     can be used with *note memoryview: 386. instances and other similar
     buffer objects.  (Backported from 3.x by Florent Xicluna;
     bpo-7703(2).)

   * Updated module: the ‘bsddb’ module has been updated from
     4.7.2devel9 to version 4.8.4 of the pybsddb package(3).  The new
     version features better Python 3.x compatibility, various bug
     fixes, and adds several new BerkeleyDB flags and methods.  (Updated
     by Jesús Cea Avión; bpo-8156(4).  The pybsddb changelog can be read
     at ‘http://hg.jcea.es/pybsddb/file/tip/ChangeLog’.)

   * The *note bz2: 13. module’s *note BZ2File: 224. now supports the
     context management protocol, so you can write ‘with
     bz2.BZ2File(...) as f:’.  (Contributed by Hagen Fürstenau;
     bpo-3860(5).)

   * New class: the *note Counter: ab9. class in the *note collections:
     1d. module is useful for tallying data.  *note Counter: ab9.
     instances behave mostly like dictionaries but return zero for
     missing keys instead of raising a *note KeyError: 3e9.:

          >>> from collections import Counter
          >>> c = Counter()
          >>> for letter in 'here is a sample of english text':
          ...   c[letter] += 1
          ...
          >>> c
          Counter({' ': 6, 'e': 5, 's': 3, 'a': 2, 'i': 2, 'h': 2,
          'l': 2, 't': 2, 'g': 1, 'f': 1, 'm': 1, 'o': 1, 'n': 1,
          'p': 1, 'r': 1, 'x': 1})
          >>> c['e']
          5
          >>> c['z']
          0

     There are three additional *note Counter: ab9. methods.  *note
     most_common(): d61. returns the N most common elements and their
     counts.  *note elements(): d62. returns an iterator over the
     contained elements, repeating each element as many times as its
     count.  *note subtract(): c2c. takes an iterable and subtracts one
     for each element instead of adding; if the argument is a dictionary
     or another ‘Counter’, the counts are subtracted.

          >>> c.most_common(5)
          [(' ', 6), ('e', 5), ('s', 3), ('a', 2), ('i', 2)]
          >>> c.elements() ->
             'a', 'a', ' ', ' ', ' ', ' ', ' ', ' ',
             'e', 'e', 'e', 'e', 'e', 'g', 'f', 'i', 'i',
             'h', 'h', 'm', 'l', 'l', 'o', 'n', 'p', 's',
             's', 's', 'r', 't', 't', 'x'
          >>> c['e']
          5
          >>> c.subtract('very heavy on the letter e')
          >>> c['e']    # Count is now lower
          -1

     Contributed by Raymond Hettinger; bpo-1696199(6).

     New class: *note OrderedDict: 2ea. is described in the earlier
     section *note PEP 372; Adding an Ordered Dictionary to collections:
     d48.

     New method: The *note deque: 62b. data type now has a *note
     count(): c2e. method that returns the number of contained elements
     equal to the supplied argument `x', and a *note reverse(): c2f.
     method that reverses the elements of the deque in-place.  *note
     deque: 62b. also exposes its maximum length as the read-only *note
     maxlen: d63. attribute.  (Both features added by Raymond
     Hettinger.)

     The *note namedtuple: 1a1. class now has an optional `rename'
     parameter.  If `rename' is true, field names that are invalid
     because they’ve been repeated or aren’t legal Python identifiers
     will be renamed to legal names that are derived from the field’s
     position within the list of fields:

          >>> from collections import namedtuple
          >>> T = namedtuple('T', ['field1', '$illegal', 'for', 'field2'], rename=True)
          >>> T._fields
          ('field1', '_1', '_2', 'field2')

     (Added by Raymond Hettinger; bpo-1818(7).)

     Finally, the ‘Mapping’ abstract base class now returns *note
     NotImplemented: 202. if a mapping is compared to another type that
     isn’t a ‘Mapping’.  (Fixed by Daniel Stutzbach; bpo-8729(8).)

   * Constructors for the parsing classes in the ‘ConfigParser’ module
     now take an `allow_no_value' parameter, defaulting to false; if
     true, options without values will be allowed.  For example:

          >>> import ConfigParser, StringIO
          >>> sample_config = """
          ... [mysqld]
          ... user = mysql
          ... pid-file = /var/run/mysqld/mysqld.pid
          ... skip-bdb
          ... """
          >>> config = ConfigParser.RawConfigParser(allow_no_value=True)
          >>> config.readfp(StringIO.StringIO(sample_config))
          >>> config.get('mysqld', 'user')
          'mysql'
          >>> print config.get('mysqld', 'skip-bdb')
          None
          >>> print config.get('mysqld', 'unknown')
          Traceback (most recent call last):
            ...
          NoOptionError: No option 'unknown' in section: 'mysqld'

     (Contributed by Mats Kindahl; bpo-7005(9).)

   * Deprecated function: ‘contextlib.nested()’, which allows handling
     more than one context manager with a single *note with: 7da.
     statement, has been deprecated, because the ‘with’ statement now
     supports multiple context managers.

   * The ‘cookielib’ module now ignores cookies that have an invalid
     version field, one that doesn’t contain an integer value.  (Fixed
     by John J. Lee; bpo-3924(10).)

   * The *note copy: 25. module’s *note deepcopy(): 4d3. function will
     now correctly copy bound instance methods.  (Implemented by Robert
     Collins; bpo-1515(11).)

   * The *note ctypes: 2a. module now always converts ‘None’ to a C
     ‘NULL’ pointer for arguments declared as pointers.  (Changed by
     Thomas Heller; bpo-4606(12).)  The underlying libffi library(13)
     has been updated to version 3.0.9, containing various fixes for
     different platforms.  (Updated by Matthias Klose; bpo-8142(14).)

   * New method: the *note datetime: 30. module’s *note timedelta: 2ca.
     class gained a *note total_seconds(): d64. method that returns the
     number of seconds in the duration.  (Contributed by Brian Quinlan;
     bpo-5788(15).)

   * New method: the *note Decimal: 2c0. class gained a *note
     from_float(): c51. class method that performs an exact conversion
     of a floating-point number to a *note Decimal: 2c0.  This exact
     conversion strives for the closest decimal approximation to the
     floating-point representation’s value; the resulting decimal value
     will therefore still include the inaccuracy, if any.  For example,
     ‘Decimal.from_float(0.1)’ returns
     ‘Decimal('0.1000000000000000055511151231257827021181583404541015625')’.
     (Implemented by Raymond Hettinger; bpo-4796(16).)

     Comparing instances of *note Decimal: 2c0. with floating-point
     numbers now produces sensible results based on the numeric values
     of the operands.  Previously such comparisons would fall back to
     Python’s default rules for comparing objects, which produced
     arbitrary results based on their type.  Note that you still cannot
     combine ‘Decimal’ and floating-point in other operations such as
     addition, since you should be explicitly choosing how to convert
     between float and *note Decimal: 2c0.  (Fixed by Mark Dickinson;
     bpo-2531(17).)

     The constructor for *note Decimal: 2c0. now accepts floating-point
     numbers (added by Raymond Hettinger; bpo-8257(18)) and non-European
     Unicode characters such as Arabic-Indic digits (contributed by Mark
     Dickinson; bpo-6595(19)).

     Most of the methods of the *note Context: acf. class now accept
     integers as well as *note Decimal: 2c0. instances; the only
     exceptions are the *note canonical(): d65. and *note
     is_canonical(): d66. methods.  (Patch by Juan José Conti;
     bpo-7633(20).)

     When using *note Decimal: 2c0. instances with a string’s *note
     format(): 5d5. method, the default alignment was previously
     left-alignment.  This has been changed to right-alignment, which is
     more sensible for numeric types.  (Changed by Mark Dickinson;
     bpo-6857(21).)

     Comparisons involving a signaling NaN value (or ‘sNAN’) now signal
     ‘InvalidOperation’ instead of silently returning a true or false
     value depending on the comparison operator.  Quiet NaN values (or
     ‘NaN’) are now hashable.  (Fixed by Mark Dickinson; bpo-7279(22).)

   * The *note difflib: 36. module now produces output that is more
     compatible with modern ‘diff’/‘patch’ tools through one small
     change, using a tab character instead of spaces as a separator in
     the header giving the filename.  (Fixed by Anatoly Techtonik;
     bpo-7585(23).)

   * The Distutils ‘sdist’ command now always regenerates the ‘MANIFEST’
     file, since even if the ‘MANIFEST.in’ or ‘setup.py’ files haven’t
     been modified, the user might have created some new files that
     should be included.  (Fixed by Tarek Ziadé; bpo-8688(24).)

   * The *note doctest: 66. module’s ‘IGNORE_EXCEPTION_DETAIL’ flag will
     now ignore the name of the module containing the exception being
     tested.  (Patch by Lennart Regebro; bpo-7490(25).)

   * The *note email: 67. module’s *note Message: 63b. class will now
     accept a Unicode-valued payload, automatically converting the
     payload to the encoding specified by ‘output_charset’.  (Added by
     R. David Murray; bpo-1368247(26).)

   * The *note Fraction: 2be. class now accepts a single float or *note
     Decimal: 2c0. instance, or two rational numbers, as arguments to
     its constructor.  (Implemented by Mark Dickinson; rationals added
     in bpo-5812(27), and float/decimal in bpo-8294(28).)

     Ordering comparisons (‘<’, ‘<=’, ‘>’, ‘>=’) between fractions and
     complex numbers now raise a *note TypeError: 1fe.  This fixes an
     oversight, making the *note Fraction: 2be. match the other numeric
     types.

   * New class: *note FTP_TLS: 1a7. in the *note ftplib: 82. module
     provides secure FTP connections using TLS encapsulation of
     authentication as well as subsequent control and data transfers.
     (Contributed by Giampaolo Rodola; bpo-2054(29).)

     The *note storbinary(): d67. method for binary uploads can now
     restart uploads thanks to an added `rest' parameter (patch by Pablo
     Mouzo; bpo-6845(30).)

   * New class decorator: *note total_ordering(): 938. in the *note
     functools: 83. module takes a class that defines an *note __eq__():
     44b. method and one of *note __lt__(): cfe, *note __le__(): d68,
     *note __gt__(): d69, or *note __ge__(): d6a, and generates the
     missing comparison methods.  Since the ‘__cmp__()’ method is being
     deprecated in Python 3.x, this decorator makes it easier to define
     ordered classes.  (Added by Raymond Hettinger; bpo-5479(31).)

     New function: *note cmp_to_key(): c28. will take an old-style
     comparison function that expects two arguments and return a new
     callable that can be used as the `key' parameter to functions such
     as *note sorted(): 547, *note min(): 8f6. and *note max(): 8f7,
     etc.  The primary intended use is to help with making code
     compatible with Python 3.x.  (Added by Raymond Hettinger.)

   * New function: the *note gc: 84. module’s *note is_tracked(): d6b.
     returns true if a given instance is tracked by the garbage
     collector, false otherwise.  (Contributed by Antoine Pitrou;
     bpo-4688(32).)

   * The *note gzip: 8b. module’s *note GzipFile: 206. now supports the
     context management protocol, so you can write ‘with
     gzip.GzipFile(...) as f:’ (contributed by Hagen Fürstenau;
     bpo-3860(33)), and it now implements the *note io.BufferedIOBase:
     67f. ABC, so you can wrap it with *note io.BufferedReader: c5b. for
     faster processing (contributed by Nir Aides; bpo-7471(34)).  It’s
     also now possible to override the modification time recorded in a
     gzipped file by providing an optional timestamp to the constructor.
     (Contributed by Jacques Frechet; bpo-4272(35).)

     Files in gzip format can be padded with trailing zero bytes; the
     *note gzip: 8b. module will now consume these trailing bytes.
     (Fixed by Tadek Pietraszek and Brian Curtin; bpo-2846(36).)

   * New attribute: the *note hashlib: 8c. module now has an
     ‘algorithms’ attribute containing a tuple naming the supported
     algorithms.  In Python 2.7, ‘hashlib.algorithms’ contains ‘('md5',
     'sha1', 'sha224', 'sha256', 'sha384', 'sha512')’.  (Contributed by
     Carl Chenet; bpo-7418(37).)

   * The default ‘HTTPResponse’ class used by the ‘httplib’ module now
     supports buffering, resulting in much faster reading of HTTP
     responses.  (Contributed by Kristján Valur Jónsson; bpo-4879(38).)

     The ‘HTTPConnection’ and ‘HTTPSConnection’ classes now support a
     `source_address' parameter, a ‘(host, port)’ 2-tuple giving the
     source address that will be used for the connection.  (Contributed
     by Eldon Ziegler; bpo-3972(39).)

   * The ‘ihooks’ module now supports relative imports.  Note that
     ‘ihooks’ is an older module for customizing imports, superseded by
     the ‘imputil’ module added in Python 2.0.  (Relative import support
     added by Neil Schemenauer.)

   * The *note imaplib: 97. module now supports IPv6 addresses.
     (Contributed by Derek Morr; bpo-1655(40).)

   * New function: the *note inspect: a0. module’s *note getcallargs():
     8a4. takes a callable and its positional and keyword arguments, and
     figures out which of the callable’s parameters will receive each
     argument, returning a dictionary mapping argument names to their
     values.  For example:

          >>> from inspect import getcallargs
          >>> def f(a, b=1, *pos, **named):
          ...     pass
          >>> getcallargs(f, 1, 2, 3)
          {'a': 1, 'b': 2, 'pos': (3,), 'named': {}}
          >>> getcallargs(f, a=2, x=4)
          {'a': 2, 'b': 1, 'pos': (), 'named': {'x': 4}}
          >>> getcallargs(f)
          Traceback (most recent call last):
          ...
          TypeError: f() takes at least 1 argument (0 given)

     Contributed by George Sakkis; bpo-3135(41).

   * Updated module: The *note io: a1. library has been upgraded to the
     version shipped with Python 3.1.  For 3.1, the I/O library was
     entirely rewritten in C and is 2 to 20 times faster depending on
     the task being performed.  The original Python version was renamed
     to the ‘_pyio’ module.

     One minor resulting change: the *note io.TextIOBase: d01. class now
     has an ‘errors’ attribute giving the error setting used for
     encoding and decoding errors (one of ‘'strict'’, ‘'replace'’,
     ‘'ignore'’).

     The *note io.FileIO: d6c. class now raises an *note OSError: 304.
     when passed an invalid file descriptor.  (Implemented by Benjamin
     Peterson; bpo-4991(42).)  The *note truncate(): d6d. method now
     preserves the file position; previously it would change the file
     position to the end of the new file.  (Fixed by Pascal Chambon;
     bpo-6939(43).)

   * New function: ‘itertools.compress(data, selectors)’ takes two
     iterators.  Elements of `data' are returned if the corresponding
     value in `selectors' is true:

          itertools.compress('ABCDEF', [1,0,1,0,1,1]) =>
            A, C, E, F

     New function: ‘itertools.combinations_with_replacement(iter, r)’
     returns all the possible `r'-length combinations of elements from
     the iterable `iter'.  Unlike *note combinations(): d6e, individual
     elements can be repeated in the generated combinations:

          itertools.combinations_with_replacement('abc', 2) =>
            ('a', 'a'), ('a', 'b'), ('a', 'c'),
            ('b', 'b'), ('b', 'c'), ('c', 'c')

     Note that elements are treated as unique depending on their
     position in the input, not their actual values.

     The *note itertools.count(): ce5. function now has a `step'
     argument that allows incrementing by values other than 1.  *note
     count(): ce5. also now allows keyword arguments, and using
     non-integer values such as floats or *note Decimal: 2c0. instances.
     (Implemented by Raymond Hettinger; bpo-5032(44).)

     *note itertools.combinations(): d6e. and *note itertools.product():
     d6f. previously raised *note ValueError: 16d. for values of `r'
     larger than the input iterable.  This was deemed a specification
     error, so they now return an empty iterator.  (Fixed by Raymond
     Hettinger; bpo-4816(45).)

   * Updated module: The *note json: a4. module was upgraded to version
     2.0.9 of the simplejson package, which includes a C extension that
     makes encoding and decoding faster.  (Contributed by Bob Ippolito;
     bpo-4136(46).)

     To support the new *note collections.OrderedDict: 2ea. type, *note
     json.load(): 659. now has an optional `object_pairs_hook' parameter
     that will be called with any object literal that decodes to a list
     of pairs.  (Contributed by Raymond Hettinger; bpo-5381(47).)

   * The *note mailbox: ae. module’s *note Maildir: d70. class now
     records the timestamp on the directories it reads, and only
     re-reads them if the modification time has subsequently changed.
     This improves performance by avoiding unneeded directory scans.
     (Fixed by A.M. Kuchling and Antoine Pitrou; bpo-1607951(48),
     bpo-6896(49).)

   * New functions: the *note math: b1. module gained *note erf(): 554.
     and *note erfc(): 555. for the error function and the complementary
     error function, *note expm1(): c3a. which computes ‘e**x - 1’ with
     more precision than using *note exp(): d71. and subtracting 1,
     *note gamma(): c3b. for the Gamma function, and *note lgamma():
     c3c. for the natural log of the Gamma function.  (Contributed by
     Mark Dickinson and nirinA raseliarison; bpo-3366(50).)

   * The *note multiprocessing: b7. module’s ‘Manager*’ classes can now
     be passed a callable that will be called whenever a subprocess is
     started, along with a set of arguments that will be passed to the
     callable.  (Contributed by lekma; bpo-5585(51).)

     The ‘Pool’ class, which controls a pool of worker processes, now
     has an optional `maxtasksperchild' parameter.  Worker processes
     will perform the specified number of tasks and then exit, causing
     the ‘Pool’ to start a new worker.  This is useful if tasks may leak
     memory or other resources, or if some tasks will cause the worker
     to become very large.  (Contributed by Charles Cazabon;
     bpo-6963(52).)

   * The *note nntplib: c0. module now supports IPv6 addresses.
     (Contributed by Derek Morr; bpo-1664(53).)

   * New functions: the *note os: c4. module wraps the following POSIX
     system calls: *note getresgid(): d72. and *note getresuid(): d73,
     which return the real, effective, and saved GIDs and UIDs; *note
     setresgid(): d74. and *note setresuid(): d75, which set real,
     effective, and saved GIDs and UIDs to new values; *note
     initgroups(): d76, which initialize the group access list for the
     current process.  (GID/UID functions contributed by Travis H.;
     bpo-6508(54).  Support for initgroups added by Jean-Paul Calderone;
     bpo-7333(55).)

     The *note os.fork(): a42. function now re-initializes the import
     lock in the child process; this fixes problems on Solaris when
     *note fork(): a42. is called from a thread.  (Fixed by Zsolt
     Cserna; bpo-7242(56).)

   * In the *note os.path: c5. module, the *note normpath(): d77. and
     *note abspath(): d78. functions now preserve Unicode; if their
     input path is a Unicode string, the return value is also a Unicode
     string.  (*note normpath(): d77. fixed by Matt Giuca in
     bpo-5827(57); *note abspath(): d78. fixed by Ezio Melotti in
     bpo-3426(58).)

   * The *note pydoc: d9. module now has help for the various symbols
     that Python uses.  You can now do ‘help('<<')’ or ‘help('@')’, for
     example.  (Contributed by David Laban; bpo-4739(59).)

   * The *note re: dd. module’s *note split(): 4d1, *note sub(): 57a,
     and *note subn(): 823. now accept an optional `flags' argument, for
     consistency with the other functions in the module.  (Added by
     Gregory P. Smith.)

   * New function: *note run_path(): d79. in the *note runpy: e2. module
     will execute the code at a provided `path' argument.  `path' can be
     the path of a Python source file (‘example.py’), a compiled
     bytecode file (‘example.pyc’), a directory (‘./package/’), or a zip
     archive (‘example.zip’).  If a directory or zip path is provided,
     it will be added to the front of ‘sys.path’ and the module *note
     __main__: 1. will be imported.  It’s expected that the directory or
     zip contains a ‘__main__.py’; if it doesn’t, some other
     ‘__main__.py’ might be imported from a location later in
     ‘sys.path’.  This makes more of the machinery of *note runpy: e2.
     available to scripts that want to mimic the way Python’s command
     line processes an explicit path name.  (Added by Nick Coghlan;
     bpo-6816(60).)

   * New function: in the *note shutil: e9. module, *note
     make_archive(): 348. takes a filename, archive type (zip or
     tar-format), and a directory path, and creates an archive
     containing the directory’s contents.  (Added by Tarek Ziadé.)

     *note shutil: e9.’s *note copyfile(): 382. and *note copytree():
     347. functions now raise a ‘SpecialFileError’ exception when asked
     to copy a named pipe.  Previously the code would treat named pipes
     like a regular file by opening them for reading, and this would
     block indefinitely.  (Fixed by Antoine Pitrou; bpo-3002(61).)

   * The *note signal: ea. module no longer re-installs the signal
     handler unless this is truly necessary, which fixes a bug that
     could make it impossible to catch the EINTR signal robustly.
     (Fixed by Charles-Francois Natali; bpo-8354(62).)

   * New functions: in the *note site: eb. module, three new functions
     return various site- and user-specific paths.  *note
     getsitepackages(): ca1. returns a list containing all global
     site-packages directories, *note getusersitepackages(): ca3.
     returns the path of the user’s site-packages directory, and *note
     getuserbase(): ca2. returns the value of the ‘USER_BASE’
     environment variable, giving the path to a directory that can be
     used to store data.  (Contributed by Tarek Ziadé; bpo-6693(63).)

     The *note site: eb. module now reports exceptions occurring when
     the ‘sitecustomize’ module is imported, and will no longer catch
     and swallow the *note KeyboardInterrupt: 2cc. exception.  (Fixed by
     Victor Stinner; bpo-3137(64).)

   * The *note create_connection(): c6f. function gained a
     `source_address' parameter, a ‘(host, port)’ 2-tuple giving the
     source address that will be used for the connection.  (Contributed
     by Eldon Ziegler; bpo-3972(65).)

     The *note recv_into(): d7a. and *note recvfrom_into(): d7b. methods
     will now write into objects that support the buffer API, most
     usefully the *note bytearray: 173. and *note memoryview: 386.
     objects.  (Implemented by Antoine Pitrou; bpo-8104(66).)

   * The ‘SocketServer’ module’s ‘TCPServer’ class now supports socket
     timeouts and disabling the Nagle algorithm.  The
     ‘disable_nagle_algorithm’ class attribute defaults to ‘False’; if
     overridden to be true, new request connections will have the
     TCP_NODELAY option set to prevent buffering many small sends into a
     single TCP packet.  The ‘timeout’ class attribute can hold a
     timeout in seconds that will be applied to the request socket; if
     no request is received within that time, ‘handle_timeout()’ will be
     called and ‘handle_request()’ will return.  (Contributed by
     Kristján Valur Jónsson; bpo-6192(67) and bpo-6267(68).)

   * Updated module: the *note sqlite3: f2. module has been updated to
     version 2.6.0 of the pysqlite package(69).  Version 2.6.0 includes
     a number of bugfixes, and adds the ability to load SQLite
     extensions from shared libraries.  Call the
     ‘enable_load_extension(True)’ method to enable extensions, and then
     call *note load_extension(): c6b. to load a particular shared
     library.  (Updated by Gerhard Häring.)

   * The *note ssl: f3. module’s *note SSLSocket: 192. objects now
     support the buffer API, which fixed a test suite failure (fix by
     Antoine Pitrou; bpo-7133(70)) and automatically set OpenSSL’s
     ‘SSL_MODE_AUTO_RETRY’, which will prevent an error code being
     returned from ‘recv()’ operations that trigger an SSL renegotiation
     (fix by Antoine Pitrou; bpo-8222(71)).

     The *note ssl.wrap_socket(): 571. constructor function now takes a
     `ciphers' argument that’s a string listing the encryption
     algorithms to be allowed; the format of the string is described in
     the OpenSSL documentation(72).  (Added by Antoine Pitrou;
     bpo-8322(73).)

     Another change makes the extension load all of OpenSSL’s ciphers
     and digest algorithms so that they’re all available.  Some SSL
     certificates couldn’t be verified, reporting an “unknown algorithm”
     error.  (Reported by Beda Kosata, and fixed by Antoine Pitrou;
     bpo-8484(74).)

     The version of OpenSSL being used is now available as the module
     attributes *note ssl.OPENSSL_VERSION: c72. (a string), *note
     ssl.OPENSSL_VERSION_INFO: c73. (a 5-tuple), and *note
     ssl.OPENSSL_VERSION_NUMBER: c74. (an integer).  (Added by Antoine
     Pitrou; bpo-8321(75).)

   * The *note struct: f8. module will no longer silently ignore
     overflow errors when a value is too large for a particular integer
     format code (one of ‘bBhHiIlLqQ’); it now always raises a *note
     struct.error: d7c. exception.  (Changed by Mark Dickinson;
     bpo-1523(76).)  The *note pack(): cd6. function will also attempt
     to use *note __index__(): 2c2. to convert and pack non-integers
     before trying the *note __int__(): 2c3. method or reporting an
     error.  (Changed by Mark Dickinson; bpo-8300(77).)

   * New function: the *note subprocess: f9. module’s *note
     check_output(): 9c1. runs a command with a specified set of
     arguments and returns the command’s output as a string when the
     command runs without error, or raises a *note CalledProcessError:
     d7d. exception otherwise.

          >>> subprocess.check_output(['df', '-h', '.'])
          'Filesystem     Size   Used  Avail Capacity  Mounted on\n
          /dev/disk0s2    52G    49G   3.0G    94%    /\n'

          >>> subprocess.check_output(['df', '-h', '/bogus'])
            ...
          subprocess.CalledProcessError: Command '['df', '-h', '/bogus']' returned non-zero exit status 1

     (Contributed by Gregory P. Smith.)

     The *note subprocess: f9. module will now retry its internal system
     calls on receiving an ‘EINTR’ signal.  (Reported by several people;
     final patch by Gregory P. Smith in bpo-1068268(78).)

   * New function: *note is_declared_global(): d7e. in the *note
     symtable: fc. module returns true for variables that are explicitly
     declared to be global, false for ones that are implicitly global.
     (Contributed by Jeremy Hylton.)

   * The *note syslog: ff. module will now use the value of
     ‘sys.argv[0]’ as the identifier instead of the previous default
     value of ‘'python'’.  (Changed by Sean Reifschneider;
     bpo-8451(79).)

   * The ‘sys.version_info’ value is now a named tuple, with attributes
     named ‘major’, ‘minor’, ‘micro’, ‘releaselevel’, and ‘serial’.
     (Contributed by Ross Light; bpo-4285(80).)

     *note sys.getwindowsversion(): 68c. also returns a named tuple,
     with attributes named ‘major’, ‘minor’, ‘build’, *note platform:
     ce, ‘service_pack’, ‘service_pack_major’, ‘service_pack_minor’,
     ‘suite_mask’, and ‘product_type’.  (Contributed by Brian Curtin;
     bpo-7766(81).)

   * The *note tarfile: 101. module’s default error handling has
     changed, to no longer suppress fatal errors.  The default error
     level was previously 0, which meant that errors would only result
     in a message being written to the debug log, but because the debug
     log is not activated by default, these errors go unnoticed.  The
     default error level is now 1, which raises an exception if there’s
     an error.  (Changed by Lars Gustäbel; bpo-7357(82).)

     *note tarfile: 101. now supports filtering the *note TarInfo: c5e.
     objects being added to a tar file.  When you call *note add(): 57b,
     you may supply an optional `filter' argument that’s a callable.
     The `filter' callable will be passed the *note TarInfo: c5e. for
     every file being added, and can modify and return it.  If the
     callable returns ‘None’, the file will be excluded from the
     resulting archive.  This is more powerful than the existing
     `exclude' argument, which has therefore been deprecated.  (Added by
     Lars Gustäbel; bpo-6856(83).)  The *note TarFile: c5d. class also
     now supports the context management protocol.  (Added by Lars
     Gustäbel; bpo-7232(84).)

   * The *note wait(): d7f. method of the *note threading.Event: b85.
     class now returns the internal flag on exit.  This means the method
     will usually return true because *note wait(): d7f. is supposed to
     block until the internal flag becomes true.  The return value will
     only be false if a timeout was provided and the operation timed
     out.  (Contributed by Tim Lesher; bpo-1674032(85).)

   * The Unicode database provided by the *note unicodedata: 123. module
     is now used internally to determine which characters are numeric,
     whitespace, or represent line breaks.  The database also includes
     information from the ‘Unihan.txt’ data file (patch by Anders
     Chrigström and Amaury Forgeot d’Arc; bpo-1571184(86)) and has been
     updated to version 5.2.0 (updated by Florent Xicluna;
     bpo-8024(87)).

   * The ‘urlparse’ module’s ‘urlsplit()’ now handles unknown URL
     schemes in a fashion compliant with RFC 3986(88): if the URL is of
     the form ‘"<something>://..."’, the text before the ‘://’ is
     treated as the scheme, even if it’s a made-up scheme that the
     module doesn’t know about.  This change may break code that worked
     around the old behaviour.  For example, Python 2.6.4 or 2.5 will
     return the following:

          >>> import urlparse
          >>> urlparse.urlsplit('invented://host/filename?query')
          ('invented', '', '//host/filename?query', '', '')

     Python 2.7 (and Python 2.6.5) will return:

          >>> import urlparse
          >>> urlparse.urlsplit('invented://host/filename?query')
          ('invented', 'host', '/filename?query', '', '')

     (Python 2.7 actually produces slightly different output, since it
     returns a named tuple instead of a standard tuple.)

     The ‘urlparse’ module also supports IPv6 literal addresses as
     defined by RFC 2732(89) (contributed by Senthil Kumaran;
     bpo-2987(90)).

          >>> urlparse.urlparse('http://[1080::8:800:200C:417A]/foo')
          ParseResult(scheme='http', netloc='[1080::8:800:200C:417A]',
                      path='/foo', params='', query='', fragment='')

   * New class: the *note WeakSet: d80. class in the *note weakref: 131.
     module is a set that only holds weak references to its elements;
     elements will be removed once there are no references pointing to
     them.  (Originally implemented in Python 3.x by Raymond Hettinger,
     and backported to 2.7 by Michael Foord.)

   * The ElementTree library, ‘xml.etree’, no longer escapes ampersands
     and angle brackets when outputting an XML processing instruction
     (which looks like ‘<?xml-stylesheet href="#style1"?>’) or comment
     (which looks like ‘<!-- comment -->’).  (Patch by Neil Muller;
     bpo-2746(91).)

   * The XML-RPC client and server, provided by the ‘xmlrpclib’ and
     ‘SimpleXMLRPCServer’ modules, have improved performance by
     supporting HTTP/1.1 keep-alive and by optionally using gzip
     encoding to compress the XML being exchanged.  The gzip compression
     is controlled by the ‘encode_threshold’ attribute of
     ‘SimpleXMLRPCRequestHandler’, which contains a size in bytes;
     responses larger than this will be compressed.  (Contributed by
     Kristján Valur Jónsson; bpo-6267(92).)

   * The *note zipfile: 14b. module’s *note ZipFile: 523. now supports
     the context management protocol, so you can write ‘with
     zipfile.ZipFile(...) as f:’.  (Contributed by Brian Curtin;
     bpo-5511(93).)

     *note zipfile: 14b. now also supports archiving empty directories
     and extracts them correctly.  (Fixed by Kuba Wieczorek;
     bpo-4710(94).)  Reading files out of an archive is faster, and
     interleaving *note read(): d81. and ‘readline()’ now works
     correctly.  (Contributed by Nir Aides; bpo-7610(95).)

     The *note is_zipfile(): d82. function now accepts a file object, in
     addition to the path names accepted in earlier versions.
     (Contributed by Gabriel Genellina; bpo-4756(96).)

     The *note writestr(): d83. method now has an optional
     `compress_type' parameter that lets you override the default
     compression method specified in the *note ZipFile: 523.
     constructor.  (Contributed by Ronald Oussoren; bpo-6003(97).)

* Menu:

* New module; importlib: New module importlib.
* New module; sysconfig: New module sysconfig.
* ttk; Themed Widgets for Tk: ttk Themed Widgets for Tk.
* Updated module; unittest: Updated module unittest.
* Updated module; ElementTree 1.3: Updated module ElementTree 1 3.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5142

   (2) https://bugs.python.org/issue7703

   (3) https://www.jcea.es/programacion/pybsddb.htm

   (4) https://bugs.python.org/issue8156

   (5) https://bugs.python.org/issue3860

   (6) https://bugs.python.org/issue1696199

   (7) https://bugs.python.org/issue1818

   (8) https://bugs.python.org/issue8729

   (9) https://bugs.python.org/issue7005

   (10) https://bugs.python.org/issue3924

   (11) https://bugs.python.org/issue1515

   (12) https://bugs.python.org/issue4606

   (13) https://sourceware.org/libffi/

   (14) https://bugs.python.org/issue8142

   (15) https://bugs.python.org/issue5788

   (16) https://bugs.python.org/issue4796

   (17) https://bugs.python.org/issue2531

   (18) https://bugs.python.org/issue8257

   (19) https://bugs.python.org/issue6595

   (20) https://bugs.python.org/issue7633

   (21) https://bugs.python.org/issue6857

   (22) https://bugs.python.org/issue7279

   (23) https://bugs.python.org/issue7585

   (24) https://bugs.python.org/issue8688

   (25) https://bugs.python.org/issue7490

   (26) https://bugs.python.org/issue1368247

   (27) https://bugs.python.org/issue5812

   (28) https://bugs.python.org/issue8294

   (29) https://bugs.python.org/issue2054

   (30) https://bugs.python.org/issue6845

   (31) https://bugs.python.org/issue5479

   (32) https://bugs.python.org/issue4688

   (33) https://bugs.python.org/issue3860

   (34) https://bugs.python.org/issue7471

   (35) https://bugs.python.org/issue4272

   (36) https://bugs.python.org/issue2846

   (37) https://bugs.python.org/issue7418

   (38) https://bugs.python.org/issue4879

   (39) https://bugs.python.org/issue3972

   (40) https://bugs.python.org/issue1655

   (41) https://bugs.python.org/issue3135

   (42) https://bugs.python.org/issue4991

   (43) https://bugs.python.org/issue6939

   (44) https://bugs.python.org/issue5032

   (45) https://bugs.python.org/issue4816

   (46) https://bugs.python.org/issue4136

   (47) https://bugs.python.org/issue5381

   (48) https://bugs.python.org/issue1607951

   (49) https://bugs.python.org/issue6896

   (50) https://bugs.python.org/issue3366

   (51) https://bugs.python.org/issue5585

   (52) https://bugs.python.org/issue6963

   (53) https://bugs.python.org/issue1664

   (54) https://bugs.python.org/issue6508

   (55) https://bugs.python.org/issue7333

   (56) https://bugs.python.org/issue7242

   (57) https://bugs.python.org/issue5827

   (58) https://bugs.python.org/issue3426

   (59) https://bugs.python.org/issue4739

   (60) https://bugs.python.org/issue6816

   (61) https://bugs.python.org/issue3002

   (62) https://bugs.python.org/issue8354

   (63) https://bugs.python.org/issue6693

   (64) https://bugs.python.org/issue3137

   (65) https://bugs.python.org/issue3972

   (66) https://bugs.python.org/issue8104

   (67) https://bugs.python.org/issue6192

   (68) https://bugs.python.org/issue6267

   (69) https://github.com/ghaering/pysqlite

   (70) https://bugs.python.org/issue7133

   (71) https://bugs.python.org/issue8222

   (72) 
https://www.openssl.org/docs/manmaster/man1/ciphers.html#CIPHER-LIST-FORMAT

   (73) https://bugs.python.org/issue8322

   (74) https://bugs.python.org/issue8484

   (75) https://bugs.python.org/issue8321

   (76) https://bugs.python.org/issue1523

   (77) https://bugs.python.org/issue8300

   (78) https://bugs.python.org/issue1068268

   (79) https://bugs.python.org/issue8451

   (80) https://bugs.python.org/issue4285

   (81) https://bugs.python.org/issue7766

   (82) https://bugs.python.org/issue7357

   (83) https://bugs.python.org/issue6856

   (84) https://bugs.python.org/issue7232

   (85) https://bugs.python.org/issue1674032

   (86) https://bugs.python.org/issue1571184

   (87) https://bugs.python.org/issue8024

   (88) https://tools.ietf.org/html/rfc3986.html

   (89) https://tools.ietf.org/html/rfc2732.html

   (90) https://bugs.python.org/issue2987

   (91) https://bugs.python.org/issue2746

   (92) https://bugs.python.org/issue6267

   (93) https://bugs.python.org/issue5511

   (94) https://bugs.python.org/issue4710

   (95) https://bugs.python.org/issue7610

   (96) https://bugs.python.org/issue4756

   (97) https://bugs.python.org/issue6003


File: python.info,  Node: New module importlib,  Next: New module sysconfig,  Up: New and Improved Modules

1.11.11.1 New module: importlib
...............................

Python 3.1 includes the *note importlib: 9a. package, a
re-implementation of the logic underlying Python’s *note import: ce7.
statement.  *note importlib: 9a. is useful for implementors of Python
interpreters and to users who wish to write new importers that can
participate in the import process.  Python 2.7 doesn’t contain the
complete *note importlib: 9a. package, but instead has a tiny subset
that contains a single function, *note import_module(): be6.

‘import_module(name, package=None)’ imports a module.  `name' is a
string containing the module or package’s name.  It’s possible to do
relative imports by providing a string that begins with a ‘.’ character,
such as ‘..utils.errors’.  For relative imports, the `package' argument
must be provided and is the name of the package that will be used as the
anchor for the relative import.  *note import_module(): be6. both
inserts the imported module into ‘sys.modules’ and returns the module
object.

Here are some examples:

     >>> from importlib import import_module
     >>> anydbm = import_module('anydbm')  # Standard absolute import
     >>> anydbm
     <module 'anydbm' from '/p/python/Lib/anydbm.py'>
     >>> # Relative import
     >>> file_util = import_module('..file_util', 'distutils.command')
     >>> file_util
     <module 'distutils.file_util' from '/python/Lib/distutils/file_util.pyc'>

*note importlib: 9a. was implemented by Brett Cannon and introduced in
Python 3.1.


File: python.info,  Node: New module sysconfig,  Next: ttk Themed Widgets for Tk,  Prev: New module importlib,  Up: New and Improved Modules

1.11.11.2 New module: sysconfig
...............................

The *note sysconfig: fe. module has been pulled out of the Distutils
package, becoming a new top-level module in its own right.  *note
sysconfig: fe. provides functions for getting information about Python’s
build process: compiler switches, installation paths, the platform name,
and whether Python is running from its source directory.

Some of the functions in the module are:

   * *note get_config_var(): a45. returns variables from Python’s
     Makefile and the ‘pyconfig.h’ file.

   * *note get_config_vars(): a46. returns a dictionary containing all
     of the configuration variables.

   * *note get_path(): d86. returns the configured path for a particular
     type of module: the standard library, site-specific modules,
     platform-specific modules, etc.

   * *note is_python_build(): d87. returns true if you’re running a
     binary from a Python source tree, and false otherwise.

Consult the *note sysconfig: fe. documentation for more details and for
a complete list of functions.

The Distutils package and *note sysconfig: fe. are now maintained by
Tarek Ziadé, who has also started a Distutils2 package (source
repository at ‘https://hg.python.org/distutils2/’) for developing a
next-generation version of Distutils.


File: python.info,  Node: ttk Themed Widgets for Tk,  Next: Updated module unittest,  Prev: New module sysconfig,  Up: New and Improved Modules

1.11.11.3 ttk: Themed Widgets for Tk
....................................

Tcl/Tk 8.5 includes a set of themed widgets that re-implement basic Tk
widgets but have a more customizable appearance and can therefore more
closely resemble the native platform’s widgets.  This widget set was
originally called Tile, but was renamed to Ttk (for “themed Tk”) on
being added to Tcl/Tck release 8.5.

To learn more, read the ‘ttk’ module documentation.  You may also wish
to read the Tcl/Tk manual page describing the Ttk theme engine,
available at ‘https://www.tcl.tk/man/tcl8.5/TkCmd/ttk_intro.htm’.  Some
screenshots of the Python/Ttk code in use are at
‘https://code.google.com/archive/p/python-ttk/wikis/Screenshots.wiki’.

The ‘ttk’ module was written by Guilherme Polo and added in bpo-2983(1).
An alternate version called ‘Tile.py’, written by Martin Franklin and
maintained by Kevin Walzer, was proposed for inclusion in bpo-2618(2),
but the authors argued that Guilherme Polo’s work was more
comprehensive.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue2983

   (2) https://bugs.python.org/issue2618


File: python.info,  Node: Updated module unittest,  Next: Updated module ElementTree 1 3,  Prev: ttk Themed Widgets for Tk,  Up: New and Improved Modules

1.11.11.4 Updated module: unittest
..................................

The *note unittest: 124. module was greatly enhanced; many new features
were added.  Most of these features were implemented by Michael Foord,
unless otherwise noted.  The enhanced version of the module is
downloadable separately for use with Python versions 2.4 to 2.6,
packaged as the ‘unittest2’ package, from
‘https://pypi.org/project/unittest2’.

When used from the command line, the module can automatically discover
tests.  It’s not as fancy as py.test(1) or nose(2), but provides a
simple way to run tests kept within a set of package directories.  For
example, the following command will search the ‘test/’ subdirectory for
any importable test files named ‘test*.py’:

     python -m unittest discover -s test

Consult the *note unittest: 124. module documentation for more details.
(Developed in bpo-6001(3).)

The *note main(): 9e8. function supports some other new options:

   * *note -b: d8b. or ‘--buffer’ will buffer the standard output and
     standard error streams during each test.  If the test passes, any
     resulting output will be discarded; on failure, the buffered output
     will be displayed.

   * *note -c: d8c. or ‘--catch’ will cause the control-C interrupt to
     be handled more gracefully.  Instead of interrupting the test
     process immediately, the currently running test will be completed
     and then the partial results up to the interruption will be
     reported.  If you’re impatient, a second press of control-C will
     cause an immediate interruption.

     This control-C handler tries to avoid causing problems when the
     code being tested or the tests being run have defined a signal
     handler of their own, by noticing that a signal handler was already
     set and calling it.  If this doesn’t work for you, there’s a *note
     removeHandler(): d8d. decorator that can be used to mark tests that
     should have the control-C handling disabled.

   * *note -f: d8e. or ‘--failfast’ makes test execution stop
     immediately when a test fails instead of continuing to execute
     further tests.  (Suggested by Cliff Dyer and implemented by Michael
     Foord; bpo-8074(4).)

The progress messages now show ‘x’ for expected failures and ‘u’ for
unexpected successes when run in verbose mode.  (Contributed by Benjamin
Peterson.)

Test cases can raise the *note SkipTest: 9e9. exception to skip a test
(bpo-1034053(5)).

The error messages for *note assertEqual(): c85, *note assertTrue():
c84, and *note assertFalse(): d8f. failures now provide more
information.  If you set the *note longMessage: d90. attribute of your
*note TestCase: 9e5. classes to true, both the standard error message
and any additional message you provide will be printed for failures.
(Added by Michael Foord; bpo-5663(6).)

The *note assertRaises(): b92. method now returns a context handler when
called without providing a callable object to run.  For example, you can
write this:

     with self.assertRaises(KeyError):
         {}['foo']

(Implemented by Antoine Pitrou; bpo-4444(7).)

Module- and class-level setup and teardown fixtures are now supported.
Modules can contain ‘setUpModule()’ and ‘tearDownModule()’ functions.
Classes can have *note setUpClass(): 376. and *note tearDownClass():
d91. methods that must be defined as class methods (using ‘@classmethod’
or equivalent).  These functions and methods are invoked when the test
runner switches to a test case in a different module or class.

The methods *note addCleanup(): 3c5. and *note doCleanups(): d92. were
added.  *note addCleanup(): 3c5. lets you add cleanup functions that
will be called unconditionally (after *note setUp(): d93. if *note
setUp(): d93. fails, otherwise after *note tearDown(): d94.).  This
allows for much simpler resource allocation and deallocation during
tests (bpo-5679(8)).

A number of new methods were added that provide more specialized tests.
Many of these methods were written by Google engineers for use in their
test suites; Gregory P. Smith, Michael Foord, and GvR worked on merging
them into Python’s version of *note unittest: 124.

   * *note assertIsNone(): d95. and *note assertIsNotNone(): d96. take
     one expression and verify that the result is or is not ‘None’.

   * *note assertIs(): d97. and *note assertIsNot(): d98. take two
     values and check whether the two values evaluate to the same object
     or not.  (Added by Michael Foord; bpo-2578(9).)

   * *note assertIsInstance(): d99. and *note assertNotIsInstance():
     d9a. check whether the resulting object is an instance of a
     particular class, or of one of a tuple of classes.  (Added by Georg
     Brandl; bpo-7031(10).)

   * *note assertGreater(): d9b, *note assertGreaterEqual(): d9c, *note
     assertLess(): d9d, and *note assertLessEqual(): d9e. compare two
     quantities.

   * *note assertMultiLineEqual(): d9f. compares two strings, and if
     they’re not equal, displays a helpful comparison that highlights
     the differences in the two strings.  This comparison is now used by
     default when Unicode strings are compared with *note assertEqual():
     c85.

   * ‘assertRegexpMatches()’ and ‘assertNotRegexpMatches()’ checks
     whether the first argument is a string matching or not matching the
     regular expression provided as the second argument (bpo-8038(11)).

   * ‘assertRaisesRegexp()’ checks whether a particular exception is
     raised, and then also checks that the string representation of the
     exception matches the provided regular expression.

   * *note assertIn(): da0. and *note assertNotIn(): da1. tests whether
     `first' is or is not in `second'.

   * ‘assertItemsEqual()’ tests whether two provided sequences contain
     the same elements.

   * *note assertSetEqual(): da2. compares whether two sets are equal,
     and only reports the differences between the sets in case of error.

   * Similarly, *note assertListEqual(): da3. and *note
     assertTupleEqual(): da4. compare the specified types and explain
     any differences without necessarily printing their full values;
     these methods are now used by default when comparing lists and
     tuples using *note assertEqual(): c85.  More generally, *note
     assertSequenceEqual(): da5. compares two sequences and can
     optionally check whether both sequences are of a particular type.

   * *note assertDictEqual(): da6. compares two dictionaries and reports
     the differences; it’s now used by default when you compare two
     dictionaries using *note assertEqual(): c85.
     ‘assertDictContainsSubset()’ checks whether all of the key/value
     pairs in `first' are found in `second'.

   * *note assertAlmostEqual(): c87. and *note assertNotAlmostEqual():
     c88. test whether `first' and `second' are approximately equal.
     This method can either round their difference to an
     optionally-specified number of `places' (the default is 7) and
     compare it to zero, or require the difference to be smaller than a
     supplied `delta' value.

   * *note loadTestsFromName(): da7. properly honors the *note
     suiteClass: da8. attribute of the *note TestLoader: 871.  (Fixed by
     Mark Roddy; bpo-6866(12).)

   * A new hook lets you extend the *note assertEqual(): c85. method to
     handle new data types.  The *note addTypeEqualityFunc(): da9.
     method takes a type object and a function.  The function will be
     used when both of the objects being compared are of the specified
     type.  This function should compare the two objects and raise an
     exception if they don’t match; it’s a good idea for the function to
     provide additional information about why the two objects aren’t
     matching, much as the new sequence comparison methods do.

*note unittest.main(): 9e8. now takes an optional ‘exit’ argument.  If
false, *note main(): 9e8. doesn’t call *note sys.exit(): daa, allowing
*note main(): 9e8. to be used from the interactive interpreter.
(Contributed by J. Pablo Fernández; bpo-3379(13).)

*note TestResult: b97. has new *note startTestRun(): dab. and *note
stopTestRun(): dac. methods that are called immediately before and after
a test run.  (Contributed by Robert Collins; bpo-5728(14).)

With all these changes, the ‘unittest.py’ was becoming awkwardly large,
so the module was turned into a package and the code split into several
files (by Benjamin Peterson).  This doesn’t affect how the module is
imported or used.

See also
........

‘http://www.voidspace.org.uk/python/articles/unittest2.shtml’

     Describes the new features, how to use them, and the rationale for
     various design decisions.  (By Michael Foord.)

   ---------- Footnotes ----------

   (1) http://pytest.org

   (2) https://nose.readthedocs.io/

   (3) https://bugs.python.org/issue6001

   (4) https://bugs.python.org/issue8074

   (5) https://bugs.python.org/issue1034053

   (6) https://bugs.python.org/issue5663

   (7) https://bugs.python.org/issue4444

   (8) https://bugs.python.org/issue5679

   (9) https://bugs.python.org/issue2578

   (10) https://bugs.python.org/issue7031

   (11) https://bugs.python.org/issue8038

   (12) https://bugs.python.org/issue6866

   (13) https://bugs.python.org/issue3379

   (14) https://bugs.python.org/issue5728


File: python.info,  Node: Updated module ElementTree 1 3,  Prev: Updated module unittest,  Up: New and Improved Modules

1.11.11.5 Updated module: ElementTree 1.3
.........................................

The version of the ElementTree library included with Python was updated
to version 1.3.  Some of the new features are:

   * The various parsing functions now take a `parser' keyword argument
     giving an *note XMLParser: 37c. instance that will be used.  This
     makes it possible to override the file’s internal encoding:

          p = ET.XMLParser(encoding='utf-8')
          t = ET.XML("""<root/>""", parser=p)

     Errors in parsing XML now raise a ‘ParseError’ exception, whose
     instances have a ‘position’ attribute containing a (`line',
     `column') tuple giving the location of the problem.

   * ElementTree’s code for converting trees to a string has been
     significantly reworked, making it roughly twice as fast in many
     cases.  The *note ElementTree.write(): 9fd. and ‘Element.write()’
     methods now have a `method' parameter that can be “xml” (the
     default), “html”, or “text”.  HTML mode will output empty elements
     as ‘<empty></empty>’ instead of ‘<empty/>’, and text mode will skip
     over elements and only output the text chunks.  If you set the
     ‘tag’ attribute of an element to ‘None’ but leave its children in
     place, the element will be omitted when the tree is written out, so
     you don’t need to do more extensive rearrangement to remove a
     single element.

     Namespace handling has also been improved.  All ‘xmlns:<whatever>’
     declarations are now output on the root element, not scattered
     throughout the resulting XML. You can set the default namespace for
     a tree by setting the ‘default_namespace’ attribute and can
     register new prefixes with *note register_namespace(): c22.  In XML
     mode, you can use the true/false `xml_declaration' parameter to
     suppress the XML declaration.

   * New *note Element: 21d. method: *note extend(): c23. appends the
     items from a sequence to the element’s children.  Elements
     themselves behave like sequences, so it’s easy to move children
     from one element to another:

          from xml.etree import ElementTree as ET

          t = ET.XML("""<list>
            <item>1</item> <item>2</item>  <item>3</item>
          </list>""")
          new = ET.XML('<root/>')
          new.extend(t)

          # Outputs <root><item>1</item>...</root>
          print ET.tostring(new)

   * New ‘Element’ method: *note iter(): daf. yields the children of the
     element as a generator.  It’s also possible to write ‘for child in
     elem:’ to loop over an element’s children.  The existing method
     ‘getiterator()’ is now deprecated, as is ‘getchildren()’ which
     constructs and returns a list of children.

   * New ‘Element’ method: *note itertext(): c25. yields all chunks of
     text that are descendants of the element.  For example:

          t = ET.XML("""<list>
            <item>1</item> <item>2</item>  <item>3</item>
          </list>""")

          # Outputs ['\n  ', '1', ' ', '2', '  ', '3', '\n']
          print list(t.itertext())

   * Deprecated: using an element as a Boolean (i.e., ‘if elem:’) would
     return true if the element had any children, or false if there were
     no children.  This behaviour is confusing – ‘None’ is false, but so
     is a childless element?  – so it will now trigger a *note
     FutureWarning: 435.  In your code, you should be explicit: write
     ‘len(elem) != 0’ if you’re interested in the number of children, or
     ‘elem is not None’.

Fredrik Lundh develops ElementTree and produced the 1.3 version; you can
read his article describing 1.3 at
‘http://effbot.org/zone/elementtree-13-intro.htm’.  Florent Xicluna
updated the version included with Python, after discussions on
python-dev and in bpo-6472(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue6472


File: python.info,  Node: Build and C API Changes<8>,  Next: Other Changes and Fixes,  Prev: New and Improved Modules,  Up: What’s New in Python 2 7

1.11.12 Build and C API Changes
-------------------------------

Changes to Python’s build process and to the C API include:

   * The latest release of the GNU Debugger, GDB 7, can be scripted
     using Python(1).  When you begin debugging an executable program P,
     GDB will look for a file named ‘P-gdb.py’ and automatically read
     it.  Dave Malcolm contributed a ‘python-gdb.py’ that adds a number
     of commands useful when debugging Python itself.  For example,
     ‘py-up’ and ‘py-down’ go up or down one Python stack frame, which
     usually corresponds to several C stack frames.  ‘py-print’ prints
     the value of a Python variable, and ‘py-bt’ prints the Python stack
     trace.  (Added as a result of bpo-8032(2).)

   * If you use the ‘.gdbinit’ file provided with Python, the “pyo”
     macro in the 2.7 version now works correctly when the thread being
     debugged doesn’t hold the GIL; the macro now acquires it before
     printing.  (Contributed by Victor Stinner; bpo-3632(3).)

   * *note Py_AddPendingCall(): 25f. is now thread-safe, letting any
     worker thread submit notifications to the main Python thread.  This
     is particularly useful for asynchronous IO operations.
     (Contributed by Kristján Valur Jónsson; bpo-4293(4).)

   * New function: *note PyCode_NewEmpty(): db1. creates an empty code
     object; only the filename, function name, and first line number are
     required.  This is useful for extension modules that are attempting
     to construct a more useful traceback stack.  Previously such
     extensions needed to call *note PyCode_New(): 39b, which had many
     more arguments.  (Added by Jeffrey Yasskin.)

   * New function: *note PyErr_NewExceptionWithDoc(): cca. creates a new
     exception class, just as the existing *note PyErr_NewException():
     ccb. does, but takes an extra ‘char *’ argument containing the
     docstring for the new exception class.  (Added by ‘lekma’ on the
     Python bug tracker; bpo-7033(5).)

   * New function: *note PyFrame_GetLineNumber(): 24b. takes a frame
     object and returns the line number that the frame is currently
     executing.  Previously code would need to get the index of the
     bytecode instruction currently executing, and then look up the line
     number corresponding to that address.  (Added by Jeffrey Yasskin.)

   * New functions: *note PyLong_AsLongAndOverflow(): cc8. and *note
     PyLong_AsLongLongAndOverflow(): cc7. approximates a Python long
     integer as a C ‘long’ or ‘long long’.  If the number is too large
     to fit into the output type, an `overflow' flag is set and returned
     to the caller.  (Contributed by Case Van Horsen; bpo-7528(6) and
     bpo-7767(7).)

   * New function: stemming from the rewrite of string-to-float
     conversion, a new *note PyOS_string_to_double(): ced. function was
     added.  The old ‘PyOS_ascii_strtod()’ and ‘PyOS_ascii_atof()’
     functions are now deprecated.

   * New function: *note PySys_SetArgvEx(): cc5. sets the value of
     ‘sys.argv’ and can optionally update ‘sys.path’ to include the
     directory containing the script named by ‘sys.argv[0]’ depending on
     the value of an `updatepath' parameter.

     This function was added to close a security hole for applications
     that embed Python.  The old function, *note PySys_SetArgv(): db2,
     would always update ‘sys.path’, and sometimes it would add the
     current directory.  This meant that, if you ran an application
     embedding Python in a directory controlled by someone else,
     attackers could put a Trojan-horse module in the directory (say, a
     file named ‘os.py’) that your application would then import and
     run.

     If you maintain a C/C++ application that embeds Python, check
     whether you’re calling *note PySys_SetArgv(): db2. and carefully
     consider whether the application should be using *note
     PySys_SetArgvEx(): cc5. with `updatepath' set to false.

     Security issue reported as CVE-2008-5983(8); discussed in
     bpo-5753(9), and fixed by Antoine Pitrou.

   * New macros: the Python header files now define the following
     macros: ‘Py_ISALNUM’, ‘Py_ISALPHA’, ‘Py_ISDIGIT’, ‘Py_ISLOWER’,
     ‘Py_ISSPACE’, ‘Py_ISUPPER’, ‘Py_ISXDIGIT’, ‘Py_TOLOWER’, and
     ‘Py_TOUPPER’.  All of these functions are analogous to the C
     standard macros for classifying characters, but ignore the current
     locale setting, because in several places Python needs to analyze
     characters in a locale-independent way.  (Added by Eric Smith;
     bpo-5793(10).)

   * Removed function: ‘PyEval_CallObject’ is now only available as a
     macro.  A function version was being kept around to preserve ABI
     linking compatibility, but that was in 1997; it can certainly be
     deleted by now.  (Removed by Antoine Pitrou; bpo-8276(11).)

   * New format codes: the ‘PyFormat_FromString()’,
     ‘PyFormat_FromStringV()’, and *note PyErr_Format(): 898. functions
     now accept ‘%lld’ and ‘%llu’ format codes for displaying C’s ‘long
     long’ types.  (Contributed by Mark Dickinson; bpo-7228(12).)

   * The complicated interaction between threads and process forking has
     been changed.  Previously, the child process created by *note
     os.fork(): a42. might fail because the child is created with only a
     single thread running, the thread performing the *note os.fork():
     a42.  If other threads were holding a lock, such as Python’s import
     lock, when the fork was performed, the lock would still be marked
     as “held” in the new process.  But in the child process nothing
     would ever release the lock, since the other threads weren’t
     replicated, and the child process would no longer be able to
     perform imports.

     Python 2.7 acquires the import lock before performing an *note
     os.fork(): a42, and will also clean up any locks created using the
     *note threading: 10b. module.  C extension modules that have
     internal locks, or that call ‘fork()’ themselves, will not benefit
     from this clean-up.

     (Fixed by Thomas Wouters; bpo-1590864(13).)

   * The *note Py_Finalize(): db3. function now calls the internal
     ‘threading._shutdown()’ function; this prevents some exceptions
     from being raised when an interpreter shuts down.  (Patch by Adam
     Olsen; bpo-1722344(14).)

   * When using the *note PyMemberDef: 52a. structure to define
     attributes of a type, Python will no longer let you try to delete
     or set a ‘T_STRING_INPLACE’ attribute.

   * Global symbols defined by the *note ctypes: 2a. module are now
     prefixed with ‘Py’, or with ‘_ctypes’.  (Implemented by Thomas
     Heller; bpo-3102(15).)

   * New configure option: the ‘--with-system-expat’ switch allows
     building the ‘pyexpat’ module to use the system Expat library.
     (Contributed by Arfrever Frehtes Taifersar Arahesis; bpo-7609(16).)

   * New configure option: the ‘--with-valgrind’ option will now disable
     the pymalloc allocator, which is difficult for the Valgrind
     memory-error detector to analyze correctly.  Valgrind will
     therefore be better at detecting memory leaks and overruns.
     (Contributed by James Henstridge; bpo-2422(17).)

   * New configure option: you can now supply an empty string to
     ‘--with-dbmliborder=’ in order to disable all of the various DBM
     modules.  (Added by Arfrever Frehtes Taifersar Arahesis;
     bpo-6491(18).)

   * The ‘configure’ script now checks for floating-point rounding bugs
     on certain 32-bit Intel chips and defines a ‘X87_DOUBLE_ROUNDING’
     preprocessor definition.  No code currently uses this definition,
     but it’s available if anyone wishes to use it.  (Added by Mark
     Dickinson; bpo-2937(19).)

     ‘configure’ also now sets a ‘LDCXXSHARED’ Makefile variable for
     supporting C++ linking.  (Contributed by Arfrever Frehtes Taifersar
     Arahesis; bpo-1222585(20).)

   * The build process now creates the necessary files for pkg-config
     support.  (Contributed by Clinton Roy; bpo-3585(21).)

   * The build process now supports Subversion 1.7.  (Contributed by
     Arfrever Frehtes Taifersar Arahesis; bpo-6094(22).)

* Menu:

* Capsules::
* Port-Specific Changes; Windows: Port-Specific Changes Windows.
* Port-Specific Changes; Mac OS X: Port-Specific Changes Mac OS X.
* Port-Specific Changes; FreeBSD: Port-Specific Changes FreeBSD.

   ---------- Footnotes ----------

   (1) https://sourceware.org/gdb/current/onlinedocs/gdb/Python.html

   (2) https://bugs.python.org/issue8032

   (3) https://bugs.python.org/issue3632

   (4) https://bugs.python.org/issue4293

   (5) https://bugs.python.org/issue7033

   (6) https://bugs.python.org/issue7528

   (7) https://bugs.python.org/issue7767

   (8) https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-5983

   (9) https://bugs.python.org/issue5753

   (10) https://bugs.python.org/issue5793

   (11) https://bugs.python.org/issue8276

   (12) https://bugs.python.org/issue7228

   (13) https://bugs.python.org/issue1590864

   (14) https://bugs.python.org/issue1722344

   (15) https://bugs.python.org/issue3102

   (16) https://bugs.python.org/issue7609

   (17) https://bugs.python.org/issue2422

   (18) https://bugs.python.org/issue6491

   (19) https://bugs.python.org/issue2937

   (20) https://bugs.python.org/issue1222585

   (21) https://bugs.python.org/issue3585

   (22) https://bugs.python.org/issue6094


File: python.info,  Node: Capsules,  Next: Port-Specific Changes Windows,  Up: Build and C API Changes<8>

1.11.12.1 Capsules
..................

Python 3.1 adds a new C datatype, *note PyCapsule: cd2, for providing a
C API to an extension module.  A capsule is essentially the holder of a
C ‘void *’ pointer, and is made available as a module attribute; for
example, the *note socket: ef. module’s API is exposed as ‘socket.CAPI’,
and *note unicodedata: 123. exposes ‘ucnhash_CAPI’.  Other extensions
can import the module, access its dictionary to get the capsule object,
and then get the ‘void *’ pointer, which will usually point to an array
of pointers to the module’s various API functions.

There is an existing data type already used for this, ‘PyCObject’, but
it doesn’t provide type safety.  Evil code written in pure Python could
cause a segmentation fault by taking a ‘PyCObject’ from module A and
somehow substituting it for the ‘PyCObject’ in module B. Capsules know
their own name, and getting the pointer requires providing the name:

     void *vtable;

     if (!PyCapsule_IsValid(capsule, "mymodule.CAPI") {
             PyErr_SetString(PyExc_ValueError, "argument type invalid");
             return NULL;
     }

     vtable = PyCapsule_GetPointer(capsule, "mymodule.CAPI");

You are assured that ‘vtable’ points to whatever you’re expecting.  If a
different capsule was passed in, *note PyCapsule_IsValid(): db6. would
detect the mismatched name and return false.  Refer to *note Providing a
C API for an Extension Module: db7. for more information on using these
objects.

Python 2.7 now uses capsules internally to provide various
extension-module APIs, but the ‘PyCObject_AsVoidPtr()’ was modified to
handle capsules, preserving compile-time compatibility with the
‘CObject’ interface.  Use of ‘PyCObject_AsVoidPtr()’ will signal a *note
PendingDeprecationWarning: 15c, which is silent by default.

Implemented in Python 3.1 and backported to 2.7 by Larry Hastings;
discussed in bpo-5630(1).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5630


File: python.info,  Node: Port-Specific Changes Windows,  Next: Port-Specific Changes Mac OS X,  Prev: Capsules,  Up: Build and C API Changes<8>

1.11.12.2 Port-Specific Changes: Windows
........................................

   * The *note msvcrt: b6. module now contains some constants from the
     ‘crtassem.h’ header file: ‘CRT_ASSEMBLY_VERSION’,
     ‘VC_ASSEMBLY_PUBLICKEYTOKEN’, and ‘LIBRARIES_ASSEMBLY_NAME_PREFIX’.
     (Contributed by David Cournapeau; bpo-4365(1).)

   * The ‘_winreg’ module for accessing the registry now implements the
     ‘CreateKeyEx()’ and ‘DeleteKeyEx()’ functions, extended versions of
     previously-supported functions that take several extra arguments.
     The ‘DisableReflectionKey()’, ‘EnableReflectionKey()’, and
     ‘QueryReflectionKey()’ were also tested and documented.
     (Implemented by Brian Curtin: bpo-7347(2).)

   * The new ‘_beginthreadex()’ API is used to start threads, and the
     native thread-local storage functions are now used.  (Contributed
     by Kristján Valur Jónsson; bpo-3582(3).)

   * The *note os.kill(): db9. function now works on Windows.  The
     signal value can be the constants ‘CTRL_C_EVENT’,
     ‘CTRL_BREAK_EVENT’, or any integer.  The first two constants will
     send ‘Control-C’ and ‘Control-Break’ keystroke events to
     subprocesses; any other value will use the ‘TerminateProcess()’
     API. (Contributed by Miki Tebeka; bpo-1220212(4).)

   * The *note os.listdir(): b1c. function now correctly fails for an
     empty path.  (Fixed by Hirokazu Yamamoto; bpo-5913(5).)

   * The ‘mimelib’ module will now read the MIME database from the
     Windows registry when initializing.  (Patch by Gabriel Genellina;
     bpo-4969(6).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4365

   (2) https://bugs.python.org/issue7347

   (3) https://bugs.python.org/issue3582

   (4) https://bugs.python.org/issue1220212

   (5) https://bugs.python.org/issue5913

   (6) https://bugs.python.org/issue4969


File: python.info,  Node: Port-Specific Changes Mac OS X,  Next: Port-Specific Changes FreeBSD,  Prev: Port-Specific Changes Windows,  Up: Build and C API Changes<8>

1.11.12.3 Port-Specific Changes: Mac OS X
.........................................

   * The path ‘/Library/Python/2.7/site-packages’ is now appended to
     ‘sys.path’, in order to share added packages between the system
     installation and a user-installed copy of the same version.
     (Changed by Ronald Oussoren; bpo-4865(1).)

          Changed in version 2.7.13: As of 2.7.13, this change was
          removed.  ‘/Library/Python/2.7/site-packages’, the
          site-packages directory used by the Apple-supplied system
          Python 2.7 is no longer appended to ‘sys.path’ for
          user-installed Pythons such as from the python.org installers.
          As of macOS 10.12, Apple changed how the system site-packages
          directory is configured, which could cause installation of pip
          components, like setuptools, to fail.  Packages installed for
          the system Python will no longer be shared with user-installed
          Pythons.  (bpo-28440(2))

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue4865

   (2) https://bugs.python.org/issue28440


File: python.info,  Node: Port-Specific Changes FreeBSD,  Prev: Port-Specific Changes Mac OS X,  Up: Build and C API Changes<8>

1.11.12.4 Port-Specific Changes: FreeBSD
........................................

   * FreeBSD 7.1’s ‘SO_SETFIB’ constant, used with
     ‘getsockopt()’/‘setsockopt()’ to select an alternate routing table,
     is now available in the *note socket: ef. module.  (Added by Kyle
     VanderBeek; bpo-8235(1).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue8235


File: python.info,  Node: Other Changes and Fixes,  Next: Porting to Python 2 7,  Prev: Build and C API Changes<8>,  Up: What’s New in Python 2 7

1.11.13 Other Changes and Fixes
-------------------------------

   * Two benchmark scripts, ‘iobench’ and ‘ccbench’, were added to the
     ‘Tools’ directory.  ‘iobench’ measures the speed of the built-in
     file I/O objects returned by *note open(): 16f. while performing
     various operations, and ‘ccbench’ is a concurrency benchmark that
     tries to measure computing throughput, thread switching latency,
     and IO processing bandwidth when performing several tasks using a
     varying number of threads.

   * The ‘Tools/i18n/msgfmt.py’ script now understands plural forms in
     ‘.po’ files.  (Fixed by Martin von Löwis; bpo-5464(1).)

   * When importing a module from a ‘.pyc’ or ‘.pyo’ file with an
     existing ‘.py’ counterpart, the ‘co_filename’ attributes of the
     resulting code objects are overwritten when the original filename
     is obsolete.  This can happen if the file has been renamed, moved,
     or is accessed through different paths.  (Patch by Ziga Seilnacht
     and Jean-Paul Calderone; bpo-1180193(2).)

   * The ‘regrtest.py’ script now takes a ‘--randseed=’ switch that
     takes an integer that will be used as the random seed for the ‘-r’
     option that executes tests in random order.  The ‘-r’ option also
     reports the seed that was used (Added by Collin Winter.)

   * Another ‘regrtest.py’ switch is ‘-j’, which takes an integer
     specifying how many tests run in parallel.  This allows reducing
     the total runtime on multi-core machines.  This option is
     compatible with several other options, including the ‘-R’ switch
     which is known to produce long runtimes.  (Added by Antoine Pitrou,
     bpo-6152(3).)  This can also be used with a new ‘-F’ switch that
     runs selected tests in a loop until they fail.  (Added by Antoine
     Pitrou; bpo-7312(4).)

   * When executed as a script, the ‘py_compile.py’ module now accepts
     ‘'-'’ as an argument, which will read standard input for the list
     of filenames to be compiled.  (Contributed by Piotr Ożarowski;
     bpo-8233(5).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5464

   (2) https://bugs.python.org/issue1180193

   (3) https://bugs.python.org/issue6152

   (4) https://bugs.python.org/issue7312

   (5) https://bugs.python.org/issue8233


File: python.info,  Node: Porting to Python 2 7,  Next: New Features Added to Python 2 7 Maintenance Releases,  Prev: Other Changes and Fixes,  Up: What’s New in Python 2 7

1.11.14 Porting to Python 2.7
-----------------------------

This section lists previously described changes and other bugfixes that
may require changes to your code:

   * The *note range(): 1f5. function processes its arguments more
     consistently; it will now call *note __int__(): 2c3. on non-float,
     non-integer arguments that are supplied to it.  (Fixed by Alexander
     Belopolsky; bpo-1533(1).)

   * The string *note format(): 5d6. method changed the default
     precision used for floating-point and complex numbers from 6
     decimal places to 12, which matches the precision used by *note
     str(): 205.  (Changed by Eric Smith; bpo-5920(2).)

   * Because of an optimization for the *note with: 7da. statement, the
     special methods *note __enter__(): d5d. and *note __exit__(): d5e.
     must belong to the object’s type, and cannot be directly attached
     to the object’s instance.  This affects new-style classes (derived
     from *note object: 3d2.) and C extension types.  (bpo-6101(3).)

   * Due to a bug in Python 2.6, the `exc_value' parameter to *note
     __exit__(): d5e. methods was often the string representation of the
     exception, not an instance.  This was fixed in 2.7, so `exc_value'
     will be an instance as expected.  (Fixed by Florent Xicluna;
     bpo-7853(4).)

   * When a restricted set of attributes were set using ‘__slots__’,
     deleting an unset attribute would not raise *note AttributeError:
     4a2. as you would expect.  Fixed by Benjamin Peterson;
     bpo-7604(5).)

In the standard library:

   * Operations with *note datetime: 1a0. instances that resulted in a
     year falling outside the supported range didn’t always raise *note
     OverflowError: a41.  Such errors are now checked more carefully and
     will now raise the exception.  (Reported by Mark Leander, patch by
     Anand B. Pillai and Alexander Belopolsky; bpo-7150(6).)

   * When using *note Decimal: 2c0. instances with a string’s *note
     format(): 5d6. method, the default alignment was previously
     left-alignment.  This has been changed to right-alignment, which
     might change the output of your programs.  (Changed by Mark
     Dickinson; bpo-6857(7).)

     Comparisons involving a signaling NaN value (or ‘sNAN’) now signal
     *note InvalidOperation: aca. instead of silently returning a true
     or false value depending on the comparison operator.  Quiet NaN
     values (or ‘NaN’) are now hashable.  (Fixed by Mark Dickinson;
     bpo-7279(8).)

   * The ElementTree library, ‘xml.etree’, no longer escapes ampersands
     and angle brackets when outputting an XML processing instruction
     (which looks like ‘<?xml-stylesheet href=”#style1”?>’) or comment
     (which looks like ‘<!– comment –>’).  (Patch by Neil Muller;
     bpo-2746(9).)

   * The ‘readline()’ method of ‘StringIO’ objects now does nothing when
     a negative length is requested, as other file-like objects do.
     (bpo-7348(10)).

   * The *note syslog: ff. module will now use the value of
     ‘sys.argv[0]’ as the identifier instead of the previous default
     value of ‘'python'’.  (Changed by Sean Reifschneider;
     bpo-8451(11).)

   * The *note tarfile: 101. module’s default error handling has
     changed, to no longer suppress fatal errors.  The default error
     level was previously 0, which meant that errors would only result
     in a message being written to the debug log, but because the debug
     log is not activated by default, these errors go unnoticed.  The
     default error level is now 1, which raises an exception if there’s
     an error.  (Changed by Lars Gustäbel; bpo-7357(12).)

   * The ‘urlparse’ module’s ‘urlsplit()’ now handles unknown URL
     schemes in a fashion compliant with RFC 3986(13): if the URL is of
     the form ‘"<something>://..."’, the text before the ‘://’ is
     treated as the scheme, even if it’s a made-up scheme that the
     module doesn’t know about.  This change may break code that worked
     around the old behaviour.  For example, Python 2.6.4 or 2.5 will
     return the following:

          >>> import urlparse
          >>> urlparse.urlsplit('invented://host/filename?query')
          ('invented', '', '//host/filename?query', '', '')

     Python 2.7 (and Python 2.6.5) will return:

          >>> import urlparse
          >>> urlparse.urlsplit('invented://host/filename?query')
          ('invented', 'host', '/filename?query', '', '')

     (Python 2.7 actually produces slightly different output, since it
     returns a named tuple instead of a standard tuple.)

For C extensions:

   * C extensions that use integer format codes with the ‘PyArg_Parse*’
     family of functions will now raise a *note TypeError: 1fe.
     exception instead of triggering a *note DeprecationWarning: 15a.
     (bpo-5080(14)).

   * Use the new *note PyOS_string_to_double(): ced. function instead of
     the old ‘PyOS_ascii_strtod()’ and ‘PyOS_ascii_atof()’ functions,
     which are now deprecated.

For applications that embed Python:

   * The *note PySys_SetArgvEx(): cc5. function was added, letting
     applications close a security hole when the existing *note
     PySys_SetArgv(): db2. function was used.  Check whether you’re
     calling *note PySys_SetArgv(): db2. and carefully consider whether
     the application should be using *note PySys_SetArgvEx(): cc5. with
     `updatepath' set to false.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1533

   (2) https://bugs.python.org/issue5920

   (3) https://bugs.python.org/issue6101

   (4) https://bugs.python.org/issue7853

   (5) https://bugs.python.org/issue7604

   (6) https://bugs.python.org/issue7150

   (7) https://bugs.python.org/issue6857

   (8) https://bugs.python.org/issue7279

   (9) https://bugs.python.org/issue2746

   (10) https://bugs.python.org/issue7348

   (11) https://bugs.python.org/issue8451

   (12) https://bugs.python.org/issue7357

   (13) https://tools.ietf.org/html/rfc3986.html

   (14) https://bugs.python.org/issue5080


File: python.info,  Node: New Features Added to Python 2 7 Maintenance Releases,  Next: Acknowledgements,  Prev: Porting to Python 2 7,  Up: What’s New in Python 2 7

1.11.15 New Features Added to Python 2.7 Maintenance Releases
-------------------------------------------------------------

New features may be added to Python 2.7 maintenance releases when the
situation genuinely calls for it.  Any such additions must go through
the Python Enhancement Proposal process, and make a compelling case for
why they can’t be adequately addressed by either adding the new feature
solely to Python 3, or else by publishing it on the Python Package
Index.

In addition to the specific proposals listed below, there is a general
exemption allowing new ‘-3’ warnings to be added in any Python 2.7
maintenance release.

* Menu:

* Two new environment variables for debug mode::
* PEP 434; IDLE Enhancement Exception for All Branches: PEP 434 IDLE Enhancement Exception for All Branches.
* PEP 466; Network Security Enhancements for Python 2.7: PEP 466 Network Security Enhancements for Python 2 7.
* PEP 477; Backport ensurepip (PEP 453) to Python 2.7: PEP 477 Backport ensurepip PEP 453 to Python 2 7.
* PEP 476; Enabling certificate verification by default for stdlib http clients: PEP 476 Enabling certificate verification by default for stdlib http clients<2>.
* PEP 493; HTTPS verification migration tools for Python 2.7: PEP 493 HTTPS verification migration tools for Python 2 7.
* New make regen-all build target: New make regen-all build target<3>.
* Removal of make touch build target: Removal of make touch build target<3>.


File: python.info,  Node: Two new environment variables for debug mode,  Next: PEP 434 IDLE Enhancement Exception for All Branches,  Up: New Features Added to Python 2 7 Maintenance Releases

1.11.15.1 Two new environment variables for debug mode
......................................................

In debug mode, the ‘[xxx refs]’ statistic is not written by default, the
‘PYTHONSHOWREFCOUNT’ environment variable now must also be set.
(Contributed by Victor Stinner; bpo-31733(1).)

When Python is compiled with ‘COUNT_ALLOC’ defined, allocation counts
are no longer dumped by default anymore: the ‘PYTHONSHOWALLOCCOUNT’
environment variable must now also be set.  Moreover, allocation counts
are now dumped into stderr, rather than stdout.  (Contributed by Victor
Stinner; bpo-31692(2).)

New in version 2.7.15.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31733

   (2) https://bugs.python.org/issue31692


File: python.info,  Node: PEP 434 IDLE Enhancement Exception for All Branches,  Next: PEP 466 Network Security Enhancements for Python 2 7,  Prev: Two new environment variables for debug mode,  Up: New Features Added to Python 2 7 Maintenance Releases

1.11.15.2 PEP 434: IDLE Enhancement Exception for All Branches
..............................................................

PEP 434(1) describes a general exemption for changes made to the IDLE
development environment shipped along with Python.  This exemption makes
it possible for the IDLE developers to provide a more consistent user
experience across all supported versions of Python 2 and 3.

For details of any IDLE changes, refer to the NEWS file for the specific
release.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0434


File: python.info,  Node: PEP 466 Network Security Enhancements for Python 2 7,  Next: PEP 477 Backport ensurepip PEP 453 to Python 2 7,  Prev: PEP 434 IDLE Enhancement Exception for All Branches,  Up: New Features Added to Python 2 7 Maintenance Releases

1.11.15.3 PEP 466: Network Security Enhancements for Python 2.7
...............................................................

PEP 466(1) describes a number of network security enhancement proposals
that have been approved for inclusion in Python 2.7 maintenance
releases, with the first of those changes appearing in the Python 2.7.7
release.

PEP 466(2) related features added in Python 2.7.7:

   * *note hmac.compare_digest(): aea. was backported from Python 3 to
     make a timing attack resistant comparison operation available to
     Python 2 applications.  (Contributed by Alex Gaynor; bpo-21306(3).)

   * OpenSSL 1.0.1g was upgraded in the official Windows installers
     published on python.org.  (Contributed by Zachary Ware;
     bpo-21462(4).)

PEP 466(5) related features added in Python 2.7.8:

   * *note hashlib.pbkdf2_hmac(): 8d3. was backported from Python 3 to
     make a hashing algorithm suitable for secure password storage
     broadly available to Python 2 applications.  (Contributed by Alex
     Gaynor; bpo-21304(6).)

   * OpenSSL 1.0.1h was upgraded for the official Windows installers
     published on python.org.  (contributed by Zachary Ware in
     bpo-21671(7) for CVE-2014-0224)

PEP 466(8) related features added in Python 2.7.9:

   * Most of Python 3.4’s *note ssl: f3. module was backported.  This
     means *note ssl: f3. now supports Server Name Indication, TLS1.x
     settings, access to the platform certificate store, the *note
     SSLContext: 4ea. class, and other features.  (Contributed by Alex
     Gaynor and David Reid; bpo-21308(9).)

     Refer to the “Version added: 2.7.9” notes in the module
     documentation for specific details.

   * *note os.urandom(): 5cc. was changed to cache a file descriptor to
     ‘/dev/urandom’ instead of reopening ‘/dev/urandom’ on every call.
     (Contributed by Alex Gaynor; bpo-21305(10).)

   * *note hashlib.algorithms_guaranteed: dc2. and *note
     hashlib.algorithms_available: dc3. were backported from Python 3 to
     make it easier for Python 2 applications to select the strongest
     available hash algorithm.  (Contributed by Alex Gaynor in
     bpo-21307(11))

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0466

   (2) https://www.python.org/dev/peps/pep-0466

   (3) https://bugs.python.org/issue21306

   (4) https://bugs.python.org/issue21462

   (5) https://www.python.org/dev/peps/pep-0466

   (6) https://bugs.python.org/issue21304

   (7) https://bugs.python.org/issue21671

   (8) https://www.python.org/dev/peps/pep-0466

   (9) https://bugs.python.org/issue21308

   (10) https://bugs.python.org/issue21305

   (11) https://bugs.python.org/issue21307


File: python.info,  Node: PEP 477 Backport ensurepip PEP 453 to Python 2 7,  Next: PEP 476 Enabling certificate verification by default for stdlib http clients<2>,  Prev: PEP 466 Network Security Enhancements for Python 2 7,  Up: New Features Added to Python 2 7 Maintenance Releases

1.11.15.4 PEP 477: Backport ensurepip (PEP 453) to Python 2.7
.............................................................

PEP 477(1) approves the inclusion of the PEP 453(2) ensurepip module and
the improved documentation that was enabled by it in the Python 2.7
maintenance releases, appearing first in the Python 2.7.9 release.

* Menu:

* Bootstrapping pip By Default: Bootstrapping pip By Default<2>.
* Documentation Changes: Documentation Changes<2>.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0477

   (2) https://www.python.org/dev/peps/pep-0453


File: python.info,  Node: Bootstrapping pip By Default<2>,  Next: Documentation Changes<2>,  Up: PEP 477 Backport ensurepip PEP 453 to Python 2 7

1.11.15.5 Bootstrapping pip By Default
......................................

The new *note ensurepip: 78. module (defined in PEP 453(1)) provides a
standard cross-platform mechanism to bootstrap the pip installer into
Python installations.  The version of ‘pip’ included with Python 2.7.9
is ‘pip’ 1.5.6, and future 2.7.x maintenance releases will update the
bundled version to the latest version of ‘pip’ that is available at the
time of creating the release candidate.

By default, the commands ‘pip’, ‘pipX’ and ‘pipX.Y’ will be installed on
all platforms (where X.Y stands for the version of the Python
installation), along with the ‘pip’ Python package and its dependencies.

For CPython *note source builds on POSIX systems: 8e0, the ‘make
install’ and ‘make altinstall’ commands do not bootstrap ‘pip’ by
default.  This behaviour can be controlled through configure options,
and overridden through Makefile options.

On Windows and Mac OS X, the CPython installers now default to
installing ‘pip’ along with CPython itself (users may opt out of
installing it during the installation process).  Window users will need
to opt in to the automatic ‘PATH’ modifications to have ‘pip’ available
from the command line by default, otherwise it can still be accessed
through the Python launcher for Windows as ‘py -m pip’.

As discussed in the PEP(2), platform packagers may choose not to install
these commands by default, as long as, when invoked, they provide clear
and simple directions on how to install them on that platform (usually
using the system package manager).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0453

   (2) 
https://www.python.org/dev/peps/pep-0477/#disabling-ensurepip-by-downstream-distributors


File: python.info,  Node: Documentation Changes<2>,  Prev: Bootstrapping pip By Default<2>,  Up: PEP 477 Backport ensurepip PEP 453 to Python 2 7

1.11.15.6 Documentation Changes
...............................

As part of this change, the *note Installing Python Modules: 8e2. and
*note Distributing Python Modules: 8e3. sections of the documentation
have been completely redesigned as short getting started and FAQ
documents.  Most packaging documentation has now been moved out to the
Python Packaging Authority maintained Python Packaging User Guide(1) and
the documentation of the individual projects.

However, as this migration is currently still incomplete, the legacy
versions of those guides remaining available as *note Installing Python
Modules (Legacy version): 8e4. and *note Distributing Python Modules
(Legacy version): 8e5.

See also
........

PEP 453(2) – Explicit bootstrapping of pip in Python installations

     PEP written by Donald Stufft and Nick Coghlan, implemented by
     Donald Stufft, Nick Coghlan, Martin von Löwis and Ned Deily.

   ---------- Footnotes ----------

   (1) http://packaging.python.org

   (2) https://www.python.org/dev/peps/pep-0453


File: python.info,  Node: PEP 476 Enabling certificate verification by default for stdlib http clients<2>,  Next: PEP 493 HTTPS verification migration tools for Python 2 7,  Prev: PEP 477 Backport ensurepip PEP 453 to Python 2 7,  Up: New Features Added to Python 2 7 Maintenance Releases

1.11.15.7 PEP 476: Enabling certificate verification by default for stdlib http clients
.......................................................................................

PEP 476(1) updated ‘httplib’ and modules which use it, such as ‘urllib2’
and ‘xmlrpclib’, to now verify that the server presents a certificate
which is signed by a Certificate Authority in the platform trust store
and whose hostname matches the hostname being requested by default,
significantly improving security for many applications.  This change was
made in the Python 2.7.9 release.

For applications which require the old previous behavior, they can pass
an alternate context:

     import urllib2
     import ssl

     # This disables all verification
     context = ssl._create_unverified_context()

     # This allows using a specific certificate for the host, which doesn't need
     # to be in the trust store
     context = ssl.create_default_context(cafile="/path/to/file.crt")

     urllib2.urlopen("https://invalid-cert", context=context)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0476


File: python.info,  Node: PEP 493 HTTPS verification migration tools for Python 2 7,  Next: New make regen-all build target<3>,  Prev: PEP 476 Enabling certificate verification by default for stdlib http clients<2>,  Up: New Features Added to Python 2 7 Maintenance Releases

1.11.15.8 PEP 493: HTTPS verification migration tools for Python 2.7
....................................................................

PEP 493(1) provides additional migration tools to support a more
incremental infrastructure upgrade process for environments containing
applications and services relying on the historically permissive
processing of server certificates when establishing client HTTPS
connections.  These additions were made in the Python 2.7.12 release.

These tools are intended for use in cases where affected applications
and services can’t be modified to explicitly pass a more permissive SSL
context when establishing the connection.

For applications and services which can’t be modified at all, the new
‘PYTHONHTTPSVERIFY’ environment variable may be set to ‘0’ to revert an
entire Python process back to the default permissive behaviour of Python
2.7.8 and earlier.

For cases where the connection establishment code can’t be modified, but
the overall application can be, the new
‘ssl._https_verify_certificates()’ function can be used to adjust the
default behaviour at runtime.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0493


File: python.info,  Node: New make regen-all build target<3>,  Next: Removal of make touch build target<3>,  Prev: PEP 493 HTTPS verification migration tools for Python 2 7,  Up: New Features Added to Python 2 7 Maintenance Releases

1.11.15.9 New ‘make regen-all’ build target
...........................................

To simplify cross-compilation, and to ensure that CPython can reliably
be compiled without requiring an existing version of Python to already
be available, the autotools-based build system no longer attempts to
implicitly recompile generated files based on file modification times.

Instead, a new ‘make regen-all’ command has been added to force
regeneration of these files when desired (e.g.  after an initial version
of Python has already been built based on the pregenerated versions).

More selective regeneration targets are also defined - see
Makefile.pre.in(1) for details.

(Contributed by Victor Stinner in bpo-23404(2).)

New in version 2.7.14.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Makefile.pre.in

   (2) https://bugs.python.org/issue23404


File: python.info,  Node: Removal of make touch build target<3>,  Prev: New make regen-all build target<3>,  Up: New Features Added to Python 2 7 Maintenance Releases

1.11.15.10 Removal of ‘make touch’ build target
...............................................

The ‘make touch’ build target previously used to request implicit
regeneration of generated files by updating their modification times has
been removed.

It has been replaced by the new ‘make regen-all’ target.

(Contributed by Victor Stinner in bpo-23404(1).)

Changed in version 2.7.14.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23404


File: python.info,  Node: Acknowledgements,  Prev: New Features Added to Python 2 7 Maintenance Releases,  Up: What’s New in Python 2 7

1.11.16 Acknowledgements
------------------------

The author would like to thank the following people for offering
suggestions, corrections and assistance with various drafts of this
article: Nick Coghlan, Philip Jenvey, Ryan Lovett, R. David Murray, Hugh
Secker-Walker.


File: python.info,  Node: What’s New in Python 2 6,  Next: What’s New in Python 2 5,  Prev: What’s New in Python 2 7,  Up: What’s New in Python

1.12 What’s New in Python 2.6
=============================


Author: A.M. Kuchling (amk at amk.ca)

This article explains the new features in Python 2.6, released on
October 1 2008.  The release schedule is described in PEP 361(1).

The major theme of Python 2.6 is preparing the migration path to Python
3.0, a major redesign of the language.  Whenever possible, Python 2.6
incorporates new features and syntax from 3.0 while remaining compatible
with existing code by not removing older features or syntax.  When it’s
not possible to do that, Python 2.6 tries to do what it can, adding
compatibility functions in a ‘future_builtins’ module and a ‘-3’ switch
to warn about usages that will become unsupported in 3.0.

Some significant new packages have been added to the standard library,
such as the *note multiprocessing: b7. and *note json: a4. modules, but
there aren’t many new features that aren’t related to Python 3.0 in some
way.

Python 2.6 also sees a number of improvements and bugfixes throughout
the source.  A search through the change logs finds there were 259
patches applied and 612 bugs fixed between Python 2.5 and 2.6.  Both
figures are likely to be underestimates.

This article doesn’t attempt to provide a complete specification of the
new features, but instead provides a convenient overview.  For full
details, you should refer to the documentation for Python 2.6.  If you
want to understand the rationale for the design and implementation,
refer to the PEP for a particular new feature.  Whenever possible,
“What’s New in Python” links to the bug/patch item for each change.

* Menu:

* Python 3.0: Python 3 0.
* Changes to the Development Process::
* PEP 343; The ‘with’ statement: PEP 343 The ‘with’ statement.
* PEP 366; Explicit Relative Imports From a Main Module: PEP 366 Explicit Relative Imports From a Main Module.
* PEP 370; Per-user site-packages Directory: PEP 370 Per-user site-packages Directory.
* PEP 371; The multiprocessing Package: PEP 371 The multiprocessing Package.
* PEP 3101; Advanced String Formatting: PEP 3101 Advanced String Formatting.
* PEP 3105; print As a Function: PEP 3105 print As a Function.
* PEP 3110; Exception-Handling Changes: PEP 3110 Exception-Handling Changes.
* PEP 3112; Byte Literals: PEP 3112 Byte Literals.
* PEP 3116; New I/O Library: PEP 3116 New I/O Library.
* PEP 3118; Revised Buffer Protocol: PEP 3118 Revised Buffer Protocol.
* PEP 3119; Abstract Base Classes: PEP 3119 Abstract Base Classes.
* PEP 3127; Integer Literal Support and Syntax: PEP 3127 Integer Literal Support and Syntax.
* PEP 3129; Class Decorators: PEP 3129 Class Decorators.
* PEP 3141; A Type Hierarchy for Numbers: PEP 3141 A Type Hierarchy for Numbers.
* Other Language Changes: Other Language Changes<11>.
* New and Improved Modules: New and Improved Modules<2>.
* Deprecations and Removals::
* Build and C API Changes: Build and C API Changes<9>.
* Porting to Python 2.6: Porting to Python 2 6.
* Acknowledgements: Acknowledgements<2>.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0361


File: python.info,  Node: Python 3 0,  Next: Changes to the Development Process,  Up: What’s New in Python 2 6

1.12.1 Python 3.0
-----------------

The development cycle for Python versions 2.6 and 3.0 was synchronized,
with the alpha and beta releases for both versions being made on the
same days.  The development of 3.0 has influenced many features in 2.6.

Python 3.0 is a far-ranging redesign of Python that breaks compatibility
with the 2.x series.  This means that existing Python code will need
some conversion in order to run on Python 3.0.  However, not all the
changes in 3.0 necessarily break compatibility.  In cases where new
features won’t cause existing code to break, they’ve been backported to
2.6 and are described in this document in the appropriate place.  Some
of the 3.0-derived features are:

   * A *note __complex__(): 2c5. method for converting objects to a
     complex number.

   * Alternate syntax for catching exceptions: ‘except TypeError as
     exc’.

   * The addition of *note functools.reduce(): d37. as a synonym for the
     built-in ‘reduce()’ function.

Python 3.0 adds several new built-in functions and changes the semantics
of some existing builtins.  Functions that are new in 3.0 such as *note
bin(): d08. have simply been added to Python 2.6, but existing builtins
haven’t been changed; instead, the ‘future_builtins’ module has versions
with the new 3.0 semantics.  Code written to be compatible with 3.0 can
do ‘from future_builtins import hex, map’ as necessary.

A new command-line switch, ‘-3’, enables warnings about features that
will be removed in Python 3.0.  You can run code with this switch to see
how much work will be necessary to port code to 3.0.  The value of this
switch is available to Python code as the boolean variable
‘sys.py3kwarning’, and to C extension code as ‘Py_Py3kWarningFlag’.

See also
........

The 3xxx series of PEPs, which contains proposals for Python 3.0.  PEP
3000(1) describes the development process for Python 3.0.  Start with
PEP 3100(2) that describes the general goals for Python 3.0, and then
explore the higher-numbered PEPS that propose specific features.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3000

   (2) https://www.python.org/dev/peps/pep-3100


File: python.info,  Node: Changes to the Development Process,  Next: PEP 343 The ‘with’ statement,  Prev: Python 3 0,  Up: What’s New in Python 2 6

1.12.2 Changes to the Development Process
-----------------------------------------

While 2.6 was being developed, the Python development process underwent
two significant changes: we switched from SourceForge’s issue tracker to
a customized Roundup installation, and the documentation was converted
from LaTeX to reStructuredText.

* Menu:

* New Issue Tracker; Roundup: New Issue Tracker Roundup.
* New Documentation Format; reStructuredText Using Sphinx: New Documentation Format reStructuredText Using Sphinx.


File: python.info,  Node: New Issue Tracker Roundup,  Next: New Documentation Format reStructuredText Using Sphinx,  Up: Changes to the Development Process

1.12.2.1 New Issue Tracker: Roundup
...................................

For a long time, the Python developers had been growing increasingly
annoyed by SourceForge’s bug tracker.  SourceForge’s hosted solution
doesn’t permit much customization; for example, it wasn’t possible to
customize the life cycle of issues.

The infrastructure committee of the Python Software Foundation therefore
posted a call for issue trackers, asking volunteers to set up different
products and import some of the bugs and patches from SourceForge.  Four
different trackers were examined: Jira(1), Launchpad(2), Roundup(3), and
Trac(4).  The committee eventually settled on Jira and Roundup as the
two candidates.  Jira is a commercial product that offers no-cost hosted
instances to free-software projects; Roundup is an open-source project
that requires volunteers to administer it and a server to host it.

After posting a call for volunteers, a new Roundup installation was set
up at ‘https://bugs.python.org’.  One installation of Roundup can host
multiple trackers, and this server now also hosts issue trackers for
Jython and for the Python web site.  It will surely find other uses in
the future.  Where possible, this edition of “What’s New in Python”
links to the bug/patch item for each change.

Hosting of the Python bug tracker is kindly provided by Upfront
Systems(5) of Stellenbosch, South Africa.  Martin von Löwis put a lot of
effort into importing existing bugs and patches from SourceForge; his
scripts for this import operation are at
‘http://svn.python.org/view/tracker/importer/’ and may be useful to
other projects wishing to move from SourceForge to Roundup.

See also
........

‘https://bugs.python.org’

     The Python bug tracker.

‘http://bugs.jython.org’:

     The Jython bug tracker.

‘http://roundup.sourceforge.net/’

     Roundup downloads and documentation.

‘http://svn.python.org/view/tracker/importer/’

     Martin von Löwis’s conversion scripts.

   ---------- Footnotes ----------

   (1) https://www.atlassian.com/software/jira/

   (2) https://launchpad.net/

   (3) http://roundup.sourceforge.net/

   (4) https://trac.edgewall.org/

   (5) http://www.upfrontsoftware.co.za


File: python.info,  Node: New Documentation Format reStructuredText Using Sphinx,  Prev: New Issue Tracker Roundup,  Up: Changes to the Development Process

1.12.2.2 New Documentation Format: reStructuredText Using Sphinx
................................................................

The Python documentation was written using LaTeX since the project
started around 1989.  In the 1980s and early 1990s, most documentation
was printed out for later study, not viewed online.  LaTeX was widely
used because it provided attractive printed output while remaining
straightforward to write once the basic rules of the markup were
learned.

Today LaTeX is still used for writing publications destined for
printing, but the landscape for programming tools has shifted.  We no
longer print out reams of documentation; instead, we browse through it
online and HTML has become the most important format to support.
Unfortunately, converting LaTeX to HTML is fairly complicated and Fred
L. Drake Jr., the long-time Python documentation editor, spent a lot of
time maintaining the conversion process.  Occasionally people would
suggest converting the documentation into SGML and later XML, but
performing a good conversion is a major task and no one ever committed
the time required to finish the job.

During the 2.6 development cycle, Georg Brandl put a lot of effort into
building a new toolchain for processing the documentation.  The
resulting package is called Sphinx, and is available from
‘http://sphinx-doc.org/’.

Sphinx concentrates on HTML output, producing attractively styled and
modern HTML; printed output is still supported through conversion to
LaTeX. The input format is reStructuredText, a markup syntax supporting
custom extensions and directives that is commonly used in the Python
community.

Sphinx is a standalone package that can be used for writing, and almost
two dozen other projects (listed on the Sphinx web site(1)) have adopted
Sphinx as their documentation tool.

See also
........

Documenting Python(2)

     Describes how to write for Python’s documentation.

Sphinx(3)

     Documentation and code for the Sphinx toolchain.

Docutils(4)

     The underlying reStructuredText parser and toolset.

   ---------- Footnotes ----------

   (1) https://www.sphinx-doc.org/en/master/examples.html

   (2) https://devguide.python.org/documenting/

   (3) http://sphinx-doc.org/

   (4) http://docutils.sourceforge.net


File: python.info,  Node: PEP 343 The ‘with’ statement,  Next: PEP 366 Explicit Relative Imports From a Main Module,  Prev: Changes to the Development Process,  Up: What’s New in Python 2 6

1.12.3 PEP 343: The ‘with’ statement
------------------------------------

The previous version, Python 2.5, added the ‘*note with: 7da.’ statement
as an optional feature, to be enabled by a ‘from __future__ import
with_statement’ directive.  In 2.6 the statement no longer needs to be
specially enabled; this means that ‘with’ is now always a keyword.  The
rest of this section is a copy of the corresponding section from the
“What’s New in Python 2.5” document; if you’re familiar with the
‘‘with’’ statement from Python 2.5, you can skip this section.

The ‘*note with: 7da.’ statement clarifies code that previously would
use ‘try...finally’ blocks to ensure that clean-up code is executed.  In
this section, I’ll discuss the statement as it will commonly be used.
In the next section, I’ll examine the implementation details and show
how to write objects for use with this statement.

The ‘*note with: 7da.’ statement is a control-flow structure whose basic
structure is:

     with expression [as variable]:
         with-block

The expression is evaluated, and it should result in an object that
supports the context management protocol (that is, has *note
__enter__(): d5d. and *note __exit__(): d5e. methods).

The object’s *note __enter__(): d5d. is called before `with-block' is
executed and therefore can run set-up code.  It also may return a value
that is bound to the name `variable', if given.  (Note carefully that
`variable' is `not' assigned the result of `expression'.)

After execution of the `with-block' is finished, the object’s *note
__exit__(): d5e. method is called, even if the block raised an
exception, and can therefore run clean-up code.

Some standard Python objects now support the context management protocol
and can be used with the ‘*note with: 7da.’ statement.  File objects are
one example:

     with open('/etc/passwd', 'r') as f:
         for line in f:
             print line
             ... more processing code ...

After this statement has executed, the file object in `f' will have been
automatically closed, even if the *note for: cfa. loop raised an
exception part-way through the block.

     Note: In this case, `f' is the same object created by *note open():
     16f, because ‘file.__enter__()’ returns `self'.

The *note threading: 10b. module’s locks and condition variables also
support the ‘*note with: 7da.’ statement:

     lock = threading.Lock()
     with lock:
         # Critical section of code
         ...

The lock is acquired before the block is executed and always released
once the block is complete.

The ‘localcontext()’ function in the *note decimal: 35. module makes it
easy to save and restore the current decimal context, which encapsulates
the desired precision and rounding characteristics for computations:

     from decimal import Decimal, Context, localcontext

     # Displays with default precision of 28 digits
     v = Decimal('578')
     print v.sqrt()

     with localcontext(Context(prec=16)):
         # All code in this block uses a precision of 16 digits.
         # The original context is restored on exiting the block.
         print v.sqrt()

* Menu:

* Writing Context Managers::
* The contextlib module::


File: python.info,  Node: Writing Context Managers,  Next: The contextlib module,  Up: PEP 343 The ‘with’ statement

1.12.3.1 Writing Context Managers
.................................

Under the hood, the ‘*note with: 7da.’ statement is fairly complicated.
Most people will only use ‘‘with’’ in company with existing objects and
don’t need to know these details, so you can skip the rest of this
section if you like.  Authors of new objects will need to understand the
details of the underlying implementation and should keep reading.

A high-level explanation of the context management protocol is:

   * The expression is evaluated and should result in an object called a
     “context manager”.  The context manager must have *note
     __enter__(): d5d. and *note __exit__(): d5e. methods.

   * The context manager’s *note __enter__(): d5d. method is called.
     The value returned is assigned to `VAR'. If no ‘as VAR’ clause is
     present, the value is simply discarded.

   * The code in `BLOCK' is executed.

   * If `BLOCK' raises an exception, the context manager’s *note
     __exit__(): d5e. method is called with three arguments, the
     exception details (‘type, value, traceback’, the same values
     returned by *note sys.exc_info(): d27, which can also be ‘None’ if
     no exception occurred).  The method’s return value controls whether
     an exception is re-raised: any false value re-raises the exception,
     and ‘True’ will result in suppressing it.  You’ll only rarely want
     to suppress the exception, because if you do the author of the code
     containing the ‘*note with: 7da.’ statement will never realize
     anything went wrong.

   * If `BLOCK' didn’t raise an exception, the *note __exit__(): d5e.
     method is still called, but `type', `value', and `traceback' are
     all ‘None’.

Let’s think through an example.  I won’t present detailed code but will
only sketch the methods necessary for a database that supports
transactions.

(For people unfamiliar with database terminology: a set of changes to
the database are grouped into a transaction.  Transactions can be either
committed, meaning that all the changes are written into the database,
or rolled back, meaning that the changes are all discarded and the
database is unchanged.  See any database textbook for more information.)

Let’s assume there’s an object representing a database connection.  Our
goal will be to let the user write code like this:

     db_connection = DatabaseConnection()
     with db_connection as cursor:
         cursor.execute('insert into ...')
         cursor.execute('delete from ...')
         # ... more operations ...

The transaction should be committed if the code in the block runs
flawlessly or rolled back if there’s an exception.  Here’s the basic
interface for ‘DatabaseConnection’ that I’ll assume:

     class DatabaseConnection:
         # Database interface
         def cursor(self):
             "Returns a cursor object and starts a new transaction"
         def commit(self):
             "Commits current transaction"
         def rollback(self):
             "Rolls back current transaction"

The *note __enter__(): d5d. method is pretty easy, having only to start
a new transaction.  For this application the resulting cursor object
would be a useful result, so the method will return it.  The user can
then add ‘as cursor’ to their ‘*note with: 7da.’ statement to bind the
cursor to a variable name.

     class DatabaseConnection:
         ...
         def __enter__(self):
             # Code to start a new transaction
             cursor = self.cursor()
             return cursor

The *note __exit__(): d5e. method is the most complicated because it’s
where most of the work has to be done.  The method has to check if an
exception occurred.  If there was no exception, the transaction is
committed.  The transaction is rolled back if there was an exception.

In the code below, execution will just fall off the end of the function,
returning the default value of ‘None’.  ‘None’ is false, so the
exception will be re-raised automatically.  If you wished, you could be
more explicit and add a *note return: 2c8. statement at the marked
location.

     class DatabaseConnection:
         ...
         def __exit__(self, type, value, tb):
             if tb is None:
                 # No exception, so commit
                 self.commit()
             else:
                 # Exception occurred, so rollback.
                 self.rollback()
                 # return False


File: python.info,  Node: The contextlib module,  Prev: Writing Context Managers,  Up: PEP 343 The ‘with’ statement

1.12.3.2 The contextlib module
..............................

The *note contextlib: 23. module provides some functions and a decorator
that are useful when writing objects for use with the ‘*note with: 7da.’
statement.

The decorator is called ‘contextmanager()’, and lets you write a single
generator function instead of defining a new class.  The generator
should yield exactly one value.  The code up to the *note yield: 2c7.
will be executed as the *note __enter__(): d5d. method, and the value
yielded will be the method’s return value that will get bound to the
variable in the ‘*note with: 7da.’ statement’s ‘as’ clause, if any.  The
code after the ‘yield’ will be executed in the *note __exit__(): d5e.
method.  Any exception raised in the block will be raised by the ‘yield’
statement.

Using this decorator, our database example from the previous section
could be written as:

     from contextlib import contextmanager

     @contextmanager
     def db_transaction(connection):
         cursor = connection.cursor()
         try:
             yield cursor
         except:
             connection.rollback()
             raise
         else:
             connection.commit()

     db = DatabaseConnection()
     with db_transaction(db) as cursor:
         ...

The *note contextlib: 23. module also has a ‘nested(mgr1, mgr2, ...)’
function that combines a number of context managers so you don’t need to
write nested ‘*note with: 7da.’ statements.  In this example, the single
‘‘with’’ statement both starts a database transaction and acquires a
thread lock:

     lock = threading.Lock()
     with nested (db_transaction(db), lock) as (cursor, locked):
         ...

Finally, the ‘closing()’ function returns its argument so that it can be
bound to a variable, and calls the argument’s ‘.close()’ method at the
end of the block.

     import urllib, sys
     from contextlib import closing

     with closing(urllib.urlopen('http://www.yahoo.com')) as f:
         for line in f:
             sys.stdout.write(line)

See also
........

PEP 343(1) - The “with” statement

     PEP written by Guido van Rossum and Nick Coghlan; implemented by
     Mike Bland, Guido van Rossum, and Neal Norwitz.  The PEP shows the
     code generated for a ‘*note with: 7da.’ statement, which can be
     helpful in learning how the statement works.

The documentation for the *note contextlib: 23. module.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0343


File: python.info,  Node: PEP 366 Explicit Relative Imports From a Main Module,  Next: PEP 370 Per-user site-packages Directory,  Prev: PEP 343 The ‘with’ statement,  Up: What’s New in Python 2 6

1.12.4 PEP 366: Explicit Relative Imports From a Main Module
------------------------------------------------------------

Python’s *note -m: 443. switch allows running a module as a script.
When you ran a module that was located inside a package, relative
imports didn’t work correctly.

The fix for Python 2.6 adds a *note __package__: a36. attribute to
modules.  When this attribute is present, relative imports will be
relative to the value of this attribute instead of the *note __name__:
dd8. attribute.

PEP 302-style importers can then set *note __package__: a36. as
necessary.  The *note runpy: e2. module that implements the *note -m:
443. switch now does this, so relative imports will now work correctly
in scripts running from inside a package.


File: python.info,  Node: PEP 370 Per-user site-packages Directory,  Next: PEP 371 The multiprocessing Package,  Prev: PEP 366 Explicit Relative Imports From a Main Module,  Up: What’s New in Python 2 6

1.12.5 PEP 370: Per-user ‘site-packages’ Directory
--------------------------------------------------

When you run Python, the module search path ‘sys.path’ usually includes
a directory whose path ends in ‘"site-packages"’.  This directory is
intended to hold locally-installed packages available to all users using
a machine or a particular site installation.

Python 2.6 introduces a convention for user-specific site directories.
The directory varies depending on the platform:

   * Unix and Mac OS X: ‘~/.local/’

   * Windows: ‘%APPDATA%/Python’

Within this directory, there will be version-specific subdirectories,
such as ‘lib/python2.6/site-packages’ on Unix/Mac OS and
‘Python26/site-packages’ on Windows.

If you don’t like the default directory, it can be overridden by an
environment variable.  *note PYTHONUSERBASE: dda. sets the root
directory used for all Python versions supporting this feature.  On
Windows, the directory for application-specific data can be changed by
setting the ‘APPDATA’ environment variable.  You can also modify the
‘site.py’ file for your Python installation.

The feature can be disabled entirely by running Python with the *note
-s: ddb. option or setting the *note PYTHONNOUSERSITE: ddc. environment
variable.

See also
........

PEP 370(1) - Per-user ‘site-packages’ Directory

     PEP written and implemented by Christian Heimes.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0370


File: python.info,  Node: PEP 371 The multiprocessing Package,  Next: PEP 3101 Advanced String Formatting,  Prev: PEP 370 Per-user site-packages Directory,  Up: What’s New in Python 2 6

1.12.6 PEP 371: The ‘multiprocessing’ Package
---------------------------------------------

The new *note multiprocessing: b7. package lets Python programs create
new processes that will perform a computation and return a result to the
parent.  The parent and child processes can communicate using queues and
pipes, synchronize their operations using locks and semaphores, and can
share simple arrays of data.

The *note multiprocessing: b7. module started out as an exact emulation
of the *note threading: 10b. module using processes instead of threads.
That goal was discarded along the path to Python 2.6, but the general
approach of the module is still similar.  The fundamental class is the
‘Process’, which is passed a callable object and a collection of
arguments.  The ‘start()’ method sets the callable running in a
subprocess, after which you can call the ‘is_alive()’ method to check
whether the subprocess is still running and the ‘join()’ method to wait
for the process to exit.

Here’s a simple example where the subprocess will calculate a factorial.
The function doing the calculation is written strangely so that it takes
significantly longer when the input argument is a multiple of 4.

     import time
     from multiprocessing import Process, Queue


     def factorial(queue, N):
         "Compute a factorial."
         # If N is a multiple of 4, this function will take much longer.
         if (N % 4) == 0:
             time.sleep(.05 * N/4)

         # Calculate the result
         fact = 1L
         for i in range(1, N+1):
             fact = fact * i

         # Put the result on the queue
         queue.put(fact)

     if __name__ == '__main__':
         queue = Queue()

         N = 5

         p = Process(target=factorial, args=(queue, N))
         p.start()
         p.join()

         result = queue.get()
         print 'Factorial', N, '=', result

A *note Queue: dde. is used to communicate the result of the factorial.
The *note Queue: dde. object is stored in a global variable.  The child
process will use the value of the variable when the child was created;
because it’s a *note Queue: dde, parent and child can use the object to
communicate.  (If the parent were to change the value of the global
variable, the child’s value would be unaffected, and vice versa.)

Two other classes, ‘Pool’ and ‘Manager’, provide higher-level
interfaces.  ‘Pool’ will create a fixed number of worker processes, and
requests can then be distributed to the workers by calling ‘apply()’ or
‘apply_async()’ to add a single request, and *note map(): cf7. or
‘map_async()’ to add a number of requests.  The following code uses a
‘Pool’ to spread requests across 5 worker processes and retrieve a list
of results:

     from multiprocessing import Pool

     def factorial(N, dictionary):
         "Compute a factorial."
         ...
     p = Pool(5)
     result = p.map(factorial, range(1, 1000, 10))
     for v in result:
         print v

This produces the following output:

     1
     39916800
     51090942171709440000
     8222838654177922817725562880000000
     33452526613163807108170062053440751665152000000000
     ...

The other high-level interface, the ‘Manager’ class, creates a separate
server process that can hold master copies of Python data structures.
Other processes can then access and modify these data structures using
proxy objects.  The following example creates a shared dictionary by
calling the *note dict(): 164. method; the worker processes then insert
values into the dictionary.  (Locking is not done for you automatically,
which doesn’t matter in this example.  ‘Manager’’s methods also include
‘Lock()’, ‘RLock()’, and ‘Semaphore()’ to create shared locks.)

     import time
     from multiprocessing import Pool, Manager

     def factorial(N, dictionary):
         "Compute a factorial."
         # Calculate the result
         fact = 1L
         for i in range(1, N+1):
             fact = fact * i

         # Store result in dictionary
         dictionary[N] = fact

     if __name__ == '__main__':
         p = Pool(5)
         mgr = Manager()
         d = mgr.dict()         # Create shared dictionary

         # Run tasks using the pool
         for N in range(1, 1000, 10):
             p.apply_async(factorial, (N, d))

         # Mark pool as closed -- no more tasks can be added.
         p.close()

         # Wait for tasks to exit
         p.join()

         # Output results
         for k, v in sorted(d.items()):
             print k, v

This will produce the output:

     1 1
     11 39916800
     21 51090942171709440000
     31 8222838654177922817725562880000000
     41 33452526613163807108170062053440751665152000000000
     51 15511187532873822802242430164693032110632597200169861120000...

See also
........

The documentation for the *note multiprocessing: b7. module.

PEP 371(1) - Addition of the multiprocessing package

     PEP written by Jesse Noller and Richard Oudkerk; implemented by
     Richard Oudkerk and Jesse Noller.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0371


File: python.info,  Node: PEP 3101 Advanced String Formatting,  Next: PEP 3105 print As a Function,  Prev: PEP 371 The multiprocessing Package,  Up: What’s New in Python 2 6

1.12.7 PEP 3101: Advanced String Formatting
-------------------------------------------

In Python 3.0, the ‘%’ operator is supplemented by a more powerful
string formatting method, *note format(): 5d6.  Support for the *note
str.format(): 5d5. method has been backported to Python 2.6.

In 2.6, both 8-bit and Unicode strings have a ‘.format()’ method that
treats the string as a template and takes the arguments to be formatted.
The formatting template uses curly brackets (‘{’, ‘}’) as special
characters:

     >>> # Substitute positional argument 0 into the string.
     >>> "User ID: {0}".format("root")
     'User ID: root'
     >>> # Use the named keyword arguments
     >>> "User ID: {uid}   Last seen: {last_login}".format(
     ...    uid="root",
     ...    last_login = "5 Mar 2008 07:20")
     'User ID: root   Last seen: 5 Mar 2008 07:20'

Curly brackets can be escaped by doubling them:

     >>> "Empty dict: {{}}".format()
     "Empty dict: {}"

Field names can be integers indicating positional arguments, such as
‘{0}’, ‘{1}’, etc.  or names of keyword arguments.  You can also supply
compound field names that read attributes or access dictionary keys:

     >>> import sys
     >>> print 'Platform: {0.platform}\nPython version: {0.version}'.format(sys)
     Platform: darwin
     Python version: 2.6a1+ (trunk:61261M, Mar  5 2008, 20:29:41)
     [GCC 4.0.1 (Apple Computer, Inc. build 5367)]'

     >>> import mimetypes
     >>> 'Content-type: {0[.mp4]}'.format(mimetypes.types_map)
     'Content-type: video/mp4'

Note that when using dictionary-style notation such as ‘[.mp4]’, you
don’t need to put any quotation marks around the string; it will look up
the value using ‘.mp4’ as the key.  Strings beginning with a number will
be converted to an integer.  You can’t write more complicated
expressions inside a format string.

So far we’ve shown how to specify which field to substitute into the
resulting string.  The precise formatting used is also controllable by
adding a colon followed by a format specifier.  For example:

     >>> # Field 0: left justify, pad to 15 characters
     >>> # Field 1: right justify, pad to 6 characters
     >>> fmt = '{0:15} ${1:>6}'
     >>> fmt.format('Registration', 35)
     'Registration    $    35'
     >>> fmt.format('Tutorial', 50)
     'Tutorial        $    50'
     >>> fmt.format('Banquet', 125)
     'Banquet         $   125'

Format specifiers can reference other fields through nesting:

     >>> fmt = '{0:{1}}'
     >>> width = 15
     >>> fmt.format('Invoice #1234', width)
     'Invoice #1234  '
     >>> width = 35
     >>> fmt.format('Invoice #1234', width)
     'Invoice #1234                      '

The alignment of a field within the desired width can be specified:

Character            Effect
                     
----------------------------------------------------------------------
                     
< (default)          Left-align
                     
                     
>                    Right-align
                     
                     
^                    Center
                     
                     
=                    (For numeric types only) Pad after the sign.
                     

Format specifiers can also include a presentation type, which controls
how the value is formatted.  For example, floating-point numbers can be
formatted as a general number or in exponential notation:

     >>> '{0:g}'.format(3.75)
     '3.75'
     >>> '{0:e}'.format(3.75)
     '3.750000e+00'

A variety of presentation types are available.  Consult the 2.6
documentation for a *note complete list: de0.; here’s a sample:

‘b’       Binary.  Outputs the number in base 2.
          
          
‘c’       Character.  Converts the integer to the corresponding Unicode character
          before printing.
          
          
‘d’       Decimal Integer.  Outputs the number in base 10.
          
          
‘o’       Octal format.  Outputs the number in base 8.
          
          
‘x’       Hex format.  Outputs the number in base 16, using lower-case letters for
          the digits above 9.
          
          
‘e’       Exponent notation.  Prints the number in scientific notation using the
          letter ‘e’ to indicate the exponent.
          
          
‘g’       General format.  This prints the number as a fixed-point number, unless
          the number is too large, in which case it switches to ‘e’ exponent
          notation.
          
          
‘n’       Number.  This is the same as ‘g’ (for floats) or ‘d’ (for integers),
          except that it uses the current locale setting to insert the appropriate
          number separator characters.
          
          
‘%’       Percentage.  Multiplies the number by 100 and displays in fixed (‘f’)
          format, followed by a percent sign.
          

Classes and types can define a *note __format__(): a2f. method to
control how they’re formatted.  It receives a single argument, the
format specifier:

     def __format__(self, format_spec):
         if isinstance(format_spec, unicode):
             return unicode(str(self))
         else:
             return str(self)

There’s also a *note format(): 5d6. builtin that will format a single
value.  It calls the type’s *note __format__(): a2f. method with the
provided specifier:

     >>> format(75.6564, '.2f')
     '75.66'

See also
........

*note Format String Syntax: de0.

     The reference documentation for format fields.

PEP 3101(1) - Advanced String Formatting

     PEP written by Talin.  Implemented by Eric Smith.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3101


File: python.info,  Node: PEP 3105 print As a Function,  Next: PEP 3110 Exception-Handling Changes,  Prev: PEP 3101 Advanced String Formatting,  Up: What’s New in Python 2 6

1.12.8 PEP 3105: ‘print’ As a Function
--------------------------------------

The ‘print’ statement becomes the *note print(): 971. function in Python
3.0.  Making *note print(): 971. a function makes it possible to replace
the function by doing ‘def print(...)’ or importing a new function from
somewhere else.

Python 2.6 has a ‘__future__’ import that removes ‘print’ as language
syntax, letting you use the functional form instead.  For example:

     >>> from __future__ import print_function
     >>> print('# of entries', len(dictionary), file=sys.stderr)

The signature of the new function is:

     def print(*args, sep=' ', end='\n', file=None)

The parameters are:

        * `args': positional arguments whose values will be printed out.

        * `sep': the separator, which will be printed between arguments.

        * `end': the ending text, which will be printed after all of the
          arguments have been output.

        * `file': the file object to which the output will be sent.

See also
........

PEP 3105(1) - Make print a function

     PEP written by Georg Brandl.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3105


File: python.info,  Node: PEP 3110 Exception-Handling Changes,  Next: PEP 3112 Byte Literals,  Prev: PEP 3105 print As a Function,  Up: What’s New in Python 2 6

1.12.9 PEP 3110: Exception-Handling Changes
-------------------------------------------

One error that Python programmers occasionally make is writing the
following code:

     try:
         ...
     except TypeError, ValueError:  # Wrong!
         ...

The author is probably trying to catch both *note TypeError: 1fe. and
*note ValueError: 16d. exceptions, but this code actually does something
different: it will catch *note TypeError: 1fe. and bind the resulting
exception object to the local name ‘"ValueError"’.  The *note
ValueError: 16d. exception will not be caught at all.  The correct code
specifies a tuple of exceptions:

     try:
         ...
     except (TypeError, ValueError):
         ...

This error happens because the use of the comma here is ambiguous: does
it indicate two different nodes in the parse tree, or a single node
that’s a tuple?

Python 3.0 makes this unambiguous by replacing the comma with the word
“as”.  To catch an exception and store the exception object in the
variable ‘exc’, you must write:

     try:
         ...
     except TypeError as exc:
         ...

Python 3.0 will only support the use of “as”, and therefore interprets
the first example as catching two different exceptions.  Python 2.6
supports both the comma and “as”, so existing code will continue to
work.  We therefore suggest using “as” when writing new Python code that
will only be executed with 2.6.

See also
........

PEP 3110(1) - Catching Exceptions in Python 3000

     PEP written and implemented by Collin Winter.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3110


File: python.info,  Node: PEP 3112 Byte Literals,  Next: PEP 3116 New I/O Library,  Prev: PEP 3110 Exception-Handling Changes,  Up: What’s New in Python 2 6

1.12.10 PEP 3112: Byte Literals
-------------------------------

Python 3.0 adopts Unicode as the language’s fundamental string type and
denotes 8-bit literals differently, either as ‘b'string'’ or using a
*note bytes: 172. constructor.  For future compatibility, Python 2.6
adds *note bytes: 172. as a synonym for the *note str: 205. type, and it
also supports the ‘b''’ notation.

The 2.6 *note str: 205. differs from 3.0’s *note bytes: 172. type in
various ways; most notably, the constructor is completely different.  In
3.0, ‘bytes([65, 66, 67])’ is 3 elements long, containing the bytes
representing ‘ABC’; in 2.6, ‘bytes([65, 66, 67])’ returns the 12-byte
string representing the *note str(): 205. of the list.

The primary use of *note bytes: 172. in 2.6 will be to write tests of
object type such as ‘isinstance(x, bytes)’.  This will help the 2to3
converter, which can’t tell whether 2.x code intends strings to contain
either characters or 8-bit bytes; you can now use either *note bytes:
172. or *note str: 205. to represent your intention exactly, and the
resulting code will also be correct in Python 3.0.

There’s also a ‘__future__’ import that causes all string literals to
become Unicode strings.  This means that ‘\u’ escape sequences can be
used to include Unicode characters:

     from __future__ import unicode_literals

     s = ('\u751f\u3080\u304e\u3000\u751f\u3054'
          '\u3081\u3000\u751f\u305f\u307e\u3054')

     print len(s)               # 12 Unicode characters

At the C level, Python 3.0 will rename the existing 8-bit string type,
called ‘PyStringObject’ in Python 2.x, to *note PyBytesObject: de4.
Python 2.6 uses ‘#define’ to support using the names *note
PyBytesObject(): de4, *note PyBytes_Check(): de5, *note
PyBytes_FromStringAndSize(): de6, and all the other functions and macros
used with strings.

Instances of the *note bytes: 172. type are immutable just as strings
are.  A new *note bytearray: 173. type stores a mutable sequence of
bytes:

     >>> bytearray([65, 66, 67])
     bytearray(b'ABC')
     >>> b = bytearray(u'\u21ef\u3244', 'utf-8')
     >>> b
     bytearray(b'\xe2\x87\xaf\xe3\x89\x84')
     >>> b[0] = '\xe3'
     >>> b
     bytearray(b'\xe3\x87\xaf\xe3\x89\x84')
     >>> unicode(str(b), 'utf-8')
     u'\u31ef \u3244'

Byte arrays support most of the methods of string types, such as
‘startswith()’/‘endswith()’, ‘find()’/‘rfind()’, and some of the methods
of lists, such as ‘append()’, ‘pop()’, and ‘reverse()’.

     >>> b = bytearray('ABC')
     >>> b.append('d')
     >>> b.append(ord('e'))
     >>> b
     bytearray(b'ABCde')

There’s also a corresponding C API, with *note PyByteArray_FromObject():
de7, *note PyByteArray_FromStringAndSize(): de8, and various other
functions.

See also
........

PEP 3112(1) - Bytes literals in Python 3000

     PEP written by Jason Orendorff; backported to 2.6 by Christian
     Heimes.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3112


File: python.info,  Node: PEP 3116 New I/O Library,  Next: PEP 3118 Revised Buffer Protocol,  Prev: PEP 3112 Byte Literals,  Up: What’s New in Python 2 6

1.12.11 PEP 3116: New I/O Library
---------------------------------

Python’s built-in file objects support a number of methods, but
file-like objects don’t necessarily support all of them.  Objects that
imitate files usually support ‘read()’ and ‘write()’, but they may not
support *note readline(): de, for example.  Python 3.0 introduces a
layered I/O library in the *note io: a1. module that separates buffering
and text-handling features from the fundamental read and write
operations.

There are three levels of abstract base classes provided by the *note
io: a1. module:

   * ‘RawIOBase’ defines raw I/O operations: ‘read()’, ‘readinto()’,
     ‘write()’, ‘seek()’, ‘tell()’, ‘truncate()’, and ‘close()’.  Most
     of the methods of this class will often map to a single system
     call.  There are also ‘readable()’, ‘writable()’, and ‘seekable()’
     methods for determining what operations a given object will allow.

     Python 3.0 has concrete implementations of this class for files and
     sockets, but Python 2.6 hasn’t restructured its file and socket
     objects in this way.

   * ‘BufferedIOBase’ is an abstract base class that buffers data in
     memory to reduce the number of system calls used, making I/O
     processing more efficient.  It supports all of the methods of
     ‘RawIOBase’, and adds a ‘raw’ attribute holding the underlying raw
     object.

     There are five concrete classes implementing this ABC.
     ‘BufferedWriter’ and ‘BufferedReader’ are for objects that support
     write-only or read-only usage that have a ‘seek()’ method for
     random access.  ‘BufferedRandom’ objects support read and write
     access upon the same underlying stream, and ‘BufferedRWPair’ is for
     objects such as TTYs that have both read and write operations
     acting upon unconnected streams of data.  The ‘BytesIO’ class
     supports reading, writing, and seeking over an in-memory buffer.

   * ‘TextIOBase’: Provides functions for reading and writing strings
     (remember, strings will be Unicode in Python 3.0), and supporting
     *note universal newlines: 6eb.  ‘TextIOBase’ defines the *note
     readline(): de. method and supports iteration upon objects.

     There are two concrete implementations.  ‘TextIOWrapper’ wraps a
     buffered I/O object, supporting all of the methods for text I/O and
     adding a ‘buffer’ attribute for access to the underlying object.
     ‘StringIO’ simply buffers everything in memory without ever writing
     anything to disk.

     (In Python 2.6, *note io.StringIO: 91a. is implemented in pure
     Python, so it’s pretty slow.  You should therefore stick with the
     existing ‘StringIO’ module or ‘cStringIO’ for now.  At some point
     Python 3.0’s *note io: a1. module will be rewritten into C for
     speed, and perhaps the C implementation will be backported to the
     2.x releases.)

In Python 2.6, the underlying implementations haven’t been restructured
to build on top of the *note io: a1. module’s classes.  The module is
being provided to make it easier to write code that’s forward-compatible
with 3.0, and to save developers the effort of writing their own
implementations of buffering and text I/O.

See also
........

PEP 3116(1) - New I/O

     PEP written by Daniel Stutzbach, Mike Verdone, and Guido van
     Rossum.  Code by Guido van Rossum, Georg Brandl, Walter Doerwald,
     Jeremy Hylton, Martin von Löwis, Tony Lownds, and others.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3116


File: python.info,  Node: PEP 3118 Revised Buffer Protocol,  Next: PEP 3119 Abstract Base Classes,  Prev: PEP 3116 New I/O Library,  Up: What’s New in Python 2 6

1.12.12 PEP 3118: Revised Buffer Protocol
-----------------------------------------

The buffer protocol is a C-level API that lets Python types exchange
pointers into their internal representations.  A memory-mapped file can
be viewed as a buffer of characters, for example, and this lets another
module such as *note re: dd. treat memory-mapped files as a string of
characters to be searched.

The primary users of the buffer protocol are numeric-processing packages
such as NumPy, which expose the internal representation of arrays so
that callers can write data directly into an array instead of going
through a slower API. This PEP updates the buffer protocol in light of
experience from NumPy development, adding a number of new features such
as indicating the shape of an array or locking a memory region.

The most important new C API function is ‘PyObject_GetBuffer(PyObject
*obj, Py_buffer *view, int flags)’, which takes an object and a set of
flags, and fills in the ‘Py_buffer’ structure with information about the
object’s memory representation.  Objects can use this operation to lock
memory in place while an external caller could be modifying the
contents, so there’s a corresponding ‘PyBuffer_Release(Py_buffer *view)’
to indicate that the external caller is done.

The `flags' argument to *note PyObject_GetBuffer(): deb. specifies
constraints upon the memory returned.  Some examples are:

        * ‘PyBUF_WRITABLE’ indicates that the memory must be writable.

        * ‘PyBUF_LOCK’ requests a read-only or exclusive lock on the
          memory.

        * ‘PyBUF_C_CONTIGUOUS’ and ‘PyBUF_F_CONTIGUOUS’ requests a
          C-contiguous (last dimension varies the fastest) or
          Fortran-contiguous (first dimension varies the fastest) array
          layout.

Two new argument codes for *note PyArg_ParseTuple(): 393, ‘s*’ and ‘z*’,
return locked buffer objects for a parameter.

See also
........

PEP 3118(1) - Revising the buffer protocol

     PEP written by Travis Oliphant and Carl Banks; implemented by
     Travis Oliphant.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3118


File: python.info,  Node: PEP 3119 Abstract Base Classes,  Next: PEP 3127 Integer Literal Support and Syntax,  Prev: PEP 3118 Revised Buffer Protocol,  Up: What’s New in Python 2 6

1.12.13 PEP 3119: Abstract Base Classes
---------------------------------------

Some object-oriented languages such as Java support interfaces,
declaring that a class has a given set of methods or supports a given
access protocol.  Abstract Base Classes (or ABCs) are an equivalent
feature for Python.  The ABC support consists of an *note abc: 3. module
containing a metaclass called ‘ABCMeta’, special handling of this
metaclass by the *note isinstance(): 552. and *note issubclass(): 553.
builtins, and a collection of basic ABCs that the Python developers
think will be widely useful.  Future versions of Python will probably
add more ABCs.

Let’s say you have a particular class and wish to know whether it
supports dictionary-style access.  The phrase “dictionary-style” is
vague, however.  It probably means that accessing items with ‘obj[1]’
works.  Does it imply that setting items with ‘obj[2] = value’ works?
Or that the object will have ‘keys()’, ‘values()’, and ‘items()’
methods?  What about the iterative variants such as ‘iterkeys()’?  *note
copy(): 25. and ‘update()’?  Iterating over the object with *note
iter(): ded.?

The Python 2.6 *note collections: 1d. module includes a number of
different ABCs that represent these distinctions.  ‘Iterable’ indicates
that a class defines *note __iter__(): 609, and ‘Container’ means the
class defines a *note __contains__(): dee. method and therefore supports
‘x in y’ expressions.  The basic dictionary interface of getting items,
setting items, and ‘keys()’, ‘values()’, and ‘items()’, is defined by
the ‘MutableMapping’ ABC.

You can derive your own classes from a particular ABC to indicate they
support that ABC’s interface:

     import collections

     class Storage(collections.MutableMapping):
         ...

Alternatively, you could write the class without deriving from the
desired ABC and instead register the class by calling the ABC’s
‘register()’ method:

     import collections

     class Storage:
         ...

     collections.MutableMapping.register(Storage)

For classes that you write, deriving from the ABC is probably clearer.
The ‘register()’ method is useful when you’ve written a new ABC that can
describe an existing type or class, or if you want to declare that some
third-party class implements an ABC. For example, if you defined a
‘PrintableType’ ABC, it’s legal to do:

     # Register Python's types
     PrintableType.register(int)
     PrintableType.register(float)
     PrintableType.register(str)

Classes should obey the semantics specified by an ABC, but Python can’t
check this; it’s up to the class author to understand the ABC’s
requirements and to implement the code accordingly.

To check whether an object supports a particular interface, you can now
write:

     def func(d):
         if not isinstance(d, collections.MutableMapping):
             raise ValueError("Mapping object expected, not %r" % d)

Don’t feel that you must now begin writing lots of checks as in the
above example.  Python has a strong tradition of duck-typing, where
explicit type-checking is never done and code simply calls methods on an
object, trusting that those methods will be there and raising an
exception if they aren’t.  Be judicious in checking for ABCs and only do
it where it’s absolutely necessary.

You can write your own ABCs by using ‘abc.ABCMeta’ as the metaclass in a
class definition:

     from abc import ABCMeta, abstractmethod

     class Drawable():
         __metaclass__ = ABCMeta

         @abstractmethod
         def draw(self, x, y, scale=1.0):
             pass

         def draw_doubled(self, x, y):
             self.draw(x, y, scale=2.0)


     class Square(Drawable):
         def draw(self, x, y, scale):
             ...

In the ‘Drawable’ ABC above, the ‘draw_doubled()’ method renders the
object at twice its size and can be implemented in terms of other
methods described in ‘Drawable’.  Classes implementing this ABC
therefore don’t need to provide their own implementation of
‘draw_doubled()’, though they can do so.  An implementation of ‘draw()’
is necessary, though; the ABC can’t provide a useful generic
implementation.

You can apply the ‘@abstractmethod’ decorator to methods such as
‘draw()’ that must be implemented; Python will then raise an exception
for classes that don’t define the method.  Note that the exception is
only raised when you actually try to create an instance of a subclass
lacking the method:

     >>> class Circle(Drawable):
     ...     pass
     ...
     >>> c = Circle()
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: Can't instantiate abstract class Circle with abstract methods draw
     >>>

Abstract data attributes can be declared using the ‘@abstractproperty’
decorator:

     from abc import abstractproperty
     ...

     @abstractproperty
     def readonly(self):
        return self._x

Subclasses must then define a ‘readonly()’ property.

See also
........

PEP 3119(1) - Introducing Abstract Base Classes

     PEP written by Guido van Rossum and Talin.  Implemented by Guido
     van Rossum.  Backported to 2.6 by Benjamin Aranguren, with Alex
     Martelli.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3119


File: python.info,  Node: PEP 3127 Integer Literal Support and Syntax,  Next: PEP 3129 Class Decorators,  Prev: PEP 3119 Abstract Base Classes,  Up: What’s New in Python 2 6

1.12.14 PEP 3127: Integer Literal Support and Syntax
----------------------------------------------------

Python 3.0 changes the syntax for octal (base-8) integer literals,
prefixing them with “0o” or “0O” instead of a leading zero, and adds
support for binary (base-2) integer literals, signalled by a “0b” or
“0B” prefix.

Python 2.6 doesn’t drop support for a leading 0 signalling an octal
number, but it does add support for “0o” and “0b”:

     >>> 0o21, 2*8 + 1
     (17, 17)
     >>> 0b101111
     47

The *note oct(): d2d. builtin still returns numbers prefixed with a
leading zero, and a new *note bin(): d08. builtin returns the binary
representation for a number:

     >>> oct(42)
     '052'
     >>> future_builtins.oct(42)
     '0o52'
     >>> bin(173)
     '0b10101101'

The *note int(): 204. and ‘long()’ builtins will now accept the “0o” and
“0b” prefixes when base-8 or base-2 are requested, or when the `base'
argument is zero (signalling that the base used should be determined
from the string):

     >>> int ('0o52', 0)
     42
     >>> int('1101', 2)
     13
     >>> int('0b1101', 2)
     13
     >>> int('0b1101', 0)
     13

See also
........

PEP 3127(1) - Integer Literal Support and Syntax

     PEP written by Patrick Maupin; backported to 2.6 by Eric Smith.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3127


File: python.info,  Node: PEP 3129 Class Decorators,  Next: PEP 3141 A Type Hierarchy for Numbers,  Prev: PEP 3127 Integer Literal Support and Syntax,  Up: What’s New in Python 2 6

1.12.15 PEP 3129: Class Decorators
----------------------------------

Decorators have been extended from functions to classes.  It’s now legal
to write:

     @foo
     @bar
     class A:
       pass

This is equivalent to:

     class A:
       pass

     A = foo(bar(A))

See also
........

PEP 3129(1) - Class Decorators

     PEP written by Collin Winter.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3129


File: python.info,  Node: PEP 3141 A Type Hierarchy for Numbers,  Next: Other Language Changes<11>,  Prev: PEP 3129 Class Decorators,  Up: What’s New in Python 2 6

1.12.16 PEP 3141: A Type Hierarchy for Numbers
----------------------------------------------

Python 3.0 adds several abstract base classes for numeric types inspired
by Scheme’s numeric tower.  These classes were backported to 2.6 as the
*note numbers: c1. module.

The most general ABC is ‘Number’.  It defines no operations at all, and
only exists to allow checking if an object is a number by doing
‘isinstance(obj, Number)’.

‘Complex’ is a subclass of ‘Number’.  Complex numbers can undergo the
basic operations of addition, subtraction, multiplication, division, and
exponentiation, and you can retrieve the real and imaginary parts and
obtain a number’s conjugate.  Python’s built-in complex type is an
implementation of ‘Complex’.

‘Real’ further derives from ‘Complex’, and adds operations that only
work on real numbers: ‘floor()’, ‘trunc()’, rounding, taking the
remainder mod N, floor division, and comparisons.

‘Rational’ numbers derive from ‘Real’, have ‘numerator’ and
‘denominator’ properties, and can be converted to floats.  Python 2.6
adds a simple rational-number class, ‘Fraction’, in the *note fractions:
81. module.  (It’s called ‘Fraction’ instead of ‘Rational’ to avoid a
name clash with *note numbers.Rational: d20.)

‘Integral’ numbers derive from ‘Rational’, and can be shifted left and
right with ‘<<’ and ‘>>’, combined using bitwise operations such as ‘&’
and ‘|’, and can be used as array indexes and slice boundaries.

In Python 3.0, the PEP slightly redefines the existing builtins *note
round(): d35, *note math.floor(): df2, *note math.ceil(): df3, and adds
a new one, *note math.trunc(): df4, that’s been backported to Python
2.6.  *note math.trunc(): df4. rounds toward zero, returning the closest
‘Integral’ that’s between the function’s argument and zero.

See also
........

PEP 3141(1) - A Type Hierarchy for Numbers

     PEP written by Jeffrey Yasskin.

Scheme’s numerical tower(2), from the Guile manual.

Scheme’s number datatypes(3) from the R5RS Scheme specification.

* Menu:

* The fractions Module::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3141

   (2) 
https://www.gnu.org/software/guile/manual/html_node/Numerical-Tower.html#Numerical-Tower

   (3) 
http://schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-9.html#%_sec_6.2


File: python.info,  Node: The fractions Module,  Up: PEP 3141 A Type Hierarchy for Numbers

1.12.16.1 The ‘fractions’ Module
................................

To fill out the hierarchy of numeric types, the *note fractions: 81.
module provides a rational-number class.  Rational numbers store their
values as a numerator and denominator forming a fraction, and can
exactly represent numbers such as ‘2/3’ that floating-point numbers can
only approximate.

The ‘Fraction’ constructor takes two ‘Integral’ values that will be the
numerator and denominator of the resulting fraction.

     >>> from fractions import Fraction
     >>> a = Fraction(2, 3)
     >>> b = Fraction(2, 5)
     >>> float(a), float(b)
     (0.66666666666666663, 0.40000000000000002)
     >>> a+b
     Fraction(16, 15)
     >>> a/b
     Fraction(5, 3)

For converting floating-point numbers to rationals, the float type now
has an ‘as_integer_ratio()’ method that returns the numerator and
denominator for a fraction that evaluates to the same floating-point
value:

     >>> (2.5) .as_integer_ratio()
     (5, 2)
     >>> (3.1415) .as_integer_ratio()
     (7074029114692207L, 2251799813685248L)
     >>> (1./3) .as_integer_ratio()
     (6004799503160661L, 18014398509481984L)

Note that values that can only be approximated by floating-point
numbers, such as 1./3, are not simplified to the number being
approximated; the fraction attempts to match the floating-point value
`exactly'.

The *note fractions: 81. module is based upon an implementation by
Sjoerd Mullender that was in Python’s ‘Demo/classes/’ directory for a
long time.  This implementation was significantly updated by Jeffrey
Yasskin.


File: python.info,  Node: Other Language Changes<11>,  Next: New and Improved Modules<2>,  Prev: PEP 3141 A Type Hierarchy for Numbers,  Up: What’s New in Python 2 6

1.12.17 Other Language Changes
------------------------------

Some smaller changes made to the core Python language are:

   * Directories and zip archives containing a ‘__main__.py’ file can
     now be executed directly by passing their name to the interpreter.
     The directory or zip archive is automatically inserted as the first
     entry in sys.path.  (Suggestion and initial patch by Andy Chu,
     subsequently revised by Phillip J. Eby and Nick Coghlan;
     bpo-1739468(1).)

   * The *note hasattr(): 54a. function was catching and ignoring all
     errors, under the assumption that they meant a *note __getattr__():
     42a. method was failing somehow and the return value of *note
     hasattr(): 54a. would therefore be ‘False’.  This logic shouldn’t
     be applied to *note KeyboardInterrupt: 2cc. and *note SystemExit:
     6f3, however; Python 2.6 will no longer discard such exceptions
     when *note hasattr(): 54a. encounters them.  (Fixed by Benjamin
     Peterson; bpo-2196(2).)

   * When calling a function using the ‘**’ syntax to provide keyword
     arguments, you are no longer required to use a Python dictionary;
     any mapping will now work:

          >>> def f(**kw):
          ...    print sorted(kw)
          ...
          >>> ud=UserDict.UserDict()
          >>> ud['a'] = 1
          >>> ud['b'] = 'string'
          >>> f(**ud)
          ['a', 'b']

     (Contributed by Alexander Belopolsky; bpo-1686487(3).)

     It’s also become legal to provide keyword arguments after a ‘*args’
     argument to a function call.

          >>> def f(*args, **kw):
          ...     print args, kw
          ...
          >>> f(1,2,3, *(4,5,6), keyword=13)
          (1, 2, 3, 4, 5, 6) {'keyword': 13}

     Previously this would have been a syntax error.  (Contributed by
     Amaury Forgeot d’Arc; bpo-3473(4).)

   * A new builtin, ‘next(iterator, [default])’ returns the next item
     from the specified iterator.  If the `default' argument is
     supplied, it will be returned if `iterator' has been exhausted;
     otherwise, the *note StopIteration: 582. exception will be raised.
     (Backported in bpo-2719(5).)

   * Tuples now have ‘index()’ and ‘count()’ methods matching the list
     type’s ‘index()’ and ‘count()’ methods:

          >>> t = (0,1,2,3,4,0,1,2)
          >>> t.index(3)
          3
          >>> t.count(0)
          2

     (Contributed by Raymond Hettinger)

   * The built-in types now have improved support for extended slicing
     syntax, accepting various combinations of ‘(start, stop, step)’.
     Previously, the support was partial and certain corner cases
     wouldn’t work.  (Implemented by Thomas Wouters.)

   * Properties now have three attributes, ‘getter’, ‘setter’ and
     ‘deleter’, that are decorators providing useful shortcuts for
     adding a getter, setter or deleter function to an existing
     property.  You would use them like this:

          class C(object):
              @property
              def x(self):
                  return self._x

              @x.setter
              def x(self, value):
                  self._x = value

              @x.deleter
              def x(self):
                  del self._x

          class D(C):
              @C.x.getter
              def x(self):
                  return self._x * 2

              @x.setter
              def x(self, value):
                  self._x = value / 2

   * Several methods of the built-in set types now accept multiple
     iterables: ‘intersection()’, ‘intersection_update()’, ‘union()’,
     ‘update()’, ‘difference()’ and ‘difference_update()’.

          >>> s=set('1234567890')
          >>> s.intersection('abc123', 'cdf246')  # Intersection between all inputs
          set(['2'])
          >>> s.difference('246', '789')
          set(['1', '0', '3', '5'])

     (Contributed by Raymond Hettinger.)

   * Many floating-point features were added.  The *note float(): 1fd.
     function will now turn the string ‘nan’ into an IEEE 754 Not A
     Number value, and ‘+inf’ and ‘-inf’ into positive or negative
     infinity.  This works on any platform with IEEE 754 semantics.
     (Contributed by Christian Heimes; bpo-1635(6).)

     Other functions in the *note math: b1. module, ‘isinf()’ and
     ‘isnan()’, return true if their floating-point argument is infinite
     or Not A Number.  (bpo-1640(7))

     Conversion functions were added to convert floating-point numbers
     into hexadecimal strings (bpo-3008(8)).  These functions convert
     floats to and from a string representation without introducing
     rounding errors from the conversion between decimal and binary.
     Floats have a *note hex(): d2e. method that returns a string
     representation, and the ‘float.fromhex()’ method converts a string
     back into a number:

          >>> a = 3.75
          >>> a.hex()
          '0x1.e000000000000p+1'
          >>> float.fromhex('0x1.e000000000000p+1')
          3.75
          >>> b=1./3
          >>> b.hex()
          '0x1.5555555555555p-2'

   * A numerical nicety: when creating a complex number from two floats
     on systems that support signed zeros (-0 and +0), the *note
     complex(): 2c1. constructor will now preserve the sign of the zero.
     (Fixed by Mark T. Dickinson; bpo-1507(9).)

   * Classes that inherit a *note __hash__(): 44c. method from a parent
     class can set ‘__hash__ = None’ to indicate that the class isn’t
     hashable.  This will make ‘hash(obj)’ raise a *note TypeError: 1fe.
     and the class will not be indicated as implementing the ‘Hashable’
     ABC.

     You should do this when you’ve defined a ‘__cmp__()’ or *note
     __eq__(): 44b. method that compares objects by their value rather
     than by identity.  All objects have a default hash method that uses
     ‘id(obj)’ as the hash value.  There’s no tidy way to remove the
     *note __hash__(): 44c. method inherited from a parent class, so
     assigning ‘None’ was implemented as an override.  At the C level,
     extensions can set ‘tp_hash’ to *note
     PyObject_HashNotImplemented(): df7.  (Fixed by Nick Coghlan and
     Amaury Forgeot d’Arc; bpo-2235(10).)

   * The *note GeneratorExit: df8. exception now subclasses *note
     BaseException: 2db. instead of *note Exception: 2dc.  This means
     that an exception handler that does ‘except Exception:’ will not
     inadvertently catch *note GeneratorExit: df8.  (Contributed by Chad
     Austin; bpo-1537(11).)

   * Generator objects now have a ‘gi_code’ attribute that refers to the
     original code object backing the generator.  (Contributed by Collin
     Winter; bpo-1473257(12).)

   * The *note compile(): 2e7. built-in function now accepts keyword
     arguments as well as positional parameters.  (Contributed by Thomas
     Wouters; bpo-1444529(13).)

   * The *note complex(): 2c1. constructor now accepts strings
     containing parenthesized complex numbers, meaning that
     ‘complex(repr(cplx))’ will now round-trip values.  For example,
     ‘complex('(3+4j)')’ now returns the value (3+4j).
     (bpo-1491866(14))

   * The string ‘translate()’ method now accepts ‘None’ as the
     translation table parameter, which is treated as the identity
     transformation.  This makes it easier to carry out operations that
     only delete characters.  (Contributed by Bengt Richter and
     implemented by Raymond Hettinger; bpo-1193128(15).)

   * The built-in *note dir(): df9. function now checks for a *note
     __dir__(): 42b. method on the objects it receives.  This method
     must return a list of strings containing the names of valid
     attributes for the object, and lets the object control the value
     that *note dir(): df9. produces.  Objects that have *note
     __getattr__(): 42a. or *note __getattribute__(): 54c. methods can
     use this to advertise pseudo-attributes they will honor.
     (bpo-1591665(16))

   * Instance method objects have new attributes for the object and
     function comprising the method; the new synonym for ‘im_self’ is
     ‘__self__’, and ‘im_func’ is also available as ‘__func__’.  The old
     names are still supported in Python 2.6, but are gone in 3.0.

   * An obscure change: when you use the *note locals(): 557. function
     inside a *note class: d32. statement, the resulting dictionary no
     longer returns free variables.  (Free variables, in this case, are
     variables referenced in the ‘class’ statement that aren’t
     attributes of the class.)

* Menu:

* Optimizations: Optimizations<10>.
* Interpreter Changes: Interpreter Changes<2>.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1739468

   (2) https://bugs.python.org/issue2196

   (3) https://bugs.python.org/issue1686487

   (4) https://bugs.python.org/issue3473

   (5) https://bugs.python.org/issue2719

   (6) https://bugs.python.org/issue1635

   (7) https://bugs.python.org/issue1640

   (8) https://bugs.python.org/issue3008

   (9) https://bugs.python.org/issue1507

   (10) https://bugs.python.org/issue2235

   (11) https://bugs.python.org/issue1537

   (12) https://bugs.python.org/issue1473257

   (13) https://bugs.python.org/issue1444529

   (14) https://bugs.python.org/issue1491866

   (15) https://bugs.python.org/issue1193128

   (16) https://bugs.python.org/issue1591665


File: python.info,  Node: Optimizations<10>,  Next: Interpreter Changes<2>,  Up: Other Language Changes<11>

1.12.17.1 Optimizations
.......................

   * The *note warnings: 12f. module has been rewritten in C. This makes
     it possible to invoke warnings from the parser, and may also make
     the interpreter’s startup faster.  (Contributed by Neal Norwitz and
     Brett Cannon; bpo-1631171(1).)

   * Type objects now have a cache of methods that can reduce the work
     required to find the correct method implementation for a particular
     class; once cached, the interpreter doesn’t need to traverse base
     classes to figure out the right method to call.  The cache is
     cleared if a base class or the class itself is modified, so the
     cache should remain correct even in the face of Python’s dynamic
     nature.  (Original optimization implemented by Armin Rigo, updated
     for Python 2.6 by Kevin Jacobs; bpo-1700288(2).)

     By default, this change is only applied to types that are included
     with the Python core.  Extension modules may not necessarily be
     compatible with this cache, so they must explicitly add
     ‘Py_TPFLAGS_HAVE_VERSION_TAG’ to the module’s ‘tp_flags’ field to
     enable the method cache.  (To be compatible with the method cache,
     the extension module’s code must not directly access and modify the
     ‘tp_dict’ member of any of the types it implements.  Most modules
     don’t do this, but it’s impossible for the Python interpreter to
     determine that.  See bpo-1878(3) for some discussion.)

   * Function calls that use keyword arguments are significantly faster
     by doing a quick pointer comparison, usually saving the time of a
     full string comparison.  (Contributed by Raymond Hettinger, after
     an initial implementation by Antoine Pitrou; bpo-1819(4).)

   * All of the functions in the *note struct: f8. module have been
     rewritten in C, thanks to work at the Need For Speed sprint.
     (Contributed by Raymond Hettinger.)

   * Some of the standard built-in types now set a bit in their type
     objects.  This speeds up checking whether an object is a subclass
     of one of these types.  (Contributed by Neal Norwitz.)

   * Unicode strings now use faster code for detecting whitespace and
     line breaks; this speeds up the ‘split()’ method by about 25% and
     ‘splitlines()’ by 35%.  (Contributed by Antoine Pitrou.)  Memory
     usage is reduced by using pymalloc for the Unicode string’s data.

   * The ‘with’ statement now stores the *note __exit__(): d5e. method
     on the stack, producing a small speedup.  (Implemented by Jeffrey
     Yasskin.)

   * To reduce memory usage, the garbage collector will now clear
     internal free lists when garbage-collecting the highest generation
     of objects.  This may return memory to the operating system sooner.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1631171

   (2) https://bugs.python.org/issue1700288

   (3) https://bugs.python.org/issue1878

   (4) https://bugs.python.org/issue1819


File: python.info,  Node: Interpreter Changes<2>,  Prev: Optimizations<10>,  Up: Other Language Changes<11>

1.12.17.2 Interpreter Changes
.............................

Two command-line options have been reserved for use by other Python
implementations.  The *note -J: dfd. switch has been reserved for use by
Jython for Jython-specific options, such as switches that are passed to
the underlying JVM. *note -X: 290. has been reserved for options
specific to a particular implementation of Python such as CPython,
Jython, or IronPython.  If either option is used with Python 2.6, the
interpreter will report that the option isn’t currently used.

Python can now be prevented from writing ‘.pyc’ or ‘.pyo’ files by
supplying the *note -B: dfe. switch to the Python interpreter, or by
setting the *note PYTHONDONTWRITEBYTECODE: dff. environment variable
before running the interpreter.  This setting is available to Python
programs as the ‘sys.dont_write_bytecode’ variable, and Python code can
change the value to modify the interpreter’s behaviour.  (Contributed by
Neal Norwitz and Georg Brandl.)

The encoding used for standard input, output, and standard error can be
specified by setting the *note PYTHONIOENCODING: a14. environment
variable before running the interpreter.  The value should be a string
in the form ‘<encoding>’ or ‘<encoding>:<errorhandler>’.  The `encoding'
part specifies the encoding’s name, e.g.  ‘utf-8’ or ‘latin-1’; the
optional `errorhandler' part specifies what to do with characters that
can’t be handled by the encoding, and should be one of “error”,
“ignore”, or “replace”.  (Contributed by Martin von Löwis.)


File: python.info,  Node: New and Improved Modules<2>,  Next: Deprecations and Removals,  Prev: Other Language Changes<11>,  Up: What’s New in Python 2 6

1.12.18 New and Improved Modules
--------------------------------

As in every release, Python’s standard library received a number of
enhancements and bug fixes.  Here’s a partial list of the most notable
changes, sorted alphabetically by module name.  Consult the ‘Misc/NEWS’
file in the source tree for a more complete list of changes, or look
through the Subversion logs for all the details.

   * The *note asyncore: a. and *note asynchat: 8. modules are being
     actively maintained again, and a number of patches and bugfixes
     were applied.  (Maintained by Josiah Carlson; see bpo-1736190(1)
     for one patch.)

   * The ‘bsddb’ module also has a new maintainer, Jesús Cea Avión, and
     the package is now available as a standalone package.  The web page
     for the package is www.jcea.es/programacion/pybsddb.htm(2).  The
     plan is to remove the package from the standard library in Python
     3.0, because its pace of releases is much more frequent than
     Python’s.

     The ‘bsddb.dbshelve’ module now uses the highest pickling protocol
     available, instead of restricting itself to protocol 1.
     (Contributed by W. Barnes.)

   * The *note cgi: 15. module will now read variables from the query
     string of an HTTP POST request.  This makes it possible to use form
     actions with URLs that include query strings such as
     “/cgi-bin/add.py?category=1”.  (Contributed by Alexandre Fiori and
     Nubis; bpo-1817(3).)

     The ‘parse_qs()’ and ‘parse_qsl()’ functions have been relocated
     from the *note cgi: 15. module to the ‘urlparse’ module.  The
     versions still available in the *note cgi: 15. module will trigger
     *note PendingDeprecationWarning: 15c. messages in 2.6
     (bpo-600362(4)).

   * The *note cmath: 18. module underwent extensive revision,
     contributed by Mark Dickinson and Christian Heimes.  Five new
     functions were added:

        * ‘polar()’ converts a complex number to polar form, returning
          the modulus and argument of the complex number.

        * ‘rect()’ does the opposite, turning a modulus, argument pair
          back into the corresponding complex number.

        * ‘phase()’ returns the argument (also called the angle) of a
          complex number.

        * ‘isnan()’ returns True if either the real or imaginary part of
          its argument is a NaN.

        * ‘isinf()’ returns True if either the real or imaginary part of
          its argument is infinite.

     The revisions also improved the numerical soundness of the *note
     cmath: 18. module.  For all functions, the real and imaginary parts
     of the results are accurate to within a few units of least
     precision (ulps) whenever possible.  See bpo-1381(5) for the
     details.  The branch cuts for ‘asinh()’, ‘atanh()’: and ‘atan()’
     have also been corrected.

     The tests for the module have been greatly expanded; nearly 2000
     new test cases exercise the algebraic functions.

     On IEEE 754 platforms, the *note cmath: 18. module now handles IEEE
     754 special values and floating-point exceptions in a manner
     consistent with Annex ‘G’ of the C99 standard.

   * A new data type in the *note collections: 1d. module:
     ‘namedtuple(typename, fieldnames)’ is a factory function that
     creates subclasses of the standard tuple whose fields are
     accessible by name as well as index.  For example:

          >>> var_type = collections.namedtuple('variable',
          ...             'id name type size')
          >>> # Names are separated by spaces or commas.
          >>> # 'id, name, type, size' would also work.
          >>> var_type._fields
          ('id', 'name', 'type', 'size')

          >>> var = var_type(1, 'frequency', 'int', 4)
          >>> print var[0], var.id    # Equivalent
          1 1
          >>> print var[2], var.type  # Equivalent
          int int
          >>> var._asdict()
          {'size': 4, 'type': 'int', 'id': 1, 'name': 'frequency'}
          >>> v2 = var._replace(name='amplitude')
          >>> v2
          variable(id=1, name='amplitude', type='int', size=4)

     Several places in the standard library that returned tuples have
     been modified to return ‘namedtuple’ instances.  For example, the
     ‘Decimal.as_tuple()’ method now returns a named tuple with ‘sign’,
     ‘digits’, and ‘exponent’ fields.

     (Contributed by Raymond Hettinger.)

   * Another change to the *note collections: 1d. module is that the
     ‘deque’ type now supports an optional `maxlen' parameter; if
     supplied, the deque’s size will be restricted to no more than
     `maxlen' items.  Adding more items to a full deque causes old items
     to be discarded.

          >>> from collections import deque
          >>> dq=deque(maxlen=3)
          >>> dq
          deque([], maxlen=3)
          >>> dq.append(1); dq.append(2); dq.append(3)
          >>> dq
          deque([1, 2, 3], maxlen=3)
          >>> dq.append(4)
          >>> dq
          deque([2, 3, 4], maxlen=3)

     (Contributed by Raymond Hettinger.)

   * The ‘Cookie’ module’s ‘Morsel’ objects now support an ‘httponly’
     attribute.  In some browsers.  cookies with this attribute set
     cannot be accessed or manipulated by JavaScript code.  (Contributed
     by Arvin Schnell; bpo-1638033(6).)

   * A new window method in the *note curses: 2b. module, ‘chgat()’,
     changes the display attributes for a certain number of characters
     on a single line.  (Contributed by Fabian Kreutz.)

          # Boldface text starting at y=0,x=21
          # and affecting the rest of the line.
          stdscr.chgat(0, 21, curses.A_BOLD)

     The ‘Textbox’ class in the *note curses.textpad: 2e. module now
     supports editing in insert mode as well as overwrite mode.  Insert
     mode is enabled by supplying a true value for the `insert_mode'
     parameter when creating the ‘Textbox’ instance.

   * The *note datetime: 30. module’s ‘strftime()’ methods now support a
     ‘%f’ format code that expands to the number of microseconds in the
     object, zero-padded on the left to six places.  (Contributed by
     Skip Montanaro; bpo-1158(7).)

   * The *note decimal: 35. module was updated to version 1.66 of the
     General Decimal Specification(8).  New features include some
     methods for some basic mathematical functions such as ‘exp()’ and
     ‘log10()’:

          >>> Decimal(1).exp()
          Decimal("2.718281828459045235360287471")
          >>> Decimal("2.7182818").ln()
          Decimal("0.9999999895305022877376682436")
          >>> Decimal(1000).log10()
          Decimal("3")

     The ‘as_tuple()’ method of ‘Decimal’ objects now returns a named
     tuple with ‘sign’, ‘digits’, and ‘exponent’ fields.

     (Implemented by Facundo Batista and Mark Dickinson.  Named tuple
     support added by Raymond Hettinger.)

   * The *note difflib: 36. module’s ‘SequenceMatcher’ class now returns
     named tuples representing matches, with ‘a’, ‘b’, and ‘size’
     attributes.  (Contributed by Raymond Hettinger.)

   * An optional ‘timeout’ parameter, specifying a timeout measured in
     seconds, was added to the *note ftplib.FTP: 1a6. class constructor
     as well as the ‘connect()’ method.  (Added by Facundo Batista.)
     Also, the ‘FTP’ class’s ‘storbinary()’ and ‘storlines()’ now take
     an optional `callback' parameter that will be called with each
     block of data after the data has been sent.  (Contributed by Phil
     Schwartz; bpo-1221598(9).)

   * The ‘reduce()’ built-in function is also available in the *note
     functools: 83. module.  In Python 3.0, the builtin has been dropped
     and ‘reduce()’ is only available from *note functools: 83.;
     currently there are no plans to drop the builtin in the 2.x series.
     (Patched by Christian Heimes; bpo-1739906(10).)

   * When possible, the *note getpass: 86. module will now use
     ‘/dev/tty’ to print a prompt message and read the password, falling
     back to standard error and standard input.  If the password may be
     echoed to the terminal, a warning is printed before the prompt is
     displayed.  (Contributed by Gregory P. Smith.)

   * The *note glob.glob(): 6bd. function can now return Unicode
     filenames if a Unicode path was used and Unicode filenames are
     matched within the directory.  (bpo-1001604(11))

   * A new function in the *note heapq: 8d. module, ‘merge(iter1, iter2,
     ...)’, takes any number of iterables returning data in sorted
     order, and returns a new generator that returns the contents of all
     the iterators, also in sorted order.  For example:

          >>> list(heapq.merge([1, 3, 5, 9], [2, 8, 16]))
          [1, 2, 3, 5, 8, 9, 16]

     Another new function, ‘heappushpop(heap, item)’, pushes `item' onto
     `heap', then pops off and returns the smallest item.  This is more
     efficient than making a call to ‘heappush()’ and then ‘heappop()’.

     *note heapq: 8d. is now implemented to only use less-than
     comparison, instead of the less-than-or-equal comparison it
     previously used.  This makes *note heapq: 8d.’s usage of a type
     match the *note list.sort(): 548. method.  (Contributed by Raymond
     Hettinger.)

   * An optional ‘timeout’ parameter, specifying a timeout measured in
     seconds, was added to the ‘httplib.HTTPConnection’ and
     ‘HTTPSConnection’ class constructors.  (Added by Facundo Batista.)

   * Most of the *note inspect: a0. module’s functions, such as
     ‘getmoduleinfo()’ and ‘getargs()’, now return named tuples.  In
     addition to behaving like tuples, the elements of the return value
     can also be accessed as attributes.  (Contributed by Raymond
     Hettinger.)

     Some new functions in the module include ‘isgenerator()’,
     ‘isgeneratorfunction()’, and ‘isabstract()’.

   * The *note itertools: a3. module gained several new functions.

     ‘izip_longest(iter1, iter2, ...[, fillvalue])’ makes tuples from
     each of the elements; if some of the iterables are shorter than
     others, the missing values are set to `fillvalue'.  For example:

          >>> tuple(itertools.izip_longest([1,2,3], [1,2,3,4,5]))
          ((1, 1), (2, 2), (3, 3), (None, 4), (None, 5))

     ‘product(iter1, iter2, ..., [repeat=N])’ returns the Cartesian
     product of the supplied iterables, a set of tuples containing every
     possible combination of the elements returned from each iterable.

          >>> list(itertools.product([1,2,3], [4,5,6]))
          [(1, 4), (1, 5), (1, 6),
           (2, 4), (2, 5), (2, 6),
           (3, 4), (3, 5), (3, 6)]

     The optional `repeat' keyword argument is used for taking the
     product of an iterable or a set of iterables with themselves,
     repeated `N' times.  With a single iterable argument, `N'-tuples
     are returned:

          >>> list(itertools.product([1,2], repeat=3))
          [(1, 1, 1), (1, 1, 2), (1, 2, 1), (1, 2, 2),
           (2, 1, 1), (2, 1, 2), (2, 2, 1), (2, 2, 2)]

     With two iterables, `2N'-tuples are returned.

          >>> list(itertools.product([1,2], [3,4], repeat=2))
          [(1, 3, 1, 3), (1, 3, 1, 4), (1, 3, 2, 3), (1, 3, 2, 4),
           (1, 4, 1, 3), (1, 4, 1, 4), (1, 4, 2, 3), (1, 4, 2, 4),
           (2, 3, 1, 3), (2, 3, 1, 4), (2, 3, 2, 3), (2, 3, 2, 4),
           (2, 4, 1, 3), (2, 4, 1, 4), (2, 4, 2, 3), (2, 4, 2, 4)]

     ‘combinations(iterable, r)’ returns sub-sequences of length `r'
     from the elements of `iterable'.

          >>> list(itertools.combinations('123', 2))
          [('1', '2'), ('1', '3'), ('2', '3')]
          >>> list(itertools.combinations('123', 3))
          [('1', '2', '3')]
          >>> list(itertools.combinations('1234', 3))
          [('1', '2', '3'), ('1', '2', '4'),
           ('1', '3', '4'), ('2', '3', '4')]

     ‘permutations(iter[, r])’ returns all the permutations of length
     `r' of the iterable’s elements.  If `r' is not specified, it will
     default to the number of elements produced by the iterable.

          >>> list(itertools.permutations([1,2,3,4], 2))
          [(1, 2), (1, 3), (1, 4),
           (2, 1), (2, 3), (2, 4),
           (3, 1), (3, 2), (3, 4),
           (4, 1), (4, 2), (4, 3)]

     ‘itertools.chain(*iterables)’ is an existing function in *note
     itertools: a3. that gained a new constructor in Python 2.6.
     ‘itertools.chain.from_iterable(iterable)’ takes a single iterable
     that should return other iterables.  ‘chain()’ will then return all
     the elements of the first iterable, then all the elements of the
     second, and so on.

          >>> list(itertools.chain.from_iterable([[1,2,3], [4,5,6]]))
          [1, 2, 3, 4, 5, 6]

     (All contributed by Raymond Hettinger.)

   * The *note logging: aa. module’s ‘FileHandler’ class and its
     subclasses ‘WatchedFileHandler’, ‘RotatingFileHandler’, and
     ‘TimedRotatingFileHandler’ now have an optional `delay' parameter
     to their constructors.  If `delay' is true, opening of the log file
     is deferred until the first ‘emit()’ call is made.  (Contributed by
     Vinay Sajip.)

     ‘TimedRotatingFileHandler’ also has a `utc' constructor parameter.
     If the argument is true, UTC time will be used in determining when
     midnight occurs and in generating filenames; otherwise local time
     will be used.

   * Several new functions were added to the *note math: b1. module:

        * *note isinf(): e01. and *note isnan(): e02. determine whether
          a given float is a (positive or negative) infinity or a NaN
          (Not a Number), respectively.

        * *note copysign(): e03. copies the sign bit of an IEEE 754
          number, returning the absolute value of `x' combined with the
          sign bit of `y'.  For example, ‘math.copysign(1, -0.0)’
          returns -1.0.  (Contributed by Christian Heimes.)

        * *note factorial(): 1fc. computes the factorial of a number.
          (Contributed by Raymond Hettinger; bpo-2138(12).)

        * *note fsum(): e04. adds up the stream of numbers from an
          iterable, and is careful to avoid loss of precision through
          using partial sums.  (Contributed by Jean Brouwers, Raymond
          Hettinger, and Mark Dickinson; bpo-2819(13).)

        * *note acosh(): e05, *note asinh(): e06. and *note atanh():
          e07. compute the inverse hyperbolic functions.

        * *note log1p(): e08. returns the natural logarithm of `1+x'
          (base `e').

        * ‘trunc()’ rounds a number toward zero, returning the closest
          ‘Integral’ that’s between the function’s argument and zero.
          Added as part of the backport of *note PEP 3141’s type
          hierarchy for numbers: d1f.

   * The *note math: b1. module has been improved to give more
     consistent behaviour across platforms, especially with respect to
     handling of floating-point exceptions and IEEE 754 special values.

     Whenever possible, the module follows the recommendations of the
     C99 standard about 754’s special values.  For example, ‘sqrt(-1.)’
     should now give a *note ValueError: 16d. across almost all
     platforms, while ‘sqrt(float('NaN'))’ should return a NaN on all
     IEEE 754 platforms.  Where Annex ‘F’ of the C99 standard recommends
     signaling ‘divide-by-zero’ or ‘invalid’, Python will raise *note
     ValueError: 16d.  Where Annex ‘F’ of the C99 standard recommends
     signaling ‘overflow’, Python will raise *note OverflowError: a41.
     (See bpo-711019(14) and bpo-1640(15).)

     (Contributed by Christian Heimes and Mark Dickinson.)

   * *note mmap: 31c. objects now have a ‘rfind()’ method that searches
     for a substring beginning at the end of the string and searching
     backwards.  The ‘find()’ method also gained an `end' parameter
     giving an index at which to stop searching.  (Contributed by John
     Lenton.)

   * The *note operator: c2. module gained a ‘methodcaller()’ function
     that takes a name and an optional set of arguments, returning a
     callable that will call the named function on any arguments passed
     to it.  For example:

          >>> # Equivalent to lambda s: s.replace('old', 'new')
          >>> replacer = operator.methodcaller('replace', 'old', 'new')
          >>> replacer('old wine in old bottles')
          'new wine in new bottles'

     (Contributed by Georg Brandl, after a suggestion by Gregory
     Petrosyan.)

     The ‘attrgetter()’ function now accepts dotted names and performs
     the corresponding attribute lookups:

          >>> inst_name = operator.attrgetter(
          ...        '__class__.__name__')
          >>> inst_name('')
          'str'
          >>> inst_name(help)
          '_Helper'

     (Contributed by Georg Brandl, after a suggestion by Barry Warsaw.)

   * The *note os: c4. module now wraps several new system calls.
     ‘fchmod(fd, mode)’ and ‘fchown(fd, uid, gid)’ change the mode and
     ownership of an opened file, and ‘lchmod(path, mode)’ changes the
     mode of a symlink.  (Contributed by Georg Brandl and Christian
     Heimes.)

     ‘chflags()’ and ‘lchflags()’ are wrappers for the corresponding
     system calls (where they’re available), changing the flags set on a
     file.  Constants for the flag values are defined in the *note stat:
     f4. module; some possible values include ‘UF_IMMUTABLE’ to signal
     the file may not be changed and ‘UF_APPEND’ to indicate that data
     can only be appended to the file.  (Contributed by M. Levinson.)

     ‘os.closerange(low, high)’ efficiently closes all file descriptors
     from `low' to `high', ignoring any errors and not including `high'
     itself.  This function is now used by the *note subprocess: f9.
     module to make starting processes faster.  (Contributed by Georg
     Brandl; bpo-1663329(16).)

   * The ‘os.environ’ object’s ‘clear()’ method will now unset the
     environment variables using *note os.unsetenv(): 1cc. in addition
     to clearing the object’s keys.  (Contributed by Martin Horcicka;
     bpo-1181(17).)

   * The *note os.walk(): 747. function now has a ‘followlinks’
     parameter.  If set to True, it will follow symlinks pointing to
     directories and visit the directory’s contents.  For backward
     compatibility, the parameter’s default value is false.  Note that
     the function can fall into an infinite recursion if there’s a
     symlink that points to a parent directory.  (bpo-1273829(18))

   * In the *note os.path: c5. module, the ‘splitext()’ function has
     been changed to not split on leading period characters.  This
     produces better results when operating on Unix’s dot-files.  For
     example, ‘os.path.splitext('.ipython')’ now returns ‘('.ipython',
     '')’ instead of ‘('', '.ipython')’.  (bpo-1115886(19))

     A new function, ‘os.path.relpath(path, start='.')’, returns a
     relative path from the ‘start’ path, if it’s supplied, or from the
     current working directory to the destination ‘path’.  (Contributed
     by Richard Barran; bpo-1339796(20).)

     On Windows, *note os.path.expandvars(): e09. will now expand
     environment variables given in the form “%var%”, and “~user” will
     be expanded into the user’s home directory path.  (Contributed by
     Josiah Carlson; bpo-957650(21).)

   * The Python debugger provided by the *note pdb: c9. module gained a
     new command: “run” restarts the Python program being debugged and
     can optionally take new command-line arguments for the program.
     (Contributed by Rocky Bernstein; bpo-1393667(22).)

   * The *note pdb.post_mortem(): e0a. function, used to begin debugging
     a traceback, will now use the traceback returned by *note
     sys.exc_info(): d27. if no traceback is supplied.  (Contributed by
     Facundo Batista; bpo-1106316(23).)

   * The *note pickletools: cb. module now has an ‘optimize()’ function
     that takes a string containing a pickle and removes some unused
     opcodes, returning a shorter pickle that contains the same data
     structure.  (Contributed by Raymond Hettinger.)

   * A ‘get_data()’ function was added to the *note pkgutil: cd. module
     that returns the contents of resource files included with an
     installed Python package.  For example:

          >>> import pkgutil
          >>> print pkgutil.get_data('test', 'exception_hierarchy.txt')
          BaseException
           +-- SystemExit
           +-- KeyboardInterrupt
           +-- GeneratorExit
           +-- Exception
                +-- StopIteration
                +-- StandardError
           ...

     (Contributed by Paul Moore; bpo-2439(24).)

   * The ‘pyexpat’ module’s ‘Parser’ objects now allow setting their
     ‘buffer_size’ attribute to change the size of the buffer used to
     hold character data.  (Contributed by Achim Gaedke; bpo-1137(25).)

   * The ‘Queue’ module now provides queue variants that retrieve
     entries in different orders.  The ‘PriorityQueue’ class stores
     queued items in a heap and retrieves them in priority order, and
     ‘LifoQueue’ retrieves the most recently added entries first,
     meaning that it behaves like a stack.  (Contributed by Raymond
     Hettinger.)

   * The *note random: dc. module’s ‘Random’ objects can now be pickled
     on a 32-bit system and unpickled on a 64-bit system, and vice
     versa.  Unfortunately, this change also means that Python 2.6’s
     ‘Random’ objects can’t be unpickled correctly on earlier versions
     of Python.  (Contributed by Shawn Ligocki; bpo-1727780(26).)

     The new ‘triangular(low, high, mode)’ function returns random
     numbers following a triangular distribution.  The returned values
     are between `low' and `high', not including `high' itself, and with
     `mode' as the most frequently occurring value in the distribution.
     (Contributed by Wladmir van der Laan and Raymond Hettinger;
     bpo-1681432(27).)

   * Long regular expression searches carried out by the *note re: dd.
     module will check for signals being delivered, so time-consuming
     searches can now be interrupted.  (Contributed by Josh Hoyt and
     Ralf Schmitt; bpo-846388(28).)

     The regular expression module is implemented by compiling bytecodes
     for a tiny regex-specific virtual machine.  Untrusted code could
     create malicious strings of bytecode directly and cause crashes, so
     Python 2.6 includes a verifier for the regex bytecode.
     (Contributed by Guido van Rossum from work for Google App Engine;
     bpo-3487(29).)

   * The *note rlcompleter: e1. module’s ‘Completer.complete()’ method
     will now ignore exceptions triggered while evaluating a name.
     (Fixed by Lorenz Quack; bpo-2250(30).)

   * The *note sched: e3. module’s ‘scheduler’ instances now have a
     read-only *note queue: da. attribute that returns the contents of
     the scheduler’s queue, represented as a list of named tuples with
     the fields ‘(time, priority, action, argument)’.  (Contributed by
     Raymond Hettinger; bpo-1861(31).)

   * The *note select: e5. module now has wrapper functions for the
     Linux ‘epoll()’ and BSD ‘kqueue()’ system calls.  ‘modify()’ method
     was added to the existing ‘poll’ objects; ‘pollobj.modify(fd,
     eventmask)’ takes a file descriptor or file object and an event
     mask, modifying the recorded event mask for that file.
     (Contributed by Christian Heimes; bpo-1657(32).)

   * The *note shutil.copytree(): 347. function now has an optional
     `ignore' argument that takes a callable object.  This callable will
     receive each directory path and a list of the directory’s contents,
     and returns a list of names that will be ignored, not copied.

     The *note shutil: e9. module also provides an ‘ignore_patterns()’
     function for use with this new parameter.  ‘ignore_patterns()’
     takes an arbitrary number of glob-style patterns and returns a
     callable that will ignore any files and directories that match any
     of these patterns.  The following example copies a directory tree,
     but skips both ‘.svn’ directories and Emacs backup files, which
     have names ending with ‘~’:

          shutil.copytree('Doc/library', '/tmp/library',
                          ignore=shutil.ignore_patterns('*~', '.svn'))

     (Contributed by Tarek Ziadé; bpo-2663(33).)

   * Integrating signal handling with GUI handling event loops like
     those used by Tkinter or GTk+ has long been a problem; most
     software ends up polling, waking up every fraction of a second to
     check if any GUI events have occurred.  The *note signal: ea.
     module can now make this more efficient.  Calling
     ‘signal.set_wakeup_fd(fd)’ sets a file descriptor to be used; when
     a signal is received, a byte is written to that file descriptor.
     There’s also a C-level function, *note PySignal_SetWakeupFd(): e0b,
     for setting the descriptor.

     Event loops will use this by opening a pipe to create two
     descriptors, one for reading and one for writing.  The writable
     descriptor will be passed to ‘set_wakeup_fd()’, and the readable
     descriptor will be added to the list of descriptors monitored by
     the event loop via ‘select()’ or ‘poll()’.  On receiving a signal,
     a byte will be written and the main event loop will be woken up,
     avoiding the need to poll.

     (Contributed by Adam Olsen; bpo-1583(34).)

     The ‘siginterrupt()’ function is now available from Python code,
     and allows changing whether signals can interrupt system calls or
     not.  (Contributed by Ralf Schmitt.)

     The ‘setitimer()’ and ‘getitimer()’ functions have also been added
     (where they’re available).  ‘setitimer()’ allows setting interval
     timers that will cause a signal to be delivered to the process
     after a specified time, measured in wall-clock time, consumed
     process time, or combined process+system time.  (Contributed by
     Guilherme Polo; bpo-2240(35).)

   * The *note smtplib: ed. module now supports SMTP over SSL thanks to
     the addition of the ‘SMTP_SSL’ class.  This class supports an
     interface identical to the existing ‘SMTP’ class.  (Contributed by
     Monty Taylor.)  Both class constructors also have an optional
     ‘timeout’ parameter that specifies a timeout for the initial
     connection attempt, measured in seconds.  (Contributed by Facundo
     Batista.)

     An implementation of the LMTP protocol ( RFC 2033(36)) was also
     added to the module.  LMTP is used in place of SMTP when
     transferring e-mail between agents that don’t manage a mail queue.
     (LMTP implemented by Leif Hedstrom; bpo-957003(37).)

     ‘SMTP.starttls()’ now complies with RFC 3207(38) and forgets any
     knowledge obtained from the server not obtained from the TLS
     negotiation itself.  (Patch contributed by Bill Fenner;
     bpo-829951(39).)

   * The *note socket: ef. module now supports TIPC
     (‘http://tipc.sourceforge.net/’), a high-performance non-IP-based
     protocol designed for use in clustered environments.  TIPC
     addresses are 4- or 5-tuples.  (Contributed by Alberto Bertogli;
     bpo-1646(40).)

     A new function, ‘create_connection()’, takes an address and
     connects to it using an optional timeout value, returning the
     connected socket object.  This function also looks up the address’s
     type and connects to it using IPv4 or IPv6 as appropriate.
     Changing your code to use ‘create_connection()’ instead of
     ‘socket(socket.AF_INET, ...)’ may be all that’s required to make
     your code work with IPv6.

   * The base classes in the ‘SocketServer’ module now support calling a
     ‘handle_timeout()’ method after a span of inactivity specified by
     the server’s ‘timeout’ attribute.  (Contributed by Michael
     Pomraning.)  The ‘serve_forever()’ method now takes an optional
     poll interval measured in seconds, controlling how often the server
     will check for a shutdown request.  (Contributed by Pedro Werneck
     and Jeffrey Yasskin; bpo-742598(41), bpo-1193577(42).)

   * The *note sqlite3: f2. module, maintained by Gerhard Häring, has
     been updated from version 2.3.2 in Python 2.5 to version 2.4.1.

   * The *note struct: f8. module now supports the C99 ‘_Bool’ type,
     using the format character ‘'?'’.  (Contributed by David Remahl.)

   * The ‘Popen’ objects provided by the *note subprocess: f9. module
     now have ‘terminate()’, ‘kill()’, and ‘send_signal()’ methods.  On
     Windows, ‘send_signal()’ only supports the ‘SIGTERM’ signal, and
     all these methods are aliases for the Win32 API function
     ‘TerminateProcess()’.  (Contributed by Christian Heimes.)

   * A new variable in the *note sys: fd. module, ‘float_info’, is an
     object containing information derived from the ‘float.h’ file about
     the platform’s floating-point support.  Attributes of this object
     include ‘mant_dig’ (number of digits in the mantissa), ‘epsilon’
     (smallest difference between 1.0 and the next largest value
     representable), and several others.  (Contributed by Christian
     Heimes; bpo-1534(43).)

     Another new variable, ‘dont_write_bytecode’, controls whether
     Python writes any ‘.pyc’ or ‘.pyo’ files on importing a module.  If
     this variable is true, the compiled files are not written.  The
     variable is initially set on start-up by supplying the *note -B:
     dfe. switch to the Python interpreter, or by setting the *note
     PYTHONDONTWRITEBYTECODE: dff. environment variable before running
     the interpreter.  Python code can subsequently change the value of
     this variable to control whether bytecode files are written or not.
     (Contributed by Neal Norwitz and Georg Brandl.)

     Information about the command-line arguments supplied to the Python
     interpreter is available by reading attributes of a named tuple
     available as ‘sys.flags’.  For example, the ‘verbose’ attribute is
     true if Python was executed in verbose mode, ‘debug’ is true in
     debugging mode, etc.  These attributes are all read-only.
     (Contributed by Christian Heimes.)

     A new function, ‘getsizeof()’, takes a Python object and returns
     the amount of memory used by the object, measured in bytes.
     Built-in objects return correct results; third-party extensions may
     not, but can define a ‘__sizeof__()’ method to return the object’s
     size.  (Contributed by Robert Schuppenies; bpo-2898(44).)

     It’s now possible to determine the current profiler and tracer
     functions by calling *note sys.getprofile(): e0c. and *note
     sys.gettrace(): e0d.  (Contributed by Georg Brandl; bpo-1648(45).)

   * The *note tarfile: 101. module now supports POSIX.1-2001 (pax)
     tarfiles in addition to the POSIX.1-1988 (ustar) and GNU tar
     formats that were already supported.  The default format is GNU
     tar; specify the ‘format’ parameter to open a file using a
     different format:

          tar = tarfile.open("output.tar", "w",
                             format=tarfile.PAX_FORMAT)

     The new ‘encoding’ and ‘errors’ parameters specify an encoding and
     an error handling scheme for character conversions.  ‘'strict'’,
     ‘'ignore'’, and ‘'replace'’ are the three standard ways Python can
     handle errors,; ‘'utf-8'’ is a special value that replaces bad
     characters with their UTF-8 representation.  (Character conversions
     occur because the PAX format supports Unicode filenames, defaulting
     to UTF-8 encoding.)

     The ‘TarFile.add()’ method now accepts an ‘exclude’ argument that’s
     a function that can be used to exclude certain filenames from an
     archive.  The function must take a filename and return true if the
     file should be excluded or false if it should be archived.  The
     function is applied to both the name initially passed to ‘add()’
     and to the names of files in recursively-added directories.

     (All changes contributed by Lars Gustäbel).

   * An optional ‘timeout’ parameter was added to the *note
     telnetlib.Telnet: 68e. class constructor, specifying a timeout
     measured in seconds.  (Added by Facundo Batista.)

   * The *note tempfile.NamedTemporaryFile: e0e. class usually deletes
     the temporary file it created when the file is closed.  This
     behaviour can now be changed by passing ‘delete=False’ to the
     constructor.  (Contributed by Damien Miller; bpo-1537850(46).)

     A new class, ‘SpooledTemporaryFile’, behaves like a temporary file
     but stores its data in memory until a maximum size is exceeded.  On
     reaching that limit, the contents will be written to an on-disk
     temporary file.  (Contributed by Dustin J. Mitchell.)

     The ‘NamedTemporaryFile’ and ‘SpooledTemporaryFile’ classes both
     work as context managers, so you can write ‘with
     tempfile.NamedTemporaryFile() as tmp: ...’.  (Contributed by
     Alexander Belopolsky; bpo-2021(47).)

   * The ‘test.test_support’ module gained a number of context managers
     useful for writing tests.  ‘EnvironmentVarGuard()’ is a context
     manager that temporarily changes environment variables and
     automatically restores them to their old values.

     Another context manager, ‘TransientResource’, can surround calls to
     resources that may or may not be available; it will catch and
     ignore a specified list of exceptions.  For example, a network test
     may ignore certain failures when connecting to an external web
     site:

          with test_support.TransientResource(IOError,
                                          errno=errno.ETIMEDOUT):
              f = urllib.urlopen('https://sf.net')
              ...

     Finally, ‘check_warnings()’ resets the ‘warning’ module’s warning
     filters and returns an object that will record all warning messages
     triggered (bpo-3781(48)):

          with test_support.check_warnings() as wrec:
              warnings.simplefilter("always")
              # ... code that triggers a warning ...
              assert str(wrec.message) == "function is outdated"
              assert len(wrec.warnings) == 1, "Multiple warnings raised"

     (Contributed by Brett Cannon.)

   * The *note textwrap: 10a. module can now preserve existing
     whitespace at the beginnings and ends of the newly-created lines by
     specifying ‘drop_whitespace=False’ as an argument:

          >>> S = """This  sentence  has a bunch   of
          ...   extra   whitespace."""
          >>> print textwrap.fill(S, width=15)
          This  sentence
          has a bunch
          of    extra
          whitespace.
          >>> print textwrap.fill(S, drop_whitespace=False, width=15)
          This  sentence
            has a bunch
             of    extra
             whitespace.
          >>>

     (Contributed by Dwayne Bailey; bpo-1581073(49).)

   * The *note threading: 10b. module API is being changed to use
     properties such as ‘daemon’ instead of ‘setDaemon()’ and
     ‘isDaemon()’ methods, and some methods have been renamed to use
     underscores instead of camel-case; for example, the ‘activeCount()’
     method is renamed to ‘active_count()’.  Both the 2.6 and 3.0
     versions of the module support the same properties and renamed
     methods, but don’t remove the old methods.  No date has been set
     for the deprecation of the old APIs in Python 3.x; the old APIs
     won’t be removed in any 2.x version.  (Carried out by several
     people, most notably Benjamin Peterson.)

     The *note threading: 10b. module’s ‘Thread’ objects gained an
     ‘ident’ property that returns the thread’s identifier, a nonzero
     integer.  (Contributed by Gregory P. Smith; bpo-2871(50).)

   * The *note timeit: 10d. module now accepts callables as well as
     strings for the statement being timed and for the setup code.  Two
     convenience functions were added for creating ‘Timer’ instances:
     ‘repeat(stmt, setup, time, repeat, number)’ and ‘timeit(stmt,
     setup, time, number)’ create an instance and call the corresponding
     method.  (Contributed by Erik Demaine; bpo-1533909(51).)

   * The ‘Tkinter’ module now accepts lists and tuples for options,
     separating the elements by spaces before passing the resulting
     value to Tcl/Tk.  (Contributed by Guilherme Polo; bpo-2906(52).)

   * The *note turtle: 11f. module for turtle graphics was greatly
     enhanced by Gregor Lingl.  New features in the module include:

        * Better animation of turtle movement and rotation.

        * Control over turtle movement using the new ‘delay()’,
          ‘tracer()’, and ‘speed()’ methods.

        * The ability to set new shapes for the turtle, and to define a
          new coordinate system.

        * Turtles now have an ‘undo()’ method that can roll back
          actions.

        * Simple support for reacting to input events such as mouse and
          keyboard activity, making it possible to write simple games.

        * A ‘turtle.cfg’ file can be used to customize the starting
          appearance of the turtle’s screen.

        * The module’s docstrings can be replaced by new docstrings that
          have been translated into another language.

     (bpo-1513695(53))

   * An optional ‘timeout’ parameter was added to the ‘urllib.urlopen()’
     function and the ‘urllib.ftpwrapper’ class constructor, as well as
     the ‘urllib2.urlopen()’ function.  The parameter specifies a
     timeout measured in seconds.  For example:

          >>> u = urllib2.urlopen("http://slow.example.com",
                                  timeout=3)
          Traceback (most recent call last):
            ...
          urllib2.URLError: <urlopen error timed out>
          >>>

     (Added by Facundo Batista.)

   * The Unicode database provided by the *note unicodedata: 123. module
     has been updated to version 5.1.0.  (Updated by Martin von Löwis;
     bpo-3811(54).)

   * The *note warnings: 12f. module’s ‘formatwarning()’ and
     ‘showwarning()’ gained an optional `line' argument that can be used
     to supply the line of source code.  (Added as part of
     bpo-1631171(55), which re-implemented part of the *note warnings:
     12f. module in C code.)

     A new function, ‘catch_warnings()’, is a context manager intended
     for testing purposes that lets you temporarily modify the warning
     filters and then restore their original values (bpo-3781(56)).

   * The XML-RPC ‘SimpleXMLRPCServer’ and ‘DocXMLRPCServer’ classes can
     now be prevented from immediately opening and binding to their
     socket by passing ‘False’ as the `bind_and_activate' constructor
     parameter.  This can be used to modify the instance’s
     ‘allow_reuse_address’ attribute before calling the ‘server_bind()’
     and ‘server_activate()’ methods to open the socket and begin
     listening for connections.  (Contributed by Peter Parente;
     bpo-1599845(57).)

     ‘SimpleXMLRPCServer’ also has a ‘_send_traceback_header’ attribute;
     if true, the exception and formatted traceback are returned as HTTP
     headers “X-Exception” and “X-Traceback”.  This feature is for
     debugging purposes only and should not be used on production
     servers because the tracebacks might reveal passwords or other
     sensitive information.  (Contributed by Alan McIntyre as part of
     his project for Google’s Summer of Code 2007.)

   * The ‘xmlrpclib’ module no longer automatically converts *note
     datetime.date: 19e. and *note datetime.time: 5ed. to the
     ‘xmlrpclib.DateTime’ type; the conversion semantics were not
     necessarily correct for all applications.  Code using ‘xmlrpclib’
     should convert ‘date’ and *note time: 5ed. instances.
     (bpo-1330538(58)) The code can also handle dates before 1900
     (contributed by Ralf Schmitt; bpo-2014(59)) and 64-bit integers
     represented by using ‘<i8>’ in XML-RPC responses (contributed by
     Riku Lindblad; bpo-2985(60)).

   * The *note zipfile: 14b. module’s ‘ZipFile’ class now has
     ‘extract()’ and ‘extractall()’ methods that will unpack a single
     file or all the files in the archive to the current directory, or
     to a specified directory:

          z = zipfile.ZipFile('python-251.zip')

          # Unpack a single file, writing it relative
          # to the /tmp directory.
          z.extract('Python/sysmodule.c', '/tmp')

          # Unpack all the files in the archive.
          z.extractall()

     (Contributed by Alan McIntyre; bpo-467924(61).)

     The *note open(): 16f, ‘read()’ and ‘extract()’ methods can now
     take either a filename or a ‘ZipInfo’ object.  This is useful when
     an archive accidentally contains a duplicated filename.
     (Contributed by Graham Horler; bpo-1775025(62).)

     Finally, *note zipfile: 14b. now supports using Unicode filenames
     for archived files.  (Contributed by Alexey Borzenkov;
     bpo-1734346(63).)

* Menu:

* The ast module::
* The future_builtins module::
* The json module; JavaScript Object Notation: The json module JavaScript Object Notation.
* The plistlib module; A Property-List Parser: The plistlib module A Property-List Parser.
* ctypes Enhancements::
* Improved SSL Support::

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1736190

   (2) https://www.jcea.es/programacion/pybsddb.htm

   (3) https://bugs.python.org/issue1817

   (4) https://bugs.python.org/issue600362

   (5) https://bugs.python.org/issue1381

   (6) https://bugs.python.org/issue1638033

   (7) https://bugs.python.org/issue1158

   (8) http://speleotrove.com/decimal/decarith.html

   (9) https://bugs.python.org/issue1221598

   (10) https://bugs.python.org/issue1739906

   (11) https://bugs.python.org/issue1001604

   (12) https://bugs.python.org/issue2138

   (13) https://bugs.python.org/issue2819

   (14) https://bugs.python.org/issue711019

   (15) https://bugs.python.org/issue1640

   (16) https://bugs.python.org/issue1663329

   (17) https://bugs.python.org/issue1181

   (18) https://bugs.python.org/issue1273829

   (19) https://bugs.python.org/issue1115886

   (20) https://bugs.python.org/issue1339796

   (21) https://bugs.python.org/issue957650

   (22) https://bugs.python.org/issue1393667

   (23) https://bugs.python.org/issue1106316

   (24) https://bugs.python.org/issue2439

   (25) https://bugs.python.org/issue1137

   (26) https://bugs.python.org/issue1727780

   (27) https://bugs.python.org/issue1681432

   (28) https://bugs.python.org/issue846388

   (29) https://bugs.python.org/issue3487

   (30) https://bugs.python.org/issue2250

   (31) https://bugs.python.org/issue1861

   (32) https://bugs.python.org/issue1657

   (33) https://bugs.python.org/issue2663

   (34) https://bugs.python.org/issue1583

   (35) https://bugs.python.org/issue2240

   (36) https://tools.ietf.org/html/rfc2033.html

   (37) https://bugs.python.org/issue957003

   (38) https://tools.ietf.org/html/rfc3207.html

   (39) https://bugs.python.org/issue829951

   (40) https://bugs.python.org/issue1646

   (41) https://bugs.python.org/issue742598

   (42) https://bugs.python.org/issue1193577

   (43) https://bugs.python.org/issue1534

   (44) https://bugs.python.org/issue2898

   (45) https://bugs.python.org/issue1648

   (46) https://bugs.python.org/issue1537850

   (47) https://bugs.python.org/issue2021

   (48) https://bugs.python.org/issue3781

   (49) https://bugs.python.org/issue1581073

   (50) https://bugs.python.org/issue2871

   (51) https://bugs.python.org/issue1533909

   (52) https://bugs.python.org/issue2906

   (53) https://bugs.python.org/issue1513695

   (54) https://bugs.python.org/issue3811

   (55) https://bugs.python.org/issue1631171

   (56) https://bugs.python.org/issue3781

   (57) https://bugs.python.org/issue1599845

   (58) https://bugs.python.org/issue1330538

   (59) https://bugs.python.org/issue2014

   (60) https://bugs.python.org/issue2985

   (61) https://bugs.python.org/issue467924

   (62) https://bugs.python.org/issue1775025

   (63) https://bugs.python.org/issue1734346


File: python.info,  Node: The ast module,  Next: The future_builtins module,  Up: New and Improved Modules<2>

1.12.18.1 The ‘ast’ module
..........................

The *note ast: 7. module provides an Abstract Syntax Tree representation
of Python code, and Armin Ronacher contributed a set of helper functions
that perform a variety of common tasks.  These will be useful for HTML
templating packages, code analyzers, and similar tools that process
Python code.

The ‘parse()’ function takes an expression and returns an AST. The
‘dump()’ function outputs a representation of a tree, suitable for
debugging:

     import ast

     t = ast.parse("""
     d = {}
     for i in 'abcdefghijklm':
         d[i + i] = ord(i) - ord('a') + 1
     print d
     """)
     print ast.dump(t)

This outputs a deeply nested tree:

     Module(body=[
       Assign(targets=[
         Name(id='d', ctx=Store())
        ], value=Dict(keys=[], values=[]))
       For(target=Name(id='i', ctx=Store()),
           iter=Str(s='abcdefghijklm'), body=[
         Assign(targets=[
           Subscript(value=
             Name(id='d', ctx=Load()),
               slice=
               Index(value=
                 BinOp(left=Name(id='i', ctx=Load()), op=Add(),
                  right=Name(id='i', ctx=Load()))), ctx=Store())
          ], value=
          BinOp(left=
           BinOp(left=
            Call(func=
             Name(id='ord', ctx=Load()), args=[
               Name(id='i', ctx=Load())
              ], keywords=[], starargs=None, kwargs=None),
            op=Sub(), right=Call(func=
             Name(id='ord', ctx=Load()), args=[
               Str(s='a')
              ], keywords=[], starargs=None, kwargs=None)),
            op=Add(), right=Num(n=1)))
         ], orelse=[])
        Print(dest=None, values=[
          Name(id='d', ctx=Load())
        ], nl=True)
      ])

The ‘literal_eval()’ method takes a string or an AST representing a
literal expression, parses and evaluates it, and returns the resulting
value.  A literal expression is a Python expression containing only
strings, numbers, dictionaries, etc.  but no statements or function
calls.  If you need to evaluate an expression but cannot accept the
security risk of using an *note eval(): c61. call, ‘literal_eval()’ will
handle it safely:

     >>> literal = '("a", "b", {2:4, 3:8, 1:2})'
     >>> print ast.literal_eval(literal)
     ('a', 'b', {1: 2, 2: 4, 3: 8})
     >>> print ast.literal_eval('"a" + "b"')
     Traceback (most recent call last):
       ...
     ValueError: malformed string

The module also includes ‘NodeVisitor’ and ‘NodeTransformer’ classes for
traversing and modifying an AST, and functions for common
transformations such as changing line numbers.


File: python.info,  Node: The future_builtins module,  Next: The json module JavaScript Object Notation,  Prev: The ast module,  Up: New and Improved Modules<2>

1.12.18.2 The ‘future_builtins’ module
......................................

Python 3.0 makes many changes to the repertoire of built-in functions,
and most of the changes can’t be introduced in the Python 2.x series
because they would break compatibility.  The ‘future_builtins’ module
provides versions of these built-in functions that can be imported when
writing 3.0-compatible code.

The functions in this module currently include:

   * ‘ascii(obj)’: equivalent to *note repr(): 8b9.  In Python 3.0,
     *note repr(): 8b9. will return a Unicode string, while *note
     ascii(): e11. will return a pure ASCII bytestring.

   * ‘filter(predicate, iterable)’, ‘map(func, iterable1, ...)’: the 3.0
     versions return iterators, unlike the 2.x builtins which return
     lists.

   * ‘hex(value)’, ‘oct(value)’: instead of calling the ‘__hex__()’ or
     ‘__oct__()’ methods, these versions will call the *note
     __index__(): 2c2. method and convert the result to hexadecimal or
     octal.  *note oct(): d2d. will use the new ‘0o’ notation for its
     result.


File: python.info,  Node: The json module JavaScript Object Notation,  Next: The plistlib module A Property-List Parser,  Prev: The future_builtins module,  Up: New and Improved Modules<2>

1.12.18.3 The ‘json’ module: JavaScript Object Notation
.......................................................

The new *note json: a4. module supports the encoding and decoding of
Python types in JSON (Javascript Object Notation).  JSON is a
lightweight interchange format often used in web applications.  For more
information about JSON, see ‘http://www.json.org’.

*note json: a4. comes with support for decoding and encoding most
built-in Python types.  The following example encodes and decodes a
dictionary:

     >>> import json
     >>> data = {"spam": "foo", "parrot": 42}
     >>> in_json = json.dumps(data) # Encode the data
     >>> in_json
     '{"parrot": 42, "spam": "foo"}'
     >>> json.loads(in_json) # Decode into a Python object
     {"spam": "foo", "parrot": 42}

It’s also possible to write your own decoders and encoders to support
more types.  Pretty-printing of the JSON strings is also supported.

*note json: a4. (originally called simplejson) was written by Bob
Ippolito.


File: python.info,  Node: The plistlib module A Property-List Parser,  Next: ctypes Enhancements,  Prev: The json module JavaScript Object Notation,  Up: New and Improved Modules<2>

1.12.18.4 The ‘plistlib’ module: A Property-List Parser
.......................................................

The ‘.plist’ format is commonly used on Mac OS X to store basic data
types (numbers, strings, lists, and dictionaries) by serializing them
into an XML-based format.  It resembles the XML-RPC serialization of
data types.

Despite being primarily used on Mac OS X, the format has nothing
Mac-specific about it and the Python implementation works on any
platform that Python supports, so the *note plistlib: cf. module has
been promoted to the standard library.

Using the module is simple:

     import sys
     import plistlib
     import datetime

     # Create data structure
     data_struct = dict(lastAccessed=datetime.datetime.now(),
                        version=1,
                        categories=('Personal','Shared','Private'))

     # Create string containing XML.
     plist_str = plistlib.writePlistToString(data_struct)
     new_struct = plistlib.readPlistFromString(plist_str)
     print data_struct
     print new_struct

     # Write data structure to a file and read it back.
     plistlib.writePlist(data_struct, '/tmp/customizations.plist')
     new_struct = plistlib.readPlist('/tmp/customizations.plist')

     # read/writePlist accepts file-like objects as well as paths.
     plistlib.writePlist(data_struct, sys.stdout)


File: python.info,  Node: ctypes Enhancements,  Next: Improved SSL Support,  Prev: The plistlib module A Property-List Parser,  Up: New and Improved Modules<2>

1.12.18.5 ctypes Enhancements
.............................

Thomas Heller continued to maintain and enhance the *note ctypes: 2a.
module.

*note ctypes: 2a. now supports a ‘c_bool’ datatype that represents the
C99 ‘bool’ type.  (Contributed by David Remahl; bpo-1649190(1).)

The *note ctypes: 2a. string, buffer and array types have improved
support for extended slicing syntax, where various combinations of
‘(start, stop, step)’ are supplied.  (Implemented by Thomas Wouters.)

All *note ctypes: 2a. data types now support ‘from_buffer()’ and
‘from_buffer_copy()’ methods that create a ctypes instance based on a
provided buffer object.  ‘from_buffer_copy()’ copies the contents of the
object, while ‘from_buffer()’ will share the same memory area.

A new calling convention tells *note ctypes: 2a. to clear the ‘errno’ or
Win32 LastError variables at the outset of each wrapped call.
(Implemented by Thomas Heller; bpo-1798(2).)

You can now retrieve the Unix ‘errno’ variable after a function call.
When creating a wrapped function, you can supply ‘use_errno=True’ as a
keyword parameter to the ‘DLL()’ function and then call the module-level
methods ‘set_errno()’ and ‘get_errno()’ to set and retrieve the error
value.

The Win32 LastError variable is similarly supported by the ‘DLL()’,
‘OleDLL()’, and ‘WinDLL()’ functions.  You supply ‘use_last_error=True’
as a keyword parameter and then call the module-level methods
‘set_last_error()’ and ‘get_last_error()’.

The ‘byref()’ function, used to retrieve a pointer to a ctypes instance,
now has an optional `offset' parameter that is a byte count that will be
added to the returned pointer.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1649190

   (2) https://bugs.python.org/issue1798


File: python.info,  Node: Improved SSL Support,  Prev: ctypes Enhancements,  Up: New and Improved Modules<2>

1.12.18.6 Improved SSL Support
..............................

Bill Janssen made extensive improvements to Python 2.6’s support for the
Secure Sockets Layer by adding a new module, *note ssl: f3, that’s built
atop the OpenSSL(1) library.  This new module provides more control over
the protocol negotiated, the X.509 certificates used, and has better
support for writing SSL servers (as opposed to clients) in Python.  The
existing SSL support in the *note socket: ef. module hasn’t been removed
and continues to work, though it will be removed in Python 3.0.

To use the new module, you must first create a TCP connection in the
usual way and then pass it to the *note ssl.wrap_socket(): 571.
function.  It’s possible to specify whether a certificate is required,
and to obtain certificate info by calling the ‘getpeercert()’ method.

See also
........

The documentation for the *note ssl: f3. module.

   ---------- Footnotes ----------

   (1) https://www.openssl.org/


File: python.info,  Node: Deprecations and Removals,  Next: Build and C API Changes<9>,  Prev: New and Improved Modules<2>,  Up: What’s New in Python 2 6

1.12.19 Deprecations and Removals
---------------------------------

   * String exceptions have been removed.  Attempting to use them raises
     a *note TypeError: 1fe.

   * Changes to the *note Exception: 2dc. interface as dictated by PEP
     352(1) continue to be made.  For 2.6, the ‘message’ attribute is
     being deprecated in favor of the ‘args’ attribute.

   * (3.0-warning mode) Python 3.0 will feature a reorganized standard
     library that will drop many outdated modules and rename others.
     Python 2.6 running in 3.0-warning mode will warn about these
     modules when they are imported.

     The list of deprecated modules is: ‘audiodev’, ‘bgenlocations’,
     ‘buildtools’, ‘bundlebuilder’, ‘Canvas’, ‘compiler’, ‘dircache’,
     ‘dl’, ‘fpformat’, ‘gensuitemodule’, ‘ihooks’, ‘imageop’, ‘imgfile’,
     ‘linuxaudiodev’, ‘mhlib’, ‘mimetools’, ‘multifile’, ‘new’, ‘pure’,
     ‘statvfs’, ‘sunaudiodev’, ‘test.testall’, and ‘toaiff’.

   * The ‘gopherlib’ module has been removed.

   * The ‘MimeWriter’ module and ‘mimify’ module have been deprecated;
     use the *note email: 67. package instead.

   * The ‘md5’ module has been deprecated; use the *note hashlib: 8c.
     module instead.

   * The ‘posixfile’ module has been deprecated; *note fcntl.lockf():
     e17. provides better locking.

   * The ‘popen2’ module has been deprecated; use the *note subprocess:
     f9. module.

   * The ‘rgbimg’ module has been removed.

   * The ‘sets’ module has been deprecated; it’s better to use the
     built-in *note set: 1f6. and *note frozenset: 1f7. types.

   * The ‘sha’ module has been deprecated; use the *note hashlib: 8c.
     module instead.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0352


File: python.info,  Node: Build and C API Changes<9>,  Next: Porting to Python 2 6,  Prev: Deprecations and Removals,  Up: What’s New in Python 2 6

1.12.20 Build and C API Changes
-------------------------------

Changes to Python’s build process and to the C API include:

   * Python now must be compiled with C89 compilers (after 19 years!).
     This means that the Python source tree has dropped its own
     implementations of ‘memmove()’ and ‘strerror()’, which are in the
     C89 standard library.

   * Python 2.6 can be built with Microsoft Visual Studio 2008 (version
     9.0), and this is the new default compiler.  See the ‘PCbuild’
     directory for the build files.  (Implemented by Christian Heimes.)

   * On Mac OS X, Python 2.6 can be compiled as a 4-way universal build.
     The ‘configure’ script can take a
     ‘--with-universal-archs=[32-bit|64-bit|all]’ switch, controlling
     whether the binaries are built for 32-bit architectures (x86,
     PowerPC), 64-bit (x86-64 and PPC-64), or both.  (Contributed by
     Ronald Oussoren.)

   * The BerkeleyDB module now has a C API object, available as
     ‘bsddb.db.api’.  This object can be used by other C extensions that
     wish to use the ‘bsddb’ module for their own purposes.
     (Contributed by Duncan Grisby.)

   * The new buffer interface, previously described in *note the PEP
     3118 section: dea, adds *note PyObject_GetBuffer(): deb. and *note
     PyBuffer_Release(): e19, as well as a few other functions.

   * Python’s use of the C stdio library is now thread-safe, or at least
     as thread-safe as the underlying library is.  A long-standing
     potential bug occurred if one thread closed a file object while
     another thread was reading from or writing to the object.  In 2.6
     file objects have a reference count, manipulated by the
     ‘PyFile_IncUseCount()’ and ‘PyFile_DecUseCount()’ functions.  File
     objects can’t be closed unless the reference count is zero.
     ‘PyFile_IncUseCount()’ should be called while the GIL is still
     held, before carrying out an I/O operation using the ‘FILE *’
     pointer, and ‘PyFile_DecUseCount()’ should be called immediately
     after the GIL is re-acquired.  (Contributed by Antoine Pitrou and
     Gregory P. Smith.)

   * Importing modules simultaneously in two different threads no longer
     deadlocks; it will now raise an *note ImportError: 16c.  A new API
     function, *note PyImport_ImportModuleNoBlock(): aa0, will look for
     a module in ‘sys.modules’ first, then try to import it after
     acquiring an import lock.  If the import lock is held by another
     thread, an *note ImportError: 16c. is raised.  (Contributed by
     Christian Heimes.)

   * Several functions return information about the platform’s
     floating-point support.  *note PyFloat_GetMax(): e1a. returns the
     maximum representable floating point value, and *note
     PyFloat_GetMin(): e1b. returns the minimum positive value.  *note
     PyFloat_GetInfo(): e1c. returns an object containing more
     information from the ‘float.h’ file, such as ‘"mant_dig"’ (number
     of digits in the mantissa), ‘"epsilon"’ (smallest difference
     between 1.0 and the next largest value representable), and several
     others.  (Contributed by Christian Heimes; bpo-1534(1).)

   * C functions and methods that use *note PyComplex_AsCComplex(): e1d.
     will now accept arguments that have a *note __complex__(): 2c5.
     method.  In particular, the functions in the *note cmath: 18.
     module will now accept objects with this method.  This is a
     backport of a Python 3.0 change.  (Contributed by Mark Dickinson;
     bpo-1675423(2).)

   * Python’s C API now includes two functions for case-insensitive
     string comparisons, ‘PyOS_stricmp(char*, char*)’ and
     ‘PyOS_strnicmp(char*, char*, Py_ssize_t)’.  (Contributed by
     Christian Heimes; bpo-1635(3).)

   * Many C extensions define their own little macro for adding integers
     and strings to the module’s dictionary in the ‘init*’ function.
     Python 2.6 finally defines standard macros for adding values to a
     module, *note PyModule_AddStringMacro: e1e. and
     ‘PyModule_AddIntMacro()’.  (Contributed by Christian Heimes.)

   * Some macros were renamed in both 3.0 and 2.6 to make it clearer
     that they are macros, not functions.  ‘Py_Size()’ became
     ‘Py_SIZE()’, ‘Py_Type()’ became ‘Py_TYPE()’, and ‘Py_Refcnt()’
     became ‘Py_REFCNT()’.  The mixed-case macros are still available in
     Python 2.6 for backward compatibility.  (bpo-1629(4))

   * Distutils now places C extensions it builds in a different
     directory when running on a debug version of Python.  (Contributed
     by Collin Winter; bpo-1530959(5).)

   * Several basic data types, such as integers and strings, maintain
     internal free lists of objects that can be re-used.  The data
     structures for these free lists now follow a naming convention: the
     variable is always named ‘free_list’, the counter is always named
     ‘numfree’, and a macro ‘Py<typename>_MAXFREELIST’ is always
     defined.

   * A new Makefile target, “make patchcheck”, prepares the Python
     source tree for making a patch: it fixes trailing whitespace in all
     modified ‘.py’ files, checks whether the documentation has been
     changed, and reports whether the ‘Misc/ACKS’ and ‘Misc/NEWS’ files
     have been updated.  (Contributed by Brett Cannon.)

     Another new target, “make profile-opt”, compiles a Python binary
     using GCC’s profile-guided optimization.  It compiles Python with
     profiling enabled, runs the test suite to obtain a set of profiling
     results, and then compiles using these results for optimization.
     (Contributed by Gregory P. Smith.)

* Menu:

* Port-Specific Changes; Windows: Port-Specific Changes Windows<2>.
* Port-Specific Changes; Mac OS X: Port-Specific Changes Mac OS X<2>.
* Port-Specific Changes; IRIX: Port-Specific Changes IRIX.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1534

   (2) https://bugs.python.org/issue1675423

   (3) https://bugs.python.org/issue1635

   (4) https://bugs.python.org/issue1629

   (5) https://bugs.python.org/issue1530959


File: python.info,  Node: Port-Specific Changes Windows<2>,  Next: Port-Specific Changes Mac OS X<2>,  Up: Build and C API Changes<9>

1.12.20.1 Port-Specific Changes: Windows
........................................

   * The support for Windows 95, 98, ME and NT4 has been dropped.
     Python 2.6 requires at least Windows 2000 SP4.

   * The new default compiler on Windows is Visual Studio 2008 (version
     9.0).  The build directories for Visual Studio 2003 (version 7.1)
     and 2005 (version 8.0) were moved into the PC/ directory.  The new
     ‘PCbuild’ directory supports cross compilation for X64, debug
     builds and Profile Guided Optimization (PGO). PGO builds are
     roughly 10% faster than normal builds.  (Contributed by Christian
     Heimes with help from Amaury Forgeot d’Arc and Martin von Löwis.)

   * The *note msvcrt: b6. module now supports both the normal and wide
     char variants of the console I/O API. The ‘getwch()’ function reads
     a keypress and returns a Unicode value, as does the ‘getwche()’
     function.  The ‘putwch()’ function takes a Unicode character and
     writes it to the console.  (Contributed by Christian Heimes.)

   * *note os.path.expandvars(): e09. will now expand environment
     variables in the form “%var%”, and “~user” will be expanded into
     the user’s home directory path.  (Contributed by Josiah Carlson;
     bpo-957650(1).)

   * The *note socket: ef. module’s socket objects now have an ‘ioctl()’
     method that provides a limited interface to the ‘WSAIoctl()’ system
     interface.

   * The ‘_winreg’ module now has a function,
     ‘ExpandEnvironmentStrings()’, that expands environment variable
     references such as ‘%NAME%’ in an input string.  The handle objects
     provided by this module now support the context protocol, so they
     can be used in *note with: 7da. statements.  (Contributed by
     Christian Heimes.)

     ‘_winreg’ also has better support for x64 systems, exposing the
     ‘DisableReflectionKey()’, ‘EnableReflectionKey()’, and
     ‘QueryReflectionKey()’ functions, which enable and disable registry
     reflection for 32-bit processes running on 64-bit systems.
     (bpo-1753245(2))

   * The *note msilib: b5. module’s ‘Record’ object gained
     ‘GetInteger()’ and ‘GetString()’ methods that return field values
     as an integer or a string.  (Contributed by Floris Bruynooghe;
     bpo-2125(3).)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue957650

   (2) https://bugs.python.org/issue1753245

   (3) https://bugs.python.org/issue2125


File: python.info,  Node: Port-Specific Changes Mac OS X<2>,  Next: Port-Specific Changes IRIX,  Prev: Port-Specific Changes Windows<2>,  Up: Build and C API Changes<9>

1.12.20.2 Port-Specific Changes: Mac OS X
.........................................

   * When compiling a framework build of Python, you can now specify the
     framework name to be used by providing the ‘--with-framework-name=’
     option to the ‘configure’ script.

   * The ‘macfs’ module has been removed.  This in turn required the
     ‘macostools.touched()’ function to be removed because it depended
     on the ‘macfs’ module.  (bpo-1490190(1))

   * Many other Mac OS modules have been deprecated and will be removed
     in Python 3.0: ‘_builtinSuites’, ‘aepack’, ‘aetools’, ‘aetypes’,
     ‘applesingle’, ‘appletrawmain’, ‘appletrunner’, ‘argvemulator’,
     ‘Audio_mac’, ‘autoGIL’, ‘Carbon’, ‘cfmfile’, ‘CodeWarrior’,
     ‘ColorPicker’, ‘EasyDialogs’, ‘Explorer’, ‘Finder’, ‘FrameWork’,
     ‘findertools’, ‘ic’, ‘icglue’, ‘icopen’, ‘macerrors’, ‘MacOS’,
     ‘macfs’, ‘macostools’, ‘macresource’, ‘MiniAEFrame’, ‘Nav’,
     ‘Netscape’, ‘OSATerminology’, ‘pimp’, ‘PixMapWrapper’, ‘StdSuites’,
     ‘SystemEvents’, ‘Terminal’, and ‘terminalcommand’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1490190


File: python.info,  Node: Port-Specific Changes IRIX,  Prev: Port-Specific Changes Mac OS X<2>,  Up: Build and C API Changes<9>

1.12.20.3 Port-Specific Changes: IRIX
.....................................

A number of old IRIX-specific modules were deprecated and will be
removed in Python 3.0: ‘al’ and ‘AL’, ‘cd’, ‘cddb’, ‘cdplayer’, ‘CL’ and
‘cl’, ‘DEVICE’, ‘ERRNO’, ‘FILE’, ‘FL’ and ‘fl’, ‘flp’, ‘fm’, ‘GET’,
‘GLWS’, ‘GL’ and ‘gl’, ‘IN’, ‘IOCTL’, ‘jpeg’, ‘panelparser’, ‘readcd’,
‘SV’ and ‘sv’, ‘torgb’, ‘videoreader’, and ‘WAIT’.


File: python.info,  Node: Porting to Python 2 6,  Next: Acknowledgements<2>,  Prev: Build and C API Changes<9>,  Up: What’s New in Python 2 6

1.12.21 Porting to Python 2.6
-----------------------------

This section lists previously described changes and other bugfixes that
may require changes to your code:

   * Classes that aren’t supposed to be hashable should set ‘__hash__ =
     None’ in their definitions to indicate the fact.

   * String exceptions have been removed.  Attempting to use them raises
     a *note TypeError: 1fe.

   * The *note __init__(): e23. method of *note collections.deque: 62b.
     now clears any existing contents of the deque before adding
     elements from the iterable.  This change makes the behavior match
     ‘list.__init__()’.

   * *note object.__init__(): e23. previously accepted arbitrary
     arguments and keyword arguments, ignoring them.  In Python 2.6,
     this is no longer allowed and will result in a *note TypeError:
     1fe.  This will affect *note __init__(): e23. methods that end up
     calling the corresponding method on *note object: 3d2. (perhaps
     through using *note super(): 5dd.).  See bpo-1683368(1) for
     discussion.

   * The ‘Decimal’ constructor now accepts leading and trailing
     whitespace when passed a string.  Previously it would raise an
     ‘InvalidOperation’ exception.  On the other hand, the
     ‘create_decimal()’ method of ‘Context’ objects now explicitly
     disallows extra whitespace, raising a ‘ConversionSyntax’ exception.

   * Due to an implementation accident, if you passed a file path to the
     built-in *note __import__(): 16b. function, it would actually
     import the specified file.  This was never intended to work,
     however, and the implementation now explicitly checks for this case
     and raises an *note ImportError: 16c.

   * C API: the *note PyImport_Import(): e24. and *note
     PyImport_ImportModule(): d3b. functions now default to absolute
     imports, not relative imports.  This will affect C extensions that
     import other modules.

   * C API: extension data types that shouldn’t be hashable should
     define their ‘tp_hash’ slot to *note PyObject_HashNotImplemented():
     df7.

   * The *note socket: ef. module exception *note socket.error: a76. now
     inherits from *note IOError: a73.  Previously it wasn’t a subclass
     of ‘StandardError’ but now it is, through *note IOError: a73.
     (Implemented by Gregory P. Smith; bpo-1706815(2).)

   * The ‘xmlrpclib’ module no longer automatically converts *note
     datetime.date: 19e. and *note datetime.time: 5ed. to the
     ‘xmlrpclib.DateTime’ type; the conversion semantics were not
     necessarily correct for all applications.  Code using ‘xmlrpclib’
     should convert ‘date’ and *note time: 5ed. instances.
     (bpo-1330538(3))

   * (3.0-warning mode) The *note Exception: 2dc. class now warns when
     accessed using slicing or index access; having *note Exception:
     2dc. behave like a tuple is being phased out.

   * (3.0-warning mode) inequality comparisons between two dictionaries
     or two objects that don’t implement comparison methods are reported
     as warnings.  ‘dict1 == dict2’ still works, but ‘dict1 < dict2’ is
     being phased out.

     Comparisons between cells, which are an implementation detail of
     Python’s scoping rules, also cause warnings because such
     comparisons are forbidden entirely in 3.0.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1683368

   (2) https://bugs.python.org/issue1706815

   (3) https://bugs.python.org/issue1330538


File: python.info,  Node: Acknowledgements<2>,  Prev: Porting to Python 2 6,  Up: What’s New in Python 2 6

1.12.22 Acknowledgements
------------------------

The author would like to thank the following people for offering
suggestions, corrections and assistance with various drafts of this
article: Georg Brandl, Steve Brown, Nick Coghlan, Ralph Corderoy, Jim
Jewett, Kent Johnson, Chris Lambacher, Martin Michlmayr, Antoine Pitrou,
Brian Warner.


File: python.info,  Node: What’s New in Python 2 5,  Next: What’s New in Python 2 4,  Prev: What’s New in Python 2 6,  Up: What’s New in Python

1.13 What’s New in Python 2.5
=============================


Author: A.M. Kuchling

This article explains the new features in Python 2.5.  The final release
of Python 2.5 is scheduled for August 2006; PEP 356(1) describes the
planned release schedule.

The changes in Python 2.5 are an interesting mix of language and library
improvements.  The library enhancements will be more important to
Python’s user community, I think, because several widely-useful packages
were added.  New modules include ElementTree for XML processing
(‘xml.etree’), the SQLite database module (‘sqlite’), and the *note
ctypes: 2a. module for calling C functions.

The language changes are of middling significance.  Some pleasant new
features were added, but most of them aren’t features that you’ll use
every day.  Conditional expressions were finally added to the language
using a novel syntax; see section *note PEP 308; Conditional
Expressions: e29.  The new ‘*note with: 7da.’ statement will make
writing cleanup code easier (section *note PEP 343; The ‘with’
statement: e2a.).  Values can now be passed into generators (section
*note PEP 342; New Generator Features: e2b.).  Imports are now visible
as either absolute or relative (section *note PEP 328; Absolute and
Relative Imports: e2c.).  Some corner cases of exception handling are
handled better (section *note PEP 341; Unified try/except/finally:
e2d.).  All these improvements are worthwhile, but they’re improvements
to one specific language feature or another; none of them are broad
modifications to Python’s semantics.

As well as the language and library additions, other improvements and
bugfixes were made throughout the source tree.  A search through the SVN
change logs finds there were 353 patches applied and 458 bugs fixed
between Python 2.4 and 2.5.  (Both figures are likely to be
underestimates.)

This article doesn’t try to be a complete specification of the new
features; instead changes are briefly introduced using helpful examples.
For full details, you should always refer to the documentation for
Python 2.5 at ‘https://docs.python.org’.  If you want to understand the
complete implementation and design rationale, refer to the PEP for a
particular new feature.

Comments, suggestions, and error reports for this document are welcome;
please e-mail them to the author or open a bug in the Python bug
tracker.

* Menu:

* PEP 308; Conditional Expressions: PEP 308 Conditional Expressions.
* PEP 309; Partial Function Application: PEP 309 Partial Function Application.
* PEP 314; Metadata for Python Software Packages v1.1: PEP 314 Metadata for Python Software Packages v1 1.
* PEP 328; Absolute and Relative Imports: PEP 328 Absolute and Relative Imports.
* PEP 338; Executing Modules as Scripts: PEP 338 Executing Modules as Scripts.
* PEP 341; Unified try/except/finally: PEP 341 Unified try/except/finally.
* PEP 342; New Generator Features: PEP 342 New Generator Features.
* PEP 343; The ‘with’ statement: PEP 343 The ‘with’ statement<2>.
* PEP 352; Exceptions as New-Style Classes: PEP 352 Exceptions as New-Style Classes.
* PEP 353; Using ssize_t as the index type: PEP 353 Using ssize_t as the index type.
* PEP 357; The ‘__index__’ method: PEP 357 The ‘__index__’ method.
* Other Language Changes: Other Language Changes<12>.
* New, Improved, and Removed Modules: New Improved and Removed Modules.
* Build and C API Changes: Build and C API Changes<10>.
* Porting to Python 2.5: Porting to Python 2 5.
* Acknowledgements: Acknowledgements<3>.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0356


File: python.info,  Node: PEP 308 Conditional Expressions,  Next: PEP 309 Partial Function Application,  Up: What’s New in Python 2 5

1.13.1 PEP 308: Conditional Expressions
---------------------------------------

For a long time, people have been requesting a way to write conditional
expressions, which are expressions that return value A or value B
depending on whether a Boolean value is true or false.  A conditional
expression lets you write a single assignment statement that has the
same effect as the following:

     if condition:
         x = true_value
     else:
         x = false_value

There have been endless tedious discussions of syntax on both python-dev
and comp.lang.python.  A vote was even held that found the majority of
voters wanted conditional expressions in some form, but there was no
syntax that was preferred by a clear majority.  Candidates included C’s
‘cond ? true_v : false_v’, ‘if cond then true_v else false_v’, and 16
other variations.

Guido van Rossum eventually chose a surprising syntax:

     x = true_value if condition else false_value

Evaluation is still lazy as in existing Boolean expressions, so the
order of evaluation jumps around a bit.  The `condition' expression in
the middle is evaluated first, and the `true_value' expression is
evaluated only if the condition was true.  Similarly, the `false_value'
expression is only evaluated when the condition is false.

This syntax may seem strange and backwards; why does the condition go in
the `middle' of the expression, and not in the front as in C’s ‘c ? x :
y’?  The decision was checked by applying the new syntax to the modules
in the standard library and seeing how the resulting code read.  In many
cases where a conditional expression is used, one value seems to be the
‘common case’ and one value is an ‘exceptional case’, used only on rarer
occasions when the condition isn’t met.  The conditional syntax makes
this pattern a bit more obvious:

     contents = ((doc + '\n') if doc else '')

I read the above statement as meaning “here `contents' is usually
assigned a value of ‘doc+'\n'’; sometimes `doc' is empty, in which
special case an empty string is returned.” I doubt I will use
conditional expressions very often where there isn’t a clear common and
uncommon case.

There was some discussion of whether the language should require
surrounding conditional expressions with parentheses.  The decision was
made to `not' require parentheses in the Python language’s grammar, but
as a matter of style I think you should always use them.  Consider these
two statements:

     # First version -- no parens
     level = 1 if logging else 0

     # Second version -- with parens
     level = (1 if logging else 0)

In the first version, I think a reader’s eye might group the statement
into ‘level = 1’, ‘if logging’, ‘else 0’, and think that the condition
decides whether the assignment to `level' is performed.  The second
version reads better, in my opinion, because it makes it clear that the
assignment is always performed and the choice is being made between two
values.

Another reason for including the brackets: a few odd combinations of
list comprehensions and lambdas could look like incorrect conditional
expressions.  See PEP 308(1) for some examples.  If you put parentheses
around your conditional expressions, you won’t run into this case.

See also
........

PEP 308(2) - Conditional Expressions

     PEP written by Guido van Rossum and Raymond D. Hettinger;
     implemented by Thomas Wouters.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0308

   (2) https://www.python.org/dev/peps/pep-0308


File: python.info,  Node: PEP 309 Partial Function Application,  Next: PEP 314 Metadata for Python Software Packages v1 1,  Prev: PEP 308 Conditional Expressions,  Up: What’s New in Python 2 5

1.13.2 PEP 309: Partial Function Application
--------------------------------------------

The *note functools: 83. module is intended to contain tools for
functional-style programming.

One useful tool in this module is the ‘partial()’ function.  For
programs written in a functional style, you’ll sometimes want to
construct variants of existing functions that have some of the
parameters filled in.  Consider a Python function ‘f(a, b, c)’; you
could create a new function ‘g(b, c)’ that was equivalent to ‘f(1, b,
c)’.  This is called “partial function application”.

‘partial()’ takes the arguments ‘(function, arg1, arg2, ...
kwarg1=value1, kwarg2=value2)’.  The resulting object is callable, so
you can just call it to invoke `function' with the filled-in arguments.

Here’s a small but realistic example:

     import functools

     def log (message, subsystem):
         "Write the contents of 'message' to the specified subsystem."
         print '%s: %s' % (subsystem, message)
         ...

     server_log = functools.partial(log, subsystem='server')
     server_log('Unable to open socket')

Here’s another example, from a program that uses PyGTK. Here a
context-sensitive pop-up menu is being constructed dynamically.  The
callback provided for the menu option is a partially applied version of
the ‘open_item()’ method, where the first argument has been provided.

     ...
     class Application:
         def open_item(self, path):
            ...
         def init (self):
             open_func = functools.partial(self.open_item, item_path)
             popup_menu.append( ("Open", open_func, 1) )

Another function in the *note functools: 83. module is the
‘update_wrapper(wrapper, wrapped)’ function that helps you write
well-behaved decorators.  ‘update_wrapper()’ copies the name, module,
and docstring attribute to a wrapper function so that tracebacks inside
the wrapped function are easier to understand.  For example, you might
write:

     def my_decorator(f):
         def wrapper(*args, **kwds):
             print 'Calling decorated function'
             return f(*args, **kwds)
         functools.update_wrapper(wrapper, f)
         return wrapper

‘wraps()’ is a decorator that can be used inside your own decorators to
copy the wrapped function’s information.  An alternate version of the
previous example would be:

     def my_decorator(f):
         @functools.wraps(f)
         def wrapper(*args, **kwds):
             print 'Calling decorated function'
             return f(*args, **kwds)
         return wrapper

See also
........

PEP 309(1) - Partial Function Application

     PEP proposed and written by Peter Harris; implemented by Hye-Shik
     Chang and Nick Coghlan, with adaptations by Raymond Hettinger.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0309


File: python.info,  Node: PEP 314 Metadata for Python Software Packages v1 1,  Next: PEP 328 Absolute and Relative Imports,  Prev: PEP 309 Partial Function Application,  Up: What’s New in Python 2 5

1.13.3 PEP 314: Metadata for Python Software Packages v1.1
----------------------------------------------------------

Some simple dependency support was added to Distutils.  The ‘setup()’
function now has ‘requires’, ‘provides’, and ‘obsoletes’ keyword
parameters.  When you build a source distribution using the ‘sdist’
command, the dependency information will be recorded in the ‘PKG-INFO’
file.

Another new keyword parameter is ‘download_url’, which should be set to
a URL for the package’s source code.  This means it’s now possible to
look up an entry in the package index, determine the dependencies for a
package, and download the required packages.

     VERSION = '1.0'
     setup(name='PyPackage',
           version=VERSION,
           requires=['numarray', 'zlib (>=1.1.4)'],
           obsoletes=['OldPackage']
           download_url=('http://www.example.com/pypackage/dist/pkg-%s.tar.gz'
                         % VERSION),
          )

Another new enhancement to the Python package index at
‘https://pypi.org’ is storing source and binary archives for a package.
The new ‘upload’ Distutils command will upload a package to the
repository.

Before a package can be uploaded, you must be able to build a
distribution using the ‘sdist’ Distutils command.  Once that works, you
can run ‘python setup.py upload’ to add your package to the PyPI
archive.  Optionally you can GPG-sign the package by supplying the
‘--sign’ and ‘--identity’ options.

Package uploading was implemented by Martin von Löwis and Richard Jones.

See also
........

PEP 314(1) - Metadata for Python Software Packages v1.1

     PEP proposed and written by A.M. Kuchling, Richard Jones, and Fred
     Drake; implemented by Richard Jones and Fred Drake.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0314


File: python.info,  Node: PEP 328 Absolute and Relative Imports,  Next: PEP 338 Executing Modules as Scripts,  Prev: PEP 314 Metadata for Python Software Packages v1 1,  Up: What’s New in Python 2 5

1.13.4 PEP 328: Absolute and Relative Imports
---------------------------------------------

The simpler part of PEP 328(1) was implemented in Python 2.4:
parentheses could now be used to enclose the names imported from a
module using the ‘from ... import ...’ statement, making it easier to
import many different names.

The more complicated part has been implemented in Python 2.5: importing
a module can be specified to use absolute or package-relative imports.
The plan is to move toward making absolute imports the default in future
versions of Python.

Let’s say you have a package directory like this:

     pkg/
     pkg/__init__.py
     pkg/main.py
     pkg/string.py

This defines a package named ‘pkg’ containing the ‘pkg.main’ and
‘pkg.string’ submodules.

Consider the code in the ‘main.py’ module.  What happens if it executes
the statement ‘import string’?  In Python 2.4 and earlier, it will first
look in the package’s directory to perform a relative import, finds
‘pkg/string.py’, imports the contents of that file as the ‘pkg.string’
module, and that module is bound to the name ‘string’ in the ‘pkg.main’
module’s namespace.

That’s fine if ‘pkg.string’ was what you wanted.  But what if you wanted
Python’s standard *note string: f6. module?  There’s no clean way to
ignore ‘pkg.string’ and look for the standard module; generally you had
to look at the contents of ‘sys.modules’, which is slightly unclean.
Holger Krekel’s ‘py.std’ package provides a tidier way to perform
imports from the standard library, ‘import py; py.std.string.join()’,
but that package isn’t available on all Python installations.

Reading code which relies on relative imports is also less clear,
because a reader may be confused about which module, *note string: f6.
or ‘pkg.string’, is intended to be used.  Python users soon learned not
to duplicate the names of standard library modules in the names of their
packages’ submodules, but you can’t protect against having your
submodule’s name being used for a new module added in a future version
of Python.

In Python 2.5, you can switch *note import: ce7.’s behaviour to absolute
imports using a ‘from __future__ import absolute_import’ directive.
This absolute-import behaviour will become the default in a future
version (probably Python 2.7).  Once absolute imports are the default,
‘import string’ will always find the standard library’s version.  It’s
suggested that users should begin using absolute imports as much as
possible, so it’s preferable to begin writing ‘from pkg import string’
in your code.

Relative imports are still possible by adding a leading period to the
module name when using the ‘from ... import’ form:

     # Import names from pkg.string
     from .string import name1, name2
     # Import pkg.string
     from . import string

This imports the *note string: f6. module relative to the current
package, so in ‘pkg.main’ this will import `name1' and `name2' from
‘pkg.string’.  Additional leading periods perform the relative import
starting from the parent of the current package.  For example, code in
the ‘A.B.C’ module can do:

     from . import D                 # Imports A.B.D
     from .. import E                # Imports A.E
     from ..F import G               # Imports A.F.G

Leading periods cannot be used with the ‘import modname’ form of the
import statement, only the ‘from ... import’ form.

See also
........

PEP 328(2) - Imports: Multi-Line and Absolute/Relative

     PEP written by Aahz; implemented by Thomas Wouters.

‘https://pylib.readthedocs.io/’

     The py library by Holger Krekel, which contains the ‘py.std’
     package.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0328

   (2) https://www.python.org/dev/peps/pep-0328


File: python.info,  Node: PEP 338 Executing Modules as Scripts,  Next: PEP 341 Unified try/except/finally,  Prev: PEP 328 Absolute and Relative Imports,  Up: What’s New in Python 2 5

1.13.5 PEP 338: Executing Modules as Scripts
--------------------------------------------

The *note -m: 443. switch added in Python 2.4 to execute a module as a
script gained a few more abilities.  Instead of being implemented in C
code inside the Python interpreter, the switch now uses an
implementation in a new module, *note runpy: e2.

The *note runpy: e2. module implements a more sophisticated import
mechanism so that it’s now possible to run modules in a package such as
‘pychecker.checker’.  The module also supports alternative import
mechanisms such as the *note zipimport: 14c. module.  This means you can
add a .zip archive’s path to ‘sys.path’ and then use the *note -m: 443.
switch to execute code from the archive.

See also
........

PEP 338(1) - Executing modules as scripts

     PEP written and implemented by Nick Coghlan.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0338


File: python.info,  Node: PEP 341 Unified try/except/finally,  Next: PEP 342 New Generator Features,  Prev: PEP 338 Executing Modules as Scripts,  Up: What’s New in Python 2 5

1.13.6 PEP 341: Unified try/except/finally
------------------------------------------

Until Python 2.5, the *note try: e37. statement came in two flavours.
You could use a *note finally: 2bc. block to ensure that code is always
executed, or one or more *note except: c10. blocks to catch specific
exceptions.  You couldn’t combine both ‘except’ blocks and a ‘finally’
block, because generating the right bytecode for the combined version
was complicated and it wasn’t clear what the semantics of the combined
statement should be.

Guido van Rossum spent some time working with Java, which does support
the equivalent of combining *note except: c10. blocks and a *note
finally: 2bc. block, and this clarified what the statement should mean.
In Python 2.5, you can now write:

     try:
         block-1 ...
     except Exception1:
         handler-1 ...
     except Exception2:
         handler-2 ...
     else:
         else-block
     finally:
         final-block

The code in `block-1' is executed.  If the code raises an exception, the
various *note except: c10. blocks are tested: if the exception is of
class ‘Exception1’, `handler-1' is executed; otherwise if it’s of class
‘Exception2’, `handler-2' is executed, and so forth.  If no exception is
raised, the `else-block' is executed.

No matter what happened previously, the `final-block' is executed once
the code block is complete and any raised exceptions handled.  Even if
there’s an error in an exception handler or the `else-block' and a new
exception is raised, the code in the `final-block' is still run.

See also
........

PEP 341(1) - Unifying try-except and try-finally

     PEP written by Georg Brandl; implementation by Thomas Lee.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0341


File: python.info,  Node: PEP 342 New Generator Features,  Next: PEP 343 The ‘with’ statement<2>,  Prev: PEP 341 Unified try/except/finally,  Up: What’s New in Python 2 5

1.13.7 PEP 342: New Generator Features
--------------------------------------

Python 2.5 adds a simple way to pass values `into' a generator.  As
introduced in Python 2.3, generators only produce output; once a
generator’s code was invoked to create an iterator, there was no way to
pass any new information into the function when its execution is
resumed.  Sometimes the ability to pass in some information would be
useful.  Hackish solutions to this include making the generator’s code
look at a global variable and then changing the global variable’s value,
or passing in some mutable object that callers then modify.

To refresh your memory of basic generators, here’s a simple example:

     def counter (maximum):
         i = 0
         while i < maximum:
             yield i
             i += 1

When you call ‘counter(10)’, the result is an iterator that returns the
values from 0 up to 9.  On encountering the *note yield: 2c7. statement,
the iterator returns the provided value and suspends the function’s
execution, preserving the local variables.  Execution resumes on the
following call to the iterator’s *note next(): 775. method, picking up
after the ‘yield’ statement.

In Python 2.3, *note yield: 2c7. was a statement; it didn’t return any
value.  In 2.5, ‘yield’ is now an expression, returning a value that can
be assigned to a variable or otherwise operated on:

     val = (yield i)

I recommend that you always put parentheses around a *note yield: 2c7.
expression when you’re doing something with the returned value, as in
the above example.  The parentheses aren’t always necessary, but it’s
easier to always add them instead of having to remember when they’re
needed.

( PEP 342(1) explains the exact rules, which are that a *note yield:
2c7.-expression must always be parenthesized except when it occurs at
the top-level expression on the right-hand side of an assignment.  This
means you can write ‘val = yield i’ but have to use parentheses when
there’s an operation, as in ‘val = (yield i) + 12’.)

Values are sent into a generator by calling its ‘send(value)’ method.
The generator’s code is then resumed and the *note yield: 2c7.
expression returns the specified `value'.  If the regular *note next():
775. method is called, the ‘yield’ returns *note None: 203.

Here’s the previous example, modified to allow changing the value of the
internal counter.

     def counter (maximum):
         i = 0
         while i < maximum:
             val = (yield i)
             # If value provided, change counter
             if val is not None:
                 i = val
             else:
                 i += 1

And here’s an example of changing the counter:

     >>> it = counter(10)
     >>> print it.next()
     0
     >>> print it.next()
     1
     >>> print it.send(8)
     8
     >>> print it.next()
     9
     >>> print it.next()
     Traceback (most recent call last):
       File "t.py", line 15, in ?
         print it.next()
     StopIteration

*note yield: 2c7. will usually return *note None: 203, so you should
always check for this case.  Don’t just use its value in expressions
unless you’re sure that the ‘send()’ method will be the only method used
to resume your generator function.

In addition to ‘send()’, there are two other new methods on generators:

   * ‘throw(type, value=None, traceback=None)’ is used to raise an
     exception inside the generator; the exception is raised by the
     *note yield: 2c7. expression where the generator’s execution is
     paused.

   * ‘close()’ raises a new *note GeneratorExit: df8. exception inside
     the generator to terminate the iteration.  On receiving this
     exception, the generator’s code must either raise *note
     GeneratorExit: df8. or *note StopIteration: 582.  Catching the
     *note GeneratorExit: df8. exception and returning a value is
     illegal and will trigger a *note RuntimeError: 3dc.; if the
     function raises some other exception, that exception is propagated
     to the caller.  ‘close()’ will also be called by Python’s garbage
     collector when the generator is garbage-collected.

     If you need to run cleanup code when a *note GeneratorExit: df8.
     occurs, I suggest using a ‘try: ... finally:’ suite instead of
     catching *note GeneratorExit: df8.

The cumulative effect of these changes is to turn generators from
one-way producers of information into both producers and consumers.

Generators also become `coroutines', a more generalized form of
subroutines.  Subroutines are entered at one point and exited at another
point (the top of the function, and a *note return: 2c8. statement), but
coroutines can be entered, exited, and resumed at many different points
(the *note yield: 2c7. statements).  We’ll have to figure out patterns
for using coroutines effectively in Python.

The addition of the ‘close()’ method has one side effect that isn’t
obvious.  ‘close()’ is called when a generator is garbage-collected, so
this means the generator’s code gets one last chance to run before the
generator is destroyed.  This last chance means that ‘try...finally’
statements in generators can now be guaranteed to work; the *note
finally: 2bc. clause will now always get a chance to run.  The syntactic
restriction that you couldn’t mix *note yield: 2c7. statements with a
‘try...finally’ suite has therefore been removed.  This seems like a
minor bit of language trivia, but using generators and ‘try...finally’
is actually necessary in order to implement the *note with: 7da.
statement described by PEP 343(2).  I’ll look at this new statement in
the following section.

Another even more esoteric effect of this change: previously, the
‘gi_frame’ attribute of a generator was always a frame object.  It’s now
possible for ‘gi_frame’ to be ‘None’ once the generator has been
exhausted.

See also
........

PEP 342(3) - Coroutines via Enhanced Generators

     PEP written by Guido van Rossum and Phillip J. Eby; implemented by
     Phillip J. Eby.  Includes examples of some fancier uses of
     generators as coroutines.

     Earlier versions of these features were proposed in PEP 288(4) by
     Raymond Hettinger and PEP 325(5) by Samuele Pedroni.

‘https://en.wikipedia.org/wiki/Coroutine’

     The Wikipedia entry for coroutines.

‘http://www.sidhe.org/~dan/blog/archives/000178.html’

     An explanation of coroutines from a Perl point of view, written by
     Dan Sugalski.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0342

   (2) https://www.python.org/dev/peps/pep-0343

   (3) https://www.python.org/dev/peps/pep-0342

   (4) https://www.python.org/dev/peps/pep-0288

   (5) https://www.python.org/dev/peps/pep-0325


File: python.info,  Node: PEP 343 The ‘with’ statement<2>,  Next: PEP 352 Exceptions as New-Style Classes,  Prev: PEP 342 New Generator Features,  Up: What’s New in Python 2 5

1.13.8 PEP 343: The ‘with’ statement
------------------------------------

The ‘*note with: 7da.’ statement clarifies code that previously would
use ‘try...finally’ blocks to ensure that clean-up code is executed.  In
this section, I’ll discuss the statement as it will commonly be used.
In the next section, I’ll examine the implementation details and show
how to write objects for use with this statement.

The ‘*note with: 7da.’ statement is a new control-flow structure whose
basic structure is:

     with expression [as variable]:
         with-block

The expression is evaluated, and it should result in an object that
supports the context management protocol (that is, has *note
__enter__(): d5d. and *note __exit__(): d5e. methods.

The object’s *note __enter__(): d5d. is called before `with-block' is
executed and therefore can run set-up code.  It also may return a value
that is bound to the name `variable', if given.  (Note carefully that
`variable' is `not' assigned the result of `expression'.)

After execution of the `with-block' is finished, the object’s *note
__exit__(): d5e. method is called, even if the block raised an
exception, and can therefore run clean-up code.

To enable the statement in Python 2.5, you need to add the following
directive to your module:

     from __future__ import with_statement

The statement will always be enabled in Python 2.6.

Some standard Python objects now support the context management protocol
and can be used with the ‘*note with: 7da.’ statement.  File objects are
one example:

     with open('/etc/passwd', 'r') as f:
         for line in f:
             print line
             ... more processing code ...

After this statement has executed, the file object in `f' will have been
automatically closed, even if the *note for: cfa. loop raised an
exception part-way through the block.

     Note: In this case, `f' is the same object created by *note open():
     16f, because ‘file.__enter__()’ returns `self'.

The *note threading: 10b. module’s locks and condition variables also
support the ‘*note with: 7da.’ statement:

     lock = threading.Lock()
     with lock:
         # Critical section of code
         ...

The lock is acquired before the block is executed and always released
once the block is complete.

The new ‘localcontext()’ function in the *note decimal: 35. module makes
it easy to save and restore the current decimal context, which
encapsulates the desired precision and rounding characteristics for
computations:

     from decimal import Decimal, Context, localcontext

     # Displays with default precision of 28 digits
     v = Decimal('578')
     print v.sqrt()

     with localcontext(Context(prec=16)):
         # All code in this block uses a precision of 16 digits.
         # The original context is restored on exiting the block.
         print v.sqrt()

* Menu:

* Writing Context Managers: Writing Context Managers<2>.
* The contextlib module: The contextlib module<2>.


File: python.info,  Node: Writing Context Managers<2>,  Next: The contextlib module<2>,  Up: PEP 343 The ‘with’ statement<2>

1.13.8.1 Writing Context Managers
.................................

Under the hood, the ‘*note with: 7da.’ statement is fairly complicated.
Most people will only use ‘‘with’’ in company with existing objects and
don’t need to know these details, so you can skip the rest of this
section if you like.  Authors of new objects will need to understand the
details of the underlying implementation and should keep reading.

A high-level explanation of the context management protocol is:

   * The expression is evaluated and should result in an object called a
     “context manager”.  The context manager must have *note
     __enter__(): d5d. and *note __exit__(): d5e. methods.

   * The context manager’s *note __enter__(): d5d. method is called.
     The value returned is assigned to `VAR'. If no ‘'as VAR'’ clause is
     present, the value is simply discarded.

   * The code in `BLOCK' is executed.

   * If `BLOCK' raises an exception, the ‘__exit__(type, value,
     traceback)’ is called with the exception details, the same values
     returned by *note sys.exc_info(): d27.  The method’s return value
     controls whether the exception is re-raised: any false value
     re-raises the exception, and ‘True’ will result in suppressing it.
     You’ll only rarely want to suppress the exception, because if you
     do the author of the code containing the ‘*note with: 7da.’
     statement will never realize anything went wrong.

   * If `BLOCK' didn’t raise an exception, the *note __exit__(): d5e.
     method is still called, but `type', `value', and `traceback' are
     all ‘None’.

Let’s think through an example.  I won’t present detailed code but will
only sketch the methods necessary for a database that supports
transactions.

(For people unfamiliar with database terminology: a set of changes to
the database are grouped into a transaction.  Transactions can be either
committed, meaning that all the changes are written into the database,
or rolled back, meaning that the changes are all discarded and the
database is unchanged.  See any database textbook for more information.)

Let’s assume there’s an object representing a database connection.  Our
goal will be to let the user write code like this:

     db_connection = DatabaseConnection()
     with db_connection as cursor:
         cursor.execute('insert into ...')
         cursor.execute('delete from ...')
         # ... more operations ...

The transaction should be committed if the code in the block runs
flawlessly or rolled back if there’s an exception.  Here’s the basic
interface for ‘DatabaseConnection’ that I’ll assume:

     class DatabaseConnection:
         # Database interface
         def cursor (self):
             "Returns a cursor object and starts a new transaction"
         def commit (self):
             "Commits current transaction"
         def rollback (self):
             "Rolls back current transaction"

The *note __enter__(): d5d. method is pretty easy, having only to start
a new transaction.  For this application the resulting cursor object
would be a useful result, so the method will return it.  The user can
then add ‘as cursor’ to their ‘*note with: 7da.’ statement to bind the
cursor to a variable name.

     class DatabaseConnection:
         ...
         def __enter__ (self):
             # Code to start a new transaction
             cursor = self.cursor()
             return cursor

The *note __exit__(): d5e. method is the most complicated because it’s
where most of the work has to be done.  The method has to check if an
exception occurred.  If there was no exception, the transaction is
committed.  The transaction is rolled back if there was an exception.

In the code below, execution will just fall off the end of the function,
returning the default value of ‘None’.  ‘None’ is false, so the
exception will be re-raised automatically.  If you wished, you could be
more explicit and add a *note return: 2c8. statement at the marked
location.

     class DatabaseConnection:
         ...
         def __exit__ (self, type, value, tb):
             if tb is None:
                 # No exception, so commit
                 self.commit()
             else:
                 # Exception occurred, so rollback.
                 self.rollback()
                 # return False


File: python.info,  Node: The contextlib module<2>,  Prev: Writing Context Managers<2>,  Up: PEP 343 The ‘with’ statement<2>

1.13.8.2 The contextlib module
..............................

The new *note contextlib: 23. module provides some functions and a
decorator that are useful for writing objects for use with the ‘*note
with: 7da.’ statement.

The decorator is called ‘contextmanager()’, and lets you write a single
generator function instead of defining a new class.  The generator
should yield exactly one value.  The code up to the *note yield: 2c7.
will be executed as the *note __enter__(): d5d. method, and the value
yielded will be the method’s return value that will get bound to the
variable in the ‘*note with: 7da.’ statement’s ‘as’ clause, if any.  The
code after the *note yield: 2c7. will be executed in the *note
__exit__(): d5e. method.  Any exception raised in the block will be
raised by the ‘yield’ statement.

Our database example from the previous section could be written using
this decorator as:

     from contextlib import contextmanager

     @contextmanager
     def db_transaction (connection):
         cursor = connection.cursor()
         try:
             yield cursor
         except:
             connection.rollback()
             raise
         else:
             connection.commit()

     db = DatabaseConnection()
     with db_transaction(db) as cursor:
         ...

The *note contextlib: 23. module also has a ‘nested(mgr1, mgr2, ...)’
function that combines a number of context managers so you don’t need to
write nested ‘*note with: 7da.’ statements.  In this example, the single
‘‘with’’ statement both starts a database transaction and acquires a
thread lock:

     lock = threading.Lock()
     with nested (db_transaction(db), lock) as (cursor, locked):
         ...

Finally, the ‘closing(object)’ function returns `object' so that it can
be bound to a variable, and calls ‘object.close’ at the end of the
block.

     import urllib, sys
     from contextlib import closing

     with closing(urllib.urlopen('http://www.yahoo.com')) as f:
         for line in f:
             sys.stdout.write(line)

See also
........

PEP 343(1) - The “with” statement

     PEP written by Guido van Rossum and Nick Coghlan; implemented by
     Mike Bland, Guido van Rossum, and Neal Norwitz.  The PEP shows the
     code generated for a ‘*note with: 7da.’ statement, which can be
     helpful in learning how the statement works.

The documentation for the *note contextlib: 23. module.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0343


File: python.info,  Node: PEP 352 Exceptions as New-Style Classes,  Next: PEP 353 Using ssize_t as the index type,  Prev: PEP 343 The ‘with’ statement<2>,  Up: What’s New in Python 2 5

1.13.9 PEP 352: Exceptions as New-Style Classes
-----------------------------------------------

Exception classes can now be new-style classes, not just classic
classes, and the built-in *note Exception: 2dc. class and all the
standard built-in exceptions (*note NameError: e40, *note ValueError:
16d, etc.)  are now new-style classes.

The inheritance hierarchy for exceptions has been rearranged a bit.  In
2.5, the inheritance relationships are:

     BaseException       # New in Python 2.5
     |- KeyboardInterrupt
     |- SystemExit
     |- Exception
        |- (all other current built-in exceptions)

This rearrangement was done because people often want to catch all
exceptions that indicate program errors.  *note KeyboardInterrupt: 2cc.
and *note SystemExit: 6f3. aren’t errors, though, and usually represent
an explicit action such as the user hitting ‘Control-C’ or code calling
*note sys.exit(): daa.  A bare ‘except:’ will catch all exceptions, so
you commonly need to list *note KeyboardInterrupt: 2cc. and *note
SystemExit: 6f3. in order to re-raise them.  The usual pattern is:

     try:
         ...
     except (KeyboardInterrupt, SystemExit):
         raise
     except:
         # Log error...
         # Continue running program...

In Python 2.5, you can now write ‘except Exception’ to achieve the same
result, catching all the exceptions that usually indicate errors but
leaving *note KeyboardInterrupt: 2cc. and *note SystemExit: 6f3. alone.
As in previous versions, a bare ‘except:’ still catches all exceptions.

The goal for Python 3.0 is to require any class raised as an exception
to derive from *note BaseException: 2db. or some descendant of *note
BaseException: 2db, and future releases in the Python 2.x series may
begin to enforce this constraint.  Therefore, I suggest you begin making
all your exception classes derive from *note Exception: 2dc. now.  It’s
been suggested that the bare ‘except:’ form should be removed in Python
3.0, but Guido van Rossum hasn’t decided whether to do this or not.

Raising of strings as exceptions, as in the statement ‘raise "Error
occurred"’, is deprecated in Python 2.5 and will trigger a warning.  The
aim is to be able to remove the string-exception feature in a few
releases.

See also
........

PEP 352(1) - Required Superclass for Exceptions

     PEP written by Brett Cannon and Guido van Rossum; implemented by
     Brett Cannon.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0352


File: python.info,  Node: PEP 353 Using ssize_t as the index type,  Next: PEP 357 The ‘__index__’ method,  Prev: PEP 352 Exceptions as New-Style Classes,  Up: What’s New in Python 2 5

1.13.10 PEP 353: Using ssize_t as the index type
------------------------------------------------

A wide-ranging change to Python’s C API, using a new ‘Py_ssize_t’ type
definition instead of ‘int’, will permit the interpreter to handle more
data on 64-bit platforms.  This change doesn’t affect Python’s capacity
on 32-bit platforms.

Various pieces of the Python interpreter used C’s ‘int’ type to store
sizes or counts; for example, the number of items in a list or tuple
were stored in an ‘int’.  The C compilers for most 64-bit platforms
still define ‘int’ as a 32-bit type, so that meant that lists could only
hold up to ‘2**31 - 1’ = 2147483647 items.  (There are actually a few
different programming models that 64-bit C compilers can use – see
‘http://www.unix.org/version2/whatsnew/lp64_wp.html’ for a discussion –
but the most commonly available model leaves ‘int’ as 32 bits.)

A limit of 2147483647 items doesn’t really matter on a 32-bit platform
because you’ll run out of memory before hitting the length limit.  Each
list item requires space for a pointer, which is 4 bytes, plus space for
a *note PyObject: 5b5. representing the item.  2147483647*4 is already
more bytes than a 32-bit address space can contain.

It’s possible to address that much memory on a 64-bit platform, however.
The pointers for a list that size would only require 16 GiB of space, so
it’s not unreasonable that Python programmers might construct lists that
large.  Therefore, the Python interpreter had to be changed to use some
type other than ‘int’, and this will be a 64-bit type on 64-bit
platforms.  The change will cause incompatibilities on 64-bit machines,
so it was deemed worth making the transition now, while the number of
64-bit users is still relatively small.  (In 5 or 10 years, we may `all'
be on 64-bit machines, and the transition would be more painful then.)

This change most strongly affects authors of C extension modules.
Python strings and container types such as lists and tuples now use
‘Py_ssize_t’ to store their size.  Functions such as *note
PyList_Size(): e43. now return ‘Py_ssize_t’.  Code in extension modules
may therefore need to have some variables changed to ‘Py_ssize_t’.

The *note PyArg_ParseTuple(): 393. and *note Py_BuildValue(): 3f0.
functions have a new conversion code, ‘n’, for ‘Py_ssize_t’.  *note
PyArg_ParseTuple(): 393.’s ‘s#’ and ‘t#’ still output ‘int’ by default,
but you can define the macro ‘PY_SSIZE_T_CLEAN’ before including
‘Python.h’ to make them return ‘Py_ssize_t’.

PEP 353(1) has a section on conversion guidelines that extension authors
should read to learn about supporting 64-bit platforms.

See also
........

PEP 353(2) - Using ssize_t as the index type

     PEP written and implemented by Martin von Löwis.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0353

   (2) https://www.python.org/dev/peps/pep-0353


File: python.info,  Node: PEP 357 The ‘__index__’ method,  Next: Other Language Changes<12>,  Prev: PEP 353 Using ssize_t as the index type,  Up: What’s New in Python 2 5

1.13.11 PEP 357: The ‘__index__’ method
---------------------------------------

The NumPy developers had a problem that could only be solved by adding a
new special method, *note __index__(): 2c2.  When using slice notation,
as in ‘[start:stop:step]’, the values of the `start', `stop', and `step'
indexes must all be either integers or long integers.  NumPy defines a
variety of specialized integer types corresponding to unsigned and
signed integers of 8, 16, 32, and 64 bits, but there was no way to
signal that these types could be used as slice indexes.

Slicing can’t just use the existing *note __int__(): 2c3. method because
that method is also used to implement coercion to integers.  If slicing
used *note __int__(): 2c3, floating-point numbers would also become
legal slice indexes and that’s clearly an undesirable behaviour.

Instead, a new special method called *note __index__(): 2c2. was added.
It takes no arguments and returns an integer giving the slice index to
use.  For example:

     class C:
         def __index__ (self):
             return self.value

The return value must be either a Python integer or long integer.  The
interpreter will check that the type returned is correct, and raises a
*note TypeError: 1fe. if this requirement isn’t met.

A corresponding ‘nb_index’ slot was added to the C-level *note
PyNumberMethods: e46. structure to let C extensions implement this
protocol.  ‘PyNumber_Index(obj)’ can be used in extension code to call
the *note __index__(): 2c2. function and retrieve its result.

See also
........

PEP 357(1) - Allowing Any Object to be Used for Slicing

     PEP written and implemented by Travis Oliphant.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0357


File: python.info,  Node: Other Language Changes<12>,  Next: New Improved and Removed Modules,  Prev: PEP 357 The ‘__index__’ method,  Up: What’s New in Python 2 5

1.13.12 Other Language Changes
------------------------------

Here are all of the changes that Python 2.5 makes to the core Python
language.

   * The *note dict: 164. type has a new hook for letting subclasses
     provide a default value when a key isn’t contained in the
     dictionary.  When a key isn’t found, the dictionary’s
     ‘__missing__(key)’ method will be called.  This hook is used to
     implement the new ‘defaultdict’ class in the *note collections: 1d.
     module.  The following example defines a dictionary that returns
     zero for any missing key:

          class zerodict (dict):
              def __missing__ (self, key):
                  return 0

          d = zerodict({1:1, 2:2})
          print d[1], d[2]   # Prints 1, 2
          print d[3], d[4]   # Prints 0, 0

   * Both 8-bit and Unicode strings have new ‘partition(sep)’ and
     ‘rpartition(sep)’ methods that simplify a common use case.

     The ‘find(S)’ method is often used to get an index which is then
     used to slice the string and obtain the pieces that are before and
     after the separator.  ‘partition(sep)’ condenses this pattern into
     a single method call that returns a 3-tuple containing the
     substring before the separator, the separator itself, and the
     substring after the separator.  If the separator isn’t found, the
     first element of the tuple is the entire string and the other two
     elements are empty.  ‘rpartition(sep)’ also returns a 3-tuple but
     starts searching from the end of the string; the ‘r’ stands for
     ‘reverse’.

     Some examples:

          >>> ('http://www.python.org').partition('://')
          ('http', '://', 'www.python.org')
          >>> ('file:/usr/share/doc/index.html').partition('://')
          ('file:/usr/share/doc/index.html', '', '')
          >>> (u'Subject: a quick question').partition(':')
          (u'Subject', u':', u' a quick question')
          >>> 'www.python.org'.rpartition('.')
          ('www.python', '.', 'org')
          >>> 'www.python.org'.rpartition(':')
          ('', '', 'www.python.org')

     (Implemented by Fredrik Lundh following a suggestion by Raymond
     Hettinger.)

   * The ‘startswith()’ and ‘endswith()’ methods of string types now
     accept tuples of strings to check for.

          def is_image_file (filename):
              return filename.endswith(('.gif', '.jpg', '.tiff'))

     (Implemented by Georg Brandl following a suggestion by Tom Lynn.)

   * The *note min(): 8f6. and *note max(): 8f7. built-in functions
     gained a ‘key’ keyword parameter analogous to the ‘key’ argument
     for ‘sort()’.  This parameter supplies a function that takes a
     single argument and is called for every value in the list; *note
     min(): 8f6./*note max(): 8f7. will return the element with the
     smallest/largest return value from this function.  For example, to
     find the longest string in a list, you can do:

          L = ['medium', 'longest', 'short']
          # Prints 'longest'
          print max(L, key=len)
          # Prints 'short', because lexicographically 'short' has the largest value
          print max(L)

     (Contributed by Steven Bethard and Raymond Hettinger.)

   * Two new built-in functions, *note any(): e49. and *note all(): e4a,
     evaluate whether an iterator contains any true or false values.
     *note any(): e49. returns *note True: 594. if any value returned by
     the iterator is true; otherwise it will return *note False: 48f.
     *note all(): e4a. returns *note True: 594. only if all of the
     values returned by the iterator evaluate as true.  (Suggested by
     Guido van Rossum, and implemented by Raymond Hettinger.)

   * The result of a class’s *note __hash__(): 44c. method can now be
     either a long integer or a regular integer.  If a long integer is
     returned, the hash of that value is taken.  In earlier versions the
     hash value was required to be a regular integer, but in 2.5 the
     *note id(): e4b. built-in was changed to always return non-negative
     numbers, and users often seem to use ‘id(self)’ in *note
     __hash__(): 44c. methods (though this is discouraged).

   * ASCII is now the default encoding for modules.  It’s now a syntax
     error if a module contains string literals with 8-bit characters
     but doesn’t have an encoding declaration.  In Python 2.4 this
     triggered a warning, not a syntax error.  See PEP 263(1) for how to
     declare a module’s encoding; for example, you might add a line like
     this near the top of the source file:

          # -*- coding: latin1 -*-

   * A new warning, *note UnicodeWarning: e4c, is triggered when you
     attempt to compare a Unicode string and an 8-bit string that can’t
     be converted to Unicode using the default ASCII encoding.  The
     result of the comparison is false:

          >>> chr(128) == unichr(128)   # Can't convert chr(128) to Unicode
          __main__:1: UnicodeWarning: Unicode equal comparison failed
            to convert both arguments to Unicode - interpreting them
            as being unequal
          False
          >>> chr(127) == unichr(127)   # chr(127) can be converted
          True

     Previously this would raise a *note UnicodeDecodeError: 32b.
     exception, but in 2.5 this could result in puzzling problems when
     accessing a dictionary.  If you looked up ‘unichr(128)’ and
     ‘chr(128)’ was being used as a key, you’d get a *note
     UnicodeDecodeError: 32b. exception.  Other changes in 2.5 resulted
     in this exception being raised instead of suppressed by the code in
     ‘dictobject.c’ that implements dictionaries.

     Raising an exception for such a comparison is strictly correct, but
     the change might have broken code, so instead *note UnicodeWarning:
     e4c. was introduced.

     (Implemented by Marc-André Lemburg.)

   * One error that Python programmers sometimes make is forgetting to
     include an ‘__init__.py’ module in a package directory.  Debugging
     this mistake can be confusing, and usually requires running Python
     with the *note -v: e4d. switch to log all the paths searched.  In
     Python 2.5, a new *note ImportWarning: 6cf. warning is triggered
     when an import would have picked up a directory as a package but no
     ‘__init__.py’ was found.  This warning is silently ignored by
     default; provide the *note -Wd: 15b. option when running the Python
     executable to display the warning message.  (Implemented by Thomas
     Wouters.)

   * The list of base classes in a class definition can now be empty.
     As an example, this is now legal:

          class C():
              pass

     (Implemented by Brett Cannon.)

* Menu:

* Interactive Interpreter Changes::
* Optimizations: Optimizations<11>.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0263


File: python.info,  Node: Interactive Interpreter Changes,  Next: Optimizations<11>,  Up: Other Language Changes<12>

1.13.12.1 Interactive Interpreter Changes
.........................................

In the interactive interpreter, ‘quit’ and ‘exit’ have long been strings
so that new users get a somewhat helpful message when they try to quit:

     >>> quit
     'Use Ctrl-D (i.e. EOF) to exit.'

In Python 2.5, ‘quit’ and ‘exit’ are now objects that still produce
string representations of themselves, but are also callable.  Newbies
who try ‘quit()’ or ‘exit()’ will now exit the interpreter as they
expect.  (Implemented by Georg Brandl.)

The Python executable now accepts the standard long options *note –help:
e50. and *note –version: 6c8.; on Windows, it also accepts the *note /?:
e51. option for displaying a help message.  (Implemented by Georg
Brandl.)


File: python.info,  Node: Optimizations<11>,  Prev: Interactive Interpreter Changes,  Up: Other Language Changes<12>

1.13.12.2 Optimizations
.......................

Several of the optimizations were developed at the NeedForSpeed sprint,
an event held in Reykjavik, Iceland, from May 21–28 2006.  The sprint
focused on speed enhancements to the CPython implementation and was
funded by EWT LLC with local support from CCP Games.  Those
optimizations added at this sprint are specially marked in the following
list.

   * When they were introduced in Python 2.4, the built-in *note set:
     1f6. and *note frozenset: 1f7. types were built on top of Python’s
     dictionary type.  In 2.5 the internal data structure has been
     customized for implementing sets, and as a result sets will use a
     third less memory and are somewhat faster.  (Implemented by Raymond
     Hettinger.)

   * The speed of some Unicode operations, such as finding substrings,
     string splitting, and character map encoding and decoding, has been
     improved.  (Substring search and splitting improvements were added
     by Fredrik Lundh and Andrew Dalke at the NeedForSpeed sprint.
     Character maps were improved by Walter Dörwald and Martin von
     Löwis.)

   * The ‘long(str, base)’ function is now faster on long digit strings
     because fewer intermediate results are calculated.  The peak is for
     strings of around 800–1000 digits where the function is 6 times
     faster.  (Contributed by Alan McIntyre and committed at the
     NeedForSpeed sprint.)

   * It’s now illegal to mix iterating over a file with ‘for line in
     file’ and calling the file object’s ‘read()’/*note readline():
     de./‘readlines()’ methods.  Iteration uses an internal buffer and
     the ‘read*()’ methods don’t use that buffer.  Instead they would
     return the data following the buffer, causing the data to appear
     out of order.  Mixing iteration and these methods will now trigger
     a *note ValueError: 16d. from the ‘read*()’ method.  (Implemented
     by Thomas Wouters.)

   * The *note struct: f8. module now compiles structure format strings
     into an internal representation and caches this representation,
     yielding a 20% speedup.  (Contributed by Bob Ippolito at the
     NeedForSpeed sprint.)

   * The *note re: dd. module got a 1 or 2% speedup by switching to
     Python’s allocator functions instead of the system’s ‘malloc()’ and
     ‘free()’.  (Contributed by Jack Diederich at the NeedForSpeed
     sprint.)

   * The code generator’s peephole optimizer now performs simple
     constant folding in expressions.  If you write something like ‘a =
     2+3’, the code generator will do the arithmetic and produce code
     corresponding to ‘a = 5’.  (Proposed and implemented by Raymond
     Hettinger.)

   * Function calls are now faster because code objects now keep the
     most recently finished frame (a “zombie frame”) in an internal
     field of the code object, reusing it the next time the code object
     is invoked.  (Original patch by Michael Hudson, modified by Armin
     Rigo and Richard Jones; committed at the NeedForSpeed sprint.)
     Frame objects are also slightly smaller, which may improve cache
     locality and reduce memory usage a bit.  (Contributed by Neal
     Norwitz.)

   * Python’s built-in exceptions are now new-style classes, a change
     that speeds up instantiation considerably.  Exception handling in
     Python 2.5 is therefore about 30% faster than in 2.4.  (Contributed
     by Richard Jones, Georg Brandl and Sean Reifschneider at the
     NeedForSpeed sprint.)

   * Importing now caches the paths tried, recording whether they exist
     or not so that the interpreter makes fewer ‘open()’ and ‘stat()’
     calls on startup.  (Contributed by Martin von Löwis and Georg
     Brandl.)


File: python.info,  Node: New Improved and Removed Modules,  Next: Build and C API Changes<10>,  Prev: Other Language Changes<12>,  Up: What’s New in Python 2 5

1.13.13 New, Improved, and Removed Modules
------------------------------------------

The standard library received many enhancements and bug fixes in Python
2.5.  Here’s a partial list of the most notable changes, sorted
alphabetically by module name.  Consult the ‘Misc/NEWS’ file in the
source tree for a more complete list of changes, or look through the SVN
logs for all the details.

   * The *note audioop: c. module now supports the a-LAW encoding, and
     the code for u-LAW encoding has been improved.  (Contributed by
     Lars Immisch.)

   * The *note codecs: 1b. module gained support for incremental codecs.
     The ‘codec.lookup()’ function now returns a ‘CodecInfo’ instance
     instead of a tuple.  ‘CodecInfo’ instances behave like a 4-tuple to
     preserve backward compatibility but also have the attributes
     ‘encode’, ‘decode’, ‘incrementalencoder’, ‘incrementaldecoder’,
     ‘streamwriter’, and ‘streamreader’.  Incremental codecs can receive
     input and produce output in multiple chunks; the output is the same
     as if the entire input was fed to the non-incremental codec.  See
     the *note codecs: 1b. module documentation for details.  (Designed
     and implemented by Walter Dörwald.)

   * The *note collections: 1d. module gained a new type, ‘defaultdict’,
     that subclasses the standard *note dict: 164. type.  The new type
     mostly behaves like a dictionary but constructs a default value
     when a key isn’t present, automatically adding it to the dictionary
     for the requested key value.

     The first argument to ‘defaultdict’’s constructor is a factory
     function that gets called whenever a key is requested but not
     found.  This factory function receives no arguments, so you can use
     built-in type constructors such as *note list(): 1f8. or *note
     int(): 204.  For example, you can make an index of words based on
     their initial letter like this:

          words = """Nel mezzo del cammin di nostra vita
          mi ritrovai per una selva oscura
          che la diritta via era smarrita""".lower().split()

          index = defaultdict(list)

          for w in words:
              init_letter = w[0]
              index[init_letter].append(w)

     Printing ‘index’ results in the following output:

          defaultdict(<type 'list'>, {'c': ['cammin', 'che'], 'e': ['era'],
                  'd': ['del', 'di', 'diritta'], 'm': ['mezzo', 'mi'],
                  'l': ['la'], 'o': ['oscura'], 'n': ['nel', 'nostra'],
                  'p': ['per'], 's': ['selva', 'smarrita'],
                  'r': ['ritrovai'], 'u': ['una'], 'v': ['vita', 'via']}

     (Contributed by Guido van Rossum.)

   * The ‘deque’ double-ended queue type supplied by the *note
     collections: 1d. module now has a ‘remove(value)’ method that
     removes the first occurrence of `value' in the queue, raising *note
     ValueError: 16d. if the value isn’t found.  (Contributed by Raymond
     Hettinger.)

   * New module: The *note contextlib: 23. module contains helper
     functions for use with the new ‘*note with: 7da.’ statement.  See
     section *note The contextlib module: e3c. for more about this
     module.

   * New module: The *note cProfile: 27. module is a C implementation of
     the existing *note profile: d3. module that has much lower
     overhead.  The module’s interface is the same as *note profile:
     d3.: you run ‘cProfile.run('main()')’ to profile a function, can
     save profile data to a file, etc.  It’s not yet known if the
     Hotshot profiler, which is also written in C but doesn’t match the
     *note profile: d3. module’s interface, will continue to be
     maintained in future versions of Python.  (Contributed by Armin
     Rigo.)

     Also, the *note pstats: d4. module for analyzing the data measured
     by the profiler now supports directing the output to any file
     object by supplying a `stream' argument to the ‘Stats’ constructor.
     (Contributed by Skip Montanaro.)

   * The *note csv: 29. module, which parses files in comma-separated
     value format, received several enhancements and a number of
     bugfixes.  You can now set the maximum size in bytes of a field by
     calling the ‘csv.field_size_limit(new_limit)’ function; omitting
     the `new_limit' argument will return the currently-set limit.  The
     ‘reader’ class now has a ‘line_num’ attribute that counts the
     number of physical lines read from the source; records can span
     multiple physical lines, so ‘line_num’ is not the same as the
     number of records read.

     The CSV parser is now stricter about multi-line quoted fields.
     Previously, if a line ended within a quoted field without a
     terminating newline character, a newline would be inserted into the
     returned field.  This behavior caused problems when reading files
     that contained carriage return characters within fields, so the
     code was changed to return the field without inserting newlines.
     As a consequence, if newlines embedded within fields are important,
     the input should be split into lines in a manner that preserves the
     newline characters.

     (Contributed by Skip Montanaro and Andrew McNamara.)

   * The *note datetime: 1a0. class in the *note datetime: 30. module
     now has a ‘strptime(string, format)’ method for parsing date
     strings, contributed by Josh Spoerri.  It uses the same format
     characters as *note time.strptime(): e56. and *note
     time.strftime(): c37.:

          from datetime import datetime

          ts = datetime.strptime('10:13:15 2006-03-07',
                                 '%H:%M:%S %Y-%m-%d')

   * The ‘SequenceMatcher.get_matching_blocks()’ method in the *note
     difflib: 36. module now guarantees to return a minimal list of
     blocks describing matching subsequences.  Previously, the algorithm
     would occasionally break a block of matching elements into two list
     entries.  (Enhancement by Tim Peters.)

   * The *note doctest: 66. module gained a ‘SKIP’ option that keeps an
     example from being executed at all.  This is intended for code
     snippets that are usage examples intended for the reader and aren’t
     actually test cases.

     An `encoding' parameter was added to the ‘testfile()’ function and
     the ‘DocFileSuite’ class to specify the file’s encoding.  This
     makes it easier to use non-ASCII characters in tests contained
     within a docstring.  (Contributed by Bjorn Tillenius.)

   * The *note email: 67. package has been updated to version 4.0.
     (Contributed by Barry Warsaw.)

   * The *note fileinput: 7e. module was made more flexible.  Unicode
     filenames are now supported, and a `mode' parameter that defaults
     to ‘"r"’ was added to the *note input(): d33. function to allow
     opening files in binary or *note universal newlines: 6eb. mode.
     Another new parameter, `openhook', lets you use a function other
     than *note open(): 16f. to open the input files.  Once you’re
     iterating over the set of files, the ‘FileInput’ object’s new
     ‘fileno()’ returns the file descriptor for the currently opened
     file.  (Contributed by Georg Brandl.)

   * In the *note gc: 84. module, the new ‘get_count()’ function returns
     a 3-tuple containing the current collection counts for the three GC
     generations.  This is accounting information for the garbage
     collector; when these counts reach a specified threshold, a garbage
     collection sweep will be made.  The existing *note gc.collect():
     35b. function now takes an optional `generation' argument of 0, 1,
     or 2 to specify which generation to collect.  (Contributed by Barry
     Warsaw.)

   * The ‘nsmallest()’ and ‘nlargest()’ functions in the *note heapq:
     8d. module now support a ‘key’ keyword parameter similar to the one
     provided by the *note min(): 8f6./*note max(): 8f7. functions and
     the ‘sort()’ methods.  For example:

          >>> import heapq
          >>> L = ["short", 'medium', 'longest', 'longer still']
          >>> heapq.nsmallest(2, L)  # Return two lowest elements, lexicographically
          ['longer still', 'longest']
          >>> heapq.nsmallest(2, L, key=len)   # Return two shortest elements
          ['short', 'medium']

     (Contributed by Raymond Hettinger.)

   * The *note itertools.islice(): 4a9. function now accepts ‘None’ for
     the start and step arguments.  This makes it more compatible with
     the attributes of slice objects, so that you can now write the
     following:

          s = slice(5)     # Create slice object
          itertools.islice(iterable, s.start, s.stop, s.step)

     (Contributed by Raymond Hettinger.)

   * The *note format(): 5d6. function in the *note locale: a9. module
     has been modified and two new functions were added,
     ‘format_string()’ and ‘currency()’.

     The *note format(): 5d6. function’s `val' parameter could
     previously be a string as long as no more than one %char specifier
     appeared; now the parameter must be exactly one %char specifier
     with no surrounding text.  An optional `monetary' parameter was
     also added which, if ‘True’, will use the locale’s rules for
     formatting currency in placing a separator between groups of three
     digits.

     To format strings with multiple %char specifiers, use the new
     ‘format_string()’ function that works like *note format(): 5d6. but
     also supports mixing %char specifiers with arbitrary text.

     A new ‘currency()’ function was also added that formats a number
     according to the current locale’s settings.

     (Contributed by Georg Brandl.)

   * The *note mailbox: ae. module underwent a massive rewrite to add
     the capability to modify mailboxes in addition to reading them.  A
     new set of classes that include ‘mbox’, ‘MH’, and ‘Maildir’ are
     used to read mailboxes, and have an ‘add(message)’ method to add
     messages, ‘remove(key)’ to remove messages, and ‘lock()’/‘unlock()’
     to lock/unlock the mailbox.  The following example converts a
     maildir-format mailbox into an mbox-format one:

          import mailbox

          # 'factory=None' uses email.Message.Message as the class representing
          # individual messages.
          src = mailbox.Maildir('maildir', factory=None)
          dest = mailbox.mbox('/tmp/mbox')

          for msg in src:
              dest.add(msg)

     (Contributed by Gregory K. Johnson.  Funding was provided by
     Google’s 2005 Summer of Code.)

   * New module: the *note msilib: b5. module allows creating Microsoft
     Installer ‘.msi’ files and CAB files.  Some support for reading the
     ‘.msi’ database is also included.  (Contributed by Martin von
     Löwis.)

   * The *note nis: bf. module now supports accessing domains other than
     the system default domain by supplying a `domain' argument to the
     *note nis.match(): e57. and *note nis.maps(): e58. functions.
     (Contributed by Ben Bell.)

   * The *note operator: c2. module’s ‘itemgetter()’ and ‘attrgetter()’
     functions now support multiple fields.  A call such as
     ‘operator.attrgetter('a', 'b')’ will return a function that
     retrieves the ‘a’ and ‘b’ attributes.  Combining this new feature
     with the ‘sort()’ method’s ‘key’ parameter lets you easily sort
     lists using multiple fields.  (Contributed by Raymond Hettinger.)

   * The *note optparse: c3. module was updated to version 1.5.1 of the
     Optik library.  The ‘OptionParser’ class gained an ‘epilog’
     attribute, a string that will be printed after the help message,
     and a ‘destroy()’ method to break reference cycles created by the
     object.  (Contributed by Greg Ward.)

   * The *note os: c4. module underwent several changes.  The
     ‘stat_float_times’ variable now defaults to true, meaning that
     *note os.stat(): 321. will now return time values as floats.  (This
     doesn’t necessarily mean that *note os.stat(): 321. will return
     times that are precise to fractions of a second; not all systems
     support such precision.)

     Constants named *note os.SEEK_SET: e59, *note os.SEEK_CUR: e5a, and
     *note os.SEEK_END: e5b. have been added; these are the parameters
     to the *note os.lseek(): b39. function.  Two new constants for
     locking are *note os.O_SHLOCK: e5c. and *note os.O_EXLOCK: e5d.

     Two new functions, ‘wait3()’ and ‘wait4()’, were added.  They’re
     similar the ‘waitpid()’ function which waits for a child process to
     exit and returns a tuple of the process ID and its exit status, but
     ‘wait3()’ and ‘wait4()’ return additional information.  ‘wait3()’
     doesn’t take a process ID as input, so it waits for any child
     process to exit and returns a 3-tuple of `process-id',
     `exit-status', `resource-usage' as returned from the *note
     resource.getrusage(): e5e. function.  ‘wait4(pid)’ does take a
     process ID. (Contributed by Chad J. Schroeder.)

     On FreeBSD, the *note os.stat(): 321. function now returns times
     with nanosecond resolution, and the returned object now has
     ‘st_gen’ and ‘st_birthtime’.  The ‘st_flags’ attribute is also
     available, if the platform supports it.  (Contributed by Antti
     Louko and Diego Pettenò.)

   * The Python debugger provided by the *note pdb: c9. module can now
     store lists of commands to execute when a breakpoint is reached and
     execution stops.  Once breakpoint #1 has been created, enter
     ‘commands 1’ and enter a series of commands to be executed,
     finishing the list with ‘end’.  The command list can include
     commands that resume execution, such as ‘continue’ or ‘next’.
     (Contributed by Grégoire Dooms.)

   * The *note pickle: ca. and ‘cPickle’ modules no longer accept a
     return value of ‘None’ from the *note __reduce__(): 2d0. method;
     the method must return a tuple of arguments instead.  The ability
     to return ‘None’ was deprecated in Python 2.4, so this completes
     the removal of the feature.

   * The *note pkgutil: cd. module, containing various utility functions
     for finding packages, was enhanced to support PEP 302(1)’s import
     hooks and now also works for packages stored in ZIP-format
     archives.  (Contributed by Phillip J. Eby.)

   * The pybench benchmark suite by Marc-André Lemburg is now included
     in the ‘Tools/pybench’ directory.  The pybench suite is an
     improvement on the commonly used ‘pystone.py’ program because
     pybench provides a more detailed measurement of the interpreter’s
     speed.  It times particular operations such as function calls,
     tuple slicing, method lookups, and numeric operations, instead of
     performing many different operations and reducing the result to a
     single number as ‘pystone.py’ does.

   * The ‘pyexpat’ module now uses version 2.0 of the Expat parser.
     (Contributed by Trent Mick.)

   * The *note Queue: dde. class provided by the ‘Queue’ module gained
     two new methods.  ‘join()’ blocks until all items in the queue have
     been retrieved and all processing work on the items have been
     completed.  Worker threads call the other new method,
     ‘task_done()’, to signal that processing for an item has been
     completed.  (Contributed by Raymond Hettinger.)

   * The old ‘regex’ and ‘regsub’ modules, which have been deprecated
     ever since Python 2.0, have finally been deleted.  Other deleted
     modules: ‘statcache’, ‘tzparse’, ‘whrandom’.

   * Also deleted: the ‘lib-old’ directory, which includes ancient
     modules such as ‘dircmp’ and ‘ni’, was removed.  ‘lib-old’ wasn’t
     on the default ‘sys.path’, so unless your programs explicitly added
     the directory to ‘sys.path’, this removal shouldn’t affect your
     code.

   * The *note rlcompleter: e1. module is no longer dependent on
     importing the *note readline: de. module and therefore now works on
     non-Unix platforms.  (Patch from Robert Kiendl.)

   * The ‘SimpleXMLRPCServer’ and ‘DocXMLRPCServer’ classes now have a
     ‘rpc_paths’ attribute that constrains XML-RPC operations to a
     limited set of URL paths; the default is to allow only ‘'/'’ and
     ‘'/RPC2'’.  Setting ‘rpc_paths’ to ‘None’ or an empty tuple
     disables this path checking.

   * The *note socket: ef. module now supports ‘AF_NETLINK’ sockets on
     Linux, thanks to a patch from Philippe Biondi.  Netlink sockets are
     a Linux-specific mechanism for communications between a user-space
     process and kernel code; an introductory article about them is at
     ‘https://www.linuxjournal.com/article/7356’.  In Python code,
     netlink addresses are represented as a tuple of 2 integers, ‘(pid,
     group_mask)’.

     Two new methods on socket objects, ‘recv_into(buffer)’ and
     ‘recvfrom_into(buffer)’, store the received data in an object that
     supports the buffer protocol instead of returning the data as a
     string.  This means you can put the data directly into an array or
     a memory-mapped file.

     Socket objects also gained ‘getfamily()’, ‘gettype()’, and
     ‘getproto()’ accessor methods to retrieve the family, type, and
     protocol values for the socket.

   * New module: the *note spwd: f1. module provides functions for
     accessing the shadow password database on systems that support
     shadow passwords.

   * The *note struct: f8. is now faster because it compiles format
     strings into ‘Struct’ objects with ‘pack()’ and ‘unpack()’ methods.
     This is similar to how the *note re: dd. module lets you create
     compiled regular expression objects.  You can still use the
     module-level ‘pack()’ and ‘unpack()’ functions; they’ll create
     ‘Struct’ objects and cache them.  Or you can use ‘Struct’ instances
     directly:

          s = struct.Struct('ih3s')

          data = s.pack(1972, 187, 'abc')
          year, number, name = s.unpack(data)

     You can also pack and unpack data to and from buffer objects
     directly using the ‘pack_into(buffer, offset, v1, v2, ...)’ and
     ‘unpack_from(buffer, offset)’ methods.  This lets you store data
     directly into an array or a memory-mapped file.

     (‘Struct’ objects were implemented by Bob Ippolito at the
     NeedForSpeed sprint.  Support for buffer objects was added by
     Martin Blais, also at the NeedForSpeed sprint.)

   * The Python developers switched from CVS to Subversion during the
     2.5 development process.  Information about the exact build version
     is available as the ‘sys.subversion’ variable, a 3-tuple of
     ‘(interpreter-name, branch-name, revision-range)’.  For example, at
     the time of writing my copy of 2.5 was reporting ‘('CPython',
     'trunk', '45313:45315')’.

     This information is also available to C extensions via the *note
     Py_GetBuildInfo(): e5f. function that returns a string of build
     information like this: ‘"trunk:45355:45356M, Apr 13 2006,
     07:42:19"’.  (Contributed by Barry Warsaw.)

   * Another new function, *note sys._current_frames(): e60, returns the
     current stack frames for all running threads as a dictionary
     mapping thread identifiers to the topmost stack frame currently
     active in that thread at the time the function is called.
     (Contributed by Tim Peters.)

   * The ‘TarFile’ class in the *note tarfile: 101. module now has an
     ‘extractall()’ method that extracts all members from the archive
     into the current working directory.  It’s also possible to set a
     different directory as the extraction target, and to unpack only a
     subset of the archive’s members.

     The compression used for a tarfile opened in stream mode can now be
     autodetected using the mode ‘'r|*'’.  (Contributed by Lars
     Gustäbel.)

   * The *note threading: 10b. module now lets you set the stack size
     used when new threads are created.  The ‘stack_size([*size*])’
     function returns the currently configured stack size, and supplying
     the optional `size' parameter sets a new value.  Not all platforms
     support changing the stack size, but Windows, POSIX threading, and
     OS/2 all do.  (Contributed by Andrew MacIntyre.)

   * The *note unicodedata: 123. module has been updated to use version
     4.1.0 of the Unicode character database.  Version 3.2.0 is required
     by some specifications, so it’s still available as *note
     unicodedata.ucd_3_2_0: e61.

   * New module: the *note uuid: 12d. module generates universally
     unique identifiers (UUIDs) according to RFC 4122(2).  The RFC
     defines several different UUID versions that are generated from a
     starting string, from system properties, or purely randomly.  This
     module contains a ‘UUID’ class and functions named ‘uuid1()’,
     ‘uuid3()’, ‘uuid4()’, and ‘uuid5()’ to generate different versions
     of UUID. (Version 2 UUIDs are not specified in RFC 4122(3) and are
     not supported by this module.)

          >>> import uuid
          >>> # make a UUID based on the host ID and current time
          >>> uuid.uuid1()
          UUID('a8098c1a-f86e-11da-bd1a-00112444be1e')

          >>> # make a UUID using an MD5 hash of a namespace UUID and a name
          >>> uuid.uuid3(uuid.NAMESPACE_DNS, 'python.org')
          UUID('6fa459ea-ee8a-3ca4-894e-db77e160355e')

          >>> # make a random UUID
          >>> uuid.uuid4()
          UUID('16fd2706-8baf-433b-82eb-8c7fada847da')

          >>> # make a UUID using a SHA-1 hash of a namespace UUID and a name
          >>> uuid.uuid5(uuid.NAMESPACE_DNS, 'python.org')
          UUID('886313e1-3b8a-5372-9b90-0c9aee199e5d')

     (Contributed by Ka-Ping Yee.)

   * The *note weakref: 131. module’s ‘WeakKeyDictionary’ and
     ‘WeakValueDictionary’ types gained new methods for iterating over
     the weak references contained in the dictionary.  ‘iterkeyrefs()’
     and ‘keyrefs()’ methods were added to ‘WeakKeyDictionary’, and
     ‘itervaluerefs()’ and ‘valuerefs()’ were added to
     ‘WeakValueDictionary’.  (Contributed by Fred L. Drake, Jr.)

   * The *note webbrowser: 132. module received a number of
     enhancements.  It’s now usable as a script with ‘python -m
     webbrowser’, taking a URL as the argument; there are a number of
     switches to control the behaviour (‘-n’ for a new browser window,
     ‘-t’ for a new tab).  New module-level functions, ‘open_new()’ and
     ‘open_new_tab()’, were added to support this.  The module’s *note
     open(): 16f. function supports an additional feature, an
     `autoraise' parameter that signals whether to raise the open window
     when possible.  A number of additional browsers were added to the
     supported list such as Firefox, Opera, Konqueror, and elinks.
     (Contributed by Oleg Broytmann and Georg Brandl.)

   * The ‘xmlrpclib’ module now supports returning *note datetime: 1a0.
     objects for the XML-RPC date type.  Supply ‘use_datetime=True’ to
     the ‘loads()’ function or the ‘Unmarshaller’ class to enable this
     feature.  (Contributed by Skip Montanaro.)

   * The *note zipfile: 14b. module now supports the ZIP64 version of
     the format, meaning that a .zip archive can now be larger than 4
     GiB and can contain individual files larger than 4 GiB.
     (Contributed by Ronald Oussoren.)

   * The *note zlib: 14d. module’s ‘Compress’ and ‘Decompress’ objects
     now support a *note copy(): 25. method that makes a copy of the
     object’s internal state and returns a new ‘Compress’ or
     ‘Decompress’ object.  (Contributed by Chris AtLee.)

* Menu:

* The ctypes package::
* The ElementTree package::
* The hashlib package::
* The sqlite3 package::
* The wsgiref package::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0302

   (2) https://tools.ietf.org/html/rfc4122.html

   (3) https://tools.ietf.org/html/rfc4122.html


File: python.info,  Node: The ctypes package,  Next: The ElementTree package,  Up: New Improved and Removed Modules

1.13.13.1 The ctypes package
............................

The *note ctypes: 2a. package, written by Thomas Heller, has been added
to the standard library.  *note ctypes: 2a. lets you call arbitrary
functions in shared libraries or DLLs.  Long-time users may remember the
‘dl’ module, which provides functions for loading shared libraries and
calling functions in them.  The *note ctypes: 2a. package is much
fancier.

To load a shared library or DLL, you must create an instance of the
‘CDLL’ class and provide the name or path of the shared library or DLL.
Once that’s done, you can call arbitrary functions by accessing them as
attributes of the ‘CDLL’ object.

     import ctypes

     libc = ctypes.CDLL('libc.so.6')
     result = libc.printf("Line of output\n")

Type constructors for the various C types are provided: ‘c_int()’,
‘c_float()’, ‘c_double()’, ‘c_char_p()’ (equivalent to ‘char *’), and so
forth.  Unlike Python’s types, the C versions are all mutable; you can
assign to their ‘value’ attribute to change the wrapped value.  Python
integers and strings will be automatically converted to the
corresponding C types, but for other types you must call the correct
type constructor.  (And I mean `must'; getting it wrong will often
result in the interpreter crashing with a segmentation fault.)

You shouldn’t use ‘c_char_p()’ with a Python string when the C function
will be modifying the memory area, because Python strings are supposed
to be immutable; breaking this rule will cause puzzling bugs.  When you
need a modifiable memory area, use ‘create_string_buffer()’:

     s = "this is a string"
     buf = ctypes.create_string_buffer(s)
     libc.strfry(buf)

C functions are assumed to return integers, but you can set the
‘restype’ attribute of the function object to change this:

     >>> libc.atof('2.71828')
     -1783957616
     >>> libc.atof.restype = ctypes.c_double
     >>> libc.atof('2.71828')
     2.71828

*note ctypes: 2a. also provides a wrapper for Python’s C API as the
‘ctypes.pythonapi’ object.  This object does `not' release the global
interpreter lock before calling a function, because the lock must be
held when calling into the interpreter’s code.  There’s a ‘py_object()’
type constructor that will create a *note PyObject *: 5b5. pointer.  A
simple usage:

     import ctypes

     d = {}
     ctypes.pythonapi.PyObject_SetItem(ctypes.py_object(d),
               ctypes.py_object("abc"),  ctypes.py_object(1))
     # d is now {'abc', 1}.

Don’t forget to use ‘py_object()’; if it’s omitted you end up with a
segmentation fault.

*note ctypes: 2a. has been around for a while, but people still write
and distribution hand-coded extension modules because you can’t rely on
*note ctypes: 2a. being present.  Perhaps developers will begin to write
Python wrappers atop a library accessed through *note ctypes: 2a.
instead of extension modules, now that *note ctypes: 2a. is included
with core Python.

See also
........

‘http://starship.python.net/crew/theller/ctypes/’

     The ctypes web page, with a tutorial, reference, and FAQ.

The documentation for the *note ctypes: 2a. module.


File: python.info,  Node: The ElementTree package,  Next: The hashlib package,  Prev: The ctypes package,  Up: New Improved and Removed Modules

1.13.13.2 The ElementTree package
.................................

A subset of Fredrik Lundh’s ElementTree library for processing XML has
been added to the standard library as ‘xml.etree’.  The available
modules are ‘ElementTree’, ‘ElementPath’, and ‘ElementInclude’ from
ElementTree 1.2.6.  The ‘cElementTree’ accelerator module is also
included.

The rest of this section will provide a brief overview of using
ElementTree.  Full documentation for ElementTree is available at
‘http://effbot.org/zone/element-index.htm’.

ElementTree represents an XML document as a tree of element nodes.  The
text content of the document is stored as the ‘text’ and ‘tail’
attributes of (This is one of the major differences between ElementTree
and the Document Object Model; in the DOM there are many different types
of node, including ‘TextNode’.)

The most commonly used parsing function is ‘parse()’, that takes either
a string (assumed to contain a filename) or a file-like object and
returns an ‘ElementTree’ instance:

     from xml.etree import ElementTree as ET

     tree = ET.parse('ex-1.xml')

     feed = urllib.urlopen(
               'http://planet.python.org/rss10.xml')
     tree = ET.parse(feed)

Once you have an ‘ElementTree’ instance, you can call its ‘getroot()’
method to get the root ‘Element’ node.

There’s also an ‘XML()’ function that takes a string literal and returns
an ‘Element’ node (not an ‘ElementTree’).  This function provides a tidy
way to incorporate XML fragments, approaching the convenience of an XML
literal:

     svg = ET.XML("""<svg width="10px" version="1.0">
                  </svg>""")
     svg.set('height', '320px')
     svg.append(elem1)

Each XML element supports some dictionary-like and some list-like access
methods.  Dictionary-like operations are used to access attribute
values, and list-like operations are used to access child nodes.

Operation                           Result
                                    
-------------------------------------------------------------------------------------
                                    
‘elem[n]’                           Returns n’th child element.
                                    
                                    
‘elem[m:n]’                         Returns list of m’th through n’th child
                                    elements.
                                    
                                    
‘len(elem)’                         Returns number of child elements.
                                    
                                    
‘list(elem)’                        Returns list of child elements.
                                    
                                    
‘elem.append(elem2)’                Adds `elem2' as a child.
                                    
                                    
‘elem.insert(index, elem2)’         Inserts `elem2' at the specified location.
                                    
                                    
‘del elem[n]’                       Deletes n’th child element.
                                    
                                    
‘elem.keys()’                       Returns list of attribute names.
                                    
                                    
‘elem.get(name)’                    Returns value of attribute `name'.
                                    
                                    
‘elem.set(name, value)’             Sets new value for attribute `name'.
                                    
                                    
‘elem.attrib’                       Retrieves the dictionary containing
                                    attributes.
                                    
                                    
‘del elem.attrib[name]’             Deletes attribute `name'.
                                    

Comments and processing instructions are also represented as ‘Element’
nodes.  To check if a node is a comment or processing instructions:

     if elem.tag is ET.Comment:
         ...
     elif elem.tag is ET.ProcessingInstruction:
         ...

To generate XML output, you should call the ‘ElementTree.write()’
method.  Like ‘parse()’, it can take either a string or a file-like
object:

     # Encoding is US-ASCII
     tree.write('output.xml')

     # Encoding is UTF-8
     f = open('output.xml', 'w')
     tree.write(f, encoding='utf-8')

(Caution: the default encoding used for output is ASCII. For general XML
work, where an element’s name may contain arbitrary Unicode characters,
ASCII isn’t a very useful encoding because it will raise an exception if
an element’s name contains any characters with values greater than 127.
Therefore, it’s best to specify a different encoding such as UTF-8 that
can handle any Unicode character.)

This section is only a partial description of the ElementTree
interfaces.  Please read the package’s official documentation for more
details.

See also
........

‘http://effbot.org/zone/element-index.htm’

     Official documentation for ElementTree.


File: python.info,  Node: The hashlib package,  Next: The sqlite3 package,  Prev: The ElementTree package,  Up: New Improved and Removed Modules

1.13.13.3 The hashlib package
.............................

A new *note hashlib: 8c. module, written by Gregory P. Smith, has been
added to replace the ‘md5’ and ‘sha’ modules.  *note hashlib: 8c. adds
support for additional secure hashes (SHA-224, SHA-256, SHA-384, and
SHA-512).  When available, the module uses OpenSSL for fast platform
optimized implementations of algorithms.

The old ‘md5’ and ‘sha’ modules still exist as wrappers around hashlib
to preserve backwards compatibility.  The new module’s interface is very
close to that of the old modules, but not identical.  The most
significant difference is that the constructor functions for creating
new hashing objects are named differently.

     # Old versions
     h = md5.md5()
     h = md5.new()

     # New version
     h = hashlib.md5()

     # Old versions
     h = sha.sha()
     h = sha.new()

     # New version
     h = hashlib.sha1()

     # Hash that weren't previously available
     h = hashlib.sha224()
     h = hashlib.sha256()
     h = hashlib.sha384()
     h = hashlib.sha512()

     # Alternative form
     h = hashlib.new('md5')          # Provide algorithm as a string

Once a hash object has been created, its methods are the same as before:
‘update(string)’ hashes the specified string into the current digest
state, ‘digest()’ and ‘hexdigest()’ return the digest value as a binary
string or a string of hex digits, and *note copy(): 25. returns a new
hashing object with the same digest state.

See also
........

The documentation for the *note hashlib: 8c. module.


File: python.info,  Node: The sqlite3 package,  Next: The wsgiref package,  Prev: The hashlib package,  Up: New Improved and Removed Modules

1.13.13.4 The sqlite3 package
.............................

The pysqlite module (‘http://www.pysqlite.org’), a wrapper for the
SQLite embedded database, has been added to the standard library under
the package name *note sqlite3: f2.

SQLite is a C library that provides a lightweight disk-based database
that doesn’t require a separate server process and allows accessing the
database using a nonstandard variant of the SQL query language.  Some
applications can use SQLite for internal data storage.  It’s also
possible to prototype an application using SQLite and then port the code
to a larger database such as PostgreSQL or Oracle.

pysqlite was written by Gerhard Häring and provides a SQL interface
compliant with the DB-API 2.0 specification described by PEP 249(1).

If you’re compiling the Python source yourself, note that the source
tree doesn’t include the SQLite code, only the wrapper module.  You’ll
need to have the SQLite libraries and headers installed before compiling
Python, and the build process will compile the module when the necessary
headers are available.

To use the module, you must first create a ‘Connection’ object that
represents the database.  Here the data will be stored in the
‘/tmp/example’ file:

     conn = sqlite3.connect('/tmp/example')

You can also supply the special name ‘:memory:’ to create a database in
RAM.

Once you have a ‘Connection’, you can create a ‘Cursor’ object and call
its ‘execute()’ method to perform SQL commands:

     c = conn.cursor()

     # Create table
     c.execute('''create table stocks
     (date text, trans text, symbol text,
      qty real, price real)''')

     # Insert a row of data
     c.execute("""insert into stocks
               values ('2006-01-05','BUY','RHAT',100,35.14)""")

Usually your SQL operations will need to use values from Python
variables.  You shouldn’t assemble your query using Python’s string
operations because doing so is insecure; it makes your program
vulnerable to an SQL injection attack.

Instead, use the DB-API’s parameter substitution.  Put ‘?’ as a
placeholder wherever you want to use a value, and then provide a tuple
of values as the second argument to the cursor’s ‘execute()’ method.
(Other database modules may use a different placeholder, such as ‘%s’ or
‘:1’.)  For example:

     # Never do this -- insecure!
     symbol = 'IBM'
     c.execute("... where symbol = '%s'" % symbol)

     # Do this instead
     t = (symbol,)
     c.execute('select * from stocks where symbol=?', t)

     # Larger example
     for t in (('2006-03-28', 'BUY', 'IBM', 1000, 45.00),
               ('2006-04-05', 'BUY', 'MSOFT', 1000, 72.00),
               ('2006-04-06', 'SELL', 'IBM', 500, 53.00),
              ):
         c.execute('insert into stocks values (?,?,?,?,?)', t)

To retrieve data after executing a SELECT statement, you can either
treat the cursor as an iterator, call the cursor’s ‘fetchone()’ method
to retrieve a single matching row, or call ‘fetchall()’ to get a list of
the matching rows.

This example uses the iterator form:

     >>> c = conn.cursor()
     >>> c.execute('select * from stocks order by price')
     >>> for row in c:
     ...    print row
     ...
     (u'2006-01-05', u'BUY', u'RHAT', 100, 35.140000000000001)
     (u'2006-03-28', u'BUY', u'IBM', 1000, 45.0)
     (u'2006-04-06', u'SELL', u'IBM', 500, 53.0)
     (u'2006-04-05', u'BUY', u'MSOFT', 1000, 72.0)
     >>>

For more information about the SQL dialect supported by SQLite, see
‘https://www.sqlite.org’.

See also
........

‘http://www.pysqlite.org’

     The pysqlite web page.

‘https://www.sqlite.org’

     The SQLite web page; the documentation describes the syntax and the
     available data types for the supported SQL dialect.

The documentation for the *note sqlite3: f2. module.

PEP 249(2) - Database API Specification 2.0

     PEP written by Marc-André Lemburg.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0249

   (2) https://www.python.org/dev/peps/pep-0249


File: python.info,  Node: The wsgiref package,  Prev: The sqlite3 package,  Up: New Improved and Removed Modules

1.13.13.5 The wsgiref package
.............................

The Web Server Gateway Interface (WSGI) v1.0 defines a standard
interface between web servers and Python web applications and is
described in PEP 333(1).  The *note wsgiref: 135. package is a reference
implementation of the WSGI specification.

The package includes a basic HTTP server that will run a WSGI
application; this server is useful for debugging but isn’t intended for
production use.  Setting up a server takes only a few lines of code:

     from wsgiref import simple_server

     wsgi_app = ...

     host = ''
     port = 8000
     httpd = simple_server.make_server(host, port, wsgi_app)
     httpd.serve_forever()

See also
........

‘http://www.wsgi.org’

     A central web site for WSGI-related resources.

PEP 333(2) - Python Web Server Gateway Interface v1.0

     PEP written by Phillip J. Eby.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0333

   (2) https://www.python.org/dev/peps/pep-0333


File: python.info,  Node: Build and C API Changes<10>,  Next: Porting to Python 2 5,  Prev: New Improved and Removed Modules,  Up: What’s New in Python 2 5

1.13.14 Build and C API Changes
-------------------------------

Changes to Python’s build process and to the C API include:

   * The Python source tree was converted from CVS to Subversion, in a
     complex migration procedure that was supervised and flawlessly
     carried out by Martin von Löwis.  The procedure was developed as
     PEP 347(1).

   * Coverity, a company that markets a source code analysis tool called
     Prevent, provided the results of their examination of the Python
     source code.  The analysis found about 60 bugs that were quickly
     fixed.  Many of the bugs were refcounting problems, often occurring
     in error-handling code.  See ‘https://scan.coverity.com’ for the
     statistics.

   * The largest change to the C API came from PEP 353(2), which
     modifies the interpreter to use a ‘Py_ssize_t’ type definition
     instead of ‘int’.  See the earlier section *note PEP 353; Using
     ssize_t as the index type: e41. for a discussion of this change.

   * The design of the bytecode compiler has changed a great deal, no
     longer generating bytecode by traversing the parse tree.  Instead
     the parse tree is converted to an abstract syntax tree (or AST),
     and it is the abstract syntax tree that’s traversed to produce the
     bytecode.

     It’s possible for Python code to obtain AST objects by using the
     *note compile(): 2e7. built-in and specifying ‘_ast.PyCF_ONLY_AST’
     as the value of the `flags' parameter:

          from _ast import PyCF_ONLY_AST
          ast = compile("""a=0
          for i in range(10):
              a += i
          """, "<string>", 'exec', PyCF_ONLY_AST)

          assignment = ast.body[0]
          for_loop = ast.body[1]

     No official documentation has been written for the AST code yet,
     but PEP 339(3) discusses the design.  To start learning about the
     code, read the definition of the various AST nodes in
     ‘Parser/Python.asdl’.  A Python script reads this file and
     generates a set of C structure definitions in
     ‘Include/Python-ast.h’.  The ‘PyParser_ASTFromString()’ and
     ‘PyParser_ASTFromFile()’, defined in ‘Include/pythonrun.h’, take
     Python source as input and return the root of an AST representing
     the contents.  This AST can then be turned into a code object by
     ‘PyAST_Compile()’.  For more information, read the source code, and
     then ask questions on python-dev.

     The AST code was developed under Jeremy Hylton’s management, and
     implemented by (in alphabetical order) Brett Cannon, Nick Coghlan,
     Grant Edwards, John Ehresman, Kurt Kaiser, Neal Norwitz, Tim
     Peters, Armin Rigo, and Neil Schemenauer, plus the participants in
     a number of AST sprints at conferences such as PyCon.

   * Evan Jones’s patch to obmalloc, first described in a talk at PyCon
     DC 2005, was applied.  Python 2.4 allocated small objects in
     256K-sized arenas, but never freed arenas.  With this patch, Python
     will free arenas when they’re empty.  The net effect is that on
     some platforms, when you allocate many objects, Python’s memory
     usage may actually drop when you delete them and the memory may be
     returned to the operating system.  (Implemented by Evan Jones, and
     reworked by Tim Peters.)

     Note that this change means extension modules must be more careful
     when allocating memory.  Python’s API has many different functions
     for allocating memory that are grouped into families.  For example,
     *note PyMem_Malloc(): 5ff, *note PyMem_Realloc(): a50, and *note
     PyMem_Free(): e6e. are one family that allocates raw memory, while
     *note PyObject_Malloc(): 602, *note PyObject_Realloc(): e6f, and
     *note PyObject_Free(): 5fe. are another family that’s supposed to
     be used for creating Python objects.

     Previously these different families all reduced to the platform’s
     ‘malloc()’ and ‘free()’ functions.  This meant it didn’t matter if
     you got things wrong and allocated memory with the ‘PyMem()’
     function but freed it with the *note PyObject(): 5b5. function.
     With 2.5’s changes to obmalloc, these families now do different
     things and mismatches will probably result in a segfault.  You
     should carefully test your C extension modules with Python 2.5.

   * The built-in set types now have an official C API. Call *note
     PySet_New(): e70. and *note PyFrozenSet_New(): e71. to create a new
     set, *note PySet_Add(): e72. and *note PySet_Discard(): e73. to add
     and remove elements, and *note PySet_Contains(): e74. and *note
     PySet_Size(): e75. to examine the set’s state.  (Contributed by
     Raymond Hettinger.)

   * C code can now obtain information about the exact revision of the
     Python interpreter by calling the *note Py_GetBuildInfo(): e5f.
     function that returns a string of build information like this:
     ‘"trunk:45355:45356M, Apr 13 2006, 07:42:19"’.  (Contributed by
     Barry Warsaw.)

   * Two new macros can be used to indicate C functions that are local
     to the current file so that a faster calling convention can be
     used.  ‘Py_LOCAL(type)’ declares the function as returning a value
     of the specified `type' and uses a fast-calling qualifier.
     ‘Py_LOCAL_INLINE(type)’ does the same thing and also requests the
     function be inlined.  If ‘PY_LOCAL_AGGRESSIVE()’ is defined before
     ‘python.h’ is included, a set of more aggressive optimizations are
     enabled for the module; you should benchmark the results to find
     out if these optimizations actually make the code faster.
     (Contributed by Fredrik Lundh at the NeedForSpeed sprint.)

   * ‘PyErr_NewException(name, base, dict)’ can now accept a tuple of
     base classes as its `base' argument.  (Contributed by Georg
     Brandl.)

   * The ‘PyErr_Warn()’ function for issuing warnings is now deprecated
     in favour of ‘PyErr_WarnEx(category, message, stacklevel)’ which
     lets you specify the number of stack frames separating this
     function and the caller.  A `stacklevel' of 1 is the function
     calling *note PyErr_WarnEx(): e76, 2 is the function above that,
     and so forth.  (Added by Neal Norwitz.)

   * The CPython interpreter is still written in C, but the code can now
     be compiled with a C++ compiler without errors.  (Implemented by
     Anthony Baxter, Martin von Löwis, Skip Montanaro.)

   * The ‘PyRange_New()’ function was removed.  It was never documented,
     never used in the core code, and had dangerously lax error
     checking.  In the unlikely case that your extensions were using it,
     you can replace it by something like the following:

          range = PyObject_CallFunction((PyObject*) &PyRange_Type, "lll",
                                        start, stop, step);

* Menu:

* Port-Specific Changes::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0347

   (2) https://www.python.org/dev/peps/pep-0353

   (3) https://www.python.org/dev/peps/pep-0339


File: python.info,  Node: Port-Specific Changes,  Up: Build and C API Changes<10>

1.13.14.1 Port-Specific Changes
...............................

   * MacOS X (10.3 and higher): dynamic loading of modules now uses the
     ‘dlopen()’ function instead of MacOS-specific functions.

   * MacOS X: an ‘--enable-universalsdk’ switch was added to the
     ‘configure’ script that compiles the interpreter as a universal
     binary able to run on both PowerPC and Intel processors.
     (Contributed by Ronald Oussoren; bpo-2573(1).)

   * Windows: ‘.dll’ is no longer supported as a filename extension for
     extension modules.  ‘.pyd’ is now the only filename extension that
     will be searched for.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue2573


File: python.info,  Node: Porting to Python 2 5,  Next: Acknowledgements<3>,  Prev: Build and C API Changes<10>,  Up: What’s New in Python 2 5

1.13.15 Porting to Python 2.5
-----------------------------

This section lists previously described changes that may require changes
to your code:

   * ASCII is now the default encoding for modules.  It’s now a syntax
     error if a module contains string literals with 8-bit characters
     but doesn’t have an encoding declaration.  In Python 2.4 this
     triggered a warning, not a syntax error.

   * Previously, the ‘gi_frame’ attribute of a generator was always a
     frame object.  Because of the PEP 342(1) changes described in
     section *note PEP 342; New Generator Features: e2b, it’s now
     possible for ‘gi_frame’ to be ‘None’.

   * A new warning, *note UnicodeWarning: e4c, is triggered when you
     attempt to compare a Unicode string and an 8-bit string that can’t
     be converted to Unicode using the default ASCII encoding.
     Previously such comparisons would raise a *note UnicodeDecodeError:
     32b. exception.

   * Library: the *note csv: 29. module is now stricter about multi-line
     quoted fields.  If your files contain newlines embedded within
     fields, the input should be split into lines in a manner which
     preserves the newline characters.

   * Library: the *note locale: a9. module’s *note format(): 5d6.
     function’s would previously accept any string as long as no more
     than one %char specifier appeared.  In Python 2.5, the argument
     must be exactly one %char specifier with no surrounding text.

   * Library: The *note pickle: ca. and ‘cPickle’ modules no longer
     accept a return value of ‘None’ from the *note __reduce__(): 2d0.
     method; the method must return a tuple of arguments instead.  The
     modules also no longer accept the deprecated `bin' keyword
     parameter.

   * Library: The ‘SimpleXMLRPCServer’ and ‘DocXMLRPCServer’ classes now
     have a ‘rpc_paths’ attribute that constrains XML-RPC operations to
     a limited set of URL paths; the default is to allow only ‘'/'’ and
     ‘'/RPC2'’.  Setting ‘rpc_paths’ to ‘None’ or an empty tuple
     disables this path checking.

   * C API: Many functions now use ‘Py_ssize_t’ instead of ‘int’ to
     allow processing more data on 64-bit machines.  Extension code may
     need to make the same change to avoid warnings and to support
     64-bit machines.  See the earlier section *note PEP 353; Using
     ssize_t as the index type: e41. for a discussion of this change.

   * C API: The obmalloc changes mean that you must be careful to not
     mix usage of the ‘PyMem_*()’ and ‘PyObject_*()’ families of
     functions.  Memory allocated with one family’s ‘*_Malloc()’ must be
     freed with the corresponding family’s ‘*_Free()’ function.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0342


File: python.info,  Node: Acknowledgements<3>,  Prev: Porting to Python 2 5,  Up: What’s New in Python 2 5

1.13.16 Acknowledgements
------------------------

The author would like to thank the following people for offering
suggestions, corrections and assistance with various drafts of this
article: Georg Brandl, Nick Coghlan, Phillip J. Eby, Lars Gustäbel,
Raymond Hettinger, Ralf W. Grosse-Kunstleve, Kent Johnson, Iain Lowe,
Martin von Löwis, Fredrik Lundh, Andrew McNamara, Skip Montanaro,
Gustavo Niemeyer, Paul Prescod, James Pryor, Mike Rovner, Scott Weikart,
Barry Warsaw, Thomas Wouters.


File: python.info,  Node: What’s New in Python 2 4,  Next: What’s New in Python 2 3,  Prev: What’s New in Python 2 5,  Up: What’s New in Python

1.14 What’s New in Python 2.4
=============================


Author: A.M. Kuchling

This article explains the new features in Python 2.4.1, released on
March 30, 2005.

Python 2.4 is a medium-sized release.  It doesn’t introduce as many
changes as the radical Python 2.2, but introduces more features than the
conservative 2.3 release.  The most significant new language features
are function decorators and generator expressions; most other changes
are to the standard library.

According to the CVS change logs, there were 481 patches applied and 502
bugs fixed between Python 2.3 and 2.4.  Both figures are likely to be
underestimates.

This article doesn’t attempt to provide a complete specification of
every single new feature, but instead provides a brief introduction to
each feature.  For full details, you should refer to the documentation
for Python 2.4, such as the Python Library Reference and the Python
Reference Manual.  Often you will be referred to the PEP for a
particular new feature for explanations of the implementation and design
rationale.

* Menu:

* PEP 218; Built-In Set Objects: PEP 218 Built-In Set Objects.
* PEP 237; Unifying Long Integers and Integers: PEP 237 Unifying Long Integers and Integers.
* PEP 289; Generator Expressions: PEP 289 Generator Expressions.
* PEP 292; Simpler String Substitutions: PEP 292 Simpler String Substitutions.
* PEP 318; Decorators for Functions and Methods: PEP 318 Decorators for Functions and Methods.
* PEP 322; Reverse Iteration: PEP 322 Reverse Iteration.
* PEP 324; New subprocess Module: PEP 324 New subprocess Module.
* PEP 327; Decimal Data Type: PEP 327 Decimal Data Type.
* PEP 328; Multi-line Imports: PEP 328 Multi-line Imports.
* PEP 331; Locale-Independent Float/String Conversions: PEP 331 Locale-Independent Float/String Conversions.
* Other Language Changes: Other Language Changes<13>.
* New, Improved, and Deprecated Modules: New Improved and Deprecated Modules<3>.
* Build and C API Changes: Build and C API Changes<11>.
* Porting to Python 2.4: Porting to Python 2 4.
* Acknowledgements: Acknowledgements<4>.


File: python.info,  Node: PEP 218 Built-In Set Objects,  Next: PEP 237 Unifying Long Integers and Integers,  Up: What’s New in Python 2 4

1.14.1 PEP 218: Built-In Set Objects
------------------------------------

Python 2.3 introduced the ‘sets’ module.  C implementations of set data
types have now been added to the Python core as two new built-in types,
‘set(iterable)’ and ‘frozenset(iterable)’.  They provide high speed
operations for membership testing, for eliminating duplicates from
sequences, and for mathematical operations like unions, intersections,
differences, and symmetric differences.

     >>> a = set('abracadabra')              # form a set from a string
     >>> 'z' in a                            # fast membership testing
     False
     >>> a                                   # unique letters in a
     set(['a', 'r', 'b', 'c', 'd'])
     >>> ''.join(a)                          # convert back into a string
     'arbcd'

     >>> b = set('alacazam')                 # form a second set
     >>> a - b                               # letters in a but not in b
     set(['r', 'd', 'b'])
     >>> a | b                               # letters in either a or b
     set(['a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'])
     >>> a & b                               # letters in both a and b
     set(['a', 'c'])
     >>> a ^ b                               # letters in a or b but not both
     set(['r', 'd', 'b', 'm', 'z', 'l'])

     >>> a.add('z')                          # add a new element
     >>> a.update('wxy')                     # add multiple new elements
     >>> a
     set(['a', 'c', 'b', 'd', 'r', 'w', 'y', 'x', 'z'])
     >>> a.remove('x')                       # take one element out
     >>> a
     set(['a', 'c', 'b', 'd', 'r', 'w', 'y', 'z'])

The *note frozenset(): 1f7. type is an immutable version of *note set():
1f6.  Since it is immutable and hashable, it may be used as a dictionary
key or as a member of another set.

The ‘sets’ module remains in the standard library, and may be useful if
you wish to subclass the ‘Set’ or ‘ImmutableSet’ classes.  There are
currently no plans to deprecate the module.

See also
........

PEP 218(1) - Adding a Built-In Set Object Type

     Originally proposed by Greg Wilson and ultimately implemented by
     Raymond Hettinger.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0218


File: python.info,  Node: PEP 237 Unifying Long Integers and Integers,  Next: PEP 289 Generator Expressions,  Prev: PEP 218 Built-In Set Objects,  Up: What’s New in Python 2 4

1.14.2 PEP 237: Unifying Long Integers and Integers
---------------------------------------------------

The lengthy transition process for this PEP, begun in Python 2.2, takes
another step forward in Python 2.4.  In 2.3, certain integer operations
that would behave differently after int/long unification triggered *note
FutureWarning: 435. warnings and returned values limited to 32 or 64
bits (depending on your platform).  In 2.4, these expressions no longer
produce a warning and instead produce a different result that’s usually
a long integer.

The problematic expressions are primarily left shifts and lengthy
hexadecimal and octal constants.  For example, ‘2 << 32’ results in a
warning in 2.3, evaluating to 0 on 32-bit platforms.  In Python 2.4,
this expression now returns the correct answer, 8589934592.

See also
........

PEP 237(1) - Unifying Long Integers and Integers

     Original PEP written by Moshe Zadka and GvR. The changes for 2.4
     were implemented by Kalle Svensson.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0237


File: python.info,  Node: PEP 289 Generator Expressions,  Next: PEP 292 Simpler String Substitutions,  Prev: PEP 237 Unifying Long Integers and Integers,  Up: What’s New in Python 2 4

1.14.3 PEP 289: Generator Expressions
-------------------------------------

The iterator feature introduced in Python 2.2 and the *note itertools:
a3. module make it easier to write programs that loop through large data
sets without having the entire data set in memory at one time.  List
comprehensions don’t fit into this picture very well because they
produce a Python list object containing all of the items.  This
unavoidably pulls all of the objects into memory, which can be a problem
if your data set is very large.  When trying to write a
functionally-styled program, it would be natural to write something
like:

     links = [link for link in get_all_links() if not link.followed]
     for link in links:
         ...

instead of

     for link in get_all_links():
         if link.followed:
             continue
         ...

The first form is more concise and perhaps more readable, but if you’re
dealing with a large number of link objects you’d have to write the
second form to avoid having all link objects in memory at the same time.

Generator expressions work similarly to list comprehensions but don’t
materialize the entire list; instead they create a generator that will
return elements one by one.  The above example could be written as:

     links = (link for link in get_all_links() if not link.followed)
     for link in links:
         ...

Generator expressions always have to be written inside parentheses, as
in the above example.  The parentheses signalling a function call also
count, so if you want to create an iterator that will be immediately
passed to a function you could write:

     print sum(obj.count for obj in list_all_objects())

Generator expressions differ from list comprehensions in various small
ways.  Most notably, the loop variable (`obj' in the above example) is
not accessible outside of the generator expression.  List comprehensions
leave the variable assigned to its last value; future versions of Python
will change this, making list comprehensions match generator expressions
in this respect.

See also
........

PEP 289(1) - Generator Expressions

     Proposed by Raymond Hettinger and implemented by Jiwon Seo with
     early efforts steered by Hye-Shik Chang.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0289


File: python.info,  Node: PEP 292 Simpler String Substitutions,  Next: PEP 318 Decorators for Functions and Methods,  Prev: PEP 289 Generator Expressions,  Up: What’s New in Python 2 4

1.14.4 PEP 292: Simpler String Substitutions
--------------------------------------------

Some new classes in the standard library provide an alternative
mechanism for substituting variables into strings; this style of
substitution may be better for applications where untrained users need
to edit templates.

The usual way of substituting variables by name is the ‘%’ operator:

     >>> '%(page)i: %(title)s' % {'page':2, 'title': 'The Best of Times'}
     '2: The Best of Times'

When writing the template string, it can be easy to forget the ‘i’ or
‘s’ after the closing parenthesis.  This isn’t a big problem if the
template is in a Python module, because you run the code, get an
“Unsupported format character” *note ValueError: 16d, and fix the
problem.  However, consider an application such as Mailman where
template strings or translations are being edited by users who aren’t
aware of the Python language.  The format string’s syntax is complicated
to explain to such users, and if they make a mistake, it’s difficult to
provide helpful feedback to them.

PEP 292 adds a ‘Template’ class to the *note string: f6. module that
uses ‘$’ to indicate a substitution:

     >>> import string
     >>> t = string.Template('$page: $title')
     >>> t.substitute({'page':2, 'title': 'The Best of Times'})
     '2: The Best of Times'

If a key is missing from the dictionary, the ‘substitute()’ method will
raise a *note KeyError: 3e9.  There’s also a ‘safe_substitute()’ method
that ignores missing keys:

     >>> t = string.Template('$page: $title')
     >>> t.safe_substitute({'page':3})
     '3: $title'

See also
........

PEP 292(1) - Simpler String Substitutions

     Written and implemented by Barry Warsaw.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0292


File: python.info,  Node: PEP 318 Decorators for Functions and Methods,  Next: PEP 322 Reverse Iteration,  Prev: PEP 292 Simpler String Substitutions,  Up: What’s New in Python 2 4

1.14.5 PEP 318: Decorators for Functions and Methods
----------------------------------------------------

Python 2.2 extended Python’s object model by adding static methods and
class methods, but it didn’t extend Python’s syntax to provide any new
way of defining static or class methods.  Instead, you had to write a
*note def: e83. statement in the usual way, and pass the resulting
method to a *note staticmethod(): 30a. or *note classmethod(): 309.
function that would wrap up the function as a method of the new type.
Your code would look like this:

     class C:
        def meth (cls):
            ...

        meth = classmethod(meth)   # Rebind name to wrapped-up class method

If the method was very long, it would be easy to miss or forget the
*note classmethod(): 309. invocation after the function body.

The intention was always to add some syntax to make such definitions
more readable, but at the time of 2.2’s release a good syntax was not
obvious.  Today a good syntax `still' isn’t obvious but users are asking
for easier access to the feature; a new syntactic feature has been added
to meet this need.

The new feature is called “function decorators”.  The name comes from
the idea that *note classmethod(): 309, *note staticmethod(): 30a, and
friends are storing additional information on a function object; they’re
`decorating' functions with more details.

The notation borrows from Java and uses the ‘'@'’ character as an
indicator.  Using the new syntax, the example above would be written:

     class C:

        @classmethod
        def meth (cls):
            ...

The ‘@classmethod’ is shorthand for the ‘meth=classmethod(meth)’
assignment.  More generally, if you have the following:

     @A
     @B
     @C
     def f ():
         ...

It’s equivalent to the following pre-decorator code:

     def f(): ...
     f = A(B(C(f)))

Decorators must come on the line before a function definition, one
decorator per line, and can’t be on the same line as the def statement,
meaning that ‘@A def f(): ...’ is illegal.  You can only decorate
function definitions, either at the module level or inside a class; you
can’t decorate class definitions.

A decorator is just a function that takes the function to be decorated
as an argument and returns either the same function or some new object.
The return value of the decorator need not be callable (though it
typically is), unless further decorators will be applied to the result.
It’s easy to write your own decorators.  The following simple example
just sets an attribute on the function object:

     >>> def deco(func):
     ...    func.attr = 'decorated'
     ...    return func
     ...
     >>> @deco
     ... def f(): pass
     ...
     >>> f
     <function f at 0x402ef0d4>
     >>> f.attr
     'decorated'
     >>>

As a slightly more realistic example, the following decorator checks
that the supplied argument is an integer:

     def require_int (func):
         def wrapper (arg):
             assert isinstance(arg, int)
             return func(arg)

         return wrapper

     @require_int
     def p1 (arg):
         print arg

     @require_int
     def p2(arg):
         print arg*2

An example in PEP 318(1) contains a fancier version of this idea that
lets you both specify the required type and check the returned type.

Decorator functions can take arguments.  If arguments are supplied, your
decorator function is called with only those arguments and must return a
new decorator function; this function must take a single function and
return a function, as previously described.  In other words, ‘@A @B
@C(args)’ becomes:

     def f(): ...
     _deco = C(args)
     f = A(B(_deco(f)))

Getting this right can be slightly brain-bending, but it’s not too
difficult.

A small related change makes the ‘func_name’ attribute of functions
writable.  This attribute is used to display function names in
tracebacks, so decorators should change the name of any new function
that’s constructed and returned.

See also
........

PEP 318(2) - Decorators for Functions, Methods and Classes

     Written by Kevin D. Smith, Jim Jewett, and Skip Montanaro.  Several
     people wrote patches implementing function decorators, but the one
     that was actually checked in was patch #979728, written by Mark
     Russell.

‘https://wiki.python.org/moin/PythonDecoratorLibrary’

     This Wiki page contains several examples of decorators.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0318

   (2) https://www.python.org/dev/peps/pep-0318


File: python.info,  Node: PEP 322 Reverse Iteration,  Next: PEP 324 New subprocess Module,  Prev: PEP 318 Decorators for Functions and Methods,  Up: What’s New in Python 2 4

1.14.6 PEP 322: Reverse Iteration
---------------------------------

A new built-in function, ‘reversed(seq)’, takes a sequence and returns
an iterator that loops over the elements of the sequence in reverse
order.

     >>> for i in reversed(xrange(1,4)):
     ...    print i
     ...
     3
     2
     1

Compared to extended slicing, such as ‘range(1,4)[::-1]’, *note
reversed(): 2c6. is easier to read, runs faster, and uses substantially
less memory.

Note that *note reversed(): 2c6. only accepts sequences, not arbitrary
iterators.  If you want to reverse an iterator, first convert it to a
list with *note list(): 1f8.

     >>> input = open('/etc/passwd', 'r')
     >>> for line in reversed(list(input)):
     ...   print line
     ...
     root:*:0:0:System Administrator:/var/root:/bin/tcsh
       ...

See also
........

PEP 322(1) - Reverse Iteration

     Written and implemented by Raymond Hettinger.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0322


File: python.info,  Node: PEP 324 New subprocess Module,  Next: PEP 327 Decimal Data Type,  Prev: PEP 322 Reverse Iteration,  Up: What’s New in Python 2 4

1.14.7 PEP 324: New subprocess Module
-------------------------------------

The standard library provides a number of ways to execute a subprocess,
offering different features and different levels of complexity.
‘os.system(command)’ is easy to use, but slow (it runs a shell process
which executes the command) and dangerous (you have to be careful about
escaping the shell’s metacharacters).  The ‘popen2’ module offers
classes that can capture standard output and standard error from the
subprocess, but the naming is confusing.  The *note subprocess: f9.
module cleans this up, providing a unified interface that offers all the
features you might need.

Instead of ‘popen2’’s collection of classes, *note subprocess: f9.
contains a single class called ‘Popen’ whose constructor supports a
number of different keyword arguments.

     class Popen(args, bufsize=0, executable=None,
                 stdin=None, stdout=None, stderr=None,
                 preexec_fn=None, close_fds=False, shell=False,
                 cwd=None, env=None, universal_newlines=False,
                 startupinfo=None, creationflags=0):

`args' is commonly a sequence of strings that will be the arguments to
the program executed as the subprocess.  (If the `shell' argument is
true, `args' can be a string which will then be passed on to the shell
for interpretation, just as *note os.system(): e86. does.)

`stdin', `stdout', and `stderr' specify what the subprocess’s input,
output, and error streams will be.  You can provide a file object or a
file descriptor, or you can use the constant ‘subprocess.PIPE’ to create
a pipe between the subprocess and the parent.

The constructor has a number of handy options:

   * `close_fds' requests that all file descriptors be closed before
     running the subprocess.

   * `cwd' specifies the working directory in which the subprocess will
     be executed (defaulting to whatever the parent’s working directory
     is).

   * `env' is a dictionary specifying environment variables.

   * `preexec_fn' is a function that gets called before the child is
     started.

   * `universal_newlines' opens the child’s input and output using
     Python’s *note universal newlines: 6eb. feature.

Once you’ve created the ‘Popen’ instance, you can call its ‘wait()’
method to pause until the subprocess has exited, ‘poll()’ to check if
it’s exited without pausing, or ‘communicate(data)’ to send the string
`data' to the subprocess’s standard input.  ‘communicate(data)’ then
reads any data that the subprocess has sent to its standard output or
standard error, returning a tuple ‘(stdout_data, stderr_data)’.

‘call()’ is a shortcut that passes its arguments along to the ‘Popen’
constructor, waits for the command to complete, and returns the status
code of the subprocess.  It can serve as a safer analog to *note
os.system(): e86.:

     sts = subprocess.call(['dpkg', '-i', '/tmp/new-package.deb'])
     if sts == 0:
         # Success
         ...
     else:
         # dpkg returned an error
         ...

The command is invoked without use of the shell.  If you really do want
to use the shell, you can add ‘shell=True’ as a keyword argument and
provide a string instead of a sequence:

     sts = subprocess.call('dpkg -i /tmp/new-package.deb', shell=True)

The PEP takes various examples of shell and Python code and shows how
they’d be translated into Python code that uses *note subprocess: f9.
Reading this section of the PEP is highly recommended.

See also
........

PEP 324(1) - subprocess - New process module

     Written and implemented by Peter Åstrand, with assistance from
     Fredrik Lundh and others.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0324


File: python.info,  Node: PEP 327 Decimal Data Type,  Next: PEP 328 Multi-line Imports,  Prev: PEP 324 New subprocess Module,  Up: What’s New in Python 2 4

1.14.8 PEP 327: Decimal Data Type
---------------------------------

Python has always supported floating-point (FP) numbers, based on the
underlying C ‘double’ type, as a data type.  However, while most
programming languages provide a floating-point type, many people (even
programmers) are unaware that floating-point numbers don’t represent
certain decimal fractions accurately.  The new ‘Decimal’ type can
represent these fractions accurately, up to a user-specified precision
limit.

* Menu:

* Why is Decimal needed?::
* The Decimal type::
* The Context type::


File: python.info,  Node: Why is Decimal needed?,  Next: The Decimal type,  Up: PEP 327 Decimal Data Type

1.14.8.1 Why is Decimal needed?
...............................

The limitations arise from the representation used for floating-point
numbers.  FP numbers are made up of three components:

   * The sign, which is positive or negative.

   * The mantissa, which is a single-digit binary number followed by a
     fractional part.  For example, ‘1.01’ in base-2 notation is ‘1 +
     0/2 + 1/4’, or 1.25 in decimal notation.

   * The exponent, which tells where the decimal point is located in the
     number represented.

For example, the number 1.25 has positive sign, a mantissa value of 1.01
(in binary), and an exponent of 0 (the decimal point doesn’t need to be
shifted).  The number 5 has the same sign and mantissa, but the exponent
is 2 because the mantissa is multiplied by 4 (2 to the power of the
exponent 2); 1.25 * 4 equals 5.

Modern systems usually provide floating-point support that conforms to a
standard called IEEE 754.  C’s ‘double’ type is usually implemented as a
64-bit IEEE 754 number, which uses 52 bits of space for the mantissa.
This means that numbers can only be specified to 52 bits of precision.
If you’re trying to represent numbers whose expansion repeats endlessly,
the expansion is cut off after 52 bits.  Unfortunately, most software
needs to produce output in base 10, and common fractions in base 10 are
often repeating decimals in binary.  For example, 1.1 decimal is binary
‘1.0001100110011 ...’; .1 = 1/16 + 1/32 + 1/256 plus an infinite number
of additional terms.  IEEE 754 has to chop off that infinitely repeated
decimal after 52 digits, so the representation is slightly inaccurate.

Sometimes you can see this inaccuracy when the number is printed:

     >>> 1.1
     1.1000000000000001

The inaccuracy isn’t always visible when you print the number because
the FP-to-decimal-string conversion is provided by the C library, and
most C libraries try to produce sensible output.  Even if it’s not
displayed, however, the inaccuracy is still there and subsequent
operations can magnify the error.

For many applications this doesn’t matter.  If I’m plotting points and
displaying them on my monitor, the difference between 1.1 and
1.1000000000000001 is too small to be visible.  Reports often limit
output to a certain number of decimal places, and if you round the
number to two or three or even eight decimal places, the error is never
apparent.  However, for applications where it does matter, it’s a lot of
work to implement your own custom arithmetic routines.

Hence, the ‘Decimal’ type was created.


File: python.info,  Node: The Decimal type,  Next: The Context type,  Prev: Why is Decimal needed?,  Up: PEP 327 Decimal Data Type

1.14.8.2 The ‘Decimal’ type
...........................

A new module, *note decimal: 35, was added to Python’s standard library.
It contains two classes, ‘Decimal’ and ‘Context’.  ‘Decimal’ instances
represent numbers, and ‘Context’ instances are used to wrap up various
settings such as the precision and default rounding mode.

‘Decimal’ instances are immutable, like regular Python integers and FP
numbers; once it’s been created, you can’t change the value an instance
represents.  ‘Decimal’ instances can be created from integers or
strings:

     >>> import decimal
     >>> decimal.Decimal(1972)
     Decimal("1972")
     >>> decimal.Decimal("1.1")
     Decimal("1.1")

You can also provide tuples containing the sign, the mantissa
represented as a tuple of decimal digits, and the exponent:

     >>> decimal.Decimal((1, (1, 4, 7, 5), -2))
     Decimal("-14.75")

Cautionary note: the sign bit is a Boolean value, so 0 is positive and 1
is negative.

Converting from floating-point numbers poses a bit of a problem: should
the FP number representing 1.1 turn into the decimal number for exactly
1.1, or for 1.1 plus whatever inaccuracies are introduced?  The decision
was to dodge the issue and leave such a conversion out of the API.
Instead, you should convert the floating-point number into a string
using the desired precision and pass the string to the ‘Decimal’
constructor:

     >>> f = 1.1
     >>> decimal.Decimal(str(f))
     Decimal("1.1")
     >>> decimal.Decimal('%.12f' % f)
     Decimal("1.100000000000")

Once you have ‘Decimal’ instances, you can perform the usual
mathematical operations on them.  One limitation: exponentiation
requires an integer exponent:

     >>> a = decimal.Decimal('35.72')
     >>> b = decimal.Decimal('1.73')
     >>> a+b
     Decimal("37.45")
     >>> a-b
     Decimal("33.99")
     >>> a*b
     Decimal("61.7956")
     >>> a/b
     Decimal("20.64739884393063583815028902")
     >>> a ** 2
     Decimal("1275.9184")
     >>> a**b
     Traceback (most recent call last):
       ...
     decimal.InvalidOperation: x ** (non-integer)

You can combine ‘Decimal’ instances with integers, but not with
floating-point numbers:

     >>> a + 4
     Decimal("39.72")
     >>> a + 4.5
     Traceback (most recent call last):
       ...
     TypeError: You can interact Decimal only with int, long or Decimal data types.
     >>>

‘Decimal’ numbers can be used with the *note math: b1. and *note cmath:
18. modules, but note that they’ll be immediately converted to
floating-point numbers before the operation is performed, resulting in a
possible loss of precision and accuracy.  You’ll also get back a regular
floating-point number and not a ‘Decimal’.

     >>> import math, cmath
     >>> d = decimal.Decimal('123456789012.345')
     >>> math.sqrt(d)
     351364.18288201344
     >>> cmath.sqrt(-d)
     351364.18288201344j

‘Decimal’ instances have a ‘sqrt()’ method that returns a ‘Decimal’, but
if you need other things such as trigonometric functions you’ll have to
implement them.

     >>> d.sqrt()
     Decimal("351364.1828820134592177245001")


File: python.info,  Node: The Context type,  Prev: The Decimal type,  Up: PEP 327 Decimal Data Type

1.14.8.3 The ‘Context’ type
...........................

Instances of the ‘Context’ class encapsulate several settings for
decimal operations:

   * ‘prec’ is the precision, the number of decimal places.

   * ‘rounding’ specifies the rounding mode.  The *note decimal: 35.
     module has constants for the various possibilities: ‘ROUND_DOWN’,
     ‘ROUND_CEILING’, ‘ROUND_HALF_EVEN’, and various others.

   * ‘traps’ is a dictionary specifying what happens on encountering
     certain error conditions: either an exception is raised or a value
     is returned.  Some examples of error conditions are division by
     zero, loss of precision, and overflow.

There’s a thread-local default context available by calling
‘getcontext()’; you can change the properties of this context to alter
the default precision, rounding, or trap handling.  The following
example shows the effect of changing the precision of the default
context:

     >>> decimal.getcontext().prec
     28
     >>> decimal.Decimal(1) / decimal.Decimal(7)
     Decimal("0.1428571428571428571428571429")
     >>> decimal.getcontext().prec = 9
     >>> decimal.Decimal(1) / decimal.Decimal(7)
     Decimal("0.142857143")

The default action for error conditions is selectable; the module can
either return a special value such as infinity or not-a-number, or
exceptions can be raised:

     >>> decimal.Decimal(1) / decimal.Decimal(0)
     Traceback (most recent call last):
       ...
     decimal.DivisionByZero: x / 0
     >>> decimal.getcontext().traps[decimal.DivisionByZero] = False
     >>> decimal.Decimal(1) / decimal.Decimal(0)
     Decimal("Infinity")
     >>>

The ‘Context’ instance also has various methods for formatting numbers
such as ‘to_eng_string()’ and ‘to_sci_string()’.

For more information, see the documentation for the *note decimal: 35.
module, which includes a quick-start tutorial and a reference.

See also
........

PEP 327(1) - Decimal Data Type

     Written by Facundo Batista and implemented by Facundo Batista, Eric
     Price, Raymond Hettinger, Aahz, and Tim Peters.

‘http://www.lahey.com/float.htm’

     The article uses Fortran code to illustrate many of the problems
     that floating-point inaccuracy can cause.

‘http://speleotrove.com/decimal/’

     A description of a decimal-based representation.  This
     representation is being proposed as a standard, and underlies the
     new Python decimal type.  Much of this material was written by Mike
     Cowlishaw, designer of the Rexx language.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0327


File: python.info,  Node: PEP 328 Multi-line Imports,  Next: PEP 331 Locale-Independent Float/String Conversions,  Prev: PEP 327 Decimal Data Type,  Up: What’s New in Python 2 4

1.14.9 PEP 328: Multi-line Imports
----------------------------------

One language change is a small syntactic tweak aimed at making it easier
to import many names from a module.  In a ‘from module import names’
statement, `names' is a sequence of names separated by commas.  If the
sequence is very long, you can either write multiple imports from the
same module, or you can use backslashes to escape the line endings like
this:

     from SimpleXMLRPCServer import SimpleXMLRPCServer,\
                 SimpleXMLRPCRequestHandler,\
                 CGIXMLRPCRequestHandler,\
                 resolve_dotted_attribute

The syntactic change in Python 2.4 simply allows putting the names
within parentheses.  Python ignores newlines within a parenthesized
expression, so the backslashes are no longer needed:

     from SimpleXMLRPCServer import (SimpleXMLRPCServer,
                                     SimpleXMLRPCRequestHandler,
                                     CGIXMLRPCRequestHandler,
                                     resolve_dotted_attribute)

The PEP also proposes that all *note import: ce7. statements be absolute
imports, with a leading ‘.’ character to indicate a relative import.
This part of the PEP was not implemented for Python 2.4, but was
completed for Python 2.5.

See also
........

PEP 328(1) - Imports: Multi-Line and Absolute/Relative

     Written by Aahz.  Multi-line imports were implemented by Dima
     Dorfman.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0328


File: python.info,  Node: PEP 331 Locale-Independent Float/String Conversions,  Next: Other Language Changes<13>,  Prev: PEP 328 Multi-line Imports,  Up: What’s New in Python 2 4

1.14.10 PEP 331: Locale-Independent Float/String Conversions
------------------------------------------------------------

The *note locale: a9. modules lets Python software select various
conversions and display conventions that are localized to a particular
country or language.  However, the module was careful to not change the
numeric locale because various functions in Python’s implementation
required that the numeric locale remain set to the ‘'C'’ locale.  Often
this was because the code was using the C library’s ‘atof()’ function.

Not setting the numeric locale caused trouble for extensions that used
third-party C libraries, however, because they wouldn’t have the correct
locale set.  The motivating example was GTK+, whose user interface
widgets weren’t displaying numbers in the current locale.

The solution described in the PEP is to add three new functions to the
Python API that perform ASCII-only conversions, ignoring the locale
setting:

   * ‘PyOS_ascii_strtod(str, ptr)’ and ‘PyOS_ascii_atof(str, ptr)’ both
     convert a string to a C ‘double’.

   * ‘PyOS_ascii_formatd(buffer, buf_len, format, d)’ converts a
     ‘double’ to an ASCII string.

The code for these functions came from the GLib library
(‘https://developer.gnome.org/glib/stable/’), whose developers kindly
relicensed the relevant functions and donated them to the Python
Software Foundation.  The *note locale: a9. module can now change the
numeric locale, letting extensions such as GTK+ produce the correct
results.

See also
........

PEP 331(1) - Locale-Independent Float/String Conversions

     Written by Christian R. Reis, and implemented by Gustavo Carneiro.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0331


File: python.info,  Node: Other Language Changes<13>,  Next: New Improved and Deprecated Modules<3>,  Prev: PEP 331 Locale-Independent Float/String Conversions,  Up: What’s New in Python 2 4

1.14.11 Other Language Changes
------------------------------

Here are all of the changes that Python 2.4 makes to the core Python
language.

   * Decorators for functions and methods were added ( PEP 318(1)).

   * Built-in *note set(): 1f6. and *note frozenset(): 1f7. types were
     added ( PEP 218(2)).  Other new built-ins include the
     ‘reversed(seq)’ function ( PEP 322(3)).

   * Generator expressions were added ( PEP 289(4)).

   * Certain numeric expressions no longer return values restricted to
     32 or 64 bits ( PEP 237(5)).

   * You can now put parentheses around the list of names in a ‘from
     module import names’ statement ( PEP 328(6)).

   * The *note dict.update(): e8e. method now accepts the same argument
     forms as the *note dict: 164. constructor.  This includes any
     mapping, any iterable of key/value pairs, and keyword arguments.
     (Contributed by Raymond Hettinger.)

   * The string methods ‘ljust()’, ‘rjust()’, and ‘center()’ now take an
     optional argument for specifying a fill character other than a
     space.  (Contributed by Raymond Hettinger.)

   * Strings also gained an ‘rsplit()’ method that works like the
     ‘split()’ method but splits from the end of the string.
     (Contributed by Sean Reifschneider.)

          >>> 'www.python.org'.split('.', 1)
          ['www', 'python.org']
          'www.python.org'.rsplit('.', 1)
          ['www.python', 'org']

   * Three keyword parameters, `cmp', `key', and `reverse', were added
     to the ‘sort()’ method of lists.  These parameters make some common
     usages of ‘sort()’ simpler.  All of these parameters are optional.

     For the `cmp' parameter, the value should be a comparison function
     that takes two parameters and returns -1, 0, or +1 depending on how
     the parameters compare.  This function will then be used to sort
     the list.  Previously this was the only parameter that could be
     provided to ‘sort()’.

     `key' should be a single-parameter function that takes a list
     element and returns a comparison key for the element.  The list is
     then sorted using the comparison keys.  The following example sorts
     a list case-insensitively:

          >>> L = ['A', 'b', 'c', 'D']
          >>> L.sort()                 # Case-sensitive sort
          >>> L
          ['A', 'D', 'b', 'c']
          >>> # Using 'key' parameter to sort list
          >>> L.sort(key=lambda x: x.lower())
          >>> L
          ['A', 'b', 'c', 'D']
          >>> # Old-fashioned way
          >>> L.sort(cmp=lambda x,y: cmp(x.lower(), y.lower()))
          >>> L
          ['A', 'b', 'c', 'D']

     The last example, which uses the `cmp' parameter, is the old way to
     perform a case-insensitive sort.  It works but is slower than using
     a `key' parameter.  Using `key' calls ‘lower()’ method once for
     each element in the list while using `cmp' will call it twice for
     each comparison, so using `key' saves on invocations of the
     ‘lower()’ method.

     For simple key functions and comparison functions, it is often
     possible to avoid a *note lambda: cf9. expression by using an
     unbound method instead.  For example, the above case-insensitive
     sort is best written as:

          >>> L.sort(key=str.lower)
          >>> L
          ['A', 'b', 'c', 'D']

     Finally, the `reverse' parameter takes a Boolean value.  If the
     value is true, the list will be sorted into reverse order.  Instead
     of ‘L.sort(); L.reverse()’, you can now write
     ‘L.sort(reverse=True)’.

     The results of sorting are now guaranteed to be stable.  This means
     that two entries with equal keys will be returned in the same order
     as they were input.  For example, you can sort a list of people by
     name, and then sort the list by age, resulting in a list sorted by
     age where people with the same age are in name-sorted order.

     (All changes to ‘sort()’ contributed by Raymond Hettinger.)

   * There is a new built-in function ‘sorted(iterable)’ that works like
     the in-place *note list.sort(): 548. method but can be used in
     expressions.  The differences are:

   * the input may be any iterable;

   * a newly formed copy is sorted, leaving the original intact; and

   * the expression returns the new sorted copy

          >>> L = [9,7,8,3,2,4,1,6,5]
          >>> [10+i for i in sorted(L)]       # usable in a list comprehension
          [11, 12, 13, 14, 15, 16, 17, 18, 19]
          >>> L                               # original is left unchanged
          [9,7,8,3,2,4,1,6,5]
          >>> sorted('Monty Python')          # any iterable may be an input
          [' ', 'M', 'P', 'h', 'n', 'n', 'o', 'o', 't', 't', 'y', 'y']

          >>> # List the contents of a dict sorted by key values
          >>> colormap = dict(red=1, blue=2, green=3, black=4, yellow=5)
          >>> for k, v in sorted(colormap.iteritems()):
          ...     print k, v
          ...
          black 4
          blue 2
          green 3
          red 1
          yellow 5

     (Contributed by Raymond Hettinger.)

   * Integer operations will no longer trigger an ‘OverflowWarning’.
     The ‘OverflowWarning’ warning will disappear in Python 2.5.

   * The interpreter gained a new switch, *note -m: 443, that takes a
     name, searches for the corresponding module on ‘sys.path’, and runs
     the module as a script.  For example, you can now run the Python
     profiler with ‘python -m profile’.  (Contributed by Nick Coghlan.)

   * The ‘eval(expr, globals, locals)’ and ‘execfile(filename, globals,
     locals)’ functions and the ‘exec’ statement now accept any mapping
     type for the `locals' parameter.  Previously this had to be a
     regular Python dictionary.  (Contributed by Raymond Hettinger.)

   * The *note zip(): cfc. built-in function and ‘itertools.izip()’ now
     return an empty list if called with no arguments.  Previously they
     raised a *note TypeError: 1fe. exception.  This makes them more
     suitable for use with variable length argument lists:

          >>> def transpose(array):
          ...    return zip(*array)
          ...
          >>> transpose([(1,2,3), (4,5,6)])
          [(1, 4), (2, 5), (3, 6)]
          >>> transpose([])
          []

     (Contributed by Raymond Hettinger.)

   * Encountering a failure while importing a module no longer leaves a
     partially-initialized module object in ‘sys.modules’.  The
     incomplete module object left behind would fool further imports of
     the same module into succeeding, leading to confusing errors.
     (Fixed by Tim Peters.)

   * *note None: 203. is now a constant; code that binds a new value to
     the name ‘None’ is now a syntax error.  (Contributed by Raymond
     Hettinger.)

* Menu:

* Optimizations: Optimizations<12>.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0318

   (2) https://www.python.org/dev/peps/pep-0218

   (3) https://www.python.org/dev/peps/pep-0322

   (4) https://www.python.org/dev/peps/pep-0289

   (5) https://www.python.org/dev/peps/pep-0237

   (6) https://www.python.org/dev/peps/pep-0328


File: python.info,  Node: Optimizations<12>,  Up: Other Language Changes<13>

1.14.11.1 Optimizations
.......................

   * The inner loops for list and tuple slicing were optimized and now
     run about one-third faster.  The inner loops for dictionaries were
     also optimized, resulting in performance boosts for ‘keys()’,
     ‘values()’, ‘items()’, ‘iterkeys()’, ‘itervalues()’, and
     ‘iteritems()’.  (Contributed by Raymond Hettinger.)

   * The machinery for growing and shrinking lists was optimized for
     speed and for space efficiency.  Appending and popping from lists
     now runs faster due to more efficient code paths and less frequent
     use of the underlying system ‘realloc()’.  List comprehensions also
     benefit.  ‘list.extend()’ was also optimized and no longer converts
     its argument into a temporary list before extending the base list.
     (Contributed by Raymond Hettinger.)

   * *note list(): 1f8, *note tuple(): 1a2, *note map(): cf7, *note
     filter(): cf8, and *note zip(): cfc. now run several times faster
     with non-sequence arguments that supply a *note __len__(): e90.
     method.  (Contributed by Raymond Hettinger.)

   * The methods ‘list.__getitem__()’, ‘dict.__getitem__()’, and
     ‘dict.__contains__()’ are now implemented as ‘method_descriptor’
     objects rather than ‘wrapper_descriptor’ objects.  This form of
     access doubles their performance and makes them more suitable for
     use as arguments to functionals: ‘map(mydict.__getitem__,
     keylist)’.  (Contributed by Raymond Hettinger.)

   * Added a new opcode, ‘LIST_APPEND’, that simplifies the generated
     bytecode for list comprehensions and speeds them up by about a
     third.  (Contributed by Raymond Hettinger.)

   * The peephole bytecode optimizer has been improved to produce
     shorter, faster bytecode; remarkably, the resulting bytecode is
     more readable.  (Enhanced by Raymond Hettinger.)

   * String concatenations in statements of the form ‘s = s + "abc"’ and
     ‘s += "abc"’ are now performed more efficiently in certain
     circumstances.  This optimization won’t be present in other Python
     implementations such as Jython, so you shouldn’t rely on it; using
     the ‘join()’ method of strings is still recommended when you want
     to efficiently glue a large number of strings together.
     (Contributed by Armin Rigo.)

The net result of the 2.4 optimizations is that Python 2.4 runs the
pystone benchmark around 5% faster than Python 2.3 and 35% faster than
Python 2.2.  (pystone is not a particularly good benchmark, but it’s the
most commonly used measurement of Python’s performance.  Your own
applications may show greater or smaller benefits from Python 2.4.)


File: python.info,  Node: New Improved and Deprecated Modules<3>,  Next: Build and C API Changes<11>,  Prev: Other Language Changes<13>,  Up: What’s New in Python 2 4

1.14.12 New, Improved, and Deprecated Modules
---------------------------------------------

As usual, Python’s standard library received a number of enhancements
and bug fixes.  Here’s a partial list of the most notable changes,
sorted alphabetically by module name.  Consult the ‘Misc/NEWS’ file in
the source tree for a more complete list of changes, or look through the
CVS logs for all the details.

   * The *note asyncore: a. module’s ‘loop()’ function now has a `count'
     parameter that lets you perform a limited number of passes through
     the polling loop.  The default is still to loop forever.

   * The *note base64: d. module now has more complete RFC 3548(1)
     support for Base64, Base32, and Base16 encoding and decoding,
     including optional case folding and optional alternative alphabets.
     (Contributed by Barry Warsaw.)

   * The *note bisect: 11. module now has an underlying C implementation
     for improved performance.  (Contributed by Dmitry Vasiliev.)

   * The CJKCodecs collections of East Asian codecs, maintained by
     Hye-Shik Chang, was integrated into 2.4.  The new encodings are:

   * Chinese (PRC): gb2312, gbk, gb18030, big5hkscs, hz

   * Chinese (ROC): big5, cp950

   * 
     Japanese: cp932, euc-jis-2004, euc-jp, euc-jisx0213, iso-2022-jp,

          iso-2022-jp-1, iso-2022-jp-2, iso-2022-jp-3, iso-2022-jp-ext,
          iso-2022-jp-2004, shift-jis, shift-jisx0213, shift-jis-2004

   * Korean: cp949, euc-kr, johab, iso-2022-kr

   * Some other new encodings were added: HP Roman8, ISO_8859-11,
     ISO_8859-16, PCTP-154, and TIS-620.

   * The UTF-8 and UTF-16 codecs now cope better with receiving partial
     input.  Previously the ‘StreamReader’ class would try to read more
     data, making it impossible to resume decoding from the stream.  The
     ‘read()’ method will now return as much data as it can and future
     calls will resume decoding where previous ones left off.
     (Implemented by Walter Dörwald.)

   * There is a new *note collections: 1d. module for various
     specialized collection datatypes.  Currently it contains just one
     type, ‘deque’, a double-ended queue that supports efficiently
     adding and removing elements from either end:

          >>> from collections import deque
          >>> d = deque('ghi')        # make a new deque with three items
          >>> d.append('j')           # add a new entry to the right side
          >>> d.appendleft('f')       # add a new entry to the left side
          >>> d                       # show the representation of the deque
          deque(['f', 'g', 'h', 'i', 'j'])
          >>> d.pop()                 # return and remove the rightmost item
          'j'
          >>> d.popleft()             # return and remove the leftmost item
          'f'
          >>> list(d)                 # list the contents of the deque
          ['g', 'h', 'i']
          >>> 'h' in d                # search the deque
          True

     Several modules, such as the ‘Queue’ and *note threading: 10b.
     modules, now take advantage of *note collections.deque: 62b. for
     improved performance.  (Contributed by Raymond Hettinger.)

   * The ‘ConfigParser’ classes have been enhanced slightly.  The
     ‘read()’ method now returns a list of the files that were
     successfully parsed, and the *note set(): 1f6. method raises *note
     TypeError: 1fe. if passed a `value' argument that isn’t a string.
     (Contributed by John Belmonte and David Goodger.)

   * The *note curses: 2b. module now supports the ncurses extension
     ‘use_default_colors()’.  On platforms where the terminal supports
     transparency, this makes it possible to use a transparent
     background.  (Contributed by Jörg Lehmann.)

   * The *note difflib: 36. module now includes an ‘HtmlDiff’ class that
     creates an HTML table showing a side by side comparison of two
     versions of a text.  (Contributed by Dan Gass.)

   * The *note email: 67. package was updated to version 3.0, which
     dropped various deprecated APIs and removes support for Python
     versions earlier than 2.3.  The 3.0 version of the package uses a
     new incremental parser for MIME messages, available in the
     ‘email.FeedParser’ module.  The new parser doesn’t require reading
     the entire message into memory, and doesn’t raise exceptions if a
     message is malformed; instead it records any problems in the
     ‘defect’ attribute of the message.  (Developed by Anthony Baxter,
     Barry Warsaw, Thomas Wouters, and others.)

   * The *note heapq: 8d. module has been converted to C. The resulting
     tenfold improvement in speed makes the module suitable for handling
     high volumes of data.  In addition, the module has two new
     functions ‘nlargest()’ and ‘nsmallest()’ that use heaps to find the
     N largest or smallest values in a dataset without the expense of a
     full sort.  (Contributed by Raymond Hettinger.)

   * The ‘httplib’ module now contains constants for HTTP status codes
     defined in various HTTP-related RFC documents.  Constants have
     names such as ‘OK’, ‘CREATED’, ‘CONTINUE’, and ‘MOVED_PERMANENTLY’;
     use pydoc to get a full list.  (Contributed by Andrew Eland.)

   * The *note imaplib: 97. module now supports IMAP’s THREAD command
     (contributed by Yves Dionne) and new ‘deleteacl()’ and ‘myrights()’
     methods (contributed by Arnaud Mazin).

   * The *note itertools: a3. module gained a ‘groupby(iterable[,
     *func*])’ function.  `iterable' is something that can be iterated
     over to return a stream of elements, and the optional `func'
     parameter is a function that takes an element and returns a key
     value; if omitted, the key is simply the element itself.
     ‘groupby()’ then groups the elements into subsequences which have
     matching values of the key, and returns a series of 2-tuples
     containing the key value and an iterator over the subsequence.

     Here’s an example to make this clearer.  The `key' function simply
     returns whether a number is even or odd, so the result of
     ‘groupby()’ is to return consecutive runs of odd or even numbers.

          >>> import itertools
          >>> L = [2, 4, 6, 7, 8, 9, 11, 12, 14]
          >>> for key_val, it in itertools.groupby(L, lambda x: x % 2):
          ...    print key_val, list(it)
          ...
          0 [2, 4, 6]
          1 [7]
          0 [8]
          1 [9, 11]
          0 [12, 14]
          >>>

     ‘groupby()’ is typically used with sorted input.  The logic for
     ‘groupby()’ is similar to the Unix ‘uniq’ filter which makes it
     handy for eliminating, counting, or identifying duplicate elements:

          >>> word = 'abracadabra'
          >>> letters = sorted(word)   # Turn string into a sorted list of letters
          >>> letters
          ['a', 'a', 'a', 'a', 'a', 'b', 'b', 'c', 'd', 'r', 'r']
          >>> for k, g in itertools.groupby(letters):
          ...    print k, list(g)
          ...
          a ['a', 'a', 'a', 'a', 'a']
          b ['b', 'b']
          c ['c']
          d ['d']
          r ['r', 'r']
          >>> # List unique letters
          >>> [k for k, g in groupby(letters)]
          ['a', 'b', 'c', 'd', 'r']
          >>> # Count letter occurrences
          >>> [(k, len(list(g))) for k, g in groupby(letters)]
          [('a', 5), ('b', 2), ('c', 1), ('d', 1), ('r', 2)]

     (Contributed by Hye-Shik Chang.)

   * *note itertools: a3. also gained a function named ‘tee(iterator,
     N)’ that returns `N' independent iterators that replicate
     `iterator'.  If `N' is omitted, the default is 2.

          >>> L = [1,2,3]
          >>> i1, i2 = itertools.tee(L)
          >>> i1,i2
          (<itertools.tee object at 0x402c2080>, <itertools.tee object at 0x402c2090>)
          >>> list(i1)               # Run the first iterator to exhaustion
          [1, 2, 3]
          >>> list(i2)               # Run the second iterator to exhaustion
          [1, 2, 3]

     Note that ‘tee()’ has to keep copies of the values returned by the
     iterator; in the worst case, it may need to keep all of them.  This
     should therefore be used carefully if the leading iterator can run
     far ahead of the trailing iterator in a long stream of inputs.  If
     the separation is large, then you might as well use *note list():
     1f8. instead.  When the iterators track closely with one another,
     ‘tee()’ is ideal.  Possible applications include bookmarking,
     windowing, or lookahead iterators.  (Contributed by Raymond
     Hettinger.)

   * A number of functions were added to the *note locale: a9. module,
     such as ‘bind_textdomain_codeset()’ to specify a particular
     encoding and a family of ‘l*gettext()’ functions that return
     messages in the chosen encoding.  (Contributed by Gustavo
     Niemeyer.)

   * Some keyword arguments were added to the *note logging: aa.
     package’s ‘basicConfig()’ function to simplify log configuration.
     The default behavior is to log messages to standard error, but
     various keyword arguments can be specified to log to a particular
     file, change the logging format, or set the logging level.  For
     example:

          import logging
          logging.basicConfig(filename='/var/log/application.log',
              level=0,  # Log all messages
              format='%(levelname):%(process):%(thread):%(message)')

     Other additions to the *note logging: aa. package include a
     ‘log(level, msg)’ convenience method, as well as a
     ‘TimedRotatingFileHandler’ class that rotates its log files at a
     timed interval.  The module already had ‘RotatingFileHandler’,
     which rotated logs once the file exceeded a certain size.  Both
     classes derive from a new ‘BaseRotatingHandler’ class that can be
     used to implement other rotating handlers.

     (Changes implemented by Vinay Sajip.)

   * The *note marshal: b0. module now shares interned strings on
     unpacking a data structure.  This may shrink the size of certain
     pickle strings, but the primary effect is to make ‘.pyc’ files
     significantly smaller.  (Contributed by Martin von Löwis.)

   * The *note nntplib: c0. module’s ‘NNTP’ class gained ‘description()’
     and ‘descriptions()’ methods to retrieve newsgroup descriptions for
     a single group or for a range of groups.  (Contributed by Jürgen A.
     Erhard.)

   * Two new functions were added to the *note operator: c2. module,
     ‘attrgetter(attr)’ and ‘itemgetter(index)’.  Both functions return
     callables that take a single argument and return the corresponding
     attribute or item; these callables make excellent data extractors
     when used with *note map(): cf7. or *note sorted(): 547.  For
     example:

          >>> L = [('c', 2), ('d', 1), ('a', 4), ('b', 3)]
          >>> map(operator.itemgetter(0), L)
          ['c', 'd', 'a', 'b']
          >>> map(operator.itemgetter(1), L)
          [2, 1, 4, 3]
          >>> sorted(L, key=operator.itemgetter(1)) # Sort list by second tuple item
          [('d', 1), ('c', 2), ('b', 3), ('a', 4)]

     (Contributed by Raymond Hettinger.)

   * The *note optparse: c3. module was updated in various ways.  The
     module now passes its messages through *note gettext.gettext():
     e92, making it possible to internationalize Optik’s help and error
     messages.  Help messages for options can now include the string
     ‘'%default'’, which will be replaced by the option’s default value.
     (Contributed by Greg Ward.)

   * The long-term plan is to deprecate the ‘rfc822’ module in some
     future Python release in favor of the *note email: 67. package.  To
     this end, the ‘email.Utils.formatdate()’ function has been changed
     to make it usable as a replacement for ‘rfc822.formatdate()’.  You
     may want to write new e-mail processing code with this in mind.
     (Change implemented by Anthony Baxter.)

   * A new ‘urandom(n)’ function was added to the *note os: c4. module,
     returning a string containing `n' bytes of random data.  This
     function provides access to platform-specific sources of randomness
     such as ‘/dev/urandom’ on Linux or the Windows CryptoAPI.
     (Contributed by Trevor Perrin.)

   * Another new function: ‘os.path.lexists(path)’ returns true if the
     file specified by `path' exists, whether or not it’s a symbolic
     link.  This differs from the existing ‘os.path.exists(path)’
     function, which returns false if `path' is a symlink that points to
     a destination that doesn’t exist.  (Contributed by Beni
     Cherniavsky.)

   * A new ‘getsid()’ function was added to the *note posix: d1. module
     that underlies the *note os: c4. module.  (Contributed by J.
     Raynor.)

   * The *note poplib: d0. module now supports POP over SSL.
     (Contributed by Hector Urtubia.)

   * The *note profile: d3. module can now profile C extension
     functions.  (Contributed by Nick Bastin.)

   * The *note random: dc. module has a new method called
     ‘getrandbits(N)’ that returns a long integer `N' bits in length.
     The existing ‘randrange()’ method now uses ‘getrandbits()’ where
     appropriate, making generation of arbitrarily large random numbers
     more efficient.  (Contributed by Raymond Hettinger.)

   * The regular expression language accepted by the *note re: dd.
     module was extended with simple conditional expressions, written as
     ‘(?(group)A|B)’.  `group' is either a numeric group ID or a group
     name defined with ‘(?P<group>...)’ earlier in the expression.  If
     the specified group matched, the regular expression pattern `A'
     will be tested against the string; if the group didn’t match, the
     pattern `B' will be used instead.  (Contributed by Gustavo
     Niemeyer.)

   * The *note re: dd. module is also no longer recursive, thanks to a
     massive amount of work by Gustavo Niemeyer.  In a recursive regular
     expression engine, certain patterns result in a large amount of C
     stack space being consumed, and it was possible to overflow the
     stack.  For example, if you matched a 30000-byte string of ‘a’
     characters against the expression ‘(a|b)+’, one stack frame was
     consumed per character.  Python 2.3 tried to check for stack
     overflow and raise a *note RuntimeError: 3dc. exception, but
     certain patterns could sidestep the checking and if you were
     unlucky Python could segfault.  Python 2.4’s regular expression
     engine can match this pattern without problems.

   * The *note signal: ea. module now performs tighter error-checking on
     the parameters to the *note signal.signal(): b58. function.  For
     example, you can’t set a handler on the ‘SIGKILL’ signal; previous
     versions of Python would quietly accept this, but 2.4 will raise a
     *note RuntimeError: 3dc. exception.

   * Two new functions were added to the *note socket: ef. module.
     ‘socketpair()’ returns a pair of connected sockets and
     ‘getservbyport(port)’ looks up the service name for a given port
     number.  (Contributed by Dave Cole and Barry Warsaw.)

   * The ‘sys.exitfunc()’ function has been deprecated.  Code should be
     using the existing *note atexit: b. module, which correctly handles
     calling multiple exit functions.  Eventually ‘sys.exitfunc()’ will
     become a purely internal interface, accessed only by *note atexit:
     b.

   * The *note tarfile: 101. module now generates GNU-format tar files
     by default.  (Contributed by Lars Gustäbel.)

   * The *note threading: 10b. module now has an elegantly simple way to
     support thread-local data.  The module contains a ‘local’ class
     whose attribute values are local to different threads.

          import threading

          data = threading.local()
          data.number = 42
          data.url = ('www.python.org', 80)

     Other threads can assign and retrieve their own values for the
     ‘number’ and ‘url’ attributes.  You can subclass ‘local’ to
     initialize attributes or to add methods.  (Contributed by Jim
     Fulton.)

   * The *note timeit: 10d. module now automatically disables periodic
     garbage collection during the timing loop.  This change makes
     consecutive timings more comparable.  (Contributed by Raymond
     Hettinger.)

   * The *note weakref: 131. module now supports a wider variety of
     objects including Python functions, class instances, sets,
     frozensets, deques, arrays, files, sockets, and regular expression
     pattern objects.  (Contributed by Raymond Hettinger.)

   * The ‘xmlrpclib’ module now supports a multi-call extension for
     transmitting multiple XML-RPC calls in a single HTTP operation.
     (Contributed by Brian Quinlan.)

   * The ‘mpz’, ‘rotor’, and ‘xreadlines’ modules have been removed.

* Menu:

* cookielib::
* doctest: doctest<3>.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3548.html


File: python.info,  Node: cookielib,  Next: doctest<3>,  Up: New Improved and Deprecated Modules<3>

1.14.12.1 cookielib
...................

The ‘cookielib’ library supports client-side handling for HTTP cookies,
mirroring the ‘Cookie’ module’s server-side cookie support.  Cookies are
stored in cookie jars; the library transparently stores cookies offered
by the web server in the cookie jar, and fetches the cookie from the jar
when connecting to the server.  As in web browsers, policy objects
control whether cookies are accepted or not.

In order to store cookies across sessions, two implementations of cookie
jars are provided: one that stores cookies in the Netscape format so
applications can use the Mozilla or Lynx cookie files, and one that
stores cookies in the same format as the Perl libwww library.

‘urllib2’ has been changed to interact with ‘cookielib’:
‘HTTPCookieProcessor’ manages a cookie jar that is used when accessing
URLs.

This module was contributed by John J. Lee.


File: python.info,  Node: doctest<3>,  Prev: cookielib,  Up: New Improved and Deprecated Modules<3>

1.14.12.2 doctest
.................

The *note doctest: 66. module underwent considerable refactoring thanks
to Edward Loper and Tim Peters.  Testing can still be as simple as
running *note doctest.testmod(): e95, but the refactorings allow
customizing the module’s operation in various ways

The new ‘DocTestFinder’ class extracts the tests from a given object’s
docstrings:

     def f (x, y):
         """>>> f(2,2)
     4
     >>> f(3,2)
     6
         """
         return x*y

     finder = doctest.DocTestFinder()

     # Get list of DocTest instances
     tests = finder.find(f)

The new ‘DocTestRunner’ class then runs individual tests and can produce
a summary of the results:

     runner = doctest.DocTestRunner()
     for t in tests:
         tried, failed = runner.run(t)

     runner.summarize(verbose=1)

The above example produces the following output:

     1 items passed all tests:
        2 tests in f
     2 tests in 1 items.
     2 passed and 0 failed.
     Test passed.

‘DocTestRunner’ uses an instance of the ‘OutputChecker’ class to compare
the expected output with the actual output.  This class takes a number
of different flags that customize its behaviour; ambitious users can
also write a completely new subclass of ‘OutputChecker’.

The default output checker provides a number of handy features.  For
example, with the *note doctest.ELLIPSIS: e96. option flag, an ellipsis
(‘...’) in the expected output matches any substring, making it easier
to accommodate outputs that vary in minor ways:

     def o (n):
         """>>> o(1)
     <__main__.C instance at 0x...>
     >>>
     """

Another special string, ‘<BLANKLINE>’, matches a blank line:

     def p (n):
         """>>> p(1)
     <BLANKLINE>
     >>>
     """

Another new capability is producing a diff-style display of the output
by specifying the *note doctest.REPORT_UDIFF: e97. (unified diffs),
*note doctest.REPORT_CDIFF: e98. (context diffs), or *note
doctest.REPORT_NDIFF: e99. (delta-style) option flags.  For example:

     def g (n):
         """>>> g(4)
     here
     is
     a
     lengthy
     >>>"""
         L = 'here is a rather lengthy list of words'.split()
         for word in L[:n]:
             print word

Running the above function’s tests with *note doctest.REPORT_UDIFF: e97.
specified, you get the following output:

     **********************************************************************
     File "t.py", line 15, in g
     Failed example:
         g(4)
     Differences (unified diff with -expected +actual):
         @@ -2,3 +2,3 @@
          is
          a
         -lengthy
         +rather
     **********************************************************************


File: python.info,  Node: Build and C API Changes<11>,  Next: Porting to Python 2 4,  Prev: New Improved and Deprecated Modules<3>,  Up: What’s New in Python 2 4

1.14.13 Build and C API Changes
-------------------------------

Some of the changes to Python’s build process and to the C API are:

   * Three new convenience macros were added for common return values
     from extension functions: *note Py_RETURN_NONE: e9b, *note
     Py_RETURN_TRUE: e9c, and *note Py_RETURN_FALSE: e9d.  (Contributed
     by Brett Cannon.)

   * Another new macro, ‘Py_CLEAR(obj)’, decreases the reference count
     of `obj' and sets `obj' to the null pointer.  (Contributed by Jim
     Fulton.)

   * A new function, ‘PyTuple_Pack(N, obj1, obj2, ..., objN)’,
     constructs tuples from a variable length argument list of Python
     objects.  (Contributed by Raymond Hettinger.)

   * A new function, ‘PyDict_Contains(d, k)’, implements fast dictionary
     lookups without masking exceptions raised during the look-up
     process.  (Contributed by Raymond Hettinger.)

   * The ‘Py_IS_NAN(X)’ macro returns 1 if its float or double argument
     `X' is a NaN. (Contributed by Tim Peters.)

   * C code can avoid unnecessary locking by using the new *note
     PyEval_ThreadsInitialized(): 20d. function to tell if any thread
     operations have been performed.  If this function returns false, no
     lock operations are needed.  (Contributed by Nick Coghlan.)

   * A new function, *note PyArg_VaParseTupleAndKeywords(): e9e, is the
     same as *note PyArg_ParseTupleAndKeywords(): 6c1. but takes a
     ‘va_list’ instead of a number of arguments.  (Contributed by Greg
     Chapman.)

   * A new method flag, ‘METH_COEXISTS’, allows a function defined in
     slots to co-exist with a *note PyCFunction: e9f. having the same
     name.  This can halve the access time for a method such as
     ‘set.__contains__()’.  (Contributed by Raymond Hettinger.)

   * Python can now be built with additional profiling for the
     interpreter itself, intended as an aid to people developing the
     Python core.  Providing ‘--enable-profiling’ to the ‘configure’
     script will let you profile the interpreter with ‘gprof’, and
     providing the ‘--with-tsc’ switch enables profiling using the
     Pentium’s Time-Stamp-Counter register.  Note that the ‘--with-tsc’
     switch is slightly misnamed, because the profiling feature also
     works on the PowerPC platform, though that processor architecture
     doesn’t call that register “the TSC register”.  (Contributed by
     Jeremy Hylton.)

   * The ‘tracebackobject’ type has been renamed to ‘PyTracebackObject’.

* Menu:

* Port-Specific Changes: Port-Specific Changes<2>.


File: python.info,  Node: Port-Specific Changes<2>,  Up: Build and C API Changes<11>

1.14.13.1 Port-Specific Changes
...............................

   * The Windows port now builds under MSVC++ 7.1 as well as version 6.
     (Contributed by Martin von Löwis.)


File: python.info,  Node: Porting to Python 2 4,  Next: Acknowledgements<4>,  Prev: Build and C API Changes<11>,  Up: What’s New in Python 2 4

1.14.14 Porting to Python 2.4
-----------------------------

This section lists previously described changes that may require changes
to your code:

   * Left shifts and hexadecimal/octal constants that are too large no
     longer trigger a *note FutureWarning: 435. and return a value
     limited to 32 or 64 bits; instead they return a long integer.

   * Integer operations will no longer trigger an ‘OverflowWarning’.
     The ‘OverflowWarning’ warning will disappear in Python 2.5.

   * The *note zip(): cfc. built-in function and ‘itertools.izip()’ now
     return an empty list instead of raising a *note TypeError: 1fe.
     exception if called with no arguments.

   * You can no longer compare the ‘date’ and *note datetime: 1a0.
     instances provided by the *note datetime: 30. module.  Two
     instances of different classes will now always be unequal, and
     relative comparisons (‘<’, ‘>’) will raise a *note TypeError: 1fe.

   * ‘dircache.listdir()’ now passes exceptions to the caller instead of
     returning empty lists.

   * ‘LexicalHandler.startDTD()’ used to receive the public and system
     IDs in the wrong order.  This has been corrected; applications
     relying on the wrong order need to be fixed.

   * *note fcntl.ioctl(): ea2. now warns if the `mutate' argument is
     omitted and relevant.

   * The *note tarfile: 101. module now generates GNU-format tar files
     by default.

   * Encountering a failure while importing a module no longer leaves a
     partially-initialized module object in ‘sys.modules’.

   * *note None: 203. is now a constant; code that binds a new value to
     the name ‘None’ is now a syntax error.

   * The ‘signals.signal()’ function now raises a *note RuntimeError:
     3dc. exception for certain illegal values; previously these errors
     would pass silently.  For example, you can no longer set a handler
     on the ‘SIGKILL’ signal.


File: python.info,  Node: Acknowledgements<4>,  Prev: Porting to Python 2 4,  Up: What’s New in Python 2 4

1.14.15 Acknowledgements
------------------------

The author would like to thank the following people for offering
suggestions, corrections and assistance with various drafts of this
article: Koray Can, Hye-Shik Chang, Michael Dyck, Raymond Hettinger,
Brian Hurt, Hamish Lawson, Fredrik Lundh, Sean Reifschneider, Sadruddin
Rejeb.


File: python.info,  Node: What’s New in Python 2 3,  Next: What’s New in Python 2 2,  Prev: What’s New in Python 2 4,  Up: What’s New in Python

1.15 What’s New in Python 2.3
=============================


Author: A.M. Kuchling

This article explains the new features in Python 2.3.  Python 2.3 was
released on July 29, 2003.

The main themes for Python 2.3 are polishing some of the features added
in 2.2, adding various small but useful enhancements to the core
language, and expanding the standard library.  The new object model
introduced in the previous version has benefited from 18 months of
bugfixes and from optimization efforts that have improved the
performance of new-style classes.  A few new built-in functions have
been added such as *note sum(): 316. and *note enumerate(): ea7.  The
*note in: 179. operator can now be used for substring searches (e.g.
‘"ab" in "abc"’ returns *note True: 594.).

Some of the many new library features include Boolean, set, heap, and
date/time data types, the ability to import modules from ZIP-format
archives, metadata support for the long-awaited Python catalog, an
updated version of IDLE, and modules for logging messages, wrapping
text, parsing CSV files, processing command-line options, using
BerkeleyDB databases… the list of new and enhanced modules is lengthy.

This article doesn’t attempt to provide a complete specification of the
new features, but instead provides a convenient overview.  For full
details, you should refer to the documentation for Python 2.3, such as
the Python Library Reference and the Python Reference Manual.  If you
want to understand the complete implementation and design rationale,
refer to the PEP for a particular new feature.

* Menu:

* PEP 218; A Standard Set Datatype: PEP 218 A Standard Set Datatype.
* PEP 255; Simple Generators: PEP 255 Simple Generators.
* PEP 263; Source Code Encodings: PEP 263 Source Code Encodings.
* PEP 273; Importing Modules from ZIP Archives: PEP 273 Importing Modules from ZIP Archives.
* PEP 277; Unicode file name support for Windows NT: PEP 277 Unicode file name support for Windows NT.
* PEP 278; Universal Newline Support: PEP 278 Universal Newline Support.
* PEP 279; enumerate(): PEP 279 enumerate.
* PEP 282; The logging Package: PEP 282 The logging Package.
* PEP 285; A Boolean Type: PEP 285 A Boolean Type.
* PEP 293; Codec Error Handling Callbacks: PEP 293 Codec Error Handling Callbacks.
* PEP 301; Package Index and Metadata for Distutils: PEP 301 Package Index and Metadata for Distutils.
* PEP 302; New Import Hooks: PEP 302 New Import Hooks.
* PEP 305; Comma-separated Files: PEP 305 Comma-separated Files.
* PEP 307; Pickle Enhancements: PEP 307 Pickle Enhancements.
* Extended Slices::
* Other Language Changes: Other Language Changes<14>.
* New, Improved, and Deprecated Modules: New Improved and Deprecated Modules<4>.
* Pymalloc; A Specialized Object Allocator: Pymalloc A Specialized Object Allocator.
* Build and C API Changes: Build and C API Changes<12>.
* Other Changes and Fixes: Other Changes and Fixes<2>.
* Porting to Python 2.3: Porting to Python 2 3.
* Acknowledgements: Acknowledgements<5>.


File: python.info,  Node: PEP 218 A Standard Set Datatype,  Next: PEP 255 Simple Generators,  Up: What’s New in Python 2 3

1.15.1 PEP 218: A Standard Set Datatype
---------------------------------------

The new ‘sets’ module contains an implementation of a set datatype.  The
‘Set’ class is for mutable sets, sets that can have members added and
removed.  The ‘ImmutableSet’ class is for sets that can’t be modified,
and instances of ‘ImmutableSet’ can therefore be used as dictionary
keys.  Sets are built on top of dictionaries, so the elements within a
set must be hashable.

Here’s a simple example:

     >>> import sets
     >>> S = sets.Set([1,2,3])
     >>> S
     Set([1, 2, 3])
     >>> 1 in S
     True
     >>> 0 in S
     False
     >>> S.add(5)
     >>> S.remove(3)
     >>> S
     Set([1, 2, 5])
     >>>

The union and intersection of sets can be computed with the ‘union()’
and ‘intersection()’ methods; an alternative notation uses the bitwise
operators ‘&’ and ‘|’.  Mutable sets also have in-place versions of
these methods, ‘union_update()’ and ‘intersection_update()’.

     >>> S1 = sets.Set([1,2,3])
     >>> S2 = sets.Set([4,5,6])
     >>> S1.union(S2)
     Set([1, 2, 3, 4, 5, 6])
     >>> S1 | S2                  # Alternative notation
     Set([1, 2, 3, 4, 5, 6])
     >>> S1.intersection(S2)
     Set([])
     >>> S1 & S2                  # Alternative notation
     Set([])
     >>> S1.union_update(S2)
     >>> S1
     Set([1, 2, 3, 4, 5, 6])
     >>>

It’s also possible to take the symmetric difference of two sets.  This
is the set of all elements in the union that aren’t in the intersection.
Another way of putting it is that the symmetric difference contains all
elements that are in exactly one set.  Again, there’s an alternative
notation (‘^’), and an in-place version with the ungainly name
‘symmetric_difference_update()’.

     >>> S1 = sets.Set([1,2,3,4])
     >>> S2 = sets.Set([3,4,5,6])
     >>> S1.symmetric_difference(S2)
     Set([1, 2, 5, 6])
     >>> S1 ^ S2
     Set([1, 2, 5, 6])
     >>>

There are also ‘issubset()’ and ‘issuperset()’ methods for checking
whether one set is a subset or superset of another:

     >>> S1 = sets.Set([1,2,3])
     >>> S2 = sets.Set([2,3])
     >>> S2.issubset(S1)
     True
     >>> S1.issubset(S2)
     False
     >>> S1.issuperset(S2)
     True
     >>>

See also
........

PEP 218(1) - Adding a Built-In Set Object Type

     PEP written by Greg V. Wilson.  Implemented by Greg V. Wilson, Alex
     Martelli, and GvR.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0218


File: python.info,  Node: PEP 255 Simple Generators,  Next: PEP 263 Source Code Encodings,  Prev: PEP 218 A Standard Set Datatype,  Up: What’s New in Python 2 3

1.15.2 PEP 255: Simple Generators
---------------------------------

In Python 2.2, generators were added as an optional feature, to be
enabled by a ‘from __future__ import generators’ directive.  In 2.3
generators no longer need to be specially enabled, and are now always
present; this means that *note yield: 2c7. is now always a keyword.  The
rest of this section is a copy of the description of generators from the
“What’s New in Python 2.2” document; if you read it back when Python 2.2
came out, you can skip the rest of this section.

You’re doubtless familiar with how function calls work in Python or C.
When you call a function, it gets a private namespace where its local
variables are created.  When the function reaches a *note return: 2c8.
statement, the local variables are destroyed and the resulting value is
returned to the caller.  A later call to the same function will get a
fresh new set of local variables.  But, what if the local variables
weren’t thrown away on exiting a function?  What if you could later
resume the function where it left off?  This is what generators provide;
they can be thought of as resumable functions.

Here’s the simplest example of a generator function:

     def generate_ints(N):
         for i in range(N):
             yield i

A new keyword, *note yield: 2c7, was introduced for generators.  Any
function containing a ‘yield’ statement is a generator function; this is
detected by Python’s bytecode compiler which compiles the function
specially as a result.

When you call a generator function, it doesn’t return a single value;
instead it returns a generator object that supports the iterator
protocol.  On executing the *note yield: 2c7. statement, the generator
outputs the value of ‘i’, similar to a *note return: 2c8. statement.
The big difference between ‘yield’ and a ‘return’ statement is that on
reaching a ‘yield’ the generator’s state of execution is suspended and
local variables are preserved.  On the next call to the generator’s
‘.next()’ method, the function will resume executing immediately after
the ‘yield’ statement.  (For complicated reasons, the ‘yield’ statement
isn’t allowed inside the *note try: e37. block of a ‘try’…‘finally’
statement; read PEP 255(1) for a full explanation of the interaction
between ‘yield’ and exceptions.)

Here’s a sample usage of the ‘generate_ints()’ generator:

     >>> gen = generate_ints(3)
     >>> gen
     <generator object at 0x8117f90>
     >>> gen.next()
     0
     >>> gen.next()
     1
     >>> gen.next()
     2
     >>> gen.next()
     Traceback (most recent call last):
       File "stdin", line 1, in ?
       File "stdin", line 2, in generate_ints
     StopIteration

You could equally write ‘for i in generate_ints(5)’, or ‘a,b,c =
generate_ints(3)’.

Inside a generator function, the *note return: 2c8. statement can only
be used without a value, and signals the end of the procession of
values; afterwards the generator cannot return any further values.
‘return’ with a value, such as ‘return 5’, is a syntax error inside a
generator function.  The end of the generator’s results can also be
indicated by raising *note StopIteration: 582. manually, or by just
letting the flow of execution fall off the bottom of the function.

You could achieve the effect of generators manually by writing your own
class and storing all the local variables of the generator as instance
variables.  For example, returning a list of integers could be done by
setting ‘self.count’ to 0, and having the *note next(): 775. method
increment ‘self.count’ and return it.  However, for a moderately
complicated generator, writing a corresponding class would be much
messier.  ‘Lib/test/test_generators.py’ contains a number of more
interesting examples.  The simplest one implements an in-order traversal
of a tree using generators recursively.

     # A recursive generator that generates Tree leaves in in-order.
     def inorder(t):
         if t:
             for x in inorder(t.left):
                 yield x
             yield t.label
             for x in inorder(t.right):
                 yield x

Two other examples in ‘Lib/test/test_generators.py’ produce solutions
for the N-Queens problem (placing $N$ queens on an $NxN$ chess board so
that no queen threatens another) and the Knight’s Tour (a route that
takes a knight to every square of an $NxN$ chessboard without visiting
any square twice).

The idea of generators comes from other programming languages,
especially Icon (‘https://www.cs.arizona.edu/icon/’), where the idea of
generators is central.  In Icon, every expression and function call
behaves like a generator.  One example from “An Overview of the Icon
Programming Language” at
‘https://www.cs.arizona.edu/icon/docs/ipd266.htm’ gives an idea of what
this looks like:

     sentence := "Store it in the neighboring harbor"
     if (i := find("or", sentence)) > 5 then write(i)

In Icon the ‘find()’ function returns the indexes at which the substring
“or” is found: 3, 23, 33.  In the *note if: eab. statement, ‘i’ is first
assigned a value of 3, but 3 is less than 5, so the comparison fails,
and Icon retries it with the second value of 23.  23 is greater than 5,
so the comparison now succeeds, and the code prints the value 23 to the
screen.

Python doesn’t go nearly as far as Icon in adopting generators as a
central concept.  Generators are considered part of the core Python
language, but learning or using them isn’t compulsory; if they don’t
solve any problems that you have, feel free to ignore them.  One novel
feature of Python’s interface as compared to Icon’s is that a
generator’s state is represented as a concrete object (the iterator)
that can be passed around to other functions or stored in a data
structure.

See also
........

PEP 255(2) - Simple Generators

     Written by Neil Schemenauer, Tim Peters, Magnus Lie Hetland.
     Implemented mostly by Neil Schemenauer and Tim Peters, with other
     fixes from the Python Labs crew.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0255

   (2) https://www.python.org/dev/peps/pep-0255


File: python.info,  Node: PEP 263 Source Code Encodings,  Next: PEP 273 Importing Modules from ZIP Archives,  Prev: PEP 255 Simple Generators,  Up: What’s New in Python 2 3

1.15.3 PEP 263: Source Code Encodings
-------------------------------------

Python source files can now be declared as being in different character
set encodings.  Encodings are declared by including a specially
formatted comment in the first or second line of the source file.  For
example, a UTF-8 file can be declared with:

     #!/usr/bin/env python
     # -*- coding: UTF-8 -*-

Without such an encoding declaration, the default encoding used is 7-bit
ASCII. Executing or importing modules that contain string literals with
8-bit characters and have no encoding declaration will result in a *note
DeprecationWarning: 15a. being signalled by Python 2.3; in 2.4 this will
be a syntax error.

The encoding declaration only affects Unicode string literals, which
will be converted to Unicode using the specified encoding.  Note that
Python identifiers are still restricted to ASCII characters, so you
can’t have variable names that use characters outside of the usual
alphanumerics.

See also
........

PEP 263(1) - Defining Python Source Code Encodings

     Written by Marc-André Lemburg and Martin von Löwis; implemented by
     Suzuki Hisao and Martin von Löwis.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0263


File: python.info,  Node: PEP 273 Importing Modules from ZIP Archives,  Next: PEP 277 Unicode file name support for Windows NT,  Prev: PEP 263 Source Code Encodings,  Up: What’s New in Python 2 3

1.15.4 PEP 273: Importing Modules from ZIP Archives
---------------------------------------------------

The new *note zipimport: 14c. module adds support for importing modules
from a ZIP-format archive.  You don’t need to import the module
explicitly; it will be automatically imported if a ZIP archive’s
filename is added to ‘sys.path’.  For example:

     amk@nyman:~/src/python$ unzip -l /tmp/example.zip
     Archive:  /tmp/example.zip
       Length     Date   Time    Name
      --------    ----   ----    ----
          8467  11-26-02 22:30   jwzthreading.py
      --------                   -------
          8467                   1 file
     amk@nyman:~/src/python$ ./python
     Python 2.3 (#1, Aug 1 2003, 19:54:32)
     >>> import sys
     >>> sys.path.insert(0, '/tmp/example.zip')  # Add .zip file to front of path
     >>> import jwzthreading
     >>> jwzthreading.__file__
     '/tmp/example.zip/jwzthreading.py'
     >>>

An entry in ‘sys.path’ can now be the filename of a ZIP archive.  The
ZIP archive can contain any kind of files, but only files named ‘*.py’,
‘*.pyc’, or ‘*.pyo’ can be imported.  If an archive only contains ‘*.py’
files, Python will not attempt to modify the archive by adding the
corresponding ‘*.pyc’ file, meaning that if a ZIP archive doesn’t
contain ‘*.pyc’ files, importing may be rather slow.

A path within the archive can also be specified to only import from a
subdirectory; for example, the path ‘/tmp/example.zip/lib/’ would only
import from the ‘lib/’ subdirectory within the archive.

See also
........

PEP 273(1) - Import Modules from Zip Archives

     Written by James C. Ahlstrom, who also provided an implementation.
     Python 2.3 follows the specification in PEP 273(2), but uses an
     implementation written by Just van Rossum that uses the import
     hooks described in PEP 302(3).  See section *note PEP 302; New
     Import Hooks: eaf. for a description of the new import hooks.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0273

   (2) https://www.python.org/dev/peps/pep-0273

   (3) https://www.python.org/dev/peps/pep-0302


File: python.info,  Node: PEP 277 Unicode file name support for Windows NT,  Next: PEP 278 Universal Newline Support,  Prev: PEP 273 Importing Modules from ZIP Archives,  Up: What’s New in Python 2 3

1.15.5 PEP 277: Unicode file name support for Windows NT
--------------------------------------------------------

On Windows NT, 2000, and XP, the system stores file names as Unicode
strings.  Traditionally, Python has represented file names as byte
strings, which is inadequate because it renders some file names
inaccessible.

Python now allows using arbitrary Unicode strings (within the
limitations of the file system) for all functions that expect file
names, most notably the *note open(): 16f. built-in function.  If a
Unicode string is passed to *note os.listdir(): b1c, Python now returns
a list of Unicode strings.  A new function, ‘os.getcwdu()’, returns the
current directory as a Unicode string.

Byte strings still work as file names, and on Windows Python will
transparently convert them to Unicode using the ‘mbcs’ encoding.

Other systems also allow Unicode strings as file names but convert them
to byte strings before passing them to the system, which can cause a
*note UnicodeError: d03. to be raised.  Applications can test whether
arbitrary Unicode strings are supported as file names by checking *note
os.path.supports_unicode_filenames: eb1, a Boolean value.

Under MacOS, *note os.listdir(): b1c. may now return Unicode filenames.

See also
........

PEP 277(1) - Unicode file name support for Windows NT

     Written by Neil Hodgson; implemented by Neil Hodgson, Martin von
     Löwis, and Mark Hammond.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0277


File: python.info,  Node: PEP 278 Universal Newline Support,  Next: PEP 279 enumerate,  Prev: PEP 277 Unicode file name support for Windows NT,  Up: What’s New in Python 2 3

1.15.6 PEP 278: Universal Newline Support
-----------------------------------------

The three major operating systems used today are Microsoft Windows,
Apple’s Macintosh OS, and the various Unix derivatives.  A minor
irritation of cross-platform work is that these three platforms all use
different characters to mark the ends of lines in text files.  Unix uses
the linefeed (ASCII character 10), MacOS uses the carriage return (ASCII
character 13), and Windows uses a two-character sequence of a carriage
return plus a newline.

Python’s file objects can now support end of line conventions other than
the one followed by the platform on which Python is running.  Opening a
file with the mode ‘'U'’ or ‘'rU'’ will open a file for reading in *note
universal newlines: 6eb. mode.  All three line ending conventions will
be translated to a ‘'\n'’ in the strings returned by the various file
methods such as ‘read()’ and *note readline(): de.

Universal newline support is also used when importing modules and when
executing a file with the ‘execfile()’ function.  This means that Python
modules can be shared between all three operating systems without
needing to convert the line-endings.

This feature can be disabled when compiling Python by specifying the
‘--without-universal-newlines’ switch when running Python’s ‘configure’
script.

See also
........

PEP 278(1) - Universal Newline Support

     Written and implemented by Jack Jansen.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0278


File: python.info,  Node: PEP 279 enumerate,  Next: PEP 282 The logging Package,  Prev: PEP 278 Universal Newline Support,  Up: What’s New in Python 2 3

1.15.7 PEP 279: enumerate()
---------------------------

A new built-in function, *note enumerate(): ea7, will make certain loops
a bit clearer.  ‘enumerate(thing)’, where `thing' is either an iterator
or a sequence, returns an iterator that will return ‘(0, thing[0])’,
‘(1, thing[1])’, ‘(2, thing[2])’, and so forth.

A common idiom to change every element of a list looks like this:

     for i in range(len(L)):
         item = L[i]
         # ... compute some result based on item ...
         L[i] = result

This can be rewritten using *note enumerate(): ea7. as:

     for i, item in enumerate(L):
         # ... compute some result based on item ...
         L[i] = result

See also
........

PEP 279(1) - The enumerate() built-in function

     Written and implemented by Raymond D. Hettinger.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0279


File: python.info,  Node: PEP 282 The logging Package,  Next: PEP 285 A Boolean Type,  Prev: PEP 279 enumerate,  Up: What’s New in Python 2 3

1.15.8 PEP 282: The logging Package
-----------------------------------

A standard package for writing logs, *note logging: aa, has been added
to Python 2.3.  It provides a powerful and flexible mechanism for
generating logging output which can then be filtered and processed in
various ways.  A configuration file written in a standard format can be
used to control the logging behavior of a program.  Python includes
handlers that will write log records to standard error or to a file or
socket, send them to the system log, or even e-mail them to a particular
address; of course, it’s also possible to write your own handler
classes.

The ‘Logger’ class is the primary class.  Most application code will
deal with one or more ‘Logger’ objects, each one used by a particular
subsystem of the application.  Each ‘Logger’ is identified by a name,
and names are organized into a hierarchy using ‘.’ as the component
separator.  For example, you might have ‘Logger’ instances named
‘server’, ‘server.auth’ and ‘server.network’.  The latter two instances
are below ‘server’ in the hierarchy.  This means that if you turn up the
verbosity for ‘server’ or direct ‘server’ messages to a different
handler, the changes will also apply to records logged to ‘server.auth’
and ‘server.network’.  There’s also a root ‘Logger’ that’s the parent of
all other loggers.

For simple uses, the *note logging: aa. package contains some
convenience functions that always use the root log:

     import logging

     logging.debug('Debugging information')
     logging.info('Informational message')
     logging.warning('Warning:config file %s not found', 'server.conf')
     logging.error('Error occurred')
     logging.critical('Critical error -- shutting down')

This produces the following output:

     WARNING:root:Warning:config file server.conf not found
     ERROR:root:Error occurred
     CRITICAL:root:Critical error -- shutting down

In the default configuration, informational and debugging messages are
suppressed and the output is sent to standard error.  You can enable the
display of informational and debugging messages by calling the
‘setLevel()’ method on the root logger.

Notice the ‘warning()’ call’s use of string formatting operators; all of
the functions for logging messages take the arguments ‘(msg, arg1, arg2,
...)’ and log the string resulting from ‘msg % (arg1, arg2, ...)’.

There’s also an ‘exception()’ function that records the most recent
traceback.  Any of the other functions will also record the traceback if
you specify a true value for the keyword argument `exc_info'.

     def f():
         try:    1/0
         except: logging.exception('Problem recorded')

     f()

This produces the following output:

     ERROR:root:Problem recorded
     Traceback (most recent call last):
       File "t.py", line 6, in f
         1/0
     ZeroDivisionError: integer division or modulo by zero

Slightly more advanced programs will use a logger other than the root
logger.  The ‘getLogger(name)’ function is used to get a particular log,
creating it if it doesn’t exist yet.  ‘getLogger(None)’ returns the root
logger.

     log = logging.getLogger('server')
      ...
     log.info('Listening on port %i', port)
      ...
     log.critical('Disk full')
      ...

Log records are usually propagated up the hierarchy, so a message logged
to ‘server.auth’ is also seen by ‘server’ and ‘root’, but a ‘Logger’ can
prevent this by setting its ‘propagate’ attribute to *note False: 48f.

There are more classes provided by the *note logging: aa. package that
can be customized.  When a ‘Logger’ instance is told to log a message,
it creates a ‘LogRecord’ instance that is sent to any number of
different ‘Handler’ instances.  Loggers and handlers can also have an
attached list of filters, and each filter can cause the ‘LogRecord’ to
be ignored or can modify the record before passing it along.  When
they’re finally output, ‘LogRecord’ instances are converted to text by a
‘Formatter’ class.  All of these classes can be replaced by your own
specially-written classes.

With all of these features the *note logging: aa. package should provide
enough flexibility for even the most complicated applications.  This is
only an incomplete overview of its features, so please see the package’s
reference documentation for all of the details.  Reading PEP 282(1) will
also be helpful.

See also
........

PEP 282(2) - A Logging System

     Written by Vinay Sajip and Trent Mick; implemented by Vinay Sajip.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0282

   (2) https://www.python.org/dev/peps/pep-0282


File: python.info,  Node: PEP 285 A Boolean Type,  Next: PEP 293 Codec Error Handling Callbacks,  Prev: PEP 282 The logging Package,  Up: What’s New in Python 2 3

1.15.9 PEP 285: A Boolean Type
------------------------------

A Boolean type was added to Python 2.3.  Two new constants were added to
the ‘__builtin__’ module, *note True: 594. and *note False: 48f.  (*note
True: 594. and *note False: 48f. constants were added to the built-ins
in Python 2.2.1, but the 2.2.1 versions are simply set to integer values
of 1 and 0 and aren’t a different type.)

The type object for this new type is named *note bool: 2bd.; the
constructor for it takes any Python value and converts it to *note True:
594. or *note False: 48f.

     >>> bool(1)
     True
     >>> bool(0)
     False
     >>> bool([])
     False
     >>> bool( (1,) )
     True

Most of the standard library modules and built-in functions have been
changed to return Booleans.

     >>> obj = []
     >>> hasattr(obj, 'append')
     True
     >>> isinstance(obj, list)
     True
     >>> isinstance(obj, tuple)
     False

Python’s Booleans were added with the primary goal of making code
clearer.  For example, if you’re reading a function and encounter the
statement ‘return 1’, you might wonder whether the ‘1’ represents a
Boolean truth value, an index, or a coefficient that multiplies some
other quantity.  If the statement is ‘return True’, however, the meaning
of the return value is quite clear.

Python’s Booleans were `not' added for the sake of strict type-checking.
A very strict language such as Pascal would also prevent you performing
arithmetic with Booleans, and would require that the expression in an
*note if: eab. statement always evaluate to a Boolean result.  Python is
not this strict and never will be, as PEP 285(1) explicitly says.  This
means you can still use any expression in an ‘if’ statement, even ones
that evaluate to a list or tuple or some random object.  The Boolean
type is a subclass of the *note int: 204. class so that arithmetic using
a Boolean still works.

     >>> True + 1
     2
     >>> False + 1
     1
     >>> False * 75
     0
     >>> True * 75
     75

To sum up *note True: 594. and *note False: 48f. in a sentence: they’re
alternative ways to spell the integer values 1 and 0, with the single
difference that *note str(): 205. and *note repr(): 8b9. return the
strings ‘'True'’ and ‘'False'’ instead of ‘'1'’ and ‘'0'’.

See also
........

PEP 285(2) - Adding a bool type

     Written and implemented by GvR.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0285

   (2) https://www.python.org/dev/peps/pep-0285


File: python.info,  Node: PEP 293 Codec Error Handling Callbacks,  Next: PEP 301 Package Index and Metadata for Distutils,  Prev: PEP 285 A Boolean Type,  Up: What’s New in Python 2 3

1.15.10 PEP 293: Codec Error Handling Callbacks
-----------------------------------------------

When encoding a Unicode string into a byte string, unencodable
characters may be encountered.  So far, Python has allowed specifying
the error processing as either “strict” (raising *note UnicodeError:
d03.), “ignore” (skipping the character), or “replace” (using a question
mark in the output string), with “strict” being the default behavior.
It may be desirable to specify alternative processing of such errors,
such as inserting an XML character reference or HTML entity reference
into the converted string.

Python now has a flexible framework to add different processing
strategies.  New error handlers can be added with *note
codecs.register_error(): eb9, and codecs then can access the error
handler with *note codecs.lookup_error(): eba.  An equivalent C API has
been added for codecs written in C. The error handler gets the necessary
state information such as the string being converted, the position in
the string where the error was detected, and the target encoding.  The
handler can then either raise an exception or return a replacement
string.

Two additional error handlers have been implemented using this
framework: “backslashreplace” uses Python backslash quoting to represent
unencodable characters and “xmlcharrefreplace” emits XML character
references.

See also
........

PEP 293(1) - Codec Error Handling Callbacks

     Written and implemented by Walter Dörwald.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0293


File: python.info,  Node: PEP 301 Package Index and Metadata for Distutils,  Next: PEP 302 New Import Hooks,  Prev: PEP 293 Codec Error Handling Callbacks,  Up: What’s New in Python 2 3

1.15.11 PEP 301: Package Index and Metadata for Distutils
---------------------------------------------------------

Support for the long-requested Python catalog makes its first appearance
in 2.3.

The heart of the catalog is the new Distutils ‘register’ command.
Running ‘python setup.py register’ will collect the metadata describing
a package, such as its name, version, maintainer, description, &c., and
send it to a central catalog server.  The resulting catalog is available
from ‘https://pypi.org’.

To make the catalog a bit more useful, a new optional `classifiers'
keyword argument has been added to the Distutils ‘setup()’ function.  A
list of Trove(1)-style strings can be supplied to help classify the
software.

Here’s an example ‘setup.py’ with classifiers, written to be compatible
with older versions of the Distutils:

     from distutils import core
     kw = {'name': "Quixote",
           'version': "0.5.1",
           'description': "A highly Pythonic Web application framework",
           # ...
           }

     if (hasattr(core, 'setup_keywords') and
         'classifiers' in core.setup_keywords):
         kw['classifiers'] = \
             ['Topic :: Internet :: WWW/HTTP :: Dynamic Content',
              'Environment :: No Input/Output (Daemon)',
              'Intended Audience :: Developers'],

     core.setup(**kw)

The full list of classifiers can be obtained by running ‘python setup.py
register --list-classifiers’.

See also
........

PEP 301(2) - Package Index and Metadata for Distutils

     Written and implemented by Richard Jones.

   ---------- Footnotes ----------

   (1) http://catb.org/~esr/trove/

   (2) https://www.python.org/dev/peps/pep-0301


File: python.info,  Node: PEP 302 New Import Hooks,  Next: PEP 305 Comma-separated Files,  Prev: PEP 301 Package Index and Metadata for Distutils,  Up: What’s New in Python 2 3

1.15.12 PEP 302: New Import Hooks
---------------------------------

While it’s been possible to write custom import hooks ever since the
‘ihooks’ module was introduced in Python 1.3, no one has ever been
really happy with it because writing new import hooks is difficult and
messy.  There have been various proposed alternatives such as the
‘imputil’ and ‘iu’ modules, but none of them has ever gained much
acceptance, and none of them were easily usable from C code.

PEP 302(1) borrows ideas from its predecessors, especially from Gordon
McMillan’s ‘iu’ module.  Three new items are added to the *note sys: fd.
module:

   * ‘sys.path_hooks’ is a list of callable objects; most often they’ll
     be classes.  Each callable takes a string containing a path and
     either returns an importer object that will handle imports from
     this path or raises an *note ImportError: 16c. exception if it
     can’t handle this path.

   * ‘sys.path_importer_cache’ caches importer objects for each path, so
     ‘sys.path_hooks’ will only need to be traversed once for each path.

   * ‘sys.meta_path’ is a list of importer objects that will be
     traversed before ‘sys.path’ is checked.  This list is initially
     empty, but user code can add objects to it.  Additional built-in
     and frozen modules can be imported by an object added to this list.

Importer objects must have a single method, ‘find_module(fullname,
path=None)’.  `fullname' will be a module or package name, e.g.
‘string’ or ‘distutils.core’.  ‘find_module()’ must return a loader
object that has a single method, ‘load_module(fullname)’, that creates
and returns the corresponding module object.

Pseudo-code for Python’s new import logic, therefore, looks something
like this (simplified a bit; see PEP 302(2) for the full details):

     for mp in sys.meta_path:
         loader = mp(fullname)
         if loader is not None:
             <module> = loader.load_module(fullname)

     for path in sys.path:
         for hook in sys.path_hooks:
             try:
                 importer = hook(path)
             except ImportError:
                 # ImportError, so try the other path hooks
                 pass
             else:
                 loader = importer.find_module(fullname)
                 <module> = loader.load_module(fullname)

     # Not found!
     raise ImportError

See also
........

PEP 302(3) - New Import Hooks

     Written by Just van Rossum and Paul Moore.  Implemented by Just van
     Rossum.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0302

   (2) https://www.python.org/dev/peps/pep-0302

   (3) https://www.python.org/dev/peps/pep-0302


File: python.info,  Node: PEP 305 Comma-separated Files,  Next: PEP 307 Pickle Enhancements,  Prev: PEP 302 New Import Hooks,  Up: What’s New in Python 2 3

1.15.13 PEP 305: Comma-separated Files
--------------------------------------

Comma-separated files are a format frequently used for exporting data
from databases and spreadsheets.  Python 2.3 adds a parser for
comma-separated files.

Comma-separated format is deceptively simple at first glance:

     Costs,150,200,3.95

Read a line and call ‘line.split(',')’: what could be simpler?  But toss
in string data that can contain commas, and things get more complicated:

     "Costs",150,200,3.95,"Includes taxes, shipping, and sundry items"

A big ugly regular expression can parse this, but using the new *note
csv: 29. package is much simpler:

     import csv

     input = open('datafile', 'rb')
     reader = csv.reader(input)
     for line in reader:
         print line

The ‘reader()’ function takes a number of different options.  The field
separator isn’t limited to the comma and can be changed to any
character, and so can the quoting and line-ending characters.

Different dialects of comma-separated files can be defined and
registered; currently there are two dialects, both used by Microsoft
Excel.  A separate *note csv.writer: ec0. class will generate
comma-separated files from a succession of tuples or lists, quoting
strings that contain the delimiter.

See also
........

PEP 305(1) - CSV File API

     Written and implemented by Kevin Altis, Dave Cole, Andrew McNamara,
     Skip Montanaro, Cliff Wells.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0305


File: python.info,  Node: PEP 307 Pickle Enhancements,  Next: Extended Slices,  Prev: PEP 305 Comma-separated Files,  Up: What’s New in Python 2 3

1.15.14 PEP 307: Pickle Enhancements
------------------------------------

The *note pickle: ca. and ‘cPickle’ modules received some attention
during the 2.3 development cycle.  In 2.2, new-style classes could be
pickled without difficulty, but they weren’t pickled very compactly; PEP
307(1) quotes a trivial example where a new-style class results in a
pickled string three times longer than that for a classic class.

The solution was to invent a new pickle protocol.  The *note
pickle.dumps(): ec3. function has supported a text-or-binary flag for a
long time.  In 2.3, this flag is redefined from a Boolean to an integer:
0 is the old text-mode pickle format, 1 is the old binary format, and
now 2 is a new 2.3-specific format.  A new constant, *note
pickle.HIGHEST_PROTOCOL: ec4, can be used to select the fanciest
protocol available.

Unpickling is no longer considered a safe operation.  2.2’s *note
pickle: ca. provided hooks for trying to prevent unsafe classes from
being unpickled (specifically, a ‘__safe_for_unpickling__’ attribute),
but none of this code was ever audited and therefore it’s all been
ripped out in 2.3.  You should not unpickle untrusted data in any
version of Python.

To reduce the pickling overhead for new-style classes, a new interface
for customizing pickling was added using three special methods: *note
__getstate__(): ec5, *note __setstate__(): 2d1, and *note
__getnewargs__(): 7a1.  Consult PEP 307(2) for the full semantics of
these methods.

As a way to compress pickles yet further, it’s now possible to use
integer codes instead of long strings to identify pickled classes.  The
Python Software Foundation will maintain a list of standardized codes;
there’s also a range of codes for private use.  Currently no codes have
been specified.

See also
........

PEP 307(3) - Extensions to the pickle protocol

     Written and implemented by Guido van Rossum and Tim Peters.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0307

   (2) https://www.python.org/dev/peps/pep-0307

   (3) https://www.python.org/dev/peps/pep-0307


File: python.info,  Node: Extended Slices,  Next: Other Language Changes<14>,  Prev: PEP 307 Pickle Enhancements,  Up: What’s New in Python 2 3

1.15.15 Extended Slices
-----------------------

Ever since Python 1.4, the slicing syntax has supported an optional
third “step” or “stride” argument.  For example, these are all legal
Python syntax: ‘L[1:10:2]’, ‘L[:-1:1]’, ‘L[::-1]’.  This was added to
Python at the request of the developers of Numerical Python, which uses
the third argument extensively.  However, Python’s built-in list, tuple,
and string sequence types have never supported this feature, raising a
*note TypeError: 1fe. if you tried it.  Michael Hudson contributed a
patch to fix this shortcoming.

For example, you can now easily extract the elements of a list that have
even indexes:

     >>> L = range(10)
     >>> L[::2]
     [0, 2, 4, 6, 8]

Negative values also work to make a copy of the same list in reverse
order:

     >>> L[::-1]
     [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

This also works for tuples, arrays, and strings:

     >>> s='abcd'
     >>> s[::2]
     'ac'
     >>> s[::-1]
     'dcba'

If you have a mutable sequence such as a list or an array you can assign
to or delete an extended slice, but there are some differences between
assignment to extended and regular slices.  Assignment to a regular
slice can be used to change the length of the sequence:

     >>> a = range(3)
     >>> a
     [0, 1, 2]
     >>> a[1:3] = [4, 5, 6]
     >>> a
     [0, 4, 5, 6]

Extended slices aren’t this flexible.  When assigning to an extended
slice, the list on the right hand side of the statement must contain the
same number of items as the slice it is replacing:

     >>> a = range(4)
     >>> a
     [0, 1, 2, 3]
     >>> a[::2]
     [0, 2]
     >>> a[::2] = [0, -1]
     >>> a
     [0, 1, -1, 3]
     >>> a[::2] = [0,1,2]
     Traceback (most recent call last):
       File "<stdin>", line 1, in ?
     ValueError: attempt to assign sequence of size 3 to extended slice of size 2

Deletion is more straightforward:

     >>> a = range(4)
     >>> a
     [0, 1, 2, 3]
     >>> a[::2]
     [0, 2]
     >>> del a[::2]
     >>> a
     [1, 3]

One can also now pass slice objects to the *note __getitem__(): 3a2.
methods of the built-in sequences:

     >>> range(10).__getitem__(slice(0, 5, 2))
     [0, 2, 4]

Or use slice objects directly in subscripts:

     >>> range(10)[slice(0, 5, 2)]
     [0, 2, 4]

To simplify implementing sequences that support extended slicing, slice
objects now have a method ‘indices(length)’ which, given the length of a
sequence, returns a ‘(start, stop, step)’ tuple that can be passed
directly to *note range(): 1f5.  ‘indices()’ handles omitted and
out-of-bounds indices in a manner consistent with regular slices (and
this innocuous phrase hides a welter of confusing details!).  The method
is intended to be used like this:

     class FakeSeq:
         ...
         def calc_item(self, i):
             ...
         def __getitem__(self, item):
             if isinstance(item, slice):
                 indices = item.indices(len(self))
                 return FakeSeq([self.calc_item(i) for i in range(*indices)])
             else:
                 return self.calc_item(i)

From this example you can also see that the built-in *note slice: ec8.
object is now the type object for the slice type, and is no longer a
function.  This is consistent with Python 2.2, where *note int: 204,
*note str: 205, etc., underwent the same change.


File: python.info,  Node: Other Language Changes<14>,  Next: New Improved and Deprecated Modules<4>,  Prev: Extended Slices,  Up: What’s New in Python 2 3

1.15.16 Other Language Changes
------------------------------

Here are all of the changes that Python 2.3 makes to the core Python
language.

   * The *note yield: 2c7. statement is now always a keyword, as
     described in section *note PEP 255; Simple Generators: eaa. of this
     document.

   * A new built-in function *note enumerate(): ea7. was added, as
     described in section *note PEP 279; enumerate(): eb4. of this
     document.

   * Two new constants, *note True: 594. and *note False: 48f. were
     added along with the built-in *note bool: 2bd. type, as described
     in section *note PEP 285; A Boolean Type: eb7. of this document.

   * The *note int(): 204. type constructor will now return a long
     integer instead of raising an *note OverflowError: a41. when a
     string or floating-point number is too large to fit into an
     integer.  This can lead to the paradoxical result that
     ‘isinstance(int(expression), int)’ is false, but that seems
     unlikely to cause problems in practice.

   * Built-in types now support the extended slicing syntax, as
     described in section *note Extended Slices: ec7. of this document.

   * A new built-in function, ‘sum(iterable, start=0)’, adds up the
     numeric items in the iterable object and returns their sum.  *note
     sum(): 316. only accepts numbers, meaning that you can’t use it to
     concatenate a bunch of strings.  (Contributed by Alex Martelli.)

   * ‘list.insert(pos, value)’ used to insert `value' at the front of
     the list when `pos' was negative.  The behaviour has now been
     changed to be consistent with slice indexing, so when `pos' is -1
     the value will be inserted before the last element, and so forth.

   * ‘list.index(value)’, which searches for `value' within the list and
     returns its index, now takes optional `start' and `stop' arguments
     to limit the search to only part of the list.

   * Dictionaries have a new method, ‘pop(key[, *default*])’, that
     returns the value corresponding to `key' and removes that key/value
     pair from the dictionary.  If the requested key isn’t present in
     the dictionary, `default' is returned if it’s specified and *note
     KeyError: 3e9. raised if it isn’t.

          >>> d = {1:2}
          >>> d
          {1: 2}
          >>> d.pop(4)
          Traceback (most recent call last):
            File "stdin", line 1, in ?
          KeyError: 4
          >>> d.pop(1)
          2
          >>> d.pop(1)
          Traceback (most recent call last):
            File "stdin", line 1, in ?
          KeyError: 'pop(): dictionary is empty'
          >>> d
          {}
          >>>

     There’s also a new class method, ‘dict.fromkeys(iterable, value)’,
     that creates a dictionary with keys taken from the supplied
     iterator `iterable' and all values set to `value', defaulting to
     ‘None’.

     (Patches contributed by Raymond Hettinger.)

     Also, the *note dict(): 164. constructor now accepts keyword
     arguments to simplify creating small dictionaries:

          >>> dict(red=1, blue=2, green=3, black=4)
          {'blue': 2, 'black': 4, 'green': 3, 'red': 1}

     (Contributed by Just van Rossum.)

   * The *note assert: 23f. statement no longer checks the ‘__debug__’
     flag, so you can no longer disable assertions by assigning to
     ‘__debug__’.  Running Python with the *note -O: 77e. switch will
     still generate code that doesn’t execute any assertions.

   * Most type objects are now callable, so you can use them to create
     new objects such as functions, classes, and modules.  (This means
     that the ‘new’ module can be deprecated in a future Python version,
     because you can now use the type objects available in the *note
     types: 121. module.)  For example, you can create a new module
     object with the following code:

          >>> import types
          >>> m = types.ModuleType('abc','docstring')
          >>> m
          <module 'abc' (built-in)>
          >>> m.__doc__
          'docstring'

   * A new warning, *note PendingDeprecationWarning: 15c. was added to
     indicate features which are in the process of being deprecated.
     The warning will `not' be printed by default.  To check for use of
     features that will be deprecated in the future, supply *note
     -Walways;;PendingDeprecationWarning;;: 15b. on the command line or
     use *note warnings.filterwarnings(): eca.

   * The process of deprecating string-based exceptions, as in ‘raise
     "Error occurred"’, has begun.  Raising a string will now trigger
     *note PendingDeprecationWarning: 15c.

   * Using ‘None’ as a variable name will now result in a *note
     SyntaxWarning: 2c9. warning.  In a future version of Python, ‘None’
     may finally become a keyword.

   * The ‘xreadlines()’ method of file objects, introduced in Python
     2.1, is no longer necessary because files now behave as their own
     iterator.  ‘xreadlines()’ was originally introduced as a faster way
     to loop over all the lines in a file, but now you can simply write
     ‘for line in file_obj’.  File objects also have a new read-only
     ‘encoding’ attribute that gives the encoding used by the file;
     Unicode strings written to the file will be automatically converted
     to bytes using the given encoding.

   * The method resolution order used by new-style classes has changed,
     though you’ll only notice the difference if you have a really
     complicated inheritance hierarchy.  Classic classes are unaffected
     by this change.  Python 2.2 originally used a topological sort of a
     class’s ancestors, but 2.3 now uses the C3 algorithm as described
     in the paper "A Monotonic Superclass Linearization for Dylan"(1).
     To understand the motivation for this change, read Michele
     Simionato’s article "Python 2.3 Method Resolution Order"(2), or
     read the thread on python-dev starting with the message at
     ‘https://mail.python.org/pipermail/python-dev/2002-October/029035.html’.
     Samuele Pedroni first pointed out the problem and also implemented
     the fix by coding the C3 algorithm.

   * Python runs multithreaded programs by switching between threads
     after executing N bytecodes.  The default value for N has been
     increased from 10 to 100 bytecodes, speeding up single-threaded
     applications by reducing the switching overhead.  Some
     multithreaded applications may suffer slower response time, but
     that’s easily fixed by setting the limit back to a lower number
     using ‘sys.setcheckinterval(N)’.  The limit can be retrieved with
     the new ‘sys.getcheckinterval()’ function.

   * One minor but far-reaching change is that the names of extension
     types defined by the modules included with Python now contain the
     module and a ‘'.'’ in front of the type name.  For example, in
     Python 2.2, if you created a socket and printed its ‘__class__’,
     you’d get this output:

          >>> s = socket.socket()
          >>> s.__class__
          <type 'socket'>

     In 2.3, you get this:

          >>> s.__class__
          <type '_socket.socket'>

   * One of the noted incompatibilities between old- and new-style
     classes has been removed: you can now assign to the *note __name__:
     d2f. and *note __bases__: ecb. attributes of new-style classes.
     There are some restrictions on what can be assigned to *note
     __bases__: ecb. along the lines of those relating to assigning to
     an instance’s *note __class__: ecc. attribute.

* Menu:

* String Changes::
* Optimizations: Optimizations<13>.

   ---------- Footnotes ----------

   (1) http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.19.3910

   (2) http://www.phyast.pitt.edu/~micheles/mro.html


File: python.info,  Node: String Changes,  Next: Optimizations<13>,  Up: Other Language Changes<14>

1.15.16.1 String Changes
........................

   * The *note in: 179. operator now works differently for strings.
     Previously, when evaluating ‘X in Y’ where `X' and `Y' are strings,
     `X' could only be a single character.  That’s now changed; `X' can
     be a string of any length, and ‘X in Y’ will return *note True:
     594. if `X' is a substring of `Y'. If `X' is the empty string, the
     result is always *note True: 594.

          >>> 'ab' in 'abcd'
          True
          >>> 'ad' in 'abcd'
          False
          >>> '' in 'abcd'
          True

     Note that this doesn’t tell you where the substring starts; if you
     need that information, use the ‘find()’ string method.

   * The ‘strip()’, ‘lstrip()’, and ‘rstrip()’ string methods now have
     an optional argument for specifying the characters to strip.  The
     default is still to remove all whitespace characters:

          >>> '   abc '.strip()
          'abc'
          >>> '><><abc<><><>'.strip('<>')
          'abc'
          >>> '><><abc<><><>\n'.strip('<>')
          'abc<><><>\n'
          >>> u'\u4000\u4001abc\u4000'.strip(u'\u4000')
          u'\u4001abc'
          >>>

     (Suggested by Simon Brunning and implemented by Walter Dörwald.)

   * The ‘startswith()’ and ‘endswith()’ string methods now accept
     negative numbers for the `start' and `end' parameters.

   * Another new string method is ‘zfill()’, originally a function in
     the *note string: f6. module.  ‘zfill()’ pads a numeric string with
     zeros on the left until it’s the specified width.  Note that the
     ‘%’ operator is still more flexible and powerful than ‘zfill()’.

          >>> '45'.zfill(4)
          '0045'
          >>> '12345'.zfill(4)
          '12345'
          >>> 'goofy'.zfill(6)
          '0goofy'

     (Contributed by Walter Dörwald.)

   * A new type object, ‘basestring’, has been added.  Both 8-bit
     strings and Unicode strings inherit from this type, so
     ‘isinstance(obj, basestring)’ will return *note True: 594. for
     either kind of string.  It’s a completely abstract type, so you
     can’t create ‘basestring’ instances.

   * Interned strings are no longer immortal and will now be
     garbage-collected in the usual way when the only reference to them
     is from the internal dictionary of interned strings.  (Implemented
     by Oren Tirosh.)


File: python.info,  Node: Optimizations<13>,  Prev: String Changes,  Up: Other Language Changes<14>

1.15.16.2 Optimizations
.......................

   * The creation of new-style class instances has been made much
     faster; they’re now faster than classic classes!

   * The ‘sort()’ method of list objects has been extensively rewritten
     by Tim Peters, and the implementation is significantly faster.

   * Multiplication of large long integers is now much faster thanks to
     an implementation of Karatsuba multiplication, an algorithm that
     scales better than the O(n*n) required for the grade-school
     multiplication algorithm.  (Original patch by Christopher A. Craig,
     and significantly reworked by Tim Peters.)

   * The ‘SET_LINENO’ opcode is now gone.  This may provide a small
     speed increase, depending on your compiler’s idiosyncrasies.  See
     section *note Other Changes and Fixes: ecf. for a longer
     explanation.  (Removed by Michael Hudson.)

   * ‘xrange()’ objects now have their own iterator, making ‘for i in
     xrange(n)’ slightly faster than ‘for i in range(n)’.  (Patch by
     Raymond Hettinger.)

   * A number of small rearrangements have been made in various hotspots
     to improve performance, such as inlining a function or removing
     some code.  (Implemented mostly by GvR, but lots of people have
     contributed single changes.)

The net result of the 2.3 optimizations is that Python 2.3 runs the
pystone benchmark around 25% faster than Python 2.2.


File: python.info,  Node: New Improved and Deprecated Modules<4>,  Next: Pymalloc A Specialized Object Allocator,  Prev: Other Language Changes<14>,  Up: What’s New in Python 2 3

1.15.17 New, Improved, and Deprecated Modules
---------------------------------------------

As usual, Python’s standard library received a number of enhancements
and bug fixes.  Here’s a partial list of the most notable changes,
sorted alphabetically by module name.  Consult the ‘Misc/NEWS’ file in
the source tree for a more complete list of changes, or look through the
CVS logs for all the details.

   * The *note array: 6. module now supports arrays of Unicode
     characters using the ‘'u'’ format character.  Arrays also now
     support using the ‘+=’ assignment operator to add another array’s
     contents, and the ‘*=’ assignment operator to repeat an array.
     (Contributed by Jason Orendorff.)

   * The ‘bsddb’ module has been replaced by version 4.1.6 of the
     PyBSDDB(1) package, providing a more complete interface to the
     transactional features of the BerkeleyDB library.

     The old version of the module has been renamed to ‘bsddb185’ and is
     no longer built automatically; you’ll have to edit ‘Modules/Setup’
     to enable it.  Note that the new ‘bsddb’ package is intended to be
     compatible with the old module, so be sure to file bugs if you
     discover any incompatibilities.  When upgrading to Python 2.3, if
     the new interpreter is compiled with a new version of the
     underlying BerkeleyDB library, you will almost certainly have to
     convert your database files to the new version.  You can do this
     fairly easily with the new scripts ‘db2pickle.py’ and
     ‘pickle2db.py’ which you will find in the distribution’s
     ‘Tools/scripts’ directory.  If you’ve already been using the
     PyBSDDB package and importing it as ‘bsddb3’, you will have to
     change your ‘import’ statements to import it as ‘bsddb’.

   * The new *note bz2: 13. module is an interface to the bz2 data
     compression library.  bz2-compressed data is usually smaller than
     corresponding *note zlib: 14d.-compressed data.  (Contributed by
     Gustavo Niemeyer.)

   * A set of standard date/time types has been added in the new *note
     datetime: 30. module.  See the following section for more details.

   * The Distutils ‘Extension’ class now supports an extra constructor
     argument named `depends' for listing additional source files that
     an extension depends on.  This lets Distutils recompile the module
     if any of the dependency files are modified.  For example, if
     ‘sampmodule.c’ includes the header file ‘sample.h’, you would
     create the ‘Extension’ object like this:

          ext = Extension("samp",
                          sources=["sampmodule.c"],
                          depends=["sample.h"])

     Modifying ‘sample.h’ would then cause the module to be recompiled.
     (Contributed by Jeremy Hylton.)

   * Other minor changes to Distutils: it now checks for the ‘CC’,
     ‘CFLAGS’, ‘CPP’, ‘LDFLAGS’, and ‘CPPFLAGS’ environment variables,
     using them to override the settings in Python’s configuration
     (contributed by Robert Weber).

   * Previously the *note doctest: 66. module would only search the
     docstrings of public methods and functions for test cases, but it
     now also examines private ones as well.  The ‘DocTestSuite()’
     function creates a *note unittest.TestSuite: 7c1. object from a set
     of *note doctest: 66. tests.

   * The new ‘gc.get_referents(object)’ function returns a list of all
     the objects referenced by `object'.

   * The *note getopt: 85. module gained a new function, ‘gnu_getopt()’,
     that supports the same arguments as the existing *note getopt():
     85. function but uses GNU-style scanning mode.  The existing *note
     getopt(): 85. stops processing options as soon as a non-option
     argument is encountered, but in GNU-style mode processing
     continues, meaning that options and arguments can be mixed.  For
     example:

          >>> getopt.getopt(['-f', 'filename', 'output', '-v'], 'f:v')
          ([('-f', 'filename')], ['output', '-v'])
          >>> getopt.gnu_getopt(['-f', 'filename', 'output', '-v'], 'f:v')
          ([('-f', 'filename'), ('-v', '')], ['output'])

     (Contributed by Peter Åstrand.)

   * The *note grp: 8a, *note pwd: d6, and *note resource: e0. modules
     now return enhanced tuples:

          >>> import grp
          >>> g = grp.getgrnam('amk')
          >>> g.gr_name, g.gr_gid
          ('amk', 500)

   * The *note gzip: 8b. module can now handle files exceeding 2 GiB.

   * The new *note heapq: 8d. module contains an implementation of a
     heap queue algorithm.  A heap is an array-like data structure that
     keeps items in a partially sorted order such that, for every index
     `k', ‘heap[k] <= heap[2*k+1]’ and ‘heap[k] <= heap[2*k+2]’.  This
     makes it quick to remove the smallest item, and inserting a new
     item while maintaining the heap property is O(lg n).  (See
     ‘https://xlinux.nist.gov/dads//HTML/priorityque.html’ for more
     information about the priority queue data structure.)

     The *note heapq: 8d. module provides ‘heappush()’ and ‘heappop()’
     functions for adding and removing items while maintaining the heap
     property on top of some other mutable Python sequence type.  Here’s
     an example that uses a Python list:

          >>> import heapq
          >>> heap = []
          >>> for item in [3, 7, 5, 11, 1]:
          ...    heapq.heappush(heap, item)
          ...
          >>> heap
          [1, 3, 5, 11, 7]
          >>> heapq.heappop(heap)
          1
          >>> heapq.heappop(heap)
          3
          >>> heap
          [5, 7, 11]

     (Contributed by Kevin O’Connor.)

   * The IDLE integrated development environment has been updated using
     the code from the IDLEfork project
     (‘http://idlefork.sourceforge.net’).  The most notable feature is
     that the code being developed is now executed in a subprocess,
     meaning that there’s no longer any need for manual ‘reload()’
     operations.  IDLE’s core code has been incorporated into the
     standard library as the ‘idlelib’ package.

   * The *note imaplib: 97. module now supports IMAP over SSL.
     (Contributed by Piers Lauder and Tino Lange.)

   * The *note itertools: a3. contains a number of useful functions for
     use with iterators, inspired by various functions provided by the
     ML and Haskell languages.  For example,
     ‘itertools.ifilter(predicate, iterator)’ returns all elements in
     the iterator for which the function ‘predicate()’ returns *note
     True: 594, and ‘itertools.repeat(obj, N)’ returns ‘obj’ `N' times.
     There are a number of other functions in the module; see the
     package’s reference documentation for details.  (Contributed by
     Raymond Hettinger.)

   * Two new functions in the *note math: b1. module, ‘degrees(rads)’
     and ‘radians(degs)’, convert between radians and degrees.  Other
     functions in the *note math: b1. module such as *note math.sin():
     ed1. and *note math.cos(): ed2. have always required input values
     measured in radians.  Also, an optional `base' argument was added
     to *note math.log(): ed3. to make it easier to compute logarithms
     for bases other than ‘e’ and ‘10’.  (Contributed by Raymond
     Hettinger.)

   * Several new POSIX functions (‘getpgid()’, ‘killpg()’, ‘lchown()’,
     ‘loadavg()’, ‘major()’, ‘makedev()’, ‘minor()’, and ‘mknod()’) were
     added to the *note posix: d1. module that underlies the *note os:
     c4. module.  (Contributed by Gustavo Niemeyer, Geert Jansen, and
     Denis S. Otkidach.)

   * In the *note os: c4. module, the ‘*stat()’ family of functions can
     now report fractions of a second in a timestamp.  Such time stamps
     are represented as floats, similar to the value returned by *note
     time.time(): 42d.

     During testing, it was found that some applications will break if
     time stamps are floats.  For compatibility, when using the tuple
     interface of the ‘stat_result’ time stamps will be represented as
     integers.  When using named fields (a feature first introduced in
     Python 2.2), time stamps are still represented as integers, unless
     ‘os.stat_float_times()’ is invoked to enable float return values:

          >>> os.stat("/tmp").st_mtime
          1034791200
          >>> os.stat_float_times(True)
          >>> os.stat("/tmp").st_mtime
          1034791200.6335014

     In Python 2.4, the default will change to always returning floats.

     Application developers should enable this feature only if all their
     libraries work properly when confronted with floating point time
     stamps, or if they use the tuple API. If used, the feature should
     be activated on an application level instead of trying to enable it
     on a per-use basis.

   * The *note optparse: c3. module contains a new parser for
     command-line arguments that can convert option values to a
     particular Python type and will automatically generate a usage
     message.  See the following section for more details.

   * The old and never-documented ‘linuxaudiodev’ module has been
     deprecated, and a new version named *note ossaudiodev: c6. has been
     added.  The module was renamed because the OSS sound drivers can be
     used on platforms other than Linux, and the interface has also been
     tidied and brought up to date in various ways.  (Contributed by
     Greg Ward and Nicholas FitzRoy-Dale.)

   * The new *note platform: ce. module contains a number of functions
     that try to determine various properties of the platform you’re
     running on.  There are functions for getting the architecture, CPU
     type, the Windows OS version, and even the Linux distribution
     version.  (Contributed by Marc-André Lemburg.)

   * The parser objects provided by the ‘pyexpat’ module can now
     optionally buffer character data, resulting in fewer calls to your
     character data handler and therefore faster performance.  Setting
     the parser object’s ‘buffer_text’ attribute to *note True: 594.
     will enable buffering.

   * The ‘sample(population, k)’ function was added to the *note random:
     dc. module.  `population' is a sequence or ‘xrange’ object
     containing the elements of a population, and ‘sample()’ chooses `k'
     elements from the population without replacing chosen elements.
     `k' can be any value up to ‘len(population)’.  For example:

          >>> days = ['Mo', 'Tu', 'We', 'Th', 'Fr', 'St', 'Sn']
          >>> random.sample(days, 3)      # Choose 3 elements
          ['St', 'Sn', 'Th']
          >>> random.sample(days, 7)      # Choose 7 elements
          ['Tu', 'Th', 'Mo', 'We', 'St', 'Fr', 'Sn']
          >>> random.sample(days, 7)      # Choose 7 again
          ['We', 'Mo', 'Sn', 'Fr', 'Tu', 'St', 'Th']
          >>> random.sample(days, 8)      # Can't choose eight
          Traceback (most recent call last):
            File "<stdin>", line 1, in ?
            File "random.py", line 414, in sample
                raise ValueError, "sample larger than population"
          ValueError: sample larger than population
          >>> random.sample(xrange(1,10000,2), 10)   # Choose ten odd nos. under 10000
          [3407, 3805, 1505, 7023, 2401, 2267, 9733, 3151, 8083, 9195]

     The *note random: dc. module now uses a new algorithm, the Mersenne
     Twister, implemented in C. It’s faster and more extensively studied
     than the previous algorithm.

     (All changes contributed by Raymond Hettinger.)

   * The *note readline: de. module also gained a number of new
     functions: ‘get_history_item()’, ‘get_current_history_length()’,
     and ‘redisplay()’.

   * The ‘rexec’ and ‘Bastion’ modules have been declared dead, and
     attempts to import them will fail with a *note RuntimeError: 3dc.
     New-style classes provide new ways to break out of the restricted
     execution environment provided by ‘rexec’, and no one has interest
     in fixing them or time to do so.  If you have applications using
     ‘rexec’, rewrite them to use something else.

     (Sticking with Python 2.2 or 2.1 will not make your applications
     any safer because there are known bugs in the ‘rexec’ module in
     those versions.  To repeat: if you’re using ‘rexec’, stop using it
     immediately.)

   * The ‘rotor’ module has been deprecated because the algorithm it
     uses for encryption is not believed to be secure.  If you need
     encryption, use one of the several AES Python modules that are
     available separately.

   * The *note shutil: e9. module gained a ‘move(src, dest)’ function
     that recursively moves a file or directory to a new location.

   * Support for more advanced POSIX signal handling was added to the
     *note signal: ea. but then removed again as it proved impossible to
     make it work reliably across platforms.

   * The *note socket: ef. module now supports timeouts.  You can call
     the ‘settimeout(t)’ method on a socket object to set a timeout of
     `t' seconds.  Subsequent socket operations that take longer than
     `t' seconds to complete will abort and raise a *note
     socket.timeout: cd9. exception.

     The original timeout implementation was by Tim O’Malley.  Michael
     Gilfix integrated it into the Python *note socket: ef. module and
     shepherded it through a lengthy review.  After the code was checked
     in, Guido van Rossum rewrote parts of it.  (This is a good example
     of a collaborative development process in action.)

   * On Windows, the *note socket: ef. module now ships with Secure
     Sockets Layer (SSL) support.

   * The value of the C ‘PYTHON_API_VERSION’ macro is now exposed at the
     Python level as ‘sys.api_version’.  The current exception can be
     cleared by calling the new ‘sys.exc_clear()’ function.

   * The new *note tarfile: 101. module allows reading from and writing
     to ‘tar’-format archive files.  (Contributed by Lars Gustäbel.)

   * The new *note textwrap: 10a. module contains functions for wrapping
     strings containing paragraphs of text.  The ‘wrap(text, width)’
     function takes a string and returns a list containing the text
     split into lines of no more than the chosen width.  The ‘fill(text,
     width)’ function returns a single string, reformatted to fit into
     lines no longer than the chosen width.  (As you can guess, ‘fill()’
     is built on top of ‘wrap()’.  For example:

          >>> import textwrap
          >>> paragraph = "Not a whit, we defy augury: ... more text ..."
          >>> textwrap.wrap(paragraph, 60)
          ["Not a whit, we defy augury: there's a special providence in",
           "the fall of a sparrow. If it be now, 'tis not to come; if it",
           ...]
          >>> print textwrap.fill(paragraph, 35)
          Not a whit, we defy augury: there's
          a special providence in the fall of
          a sparrow. If it be now, 'tis not
          to come; if it be not to come, it
          will be now; if it be not now, yet
          it will come: the readiness is all.
          >>>

     The module also contains a ‘TextWrapper’ class that actually
     implements the text wrapping strategy.  Both the ‘TextWrapper’
     class and the ‘wrap()’ and ‘fill()’ functions support a number of
     additional keyword arguments for fine-tuning the formatting;
     consult the module’s documentation for details.  (Contributed by
     Greg Ward.)

   * The ‘thread’ and *note threading: 10b. modules now have companion
     modules, ‘dummy_thread’ and ‘dummy_threading’, that provide a
     do-nothing implementation of the ‘thread’ module’s interface for
     platforms where threads are not supported.  The intention is to
     simplify thread-aware modules (ones that `don’t' rely on threads to
     run) by putting the following code at the top:

          try:
              import threading as _threading
          except ImportError:
              import dummy_threading as _threading

     In this example, ‘_threading’ is used as the module name to make it
     clear that the module being used is not necessarily the actual
     *note threading: 10b. module.  Code can call functions and use
     classes in ‘_threading’ whether or not threads are supported,
     avoiding an *note if: eab. statement and making the code slightly
     clearer.  This module will not magically make multithreaded code
     run without threads; code that waits for another thread to return
     or to do something will simply hang forever.

   * The *note time: 10c. module’s ‘strptime()’ function has long been
     an annoyance because it uses the platform C library’s ‘strptime()’
     implementation, and different platforms sometimes have odd bugs.
     Brett Cannon contributed a portable implementation that’s written
     in pure Python and should behave identically on all platforms.

   * The new *note timeit: 10d. module helps measure how long snippets
     of Python code take to execute.  The ‘timeit.py’ file can be run
     directly from the command line, or the module’s ‘Timer’ class can
     be imported and used directly.  Here’s a short example that figures
     out whether it’s faster to convert an 8-bit string to Unicode by
     appending an empty Unicode string to it or by using the ‘unicode()’
     function:

          import timeit

          timer1 = timeit.Timer('unicode("abc")')
          timer2 = timeit.Timer('"abc" + u""')

          # Run three trials
          print timer1.repeat(repeat=3, number=100000)
          print timer2.repeat(repeat=3, number=100000)

          # On my laptop this outputs:
          # [0.36831796169281006, 0.37441694736480713, 0.35304892063140869]
          # [0.17574405670166016, 0.18193507194519043, 0.17565798759460449]

   * The ‘Tix’ module has received various bug fixes and updates for the
     current version of the Tix package.

   * The ‘Tkinter’ module now works with a thread-enabled version of
     Tcl.  Tcl’s threading model requires that widgets only be accessed
     from the thread in which they’re created; accesses from another
     thread can cause Tcl to panic.  For certain Tcl interfaces,
     ‘Tkinter’ will now automatically avoid this when a widget is
     accessed from a different thread by marshalling a command, passing
     it to the correct thread, and waiting for the results.  Other
     interfaces can’t be handled automatically but ‘Tkinter’ will now
     raise an exception on such an access so that you can at least find
     out about the problem.  See
     ‘https://mail.python.org/pipermail/python-dev/2002-December/031107.html’
     for a more detailed explanation of this change.  (Implemented by
     Martin von Löwis.)

   * Calling Tcl methods through ‘_tkinter’ no longer returns only
     strings.  Instead, if Tcl returns other objects those objects are
     converted to their Python equivalent, if one exists, or wrapped
     with a ‘_tkinter.Tcl_Obj’ object if no Python equivalent exists.
     This behavior can be controlled through the ‘wantobjects()’ method
     of ‘tkapp’ objects.

     When using ‘_tkinter’ through the ‘Tkinter’ module (as most Tkinter
     applications will), this feature is always activated.  It should
     not cause compatibility problems, since Tkinter would always
     convert string results to Python types where possible.

     If any incompatibilities are found, the old behavior can be
     restored by setting the ‘wantobjects’ variable in the ‘Tkinter’
     module to false before creating the first ‘tkapp’ object.

          import Tkinter
          Tkinter.wantobjects = 0

     Any breakage caused by this change should be reported as a bug.

   * The ‘UserDict’ module has a new ‘DictMixin’ class which defines all
     dictionary methods for classes that already have a minimum mapping
     interface.  This greatly simplifies writing classes that need to be
     substitutable for dictionaries, such as the classes in the *note
     shelve: e7. module.

     Adding the mix-in as a superclass provides the full dictionary
     interface whenever the class defines *note __getitem__(): 3a2,
     *note __setitem__(): d2a, *note __delitem__(): d2b, and ‘keys()’.
     For example:

          >>> import UserDict
          >>> class SeqDict(UserDict.DictMixin):
          ...     """Dictionary lookalike implemented with lists."""
          ...     def __init__(self):
          ...         self.keylist = []
          ...         self.valuelist = []
          ...     def __getitem__(self, key):
          ...         try:
          ...             i = self.keylist.index(key)
          ...         except ValueError:
          ...             raise KeyError
          ...         return self.valuelist[i]
          ...     def __setitem__(self, key, value):
          ...         try:
          ...             i = self.keylist.index(key)
          ...             self.valuelist[i] = value
          ...         except ValueError:
          ...             self.keylist.append(key)
          ...             self.valuelist.append(value)
          ...     def __delitem__(self, key):
          ...         try:
          ...             i = self.keylist.index(key)
          ...         except ValueError:
          ...             raise KeyError
          ...         self.keylist.pop(i)
          ...         self.valuelist.pop(i)
          ...     def keys(self):
          ...         return list(self.keylist)
          ...
          >>> s = SeqDict()
          >>> dir(s)      # See that other dictionary methods are implemented
          ['__cmp__', '__contains__', '__delitem__', '__doc__', '__getitem__',
           '__init__', '__iter__', '__len__', '__module__', '__repr__',
           '__setitem__', 'clear', 'get', 'has_key', 'items', 'iteritems',
           'iterkeys', 'itervalues', 'keylist', 'keys', 'pop', 'popitem',
           'setdefault', 'update', 'valuelist', 'values']

     (Contributed by Raymond Hettinger.)

   * The DOM implementation in *note xml.dom.minidom: 13e. can now
     generate XML output in a particular encoding by providing an
     optional encoding argument to the ‘toxml()’ and ‘toprettyxml()’
     methods of DOM nodes.

   * The ‘xmlrpclib’ module now supports an XML-RPC extension for
     handling nil data values such as Python’s ‘None’.  Nil values are
     always supported on unmarshalling an XML-RPC response.  To generate
     requests containing ‘None’, you must supply a true value for the
     `allow_none' parameter when creating a ‘Marshaller’ instance.

   * The new ‘DocXMLRPCServer’ module allows writing self-documenting
     XML-RPC servers.  Run it in demo mode (as a program) to see it in
     action.  Pointing the Web browser to the RPC server produces
     pydoc-style documentation; pointing xmlrpclib to the server allows
     invoking the actual methods.  (Contributed by Brian Quinlan.)

   * Support for internationalized domain names (RFCs 3454, 3490, 3491,
     and 3492) has been added.  The “idna” encoding can be used to
     convert between a Unicode domain name and the ASCII-compatible
     encoding (ACE) of that name.

          >{}>{}> u"www.Alliancefrançaise.nu".encode("idna")
          'www.xn--alliancefranaise-npb.nu'

     The *note socket: ef. module has also been extended to
     transparently convert Unicode hostnames to the ACE version before
     passing them to the C library.  Modules that deal with hostnames
     such as ‘httplib’ and *note ftplib: 82.) also support Unicode host
     names; ‘httplib’ also sends HTTP ‘Host’ headers using the ACE
     version of the domain name.  *note urllib: 126. supports Unicode
     URLs with non-ASCII host names as long as the ‘path’ part of the
     URL is ASCII only.

     To implement this change, the *note stringprep: f7. module, the
     ‘mkstringprep’ tool and the ‘punycode’ encoding have been added.

* Menu:

* Date/Time Type::
* The optparse Module::

   ---------- Footnotes ----------

   (1) http://pybsddb.sourceforge.net


File: python.info,  Node: Date/Time Type,  Next: The optparse Module,  Up: New Improved and Deprecated Modules<4>

1.15.17.1 Date/Time Type
........................

Date and time types suitable for expressing timestamps were added as the
*note datetime: 30. module.  The types don’t support different calendars
or many fancy features, and just stick to the basics of representing
time.

The three primary types are: ‘date’, representing a day, month, and
year; *note time: 5ed, consisting of hour, minute, and second; and *note
datetime: 1a0, which contains all the attributes of both ‘date’ and
*note time: 5ed.  There’s also a ‘timedelta’ class representing
differences between two points in time, and time zone logic is
implemented by classes inheriting from the abstract ‘tzinfo’ class.

You can create instances of ‘date’ and *note time: 5ed. by either
supplying keyword arguments to the appropriate constructor, e.g.
‘datetime.date(year=1972, month=10, day=15)’, or by using one of a
number of class methods.  For example, the ‘date.today()’ class method
returns the current local date.

Once created, instances of the date/time classes are all immutable.
There are a number of methods for producing formatted strings from
objects:

     >>> import datetime
     >>> now = datetime.datetime.now()
     >>> now.isoformat()
     '2002-12-30T21:27:03.994956'
     >>> now.ctime()  # Only available on date, datetime
     'Mon Dec 30 21:27:03 2002'
     >>> now.strftime('%Y %d %b')
     '2002 30 Dec'

The ‘replace()’ method allows modifying one or more fields of a ‘date’
or *note datetime: 1a0. instance, returning a new instance:

     >>> d = datetime.datetime.now()
     >>> d
     datetime.datetime(2002, 12, 30, 22, 15, 38, 827738)
     >>> d.replace(year=2001, hour = 12)
     datetime.datetime(2001, 12, 30, 12, 15, 38, 827738)
     >>>

Instances can be compared, hashed, and converted to strings (the result
is the same as that of ‘isoformat()’).  ‘date’ and *note datetime: 1a0.
instances can be subtracted from each other, and added to ‘timedelta’
instances.  The largest missing feature is that there’s no standard
library support for parsing strings and getting back a ‘date’ or *note
datetime: 1a0.

For more information, refer to the module’s reference documentation.
(Contributed by Tim Peters.)


File: python.info,  Node: The optparse Module,  Prev: Date/Time Type,  Up: New Improved and Deprecated Modules<4>

1.15.17.2 The optparse Module
.............................

The *note getopt: 85. module provides simple parsing of command-line
arguments.  The new *note optparse: c3. module (originally named Optik)
provides more elaborate command-line parsing that follows the Unix
conventions, automatically creates the output for ‘--help’, and can
perform different actions for different options.

You start by creating an instance of ‘OptionParser’ and telling it what
your program’s options are.

     import sys
     from optparse import OptionParser

     op = OptionParser()
     op.add_option('-i', '--input',
                   action='store', type='string', dest='input',
                   help='set input filename')
     op.add_option('-l', '--length',
                   action='store', type='int', dest='length',
                   help='set maximum length of output')

Parsing a command line is then done by calling the ‘parse_args()’
method.

     options, args = op.parse_args(sys.argv[1:])
     print options
     print args

This returns an object containing all of the option values, and a list
of strings containing the remaining arguments.

Invoking the script with the various arguments now works as you’d expect
it to.  Note that the length argument is automatically converted to an
integer.

     $ ./python opt.py -i data arg1
     <Values at 0x400cad4c: {'input': 'data', 'length': None}>
     ['arg1']
     $ ./python opt.py --input=data --length=4
     <Values at 0x400cad2c: {'input': 'data', 'length': 4}>
     []
     $

The help message is automatically generated for you:

     $ ./python opt.py --help
     usage: opt.py [options]

     options:
       -h, --help            show this help message and exit
       -iINPUT, --input=INPUT
                             set input filename
       -lLENGTH, --length=LENGTH
                             set maximum length of output
     $

See the module’s documentation for more details.

Optik was written by Greg Ward, with suggestions from the readers of the
Getopt SIG.


File: python.info,  Node: Pymalloc A Specialized Object Allocator,  Next: Build and C API Changes<12>,  Prev: New Improved and Deprecated Modules<4>,  Up: What’s New in Python 2 3

1.15.18 Pymalloc: A Specialized Object Allocator
------------------------------------------------

Pymalloc, a specialized object allocator written by Vladimir Marangozov,
was a feature added to Python 2.1.  Pymalloc is intended to be faster
than the system ‘malloc()’ and to have less memory overhead for
allocation patterns typical of Python programs.  The allocator uses C’s
‘malloc()’ function to get large pools of memory and then fulfills
smaller memory requests from these pools.

In 2.1 and 2.2, pymalloc was an experimental feature and wasn’t enabled
by default; you had to explicitly enable it when compiling Python by
providing the ‘--with-pymalloc’ option to the ‘configure’ script.  In
2.3, pymalloc has had further enhancements and is now enabled by
default; you’ll have to supply ‘--without-pymalloc’ to disable it.

This change is transparent to code written in Python; however, pymalloc
may expose bugs in C extensions.  Authors of C extension modules should
test their code with pymalloc enabled, because some incorrect code may
cause core dumps at runtime.

There’s one particularly common error that causes problems.  There are a
number of memory allocation functions in Python’s C API that have
previously just been aliases for the C library’s ‘malloc()’ and
‘free()’, meaning that if you accidentally called mismatched functions
the error wouldn’t be noticeable.  When the object allocator is enabled,
these functions aren’t aliases of ‘malloc()’ and ‘free()’ any more, and
calling the wrong function to free memory may get you a core dump.  For
example, if memory was allocated using *note PyObject_Malloc(): 602, it
has to be freed using *note PyObject_Free(): 5fe, not ‘free()’.  A few
modules included with Python fell afoul of this and had to be fixed;
doubtless there are more third-party modules that will have the same
problem.

As part of this change, the confusing multiple interfaces for allocating
memory have been consolidated down into two API families.  Memory
allocated with one family must not be manipulated with functions from
the other family.  There is one family for allocating chunks of memory
and another family of functions specifically for allocating Python
objects.

   * To allocate and free an undistinguished chunk of memory use the
     “raw memory” family: *note PyMem_Malloc(): 5ff, *note
     PyMem_Realloc(): a50, and *note PyMem_Free(): e6e.

   * The “object memory” family is the interface to the pymalloc
     facility described above and is biased towards a large number of
     “small” allocations: *note PyObject_Malloc(): 602, *note
     PyObject_Realloc(): e6f, and *note PyObject_Free(): 5fe.

   * To allocate and free Python objects, use the “object” family *note
     PyObject_New(): 268, *note PyObject_NewVar(): 269, and *note
     PyObject_Del(): ed8.

Thanks to lots of work by Tim Peters, pymalloc in 2.3 also provides
debugging features to catch memory overwrites and doubled frees in both
extension modules and in the interpreter itself.  To enable this
support, compile a debugging version of the Python interpreter by
running ‘configure’ with ‘--with-pydebug’.

To aid extension writers, a header file ‘Misc/pymemcompat.h’ is
distributed with the source to Python 2.3 that allows Python extensions
to use the 2.3 interfaces to memory allocation while compiling against
any version of Python since 1.5.2.  You would copy the file from
Python’s source distribution and bundle it with the source of your
extension.

See also
........

‘https://hg.python.org/cpython/file/default/Objects/obmalloc.c’

     For the full details of the pymalloc implementation, see the
     comments at the top of the file ‘Objects/obmalloc.c’ in the Python
     source code.  The above link points to the file within the
     python.org SVN browser.


File: python.info,  Node: Build and C API Changes<12>,  Next: Other Changes and Fixes<2>,  Prev: Pymalloc A Specialized Object Allocator,  Up: What’s New in Python 2 3

1.15.19 Build and C API Changes
-------------------------------

Changes to Python’s build process and to the C API include:

   * The cycle detection implementation used by the garbage collection
     has proven to be stable, so it’s now been made mandatory.  You can
     no longer compile Python without it, and the ‘--with-cycle-gc’
     switch to ‘configure’ has been removed.

   * Python can now optionally be built as a shared library
     (‘libpython2.3.so’) by supplying ‘--enable-shared’ when running
     Python’s ‘configure’ script.  (Contributed by Ondrej Palkovsky.)

   * The ‘DL_EXPORT’ and ‘DL_IMPORT’ macros are now deprecated.
     Initialization functions for Python extension modules should now be
     declared using the new macro ‘PyMODINIT_FUNC’, while the Python
     core will generally use the ‘PyAPI_FUNC’ and ‘PyAPI_DATA’ macros.

   * The interpreter can be compiled without any docstrings for the
     built-in functions and modules by supplying ‘--without-doc-strings’
     to the ‘configure’ script.  This makes the Python executable about
     10% smaller, but will also mean that you can’t get help for
     Python’s built-ins.  (Contributed by Gustavo Niemeyer.)

   * The ‘PyArg_NoArgs()’ macro is now deprecated, and code that uses it
     should be changed.  For Python 2.2 and later, the method definition
     table can specify the *note METH_NOARGS: eda. flag, signalling that
     there are no arguments, and the argument checking can then be
     removed.  If compatibility with pre-2.2 versions of Python is
     important, the code could use ‘PyArg_ParseTuple(args, "")’ instead,
     but this will be slower than using *note METH_NOARGS: eda.

   * *note PyArg_ParseTuple(): 393. accepts new format characters for
     various sizes of unsigned integers: ‘B’ for ‘unsigned char’, ‘H’
     for ‘unsigned short int’, ‘I’ for ‘unsigned int’, and ‘K’ for
     ‘unsigned long long’.

   * A new function, ‘PyObject_DelItemString(mapping, char *key)’ was
     added as shorthand for ‘PyObject_DelItem(mapping,
     PyString_New(key))’.

   * File objects now manage their internal string buffer differently,
     increasing it exponentially when needed.  This results in the
     benchmark tests in ‘Lib/test/test_bufio.py’ speeding up
     considerably (from 57 seconds to 1.7 seconds, according to one
     measurement).

   * It’s now possible to define class and static methods for a C
     extension type by setting either the *note METH_CLASS: edb. or
     *note METH_STATIC: edc. flags in a method’s *note PyMethodDef: edd.
     structure.

   * Python now includes a copy of the Expat XML parser’s source code,
     removing any dependence on a system version or local installation
     of Expat.

   * If you dynamically allocate type objects in your extension, you
     should be aware of a change in the rules relating to the
     ‘__module__’ and *note __name__: d2f. attributes.  In summary, you
     will want to ensure the type’s dictionary contains a ‘'__module__'’
     key; making the module name the part of the type name leading up to
     the final period will no longer have the desired effect.  For more
     detail, read the API reference documentation or the source.

* Menu:

* Port-Specific Changes: Port-Specific Changes<3>.


File: python.info,  Node: Port-Specific Changes<3>,  Up: Build and C API Changes<12>

1.15.19.1 Port-Specific Changes
...............................

Support for a port to IBM’s OS/2 using the EMX runtime environment was
merged into the main Python source tree.  EMX is a POSIX emulation layer
over the OS/2 system APIs.  The Python port for EMX tries to support all
the POSIX-like capability exposed by the EMX runtime, and mostly
succeeds; ‘fork()’ and *note fcntl(): 7c. are restricted by the
limitations of the underlying emulation layer.  The standard OS/2 port,
which uses IBM’s Visual Age compiler, also gained support for
case-sensitive import semantics as part of the integration of the EMX
port into CVS. (Contributed by Andrew MacIntyre.)

On MacOS, most toolbox modules have been weaklinked to improve backward
compatibility.  This means that modules will no longer fail to load if a
single routine is missing on the current OS version.  Instead calling
the missing routine will raise an exception.  (Contributed by Jack
Jansen.)

The RPM spec files, found in the ‘Misc/RPM/’ directory in the Python
source distribution, were updated for 2.3.  (Contributed by Sean
Reifschneider.)

Other new platforms now supported by Python include AtheOS
(‘http://www.atheos.cx/’), GNU/Hurd, and OpenVMS.


File: python.info,  Node: Other Changes and Fixes<2>,  Next: Porting to Python 2 3,  Prev: Build and C API Changes<12>,  Up: What’s New in Python 2 3

1.15.20 Other Changes and Fixes
-------------------------------

As usual, there were a bunch of other improvements and bugfixes
scattered throughout the source tree.  A search through the CVS change
logs finds there were 523 patches applied and 514 bugs fixed between
Python 2.2 and 2.3.  Both figures are likely to be underestimates.

Some of the more notable changes are:

   * If the *note PYTHONINSPECT: ee0. environment variable is set, the
     Python interpreter will enter the interactive prompt after running
     a Python program, as if Python had been invoked with the *note -i:
     ee1. option.  The environment variable can be set before running
     the Python interpreter, or it can be set by the Python program as
     part of its execution.

   * The ‘regrtest.py’ script now provides a way to allow “all resources
     except `foo'.” A resource name passed to the ‘-u’ option can now be
     prefixed with a hyphen (‘'-'’) to mean “remove this resource.” For
     example, the option ‘‘-uall,-bsddb’’ could be used to enable the
     use of all resources except ‘bsddb’.

   * The tools used to build the documentation now work under Cygwin as
     well as Unix.

   * The ‘SET_LINENO’ opcode has been removed.  Back in the mists of
     time, this opcode was needed to produce line numbers in tracebacks
     and support trace functions (for, e.g., *note pdb: c9.).  Since
     Python 1.5, the line numbers in tracebacks have been computed using
     a different mechanism that works with “python -O”.  For Python 2.3
     Michael Hudson implemented a similar scheme to determine when to
     call the trace function, removing the need for ‘SET_LINENO’
     entirely.

     It would be difficult to detect any resulting difference from
     Python code, apart from a slight speed up when Python is run
     without *note -O: 77e.

     C extensions that access the ‘f_lineno’ field of frame objects
     should instead call ‘PyCode_Addr2Line(f->f_code, f->f_lasti)’.
     This will have the added effect of making the code work as desired
     under “python -O” in earlier versions of Python.

     A nifty new feature is that trace functions can now assign to the
     ‘f_lineno’ attribute of frame objects, changing the line that will
     be executed next.  A ‘jump’ command has been added to the *note
     pdb: c9. debugger taking advantage of this new feature.
     (Implemented by Richie Hindle.)


File: python.info,  Node: Porting to Python 2 3,  Next: Acknowledgements<5>,  Prev: Other Changes and Fixes<2>,  Up: What’s New in Python 2 3

1.15.21 Porting to Python 2.3
-----------------------------

This section lists previously described changes that may require changes
to your code:

   * *note yield: 2c7. is now always a keyword; if it’s used as a
     variable name in your code, a different name must be chosen.

   * For strings `X' and `Y', ‘X in Y’ now works if `X' is more than one
     character long.

   * The *note int(): 204. type constructor will now return a long
     integer instead of raising an *note OverflowError: a41. when a
     string or floating-point number is too large to fit into an
     integer.

   * If you have Unicode strings that contain 8-bit characters, you must
     declare the file’s encoding (UTF-8, Latin-1, or whatever) by adding
     a comment to the top of the file.  See section *note PEP 263;
     Source Code Encodings: ead. for more information.

   * Calling Tcl methods through ‘_tkinter’ no longer returns only
     strings.  Instead, if Tcl returns other objects those objects are
     converted to their Python equivalent, if one exists, or wrapped
     with a ‘_tkinter.Tcl_Obj’ object if no Python equivalent exists.

   * Large octal and hex literals such as ‘0xffffffff’ now trigger a
     *note FutureWarning: 435.  Currently they’re stored as 32-bit
     numbers and result in a negative value, but in Python 2.4 they’ll
     become positive long integers.

     There are a few ways to fix this warning.  If you really need a
     positive number, just add an ‘L’ to the end of the literal.  If
     you’re trying to get a 32-bit integer with low bits set and have
     previously used an expression such as ‘~(1 << 31)’, it’s probably
     clearest to start with all bits set and clear the desired upper
     bits.  For example, to clear just the top bit (bit 31), you could
     write ‘0xffffffffL &~(1L<<31)’.

   * You can no longer disable assertions by assigning to ‘__debug__’.

   * The Distutils ‘setup()’ function has gained various new keyword
     arguments such as `depends'.  Old versions of the Distutils will
     abort if passed unknown keywords.  A solution is to check for the
     presence of the new ‘get_distutil_options()’ function in your
     ‘setup.py’ and only uses the new keywords with a version of the
     Distutils that supports them:

          from distutils import core

          kw = {'sources': 'foo.c', ...}
          if hasattr(core, 'get_distutil_options'):
              kw['depends'] = ['foo.h']
          ext = Extension(**kw)

   * Using ‘None’ as a variable name will now result in a *note
     SyntaxWarning: 2c9. warning.

   * Names of extension types defined by the modules included with
     Python now contain the module and a ‘'.'’ in front of the type
     name.


File: python.info,  Node: Acknowledgements<5>,  Prev: Porting to Python 2 3,  Up: What’s New in Python 2 3

1.15.22 Acknowledgements
------------------------

The author would like to thank the following people for offering
suggestions, corrections and assistance with various drafts of this
article: Jeff Bauer, Simon Brunning, Brett Cannon, Michael Chermside,
Andrew Dalke, Scott David Daniels, Fred L. Drake, Jr., David Fraser,
Kelly Gerber, Raymond Hettinger, Michael Hudson, Chris Lambert, Detlef
Lannert, Martin von Löwis, Andrew MacIntyre, Lalo Martins, Chad Netzer,
Gustavo Niemeyer, Neal Norwitz, Hans Nowak, Chris Reedy, Francesco
Ricciardi, Vinay Sajip, Neil Schemenauer, Roman Suzi, Jason Tishler,
Just van Rossum.


File: python.info,  Node: What’s New in Python 2 2,  Next: What’s New in Python 2 1,  Prev: What’s New in Python 2 3,  Up: What’s New in Python

1.16 What’s New in Python 2.2
=============================


Author: A.M. Kuchling

* Menu:

* Introduction::
* PEPs 252 and 253; Type and Class Changes: PEPs 252 and 253 Type and Class Changes.
* PEP 234; Iterators: PEP 234 Iterators.
* PEP 255; Simple Generators: PEP 255 Simple Generators<2>.
* PEP 237; Unifying Long Integers and Integers: PEP 237 Unifying Long Integers and Integers<2>.
* PEP 238; Changing the Division Operator: PEP 238 Changing the Division Operator.
* Unicode Changes::
* PEP 227; Nested Scopes: PEP 227 Nested Scopes.
* New and Improved Modules: New and Improved Modules<3>.
* Interpreter Changes and Fixes::
* Other Changes and Fixes: Other Changes and Fixes<3>.
* Acknowledgements: Acknowledgements<6>.


File: python.info,  Node: Introduction,  Next: PEPs 252 and 253 Type and Class Changes,  Up: What’s New in Python 2 2

1.16.1 Introduction
-------------------

This article explains the new features in Python 2.2.2, released on
October 14, 2002.  Python 2.2.2 is a bugfix release of Python 2.2,
originally released on December 21, 2001.

Python 2.2 can be thought of as the “cleanup release”.  There are some
features such as generators and iterators that are completely new, but
most of the changes, significant and far-reaching though they may be,
are aimed at cleaning up irregularities and dark corners of the language
design.

This article doesn’t attempt to provide a complete specification of the
new features, but instead provides a convenient overview.  For full
details, you should refer to the documentation for Python 2.2, such as
the Python Library Reference(1) and the Python Reference Manual(2).  If
you want to understand the complete implementation and design rationale
for a change, refer to the PEP for a particular new feature.

   ---------- Footnotes ----------

   (1) https://docs.python.org/2.2/lib/lib.html

   (2) https://docs.python.org/2.2/ref/ref.html


File: python.info,  Node: PEPs 252 and 253 Type and Class Changes,  Next: PEP 234 Iterators,  Prev: Introduction,  Up: What’s New in Python 2 2

1.16.2 PEPs 252 and 253: Type and Class Changes
-----------------------------------------------

The largest and most far-reaching changes in Python 2.2 are to Python’s
model of objects and classes.  The changes should be backward
compatible, so it’s likely that your code will continue to run
unchanged, but the changes provide some amazing new capabilities.
Before beginning this, the longest and most complicated section of this
article, I’ll provide an overview of the changes and offer some
comments.

A long time ago I wrote a Web page listing flaws in Python’s design.
One of the most significant flaws was that it’s impossible to subclass
Python types implemented in C. In particular, it’s not possible to
subclass built-in types, so you can’t just subclass, say, lists in order
to add a single useful method to them.  The ‘UserList’ module provides a
class that supports all of the methods of lists and that can be
subclassed further, but there’s lots of C code that expects a regular
Python list and won’t accept a ‘UserList’ instance.

Python 2.2 fixes this, and in the process adds some exciting new
capabilities.  A brief summary:

   * You can subclass built-in types such as lists and even integers,
     and your subclasses should work in every place that requires the
     original type.

   * It’s now possible to define static and class methods, in addition
     to the instance methods available in previous versions of Python.

   * It’s also possible to automatically call methods on accessing or
     setting an instance attribute by using a new mechanism called
     `properties'.  Many uses of *note __getattr__(): 42a. can be
     rewritten to use properties instead, making the resulting code
     simpler and faster.  As a small side benefit, attributes can now
     have docstrings, too.

   * The list of legal attributes for an instance can be limited to a
     particular set using `slots', making it possible to safeguard
     against typos and perhaps make more optimizations possible in
     future versions of Python.

Some users have voiced concern about all these changes.  Sure, they say,
the new features are neat and lend themselves to all sorts of tricks
that weren’t possible in previous versions of Python, but they also make
the language more complicated.  Some people have said that they’ve
always recommended Python for its simplicity, and feel that its
simplicity is being lost.

Personally, I think there’s no need to worry.  Many of the new features
are quite esoteric, and you can write a lot of Python code without ever
needed to be aware of them.  Writing a simple class is no more difficult
than it ever was, so you don’t need to bother learning or teaching them
unless they’re actually needed.  Some very complicated tasks that were
previously only possible from C will now be possible in pure Python, and
to my mind that’s all for the better.

I’m not going to attempt to cover every single corner case and small
change that were required to make the new features work.  Instead this
section will paint only the broad strokes.  See section *note Related
Links: ee9, “Related Links”, for further sources of information about
Python 2.2’s new object model.

* Menu:

* Old and New Classes::
* Descriptors::
* Multiple Inheritance; The Diamond Rule: Multiple Inheritance The Diamond Rule.
* Attribute Access::
* Related Links::


File: python.info,  Node: Old and New Classes,  Next: Descriptors,  Up: PEPs 252 and 253 Type and Class Changes

1.16.2.1 Old and New Classes
............................

First, you should know that Python 2.2 really has two kinds of classes:
classic or old-style classes, and new-style classes.  The old-style
class model is exactly the same as the class model in earlier versions
of Python.  All the new features described in this section apply only to
new-style classes.  This divergence isn’t intended to last forever;
eventually old-style classes will be dropped, possibly in Python 3.0.

So how do you define a new-style class?  You do it by subclassing an
existing new-style class.  Most of Python’s built-in types, such as
integers, lists, dictionaries, and even files, are new-style classes
now.  A new-style class named *note object: 3d2, the base class for all
built-in types, has also been added so if no built-in type is suitable,
you can just subclass *note object: 3d2.:

     class C(object):
         def __init__ (self):
             ...
         ...

This means that *note class: d32. statements that don’t have any base
classes are always classic classes in Python 2.2.  (Actually you can
also change this by setting a module-level variable named
‘__metaclass__’ — see PEP 253(1) for the details — but it’s easier to
just subclass *note object: 3d2.)

The type objects for the built-in types are available as built-ins,
named using a clever trick.  Python has always had built-in functions
named *note int(): 204, *note float(): 1fd, and *note str(): 205.  In
2.2, they aren’t functions any more, but type objects that behave as
factories when called.

     >>> int
     <type 'int'>
     >>> int('123')
     123

To make the set of types complete, new type objects such as *note
dict(): 164. and ‘file()’ have been added.  Here’s a more interesting
example, adding a ‘lock()’ method to file objects:

     class LockableFile(file):
         def lock (self, operation, length=0, start=0, whence=0):
             import fcntl
             return fcntl.lockf(self.fileno(), operation,
                                length, start, whence)

The now-obsolete ‘posixfile’ module contained a class that emulated all
of a file object’s methods and also added a ‘lock()’ method, but this
class couldn’t be passed to internal functions that expected a built-in
file, something which is possible with our new ‘LockableFile’.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0253


File: python.info,  Node: Descriptors,  Next: Multiple Inheritance The Diamond Rule,  Prev: Old and New Classes,  Up: PEPs 252 and 253 Type and Class Changes

1.16.2.2 Descriptors
....................

In previous versions of Python, there was no consistent way to discover
what attributes and methods were supported by an object.  There were
some informal conventions, such as defining ‘__members__’ and
‘__methods__’ attributes that were lists of names, but often the author
of an extension type or a class wouldn’t bother to define them.  You
could fall back on inspecting the *note __dict__: 5f6. of an object, but
when class inheritance or an arbitrary *note __getattr__(): 42a. hook
were in use this could still be inaccurate.

The one big idea underlying the new class model is that an API for
describing the attributes of an object using `descriptors' has been
formalized.  Descriptors specify the value of an attribute, stating
whether it’s a method or a field.  With the descriptor API, static
methods and class methods become possible, as well as more exotic
constructs.

Attribute descriptors are objects that live inside class objects, and
have a few attributes of their own:

   * *note __name__: d2f. is the attribute’s name.

   * ‘__doc__’ is the attribute’s docstring.

   * ‘__get__(object)’ is a method that retrieves the attribute value
     from `object'.

   * ‘__set__(object, value)’ sets the attribute on `object' to `value'.

   * ‘__delete__(object, value)’ deletes the `value' attribute of
     `object'.

For example, when you write ‘obj.x’, the steps that Python actually
performs are:

     descriptor = obj.__class__.x
     descriptor.__get__(obj)

For methods, ‘descriptor.__get__()’ returns a temporary object that’s
callable, and wraps up the instance and the method to be called on it.
This is also why static methods and class methods are now possible; they
have descriptors that wrap up just the method, or the method and the
class.  As a brief explanation of these new kinds of methods, static
methods aren’t passed the instance, and therefore resemble regular
functions.  Class methods are passed the class of the object, but not
the object itself.  Static and class methods are defined like this:

     class C(object):
         def f(arg1, arg2):
             ...
         f = staticmethod(f)

         def g(cls, arg1, arg2):
             ...
         g = classmethod(g)

The *note staticmethod(): 30a. function takes the function ‘f()’, and
returns it wrapped up in a descriptor so it can be stored in the class
object.  You might expect there to be special syntax for creating such
methods (‘def static f’, ‘defstatic f()’, or something like that) but no
such syntax has been defined yet; that’s been left for future versions
of Python.

More new features, such as slots and properties, are also implemented as
new kinds of descriptors, and it’s not difficult to write a descriptor
class that does something novel.  For example, it would be possible to
write a descriptor class that made it possible to write Eiffel-style
preconditions and postconditions for a method.  A class that used this
feature might be defined like this:

     from eiffel import eiffelmethod

     class C(object):
         def f(self, arg1, arg2):
             # The actual function
             ...
         def pre_f(self):
             # Check preconditions
             ...
         def post_f(self):
             # Check postconditions
             ...

         f = eiffelmethod(f, pre_f, post_f)

Note that a person using the new ‘eiffelmethod()’ doesn’t have to
understand anything about descriptors.  This is why I think the new
features don’t increase the basic complexity of the language.  There
will be a few wizards who need to know about it in order to write
‘eiffelmethod()’ or the ZODB or whatever, but most users will just write
code on top of the resulting libraries and ignore the implementation
details.


File: python.info,  Node: Multiple Inheritance The Diamond Rule,  Next: Attribute Access,  Prev: Descriptors,  Up: PEPs 252 and 253 Type and Class Changes

1.16.2.3 Multiple Inheritance: The Diamond Rule
...............................................

Multiple inheritance has also been made more useful through changing the
rules under which names are resolved.  Consider this set of classes
(diagram taken from PEP 253(1) by Guido van Rossum):

           class A:
             ^ ^  def save(self): ...
            /   \
           /     \
          /       \
         /         \
     class B     class C:
         ^         ^  def save(self): ...
          \       /
           \     /
            \   /
             \ /
           class D

The lookup rule for classic classes is simple but not very smart; the
base classes are searched depth-first, going from left to right.  A
reference to ‘D.save()’ will search the classes ‘D’, ‘B’, and then ‘A’,
where ‘save()’ would be found and returned.  ‘C.save()’ would never be
found at all.  This is bad, because if ‘C’’s ‘save()’ method is saving
some internal state specific to ‘C’, not calling it will result in that
state never getting saved.

New-style classes follow a different algorithm that’s a bit more
complicated to explain, but does the right thing in this situation.
(Note that Python 2.3 changes this algorithm to one that produces the
same results in most cases, but produces more useful results for really
complicated inheritance graphs.)

  1. List all the base classes, following the classic lookup rule and
     include a class multiple times if it’s visited repeatedly.  In the
     above example, the list of visited classes is [‘D’, ‘B’, ‘A’, ‘C’,
     ‘A’].

  2. Scan the list for duplicated classes.  If any are found, remove all
     but one occurrence, leaving the `last' one in the list.  In the
     above example, the list becomes [‘D’, ‘B’, ‘C’, ‘A’] after dropping
     duplicates.

Following this rule, referring to ‘D.save()’ will return ‘C.save()’,
which is the behaviour we’re after.  This lookup rule is the same as the
one followed by Common Lisp.  A new built-in function, *note super():
5dd, provides a way to get at a class’s superclasses without having to
reimplement Python’s algorithm.  The most commonly used form will be
‘super(class, obj)’, which returns a bound superclass object (not the
actual class object).  This form will be used in methods to call a
method in the superclass; for example, ‘D’’s ‘save()’ method would look
like this:

     class D (B,C):
         def save (self):
             # Call superclass .save()
             super(D, self).save()
             # Save D's private information here
             ...

*note super(): 5dd. can also return unbound superclass objects when
called as ‘super(class)’ or ‘super(class1, class2)’, but this probably
won’t often be useful.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0253


File: python.info,  Node: Attribute Access,  Next: Related Links,  Prev: Multiple Inheritance The Diamond Rule,  Up: PEPs 252 and 253 Type and Class Changes

1.16.2.4 Attribute Access
.........................

A fair number of sophisticated Python classes define hooks for attribute
access using *note __getattr__(): 42a.; most commonly this is done for
convenience, to make code more readable by automatically mapping an
attribute access such as ‘obj.parent’ into a method call such as
‘obj.get_parent’.  Python 2.2 adds some new ways of controlling
attribute access.

First, ‘__getattr__(attr_name)’ is still supported by new-style classes,
and nothing about it has changed.  As before, it will be called when an
attempt is made to access ‘obj.foo’ and no attribute named ‘foo’ is
found in the instance’s dictionary.

New-style classes also support a new method,
‘__getattribute__(attr_name)’.  The difference between the two methods
is that *note __getattribute__(): 54c. is `always' called whenever any
attribute is accessed, while the old *note __getattr__(): 42a. is only
called if ‘foo’ isn’t found in the instance’s dictionary.

However, Python 2.2’s support for `properties' will often be a simpler
way to trap attribute references.  Writing a *note __getattr__(): 42a.
method is complicated because to avoid recursion you can’t use regular
attribute accesses inside them, and instead have to mess around with the
contents of *note __dict__: 5f6.  *note __getattr__(): 42a. methods also
end up being called by Python when it checks for other methods such as
*note __repr__(): 44a. or ‘__coerce__()’, and so have to be written with
this in mind.  Finally, calling a function on every attribute access
results in a sizable performance loss.

*note property: 308. is a new built-in type that packages up three
functions that get, set, or delete an attribute, and a docstring.  For
example, if you want to define a ‘size’ attribute that’s computed, but
also settable, you could write:

     class C(object):
         def get_size (self):
             result = ... computation ...
             return result
         def set_size (self, size):
             ... compute something based on the size
             and set internal state appropriately ...

         # Define a property.  The 'delete this attribute'
         # method is defined as None, so the attribute
         # can't be deleted.
         size = property(get_size, set_size,
                         None,
                         "Storage size of this instance")

That is certainly clearer and easier to write than a pair of *note
__getattr__(): 42a./*note __setattr__(): eee. methods that check for the
‘size’ attribute and handle it specially while retrieving all other
attributes from the instance’s *note __dict__: 5f6.  Accesses to ‘size’
are also the only ones which have to perform the work of calling a
function, so references to other attributes run at their usual speed.

Finally, it’s possible to constrain the list of attributes that can be
referenced on an object using the new *note __slots__: eef. class
attribute.  Python objects are usually very dynamic; at any time it’s
possible to define a new attribute on an instance by just doing
‘obj.new_attr=1’.  A new-style class can define a class attribute named
*note __slots__: eef. to limit the legal attributes to a particular set
of names.  An example will make this clear:

     >>> class C(object):
     ...     __slots__ = ('template', 'name')
     ...
     >>> obj = C()
     >>> print obj.template
     None
     >>> obj.template = 'Test'
     >>> print obj.template
     Test
     >>> obj.newattr = None
     Traceback (most recent call last):
       File "<stdin>", line 1, in ?
     AttributeError: 'C' object has no attribute 'newattr'

Note how you get an *note AttributeError: 4a2. on the attempt to assign
to an attribute not listed in *note __slots__: eef.


File: python.info,  Node: Related Links,  Prev: Attribute Access,  Up: PEPs 252 and 253 Type and Class Changes

1.16.2.5 Related Links
......................

This section has just been a quick overview of the new features, giving
enough of an explanation to start you programming, but many details have
been simplified or ignored.  Where should you go to get a more complete
picture?

‘https://docs.python.org/dev/howto/descriptor.html’ is a lengthy
tutorial introduction to the descriptor features, written by Guido van
Rossum.  If my description has whetted your appetite, go read this
tutorial next, because it goes into much more detail about the new
features while still remaining quite easy to read.

Next, there are two relevant PEPs, PEP 252(1) and PEP 253(2).  PEP
252(3) is titled “Making Types Look More Like Classes”, and covers the
descriptor API. PEP 253(4) is titled “Subtyping Built-in Types”, and
describes the changes to type objects that make it possible to subtype
built-in objects.  PEP 253(5) is the more complicated PEP of the two,
and at a few points the necessary explanations of types and meta-types
may cause your head to explode.  Both PEPs were written and implemented
by Guido van Rossum, with substantial assistance from the rest of the
Zope Corp.  team.

Finally, there’s the ultimate authority: the source code.  Most of the
machinery for the type handling is in ‘Objects/typeobject.c’, but you
should only resort to it after all other avenues have been exhausted,
including posting a question to python-list or python-dev.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0252

   (2) https://www.python.org/dev/peps/pep-0253

   (3) https://www.python.org/dev/peps/pep-0252

   (4) https://www.python.org/dev/peps/pep-0253

   (5) https://www.python.org/dev/peps/pep-0253


File: python.info,  Node: PEP 234 Iterators,  Next: PEP 255 Simple Generators<2>,  Prev: PEPs 252 and 253 Type and Class Changes,  Up: What’s New in Python 2 2

1.16.3 PEP 234: Iterators
-------------------------

Another significant addition to 2.2 is an iteration interface at both
the C and Python levels.  Objects can define how they can be looped over
by callers.

In Python versions up to 2.1, the usual way to make ‘for item in obj’
work is to define a *note __getitem__(): 3a2. method that looks
something like this:

     def __getitem__(self, index):
         return <next item>

*note __getitem__(): 3a2. is more properly used to define an indexing
operation on an object so that you can write ‘obj[5]’ to retrieve the
sixth element.  It’s a bit misleading when you’re using this only to
support *note for: cfa. loops.  Consider some file-like object that
wants to be looped over; the `index' parameter is essentially
meaningless, as the class probably assumes that a series of *note
__getitem__(): 3a2. calls will be made with `index' incrementing by one
each time.  In other words, the presence of the *note __getitem__():
3a2. method doesn’t mean that using ‘file[5]’ to randomly access the
sixth element will work, though it really should.

In Python 2.2, iteration can be implemented separately, and *note
__getitem__(): 3a2. methods can be limited to classes that really do
support random access.  The basic idea of iterators is simple.  A new
built-in function, ‘iter(obj)’ or ‘iter(C, sentinel)’, is used to get an
iterator.  ‘iter(obj)’ returns an iterator for the object `obj', while
‘iter(C, sentinel)’ returns an iterator that will invoke the callable
object `C' until it returns `sentinel' to signal that the iterator is
done.

Python classes can define an *note __iter__(): 609. method, which should
create and return a new iterator for the object; if the object is its
own iterator, this method can just return ‘self’.  In particular,
iterators will usually be their own iterators.  Extension types
implemented in C can implement a *note tp_iter: ef2. function in order
to return an iterator, and extension types that want to behave as
iterators can define a *note tp_iternext: ef3. function.

So, after all this, what do iterators actually do?  They have one
required method, *note next(): 775, which takes no arguments and returns
the next value.  When there are no more values to be returned, calling
*note next(): 775. should raise the *note StopIteration: 582. exception.

     >>> L = [1,2,3]
     >>> i = iter(L)
     >>> print i
     <iterator object at 0x8116870>
     >>> i.next()
     1
     >>> i.next()
     2
     >>> i.next()
     3
     >>> i.next()
     Traceback (most recent call last):
       File "<stdin>", line 1, in ?
     StopIteration
     >>>

In 2.2, Python’s *note for: cfa. statement no longer expects a sequence;
it expects something for which *note iter(): ded. will return an
iterator.  For backward compatibility and convenience, an iterator is
automatically constructed for sequences that don’t implement *note
__iter__(): 609. or a *note tp_iter: ef2. slot, so ‘for i in [1,2,3]’
will still work.  Wherever the Python interpreter loops over a sequence,
it’s been changed to use the iterator protocol.  This means you can do
things like this:

     >>> L = [1,2,3]
     >>> i = iter(L)
     >>> a,b,c = i
     >>> a,b,c
     (1, 2, 3)

Iterator support has been added to some of Python’s basic types.
Calling *note iter(): ded. on a dictionary will return an iterator which
loops over its keys:

     >>> m = {'Jan': 1, 'Feb': 2, 'Mar': 3, 'Apr': 4, 'May': 5, 'Jun': 6,
     ...      'Jul': 7, 'Aug': 8, 'Sep': 9, 'Oct': 10, 'Nov': 11, 'Dec': 12}
     >>> for key in m: print key, m[key]
     ...
     Mar 3
     Feb 2
     Aug 8
     Sep 9
     May 5
     Jun 6
     Jul 7
     Jan 1
     Apr 4
     Nov 11
     Dec 12
     Oct 10

That’s just the default behaviour.  If you want to iterate over keys,
values, or key/value pairs, you can explicitly call the ‘iterkeys()’,
‘itervalues()’, or ‘iteritems()’ methods to get an appropriate iterator.
In a minor related change, the *note in: 179. operator now works on
dictionaries, so ‘key in dict’ is now equivalent to ‘dict.has_key(key)’.

Files also provide an iterator, which calls the *note readline(): de.
method until there are no more lines in the file.  This means you can
now read each line of a file using code like this:

     for line in file:
         # do something for each line
         ...

Note that you can only go forward in an iterator; there’s no way to get
the previous element, reset the iterator, or make a copy of it.  An
iterator object could provide such additional capabilities, but the
iterator protocol only requires a *note next(): 775. method.

See also
........

PEP 234(1) - Iterators

     Written by Ka-Ping Yee and GvR; implemented by the Python Labs
     crew, mostly by GvR and Tim Peters.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0234


File: python.info,  Node: PEP 255 Simple Generators<2>,  Next: PEP 237 Unifying Long Integers and Integers<2>,  Prev: PEP 234 Iterators,  Up: What’s New in Python 2 2

1.16.4 PEP 255: Simple Generators
---------------------------------

Generators are another new feature, one that interacts with the
introduction of iterators.

You’re doubtless familiar with how function calls work in Python or C.
When you call a function, it gets a private namespace where its local
variables are created.  When the function reaches a *note return: 2c8.
statement, the local variables are destroyed and the resulting value is
returned to the caller.  A later call to the same function will get a
fresh new set of local variables.  But, what if the local variables
weren’t thrown away on exiting a function?  What if you could later
resume the function where it left off?  This is what generators provide;
they can be thought of as resumable functions.

Here’s the simplest example of a generator function:

     def generate_ints(N):
         for i in range(N):
             yield i

A new keyword, *note yield: 2c7, was introduced for generators.  Any
function containing a ‘yield’ statement is a generator function; this is
detected by Python’s bytecode compiler which compiles the function
specially as a result.  Because a new keyword was introduced, generators
must be explicitly enabled in a module by including a ‘from __future__
import generators’ statement near the top of the module’s source code.
In Python 2.3 this statement will become unnecessary.

When you call a generator function, it doesn’t return a single value;
instead it returns a generator object that supports the iterator
protocol.  On executing the *note yield: 2c7. statement, the generator
outputs the value of ‘i’, similar to a *note return: 2c8. statement.
The big difference between ‘yield’ and a ‘return’ statement is that on
reaching a ‘yield’ the generator’s state of execution is suspended and
local variables are preserved.  On the next call to the generator’s
‘next()’ method, the function will resume executing immediately after
the ‘yield’ statement.  (For complicated reasons, the ‘yield’ statement
isn’t allowed inside the ‘try’ block of a *note try: e37.…*note finally:
2bc. statement; read PEP 255(1) for a full explanation of the
interaction between ‘yield’ and exceptions.)

Here’s a sample usage of the ‘generate_ints()’ generator:

     >>> gen = generate_ints(3)
     >>> gen
     <generator object at 0x8117f90>
     >>> gen.next()
     0
     >>> gen.next()
     1
     >>> gen.next()
     2
     >>> gen.next()
     Traceback (most recent call last):
       File "<stdin>", line 1, in ?
       File "<stdin>", line 2, in generate_ints
     StopIteration

You could equally write ‘for i in generate_ints(5)’, or ‘a,b,c =
generate_ints(3)’.

Inside a generator function, the *note return: 2c8. statement can only
be used without a value, and signals the end of the procession of
values; afterwards the generator cannot return any further values.
‘return’ with a value, such as ‘return 5’, is a syntax error inside a
generator function.  The end of the generator’s results can also be
indicated by raising *note StopIteration: 582. manually, or by just
letting the flow of execution fall off the bottom of the function.

You could achieve the effect of generators manually by writing your own
class and storing all the local variables of the generator as instance
variables.  For example, returning a list of integers could be done by
setting ‘self.count’ to 0, and having the *note next(): 775. method
increment ‘self.count’ and return it.  However, for a moderately
complicated generator, writing a corresponding class would be much
messier.  ‘Lib/test/test_generators.py’ contains a number of more
interesting examples.  The simplest one implements an in-order traversal
of a tree using generators recursively.

     # A recursive generator that generates Tree leaves in in-order.
     def inorder(t):
         if t:
             for x in inorder(t.left):
                 yield x
             yield t.label
             for x in inorder(t.right):
                 yield x

Two other examples in ‘Lib/test/test_generators.py’ produce solutions
for the N-Queens problem (placing $N$ queens on an $NxN$ chess board so
that no queen threatens another) and the Knight’s Tour (a route that
takes a knight to every square of an $NxN$ chessboard without visiting
any square twice).

The idea of generators comes from other programming languages,
especially Icon (‘https://www.cs.arizona.edu/icon/’), where the idea of
generators is central.  In Icon, every expression and function call
behaves like a generator.  One example from “An Overview of the Icon
Programming Language” at
‘https://www.cs.arizona.edu/icon/docs/ipd266.htm’ gives an idea of what
this looks like:

     sentence := "Store it in the neighboring harbor"
     if (i := find("or", sentence)) > 5 then write(i)

In Icon the ‘find()’ function returns the indexes at which the substring
“or” is found: 3, 23, 33.  In the *note if: eab. statement, ‘i’ is first
assigned a value of 3, but 3 is less than 5, so the comparison fails,
and Icon retries it with the second value of 23.  23 is greater than 5,
so the comparison now succeeds, and the code prints the value 23 to the
screen.

Python doesn’t go nearly as far as Icon in adopting generators as a
central concept.  Generators are considered a new part of the core
Python language, but learning or using them isn’t compulsory; if they
don’t solve any problems that you have, feel free to ignore them.  One
novel feature of Python’s interface as compared to Icon’s is that a
generator’s state is represented as a concrete object (the iterator)
that can be passed around to other functions or stored in a data
structure.

See also
........

PEP 255(2) - Simple Generators

     Written by Neil Schemenauer, Tim Peters, Magnus Lie Hetland.
     Implemented mostly by Neil Schemenauer and Tim Peters, with other
     fixes from the Python Labs crew.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0255

   (2) https://www.python.org/dev/peps/pep-0255


File: python.info,  Node: PEP 237 Unifying Long Integers and Integers<2>,  Next: PEP 238 Changing the Division Operator,  Prev: PEP 255 Simple Generators<2>,  Up: What’s New in Python 2 2

1.16.5 PEP 237: Unifying Long Integers and Integers
---------------------------------------------------

In recent versions, the distinction between regular integers, which are
32-bit values on most machines, and long integers, which can be of
arbitrary size, was becoming an annoyance.  For example, on platforms
that support files larger than ‘2**32’ bytes, the ‘tell()’ method of
file objects has to return a long integer.  However, there were various
bits of Python that expected plain integers and would raise an error if
a long integer was provided instead.  For example, in Python 1.5, only
regular integers could be used as a slice index, and ‘'abc'[1L:]’ would
raise a *note TypeError: 1fe. exception with the message ‘slice index
must be int’.

Python 2.2 will shift values from short to long integers as required.
The ‘L’ suffix is no longer needed to indicate a long integer literal,
as now the compiler will choose the appropriate type.  (Using the ‘L’
suffix will be discouraged in future 2.x versions of Python, triggering
a warning in Python 2.4, and probably dropped in Python 3.0.)  Many
operations that used to raise an *note OverflowError: a41. will now
return a long integer as their result.  For example:

     >>> 1234567890123
     1234567890123L
     >>> 2 ** 64
     18446744073709551616L

In most cases, integers and long integers will now be treated
identically.  You can still distinguish them with the *note type(): 6ff.
built-in function, but that’s rarely needed.

See also
........

PEP 237(1) - Unifying Long Integers and Integers

     Written by Moshe Zadka and Guido van Rossum.  Implemented mostly by
     Guido van Rossum.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0237


File: python.info,  Node: PEP 238 Changing the Division Operator,  Next: Unicode Changes,  Prev: PEP 237 Unifying Long Integers and Integers<2>,  Up: What’s New in Python 2 2

1.16.6 PEP 238: Changing the Division Operator
----------------------------------------------

The most controversial change in Python 2.2 heralds the start of an
effort to fix an old design flaw that’s been in Python from the
beginning.  Currently Python’s division operator, ‘/’, behaves like C’s
division operator when presented with two integer arguments: it returns
an integer result that’s truncated down when there would be a fractional
part.  For example, ‘3/2’ is 1, not 1.5, and ‘(-1)/2’ is -1, not -0.5.
This means that the results of division can vary unexpectedly depending
on the type of the two operands and because Python is dynamically typed,
it can be difficult to determine the possible types of the operands.

(The controversy is over whether this is `really' a design flaw, and
whether it’s worth breaking existing code to fix this.  It’s caused
endless discussions on python-dev, and in July 2001 erupted into a storm
of acidly sarcastic postings on ‘comp.lang.python’.  I won’t argue for
either side here and will stick to describing what’s implemented in 2.2.
Read PEP 238(1) for a summary of arguments and counter-arguments.)

Because this change might break code, it’s being introduced very
gradually.  Python 2.2 begins the transition, but the switch won’t be
complete until Python 3.0.

First, I’ll borrow some terminology from PEP 238(2).  “True division” is
the division that most non-programmers are familiar with: 3/2 is 1.5,
1/4 is 0.25, and so forth.  “Floor division” is what Python’s ‘/’
operator currently does when given integer operands; the result is the
floor of the value returned by true division.  “Classic division” is the
current mixed behaviour of ‘/’; it returns the result of floor division
when the operands are integers, and returns the result of true division
when one of the operands is a floating-point number.

Here are the changes 2.2 introduces:

   * A new operator, ‘//’, is the floor division operator.  (Yes, we
     know it looks like C++’s comment symbol.)  ‘//’ `always' performs
     floor division no matter what the types of its operands are, so ‘1
     // 2’ is 0 and ‘1.0 // 2.0’ is also 0.0.

     ‘//’ is always available in Python 2.2; you don’t need to enable it
     using a ‘__future__’ statement.

   * By including a ‘from __future__ import division’ in a module, the
     ‘/’ operator will be changed to return the result of true division,
     so ‘1/2’ is 0.5.  Without the ‘__future__’ statement, ‘/’ still
     means classic division.  The default meaning of ‘/’ will not change
     until Python 3.0.

   * Classes can define methods called *note __truediv__(): 875. and
     *note __floordiv__(): ef7. to overload the two division operators.
     At the C level, there are also slots in the *note PyNumberMethods:
     e46. structure so extension types can define the two operators.

   * Python 2.2 supports some command-line arguments for testing whether
     code will work with the changed division semantics.  Running python
     with ‘-Q warn’ will cause a warning to be issued whenever division
     is applied to two integers.  You can use this to find code that’s
     affected by the change and fix it.  By default, Python 2.2 will
     simply perform classic division without a warning; the warning will
     be turned on by default in Python 2.3.

See also
........

PEP 238(3) - Changing the Division Operator

     Written by Moshe Zadka and Guido van Rossum.  Implemented by Guido
     van Rossum..

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0238

   (2) https://www.python.org/dev/peps/pep-0238

   (3) https://www.python.org/dev/peps/pep-0238


File: python.info,  Node: Unicode Changes,  Next: PEP 227 Nested Scopes,  Prev: PEP 238 Changing the Division Operator,  Up: What’s New in Python 2 2

1.16.7 Unicode Changes
----------------------

Python’s Unicode support has been enhanced a bit in 2.2.  Unicode
strings are usually stored as UCS-2, as 16-bit unsigned integers.
Python 2.2 can also be compiled to use UCS-4, 32-bit unsigned integers,
as its internal encoding by supplying ‘--enable-unicode=ucs4’ to the
configure script.  (It’s also possible to specify ‘--disable-unicode’ to
completely disable Unicode support.)

When built to use UCS-4 (a “wide Python”), the interpreter can natively
handle Unicode characters from U+000000 to U+110000, so the range of
legal values for the ‘unichr()’ function is expanded accordingly.  Using
an interpreter compiled to use UCS-2 (a “narrow Python”), values greater
than 65535 will still cause ‘unichr()’ to raise a *note ValueError: 16d.
exception.  This is all described in PEP 261(1), “Support for ‘wide’
Unicode characters”; consult it for further details.

Another change is simpler to explain.  Since their introduction, Unicode
strings have supported an ‘encode()’ method to convert the string to a
selected encoding such as UTF-8 or Latin-1.  A symmetric
‘decode([*encoding*])’ method has been added to 8-bit strings (though
not to Unicode strings) in 2.2.  ‘decode()’ assumes that the string is
in the specified encoding and decodes it, returning whatever is returned
by the codec.

Using this new feature, codecs have been added for tasks not directly
related to Unicode.  For example, codecs have been added for
uu-encoding, MIME’s base64 encoding, and compression with the *note
zlib: 14d. module:

     >>> s = """Here is a lengthy piece of redundant, overly verbose,
     ... and repetitive text.
     ... """
     >>> data = s.encode('zlib')
     >>> data
     'x\x9c\r\xc9\xc1\r\x80 \x10\x04\xc0?Ul...'
     >>> data.decode('zlib')
     'Here is a lengthy piece of redundant, overly verbose,\nand repetitive text.\n'
     >>> print s.encode('uu')
     begin 666 <data>
     M2&5R92!I<R!A(&QE;F=T:'D@<&EE8V4@;V8@<F5D=6YD86YT+"!O=F5R;'D@
     >=F5R8F]S92P*86YD(')E<&5T:71I=F4@=&5X="X*

     end
     >>> "sheesh".encode('rot-13')
     'furrfu'

To convert a class instance to Unicode, a ‘__unicode__()’ method can be
defined by a class, analogous to *note __str__(): ef9.

‘encode()’, ‘decode()’, and ‘__unicode__()’ were implemented by
Marc-André Lemburg.  The changes to support using UCS-4 internally were
implemented by Fredrik Lundh and Martin von Löwis.

See also
........

PEP 261(2) - Support for ‘wide’ Unicode characters

     Written by Paul Prescod.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0261

   (2) https://www.python.org/dev/peps/pep-0261


File: python.info,  Node: PEP 227 Nested Scopes,  Next: New and Improved Modules<3>,  Prev: Unicode Changes,  Up: What’s New in Python 2 2

1.16.8 PEP 227: Nested Scopes
-----------------------------

In Python 2.1, statically nested scopes were added as an optional
feature, to be enabled by a ‘from __future__ import nested_scopes’
directive.  In 2.2 nested scopes no longer need to be specially enabled,
and are now always present.  The rest of this section is a copy of the
description of nested scopes from my “What’s New in Python 2.1”
document; if you read it when 2.1 came out, you can skip the rest of
this section.

The largest change introduced in Python 2.1, and made complete in 2.2,
is to Python’s scoping rules.  In Python 2.0, at any given time there
are at most three namespaces used to look up variable names: local,
module-level, and the built-in namespace.  This often surprised people
because it didn’t match their intuitive expectations.  For example, a
nested recursive function definition doesn’t work:

     def f():
         ...
         def g(value):
             ...
             return g(value-1) + 1
         ...

The function ‘g()’ will always raise a *note NameError: e40. exception,
because the binding of the name ‘g’ isn’t in either its local namespace
or in the module-level namespace.  This isn’t much of a problem in
practice (how often do you recursively define interior functions like
this?), but this also made using the *note lambda: cf9. expression
clumsier, and this was a problem in practice.  In code which uses
‘lambda’ you can often find local variables being copied by passing them
as the default values of arguments.

     def find(self, name):
         "Return list of any entries equal to 'name'"
         L = filter(lambda x, name=name: x == name,
                    self.list_attribute)
         return L

The readability of Python code written in a strongly functional style
suffers greatly as a result.

The most significant change to Python 2.2 is that static scoping has
been added to the language to fix this problem.  As a first effect, the
‘name=name’ default argument is now unnecessary in the above example.
Put simply, when a given variable name is not assigned a value within a
function (by an assignment, or the *note def: e83, *note class: d32, or
*note import: ce7. statements), references to the variable will be
looked up in the local namespace of the enclosing scope.  A more
detailed explanation of the rules, and a dissection of the
implementation, can be found in the PEP.

This change may cause some compatibility problems for code where the
same variable name is used both at the module level and as a local
variable within a function that contains further function definitions.
This seems rather unlikely though, since such code would have been
pretty confusing to read in the first place.

One side effect of the change is that the ‘from module import *’ and
‘exec’ statements have been made illegal inside a function scope under
certain conditions.  The Python reference manual has said all along that
‘from module import *’ is only legal at the top level of a module, but
the CPython interpreter has never enforced this before.  As part of the
implementation of nested scopes, the compiler which turns Python source
into bytecodes has to generate different code to access variables in a
containing scope.  ‘from module import *’ and ‘exec’ make it impossible
for the compiler to figure this out, because they add names to the local
namespace that are unknowable at compile time.  Therefore, if a function
contains function definitions or *note lambda: cf9. expressions with
free variables, the compiler will flag this by raising a *note
SyntaxError: 55a. exception.

To make the preceding explanation a bit clearer, here’s an example:

     x = 1
     def f():
         # The next line is a syntax error
         exec 'x=2'
         def g():
             return x

Line 4 containing the ‘exec’ statement is a syntax error, since ‘exec’
would define a new local variable named ‘x’ whose value should be
accessed by ‘g()’.

This shouldn’t be much of a limitation, since ‘exec’ is rarely used in
most Python code (and when it is used, it’s often a sign of a poor
design anyway).

See also
........

PEP 227(1) - Statically Nested Scopes

     Written and implemented by Jeremy Hylton.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0227


File: python.info,  Node: New and Improved Modules<3>,  Next: Interpreter Changes and Fixes,  Prev: PEP 227 Nested Scopes,  Up: What’s New in Python 2 2

1.16.9 New and Improved Modules
-------------------------------

   * The ‘xmlrpclib’ module was contributed to the standard library by
     Fredrik Lundh, providing support for writing XML-RPC clients.
     XML-RPC is a simple remote procedure call protocol built on top of
     HTTP and XML. For example, the following snippet retrieves a list
     of RSS channels from the O’Reilly Network, and then lists the
     recent headlines for one channel:

          import xmlrpclib
          s = xmlrpclib.Server(
                'http://www.oreillynet.com/meerkat/xml-rpc/server.php')
          channels = s.meerkat.getChannels()
          # channels is a list of dictionaries, like this:
          # [{'id': 4, 'title': 'Freshmeat Daily News'}
          #  {'id': 190, 'title': '32Bits Online'},
          #  {'id': 4549, 'title': '3DGamers'}, ... ]

          # Get the items for one channel
          items = s.meerkat.getItems( {'channel': 4} )

          # 'items' is another list of dictionaries, like this:
          # [{'link': 'http://freshmeat.net/releases/52719/',
          #   'description': 'A utility which converts HTML to XSL FO.',
          #   'title': 'html2fo 0.3 (Default)'}, ... ]

     The ‘SimpleXMLRPCServer’ module makes it easy to create
     straightforward XML-RPC servers.  See
     ‘http://xmlrpc.scripting.com/’ for more information about XML-RPC.

   * The new *note hmac: 8e. module implements the HMAC algorithm
     described by RFC 2104(1).  (Contributed by Gerhard Häring.)

   * Several functions that originally returned lengthy tuples now
     return pseudo-sequences that still behave like tuples but also have
     mnemonic attributes such as memberst_mtime or ‘tm_year’.  The
     enhanced functions include *note stat(): f4, ‘fstat()’,
     ‘statvfs()’, and ‘fstatvfs()’ in the *note os: c4. module, and
     ‘localtime()’, ‘gmtime()’, and ‘strptime()’ in the *note time: 10c.
     module.

     For example, to obtain a file’s size using the old tuples, you’d
     end up writing something like ‘file_size =
     os.stat(filename)[stat.ST_SIZE]’, but now this can be written more
     clearly as ‘file_size = os.stat(filename).st_size’.

     The original patch for this feature was contributed by Nick
     Mathewson.

   * The Python profiler has been extensively reworked and various
     errors in its output have been corrected.  (Contributed by Fred L.
     Drake, Jr.  and Tim Peters.)

   * The *note socket: ef. module can be compiled to support IPv6;
     specify the ‘--enable-ipv6’ option to Python’s configure script.
     (Contributed by Jun-ichiro “itojun” Hagino.)

   * Two new format characters were added to the *note struct: f8.
     module for 64-bit integers on platforms that support the C ‘long
     long’ type.  ‘q’ is for a signed 64-bit integer, and ‘Q’ is for an
     unsigned one.  The value is returned in Python’s long integer type.
     (Contributed by Tim Peters.)

   * In the interpreter’s interactive mode, there’s a new built-in
     function *note help(): 175. that uses the *note pydoc: d9. module
     introduced in Python 2.1 to provide interactive help.
     ‘help(object)’ displays any available help text about `object'.
     *note help(): 175. with no argument puts you in an online help
     utility, where you can enter the names of functions, classes, or
     modules to read their help text.  (Contributed by Guido van Rossum,
     using Ka-Ping Yee’s *note pydoc: d9. module.)

   * Various bugfixes and performance improvements have been made to the
     SRE engine underlying the *note re: dd. module.  For example, the
     *note re.sub(): 57a. and *note re.split(): 4d1. functions have been
     rewritten in C. Another contributed patch speeds up certain Unicode
     character ranges by a factor of two, and a new ‘finditer()’ method
     that returns an iterator over all the non-overlapping matches in a
     given string.  (SRE is maintained by Fredrik Lundh.  The BIGCHARSET
     patch was contributed by Martin von Löwis.)

   * The *note smtplib: ed. module now supports RFC 2487(2), “Secure
     SMTP over TLS”, so it’s now possible to encrypt the SMTP traffic
     between a Python program and the mail transport agent being handed
     a message.  *note smtplib: ed. also supports SMTP authentication.
     (Contributed by Gerhard Häring.)

   * The *note imaplib: 97. module, maintained by Piers Lauder, has
     support for several new extensions: the NAMESPACE extension defined
     in RFC 2342(3), SORT, GETACL and SETACL. (Contributed by Anthony
     Baxter and Michel Pelletier.)

   * The ‘rfc822’ module’s parsing of email addresses is now compliant
     with RFC 2822(4), an update to RFC 822(5).  (The module’s name is
     `not' going to be changed to ‘rfc2822’.)  A new package, *note
     email: 67, has also been added for parsing and generating e-mail
     messages.  (Contributed by Barry Warsaw, and arising out of his
     work on Mailman.)

   * The *note difflib: 36. module now contains a new ‘Differ’ class for
     producing human-readable lists of changes (a “delta”) between two
     sequences of lines of text.  There are also two generator
     functions, ‘ndiff()’ and ‘restore()’, which respectively return a
     delta from two sequences, or one of the original sequences from a
     delta.  (Grunt work contributed by David Goodger, from ndiff.py
     code by Tim Peters who then did the generatorization.)

   * New constants ‘ascii_letters’, ‘ascii_lowercase’, and
     ‘ascii_uppercase’ were added to the *note string: f6. module.
     There were several modules in the standard library that used
     ‘string.letters’ to mean the ranges A-Za-z, but that assumption is
     incorrect when locales are in use, because ‘string.letters’ varies
     depending on the set of legal characters defined by the current
     locale.  The buggy modules have all been fixed to use
     ‘ascii_letters’ instead.  (Reported by an unknown person; fixed by
     Fred L. Drake, Jr.)

   * The *note mimetypes: b2. module now makes it easier to use
     alternative MIME-type databases by the addition of a ‘MimeTypes’
     class, which takes a list of filenames to be parsed.  (Contributed
     by Fred L. Drake, Jr.)

   * A ‘Timer’ class was added to the *note threading: 10b. module that
     allows scheduling an activity to happen at some future time.
     (Contributed by Itamar Shtull-Trauring.)

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2104.html

   (2) https://tools.ietf.org/html/rfc2487.html

   (3) https://tools.ietf.org/html/rfc2342.html

   (4) https://tools.ietf.org/html/rfc2822.html

   (5) https://tools.ietf.org/html/rfc822.html


File: python.info,  Node: Interpreter Changes and Fixes,  Next: Other Changes and Fixes<3>,  Prev: New and Improved Modules<3>,  Up: What’s New in Python 2 2

1.16.10 Interpreter Changes and Fixes
-------------------------------------

Some of the changes only affect people who deal with the Python
interpreter at the C level because they’re writing Python extension
modules, embedding the interpreter, or just hacking on the interpreter
itself.  If you only write Python code, none of the changes described
here will affect you very much.

   * Profiling and tracing functions can now be implemented in C, which
     can operate at much higher speeds than Python-based functions and
     should reduce the overhead of profiling and tracing.  This will be
     of interest to authors of development environments for Python.  Two
     new C functions were added to Python’s API, *note
     PyEval_SetProfile(): efd. and *note PyEval_SetTrace(): efe.  The
     existing *note sys.setprofile(): eff. and *note sys.settrace():
     f00. functions still exist, and have simply been changed to use the
     new C-level interface.  (Contributed by Fred L. Drake, Jr.)

   * Another low-level API, primarily of interest to implementors of
     Python debuggers and development tools, was added.  *note
     PyInterpreterState_Head(): f01. and *note
     PyInterpreterState_Next(): f02. let a caller walk through all the
     existing interpreter objects; *note
     PyInterpreterState_ThreadHead(): f03. and *note
     PyThreadState_Next(): f04. allow looping over all the thread states
     for a given interpreter.  (Contributed by David Beazley.)

   * The C-level interface to the garbage collector has been changed to
     make it easier to write extension types that support garbage
     collection and to debug misuses of the functions.  Various
     functions have slightly different semantics, so a bunch of
     functions had to be renamed.  Extensions that use the old API will
     still compile but will `not' participate in garbage collection, so
     updating them for 2.2 should be considered fairly high priority.

     To upgrade an extension module to the new API, perform the
     following steps:

   * Rename ‘Py_TPFLAGS_GC()’ to ‘PyTPFLAGS_HAVE_GC()’.

   * 
     Use *note PyObject_GC_New(): 3f3. or *note PyObject_GC_NewVar(): 3f4. to allocate

          objects, and *note PyObject_GC_Del(): f05. to deallocate them.

   * 
     Rename ‘PyObject_GC_Init()’ to *note PyObject_GC_Track(): f06. and

          ‘PyObject_GC_Fini()’ to *note PyObject_GC_UnTrack(): f07.

   * Remove ‘PyGC_HEAD_SIZE()’ from object size calculations.

   * Remove calls to ‘PyObject_AS_GC()’ and ‘PyObject_FROM_GC()’.

   * A new ‘et’ format sequence was added to *note PyArg_ParseTuple():
     393.; ‘et’ takes both a parameter and an encoding name, and
     converts the parameter to the given encoding if the parameter turns
     out to be a Unicode string, or leaves it alone if it’s an 8-bit
     string, assuming it to already be in the desired encoding.  This
     differs from the ‘es’ format character, which assumes that 8-bit
     strings are in Python’s default ASCII encoding and converts them to
     the specified new encoding.  (Contributed by M.-A. Lemburg, and
     used for the MBCS support on Windows described in the following
     section.)

   * A different argument parsing function, *note PyArg_UnpackTuple():
     f08, has been added that’s simpler and presumably faster.  Instead
     of specifying a format string, the caller simply gives the minimum
     and maximum number of arguments expected, and a set of pointers to
     *note PyObject*: 5b5. variables that will be filled in with
     argument values.

   * Two new flags *note METH_NOARGS: eda. and *note METH_O: f09. are
     available in method definition tables to simplify implementation of
     methods with no arguments or a single untyped argument.  Calling
     such methods is more efficient than calling a corresponding method
     that uses *note METH_VARARGS: f0a.  Also, the old ‘METH_OLDARGS’
     style of writing C methods is now officially deprecated.

   * Two new wrapper functions, *note PyOS_snprintf(): f0b. and *note
     PyOS_vsnprintf(): f0c. were added to provide cross-platform
     implementations for the relatively new ‘snprintf()’ and
     ‘vsnprintf()’ C lib APIs.  In contrast to the standard ‘sprintf()’
     and ‘vsprintf()’ functions, the Python versions check the bounds of
     the buffer used to protect against buffer overruns.  (Contributed
     by M.-A. Lemburg.)

   * The *note _PyTuple_Resize(): f0d. function has lost an unused
     parameter, so now it takes 2 parameters instead of 3.  The third
     argument was never used, and can simply be discarded when porting
     code from earlier versions to Python 2.2.


File: python.info,  Node: Other Changes and Fixes<3>,  Next: Acknowledgements<6>,  Prev: Interpreter Changes and Fixes,  Up: What’s New in Python 2 2

1.16.11 Other Changes and Fixes
-------------------------------

As usual there were a bunch of other improvements and bugfixes scattered
throughout the source tree.  A search through the CVS change logs finds
there were 527 patches applied and 683 bugs fixed between Python 2.1 and
2.2; 2.2.1 applied 139 patches and fixed 143 bugs; 2.2.2 applied 106
patches and fixed 82 bugs.  These figures are likely to be
underestimates.

Some of the more notable changes are:

   * The code for the MacOS port for Python, maintained by Jack Jansen,
     is now kept in the main Python CVS tree, and many changes have been
     made to support MacOS X.

     The most significant change is the ability to build Python as a
     framework, enabled by supplying the ‘--enable-framework’ option to
     the configure script when compiling Python.  According to Jack
     Jansen, “This installs a self-contained Python installation plus
     the OS X framework “glue” into
     ‘/Library/Frameworks/Python.framework’ (or another location of
     choice).  For now there is little immediate added benefit to this
     (actually, there is the disadvantage that you have to change your
     PATH to be able to find Python), but it is the basis for creating a
     full-blown Python application, porting the MacPython IDE, possibly
     using Python as a standard OSA scripting language and much more.”

     Most of the MacPython toolbox modules, which interface to MacOS
     APIs such as windowing, QuickTime, scripting, etc.  have been
     ported to OS X, but they’ve been left commented out in ‘setup.py’.
     People who want to experiment with these modules can uncomment them
     manually.

   * Keyword arguments passed to built-in functions that don’t take them
     now cause a *note TypeError: 1fe. exception to be raised, with the
     message “`function' takes no keyword arguments”.

   * Weak references, added in Python 2.1 as an extension module, are
     now part of the core because they’re used in the implementation of
     new-style classes.  The *note ReferenceError: f0f. exception has
     therefore moved from the *note weakref: 131. module to become a
     built-in exception.

   * A new script, ‘Tools/scripts/cleanfuture.py’ by Tim Peters,
     automatically removes obsolete ‘__future__’ statements from Python
     source code.

   * An additional `flags' argument has been added to the built-in
     function *note compile(): 2e7, so the behaviour of ‘__future__’
     statements can now be correctly observed in simulated shells, such
     as those presented by IDLE and other development environments.
     This is described in PEP 264(1).  (Contributed by Michael Hudson.)

   * The new license introduced with Python 1.6 wasn’t GPL-compatible.
     This is fixed by some minor textual changes to the 2.2 license, so
     it’s now legal to embed Python inside a GPLed program again.  Note
     that Python itself is not GPLed, but instead is under a license
     that’s essentially equivalent to the BSD license, same as it always
     was.  The license changes were also applied to the Python 2.0.1 and
     2.1.1 releases.

   * When presented with a Unicode filename on Windows, Python will now
     convert it to an MBCS encoded string, as used by the Microsoft file
     APIs.  As MBCS is explicitly used by the file APIs, Python’s choice
     of ASCII as the default encoding turns out to be an annoyance.  On
     Unix, the locale’s character set is used if
     ‘locale.nl_langinfo(CODESET)’ is available.  (Windows support was
     contributed by Mark Hammond with assistance from Marc-André
     Lemburg.  Unix support was added by Martin von Löwis.)

   * Large file support is now enabled on Windows.  (Contributed by Tim
     Peters.)

   * The ‘Tools/scripts/ftpmirror.py’ script now parses a ‘.netrc’ file,
     if you have one.  (Contributed by Mike Romberg.)

   * Some features of the object returned by the ‘xrange()’ function are
     now deprecated, and trigger warnings when they’re accessed; they’ll
     disappear in Python 2.3.  ‘xrange’ objects tried to pretend they
     were full sequence types by supporting slicing, sequence
     multiplication, and the *note in: 179. operator, but these features
     were rarely used and therefore buggy.  The ‘tolist()’ method and
     the ‘start’, ‘stop’, and ‘step’ attributes are also being
     deprecated.  At the C level, the fourth argument to the
     ‘PyRange_New()’ function, ‘repeat’, has also been deprecated.

   * There were a bunch of patches to the dictionary implementation,
     mostly to fix potential core dumps if a dictionary contains objects
     that sneakily changed their hash value, or mutated the dictionary
     they were contained in.  For a while python-dev fell into a gentle
     rhythm of Michael Hudson finding a case that dumped core, Tim
     Peters fixing the bug, Michael finding another case, and round and
     round it went.

   * On Windows, Python can now be compiled with Borland C thanks to a
     number of patches contributed by Stephen Hansen, though the result
     isn’t fully functional yet.  (But this `is' progress…)

   * Another Windows enhancement: Wise Solutions generously offered
     PythonLabs use of their InstallerMaster 8.1 system.  Earlier
     PythonLabs Windows installers used Wise 5.0a, which was beginning
     to show its age.  (Packaged up by Tim Peters.)

   * Files ending in ‘.pyw’ can now be imported on Windows.  ‘.pyw’ is a
     Windows-only thing, used to indicate that a script needs to be run
     using PYTHONW.EXE instead of PYTHON.EXE in order to prevent a DOS
     console from popping up to display the output.  This patch makes it
     possible to import such scripts, in case they’re also usable as
     modules.  (Implemented by David Bolen.)

   * On platforms where Python uses the C ‘dlopen()’ function to load
     extension modules, it’s now possible to set the flags used by
     ‘dlopen()’ using the *note sys.getdlopenflags(): f10. and *note
     sys.setdlopenflags(): b41. functions.  (Contributed by Bram Stolk.)

   * The *note pow(): 2cf. built-in function no longer supports 3
     arguments when floating-point numbers are supplied.  ‘pow(x, y, z)’
     returns ‘(x**y) % z’, but this is never useful for floating point
     numbers, and the final result varies unpredictably depending on the
     platform.  A call such as ‘pow(2.0, 8.0, 7.0)’ will now raise a
     *note TypeError: 1fe. exception.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0264


File: python.info,  Node: Acknowledgements<6>,  Prev: Other Changes and Fixes<3>,  Up: What’s New in Python 2 2

1.16.12 Acknowledgements
------------------------

The author would like to thank the following people for offering
suggestions, corrections and assistance with various drafts of this
article: Fred Bremmer, Keith Briggs, Andrew Dalke, Fred L. Drake, Jr.,
Carel Fellinger, David Goodger, Mark Hammond, Stephen Hansen, Michael
Hudson, Jack Jansen, Marc-André Lemburg, Martin von Löwis, Fredrik
Lundh, Michael McLay, Nick Mathewson, Paul Moore, Gustavo Niemeyer, Don
O’Donnell, Joonas Paalasma, Tim Peters, Jens Quade, Tom Reinhardt, Neil
Schemenauer, Guido van Rossum, Greg Ward, Edward Welbourne.


File: python.info,  Node: What’s New in Python 2 1,  Next: What’s New in Python 2 0,  Prev: What’s New in Python 2 2,  Up: What’s New in Python

1.17 What’s New in Python 2.1
=============================


Author: A.M. Kuchling

* Menu:

* Introduction: Introduction<2>.
* PEP 227; Nested Scopes: PEP 227 Nested Scopes<2>.
* PEP 236; __future__ Directives: PEP 236 __future__ Directives.
* PEP 207; Rich Comparisons: PEP 207 Rich Comparisons.
* PEP 230; Warning Framework: PEP 230 Warning Framework.
* PEP 229; New Build System: PEP 229 New Build System.
* PEP 205; Weak References: PEP 205 Weak References.
* PEP 232; Function Attributes: PEP 232 Function Attributes.
* PEP 235; Importing Modules on Case-Insensitive Platforms: PEP 235 Importing Modules on Case-Insensitive Platforms.
* PEP 217; Interactive Display Hook: PEP 217 Interactive Display Hook.
* PEP 208; New Coercion Model: PEP 208 New Coercion Model.
* PEP 241; Metadata in Python Packages: PEP 241 Metadata in Python Packages.
* New and Improved Modules: New and Improved Modules<4>.
* Other Changes and Fixes: Other Changes and Fixes<4>.
* Acknowledgements: Acknowledgements<7>.


File: python.info,  Node: Introduction<2>,  Next: PEP 227 Nested Scopes<2>,  Up: What’s New in Python 2 1

1.17.1 Introduction
-------------------

This article explains the new features in Python 2.1.  While there
aren’t as many changes in 2.1 as there were in Python 2.0, there are
still some pleasant surprises in store.  2.1 is the first release to be
steered through the use of Python Enhancement Proposals, or PEPs, so
most of the sizable changes have accompanying PEPs that provide more
complete documentation and a design rationale for the change.  This
article doesn’t attempt to document the new features completely, but
simply provides an overview of the new features for Python programmers.
Refer to the Python 2.1 documentation, or to the specific PEP, for more
details about any new feature that particularly interests you.

One recent goal of the Python development team has been to accelerate
the pace of new releases, with a new release coming every 6 to 9 months.
2.1 is the first release to come out at this faster pace, with the first
alpha appearing in January, 3 months after the final version of 2.0 was
released.

The final release of Python 2.1 was made on April 17, 2001.


File: python.info,  Node: PEP 227 Nested Scopes<2>,  Next: PEP 236 __future__ Directives,  Prev: Introduction<2>,  Up: What’s New in Python 2 1

1.17.2 PEP 227: Nested Scopes
-----------------------------

The largest change in Python 2.1 is to Python’s scoping rules.  In
Python 2.0, at any given time there are at most three namespaces used to
look up variable names: local, module-level, and the built-in namespace.
This often surprised people because it didn’t match their intuitive
expectations.  For example, a nested recursive function definition
doesn’t work:

     def f():
         ...
         def g(value):
             ...
             return g(value-1) + 1
         ...

The function ‘g()’ will always raise a *note NameError: e40. exception,
because the binding of the name ‘g’ isn’t in either its local namespace
or in the module-level namespace.  This isn’t much of a problem in
practice (how often do you recursively define interior functions like
this?), but this also made using the *note lambda: cf9. expression
clumsier, and this was a problem in practice.  In code which uses *note
lambda: cf9. you can often find local variables being copied by passing
them as the default values of arguments.

     def find(self, name):
         "Return list of any entries equal to 'name'"
         L = filter(lambda x, name=name: x == name,
                    self.list_attribute)
         return L

The readability of Python code written in a strongly functional style
suffers greatly as a result.

The most significant change to Python 2.1 is that static scoping has
been added to the language to fix this problem.  As a first effect, the
‘name=name’ default argument is now unnecessary in the above example.
Put simply, when a given variable name is not assigned a value within a
function (by an assignment, or the *note def: e83, *note class: d32, or
*note import: ce7. statements), references to the variable will be
looked up in the local namespace of the enclosing scope.  A more
detailed explanation of the rules, and a dissection of the
implementation, can be found in the PEP.

This change may cause some compatibility problems for code where the
same variable name is used both at the module level and as a local
variable within a function that contains further function definitions.
This seems rather unlikely though, since such code would have been
pretty confusing to read in the first place.

One side effect of the change is that the ‘from module import *’ and
‘exec’ statements have been made illegal inside a function scope under
certain conditions.  The Python reference manual has said all along that
‘from module import *’ is only legal at the top level of a module, but
the CPython interpreter has never enforced this before.  As part of the
implementation of nested scopes, the compiler which turns Python source
into bytecodes has to generate different code to access variables in a
containing scope.  ‘from module import *’ and ‘exec’ make it impossible
for the compiler to figure this out, because they add names to the local
namespace that are unknowable at compile time.  Therefore, if a function
contains function definitions or *note lambda: cf9. expressions with
free variables, the compiler will flag this by raising a *note
SyntaxError: 55a. exception.

To make the preceding explanation a bit clearer, here’s an example:

     x = 1
     def f():
         # The next line is a syntax error
         exec 'x=2'
         def g():
             return x

Line 4 containing the ‘exec’ statement is a syntax error, since ‘exec’
would define a new local variable named ‘x’ whose value should be
accessed by ‘g()’.

This shouldn’t be much of a limitation, since ‘exec’ is rarely used in
most Python code (and when it is used, it’s often a sign of a poor
design anyway).

Compatibility concerns have led to nested scopes being introduced
gradually; in Python 2.1, they aren’t enabled by default, but can be
turned on within a module by using a future statement as described in
PEP 236(1).  (See the following section for further discussion of PEP
236(2).)  In Python 2.2, nested scopes will become the default and there
will be no way to turn them off, but users will have had all of 2.1’s
lifetime to fix any breakage resulting from their introduction.

See also
........

PEP 227(3) - Statically Nested Scopes

     Written and implemented by Jeremy Hylton.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0236

   (2) https://www.python.org/dev/peps/pep-0236

   (3) https://www.python.org/dev/peps/pep-0227


File: python.info,  Node: PEP 236 __future__ Directives,  Next: PEP 207 Rich Comparisons,  Prev: PEP 227 Nested Scopes<2>,  Up: What’s New in Python 2 1

1.17.3 PEP 236: __future__ Directives
-------------------------------------

The reaction to nested scopes was widespread concern about the dangers
of breaking code with the 2.1 release, and it was strong enough to make
the Pythoneers take a more conservative approach.  This approach
consists of introducing a convention for enabling optional functionality
in release N that will become compulsory in release N+1.

The syntax uses a ‘from...import’ statement using the reserved module
name *note __future__: 0.  Nested scopes can be enabled by the following
statement:

     from __future__ import nested_scopes

While it looks like a normal *note import: ce7. statement, it’s not;
there are strict rules on where such a future statement can be put.
They can only be at the top of a module, and must precede any Python
code or regular ‘import’ statements.  This is because such statements
can affect how the Python bytecode compiler parses code and generates
bytecode, so they must precede any statement that will result in
bytecodes being produced.

See also
........

PEP 236(1) - Back to the *note __future__: 0.

     Written by Tim Peters, and primarily implemented by Jeremy Hylton.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0236


File: python.info,  Node: PEP 207 Rich Comparisons,  Next: PEP 230 Warning Framework,  Prev: PEP 236 __future__ Directives,  Up: What’s New in Python 2 1

1.17.4 PEP 207: Rich Comparisons
--------------------------------

In earlier versions, Python’s support for implementing comparisons on
user-defined classes and extension types was quite simple.  Classes
could implement a ‘__cmp__()’ method that was given two instances of a
class, and could only return 0 if they were equal or +1 or -1 if they
weren’t; the method couldn’t raise an exception or return anything other
than a Boolean value.  Users of Numeric Python often found this model
too weak and restrictive, because in the number-crunching programs that
numeric Python is used for, it would be more useful to be able to
perform elementwise comparisons of two matrices, returning a matrix
containing the results of a given comparison for each element.  If the
two matrices are of different sizes, then the compare has to be able to
raise an exception to signal the error.

In Python 2.1, rich comparisons were added in order to support this
need.  Python classes can now individually overload each of the ‘<’,
‘<=’, ‘>’, ‘>=’, ‘==’, and ‘!=’ operations.  The new magic method names
are:

Operation       Method name
                
-------------------------------------
                
‘<’             *note __lt__(): cfe.
                
                
‘<=’            *note __le__(): d68.
                
                
‘>’             *note __gt__(): d69.
                
                
‘>=’            *note __ge__(): d6a.
                
                
‘==’            *note __eq__(): 44b.
                
                
‘!=’            *note __ne__(): f18.
                

(The magic methods are named after the corresponding Fortran operators
‘.LT.’.  ‘.LE.’, &c.  Numeric programmers are almost certainly quite
familiar with these names and will find them easy to remember.)

Each of these magic methods is of the form ‘method(self, other)’, where
‘self’ will be the object on the left-hand side of the operator, while
‘other’ will be the object on the right-hand side.  For example, the
expression ‘A < B’ will cause ‘A.__lt__(B)’ to be called.

Each of these magic methods can return anything at all: a Boolean, a
matrix, a list, or any other Python object.  Alternatively they can
raise an exception if the comparison is impossible, inconsistent, or
otherwise meaningless.

The built-in ‘cmp(A,B)’ function can use the rich comparison machinery,
and now accepts an optional argument specifying which comparison
operation to use; this is given as one of the strings ‘"<"’, ‘"<="’,
‘">"’, ‘">="’, ‘"=="’, or ‘"!="’.  If called without the optional third
argument, ‘cmp()’ will only return -1, 0, or +1 as in previous versions
of Python; otherwise it will call the appropriate method and can return
any Python object.

There are also corresponding changes of interest to C programmers;
there’s a new slot ‘tp_richcmp’ in type objects and an API for
performing a given rich comparison.  I won’t cover the C API here, but
will refer you to PEP 207(1), or to 2.1’s C API documentation, for the
full list of related functions.

See also
........

PEP 207(2) - Rich Comparisons

     Written by Guido van Rossum, heavily based on earlier work by David
     Ascher, and implemented by Guido van Rossum.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0207

   (2) https://www.python.org/dev/peps/pep-0207


File: python.info,  Node: PEP 230 Warning Framework,  Next: PEP 229 New Build System,  Prev: PEP 207 Rich Comparisons,  Up: What’s New in Python 2 1

1.17.5 PEP 230: Warning Framework
---------------------------------

Over its 10 years of existence, Python has accumulated a certain number
of obsolete modules and features along the way.  It’s difficult to know
when a feature is safe to remove, since there’s no way of knowing how
much code uses it — perhaps no programs depend on the feature, or
perhaps many do.  To enable removing old features in a more structured
way, a warning framework was added.  When the Python developers want to
get rid of a feature, it will first trigger a warning in the next
version of Python.  The following Python version can then drop the
feature, and users will have had a full release cycle to remove uses of
the old feature.

Python 2.1 adds the warning framework to be used in this scheme.  It
adds a *note warnings: 12f. module that provide functions to issue
warnings, and to filter out warnings that you don’t want to be
displayed.  Third-party modules can also use this framework to deprecate
old features that they no longer wish to support.

For example, in Python 2.1 the ‘regex’ module is deprecated, so
importing it causes a warning to be printed:

     >>> import regex
     __main__:1: DeprecationWarning: the regex module
              is deprecated; please use the re module
     >>>

Warnings can be issued by calling the *note warnings.warn(): f1a.
function:

     warnings.warn("feature X no longer supported")

The first parameter is the warning message; an additional optional
parameters can be used to specify a particular warning category.

Filters can be added to disable certain warnings; a regular expression
pattern can be applied to the message or to the module name in order to
suppress a warning.  For example, you may have a program that uses the
‘regex’ module and not want to spare the time to convert it to use the
*note re: dd. module right now.  The warning can be suppressed by
calling

     import warnings
     warnings.filterwarnings(action = 'ignore',
                             message='.*regex module is deprecated',
                             category=DeprecationWarning,
                             module = '__main__')

This adds a filter that will apply only to warnings of the class *note
DeprecationWarning: 15a. triggered in the *note __main__: 1. module, and
applies a regular expression to only match the message about the ‘regex’
module being deprecated, and will cause such warnings to be ignored.
Warnings can also be printed only once, printed every time the offending
code is executed, or turned into exceptions that will cause the program
to stop (unless the exceptions are caught in the usual way, of course).

Functions were also added to Python’s C API for issuing warnings; refer
to PEP 230 or to Python’s API documentation for the details.

See also
........

PEP 5(1) - Guidelines for Language Evolution

     Written by Paul Prescod, to specify procedures to be followed when
     removing old features from Python.  The policy described in this
     PEP hasn’t been officially adopted, but the eventual policy
     probably won’t be too different from Prescod’s proposal.

PEP 230(2) - Warning Framework

     Written and implemented by Guido van Rossum.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0005

   (2) https://www.python.org/dev/peps/pep-0230


File: python.info,  Node: PEP 229 New Build System,  Next: PEP 205 Weak References,  Prev: PEP 230 Warning Framework,  Up: What’s New in Python 2 1

1.17.6 PEP 229: New Build System
--------------------------------

When compiling Python, the user had to go in and edit the
‘Modules/Setup’ file in order to enable various additional modules; the
default set is relatively small and limited to modules that compile on
most Unix platforms.  This means that on Unix platforms with many more
features, most notably Linux, Python installations often don’t contain
all useful modules they could.

Python 2.0 added the Distutils, a set of modules for distributing and
installing extensions.  In Python 2.1, the Distutils are used to compile
much of the standard library of extension modules, autodetecting which
ones are supported on the current machine.  It’s hoped that this will
make Python installations easier and more featureful.

Instead of having to edit the ‘Modules/Setup’ file in order to enable
modules, a ‘setup.py’ script in the top directory of the Python source
distribution is run at build time, and attempts to discover which
modules can be enabled by examining the modules and header files on the
system.  If a module is configured in ‘Modules/Setup’, the ‘setup.py’
script won’t attempt to compile that module and will defer to the
‘Modules/Setup’ file’s contents.  This provides a way to specific any
strange command-line flags or libraries that are required for a specific
platform.

In another far-reaching change to the build mechanism, Neil Schemenauer
restructured things so Python now uses a single makefile that isn’t
recursive, instead of makefiles in the top directory and in each of the
‘Python/’, ‘Parser/’, ‘Objects/’, and ‘Modules/’ subdirectories.  This
makes building Python faster and also makes hacking the Makefiles
clearer and simpler.

See also
........

PEP 229(1) - Using Distutils to Build Python

     Written and implemented by A.M. Kuchling.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0229


File: python.info,  Node: PEP 205 Weak References,  Next: PEP 232 Function Attributes,  Prev: PEP 229 New Build System,  Up: What’s New in Python 2 1

1.17.7 PEP 205: Weak References
-------------------------------

Weak references, available through the *note weakref: 131. module, are a
minor but useful new data type in the Python programmer’s toolbox.

Storing a reference to an object (say, in a dictionary or a list) has
the side effect of keeping that object alive forever.  There are a few
specific cases where this behaviour is undesirable, object caches being
the most common one, and another being circular references in data
structures such as trees.

For example, consider a memoizing function that caches the results of
another function ‘f(x)’ by storing the function’s argument and its
result in a dictionary:

     _cache = {}
     def memoize(x):
         if _cache.has_key(x):
             return _cache[x]

         retval = f(x)

         # Cache the returned object
         _cache[x] = retval

         return retval

This version works for simple things such as integers, but it has a side
effect; the ‘_cache’ dictionary holds a reference to the return values,
so they’ll never be deallocated until the Python process exits and
cleans up.  This isn’t very noticeable for integers, but if ‘f()’
returns an object, or a data structure that takes up a lot of memory,
this can be a problem.

Weak references provide a way to implement a cache that won’t keep
objects alive beyond their time.  If an object is only accessible
through weak references, the object will be deallocated and the weak
references will now indicate that the object it referred to no longer
exists.  A weak reference to an object `obj' is created by calling ‘wr =
weakref.ref(obj)’.  The object being referred to is returned by calling
the weak reference as if it were a function: ‘wr()’.  It will return the
referenced object, or ‘None’ if the object no longer exists.

This makes it possible to write a ‘memoize()’ function whose cache
doesn’t keep objects alive, by storing weak references in the cache.

     _cache = {}
     def memoize(x):
         if _cache.has_key(x):
             obj = _cache[x]()
             # If weak reference object still exists,
             # return it
             if obj is not None: return obj

         retval = f(x)

         # Cache a weak reference
         _cache[x] = weakref.ref(retval)

         return retval

The *note weakref: 131. module also allows creating proxy objects which
behave like weak references — an object referenced only by proxy objects
is deallocated – but instead of requiring an explicit call to retrieve
the object, the proxy transparently forwards all operations to the
object as long as the object still exists.  If the object is
deallocated, attempting to use a proxy will cause a
‘weakref.ReferenceError’ exception to be raised.

     proxy = weakref.proxy(obj)
     proxy.attr   # Equivalent to obj.attr
     proxy.meth() # Equivalent to obj.meth()
     del obj
     proxy.attr   # raises weakref.ReferenceError

See also
........

PEP 205(1) - Weak References

     Written and implemented by Fred L. Drake, Jr.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0205


File: python.info,  Node: PEP 232 Function Attributes,  Next: PEP 235 Importing Modules on Case-Insensitive Platforms,  Prev: PEP 205 Weak References,  Up: What’s New in Python 2 1

1.17.8 PEP 232: Function Attributes
-----------------------------------

In Python 2.1, functions can now have arbitrary information attached to
them.  People were often using docstrings to hold information about
functions and methods, because the ‘__doc__’ attribute was the only way
of attaching any information to a function.  For example, in the Zope
Web application server, functions are marked as safe for public access
by having a docstring, and in John Aycock’s SPARK parsing framework,
docstrings hold parts of the BNF grammar to be parsed.  This overloading
is unfortunate, since docstrings are really intended to hold a
function’s documentation; for example, it means you can’t properly
document functions intended for private use in Zope.

Arbitrary attributes can now be set and retrieved on functions using the
regular Python syntax:

     def f(): pass

     f.publish = 1
     f.secure = 1
     f.grammar = "A ::= B (C D)*"

The dictionary containing attributes can be accessed as the function’s
*note __dict__: 5f6.  Unlike the *note __dict__: 5f6. attribute of class
instances, in functions you can actually assign a new dictionary to
*note __dict__: 5f6, though the new value is restricted to a regular
Python dictionary; you `can’t' be tricky and set it to a ‘UserDict’
instance, or any other random object that behaves like a mapping.

See also
........

PEP 232(1) - Function Attributes

     Written and implemented by Barry Warsaw.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0232


File: python.info,  Node: PEP 235 Importing Modules on Case-Insensitive Platforms,  Next: PEP 217 Interactive Display Hook,  Prev: PEP 232 Function Attributes,  Up: What’s New in Python 2 1

1.17.9 PEP 235: Importing Modules on Case-Insensitive Platforms
---------------------------------------------------------------

Some operating systems have filesystems that are case-insensitive, MacOS
and Windows being the primary examples; on these systems, it’s
impossible to distinguish the filenames ‘FILE.PY’ and ‘file.py’, even
though they do store the file’s name in its original case (they’re
case-preserving, too).

In Python 2.1, the *note import: ce7. statement will work to simulate
case-sensitivity on case-insensitive platforms.  Python will now search
for the first case-sensitive match by default, raising an *note
ImportError: 16c. if no such file is found, so ‘import file’ will not
import a module named ‘FILE.PY’.  Case-insensitive matching can be
requested by setting the *note PYTHONCASEOK: 230. environment variable
before starting the Python interpreter.


File: python.info,  Node: PEP 217 Interactive Display Hook,  Next: PEP 208 New Coercion Model,  Prev: PEP 235 Importing Modules on Case-Insensitive Platforms,  Up: What’s New in Python 2 1

1.17.10 PEP 217: Interactive Display Hook
-----------------------------------------

When using the Python interpreter interactively, the output of commands
is displayed using the built-in *note repr(): 8b9. function.  In Python
2.1, the variable *note sys.displayhook(): f20. can be set to a callable
object which will be called instead of *note repr(): 8b9.  For example,
you can set it to a special pretty-printing function:

     >>> # Create a recursive data structure
     ... L = [1,2,3]
     >>> L.append(L)
     >>> L # Show Python's default output
     [1, 2, 3, [...]]
     >>> # Use pprint.pprint() as the display function
     ... import sys, pprint
     >>> sys.displayhook = pprint.pprint
     >>> L
     [1, 2, 3,  <Recursion on list with id=135143996>]
     >>>

See also
........

PEP 217(1) - Display Hook for Interactive Use

     Written and implemented by Moshe Zadka.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0217


File: python.info,  Node: PEP 208 New Coercion Model,  Next: PEP 241 Metadata in Python Packages,  Prev: PEP 217 Interactive Display Hook,  Up: What’s New in Python 2 1

1.17.11 PEP 208: New Coercion Model
-----------------------------------

How numeric coercion is done at the C level was significantly modified.
This will only affect the authors of C extensions to Python, allowing
them more flexibility in writing extension types that support numeric
operations.

Extension types can now set the type flag ‘Py_TPFLAGS_CHECKTYPES’ in
their ‘PyTypeObject’ structure to indicate that they support the new
coercion model.  In such extension types, the numeric slot functions can
no longer assume that they’ll be passed two arguments of the same type;
instead they may be passed two arguments of differing types, and can
then perform their own internal coercion.  If the slot function is
passed a type it can’t handle, it can indicate the failure by returning
a reference to the ‘Py_NotImplemented’ singleton value.  The numeric
functions of the other type will then be tried, and perhaps they can
handle the operation; if the other type also returns
‘Py_NotImplemented’, then a *note TypeError: 1fe. will be raised.
Numeric methods written in Python can also return ‘Py_NotImplemented’,
causing the interpreter to act as if the method did not exist (perhaps
raising a *note TypeError: 1fe, perhaps trying another object’s numeric
methods).

See also
........

PEP 208(1) - Reworking the Coercion Model

     Written and implemented by Neil Schemenauer, heavily based upon
     earlier work by Marc-André Lemburg.  Read this to understand the
     fine points of how numeric operations will now be processed at the
     C level.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0208


File: python.info,  Node: PEP 241 Metadata in Python Packages,  Next: New and Improved Modules<4>,  Prev: PEP 208 New Coercion Model,  Up: What’s New in Python 2 1

1.17.12 PEP 241: Metadata in Python Packages
--------------------------------------------

A common complaint from Python users is that there’s no single catalog
of all the Python modules in existence.  T. Middleton’s Vaults of
Parnassus at ‘http://www.vex.net/parnassus/’ are the largest catalog of
Python modules, but registering software at the Vaults is optional, and
many people don’t bother.

As a first small step toward fixing the problem, Python software
packaged using the Distutils ‘sdist’ command will include a file named
‘PKG-INFO’ containing information about the package such as its name,
version, and author (metadata, in cataloguing terminology).  PEP 241(1)
contains the full list of fields that can be present in the ‘PKG-INFO’
file.  As people began to package their software using Python 2.1, more
and more packages will include metadata, making it possible to build
automated cataloguing systems and experiment with them.  With the result
experience, perhaps it’ll be possible to design a really good catalog
and then build support for it into Python 2.2.  For example, the
Distutils ‘sdist’ and ‘bdist_*’ commands could support an ‘upload’
option that would automatically upload your package to a catalog server.

You can start creating packages containing ‘PKG-INFO’ even if you’re not
using Python 2.1, since a new release of the Distutils will be made for
users of earlier Python versions.  Version 1.0.2 of the Distutils
includes the changes described in PEP 241(2), as well as various
bugfixes and enhancements.  It will be available from the Distutils SIG
at ‘https://www.python.org/community/sigs/current/distutils-sig/’.

See also
........

PEP 241(3) - Metadata for Python Software Packages

     Written and implemented by A.M. Kuchling.

PEP 243(4) - Module Repository Upload Mechanism

     Written by Sean Reifschneider, this draft PEP describes a proposed
     mechanism for uploading Python packages to a central server.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0241

   (2) https://www.python.org/dev/peps/pep-0241

   (3) https://www.python.org/dev/peps/pep-0241

   (4) https://www.python.org/dev/peps/pep-0243


File: python.info,  Node: New and Improved Modules<4>,  Next: Other Changes and Fixes<4>,  Prev: PEP 241 Metadata in Python Packages,  Up: What’s New in Python 2 1

1.17.13 New and Improved Modules
--------------------------------

   * Ka-Ping Yee contributed two new modules: ‘inspect.py’, a module for
     getting information about live Python code, and ‘pydoc.py’, a
     module for interactively converting docstrings to HTML or text.  As
     a bonus, ‘Tools/scripts/pydoc’, which is now automatically
     installed, uses ‘pydoc.py’ to display documentation given a Python
     module, package, or class name.  For example, ‘pydoc xml.dom’
     displays the following:

          Python Library Documentation: package xml.dom in xml

          NAME
              xml.dom - W3C Document Object Model implementation for Python.

          FILE
              /usr/local/lib/python2.1/xml/dom/__init__.pyc

          DESCRIPTION
              The Python mapping of the Document Object Model is documented in the
              Python Library Reference in the section on the xml.dom package.

              This package contains the following modules:
                ...

     ‘pydoc’ also includes a Tk-based interactive help browser.  ‘pydoc’
     quickly becomes addictive; try it out!

   * Two different modules for unit testing were added to the standard
     library.  The *note doctest: 66. module, contributed by Tim Peters,
     provides a testing framework based on running embedded examples in
     docstrings and comparing the results against the expected output.
     PyUnit, contributed by Steve Purcell, is a unit testing framework
     inspired by JUnit, which was in turn an adaptation of Kent Beck’s
     Smalltalk testing framework.  See ‘http://pyunit.sourceforge.net/’
     for more information about PyUnit.

   * The *note difflib: 36. module contains a class, ‘SequenceMatcher’,
     which compares two sequences and computes the changes required to
     transform one sequence into the other.  For example, this module
     can be used to write a tool similar to the Unix ‘diff’ program, and
     in fact the sample program ‘Tools/scripts/ndiff.py’ demonstrates
     how to write such a script.

   * *note curses.panel: 2d, a wrapper for the panel library, part of
     ncurses and of SYSV curses, was contributed by Thomas Gellekum.
     The panel library provides windows with the additional feature of
     depth.  Windows can be moved higher or lower in the depth ordering,
     and the panel library figures out where panels overlap and which
     sections are visible.

   * The PyXML package has gone through a few releases since Python 2.0,
     and Python 2.1 includes an updated version of the *note xml: 13c.
     package.  Some of the noteworthy changes include support for Expat
     1.2 and later versions, the ability for Expat parsers to handle
     files in any encoding supported by Python, and various bugfixes for
     SAX, DOM, and the ‘minidom’ module.

   * Ping also contributed another hook for handling uncaught
     exceptions.  *note sys.excepthook(): f24. can be set to a callable
     object.  When an exception isn’t caught by any *note try:
     e37.…*note except: c10. blocks, the exception will be passed to
     *note sys.excepthook(): f24, which can then do whatever it likes.
     At the Ninth Python Conference, Ping demonstrated an application
     for this hook: printing an extended traceback that not only lists
     the stack frames, but also lists the function arguments and the
     local variables for each frame.

   * Various functions in the *note time: 10c. module, such as
     ‘asctime()’ and ‘localtime()’, require a floating point argument
     containing the time in seconds since the epoch.  The most common
     use of these functions is to work with the current time, so the
     floating point argument has been made optional; when a value isn’t
     provided, the current time will be used.  For example, log file
     entries usually need a string containing the current time; in
     Python 2.1, ‘time.asctime()’ can be used, instead of the lengthier
     ‘time.asctime(time.localtime(time.time()))’ that was previously
     required.

     This change was proposed and implemented by Thomas Wouters.

   * The *note ftplib: 82. module now defaults to retrieving files in
     passive mode, because passive mode is more likely to work from
     behind a firewall.  This request came from the Debian bug tracking
     system, since other Debian packages use *note ftplib: 82. to
     retrieve files and then don’t work from behind a firewall.  It’s
     deemed unlikely that this will cause problems for anyone, because
     Netscape defaults to passive mode and few people complain, but if
     passive mode is unsuitable for your application or network setup,
     call ‘set_pasv(0)’ on FTP objects to disable passive mode.

   * Support for raw socket access has been added to the *note socket:
     ef. module, contributed by Grant Edwards.

   * The *note pstats: d4. module now contains a simple interactive
     statistics browser for displaying timing profiles for Python
     programs, invoked when the module is run as a script.  Contributed
     by Eric S. Raymond.

   * A new implementation-dependent function, ‘sys._getframe([depth])’,
     has been added to return a given frame object from the current call
     stack.  *note sys._getframe(): f25. returns the frame at the top of
     the call stack; if the optional integer argument `depth' is
     supplied, the function returns the frame that is `depth' calls
     below the top of the stack.  For example, ‘sys._getframe(1)’
     returns the caller’s frame object.

     This function is only present in CPython, not in Jython or the .NET
     implementation.  Use it for debugging, and resist the temptation to
     put it into production code.


File: python.info,  Node: Other Changes and Fixes<4>,  Next: Acknowledgements<7>,  Prev: New and Improved Modules<4>,  Up: What’s New in Python 2 1

1.17.14 Other Changes and Fixes
-------------------------------

There were relatively few smaller changes made in Python 2.1 due to the
shorter release cycle.  A search through the CVS change logs turns up
117 patches applied, and 136 bugs fixed; both figures are likely to be
underestimates.  Some of the more notable changes are:

   * A specialized object allocator is now optionally available, that
     should be faster than the system ‘malloc()’ and have less memory
     overhead.  The allocator uses C’s ‘malloc()’ function to get large
     pools of memory, and then fulfills smaller memory requests from
     these pools.  It can be enabled by providing the ‘--with-pymalloc’
     option to the ‘configure’ script; see ‘Objects/obmalloc.c’ for the
     implementation details.

     Authors of C extension modules should test their code with the
     object allocator enabled, because some incorrect code may break,
     causing core dumps at runtime.  There are a bunch of memory
     allocation functions in Python’s C API that have previously been
     just aliases for the C library’s ‘malloc()’ and ‘free()’, meaning
     that if you accidentally called mismatched functions, the error
     wouldn’t be noticeable.  When the object allocator is enabled,
     these functions aren’t aliases of ‘malloc()’ and ‘free()’ any more,
     and calling the wrong function to free memory will get you a core
     dump.  For example, if memory was allocated using ‘PyMem_New()’, it
     has to be freed using ‘PyMem_Del()’, not ‘free()’.  A few modules
     included with Python fell afoul of this and had to be fixed;
     doubtless there are more third-party modules that will have the
     same problem.

     The object allocator was contributed by Vladimir Marangozov.

   * The speed of line-oriented file I/O has been improved because
     people often complain about its lack of speed, and because it’s
     often been used as a naïve benchmark.  The *note readline(): de.
     method of file objects has therefore been rewritten to be much
     faster.  The exact amount of the speedup will vary from platform to
     platform depending on how slow the C library’s ‘getc()’ was, but is
     around 66%, and potentially much faster on some particular
     operating systems.  Tim Peters did much of the benchmarking and
     coding for this change, motivated by a discussion in
     comp.lang.python.

     A new module and method for file objects was also added,
     contributed by Jeff Epler.  The new method, ‘xreadlines()’, is
     similar to the existing ‘xrange()’ built-in.  ‘xreadlines()’
     returns an opaque sequence object that only supports being iterated
     over, reading a line on every iteration but not reading the entire
     file into memory as the existing ‘readlines()’ method does.  You’d
     use it like this:

          for line in sys.stdin.xreadlines():
              # ... do something for each line ...
              ...

     For a fuller discussion of the line I/O changes, see the python-dev
     summary for January 1–15, 2001 at
     ‘https://mail.python.org/pipermail/python-dev/2001-January/’.

   * A new method, ‘popitem()’, was added to dictionaries to enable
     destructively iterating through the contents of a dictionary; this
     can be faster for large dictionaries because there’s no need to
     construct a list containing all the keys or values.  ‘D.popitem()’
     removes a random ‘(key, value)’ pair from the dictionary ‘D’ and
     returns it as a 2-tuple.  This was implemented mostly by Tim Peters
     and Guido van Rossum, after a suggestion and preliminary patch by
     Moshe Zadka.

   * Modules can now control which names are imported when ‘from module
     import *’ is used, by defining an ‘__all__’ attribute containing a
     list of names that will be imported.  One common complaint is that
     if the module imports other modules such as *note sys: fd. or *note
     string: f6, ‘from module import *’ will add them to the importing
     module’s namespace.  To fix this, simply list the public names in
     ‘__all__’:

          # List public names
          __all__ = ['Database', 'open']

     A stricter version of this patch was first suggested and
     implemented by Ben Wolfson, but after some python-dev discussion, a
     weaker final version was checked in.

   * Applying *note repr(): 8b9. to strings previously used octal
     escapes for non-printable characters; for example, a newline was
     ‘'\012'’.  This was a vestigial trace of Python’s C ancestry, but
     today octal is of very little practical use.  Ka-Ping Yee suggested
     using hex escapes instead of octal ones, and using the ‘\n’, ‘\t’,
     ‘\r’ escapes for the appropriate characters, and implemented this
     new formatting.

   * Syntax errors detected at compile-time can now raise exceptions
     containing the filename and line number of the error, a pleasant
     side effect of the compiler reorganization done by Jeremy Hylton.

   * C extensions which import other modules have been changed to use
     ‘PyImport_ImportModule()’, which means that they will use any
     import hooks that have been installed.  This is also encouraged for
     third-party extensions that need to import some other module from C
     code.

   * The size of the Unicode character database was shrunk by another
     340K thanks to Fredrik Lundh.

   * Some new ports were contributed: MacOS X (by Steven Majewski),
     Cygwin (by Jason Tishler); RISCOS (by Dietmar Schwertberger);
     Unixware 7 (by Billy G. Allie).

And there’s the usual list of minor bugfixes, minor memory leaks,
docstring edits, and other tweaks, too lengthy to be worth itemizing;
see the CVS logs for the full details if you want them.


File: python.info,  Node: Acknowledgements<7>,  Prev: Other Changes and Fixes<4>,  Up: What’s New in Python 2 1

1.17.15 Acknowledgements
------------------------

The author would like to thank the following people for offering
suggestions on various drafts of this article: Graeme Cross, David
Goodger, Jay Graves, Michael Hudson, Marc-André Lemburg, Fredrik Lundh,
Neil Schemenauer, Thomas Wouters.


File: python.info,  Node: What’s New in Python 2 0,  Next: Changelog,  Prev: What’s New in Python 2 1,  Up: What’s New in Python

1.18 What’s New in Python 2.0
=============================


Author: A.M. Kuchling and Moshe Zadka

* Menu:

* Introduction: Introduction<3>.
* What About Python 1.6?: What About Python 1 6?.
* New Development Process::
* Unicode: Unicode<2>.
* List Comprehensions::
* Augmented Assignment::
* String Methods::
* Garbage Collection of Cycles::
* Other Core Changes::
* Porting to 2.0: Porting to 2 0.
* Extending/Embedding Changes::
* Distutils; Making Modules Easy to Install: Distutils Making Modules Easy to Install.
* XML Modules::
* Module changes::
* New modules::
* IDLE Improvements::
* Deleted and Deprecated Modules::
* Acknowledgements: Acknowledgements<8>.


File: python.info,  Node: Introduction<3>,  Next: What About Python 1 6?,  Up: What’s New in Python 2 0

1.18.1 Introduction
-------------------

A new release of Python, version 2.0, was released on October 16, 2000.
This article covers the exciting new features in 2.0, highlights some
other useful changes, and points out a few incompatible changes that may
require rewriting code.

Python’s development never completely stops between releases, and a
steady flow of bug fixes and improvements are always being submitted.  A
host of minor fixes, a few optimizations, additional docstrings, and
better error messages went into 2.0; to list them all would be
impossible, but they’re certainly significant.  Consult the
publicly-available CVS logs if you want to see the full list.  This
progress is due to the five developers working for PythonLabs are now
getting paid to spend their days fixing bugs, and also due to the
improved communication resulting from moving to SourceForge.


File: python.info,  Node: What About Python 1 6?,  Next: New Development Process,  Prev: Introduction<3>,  Up: What’s New in Python 2 0

1.18.2 What About Python 1.6?
-----------------------------

Python 1.6 can be thought of as the Contractual Obligations Python
release.  After the core development team left CNRI in May 2000, CNRI
requested that a 1.6 release be created, containing all the work on
Python that had been performed at CNRI. Python 1.6 therefore represents
the state of the CVS tree as of May 2000, with the most significant new
feature being Unicode support.  Development continued after May, of
course, so the 1.6 tree received a few fixes to ensure that it’s
forward-compatible with Python 2.0.  1.6 is therefore part of Python’s
evolution, and not a side branch.

So, should you take much interest in Python 1.6?  Probably not.  The
1.6final and 2.0beta1 releases were made on the same day (September 5,
2000), the plan being to finalize Python 2.0 within a month or so.  If
you have applications to maintain, there seems little point in breaking
things by moving to 1.6, fixing them, and then having another round of
breakage within a month by moving to 2.0; you’re better off just going
straight to 2.0.  Most of the really interesting features described in
this document are only in 2.0, because a lot of work was done between
May and September.


File: python.info,  Node: New Development Process,  Next: Unicode<2>,  Prev: What About Python 1 6?,  Up: What’s New in Python 2 0

1.18.3 New Development Process
------------------------------

The most important change in Python 2.0 may not be to the code at all,
but to how Python is developed: in May 2000 the Python developers began
using the tools made available by SourceForge for storing source code,
tracking bug reports, and managing the queue of patch submissions.  To
report bugs or submit patches for Python 2.0, use the bug tracking and
patch manager tools available from Python’s project page, located at
‘https://sourceforge.net/projects/python/’.

The most important of the services now hosted at SourceForge is the
Python CVS tree, the version-controlled repository containing the source
code for Python.  Previously, there were roughly 7 or so people who had
write access to the CVS tree, and all patches had to be inspected and
checked in by one of the people on this short list.  Obviously, this
wasn’t very scalable.  By moving the CVS tree to SourceForge, it became
possible to grant write access to more people; as of September 2000
there were 27 people able to check in changes, a fourfold increase.
This makes possible large-scale changes that wouldn’t be attempted if
they’d have to be filtered through the small group of core developers.
For example, one day Peter Schneider-Kamp took it into his head to drop
K&R C compatibility and convert the C source for Python to ANSI C. After
getting approval on the python-dev mailing list, he launched into a
flurry of checkins that lasted about a week, other developers joined in
to help, and the job was done.  If there were only 5 people with write
access, probably that task would have been viewed as “nice, but not
worth the time and effort needed” and it would never have gotten done.

The shift to using SourceForge’s services has resulted in a remarkable
increase in the speed of development.  Patches now get submitted,
commented on, revised by people other than the original submitter, and
bounced back and forth between people until the patch is deemed worth
checking in.  Bugs are tracked in one central location and can be
assigned to a specific person for fixing, and we can count the number of
open bugs to measure progress.  This didn’t come without a cost:
developers now have more e-mail to deal with, more mailing lists to
follow, and special tools had to be written for the new environment.
For example, SourceForge sends default patch and bug notification e-mail
messages that are completely unhelpful, so Ka-Ping Yee wrote an HTML
screen-scraper that sends more useful messages.

The ease of adding code caused a few initial growing pains, such as code
was checked in before it was ready or without getting clear agreement
from the developer group.  The approval process that has emerged is
somewhat similar to that used by the Apache group.  Developers can vote
+1, +0, -0, or -1 on a patch; +1 and -1 denote acceptance or rejection,
while +0 and -0 mean the developer is mostly indifferent to the change,
though with a slight positive or negative slant.  The most significant
change from the Apache model is that the voting is essentially advisory,
letting Guido van Rossum, who has Benevolent Dictator For Life status,
know what the general opinion is.  He can still ignore the result of a
vote, and approve or reject a change even if the community disagrees
with him.

Producing an actual patch is the last step in adding a new feature, and
is usually easy compared to the earlier task of coming up with a good
design.  Discussions of new features can often explode into lengthy
mailing list threads, making the discussion hard to follow, and no one
can read every posting to python-dev.  Therefore, a relatively formal
process has been set up to write Python Enhancement Proposals (PEPs),
modelled on the Internet RFC process.  PEPs are draft documents that
describe a proposed new feature, and are continually revised until the
community reaches a consensus, either accepting or rejecting the
proposal.  Quoting from the introduction to PEP 1(1), “PEP Purpose and
Guidelines”:

     PEP stands for Python Enhancement Proposal.  A PEP is a design
     document providing information to the Python community, or
     describing a new feature for Python.  The PEP should provide a
     concise technical specification of the feature and a rationale for
     the feature.

     We intend PEPs to be the primary mechanisms for proposing new
     features, for collecting community input on an issue, and for
     documenting the design decisions that have gone into Python.  The
     PEP author is responsible for building consensus within the
     community and documenting dissenting opinions.

Read the rest of PEP 1(2) for the details of the PEP editorial process,
style, and format.  PEPs are kept in the Python CVS tree on SourceForge,
though they’re not part of the Python 2.0 distribution, and are also
available in HTML form from ‘https://www.python.org/dev/peps/’.  As of
September 2000, there are 25 PEPS, ranging from PEP 201(3), “Lockstep
Iteration”, to PEP 225, “Elementwise/Objectwise Operators”.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0001

   (2) https://www.python.org/dev/peps/pep-0001

   (3) https://www.python.org/dev/peps/pep-0201


File: python.info,  Node: Unicode<2>,  Next: List Comprehensions,  Prev: New Development Process,  Up: What’s New in Python 2 0

1.18.4 Unicode
--------------

The largest new feature in Python 2.0 is a new fundamental data type:
Unicode strings.  Unicode uses 16-bit numbers to represent characters
instead of the 8-bit number used by ASCII, meaning that 65,536 distinct
characters can be supported.

The final interface for Unicode support was arrived at through countless
often-stormy discussions on the python-dev mailing list, and mostly
implemented by Marc-André Lemburg, based on a Unicode string type
implementation by Fredrik Lundh.  A detailed explanation of the
interface was written up as PEP 100(1), “Python Unicode Integration”.
This article will simply cover the most significant points about the
Unicode interfaces.

In Python source code, Unicode strings are written as ‘u"string"’.
Arbitrary Unicode characters can be written using a new escape sequence,
‘\uHHHH’, where `HHHH' is a 4-digit hexadecimal number from 0000 to
FFFF. The existing ‘\xHHHH’ escape sequence can also be used, and octal
escapes can be used for characters up to U+01FF, which is represented by
‘\777’.

Unicode strings, just like regular strings, are an immutable sequence
type.  They can be indexed and sliced, but not modified in place.
Unicode strings have an ‘encode( [encoding] )’ method that returns an
8-bit string in the desired encoding.  Encodings are named by strings,
such as ‘'ascii'’, ‘'utf-8'’, ‘'iso-8859-1'’, or whatever.  A codec API
is defined for implementing and registering new encodings that are then
available throughout a Python program.  If an encoding isn’t specified,
the default encoding is usually 7-bit ASCII, though it can be changed
for your Python installation by calling the
‘sys.setdefaultencoding(encoding)’ function in a customized version of
‘site.py’.

Combining 8-bit and Unicode strings always coerces to Unicode, using the
default ASCII encoding; the result of ‘'a' + u'bc'’ is ‘u'abc'’.

New built-in functions have been added, and existing built-ins modified
to support Unicode:

   * ‘unichr(ch)’ returns a Unicode string 1 character long, containing
     the character `ch'.

   * ‘ord(u)’, where `u' is a 1-character regular or Unicode string,
     returns the number of the character as an integer.

   * ‘unicode(string [, encoding] [, errors] )’ creates a Unicode string
     from an 8-bit string.  ‘encoding’ is a string naming the encoding
     to use.  The ‘errors’ parameter specifies the treatment of
     characters that are invalid for the current encoding; passing
     ‘'strict'’ as the value causes an exception to be raised on any
     encoding error, while ‘'ignore'’ causes errors to be silently
     ignored and ‘'replace'’ uses U+FFFD, the official replacement
     character, in case of any problems.

   * The ‘exec’ statement, and various built-ins such as ‘eval()’,
     ‘getattr()’, and ‘setattr()’ will also accept Unicode strings as
     well as regular strings.  (It’s possible that the process of fixing
     this missed some built-ins; if you find a built-in function that
     accepts strings but doesn’t accept Unicode strings at all, please
     report it as a bug.)

A new module, *note unicodedata: 123, provides an interface to Unicode
character properties.  For example, ‘unicodedata.category(u'A')’ returns
the 2-character string ‘Lu’, the ‘L’ denoting it’s a letter, and ‘u’
meaning that it’s uppercase.  ‘unicodedata.bidirectional(u'\u0660')’
returns ‘AN’, meaning that U+0660 is an Arabic number.

The *note codecs: 1b. module contains functions to look up existing
encodings and register new ones.  Unless you want to implement a new
encoding, you’ll most often use the ‘codecs.lookup(encoding)’ function,
which returns a 4-element tuple: ‘(encode_func, decode_func,
stream_reader, stream_writer)’.

   * `encode_func' is a function that takes a Unicode string, and
     returns a 2-tuple ‘(string, length)’.  `string' is an 8-bit string
     containing a portion (perhaps all) of the Unicode string converted
     into the given encoding, and `length' tells you how much of the
     Unicode string was converted.

   * `decode_func' is the opposite of `encode_func', taking an 8-bit
     string and returning a 2-tuple ‘(ustring, length)’, consisting of
     the resulting Unicode string `ustring' and the integer `length'
     telling how much of the 8-bit string was consumed.

   * `stream_reader' is a class that supports decoding input from a
     stream.  `stream_reader(file_obj)' returns an object that supports
     the ‘read()’, *note readline(): de, and ‘readlines()’ methods.
     These methods will all translate from the given encoding and return
     Unicode strings.

   * `stream_writer', similarly, is a class that supports encoding
     output to a stream.  `stream_writer(file_obj)' returns an object
     that supports the ‘write()’ and ‘writelines()’ methods.  These
     methods expect Unicode strings, translating them to the given
     encoding on output.

For example, the following code writes a Unicode string into a file,
encoding it as UTF-8:

     import codecs

     unistr = u'\u0660\u2000ab ...'

     (UTF8_encode, UTF8_decode,
      UTF8_streamreader, UTF8_streamwriter) = codecs.lookup('UTF-8')

     output = UTF8_streamwriter( open( '/tmp/output', 'wb') )
     output.write( unistr )
     output.close()

The following code would then read UTF-8 input from the file:

     input = UTF8_streamreader( open( '/tmp/output', 'rb') )
     print repr(input.read())
     input.close()

Unicode-aware regular expressions are available through the *note re:
dd. module, which has a new underlying implementation called SRE written
by Fredrik Lundh of Secret Labs AB.

A ‘-U’ command line option was added which causes the Python compiler to
interpret all string literals as Unicode string literals.  This is
intended to be used in testing and future-proofing your Python code,
since some future version of Python may drop support for 8-bit strings
and provide only Unicode strings.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0100


File: python.info,  Node: List Comprehensions,  Next: Augmented Assignment,  Prev: Unicode<2>,  Up: What’s New in Python 2 0

1.18.5 List Comprehensions
--------------------------

Lists are a workhorse data type in Python, and many programs manipulate
a list at some point.  Two common operations on lists are to loop over
them, and either pick out the elements that meet a certain criterion, or
apply some function to each element.  For example, given a list of
strings, you might want to pull out all the strings containing a given
substring, or strip off trailing whitespace from each line.

The existing *note map(): cf7. and *note filter(): cf8. functions can be
used for this purpose, but they require a function as one of their
arguments.  This is fine if there’s an existing built-in function that
can be passed directly, but if there isn’t, you have to create a little
function to do the required work, and Python’s scoping rules make the
result ugly if the little function needs additional information.  Take
the first example in the previous paragraph, finding all the strings in
the list containing a given substring.  You could write the following to
do it:

     # Given the list L, make a list of all strings
     # containing the substring S.
     sublist = filter( lambda s, substring=S:
                          string.find(s, substring) != -1,
                       L)

Because of Python’s scoping rules, a default argument is used so that
the anonymous function created by the *note lambda: cf9. expression
knows what substring is being searched for.  List comprehensions make
this cleaner:

     sublist = [ s for s in L if string.find(s, S) != -1 ]

List comprehensions have the form:

     [ expression for expr in sequence1
                  for expr2 in sequence2 ...
                  for exprN in sequenceN
                  if condition ]

The ‘for’…‘in’ clauses contain the sequences to be iterated over.  The
sequences do not have to be the same length, because they are `not'
iterated over in parallel, but from left to right; this is explained
more clearly in the following paragraphs.  The elements of the generated
list will be the successive values of `expression'.  The final ‘if’
clause is optional; if present, `expression' is only evaluated and added
to the result if `condition' is true.

To make the semantics very clear, a list comprehension is equivalent to
the following Python code:

     for expr1 in sequence1:
         for expr2 in sequence2:
         ...
             for exprN in sequenceN:
                  if (condition):
                       # Append the value of
                       # the expression to the
                       # resulting list.

This means that when there are multiple ‘for’…‘in’ clauses, the
resulting list will be equal to the product of the lengths of all the
sequences.  If you have two lists of length 3, the output list is 9
elements long:

     seq1 = 'abc'
     seq2 = (1,2,3)
     >>> [ (x,y) for x in seq1 for y in seq2]
     [('a', 1), ('a', 2), ('a', 3), ('b', 1), ('b', 2), ('b', 3), ('c', 1),
     ('c', 2), ('c', 3)]

To avoid introducing an ambiguity into Python’s grammar, if `expression'
is creating a tuple, it must be surrounded with parentheses.  The first
list comprehension below is a syntax error, while the second one is
correct:

     # Syntax error
     [ x,y for x in seq1 for y in seq2]
     # Correct
     [ (x,y) for x in seq1 for y in seq2]

The idea of list comprehensions originally comes from the functional
programming language Haskell (‘https://www.haskell.org’).  Greg Ewing
argued most effectively for adding them to Python and wrote the initial
list comprehension patch, which was then discussed for a seemingly
endless time on the python-dev mailing list and kept up-to-date by Skip
Montanaro.


File: python.info,  Node: Augmented Assignment,  Next: String Methods,  Prev: List Comprehensions,  Up: What’s New in Python 2 0

1.18.6 Augmented Assignment
---------------------------

Augmented assignment operators, another long-requested feature, have
been added to Python 2.0.  Augmented assignment operators include ‘+=’,
‘-=’, ‘*=’, and so forth.  For example, the statement ‘a += 2’
increments the value of the variable ‘a’ by 2, equivalent to the
slightly lengthier ‘a = a + 2’.

The full list of supported assignment operators is ‘+=’, ‘-=’, ‘*=’,
‘/=’, ‘%=’, ‘**=’, ‘&=’, ‘|=’, ‘^=’, ‘>>=’, and ‘<<=’.  Python classes
can override the augmented assignment operators by defining methods
named *note __iadd__(): f30, *note __isub__(): f31, etc.  For example,
the following ‘Number’ class stores a number and supports using += to
create a new instance with an incremented value.

     class Number:
         def __init__(self, value):
             self.value = value
         def __iadd__(self, increment):
             return Number( self.value + increment)

     n = Number(5)
     n += 3
     print n.value

The *note __iadd__(): f30. special method is called with the value of
the increment, and should return a new instance with an appropriately
modified value; this return value is bound as the new value of the
variable on the left-hand side.

Augmented assignment operators were first introduced in the C
programming language, and most C-derived languages, such as ‘awk’, C++,
Java, Perl, and PHP also support them.  The augmented assignment patch
was implemented by Thomas Wouters.


File: python.info,  Node: String Methods,  Next: Garbage Collection of Cycles,  Prev: Augmented Assignment,  Up: What’s New in Python 2 0

1.18.7 String Methods
---------------------

Until now string-manipulation functionality was in the *note string: f6.
module, which was usually a front-end for the ‘strop’ module written in
C. The addition of Unicode posed a difficulty for the ‘strop’ module,
because the functions would all need to be rewritten in order to accept
either 8-bit or Unicode strings.  For functions such as
‘string.replace()’, which takes 3 string arguments, that means eight
possible permutations, and correspondingly complicated code.

Instead, Python 2.0 pushes the problem onto the string type, making
string manipulation functionality available through methods on both
8-bit strings and Unicode strings.

     >>> 'andrew'.capitalize()
     'Andrew'
     >>> 'hostname'.replace('os', 'linux')
     'hlinuxtname'
     >>> 'moshe'.find('sh')
     2

One thing that hasn’t changed, a noteworthy April Fools’ joke
notwithstanding, is that Python strings are immutable.  Thus, the string
methods return new strings, and do not modify the string on which they
operate.

The old *note string: f6. module is still around for backwards
compatibility, but it mostly acts as a front-end to the new string
methods.

Two methods which have no parallel in pre-2.0 versions, although they
did exist in JPython for quite some time, are ‘startswith()’ and
‘endswith()’.  ‘s.startswith(t)’ is equivalent to ‘s[:len(t)] == t’,
while ‘s.endswith(t)’ is equivalent to ‘s[-len(t):] == t’.

One other method which deserves special mention is ‘join()’.  The
‘join()’ method of a string receives one parameter, a sequence of
strings, and is equivalent to the ‘string.join()’ function from the old
*note string: f6. module, with the arguments reversed.  In other words,
‘s.join(seq)’ is equivalent to the old ‘string.join(seq, s)’.


File: python.info,  Node: Garbage Collection of Cycles,  Next: Other Core Changes,  Prev: String Methods,  Up: What’s New in Python 2 0

1.18.8 Garbage Collection of Cycles
-----------------------------------

The C implementation of Python uses reference counting to implement
garbage collection.  Every Python object maintains a count of the number
of references pointing to itself, and adjusts the count as references
are created or destroyed.  Once the reference count reaches zero, the
object is no longer accessible, since you need to have a reference to an
object to access it, and if the count is zero, no references exist any
longer.

Reference counting has some pleasant properties: it’s easy to understand
and implement, and the resulting implementation is portable, fairly
fast, and reacts well with other libraries that implement their own
memory handling schemes.  The major problem with reference counting is
that it sometimes doesn’t realise that objects are no longer accessible,
resulting in a memory leak.  This happens when there are cycles of
references.

Consider the simplest possible cycle, a class instance which has a
reference to itself:

     instance = SomeClass()
     instance.myself = instance

After the above two lines of code have been executed, the reference
count of ‘instance’ is 2; one reference is from the variable named
‘'instance'’, and the other is from the ‘myself’ attribute of the
instance.

If the next line of code is ‘del instance’, what happens?  The reference
count of ‘instance’ is decreased by 1, so it has a reference count of 1;
the reference in the ‘myself’ attribute still exists.  Yet the instance
is no longer accessible through Python code, and it could be deleted.
Several objects can participate in a cycle if they have references to
each other, causing all of the objects to be leaked.

Python 2.0 fixes this problem by periodically executing a cycle
detection algorithm which looks for inaccessible cycles and deletes the
objects involved.  A new *note gc: 84. module provides functions to
perform a garbage collection, obtain debugging statistics, and tuning
the collector’s parameters.

Running the cycle detection algorithm takes some time, and therefore
will result in some additional overhead.  It is hoped that after we’ve
gotten experience with the cycle collection from using 2.0, Python 2.1
will be able to minimize the overhead with careful tuning.  It’s not yet
obvious how much performance is lost, because benchmarking this is
tricky and depends crucially on how often the program creates and
destroys objects.  The detection of cycles can be disabled when Python
is compiled, if you can’t afford even a tiny speed penalty or suspect
that the cycle collection is buggy, by specifying the
‘--without-cycle-gc’ switch when running the ‘configure’ script.

Several people tackled this problem and contributed to a solution.  An
early implementation of the cycle detection approach was written by Toby
Kelsey.  The current algorithm was suggested by Eric Tiedemann during a
visit to CNRI, and Guido van Rossum and Neil Schemenauer wrote two
different implementations, which were later integrated by Neil.  Lots of
other people offered suggestions along the way; the March 2000 archives
of the python-dev mailing list contain most of the relevant discussion,
especially in the threads titled “Reference cycle collection for Python”
and “Finalization again”.


File: python.info,  Node: Other Core Changes,  Next: Porting to 2 0,  Prev: Garbage Collection of Cycles,  Up: What’s New in Python 2 0

1.18.9 Other Core Changes
-------------------------

Various minor changes have been made to Python’s syntax and built-in
functions.  None of the changes are very far-reaching, but they’re handy
conveniences.

* Menu:

* Minor Language Changes::
* Changes to Built-in Functions::


File: python.info,  Node: Minor Language Changes,  Next: Changes to Built-in Functions,  Up: Other Core Changes

1.18.9.1 Minor Language Changes
...............................

A new syntax makes it more convenient to call a given function with a
tuple of arguments and/or a dictionary of keyword arguments.  In Python
1.5 and earlier, you’d use the ‘apply()’ built-in function: ‘apply(f,
args, kw)’ calls the function ‘f()’ with the argument tuple `args' and
the keyword arguments in the dictionary `kw'.  ‘apply()’ is the same in
2.0, but thanks to a patch from Greg Ewing, ‘f(*args, **kw)’ is a
shorter and clearer way to achieve the same effect.  This syntax is
symmetrical with the syntax for defining functions:

     def f(*args, **kw):
         # args is a tuple of positional args,
         # kw is a dictionary of keyword args
         ...

The ‘print’ statement can now have its output directed to a file-like
object by following the ‘print’ with ‘>> file’, similar to the
redirection operator in Unix shells.  Previously you’d either have to
use the ‘write()’ method of the file-like object, which lacks the
convenience and simplicity of ‘print’, or you could assign a new value
to ‘sys.stdout’ and then restore the old value.  For sending output to
standard error, it’s much easier to write this:

     print >> sys.stderr, "Warning: action field not supplied"

Modules can now be renamed on importing them, using the syntax ‘import
module as name’ or ‘from module import name as othername’.  The patch
was submitted by Thomas Wouters.

A new format style is available when using the ‘%’ operator; ‘%r’ will
insert the *note repr(): 8b9. of its argument.  This was also added from
symmetry considerations, this time for symmetry with the existing ‘%s’
format style, which inserts the *note str(): 205. of its argument.  For
example, ‘'%r %s' % ('abc', 'abc')’ returns a string containing ‘'abc'
abc’.

Previously there was no way to implement a class that overrode Python’s
built-in *note in: 179. operator and implemented a custom version.  ‘obj
in seq’ returns true if `obj' is present in the sequence `seq'; Python
computes this by simply trying every index of the sequence until either
`obj' is found or an *note IndexError: f36. is encountered.  Moshe Zadka
contributed a patch which adds a *note __contains__(): dee. magic method
for providing a custom implementation for ‘in’.  Additionally, new
built-in objects written in C can define what ‘in’ means for them via a
new slot in the sequence protocol.

Earlier versions of Python used a recursive algorithm for deleting
objects.  Deeply nested data structures could cause the interpreter to
fill up the C stack and crash; Christian Tismer rewrote the deletion
logic to fix this problem.  On a related note, comparing recursive
objects recursed infinitely and crashed; Jeremy Hylton rewrote the code
to no longer crash, producing a useful result instead.  For example,
after this code:

     a = []
     b = []
     a.append(a)
     b.append(b)

The comparison ‘a==b’ returns true, because the two recursive data
structures are isomorphic.  See the thread “trashcan and PR#7” in the
April 2000 archives of the python-dev mailing list for the discussion
leading up to this implementation, and some useful relevant links.  Note
that comparisons can now also raise exceptions.  In earlier versions of
Python, a comparison operation such as ‘cmp(a,b)’ would always produce
an answer, even if a user-defined ‘__cmp__()’ method encountered an
error, since the resulting exception would simply be silently swallowed.

Work has been done on porting Python to 64-bit Windows on the Itanium
processor, mostly by Trent Mick of ActiveState.  (Confusingly,
‘sys.platform’ is still ‘'win32'’ on Win64 because it seems that for
ease of porting, MS Visual C++ treats code as 32 bit on Itanium.)
PythonWin also supports Windows CE; see the Python CE page at
‘http://pythonce.sourceforge.net/’ for more information.

Another new platform is Darwin/MacOS X; initial support for it is in
Python 2.0.  Dynamic loading works, if you specify “configure –with-dyld
–with-suffix=.x”.  Consult the README in the Python source distribution
for more instructions.

An attempt has been made to alleviate one of Python’s warts, the
often-confusing *note NameError: e40. exception when code refers to a
local variable before the variable has been assigned a value.  For
example, the following code raises an exception on the ‘print’ statement
in both 1.5.2 and 2.0; in 1.5.2 a *note NameError: e40. exception is
raised, while 2.0 raises a new *note UnboundLocalError: f37. exception.
*note UnboundLocalError: f37. is a subclass of *note NameError: e40, so
any existing code that expects *note NameError: e40. to be raised should
still work.

     def f():
         print "i=",i
         i = i + 1
     f()

Two new exceptions, *note TabError: f38. and *note IndentationError:
f39, have been introduced.  They’re both subclasses of *note
SyntaxError: 55a, and are raised when Python code is found to be
improperly indented.


File: python.info,  Node: Changes to Built-in Functions,  Prev: Minor Language Changes,  Up: Other Core Changes

1.18.9.2 Changes to Built-in Functions
......................................

A new built-in, ‘zip(seq1, seq2, ...)’, has been added.  *note zip():
cfc. returns a list of tuples where each tuple contains the i-th element
from each of the argument sequences.  The difference between *note
zip(): cfc. and ‘map(None, seq1, seq2)’ is that *note map(): cf7. pads
the sequences with ‘None’ if the sequences aren’t all of the same
length, while *note zip(): cfc. truncates the returned list to the
length of the shortest argument sequence.

The *note int(): 204. and ‘long()’ functions now accept an optional
“base” parameter when the first argument is a string.  ‘int('123', 10)’
returns 123, while ‘int('123', 16)’ returns 291.  ‘int(123, 16)’ raises
a *note TypeError: 1fe. exception with the message “can’t convert
non-string with explicit base”.

A new variable holding more detailed version information has been added
to the *note sys: fd. module.  ‘sys.version_info’ is a tuple ‘(major,
minor, micro, level, serial)’ For example, in a hypothetical 2.0.1beta1,
‘sys.version_info’ would be ‘(2, 0, 1, 'beta', 1)’.  `level' is a string
such as ‘"alpha"’, ‘"beta"’, or ‘"final"’ for a final release.

Dictionaries have an odd new method, ‘setdefault(key, default)’, which
behaves similarly to the existing ‘get()’ method.  However, if the key
is missing, ‘setdefault()’ both returns the value of `default' as
‘get()’ would do, and also inserts it into the dictionary as the value
for `key'.  Thus, the following lines of code:

     if dict.has_key( key ): return dict[key]
     else:
         dict[key] = []
         return dict[key]

can be reduced to a single ‘return dict.setdefault(key, [])’ statement.

The interpreter sets a maximum recursion depth in order to catch runaway
recursion before filling the C stack and causing a core dump or GPF..
Previously this limit was fixed when you compiled Python, but in 2.0 the
maximum recursion depth can be read and modified using *note
sys.getrecursionlimit(): f3b. and *note sys.setrecursionlimit(): f3c.
The default value is 1000, and a rough maximum value for a given
platform can be found by running a new script,
‘Misc/find_recursionlimit.py’.


File: python.info,  Node: Porting to 2 0,  Next: Extending/Embedding Changes,  Prev: Other Core Changes,  Up: What’s New in Python 2 0

1.18.10 Porting to 2.0
----------------------

New Python releases try hard to be compatible with previous releases,
and the record has been pretty good.  However, some changes are
considered useful enough, usually because they fix initial design
decisions that turned out to be actively mistaken, that breaking
backward compatibility can’t always be avoided.  This section lists the
changes in Python 2.0 that may cause old Python code to break.

The change which will probably break the most code is tightening up the
arguments accepted by some methods.  Some methods would take multiple
arguments and treat them as a tuple, particularly various list methods
such as ‘append()’ and ‘insert()’.  In earlier versions of Python, if
‘L’ is a list, ‘L.append( 1,2 )’ appends the tuple ‘(1,2)’ to the list.
In Python 2.0 this causes a *note TypeError: 1fe. exception to be
raised, with the message: ‘append requires exactly 1 argument; 2 given’.
The fix is to simply add an extra set of parentheses to pass both values
as a tuple: ‘L.append( (1,2) )’.

The earlier versions of these methods were more forgiving because they
used an old function in Python’s C interface to parse their arguments;
2.0 modernizes them to use ‘PyArg_ParseTuple()’, the current argument
parsing function, which provides more helpful error messages and treats
multi-argument calls as errors.  If you absolutely must use 2.0 but
can’t fix your code, you can edit ‘Objects/listobject.c’ and define the
preprocessor symbol ‘NO_STRICT_LIST_APPEND’ to preserve the old
behaviour; this isn’t recommended.

Some of the functions in the *note socket: ef. module are still
forgiving in this way.  For example, ‘socket.connect( ('hostname', 25)
)()’ is the correct form, passing a tuple representing an IP address,
but ‘socket.connect( 'hostname', 25 )()’ also works.
‘socket.connect_ex()’ and ‘socket.bind()’ are similarly easy-going.
2.0alpha1 tightened these functions up, but because the documentation
actually used the erroneous multiple argument form, many people wrote
code which would break with the stricter checking.  GvR backed out the
changes in the face of public reaction, so for the *note socket: ef.
module, the documentation was fixed and the multiple argument form is
simply marked as deprecated; it `will' be tightened up again in a future
Python version.

The ‘\x’ escape in string literals now takes exactly 2 hex digits.
Previously it would consume all the hex digits following the ‘x’ and
take the lowest 8 bits of the result, so ‘\x123456’ was equivalent to
‘\x56’.

The *note AttributeError: 4a2. and *note NameError: e40. exceptions have
a more friendly error message, whose text will be something like ‘'Spam'
instance has no attribute 'eggs'’ or ‘name 'eggs' is not defined’.
Previously the error message was just the missing attribute name ‘eggs’,
and code written to take advantage of this fact will break in 2.0.

Some work has been done to make integers and long integers a bit more
interchangeable.  In 1.5.2, large-file support was added for Solaris, to
allow reading files larger than 2 GiB; this made the ‘tell()’ method of
file objects return a long integer instead of a regular integer.  Some
code would subtract two file offsets and attempt to use the result to
multiply a sequence or slice a string, but this raised a *note
TypeError: 1fe.  In 2.0, long integers can be used to multiply or slice
a sequence, and it’ll behave as you’d intuitively expect it to; ‘3L *
'abc'’ produces ‘abcabcabc’, and ‘(0,1,2,3)[2L:4L]’ produces (2,3).
Long integers can also be used in various contexts where previously only
integers were accepted, such as in the ‘seek()’ method of file objects,
and in the formats supported by the ‘%’ operator (‘%d’, ‘%i’, ‘%x’,
etc.).  For example, ‘"%d" % 2L**64’ will produce the string
‘18446744073709551616’.

The subtlest long integer change of all is that the *note str(): 205. of
a long integer no longer has a trailing ‘L’ character, though *note
repr(): 8b9. still includes it.  The ‘L’ annoyed many people who wanted
to print long integers that looked just like regular integers, since
they had to go out of their way to chop off the character.  This is no
longer a problem in 2.0, but code which does ‘str(longval)[:-1]’ and
assumes the ‘L’ is there, will now lose the final digit.

Taking the *note repr(): 8b9. of a float now uses a different formatting
precision than *note str(): 205.  *note repr(): 8b9. uses ‘%.17g’ format
string for C’s ‘sprintf()’, while *note str(): 205. uses ‘%.12g’ as
before.  The effect is that *note repr(): 8b9. may occasionally show
more decimal places than *note str(): 205, for certain numbers.  For
example, the number 8.1 can’t be represented exactly in binary, so
‘repr(8.1)’ is ‘'8.0999999999999996'’, while str(8.1) is ‘'8.1'’.

The ‘-X’ command-line option, which turned all standard exceptions into
strings instead of classes, has been removed; the standard exceptions
will now always be classes.  The ‘exceptions’ module containing the
standard exceptions was translated from Python to a built-in C module,
written by Barry Warsaw and Fredrik Lundh.


File: python.info,  Node: Extending/Embedding Changes,  Next: Distutils Making Modules Easy to Install,  Prev: Porting to 2 0,  Up: What’s New in Python 2 0

1.18.11 Extending/Embedding Changes
-----------------------------------

Some of the changes are under the covers, and will only be apparent to
people writing C extension modules or embedding a Python interpreter in
a larger application.  If you aren’t dealing with Python’s C API, you
can safely skip this section.

The version number of the Python C API was incremented, so C extensions
compiled for 1.5.2 must be recompiled in order to work with 2.0.  On
Windows, it’s not possible for Python 2.0 to import a third party
extension built for Python 1.5.x due to how Windows DLLs work, so Python
will raise an exception and the import will fail.

Users of Jim Fulton’s ExtensionClass module will be pleased to find out
that hooks have been added so that ExtensionClasses are now supported by
*note isinstance(): 552. and *note issubclass(): 553.  This means you no
longer have to remember to write code such as ‘if type(obj) ==
myExtensionClass’, but can use the more natural ‘if isinstance(obj,
myExtensionClass)’.

The ‘Python/importdl.c’ file, which was a mass of #ifdefs to support
dynamic loading on many different platforms, was cleaned up and
reorganised by Greg Stein.  ‘importdl.c’ is now quite small, and
platform-specific code has been moved into a bunch of
‘Python/dynload_*.c’ files.  Another cleanup: there were also a number
of ‘my*.h’ files in the Include/ directory that held various portability
hacks; they’ve been merged into a single file, ‘Include/pyport.h’.

Vladimir Marangozov’s long-awaited malloc restructuring was completed,
to make it easy to have the Python interpreter use a custom allocator
instead of C’s standard ‘malloc()’.  For documentation, read the
comments in ‘Include/pymem.h’ and ‘Include/objimpl.h’.  For the lengthy
discussions during which the interface was hammered out, see the Web
archives of the ‘patches’ and ‘python-dev’ lists at python.org.

Recent versions of the GUSI development environment for MacOS support
POSIX threads.  Therefore, Python’s POSIX threading support now works on
the Macintosh.  Threading support using the user-space GNU ‘pth’ library
was also contributed.

Threading support on Windows was enhanced, too.  Windows supports thread
locks that use kernel objects only in case of contention; in the common
case when there’s no contention, they use simpler functions which are an
order of magnitude faster.  A threaded version of Python 1.5.2 on NT is
twice as slow as an unthreaded version; with the 2.0 changes, the
difference is only 10%.  These improvements were contributed by Yakov
Markovitch.

Python 2.0’s source now uses only ANSI C prototypes, so compiling Python
now requires an ANSI C compiler, and can no longer be done using a
compiler that only supports K&R C.

Previously the Python virtual machine used 16-bit numbers in its
bytecode, limiting the size of source files.  In particular, this
affected the maximum size of literal lists and dictionaries in Python
source; occasionally people who are generating Python code would run
into this limit.  A patch by Charles G. Waldman raises the limit from
‘2**16’ to ‘2**32’.

Three new convenience functions intended for adding constants to a
module’s dictionary at module initialization time were added:
‘PyModule_AddObject()’, ‘PyModule_AddIntConstant()’, and
‘PyModule_AddStringConstant()’.  Each of these functions takes a module
object, a null-terminated C string containing the name to be added, and
a third argument for the value to be assigned to the name.  This third
argument is, respectively, a Python object, a C long, or a C string.

A wrapper API was added for Unix-style signal handlers.  ‘PyOS_getsig()’
gets a signal handler and ‘PyOS_setsig()’ will set a new handler.


File: python.info,  Node: Distutils Making Modules Easy to Install,  Next: XML Modules,  Prev: Extending/Embedding Changes,  Up: What’s New in Python 2 0

1.18.12 Distutils: Making Modules Easy to Install
-------------------------------------------------

Before Python 2.0, installing modules was a tedious affair – there was
no way to figure out automatically where Python is installed, or what
compiler options to use for extension modules.  Software authors had to
go through an arduous ritual of editing Makefiles and configuration
files, which only really work on Unix and leave Windows and MacOS
unsupported.  Python users faced wildly differing installation
instructions which varied between different extension packages, which
made administering a Python installation something of a chore.

The SIG for distribution utilities, shepherded by Greg Ward, has created
the Distutils, a system to make package installation much easier.  They
form the *note distutils: 38. package, a new part of Python’s standard
library.  In the best case, installing a Python module from source will
require the same steps: first you simply mean unpack the tarball or zip
archive, and the run “‘python setup.py install’”.  The platform will be
automatically detected, the compiler will be recognized, C extension
modules will be compiled, and the distribution installed into the proper
directory.  Optional command-line arguments provide more control over
the installation process, the distutils package offers many places to
override defaults – separating the build from the install, building or
installing in non-default directories, and more.

In order to use the Distutils, you need to write a ‘setup.py’ script.
For the simple case, when the software contains only .py files, a
minimal ‘setup.py’ can be just a few lines long:

     from distutils.core import setup
     setup (name = "foo", version = "1.0",
            py_modules = ["module1", "module2"])

The ‘setup.py’ file isn’t much more complicated if the software consists
of a few packages:

     from distutils.core import setup
     setup (name = "foo", version = "1.0",
            packages = ["package", "package.subpackage"])

A C extension can be the most complicated case; here’s an example taken
from the PyXML package:

     from distutils.core import setup, Extension

     expat_extension = Extension('xml.parsers.pyexpat',
          define_macros = [('XML_NS', None)],
          include_dirs = [ 'extensions/expat/xmltok',
                           'extensions/expat/xmlparse' ],
          sources = [ 'extensions/pyexpat.c',
                      'extensions/expat/xmltok/xmltok.c',
                      'extensions/expat/xmltok/xmlrole.c', ]
            )
     setup (name = "PyXML", version = "0.5.4",
            ext_modules =[ expat_extension ] )

The Distutils can also take care of creating source and binary
distributions.  The “sdist” command, run by “‘python setup.py sdist’’,
builds a source distribution such as ‘foo-1.0.tar.gz’.  Adding new
commands isn’t difficult, “bdist_rpm” and “bdist_wininst” commands have
already been contributed to create an RPM distribution and a Windows
installer for the software, respectively.  Commands to create other
distribution formats such as Debian packages and Solaris ‘.pkg’ files
are in various stages of development.

All this is documented in a new manual, `Distributing Python Modules',
that joins the basic set of Python documentation.


File: python.info,  Node: XML Modules,  Next: Module changes,  Prev: Distutils Making Modules Easy to Install,  Up: What’s New in Python 2 0

1.18.13 XML Modules
-------------------

Python 1.5.2 included a simple XML parser in the form of the ‘xmllib’
module, contributed by Sjoerd Mullender.  Since 1.5.2’s release, two
different interfaces for processing XML have become common: SAX2
(version 2 of the Simple API for XML) provides an event-driven interface
with some similarities to ‘xmllib’, and the DOM (Document Object Model)
provides a tree-based interface, transforming an XML document into a
tree of nodes that can be traversed and modified.  Python 2.0 includes a
SAX2 interface and a stripped-down DOM interface as part of the *note
xml: 13c. package.  Here we will give a brief overview of these new
interfaces; consult the Python documentation or the source code for
complete details.  The Python XML SIG is also working on improved
documentation.

* Menu:

* SAX2 Support::
* DOM Support::
* Relationship to PyXML::


File: python.info,  Node: SAX2 Support,  Next: DOM Support,  Up: XML Modules

1.18.13.1 SAX2 Support
......................

SAX defines an event-driven interface for parsing XML. To use SAX, you
must write a SAX handler class.  Handler classes inherit from various
classes provided by SAX, and override various methods that will then be
called by the XML parser.  For example, the ‘startElement()’ and
‘endElement()’ methods are called for every starting and end tag
encountered by the parser, the ‘characters()’ method is called for every
chunk of character data, and so forth.

The advantage of the event-driven approach is that the whole document
doesn’t have to be resident in memory at any one time, which matters if
you are processing really huge documents.  However, writing the SAX
handler class can get very complicated if you’re trying to modify the
document structure in some elaborate way.

For example, this little example program defines a handler that prints a
message for every starting and ending tag, and then parses the file
‘hamlet.xml’ using it:

     from xml import sax

     class SimpleHandler(sax.ContentHandler):
         def startElement(self, name, attrs):
             print 'Start of element:', name, attrs.keys()

         def endElement(self, name):
             print 'End of element:', name

     # Create a parser object
     parser = sax.make_parser()

     # Tell it what handler to use
     handler = SimpleHandler()
     parser.setContentHandler( handler )

     # Parse a file!
     parser.parse( 'hamlet.xml' )

For more information, consult the Python documentation, or the XML HOWTO
at ‘http://pyxml.sourceforge.net/topics/howto/xml-howto.html’.


File: python.info,  Node: DOM Support,  Next: Relationship to PyXML,  Prev: SAX2 Support,  Up: XML Modules

1.18.13.2 DOM Support
.....................

The Document Object Model is a tree-based representation for an XML
document.  A top-level ‘Document’ instance is the root of the tree, and
has a single child which is the top-level ‘Element’ instance.  This
‘Element’ has children nodes representing character data and any
sub-elements, which may have further children of their own, and so
forth.  Using the DOM you can traverse the resulting tree any way you
like, access element and attribute values, insert and delete nodes, and
convert the tree back into XML.

The DOM is useful for modifying XML documents, because you can create a
DOM tree, modify it by adding new nodes or rearranging subtrees, and
then produce a new XML document as output.  You can also construct a DOM
tree manually and convert it to XML, which can be a more flexible way of
producing XML output than simply writing ‘<tag1>’…‘</tag1>’ to a file.

The DOM implementation included with Python lives in the *note
xml.dom.minidom: 13e. module.  It’s a lightweight implementation of the
Level 1 DOM with support for XML namespaces.  The ‘parse()’ and
‘parseString()’ convenience functions are provided for generating a DOM
tree:

     from xml.dom import minidom
     doc = minidom.parse('hamlet.xml')

‘doc’ is a ‘Document’ instance.  ‘Document’, like all the other DOM
classes such as ‘Element’ and ‘Text’, is a subclass of the ‘Node’ base
class.  All the nodes in a DOM tree therefore support certain common
methods, such as ‘toxml()’ which returns a string containing the XML
representation of the node and its children.  Each class also has
special methods of its own; for example, ‘Element’ and ‘Document’
instances have a method to find all child elements with a given tag
name.  Continuing from the previous 2-line example:

     perslist = doc.getElementsByTagName( 'PERSONA' )
     print perslist[0].toxml()
     print perslist[1].toxml()

For the `Hamlet' XML file, the above few lines output:

     <PERSONA>CLAUDIUS, king of Denmark. </PERSONA>
     <PERSONA>HAMLET, son to the late, and nephew to the present king.</PERSONA>

The root element of the document is available as ‘doc.documentElement’,
and its children can be easily modified by deleting, adding, or removing
nodes:

     root = doc.documentElement

     # Remove the first child
     root.removeChild( root.childNodes[0] )

     # Move the new first child to the end
     root.appendChild( root.childNodes[0] )

     # Insert the new first child (originally,
     # the third child) before the 20th child.
     root.insertBefore( root.childNodes[0], root.childNodes[20] )

Again, I will refer you to the Python documentation for a complete
listing of the different ‘Node’ classes and their various methods.


File: python.info,  Node: Relationship to PyXML,  Prev: DOM Support,  Up: XML Modules

1.18.13.3 Relationship to PyXML
...............................

The XML Special Interest Group has been working on XML-related Python
code for a while.  Its code distribution, called PyXML, is available
from the SIG’s Web pages at
‘https://www.python.org/community/sigs/current/xml-sig’.  The PyXML
distribution also used the package name ‘xml’.  If you’ve written
programs that used PyXML, you’re probably wondering about its
compatibility with the 2.0 *note xml: 13c. package.

The answer is that Python 2.0’s *note xml: 13c. package isn’t compatible
with PyXML, but can be made compatible by installing a recent version
PyXML. Many applications can get by with the XML support that is
included with Python 2.0, but more complicated applications will require
that the full PyXML package will be installed.  When installed, PyXML
versions 0.6.0 or greater will replace the *note xml: 13c. package
shipped with Python, and will be a strict superset of the standard
package, adding a bunch of additional features.  Some of the additional
features in PyXML include:

   * 4DOM, a full DOM implementation from FourThought, Inc.

   * The xmlproc validating parser, written by Lars Marius Garshol.

   * The ‘sgmlop’ parser accelerator module, written by Fredrik Lundh.


File: python.info,  Node: Module changes,  Next: New modules,  Prev: XML Modules,  Up: What’s New in Python 2 0

1.18.14 Module changes
----------------------

Lots of improvements and bugfixes were made to Python’s extensive
standard library; some of the affected modules include *note readline:
de, ‘ConfigParser’, *note cgi: 15, *note calendar: 14, *note posix: d1,
*note readline: de, ‘xmllib’, *note aifc: 4, ‘chunk, wave’, *note
random: dc, *note shelve: e7, and *note nntplib: c0.  Consult the CVS
logs for the exact patch-by-patch details.

Brian Gallew contributed OpenSSL support for the *note socket: ef.
module.  OpenSSL is an implementation of the Secure Socket Layer, which
encrypts the data being sent over a socket.  When compiling Python, you
can edit ‘Modules/Setup’ to include SSL support, which adds an
additional function to the *note socket: ef. module: ‘socket.ssl(socket,
keyfile, certfile)’, which takes a socket object and returns an SSL
socket.  The ‘httplib’ and *note urllib: 126. modules were also changed
to support ‘https://’ URLs, though no one has implemented FTP or SMTP
over SSL.

The ‘httplib’ module has been rewritten by Greg Stein to support
HTTP/1.1.  Backward compatibility with the 1.5 version of ‘httplib’ is
provided, though using HTTP/1.1 features such as pipelining will require
rewriting code to use a different set of interfaces.

The ‘Tkinter’ module now supports Tcl/Tk version 8.1, 8.2, or 8.3, and
support for the older 7.x versions has been dropped.  The Tkinter module
now supports displaying Unicode strings in Tk widgets.  Also, Fredrik
Lundh contributed an optimization which makes operations like
‘create_line’ and ‘create_polygon’ much faster, especially when using
lots of coordinates.

The *note curses: 2b. module has been greatly extended, starting from
Oliver Andrich’s enhanced version, to provide many additional functions
from ncurses and SYSV curses, such as colour, alternative character set
support, pads, and mouse support.  This means the module is no longer
compatible with operating systems that only have BSD curses, but there
don’t seem to be any currently maintained OSes that fall into this
category.

As mentioned in the earlier discussion of 2.0’s Unicode support, the
underlying implementation of the regular expressions provided by the
*note re: dd. module has been changed.  SRE, a new regular expression
engine written by Fredrik Lundh and partially funded by Hewlett Packard,
supports matching against both 8-bit strings and Unicode strings.


File: python.info,  Node: New modules,  Next: IDLE Improvements,  Prev: Module changes,  Up: What’s New in Python 2 0

1.18.15 New modules
-------------------

A number of new modules were added.  We’ll simply list them with brief
descriptions; consult the 2.0 documentation for the details of a
particular module.

   * *note atexit: b.: For registering functions to be called before the
     Python interpreter exits.  Code that currently sets ‘sys.exitfunc’
     directly should be changed to use the *note atexit: b. module
     instead, importing *note atexit: b. and calling *note
     atexit.register(): f46. with the function to be called on exit.
     (Contributed by Skip Montanaro.)

   * *note codecs: 1b, ‘encodings’, *note unicodedata: 123.: Added as
     part of the new Unicode support.

   * *note filecmp: 7d.: Supersedes the old ‘cmp’, ‘cmpcache’ and
     ‘dircmp’ modules, which have now become deprecated.  (Contributed
     by Gordon MacMillan and Moshe Zadka.)

   * *note gettext: 87.: This module provides internationalization
     (I18N) and localization (L10N) support for Python programs by
     providing an interface to the GNU gettext message catalog library.
     (Integrated by Barry Warsaw, from separate contributions by Martin
     von Löwis, Peter Funk, and James Henstridge.)

   * ‘linuxaudiodev’: Support for the ‘/dev/audio’ device on Linux, a
     twin to the existing ‘sunaudiodev’ module.  (Contributed by Peter
     Bosch, with fixes by Jeremy Hylton.)

   * *note mmap: b3.: An interface to memory-mapped files on both
     Windows and Unix.  A file’s contents can be mapped directly into
     memory, at which point it behaves like a mutable string, so its
     contents can be read and modified.  They can even be passed to
     functions that expect ordinary strings, such as the *note re: dd.
     module.  (Contributed by Sam Rushing, with some extensions by A.M.
     Kuchling.)

   * ‘pyexpat’: An interface to the Expat XML parser.  (Contributed by
     Paul Prescod.)

   * ‘robotparser’: Parse a ‘robots.txt’ file, which is used for writing
     Web spiders that politely avoid certain areas of a Web site.  The
     parser accepts the contents of a ‘robots.txt’ file, builds a set of
     rules from it, and can then answer questions about the fetchability
     of a given URL. (Contributed by Skip Montanaro.)

   * *note tabnanny: 100.: A module/script to check Python source code
     for ambiguous indentation.  (Contributed by Tim Peters.)

   * ‘UserString’: A base class useful for deriving objects that behave
     like strings.

   * *note webbrowser: 132.: A module that provides a platform
     independent way to launch a web browser on a specific URL. For each
     platform, various browsers are tried in a specific order.  The user
     can alter which browser is launched by setting the `BROWSER'
     environment variable.  (Originally inspired by Eric S. Raymond’s
     patch to *note urllib: 126. which added similar functionality, but
     the final module comes from code originally implemented by Fred
     Drake as ‘Tools/idle/BrowserControl.py’, and adapted for the
     standard library by Fred.)

   * ‘_winreg’: An interface to the Windows registry.  ‘_winreg’ is an
     adaptation of functions that have been part of PythonWin since
     1995, but has now been added to the core distribution, and enhanced
     to support Unicode.  ‘_winreg’ was written by Bill Tutt and Mark
     Hammond.

   * *note zipfile: 14b.: A module for reading and writing ZIP-format
     archives.  These are archives produced by ‘PKZIP’ on DOS/Windows or
     ‘zip’ on Unix, not to be confused with ‘gzip’-format files (which
     are supported by the *note gzip: 8b. module) (Contributed by James
     C. Ahlstrom.)

   * ‘imputil’: A module that provides a simpler way for writing
     customized import hooks, in comparison to the existing ‘ihooks’
     module.  (Implemented by Greg Stein, with much discussion on
     python-dev along the way.)


File: python.info,  Node: IDLE Improvements,  Next: Deleted and Deprecated Modules,  Prev: New modules,  Up: What’s New in Python 2 0

1.18.16 IDLE Improvements
-------------------------

IDLE is the official Python cross-platform IDE, written using Tkinter.
Python 2.0 includes IDLE 0.6, which adds a number of new features and
improvements.  A partial list:

   * UI improvements and optimizations, especially in the area of syntax
     highlighting and auto-indentation.

   * The class browser now shows more information, such as the top level
     functions in a module.

   * Tab width is now a user settable option.  When opening an existing
     Python file, IDLE automatically detects the indentation
     conventions, and adapts.

   * There is now support for calling browsers on various platforms,
     used to open the Python documentation in a browser.

   * IDLE now has a command line, which is largely similar to the
     vanilla Python interpreter.

   * Call tips were added in many places.

   * IDLE can now be installed as a package.

   * In the editor window, there is now a line/column bar at the bottom.

   * Three new keystroke commands: Check module (‘Alt-F5’), Import
     module (‘F5’) and Run script (‘Ctrl-F5’).


File: python.info,  Node: Deleted and Deprecated Modules,  Next: Acknowledgements<8>,  Prev: IDLE Improvements,  Up: What’s New in Python 2 0

1.18.17 Deleted and Deprecated Modules
--------------------------------------

A few modules have been dropped because they’re obsolete, or because
there are now better ways to do the same thing.  The ‘stdwin’ module is
gone; it was for a platform-independent windowing toolkit that’s no
longer developed.

A number of modules have been moved to the ‘lib-old’ subdirectory:
‘cmp’, ‘cmpcache’, ‘dircmp’, ‘dump’, ‘find’, ‘grep’, ‘packmail’, ‘poly’,
‘util’, ‘whatsound’, ‘zmod’.  If you have code which relies on a module
that’s been moved to ‘lib-old’, you can simply add that directory to
‘sys.path’ to get them back, but you’re encouraged to update any code
that uses these modules.


File: python.info,  Node: Acknowledgements<8>,  Prev: Deleted and Deprecated Modules,  Up: What’s New in Python 2 0

1.18.18 Acknowledgements
------------------------

The authors would like to thank the following people for offering
suggestions on various drafts of this article: David Bolen, Mark
Hammond, Gregg Hauser, Jeremy Hylton, Fredrik Lundh, Detlef Lannert,
Aahz Maruch, Skip Montanaro, Vladimir Marangozov, Tobias Polzin, Guido
van Rossum, Neil Schemenauer, and Russ Schmidt.

The “Changelog” is an HTML version of the file built(1) from the
contents of the Misc/NEWS.d(2) directory tree, which contains `all'
nontrivial changes to Python for the current version.

   ---------- Footnotes ----------

   (1) https://pypi.org/project/blurb

   (2) https://github.com/python/cpython/tree/3.9/Misc/NEWS.d


File: python.info,  Node: Changelog,  Prev: What’s New in Python 2 0,  Up: What’s New in Python

1.19 Changelog
==============

* Menu:

* Python 3.9.10 final: Python 3 9 10 final.
* Python 3.9.9 final: Python 3 9 9 final.
* Python 3.9.8 final: Python 3 9 8 final.
* Python 3.9.7 final: Python 3 9 7 final.
* Python 3.9.6 final: Python 3 9 6 final.
* Python 3.9.5 final: Python 3 9 5 final.
* Python 3.9.4 final: Python 3 9 4 final.
* Python 3.9.3 final: Python 3 9 3 final.
* Python 3.9.2 final: Python 3 9 2 final.
* Python 3.9.2 release candidate 1: Python 3 9 2 release candidate 1.
* Python 3.9.1 final: Python 3 9 1 final.
* Python 3.9.1 release candidate 1: Python 3 9 1 release candidate 1.
* Python 3.9.0 final: Python 3 9 0 final.
* Python 3.9.0 release candidate 2: Python 3 9 0 release candidate 2.
* Python 3.9.0 release candidate 1: Python 3 9 0 release candidate 1.
* Python 3.9.0 beta 5: Python 3 9 0 beta 5.
* Python 3.9.0 beta 4: Python 3 9 0 beta 4.
* Python 3.9.0 beta 3: Python 3 9 0 beta 3.
* Python 3.9.0 beta 2: Python 3 9 0 beta 2.
* Python 3.9.0 beta 1: Python 3 9 0 beta 1.
* Python 3.9.0 alpha 6: Python 3 9 0 alpha 6.
* Python 3.9.0 alpha 5: Python 3 9 0 alpha 5.
* Python 3.9.0 alpha 4: Python 3 9 0 alpha 4.
* Python 3.9.0 alpha 3: Python 3 9 0 alpha 3.
* Python 3.9.0 alpha 2: Python 3 9 0 alpha 2.
* Python 3.9.0 alpha 1: Python 3 9 0 alpha 1.
* Python 3.8.0 beta 1: Python 3 8 0 beta 1.
* Python 3.8.0 alpha 4: Python 3 8 0 alpha 4.
* Python 3.8.0 alpha 3: Python 3 8 0 alpha 3.
* Python 3.8.0 alpha 2: Python 3 8 0 alpha 2.
* Python 3.8.0 alpha 1: Python 3 8 0 alpha 1.
* Python 3.7.0 final: Python 3 7 0 final.
* Python 3.7.0 release candidate 1: Python 3 7 0 release candidate 1.
* Python 3.7.0 beta 5: Python 3 7 0 beta 5.
* Python 3.7.0 beta 4: Python 3 7 0 beta 4.
* Python 3.7.0 beta 3: Python 3 7 0 beta 3.
* Python 3.7.0 beta 2: Python 3 7 0 beta 2.
* Python 3.7.0 beta 1: Python 3 7 0 beta 1.
* Python 3.7.0 alpha 4: Python 3 7 0 alpha 4.
* Python 3.7.0 alpha 3: Python 3 7 0 alpha 3.
* Python 3.7.0 alpha 2: Python 3 7 0 alpha 2.
* Python 3.7.0 alpha 1: Python 3 7 0 alpha 1.
* Python 3.6.6 final: Python 3 6 6 final.
* Python 3.6.6 release candidate 1: Python 3 6 6 release candidate 1.
* Python 3.6.5 final: Python 3 6 5 final.
* Python 3.6.5 release candidate 1: Python 3 6 5 release candidate 1.
* Python 3.6.4 final: Python 3 6 4 final.
* Python 3.6.4 release candidate 1: Python 3 6 4 release candidate 1.
* Python 3.6.3 final: Python 3 6 3 final.
* Python 3.6.3 release candidate 1: Python 3 6 3 release candidate 1.
* Python 3.6.2 final: Python 3 6 2 final.
* Python 3.6.2 release candidate 2: Python 3 6 2 release candidate 2.
* Python 3.6.2 release candidate 1: Python 3 6 2 release candidate 1.
* Python 3.6.1 final: Python 3 6 1 final.
* Python 3.6.1 release candidate 1: Python 3 6 1 release candidate 1.
* Python 3.6.0 final: Python 3 6 0 final.
* Python 3.6.0 release candidate 2: Python 3 6 0 release candidate 2.
* Python 3.6.0 release candidate 1: Python 3 6 0 release candidate 1.
* Python 3.6.0 beta 4: Python 3 6 0 beta 4.
* Python 3.6.0 beta 3: Python 3 6 0 beta 3.
* Python 3.6.0 beta 2: Python 3 6 0 beta 2.
* Python 3.6.0 beta 1: Python 3 6 0 beta 1.
* Python 3.6.0 alpha 4: Python 3 6 0 alpha 4.
* Python 3.6.0 alpha 3: Python 3 6 0 alpha 3.
* Python 3.6.0 alpha 2: Python 3 6 0 alpha 2.
* Python 3.6.0 alpha 1: Python 3 6 0 alpha 1.
* Python 3.5.5 final: Python 3 5 5 final.
* Python 3.5.5 release candidate 1: Python 3 5 5 release candidate 1.
* Python 3.5.4 final: Python 3 5 4 final.
* Python 3.5.4 release candidate 1: Python 3 5 4 release candidate 1.
* Python 3.5.3 final: Python 3 5 3 final.
* Python 3.5.3 release candidate 1: Python 3 5 3 release candidate 1.
* Python 3.5.2 final: Python 3 5 2 final.
* Python 3.5.2 release candidate 1: Python 3 5 2 release candidate 1.
* Python 3.5.1 final: Python 3 5 1 final.
* Python 3.5.1 release candidate 1: Python 3 5 1 release candidate 1.
* Python 3.5.0 final: Python 3 5 0 final.
* Python 3.5.0 release candidate 4: Python 3 5 0 release candidate 4.
* Python 3.5.0 release candidate 3: Python 3 5 0 release candidate 3.
* Python 3.5.0 release candidate 2: Python 3 5 0 release candidate 2.
* Python 3.5.0 release candidate 1: Python 3 5 0 release candidate 1.
* Python 3.5.0 beta 4: Python 3 5 0 beta 4.
* Python 3.5.0 beta 3: Python 3 5 0 beta 3.
* Python 3.5.0 beta 2: Python 3 5 0 beta 2.
* Python 3.5.0 beta 1: Python 3 5 0 beta 1.
* Python 3.5.0 alpha 4: Python 3 5 0 alpha 4.
* Python 3.5.0 alpha 3: Python 3 5 0 alpha 3.
* Python 3.5.0 alpha 2: Python 3 5 0 alpha 2.
* Python 3.5.0 alpha 1: Python 3 5 0 alpha 1.


File: python.info,  Node: Python 3 9 10 final,  Next: Python 3 9 9 final,  Up: Changelog

1.19.1 Python 3.9.10 final
--------------------------

`Release date: 2022-01-13'

* Menu:

* Core and Builtins::
* Library::
* Documentation: Documentation<2>.
* Tests::
* Build::
* Windows::
* macOS::
* Tools/Demos::
* C API::


File: python.info,  Node: Core and Builtins,  Next: Library,  Up: Python 3 9 10 final

1.19.1.1 Core and Builtins
..........................

   - bpo-46070(1): *note Py_EndInterpreter(): f4e. now explicitly
     untracks all objects currently tracked by the GC. Previously, if an
     object was used later by another interpreter, calling *note
     PyObject_GC_UnTrack(): f07. on the object crashed if the previous
     or the next object of the ‘PyGC_Head’ structure became a dangling
     pointer.  Patch by Victor Stinner.

   - bpo-46085(2): Fix iterator cache mechanism of ‘OrderedDict’.

   - bpo-46110(3): Add a maximum recursion check to the PEG parser to
     avoid stack overflow.  Patch by Pablo Galindo

   - bpo-46000(4): Improve compatibility of the *note curses: 2b. module
     with NetBSD curses.

   - bpo-45614(5): Fix *note traceback: 11c. display for exceptions with
     invalid module name.

   - bpo-45806(6): Re-introduced fix that allows recovery from stack
     overflow without crashing the interpreter.  The original fix as
     part of bpo-42500(7) was reverted (see release notes for Python
     3.9.4) since it introduced an ABI change in a bugfix release which
     is not allowed.  The new fix doesn’t introduce any ABI changes.
     Patch by Mark Shannon.

   - bpo-45822(8): Fixed a bug in the parser that was causing it to not
     respect PEP 263(9) coding cookies when no flags are provided.
     Patch by Pablo Galindo

   - bpo-45820(10): Fix a segfault when the parser fails without reading
     any input.  Patch by Pablo Galindo

   - bpo-42540(11): Fix crash when *note os.fork(): a42. is called with
     an active non-default memory allocator.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue46070

   (2) https://bugs.python.org/issue46085

   (3) https://bugs.python.org/issue46110

   (4) https://bugs.python.org/issue46000

   (5) https://bugs.python.org/issue45614

   (6) https://bugs.python.org/issue45806

   (7) https://bugs.python.org/issue42500

   (8) https://bugs.python.org/issue45822

   (9) https://www.python.org/dev/peps/pep-0263

   (10) https://bugs.python.org/issue45820

   (11) https://bugs.python.org/issue42540


File: python.info,  Node: Library,  Next: Documentation<2>,  Prev: Core and Builtins,  Up: Python 3 9 10 final

1.19.1.2 Library
................

   - bpo-40479(1): Fix *note hashlib: 8c. `usedforsecurity' option to
     work correctly with OpenSSL 3.0.0 in FIPS mode.

   - bpo-46070(2): Fix possible segfault when importing the *note
     asyncio: 9. module from different sub-interpreters in parallel.
     Patch by Erlend E. Aasland.

   - bpo-46278(3): Reflect ‘context’ argument in
     ‘AbstractEventLoop.call_*()’ methods.  Loop implementations already
     support it.

   - bpo-46239(4): Improve error message when importing
     ‘asyncio.windows_events’ on non-Windows.

   - bpo-20369(5): *note concurrent.futures.wait(): f50. no longer
     blocks forever when given duplicate Futures.  Patch by Kumar
     Aditya.

   - bpo-46105(6): Honor spec when generating requirement specs with
     urls and extras (importlib_metadata 4.8.3).

   - bpo-26952(7): *note argparse: 5. raises *note ValueError: 16d. with
     clear message when trying to render usage for an empty
     mutually-exclusive group.  Previously it raised a cryptic *note
     IndexError: f36.

   - bpo-27718(8): Fix help for the *note signal: ea. module.  Some
     functions (e.g.  ‘signal()’ and ‘getsignal()’) were omitted.

   - bpo-46032(9): The ‘registry()’ method of *note
     functools.singledispatch(): 491. functions checks now the first
     argument or the first parameter annotation and raises a TypeError
     if it is not supported.  Previously unsupported “types” were
     ignored (e.g.  ‘typing.List[int]’) or caused an error at calling
     time (e.g.  ‘list[int]’).

   - bpo-46018(10): Ensure that *note math.expm1(): c3a. does not raise
     on underflow.

   - bpo-27946(11): Fix possible crash when getting an attribute of
     class:*note xml.etree.ElementTree.Element: 21d. simultaneously with
     replacing the ‘attrib’ dict.

   - bpo-13236(12): *note unittest.TextTestResult: f51. and *note
     unittest.TextTestRunner: f52. flush now the output stream more
     often.

   - bpo-37658(13): Fix issue when on certain conditions
     ‘asyncio.wait_for()’ may allow a coroutine to complete
     successfully, but fail to return the result, potentially causing
     memory leaks or other issues.

   - bpo-45831(14): *note faulthandler: 7b. can now write ASCII-only
     strings (like filenames and function names) with a single write()
     syscall when dumping a traceback.  It reduces the risk of getting
     an unreadable dump when two threads or two processes dump a
     traceback to the same file (like stderr) at the same time.  Patch
     by Victor Stinner.

   - bpo-41735(15): Fix thread lock in ‘zlib.Decompress.flush()’ method
     before ‘PyObject_GetBuffer’.

   - bpo-45664(16): Fix *note types.resolve_bases(): 50b. and *note
     types.new_class(): b8f. for *note types.GenericAlias: 27c. instance
     as a base.

   - bpo-45663(17): Fix *note dataclasses.is_dataclass(): f53. for
     dataclasses which are subclasses of *note types.GenericAlias: 27c.

   - bpo-45662(18): Fix the repr of ‘dataclasses.InitVar’ with a type
     alias to the built-in class, e.g.  ‘InitVar[list[int]]’.

   - bpo-43498(19): Avoid a possible `“RuntimeError: dictionary changed
     size during iteration”' when adjusting the process count of
     ‘ProcessPoolExecutor’.

   - bpo-29620(20): *note assertWarns(): b94. no longer raises a
     ‘RuntimeException’ when accessing a module’s ‘__warningregistry__’
     causes importation of a new module, or when a new module is
     imported in another thread.  Patch by Kernc.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40479

   (2) https://bugs.python.org/issue46070

   (3) https://bugs.python.org/issue46278

   (4) https://bugs.python.org/issue46239

   (5) https://bugs.python.org/issue20369

   (6) https://bugs.python.org/issue46105

   (7) https://bugs.python.org/issue26952

   (8) https://bugs.python.org/issue27718

   (9) https://bugs.python.org/issue46032

   (10) https://bugs.python.org/issue46018

   (11) https://bugs.python.org/issue27946

   (12) https://bugs.python.org/issue13236

   (13) https://bugs.python.org/issue37658

   (14) https://bugs.python.org/issue45831

   (15) https://bugs.python.org/issue41735

   (16) https://bugs.python.org/issue45664

   (17) https://bugs.python.org/issue45663

   (18) https://bugs.python.org/issue45662

   (19) https://bugs.python.org/issue43498

   (20) https://bugs.python.org/issue29620


File: python.info,  Node: Documentation<2>,  Next: Tests,  Prev: Library,  Up: Python 3 9 10 final

1.19.1.3 Documentation
......................

   - bpo-19737(1): Update the documentation for the *note globals():
     f55. function.

   - bpo-45840(2): Improve cross-references in the documentation for the
     data model.

   - bpo-45788(3): Link doc for sys.prefix to sysconfig doc on
     installation paths.

   - bpo-25381(4): In the extending chapter of the extending doc, update
     a paragraph about the global variables containing exception
     information.

   - bpo-43905(5): Expanded *note astuple(): f56. and *note asdict():
     f57. docs, warning about deepcopy being applied and providing a
     workaround.

   - bpo-41028(6): Language and version switchers, previously maintained
     in every cpython branches, are now handled by docsbuild-script.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19737

   (2) https://bugs.python.org/issue45840

   (3) https://bugs.python.org/issue45788

   (4) https://bugs.python.org/issue25381

   (5) https://bugs.python.org/issue43905

   (6) https://bugs.python.org/issue41028


File: python.info,  Node: Tests,  Next: Build,  Prev: Documentation<2>,  Up: Python 3 9 10 final

1.19.1.4 Tests
..............

   - bpo-46205(1): Fix hang in runtest_mp due to race condition

   - bpo-46263(2): Fix test_capi on FreeBSD 14-dev: instruct jemalloc to
     not fill freed memory with junk byte.

   - bpo-46150(3): Now ‘fakename’ in
     ‘test_pathlib.PosixPathTest.test_expanduser’ is checked to be
     non-existent.

   - bpo-46129(4): Rewrite ‘asyncio.locks’ tests with *note
     unittest.IsolatedAsyncioTestCase: 377. usage.

   - bpo-23819(5): Fixed *note asyncio: 9. tests in python optimized
     mode.  Patch by Kumar Aditya.

   - bpo-46114(6): Fix test case for OpenSSL 3.0.1 version.  OpenSSL 3.0
     uses ‘0xMNN00PP0L’.

   - bpo-19460(7): Add new Test for *note
     email.mime.nonmultipart.MIMENonMultipart: f59.

   - bpo-45835(8): Fix race condition in test_queue tests with multiple
     “feeder” threads.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue46205

   (2) https://bugs.python.org/issue46263

   (3) https://bugs.python.org/issue46150

   (4) https://bugs.python.org/issue46129

   (5) https://bugs.python.org/issue23819

   (6) https://bugs.python.org/issue46114

   (7) https://bugs.python.org/issue19460

   (8) https://bugs.python.org/issue45835


File: python.info,  Node: Build,  Next: Windows,  Prev: Tests,  Up: Python 3 9 10 final

1.19.1.5 Build
..............

   - bpo-46263(1): ‘configure’ no longer sets ‘MULTIARCH’ on FreeBSD
     platforms.

   - bpo-46106(2): Updated OpenSSL to 1.1.1m in Windows builds, macOS
     installer builds, and CI. Patch by Kumar Aditya.

   - bpo-44035(3): CI now verifies that autoconf files have been
     regenerated with a current and unpatched autoconf package.

   - bpo-33393(4): Update ‘config.guess’ to 2021-06-03 and ‘config.sub’
     to 2021-08-14.  ‘Makefile’ now has an ‘update-config’ target to
     make updating more convenient.

   - bpo-45866(5): ‘make regen-all’ now produces the same output when
     run from a directory other than the source tree: when building
     Python out of the source tree.  pegen now strips directory of the
     “generated by pygen from <FILENAME>” header Patch by Victor
     Stinner.

   - bpo-41498(6): Python now compiles on platforms without ‘sigset_t’.
     Several functions in *note signal: ea. are not available when
     ‘sigset_t’ is missing.

     Based on patch by Roman Yurchak for pyodide.

   - bpo-45881(7): ‘setup.py’ now uses ‘CC’ from environment first to
     discover multiarch and cross compile paths.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue46263

   (2) https://bugs.python.org/issue46106

   (3) https://bugs.python.org/issue44035

   (4) https://bugs.python.org/issue33393

   (5) https://bugs.python.org/issue45866

   (6) https://bugs.python.org/issue41498

   (7) https://bugs.python.org/issue45881


File: python.info,  Node: Windows,  Next: macOS,  Prev: Build,  Up: Python 3 9 10 final

1.19.1.6 Windows
................

   - bpo-45901(1): When installed through the Microsoft Store and set as
     the default app for ‘*.py’ files, command line arguments will now
     be passed to Python when invoking a script without explicitly
     launching Python (that is, ‘script.py args’ rather than ‘python
     script.py args’).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45901


File: python.info,  Node: macOS,  Next: Tools/Demos,  Prev: Windows,  Up: Python 3 9 10 final

1.19.1.7 macOS
..............

   - bpo-40477(1): The Python Launcher app for macOS now properly
     launches scripts and, if necessary, the Terminal app when running
     on recent macOS releases.

   - bpo-45732(2): Update python.org macOS installer to use Tcl/Tk
     8.6.12.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40477

   (2) https://bugs.python.org/issue45732


File: python.info,  Node: Tools/Demos,  Next: C API,  Prev: macOS,  Up: Python 3 9 10 final

1.19.1.8 Tools/Demos
....................

   - bpo-45838(1): Fix line number calculation when debugging Python
     with GDB.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45838


File: python.info,  Node: C API,  Prev: Tools/Demos,  Up: Python 3 9 10 final

1.19.1.9 C API
..............

   - bpo-39026(1): Fix Python.h to build C extensions with Xcode: remove
     a relative include from ‘Include/cpython/pystate.h’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39026


File: python.info,  Node: Python 3 9 9 final,  Next: Python 3 9 8 final,  Prev: Python 3 9 10 final,  Up: Changelog

1.19.2 Python 3.9.9 final
-------------------------

`Release date: 2021-11-15'

* Menu:

* Core and Builtins: Core and Builtins<2>.
* Library: Library<2>.
* Documentation: Documentation<3>.
* Windows: Windows<2>.


File: python.info,  Node: Core and Builtins<2>,  Next: Library<2>,  Up: Python 3 9 9 final

1.19.2.1 Core and Builtins
..........................

   - bpo-45738(1): Fix computation of error location for invalid
     continuation characters in the parser.  Patch by Pablo Galindo.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45738


File: python.info,  Node: Library<2>,  Next: Documentation<3>,  Prev: Core and Builtins<2>,  Up: Python 3 9 9 final

1.19.2.2 Library
................

   - bpo-45235(1): Reverted an argparse bugfix that caused regression in
     the handling of default arguments for subparsers.  This prevented
     leaf level arguments from taking precedence over root level
     arguments.

   - bpo-45765(2): In importlib.metadata, fix distribution discovery for
     an empty path.

   - bpo-45644(3): In-place JSON file formatting using ‘python3 -m
     json.tool infile infile’ now works correctly, previously it left
     the file empty.  Patch by Chris Wesseling.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45235

   (2) https://bugs.python.org/issue45765

   (3) https://bugs.python.org/issue45644


File: python.info,  Node: Documentation<3>,  Next: Windows<2>,  Prev: Library<2>,  Up: Python 3 9 9 final

1.19.2.3 Documentation
......................

   - bpo-45772(1): ‘socket.socket’ documentation is corrected to a class
     from a function.

   - bpo-45392(2): Update the docstring of the *note type: 6ff. built-in
     to remove a redundant line and to mention keyword arguments for the
     constructor.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45772

   (2) https://bugs.python.org/issue45392


File: python.info,  Node: Windows<2>,  Prev: Documentation<3>,  Up: Python 3 9 9 final

1.19.2.4 Windows
................

   - bpo-45732(1): Updates bundled Tcl/Tk to 8.6.12.

   - bpo-45720(2): Internal reference to ‘shlwapi.dll’ was dropped to
     help improve startup time.  This DLL will no longer be loaded at
     the start of every Python process.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45732

   (2) https://bugs.python.org/issue45720


File: python.info,  Node: Python 3 9 8 final,  Next: Python 3 9 7 final,  Prev: Python 3 9 9 final,  Up: Changelog

1.19.3 Python 3.9.8 final
-------------------------

`Release date: 2021-11-05'

* Menu:

* Core and Builtins: Core and Builtins<3>.
* Library: Library<3>.
* Documentation: Documentation<4>.
* Tests: Tests<2>.
* Build: Build<2>.
* Windows: Windows<3>.
* macOS: macOS<2>.
* IDLE: IDLE<3>.
* C API: C API<2>.


File: python.info,  Node: Core and Builtins<3>,  Next: Library<3>,  Up: Python 3 9 8 final

1.19.3.1 Core and Builtins
..........................

   - bpo-30570(1): Fixed a crash in ‘issubclass()’ from infinite
     recursion when searching pathological ‘__bases__’ tuples.

   - bpo-45494(2): Fix parser crash when reporting errors involving
     invalid continuation characters.  Patch by Pablo Galindo.

   - bpo-45385(3): Fix reference leak from descr_check.  Patch by
     Dong-hee Na.

   - bpo-45167(4): Fix deepcopying of *note types.GenericAlias: 27c.
     objects.

   - bpo-44219(5): Release the GIL while performing ‘isatty’ system
     calls on arbitrary file descriptors.  In particular, this affects
     *note os.isatty(): f66, *note os.device_encoding(): f67. and *note
     io.TextIOWrapper: 6ea.  By extension, *note io.open(): 74d. in text
     mode is also affected.  This change solves a deadlock in *note
     os.isatty(): f66.  Patch by Vincent Michel in bpo-44219(6).

   - bpo-44959(7): Added fallback to extension modules with ‘.sl’ suffix
     on HP-UX

   - bpo-44050(8): Extensions that indicate they use global state (by
     setting ‘m_size’ to -1) can again be used in multiple interpreters.
     This reverts to behavior of Python 3.8.

   - bpo-45121(9): Fix issue where ‘Protocol.__init__’ raises
     ‘RecursionError’ when it’s called directly or via ‘super()’.  Patch
     provided by Yurii Karabas.

   - bpo-45083(10): When the interpreter renders an exception, its name
     now has a complete qualname.  Previously only the class name was
     concatenated to the module name, which sometimes resulted in an
     incorrect full name being displayed.

     (This issue impacted only the C code exception rendering, the *note
     traceback: 11c. module was using qualname already).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30570

   (2) https://bugs.python.org/issue45494

   (3) https://bugs.python.org/issue45385

   (4) https://bugs.python.org/issue45167

   (5) https://bugs.python.org/issue44219

   (6) https://bugs.python.org/issue44219

   (7) https://bugs.python.org/issue44959

   (8) https://bugs.python.org/issue44050

   (9) https://bugs.python.org/issue45121

   (10) https://bugs.python.org/issue45083


File: python.info,  Node: Library<3>,  Next: Documentation<4>,  Prev: Core and Builtins<3>,  Up: Python 3 9 8 final

1.19.3.2 Library
................

   - bpo-45678(1): Fix bug in Python 3.9 that meant
     ‘functools.singledispatchmethod’ failed to properly wrap the
     attributes of the target method.  Patch by Alex Waygood.

   - bpo-45679(2): Fix caching of multi-value *note typing.Literal: 275.
     ‘Literal[True, 2]’ is no longer equal to ‘Literal[1, 2]’.

   - bpo-45438(3): Fix typing.Signature string representation for
     generic builtin types.

   - bpo-45581(4): *note sqlite3.connect(): 4e1. now correctly raises
     *note MemoryError: f69. if the underlying SQLite API signals memory
     error.  Patch by Erlend E. Aasland.

   - bpo-39679(5): Fix bug in *note functools.singledispatchmethod: 2fa.
     that caused it to fail when attempting to register a *note
     classmethod(): 309. or *note staticmethod(): 30a. using type
     annotations.  Patch contributed by Alex Waygood.

   - bpo-45515(6): Add references to *note zoneinfo: 14e. in the *note
     datetime: 30. documentation, mostly replacing outdated references
     to ‘dateutil.tz’.  Change by Paul Ganssle.

   - bpo-45467(7): Fix incremental decoder and stream reader in the
     “raw-unicode-escape” codec.  Previously they failed if the escape
     sequence was split.

   - bpo-45461(8): Fix incremental decoder and stream reader in the
     “unicode-escape” codec.  Previously they failed if the escape
     sequence was split.

   - bpo-45239(9): Fixed *note email.utils.parsedate_tz(): f6a. crashing
     with *note UnboundLocalError: f37. on certain invalid input instead
     of returning ‘None’.  Patch by Ben Hoyt.

   - bpo-44904(10): Fix bug in the *note doctest: 66. module that caused
     it to fail if a docstring included an example with a ‘classmethod’
     ‘property’.  Patch by Alex Waygood.

   - bpo-45406(11): Make *note inspect.getmodule(): f6b. catch
     ‘FileNotFoundError’ raised by :’func:‘inspect.getabsfile’, and
     return ‘None’ to indicate that the module could not be determined.

   - bpo-45262(12): Prevent use-after-free in asyncio.  Make sure the
     cached running loop holder gets cleared on dealloc to prevent
     use-after-free in get_running_loop

   - bpo-45386(13): Make *note xmlrpc.client: 148. more robust to C
     runtimes where the underlying C ‘strftime’ function results in a
     ‘ValueError’ when testing for year formatting options.

   - bpo-45371(14): Fix clang rpath issue in *note distutils: 38.  The
     UnixCCompiler now uses correct clang option to add a runtime
     library directory (rpath) to a shared library.

   - bpo-20028(15): Improve error message of *note csv.Dialect: f6c.
     when initializing.  Patch by Vajrasky Kok and Dong-hee Na.

   - bpo-45343(16): Update bundled pip to 21.2.4 and setuptools to
     58.1.0

   - bpo-41710(17): On Unix, if the ‘sem_clockwait()’ function is
     available in the C library (glibc 2.30 and newer), the *note
     threading.Lock.acquire(): 85b. method now uses the monotonic clock
     (*note time.CLOCK_MONOTONIC: 4fc.) for the timeout, rather than
     using the system clock (*note time.CLOCK_REALTIME: f6d.), to not be
     affected by system clock changes.  Patch by Victor Stinner.

   - bpo-45328(18): Fixed *note http.client.HTTPConnection: 499. to work
     properly in OSs that don’t support the ‘TCP_NODELAY’ socket option.

   - bpo-1596321(19): Fix the ‘threading._shutdown()’ function when the
     *note threading: 10b. module was imported first from a thread
     different than the main thread: no longer log an error at Python
     exit.

   - bpo-45274(20): Fix a race condition in the *note Thread.join():
     c32. method of the *note threading: 10b. module.  If the function
     is interrupted by a signal and the signal handler raises an
     exception, make sure that the thread remains in a consistent state
     to prevent a deadlock.  Patch by Victor Stinner.

   - bpo-45238(21): Fix ‘unittest.IsolatedAsyncioTestCase.debug()’: it
     runs now asynchronous methods and callbacks.

   - bpo-36674(22): *note unittest.TestCase.debug(): f6e. raises now a
     *note unittest.SkipTest: 9e9. if the class or the test method are
     decorated with the skipping decorator.

   - bpo-45235(23): Fix an issue where argparse would not preserve
     values in a provided namespace when using a subparser with
     defaults.

   - bpo-45234(24): Fixed a regression in *note copyfile(): 382, *note
     copy(): 383, *note copy2(): 384. raising *note FileNotFoundError:
     8ad. when source is a directory, which should raise *note
     IsADirectoryError: a7a.

   - bpo-45228(25): Fix stack buffer overflow in parsing J1939 network
     address.

   - bpo-45192(26): Fix the ‘tempfile._infer_return_type’ function so
     that the ‘dir’ argument of the *note tempfile: 103. functions
     accepts an object implementing the ‘os.PathLike’ protocol.

     Patch by Kyungmin Lee.

   - bpo-45160(27): When tracing a tkinter variable used by a ttk
     OptionMenu, callbacks are no longer made twice.

   - bpo-35474(28): Calling *note mimetypes.guess_all_extensions(): f6f.
     with ‘strict=False’ no longer affects the result of the following
     call with ‘strict=True’.  Also, mutating the returned list no
     longer affects the global state.

   - bpo-45166(29): *note typing.get_type_hints(): 1ef. now works with
     *note Final: 368. wrapped in *note ForwardRef: f70.

   - bpo-45097(30): Remove deprecation warnings about the loop argument
     in *note asyncio: 9. incorrectly emitted in cases when the user
     does not pass the loop argument.

   - bpo-45081(31): Fix issue when dataclasses that inherit from
     ‘typing.Protocol’ subclasses have wrong ‘__init__’.  Patch provided
     by Yurii Karabas.

   - bpo-24444(32): Fixed an error raised in *note argparse: 5. help
     display when help for an option is set to 1+ blank spaces or when
     `choices' arg is an empty container.

   - bpo-45021(33): Fix a potential deadlock at shutdown of forked
     children when using *note concurrent.futures: 21. module

   - bpo-45030(34): Fix integer overflow in pickling and copying the
     range iterator.

   - bpo-39039(35): tarfile.open raises *note ReadError: f71. when a
     zlib error occurs during file extraction.

   - bpo-44594(36): Fix an edge case of ‘ExitStack’ and ‘AsyncExitStack’
     exception chaining.  They will now match ‘with’ block behavior when
     ‘__context__’ is explicitly set to ‘None’ when the exception is in
     flight.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45678

   (2) https://bugs.python.org/issue45679

   (3) https://bugs.python.org/issue45438

   (4) https://bugs.python.org/issue45581

   (5) https://bugs.python.org/issue39679

   (6) https://bugs.python.org/issue45515

   (7) https://bugs.python.org/issue45467

   (8) https://bugs.python.org/issue45461

   (9) https://bugs.python.org/issue45239

   (10) https://bugs.python.org/issue44904

   (11) https://bugs.python.org/issue45406

   (12) https://bugs.python.org/issue45262

   (13) https://bugs.python.org/issue45386

   (14) https://bugs.python.org/issue45371

   (15) https://bugs.python.org/issue20028

   (16) https://bugs.python.org/issue45343

   (17) https://bugs.python.org/issue41710

   (18) https://bugs.python.org/issue45328

   (19) https://bugs.python.org/issue1596321

   (20) https://bugs.python.org/issue45274

   (21) https://bugs.python.org/issue45238

   (22) https://bugs.python.org/issue36674

   (23) https://bugs.python.org/issue45235

   (24) https://bugs.python.org/issue45234

   (25) https://bugs.python.org/issue45228

   (26) https://bugs.python.org/issue45192

   (27) https://bugs.python.org/issue45160

   (28) https://bugs.python.org/issue35474

   (29) https://bugs.python.org/issue45166

   (30) https://bugs.python.org/issue45097

   (31) https://bugs.python.org/issue45081

   (32) https://bugs.python.org/issue24444

   (33) https://bugs.python.org/issue45021

   (34) https://bugs.python.org/issue45030

   (35) https://bugs.python.org/issue39039

   (36) https://bugs.python.org/issue44594


File: python.info,  Node: Documentation<4>,  Next: Tests<2>,  Prev: Library<3>,  Up: Python 3 9 8 final

1.19.3.3 Documentation
......................

   - bpo-45726(1): Improve documentation for *note
     functools.singledispatch(): 491. and *note
     functools.singledispatchmethod: 2fa.

   - bpo-45680(2): Amend the docs on ‘GenericAlias’ objects to clarify
     that non-container classes can also implement ‘__class_getitem__’.
     Patch contributed by Alex Waygood.

   - bpo-45655(3): Add a new “relevant PEPs” section to the top of the
     documentation for the ‘typing’ module.  Patch by Alex Waygood.

   - bpo-45604(4): Add ‘level’ argument to
     ‘multiprocessing.log_to_stderr’ function docs.

   - bpo-45464(5): Mention in the documentation of *note Built-in
     Exceptions: f73. that inheriting from multiple exception types in a
     single subclass is not recommended due to possible memory layout
     incompatibility.

   - bpo-45449(6): Add note about PEP 585(7) in *note collections.abc:
     1e.

   - bpo-45516(8): Add protocol description to the *note
     importlib.abc.Traversable: f74. documentation.

   - bpo-20692(9): Add Programming FAQ entry explaining that int literal
     attribute access requires either a space after or parentheses
     around the literal.

   - bpo-45216(10): Remove extra documentation listing methods in
     ‘difflib’.  It was rendering twice in pydoc and was outdated in
     some places.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45726

   (2) https://bugs.python.org/issue45680

   (3) https://bugs.python.org/issue45655

   (4) https://bugs.python.org/issue45604

   (5) https://bugs.python.org/issue45464

   (6) https://bugs.python.org/issue45449

   (7) https://www.python.org/dev/peps/pep-0585

   (8) https://bugs.python.org/issue45516

   (9) https://bugs.python.org/issue20692

   (10) https://bugs.python.org/issue45216


File: python.info,  Node: Tests<2>,  Next: Build<2>,  Prev: Documentation<4>,  Up: Python 3 9 8 final

1.19.3.4 Tests
..............

   - bpo-45578(1): Add tests for *note dis.distb(): 920.

   - bpo-45577(2): Add subtests for all ‘pickle’ protocols in
     ‘test_zoneinfo’.

   - bpo-43592(3): ‘test.libregrtest’ now raises the soft resource limit
     for the maximum number of file descriptors when the default is too
     low for our test suite as was often the case on macOS.

   - bpo-40173(4): Fix
     ‘test.support.import_helper.import_fresh_module()’.

   - bpo-45280(5): Add a test case for empty *note typing.NamedTuple:
     227.

   - bpo-45269(6): Cover case when invalid ‘markers’ type is supplied to
     ‘c_make_encoder’.

   - bpo-45209(7): Fix ‘UserWarning: resource_tracker’ warning in
     ‘_test_multiprocessing._TestSharedMemory.test_shared_memory_cleaned_after_process_termination’

   - bpo-45195(8): Fix test_readline.test_nonascii(): sometimes, the
     newline character is not written at the end, so don’t expect it in
     the output.  Patch by Victor Stinner.

   - bpo-45156(9): Fixes infinite loop on *note unittest.mock.seal():
     510. of mocks created by ‘create_autospec()’.

   - bpo-45042(10): Fixes that test classes decorated with
     ‘@hashlib_helper.requires_hashdigest’ were skipped all the time.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45578

   (2) https://bugs.python.org/issue45577

   (3) https://bugs.python.org/issue43592

   (4) https://bugs.python.org/issue40173

   (5) https://bugs.python.org/issue45280

   (6) https://bugs.python.org/issue45269

   (7) https://bugs.python.org/issue45209

   (8) https://bugs.python.org/issue45195

   (9) https://bugs.python.org/issue45156

   (10) https://bugs.python.org/issue45042


File: python.info,  Node: Build<2>,  Next: Windows<3>,  Prev: Tests<2>,  Up: Python 3 9 8 final

1.19.3.5 Build
..............

   - bpo-43158(1): ‘setup.py’ now uses values from configure script to
     build the ‘_uuid’ extension module.  Configure now detects
     util-linux’s ‘libuuid’, too.

   - bpo-45571(2): ‘Modules/Setup’ now use ‘PY_CFLAGS_NODIST’ instead of
     ‘PY_CFLAGS’ to compile shared modules.

   - bpo-45532(3): Update *note sys.version: 6ca. to use ‘main’ as
     fallback information.  Patch by Jeong YunWon.

   - bpo-45405(4): Prevent ‘internal configure error’ when running
     ‘configure’ with recent versions of non-Apple clang.  Patch by
     David Bohman.

   - bpo-45220(5): Avoid building with the Windows 11 SDK previews
     automatically.  This may be overridden by setting the
     ‘DefaultWindowsSDKVersion’ environment variable before building.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43158

   (2) https://bugs.python.org/issue45571

   (3) https://bugs.python.org/issue45532

   (4) https://bugs.python.org/issue45405

   (5) https://bugs.python.org/issue45220


File: python.info,  Node: Windows<3>,  Next: macOS<2>,  Prev: Build<2>,  Up: Python 3 9 8 final

1.19.3.6 Windows
................

   - bpo-45337(1): venv now warns when the created environment may need
     to be accessed at a different path, due to redirections, links or
     junctions.  It also now correctly installs or upgrades components
     when the alternate path is required.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45337


File: python.info,  Node: macOS<2>,  Next: IDLE<3>,  Prev: Windows<3>,  Up: Python 3 9 8 final

1.19.3.7 macOS
..............

   - bpo-44828(1): Avoid tkinter file dialog failure on macOS 12
     Monterey when using the Tk 8.6.11 provided by python.org macOS
     installers.  Patch by Marc Culler of the Tk project.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue44828


File: python.info,  Node: IDLE<3>,  Next: C API<2>,  Prev: macOS<2>,  Up: Python 3 9 8 final

1.19.3.8 IDLE
.............

   - bpo-45296(1): On Windows, change exit/quit message to suggest
     Ctrl-D, which works, instead of <Ctrl-Z Return>, which does not
     work in IDLE.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45296


File: python.info,  Node: C API<2>,  Prev: IDLE<3>,  Up: Python 3 9 8 final

1.19.3.9 C API
..............

   - bpo-44687(1): ‘BufferedReader.peek()’ no longer raises *note
     ValueError: 16d. when the entire file has already been buffered.

   - bpo-44751(2): Remove ‘crypt.h’ include from the public ‘Python.h’
     header.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue44687

   (2) https://bugs.python.org/issue44751


File: python.info,  Node: Python 3 9 7 final,  Next: Python 3 9 6 final,  Prev: Python 3 9 8 final,  Up: Changelog

1.19.4 Python 3.9.7 final
-------------------------

`Release date: 2021-08-30'

* Menu:

* Security::
* Core and Builtins: Core and Builtins<4>.
* Library: Library<4>.
* Documentation: Documentation<5>.
* Tests: Tests<3>.
* Build: Build<3>.
* Windows: Windows<4>.
* macOS: macOS<3>.


File: python.info,  Node: Security,  Next: Core and Builtins<4>,  Up: Python 3 9 7 final

1.19.4.1 Security
.................

   - bpo-42278(1): Replaced usage of *note tempfile.mktemp(): f7d. with
     *note TemporaryDirectory: c96. to avoid a potential race condition.

   - bpo-41180(2): Add auditing events to the *note marshal: b0. module,
     and stop raising ‘code.__init__’ events for every unmarshalled code
     object.  Directly instantiated code objects will continue to raise
     an event, and audit event handlers should inspect or collect the
     raw marshal data.  This reduces a significant performance overhead
     when loading from ‘.pyc’ files.

   - bpo-44394(3): Update the vendored copy of libexpat to 2.4.1 (from
     2.2.8) to get the fix for the CVE-2013-0340 “Billion Laughs”
     vulnerability.  This copy is most used on Windows and macOS.

   - bpo-43124(4): Made the internal ‘putcmd’ function in *note smtplib:
     ed. sanitize input for presence of ‘\r’ and ‘\n’ characters to
     avoid (unlikely) command injection.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42278

   (2) https://bugs.python.org/issue41180

   (3) https://bugs.python.org/issue44394

   (4) https://bugs.python.org/issue43124


File: python.info,  Node: Core and Builtins<4>,  Next: Library<4>,  Prev: Security,  Up: Python 3 9 7 final

1.19.4.2 Core and Builtins
..........................

   - bpo-45018(1): Fixed pickling of range iterators that iterated for
     over 2**32 times.

   - bpo-44962(2): Fix a race in WeakKeyDictionary, WeakValueDictionary
     and WeakSet when two threads attempt to commit the last pending
     removal.  This fixes asyncio.create_task and fixes a data loss in
     asyncio.run where shutdown_asyncgens is not run

   - bpo-44954(3): Fixed a corner case bug where the result of
     ‘float.fromhex('0x.8p-1074')’ was rounded the wrong way.

   - bpo-44947(4): Refine the syntax error for trailing commas in import
     statements.  Patch by Pablo Galindo.

   - bpo-44698(5): Restore behaviour of complex exponentiation with
     integer-valued exponent of type *note float: 1fd. or *note complex:
     2c1.

   - bpo-44885(6): Correct the ast locations of f-strings with format
     specs and repeated expressions.  Patch by Pablo Galindo

   - bpo-44872(7): Use new trashcan macros (Py_TRASHCAN_BEGIN/END) in
     frameobject.c instead of the old ones (Py_TRASHCAN_SAFE_BEGIN/END).

   - bpo-33930(8): Fix segmentation fault with deep recursion when
     cleaning method objects.  Patch by Augusto Goulart and Pablo
     Galindo.

   - bpo-25782(9): Fix bug where ‘PyErr_SetObject’ hangs when the
     current exception has a cycle in its context chain.

   - bpo-44856(10): Fix reference leaks in the error paths of
     ‘update_bases()’ and ‘__build_class__’.  Patch by Pablo Galindo.

   - bpo-44698(11): Fix undefined behaviour in complex object
     exponentiation.

   - bpo-44562(12): Remove uses of *note PyObject_GC_Del(): f05. in
     error path when initializing *note types.GenericAlias: 27c.

   - bpo-44523(13): Remove the pass-through for *note hash(): aa3. of
     *note weakref.proxy: 37a. objects to prevent unintended
     consequences when the original referred object dies while the proxy
     is part of a hashable object.  Patch by Pablo Galindo.

   - bpo-44472(14): Fix ltrace functionality when exceptions are raised.
     Patch by Pablo Galindo

   - bpo-44184(15): Fix a crash at Python exit when a deallocator
     function removes the last strong reference to a heap type.  Patch
     by Victor Stinner.

   - bpo-39091(16): Fix crash when using passing a non-exception to a
     generator’s ‘throw()’ method.  Patch by Noah Oxer

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45018

   (2) https://bugs.python.org/issue44962

   (3) https://bugs.python.org/issue44954

   (4) https://bugs.python.org/issue44947

   (5) https://bugs.python.org/issue44698

   (6) https://bugs.python.org/issue44885

   (7) https://bugs.python.org/issue44872

   (8) https://bugs.python.org/issue33930

   (9) https://bugs.python.org/issue25782

   (10) https://bugs.python.org/issue44856

   (11) https://bugs.python.org/issue44698

   (12) https://bugs.python.org/issue44562

   (13) https://bugs.python.org/issue44523

   (14) https://bugs.python.org/issue44472

   (15) https://bugs.python.org/issue44184

   (16) https://bugs.python.org/issue39091


File: python.info,  Node: Library<4>,  Next: Documentation<5>,  Prev: Core and Builtins<4>,  Up: Python 3 9 7 final

1.19.4.3 Library
................

   - bpo-41620(1): *note run(): b96. now always return a *note
     TestResult: b97. instance.  Previously it returned ‘None’ if the
     test class or method was decorated with a skipping decorator.

   - bpo-43913(2): Fix bugs in cleaning up classes and modules in *note
     unittest: 124.:

        * Functions registered with *note addModuleCleanup(): 374. were
          not called unless the user defines ‘tearDownModule()’ in their
          test module.

        * Functions registered with *note addClassCleanup(): 375. were
          not called if ‘tearDownClass’ is set to ‘None’.

        * Buffering in *note TestResult: b97. did not work with
          functions registered with ‘addClassCleanup()’ and
          ‘addModuleCleanup()’.

        * Errors in functions registered with ‘addClassCleanup()’ and
          ‘addModuleCleanup()’ were not handled correctly in buffered
          and debug modes.

        * Errors in ‘setUpModule()’ and functions registered with
          ‘addModuleCleanup()’ were reported in wrong order.

        * And several lesser bugs.

   - bpo-45001(3): Made email date parsing more robust against malformed
     input, namely a whitespace-only ‘Date:’ header.  Patch by Wouter
     Bolsterlee.

   - bpo-44449(4): Fix a crash in the signal handler of the *note
     faulthandler: 7b. module: no longer modify the reference count of
     frame objects.  Patch by Victor Stinner.

   - bpo-44955(5): Method *note stopTestRun(): dac. is now always called
     in pair with method *note startTestRun(): dab. for *note
     TestResult: b97. objects implicitly created in *note run(): b96.
     Previously it was not called for test methods and classes decorated
     with a skipping decorator.

   - bpo-38956(6): ‘argparse.BooleanOptionalAction’’s default value is
     no longer printed twice when used with *note
     argparse.ArgumentDefaultsHelpFormatter: f80.

   - bpo-44581(7): Upgrade bundled pip to 21.2.3 and setuptools to
     57.4.0

   - bpo-44849(8): Fix the *note os.set_inheritable(): 8e9. function on
     FreeBSD 14 for file descriptor opened with the *note O_PATH: 96e.
     flag: ignore the *note EBADF: 22f. error on ‘ioctl()’, fallback on
     the ‘fcntl()’ implementation.  Patch by Victor Stinner.

   - bpo-44605(9): The @functools.total_ordering() decorator now works
     with metaclasses.

   - bpo-44822(10): *note sqlite3: f2. user-defined functions and
     aggregators returning *note strings: 205. with embedded NUL
     characters are no longer truncated.  Patch by Erlend E. Aasland.

   - bpo-44815(11): Always show ‘loop=’ arg deprecations in *note
     asyncio.gather(): 3ab. and *note asyncio.sleep(): 3aa.

   - bpo-44806(12): Non-protocol subclasses of *note typing.Protocol:
     36a. ignore now the ‘__init__’ method inherited from protocol base
     classes.

   - bpo-44667(13): The *note tokenize.tokenize(): d23. doesn’t
     incorrectly generate a ‘NEWLINE’ token if the source doesn’t end
     with a new line character but the last line is a comment, as the
     function is already generating a ‘NL’ token.  Patch by Pablo
     Galindo

   - bpo-42853(14): Fix ‘http.client.HTTPSConnection’ fails to download
     >2GiB data.

   - bpo-44752(15): ‘rcompleter’ does not call *note getattr(): 54b. on
     *note property: 308. objects to avoid the side-effect of evaluating
     the corresponding method.

   - bpo-44720(16): ‘weakref.proxy’ objects referencing non-iterators
     now raise ‘TypeError’ rather than dereferencing the null
     ‘tp_iternext’ slot and crashing.

   - bpo-44704(17): The implementation of ‘collections.abc.Set._hash()’
     now matches that of ‘frozenset.__hash__()’.

   - bpo-44666(18): Fixed issue in *note compileall.compile_file(): 7ae.
     when ‘sys.stdout’ is redirected.  Patch by Stefan Hölzl.

   - bpo-40897(19): Give priority to using the current class constructor
     in *note inspect.signature(): 655.  Patch by Weipeng Hong.

   - bpo-44608(20): Fix memory leak in ‘_tkinter._flatten()’ if it is
     called with a sequence or set, but not list or tuple.

   - bpo-41928(21): Update *note shutil.copyfile(): 382. to raise *note
     FileNotFoundError: 8ad. instead of confusing *note
     IsADirectoryError: a7a. when a path ending with a ‘os.path.sep’
     does not exist; *note shutil.copy(): 383. and *note shutil.copy2():
     384. are also affected.

   - bpo-44566(22): handle StopIteration subclass raised from
     @contextlib.contextmanager generator

   - bpo-44558(23): Make the implementation consistency of *note
     indexOf(): 17b. between C and Python versions.  Patch by Dong-hee
     Na.

   - bpo-41249(24): Fixes ‘TypedDict’ to work with
     ‘typing.get_type_hints()’ and postponed evaluation of annotations
     across modules.

   - bpo-44461(25): Fix bug with *note pdb: c9.’s handling of import
     error due to a package which does not have a ‘__main__’ module

   - bpo-42892(26): Fixed an exception thrown while parsing a malformed
     multipart email by *note email.message.EmailMessage: 63c.

   - bpo-27827(27): ‘pathlib.PureWindowsPath.is_reserved()’ now
     identifies a greater range of reserved filenames, including those
     with trailing spaces or colons.

   - bpo-34266(28): Handle exceptions from parsing the arg of *note pdb:
     c9.’s run/restart command.

   - bpo-27334(29): The *note sqlite3: f2. context manager now performs
     a rollback (thus releasing the database lock) if commit failed.
     Patch by Luca Citi and Erlend E. Aasland.

   - bpo-43853(30): Improved string handling for *note sqlite3: f2.
     user-defined functions and aggregates:

        * It is now possible to pass strings with embedded null
          characters to UDFs

        * Conversion failures now correctly raise *note MemoryError:
          f69.

     Patch by Erlend E. Aasland.

   - bpo-43048(31): Handle *note RecursionError: 727. in *note
     TracebackException: 865.’s constructor, so that long exceptions
     chains are truncated instead of causing traceback formatting to
     fail.

   - bpo-41402(32): Fix *note email.message.EmailMessage.set_content():
     f81. when called with binary data and ‘7bit’ content transfer
     encoding.

   - bpo-32695(33): The `compresslevel' and `preset' keyword arguments
     of *note tarfile.open(): 855. are now both documented and tested.

   - bpo-34990(34): Fixed a Y2k38 bug in the compileall module where it
     would fail to compile files with a modification time after the year
     2038.

   - bpo-38840(35): Fix ‘test___all__’ on platforms lacking a shared
     memory implementation.

   - bpo-30256(36): Pass multiprocessing BaseProxy argument
     ‘manager_owned’ through AutoProxy.

   - bpo-27513(37): *note email.utils.getaddresses(): f82. now accepts
     *note email.header.Header: f83. objects along with string values.
     Patch by Zackery Spytz.

   - bpo-33349(38): lib2to3 now recognizes async generators everywhere.

   - bpo-29298(39): Fix ‘TypeError’ when required subparsers without
     ‘dest’ do not receive arguments.  Patch by Anthony Sottile.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41620

   (2) https://bugs.python.org/issue43913

   (3) https://bugs.python.org/issue45001

   (4) https://bugs.python.org/issue44449

   (5) https://bugs.python.org/issue44955

   (6) https://bugs.python.org/issue38956

   (7) https://bugs.python.org/issue44581

   (8) https://bugs.python.org/issue44849

   (9) https://bugs.python.org/issue44605

   (10) https://bugs.python.org/issue44822

   (11) https://bugs.python.org/issue44815

   (12) https://bugs.python.org/issue44806

   (13) https://bugs.python.org/issue44667

   (14) https://bugs.python.org/issue42853

   (15) https://bugs.python.org/issue44752

   (16) https://bugs.python.org/issue44720

   (17) https://bugs.python.org/issue44704

   (18) https://bugs.python.org/issue44666

   (19) https://bugs.python.org/issue40897

   (20) https://bugs.python.org/issue44608

   (21) https://bugs.python.org/issue41928

   (22) https://bugs.python.org/issue44566

   (23) https://bugs.python.org/issue44558

   (24) https://bugs.python.org/issue41249

   (25) https://bugs.python.org/issue44461

   (26) https://bugs.python.org/issue42892

   (27) https://bugs.python.org/issue27827

   (28) https://bugs.python.org/issue34266

   (29) https://bugs.python.org/issue27334

   (30) https://bugs.python.org/issue43853

   (31) https://bugs.python.org/issue43048

   (32) https://bugs.python.org/issue41402

   (33) https://bugs.python.org/issue32695

   (34) https://bugs.python.org/issue34990

   (35) https://bugs.python.org/issue38840

   (36) https://bugs.python.org/issue30256

   (37) https://bugs.python.org/issue27513

   (38) https://bugs.python.org/issue33349

   (39) https://bugs.python.org/issue29298


File: python.info,  Node: Documentation<5>,  Next: Tests<3>,  Prev: Library<4>,  Up: Python 3 9 7 final

1.19.4.4 Documentation
......................

   - bpo-44903(1): Removed the othergui.rst file, any references to it,
     and the list of GUI frameworks in the FAQ. In their place I’ve
     added links to the Python Wiki ‘page on GUI frameworks’.

   - bpo-44693(2): Update the definition of __future__ in the glossary
     by replacing the confusing word “pseudo-module” with a more
     accurate description.

   - bpo-35183(3): Add typical examples to os.path.splitext docs

   - bpo-30511(4): Clarify that *note shutil.make_archive(): 348. is not
     thread-safe due to reliance on changing the current working
     directory.

   - bpo-44561(5): Update of three expired hyperlinks in
     Doc/distributing/index.rst: “Project structure”, “Building and
     packaging the project”, and “Uploading the project to the Python
     Packaging Index”.

   - bpo-42958(6): Updated the docstring and docs of *note
     filecmp.cmp(): f85. to be more accurate and less confusing
     especially in respect to `shallow' arg.

   - bpo-44558(7): Match the docstring and python implementation of
     *note countOf(): 17c. to the behavior of its c implementation.

   - bpo-44544(8): List all kwargs for *note textwrap.wrap(): f86, *note
     textwrap.fill(): f87, and *note textwrap.shorten(): 9d3.  Now,
     there are nav links to attributes of ‘TextWrap’, which makes
     navigation much easier while minimizing duplication in the
     documentation.

   - bpo-38062(9): Clarify that atexit uses equality comparisons
     internally.

   - bpo-43066(10): Added a warning to *note zipfile: 14b. docs:
     filename arg with a leading slash may cause archive to be
     un-openable on Windows systems.

   - bpo-27752(11): Documentation of csv.Dialect is more descriptive.

   - bpo-44453(12): Fix documentation for the return type of *note
     sysconfig.get_path(): d86.

   - bpo-39498(13): Add a “Security Considerations” index which links to
     standard library modules that have explicitly documented security
     considerations.

   - bpo-33479(14): Remove the unqualified claim that tkinter is
     threadsafe.  It has not been true for several years and likely
     never was.  An explanation of what is true may be added later,
     after more discussion, and possibly after patching _tkinter.c,

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue44903

   (2) https://bugs.python.org/issue44693

   (3) https://bugs.python.org/issue35183

   (4) https://bugs.python.org/issue30511

   (5) https://bugs.python.org/issue44561

   (6) https://bugs.python.org/issue42958

   (7) https://bugs.python.org/issue44558

   (8) https://bugs.python.org/issue44544

   (9) https://bugs.python.org/issue38062

   (10) https://bugs.python.org/issue43066

   (11) https://bugs.python.org/issue27752

   (12) https://bugs.python.org/issue44453

   (13) https://bugs.python.org/issue39498

   (14) https://bugs.python.org/issue33479


File: python.info,  Node: Tests<3>,  Next: Build<3>,  Prev: Documentation<5>,  Up: Python 3 9 7 final

1.19.4.5 Tests
..............

   - bpo-25130(1): Add calls of *note gc.collect(): 35b. in tests to
     support PyPy.

   - bpo-45011(2): Made tests relying on the ‘_asyncio’ C extension
     module optional to allow running on alternative Python
     implementations.  Patch by Serhiy Storchaka.

   - bpo-44949(3): Fix auto history tests of test_readline: sometimes,
     the newline character is not written at the end, so don’t expect it
     in the output.

   - bpo-44852(4): Add ability to wholesale silence DeprecationWarnings
     while running the regression test suite.

   - bpo-40928(5): Notify users running test_decimal regression tests on
     macOS of potential harmless “malloc can’t allocate region” messages
     spewed by test_decimal.

   - bpo-44734(6): Fixed floating point precision issue in turtle tests.

   - bpo-44708(7): Regression tests, when run with -w, are now
     re-running only the affected test methods instead of re-running the
     entire test file.

   - bpo-30256(8): Add test for nested queues when using
     ‘multiprocessing’ shared objects ‘AutoProxy[Queue]’ inside
     ‘ListProxy’ and ‘DictProxy’

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25130

   (2) https://bugs.python.org/issue45011

   (3) https://bugs.python.org/issue44949

   (4) https://bugs.python.org/issue44852

   (5) https://bugs.python.org/issue40928

   (6) https://bugs.python.org/issue44734

   (7) https://bugs.python.org/issue44708

   (8) https://bugs.python.org/issue30256


File: python.info,  Node: Build<3>,  Next: Windows<4>,  Prev: Tests<3>,  Up: Python 3 9 7 final

1.19.4.6 Build
..............

   - bpo-44535(1): Enable building using a Visual Studio 2022 install on
     Windows.

   - bpo-43298(2): Improved error message when building without a
     Windows SDK installed.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue44535

   (2) https://bugs.python.org/issue43298


File: python.info,  Node: Windows<4>,  Next: macOS<3>,  Prev: Build<3>,  Up: Python 3 9 7 final

1.19.4.7 Windows
................

   - bpo-45007(1): Update to OpenSSL 1.1.1l in Windows build

   - bpo-44572(2): Avoid consuming standard input in the *note platform:
     ce. module

   - bpo-40263(3): This is a follow-on bug from
     ‘https://bugs.python.org/issue26903’.  Once that is applied we run
     into an off-by-one assertion problem.  The assert was not correct.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45007

   (2) https://bugs.python.org/issue44572

   (3) https://bugs.python.org/issue40263


File: python.info,  Node: macOS<3>,  Prev: Windows<4>,  Up: Python 3 9 7 final

1.19.4.8 macOS
..............

   - bpo-45007(1): Update macOS installer builds to use OpenSSL 1.1.1l.

   - bpo-44689(2): *note ctypes.util.find_library(): 701. now works
     correctly on macOS 11 Big Sur even if Python is built on an older
     version of macOS. Previously, when built on older macOS systems,
     ‘find_library’ was not able to find macOS system libraries when
     running on Big Sur due to changes in how system libraries are
     stored.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue45007

   (2) https://bugs.python.org/issue44689


File: python.info,  Node: Python 3 9 6 final,  Next: Python 3 9 5 final,  Prev: Python 3 9 7 final,  Up: Changelog

1.19.5 Python 3.9.6 final
-------------------------

`Release date: 2021-06-28'

* Menu:

* Security: Security<2>.
* Core and Builtins: Core and Builtins<5>.
* Library: Library<5>.
* Documentation: Documentation<6>.
* Tests: Tests<4>.
* Build: Build<4>.
* Windows: Windows<5>.
* macOS: macOS<4>.
* IDLE: IDLE<4>.
* Tools/Demos: Tools/Demos<2>.
* C API: C API<3>.


File: python.info,  Node: Security<2>,  Next: Core and Builtins<5>,  Up: Python 3 9 6 final

1.19.5.1 Security
.................

   - bpo-44022(1): mod:*note http.client: 93. now avoids infinitely
     reading potential HTTP headers after a ‘100 Continue’ status
     response from the server.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue44022


File: python.info,  Node: Core and Builtins<5>,  Next: Library<5>,  Prev: Security<2>,  Up: Python 3 9 6 final

1.19.5.2 Core and Builtins
..........................

   - bpo-44409(1): Fix error location information for tokenizer errors
     raised on initialization of the tokenizer.  Patch by Pablo Galindo.

   - bpo-43667(2): Improve Unicode support in non-UTF locales on Oracle
     Solaris.  This issue does not affect other Solaris systems.

   - bpo-44168(3): Fix error message in the parser involving keyword
     arguments with invalid expressions.  Patch by Pablo Galindo

   - bpo-44114(4): Fix incorrect dictkeys_reversed and
     dictitems_reversed function signatures in C code, which broke
     webassembly builds.

   - bpo-44070(5): No longer eagerly makes import filenames absolute,
     except for extension modules, which was introduced in 3.9.5.

   - bpo-28146(6): Fix a confusing error message in *note str.format():
     5d5.

   - bpo-11105(7): When compiling *note ast.AST: 187. objects with
     recursive references through *note compile(): 2e7, the interpreter
     doesn’t crash anymore instead it raises a *note RecursionError:
     727.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue44409

   (2) https://bugs.python.org/issue43667

   (3) https://bugs.python.org/issue44168

   (4) https://bugs.python.org/issue44114

   (5) https://bugs.python.org/issue44070

   (6) https://bugs.python.org/issue28146

   (7) https://bugs.python.org/issue11105


File: python.info,  Node: Library<5>,  Next: Documentation<6>,  Prev: Core and Builtins<5>,  Up: Python 3 9 6 final

1.19.5.3 Library
................

   - bpo-44516(1): Update vendored pip to 21.1.3

   - bpo-44482(2): Fix very unlikely resource leak in *note glob: 88. in
     alternate Python implementations.

   - bpo-44439(3): Fix in ‘bz2.BZ2File.write()’ /
     ‘lzma.LZMAFile.write()’ methods, when the input data is an object
     that supports the buffer protocol, the file length may be wrong.

   - bpo-44434(4): _thread.start_new_thread() no longer calls
     PyThread_exit_thread() explicitly at the thread exit, the call was
     redundant.  On Linux with the glibc, pthread_exit() aborts the
     whole process if dlopen() fails to open libgcc_s.so file (ex:
     EMFILE error).  Patch by Victor Stinner.

   - bpo-44422(5): The *note threading.enumerate(): f90. function now
     uses a reentrant lock to prevent a hang on reentrant call.  Patch
     by Victor Stinner.

   - bpo-44395(6): Fix ‘as_string()’ to pass unixfrom properly.  Patch
     by Dong-hee Na.

   - bpo-44342(7): [Enum] Be more robust in searching for pickle support
     before making an enum class unpicklable.

   - bpo-44356(8): [Enum] Allow multiple data-type mixins if they are
     all the same.

   - bpo-44254(9): On Mac, give turtledemo button text a color that
     works on both light or dark background.  Programmers cannot control
     the latter.

   - bpo-44145(10): *note hmac: 8e. computations were not releasing the
     GIL while calling the OpenSSL ‘HMAC_Update’ C API (a new feature in
     3.9).  This unintentionally prevented parallel computation as other
     *note hashlib: 8c. algorithms support.

   - bpo-37788(11): Fix a reference leak when a Thread object is never
     joined.

   - bpo-44061(12): Fix regression in previous release when calling
     *note pkgutil.iter_modules(): 702. with a list of *note
     pathlib.Path: 32f. objects

   - bpo-36515(13): The *note hashlib: 8c. module no longer does
     unaligned memory accesses when compiled for ARM platforms.

   - bpo-44018(14): random.seed() no longer mutates bytearray inputs.

   - bpo-38352(15): Add ‘IO’, ‘BinaryIO’, ‘TextIO’, ‘Match’, and
     ‘Pattern’ to ‘typing.__all__’.  Patch by Jelle Zijlstra.

   - bpo-43972(16): When *note http.server.SimpleHTTPRequestHandler:
     49c. sends a ‘301 (Moved Permanently)’ for a directory path not
     ending with ‘/’, add a ‘Content-Length: 0’ header.  This improves
     the behavior for certain clients.

   - bpo-28528(17): Fix a bug in *note pdb: c9. where ‘checkline()’
     raises *note AttributeError: 4a2. if it is called after ‘reset()’.

   - bpo-43776(18): When *note subprocess.Popen: 3db. args are provided
     as a string or as *note pathlib.Path: 32f, the Popen instance repr
     now shows the right thing.

   - bpo-43666(19): AIX: ‘Lib/_aix_support.get_platform()’ may fail in
     an AIX WPAR. The fileset bos.rte appears to have a builddate in
     both LPAR and WPAR so this fileset is queried rather than bos.mp64.
     To prevent a similiar situation (no builddate in ODM) a value
     (9988) sufficient for completing a build is provided.  Patch by M
     Felt.

   - bpo-43650(20): Fix *note MemoryError: f69. in *note
     shutil.unpack_archive(): c68. which fails inside
     ‘shutil._unpack_zipfile()’ on large files.  Patch by Igor
     Bolshakov.

   - bpo-43318(21): Fix a bug where *note pdb: c9. does not always echo
     cleared breakpoints.

   - bpo-43295(22): *note datetime.datetime.strptime(): f91. now raises
     ‘ValueError’ instead of ‘IndexError’ when matching ‘'z'’ with the
     ‘%z’ format specifier.

   - bpo-37022(23): *note pdb: c9. now displays exceptions from ‘repr()’
     with its ‘p’ and ‘pp’ commands.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue44516

   (2) https://bugs.python.org/issue44482

   (3) https://bugs.python.org/issue44439

   (4) https://bugs.python.org/issue44434

   (5) https://bugs.python.org/issue44422

   (6) https://bugs.python.org/issue44395

   (7) https://bugs.python.org/issue44342

   (8) https://bugs.python.org/issue44356

   (9) https://bugs.python.org/issue44254

   (10) https://bugs.python.org/issue44145

   (11) https://bugs.python.org/issue37788

   (12) https://bugs.python.org/issue44061

   (13) https://bugs.python.org/issue36515

   (14) https://bugs.python.org/issue44018

   (15) https://bugs.python.org/issue38352

   (16) https://bugs.python.org/issue43972

   (17) https://bugs.python.org/issue28528

   (18) https://bugs.python.org/issue43776

   (19) https://bugs.python.org/issue43666

   (20) https://bugs.python.org/issue43650

   (21) https://bugs.python.org/issue43318

   (22) https://bugs.python.org/issue43295

   (23) https://bugs.python.org/issue37022


File: python.info,  Node: Documentation<6>,  Next: Tests<4>,  Prev: Library<5>,  Up: Python 3 9 6 final

1.19.5.4 Documentation
......................

   - bpo-40620(1): Convert examples in tutorial controlflow.rst section
     4.3 to be interpreter-demo style.

   - bpo-13814(2): In the Design FAQ, answer “Why don’t generators
     support the with statement?”

   - bpo-44392(3): Added a new section in the C API documentation for
     types used in type hinting.  Documented ‘Py_GenericAlias’ and
     ‘Py_GenericAliasType’.

   - bpo-38291(4): Mark ‘typing.io’ and ‘typing.re’ as deprecated since
     Python 3.8 in the documentation.  They were never properly
     supported by type checkers.

   - bpo-44322(5): Document that SyntaxError args have a details tuple
     and that details are adjusted for errors in f-string field
     replacement expressions.

   - bpo-44195(6): Corrected references to ‘TraversableResources’ in
     docs.  There is no ‘TraversableReader’.

   - bpo-41963(7): Document that ‘ConfigParser’ strips off comments when
     reading configuration files.

   - bpo-44072(8): Correct where in the numeric ABC hierarchy ‘**’
     support is added, i.e., in numbers.Complex, not numbers.Integral.

   - bpo-43558(9): Add the remark to *note dataclasses: 2f.
     documentation that the *note __init__(): e23. of any base class has
     to be called in ‘__post_init__()’, along with a code example.

   - bpo-41621(10): Document that *note collections.defaultdict: c0c.
     parameter ‘default_factory’ defaults to None and is
     positional-only.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40620

   (2) https://bugs.python.org/issue13814

   (3) https://bugs.python.org/issue44392

   (4) https://bugs.python.org/issue38291

   (5) https://bugs.python.org/issue44322

   (6) https://bugs.python.org/issue44195

   (7) https://bugs.python.org/issue41963

   (8) https://bugs.python.org/issue44072

   (9) https://bugs.python.org/issue43558

   (10) https://bugs.python.org/issue41621


File: python.info,  Node: Tests<4>,  Next: Build<4>,  Prev: Documentation<6>,  Up: Python 3 9 6 final

1.19.5.5 Tests
..............

   - bpo-44287(1): Fix asyncio test_popen() of test_windows_utils by
     using a longer timeout.  Use military grade battle-tested *note
     test.support.SHORT_TIMEOUT: f94. timeout rather than a hardcoded
     timeout of 10 seconds: it’s 30 seconds by default, but it is made
     longer on slow buildbots.  Patch by Victor Stinner.

   - bpo-44363(2): Account for address sanitizer in test_capi.
     test_capi now passes when run GCC address sanitizer.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue44287

   (2) https://bugs.python.org/issue44363


File: python.info,  Node: Build<4>,  Next: Windows<5>,  Prev: Tests<4>,  Up: Python 3 9 6 final

1.19.5.6 Build
..............

   - bpo-44381(1): The Windows build now accepts
     ‘EnableControlFlowGuard’ set to ‘guard’ to enable CFG.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue44381


File: python.info,  Node: Windows<5>,  Next: macOS<4>,  Prev: Build<4>,  Up: Python 3 9 6 final

1.19.5.7 Windows
................

   - bpo-41299(1): Fix 16ms jitter when using timeouts in *note
     threading: 10b, such as with *note threading.Lock.acquire(): 85b.
     or *note threading.Condition.wait(): f97.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41299


File: python.info,  Node: macOS<4>,  Next: IDLE<4>,  Prev: Windows<5>,  Up: Python 3 9 6 final

1.19.5.8 macOS
..............

   - bpo-43568(1): Relax unnecessarily restrictive
     MACOSX_DEPLOYMENT_TARGET check when building extension modules for
     macOS. Patch by Joshua Root.

   - bpo-43109(2): Allow –with-lto configure option to work with
     Apple-supplied Xcode or Command Line Tools.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43568

   (2) https://bugs.python.org/issue43109


File: python.info,  Node: IDLE<4>,  Next: Tools/Demos<2>,  Prev: macOS<4>,  Up: Python 3 9 6 final

1.19.5.9 IDLE
.............

   - bpo-40128(1): Mostly fix completions on macOS when not using tcl/tk
     8.6.11 (as with 3.9).  The added update_idletask call should be
     harmless and possibly helpful otherwise.

   - bpo-33962(2): Move the indent space setting from the Font tab to
     the new Windows tab.  Patch by Mark Roseman and Terry Jan Reedy.

   - bpo-40468(3): Split the settings dialog General tab into Windows
     and Shell/ED tabs.  Move help sources, which extend the Help menu,
     to the Extensions tab.  Make space for new options and shorten the
     dialog.  The latter makes the dialog better fit small screens.

   - bpo-41611(4): Avoid uncaught exceptions in
     ‘AutoCompleteWindow.winconfig_event()’.

   - bpo-41611(5): Fix IDLE sometimes freezing upon tab-completion on
     macOS.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40128

   (2) https://bugs.python.org/issue33962

   (3) https://bugs.python.org/issue40468

   (4) https://bugs.python.org/issue41611

   (5) https://bugs.python.org/issue41611


File: python.info,  Node: Tools/Demos<2>,  Next: C API<3>,  Prev: IDLE<4>,  Up: Python 3 9 6 final

1.19.5.10 Tools/Demos
.....................

   - bpo-44074(1): Make patchcheck automatically detect the correct base
     branch name (previously it was hardcoded to ‘master’)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue44074


File: python.info,  Node: C API<3>,  Prev: Tools/Demos<2>,  Up: Python 3 9 6 final

1.19.5.11 C API
...............

   - bpo-44441(1): *note Py_RunMain(): 2b5. now resets
     ‘PyImport_Inittab’ to its initial value at exit.  It must be
     possible to call *note PyImport_AppendInittab(): f9c. or *note
     PyImport_ExtendInittab(): f9d. at each Python initialization.
     Patch by Victor Stinner.

   - bpo-42083(2): Fix crash in *note PyStructSequence_NewType(): f9e.
     when passed ‘NULL’ in the documentation string slot.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue44441

   (2) https://bugs.python.org/issue42083


File: python.info,  Node: Python 3 9 5 final,  Next: Python 3 9 4 final,  Prev: Python 3 9 6 final,  Up: Changelog

1.19.6 Python 3.9.5 final
-------------------------

`Release date: 2021-05-03'

* Menu:

* Security: Security<3>.
* Core and Builtins: Core and Builtins<6>.
* Library: Library<6>.
* Documentation: Documentation<7>.
* Tests: Tests<5>.
* Windows: Windows<6>.
* macOS: macOS<5>.
* IDLE: IDLE<5>.


File: python.info,  Node: Security<3>,  Next: Core and Builtins<6>,  Up: Python 3 9 5 final

1.19.6.1 Security
.................

   - bpo-43434(1): Creating a *note sqlite3.Connection: 4df. object now
     also produces a ‘sqlite3.connect’ *note auditing event: fa1.
     Previously this event was only produced by *note sqlite3.connect():
     4e1. calls.  Patch by Erlend E. Aasland.

   - bpo-43882(2): The presence of newline or tab characters in parts of
     a URL could allow some forms of attacks.

     Following the controlling specification for URLs defined by WHATWG
     *note urllib.parse(): 128. now removes ASCII newlines and tabs from
     URLs, preventing such attacks.

   - bpo-43472(3): Ensures interpreter-level audit hooks receive the
     ‘cpython.PyInterpreterState_New’ event when called through the
     ‘_xxsubinterpreters’ module.

   - bpo-36384(4): *note ipaddress: a2. module no longer accepts any
     leading zeros in IPv4 address strings.  Leading zeros are ambiguous
     and interpreted as octal notation by some libraries.  For example
     the legacy function *note socket.inet_aton(): 236. treats leading
     zeros as octal notatation.  glibc implementation of modern *note
     inet_pton(): 237. does not accept any leading zeros.  For a while
     the *note ipaddress: a2. module used to accept ambiguous leading
     zeros.

   - bpo-43075(5): Fix Regular Expression Denial of Service (ReDoS)
     vulnerability in *note urllib.request.AbstractBasicAuthHandler:
     fa2.  The ReDoS-vulnerable regex has quadratic worst-case
     complexity and it allows cause a denial of service when identifying
     crafted invalid RFCs.  This ReDoS issue is on the client side and
     needs remote attackers to control the HTTP server.

   - bpo-42800(6): Audit hooks are now fired for frame.f_code,
     traceback.tb_frame, and generator code/frame attribute access.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43434

   (2) https://bugs.python.org/issue43882

   (3) https://bugs.python.org/issue43472

   (4) https://bugs.python.org/issue36384

   (5) https://bugs.python.org/issue43075

   (6) https://bugs.python.org/issue42800


File: python.info,  Node: Core and Builtins<6>,  Next: Library<6>,  Prev: Security<3>,  Up: Python 3 9 5 final

1.19.6.2 Core and Builtins
..........................

   - bpo-43105(1): Importlib now resolves relative paths when creating
     module spec objects from file locations.

   - bpo-42924(2): Fix ‘bytearray’ repetition incorrectly copying data
     from the start of the buffer, even if the data is offset within the
     buffer (e.g.  after reassigning a slice at the start of the
     ‘bytearray’ to a shorter byte string).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43105

   (2) https://bugs.python.org/issue42924


File: python.info,  Node: Library<6>,  Next: Documentation<7>,  Prev: Core and Builtins<6>,  Up: Python 3 9 5 final

1.19.6.3 Library
................

   - bpo-43993(1): Update bundled pip to 21.1.1.

   - bpo-43937(2): Fixed the *note turtle: 11f. module working with
     non-default root window.

   - bpo-43930(3): Update bundled pip to 21.1 and setuptools to 56.0.0

   - bpo-43920(4): OpenSSL 3.0.0: *note load_verify_locations(): 8d8.
     now returns a consistent error message when cadata contains no
     valid certificate.

   - bpo-43607(5): *note urllib: 126. can now convert Windows paths with
     ‘\\?\’ prefixes into URL paths.

   - bpo-43284(6): platform.win32_ver derives the windows version from
     sys.getwindowsversion().platform_version which in turn derives the
     version from kernel32.dll (which can be of a different version than
     Windows itself).  Therefore change the platform.win32_ver to
     determine the version using the platform module’s _syscmd_ver
     private function to return an accurate version.

   - bpo-42248(7): [Enum] ensure exceptions raised in ‘_missing_’ are
     released.

   - bpo-43799(8): OpenSSL 3.0.0: define ‘OPENSSL_API_COMPAT’ 1.1.1 to
     suppress deprecation warnings.  Python requires OpenSSL 1.1.1 APIs.

   - bpo-43794(9): Add *note ssl.OP_IGNORE_UNEXPECTED_EOF: fa5.
     constants (OpenSSL 3.0.0)

   - bpo-43789(10): OpenSSL 3.0.0: Don’t call the password callback
     function a second time when first call has signaled an error
     condition.

   - bpo-43788(11): The header files for *note ssl: f3. error codes are
     now OpenSSL version-specific.  Exceptions will now show correct
     reason and library codes.  The ‘make_ssl_data.py’ script has been
     rewritten to use OpenSSL’s text file with error codes.

   - bpo-43655(12): *note tkinter: 10e. dialog windows are now
     recognized as dialogs by window managers on macOS and X Window.

   - bpo-43534(13): *note turtle.textinput(): fa6. and *note
     turtle.numinput(): fa7. create now a transient window working on
     behalf of the canvas window.

   - bpo-43522(14): Fix problem with *note hostname_checks_common_name:
     4e5.  OpenSSL does not copy hostflags from `struct SSL_CTX' to
     `struct SSL'.

   - bpo-42967(15): Allow *note bytes: 172. ‘separator’ argument in
     ‘urllib.parse.parse_qs’ and ‘urllib.parse.parse_qsl’ when parsing
     *note str: 205. query strings.  Previously, this raised a
     ‘TypeError’.

   - bpo-43176(16): Fixed processing of a dataclass that inherits from a
     frozen dataclass with no fields.  It is now correctly detected as
     an error.

   - bpo-41735(17): Fix thread locks in zlib module may go wrong in rare
     case.  Patch by Ma Lin.

   - bpo-36470(18): Fix dataclasses with ‘InitVar’s and *note replace():
     fa8.  Patch by Claudiu Popa.

   - bpo-32745(19): Fix a regression in the handling of ctypes’ *note
     ctypes.c_wchar_p: fa9. type: embedded null characters would cause a
     *note ValueError: 16d. to be raised.  Patch by Zackery Spytz.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43993

   (2) https://bugs.python.org/issue43937

   (3) https://bugs.python.org/issue43930

   (4) https://bugs.python.org/issue43920

   (5) https://bugs.python.org/issue43607

   (6) https://bugs.python.org/issue43284

   (7) https://bugs.python.org/issue42248

   (8) https://bugs.python.org/issue43799

   (9) https://bugs.python.org/issue43794

   (10) https://bugs.python.org/issue43789

   (11) https://bugs.python.org/issue43788

   (12) https://bugs.python.org/issue43655

   (13) https://bugs.python.org/issue43534

   (14) https://bugs.python.org/issue43522

   (15) https://bugs.python.org/issue42967

   (16) https://bugs.python.org/issue43176

   (17) https://bugs.python.org/issue41735

   (18) https://bugs.python.org/issue36470

   (19) https://bugs.python.org/issue32745


File: python.info,  Node: Documentation<7>,  Next: Tests<5>,  Prev: Library<6>,  Up: Python 3 9 5 final

1.19.6.4 Documentation
......................

   - bpo-43959(1): The documentation on the PyContextVar C-API was
     clarified.

   - bpo-43938(2): Update dataclasses documentation to express that
     FrozenInstanceError is derived from AttributeError.

   - bpo-43755(3): Update documentation to reflect that unparenthesized
     lambda expressions can no longer be the expression part in an ‘if’
     clause in comprehensions and generator expressions since Python
     3.9.

   - bpo-43739(4): Fixing the example code in
     Doc/extending/extending.rst to declare and initialize the pmodule
     variable to be of the right type.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43959

   (2) https://bugs.python.org/issue43938

   (3) https://bugs.python.org/issue43755

   (4) https://bugs.python.org/issue43739


File: python.info,  Node: Tests<5>,  Next: Windows<6>,  Prev: Documentation<7>,  Up: Python 3 9 5 final

1.19.6.5 Tests
..............

   - bpo-43961(1): Fix test_logging.test_namer_rotator_inheritance() on
     Windows: use *note os.replace(): b15. rather than *note
     os.rename(): b14.  Patch by Victor Stinner.

   - bpo-43842(2): Fix a race condition in the SMTP test of
     test_logging.  Don’t close a file descriptor (socket) from a
     different thread while asyncore.loop() is polling the file
     descriptor.  Patch by Victor Stinner.

   - bpo-43811(3): Tests multiple OpenSSL versions on GitHub Actions.
     Use ccache to speed up testing.

   - bpo-43791(4): OpenSSL 3.0.0: Disable testing of legacy protocols
     TLS 1.0 and 1.1.  Tests are failing with
     TLSV1_ALERT_INTERNAL_ERROR.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43961

   (2) https://bugs.python.org/issue43842

   (3) https://bugs.python.org/issue43811

   (4) https://bugs.python.org/issue43791


File: python.info,  Node: Windows<6>,  Next: macOS<5>,  Prev: Tests<5>,  Up: Python 3 9 5 final

1.19.6.6 Windows
................

   - bpo-35306(1): Avoid raising errors from *note
     pathlib.Path.exists(): 330. when passed an invalid filename.

   - bpo-38822(2): Fixed *note os.stat(): 321. failing on inaccessible
     directories with a trailing slash, rather than falling back to the
     parent directory’s metadata.  This implicitly affected *note
     os.path.exists(): 325. and *note os.path.isdir(): 327.

   - bpo-26227(3): Fixed decoding of host names in *note
     socket.gethostbyaddr(): fad. and *note socket.gethostbyname_ex():
     fae.

   - bpo-40432(4): Updated pegen regeneration script on Windows to find
     and use Python 3.8 or higher.  Prior to this, pegen regeneration
     already required 3.8 or higher, but the script may have used lower
     versions of Python.

   - bpo-43745(5): Actually updates Windows release to OpenSSL 1.1.1k.
     Earlier releases were mislabelled and actually included 1.1.1i
     again.

   - bpo-43492(6): Upgrade Windows installer to use SQLite 3.35.5.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35306

   (2) https://bugs.python.org/issue38822

   (3) https://bugs.python.org/issue26227

   (4) https://bugs.python.org/issue40432

   (5) https://bugs.python.org/issue43745

   (6) https://bugs.python.org/issue43492


File: python.info,  Node: macOS<5>,  Next: IDLE<5>,  Prev: Windows<6>,  Up: Python 3 9 5 final

1.19.6.7 macOS
..............

   - bpo-42119(1): Fix check for macOS SDK paths when building Python.
     Narrow search to match contents of SDKs, namely only files in
     ‘/System/Library’, ‘/System/IOSSupport’, and ‘/usr’ other than
     ‘/usr/local’.  Previously, anything under ‘/System’ was assumed to
     be in an SDK which causes problems with the new file system layout
     in 10.15+ where user file systems may appear to be mounted under
     ‘/System’.  Paths in ‘/Library’ were also incorrectly treated as
     SDK locations.

   - bpo-44009(2): Provide “python3.x-intel64” executable to allow
     reliably forcing macOS universal2 framework builds to run under
     Rosetta 2 Intel-64 emulation on Apple Silicon Macs.  This can be
     useful for testing or when universal2 wheels are not yet available.

   - bpo-43492(3): Update macOS installer to use SQLite 3.35.4.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42119

   (2) https://bugs.python.org/issue44009

   (3) https://bugs.python.org/issue43492


File: python.info,  Node: IDLE<5>,  Prev: macOS<5>,  Up: Python 3 9 5 final

1.19.6.8 IDLE
.............

   - bpo-43655(1): IDLE dialog windows are now recognized as dialogs by
     window managers on macOS and X Window.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43655


File: python.info,  Node: Python 3 9 4 final,  Next: Python 3 9 3 final,  Prev: Python 3 9 5 final,  Up: Changelog

1.19.7 Python 3.9.4 final
-------------------------

`Release date: 2021-04-04'

* Menu:

* Core and Builtins: Core and Builtins<7>.
* Library: Library<7>.


File: python.info,  Node: Core and Builtins<7>,  Next: Library<7>,  Up: Python 3 9 4 final

1.19.7.1 Core and Builtins
..........................

   - bpo-43710(1): Reverted the fix for
     ‘https://bugs.python.org/issue42500’ as it changed the
     PyThreadState struct size and broke the 3.9.x ABI in the 3.9.3
     release (visible on 32-bit platforms using binaries compiled using
     an earlier version of Python 3.9.x headers).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43710


File: python.info,  Node: Library<7>,  Prev: Core and Builtins<7>,  Up: Python 3 9 4 final

1.19.7.2 Library
................

   - bpo-26053(1): Fixed bug where the *note pdb: c9. interactive run
     command echoed the args from the shell command line, even if those
     have been overridden at the pdb prompt.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26053


File: python.info,  Node: Python 3 9 3 final,  Next: Python 3 9 2 final,  Prev: Python 3 9 4 final,  Up: Changelog

1.19.8 Python 3.9.3 final
-------------------------

`Release date: 2021-04-02'

* Menu:

* Security: Security<4>.
* Core and Builtins: Core and Builtins<8>.
* Library: Library<8>.
* Documentation: Documentation<8>.
* Tests: Tests<6>.
* Build: Build<5>.
* macOS: macOS<6>.
* IDLE: IDLE<6>.


File: python.info,  Node: Security<4>,  Next: Core and Builtins<8>,  Up: Python 3 9 3 final

1.19.8.1 Security
.................

   - bpo-42988(1): CVE-2021-3426: Remove the ‘getfile’ feature of the
     *note pydoc: d9. module which could be abused to read arbitrary
     files on the disk (directory traversal vulnerability).  Moreover,
     even source code of Python modules can contain sensitive data like
     passwords.  Vulnerability reported by David Schwörer.

   - bpo-43285(2): *note ftplib: 82. no longer trusts the IP address
     value returned from the server in response to the PASV command by
     default.  This prevents a malicious FTP server from using the
     response to probe IPv4 address and port combinations on the client
     network.

     Code that requires the former vulnerable behavior may set a
     ‘trust_server_pasv_ipv4_address’ attribute on their *note
     ftplib.FTP: 1a6. instances to ‘True’ to re-enable it.

   - bpo-43439(3): Add audit hooks for *note gc.get_objects(): 2fe,
     *note gc.get_referrers(): fb6. and *note gc.get_referents(): fb7.
     Patch by Pablo Galindo.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42988

   (2) https://bugs.python.org/issue43285

   (3) https://bugs.python.org/issue43439


File: python.info,  Node: Core and Builtins<8>,  Next: Library<8>,  Prev: Security<4>,  Up: Python 3 9 3 final

1.19.8.2 Core and Builtins
..........................

   - bpo-43660(1): Fix crash that happens when replacing ‘sys.stderr’
     with a callable that can remove the object while an exception is
     being printed.  Patch by Pablo Galindo.

   - bpo-43555(2): Report the column offset for *note SyntaxError: 55a.
     for invalid line continuation characters.  Patch by Pablo Galindo.

   - bpo-43517(3): Fix misdetection of circular imports when using ‘from
     pkg.mod import attr’, which caused false positives in non-trivial
     multi-threaded code.

   - bpo-35883(4): Python no longer fails at startup with a fatal error
     if a command line argument contains an invalid Unicode character.
     The *note Py_DecodeLocale(): 53f. function now escapes byte
     sequences which would be decoded as Unicode characters outside the
     [U+0000; U+10ffff] range.

   - bpo-43406(5): Fix a possible race condition where
     ‘PyErr_CheckSignals’ tries to execute a non-Python signal handler.

   - bpo-42500(6): Improve handling of exceptions near recursion limit.
     Converts a number of Fatal Errors in RecursionErrors.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43660

   (2) https://bugs.python.org/issue43555

   (3) https://bugs.python.org/issue43517

   (4) https://bugs.python.org/issue35883

   (5) https://bugs.python.org/issue43406

   (6) https://bugs.python.org/issue42500


File: python.info,  Node: Library<8>,  Next: Documentation<8>,  Prev: Core and Builtins<8>,  Up: Python 3 9 3 final

1.19.8.3 Library
................

   - bpo-43433(1): *note xmlrpc.client.ServerProxy: 37f. no longer
     ignores query and fragment in the URL of the server.

   - bpo-35930(2): Raising an exception raised in a “future” instance
     will create reference cycles.

   - bpo-43577(3): Fix deadlock when using *note ssl.SSLContext: 4ea.
     debug callback with *note ssl.SSLContext.sni_callback(): fba.

   - bpo-43521(4): ‘ast.unparse’ can now render NaNs and empty sets.

   - bpo-43423(5): ‘subprocess.communicate()’ no longer raises an
     IndexError when there is an empty stdout or stderr IO buffer during
     a timeout on Windows.

   - bpo-27820(6): Fixed long-standing bug of smtplib.SMTP where doing
     AUTH LOGIN with initial_response_ok=False will fail.

     The cause is that SMTP.auth_login _always_ returns a password if
     provided with a challenge string, thus non-compliant with the
     standard for AUTH LOGIN.

     Also fixes bug with the test for smtpd.

   - bpo-43332(7): Improves the networking efficiency of *note
     http.client: 93. when using a proxy via ‘set_tunnel()’.  Fewer
     small send calls are made during connection setup.

   - bpo-43399(8): Fix ‘ElementTree.extend’ not working on iterators
     when using the Python implementation

   - bpo-43316(9): The ‘python -m gzip’ command line application now
     properly fails when detecting an unsupported extension.  It exits
     with a non-zero exit code and prints an error message to stderr.

   - bpo-43260(10): Fix TextIOWrapper can not flush internal buffer
     forever after very large text is written.

   - bpo-42782(11): Fail fast in *note shutil.move(): 385. to avoid
     creating destination directories on failure.

   - bpo-37193(12): Fixed memory leak in ‘socketserver.ThreadingMixIn’
     introduced in Python 3.7.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43433

   (2) https://bugs.python.org/issue35930

   (3) https://bugs.python.org/issue43577

   (4) https://bugs.python.org/issue43521

   (5) https://bugs.python.org/issue43423

   (6) https://bugs.python.org/issue27820

   (7) https://bugs.python.org/issue43332

   (8) https://bugs.python.org/issue43399

   (9) https://bugs.python.org/issue43316

   (10) https://bugs.python.org/issue43260

   (11) https://bugs.python.org/issue42782

   (12) https://bugs.python.org/issue37193


File: python.info,  Node: Documentation<8>,  Next: Tests<6>,  Prev: Library<8>,  Up: Python 3 9 3 final

1.19.8.4 Documentation
......................

   - bpo-43199(1): Answer “Why is there no goto?” in the Design and
     History FAQ.

   - bpo-43407(2): Clarified that a result from *note time.monotonic():
     85e, *note time.perf_counter(): 3cc, *note time.process_time():
     3cd, or *note time.thread_time(): 1e7. can be compared with the
     result from any following call to the same function - not just the
     next immediate call.

   - bpo-27646(3): Clarify that ‘yield from <expr>’ works with any
     iterable, not just iterators.

   - bpo-36346(4): Update some deprecated unicode APIs which are
     documented as “will be removed in 4.0” to “3.12”.  See PEP 623(5)
     for detail.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43199

   (2) https://bugs.python.org/issue43407

   (3) https://bugs.python.org/issue27646

   (4) https://bugs.python.org/issue36346

   (5) https://www.python.org/dev/peps/pep-0623


File: python.info,  Node: Tests<6>,  Next: Build<5>,  Prev: Documentation<8>,  Up: Python 3 9 3 final

1.19.8.5 Tests
..............

   - bpo-37945(1): Fix test_getsetlocale_issue1813() of test_locale:
     skip the test if ‘setlocale()’ fails.  Patch by Victor Stinner.

   - bpo-41561(2): Add workaround for Ubuntu’s custom OpenSSL security
     level policy.

   - bpo-43288(3): Fix test_importlib to correctly skip Unicode file
     tests if the fileystem does not support them.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37945

   (2) https://bugs.python.org/issue41561

   (3) https://bugs.python.org/issue43288


File: python.info,  Node: Build<5>,  Next: macOS<6>,  Prev: Tests<6>,  Up: Python 3 9 3 final

1.19.8.6 Build
..............

   - bpo-43631(1): Update macOS, Windows, and CI to OpenSSL 1.1.1k.

   - bpo-43617(2): Improve configure.ac: Check for presence of
     autoconf-archive package and remove our copies of M4 macros.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43631

   (2) https://bugs.python.org/issue43617


File: python.info,  Node: macOS<6>,  Next: IDLE<6>,  Prev: Build<5>,  Up: Python 3 9 3 final

1.19.8.7 macOS
..............

   - bpo-41837(1): Update macOS installer build to use OpenSSL 1.1.1j.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41837


File: python.info,  Node: IDLE<6>,  Prev: macOS<6>,  Up: Python 3 9 3 final

1.19.8.8 IDLE
.............

   - bpo-42225(1): Document that IDLE can fail on Unix either from
     misconfigured IP masquerage rules or failure displaying complex
     colored (non-ascii) characters.

   - bpo-43283(2): Document why printing to IDLE’s Shell is often slower
     than printing to a system terminal and that it can be made faster
     by pre-formatting a single string before printing.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42225

   (2) https://bugs.python.org/issue43283


File: python.info,  Node: Python 3 9 2 final,  Next: Python 3 9 2 release candidate 1,  Prev: Python 3 9 3 final,  Up: Changelog

1.19.9 Python 3.9.2 final
-------------------------

`Release date: 2021-02-19'

* Menu:

* Windows: Windows<7>.


File: python.info,  Node: Windows<7>,  Up: Python 3 9 2 final

1.19.9.1 Windows
................

   - bpo-43155(1): ‘PyCMethod_New()’ is now present in ‘python3.lib’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43155


File: python.info,  Node: Python 3 9 2 release candidate 1,  Next: Python 3 9 1 final,  Prev: Python 3 9 2 final,  Up: Changelog

1.19.10 Python 3.9.2 release candidate 1
----------------------------------------

`Release date: 2021-02-16'

* Menu:

* Security: Security<5>.
* Core and Builtins: Core and Builtins<9>.
* Library: Library<9>.
* Documentation: Documentation<9>.
* Tests: Tests<7>.
* Build: Build<6>.
* Windows: Windows<8>.
* macOS: macOS<7>.
* IDLE: IDLE<7>.
* Tools/Demos: Tools/Demos<3>.
* C API: C API<4>.


File: python.info,  Node: Security<5>,  Next: Core and Builtins<9>,  Up: Python 3 9 2 release candidate 1

1.19.10.1 Security
..................

   - bpo-42967(1): Fix web cache poisoning vulnerability by defaulting
     the query args separator to ‘&’, and allowing the user to choose a
     custom separator.

   - bpo-42938(2): Avoid static buffers when computing the repr of *note
     ctypes.c_double: fc4. and *note ctypes.c_longdouble: fc5. values.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42967

   (2) https://bugs.python.org/issue42938


File: python.info,  Node: Core and Builtins<9>,  Next: Library<9>,  Prev: Security<5>,  Up: Python 3 9 2 release candidate 1

1.19.10.2 Core and Builtins
...........................

   - bpo-42819(1): *note readline: de.: Explicitly disable bracketed
     paste in the interactive interpreter, even if it’s set in the
     inputrc, is enabled by default (eg GNU Readline 8.1), or a user
     calls ‘readline.read_init_file()’.  The Python REPL has not
     implemented bracketed paste support.  Also, bracketed mode writes
     the ‘"\x1b[?2004h"’ escape sequence into stdout which causes test
     failures in applications that don’t support it.  It can still be
     explicitly enabled by calling ‘readline.parse_and_bind("set
     enable-bracketed-paste on")’.  Patch by Dustin Rodrigues.

   - bpo-42806(2): Fix the column offsets for f-strings *note ast: 7.
     nodes surrounded by parentheses and for nodes that spawn multiple
     lines.  Patch by Pablo Galindo.

   - bpo-40631(3): Fix regression where a single parenthesized starred
     expression was a valid assignment target.

   - bpo-32381(4): Fix encoding name when running a ‘.pyc’ file on
     Windows: *note PyRun_SimpleFileExFlags(): fc7. now uses the correct
     encoding to decode the filename.

   - bpo-42536(5): Several built-in and standard library types now
     ensure that their internal result tuples are always tracked by the
     *note garbage collector: fc8.:

        - *note collections.OrderedDict.items(): 2ea.

        - *note dict.items(): cf5.

        - *note enumerate(): ea7.

        - *note functools.reduce(): d37.

        - *note itertools.combinations(): d6e.

        - *note itertools.combinations_with_replacement(): ce3.

        - *note itertools.permutations(): fc9.

        - *note itertools.product(): d6f.

        - *note itertools.zip_longest(): cfb.

        - *note zip(): cfc.

     Previously, they could have become untracked by a prior garbage
     collection.  Patch by Brandt Bucher.

   - bpo-42195(6): The ‘__args__’ of the parameterized generics for
     *note typing.Callable: 27b. and *note collections.abc.Callable:
     27a. are now consistent.  The ‘__args__’ for *note
     collections.abc.Callable: 27a. are now flattened while *note
     typing.Callable: 27b.’s have not changed.  To allow this change,
     *note types.GenericAlias: 27c. can now be subclassed and
     ‘collections.abc.Callable’’s ‘__class_getitem__’ will now return a
     subclass of ‘types.GenericAlias’.  Tests for typing were also
     updated to not subclass things like ‘Callable[..., T]’ as that is
     not a valid base class.  Finally, both types no longer validate
     their ‘argtypes’, in ‘Callable[[argtypes], resulttype]’ to prepare
     for PEP 612(7).  Patch by Ken Jin.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42819

   (2) https://bugs.python.org/issue42806

   (3) https://bugs.python.org/issue40631

   (4) https://bugs.python.org/issue32381

   (5) https://bugs.python.org/issue42536

   (6) https://bugs.python.org/issue42195

   (7) https://www.python.org/dev/peps/pep-0612


File: python.info,  Node: Library<9>,  Next: Documentation<9>,  Prev: Core and Builtins<9>,  Up: Python 3 9 2 release candidate 1

1.19.10.3 Library
.................

   - bpo-43102(1): The namedtuple __new__ method had its __builtins__
     set to None instead of an actual dictionary.  This created problems
     for introspection tools.

   - bpo-43108(2): Fixed a reference leak in the *note curses: 2b.
     module.  Patch by Pablo Galindo

   - bpo-42944(3): Fix ‘random.Random.sample’ when ‘counts’ argument is
     not ‘None’.

   - bpo-42931(4): Add ‘randbytes()’ to ‘random.__all__’.

   - bpo-42780(5): Fix os.set_inheritable() for O_PATH file descriptors
     on Linux.

   - bpo-42851(6): remove __init_subclass__ support for Enum members

   - bpo-41748(7): Fix HTMLParser parsing rules for element attributes
     containing commas with spaces.  Patch by Karl Dubost.

   - bpo-42759(8): Fixed equality comparison of ‘tkinter.Variable’ and
     *note tkinter.font.Font: fcb.  Objects which belong to different
     Tcl interpreters are now always different, even if they have the
     same name.

   - bpo-42756(9): Configure LMTP Unix-domain socket to use socket
     global default timeout when a timeout is not explicitly provided.

   - bpo-23328(10): Allow / character in username, password fields on
     _PROXY envars.

   - bpo-42655(11): *note subprocess: f9. `extra_groups' is now
     correctly passed into setgroups() system call.

   - bpo-42727(12): ‘EnumMeta.__prepare__’ now accepts ‘**kwds’ to
     properly support ‘__init_subclass__’

   - bpo-42681(13): Fixed range checks for color and pair numbers in
     *note curses: 2b.

   - bpo-37961(14): Fix crash in ‘tracemalloc.Traceback.__repr__()’
     (regressed in Python 3.9).

   - bpo-42630(15): *note tkinter: 10e. functions and constructors which
     need a default root window raise now *note RuntimeError: 3dc. with
     descriptive message instead of obscure *note AttributeError: 4a2.
     or *note NameError: e40. if it is not created yet or cannot be
     created automatically.

   - bpo-42644(16): *note logging.disable: fcc. will now validate the
     types and value of its parameter.  It also now accepts strings
     representing the levels (as does ‘loging.setLevel’) instead of only
     the numerical values.

   - bpo-36541(17): Fixed lib2to3.pgen2 to be able to parse PEP-570
     positional only argument syntax.

   - bpo-42517(18): Enum: private names will raise a DeprecationWarning;
     in 3.10 they will become normal attributes

   - bpo-42678(19): ‘Enum’: call ‘__init_subclass__’ after members have
     been added

   - bpo-42532(20): Remove unexpected call of ‘__bool__’ when passing a
     ‘spec_arg’ argument to a Mock.

   - bpo-42388(21): Fix subprocess.check_output(…, input=None) behavior
     when text=True to be consistent with that of the documentation and
     universal_newlines=True.

   - bpo-34463(22): Fixed discrepancy between *note traceback: 11c. and
     the interpreter in formatting of SyntaxError with lineno not set
     (*note traceback: 11c. was changed to match interpreter).

   - bpo-42375(23): subprocess module update for DragonFlyBSD support.

   - bpo-42384(24): Make pdb populate sys.path[0] exactly the same as
     regular python execution.

   - bpo-42383(25): Fix pdb: previously pdb would fail to restart the
     debugging target if it was specified using a relative path and the
     current directory changed.

   - bpo-42318(26): Fixed support of non-BMP characters in *note
     tkinter: 10e. on macOS.

   - bpo-42163(27): Restore compatibility for ‘uname_result’ around
     deepcopy and _replace.

   - bpo-39825(28): Windows: Change
     ‘sysconfig.get_config_var('EXT_SUFFIX')’ to the expected full
     ‘platform_tag.extension’ format.  Previously it was hard-coded to
     ‘.pyd’, now it is compatible with ‘distutils.sysconfig’ and will
     result in something like ‘.cp38-win_amd64.pyd’.  This brings
     windows into conformance with the other platforms.

   - bpo-42059(29): *note typing.TypedDict: 367. types created using the
     alternative call-style syntax now correctly respect the ‘total’
     keyword argument when setting their ‘__required_keys__’ and
     ‘__optional_keys__’ class attributes.

   - bpo-39101(30): Fixed tests using IsolatedAsyncioTestCase from
     hanging on BaseExceptions.

   - bpo-42005(31): Fix CLI of *note cProfile: 27. and *note profile:
     d3. to catch *note BrokenPipeError: a7e.

   - bpo-41907(32): fix *note format(): 5d6. behavior for ‘IntFlag’

   - bpo-41889(33): Enum: fix regression involving inheriting a
     multiply-inherited enum

   - bpo-41891(34): Ensure asyncio.wait_for waits for task completion

   - bpo-41604(35): Don’t decrement the reference count of the previous
     user_ptr when set_panel_userptr fails.

   - bpo-40219(36): Lowered ‘tkinter.ttk.LabeledScale’ dummy widget to
     prevent hiding part of the content label.

   - bpo-40084(37): Fix ‘Enum.__dir__’: dir(Enum.member) now includes
     attributes as well as methods.

   - bpo-39068(38): Fix initialization race condition in ‘a85encode()’
     and ‘b85encode()’ in *note base64: d.  Patch by Brandon Stansbury.

   - bpo-33289(39): Correct call to *note tkinter.colorchooser: 10f. to
     return RGB triplet of ints instead of floats.  Patch by Cheryl
     Sabella.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43102

   (2) https://bugs.python.org/issue43108

   (3) https://bugs.python.org/issue42944

   (4) https://bugs.python.org/issue42931

   (5) https://bugs.python.org/issue42780

   (6) https://bugs.python.org/issue42851

   (7) https://bugs.python.org/issue41748

   (8) https://bugs.python.org/issue42759

   (9) https://bugs.python.org/issue42756

   (10) https://bugs.python.org/issue23328

   (11) https://bugs.python.org/issue42655

   (12) https://bugs.python.org/issue42727

   (13) https://bugs.python.org/issue42681

   (14) https://bugs.python.org/issue37961

   (15) https://bugs.python.org/issue42630

   (16) https://bugs.python.org/issue42644

   (17) https://bugs.python.org/issue36541

   (18) https://bugs.python.org/issue42517

   (19) https://bugs.python.org/issue42678

   (20) https://bugs.python.org/issue42532

   (21) https://bugs.python.org/issue42388

   (22) https://bugs.python.org/issue34463

   (23) https://bugs.python.org/issue42375

   (24) https://bugs.python.org/issue42384

   (25) https://bugs.python.org/issue42383

   (26) https://bugs.python.org/issue42318

   (27) https://bugs.python.org/issue42163

   (28) https://bugs.python.org/issue39825

   (29) https://bugs.python.org/issue42059

   (30) https://bugs.python.org/issue39101

   (31) https://bugs.python.org/issue42005

   (32) https://bugs.python.org/issue41907

   (33) https://bugs.python.org/issue41889

   (34) https://bugs.python.org/issue41891

   (35) https://bugs.python.org/issue41604

   (36) https://bugs.python.org/issue40219

   (37) https://bugs.python.org/issue40084

   (38) https://bugs.python.org/issue39068

   (39) https://bugs.python.org/issue33289


File: python.info,  Node: Documentation<9>,  Next: Tests<7>,  Prev: Library<9>,  Up: Python 3 9 2 release candidate 1

1.19.10.4 Documentation
.......................

   - bpo-40304(1): Fix doc for type(name, bases, dict).  Patch by Boris
     Verkhovskiy and Éric Araujo.

   - bpo-42811(2): Updated importlib.utils.resolve_name() doc to use
     __spec__.parent instead of __package__.  (Thanks Yair Frid.)

   - bpo-17140(3): Add documentation for the *note
     multiprocessing.pool.ThreadPool: fce. class.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40304

   (2) https://bugs.python.org/issue42811

   (3) https://bugs.python.org/issue17140


File: python.info,  Node: Tests<7>,  Next: Build<6>,  Prev: Documentation<9>,  Up: Python 3 9 2 release candidate 1

1.19.10.5 Tests
...............

   - bpo-42794(1): Update test_nntplib to use offical group name of
     news.aioe.org for testing.  Patch by Dong-hee Na.

   - bpo-40810(2): In *note sqlite3: f2, fix ‘CheckTraceCallbackContent’
     for SQLite pre 3.7.15.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42794

   (2) https://bugs.python.org/issue40810


File: python.info,  Node: Build<6>,  Next: Windows<8>,  Prev: Tests<7>,  Up: Python 3 9 2 release candidate 1

1.19.10.6 Build
...............

   - bpo-43174(1): Windows build now uses ‘/utf-8’ compiler option.

   - bpo-42692(2): Fix __builtin_available check on older compilers.
     Patch by Joshua Root.

   - bpo-42604(3): Now all platforms use a value for the “EXT_SUFFIX”
     build variable derived from SOABI (for instance in freeBSD,
     “EXT_SUFFIX” is now “.cpython-310d.so” instead of “.so”).
     Previosuly only Linux, Mac and VxWorks were using a value for
     “EXT_SUFFIX” that included “SOABI”.

   - bpo-42598(4): Fix implicit function declarations in configure which
     could have resulted in incorrect configuration checks.  Patch
     contributed by Joshua Root.

   - bpo-29076(5): Add fish shell support to macOS installer.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43174

   (2) https://bugs.python.org/issue42692

   (3) https://bugs.python.org/issue42604

   (4) https://bugs.python.org/issue42598

   (5) https://bugs.python.org/issue29076


File: python.info,  Node: Windows<8>,  Next: macOS<7>,  Prev: Build<6>,  Up: Python 3 9 2 release candidate 1

1.19.10.7 Windows
.................

   - bpo-41837(1): Updated Windows installer to include OpenSSL 1.1.1i

   - bpo-42584(2): Upgrade Windows installer to use SQLite 3.34.0.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41837

   (2) https://bugs.python.org/issue42584


File: python.info,  Node: macOS<7>,  Next: IDLE<7>,  Prev: Windows<8>,  Up: Python 3 9 2 release candidate 1

1.19.10.8 macOS
...............

   - bpo-42504(1): Ensure that the value of
     sysconfig.get_config_var(‘MACOSX_DEPLOYMENT_TARGET’) is always a
     string, even in when the value is parsable as an integer.

   - bpo-42361(2): Update macOS installer build to use Tcl/Tk 8.6.11
     (rc2, expected to be final release).

   - bpo-41837(3): Update macOS installer build to use OpenSSL 1.1.1i.

   - bpo-42584(4): Update macOS installer to use SQLite 3.34.0.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42504

   (2) https://bugs.python.org/issue42361

   (3) https://bugs.python.org/issue41837

   (4) https://bugs.python.org/issue42584


File: python.info,  Node: IDLE<7>,  Next: Tools/Demos<3>,  Prev: macOS<7>,  Up: Python 3 9 2 release candidate 1

1.19.10.9 IDLE
..............

   - bpo-43008(1): Make IDLE invoke *note sys.excepthook(): f24. in
     normal, 2-process mode.  Patch by Ken Hilton.

   - bpo-33065(2): Fix problem debugging user classes with __repr__
     method.

   - bpo-23544(3): Disable Debug=>Stack Viewer when user code is running
     or Debugger is active, to prevent hang or crash.  Patch by Zackery
     Spytz.

   - bpo-32631(4): Finish zzdummy example extension module: make menu
     entries work; add docstrings and tests with 100% coverage.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43008

   (2) https://bugs.python.org/issue33065

   (3) https://bugs.python.org/issue23544

   (4) https://bugs.python.org/issue32631


File: python.info,  Node: Tools/Demos<3>,  Next: C API<4>,  Prev: IDLE<7>,  Up: Python 3 9 2 release candidate 1

1.19.10.10 Tools/Demos
......................

   - bpo-42726(1): Fixed Python 3 compatibility issue with
     gdb/libpython.py handling of attribute dictionaries.

   - bpo-42613(2): Fix ‘freeze.py’ tool to use the prope config and
     library directories.  Patch by Victor Stinner.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42726

   (2) https://bugs.python.org/issue42613


File: python.info,  Node: C API<4>,  Prev: Tools/Demos<3>,  Up: Python 3 9 2 release candidate 1

1.19.10.11 C API
................

   - bpo-43030(1): Fixed a compiler warning in *note
     Py_UNICODE_ISSPACE(): fd6. on platforms with signed ‘wchar_t’.

   - bpo-42591(2): Export the ‘Py_FrozenMain()’ function: fix a Python
     3.9.0 regression.  Python 3.9 uses ‘-fvisibility=hidden’ and the
     function was not exported explicitly and so not exported.

   - bpo-40052(3): Fix an alignment build warning/error in function
     ‘PyVectorcall_Function()’.  Patch by Andreas Schneider, Antoine
     Pitrou and Petr Viktorin.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue43030

   (2) https://bugs.python.org/issue42591

   (3) https://bugs.python.org/issue40052


File: python.info,  Node: Python 3 9 1 final,  Next: Python 3 9 1 release candidate 1,  Prev: Python 3 9 2 release candidate 1,  Up: Changelog

1.19.11 Python 3.9.1 final
--------------------------

`Release date: 2020-12-07'

* Menu:

* Core and Builtins: Core and Builtins<10>.
* Library: Library<10>.
* Tests: Tests<8>.
* macOS: macOS<8>.
* IDLE: IDLE<8>.


File: python.info,  Node: Core and Builtins<10>,  Next: Library<10>,  Up: Python 3 9 1 final

1.19.11.1 Core and Builtins
...........................

   - bpo-42576(1): ‘types.GenericAlias’ will now raise a ‘TypeError’
     when attempting to initialize with a keyword argument.  Previously,
     this would cause the interpreter to crash if the interpreter was
     compiled with debug symbols.  This does not affect interpreters
     compiled for release.  Patch by Ken Jin.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42576


File: python.info,  Node: Library<10>,  Next: Tests<8>,  Prev: Core and Builtins<10>,  Up: Python 3 9 1 final

1.19.11.2 Library
.................

   - bpo-5054(1): CGIHTTPRequestHandler.run_cgi() HTTP_ACCEPT improperly
     parsed.  Replace the special purpose getallmatchingheaders with
     generic get_all method and add relevant tests.

     Original Patch by Martin Panter.  Modified by Senthil Kumaran.

   - bpo-17735(2): ‘inspect.findsource()’ now raises *note OSError: 304.
     instead of *note IndexError: f36. when ‘co_lineno’ of a code object
     is greater than the file length.  This can happen, for example,
     when a file is edited after it was imported.  PR by Irit Katriel.

   - bpo-42116(3): Fix handling of trailing comments by *note
     inspect.getsource(): fda.

   - bpo-42487(4): ChainMap.__iter__ no longer calls __getitem__ on
     underlying maps

   - bpo-42482(5): *note TracebackException: 865. no longer holds a
     reference to the exception’s traceback object.  Consequently,
     instances of TracebackException for equivalent but non-equal
     exceptions now compare as equal.

   - bpo-42406(6): We fixed an issue in ‘pickle.whichmodule’ in which
     importing *note multiprocessing: b7. could change the how pickle
     identifies which module an object belongs to, potentially breaking
     the unpickling of those objects.

   - bpo-34215(7): Clarify the error message for *note
     asyncio.IncompleteReadError: fdb. when ‘expected’ is ‘None’.

   - bpo-12800(8): Extracting a symlink from a tarball should succeed
     and overwrite the symlink if it already exists.  The fix is to
     remove the existing file or symlink before extraction.  Based on
     patch by Chris AtLee, Jeffrey Kintscher, and Senthil Kumaran.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5054

   (2) https://bugs.python.org/issue17735

   (3) https://bugs.python.org/issue42116

   (4) https://bugs.python.org/issue42487

   (5) https://bugs.python.org/issue42482

   (6) https://bugs.python.org/issue42406

   (7) https://bugs.python.org/issue34215

   (8) https://bugs.python.org/issue12800


File: python.info,  Node: Tests<8>,  Next: macOS<8>,  Prev: Library<10>,  Up: Python 3 9 1 final

1.19.11.3 Tests
...............

   - bpo-41473(1): Reenable test_gdb on gdb 9.2 and newer:
     ‘https://bugzilla.redhat.com/show_bug.cgi?id=1866884’ bug is fixed
     in gdb 10.1.

   - bpo-42553(2): Fix ‘test_asyncio.test_call_later()’ race condition:
     don’t measure asyncio performance in the ‘call_later()’ unit test.
     The test failed randomly on the CI.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41473

   (2) https://bugs.python.org/issue42553


File: python.info,  Node: macOS<8>,  Next: IDLE<8>,  Prev: Tests<8>,  Up: Python 3 9 1 final

1.19.11.4 macOS
...............

   - bpo-41116(1): If no explicit macOS SDK was specified, setup.py
     should check for Tcl and TK frameworks in /Library/Frameworks; the
     previous commit inadvertently broke that test.

   - bpo-42504(2): Fix build on macOS Big Sur when
     MACOSX_DEPLOYMENT_TARGET=11

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41116

   (2) https://bugs.python.org/issue42504


File: python.info,  Node: IDLE<8>,  Prev: macOS<8>,  Up: Python 3 9 1 final

1.19.11.5 IDLE
..............

   - bpo-42508(1): Keep IDLE running on macOS. Remove obsolete
     workaround that prevented running files with shortcuts when using
     new universal2 installers built on macOS 11.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42508


File: python.info,  Node: Python 3 9 1 release candidate 1,  Next: Python 3 9 0 final,  Prev: Python 3 9 1 final,  Up: Changelog

1.19.12 Python 3.9.1 release candidate 1
----------------------------------------

`Release date: 2020-11-24'

* Menu:

* Security: Security<6>.
* Core and Builtins: Core and Builtins<11>.
* Library: Library<11>.
* Documentation: Documentation<10>.
* Tests: Tests<9>.
* Build: Build<7>.
* Windows: Windows<9>.
* macOS: macOS<9>.
* IDLE: IDLE<9>.
* C API: C API<5>.


File: python.info,  Node: Security<6>,  Next: Core and Builtins<11>,  Up: Python 3 9 1 release candidate 1

1.19.12.1 Security
..................

   - bpo-42103(1): Prevented potential DoS attack via CPU and RAM
     exhaustion when processing malformed Apple Property List files in
     binary format.

   - bpo-42051(2): The *note plistlib: cf. module no longer accepts
     entity declarations in XML plist files to avoid XML
     vulnerabilities.  This should not affect users as entity
     declarations are not used in regular plist files.

   - bpo-40791(3): Add ‘volatile’ to the accumulator variable in
     ‘hmac.compare_digest’, making constant-time-defeating optimizations
     less likely.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42103

   (2) https://bugs.python.org/issue42051

   (3) https://bugs.python.org/issue40791


File: python.info,  Node: Core and Builtins<11>,  Next: Library<11>,  Prev: Security<6>,  Up: Python 3 9 1 release candidate 1

1.19.12.2 Core and Builtins
...........................

   - bpo-41686(1): On Windows, the ‘SIGINT’ event,
     ‘_PyOS_SigintEvent()’, is now created even if Python is configured
     to not install signal handlers (if *note
     PyConfig.install_signal_handlers: fe2. equals to 0, or
     ‘Py_InitializeEx(0)’).

   - bpo-42381(2): Allow assignment expressions in set literals and set
     comprehensions as per PEP 572.  Patch by Pablo Galindo.

   - bpo-42374(3): Fix a regression introduced by the new parser, where
     an unparenthesized walrus operator was not allowed within generator
     expressions.

   - bpo-42296(4): On Windows, fix a regression in signal handling which
     prevented to interrupt a program using CTRL+C. The signal handler
     can be run in a thread different than the Python thread, in which
     case the test deciding if the thread can handle signals is wrong.

   - bpo-42332(5): *note types.GenericAlias: 27c. objects can now be the
     targets of weakrefs.

   - bpo-42218(6): Fixed a bug in the PEG parser that was causing
     crashes in debug mode.  Now errors are checked in left-recursive
     rules to avoid cases where such errors do not get handled in time
     and appear as long-distance crashes in other places.

   - bpo-42214(7): Fixed a possible crash in the PEG parser when
     checking for the ‘!=’ token in the ‘barry_as_flufl’ rule.  Patch by
     Pablo Galindo.

   - bpo-42143(8): Fix handling of errors during creation of
     ‘PyFunctionObject’, which resulted in operations on uninitialized
     memory.  Patch by Yonatan Goldschmidt.

   - bpo-41659(9): Fix a bug in the parser, where a curly brace
     following a ‘primary’ didn’t fail immediately.  This led to invalid
     expressions like ‘a {b}’ to throw a *note SyntaxError: 55a. with a
     wrong offset, or invalid expressions ending with a curly brace like
     ‘a {’ to not fail immediately in the REPL.

   - bpo-42150(10): Fix possible buffer overflow in the new parser when
     checking for continuation lines.  Patch by Pablo Galindo.

   - bpo-42123(11): Run the parser two times.  On the first run, disable
     all the rules that only generate better error messages to gain
     performance.  If there’s a parse failure, run the parser a second
     time with those enabled.

   - bpo-42057(12): Fix peephole optimizer misoptimize conditional jump
     + JUMP_IF_NOT_EXC_MATCH pair.

   - bpo-41984(13): The garbage collector now tracks all user-defined
     classes.  Patch by Brandt Bucher.

   - bpo-41993(14): Fixed potential issues with removing not completely
     initialized module from ‘sys.modules’ when import fails.

   - bpo-41979(15): Star-unpacking is now allowed for with item’s
     targets in the PEG parser.

   - bpo-41909(16): Fixed stack overflow in *note issubclass(): 553. and
     *note isinstance(): 552. when getting the ‘__bases__’ attribute
     leads to infinite recursion.

   - bpo-41894(17): When loading a native module and a load failure
     occurs, prevent a possible UnicodeDecodeError when not running in a
     UTF-8 locale by decoding the load error message using the current
     locale’s encoding.

   - bpo-39934(18): Correctly count control blocks in ‘except’ in
     compiler.  Ensures that a syntax error, rather a fatal error,
     occurs for deeply nested, named exception handlers.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41686

   (2) https://bugs.python.org/issue42381

   (3) https://bugs.python.org/issue42374

   (4) https://bugs.python.org/issue42296

   (5) https://bugs.python.org/issue42332

   (6) https://bugs.python.org/issue42218

   (7) https://bugs.python.org/issue42214

   (8) https://bugs.python.org/issue42143

   (9) https://bugs.python.org/issue41659

   (10) https://bugs.python.org/issue42150

   (11) https://bugs.python.org/issue42123

   (12) https://bugs.python.org/issue42057

   (13) https://bugs.python.org/issue41984

   (14) https://bugs.python.org/issue41993

   (15) https://bugs.python.org/issue41979

   (16) https://bugs.python.org/issue41909

   (17) https://bugs.python.org/issue41894

   (18) https://bugs.python.org/issue39934


File: python.info,  Node: Library<11>,  Next: Documentation<10>,  Prev: Core and Builtins<11>,  Up: Python 3 9 1 release candidate 1

1.19.12.3 Library
.................

   - bpo-42328(1): Fixed *note tkinter.ttk.Style.map(): fe4.  The
     function accepts now the representation of the default state as
     empty sequence (as returned by ‘Style.map()’).  The structure of
     the result is now the same on all platform and does not depend on
     the value of ‘wantobjects’.

   - bpo-42345(2): Fix various issues with ‘typing.Literal’ parameter
     handling (flatten, deduplicate, use type to cache key).  Patch
     provided by Yurii Karabas.

   - bpo-42350(3): Fix the *note threading.Thread: 21a. class at fork:
     do nothing if the thread is already stopped (ex: fork called at
     Python exit).  Previously, an error was logged in the child
     process.

   - bpo-42014(4): The ‘onerror’ callback from ‘shutil.rmtree’ now
     receives correct function when ‘os.open’ fails.

   - bpo-42237(5): Fix *note os.sendfile(): 461. on illumos.

   - bpo-42249(6): Fixed writing binary Plist files larger than 4 GiB.

   - bpo-35455(7): On Solaris, *note thread_time(): 1e7. is now
     implemented with ‘gethrvtime()’ because
     ‘clock_gettime(CLOCK_THREAD_CPUTIME_ID)’ is not always available.
     Patch by Jakub Kulik.

   - bpo-42233(8): The *note repr(): 8b9. of *note typing: 122. types
     containing *note Generic Alias Types: fe5. previously did not show
     the parameterized types in the ‘GenericAlias’.  They have now been
     changed to do so.

   - bpo-41754(9): webbrowser: Ignore `NotADirectoryError' when calling
     ‘xdg-settings’.

   - bpo-29566(10): ‘binhex.binhex()’ consistently writes macOS 9 line
     endings.

   - bpo-42183(11): Fix a stack overflow error for asyncio Task or
     Future repr().

     The overflow occurs under some circumstances when a Task or Future
     recursively returns itself.

   - bpo-42146(12): Fix memory leak in *note subprocess.Popen(): 3db. in
     case an uid (gid) specified in ‘user’ (‘group’, ‘extra_groups’)
     overflows ‘uid_t’ (‘gid_t’).

   - bpo-42140(13): Improve asyncio.wait function to create the futures
     set just one time.

   - bpo-42103(14): ‘InvalidFileException’ and *note RecursionError:
     727. are now the only errors caused by loading malformed binary
     Plist file (previously ValueError and TypeError could be raised in
     some specific cases).

   - bpo-41052(15): Pickling heap types implemented in C with protocols
     0 and 1 raises now an error instead of producing incorrect data.

   - bpo-41491(16): plistlib: fix parsing XML plists with hexadecimal
     integer values

   - bpo-42065(17): Fix an incorrectly formatted error from
     ‘_codecs.charmap_decode()’ when called with a mapped value outside
     the range of valid Unicode code points.  PR by Max Bernstein.

   - bpo-41966(18): Fix pickling pure Python *note datetime.time: 5ed.
     subclasses.  Patch by Dean Inwood.

   - bpo-41976(19): Fixed a bug that was causing *note
     ctypes.util.find_library(): 701. to return ‘None’ when triying to
     locate a library in an environment when gcc>=9 is available and
     ‘ldconfig’ is not.  Patch by Pablo Galindo

   - bpo-41900(20): C14N 2.0 serialisation in xml.etree.ElementTree
     failed for unprefixed attributes when a default namespace was
     defined.

   - bpo-41840(21): Fix a bug in the *note symtable: fc. module that was
     causing module-scope global variables to not be reported as both
     local and global.  Patch by Pablo Galindo.

   - bpo-41831(22): ‘str()’ for the ‘type’ attribute of the
     ‘tkinter.Event’ object always returns now the numeric code returned
     by Tk instead of the name of the event type.

   - bpo-41817(23): fix ‘tkinter.EventType’ Enum so all members are
     strings, and none are tuples

   - bpo-41815(24): Fix SQLite3 segfault when backing up closed
     database.  Patch contributed by Peter David McCormick.

   - bpo-41316(25): Fix the *note tarfile: 101. module to write only
     basename of TAR file to GZIP compression header.

   - bpo-16396(26): Allow ‘ctypes.wintypes’ to be imported on
     non-Windows systems.

   - bpo-40592(27): *note shutil.which(): fe6. now ignores empty entries
     in ‘PATHEXT’ instead of treating them as a match.

   - bpo-40550(28): Fix time-of-check/time-of-action issue in
     subprocess.Popen.send_signal.

   - bpo-40492(29): Fix ‘--outfile’ for *note cProfile: 27. / *note
     profile: d3. not writing the output file in the original directory
     when the program being profiled changes the working directory.  PR
     by Anthony Sottile.

   - bpo-40105(30): ZipFile truncates files to avoid corruption when a
     shorter comment is provided in append (“a”) mode.  Patch by Jan
     Mazur.

   - bpo-27321(31): Fixed KeyError exception when flattening an email to
     a string attempts to replace a non-existent
     Content-Transfer-Encoding header.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42328

   (2) https://bugs.python.org/issue42345

   (3) https://bugs.python.org/issue42350

   (4) https://bugs.python.org/issue42014

   (5) https://bugs.python.org/issue42237

   (6) https://bugs.python.org/issue42249

   (7) https://bugs.python.org/issue35455

   (8) https://bugs.python.org/issue42233

   (9) https://bugs.python.org/issue41754

   (10) https://bugs.python.org/issue29566

   (11) https://bugs.python.org/issue42183

   (12) https://bugs.python.org/issue42146

   (13) https://bugs.python.org/issue42140

   (14) https://bugs.python.org/issue42103

   (15) https://bugs.python.org/issue41052

   (16) https://bugs.python.org/issue41491

   (17) https://bugs.python.org/issue42065

   (18) https://bugs.python.org/issue41966

   (19) https://bugs.python.org/issue41976

   (20) https://bugs.python.org/issue41900

   (21) https://bugs.python.org/issue41840

   (22) https://bugs.python.org/issue41831

   (23) https://bugs.python.org/issue41817

   (24) https://bugs.python.org/issue41815

   (25) https://bugs.python.org/issue41316

   (26) https://bugs.python.org/issue16396

   (27) https://bugs.python.org/issue40592

   (28) https://bugs.python.org/issue40550

   (29) https://bugs.python.org/issue40492

   (30) https://bugs.python.org/issue40105

   (31) https://bugs.python.org/issue27321


File: python.info,  Node: Documentation<10>,  Next: Tests<9>,  Prev: Library<11>,  Up: Python 3 9 1 release candidate 1

1.19.12.4 Documentation
.......................

   - bpo-42153(1): Fix the URL for the IMAP protocol documents.

   - bpo-42061(2): Document __format__ functionality for IP addresses.

   - bpo-41910(3): Document the default implementation of *note
     object.__eq__: 44b.

   - bpo-42010(4): Clarify that subscription expressions are also valid
     for certain *note classes: fe8. and *note types: fe9. in the
     standard library, and for user-defined classes and types if the
     classmethod *note __class_getitem__(): 437. is provided.

   - bpo-41805(5): Documented *note generic alias type: fe5. and *note
     types.GenericAlias: 27c.  Also added an entry in glossary for *note
     generic types: fea.

   - bpo-41774(6): In Programming FAQ “Sequences (Tuples/Lists)”
     section, add “How do you remove multiple items from a list”.

   - bpo-35293(7): Fix RemovedInSphinx40Warning when building the
     documentation.  Patch by Dong-hee Na.

   - bpo-41726(8): Update the refcounts info of
     ‘PyType_FromModuleAndSpec’.

   - bpo-39693(9): Fix tarfile’s extractfile documentation

   - bpo-39416(10): Document some restrictions on the default string
     representations of numeric classes.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42153

   (2) https://bugs.python.org/issue42061

   (3) https://bugs.python.org/issue41910

   (4) https://bugs.python.org/issue42010

   (5) https://bugs.python.org/issue41805

   (6) https://bugs.python.org/issue41774

   (7) https://bugs.python.org/issue35293

   (8) https://bugs.python.org/issue41726

   (9) https://bugs.python.org/issue39693

   (10) https://bugs.python.org/issue39416


File: python.info,  Node: Tests<9>,  Next: Build<7>,  Prev: Documentation<10>,  Up: Python 3 9 1 release candidate 1

1.19.12.5 Tests
...............

   - bpo-40754(1): Include ‘_testinternalcapi’ module in Windows
     installer for test suite

   - bpo-41739(2): Fix
     test_logging.test_race_between_set_target_and_flush(): the test now
     waits until all threads complete to avoid leaking running threads.

   - bpo-41970(3): Avoid a test failure in ‘test_lib2to3’ if the module
     has already imported at the time the test executes.  Patch by Pablo
     Galindo.

   - bpo-41944(4): Tests for CJK codecs no longer call ‘eval()’ on
     content received via HTTP.

   - bpo-41939(5): Fix test_site.test_license_exists_at_url(): call
     ‘urllib.request.urlcleanup()’ to reset the global
     ‘urllib.request._opener’.  Patch by Victor Stinner.

   - bpo-41561(6): test_ssl: skip test_min_max_version_mismatch when TLS
     1.0 is not available

   - bpo-41602(7): Add tests for SIGINT handling in the runpy module.

   - bpo-41306(8): Fixed a failure in ‘test_tk.test_widgets.ScaleTest’
     happening when executing the test with Tk 8.6.10.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40754

   (2) https://bugs.python.org/issue41739

   (3) https://bugs.python.org/issue41970

   (4) https://bugs.python.org/issue41944

   (5) https://bugs.python.org/issue41939

   (6) https://bugs.python.org/issue41561

   (7) https://bugs.python.org/issue41602

   (8) https://bugs.python.org/issue41306


File: python.info,  Node: Build<7>,  Next: Windows<9>,  Prev: Tests<9>,  Up: Python 3 9 1 release candidate 1

1.19.12.6 Build
...............

   - bpo-42398(1): Fix a race condition in “make regen-all” when make
     -jN option is used to run jobs in parallel.  The clinic.py script
     now only use atomic write to write files.  Moveover, generated
     files are now left unchanged if the content does not change, to not
     change the file modification time.

   - bpo-41617(2): Fix building ‘pycore_bitutils.h’ internal header on
     old clang version without ‘__builtin_bswap16()’ (ex: Xcode 4.6.3 on
     Mac OS X 10.7).  Patch by Joshua Root and Victor Stinner.

   - bpo-38249(3): Update *note Py_UNREACHABLE: 527. to use
     __builtin_unreachable() if only the compiler is able to use it.
     Patch by Dong-hee Na.

   - bpo-40998(4): Addressed three compiler warnings found by undefined
     behavior sanitizer (ubsan).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42398

   (2) https://bugs.python.org/issue41617

   (3) https://bugs.python.org/issue38249

   (4) https://bugs.python.org/issue40998


File: python.info,  Node: Windows<9>,  Next: macOS<9>,  Prev: Build<7>,  Up: Python 3 9 1 release candidate 1

1.19.12.7 Windows
.................

   - bpo-42120(1): Remove macro definition of ‘copysign’ (to
     ‘_copysign’) in headers.

   - bpo-38439(2): Updates the icons for IDLE in the Windows Store
     package.

   - bpo-41744(3): Fixes automatic import of props file when using the
     Nuget package.

   - bpo-41557(4): Update Windows installer to use SQLite 3.33.0.

   - bpo-38324(5): Avoid Unicode errors when accessing certain locale
     data on Windows.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42120

   (2) https://bugs.python.org/issue38439

   (3) https://bugs.python.org/issue41744

   (4) https://bugs.python.org/issue41557

   (5) https://bugs.python.org/issue38324


File: python.info,  Node: macOS<9>,  Next: IDLE<9>,  Prev: Windows<9>,  Up: Python 3 9 1 release candidate 1

1.19.12.8 macOS
...............

   - bpo-41116(1): Ensure distutils.unixxcompiler.find_library_file can
     find system provided libraries on macOS 11.

   - bpo-41100(2): Add support for macOS 11 and Apple Silicon systems.

     It is now possible to build “Universal 2” binaries using
     “–enable-universalsdk –with-universal-archs=universal2”.

     Binaries build on later macOS versions can be deployed back to
     older versions (tested up to macOS 10.9), when using the correct
     deployment target.  This is tested using Xcode 11 and later.

   - bpo-38443(3): The ‘--enable-universalsdk’ and
     ‘--with-universal-archs’ options for the configure script now check
     that the specified architectures can be used.

   - bpo-41471(4): Ignore invalid prefix lengths in system proxy
     excludes.

   - bpo-41557(5): Update macOS installer to use SQLite 3.33.0.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41116

   (2) https://bugs.python.org/issue41100

   (3) https://bugs.python.org/issue38443

   (4) https://bugs.python.org/issue41471

   (5) https://bugs.python.org/issue41557


File: python.info,  Node: IDLE<9>,  Next: C API<5>,  Prev: macOS<9>,  Up: Python 3 9 1 release candidate 1

1.19.12.9 IDLE
..............

   - bpo-42426(1): Fix reporting offset of the RE error in searchengine.

   - bpo-42415(2): Get docstrings for IDLE calltips more often by using
     inspect.getdoc.

   - bpo-33987(3): Mostly finish using ttk widgets, mainly for editor,
     settings, and searches.  Some patches by Mark Roseman.

   - bpo-41775(4): Use ‘IDLE Shell’ as shell title

   - bpo-35764(5): Rewrite the Calltips doc section.

   - bpo-40181(6): In calltips, stop reminding that ‘/’ marks the end of
     positional-only arguments.

   - bpo-40511(7): Typing opening and closing parentheses inside the
     parentheses of a function call will no longer cause unnecessary
     “flashing” off and on of an existing open call-tip, e.g.  when
     typed in a string literal.

   - bpo-38439(8): Add a 256×256 pixel IDLE icon to the Windows .ico
     file.  Created by Andrew Clover.  Remove the low-color gif
     variations from the .ico file.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42426

   (2) https://bugs.python.org/issue42415

   (3) https://bugs.python.org/issue33987

   (4) https://bugs.python.org/issue41775

   (5) https://bugs.python.org/issue35764

   (6) https://bugs.python.org/issue40181

   (7) https://bugs.python.org/issue40511

   (8) https://bugs.python.org/issue38439


File: python.info,  Node: C API<5>,  Prev: IDLE<9>,  Up: Python 3 9 1 release candidate 1

1.19.12.10 C API
................

   - bpo-42015(1): Fix potential crash in deallocating method objects
     when dynamically allocated ‘PyMethodDef’’s lifetime is managed
     through the ‘self’ argument of a ‘PyCFunction’.

   - bpo-41986(2): ‘Py_FileSystemDefaultEncodeErrors’ and ‘Py_UTF8Mode’
     are available again in limited API.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue42015

   (2) https://bugs.python.org/issue41986


File: python.info,  Node: Python 3 9 0 final,  Next: Python 3 9 0 release candidate 2,  Prev: Python 3 9 1 release candidate 1,  Up: Changelog

1.19.13 Python 3.9.0 final
--------------------------

`Release date: 2020-10-04'

* Menu:

* Library: Library<12>.
* Tests: Tests<10>.
* Build: Build<8>.


File: python.info,  Node: Library<12>,  Next: Tests<10>,  Up: Python 3 9 0 final

1.19.13.1 Library
.................

   - bpo-41815(1): Fix SQLite3 segfault when backing up closed database.
     Patch contributed by Peter David McCormick.

   - bpo-41662(2): No longer override exceptions raised in ‘__len__()’
     of a sequence of parameters in *note sqlite3: f2. with *note
     ProgrammingError: ff3.

   - bpo-41662(3): Fixed crash when mutate list of parameters during
     iteration in *note sqlite3: f2.

   - bpo-39728(4): fix default ‘_missing_’ so a duplicate *note
     ValueError: 16d. is not set as the ‘__context__’ of the original
     *note ValueError: 16d.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41815

   (2) https://bugs.python.org/issue41662

   (3) https://bugs.python.org/issue41662

   (4) https://bugs.python.org/issue39728


File: python.info,  Node: Tests<10>,  Next: Build<8>,  Prev: Library<12>,  Up: Python 3 9 0 final

1.19.13.2 Tests
...............

   - bpo-41602(1): Add tests for SIGINT handling in the runpy module.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41602


File: python.info,  Node: Build<8>,  Prev: Tests<10>,  Up: Python 3 9 0 final

1.19.13.3 Build
...............

   - bpo-38249(1): Update *note Py_UNREACHABLE: 527. to use
     __builtin_unreachable() if only the compiler is able to use it.
     Patch by Dong-hee Na.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38249


File: python.info,  Node: Python 3 9 0 release candidate 2,  Next: Python 3 9 0 release candidate 1,  Prev: Python 3 9 0 final,  Up: Changelog

1.19.14 Python 3.9.0 release candidate 2
----------------------------------------

`Release date: 2020-09-16'

* Menu:

* Core and Builtins: Core and Builtins<12>.
* Library: Library<13>.
* Documentation: Documentation<11>.
* Tests: Tests<11>.
* Build: Build<9>.
* Windows: Windows<10>.
* C API: C API<6>.


File: python.info,  Node: Core and Builtins<12>,  Next: Library<13>,  Up: Python 3 9 0 release candidate 2

1.19.14.1 Core and Builtins
...........................

   - bpo-41780(1): Fix *note __dir__(): 42b. of *note
     types.GenericAlias: 27c.  Patch by Batuhan Taskaya.

   - bpo-41690(2): Fix a possible stack overflow in the parser when
     parsing functions and classes with a huge ammount of arguments.
     Patch by Pablo Galindo.

   - bpo-41681(3): Fixes the wrong error description in the error raised
     by using 2 ‘,’ in format string in f-string and *note str.format():
     5d5.

   - bpo-41654(4): Fix a crash that occurred when destroying subclasses
     of *note MemoryError: f69.  Patch by Pablo Galindo.

   - bpo-41631(5): The ‘_ast’ module uses again a global state.  Using a
     module state per module instance is causing subtle practical
     problems.  For example, the Mercurial project replaces the
     ‘__import__()’ function to implement lazy import, whereas Python
     expected that ‘import _ast’ always return a fully initialized
     ‘_ast’ module.

   - bpo-41533(6): Free the stack allocated in ‘va_build_stack’ if
     ‘do_mkstack’ fails and the stack is not a ‘small_stack’.

   - bpo-41531(7): Fix a bug that was dropping keys when compiling dict
     literals with more than 0xFFFF elements.  Patch by Pablo Galindo.

   - bpo-41525(8): The output of ‘python --help’ contains now only ASCII
     characters.

   - bpo-29590(9): Make the stack trace correct after calling *note
     generator.throw(): ff8. on a generator that has yielded from a
     ‘yield from’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41780

   (2) https://bugs.python.org/issue41690

   (3) https://bugs.python.org/issue41681

   (4) https://bugs.python.org/issue41654

   (5) https://bugs.python.org/issue41631

   (6) https://bugs.python.org/issue41533

   (7) https://bugs.python.org/issue41531

   (8) https://bugs.python.org/issue41525

   (9) https://bugs.python.org/issue29590


File: python.info,  Node: Library<13>,  Next: Documentation<11>,  Prev: Core and Builtins<12>,  Up: Python 3 9 0 release candidate 2

1.19.14.2 Library
.................

   - bpo-41517(1): fix bug allowing Enums to be extended via multiple
     inheritance

   - bpo-39587(2): use the correct mix-in data type when constructing
     Enums

   - bpo-41789(3): Honor *note object: 3d2. overrides in ‘Enum’ class
     creation (specifically, ‘__str__’, ‘__repr__’, ‘__format__’, and
     ‘__reduce_ex__’).

   - bpo-39651(4): Fix a race condition in the ‘call_soon_threadsafe()’
     method of ‘asyncio.ProactorEventLoop’: do nothing if the self-pipe
     socket has been closed.

   - bpo-41720(5): Fixed ‘turtle.Vec2D.__rmul__()’ for arguments which
     are not int or float.

   - bpo-41696(6): Fix handling of debug mode in *note asyncio.run():
     18d.  This allows setting ‘PYTHONASYNCIODEBUG’ or ‘-X dev’ to
     enable asyncio debug mode when using *note asyncio.run(): 18d.

   - bpo-41687(7): Fix implementation of sendfile to be compatible with
     Solaris.

   - bpo-39010(8): Restarting a ‘ProactorEventLoop’ on Windows no longer
     logs spurious ‘ConnectionResetErrors’.

   - bpo-41609(9): The pdb whatis command correctly reports instance
     methods as ‘Method’ rather than ‘Function’.

   - bpo-32751(10): When cancelling the task due to a timeout, *note
     asyncio.wait_for(): 191. will now wait until the cancellation is
     complete also in the case when `timeout' is <= 0, like it does with
     positive timeouts.

   - bpo-37658(11): *note asyncio.wait_for(): 191. now properly handles
     races between cancellation of itself and the completion of the
     wrapped awaitable.

   - bpo-40782(12): Change the method
     asyncio.AbstractEventLoop.run_in_executor to not be a coroutine.

   - bpo-41520(13): Fix *note codeop: 1c. regression that prevented
     turning compile warnings into errors.

   - bpo-41503(14): Fixed a race between setTarget and flush in
     logging.handlers.MemoryHandler.

   - bpo-41344(15): Prevent creating ‘shared_memory.SharedMemory’
     objects with ‘size=0’.

   - bpo-41025(16): Fixed an issue preventing the C implementation of
     *note zoneinfo.ZoneInfo: 17f. from being subclassed.

   - bpo-31122(17): ssl.wrap_socket() now raises ssl.SSLEOFError rather
     than OSError when peer closes connection during TLS negotiation

   - bpo-33660(18): Fix pathlib.PosixPath to resolve a relative path
     located on the root directory properly.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41517

   (2) https://bugs.python.org/issue39587

   (3) https://bugs.python.org/issue41789

   (4) https://bugs.python.org/issue39651

   (5) https://bugs.python.org/issue41720

   (6) https://bugs.python.org/issue41696

   (7) https://bugs.python.org/issue41687

   (8) https://bugs.python.org/issue39010

   (9) https://bugs.python.org/issue41609

   (10) https://bugs.python.org/issue32751

   (11) https://bugs.python.org/issue37658

   (12) https://bugs.python.org/issue40782

   (13) https://bugs.python.org/issue41520

   (14) https://bugs.python.org/issue41503

   (15) https://bugs.python.org/issue41344

   (16) https://bugs.python.org/issue41025

   (17) https://bugs.python.org/issue31122

   (18) https://bugs.python.org/issue33660


File: python.info,  Node: Documentation<11>,  Next: Tests<11>,  Prev: Library<13>,  Up: Python 3 9 0 release candidate 2

1.19.14.3 Documentation
.......................

   - bpo-37149(1): Change Shipman tkinter doc link from archive.org to
     TkDocs.  (The doc has been removed from the NMT server.)  The new
     link responds much faster and includes a short explanatory note.

   - bpo-41624(2): Fix the signature of *note typing.Coroutine: ffb.

   - bpo-40204(3): Enable Sphinx 3.2 ‘c_allow_pre_v3’ option and disable
     ‘c_warn_on_allowed_pre_v3’ option to make the documentation
     compatible with Sphinx 2 and Sphinx 3.

   - bpo-40979(4): Refactored typing.rst, arranging more than 70
     classes, functions, and decorators into new sub-sections.

   - bpo-39883(5): Make code, examples, and recipes in the Python
     documentation be licensed under the more permissive BSD0 license in
     addition to the existing Python 2.0 license.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37149

   (2) https://bugs.python.org/issue41624

   (3) https://bugs.python.org/issue40204

   (4) https://bugs.python.org/issue40979

   (5) https://bugs.python.org/issue39883


File: python.info,  Node: Tests<11>,  Next: Build<9>,  Prev: Documentation<11>,  Up: Python 3 9 0 release candidate 2

1.19.14.4 Tests
...............

   - bpo-41731(1): Make test_cmd_line_script pass with option ‘-vv’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41731


File: python.info,  Node: Build<9>,  Next: Windows<10>,  Prev: Tests<11>,  Up: Python 3 9 0 release candidate 2

1.19.14.5 Build
...............

   - bpo-41617(1): Fix ‘pycore_byteswap.h’ header file to support old
     clang versions: ‘__builtin_bswap16()’ is not available in LLVM
     clang 3.0.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41617


File: python.info,  Node: Windows<10>,  Next: C API<6>,  Prev: Build<9>,  Up: Python 3 9 0 release candidate 2

1.19.14.6 Windows
.................

   - bpo-41526(1): Fixed layout of final page of the installer by
     removing the special thanks to Mark Hammond (with his permission).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41526


File: python.info,  Node: C API<6>,  Prev: Windows<10>,  Up: Python 3 9 0 release candidate 2

1.19.14.7 C API
...............

   - bpo-41524(1): Fix bug in PyOS_mystrnicmp and PyOS_mystricmp that
     incremented pointers beyond the end of a string.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41524


File: python.info,  Node: Python 3 9 0 release candidate 1,  Next: Python 3 9 0 beta 5,  Prev: Python 3 9 0 release candidate 2,  Up: Changelog

1.19.15 Python 3.9.0 release candidate 1
----------------------------------------

`Release date: 2020-08-11'

* Menu:

* Core and Builtins: Core and Builtins<13>.
* Library: Library<14>.
* Documentation: Documentation<12>.
* Windows: Windows<11>.
* IDLE: IDLE<10>.


File: python.info,  Node: Core and Builtins<13>,  Next: Library<14>,  Up: Python 3 9 0 release candidate 1

1.19.15.1 Core and Builtins
...........................

   - bpo-38156(1): Handle interrupts that come after EOF correctly in
     ‘PyOS_StdioReadline’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38156


File: python.info,  Node: Library<14>,  Next: Documentation<12>,  Prev: Core and Builtins<13>,  Up: Python 3 9 0 release candidate 1

1.19.15.2 Library
.................

   - bpo-41497(1): Fix potential UnicodeDecodeError in dis module.

   - bpo-41490(2): Update *note ensurepip: 78. to install pip 20.2.1 and
     setuptools 49.2.1.

   - bpo-41467(3): On Windows, fix asyncio ‘recv_into()’ return value
     when the socket/pipe is closed (*note BrokenPipeError: a7e.):
     return ‘0’ rather than an empty byte string (‘b''’).

   - bpo-41425(4): Make tkinter doc example runnable.

   - bpo-41384(5): Raise TclError instead of TypeError when an unknown
     option is passed to tkinter.OptionMenu.

   - bpo-38731(6): Fix *note NameError: e40. in command-line interface
     of *note py_compile: d7.

   - bpo-41317(7): Use add_done_callback() in asyncio.loop.sock_accept()
     to unsubscribe reader early on cancellation.

   - bpo-41364(8): Reduce import overhead of *note uuid: 12d.

   - bpo-41341(9): Recursive evaluation of *note typing.ForwardRef: f70.
     in ‘get_type_hints’.

   - bpo-41182(10): selector: use DefaultSelector based upon
     implementation

   - bpo-40726(11): Handle cases where the ‘end_lineno’ is ‘None’ on
     *note ast.increment_lineno(): 1003.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41497

   (2) https://bugs.python.org/issue41490

   (3) https://bugs.python.org/issue41467

   (4) https://bugs.python.org/issue41425

   (5) https://bugs.python.org/issue41384

   (6) https://bugs.python.org/issue38731

   (7) https://bugs.python.org/issue41317

   (8) https://bugs.python.org/issue41364

   (9) https://bugs.python.org/issue41341

   (10) https://bugs.python.org/issue41182

   (11) https://bugs.python.org/issue40726


File: python.info,  Node: Documentation<12>,  Next: Windows<11>,  Prev: Library<14>,  Up: Python 3 9 0 release candidate 1

1.19.15.3 Documentation
.......................

   - bpo-41045(1): Add documentation for debug feature of f-strings.

   - bpo-41314(2): Changed the release when ‘from __future__ import
     annotations’ becomes the default from ‘4.0’ to ‘3.10’ (following a
     change in PEP 563).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41045

   (2) https://bugs.python.org/issue41314


File: python.info,  Node: Windows<11>,  Next: IDLE<10>,  Prev: Documentation<12>,  Up: Python 3 9 0 release candidate 1

1.19.15.4 Windows
.................

   - bpo-41492(1): Fixes the description that appears in UAC prompts.

   - bpo-40948(2): Improve post-install message to direct people to the
     “py” command.

   - bpo-41412(3): The installer will now fail to install on Windows 7
     and Windows 8.  Further, the UCRT dependency is now always
     downloaded on demand.

   - bpo-40741(4): Update Windows release to include SQLite 3.32.3.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41492

   (2) https://bugs.python.org/issue40948

   (3) https://bugs.python.org/issue41412

   (4) https://bugs.python.org/issue40741


File: python.info,  Node: IDLE<10>,  Prev: Windows<11>,  Up: Python 3 9 0 release candidate 1

1.19.15.5 IDLE
..............

   - bpo-41468(1): Improve IDLE run crash error message (which users
     should never see).

   - bpo-41373(2): Save files loaded with no line ending, as when blank,
     or different line endings, by setting its line ending to the system
     default.  Fix regression in 3.8.4 and 3.9.0b4.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41468

   (2) https://bugs.python.org/issue41373


File: python.info,  Node: Python 3 9 0 beta 5,  Next: Python 3 9 0 beta 4,  Prev: Python 3 9 0 release candidate 1,  Up: Changelog

1.19.16 Python 3.9.0 beta 5
---------------------------

`Release date: 2020-07-20'

* Menu:

* Security: Security<7>.
* Core and Builtins: Core and Builtins<14>.
* Library: Library<15>.
* Documentation: Documentation<13>.
* macOS: macOS<10>.
* IDLE: IDLE<11>.
* C API: C API<7>.


File: python.info,  Node: Security<7>,  Next: Core and Builtins<14>,  Up: Python 3 9 0 beta 5

1.19.16.1 Security
..................

   - bpo-41304(1): Fixes ‘python3x._pth’ being ignored on Windows,
     caused by the fix for bpo-29778(2) (CVE-2020-15801).

   - bpo-41162(3): Audit hooks are now cleared later during finalization
     to avoid missing events.

   - bpo-29778(4): Ensure ‘python3.dll’ is loaded from correct locations
     when Python is embedded (CVE-2020-15523).

   - bpo-39603(5): Prevent http header injection by rejecting control
     characters in http.client.putrequest(…).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41304

   (2) https://bugs.python.org/issue29778

   (3) https://bugs.python.org/issue41162

   (4) https://bugs.python.org/issue29778

   (5) https://bugs.python.org/issue39603


File: python.info,  Node: Core and Builtins<14>,  Next: Library<15>,  Prev: Security<7>,  Up: Python 3 9 0 beta 5

1.19.16.2 Core and Builtins
...........................

   - bpo-41295(1): Resolve a regression in CPython 3.8.4 where defining
     “__setattr__” in a multi-inheritance setup and calling up the
     hierarchy chain could fail if builtins/extension types were
     involved in the base types.

   - bpo-41247(2): Always cache the running loop holder when running
     ‘asyncio.set_running_loop’.

   - bpo-41252(3): Fix incorrect refcounting in _ssl.c’s
     ‘_servername_callback()’.

   - bpo-41215(4): Use non-NULL default values in the PEG parser keyword
     list to overcome a bug that was preventing Python from being
     properly compiled when using the XLC compiler.  Patch by Pablo
     Galindo.

   - bpo-41218(5): Python 3.8.3 had a regression where compiling with
     ast.PyCF_ALLOW_TOP_LEVEL_AWAIT would aggressively mark list
     comprehension with CO_COROUTINE. Now only list comprehension making
     use of async/await will tagged as so.

   - bpo-41175(6): Guard against a NULL pointer dereference within
     bytearrayobject triggered by the ‘bytearray() + bytearray()’
     operation.

   - bpo-39960(7): The “hackcheck” that prevents sneaking around a
     type’s __setattr__() by calling the superclass method was rewritten
     to allow C implemented heap types.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41295

   (2) https://bugs.python.org/issue41247

   (3) https://bugs.python.org/issue41252

   (4) https://bugs.python.org/issue41215

   (5) https://bugs.python.org/issue41218

   (6) https://bugs.python.org/issue41175

   (7) https://bugs.python.org/issue39960


File: python.info,  Node: Library<15>,  Next: Documentation<13>,  Prev: Core and Builtins<14>,  Up: Python 3 9 0 beta 5

1.19.16.3 Library
.................

   - bpo-41288(1): Unpickling invalid NEWOBJ_EX opcode with the C
     implementation raises now UnpicklingError instead of crashing.

   - bpo-39017(2): Avoid infinite loop when reading specially crafted
     TAR files using the tarfile module (CVE-2019-20907).

   - bpo-41235(3): Fix the error handling in *note
     ssl.SSLContext.load_dh_params(): b6a.

   - bpo-41207(4): In distutils.spawn, restore expectation that
     DistutilsExecError is raised when the command is not found.

   - bpo-39168(5): Remove the ‘__new__’ method of *note typing.Generic:
     100b.

   - bpo-41194(6): Fix a crash in the ‘_ast’ module: it can no longer be
     loaded more than once.  It now uses a global state rather than a
     module state.

   - bpo-39384(7): Fixed email.contentmanager to allow set_content() to
     set a null string.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41288

   (2) https://bugs.python.org/issue39017

   (3) https://bugs.python.org/issue41235

   (4) https://bugs.python.org/issue41207

   (5) https://bugs.python.org/issue39168

   (6) https://bugs.python.org/issue41194

   (7) https://bugs.python.org/issue39384


File: python.info,  Node: Documentation<13>,  Next: macOS<10>,  Prev: Library<15>,  Up: Python 3 9 0 beta 5

1.19.16.4 Documentation
.......................

   - bpo-37703(1): Updated Documentation to comprehensively elaborate on
     the behaviour of gather.cancel()

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37703


File: python.info,  Node: macOS<10>,  Next: IDLE<11>,  Prev: Documentation<13>,  Up: Python 3 9 0 beta 5

1.19.16.5 macOS
...............

   - bpo-40741(1): Update macOS installer to use SQLite 3.32.3.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40741


File: python.info,  Node: IDLE<11>,  Next: C API<7>,  Prev: macOS<10>,  Up: Python 3 9 0 beta 5

1.19.16.6 IDLE
..............

   - bpo-41300(1): Save files with non-ascii chars.  Fix regression
     released in 3.9.0b4 and 3.8.4.

   - bpo-37765(2): Add keywords to module name completion list.  Rewrite
     Completions section of IDLE doc.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41300

   (2) https://bugs.python.org/issue37765


File: python.info,  Node: C API<7>,  Prev: IDLE<11>,  Up: Python 3 9 0 beta 5

1.19.16.7 C API
...............

   - bpo-40170(1): Revert *note PyType_HasFeature(): 1010. change: it
     reads again directly the *note PyTypeObject.tp_flags: 1011. member
     when the limited C API is not used, rather than always calling
     *note PyType_GetFlags(): 1012. which hides implementation details.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40170


File: python.info,  Node: Python 3 9 0 beta 4,  Next: Python 3 9 0 beta 3,  Prev: Python 3 9 0 beta 5,  Up: Changelog

1.19.17 Python 3.9.0 beta 4
---------------------------

`Release date: 2020-07-02'

* Menu:

* Security: Security<8>.
* Core and Builtins: Core and Builtins<15>.
* Library: Library<16>.
* Tests: Tests<12>.
* Build: Build<10>.
* Windows: Windows<12>.
* macOS: macOS<11>.
* IDLE: IDLE<12>.
* C API: C API<8>.


File: python.info,  Node: Security<8>,  Next: Core and Builtins<15>,  Up: Python 3 9 0 beta 4

1.19.17.1 Security
..................

   - bpo-41004(1): The __hash__() methods of ipaddress.IPv4Interface and
     ipaddress.IPv6Interface incorrectly generated constant hash values
     of 32 and 128 respectively.  This resulted in always causing hash
     collisions.  The fix uses hash() to generate hash values for the
     tuple of (address, mask length, network address).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41004


File: python.info,  Node: Core and Builtins<15>,  Next: Library<16>,  Prev: Security<8>,  Up: Python 3 9 0 beta 4

1.19.17.2 Core and Builtins
...........................

   - bpo-41094(1): Fix decoding errors with audit when open files with
     non-ASCII names on non-UTF-8 locale.

   - bpo-41084(2): Prefix the error message with ‘f-string: ‘, when
     parsing an f-string expression which throws a *note SyntaxError:
     55a.

   - bpo-41076(3): Pre-feed the parser with the location of the f-string
     expression, not the f-string itself, which allows us to skip the
     shifting of the AST node locations after the parsing is completed.

   - bpo-40939(4): Deprecate ‘PyNode_Compile()’.

   - bpo-41056(5): Fixes a reference to deallocated stack space during
     startup when constructing sys.path involving a relative symlink
     when code was supplied via -c.  (discovered via Coverity)

   - bpo-41061(6): Fix incorrect expressions and asserts in hashtable
     code and tests.

   - bpo-41052(7): Opt out serialization/deserialization for
     _random.Random

   - bpo-40939(8): Deprecate *note PyParser_SimpleParseStringFlags():
     1ff, *note PyParser_SimpleParseStringFlagsFilename(): 200. and
     *note PyParser_SimpleParseFileFlags(): 201.

   - bpo-35975(9): Stefan Behnel reported that cf_feature_version is
     used even when PyCF_ONLY_AST is not set.  This is against the
     intention and against the documented behavior, so it’s been fixed.

   - bpo-40985(10): Fix a bug that caused the *note SyntaxError: 55a.
     text to be empty when a file ends with a line ending in a line
     continuation character (i.e.  backslash).  The error text should
     contain the text of the last line.

   - bpo-40958(11): Fix a possible buffer overflow in the PEG parser
     when gathering information for emitting syntax errors.  Patch by
     Pablo Galindo.

   - bpo-40957(12): Fix refleak in _Py_fopen_obj() when PySys_Audit()
     fails

   - bpo-40947(13): The Python *note Path Configuration: 1016. now takes
     *note PyConfig.platlibdir: 1017. in account.

   - bpo-40847(14): Fix a bug where a line with only a line continuation
     character is not considered a blank line at tokenizer level.  In
     such cases, more than a single ‘NEWLINE’ token was emitted.  The
     old parser was working around the issue, but the new parser threw a
     *note SyntaxError: 55a. for valid input due to this.  For example,
     an empty line following a line continuation character was
     interpreted as a *note SyntaxError: 55a.

   - bpo-40824(15): Unexpected errors in calling the ‘__iter__’ method
     are no longer masked by ‘TypeError’ in the *note in: 179. operator
     and functions *note contains(): 17a, *note indexOf(): 17b. and
     *note countOf(): 17c. of the *note operator: c2. module.

   - bpo-19569(16): Add the private macros ‘_Py_COMP_DIAG_PUSH’,
     ‘_Py_COMP_DIAG_IGNORE_DEPR_DECLS’, and ‘_Py_COMP_DIAG_POP’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41094

   (2) https://bugs.python.org/issue41084

   (3) https://bugs.python.org/issue41076

   (4) https://bugs.python.org/issue40939

   (5) https://bugs.python.org/issue41056

   (6) https://bugs.python.org/issue41061

   (7) https://bugs.python.org/issue41052

   (8) https://bugs.python.org/issue40939

   (9) https://bugs.python.org/issue35975

   (10) https://bugs.python.org/issue40985

   (11) https://bugs.python.org/issue40958

   (12) https://bugs.python.org/issue40957

   (13) https://bugs.python.org/issue40947

   (14) https://bugs.python.org/issue40847

   (15) https://bugs.python.org/issue40824

   (16) https://bugs.python.org/issue19569


File: python.info,  Node: Library<16>,  Next: Tests<12>,  Prev: Core and Builtins<15>,  Up: Python 3 9 0 beta 4

1.19.17.3 Library
.................

   - bpo-41193(1): The ‘write_history()’ atexit function of the readline
     completer now ignores any *note OSError: 304. to ignore error if
     the filesystem is read-only, instead of only ignoring *note
     FileNotFoundError: 8ad. and *note PermissionError: 6f6.

   - bpo-41161(2): The decimal module now requires libmpdec-2.5.0.
     Users of –with-system-libmpdec should update their system library.

   - bpo-40874(3): The decimal module now requires libmpdec-2.5.0.

   - bpo-41138(4): Fixed the *note trace: 11b. module CLI for Python
     source files with non-UTF-8 encoding.

   - bpo-31938(5): Fix default-value signatures of several functions in
     the *note select: e5. module - by Anthony Sottile.

   - bpo-41068(6): Fixed reading files with non-ASCII names from ZIP
     archive directly after writing them.

   - bpo-41058(7): ‘pdb.find_function()’ now correctly determines the
     source file encoding.

   - bpo-41056(8): Fix a NULL pointer dereference within the ssl module
     during a MemoryError in the keylog callback.  (discovered by
     Coverity)

   - bpo-41056(9): Fixed an instance where a MemoryError within the
     zoneinfo module might not be reported or not reported at its
     source.  (found by Coverity)

   - bpo-41048(10): *note mimetypes.read_mime_types(): 1019. function
     reads the rule file using UTF-8 encoding, not the locale encoding.
     Patch by Srinivas Reddy Thatiparthy.

   - bpo-41043(11): Fixed the use of *note glob(): 6bd. in the stdlib:
     literal part of the path is now always correctly escaped.

   - bpo-40448(12): *note ensurepip: 78. now disables the use of ‘pip’
     cache when installing the bundled versions of ‘pip’ and
     ‘setuptools’.  Patch by Krzysztof Konopko.

   - bpo-40967(13): Removed ‘asyncio.Task.current_task()’ and
     ‘asyncio.Task.all_tasks()’.  Patch contributed by Rémi Lapeyre.

   - bpo-40955(14): Fix a minor memory leak in *note subprocess: f9.
     module when extra_groups was specified.

   - bpo-40855(15): The standard deviation and variance functions in the
     statistics module were ignoring their mu and xbar arguments.

   - bpo-40924(16): Removed support for loaders implementing .files and
     supplying TraversableResources.

   - bpo-40939(17): Use the new PEG parser when generating the stdlib
     *note keyword: a6. module.

   - bpo-40834(18): Fix truncate when sending str object
     with_xxsubinterpreters.channel_send.

   - bpo-26407(19): Unexpected errors in calling the ‘__iter__’ method
     are no longer masked by ‘TypeError’ in *note csv.reader(): 101a,
     ‘csv.writer.writerow()’ and ‘csv.writer.writerows()’.

   - bpo-38488(20): Update ensurepip to install pip 20.1.1 and
     setuptools 47.1.0.

   - bpo-36543(21): Restored the deprecated ‘xml.etree.cElementTree’
     module.

   - bpo-34226(22): Fix *note cgi.parse_multipart: 282. without
     content_length.  Patch by Roger Duran

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41193

   (2) https://bugs.python.org/issue41161

   (3) https://bugs.python.org/issue40874

   (4) https://bugs.python.org/issue41138

   (5) https://bugs.python.org/issue31938

   (6) https://bugs.python.org/issue41068

   (7) https://bugs.python.org/issue41058

   (8) https://bugs.python.org/issue41056

   (9) https://bugs.python.org/issue41056

   (10) https://bugs.python.org/issue41048

   (11) https://bugs.python.org/issue41043

   (12) https://bugs.python.org/issue40448

   (13) https://bugs.python.org/issue40967

   (14) https://bugs.python.org/issue40955

   (15) https://bugs.python.org/issue40855

   (16) https://bugs.python.org/issue40924

   (17) https://bugs.python.org/issue40939

   (18) https://bugs.python.org/issue40834

   (19) https://bugs.python.org/issue26407

   (20) https://bugs.python.org/issue38488

   (21) https://bugs.python.org/issue36543

   (22) https://bugs.python.org/issue34226


File: python.info,  Node: Tests<12>,  Next: Build<10>,  Prev: Library<16>,  Up: Python 3 9 0 beta 4

1.19.17.4 Tests
...............

   - bpo-41085(1): Fix integer overflow in the *note
     array.array.index(): 101c. method on 64-bit Windows for index
     larger than ‘2**31’.

   - bpo-41069(2): *note test.support.TESTFN: 101d. and the current
     directory for tests when run via ‘test.regrtest’ contain now
     non-ascii characters if possible.

   - bpo-38377(3): On Linux, skip tests using multiprocessing if the
     current user cannot create a file in ‘/dev/shm/’ directory.  Add
     the ‘skip_if_broken_multiprocessing_synchronize()’ function to the
     *note test.support: 106. module.

   - bpo-41009(4): Fix use of
     ‘support.require_{linux|mac|freebsd}_version()’ decorators as class
     decorator.

   - bpo-41003(5): Fix ‘test_copyreg’ when ‘numpy’ is installed:
     ‘test.pickletester’ now saves/restores warnings filters when
     importing ‘numpy’, to ignore filters installed by ‘numpy’.

   - bpo-40964(6): Disable remote *note imaplib: 97. tests, host
     cyrus.andrew.cmu.edu is blocking incoming connections.

   - bpo-40927(7): Fix test_binhex when run twice: it now uses
     import_fresh_module() to ensure that it raises DeprecationWarning
     each time.

   - bpo-34401(8): Make test_gdb properly run on HP-UX. Patch by Michael
     Osipov.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41085

   (2) https://bugs.python.org/issue41069

   (3) https://bugs.python.org/issue38377

   (4) https://bugs.python.org/issue41009

   (5) https://bugs.python.org/issue41003

   (6) https://bugs.python.org/issue40964

   (7) https://bugs.python.org/issue40927

   (8) https://bugs.python.org/issue34401


File: python.info,  Node: Build<10>,  Next: Windows<12>,  Prev: Tests<12>,  Up: Python 3 9 0 beta 4

1.19.17.5 Build
...............

   - bpo-40204(1): Pin Sphinx version to 2.3.1 in ‘Doc/Makefile’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40204


File: python.info,  Node: Windows<12>,  Next: macOS<11>,  Prev: Build<10>,  Up: Python 3 9 0 beta 4

1.19.17.6 Windows
.................

   - bpo-41074(1): Fixed support of non-ASCII names in functions *note
     msilib.OpenDatabase(): 1020. and *note msilib.init_database():
     1021. and non-ASCII SQL in method *note msilib.Database.OpenView():
     1022.

   - bpo-40164(2): Updates Windows OpenSSL to 1.1.1g

   - bpo-37556(3): Extend py.exe help to mention overrides via venv,
     shebang, environmental variables & ini files.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41074

   (2) https://bugs.python.org/issue40164

   (3) https://bugs.python.org/issue37556


File: python.info,  Node: macOS<11>,  Next: IDLE<12>,  Prev: Windows<12>,  Up: Python 3 9 0 beta 4

1.19.17.7 macOS
...............

   - bpo-39580(1): Avoid opening Finder window if running installer from
     the command line.  Patch contributed by Rick Heil.

   - bpo-41100(2): Fix configure error when building on macOS 11.  Note
     that the current Python release was released shortly after the
     first developer preview of macOS 11 (Big Sur); there are other
     known issues with building and running on the developer preview.
     Big Sur is expected to be fully supported in a future bugfix
     release of Python 3.8.x and with 3.9.0.

   - bpo-41005(3): fixed an XDG settings issue not allowing macos to
     open browser in webbrowser.py

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39580

   (2) https://bugs.python.org/issue41100

   (3) https://bugs.python.org/issue41005


File: python.info,  Node: IDLE<12>,  Next: C API<8>,  Prev: macOS<11>,  Up: Python 3 9 0 beta 4

1.19.17.8 IDLE
..............

   - bpo-41152(1): The encoding of ‘stdin’, ‘stdout’ and ‘stderr’ in
     IDLE is now always UTF-8.

   - bpo-41144(2): Make Open Module open a special module such as
     os.path.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue41152

   (2) https://bugs.python.org/issue41144


File: python.info,  Node: C API<8>,  Prev: IDLE<12>,  Up: Python 3 9 0 beta 4

1.19.17.9 C API
...............

   - bpo-36346(1): Mark ‘Py_UNICODE_COPY’, ‘Py_UNICODE_FILL’,
     ‘PyUnicode_WSTR_LENGTH’, ‘PyUnicode_FromUnicode’,
     ‘PyUnicode_AsUnicode’, ‘_PyUnicode_AsUnicode’, and
     ‘PyUnicode_AsUnicodeAndSize’ as deprecated in C. Remove
     ‘Py_UNICODE_MATCH’ which was deprecated and broken since Python
     3.3.

   - bpo-36020(2): On Windows, ‘#include "pyerrors.h"’ no longer defines
     ‘snprintf’ and ‘vsnprintf’ macros.

   - bpo-40703(3): The PyType_FromSpec*() functions no longer overwrite
     the type’s “__module__” attribute if it is set via “Py_tp_members”
     or “Py_tp_getset”.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36346

   (2) https://bugs.python.org/issue36020

   (3) https://bugs.python.org/issue40703


File: python.info,  Node: Python 3 9 0 beta 3,  Next: Python 3 9 0 beta 2,  Prev: Python 3 9 0 beta 4,  Up: Changelog

1.19.18 Python 3.9.0 beta 3
---------------------------

`Release date: 2020-06-09'

* Menu:

* Library: Library<17>.
* Build: Build<11>.


File: python.info,  Node: Library<17>,  Next: Build<11>,  Up: Python 3 9 0 beta 3

1.19.18.1 Library
.................

   - bpo-40924(1): *note importlib.resources: 9e.: Reverted
     ‘TraversableResources’ implementations from the built-in loaders
     (SourceFileLoader and ZipImporter) as it was an incompatible change
     introduced in 3.9.0 beta 2 causing through a chain of events for
     root TLS certificates to be missing.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40924


File: python.info,  Node: Build<11>,  Prev: Library<17>,  Up: Python 3 9 0 beta 3

1.19.18.2 Build
...............

   - bpo-40684(1): ‘make install’ now uses the ‘PLATLIBDIR’ variable for
     the destination ‘lib-dynload/’ directory when ‘./configure
     --with-platlibdir’ is used.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40684


File: python.info,  Node: Python 3 9 0 beta 2,  Next: Python 3 9 0 beta 1,  Prev: Python 3 9 0 beta 3,  Up: Changelog

1.19.19 Python 3.9.0 beta 2
---------------------------

`Release date: 2020-06-08'

* Menu:

* Core and Builtins: Core and Builtins<16>.
* Library: Library<18>.
* Tests: Tests<13>.
* Build: Build<12>.
* Windows: Windows<13>.
* macOS: macOS<12>.
* IDLE: IDLE<13>.
* C API: C API<9>.


File: python.info,  Node: Core and Builtins<16>,  Next: Library<18>,  Up: Python 3 9 0 beta 2

1.19.19.1 Core and Builtins
...........................

   - bpo-40904(1): Fix possible segfault in the new PEG parser when
     parsing f-string containing yield statements with no value
     (‘f"{yield}"’).  Patch by Pablo Galindo

   - bpo-40903(2): Fixed a possible segfault in the new PEG parser when
     producing error messages for invalid assignments of the form
     ‘p=p=’.  Patch by Pablo Galindo

   - bpo-40880(3): Fix invalid memory read in the new parser when
     checking newlines in string literals.  Patch by Pablo Galindo.

   - bpo-40883(4): Fix memory leak in when parsing f-strings in the new
     parser.  Patch by Pablo Galindo

   - bpo-40870(5): Raise *note ValueError: 16d. when validating custom
     AST’s where the constants ‘True’, ‘False’ and ‘None’ are used
     within a *note ast.Name: 102b. node.

   - bpo-40854(6): Allow overriding *note sys.platlibdir: 1e9. via a new
     *note PYTHONPLATLIBDIR: 102c. environment variable.

   - bpo-40826(7): Fix GIL usage in ‘PyOS_Readline()’: lock the GIL to
     set an exception and pass the Python thread state when checking if
     there is a pending signal.

   - bpo-40780(8): Fix a corner case where g-style string formatting of
     a float failed to remove trailing zeros.

   - bpo-38964(9): When there’s a *note SyntaxError: 55a. in the
     expression part of an fstring, the filename attribute of the *note
     SyntaxError: 55a. gets correctly set to the name of the file the
     fstring resides in.

   - bpo-40750(10): Support the “-d” debug flag in the new PEG parser.
     Patch by Pablo Galindo

   - bpo-40217(11): Instances of types created with *note
     PyType_FromSpecWithBases(): 102d. will no longer automatically
     visit their class object when traversing references in the garbage
     collector.  The user is expected to manually visit the object’s
     class.  Patch by Pablo Galindo.

   - bpo-40696(12): Fix a hang that can arise after *note
     generator.throw(): ff8. due to a cycle in the exception context
     chain.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40904

   (2) https://bugs.python.org/issue40903

   (3) https://bugs.python.org/issue40880

   (4) https://bugs.python.org/issue40883

   (5) https://bugs.python.org/issue40870

   (6) https://bugs.python.org/issue40854

   (7) https://bugs.python.org/issue40826

   (8) https://bugs.python.org/issue40780

   (9) https://bugs.python.org/issue38964

   (10) https://bugs.python.org/issue40750

   (11) https://bugs.python.org/issue40217

   (12) https://bugs.python.org/issue40696


File: python.info,  Node: Library<18>,  Next: Tests<13>,  Prev: Core and Builtins<16>,  Up: Python 3 9 0 beta 2

1.19.19.2 Library
.................

   - bpo-39791(1): Refresh importlib.metadata from importlib_metadata
     1.6.1.

   - bpo-40807(2): Stop codeop._maybe_compile, used by
     code.InteractiveInterpreter (and IDLE). from from emitting each
     warning three times.

   - bpo-39791(3): Built-in loaders (SourceFileLoader and ZipImporter)
     now supply ‘TraversableResources’ implementations for
     ‘ResourceReader’, and the fallback function has been removed.

   - bpo-17005(4): The topological sort functionality that was
     introduced initially in the *note functools: 83. module has been
     moved to a new *note graphlib: 89. module to better accommodate the
     new tools and keep the original scope of the *note functools: 83.
     module.  Patch by Pablo Galindo

   - bpo-40777(5): Initialize PyDateTime_IsoCalendarDateType.tp_base at
     run-time to avoid errors on some compilers.

   - bpo-40767(6): *note webbrowser: 132. now properly finds the default
     browser in pure Wayland systems by checking the WAYLAND_DISPLAY
     environment variable.  Patch contributed by Jérémy Attali.

   - bpo-40791(7): ‘hashlib.compare_digest()’ uses OpenSSL’s
     ‘CRYPTO_memcmp()’ function when OpenSSL is available.

   - bpo-40795(8): *note ctypes: 2a. module: If ctypes fails to convert
     the result of a callback or if a ctypes callback function raises an
     exception, sys.unraisablehook is now called with an exception set.
     Previously, the error was logged into stderr by *note
     PyErr_Print(): 102f.

   - bpo-30008(9): Fix *note ssl: f3. code to be compatible with OpenSSL
     1.1.x builds that use ‘no-deprecated’ and ‘--api=1.1.0’.

   - bpo-30064(10): Fix asyncio ‘loop.sock_*’ race condition issue

   - bpo-40759(11): Deprecate the *note symbol: fb. module.

   - bpo-40737(12): Fix possible reference leak for *note sqlite3: f2.
     initialization.

   - bpo-40698(13): *note distutils: 38. upload creates SHA2-256 and
     Blake2b-256 digests.  MD5 digests is skipped if platform blocks
     MD5.

   - bpo-40695(14): *note hashlib: 8c. no longer falls back to builtin
     hash implementations when OpenSSL provides a hash digest and the
     algorithm is blocked by security policy.

   - bpo-9216(15): func:*note hashlib.new: 1030. passed
     ‘usedforsecurity’ to OpenSSL EVP constructor ‘_hashlib.new()’.
     test_hashlib and test_smtplib handle strict security policy better.

   - bpo-40614(16): *note ast.parse(): 2d6. will not parse self
     documenting expressions in f-strings when passed ‘feature_version’
     is less than ‘(3, 8)’.

   - bpo-40671(17): Prepare ‘_hashlib’ for PEP 489(18) and use *note
     PyModule_AddType(): 253.

   - bpo-32309(19): Added a new *note coroutine: 18a. *note
     asyncio.to_thread(): 18f.  It is mainly used for running IO-bound
     functions in a separate thread to avoid blocking the event loop,
     and essentially works as a high-level version of *note
     run_in_executor(): 190. that can directly take keyword arguments.

   - bpo-40630(20): Added *note tracemalloc.reset_peak(): 1ec. to set
     the peak size of traced memory blocks to the current size, to
     measure the peak of specific pieces of code.

   - bpo-13097(21): ‘ctypes’ now raises an ‘ArgumentError’ when a
     callback is invoked with more than 1024 arguments.

   - bpo-23082(22): Updated the error message and docs of
     PurePath.relative_to() to better reflect the function behaviour.

   - bpo-39244(23): Fixed
     ‘multiprocessing.context.get_all_start_methods’ to properly return
     the default method first on macOS.

   - bpo-39040(24): Fix parsing of invalid mime headers parameters by
     collapsing whitespace between encoded words in a bare-quote-string.

   - bpo-35714(25): *note struct.error: d7c. is now raised if there is a
     null character in a *note struct: f8. format string.

   - bpo-36290(26): AST nodes are now raising *note TypeError: 1fe. on
     conflicting keyword arguments.  Patch contributed by Rémi Lapeyre.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39791

   (2) https://bugs.python.org/issue40807

   (3) https://bugs.python.org/issue39791

   (4) https://bugs.python.org/issue17005

   (5) https://bugs.python.org/issue40777

   (6) https://bugs.python.org/issue40767

   (7) https://bugs.python.org/issue40791

   (8) https://bugs.python.org/issue40795

   (9) https://bugs.python.org/issue30008

   (10) https://bugs.python.org/issue30064

   (11) https://bugs.python.org/issue40759

   (12) https://bugs.python.org/issue40737

   (13) https://bugs.python.org/issue40698

   (14) https://bugs.python.org/issue40695

   (15) https://bugs.python.org/issue9216

   (16) https://bugs.python.org/issue40614

   (17) https://bugs.python.org/issue40671

   (18) https://www.python.org/dev/peps/pep-0489

   (19) https://bugs.python.org/issue32309

   (20) https://bugs.python.org/issue40630

   (21) https://bugs.python.org/issue13097

   (22) https://bugs.python.org/issue23082

   (23) https://bugs.python.org/issue39244

   (24) https://bugs.python.org/issue39040

   (25) https://bugs.python.org/issue35714

   (26) https://bugs.python.org/issue36290


File: python.info,  Node: Tests<13>,  Next: Build<12>,  Prev: Library<18>,  Up: Python 3 9 0 beta 2

1.19.19.3 Tests
...............

   - bpo-17258(1): Skip some *note multiprocessing: b7. tests when MD5
     hash digest is blocked.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17258


File: python.info,  Node: Build<12>,  Next: Windows<13>,  Prev: Tests<13>,  Up: Python 3 9 0 beta 2

1.19.19.4 Build
...............

   - bpo-40514(1): Remove ‘--with-experimental-isolated-subinterpreters’
     configure option in Python 3.9: the experiment continues in the
     master branch, but it’s no longer needed in 3.9.

   - bpo-40683(2): Fixed an issue where the *note zoneinfo: 14e. module
     and its tests were not included when Python is installed with
     ‘make’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40514

   (2) https://bugs.python.org/issue40683


File: python.info,  Node: Windows<13>,  Next: macOS<12>,  Prev: Build<12>,  Up: Python 3 9 0 beta 2

1.19.19.5 Windows
.................

   - bpo-39631(1): Changes the registered MIME type for ‘.py’ files on
     Windows to ‘text/x-python’ instead of ‘text/plain’.

   - bpo-40677(2): Manually define IO_REPARSE_TAG_APPEXECLINK in case
     some old Windows SDK doesn’t have it.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39631

   (2) https://bugs.python.org/issue40677


File: python.info,  Node: macOS<12>,  Next: IDLE<13>,  Prev: Windows<13>,  Up: Python 3 9 0 beta 2

1.19.19.6 macOS
...............

   - bpo-40741(1): Update macOS installer to use SQLite 3.32.2.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40741


File: python.info,  Node: IDLE<13>,  Next: C API<9>,  Prev: macOS<12>,  Up: Python 3 9 0 beta 2

1.19.19.7 IDLE
..............

   - bpo-39885(1): Make context menu Cut and Copy work again when
     right-clicking within a selection.

   - bpo-40723(2): Make test_idle pass when run after import.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39885

   (2) https://bugs.python.org/issue40723


File: python.info,  Node: C API<9>,  Prev: IDLE<13>,  Up: Python 3 9 0 beta 2

1.19.19.8 C API
...............

   - bpo-40910(1): Export explicitly the *note Py_GetArgcArgv(): 1037.
     function to the C API and document the function.  Previously, it
     was exported implicitly which no longer works since Python is built
     with ‘-fvisibility=hidden’.

   - bpo-40724(2): Allow defining buffer slots in type specs.

   - bpo-40826(3): ‘PyOS_InterruptOccurred()’ now fails with a fatal
     error if it is called with the GIL released.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40910

   (2) https://bugs.python.org/issue40724

   (3) https://bugs.python.org/issue40826


File: python.info,  Node: Python 3 9 0 beta 1,  Next: Python 3 9 0 alpha 6,  Prev: Python 3 9 0 beta 2,  Up: Changelog

1.19.20 Python 3.9.0 beta 1
---------------------------

`Release date: 2020-05-19'

* Menu:

* Security: Security<9>.
* Core and Builtins: Core and Builtins<17>.
* Library: Library<19>.
* Documentation: Documentation<14>.
* Tests: Tests<14>.
* Build: Build<13>.
* Windows: Windows<14>.
* macOS: macOS<13>.
* Tools/Demos: Tools/Demos<4>.
* C API: C API<10>.


File: python.info,  Node: Security<9>,  Next: Core and Builtins<17>,  Up: Python 3 9 0 beta 1

1.19.20.1 Security
..................

   - bpo-40501(1): *note uuid: 12d. no longer uses *note ctypes: 2a. to
     load ‘libuuid’ or ‘rpcrt4.dll’ at runtime.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40501


File: python.info,  Node: Core and Builtins<17>,  Next: Library<19>,  Prev: Security<9>,  Up: Python 3 9 0 beta 1

1.19.20.2 Core and Builtins
...........................

   - bpo-40663(1): Correctly generate annotations where parentheses are
     omitted but required (e.g: ‘Type[(str, int, *other))]’.

   - bpo-40596(2): Fixed *note str.isidentifier(): 103b. for
     non-canonicalized strings containing non-BMP characters on Windows.

   - bpo-40593(3): Improved syntax errors for invalid characters in
     source code.

   - bpo-40585(4): Fixed a bug when using *note
     codeop.compile_command(): 103c. that was causing exceptions to be
     swallowed with the new parser.  Patch by Pablo Galindo

   - bpo-40566(5): Apply PEP 573(6) to *note abc: 3.

   - bpo-40502(7): Initialize ‘n->n_col_offset’.  (Patch by Joannah
     Nanjekye)

   - bpo-40527(8): Fix command line argument parsing: no longer write
     errors multiple times into stderr.

   - bpo-1635741(9): Port *note errno: 7a. to multiphase initialization
     ( PEP 489(10)).

   - bpo-40523(11): Add pass-throughs for *note hash(): aa3. and *note
     reversed(): 2c6. to *note weakref.proxy: 37a. objects.  Patch by
     Pablo Galindo.

   - bpo-1635741(12): Port *note syslog: ff. to multiphase
     initialization ( PEP 489(13)).

   - bpo-40246(14): Reporting a specialised error message for invalid
     string prefixes, which was introduced in bpo-40246(15), is being
     reverted due to backwards compatibility concerns for strings that
     immediately follow a reserved keyword without whitespace between
     them.  Constructs like ‘bg="#d00" if clear else"#fca"’ were failing
     to parse, which is not an acceptable breakage on such short notice.

   - bpo-40417(16): Fix imp module deprecation warning when
     PyImport_ReloadModule is called.  Patch by Robert Rouhani.

   - bpo-40408(17): Fixed support of nested type variables in
     GenericAlias (e.g.  ‘list[list[T]]’).

   - bpo-1635741(18): Port _stat module to multiphase initialization (
     PEP 489(19)).

   - bpo-29587(20): Enable implicit exception chaining when calling
     *note generator.throw(): ff8.

   - bpo-40328(21): Add tools for generating mappings headers for
     CJKCodecs.

   - bpo-40228(22): Setting frame.f_lineno is now robust w.r.t.  changes
     in the source-to-bytecode compiler

   - bpo-38880(23): Added the ability to list interpreters associated
     with channel ends in the internal subinterpreters module.

   - bpo-37986(24): Improve performance of *note PyLong_FromDouble():
     1f4. for values that fit into ‘long’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40663

   (2) https://bugs.python.org/issue40596

   (3) https://bugs.python.org/issue40593

   (4) https://bugs.python.org/issue40585

   (5) https://bugs.python.org/issue40566

   (6) https://www.python.org/dev/peps/pep-0573

   (7) https://bugs.python.org/issue40502

   (8) https://bugs.python.org/issue40527

   (9) https://bugs.python.org/issue1635741

   (10) https://www.python.org/dev/peps/pep-0489

   (11) https://bugs.python.org/issue40523

   (12) https://bugs.python.org/issue1635741

   (13) https://www.python.org/dev/peps/pep-0489

   (14) https://bugs.python.org/issue40246

   (15) https://bugs.python.org/issue40246

   (16) https://bugs.python.org/issue40417

   (17) https://bugs.python.org/issue40408

   (18) https://bugs.python.org/issue1635741

   (19) https://www.python.org/dev/peps/pep-0489

   (20) https://bugs.python.org/issue29587

   (21) https://bugs.python.org/issue40328

   (22) https://bugs.python.org/issue40228

   (23) https://bugs.python.org/issue38880

   (24) https://bugs.python.org/issue37986


File: python.info,  Node: Library<19>,  Next: Documentation<14>,  Prev: Core and Builtins<17>,  Up: Python 3 9 0 beta 1

1.19.20.3 Library
.................

   - bpo-40662(1): Fixed *note ast.get_source_segment(): 2d5. for ast
     nodes that have incomplete location information.  Patch by Irit
     Katriel.

   - bpo-40665(2): Convert *note bisect: 11. to use Argument Clinic.

   - bpo-40536(3): Added the *note available_timezones(): 103e. function
     to the *note zoneinfo: 14e. module.  Patch by Paul Ganssle.

   - bpo-40645(4): The ‘hmac.HMAC’ exposes internal implementation
     details.  The attributes ‘digest_cons’, ‘inner’, and ‘outer’ are
     deprecated and will be removed in the future.

   - bpo-40645(5): The internal module ‘_hashlib’ wraps and exposes
     OpenSSL’s HMAC API. The new code will be used in Python 3.10 after
     the internal implementation details of the pure Python HMAC module
     are no longer part of the public API.

   - bpo-40637(6): Builtin hash modules can now be disabled or
     selectively enabled with ‘configure
     --with-builtin-hashlib-hashes=sha3,blake1’ or
     ‘--without-builtin-hashlib-hashes’.

   - bpo-37630(7): The *note hashlib: 8c. module can now use SHA3 hashes
     and SHAKE XOF from OpenSSL when available.

   - bpo-40479(8): The *note hashlib: 8c. now compiles with OpenSSL
     3.0.0-alpha2.

   - bpo-40257(9): Revert changes to *note inspect.getdoc(): 307.

   - bpo-40607(10): When cancelling a task due to timeout, *note
     asyncio.wait_for(): 191. will now propagate the exception if an
     error happens during cancellation.  Patch by Roman Skurikhin.

   - bpo-40612(11): Fix edge cases in SyntaxError formatting.  If the
     offset is <= 0, no caret is printed.  If the offset is > line
     length, the caret is printed pointing just after the last
     character.

   - bpo-40597(12): If text content lines are longer than
     policy.max_line_length, always use a content-encoding to make sure
     they are wrapped.

   - bpo-40571(13): Added functools.cache() as a simpler, more
     discoverable way to access the unbounded cache variant of
     lru_cache(maxsize=None).

   - bpo-40503(14): PEP 615(15), the *note zoneinfo: 14e. module.  Adds
     support for the IANA time zone database.

   - bpo-40397(16): Removed attributes ‘__args__’ and ‘__parameters__’
     from special generic aliases like ‘typing.List’ (not subscripted).

   - bpo-40549(17): Convert posixmodule.c (“posix” or “nt” module) to
     the multiphase initialization (PEP 489).

   - bpo-31033(18): Add a ‘msg’ argument to ‘Future.cancel()’ and
     ‘Task.cancel()’.

   - bpo-40541(19): Added an optional `counts' parameter to
     random.sample().

   - bpo-40515(20): The *note ssl: f3. and *note hashlib: 8c. modules
     now actively check that OpenSSL is build with thread support.
     Python 3.7.0 made thread support mandatory and no longer works
     safely with a no-thread builds.

   - bpo-31033(21): When a *note asyncio.Task: 2e0. is cancelled, the
     exception traceback now chains all the way back to where the task
     was first interrupted.

   - bpo-40504(22): *note functools.lru_cache(): 2f8. objects can now be
     the targets of weakrefs.

   - bpo-40559(23): Fix possible memory leak in the C implementation of
     *note asyncio.Task: 2e0.

   - bpo-40480(24): ‘fnmatch.fnmatch()’ could take exponential time in
     the presence of multiple ‘*’ pattern characters.  This was repaired
     by generating more elaborate regular expressions to avoid futile
     backtracking.

   - bpo-40495(25): *note compileall: 20. is now able to use hardlinks
     to prevent duplicates in a case when ‘.pyc’ files for different
     optimization levels have the same content.

   - bpo-40457(26): The ssl module now support OpenSSL builds without
     TLS 1.0 and 1.1 methods.

   - bpo-40355(27): Improve error reporting in *note ast.literal_eval():
     5a0. in the presence of malformed *note ast.Dict: 103f. nodes
     instead of silently ignoring any non-conforming elements.  Patch by
     Curtis Bucher.

   - bpo-40465(28): Deprecated the optional `random' argument to
     `random.shuffle()'.

   - bpo-40459(29): *note platform.win32_ver(): 1040. now produces
     correct `ptype' strings instead of empty strings.

   - bpo-39435(30): The first argument of *note pickle.loads(): 6ba. is
     now positional-only.

   - bpo-39305(31): Update *note nntplib: c0. to merge *note
     nntplib.NNTP: 1c6. and ‘nntplib._NNTPBase’.  Patch by Dong-hee Na.

   - bpo-32494(32): Update *note dbm.gnu: 33. to use gdbm_count if
     possible when calling *note len(): 28b.  Patch by Dong-hee Na.

   - bpo-40453(33): Add ‘isolated=True’ keyword-only parameter to
     ‘_xxsubinterpreters.create()’.  An isolated subinterpreter cannot
     spawn threads, spawn a child process or call ‘os.fork()’.

   - bpo-40286(34): Remove ‘_random.Random.randbytes()’: the C
     implementation of ‘randbytes()’.  Implement the method in Python to
     ease subclassing: ‘randbytes()’ now directly reuses
     ‘getrandbits()’.

   - bpo-40394(35): Added default arguments to *note
     difflib.SequenceMatcher.find_longest_match(): 1041.

   - bpo-39995(36): Fix a race condition in
     concurrent.futures._ThreadWakeup: access to _ThreadWakeup is now
     protected with the shutdown lock.

   - bpo-30966(37): ‘Process.shutdown(wait=True)’ of *note
     concurrent.futures: 21. now closes explicitly the result queue.

   - bpo-30966(38): Add a new *note close(): 1c4. method to the *note
     SimpleQueue: 1c3. class to explicitly close the queue.

   - bpo-39966(39): Revert bpo-25597(40).  *note
     unittest.mock.MagicMock: 874. with wraps’ set uses default return
     values for magic methods.

   - bpo-39791(41): Added ‘files()’ function to importlib.resources with
     support for subdirectories in package data, matching backport in
     importlib_resources 1.5.

   - bpo-40375(42): *note imaplib.IMAP4.unselect(): 1b3. is added.
     Patch by Dong-hee Na.

   - bpo-40389(43): ‘repr()’ now returns ‘typing.Optional[T]’ when
     called for ‘typing.Union’ of two types, one of which is ‘NoneType’.

   - bpo-40291(44): Add support for CAN_J1939 sockets (available on
     Linux 5.4+)

   - bpo-40273(45): *note types.MappingProxyType: b8e. is now
     reversible.

   - bpo-39075(46): The repr for *note types.SimpleNamespace: 1d8. is
     now insertion ordered rather than alphabetical.

   - bpo-40192(47): On AIX, *note thread_time(): 1e7. is now implemented
     with ‘thread_cputime()’ which has nanosecond resolution, rather
     than ‘clock_gettime(CLOCK_THREAD_CPUTIME_ID)’ which has a
     resolution of 10 ms.  Patch by Batuhan Taskaya.

   - bpo-40025(48): Raise TypeError when _generate_next_value_ is
     defined after members.  Patch by Ethan Onstott.

   - bpo-39058(49): In the argparse module, the repr for Namespace() and
     other argument holders now displayed in the order attributes were
     added.  Formerly, it displayed in alphabetical order even though
     argument order is preserved the user visible parts of the module.

   - bpo-24416(50): The ‘isocalendar()’ methods of *note datetime.date:
     19e. and *note datetime.datetime: 1a0. now return a *note named
     tuple: b7b. instead of a *note tuple: 1a2.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40662

   (2) https://bugs.python.org/issue40665

   (3) https://bugs.python.org/issue40536

   (4) https://bugs.python.org/issue40645

   (5) https://bugs.python.org/issue40645

   (6) https://bugs.python.org/issue40637

   (7) https://bugs.python.org/issue37630

   (8) https://bugs.python.org/issue40479

   (9) https://bugs.python.org/issue40257

   (10) https://bugs.python.org/issue40607

   (11) https://bugs.python.org/issue40612

   (12) https://bugs.python.org/issue40597

   (13) https://bugs.python.org/issue40571

   (14) https://bugs.python.org/issue40503

   (15) https://www.python.org/dev/peps/pep-0615

   (16) https://bugs.python.org/issue40397

   (17) https://bugs.python.org/issue40549

   (18) https://bugs.python.org/issue31033

   (19) https://bugs.python.org/issue40541

   (20) https://bugs.python.org/issue40515

   (21) https://bugs.python.org/issue31033

   (22) https://bugs.python.org/issue40504

   (23) https://bugs.python.org/issue40559

   (24) https://bugs.python.org/issue40480

   (25) https://bugs.python.org/issue40495

   (26) https://bugs.python.org/issue40457

   (27) https://bugs.python.org/issue40355

   (28) https://bugs.python.org/issue40465

   (29) https://bugs.python.org/issue40459

   (30) https://bugs.python.org/issue39435

   (31) https://bugs.python.org/issue39305

   (32) https://bugs.python.org/issue32494

   (33) https://bugs.python.org/issue40453

   (34) https://bugs.python.org/issue40286

   (35) https://bugs.python.org/issue40394

   (36) https://bugs.python.org/issue39995

   (37) https://bugs.python.org/issue30966

   (38) https://bugs.python.org/issue30966

   (39) https://bugs.python.org/issue39966

   (40) https://bugs.python.org/issue25597

   (41) https://bugs.python.org/issue39791

   (42) https://bugs.python.org/issue40375

   (43) https://bugs.python.org/issue40389

   (44) https://bugs.python.org/issue40291

   (45) https://bugs.python.org/issue40273

   (46) https://bugs.python.org/issue39075

   (47) https://bugs.python.org/issue40192

   (48) https://bugs.python.org/issue40025

   (49) https://bugs.python.org/issue39058

   (50) https://bugs.python.org/issue24416


File: python.info,  Node: Documentation<14>,  Next: Tests<14>,  Prev: Library<19>,  Up: Python 3 9 0 beta 1

1.19.20.4 Documentation
.......................

   - bpo-34790(1): Add version of removal for explicit passing of coros
     to *note asyncio.wait(): 207.’s documentation

   - bpo-40561(2): Provide docstrings for webbrowser open functions.

   - bpo-40499(3): Mention that *note asyncio.wait(): 207. requires a
     non-empty set of awaitables.

   - bpo-39705(4): Tutorial example for sorted() in the Loop Techniques
     section is given a better explanation.  Also a new example is
     included to explain sorted()’s basic behavior.

   - bpo-39435(5): Fix an incorrect signature for *note pickle.loads():
     6ba. in the docs

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34790

   (2) https://bugs.python.org/issue40561

   (3) https://bugs.python.org/issue40499

   (4) https://bugs.python.org/issue39705

   (5) https://bugs.python.org/issue39435


File: python.info,  Node: Tests<14>,  Next: Build<13>,  Prev: Documentation<14>,  Up: Python 3 9 0 beta 1

1.19.20.5 Tests
...............

   - bpo-40055(1): distutils.tests now saves/restores warnings filters
     to leave them unchanged.  Importing tests imports docutils which
     imports pkg_resources which adds a warnings filter.

   - bpo-40436(2): test_gdb and test.pythoninfo now check gdb command
     exit code.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40055

   (2) https://bugs.python.org/issue40436


File: python.info,  Node: Build<13>,  Next: Windows<14>,  Prev: Tests<14>,  Up: Python 3 9 0 beta 1

1.19.20.6 Build
...............

   - bpo-40653(1): Move _dirnameW out of HAVE_SYMLINK to fix a potential
     compiling issue.

   - bpo-40514(2): Add ‘--with-experimental-isolated-subinterpreters’
     build option to ‘configure’: better isolate subinterpreters,
     experimental build mode.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40653

   (2) https://bugs.python.org/issue40514


File: python.info,  Node: Windows<14>,  Next: macOS<13>,  Prev: Build<13>,  Up: Python 3 9 0 beta 1

1.19.20.7 Windows
.................

   - bpo-40650(1): Include winsock2.h in pytime.c for timeval.

   - bpo-40458(2): Increase reserved stack space to prevent overflow
     crash on Windows.

   - bpo-39148(3): Add IPv6 support to *note asyncio: 9. datagram
     endpoints in ProactorEventLoop.  Change the raised exception for
     unknown address families to ValueError as it’s not coming from
     Windows API.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40650

   (2) https://bugs.python.org/issue40458

   (3) https://bugs.python.org/issue39148


File: python.info,  Node: macOS<13>,  Next: Tools/Demos<4>,  Prev: Windows<14>,  Up: Python 3 9 0 beta 1

1.19.20.8 macOS
...............

   - bpo-34956(1): When building Python on macOS from source, ‘_tkinter’
     now links with non-system Tcl and Tk frameworks if they are
     installed in ‘/Library/Frameworks’, as had been the case on older
     releases of macOS. If a macOS SDK is explicitly configured, by
     using ‘--enable-universalsdk=’ or ‘-isysroot’, only the SDK itself
     is searched.  The default behavior can still be overridden with
     ‘--with-tcltk-includes’ and ‘--with-tcltk-libs’.

   - bpo-35569(2): Expose RFC 3542 IPv6 socket options.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34956

   (2) https://bugs.python.org/issue35569


File: python.info,  Node: Tools/Demos<4>,  Next: C API<10>,  Prev: macOS<13>,  Up: Python 3 9 0 beta 1

1.19.20.9 Tools/Demos
.....................

   - bpo-40479(1): Update multissltest helper to test with latest
     OpenSSL 1.0.2, 1.1.0, 1.1.1, and 3.0.0-alpha.

   - bpo-40431(2): Fix a syntax typo in ‘turtledemo’ that now raises a
     ‘SyntaxError’.

   - bpo-40163(3): Fix multissltest tool.  OpenSSL has changed download
     URL for old releases.  The multissltest tool now tries to download
     from current and old download URLs.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40479

   (2) https://bugs.python.org/issue40431

   (3) https://bugs.python.org/issue40163


File: python.info,  Node: C API<10>,  Prev: Tools/Demos<4>,  Up: Python 3 9 0 beta 1

1.19.20.10 C API
................

   - bpo-39465(1): Remove the ‘_PyUnicode_ClearStaticStrings()’ function
     from the C API.

   - bpo-38787(2): Add PyCFunction_CheckExact() macro for exact type
     checks now that we allow subtypes of PyCFunction, as well as
     PyCMethod_CheckExact() and PyCMethod_Check() for the new PyCMethod
     subtype.

   - bpo-40545(3): Declare ‘_PyErr_GetTopmostException()’ with
     ‘PyAPI_FUNC()’ to properly export the function in the C API. The
     function remains private (‘_Py’) prefix.

   - bpo-40412(4): Nullify inittab_copy during finalization, preventing
     future interpreter initializations in an embedded situation from
     crashing.  Patch by Gregory Szorc.

   - bpo-40429(5): The *note PyThreadState_GetFrame(): 24e. function now
     returns a strong reference to the frame.

   - bpo-40428(6): Remove the following functions from the C API. Call
     ‘PyGC_Collect()’ explicitly to free all free lists.

        * ‘PyAsyncGen_ClearFreeLists()’

        * ‘PyContext_ClearFreeList()’

        * ‘PyDict_ClearFreeList()’

        * ‘PyFloat_ClearFreeList()’

        * ‘PyFrame_ClearFreeList()’

        * ‘PyList_ClearFreeList()’

        * ‘PySet_ClearFreeList()’

        * ‘PyTuple_ClearFreeList()’

   - bpo-40421(7): New *note PyFrame_GetBack(): 24a. function: get the
     frame next outer frame.

   - bpo-40421(8): New *note PyFrame_GetCode(): 249. function: return a
     borrowed reference to the frame code.

   - bpo-40217(9): Ensure that instances of types created with *note
     PyType_FromSpecWithBases(): 102d. will visit its class object when
     traversing references in the garbage collector (implemented as an
     extension of the provided *note tp_traverse: 23b.).  Patch by Pablo
     Galindo.

   - bpo-38787(10): Module C state is now accessible from C-defined heap
     type methods ( PEP 573(11)).  Patch by Marcel Plch and Petr
     Viktorin.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39465

   (2) https://bugs.python.org/issue38787

   (3) https://bugs.python.org/issue40545

   (4) https://bugs.python.org/issue40412

   (5) https://bugs.python.org/issue40429

   (6) https://bugs.python.org/issue40428

   (7) https://bugs.python.org/issue40421

   (8) https://bugs.python.org/issue40421

   (9) https://bugs.python.org/issue40217

   (10) https://bugs.python.org/issue38787

   (11) https://www.python.org/dev/peps/pep-0573


File: python.info,  Node: Python 3 9 0 alpha 6,  Next: Python 3 9 0 alpha 5,  Prev: Python 3 9 0 beta 1,  Up: Changelog

1.19.21 Python 3.9.0 alpha 6
----------------------------

`Release date: 2020-04-27'

* Menu:

* Security: Security<10>.
* Core and Builtins: Core and Builtins<18>.
* Library: Library<20>.
* Documentation: Documentation<15>.
* Tests: Tests<15>.
* Build: Build<14>.
* Windows: Windows<15>.
* macOS: macOS<14>.
* IDLE: IDLE<14>.
* Tools/Demos: Tools/Demos<5>.
* C API: C API<11>.


File: python.info,  Node: Security<10>,  Next: Core and Builtins<18>,  Up: Python 3 9 0 alpha 6

1.19.21.1 Security
..................

   - bpo-40121(1): Fixes audit events raised on creating a new socket.

   - bpo-39073(2): Disallow CR or LF in email.headerregistry.Address
     arguments to guard against header injection attacks.

   - bpo-39503(3): CVE-2020-8492: The *note AbstractBasicAuthHandler:
     fa2. class of the *note urllib.request: 129. module uses an
     inefficient regular expression which can be exploited by an
     attacker to cause a denial of service.  Fix the regex to prevent
     the catastrophic backtracking.  Vulnerability reported by Ben
     Caller and Matt Schwager.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40121

   (2) https://bugs.python.org/issue39073

   (3) https://bugs.python.org/issue39503


File: python.info,  Node: Core and Builtins<18>,  Next: Library<20>,  Prev: Security<10>,  Up: Python 3 9 0 alpha 6

1.19.21.2 Core and Builtins
...........................

   - bpo-40313(1): Improve the performance of bytes.hex().

   - bpo-40334(2): Switch to a new parser, based on PEG. For more
     details see PEP 617.  To temporarily switch back to the old parser,
     use ‘-X oldparser’ or ‘PYTHONOLDPARSER=1’.  In Python 3.10 we will
     remove the old parser completely, including the ‘parser’ module
     (already deprecated) and anything that depends on it.

   - bpo-40267(3): Fix the tokenizer to display the correct error
     message, when there is a SyntaxError on the last input character
     and no newline follows.  It used to be ‘unexpected EOF while
     parsing’, while it should be ‘invalid syntax’.

   - bpo-39522(4): Correctly unparse explicit ‘u’ prefix for strings
     when postponed evaluation for annotations activated.  Patch by
     Batuhan Taskaya.

   - bpo-40246(5): Report a specialized error message, ‘invalid string
     prefix’, when the tokenizer encounters a string with an invalid
     prefix.

   - bpo-40082(6): Fix the signal handler: it now always uses the main
     interpreter, rather than trying to get the current Python thread
     state.

   - bpo-37388(7): str.encode() and str.decode() no longer check the
     encoding and errors in development mode or in debug mode during
     Python finalization.  The codecs machinery can no longer work on
     very late calls to str.encode() and str.decode().

   - bpo-40077(8): Fix possible refleaks in ‘_json’, memo of
     PyScannerObject should be traversed.

   - bpo-37207(9): Speed up calls to ‘dict()’ by using the PEP 590(10)
     ‘vectorcall’ calling convention.

   - bpo-40141(11): Add column and line information to ‘ast.keyword’
     nodes.  Patch by Pablo Galindo.

   - bpo-1635741(12): Port *note resource: e0. to multiphase
     initialization ( PEP 489(13)).

   - bpo-1635741(14): Port *note math: b1. to multiphase initialization
     ( PEP 489(15)).

   - bpo-1635741(16): Port _uuid module to multiphase initialization (
     PEP 489(17)).

   - bpo-40077(18): Convert json module to use *note PyType_FromSpec():
     23a.

   - bpo-40067(19): Improve the error message for multiple star
     expressions in an assignment.  Patch by Furkan Onder

   - bpo-1635741(20): Port _functools module to multiphase
     initialization (PEP 489).  Patch by Paulo Henrique Silva.

   - bpo-1635741(21): Port operator module to multiphase initialization
     (PEP 489).  Patch by Paulo Henrique Silva.

   - bpo-20526(22): Fix *note PyThreadState_Clear(): 104c.
     ‘PyThreadState.frame’ is a borrowed reference, not a strong
     reference: ‘PyThreadState_Clear()’ must not call
     ‘Py_CLEAR(tstate->frame)’.

   - bpo-1635741(23): Port time module to multiphase initialization (
     PEP 489(24)).  Patch by Paulo Henrique Silva.

   - bpo-1635741(25): Port _weakref extension module to multiphase
     initialization ( PEP 489(26)).

   - bpo-40020(27): Fix a leak and subsequent crash in parsetok.c caused
     by realloc misuse on a rare codepath.

   - bpo-39939(28): Added str.removeprefix and str.removesuffix methods
     and corresponding bytes, bytearray, and collections.UserString
     methods to remove affixes from a string if present.  See PEP
     616(29) for a full description.  Patch by Dennis Sweeney.

   - bpo-39481(30): Implement PEP 585.  This supports list[int],
     tuple[str, …] etc.

   - bpo-32894(31): Support unparsing of infinity numbers in postponed
     annotations.  Patch by Batuhan Taşkaya.

   - bpo-37207(32): Speed up calls to ‘list()’ by using the PEP 590(33)
     ‘vectorcall’ calling convention.  Patch by Mark Shannon.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40313

   (2) https://bugs.python.org/issue40334

   (3) https://bugs.python.org/issue40267

   (4) https://bugs.python.org/issue39522

   (5) https://bugs.python.org/issue40246

   (6) https://bugs.python.org/issue40082

   (7) https://bugs.python.org/issue37388

   (8) https://bugs.python.org/issue40077

   (9) https://bugs.python.org/issue37207

   (10) https://www.python.org/dev/peps/pep-0590

   (11) https://bugs.python.org/issue40141

   (12) https://bugs.python.org/issue1635741

   (13) https://www.python.org/dev/peps/pep-0489

   (14) https://bugs.python.org/issue1635741

   (15) https://www.python.org/dev/peps/pep-0489

   (16) https://bugs.python.org/issue1635741

   (17) https://www.python.org/dev/peps/pep-0489

   (18) https://bugs.python.org/issue40077

   (19) https://bugs.python.org/issue40067

   (20) https://bugs.python.org/issue1635741

   (21) https://bugs.python.org/issue1635741

   (22) https://bugs.python.org/issue20526

   (23) https://bugs.python.org/issue1635741

   (24) https://www.python.org/dev/peps/pep-0489

   (25) https://bugs.python.org/issue1635741

   (26) https://www.python.org/dev/peps/pep-0489

   (27) https://bugs.python.org/issue40020

   (28) https://bugs.python.org/issue39939

   (29) https://www.python.org/dev/peps/pep-0616

   (30) https://bugs.python.org/issue39481

   (31) https://bugs.python.org/issue32894

   (32) https://bugs.python.org/issue37207

   (33) https://www.python.org/dev/peps/pep-0590


File: python.info,  Node: Library<20>,  Next: Documentation<15>,  Prev: Core and Builtins<18>,  Up: Python 3 9 0 alpha 6

1.19.21.3 Library
.................

   - bpo-40398(1): *note typing.get_args(): 27d. now always returns an
     empty tuple for special generic aliases.

   - bpo-40396(2): Functions *note typing.get_origin(): 36e, *note
     typing.get_args(): 27d. and *note typing.get_type_hints(): 1ef.
     support now generic aliases like ‘list[int]’.

   - bpo-38061(3): Optimize the *note subprocess: f9. module on FreeBSD
     using ‘closefrom()’.  A single ‘close(fd)’ syscall is cheap, but
     when ‘sysconf(_SC_OPEN_MAX)’ is high, the loop calling ‘close(fd)’
     on each file descriptor can take several milliseconds.

     The workaround on FreeBSD to improve performance was to load and
     mount the fdescfs kernel module, but this is not enabled by
     default.

     Initial patch by Ed Maste (emaste), Conrad Meyer (cem), Kyle Evans
     (kevans) and Kubilay Kocak (koobs):
     ‘https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274’

   - bpo-38061(4): On FreeBSD, ‘os.closerange(fd_low, fd_high)’ now
     calls ‘closefrom(fd_low)’ if `fd_high' is greater than or equal to
     ‘sysconf(_SC_OPEN_MAX)’.

     Initial patch by Ed Maste (emaste), Conrad Meyer (cem), Kyle Evans
     (kevans) and Kubilay Kocak (koobs):
     ‘https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274’

   - bpo-40360(5): The *note lib2to3: a7. module is pending deprecation
     due to PEP 617(6).

   - bpo-40138(7): Fix the Windows implementation of *note os.waitpid():
     760. for exit code larger than ‘INT_MAX >> 8’.  The exit status is
     now interpreted as an unsigned number.

   - bpo-39942(8): Set “__main__” as the default module name when
     “__name__” is missing in *note typing.TypeVar: 104e.  Patch by
     Weipeng Hong.

   - bpo-40275(9): The *note logging: aa. package is now imported lazily
     in *note unittest: 124. only when the *note assertLogs(): 9eb.
     assertion is used.

   - bpo-40275(10): The *note asyncio: 9. package is now imported lazily
     in *note unittest: 124. only when the *note
     IsolatedAsyncioTestCase: 377. class is used.

   - bpo-40330(11): In ‘ShareableList.__setitem__()’, check the size of
     a new string item after encoding it to utf-8, not before.

   - bpo-40148(12): Added ‘pathlib.Path.with_stem()’ to create a new
     Path with the stem replaced.

   - bpo-40325(13): Deprecated support for set objects in
     random.sample().

   - bpo-40257(14): Improved help for the *note typing: 122. module.
     Docstrings are now shown for all special forms and special generic
     aliases (like ‘Union’ and ‘List’).  Using ‘help()’ with generic
     alias like ‘List[int]’ will show the help for the correspondent
     concrete type (‘list’ in this case).

   - bpo-40257(15): func:*note inspect.getdoc: 307. no longer returns
     docstring inherited from the type of the object or from parent
     class if it is a class if it is not defined in the object itself.
     In *note pydoc: d9. the documentation string is now shown not only
     for class, function, method etc, but for any object that has its
     own ‘__doc__’ attribute.

   - bpo-40287(16): Fixed ‘SpooledTemporaryFile.seek()’ to return the
     position.

   - bpo-40290(17): Added zscore() to statistics.NormalDist().

   - bpo-40282(18): Allow ‘random.getrandbits(0)’ to succeed and to
     return 0.

   - bpo-40286(19): Add *note random.randbytes(): 104f. function and
     ‘random.Random.randbytes()’ method to generate random bytes.

   - bpo-40277(20): *note collections.namedtuple(): 1a1. now provides a
     human-readable repr for its field accessors.

   - bpo-40270(21): The included copy of sqlite3 on Windows is now
     compiled with the json extension.  This allows the use of functions
     such as ‘json_object’.

   - bpo-29255(22): Wait in ‘KqueueSelector.select’ when no fds are
     registered

   - bpo-40260(23): Ensure *note modulefinder: b4. uses *note
     io.open_code(): 1050. and respects coding comments.

   - bpo-40234(24): Allow again to spawn daemon threads in
     subinterpreters (revert change which denied them).

   - bpo-39207(25): Workers in *note ProcessPoolExecutor: 196. are now
     spawned on demand, only when there are no available idle workers to
     reuse.  This optimizes startup overhead and reduces the amount of
     lost CPU time to idle workers.  Patch by Kyle Stanley.

   - bpo-40091(26): Fix a hang at fork in the logging module: the new
     private _at_fork_reinit() method is now used to reinitialize locks
     at fork in the child process.

   - bpo-40149(27): Implement traverse and clear slots in _abc._abc_data
     type.

   - bpo-40208(28): Remove deprecated ‘symtable.SymbolTable.has_exec()’.

   - bpo-40196(29): Fix a bug in the *note symtable: fc. module that was
     causing incorrectly report global variables as local.  Patch by
     Pablo Galindo.

   - bpo-40190(30): Add support for ‘_SC_AIX_REALMEM’ to
     ‘posix.sysconf()’.

   - bpo-40182(31): Removed the ‘_field_types’ attribute of the *note
     typing.NamedTuple: 227. class.

   - bpo-36517(32): Multiple inheritance with *note typing.NamedTuple:
     227. now raises an error instead of silently ignoring other types.

   - bpo-40126(33): Fixed reverting multiple patches in unittest.mock.
     Patcher’s ‘__exit__()’ is now never called if its ‘__enter__()’ is
     failed.  Returning true from ‘__exit__()’ silences now the
     exception.

   - bpo-40094(34): CGIHTTPRequestHandler of http.server now logs the
     CGI script exit code, rather than the CGI script exit status of
     os.waitpid().  For example, if the script is killed by signal 11,
     it now logs: “CGI script exit code -11.”

   - bpo-40108(35): Improve the error message when triying to import a
     module using *note runpy: e2. and incorrently use the “.py”
     extension at the end of the module name.  Patch by Pablo Galindo.

   - bpo-40094(36): Add *note os.waitstatus_to_exitcode(): 1ce.
     function: convert a wait status to an exit code.

   - bpo-40089(37): Fix threading._after_fork(): if fork was not called
     by a thread spawned by threading.Thread, threading._after_fork()
     now creates a _MainThread instance for _main_thread, instead of a
     _DummyThread instance.

   - bpo-40089(38): Add a private ‘_at_fork_reinit()’ method to
     ‘_thread.Lock’, ‘_thread.RLock’, *note threading.RLock: cba. and
     *note threading.Condition: b82. classes: reinitialize the lock at
     fork in the child process, reset the lock to the unlocked state.
     Rename also the private ‘_reset_internal_locks()’ method of *note
     threading.Event: b85. to ‘_at_fork_reinit()’.

   - bpo-25780(39): Expose *note CAN_RAW_JOIN_FILTERS: 1e2. in the *note
     socket: ef. module.

   - bpo-39503(40): *note AbstractBasicAuthHandler: fa2. of *note
     urllib.request: 129. now parses all WWW-Authenticate HTTP headers
     and accepts multiple challenges per header: use the realm of the
     first Basic challenge.

   - bpo-39812(41): Removed daemon threads from *note
     concurrent.futures: 21. by adding an internal
     ‘threading._register_atexit()’, which calls registered functions
     prior to joining all non-daemon threads.  This allows for
     compatibility with subinterpreters, which don’t support daemon
     threads.

   - bpo-40050(42): Fix ‘importlib._bootstrap_external’: avoid creating
     a new ‘winreg’ builtin module if it’s already available in *note
     sys.modules: 1051, and remove redundant imports.

   - bpo-40014(43): Fix ‘os.getgrouplist()’: if ‘getgrouplist()’
     function fails because the group list is too small, retry with a
     larger group list.  On failure, the glibc implementation of
     ‘getgrouplist()’ sets ‘ngroups’ to the total number of groups.  For
     other implementations, double the group list size.

   - bpo-40017(44): Add *note time.CLOCK_TAI: 1052. constant if the
     operating system support it.

   - bpo-40016(45): In re docstring, clarify the relationship between
     inline and argument compile flags.

   - bpo-39953(46): Update internal table of OpenSSL error codes in the
     ‘ssl’ module.

   - bpo-36144(47): Added PEP 584(48) operators to *note
     weakref.WeakValueDictionary: 1053.

   - bpo-36144(49): Added PEP 584(50) operators to *note
     weakref.WeakKeyDictionary: 1054.

   - bpo-38891(51): Fix linear runtime behaviour of the ‘__getitem__’
     and ‘__setitem__’ methods in *note
     multiprocessing.shared_memory.ShareableList: 1055.  This avoids
     quadratic performance when iterating a ‘ShareableList’.  Patch by
     Thomas Krennwallner.

   - bpo-39682(52): Remove undocumented support for `closing' a *note
     pathlib.Path: 32f. object via its context manager.  The context
     manager magic methods remain, but they are now a no-op, making
     ‘Path’ objects immutable.

   - bpo-36144(53): Added PEP 584(54) operators (‘|’ and ‘|=’) to *note
     collections.ChainMap: 5a4.

   - bpo-39011(55): Normalization of line endings in ElementTree
     attributes was removed, as line endings which were replaced by
     entity numbers should be preserved in original form.

   - bpo-38410(56): Properly handle *note sys.audit(): 1056. failures in
     *note sys.set_asyncgen_hooks(): 1057.

   - bpo-36541(57): lib2to3 now recognizes named assignment expressions
     (the walrus operator, ‘:=’)

   - bpo-35967(58): In platform, delay the invocation of ‘uname -p’
     until the processor attribute is requested.

   - bpo-35113(59): *note inspect.getsource(): fda. now returns correct
     source code for inner class with same name as module level class.
     Decorators are also returned as part of source of the class.  Patch
     by Karthikeyan Singaravelan.

   - bpo-33262(60): Deprecate passing None as an argument for *note
     shlex.split(): 210.’s ‘s’ parameter.  Patch by Zackery Spytz.

   - bpo-31758(61): Prevent crashes when using an uninitialized
     ‘_elementtree.XMLParser’ object.  Patch by Oren Milman.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40398

   (2) https://bugs.python.org/issue40396

   (3) https://bugs.python.org/issue38061

   (4) https://bugs.python.org/issue38061

   (5) https://bugs.python.org/issue40360

   (6) https://www.python.org/dev/peps/pep-0617

   (7) https://bugs.python.org/issue40138

   (8) https://bugs.python.org/issue39942

   (9) https://bugs.python.org/issue40275

   (10) https://bugs.python.org/issue40275

   (11) https://bugs.python.org/issue40330

   (12) https://bugs.python.org/issue40148

   (13) https://bugs.python.org/issue40325

   (14) https://bugs.python.org/issue40257

   (15) https://bugs.python.org/issue40257

   (16) https://bugs.python.org/issue40287

   (17) https://bugs.python.org/issue40290

   (18) https://bugs.python.org/issue40282

   (19) https://bugs.python.org/issue40286

   (20) https://bugs.python.org/issue40277

   (21) https://bugs.python.org/issue40270

   (22) https://bugs.python.org/issue29255

   (23) https://bugs.python.org/issue40260

   (24) https://bugs.python.org/issue40234

   (25) https://bugs.python.org/issue39207

   (26) https://bugs.python.org/issue40091

   (27) https://bugs.python.org/issue40149

   (28) https://bugs.python.org/issue40208

   (29) https://bugs.python.org/issue40196

   (30) https://bugs.python.org/issue40190

   (31) https://bugs.python.org/issue40182

   (32) https://bugs.python.org/issue36517

   (33) https://bugs.python.org/issue40126

   (34) https://bugs.python.org/issue40094

   (35) https://bugs.python.org/issue40108

   (36) https://bugs.python.org/issue40094

   (37) https://bugs.python.org/issue40089

   (38) https://bugs.python.org/issue40089

   (39) https://bugs.python.org/issue25780

   (40) https://bugs.python.org/issue39503

   (41) https://bugs.python.org/issue39812

   (42) https://bugs.python.org/issue40050

   (43) https://bugs.python.org/issue40014

   (44) https://bugs.python.org/issue40017

   (45) https://bugs.python.org/issue40016

   (46) https://bugs.python.org/issue39953

   (47) https://bugs.python.org/issue36144

   (48) https://www.python.org/dev/peps/pep-0584

   (49) https://bugs.python.org/issue36144

   (50) https://www.python.org/dev/peps/pep-0584

   (51) https://bugs.python.org/issue38891

   (52) https://bugs.python.org/issue39682

   (53) https://bugs.python.org/issue36144

   (54) https://www.python.org/dev/peps/pep-0584

   (55) https://bugs.python.org/issue39011

   (56) https://bugs.python.org/issue38410

   (57) https://bugs.python.org/issue36541

   (58) https://bugs.python.org/issue35967

   (59) https://bugs.python.org/issue35113

   (60) https://bugs.python.org/issue33262

   (61) https://bugs.python.org/issue31758


File: python.info,  Node: Documentation<15>,  Next: Tests<15>,  Prev: Library<20>,  Up: Python 3 9 0 alpha 6

1.19.21.4 Documentation
.......................

   - bpo-27635(1): The pickle documentation incorrectly claimed that
     ‘__new__’ isn’t called by default when unpickling.

   - bpo-39879(2): Updated *note Data model: 1059. docs to include *note
     dict(): 164. insertion order preservation.  Patch by Furkan Onder
     and Samy Lahfa.

   - bpo-38387(3): Document *note PyDoc_STRVAR: 105a. macro in the C-API
     reference.

   - bpo-13743(4): Some methods within xml.dom.minidom.Element class are
     now better documented.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27635

   (2) https://bugs.python.org/issue39879

   (3) https://bugs.python.org/issue38387

   (4) https://bugs.python.org/issue13743


File: python.info,  Node: Tests<15>,  Next: Build<14>,  Prev: Documentation<15>,  Up: Python 3 9 0 alpha 6

1.19.21.5 Tests
...............

   - bpo-31904(1): Set expected default encoding in
     test_c_locale_coercion.py for VxWorks RTOS.

   - bpo-40162(2): Update Travis CI configuration to OpenSSL 1.1.1f.

   - bpo-40146(3): Update OpenSSL to 1.1.1f in Azure Pipelines.

   - bpo-40094(4): Add *note test.support.wait_process(): 105c.
     function.

   - bpo-40003(5): ‘test.bisect_cmd’ now copies Python command line
     options like ‘-O’ or ‘-W’.  Moreover, emit a warning if
     ‘test.bisect_cmd’ is used with ‘-w’/‘--verbose2’ option.

   - bpo-39380(6): Add the encoding in *note ftplib.FTP: 1a6. and *note
     ftplib.FTP_TLS: 1a7. to the constructor as keyword-only and change
     the default from ‘latin-1’ to ‘utf-8’ to follow RFC 2640(7).

   - bpo-39793(8): Use the same domain when testing ‘make_msgid’.  Patch
     by Batuhan Taskaya.

   - bpo-1812(9): Fix newline handling in doctest.testfile when loading
     from a package whose loader has a get_data method.  Patch by Peter
     Donis.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31904

   (2) https://bugs.python.org/issue40162

   (3) https://bugs.python.org/issue40146

   (4) https://bugs.python.org/issue40094

   (5) https://bugs.python.org/issue40003

   (6) https://bugs.python.org/issue39380

   (7) https://tools.ietf.org/html/rfc2640.html

   (8) https://bugs.python.org/issue39793

   (9) https://bugs.python.org/issue1812


File: python.info,  Node: Build<14>,  Next: Windows<15>,  Prev: Tests<15>,  Up: Python 3 9 0 alpha 6

1.19.21.6 Build
...............

   - bpo-38360(1): Support single-argument form of macOS -isysroot flag.

   - bpo-40158(2): Fix CPython MSBuild Properties in NuGet Package
     (build/native/python.props)

   - bpo-38527(3): Fix configure check on Solaris for “float word
     ordering”: sometimes, the correct “grep” command was not being
     used.  Patch by Arnon Yaari.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38360

   (2) https://bugs.python.org/issue40158

   (3) https://bugs.python.org/issue38527


File: python.info,  Node: Windows<15>,  Next: macOS<14>,  Prev: Build<14>,  Up: Python 3 9 0 alpha 6

1.19.21.7 Windows
.................

   - bpo-40164(1): Updates Windows to OpenSSL 1.1.1f

   - bpo-8901(2): Ignore the Windows registry when the ‘-E’ option is
     used.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40164

   (2) https://bugs.python.org/issue8901


File: python.info,  Node: macOS<14>,  Next: IDLE<14>,  Prev: Windows<15>,  Up: Python 3 9 0 alpha 6

1.19.21.8 macOS
...............

   - bpo-38329(1): python.org macOS installers now update the Current
     version symlink of /Library/Frameworks/Python.framework/Versions
     for 3.9 installs.  Previously, Current was only updated for Python
     2.x installs.  This should make it easier to embed Python 3 into
     other macOS applications.

   - bpo-40164(2): Update macOS installer builds to use OpenSSL 1.1.1g.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38329

   (2) https://bugs.python.org/issue40164


File: python.info,  Node: IDLE<14>,  Next: Tools/Demos<5>,  Prev: macOS<14>,  Up: Python 3 9 0 alpha 6

1.19.21.9 IDLE
..............

   - bpo-38439(1): Add a 256×256 pixel IDLE icon to support more modern
     environments.  Created by Andrew Clover.  Delete the unused macOS
     idle.icns icon file.

   - bpo-38689(2): IDLE will no longer freeze when inspect.signature
     fails when fetching a calltip.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38439

   (2) https://bugs.python.org/issue38689


File: python.info,  Node: Tools/Demos<5>,  Next: C API<11>,  Prev: IDLE<14>,  Up: Python 3 9 0 alpha 6

1.19.21.10 Tools/Demos
......................

   - bpo-40385(1): Removed the checkpyc.py tool.  Please see compileall
     without force mode as a potential alternative.

   - bpo-40179(2): Fixed translation of ‘#elif’ in Argument Clinic.

   - bpo-40094(3): Fix ‘which.py’ script exit code: it now uses *note
     os.waitstatus_to_exitcode(): 1ce. to convert *note os.system():
     e86. exit status into an exit code.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40385

   (2) https://bugs.python.org/issue40179

   (3) https://bugs.python.org/issue40094


File: python.info,  Node: C API<11>,  Prev: Tools/Demos<5>,  Up: Python 3 9 0 alpha 6

1.19.21.11 C API
................

   - bpo-40241(1): Move the ‘PyGC_Head’ structure to the internal C API.

   - bpo-40170(2): Convert *note PyObject_IS_GC(): 267. macro to a
     function to hide implementation details.

   - bpo-40241(3): Add the functions *note PyObject_GC_IsTracked(): 254.
     and *note PyObject_GC_IsFinalized(): 255. to the public API to
     allow to query if Python objects are being currently tracked or
     have been already finalized by the garbage collector respectively.
     Patch by Pablo Galindo.

   - bpo-40170(4): The ‘PyObject_NEW()’ macro becomes an alias to the
     *note PyObject_New(): 268. macro, and the ‘PyObject_NEW_VAR()’
     macro becomes an alias to the *note PyObject_NewVar(): 269. macro,
     to hide implementation details.  They no longer access directly the
     *note PyTypeObject.tp_basicsize: 26a. member.

   - bpo-40170(5): *note PyType_HasFeature(): 1010. now always calls
     *note PyType_GetFlags(): 1012. to hide implementation details.
     Previously, it accessed directly the *note PyTypeObject.tp_flags:
     1011. member when the limited C API was not used.

   - bpo-40170(6): Convert the ‘PyObject_GET_WEAKREFS_LISTPTR()’ macro
     to a function to hide implementation details: the macro accessed
     directly to the *note PyTypeObject.tp_weaklistoffset: 26b. member.

   - bpo-40170(7): Convert *note PyObject_CheckBuffer(): 26c. macro to a
     function to hide implementation details: the macro accessed
     directly the *note PyTypeObject.tp_as_buffer: 26d. member.

   - bpo-40170(8): Always declare *note PyIndex_Check(): 26e. as an
     opaque function to hide implementation details: remove
     ‘PyIndex_Check()’ macro.  The macro accessed directly the *note
     PyTypeObject.tp_as_number: 26f. member.

   - bpo-39947(9): Add *note PyThreadState_GetID(): 24f. function: get
     the unique identifier of a Python thread state.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40241

   (2) https://bugs.python.org/issue40170

   (3) https://bugs.python.org/issue40241

   (4) https://bugs.python.org/issue40170

   (5) https://bugs.python.org/issue40170

   (6) https://bugs.python.org/issue40170

   (7) https://bugs.python.org/issue40170

   (8) https://bugs.python.org/issue40170

   (9) https://bugs.python.org/issue39947


File: python.info,  Node: Python 3 9 0 alpha 5,  Next: Python 3 9 0 alpha 4,  Prev: Python 3 9 0 alpha 6,  Up: Changelog

1.19.22 Python 3.9.0 alpha 5
----------------------------

`Release date: 2020-03-23'

* Menu:

* Security: Security<11>.
* Core and Builtins: Core and Builtins<19>.
* Library: Library<21>.
* Documentation: Documentation<16>.
* Tests: Tests<16>.
* Build: Build<15>.
* Windows: Windows<16>.
* macOS: macOS<15>.
* IDLE: IDLE<15>.
* Tools/Demos: Tools/Demos<6>.
* C API: C API<12>.


File: python.info,  Node: Security<11>,  Next: Core and Builtins<19>,  Up: Python 3 9 0 alpha 5

1.19.22.1 Security
..................

   - bpo-38576(1): Disallow control characters in hostnames in
     http.client, addressing CVE-2019-18348.  Such potentially malicious
     header injection URLs now cause a InvalidURL to be raised.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38576


File: python.info,  Node: Core and Builtins<19>,  Next: Library<21>,  Prev: Security<11>,  Up: Python 3 9 0 alpha 5

1.19.22.2 Core and Builtins
...........................

   - bpo-40010(1): Optimize pending calls in multithreaded applications.
     If a thread different than the main thread schedules a pending call
     (*note Py_AddPendingCall(): 25f.), the bytecode evaluation loop is
     no longer interrupted at each bytecode instruction to check for
     pending calls which cannot be executed.  Only the main thread can
     execute pending calls.

     Previously, the bytecode evaluation loop was interrupted at each
     instruction until the main thread executes pending calls.

   - bpo-1635741(2): Port _weakref extension module to multiphase
     initialization ( PEP 489(3)).

   - bpo-1635741(4): Port _collections module to multiphase
     initialization ( PEP 489(5)).

   - bpo-40010(6): Optimize signal handling in multithreaded
     applications.  If a thread different than the main thread gets a
     signal, the bytecode evaluation loop is no longer interrupted at
     each bytecode instruction to check for pending signals which cannot
     be handled.  Only the main thread of the main interpreter can
     handle signals.

     Previously, the bytecode evaluation loop was interrupted at each
     instruction until the main thread handles signals.

   - bpo-39984(7): If *note Py_AddPendingCall(): 25f. is called in a
     subinterpreter, the function is now scheduled to be called from the
     subinterpreter, rather than being called from the main interpreter.
     Each subinterpreter now has its own list of scheduled calls.

   - bpo-1635741(8): Port _heapq module to multiphase initialization.

   - bpo-1635741(9): Port itertools module to multiphase initialization
     ( PEP 489(10)).

   - bpo-37207(11): Speed up calls to ‘frozenset()’ by using the PEP
     590(12) ‘vectorcall’ calling convention.  Patch by Dong-hee Na.

   - bpo-39984(13): subinterpreters: Move
     ‘_PyRuntimeState.ceval.tracing_possible’ to
     ‘PyInterpreterState.ceval.tracing_possible’: each interpreter now
     has its own variable.

   - bpo-37207(14): Speed up calls to ‘set()’ by using the PEP 590(15)
     ‘vectorcall’ calling convention.  Patch by Dong-hee Na.

   - bpo-1635741(16): Port _statistics module to multiphase
     initialization ( PEP 489(17)).

   - bpo-39968(18): Use inline function to replace extension modules’
     get_module_state macros.

   - bpo-39965(19): Correctly raise ‘SyntaxError’ if `await' is used
     inside non-async functions and ‘PyCF_ALLOW_TOP_LEVEL_AWAIT’ is set
     (like in the asyncio REPL). Patch by Pablo Galindo.

   - bpo-39562(20): Allow executing asynchronous comprehensions on the
     top level when the ‘PyCF_ALLOW_TOP_LEVEL_AWAIT’ flag is given.
     Patch by Batuhan Taskaya.

   - bpo-37207(21): Speed up calls to ‘tuple()’ by using the PEP 590(22)
     ‘vectorcall’ calling convention.  Patch by Dong-hee Na.

   - bpo-38373(23): Changed list overallocation strategy.  It no longer
     overallocates if the new size is closer to overalocated size than
     to the old size and adds padding.

   - bpo-39926(24): Update Unicode database to Unicode version 13.0.0.

   - bpo-19466(25): Clear the frames of daemon threads earlier during
     the Python shutdown to call objects destructors.  So “unclosed
     file” resource warnings are now emitted for daemon threads in a
     more reliable way.

   - bpo-38894(26): Fix a bug that was causing incomplete results when
     calling ‘pathlib.Path.glob’ in the presence of symlinks that point
     to files where the user does not have read access.  Patch by Pablo
     Galindo and Matt Wozniski.

   - bpo-39877(27): Fix *note PyEval_RestoreThread(): 3d6. random crash
     at exit with daemon threads.  It now accesses the ‘_PyRuntime’
     variable directly instead of using ‘tstate->interp->runtime’, since
     ‘tstate’ can be a dangling pointer after *note Py_Finalize(): db3.
     has been called.  Moreover, the daemon thread now exits before
     trying to take the GIL.

   - bpo-39871(28): Fix a possible *note SystemError: 6f2. in
     ‘math.{atan2,copysign,remainder}()’ when the first argument cannot
     be converted to a *note float: 1fd.  Patch by Zackery Spytz.

   - bpo-39776(29): Fix race condition where threads created by
     PyGILState_Ensure() could get a duplicate id.

     This affects consumers of tstate->id like the contextvar caching
     machinery, which could return invalid cached objects under heavy
     thread load (observed in embedded scenarios).

   - bpo-39778(30): Fixed a crash due to incorrect handling of weak
     references in ‘collections.OrderedDict’ classes.  Patch by Pablo
     Galindo.

   - bpo-1635741(31): Port audioop extension module to multiphase
     initialization ( PEP 489(32)).

   - bpo-39702(33): Relax *note decorator: 174. grammar restrictions to
     allow any valid expression ( PEP 614(34)).

   - bpo-38091(35): Tweak import deadlock detection code to not deadlock
     itself.

   - bpo-1635741(36): Port _locale extension module to multiphase
     initialization ( PEP 489(37)).

   - bpo-39087(38): Optimize *note PyUnicode_AsUTF8(): 52f. and *note
     PyUnicode_AsUTF8AndSize(): 52e. slightly when they need to create
     internal UTF-8 cache.

   - bpo-39520(39): Fix unparsing of ext slices with no items
     (‘foo[:,]’).  Patch by Batuhan Taskaya.

   - bpo-39220(40): Do not optimize annotations if ‘from __future__
     import annotations’ is used.  Patch by Pablo Galindo.

   - bpo-35712(41): Using *note NotImplemented: 202. in a boolean
     context has been deprecated.  Patch contributed by Josh Rosenberg.

   - bpo-22490(42): Don’t leak environment variable
     ‘__PYVENV_LAUNCHER__’ into the interpreter session on macOS.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40010

   (2) https://bugs.python.org/issue1635741

   (3) https://www.python.org/dev/peps/pep-0489

   (4) https://bugs.python.org/issue1635741

   (5) https://www.python.org/dev/peps/pep-0489

   (6) https://bugs.python.org/issue40010

   (7) https://bugs.python.org/issue39984

   (8) https://bugs.python.org/issue1635741

   (9) https://bugs.python.org/issue1635741

   (10) https://www.python.org/dev/peps/pep-0489

   (11) https://bugs.python.org/issue37207

   (12) https://www.python.org/dev/peps/pep-0590

   (13) https://bugs.python.org/issue39984

   (14) https://bugs.python.org/issue37207

   (15) https://www.python.org/dev/peps/pep-0590

   (16) https://bugs.python.org/issue1635741

   (17) https://www.python.org/dev/peps/pep-0489

   (18) https://bugs.python.org/issue39968

   (19) https://bugs.python.org/issue39965

   (20) https://bugs.python.org/issue39562

   (21) https://bugs.python.org/issue37207

   (22) https://www.python.org/dev/peps/pep-0590

   (23) https://bugs.python.org/issue38373

   (24) https://bugs.python.org/issue39926

   (25) https://bugs.python.org/issue19466

   (26) https://bugs.python.org/issue38894

   (27) https://bugs.python.org/issue39877

   (28) https://bugs.python.org/issue39871

   (29) https://bugs.python.org/issue39776

   (30) https://bugs.python.org/issue39778

   (31) https://bugs.python.org/issue1635741

   (32) https://www.python.org/dev/peps/pep-0489

   (33) https://bugs.python.org/issue39702

   (34) https://www.python.org/dev/peps/pep-0614

   (35) https://bugs.python.org/issue38091

   (36) https://bugs.python.org/issue1635741

   (37) https://www.python.org/dev/peps/pep-0489

   (38) https://bugs.python.org/issue39087

   (39) https://bugs.python.org/issue39520

   (40) https://bugs.python.org/issue39220

   (41) https://bugs.python.org/issue35712

   (42) https://bugs.python.org/issue22490


File: python.info,  Node: Library<21>,  Next: Documentation<16>,  Prev: Core and Builtins<19>,  Up: Python 3 9 0 alpha 5

1.19.22.3 Library
.................

   - bpo-39830(1): Add *note zipfile.Path: 1067. to ‘__all__’ in the
     *note zipfile: 14b. module.

   - bpo-40000(2): Improved error messages for validation of
     ‘ast.Constant’ nodes.  Patch by Batuhan Taskaya.

   - bpo-39999(3): ‘__module__’ of the AST node classes is now set to
     “ast” instead of “_ast”.  Added docstrings for dummy AST node
     classes and deprecated attributes.

   - bpo-39991(4): *note uuid.getnode(): 517. now skips IPv6 addresses
     with the same string length than a MAC address (17 characters):
     only use MAC addresses.

   - bpo-39988(5): Deprecated ‘ast.AugLoad’ and ‘ast.AugStore’ node
     classes because they are no longer used.

   - bpo-39656(6): Ensure ‘bin/python3.#’ is always present in virtual
     environments on POSIX platforms - by Anthony Sottile.

   - bpo-39969(7): Deprecated ‘ast.Param’ node class because it’s no
     longer used.  Patch by Batuhan Taskaya.

   - bpo-39360(8): Ensure all workers exit when finalizing a
     ‘multiprocessing.Pool’ implicitly via the module finalization
     handlers of multiprocessing.  This fixes a deadlock situation that
     can be experienced when the Pool is not properly finalized via the
     context manager or a call to ‘multiprocessing.Pool.terminate’.
     Patch by Batuhan Taskaya and Pablo Galindo.

   - bpo-35370(9): sys.settrace(), sys.setprofile() and
     _lsprof.Profiler.enable() now properly report *note PySys_Audit():
     1068. error if “sys.setprofile” or “sys.settrace” audit event is
     denied.

   - bpo-39936(10): AIX: Fix _aix_support module when the subprocess is
     not available, when building Python from scratch.  It now uses new
     private _bootsubprocess module, rather than having two
     implementations depending if subprocess is available or not.  So
     _aix_support.aix_platform() result is now the same if subprocess is
     available or not.

   - bpo-36144(11): *note collections.OrderedDict: 2ea. now implements
     ‘|’ and ‘|=’ ( PEP 584(12)).

   - bpo-39652(13): The column name found in
     ‘sqlite3.Cursor.description’ is now truncated on the first ‘[’ only
     if the PARSE_COLNAMES option is set.

   - bpo-39915(14): Ensure *note
     unittest.mock.AsyncMock.await_args_list: 1069. has call objects in
     the order of awaited arguments instead of using *note
     unittest.mock.Mock.call_args: 106a. which has the last value of the
     call.  Patch by Karthikeyan Singaravelan.

   - bpo-36144(15): Updated *note os.environ: c09. and *note
     os.environb: c65. to support PEP 584(16)’s merge (‘|’) and update
     (‘|=’) operators.

   - bpo-38662(17): The ‘ensurepip’ module now invokes ‘pip’ via the
     ‘runpy’ module.  Hence it is no longer tightly coupled with the
     internal API of the bundled ‘pip’ version, allowing easier updates
     to a newer ‘pip’ version both internally and for distributors.

   - bpo-38075(18): Fix the ‘random.Random.seed()’ method when a *note
     bool: 2bd. is passed as the seed.

   - bpo-39916(19): More reliable use of ‘os.scandir()’ in
     ‘Path.glob()’.  It no longer emits a ResourceWarning when
     interrupted.

   - bpo-39850(20): *note multiprocessing: b7. now supports abstract
     socket addresses (if abstract sockets are supported in the running
     platform).  When creating arbitrary addresses (like when
     default-constructing *note multiprocessing.connection.Listener:
     106b. objects) abstract sockets are preferred to avoid the case
     when the temporary-file-generated address is too large for an
     AF_UNIX socket address.  Patch by Pablo Galindo.

   - bpo-36287(21): *note ast.dump(): 185. no longer outputs optional
     fields and attributes with default values.  The default values for
     optional fields and attributes of AST nodes are now set as class
     attributes (e.g.  ‘Constant.kind’ is set to ‘None’).

   - bpo-39889(22): Fixed *note ast.unparse(): 186. for extended slices
     containing a single element (e.g.  ‘a[i:j,]’).  Remove redundant
     tuples when index with a tuple (e.g.  ‘a[i, j]’).

   - bpo-39828(23): Fix *note json.tool: a5. to catch *note
     BrokenPipeError: a7e.  Patch by Dong-hee Na.

   - bpo-13487(24): Avoid a possible `“RuntimeError: dictionary changed
     size during iteration”' from *note inspect.getmodule(): f6b. when
     it tried to loop through *note sys.modules: 1051.

   - bpo-39674(25): Revert “bpo-37330(26): open() no longer accept ‘U’
     in file mode”.  The “U” mode of open() is kept in Python 3.9 to
     ease transition from Python 2.7, but will be removed in Python
     3.10.

   - bpo-28577(27): The hosts method on 32-bit prefix length
     IPv4Networks and 128-bit prefix IPv6Networks now returns a list
     containing the single Address instead of an empty list.

   - bpo-39826(28): Add getConnection method to logging HTTPHandler to
     enable custom connections.

   - bpo-39763(29): Reimplement ‘distutils.spawn.spawn()’ function with
     the *note subprocess: f9. module.

   - bpo-39794(30): Add –without-decimal-contextvar build option.  This
     enables a thread-local rather than a coroutine local context.

   - bpo-36144(31): *note collections.defaultdict: c0c. now implements
     ‘|’ ( PEP 584(32)).

   - bpo-39517(33): Fix runpy.run_path() when using pathlike objects

   - bpo-39775(34): Change ‘inspect.Signature.parameters’ back to
     ‘collections.OrderedDict’.  This was changed to ‘dict’ in Python
     3.9.0a4.

   - bpo-39678(35): Refactor queue_manager in *note
     concurrent.futures.ProcessPoolExecutor: 196. to make it easier to
     maintain.

   - bpo-39764(36): Fix AttributeError when calling get_stack on a
     PyAsyncGenObject Task

   - bpo-39769(37): The *note compileall.compile_dir(): 47a. function’s
     `ddir' parameter and the compileall command line flag ‘-d’ no
     longer write the wrong pathname to the generated pyc file for
     submodules beneath the root of the directory tree being compiled.
     This fixes a regression introduced with Python 3.5.

   - bpo-36144(38): *note types.MappingProxyType: b8e. objects now
     support the merge (‘|’) operator from PEP 584(39).

   - bpo-38691(40): The *note importlib: 9a. module now ignores the
     *note PYTHONCASEOK: 230. environment variable when the *note -E:
     231. or *note -I: 232. command line options are being used.

   - bpo-39719(41): Remove ‘tempfile.SpooledTemporaryFile.softspace()’
     as files no longer have the ‘softspace’ attribute in Python 3.
     Patch by Shantanu.

   - bpo-39667(42): Improve pathlib.Path compatibility on zipfile.Path
     and correct performance degradation as found in zipp 3.0.

   - bpo-39638(43): Keep ASDL signatures in the docstrings for ‘AST’
     nodes.  Patch by Batuhan Taskaya

   - bpo-39639(44): Deprecated ‘ast.Suite’ node class because it’s no
     longer used.  Patch by Batuhan Taskaya.

   - bpo-39609(45): Add thread_name_prefix to default asyncio executor

   - bpo-39548(46): Fix handling of header in *note
     urllib.request.AbstractDigestAuthHandler: 106c. when the optional
     ‘qop’ parameter is not present.

   - bpo-39509(47): HTTP status codes ‘103 EARLY_HINTS’ and ‘425
     TOO_EARLY’ are added to *note http.HTTPStatus: 1ac.  Patch by
     Dong-hee Na.

   - bpo-39507(48): Adding HTTP status 418 “I’m a Teapot” to HTTPStatus
     in http library.  Patch by Ross Rhodes.

   - bpo-39495(49): Remove default value from `attrs' parameter of *note
     xml.etree.ElementTree.TreeBuilder.start(): 106d. for consistency
     between Python and C implementations.

   - bpo-38971(50): Open issue in the BPO indicated a desire to make the
     implementation of codecs.open() at parity with io.open(), which
     implements a try/except to assure file stream gets closed before an
     exception is raised.

   - bpo-38641(51): Added starred expressions support to ‘return’ and
     ‘yield’ statements for ‘lib2to3’.  Patch by Vlad Emelianov.

   - bpo-37534(52): When using minidom module to generate XML documents
     the ability to add Standalone Document Declaration is added.  All
     the changes are made to generate a document in compliance with
     Extensible Markup Language (XML) 1.0 (Fifth Edition) W3C
     Recommendation (available here:
     ‘https://www.w3.org/TR/xml/#sec-prolog-dtd’).

   - bpo-34788(53): Add support for scoped IPv6 addresses to *note
     ipaddress: a2.  Patch by Oleksandr Pavliuk.

   - bpo-34822(54): Simplified AST for subscription.  Simple indices are
     now represented by their value, extended slices are represented as
     tuples.  *note ast: 7. classes ‘Index’ and ‘ExtSlice’ are
     considered deprecated and will be removed in future Python
     versions.  In the meantime, ‘Index(value)’ now returns a ‘value’
     itself, ‘ExtSlice(slices)’ returns ‘Tuple(slices, Load())’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39830

   (2) https://bugs.python.org/issue40000

   (3) https://bugs.python.org/issue39999

   (4) https://bugs.python.org/issue39991

   (5) https://bugs.python.org/issue39988

   (6) https://bugs.python.org/issue39656

   (7) https://bugs.python.org/issue39969

   (8) https://bugs.python.org/issue39360

   (9) https://bugs.python.org/issue35370

   (10) https://bugs.python.org/issue39936

   (11) https://bugs.python.org/issue36144

   (12) https://www.python.org/dev/peps/pep-0584

   (13) https://bugs.python.org/issue39652

   (14) https://bugs.python.org/issue39915

   (15) https://bugs.python.org/issue36144

   (16) https://www.python.org/dev/peps/pep-0584

   (17) https://bugs.python.org/issue38662

   (18) https://bugs.python.org/issue38075

   (19) https://bugs.python.org/issue39916

   (20) https://bugs.python.org/issue39850

   (21) https://bugs.python.org/issue36287

   (22) https://bugs.python.org/issue39889

   (23) https://bugs.python.org/issue39828

   (24) https://bugs.python.org/issue13487

   (25) https://bugs.python.org/issue39674

   (26) https://bugs.python.org/issue37330

   (27) https://bugs.python.org/issue28577

   (28) https://bugs.python.org/issue39826

   (29) https://bugs.python.org/issue39763

   (30) https://bugs.python.org/issue39794

   (31) https://bugs.python.org/issue36144

   (32) https://www.python.org/dev/peps/pep-0584

   (33) https://bugs.python.org/issue39517

   (34) https://bugs.python.org/issue39775

   (35) https://bugs.python.org/issue39678

   (36) https://bugs.python.org/issue39764

   (37) https://bugs.python.org/issue39769

   (38) https://bugs.python.org/issue36144

   (39) https://www.python.org/dev/peps/pep-0584

   (40) https://bugs.python.org/issue38691

   (41) https://bugs.python.org/issue39719

   (42) https://bugs.python.org/issue39667

   (43) https://bugs.python.org/issue39638

   (44) https://bugs.python.org/issue39639

   (45) https://bugs.python.org/issue39609

   (46) https://bugs.python.org/issue39548

   (47) https://bugs.python.org/issue39509

   (48) https://bugs.python.org/issue39507

   (49) https://bugs.python.org/issue39495

   (50) https://bugs.python.org/issue38971

   (51) https://bugs.python.org/issue38641

   (52) https://bugs.python.org/issue37534

   (53) https://bugs.python.org/issue34788

   (54) https://bugs.python.org/issue34822


File: python.info,  Node: Documentation<16>,  Next: Tests<16>,  Prev: Library<21>,  Up: Python 3 9 0 alpha 5

1.19.22.4 Documentation
.......................

   - bpo-39868(1): Updated the Language Reference for PEP 572(2).

   - bpo-13790(3): Change ‘string’ to ‘specification’ in format doc.

   - bpo-17422(4): The language reference no longer restricts default
     class namespaces to dicts only.

   - bpo-39530(5): Fix misleading documentation about mixed-type numeric
     comparisons.

   - bpo-39718(6): Update *note token: 119. documentation to reflect
     additions in Python 3.8

   - bpo-39677(7): Changed operand name of `MAKE_FUNCTION' from `argc'
     to `flags' for module *note dis: 37.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39868

   (2) https://www.python.org/dev/peps/pep-0572

   (3) https://bugs.python.org/issue13790

   (4) https://bugs.python.org/issue17422

   (5) https://bugs.python.org/issue39530

   (6) https://bugs.python.org/issue39718

   (7) https://bugs.python.org/issue39677


File: python.info,  Node: Tests<16>,  Next: Build<15>,  Prev: Documentation<16>,  Up: Python 3 9 0 alpha 5

1.19.22.5 Tests
...............

   - bpo-40019(1): test_gdb now skips tests if it detects that gdb
     failed to read debug information because the Python binary is
     optimized.

   - bpo-27807(2): ‘test_site.test_startup_imports()’ is now skipped if
     a path of *note sys.path: 260. contains a ‘.pth’ file.

   - bpo-26067(3): Do not fail test_shutil test_chown test when uid or
     gid of user cannot be resolved to a name.

   - bpo-39855(4): test_subprocess.test_user() now skips the test on an
     user name if the user name doesn’t exist.  For example, skip the
     test if the user “nobody” doesn’t exist on Linux.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40019

   (2) https://bugs.python.org/issue27807

   (3) https://bugs.python.org/issue26067

   (4) https://bugs.python.org/issue39855


File: python.info,  Node: Build<15>,  Next: Windows<16>,  Prev: Tests<16>,  Up: Python 3 9 0 alpha 5

1.19.22.6 Build
...............

   - bpo-39761(1): Fix build with DTrace but without additional DFLAGS.

   - bpo-39763(2): setup.py now uses a basic implementation of the *note
     subprocess: f9. module if the *note subprocess: f9. module is not
     available: before required C extension modules are built.

   - bpo-1294959(3): Add ‘--with-platlibdir’ option to the configure
     script: name of the platform-specific library directory, stored in
     the new *note sys.platlibdir: 1e9. attribute.  It is used to build
     the path of platform-specific extension modules and the path of the
     standard library.  It is equal to ‘"lib"’ on most platforms.  On
     Fedora and SuSE, it is equal to ‘"lib64"’ on 64-bit platforms.
     Patch by Jan Matějek, Matěj Cepl, Charalampos Stratakis and Victor
     Stinner.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39761

   (2) https://bugs.python.org/issue39763

   (3) https://bugs.python.org/issue1294959


File: python.info,  Node: Windows<16>,  Next: macOS<15>,  Prev: Build<15>,  Up: Python 3 9 0 alpha 5

1.19.22.7 Windows
.................

   - bpo-39930(1): Ensures the required ‘vcruntime140.dll’ is included
     in install packages.

   - bpo-39847(2): Avoid hang when computer is hibernated whilst waiting
     for a mutex (for lock-related objects from *note threading: 10b.)
     around 49-day uptime.

   - bpo-38597(3): *note distutils: 38. will no longer statically link
     ‘vcruntime140.dll’ when a redistributable version is unavailable.
     All future releases of CPython will include a copy of this DLL to
     ensure distributed extensions can continue to load.

   - bpo-38380(4): Update Windows builds to use SQLite 3.31.1

   - bpo-39789(5): Update Windows release build machines to Visual
     Studio 2019 (MSVC 14.2).

   - bpo-34803(6): Package for nuget.org now includes repository
     reference and bundled icon image.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39930

   (2) https://bugs.python.org/issue39847

   (3) https://bugs.python.org/issue38597

   (4) https://bugs.python.org/issue38380

   (5) https://bugs.python.org/issue39789

   (6) https://bugs.python.org/issue34803


File: python.info,  Node: macOS<15>,  Next: IDLE<15>,  Prev: Windows<16>,  Up: Python 3 9 0 alpha 5

1.19.22.8 macOS
...............

   - bpo-38380(1): Update macOS builds to use SQLite 3.31.1

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38380


File: python.info,  Node: IDLE<15>,  Next: Tools/Demos<6>,  Prev: macOS<15>,  Up: Python 3 9 0 alpha 5

1.19.22.9 IDLE
..............

   - bpo-27115(1): For ‘Go to Line’, use a Query box subclass with IDLE
     standard behavior and improved error checking.

   - bpo-39885(2): Since clicking to get an IDLE context menu moves the
     cursor, any text selection should be and now is cleared.

   - bpo-39852(3): Edit “Go to line” now clears any selection,
     preventing accidental deletion.  It also updates Ln and Col on the
     status bar.

   - bpo-39781(4): Selecting code context lines no longer causes a jump.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27115

   (2) https://bugs.python.org/issue39885

   (3) https://bugs.python.org/issue39852

   (4) https://bugs.python.org/issue39781


File: python.info,  Node: Tools/Demos<6>,  Next: C API<12>,  Prev: IDLE<15>,  Up: Python 3 9 0 alpha 5

1.19.22.10 Tools/Demos
......................

   - bpo-36184(1): Port python-gdb.py to FreeBSD. python-gdb.py now
     checks for “take_gil” function name to check if a frame tries to
     acquire the GIL, instead of checking for “pthread_cond_timedwait”
     which is specific to Linux and can be a different condition than
     the GIL.

   - bpo-38080(2): Added support to fix ‘getproxies’ in the
     ‘lib2to3.fixes.fix_urllib’ module.  Patch by José Roberto Meza
     Cabrera.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36184

   (2) https://bugs.python.org/issue38080


File: python.info,  Node: C API<12>,  Prev: Tools/Demos<6>,  Up: Python 3 9 0 alpha 5

1.19.22.11 C API
................

   - bpo-40024(1): Add *note PyModule_AddType(): 253. helper function:
     add a type to a module.  Patch by Dong-hee Na.

   - bpo-39946(2): Remove ‘_PyRuntime.getframe’ hook and remove
     ‘_PyThreadState_GetFrame’ macro which was an alias to
     ‘_PyRuntime.getframe’.  They were only exposed by the internal C
     API. Remove also ‘PyThreadFrameGetter’ type.

   - bpo-39947(3): Add *note PyThreadState_GetFrame(): 24e. function:
     get the current frame of a Python thread state.

   - bpo-37207(4): Add _PyArg_NoKwnames helper function.  Patch by
     Dong-hee Na.

   - bpo-39947(5): Add *note PyThreadState_GetInterpreter(): 24c.: get
     the interpreter of a Python thread state.

   - bpo-39947(6): Add *note PyInterpreterState_Get(): 24d. function to
     the limited C API.

   - bpo-35370(7): If *note PySys_Audit(): 1068. fails in *note
     PyEval_SetProfile(): efd. or *note PyEval_SetTrace(): efe, log the
     error as an unraisable exception.

   - bpo-39947(8): Move the static inline function flavor of
     Py_EnterRecursiveCall() and Py_LeaveRecursiveCall() to the internal
     C API: they access PyThreadState attributes.  The limited C API
     provides regular functions which hide implementation details.

   - bpo-39947(9): Py_TRASHCAN_BEGIN_CONDITION and Py_TRASHCAN_END macro
     no longer access PyThreadState attributes, but call new private
     _PyTrash_begin() and _PyTrash_end() functions which hide
     implementation details.

   - bpo-39884(10): *note PyDescr_NewMethod(): 1076. and
     ‘PyCFunction_NewEx()’ now include the method name in the
     SystemError “bad call flags” error message to ease debug.

   - bpo-39877(11): Deprecated *note PyEval_InitThreads(): 20c. and
     *note PyEval_ThreadsInitialized(): 20d.  Calling *note
     PyEval_InitThreads(): 20c. now does nothing.

   - bpo-38249(12): *note Py_UNREACHABLE: 527. is now implemented with
     ‘__builtin_unreachable()’ and analogs in release mode.

   - bpo-38643(13): *note PyNumber_ToBase(): 1077. now raises a *note
     SystemError: 6f2. instead of crashing when called with invalid
     base.

   - bpo-39882(14): The *note Py_FatalError(): 266. function is replaced
     with a macro which logs automatically the name of the current
     function, unless the ‘Py_LIMITED_API’ macro is defined.

   - bpo-39824(15): Extension modules: *note m_traverse: 258, *note
     m_clear: 259. and *note m_free: 25a. functions of *note
     PyModuleDef: 25b. are no longer called if the module state was
     requested but is not allocated yet.  This is the case immediately
     after the module is created and before the module is executed
     (*note Py_mod_exec: 25c. function).  More precisely, these
     functions are not called if *note m_size: 25d. is greater than 0
     and the module state (as returned by *note PyModule_GetState():
     25e.) is ‘NULL’.

     Extension modules without module state (‘m_size <= 0’) are not
     affected.

   - bpo-38913(16): Fixed segfault in ‘Py_BuildValue()’ called with a
     format containing “#” and undefined PY_SSIZE_T_CLEAN whwn an
     exception is set.

   - bpo-38500(17): Add a private API to get and set the frame
     evaluation function: add *note
     _PyInterpreterState_GetEvalFrameFunc(): 1078. and *note
     _PyInterpreterState_SetEvalFrameFunc(): 1079. C functions.  The
     *note _PyFrameEvalFunction: 107a. function type now takes a
     `tstate' parameter.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40024

   (2) https://bugs.python.org/issue39946

   (3) https://bugs.python.org/issue39947

   (4) https://bugs.python.org/issue37207

   (5) https://bugs.python.org/issue39947

   (6) https://bugs.python.org/issue39947

   (7) https://bugs.python.org/issue35370

   (8) https://bugs.python.org/issue39947

   (9) https://bugs.python.org/issue39947

   (10) https://bugs.python.org/issue39884

   (11) https://bugs.python.org/issue39877

   (12) https://bugs.python.org/issue38249

   (13) https://bugs.python.org/issue38643

   (14) https://bugs.python.org/issue39882

   (15) https://bugs.python.org/issue39824

   (16) https://bugs.python.org/issue38913

   (17) https://bugs.python.org/issue38500


File: python.info,  Node: Python 3 9 0 alpha 4,  Next: Python 3 9 0 alpha 3,  Prev: Python 3 9 0 alpha 5,  Up: Changelog

1.19.23 Python 3.9.0 alpha 4
----------------------------

`Release date: 2020-02-25'

* Menu:

* Security: Security<12>.
* Core and Builtins: Core and Builtins<20>.
* Library: Library<22>.
* Documentation: Documentation<17>.
* Tests: Tests<17>.
* Build: Build<16>.
* Windows: Windows<17>.
* IDLE: IDLE<16>.
* C API: C API<13>.


File: python.info,  Node: Security<12>,  Next: Core and Builtins<20>,  Up: Python 3 9 0 alpha 4

1.19.23.1 Security
..................

   - bpo-39184(1): Add audit events to functions in *note fcntl: 7c,
     *note msvcrt: b6, *note os: c4, *note resource: e0, *note shutil:
     e9, *note signal: ea. and *note syslog: ff.

   - bpo-39401(2): Avoid unsafe DLL load at startup on Windows 7 and
     earlier.

   - bpo-39184(3): Add audit events to command execution functions in os
     and pty modules.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39184

   (2) https://bugs.python.org/issue39401

   (3) https://bugs.python.org/issue39184


File: python.info,  Node: Core and Builtins<20>,  Next: Library<22>,  Prev: Security<12>,  Up: Python 3 9 0 alpha 4

1.19.23.2 Core and Builtins
...........................

   - bpo-39382(1): Fix a use-after-free in the single inheritance path
     of ‘issubclass()’, when the ‘__bases__’ of an object has a single
     reference, and so does its first item.  Patch by Yonatan
     Goldschmidt.

   - bpo-39573(2): Update clinic tool to use *note Py_IS_TYPE(): 107e.
     Patch by Dong-hee Na.

   - bpo-39619(3): Enable use of *note os.chroot(): 107f. on HP-UX
     systems.

   - bpo-39573(4): Add *note Py_IS_TYPE(): 107e. static inline function
     to check whether the object `o' type is `type'.

   - bpo-39606(5): Fix regression caused by fix for bpo-39386(6), that
     prevented calling ‘aclose’ on an async generator that had already
     been closed or exhausted.

   - bpo-39579(7): Change the ending column offset of ‘Attribute’ nodes
     constructed in ‘ast_for_dotted_name’ to point at the end of the
     current node and not at the end of the last ‘NAME’ node.

   - bpo-1635741(8): Port _crypt extension module to multiphase
     initialization ( PEP 489(9)).

   - bpo-1635741(10): Port _contextvars extension module to multiphase
     initialization ( PEP 489(11)).

   - bpo-39510(12): Fix segfault in ‘readinto()’ method on closed
     BufferedReader.

   - bpo-39502(13): Fix *note time.localtime(): 1080. on 64-bit AIX to
     support years before 1902 and after 2038.  Patch by M Felt.

   - bpo-39492(14): Fix a reference cycle in the C Pickler that was
     preventing the garbage collection of deleted, pickled objects.

   - bpo-39453(15): Fixed a possible crash in ‘list.__contains__()’ when
     a list is changed during comparing items.  Patch by Dong-hee Na.

   - bpo-39434(16): *note floor division: 1f9. of float operation now
     has a better performance.  Also the message of *note
     ZeroDivisionError: 1fa. for this operation is updated.  Patch by
     Dong-hee Na.

   - bpo-1635741(17): Port _codecs extension module to multiphase
     initialization ( PEP 489(18)).

   - bpo-1635741(19): Port _bz2 extension module to multiphase
     initialization ( PEP 489(20)).

   - bpo-1635741(21): Port _abc extension module to multiphase
     initialization ( PEP 489(22)).

   - bpo-39320(23): Replace two complex bytecodes for building dicts
     with two simpler ones.  The new bytecodes ‘DICT_MERGE’ and
     ‘DICT_UPDATE’ have been added The old bytecodes ‘BUILD_MAP_UNPACK’
     and ‘BUILD_MAP_UNPACK_WITH_CALL’ have been removed.

   - bpo-39219(24): Syntax errors raised in the tokenizer now always set
     correct “text” and “offset” attributes.

   - bpo-36051(25): Drop the GIL during large ‘bytes.join’ operations.
     Patch by Bruce Merry.

   - bpo-38960(26): Fix DTrace build issues on FreeBSD. Patch by David
     Carlier.

   - bpo-37207(27): Speed up calls to ‘range()’ by about 30%, by using
     the PEP 590 ‘vectorcall’ calling convention.  Patch by Mark
     Shannon.

   - bpo-36144(28): *note dict: 164. (and *note collections.UserDict:
     1081.) objects now support PEP 584’s merge (‘|’) and update (‘|=’)
     operators.  Patch by Brandt Bucher.

   - bpo-32856(29): Optimized the idiom for assignment a temporary
     variable in comprehensions.  Now ‘for y in [expr]’ in
     comprehensions is as fast as a simple assignment ‘y = expr’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39382

   (2) https://bugs.python.org/issue39573

   (3) https://bugs.python.org/issue39619

   (4) https://bugs.python.org/issue39573

   (5) https://bugs.python.org/issue39606

   (6) https://bugs.python.org/issue39386

   (7) https://bugs.python.org/issue39579

   (8) https://bugs.python.org/issue1635741

   (9) https://www.python.org/dev/peps/pep-0489

   (10) https://bugs.python.org/issue1635741

   (11) https://www.python.org/dev/peps/pep-0489

   (12) https://bugs.python.org/issue39510

   (13) https://bugs.python.org/issue39502

   (14) https://bugs.python.org/issue39492

   (15) https://bugs.python.org/issue39453

   (16) https://bugs.python.org/issue39434

   (17) https://bugs.python.org/issue1635741

   (18) https://www.python.org/dev/peps/pep-0489

   (19) https://bugs.python.org/issue1635741

   (20) https://www.python.org/dev/peps/pep-0489

   (21) https://bugs.python.org/issue1635741

   (22) https://www.python.org/dev/peps/pep-0489

   (23) https://bugs.python.org/issue39320

   (24) https://bugs.python.org/issue39219

   (25) https://bugs.python.org/issue36051

   (26) https://bugs.python.org/issue38960

   (27) https://bugs.python.org/issue37207

   (28) https://bugs.python.org/issue36144

   (29) https://bugs.python.org/issue32856


File: python.info,  Node: Library<22>,  Next: Documentation<17>,  Prev: Core and Builtins<20>,  Up: Python 3 9 0 alpha 4

1.19.23.3 Library
.................

   - bpo-30566(1): Fix *note IndexError: f36. when trying to decode an
     invalid string with punycode codec.

   - bpo-39649(2): Remove obsolete check for ‘__args__’ in
     bdb.Bdb.format_stack_entry.

   - bpo-39648(3): Expanded *note math.gcd(): 1be. and *note math.lcm():
     1bf. to handle multiple arguments.

   - bpo-39681(4): Fix a regression where the C pickle module wouldn’t
     allow unpickling from a file-like object that doesn’t expose a
     readinto() method.

   - bpo-35950(5): Raise *note io.UnsupportedOperation: 1083. in
     ‘io.BufferedReader.truncate()’ when it is called on a read-only
     *note io.BufferedReader: c5b. instance.

   - bpo-39479(6): Add *note math.lcm(): 1bf. function: least common
     multiple.

   - bpo-39674(7): Revert “Do not expose abstract collection classes in
     the collections module” change (bpo-25988(8)).  Aliases to ABC like
     collections.Mapping are kept in Python 3.9 to ease transition from
     Python 2.7, but will be removed in Python 3.10.

   - bpo-39104(9): Fix hanging ProcessPoolExcutor on
     ‘shutdown(wait=False)’ when a task has failed pickling.

   - bpo-39627(10): Fixed TypedDict totality check for inherited keys.

   - bpo-39474(11): Fixed starting position of AST for expressions like
     ‘(a)(b)’, ‘(a)[b]’ and ‘(a).b’.

   - bpo-21016(12): The *note pydoc: d9. and *note trace: 11b. modules
     now use the *note sysconfig: fe. module to get the path to the
     Python standard library, to support uncommon installation path like
     ‘/usr/lib64/python3.9/’ on Fedora.  Patch by Jan Matějek.

   - bpo-39590(13): Collections.deque now holds strong references during
     deque.__contains__ and deque.count, fixing crashes.

   - bpo-39586(14): The distutils ‘bdist_msi’ command is deprecated in
     Python 3.9, use ‘bdist_wheel’ (wheel packages) instead.

   - bpo-39595(15): Improved performance of zipfile.Path for files with
     a large number of entries.  Also improved performance and fixed
     minor issue as published with importlib_metadata 1.5(16).

   - bpo-39350(17): Fix regression in *note fractions.Fraction: 2be. if
     the numerator and/or the denominator is an *note int: 204.
     subclass.  The *note math.gcd(): 1be. function is now used to
     normalize the `numerator' and `denominator'.  *note math.gcd():
     1be. always return a *note int: 204. type.  Previously, the GCD
     type depended on `numerator' and `denominator'.

   - bpo-39567(18): Added audit for *note os.walk(): 747, *note
     os.fwalk(): 4bb, *note pathlib.Path.glob(): 1084. and *note
     pathlib.Path.rglob(): 1085.

   - bpo-39559(19): Remove unused, undocumented argument ‘getters’ from
     *note uuid.getnode(): 517.

   - bpo-38149(20): *note sys.audit(): 1056. is now called only once per
     call of *note glob.glob(): 6bd. and *note glob.iglob(): 6be.

   - bpo-39546(21): Fix a regression in *note ArgumentParser: 788. where
     ‘allow_abbrev=False’ was ignored for long options that used a
     prefix character other than “-“.

   - bpo-39450(22): Striped whitespace from docstring before returning
     it from ‘unittest.case.shortDescription()’.

   - bpo-12915(23): A new function ‘resolve_name’ has been added to the
     ‘pkgutil’ module.  This resolves a string of the form ‘'a.b.c.d'’
     or ‘'a.b:c.d'’ to an object.  In the example, ‘a.b’ is a
     package/module and ‘c.d’ is an object within that package/module
     reached via recursive attribute access.

   - bpo-39353(24): The *note binascii.crc_hqx(): 1086. function is no
     longer deprecated.

   - bpo-39493(25): Mark ‘typing.IO.closed’ as a property

   - bpo-39491(26): Add *note typing.Annotated: 1ee. and
     ‘include_extras’ parameter to *note typing.get_type_hints(): 1ef.
     as part of PEP 593(27).  Patch by Till Varoquaux, documentation by
     Till Varoquaux and Konstantin Kashin.

   - bpo-39485(28): Fix a bug in *note unittest.mock.create_autospec():
     1087. that would complain about the wrong number of arguments for
     custom descriptors defined in an extension module returning
     functions.

   - bpo-38932(29): Mock fully resets child objects on reset_mock().
     Patch by Vegard Stikbakke

   - bpo-39082(30): Allow AsyncMock to correctly patch static/class
     methods

   - bpo-39432(31): Implement PEP-489 algorithm for non-ascii “PyInit_…”
     symbol names in distutils to make it export the correct init symbol
     also on Windows.

   - bpo-18819(32): Omit ‘devmajor’ and ‘devminor’ fields for non-device
     files in *note tarfile: 101. archives, enabling bit-for-bit
     compatibility with GNU ‘tar(1)’.

   - bpo-39349(33): Added a new `cancel_futures' parameter to *note
     concurrent.futures.Executor.shutdown(): 195. that cancels all
     pending futures which have not started running, instead of waiting
     for them to complete before shutting down the executor.

   - bpo-39274(34): ‘bool(fraction.Fraction)’ now returns a boolean even
     if (numerator != 0) does not return a boolean (ex: numpy number).

   - bpo-34793(35): Remove support for ‘with (await asyncio.lock):’ and
     ‘with (yield from asyncio.lock):’.  The same is correct for
     ‘asyncio.Condition’ and ‘asyncio.Semaphore’.

   - bpo-25597(36): Ensure, if ‘wraps’ is supplied to *note
     unittest.mock.MagicMock: 874, it is used to calculate return values
     for the magic methods instead of using the default return values.
     Patch by Karthikeyan Singaravelan.

   - bpo-36350(37): *note inspect.Signature.parameters: 1088. and *note
     inspect.BoundArguments.arguments: 1b9. are now dicts instead of
     OrderedDicts.  Patch contributed by Rémi Lapeyre.

   - bpo-35727(38): Fix sys.exit() and sys.exit(None) exit code
     propagation when used in multiprocessing.Process.

   - bpo-32173(39): * Add ‘lazycache’ function to ‘__all__’.  * Use
     *note dict.clear: 1089. to clear the cache.  * Refactoring
     ‘getline’ function and ‘checkcache’ function.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30566

   (2) https://bugs.python.org/issue39649

   (3) https://bugs.python.org/issue39648

   (4) https://bugs.python.org/issue39681

   (5) https://bugs.python.org/issue35950

   (6) https://bugs.python.org/issue39479

   (7) https://bugs.python.org/issue39674

   (8) https://bugs.python.org/issue25988

   (9) https://bugs.python.org/issue39104

   (10) https://bugs.python.org/issue39627

   (11) https://bugs.python.org/issue39474

   (12) https://bugs.python.org/issue21016

   (13) https://bugs.python.org/issue39590

   (14) https://bugs.python.org/issue39586

   (15) https://bugs.python.org/issue39595

   (16) 
https://importlib-metadata.readthedocs.io/en/latest/changelog%20(links).html#v1-5-0

   (17) https://bugs.python.org/issue39350

   (18) https://bugs.python.org/issue39567

   (19) https://bugs.python.org/issue39559

   (20) https://bugs.python.org/issue38149

   (21) https://bugs.python.org/issue39546

   (22) https://bugs.python.org/issue39450

   (23) https://bugs.python.org/issue12915

   (24) https://bugs.python.org/issue39353

   (25) https://bugs.python.org/issue39493

   (26) https://bugs.python.org/issue39491

   (27) https://www.python.org/dev/peps/pep-0593

   (28) https://bugs.python.org/issue39485

   (29) https://bugs.python.org/issue38932

   (30) https://bugs.python.org/issue39082

   (31) https://bugs.python.org/issue39432

   (32) https://bugs.python.org/issue18819

   (33) https://bugs.python.org/issue39349

   (34) https://bugs.python.org/issue39274

   (35) https://bugs.python.org/issue34793

   (36) https://bugs.python.org/issue25597

   (37) https://bugs.python.org/issue36350

   (38) https://bugs.python.org/issue35727

   (39) https://bugs.python.org/issue32173


File: python.info,  Node: Documentation<17>,  Next: Tests<17>,  Prev: Library<22>,  Up: Python 3 9 0 alpha 4

1.19.23.4 Documentation
.......................

   - bpo-17422(1): The language reference now specifies restrictions on
     class namespaces.  Adapted from a patch by Ethan Furman.

   - bpo-39572(2): Updated documentation of ‘total’ flag of ‘TypedDict’.

   - bpo-39654(3): In pyclbr doc, update ‘class’ to ‘module’ where
     appropriate and add readmodule comment.  Patch by Hakan Çelik.

   - bpo-39153(4): Clarify refcounting semantics for the following
     functions: - PyObject_SetItem - PyMapping_SetItemString -
     PyDict_SetItem - PyDict_SetItemString

   - bpo-39392(5): Explain that when filling with turtle, overlap
     regions may be left unfilled.

   - bpo-39369(6): Update mmap readline method description.  The fact
     that the readline method does update the file position should not
     be ignored since this might give the impression for the programmer
     that it doesn’t update it.

   - bpo-9056(7): Include subsection in TOC for PDF version of docs.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17422

   (2) https://bugs.python.org/issue39572

   (3) https://bugs.python.org/issue39654

   (4) https://bugs.python.org/issue39153

   (5) https://bugs.python.org/issue39392

   (6) https://bugs.python.org/issue39369

   (7) https://bugs.python.org/issue9056


File: python.info,  Node: Tests<17>,  Next: Build<16>,  Prev: Documentation<17>,  Up: Python 3 9 0 alpha 4

1.19.23.5 Tests
...............

   - bpo-38325(1): Skip tests on non-BMP characters of
     test_winconsoleio.

   - bpo-39502(2): Skip test_zipfile.test_add_file_after_2107() if *note
     time.localtime(): 1080. fails with *note OverflowError: a41.  It is
     the case on AIX 6.1 for example.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38325

   (2) https://bugs.python.org/issue39502


File: python.info,  Node: Build<16>,  Next: Windows<17>,  Prev: Tests<17>,  Up: Python 3 9 0 alpha 4

1.19.23.6 Build
...............

   - bpo-39489(1): Remove ‘COUNT_ALLOCS’ special build.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39489


File: python.info,  Node: Windows<17>,  Next: IDLE<16>,  Prev: Build<16>,  Up: Python 3 9 0 alpha 4

1.19.23.7 Windows
.................

   - bpo-39553(1): Delete unused code related to SxS manifests.

   - bpo-39439(2): Honor the Python path when a virtualenv is active on
     Windows.

   - bpo-39393(3): Improve the error message when attempting to load a
     DLL with unresolved dependencies.

   - bpo-38883(4): *note home(): 81a. and *note expanduser(): 819. on
     Windows now prefer ‘USERPROFILE’ and no longer use ‘HOME’, which is
     not normally set for regular user accounts.  This makes them again
     behave like *note os.path.expanduser(): 32c, which was changed to
     ignore ‘HOME’ in 3.8, see bpo-36264(5).

   - bpo-39185(6): The build.bat script has additional options for
     very-quiet output (-q) and very-verbose output (-vv)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39553

   (2) https://bugs.python.org/issue39439

   (3) https://bugs.python.org/issue39393

   (4) https://bugs.python.org/issue38883

   (5) https://bugs.python.org/issue36264

   (6) https://bugs.python.org/issue39185


File: python.info,  Node: IDLE<16>,  Next: C API<13>,  Prev: Windows<17>,  Up: Python 3 9 0 alpha 4

1.19.23.8 IDLE
..............

   - bpo-39663(1): Add tests for pyparse find_good_parse_start().

   - bpo-39600(2): In the font configuration window, remove duplicated
     font names.

   - bpo-30780(3): Add remaining configdialog tests for buttons and
     highlights and keys tabs.

   - bpo-39388(4): IDLE Settings Cancel button now cancels pending
     changes

   - bpo-38792(5): Close an IDLE shell calltip if a *note
     KeyboardInterrupt: 2cc. or shell restart occurs.  Patch by Zackery
     Spytz.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39663

   (2) https://bugs.python.org/issue39600

   (3) https://bugs.python.org/issue30780

   (4) https://bugs.python.org/issue39388

   (5) https://bugs.python.org/issue38792


File: python.info,  Node: C API<13>,  Prev: IDLE<16>,  Up: Python 3 9 0 alpha 4

1.19.23.9 C API
...............

   - bpo-35081(1): Move the ‘bytes_methods.h’ header file to the
     internal C API as ‘pycore_bytes_methods.h’: it only contains
     private symbols (prefixed by ‘_Py’), except of the
     ‘PyDoc_STRVAR_shared()’ macro.

   - bpo-35081(2): Move the ‘dtoa.h’ header file to the internal C API
     as ‘pycore_dtoa.h’: it only contains private functions (prefixed by
     ‘_Py’).  The *note math: b1. and *note cmath: 18. modules must now
     be compiled with the ‘Py_BUILD_CORE’ macro defined.

   - bpo-39573(3): Add *note Py_SET_SIZE(): 1090. function to set the
     size of an object.

   - bpo-39500(4): *note PyUnicode_IsIdentifier(): 1091. does not call
     *note Py_FatalError(): 266. anymore if the string is not ready.

   - bpo-39573(5): Add *note Py_SET_TYPE(): 1092. function to set the
     type of an object.

   - bpo-39573(6): Add a *note Py_SET_REFCNT(): 1093. function to set
     the reference counter of an object.

   - bpo-39542(7): Convert *note PyType_HasFeature(): 1010, *note
     PyType_Check(): 1094. and *note PyType_CheckExact(): 1095. macros
     to static inline functions.

   - bpo-39542(8): In the limited C API, ‘PyObject_INIT()’ and
     ‘PyObject_INIT_VAR()’ are now defined as aliases to *note
     PyObject_Init(): 398. and *note PyObject_InitVar(): 1096. to make
     their implementation opaque.  It avoids to leak implementation
     details in the limited C API. Exclude the following functions from
     the limited C API: ‘_Py_NewReference()’, ‘_Py_ForgetReference()’,
     ‘_PyTraceMalloc_NewReference()’ and ‘_Py_GetRefTotal()’.

   - bpo-39542(9): Exclude trashcan mechanism from the limited C API: it
     requires access to PyTypeObject and PyThreadState structure fields,
     whereas these structures are opaque in the limited C API.

   - bpo-39511(10): The *note PyThreadState_Clear(): 104c. function now
     calls the ‘PyThreadState.on_delete’ callback.  Previously, that
     happened in *note PyThreadState_Delete(): 1097.

   - bpo-38076(11): Fix to clear the interpreter state only after
     clearing module globals to guarantee module state access from C
     Extensions during runtime destruction

   - bpo-39245(12): The Vectorcall API (PEP 590) was made public, adding
     the functions ‘PyObject_Vectorcall’, ‘PyObject_VectorcallMethod’,
     ‘PyVectorcall_Function’, ‘PyObject_CallOneArg’,
     ‘PyObject_CallMethodNoArgs’, ‘PyObject_CallMethodOneArg’,
     ‘PyObject_FastCallDict’, and the flag ‘Py_TPFLAGS_HAVE_VECTORCALL’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35081

   (2) https://bugs.python.org/issue35081

   (3) https://bugs.python.org/issue39573

   (4) https://bugs.python.org/issue39500

   (5) https://bugs.python.org/issue39573

   (6) https://bugs.python.org/issue39573

   (7) https://bugs.python.org/issue39542

   (8) https://bugs.python.org/issue39542

   (9) https://bugs.python.org/issue39542

   (10) https://bugs.python.org/issue39511

   (11) https://bugs.python.org/issue38076

   (12) https://bugs.python.org/issue39245


File: python.info,  Node: Python 3 9 0 alpha 3,  Next: Python 3 9 0 alpha 2,  Prev: Python 3 9 0 alpha 4,  Up: Changelog

1.19.24 Python 3.9.0 alpha 3
----------------------------

`Release date: 2020-01-24'

* Menu:

* Core and Builtins: Core and Builtins<21>.
* Library: Library<23>.
* Documentation: Documentation<18>.
* Build: Build<17>.
* IDLE: IDLE<17>.
* C API: C API<14>.


File: python.info,  Node: Core and Builtins<21>,  Next: Library<23>,  Up: Python 3 9 0 alpha 3

1.19.24.1 Core and Builtins
...........................

   - bpo-39427(1): Document all possibilities for the ‘-X’ options in
     the command line help section.  Patch by Pablo Galindo.

   - bpo-39421(2): Fix possible crashes when operating with the
     functions in the *note heapq: 8d. module and custom comparison
     operators.

   - bpo-39386(3): Prevent double awaiting of async iterator.

   - bpo-17005(4): Add ‘functools.TopologicalSorter’ to the *note
     functools: 83. module to offers functionality to perform
     topological sorting of graphs.  Patch by Pablo Galindo, Tim Peters
     and Larry Hastings.

   - bpo-39320(5): Replace four complex bytecodes for building sequences
     with three simpler ones.

     The following four bytecodes have been removed:

        * BUILD_LIST_UNPACK

        * BUILD_TUPLE_UNPACK

        * BUILD_SET_UNPACK

        * BUILD_TUPLE_UNPACK_WITH_CALL

     The following three bytecodes have been added:

        * LIST_TO_TUPLE

        * LIST_EXTEND

        * SET_UPDATE

   - bpo-39336(6): Import loaders which publish immutable module objects
     can now publish immutable packages in addition to individual
     modules.

   - bpo-39322(7): Added a new function *note gc.is_finalized(): 1a9. to
     check if an object has been finalized by the garbage collector.
     Patch by Pablo Galindo.

   - bpo-39048(8): Improve the displayed error message when incorrect
     types are passed to ‘async with’ statements by looking up the *note
     __aenter__(): 109a. special method before the *note __aexit__():
     109b. special method when entering an asynchronous context manager.
     Patch by Géry Ogam.

   - bpo-39235(9): Fix AST end location for lone generator expression in
     function call, e.g.  f(i for i in a).

   - bpo-39209(10): Correctly handle multi-line tokens in interactive
     mode.  Patch by Pablo Galindo.

   - bpo-1635741(11): Port _json extension module to multiphase
     initialization ( PEP 489(12)).

   - bpo-39216(13): Fix constant folding optimization for positional
     only arguments - by Anthony Sottile.

   - bpo-39215(14): Fix ‘SystemError’ when nested function has
     annotation on positional-only argument - by Anthony Sottile.

   - bpo-39200(15): Correct the error message when calling the *note
     min(): 8f6. or *note max(): 8f7. with no arguments.  Patch by
     Dong-hee Na.

   - bpo-39200(16): Correct the error message when trying to construct
     *note range: 1f5. objects with no arguments.  Patch by Pablo
     Galindo.

   - bpo-39166(17): Fix incorrect line execution reporting in trace
     functions when tracing the last iteration of asynchronous for
     loops.  Patch by Pablo Galindo.

   - bpo-39114(18): Fix incorrect line execution reporting in trace
     functions when tracing exception handlers with name binding.  Patch
     by Pablo Galindo.

   - bpo-39156(19): Split the COMPARE_OP bytecode instruction into four
     distinct instructions.

        * COMPARE_OP for rich comparisons

        * IS_OP for ‘is’ and ‘is not’ tests

        * CONTAINS_OP for ‘in’ and ‘is not’ tests

        * JUMP_IF_NOT_EXC_MATCH for checking exceptions in ‘try-except’
          statements.

     This improves the clarity of the interpreter and should provide a
     modest speedup.

   - bpo-38588(20): Fix possible crashes in dict and list when calling
     *note PyObject_RichCompareBool(): 109c.

   - bpo-13601(21): By default, ‘sys.stderr’ is line-buffered now, even
     if ‘stderr’ is redirected to a file.  You can still make
     ‘sys.stderr’ unbuffered by passing the *note -u: 109d. command-line
     option or setting the *note PYTHONUNBUFFERED: 109e. environment
     variable.

     (Contributed by Jendrik Seipp in bpo-13601(22).)

   - bpo-38610(23): Fix possible crashes in several list methods by
     holding strong references to list elements when calling *note
     PyObject_RichCompareBool(): 109c.

   - bpo-32021(24): Include brotli .br encoding in mimetypes
     encodings_map

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39427

   (2) https://bugs.python.org/issue39421

   (3) https://bugs.python.org/issue39386

   (4) https://bugs.python.org/issue17005

   (5) https://bugs.python.org/issue39320

   (6) https://bugs.python.org/issue39336

   (7) https://bugs.python.org/issue39322

   (8) https://bugs.python.org/issue39048

   (9) https://bugs.python.org/issue39235

   (10) https://bugs.python.org/issue39209

   (11) https://bugs.python.org/issue1635741

   (12) https://www.python.org/dev/peps/pep-0489

   (13) https://bugs.python.org/issue39216

   (14) https://bugs.python.org/issue39215

   (15) https://bugs.python.org/issue39200

   (16) https://bugs.python.org/issue39200

   (17) https://bugs.python.org/issue39166

   (18) https://bugs.python.org/issue39114

   (19) https://bugs.python.org/issue39156

   (20) https://bugs.python.org/issue38588

   (21) https://bugs.python.org/issue13601

   (22) https://bugs.python.org/issue13601

   (23) https://bugs.python.org/issue38610

   (24) https://bugs.python.org/issue32021


File: python.info,  Node: Library<23>,  Next: Documentation<18>,  Prev: Core and Builtins<21>,  Up: Python 3 9 0 alpha 3

1.19.24.2 Library
.................

   - bpo-39430(1): Fixed race condition in lazy imports in *note
     tarfile: 101.

   - bpo-39413(2): The *note os.unsetenv(): 1cc. function is now also
     available on Windows.

   - bpo-39390(3): Fixed a regression with the ‘ignore’ callback of
     *note shutil.copytree(): 347.  The argument types are now str and
     List[str] again.

   - bpo-39395(4): The *note os.putenv(): 1cd. and *note os.unsetenv():
     1cc. functions are now always available.

   - bpo-39406(5): If ‘setenv()’ C function is available, *note
     os.putenv(): 1cd. is now implemented with ‘setenv()’ instead of
     ‘putenv()’, so Python doesn’t have to handle the environment
     variable memory.

   - bpo-39396(6): Fix ‘math.nextafter(-0.0, +0.0)’ on AIX 7.1.

   - bpo-29435(7): Allow *note tarfile.is_tarfile(): 10a0. to be used
     with file and file-like objects, like *note zipfile.is_zipfile():
     d82.  Patch by William Woodruff.

   - bpo-39377(8): Removed ‘encoding’ option from *note json.loads():
     225.  It has been deprecated since Python 3.1.

   - bpo-39389(9): Write accurate compression level metadata in *note
     gzip: 8b. archives, rather than always signaling maximum
     compression.

   - bpo-39366(10): The previously deprecated ‘xpath()’ and ‘xgtitle()’
     methods of *note nntplib.NNTP: 1c6. have been removed.

   - bpo-39357(11): Remove the `buffering' parameter of *note
     bz2.BZ2File: 224.  Since Python 3.0, it was ignored and using it
     was emitting *note DeprecationWarning: 15a.  Pass an open file
     object, to control how the file is opened.  The `compresslevel'
     parameter becomes keyword-only.

   - bpo-39353(12): Deprecate binhex4 and hexbin4 standards.  Deprecate
     the *note binhex: 10. module and the following *note binascii: f.
     functions: *note b2a_hqx(): 208, *note a2b_hqx(): 209, *note
     rlecode_hqx(): 20a, *note rledecode_hqx(): 20b, *note crc_hqx():
     1086.

   - bpo-39351(13): Remove ‘base64.encodestring()’ and
     ‘base64.decodestring()’, aliases deprecated since Python 3.1: use
     *note base64.encodebytes(): 222. and *note base64.decodebytes():
     223. instead.

   - bpo-39350(14): Remove ‘fractions.gcd()’ function, deprecated since
     Python 3.5 (bpo-22486(15)): use *note math.gcd(): 1be. instead.

   - bpo-39329(16): *note LMTP: 1e0. constructor now has an optional
     `timeout' parameter.  Patch by Dong-hee Na.

   - bpo-39313(17): Add a new ‘exec_function’ option (`–exec-function'
     in the CLI) to ‘RefactoringTool’ for making ‘exec’ a function.
     Patch by Batuhan Taskaya.

   - bpo-39259(18): *note FTP_TLS: 1a7. and *note FTP_TLS: 1a7. now
     raise a *note ValueError: 16d. if the given timeout for their
     constructor is zero to prevent the creation of a non-blocking
     socket.  Patch by Dong-hee Na.

   - bpo-39259(19): *note SMTP: 1de. and *note SMTP_SSL: 1df. now raise
     a *note ValueError: 16d. if the given timeout for their constructor
     is zero to prevent the creation of a non-blocking socket.  Patch by
     Dong-hee Na.

   - bpo-39310(20): Add *note math.ulp(): 1c1.: return the value of the
     least significant bit of a float.

   - bpo-39297(21): Improved performance of importlib.metadata
     distribution discovery and resilients to inaccessible sys.path
     entries (importlib_metadata v1.4.0).

   - bpo-39259(22): *note NNTP: 1c6. and *note NNTP_SSL: 1c7. now raise
     a *note ValueError: 16d. if the given timeout for their constructor
     is zero to prevent the creation of a non-blocking socket.  Patch by
     Dong-hee Na.

   - bpo-38901(23): When you specify prompt=’.’ or equivalently python
     -m venv –prompt .  … the basename of the current directory is used
     to set the created venv’s prompt when it’s activated.

   - bpo-39288(24): Add *note math.nextafter(): 1c0.: return the next
     floating-point value after `x' towards `y'.

   - bpo-39259(25): *note POP3: 1d5. and *note POP3_SSL: 1d6. now raise
     a *note ValueError: 16d. if the given timeout for their constructor
     is zero to prevent the creation of a non-blocking socket.  Patch by
     Dong-hee Na.

   - bpo-39242(26): Updated the Gmane domain from news.gmane.org to
     news.gmane.io which is used for examples of *note NNTP: 1c6. news
     reader server and nntplib tests.

   - bpo-35292(27): Proxy the ‘SimpleHTTPRequestHandler.guess_type’ to
     *note mimetypes.guess_type: 10a1. so the *note mimetypes.init:
     10a2. is called lazily to avoid unnecessary costs when *note
     http.server: 96. module is imported.

   - bpo-39239(28): The *note select.epoll.unregister(): 22e. method no
     longer ignores the *note EBADF: 22f. error.

   - bpo-38907(29): In http.server script, restore binding to IPv4 on
     Windows.

   - bpo-39152(30): Fix ttk.Scale.configure([name]) to return
     configuration tuple for name or all options.  Giovanni Lombardo
     contributed part of the patch.

   - bpo-39198(31): If an exception were to be thrown in
     ‘Logger.isEnabledFor’ (say, by asyncio timeouts or stopit) , the
     *note logging: aa. global lock may not be released appropriately,
     resulting in deadlock.  This change wraps that block of code with
     ‘try...finally’ to ensure the lock is released.

   - bpo-39191(32): Perform a check for running loop before starting a
     new task in ‘loop.run_until_complete()’ to fail fast; it prevents
     the side effect of new task spawning before exception raising.

   - bpo-38871(33): Correctly parenthesize filter-based statements that
     contain lambda expressions in mod:*note lib2to3: a7.  Patch by
     Dong-hee Na.

   - bpo-39142(34): A change was made to logging.config.dictConfig to
     avoid converting instances of named tuples to ConvertingTuple.
     It’s assumed that named tuples are too specialised to be treated
     like ordinary tuples; if a user of named tuples requires
     ConvertingTuple functionality, they will have to implement that
     themselves in their named tuple class.

   - bpo-39158(35): ast.literal_eval() now supports empty sets.

   - bpo-39129(36): Fix import path for ‘asyncio.TimeoutError’

   - bpo-39057(37): ‘urllib.request.proxy_bypass_environment()’ now
     ignores leading dots and no longer ignores a trailing newline.

   - bpo-39056(38): Fixed handling invalid warning category in the -W
     option.  No longer import the re module if it is not needed.

   - bpo-39055(39): *note base64.b64decode(): 10a3. with ‘validate=True’
     raises now a binascii.Error if the input ends with a single ‘\n’.

   - bpo-21600(40): Fix ‘mock.patch.stopall()’ to stop active patches
     that were created with ‘mock.patch.dict()’.

   - bpo-39019(41): Implement dummy ‘__class_getitem__’ for *note
     tempfile.SpooledTemporaryFile: b7e.

   - bpo-39019(42): Implement dummy ‘__class_getitem__’ for
     ‘subprocess.Popen’, ‘subprocess.CompletedProcess’

   - bpo-38914(43): Adjusted the wording of the warning issued by
     distutils’ ‘check’ command when the ‘author’ and ‘maintainer’
     fields are supplied but no corresponding e-mail field
     (‘author_email’ or ‘maintainer_email’) is found.  The wording now
     reflects the fact that these fields are suggested, but not
     required.  Patch by Juergen Gmach.

   - bpo-38878(44): Fixed __subclasshook__ of *note os.PathLike: 5e6. to
     return a correct result upon inheritance.  Patch by Bar Harel.

   - bpo-38615(45): *note IMAP4: 1af. and *note IMAP4_SSL: 1b0. now have
     an optional `timeout' parameter for their constructors.  Also, the
     *note open(): 1b1. method now has an optional `timeout' parameter
     with this change.  The overridden methods of *note IMAP4_SSL: 1b0.
     and *note IMAP4_stream: 1b2. were applied to this change.  Patch by
     Dong-hee Na.

   - bpo-35182(46): Fixed ‘Popen.communicate()’ subsequent call crash
     when the child process has already closed any piped standard
     stream, but still continues to be running.  Patch by Andriy
     Maletsky.

   - bpo-38630(47): On Unix, *note subprocess.Popen.send_signal(): 10a4.
     now polls the process status.  Polling reduces the risk of sending
     a signal to the wrong process if the process completed, the *note
     subprocess.Popen.returncode: 10a5. attribute is still ‘None’, and
     the pid has been reassigned (recycled) to a new different process.

   - bpo-38536(48): Removes trailing space in formatted currency with
     ‘international=True’ and a locale with symbol following value.
     E.g.  ‘locale.currency(12.34, international=True)’ returned ‘'12,34
     EUR '’ instead of ‘'12,34 EUR'’.

   - bpo-38473(49): Use signature from inner mock for autospecced
     methods attached with ‘unittest.mock.attach_mock()’.  Patch by
     Karthikeyan Singaravelan.

   - bpo-38361(50): Fixed an issue where ‘ident’ could include a leading
     path separator when *note syslog.openlog(): 10a6. was called
     without arguments.

   - bpo-38293(51): Add *note copy.copy(): 4d2. and *note
     copy.deepcopy(): 4d3. support to *note property(): 308. objects.

   - bpo-37958(52): Added the pstats.Stats.get_profile_dict() method to
     return the profile data as a StatsProfile instance.

   - bpo-28367(53): Termios magic constants for the following baud
     rates: - B500000 - B576000 - B921600 - B1000000 - B1152000 -
     B1500000 - B2000000 - B2500000 - B3000000 - B3500000 - B4000000
     Patch by Andrey Smirnov

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39430

   (2) https://bugs.python.org/issue39413

   (3) https://bugs.python.org/issue39390

   (4) https://bugs.python.org/issue39395

   (5) https://bugs.python.org/issue39406

   (6) https://bugs.python.org/issue39396

   (7) https://bugs.python.org/issue29435

   (8) https://bugs.python.org/issue39377

   (9) https://bugs.python.org/issue39389

   (10) https://bugs.python.org/issue39366

   (11) https://bugs.python.org/issue39357

   (12) https://bugs.python.org/issue39353

   (13) https://bugs.python.org/issue39351

   (14) https://bugs.python.org/issue39350

   (15) https://bugs.python.org/issue22486

   (16) https://bugs.python.org/issue39329

   (17) https://bugs.python.org/issue39313

   (18) https://bugs.python.org/issue39259

   (19) https://bugs.python.org/issue39259

   (20) https://bugs.python.org/issue39310

   (21) https://bugs.python.org/issue39297

   (22) https://bugs.python.org/issue39259

   (23) https://bugs.python.org/issue38901

   (24) https://bugs.python.org/issue39288

   (25) https://bugs.python.org/issue39259

   (26) https://bugs.python.org/issue39242

   (27) https://bugs.python.org/issue35292

   (28) https://bugs.python.org/issue39239

   (29) https://bugs.python.org/issue38907

   (30) https://bugs.python.org/issue39152

   (31) https://bugs.python.org/issue39198

   (32) https://bugs.python.org/issue39191

   (33) https://bugs.python.org/issue38871

   (34) https://bugs.python.org/issue39142

   (35) https://bugs.python.org/issue39158

   (36) https://bugs.python.org/issue39129

   (37) https://bugs.python.org/issue39057

   (38) https://bugs.python.org/issue39056

   (39) https://bugs.python.org/issue39055

   (40) https://bugs.python.org/issue21600

   (41) https://bugs.python.org/issue39019

   (42) https://bugs.python.org/issue39019

   (43) https://bugs.python.org/issue38914

   (44) https://bugs.python.org/issue38878

   (45) https://bugs.python.org/issue38615

   (46) https://bugs.python.org/issue35182

   (47) https://bugs.python.org/issue38630

   (48) https://bugs.python.org/issue38536

   (49) https://bugs.python.org/issue38473

   (50) https://bugs.python.org/issue38361

   (51) https://bugs.python.org/issue38293

   (52) https://bugs.python.org/issue37958

   (53) https://bugs.python.org/issue28367


File: python.info,  Node: Documentation<18>,  Next: Build<17>,  Prev: Library<23>,  Up: Python 3 9 0 alpha 3

1.19.24.3 Documentation
.......................

   - bpo-39381(1): Mention in docs that *note asyncio.get_event_loop():
     45d. implicitly creates new event loop only if called from the main
     thread.

   - bpo-38918(2): Add an entry for ‘__module__’ in the “function” &
     “method” sections of the inspect docs types and members table(3)

   - bpo-3530(4): In the *note ast: 7. module documentation, fix a
     misleading ‘NodeTransformer’ example and add advice on when to use
     the ‘fix_missing_locations’ function.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39381

   (2) https://bugs.python.org/issue38918

   (3) https://docs.python.org/3/library/inspect.html#types-and-members

   (4) https://bugs.python.org/issue3530


File: python.info,  Node: Build<17>,  Next: IDLE<17>,  Prev: Documentation<18>,  Up: Python 3 9 0 alpha 3

1.19.24.4 Build
...............

   - bpo-39395(1): On non-Windows platforms, the ‘setenv()’ and
     ‘unsetenv()’ functions are now required to build Python.

   - bpo-39160(2): Updated the documentation in ‘/configure --help’ to
     show default values, reference documentation where required and add
     additional explanation where needed.

   - bpo-39144(3): The ctags and etags build targets both include
     Modules/_ctypes and Python standard library source files.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39395

   (2) https://bugs.python.org/issue39160

   (3) https://bugs.python.org/issue39144


File: python.info,  Node: IDLE<17>,  Next: C API<14>,  Prev: Build<17>,  Up: Python 3 9 0 alpha 3

1.19.24.5 IDLE
..............

   - bpo-39050(1): Make IDLE Settings dialog Help button work again.

   - bpo-34118(2): Tag memoryview, range, and tuple as classes, the same
     as list, etcetera, in the library manual built-in functions list.

   - bpo-32989(3): Add tests for editor newline_and_indent_event method.
     Remove dead code from pyparse find_good_parse_start method.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39050

   (2) https://bugs.python.org/issue34118

   (3) https://bugs.python.org/issue32989


File: python.info,  Node: C API<14>,  Prev: IDLE<17>,  Up: Python 3 9 0 alpha 3

1.19.24.6 C API
...............

   - bpo-39372(1): Clean header files of interfaces defined but with no
     implementation.  The public API symbols being removed are:
     ‘_PyBytes_InsertThousandsGroupingLocale’,
     ‘_PyBytes_InsertThousandsGrouping’, ‘_Py_InitializeFromArgs’,
     ‘_Py_InitializeFromWideArgs’, ‘_PyFloat_Repr’, ‘_PyFloat_Digits’,
     ‘_PyFloat_DigitsInit’, ‘PyFrame_ExtendStack’,
     ‘_PyAIterWrapper_Type’, ‘PyNullImporter_Type’, ‘PyCmpWrapper_Type’,
     ‘PySortWrapper_Type’, ‘PyNoArgsFunction’.

   - bpo-39164(2): Add a private ‘_PyErr_GetExcInfo()’ function to
     retrieve exception information of the specified Python thread
     state.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39372

   (2) https://bugs.python.org/issue39164


File: python.info,  Node: Python 3 9 0 alpha 2,  Next: Python 3 9 0 alpha 1,  Prev: Python 3 9 0 alpha 3,  Up: Changelog

1.19.25 Python 3.9.0 alpha 2
----------------------------

`Release date: 2019-12-18'

* Menu:

* Security: Security<13>.
* Core and Builtins: Core and Builtins<22>.
* Library: Library<24>.
* Documentation: Documentation<19>.
* Tests: Tests<18>.
* Build: Build<18>.
* Windows: Windows<18>.
* macOS: macOS<16>.
* IDLE: IDLE<18>.
* C API: C API<15>.


File: python.info,  Node: Security<13>,  Next: Core and Builtins<22>,  Up: Python 3 9 0 alpha 2

1.19.25.1 Security
..................

   - bpo-38945(1): Newline characters have been escaped when performing
     uu encoding to prevent them from overflowing into to content
     section of the encoded file.  This prevents malicious or accidental
     modification of data during the decoding process.

   - bpo-37228(2): Due to significant security concerns, the
     `reuse_address' parameter of *note
     asyncio.loop.create_datagram_endpoint(): 189. is no longer
     supported.  This is because of the behavior of ‘SO_REUSEADDR’ in
     UDP. For more details, see the documentation for
     ‘loop.create_datagram_endpoint()’.  (Contributed by Kyle Stanley,
     Antoine Pitrou, and Yury Selivanov in bpo-37228(3).)

   - bpo-38804(4): Fixes a ReDoS vulnerability in *note http.cookiejar:
     94.  Patch by Ben Caller.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38945

   (2) https://bugs.python.org/issue37228

   (3) https://bugs.python.org/issue37228

   (4) https://bugs.python.org/issue38804


File: python.info,  Node: Core and Builtins<22>,  Next: Library<24>,  Prev: Security<13>,  Up: Python 3 9 0 alpha 2

1.19.25.2 Core and Builtins
...........................

   - bpo-39028(1): Slightly improve the speed of keyword argument
     parsing with many kwargs by strengthening the assumption that
     kwargs are interned strings.

   - bpo-39080(2): Fix the value of `end_col_offset' for Starred
     Expression AST nodes when they are among the elements in the `args'
     attribute of Call AST nodes.

   - bpo-39031(3): When parsing an “elif” node, lineno and col_offset of
     the node now point to the “elif” keyword and not to its condition,
     making it consistent with the “if” node.  Patch by Lysandros
     Nikolaou.

   - bpo-20443(4): In Python 3.9.0a1, sys.argv[0] was made an absolute
     path if a filename was specified on the command line.  Revert this
     change, since most users expect sys.argv to be unmodified.

   - bpo-39008(5): *note PySys_Audit(): 1068. now requires ‘Py_ssize_t’
     to be used for size arguments in the format string, regardless of
     whether ‘PY_SSIZE_T_CLEAN’ was defined at include time.

   - bpo-38673(6): In REPL mode, don’t switch to PS2 if the line starts
     with comment or whitespace.  Based on work by Batuhan Taşkaya.

   - bpo-38922(7): Calling ‘replace’ on a code object now raises the
     ‘code.__new__’ audit event.

   - bpo-38920(8): Add audit hooks for when *note sys.excepthook(): f24.
     and *note sys.unraisablehook(): 35a. are invoked.

   - bpo-38892(9): Improve documentation for audit events table and
     functions.

   - bpo-38852(10): Set the thread stack size to 8 Mb for debug builds
     on android platforms.

   - bpo-38858(11): Each Python subinterpreter now has its own “small
     integer singletons”: numbers in [-5; 257] range.  It is no longer
     possible to change the number of small integers at build time by
     overriding ‘NSMALLNEGINTS’ and ‘NSMALLPOSINTS’ macros: macros
     should now be modified manually in ‘pycore_pystate.h’ header file.

   - bpo-36854(12): The garbage collector state becomes per interpreter
     (‘PyInterpreterState.gc’), rather than being global
     (‘_PyRuntimeState.gc’).

   - bpo-38835(13): The ‘PyFPE_START_PROTECT()’ and
     ‘PyFPE_END_PROTECT()’ macros are empty: they have been doing
     nothing for the last year, so stop using them.

   - bpo-38328(14): Sped up the creation time of constant *note list:
     1f8. and *note set: 1f6. displays.  Patch by Brandt Bucher.

   - bpo-38707(15): ‘MainThread.native_id’ is now correctly reset in
     child processes spawned using *note multiprocessing.Process: 4b9,
     instead of retaining the parent’s value.

   - bpo-38629(16): Added ‘__floor__’ and ‘__ceil__’ methods to float
     object.  Patch by Batuhan Taşkaya.

   - bpo-27145(17): int + int and int - int operators can now return
     small integer singletons.  Patch by hongweipeng.

   - bpo-38021(18): Provide a platform tag for AIX that is sufficient
     for PEP425 binary distribution identification.  Patch by Michael
     Felt.

   - bpo-35409(19): Ignore GeneratorExit exceptions when throwing an
     exception into the aclose coroutine of an asynchronous generator.

   - bpo-33387(20): Removed WITH_CLEANUP_START, WITH_CLEANUP_FINISH,
     BEGIN_FINALLY, END_FINALLY, CALL_FINALLY and POP_FINALLY bytecodes.
     Replaced with RERAISE and WITH_EXCEPT_START bytecodes.  The
     compiler now generates different code for exceptional and
     non-exceptional branches for ‘with’ and ‘try-except’ statements.
     For ‘try-finally’ statements the ‘finally’ block is replicated for
     each exit from the ‘try’ body.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39028

   (2) https://bugs.python.org/issue39080

   (3) https://bugs.python.org/issue39031

   (4) https://bugs.python.org/issue20443

   (5) https://bugs.python.org/issue39008

   (6) https://bugs.python.org/issue38673

   (7) https://bugs.python.org/issue38922

   (8) https://bugs.python.org/issue38920

   (9) https://bugs.python.org/issue38892

   (10) https://bugs.python.org/issue38852

   (11) https://bugs.python.org/issue38858

   (12) https://bugs.python.org/issue36854

   (13) https://bugs.python.org/issue38835

   (14) https://bugs.python.org/issue38328

   (15) https://bugs.python.org/issue38707

   (16) https://bugs.python.org/issue38629

   (17) https://bugs.python.org/issue27145

   (18) https://bugs.python.org/issue38021

   (19) https://bugs.python.org/issue35409

   (20) https://bugs.python.org/issue33387


File: python.info,  Node: Library<24>,  Next: Documentation<19>,  Prev: Core and Builtins<22>,  Up: Python 3 9 0 alpha 2

1.19.25.3 Library
.................

   - bpo-39033(1): Fix *note NameError: e40. in *note zipimport: 14c.
     Patch by Karthikeyan Singaravelan.

   - bpo-39022(2): Update importlib.metadata to include improvements
     from importlib_metadata 1.3 including better serialization of
     EntryPoints and improved documentation for custom finders.

   - bpo-39006(3): Fix asyncio when the ssl module is missing: only
     check for ssl.SSLSocket instance if the ssl module is available.

   - bpo-38708(4): Fix a potential IndexError in email parser when
     parsing an empty msg-id.

   - bpo-38698(5): Add a new ‘InvalidMessageID’ token to email parser to
     represent invalid Message-ID headers.  Also, add defects when there
     is remaining value after parsing the header.

   - bpo-38994(6): Implement ‘__class_getitem__’ for ‘os.PathLike’,
     ‘pathlib.Path’.

   - bpo-38979(7): Return class from ‘ContextVar.__class_getitem__’ to
     simplify subclassing.

   - bpo-38978(8): Implement ‘__class_getitem__’ on asyncio objects
     (Future, Task, Queue).  Patch by Batuhan Taskaya.

   - bpo-38916(9): *note array.array: 216.: Remove ‘tostring()’ and
     ‘fromstring()’ methods.  They were aliases to ‘tobytes()’ and
     ‘frombytes()’, deprecated since Python 3.2.

   - bpo-38986(10): Make repr of C accelerated TaskWakeupMethWrapper the
     same as of pure Python version.

   - bpo-38982(11): Fix asyncio ‘PidfdChildWatcher’: handle ‘waitpid()’
     error.  If ‘waitpid()’ is called elsewhere, ‘waitpid()’ call fails
     with *note ChildProcessError: a79.: use return code 255 in this
     case, and log a warning.  It ensures that the pidfd file descriptor
     is closed if this error occurs.

   - bpo-38529(12): Drop too noisy asyncio warning about deletion of a
     stream without explicit ‘.close()’ call.

   - bpo-27413(13): Added ability to pass through ‘ensure_ascii’ options
     to json.dumps in the ‘json.tool’ command-line interface.

   - bpo-38634(14): The *note readline: de. module now detects if Python
     is linked to libedit at runtime on all platforms.  Previously, the
     check was only done on macOS.

   - bpo-33684(15): Fix ‘json.tool’ failed to read a JSON file with
     non-ASCII characters when locale encoding is not UTF-8.

   - bpo-38698(16): Prevent UnboundLocalError to pop up in
     parse_message_id.

     parse_message_id() was improperly using a token defined inside an
     exception handler, which was raising *note UnboundLocalError: f37.
     on parsing an invalid value.  Patch by Claudiu Popa.

   - bpo-38927(17): Use ‘python -m pip’ instead of ‘pip’ to upgrade
     dependencies in venv.

   - bpo-26730(18): Fix ‘SpooledTemporaryFile.rollover()’ might corrupt
     the file when it is in text mode.  Patch by Serhiy Storchaka.

   - bpo-38881(19): random.choices() now raises a ValueError when all
     the weights are zero.

   - bpo-38876(20): Raise pickle.UnpicklingError when loading an item
     from memo for invalid input.

     The previous code was raising a *note KeyError: 3e9. for both the
     Python and C implementation.  This was caused by the specified
     index of an invalid input which did not exist in the memo
     structure, where the pickle stores what objects it has seen.  The
     malformed input would have caused either a ‘BINGET’ or
     ‘LONG_BINGET’ load from the memo, leading to a *note KeyError: 3e9.
     as the determined index was bogus.  Patch by Claudiu Popa

   - bpo-38688(21): Calling func:*note shutil.copytree: 347. to copy a
     directory tree from one directory to another subdirectory resulted
     in an endless loop and a RecursionError.  A fix was added to
     consume an iterator and create the list of the entries to be
     copied, avoiding the recursion for newly created directories.
     Patch by Bruno P. Kinoshita.

   - bpo-38863(22): Improve ‘is_cgi()’ function in *note http.server:
     96, which enables processing the case that cgi directory is a child
     of another directory other than root.

   - bpo-37838(23): *note typing.get_type_hints(): 1ef. properly handles
     functions decorated with *note functools.wraps(): 955.

   - bpo-38870(24): Expose *note ast.unparse(): 186. as a function of
     the *note ast: 7. module that can be used to unparse an *note
     ast.AST: 187. object and produce a string with code that would
     produce an equivalent *note ast.AST: 187. object when parsed.
     Patch by Pablo Galindo and Batuhan Taskaya.

   - bpo-38859(25): AsyncMock now returns StopAsyncIteration on the
     exhaustion of a side_effects iterable.  Since PEP-479 its
     Impossible to raise a StopIteration exception from a coroutine.

   - bpo-38857(26): AsyncMock fix for return values that are awaitable
     types.  This also covers side_effect iterable values that happened
     to be awaitable, and wraps callables that return an awaitable type.
     Before these awaitables were being awaited instead of being
     returned as is.

   - bpo-38834(27): *note typing.TypedDict: 367. subclasses now track
     which keys are optional using the ‘__required_keys__’ and
     ‘__optional_keys__’ attributes, to enable runtime validation by
     downstream projects.  Patch by Zac Hatfield-Dodds.

   - bpo-38821(28): Fix unhandled exceptions in *note argparse: 5. when
     internationalizing error messages for arguments with ‘nargs’ set to
     special (non-integer) values.  Patch by Federico Bond.

   - bpo-38820(29): Make Python compatible with OpenSSL 3.0.0.  *note
     ssl.SSLSocket.getpeercert(): 9b7. no longer returns IPv6 addresses
     with a trailing new line.

   - bpo-38811(30): Fix an unhandled exception in *note pathlib: c8.
     when *note os.link(): b11. is missing.  Patch by Toke
     Høiland-Jørgensen.

   - bpo-38686(31): Added support for multiple ‘qop’ values in *note
     urllib.request.AbstractDigestAuthHandler: 106c.

   - bpo-38712(32): Add the Linux-specific *note
     signal.pidfd_send_signal(): 1dc. function, which allows sending a
     signal to a process identified by a file descriptor rather than a
     pid.

   - bpo-38348(33): Add ‘-i’ and ‘--indent’ (indentation level), and
     ‘--no-type-comments’ (type comments) command line options to ast
     parsing tool.

   - bpo-37523(34): Change ‘zipfile.ZipExtFile’ to raise ‘ValueError’
     when trying to access the underlying file object after it has been
     closed.  This new behavior is consistent with how accessing closed
     files is handled in other parts of Python.

   - bpo-38045(35): Improve the performance of ‘enum._decompose()’ in
     *note enum: 79.  Patch by hongweipeng.

   - bpo-36820(36): Break cycle generated when saving an exception in
     socket.py, codeop.py and dyld.py as they keep alive not only the
     exception but user objects through the ‘__traceback__’ attribute.
     Patch by Mario Corchero.

   - bpo-36406(37): Handle namespace packages in *note doctest: 66.
     Patch by Karthikeyan Singaravelan.

   - bpo-34776(38): Fix dataclasses to support forward references in
     type annotations

   - bpo-20928(39): ElementTree supports recursive XInclude processing.
     Patch by Stefan Behnel.

   - bpo-29636(40): Add whitespace options for formatting JSON with the
     ‘json.tool’ CLI. The following mutually exclusive options are now
     supported: ‘--indent’ for setting the indent level in spaces;
     ‘--tab’ for indenting with tabs; ‘--no-indent’ for suppressing
     newlines; and ‘--compact’ for suppressing all whitespace.  The
     default behavior remains the same as ‘--indent=4’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39033

   (2) https://bugs.python.org/issue39022

   (3) https://bugs.python.org/issue39006

   (4) https://bugs.python.org/issue38708

   (5) https://bugs.python.org/issue38698

   (6) https://bugs.python.org/issue38994

   (7) https://bugs.python.org/issue38979

   (8) https://bugs.python.org/issue38978

   (9) https://bugs.python.org/issue38916

   (10) https://bugs.python.org/issue38986

   (11) https://bugs.python.org/issue38982

   (12) https://bugs.python.org/issue38529

   (13) https://bugs.python.org/issue27413

   (14) https://bugs.python.org/issue38634

   (15) https://bugs.python.org/issue33684

   (16) https://bugs.python.org/issue38698

   (17) https://bugs.python.org/issue38927

   (18) https://bugs.python.org/issue26730

   (19) https://bugs.python.org/issue38881

   (20) https://bugs.python.org/issue38876

   (21) https://bugs.python.org/issue38688

   (22) https://bugs.python.org/issue38863

   (23) https://bugs.python.org/issue37838

   (24) https://bugs.python.org/issue38870

   (25) https://bugs.python.org/issue38859

   (26) https://bugs.python.org/issue38857

   (27) https://bugs.python.org/issue38834

   (28) https://bugs.python.org/issue38821

   (29) https://bugs.python.org/issue38820

   (30) https://bugs.python.org/issue38811

   (31) https://bugs.python.org/issue38686

   (32) https://bugs.python.org/issue38712

   (33) https://bugs.python.org/issue38348

   (34) https://bugs.python.org/issue37523

   (35) https://bugs.python.org/issue38045

   (36) https://bugs.python.org/issue36820

   (37) https://bugs.python.org/issue36406

   (38) https://bugs.python.org/issue34776

   (39) https://bugs.python.org/issue20928

   (40) https://bugs.python.org/issue29636


File: python.info,  Node: Documentation<19>,  Next: Tests<18>,  Prev: Library<24>,  Up: Python 3 9 0 alpha 2

1.19.25.4 Documentation
.......................

   - bpo-38928(1): Correct when venv’s ‘upgrade_dependencies()’ and
     ‘--upgrade-deps’ are added.

   - bpo-38899(2): Update documentation to state that to activate
     virtual environments under fish one should use ‘source’, not ‘’ as
     documented at
     ‘https://fishshell.com/docs/current/commands.html#source’.

   - bpo-22377(3): Improves documentation of the values that *note
     datetime.datetime.strptime(): f91. accepts for ‘%Z’.  Patch by Karl
     Dubost.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38928

   (2) https://bugs.python.org/issue38899

   (3) https://bugs.python.org/issue22377


File: python.info,  Node: Tests<18>,  Next: Build<18>,  Prev: Documentation<19>,  Up: Python 3 9 0 alpha 2

1.19.25.5 Tests
...............

   - bpo-38546(1): Fix test_ressources_gced_in_workers() of
     test_concurrent_futures: explicitly stop the manager to prevent
     leaking a child process running in the background after the test
     completes.

   - bpo-38546(2): Multiprocessing and concurrent.futures tests now stop
     the resource tracker process when tests complete.

   - bpo-38614(3): Replace hardcoded timeout constants in tests with new
     *note test.support: 106. constants: *note LOOPBACK_TIMEOUT: 10b1,
     *note INTERNET_TIMEOUT: 10b2, *note SHORT_TIMEOUT: f94. and *note
     LONG_TIMEOUT: 10b3.  It becomes easier to adjust these four timeout
     constants for all tests at once, rather than having to adjust every
     single test file.

   - bpo-38547(4): Fix test_pty: if the process is the session leader,
     closing the master file descriptor raises a SIGHUP signal: simply
     ignore SIGHUP when running the tests.

   - bpo-38992(5): Fix a test for *note math.fsum(): e04. that was
     failing due to constant folding.

   - bpo-38991(6): *note test.support: 106.: ‘run_python_until_end()’,
     ‘assert_python_ok()’ and ‘assert_python_failure()’ functions no
     longer strip whitespaces from stderr.  Remove
     ‘test.support.strip_python_stderr()’ function.

   - bpo-38965(7): Fix test_faulthandler on GCC 10.  Use the “volatile”
     keyword in ‘faulthandler._stack_overflow()’ to prevent tail call
     optimization on any compiler, rather than relying on compiler
     specific pragma.

   - bpo-38875(8): test_capi: trashcan tests now require the test “cpu”
     resource.

   - bpo-38841(9): Skip asyncio
     test_create_datagram_endpoint_existing_sock_unix on platforms
     lacking a functional bind() for named unix domain sockets.

   - bpo-38692(10): Skip the test_posix.test_pidfd_open() test if
     ‘os.pidfd_open()’ fails with a *note PermissionError: 6f6.  This
     situation can happen in a Linux sandbox using a syscall whitelist
     which doesn’t allow the ‘pidfd_open()’ syscall yet.

   - bpo-38839(11): Fix some unused functions in tests.  Patch by Adam
     Johnson.

   - bpo-38669(12): Raise *note TypeError: 1fe. when passing target as a
     string with *note unittest.mock.patch.object(): 10b4.

   - bpo-37957(13): test.regrtest now can receive a list of test
     patterns to ignore (using the -i/–ignore argument) or a file with a
     list of patterns to ignore (using the –ignore-file argument).
     Patch by Pablo Galindo.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38546

   (2) https://bugs.python.org/issue38546

   (3) https://bugs.python.org/issue38614

   (4) https://bugs.python.org/issue38547

   (5) https://bugs.python.org/issue38992

   (6) https://bugs.python.org/issue38991

   (7) https://bugs.python.org/issue38965

   (8) https://bugs.python.org/issue38875

   (9) https://bugs.python.org/issue38841

   (10) https://bugs.python.org/issue38692

   (11) https://bugs.python.org/issue38839

   (12) https://bugs.python.org/issue38669

   (13) https://bugs.python.org/issue37957


File: python.info,  Node: Build<18>,  Next: Windows<18>,  Prev: Tests<18>,  Up: Python 3 9 0 alpha 2

1.19.25.6 Build
...............

   - bpo-37404(1): *note asyncio: 9. now raises ‘TyperError’ when
     calling incompatible methods with an *note ssl.SSLSocket: 192.
     socket.  Patch by Ido Michael.

   - bpo-36500(2): Added an optional “regen” project to the Visual
     Studio solution that will regenerate all grammar, tokens, and
     opcodes.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37404

   (2) https://bugs.python.org/issue36500


File: python.info,  Node: Windows<18>,  Next: macOS<16>,  Prev: Build<18>,  Up: Python 3 9 0 alpha 2

1.19.25.7 Windows
.................

   - bpo-39007(1): Add auditing events to functions in *note winreg:
     133.

   - bpo-33125(2): Add support for building and releasing Windows ARM64
     packages.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue39007

   (2) https://bugs.python.org/issue33125


File: python.info,  Node: macOS<16>,  Next: IDLE<18>,  Prev: Windows<18>,  Up: Python 3 9 0 alpha 2

1.19.25.8 macOS
...............

   - bpo-37931(1): Fixed a crash on OSX dynamic builds that occurred
     when re-initializing the posix module after a Py_Finalize if the
     environment had changed since the previous ‘import posix’.  Patch
     by Benoît Hudson.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37931


File: python.info,  Node: IDLE<18>,  Next: C API<15>,  Prev: macOS<16>,  Up: Python 3 9 0 alpha 2

1.19.25.9 IDLE
..............

   - bpo-38944(1): Escape key now closes IDLE completion windows.  Patch
     by Johnny Najera.

   - bpo-38943(2): Fix IDLE autocomplete windows not always appearing on
     some systems.  Patch by Johnny Najera.

   - bpo-38862(3): ‘Strip Trailing Whitespace’ on the Format menu
     removes extra newlines at the end of non-shell files.

   - bpo-38636(4): Fix IDLE Format menu tab toggle and file indent
     width.  These functions (default shortcuts Alt-T and Alt-U) were
     mistakenly disabled in 3.7.5 and 3.8.0.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38944

   (2) https://bugs.python.org/issue38943

   (3) https://bugs.python.org/issue38862

   (4) https://bugs.python.org/issue38636


File: python.info,  Node: C API<15>,  Prev: IDLE<18>,  Up: Python 3 9 0 alpha 2

1.19.25.10 C API
................

   - bpo-38896(1): Remove ‘PyUnicode_ClearFreeList()’ function: the
     Unicode free list has been removed in Python 3.3.

   - bpo-37340(2): Remove ‘PyMethod_ClearFreeList()’ and
     ‘PyCFunction_ClearFreeList()’ functions: the free lists of bound
     method objects have been removed.

   - bpo-38835(3): Exclude ‘PyFPE_START_PROTECT()’ and
     ‘PyFPE_END_PROTECT()’ macros of ‘pyfpe.h’ from ‘Py_LIMITED_API’
     (stable API).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38896

   (2) https://bugs.python.org/issue37340

   (3) https://bugs.python.org/issue38835


File: python.info,  Node: Python 3 9 0 alpha 1,  Next: Python 3 8 0 beta 1,  Prev: Python 3 9 0 alpha 2,  Up: Changelog

1.19.26 Python 3.9.0 alpha 1
----------------------------

`Release date: 2019-11-19'

* Menu:

* Security: Security<14>.
* Core and Builtins: Core and Builtins<23>.
* Library: Library<25>.
* Documentation: Documentation<20>.
* Tests: Tests<19>.
* Build: Build<19>.
* Windows: Windows<19>.
* macOS: macOS<17>.
* IDLE: IDLE<19>.
* Tools/Demos: Tools/Demos<7>.
* C API: C API<16>.


File: python.info,  Node: Security<14>,  Next: Core and Builtins<23>,  Up: Python 3 9 0 alpha 1

1.19.26.1 Security
..................

   - bpo-38722(1): *note runpy: e2. now uses *note io.open_code(): 1050.
     to open code files.  Patch by Jason Killen.

   - bpo-38622(2): Add additional audit events for the *note ctypes: 2a.
     module.

   - bpo-38418(3): Fixes audit event for *note os.system(): e86. to be
     named ‘os.system’.

   - bpo-38243(4): Escape the server title of *note
     xmlrpc.server.DocXMLRPCServer: 10bc. when rendering the document
     page as HTML. (Contributed by Dong-hee Na in bpo-38243(5).)

   - bpo-38174(6): Update vendorized expat library version to 2.2.8,
     which resolves CVE-2019-15903.

   - bpo-37764(7): Fixes email._header_value_parser.get_unstructured
     going into an infinite loop for a specific case in which the email
     header does not have trailing whitespace, and the case in which it
     contains an invalid encoded word.  Patch by Ashwin Ramaswami.

   - bpo-37461(8): Fix an infinite loop when parsing specially crafted
     email headers.  Patch by Abhilash Raj.

   - bpo-37363(9): Adds audit events for the range of supported run
     commands (see *note Command line and environment: 10bd.).

   - bpo-37463(10): ssl.match_hostname() no longer accepts IPv4
     addresses with additional text after the address and only
     quad-dotted notation without trailing whitespaces.  Some
     inet_aton() implementations ignore whitespace and all data after
     whitespace, e.g.  ‘127.0.0.1 whatever’.

   - bpo-37363(11): Adds audit events for *note ensurepip: 78, *note
     ftplib: 82, *note glob: 88, *note imaplib: 97, *note nntplib: c0,
     *note pdb: c9, *note poplib: d0, *note shutil: e9, *note smtplib:
     ed, *note sqlite3: f2, *note subprocess: f9, *note telnetlib: 102,
     *note tempfile: 103. and *note webbrowser: 132, as well as *note
     os.listdir(): b1c, *note os.scandir(): 389. and *note breakpoint():
     40b.

   - bpo-37364(12): *note io.open_code(): 1050. is now used when reading
     ‘.pth’ files.

   - bpo-34631(13): Updated OpenSSL to 1.1.1c in Windows installer

   - bpo-34155(14): Fix parsing of invalid email addresses with more
     than one ‘@’ (e.g.  a@b@c.com.)  to not return the part before 2nd
     ‘@’ as valid email address.  Patch by maxking & jpic.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38722

   (2) https://bugs.python.org/issue38622

   (3) https://bugs.python.org/issue38418

   (4) https://bugs.python.org/issue38243

   (5) https://bugs.python.org/issue38243

   (6) https://bugs.python.org/issue38174

   (7) https://bugs.python.org/issue37764

   (8) https://bugs.python.org/issue37461

   (9) https://bugs.python.org/issue37363

   (10) https://bugs.python.org/issue37463

   (11) https://bugs.python.org/issue37363

   (12) https://bugs.python.org/issue37364

   (13) https://bugs.python.org/issue34631

   (14) https://bugs.python.org/issue34155


File: python.info,  Node: Core and Builtins<23>,  Next: Library<25>,  Prev: Security<14>,  Up: Python 3 9 0 alpha 1

1.19.26.2 Core and Builtins
...........................

   - bpo-38631(1): Replace ‘Py_FatalError()’ call with a regular *note
     RuntimeError: 3dc. exception in ‘float.__getformat__()’.

   - bpo-38639(2): Optimized *note math.floor(): df2, *note math.ceil():
     df3. and *note math.trunc(): df4. for floats.

   - bpo-38640(3): Fixed a bug in the compiler that was causing to raise
     in the presence of break statements and continue statements inside
     always false while loops.  Patch by Pablo Galindo.

   - bpo-38613(4): Optimized some set operations (e.g.  ‘|’, ‘^’, and
     ‘-’) of ‘dict_keys’.  ‘d.keys() | other’ was slower than ‘set(d) |
     other’ but they are almost same performance for now.

   - bpo-28029(5): ‘"".replace("", s, n)’ now returns ‘s’ instead of an
     empty string for all non-zero ‘n’.  There are similar changes for
     *note bytes: 172. and *note bytearray: 173. objects.

   - bpo-38535(6): Fixed line numbers and column offsets for AST nodes
     for calls without arguments in decorators.

   - bpo-38525(7): Fix a segmentation fault when using reverse iterators
     of empty ‘dict’ objects.  Patch by Dong-hee Na and Inada Naoki.

   - bpo-38465(8): *note bytearray: 173, *note array: 216. and *note
     mmap: 31c. objects allow now to export more than ‘2**31’ buffers at
     a time.

   - bpo-38469(9): Fixed a bug where the scope of named expressions was
     not being resolved correctly in the presence of the `global'
     keyword.  Patch by Pablo Galindo.

   - bpo-38437(10): Activate the ‘GC_DEBUG’ macro for debug builds of
     the interpreter (when ‘Py_DEBUG’ is set).  Patch by Pablo Galindo.

   - bpo-38379(11): When the garbage collector makes a collection in
     which some objects resurrect (they are reachable from outside the
     isolated cycles after the finalizers have been executed), do not
     block the collection of all objects that are still unreachable.
     Patch by Pablo Galindo and Tim Peters.

   - bpo-38379(12): When cyclic garbage collection (gc) runs finalizers
     that resurrect unreachable objects, the current gc run ends,
     without collecting any cyclic trash.  However, the statistics
     reported by ‘collect()’ and ‘get_stats()’ claimed that all cyclic
     trash found was collected, and that the resurrected objects were
     collected.  Changed the stats to report that none were collected.

   - bpo-38392(13): In debug mode, *note PyObject_GC_Track(): f06. now
     calls ‘tp_traverse()’ of the object type to ensure that the object
     is valid: test that objects visited by ‘tp_traverse()’ are valid.

   - bpo-38210(14): Remove unnecessary intersection and update set
     operation in dictview with empty set.  (Contributed by Dong-hee Na
     in bpo-38210(15).)

   - bpo-38402(16): Check the error from the system’s underlying ‘crypt’
     or ‘crypt_r’.

   - bpo-37474(17): On FreeBSD, Python no longer calls
     ‘fedisableexcept()’ at startup to control the floating point
     control mode.  The call became useless since FreeBSD 6: it became
     the default mode.

   - bpo-38006(18): Fix a bug due to the interaction of weakrefs and the
     cyclic garbage collector.  We must clear any weakrefs in garbage in
     order to prevent their callbacks from executing and causing a
     crash.

   - bpo-38317(19): Fix warnings options priority:
     ‘PyConfig.warnoptions’ has the highest priority, as stated in the
     PEP 587(20).

   - bpo-38310(21): Predict ‘BUILD_MAP_UNPACK_WITH_CALL’ ->
     ‘CALL_FUNCTION_EX’ opcode pairs in the main interpreter loop.
     Patch by Brandt Bucher.

   - bpo-36871(22): Improve error handling for the assert_has_calls and
     assert_has_awaits methods of mocks.  Fixed a bug where any errors
     encountered while binding the expected calls to the mock’s spec
     were silently swallowed, leading to misleading error output.

   - bpo-11410(23): Better control over symbol visibility is provided
     through use of the visibility attributes available in gcc >= 4.0,
     provided in a uniform way across POSIX and Windows.  The POSIX
     build files have been updated to compile with -fvisibility=hidden,
     minimising exported symbols.

   - bpo-38219(24): Optimized the *note dict: 164. constructor and the
     *note update(): e8e. method for the case when the argument is a
     dict.

   - bpo-38236(25): Python now dumps path configuration if it fails to
     import the Python codecs of the filesystem and stdio encodings.

   - bpo-38013(26): Allow to call ‘async_generator_athrow().throw(...)’
     even for non-started async generator helper.  It fixes annoying
     warning at the end of *note asyncio.run(): 18d. call.

   - bpo-38124(27): Fix an off-by-one error in PyState_AddModule that
     could cause out-of-bounds memory access.

   - bpo-38116(28): The select module is now PEP-384 compliant and no
     longer has static state

   - bpo-38113(29): ast module updated to PEP-384 and all statics
     removed

   - bpo-38076(30): The struct module is now PEP-384 compatible

   - bpo-38075(31): The random module is now PEP-384 compatible

   - bpo-38074(32): zlib module made PEP-384 compatible

   - bpo-38073(33): Make pwd extension module PEP-384 compatible

   - bpo-38072(34): grp module made PEP-384 compatible

   - bpo-38069(35): Make _posixsubprocess PEP-384 compatible

   - bpo-38071(36): Make termios extension module PEP-384 compatible

   - bpo-38005(37): Fixed comparing and creating of InterpreterID and
     ChannelID.

   - bpo-36946(38): Fix possible signed integer overflow when handling
     slices.  Patch by hongweipeng.

   - bpo-37994(39): Fixed silencing arbitrary errors if an attribute
     lookup fails in several sites.  Only AttributeError should be
     silenced.

   - bpo-8425(40): Optimize set difference_update for the case when the
     other set is much larger than the base set.  (Suggested by Evgeny
     Kapun with code contributed by Michele Orrù).

   - bpo-37966(41): The implementation of *note is_normalized(): 370.
     has been greatly sped up on strings that aren’t normalized, by
     implementing the full normalization-quick-check algorithm from the
     Unicode standard.

   - bpo-37947(42): Adjust correctly the recursion level in the symtable
     generation for named expressions.  Patch by Pablo Galindo.

   - bpo-37812(43): The ‘CHECK_SMALL_INT’ macro used inside
     ‘Object/longobject.c’ has been replaced with an explicit ‘return’
     at each call site.

   - bpo-37751(44): Fix *note codecs.lookup(): 238. to normalize the
     encoding name the same way than ‘encodings.normalize_encoding()’,
     except that *note codecs.lookup(): 238. also converts the name to
     lower case.

   - bpo-37830(45): Fixed compilation of *note break: 3fa. and *note
     continue: 2bb. in the *note finally: 2bc. block when the
     corresponding *note try: e37. block contains *note return: 2c8.
     with a non-constant value.

   - bpo-20490(46): Improve import error message for partially
     initialized module on circular ‘from’ imports - by Anthony Sottile.

   - bpo-37840(47): Fix handling of negative indices in *note sq_item:
     10bf. of *note bytearray: 173.  Patch by Sergey Fedoseev.

   - bpo-37802(48): Slightly improve performance of *note
     PyLong_FromUnsignedLong(): 10c0, *note
     PyLong_FromUnsignedLongLong(): 10c1. and *note PyLong_FromSize_t():
     10c2.  Patch by Sergey Fedoseev.

   - bpo-37409(49): Ensure explicit relative imports from interactive
     sessions and scripts (having no parent package) always raise
     ImportError, rather than treating the current module as the
     package.  Patch by Ben Lewis.

   - bpo-32912(50): Reverted bpo-32912(51): emitting *note
     SyntaxWarning: 2c9. instead of *note DeprecationWarning: 15a. for
     invalid escape sequences in string and bytes literals.

   - bpo-37757(52): PEP 572(53): As described in the PEP, assignment
     expressions now raise *note SyntaxError: 55a. when their
     interaction with comprehension scoping results in an ambiguous
     target scope.

     The ‘TargetScopeError’ subclass originally proposed by the PEP has
     been removed in favour of just raising regular syntax errors for
     the disallowed cases.

   - bpo-36279(54): Fix potential use of uninitialized memory in *note
     os.wait3(): 75c.

   - bpo-36311(55): Decoding bytes objects larger than 2GiB is faster
     and no longer fails when a multibyte characters spans a chunk
     boundary.

   - bpo-34880(56): The *note assert: 23f. statement now works properly
     if the *note AssertionError: 240. exception is being shadowed.
     Patch by Zackery Spytz.

   - bpo-37340(57): Removed object cache (‘free_list’) for bound method
     objects.  Temporary bound method objects are less used than before
     thanks to the ‘LOAD_METHOD’ opcode and the
     ‘_PyObject_VectorcallMethod’ C API.

   - bpo-37648(58): Fixed minor inconsistency in ‘list.__contains__()’,
     ‘tuple.__contains__()’ and a few other places.  The collection’s
     item is now always at the left and the needle is on the right of
     ‘==’.

   - bpo-37444(59): Update differing exception between
     ‘builtins.__import__()’ and *note importlib.__import__(): a8e.

   - bpo-37619(60): When adding a wrapper descriptor from one class to a
     different class (for example, setting ‘__add__ = str.__add__’ on an
     ‘int’ subclass), an exception is correctly raised when the operator
     is called.

   - bpo-37593(61): Swap the positions of the `posonlyargs' and `args'
     parameters in the constructor of ‘ast.parameters’ nodes.

   - bpo-37543(62): Optimized pymalloc for non PGO build.

   - bpo-37537(63): Compute allocated pymalloc blocks inside
     _Py_GetAllocatedBlocks().  This slows down _Py_GetAllocatedBlocks()
     but gives a small speedup to _PyObject_Malloc() and
     _PyObject_Free().

   - bpo-37467(64): Fix *note sys.excepthook(): f24. and
     ‘PyErr_Display()’ if a filename is a bytes string.  For example,
     for a SyntaxError exception where the filename attribute is a bytes
     string.

   - bpo-37433(65): Fix ‘SyntaxError’ indicator printing too many spaces
     for multi-line strings - by Anthony Sottile.

   - bpo-37417(66): ‘bytearray.extend()’ now correctly handles errors
     that arise during iteration.  Patch by Brandt Bucher.

   - bpo-37414(67): The undocumented ‘sys.callstats()’ function has been
     removed.  Since Python 3.7, it was deprecated and always returned
     ‘None’.  It required a special build option ‘CALL_PROFILE’ which
     was already removed in Python 3.7.

   - bpo-37392(68): Remove ‘sys.getcheckinterval()’ and
     ‘sys.setcheckinterval()’ functions.  They were deprecated since
     Python 3.2.  Use *note sys.getswitchinterval(): 217. and *note
     sys.setswitchinterval(): 218. instead.  Remove also
     ‘check_interval’ field of the ‘PyInterpreterState’ structure.

   - bpo-37388(69): In development mode and in debug build, `encoding'
     and `errors' arguments are now checked on string encoding and
     decoding operations.  Examples: *note open(): 16f, *note
     str.encode(): 170. and *note bytes.decode(): 171.

     By default, for best performances, the `errors' argument is only
     checked at the first encoding/decoding error, and the `encoding'
     argument is sometimes ignored for empty strings.

   - bpo-37348(70): Optimized decoding short ASCII string with UTF-8 and
     ascii codecs.  ‘b"foo".decode()’ is about 15% faster.  Patch by
     Inada Naoki.

   - bpo-24214(71): Improved support of the surrogatepass error handler
     in the UTF-8 and UTF-16 incremental decoders.

   - bpo-37330(72): *note open(): 16f, *note io.open(): 74d, *note
     codecs.open(): 10c3. and *note fileinput.FileInput: 3a5. no longer
     accept ‘'U'’ (“universal newline”) in the file mode.  This flag was
     deprecated since Python 3.3.

   - bpo-35224(73): Reverse evaluation order of key: value in dict
     comprehensions as proposed in PEP 572.  I.e.  in ‘{k: v for ...}’,
     ‘k’ will be evaluated before ‘v’.

   - bpo-37316(74): Fix the *note PySys_Audit(): 1068. call in *note
     mmap.mmap: 31c.

   - bpo-37300(75): Remove an unnecessary Py_XINCREF in classobject.c.

   - bpo-37269(76): Fix a bug in the peephole optimizer that was not
     treating correctly constant conditions with binary operators.
     Patch by Pablo Galindo.

   - bpo-20443(77): Python now gets the absolute path of the script
     filename specified on the command line (ex: “python3 script.py”):
     the __file__ attribute of the __main__ module and sys.path[0]
     become an absolute path, rather than a relative path.

   - bpo-37257(78): Python’s small object allocator (‘obmalloc.c’) now
     allows (no more than) one empty arena to remain available for
     immediate reuse, without returning it to the OS. This prevents
     thrashing in simple loops where an arena could be created and
     destroyed anew on each iteration.

   - bpo-37231(79): The dispatching of type slots to special methods
     (for example calling ‘__mul__’ when doing ‘x * y’) has been made
     faster.

   - bpo-36974(80): Implemented separate vectorcall functions for every
     calling convention of builtin functions and methods.  This improves
     performance for calls.

   - bpo-37213(81): Handle correctly negative line offsets in the
     peephole optimizer.  Patch by Pablo Galindo.

   - bpo-37219(82): Remove erroneous optimization for empty set
     differences.

   - bpo-15913(83): Implement *note PyBuffer_SizeFromFormat(): 10c4.
     function (previously documented but not implemented): call *note
     struct.calcsize(): 10c5.  Patch by Joannah Nanjekye.

   - bpo-36922(84): Slot functions optimize any callable with
     ‘Py_TPFLAGS_METHOD_DESCRIPTOR’ instead of only instances of
     ‘function’.

   - bpo-36974(85): The slot ‘tp_vectorcall_offset’ is inherited
     unconditionally to support ‘super().__call__()’ when the base class
     uses vectorcall.

   - bpo-37160(86): *note threading.get_native_id(): 360. now also
     supports NetBSD.

   - bpo-37077(87): Add *note threading.get_native_id(): 360. support
     for AIX. Patch by M. Felt

   - bpo-36781(88): *note sum(): 316. has been optimized for boolean
     values.

   - bpo-34556(89): Add ‘--upgrade-deps’ to venv module.  Patch by
     Cooper Ry Lees

   - bpo-20523(90): ‘pdb.Pdb’ supports ~/.pdbrc in Windows 7.  Patch by
     Tim Hopper and Dan Lidral-Porter.

   - bpo-35551(91): Updated encodings: - Removed the “tis260” encoding,
     which was an alias for the nonexistent “tactis” codec.  - Added
     “mac_centeuro” as an alias for the mac_latin2 encoding.

   - bpo-19072(92): The *note classmethod: 309. decorator can now wrap
     other descriptors such as property objects.  Adapted from a patch
     written by Graham Dumpleton.

   - bpo-27575(93): Improve speed of dictview intersection by directly
     using set intersection logic.  Patch by David Su.

   - bpo-30773(94): Prohibit parallel running of aclose() / asend() /
     athrow().  Fix ag_running to reflect the actual running status of
     the AG.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38631

   (2) https://bugs.python.org/issue38639

   (3) https://bugs.python.org/issue38640

   (4) https://bugs.python.org/issue38613

   (5) https://bugs.python.org/issue28029

   (6) https://bugs.python.org/issue38535

   (7) https://bugs.python.org/issue38525

   (8) https://bugs.python.org/issue38465

   (9) https://bugs.python.org/issue38469

   (10) https://bugs.python.org/issue38437

   (11) https://bugs.python.org/issue38379

   (12) https://bugs.python.org/issue38379

   (13) https://bugs.python.org/issue38392

   (14) https://bugs.python.org/issue38210

   (15) https://bugs.python.org/issue38210

   (16) https://bugs.python.org/issue38402

   (17) https://bugs.python.org/issue37474

   (18) https://bugs.python.org/issue38006

   (19) https://bugs.python.org/issue38317

   (20) https://www.python.org/dev/peps/pep-0587

   (21) https://bugs.python.org/issue38310

   (22) https://bugs.python.org/issue36871

   (23) https://bugs.python.org/issue11410

   (24) https://bugs.python.org/issue38219

   (25) https://bugs.python.org/issue38236

   (26) https://bugs.python.org/issue38013

   (27) https://bugs.python.org/issue38124

   (28) https://bugs.python.org/issue38116

   (29) https://bugs.python.org/issue38113

   (30) https://bugs.python.org/issue38076

   (31) https://bugs.python.org/issue38075

   (32) https://bugs.python.org/issue38074

   (33) https://bugs.python.org/issue38073

   (34) https://bugs.python.org/issue38072

   (35) https://bugs.python.org/issue38069

   (36) https://bugs.python.org/issue38071

   (37) https://bugs.python.org/issue38005

   (38) https://bugs.python.org/issue36946

   (39) https://bugs.python.org/issue37994

   (40) https://bugs.python.org/issue8425

   (41) https://bugs.python.org/issue37966

   (42) https://bugs.python.org/issue37947

   (43) https://bugs.python.org/issue37812

   (44) https://bugs.python.org/issue37751

   (45) https://bugs.python.org/issue37830

   (46) https://bugs.python.org/issue20490

   (47) https://bugs.python.org/issue37840

   (48) https://bugs.python.org/issue37802

   (49) https://bugs.python.org/issue37409

   (50) https://bugs.python.org/issue32912

   (51) https://bugs.python.org/issue32912

   (52) https://bugs.python.org/issue37757

   (53) https://www.python.org/dev/peps/pep-0572

   (54) https://bugs.python.org/issue36279

   (55) https://bugs.python.org/issue36311

   (56) https://bugs.python.org/issue34880

   (57) https://bugs.python.org/issue37340

   (58) https://bugs.python.org/issue37648

   (59) https://bugs.python.org/issue37444

   (60) https://bugs.python.org/issue37619

   (61) https://bugs.python.org/issue37593

   (62) https://bugs.python.org/issue37543

   (63) https://bugs.python.org/issue37537

   (64) https://bugs.python.org/issue37467

   (65) https://bugs.python.org/issue37433

   (66) https://bugs.python.org/issue37417

   (67) https://bugs.python.org/issue37414

   (68) https://bugs.python.org/issue37392

   (69) https://bugs.python.org/issue37388

   (70) https://bugs.python.org/issue37348

   (71) https://bugs.python.org/issue24214

   (72) https://bugs.python.org/issue37330

   (73) https://bugs.python.org/issue35224

   (74) https://bugs.python.org/issue37316

   (75) https://bugs.python.org/issue37300

   (76) https://bugs.python.org/issue37269

   (77) https://bugs.python.org/issue20443

   (78) https://bugs.python.org/issue37257

   (79) https://bugs.python.org/issue37231

   (80) https://bugs.python.org/issue36974

   (81) https://bugs.python.org/issue37213

   (82) https://bugs.python.org/issue37219

   (83) https://bugs.python.org/issue15913

   (84) https://bugs.python.org/issue36922

   (85) https://bugs.python.org/issue36974

   (86) https://bugs.python.org/issue37160

   (87) https://bugs.python.org/issue37077

   (88) https://bugs.python.org/issue36781

   (89) https://bugs.python.org/issue34556

   (90) https://bugs.python.org/issue20523

   (91) https://bugs.python.org/issue35551

   (92) https://bugs.python.org/issue19072

   (93) https://bugs.python.org/issue27575

   (94) https://bugs.python.org/issue30773


File: python.info,  Node: Library<25>,  Next: Documentation<20>,  Prev: Core and Builtins<23>,  Up: Python 3 9 0 alpha 1

1.19.26.3 Library
.................

   - bpo-36589(1): The *note curses.update_lines_cols(): 7b9. function
     now returns ‘None’ instead of ‘1’ on success.

   - bpo-38807(2): Update *note TypeError: 1fe. messages for *note
     os.path.join(): 10c7. to include *note os.PathLike: 5e6. objects as
     acceptable input types.

   - bpo-38724(3): Add a repr for ‘subprocess.Popen’ objects.  Patch by
     Andrey Doroschenko.

   - bpo-38786(4): pydoc now recognizes and parses HTTPS URLs.  Patch by
     python273.

   - bpo-38785(5): Prevent asyncio from crashing if parent ‘__init__’ is
     not called from a constructor of object derived from
     ‘asyncio.Future’.

   - bpo-38723(6): *note pdb: c9. now uses *note io.open_code(): 1050.
     to trigger auditing events.

   - bpo-27805(7): Allow opening pipes and other non-seekable files in
     append mode with *note open(): 16f.

   - bpo-38438(8): Simplify the *note argparse: 5. usage message for
     ‘nargs="*"’.

   - bpo-38761(9): WeakSet is now registered as a
     collections.abc.MutableSet.

   - bpo-38716(10): logging: change RotatingHandler namer and rotator to
     class-level attributes.  This stops __init__ from setting them to
     None in the case where a subclass defines them with eponymous
     methods.

   - bpo-38713(11): Add *note os.P_PIDFD: 1cb. constant, which may be
     passed to *note os.waitid(): 75f. to wait on a Linux process file
     descriptor.

   - bpo-38692(12): Add *note asyncio.PidfdChildWatcher: 18e, a
     Linux-specific child watcher implementation that polls process file
     descriptors.

   - bpo-38692(13): Expose the Linux ‘pidfd_open’ syscall as *note
     os.pidfd_open(): 158.

   - bpo-38602(14): Added constants ‘F_OFD_GETLK’, ‘F_OFD_SETLK’ and
     ‘F_OFD_SETLKW’ to the *note fcntl: 7c. module.  Patch by Dong-hee
     Na.

   - bpo-38334(15): Fixed seeking backward on an encrypted
     ‘zipfile.ZipExtFile’.

   - bpo-38312(16): Add *note curses.get_escdelay(): 198, *note
     curses.set_escdelay(): 199, *note curses.get_tabsize(): 19a, and
     *note curses.set_tabsize(): 19b. functions - by Anthony Sottile.

   - bpo-38586(17): Now *note fileConfig(): 4b0. correctly sets the
     .name of handlers loaded.

   - bpo-38565(18): Add new cache_parameters() method for
     functools.lru_cache() to better support pickling.

   - bpo-34679(19): asynci.ProactorEventLoop.close() now only calls
     signal.set_wakeup_fd() in the main thread.

   - bpo-31202(20): The case the result of ‘pathlib.WindowsPath.glob()’
     matches now the case of the pattern for literal parts.

   - bpo-36321(21): Remove misspelled attribute.  The 3.8 changelog
     noted that this would be removed in 3.9.

   - bpo-38521(22): Fixed erroneous equality comparison in
     statistics.NormalDist().

   - bpo-38493(23): Added *note CLD_KILLED: 1c9. and *note CLD_STOPPED:
     1ca. for ‘si_code’.  Patch by Dong-hee Na.

   - bpo-38478(24): Fixed a bug in ‘inspect.signature.bind()’ that was
     causing it to fail when handling a keyword argument with same name
     as positional-only parameter.  Patch by Pablo Galindo.

   - bpo-33604(25): Fixed *note hmac.new: 940. and ‘hmac.HMAC’ to raise
     TypeError instead of ValueError when the digestmod parameter, now
     required in 3.8, is omitted.  Also clarified the hmac module
     documentation and docstrings.

   - bpo-38378(26): Parameters `out' and `in' of *note os.sendfile():
     461. was renamed to `out_fd' and `in_fd'.

   - bpo-38417(27): Added support for setting the umask in the child
     process to the subprocess module on POSIX systems.

   - bpo-38449(28): Revert GH-15522, which introduces a regression in
     *note mimetypes.guess_type(): 10a1. due to improper handling of
     filenames as urls.

   - bpo-38431(29): Fix ‘__repr__’ method for ‘dataclasses.InitVar’ to
     support typing objects, patch by Samuel Colvin.

   - bpo-38109(30): Add missing *note stat.S_IFDOOR: 9ba, *note
     stat.S_IFPORT: 9bb, *note stat.S_IFWHT: 9bc, *note stat.S_ISDOOR():
     10c8, *note stat.S_ISPORT(): 10c9, and *note stat.S_ISWHT(): 10ca.
     values to the Python implementation of *note stat: f4.

   - bpo-38422(31): Clarify docstrings of pathlib suffix(es)

   - bpo-38405(32): Nested subclasses of *note typing.NamedTuple: 227.
     are now pickleable.

   - bpo-38332(33): Prevent *note KeyError: 3e9. thrown by
     ‘_encoded_words.decode()’ when given an encoded-word with invalid
     content-type encoding from propagating all the way to
     ‘email.message.get()’.

   - bpo-38371(34): Deprecated the ‘split()’ method in
     ‘_tkinter.TkappType’ in favour of the ‘splitlist()’ method which
     has more consistent and predicable behavior.

   - bpo-38341(35): Add *note smtplib.SMTPNotSupportedError: 10cb. to
     the *note smtplib: ed. exported names.

   - bpo-38319(36): sendfile() used in socket and shutil modules was
     raising OverflowError for files >= 2GiB on 32-bit architectures.
     (patch by Giampaolo Rodola)

   - bpo-38242(37): Revert the new asyncio Streams API

   - bpo-13153(38): OS native encoding is now used for converting
     between Python strings and Tcl objects.  This allows to display,
     copy and paste to clipboard emoji and other non-BMP characters.
     Converting strings from Tcl to Python and back now never fails
     (except MemoryError).

   - bpo-38019(39): Correctly handle pause/resume reading of closed
     asyncio unix pipe.

   - bpo-38163(40): Child mocks will now detect their type as either
     synchronous or asynchronous, asynchronous child mocks will be
     AsyncMocks and synchronous child mocks will be either MagicMock or
     Mock (depending on their parent type).

   - bpo-38161(41): Removes _AwaitEvent from AsyncMock.

   - bpo-38216(42): Allow the rare code that wants to send invalid http
     requests from the *note http.client: 93. library a way to do so.
     The fixes for bpo-30458(43) led to breakage for some projects that
     were relying on this ability to test their own behavior in the face
     of bad requests.

   - bpo-28286(44): Deprecate opening *note GzipFile: 206. for writing
     implicitly.  Always specify the `mode' argument for writing.

   - bpo-38108(45): Any synchronous magic methods on an AsyncMock now
     return a MagicMock.  Any asynchronous magic methods on a MagicMock
     now return an AsyncMock.

   - bpo-38265(46): Update the `length' parameter of *note os.pread():
     4c0. to accept ‘Py_ssize_t’ instead of ‘int’.

   - bpo-38112(47): *note compileall: 20. has a higher default recursion
     limit and new command-line arguments for path manipulation,
     symlinks handling, and multiple optimization levels.

   - bpo-38248(48): asyncio: Fix inconsistent immediate Task
     cancellation

   - bpo-38237(49): The arguments for the builtin pow function are more
     descriptive.  They can now also be passed in as keywords.

   - bpo-34002(50): Improve efficiency in parts of email package by
     changing while-pop to a for loop, using isdisjoint instead of set
     intersections.

   - bpo-38191(51): Constructors of *note NamedTuple: 227. and *note
     TypedDict: 367. types now accept arbitrary keyword argument names,
     including “cls”, “self”, “typename”, “_typename”, “fields” and
     “_fields”.

   - bpo-38155(52): Add ‘__all__’ to *note datetime: 30.  Patch by Tahia
     Khan.

   - bpo-38185(53): Fixed case-insensitive string comparison in *note
     sqlite3.Row: 84d. indexing.

   - bpo-38136(54): Changes AsyncMock call count and await count to be
     two different counters.  Now await count only counts when a
     coroutine has been awaited, not when it has been called, and
     vice-versa.  Update the documentation around this.

   - bpo-37828(55): Fix default mock name in *note
     unittest.mock.Mock.assert_called(): 69f. exceptions.  Patch by
     Abraham Toriz Cruz.

   - bpo-38175(56): Fix a memory leak in comparison of *note
     sqlite3.Row: 84d. objects.

   - bpo-33936(57): _hashlib no longer calls obsolete OpenSSL
     initialization function with OpenSSL 1.1.0+.

   - bpo-34706(58): Preserve subclassing in
     inspect.Signature.from_callable.

   - bpo-38153(59): Names of hashing algorithms from OpenSSL are now
     normalized to follow Python’s naming conventions.  For example
     OpenSSL uses sha3-512 instead of sha3_512 or blake2b512 instead of
     blake2b.

   - bpo-38115(60): Fix a bug in dis.findlinestarts() where it would
     return invalid bytecode offsets.  Document that a code object’s
     co_lnotab can contain invalid bytecode offsets.

   - bpo-38148(61): Add slots to *note asyncio: 9. transport classes,
     which can reduce memory usage.

   - bpo-38142(62): The _hashlib OpenSSL wrapper extension module is now
     PEP-384 compliant.

   - bpo-9216(63): hashlib constructors now support usedforsecurity flag
     to signal that a hashing algorithm is not used in a security
     context.

   - bpo-36991(64): Fixes a potential incorrect AttributeError exception
     escaping ZipFile.extract() in some unsupported input error
     situations.

   - bpo-38134(65): Remove obsolete copy of PBKDF2_HMAC_fast.  All
     supported OpenSSL versions contain a fast implementation.

   - bpo-38132(66): The OpenSSL hashlib wrapper uses a simpler
     implementation.  Several Macros and pointless caches are gone.  The
     hash name now comes from OpenSSL’s EVP. The algorithm name stays
     the same, except it is now always lower case.

   - bpo-38008(67): Fix parent class check in protocols to correctly
     identify the module that provides a builtin protocol, instead of
     assuming they all come from the *note collections.abc: 1e. module

   - bpo-34037(68): For *note asyncio: 9, add a new coroutine
     ‘loop.shutdown_default_executor()’.  The new coroutine provides an
     API to schedule an executor shutdown that waits on the threadpool
     to finish closing.  Also, *note asyncio.run(): 18d. has been
     updated to utilize the new coroutine.  Patch by Kyle Stanley.

   - bpo-37405(69): Fixed regression bug for socket.getsockname() for
     non-CAN_ISOTP AF_CAN address family sockets by returning a 1-tuple
     instead of string.

   - bpo-38121(70): Update parameter names on functions in
     importlib.metadata matching the changes in the 0.22 release of
     importlib_metadata.

   - bpo-38110(71): The os.closewalk() implementation now uses the libc
     fdwalk() API on platforms where it is available.

   - bpo-38093(72): Fixes AsyncMock so it doesn’t crash when used with
     AsyncContextManagers or AsyncIterators.

   - bpo-37488(73): Add warning to ‘datetime.utctimetuple()’,
     ‘datetime.utcnow()’ and ‘datetime.utcfromtimestamp()’ .

   - bpo-35640(74): Allow passing a *note path-like object: 472. as
     ‘directory’ argument to the *note
     http.server.SimpleHTTPRequestHandler: 49c. class.  Patch by Géry
     Ogam.

   - bpo-38086(75): Update importlib.metadata with changes from
     importlib_metadata 0.21(76).

   - bpo-37251(77): Remove ‘__code__’ check in AsyncMock that
     incorrectly evaluated function specs as async objects but failed to
     evaluate classes with ‘__await__’ but no ‘__code__’ attribute
     defined as async objects.

   - bpo-38037(78): Fix reference counters in the *note signal: ea.
     module.

   - bpo-38066(79): Hide internal asyncio.Stream methods: feed_eof(),
     feed_data(), set_exception() and set_transport().

   - bpo-38059(80): inspect.py now uses sys.exit() instead of exit()

   - bpo-38049(81): Added command-line interface for the *note ast: 7.
     module.

   - bpo-37953(82): In *note typing: 122, improved the ‘__hash__’ and
     ‘__eq__’ methods for ‘ForwardReferences’.

   - bpo-38026(83): Fixed *note inspect.getattr_static(): c99. used
     ‘isinstance’ while it should avoid dynamic lookup.

   - bpo-35923(84): Update *note importlib.machinery.BuiltinImporter:
     64f. to use ‘loader._ORIGIN’ instead of a hardcoded value.  Patch
     by Dong-hee Na.

   - bpo-38010(85): In ‘importlib.metadata’ sync with
     ‘importlib_metadata’ 0.20, clarifying behavior of ‘files()’ and
     fixing issue where only one requirement was returned for
     ‘requires()’ on ‘dist-info’ packages.

   - bpo-38006(86): weakref.WeakValueDictionary defines a local remove()
     function used as callback for weak references.  This function was
     created with a closure.  Modify the implementation to avoid the
     closure.

   - bpo-37995(87): Added the `indent' option to *note ast.dump(): 185.
     which allows it to produce a multiline indented output.

   - bpo-34410(88): Fixed a crash in the ‘tee()’ iterator when re-enter
     it.  RuntimeError is now raised in this case.

   - bpo-37140(89): Fix a ctypes regression of Python 3.8.  When a
     ctypes.Structure is passed by copy to a function, ctypes internals
     created a temporary object which had the side effect of calling the
     structure finalizer (__del__) twice.  The Python semantics requires
     a finalizer to be called exactly once.  Fix ctypes internals to no
     longer call the finalizer twice.

   - bpo-37587(90): ‘_json.scanstring’ is now up to 3x faster when there
     are many backslash escaped characters in the JSON string.

   - bpo-37834(91): Prevent shutil.rmtree exception when built on
     non-Windows system without fd system call support, like older
     versions of macOS.

   - bpo-10978(92): Semaphores and BoundedSemaphores can now release
     more than one waiting thread at a time.

   - bpo-37972(93): Subscripts to the *note unittest.mock.call: 10cc.
     objects now receive the same chaining mechanism as any other custom
     attributes, so that the following usage no longer raises a *note
     TypeError: 1fe.:

     call().foo().__getitem__(‘bar’)

     Patch by blhsing

   - bpo-37965(94): Fix C compiler warning caused by
     distutils.ccompiler.CCompiler.has_function.

   - bpo-37964(95): Add ‘F_GETPATH’ command to *note fcntl: 7c.

   - bpo-37960(96): ‘repr()’ of buffered and text streams now silences
     only expected exceptions when get the value of “name” and “mode”
     attributes.

   - bpo-37961(97): Add a ‘total_nframe’ field to the traces collected
     by the tracemalloc module.  This field indicates the original
     number of frames before it was truncated.

   - bpo-37951(98): Most features of the subprocess module now work
     again in subinterpreters.  Only `preexec_fn' is restricted in
     subinterpreters.

   - bpo-36205(99): Fix the rusage implementation of time.process_time()
     to correctly report the sum of the system and user CPU time.

   - bpo-37950(100): Fix *note ast.dump(): 185. when call with
     incompletely initialized node.

   - bpo-34679(101): Restores instantiation of Windows IOCP event loops
     from the non-main thread.

   - bpo-36917(102): Add default implementation of the
     ‘ast.NodeVisitor.visit_Constant()’ method which emits a deprecation
     warning and calls corresponding methody ‘visit_Num()’,
     ‘visit_Str()’, etc.

   - bpo-37798(103): Update test_statistics.py to verify that the
     statistics module works well for both C and Python implementations.
     Patch by Dong-hee Na

   - bpo-26589(104): Added a new status code to the http module: 451
     UNAVAILABLE_FOR_LEGAL_REASONS

   - bpo-37915(105): Fix a segmentation fault that appeared when
     comparing instances of ‘datetime.timezone’ and ‘datetime.tzinfo’
     objects.  Patch by Pablo Galindo.

   - bpo-32554(106): Deprecate having random.seed() call hash on
     arbitrary types.

   - bpo-9938(107): Add optional keyword argument ‘exit_on_error’ for
     ‘ArgumentParser’.

   - bpo-37851(108): The *note faulthandler: 7b. module no longer
     allocates its alternative stack at Python startup.  Now the stack
     is only allocated at the first faulthandler usage.

   - bpo-32793(109): Fix a duplicated debug message when *note
     smtplib.SMTP.connect(): 10cd. is called.

   - bpo-37885(110): venv: Don’t generate unset variable warning on
     deactivate.

   - bpo-37868(111): Fix dataclasses.is_dataclass when given an instance
     that never raises AttributeError in __getattr__.  That is, an
     object that returns something for __dataclass_fields__ even if it’s
     not a dataclass.

   - bpo-37811(112): Fix ‘socket’ module’s ‘socket.connect(address)’
     function being unable to establish connection in case of
     interrupted system call.  The problem was observed on all OSes
     which ‘poll(2)’ system call can take only non-negative integers and
     -1 as a timeout value.

   - bpo-37863(113): Optimizations for Fraction.__hash__ suggested by
     Tim Peters.

   - bpo-21131(114): Fix ‘faulthandler.register(chain=True)’ stack.
     faulthandler now allocates a dedicated stack of ‘SIGSTKSZ*2’ bytes,
     instead of just ‘SIGSTKSZ’ bytes.  Calling the previous signal
     handler in faulthandler signal handler uses more than ‘SIGSTKSZ’
     bytes of stack memory on some platforms.

   - bpo-37798(115): Add C fastpath for statistics.NormalDist.inv_cdf()
     Patch by Dong-hee Na

   - bpo-37804(116): Remove the deprecated method
     ‘threading.Thread.isAlive()’.  Patch by Dong-hee Na.

   - bpo-37819(117): Add Fraction.as_integer_ratio() to match the
     corresponding methods in bool, int, float, and decimal.

   - bpo-14465(118): Add an xml.etree.ElementTree.indent() function for
     pretty-printing XML trees.  Contributed by Stefan Behnel.

   - bpo-37810(119): Fix *note difflib: 36. ‘?’ hint in diff output when
     dealing with tabs.  Patch by Anthony Sottile.

   - bpo-37772(120): In ‘zipfile.Path’, when adding implicit dirs,
     ensure that ancestral directories are added and that duplicates are
     excluded.

   - bpo-18578(121): Renamed and documented ‘test.bytecode_helper’ as
     *note test.support.bytecode_helper: 107.  Patch by Joannah
     Nanjekye.

   - bpo-37785(122): Fix xgettext warnings in *note argparse: 5.

   - bpo-34488(123): ‘writelines()’ method of *note io.BytesIO: 88a. is
     now slightly faster when many small lines are passed.  Patch by
     Sergey Fedoseev.

   - bpo-37449(124): *note ensurepip: 78. now uses *note
     importlib.resources.read_binary(): 10ce. to read data instead of
     *note pkgutil.get_data(): 10cf.  Patch by Joannah Nanjekye.

   - bpo-28292(125): Mark calendar.py helper functions as being private.
     The follows PEP 8 guidance to maintain the style conventions in the
     module and it addresses a known case of user confusion.

   - bpo-18049(126): Add definition of THREAD_STACK_SIZE for AIX in
     Python/thread_pthread.h The default thread stacksize caused crashes
     with the default recursion limit Patch by M Felt

   - bpo-37742(127): The logging.getLogger() API now returns the root
     logger when passed the name ‘root’, whereas previously it returned
     a non-root logger named ‘root’.  This could affect cases where user
     code explicitly wants a non-root logger named ‘root’, or
     instantiates a logger using logging.getLogger(__name__) in some
     top-level module called ‘root.py’.

   - bpo-37738(128): Fix the implementation of curses ‘addch(str,
     color_pair)’: pass the color pair to ‘setcchar()’, instead of
     always passing 0 as the color pair.

   - bpo-37723(129): Fix performance regression on regular expression
     parsing with huge character sets.  Patch by Yann Vaginay.

   - bpo-35943(130): The function *note PyImport_GetModule(): 525. now
     ensures any module it returns is fully initialized.  Patch by
     Joannah Nanjekye.

   - bpo-32178(131): Fix IndexError in *note email: 67. package when
     trying to parse invalid address fields starting with ‘:’.

   - bpo-37268(132): The *note parser: c7. module is deprecated and will
     be removed in future versions of Python.

   - bpo-11953(133): Completing WSA* error codes in *note socket: ef.

   - bpo-37685(134): Fixed comparisons of *note datetime.timedelta: 2ca.
     and *note datetime.timezone: ae0.

   - bpo-37697(135): Synchronize ‘importlib.metadata’ with
     importlib_metadata 0.19(136), improving handling of EGG-INFO files
     and fixing a crash when entry point names contained colons.

   - bpo-37695(137): Correct *note curses.unget_wch(): abf. error
     message.  Patch by Anthony Sottile.

   - bpo-37689(138): Add ‘is_relative_to()’ in ‘PurePath’ to determine
     whether or not one path is relative to another.

   - bpo-29553(139): Fixed *note argparse.ArgumentParser.format_usage():
     10d0. for mutually exclusive groups.  Patch by Andrew Nester.

   - bpo-37691(140): Let math.dist() accept coordinates as sequences (or
     iterables) rather than just tuples.

   - bpo-37685(141): Fixed ‘__eq__’, ‘__lt__’ etc implementations in
     some classes.  They now return *note NotImplemented: 202. for
     unsupported type of the other operand.  This allows the other
     operand to play role (for example the equality comparison with
     *note ANY: 10d1. will return ‘True’).

   - bpo-37354(142): Make Activate.ps1 Powershell script static to allow
     for signing it.

   - bpo-37664(143): Update wheels bundled with ensurepip (pip 19.2.3
     and setuptools 41.2.0)

   - bpo-37663(144): Bring consistency to venv shell activation scripts
     by always using __VENV_PROMPT__.

   - bpo-37642(145): Allowed the pure Python implementation of *note
     datetime.timezone: ae0. to represent sub-minute offsets close to
     minimum and maximum boundaries, specifically in the ranges (23:59,
     24:00) and (-23:59, 24:00).  Patch by Ngalim Siregar

   - bpo-36161(146): In *note posix: d1, use ‘ttyname_r’ instead of
     ‘ttyname’ for thread safety.

   - bpo-36324(147): Make internal attributes for
     statistics.NormalDist() private.

   - bpo-37555(148): Fix ‘NonCallableMock._call_matcher’ returning tuple
     instead of ‘_Call’ object when ‘self._spec_signature’ exists.
     Patch by Elizabeth Uselton

   - bpo-29446(149): Make ‘from tkinter import *’ import only the
     expected objects.

   - bpo-16970(150): Adding a value error when an invalid value in
     passed to nargs Patch by Robert Leenders

   - bpo-34443(151): Exceptions from *note enum: 79. now use the
     ‘__qualname’ of the enum class in the exception message instead of
     the ‘__name__’.

   - bpo-37491(152): Fix ‘IndexError’ when parsing email headers with
     unexpectedly ending bare-quoted string value.  Patch by Abhilash
     Raj.

   - bpo-37587(153): Make json.loads faster for long strings.  (Patch by
     Marco Paolini)

   - bpo-18378(154): Recognize “UTF-8” as a valid value for LC_CTYPE in
     locale._parse_localename.

   - bpo-37579(155): Return *note NotImplemented: 202. in Python
     implementation of ‘__eq__’ for *note timedelta: 2ca. and *note
     time: 5ed. when the other object being compared is not of the same
     type to match C implementation.  Patch by Karthikeyan Singaravelan.

   - bpo-21478(156): Record calls to parent when autospecced object is
     attached to a mock using ‘unittest.mock.attach_mock()’.  Patch by
     Karthikeyan Singaravelan.

   - bpo-37531(157): “python3 -m test -jN –timeout=TIMEOUT” now kills a
     worker process if it runs longer than `TIMEOUT' seconds.

   - bpo-37482(158): Fix serialization of display name in originator or
     destination address fields with both encoded words and special
     chars.

   - bpo-36993(159): Improve error reporting for corrupt zip files with
     bad zip64 extra data.  Patch by Daniel Hillier.

   - bpo-37502(160): pickle.loads() no longer raises TypeError when the
     buffers argument is set to None

   - bpo-37520(161): Correct behavior for zipfile.Path.parent when the
     path object identifies a subdirectory.

   - bpo-18374(162): Fix the ‘.col_offset’ attribute of nested *note
     ast.BinOp: 10d2. instances which had a too large value in some
     situations.

   - bpo-37424(163): Fixes a possible hang when using a timeout on *note
     subprocess.run(): 4f3. while capturing output.  If the child
     process spawned its own children or otherwise connected its stdout
     or stderr handles with another process, we could hang after the
     timeout was reached and our child was killed when attempting to
     read final output from the pipes.

   - bpo-37421(164): Fix ‘multiprocessing.util.get_temp_dir()’
     finalizer: clear also the ‘tempdir’ configuration of the current
     process, so next call to ‘get_temp_dir()’ will create a new
     temporary directory, rather than reusing the removed temporary
     directory.

   - bpo-37481(165): The distutils ‘bdist_wininst’ command is deprecated
     in Python 3.8, use ‘bdist_wheel’ (wheel packages) instead.

   - bpo-37479(166): When ‘Enum.__str__’ is overridden in a derived
     class, the override will be used by ‘Enum.__format__’ regardless of
     whether mixin classes are present.

   - bpo-37440(167): http.client now enables TLS 1.3 post-handshake
     authentication for default context or if a cert_file is passed to
     HTTPSConnection.

   - bpo-37437(168): Update vendorized expat version to 2.2.7.

   - bpo-37428(169): SSLContext.post_handshake_auth = True no longer
     sets SSL_VERIFY_POST_HANDSHAKE verify flag for client connections.
     Although the option is documented as ignored for clients, OpenSSL
     implicitly enables cert chain validation when the flag is set.

   - bpo-37420(170): *note os.sched_setaffinity(): b30. now correctly
     handles errors that arise during iteration over its ‘mask’
     argument.  Patch by Brandt Bucher.

   - bpo-37412(171): The *note os.getcwdb(): 3da. function now uses the
     UTF-8 encoding on Windows, rather than the ANSI code page: see PEP
     529(172) for the rationale.  The function is no longer deprecated
     on Windows.

   - bpo-37406(173): The sqlite3 module now raises TypeError, rather
     than ValueError, if operation argument type is not str: execute(),
     executemany() and calling a connection.

   - bpo-29412(174): Fix IndexError in parsing a header value ending
     unexpectedly.  Patch by Abhilash Raj.

   - bpo-36546(175): The `dist' argument for statistics.quantiles() is
     now positional only.  The current name doesn’t reflect that the
     argument can be either a dataset or a distribution.  Marking the
     parameter as positional avoids confusion and makes it possible to
     change the name later.

   - bpo-37394(176): Fix a bug that was causing the *note queue: da.
     module to fail if the accelerator module was not available.  Patch
     by Pablo Galindo.

   - bpo-37376(177): *note pprint: d2. now has support for *note
     types.SimpleNamespace: 1d8.  Patch by Carl Bordum Hansen.

   - bpo-26967(178): An *note ArgumentParser: 788. with
     ‘allow_abbrev=False’ no longer disables grouping of short flags,
     such as ‘-vv’, but only disables abbreviation of long flags as
     documented.  Patch by Zac Hatfield-Dodds.

   - bpo-37212(179): *note unittest.mock.call(): 10cc. now preserves the
     order of keyword arguments in repr output.  Patch by Karthikeyan
     Singaravelan.

   - bpo-37372(180): Fix error unpickling datetime.time objects from
     Python 2 with seconds>=24.  Patch by Justin Blanchard.

   - bpo-37345(181): Add formal support for UDPLITE sockets.  Support
     was present before, but it is now easier to detect support with
     ‘hasattr(socket, 'IPPROTO_UDPLITE')’ and there are constants
     defined for each of the values needed: ‘socket.IPPROTO_UDPLITE’,
     ‘UDPLITE_SEND_CSCOV’, and ‘UDPLITE_RECV_CSCOV’.  Patch by Gabe
     Appleton.

   - bpo-37358(182): Optimized ‘functools.partial’ by using vectorcall.

   - bpo-37347(183): *note sqlite3.Connection.create_aggregate(): 10d3,
     *note sqlite3.Connection.create_function(): 10d4, *note
     sqlite3.Connection.set_authorizer(): 10d5, *note
     sqlite3.Connection.set_progress_handler(): 10d6. *note
     sqlite3.Connection.set_trace_callback(): b65. methods lead to
     segfaults if some of these methods are called twice with an equal
     object but not the same.  Now callbacks are stored more carefully.
     Patch by Aleksandr Balezin.

   - bpo-37163(184): The `obj' argument of *note dataclasses.replace():
     fa8. is positional-only now.

   - bpo-37085(185): Add the optional Linux SocketCAN Broadcast Manager
     constants, used as flags to configure the BCM behaviour, in the
     socket module.  Patch by Karl Ding.

   - bpo-37328(186): ‘HTMLParser.unescape’ is removed.  It was
     undocumented and deprecated since Python 3.4.

   - bpo-37305(187): Add .webmanifest -> application/manifest+json to
     list of recognized file types and content type headers

   - bpo-37320(188): ‘aifc.openfp()’ alias to ‘aifc.open()’,
     ‘sunau.openfp()’ alias to ‘sunau.open()’, and ‘wave.openfp()’ alias
     to ‘wave.open()’ have been removed.  They were deprecated since
     Python 3.7.

   - bpo-37315(189): Deprecated accepting floats with integral value
     (like ‘5.0’) in *note math.factorial(): 1fc.

   - bpo-37312(190): ‘_dummy_thread’ and ‘dummy_threading’ modules have
     been removed.  These modules were deprecated since Python 3.7 which
     requires threading support.

   - bpo-33972(191): Email with single part but content-type set to
     ‘multipart/*’ doesn’t raise AttributeError anymore.

   - bpo-37280(192): Use threadpool for reading from file for sendfile
     fallback mode.

   - bpo-37279(193): Fix asyncio sendfile support when sendfile sends
     extra data in fallback mode.

   - bpo-19865(194): *note ctypes.create_unicode_buffer(): 10d7. now
     also supports non-BMP characters on platforms with 16-bit ‘wchar_t’
     (for example, Windows and AIX).

   - bpo-37266(195): In a subinterpreter, spawning a daemon thread now
     raises an exception.  Daemon threads were never supported in
     subinterpreters.  Previously, the subinterpreter finalization
     crashed with a Python fatal error if a daemon thread was still
     running.

   - bpo-37210(196): Allow pure Python implementation of *note pickle:
     ca. to work even when the C ‘_pickle’ module is unavailable.

   - bpo-21872(197): Fix *note lzma: ad.: module decompresses data
     incompletely.  When decompressing a FORMAT_ALONE format file, and
     it doesn’t have the end marker, sometimes the last one to dozens
     bytes can’t be output.  Patch by Ma Lin.

   - bpo-35922(198): Fix ‘RobotFileParser.crawl_delay()’ and
     ‘RobotFileParser.request_rate()’ to return ‘None’ rather than raise
     *note AttributeError: 4a2. when no relevant rule is defined in the
     robots.txt file.  Patch by Rémi Lapeyre.

   - bpo-35766(199): Change the format of feature_version to be a
     (major, minor) tuple.

   - bpo-36607(200): Eliminate *note RuntimeError: 3dc. raised by *note
     asyncio.all_tasks(): 229. if internal tasks weak set is changed by
     another thread during iteration.

   - bpo-18748(201): ‘_pyio.IOBase’ destructor now does nothing if
     getting the ‘closed’ attribute fails to better mimic ‘_io.IOBase’
     finalizer.

   - bpo-36402(202): Fix a race condition at Python shutdown when
     waiting for threads.  Wait until the Python thread state of all
     non-daemon threads get deleted (join all non-daemon threads),
     rather than just wait until non-daemon Python threads complete.

   - bpo-37206(203): Default values which cannot be represented as
     Python objects no longer improperly represented as ‘None’ in
     function signatures.

   - bpo-37111(204): Added ‘encoding’ and ‘errors’ keyword parameters to
     ‘logging.basicConfig’.

   - bpo-12144(205): Ensure cookies with ‘expires’ attribute are handled
     in ‘CookieJar.make_cookies()’.

   - bpo-34886(206): Fix an unintended ValueError from *note
     subprocess.run(): 4f3. when checking for conflicting *note input:
     d33. and ‘stdin’ or ‘capture_output’ and ‘stdout’ or ‘stderr’ args
     when they were explicitly provided but with *note None: 203. values
     within a passed in ‘**kwargs’ dict rather than as passed directly
     by name.  Patch contributed by Rémi Lapeyre.

   - bpo-37173(207): The exception message for ‘inspect.getfile()’ now
     correctly reports the passed class rather than the builtins module.

   - bpo-37178(208): Give math.perm() a one argument form that means the
     same as math.factorial().

   - bpo-37178(209): For math.perm(n, k), let k default to n, giving the
     same result as factorial.

   - bpo-37165(210): Converted _collections._count_elements to use the
     Argument Clinic.

   - bpo-34767(211): Do not always create a *note collections.deque:
     62b. in *note asyncio.Lock: 3ae.

   - bpo-37158(212): Speed-up statistics.fmean() by switching from a
     function to a generator.

   - bpo-34282(213): Remove ‘Enum._convert’ method, deprecated in 3.8.

   - bpo-37150(214): ‘argparse._ActionsContainer.add_argument’ now
     throws error, if someone accidentally pass FileType class object
     instead of instance of FileType as *note type: 6ff. argument

   - bpo-28724(215): The socket module now has the *note
     socket.send_fds(): 1e4. and ‘socket.recv.fds()’ methods.
     Contributed by Joannah Nanjekye, Shinya Okano and Victor Stinner.

   - bpo-35621(216): Support running asyncio subprocesses when execution
     event loop in a thread on UNIX.

   - bpo-36520(217): Lengthy email headers with UTF-8 characters are now
     properly encoded when they are folded.  Patch by Jeffrey Kintscher.

   - bpo-30835(218): Fixed a bug in email parsing where a message with
     invalid bytes in content-transfer-encoding of a multipart message
     can cause an AttributeError.  Patch by Andrew Donnellan.

   - bpo-31163(219): pathlib.Path instance’s rename and replace methods
     now return the new Path instance.

   - bpo-25068(220): *note urllib.request.ProxyHandler: 10d8. now
     lowercases the keys of the passed dictionary.

   - bpo-26185(221): Fix *note repr(): 8b9. on empty ‘ZipInfo’ object.
     Patch by Mickaël Schoentgen.

   - bpo-21315(222): Email headers containing RFC2047 encoded words are
     parsed despite the missing whitespace, and a defect registered.
     Also missing trailing whitespace after encoded words is now
     registered as a defect.

   - bpo-31904(223): Port test_datetime to VxWorks: skip zoneinfo tests
     on VxWorks

   - bpo-35805(224): Add parser for Message-ID header and add it to
     default HeaderRegistry.  This should prevent folding of Message-ID
     using RFC 2048 encoded words.

   - bpo-36871(225): Ensure method signature is used instead of
     constructor signature of a class while asserting mock object
     against method calls.  Patch by Karthikeyan Singaravelan.

   - bpo-35070(226): posix.getgrouplist() now works correctly when the
     user belongs to NGROUPS_MAX supplemental groups.  Patch by Jeffrey
     Kintscher.

   - bpo-31783(227): Fix race condition in ThreadPoolExecutor when
     worker threads are created during interpreter shutdown.

   - bpo-36582(228): Fix ‘UserString.encode()’ to correctly return
     ‘bytes’ rather than a ‘UserString’ instance.

   - bpo-32424(229): Deprecate xml.etree.ElementTree.Element.copy() in
     favor of copy.copy().

     Patch by Gordon P. Hemsley

   - bpo-36564(230): Fix infinite loop in email header folding logic
     that would be triggered when an email policy’s max_line_length is
     not long enough to include the required markup and any values in
     the message.  Patch by Paul Ganssle

   - bpo-36543(231): Removed methods Element.getchildren(),
     Element.getiterator() and ElementTree.getiterator() and the
     xml.etree.cElementTree module.

   - bpo-36409(232): Remove the old plistlib API deprecated in Python
     3.4

   - bpo-36302(233): distutils sorts source file lists so that Extension
     .so files build more reproducibly by default

   - bpo-36250(234): Ignore ‘ValueError’ from ‘signal’ with
     ‘interaction’ in non-main thread.

   - bpo-36046(235): Added ‘user’, ‘group’ and ‘extra_groups’ parameters
     to the subprocess.Popen constructor.  Patch by Patrick McLean.

   - bpo-32627(236): Fix compile error when ‘_uuid’ headers conflicting
     included.

   - bpo-35800(237): Deprecate ‘smtpd.MailmanProxy’ ready for future
     removal.

   - bpo-35168(238): *note shlex.shlex.punctuation_chars: 10d9. is now a
     read-only property.

   - bpo-8538(239): Add support for boolean actions like ‘--foo’ and
     ‘--no-foo’ to argparse.  Patch contributed by Rémi Lapeyre.

   - bpo-20504(240): Fixes a bug in *note cgi: 15. module when a
     multipart/form-data request has no ‘Content-Length’ header.

   - bpo-25988(241): The abstract base classes in *note collections.abc:
     1e. no longer are exposed in the regular *note collections: 1d.
     module.

   - bpo-11122(242): Distutils won’t check for rpmbuild in specified
     paths only.

   - bpo-34775(243): Division handling of PurePath now returns
     NotImplemented instead of raising a TypeError when passed something
     other than an instance of str or PurePath.  Patch by Roger Aiudi.

   - bpo-34749(244): *note binascii.a2b_base64(): 10da. is now up to 2
     times faster.  Patch by Sergey Fedoseev.

   - bpo-34519(245): Add additional aliases for HP Roman 8.  Patch by
     Michael Osipov.

   - bpo-28009(246): Fix uuid.getnode() on platforms with ‘.’ as MAC
     Addr delimiter as well fix for MAC Addr format that omits a leading
     0 in MAC Addr values.  Currently, AIX is the only know platform
     with these settings.  Patch by Michael Felt.

   - bpo-30618(247): Add *note readlink(): 1d0.  Patch by Girts
     Folkmanis.

   - bpo-32498(248): Made *note urllib.parse.unquote(): 10db. accept
     bytes in addition to strings.  Patch by Stein Karlsen.

   - bpo-33348(249): lib2to3 now recognizes expressions after ‘*’ and
     ‘**’ like in ‘f(*[] or [])’.

   - bpo-32689(250): Update *note shutil.move(): 385. function to allow
     for Path objects to be used as source argument.  Patch by Emily
     Morehouse and Maxwell “5.13b” McKinnon.

   - bpo-32820(251): Added __format__ to IPv4 and IPv6 classes.  Always
     outputs a fully zero- padded string.  Supports b/x/n modifiers
     (bin/hex/native format).  Native format for IPv4 is bin, native
     format for IPv6 is hex.  Also supports ‘#’ and ‘_’ modifiers.

   - bpo-27657(252): Fix urllib.parse.urlparse() with numeric paths.  A
     string like “path:80” is no longer parsed as a path but as a scheme
     (“path”) and a path (“80”).

   - bpo-4963(253): Fixed non-deterministic behavior related to
     mimetypes extension mapping and module reinitialization.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36589

   (2) https://bugs.python.org/issue38807

   (3) https://bugs.python.org/issue38724

   (4) https://bugs.python.org/issue38786

   (5) https://bugs.python.org/issue38785

   (6) https://bugs.python.org/issue38723

   (7) https://bugs.python.org/issue27805

   (8) https://bugs.python.org/issue38438

   (9) https://bugs.python.org/issue38761

   (10) https://bugs.python.org/issue38716

   (11) https://bugs.python.org/issue38713

   (12) https://bugs.python.org/issue38692

   (13) https://bugs.python.org/issue38692

   (14) https://bugs.python.org/issue38602

   (15) https://bugs.python.org/issue38334

   (16) https://bugs.python.org/issue38312

   (17) https://bugs.python.org/issue38586

   (18) https://bugs.python.org/issue38565

   (19) https://bugs.python.org/issue34679

   (20) https://bugs.python.org/issue31202

   (21) https://bugs.python.org/issue36321

   (22) https://bugs.python.org/issue38521

   (23) https://bugs.python.org/issue38493

   (24) https://bugs.python.org/issue38478

   (25) https://bugs.python.org/issue33604

   (26) https://bugs.python.org/issue38378

   (27) https://bugs.python.org/issue38417

   (28) https://bugs.python.org/issue38449

   (29) https://bugs.python.org/issue38431

   (30) https://bugs.python.org/issue38109

   (31) https://bugs.python.org/issue38422

   (32) https://bugs.python.org/issue38405

   (33) https://bugs.python.org/issue38332

   (34) https://bugs.python.org/issue38371

   (35) https://bugs.python.org/issue38341

   (36) https://bugs.python.org/issue38319

   (37) https://bugs.python.org/issue38242

   (38) https://bugs.python.org/issue13153

   (39) https://bugs.python.org/issue38019

   (40) https://bugs.python.org/issue38163

   (41) https://bugs.python.org/issue38161

   (42) https://bugs.python.org/issue38216

   (43) https://bugs.python.org/issue30458

   (44) https://bugs.python.org/issue28286

   (45) https://bugs.python.org/issue38108

   (46) https://bugs.python.org/issue38265

   (47) https://bugs.python.org/issue38112

   (48) https://bugs.python.org/issue38248

   (49) https://bugs.python.org/issue38237

   (50) https://bugs.python.org/issue34002

   (51) https://bugs.python.org/issue38191

   (52) https://bugs.python.org/issue38155

   (53) https://bugs.python.org/issue38185

   (54) https://bugs.python.org/issue38136

   (55) https://bugs.python.org/issue37828

   (56) https://bugs.python.org/issue38175

   (57) https://bugs.python.org/issue33936

   (58) https://bugs.python.org/issue34706

   (59) https://bugs.python.org/issue38153

   (60) https://bugs.python.org/issue38115

   (61) https://bugs.python.org/issue38148

   (62) https://bugs.python.org/issue38142

   (63) https://bugs.python.org/issue9216

   (64) https://bugs.python.org/issue36991

   (65) https://bugs.python.org/issue38134

   (66) https://bugs.python.org/issue38132

   (67) https://bugs.python.org/issue38008

   (68) https://bugs.python.org/issue34037

   (69) https://bugs.python.org/issue37405

   (70) https://bugs.python.org/issue38121

   (71) https://bugs.python.org/issue38110

   (72) https://bugs.python.org/issue38093

   (73) https://bugs.python.org/issue37488

   (74) https://bugs.python.org/issue35640

   (75) https://bugs.python.org/issue38086

   (76) 
https://gitlab.com/python-devs/importlib_metadata/blob/0.21/importlib_metadata/docs/changelog.rst

   (77) https://bugs.python.org/issue37251

   (78) https://bugs.python.org/issue38037

   (79) https://bugs.python.org/issue38066

   (80) https://bugs.python.org/issue38059

   (81) https://bugs.python.org/issue38049

   (82) https://bugs.python.org/issue37953

   (83) https://bugs.python.org/issue38026

   (84) https://bugs.python.org/issue35923

   (85) https://bugs.python.org/issue38010

   (86) https://bugs.python.org/issue38006

   (87) https://bugs.python.org/issue37995

   (88) https://bugs.python.org/issue34410

   (89) https://bugs.python.org/issue37140

   (90) https://bugs.python.org/issue37587

   (91) https://bugs.python.org/issue37834

   (92) https://bugs.python.org/issue10978

   (93) https://bugs.python.org/issue37972

   (94) https://bugs.python.org/issue37965

   (95) https://bugs.python.org/issue37964

   (96) https://bugs.python.org/issue37960

   (97) https://bugs.python.org/issue37961

   (98) https://bugs.python.org/issue37951

   (99) https://bugs.python.org/issue36205

   (100) https://bugs.python.org/issue37950

   (101) https://bugs.python.org/issue34679

   (102) https://bugs.python.org/issue36917

   (103) https://bugs.python.org/issue37798

   (104) https://bugs.python.org/issue26589

   (105) https://bugs.python.org/issue37915

   (106) https://bugs.python.org/issue32554

   (107) https://bugs.python.org/issue9938

   (108) https://bugs.python.org/issue37851

   (109) https://bugs.python.org/issue32793

   (110) https://bugs.python.org/issue37885

   (111) https://bugs.python.org/issue37868

   (112) https://bugs.python.org/issue37811

   (113) https://bugs.python.org/issue37863

   (114) https://bugs.python.org/issue21131

   (115) https://bugs.python.org/issue37798

   (116) https://bugs.python.org/issue37804

   (117) https://bugs.python.org/issue37819

   (118) https://bugs.python.org/issue14465

   (119) https://bugs.python.org/issue37810

   (120) https://bugs.python.org/issue37772

   (121) https://bugs.python.org/issue18578

   (122) https://bugs.python.org/issue37785

   (123) https://bugs.python.org/issue34488

   (124) https://bugs.python.org/issue37449

   (125) https://bugs.python.org/issue28292

   (126) https://bugs.python.org/issue18049

   (127) https://bugs.python.org/issue37742

   (128) https://bugs.python.org/issue37738

   (129) https://bugs.python.org/issue37723

   (130) https://bugs.python.org/issue35943

   (131) https://bugs.python.org/issue32178

   (132) https://bugs.python.org/issue37268

   (133) https://bugs.python.org/issue11953

   (134) https://bugs.python.org/issue37685

   (135) https://bugs.python.org/issue37697

   (136) 
https://gitlab.com/python-devs/importlib_metadata/-/milestones/20

   (137) https://bugs.python.org/issue37695

   (138) https://bugs.python.org/issue37689

   (139) https://bugs.python.org/issue29553

   (140) https://bugs.python.org/issue37691

   (141) https://bugs.python.org/issue37685

   (142) https://bugs.python.org/issue37354

   (143) https://bugs.python.org/issue37664

   (144) https://bugs.python.org/issue37663

   (145) https://bugs.python.org/issue37642

   (146) https://bugs.python.org/issue36161

   (147) https://bugs.python.org/issue36324

   (148) https://bugs.python.org/issue37555

   (149) https://bugs.python.org/issue29446

   (150) https://bugs.python.org/issue16970

   (151) https://bugs.python.org/issue34443

   (152) https://bugs.python.org/issue37491

   (153) https://bugs.python.org/issue37587

   (154) https://bugs.python.org/issue18378

   (155) https://bugs.python.org/issue37579

   (156) https://bugs.python.org/issue21478

   (157) https://bugs.python.org/issue37531

   (158) https://bugs.python.org/issue37482

   (159) https://bugs.python.org/issue36993

   (160) https://bugs.python.org/issue37502

   (161) https://bugs.python.org/issue37520

   (162) https://bugs.python.org/issue18374

   (163) https://bugs.python.org/issue37424

   (164) https://bugs.python.org/issue37421

   (165) https://bugs.python.org/issue37481

   (166) https://bugs.python.org/issue37479

   (167) https://bugs.python.org/issue37440

   (168) https://bugs.python.org/issue37437

   (169) https://bugs.python.org/issue37428

   (170) https://bugs.python.org/issue37420

   (171) https://bugs.python.org/issue37412

   (172) https://www.python.org/dev/peps/pep-0529

   (173) https://bugs.python.org/issue37406

   (174) https://bugs.python.org/issue29412

   (175) https://bugs.python.org/issue36546

   (176) https://bugs.python.org/issue37394

   (177) https://bugs.python.org/issue37376

   (178) https://bugs.python.org/issue26967

   (179) https://bugs.python.org/issue37212

   (180) https://bugs.python.org/issue37372

   (181) https://bugs.python.org/issue37345

   (182) https://bugs.python.org/issue37358

   (183) https://bugs.python.org/issue37347

   (184) https://bugs.python.org/issue37163

   (185) https://bugs.python.org/issue37085

   (186) https://bugs.python.org/issue37328

   (187) https://bugs.python.org/issue37305

   (188) https://bugs.python.org/issue37320

   (189) https://bugs.python.org/issue37315

   (190) https://bugs.python.org/issue37312

   (191) https://bugs.python.org/issue33972

   (192) https://bugs.python.org/issue37280

   (193) https://bugs.python.org/issue37279

   (194) https://bugs.python.org/issue19865

   (195) https://bugs.python.org/issue37266

   (196) https://bugs.python.org/issue37210

   (197) https://bugs.python.org/issue21872

   (198) https://bugs.python.org/issue35922

   (199) https://bugs.python.org/issue35766

   (200) https://bugs.python.org/issue36607

   (201) https://bugs.python.org/issue18748

   (202) https://bugs.python.org/issue36402

   (203) https://bugs.python.org/issue37206

   (204) https://bugs.python.org/issue37111

   (205) https://bugs.python.org/issue12144

   (206) https://bugs.python.org/issue34886

   (207) https://bugs.python.org/issue37173

   (208) https://bugs.python.org/issue37178

   (209) https://bugs.python.org/issue37178

   (210) https://bugs.python.org/issue37165

   (211) https://bugs.python.org/issue34767

   (212) https://bugs.python.org/issue37158

   (213) https://bugs.python.org/issue34282

   (214) https://bugs.python.org/issue37150

   (215) https://bugs.python.org/issue28724

   (216) https://bugs.python.org/issue35621

   (217) https://bugs.python.org/issue36520

   (218) https://bugs.python.org/issue30835

   (219) https://bugs.python.org/issue31163

   (220) https://bugs.python.org/issue25068

   (221) https://bugs.python.org/issue26185

   (222) https://bugs.python.org/issue21315

   (223) https://bugs.python.org/issue31904

   (224) https://bugs.python.org/issue35805

   (225) https://bugs.python.org/issue36871

   (226) https://bugs.python.org/issue35070

   (227) https://bugs.python.org/issue31783

   (228) https://bugs.python.org/issue36582

   (229) https://bugs.python.org/issue32424

   (230) https://bugs.python.org/issue36564

   (231) https://bugs.python.org/issue36543

   (232) https://bugs.python.org/issue36409

   (233) https://bugs.python.org/issue36302

   (234) https://bugs.python.org/issue36250

   (235) https://bugs.python.org/issue36046

   (236) https://bugs.python.org/issue32627

   (237) https://bugs.python.org/issue35800

   (238) https://bugs.python.org/issue35168

   (239) https://bugs.python.org/issue8538

   (240) https://bugs.python.org/issue20504

   (241) https://bugs.python.org/issue25988

   (242) https://bugs.python.org/issue11122

   (243) https://bugs.python.org/issue34775

   (244) https://bugs.python.org/issue34749

   (245) https://bugs.python.org/issue34519

   (246) https://bugs.python.org/issue28009

   (247) https://bugs.python.org/issue30618

   (248) https://bugs.python.org/issue32498

   (249) https://bugs.python.org/issue33348

   (250) https://bugs.python.org/issue32689

   (251) https://bugs.python.org/issue32820

   (252) https://bugs.python.org/issue27657

   (253) https://bugs.python.org/issue4963


File: python.info,  Node: Documentation<20>,  Next: Tests<19>,  Prev: Library<25>,  Up: Python 3 9 0 alpha 1

1.19.26.4 Documentation
.......................

   - bpo-21767(1): Explicitly mention abc support in
     functools.singledispatch

   - bpo-38816(2): Provides more details about the interaction between
     ‘fork()’ and CPython’s runtime, focusing just on the C-API. This
     includes cautions about where ‘fork()’ should and shouldn’t be
     called.

   - bpo-38351(3): Modernize *note email: 67. examples from %-formatting
     to f-strings.

   - bpo-38778(4): Document the fact that *note RuntimeError: 3dc. is
     raised if *note os.fork(): a42. is called in a subinterpreter.

   - bpo-38592(5): Add Brazilian Portuguese to the language switcher at
     Python Documentation website.

   - bpo-38294(6): Add list of no-longer-escaped chars to re.escape
     documentation

   - bpo-38053(7): Modernized the plistlib documentation

   - bpo-26868(8): Fix example usage of *note PyModule_AddObject():
     10dd. to properly handle errors.

   - bpo-36797(9): Fix a dead link in the distutils API Reference.

   - bpo-37977(10): Warn more strongly and clearly about pickle
     insecurity

   - bpo-37979(11): Added a link to dateutil.parser.isoparse in the
     datetime.fromisoformat documentation.  Patch by Paul Ganssle

   - bpo-12707(12): Deprecate info(), geturl(), getcode() methods in
     favor of the headers, url, and status properties, respectively, for
     HTTPResponse and addinfourl.  Also deprecate the code attribute of
     addinfourl in favor of the status attribute.  Patch by Ashwin
     Ramaswami

   - bpo-37937(13): Mention ‘frame.f_trace’ in *note sys.settrace():
     f00. docs.

   - bpo-37878(14): Make *note PyThreadState_DeleteCurrent(): 10de.
     Internal.

   - bpo-37759(15): Beginning edits to Whatsnew 3.8

   - bpo-37726(16): Stop recommending getopt in the tutorial for command
     line argument parsing and promote argparse.

   - bpo-32910(17): Remove implementation-specific behaviour of how
     venv’s Deactivate works.

   - bpo-37256(18): Fix wording of arguments for ‘Request’ in *note
     urllib.request: 129.

   - bpo-37284(19): Add a brief note to indicate that any new
     ‘sys.implementation’ required attributes must go through the PEP
     process.

   - bpo-30088(20): Documented that *note mailbox.Maildir: d70.
     constructor doesn’t attempt to verify the maildir folder layout
     correctness.  Patch by Sviatoslav Sydorenko.

   - bpo-37521(21): Fix *note importlib: 9a. examples to insert any
     newly created modules via importlib.util.module_from_spec()
     immediately into sys.modules instead of after calling
     loader.exec_module().

     Thanks to Benjamin Mintz for finding the bug.

   - bpo-37456(22): Slash (‘/’) is now part of syntax.

   - bpo-37487(23): Fix PyList_GetItem index description to include 0.

   - bpo-37149(24): Replace the dead link to the Tkinter 8.5 reference
     by John Shipman, New Mexico Tech, with a link to the archive.org
     copy.

   - bpo-37478(25): Added possible exceptions to the description of
     os.chdir().

   - bpo-34903(26): Documented that in *note
     datetime.datetime.strptime(): f91, the leading zero in some
     two-digit formats is optional.  Patch by Mike Gleen.

   - bpo-36260(27): Add decompression pitfalls to zipfile module
     documentation.

   - bpo-37004(28): In the documentation for difflib, a note was added
     explicitly warning that the results of SequenceMatcher’s ratio
     method may depend on the order of the input strings.

   - bpo-36960(29): Restructured the *note datetime: 30. docs in the
     interest of making them more user-friendly and improving
     readability.  Patch by Brad Solomon.

   - bpo-36487(30): Make C-API docs clear about what the “main”
     interpreter is.

   - bpo-23460(31): The documentation for decimal string formatting
     using the ‘:g’ specifier has been updated to reflect the correct
     exponential notation cutoff point.  Original patch contributed by
     Tuomas Suutari.

   - bpo-35803(32): Document and test that ‘tempfile’ functions may
     accept a *note path-like object: 472. for the ‘dir’ argument.
     Patch by Anthony Sottile.

   - bpo-33944(33): Added a note about the intended use of code in .pth
     files.

   - bpo-34293(34): Fix the Doc/Makefile regarding PAPER environment
     variable and PDF builds

   - bpo-25237(35): Add documentation for tkinter modules

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21767

   (2) https://bugs.python.org/issue38816

   (3) https://bugs.python.org/issue38351

   (4) https://bugs.python.org/issue38778

   (5) https://bugs.python.org/issue38592

   (6) https://bugs.python.org/issue38294

   (7) https://bugs.python.org/issue38053

   (8) https://bugs.python.org/issue26868

   (9) https://bugs.python.org/issue36797

   (10) https://bugs.python.org/issue37977

   (11) https://bugs.python.org/issue37979

   (12) https://bugs.python.org/issue12707

   (13) https://bugs.python.org/issue37937

   (14) https://bugs.python.org/issue37878

   (15) https://bugs.python.org/issue37759

   (16) https://bugs.python.org/issue37726

   (17) https://bugs.python.org/issue32910

   (18) https://bugs.python.org/issue37256

   (19) https://bugs.python.org/issue37284

   (20) https://bugs.python.org/issue30088

   (21) https://bugs.python.org/issue37521

   (22) https://bugs.python.org/issue37456

   (23) https://bugs.python.org/issue37487

   (24) https://bugs.python.org/issue37149

   (25) https://bugs.python.org/issue37478

   (26) https://bugs.python.org/issue34903

   (27) https://bugs.python.org/issue36260

   (28) https://bugs.python.org/issue37004

   (29) https://bugs.python.org/issue36960

   (30) https://bugs.python.org/issue36487

   (31) https://bugs.python.org/issue23460

   (32) https://bugs.python.org/issue35803

   (33) https://bugs.python.org/issue33944

   (34) https://bugs.python.org/issue34293

   (35) https://bugs.python.org/issue25237


File: python.info,  Node: Tests<19>,  Next: Build<19>,  Prev: Documentation<20>,  Up: Python 3 9 0 alpha 1

1.19.26.5 Tests
...............

   - bpo-38614(1): Fix test_communicate() of
     test_asyncio.test_subprocess: use ‘support.LONG_TIMEOUT’ (5
     minutes), instead of just 1 minute.

   - bpo-38614(2): Add timeout constants to *note test.support: 106.:
     *note LOOPBACK_TIMEOUT: 10b1, *note INTERNET_TIMEOUT: 10b2, *note
     SHORT_TIMEOUT: f94. and *note LONG_TIMEOUT: 10b3.

   - bpo-38502(3): test.regrtest now uses process groups in the
     multiprocessing mode (-jN command line option) if process groups
     are available: if *note os.setsid(): 10e0. and *note os.killpg():
     10e1. functions are available.

   - bpo-35998(4): Fix a race condition in
     test_asyncio.test_start_tls_server_1().  Previously, there was a
     race condition between the test main() function which replaces the
     protocol and the test ServerProto protocol which sends ANSWER once
     it gets HELLO. Now, only the test main() function is responsible to
     send data, ServerProto no longer sends data.

   - bpo-38470(5): Fix ‘test_compileall.test_compile_dir_maxlevels()’ on
     Windows without long path support: only create 3 subdirectories
     instead of between 20 and 100 subdirectories.

   - bpo-37531(6): On timeout, regrtest no longer attempts to call
     ‘popen.communicate()’ again: it can hang until all child processes
     using stdout and stderr pipes completes.  Kill the worker process
     and ignores its output.  Change also the faulthandler timeout of
     the main process from 1 minute to 5 minutes, for Python slowest
     buildbots.

   - bpo-38239(7): Fix test_gdb for Link Time Optimization (LTO) builds.

   - bpo-38275(8): test_ssl now handles disabled TLS/SSL versions
     better.  OpenSSL’s crypto policy and run-time settings are
     recognized and tests for disabled versions are skipped.  Tests also
     accept more TLS minimum_versions for platforms that override
     OpenSSL’s default with strict settings.

   - bpo-38271(9): The private keys for test_ssl were encrypted with
     3DES in traditional PKCS#5 format.  3DES and the digest algorithm
     of PKCS#5 are blocked by some strict crypto policies.  Use PKCS#8
     format with AES256 encryption instead.

   - bpo-38270(10): test.support now has a helper function to check for
     availability of a hash digest function.  Several tests are
     refactored avoid MD5 and use SHA256 instead.  Other tests are
     marked to use MD5 and skipped when MD5 is disabled.

   - bpo-37123(11): Multiprocessing test test_mymanager() now also
     expects -SIGTERM, not only exitcode 0.
     BaseManager._finalize_manager() sends SIGTERM to the manager
     process if it takes longer than 1 second to stop, which happens on
     slow buildbots.

   - bpo-38212(12): Multiprocessing tests: increase
     test_queue_feeder_donot_stop_onexc() timeout from 1 to 60 seconds.

   - bpo-38117(13): Test with OpenSSL 1.1.1d

   - bpo-38018(14): Increase code coverage for
     multiprocessing.shared_memory.

   - bpo-37805(15): Add tests for json.dump(…, skipkeys=True).  Patch by
     Dong-hee Na.

   - bpo-37531(16): Enhance regrtest multiprocess timeout: write a
     message when killing a worker process, catch popen.kill() and
     popen.wait() exceptions, put a timeout on the second call to
     popen.communicate().

   - bpo-37876(17): Add tests for ROT-13 codec.

   - bpo-36833(18): Added tests for PyDateTime_xxx_GET_xxx() macros of
     the C API of the *note datetime: 30. module.  Patch by Joannah
     Nanjekye.

   - bpo-37558(19): Fix
     test_shared_memory_cleaned_after_process_termination name handling

   - bpo-37526(20): Add *note test.support.catch_threading_exception():
     10e2.: context manager catching *note threading.Thread: 21a.
     exception using *note threading.excepthook(): 35e.

   - bpo-37421(21): test_concurrent_futures now explicitly stops the
     ForkServer instance if it’s running.

   - bpo-37421(22): multiprocessing tests now stop the ForkServer
     instance if it’s running: close the “alive” file descriptor to ask
     the server to stop and then remove its UNIX address.

   - bpo-37421(23): test_distutils.test_build_ext() is now able to
     remove the temporary directory on Windows: don’t import the newly
     built C extension (“xx”) in the current process, but test it in a
     separated process.

   - bpo-37421(24): test_concurrent_futures now cleans up
     multiprocessing to remove immediately temporary directories created
     by multiprocessing.util.get_temp_dir().

   - bpo-37421(25): test_winconsoleio doesn’t leak a temporary file
     anymore: use tempfile.TemporaryFile() to remove it when the test
     completes.

   - bpo-37421(26): multiprocessing tests now explicitly call
     ‘_run_finalizers()’ to immediately remove temporary directories
     created by tests.

   - bpo-37421(27): urllib.request tests now call *note urlcleanup():
     10e3. to remove temporary files created by ‘urlretrieve()’ tests
     and to clear the ‘_opener’ global variable set by ‘urlopen()’ and
     functions calling indirectly ‘urlopen()’.

   - bpo-37472(28): Remove ‘Lib/test/outstanding_bugs.py’.

   - bpo-37199(29): Fix test failures when IPv6 is unavailable or
     disabled.

   - bpo-19696(30): Replace deprecated method “random.choose” with
     “random.choice” in “test_pkg_import.py”.

   - bpo-37335(31): Remove no longer necessary code from c locale
     coercion tests

   - bpo-37421(32): Fix test_shutil to no longer leak temporary files.

   - bpo-37411(33): Fix test_wsgiref.testEnviron() to no longer depend
     on the environment variables (don’t fail if “X” variable is set).

   - bpo-37400(34): Fix test_os.test_chown(): use os.getgroups() rather
     than grp.getgrall() to get groups.  Rename also the test to
     test_chown_gid().

   - bpo-37359(35): Add –cleanup option to python3 -m test to remove
     ‘test_python_*’ directories of previous failed jobs.  Add “make
     cleantest” to run ‘python3 -m test --cleanup’.

   - bpo-37362(36): test_gdb no longer fails if it gets an “unexpected”
     message on stderr: it now ignores stderr.  The purpose of test_gdb
     is to test that python-gdb.py commands work as expected, not to
     test gdb.

   - bpo-35998(37): Avoid TimeoutError in test_asyncio:
     test_start_tls_server_1()

   - bpo-37278(38): Fix test_asyncio ProactorLoopCtrlC: join the thread
     to prevent leaking a running thread and leaking a reference.

   - bpo-37261(39): Fix *note test.support.catch_unraisable_exception():
     10e4.: its __exit__() method now ignores unraisable exception
     raised when clearing its ‘unraisable’ attribute.

   - bpo-37069(40): regrtest now uses *note sys.unraisablehook(): 35a.
     to mark a test as “environment altered” (ENV_CHANGED) if it emits
     an “unraisable exception”.  Moreover, regrtest logs a warning in
     this case.

     Use ‘python3 -m test --fail-env-changed’ to catch unraisable
     exceptions in tests.

   - bpo-37252(41): Fix assertions in ‘test_close’ and
     ‘test_events_mask_overflow’ devpoll tests.

   - bpo-37169(42): Rewrite ‘_PyObject_IsFreed()’ unit tests.

   - bpo-37153(43): ‘test_venv.test_multiprocessing()’ now explicitly
     calls ‘pool.terminate()’ to wait until the pool completes.

   - bpo-34001(44): Make test_ssl pass with LibreSSL. LibreSSL handles
     minimum and maximum TLS version differently than OpenSSL.

   - bpo-36919(45): Make ‘test_source_encoding.test_issue2301’
     implementation independent.  The test will work now for both
     CPython and IronPython.

   - bpo-30202(46): Update ‘test.test_importlib.test_abc’ to test
     ‘find_spec()’.

   - bpo-28009(47): Modify the test_uuid logic to test when a program is
     available AND can be used to obtain a MACADDR as basis for an UUID.
     Patch by M. Felt

   - bpo-34596(48): Fallback to a default reason when *note
     unittest.skip(): 10e5. is uncalled.  Patch by Naitree Zhu.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38614

   (2) https://bugs.python.org/issue38614

   (3) https://bugs.python.org/issue38502

   (4) https://bugs.python.org/issue35998

   (5) https://bugs.python.org/issue38470

   (6) https://bugs.python.org/issue37531

   (7) https://bugs.python.org/issue38239

   (8) https://bugs.python.org/issue38275

   (9) https://bugs.python.org/issue38271

   (10) https://bugs.python.org/issue38270

   (11) https://bugs.python.org/issue37123

   (12) https://bugs.python.org/issue38212

   (13) https://bugs.python.org/issue38117

   (14) https://bugs.python.org/issue38018

   (15) https://bugs.python.org/issue37805

   (16) https://bugs.python.org/issue37531

   (17) https://bugs.python.org/issue37876

   (18) https://bugs.python.org/issue36833

   (19) https://bugs.python.org/issue37558

   (20) https://bugs.python.org/issue37526

   (21) https://bugs.python.org/issue37421

   (22) https://bugs.python.org/issue37421

   (23) https://bugs.python.org/issue37421

   (24) https://bugs.python.org/issue37421

   (25) https://bugs.python.org/issue37421

   (26) https://bugs.python.org/issue37421

   (27) https://bugs.python.org/issue37421

   (28) https://bugs.python.org/issue37472

   (29) https://bugs.python.org/issue37199

   (30) https://bugs.python.org/issue19696

   (31) https://bugs.python.org/issue37335

   (32) https://bugs.python.org/issue37421

   (33) https://bugs.python.org/issue37411

   (34) https://bugs.python.org/issue37400

   (35) https://bugs.python.org/issue37359

   (36) https://bugs.python.org/issue37362

   (37) https://bugs.python.org/issue35998

   (38) https://bugs.python.org/issue37278

   (39) https://bugs.python.org/issue37261

   (40) https://bugs.python.org/issue37069

   (41) https://bugs.python.org/issue37252

   (42) https://bugs.python.org/issue37169

   (43) https://bugs.python.org/issue37153

   (44) https://bugs.python.org/issue34001

   (45) https://bugs.python.org/issue36919

   (46) https://bugs.python.org/issue30202

   (47) https://bugs.python.org/issue28009

   (48) https://bugs.python.org/issue34596


File: python.info,  Node: Build<19>,  Next: Windows<19>,  Prev: Tests<19>,  Up: Python 3 9 0 alpha 1

1.19.26.6 Build
...............

   - bpo-38809(1): On Windows, build scripts will now recognize and use
     python.exe from an active virtual env.

   - bpo-38684(2): Fix _hashlib build when Blake2 is disabled, but
     OpenSSL supports it.

   - bpo-38468(3): Misc/python-config.in now uses ‘getvar()’ for all
     still existing *note sysconfig.get_config_var(): a45. calls.  Patch
     by Joannah Nanjekye.

   - bpo-37415(4): Fix stdatomic.h header check for ICC compiler: the
     ICC implementation lacks atomic_uintptr_t type which is needed by
     Python.

   - bpo-38301(5): In Solaris family, we must be sure to use
     ‘-D_REENTRANT’.  Patch by Jesús Cea Avión.

   - bpo-36002(6): Locate ‘llvm-profdata’ and ‘llvm-ar’ binaries using
     ‘AC_PATH_TOOL’ rather than ‘AC_PATH_TARGET_TOOL’.

   - bpo-37936(7): The ‘.gitignore’ file systematically keeps “rooted”,
     with a non-trailing slash, all the rules that are meant to apply to
     files in a specific place in the repo.  Previously, when the
     intended file to ignore happened to be at the root of the repo,
     we’d most often accidentally also ignore files and directories with
     the same name anywhere in the tree.

   - bpo-37760(8): The ‘Tools/unicode/makeunicodedata.py’ script, which
     is used for converting information from the Unicode Character
     Database into generated code and data used by the methods of *note
     str: 205. and by the *note unicodedata: 123. module, now handles
     each character’s data as a ‘dataclass’ with named attributes,
     rather than a length-18 list of different fields.

   - bpo-37936(9): The ‘.gitignore’ file no longer applies to any files
     that are in fact tracked in the Git repository.  Patch by Greg
     Price.

   - bpo-37725(10): Change “clean” makefile target to also clean the
     program guided optimization (PGO) data.  Previously you would have
     to use “make clean” and “make profile-removal”, or “make clobber”.

   - bpo-37707(11): Mark some individual tests to skip when –pgo is
     used.  The tests marked increase the PGO task time significantly
     and likely don’t help improve optimization of the final executable.

   - bpo-36044(12): Reduce the number of unit tests run for the PGO
     generation task.  This speeds up the task by a factor of about 15x.
     Running the full unit test suite is slow.  This change may result
     in a slightly less optimized build since not as many code branches
     will be executed.  If you are willing to wait for the much slower
     build, the old behavior can be restored using ‘./configure [..]
     PROFILE_TASK=”-m test –pgo-extended”’.  We make no guarantees as to
     which PGO task set produces a faster build.  Users who care should
     run their own relevant benchmarks as results can depend on the
     environment, workload, and compiler tool chain.

   - bpo-37468(13): ‘make install’ no longer installs ‘wininst-*.exe’
     files used by distutils bdist_wininst: bdist_wininst only works on
     Windows.

   - bpo-37189(14): Many ‘PyRun_XXX()’ functions like *note
     PyRun_String(): 10e7. were no longer exported in ‘libpython38.dll’
     by mistake.  Export them again to fix the ABI compatibility.

   - bpo-25361(15): Enables use of SSE2 instructions in Windows 32-bit
     build.

   - bpo-36210(16): Update optional extension module detection for AIX.
     ossaudiodev and spwd are not applicable for AIX, and are no longer
     reported as missing.  3rd-party packaging of ncurses (with ASIS
     support) conflicts with officially supported AIX curses library, so
     configure AIX to use libcurses.a.  However, skip trying to build
     _curses_panel.

     patch by M Felt

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38809

   (2) https://bugs.python.org/issue38684

   (3) https://bugs.python.org/issue38468

   (4) https://bugs.python.org/issue37415

   (5) https://bugs.python.org/issue38301

   (6) https://bugs.python.org/issue36002

   (7) https://bugs.python.org/issue37936

   (8) https://bugs.python.org/issue37760

   (9) https://bugs.python.org/issue37936

   (10) https://bugs.python.org/issue37725

   (11) https://bugs.python.org/issue37707

   (12) https://bugs.python.org/issue36044

   (13) https://bugs.python.org/issue37468

   (14) https://bugs.python.org/issue37189

   (15) https://bugs.python.org/issue25361

   (16) https://bugs.python.org/issue36210


File: python.info,  Node: Windows<19>,  Next: macOS<17>,  Prev: Build<19>,  Up: Python 3 9 0 alpha 1

1.19.26.7 Windows
.................

   - bpo-38589(1): Fixes HTML Help shortcut when Windows is not
     installed to C drive

   - bpo-38453(2): Ensure ntpath.realpath() correctly resolves relative
     paths.

   - bpo-38519(3): Restores the internal C headers that were missing
     from the nuget.org and Microsoft Store packages.

   - bpo-38492(4): Remove ‘pythonw.exe’ dependency on the Microsoft C++
     runtime.

   - bpo-38344(5): Fix error message in activate.bat

   - bpo-38359(6): Ensures ‘pyw.exe’ launcher reads correct registry
     key.

   - bpo-38355(7): Fixes ‘ntpath.realpath’ failing on ‘sys.executable’.

   - bpo-38117(8): Update bundled OpenSSL to 1.1.1d

   - bpo-38092(9): Reduce overhead when using multiprocessing in a
     Windows virtual environment.

   - bpo-38133(10): Allow py.exe launcher to locate installations from
     the Microsoft Store and improve display of active virtual
     environments.

   - bpo-38114(11): The ‘pip.ini’ is no longer included in the Nuget
     package.

   - bpo-32592(12): Set Windows 8 as the minimum required version for
     API support

   - bpo-36634(13): *note os.cpu_count(): 96a. now returns active
     processors rather than maximum processors.

   - bpo-36634(14): venv activate.bat now works when the existing
     variables contain double quote characters.

   - bpo-38081(15): Prevent error calling *note os.path.realpath(): 32d.
     on ‘'NUL'’.

   - bpo-38087(16): Fix case sensitivity in test_pathlib and
     test_ntpath.

   - bpo-38088(17): Fixes distutils not finding vcruntime140.dll with
     only the v142 toolset installed.

   - bpo-37283(18): Ensure command-line and unattend.xml setting
     override previously detected states in Windows installer.

   - bpo-38030(19): Fixes *note os.stat(): 321. failing for block
     devices on Windows

   - bpo-38020(20): Fixes potential crash when calling *note
     os.readlink(): 1d1. (or indirectly through *note realpath(): 32d.)
     on a file that is not a supported link.

   - bpo-37705(21): Improve the implementation of ‘winerror_to_errno()’.

   - bpo-37549(22): *note os.dup(): 10e9. no longer fails for standard
     streams on Windows 7.

   - bpo-1311(23): The ‘nul’ file on Windows now returns True from *note
     exists(): 325. and a valid result from *note os.stat(): 321. with
     ‘S_IFCHR’ set.

   - bpo-9949(24): Enable support for following symlinks in
     ‘os.realpath()’.

   - bpo-37834(25): Treat all name surrogate reparse points on Windows
     in *note os.lstat(): 322. and other reparse points as regular files
     in *note os.stat(): 321.

   - bpo-36266(26): Add the module name in the formatted error message
     when DLL load fail happens during module import in
     ‘_PyImport_FindSharedFuncptrWindows()’.  Patch by Srinivas
     Nyayapati.

   - bpo-25172(27): Trying to import the *note crypt: 28. module on
     Windows will result in an *note ImportError: 16c. with a message
     explaining that the module isn’t supported on Windows.  On other
     platforms, if the underlying ‘_crypt’ module is not available, the
     ImportError will include a message explaining the problem.

   - bpo-37778(28): Fixes the icons used for file associations to the
     Microsoft Store package.

   - bpo-37734(29): Fix use of registry values to launch Python from
     Microsoft Store app.

   - bpo-37702(30): Fix memory leak on Windows in creating an SSLContext
     object or running urllib.request.urlopen(’‘https://’…’).

   - bpo-37672(31): Switch Windows Store package’s pip to use bundled
     ‘pip.ini’ instead of ‘PIP_USER’ variable.

   - bpo-10945(32): Officially drop support for creating bdist_wininst
     installers on non-Windows systems.

   - bpo-37445(33): Include the ‘FORMAT_MESSAGE_IGNORE_INSERTS’ flag in
     ‘FormatMessageW()’ calls.

   - bpo-37369(34): Fixes path for *note sys.executable: 39d. when
     running from the Microsoft Store.

   - bpo-37380(35): Don’t collect unfinished processes with
     ‘subprocess._active’ on Windows to cleanup later.  Patch by Ruslan
     Kuprieiev.

   - bpo-37351(36): Removes libpython38.a from standard Windows
     distribution.

   - bpo-35360(37): Update Windows builds to use SQLite 3.28.0.

   - bpo-37267(38): On Windows, *note os.dup(): 10e9. no longer creates
     an inheritable fd when handling a character file.

   - bpo-36779(39): Ensure ‘time.tzname’ is correct on Windows when the
     active code page is set to CP_UTF7 or CP_UTF8.

   - bpo-32587(40): Make *note winreg.REG_MULTI_SZ: 10ea. support
     zero-length strings.

   - bpo-28269(41): Replace use of ‘strcasecmp()’ for the system
     function ‘_stricmp()’.  Patch by Minmin Gong.

   - bpo-36590(42): Add native Bluetooth RFCOMM support to socket
     module.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38589

   (2) https://bugs.python.org/issue38453

   (3) https://bugs.python.org/issue38519

   (4) https://bugs.python.org/issue38492

   (5) https://bugs.python.org/issue38344

   (6) https://bugs.python.org/issue38359

   (7) https://bugs.python.org/issue38355

   (8) https://bugs.python.org/issue38117

   (9) https://bugs.python.org/issue38092

   (10) https://bugs.python.org/issue38133

   (11) https://bugs.python.org/issue38114

   (12) https://bugs.python.org/issue32592

   (13) https://bugs.python.org/issue36634

   (14) https://bugs.python.org/issue36634

   (15) https://bugs.python.org/issue38081

   (16) https://bugs.python.org/issue38087

   (17) https://bugs.python.org/issue38088

   (18) https://bugs.python.org/issue37283

   (19) https://bugs.python.org/issue38030

   (20) https://bugs.python.org/issue38020

   (21) https://bugs.python.org/issue37705

   (22) https://bugs.python.org/issue37549

   (23) https://bugs.python.org/issue1311

   (24) https://bugs.python.org/issue9949

   (25) https://bugs.python.org/issue37834

   (26) https://bugs.python.org/issue36266

   (27) https://bugs.python.org/issue25172

   (28) https://bugs.python.org/issue37778

   (29) https://bugs.python.org/issue37734

   (30) https://bugs.python.org/issue37702

   (31) https://bugs.python.org/issue37672

   (32) https://bugs.python.org/issue10945

   (33) https://bugs.python.org/issue37445

   (34) https://bugs.python.org/issue37369

   (35) https://bugs.python.org/issue37380

   (36) https://bugs.python.org/issue37351

   (37) https://bugs.python.org/issue35360

   (38) https://bugs.python.org/issue37267

   (39) https://bugs.python.org/issue36779

   (40) https://bugs.python.org/issue32587

   (41) https://bugs.python.org/issue28269

   (42) https://bugs.python.org/issue36590


File: python.info,  Node: macOS<17>,  Next: IDLE<19>,  Prev: Windows<19>,  Up: Python 3 9 0 alpha 1

1.19.26.8 macOS
...............

   - bpo-38117(1): Updated OpenSSL to 1.1.1d in macOS installer.

   - bpo-38089(2): Move Azure Pipelines to latest VM versions and make
     macOS tests optional

   - bpo-18049(3): Increase the default stack size of threads from 5MB
     to 16MB on macOS, to match the stack size of the main thread.  This
     avoids crashes on deep recursion in threads.

   - bpo-34602(4): Avoid test suite failures on macOS by no longer
     calling resource.setrlimit to increase the process stack size limit
     at runtime.  The runtime change is no longer needed since the
     interpreter is being built with a larger default stack size.

   - bpo-35360(5): Update macOS installer to use SQLite 3.28.0.

   - bpo-34631(6): Updated OpenSSL to 1.1.1c in macOS installer.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38117

   (2) https://bugs.python.org/issue38089

   (3) https://bugs.python.org/issue18049

   (4) https://bugs.python.org/issue34602

   (5) https://bugs.python.org/issue35360

   (6) https://bugs.python.org/issue34631


File: python.info,  Node: IDLE<19>,  Next: Tools/Demos<7>,  Prev: macOS<17>,  Up: Python 3 9 0 alpha 1

1.19.26.9 IDLE
..............

   - bpo-26353(1): Stop adding newline when saving an IDLE shell window.

   - bpo-4630(2): Add an option to toggle IDLE’s cursor blink for shell,
     editor, and output windows.  See Settings, General, Window
     Preferences, Cursor Blink.  Patch by Zackery Spytz.

   - bpo-38598(3): Do not try to compile IDLE shell or output windows

   - bpo-36698(4): IDLE no longer fails when write non-encodable
     characters to stderr.  It now escapes them with a backslash, as the
     regular Python interpreter.  Added the ‘errors’ field to the
     standard streams.

   - bpo-35379(5): When exiting IDLE, catch any AttributeError.  One
     happens when EditorWindow.close is called twice.  Printing a
     traceback, when IDLE is run from a terminal, is useless and
     annoying.

   - bpo-38183(6): To avoid problems, test_idle ignores the user config
     directory.  It no longer tries to create or access .idlerc or any
     files within.  Users must run IDLE to discover problems with saving
     settings.

   - bpo-38077(7): IDLE no longer adds ‘argv’ to the user namespace when
     initializing it.  This bug only affected 3.7.4 and 3.8.0b2 to
     3.8.0b4.

   - bpo-38041(8): Shell restart lines now fill the window width, always
     start with ‘=’, and avoid wrapping unnecessarily.  The line will
     still wrap if the included file name is long relative to the width.

   - bpo-35771(9): To avoid occasional spurious test_idle failures on
     slower machines, increase the ‘hover_delay’ in test_tooltip.

   - bpo-37824(10): Properly handle user input warnings in IDLE shell.
     Cease turning SyntaxWarnings into SyntaxErrors.

   - bpo-37929(11): IDLE Settings dialog now closes properly when there
     is no shell window.

   - bpo-37902(12): Add mousewheel scrolling for IDLE module, path, and
     stack browsers.  Patch by George Zhang.

   - bpo-37849(13): Fixed completions list appearing too high or low
     when shown above the current line.

   - bpo-36419(14): Refactor IDLE autocomplete and improve testing.

   - bpo-37748(15): Reorder the Run menu.  Put the most common choice,
     Run Module, at the top.

   - bpo-37692(16): Improve highlight config sample with example shell
     interaction and better labels for shell elements.

   - bpo-37628(17): Settings dialog no longer expands with font size.

   - bpo-37627(18): Initialize the Customize Run dialog with the command
     line arguments most recently entered before.  The user can
     optionally edit before submitting them.

   - bpo-33610(19): Fix code context not showing the correct context
     when first toggled on.

   - bpo-37530(20): Optimize code context to reduce unneeded background
     activity.  Font and highlight changes now occur along with text
     changes instead of after a random delay.

   - bpo-27452(21): Cleanup ‘config.py’ by inlining ‘RemoveFile’ and
     simplifying the handling of ‘file’ in ‘CreateConfigHandlers’.

   - bpo-37325(22): Fix tab focus traversal order for help source and
     custom run dialogs.

   - bpo-37321(23): Both subprocess connection error messages now refer
     to the ‘Startup failure’ section of the IDLE doc.

   - bpo-17535(24): Add optional line numbers for IDLE editor windows.
     Windows open without line numbers unless set otherwise in the
     General tab of the configuration dialog.

   - bpo-26806(25): To compensate for stack frames added by IDLE and
     avoid possible problems with low recursion limits, add 30 to limits
     in the user code execution process.  Subtract 30 when reporting
     recursion limits to make this addition mostly transparent.

   - bpo-37177(26): Properly ‘attach’ search dialogs to their main
     window so that they behave like other dialogs and do not get hidden
     behind their main window.

   - bpo-37039(27): Adjust “Zoom Height” to individual screens by
     momentarily maximizing the window on first use with a particular
     screen.  Changing screen settings may invalidate the saved height.
     While a window is maximized, “Zoom Height” has no effect.

   - bpo-35763(28): Make calltip reminder about ‘/’ meaning
     positional-only less obtrusive by only adding it when there is room
     on the first line.

   - bpo-5680(29): Add ‘Run… Customized’ to the Run menu to run a module
     with customized settings.  Any ‘command line arguments’ entered are
     added to sys.argv.  One can suppress the normal Shell main module
     restart.

   - bpo-36390(30): Gather Format menu functions into format.py.
     Combine paragraph.py, rstrip.py, and format methods from editor.py.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26353

   (2) https://bugs.python.org/issue4630

   (3) https://bugs.python.org/issue38598

   (4) https://bugs.python.org/issue36698

   (5) https://bugs.python.org/issue35379

   (6) https://bugs.python.org/issue38183

   (7) https://bugs.python.org/issue38077

   (8) https://bugs.python.org/issue38041

   (9) https://bugs.python.org/issue35771

   (10) https://bugs.python.org/issue37824

   (11) https://bugs.python.org/issue37929

   (12) https://bugs.python.org/issue37902

   (13) https://bugs.python.org/issue37849

   (14) https://bugs.python.org/issue36419

   (15) https://bugs.python.org/issue37748

   (16) https://bugs.python.org/issue37692

   (17) https://bugs.python.org/issue37628

   (18) https://bugs.python.org/issue37627

   (19) https://bugs.python.org/issue33610

   (20) https://bugs.python.org/issue37530

   (21) https://bugs.python.org/issue27452

   (22) https://bugs.python.org/issue37325

   (23) https://bugs.python.org/issue37321

   (24) https://bugs.python.org/issue17535

   (25) https://bugs.python.org/issue26806

   (26) https://bugs.python.org/issue37177

   (27) https://bugs.python.org/issue37039

   (28) https://bugs.python.org/issue35763

   (29) https://bugs.python.org/issue5680

   (30) https://bugs.python.org/issue36390


File: python.info,  Node: Tools/Demos<7>,  Next: C API<16>,  Prev: IDLE<19>,  Up: Python 3 9 0 alpha 1

1.19.26.10 Tools/Demos
......................

   - bpo-38118(1): Update Valgrind suppression file to ignore a false
     alarm in *note PyUnicode_Decode(): 10ee. when using GCC builtin
     strcmp().

   - bpo-38347(2): pathfix.py: Assume all files that end on ‘.py’ are
     Python scripts when working recursively.

   - bpo-37803(3): pdb’s ‘--help’ and ‘--version’ long options now work.

   - bpo-37942(4): Improve ArgumentClinic converter for floats.

   - bpo-37704(5): Remove ‘Tools/scripts/h2py.py’: use cffi to access a
     C API in Python.

   - bpo-37675(6): 2to3 now works when run from a zipped standard
     library.

   - bpo-37034(7): Argument Clinic now uses the argument name on errors
     with keyword-only argument instead of their position.  Patch
     contributed by Rémi Lapeyre.

   - bpo-37064(8): Add option -k to pathscript.py script: preserve
     shebang flags.  Add option -a to pathscript.py script: add flags.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue38118

   (2) https://bugs.python.org/issue38347

   (3) https://bugs.python.org/issue37803

   (4) https://bugs.python.org/issue37942

   (5) https://bugs.python.org/issue37704

   (6) https://bugs.python.org/issue37675

   (7) https://bugs.python.org/issue37034

   (8) https://bugs.python.org/issue37064


File: python.info,  Node: C API<16>,  Prev: Tools/Demos<7>,  Up: Python 3 9 0 alpha 1

1.19.26.11 C API
................

   - bpo-37633(1): Re-export some function compatibility wrappers for
     macros in ‘pythonrun.h’.

   - bpo-38644(2): Provide *note Py_EnterRecursiveCall(): 251. and *note
     Py_LeaveRecursiveCall(): 252. as regular functions for the limited
     API. Previously, there were defined as macros, but these macros
     didn’t work with the limited API which cannot access
     ‘PyThreadState.recursion_depth’ field.  Remove
     ‘_Py_CheckRecursionLimit’ from the stable ABI.

   - bpo-38650(3): The global variable *note
     PyStructSequence_UnnamedField: 262. is now a constant and refers to
     a constant string.

   - bpo-38540(4): Fixed possible leak in *note PyArg_Parse(): 10f0. and
     similar functions for format units ‘"es#"’ and ‘"et#"’ when the
     macro ‘PY_SSIZE_T_CLEAN’ is not defined.

   - bpo-38395(5): Fix a crash in *note weakref.proxy: 37a. objects due
     to incorrect lifetime management when calling some associated
     methods that may delete the last reference to object being
     referenced by the proxy.  Patch by Pablo Galindo.

   - bpo-36389(6): The ‘_PyObject_CheckConsistency()’ function is now
     also available in release mode.  For example, it can be used to
     debug a crash in the ‘visit_decref()’ function of the GC.

   - bpo-38266(7): Revert the removal of PyThreadState_DeleteCurrent()
     with documentation.

   - bpo-38303(8): Update audioop extension module to use the stable ABI
     (PEP-384).  Patch by Tyler Kieft.

   - bpo-38234(9): *note Py_SetPath(): 39c. now sets *note
     sys.executable: 39d. to the program full path (*note
     Py_GetProgramFullPath(): 39e.) rather than to the program name
     (*note Py_GetProgramName(): 39f.).

   - bpo-38234(10): Python ignored arguments passed to *note
     Py_SetPath(): 39c, *note Py_SetPythonHome(): 10f1. and *note
     Py_SetProgramName(): 10f2.: fix Python initialization to use
     specified arguments.

   - bpo-38205(11): The *note Py_UNREACHABLE(): 527. macro now calls
     *note Py_FatalError(): 266.

   - bpo-38140(12): Make dict and weakref offsets opaque for C heap
     types by passing the offsets through PyMemberDef

   - bpo-15088(13): The C function ‘PyGen_NeedsFinalizing’ has been
     removed.  It was not documented, tested or used anywhere within
     CPython after the implementation of PEP 442(14).  Patch by Joannah
     Nanjekye.  (Patch by Joannah Nanjekye)

   - bpo-36763(15): Options added by ‘PySys_AddXOption()’ are now
     handled the same way than ‘PyConfig.xoptions’ and command line ‘-X’
     options.

   - bpo-37926(16): Fix a crash in ‘PySys_SetArgvEx(0, NULL, 0)’.

   - bpo-37879(17): Fix subtype_dealloc to suppress the type decref when
     the base type is a C heap type

   - bpo-37645(18): Add ‘_PyObject_FunctionStr()’ to get a user-friendly
     string representation of a function-like object.  Patch by Jeroen
     Demeyer.

   - bpo-29548(19): The functions ‘PyEval_CallObject’,
     ‘PyEval_CallFunction’, ‘PyEval_CallMethod’ and
     ‘PyEval_CallObjectWithKeywords’ are deprecated.  Use *note
     PyObject_Call(): 23c. and its variants instead.

   - bpo-37151(20): ‘PyCFunction_Call’ is now a deprecated alias of
     *note PyObject_Call(): 23c.

   - bpo-37540(21): The vectorcall protocol now requires that the caller
     passes only strings as keyword names.

   - bpo-37207(22): The vectorcall protocol is now enabled for ‘type’
     objects: set ‘tp_vectorcall’ to a vectorcall function to be used
     instead of ‘tp_new’ and ‘tp_init’ when calling the class itself.

   - bpo-21120(23): Exclude Python-ast.h, ast.h and asdl.h from the
     limited API.

   - bpo-37483(24): Add new function ‘_PyObject_CallOneArg’ for calling
     an object with one positional argument.

   - bpo-36763(25): Add ‘PyConfig_SetWideStringList()’ function.

   - bpo-37337(26): Add fast functions for calling methods:
     ‘_PyObject_VectorcallMethod()’, ‘_PyObject_CallMethodNoArgs()’ and
     ‘_PyObject_CallMethodOneArg()’.

   - bpo-28805(27): The *note METH_FASTCALL: 10f3. calling convention
     has been documented.

   - bpo-37221(28): The new function *note PyCode_NewWithPosOnlyArgs():
     39a. allows to create code objects like *note PyCode_New(): 39b,
     but with an extra `posonlyargcount' parameter for indicating the
     number of positonal-only arguments.

   - bpo-37215(29): Fix dtrace issue introduce by bpo-36842(30)

   - bpo-37194(31): Add a new public *note PyObject_CallNoArgs(): 250.
     function to the C API: call a callable Python object without any
     arguments.  It is the most efficient way to call a callback without
     any argument.  On x86-64, for example,
     ‘PyObject_CallFunctionObjArgs(func, NULL)’ allocates 960 bytes on
     the stack per call, whereas ‘PyObject_CallNoArgs(func)’ only
     allocates 624 bytes per call.

   - bpo-37170(32): Fix the cast on error in *note
     PyLong_AsUnsignedLongLongMask(): 10f4.

   - bpo-35381(33): Convert posixmodule.c statically allocated types
     ‘DirEntryType’ and ‘ScandirIteratorType’ to heap-allocated types.

   - bpo-34331(34): Use singular/plural noun in error message when
     instantiating an abstract class with non-overriden abstract
     method(s).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37633

   (2) https://bugs.python.org/issue38644

   (3) https://bugs.python.org/issue38650

   (4) https://bugs.python.org/issue38540

   (5) https://bugs.python.org/issue38395

   (6) https://bugs.python.org/issue36389

   (7) https://bugs.python.org/issue38266

   (8) https://bugs.python.org/issue38303

   (9) https://bugs.python.org/issue38234

   (10) https://bugs.python.org/issue38234

   (11) https://bugs.python.org/issue38205

   (12) https://bugs.python.org/issue38140

   (13) https://bugs.python.org/issue15088

   (14) https://www.python.org/dev/peps/pep-0442

   (15) https://bugs.python.org/issue36763

   (16) https://bugs.python.org/issue37926

   (17) https://bugs.python.org/issue37879

   (18) https://bugs.python.org/issue37645

   (19) https://bugs.python.org/issue29548

   (20) https://bugs.python.org/issue37151

   (21) https://bugs.python.org/issue37540

   (22) https://bugs.python.org/issue37207

   (23) https://bugs.python.org/issue21120

   (24) https://bugs.python.org/issue37483

   (25) https://bugs.python.org/issue36763

   (26) https://bugs.python.org/issue37337

   (27) https://bugs.python.org/issue28805

   (28) https://bugs.python.org/issue37221

   (29) https://bugs.python.org/issue37215

   (30) https://bugs.python.org/issue36842

   (31) https://bugs.python.org/issue37194

   (32) https://bugs.python.org/issue37170

   (33) https://bugs.python.org/issue35381

   (34) https://bugs.python.org/issue34331


File: python.info,  Node: Python 3 8 0 beta 1,  Next: Python 3 8 0 alpha 4,  Prev: Python 3 9 0 alpha 1,  Up: Changelog

1.19.27 Python 3.8.0 beta 1
---------------------------

`Release date: 2019-06-04'

* Menu:

* Security: Security<15>.
* Core and Builtins: Core and Builtins<24>.
* Library: Library<26>.
* Documentation: Documentation<21>.
* Tests: Tests<20>.
* Build: Build<20>.
* Windows: Windows<20>.
* macOS: macOS<18>.
* IDLE: IDLE<20>.
* Tools/Demos: Tools/Demos<8>.
* C API: C API<17>.


File: python.info,  Node: Security<15>,  Next: Core and Builtins<24>,  Up: Python 3 8 0 beta 1

1.19.27.1 Security
..................

   - bpo-35907(1): CVE-2019-9948: Avoid file reading by disallowing
     ‘local-file://’ and ‘local_file://’ URL schemes in
     ‘URLopener().open()’ and ‘URLopener().retrieve()’ of *note
     urllib.request: 129.

   - bpo-33529(2): Prevent fold function used in email header encoding
     from entering infinite loop when there are too many non-ASCII
     characters in a header.

   - bpo-33164(3): Updated blake2 implementation which uses secure
     memset implementation provided by platform.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35907

   (2) https://bugs.python.org/issue33529

   (3) https://bugs.python.org/issue33164


File: python.info,  Node: Core and Builtins<24>,  Next: Library<26>,  Prev: Security<15>,  Up: Python 3 8 0 beta 1

1.19.27.2 Core and Builtins
...........................

   - bpo-35814(1): Allow unpacking in the right hand side of annotated
     assignments.  In particular, ‘t: Tuple[int, ...] = x, y, *z’ is now
     allowed.

   - bpo-37126(2): All structseq objects are now tracked by the garbage
     collector.  Patch by Pablo Galindo.

   - bpo-37122(3): Make the `co_argcount' attribute of code objects
     represent the total number of positional arguments (including
     positional-only arguments).  The value of `co_posonlyargcount' can
     be used to distinguish which arguments are positional only, and the
     difference (`co_argcount' - `co_posonlyargcount') is the number of
     positional-or-keyword arguments.  Patch by Pablo Galindo.

   - bpo-20092(4): Constructors of *note int: 204, *note float: 1fd. and
     *note complex: 2c1. will now use the *note __index__(): 2c2.
     special method, if available and the corresponding method *note
     __int__(): 2c3, *note __float__(): 2c4. or *note __complex__():
     2c5. is not available.

   - bpo-37087(5): Add native thread ID (TID) support to OpenBSD.

   - bpo-26219(6): Implemented per opcode cache mechanism and
     ‘LOAD_GLOBAL’ instruction use it.  ‘LOAD_GLOBAL’ is now about 40%
     faster.  Contributed by Yury Selivanov, and Inada Naoki.

   - bpo-37072(7): Fix crash in PyAST_FromNodeObject() when flags is
     NULL.

   - bpo-37029(8): Freeing a great many small objects could take time
     quadratic in the number of arenas, due to using linear search to
     keep ‘obmalloc.c’’s list of usable arenas sorted by order of number
     of free memory pools.  This is accomplished without search now,
     leaving the worst-case time linear in the number of arenas.  For
     programs where this quite visibly matters (typically with more than
     100 thousand small objects alive simultaneously), this can greatly
     reduce the time needed to release their memory.

   - bpo-26423(9): Fix possible overflow in ‘wrap_lenfunc()’ when
     ‘sizeof(long) < sizeof(Py_ssize_t)’ (e.g., 64-bit Windows).

   - bpo-37050(10): Improve the AST for “debug” f-strings, which use ‘=’
     to print out the source of the expression being evaluated.  Delete
     expr_text from the FormattedValue node, and instead use a Constant
     string node (possibly merged with adjacent constant expressions
     inside the f-string).

   - bpo-22385(11): The *note bytes.hex: 724, *note bytearray.hex: 725,
     and *note memoryview.hex: 726. methods as well as the *note
     binascii.hexlify: 10f8. and ‘b2a_hex’ functions now have the
     ability to include an optional separator between hex bytes.  This
     functionality was inspired by MicroPython’s hexlify implementation.

   - bpo-26836(12): Add *note os.memfd_create(): 320.

   - bpo-37032(13): Added new ‘replace()’ method to the code type (*note
     types.CodeType: 2cd.).

   - bpo-37007(14): Implement *note socket.if_nameindex(): 34d, *note
     socket.if_nametoindex(): 34e, and *note socket.if_indextoname():
     34f. on Windows.

   - bpo-36829(15): *note PyErr_WriteUnraisable(): 10f9. now creates a
     traceback object if there is no current traceback.  Moreover, call
     *note PyErr_NormalizeException(): 10fa. and *note
     PyException_SetTraceback(): 10fb. to normalize the exception value.
     Ignore any error.

   - bpo-36878(16): Only accept text after ‘# type: ignore’ if the first
     character is ASCII. This is to disallow things like ‘# type:
     ignoreé’.

   - bpo-36878(17): Store text appearing after a ‘# type: ignore’
     comment in the AST. For example a type ignore like ‘# type:
     ignore[E1000]’ will have the string ‘"[E1000]"’ stored in its AST
     node.

   - bpo-2180(18): Treat line continuation at EOF as a ‘SyntaxError’ by
     Anthony Sottile.

   - bpo-36907(19): Fix a crash when calling a C function with a keyword
     dict (‘f(**kwargs)’) and changing the dict ‘kwargs’ while that
     function is running.

   - bpo-36946(20): Fix possible signed integer overflow when handling
     slices.

   - bpo-36826(21): Add NamedExpression kind support to ast_unparse.c

   - bpo-1875(22): A *note SyntaxError: 55a. is now raised if a code
     blocks that will be optimized away (e.g.  if conditions that are
     always false) contains syntax errors.  Patch by Pablo Galindo.

   - bpo-36027(23): Allow computation of modular inverses via
     three-argument ‘pow’: the second argument is now permitted to be
     negative in the case where the first and third arguments are
     relatively prime.

   - bpo-36861(24): Update the Unicode database to version 12.1.0.

   - bpo-28866(25): Avoid caching attributes of classes which type
     defines mro() to avoid a hard cache invalidation problem.

   - bpo-36851(26): The ‘FrameType’ stack is now correctly cleaned up if
     the execution ends with a return and the stack is not empty.

   - bpo-34616(27): The ‘compile()’ builtin functions now support the
     ‘ast.PyCF_ALLOW_TOP_LEVEL_AWAIT’ flag, which allow to compile
     sources that contains top-level ‘await’, ‘async with’ or ‘async
     for’.  This is useful to evaluate async-code from with an already
     async functions; for example in a custom REPL.

   - bpo-36842(28): Implement PEP 578, adding sys.audit, io.open_code
     and related APIs.

   - bpo-27639(29): Correct return type for UserList slicing operations.
     Patch by Michael Blahay, Erick Cervantes, and vaultah

   - bpo-36737(30): Move PyRuntimeState.warnings into per-interpreter
     state (via “module state”).

   - bpo-36793(31): Removed ‘__str__’ implementations from builtin types
     *note bool: 2bd, *note int: 204, *note float: 1fd, *note complex:
     2c1. and few classes from the standard library.  They now inherit
     ‘__str__()’ from *note object: 3d2.

   - bpo-36817(32): Add a ‘=’ feature f-strings for debugging.  This can
     precede ‘!s’, ‘!r’, or ‘!a’.  It produces the text of the
     expression, followed by an equal sign, followed by the repr of the
     value of the expression.  So ‘f'{3*9+15=}'’ would be equal to the
     string ‘'3*9+15=42'’.  If ‘=’ is specified, the default conversion
     is set to ‘!r’, unless a format spec is given, in which case the
     formatting behavior is unchanged, and __format__ will be used.

   - bpo-24048(33): Save the live exception during import.c’s
     ‘remove_module()’.

   - bpo-27987(34): pymalloc returns memory blocks aligned by 16 bytes,
     instead of 8 bytes, on 64-bit platforms to conform x86-64 ABI.
     Recent compilers assume this alignment more often.  Patch by Inada
     Naoki.

   - bpo-36601(35): A long-since-meaningless check for ‘getpid() ==
     main_pid’ was removed from Python’s internal C signal handler.

   - bpo-36594(36): Fix incorrect use of ‘%p’ in format strings.  Patch
     by Zackery Spytz.

   - bpo-36045(37): builtins.help() now prefixes ‘async’ for async
     functions

   - bpo-36084(38): Add native thread ID (TID) to threading.Thread
     objects (supported platforms: Windows, FreeBSD, Linux, macOS)

   - bpo-36035(39): Added fix for broken symlinks in combination with
     pathlib

   - bpo-35983(40): Added new trashcan macros to deal with a double
     deallocation that could occur when the ‘tp_dealloc’ of a subclass
     calls the ‘tp_dealloc’ of a base class and that base class uses the
     trashcan mechanism.  Patch by Jeroen Demeyer.

   - bpo-20602(41): Do not clear *note sys.flags: c0e. and *note
     sys.float_info: 10fc. during shutdown.  Patch by Zackery Spytz.

   - bpo-26826(42): Expose ‘copy_file_range()’ as a low level API in the
     *note os: c4. module.

   - bpo-32388(43): Remove cross-version binary compatibility
     requirement in tp_flags.

   - bpo-31862(44): Port binascii to PEP 489 multiphase initialization.
     Patch by Marcel Plch.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35814

   (2) https://bugs.python.org/issue37126

   (3) https://bugs.python.org/issue37122

   (4) https://bugs.python.org/issue20092

   (5) https://bugs.python.org/issue37087

   (6) https://bugs.python.org/issue26219

   (7) https://bugs.python.org/issue37072

   (8) https://bugs.python.org/issue37029

   (9) https://bugs.python.org/issue26423

   (10) https://bugs.python.org/issue37050

   (11) https://bugs.python.org/issue22385

   (12) https://bugs.python.org/issue26836

   (13) https://bugs.python.org/issue37032

   (14) https://bugs.python.org/issue37007

   (15) https://bugs.python.org/issue36829

   (16) https://bugs.python.org/issue36878

   (17) https://bugs.python.org/issue36878

   (18) https://bugs.python.org/issue2180

   (19) https://bugs.python.org/issue36907

   (20) https://bugs.python.org/issue36946

   (21) https://bugs.python.org/issue36826

   (22) https://bugs.python.org/issue1875

   (23) https://bugs.python.org/issue36027

   (24) https://bugs.python.org/issue36861

   (25) https://bugs.python.org/issue28866

   (26) https://bugs.python.org/issue36851

   (27) https://bugs.python.org/issue34616

   (28) https://bugs.python.org/issue36842

   (29) https://bugs.python.org/issue27639

   (30) https://bugs.python.org/issue36737

   (31) https://bugs.python.org/issue36793

   (32) https://bugs.python.org/issue36817

   (33) https://bugs.python.org/issue24048

   (34) https://bugs.python.org/issue27987

   (35) https://bugs.python.org/issue36601

   (36) https://bugs.python.org/issue36594

   (37) https://bugs.python.org/issue36045

   (38) https://bugs.python.org/issue36084

   (39) https://bugs.python.org/issue36035

   (40) https://bugs.python.org/issue35983

   (41) https://bugs.python.org/issue20602

   (42) https://bugs.python.org/issue26826

   (43) https://bugs.python.org/issue32388

   (44) https://bugs.python.org/issue31862


File: python.info,  Node: Library<26>,  Next: Documentation<21>,  Prev: Core and Builtins<24>,  Up: Python 3 8 0 beta 1

1.19.27.3 Library
.................

   - bpo-37128(1): Added *note math.perm(): 317.

   - bpo-37120(2): Add SSLContext.num_tickets to control the number of
     TLSv1.3 session tickets.

   - bpo-12202(3): Fix the error handling in *note
     msilib.SummaryInformation.GetProperty(): 10fe.  Patch by Zackery
     Spytz.

   - bpo-26835(4): The fcntl module now contains file sealing constants
     for sealing of memfds.

   - bpo-29262(5): Add ‘get_origin()’ and ‘get_args()’ introspection
     helpers to ‘typing’ module.

   - bpo-12639(6): *note msilib.Directory.start_component(): 10ff. no
     longer fails if `keyfile' is not ‘None’.

   - bpo-36999(7): Add the ‘asyncio.Task.get_coro()’ method to publicly
     expose the tasks’s coroutine object.

   - bpo-35246(8): Make *note asyncio.create_subprocess_exec(): 3b4.
     accept path-like arguments.

   - bpo-35279(9): Change default `max_workers' of ‘ThreadPoolExecutor’
     from ‘cpu_count() * 5’ to ‘min(32, cpu_count() + 4)’.  Previous
     value was unreasonably large on many cores machines.

   - bpo-37076(10): *note _thread.start_new_thread(): 1100. now logs
     uncaught exception raised by the function using *note
     sys.unraisablehook(): 35a, rather than *note sys.excepthook(): f24,
     so the hook gets access to the function which raised the exception.

   - bpo-33725(11): On macOS, the *note multiprocessing: b7. module now
     uses `spawn' start method by default.

   - bpo-37054(12): Fix destructor ‘_pyio.BytesIO’ and
     ‘_pyio.TextIOWrapper’: initialize their ‘_buffer’ attribute as soon
     as possible (in the class body), because it’s used by ‘__del__()’
     which calls ‘close()’.

   - bpo-37058(13): PEP 544: Add ‘Protocol’ and ‘@runtime_checkable’ to
     the ‘typing’ module.

   - bpo-36933(14): The functions ‘sys.set_coroutine_wrapper’ and
     ‘sys.get_coroutine_wrapper’ that were deprecated and marked for
     removal in 3.8 have been removed.

   - bpo-37047(15): Handle late binding and attribute access in *note
     unittest.mock.AsyncMock: 372. setup for autospeccing.  Document
     newly implemented async methods in *note unittest.mock.MagicMock:
     874.

   - bpo-37049(16): PEP 589: Add ‘TypedDict’ to the ‘typing’ module.

   - bpo-37046(17): PEP 586: Add ‘Literal’ to the ‘typing’ module.

   - bpo-37045(18): PEP 591: Add ‘Final’ qualifier and ‘@final’
     decorator to the ‘typing’ module.

   - bpo-37035(19): Don’t log OSError based exceptions if a fatal error
     has occurred in asyncio transport.  Peer can generate almost any
     OSError, user cannot avoid these exceptions by fixing own code.
     Errors are still propagated to user code, it’s just logging them is
     pointless and pollute asyncio logs.

   - bpo-37001(20): *note symtable.symtable(): 1101. now accepts the
     same input types for source code as the built-in *note compile():
     2e7. function.  Patch by Dino Viehland.

   - bpo-37028(21): Implement asyncio REPL

   - bpo-37027(22): Return safe to use proxy socket object from
     transport.get_extra_info(‘socket’)

   - bpo-32528(23): Make asyncio.CancelledError a BaseException.

     This will address the common mistake many asyncio users make: an
     “except Exception” clause breaking Tasks cancellation.

     In addition to this change, we stop inheriting asyncio.TimeoutError
     and asyncio.InvalidStateError from their concurrent.futures.*
     counterparts.  There’s no point for these exceptions to share the
     inheritance chain.

   - bpo-1230540(24): Add a new *note threading.excepthook(): 35e.
     function which handles uncaught *note threading.Thread.run(): 35f.
     exception.  It can be overridden to control how uncaught *note
     threading.Thread.run(): 35f. exceptions are handled.

   - bpo-36996(25): Handle *note unittest.mock.patch(): 877. used as a
     decorator on async functions.

   - bpo-37008(26): Add support for calling *note next(): 775. with the
     mock resulting from *note unittest.mock.mock_open(): 1102.

   - bpo-27737(27): Allow whitespace only header encoding in
     ‘email.header’ - by Batuhan Taskaya

   - bpo-36969(28): PDB command ‘args’ now display positional only
     arguments.  Patch contributed by Rémi Lapeyre.

   - bpo-36969(29): PDB command ‘args’ now display keyword only
     arguments.  Patch contributed by Rémi Lapeyre.

   - bpo-36983(30): Add missing names to ‘typing.__all__’: ‘ChainMap’,
     ‘ForwardRef’, ‘OrderedDict’ - by Anthony Sottile.

   - bpo-36972(31): Add SupportsIndex protocol to the typing module to
     allow type checking to detect classes that can be passed to *note
     hex(): d2e, *note oct(): d2d. and *note bin(): d08.

   - bpo-32972(32): Implement ‘unittest.IsolatedAsyncioTestCase’ to help
     testing asyncio-based code.

   - bpo-36952(33): *note fileinput.input(): 3cf. and *note
     fileinput.FileInput: 3a5. `bufsize' argument has been removed (was
     deprecated and ignored since Python 3.6), and as a result the
     `mode' and `openhook' arguments have been made keyword-only.

   - bpo-36952(34): Starting with Python 3.3, importing ABCs from *note
     collections: 1d. is deprecated, and import should be done from
     *note collections.abc: 1e.  Still being able to import from *note
     collections: 1d. was marked for removal in 3.8, but has been
     delayed to 3.9; documentation and ‘DeprecationWarning’ clarified.

   - bpo-36949(35): Implement __repr__ for WeakSet objects.

   - bpo-36948(36): Fix *note NameError: e40. in *note
     urllib.request.URLopener.retrieve(): 1103.  Patch by Karthikeyan
     Singaravelan.

   - bpo-33524(37): Fix the folding of email header when the
     max_line_length is 0 or None and the header contains non-ascii
     characters.  Contributed by Licht Takeuchi (@Licht-T).

   - bpo-24564(38): *note shutil.copystat(): b52. now ignores *note
     errno.EINVAL: 1104. on *note os.setxattr(): b29. which may occur
     when copying files on filesystems without extended attributes
     support.

     Original patch by Giampaolo Rodola, updated by Ying Wang.

   - bpo-36888(39): Python child processes can now access the status of
     their parent process using multiprocessing.process.parent_process

   - bpo-36921(40): Deprecate ‘@coroutine’ for sake of ‘async def’.

   - bpo-25652(41): Fix bug in ‘__rmod__’ of ‘UserString’ - by Batuhan
     Taskaya.

   - bpo-36916(42): Remove a message about an unhandled exception in a
     task when writer.write() is used without await and writer.drain()
     fails with an exception.

   - bpo-36889(43): Introduce ‘asyncio.Stream’ class that merges *note
     asyncio.StreamReader: 1105. and *note asyncio.StreamWriter: 1106.
     functionality.  ‘asyncio.Stream’ can work in readonly, writeonly
     and readwrite modes.  Provide ‘asyncio.connect()’,
     ‘asyncio.connect_unix()’, ‘asyncio.connect_read_pipe()’ and
     ‘asyncio.connect_write_pipe()’ factories to open ‘asyncio.Stream’
     connections.  Provide ‘asyncio.StreamServer’ and ‘UnixStreamServer’
     to serve servers with asyncio.Stream API. Modify *note
     asyncio.create_subprocess_shell(): 3b5. and *note
     asyncio.create_subprocess_exec(): 3b4. to use ‘asyncio.Stream’
     instead of deprecated ‘StreamReader’ and ‘StreamWriter’.  Deprecate
     *note asyncio.StreamReader: 1105. and *note asyncio.StreamWriter:
     1106.  Deprecate usage of private classes, e.g.
     ‘asyncio.FlowControlMixing’ and ‘asyncio.StreamReaderProtocol’
     outside of asyncio package.

   - bpo-36845(44): Added validation of integer prefixes to the
     construction of IP networks and interfaces in the ipaddress module.

   - bpo-23378(45): Add an extend action to argparser.

   - bpo-36867(46): Fix a bug making a SharedMemoryManager instance and
     its parent process use two separate resource_tracker processes.

   - bpo-23896(47): Adds a grammar to lib2to3.pygram that contains exec
     as a function not as statement.

   - bpo-36895(48): The function ‘time.clock()’ was deprecated in 3.3 in
     favor of ‘time.perf_counter()’ and marked for removal in 3.8, it
     has removed.

   - bpo-35545(49): Fix asyncio discarding IPv6 scopes when ensuring
     hostname resolutions internally

   - bpo-36887(50): Add new function *note math.isqrt(): 319. to compute
     integer square roots.

   - bpo-34632(51): Introduce the ‘importlib.metadata’ module with
     (provisional) support for reading metadata from third-party
     packages.

   - bpo-36878(52): When using ‘type_comments=True’ in *note ast.parse:
     2d6, treat ‘# type: ignore’ followed by a non-alphanumeric
     character and then arbitrary text as a type ignore, instead of
     requiring nothing but whitespace or another comment.  This is to
     permit formations such as ‘# type: ignore[E1000]’.

   - bpo-36778(53): ‘cp65001’ encoding (Windows code page 65001) becomes
     an alias to ‘utf_8’ encoding.

   - bpo-36867(54): The multiprocessing.resource_tracker replaces the
     multiprocessing.semaphore_tracker module.  Other than semaphores,
     resource_tracker also tracks shared_memory segments.

   - bpo-30262(55): The ‘Cache’ and ‘Statement’ objects of the *note
     sqlite3: f2. module are not exposed to the user.  Patch by Aviv
     Palivoda.

   - bpo-24538(56): In *note shutil.copystat(): b52, first copy extended
     file attributes and then file permissions, since extended
     attributes can only be set on the destination while it is still
     writeable.

   - bpo-36829(57): Add new *note sys.unraisablehook(): 35a. function
     which can be overridden to control how “unraisable exceptions” are
     handled.  It is called when an exception has occurred but there is
     no way for Python to handle it.  For example, when a destructor
     raises an exception or during garbage collection (*note
     gc.collect(): 35b.).

   - bpo-36832(58): Introducing ‘zipfile.Path’, a pathlib-compatible
     wrapper for traversing zip files.

   - bpo-36814(59): Fix an issue where os.posix_spawnp() would
     incorrectly raise a TypeError when file_actions is None.

   - bpo-33110(60): Handle exceptions raised by functions added by
     concurrent.futures add_done_callback correctly when the Future has
     already completed.

   - bpo-26903(61): Limit ‘max_workers’ in ‘ProcessPoolExecutor’ to 61
     to work around a WaitForMultipleObjects limitation.

   - bpo-36813(62): Fix *note QueueListener: 803. to call
     ‘queue.task_done()’ upon stopping.  Patch by Bar Harel.

   - bpo-36806(63): Forbid creation of asyncio stream objects like
     StreamReader, StreamWriter, Process, and their protocols outside of
     asyncio package.

   - bpo-36802(64): Provide both sync and async calls for
     StreamWriter.write() and StreamWriter.close()

   - bpo-36801(65): Properly handle SSL connection closing in asyncio
     StreamWriter.drain() call.

   - bpo-36785(66): Implement PEP 574 (pickle protocol 5 with
     out-of-band buffers).

   - bpo-36772(67): functools.lru_cache() can now be used as a straight
     decorator in addition to its existing usage as a function that
     returns a decorator.

   - bpo-6584(68): Add a *note BadGzipFile: 303. exception to the *note
     gzip: 8b. module.

   - bpo-36748(69): Optimized write buffering in C implementation of
     ‘TextIOWrapper’.  Writing ASCII string to ‘TextIOWrapper’ with
     ascii, latin1, or utf-8 encoding is about 20% faster.  Patch by
     Inada Naoki.

   - bpo-8138(70): Don’t mark ‘wsgiref.simple_server.SimpleServer’ as
     multi-threaded since ‘wsgiref.simple_server.WSGIServer’ is
     single-threaded.

   - bpo-22640(71): *note py_compile.compile(): 343. now supports silent
     mode.  Patch by Joannah Nanjekye

   - bpo-29183(72): Fix double exceptions in *note
     wsgiref.handlers.BaseHandler: 1107. by calling its ‘close()’ method
     only when no exception is raised.

   - bpo-36548(73): Improved the repr of regular expression flags.

   - bpo-36542(74): The signature of Python functions can now be
     overridden by specifying the ‘__text_signature__’ attribute.

   - bpo-36533(75): Reinitialize logging.Handler locks in forked child
     processes instead of attempting to acquire them all in the parent
     before forking only to be released in the child process.  The
     acquire/release pattern was leading to deadlocks in code that has
     implemented any form of chained logging handlers that depend upon
     one another as the lock acquisition order cannot be guaranteed.

   - bpo-35252(76): Throw a TypeError instead of an AssertionError when
     using an invalid type annotation with singledispatch.

   - bpo-35900(77): Allow reduction methods to return a 6-item tuple
     where the 6th item specifies a custom state-setting method that’s
     called instead of the regular ‘__setstate__’ method.

   - bpo-35900(78): enable custom reduction callback registration for
     functions and classes in _pickle.c, using the new Pickler’s
     attribute ‘reducer_override’

   - bpo-36368(79): Fix a bug crashing SharedMemoryManager instances in
     interactive sessions after a ctrl-c (KeyboardInterrupt) was sent

   - bpo-31904(80): Fix mmap fail for VxWorks

   - bpo-27497(81): *note csv.DictWriter.writeheader(): c4c. now returns
     the return value of the underlying ‘csv.Writer.writerow()’ method.
     Patch contributed by Ashish Nitin Patil.

   - bpo-36239(82): Parsing .mo files now ignores comments starting and
     ending with #-#-#-#-#.

   - bpo-26707(83): Enable plistlib to read and write binary plist files
     that were created as a KeyedArchive file.  Specifically, this
     allows the plistlib to process 0x80 tokens as UID objects.

   - bpo-31904(84): Add posix module support for VxWorks.

   - bpo-35125(85): Asyncio: Remove inner callback on outer cancellation
     in shield

   - bpo-35721(86): Fix ‘asyncio.SelectorEventLoop.subprocess_exec()’
     leaks file descriptors if ‘Popen’ fails and called with
     ‘stdin=subprocess.PIPE’.  Patch by Niklas Fiekas.

   - bpo-31855(87): *note unittest.mock.mock_open(): 1102. results now
     respects the argument of read([size]).  Patch contributed by Rémi
     Lapeyre.

   - bpo-35431(88): Implement *note math.comb(): 318. that returns
     binomial coefficient, that computes the number of ways to choose k
     items from n items without repetition and without order.  Patch by
     Yash Aggarwal and Keller Fuchs.

   - bpo-26660(89): Fixed permission errors in *note TemporaryDirectory:
     c96. clean up.  Previously ‘TemporaryDirectory.cleanup()’ failed
     when non-writeable or non-searchable files or directories were
     created inside a temporary directory.

   - bpo-34271(90): Add debugging helpers to ssl module.  It’s now
     possible to dump key material and to trace TLS protocol.  The
     default and stdlib contexts also support SSLKEYLOGFILE env var.

   - bpo-26467(91): Added AsyncMock to support using unittest to mock
     asyncio coroutines.  Patch by Lisa Roach.

   - bpo-33569(92): dataclasses.InitVar: Exposes the type used to create
     the init var.

   - bpo-34424(93): Fix serialization of messages containing encoded
     strings when the policy.linesep is set to a multi-character string.
     Patch by Jens Troeger.

   - bpo-34303(94): Performance of *note functools.reduce(): d37. is
     slightly improved.  Patch by Sergey Fedoseev.

   - bpo-33361(95): Fix a bug in *note codecs.StreamRecoder: 1108. where
     seeking might leave old data in a buffer and break subsequent read
     calls.  Patch by Ammar Askar.

   - bpo-22454(96): The *note shlex: e8. module now exposes *note
     shlex.join(): 345, the inverse of *note shlex.split(): 210.  Patch
     by Bo Bayles.

   - bpo-31922(97):
     ‘asyncio.AbstractEventLoop.create_datagram_endpoint()’: Do not
     connect UDP socket when broadcast is allowed.  This allows to
     receive replies after a UDP broadcast.

   - bpo-24882(98): Change ThreadPoolExecutor to use existing idle
     threads before spinning up new ones.

   - bpo-31961(99): Added support for bytes and path-like objects in
     *note subprocess.Popen(): 3db. on Windows.  The `args' parameter
     now accepts a *note path-like object: 472. if `shell' is ‘False’
     and a sequence containing bytes and path-like objects.  The
     `executable' parameter now accepts a bytes and *note path-like
     object: 472.  The `cwd' parameter now accepts a bytes object.
     Based on patch by Anders Lorentsen.

   - bpo-33123(100): *note pathlib.Path.unlink: 1109. now accepts a
     `missing_ok' parameter to avoid a *note FileNotFoundError: 8ad.
     from being raised.  Patch by Robert Buchholz.

   - bpo-32941(101): Allow *note mmap.mmap: 31c. objects to access the
     madvise() system call (through *note mmap.mmap.madvise(): 31d.).

   - bpo-22102(102): Added support for ZIP files with disks set to 0.
     Such files are commonly created by builtin tools on Windows when
     use ZIP64 extension.  Patch by Francisco Facioni.

   - bpo-32515(103): trace.py can now run modules via python3 -m trace
     -t –module module_name

   - bpo-32299(104): Changed *note unittest.mock.patch.dict(): 110a. to
     return the patched dictionary when used as context manager.  Patch
     by Vadim Tsander.

   - bpo-27141(105): Added a ‘__copy__()’ to ‘collections.UserList’ and
     ‘collections.UserDict’ in order to correctly implement shallow
     copying of the objects.  Patch by Bar Harel.

   - bpo-31829(106): ‘\r’, ‘\0’ and ‘\x1a’ (end-of-file on Windows) are
     now escaped in protocol 0 pickles of Unicode strings.  This allows
     to load them without loss from files open in text mode in Python 2.

   - bpo-23395(107): ‘_thread.interrupt_main()’ now avoids setting the
     Python error status if the ‘SIGINT’ signal is ignored or not
     handled by Python.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37128

   (2) https://bugs.python.org/issue37120

   (3) https://bugs.python.org/issue12202

   (4) https://bugs.python.org/issue26835

   (5) https://bugs.python.org/issue29262

   (6) https://bugs.python.org/issue12639

   (7) https://bugs.python.org/issue36999

   (8) https://bugs.python.org/issue35246

   (9) https://bugs.python.org/issue35279

   (10) https://bugs.python.org/issue37076

   (11) https://bugs.python.org/issue33725

   (12) https://bugs.python.org/issue37054

   (13) https://bugs.python.org/issue37058

   (14) https://bugs.python.org/issue36933

   (15) https://bugs.python.org/issue37047

   (16) https://bugs.python.org/issue37049

   (17) https://bugs.python.org/issue37046

   (18) https://bugs.python.org/issue37045

   (19) https://bugs.python.org/issue37035

   (20) https://bugs.python.org/issue37001

   (21) https://bugs.python.org/issue37028

   (22) https://bugs.python.org/issue37027

   (23) https://bugs.python.org/issue32528

   (24) https://bugs.python.org/issue1230540

   (25) https://bugs.python.org/issue36996

   (26) https://bugs.python.org/issue37008

   (27) https://bugs.python.org/issue27737

   (28) https://bugs.python.org/issue36969

   (29) https://bugs.python.org/issue36969

   (30) https://bugs.python.org/issue36983

   (31) https://bugs.python.org/issue36972

   (32) https://bugs.python.org/issue32972

   (33) https://bugs.python.org/issue36952

   (34) https://bugs.python.org/issue36952

   (35) https://bugs.python.org/issue36949

   (36) https://bugs.python.org/issue36948

   (37) https://bugs.python.org/issue33524

   (38) https://bugs.python.org/issue24564

   (39) https://bugs.python.org/issue36888

   (40) https://bugs.python.org/issue36921

   (41) https://bugs.python.org/issue25652

   (42) https://bugs.python.org/issue36916

   (43) https://bugs.python.org/issue36889

   (44) https://bugs.python.org/issue36845

   (45) https://bugs.python.org/issue23378

   (46) https://bugs.python.org/issue36867

   (47) https://bugs.python.org/issue23896

   (48) https://bugs.python.org/issue36895

   (49) https://bugs.python.org/issue35545

   (50) https://bugs.python.org/issue36887

   (51) https://bugs.python.org/issue34632

   (52) https://bugs.python.org/issue36878

   (53) https://bugs.python.org/issue36778

   (54) https://bugs.python.org/issue36867

   (55) https://bugs.python.org/issue30262

   (56) https://bugs.python.org/issue24538

   (57) https://bugs.python.org/issue36829

   (58) https://bugs.python.org/issue36832

   (59) https://bugs.python.org/issue36814

   (60) https://bugs.python.org/issue33110

   (61) https://bugs.python.org/issue26903

   (62) https://bugs.python.org/issue36813

   (63) https://bugs.python.org/issue36806

   (64) https://bugs.python.org/issue36802

   (65) https://bugs.python.org/issue36801

   (66) https://bugs.python.org/issue36785

   (67) https://bugs.python.org/issue36772

   (68) https://bugs.python.org/issue6584

   (69) https://bugs.python.org/issue36748

   (70) https://bugs.python.org/issue8138

   (71) https://bugs.python.org/issue22640

   (72) https://bugs.python.org/issue29183

   (73) https://bugs.python.org/issue36548

   (74) https://bugs.python.org/issue36542

   (75) https://bugs.python.org/issue36533

   (76) https://bugs.python.org/issue35252

   (77) https://bugs.python.org/issue35900

   (78) https://bugs.python.org/issue35900

   (79) https://bugs.python.org/issue36368

   (80) https://bugs.python.org/issue31904

   (81) https://bugs.python.org/issue27497

   (82) https://bugs.python.org/issue36239

   (83) https://bugs.python.org/issue26707

   (84) https://bugs.python.org/issue31904

   (85) https://bugs.python.org/issue35125

   (86) https://bugs.python.org/issue35721

   (87) https://bugs.python.org/issue31855

   (88) https://bugs.python.org/issue35431

   (89) https://bugs.python.org/issue26660

   (90) https://bugs.python.org/issue34271

   (91) https://bugs.python.org/issue26467

   (92) https://bugs.python.org/issue33569

   (93) https://bugs.python.org/issue34424

   (94) https://bugs.python.org/issue34303

   (95) https://bugs.python.org/issue33361

   (96) https://bugs.python.org/issue22454

   (97) https://bugs.python.org/issue31922

   (98) https://bugs.python.org/issue24882

   (99) https://bugs.python.org/issue31961

   (100) https://bugs.python.org/issue33123

   (101) https://bugs.python.org/issue32941

   (102) https://bugs.python.org/issue22102

   (103) https://bugs.python.org/issue32515

   (104) https://bugs.python.org/issue32299

   (105) https://bugs.python.org/issue27141

   (106) https://bugs.python.org/issue31829

   (107) https://bugs.python.org/issue23395


File: python.info,  Node: Documentation<21>,  Next: Tests<20>,  Prev: Library<26>,  Up: Python 3 8 0 beta 1

1.19.27.4 Documentation
.......................

   - bpo-36896(1): Clarify that some types have unstable constructor
     signature between Python versions.

   - bpo-36686(2): Improve documentation of the stdin, stdout, and
     stderr arguments of the ‘asyncio.subprocess_exec’ function to
     specify which values are supported.  Also mention that decoding as
     text is not supported.

     Add a few tests to verify that the various values passed to the
     std* arguments actually work.

   - bpo-36984(3): Improve version added references in ‘typing’ module -
     by Anthony Sottile.

   - bpo-36868(4): What’s new now mentions
     SSLContext.hostname_checks_common_name instead of
     SSLContext.host_flags.

   - bpo-35924(5): Add a note to the ‘curses.addstr()’ documentation to
     warn that multiline strings can cause segfaults because of an
     ncurses bug.

   - bpo-36783(6): Added C API Documentation for Time_FromTimeAndFold
     and PyDateTime_FromDateAndTimeAndFold as per PEP 495.  Patch by
     Edison Abahurire.

   - bpo-36797(7): More of the legacy distutils documentation has been
     either pruned, or else more clearly marked as being retained solely
     until the setuptools documentation covers it independently.

   - bpo-22865(8): Add detail to the documentation on the *note
     pty.spawn: 97f. function.

   - bpo-35397(9): Remove deprecation and document
     urllib.parse.unwrap().  Patch contributed by Rémi Lapeyre.

   - bpo-32995(10): Added the context variable in glossary.

   - bpo-33519(11): Clarify that *note copy(): 25. is not part of the
     ‘MutableSequence’ ABC.

   - bpo-33482(12): Make ‘codecs.StreamRecoder.writelines’ take a list
     of bytes.

   - bpo-25735(13): Added documentation for func factorial to indicate
     that returns integer values

   - bpo-20285(14): Expand object.__doc__ (docstring) to make it
     clearer.  Modify pydoc.py so that help(object) lists object methods
     (for other classes, help omits methods of the object base class.)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36896

   (2) https://bugs.python.org/issue36686

   (3) https://bugs.python.org/issue36984

   (4) https://bugs.python.org/issue36868

   (5) https://bugs.python.org/issue35924

   (6) https://bugs.python.org/issue36783

   (7) https://bugs.python.org/issue36797

   (8) https://bugs.python.org/issue22865

   (9) https://bugs.python.org/issue35397

   (10) https://bugs.python.org/issue32995

   (11) https://bugs.python.org/issue33519

   (12) https://bugs.python.org/issue33482

   (13) https://bugs.python.org/issue25735

   (14) https://bugs.python.org/issue20285


File: python.info,  Node: Tests<20>,  Next: Build<20>,  Prev: Documentation<21>,  Up: Python 3 8 0 beta 1

1.19.27.5 Tests
...............

   - bpo-37069(1): Modify test_coroutines, test_cprofile,
     test_generators, test_raise, test_ssl and test_yield_from to use
     *note test.support.catch_unraisable_exception(): 10e4. rather than
     *note test.support.captured_stderr(): 110d.

   - bpo-37098(2): Fix test_memfd_create on older Linux Kernels.

   - bpo-37081(3): Test with OpenSSL 1.1.1c

   - bpo-36829(4): Add *note test.support.catch_unraisable_exception():
     10e4.: context manager catching unraisable exception using *note
     sys.unraisablehook(): 35a.

   - bpo-36915(5): The main regrtest process now always removes all
     temporary directories of worker processes even if they crash or if
     they are killed on KeyboardInterrupt (CTRL+c).

   - bpo-36719(6): “python3 -m test -jN …” now continues the execution
     of next tests when a worker process crash (CHILD_ERROR state).
     Previously, the test suite stopped immediately.  Use –failfast to
     stop at the first error.

   - bpo-36816(7): Update Lib/test/selfsigned_pythontestdotnet.pem to
     match self-signed.pythontest.net’s new TLS certificate.

   - bpo-35925(8): Skip httplib and nntplib networking tests when they
     would otherwise fail due to a modern OS or distro with a default
     OpenSSL policy of rejecting connections to servers with weak
     certificates.

   - bpo-36782(9): Add tests for several C API functions in the *note
     datetime: 30. module.  Patch by Edison Abahurire.

   - bpo-36342(10): Fix test_multiprocessing in test_venv if platform
     lacks functioning sem_open.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37069

   (2) https://bugs.python.org/issue37098

   (3) https://bugs.python.org/issue37081

   (4) https://bugs.python.org/issue36829

   (5) https://bugs.python.org/issue36915

   (6) https://bugs.python.org/issue36719

   (7) https://bugs.python.org/issue36816

   (8) https://bugs.python.org/issue35925

   (9) https://bugs.python.org/issue36782

   (10) https://bugs.python.org/issue36342


File: python.info,  Node: Build<20>,  Next: Windows<20>,  Prev: Tests<20>,  Up: Python 3 8 0 beta 1

1.19.27.6 Build
...............

   - bpo-36721(1): To embed Python into an application, a new ‘--embed’
     option must be passed to ‘python3-config --libs --embed’ to get
     ‘-lpython3.8’ (link the application to libpython).  To support both
     3.8 and older, try ‘python3-config --libs --embed’ first and
     fallback to ‘python3-config --libs’ (without ‘--embed’) if the
     previous command fails.

     Add a pkg-config ‘python-3.8-embed’ module to embed Python into an
     application: ‘pkg-config python-3.8-embed --libs’ includes
     ‘-lpython3.8’.  To support both 3.8 and older, try ‘pkg-config
     python-X.Y-embed --libs’ first and fallback to ‘pkg-config
     python-X.Y --libs’ (without ‘--embed’) if the previous command
     fails (replace ‘X.Y’ with the Python version).

     On the other hand, ‘pkg-config python3.8 --libs’ no longer contains
     ‘-lpython3.8’.  C extensions must not be linked to libpython
     (except on Android, case handled by the script); this change is
     backward incompatible on purpose.

   - bpo-36786(2): “make install” now runs compileall in parallel.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36721

   (2) https://bugs.python.org/issue36786


File: python.info,  Node: Windows<20>,  Next: macOS<18>,  Prev: Build<20>,  Up: Python 3 8 0 beta 1

1.19.27.7 Windows
.................

   - bpo-36965(1): include of STATUS_CONTROL_C_EXIT without depending on
     MSC compiler

   - bpo-35926(2): Update to OpenSSL 1.1.1b for Windows.

   - bpo-29883(3): Add Windows support for UDP transports for the
     Proactor Event Loop.  Patch by Adam Meily.

   - bpo-33407(4): The ‘Py_DEPRECATED()’ macro has been implemented for
     MSVC.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36965

   (2) https://bugs.python.org/issue35926

   (3) https://bugs.python.org/issue29883

   (4) https://bugs.python.org/issue33407


File: python.info,  Node: macOS<18>,  Next: IDLE<20>,  Prev: Windows<20>,  Up: Python 3 8 0 beta 1

1.19.27.8 macOS
...............

   - bpo-36231(1): Support building Python on macOS without /usr/include
     installed.  As of macOS 10.14, system header files are only
     available within an SDK provided by either the Command Line Tools
     or the Xcode app.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36231


File: python.info,  Node: IDLE<20>,  Next: Tools/Demos<8>,  Prev: macOS<18>,  Up: Python 3 8 0 beta 1

1.19.27.9 IDLE
..............

   - bpo-35610(1): Replace now redundant .context_use_ps1 with
     .prompt_last_line.  This finishes change started in bpo-31858(2).

   - bpo-37038(3): Make idlelib.run runnable; add test clause.

   - bpo-36958(4): Print any argument other than None or int passed to
     SystemExit or sys.exit().

   - bpo-36807(5): When saving a file, call os.fsync() so bits are
     flushed to e.g.  USB drive.

   - bpo-32411(6): In browser.py, remove extraneous sorting by line
     number since dictionary was created in line number order.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35610

   (2) https://bugs.python.org/issue31858

   (3) https://bugs.python.org/issue37038

   (4) https://bugs.python.org/issue36958

   (5) https://bugs.python.org/issue36807

   (6) https://bugs.python.org/issue32411


File: python.info,  Node: Tools/Demos<8>,  Next: C API<17>,  Prev: IDLE<20>,  Up: Python 3 8 0 beta 1

1.19.27.10 Tools/Demos
......................

   - bpo-37053(1): Handle strings like u”bar” correctly in
     Tools/parser/unparse.py.  Patch by Chih-Hsuan Yen.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue37053


File: python.info,  Node: C API<17>,  Prev: Tools/Demos<8>,  Up: Python 3 8 0 beta 1

1.19.27.11 C API
................

   - bpo-36763(1): Implement the PEP 587(2) “Python Initialization
     Configuration”.

   - bpo-36379(3): Fix crashes when attempting to use the `modulo'
     parameter when ‘__ipow__’ is implemented in C.

   - bpo-37107(4): Update *note PyObject_CallMethodObjArgs(): 1114. and
     ‘_PyObject_CallMethodIdObjArgs’ to use ‘_PyObject_GetMethod’ to
     avoid creating a bound method object in many cases.  Patch by
     Michael J. Sullivan.

   - bpo-36974(5): Implement PEP 590(6): Vectorcall: a fast calling
     protocol for CPython.  This is a new protocol to optimize calls of
     custom callable objects.

   - bpo-36763(7): ‘Py_Main()’ now returns the exitcode rather than
     calling ‘Py_Exit(exitcode)’ when calling ‘PyErr_Print()’ if the
     current exception type is ‘SystemExit’.

   - bpo-36922(8): Add new type flag ‘Py_TPFLAGS_METHOD_DESCRIPTOR’ for
     objects behaving like unbound methods.  These are objects
     supporting the optimization given by the
     ‘LOAD_METHOD’/‘CALL_METHOD’ opcodes.  See PEP 590.

   - bpo-36728(9): The ‘PyEval_ReInitThreads()’ function has been
     removed from the C API. It should not be called explicitly: use
     *note PyOS_AfterFork_Child(): 3ef. instead.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36763

   (2) https://www.python.org/dev/peps/pep-0587

   (3) https://bugs.python.org/issue36379

   (4) https://bugs.python.org/issue37107

   (5) https://bugs.python.org/issue36974

   (6) https://www.python.org/dev/peps/pep-0590

   (7) https://bugs.python.org/issue36763

   (8) https://bugs.python.org/issue36922

   (9) https://bugs.python.org/issue36728


File: python.info,  Node: Python 3 8 0 alpha 4,  Next: Python 3 8 0 alpha 3,  Prev: Python 3 8 0 beta 1,  Up: Changelog

1.19.28 Python 3.8.0 alpha 4
----------------------------

`Release date: 2019-05-06'

* Menu:

* Security: Security<16>.
* Core and Builtins: Core and Builtins<25>.
* Library: Library<27>.
* Documentation: Documentation<22>.
* Tests: Tests<21>.
* Build: Build<21>.
* Windows: Windows<21>.
* macOS: macOS<19>.
* IDLE: IDLE<21>.
* Tools/Demos: Tools/Demos<9>.
* C API: C API<18>.


File: python.info,  Node: Security<16>,  Next: Core and Builtins<25>,  Up: Python 3 8 0 alpha 4

1.19.28.1 Security
..................

   - bpo-36742(1): Fixes mishandling of pre-normalization characters in
     urlsplit().

   - bpo-30458(2): Address CVE-2019-9740 by disallowing URL paths with
     embedded whitespace or control characters through into the
     underlying http client request.  Such potentially malicious header
     injection URLs now cause an http.client.InvalidURL exception to be
     raised.

   - bpo-35755(3): *note shutil.which(): fe6. now uses
     ‘os.confstr("CS_PATH")’ if available and if the ‘PATH’ environment
     variable is not set.  Remove also the current directory from
     ‘posixpath.defpath’.  On Unix, *note shutil.which(): fe6. and the
     *note subprocess: f9. module no longer search the executable in the
     current directory if the ‘PATH’ environment variable is not set.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36742

   (2) https://bugs.python.org/issue30458

   (3) https://bugs.python.org/issue35755


File: python.info,  Node: Core and Builtins<25>,  Next: Library<27>,  Prev: Security<16>,  Up: Python 3 8 0 alpha 4

1.19.28.2 Core and Builtins
...........................

   - bpo-36722(1): In debug build, import now also looks for C
     extensions compiled in release mode and for C extensions compiled
     in the stable ABI.

   - bpo-32849(2): Fix Python Initialization code on FreeBSD to detect
     properly when stdin file descriptor (fd 0) is invalid.

   - bpo-36623(3): Remove parser headers and related function
     declarations that lack implementations after the removal of pgen.

   - bpo-20180(4): ‘dict.pop()’ is now up to 33% faster thanks to
     Argument Clinic.  Patch by Inada Naoki.

   - bpo-36611(5): Debug memory allocators: disable serialno field by
     default from debug hooks on Python memory allocators to reduce the
     memory footprint by 5%.  Enable *note tracemalloc: 11d. to get the
     traceback where a memory block has been allocated when a fatal
     memory error is logged to decide where to put a breakpoint.
     Compile Python with ‘PYMEM_DEBUG_SERIALNO’ defined to get back the
     field.

   - bpo-36588(6): On AIX, *note sys.platform: 3d3. doesn’t contain the
     major version anymore.  Always return ‘'aix'’, instead of ‘'aix3'’
     ..  ‘'aix7'’.  Since older Python versions include the version
     number, it is recommended to always use
     ‘sys.platform.startswith('aix')’.  Contributed by M. Felt.

   - bpo-36549(7): Change str.capitalize to use titlecase for the first
     character instead of uppercase.

   - bpo-36540(8): Implement PEP 570(9) (Python positional-only
     parameters).  Patch by Pablo Galindo.

   - bpo-36475(10): *note PyEval_AcquireLock(): 3d4. and *note
     PyEval_AcquireThread(): 3d5. now terminate the current thread if
     called while the interpreter is finalizing, making them consistent
     with *note PyEval_RestoreThread(): 3d6, *note
     Py_END_ALLOW_THREADS(): 3d7, and *note PyGILState_Ensure(): 3d8.

   - bpo-36504(11): Fix signed integer overflow in _ctypes.c’s
     ‘PyCArrayType_new()’.

   - bpo-20844(12): Fix running script with encoding cookie and LF line
     ending may fail on Windows.

   - bpo-24214(13): Fixed support of the surrogatepass error handler in
     the UTF-8 incremental decoder.

   - bpo-36452(14): Changing ‘dict’ keys during iteration of the dict
     itself, ‘keys()’, ‘values()’, or ‘items()’ will now be detected in
     certain corner cases where keys are deleted/added so that the
     number of keys isn’t changed.  A *note RuntimeError: 3dc. will be
     raised after ‘len(dict)’ iterations.  Contributed by Thomas Perl.

   - bpo-36459(15): Fix a possible double ‘PyMem_FREE()’ due to
     tokenizer.c’s ‘tok_nextc()’.

   - bpo-36433(16): Fixed TypeError message in classmethoddescr_call.

   - bpo-36430(17): Fix a possible reference leak in *note
     itertools.count(): ce5.

   - bpo-36440(18): Include node names in ‘ParserError’ messages,
     instead of numeric IDs.  Patch by A. Skrobov.

   - bpo-36143(19): Regenerate *note keyword: a6. from the Grammar and
     Tokens file using pgen.  Patch by Pablo Galindo.

   - bpo-18372(20): Add missing *note PyObject_GC_Track(): f06. calls in
     the *note pickle: ca. module.  Patch by Zackery Spytz.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36722

   (2) https://bugs.python.org/issue32849

   (3) https://bugs.python.org/issue36623

   (4) https://bugs.python.org/issue20180

   (5) https://bugs.python.org/issue36611

   (6) https://bugs.python.org/issue36588

   (7) https://bugs.python.org/issue36549

   (8) https://bugs.python.org/issue36540

   (9) https://www.python.org/dev/peps/pep-0570

   (10) https://bugs.python.org/issue36475

   (11) https://bugs.python.org/issue36504

   (12) https://bugs.python.org/issue20844

   (13) https://bugs.python.org/issue24214

   (14) https://bugs.python.org/issue36452

   (15) https://bugs.python.org/issue36459

   (16) https://bugs.python.org/issue36433

   (17) https://bugs.python.org/issue36430

   (18) https://bugs.python.org/issue36440

   (19) https://bugs.python.org/issue36143

   (20) https://bugs.python.org/issue18372


File: python.info,  Node: Library<27>,  Next: Documentation<22>,  Prev: Core and Builtins<25>,  Up: Python 3 8 0 alpha 4

1.19.28.3 Library
.................

   - bpo-35952(1): Fix pythoninfo when the compiler is missing.

   - bpo-28238(2): The ‘.find*()’ methods of xml.etree.ElementTree can
     now search for wildcards like ‘{*}tag’ and ‘{ns}*’ that match a tag
     in any namespace or all tags in a namespace.  Patch by Stefan
     Behnel.

   - bpo-26978(3): ‘pathlib.path.link_to()’ is now implemented.  It
     creates a hard link pointing to a path.

   - bpo-1613500(4): *note fileinput.FileInput: 3a5. now uses the input
     file mode to correctly set the output file mode (previously it was
     hardcoded to ‘'w'’) when ‘inplace=True’ is passed to its
     constructor.

   - bpo-36734(5): Fix compilation of ‘faulthandler.c’ on HP-UX.
     Initialize ‘stack_t current_stack’ to zero using ‘memset()’.

   - bpo-13611(6): The xml.etree.ElementTree packages gained support for
     C14N 2.0 serialisation.  Patch by Stefan Behnel.

   - bpo-36669(7): Add missing matrix multiplication operator support to
     weakref.proxy.

   - bpo-36676(8): The XMLParser() in xml.etree.ElementTree provides
     namespace prefix context to the parser target if it defines the
     callback methods “start_ns()” and/or “end_ns()”.  Patch by Stefan
     Behnel.

   - bpo-36673(9): The TreeBuilder and XMLPullParser in
     xml.etree.ElementTree gained support for parsing comments and
     processing instructions.  Patch by Stefan Behnel.

   - bpo-36650(10): The C version of functools.lru_cache() was treating
     calls with an empty ‘**kwargs’ dictionary as being distinct from
     calls with no keywords at all.  This did not result in an incorrect
     answer, but it did trigger an unexpected cache miss.

   - bpo-28552(11): Fix *note distutils.sysconfig: 61. if *note
     sys.executable: 39d. is ‘None’ or an empty string: use *note
     os.getcwd(): 1119. to initialize ‘project_base’.  Fix also the
     distutils build command: don’t use *note sys.executable: 39d. if it
     is ‘None’ or an empty string.

   - bpo-35755(12): *note shutil.which(): fe6. and
     ‘distutils.spawn.find_executable()’ now use ‘os.confstr("CS_PATH")’
     if available instead of *note os.defpath: 111a, if the ‘PATH’
     environment variable is not set.  Moreover, don’t use
     ‘os.confstr("CS_PATH")’ nor *note os.defpath: 111a. if the ‘PATH’
     environment variable is set to an empty string.

   - bpo-25430(13): improve performance of ‘IPNetwork.__contains__()’

   - bpo-30485(14): Path expressions in xml.etree.ElementTree can now
     avoid explicit namespace prefixes for tags (or the “{namespace}tag”
     notation) by passing a default namespace with an empty string
     prefix.

   - bpo-36613(15): Fix *note asyncio: 9. wait() not removing callback
     if exception

   - bpo-36598(16): Fix ‘isinstance’ check for Mock objects with spec
     when the code is executed under tracing.  Patch by Karthikeyan
     Singaravelan.

   - bpo-18748(17): In development mode (*note -X: 290. ‘dev’) and in
     debug build, the *note io.IOBase: 30c. destructor now logs
     ‘close()’ exceptions.  These exceptions are silent by default in
     release mode.

   - bpo-36575(18): The ‘_lsprof’ module now uses internal timer same to
     ‘time.perf_counter()’ by default.  ‘gettimeofday(2)’ was used on
     Unix.  New timer has better resolution on most Unix platforms and
     timings are no longer impacted by system clock updates since
     ‘perf_counter()’ is monotonic.  Patch by Inada Naoki.

   - bpo-33461(19): ‘json.loads’ now emits ‘DeprecationWarning’ when
     ‘encoding’ option is specified.  Patch by Matthias Bussonnier.

   - bpo-36559(20): The random module now prefers the lean internal
     _sha512 module over hashlib for seed(version=2) to optimize import
     time.

   - bpo-17561(21): Set backlog=None as the default for
     socket.create_server.

   - bpo-34373(22): Fix *note time.mktime(): c36. error handling on AIX
     for year before 1970.

   - bpo-36232(23): Improve error message when trying to open existing
     DBM database that actually doesn’t exist.  Patch by Marco Rougeth.

   - bpo-36546(24): Add statistics.quantiles()

   - bpo-36050(25): Optimized ‘http.client.HTTPResponse.read()’ for
     large response.  Patch by Inada Naoki.

   - bpo-36522(26): If `debuglevel' is set to >0 in *note http.client:
     93, print all values for headers with multiple values for the same
     header name.  Patch by Matt Houglum.

   - bpo-36492(27): Deprecated passing required arguments like `func' as
     keyword arguments in functions which should accept arbitrary
     keyword arguments and pass them to other function.  Arbitrary
     keyword arguments (even with names “self” and “func”) can now be
     passed to these functions if the required arguments are passed as
     positional arguments.

   - bpo-27181(28): Add statistics.geometric_mean().

   - bpo-30427(29): ‘os.path.normcase()’ relies on ‘os.fspath()’ to
     check the type of its argument.  Redundant checks have been removed
     from its ‘posixpath.normcase()’ and ‘ntpath.normcase()’
     implementations.  Patch by Wolfgang Maier.

   - bpo-36385(30): Stop rejecting IPv4 octets for being ambiguously
     octal.  Leading zeros are ignored, and no longer are assumed to
     specify octal octets.  Octets are always decimal numbers.  Octets
     must still be no more than three digits, including leading zeroes.

   - bpo-36434(31): Errors during writing to a ZIP file no longer
     prevent to properly close it.

   - bpo-36407(32): Fixed wrong indentation writing for CDATA section in
     xml.dom.minidom.  Patch by Vladimir Surjaninov.

   - bpo-36326(33): inspect.getdoc() can now find docstrings for member
     objects when __slots__ is a dictionary.

   - bpo-36366(34): Calling ‘stop()’ on an unstarted or stopped *note
     unittest.mock.patch(): 877. object will now return *note None: 203.
     instead of raising *note RuntimeError: 3dc, making the method
     idempotent.  Patch by Karthikeyan Singaravelan.

   - bpo-36348(35): The ‘imap.IMAP4.logout()’ method no longer ignores
     silently arbitrary exceptions.

   - bpo-31904(36): Add time module support and fix test_time faiures
     for VxWorks.

   - bpo-36227(37): Added support for keyword arguments
     ‘default_namespace’ and ‘xml_declaration’ in functions
     ElementTree.tostring() and ElementTree.tostringlist().

   - bpo-36004(38): Added new alternate constructors *note
     datetime.date.fromisocalendar(): 2f5. and *note
     datetime.datetime.fromisocalendar(): 2f6, which construct date
     objects from ISO year, week number and weekday; these are the
     inverse of each class’s ‘isocalendar’ method.  Patch by Paul
     Ganssle.

   - bpo-35936(39): *note modulefinder: b4. no longer depends on the
     deprecated *note imp: 99. module, and the initializer for *note
     modulefinder.ModuleFinder: 111b. now has immutable default
     arguments.  Patch by Brandt Bucher.

   - bpo-35376(40): *note modulefinder: b4. correctly handles modules
     that have the same name as a bad package.  Patch by Brandt Bucher.

   - bpo-17396(41): *note modulefinder: b4. no longer crashes when
     encountering syntax errors in followed imports.  Patch by Brandt
     Bucher.

   - bpo-35934(42): Added *note create_server(): 34b. and *note
     has_dualstack_ipv6(): 34c. convenience functions to automate the
     necessary tasks usually involved when creating a server socket,
     including accepting both IPv4 and IPv6 connections on the same
     socket.  (Contributed by Giampaolo Rodola in bpo-17561(43).)

   - bpo-23078(44): Add support for *note classmethod(): 309. and *note
     staticmethod(): 30a. to *note unittest.mock.create_autospec():
     1087.  Initial patch by Felipe Ochoa.

   - bpo-35416(45): Fix potential resource warnings in distutils.  Patch
     by Mickaël Schoentgen.

   - bpo-25451(46): Add transparency methods to ‘tkinter.PhotoImage’.
     Patch by Zackery Spytz.

   - bpo-35082(47): Don’t return deleted attributes when calling dir on
     a *note unittest.mock.Mock: 373.

   - bpo-34547(48): *note wsgiref.handlers.BaseHandler: 1107. now
     handles abrupt client connection terminations gracefully.  Patch by
     Petter Strandmark.

   - bpo-31658(49): *note xml.sax.parse(): 111c. now supports *note
     path-like: 472.  Patch by Mickaël Schoentgen.

   - bpo-34139(50): Remove stale unix datagram socket before binding

   - bpo-33530(51): Implemented Happy Eyeballs in
     ‘asyncio.create_connection()’.  Added two new arguments,
     `happy_eyeballs_delay' and `interleave', to specify Happy Eyeballs
     behavior.

   - bpo-33291(52): Do not raise AttributeError when calling the inspect
     functions isgeneratorfunction, iscoroutinefunction,
     isasyncgenfunction on a method created from an arbitrary callable.
     Instead, return False.

   - bpo-31310(53): Fix the multiprocessing.semaphore_tracker so it is
     reused by child processes

   - bpo-31292(54): Fix ‘setup.py check --restructuredtext’ for files
     containing ‘include’ directives.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35952

   (2) https://bugs.python.org/issue28238

   (3) https://bugs.python.org/issue26978

   (4) https://bugs.python.org/issue1613500

   (5) https://bugs.python.org/issue36734

   (6) https://bugs.python.org/issue13611

   (7) https://bugs.python.org/issue36669

   (8) https://bugs.python.org/issue36676

   (9) https://bugs.python.org/issue36673

   (10) https://bugs.python.org/issue36650

   (11) https://bugs.python.org/issue28552

   (12) https://bugs.python.org/issue35755

   (13) https://bugs.python.org/issue25430

   (14) https://bugs.python.org/issue30485

   (15) https://bugs.python.org/issue36613

   (16) https://bugs.python.org/issue36598

   (17) https://bugs.python.org/issue18748

   (18) https://bugs.python.org/issue36575

   (19) https://bugs.python.org/issue33461

   (20) https://bugs.python.org/issue36559

   (21) https://bugs.python.org/issue17561

   (22) https://bugs.python.org/issue34373

   (23) https://bugs.python.org/issue36232

   (24) https://bugs.python.org/issue36546

   (25) https://bugs.python.org/issue36050

   (26) https://bugs.python.org/issue36522

   (27) https://bugs.python.org/issue36492

   (28) https://bugs.python.org/issue27181

   (29) https://bugs.python.org/issue30427

   (30) https://bugs.python.org/issue36385

   (31) https://bugs.python.org/issue36434

   (32) https://bugs.python.org/issue36407

   (33) https://bugs.python.org/issue36326

   (34) https://bugs.python.org/issue36366

   (35) https://bugs.python.org/issue36348

   (36) https://bugs.python.org/issue31904

   (37) https://bugs.python.org/issue36227

   (38) https://bugs.python.org/issue36004

   (39) https://bugs.python.org/issue35936

   (40) https://bugs.python.org/issue35376

   (41) https://bugs.python.org/issue17396

   (42) https://bugs.python.org/issue35934

   (43) https://bugs.python.org/issue17561

   (44) https://bugs.python.org/issue23078

   (45) https://bugs.python.org/issue35416

   (46) https://bugs.python.org/issue25451

   (47) https://bugs.python.org/issue35082

   (48) https://bugs.python.org/issue34547

   (49) https://bugs.python.org/issue31658

   (50) https://bugs.python.org/issue34139

   (51) https://bugs.python.org/issue33530

   (52) https://bugs.python.org/issue33291

   (53) https://bugs.python.org/issue31310

   (54) https://bugs.python.org/issue31292


File: python.info,  Node: Documentation<22>,  Next: Tests<21>,  Prev: Library<27>,  Up: Python 3 8 0 alpha 4

1.19.28.4 Documentation
.......................

   - bpo-36625(1): Remove obsolete comments from docstrings in
     fractions.Fraction

   - bpo-30840(2): Document relative imports

   - bpo-36523(3): Add docstring for io.IOBase.writelines().

   - bpo-36425(4): New documentation translation: Simplified Chinese(5).

   - bpo-36345(6): Avoid the duplication of code from
     ‘Tools/scripts/serve.py’ in using the ‘literalinclude’ directive
     for the basic wsgiref-based web server in the documentation of
     *note wsgiref: 135.  Contributed by Stéphane Wirtel.

   - bpo-36345(7): Using the code of the ‘Tools/scripts/serve.py’ script
     as an example in the *note wsgiref: 135. documentation.
     Contributed by Stéphane Wirtel.

   - bpo-36157(8): Added Documention for PyInterpreterState_Main().

   - bpo-33043(9): Updates the docs.python.org page with the addition of
     a ‘Contributing to Docs’ link at the end of the page (between
     ‘Reporting Bugs’ and ‘About Documentation’).  Updates the ‘Found a
     Bug’ page with additional links and information in the
     Documentation Bugs section.

   - bpo-35581(10): @typing.type_check_only now allows type stubs to
     mark functions and classes not available during runtime.

   - bpo-33832(11): Add glossary entry for ‘magic method’.

   - bpo-32913(12): Added re.Match.groupdict example to regex HOWTO.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36625

   (2) https://bugs.python.org/issue30840

   (3) https://bugs.python.org/issue36523

   (4) https://bugs.python.org/issue36425

   (5) https://docs.python.org/zh-cn/

   (6) https://bugs.python.org/issue36345

   (7) https://bugs.python.org/issue36345

   (8) https://bugs.python.org/issue36157

   (9) https://bugs.python.org/issue33043

   (10) https://bugs.python.org/issue35581

   (11) https://bugs.python.org/issue33832

   (12) https://bugs.python.org/issue32913


File: python.info,  Node: Tests<21>,  Next: Build<21>,  Prev: Documentation<22>,  Up: Python 3 8 0 alpha 4

1.19.28.5 Tests
...............

   - bpo-36719(1): regrtest now always detects uncollectable objects.
     Previously, the check was only enabled by ‘--findleaks’.  The check
     now also works with ‘-jN/--multiprocess N’.  ‘--findleaks’ becomes
     a deprecated alias to ‘--fail-env-changed’.

   - bpo-36725(2): When using multiprocessing mode (-jN), regrtest now
     better reports errors if a worker process fails, and it exits
     immediately on a worker thread failure or when interrupted.

   - bpo-36454(3): Change test_time.test_monotonic() to test only the
     lower bound of elapsed time after a sleep command rather than the
     upper bound.  This prevents unnecessary test failures on slow
     buildbots.  Patch by Victor Stinner.

   - bpo-32424(4): Improve test coverage for xml.etree.ElementTree.
     Patch by Gordon P. Hemsley.

   - bpo-32424(5): Fix typo in test_cyclic_gc() test for
     xml.etree.ElementTree.  Patch by Gordon P. Hemsley.

   - bpo-36635(6): Add a new ‘_testinternalcapi’ module to test the
     internal C API.

   - bpo-36629(7): Fix ‘test_imap4_host_default_value()’ of
     ‘test_imaplib’: catch also *note errno.ENETUNREACH: 111f. error.

   - bpo-36611(8): Fix ‘test_sys.test_getallocatedblocks()’ when *note
     tracemalloc: 11d. is enabled.

   - bpo-36560(9): Fix reference leak hunting in regrtest: compute also
     deltas (of reference count, allocated memory blocks, file
     descriptor count) during warmup, to ensure that everything is
     initialized before starting to hunt reference leaks.

   - bpo-36565(10): Fix reference hunting (‘python3 -m test -R 3:3’)
     when Python has no built-in abc module.

   - bpo-31904(11): Port test_resource to VxWorks: skip tests cases
     setting RLIMIT_FSIZE and RLIMIT_CPU.

   - bpo-31904(12): Fix test_tabnanny on VxWorks: adjust ENOENT error
     message.

   - bpo-36436(13): Fix ‘_testcapi.pymem_buffer_overflow()’: handle
     memory allocation failure.

   - bpo-31904(14): Fix test_utf8_mode on VxWorks: Python always use
     UTF-8 on VxWorks.

   - bpo-36341(15): Fix tests that may fail with PermissionError upon
     calling bind() on AF_UNIX sockets.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36719

   (2) https://bugs.python.org/issue36725

   (3) https://bugs.python.org/issue36454

   (4) https://bugs.python.org/issue32424

   (5) https://bugs.python.org/issue32424

   (6) https://bugs.python.org/issue36635

   (7) https://bugs.python.org/issue36629

   (8) https://bugs.python.org/issue36611

   (9) https://bugs.python.org/issue36560

   (10) https://bugs.python.org/issue36565

   (11) https://bugs.python.org/issue31904

   (12) https://bugs.python.org/issue31904

   (13) https://bugs.python.org/issue36436

   (14) https://bugs.python.org/issue31904

   (15) https://bugs.python.org/issue36341


File: python.info,  Node: Build<21>,  Next: Windows<21>,  Prev: Tests<21>,  Up: Python 3 8 0 alpha 4

1.19.28.6 Build
...............

   - bpo-36747(1): Remove the stale scriptsinstall Makefile target.

   - bpo-21536(2): On Unix, C extensions are no longer linked to
     libpython except on Android and Cygwin.

     It is now possible for a statically linked Python to load a C
     extension built using a shared library Python.

     When Python is embedded, ‘libpython’ must not be loaded with
     ‘RTLD_LOCAL’, but ‘RTLD_GLOBAL’ instead.  Previously, using
     ‘RTLD_LOCAL’, it was already not possible to load C extensions
     which were not linked to ‘libpython’, such as C extensions of the
     standard library built by the ‘*shared*’ section of
     ‘Modules/Setup’.

     distutils, python-config and python-config.py have been modified.

   - bpo-36707(3): ‘./configure --with-pymalloc’ no longer adds the ‘m’
     flag to SOABI (sys.implementation.cache_tag).  Enabling or
     disabling pymalloc has no impact on the ABI.

   - bpo-36635(4): Change ‘PyAPI_FUNC(type)’, ‘PyAPI_DATA(type)’ and
     ‘PyMODINIT_FUNC’ macros of ‘pyport.h’ when ‘Py_BUILD_CORE_MODULE’
     is defined.  The ‘Py_BUILD_CORE_MODULE’ define must be now be used
     to build a C extension as a dynamic library accessing Python
     internals: export the PyInit_xxx() function in DLL exports on
     Windows.

   - bpo-31904(5): Don’t build the ‘_crypt’ extension on VxWorks.

   - bpo-36618(6): Add ‘-fmax-type-align=8’ to CFLAGS when clang
     compiler is detected.  The pymalloc memory allocator aligns memory
     on 8 bytes.  On x86-64, clang expects alignment on 16 bytes by
     default and so uses MOVAPS instruction which can lead to
     segmentation fault.  Instruct clang that Python is limited to
     alignment on 8 bytes to use MOVUPS instruction instead: slower but
     don’t trigger a SIGSEGV if the memory is not aligned on 16 bytes.
     Sadly, the flag must be added to ‘CFLAGS’ and not just
     ‘CFLAGS_NODIST’, since third party C extensions can have the same
     issue.

   - bpo-36605(7): ‘make tags’ and ‘make TAGS’ now also parse
     ‘Modules/_io/*.c’ and ‘Modules/_io/*.h’.

   - bpo-36465(8): Release builds and debug builds are now ABI
     compatible: defining the ‘Py_DEBUG’ macro no longer implies the
     ‘Py_TRACE_REFS’ macro, which introduces the only ABI
     incompatibility.  The ‘Py_TRACE_REFS’ macro, which adds the
     ‘sys.getobjects()’ function and the *note PYTHONDUMPREFS: 293.
     environment variable, can be set using the new ‘./configure
     --with-trace-refs’ build option.

   - bpo-36577(9): setup.py now correctly reports missing OpenSSL
     headers and libraries again.

   - bpo-36544(10): Fix regression introduced in bpo-36146(11)
     refactoring setup.py

   - bpo-36508(12): ‘python-config --ldflags’ no longer includes flags
     of the ‘LINKFORSHARED’ variable.  The ‘LINKFORSHARED’ variable must
     only be used to build executables.

   - bpo-36503(13): Remove references to “aix3” and “aix4”.  Patch by M.
     Felt.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36747

   (2) https://bugs.python.org/issue21536

   (3) https://bugs.python.org/issue36707

   (4) https://bugs.python.org/issue36635

   (5) https://bugs.python.org/issue31904

   (6) https://bugs.python.org/issue36618

   (7) https://bugs.python.org/issue36605

   (8) https://bugs.python.org/issue36465

   (9) https://bugs.python.org/issue36577

   (10) https://bugs.python.org/issue36544

   (11) https://bugs.python.org/issue36146

   (12) https://bugs.python.org/issue36508

   (13) https://bugs.python.org/issue36503


File: python.info,  Node: Windows<21>,  Next: macOS<19>,  Prev: Build<21>,  Up: Python 3 8 0 alpha 4

1.19.28.7 Windows
.................

   - bpo-35920(1): Added platform.win32_edition() and
     platform.win32_is_iot().  Added support for cross-compiling
     packages for Windows ARM32.  Skip tests that are not expected to
     work on Windows IoT Core ARM32.

   - bpo-36649(2): Remove trailing spaces for registry keys when
     installed via the Store.

   - bpo-34144(3): Fixed activate.bat to correctly update codepage when
     chcp.com returns dots in output.  Patch by Lorenz Mende.

   - bpo-36509(4): Added preset-iot layout for Windows IoT ARM
     containers.  This layout doesn’t contain UI components like tkinter
     or IDLE. It also doesn’t contain files to support on-target builds
     since Windows ARM32 builds must be cross-compiled when using MSVC.

   - bpo-35941(5): enum_certificates function of the ssl module now
     returns certificates from all available certificate stores inside
     windows in a query instead of returning only certificates from the
     system wide certificate store.  This includes certificates from
     these certificate stores: local machine, local machine enterprise,
     local machine group policy, current user, current user group
     policy, services, users.  ssl.enum_crls() function is changed in
     the same way to return all certificate revocation lists inside the
     windows certificate revocation list stores.

   - bpo-36441(6): Fixes creating a venv when debug binaries are
     installed.

   - bpo-36085(7): Enable better DLL resolution on Windows by using safe
     DLL search paths and adding *note os.add_dll_directory(): 2f3.

   - bpo-36010(8): Add the venv standard library module to the nuget
     distribution for Windows.

   - bpo-29515(9): Add the following socket module constants on Windows:
     IPPROTO_AH IPPROTO_CBT IPPROTO_DSTOPTS IPPROTO_EGP IPPROTO_ESP
     IPPROTO_FRAGMENT IPPROTO_GGP IPPROTO_HOPOPTS IPPROTO_ICLFXBM
     IPPROTO_ICMPV6 IPPROTO_IDP IPPROTO_IGMP IPPROTO_IGP IPPROTO_IPV4
     IPPROTO_IPV6 IPPROTO_L2TP IPPROTO_MAX IPPROTO_ND IPPROTO_NONE
     IPPROTO_PGM IPPROTO_PIM IPPROTO_PUP IPPROTO_RDP IPPROTO_ROUTING
     IPPROTO_SCTP IPPROTO_ST

   - bpo-35947(10): Added current version of libffi to
     cpython-source-deps.  Change _ctypes to use current version of
     libffi on Windows.

   - bpo-34060(11): Report system load when running test suite on
     Windows.  Patch by Ammar Askar.  Based on prior work by Jeremy
     Kloth.

   - bpo-31512(12): With the Windows 10 Creators Update, non-elevated
     users can now create symlinks as long as the computer has Developer
     Mode enabled.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35920

   (2) https://bugs.python.org/issue36649

   (3) https://bugs.python.org/issue34144

   (4) https://bugs.python.org/issue36509

   (5) https://bugs.python.org/issue35941

   (6) https://bugs.python.org/issue36441

   (7) https://bugs.python.org/issue36085

   (8) https://bugs.python.org/issue36010

   (9) https://bugs.python.org/issue29515

   (10) https://bugs.python.org/issue35947

   (11) https://bugs.python.org/issue34060

   (12) https://bugs.python.org/issue31512


File: python.info,  Node: macOS<19>,  Next: IDLE<21>,  Prev: Windows<21>,  Up: Python 3 8 0 alpha 4

1.19.28.8 macOS
...............

   - bpo-34602(1): Avoid failures setting macOS stack resource limit
     with resource.setrlimit.  This reverts an earlier fix for
     bpo-18075(2) which forced a non-default stack size when building
     the interpreter executable on macOS.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34602

   (2) https://bugs.python.org/issue18075


File: python.info,  Node: IDLE<21>,  Next: Tools/Demos<9>,  Prev: macOS<19>,  Up: Python 3 8 0 alpha 4

1.19.28.9 IDLE
..............

   - bpo-36429(1): Fix starting IDLE with pyshell.  Add idlelib.pyshell
     alias at top; remove pyshell alias at bottom.  Remove obsolete
     __name__==’__main__’ command.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36429


File: python.info,  Node: Tools/Demos<9>,  Next: C API<18>,  Prev: IDLE<21>,  Up: Python 3 8 0 alpha 4

1.19.28.10 Tools/Demos
......................

   - bpo-14546(1): Fix the argument handling in Tools/scripts/lll.py.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14546


File: python.info,  Node: C API<18>,  Prev: Tools/Demos<9>,  Up: Python 3 8 0 alpha 4

1.19.28.11 C API
................

   - bpo-36763(1): Fix memory leak in *note
     Py_SetStandardStreamEncoding(): a0a.: release memory if the
     function is called twice.

   - bpo-36641(2): ‘PyDoc_VAR(name)’ and ‘PyDoc_STRVAR(name,str)’ now
     create ‘static const char name[]’ instead of ‘static char name[]’.
     Patch by Inada Naoki.

   - bpo-36389(3): Change the value of ‘CLEANBYTE’, ‘DEADDYTE’ and
     ‘FORBIDDENBYTE’ internal constants used by debug hooks on Python
     memory allocators (*note PyMem_SetupDebugHooks(): 604. function).
     Byte patterns ‘0xCB’, ‘0xDB’ and ‘0xFB’ have been replaced with
     ‘0xCD’, ‘0xDD’ and ‘0xFD’ to use the same values than Windows CRT
     debug ‘malloc()’ and ‘free()’.

   - bpo-36443(4): Since Python 3.7.0, calling *note Py_DecodeLocale():
     53f. before *note Py_Initialize(): 20f. produces mojibake if the
     ‘LC_CTYPE’ locale is coerced and/or if the UTF-8 Mode is enabled by
     the user configuration.  The LC_CTYPE coercion and UTF-8 Mode are
     now disabled by default to fix the mojibake issue.  They must now
     be enabled explicitly (opt-in) using the new ‘_Py_PreInitialize()’
     API with ‘_PyPreConfig’.

   - bpo-36025(5): Fixed an accidental change to the datetime C API
     where the arguments to the *note PyDate_FromTimestamp(): 1126.
     function were incorrectly interpreted as a single timestamp rather
     than an arguments tuple, which causes existing code to start
     raising *note TypeError: 1fe.  The backwards-incompatible change
     was only present in alpha releases of Python 3.8.  Patch by Paul
     Ganssle.

   - bpo-35810(6): Modify ‘PyObject_Init’ to correctly increase the
     refcount of heap- allocated Type objects.  Also fix the refcounts
     of the heap-allocated types that were either doing this manually or
     not decreasing the type’s refcount in tp_dealloc

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36763

   (2) https://bugs.python.org/issue36641

   (3) https://bugs.python.org/issue36389

   (4) https://bugs.python.org/issue36443

   (5) https://bugs.python.org/issue36025

   (6) https://bugs.python.org/issue35810


File: python.info,  Node: Python 3 8 0 alpha 3,  Next: Python 3 8 0 alpha 2,  Prev: Python 3 8 0 alpha 4,  Up: Changelog

1.19.29 Python 3.8.0 alpha 3
----------------------------

`Release date: 2019-03-25'

* Menu:

* Security: Security<17>.
* Core and Builtins: Core and Builtins<26>.
* Library: Library<28>.
* Documentation: Documentation<23>.
* Tests: Tests<22>.
* Build: Build<22>.
* Windows: Windows<22>.
* IDLE: IDLE<22>.
* Tools/Demos: Tools/Demos<10>.
* C API: C API<19>.


File: python.info,  Node: Security<17>,  Next: Core and Builtins<26>,  Up: Python 3 8 0 alpha 3

1.19.29.1 Security
..................

   - bpo-36216(1): Changes urlsplit() to raise ValueError when the URL
     contains characters that decompose under IDNA encoding
     (NFKC-normalization) into characters that affect how the URL is
     parsed.

   - bpo-35121(2): Don’t send cookies of domain A without Domain
     attribute to domain B when domain A is a suffix match of domain B
     while using a cookiejar with *note
     http.cookiejar.DefaultCookiePolicy: 1129. policy.  Patch by
     Karthikeyan Singaravelan.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36216

   (2) https://bugs.python.org/issue35121


File: python.info,  Node: Core and Builtins<26>,  Next: Library<28>,  Prev: Security<17>,  Up: Python 3 8 0 alpha 3

1.19.29.2 Core and Builtins
...........................

   - bpo-36421(1): Fix a possible double decref in _ctypes.c’s
     ‘PyCArrayType_new()’.

   - bpo-36412(2): Fix a possible crash when creating a new dictionary.

   - bpo-36398(3): Fix a possible crash in ‘structseq_repr()’.

   - bpo-36256(4): Fix bug in parsermodule when parsing a state in a DFA
     that has two or more arcs with labels of the same type.  Patch by
     Pablo Galindo.

   - bpo-36365(5): repr(structseq) is no longer limited to 512 bytes.

   - bpo-36374(6): Fix a possible null pointer dereference in
     ‘merge_consts_recursive()’.  Patch by Zackery Spytz.

   - bpo-36236(7): At Python initialization, the current directory is no
     longer prepended to *note sys.path: 260. if it has been removed.

   - bpo-36352(8): Python initialization now fails with an error, rather
     than silently truncating paths, if a path is too long.

   - bpo-36301(9): Python initialization now fails if decoding
     ‘pybuilddir.txt’ configuration file fails at startup.

   - bpo-36333(10): Fix leak in _PyRuntimeState_Fini.  Contributed by
     Stéphane Wirtel.

   - bpo-36332(11): The builtin *note compile(): 2e7. can now handle AST
     objects that contain assignment expressions.  Patch by Pablo
     Galindo.

   - bpo-36282(12): Improved error message for too much positional
     arguments in some builtin functions.

   - bpo-30040(13): New empty dict uses fewer memory for now.  It used
     more memory than empty dict created by ‘dict.clear()’.  And empty
     dict creation and deletion is about 2x faster.  Patch by Inada
     Naoki.

   - bpo-36262(14): Fix an unlikely memory leak on conversion from
     string to float in the function ‘_Py_dg_strtod()’ used by
     ‘float(str)’, ‘complex(str)’, *note pickle.load(): 6b9, *note
     marshal.load(): 112b, etc.

   - bpo-36252(15): Update Unicode databases to version 12.0.0.

   - bpo-36218(16): Fix a segfault occurring when sorting a list of
     heterogeneous values.  Patch contributed by Rémi Lapeyre and Elliot
     Gorokhovsky.

   - bpo-36188(17): Cleaned up left-over vestiges of Python 2 unbound
     method handling in method objects and documentation.  Patch by
     Martijn Pieters

   - bpo-36124(18): Add a new interpreter-specific dict and expose it in
     the C-API via PyInterpreterState_GetDict().  This parallels
     PyThreadState_GetDict().  However, extension modules should
     continue using PyModule_GetState() for their own internal
     per-interpreter state.

   - bpo-35975(19): Add a ‘feature_version’ flag to ‘ast.parse()’
     (documented) and ‘compile()’ (hidden) that allows tweaking the
     parser to support older versions of the grammar.  In particular, if
     ‘feature_version’ is 5 or 6, the hacks for the ‘async’ and ‘await’
     keyword from PEP 492 are reinstated.  (For 7 or higher, these are
     unconditionally treated as keywords, but they are still special
     tokens rather than ‘NAME’ tokens that the parser driver
     recognizes.)

   - bpo-31904(20): Use UTF-8 as the system encoding on VxWorks.

   - bpo-36048(21): The *note __index__(): 2c2. special method will be
     used instead of *note __int__(): 2c3. for implicit conversion of
     Python numbers to C integers.  Using the ‘__int__()’ method in
     implicit conversions has been deprecated.

   - bpo-35808(22): Retire pgen and use a modified version of pgen2 to
     generate the parser.  Patch by Pablo Galindo.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36421

   (2) https://bugs.python.org/issue36412

   (3) https://bugs.python.org/issue36398

   (4) https://bugs.python.org/issue36256

   (5) https://bugs.python.org/issue36365

   (6) https://bugs.python.org/issue36374

   (7) https://bugs.python.org/issue36236

   (8) https://bugs.python.org/issue36352

   (9) https://bugs.python.org/issue36301

   (10) https://bugs.python.org/issue36333

   (11) https://bugs.python.org/issue36332

   (12) https://bugs.python.org/issue36282

   (13) https://bugs.python.org/issue30040

   (14) https://bugs.python.org/issue36262

   (15) https://bugs.python.org/issue36252

   (16) https://bugs.python.org/issue36218

   (17) https://bugs.python.org/issue36188

   (18) https://bugs.python.org/issue36124

   (19) https://bugs.python.org/issue35975

   (20) https://bugs.python.org/issue31904

   (21) https://bugs.python.org/issue36048

   (22) https://bugs.python.org/issue35808


File: python.info,  Node: Library<28>,  Next: Documentation<23>,  Prev: Core and Builtins<26>,  Up: Python 3 8 0 alpha 3

1.19.29.3 Library
.................

   - bpo-36401(1): The class documentation created by pydoc now has a
     separate section for readonly properties.

   - bpo-36320(2): The typing.NamedTuple() class has deprecated the
     _field_types attribute in favor of the __annotations__ attribute
     which carried the same information.  Also, both attributes were
     converted from OrderedDict to a regular dict.

   - bpo-34745(3): Fix *note asyncio: 9. ssl memory issues caused by
     circular references

   - bpo-36324(4): Add method to statistics.NormalDist for computing the
     inverse cumulative normal distribution.

   - bpo-36321(5): collections.namedtuple() misspelled the name of an
     attribute.  To be consistent with typing.NamedTuple, the attribute
     name should have been “_field_defaults” instead of
     “_fields_defaults”.  For backwards compatibility, both spellings
     are now created.  The misspelled version may be removed in the
     future.

   - bpo-36297(6): “unicode_internal” codec is removed.  It was
     deprecated since Python 3.3.  Patch by Inada Naoki.

   - bpo-36298(7): Raise ModuleNotFoundError in pyclbr when a module
     can’t be found.  Thanks to ‘mental’ for the bug report.

   - bpo-36268(8): Switch the default format used for writing tars with
     mod:*note tarfile: 101. to the modern POSIX.1-2001 pax standard,
     from the vendor-specific GNU. Contributed by C.A.M. Gerlach.

   - bpo-36285(9): Fix integer overflows in the array module.  Patch by
     Stephan Hohe.

   - bpo-31904(10): Add _signal module support for VxWorks.

   - bpo-36272(11): *note logging: aa. does not silently ignore
     RecursionError anymore.  Patch contributed by Rémi Lapeyre.

   - bpo-36280(12): Add a kind field to ast.Constant.  It is ‘u’ if the
     literal has a ‘u’ prefix (i.e.  a Python 2 style unicode literal),
     else None.

   - bpo-35931(13): The *note pdb: c9. ‘debug’ command now gracefully
     handles all exceptions.

   - bpo-36251(14): Fix format strings used for stderrprinter and
     re.Match reprs.  Patch by Stephan Hohe.

   - bpo-36235(15): Fix ‘CFLAGS’ in ‘customize_compiler()’ of
     ‘distutils.sysconfig’: when the ‘CFLAGS’ environment variable is
     defined, don’t override ‘CFLAGS’ variable with the ‘OPT’ variable
     anymore.  Initial patch written by David Malcolm.

   - bpo-35807(16): Update ensurepip to install pip 19.0.3 and
     setuptools 40.8.0.

   - bpo-36139(17): Release GIL when closing *note mmap: 31c. objects.

   - bpo-36179(18): Fix two unlikely reference leaks in _hashopenssl.
     The leaks only occur in out-of-memory cases.

   - bpo-36169(19): Add overlap() method to statistics.NormalDist.
     Computes the overlapping coefficient for two normal distributions.

   - bpo-36103(20): Default buffer size used by ‘shutil.copyfileobj()’
     is changed from 16 KiB to 64 KiB on non-Windows platform to reduce
     system call overhead.  Contributed by Inada Naoki.

   - bpo-36130(21): Fix ‘pdb’ with ‘skip=...’ when stepping into a frame
     without a ‘__name__’ global.  Patch by Anthony Sottile.

   - bpo-35652(22): shutil.copytree(copy_function=…) erroneously pass
     DirEntry instead of a path string.

   - bpo-35178(23): Ensure custom *note warnings.formatwarning(): 112d.
     function can receive ‘line’ as positional argument.  Based on patch
     by Tashrif Billah.

   - bpo-36106(24): Resolve potential name clash with libm’s sinpi().
     Patch by Dmitrii Pasechnik.

   - bpo-36091(25): Clean up reference to async generator in Lib/types.
     Patch by Henry Chen.

   - bpo-36043(26): ‘FileCookieJar’ supports *note path-like object:
     472.  Contributed by Stéphane Wirtel

   - bpo-35899(27): Enum has been fixed to correctly handle empty
     strings and strings with non-Latin characters (ie.  ‘α’, ‘א’)
     without crashing.  Original patch contributed by Maxwell.  Assisted
     by Stéphane Wirtel.

   - bpo-21269(28): Add ‘args’ and ‘kwargs’ properties to mock call
     objects.  Contributed by Kumar Akshay.

   - bpo-30670(29): *note pprint.pp: 340. has been added to pretty-print
     objects with dictionary keys being sorted with their insertion
     order by default.  Parameter `sort_dicts' has been added to *note
     pprint.pprint: 341, *note pprint.pformat: 97d. and *note
     pprint.PrettyPrinter: 97c.  Contributed by Rémi Lapeyre.

   - bpo-35843(30): Implement ‘__getitem__’ for ‘_NamespacePath’.  Patch
     by Anthony Sottile.

   - bpo-35802(31): Clean up code which checked presence of ‘os.stat’ /
     ‘os.lstat’ / ‘os.chmod’ which are always present.  Patch by Anthony
     Sottile.

   - bpo-35715(32): Librates the return value of a ProcessPoolExecutor
     _process_worker after it’s no longer needed to free memory

   - bpo-35493(33): Use *note multiprocessing.connection.wait(): b01.
     instead of polling each 0.2 seconds for worker updates in
     ‘multiprocessing.Pool’.  Patch by Pablo Galindo.

   - bpo-35661(34): Store the venv prompt in pyvenv.cfg.

   - bpo-35121(35): Don’t set cookie for a request when the request path
     is a prefix match of the cookie’s path attribute but doesn’t end
     with “/”.  Patch by Karthikeyan Singaravelan.

   - bpo-21478(36): Calls to a child function created with *note
     unittest.mock.create_autospec(): 1087. should propagate to the
     parent.  Patch by Karthikeyan Singaravelan.

   - bpo-35198(37): Fix C++ extension compilation on AIX

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36401

   (2) https://bugs.python.org/issue36320

   (3) https://bugs.python.org/issue34745

   (4) https://bugs.python.org/issue36324

   (5) https://bugs.python.org/issue36321

   (6) https://bugs.python.org/issue36297

   (7) https://bugs.python.org/issue36298

   (8) https://bugs.python.org/issue36268

   (9) https://bugs.python.org/issue36285

   (10) https://bugs.python.org/issue31904

   (11) https://bugs.python.org/issue36272

   (12) https://bugs.python.org/issue36280

   (13) https://bugs.python.org/issue35931

   (14) https://bugs.python.org/issue36251

   (15) https://bugs.python.org/issue36235

   (16) https://bugs.python.org/issue35807

   (17) https://bugs.python.org/issue36139

   (18) https://bugs.python.org/issue36179

   (19) https://bugs.python.org/issue36169

   (20) https://bugs.python.org/issue36103

   (21) https://bugs.python.org/issue36130

   (22) https://bugs.python.org/issue35652

   (23) https://bugs.python.org/issue35178

   (24) https://bugs.python.org/issue36106

   (25) https://bugs.python.org/issue36091

   (26) https://bugs.python.org/issue36043

   (27) https://bugs.python.org/issue35899

   (28) https://bugs.python.org/issue21269

   (29) https://bugs.python.org/issue30670

   (30) https://bugs.python.org/issue35843

   (31) https://bugs.python.org/issue35802

   (32) https://bugs.python.org/issue35715

   (33) https://bugs.python.org/issue35493

   (34) https://bugs.python.org/issue35661

   (35) https://bugs.python.org/issue35121

   (36) https://bugs.python.org/issue21478

   (37) https://bugs.python.org/issue35198


File: python.info,  Node: Documentation<23>,  Next: Tests<22>,  Prev: Library<28>,  Up: Python 3 8 0 alpha 3

1.19.29.4 Documentation
.......................

   - bpo-36329(1): Declare the path of the Python binary for the usage
     of ‘Tools/scripts/serve.py’ when executing ‘make -C Doc/ serve’.
     Contributed by Stéphane Wirtel

   - bpo-36138(2): Improve documentation about converting
     datetime.timedelta to scalars.

   - bpo-21314(3): A new entry was added to the Core Language Section of
     the Programming FAQ, which explaines the usage of slash(/) in the
     signature of a function.  Patch by Lysandros Nikolaou

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36329

   (2) https://bugs.python.org/issue36138

   (3) https://bugs.python.org/issue21314


File: python.info,  Node: Tests<22>,  Next: Build<22>,  Prev: Documentation<23>,  Up: Python 3 8 0 alpha 3

1.19.29.5 Tests
...............

   - bpo-36234(1): test_posix.PosixUidGidTests: add tests for invalid
     uid/gid type (str).  Initial patch written by David Malcolm.

   - bpo-29571(2): Fix ‘test_re.test_locale_flag()’: use
     ‘locale.getpreferredencoding()’ rather than ‘locale.getlocale()’ to
     get the locale encoding.  With some locales, ‘locale.getlocale()’
     returns the wrong encoding.

   - bpo-36123(3): Fix race condition in test_socket.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36234

   (2) https://bugs.python.org/issue29571

   (3) https://bugs.python.org/issue36123


File: python.info,  Node: Build<22>,  Next: Windows<22>,  Prev: Tests<22>,  Up: Python 3 8 0 alpha 3

1.19.29.6 Build
...............

   - bpo-36356(1): Fix leaks that led to build failure when configured
     with address sanitizer.

   - bpo-36146(2): Add ‘TEST_EXTENSIONS’ constant to ‘setup.py’ to allow
     to not build test extensions like ‘_testcapi’.

   - bpo-36146(3): Fix setup.py on macOS: only add ‘/usr/include/ffi’ to
     include directories of _ctypes, not for all extensions.

   - bpo-31904(4): Enable build system to cross-build for VxWorks RTOS.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36356

   (2) https://bugs.python.org/issue36146

   (3) https://bugs.python.org/issue36146

   (4) https://bugs.python.org/issue31904


File: python.info,  Node: Windows<22>,  Next: IDLE<22>,  Prev: Build<22>,  Up: Python 3 8 0 alpha 3

1.19.29.7 Windows
.................

   - bpo-36312(1): Fixed decoders for the following code pages: 50220,
     50221, 50222, 50225, 50227, 50229, 57002 through 57011, 65000 and
     42.

   - bpo-36264(2): Don’t honor POSIX ‘HOME’ in ‘os.path.expanduser’ on
     windows.  Patch by Anthony Sottile.

   - bpo-24643(3): Fix name collisions due to ‘#define timezone
     _timezone’ in PC/pyconfig.h.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36312

   (2) https://bugs.python.org/issue36264

   (3) https://bugs.python.org/issue24643


File: python.info,  Node: IDLE<22>,  Next: Tools/Demos<10>,  Prev: Windows<22>,  Up: Python 3 8 0 alpha 3

1.19.29.8 IDLE
..............

   - bpo-36405(1): Use dict unpacking in idlelib.

   - bpo-36396(2): Remove fgBg param of idlelib.config.GetHighlight().
     This param was only used twice and changed the return type.

   - bpo-36176(3): Fix IDLE autocomplete & calltip popup colors.
     Prevent conflicts with Linux dark themes (and slightly darken
     calltip background).

   - bpo-23205(4): For the grep module, add tests for findfiles,
     refactor findfiles to be a module-level function, and refactor
     findfiles to use os.walk.

   - bpo-23216(5): Add docstrings to IDLE search modules.

   - bpo-36152(6): Remove colorizer.ColorDelegator.close_when_done and
     the corresponding argument of .close().  In IDLE, both have always
     been None or False since 2007.

   - bpo-32129(7): Avoid blurry IDLE application icon on macOS with Tk
     8.6.  Patch by Kevin Walzer.

   - bpo-36096(8): Refactor class variables to instance variables in
     colorizer.

   - bpo-30348(9): Increase test coverage of idlelib.autocomplete by
     30%.  Patch by Louie Lu

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36405

   (2) https://bugs.python.org/issue36396

   (3) https://bugs.python.org/issue36176

   (4) https://bugs.python.org/issue23205

   (5) https://bugs.python.org/issue23216

   (6) https://bugs.python.org/issue36152

   (7) https://bugs.python.org/issue32129

   (8) https://bugs.python.org/issue36096

   (9) https://bugs.python.org/issue30348


File: python.info,  Node: Tools/Demos<10>,  Next: C API<19>,  Prev: IDLE<22>,  Up: Python 3 8 0 alpha 3

1.19.29.9 Tools/Demos
.....................

   - bpo-35132(1): Fix py-list and py-bt commands of python-gdb.py on
     gdb7.

   - bpo-32217(2): Fix freeze script on Windows.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35132

   (2) https://bugs.python.org/issue32217


File: python.info,  Node: C API<19>,  Prev: Tools/Demos<10>,  Up: Python 3 8 0 alpha 3

1.19.29.10 C API
................

   - bpo-36381(1): Raise ‘DeprecationWarning’ when ‘#’ formats are used
     for building or parsing values without ‘PY_SSIZE_T_CLEAN’.

   - bpo-36142(2): The whole coreconfig.h header is now excluded from
     Py_LIMITED_API. Move functions definitions into a new internal
     pycore_coreconfig.h header.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36381

   (2) https://bugs.python.org/issue36142


File: python.info,  Node: Python 3 8 0 alpha 2,  Next: Python 3 8 0 alpha 1,  Prev: Python 3 8 0 alpha 3,  Up: Changelog

1.19.30 Python 3.8.0 alpha 2
----------------------------

`Release date: 2019-02-25'

* Menu:

* Core and Builtins: Core and Builtins<27>.
* Library: Library<29>.
* Documentation: Documentation<24>.
* Tests: Tests<23>.
* Windows: Windows<23>.
* IDLE: IDLE<23>.


File: python.info,  Node: Core and Builtins<27>,  Next: Library<29>,  Up: Python 3 8 0 alpha 2

1.19.30.1 Core and Builtins
...........................

   - bpo-36052(1): Raise a *note SyntaxError: 55a. when assigning a
     value to *note __debug__: 1137. with the Assignment Operator.
     Contributed by Stéphane Wirtel and Pablo Galindo.

   - bpo-36012(2): Doubled the speed of class variable writes.  When a
     non-dunder attribute was updated, there was an unnecessary call to
     update slots.

   - bpo-35942(3): The error message emitted when returning invalid
     types from ‘__fspath__’ in interfaces that allow passing *note
     PathLike: 5e6. objects has been improved and now it does explain
     the origin of the error.

   - bpo-36016(4): ‘gc.get_objects’ can now receive an optional
     parameter indicating a generation to get objects from.  Patch by
     Pablo Galindo.

   - bpo-1054041(5): When the main interpreter exits due to an uncaught
     KeyboardInterrupt, the process now exits in the appropriate manner
     for its parent process to detect that a SIGINT or ^C terminated the
     process.  This allows shells and batch scripts to understand that
     the user has asked them to stop.

   - bpo-35992(6): Fix ‘__class_getitem__()’ not being called on a class
     with a custom non-subscriptable metaclass.

   - bpo-35993(7): Fix a crash on fork when using subinterpreters.
     Contributed by Stéphane Wirtel

   - bpo-35991(8): Fix a potential double free in
     Modules/_randommodule.c.

   - bpo-35961(9): Fix a crash in slice_richcompare(): use strong
     references rather than stolen references for the two temporary
     internal tuples.

   - bpo-35911(10): Enable the creation of cell objects by adding a
     ‘cell.__new__’ method, and expose the type ‘cell’ in ‘Lib/types.py’
     under the name CellType.  Patch by Pierre Glaser.

   - bpo-12822(11): Use monotonic clock for ‘pthread_cond_timedwait’
     when ‘pthread_condattr_setclock’ and ‘CLOCK_MONOTONIC’ are
     available.

   - bpo-15248(12): The compiler emits now syntax warnings in the case
     when a comma is likely missed before tuple or list.

   - bpo-35886(13): The implementation of PyInterpreterState has been
     moved into the internal header files (guarded by Py_BUILD_CORE).

   - bpo-31506(14): Clarify the errors reported when ‘object.__new__’
     and ‘object.__init__’ receive more than one argument.  Contributed
     by Sanyam Khurana.

   - bpo-35724(15): Signal-handling is now guaranteed to happen relative
     to the main interpreter.

   - bpo-33608(16): We added a new internal _Py_AddPendingCall() that
     operates relative to the provided interpreter.  This allows us to
     use the existing implementation to ask another interpreter to do
     work that cannot be done in the current interpreter, like decref an
     object the other interpreter owns.  The existing
     Py_AddPendingCall() only operates relative to the main interpreter.

   - bpo-33989(17): Fix a possible crash in *note list.sort(): 548. when
     sorting objects with ‘ob_type->tp_richcompare == NULL’.  Patch by
     Zackery Spytz.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36052

   (2) https://bugs.python.org/issue36012

   (3) https://bugs.python.org/issue35942

   (4) https://bugs.python.org/issue36016

   (5) https://bugs.python.org/issue1054041

   (6) https://bugs.python.org/issue35992

   (7) https://bugs.python.org/issue35993

   (8) https://bugs.python.org/issue35991

   (9) https://bugs.python.org/issue35961

   (10) https://bugs.python.org/issue35911

   (11) https://bugs.python.org/issue12822

   (12) https://bugs.python.org/issue15248

   (13) https://bugs.python.org/issue35886

   (14) https://bugs.python.org/issue31506

   (15) https://bugs.python.org/issue35724

   (16) https://bugs.python.org/issue33608

   (17) https://bugs.python.org/issue33989


File: python.info,  Node: Library<29>,  Next: Documentation<24>,  Prev: Core and Builtins<27>,  Up: Python 3 8 0 alpha 2

1.19.30.2 Library
.................

   - bpo-35512(1): *note unittest.mock.patch.dict(): 110a. used as a
     decorator with string target resolves the target during function
     call instead of during decorator construction.  Patch by
     Karthikeyan Singaravelan.

   - bpo-36018(2): Add statistics.NormalDist, a tool for creating and
     manipulating normal distributions of random variable.  Features a
     composite class that treats the mean and standard deviation of
     measurement data as single entity.

   - bpo-35904(3): Added statistics.fmean() as a faster, floating point
     variant of the existing mean() function.

   - bpo-35918(4): Removed broken ‘has_key’ method from
     multiprocessing.managers.SyncManager.dict.  Contributed by Rémi
     Lapeyre.

   - bpo-18283(5): Add support for bytes to *note shutil.which(): fe6.

   - bpo-35960(6): Fix *note dataclasses.field(): 1139. throwing away
     empty mapping objects passed as metadata.

   - bpo-35500(7): Write expected and actual call parameters on separate
     lines in *note unittest.mock.Mock.assert_called_with(): 113a.
     assertion errors.  Contributed by Susan Su.

   - bpo-35931(8): The *note pdb: c9. ‘debug’ command now gracefully
     handles syntax errors.

   - bpo-24209(9): In http.server script, rely on getaddrinfo to bind to
     preferred address based on the bind parameter.  Now default bind or
     binding to a name may bind to IPv6 or dual-stack, depending on the
     environment.

   - bpo-35321(10): Set ‘__spec__.origin’ of ‘_frozen_importlib’ to
     frozen so that it matches the behavior of
     ‘_frozen_importlib_external’.  Patch by Nina Zakharenko.

   - bpo-35378(11): Fix a reference issue inside ‘multiprocessing.Pool’
     that caused the pool to remain alive if it was deleted without
     being closed or terminated explicitly.  A new strong reference is
     added to the pool iterators to link the lifetime of the pool to the
     lifetime of its iterators so the pool does not get destroyed if a
     pool iterator is still alive.

   - bpo-34294(12): re module, fix wrong capturing groups in rare cases.
     *note re.search(): c82, *note re.findall(): a44, *note re.sub():
     57a. and other functions that scan through string looking for a
     match, should reset capturing groups between two match attempts.
     Patch by Ma Lin.

   - bpo-35615(13): *note weakref: 131.: Fix a RuntimeError when copying
     a WeakKeyDictionary or a WeakValueDictionary, due to some keys or
     values disappearing while iterating.

   - bpo-35606(14): Implement *note math.prod(): 315. as analogous
     function to *note sum(): 316. that returns the product of a ‘start’
     value (default: 1) times an iterable of numbers.  Patch by Pablo
     Galindo.

   - bpo-32417(15): Performing arithmetic between *note
     datetime.datetime: 1a0. subclasses and *note datetime.timedelta:
     2ca. now returns an object of the same type as the *note
     datetime.datetime: 1a0. subclass.  As a result, *note
     datetime.datetime.astimezone(): 2cb. and alternate constructors
     like *note datetime.datetime.now(): 113b. and
     ‘datetime.fromtimestamp()’ called with a ‘tz’ argument now `also'
     retain their subclass.

   - bpo-35153(16): Add `headers' optional keyword-only parameter to
     *note xmlrpc.client.ServerProxy: 37f, ‘xmlrpc.client.Transport’ and
     ‘xmlrpc.client.SafeTransport’.  Patch by Cédric Krier.

   - bpo-34572(17): Fix C implementation of pickle.loads to use
     importlib’s locking mechanisms, and thereby avoid using
     partially-loaded modules.  Patch by Tim Burgess.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35512

   (2) https://bugs.python.org/issue36018

   (3) https://bugs.python.org/issue35904

   (4) https://bugs.python.org/issue35918

   (5) https://bugs.python.org/issue18283

   (6) https://bugs.python.org/issue35960

   (7) https://bugs.python.org/issue35500

   (8) https://bugs.python.org/issue35931

   (9) https://bugs.python.org/issue24209

   (10) https://bugs.python.org/issue35321

   (11) https://bugs.python.org/issue35378

   (12) https://bugs.python.org/issue34294

   (13) https://bugs.python.org/issue35615

   (14) https://bugs.python.org/issue35606

   (15) https://bugs.python.org/issue32417

   (16) https://bugs.python.org/issue35153

   (17) https://bugs.python.org/issue34572


File: python.info,  Node: Documentation<24>,  Next: Tests<23>,  Prev: Library<29>,  Up: Python 3 8 0 alpha 2

1.19.30.3 Documentation
.......................

   - bpo-36083(1): Fix formatting of –check-hash-based-pycs options in
     the manpage Synopsis.

   - bpo-36007(2): Bump minimum sphinx version to 1.8.  Patch by Anthony
     Sottile.

   - bpo-22062(3): Update documentation and docstrings for pathlib.
     Original patch by Mike Short.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue36083

   (2) https://bugs.python.org/issue36007

   (3) https://bugs.python.org/issue22062


File: python.info,  Node: Tests<23>,  Next: Windows<23>,  Prev: Documentation<24>,  Up: Python 3 8 0 alpha 2

1.19.30.4 Tests
...............

   - bpo-27313(1): Avoid test_ttk_guionly ComboboxTest failure with
     macOS Cocoa Tk.

   - bpo-36019(2): Add test.support.TEST_HTTP_URL and replace references
     of ‘http://www.example.com’ by this new constant.  Contributed by
     Stéphane Wirtel.

   - bpo-36037(3): Fix test_ssl for strict OpenSSL configuration like
     RHEL8 strict crypto policy.  Use older TLS version for minimum TLS
     version of the server SSL context if needed, to test TLS version
     older than default minimum TLS version.

   - bpo-35798(4): Added *note test.support.check_syntax_warning():
     113e.

   - bpo-35505(5): Make test_imap4_host_default_value independent on
     whether the local IMAP server is running.

   - bpo-35917(6): multiprocessing: provide unit tests for SyncManager
     and SharedMemoryManager classes + all the shareable types which are
     supposed to be supported by them.  (patch by Giampaolo Rodola)

   - bpo-35704(7): Skip ‘test_shutil.test_unpack_archive_xztar’ to
     prevent a MemoryError on 32-bit AIX when MAXDATA setting is less
     than 0x20000000.

     Patch by Michael Felt (aixtools)

   - bpo-34720(8): Assert m_state != NULL to mimic GC traversal
     functions that do not correctly handle module creation when the
     module state has not been created.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27313

   (2) https://bugs.python.org/issue36019

   (3) https://bugs.python.org/issue36037

   (4) https://bugs.python.org/issue35798

   (5) https://bugs.python.org/issue35505

   (6) https://bugs.python.org/issue35917

   (7) https://bugs.python.org/issue35704

   (8) https://bugs.python.org/issue34720


File: python.info,  Node: Windows<23>,  Next: IDLE<23>,  Prev: Tests<23>,  Up: Python 3 8 0 alpha 2

1.19.30.5 Windows
.................

   - bpo-35976(1): Added ARM build support to Windows build files in
     PCBuild.

   - bpo-35692(2): ‘pathlib’ no longer raises when checking file and
     directory existence on drives that are not ready

   - bpo-35872(3): Uses the base Python executable when invoking venv in
     a virtual environment

   - bpo-35873(4): Prevents venv paths being inherited by child
     processes

   - bpo-35299(5): Fix sysconfig detection of the source directory and
     distutils handling of pyconfig.h during PGO profiling

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35976

   (2) https://bugs.python.org/issue35692

   (3) https://bugs.python.org/issue35872

   (4) https://bugs.python.org/issue35873

   (5) https://bugs.python.org/issue35299


File: python.info,  Node: IDLE<23>,  Prev: Windows<23>,  Up: Python 3 8 0 alpha 2

1.19.30.6 IDLE
..............

   - bpo-24310(1): IDLE – Document settings dialog font tab sample.

   - bpo-35833(2): Revise IDLE doc for control codes sent to Shell.  Add
     a code example block.

   - bpo-35689(3): Add docstrings and unittests for colorizer.py.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24310

   (2) https://bugs.python.org/issue35833

   (3) https://bugs.python.org/issue35689


File: python.info,  Node: Python 3 8 0 alpha 1,  Next: Python 3 7 0 final,  Prev: Python 3 8 0 alpha 2,  Up: Changelog

1.19.31 Python 3.8.0 alpha 1
----------------------------

`Release date: 2019-02-03'

* Menu:

* Security: Security<18>.
* Core and Builtins: Core and Builtins<28>.
* Library: Library<30>.
* Documentation: Documentation<25>.
* Tests: Tests<24>.
* Build: Build<23>.
* Windows: Windows<24>.
* macOS: macOS<20>.
* IDLE: IDLE<24>.
* Tools/Demos: Tools/Demos<11>.
* C API: C API<20>.


File: python.info,  Node: Security<18>,  Next: Core and Builtins<28>,  Up: Python 3 8 0 alpha 1

1.19.31.1 Security
..................

   - bpo-35746(1): [CVE-2019-5010] Fix a NULL pointer deref in ssl
     module.  The cert parser did not handle CRL distribution points
     with empty DP or URI correctly.  A malicious or buggy certificate
     can result into segfault.  Vulnerability (TALOS-2018-0758) reported
     by Colin Read and Nicolas Edet of Cisco.

   - bpo-34812(2): The *note -I: 232. command line option (run Python in
     isolated mode) is now also copied by the *note multiprocessing: b7.
     and *note distutils: 38. modules when spawning child processes.
     Previously, only *note -E: 231. and *note -s: ddb. options (enabled
     by *note -I: 232.) were copied.

   - bpo-34791(3): The xml.sax and xml.dom.domreg no longer use
     environment variables to override parser implementations when
     sys.flags.ignore_environment is set by -E or -I arguments.

   - bpo-17239(4): The xml.sax and xml.dom.minidom parsers no longer
     processes external entities by default.  External DTD and ENTITY
     declarations no longer load files or create network connections.

   - bpo-34623(5): CVE-2018-14647: The C accelerated _elementtree module
     now initializes hash randomization salt from _Py_HashSecret instead
     of libexpat’s default CSPRNG.

   - bpo-34405(6): Updated to OpenSSL 1.1.0i for Windows builds.

   - bpo-33871(7): Fixed sending the part of the file in *note
     os.sendfile(): 461. on macOS. Using the `trailers' argument could
     cause sending more bytes from the input file than was specified.

   - bpo-32533(8): Fixed thread-safety of error handling in _ssl.

   - bpo-33136(9): Harden ssl module against LibreSSL CVE-2018-8970.
     X509_VERIFY_PARAM_set1_host() is called with an explicit namelen.
     A new test ensures that NULL bytes are not allowed.

   - bpo-33001(10): Minimal fix to prevent buffer overrun in os.symlink
     on Windows

   - bpo-32981(11): Regexes in difflib and poplib were vulnerable to
     catastrophic backtracking.  These regexes formed potential DOS
     vectors (REDOS). They have been refactored.  This resolves
     CVE-2018-1060 and CVE-2018-1061.  Patch by Jamie Davis.

   - bpo-28414(12): The ssl module now allows users to perform their own
     IDN en/decoding when using SNI.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35746

   (2) https://bugs.python.org/issue34812

   (3) https://bugs.python.org/issue34791

   (4) https://bugs.python.org/issue17239

   (5) https://bugs.python.org/issue34623

   (6) https://bugs.python.org/issue34405

   (7) https://bugs.python.org/issue33871

   (8) https://bugs.python.org/issue32533

   (9) https://bugs.python.org/issue33136

   (10) https://bugs.python.org/issue33001

   (11) https://bugs.python.org/issue32981

   (12) https://bugs.python.org/issue28414


File: python.info,  Node: Core and Builtins<28>,  Next: Library<30>,  Prev: Security<18>,  Up: Python 3 8 0 alpha 1

1.19.31.2 Core and Builtins
...........................

   - bpo-35877(1): Make parenthesis optional for named expressions in
     while statement.  Patch by Karthikeyan Singaravelan.

   - bpo-35814(2): Allow same right hand side expressions in annotated
     assignments as in normal ones.  In particular, ‘x: Tuple[int, int]
     = 1, 2’ (without parentheses on the right) is now allowed.

   - bpo-35766(3): Add the option to parse PEP 484 type comments in the
     ast module.  (Off by default.)  This is merging the key
     functionality of the third party fork thereof,
     [typed_ast](‘https://github.com/python/typed_ast’).

   - bpo-35713(4): Reorganize Python initialization to get working
     exceptions and sys.stderr earlier.

   - bpo-33416(5): Add end line and end column position information to
     the Python AST nodes.  This is a C-level backwards incompatible
     change.

   - bpo-35720(6): Fixed a minor memory leak in
     pymain_parse_cmdline_impl function in Modules/main.c

   - bpo-35634(7): ‘func(**kwargs)’ will now raise an error when
     ‘kwargs’ is a mapping containing multiple entries with the same
     key.  An error was already raised when other keyword arguments are
     passed before ‘**kwargs’ since Python 3.6.

   - bpo-35623(8): Fix a crash when sorting very long lists.  Patch by
     Stephan Hohe.

   - bpo-35214(9): clang Memory Sanitizer build instrumentation was
     added to work around false positives from posix, socket, time,
     test_io, and test_faulthandler.

   - bpo-35560(10): Fix an assertion error in *note format(): 5d6. in
     debug build for floating point formatting with “n” format, zero
     padding and small width.  Release build is not impacted.  Patch by
     Karthikeyan Singaravelan.

   - bpo-35552(11): Format characters ‘%s’ and ‘%V’ in *note
     PyUnicode_FromFormat(): 8b8. and ‘%s’ in *note
     PyBytes_FromFormat(): 1144. no longer read memory past the limit if
     `precision' is specified.

   - bpo-35504(12): Fix segfaults and *note SystemError: 6f2.s when
     deleting certain attributes.  Patch by Zackery Spytz.

   - bpo-35504(13): Fixed a SystemError when delete the
     characters_written attribute of an OSError.

   - bpo-35494(14): Improved syntax error messages for unbalanced
     parentheses in f-string.

   - bpo-35444(15): Fixed error handling in pickling methods when fail
     to look up builtin “getattr”.  Sped up pickling iterators.

   - bpo-35436(16): Fix various issues with memory allocation error
     handling.  Patch by Zackery Spytz.

   - bpo-35423(17): Separate the signal handling trigger in the eval
     loop from the “pending calls” machinery.  There is no semantic
     change and the difference in performance is insignificant.

   - bpo-35357(18): Internal attributes’ names of unittest.mock._Call
     and unittest.mock.MagicProxy (name, parent & from_kall) are now
     prefixed with _mock_ in order to prevent clashes with widely used
     object attributes.  Fixed minor typo in test function name.

   - bpo-35372(19): Fixed the code page decoder for input longer than 2
     GiB containing undecodable bytes.

   - bpo-35336(20): Fix PYTHONCOERCECLOCALE=1 environment variable: only
     coerce the C locale if the LC_CTYPE locale is “C”.

   - bpo-31241(21): The `lineno' and `col_offset' attributes of AST
     nodes for list comprehensions, generator expressions and tuples are
     now point to the opening parenthesis or square brace.  For tuples
     without parenthesis they point to the position of the first item.

   - bpo-33954(22): For *note str.format(): 5d5, ‘float.__format__()’
     and ‘complex.__format__()’ methods for non-ASCII decimal point when
     using the “n” formatter.

   - bpo-35269(23): Fix a possible segfault involving a newly-created
     coroutine.  Patch by Zackery Spytz.

   - bpo-35224(24): Implement PEP 572(25) (assignment expressions).
     Patch by Emily Morehouse.

   - bpo-32492(26): Speed up ‘namedtuple’ attribute access by 1.6x using
     a C fast-path for the name descriptors.  Patch by Pablo Galindo.

   - bpo-35214(27): Fixed an out of bounds memory access when parsing a
     truncated unicode escape sequence at the end of a string such as
     ‘'\N'’.  It would read one byte beyond the end of the memory
     allocation.

   - bpo-35214(28): The interpreter and extension modules have had
     annotations added so that they work properly under clang’s Memory
     Sanitizer.  A new configure flag –with-memory-sanitizer has been
     added to make test builds of this nature easier to perform.

   - bpo-35193(29): Fix an off by one error in the bytecode peephole
     optimizer where it could read bytes beyond the end of bounds of an
     array when removing unreachable code.  This bug was present in
     every release of Python 3.6 and 3.7 until now.

   - bpo-35169(30): Improved error messages for forbidden assignments.

   - bpo-34022(31): Fix handling of hash-based bytecode files in *note
     zipimport: 14c.  Patch by Elvis Pranskevichus.

   - bpo-28401(32): Debug builds will no longer to attempt to import
     extension modules built for the ABI as they were never compatible
     to begin with.  Patch by Stefano Rivera.

   - bpo-29341(33): Clarify in the docstrings of *note os: c4. methods
     that path-like objects are also accepted as input parameters.

   - bpo-35050(34): *note socket: ef.: Fix off-by-one bug in length
     check for ‘AF_ALG’ name and type.

   - bpo-29743(35): Raise *note ValueError: 16d. instead of *note
     OverflowError: a41. in case of a negative ‘_length_’ in a *note
     ctypes.Array: 1145. subclass.  Also raise *note TypeError: 1fe.
     instead of *note AttributeError: 4a2. for non-integer ‘_length_’.
     Original patch by Oren Milman.

   - bpo-16806(36): Fix ‘lineno’ and ‘col_offset’ for multi-line string
     tokens.

   - bpo-35029(37): *note SyntaxWarning: 2c9. raised as an exception at
     code generation time will be now replaced with a *note SyntaxError:
     55a. for better error reporting.

   - bpo-34983(38): Expose *note symtable.Symbol.is_nonlocal(): 1146. in
     the symtable module.  Patch by Pablo Galindo.

   - bpo-34974(39): *note bytes: 172. and *note bytearray: 173.
     constructors no longer convert unexpected exceptions (e.g.  *note
     MemoryError: f69. and *note KeyboardInterrupt: 2cc.) to *note
     TypeError: 1fe.

   - bpo-34939(40): Allow annotated names in module namespace that are
     declared global before the annotation happens.  Patch by Pablo
     Galindo.

   - bpo-34973(41): Fixed crash in *note bytes(): 172. when the *note
     list: 1f8. argument is mutated while it is iterated.

   - bpo-34876(42): The `lineno' and `col_offset' attributes of the AST
     for decorated function and class refer now to the position of the
     corresponding ‘def’, ‘async def’ and ‘class’ instead of the
     position of the first decorator.  This leads to more correct line
     reporting in tracing.  This is the only case when the position of
     child AST nodes can precede the position of the parent AST node.

   - bpo-34879(43): Fix a possible null pointer dereference in
     bytesobject.c.  Patch by Zackery Spytz.

   - bpo-34784(44): Fix the implementation of PyStructSequence_NewType
     in order to create heap allocated StructSequences.

   - bpo-32912(45): A *note SyntaxWarning: 2c9. is now emitted instead
     of a *note DeprecationWarning: 15a. for invalid escape sequences in
     string and bytes literals.

   - bpo-34854(46): Fixed a crash in compiling string annotations
     containing a lambda with a keyword-only argument that doesn’t have
     a default value.

   - bpo-34850(47): The compiler now produces a *note SyntaxWarning:
     2c9. when identity checks (‘is’ and ‘is not’) are used with certain
     types of literals (e.g.  strings, ints).  These can often work by
     accident in CPython, but are not guaranteed by the language spec.
     The warning advises users to use equality tests (‘==’ and ‘!=’)
     instead.

   - bpo-34824(48): Fix a possible null pointer dereference in
     Modules/_ssl.c.  Patch by Zackery Spytz.

   - bpo-30156(49): The C function ‘property_descr_get()’ uses a
     “cached” tuple to optimize function calls.  But this tuple can be
     discovered in debug mode with ‘sys.getobjects()’.  Remove the
     optimization, it’s not really worth it and it causes 3 different
     crashes last years.

   - bpo-34762(50): Fix contextvars C API to use PyObject* pointer
     types.

   - bpo-34751(51): The hash function for tuples is now based on xxHash
     which gives better collision results on (formerly) pathological
     cases.  Additionally, on 64-bit systems it improves tuple hashes in
     general.  Patch by Jeroen Demeyer with substantial contributions by
     Tim Peters.

   - bpo-34735(52): Fix a memory leak in Modules/timemodule.c.  Patch by
     Zackery Spytz.

   - bpo-34683(53): Fixed a bug where some SyntaxError error pointed to
     locations that were off-by-one.

   - bpo-34651(54): Only allow the main interpreter to fork.  The avoids
     the possibility of affecting the main interpreter, which is
     critical to operation of the runtime.

   - bpo-34653(55): Remove unused function
     PyParser_SimpleParseStringFilename.

   - bpo-32236(56): Warn that line buffering is not supported if *note
     open(): 16f. is called with binary mode and ‘buffering=1’.

   - bpo-34641(57): Further restrict the syntax of the left-hand side of
     keyword arguments in function calls.  In particular,
     ‘f((keyword)=arg)’ is now disallowed.

   - bpo-34637(58): Make the `start' argument to `sum()' visible as a
     keyword argument.

   - bpo-1621(59): Do not assume signed integer overflow behavior (C
     undefined behavior) when performing set hash table resizing.

   - bpo-34588(60): Fix an off-by-one in the recursive call pruning
     feature of traceback formatting.

   - bpo-34485(61): On Windows, the LC_CTYPE is now set to the user
     preferred locale at startup.  Previously, the LC_CTYPE locale was
     “C” at startup, but changed when calling setlocale(LC_CTYPE, “”) or
     setlocale(LC_ALL, “”).

   - bpo-34485(62): Standard streams like sys.stdout now use the
     “surrogateescape” error handler, instead of “strict”, on the POSIX
     locale (when the C locale is not coerced and the UTF-8 Mode is
     disabled).

   - bpo-34485(63): Fix the error handler of standard streams like
     sys.stdout: PYTHONIOENCODING=”:” is now ignored instead of setting
     the error handler to “strict”.

   - bpo-34485(64): Python now gets the locale encoding with C code to
     initialize the encoding of standard streams like sys.stdout.
     Moreover, the encoding is now initialized to the Python codec name
     to get a normalized encoding name and to ensure that the codec is
     loaded.  The change avoids importing _bootlocale and _locale
     modules at startup by default.

   - bpo-34527(65): On FreeBSD, Py_DecodeLocale() and Py_EncodeLocale()
     now also forces the ASCII encoding if the LC_CTYPE locale is
     “POSIX”, not only if the LC_CTYPE locale is “C”.

   - bpo-34527(66): The UTF-8 Mode is now also enabled by the “POSIX”
     locale, not only by the “C” locale.

   - bpo-34403(67): On HP-UX with C or POSIX locale,
     sys.getfilesystemencoding() now returns “ascii” instead of “roman8”
     (when the UTF-8 Mode is disabled and the C locale is not coerced).

   - bpo-34523(68): The Python filesystem encoding is now read earlier
     during the Python initialization.

   - bpo-12458(69): Tracebacks show now correct line number for
     subexpressions in multiline expressions.  Tracebacks show now the
     line number of the first line for multiline expressions instead of
     the line number of the last subexpression.

   - bpo-34408(70): Prevent a null pointer dereference and resource
     leakage in ‘PyInterpreterState_New()’.

   - bpo-34400(71): Fix undefined behavior in parsetok.c.  Patch by
     Zackery Spytz.

   - bpo-33073(72): Added as_integer_ratio to ints to make them more
     interoperable with floats.

   - bpo-34377(73): Update valgrind suppression list to use
     ‘_PyObject_Free’/‘_PyObject_Realloc’ instead of
     ‘PyObject_Free’/‘PyObject_Realloc’.

   - bpo-34353(74): Added the “socket” option in the *note
     stat.filemode(): b75. Python implementation to match the C
     implementation.

   - bpo-34320(75): Fix ‘dict(od)’ didn’t copy iteration order of
     OrderedDict.

   - bpo-34113(76): Fixed crash on debug builds when opcode stack was
     adjusted with negative numbers.  Patch by Constantin Petrisor.

   - bpo-34100(77): Compiler now merges constants in tuples and
     frozensets recursively.  Code attributes like ‘co_names’ are merged
     too.

   - bpo-34151(78): Performance of list concatenation, repetition and
     slicing operations is slightly improved.  Patch by Sergey Fedoseev.

   - bpo-34170(79): -X dev: it is now possible to override the memory
     allocator using PYTHONMALLOC even if the developer mode is enabled.

   - bpo-33237(80): Improved *note AttributeError: 4a2. message for
     partially initialized module.

   - bpo-34149(81): Fix min and max functions to get default behavior
     when key is None.

   - bpo-34125(82): Profiling of unbound built-in methods now works when
     ‘**kwargs’ is given.

   - bpo-34141(83): Optimized pickling atomic types (None, bool, int,
     float, bytes, str).

   - bpo-34126(84): Fix crashes when profiling certain invalid calls of
     unbound methods.  Patch by Jeroen Demeyer.

   - bpo-24618(85): Fixed reading invalid memory when create the code
     object with too small varnames tuple or too large argument counts.

   - bpo-34068(86): In *note io.IOBase.close(): 1147, ensure that the
     *note closed: 1148. attribute is not set with a live exception.
     Patch by Zackery Spytz and Serhiy Storchaka.

   - bpo-34087(87): Fix buffer overflow while converting unicode to
     numeric values.

   - bpo-34080(88): Fixed a memory leak in the compiler when it raised
     some uncommon errors during tokenizing.

   - bpo-34066(89): Disabled interruption by Ctrl-C between calling
     ‘open()’ and entering a `with' block in ‘with open()’.

   - bpo-34042(90): Fix dict.copy() to maintain correct total refcount
     (as reported by sys.gettotalrefcount()).

   - bpo-33418(91): Fix potential memory leak in function object when it
     creates reference cycle.

   - bpo-33985(92): Implement contextvars.ContextVar.name attribute.

   - bpo-33956(93): Update vendored Expat library copy to version 2.2.5.

   - bpo-24596(94): Decref the module object in *note
     PyRun_SimpleFileExFlags(): fc7. before calling *note PyErr_Print():
     102f.  Patch by Zackery Spytz.

   - bpo-33451(95): Close directly executed pyc files before calling
     ‘PyEval_EvalCode()’.

   - bpo-1617161(96): The hash of ‘BuiltinMethodType’ instances (methods
     of built-in classes) now depends on the hash of the identity of
     `__self__' instead of its value.  The hash and equality of
     ‘ModuleType’ and ‘MethodWrapperType’ instances (methods of
     user-defined classes and some methods of built-in classes like
     ‘str.__add__’) now depend on the hash and equality of the identity
     of `__self__' instead of its value.  ‘MethodWrapperType’ instances
     no longer support ordering.

   - bpo-33824(97): Fix “LC_ALL=C python3.7 -V”: reset properly the
     command line parser when the encoding changes after reading the
     Python configuration.

   - bpo-33803(98): Fix a crash in hamt.c caused by enabling GC tracking
     for an object that hadn’t all of its fields set to NULL.

   - bpo-33738(99): Seven macro incompatibilities with the Limited API
     were fixed, and the macros *note PyIter_Check(): 1149, *note
     PyIndex_Check(): 26e. and ‘PyExceptionClass_Name()’ were added as
     functions.  A script for automatic macro checks was added.

   - bpo-33786(100): Fix asynchronous generators to handle GeneratorExit
     in athrow() correctly

   - bpo-30167(101): ‘PyRun_SimpleFileExFlags’ removes ‘__cached__’ from
     module in addition to ‘__file__’.

   - bpo-33706(102): Fix a crash in Python initialization when parsing
     the command line options.  Thanks Christoph Gohlke for the bug
     report and the fix!

   - bpo-33597(103): Reduce ‘PyGC_Head’ size from 3 words to 2 words.

   - bpo-30654(104): Fixed reset of the SIGINT handler to SIG_DFL on
     interpreter shutdown even when there was a custom handler set
     previously.  Patch by Philipp Kerling.

   - bpo-33622(105): Fixed a leak when the garbage collector fails to
     add an object with the ‘__del__’ method or referenced by it into
     the *note gc.garbage: c12. list.  ‘PyGC_Collect()’ can now be
     called when an exception is set and preserves it.

   - bpo-33462(106): Make dict and dict views reversible.  Patch by Rémi
     Lapeyre.

   - bpo-23722(107): A *note RuntimeError: 3dc. is now raised when the
     custom metaclass doesn’t provide the ‘__classcell__’ entry in the
     namespace passed to ‘type.__new__’.  A *note DeprecationWarning:
     15a. was emitted in Python 3.6–3.7.

   - bpo-33499(108): Add *note PYTHONPYCACHEPREFIX: 28f. environment
     variable and *note -X: 290. ‘pycache_prefix’ command-line option to
     set an alternate root directory for writing module bytecode cache
     files.

   - bpo-25711(109): The *note zipimport: 14c. module has been rewritten
     in pure Python.

   - bpo-33509(110): Fix module_globals parameter of
     warnings.warn_explicit(): don’t crash if module_globals is not a
     dict.

   - bpo-31849(111): Fix signed/unsigned comparison warning in pyhash.c.

   - bpo-33475(112): Fixed miscellaneous bugs in converting annotations
     to strings and optimized parentheses in the string representation.

   - bpo-20104(113): Added support for the ‘setpgroup’, ‘resetids’,
     ‘setsigmask’, ‘setsigdef’ and ‘scheduler’ parameters of
     ‘posix_spawn’.  Patch by Pablo Galindo.

   - bpo-33391(114): Fix a leak in set_symmetric_difference().

   - bpo-33363(115): Raise a SyntaxError for ‘async with’ and ‘async
     for’ statements outside of async functions.

   - bpo-28055(116): Fix unaligned accesses in siphash24().  Patch by
     Rolf Eike Beer.

   - bpo-33128(117): Fix a bug that causes PathFinder to appear twice on
     sys.meta_path.  Patch by Pablo Galindo Salgado.

   - bpo-33331(118): Modules imported last are now cleared first at
     interpreter shutdown.

   - bpo-33312(119): Fixed clang ubsan (undefined behavior sanitizer)
     warnings in dictobject.c by adjusting how the internal struct
     _dictkeysobject shared keys structure is declared.

   - bpo-33305(120): Improved syntax error messages for invalid
     numerical literals.

   - bpo-33306(121): Improved syntax error messages for unbalanced
     parentheses.

   - bpo-33234(122): The list constructor will pre-size and not
     over-allocate when the input length is known.

   - bpo-33270(123): Intern the names for all anonymous code objects.
     Patch by Zackery Spytz.

   - bpo-30455(124): The C and Python code and the documentation related
     to tokens are now generated from a single source file
     ‘Grammar/Tokens’.

   - bpo-33176(125): Add a ‘toreadonly()’ method to memoryviews.

   - bpo-33231(126): Fix potential memory leak in ‘normalizestring()’.

   - bpo-33205(127): Change dict growth function from
     ‘round_up_to_power_2(used*2+hashtable_size/2)’ to
     ‘round_up_to_power_2(used*3)’.  Previously, dict is shrinked only
     when ‘used == 0’.  Now dict has more chance to be shrinked.

   - bpo-29922(128): Improved error messages in ‘async with’ when
     ‘__aenter__()’ or ‘__aexit__()’ return non-awaitable object.

   - bpo-33199(129): Fix ‘ma_version_tag’ in dict implementation is
     uninitialized when copying from key-sharing dict.

   - bpo-33053(130): When using the -m switch, sys.path[0] is now
     explicitly expanded as the `starting' working directory, rather
     than being left as the empty path (which allows imports from the
     current working directory at the time of the import)

   - bpo-33138(131): Changed standard error message for non-pickleable
     and non-copyable types.  It now says “cannot pickle” instead of
     “can’t pickle” or “cannot serialize”.

   - bpo-33018(132): Improve consistency of errors raised by
     ‘issubclass()’ when called with a non-class and an abstract base
     class as the first and second arguments, respectively.  Patch by
     Josh Bronson.

   - bpo-33083(133): ‘math.factorial’ no longer accepts arguments that
     are not int-like.  Patch by Pablo Galindo.

   - bpo-33041(134): Added new opcode *note END_ASYNC_FOR: 3fc. and
     fixes the following issues:

        * Setting global *note StopAsyncIteration: 114a. no longer
          breaks ‘async for’ loops.

        * Jumping into an ‘async for’ loop is now disabled.

        * Jumping out of an ‘async for’ loop no longer corrupts the
          stack.

   - bpo-25750(135): Fix rare Python crash due to bad refcounting in
     ‘type_getattro()’ if a descriptor deletes itself from the class.
     Patch by Jeroen Demeyer.

   - bpo-33041(136): Fixed bytecode generation for “async for” with a
     complex target.  A StopAsyncIteration raised on assigning or
     unpacking will be now propagated instead of stopping the iteration.

   - bpo-33026(137): Fixed jumping out of “with” block by setting
     f_lineno.

   - bpo-33005(138): Fix a crash on fork when using a custom memory
     allocator (ex: using PYTHONMALLOC env var).  _PyGILState_Reinit()
     and _PyInterpreterState_Enable() now use the default RAW memory
     allocator to allocate a new interpreters mutex on fork.

   - bpo-32911(139): Due to unexpected compatibility issues discovered
     during downstream beta testing, reverted bpo-29463(140).
     ‘docstring’ field is removed from Module, ClassDef, FunctionDef,
     and AsyncFunctionDef ast nodes which was added in 3.7a1.  Docstring
     expression is restored as a first statement in their body.  Based
     on patch by Inada Naoki.

   - bpo-17288(141): Prevent jumps from ‘return’ and ‘exception’ trace
     events.

   - bpo-32946(142): Importing names from already imported module with
     “from … import …” is now 30% faster if the module is not a package.

   - bpo-32932(143): Make error message more revealing when there are
     non-str objects in ‘__all__’.

   - bpo-32925(144): Optimized iterating and containing test for literal
     lists consisting of non-constants: ‘x in [a, b]’ and ‘for x in [a,
     b]’.  The case of all constant elements already was optimized.

   - bpo-32889(145): Update Valgrind suppression list to account for the
     rename of ‘Py_ADDRESS_IN_RANG’ to ‘address_in_range’.

   - bpo-32836(146): Don’t use temporary variables in cases of
     list/dict/set comprehensions

   - bpo-31356(147): Remove the new API added in bpo-31356(148)
     (gc.ensure_disabled() context manager).

   - bpo-32305(149): For namespace packages, ensure that both ‘__file__’
     and ‘__spec__.origin’ are set to None.

   - bpo-32303(150): Make sure ‘__spec__.loader’ matches ‘__loader__’
     for namespace packages.

   - bpo-32711(151): Fix the warning messages for Python/ast_unparse.c.
     Patch by Stéphane Wirtel

   - bpo-32583(152): Fix possible crashing in builtin Unicode decoders
     caused by write out-of-bound errors when using customized decode
     error handlers.

   - bpo-32489(153): A *note continue: 2bb. statement is now allowed in
     the *note finally: 2bc. clause.

   - bpo-17611(154): Simplified the interpreter loop by moving the logic
     of unrolling the stack of blocks into the compiler.  The compiler
     emits now explicit instructions for adjusting the stack of values
     and calling the cleaning up code for *note break: 3fa, *note
     continue: 2bb. and *note return: 2c8.

     Removed opcodes ‘BREAK_LOOP’, ‘CONTINUE_LOOP’, ‘SETUP_LOOP’ and
     ‘SETUP_EXCEPT’.  Added new opcodes *note ROT_FOUR: 3fb,
     ‘BEGIN_FINALLY’ and ‘CALL_FINALLY’ and ‘POP_FINALLY’.  Changed the
     behavior of ‘END_FINALLY’ and ‘WITH_CLEANUP_START’.

   - bpo-32285(155): New function unicodedata.is_normalized, which can
     check whether a string is in a specific normal form.

   - bpo-10544(156): Yield expressions are now disallowed in
     comprehensions and generator expressions except the expression for
     the outermost iterable.

   - bpo-32117(157): Iterable unpacking is now allowed without
     parentheses in yield and return statements, e.g.  ‘yield 1, 2, 3,
     *rest’.  Thanks to David Cuthbert for the change and Jordan Chapman
     for added tests.

   - bpo-31902(158): Fix the ‘col_offset’ attribute for ast nodes
     ‘ast.AsyncFor’, ‘ast.AsyncFunctionDef’, and ‘ast.AsyncWith’.
     Previously, ‘col_offset’ pointed to the keyword after ‘async’.

   - bpo-25862(159): Fix assertion failures in the ‘tell()’ method of
     ‘io.TextIOWrapper’.  Patch by Zackery Spytz.

   - bpo-21983(160): Fix a crash in *note ctypes.cast(): 114b. in case
     the type argument is a ctypes structured data type.  Patch by Eryk
     Sun and Oren Milman.

   - bpo-31577(161): Fix a crash in *note os.utime(): b19. in case of a
     bad ns argument.  Patch by Oren Milman.

   - bpo-29832(162): Remove references to ‘getsockaddrarg’ from various
     socket error messages.  Patch by Oren Milman.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35877

   (2) https://bugs.python.org/issue35814

   (3) https://bugs.python.org/issue35766

   (4) https://bugs.python.org/issue35713

   (5) https://bugs.python.org/issue33416

   (6) https://bugs.python.org/issue35720

   (7) https://bugs.python.org/issue35634

   (8) https://bugs.python.org/issue35623

   (9) https://bugs.python.org/issue35214

   (10) https://bugs.python.org/issue35560

   (11) https://bugs.python.org/issue35552

   (12) https://bugs.python.org/issue35504

   (13) https://bugs.python.org/issue35504

   (14) https://bugs.python.org/issue35494

   (15) https://bugs.python.org/issue35444

   (16) https://bugs.python.org/issue35436

   (17) https://bugs.python.org/issue35423

   (18) https://bugs.python.org/issue35357

   (19) https://bugs.python.org/issue35372

   (20) https://bugs.python.org/issue35336

   (21) https://bugs.python.org/issue31241

   (22) https://bugs.python.org/issue33954

   (23) https://bugs.python.org/issue35269

   (24) https://bugs.python.org/issue35224

   (25) https://www.python.org/dev/peps/pep-0572

   (26) https://bugs.python.org/issue32492

   (27) https://bugs.python.org/issue35214

   (28) https://bugs.python.org/issue35214

   (29) https://bugs.python.org/issue35193

   (30) https://bugs.python.org/issue35169

   (31) https://bugs.python.org/issue34022

   (32) https://bugs.python.org/issue28401

   (33) https://bugs.python.org/issue29341

   (34) https://bugs.python.org/issue35050

   (35) https://bugs.python.org/issue29743

   (36) https://bugs.python.org/issue16806

   (37) https://bugs.python.org/issue35029

   (38) https://bugs.python.org/issue34983

   (39) https://bugs.python.org/issue34974

   (40) https://bugs.python.org/issue34939

   (41) https://bugs.python.org/issue34973

   (42) https://bugs.python.org/issue34876

   (43) https://bugs.python.org/issue34879

   (44) https://bugs.python.org/issue34784

   (45) https://bugs.python.org/issue32912

   (46) https://bugs.python.org/issue34854

   (47) https://bugs.python.org/issue34850

   (48) https://bugs.python.org/issue34824

   (49) https://bugs.python.org/issue30156

   (50) https://bugs.python.org/issue34762

   (51) https://bugs.python.org/issue34751

   (52) https://bugs.python.org/issue34735

   (53) https://bugs.python.org/issue34683

   (54) https://bugs.python.org/issue34651

   (55) https://bugs.python.org/issue34653

   (56) https://bugs.python.org/issue32236

   (57) https://bugs.python.org/issue34641

   (58) https://bugs.python.org/issue34637

   (59) https://bugs.python.org/issue1621

   (60) https://bugs.python.org/issue34588

   (61) https://bugs.python.org/issue34485

   (62) https://bugs.python.org/issue34485

   (63) https://bugs.python.org/issue34485

   (64) https://bugs.python.org/issue34485

   (65) https://bugs.python.org/issue34527

   (66) https://bugs.python.org/issue34527

   (67) https://bugs.python.org/issue34403

   (68) https://bugs.python.org/issue34523

   (69) https://bugs.python.org/issue12458

   (70) https://bugs.python.org/issue34408

   (71) https://bugs.python.org/issue34400

   (72) https://bugs.python.org/issue33073

   (73) https://bugs.python.org/issue34377

   (74) https://bugs.python.org/issue34353

   (75) https://bugs.python.org/issue34320

   (76) https://bugs.python.org/issue34113

   (77) https://bugs.python.org/issue34100

   (78) https://bugs.python.org/issue34151

   (79) https://bugs.python.org/issue34170

   (80) https://bugs.python.org/issue33237

   (81) https://bugs.python.org/issue34149

   (82) https://bugs.python.org/issue34125

   (83) https://bugs.python.org/issue34141

   (84) https://bugs.python.org/issue34126

   (85) https://bugs.python.org/issue24618

   (86) https://bugs.python.org/issue34068

   (87) https://bugs.python.org/issue34087

   (88) https://bugs.python.org/issue34080

   (89) https://bugs.python.org/issue34066

   (90) https://bugs.python.org/issue34042

   (91) https://bugs.python.org/issue33418

   (92) https://bugs.python.org/issue33985

   (93) https://bugs.python.org/issue33956

   (94) https://bugs.python.org/issue24596

   (95) https://bugs.python.org/issue33451

   (96) https://bugs.python.org/issue1617161

   (97) https://bugs.python.org/issue33824

   (98) https://bugs.python.org/issue33803

   (99) https://bugs.python.org/issue33738

   (100) https://bugs.python.org/issue33786

   (101) https://bugs.python.org/issue30167

   (102) https://bugs.python.org/issue33706

   (103) https://bugs.python.org/issue33597

   (104) https://bugs.python.org/issue30654

   (105) https://bugs.python.org/issue33622

   (106) https://bugs.python.org/issue33462

   (107) https://bugs.python.org/issue23722

   (108) https://bugs.python.org/issue33499

   (109) https://bugs.python.org/issue25711

   (110) https://bugs.python.org/issue33509

   (111) https://bugs.python.org/issue31849

   (112) https://bugs.python.org/issue33475

   (113) https://bugs.python.org/issue20104

   (114) https://bugs.python.org/issue33391

   (115) https://bugs.python.org/issue33363

   (116) https://bugs.python.org/issue28055

   (117) https://bugs.python.org/issue33128

   (118) https://bugs.python.org/issue33331

   (119) https://bugs.python.org/issue33312

   (120) https://bugs.python.org/issue33305

   (121) https://bugs.python.org/issue33306

   (122) https://bugs.python.org/issue33234

   (123) https://bugs.python.org/issue33270

   (124) https://bugs.python.org/issue30455

   (125) https://bugs.python.org/issue33176

   (126) https://bugs.python.org/issue33231

   (127) https://bugs.python.org/issue33205

   (128) https://bugs.python.org/issue29922

   (129) https://bugs.python.org/issue33199

   (130) https://bugs.python.org/issue33053

   (131) https://bugs.python.org/issue33138

   (132) https://bugs.python.org/issue33018

   (133) https://bugs.python.org/issue33083

   (134) https://bugs.python.org/issue33041

   (135) https://bugs.python.org/issue25750

   (136) https://bugs.python.org/issue33041

   (137) https://bugs.python.org/issue33026

   (138) https://bugs.python.org/issue33005

   (139) https://bugs.python.org/issue32911

   (140) https://bugs.python.org/issue29463

   (141) https://bugs.python.org/issue17288

   (142) https://bugs.python.org/issue32946

   (143) https://bugs.python.org/issue32932

   (144) https://bugs.python.org/issue32925

   (145) https://bugs.python.org/issue32889

   (146) https://bugs.python.org/issue32836

   (147) https://bugs.python.org/issue31356

   (148) https://bugs.python.org/issue31356

   (149) https://bugs.python.org/issue32305

   (150) https://bugs.python.org/issue32303

   (151) https://bugs.python.org/issue32711

   (152) https://bugs.python.org/issue32583

   (153) https://bugs.python.org/issue32489

   (154) https://bugs.python.org/issue17611

   (155) https://bugs.python.org/issue32285

   (156) https://bugs.python.org/issue10544

   (157) https://bugs.python.org/issue32117

   (158) https://bugs.python.org/issue31902

   (159) https://bugs.python.org/issue25862

   (160) https://bugs.python.org/issue21983

   (161) https://bugs.python.org/issue31577

   (162) https://bugs.python.org/issue29832


File: python.info,  Node: Library<30>,  Next: Documentation<25>,  Prev: Core and Builtins<28>,  Up: Python 3 8 0 alpha 1

1.19.31.3 Library
.................

   - bpo-35845(1): Add ‘order’ parameter to memoryview.tobytes().

   - bpo-35864(2): The _asdict() method for collections.namedtuple now
     returns a regular dict instead of an OrderedDict.

   - bpo-35537(3): An ExitStack is now used internally within
     subprocess.POpen to clean up pipe file handles.  No behavior change
     in normal operation.  But if closing one handle were ever to cause
     an exception, the others will now be closed instead of leaked.
     (patch by Giampaolo Rodola)

   - bpo-35847(4): RISC-V needed the CTYPES_PASS_BY_REF_HACK. Fixes
     ctypes Structure test_pass_by_value.

   - bpo-35813(5): Shared memory submodule added to multiprocessing to
     avoid need for serialization between processes

   - bpo-35780(6): Fix lru_cache() errors arising in recursive,
     reentrant, or multi-threaded code.  These errors could result in
     orphan links and in the cache being trapped in a state with fewer
     than the specified maximum number of links.  Fix handling of
     negative maxsize which should have been treated as zero.  Fix
     errors in toggling the “full” status flag.  Fix misordering of
     links when errors are encountered.  Sync-up the C code and pure
     Python code for the space saving path in functions with a single
     positional argument.  In this common case, the space overhead of an
     lru cache entry is reduced by almost half.  Fix counting of cache
     misses.  In error cases, the miss count was out of sync with the
     actual number of times the underlying user function was called.

   - bpo-35537(7): *note os.posix_spawn(): 381. and *note
     os.posix_spawnp(): 114d. now have a `setsid' parameter.

   - bpo-23846(8): *note asyncio.ProactorEventLoop: 2de. now catches and
     logs send errors when the self-pipe is full.

   - bpo-34323(9): *note asyncio: 9.: Enhance ‘IocpProactor.close()’
     log: wait 1 second before the first log, then log every second.
     Log also the number of seconds since ‘close()’ was called.

   - bpo-35674(10): Add a new *note os.posix_spawnp(): 114d. function.
     Patch by Joannah Nanjekye.

   - bpo-35733(11): ‘ast.Constant(boolean)’ no longer an instance of
     ‘ast.Num’.  Patch by Anthony Sottile.

   - bpo-35726(12): QueueHandler.prepare() now makes a copy of the
     record before modifying and enqueueing it, to avoid affecting other
     handlers in the chain.

   - bpo-35719(13): Sped up multi-argument *note math: b1. functions
     atan2(), copysign(), remainder() and hypot() by 1.3–2.5 times.

   - bpo-35717(14): Fix KeyError exception raised when using enums and
     compile.  Patch contributed by Rémi Lapeyre.

   - bpo-35699(15): Fixed detection of Visual Studio Build Tools 2017 in
     distutils

   - bpo-32710(16): Fix memory leaks in asyncio ProactorEventLoop on
     overlapped operation failure.

   - bpo-35702(17): The *note time.CLOCK_UPTIME_RAW: 365. constant is
     now available for macOS 10.12.

   - bpo-32710(18): Fix a memory leak in asyncio in the
     ProactorEventLoop when ‘ReadFile()’ or ‘WSASend()’ overlapped
     operation fail immediately: release the internal buffer.

   - bpo-35682(19): Fix ‘asyncio.ProactorEventLoop.sendfile()’: don’t
     attempt to set the result of an internal future if it’s already
     done.

   - bpo-35283(20): Add a deprecated warning for the
     ‘threading.Thread.isAlive()’ method.  Patch by Dong-hee Na.

   - bpo-35664(21): Improve operator.itemgetter() performance by 33%
     with optimized argument handling and with adding a fast path for
     the common case of a single non-negative integer index into a tuple
     (which is the typical use case in the standard library).

   - bpo-35643(22): Fixed a SyntaxWarning: invalid escape sequence in
     Modules/_sha3/cleanup.py.  Patch by Mickaël Schoentgen.

   - bpo-35619(23): Improved support of custom data descriptors in *note
     help(): 175. and *note pydoc: d9.

   - bpo-28503(24): The *note crypt: 28. module now internally uses the
     ‘crypt_r()’ library function instead of *note crypt(): 28. when
     available.

   - bpo-35614(25): Fixed help() on metaclasses.  Patch by Sanyam
     Khurana.

   - bpo-35568(26): Expose ‘raise(signum)’ as ‘raise_signal’

   - bpo-35588(27): The floor division and modulo operations and the
     *note divmod(): 28d. function on *note fractions.Fraction: 2be.
     types are 2–4x faster.  Patch by Stefan Behnel.

   - bpo-35585(28): Speed-up building enums by value, e.g.
     http.HTTPStatus(200).

   - bpo-30561(29): random.gammavariate(1.0, beta) now computes the same
     result as random.expovariate(1.0 / beta).  This synchronizes the
     two algorithms and eliminates some idiosyncrasies in the old
     implementation.  It does however produce a difference stream of
     random variables than it used to.

   - bpo-35537(30): The *note subprocess: f9. module can now use the
     *note os.posix_spawn(): 381. function in some cases for better
     performance.

   - bpo-35526(31): Delaying the ‘joke’ of barry_as_FLUFL.mandatory to
     Python version 4.0

   - bpo-35523(32): Remove *note ctypes: 2a. callback workaround: no
     longer create a callback at startup.  Avoid SELinux alert on
     ‘import ctypes’ and ‘import uuid’.

   - bpo-31784(33): *note uuid.uuid1(): 518. now calls *note
     time.time_ns(): 433. rather than ‘int(time.time() * 1e9)’.

   - bpo-35513(34): ‘TextTestRunner’ of ‘unittest.runner’ now uses *note
     time.perf_counter(): 3cc. rather than *note time.time(): 42d. to
     measure the execution time of a test: *note time.time(): 42d. can
     go backwards, whereas *note time.perf_counter(): 3cc. is monotonic.

   - bpo-35502(35): Fixed reference leaks in *note
     xml.etree.ElementTree.TreeBuilder: 37d. in case of unfinished
     building of the tree (in particular when an error was raised during
     parsing XML).

   - bpo-35348(36): Make *note platform.architecture(): 114e. parsing of
     ‘file’ command output more reliable: add the ‘-b’ option to the
     ‘file’ command to omit the filename, force the usage of the C
     locale, and search also the “shared object” pattern.

   - bpo-35491(37): *note multiprocessing: b7.: Add ‘Pool.__repr__()’
     and enhance ‘BaseProcess.__repr__()’ (add pid and parent pid) to
     ease debugging.  Pool state constant values are now strings instead
     of integers, for example ‘RUN’ value becomes ‘'RUN'’ instead of
     ‘0’.

   - bpo-35477(38): ‘multiprocessing.Pool.__enter__()’ now fails if the
     pool is not running: ‘with pool:’ fails if used more than once.

   - bpo-31446(39): Copy command line that was passed to CreateProcessW
     since this function can change the content of the input buffer.

   - bpo-35471(40): Python 2.4 dropped MacOS 9 support.  The macpath
     module was deprecated in Python 3.7.  The module is now removed.

   - bpo-23057(41): Unblock Proactor event loop when keyboard interrupt
     is received on Windows

   - bpo-35052(42): Fix xml.dom.minidom cloneNode() on a document with
     an entity: pass the correct arguments to the user data handler of
     an entity.

   - bpo-20239(43): Allow repeated assignment deletion of *note
     unittest.mock.Mock: 373. attributes.  Patch by Pablo Galindo.

   - bpo-17185(44): Set ‘__signature__’ on mock for *note inspect: a0.
     to get signature.  Patch by Karthikeyan Singaravelan.

   - bpo-35445(45): Memory errors during creating posix.environ no
     longer ignored.

   - bpo-35415(46): Validate fileno= argument to socket.socket().

   - bpo-35424(47): ‘multiprocessing.Pool’ destructor now emits *note
     ResourceWarning: 5cb. if the pool is still running.

   - bpo-35330(48): When a ‘Mock’ instance was used to wrap an object,
     if ‘side_effect’ is used in one of the mocks of it methods, don’t
     call the original implementation and return the result of using the
     side effect the same way that it is done with return_value.

   - bpo-35346(49): Drop Mac OS 9 and Rhapsody support from the *note
     platform: ce. module.  Rhapsody last release was in 2000.  Mac OS 9
     last release was in 2001.

   - bpo-10496(50): ‘check_environ()’ of ‘distutils.utils’ now catches
     *note KeyError: 3e9. on calling *note pwd.getpwuid(): 114f.: don’t
     create the ‘HOME’ environment variable in this case.

   - bpo-10496(51): ‘posixpath.expanduser()’ now returns the input
     `path' unchanged if the ‘HOME’ environment variable is not set and
     the current user has no home directory (if the current user
     identifier doesn’t exist in the password database).  This change
     fix the *note site: eb. module if the current user doesn’t exist in
     the password database (if the user has no home directory).

   - bpo-35389(52): *note platform.libc_ver(): 1150. now uses
     ‘os.confstr('CS_GNU_LIBC_VERSION')’ if available and the
     `executable' parameter is not set.

   - bpo-35394(53): Add empty slots to asyncio abstract protocols.

   - bpo-35310(54): Fix a bug in *note select.select(): 766. where, in
     some cases, the file descriptor sequences were returned unmodified
     after a signal interruption, even though the file descriptors might
     not be ready yet.  *note select.select(): 766. will now always
     return empty lists if a timeout has occurred.  Patch by Oran
     Avraham.

   - bpo-35380(55): Enable TCP_NODELAY on Windows for proactor asyncio
     event loop.

   - bpo-35341(56): Add generic version of ‘collections.OrderedDict’ to
     the ‘typing’ module.  Patch by Ismo Toijala.

   - bpo-35371(57): Fixed possible crash in ‘os.utime()’ on Windows when
     pass incorrect arguments.

   - bpo-35346(58): *note platform.uname(): 1151. now redirects ‘stderr’
     to *note os.devnull: 1152. when running external programs like ‘cmd
     /c ver’.

   - bpo-35066(59): Previously, calling the strftime() method on a
     datetime object with a trailing ‘%’ in the format string would
     result in an exception.  However, this only occurred when the
     datetime C module was being used; the python implementation did not
     match this behavior.  Datetime is now PEP-399 compliant, and will
     not throw an exception on a trailing ‘%’.

   - bpo-35345(60): The function ‘platform.popen’ has been removed, it
     was deprecated since Python 3.3: use *note os.popen(): 3cb.
     instead.

   - bpo-35344(61): On macOS, *note platform.platform(): 1153. now uses
     *note platform.mac_ver(): 1154, if it returns a non-empty release
     string, to get the macOS version rather than the darwin version.

   - bpo-35312(62): Make ‘lib2to3.pgen2.parse.ParseError’ round-trip
     pickle-able.  Patch by Anthony Sottile.

   - bpo-35308(63): Fix regression in ‘webbrowser’ where default
     browsers may be preferred over browsers in the ‘BROWSER’
     environment variable.

   - bpo-24746(64): Avoid stripping trailing whitespace in doctest fancy
     diff.  Original patch by R. David Murray & Jairo Trad.  Enhanced by
     Sanyam Khurana.

   - bpo-28604(65): *note locale.localeconv(): 585. now sets temporarily
     the ‘LC_CTYPE’ locale to the ‘LC_MONETARY’ locale if the two
     locales are different and monetary strings are non-ASCII. This
     temporary change affects other threads.

   - bpo-35277(66): Update ensurepip to install pip 18.1 and setuptools
     40.6.2.

   - bpo-24209(67): Adds IPv6 support when invoking http.server
     directly.

   - bpo-35226(68): Recursively check arguments when testing for
     equality of *note unittest.mock.call: 10cc. objects and add note
     that tracking of parameters used to create ancestors of mocks in
     ‘mock_calls’ is not possible.

   - bpo-29564(69): The warnings module now suggests to enable
     tracemalloc if the source is specified, the tracemalloc module is
     available, but tracemalloc is not tracing memory allocations.

   - bpo-35189(70): Modify the following fnctl function to retry if
     interrupted by a signal (EINTR): flock, lockf, fnctl

   - bpo-30064(71): Use add_done_callback() in sock_* asyncio API to
     unsubscribe reader/writer early on calcellation.

   - bpo-35186(72): Removed the “built with” comment added when
     ‘setup.py upload’ is used with either ‘bdist_rpm’ or ‘bdist_dumb’.

   - bpo-35152(73): Allow sending more than 2 GB at once on a
     multiprocessing connection on non-Windows systems.

   - bpo-35062(74): Fix incorrect parsing of
     ‘_io.IncrementalNewlineDecoder’’s `translate' argument.

   - bpo-35065(75): Remove ‘StreamReaderProtocol._untrack_reader’.  The
     call to ‘_untrack_reader’ is currently performed too soon, causing
     the protocol to forget about the reader before ‘connection_lost’
     can run and feed the EOF to the reader.

   - bpo-34160(76): ElementTree and minidom now preserve the attribute
     order specified by the user.

   - bpo-35079(77): Improve difflib.SequenceManager.get_matching_blocks
     doc by adding ‘non-overlapping’ and changing ‘!=’ to ‘<’.

   - bpo-33710(78): Deprecated ‘l*gettext()’ functions and methods in
     the *note gettext: 87. module.  They return encoded bytes instead
     of Unicode strings and are artifacts from Python 2 times.  Also
     deprecated functions and methods related to setting the charset for
     ‘l*gettext()’ functions and methods.

   - bpo-35017(79): *note socketserver.BaseServer.serve_forever(): b63.
     now exits immediately if it’s *note shutdown(): 1155. method is
     called while it is polling for new events.

   - bpo-35024(80): *note importlib: 9a. no longer logs ‘wrote’
     redundantly after ‘(created|could not create)’ is already logged.
     Patch by Quentin Agren.

   - bpo-35047(81): ‘unittest.mock’ now includes mock calls in exception
     messages if ‘assert_not_called’, ‘assert_called_once’, or
     ‘assert_called_once_with’ fails.  Patch by Petter Strandmark.

   - bpo-31047(82): Fix ‘ntpath.abspath’ regression where it didn’t
     remove a trailing separator on Windows.  Patch by Tim Graham.

   - bpo-35053(83): tracemalloc now tries to update the traceback when
     an object is reused from a “free list” (optimization for faster
     object creation, used by the builtin list type for example).

   - bpo-31553(84): Add the –json-lines option to json.tool.  Patch by
     hongweipeng.

   - bpo-34794(85): Fixed a leak in Tkinter when pass the Python wrapper
     around Tcl_Obj back to Tcl/Tk.

   - bpo-34909(86): Enum: fix grandchildren subclassing when parent
     mixed with concrete data types.

   - bpo-35022(87): *note unittest.mock.MagicMock: 874. now supports the
     ‘__fspath__’ method (from *note os.PathLike: 5e6.).

   - bpo-35008(88): Fixed references leaks when call the
     ‘__setstate__()’ method of *note xml.etree.ElementTree.Element:
     21d. in the C implementation for already initialized element.

   - bpo-23420(89): Verify the value for the parameter ‘-s’ of the
     cProfile CLI. Patch by Robert Kuska

   - bpo-33947(90): dataclasses now handle recursive reprs without
     raising RecursionError.

   - bpo-34890(91): Make *note inspect.iscoroutinefunction(): 7e9, *note
     inspect.isgeneratorfunction(): 1156. and *note
     inspect.isasyncgenfunction(): 1157. work with *note
     functools.partial(): 8b5.  Patch by Pablo Galindo.

   - bpo-34521(92): Use *note socket.CMSG_SPACE(): 1158. to calculate
     ancillary data size instead of *note socket.CMSG_LEN(): 1159. in
     ‘multiprocessing.reduction.recvfds()’ as RFC 3542(93) requires the
     use of the former for portable applications.

   - bpo-31522(94): The ‘mailbox.mbox.get_string’ function `from_'
     parameter can now successfully be set to a non-default value.

   - bpo-34970(95): Protect tasks weak set manipulation in
     ‘asyncio.all_tasks()’

   - bpo-34969(96): gzip: Add –fast, –best on the gzip CLI, these
     parameters will be used for the fast compression method (quick) or
     the best method compress (slower, but smaller file).  Also, change
     the default compression level to 6 (tradeoff).

   - bpo-16965(97): The *note 2to3: 115a. *note execfile: 115b. fixer
     now opens the file with mode ‘'rb'’.  Patch by Zackery Spytz.

   - bpo-34966(98): *note pydoc: d9. now supports aliases not only to
     methods defined in the end class, but also to inherited methods.
     The docstring is not duplicated for aliases.

   - bpo-34926(99): *note mimetypes.MimeTypes.guess_type(): 115c. now
     accepts *note path-like object: 472. in addition to url strings.
     Patch by Mayank Asthana.

   - bpo-23831(100): Add ‘moveto()’ method to the ‘tkinter.Canvas’
     widget.  Patch by Juliette Monsel.

   - bpo-34941(101): Methods ‘find()’, ‘findtext()’ and ‘findall()’ of
     the ‘Element’ class in the *note xml.etree.ElementTree: 140. module
     are now able to find children which are instances of ‘Element’
     subclasses.

   - bpo-32680(102): *note smtplib.SMTP: 1de. objects now always have a
     ‘sock’ attribute present

   - bpo-34769(103): Fix for async generators not finalizing when event
     loop is in debug mode and garbage collector runs in another thread.

   - bpo-34936(104): Fix ‘TclError’ in
     ‘tkinter.Spinbox.selection_element()’.  Patch by Juliette Monsel.

   - bpo-34829(105): Add methods ‘selection_from’, ‘selection_range’,
     ‘selection_present’ and ‘selection_to’ to the ‘tkinter.Spinbox’ for
     consistency with the ‘tkinter.Entry’ widget.  Patch by Juliette
     Monsel.

   - bpo-34911(106): Added `secure_protocols' argument to
     `http.cookiejar.DefaultCookiePolicy' to allow for tweaking of
     protocols and also to add support by default for `wss', the secure
     websocket protocol.

   - bpo-34922(107): Fixed integer overflow in the *note digest(): 115d.
     and *note hexdigest(): 115e. methods for the SHAKE algorithm in the
     *note hashlib: 8c. module.

   - bpo-34925(108): 25% speedup in argument parsing for the functions
     in the bisect module.

   - bpo-34900(109): Fixed *note unittest.TestCase.debug(): f6e. when
     used to call test methods with subtests.  Patch by Bruno Oliveira.

   - bpo-34844(110): logging.Formatter enhancement - Ensure styles and
     fmt matches in logging.Formatter - Added validate method in each
     format style class: StrFormatStyle, PercentStyle,
     StringTemplateStyle.  - This method is called in the constructor of
     logging.Formatter class - Also re-raise the KeyError in the format
     method of each style class, so it would a bit clear that it’s an
     error with the invalid format fields.

   - bpo-34897(111): Adjust test.support.missing_compiler_executable
     check so that a nominal command name of “” is ignored.  Patch by
     Michael Felt.

   - bpo-34871(112): Fix inspect module polluted ‘sys.modules’ when
     parsing ‘__text_signature__’ of callable.

   - bpo-34898(113): Add ‘mtime’ argument to *note gzip.compress: 302.
     for reproducible output.  Patch by Guo Ci Teo.

   - bpo-28441(114): On Cygwin and MinGW, ensure that ‘sys.executable’
     always includes the full filename in the path, including the ‘.exe’
     suffix (unless it is a symbolic link).

   - bpo-34866(115): Adding ‘max_num_fields’ to ‘cgi.FieldStorage’ to
     make DOS attacks harder by limiting the number of
     ‘MiniFieldStorage’ objects created by ‘FieldStorage’.

   - bpo-34711(116): http.server ensures it reports HTTPStatus.NOT_FOUND
     when the local path ends with “/” and is not a directory, even if
     the underlying OS (e.g.  AIX) accepts such paths as a valid file
     reference.  Patch by Michael Felt.

   - bpo-34872(117): Fix self-cancellation in C implementation of
     asyncio.Task

   - bpo-34849(118): Don’t log waiting for ‘selector.select’ in asyncio
     loop iteration.  The waiting is pretty normal for any asyncio
     program, logging its time just adds a noise to logs without any
     useful information provided.

   - bpo-34022(119): The ‘SOURCE_DATE_EPOCH’ environment variable no
     longer overrides the value of the `invalidation_mode' argument to
     *note py_compile.compile(): 343, and determines its default value
     instead.

   - bpo-34819(120): Use a monotonic clock to compute timeouts in
     ‘Executor.map()’ and ‘as_completed()’, in order to prevent timeouts
     from deviating when the system clock is adjusted.

   - bpo-34758(121): Add .wasm -> application/wasm to list of recognized
     file types and content type headers

   - bpo-34789(122): *note xml.sax.make_parser(): 115f. now accepts any
     iterable as its `parser_list' argument.  Patch by Andrés Delfino.

   - bpo-34334(123): In ‘QueueHandler’, clear ‘exc_text’ from
     ‘LogRecord’ to prevent traceback from being written twice.

   - bpo-34687(124): On Windows, asyncio now uses ProactorEventLoop,
     instead of SelectorEventLoop, by default.

   - bpo-5950(125): Support reading zip files with archive comments in
     *note zipimport: 14c.

   - bpo-32892(126): The parser now represents all constants as *note
     ast.Constant: 3a6. instead of using specific constant AST types
     (‘Num’, ‘Str’, ‘Bytes’, ‘NameConstant’ and ‘Ellipsis’).  These
     classes are considered deprecated and will be removed in future
     Python versions.

   - bpo-34728(127): Add deprecation warning when ‘loop’ is used in
     methods: *note asyncio.sleep: 3aa, *note asyncio.wait: 207. and
     *note asyncio.wait_for: 191.

   - bpo-34738(128): ZIP files created by *note distutils: 38. will now
     include entries for directories.

   - bpo-34659(129): Add an optional `initial' argument to
     itertools.accumulate().

   - bpo-29577(130): Support multiple mixin classes when creating Enums.

   - bpo-34670(131): Add SSLContext.post_handshake_auth and
     SSLSocket.verify_client_post_handshake for TLS 1.3’s post handshake
     authentication feature.

   - bpo-32718(132): The Activate.ps1 script from venv works with
     PowerShell Core 6.1 and is now available under all operating
     systems.

   - bpo-31177(133): Fix bug that prevented using *note reset_mock: 6a1.
     on mock instances with deleted attributes

   - bpo-34672(134): Add a workaround, so the ‘'Z'’ *note
     time.strftime(): c37. specifier on the musl C library can work in
     some cases.

   - bpo-34666(135): Implement ‘asyncio.StreamWriter.awrite’ and
     ‘asyncio.StreamWriter.aclose()’ coroutines.  Methods are needed for
     providing a consistent stream API with control flow switched on by
     default.

   - bpo-6721(136): Acquire the logging module’s commonly used internal
     locks while fork()ing to avoid deadlocks in the child process.

   - bpo-34658(137): Fix a rare interpreter unhandled exception state
     SystemError only seen when using subprocess with a preexec_fn while
     an after_parent handler has been registered with
     os.register_at_fork and the fork system call fails.

   - bpo-34652(138): Ensure *note os.lchmod(): 1160. is never defined on
     Linux.

   - bpo-34638(139): Store a weak reference to stream reader to break
     strong references loop between reader and protocol.  It allows to
     detect and close the socket if the stream is deleted (garbage
     collected) without ‘close()’ call.

   - bpo-34536(140): ‘Enum._missing_’: raise *note ValueError: 16d. if
     None returned and *note TypeError: 1fe. if non-member is returned.

   - bpo-34636(141): Speed up re scanning of many non-matching
     characters for s w and d within bytes objects.  (microoptimization)

   - bpo-24412(142): Add *note addModuleCleanup(): 374. and *note
     addClassCleanup(): 375. to unittest to support cleanups for
     ‘setUpModule()’ and *note setUpClass(): 376.  Patch by Lisa Roach.

   - bpo-34630(143): Don’t log SSL certificate errors in asyncio code
     (connection error logging is skipped already).

   - bpo-32490(144): Prevent filename duplication in *note subprocess:
     f9. exception messages.  Patch by Zackery Spytz.

   - bpo-34363(145): dataclasses.asdict() and .astuple() now handle
     namedtuples correctly.

   - bpo-34625(146): Update vendorized expat library version to 2.2.6.

   - bpo-32270(147): The subprocess module no longer mistakenly closes
     redirected fds even when they were in pass_fds when outside of the
     default {0, 1, 2} set.

   - bpo-34622(148): Create a dedicated ‘asyncio.CancelledError’,
     ‘asyncio.InvalidStateError’ and ‘asyncio.TimeoutError’ exception
     classes.  Inherit them from corresponding exceptions from
     ‘concurrent.futures’ package.  Extract ‘asyncio’ exceptions into a
     separate file.

   - bpo-34610(149): Fixed iterator of
     ‘multiprocessing.managers.DictProxy’.

   - bpo-34421(150): Fix distutils logging for non-ASCII strings.  This
     caused installation issues on Windows.

   - bpo-34604(151): Fix possible mojibake in the error message of *note
     pwd.getpwnam: 1161. and *note grp.getgrnam: 1162. using string
     representation because of invisible characters or trailing
     whitespaces.  Patch by William Grzybowski.

   - bpo-30977(152): Make uuid.UUID use ‘__slots__’ to reduce its memory
     footprint.  Based on original patch by Wouter Bolsterlee.

   - bpo-34574(153): OrderedDict iterators are not exhausted during
     pickling anymore.  Patch by Sergey Fedoseev.

   - bpo-8110(154): Refactored *note subprocess: f9. to check for
     Windows-specific modules rather than ‘sys.platform == 'win32'’.

   - bpo-34530(155): ‘distutils.spawn.find_executable()’ now falls back
     on *note os.defpath: 111a. if the ‘PATH’ environment variable is
     not set.

   - bpo-34563(156): On Windows, fix multiprocessing.Connection for very
     large read: fix _winapi.PeekNamedPipe() and _winapi.ReadFile() for
     read larger than INT_MAX (usually ‘2**31-1’).

   - bpo-34558(157): Correct typo in Lib/ctypes/_aix.py

   - bpo-34282(158): Move ‘Enum._convert’ to ‘EnumMeta._convert_’ and
     fix enum members getting shadowed by parent attributes.

   - bpo-22872(159): When the queue is closed, *note ValueError: 16d. is
     now raised by *note multiprocessing.Queue.put(): 1163. and *note
     multiprocessing.Queue.get(): 1164. instead of *note AssertionError:
     240. and *note OSError: 304, respectively.  Patch by Zackery Spytz.

   - bpo-34515(160): Fix parsing non-ASCII identifiers in
     ‘lib2to3.pgen2.tokenize’ (PEP 3131).

   - bpo-13312(161): Avoids a possible integer underflow (undefined
     behavior) in the time module’s year handling code when passed a
     very low negative year value.

   - bpo-34472(162): Improved compatibility for streamed files in *note
     zipfile: 14b.  Previously an optional signature was not being
     written and certain ZIP applications were not supported.  Patch by
     Silas Sewell.

   - bpo-34454(163): Fix the .fromisoformat() methods of datetime types
     crashing when given unicode with non-UTF-8-encodable code points.
     Specifically, datetime.fromisoformat() now accepts surrogate
     unicode code points used as the separator.  Report and tests by
     Alexey Izbyshev, patch by Paul Ganssle.

   - bpo-6700(164): Fix inspect.getsourcelines for module level
     frames/tracebacks.  Patch by Vladimir Matveev.

   - bpo-34171(165): Running the *note trace: 11b. module no longer
     creates the ‘trace.cover’ file.

   - bpo-34441(166): Fix crash when an ‘ABC’-derived class with invalid
     ‘__subclasses__’ is passed as the second argument to *note
     issubclass(): 553.  Patch by Alexey Izbyshev.

   - bpo-34427(167): Fix infinite loop in ‘a.extend(a)’ for
     ‘MutableSequence’ subclasses.

   - bpo-34412(168): Make *note signal.strsignal(): 1165. work on HP-UX.
     Patch by Michael Osipov.

   - bpo-20849(169): shutil.copytree now accepts a new ‘dirs_exist_ok’
     keyword argument.  Patch by Josh Bronson.

   - bpo-31715(170): Associate ‘.mjs’ file extension with
     ‘application/javascript’ MIME Type.

   - bpo-34384(171): *note os.readlink(): 1d1. now accepts *note
     path-like: 472. and *note bytes: 172. objects on Windows.

   - bpo-22602(172): The UTF-7 decoder now raises *note
     UnicodeDecodeError: 32b. for ill-formed sequences starting with “+”
     (as specified in RFC 2152).  Patch by Zackery Spytz.

   - bpo-2122(173): The *note mmap.flush(): 3e5. method now returns
     ‘None’ on success, raises an exception on error under all
     platforms.

   - bpo-34341(174): Appending to the ZIP archive with the ZIP64
     extension no longer grows the size of extra fields of existing
     entries.

   - bpo-34333(175): Fix %-formatting in *note
     pathlib.PurePath.with_suffix(): 1166. when formatting an error
     message.

   - bpo-18540(176): The *note imaplib.IMAP4: 1af. and *note
     imaplib.IMAP4_SSL: 1b0. classes now resolve to the local host IP
     correctly when the default value of `host' parameter (‘''’) is
     used.

   - bpo-26502(177): Implement ‘traceback.FrameSummary.__len__()’ method
     to preserve compatibility with the old tuple API.

   - bpo-34318(178): *note assertRaises(): b92, *note
     assertRaisesRegex(): b93, *note assertWarns(): b94. and *note
     assertWarnsRegex(): b95. no longer success if the passed callable
     is None.  They no longer ignore unknown keyword arguments in the
     context manager mode.  A DeprecationWarning was raised in these
     cases since Python 3.5.

   - bpo-9372(179): Deprecate *note __getitem__(): 3a2. methods of *note
     xml.dom.pulldom.DOMEventStream: 3a3, *note
     wsgiref.util.FileWrapper: 3a4. and *note fileinput.FileInput: 3a5.

   - bpo-33613(180): Fix a race condition in
     ‘multiprocessing.semaphore_tracker’ when the tracker receives
     SIGINT before it can register signal handlers for ignoring it.

   - bpo-34248(181): Report filename in the exception raised when the
     database file cannot be opened by *note dbm.gnu.open(): 1167. and
     *note dbm.ndbm.open(): 1168. due to OS-related error.  Patch by
     Zsolt Cserna.

   - bpo-33089(182): Add math.dist() to compute the Euclidean distance
     between two points.

   - bpo-34246(183): *note smtplib.SMTP.send_message(): 834. no longer
     modifies the content of the `mail_options' argument.  Patch by
     Pablo S. Blum de Aguiar.

   - bpo-31047(184): Fix ‘ntpath.abspath’ for invalid paths on windows.
     Patch by Franz Woellert.

   - bpo-32321(185): Add pure Python fallback for functools.reduce.
     Patch by Robert Wright.

   - bpo-34270(186): The default asyncio task class now always has a
     name which can be get or set using two new methods (*note
     get_name(): 2e4. and *note set_name(): 2e3.) and is visible in the
     *note repr(): 8b9. output.  An initial name can also be set using
     the new ‘name’ keyword argument to *note asyncio.create_task():
     2e1. or the ‘create_task()’ method of the event loop.  If no
     initial name is set, the default Task implementation generates a
     name like ‘Task-1’ using a monotonic counter.

   - bpo-34263(187): asyncio’s event loop will not pass timeouts longer
     than one day to epoll/select etc.

   - bpo-34035(188): Fix several AttributeError in zipfile seek()
     methods.  Patch by Mickaël Schoentgen.

   - bpo-32215(189): Fix performance regression in *note sqlite3: f2.
     when a DML statement appeared in a different line than the rest of
     the SQL query.

   - bpo-34075(190): Deprecate passing non-ThreadPoolExecutor instances
     to ‘AbstractEventLoop.set_default_executor()’.

   - bpo-34251(191): Restore ‘msilib.Win64’ to preserve backwards
     compatibility since it’s already used by *note distutils: 38.’
     ‘bdist_msi’ command.

   - bpo-19891(192): Ignore errors caused by missing / non-writable
     homedir while writing history during exit of an interactive
     session.  Patch by Anthony Sottile.

   - bpo-33089(193): Enhanced math.hypot() to support more than two
     dimensions.

   - bpo-34228(194): tracemalloc: PYTHONTRACEMALLOC=0 environment
     variable and -X tracemalloc=0 command line option are now allowed
     to disable explicitly tracemalloc at startup.

   - bpo-13041(195): Use *note shutil.get_terminal_size(): b25. to
     calculate the terminal width correctly in the
     ‘argparse.HelpFormatter’ class.  Initial patch by Zbyszek
     Jędrzejewski-Szmek.

   - bpo-34213(196): Allow frozen dataclasses to have a field named
     “object”.  Previously this conflicted with an internal use of
     “object”.

   - bpo-34052(197): *note sqlite3.Connection.create_aggregate(): 10d3,
     *note sqlite3.Connection.create_function(): 10d4, *note
     sqlite3.Connection.set_authorizer(): 10d5, *note
     sqlite3.Connection.set_progress_handler(): 10d6. methods raises
     TypeError when unhashable objects are passed as callable.  These
     methods now don’t pass such objects to SQLite API. Previous
     behavior could lead to segfaults.  Patch by Sergey Fedoseev.

   - bpo-34197(198): Attributes `skipinitialspace', `doublequote' and
     `strict' of the `dialect' attribute of the *note csv: 29. reader
     are now *note bool: 2bd. instances instead of integers 0 or 1.

   - bpo-32788(199): Errors other than *note TypeError: 1fe. raised in
     methods ‘__adapt__()’ and ‘__conform__()’ in the *note sqlite3: f2.
     module are now propagated to the user.

   - bpo-21446(200): The *note reload: 1169. fixer now uses *note
     importlib.reload(): 4a0. instead of deprecated *note imp.reload():
     d38.

   - bpo-940286(201): pydoc’s ‘Helper.showtopic()’ method now prints the
     cross references of a topic correctly.

   - bpo-34164(202): *note base64.b32decode(): a3e. could raise
     UnboundLocalError or OverflowError for incorrect padding.  Now it
     always raises ‘base64.Error’ in these cases.

   - bpo-33729(203): Fixed issues with arguments parsing in *note
     hashlib: 8c.

   - bpo-34097(204): ZipFile can zip files older than 1980-01-01 and
     newer than 2107-12-31 using a new ‘strict_timestamps’ parameter at
     the cost of setting the timestamp to the limit.

   - bpo-34108(205): Remove extraneous CR in 2to3 refactor.

   - bpo-34070(206): Make sure to only check if the handle is a tty,
     when opening a file with ‘buffering=-1’.

   - bpo-27494(207): Reverted bpo-27494(208).  2to3 rejects now a
     trailing comma in generator expressions.

   - bpo-33967(209): functools.singledispatch now raises TypeError
     instead of IndexError when no positional arguments are passed.

   - bpo-34041(210): Add the parameter `deterministic' to the *note
     sqlite3.Connection.create_function(): 10d4. method.  Patch by
     Sergey Fedoseev.

   - bpo-34056(211): Ensure the loader shim created by ‘imp.load_module’
     always returns bytes from its ‘get_data()’ function.  This fixes
     using ‘imp.load_module’ with PEP 552(212) hash-based pycs.

   - bpo-34054(213): The multiprocessing module now uses the monotonic
     clock *note time.monotonic(): 85e. instead of the system clock
     *note time.time(): 42d. to implement timeout.

   - bpo-34043(214): Optimize tarfile uncompress performance about 15%
     when gzip is used.

   - bpo-34044(215): ‘subprocess.Popen’ now copies the `startupinfo'
     argument to leave it unchanged: it will modify the copy, so that
     the same ‘STARTUPINFO’ object can be used multiple times.

   - bpo-34010(216): Fixed a performance regression for reading streams
     with tarfile.  The buffered read should use a list, instead of
     appending to a bytes object.

   - bpo-34019(217): webbrowser: Correct the arguments passed to Opera
     Browser when opening a new URL using the ‘webbrowser’ module.
     Patch by Bumsik Kim.

   - bpo-34003(218): csv.DictReader now creates dicts instead of
     OrderedDicts.  Patch by Michael Selik.

   - bpo-33978(219): Closed existing logging handlers before
     reconfiguration via fileConfig and dictConfig.  Patch by
     Karthikeyan Singaravelan.

   - bpo-14117(220): Make minor tweaks to turtledemo.  The ‘wikipedia’
     example is now ‘rosette’, describing what it draws.  The ‘penrose’
     print output is reduced.  The’1024’ output of ‘tree’ is eliminated.

   - bpo-33974(221): Fixed passing lists and tuples of strings
     containing special characters ‘"’, ‘\’, ‘{’, ‘}’ and ‘\n’ as
     options to *note ttk: 118. widgets.

   - bpo-27500(222): Fix getaddrinfo to resolve IPv6 addresses
     correctly.

   - bpo-24567(223): Improve random.choices() to handle subnormal input
     weights that could occasionally trigger an IndexError.

   - bpo-33871(224): Fixed integer overflow in *note os.readv(): 4bf,
     *note os.writev(): 4c2, *note os.preadv(): 4be. and *note
     os.pwritev(): 4c1. and in *note os.sendfile(): 461. with `headers'
     or `trailers' arguments (on BSD-based OSes and macOS).

   - bpo-25007(225): Add *note copy.copy(): 4d2. and *note
     copy.deepcopy(): 4d3. support to zlib compressors and
     decompressors.  Patch by Zackery Spytz.

   - bpo-33929(226): multiprocessing: Fix a race condition in Popen of
     multiprocessing.popen_spawn_win32.  The child process now
     duplicates the read end of pipe instead of “stealing” it.
     Previously, the read end of pipe was “stolen” by the child process,
     but it leaked a handle if the child process had been terminated
     before it could steal the handle from the parent process.

   - bpo-33899(227): Tokenize module now implicitly emits a NEWLINE when
     provided with input that does not have a trailing new line.  This
     behavior now matches what the C tokenizer does internally.
     Contributed by Ammar Askar.

   - bpo-33897(228): Added a ‘force’ keyword argument to
     logging.basicConfig().

   - bpo-33695(229): *note shutil.copytree(): 347. uses *note
     os.scandir(): 389. function and all copy functions depending from
     it use cached *note os.stat(): 321. values.  The speedup for
     copying a directory with 8000 files is around +9% on Linux, +20% on
     Windows and + 30% on a Windows SMB share.  Also the number of *note
     os.stat(): 321. syscalls is reduced by 38% making *note
     shutil.copytree(): 347. especially faster on network filesystems.
     (Contributed by Giampaolo Rodola’ in bpo-33695(230).)

   - bpo-33916(231): bz2 and lzma: When Decompressor.__init__() is
     called twice, free the old lock to not leak memory.

   - bpo-32568(232): Make select.epoll() and its documentation
     consistent regarding `sizehint' and `flags'.

   - bpo-33833(233): Fixed bug in asyncio where ProactorSocketTransport
     logs AssertionError if force closed during write.

   - bpo-33663(234): Convert content length to string before putting to
     header.

   - bpo-33721(235): *note os.path: c5. functions that return a boolean
     result like *note exists(): 325, *note lexists(): 326, *note
     isdir(): 327, *note isfile(): 328, *note islink(): 323, and *note
     ismount(): 329, and *note pathlib.Path: 32f. methods that return a
     boolean result like *note exists(): 330, *note is_dir(): 331, *note
     is_file(): 332, *note is_mount(): 333, *note is_symlink(): 334,
     *note is_block_device(): 335, *note is_char_device(): 336, *note
     is_fifo(): 337, *note is_socket(): 338. now return ‘False’ instead
     of raising *note ValueError: 16d. or its subclasses *note
     UnicodeEncodeError: 32a. and *note UnicodeDecodeError: 32b. for
     paths that contain characters or bytes unrepresentable at the OS
     level.

   - bpo-26544(236): Fixed implementation of *note platform.libc_ver():
     1150.  It almost always returned version ‘2.9’ for glibc.

   - bpo-33843(237): Remove deprecated ‘cgi.escape’, ‘cgi.parse_qs’ and
     ‘cgi.parse_qsl’.

   - bpo-33842(238): Remove ‘tarfile.filemode’ which is deprecated since
     Python 3.3.

   - bpo-30167(239): Prevent site.main() exception if PYTHONSTARTUP is
     set.  Patch by Steve Weber.

   - bpo-33805(240): Improve error message of dataclasses.replace() when
     an InitVar is not specified

   - bpo-33687(241): Fix the call to ‘os.chmod()’ for ‘uu.decode()’ if a
     mode is given or decoded.  Patch by Timo Furrer.

   - bpo-33812(242): Datetime instance d with non-None tzinfo, but with
     d.tzinfo.utcoffset(d) returning None is now treated as naive by the
     astimezone() method.

   - bpo-32108(243): In configparser, don’t clear section when it is
     assigned to itself.

   - bpo-27397(244): Make email module properly handle invalid-length
     base64 strings.

   - bpo-33578(245): Implement multibyte encoder/decoder state methods

   - bpo-30805(246): Avoid race condition with debug logging

   - bpo-33476(247): Fix _header_value_parser.py when address group is
     missing final ‘;’.  Contributed by Enrique Perez-Terron

   - bpo-33694(248): asyncio: Fix a race condition causing data loss on
     pause_reading()/resume_reading() when using the ProactorEventLoop.

   - bpo-32493(249): Correct test for ‘uuid_enc_be’ availability in
     ‘configure.ac’.  Patch by Michael Felt.

   - bpo-33792(250): Add asyncio.WindowsSelectorEventLoopPolicy and
     asyncio.WindowsProactorEventLoopPolicy.

   - bpo-33274(251): W3C DOM Level 1 specifies return value of
     Element.removeAttributeNode() as “The Attr node that was removed.”
     xml.dom.minidom now complies with this requirement.

   - bpo-33778(252): Update ‘unicodedata’’s database to Unicode version
     11.0.0.

   - bpo-33165(253): Added a stacklevel parameter to logging calls to
     allow use of wrapper/helper functions for logging APIs.

   - bpo-33770(254): improve base64 exception message for encoded inputs
     of invalid length

   - bpo-33769(255): asyncio/start_tls: Fix error message; cancel
     callbacks in case of an unhandled error; mark SSLTransport as
     closed if it is aborted.

   - bpo-33767(256): The concatenation (‘+’) and repetition (‘*’)
     sequence operations now raise *note TypeError: 1fe. instead of
     *note SystemError: 6f2. when performed on *note mmap.mmap: 31c.
     objects.  Patch by Zackery Spytz.

   - bpo-33734(257): asyncio/ssl: Fix AttributeError, increase default
     handshake timeout

   - bpo-31014(258): Fixed creating a controller for *note webbrowser:
     132. when a user specifies a path to an entry in the BROWSER
     environment variable.  Based on patch by John Still.

   - bpo-2504(259): Add gettext.pgettext() and variants.

   - bpo-33197(260): Add description property for _ParameterKind

   - bpo-32751(261): When cancelling the task due to a timeout, *note
     asyncio.wait_for(): 191. will now wait until the cancellation is
     complete.

   - bpo-32684(262): Fix gather to propagate cancellation of itself even
     with return_exceptions.

   - bpo-33654(263): Support protocol type switching in
     SSLTransport.set_protocol().

   - bpo-33674(264): Pause the transport as early as possible to further
     reduce the risk of data_received() being called before
     connection_made().

   - bpo-33671(265): *note shutil.copyfile(): 382, *note shutil.copy():
     383, *note shutil.copy2(): 384, *note shutil.copytree(): 347. and
     *note shutil.move(): 385. use platform-specific fast-copy syscalls
     on Linux and macOS in order to copy the file more efficiently.  On
     Windows *note shutil.copyfile(): 382. uses a bigger default buffer
     size (1 MiB instead of 16 KiB) and a *note memoryview(): 386.-based
     variant of *note shutil.copyfileobj(): 387. is used.  The speedup
     for copying a 512MiB file is about +26% on Linux, +50% on macOS and
     +40% on Windows.  Also, much less CPU cycles are consumed.
     (Contributed by Giampaolo Rodola’ in bpo-25427(266).)

   - bpo-33674(267): Fix a race condition in
     SSLProtocol.connection_made() of asyncio.sslproto: start
     immediately the handshake instead of using call_soon().
     Previously, data_received() could be called before the handshake
     started, causing the handshake to hang or fail.

   - bpo-31647(268): Fixed bug where calling write_eof() on a
     _SelectorSocketTransport after it’s already closed raises
     AttributeError.

   - bpo-32610(269): Make asyncio.all_tasks() return only pending tasks.

   - bpo-32410(270): Avoid blocking on file IO in sendfile fallback code

   - bpo-33469(271): Fix RuntimeError after closing loop that used
     run_in_executor

   - bpo-33672(272): Fix Task.__repr__ crash with Cython’s bogus
     coroutines

   - bpo-33654(273): Fix transport.set_protocol() to support switching
     between asyncio.Protocol and asyncio.BufferedProtocol.  Fix
     loop.start_tls() to work with asyncio.BufferedProtocols.

   - bpo-33652(274): Pickles of type variables and subscripted generics
     are now future-proof and compatible with older Python versions.

   - bpo-32493(275): Fixed *note uuid.uuid1(): 518. on FreeBSD.

   - bpo-33238(276): Add ‘InvalidStateError’ to *note
     concurrent.futures: 21.  ‘Future.set_result’ and
     ‘Future.set_exception’ now raise ‘InvalidStateError’ if the futures
     are not pending or running.  Patch by Jason Haydaman.

   - bpo-33618(277): Finalize and document preliminary and experimental
     TLS 1.3 support with OpenSSL 1.1.1

   - bpo-33625(278): Release GIL on *note grp.getgrnam: 1162, *note
     grp.getgrgid: 6d6, *note pwd.getpwnam: 1161. and *note
     pwd.getpwuid: 114f. if reentrant variants of these functions are
     available.  Patch by William Grzybowski.

   - bpo-33623(279): Fix possible SIGSGV when asyncio.Future is created
     in __del__

   - bpo-11874(280): Use a better regex when breaking usage into
     wrappable parts.  Avoids bogus assertion errors from custom metavar
     strings.

   - bpo-30877(281): Fixed a bug in the Python implementation of the
     JSON decoder that prevented the cache of parsed strings from
     clearing after finishing the decoding.  Based on patch by c-fos.

   - bpo-33604(282): Remove HMAC default to md5 marked for removal in
     3.8 (removal originally planned in 3.6, bump to 3.8 in gh-7062).

   - bpo-33582(283): Emit a deprecation warning for
     inspect.formatargspec

   - bpo-21145(284): Add ‘functools.cached_property’ decorator, for
     computed properties cached for the life of the instance.

   - bpo-33570(285): Change TLS 1.3 cipher suite settings for
     compatibility with OpenSSL 1.1.1-pre6 and newer.  OpenSSL 1.1.1
     will have TLS 1.3 ciphers enabled by default.

   - bpo-28556(286): Do not simplify arguments to *note typing.Union:
     116a.  Now ‘Union[Manager, Employee]’ is not simplified to
     ‘Employee’ at runtime.  Such simplification previously caused
     several bugs and limited possibilities for introspection.

   - bpo-12486(287): *note tokenize.generate_tokens(): 116b. is now
     documented as a public API to tokenize unicode strings.  It was
     previously present but undocumented.

   - bpo-33540(288): Add a new ‘block_on_close’ class attribute to
     ‘ForkingMixIn’ and ‘ThreadingMixIn’ classes of *note socketserver:
     f0.

   - bpo-33548(289): tempfile._candidate_tempdir_list should consider
     common TEMP locations

   - bpo-33109(290): argparse subparsers are once again not required by
     default, reverting the change in behavior introduced by
     bpo-26510(291) in 3.7.0a2.

   - bpo-33541(292): Remove unused private method
     ‘_strptime.LocaleTime.__pad’ (a.k.a.  ‘_LocaleTime__pad’).

   - bpo-33536(293): dataclasses.make_dataclass now checks for invalid
     field names and duplicate fields.  Also, added a check for invalid
     field specifications.

   - bpo-33542(294): Prevent ‘uuid.get_node’ from using a DUID instead
     of a MAC on Windows.  Patch by Zvi Effron

   - bpo-26819(295): Fix race condition with
     ‘ReadTransport.resume_reading’ in Windows proactor event loop.

   - Fix failure in *note typing.get_type_hints(): 1ef. when ClassVar
     was provided as a string forward reference.

   - bpo-33516(296): *note unittest.mock.MagicMock: 874. now supports
     the ‘__round__’ magic method.

   - bpo-28612(297): Added support for Site Maps to urllib’s
     ‘RobotFileParser’ as *note RobotFileParser.site_maps(): 116c.
     Patch by Lady Red, based on patch by Peter Wirtz.

   - bpo-28167(298): Remove platform.linux_distribution, which was
     deprecated since 3.5.

   - bpo-33504(299): Switch the default dictionary implementation for
     *note configparser: 22. from *note collections.OrderedDict: 2ea. to
     the standard *note dict: 164. type.

   - bpo-33505(300): Optimize asyncio.ensure_future() by reordering if
     checks: 1.17x faster.

   - bpo-33497(301): Add errors param to cgi.parse_multipart and make an
     encoding in FieldStorage use the given errors (needed for Twisted).
     Patch by Amber Brown.

   - bpo-29235(302): The ‘cProfile.Profile’ class can now be used as a
     context manager.  Patch by Scott Sanderson.

   - bpo-33495(303): Change dataclasses.Fields repr to use the repr of
     each of its members, instead of str.  This makes it more clear what
     each field actually represents.  This is especially true for the
     ‘type’ member.

   - bpo-26103(304): Correct ‘inspect.isdatadescriptor’ to look for
     ‘__set__’ or ‘__delete__’.  Patch by Aaron Hall.

   - bpo-29209(305): Removed the ‘doctype()’ method and the `html'
     parameter of the constructor of *note XMLParser: 37c.  The
     ‘doctype()’ method defined in a subclass will no longer be called.
     Deprecated methods ‘getchildren()’ and ‘getiterator()’ in the *note
     ElementTree: 140. module emit now a *note DeprecationWarning: 15a.
     instead of *note PendingDeprecationWarning: 15c.

   - bpo-33453(306): Fix dataclasses to work if using literal string
     type annotations or if using PEP 563 “Postponed Evaluation of
     Annotations”.  Only specific string prefixes are detected for both
     ClassVar (“ClassVar” and “typing.ClassVar”) and InitVar (“InitVar”
     and “dataclasses.InitVar”).

   - bpo-28556(307): Minor fixes in typing module: add annotations to
     ‘NamedTuple.__new__’, pass ‘*args’ and ‘**kwds’ in
     ‘Generic.__new__’.  Original PRs by Paulius Šarka and Chad
     Dombrova.

   - bpo-33365(308): Print the header values besides the header keys
     instead just the header keys if `debuglevel' is set to >0 in *note
     http.client: 93.  Patch by Marco Strigl.

   - bpo-20087(309): Updated alias mapping with glibc 2.27 supported
     locales.

   - bpo-33422(310): Fix trailing quotation marks getting deleted when
     looking up byte/string literals on pydoc.  Patch by Andrés Delfino.

   - bpo-28167(311): The function ‘platform.linux_distribution’ and
     ‘platform.dist’ now trigger a ‘DeprecationWarning’ and have been
     marked for removal in Python 3.8

   - bpo-33281(312): Fix ctypes.util.find_library regression on macOS.

   - bpo-33311(313): Text and html output generated by cgitb does not
     display parentheses if the current call is done directly in the
     module.  Patch by Stéphane Blondon.

   - bpo-27300(314): The file classes in `tempfile' now accept an
     `errors' parameter that complements the already existing
     `encoding'.  Patch by Stephan Hohe.

   - bpo-32933(315): *note unittest.mock.mock_open(): 1102. now supports
     iteration over the file contents.  Patch by Tony Flury.

   - bpo-33217(316): Raise *note TypeError: 1fe. when looking up
     non-Enum objects in Enum classes and Enum members.

   - bpo-33197(317): Update error message when constructing invalid
     inspect.Parameters Patch by Dong-hee Na.

   - bpo-33383(318): Fixed crash in the get() method of the *note
     dbm.ndbm: 34. database object when it is called with a single
     argument.

   - bpo-33375(319): The warnings module now finds the Python file
     associated with a warning from the code object, rather than the
     frame’s global namespace.  This is consistent with how tracebacks
     and pdb find filenames, and should work better for dynamically
     executed code.

   - bpo-33336(320): ‘imaplib’ now allows ‘MOVE’ command in
     ‘IMAP4.uid()’ (RFC 6851: IMAP MOVE Extension) and potentially as a
     name of supported method of ‘IMAP4’ object.

   - bpo-32455(321): Added `jump' parameter to *note dis.stack_effect():
     927.

   - bpo-27485(322): Rename and deprecate undocumented functions in
     *note urllib.parse(): 128.

   - bpo-33332(323): Add ‘signal.valid_signals()’ to expose the POSIX
     sigfillset() functionality.

   - bpo-33251(324): ‘ConfigParser.items()’ was fixed so that key-value
     pairs passed in via *note vars: 116d. are not included in the
     resulting output.

   - bpo-33329(325): Fix multiprocessing regression on newer glibcs

   - bpo-33334(326): *note dis.stack_effect(): 927. now supports all
     defined opcodes including NOP and EXTENDED_ARG.

   - bpo-991266(327): Fix quoting of the ‘Comment’ attribute of *note
     http.cookies.SimpleCookie: 116e.

   - bpo-33131(328): Upgrade bundled version of pip to 10.0.1.

   - bpo-33308(329): Fixed a crash in the *note parser: c7. module when
     converting an ST object to a tree of tuples or lists with
     ‘line_info=False’ and ‘col_info=True’.

   - bpo-23403(330): lib2to3 now uses pickle protocol 4 for pre-computed
     grammars.

   - bpo-33266(331): lib2to3 now recognizes ‘rf'...'’ strings.

   - bpo-11594(332): Ensure line-endings are respected when using
     lib2to3.

   - bpo-33254(333): Have *note importlib.resources.contents(): 116f.
     and *note importlib.abc.ResourceReader.contents(): 1170. return an
     *note iterable: c7c. instead of an *note iterator: 1171.

   - bpo-33265(334): ‘contextlib.ExitStack’ and
     ‘contextlib.AsyncExitStack’ now use a method instead of a wrapper
     function for exit callbacks.

   - bpo-33263(335): Fix FD leak in ‘_SelectorSocketTransport’ Patch by
     Vlad Starostin.

   - bpo-33256(336): Fix display of ‘<module>’ call in the html produced
     by ‘cgitb.html()’.  Patch by Stéphane Blondon.

   - bpo-33144(337): ‘random.Random()’ and its subclassing mechanism got
     optimized to check only once at class/subclass instantiation time
     whether its ‘getrandbits()’ method can be relied on by other
     methods, including ‘randrange()’, for the generation of arbitrarily
     large random integers.  Patch by Wolfgang Maier.

   - bpo-33185(338): Fixed regression when running pydoc with the *note
     -m: 443. switch.  (The regression was introduced in 3.7.0b3 by the
     resolution of bpo-33053(339))

     This fix also changed pydoc to add ‘os.getcwd()’ to *note sys.path:
     260. when necessary, rather than adding ‘"."’.

   - bpo-29613(340): Added support for the ‘SameSite’ cookie flag to the
     ‘http.cookies’ module.

   - bpo-33169(341): Delete entries of ‘None’ in *note
     sys.path_importer_cache: 598. when
     ‘importlib.machinery.invalidate_caches()’ is called.

   - bpo-33203(342): ‘random.Random.choice()’ now raises ‘IndexError’
     for empty sequences consistently even when called from subclasses
     without a ‘getrandbits()’ implementation.

   - bpo-33224(343): Update difflib.mdiff() for PEP 479(344).  Convert
     an uncaught StopIteration in a generator into a return-statement.

   - bpo-33209(345): End framing at the end of C implementation of *note
     pickle.Pickler.dump(): 1172.

   - bpo-32861(346): The urllib.robotparser’s ‘__str__’ representation
     now includes wildcard entries and the “Crawl-delay” and
     “Request-rate” fields.  Also removes extra newlines that were being
     appended to the end of the string.  Patch by Michael Lazar.

   - bpo-23403(347): ‘DEFAULT_PROTOCOL’ in *note pickle: ca. was bumped
     to 4.  Protocol 4 is described in PEP 3154(348) and available since
     Python 3.4.  It offers better performance and smaller size compared
     to protocol 3 introduced in Python 3.0.

   - bpo-20104(349): Improved error handling and fixed a reference leak
     in *note os.posix_spawn(): 381.

   - bpo-33106(350): Deleting a key from a read-only dbm database raises
     module specific error instead of KeyError.

   - bpo-33175(351): In dataclasses, Field.__set_name__ now looks up the
     __set_name__ special method on the class, not the instance, of the
     default value.

   - bpo-32380(352): Create functools.singledispatchmethod to support
     generic single dispatch on descriptors and methods.

   - bpo-33141(353): Have Field objects pass through __set_name__ to
     their default values, if they have their own __set_name__.

   - bpo-33096(354): Allow ttk.Treeview.insert to insert iid that has a
     false boolean value.  Note iid=0 and iid=False would be same.
     Patch by Garvit Khatri.

   - bpo-32873(355): Treat type variables and special typing forms as
     immutable by copy and pickle.  This fixes several minor issues and
     inconsistencies, and improves backwards compatibility with Python
     3.6.

   - bpo-33134(356): When computing dataclass’s __hash__, use the lookup
     table to contain the function which returns the __hash__ value.
     This is an improvement over looking up a string, and then testing
     that string to see what to do.

   - bpo-33127(357): The ssl module now compiles with LibreSSL 2.7.1.

   - bpo-32505(358): Raise TypeError if a member variable of a dataclass
     is of type Field, but doesn’t have a type annotation.

   - bpo-33078(359): Fix the failure on OSX caused by the tests relying
     on sem_getvalue

   - bpo-33116(360): Add ‘Field’ to dataclasses.__all__.

   - bpo-32896(361): Fix an error where subclassing a dataclass with a
     field that uses a default_factory would generate an incorrect
     class.

   - bpo-33100(362): Dataclasses: If a field has a default value that’s
     a MemberDescriptorType, then it’s from that field being in
     __slots__, not an actual default value.

   - bpo-32953(363): If a non-dataclass inherits from a frozen
     dataclass, allow attributes to be added to the derived class.  Only
     attributes from the frozen dataclass cannot be assigned to.
     Require all dataclasses in a hierarchy to be either all frozen or
     all non-frozen.

   - bpo-33097(364): Raise RuntimeError when ‘executor.submit’ is called
     during interpreter shutdown.

   - bpo-32968(365): Modulo and floor division involving Fraction and
     float should return float.

   - bpo-33061(366): Add missing ‘NoReturn’ to ‘__all__’ in typing.py

   - bpo-33078(367): Fix the size handling in multiprocessing.Queue when
     a pickling error occurs.

   - bpo-33064(368): lib2to3 now properly supports trailing commas after
     ‘*args’ and ‘**kwargs’ in function signatures.

   - bpo-33056(369): FIX properly close leaking fds in
     concurrent.futures.ProcessPoolExecutor.

   - bpo-33021(370): Release the GIL during fstat() calls, avoiding hang
     of all threads when calling mmap.mmap(), os.urandom(), and
     random.seed().  Patch by Nir Soffer.

   - bpo-31804(371): Avoid failing in multiprocessing.Process if the
     standard streams are closed or None at exit.

   - bpo-33034(372): Providing an explicit error message when casting
     the port property to anything that is not an integer value using
     ‘urlparse()’ and ‘urlsplit()’.  Patch by Matt Eaton.

   - bpo-30249(373): Improve struct.unpack_from() exception messages for
     problems with the buffer size and offset.

   - bpo-33037(374): Skip sending/receiving data after SSL transport
     closing.

   - bpo-27683(375): Fix a regression in *note ipaddress: a2. that
     result of ‘hosts()’ is empty when the network is constructed by a
     tuple containing an integer mask and only 1 bit left for addresses.

   - bpo-22674(376): Add the strsignal() function in the signal module
     that returns the system description of the given signal, as
     returned by strsignal(3).

   - bpo-32999(377): Fix C implementation of ‘ABC.__subclasscheck__(cls,
     subclass)’ crashed when ‘subclass’ is not a type object.

   - bpo-33009(378): Fix inspect.signature() for single-parameter
     partialmethods.

   - bpo-32969(379): Expose several missing constants in zlib and fix
     corresponding documentation.

   - bpo-32056(380): Improved exceptions raised for invalid number of
     channels and sample width when read an audio file in modules *note
     aifc: 4, *note wave: 130. and *note sunau: fa.

   - bpo-32970(381): Improved disassembly of the MAKE_FUNCTION
     instruction.

   - bpo-32844(382): Fix wrong redirection of a low descriptor (0 or 1)
     to stderr in subprocess if another low descriptor is closed.

   - bpo-32960(383): For dataclasses, disallow inheriting frozen from
     non-frozen classes, and also disallow inheriting non-frozen from
     frozen classes.  This restriction will be relaxed at a future date.

   - bpo-32713(384): Fixed tarfile.itn handling of out-of-bounds float
     values.  Patch by Joffrey Fuhrer.

   - bpo-32257(385): The ssl module now contains OP_NO_RENEGOTIATION
     constant, available with OpenSSL 1.1.0h or 1.1.1.

   - bpo-32951(386): Direct instantiation of SSLSocket and SSLObject
     objects is now prohibited.  The constructors were never documented,
     tested, or designed as public constructors.  Users were suppose to
     use ssl.wrap_socket() or SSLContext.

   - bpo-32929(387): Remove the tri-state parameter “hash”, and add the
     boolean “unsafe_hash”.  If unsafe_hash is True, add a __hash__
     function, but if a __hash__ exists, raise TypeError.  If
     unsafe_hash is False, add a __hash__ based on the values of eq= and
     frozen=.  The unsafe_hash=False behavior is the same as the old
     hash=None behavior.  unsafe_hash=False is the default, just as
     hash=None used to be.

   - bpo-32947(388): Add OP_ENABLE_MIDDLEBOX_COMPAT and test workaround
     for TLSv1.3 for future compatibility with OpenSSL 1.1.1.

   - bpo-32146(389): Document the interaction between frozen executables
     and the spawn and forkserver start methods in multiprocessing.

   - bpo-30622(390): The ssl module now detects missing NPN support in
     LibreSSL.

   - bpo-32922(391): dbm.open() now encodes filename with the filesystem
     encoding rather than default encoding.

   - bpo-32759(392): Free unused arenas in multiprocessing.heap.

   - bpo-32859(393): In ‘os.dup2’, don’t check every call whether the
     ‘dup3’ syscall exists or not.

   - bpo-32556(394): nt._getfinalpathname, nt._getvolumepathname and
     nt._getdiskusage now correctly convert from bytes.

   - bpo-21060(395): Rewrite confusing message from setup.py upload from
     “No dist file created in earlier command” to the more helpful “Must
     create and upload files in one command”.

   - bpo-32857(396): In *note tkinter: 10e, ‘after_cancel(None)’ now
     raises a *note ValueError: 16d. instead of canceling the first
     scheduled function.  Patch by Cheryl Sabella.

   - bpo-32852(397): Make sure sys.argv remains as a list when running
     trace.

   - bpo-31333(398): ‘_abc’ module is added.  It is a speedup module
     with C implementations for various functions and methods in ‘abc’.
     Creating an ABC subclass and calling ‘isinstance’ or ‘issubclass’
     with an ABC subclass are up to 1.5x faster.  In addition, this
     makes Python start-up up to 10% faster.

     Note that the new implementation hides internal registry and
     caches, previously accessible via private attributes
     ‘_abc_registry’, ‘_abc_cache’, and ‘_abc_negative_cache’.  There
     are three debugging helper methods that can be used instead
     ‘_dump_registry’, ‘_abc_registry_clear’, and ‘_abc_caches_clear’.

   - bpo-32841(399): Fixed *note asyncio.Condition: 3b0. issue which
     silently ignored cancellation after notifying and cancelling a
     conditional lock.  Patch by Bar Harel.

   - bpo-32819(400): ssl.match_hostname() has been simplified and no
     longer depends on re and ipaddress module for wildcard and IP
     addresses.  Error reporting for invalid wildcards has been
     improved.

   - bpo-19675(401): ‘multiprocessing.Pool’ no longer leaks processes if
     its initialization fails.

   - bpo-32394(402): socket: Remove
     TCP_FASTOPEN,TCP_KEEPCNT,TCP_KEEPIDLE,TCP_KEEPINTVL flags on older
     version Windows during run-time.

   - bpo-31787(403): Fixed refleaks of ‘__init__()’ methods in various
     modules.  (Contributed by Oren Milman)

   - bpo-30157(404): Fixed guessing quote and delimiter in
     csv.Sniffer.sniff() when only the last field is quoted.  Patch by
     Jake Davis.

   - bpo-30688(405): Added support of ‘\N{name}’ escapes in regular
     expressions.  Based on patch by Jonathan Eunice.

   - bpo-32792(406): collections.ChainMap() preserves the order of the
     underlying mappings.

   - bpo-32775(407): *note fnmatch.translate(): 1173. no longer produces
     patterns which contain set operations.  Sets starting with ‘[’ or
     containing ‘–’, ‘&&’, ‘~~’ or ‘||’ will be interpreted differently
     in regular expressions in future versions.  Currently they emit
     warnings.  fnmatch.translate() now avoids producing patterns
     containing such sets by accident.

   - bpo-32622(408): Implement native fast sendfile for Windows proactor
     event loop.

   - bpo-32777(409): Fix a rare but potential pre-exec child process
     deadlock in subprocess on POSIX systems when marking file
     descriptors inheritable on exec in the child process.  This bug
     appears to have been introduced in 3.4.

   - bpo-32647(410): The ctypes module used to depend on indirect
     linking for dlopen.  The shared extension is now explicitly linked
     against libdl on platforms with dl.

   - bpo-32749(411): A *note dbm.dumb: 32. database opened with flags
     ‘r’ is now read-only.  *note dbm.dumb.open(): 3e1. with flags ‘r’
     and ‘w’ no longer creates a database if it does not exist.

   - bpo-32741(412): Implement ‘asyncio.TimerHandle.when()’ method.

   - bpo-32691(413): Use mod_spec.parent when running modules with pdb

   - bpo-32734(414): Fixed ‘asyncio.Lock()’ safety issue which allowed
     acquiring and locking the same lock multiple times, without it
     being free.  Patch by Bar Harel.

   - bpo-32727(415): Do not include name field in SMTP envelope from
     address.  Patch by Stéphane Wirtel

   - bpo-31453(416): Add TLSVersion constants and
     SSLContext.maximum_version / minimum_version attributes.  The new
     API wraps OpenSSL 1.1
     ‘https://www.openssl.org/docs/man1.1.0/ssl/SSL_CTX_set_min_proto_version.html’
     feature.

   - bpo-24334(417): Internal implementation details of ssl module were
     cleaned up.  The SSLSocket has one less layer of indirection.
     Owner and session information are now handled by the SSLSocket and
     SSLObject constructor.  Channel binding implementation has been
     simplified.

   - bpo-31848(418): Fix the error handling in Aifc_read.initfp() when
     the SSND chunk is not found.  Patch by Zackery Spytz.

   - bpo-32585(419): Add Ttk spinbox widget to *note tkinter.ttk: 118.
     Patch by Alan D Moore.

   - bpo-32512(420): *note profile: d3. CLI accepts ‘-m module_name’ as
     an alternative to script path.

   - bpo-8525(421): help() on a type now displays builtin subclasses.
     This is intended primarily to help with notification of more
     specific exception subclasses.

     Patch by Sanyam Khurana.

   - bpo-31639(422): http.server now exposes a ThreadingHTTPServer class
     and uses it when the module is run with ‘-m’ to cope with web
     browsers pre-opening sockets.

   - bpo-29877(423): compileall: import ProcessPoolExecutor only when
     needed, preventing hangs on low resource platforms

   - bpo-32221(424): Various functions returning tuple containing IPv6
     addresses now omit ‘%scope’ part since the same information is
     already encoded in `scopeid' tuple item.  Especially this speeds up
     ‘socket.recvfrom()’ when it receives multicast packet since useless
     resolving of network interface name is omitted.

   - bpo-32147(425): *note binascii.unhexlify(): 1174. is now up to 2
     times faster.  Patch by Sergey Fedoseev.

   - bpo-30693(426): The TarFile class now recurses directories in a
     reproducible way.

   - bpo-30693(427): The ZipFile class now recurses directories in a
     reproducible way.

   - bpo-31680(428): Added *note curses.ncurses_version: 2f0.

   - bpo-31908(429): Fix output of cover files for ‘trace’ module
     command-line tool.  Previously emitted cover files only when
     ‘--missing’ option was used.  Patch by Michael Selik.

   - bpo-31608(430): Raise a ‘TypeError’ instead of crashing if a
     ‘collections.deque’ subclass returns a non-deque from ‘__new__’.
     Patch by Oren Milman.

   - bpo-31425(431): Add support for sockets of the AF_QIPCRTR address
     family, supported by the Linux kernel.  This is used to communicate
     with services, such as GPS or radio, running on Qualcomm devices.
     Patch by Bjorn Andersson.

   - bpo-22005(432): Implemented unpickling instances of *note datetime:
     1a0, *note date: 19e. and *note time: 5ed. pickled by Python 2.
     ‘encoding='latin1'’ should be used for successful decoding.

   - bpo-27645(433): *note sqlite3.Connection: 4df. now exposes a *note
     backup: 4e0. method, if the underlying SQLite library is at version
     3.6.11 or higher.  Patch by Lele Gaifax.

   - bpo-16865(434): Support arrays >=2GiB in *note ctypes: 2a.  Patch
     by Segev Finer.

   - bpo-31508(435): Removed support of arguments in *note
     tkinter.ttk.Treeview.selection: 3de.  It was deprecated in 3.6.
     Use specialized methods like ‘selection_set’ for changing the
     selection.

   - bpo-29456(436): Fix bugs in hangul normalization: u1176, u11a7 and
     u11c3

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35845

   (2) https://bugs.python.org/issue35864

   (3) https://bugs.python.org/issue35537

   (4) https://bugs.python.org/issue35847

   (5) https://bugs.python.org/issue35813

   (6) https://bugs.python.org/issue35780

   (7) https://bugs.python.org/issue35537

   (8) https://bugs.python.org/issue23846

   (9) https://bugs.python.org/issue34323

   (10) https://bugs.python.org/issue35674

   (11) https://bugs.python.org/issue35733

   (12) https://bugs.python.org/issue35726

   (13) https://bugs.python.org/issue35719

   (14) https://bugs.python.org/issue35717

   (15) https://bugs.python.org/issue35699

   (16) https://bugs.python.org/issue32710

   (17) https://bugs.python.org/issue35702

   (18) https://bugs.python.org/issue32710

   (19) https://bugs.python.org/issue35682

   (20) https://bugs.python.org/issue35283

   (21) https://bugs.python.org/issue35664

   (22) https://bugs.python.org/issue35643

   (23) https://bugs.python.org/issue35619

   (24) https://bugs.python.org/issue28503

   (25) https://bugs.python.org/issue35614

   (26) https://bugs.python.org/issue35568

   (27) https://bugs.python.org/issue35588

   (28) https://bugs.python.org/issue35585

   (29) https://bugs.python.org/issue30561

   (30) https://bugs.python.org/issue35537

   (31) https://bugs.python.org/issue35526

   (32) https://bugs.python.org/issue35523

   (33) https://bugs.python.org/issue31784

   (34) https://bugs.python.org/issue35513

   (35) https://bugs.python.org/issue35502

   (36) https://bugs.python.org/issue35348

   (37) https://bugs.python.org/issue35491

   (38) https://bugs.python.org/issue35477

   (39) https://bugs.python.org/issue31446

   (40) https://bugs.python.org/issue35471

   (41) https://bugs.python.org/issue23057

   (42) https://bugs.python.org/issue35052

   (43) https://bugs.python.org/issue20239

   (44) https://bugs.python.org/issue17185

   (45) https://bugs.python.org/issue35445

   (46) https://bugs.python.org/issue35415

   (47) https://bugs.python.org/issue35424

   (48) https://bugs.python.org/issue35330

   (49) https://bugs.python.org/issue35346

   (50) https://bugs.python.org/issue10496

   (51) https://bugs.python.org/issue10496

   (52) https://bugs.python.org/issue35389

   (53) https://bugs.python.org/issue35394

   (54) https://bugs.python.org/issue35310

   (55) https://bugs.python.org/issue35380

   (56) https://bugs.python.org/issue35341

   (57) https://bugs.python.org/issue35371

   (58) https://bugs.python.org/issue35346

   (59) https://bugs.python.org/issue35066

   (60) https://bugs.python.org/issue35345

   (61) https://bugs.python.org/issue35344

   (62) https://bugs.python.org/issue35312

   (63) https://bugs.python.org/issue35308

   (64) https://bugs.python.org/issue24746

   (65) https://bugs.python.org/issue28604

   (66) https://bugs.python.org/issue35277

   (67) https://bugs.python.org/issue24209

   (68) https://bugs.python.org/issue35226

   (69) https://bugs.python.org/issue29564

   (70) https://bugs.python.org/issue35189

   (71) https://bugs.python.org/issue30064

   (72) https://bugs.python.org/issue35186

   (73) https://bugs.python.org/issue35152

   (74) https://bugs.python.org/issue35062

   (75) https://bugs.python.org/issue35065

   (76) https://bugs.python.org/issue34160

   (77) https://bugs.python.org/issue35079

   (78) https://bugs.python.org/issue33710

   (79) https://bugs.python.org/issue35017

   (80) https://bugs.python.org/issue35024

   (81) https://bugs.python.org/issue35047

   (82) https://bugs.python.org/issue31047

   (83) https://bugs.python.org/issue35053

   (84) https://bugs.python.org/issue31553

   (85) https://bugs.python.org/issue34794

   (86) https://bugs.python.org/issue34909

   (87) https://bugs.python.org/issue35022

   (88) https://bugs.python.org/issue35008

   (89) https://bugs.python.org/issue23420

   (90) https://bugs.python.org/issue33947

   (91) https://bugs.python.org/issue34890

   (92) https://bugs.python.org/issue34521

   (93) https://tools.ietf.org/html/rfc3542.html

   (94) https://bugs.python.org/issue31522

   (95) https://bugs.python.org/issue34970

   (96) https://bugs.python.org/issue34969

   (97) https://bugs.python.org/issue16965

   (98) https://bugs.python.org/issue34966

   (99) https://bugs.python.org/issue34926

   (100) https://bugs.python.org/issue23831

   (101) https://bugs.python.org/issue34941

   (102) https://bugs.python.org/issue32680

   (103) https://bugs.python.org/issue34769

   (104) https://bugs.python.org/issue34936

   (105) https://bugs.python.org/issue34829

   (106) https://bugs.python.org/issue34911

   (107) https://bugs.python.org/issue34922

   (108) https://bugs.python.org/issue34925

   (109) https://bugs.python.org/issue34900

   (110) https://bugs.python.org/issue34844

   (111) https://bugs.python.org/issue34897

   (112) https://bugs.python.org/issue34871

   (113) https://bugs.python.org/issue34898

   (114) https://bugs.python.org/issue28441

   (115) https://bugs.python.org/issue34866

   (116) https://bugs.python.org/issue34711

   (117) https://bugs.python.org/issue34872

   (118) https://bugs.python.org/issue34849

   (119) https://bugs.python.org/issue34022

   (120) https://bugs.python.org/issue34819

   (121) https://bugs.python.org/issue34758

   (122) https://bugs.python.org/issue34789

   (123) https://bugs.python.org/issue34334

   (124) https://bugs.python.org/issue34687

   (125) https://bugs.python.org/issue5950

   (126) https://bugs.python.org/issue32892

   (127) https://bugs.python.org/issue34728

   (128) https://bugs.python.org/issue34738

   (129) https://bugs.python.org/issue34659

   (130) https://bugs.python.org/issue29577

   (131) https://bugs.python.org/issue34670

   (132) https://bugs.python.org/issue32718

   (133) https://bugs.python.org/issue31177

   (134) https://bugs.python.org/issue34672

   (135) https://bugs.python.org/issue34666

   (136) https://bugs.python.org/issue6721

   (137) https://bugs.python.org/issue34658

   (138) https://bugs.python.org/issue34652

   (139) https://bugs.python.org/issue34638

   (140) https://bugs.python.org/issue34536

   (141) https://bugs.python.org/issue34636

   (142) https://bugs.python.org/issue24412

   (143) https://bugs.python.org/issue34630

   (144) https://bugs.python.org/issue32490

   (145) https://bugs.python.org/issue34363

   (146) https://bugs.python.org/issue34625

   (147) https://bugs.python.org/issue32270

   (148) https://bugs.python.org/issue34622

   (149) https://bugs.python.org/issue34610

   (150) https://bugs.python.org/issue34421

   (151) https://bugs.python.org/issue34604

   (152) https://bugs.python.org/issue30977

   (153) https://bugs.python.org/issue34574

   (154) https://bugs.python.org/issue8110

   (155) https://bugs.python.org/issue34530

   (156) https://bugs.python.org/issue34563

   (157) https://bugs.python.org/issue34558

   (158) https://bugs.python.org/issue34282

   (159) https://bugs.python.org/issue22872

   (160) https://bugs.python.org/issue34515

   (161) https://bugs.python.org/issue13312

   (162) https://bugs.python.org/issue34472

   (163) https://bugs.python.org/issue34454

   (164) https://bugs.python.org/issue6700

   (165) https://bugs.python.org/issue34171

   (166) https://bugs.python.org/issue34441

   (167) https://bugs.python.org/issue34427

   (168) https://bugs.python.org/issue34412

   (169) https://bugs.python.org/issue20849

   (170) https://bugs.python.org/issue31715

   (171) https://bugs.python.org/issue34384

   (172) https://bugs.python.org/issue22602

   (173) https://bugs.python.org/issue2122

   (174) https://bugs.python.org/issue34341

   (175) https://bugs.python.org/issue34333

   (176) https://bugs.python.org/issue18540

   (177) https://bugs.python.org/issue26502

   (178) https://bugs.python.org/issue34318

   (179) https://bugs.python.org/issue9372

   (180) https://bugs.python.org/issue33613

   (181) https://bugs.python.org/issue34248

   (182) https://bugs.python.org/issue33089

   (183) https://bugs.python.org/issue34246

   (184) https://bugs.python.org/issue31047

   (185) https://bugs.python.org/issue32321

   (186) https://bugs.python.org/issue34270

   (187) https://bugs.python.org/issue34263

   (188) https://bugs.python.org/issue34035

   (189) https://bugs.python.org/issue32215

   (190) https://bugs.python.org/issue34075

   (191) https://bugs.python.org/issue34251

   (192) https://bugs.python.org/issue19891

   (193) https://bugs.python.org/issue33089

   (194) https://bugs.python.org/issue34228

   (195) https://bugs.python.org/issue13041

   (196) https://bugs.python.org/issue34213

   (197) https://bugs.python.org/issue34052

   (198) https://bugs.python.org/issue34197

   (199) https://bugs.python.org/issue32788

   (200) https://bugs.python.org/issue21446

   (201) https://bugs.python.org/issue940286

   (202) https://bugs.python.org/issue34164

   (203) https://bugs.python.org/issue33729

   (204) https://bugs.python.org/issue34097

   (205) https://bugs.python.org/issue34108

   (206) https://bugs.python.org/issue34070

   (207) https://bugs.python.org/issue27494

   (208) https://bugs.python.org/issue27494

   (209) https://bugs.python.org/issue33967

   (210) https://bugs.python.org/issue34041

   (211) https://bugs.python.org/issue34056

   (212) https://www.python.org/dev/peps/pep-0552

   (213) https://bugs.python.org/issue34054

   (214) https://bugs.python.org/issue34043

   (215) https://bugs.python.org/issue34044

   (216) https://bugs.python.org/issue34010

   (217) https://bugs.python.org/issue34019

   (218) https://bugs.python.org/issue34003

   (219) https://bugs.python.org/issue33978

   (220) https://bugs.python.org/issue14117

   (221) https://bugs.python.org/issue33974

   (222) https://bugs.python.org/issue27500

   (223) https://bugs.python.org/issue24567

   (224) https://bugs.python.org/issue33871

   (225) https://bugs.python.org/issue25007

   (226) https://bugs.python.org/issue33929

   (227) https://bugs.python.org/issue33899

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   (229) https://bugs.python.org/issue33695

   (230) https://bugs.python.org/issue33695

   (231) https://bugs.python.org/issue33916

   (232) https://bugs.python.org/issue32568

   (233) https://bugs.python.org/issue33833

   (234) https://bugs.python.org/issue33663

   (235) https://bugs.python.org/issue33721

   (236) https://bugs.python.org/issue26544

   (237) https://bugs.python.org/issue33843

   (238) https://bugs.python.org/issue33842

   (239) https://bugs.python.org/issue30167

   (240) https://bugs.python.org/issue33805

   (241) https://bugs.python.org/issue33687

   (242) https://bugs.python.org/issue33812

   (243) https://bugs.python.org/issue32108

   (244) https://bugs.python.org/issue27397

   (245) https://bugs.python.org/issue33578

   (246) https://bugs.python.org/issue30805

   (247) https://bugs.python.org/issue33476

   (248) https://bugs.python.org/issue33694

   (249) https://bugs.python.org/issue32493

   (250) https://bugs.python.org/issue33792

   (251) https://bugs.python.org/issue33274

   (252) https://bugs.python.org/issue33778

   (253) https://bugs.python.org/issue33165

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   (255) https://bugs.python.org/issue33769

   (256) https://bugs.python.org/issue33767

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   (258) https://bugs.python.org/issue31014

   (259) https://bugs.python.org/issue2504

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   (261) https://bugs.python.org/issue32751

   (262) https://bugs.python.org/issue32684

   (263) https://bugs.python.org/issue33654

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   (277) https://bugs.python.org/issue33618

   (278) https://bugs.python.org/issue33625

   (279) https://bugs.python.org/issue33623

   (280) https://bugs.python.org/issue11874

   (281) https://bugs.python.org/issue30877

   (282) https://bugs.python.org/issue33604

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   (284) https://bugs.python.org/issue21145

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   (287) https://bugs.python.org/issue12486

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   (290) https://bugs.python.org/issue33109

   (291) https://bugs.python.org/issue26510

   (292) https://bugs.python.org/issue33541

   (293) https://bugs.python.org/issue33536

   (294) https://bugs.python.org/issue33542

   (295) https://bugs.python.org/issue26819

   (296) https://bugs.python.org/issue33516

   (297) https://bugs.python.org/issue28612

   (298) https://bugs.python.org/issue28167

   (299) https://bugs.python.org/issue33504

   (300) https://bugs.python.org/issue33505

   (301) https://bugs.python.org/issue33497

   (302) https://bugs.python.org/issue29235

   (303) https://bugs.python.org/issue33495

   (304) https://bugs.python.org/issue26103

   (305) https://bugs.python.org/issue29209

   (306) https://bugs.python.org/issue33453

   (307) https://bugs.python.org/issue28556

   (308) https://bugs.python.org/issue33365

   (309) https://bugs.python.org/issue20087

   (310) https://bugs.python.org/issue33422

   (311) https://bugs.python.org/issue28167

   (312) https://bugs.python.org/issue33281

   (313) https://bugs.python.org/issue33311

   (314) https://bugs.python.org/issue27300

   (315) https://bugs.python.org/issue32933

   (316) https://bugs.python.org/issue33217

   (317) https://bugs.python.org/issue33197

   (318) https://bugs.python.org/issue33383

   (319) https://bugs.python.org/issue33375

   (320) https://bugs.python.org/issue33336

   (321) https://bugs.python.org/issue32455

   (322) https://bugs.python.org/issue27485

   (323) https://bugs.python.org/issue33332

   (324) https://bugs.python.org/issue33251

   (325) https://bugs.python.org/issue33329

   (326) https://bugs.python.org/issue33334

   (327) https://bugs.python.org/issue991266

   (328) https://bugs.python.org/issue33131

   (329) https://bugs.python.org/issue33308

   (330) https://bugs.python.org/issue23403

   (331) https://bugs.python.org/issue33266

   (332) https://bugs.python.org/issue11594

   (333) https://bugs.python.org/issue33254

   (334) https://bugs.python.org/issue33265

   (335) https://bugs.python.org/issue33263

   (336) https://bugs.python.org/issue33256

   (337) https://bugs.python.org/issue33144

   (338) https://bugs.python.org/issue33185

   (339) https://bugs.python.org/issue33053

   (340) https://bugs.python.org/issue29613

   (341) https://bugs.python.org/issue33169

   (342) https://bugs.python.org/issue33203

   (343) https://bugs.python.org/issue33224

   (344) https://www.python.org/dev/peps/pep-0479

   (345) https://bugs.python.org/issue33209

   (346) https://bugs.python.org/issue32861

   (347) https://bugs.python.org/issue23403

   (348) https://www.python.org/dev/peps/pep-3154

   (349) https://bugs.python.org/issue20104

   (350) https://bugs.python.org/issue33106

   (351) https://bugs.python.org/issue33175

   (352) https://bugs.python.org/issue32380

   (353) https://bugs.python.org/issue33141

   (354) https://bugs.python.org/issue33096

   (355) https://bugs.python.org/issue32873

   (356) https://bugs.python.org/issue33134

   (357) https://bugs.python.org/issue33127

   (358) https://bugs.python.org/issue32505

   (359) https://bugs.python.org/issue33078

   (360) https://bugs.python.org/issue33116

   (361) https://bugs.python.org/issue32896

   (362) https://bugs.python.org/issue33100

   (363) https://bugs.python.org/issue32953

   (364) https://bugs.python.org/issue33097

   (365) https://bugs.python.org/issue32968

   (366) https://bugs.python.org/issue33061

   (367) https://bugs.python.org/issue33078

   (368) https://bugs.python.org/issue33064

   (369) https://bugs.python.org/issue33056

   (370) https://bugs.python.org/issue33021

   (371) https://bugs.python.org/issue31804

   (372) https://bugs.python.org/issue33034

   (373) https://bugs.python.org/issue30249

   (374) https://bugs.python.org/issue33037

   (375) https://bugs.python.org/issue27683

   (376) https://bugs.python.org/issue22674

   (377) https://bugs.python.org/issue32999

   (378) https://bugs.python.org/issue33009

   (379) https://bugs.python.org/issue32969

   (380) https://bugs.python.org/issue32056

   (381) https://bugs.python.org/issue32970

   (382) https://bugs.python.org/issue32844

   (383) https://bugs.python.org/issue32960

   (384) https://bugs.python.org/issue32713

   (385) https://bugs.python.org/issue32257

   (386) https://bugs.python.org/issue32951

   (387) https://bugs.python.org/issue32929

   (388) https://bugs.python.org/issue32947

   (389) https://bugs.python.org/issue32146

   (390) https://bugs.python.org/issue30622

   (391) https://bugs.python.org/issue32922

   (392) https://bugs.python.org/issue32759

   (393) https://bugs.python.org/issue32859

   (394) https://bugs.python.org/issue32556

   (395) https://bugs.python.org/issue21060

   (396) https://bugs.python.org/issue32857

   (397) https://bugs.python.org/issue32852

   (398) https://bugs.python.org/issue31333

   (399) https://bugs.python.org/issue32841

   (400) https://bugs.python.org/issue32819

   (401) https://bugs.python.org/issue19675

   (402) https://bugs.python.org/issue32394

   (403) https://bugs.python.org/issue31787

   (404) https://bugs.python.org/issue30157

   (405) https://bugs.python.org/issue30688

   (406) https://bugs.python.org/issue32792

   (407) https://bugs.python.org/issue32775

   (408) https://bugs.python.org/issue32622

   (409) https://bugs.python.org/issue32777

   (410) https://bugs.python.org/issue32647

   (411) https://bugs.python.org/issue32749

   (412) https://bugs.python.org/issue32741

   (413) https://bugs.python.org/issue32691

   (414) https://bugs.python.org/issue32734

   (415) https://bugs.python.org/issue32727

   (416) https://bugs.python.org/issue31453

   (417) https://bugs.python.org/issue24334

   (418) https://bugs.python.org/issue31848

   (419) https://bugs.python.org/issue32585

   (420) https://bugs.python.org/issue32512

   (421) https://bugs.python.org/issue8525

   (422) https://bugs.python.org/issue31639

   (423) https://bugs.python.org/issue29877

   (424) https://bugs.python.org/issue32221

   (425) https://bugs.python.org/issue32147

   (426) https://bugs.python.org/issue30693

   (427) https://bugs.python.org/issue30693

   (428) https://bugs.python.org/issue31680

   (429) https://bugs.python.org/issue31908

   (430) https://bugs.python.org/issue31608

   (431) https://bugs.python.org/issue31425

   (432) https://bugs.python.org/issue22005

   (433) https://bugs.python.org/issue27645

   (434) https://bugs.python.org/issue16865

   (435) https://bugs.python.org/issue31508

   (436) https://bugs.python.org/issue29456


File: python.info,  Node: Documentation<25>,  Next: Tests<24>,  Prev: Library<30>,  Up: Python 3 8 0 alpha 1

1.19.31.4 Documentation
.......................

   - bpo-21257(1): Document *note http.client.parse_headers(): 1176.

   - bpo-34764(2): Improve example of iter() with 2nd sentinel argument.

   - bpo-35564(3): Explicitly set master_doc variable in conf.py for
     compliance with Sphinx 2.0

   - bpo-35511(4): Specified that profile.Profile class doesn’t not
     support enable or disable methods.  Also, elaborated that Profile
     object as a context manager is only supported in cProfile module.

   - bpo-10536(5): Enhance the gettext docs.  Patch by Éric Araujo

   - bpo-35089(6): Remove mention of ‘typing.io’ and ‘typing.re’.  Their
     types should be imported from ‘typing’ directly.

   - bpo-35038(7): Fix the documentation about an unexisting
     ‘f_restricted’ attribute in the frame object.  Patch by Stéphane
     Wirtel

   - bpo-35042(8): Replace PEP XYZ by the pep role and allow to use the
     direct links to the PEPs.

   - bpo-35044(9): Fix the documentation with the role ‘exc’ for the
     appropriated exception.  Patch by Stéphane Wirtel

   - bpo-35035(10): Rename documentation for *note email.utils: 74. to
     ‘email.utils.rst’.

   - bpo-34967(11): Use app.add_object_type() instead of the deprecated
     Sphinx function app.description_unit()

   - bpo-34913(12): Add documentation about the new command line
     interface of the gzip module.

   - bpo-32174(13): chm document displays non-ASCII charaters properly
     on some MBCS Windows systems.

   - bpo-11233(14): Create availability directive for documentation.
     Original patch by Georg Brandl.

   - bpo-34790(15): Document how passing coroutines to asyncio.wait()
     can be confusing.

   - bpo-34552(16): Make clear that ‘==’ operator sometimes is
     equivalent to ‘is’.  The ‘<’, ‘<=’, ‘>’ and ‘>=’ operators are only
     defined where they make sense.

   - bpo-28617(17): Fixed info in the stdtypes docs concerning the types
     that support membership tests.

   - bpo-20177(18): Migrate datetime.date.fromtimestamp to Argument
     Clinic.  Patch by Tim Hoffmann.

   - bpo-34065(19): Fix wrongly written basicConfig documentation markup
     syntax

   - bpo-33460(20): replaced ellipsis with correct error codes in
     tutorial chapter 3.

   - bpo-33847(21): Add ‘@’ operator entry to index.

   - bpo-33409(22): Clarified the relationship between PEP 538(23)’s
     PYTHONCOERCECLOCALE and PEP 540’s PYTHONUTF8 mode.

   - bpo-33197(24): Add versionadded tag to the documentation of
     ParameterKind.description

   - bpo-17045(25): Improve the C-API doc for PyTypeObject.  This
     includes adding several quick-reference tables and a lot of missing
     slot/typedef entries.  The existing entries were also cleaned up
     with a slightly more consistent format.

   - bpo-33736(26): Improve the documentation of *note
     asyncio.open_connection(): 46b, *note asyncio.start_server(): 46c.
     and their UNIX socket counterparts.

   - bpo-23859(27): Document that *note asyncio.wait(): 207. does not
     cancel its futures on timeout.

   - bpo-32436(28): Document PEP 567(29) changes to asyncio.

   - bpo-33604(30): Update HMAC md5 default to a DeprecationWarning,
     bump removal to 3.8.

   - bpo-33594(31): Document ‘getargspec’, ‘from_function’ and
     ‘from_builtin’ as deprecated in their respective docstring, and
     include version since deprecation in DeprecationWarning message.

   - bpo-33503(32): Fix broken pypi link

   - bpo-33421(33): Add missing documentation for
     ‘typing.AsyncContextManager’.

   - bpo-33487(34): BZ2file now emit a DeprecationWarning when
     buffering=None is passed, the deprecation message and documentation
     also now explicitly state it is deprecated since 3.0.

   - bpo-33378(35): Add Korean language switcher for
     ‘https://docs.python.org/3/’

   - bpo-33276(36): Clarify that the ‘__path__’ attribute on modules
     cannot be just any value.

   - bpo-33201(37): Modernize documentation for writing C extension
     types.

   - bpo-33195(38): Deprecate ‘Py_UNICODE’ usage in ‘c-api/arg’
     document.  ‘Py_UNICODE’ related APIs are deprecated since Python
     3.3, but it is missed in the document.

   - bpo-33126(39): Document PyBuffer_ToContiguous().

   - bpo-27212(40): Modify documentation for the ‘islice()’ recipe to
     consume initial values up to the start index.

   - bpo-28247(41): Update *note zipapp: 14a. documentation to describe
     how to make standalone applications.

   - bpo-18802(42): Documentation changes for ipaddress.  Patch by Jon
     Foster and Berker Peksag.

   - bpo-27428(43): Update documentation to clarify that
     ‘WindowsRegistryFinder’ implements ‘MetaPathFinder’.  (Patch by
     Himanshu Lakhara)

   - bpo-28124(44): The ssl module function ssl.wrap_socket() has been
     de-emphasized and deprecated in favor of the more secure and
     efficient SSLContext.wrap_socket() method.

   - bpo-17232(45): Clarify docs for -O and -OO. Patch by Terry Reedy.

   - bpo-32436(46): Add documentation for the contextvars module (PEP
     567).

   - bpo-32800(47): Update link to w3c doc for xml default namespaces.

   - bpo-11015(48): Update *note test.support: 106. documentation.

   - bpo-32613(49): Update the faq/windows.html to use the py command
     from PEP 397 instead of python.

   - bpo-8722(50): Document *note __getattr__(): 42a. behavior when
     property ‘get()’ method raises *note AttributeError: 4a2.

   - bpo-32614(51): Modify RE examples in documentation to use raw
     strings to prevent *note DeprecationWarning: 15a. and add text to
     REGEX HOWTO to highlight the deprecation.

   - bpo-20709(52): Remove the paragraph where we explain that
     os.utime() does not support a directory as path under Windows.
     Patch by Jan-Philip Gehrcke

   - bpo-32722(53): Remove the bad example in the tutorial of the
     Generator Expression.  Patch by Stéphane Wirtel

   - bpo-31972(54): Improve docstrings for *note pathlib.PurePath: 235.
     subclasses.

   - bpo-30607(55): Use the externalized ‘python-docs-theme’ package
     when building the documentation.

   - bpo-8243(56): Add a note about curses.addch and curses.addstr
     exception behavior when writing outside a window, or pad.

   - bpo-32337(57): Update documentation related with ‘dict’ order.

   - bpo-25041(58): Document ‘AF_PACKET’ in the *note socket: ef.
     module.

   - bpo-31432(59): Clarify meaning of CERT_NONE, CERT_OPTIONAL, and
     CERT_REQUIRED flags for ssl.SSLContext.verify_mode.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21257

   (2) https://bugs.python.org/issue34764

   (3) https://bugs.python.org/issue35564

   (4) https://bugs.python.org/issue35511

   (5) https://bugs.python.org/issue10536

   (6) https://bugs.python.org/issue35089

   (7) https://bugs.python.org/issue35038

   (8) https://bugs.python.org/issue35042

   (9) https://bugs.python.org/issue35044

   (10) https://bugs.python.org/issue35035

   (11) https://bugs.python.org/issue34967

   (12) https://bugs.python.org/issue34913

   (13) https://bugs.python.org/issue32174

   (14) https://bugs.python.org/issue11233

   (15) https://bugs.python.org/issue34790

   (16) https://bugs.python.org/issue34552

   (17) https://bugs.python.org/issue28617

   (18) https://bugs.python.org/issue20177

   (19) https://bugs.python.org/issue34065

   (20) https://bugs.python.org/issue33460

   (21) https://bugs.python.org/issue33847

   (22) https://bugs.python.org/issue33409

   (23) https://www.python.org/dev/peps/pep-0538

   (24) https://bugs.python.org/issue33197

   (25) https://bugs.python.org/issue17045

   (26) https://bugs.python.org/issue33736

   (27) https://bugs.python.org/issue23859

   (28) https://bugs.python.org/issue32436

   (29) https://www.python.org/dev/peps/pep-0567

   (30) https://bugs.python.org/issue33604

   (31) https://bugs.python.org/issue33594

   (32) https://bugs.python.org/issue33503

   (33) https://bugs.python.org/issue33421

   (34) https://bugs.python.org/issue33487

   (35) https://bugs.python.org/issue33378

   (36) https://bugs.python.org/issue33276

   (37) https://bugs.python.org/issue33201

   (38) https://bugs.python.org/issue33195

   (39) https://bugs.python.org/issue33126

   (40) https://bugs.python.org/issue27212

   (41) https://bugs.python.org/issue28247

   (42) https://bugs.python.org/issue18802

   (43) https://bugs.python.org/issue27428

   (44) https://bugs.python.org/issue28124

   (45) https://bugs.python.org/issue17232

   (46) https://bugs.python.org/issue32436

   (47) https://bugs.python.org/issue32800

   (48) https://bugs.python.org/issue11015

   (49) https://bugs.python.org/issue32613

   (50) https://bugs.python.org/issue8722

   (51) https://bugs.python.org/issue32614

   (52) https://bugs.python.org/issue20709

   (53) https://bugs.python.org/issue32722

   (54) https://bugs.python.org/issue31972

   (55) https://bugs.python.org/issue30607

   (56) https://bugs.python.org/issue8243

   (57) https://bugs.python.org/issue32337

   (58) https://bugs.python.org/issue25041

   (59) https://bugs.python.org/issue31432


File: python.info,  Node: Tests<24>,  Next: Build<23>,  Prev: Documentation<25>,  Up: Python 3 8 0 alpha 1

1.19.31.5 Tests
...............

   - bpo-35772(1): Fix sparse file tests of test_tarfile on ppc64 with
     the tmpfs filesystem.  Fix the function testing if the filesystem
     supports sparse files: create a file which contains data and
     “holes”, instead of creating a file which contains no data.  tmpfs
     effective block size is a page size (tmpfs lives in the page
     cache).  RHEL uses 64 KiB pages on aarch64, ppc64, ppc64le, only
     s390x and x86_64 use 4 KiB pages, whereas the test punch holes of 4
     KiB.

   - bpo-35045(2): Make ssl tests less strict and also accept TLSv1 as
     system default.  The changes unbreaks test_min_max_version on
     Fedora 29.

   - bpo-32710(3): ‘test_asyncio/test_sendfile.py’ now resets the event
     loop policy using ‘tearDownModule()’ as done in other tests, to
     prevent a warning when running tests on Windows.

   - bpo-33717(4): test.pythoninfo now logs information of all clocks,
     not only time.time() and time.perf_counter().

   - bpo-35488(5): Add a test to pathlib’s Path.match() to verify it
     does not support glob-style ** recursive pattern matching.

   - bpo-31731(6): Fix a race condition in ‘check_interrupted_write()’
     of test_io: create directly the thread with SIGALRM signal blocked,
     rather than blocking the signal later from the thread.  Previously,
     it was possible that the thread gets the signal before the signal
     is blocked.

   - bpo-35424(7): Fix test_multiprocessing_main_handling: use
     ‘multiprocessing.Pool’ with a context manager and then explicitly
     join the pool.

   - bpo-35519(8): Rename ‘test.bisect’ module to ‘test.bisect_cmd’ to
     avoid conflict with *note bisect: 11. module when running directly
     a test like ‘./python Lib/test/test_xmlrpc.py’.

   - bpo-35513(9): Replace *note time.time(): 42d. with *note
     time.monotonic(): 85e. in tests to measure time delta.

   - bpo-34279(10): *note test.support.run_unittest(): 1178. no longer
     raise ‘TestDidNotRun’ if the test result contains skipped tests.
     The exception is now only raised if no test have been run and no
     test have been skipped.

   - bpo-35412(11): Add testcase to ‘test_future4’: check unicode
     literal.

   - bpo-26704(12): Added test demonstrating double-patching of an
     instance method.  Patch by Anthony Sottile.

   - bpo-33725(13): test_multiprocessing_fork may crash on recent
     versions of macOS. Until the issue is resolved, skip the test on
     macOS.

   - bpo-35352(14): Modify test_asyncio to use the certificate set from
     the test directory.

   - bpo-35317(15): Fix ‘mktime()’ overflow error in ‘test_email’: run
     ‘test_localtime_daylight_true_dst_true()’ and
     ‘test_localtime_daylight_false_dst_true()’ with a specific
     timezone.

   - bpo-21263(16): After several reports that test_gdb does not work
     properly on macOS and since gdb is not shipped by default anymore,
     test_gdb is now skipped on macOS when LLVM Clang has been used to
     compile Python.  Patch by Lysandros Nikolaou

   - bpo-34279(17): regrtest issue a warning when no tests have been
     executed in a particular test file.  Also, a new final result state
     is issued if no test have been executed across all test files.
     Patch by Pablo Galindo.

   - bpo-34962(18): make docstest in Doc now passes., and is enforced in
     CI

   - bpo-23596(19): Use argparse for the command line of the gzip
     module.  Patch by Antony Lee

   - bpo-34537(20): Fix ‘test_gdb.test_strings()’ when ‘LC_ALL=C’ and
     GDB was compiled with Python 3.6 or earlier.

   - bpo-34587(21): test_socket: Remove RDSTest.testCongestion().  The
     test tries to fill the receiver’s socket buffer and expects an
     error.  But the RDS protocol doesn’t require that.  Moreover, the
     Linux implementation of RDS expects that the producer of the
     messages reduces its rate, it’s not the role of the receiver to
     trigger an error.  The test fails on Fedora 28 by design, so just
     remove it.

   - bpo-34661(22): Fix test_shutil if unzip doesn’t support -t.

   - bpo-34200(23): Fixed non-deterministic flakiness of test_pkg by not
     using the scary test.support.module_cleanup() logic to save and
     restore sys.modules contents between test cases.

   - bpo-34569(24): The experimental PEP 554 data channels now correctly
     pass negative PyLong objects between subinterpreters on 32-bit
     systems.  Patch by Michael Felt.

   - bpo-34594(25): Fix usage of hardcoded ‘errno’ values in the tests.

   - bpo-34579(26): Fix test_embed for AIX Patch by Michael Felt

   - bpo-34542(27): Use 3072 RSA keys and SHA-256 signature for test
     certs and keys.

   - bpo-11193(28): Remove special condition for AIX in
     ‘test_subprocess.test_undecodable_env’

   - bpo-34347(29): Fix ‘test_utf8_mode.test_cmd_line’ for AIX

   - bpo-34490(30): On AIX with AF_UNIX family sockets getsockname()
     does not provide ‘sockname’, so skip calls to
     transport.get_extra_info(‘sockname’)

   - bpo-34391(31): Fix ftplib test for TLS 1.3 by reading from data
     socket.

   - bpo-11192(32): Fix ‘test_socket’ on AIX 6.1 and later IPv6 zone id
     supports only supported by inet_pton6_zone() Switch to
     runtime-based platform.system() to establish current platform
     rather than build-time based sys.platform()

   - bpo-34399(33): Update all RSA keys and DH params to use at least
     2048 bits.

   - bpo-34373(34): Fix ‘test_mktime’ and ‘test_pthread_getcpuclickid’
     tests for AIX Add range checking for ‘_PyTime_localtime’ for AIX
     Patch by Michael Felt

   - bpo-11191(35): Skip the distutils test ‘test_search_cpp’ when using
     XLC as compiler patch by aixtools (Michael Felt)

   - Improved an error message when mock assert_has_calls fails.

   - bpo-33746(36): Fix test_unittest when run in verbose mode.

   - bpo-33901(37): Fix test_dbm_gnu on macOS with gdbm 1.15: add a
     larger value to make sure that the file size changes.

   - bpo-33873(38): Fix a bug in ‘regrtest’ that caused an extra test to
     run if –huntrleaks/-R was used.  Exit with error in case that
     invalid parameters are specified to –huntrleaks/-R (at least one
     warmup run and one repetition must be used).

   - bpo-33562(39): Check that a global asyncio event loop policy is not
     left behind by any tests.

   - bpo-33655(40): Ignore test_posix_fallocate failures on BSD
     platforms that might be due to running on ZFS.

   - bpo-32962(41): Fixed test_gdb when Python is compiled with flags
     -mcet -fcf-protection -O0.

   - bpo-33358(42): Fix
     ‘test_embed.test_pre_initialization_sys_options()’ when the
     interpreter is built with ‘--enable-shared’.

   - bpo-32872(43): Avoid regrtest compatibility issue with namespace
     packages.

   - bpo-32517(44): Fix failing ‘test_asyncio’ on macOS 10.12.2+ due to
     transport of ‘KqueueSelector’ loop was not being closed.

   - bpo-32663(45): Making sure the ‘SMTPUTF8SimTests’ class of tests
     gets run in test_smtplib.py.

   - bpo-27643(46): Test_C test case needs “signed short” bitfields, but
     the IBM XLC compiler (on AIX) does not support this Skip the code
     and test when AIX and XLC are used

     Applicable to Python2-2.7 and later

   - bpo-19417(47): Add test_bdb.py.

   - bpo-31809(48): Add tests to verify connection with secp ECDH
     curves.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35772

   (2) https://bugs.python.org/issue35045

   (3) https://bugs.python.org/issue32710

   (4) https://bugs.python.org/issue33717

   (5) https://bugs.python.org/issue35488

   (6) https://bugs.python.org/issue31731

   (7) https://bugs.python.org/issue35424

   (8) https://bugs.python.org/issue35519

   (9) https://bugs.python.org/issue35513

   (10) https://bugs.python.org/issue34279

   (11) https://bugs.python.org/issue35412

   (12) https://bugs.python.org/issue26704

   (13) https://bugs.python.org/issue33725

   (14) https://bugs.python.org/issue35352

   (15) https://bugs.python.org/issue35317

   (16) https://bugs.python.org/issue21263

   (17) https://bugs.python.org/issue34279

   (18) https://bugs.python.org/issue34962

   (19) https://bugs.python.org/issue23596

   (20) https://bugs.python.org/issue34537

   (21) https://bugs.python.org/issue34587

   (22) https://bugs.python.org/issue34661

   (23) https://bugs.python.org/issue34200

   (24) https://bugs.python.org/issue34569

   (25) https://bugs.python.org/issue34594

   (26) https://bugs.python.org/issue34579

   (27) https://bugs.python.org/issue34542

   (28) https://bugs.python.org/issue11193

   (29) https://bugs.python.org/issue34347

   (30) https://bugs.python.org/issue34490

   (31) https://bugs.python.org/issue34391

   (32) https://bugs.python.org/issue11192

   (33) https://bugs.python.org/issue34399

   (34) https://bugs.python.org/issue34373

   (35) https://bugs.python.org/issue11191

   (36) https://bugs.python.org/issue33746

   (37) https://bugs.python.org/issue33901

   (38) https://bugs.python.org/issue33873

   (39) https://bugs.python.org/issue33562

   (40) https://bugs.python.org/issue33655

   (41) https://bugs.python.org/issue32962

   (42) https://bugs.python.org/issue33358

   (43) https://bugs.python.org/issue32872

   (44) https://bugs.python.org/issue32517

   (45) https://bugs.python.org/issue32663

   (46) https://bugs.python.org/issue27643

   (47) https://bugs.python.org/issue19417

   (48) https://bugs.python.org/issue31809


File: python.info,  Node: Build<23>,  Next: Windows<24>,  Prev: Tests<24>,  Up: Python 3 8 0 alpha 1

1.19.31.6 Build
...............

   - bpo-34691(1): The _contextvars module is now built into the core
     Python library on Windows.

   - bpo-35683(2): Improved Azure Pipelines build steps and now
     verifying layouts correctly

   - bpo-35642(3): Remove asynciomodule.c from pythoncore.vcxproj

   - bpo-35550(4): Fix incorrect Solaris #ifdef checks to look for __sun
     && __SVR4 instead of sun when compiling.

   - bpo-35499(5): ‘make profile-opt’ no longer replaces ‘CFLAGS_NODIST’
     with ‘CFLAGS’.  It now adds profile-guided optimization (PGO) flags
     to ‘CFLAGS_NODIST’: existing ‘CFLAGS_NODIST’ flags are kept.

   - bpo-35257(6): Avoid leaking the linker flags from Link Time
     Optimizations (LTO) into distutils when compiling C extensions.

   - bpo-35351(7): When building Python with clang and LTO, LTO flags
     are no longer passed into CFLAGS to build third-party C extensions
     through distutils.

   - bpo-35139(8): Fix a compiler error when statically linking
     ‘pyexpat’ in ‘Modules/Setup’.

   - bpo-35059(9): PCbuild: Set InlineFunctionExpansion to
     OnlyExplicitInline (“/Ob1” option) in pyproject.props in Debug mode
     to expand functions marked as inline.  This change should make
     Python compiled in Debug mode a little bit faster on Windows.

   - bpo-35011(10): Restores the use of pyexpatns.h to isolate our
     embedded copy of the expat C library so that its symbols do not
     conflict at link or dynamic loading time with an embedding
     application or other extension modules with their own version of
     libexpat.

   - bpo-28015(11): Have –with-lto works correctly with clang.

   - bpo-34765(12): Update the outdated install-sh file to the latest
     revision from automake v1.16.1

   - bpo-34585(13): Check for floating-point byte order in configure.ac
     using compilation tests instead of executing code, so that these
     checks work in cross-compiled builds.

   - bpo-34710(14): Fixed SSL module build with OpenSSL & pedantic
     CFLAGS.

   - bpo-34582(15): Add JUnit XML output for regression tests and update
     Azure DevOps builds.

   - bpo-34081(16): Make Sphinx warnings as errors in the Docs Makefile.

   - bpo-34555(17): Fix for case where it was not possible to have both
     ‘HAVE_LINUX_VM_SOCKETS_H’ and ‘HAVE_SOCKADDR_ALG’ be undefined.

   - bpo-33015(18): Fix an undefined behaviour in the pthread
     implementation of ‘PyThread_start_new_thread()’: add a function
     wrapper to always return ‘NULL’.

   - bpo-34245(19): The Python shared library is now installed with
     write permission (mode 0755), which is the standard way of
     installing such libraries.

   - bpo-34121(20): Fix detection of C11 atomic support on clang.

   - bpo-32430(21): Rename Modules/Setup.dist to Modules/Setup, and
     remove the necessity to copy the former manually to the latter when
     updating the local source tree.

   - bpo-30345(22): Add -g to LDFLAGS when compiling with LTO to get
     debug symbols.

   - bpo-5755(23): Move ‘-Wstrict-prototypes’ option to ‘CFLAGS_NODIST’
     from ‘OPT’.  This option emitted annoying warnings when building
     extension modules written in C++.

   - bpo-33614(24): Ensures module definition files for the stable ABI
     on Windows are correctly regenerated.

   - bpo-33648(25): The –with-c-locale-warning configuration flag has
     been removed.  It has had no effect for about a year.

   - bpo-33522(26): Enable CI builds on Visual Studio Team Services at
     ‘https://python.visualstudio.com/cpython’

   - bpo-33512(27): configure’s check for “long double” has been
     simplified

   - bpo-33483(28): C compiler is now correctly detected from the
     standard environment variables.  –without-gcc and –with-icc options
     have been removed.

   - bpo-33394(29): Enable the verbose build for extension modules, when
     GNU make is passed macros on the command line.

   - bpo-33393(30): Update config.guess and config.sub files.

   - bpo-33377(31): Add new triplets for mips r6 and riscv variants
     (used in extension suffixes).

   - bpo-32232(32): By default, modules configured in ‘Modules/Setup’
     are no longer built with ‘-DPy_BUILD_CORE’.  Instead, modules that
     specifically need that preprocessor definition include it in their
     individual entries.

   - bpo-33182(33): The embedding tests can once again be built with
     clang 6.0

   - bpo-33163(34): Upgrade pip to 9.0.3 and setuptools to v39.0.1.

   - bpo-33012(35): gcc 8 has added a new warning heuristic to detect
     invalid function casts and a stock python build seems to hit that
     warning quite often.  The most common is the cast of a METH_NOARGS
     function (that uses just one argument) to a PyCFunction.  Fix this
     by adding a dummy argument to all functions that implement
     METH_NOARGS.

   - bpo-32898(36): Fix the python debug build when using COUNT_ALLOCS.

   - bpo-29442(37): Replace optparse with argparse in setup.py

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34691

   (2) https://bugs.python.org/issue35683

   (3) https://bugs.python.org/issue35642

   (4) https://bugs.python.org/issue35550

   (5) https://bugs.python.org/issue35499

   (6) https://bugs.python.org/issue35257

   (7) https://bugs.python.org/issue35351

   (8) https://bugs.python.org/issue35139

   (9) https://bugs.python.org/issue35059

   (10) https://bugs.python.org/issue35011

   (11) https://bugs.python.org/issue28015

   (12) https://bugs.python.org/issue34765

   (13) https://bugs.python.org/issue34585

   (14) https://bugs.python.org/issue34710

   (15) https://bugs.python.org/issue34582

   (16) https://bugs.python.org/issue34081

   (17) https://bugs.python.org/issue34555

   (18) https://bugs.python.org/issue33015

   (19) https://bugs.python.org/issue34245

   (20) https://bugs.python.org/issue34121

   (21) https://bugs.python.org/issue32430

   (22) https://bugs.python.org/issue30345

   (23) https://bugs.python.org/issue5755

   (24) https://bugs.python.org/issue33614

   (25) https://bugs.python.org/issue33648

   (26) https://bugs.python.org/issue33522

   (27) https://bugs.python.org/issue33512

   (28) https://bugs.python.org/issue33483

   (29) https://bugs.python.org/issue33394

   (30) https://bugs.python.org/issue33393

   (31) https://bugs.python.org/issue33377

   (32) https://bugs.python.org/issue32232

   (33) https://bugs.python.org/issue33182

   (34) https://bugs.python.org/issue33163

   (35) https://bugs.python.org/issue33012

   (36) https://bugs.python.org/issue32898

   (37) https://bugs.python.org/issue29442


File: python.info,  Node: Windows<24>,  Next: macOS<20>,  Prev: Build<23>,  Up: Python 3 8 0 alpha 1

1.19.31.7 Windows
.................

   - bpo-35890(1): Fix API calling consistency of GetVersionEx and
     wcstok.

   - bpo-32560(2): The ‘py’ launcher now forwards its ‘STARTUPINFO’
     structure to child processes.

   - bpo-35854(3): Fix EnvBuilder and –symlinks in venv on Windows

   - bpo-35811(4): Avoid propagating venv settings when launching via
     py.exe

   - bpo-35797(5): Fix default executable used by the multiprocessing
     module

   - bpo-35758(6): Allow building on ARM with MSVC.

   - bpo-29734(7): Fix handle leaks in os.stat on Windows.

   - bpo-35596(8): Use unchecked PYCs for the embeddable distro to avoid
     zipimport restrictions.

   - bpo-35596(9): Fix vcruntime140.dll being added to embeddable distro
     multiple times.

   - bpo-35402(10): Update Windows build to use Tcl and Tk 8.6.9

   - bpo-35401(11): Updates Windows build to OpenSSL 1.1.0j

   - bpo-34977(12): venv on Windows will now use a python.exe redirector
     rather than copying the actual binaries from the base environment.

   - bpo-34977(13): Adds support for building a Windows App Store
     package

   - bpo-35067(14): Remove _distutils_findvs module and use vswhere.exe
     instead.

   - bpo-32557(15): Allow shutil.disk_usage to take a file path on
     Windows

   - bpo-34770(16): Fix a possible null pointer dereference in
     pyshellext.cpp.

   - bpo-34603(17): Fix returning structs from functions produced by
     MSVC

   - bpo-34581(18): Guard MSVC-specific code in socketmodule.c with
     ‘#ifdef _MSC_VER’.

   - bpo-34532(19): Fixes exit code of list version arguments for
     py.exe.

   - bpo-34062(20): Fixed the ‘–list’ and ‘–list-paths’ arguments for
     the py.exe launcher

   - bpo-34225(21): Ensure INCLUDE and LIB directories do not end with a
     backslash.

   - bpo-34011(22): A suite of code has been changed which copied across
     DLLs and init.tcl from the running Python location into a venv
     being created.  These copies are needed only when running from a
     Python source build, and the copying code is now only run when that
     is the case, rather than whenever a venv is created.

   - bpo-34006(23): Revert line length limit for Windows help docs.  The
     line-length limit is not needed because the pages appear in a
     separate app rather than on a browser tab.  It can also interact
     badly with the DPI setting.

   - bpo-31546(24): Restore running PyOS_InputHook while waiting for
     user input at the prompt.  The restores integration of interactive
     GUI windows (such as Matplotlib figures) with the prompt on
     Windows.

   - bpo-30237(25): Output error when ReadConsole is canceled by
     CancelSynchronousIo instead of crashing.

   - bpo-33895(26): GIL is released while calling functions that acquire
     Windows loader lock.

   - bpo-33720(27): Reduces maximum marshal recursion depth on release
     builds.

   - bpo-29097(28): Fix bug where ‘datetime.fromtimestamp()’ erroneously
     throws an *note OSError: 304. on Windows for values between 0 and
     86400.  Patch by Ammar Askar.

   - bpo-33316(29): PyThread_release_lock always fails

   - bpo-33184(30): Update Windows installer to use OpenSSL 1.1.0h.

   - bpo-32890(31): Fix usage of GetLastError() instead of errno in
     os.execve() and os.truncate().

   - bpo-33016(32): Fix potential use of uninitialized memory in
     nt._getfinalpathname

   - bpo-32903(33): Fix a memory leak in os.chdir() on Windows if the
     current directory is set to a UNC path.

   - bpo-32901(34): Update Tcl and Tk versions to 8.6.8

   - bpo-31966(35): Fixed WindowsConsoleIO.write() for writing empty
     data.

   - bpo-32409(36): Ensures activate.bat can handle Unicode contents.

   - bpo-32457(37): Improves handling of denormalized executable path
     when launching Python.

   - bpo-32370(38): Use the correct encoding for ipconfig output in the
     uuid module.  Patch by Segev Finer.

   - bpo-29248(39): Fix *note os.readlink(): 1d1. on Windows, which was
     mistakenly treating the ‘PrintNameOffset’ field of the reparse data
     buffer as a number of characters instead of bytes.  Patch by Craig
     Holmquist and SSE4.

   - bpo-1104(40): Correctly handle string length in
     ‘msilib.SummaryInfo.GetProperty()’ to prevent it from truncating
     the last character.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35890

   (2) https://bugs.python.org/issue32560

   (3) https://bugs.python.org/issue35854

   (4) https://bugs.python.org/issue35811

   (5) https://bugs.python.org/issue35797

   (6) https://bugs.python.org/issue35758

   (7) https://bugs.python.org/issue29734

   (8) https://bugs.python.org/issue35596

   (9) https://bugs.python.org/issue35596

   (10) https://bugs.python.org/issue35402

   (11) https://bugs.python.org/issue35401

   (12) https://bugs.python.org/issue34977

   (13) https://bugs.python.org/issue34977

   (14) https://bugs.python.org/issue35067

   (15) https://bugs.python.org/issue32557

   (16) https://bugs.python.org/issue34770

   (17) https://bugs.python.org/issue34603

   (18) https://bugs.python.org/issue34581

   (19) https://bugs.python.org/issue34532

   (20) https://bugs.python.org/issue34062

   (21) https://bugs.python.org/issue34225

   (22) https://bugs.python.org/issue34011

   (23) https://bugs.python.org/issue34006

   (24) https://bugs.python.org/issue31546

   (25) https://bugs.python.org/issue30237

   (26) https://bugs.python.org/issue33895

   (27) https://bugs.python.org/issue33720

   (28) https://bugs.python.org/issue29097

   (29) https://bugs.python.org/issue33316

   (30) https://bugs.python.org/issue33184

   (31) https://bugs.python.org/issue32890

   (32) https://bugs.python.org/issue33016

   (33) https://bugs.python.org/issue32903

   (34) https://bugs.python.org/issue32901

   (35) https://bugs.python.org/issue31966

   (36) https://bugs.python.org/issue32409

   (37) https://bugs.python.org/issue32457

   (38) https://bugs.python.org/issue32370

   (39) https://bugs.python.org/issue29248

   (40) https://bugs.python.org/issue1104


File: python.info,  Node: macOS<20>,  Next: IDLE<24>,  Prev: Windows<24>,  Up: Python 3 8 0 alpha 1

1.19.31.8 macOS
...............

   - bpo-35401(1): Update macOS installer to use OpenSSL 1.1.0j.

   - bpo-35025(2): Properly guard the use of the ‘CLOCK_GETTIME’ et al.
     macros in ‘timemodule’ on macOS.

   - bpo-24658(3): On macOS, fix reading from and writing into a file
     with a size larger than 2 GiB.

   - bpo-34405(4): Update to OpenSSL 1.1.0i for macOS installer builds.

   - bpo-33635(5): In macOS stat on some file descriptors (/dev/fd/3
     f.e) will result in bad file descriptor OSError.  Guard against
     this exception was added in is_dir, is_file and similar methods.
     DirEntry.is_dir can also throw this exception so
     _RecursiveWildcardSelector._iterate_directories was also extended
     with the same error ignoring pattern.

   - bpo-13631(6): The .editrc file in user’s home directory is now
     processed correctly during the readline initialization through
     editline emulation on macOS.

   - bpo-33184(7): Update macOS installer build to use OpenSSL 1.1.0h.

   - bpo-32726(8): Build and link with private copy of Tcl/Tk 8.6 for
     the macOS 10.6+ installer.  The 10.9+ installer variant already
     does this.  This means that the Python 3.7 provided by the
     python.org macOS installers no longer need or use any external
     versions of Tcl/Tk, either system-provided or user-installed, such
     as ActiveTcl.

   - bpo-32901(9): Update macOS 10.9+ installer to Tcl/Tk 8.6.8.

   - bpo-31903(10): In ‘_scproxy’, drop the GIL when calling into
     ‘SystemConfiguration’ to avoid deadlocks.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35401

   (2) https://bugs.python.org/issue35025

   (3) https://bugs.python.org/issue24658

   (4) https://bugs.python.org/issue34405

   (5) https://bugs.python.org/issue33635

   (6) https://bugs.python.org/issue13631

   (7) https://bugs.python.org/issue33184

   (8) https://bugs.python.org/issue32726

   (9) https://bugs.python.org/issue32901

   (10) https://bugs.python.org/issue31903


File: python.info,  Node: IDLE<24>,  Next: Tools/Demos<11>,  Prev: macOS<20>,  Up: Python 3 8 0 alpha 1

1.19.31.9 IDLE
..............

   - bpo-35770(1): IDLE macosx deletes Options => Configure IDLE. It
     previously deleted Window => Zoom Height by mistake.  (Zoom Height
     is now on the Options menu).  On Mac, the settings dialog is
     accessed via Preferences on the IDLE menu.

   - bpo-35769(2): Change IDLE’s new file name from ‘Untitled’ to
     ‘untitled’

   - bpo-35660(3): Fix imports in idlelib.window.

   - bpo-35641(4): Proper format ‘calltip’ when the function has no
     docstring.

   - bpo-33987(5): Use ttk Frame for ttk widgets.

   - bpo-34055(6): Fix erroneous ‘smart’ indents and newlines in IDLE
     Shell.

   - bpo-35591(7): Find Selection now works when selection not found.

   - bpo-35196(8): Speed up squeezer line counting.

   - bpo-35598(9): Update config_key: use PEP 8 names and ttk widgets,
     make some objects global, and add tests.

   - bpo-28097(10): Add Previous/Next History entries to Shell menu.

   - bpo-35208(11): Squeezer now properly counts wrapped lines before
     newlines.

   - bpo-35555(12): Gray out Code Context menu entry when it’s not
     applicable.

   - bpo-35521(13): Document the IDLE editor code context feature.  Add
     some internal references within the IDLE doc.

   - bpo-22703(14): The Code Context menu label now toggles between
     Show/Hide Code Context.  The Zoom Height menu now toggles between
     Zoom/Restore Height.  Zoom Height has moved from the Window menu to
     the Options menu.

   - bpo-35213(15): Where appropriate, use ‘macOS’ in idlelib.

   - bpo-34864(16): On macOS, warn if the system preference “Prefer tabs
     when opening documents” is set to “Always”.

   - bpo-34864(17): Document two IDLE on MacOS issues.  The System
     Preferences Dock “prefer tabs always” setting disables some IDLE
     features.  Menus are a bit different than as described for Windows
     and Linux.

   - bpo-35202(18): Remove unused imports from lib/idlelib

   - bpo-33000(19): Document that IDLE’s shell has no line limit.  A
     program that runs indefinitely can overfill memory.

   - bpo-23220(20): Explain how IDLE’s Shell displays output.

   - bpo-35099(21): Improve the doc about IDLE running user code.  The
     section is renamed from “IDLE – console differences” is renamed
     “Running user code”.  It mostly covers the implications of using
     custom sys.stdxxx objects.

   - bpo-35097(22): Add IDLE doc subsection explaining editor windows.
     Topics include opening, title and status bar, .py* extension, and
     running.

   - bpo-35093(23): Document the IDLE document viewer in the IDLE doc.
     Add a paragraph in “Help and preferences”, “Help sources”
     subsection.

   - bpo-35088(24): Update idlelib.help.copy_string docstring.  We now
     use git and backporting instead of hg and forward merging.

   - bpo-35087(25): Update idlelib help files for the current doc build.
     The main change is the elimination of chapter-section numbers.

   - bpo-34548(26): Use configured color theme for read-only text views.

   - bpo-1529353(27): Enable “squeezing” of long outputs in the shell,
     to avoid performance degradation and to clean up the history
     without losing it.  Squeezed outputs may be copied, viewed in a
     separate window, and “unsqueezed”.

   - bpo-34047(28): Fixed mousewheel scrolling direction on macOS.

   - bpo-34275(29): Make IDLE calltips always visible on Mac.  Some
     MacOS-tk combinations need .update_idletasks().  Patch by Kevin
     Walzer.

   - bpo-34120(30): Fix unresponsiveness after closing certain windows
     and dialogs.

   - bpo-33975(31): Avoid small type when running htests.  Since part of
     the purpose of human-viewed tests is to determine that widgets look
     right, it is important that they look the same for testing as when
     running IDLE.

   - bpo-33905(32): Add test for idlelib.stackview.StackBrowser.

   - bpo-33924(33): Change mainmenu.menudefs key ‘windows’ to ‘window’.
     Every other menudef key is lowercase version of main menu entry.

   - bpo-33906(34): Rename idlelib.windows as window Match Window on the
     main menu and remove last plural module name.

   - bpo-33917(35): Fix and document idlelib/idle_test/template.py.  The
     revised file compiles, runs, and tests OK. idle_test/README.txt
     explains how to use it to create new IDLE test files.

   - bpo-33904(36): IDLE: In rstrip, rename class RstripExtension as
     Rstrip

   - bpo-33907(37): For consistency and clarity, rename an IDLE module
     and classes.  Module calltips and its class CallTips are now
     calltip and Calltip.  In module calltip_w, class CallTip is now
     CalltipWindow.

   - bpo-33856(38): Add “help” in the welcome message of IDLE

   - bpo-33839(39): IDLE: refactor ToolTip and CallTip and add
     documentation and tests

   - bpo-33855(40): Minimally test all IDLE modules.  Add missing files,
     import module, instantiate classes, and check coverage.  Check
     existing files.

   - bpo-33656(41): On Windows, add API call saying that tk scales for
     DPI. On Windows 8.1+ or 10, with DPI compatibility properties of
     the Python binary unchanged, and a monitor resolution greater than
     96 DPI, this should make text and lines sharper.  It should
     otherwise have no effect.

   - bpo-33768(42): Clicking on a context line moves that line to the
     top of the editor window.

   - bpo-33763(43): IDLE: Use read-only text widget for code context
     instead of label widget.

   - bpo-33664(44): Scroll IDLE editor text by lines.  Previously, the
     mouse wheel and scrollbar slider moved text by a fixed number of
     pixels, resulting in partial lines at the top of the editor box.
     The change also applies to the shell and grep output windows, but
     not to read-only text views.

   - bpo-33679(45): Enable theme-specific color configuration for Code
     Context.  Use the Highlights tab to see the setting for built-in
     themes or add settings to custom themes.

   - bpo-33642(46): Display up to maxlines non-blank lines for Code
     Context.  If there is no current context, show a single blank line.

   - bpo-33628(47): IDLE: Cleanup codecontext.py and its test.

   - bpo-33564(48): IDLE’s code context now recognizes async as a block
     opener.

   - bpo-21474(49): Update word/identifier definition from ascii to
     unicode.  In text and entry boxes, this affects selection by
     double-click, movement left/right by control-left/right, and
     deletion left/right by control-BACKSPACE/DEL.

   - bpo-33204(50): IDLE: consistently color invalid string prefixes.  A
     ‘u’ string prefix cannot be paired with either ‘r’ or ‘f’.
     Consistently color as much of the prefix, starting at the right, as
     is valid.  Revise and extend colorizer test.

   - bpo-32984(51): Set ‘__file__’ while running a startup file.  Like
     Python, IDLE optionally runs one startup file in the Shell window
     before presenting the first interactive input prompt.  For IDLE,
     ‘-s’ runs a file named in environmental variable ‘IDLESTARTUP’ or
     *note PYTHONSTARTUP: 9cb.; ‘-r file’ runs ‘file’.  Python sets
     ‘__file__’ to the startup file name before running the file and
     unsets it before the first prompt.  IDLE now does the same when run
     normally, without the ‘-n’ option.

   - bpo-32940(52): Simplify and rename StringTranslatePseudoMapping in
     pyparse.

   - bpo-32916(53): Change ‘str’ to ‘code’ in pyparse.

   - bpo-32905(54): Remove unused code in pyparse module.

   - bpo-32874(55): Add tests for pyparse.

   - bpo-32837(56): Using the system and place-dependent default
     encoding for open() is a bad idea for IDLE’s system and
     location-independent files.

   - bpo-32826(57): Add “encoding=utf-8” to open() in IDLE’s
     test_help_about.  GUI test test_file_buttons() only looks at
     initial ascii-only lines, but failed on systems where open()
     defaults to ‘ascii’ because readline() internally reads and decodes
     far enough ahead to encounter a non-ascii character in CREDITS.txt.

   - bpo-32831(58): Add docstrings and tests for codecontext.

   - bpo-32765(59): Update configdialog General tab docstring to add new
     widgets to the widget list.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35770

   (2) https://bugs.python.org/issue35769

   (3) https://bugs.python.org/issue35660

   (4) https://bugs.python.org/issue35641

   (5) https://bugs.python.org/issue33987

   (6) https://bugs.python.org/issue34055

   (7) https://bugs.python.org/issue35591

   (8) https://bugs.python.org/issue35196

   (9) https://bugs.python.org/issue35598

   (10) https://bugs.python.org/issue28097

   (11) https://bugs.python.org/issue35208

   (12) https://bugs.python.org/issue35555

   (13) https://bugs.python.org/issue35521

   (14) https://bugs.python.org/issue22703

   (15) https://bugs.python.org/issue35213

   (16) https://bugs.python.org/issue34864

   (17) https://bugs.python.org/issue34864

   (18) https://bugs.python.org/issue35202

   (19) https://bugs.python.org/issue33000

   (20) https://bugs.python.org/issue23220

   (21) https://bugs.python.org/issue35099

   (22) https://bugs.python.org/issue35097

   (23) https://bugs.python.org/issue35093

   (24) https://bugs.python.org/issue35088

   (25) https://bugs.python.org/issue35087

   (26) https://bugs.python.org/issue34548

   (27) https://bugs.python.org/issue1529353

   (28) https://bugs.python.org/issue34047

   (29) https://bugs.python.org/issue34275

   (30) https://bugs.python.org/issue34120

   (31) https://bugs.python.org/issue33975

   (32) https://bugs.python.org/issue33905

   (33) https://bugs.python.org/issue33924

   (34) https://bugs.python.org/issue33906

   (35) https://bugs.python.org/issue33917

   (36) https://bugs.python.org/issue33904

   (37) https://bugs.python.org/issue33907

   (38) https://bugs.python.org/issue33856

   (39) https://bugs.python.org/issue33839

   (40) https://bugs.python.org/issue33855

   (41) https://bugs.python.org/issue33656

   (42) https://bugs.python.org/issue33768

   (43) https://bugs.python.org/issue33763

   (44) https://bugs.python.org/issue33664

   (45) https://bugs.python.org/issue33679

   (46) https://bugs.python.org/issue33642

   (47) https://bugs.python.org/issue33628

   (48) https://bugs.python.org/issue33564

   (49) https://bugs.python.org/issue21474

   (50) https://bugs.python.org/issue33204

   (51) https://bugs.python.org/issue32984

   (52) https://bugs.python.org/issue32940

   (53) https://bugs.python.org/issue32916

   (54) https://bugs.python.org/issue32905

   (55) https://bugs.python.org/issue32874

   (56) https://bugs.python.org/issue32837

   (57) https://bugs.python.org/issue32826

   (58) https://bugs.python.org/issue32831

   (59) https://bugs.python.org/issue32765


File: python.info,  Node: Tools/Demos<11>,  Next: C API<20>,  Prev: IDLE<24>,  Up: Python 3 8 0 alpha 1

1.19.31.10 Tools/Demos
......................

   - bpo-35884(1): Add a benchmark script for timing various ways to
     access variables: ‘Tools/scripts/var_access_benchmark.py’.

   - bpo-34989(2): python-gdb.py now handles errors on computing the
     line number of a Python frame.

   - bpo-20260(3): Argument Clinic now has non-bitwise unsigned int
     converters.

   - bpo-32962(4): python-gdb now catches ‘UnicodeDecodeError’
     exceptions when calling ‘string()’.

   - bpo-32962(5): python-gdb now catches ValueError on read_var(): when
     Python has no debug symbols for example.

   - bpo-33189(6): ‘pygettext.py’ now recognizes only literal strings as
     docstrings and translatable strings, and rejects bytes literals and
     f-string expressions.

   - bpo-31920(7): Fixed handling directories as arguments in the
     ‘pygettext’ script.  Based on patch by Oleg Krasnikov.

   - bpo-29673(8): Fix pystackv and pystack gdbinit macros.

   - bpo-25427(9): Remove the pyvenv script in favor of ‘python3 -m
     venv’ in order to lower confusion as to what Python interpreter a
     virtual environment will be created for.

   - bpo-32885(10): Add an ‘-n’ flag for ‘Tools/scripts/pathfix.py’ to
     disable automatic backup creation (files with ‘~’ suffix).

   - bpo-32222(11): Fix pygettext not extracting docstrings for
     functions with type annotated arguments.  Patch by Toby Harradine.

   - bpo-31583(12): Fix 2to3 for using with –add-suffix option but
     without –output-dir option for relative path to files in current
     directory.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35884

   (2) https://bugs.python.org/issue34989

   (3) https://bugs.python.org/issue20260

   (4) https://bugs.python.org/issue32962

   (5) https://bugs.python.org/issue32962

   (6) https://bugs.python.org/issue33189

   (7) https://bugs.python.org/issue31920

   (8) https://bugs.python.org/issue29673

   (9) https://bugs.python.org/issue25427

   (10) https://bugs.python.org/issue32885

   (11) https://bugs.python.org/issue32222

   (12) https://bugs.python.org/issue31583


File: python.info,  Node: C API<20>,  Prev: Tools/Demos<11>,  Up: Python 3 8 0 alpha 1

1.19.31.11 C API
................

   - bpo-35713(1): The ‘PyByteArray_Init()’ and ‘PyByteArray_Fini()’
     functions have been removed.  They did nothing since Python 2.7.4
     and Python 3.2.0, were excluded from the limited API (stable ABI),
     and were not documented.

   - bpo-33817(2): Fixed *note _PyBytes_Resize(): 117f. for empty bytes
     objects.

   - bpo-35322(3): Fix memory leak in *note PyUnicode_EncodeLocale():
     542. and *note PyUnicode_EncodeFSDefault(): 1180. on error
     handling.

   - bpo-35059(4): The following C macros have been converted to static
     inline functions: *note Py_INCREF(): 38e, *note Py_DECREF(): 38f,
     *note Py_XINCREF(): 390, *note Py_XDECREF(): 391,
     ‘PyObject_INIT()’, ‘PyObject_INIT_VAR()’.

   - bpo-35296(5): ‘make install’ now also installs the internal API:
     ‘Include/internal/*.h’ header files.

   - bpo-35081(6): Internal APIs surrounded by ‘#ifdef Py_BUILD_CORE’
     have been moved from ‘Include/*.h’ headers to new header files
     ‘Include/internal/pycore_*.h’.

   - bpo-35259(7): Conditionally declare *note Py_FinalizeEx(): 6c0.
     (new in 3.6) based on Py_LIMITED_API. Patch by Arthur Neufeld.

   - bpo-35081(8): The ‘_PyObject_GC_TRACK()’ and
     ‘_PyObject_GC_UNTRACK()’ macros have been removed from the public C
     API.

   - bpo-35134(9): Creation of a new ‘Include/cpython/’ subdirectory.

   - bpo-34725(10): Adds _Py_SetProgramFullPath so embedders may
     override sys.executable

   - bpo-34910(11): Ensure that *note PyObject_Print(): 1181. always
     returns ‘-1’ on error.  Patch by Zackery Spytz.

   - bpo-34523(12): Py_DecodeLocale() and Py_EncodeLocale() now use the
     UTF-8 encoding on Windows if Py_LegacyWindowsFSEncodingFlag is
     zero.

   - bpo-34193(13): Fix pluralization in TypeError messages in getargs.c
     and typeobject.c: ‘1 argument’ instead of ‘1 arguments’ and ‘1
     element’ instead of ‘1 elements’.

   - bpo-34127(14): Return grammatically correct error message based on
     argument count.  Patch by Karthikeyan Singaravelan.

   - bpo-23927(15): Fixed *note SystemError: 6f2. in *note
     PyArg_ParseTupleAndKeywords(): 6c1. when the ‘w*’ format unit is
     used for optional parameter.

   - bpo-32455(16): Added ‘PyCompile_OpcodeStackEffectWithJump()’.

   - bpo-34008(17): Py_Main() can again be called after Py_Initialize(),
     as in Python 3.6.

   - bpo-32500(18): Fixed error messages for *note PySequence_Size():
     1182, *note PySequence_GetItem(): 1183, *note PySequence_SetItem():
     1184. and *note PySequence_DelItem(): 1185. called with a mapping
     and *note PyMapping_Size(): 1186. called with a sequence.

   - bpo-33818(19): ‘PyExceptionClass_Name()’ will now return ‘const
     char *’ instead of ‘char *’.

   - bpo-33042(20): Embedding applications may once again call
     PySys_ResetWarnOptions, PySys_AddWarnOption, and PySys_AddXOption
     prior to calling Py_Initialize.

   - bpo-32374(21): Document that m_traverse for multi-phase initialized
     modules can be called with m_state=NULL, and add a sanity check

   - bpo-30863(22): *note PyUnicode_AsWideChar(): 1187. and *note
     PyUnicode_AsWideCharString(): 53c. no longer cache the ‘wchar_t*’
     representation of string objects.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35713

   (2) https://bugs.python.org/issue33817

   (3) https://bugs.python.org/issue35322

   (4) https://bugs.python.org/issue35059

   (5) https://bugs.python.org/issue35296

   (6) https://bugs.python.org/issue35081

   (7) https://bugs.python.org/issue35259

   (8) https://bugs.python.org/issue35081

   (9) https://bugs.python.org/issue35134

   (10) https://bugs.python.org/issue34725

   (11) https://bugs.python.org/issue34910

   (12) https://bugs.python.org/issue34523

   (13) https://bugs.python.org/issue34193

   (14) https://bugs.python.org/issue34127

   (15) https://bugs.python.org/issue23927

   (16) https://bugs.python.org/issue32455

   (17) https://bugs.python.org/issue34008

   (18) https://bugs.python.org/issue32500

   (19) https://bugs.python.org/issue33818

   (20) https://bugs.python.org/issue33042

   (21) https://bugs.python.org/issue32374

   (22) https://bugs.python.org/issue30863


File: python.info,  Node: Python 3 7 0 final,  Next: Python 3 7 0 release candidate 1,  Prev: Python 3 8 0 alpha 1,  Up: Changelog

1.19.32 Python 3.7.0 final
--------------------------

`Release date: 2018-06-27'

* Menu:

* Library: Library<31>.
* C API: C API<21>.


File: python.info,  Node: Library<31>,  Next: C API<21>,  Up: Python 3 7 0 final

1.19.32.1 Library
.................

   - bpo-33851(1): Fix *note ast.get_docstring(): 118a. for a node that
     lacks a docstring.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33851


File: python.info,  Node: C API<21>,  Prev: Library<31>,  Up: Python 3 7 0 final

1.19.32.2 C API
...............

   - bpo-33932(1): Calling Py_Initialize() twice does nothing, instead
     of failing with a fatal error: restore the Python 3.6 behaviour.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33932


File: python.info,  Node: Python 3 7 0 release candidate 1,  Next: Python 3 7 0 beta 5,  Prev: Python 3 7 0 final,  Up: Changelog

1.19.33 Python 3.7.0 release candidate 1
----------------------------------------

`Release date: 2018-06-12'

* Menu:

* Core and Builtins: Core and Builtins<29>.
* Library: Library<32>.
* Documentation: Documentation<26>.
* Build: Build<24>.
* Windows: Windows<25>.
* IDLE: IDLE<25>.


File: python.info,  Node: Core and Builtins<29>,  Next: Library<32>,  Up: Python 3 7 0 release candidate 1

1.19.33.1 Core and Builtins
...........................

   - bpo-33803(1): Fix a crash in hamt.c caused by enabling GC tracking
     for an object that hadn’t all of its fields set to NULL.

   - bpo-33706(2): Fix a crash in Python initialization when parsing the
     command line options.  Thanks Christoph Gohlke for the bug report
     and the fix!

   - bpo-30654(3): Fixed reset of the SIGINT handler to SIG_DFL on
     interpreter shutdown even when there was a custom handler set
     previously.  Patch by Philipp Kerling.

   - bpo-31849(4): Fix signed/unsigned comparison warning in pyhash.c.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33803

   (2) https://bugs.python.org/issue33706

   (3) https://bugs.python.org/issue30654

   (4) https://bugs.python.org/issue31849


File: python.info,  Node: Library<32>,  Next: Documentation<26>,  Prev: Core and Builtins<29>,  Up: Python 3 7 0 release candidate 1

1.19.33.2 Library
.................

   - bpo-30167(1): Prevent site.main() exception if PYTHONSTARTUP is
     set.  Patch by Steve Weber.

   - bpo-33812(2): Datetime instance d with non-None tzinfo, but with
     d.tzinfo.utcoffset(d) returning None is now treated as naive by the
     astimezone() method.

   - bpo-30805(3): Avoid race condition with debug logging

   - bpo-33694(4): asyncio: Fix a race condition causing data loss on
     pause_reading()/resume_reading() when using the ProactorEventLoop.

   - bpo-32493(5): Correct test for ‘uuid_enc_be’ availability in
     ‘configure.ac’.  Patch by Michael Felt.

   - bpo-33792(6): Add asyncio.WindowsSelectorEventLoopPolicy and
     asyncio.WindowsProactorEventLoopPolicy.

   - bpo-33778(7): Update ‘unicodedata’’s database to Unicode version
     11.0.0.

   - bpo-33770(8): improve base64 exception message for encoded inputs
     of invalid length

   - bpo-33769(9): asyncio/start_tls: Fix error message; cancel
     callbacks in case of an unhandled error; mark SSLTransport as
     closed if it is aborted.

   - bpo-33767(10): The concatenation (‘+’) and repetition (‘*’)
     sequence operations now raise *note TypeError: 1fe. instead of
     *note SystemError: 6f2. when performed on *note mmap.mmap: 31c.
     objects.  Patch by Zackery Spytz.

   - bpo-33734(11): asyncio/ssl: Fix AttributeError, increase default
     handshake timeout

   - bpo-11874(12): Use a better regex when breaking usage into
     wrappable parts.  Avoids bogus assertion errors from custom metavar
     strings.

   - bpo-33582(13): Emit a deprecation warning for inspect.formatargspec

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30167

   (2) https://bugs.python.org/issue33812

   (3) https://bugs.python.org/issue30805

   (4) https://bugs.python.org/issue33694

   (5) https://bugs.python.org/issue32493

   (6) https://bugs.python.org/issue33792

   (7) https://bugs.python.org/issue33778

   (8) https://bugs.python.org/issue33770

   (9) https://bugs.python.org/issue33769

   (10) https://bugs.python.org/issue33767

   (11) https://bugs.python.org/issue33734

   (12) https://bugs.python.org/issue11874

   (13) https://bugs.python.org/issue33582


File: python.info,  Node: Documentation<26>,  Next: Build<24>,  Prev: Library<32>,  Up: Python 3 7 0 release candidate 1

1.19.33.3 Documentation
.......................

   - bpo-33409(1): Clarified the relationship between PEP 538(2)’s
     PYTHONCOERCECLOCALE and PEP 540’s PYTHONUTF8 mode.

   - bpo-33736(3): Improve the documentation of *note
     asyncio.open_connection(): 46b, *note asyncio.start_server(): 46c.
     and their UNIX socket counterparts.

   - bpo-31432(4): Clarify meaning of CERT_NONE, CERT_OPTIONAL, and
     CERT_REQUIRED flags for ssl.SSLContext.verify_mode.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33409

   (2) https://www.python.org/dev/peps/pep-0538

   (3) https://bugs.python.org/issue33736

   (4) https://bugs.python.org/issue31432


File: python.info,  Node: Build<24>,  Next: Windows<25>,  Prev: Documentation<26>,  Up: Python 3 7 0 release candidate 1

1.19.33.4 Build
...............

   - bpo-5755(1): Move ‘-Wstrict-prototypes’ option to ‘CFLAGS_NODIST’
     from ‘OPT’.  This option emitted annoying warnings when building
     extension modules written in C++.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5755


File: python.info,  Node: Windows<25>,  Next: IDLE<25>,  Prev: Build<24>,  Up: Python 3 7 0 release candidate 1

1.19.33.5 Windows
.................

   - bpo-33720(1): Reduces maximum marshal recursion depth on release
     builds.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33720


File: python.info,  Node: IDLE<25>,  Prev: Windows<25>,  Up: Python 3 7 0 release candidate 1

1.19.33.6 IDLE
..............

   - bpo-33656(1): On Windows, add API call saying that tk scales for
     DPI. On Windows 8.1+ or 10, with DPI compatibility properties of
     the Python binary unchanged, and a monitor resolution greater than
     96 DPI, this should make text and lines sharper.  It should
     otherwise have no effect.

   - bpo-33768(2): Clicking on a context line moves that line to the top
     of the editor window.

   - bpo-33763(3): IDLE: Use read-only text widget for code context
     instead of label widget.

   - bpo-33664(4): Scroll IDLE editor text by lines.  Previously, the
     mouse wheel and scrollbar slider moved text by a fixed number of
     pixels, resulting in partial lines at the top of the editor box.
     The change also applies to the shell and grep output windows, but
     not to read-only text views.

   - bpo-33679(5): Enable theme-specific color configuration for Code
     Context.  Use the Highlights tab to see the setting for built-in
     themes or add settings to custom themes.

   - bpo-33642(6): Display up to maxlines non-blank lines for Code
     Context.  If there is no current context, show a single blank line.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33656

   (2) https://bugs.python.org/issue33768

   (3) https://bugs.python.org/issue33763

   (4) https://bugs.python.org/issue33664

   (5) https://bugs.python.org/issue33679

   (6) https://bugs.python.org/issue33642


File: python.info,  Node: Python 3 7 0 beta 5,  Next: Python 3 7 0 beta 4,  Prev: Python 3 7 0 release candidate 1,  Up: Changelog

1.19.34 Python 3.7.0 beta 5
---------------------------

`Release date: 2018-05-30'

* Menu:

* Core and Builtins: Core and Builtins<30>.
* Library: Library<33>.
* Documentation: Documentation<27>.
* Tests: Tests<25>.
* Build: Build<25>.
* macOS: macOS<21>.
* IDLE: IDLE<26>.


File: python.info,  Node: Core and Builtins<30>,  Next: Library<33>,  Up: Python 3 7 0 beta 5

1.19.34.1 Core and Builtins
...........................

   - bpo-33622(1): Fixed a leak when the garbage collector fails to add
     an object with the ‘__del__’ method or referenced by it into the
     *note gc.garbage: c12. list.  ‘PyGC_Collect()’ can now be called
     when an exception is set and preserves it.

   - bpo-33509(2): Fix module_globals parameter of
     warnings.warn_explicit(): don’t crash if module_globals is not a
     dict.

   - bpo-20104(3): The new *note os.posix_spawn: 381. added in 3.7.0b1
     was removed as we are still working on what the API should look
     like.  Expect this in 3.8 instead.

   - bpo-33475(4): Fixed miscellaneous bugs in converting annotations to
     strings and optimized parentheses in the string representation.

   - bpo-33391(5): Fix a leak in set_symmetric_difference().

   - bpo-28055(6): Fix unaligned accesses in siphash24().  Patch by Rolf
     Eike Beer.

   - bpo-32911(7): Due to unexpected compatibility issues discovered
     during downstream beta testing, reverted bpo-29463(8).  ‘docstring’
     field is removed from Module, ClassDef, FunctionDef, and
     AsyncFunctionDef ast nodes which was added in 3.7a1.  Docstring
     expression is restored as a first statement in their body.  Based
     on patch by Inada Naoki.

   - bpo-21983(9): Fix a crash in *note ctypes.cast(): 114b. in case the
     type argument is a ctypes structured data type.  Patch by Eryk Sun
     and Oren Milman.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33622

   (2) https://bugs.python.org/issue33509

   (3) https://bugs.python.org/issue20104

   (4) https://bugs.python.org/issue33475

   (5) https://bugs.python.org/issue33391

   (6) https://bugs.python.org/issue28055

   (7) https://bugs.python.org/issue32911

   (8) https://bugs.python.org/issue29463

   (9) https://bugs.python.org/issue21983


File: python.info,  Node: Library<33>,  Next: Documentation<27>,  Prev: Core and Builtins<30>,  Up: Python 3 7 0 beta 5

1.19.34.2 Library
.................

   - bpo-32751(1): When cancelling the task due to a timeout, *note
     asyncio.wait_for(): 191. will now wait until the cancellation is
     complete.

   - bpo-32684(2): Fix gather to propagate cancellation of itself even
     with return_exceptions.

   - bpo-33654(3): Support protocol type switching in
     SSLTransport.set_protocol().

   - bpo-33674(4): Pause the transport as early as possible to further
     reduce the risk of data_received() being called before
     connection_made().

   - bpo-33674(5): Fix a race condition in SSLProtocol.connection_made()
     of asyncio.sslproto: start immediately the handshake instead of
     using call_soon().  Previously, data_received() could be called
     before the handshake started, causing the handshake to hang or
     fail.

   - bpo-31647(6): Fixed bug where calling write_eof() on a
     _SelectorSocketTransport after it’s already closed raises
     AttributeError.

   - bpo-32610(7): Make asyncio.all_tasks() return only pending tasks.

   - bpo-32410(8): Avoid blocking on file IO in sendfile fallback code

   - bpo-33469(9): Fix RuntimeError after closing loop that used
     run_in_executor

   - bpo-33672(10): Fix Task.__repr__ crash with Cython’s bogus
     coroutines

   - bpo-33654(11): Fix transport.set_protocol() to support switching
     between asyncio.Protocol and asyncio.BufferedProtocol.  Fix
     loop.start_tls() to work with asyncio.BufferedProtocols.

   - bpo-33652(12): Pickles of type variables and subscripted generics
     are now future-proof and compatible with older Python versions.

   - bpo-32493(13): Fixed *note uuid.uuid1(): 518. on FreeBSD.

   - bpo-33618(14): Finalize and document preliminary and experimental
     TLS 1.3 support with OpenSSL 1.1.1

   - bpo-33623(15): Fix possible SIGSGV when asyncio.Future is created
     in __del__

   - bpo-30877(16): Fixed a bug in the Python implementation of the JSON
     decoder that prevented the cache of parsed strings from clearing
     after finishing the decoding.  Based on patch by c-fos.

   - bpo-33570(17): Change TLS 1.3 cipher suite settings for
     compatibility with OpenSSL 1.1.1-pre6 and newer.  OpenSSL 1.1.1
     will have TLS 1.3 ciphers enabled by default.

   - bpo-28556(18): Do not simplify arguments to *note typing.Union:
     116a.  Now ‘Union[Manager, Employee]’ is not simplified to
     ‘Employee’ at runtime.  Such simplification previously caused
     several bugs and limited possibilities for introspection.

   - bpo-33540(19): Add a new ‘block_on_close’ class attribute to
     ‘ForkingMixIn’ and ‘ThreadingMixIn’ classes of *note socketserver:
     f0.

   - bpo-33548(20): tempfile._candidate_tempdir_list should consider
     common TEMP locations

   - bpo-33109(21): argparse subparsers are once again not required by
     default, reverting the change in behavior introduced by
     bpo-26510(22) in 3.7.0a2.

   - bpo-33536(23): dataclasses.make_dataclass now checks for invalid
     field names and duplicate fields.  Also, added a check for invalid
     field specifications.

   - bpo-33542(24): Prevent ‘uuid.get_node’ from using a DUID instead of
     a MAC on Windows.  Patch by Zvi Effron

   - bpo-26819(25): Fix race condition with
     ‘ReadTransport.resume_reading’ in Windows proactor event loop.

   - Fix failure in *note typing.get_type_hints(): 1ef. when ClassVar
     was provided as a string forward reference.

   - bpo-33505(26): Optimize asyncio.ensure_future() by reordering if
     checks: 1.17x faster.

   - bpo-33497(27): Add errors param to cgi.parse_multipart and make an
     encoding in FieldStorage use the given errors (needed for Twisted).
     Patch by Amber Brown.

   - bpo-33495(28): Change dataclasses.Fields repr to use the repr of
     each of its members, instead of str.  This makes it more clear what
     each field actually represents.  This is especially true for the
     ‘type’ member.

   - bpo-33453(29): Fix dataclasses to work if using literal string type
     annotations or if using PEP 563 “Postponed Evaluation of
     Annotations”.  Only specific string prefixes are detected for both
     ClassVar (“ClassVar” and “typing.ClassVar”) and InitVar (“InitVar”
     and “dataclasses.InitVar”).

   - bpo-28556(30): Minor fixes in typing module: add annotations to
     ‘NamedTuple.__new__’, pass ‘*args’ and ‘**kwds’ in
     ‘Generic.__new__’.  Original PRs by Paulius Šarka and Chad
     Dombrova.

   - bpo-20087(31): Updated alias mapping with glibc 2.27 supported
     locales.

   - bpo-33422(32): Fix trailing quotation marks getting deleted when
     looking up byte/string literals on pydoc.  Patch by Andrés Delfino.

   - bpo-28167(33): The function ‘platform.linux_distribution’ and
     ‘platform.dist’ now trigger a ‘DeprecationWarning’ and have been
     marked for removal in Python 3.8

   - bpo-33197(34): Update error message when constructing invalid
     inspect.Parameters Patch by Dong-hee Na.

   - bpo-33263(35): Fix FD leak in ‘_SelectorSocketTransport’ Patch by
     Vlad Starostin.

   - bpo-32861(36): The urllib.robotparser’s ‘__str__’ representation
     now includes wildcard entries and the “Crawl-delay” and
     “Request-rate” fields.  Patch by Michael Lazar.

   - bpo-32257(37): The ssl module now contains OP_NO_RENEGOTIATION
     constant, available with OpenSSL 1.1.0h or 1.1.1.

   - bpo-16865(38): Support arrays >=2GiB in *note ctypes: 2a.  Patch by
     Segev Finer.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32751

   (2) https://bugs.python.org/issue32684

   (3) https://bugs.python.org/issue33654

   (4) https://bugs.python.org/issue33674

   (5) https://bugs.python.org/issue33674

   (6) https://bugs.python.org/issue31647

   (7) https://bugs.python.org/issue32610

   (8) https://bugs.python.org/issue32410

   (9) https://bugs.python.org/issue33469

   (10) https://bugs.python.org/issue33672

   (11) https://bugs.python.org/issue33654

   (12) https://bugs.python.org/issue33652

   (13) https://bugs.python.org/issue32493

   (14) https://bugs.python.org/issue33618

   (15) https://bugs.python.org/issue33623

   (16) https://bugs.python.org/issue30877

   (17) https://bugs.python.org/issue33570

   (18) https://bugs.python.org/issue28556

   (19) https://bugs.python.org/issue33540

   (20) https://bugs.python.org/issue33548

   (21) https://bugs.python.org/issue33109

   (22) https://bugs.python.org/issue26510

   (23) https://bugs.python.org/issue33536

   (24) https://bugs.python.org/issue33542

   (25) https://bugs.python.org/issue26819

   (26) https://bugs.python.org/issue33505

   (27) https://bugs.python.org/issue33497

   (28) https://bugs.python.org/issue33495

   (29) https://bugs.python.org/issue33453

   (30) https://bugs.python.org/issue28556

   (31) https://bugs.python.org/issue20087

   (32) https://bugs.python.org/issue33422

   (33) https://bugs.python.org/issue28167

   (34) https://bugs.python.org/issue33197

   (35) https://bugs.python.org/issue33263

   (36) https://bugs.python.org/issue32861

   (37) https://bugs.python.org/issue32257

   (38) https://bugs.python.org/issue16865


File: python.info,  Node: Documentation<27>,  Next: Tests<25>,  Prev: Library<33>,  Up: Python 3 7 0 beta 5

1.19.34.3 Documentation
.......................

   - bpo-23859(1): Document that *note asyncio.wait(): 207. does not
     cancel its futures on timeout.

   - bpo-32436(2): Document PEP 567(3) changes to asyncio.

   - bpo-33604(4): Update HMAC md5 default to a DeprecationWarning, bump
     removal to 3.8.

   - bpo-33503(5): Fix broken pypi link

   - bpo-33421(6): Add missing documentation for
     ‘typing.AsyncContextManager’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23859

   (2) https://bugs.python.org/issue32436

   (3) https://www.python.org/dev/peps/pep-0567

   (4) https://bugs.python.org/issue33604

   (5) https://bugs.python.org/issue33503

   (6) https://bugs.python.org/issue33421


File: python.info,  Node: Tests<25>,  Next: Build<25>,  Prev: Documentation<27>,  Up: Python 3 7 0 beta 5

1.19.34.4 Tests
...............

   - bpo-33655(1): Ignore test_posix_fallocate failures on BSD platforms
     that might be due to running on ZFS.

   - bpo-32604(2): Remove the _xxsubinterpreters module (meant for
     testing) and associated helpers.  This module was originally added
     recently in 3.7b1.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33655

   (2) https://bugs.python.org/issue32604


File: python.info,  Node: Build<25>,  Next: macOS<21>,  Prev: Tests<25>,  Up: Python 3 7 0 beta 5

1.19.34.5 Build
...............

   - bpo-33614(1): Ensures module definition files for the stable ABI on
     Windows are correctly regenerated.

   - bpo-33522(2): Enable CI builds on Visual Studio Team Services at
     ‘https://python.visualstudio.com/cpython’

   - bpo-33012(3): Add ‘-Wno-cast-function-type’ for gcc 8 for silencing
     warnings about function casts like casting to PyCFunction in method
     definition lists.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33614

   (2) https://bugs.python.org/issue33522

   (3) https://bugs.python.org/issue33012


File: python.info,  Node: macOS<21>,  Next: IDLE<26>,  Prev: Build<25>,  Up: Python 3 7 0 beta 5

1.19.34.6 macOS
...............

   - bpo-13631(1): The .editrc file in user’s home directory is now
     processed correctly during the readline initialization through
     editline emulation on macOS.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13631


File: python.info,  Node: IDLE<26>,  Prev: macOS<21>,  Up: Python 3 7 0 beta 5

1.19.34.7 IDLE
..............

   - bpo-33628(1): IDLE: Cleanup codecontext.py and its test.

   - bpo-33564(2): IDLE’s code context now recognizes async as a block
     opener.

   - bpo-32831(3): Add docstrings and tests for codecontext.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33628

   (2) https://bugs.python.org/issue33564

   (3) https://bugs.python.org/issue32831


File: python.info,  Node: Python 3 7 0 beta 4,  Next: Python 3 7 0 beta 3,  Prev: Python 3 7 0 beta 5,  Up: Changelog

1.19.35 Python 3.7.0 beta 4
---------------------------

`Release date: 2018-05-02'

* Menu:

* Core and Builtins: Core and Builtins<31>.
* Library: Library<34>.
* Documentation: Documentation<28>.
* Tests: Tests<26>.
* Build: Build<26>.
* Windows: Windows<26>.
* macOS: macOS<22>.
* IDLE: IDLE<27>.
* Tools/Demos: Tools/Demos<12>.


File: python.info,  Node: Core and Builtins<31>,  Next: Library<34>,  Up: Python 3 7 0 beta 4

1.19.35.1 Core and Builtins
...........................

   - bpo-33363(1): Raise a SyntaxError for ‘async with’ and ‘async for’
     statements outside of async functions.

   - bpo-33128(2): Fix a bug that causes PathFinder to appear twice on
     sys.meta_path.  Patch by Pablo Galindo Salgado.

   - bpo-33312(3): Fixed clang ubsan (undefined behavior sanitizer)
     warnings in dictobject.c by adjusting how the internal struct
     _dictkeysobject shared keys structure is declared.

   - bpo-33231(4): Fix potential memory leak in ‘normalizestring()’.

   - bpo-33205(5): Change dict growth function from
     ‘round_up_to_power_2(used*2+hashtable_size/2)’ to
     ‘round_up_to_power_2(used*3)’.  Previously, dict is shrinked only
     when ‘used == 0’.  Now dict has more chance to be shrinked.

   - bpo-29922(6): Improved error messages in ‘async with’ when
     ‘__aenter__()’ or ‘__aexit__()’ return non-awaitable object.

   - bpo-33199(7): Fix ‘ma_version_tag’ in dict implementation is
     uninitialized when copying from key-sharing dict.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33363

   (2) https://bugs.python.org/issue33128

   (3) https://bugs.python.org/issue33312

   (4) https://bugs.python.org/issue33231

   (5) https://bugs.python.org/issue33205

   (6) https://bugs.python.org/issue29922

   (7) https://bugs.python.org/issue33199


File: python.info,  Node: Library<34>,  Next: Documentation<28>,  Prev: Core and Builtins<31>,  Up: Python 3 7 0 beta 4

1.19.35.2 Library
.................

   - bpo-33281(1): Fix ctypes.util.find_library regression on macOS.

   - bpo-33383(2): Fixed crash in the get() method of the *note
     dbm.ndbm: 34. database object when it is called with a single
     argument.

   - bpo-33329(3): Fix multiprocessing regression on newer glibcs

   - bpo-991266(4): Fix quoting of the ‘Comment’ attribute of *note
     http.cookies.SimpleCookie: 116e.

   - bpo-33131(5): Upgrade bundled version of pip to 10.0.1.

   - bpo-33308(6): Fixed a crash in the *note parser: c7. module when
     converting an ST object to a tree of tuples or lists with
     ‘line_info=False’ and ‘col_info=True’.

   - bpo-33266(7): lib2to3 now recognizes ‘rf'...'’ strings.

   - bpo-11594(8): Ensure line-endings are respected when using lib2to3.

   - bpo-33254(9): Have *note importlib.resources.contents(): 116f. and
     *note importlib.abc.ResourceReader.contents(): 1170. return an
     *note iterable: c7c. instead of an *note iterator: 1171.

   - bpo-33256(10): Fix display of ‘<module>’ call in the html produced
     by ‘cgitb.html()’.  Patch by Stéphane Blondon.

   - bpo-33185(11): Fixed regression when running pydoc with the *note
     -m: 443. switch.  (The regression was introduced in 3.7.0b3 by the
     resolution of bpo-33053(12)) This fix also changed pydoc to add
     ‘os.getcwd()’ to *note sys.path: 260. when necessary, rather than
     adding ‘"."’.

   - bpo-33169(13): Delete entries of ‘None’ in *note
     sys.path_importer_cache: 598. when
     ‘importlib.machinery.invalidate_caches()’ is called.

   - bpo-33217(14): Deprecate looking up non-Enum objects in Enum
     classes and Enum members (will raise *note TypeError: 1fe. in
     3.8+).

   - bpo-33203(15): ‘random.Random.choice()’ now raises ‘IndexError’ for
     empty sequences consistently even when called from subclasses
     without a ‘getrandbits()’ implementation.

   - bpo-33224(16): Update difflib.mdiff() for PEP 479(17).  Convert an
     uncaught StopIteration in a generator into a return-statement.

   - bpo-33209(18): End framing at the end of C implementation of *note
     pickle.Pickler.dump(): 1172.

   - bpo-20104(19): Improved error handling and fixed a reference leak
     in *note os.posix_spawn(): 381.

   - bpo-33175(20): In dataclasses, Field.__set_name__ now looks up the
     __set_name__ special method on the class, not the instance, of the
     default value.

   - bpo-33097(21): Raise RuntimeError when ‘executor.submit’ is called
     during interpreter shutdown.

   - bpo-31908(22): Fix output of cover files for ‘trace’ module
     command-line tool.  Previously emitted cover files only when
     ‘--missing’ option was used.  Patch by Michael Selik.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33281

   (2) https://bugs.python.org/issue33383

   (3) https://bugs.python.org/issue33329

   (4) https://bugs.python.org/issue991266

   (5) https://bugs.python.org/issue33131

   (6) https://bugs.python.org/issue33308

   (7) https://bugs.python.org/issue33266

   (8) https://bugs.python.org/issue11594

   (9) https://bugs.python.org/issue33254

   (10) https://bugs.python.org/issue33256

   (11) https://bugs.python.org/issue33185

   (12) https://bugs.python.org/issue33053

   (13) https://bugs.python.org/issue33169

   (14) https://bugs.python.org/issue33217

   (15) https://bugs.python.org/issue33203

   (16) https://bugs.python.org/issue33224

   (17) https://www.python.org/dev/peps/pep-0479

   (18) https://bugs.python.org/issue33209

   (19) https://bugs.python.org/issue20104

   (20) https://bugs.python.org/issue33175

   (21) https://bugs.python.org/issue33097

   (22) https://bugs.python.org/issue31908


File: python.info,  Node: Documentation<28>,  Next: Tests<26>,  Prev: Library<34>,  Up: Python 3 7 0 beta 4

1.19.35.3 Documentation
.......................

   - bpo-33378(1): Add Korean language switcher for
     ‘https://docs.python.org/3/’

   - bpo-33276(2): Clarify that the ‘__path__’ attribute on modules
     cannot be just any value.

   - bpo-33201(3): Modernize documentation for writing C extension
     types.

   - bpo-33195(4): Deprecate ‘Py_UNICODE’ usage in ‘c-api/arg’ document.
     ‘Py_UNICODE’ related APIs are deprecated since Python 3.3, but it
     is missed in the document.

   - bpo-8243(5): Add a note about curses.addch and curses.addstr
     exception behavior when writing outside a window, or pad.

   - bpo-32337(6): Update documentation related with ‘dict’ order.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33378

   (2) https://bugs.python.org/issue33276

   (3) https://bugs.python.org/issue33201

   (4) https://bugs.python.org/issue33195

   (5) https://bugs.python.org/issue8243

   (6) https://bugs.python.org/issue32337


File: python.info,  Node: Tests<26>,  Next: Build<26>,  Prev: Documentation<28>,  Up: Python 3 7 0 beta 4

1.19.35.4 Tests
...............

   - bpo-33358(1): Fix
     ‘test_embed.test_pre_initialization_sys_options()’ when the
     interpreter is built with ‘--enable-shared’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33358


File: python.info,  Node: Build<26>,  Next: Windows<26>,  Prev: Tests<26>,  Up: Python 3 7 0 beta 4

1.19.35.5 Build
...............

   - bpo-33394(1): Enable the verbose build for extension modules, when
     GNU make is passed macros on the command line.

   - bpo-33393(2): Update config.guess and config.sub files.

   - bpo-33377(3): Add new triplets for mips r6 and riscv variants (used
     in extension suffixes).

   - bpo-32232(4): By default, modules configured in ‘Modules/Setup’ are
     no longer built with ‘-DPy_BUILD_CORE’.  Instead, modules that
     specifically need that preprocessor definition include it in their
     individual entries.

   - bpo-33182(5): The embedding tests can once again be built with
     clang 6.0

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33394

   (2) https://bugs.python.org/issue33393

   (3) https://bugs.python.org/issue33377

   (4) https://bugs.python.org/issue32232

   (5) https://bugs.python.org/issue33182


File: python.info,  Node: Windows<26>,  Next: macOS<22>,  Prev: Build<26>,  Up: Python 3 7 0 beta 4

1.19.35.6 Windows
.................

   - bpo-33184(1): Update Windows installer to use OpenSSL 1.1.0h.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33184


File: python.info,  Node: macOS<22>,  Next: IDLE<27>,  Prev: Windows<26>,  Up: Python 3 7 0 beta 4

1.19.35.7 macOS
...............

   - bpo-33184(1): Update macOS installer build to use OpenSSL 1.1.0h.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33184


File: python.info,  Node: IDLE<27>,  Next: Tools/Demos<12>,  Prev: macOS<22>,  Up: Python 3 7 0 beta 4

1.19.35.8 IDLE
..............

   - bpo-21474(1): Update word/identifier definition from ascii to
     unicode.  In text and entry boxes, this affects selection by
     double-click, movement left/right by control-left/right, and
     deletion left/right by control-BACKSPACE/DEL.

   - bpo-33204(2): IDLE: consistently color invalid string prefixes.  A
     ‘u’ string prefix cannot be paired with either ‘r’ or ‘f’.
     Consistently color as much of the prefix, starting at the right, as
     is valid.  Revise and extend colorizer test.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21474

   (2) https://bugs.python.org/issue33204


File: python.info,  Node: Tools/Demos<12>,  Prev: IDLE<27>,  Up: Python 3 7 0 beta 4

1.19.35.9 Tools/Demos
.....................

   - bpo-33189(1): ‘pygettext.py’ now recognizes only literal strings as
     docstrings and translatable strings, and rejects bytes literals and
     f-string expressions.

   - bpo-31920(2): Fixed handling directories as arguments in the
     ‘pygettext’ script.  Based on patch by Oleg Krasnikov.

   - bpo-29673(3): Fix pystackv and pystack gdbinit macros.

   - bpo-31583(4): Fix 2to3 for using with –add-suffix option but
     without –output-dir option for relative path to files in current
     directory.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33189

   (2) https://bugs.python.org/issue31920

   (3) https://bugs.python.org/issue29673

   (4) https://bugs.python.org/issue31583


File: python.info,  Node: Python 3 7 0 beta 3,  Next: Python 3 7 0 beta 2,  Prev: Python 3 7 0 beta 4,  Up: Changelog

1.19.36 Python 3.7.0 beta 3
---------------------------

`Release date: 2018-03-29'

* Menu:

* Security: Security<19>.
* Core and Builtins: Core and Builtins<32>.
* Library: Library<35>.
* Documentation: Documentation<29>.
* Tests: Tests<27>.
* Build: Build<27>.
* Windows: Windows<27>.
* macOS: macOS<23>.
* IDLE: IDLE<28>.
* Tools/Demos: Tools/Demos<13>.
* C API: C API<22>.


File: python.info,  Node: Security<19>,  Next: Core and Builtins<32>,  Up: Python 3 7 0 beta 3

1.19.36.1 Security
..................

   - bpo-33136(1): Harden ssl module against LibreSSL CVE-2018-8970.
     X509_VERIFY_PARAM_set1_host() is called with an explicit namelen.
     A new test ensures that NULL bytes are not allowed.

   - bpo-33001(2): Minimal fix to prevent buffer overrun in os.symlink
     on Windows

   - bpo-32981(3): Regexes in difflib and poplib were vulnerable to
     catastrophic backtracking.  These regexes formed potential DOS
     vectors (REDOS). They have been refactored.  This resolves
     CVE-2018-1060 and CVE-2018-1061.  Patch by Jamie Davis.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33136

   (2) https://bugs.python.org/issue33001

   (3) https://bugs.python.org/issue32981


File: python.info,  Node: Core and Builtins<32>,  Next: Library<35>,  Prev: Security<19>,  Up: Python 3 7 0 beta 3

1.19.36.2 Core and Builtins
...........................

   - bpo-33053(1): When using the -m switch, sys.path[0] is now
     explicitly expanded as the `starting' working directory, rather
     than being left as the empty path (which allows imports from the
     current working directory at the time of the import)

   - bpo-33018(2): Improve consistency of errors raised by
     ‘issubclass()’ when called with a non-class and an abstract base
     class as the first and second arguments, respectively.  Patch by
     Josh Bronson.

   - bpo-33041(3): Fixed jumping when the function contains an ‘async
     for’ loop.

   - bpo-33026(4): Fixed jumping out of “with” block by setting
     f_lineno.

   - bpo-33005(5): Fix a crash on fork when using a custom memory
     allocator (ex: using PYTHONMALLOC env var).  _PyGILState_Reinit()
     and _PyInterpreterState_Enable() now use the default RAW memory
     allocator to allocate a new interpreters mutex on fork.

   - bpo-17288(6): Prevent jumps from ‘return’ and ‘exception’ trace
     events.

   - bpo-32836(7): Don’t use temporary variables in cases of
     list/dict/set comprehensions

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33053

   (2) https://bugs.python.org/issue33018

   (3) https://bugs.python.org/issue33041

   (4) https://bugs.python.org/issue33026

   (5) https://bugs.python.org/issue33005

   (6) https://bugs.python.org/issue17288

   (7) https://bugs.python.org/issue32836


File: python.info,  Node: Library<35>,  Next: Documentation<29>,  Prev: Core and Builtins<32>,  Up: Python 3 7 0 beta 3

1.19.36.3 Library
.................

   - bpo-33141(1): Have Field objects pass through __set_name__ to their
     default values, if they have their own __set_name__.

   - bpo-33096(2): Allow ttk.Treeview.insert to insert iid that has a
     false boolean value.  Note iid=0 and iid=False would be same.
     Patch by Garvit Khatri.

   - bpo-32873(3): Treat type variables and special typing forms as
     immutable by copy and pickle.  This fixes several minor issues and
     inconsistencies, and improves backwards compatibility with Python
     3.6.

   - bpo-33134(4): When computing dataclass’s __hash__, use the lookup
     table to contain the function which returns the __hash__ value.
     This is an improvement over looking up a string, and then testing
     that string to see what to do.

   - bpo-33127(5): The ssl module now compiles with LibreSSL 2.7.1.

   - bpo-32505(6): Raise TypeError if a member variable of a dataclass
     is of type Field, but doesn’t have a type annotation.

   - bpo-33078(7): Fix the failure on OSX caused by the tests relying on
     sem_getvalue

   - bpo-33116(8): Add ‘Field’ to dataclasses.__all__.

   - bpo-32896(9): Fix an error where subclassing a dataclass with a
     field that uses a default_factory would generate an incorrect
     class.

   - bpo-33100(10): Dataclasses: If a field has a default value that’s a
     MemberDescriptorType, then it’s from that field being in __slots__,
     not an actual default value.

   - bpo-32953(11): If a non-dataclass inherits from a frozen dataclass,
     allow attributes to be added to the derived class.  Only attributes
     from the frozen dataclass cannot be assigned to.  Require all
     dataclasses in a hierarchy to be either all frozen or all
     non-frozen.

   - bpo-33061(12): Add missing ‘NoReturn’ to ‘__all__’ in typing.py

   - bpo-33078(13): Fix the size handling in multiprocessing.Queue when
     a pickling error occurs.

   - bpo-33064(14): lib2to3 now properly supports trailing commas after
     ‘*args’ and ‘**kwargs’ in function signatures.

   - bpo-33056(15): FIX properly close leaking fds in
     concurrent.futures.ProcessPoolExecutor.

   - bpo-33021(16): Release the GIL during fstat() calls, avoiding hang
     of all threads when calling mmap.mmap(), os.urandom(), and
     random.seed().  Patch by Nir Soffer.

   - bpo-31804(17): Avoid failing in multiprocessing.Process if the
     standard streams are closed or None at exit.

   - bpo-33037(18): Skip sending/receiving data after SSL transport
     closing.

   - bpo-27683(19): Fix a regression in *note ipaddress: a2. that result
     of ‘hosts()’ is empty when the network is constructed by a tuple
     containing an integer mask and only 1 bit left for addresses.

   - bpo-32999(20): Fix C implementation of ‘ABC.__subclasscheck__(cls,
     subclass)’ crashed when ‘subclass’ is not a type object.

   - bpo-33009(21): Fix inspect.signature() for single-parameter
     partialmethods.

   - bpo-32969(22): Expose several missing constants in zlib and fix
     corresponding documentation.

   - bpo-32056(23): Improved exceptions raised for invalid number of
     channels and sample width when read an audio file in modules *note
     aifc: 4, *note wave: 130. and *note sunau: fa.

   - bpo-32844(24): Fix wrong redirection of a low descriptor (0 or 1)
     to stderr in subprocess if another low descriptor is closed.

   - bpo-32857(25): In *note tkinter: 10e, ‘after_cancel(None)’ now
     raises a *note ValueError: 16d. instead of canceling the first
     scheduled function.  Patch by Cheryl Sabella.

   - bpo-31639(26): http.server now exposes a ThreadedHTTPServer class
     and uses it when the module is run with ‘-m’ to cope with web
     browsers pre-opening sockets.

   - bpo-27645(27): *note sqlite3.Connection: 4df. now exposes a *note
     backup: 4e0. method, if the underlying SQLite library is at version
     3.6.11 or higher.  Patch by Lele Gaifax.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33141

   (2) https://bugs.python.org/issue33096

   (3) https://bugs.python.org/issue32873

   (4) https://bugs.python.org/issue33134

   (5) https://bugs.python.org/issue33127

   (6) https://bugs.python.org/issue32505

   (7) https://bugs.python.org/issue33078

   (8) https://bugs.python.org/issue33116

   (9) https://bugs.python.org/issue32896

   (10) https://bugs.python.org/issue33100

   (11) https://bugs.python.org/issue32953

   (12) https://bugs.python.org/issue33061

   (13) https://bugs.python.org/issue33078

   (14) https://bugs.python.org/issue33064

   (15) https://bugs.python.org/issue33056

   (16) https://bugs.python.org/issue33021

   (17) https://bugs.python.org/issue31804

   (18) https://bugs.python.org/issue33037

   (19) https://bugs.python.org/issue27683

   (20) https://bugs.python.org/issue32999

   (21) https://bugs.python.org/issue33009

   (22) https://bugs.python.org/issue32969

   (23) https://bugs.python.org/issue32056

   (24) https://bugs.python.org/issue32844

   (25) https://bugs.python.org/issue32857

   (26) https://bugs.python.org/issue31639

   (27) https://bugs.python.org/issue27645


File: python.info,  Node: Documentation<29>,  Next: Tests<27>,  Prev: Library<35>,  Up: Python 3 7 0 beta 3

1.19.36.4 Documentation
.......................

   - bpo-33126(1): Document PyBuffer_ToContiguous().

   - bpo-27212(2): Modify documentation for the ‘islice()’ recipe to
     consume initial values up to the start index.

   - bpo-28247(3): Update *note zipapp: 14a. documentation to describe
     how to make standalone applications.

   - bpo-18802(4): Documentation changes for ipaddress.  Patch by Jon
     Foster and Berker Peksag.

   - bpo-27428(5): Update documentation to clarify that
     ‘WindowsRegistryFinder’ implements ‘MetaPathFinder’.  (Patch by
     Himanshu Lakhara)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33126

   (2) https://bugs.python.org/issue27212

   (3) https://bugs.python.org/issue28247

   (4) https://bugs.python.org/issue18802

   (5) https://bugs.python.org/issue27428


File: python.info,  Node: Tests<27>,  Next: Build<27>,  Prev: Documentation<29>,  Up: Python 3 7 0 beta 3

1.19.36.5 Tests
...............

   - bpo-32872(1): Avoid regrtest compatibility issue with namespace
     packages.

   - bpo-32517(2): Fix failing ‘test_asyncio’ on macOS 10.12.2+ due to
     transport of ‘KqueueSelector’ loop was not being closed.

   - bpo-19417(3): Add test_bdb.py.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32872

   (2) https://bugs.python.org/issue32517

   (3) https://bugs.python.org/issue19417


File: python.info,  Node: Build<27>,  Next: Windows<27>,  Prev: Tests<27>,  Up: Python 3 7 0 beta 3

1.19.36.6 Build
...............

   - bpo-33163(1): Upgrade pip to 9.0.3 and setuptools to v39.0.1.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33163


File: python.info,  Node: Windows<27>,  Next: macOS<23>,  Prev: Build<27>,  Up: Python 3 7 0 beta 3

1.19.36.7 Windows
.................

   - bpo-33016(1): Fix potential use of uninitialized memory in
     nt._getfinalpathname

   - bpo-32903(2): Fix a memory leak in os.chdir() on Windows if the
     current directory is set to a UNC path.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33016

   (2) https://bugs.python.org/issue32903


File: python.info,  Node: macOS<23>,  Next: IDLE<28>,  Prev: Windows<27>,  Up: Python 3 7 0 beta 3

1.19.36.8 macOS
...............

   - bpo-32726(1): Build and link with private copy of Tcl/Tk 8.6 for
     the macOS 10.6+ installer.  The 10.9+ installer variant already
     does this.  This means that the Python 3.7 provided by the
     python.org macOS installers no longer need or use any external
     versions of Tcl/Tk, either system-provided or user-installed, such
     as ActiveTcl.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32726


File: python.info,  Node: IDLE<28>,  Next: Tools/Demos<13>,  Prev: macOS<23>,  Up: Python 3 7 0 beta 3

1.19.36.9 IDLE
..............

   - bpo-32984(1): Set ‘__file__’ while running a startup file.  Like
     Python, IDLE optionally runs one startup file in the Shell window
     before presenting the first interactive input prompt.  For IDLE,
     ‘-s’ runs a file named in environmental variable ‘IDLESTARTUP’ or
     *note PYTHONSTARTUP: 9cb.; ‘-r file’ runs ‘file’.  Python sets
     ‘__file__’ to the startup file name before running the file and
     unsets it before the first prompt.  IDLE now does the same when run
     normally, without the ‘-n’ option.

   - bpo-32940(2): Simplify and rename StringTranslatePseudoMapping in
     pyparse.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32984

   (2) https://bugs.python.org/issue32940


File: python.info,  Node: Tools/Demos<13>,  Next: C API<22>,  Prev: IDLE<28>,  Up: Python 3 7 0 beta 3

1.19.36.10 Tools/Demos
......................

   - bpo-32885(1): Add an ‘-n’ flag for ‘Tools/scripts/pathfix.py’ to
     disable automatic backup creation (files with ‘~’ suffix).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32885


File: python.info,  Node: C API<22>,  Prev: Tools/Demos<13>,  Up: Python 3 7 0 beta 3

1.19.36.11 C API
................

   - bpo-33042(1): Embedding applications may once again call
     PySys_ResetWarnOptions, PySys_AddWarnOption, and PySys_AddXOption
     prior to calling Py_Initialize.

   - bpo-32374(2): Document that m_traverse for multi-phase initialized
     modules can be called with m_state=NULL, and add a sanity check

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33042

   (2) https://bugs.python.org/issue32374


File: python.info,  Node: Python 3 7 0 beta 2,  Next: Python 3 7 0 beta 1,  Prev: Python 3 7 0 beta 3,  Up: Changelog

1.19.37 Python 3.7.0 beta 2
---------------------------

`Release date: 2018-02-27'

* Menu:

* Security: Security<20>.
* Core and Builtins: Core and Builtins<33>.
* Library: Library<36>.
* Documentation: Documentation<30>.
* Tests: Tests<28>.
* Build: Build<28>.
* Windows: Windows<28>.
* macOS: macOS<24>.
* IDLE: IDLE<29>.
* Tools/Demos: Tools/Demos<14>.


File: python.info,  Node: Security<20>,  Next: Core and Builtins<33>,  Up: Python 3 7 0 beta 2

1.19.37.1 Security
..................

   - bpo-28414(1): The ssl module now allows users to perform their own
     IDN en/decoding when using SNI.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28414


File: python.info,  Node: Core and Builtins<33>,  Next: Library<36>,  Prev: Security<20>,  Up: Python 3 7 0 beta 2

1.19.37.2 Core and Builtins
...........................

   - bpo-32889(1): Update Valgrind suppression list to account for the
     rename of ‘Py_ADDRESS_IN_RANG’ to ‘address_in_range’.

   - bpo-31356(2): Remove the new API added in bpo-31356(3)
     (gc.ensure_disabled() context manager).

   - bpo-32305(4): For namespace packages, ensure that both ‘__file__’
     and ‘__spec__.origin’ are set to None.

   - bpo-32303(5): Make sure ‘__spec__.loader’ matches ‘__loader__’ for
     namespace packages.

   - bpo-32711(6): Fix the warning messages for Python/ast_unparse.c.
     Patch by Stéphane Wirtel

   - bpo-32583(7): Fix possible crashing in builtin Unicode decoders
     caused by write out-of-bound errors when using customized decode
     error handlers.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32889

   (2) https://bugs.python.org/issue31356

   (3) https://bugs.python.org/issue31356

   (4) https://bugs.python.org/issue32305

   (5) https://bugs.python.org/issue32303

   (6) https://bugs.python.org/issue32711

   (7) https://bugs.python.org/issue32583


File: python.info,  Node: Library<36>,  Next: Documentation<30>,  Prev: Core and Builtins<33>,  Up: Python 3 7 0 beta 2

1.19.37.3 Library
.................

   - bpo-32960(1): For dataclasses, disallow inheriting frozen from
     non-frozen classes, and also disallow inheriting non-frozen from
     frozen classes.  This restriction will be relaxed at a future date.

   - bpo-32713(2): Fixed tarfile.itn handling of out-of-bounds float
     values.  Patch by Joffrey Fuhrer.

   - bpo-32951(3): Direct instantiation of SSLSocket and SSLObject
     objects is now prohibited.  The constructors were never documented,
     tested, or designed as public constructors.  Users were suppose to
     use ssl.wrap_socket() or SSLContext.

   - bpo-32929(4): Remove the tri-state parameter “hash”, and add the
     boolean “unsafe_hash”.  If unsafe_hash is True, add a __hash__
     function, but if a __hash__ exists, raise TypeError.  If
     unsafe_hash is False, add a __hash__ based on the values of eq= and
     frozen=.  The unsafe_hash=False behavior is the same as the old
     hash=None behavior.  unsafe_hash=False is the default, just as
     hash=None used to be.

   - bpo-32947(5): Add OP_ENABLE_MIDDLEBOX_COMPAT and test workaround
     for TLSv1.3 for future compatibility with OpenSSL 1.1.1.

   - bpo-30622(6): The ssl module now detects missing NPN support in
     LibreSSL.

   - bpo-32922(7): dbm.open() now encodes filename with the filesystem
     encoding rather than default encoding.

   - bpo-32859(8): In ‘os.dup2’, don’t check every call whether the
     ‘dup3’ syscall exists or not.

   - bpo-32556(9): nt._getfinalpathname, nt._getvolumepathname and
     nt._getdiskusage now correctly convert from bytes.

   - bpo-25988(10): Emit a *note DeprecationWarning: 15a. when using or
     importing an ABC directly from *note collections: 1d. rather than
     from *note collections.abc: 1e.

   - bpo-21060(11): Rewrite confusing message from setup.py upload from
     “No dist file created in earlier command” to the more helpful “Must
     create and upload files in one command”.

   - bpo-32852(12): Make sure sys.argv remains as a list when running
     trace.

   - bpo-31333(13): ‘_abc’ module is added.  It is a speedup module with
     C implementations for various functions and methods in ‘abc’.
     Creating an ABC subclass and calling ‘isinstance’ or ‘issubclass’
     with an ABC subclass are up to 1.5x faster.  In addition, this
     makes Python start-up up to 10% faster.  Note that the new
     implementation hides internal registry and caches, previously
     accessible via private attributes ‘_abc_registry’, ‘_abc_cache’,
     and ‘_abc_negative_cache’.  There are three debugging helper
     methods that can be used instead ‘_dump_registry’,
     ‘_abc_registry_clear’, and ‘_abc_caches_clear’.

   - bpo-32841(14): Fixed *note asyncio.Condition: 3b0. issue which
     silently ignored cancellation after notifying and cancelling a
     conditional lock.  Patch by Bar Harel.

   - bpo-32819(15): ssl.match_hostname() has been simplified and no
     longer depends on re and ipaddress module for wildcard and IP
     addresses.  Error reporting for invalid wildcards has been
     improved.

   - bpo-32394(16): socket: Remove
     TCP_FASTOPEN,TCP_KEEPCNT,TCP_KEEPIDLE,TCP_KEEPINTVL flags on older
     version Windows during run-time.

   - bpo-31787(17): Fixed refleaks of ‘__init__()’ methods in various
     modules.  (Contributed by Oren Milman)

   - bpo-30157(18): Fixed guessing quote and delimiter in
     csv.Sniffer.sniff() when only the last field is quoted.  Patch by
     Jake Davis.

   - bpo-32792(19): collections.ChainMap() preserves the order of the
     underlying mappings.

   - bpo-32775(20): *note fnmatch.translate(): 1173. no longer produces
     patterns which contain set operations.  Sets starting with ‘[’ or
     containing ‘–’, ‘&&’, ‘~~’ or ‘||’ will be interpreted differently
     in regular expressions in future versions.  Currently they emit
     warnings.  fnmatch.translate() now avoids producing patterns
     containing such sets by accident.

   - bpo-32622(21): Implement native fast sendfile for Windows proactor
     event loop.

   - bpo-32777(22): Fix a rare but potential pre-exec child process
     deadlock in subprocess on POSIX systems when marking file
     descriptors inheritable on exec in the child process.  This bug
     appears to have been introduced in 3.4.

   - bpo-32647(23): The ctypes module used to depend on indirect linking
     for dlopen.  The shared extension is now explicitly linked against
     libdl on platforms with dl.

   - bpo-32741(24): Implement ‘asyncio.TimerHandle.when()’ method.

   - bpo-32691(25): Use mod_spec.parent when running modules with pdb

   - bpo-32734(26): Fixed ‘asyncio.Lock()’ safety issue which allowed
     acquiring and locking the same lock multiple times, without it
     being free.  Patch by Bar Harel.

   - bpo-32727(27): Do not include name field in SMTP envelope from
     address.  Patch by Stéphane Wirtel

   - bpo-31453(28): Add TLSVersion constants and
     SSLContext.maximum_version / minimum_version attributes.  The new
     API wraps OpenSSL 1.1
     ‘https://www.openssl.org/docs/man1.1.0/ssl/SSL_CTX_set_min_proto_version.html’
     feature.

   - bpo-24334(29): Internal implementation details of ssl module were
     cleaned up.  The SSLSocket has one less layer of indirection.
     Owner and session information are now handled by the SSLSocket and
     SSLObject constructor.  Channel binding implementation has been
     simplified.

   - bpo-31848(30): Fix the error handling in Aifc_read.initfp() when
     the SSND chunk is not found.  Patch by Zackery Spytz.

   - bpo-32585(31): Add Ttk spinbox widget to *note tkinter.ttk: 118.
     Patch by Alan D Moore.

   - bpo-32221(32): Various functions returning tuple containing IPv6
     addresses now omit ‘%scope’ part since the same information is
     already encoded in `scopeid' tuple item.  Especially this speeds up
     ‘socket.recvfrom()’ when it receives multicast packet since useless
     resolving of network interface name is omitted.

   - bpo-30693(33): The TarFile class now recurses directories in a
     reproducible way.

   - bpo-30693(34): The ZipFile class now recurses directories in a
     reproducible way.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32960

   (2) https://bugs.python.org/issue32713

   (3) https://bugs.python.org/issue32951

   (4) https://bugs.python.org/issue32929

   (5) https://bugs.python.org/issue32947

   (6) https://bugs.python.org/issue30622

   (7) https://bugs.python.org/issue32922

   (8) https://bugs.python.org/issue32859

   (9) https://bugs.python.org/issue32556

   (10) https://bugs.python.org/issue25988

   (11) https://bugs.python.org/issue21060

   (12) https://bugs.python.org/issue32852

   (13) https://bugs.python.org/issue31333

   (14) https://bugs.python.org/issue32841

   (15) https://bugs.python.org/issue32819

   (16) https://bugs.python.org/issue32394

   (17) https://bugs.python.org/issue31787

   (18) https://bugs.python.org/issue30157

   (19) https://bugs.python.org/issue32792

   (20) https://bugs.python.org/issue32775

   (21) https://bugs.python.org/issue32622

   (22) https://bugs.python.org/issue32777

   (23) https://bugs.python.org/issue32647

   (24) https://bugs.python.org/issue32741

   (25) https://bugs.python.org/issue32691

   (26) https://bugs.python.org/issue32734

   (27) https://bugs.python.org/issue32727

   (28) https://bugs.python.org/issue31453

   (29) https://bugs.python.org/issue24334

   (30) https://bugs.python.org/issue31848

   (31) https://bugs.python.org/issue32585

   (32) https://bugs.python.org/issue32221

   (33) https://bugs.python.org/issue30693

   (34) https://bugs.python.org/issue30693


File: python.info,  Node: Documentation<30>,  Next: Tests<28>,  Prev: Library<36>,  Up: Python 3 7 0 beta 2

1.19.37.4 Documentation
.......................

   - bpo-28124(1): The ssl module function ssl.wrap_socket() has been
     de-emphasized and deprecated in favor of the more secure and
     efficient SSLContext.wrap_socket() method.

   - bpo-17232(2): Clarify docs for -O and -OO. Patch by Terry Reedy.

   - bpo-32436(3): Add documentation for the contextvars module (PEP
     567).

   - bpo-32800(4): Update link to w3c doc for xml default namespaces.

   - bpo-11015(5): Update *note test.support: 106. documentation.

   - bpo-8722(6): Document *note __getattr__(): 42a. behavior when
     property ‘get()’ method raises *note AttributeError: 4a2.

   - bpo-32614(7): Modify RE examples in documentation to use raw
     strings to prevent *note DeprecationWarning: 15a. and add text to
     REGEX HOWTO to highlight the deprecation.

   - bpo-31972(8): Improve docstrings for *note pathlib.PurePath: 235.
     subclasses.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28124

   (2) https://bugs.python.org/issue17232

   (3) https://bugs.python.org/issue32436

   (4) https://bugs.python.org/issue32800

   (5) https://bugs.python.org/issue11015

   (6) https://bugs.python.org/issue8722

   (7) https://bugs.python.org/issue32614

   (8) https://bugs.python.org/issue31972


File: python.info,  Node: Tests<28>,  Next: Build<28>,  Prev: Documentation<30>,  Up: Python 3 7 0 beta 2

1.19.37.5 Tests
...............

   - bpo-31809(1): Add tests to verify connection with secp ECDH curves.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31809


File: python.info,  Node: Build<28>,  Next: Windows<28>,  Prev: Tests<28>,  Up: Python 3 7 0 beta 2

1.19.37.6 Build
...............

   - bpo-32898(1): Fix the python debug build when using COUNT_ALLOCS.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32898


File: python.info,  Node: Windows<28>,  Next: macOS<24>,  Prev: Build<28>,  Up: Python 3 7 0 beta 2

1.19.37.7 Windows
.................

   - bpo-32901(1): Update Tcl and Tk versions to 8.6.8

   - bpo-31966(2): Fixed WindowsConsoleIO.write() for writing empty
     data.

   - bpo-32409(3): Ensures activate.bat can handle Unicode contents.

   - bpo-32457(4): Improves handling of denormalized executable path
     when launching Python.

   - bpo-32370(5): Use the correct encoding for ipconfig output in the
     uuid module.  Patch by Segev Finer.

   - bpo-29248(6): Fix *note os.readlink(): 1d1. on Windows, which was
     mistakenly treating the ‘PrintNameOffset’ field of the reparse data
     buffer as a number of characters instead of bytes.  Patch by Craig
     Holmquist and SSE4.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32901

   (2) https://bugs.python.org/issue31966

   (3) https://bugs.python.org/issue32409

   (4) https://bugs.python.org/issue32457

   (5) https://bugs.python.org/issue32370

   (6) https://bugs.python.org/issue29248


File: python.info,  Node: macOS<24>,  Next: IDLE<29>,  Prev: Windows<28>,  Up: Python 3 7 0 beta 2

1.19.37.8 macOS
...............

   - bpo-32901(1): Update macOS 10.9+ installer to Tcl/Tk 8.6.8.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32901


File: python.info,  Node: IDLE<29>,  Next: Tools/Demos<14>,  Prev: macOS<24>,  Up: Python 3 7 0 beta 2

1.19.37.9 IDLE
..............

   - bpo-32916(1): Change ‘str’ to ‘code’ in pyparse.

   - bpo-32905(2): Remove unused code in pyparse module.

   - bpo-32874(3): Add tests for pyparse.

   - bpo-32837(4): Using the system and place-dependent default encoding
     for open() is a bad idea for IDLE’s system and location-independent
     files.

   - bpo-32826(5): Add “encoding=utf-8” to open() in IDLE’s
     test_help_about.  GUI test test_file_buttons() only looks at
     initial ascii-only lines, but failed on systems where open()
     defaults to ‘ascii’ because readline() internally reads and decodes
     far enough ahead to encounter a non-ascii character in CREDITS.txt.

   - bpo-32765(6): Update configdialog General tab docstring to add new
     widgets to the widget list.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32916

   (2) https://bugs.python.org/issue32905

   (3) https://bugs.python.org/issue32874

   (4) https://bugs.python.org/issue32837

   (5) https://bugs.python.org/issue32826

   (6) https://bugs.python.org/issue32765


File: python.info,  Node: Tools/Demos<14>,  Prev: IDLE<29>,  Up: Python 3 7 0 beta 2

1.19.37.10 Tools/Demos
......................

   - bpo-32222(1): Fix pygettext not extracting docstrings for functions
     with type annotated arguments.  Patch by Toby Harradine.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32222


File: python.info,  Node: Python 3 7 0 beta 1,  Next: Python 3 7 0 alpha 4,  Prev: Python 3 7 0 beta 2,  Up: Changelog

1.19.38 Python 3.7.0 beta 1
---------------------------

`Release date: 2018-01-30'

* Menu:

* Core and Builtins: Core and Builtins<34>.
* Library: Library<37>.
* Documentation: Documentation<31>.
* Tests: Tests<29>.
* Build: Build<29>.
* Windows: Windows<29>.
* macOS: macOS<25>.
* C API: C API<23>.


File: python.info,  Node: Core and Builtins<34>,  Next: Library<37>,  Up: Python 3 7 0 beta 1

1.19.38.1 Core and Builtins
...........................

   - bpo-32703(1): Fix coroutine’s ResourceWarning when there’s an
     active error set when it’s being finalized.

   - bpo-32650(2): Pdb and other debuggers dependent on bdb.py will
     correctly step over (next command) native coroutines.  Patch by
     Pablo Galindo.

   - bpo-28685(3): Optimize list.sort() and sorted() by using type
     specialized comparisons when possible.

   - bpo-32685(4): Improve suggestion when the Python 2 form of print
     statement is either present on the same line as the header of a
     compound statement or else terminated by a semi-colon instead of a
     newline.  Patch by Nitish Chandra.

   - bpo-32697(5): Python now explicitly preserves the definition order
     of keyword-only parameters.  It’s always preserved their order, but
     this behavior was never guaranteed before; this behavior is now
     guaranteed and tested.

   - bpo-32690(6): The locals() dictionary now displays in the lexical
     order that variables were defined.  Previously, the order was
     reversed.

   - bpo-32677(7): Add ‘.isascii()’ method to ‘str’, ‘bytes’ and
     ‘bytearray’.  It can be used to test that string contains only
     ASCII characters.

   - bpo-32670(8): Enforce PEP 479(9) for all code.  This means that
     manually raising a StopIteration exception from a generator is
     prohibited for all code, regardless of whether ‘from __future__
     import generator_stop’ was used or not.

   - bpo-32591(10): Added built-in support for tracking the origin of
     coroutine objects; see sys.set_coroutine_origin_tracking_depth and
     CoroutineType.cr_origin.  This replaces the asyncio debug mode’s
     use of coroutine wrapping for native coroutine objects.

   - bpo-31368(11): Expose preadv and pwritev system calls in the os
     module.  Patch by Pablo Galindo

   - bpo-32544(12): ‘hasattr(obj, name)’ and ‘getattr(obj, name,
     default)’ are about 4 times faster than before when ‘name’ is not
     found and ‘obj’ doesn’t override ‘__getattr__’ or
     ‘__getattribute__’.

   - bpo-26163(13): Improved frozenset() hash to create more distinct
     hash values when faced with datasets containing many similar
     values.

   - bpo-32550(14): Remove the STORE_ANNOTATION bytecode.

   - bpo-20104(15): Expose posix_spawn as a low level API in the os
     module.  (removed before 3.7.0rc1)

   - bpo-24340(16): Fixed estimation of the code stack size.

   - bpo-32436(17): Implement PEP 567(18) Context Variables.

   - bpo-18533(19): ‘repr()’ on a dict containing its own ‘values()’ or
     ‘items()’ no longer raises ‘RecursionError’; OrderedDict similarly.
     Instead, use ‘...’, as for other recursive structures.  Patch by
     Ben North.

   - bpo-20891(20): Py_Initialize() now creates the GIL. The GIL is no
     longer created “on demand” to fix a race condition when
     PyGILState_Ensure() is called in a non-Python thread.

   - bpo-32028(21): Leading whitespace is now correctly ignored when
     generating suggestions for converting Py2 print statements to Py3
     builtin print function calls.  Patch by Sanyam Khurana.

   - bpo-31179(22): Make dict.copy() up to 5.5 times faster.

   - bpo-31113(23): Get rid of recursion in the compiler for normal
     control flow.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32703

   (2) https://bugs.python.org/issue32650

   (3) https://bugs.python.org/issue28685

   (4) https://bugs.python.org/issue32685

   (5) https://bugs.python.org/issue32697

   (6) https://bugs.python.org/issue32690

   (7) https://bugs.python.org/issue32677

   (8) https://bugs.python.org/issue32670

   (9) https://www.python.org/dev/peps/pep-0479

   (10) https://bugs.python.org/issue32591

   (11) https://bugs.python.org/issue31368

   (12) https://bugs.python.org/issue32544

   (13) https://bugs.python.org/issue26163

   (14) https://bugs.python.org/issue32550

   (15) https://bugs.python.org/issue20104

   (16) https://bugs.python.org/issue24340

   (17) https://bugs.python.org/issue32436

   (18) https://www.python.org/dev/peps/pep-0567

   (19) https://bugs.python.org/issue18533

   (20) https://bugs.python.org/issue20891

   (21) https://bugs.python.org/issue32028

   (22) https://bugs.python.org/issue31179

   (23) https://bugs.python.org/issue31113


File: python.info,  Node: Library<37>,  Next: Documentation<31>,  Prev: Core and Builtins<34>,  Up: Python 3 7 0 beta 1

1.19.38.2 Library
.................

   - bpo-25988(1): Deprecate exposing the contents of collections.abc in
     the regular collections module.

   - bpo-31429(2): The default cipher suite selection of the ssl module
     now uses a blacklist approach rather than a hard-coded whitelist.
     Python no longer re-enables ciphers that have been blocked by
     OpenSSL security update.  Default cipher suite selection can be
     configured on compile time.

   - bpo-30306(3): contextlib.contextmanager now releases the arguments
     passed to the underlying generator as soon as the context manager
     is entered.  Previously it would keep them alive for as long as the
     context manager was alive, even when not being used as a function
     decorator.  Patch by Martin Teichmann.

   - bpo-21417(4): Added support for setting the compression level for
     zipfile.ZipFile.

   - bpo-32251(5): Implement asyncio.BufferedProtocol (provisional API).

   - bpo-32513(6): In dataclasses, allow easier overriding of dunder
     methods without specifying decorator parameters.

   - bpo-32660(7): *note termios: 104. makes available ‘FIONREAD’,
     ‘FIONCLEX’, ‘FIOCLEX’, ‘FIOASYNC’ and ‘FIONBIO’ also under
     Solaris/derivatives.

   - bpo-27931(8): Fix email address header parsing error when the
     username is an empty quoted string.  Patch by Xiang Zhang.

   - bpo-32659(9): Under Solaris and derivatives, *note os.stat_result:
     11bf. provides a st_fstype attribute.

   - bpo-32662(10): Implement Server.start_serving(),
     Server.serve_forever(), and Server.is_serving() methods.  Add
     ‘start_serving’ keyword parameter to loop.create_server() and
     loop.create_unix_server().

   - bpo-32391(11): Implement *note asyncio.StreamWriter.wait_closed():
     45e. and *note asyncio.StreamWriter.is_closing(): 45f. methods

   - bpo-32643(12): Make Task._step, Task._wakeup and
     Future._schedule_callbacks methods private.

   - bpo-32630(13): Refactor decimal module to use contextvars to store
     decimal context.

   - bpo-32622(14): Add ‘asyncio.AbstractEventLoop.sendfile()’ method.

   - bpo-32304(15): distutils’ upload command no longer corrupts tar
     files ending with a CR byte, and no longer tries to convert CR to
     CRLF in any of the upload text fields.

   - bpo-32502(16): uuid.uuid1 no longer raises an exception if a 64-bit
     hardware address is encountered.

   - bpo-32596(17): ‘concurrent.futures’ imports ‘ThreadPoolExecutor’
     and ‘ProcessPoolExecutor’ lazily (using PEP 562(18)).  It makes
     ‘import asyncio’ about 15% faster because asyncio uses only
     ‘ThreadPoolExecutor’ by default.

   - bpo-31801(19): Add ‘_ignore_’ to ‘Enum’ so temporary variables can
     be used during class construction without being turned into
     members.

   - bpo-32576(20): Use queue.SimpleQueue() in places where it can be
     invoked from a weakref callback.

   - bpo-32574(21): Fix memory leak in asyncio.Queue, when the queue has
     limited size and it is full, the cancelation of queue.put() can
     cause a memory leak.  Patch by: José Melero.

   - bpo-32521(22): The nis module is now compatible with new libnsl and
     headers location.

   - bpo-32467(23): collections.abc.ValuesView now inherits from
     collections.abc.Collection.

   - bpo-32473(24): Improve ABCMeta._dump_registry() output readability

   - bpo-32102(25): New argument ‘capture_output’ for subprocess.run

   - bpo-32521(26): glibc has removed Sun RPC. Use replacement libtirpc
     headers and library in nis module.

   - bpo-32493(27): UUID module fixes build for FreeBSD/OpenBSD

   - bpo-32503(28): Pickling with protocol 4 no longer creates too small
     frames.

   - bpo-29237(29): Create enum for pstats sorting options

   - bpo-32454(30): Add close(fd) function to the socket module.

   - bpo-25942(31): The subprocess module is now more graceful when
     handling a Ctrl-C KeyboardInterrupt during subprocess.call,
     subprocess.run, or a Popen context manager.  It now waits a short
     amount of time for the child (presumed to have also gotten the
     SIGINT) to exit, before continuing the KeyboardInterrupt exception
     handling.  This still includes a SIGKILL in the call() and run()
     APIs, but at least the child had a chance first.

   - bpo-32433(32): The hmac module now has hmac.digest(), which
     provides an optimized HMAC digest.

   - bpo-28134(33): Sockets now auto-detect family, type and protocol
     from file descriptor by default.

   - bpo-32404(34): Fix bug where *note
     datetime.datetime.fromtimestamp(): 11c0. did not call __new__ in
     *note datetime.datetime: 1a0. subclasses.

   - bpo-32403(35): Improved speed of *note datetime.date: 19e. and
     *note datetime.datetime: 1a0. alternate constructors.

   - bpo-32228(36): Ensure that ‘truncate()’ preserves the file position
     (as reported by ‘tell()’) after writes longer than the buffer size.

   - bpo-32410(37): Implement ‘loop.sock_sendfile’ for asyncio event
     loop.

   - bpo-22908(38): Added seek and tell to the ZipExtFile class.  This
     only works if the file object used to open the zipfile is seekable.

   - bpo-32373(39): Add socket.getblocking() method.

   - bpo-32248(40): Add *note importlib.resources: 9e. and *note
     importlib.abc.ResourceReader: 44e. as the unified API for reading
     resources contained within packages.  Loaders wishing to support
     resource reading must implement the ‘get_resource_reader()’ method.
     File-based and zipimport-based loaders both implement these APIs.
     *note importlib.abc.ResourceLoader: 568. is deprecated in favor of
     these new APIs.

   - bpo-32320(41): collections.namedtuple() now supports default
     values.

   - bpo-29302(42): Add contextlib.AsyncExitStack.  Patch by Alexander
     Mohr and Ilya Kulakov.

   - bpo-31961(43): `Removed in Python 3.7.0b2.'  The `args' argument of
     subprocess.Popen can now be a *note path-like object: 472.  If
     `args' is given as a sequence, it’s first element can now be a
     *note path-like object: 472. as well.

   - bpo-31900(44): The *note locale.localeconv(): 585. function now
     sets temporarily the ‘LC_CTYPE’ locale to the ‘LC_NUMERIC’ locale
     to decode ‘decimal_point’ and ‘thousands_sep’ byte strings if they
     are non-ASCII or longer than 1 byte, and the ‘LC_NUMERIC’ locale is
     different than the ‘LC_CTYPE’ locale.  This temporary change
     affects other threads.  Same change for the *note str.format():
     5d5. method when formatting a number (*note int: 204, *note float:
     1fd, *note float: 1fd. and subclasses) with the ‘n’ type (ex:
     ‘'{:n}'.format(1234)’).

   - bpo-31853(45): Use super().method instead of socket.method in
     SSLSocket.  They were there most likely for legacy reasons.

   - bpo-31399(46): The ssl module now uses OpenSSL’s
     X509_VERIFY_PARAM_set1_host() and X509_VERIFY_PARAM_set1_ip() API
     to verify hostname and IP addresses.  Subject common name fallback
     can be disabled with SSLContext.hostname_checks_common_name.

   - bpo-14976(47): Add a queue.SimpleQueue class, an unbounded FIFO
     queue with a reentrant C implementation of put().

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25988

   (2) https://bugs.python.org/issue31429

   (3) https://bugs.python.org/issue30306

   (4) https://bugs.python.org/issue21417

   (5) https://bugs.python.org/issue32251

   (6) https://bugs.python.org/issue32513

   (7) https://bugs.python.org/issue32660

   (8) https://bugs.python.org/issue27931

   (9) https://bugs.python.org/issue32659

   (10) https://bugs.python.org/issue32662

   (11) https://bugs.python.org/issue32391

   (12) https://bugs.python.org/issue32643

   (13) https://bugs.python.org/issue32630

   (14) https://bugs.python.org/issue32622

   (15) https://bugs.python.org/issue32304

   (16) https://bugs.python.org/issue32502

   (17) https://bugs.python.org/issue32596

   (18) https://www.python.org/dev/peps/pep-0562

   (19) https://bugs.python.org/issue31801

   (20) https://bugs.python.org/issue32576

   (21) https://bugs.python.org/issue32574

   (22) https://bugs.python.org/issue32521

   (23) https://bugs.python.org/issue32467

   (24) https://bugs.python.org/issue32473

   (25) https://bugs.python.org/issue32102

   (26) https://bugs.python.org/issue32521

   (27) https://bugs.python.org/issue32493

   (28) https://bugs.python.org/issue32503

   (29) https://bugs.python.org/issue29237

   (30) https://bugs.python.org/issue32454

   (31) https://bugs.python.org/issue25942

   (32) https://bugs.python.org/issue32433

   (33) https://bugs.python.org/issue28134

   (34) https://bugs.python.org/issue32404

   (35) https://bugs.python.org/issue32403

   (36) https://bugs.python.org/issue32228

   (37) https://bugs.python.org/issue32410

   (38) https://bugs.python.org/issue22908

   (39) https://bugs.python.org/issue32373

   (40) https://bugs.python.org/issue32248

   (41) https://bugs.python.org/issue32320

   (42) https://bugs.python.org/issue29302

   (43) https://bugs.python.org/issue31961

   (44) https://bugs.python.org/issue31900

   (45) https://bugs.python.org/issue31853

   (46) https://bugs.python.org/issue31399

   (47) https://bugs.python.org/issue14976


File: python.info,  Node: Documentation<31>,  Next: Tests<29>,  Prev: Library<37>,  Up: Python 3 7 0 beta 1

1.19.38.3 Documentation
.......................

   - bpo-32724(1): Add references to some commands in the documentation
     of Pdb.  Patch by Stéphane Wirtel

   - bpo-32649(2): Complete the C API documentation, profiling and
     tracing part with the newly added per-opcode events.

   - bpo-17799(3): Explain real behaviour of sys.settrace and
     sys.setprofile and their C-API counterparts regarding which type of
     events are received in each function.  Patch by Pablo Galindo
     Salgado.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32724

   (2) https://bugs.python.org/issue32649

   (3) https://bugs.python.org/issue17799


File: python.info,  Node: Tests<29>,  Next: Build<29>,  Prev: Documentation<31>,  Up: Python 3 7 0 beta 1

1.19.38.4 Tests
...............

   - bpo-32721(1): Fix test_hashlib to not fail if the _md5 module is
     not built.

   - bpo-28414(2): Add test cases for IDNA 2003 and 2008 host names.
     IDNA 2003 internationalized host names are working since
     bpo-31399(3) has landed.  IDNA 2008 are still broken.

   - bpo-32604(4): Add a new “_xxsubinterpreters” extension module that
     exposes the existing subinterpreter C-API and a new
     cross-interpreter data sharing mechanism.  The module is primarily
     intended for more thorough testing of the existing subinterpreter
     support.  Note that the _xxsubinterpreters module has been removed
     in 3.7.0rc1.

   - bpo-32602(5): Add test certs and test for ECDSA cert and EC/RSA
     dual mode.

   - bpo-32549(6): On Travis CI, Python now Compiles and uses a local
     copy of OpenSSL 1.1.0g for testing.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32721

   (2) https://bugs.python.org/issue28414

   (3) https://bugs.python.org/issue31399

   (4) https://bugs.python.org/issue32604

   (5) https://bugs.python.org/issue32602

   (6) https://bugs.python.org/issue32549


File: python.info,  Node: Build<29>,  Next: Windows<29>,  Prev: Tests<29>,  Up: Python 3 7 0 beta 1

1.19.38.5 Build
...............

   - bpo-32635(1): Fix segfault of the crypt module when libxcrypt is
     provided instead of libcrypt at the system.

   - bpo-32598(2): Use autoconf to detect OpenSSL libs, headers and
     supported features.  The ax_check_openssl M4 macro uses pkg-config
     to locate OpenSSL and falls back to manual search.

   - bpo-32593(3): Drop support of FreeBSD 9 and older.

   - bpo-29708(4): If the ‘SOURCE_DATE_EPOCH’ environment variable is
     set, *note py_compile: d7. will always create hash-based ‘.pyc’
     files.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32635

   (2) https://bugs.python.org/issue32598

   (3) https://bugs.python.org/issue32593

   (4) https://bugs.python.org/issue29708


File: python.info,  Node: Windows<29>,  Next: macOS<25>,  Prev: Build<29>,  Up: Python 3 7 0 beta 1

1.19.38.6 Windows
.................

   - bpo-32588(1): Create standalone _distutils_findvs module and add
     missing _queue module to installer.

   - bpo-29911(2): Ensure separate Modify and Uninstall buttons are
     displayed.

   - bpo-32507(3): Use app-local UCRT install rather than the proper
     update for old versions of Windows.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32588

   (2) https://bugs.python.org/issue29911

   (3) https://bugs.python.org/issue32507


File: python.info,  Node: macOS<25>,  Next: C API<23>,  Prev: Windows<29>,  Up: Python 3 7 0 beta 1

1.19.38.7 macOS
...............

   - bpo-32726(1): Provide an additional, more modern macOS installer
     variant that supports macOS 10.9+ systems in 64-bit mode only.
     Upgrade the supplied third-party libraries to OpenSSL 1.1.0g and to
     SQLite 3.22.0.  The 10.9+ installer now links with and supplies its
     own copy of Tcl/Tk 8.6.

   - bpo-28440(2): No longer add /Library/Python/3.x/site-packages to
     sys.path for macOS framework builds to avoid future conflicts.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32726

   (2) https://bugs.python.org/issue28440


File: python.info,  Node: C API<23>,  Prev: macOS<25>,  Up: Python 3 7 0 beta 1

1.19.38.8 C API
...............

   - bpo-32681(1): Fix uninitialized variable ‘res’ in the C
     implementation of os.dup2.  Patch by Stéphane Wirtel

   - bpo-10381(2): Add C API access to the ‘datetime.timezone’
     constructor and ‘datetime.timzone.UTC’ singleton.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32681

   (2) https://bugs.python.org/issue10381


File: python.info,  Node: Python 3 7 0 alpha 4,  Next: Python 3 7 0 alpha 3,  Prev: Python 3 7 0 beta 1,  Up: Changelog

1.19.39 Python 3.7.0 alpha 4
----------------------------

`Release date: 2018-01-08'

* Menu:

* Core and Builtins: Core and Builtins<35>.
* Library: Library<38>.
* Documentation: Documentation<32>.
* Tests: Tests<30>.
* Windows: Windows<30>.
* Tools/Demos: Tools/Demos<15>.
* C API: C API<24>.


File: python.info,  Node: Core and Builtins<35>,  Next: Library<38>,  Up: Python 3 7 0 alpha 4

1.19.39.1 Core and Builtins
...........................

   - bpo-31975(1): The default warning filter list now starts with a
     “default::DeprecationWarning:__main__” entry, so deprecation
     warnings are once again shown by default in single-file scripts and
     at the interactive prompt.

   - bpo-32226(2): ‘__class_getitem__’ is now an automatic class method.

   - bpo-32399(3): Add AIX uuid library support for RFC4122 using
     uuid_create() in libc.a

   - bpo-32390(4): Fix the compilation failure on AIX after the f_fsid
     field has been added to the object returned by os.statvfs()
     (bpo-32143(5)).  Original patch by Michael Felt.

   - bpo-32379(6): Make MRO computation faster when a class inherits
     from a single base.

   - bpo-32259(7): The error message of a TypeError raised when unpack
     non-iterable is now more specific.

   - bpo-27169(8): The ‘__debug__’ constant is now optimized out at
     compile time.  This fixes also bpo-22091(9).

   - bpo-32329(10): The *note -R: 11c9. option now turns on hash
     randomization when the *note PYTHONHASHSEED: aa4. environment
     variable is set to ‘0’.  Previously, the option was ignored.
     Moreover, ‘sys.flags.hash_randomization’ is now properly set to 0
     when hash randomization is turned off by ‘PYTHONHASHSEED=0’.

   - bpo-30416(11): The optimizer is now protected from spending much
     time doing complex calculations and consuming much memory for
     creating large constants in constant folding.  Increased limits for
     constants that can be produced in constant folding.

   - bpo-32282(12): Fix an unnecessary ifdef in the include of
     VersionHelpers.h in socketmodule on Windows.

   - bpo-30579(13): Implement TracebackType.__new__ to allow
     Python-level creation of traceback objects, and make
     TracebackType.tb_next mutable.

   - bpo-32260(14): Don’t byte swap the input keys to the SipHash
     algorithm on big-endian platforms.  This should ensure siphash
     gives consistent results across platforms.

   - bpo-31506(15): Improve the error message logic for object.__new__
     and object.__init__.  Patch by Sanyam Khurana.

   - bpo-20361(16): ‘-b’ and ‘-bb’ now inject ‘'default::BytesWarning'’
     and ‘error::BytesWarning’ entries into ‘sys.warnoptions’, ensuring
     that they take precedence over any other warning filters configured
     via the ‘-W’ option or the ‘PYTHONWARNINGS’ environment variable.

   - bpo-32230(17): ‘-X dev’ now injects a ‘'default'’ entry into
     sys.warnoptions, ensuring that it behaves identically to actually
     passing ‘-Wdefault’ at the command line.

   - bpo-29240(18): Add a new UTF-8 mode: implementation of the PEP
     540(19).

   - bpo-32226(20): PEP 560(21): Add support for ‘__mro_entries__’ and
     ‘__class_getitem__’.  Implemented by Ivan Levkivskyi.

   - bpo-32225(22): PEP 562(23): Add support for module ‘__getattr__’
     and ‘__dir__’.  Implemented by Ivan Levkivskyi.

   - bpo-31901(24): The *note atexit: b. module now has its callback
     stored per interpreter.

   - bpo-31650(25): Implement PEP 552(26) (Deterministic pycs).  Python
     now supports invalidating bytecode cache files bashed on a source
     content hash rather than source last-modified time.

   - bpo-29469(27): Move constant folding from bytecode layer to AST
     layer.  Original patch by Eugene Toder.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31975

   (2) https://bugs.python.org/issue32226

   (3) https://bugs.python.org/issue32399

   (4) https://bugs.python.org/issue32390

   (5) https://bugs.python.org/issue32143

   (6) https://bugs.python.org/issue32379

   (7) https://bugs.python.org/issue32259

   (8) https://bugs.python.org/issue27169

   (9) https://bugs.python.org/issue22091

   (10) https://bugs.python.org/issue32329

   (11) https://bugs.python.org/issue30416

   (12) https://bugs.python.org/issue32282

   (13) https://bugs.python.org/issue30579

   (14) https://bugs.python.org/issue32260

   (15) https://bugs.python.org/issue31506

   (16) https://bugs.python.org/issue20361

   (17) https://bugs.python.org/issue32230

   (18) https://bugs.python.org/issue29240

   (19) https://www.python.org/dev/peps/pep-0540

   (20) https://bugs.python.org/issue32226

   (21) https://www.python.org/dev/peps/pep-0560

   (22) https://bugs.python.org/issue32225

   (23) https://www.python.org/dev/peps/pep-0562

   (24) https://bugs.python.org/issue31901

   (25) https://bugs.python.org/issue31650

   (26) https://www.python.org/dev/peps/pep-0552

   (27) https://bugs.python.org/issue29469


File: python.info,  Node: Library<38>,  Next: Documentation<32>,  Prev: Core and Builtins<35>,  Up: Python 3 7 0 alpha 4

1.19.39.2 Library
.................

   - bpo-32506(1): Now that dict is defined as keeping insertion order,
     drop OrderedDict and just use plain dict.

   - bpo-32279(2): Add params to dataclasses.make_dataclasses(): init,
     repr, eq, order, hash, and frozen.  Pass them through to
     dataclass().

   - bpo-32278(3): Make type information optional on
     dataclasses.make_dataclass().  If omitted, the string ‘typing.Any’
     is used.

   - bpo-32499(4): Add dataclasses.is_dataclass(obj), which returns True
     if obj is a dataclass or an instance of one.

   - bpo-32468(5): Improve frame repr() to mention filename, code name
     and current line number.

   - bpo-23749(6): asyncio: Implement loop.start_tls()

   - bpo-32441(7): Return the new file descriptor (i.e., the second
     argument) from ‘os.dup2’.  Previously, ‘None’ was always returned.

   - bpo-32422(8): ‘functools.lru_cache’ uses less memory (3 words for
     each cached key) and takes about 1/3 time for cyclic GC.

   - bpo-31721(9): Prevent Python crash from happening when
     Future._log_traceback is set to True manually.  Now it can only be
     set to False, or a ValueError is raised.

   - bpo-32415(10): asyncio: Add Task.get_loop() and Future.get_loop()

   - bpo-26133(11): Don’t unsubscribe signals in asyncio UNIX event loop
     on interpreter shutdown.

   - bpo-32363(12): Make asyncio.Task.set_exception() and set_result()
     raise NotImplementedError.  Task._step() and Future.__await__()
     raise proper exceptions when they are in an invalid state, instead
     of raising an AssertionError.

   - bpo-32357(13): Optimize asyncio.iscoroutine() and
     loop.create_task() for non-native coroutines (e.g.  async/await
     compiled with Cython).  ‘loop.create_task(python_coroutine)’ used
     to be 20% faster than ‘loop.create_task(cython_coroutine)’.  Now,
     the latter is as fast.

   - bpo-32356(14): asyncio.transport.resume_reading() and
     pause_reading() are now idempotent.  New transport.is_reading()
     method is added.

   - bpo-32355(15): Optimize asyncio.gather(); now up to 15% faster.

   - bpo-32351(16): Use fastpath in asyncio.sleep if delay<0 (2x boost)

   - bpo-32348(17): Optimize asyncio.Future schedule/add/remove
     callback.  The optimization shows 3-6% performance improvements of
     async/await code.

   - bpo-32331(18): Fix socket.settimeout() and socket.setblocking() to
     keep socket.type as is.  Fix socket.socket() constructor to reset
     any bit flags applied to socket’s type.  This change only affects
     OSes that have SOCK_NONBLOCK and/or SOCK_CLOEXEC.

   - bpo-32248(19): Add *note importlib.abc.ResourceReader: 44e. as an
     ABC for loaders to provide a unified API for reading resources
     contained within packages.  Also add *note importlib.resources: 9e.
     as the port of ‘importlib_resources’.

   - bpo-32311(20): Implement asyncio.create_task(coro) shortcut

   - bpo-32327(21): Convert asyncio functions that were documented as
     coroutines to coroutines.  Affected functions: loop.sock_sendall,
     loop.sock_recv, loop.sock_accept, loop.getaddrinfo,
     loop.getnameinfo.

   - bpo-32323(22): *note urllib.parse.urlsplit(): 6f0. does not convert
     zone-id (scope) to lower case for scoped IPv6 addresses in
     hostnames now.

   - bpo-32302(23): Fix bdist_wininst of distutils for CRT v142: it
     binary compatible with CRT v140.

   - bpo-29711(24): Fix ‘stop_serving’ in asyncio proactor loop kill all
     listening servers

   - bpo-32308(25): *note re.sub(): 57a. now replaces empty matches
     adjacent to a previous non-empty match.

   - bpo-29970(26): Abort asyncio SSLProtocol connection if handshake
     not complete within 10s

   - bpo-32314(27): Implement asyncio.run().

   - bpo-17852(28): Revert incorrect fix based on misunderstanding of
     _Py_PyAtExit() semantics.

   - bpo-32296(29): Implement asyncio._get_running_loop() and
     get_event_loop() in C. This makes them 4x faster.

   - bpo-32250(30): Implement ‘asyncio.current_task()’ and
     ‘asyncio.all_tasks()’.  Add helpers intended to be used by
     alternative task implementations: ‘asyncio._register_task’,
     ‘asyncio._enter_task’, ‘asyncio._leave_task’ and
     ‘asyncio._unregister_task’.  Deprecate
     ‘asyncio.Task.current_task()’ and ‘asyncio.Task.all_tasks()’.

   - bpo-32255(31): A single empty field is now always quoted when
     written into a CSV file.  This allows to distinguish an empty row
     from a row consisting of a single empty field.  Patch by Licht
     Takeuchi.

   - bpo-32277(32): Raise ‘NotImplementedError’ instead of ‘SystemError’
     on platforms where ‘chmod(..., follow_symlinks=False)’ is not
     supported.  Patch by Anthony Sottile.

   - bpo-30050(33): New argument warn_on_full_buffer to
     signal.set_wakeup_fd lets you control whether Python prints a
     warning on stderr when the wakeup fd buffer overflows.

   - bpo-29137(34): The ‘fpectl’ library has been removed.  It was never
     enabled by default, never worked correctly on x86-64, and it
     changed the Python ABI in ways that caused unexpected breakage of C
     extensions.

   - bpo-32273(35): Move asyncio.test_utils to test.test_asyncio.

   - bpo-32272(36): Remove asyncio.async() function.

   - bpo-32269(37): Add asyncio.get_running_loop() function.

   - bpo-32265(38): All class and static methods of builtin types now
     are correctly classified by inspect.classify_class_attrs() and
     grouped in pydoc ouput.  Added types.ClassMethodDescriptorType for
     unbound class methods of builtin types.

   - bpo-32253(39): Deprecate ‘yield from lock’, ‘await lock’, ‘with
     (yield from lock)’ and ‘with await lock’ for asyncio
     synchronization primitives.

   - bpo-22589(40): Changed MIME type of .bmp from ‘image/x-ms-bmp’ to
     ‘image/bmp’

   - bpo-32193(41): Convert asyncio to use `async/await' syntax.  Old
     styled ‘yield from’ is still supported too.

   - bpo-32206(42): Add support to run modules with pdb

   - bpo-32227(43): ‘functools.singledispatch’ now supports registering
     implementations using type annotations.

   - bpo-15873(44): Added new alternate constructors *note
     datetime.datetime.fromisoformat(): 486, *note
     datetime.time.fromisoformat(): 11cb. and *note
     datetime.date.fromisoformat(): 11cc. as the inverse operation of
     each classes’s respective ‘isoformat’ methods.

   - bpo-32199(45): The getnode() ip getter now uses ‘ip link’ instead
     of ‘ip link list’.

   - bpo-32143(46): os.statvfs() includes the f_fsid field from
     statvfs(2)

   - bpo-26439(47): Fix ctypes.util.find_library() for AIX by
     implementing ctypes._aix.find_library() Patch by: Michael Felt

   - bpo-31993(48): The pickler now uses less memory when serializing
     large bytes and str objects into a file.  Pickles created with
     protocol 4 will require less memory for unpickling large bytes and
     str objects.

   - bpo-27456(49): Ensure TCP_NODELAY is set on Linux.  Tests by Victor
     Stinner.

   - bpo-31778(50): ast.literal_eval() is now more strict.  Addition and
     subtraction of arbitrary numbers no longer allowed.

   - bpo-31802(51): Importing native path module (‘posixpath’, ‘ntpath’)
     now works even if the ‘os’ module still is not imported.

   - bpo-30241(52): Add contextlib.AbstractAsyncContextManager.  Patch
     by Jelle Zijlstra.

   - bpo-31699(53): Fix deadlocks in *note
     concurrent.futures.ProcessPoolExecutor: 196. when task arguments or
     results cause pickling or unpickling errors.  This should make sure
     that calls to the ‘ProcessPoolExecutor’ API always eventually
     return.

   - bpo-15216(54): ‘TextIOWrapper.reconfigure()’ supports changing
     `encoding', `errors', and `newline'.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32506

   (2) https://bugs.python.org/issue32279

   (3) https://bugs.python.org/issue32278

   (4) https://bugs.python.org/issue32499

   (5) https://bugs.python.org/issue32468

   (6) https://bugs.python.org/issue23749

   (7) https://bugs.python.org/issue32441

   (8) https://bugs.python.org/issue32422

   (9) https://bugs.python.org/issue31721

   (10) https://bugs.python.org/issue32415

   (11) https://bugs.python.org/issue26133

   (12) https://bugs.python.org/issue32363

   (13) https://bugs.python.org/issue32357

   (14) https://bugs.python.org/issue32356

   (15) https://bugs.python.org/issue32355

   (16) https://bugs.python.org/issue32351

   (17) https://bugs.python.org/issue32348

   (18) https://bugs.python.org/issue32331

   (19) https://bugs.python.org/issue32248

   (20) https://bugs.python.org/issue32311

   (21) https://bugs.python.org/issue32327

   (22) https://bugs.python.org/issue32323

   (23) https://bugs.python.org/issue32302

   (24) https://bugs.python.org/issue29711

   (25) https://bugs.python.org/issue32308

   (26) https://bugs.python.org/issue29970

   (27) https://bugs.python.org/issue32314

   (28) https://bugs.python.org/issue17852

   (29) https://bugs.python.org/issue32296

   (30) https://bugs.python.org/issue32250

   (31) https://bugs.python.org/issue32255

   (32) https://bugs.python.org/issue32277

   (33) https://bugs.python.org/issue30050

   (34) https://bugs.python.org/issue29137

   (35) https://bugs.python.org/issue32273

   (36) https://bugs.python.org/issue32272

   (37) https://bugs.python.org/issue32269

   (38) https://bugs.python.org/issue32265

   (39) https://bugs.python.org/issue32253

   (40) https://bugs.python.org/issue22589

   (41) https://bugs.python.org/issue32193

   (42) https://bugs.python.org/issue32206

   (43) https://bugs.python.org/issue32227

   (44) https://bugs.python.org/issue15873

   (45) https://bugs.python.org/issue32199

   (46) https://bugs.python.org/issue32143

   (47) https://bugs.python.org/issue26439

   (48) https://bugs.python.org/issue31993

   (49) https://bugs.python.org/issue27456

   (50) https://bugs.python.org/issue31778

   (51) https://bugs.python.org/issue31802

   (52) https://bugs.python.org/issue30241

   (53) https://bugs.python.org/issue31699

   (54) https://bugs.python.org/issue15216


File: python.info,  Node: Documentation<32>,  Next: Tests<30>,  Prev: Library<38>,  Up: Python 3 7 0 alpha 4

1.19.39.3 Documentation
.......................

   - bpo-32418(1): Add get_loop() method to Server and AbstractServer
     classes.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32418


File: python.info,  Node: Tests<30>,  Next: Windows<30>,  Prev: Documentation<32>,  Up: Python 3 7 0 alpha 4

1.19.39.4 Tests
...............

   - bpo-32252(1): Fix faulthandler_suppress_crash_report() used to
     prevent core dump files when testing crashes.  getrlimit() returns
     zero on success.

   - bpo-32002(2): Adjust C locale coercion testing for the empty locale
     and POSIX locale cases to more readily adjust to platform dependent
     behaviour.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32252

   (2) https://bugs.python.org/issue32002


File: python.info,  Node: Windows<30>,  Next: Tools/Demos<15>,  Prev: Tests<30>,  Up: Python 3 7 0 alpha 4

1.19.39.5 Windows
.................

   - bpo-19764(1): Implement support for
     ‘subprocess.Popen(close_fds=True)’ on Windows.  Patch by Segev
     Finer.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19764


File: python.info,  Node: Tools/Demos<15>,  Next: C API<24>,  Prev: Windows<30>,  Up: Python 3 7 0 alpha 4

1.19.39.6 Tools/Demos
.....................

   - bpo-24960(1): 2to3 and lib2to3 can now read pickled grammar files
     using pkgutil.get_data() rather than probing the filesystem.  This
     lets 2to3 and lib2to3 work when run from a zipfile.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24960


File: python.info,  Node: C API<24>,  Prev: Tools/Demos<15>,  Up: Python 3 7 0 alpha 4

1.19.39.7 C API
...............

   - bpo-32030(1): Py_Initialize() doesn’t reset the memory allocators
     to default if the ‘PYTHONMALLOC’ environment variable is not set.

   - bpo-29084(2): Undocumented C API for OrderedDict has been excluded
     from the limited C API. It was added by mistake and actually never
     worked in the limited C API.

   - bpo-32264(3): Moved the pygetopt.h header into internal/, since it
     has no public APIs.

   - bpo-32241(4): *note Py_SetProgramName(): 10f2. and *note
     Py_SetPythonHome(): 10f1. now take the ‘const wchar *’ arguments
     instead of ‘wchar *’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32030

   (2) https://bugs.python.org/issue29084

   (3) https://bugs.python.org/issue32264

   (4) https://bugs.python.org/issue32241


File: python.info,  Node: Python 3 7 0 alpha 3,  Next: Python 3 7 0 alpha 2,  Prev: Python 3 7 0 alpha 4,  Up: Changelog

1.19.40 Python 3.7.0 alpha 3
----------------------------

`Release date: 2017-12-05'

* Menu:

* Core and Builtins: Core and Builtins<36>.
* Library: Library<39>.
* Documentation: Documentation<33>.
* Tests: Tests<31>.
* Build: Build<30>.
* Windows: Windows<31>.
* macOS: macOS<26>.
* IDLE: IDLE<30>.
* Tools/Demos: Tools/Demos<16>.
* C API: C API<25>.


File: python.info,  Node: Core and Builtins<36>,  Next: Library<39>,  Up: Python 3 7 0 alpha 3

1.19.40.1 Core and Builtins
...........................

   - bpo-32176(1): co_flags.CO_NOFREE is now always set correctly by the
     code object constructor based on freevars and cellvars, rather than
     needing to be set correctly by the caller.  This ensures it will be
     cleared automatically when additional cell references are injected
     into a modified code object and function.

   - bpo-10544(2): Yield expressions are now deprecated in
     comprehensions and generator expressions.  They are still permitted
     in the definition of the outermost iterable, as that is evaluated
     directly in the enclosing scope.

   - bpo-32137(3): The repr of deeply nested dict now raises a
     RecursionError instead of crashing due to a stack overflow.

   - bpo-32096(4): Revert memory allocator changes in the C API: move
     structures back from _PyRuntime to Objects/obmalloc.c.  The memory
     allocators are once again initialized statically, and so
     PyMem_RawMalloc() and Py_DecodeLocale() can be called before
     _PyRuntime_Initialize().

   - bpo-32043(5): Add a new “developer mode”: new “-X dev” command line
     option to enable debug checks at runtime.

   - bpo-32023(6): SyntaxError is now correctly raised when a generator
     expression without parenthesis is used instead of an inheritance
     list in a class definition.  The duplication of the parentheses can
     be omitted only on calls.

   - bpo-32012(7): SyntaxError is now correctly raised when a generator
     expression without parenthesis is passed as an argument, but
     followed by a trailing comma.  A generator expression always needs
     to be directly inside a set of parentheses and cannot have a comma
     on either side.

   - bpo-28180(8): A new internal ‘_Py_SetLocaleFromEnv(category)’
     helper function has been added in order to improve the consistency
     of behaviour across different ‘libc’ implementations (e.g.  Android
     doesn’t support setting the locale from the environment by
     default).

   - bpo-31949(9): Fixed several issues in printing tracebacks
     (PyTraceBack_Print()).  Setting sys.tracebacklimit to 0 or less now
     suppresses printing tracebacks.  Setting sys.tracebacklimit to None
     now causes using the default limit.  Setting sys.tracebacklimit to
     an integer larger than LONG_MAX now means using the limit LONG_MAX
     rather than the default limit.  Fixed integer overflows in the case
     of more than ‘2**31’ traceback items on Windows.  Fixed output
     errors handling.

   - bpo-30696(10): Fix the interactive interpreter looping endlessly
     when no memory.

   - bpo-20047(11): Bytearray methods partition() and rpartition() now
     accept only bytes-like objects as separator, as documented.  In
     particular they now raise TypeError rather of returning a bogus
     result when an integer is passed as a separator.

   - bpo-21720(12): BytesWarning no longer emitted when the `fromlist'
     argument of ‘__import__()’ or the ‘__all__’ attribute of the module
     contain bytes instances.

   - bpo-31845(13): Environment variables are once more read correctly
     at interpreter startup.

   - bpo-28936(14): Ensure that lexically first syntax error involving a
     parameter and ‘global’ or ‘nonlocal’ is detected first at a given
     scope.  Patch by Ivan Levkivskyi.

   - bpo-31825(15): Fixed OverflowError in the ‘unicode-escape’ codec
     and in codecs.escape_decode() when decode an escaped non-ascii
     byte.

   - bpo-31618(16): The per-frame tracing logic added in 3.7a1 has been
     altered so that ‘frame->f_lineno’ is updated before either ‘"line"’
     or ‘"opcode"’ events are emitted.  Previously, opcode events were
     emitted first, and therefore would occasionally see stale line
     numbers on the frame.  The behavior of this feature has changed
     slightly as a result: when both ‘f_trace_lines’ and
     ‘f_trace_opcodes’ are enabled, line events now occur first.

   - bpo-28603(17): Print the full context/cause chain of exceptions on
     interpreter exit, even if an exception in the chain is unhashable
     or compares equal to later ones.  Patch by Zane Bitter.

   - bpo-31786(18): Fix timeout rounding in the select module to round
     correctly negative timeouts between -1.0 and 0.0.  The functions
     now block waiting for events as expected.  Previously, the call was
     incorrectly non-blocking.  Patch by Pablo Galindo.

   - bpo-31781(19): Prevent crashes when calling methods of an
     uninitialized ‘zipimport.zipimporter’ object.  Patch by Oren
     Milman.

   - bpo-30399(20): Standard repr() of BaseException with a single
     argument no longer contains redundant trailing comma.

   - bpo-31626(21): Fixed a bug in debug memory allocator.  There was a
     write to freed memory after shrinking a memory block.

   - bpo-30817(22): ‘PyErr_PrintEx()’ clears now the ignored exception
     that may be raised by ‘_PySys_SetObjectId()’, for example when no
     memory.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32176

   (2) https://bugs.python.org/issue10544

   (3) https://bugs.python.org/issue32137

   (4) https://bugs.python.org/issue32096

   (5) https://bugs.python.org/issue32043

   (6) https://bugs.python.org/issue32023

   (7) https://bugs.python.org/issue32012

   (8) https://bugs.python.org/issue28180

   (9) https://bugs.python.org/issue31949

   (10) https://bugs.python.org/issue30696

   (11) https://bugs.python.org/issue20047

   (12) https://bugs.python.org/issue21720

   (13) https://bugs.python.org/issue31845

   (14) https://bugs.python.org/issue28936

   (15) https://bugs.python.org/issue31825

   (16) https://bugs.python.org/issue31618

   (17) https://bugs.python.org/issue28603

   (18) https://bugs.python.org/issue31786

   (19) https://bugs.python.org/issue31781

   (20) https://bugs.python.org/issue30399

   (21) https://bugs.python.org/issue31626

   (22) https://bugs.python.org/issue30817


File: python.info,  Node: Library<39>,  Next: Documentation<33>,  Prev: Core and Builtins<36>,  Up: Python 3 7 0 alpha 3

1.19.40.2 Library
.................

   - bpo-28556(1): Two minor fixes for ‘typing’ module: allow shallow
     copying instances of generic classes, improve interaction of
     ‘__init_subclass__’ with generics.  Original PRs by Ivan
     Levkivskyi.

   - bpo-32214(2): PEP 557, Data Classes.  Provides a decorator which
     adds boilerplate methods to classes which use type annotations so
     specify fields.

   - bpo-27240(3): The header folding algorithm for the new email
     policies has been rewritten, which also fixes bpo-30788(4),
     bpo-31831(5), and bpo-32182(6).  In particular, RFC2231 folding is
     now done correctly.

   - bpo-32186(7): io.FileIO.readall() and io.FileIO.read() now release
     the GIL when getting the file size.  Fixed hang of all threads with
     inaccessible NFS server.  Patch by Nir Soffer.

   - bpo-321010(8): Add ‘sys.flags.dev_mode’ flag

   - bpo-32154(9): The ‘asyncio.windows_utils.socketpair()’ function has
     been removed: use directly *note socket.socketpair(): 57d. which is
     available on all platforms since Python 3.5 (before, it wasn’t
     available on Windows).  ‘asyncio.windows_utils.socketpair()’ was
     just an alias to ‘socket.socketpair’ on Python 3.5 and newer.

   - bpo-32089(10): warnings: In development (-X dev) and debug mode
     (pydebug build), use the “default” action for ResourceWarning,
     rather than the “always” action, in the default warnings filters.

   - bpo-32107(11): ‘uuid.getnode()’ now preferentially returns
     universally administered MAC addresses if available, over locally
     administered MAC addresses.  This makes a better guarantee for
     global uniqueness of UUIDs returned from ‘uuid.uuid1()’.  If only
     locally administered MAC addresses are available, the first such
     one found is returned.

   - bpo-23033(12): Wildcard is now supported in hostname when it is one
     and only character in the left most segment of hostname in second
     argument of *note ssl.match_hostname(): 4e3.  Patch by Mandeep
     Singh.

   - bpo-12239(13): Make *note msilib.SummaryInformation.GetProperty():
     10fe. return ‘None’ when the value of property is ‘VT_EMPTY’.
     Initial patch by Mark Mc Mahon.

   - bpo-28334(14): Use *note os.path.expanduser(): 32c. to find the
     ‘~/.netrc’ file in *note netrc.netrc: 11d5.  If it does not exist,
     *note FileNotFoundError: 8ad. is raised.  Patch by Dimitri
     Merejkowsky.

   - bpo-32121(15): Made ‘tracemalloc.Traceback’ behave more like the
     traceback module, sorting the frames from oldest to most recent.
     ‘Traceback.format()’ now accepts negative `limit', truncating the
     result to the ‘abs(limit)’ oldest frames.  To get the old
     behaviour, one can use the new `most_recent_first' argument to
     ‘Traceback.format()’.  (Patch by Jesse Bakker.)

   - bpo-31325(16): Fix wrong usage of *note collections.namedtuple():
     1a1. in the *note RobotFileParser.parse(): 11d6. method.  Initial
     patch by Robin Wellner.

   - bpo-12382(17): *note msilib.OpenDatabase(): 1020. now raises a
     better exception message when it couldn’t open or create an MSI
     file.  Initial patch by William Tisäter.

   - bpo-19610(18): ‘setup()’ now warns about invalid types for some
     fields.  The ‘distutils.dist.Distribution’ class now warns when
     ‘classifiers’, ‘keywords’ and ‘platforms’ fields are not specified
     as a list or a string.

   - bpo-32071(19): Added the ‘-k’ command-line option to ‘python -m
     unittest’ to run only tests that match the given pattern(s).

   - bpo-10049(20): Added `nullcontext' no-op context manager to
     contextlib.  This provides a simpler and faster alternative to
     ExitStack() when handling optional context managers.

   - bpo-28684(21): The new test.support.skip_unless_bind_unix_socket()
     decorator is used here to skip asyncio tests that fail because the
     platform lacks a functional bind() function for unix domain sockets
     (as it is the case for non root users on the recent Android
     versions that run now SELinux in enforcing mode).

   - bpo-32110(22): ‘codecs.StreamReader.read(n)’ now returns not more
     than `n' characters/bytes for non-negative `n'.  This makes it
     compatible with ‘read()’ methods of other file-like objects.

   - bpo-27535(23): The warnings module doesn’t leak memory anymore in
     the hidden warnings registry for the “ignore” action of warnings
     filters.  warn_explicit() function doesn’t add the warning key to
     the registry anymore for the “ignore” action.

   - bpo-32088(24): warnings: When Python is build is debug mode
     (‘Py_DEBUG’), *note DeprecationWarning: 15a, *note
     PendingDeprecationWarning: 15c. and *note ImportWarning: 6cf.
     warnings are now displayed by default.

   - bpo-1647489(25): Fixed searching regular expression patterns that
     could match an empty string.  Non-empty string can now be correctly
     found after matching an empty string.

   - bpo-25054(26): Added support of splitting on a pattern that could
     match an empty string.

   - bpo-32072(27): Fixed issues with binary plists: Fixed saving
     bytearrays.  Identical objects will be saved only once.  Equal
     references will be load as identical objects.  Added support for
     saving and loading recursive data structures.

   - bpo-32069(28): Drop legacy SSL transport from asyncio,
     ssl.MemoryBIO is always used anyway.

   - bpo-32066(29): asyncio: Support pathlib.Path in
     create_unix_connection; sock arg should be optional

   - bpo-32046(30): Updates 2to3 to convert from
     operator.isCallable(obj) to callable(obj).  Patch by Dong-hee Na.

   - bpo-32018(31): inspect.signature should follow PEP 8(32), if the
     parameter has an annotation and a default value.  Patch by Dong-hee
     Na.

   - bpo-32025(33): Add time.thread_time() and time.thread_time_ns()

   - bpo-32037(34): Integers that fit in a signed 32-bit integer will be
     now pickled with protocol 0 using the INT opcode.  This will
     decrease the size of a pickle, speed up pickling and unpickling,
     and make these integers be unpickled as int instances in Python 2.

   - bpo-32034(35): Make asyncio.IncompleteReadError and
     LimitOverrunError pickleable.

   - bpo-32015(36): Fixed the looping of asyncio in the case of
     reconnection the socket during waiting async read/write from/to the
     socket.

   - bpo-32011(37): Restored support of loading marshal files with the
     TYPE_INT64 code.  These files can be produced in Python 2.7.

   - bpo-28369(38): Enhance add_reader/writer check that socket is not
     used by some transport.  Before, only cases when add_reader/writer
     were called with an int FD were supported.  Now the check is
     implemented correctly for all file-like objects.

   - bpo-31976(39): Fix race condition when flushing a file is slow,
     which can cause a segfault if closing the file from another thread.

   - bpo-31985(40): Formally deprecated aifc.openfp, sunau.openfp, and
     wave.openfp.  Since change 7bc817d5ba917528e8bd07ec461c635291e7b06a
     in 1993, openfp in each of the three modules had been pointing to
     that module’s open function as a matter of backwards compatibility,
     though it had been both untested and undocumented.

   - bpo-21862(41): cProfile command line now accepts ‘-m module_name’
     as an alternative to script path.  Patch by Sanyam Khurana.

   - bpo-31970(42): Reduce performance overhead of asyncio debug mode.

   - bpo-31843(43): `database' argument of sqlite3.connect() now accepts
     a *note path-like object: 472, instead of just a string.

   - bpo-31945(44): Add Configurable `blocksize' to ‘HTTPConnection’ and
     ‘HTTPSConnection’ for improved upload throughput.  Patch by Nir
     Soffer.

   - bpo-31943(45): Add a ‘cancelled()’ method to *note asyncio.Handle:
     11d7.  Patch by Marat Sharafutdinov.

   - bpo-9678(46): Fixed determining the MAC address in the uuid module:
     Using ifconfig on NetBSD and OpenBSD. Using arp on Linux, FreeBSD,
     NetBSD and OpenBSD. Based on patch by Takayuki Shimizukawa.

   - bpo-30057(47): Fix potential missed signal in signal.signal().

   - bpo-31933(48): Fix Blake2 params leaf_size and node_offset on big
     endian platforms.  Patch by Jack O’Connor.

   - bpo-21423(49): Add an initializer argument to
     {Process,Thread}PoolExecutor

   - bpo-31927(50): Fixed compilation of the socket module on NetBSD 8.
     Fixed assertion failure or reading arbitrary data when parse a
     AF_BLUETOOTH address on NetBSD and DragonFly BSD.

   - bpo-27666(51): Fixed stack corruption in curses.box() and
     curses.ungetmouse() when the size of types chtype or mmask_t is
     less than the size of C long.  curses.box() now accepts characters
     as arguments.  Based on patch by Steve Fink.

   - bpo-31917(52): Add 3 new clock identifiers: *note
     time.CLOCK_BOOTTIME: 4fb, *note time.CLOCK_PROF: 4fd. and *note
     time.CLOCK_UPTIME: 4fe.

   - bpo-31897(53): plistlib now catches more errors when read binary
     plists and raises InvalidFileException instead of unexpected
     exceptions.

   - bpo-25720(54): Fix the method for checking pad state of curses
     WINDOW. Patch by Masayuki Yamamoto.

   - bpo-31893(55): Fixed the layout of the kqueue_event structure on
     OpenBSD and NetBSD. Fixed the comparison of the kqueue_event
     objects.

   - bpo-31891(56): Fixed building the curses module on NetBSD.

   - bpo-31884(57): added required constants to subprocess module for
     setting priority on windows

   - bpo-28281(58): Remove year (1-9999) limits on the
     Calendar.weekday() function.  Patch by Mark Gollahon.

   - bpo-31702(59): crypt.mksalt() now allows to specify the number of
     rounds for SHA-256 and SHA-512 hashing.

   - bpo-30639(60): *note inspect.getfile(): 11d8. no longer computes
     the repr of unknown objects to display in an error message, to
     protect against badly behaved custom reprs.

   - bpo-30768(61): Fix the pthread+semaphore implementation of
     PyThread_acquire_lock_timed() when called with timeout > 0 and
     intr_flag=0: recompute the timeout if sem_timedwait() is
     interrupted by a signal (EINTR). See also the PEP 475(62).

   - bpo-31854(63): Add ‘mmap.ACCESS_DEFAULT’ constant.

   - bpo-31834(64): Use optimized code for BLAKE2 only with SSSE3+.  The
     pure SSE2 implementation is slower than the pure C reference
     implementation.

   - bpo-28292(65): Calendar.itermonthdates() will now consistently
     raise an exception when a date falls outside of the 0001-01-01
     through 9999-12-31 range.  To support applications that cannot
     tolerate such exceptions, the new methods itermonthdays3() and
     itermonthdays4() are added.  The new methods return tuples and are
     not restricted by the range supported by datetime.date.

   - bpo-28564(66): The shutil.rmtree() function has been sped up to
     20–40%.  This was done using the os.scandir() function.

   - bpo-28416(67): Instances of pickle.Pickler subclass with the
     persistent_id() method and pickle.Unpickler subclass with the
     persistent_load() method no longer create reference cycles.

   - bpo-31653(68): Don’t release the GIL if we can acquire a
     multiprocessing semaphore immediately.

   - bpo-28326(69): Fix multiprocessing.Process when stdout and/or
     stderr is closed or None.

   - bpo-20825(70): Add ‘subnet_of’ and ‘superset_of’ containment tests
     to *note ipaddress.IPv6Network: 4a6. and *note
     ipaddress.IPv4Network: 4a7.  Patch by Michel Albert and Cheryl
     Sabella.

   - bpo-31827(71): Remove the os.stat_float_times() function.  It was
     introduced in Python 2.3 for backward compatibility with Python
     2.2, and was deprecated since Python 3.1.

   - bpo-31756(72): Add a ‘subprocess.Popen(text=False)’ keyword
     argument to *note subprocess: f9. functions to be more explicit
     about when the library should attempt to decode outputs into text.
     Patch by Andrew Clegg.

   - bpo-31819(73): Add AbstractEventLoop.sock_recv_into().

   - bpo-31457(74): If nested log adapters are used, the inner
     ‘process()’ methods are no longer omitted.

   - bpo-31457(75): The ‘manager’ property on LoggerAdapter objects is
     now properly settable.

   - bpo-31806(76): Fix timeout rounding in time.sleep(),
     threading.Lock.acquire() and socket.socket.settimeout() to round
     correctly negative timeouts between -1.0 and 0.0.  The functions
     now block waiting for events as expected.  Previously, the call was
     incorrectly non-blocking.  Patch by Pablo Galindo.

   - bpo-31803(77): time.clock() and time.get_clock_info(‘clock’) now
     emit a DeprecationWarning warning.

   - bpo-31800(78): Extended support for parsing UTC offsets.  strptime
     ‘%z’ can now parse the output generated by datetime.isoformat,
     including seconds and microseconds.

   - bpo-28603(79): traceback: Fix a TypeError that occurred during
     printing of exception tracebacks when either the current exception
     or an exception in its context/cause chain is unhashable.  Patch by
     Zane Bitter.

   - bpo-30541(80): Add new function to seal a mock and prevent the
     automatically creation of child mocks.  Patch by Mario Corchero.

   - bpo-31784(81): Implement the PEP 564(82), add new 6 new functions
     with nanosecond resolution to the *note time: 10c. module: *note
     clock_gettime_ns(): 42e, *note clock_settime_ns(): 42f, *note
     monotonic_ns(): 430, *note perf_counter_ns(): 431, *note
     process_time_ns(): 432, *note time_ns(): 433.

   - bpo-30143(83): 2to3 now generates a code that uses abstract
     collection classes from collections.abc rather than collections.

   - bpo-31770(84): Prevent a crash when calling the ‘__init__()’ method
     of a ‘sqlite3.Cursor’ object more than once.  Patch by Oren Milman.

   - bpo-31764(85): Prevent a crash in ‘sqlite3.Cursor.close()’ in case
     the ‘Cursor’ object is uninitialized.  Patch by Oren Milman.

   - bpo-31752(86): Fix possible crash in timedelta constructor called
     with custom integers.

   - bpo-31620(87): an empty asyncio.Queue now doesn’t leak memory when
     queue.get pollers timeout

   - bpo-31690(88): Allow the flags re.ASCII, re.LOCALE, and re.UNICODE
     to be used as group flags for regular expressions.

   - bpo-30349(89): FutureWarning is now emitted if a regular expression
     contains character set constructs that will change semantically in
     the future (nested sets and set operations).

   - bpo-31664(90): Added support for the Blowfish hashing in the crypt
     module.

   - bpo-31632(91): Fix method set_protocol() of class
     _SSLProtocolTransport in asyncio module.  This method was
     previously modifying a wrong reference to the protocol.

   - bpo-15037(92): Added a workaround for getkey() in curses for
     ncurses 5.7 and earlier.

   - bpo-31307(93): Allow use of bytes objects for arguments to *note
     configparser.ConfigParser.read(): 11d9.  Patch by Vincent Michel.

   - bpo-31334(94): Fix ‘poll.poll([timeout])’ in the ‘select’ module
     for arbitrary negative timeouts on all OSes where it can only be a
     non-negative integer or -1.  Patch by Riccardo Coccioli.

   - bpo-31310(95): multiprocessing’s semaphore tracker should be
     launched again if crashed.

   - bpo-31308(96): Make multiprocessing’s forkserver process immune to
     Ctrl-C and other user interruptions.  If it crashes, restart it
     when necessary.

   - bpo-31245(97): Added support for AF_UNIX socket in asyncio
     ‘create_datagram_endpoint’.

   - bpo-30553(98): Add HTTP/2 status code 421 (Misdirected Request) to
     *note http.HTTPStatus: 1ac.  Patch by Vitor Pereira.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28556

   (2) https://bugs.python.org/issue32214

   (3) https://bugs.python.org/issue27240

   (4) https://bugs.python.org/issue30788

   (5) https://bugs.python.org/issue31831

   (6) https://bugs.python.org/issue32182

   (7) https://bugs.python.org/issue32186

   (8) https://bugs.python.org/issue321010

   (9) https://bugs.python.org/issue32154

   (10) https://bugs.python.org/issue32089

   (11) https://bugs.python.org/issue32107

   (12) https://bugs.python.org/issue23033

   (13) https://bugs.python.org/issue12239

   (14) https://bugs.python.org/issue28334

   (15) https://bugs.python.org/issue32121

   (16) https://bugs.python.org/issue31325

   (17) https://bugs.python.org/issue12382

   (18) https://bugs.python.org/issue19610

   (19) https://bugs.python.org/issue32071

   (20) https://bugs.python.org/issue10049

   (21) https://bugs.python.org/issue28684

   (22) https://bugs.python.org/issue32110

   (23) https://bugs.python.org/issue27535

   (24) https://bugs.python.org/issue32088

   (25) https://bugs.python.org/issue1647489

   (26) https://bugs.python.org/issue25054

   (27) https://bugs.python.org/issue32072

   (28) https://bugs.python.org/issue32069

   (29) https://bugs.python.org/issue32066

   (30) https://bugs.python.org/issue32046

   (31) https://bugs.python.org/issue32018

   (32) https://www.python.org/dev/peps/pep-0008

   (33) https://bugs.python.org/issue32025

   (34) https://bugs.python.org/issue32037

   (35) https://bugs.python.org/issue32034

   (36) https://bugs.python.org/issue32015

   (37) https://bugs.python.org/issue32011

   (38) https://bugs.python.org/issue28369

   (39) https://bugs.python.org/issue31976

   (40) https://bugs.python.org/issue31985

   (41) https://bugs.python.org/issue21862

   (42) https://bugs.python.org/issue31970

   (43) https://bugs.python.org/issue31843

   (44) https://bugs.python.org/issue31945

   (45) https://bugs.python.org/issue31943

   (46) https://bugs.python.org/issue9678

   (47) https://bugs.python.org/issue30057

   (48) https://bugs.python.org/issue31933

   (49) https://bugs.python.org/issue21423

   (50) https://bugs.python.org/issue31927

   (51) https://bugs.python.org/issue27666

   (52) https://bugs.python.org/issue31917

   (53) https://bugs.python.org/issue31897

   (54) https://bugs.python.org/issue25720

   (55) https://bugs.python.org/issue31893

   (56) https://bugs.python.org/issue31891

   (57) https://bugs.python.org/issue31884

   (58) https://bugs.python.org/issue28281

   (59) https://bugs.python.org/issue31702

   (60) https://bugs.python.org/issue30639

   (61) https://bugs.python.org/issue30768

   (62) https://www.python.org/dev/peps/pep-0475

   (63) https://bugs.python.org/issue31854

   (64) https://bugs.python.org/issue31834

   (65) https://bugs.python.org/issue28292

   (66) https://bugs.python.org/issue28564

   (67) https://bugs.python.org/issue28416

   (68) https://bugs.python.org/issue31653

   (69) https://bugs.python.org/issue28326

   (70) https://bugs.python.org/issue20825

   (71) https://bugs.python.org/issue31827

   (72) https://bugs.python.org/issue31756

   (73) https://bugs.python.org/issue31819

   (74) https://bugs.python.org/issue31457

   (75) https://bugs.python.org/issue31457

   (76) https://bugs.python.org/issue31806

   (77) https://bugs.python.org/issue31803

   (78) https://bugs.python.org/issue31800

   (79) https://bugs.python.org/issue28603

   (80) https://bugs.python.org/issue30541

   (81) https://bugs.python.org/issue31784

   (82) https://www.python.org/dev/peps/pep-0564

   (83) https://bugs.python.org/issue30143

   (84) https://bugs.python.org/issue31770

   (85) https://bugs.python.org/issue31764

   (86) https://bugs.python.org/issue31752

   (87) https://bugs.python.org/issue31620

   (88) https://bugs.python.org/issue31690

   (89) https://bugs.python.org/issue30349

   (90) https://bugs.python.org/issue31664

   (91) https://bugs.python.org/issue31632

   (92) https://bugs.python.org/issue15037

   (93) https://bugs.python.org/issue31307

   (94) https://bugs.python.org/issue31334

   (95) https://bugs.python.org/issue31310

   (96) https://bugs.python.org/issue31308

   (97) https://bugs.python.org/issue31245

   (98) https://bugs.python.org/issue30553


File: python.info,  Node: Documentation<33>,  Next: Tests<31>,  Prev: Library<39>,  Up: Python 3 7 0 alpha 3

1.19.40.3 Documentation
.......................

   - bpo-32105(1): Added asyncio.BaseEventLoop.connect_accepted_socket
     versionadded marker.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32105


File: python.info,  Node: Tests<31>,  Next: Build<30>,  Prev: Documentation<33>,  Up: Python 3 7 0 alpha 3

1.19.40.4 Tests
...............

   - bpo-31380(1): Skip test_httpservers test_undecodable_file on macOS:
     fails on APFS.

   - bpo-31705(2): Skip test_socket.test_sha256() on Linux kernel older
     than 4.5.  The test fails with ENOKEY on kernel 3.10 (on ppc64le).
     A fix was merged into the kernel 4.5.

   - bpo-32138(3): Skip on Android test_faulthandler tests that raise
     SIGSEGV and remove the test.support.requires_android_level
     decorator.

   - bpo-32136(4): The runtime embedding tests have been split out from
     ‘Lib/test/test_capi.py’ into a new ‘Lib/test/test_embed.py’ file.

   - bpo-28668(5): test.support.requires_multiprocessing_queue is
     removed.  Skip tests with
     test.support.import_module(‘multiprocessing.synchronize’) instead
     when the semaphore implementation is broken or missing.

   - bpo-32126(6): Skip test_get_event_loop_new_process in
     test.test_asyncio.test_events when sem_open() is not functional.

   - bpo-31174(7): Fix test_tools.test_unparse: DirectoryTestCase now
     stores the names sample to always test the same files.  It prevents
     false alarms when hunting reference leaks.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31380

   (2) https://bugs.python.org/issue31705

   (3) https://bugs.python.org/issue32138

   (4) https://bugs.python.org/issue32136

   (5) https://bugs.python.org/issue28668

   (6) https://bugs.python.org/issue32126

   (7) https://bugs.python.org/issue31174


File: python.info,  Node: Build<30>,  Next: Windows<31>,  Prev: Tests<31>,  Up: Python 3 7 0 alpha 3

1.19.40.5 Build
...............

   - bpo-28538(1): Revert the previous changes, the if_nameindex
     structure is defined by Unified Headers.

   - bpo-28762(2): Revert the last commit, the F_LOCK macro is defined
     by Android Unified Headers.

   - bpo-29040(3): Support building Android with Unified Headers.  The
     first NDK release to support Unified Headers is android-ndk-r14.

   - bpo-32059(4): ‘detect_modules()’ in ‘setup.py’ now also searches
     the sysroot paths when cross-compiling.

   - bpo-31957(5): Fixes Windows SDK version detection when building for
     Windows.

   - bpo-31609(6): Fixes quotes in PCbuild/clean.bat

   - bpo-31934(7): Abort the build when building out of a not clean
     source tree.

   - bpo-31926(8): Fixed Argument Clinic sometimes causing compilation
     errors when there was more than one function and/or method in a .c
     file with the same name.

   - bpo-28791(9): Update Windows builds to use SQLite 3.21.0.

   - bpo-28791(10): Update OS X installer to use SQLite 3.21.0.

   - bpo-28643(11): Record profile-opt build progress with stamp files.

   - bpo-31866(12): Finish removing support for AtheOS.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28538

   (2) https://bugs.python.org/issue28762

   (3) https://bugs.python.org/issue29040

   (4) https://bugs.python.org/issue32059

   (5) https://bugs.python.org/issue31957

   (6) https://bugs.python.org/issue31609

   (7) https://bugs.python.org/issue31934

   (8) https://bugs.python.org/issue31926

   (9) https://bugs.python.org/issue28791

   (10) https://bugs.python.org/issue28791

   (11) https://bugs.python.org/issue28643

   (12) https://bugs.python.org/issue31866


File: python.info,  Node: Windows<31>,  Next: macOS<26>,  Prev: Build<30>,  Up: Python 3 7 0 alpha 3

1.19.40.6 Windows
.................

   - bpo-1102(1): Return ‘None’ when ‘View.Fetch()’ returns
     ‘ERROR_NO_MORE_ITEMS’ instead of raising ‘MSIError’.  Initial patch
     by Anthony Tuininga.

   - bpo-31944(2): Fixes Modify button in Apps and Features dialog.

   - bpo-20486(3): Implement the ‘Database.Close()’ method to help
     closing MSI database objects.

   - bpo-31857(4): Make the behavior of USE_STACKCHECK deterministic in
     a multi-threaded environment.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1102

   (2) https://bugs.python.org/issue31944

   (3) https://bugs.python.org/issue20486

   (4) https://bugs.python.org/issue31857


File: python.info,  Node: macOS<26>,  Next: IDLE<30>,  Prev: Windows<31>,  Up: Python 3 7 0 alpha 3

1.19.40.7 macOS
...............

   - bpo-31392(1): Update macOS installer to use OpenSSL 1.0.2m

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31392


File: python.info,  Node: IDLE<30>,  Next: Tools/Demos<16>,  Prev: macOS<26>,  Up: Python 3 7 0 alpha 3

1.19.40.8 IDLE
..............

   - bpo-32207(1): Improve tk event exception tracebacks in IDLE. When
     tk event handling is driven by IDLE’s run loop, a confusing and
     distracting queue.EMPTY traceback context is no longer added to tk
     event exception tracebacks.  The traceback is now the same as when
     event handling is driven by user code.  Patch based on a suggestion
     by Serhiy Storchaka.

   - bpo-32164(2): Delete unused file idlelib/tabbedpages.py.  Use of
     TabbedPageSet in configdialog was replaced by ttk.Notebook.

   - bpo-32100(3): IDLE: Fix old and new bugs in pathbrowser; improve
     tests.  Patch mostly by Cheryl Sabella.

   - bpo-31858(4): IDLE – Restrict shell prompt manipulation to the
     shell.  Editor and output windows only see an empty last prompt
     line.  This simplifies the code and fixes a minor bug when newline
     is inserted.  Sys.ps1, if present, is read on Shell start-up, but
     is not set or changed.

   - bpo-31860(5): The font sample in the IDLE configuration dialog is
     now editable.  Changes persist while IDLE remains open

   - bpo-31836(6): Test_code_module now passes if run after test_idle,
     which sets ps1.  The code module uses sys.ps1 if present or sets it
     to ‘>>> ‘ if not.  Test_code_module now properly tests both
     behaviors.  Ditto for ps2.

   - bpo-28603(7): Fix a TypeError that caused a shell restart when
     printing a traceback that includes an exception that is unhashable.
     Patch by Zane Bitter.

   - bpo-13802(8): Use non-Latin characters in the IDLE’s Font settings
     sample.  Even if one selects a font that defines a limited subset
     of the unicode Basic Multilingual Plane, tcl/tk will use other
     fonts that define a character.  The expanded example give users of
     non-Latin characters a better idea of what they might see in IDLE’s
     shell and editors.  To make room for the expanded sample, frames on
     the Font tab are re-arranged.  The Font/Tabs help explains a bit
     about the additions.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32207

   (2) https://bugs.python.org/issue32164

   (3) https://bugs.python.org/issue32100

   (4) https://bugs.python.org/issue31858

   (5) https://bugs.python.org/issue31860

   (6) https://bugs.python.org/issue31836

   (7) https://bugs.python.org/issue28603

   (8) https://bugs.python.org/issue13802


File: python.info,  Node: Tools/Demos<16>,  Next: C API<25>,  Prev: IDLE<30>,  Up: Python 3 7 0 alpha 3

1.19.40.9 Tools/Demos
.....................

   - bpo-32159(1): Remove CVS and Subversion tools: remove svneol.py and
     treesync.py scripts.  CPython migrated from CVS to Subversion, to
     Mercurial, and then to Git.  CVS and Subversion are no longer used
     to develop CPython.

   - bpo-30722(2): Make redemo work with Python 3.6 and newer versions.
     Also, remove the ‘LOCALE’ option since it doesn’t work with string
     patterns in Python 3.  Patch by Christoph Sarnowski.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32159

   (2) https://bugs.python.org/issue30722


File: python.info,  Node: C API<25>,  Prev: Tools/Demos<16>,  Up: Python 3 7 0 alpha 3

1.19.40.10 C API
................

   - bpo-20891(1): Fix PyGILState_Ensure().  When PyGILState_Ensure() is
     called in a non-Python thread before PyEval_InitThreads(), only
     call PyEval_InitThreads() after calling PyThreadState_New() to fix
     a crash.

   - bpo-32125(2): The ‘Py_UseClassExceptionsFlag’ flag has been
     removed.  It was deprecated and wasn’t used anymore since Python
     2.0.

   - bpo-25612(3): Move the current exception state from the frame
     object to the co-routine.  This simplifies the interpreter and
     fixes a couple of obscure bugs caused by having swap exception
     state when entering or exiting a generator.

   - bpo-23699(4): Add Py_RETURN_RICHCOMPARE macro to reduce boilerplate
     code in rich comparison functions.

   - bpo-30697(5): The ‘PyExc_RecursionErrorInst’ singleton is removed
     and ‘PyErr_NormalizeException()’ does not use it anymore.  This
     singleton is persistent and its members being never cleared may
     cause a segfault during finalization of the interpreter.  See also
     bpo-22898(6).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20891

   (2) https://bugs.python.org/issue32125

   (3) https://bugs.python.org/issue25612

   (4) https://bugs.python.org/issue23699

   (5) https://bugs.python.org/issue30697

   (6) https://bugs.python.org/issue22898


File: python.info,  Node: Python 3 7 0 alpha 2,  Next: Python 3 7 0 alpha 1,  Prev: Python 3 7 0 alpha 3,  Up: Changelog

1.19.41 Python 3.7.0 alpha 2
----------------------------

`Release date: 2017-10-16'

* Menu:

* Core and Builtins: Core and Builtins<37>.
* Library: Library<40>.
* Documentation: Documentation<34>.
* Build: Build<31>.
* IDLE: IDLE<31>.
* C API: C API<26>.


File: python.info,  Node: Core and Builtins<37>,  Next: Library<40>,  Up: Python 3 7 0 alpha 2

1.19.41.1 Core and Builtins
...........................

   - bpo-31558(1): ‘gc.freeze()’ is a new API that allows for moving all
     objects currently tracked by the garbage collector to a permanent
     generation, effectively removing them from future collection
     events.  This can be used to protect those objects from having
     their PyGC_Head mutated.  In effect, this enables great
     copy-on-write stability at fork().

   - bpo-31642(2): Restored blocking “from package import module” by
     setting sys.modules[“package.module”] to None.

   - bpo-31708(3): Allow use of asynchronous generator expressions in
     synchronous functions.

   - bpo-31709(4): Drop support of asynchronous __aiter__.

   - bpo-30404(5): The -u option now makes the stdout and stderr streams
     unbuffered rather than line-buffered.

   - bpo-31619(6): Fixed a ValueError when convert a string with large
     number of underscores to integer with binary base.

   - bpo-31602(7): Fix an assertion failure in
     ‘zipimporter.get_source()’ in case of a bad *note
     zlib.decompress(): 6b6.  Patch by Oren Milman.

   - bpo-31592(8): Fixed an assertion failure in Python parser in case
     of a bad *note unicodedata.normalize(): 11e4.  Patch by Oren
     Milman.

   - bpo-31588(9): Raise a *note TypeError: 1fe. with a helpful error
     message when class creation fails due to a metaclass with a bad
     ‘__prepare__()’ method.  Patch by Oren Milman.

   - bpo-31574(10): Importlib was instrumented with two dtrace probes to
     profile import timing.

   - bpo-31566(11): Fix an assertion failure in ‘_warnings.warn()’ in
     case of a bad ‘__name__’ global.  Patch by Oren Milman.

   - bpo-31506(12): Improved the error message logic for object.__new__
     and object.__init__.

   - bpo-31505(13): Fix an assertion failure in *note json: a4, in case
     ‘_json.make_encoder()’ received a bad ‘encoder()’ argument.  Patch
     by Oren Milman.

   - bpo-31492(14): Fix assertion failures in case of failing to import
     from a module with a bad ‘__name__’ attribute, and in case of
     failing to access an attribute of such a module.  Patch by Oren
     Milman.

   - bpo-31478(15): Fix an assertion failure in ‘_random.Random.seed()’
     in case the argument has a bad ‘__abs__()’ method.  Patch by Oren
     Milman.

   - bpo-31336(16): Speed up class creation by 10-20% by reducing the
     overhead in the necessary special method lookups.  Patch by Stefan
     Behnel.

   - bpo-31415(17): Add ‘-X importtime’ option to show how long each
     import takes.  It can be used to optimize application’s startup
     time.  Support the *note PYTHONPROFILEIMPORTTIME: 444. as an
     equivalent way to enable this.

   - bpo-31410(18): Optimized calling wrapper and classmethod
     descriptors.

   - bpo-31353(19): PEP 553(20) - Add a new built-in called
     ‘breakpoint()’ which calls ‘sys.breakpointhook()’.  By default this
     imports ‘pdb’ and calls ‘pdb.set_trace()’, but users may override
     ‘sys.breakpointhook()’ to call whatever debugger they want.  The
     original value of the hook is saved in ‘sys.__breakpointhook__’.

   - bpo-17852(21): Maintain a list of open buffered files, flush them
     before exiting the interpreter.  Based on a patch from Armin Rigo.

   - bpo-31315(22): Fix an assertion failure in imp.create_dynamic(),
     when spec.name is not a string.  Patch by Oren Milman.

   - bpo-31311(23): Fix a crash in the ‘__setstate__()’ method of *note
     ctypes._CData: 11e5, in case of a bad ‘__dict__’.  Patch by Oren
     Milman.

   - bpo-31293(24): Fix crashes in true division and multiplication of a
     timedelta object by a float with a bad as_integer_ratio() method.
     Patch by Oren Milman.

   - bpo-31285(25): Fix an assertion failure in *note
     warnings.warn_explicit: 6a7, when the return value of the received
     loader’s get_source() has a bad splitlines() method.  Patch by Oren
     Milman.

   - bpo-30406(26): Make ‘async’ and ‘await’ proper keywords, as
     specified in PEP 492(27).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31558

   (2) https://bugs.python.org/issue31642

   (3) https://bugs.python.org/issue31708

   (4) https://bugs.python.org/issue31709

   (5) https://bugs.python.org/issue30404

   (6) https://bugs.python.org/issue31619

   (7) https://bugs.python.org/issue31602

   (8) https://bugs.python.org/issue31592

   (9) https://bugs.python.org/issue31588

   (10) https://bugs.python.org/issue31574

   (11) https://bugs.python.org/issue31566

   (12) https://bugs.python.org/issue31506

   (13) https://bugs.python.org/issue31505

   (14) https://bugs.python.org/issue31492

   (15) https://bugs.python.org/issue31478

   (16) https://bugs.python.org/issue31336

   (17) https://bugs.python.org/issue31415

   (18) https://bugs.python.org/issue31410

   (19) https://bugs.python.org/issue31353

   (20) https://www.python.org/dev/peps/pep-0553

   (21) https://bugs.python.org/issue17852

   (22) https://bugs.python.org/issue31315

   (23) https://bugs.python.org/issue31311

   (24) https://bugs.python.org/issue31293

   (25) https://bugs.python.org/issue31285

   (26) https://bugs.python.org/issue30406

   (27) https://www.python.org/dev/peps/pep-0492


File: python.info,  Node: Library<40>,  Next: Documentation<34>,  Prev: Core and Builtins<37>,  Up: Python 3 7 0 alpha 2

1.19.41.2 Library
.................

   - bpo-30058(1): Fixed buffer overflow in select.kqueue.control().

   - bpo-31672(2): ‘idpattern’ in ‘string.Template’ matched some
     non-ASCII characters.  Now it uses ‘-i’ regular expression local
     flag to avoid non-ASCII characters.

   - bpo-31701(3): On Windows, faulthandler.enable() now ignores MSC and
     COM exceptions.

   - bpo-31728(4): Prevent crashes in ‘_elementtree’ due to unsafe
     cleanup of ‘Element.text’ and ‘Element.tail’.  Patch by Oren
     Milman.

   - bpo-31671(5): Now ‘re.compile()’ converts passed RegexFlag to
     normal int object before compiling.  bm_regex_compile benchmark
     shows 14% performance improvements.

   - bpo-30397(6): The types of compiled regular objects and match
     objects are now exposed as ‘re.Pattern’ and ‘re.Match’.  This adds
     information in pydoc output for the re module.

   - bpo-31675(7): Fixed memory leaks in Tkinter’s methods splitlist()
     and split() when pass a string larger than 2 GiB.

   - bpo-31673(8): Fixed typo in the name of Tkinter’s method
     adderrorinfo().

   - bpo-31648(9): Improvements to path predicates in ElementTree: Allow
     whitespace around predicate parts, i.e.  “[a = ‘text’]” instead of
     requiring the less readable “[a=’text’]”.  Add support for text
     comparison of the current node, like “[.=’text’]”.  Patch by Stefan
     Behnel.

   - bpo-30806(10): Fix the string representation of a netrc object.

   - bpo-31638(11): Add optional argument ‘compressed’ to
     ‘zipapp.create_archive’, and add option ‘--compress’ to the command
     line interface of ‘zipapp’.

   - bpo-25351(12): Avoid venv activate failures with undefined
     variables

   - bpo-20519(13): Avoid ctypes use (if possible) and improve import
     time for uuid.

   - bpo-28293(14): The regular expression cache is no longer completely
     dumped when it is full.

   - bpo-31596(15): Added pthread_getcpuclockid() to the time module

   - bpo-27494(16): Make 2to3 accept a trailing comma in generator
     expressions.  For example, ‘set(x for x in [],)’ is now allowed.

   - bpo-30347(17): Stop crashes when concurrently iterate over
     itertools.groupby() iterators.

   - bpo-30346(18): An iterator produced by itertools.groupby() iterator
     now becomes exhausted after advancing the groupby iterator.

   - bpo-31556(19): Cancel asyncio.wait_for future faster if timeout <=
     0

   - bpo-31540(20): Allow passing a context object in *note
     concurrent.futures.ProcessPoolExecutor: 196. constructor.  Also,
     free job resources in *note concurrent.futures.ProcessPoolExecutor:
     196. earlier to improve memory usage when a worker waits for new
     jobs.

   - bpo-31516(21): ‘threading.current_thread()’ should not return a
     dummy thread at shutdown.

   - bpo-31525(22): In the sqlite module, require the sqlite3_prepare_v2
     API. Thus, the sqlite module now requires sqlite version at least
     3.3.9.

   - bpo-26510(23): argparse subparsers are now required by default.
     This matches behaviour in Python 2.  For optional subparsers, use
     the new parameter ‘add_subparsers(required=False)’.  Patch by
     Anthony Sottile.  (As of 3.7.0rc1, the default was changed to not
     required as had been the case since Python 3.3.)

   - bpo-27541(24): Reprs of subclasses of some collection and iterator
     classes (*note bytearray: 173, *note array.array: 216, *note
     collections.deque: 62b, *note collections.defaultdict: c0c, *note
     itertools.count: ce5, *note itertools.repeat: 11e7.) now contain
     actual type name insteads of hardcoded name of the base class.

   - bpo-31351(25): python -m ensurepip now exits with non-zero exit
     code if pip bootstrapping has failed.

   - bpo-31389(26): ‘pdb.set_trace()’ now takes an optional keyword-only
     argument ‘header’.  If given, this is printed to the console just
     before debugging begins.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30058

   (2) https://bugs.python.org/issue31672

   (3) https://bugs.python.org/issue31701

   (4) https://bugs.python.org/issue31728

   (5) https://bugs.python.org/issue31671

   (6) https://bugs.python.org/issue30397

   (7) https://bugs.python.org/issue31675

   (8) https://bugs.python.org/issue31673

   (9) https://bugs.python.org/issue31648

   (10) https://bugs.python.org/issue30806

   (11) https://bugs.python.org/issue31638

   (12) https://bugs.python.org/issue25351

   (13) https://bugs.python.org/issue20519

   (14) https://bugs.python.org/issue28293

   (15) https://bugs.python.org/issue31596

   (16) https://bugs.python.org/issue27494

   (17) https://bugs.python.org/issue30347

   (18) https://bugs.python.org/issue30346

   (19) https://bugs.python.org/issue31556

   (20) https://bugs.python.org/issue31540

   (21) https://bugs.python.org/issue31516

   (22) https://bugs.python.org/issue31525

   (23) https://bugs.python.org/issue26510

   (24) https://bugs.python.org/issue27541

   (25) https://bugs.python.org/issue31351

   (26) https://bugs.python.org/issue31389


File: python.info,  Node: Documentation<34>,  Next: Build<31>,  Prev: Library<40>,  Up: Python 3 7 0 alpha 2

1.19.41.3 Documentation
.......................

   - bpo-31537(1): Fix incorrect usage of ‘get_history_length’ in
     readline documentation example code.  Patch by Brad Smith.

   - bpo-30085(2): The operator functions without double underscores are
     preferred for clarity.  The one with underscores are only kept for
     back-compatibility.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31537

   (2) https://bugs.python.org/issue30085


File: python.info,  Node: Build<31>,  Next: IDLE<31>,  Prev: Documentation<34>,  Up: Python 3 7 0 alpha 2

1.19.41.4 Build
...............

   - bpo-31696(1): Improve compiler version information in *note
     sys.version: 6ca. when Python is built with Clang.

   - bpo-31625(2): Stop using ranlib on static libraries.  Instead, we
     assume ar supports the ‘s’ flag.

   - bpo-31624(3): Remove support for BSD/OS.

   - bpo-22140(4): Prevent double substitution of prefix in
     python-config.sh.

   - bpo-31569(5): Correct PCBuild/ case to PCbuild/ in build scripts
     and documentation.

   - bpo-31536(6): Avoid wholesale rebuild after ‘make regen-all’ if
     nothing changed.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31696

   (2) https://bugs.python.org/issue31625

   (3) https://bugs.python.org/issue31624

   (4) https://bugs.python.org/issue22140

   (5) https://bugs.python.org/issue31569

   (6) https://bugs.python.org/issue31536


File: python.info,  Node: IDLE<31>,  Next: C API<26>,  Prev: Build<31>,  Up: Python 3 7 0 alpha 2

1.19.41.5 IDLE
..............

   - bpo-31460(1): Simplify the API of IDLE’s Module Browser.  Passing a
     widget instead of an flist with a root widget opens the option of
     creating a browser frame that is only part of a window.  Passing a
     full file name instead of pieces assumed to come from a .py file
     opens the possibility of browsing python files that do not end in
     .py.

   - bpo-31649(2): IDLE - Make _htest, _utest parameters keyword only.

   - bpo-31559(3): Remove test order dependence in
     idle_test.test_browser.

   - bpo-31459(4): Rename IDLE’s module browser from Class Browser to
     Module Browser.  The original module-level class and method browser
     became a module browser, with the addition of module-level
     functions, years ago.  Nested classes and functions were added
     yesterday.  For back-compatibility, the virtual event
     <<open-class-browser>>, which appears on the Keys tab of the
     Settings dialog, is not changed.  Patch by Cheryl Sabella.

   - bpo-31500(5): Default fonts now are scaled on HiDPI displays.

   - bpo-1612262(6): IDLE module browser now shows nested classes and
     functions.  Original patches for code and tests by Guilherme Polo
     and Cheryl Sabella, respectively.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31460

   (2) https://bugs.python.org/issue31649

   (3) https://bugs.python.org/issue31559

   (4) https://bugs.python.org/issue31459

   (5) https://bugs.python.org/issue31500

   (6) https://bugs.python.org/issue1612262


File: python.info,  Node: C API<26>,  Prev: IDLE<31>,  Up: Python 3 7 0 alpha 2

1.19.41.6 C API
...............

   - bpo-28280(1): Make ‘PyMapping_Keys()’, ‘PyMapping_Values()’ and
     ‘PyMapping_Items()’ always return a *note list: 1f8. (rather than a
     *note list: 1f8. or a *note tuple: 1a2.).  Patch by Oren Milman.

   - bpo-31532(2): Fix memory corruption due to allocator mix in
     getpath.c between Py_GetPath() and Py_SetPath()

   - bpo-25658(3): Implement PEP 539(4) for Thread Specific Storage
     (TSS) API: it is a new Thread Local Storage (TLS) API to CPython
     which would supersede use of the existing TLS API within the
     CPython interpreter, while deprecating the existing API. PEP
     written by Erik M. Bray, patch by Masayuki Yamamoto.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28280

   (2) https://bugs.python.org/issue31532

   (3) https://bugs.python.org/issue25658

   (4) https://www.python.org/dev/peps/pep-0539


File: python.info,  Node: Python 3 7 0 alpha 1,  Next: Python 3 6 6 final,  Prev: Python 3 7 0 alpha 2,  Up: Changelog

1.19.42 Python 3.7.0 alpha 1
----------------------------

`Release date: 2017-09-19'

* Menu:

* Security: Security<21>.
* Core and Builtins: Core and Builtins<38>.
* Library: Library<41>.
* Documentation: Documentation<35>.
* Tests: Tests<32>.
* Build: Build<32>.
* Windows: Windows<32>.
* IDLE: IDLE<32>.
* Tools/Demos: Tools/Demos<17>.
* C API: C API<27>.


File: python.info,  Node: Security<21>,  Next: Core and Builtins<38>,  Up: Python 3 7 0 alpha 1

1.19.42.1 Security
..................

   - bpo-29781(1): SSLObject.version() now correctly returns None when
     handshake over BIO has not been performed yet.

   - bpo-29505(2): Add fuzz tests for float(str), int(str),
     unicode(str); for oss-fuzz.

   - bpo-30947(3): Upgrade libexpat embedded copy from version 2.2.1 to
     2.2.3 to get security fixes.

   - bpo-30730(4): Prevent environment variables injection in subprocess
     on Windows.  Prevent passing other environment variables and
     command arguments.

   - bpo-30694(5): Upgrade expat copy from 2.2.0 to 2.2.1 to get fixes
     of multiple security vulnerabilities including: CVE-2017-9233
     (External entity infinite loop DoS), CVE-2016-9063 (Integer
     overflow, re-fix), CVE-2016-0718 (Fix regression bugs from 2.2.0’s
     fix to CVE-2016-0718) and CVE-2012-0876 (Counter hash flooding with
     SipHash).  Note: the CVE-2016-5300 (Use os-specific entropy sources
     like getrandom) doesn’t impact Python, since Python already gets
     entropy from the OS to set the expat secret using
     ‘XML_SetHashSalt()’.

   - bpo-30500(6): Fix urllib.parse.splithost() to correctly parse
     fragments.  For example, ‘splithost('//127.0.0.1#@evil.com/')’ now
     correctly returns the ‘127.0.0.1’ host, instead of treating
     ‘@evil.com’ as the host in an authentication (‘login@host’).

   - bpo-29591(7): Update expat copy from 2.1.1 to 2.2.0 to get fixes of
     CVE-2016-0718 and CVE-2016-4472.  See
     ‘https://sourceforge.net/p/expat/bugs/537/’ for more information.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29781

   (2) https://bugs.python.org/issue29505

   (3) https://bugs.python.org/issue30947

   (4) https://bugs.python.org/issue30730

   (5) https://bugs.python.org/issue30694

   (6) https://bugs.python.org/issue30500

   (7) https://bugs.python.org/issue29591


File: python.info,  Node: Core and Builtins<38>,  Next: Library<41>,  Prev: Security<21>,  Up: Python 3 7 0 alpha 1

1.19.42.2 Core and Builtins
...........................

   - bpo-31490(1): Fix an assertion failure in *note ctypes: 2a. class
     definition, in case the class has an attribute whose name is
     specified in ‘_anonymous_’ but not in ‘_fields_’.  Patch by Oren
     Milman.

   - bpo-31471(2): Fix an assertion failure in *note subprocess.Popen():
     3db. on Windows, in case the env argument has a bad keys() method.
     Patch by Oren Milman.

   - bpo-31418(3): Fix an assertion failure in ‘PyErr_WriteUnraisable()’
     in case of an exception with a bad ‘__module__’ attribute.  Patch
     by Oren Milman.

   - bpo-31416(4): Fix assertion failures in case of a bad
     warnings.filters or warnings.defaultaction.  Patch by Oren Milman.

   - bpo-28411(5): Change direct usage of PyInterpreterState.modules to
     PyImport_GetModuleDict().  Also introduce more uniformity in other
     code that deals with sys.modules.  This helps reduce complications
     when working on sys.modules.

   - bpo-28411(6): Switch to the abstract API when dealing with
     ‘PyInterpreterState.modules’.  This allows later support for all
     dict subclasses and other Mapping implementations.  Also add a
     ‘PyImport_GetModule()’ function to reduce a bunch of duplicated
     code.

   - bpo-31411(7): Raise a TypeError instead of SystemError in case
     warnings.onceregistry is not a dictionary.  Patch by Oren Milman.

   - bpo-31344(8): For finer control of tracing behaviour when testing
     the interpreter, two new frame attributes have been added to
     control the emission of particular trace events: ‘f_trace_lines’
     (‘True’ by default) to turn off per-line trace events; and
     ‘f_trace_opcodes’ (‘False’ by default) to turn on per-opcode trace
     events.

   - bpo-31373(9): Fix several possible instances of undefined behavior
     due to floating-point demotions.

   - bpo-30465(10): Location information (‘lineno’ and ‘col_offset’) in
     f-strings is now (mostly) correct.  This fixes tools like flake8
     from showing warnings on the wrong line (typically the first line
     of the file).

   - bpo-30860(11): Consolidate CPython’s global runtime state under a
     single struct.  This improves discoverability of the runtime state.

   - bpo-31347(12): Fix possible undefined behavior in
     _PyObject_FastCall_Prepend.

   - bpo-31343(13): Include sys/sysmacros.h for major(), minor(), and
     makedev().  GNU C libray plans to remove the functions from
     sys/types.h.

   - bpo-31291(14): Fix an assertion failure in *note
     zipimport.zipimporter.get_data: 11ef. on Windows, when the return
     value of ‘pathname.replace('/','\\')’ isn’t a string.  Patch by
     Oren Milman.

   - bpo-31271(15): Fix an assertion failure in the write() method of
     *note io.TextIOWrapper: 6ea, when the encoder doesn’t return a
     bytes object.  Patch by Oren Milman.

   - bpo-31243(16): Fix a crash in some methods of *note
     io.TextIOWrapper: 6ea, when the decoder’s state is invalid.  Patch
     by Oren Milman.

   - bpo-30721(17): ‘print’ now shows correct usage hint for using
     Python 2 redirection syntax.  Patch by Sanyam Khurana.

   - bpo-31070(18): Fix a race condition in importlib
     _get_module_lock().

   - bpo-30747(19): Add a non-dummy implementation of _Py_atomic_store
     and _Py_atomic_load on MSVC.

   - bpo-31095(20): Fix potential crash during GC caused by ‘tp_dealloc’
     which doesn’t call ‘PyObject_GC_UnTrack()’.

   - bpo-31071(21): Avoid masking original TypeError in call with *
     unpacking when other arguments are passed.

   - bpo-30978(22): str.format_map() now passes key lookup exceptions
     through.  Previously any exception was replaced with a KeyError
     exception.

   - bpo-30808(23): Use _Py_atomic API for concurrency-sensitive signal
     state.

   - bpo-30876(24): Relative import from unloaded package now reimports
     the package instead of failing with SystemError.  Relative import
     from non-package now fails with ImportError rather than
     SystemError.

   - bpo-30703(25): Improve signal delivery.  Avoid using
     Py_AddPendingCall from signal handler, to avoid calling
     signal-unsafe functions.  The tests I’m adding here fail without
     the rest of the patch, on Linux and OS X. This means our signal
     delivery logic had defects (some signals could be lost).

   - bpo-30765(26): Avoid blocking in pthread_mutex_lock() when
     PyThread_acquire_lock() is asked not to block.

   - bpo-31161(27): Make sure the ‘Missing parentheses’ syntax error
     message is only applied to SyntaxError, not to subclasses.  Patch
     by Martijn Pieters.

   - bpo-30814(28): Fixed a race condition when import a submodule from
     a package.

   - bpo-30736(29): The internal unicodedata database has been upgraded
     to Unicode 10.0.

   - bpo-30604(30): Move co_extra_freefuncs from per-thread to
     per-interpreter to avoid crashes.

   - bpo-30597(31): ‘print’ now shows expected input in custom error
     message when used as a Python 2 statement.  Patch by Sanyam
     Khurana.

   - bpo-30682(32): Removed a too-strict assertion that failed for
     certain f-strings, such as eval(“f’\n’”) and eval(“f’\r’”).

   - bpo-30501(33): The compiler now produces more optimal code for
     complex condition expressions in the “if”, “while” and “assert”
     statement, the “if” expression, and generator expressions and
     comprehensions.

   - bpo-28180(34): Implement PEP 538(35) (legacy C locale coercion).
     This means that when a suitable coercion target locale is
     available, both the core interpreter and locale-aware C extensions
     will assume the use of UTF-8 as the default text encoding, rather
     than ASCII.

   - bpo-30486(36): Allows setting cell values for __closure__.  Patch
     by Lisa Roach.

   - bpo-30537(37): itertools.islice now accepts integer-like objects
     (having an __index__ method) as start, stop, and slice arguments

   - bpo-25324(38): Tokens needed for parsing in Python moved to C.
     ‘COMMENT’, ‘NL’ and ‘ENCODING’.  This way the tokens and tok_names
     in the token module don’t get changed when you import the tokenize
     module.

   - bpo-29104(39): Fixed parsing backslashes in f-strings.

   - bpo-27945(40): Fixed various segfaults with dict when input
     collections are mutated during searching, inserting or comparing.
     Based on patches by Duane Griffin and Tim Mitchell.

   - bpo-25794(41): Fixed type.__setattr__() and type.__delattr__() for
     non-interned attribute names.  Based on patch by Eryk Sun.

   - bpo-30039(42): If a KeyboardInterrupt happens when the interpreter
     is in the middle of resuming a chain of nested ‘yield from’ or
     ‘await’ calls, it’s now correctly delivered to the innermost frame.

   - bpo-28974(43): ‘object.__format__(x, '')’ is now equivalent to
     ‘str(x)’ rather than ‘format(str(self), '')’.

   - bpo-30024(44): Circular imports involving absolute imports with
     binding a submodule to a name are now supported.

   - bpo-12414(45): sys.getsizeof() on a code object now returns the
     sizes which includes the code struct and sizes of objects which it
     references.  Patch by Dong-hee Na.

   - bpo-29839(46): len() now raises ValueError rather than
     OverflowError if __len__() returned a large negative integer.

   - bpo-11913(47): README.rst is now included in the list of distutils
     standard READMEs and therefore included in source distributions.

   - bpo-29914(48): Fixed default implementations of __reduce__ and
     __reduce_ex__().  object.__reduce__() no longer takes arguments,
     object.__reduce_ex__() now requires one argument.

   - bpo-29949(49): Fix memory usage regression of set and frozenset
     object.

   - bpo-29935(50): Fixed error messages in the index() method of tuple,
     list and deque when pass indices of wrong type.

   - bpo-29816(51): Shift operation now has less opportunity to raise
     OverflowError.  ValueError always is raised rather than
     OverflowError for negative counts.  Shifting zero with non-negative
     count always returns zero.

   - bpo-24821(52): Fixed the slowing down to 25 times in the searching
     of some unlucky Unicode characters.

   - bpo-29102(53): Add a unique ID to PyInterpreterState.  This makes
     it easier to identify each subinterpreter.

   - bpo-29894(54): The deprecation warning is emitted if __complex__
     returns an instance of a strict subclass of complex.  In a future
     versions of Python this can be an error.

   - bpo-29859(55): Show correct error messages when any of the
     pthread_* calls in thread_pthread.h fails.

   - bpo-29849(56): Fix a memory leak when an ImportError is raised
     during from import.

   - bpo-28856(57): Fix an oversight that %b format for bytes should
     support objects follow the buffer protocol.

   - bpo-29723(58): The ‘sys.path[0]’ initialization change for
     bpo-29139(59) caused a regression by revealing an inconsistency in
     how sys.path is initialized when executing ‘__main__’ from a
     zipfile, directory, or other import location.  The interpreter now
     consistently avoids ever adding the import location’s parent
     directory to ‘sys.path’, and ensures no other ‘sys.path’ entries
     are inadvertently modified when inserting the import location named
     on the command line.

   - bpo-29568(60): Escaped percent “%%” in the format string for
     classic string formatting no longer allows any characters between
     two percents.

   - bpo-29714(61): Fix a regression that bytes format may fail when
     containing zero bytes inside.

   - bpo-29695(62): bool(), float(), list() and tuple() no longer take
     keyword arguments.  The first argument of int() can now be passes
     only as positional argument.

   - bpo-28893(63): Set correct __cause__ for errors about invalid
     awaitables returned from __aiter__ and __anext__.

   - bpo-28876(64): ‘bool(range)’ works even if ‘len(range)’ raises
     *note OverflowError: a41.

   - bpo-29683(65): Fixes to memory allocation in _PyCode_SetExtra.
     Patch by Brian Coleman.

   - bpo-29684(66): Fix minor regression of
     PyEval_CallObjectWithKeywords.  It should raise TypeError when
     kwargs is not a dict.  But it might cause segv when args=NULL and
     kwargs is not a dict.

   - bpo-28598(67): Support __rmod__ for subclasses of str being called
     before str.__mod__.  Patch by Martijn Pieters.

   - bpo-29607(68): Fix stack_effect computation for CALL_FUNCTION_EX.
     Patch by Matthieu Dartiailh.

   - bpo-29602(69): Fix incorrect handling of signed zeros in complex
     constructor for complex subclasses and for inputs having a
     __complex__ method.  Patch by Serhiy Storchaka.

   - bpo-29347(70): Fixed possibly dereferencing undefined pointers when
     creating weakref objects.

   - bpo-29463(71): Add ‘docstring’ field to Module, ClassDef,
     FunctionDef, and AsyncFunctionDef ast nodes.  docstring is not
     first stmt in their body anymore.  It affects ‘co_firstlineno’ and
     ‘co_lnotab’ of code object for module and class.  (Reverted in
     bpo-32911(72).)

   - bpo-29438(73): Fixed use-after-free problem in key sharing dict.

   - bpo-29546(74): Set the ‘path’ and ‘name’ attribute on ImportError
     for ‘from ... import ...’.

   - bpo-29546(75): Improve from-import error message with location

   - bpo-29478(76): If max_line_length=None is specified while using the
     Compat32 policy, it is no longer ignored.  Patch by Mircea Cosbuc.

   - bpo-29319(77): Prevent RunMainFromImporter overwriting sys.path[0].

   - bpo-29337(78): Fixed possible BytesWarning when compare the code
     objects.  Warnings could be emitted at compile time.

   - bpo-29327(79): Fixed a crash when pass the iterable keyword
     argument to sorted().

   - bpo-29034(80): Fix memory leak and use-after-free in os module
     (path_converter).

   - bpo-29159(81): Fix regression in bytes(x) when x.__index__() raises
     Exception.

   - bpo-29049(82): Call _PyObject_GC_TRACK() lazily when calling Python
     function.  Calling function is up to 5% faster.

   - bpo-28927(83): bytes.fromhex() and bytearray.fromhex() now ignore
     all ASCII whitespace, not only spaces.  Patch by Robert Xiao.

   - bpo-28932(84): Do not include <sys/random.h> if it does not exist.

   - bpo-25677(85): Correct the positioning of the syntax error caret
     for indented blocks.  Based on patch by Michael Layzell.

   - bpo-29000(86): Fixed bytes formatting of octals with zero padding
     in alternate form.

   - bpo-18896(87): Python function can now have more than 255
     parameters.  collections.namedtuple() now supports tuples with more
     than 255 elements.

   - bpo-28596(88): The preferred encoding is UTF-8 on Android.  Patch
     written by Chi Hsuan Yen.

   - bpo-22257(89): Clean up interpreter startup (see PEP 432(90)).

   - bpo-26919(91): On Android, operating system data is now always
     encoded/decoded to/from UTF-8, instead of the locale encoding to
     avoid inconsistencies with os.fsencode() and os.fsdecode() which
     are already using UTF-8.

   - bpo-28991(92): functools.lru_cache() was susceptible to an obscure
     reentrancy bug triggerable by a monkey-patched len() function.

   - bpo-28147(93): Fix a memory leak in split-table dictionaries:
     setattr() must not convert combined table into split table.  Patch
     written by INADA Naoki.

   - bpo-28739(94): f-string expressions are no longer accepted as
     docstrings and by ast.literal_eval() even if they do not include
     expressions.

   - bpo-28512(95): Fixed setting the offset attribute of SyntaxError by
     PyErr_SyntaxLocationEx() and PyErr_SyntaxLocationObject().

   - bpo-28918(96): Fix the cross compilation of xxlimited when Python
     has been built with Py_DEBUG defined.

   - bpo-23722(97): Rather than silently producing a class that doesn’t
     support zero-argument ‘super()’ in methods, failing to pass the new
     ‘__classcell__’ namespace entry up to ‘type.__new__’ now results in
     a ‘DeprecationWarning’ and a class that supports zero-argument
     ‘super()’.

   - bpo-28797(98): Modifying the class __dict__ inside the __set_name__
     method of a descriptor that is used inside that class no longer
     prevents calling the __set_name__ method of other descriptors.

   - bpo-28799(99): Remove the ‘PyEval_GetCallStats()’ function and
     deprecate the untested and undocumented ‘sys.callstats()’ function.
     Remove the ‘CALL_PROFILE’ special build: use the *note
     sys.setprofile(): eff. function, *note cProfile: 27. or *note
     profile: d3. to profile function calls.

   - bpo-12844(100): More than 255 arguments can now be passed to a
     function.

   - bpo-28782(101): Fix a bug in the implementation ‘yield from’ when
     checking if the next instruction is YIELD_FROM. Regression
     introduced by WORDCODE (bpo-26647(102)).

   - bpo-28774(103): Fix error position of the unicode error in ASCII
     and Latin1 encoders when a string returned by the error handler
     contains multiple non-encodable characters (non-ASCII for the ASCII
     codec, characters out of the U+0000-U+00FF range for Latin1).

   - bpo-28731(104): Optimize _PyDict_NewPresized() to create correct
     size dict.  Improve speed of dict literal with constant keys up to
     30%.

   - bpo-28532(105): Show sys.version when -V option is supplied twice.

   - bpo-27100(106): The with-statement now checks for __enter__ before
     it checks for __exit__.  This gives less confusing error messages
     when both methods are missing.  Patch by Jonathan Ellington.

   - bpo-28746(107): Fix the set_inheritable() file descriptor method on
     platforms that do not have the ioctl FIOCLEX and FIONCLEX commands.

   - bpo-26920(108): Fix not getting the locale’s charset upon
     initializing the interpreter, on platforms that do not have
     langinfo.

   - bpo-28648(109): Fixed crash in Py_DecodeLocale() in debug build on
     Mac OS X when decode astral characters.  Patch by Xiang Zhang.

   - bpo-28665(110): Improve speed of the STORE_DEREF opcode by 40%.

   - bpo-19398(111): Extra slash no longer added to sys.path components
     in case of empty compile-time PYTHONPATH components.

   - bpo-28621(112): Sped up converting int to float by reusing faster
     bits counting implementation.  Patch by Adrian Wielgosik.

   - bpo-28580(113): Optimize iterating split table values.  Patch by
     Xiang Zhang.

   - bpo-28583(114): PyDict_SetDefault didn’t combine split table when
     needed.  Patch by Xiang Zhang.

   - bpo-28128(115): Deprecation warning for invalid str and byte escape
     sequences now prints better information about where the error
     occurs.  Patch by Serhiy Storchaka and Eric Smith.

   - bpo-28509(116): dict.update() no longer allocate unnecessary large
     memory.

   - bpo-28426(117): Fixed potential crash in
     PyUnicode_AsDecodedObject() in debug build.

   - bpo-28517(118): Fixed of-by-one error in the peephole optimizer
     that caused keeping unreachable code.

   - bpo-28214(119): Improved exception reporting for problematic
     __set_name__ attributes.

   - bpo-23782(120): Fixed possible memory leak in _PyTraceback_Add()
     and exception loss in PyTraceBack_Here().

   - bpo-28183(121): Optimize and cleanup dict iteration.

   - bpo-26081(122): Added C implementation of asyncio.Future.  Original
     patch by Yury Selivanov.

   - bpo-28379(123): Added sanity checks and tests for
     PyUnicode_CopyCharacters().  Patch by Xiang Zhang.

   - bpo-28376(124): The type of long range iterator is now registered
     as Iterator.  Patch by Oren Milman.

   - bpo-28376(125): Creating instances of range_iterator by calling
     range_iterator type now is disallowed.  Calling iter() on range
     instance is the only way.  Patch by Oren Milman.

   - bpo-26906(126): Resolving special methods of uninitialized type now
     causes implicit initialization of the type instead of a fail.

   - bpo-18287(127): PyType_Ready() now checks that tp_name is not NULL.
     Original patch by Niklas Koep.

   - bpo-24098(128): Fixed possible crash when AST is changed in process
     of compiling it.

   - bpo-28201(129): Dict reduces possibility of 2nd conflict in hash
     table when hashes have same lower bits.

   - bpo-28350(130): String constants with null character no longer
     interned.

   - bpo-26617(131): Fix crash when GC runs during weakref callbacks.

   - bpo-27942(132): String constants now interned recursively in tuples
     and frozensets.

   - bpo-28289(133): ImportError.__init__ now resets not specified
     attributes.

   - bpo-21578(134): Fixed misleading error message when ImportError
     called with invalid keyword args.

   - bpo-28203(135): Fix incorrect type in complex(1.0, {2:3}) error
     message.  Patch by Soumya Sharma.

   - bpo-28086(136): Single var-positional argument of tuple subtype was
     passed unscathed to the C-defined function.  Now it is converted to
     exact tuple.

   - bpo-28214(137): Now __set_name__ is looked up on the class instead
     of the instance.

   - bpo-27955(138): Fallback on reading /dev/urandom device when the
     getrandom() syscall fails with EPERM, for example when blocked by
     SECCOMP.

   - bpo-28192(139): Don’t import readline in isolated mode.

   - bpo-27441(140): Remove some redundant assignments to ob_size in
     longobject.c.  Thanks Oren Milman.

   - bpo-27222(141): Clean up redundant code in long_rshift function.
     Thanks Oren Milman.

   - Upgrade internal unicode databases to Unicode version 9.0.0.

   - bpo-28131(142): Fix a regression in zipimport’s compile_source().
     zipimport should use the same optimization level as the
     interpreter.

   - bpo-28126(143): Replace Py_MEMCPY with memcpy().  Visual Studio can
     properly optimize memcpy().

   - bpo-28120(144): Fix dict.pop() for splitted dictionary when trying
     to remove a “pending key” (Not yet inserted in split-table).  Patch
     by Xiang Zhang.

   - bpo-26182(145): Raise DeprecationWarning when async and await
     keywords are used as variable/attribute/class/function name.

   - bpo-26182(146): Fix a refleak in code that raises
     DeprecationWarning.

   - bpo-28721(147): Fix asynchronous generators aclose() and athrow()
     to handle StopAsyncIteration propagation properly.

   - bpo-26110(148): Speed-up method calls: add LOAD_METHOD and
     CALL_METHOD opcodes.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31490

   (2) https://bugs.python.org/issue31471

   (3) https://bugs.python.org/issue31418

   (4) https://bugs.python.org/issue31416

   (5) https://bugs.python.org/issue28411

   (6) https://bugs.python.org/issue28411

   (7) https://bugs.python.org/issue31411

   (8) https://bugs.python.org/issue31344

   (9) https://bugs.python.org/issue31373

   (10) https://bugs.python.org/issue30465

   (11) https://bugs.python.org/issue30860

   (12) https://bugs.python.org/issue31347

   (13) https://bugs.python.org/issue31343

   (14) https://bugs.python.org/issue31291

   (15) https://bugs.python.org/issue31271

   (16) https://bugs.python.org/issue31243

   (17) https://bugs.python.org/issue30721

   (18) https://bugs.python.org/issue31070

   (19) https://bugs.python.org/issue30747

   (20) https://bugs.python.org/issue31095

   (21) https://bugs.python.org/issue31071

   (22) https://bugs.python.org/issue30978

   (23) https://bugs.python.org/issue30808

   (24) https://bugs.python.org/issue30876

   (25) https://bugs.python.org/issue30703

   (26) https://bugs.python.org/issue30765

   (27) https://bugs.python.org/issue31161

   (28) https://bugs.python.org/issue30814

   (29) https://bugs.python.org/issue30736

   (30) https://bugs.python.org/issue30604

   (31) https://bugs.python.org/issue30597

   (32) https://bugs.python.org/issue30682

   (33) https://bugs.python.org/issue30501

   (34) https://bugs.python.org/issue28180

   (35) https://www.python.org/dev/peps/pep-0538

   (36) https://bugs.python.org/issue30486

   (37) https://bugs.python.org/issue30537

   (38) https://bugs.python.org/issue25324

   (39) https://bugs.python.org/issue29104

   (40) https://bugs.python.org/issue27945

   (41) https://bugs.python.org/issue25794

   (42) https://bugs.python.org/issue30039

   (43) https://bugs.python.org/issue28974

   (44) https://bugs.python.org/issue30024

   (45) https://bugs.python.org/issue12414

   (46) https://bugs.python.org/issue29839

   (47) https://bugs.python.org/issue11913

   (48) https://bugs.python.org/issue29914

   (49) https://bugs.python.org/issue29949

   (50) https://bugs.python.org/issue29935

   (51) https://bugs.python.org/issue29816

   (52) https://bugs.python.org/issue24821

   (53) https://bugs.python.org/issue29102

   (54) https://bugs.python.org/issue29894

   (55) https://bugs.python.org/issue29859

   (56) https://bugs.python.org/issue29849

   (57) https://bugs.python.org/issue28856

   (58) https://bugs.python.org/issue29723

   (59) https://bugs.python.org/issue29139

   (60) https://bugs.python.org/issue29568

   (61) https://bugs.python.org/issue29714

   (62) https://bugs.python.org/issue29695

   (63) https://bugs.python.org/issue28893

   (64) https://bugs.python.org/issue28876

   (65) https://bugs.python.org/issue29683

   (66) https://bugs.python.org/issue29684

   (67) https://bugs.python.org/issue28598

   (68) https://bugs.python.org/issue29607

   (69) https://bugs.python.org/issue29602

   (70) https://bugs.python.org/issue29347

   (71) https://bugs.python.org/issue29463

   (72) https://bugs.python.org/issue32911

   (73) https://bugs.python.org/issue29438

   (74) https://bugs.python.org/issue29546

   (75) https://bugs.python.org/issue29546

   (76) https://bugs.python.org/issue29478

   (77) https://bugs.python.org/issue29319

   (78) https://bugs.python.org/issue29337

   (79) https://bugs.python.org/issue29327

   (80) https://bugs.python.org/issue29034

   (81) https://bugs.python.org/issue29159

   (82) https://bugs.python.org/issue29049

   (83) https://bugs.python.org/issue28927

   (84) https://bugs.python.org/issue28932

   (85) https://bugs.python.org/issue25677

   (86) https://bugs.python.org/issue29000

   (87) https://bugs.python.org/issue18896

   (88) https://bugs.python.org/issue28596

   (89) https://bugs.python.org/issue22257

   (90) https://www.python.org/dev/peps/pep-0432

   (91) https://bugs.python.org/issue26919

   (92) https://bugs.python.org/issue28991

   (93) https://bugs.python.org/issue28147

   (94) https://bugs.python.org/issue28739

   (95) https://bugs.python.org/issue28512

   (96) https://bugs.python.org/issue28918

   (97) https://bugs.python.org/issue23722

   (98) https://bugs.python.org/issue28797

   (99) https://bugs.python.org/issue28799

   (100) https://bugs.python.org/issue12844

   (101) https://bugs.python.org/issue28782

   (102) https://bugs.python.org/issue26647

   (103) https://bugs.python.org/issue28774

   (104) https://bugs.python.org/issue28731

   (105) https://bugs.python.org/issue28532

   (106) https://bugs.python.org/issue27100

   (107) https://bugs.python.org/issue28746

   (108) https://bugs.python.org/issue26920

   (109) https://bugs.python.org/issue28648

   (110) https://bugs.python.org/issue28665

   (111) https://bugs.python.org/issue19398

   (112) https://bugs.python.org/issue28621

   (113) https://bugs.python.org/issue28580

   (114) https://bugs.python.org/issue28583

   (115) https://bugs.python.org/issue28128

   (116) https://bugs.python.org/issue28509

   (117) https://bugs.python.org/issue28426

   (118) https://bugs.python.org/issue28517

   (119) https://bugs.python.org/issue28214

   (120) https://bugs.python.org/issue23782

   (121) https://bugs.python.org/issue28183

   (122) https://bugs.python.org/issue26081

   (123) https://bugs.python.org/issue28379

   (124) https://bugs.python.org/issue28376

   (125) https://bugs.python.org/issue28376

   (126) https://bugs.python.org/issue26906

   (127) https://bugs.python.org/issue18287

   (128) https://bugs.python.org/issue24098

   (129) https://bugs.python.org/issue28201

   (130) https://bugs.python.org/issue28350

   (131) https://bugs.python.org/issue26617

   (132) https://bugs.python.org/issue27942

   (133) https://bugs.python.org/issue28289

   (134) https://bugs.python.org/issue21578

   (135) https://bugs.python.org/issue28203

   (136) https://bugs.python.org/issue28086

   (137) https://bugs.python.org/issue28214

   (138) https://bugs.python.org/issue27955

   (139) https://bugs.python.org/issue28192

   (140) https://bugs.python.org/issue27441

   (141) https://bugs.python.org/issue27222

   (142) https://bugs.python.org/issue28131

   (143) https://bugs.python.org/issue28126

   (144) https://bugs.python.org/issue28120

   (145) https://bugs.python.org/issue26182

   (146) https://bugs.python.org/issue26182

   (147) https://bugs.python.org/issue28721

   (148) https://bugs.python.org/issue26110


File: python.info,  Node: Library<41>,  Next: Documentation<35>,  Prev: Core and Builtins<38>,  Up: Python 3 7 0 alpha 1

1.19.42.3 Library
.................

   - bpo-31499(1): xml.etree: Fix a crash when a parser is part of a
     reference cycle.

   - bpo-31482(2): ‘random.seed()’ now works with bytes in version=1

   - bpo-28556(3): typing.get_type_hints now finds the right globalns
     for classes and modules by default (when no ‘globalns’ was
     specified by the caller).

   - bpo-28556(4): Speed improvements to the ‘typing’ module.  Original
     PRs by Ivan Levkivskyi and Mitar.

   - bpo-31544(5): The C accelerator module of ElementTree ignored
     exceptions raised when looking up TreeBuilder target methods in
     XMLParser().

   - bpo-31234(6): socket.create_connection() now fixes manually a
     reference cycle: clear the variable storing the last exception on
     success.

   - bpo-31457(7): LoggerAdapter objects can now be nested.

   - bpo-31431(8): SSLContext.check_hostname now automatically sets
     SSLContext.verify_mode to ssl.CERT_REQUIRED instead of failing with
     a ValueError.

   - bpo-31233(9): socketserver.ThreadingMixIn now keeps a list of
     non-daemonic threads to wait until all these threads complete in
     server_close().

   - bpo-28638(10): Changed the implementation strategy for
     collections.namedtuple() to substantially reduce the use of exec()
     in favor of precomputed methods.  As a result, the `verbose'
     parameter and `_source' attribute are no longer supported.  The
     benefits include 1) having a smaller memory footprint for
     applications using multiple named tuples, 2) faster creation of the
     named tuple class (approx 4x to 6x depending on how it is
     measured), and 3) minor speed-ups for instance creation using
     __new__, _make, and _replace.  (The primary patch contributor is
     Jelle Zijlstra with further improvements by INADA Naoki, Serhiy
     Storchaka, and Raymond Hettinger.)

   - bpo-31400(11): Improves SSL error handling to avoid losing error
     numbers.

   - bpo-27629(12): Make return types of SSLContext.wrap_bio() and
     SSLContext.wrap_socket() customizable.

   - bpo-28958(13): ssl.SSLContext() now uses OpenSSL error information
     when a context cannot be instantiated.

   - bpo-28182(14): The SSL module now raises SSLCertVerificationError
     when OpenSSL fails to verify the peer’s certificate.  The exception
     contains more information about the error.

   - bpo-27340(15): SSLSocket.sendall() now uses memoryview to create
     slices of data.  This fixes support for all bytes-like object.  It
     is also more efficient and avoids costly copies.

   - bpo-14191(16): A new function
     ‘argparse.ArgumentParser.parse_intermixed_args’ provides the
     ability to parse command lines where there user intermixes options
     and positional arguments.

   - bpo-31178(17): Fix string concatenation bug in rare error path in
     the subprocess module

   - bpo-31350(18): Micro-optimize ‘asyncio._get_running_loop()’ to
     become up to 10% faster.

   - bpo-31170(19): expat: Update libexpat from 2.2.3 to 2.2.4.  Fix
     copying of partial characters for UTF-8 input (libexpat bug 115):
     ‘https://github.com/libexpat/libexpat/issues/115’

   - bpo-29136(20): Add TLS 1.3 cipher suites and OP_NO_TLSv1_3.

   - bpo-1198569(21): ‘string.Template’ subclasses can optionally define
     ‘braceidpattern’ if they want to specify different placeholder
     patterns inside and outside the braces.  If None (the default) it
     falls back to ‘idpattern’.

   - bpo-31326(22): concurrent.futures.ProcessPoolExecutor.shutdown()
     now explicitly closes the call queue.  Moreover,
     shutdown(wait=True) now also join the call queue thread, to prevent
     leaking a dangling thread.

   - bpo-27144(23): The ‘map()’ and ‘as_completed()’ iterators in
     ‘concurrent.futures’ now avoid keeping a reference to yielded
     objects.

   - bpo-31281(24): Fix ‘fileinput.FileInput(files, inplace=True)’ when
     ‘files’ contain ‘pathlib.Path’ objects.

   - bpo-10746(25): Fix ctypes producing wrong PEP 3118(26) type codes
     for integer types.

   - bpo-27584(27): ‘AF_VSOCK’ has been added to the socket interface
     which allows communication between virtual machines and their host.

   - bpo-22536(28): The subprocess module now sets the filename when
     FileNotFoundError is raised on POSIX systems due to the executable
     or cwd not being found.

   - bpo-29741(29): Update some methods in the _pyio module to also
     accept integer types.  Patch by Oren Milman.

   - bpo-31249(30): concurrent.futures: WorkItem.run() used by
     ThreadPoolExecutor now breaks a reference cycle between an
     exception object and the WorkItem object.

   - bpo-31247(31): xmlrpc.server now explicitly breaks reference cycles
     when using sys.exc_info() in code handling exceptions.

   - bpo-23835(32): configparser: reading defaults in the
     ‘ConfigParser()’ constructor is now using ‘read_dict()’, making its
     behavior consistent with the rest of the parser.  Non-string keys
     and values in the defaults dictionary are now being implicitly
     converted to strings.  Patch by James Tocknell.

   - bpo-31238(33): pydoc: the stop() method of the private ServerThread
     class now waits until DocServer.serve_until_quit() completes and
     then explicitly sets its docserver attribute to None to break a
     reference cycle.

   - bpo-5001(34): Many asserts in *note multiprocessing: b7. are now
     more informative, and some error types have been changed to more
     specific ones.

   - bpo-31109(35): Convert zipimport to use Argument Clinic.

   - bpo-30102(36): The ssl and hashlib modules now call
     OPENSSL_add_all_algorithms_noconf() on OpenSSL < 1.1.0.  The
     function detects CPU features and enables optimizations on some CPU
     architectures such as POWER8.  Patch is based on research from
     Gustavo Serra Scalet.

   - bpo-18966(37): Non-daemonic threads created by a
     multiprocessing.Process are now joined on child exit.

   - bpo-31183(38): *note dis: 37. now works with asynchronous generator
     and coroutine objects.  Patch by George Collins based on diagnosis
     by Luciano Ramalho.

   - bpo-5001(39): There are a number of uninformative asserts in the
     *note multiprocessing: b7. module, as noted in issue 5001.  This
     change fixes two of the most potentially problematic ones, since
     they are in error-reporting code, in the
     ‘multiprocessing.managers.convert_to_error’ function.  (It also
     makes more informative a ValueError message.)  The only potentially
     problematic change is that the AssertionError is now a TypeError;
     however, this should also help distinguish it from an
     AssertionError being `reported' by the function/its caller (such as
     in issue 31169).  - Patch by Allen W. Smith (drallensmith on
     github).

   - bpo-31185(40): Fixed miscellaneous errors in asyncio speedup
     module.

   - bpo-31151(41): socketserver.ForkingMixIn.server_close() now waits
     until all child processes completed to prevent leaking zombie
     processes.

   - bpo-31072(42): Add an ‘include_file’ parameter to
     ‘zipapp.create_archive()’

   - bpo-24700(43): Optimize array.array comparison.  It is now from 10x
     up to 70x faster when comparing arrays holding values of the same
     integer type.

   - bpo-31135(44): ttk: fix the destroy() method of LabeledScale and
     OptionMenu classes.  Call the parent destroy() method even if the
     used attribute doesn’t exist.  The LabeledScale.destroy() method
     now also explicitly clears label and scale attributes to help the
     garbage collector to destroy all widgets.

   - bpo-31107(45): Fix ‘copyreg._slotnames()’ mangled attribute
     calculation for classes whose name begins with an underscore.
     Patch by Shane Harvey.

   - bpo-31080(46): Allow *note logging.config.fileConfig: 4b0. to
     accept kwargs and/or args.

   - bpo-30897(47): ‘pathlib.Path’ objects now include an ‘is_mount()’
     method (only implemented on POSIX). This is similar to
     ‘os.path.ismount(p)’.  Patch by Cooper Ry Lees.

   - bpo-31061(48): Fixed a crash when using asyncio and threads.

   - bpo-30987(49): Added support for CAN ISO-TP protocol in the socket
     module.

   - bpo-30522(50): Added a ‘setStream’ method to
     ‘logging.StreamHandler’ to allow the stream to be set after
     creation.

   - bpo-30502(51): Fix handling of long oids in ssl.  Based on patch by
     Christian Heimes.

   - bpo-5288(52): Support tzinfo objects with sub-minute offsets.

   - bpo-30919(53): Fix shared memory performance regression in
     multiprocessing in 3.x.  Shared memory used anonymous memory
     mappings in 2.x, while 3.x mmaps actual files.  Try to be careful
     to do as little disk I/O as possible.

   - bpo-26732(54): Fix too many fds in processes started with the
     “forkserver” method.  A child process would inherit as many fds as
     the number of still-running children.

   - bpo-29403(55): Fix ‘unittest.mock’’s autospec to not fail on
     method-bound builtin functions.  Patch by Aaron Gallagher.

   - bpo-30961(56): Fix decrementing a borrowed reference in
     tracemalloc.

   - bpo-19896(57): Fix multiprocessing.sharedctypes to recognize
     typecodes ‘'q'’ and ‘'Q'’.

   - bpo-30946(58): Remove obsolete code in readline module for
     platforms where GNU readline is older than 2.1 or where select() is
     not available.

   - bpo-25684(59): Change ‘ttk.OptionMenu’ radiobuttons to be unique
     across instances of ‘OptionMenu’.

   - bpo-30886(60): Fix multiprocessing.Queue.join_thread(): it now
     waits until the thread completes, even if the thread was started by
     the same process which created the queue.

   - bpo-29854(61): Fix segfault in readline when using readline’s
     history-size option.  Patch by Nir Soffer.

   - bpo-30794(62): Added multiprocessing.Process.kill method to
     terminate using the SIGKILL signal on Unix.

   - bpo-30319(63): socket.close() now ignores ECONNRESET error.

   - bpo-30828(64): Fix out of bounds write in
     ‘asyncio.CFuture.remove_done_callback()’.

   - bpo-30302(65): Use keywords in the ‘repr’ of ‘datetime.timedelta’.

   - bpo-30807(66): signal.setitimer() may disable the timer when passed
     a tiny value.  Tiny values (such as 1e-6) are valid non-zero values
     for setitimer(), which is specified as taking
     microsecond-resolution intervals.  However, on some platform, our
     conversion routine could convert 1e-6 into a zero interval,
     therefore disabling the timer instead of (re-)scheduling it.

   - bpo-30441(67): Fix bug when modifying os.environ while iterating
     over it

   - bpo-29585(68): Avoid importing ‘sysconfig’ from ‘site’ to improve
     startup speed.  Python startup is about 5% faster on Linux and 30%
     faster on macOS.

   - bpo-29293(69): Add missing parameter “n” on
     multiprocessing.Condition.notify().  The doc claims
     multiprocessing.Condition behaves like threading.Condition, but its
     notify() method lacked the optional “n” argument (to specify the
     number of sleepers to wake up) that threading.Condition.notify()
     accepts.

   - bpo-30532(70): Fix email header value parser dropping folding white
     space in certain cases.

   - bpo-30596(71): Add a ‘close()’ method to ‘multiprocessing.Process’.

   - bpo-9146(72): Fix a segmentation fault in _hashopenssl when
     standard hash functions such as md5 are not available in the linked
     OpenSSL library.  As in some special FIPS-140 build environments.

   - bpo-29169(73): Update zlib to 1.2.11.

   - bpo-30119(74): ftplib.FTP.putline() now throws ValueError on
     commands that contains CR or LF. Patch by Dong-hee Na.

   - bpo-30879(75): os.listdir() and os.scandir() now emit bytes names
     when called with bytes-like argument.

   - bpo-30746(76): Prohibited the ‘=’ character in environment variable
     names in ‘os.putenv()’ and ‘os.spawn*()’.

   - bpo-30664(77): The description of a unittest subtest now preserves
     the order of keyword arguments of TestCase.subTest().

   - bpo-21071(78): struct.Struct.format type is now *note str: 205.
     instead of *note bytes: 172.

   - bpo-29212(79): Fix concurrent.futures.thread.ThreadPoolExecutor
     threads to have a non repr() based thread name by default when no
     thread_name_prefix is supplied.  They will now identify themselves
     as “ThreadPoolExecutor-y_n”.

   - bpo-29755(80): Fixed the lgettext() family of functions in the
     gettext module.  They now always return bytes.

   - bpo-30616(81): Functional API of enum allows to create empty enums.
     Patched by Dong-hee Na

   - bpo-30038(82): Fix race condition between signal delivery and
     wakeup file descriptor.  Patch by Nathaniel Smith.

   - bpo-23894(83): lib2to3 now recognizes ‘rb'...'’ and ‘f'...'’
     strings.

   - bpo-24744(84): pkgutil.walk_packages function now raises ValueError
     if `path' is a string.  Patch by Sanyam Khurana.

   - bpo-24484(85): Avoid race condition in multiprocessing cleanup.

   - bpo-30589(86): Fix multiprocessing.Process.exitcode to return the
     opposite of the signal number when the process is killed by a
     signal (instead of 255) when using the “forkserver” method.

   - bpo-28994(87): The traceback no longer displayed for SystemExit
     raised in a callback registered by atexit.

   - bpo-30508(88): Don’t log exceptions if Task/Future “cancel()”
     method was called.

   - bpo-30645(89): Fix path calculation in ‘imp.load_package()’, fixing
     it for cases when a package is only shipped with bytecodes.  Patch
     by Alexandru Ardelean.

   - bpo-11822(90): The dis.dis() function now is able to disassemble
     nested code objects.

   - bpo-30624(91): selectors does not take KeyboardInterrupt and
     SystemExit into account, leaving a fd in a bad state in case of
     error.  Patch by Giampaolo Rodola’.

   - bpo-30595(92): multiprocessing.Queue.get() with a timeout now polls
     its reader in non-blocking mode if it succeeded to acquire the lock
     but the acquire took longer than the timeout.

   - bpo-28556(93): Updates to typing module: Add generic
     AsyncContextManager, add support for ContextManager on all
     versions.  Original PRs by Jelle Zijlstra and Ivan Levkivskyi

   - bpo-30605(94): re.compile() no longer raises a BytesWarning when
     compiling a bytes instance with misplaced inline modifier.  Patch
     by Roy Williams.

   - bpo-29870(95): Fix ssl sockets leaks when connection is aborted in
     asyncio/ssl implementation.  Patch by Michaël Sghaïer.

   - bpo-29743(96): Closing transport during handshake process leaks
     open socket.  Patch by Nikolay Kim

   - bpo-27585(97): Fix waiter cancellation in asyncio.Lock.  Patch by
     Mathieu Sornay.

   - bpo-30014(98): modify() method of poll(), epoll() and devpoll()
     based classes of selectors module is around 10% faster.  Patch by
     Giampaolo Rodola’.

   - bpo-30418(99): On Windows, subprocess.Popen.communicate() now also
     ignore EINVAL on stdin.write() if the child process is still
     running but closed the pipe.

   - bpo-30463(100): Addded empty __slots__ to abc.ABC. This allows
     subclassers to deny __dict__ and __weakref__ creation.  Patch by
     Aaron Hall.

   - bpo-30520(101): Loggers are now pickleable.

   - bpo-30557(102): faulthandler now correctly filters and displays
     exception codes on Windows

   - bpo-30526(103): Add TextIOWrapper.reconfigure() and a
     TextIOWrapper.write_through attribute.

   - bpo-30245(104): Fix possible overflow when organize
     struct.pack_into error message.  Patch by Yuan Liu.

   - bpo-30378(105): Fix the problem that logging.handlers.SysLogHandler
     cannot handle IPv6 addresses.

   - bpo-16500(106): Allow registering at-fork handlers.

   - bpo-30470(107): Deprecate invalid ctypes call protection on
     Windows.  Patch by Mariatta Wijaya.

   - bpo-30414(108): multiprocessing.Queue._feed background running
     thread do not break from main loop on exception.

   - bpo-30003(109): Fix handling escape characters in HZ codec.  Based
     on patch by Ma Lin.

   - bpo-30149(110): inspect.signature() now supports callables with
     variable-argument parameters wrapped with partialmethod.  Patch by
     Dong-hee Na.

   - bpo-30436(111): importlib.find_spec() raises ModuleNotFoundError
     instead of AttributeError if the specified parent module is not a
     package (i.e.  lacks a __path__ attribute).

   - bpo-30301(112): Fix AttributeError when using SimpleQueue.empty()
     under `spawn' and `forkserver' start methods.

   - bpo-30375(113): Warnings emitted when compile a regular expression
     now always point to the line in the user code.  Previously they
     could point into inners of the re module if emitted from inside of
     groups or conditionals.

   - bpo-30329(114): imaplib and poplib now catch the Windows socket
     WSAEINVAL error (code 10022) on shutdown(SHUT_RDWR): An invalid
     operation was attempted.  This error occurs sometimes on SSL
     connections.

   - bpo-29196(115): Removed previously deprecated in Python 2.4 classes
     Plist, Dict and _InternalDict in the plistlib module.  Dict values
     in the result of functions readPlist() and readPlistFromBytes() are
     now normal dicts.  You no longer can use attribute access to access
     items of these dictionaries.

   - bpo-9850(116): The ‘macpath’ is now deprecated and will be removed
     in Python 3.8.

   - bpo-30299(117): Compiling regular expression in debug mode on
     CPython now displays the compiled bytecode in human readable form.

   - bpo-30048(118): Fixed ‘Task.cancel()’ can be ignored when the task
     is running coroutine and the coroutine returned without any more
     ‘await’.

   - bpo-30266(119): contextlib.AbstractContextManager now supports
     anti-registration by setting __enter__ = None or __exit__ = None,
     following the pattern introduced in bpo-25958(120).  Patch by Jelle
     Zijlstra.

   - bpo-30340(121): Enhanced regular expressions optimization.  This
     increased the performance of matching some patterns up to 25 times.

   - bpo-30298(122): Weaken the condition of deprecation warnings for
     inline modifiers.  Now allowed several subsequential inline
     modifiers at the start of the pattern (e.g.  ‘'(?i)(?s)...'’).  In
     verbose mode whitespaces and comments now are allowed before and
     between inline modifiers (e.g.  ‘'(?x) (?i) (?s)...'’).

   - bpo-30285(123): Optimized case-insensitive matching and searching
     of regular expressions.

   - bpo-29990(124): Fix range checking in GB18030 decoder.  Original
     patch by Ma Lin.

   - bpo-29979(125): rewrite cgi.parse_multipart, reusing the
     FieldStorage class and making its results consistent with those of
     FieldStorage for multipart/form-data requests.  Patch by Pierre
     Quentel.

   - bpo-30243(126): Removed the __init__ methods of _json’s scanner and
     encoder.  Misusing them could cause memory leaks or crashes.  Now
     scanner and encoder objects are completely initialized in the
     __new__ methods.

   - bpo-30215(127): Compiled regular expression objects with the
     re.LOCALE flag no longer depend on the locale at compile time.
     Only the locale at matching time affects the result of matching.

   - bpo-30185(128): Avoid KeyboardInterrupt tracebacks in forkserver
     helper process when Ctrl-C is received.

   - bpo-30103(129): binascii.b2a_uu() and uu.encode() now support using
     ‘'`'’ as zero instead of space.

   - bpo-28556(130): Various updates to typing module: add
     typing.NoReturn type, use WrapperDescriptorType, minor bug-fixes.
     Original PRs by Jim Fasarakis-Hilliard and Ivan Levkivskyi.

   - bpo-30205(131): Fix getsockname() for unbound AF_UNIX sockets on
     Linux.

   - bpo-30228(132): The seek() and tell() methods of io.FileIO now set
     the internal seekable attribute to avoid one syscall on open() (in
     buffered or text mode).

   - bpo-30190(133): unittest’s assertAlmostEqual and
     assertNotAlmostEqual provide a better message in case of failure
     which includes the difference between left and right arguments.
     (patch by Giampaolo Rodola’)

   - bpo-30101(134): Add support for curses.A_ITALIC.

   - bpo-29822(135): inspect.isabstract() now works during
     __init_subclass__.  Patch by Nate Soares.

   - bpo-29960(136): Preserve generator state when
     _random.Random.setstate() raises an exception.  Patch by Bryan
     Olson.

   - bpo-30070(137): Fixed leaks and crashes in errors handling in the
     parser module.

   - bpo-22352(138): Column widths in the output of dis.dis() are now
     adjusted for large line numbers and instruction offsets.

   - bpo-30061(139): Fixed crashes in IOBase methods __next__() and
     readlines() when readline() or __next__() respectively return
     non-sizeable object.  Fixed possible other errors caused by not
     checking results of PyObject_Size(), PySequence_Size(), or
     PyMapping_Size().

   - bpo-30218(140): Fix PathLike support for shutil.unpack_archive.
     Patch by Jelle Zijlstra.

   - bpo-10076(141): Compiled regular expression and match objects in
     the re module now support copy.copy() and copy.deepcopy() (they are
     considered atomic).

   - bpo-30068(142): _io._IOBase.readlines will check if it’s closed
     first when hint is present.

   - bpo-29694(143): Fixed race condition in pathlib mkdir with flags
     parents=True.  Patch by Armin Rigo.

   - bpo-29692(144): Fixed arbitrary unchaining of RuntimeError
     exceptions in contextlib.contextmanager.  Patch by Siddharth
     Velankar.

   - bpo-26187(145): Test that sqlite3 trace callback is not called
     multiple times when schema is changing.  Indirectly fixed by
     switching to use sqlite3_prepare_v2() in bpo-9303(146).  Patch by
     Aviv Palivoda.

   - bpo-30017(147): Allowed calling the close() method of the zip entry
     writer object multiple times.  Writing to a closed writer now
     always produces a ValueError.

   - bpo-29998(148): Pickling and copying ImportError now preserves name
     and path attributes.

   - bpo-29995(149): re.escape() now escapes only regex special
     characters.

   - bpo-29962(150): Add math.remainder operation, implementing
     remainder as specified in IEEE 754.

   - bpo-29649(151): Improve struct.pack_into() exception messages for
     problems with the buffer size and offset.  Patch by Andrew Nester.

   - bpo-29654(152): Support If-Modified-Since HTTP header (browser
     cache).  Patch by Pierre Quentel.

   - bpo-29931(153): Fixed comparison check for ipaddress.ip_interface
     objects.  Patch by Sanjay Sundaresan.

   - bpo-29953(154): Fixed memory leaks in the replace() method of
     datetime and time objects when pass out of bound fold argument.

   - bpo-29942(155): Fix a crash in itertools.chain.from_iterable when
     encountering long runs of empty iterables.

   - bpo-10030(156): Sped up reading encrypted ZIP files by 2 times.

   - bpo-29204(157): Element.getiterator() and the html parameter of
     XMLParser() were deprecated only in the documentation (since Python
     3.2 and 3.4 correspondingly).  Now using them emits a deprecation
     warning.

   - bpo-27863(158): Fixed multiple crashes in ElementTree caused by
     race conditions and wrong types.

   - bpo-25996(159): Added support of file descriptors in os.scandir()
     on Unix.  os.fwalk() is sped up by 2 times by using os.scandir().

   - bpo-28699(160): Fixed a bug in pools in multiprocessing.pool that
     raising an exception at the very first of an iterable may swallow
     the exception or make the program hang.  Patch by Davin Potts and
     Xiang Zhang.

   - bpo-23890(161): unittest.TestCase.assertRaises() now manually
     breaks a reference cycle to not keep objects alive longer than
     expected.

   - bpo-29901(162): The zipapp module now supports general path-like
     objects, not just pathlib.Path.

   - bpo-25803(163): Avoid incorrect errors raised by
     Path.mkdir(exist_ok=True) when the OS gives priority to errors such
     as EACCES over EEXIST.

   - bpo-29861(164): Release references to tasks, their arguments and
     their results as soon as they are finished in multiprocessing.Pool.

   - bpo-19930(165): The mode argument of os.makedirs() no longer
     affects the file permission bits of newly-created
     intermediate-level directories.

   - bpo-29884(166): faulthandler: Restore the old sigaltstack during
     teardown.  Patch by Christophe Zeitouny.

   - bpo-25455(167): Fixed crashes in repr of recursive buffered
     file-like objects.

   - bpo-29800(168): Fix crashes in partial.__repr__ if the keys of
     partial.keywords are not strings.  Patch by Michael Seifert.

   - bpo-8256(169): Fixed possible failing or crashing input() if
     attributes “encoding” or “errors” of sys.stdin or sys.stdout are
     not set or are not strings.

   - bpo-28692(170): Using non-integer value for selecting a plural form
     in gettext is now deprecated.

   - bpo-26121(171): Use C library implementation for math functions
     erf() and erfc().

   - bpo-29619(172): os.stat() and os.DirEntry.inode() now convert inode
     (st_ino) using unsigned integers.

   - bpo-28298(173): Fix a bug that prevented array ‘Q’, ‘L’ and ‘I’
     from accepting big intables (objects that have __int__) as
     elements.

   - bpo-29645(174): Speed up importing the webbrowser module.
     webbrowser.register() is now thread-safe.

   - bpo-28231(175): The zipfile module now accepts path-like objects
     for external paths.

   - bpo-26915(176): index() and count() methods of
     collections.abc.Sequence now check identity before checking
     equality when do comparisons.

   - bpo-28682(177): Added support for bytes paths in os.fwalk().

   - bpo-29728(178): Add new ‘socket.TCP_NOTSENT_LOWAT’ (Linux 3.12)
     constant.  Patch by Nathaniel J. Smith.

   - bpo-29623(179): Allow use of path-like object as a single argument
     in ConfigParser.read().  Patch by David Ellis.

   - bpo-9303(180): Migrate sqlite3 module to _v2 API. Patch by Aviv
     Palivoda.

   - bpo-28963(181): Fix out of bound iteration in
     asyncio.Future.remove_done_callback implemented in C.

   - bpo-29704(182): asyncio.subprocess.SubprocessStreamProtocol no
     longer closes before all pipes are closed.

   - bpo-29271(183): Fix Task.current_task and Task.all_tasks
     implemented in C to accept None argument as their pure Python
     implementation.

   - bpo-29703(184): Fix asyncio to support instantiation of new event
     loops in child processes.

   - bpo-29615(185): SimpleXMLRPCDispatcher no longer chains KeyError
     (or any other exception) to exception(s) raised in the dispatched
     methods.  Patch by Petr Motejlek.

   - bpo-7769(186): Method register_function() of
     xmlrpc.server.SimpleXMLRPCDispatcher and its subclasses can now be
     used as a decorator.

   - bpo-29376(187): Fix assertion error in
     threading._DummyThread.is_alive().

   - bpo-28624(188): Add a test that checks that cwd parameter of
     Popen() accepts PathLike objects.  Patch by Sayan Chowdhury.

   - bpo-28518(189): Start a transaction implicitly before a DML
     statement.  Patch by Aviv Palivoda.

   - bpo-29742(190): get_extra_info() raises exception if get called on
     closed ssl transport.  Patch by Nikolay Kim.

   - bpo-16285(191): urllib.parse.quote is now based on RFC 3986 and
     hence includes ‘~’ in the set of characters that is not quoted by
     default.  Patch by Christian Theune and Ratnadeep Debnath.

   - bpo-29532(192): Altering a kwarg dictionary passed to
     functools.partial() no longer affects a partial object after
     creation.

   - bpo-29110(193): Fix file object leak in aifc.open() when file is
     given as a filesystem path and is not in valid AIFF format.  Patch
     by Anthony Zhang.

   - bpo-22807(194): Add uuid.SafeUUID and uuid.UUID.is_safe to relay
     information from the platform about whether generated UUIDs are
     generated with a multiprocessing safe method.

   - bpo-29576(195): Improve some deprecations in importlib.  Some
     deprecated methods now emit DeprecationWarnings and have better
     descriptive messages.

   - bpo-29534(196): Fixed different behaviour of Decimal.from_float()
     for _decimal and _pydecimal.  Thanks Andrew Nester.

   - bpo-10379(197): locale.format_string now supports the ‘monetary’
     keyword argument, and locale.format is deprecated.

   - bpo-29851(198): importlib.reload() now raises ModuleNotFoundError
     if the module lacks a spec.

   - bpo-28556(199): Various updates to typing module: typing.Counter,
     typing.ChainMap, improved ABC caching, etc.  Original PRs by Jelle
     Zijlstra, Ivan Levkivskyi, Manuel Krebber, and Łukasz Langa.

   - bpo-29100(200): Fix datetime.fromtimestamp() regression introduced
     in Python 3.6.0: check minimum and maximum years.

   - bpo-29416(201): Prevent infinite loop in pathlib.Path.mkdir

   - bpo-29444(202): Fixed out-of-bounds buffer access in the group()
     method of the match object.  Based on patch by WGH.

   - bpo-29377(203): Add WrapperDescriptorType, MethodWrapperType, and
     MethodDescriptorType built-in types to types module.  Original
     patch by Manuel Krebber.

   - bpo-29218(204): Unused install_misc command is now removed.  It has
     been documented as unused since 2000.  Patch by Eric N. Vander
     Weele.

   - bpo-29368(205): The extend() method is now called instead of the
     append() method when unpickle collections.deque and other list-like
     objects.  This can speed up unpickling to 2 times.

   - bpo-29338(206): The help of a builtin or extension class now
     includes the constructor signature if __text_signature__ is
     provided for the class.

   - bpo-29335(207): Fix subprocess.Popen.wait() when the child process
     has exited to a stopped instead of terminated state (ex: when under
     ptrace).

   - bpo-29290(208): Fix a regression in argparse that help messages
     would wrap at non-breaking spaces.

   - bpo-28735(209): Fixed the comparison of mock.MagickMock with
     mock.ANY.

   - bpo-29197(210): Removed deprecated function ntpath.splitunc().

   - bpo-29210(211): Removed support of deprecated argument “exclude” in
     tarfile.TarFile.add().

   - bpo-29219(212): Fixed infinite recursion in the repr of
     uninitialized ctypes.CDLL instances.

   - bpo-29192(213): Removed deprecated features in the http.cookies
     module.

   - bpo-29193(214): A format string argument for
     string.Formatter.format() is now positional-only.

   - bpo-29195(215): Removed support of deprecated undocumented keyword
     arguments in methods of regular expression objects.

   - bpo-28969(216): Fixed race condition in C implementation of
     functools.lru_cache.  KeyError could be raised when cached function
     with full cache was simultaneously called from different threads
     with the same uncached arguments.

   - bpo-20804(217): The unittest.mock.sentinel attributes now preserve
     their identity when they are copied or pickled.

   - bpo-29142(218): In urllib.request, suffixes in no_proxy environment
     variable with leading dots could match related hostnames again
     (e.g.  .b.c matches a.b.c).  Patch by Milan Oberkirch.

   - bpo-28961(219): Fix unittest.mock._Call helper: don’t ignore the
     name parameter anymore.  Patch written by Jiajun Huang.

   - bpo-15812(220): inspect.getframeinfo() now correctly shows the
     first line of a context.  Patch by Sam Breese.

   - bpo-28985(221): Update authorizer constants in sqlite3 module.
     Patch by Dingyuan Wang.

   - bpo-29079(222): Prevent infinite loop in pathlib.resolve() on
     Windows

   - bpo-13051(223): Fixed recursion errors in large or resized
     curses.textpad.Textbox.  Based on patch by Tycho Andersen.

   - bpo-9770(224): curses.ascii predicates now work correctly with
     negative integers.

   - bpo-28427(225): old keys should not remove new values from
     WeakValueDictionary when collecting from another thread.

   - bpo-28923(226): Remove editor artifacts from Tix.py.

   - bpo-28871(227): Fixed a crash when deallocate deep ElementTree.

   - bpo-19542(228): Fix bugs in WeakValueDictionary.setdefault() and
     WeakValueDictionary.pop() when a GC collection happens in another
     thread.

   - bpo-20191(229): Fixed a crash in resource.prlimit() when passing a
     sequence that doesn’t own its elements as limits.

   - bpo-16255(230): subprocess.Popen uses /system/bin/sh on Android as
     the shell, instead of /bin/sh.

   - bpo-28779(231): multiprocessing.set_forkserver_preload() would
     crash the forkserver process if a preloaded module instantiated
     some multiprocessing objects such as locks.

   - bpo-26937(232): The chown() method of the tarfile.TarFile class
     does not fail now when the grp module cannot be imported, as for
     example on Android platforms.

   - bpo-28847(233): dbm.dumb now supports reading read-only files and
     no longer writes the index file when it is not changed.  A
     deprecation warning is now emitted if the index file is missed and
     recreated in the ‘r’ and ‘w’ modes (will be an error in future
     Python releases).

   - bpo-27030(234): Unknown escapes consisting of ‘'\'’ and an ASCII
     letter in re.sub() replacement templates regular expressions now
     are errors.

   - bpo-28835(235): Fix a regression introduced in
     warnings.catch_warnings(): call warnings.showwarning() if it was
     overridden inside the context manager.

   - bpo-27172(236): To assist with upgrades from 2.7, the previously
     documented deprecation of ‘inspect.getfullargspec()’ has been
     reversed.  This decision may be revisited again after the Python
     2.7 branch is no longer officially supported.

   - bpo-28740(237): Add sys.getandroidapilevel(): return the build time
     API version of Android as an integer.  Function only available on
     Android.

   - bpo-26273(238): Add new ‘socket.TCP_CONGESTION’ (Linux 2.6.13) and
     ‘socket.TCP_USER_TIMEOUT’ (Linux 2.6.37) constants.  Patch written
     by Omar Sandoval.

   - bpo-28752(239): Restored the __reduce__() methods of datetime
     objects.

   - bpo-28727(240): Regular expression patterns, _sre.SRE_Pattern
     objects created by re.compile(), become comparable (only x==y and
     x!=y operators).  This change should fix the bpo-18383(241): don’t
     duplicate warning filters when the warnings module is reloaded
     (thing usually only done in unit tests).

   - bpo-20572(242): Remove the subprocess.Popen.wait endtime parameter.
     It was deprecated in 3.4 and undocumented prior to that.

   - bpo-25659(243): In ctypes, prevent a crash calling the
     from_buffer() and from_buffer_copy() methods on abstract classes
     like Array.

   - bpo-28548(244): In the “http.server” module, parse the protocol
     version if possible, to avoid using HTTP 0.9 in some error
     responses.

   - bpo-19717(245): Makes Path.resolve() succeed on paths that do not
     exist.  Patch by Vajrasky Kok

   - bpo-28563(246): Fixed possible DoS and arbitrary code execution
     when handle plural form selections in the gettext module.  The
     expression parser now supports exact syntax supported by GNU
     gettext.

   - bpo-28387(247): Fixed possible crash in _io.TextIOWrapper
     deallocator when the garbage collector is invoked in other thread.
     Based on patch by Sebastian Cufre.

   - bpo-27517(248): LZMA compressor and decompressor no longer raise
     exceptions if given empty data twice.  Patch by Benjamin Fogle.

   - bpo-28549(249): Fixed segfault in curses’s addch() with ncurses6.

   - bpo-28449(250): tarfile.open() with mode “r” or “r:” now tries to
     open a tar file with compression before trying to open it without
     compression.  Otherwise it had 50% chance failed with
     ignore_zeros=True.

   - bpo-23262(251): The webbrowser module now supports Firefox 36+ and
     derived browsers.  Based on patch by Oleg Broytman.

   - bpo-24241(252): The webbrowser in an X environment now prefers
     using the default browser directly.  Also, the webbrowser
     register() function now has a documented ‘preferred’ argument, to
     specify browsers to be returned by get() with no arguments.  Patch
     by David Steele

   - bpo-27939(253): Fixed bugs in tkinter.ttk.LabeledScale and
     tkinter.Scale caused by representing the scale as float value
     internally in Tk.  tkinter.IntVar now works if float value is set
     to underlying Tk variable.

   - bpo-28255(254): calendar.TextCalendar.prweek() no longer prints a
     space after a weeks’s calendar.  calendar.TextCalendar.pryear() no
     longer prints redundant newline after a year’s calendar.  Based on
     patch by Xiang Zhang.

   - bpo-28255(255): calendar.TextCalendar.prmonth() no longer prints a
     space at the start of new line after printing a month’s calendar.
     Patch by Xiang Zhang.

   - bpo-20491(256): The textwrap.TextWrapper class now honors
     non-breaking spaces.  Based on patch by Kaarle Ritvanen.

   - bpo-28353(257): os.fwalk() no longer fails on broken links.

   - bpo-28430(258): Fix iterator of C implemented asyncio.Future
     doesn’t accept non-None value is passed to it.send(val).

   - bpo-27025(259): Generated names for Tkinter widgets now start by
     the “!” prefix for readability.

   - bpo-25464(260): Fixed HList.header_exists() in tkinter.tix module
     by addin a workaround to Tix library bug.

   - bpo-28488(261): shutil.make_archive() no longer adds entry “./” to
     ZIP archive.

   - bpo-25953(262): re.sub() now raises an error for invalid numerical
     group reference in replacement template even if the pattern is not
     found in the string.  Error message for invalid group reference now
     includes the group index and the position of the reference.  Based
     on patch by SilentGhost.

   - bpo-28469(263): timeit now uses the sequence 1, 2, 5, 10, 20, 50,…
     instead of 1, 10, 100,… for autoranging.

   - bpo-28115(264): Command-line interface of the zipfile module now
     uses argparse.  Added support of long options.

   - bpo-18219(265): Optimize csv.DictWriter for large number of
     columns.  Patch by Mariatta Wijaya.

   - bpo-28448(266): Fix C implemented asyncio.Future didn’t work on
     Windows.

   - bpo-23214(267): In the “io” module, the argument to BufferedReader
     and BytesIO’s read1() methods is now optional and can be -1,
     matching the BufferedIOBase specification.

   - bpo-28480(268): Fix error building socket module when
     multithreading is disabled.

   - bpo-28240(269): timeit: remove ‘-c/--clock’ and ‘-t/--time’ command
     line options which were deprecated since Python 3.3.

   - bpo-28240(270): timeit now repeats the benchmarks 5 times instead
     of only 3 to make benchmarks more reliable.

   - bpo-28240(271): timeit autorange now uses a single loop iteration
     if the benchmark takes less than 10 seconds, instead of 10
     iterations.  “python3 -m timeit -s ‘import time’ ‘time.sleep(1)’”
     now takes 4 seconds instead of 40 seconds.

   - Distutils.sdist now looks for README and setup.py files with case
     sensitivity.  This behavior matches that found in Setuptools 6.0
     and later.  See setuptools 100(272) for rationale.

   - bpo-24452(273): Make webbrowser support Chrome on Mac OS X. Patch
     by Ned Batchelder.

   - bpo-20766(274): Fix references leaked by pdb in the handling of
     SIGINT handlers.

   - bpo-27998(275): Fixed bytes path support in os.scandir() on
     Windows.  Patch by Eryk Sun.

   - bpo-28317(276): The disassembler now decodes FORMAT_VALUE argument.

   - bpo-28380(277): unittest.mock Mock autospec functions now properly
     support assert_called, assert_not_called, and assert_called_once.

   - bpo-28229(278): lzma module now supports pathlib.

   - bpo-28321(279): Fixed writing non-BMP characters with binary format
     in plistlib.

   - bpo-28225(280): bz2 module now supports pathlib.  Initial patch by
     Ethan Furman.

   - bpo-28227(281): gzip now supports pathlib.  Patch by Ethan Furman.

   - bpo-28332(282): Deprecated silent truncations in socket.htons and
     socket.ntohs.  Original patch by Oren Milman.

   - bpo-27358(283): Optimized merging var-keyword arguments and
     improved error message when passing a non-mapping as a var-keyword
     argument.

   - bpo-28257(284): Improved error message when passing a non-iterable
     as a var-positional argument.  Added opcode
     BUILD_TUPLE_UNPACK_WITH_CALL.

   - bpo-28322(285): Fixed possible crashes when unpickle itertools
     objects from incorrect pickle data.  Based on patch by John Leitch.

   - bpo-28228(286): imghdr now supports pathlib.

   - bpo-28226(287): compileall now supports pathlib.

   - bpo-28314(288): Fix function declaration (C flags) for the
     getiterator() method of xml.etree.ElementTree.Element.

   - bpo-28148(289): Stop using localtime() and gmtime() in the time
     module.  Introduced platform independent _PyTime_localtime API that
     is similar to POSIX localtime_r, but available on all platforms.
     Patch by Ed Schouten.

   - bpo-28253(290): Fixed calendar functions for extreme months:
     0001-01 and 9999-12.  Methods itermonthdays() and itermonthdays2()
     are reimplemented so that they don’t call itermonthdates() which
     can cause datetime.date under/overflow.

   - bpo-28275(291): Fixed possible use after free in the decompress()
     methods of the LZMADecompressor and BZ2Decompressor classes.
     Original patch by John Leitch.

   - bpo-27897(292): Fixed possible crash in
     sqlite3.Connection.create_collation() if pass invalid string-like
     object as a name.  Patch by Xiang Zhang.

   - bpo-18844(293): random.choices() now has k as a keyword-only
     argument to improve the readability of common cases and come into
     line with the signature used in other languages.

   - bpo-18893(294): Fix invalid exception handling in
     Lib/ctypes/macholib/dyld.py.  Patch by Madison May.

   - bpo-27611(295): Fixed support of default root window in the
     tkinter.tix module.  Added the master parameter in the DisplayStyle
     constructor.

   - bpo-27348(296): In the traceback module, restore the formatting of
     exception messages like “Exception: None”.  This fixes a regression
     introduced in 3.5a2.

   - bpo-25651(297): Allow falsy values to be used for msg parameter of
     subTest().

   - bpo-27778(298): Fix a memory leak in os.getrandom() when the
     getrandom() is interrupted by a signal and a signal handler raises
     a Python exception.

   - bpo-28200(299): Fix memory leak on Windows in the os module (fix
     path_converter() function).

   - bpo-25400(300): RobotFileParser now correctly returns default
     values for crawl_delay and request_rate.  Initial patch by Peter
     Wirtz.

   - bpo-27932(301): Prevent memory leak in win32_ver().

   - Fix UnboundLocalError in socket._sendfile_use_sendfile.

   - bpo-28075(302): Check for ERROR_ACCESS_DENIED in Windows
     implementation of os.stat().  Patch by Eryk Sun.

   - bpo-22493(303): Warning message emitted by using inline flags in
     the middle of regular expression now contains a (truncated) regex
     pattern.  Patch by Tim Graham.

   - bpo-25270(304): Prevent codecs.escape_encode() from raising
     SystemError when an empty bytestring is passed.

   - bpo-28181(305): Get antigravity over HTTPS. Patch by Kaartic
     Sivaraam.

   - bpo-25895(306): Enable WebSocket URL schemes in
     urllib.parse.urljoin.  Patch by Gergely Imreh and Markus
     Holtermann.

   - bpo-28114(307): Fix a crash in parse_envlist() when env contains
     byte strings.  Patch by Eryk Sun.

   - bpo-27599(308): Fixed buffer overrun in binascii.b2a_qp() and
     binascii.a2b_qp().

   - bpo-27906(309): Fix socket accept exhaustion during high TCP
     traffic.  Patch by Kevin Conway.

   - bpo-28174(310): Handle when SO_REUSEPORT isn’t properly supported.
     Patch by Seth Michael Larson.

   - bpo-26654(311): Inspect functools.partial in
     asyncio.Handle.__repr__.  Patch by iceboy.

   - bpo-26909(312): Fix slow pipes IO in asyncio.  Patch by INADA
     Naoki.

   - bpo-28176(313): Fix callbacks race in
     asyncio.SelectorLoop.sock_connect.

   - bpo-27759(314): Fix selectors incorrectly retain invalid file
     descriptors.  Patch by Mark Williams.

   - bpo-28325(315): Remove vestigial MacOS 9 macurl2path module and its
     tests.

   - bpo-28368(316): Refuse monitoring processes if the child watcher
     has no loop attached.  Patch by Vincent Michel.

   - bpo-28369(317): Raise RuntimeError when transport’s FD is used with
     add_reader, add_writer, etc.

   - bpo-28370(318): Speedup asyncio.StreamReader.readexactly.  Patch by
     Коренберг Марк.

   - bpo-28371(319): Deprecate passing asyncio.Handles to
     run_in_executor.

   - bpo-28372(320): Fix asyncio to support formatting of non-python
     coroutines.

   - bpo-28399(321): Remove UNIX socket from FS before binding.  Patch
     by Коренберг Марк.

   - bpo-27972(322): Prohibit Tasks to await on themselves.

   - bpo-24142(323): Reading a corrupt config file left configparser in
     an invalid state.  Original patch by Florian Höch.

   - bpo-29581(324): ABCMeta.__new__ now accepts ‘**kwargs’, allowing
     abstract base classes to use keyword parameters in
     __init_subclass__.  Patch by Nate Soares.

   - bpo-25532(325): inspect.unwrap() will now only try to unwrap an
     object sys.getrecursionlimit() times, to protect against objects
     which create a new object on every attribute access.

   - bpo-30177(326): path.resolve(strict=False) no longer cuts the path
     after the first element not present in the filesystem.  Patch by
     Antoine Pietri.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31499

   (2) https://bugs.python.org/issue31482

   (3) https://bugs.python.org/issue28556

   (4) https://bugs.python.org/issue28556

   (5) https://bugs.python.org/issue31544

   (6) https://bugs.python.org/issue31234

   (7) https://bugs.python.org/issue31457

   (8) https://bugs.python.org/issue31431

   (9) https://bugs.python.org/issue31233

   (10) https://bugs.python.org/issue28638

   (11) https://bugs.python.org/issue31400

   (12) https://bugs.python.org/issue27629

   (13) https://bugs.python.org/issue28958

   (14) https://bugs.python.org/issue28182

   (15) https://bugs.python.org/issue27340

   (16) https://bugs.python.org/issue14191

   (17) https://bugs.python.org/issue31178

   (18) https://bugs.python.org/issue31350

   (19) https://bugs.python.org/issue31170

   (20) https://bugs.python.org/issue29136

   (21) https://bugs.python.org/issue1198569

   (22) https://bugs.python.org/issue31326

   (23) https://bugs.python.org/issue27144

   (24) https://bugs.python.org/issue31281

   (25) https://bugs.python.org/issue10746

   (26) https://www.python.org/dev/peps/pep-3118

   (27) https://bugs.python.org/issue27584

   (28) https://bugs.python.org/issue22536

   (29) https://bugs.python.org/issue29741

   (30) https://bugs.python.org/issue31249

   (31) https://bugs.python.org/issue31247

   (32) https://bugs.python.org/issue23835

   (33) https://bugs.python.org/issue31238

   (34) https://bugs.python.org/issue5001

   (35) https://bugs.python.org/issue31109

   (36) https://bugs.python.org/issue30102

   (37) https://bugs.python.org/issue18966

   (38) https://bugs.python.org/issue31183

   (39) https://bugs.python.org/issue5001

   (40) https://bugs.python.org/issue31185

   (41) https://bugs.python.org/issue31151

   (42) https://bugs.python.org/issue31072

   (43) https://bugs.python.org/issue24700

   (44) https://bugs.python.org/issue31135

   (45) https://bugs.python.org/issue31107

   (46) https://bugs.python.org/issue31080

   (47) https://bugs.python.org/issue30897

   (48) https://bugs.python.org/issue31061

   (49) https://bugs.python.org/issue30987

   (50) https://bugs.python.org/issue30522

   (51) https://bugs.python.org/issue30502

   (52) https://bugs.python.org/issue5288

   (53) https://bugs.python.org/issue30919

   (54) https://bugs.python.org/issue26732

   (55) https://bugs.python.org/issue29403

   (56) https://bugs.python.org/issue30961

   (57) https://bugs.python.org/issue19896

   (58) https://bugs.python.org/issue30946

   (59) https://bugs.python.org/issue25684

   (60) https://bugs.python.org/issue30886

   (61) https://bugs.python.org/issue29854

   (62) https://bugs.python.org/issue30794

   (63) https://bugs.python.org/issue30319

   (64) https://bugs.python.org/issue30828

   (65) https://bugs.python.org/issue30302

   (66) https://bugs.python.org/issue30807

   (67) https://bugs.python.org/issue30441

   (68) https://bugs.python.org/issue29585

   (69) https://bugs.python.org/issue29293

   (70) https://bugs.python.org/issue30532

   (71) https://bugs.python.org/issue30596

   (72) https://bugs.python.org/issue9146

   (73) https://bugs.python.org/issue29169

   (74) https://bugs.python.org/issue30119

   (75) https://bugs.python.org/issue30879

   (76) https://bugs.python.org/issue30746

   (77) https://bugs.python.org/issue30664

   (78) https://bugs.python.org/issue21071

   (79) https://bugs.python.org/issue29212

   (80) https://bugs.python.org/issue29755

   (81) https://bugs.python.org/issue30616

   (82) https://bugs.python.org/issue30038

   (83) https://bugs.python.org/issue23894

   (84) https://bugs.python.org/issue24744

   (85) https://bugs.python.org/issue24484

   (86) https://bugs.python.org/issue30589

   (87) https://bugs.python.org/issue28994

   (88) https://bugs.python.org/issue30508

   (89) https://bugs.python.org/issue30645

   (90) https://bugs.python.org/issue11822

   (91) https://bugs.python.org/issue30624

   (92) https://bugs.python.org/issue30595

   (93) https://bugs.python.org/issue28556

   (94) https://bugs.python.org/issue30605

   (95) https://bugs.python.org/issue29870

   (96) https://bugs.python.org/issue29743

   (97) https://bugs.python.org/issue27585

   (98) https://bugs.python.org/issue30014

   (99) https://bugs.python.org/issue30418

   (100) https://bugs.python.org/issue30463

   (101) https://bugs.python.org/issue30520

   (102) https://bugs.python.org/issue30557

   (103) https://bugs.python.org/issue30526

   (104) https://bugs.python.org/issue30245

   (105) https://bugs.python.org/issue30378

   (106) https://bugs.python.org/issue16500

   (107) https://bugs.python.org/issue30470

   (108) https://bugs.python.org/issue30414

   (109) https://bugs.python.org/issue30003

   (110) https://bugs.python.org/issue30149

   (111) https://bugs.python.org/issue30436

   (112) https://bugs.python.org/issue30301

   (113) https://bugs.python.org/issue30375

   (114) https://bugs.python.org/issue30329

   (115) https://bugs.python.org/issue29196

   (116) https://bugs.python.org/issue9850

   (117) https://bugs.python.org/issue30299

   (118) https://bugs.python.org/issue30048

   (119) https://bugs.python.org/issue30266

   (120) https://bugs.python.org/issue25958

   (121) https://bugs.python.org/issue30340

   (122) https://bugs.python.org/issue30298

   (123) https://bugs.python.org/issue30285

   (124) https://bugs.python.org/issue29990

   (125) https://bugs.python.org/issue29979

   (126) https://bugs.python.org/issue30243

   (127) https://bugs.python.org/issue30215

   (128) https://bugs.python.org/issue30185

   (129) https://bugs.python.org/issue30103

   (130) https://bugs.python.org/issue28556

   (131) https://bugs.python.org/issue30205

   (132) https://bugs.python.org/issue30228

   (133) https://bugs.python.org/issue30190

   (134) https://bugs.python.org/issue30101

   (135) https://bugs.python.org/issue29822

   (136) https://bugs.python.org/issue29960

   (137) https://bugs.python.org/issue30070

   (138) https://bugs.python.org/issue22352

   (139) https://bugs.python.org/issue30061

   (140) https://bugs.python.org/issue30218

   (141) https://bugs.python.org/issue10076

   (142) https://bugs.python.org/issue30068

   (143) https://bugs.python.org/issue29694

   (144) https://bugs.python.org/issue29692

   (145) https://bugs.python.org/issue26187

   (146) https://bugs.python.org/issue9303

   (147) https://bugs.python.org/issue30017

   (148) https://bugs.python.org/issue29998

   (149) https://bugs.python.org/issue29995

   (150) https://bugs.python.org/issue29962

   (151) https://bugs.python.org/issue29649

   (152) https://bugs.python.org/issue29654

   (153) https://bugs.python.org/issue29931

   (154) https://bugs.python.org/issue29953

   (155) https://bugs.python.org/issue29942

   (156) https://bugs.python.org/issue10030

   (157) https://bugs.python.org/issue29204

   (158) https://bugs.python.org/issue27863

   (159) https://bugs.python.org/issue25996

   (160) https://bugs.python.org/issue28699

   (161) https://bugs.python.org/issue23890

   (162) https://bugs.python.org/issue29901

   (163) https://bugs.python.org/issue25803

   (164) https://bugs.python.org/issue29861

   (165) https://bugs.python.org/issue19930

   (166) https://bugs.python.org/issue29884

   (167) https://bugs.python.org/issue25455

   (168) https://bugs.python.org/issue29800

   (169) https://bugs.python.org/issue8256

   (170) https://bugs.python.org/issue28692

   (171) https://bugs.python.org/issue26121

   (172) https://bugs.python.org/issue29619

   (173) https://bugs.python.org/issue28298

   (174) https://bugs.python.org/issue29645

   (175) https://bugs.python.org/issue28231

   (176) https://bugs.python.org/issue26915

   (177) https://bugs.python.org/issue28682

   (178) https://bugs.python.org/issue29728

   (179) https://bugs.python.org/issue29623

   (180) https://bugs.python.org/issue9303

   (181) https://bugs.python.org/issue28963

   (182) https://bugs.python.org/issue29704

   (183) https://bugs.python.org/issue29271

   (184) https://bugs.python.org/issue29703

   (185) https://bugs.python.org/issue29615

   (186) https://bugs.python.org/issue7769

   (187) https://bugs.python.org/issue29376

   (188) https://bugs.python.org/issue28624

   (189) https://bugs.python.org/issue28518

   (190) https://bugs.python.org/issue29742

   (191) https://bugs.python.org/issue16285

   (192) https://bugs.python.org/issue29532

   (193) https://bugs.python.org/issue29110

   (194) https://bugs.python.org/issue22807

   (195) https://bugs.python.org/issue29576

   (196) https://bugs.python.org/issue29534

   (197) https://bugs.python.org/issue10379

   (198) https://bugs.python.org/issue29851

   (199) https://bugs.python.org/issue28556

   (200) https://bugs.python.org/issue29100

   (201) https://bugs.python.org/issue29416

   (202) https://bugs.python.org/issue29444

   (203) https://bugs.python.org/issue29377

   (204) https://bugs.python.org/issue29218

   (205) https://bugs.python.org/issue29368

   (206) https://bugs.python.org/issue29338

   (207) https://bugs.python.org/issue29335

   (208) https://bugs.python.org/issue29290

   (209) https://bugs.python.org/issue28735

   (210) https://bugs.python.org/issue29197

   (211) https://bugs.python.org/issue29210

   (212) https://bugs.python.org/issue29219

   (213) https://bugs.python.org/issue29192

   (214) https://bugs.python.org/issue29193

   (215) https://bugs.python.org/issue29195

   (216) https://bugs.python.org/issue28969

   (217) https://bugs.python.org/issue20804

   (218) https://bugs.python.org/issue29142

   (219) https://bugs.python.org/issue28961

   (220) https://bugs.python.org/issue15812

   (221) https://bugs.python.org/issue28985

   (222) https://bugs.python.org/issue29079

   (223) https://bugs.python.org/issue13051

   (224) https://bugs.python.org/issue9770

   (225) https://bugs.python.org/issue28427

   (226) https://bugs.python.org/issue28923

   (227) https://bugs.python.org/issue28871

   (228) https://bugs.python.org/issue19542

   (229) https://bugs.python.org/issue20191

   (230) https://bugs.python.org/issue16255

   (231) https://bugs.python.org/issue28779

   (232) https://bugs.python.org/issue26937

   (233) https://bugs.python.org/issue28847

   (234) https://bugs.python.org/issue27030

   (235) https://bugs.python.org/issue28835

   (236) https://bugs.python.org/issue27172

   (237) https://bugs.python.org/issue28740

   (238) https://bugs.python.org/issue26273

   (239) https://bugs.python.org/issue28752

   (240) https://bugs.python.org/issue28727

   (241) https://bugs.python.org/issue18383

   (242) https://bugs.python.org/issue20572

   (243) https://bugs.python.org/issue25659

   (244) https://bugs.python.org/issue28548

   (245) https://bugs.python.org/issue19717

   (246) https://bugs.python.org/issue28563

   (247) https://bugs.python.org/issue28387

   (248) https://bugs.python.org/issue27517

   (249) https://bugs.python.org/issue28549

   (250) https://bugs.python.org/issue28449

   (251) https://bugs.python.org/issue23262

   (252) https://bugs.python.org/issue24241

   (253) https://bugs.python.org/issue27939

   (254) https://bugs.python.org/issue28255

   (255) https://bugs.python.org/issue28255

   (256) https://bugs.python.org/issue20491

   (257) https://bugs.python.org/issue28353

   (258) https://bugs.python.org/issue28430

   (259) https://bugs.python.org/issue27025

   (260) https://bugs.python.org/issue25464

   (261) https://bugs.python.org/issue28488

   (262) https://bugs.python.org/issue25953

   (263) https://bugs.python.org/issue28469

   (264) https://bugs.python.org/issue28115

   (265) https://bugs.python.org/issue18219

   (266) https://bugs.python.org/issue28448

   (267) https://bugs.python.org/issue23214

   (268) https://bugs.python.org/issue28480

   (269) https://bugs.python.org/issue28240

   (270) https://bugs.python.org/issue28240

   (271) https://bugs.python.org/issue28240

   (272) https://github.com/pypa/setuptools/issues/100

   (273) https://bugs.python.org/issue24452

   (274) https://bugs.python.org/issue20766

   (275) https://bugs.python.org/issue27998

   (276) https://bugs.python.org/issue28317

   (277) https://bugs.python.org/issue28380

   (278) https://bugs.python.org/issue28229

   (279) https://bugs.python.org/issue28321

   (280) https://bugs.python.org/issue28225

   (281) https://bugs.python.org/issue28227

   (282) https://bugs.python.org/issue28332

   (283) https://bugs.python.org/issue27358

   (284) https://bugs.python.org/issue28257

   (285) https://bugs.python.org/issue28322

   (286) https://bugs.python.org/issue28228

   (287) https://bugs.python.org/issue28226

   (288) https://bugs.python.org/issue28314

   (289) https://bugs.python.org/issue28148

   (290) https://bugs.python.org/issue28253

   (291) https://bugs.python.org/issue28275

   (292) https://bugs.python.org/issue27897

   (293) https://bugs.python.org/issue18844

   (294) https://bugs.python.org/issue18893

   (295) https://bugs.python.org/issue27611

   (296) https://bugs.python.org/issue27348

   (297) https://bugs.python.org/issue25651

   (298) https://bugs.python.org/issue27778

   (299) https://bugs.python.org/issue28200

   (300) https://bugs.python.org/issue25400

   (301) https://bugs.python.org/issue27932

   (302) https://bugs.python.org/issue28075

   (303) https://bugs.python.org/issue22493

   (304) https://bugs.python.org/issue25270

   (305) https://bugs.python.org/issue28181

   (306) https://bugs.python.org/issue25895

   (307) https://bugs.python.org/issue28114

   (308) https://bugs.python.org/issue27599

   (309) https://bugs.python.org/issue27906

   (310) https://bugs.python.org/issue28174

   (311) https://bugs.python.org/issue26654

   (312) https://bugs.python.org/issue26909

   (313) https://bugs.python.org/issue28176

   (314) https://bugs.python.org/issue27759

   (315) https://bugs.python.org/issue28325

   (316) https://bugs.python.org/issue28368

   (317) https://bugs.python.org/issue28369

   (318) https://bugs.python.org/issue28370

   (319) https://bugs.python.org/issue28371

   (320) https://bugs.python.org/issue28372

   (321) https://bugs.python.org/issue28399

   (322) https://bugs.python.org/issue27972

   (323) https://bugs.python.org/issue24142

   (324) https://bugs.python.org/issue29581

   (325) https://bugs.python.org/issue25532

   (326) https://bugs.python.org/issue30177


File: python.info,  Node: Documentation<35>,  Next: Tests<32>,  Prev: Library<41>,  Up: Python 3 7 0 alpha 1

1.19.42.4 Documentation
.......................

   - bpo-31294(1): Fix incomplete code snippet in the
     ZeroMQSocketListener and ZeroMQSocketHandler examples and adapt
     them to Python 3.

   - bpo-21649(2): Add RFC 7525 and Mozilla server side TLS links to SSL
     documentation.

   - bpo-31128(3): Allow the pydoc server to bind to arbitrary
     hostnames.

   - bpo-30803(4): Clarify doc on truth value testing.  Original patch
     by Peter Thomassen.

   - bpo-30176(5): Add missing attribute related constants in curses
     documentation.

   - bpo-30052(6): the link targets for *note bytes(): 172. and *note
     bytearray(): 173. are now their respective type definitions, rather
     than the corresponding builtin function entries.  Use *note bytes:
     11f2. and *note bytearray: 11f3. to reference the latter.  In order
     to ensure this and future cross-reference updates are applied
     automatically, the daily documentation builds now disable the
     default output caching features in Sphinx.

   - bpo-26985(7): Add missing info of code object in inspect
     documentation.

   - bpo-19824(8): Improve the documentation for, and links to, template
     strings by emphasizing their utility for internationalization, and
     by clarifying some usage constraints.  (See also: bpo-20314(9),
     bpo-12518(10))

   - bpo-28929(11): Link the documentation to its source file on GitHub.

   - bpo-25008(12): Document smtpd.py as effectively deprecated and add
     a pointer to aiosmtpd, a third-party asyncio-based replacement.

   - bpo-26355(13): Add canonical header link on each page to
     corresponding major version of the documentation.  Patch by
     Matthias Bussonnier.

   - bpo-29349(14): Fix Python 2 syntax in code for building the
     documentation.

   - bpo-23722(15): The data model reference and the porting section in
     the 3.6 What’s New guide now cover the additional ‘__classcell__’
     handling needed for custom metaclasses to fully support PEP 487(16)
     and zero-argument ‘super()’.

   - bpo-28513(17): Documented command-line interface of zipfile.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31294

   (2) https://bugs.python.org/issue21649

   (3) https://bugs.python.org/issue31128

   (4) https://bugs.python.org/issue30803

   (5) https://bugs.python.org/issue30176

   (6) https://bugs.python.org/issue30052

   (7) https://bugs.python.org/issue26985

   (8) https://bugs.python.org/issue19824

   (9) https://bugs.python.org/issue20314

   (10) https://bugs.python.org/issue12518

   (11) https://bugs.python.org/issue28929

   (12) https://bugs.python.org/issue25008

   (13) https://bugs.python.org/issue26355

   (14) https://bugs.python.org/issue29349

   (15) https://bugs.python.org/issue23722

   (16) https://www.python.org/dev/peps/pep-0487

   (17) https://bugs.python.org/issue28513


File: python.info,  Node: Tests<32>,  Next: Build<32>,  Prev: Documentation<35>,  Up: Python 3 7 0 alpha 1

1.19.42.5 Tests
...............

   - bpo-29639(1): test.support.HOST is now “localhost”, a new HOSTv4
     constant has been added for your ‘127.0.0.1’ needs, similar to the
     existing HOSTv6 constant.

   - bpo-31320(2): Silence traceback in test_ssl

   - bpo-31346(3): Prefer PROTOCOL_TLS_CLIENT and PROTOCOL_TLS_SERVER
     protocols for SSLContext.

   - bpo-25674(4): Remove sha256.tbs-internet.com ssl test

   - bpo-30715(5): Address ALPN callback changes for OpenSSL 1.1.0f.
     The latest version behaves like OpenSSL 1.0.2 and no longer aborts
     handshake.

   - bpo-30822(6): regrtest: Exclude tzdata from regrtest –all.  When
     running the test suite using –use=all / -u all, exclude tzdata
     since it makes test_datetime too slow (15-20 min on some buildbots)
     which then times out on some buildbots.  Fix also regrtest command
     line parser to allow passing -u extralargefile to run
     test_zipfile64.

   - bpo-30695(7): Add the ‘set_nomemory(start, stop)’ and
     ‘remove_mem_hooks()’ functions to the _testcapi module.

   - bpo-30357(8): test_thread: setUp() now uses
     support.threading_setup() and support.threading_cleanup() to wait
     until threads complete to avoid random side effects on following
     tests.  Initial patch written by Grzegorz Grzywacz.

   - bpo-30197(9): Enhanced functions swap_attr() and swap_item() in the
     test.support module.  They now work when delete replaced attribute
     or item inside the with statement.  The old value of the attribute
     or item (or None if it doesn’t exist) now will be assigned to the
     target of the “as” clause, if there is one.

   - bpo-24932(10): Use proper command line parsing in _testembed

   - bpo-28950(11): Disallow -j0 to be combined with -T/-l in regrtest
     command line arguments.

   - bpo-28683(12): Fix the tests that bind() a unix socket and raise
     PermissionError on Android for a non-root user.

   - bpo-26936(13): Fix the test_socket failures on Android -
     getservbyname(), getservbyport() and getaddrinfo() are broken on
     some Android API levels.

   - bpo-28666(14): Now test.support.rmtree is able to remove unwritable
     or unreadable directories.

   - bpo-23839(15): Various caches now are cleared before running every
     test file.

   - bpo-26944(16): Fix test_posix for Android where ‘id -G’ is entirely
     wrong or missing the effective gid.

   - bpo-28409(17): regrtest: fix the parser of command line arguments.

   - bpo-28217(18): Adds _testconsole module to test console input.

   - bpo-26939(19): Add the support.setswitchinterval() function to fix
     test_functools hanging on the Android armv7 qemu emulator.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29639

   (2) https://bugs.python.org/issue31320

   (3) https://bugs.python.org/issue31346

   (4) https://bugs.python.org/issue25674

   (5) https://bugs.python.org/issue30715

   (6) https://bugs.python.org/issue30822

   (7) https://bugs.python.org/issue30695

   (8) https://bugs.python.org/issue30357

   (9) https://bugs.python.org/issue30197

   (10) https://bugs.python.org/issue24932

   (11) https://bugs.python.org/issue28950

   (12) https://bugs.python.org/issue28683

   (13) https://bugs.python.org/issue26936

   (14) https://bugs.python.org/issue28666

   (15) https://bugs.python.org/issue23839

   (16) https://bugs.python.org/issue26944

   (17) https://bugs.python.org/issue28409

   (18) https://bugs.python.org/issue28217

   (19) https://bugs.python.org/issue26939


File: python.info,  Node: Build<32>,  Next: Windows<32>,  Prev: Tests<32>,  Up: Python 3 7 0 alpha 1

1.19.42.6 Build
...............

   - bpo-31354(1): Allow –with-lto to be used on all builds, not just
     ‘make profile-opt’.

   - bpo-31370(2): Remove support for building –without-threads.  This
     option is not really useful anymore in the 21st century.  Removing
     lots of conditional paths allows us to simplify the code base,
     including in difficult to maintain low-level internal code.

   - bpo-31341(3): Per PEP 11(4), support for the IRIX operating system
     was removed.

   - bpo-30854(5): Fix compile error when compiling –without-threads.
     Patch by Masayuki Yamamoto.

   - bpo-30687(6): Locate msbuild.exe on Windows when building rather
     than vcvarsall.bat

   - bpo-20210(7): Support the `disabled' marker in Setup files.
     Extension modules listed after this marker are not built at all,
     neither by the Makefile nor by setup.py.

   - bpo-29941(8): Add ‘--with-assertions’ configure flag to explicitly
     enable C ‘assert()’ checks.  Defaults to off.  ‘--with-pydebug’
     implies ‘--with-assertions’.

   - bpo-28787(9): Fix out-of-tree builds of Python when configured with
     ‘--with--dtrace’.

   - bpo-29243(10): Prevent unnecessary rebuilding of Python during
     ‘make test’, ‘make install’ and some other make targets when
     configured with ‘--enable-optimizations’.

   - bpo-23404(11): Don’t regenerate generated files based on file
     modification time anymore: the action is now explicit.  Replace
     ‘make touch’ with ‘make regen-all’.

   - bpo-29643(12): Fix ‘--enable-optimization’ didn’t work.

   - bpo-27593(13): sys.version and the platform module python_build(),
     python_branch(), and python_revision() functions now use git
     information rather than hg when building from a repo.

   - bpo-29572(14): Update Windows build and OS X installers to use
     OpenSSL 1.0.2k.

   - bpo-27659(15): Prohibit implicit C function declarations: use
     ‘-Werror=implicit-function-declaration’ when possible (GCC and
     Clang, but it depends on the compiler version).  Patch written by
     Chi Hsuan Yen.

   - bpo-29384(16): Remove old Be OS helper scripts.

   - bpo-26851(17): Set Android compilation and link flags.

   - bpo-28768(18): Fix implicit declaration of function _setmode.
     Patch by Masayuki Yamamoto

   - bpo-29080(19): Removes hard dependency on hg.exe from
     PCBuild/build.bat

   - bpo-23903(20): Added missed names to PC/python3.def.

   - bpo-28762(21): lockf() is available on Android API level 24, but
     the F_LOCK macro is not defined in android-ndk-r13.

   - bpo-28538(22): Fix the compilation error that occurs because
     if_nameindex() is available on Android API level 24, but the
     if_nameindex structure is not defined.

   - bpo-20211(23): Do not add the directory for installing C header
     files and the directory for installing object code libraries to the
     cross compilation search paths.  Original patch by Thomas
     Petazzoni.

   - bpo-28849(24): Do not define sys.implementation._multiarch on
     Android.

   - bpo-10656(25): Fix out-of-tree building on AIX. Patch by Tristan
     Carel and Michael Haubenwallner.

   - bpo-26359(26): Rename –with-optimiations to –enable-optimizations.

   - bpo-28444(27): Fix missing extensions modules when cross compiling.

   - bpo-28208(28): Update Windows build and OS X installers to use
     SQLite 3.14.2.

   - bpo-28248(29): Update Windows build and OS X installers to use
     OpenSSL 1.0.2j.

   - bpo-21124(30): Fix building the _struct module on Cygwin by passing
     ‘NULL’ instead of ‘&PyType_Type’ to PyVarObject_HEAD_INIT. Patch by
     Masayuki Yamamoto.

   - bpo-13756(31): Fix building extensions modules on Cygwin.  Patch by
     Roumen Petrov, based on original patch by Jason Tishler.

   - bpo-21085(32): Add configure check for siginfo_t.si_band, which
     Cygwin does not provide.  Patch by Masayuki Yamamoto with review
     and rebase by Erik Bray.

   - bpo-28258(33): Fixed build with Estonian locale (python-config and
     distclean targets in Makefile).  Patch by Arfrever Frehtes
     Taifersar Arahesis.

   - bpo-26661(34): setup.py now detects system libffi with multiarch
     wrapper.

   - bpo-27979(35): A full copy of libffi is no longer bundled for use
     when building _ctypes on non-OSX UNIX platforms.  An installed copy
     of libffi is now required when building _ctypes on such platforms.

   - bpo-15819(36): Remove redundant include search directory option for
     building outside the source tree.

   - bpo-28676(37): Prevent missing ‘getentropy’ declaration warning on
     macOS. Patch by Gareth Rees.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31354

   (2) https://bugs.python.org/issue31370

   (3) https://bugs.python.org/issue31341

   (4) https://www.python.org/dev/peps/pep-0011

   (5) https://bugs.python.org/issue30854

   (6) https://bugs.python.org/issue30687

   (7) https://bugs.python.org/issue20210

   (8) https://bugs.python.org/issue29941

   (9) https://bugs.python.org/issue28787

   (10) https://bugs.python.org/issue29243

   (11) https://bugs.python.org/issue23404

   (12) https://bugs.python.org/issue29643

   (13) https://bugs.python.org/issue27593

   (14) https://bugs.python.org/issue29572

   (15) https://bugs.python.org/issue27659

   (16) https://bugs.python.org/issue29384

   (17) https://bugs.python.org/issue26851

   (18) https://bugs.python.org/issue28768

   (19) https://bugs.python.org/issue29080

   (20) https://bugs.python.org/issue23903

   (21) https://bugs.python.org/issue28762

   (22) https://bugs.python.org/issue28538

   (23) https://bugs.python.org/issue20211

   (24) https://bugs.python.org/issue28849

   (25) https://bugs.python.org/issue10656

   (26) https://bugs.python.org/issue26359

   (27) https://bugs.python.org/issue28444

   (28) https://bugs.python.org/issue28208

   (29) https://bugs.python.org/issue28248

   (30) https://bugs.python.org/issue21124

   (31) https://bugs.python.org/issue13756

   (32) https://bugs.python.org/issue21085

   (33) https://bugs.python.org/issue28258

   (34) https://bugs.python.org/issue26661

   (35) https://bugs.python.org/issue27979

   (36) https://bugs.python.org/issue15819

   (37) https://bugs.python.org/issue28676


File: python.info,  Node: Windows<32>,  Next: IDLE<32>,  Prev: Build<32>,  Up: Python 3 7 0 alpha 1

1.19.42.7 Windows
.................

   - bpo-31392(1): Update Windows build to use OpenSSL 1.1.0f

   - bpo-30389(2): Adds detection of Visual Studio 2017 to distutils on
     Windows.

   - bpo-31358(3): zlib is no longer bundled in the CPython source,
     instead it is downloaded on demand just like bz2, lzma, OpenSSL,
     Tcl/Tk, and SQLite.

   - bpo-31340(4): Change to building with MSVC v141 (included with
     Visual Studio 2017)

   - bpo-30581(5): os.cpu_count() now returns the correct number of
     processors on Windows when the number of logical processors is
     greater than 64.

   - bpo-30916(6): Pre-build OpenSSL, Tcl and Tk and include the
     binaries in the build.

   - bpo-30731(7): Add a missing xmlns to python.manifest so that it
     matches the schema.

   - bpo-30291(8): Allow requiring 64-bit interpreters from py.exe using
     -64 suffix.  Contributed by Steve (Gadget) Barnes.

   - bpo-30362(9): Adds list options (-0, -0p) to py.exe launcher.
     Contributed by Steve Barnes.

   - bpo-23451(10): Fix socket deprecation warnings in socketmodule.c.
     Patch by Segev Finer.

   - bpo-30450(11): The build process on Windows no longer depends on
     Subversion, instead pulling external code from GitHub via a Python
     script.  If Python 3.6 is not found on the system (via ‘py -3.6’),
     NuGet is used to download a copy of 32-bit Python.

   - bpo-29579(12): Removes readme.txt from the installer.

   - bpo-25778(13): winreg does not truncate string correctly (Patch by
     Eryk Sun)

   - bpo-28896(14): Deprecate WindowsRegistryFinder and disable it by
     default

   - bpo-28522(15): Fixes mishandled buffer reallocation in getpathp.c

   - bpo-28402(16): Adds signed catalog files for stdlib on Windows.

   - bpo-28333(17): Enables Unicode for ps1/ps2 and input() prompts.
     (Patch by Eryk Sun)

   - bpo-28251(18): Improvements to help manuals on Windows.

   - bpo-28110(19): launcher.msi has different product codes between
     32-bit and 64-bit

   - bpo-28161(20): Opening CON for write access fails

   - bpo-28162(21): WindowsConsoleIO readall() fails if first line
     starts with Ctrl+Z

   - bpo-28163(22): WindowsConsoleIO fileno() passes wrong flags to
     _open_osfhandle

   - bpo-28164(23): _PyIO_get_console_type fails for various paths

   - bpo-28137(24): Renames Windows path file to ._pth

   - bpo-28138(25): Windows ._pth file should allow import site

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31392

   (2) https://bugs.python.org/issue30389

   (3) https://bugs.python.org/issue31358

   (4) https://bugs.python.org/issue31340

   (5) https://bugs.python.org/issue30581

   (6) https://bugs.python.org/issue30916

   (7) https://bugs.python.org/issue30731

   (8) https://bugs.python.org/issue30291

   (9) https://bugs.python.org/issue30362

   (10) https://bugs.python.org/issue23451

   (11) https://bugs.python.org/issue30450

   (12) https://bugs.python.org/issue29579

   (13) https://bugs.python.org/issue25778

   (14) https://bugs.python.org/issue28896

   (15) https://bugs.python.org/issue28522

   (16) https://bugs.python.org/issue28402

   (17) https://bugs.python.org/issue28333

   (18) https://bugs.python.org/issue28251

   (19) https://bugs.python.org/issue28110

   (20) https://bugs.python.org/issue28161

   (21) https://bugs.python.org/issue28162

   (22) https://bugs.python.org/issue28163

   (23) https://bugs.python.org/issue28164

   (24) https://bugs.python.org/issue28137

   (25) https://bugs.python.org/issue28138


File: python.info,  Node: IDLE<32>,  Next: Tools/Demos<17>,  Prev: Windows<32>,  Up: Python 3 7 0 alpha 1

1.19.42.8 IDLE
..............

   - bpo-31493(1): IDLE code context – fix code update and font update
     timers.  Canceling timers prevents a warning message when test_idle
     completes.

   - bpo-31488(2): IDLE - Update non-key options in former extension
     classes.  When applying configdialog changes, call .reload for each
     feature class.  Change ParenMatch so updated options affect
     existing instances attached to existing editor windows.

   - bpo-31477(3): IDLE - Improve rstrip entry in doc.  Strip trailing
     whitespace strips more than blank spaces.  Multiline string
     literals are not skipped.

   - bpo-31480(4): IDLE - make tests pass with zzdummy extension
     disabled by default.

   - bpo-31421(5): Document how IDLE runs tkinter programs.  IDLE calls
     tcl/tk update in the background in order to make live interaction
     and experimentation with tkinter applications much easier.

   - bpo-31414(6): IDLE – fix tk entry box tests by deleting first.
     Adding to an int entry is not the same as deleting and inserting
     because int(‘’) will fail.

   - bpo-31051(7): Rearrange IDLE configdialog GenPage into Window,
     Editor, and Help sections.

   - bpo-30617(8): IDLE - Add docstrings and tests for outwin subclass
     of editor.  Move some data and functions from the class to module
     level.  Patch by Cheryl Sabella.

   - bpo-31287(9): IDLE - Do not modify tkinter.message in
     test_configdialog.

   - bpo-27099(10): Convert IDLE’s built-in ‘extensions’ to regular
     features.  About 10 IDLE features were implemented as supposedly
     optional extensions.  Their different behavior could be confusing
     or worse for users and not good for maintenance.  Hence the
     conversion.  The main difference for users is that user
     configurable key bindings for builtin features are now handled
     uniformly.  Now, editing a binding in a keyset only affects its
     value in the keyset.  All bindings are defined together in the
     system-specific default keysets in config-extensions.def.  All
     custom keysets are saved as a whole in config-extension.cfg.  All
     take effect as soon as one clicks Apply or Ok.  The affected events
     are ‘<<force-open-completions>>’, ‘<<expand-word>>’,
     ‘<<force-open-calltip>>’, ‘<<flash-paren>>’,
     ‘<<format-paragraph>>’, ‘<<run-module>>’, ‘<<check-module>>’, and
     ‘<<zoom-height>>’.  Any (global) customizations made before 3.6.3
     will not affect their keyset-specific customization after 3.6.3.
     and vice versa.  Initial patch by Charles Wohlganger.

   - bpo-31206(11): IDLE: Factor HighPage(Frame) class from
     ConfigDialog.  Patch by Cheryl Sabella.

   - bpo-31001(12): Add tests for configdialog highlight tab.  Patch by
     Cheryl Sabella.

   - bpo-31205(13): IDLE: Factor KeysPage(Frame) class from
     ConfigDialog.  The slightly modified tests continue to pass.  Patch
     by Cheryl Sabella.

   - bpo-31130(14): IDLE – stop leaks in test_configdialog.  Initial
     patch by Victor Stinner.

   - bpo-31002(15): Add tests for configdialog keys tab.  Patch by
     Cheryl Sabella.

   - bpo-19903(16): IDLE: Calltips use *note inspect.signature: 655.
     instead of *note inspect.getfullargspec: 657.  This improves
     calltips for builtins converted to use Argument Clinic.  Patch by
     Louie Lu.

   - bpo-31083(17): IDLE - Add an outline of a TabPage class in
     configdialog.  Update existing classes to match outline.  Initial
     patch by Cheryl Sabella.

   - bpo-31050(18): Factor GenPage(Frame) class from ConfigDialog.  The
     slightly modified tests continue to pass.  Patch by Cheryl Sabella.

   - bpo-31004(19): IDLE - Factor FontPage(Frame) class from
     ConfigDialog.  Slightly modified tests continue to pass.  Fix
     General tests.  Patch mostly by Cheryl Sabella.

   - bpo-30781(20): IDLE - Use ttk widgets in ConfigDialog.  Patches by
     Terry Jan Reedy and Cheryl Sabella.

   - bpo-31060(21): IDLE - Finish rearranging methods of ConfigDialog
     Grouping methods pertaining to each tab and the buttons will aid
     writing tests and improving the tabs and will enable splitting the
     groups into classes.

   - bpo-30853(22): IDLE – Factor a VarTrace class out of ConfigDialog.
     Instance tracers manages pairs consisting of a tk variable and a
     callback function.  When tracing is turned on, setting the variable
     calls the function.  Test coverage for the new class is 100%.

   - bpo-31003(23): IDLE: Add more tests for General tab.

   - bpo-30993(24): IDLE - Improve configdialog font page and tests.  In
     configdialog: Document causal pathways in create_font_tab
     docstring.  Simplify some attribute names.  Move set_samples calls
     to var_changed_font (idea from Cheryl Sabella).  Move related
     functions to positions after the create widgets function.  In
     test_configdialog: Fix test_font_set so not order dependent.  Fix
     renamed test_indent_scale so it tests the widget.  Adjust tests for
     movement of set_samples call.  Add tests for load functions.  Put
     all font tests in one class and tab indent tests in another.
     Except for two lines, these tests completely cover the related
     functions.

   - bpo-30981(25): IDLE – Add more configdialog font page tests.

   - bpo-28523(26): IDLE: replace ‘colour’ with ‘color’ in configdialog.

   - bpo-30917(27): Add tests for idlelib.config.IdleConf.  Increase
     coverage from 46% to 96%.  Patch by Louie Lu.

   - bpo-30934(28): Document coverage details for idlelib tests.  Add
     section to idlelib/idle-test/README.txt.  Include check that
     branches are taken both ways.  Exclude IDLE-specific code that does
     not run during unit tests.

   - bpo-30913(29): IDLE: Document ConfigDialog tk Vars, methods, and
     widgets in docstrings This will facilitate improving the dialog and
     splitting up the class.  Original patch by Cheryl Sabella.

   - bpo-30899(30): IDLE: Add tests for ConfigParser subclasses in
     config.  Patch by Louie Lu.

   - bpo-30881(31): IDLE: Add docstrings to browser.py.  Patch by Cheryl
     Sabella.

   - bpo-30851(32): IDLE: Remove unused variables in configdialog.  One
     is a duplicate, one is set but cannot be altered by users.  Patch
     by Cheryl Sabella.

   - bpo-30870(33): IDLE: In Settings dialog, select font with Up, Down
     keys as well as mouse.  Initial patch by Louie Lu.

   - bpo-8231(34): IDLE: call config.IdleConf.GetUserCfgDir only once.

   - bpo-30779(35): IDLE: Factor ConfigChanges class from configdialog,
     put in config; test.  * In config, put dump test code in a
     function; run it and unittest in ‘if __name__ == ‘__main__’.  * Add
     class config.ConfigChanges based on changes_class_v4.py on bpo
     issue.  * Add class test_config.ChangesTest, partly using
     configdialog_tests_v1.py.  * Revise configdialog to use
     ConfigChanges; see tracker msg297804.  * Revise test_configdialog
     to match configdialog changes.  * Remove configdialog functions
     unused or moved to ConfigChanges.  Cheryl Sabella contributed parts
     of the patch.

   - bpo-30777(36): IDLE: configdialog - Add docstrings and fix
     comments.  Patch by Cheryl Sabella.

   - bpo-30495(37): IDLE: Improve textview with docstrings, PEP8 names,
     and more tests.  Patch by Cheryl Sabella.

   - bpo-30723(38): IDLE: Make several improvements to parenmatch.  Add
     ‘parens’ style to highlight both opener and closer.  Make ‘default’
     style, which is not default, a synonym for ‘opener’.  Make
     time-delay work the same with all styles.  Add help for config
     dialog extensions tab, including help for parenmatch.  Add new
     tests.  Original patch by Charles Wohlganger.

   - bpo-30674(39): IDLE: add docstrings to grep module.  Patch by
     Cheryl Sabella

   - bpo-21519(40): IDLE’s basic custom key entry dialog now detects
     duplicates properly.  Original patch by Saimadhav Heblikar.

   - bpo-29910(41): IDLE no longer deletes a character after commenting
     out a region by a key shortcut.  Add ‘return 'break'’ for this and
     other potential conflicts between IDLE and default key bindings.

   - bpo-30728(42): Review and change idlelib.configdialog names.
     Lowercase method and attribute names.  Replace ‘colour’ with
     ‘color’, expand overly cryptic names, delete unneeded underscores.
     Replace ‘import *’ with specific imports.  Patches by Cheryl
     Sabella.

   - bpo-6739(43): IDLE: Verify user-entered key sequences by trying to
     bind them with tk.  Add tests for all 3 validation functions.
     Original patch by G Polo.  Tests added by Cheryl Sabella.

   - bpo-15786(44): Fix several problems with IDLE’s autocompletion box.
     The following should now work: clicking on selection box items;
     using the scrollbar; selecting an item by hitting Return.  Hangs on
     MacOSX should no longer happen.  Patch by Louie Lu.

   - bpo-25514(45): Add doc subsubsection about IDLE failure to start.
     Popup no-connection message directs users to this section.

   - bpo-30642(46): Fix reference leaks in IDLE tests.  Patches by Louie
     Lu and Terry Jan Reedy.

   - bpo-30495(47): Add docstrings for textview.py and use PEP8 names.
     Patches by Cheryl Sabella and Terry Jan Reedy.

   - bpo-30290(48): Help-about: use pep8 names and add tests.  Increase
     coverage to 100%.  Patches by Louie Lu, Cheryl Sabella, and Terry
     Jan Reedy.

   - bpo-30303(49): Add _utest option to textview; add new tests.
     Increase coverage to 100%.  Patches by Louie Lu and Terry Jan
     Reedy.

   - bpo-29071(50): IDLE colors f-string prefixes (but not invalid ur
     prefixes).

   - bpo-28572(51): Add 10% to coverage of IDLE’s test_configdialog.
     Update and augment description of the configuration system.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31493

   (2) https://bugs.python.org/issue31488

   (3) https://bugs.python.org/issue31477

   (4) https://bugs.python.org/issue31480

   (5) https://bugs.python.org/issue31421

   (6) https://bugs.python.org/issue31414

   (7) https://bugs.python.org/issue31051

   (8) https://bugs.python.org/issue30617

   (9) https://bugs.python.org/issue31287

   (10) https://bugs.python.org/issue27099

   (11) https://bugs.python.org/issue31206

   (12) https://bugs.python.org/issue31001

   (13) https://bugs.python.org/issue31205

   (14) https://bugs.python.org/issue31130

   (15) https://bugs.python.org/issue31002

   (16) https://bugs.python.org/issue19903

   (17) https://bugs.python.org/issue31083

   (18) https://bugs.python.org/issue31050

   (19) https://bugs.python.org/issue31004

   (20) https://bugs.python.org/issue30781

   (21) https://bugs.python.org/issue31060

   (22) https://bugs.python.org/issue30853

   (23) https://bugs.python.org/issue31003

   (24) https://bugs.python.org/issue30993

   (25) https://bugs.python.org/issue30981

   (26) https://bugs.python.org/issue28523

   (27) https://bugs.python.org/issue30917

   (28) https://bugs.python.org/issue30934

   (29) https://bugs.python.org/issue30913

   (30) https://bugs.python.org/issue30899

   (31) https://bugs.python.org/issue30881

   (32) https://bugs.python.org/issue30851

   (33) https://bugs.python.org/issue30870

   (34) https://bugs.python.org/issue8231

   (35) https://bugs.python.org/issue30779

   (36) https://bugs.python.org/issue30777

   (37) https://bugs.python.org/issue30495

   (38) https://bugs.python.org/issue30723

   (39) https://bugs.python.org/issue30674

   (40) https://bugs.python.org/issue21519

   (41) https://bugs.python.org/issue29910

   (42) https://bugs.python.org/issue30728

   (43) https://bugs.python.org/issue6739

   (44) https://bugs.python.org/issue15786

   (45) https://bugs.python.org/issue25514

   (46) https://bugs.python.org/issue30642

   (47) https://bugs.python.org/issue30495

   (48) https://bugs.python.org/issue30290

   (49) https://bugs.python.org/issue30303

   (50) https://bugs.python.org/issue29071

   (51) https://bugs.python.org/issue28572


File: python.info,  Node: Tools/Demos<17>,  Next: C API<27>,  Prev: IDLE<32>,  Up: Python 3 7 0 alpha 1

1.19.42.9 Tools/Demos
.....................

   - bpo-30983(1): gdb integration commands (py-bt, etc.)  work on
     optimized shared builds now, too.  PEP 523(2) introduced
     _PyEval_EvalFrameDefault which inlines PyEval_EvalFrameEx on
     non-debug shared builds.  This broke the ability to use py-bt,
     py-up, and a few other Python-specific gdb integrations.  The
     problem is fixed by only looking for _PyEval_EvalFrameDefault
     frames in python-gdb.py.  Original patch by Bruno “Polaco”
     Penteado.

   - bpo-29748(3): Added the slice index converter in Argument Clinic.

   - bpo-24037(4): Argument Clinic now uses the converter
     ‘bool(accept={int})’ rather than *note int: 204. for semantical
     booleans.  This avoids repeating the default value for Python and C
     and will help in converting to *note bool: 2bd. in future.

   - bpo-29367(5): python-gdb.py now supports also ‘method-wrapper’
     (‘wrapperobject’) objects.

   - bpo-28023(6): Fix python-gdb.py didn’t support new dict
     implementation.

   - bpo-15369(7): The pybench and pystone microbenchmark have been
     removed from Tools.  Please use the new Python benchmark suite
     ‘https://github.com/python/performance’ which is more reliable and
     includes a portable version of pybench working on Python 2 and
     Python 3.

   - bpo-28102(8): The zipfile module CLI now prints usage to stderr.
     Patch by Stephen J. Turnbull.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30983

   (2) https://www.python.org/dev/peps/pep-0523

   (3) https://bugs.python.org/issue29748

   (4) https://bugs.python.org/issue24037

   (5) https://bugs.python.org/issue29367

   (6) https://bugs.python.org/issue28023

   (7) https://bugs.python.org/issue15369

   (8) https://bugs.python.org/issue28102


File: python.info,  Node: C API<27>,  Prev: Tools/Demos<17>,  Up: Python 3 7 0 alpha 1

1.19.42.10 C API
................

   - bpo-31338(1): Added the ‘Py_UNREACHABLE()’ macro for code paths
     which are never expected to be reached.  This and a few other
     useful macros are now documented in the C API manual.

   - bpo-30832(2): Remove own implementation for thread-local storage.
     CPython has provided the own implementation for thread-local
     storage (TLS) on Python/thread.c, it’s used in the case which a
     platform has not supplied native TLS. However, currently all
     supported platforms (Windows and pthreads) have provided native TLS
     and defined the Py_HAVE_NATIVE_TLS macro with unconditional in any
     case.

   - bpo-30708(3): PyUnicode_AsWideCharString() now raises a ValueError
     if the second argument is NULL and the wchar_t* string contains
     null characters.

   - bpo-16500(4): Deprecate PyOS_AfterFork() and add PyOS_BeforeFork(),
     PyOS_AfterFork_Parent() and PyOS_AfterFork_Child().

   - bpo-6532(5): The type of results of PyThread_start_new_thread() and
     PyThread_get_thread_ident(), and the id parameter of
     PyThreadState_SetAsyncExc() changed from “long” to “unsigned long”.

   - bpo-27867(6): Function PySlice_GetIndicesEx() is deprecated and
     replaced with a macro if Py_LIMITED_API is not set or set to the
     value between 0x03050400 and 0x03060000 (not including) or
     0x03060100 or higher.  Added functions PySlice_Unpack() and
     PySlice_AdjustIndices().

   - bpo-29083(7): Fixed the declaration of some public API functions.
     PyArg_VaParse() and PyArg_VaParseTupleAndKeywords() were not
     available in limited API. PyArg_ValidateKeywordArguments(),
     PyArg_UnpackTuple() and Py_BuildValue() were not available in
     limited API of version < 3.3 when PY_SSIZE_T_CLEAN is defined.

   - bpo-28769(8): The result of PyUnicode_AsUTF8AndSize() and
     PyUnicode_AsUTF8() is now of type ‘const char *’ rather of ‘char
     *’.

   - bpo-29058(9): All stable API extensions added after Python 3.2 are
     now available only when Py_LIMITED_API is set to the PY_VERSION_HEX
     value of the minimum Python version supporting this API.

   - bpo-28822(10): The index parameters `start' and `end' of
     PyUnicode_FindChar() are now adjusted to behave like
     ‘str[start:end]’.

   - bpo-28808(11): PyUnicode_CompareWithASCIIString() now never raises
     exceptions.

   - bpo-28761(12): The fields name and doc of structures PyMemberDef,
     PyGetSetDef, PyStructSequence_Field, PyStructSequence_Desc, and
     wrapperbase are now of type ‘const char *’ rather of ‘char *’.

   - bpo-28748(13): Private variable _Py_PackageContext is now of type
     ‘const char *’ rather of ‘char *’.

   - bpo-19569(14): Compiler warnings are now emitted if use most of
     deprecated functions.

   - bpo-28426(15): Deprecated undocumented functions
     PyUnicode_AsEncodedObject(), PyUnicode_AsDecodedObject(),
     PyUnicode_AsDecodedUnicode() and PyUnicode_AsEncodedUnicode().

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31338

   (2) https://bugs.python.org/issue30832

   (3) https://bugs.python.org/issue30708

   (4) https://bugs.python.org/issue16500

   (5) https://bugs.python.org/issue6532

   (6) https://bugs.python.org/issue27867

   (7) https://bugs.python.org/issue29083

   (8) https://bugs.python.org/issue28769

   (9) https://bugs.python.org/issue29058

   (10) https://bugs.python.org/issue28822

   (11) https://bugs.python.org/issue28808

   (12) https://bugs.python.org/issue28761

   (13) https://bugs.python.org/issue28748

   (14) https://bugs.python.org/issue19569

   (15) https://bugs.python.org/issue28426


File: python.info,  Node: Python 3 6 6 final,  Next: Python 3 6 6 release candidate 1,  Prev: Python 3 7 0 alpha 1,  Up: Changelog

1.19.43 Python 3.6.6 final
--------------------------

`Release date: 2018-06-27'

There were no new changes in version 3.6.6.


File: python.info,  Node: Python 3 6 6 release candidate 1,  Next: Python 3 6 5 final,  Prev: Python 3 6 6 final,  Up: Changelog

1.19.44 Python 3.6.6 release candidate 1
----------------------------------------

`Release date: 2018-06-11'

* Menu:

* Core and Builtins: Core and Builtins<39>.
* Library: Library<42>.
* Documentation: Documentation<36>.
* Tests: Tests<33>.
* Build: Build<33>.
* Windows: Windows<33>.
* macOS: macOS<27>.
* IDLE: IDLE<33>.
* Tools/Demos: Tools/Demos<18>.
* C API: C API<28>.


File: python.info,  Node: Core and Builtins<39>,  Next: Library<42>,  Up: Python 3 6 6 release candidate 1

1.19.44.1 Core and Builtins
...........................

   - bpo-33786(1): Fix asynchronous generators to handle GeneratorExit
     in athrow() correctly

   - bpo-30654(2): Fixed reset of the SIGINT handler to SIG_DFL on
     interpreter shutdown even when there was a custom handler set
     previously.  Patch by Philipp Kerling.

   - bpo-33622(3): Fixed a leak when the garbage collector fails to add
     an object with the ‘__del__’ method or referenced by it into the
     *note gc.garbage: c12. list.  ‘PyGC_Collect()’ can now be called
     when an exception is set and preserves it.

   - bpo-31849(4): Fix signed/unsigned comparison warning in pyhash.c.

   - bpo-33391(5): Fix a leak in set_symmetric_difference().

   - bpo-28055(6): Fix unaligned accesses in siphash24().  Patch by Rolf
     Eike Beer.

   - bpo-33231(7): Fix potential memory leak in ‘normalizestring()’.

   - bpo-29922(8): Improved error messages in ‘async with’ when
     ‘__aenter__()’ or ‘__aexit__()’ return non-awaitable object.

   - bpo-33199(9): Fix ‘ma_version_tag’ in dict implementation is
     uninitialized when copying from key-sharing dict.

   - bpo-33041(10): Fixed jumping when the function contains an ‘async
     for’ loop.

   - bpo-32282(11): Fix an unnecessary ifdef in the include of
     VersionHelpers.h in socketmodule on Windows.

   - bpo-21983(12): Fix a crash in *note ctypes.cast(): 114b. in case
     the type argument is a ctypes structured data type.  Patch by Eryk
     Sun and Oren Milman.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33786

   (2) https://bugs.python.org/issue30654

   (3) https://bugs.python.org/issue33622

   (4) https://bugs.python.org/issue31849

   (5) https://bugs.python.org/issue33391

   (6) https://bugs.python.org/issue28055

   (7) https://bugs.python.org/issue33231

   (8) https://bugs.python.org/issue29922

   (9) https://bugs.python.org/issue33199

   (10) https://bugs.python.org/issue33041

   (11) https://bugs.python.org/issue32282

   (12) https://bugs.python.org/issue21983


File: python.info,  Node: Library<42>,  Next: Documentation<36>,  Prev: Core and Builtins<39>,  Up: Python 3 6 6 release candidate 1

1.19.44.2 Library
.................

   - bpo-30167(1): Prevent site.main() exception if PYTHONSTARTUP is
     set.  Patch by Steve Weber.

   - bpo-33812(2): Datetime instance d with non-None tzinfo, but with
     d.tzinfo.utcoffset(d) returning None is now treated as naive by the
     astimezone() method.

   - bpo-30805(3): Avoid race condition with debug logging

   - bpo-33767(4): The concatenation (‘+’) and repetition (‘*’) sequence
     operations now raise *note TypeError: 1fe. instead of *note
     SystemError: 6f2. when performed on *note mmap.mmap: 31c. objects.
     Patch by Zackery Spytz.

   - bpo-32684(5): Fix gather to propagate cancellation of itself even
     with return_exceptions.

   - bpo-33674(6): Fix a race condition in SSLProtocol.connection_made()
     of asyncio.sslproto: start immediately the handshake instead of
     using call_soon().  Previously, data_received() could be called
     before the handshake started, causing the handshake to hang or
     fail.

   - bpo-31647(7): Fixed bug where calling write_eof() on a
     _SelectorSocketTransport after it’s already closed raises
     AttributeError.

   - bpo-33672(8): Fix Task.__repr__ crash with Cython’s bogus
     coroutines

   - bpo-33469(9): Fix RuntimeError after closing loop that used
     run_in_executor

   - bpo-11874(10): Use a better regex when breaking usage into
     wrappable parts.  Avoids bogus assertion errors from custom metavar
     strings.

   - bpo-30877(11): Fixed a bug in the Python implementation of the JSON
     decoder that prevented the cache of parsed strings from clearing
     after finishing the decoding.  Based on patch by c-fos.

   - bpo-33548(12): tempfile._candidate_tempdir_list should consider
     common TEMP locations

   - bpo-33542(13): Prevent ‘uuid.get_node’ from using a DUID instead of
     a MAC on Windows.  Patch by Zvi Effron

   - bpo-26819(14): Fix race condition with
     ‘ReadTransport.resume_reading’ in Windows proactor event loop.

   - bpo-28556(15): Minor fixes in typing module: add annotations to
     ‘NamedTuple.__new__’, pass ‘*args’ and ‘**kwds’ in
     ‘Generic.__new__’.  Original PRs by Paulius Šarka and Chad
     Dombrova.

   - bpo-20087(16): Updated alias mapping with glibc 2.27 supported
     locales.

   - bpo-33422(17): Fix trailing quotation marks getting deleted when
     looking up byte/string literals on pydoc.  Patch by Andrés Delfino.

   - bpo-33197(18): Update error message when constructing invalid
     inspect.Parameters Patch by Dong-hee Na.

   - bpo-33383(19): Fixed crash in the get() method of the *note
     dbm.ndbm: 34. database object when it is called with a single
     argument.

   - bpo-33329(20): Fix multiprocessing regression on newer glibcs

   - bpo-991266(21): Fix quoting of the ‘Comment’ attribute of *note
     http.cookies.SimpleCookie: 116e.

   - bpo-33131(22): Upgrade bundled version of pip to 10.0.1.

   - bpo-33308(23): Fixed a crash in the *note parser: c7. module when
     converting an ST object to a tree of tuples or lists with
     ‘line_info=False’ and ‘col_info=True’.

   - bpo-33263(24): Fix FD leak in ‘_SelectorSocketTransport’ Patch by
     Vlad Starostin.

   - bpo-33256(25): Fix display of ‘<module>’ call in the html produced
     by ‘cgitb.html()’.  Patch by Stéphane Blondon.

   - bpo-33203(26): ‘random.Random.choice()’ now raises ‘IndexError’ for
     empty sequences consistently even when called from subclasses
     without a ‘getrandbits()’ implementation.

   - bpo-33224(27): Update difflib.mdiff() for PEP 479(28).  Convert an
     uncaught StopIteration in a generator into a return-statement.

   - bpo-33209(29): End framing at the end of C implementation of *note
     pickle.Pickler.dump(): 1172.

   - bpo-32861(30): The urllib.robotparser’s ‘__str__’ representation
     now includes wildcard entries and the “Crawl-delay” and
     “Request-rate” fields.  Patch by Michael Lazar.

   - bpo-33096(31): Allow ttk.Treeview.insert to insert iid that has a
     false boolean value.  Note iid=0 and iid=False would be same.
     Patch by Garvit Khatri.

   - bpo-33127(32): The ssl module now compiles with LibreSSL 2.7.1.

   - bpo-33021(33): Release the GIL during fstat() calls, avoiding hang
     of all threads when calling mmap.mmap(), os.urandom(), and
     random.seed().  Patch by Nir Soffer.

   - bpo-27683(34): Fix a regression in *note ipaddress: a2. that result
     of ‘hosts()’ is empty when the network is constructed by a tuple
     containing an integer mask and only 1 bit left for addresses.

   - bpo-32844(35): Fix wrong redirection of a low descriptor (0 or 1)
     to stderr in subprocess if another low descriptor is closed.

   - bpo-31908(36): Fix output of cover files for ‘trace’ module
     command-line tool.  Previously emitted cover files only when
     ‘--missing’ option was used.  Patch by Michael Selik.

   - bpo-31457(37): If nested log adapters are used, the inner
     ‘process()’ methods are no longer omitted.

   - bpo-16865(38): Support arrays >=2GiB in *note ctypes: 2a.  Patch by
     Segev Finer.

   - bpo-31238(39): pydoc: the stop() method of the private ServerThread
     class now waits until DocServer.serve_until_quit() completes and
     then explicitly sets its docserver attribute to None to break a
     reference cycle.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30167

   (2) https://bugs.python.org/issue33812

   (3) https://bugs.python.org/issue30805

   (4) https://bugs.python.org/issue33767

   (5) https://bugs.python.org/issue32684

   (6) https://bugs.python.org/issue33674

   (7) https://bugs.python.org/issue31647

   (8) https://bugs.python.org/issue33672

   (9) https://bugs.python.org/issue33469

   (10) https://bugs.python.org/issue11874

   (11) https://bugs.python.org/issue30877

   (12) https://bugs.python.org/issue33548

   (13) https://bugs.python.org/issue33542

   (14) https://bugs.python.org/issue26819

   (15) https://bugs.python.org/issue28556

   (16) https://bugs.python.org/issue20087

   (17) https://bugs.python.org/issue33422

   (18) https://bugs.python.org/issue33197

   (19) https://bugs.python.org/issue33383

   (20) https://bugs.python.org/issue33329

   (21) https://bugs.python.org/issue991266

   (22) https://bugs.python.org/issue33131

   (23) https://bugs.python.org/issue33308

   (24) https://bugs.python.org/issue33263

   (25) https://bugs.python.org/issue33256

   (26) https://bugs.python.org/issue33203

   (27) https://bugs.python.org/issue33224

   (28) https://www.python.org/dev/peps/pep-0479

   (29) https://bugs.python.org/issue33209

   (30) https://bugs.python.org/issue32861

   (31) https://bugs.python.org/issue33096

   (32) https://bugs.python.org/issue33127

   (33) https://bugs.python.org/issue33021

   (34) https://bugs.python.org/issue27683

   (35) https://bugs.python.org/issue32844

   (36) https://bugs.python.org/issue31908

   (37) https://bugs.python.org/issue31457

   (38) https://bugs.python.org/issue16865

   (39) https://bugs.python.org/issue31238


File: python.info,  Node: Documentation<36>,  Next: Tests<33>,  Prev: Library<42>,  Up: Python 3 6 6 release candidate 1

1.19.44.3 Documentation
.......................

   - bpo-33503(1): Fix broken pypi link

   - bpo-33421(2): Add missing documentation for
     ‘typing.AsyncContextManager’.

   - bpo-33378(3): Add Korean language switcher for
     ‘https://docs.python.org/3/’

   - bpo-33276(4): Clarify that the ‘__path__’ attribute on modules
     cannot be just any value.

   - bpo-33201(5): Modernize documentation for writing C extension
     types.

   - bpo-33195(6): Deprecate ‘Py_UNICODE’ usage in ‘c-api/arg’ document.
     ‘Py_UNICODE’ related APIs are deprecated since Python 3.3, but it
     is missed in the document.

   - bpo-33126(7): Document PyBuffer_ToContiguous().

   - bpo-27212(8): Modify documentation for the ‘islice()’ recipe to
     consume initial values up to the start index.

   - bpo-28247(9): Update *note zipapp: 14a. documentation to describe
     how to make standalone applications.

   - bpo-18802(10): Documentation changes for ipaddress.  Patch by Jon
     Foster and Berker Peksag.

   - bpo-27428(11): Update documentation to clarify that
     ‘WindowsRegistryFinder’ implements ‘MetaPathFinder’.  (Patch by
     Himanshu Lakhara)

   - bpo-8243(12): Add a note about curses.addch and curses.addstr
     exception behavior when writing outside a window, or pad.

   - bpo-31432(13): Clarify meaning of CERT_NONE, CERT_OPTIONAL, and
     CERT_REQUIRED flags for ssl.SSLContext.verify_mode.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33503

   (2) https://bugs.python.org/issue33421

   (3) https://bugs.python.org/issue33378

   (4) https://bugs.python.org/issue33276

   (5) https://bugs.python.org/issue33201

   (6) https://bugs.python.org/issue33195

   (7) https://bugs.python.org/issue33126

   (8) https://bugs.python.org/issue27212

   (9) https://bugs.python.org/issue28247

   (10) https://bugs.python.org/issue18802

   (11) https://bugs.python.org/issue27428

   (12) https://bugs.python.org/issue8243

   (13) https://bugs.python.org/issue31432


File: python.info,  Node: Tests<33>,  Next: Build<33>,  Prev: Documentation<36>,  Up: Python 3 6 6 release candidate 1

1.19.44.4 Tests
...............

   - bpo-33655(1): Ignore test_posix_fallocate failures on BSD platforms
     that might be due to running on ZFS.

   - bpo-19417(2): Add test_bdb.py.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33655

   (2) https://bugs.python.org/issue19417


File: python.info,  Node: Build<33>,  Next: Windows<33>,  Prev: Tests<33>,  Up: Python 3 6 6 release candidate 1

1.19.44.5 Build
...............

   - bpo-5755(1): Move ‘-Wstrict-prototypes’ option to ‘CFLAGS_NODIST’
     from ‘OPT’.  This option emitted annoying warnings when building
     extension modules written in C++.

   - bpo-33614(2): Ensures module definition files for the stable ABI on
     Windows are correctly regenerated.

   - bpo-33522(3): Enable CI builds on Visual Studio Team Services at
     ‘https://python.visualstudio.com/cpython’

   - bpo-33012(4): Add ‘-Wno-cast-function-type’ for gcc 8 for silencing
     warnings about function casts like casting to PyCFunction in method
     definition lists.

   - bpo-33394(5): Enable the verbose build for extension modules, when
     GNU make is passed macros on the command line.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5755

   (2) https://bugs.python.org/issue33614

   (3) https://bugs.python.org/issue33522

   (4) https://bugs.python.org/issue33012

   (5) https://bugs.python.org/issue33394


File: python.info,  Node: Windows<33>,  Next: macOS<27>,  Prev: Build<33>,  Up: Python 3 6 6 release candidate 1

1.19.44.6 Windows
.................

   - bpo-33184(1): Update Windows installer to OpenSSL 1.0.2o.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33184


File: python.info,  Node: macOS<27>,  Next: IDLE<33>,  Prev: Windows<33>,  Up: Python 3 6 6 release candidate 1

1.19.44.7 macOS
...............

   - bpo-33184(1): Update macOS installer build to use OpenSSL 1.0.2o.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33184


File: python.info,  Node: IDLE<33>,  Next: Tools/Demos<18>,  Prev: macOS<27>,  Up: Python 3 6 6 release candidate 1

1.19.44.8 IDLE
..............

   - bpo-33656(1): On Windows, add API call saying that tk scales for
     DPI. On Windows 8.1+ or 10, with DPI compatibility properties of
     the Python binary unchanged, and a monitor resolution greater than
     96 DPI, this should make text and lines sharper.  It should
     otherwise have no effect.

   - bpo-33768(2): Clicking on a context line moves that line to the top
     of the editor window.

   - bpo-33763(3): IDLE: Use read-only text widget for code context
     instead of label widget.

   - bpo-33664(4): Scroll IDLE editor text by lines.  Previously, the
     mouse wheel and scrollbar slider moved text by a fixed number of
     pixels, resulting in partial lines at the top of the editor box.
     The change also applies to the shell and grep output windows, but
     not to read-only text views.

   - bpo-33679(5): Enable theme-specific color configuration for Code
     Context.  Use the Highlights tab to see the setting for built-in
     themes or add settings to custom themes.

   - bpo-33642(6): Display up to maxlines non-blank lines for Code
     Context.  If there is no current context, show a single blank line.

   - bpo-33628(7): IDLE: Cleanup codecontext.py and its test.

   - bpo-33564(8): IDLE’s code context now recognizes async as a block
     opener.

   - bpo-29706(9): IDLE now colors async and await as keywords in 3.6.
     They become full keywords in 3.7.

   - bpo-21474(10): Update word/identifier definition from ascii to
     unicode.  In text and entry boxes, this affects selection by
     double-click, movement left/right by control-left/right, and
     deletion left/right by control-BACKSPACE/DEL.

   - bpo-33204(11): IDLE: consistently color invalid string prefixes.  A
     ‘u’ string prefix cannot be paired with either ‘r’ or ‘f’.
     Consistently color as much of the prefix, starting at the right, as
     is valid.  Revise and extend colorizer test.

   - bpo-32831(12): Add docstrings and tests for codecontext.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33656

   (2) https://bugs.python.org/issue33768

   (3) https://bugs.python.org/issue33763

   (4) https://bugs.python.org/issue33664

   (5) https://bugs.python.org/issue33679

   (6) https://bugs.python.org/issue33642

   (7) https://bugs.python.org/issue33628

   (8) https://bugs.python.org/issue33564

   (9) https://bugs.python.org/issue29706

   (10) https://bugs.python.org/issue21474

   (11) https://bugs.python.org/issue33204

   (12) https://bugs.python.org/issue32831


File: python.info,  Node: Tools/Demos<18>,  Next: C API<28>,  Prev: IDLE<33>,  Up: Python 3 6 6 release candidate 1

1.19.44.9 Tools/Demos
.....................

   - bpo-33189(1): ‘pygettext.py’ now recognizes only literal strings as
     docstrings and translatable strings, and rejects bytes literals and
     f-string expressions.

   - bpo-31920(2): Fixed handling directories as arguments in the
     ‘pygettext’ script.  Based on patch by Oleg Krasnikov.

   - bpo-29673(3): Fix pystackv and pystack gdbinit macros.

   - bpo-32885(4): Add an ‘-n’ flag for ‘Tools/scripts/pathfix.py’ to
     disable automatic backup creation (files with ‘~’ suffix).

   - bpo-31583(5): Fix 2to3 for using with –add-suffix option but
     without –output-dir option for relative path to files in current
     directory.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33189

   (2) https://bugs.python.org/issue31920

   (3) https://bugs.python.org/issue29673

   (4) https://bugs.python.org/issue32885

   (5) https://bugs.python.org/issue31583


File: python.info,  Node: C API<28>,  Prev: Tools/Demos<18>,  Up: Python 3 6 6 release candidate 1

1.19.44.10 C API
................

   - bpo-32374(1): Document that m_traverse for multi-phase initialized
     modules can be called with m_state=NULL, and add a sanity check

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32374


File: python.info,  Node: Python 3 6 5 final,  Next: Python 3 6 5 release candidate 1,  Prev: Python 3 6 6 release candidate 1,  Up: Changelog

1.19.45 Python 3.6.5 final
--------------------------

`Release date: 2018-03-28'

* Menu:

* Tests: Tests<34>.
* Build: Build<34>.


File: python.info,  Node: Tests<34>,  Next: Build<34>,  Up: Python 3 6 5 final

1.19.45.1 Tests
...............

   - bpo-32872(1): Avoid regrtest compatibility issue with namespace
     packages.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32872


File: python.info,  Node: Build<34>,  Prev: Tests<34>,  Up: Python 3 6 5 final

1.19.45.2 Build
...............

   - bpo-33163(1): Upgrade pip to 9.0.3 and setuptools to v39.0.1.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33163


File: python.info,  Node: Python 3 6 5 release candidate 1,  Next: Python 3 6 4 final,  Prev: Python 3 6 5 final,  Up: Changelog

1.19.46 Python 3.6.5 release candidate 1
----------------------------------------

`Release date: 2018-03-13'

* Menu:

* Security: Security<22>.
* Core and Builtins: Core and Builtins<40>.
* Library: Library<43>.
* Documentation: Documentation<37>.
* Tests: Tests<35>.
* Build: Build<35>.
* Windows: Windows<34>.
* macOS: macOS<28>.
* IDLE: IDLE<34>.
* Tools/Demos: Tools/Demos<19>.
* C API: C API<29>.


File: python.info,  Node: Security<22>,  Next: Core and Builtins<40>,  Up: Python 3 6 5 release candidate 1

1.19.46.1 Security
..................

   - bpo-33001(1): Minimal fix to prevent buffer overrun in os.symlink
     on Windows

   - bpo-32981(2): Regexes in difflib and poplib were vulnerable to
     catastrophic backtracking.  These regexes formed potential DOS
     vectors (REDOS). They have been refactored.  This resolves
     CVE-2018-1060 and CVE-2018-1061.  Patch by Jamie Davis.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33001

   (2) https://bugs.python.org/issue32981


File: python.info,  Node: Core and Builtins<40>,  Next: Library<43>,  Prev: Security<22>,  Up: Python 3 6 5 release candidate 1

1.19.46.2 Core and Builtins
...........................

   - bpo-33026(1): Fixed jumping out of “with” block by setting
     f_lineno.

   - bpo-17288(2): Prevent jumps from ‘return’ and ‘exception’ trace
     events.

   - bpo-32889(3): Update Valgrind suppression list to account for the
     rename of ‘Py_ADDRESS_IN_RANG’ to ‘address_in_range’.

   - bpo-32650(4): Pdb and other debuggers dependent on bdb.py will
     correctly step over (next command) native coroutines.  Patch by
     Pablo Galindo.

   - bpo-32685(5): Improve suggestion when the Python 2 form of print
     statement is either present on the same line as the header of a
     compound statement or else terminated by a semi-colon instead of a
     newline.  Patch by Nitish Chandra.

   - bpo-32583(6): Fix possible crashing in builtin Unicode decoders
     caused by write out-of-bound errors when using customized decode
     error handlers.

   - bpo-26163(7): Improved frozenset() hash to create more distinct
     hash values when faced with datasets containing many similar
     values.

   - bpo-27169(8): The ‘__debug__’ constant is now optimized out at
     compile time.  This fixes also bpo-22091(9).

   - bpo-32329(10): ‘sys.flags.hash_randomization’ is now properly set
     to 0 when hash randomization is turned off by ‘PYTHONHASHSEED=0’.

   - bpo-30416(11): The optimizer is now protected from spending much
     time doing complex calculations and consuming much memory for
     creating large constants in constant folding.

   - bpo-18533(12): ‘repr()’ on a dict containing its own ‘values()’ or
     ‘items()’ no longer raises ‘RecursionError’; OrderedDict similarly.
     Instead, use ‘...’, as for other recursive structures.  Patch by
     Ben North.

   - bpo-32028(13): Leading whitespace is now correctly ignored when
     generating suggestions for converting Py2 print statements to Py3
     builtin print function calls.  Patch by Sanyam Khurana.

   - bpo-32137(14): The repr of deeply nested dict now raises a
     RecursionError instead of crashing due to a stack overflow.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33026

   (2) https://bugs.python.org/issue17288

   (3) https://bugs.python.org/issue32889

   (4) https://bugs.python.org/issue32650

   (5) https://bugs.python.org/issue32685

   (6) https://bugs.python.org/issue32583

   (7) https://bugs.python.org/issue26163

   (8) https://bugs.python.org/issue27169

   (9) https://bugs.python.org/issue22091

   (10) https://bugs.python.org/issue32329

   (11) https://bugs.python.org/issue30416

   (12) https://bugs.python.org/issue18533

   (13) https://bugs.python.org/issue32028

   (14) https://bugs.python.org/issue32137


File: python.info,  Node: Library<43>,  Next: Documentation<37>,  Prev: Core and Builtins<40>,  Up: Python 3 6 5 release candidate 1

1.19.46.3 Library
.................

   - bpo-33064(1): lib2to3 now properly supports trailing commas after
     ‘*args’ and ‘**kwargs’ in function signatures.

   - bpo-31804(2): Avoid failing in multiprocessing.Process if the
     standard streams are closed or None at exit.

   - bpo-33037(3): Skip sending/receiving data after SSL transport
     closing.

   - bpo-30353(4): Fix ctypes pass-by-value for structs on 64-bit
     Cygwin/MinGW.

   - bpo-33009(5): Fix inspect.signature() for single-parameter
     partialmethods.

   - bpo-32969(6): Expose several missing constants in zlib and fix
     corresponding documentation.

   - bpo-32713(7): Fixed tarfile.itn handling of out-of-bounds float
     values.  Patch by Joffrey Fuhrer.

   - bpo-30622(8): The ssl module now detects missing NPN support in
     LibreSSL.

   - bpo-32922(9): dbm.open() now encodes filename with the filesystem
     encoding rather than default encoding.

   - bpo-32859(10): In ‘os.dup2’, don’t check every call whether the
     ‘dup3’ syscall exists or not.

   - bpo-21060(11): Rewrite confusing message from setup.py upload from
     “No dist file created in earlier command” to the more helpful “Must
     create and upload files in one command”.

   - bpo-32857(12): In *note tkinter: 10e, ‘after_cancel(None)’ now
     raises a *note ValueError: 16d. instead of canceling the first
     scheduled function.  Patch by Cheryl Sabella.

   - bpo-32852(13): Make sure sys.argv remains as a list when running
     trace.

   - bpo-32841(14): Fixed *note asyncio.Condition: 3b0. issue which
     silently ignored cancellation after notifying and cancelling a
     conditional lock.  Patch by Bar Harel.

   - bpo-31787(15): Fixed refleaks of ‘__init__()’ methods in various
     modules.  (Contributed by Oren Milman)

   - bpo-30157(16): Fixed guessing quote and delimiter in
     csv.Sniffer.sniff() when only the last field is quoted.  Patch by
     Jake Davis.

   - bpo-32394(17): socket: Remove TCP_FASTOPEN, TCP_KEEPCNT flags on
     older version Windows during run-time.

   - bpo-32777(18): Fix a rare but potential pre-exec child process
     deadlock in subprocess on POSIX systems when marking file
     descriptors inheritable on exec in the child process.  This bug
     appears to have been introduced in 3.4.

   - bpo-32647(19): The ctypes module used to depend on indirect linking
     for dlopen.  The shared extension is now explicitly linked against
     libdl on platforms with dl.

   - bpo-32734(20): Fixed ‘asyncio.Lock()’ safety issue which allowed
     acquiring and locking the same lock multiple times, without it
     being free.  Patch by Bar Harel.

   - bpo-32727(21): Do not include name field in SMTP envelope from
     address.  Patch by Stéphane Wirtel

   - bpo-27931(22): Fix email address header parsing error when the
     username is an empty quoted string.  Patch by Xiang Zhang.

   - bpo-32304(23): distutils’ upload command no longer corrupts tar
     files ending with a CR byte, and no longer tries to convert CR to
     CRLF in any of the upload text fields.

   - bpo-32502(24): uuid.uuid1 no longer raises an exception if a 64-bit
     hardware address is encountered.

   - bpo-31848(25): Fix the error handling in Aifc_read.initfp() when
     the SSND chunk is not found.  Patch by Zackery Spytz.

   - bpo-32555(26): On FreeBSD and Solaris, os.strerror() now always
     decode the byte string from the current locale encoding, rather
     than using ASCII/surrogateescape in some cases.

   - bpo-32521(27): The nis module is now compatible with new libnsl and
     headers location.

   - bpo-32473(28): Improve ABCMeta._dump_registry() output readability

   - bpo-32521(29): glibc has removed Sun RPC. Use replacement libtirpc
     headers and library in nis module.

   - bpo-32228(30): Ensure that ‘truncate()’ preserves the file position
     (as reported by ‘tell()’) after writes longer than the buffer size.

   - bpo-26133(31): Don’t unsubscribe signals in asyncio UNIX event loop
     on interpreter shutdown.

   - bpo-32185(32): The SSL module no longer sends IP addresses in SNI
     TLS extension on platforms with OpenSSL 1.0.2+ or inet_pton.

   - bpo-32323(33): *note urllib.parse.urlsplit(): 6f0. does not convert
     zone-id (scope) to lower case for scoped IPv6 addresses in
     hostnames now.

   - bpo-32302(34): Fix bdist_wininst of distutils for CRT v142: it
     binary compatible with CRT v140.

   - bpo-32255(35): A single empty field is now always quoted when
     written into a CSV file.  This allows to distinguish an empty row
     from a row consisting of a single empty field.  Patch by Licht
     Takeuchi.

   - bpo-32277(36): Raise ‘NotImplementedError’ instead of ‘SystemError’
     on platforms where ‘chmod(..., follow_symlinks=False)’ is not
     supported.  Patch by Anthony Sottile.

   - bpo-32199(37): The getnode() ip getter now uses ‘ip link’ instead
     of ‘ip link list’.

   - bpo-27456(38): Ensure TCP_NODELAY is set on Linux.  Tests by Victor
     Stinner.

   - bpo-31900(39): The *note locale.localeconv(): 585. function now
     sets temporarily the ‘LC_CTYPE’ locale to the ‘LC_NUMERIC’ locale
     to decode ‘decimal_point’ and ‘thousands_sep’ byte strings if they
     are non-ASCII or longer than 1 byte, and the ‘LC_NUMERIC’ locale is
     different than the ‘LC_CTYPE’ locale.  This temporary change
     affects other threads.  Same change for the *note str.format():
     5d5. method when formatting a number (*note int: 204, *note float:
     1fd, *note float: 1fd. and subclasses) with the ‘n’ type (ex:
     ‘'{:n}'.format(1234)’).

   - bpo-31802(40): Importing native path module (‘posixpath’, ‘ntpath’)
     now works even if the ‘os’ module still is not imported.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33064

   (2) https://bugs.python.org/issue31804

   (3) https://bugs.python.org/issue33037

   (4) https://bugs.python.org/issue30353

   (5) https://bugs.python.org/issue33009

   (6) https://bugs.python.org/issue32969

   (7) https://bugs.python.org/issue32713

   (8) https://bugs.python.org/issue30622

   (9) https://bugs.python.org/issue32922

   (10) https://bugs.python.org/issue32859

   (11) https://bugs.python.org/issue21060

   (12) https://bugs.python.org/issue32857

   (13) https://bugs.python.org/issue32852

   (14) https://bugs.python.org/issue32841

   (15) https://bugs.python.org/issue31787

   (16) https://bugs.python.org/issue30157

   (17) https://bugs.python.org/issue32394

   (18) https://bugs.python.org/issue32777

   (19) https://bugs.python.org/issue32647

   (20) https://bugs.python.org/issue32734

   (21) https://bugs.python.org/issue32727

   (22) https://bugs.python.org/issue27931

   (23) https://bugs.python.org/issue32304

   (24) https://bugs.python.org/issue32502

   (25) https://bugs.python.org/issue31848

   (26) https://bugs.python.org/issue32555

   (27) https://bugs.python.org/issue32521

   (28) https://bugs.python.org/issue32473

   (29) https://bugs.python.org/issue32521

   (30) https://bugs.python.org/issue32228

   (31) https://bugs.python.org/issue26133

   (32) https://bugs.python.org/issue32185

   (33) https://bugs.python.org/issue32323

   (34) https://bugs.python.org/issue32302

   (35) https://bugs.python.org/issue32255

   (36) https://bugs.python.org/issue32277

   (37) https://bugs.python.org/issue32199

   (38) https://bugs.python.org/issue27456

   (39) https://bugs.python.org/issue31900

   (40) https://bugs.python.org/issue31802


File: python.info,  Node: Documentation<37>,  Next: Tests<35>,  Prev: Library<43>,  Up: Python 3 6 5 release candidate 1

1.19.46.4 Documentation
.......................

   - bpo-17232(1): Clarify docs for -O and -OO. Patch by Terry Reedy.

   - bpo-32800(2): Update link to w3c doc for xml default namespaces.

   - bpo-8722(3): Document *note __getattr__(): 42a. behavior when
     property ‘get()’ method raises *note AttributeError: 4a2.

   - bpo-32614(4): Modify RE examples in documentation to use raw
     strings to prevent *note DeprecationWarning: 15a. and add text to
     REGEX HOWTO to highlight the deprecation.

   - bpo-31972(5): Improve docstrings for *note pathlib.PurePath: 235.
     subclasses.

   - bpo-17799(6): Explain real behaviour of sys.settrace and
     sys.setprofile and their C-API counterparts regarding which type of
     events are received in each function.  Patch by Pablo Galindo
     Salgado.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17232

   (2) https://bugs.python.org/issue32800

   (3) https://bugs.python.org/issue8722

   (4) https://bugs.python.org/issue32614

   (5) https://bugs.python.org/issue31972

   (6) https://bugs.python.org/issue17799


File: python.info,  Node: Tests<35>,  Next: Build<35>,  Prev: Documentation<37>,  Up: Python 3 6 5 release candidate 1

1.19.46.5 Tests
...............

   - bpo-32517(1): Fix failing ‘test_asyncio’ on macOS 10.12.2+ due to
     transport of ‘KqueueSelector’ loop was not being closed.

   - bpo-32721(2): Fix test_hashlib to not fail if the _md5 module is
     not built.

   - bpo-32252(3): Fix faulthandler_suppress_crash_report() used to
     prevent core dump files when testing crashes.  getrlimit() returns
     zero on success.

   - bpo-31518(4): Debian Unstable has disabled TLS 1.0 and 1.1 for
     SSLv23_METHOD().  Change TLS/SSL protocol of some tests to
     PROTOCOL_TLS or PROTOCOL_TLSv1_2 to make them pass on Debian.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32517

   (2) https://bugs.python.org/issue32721

   (3) https://bugs.python.org/issue32252

   (4) https://bugs.python.org/issue31518


File: python.info,  Node: Build<35>,  Next: Windows<34>,  Prev: Tests<35>,  Up: Python 3 6 5 release candidate 1

1.19.46.6 Build
...............

   - bpo-32635(1): Fix segfault of the crypt module when libxcrypt is
     provided instead of libcrypt at the system.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32635


File: python.info,  Node: Windows<34>,  Next: macOS<28>,  Prev: Build<35>,  Up: Python 3 6 5 release candidate 1

1.19.46.7 Windows
.................

   - bpo-33016(1): Fix potential use of uninitialized memory in
     nt._getfinalpathname

   - bpo-32903(2): Fix a memory leak in os.chdir() on Windows if the
     current directory is set to a UNC path.

   - bpo-31966(3): Fixed WindowsConsoleIO.write() for writing empty
     data.

   - bpo-32409(4): Ensures activate.bat can handle Unicode contents.

   - bpo-32457(5): Improves handling of denormalized executable path
     when launching Python.

   - bpo-32370(6): Use the correct encoding for ipconfig output in the
     uuid module.  Patch by Segev Finer.

   - bpo-29248(7): Fix *note os.readlink(): 1d1. on Windows, which was
     mistakenly treating the ‘PrintNameOffset’ field of the reparse data
     buffer as a number of characters instead of bytes.  Patch by Craig
     Holmquist and SSE4.

   - bpo-32588(8): Create standalone _distutils_findvs module.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33016

   (2) https://bugs.python.org/issue32903

   (3) https://bugs.python.org/issue31966

   (4) https://bugs.python.org/issue32409

   (5) https://bugs.python.org/issue32457

   (6) https://bugs.python.org/issue32370

   (7) https://bugs.python.org/issue29248

   (8) https://bugs.python.org/issue32588


File: python.info,  Node: macOS<28>,  Next: IDLE<34>,  Prev: Windows<34>,  Up: Python 3 6 5 release candidate 1

1.19.46.8 macOS
...............

   - bpo-32726(1): Provide an additional, more modern macOS installer
     variant that supports macOS 10.9+ systems in 64-bit mode only.
     Upgrade the supplied third-party libraries to OpenSSL 1.0.2n, XZ
     5.2.3, and SQLite 3.22.0.  The 10.9+ installer now links with and
     supplies its own copy of Tcl/Tk 8.6.8.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32726


File: python.info,  Node: IDLE<34>,  Next: Tools/Demos<19>,  Prev: macOS<28>,  Up: Python 3 6 5 release candidate 1

1.19.46.9 IDLE
..............

   - bpo-32984(1): Set ‘__file__’ while running a startup file.  Like
     Python, IDLE optionally runs one startup file in the Shell window
     before presenting the first interactive input prompt.  For IDLE,
     ‘-s’ runs a file named in environmental variable ‘IDLESTARTUP’ or
     *note PYTHONSTARTUP: 9cb.; ‘-r file’ runs ‘file’.  Python sets
     ‘__file__’ to the startup file name before running the file and
     unsets it before the first prompt.  IDLE now does the same when run
     normally, without the ‘-n’ option.

   - bpo-32940(2): Simplify and rename StringTranslatePseudoMapping in
     pyparse.

   - bpo-32916(3): Change ‘str’ to ‘code’ in pyparse.

   - bpo-32905(4): Remove unused code in pyparse module.

   - bpo-32874(5): Add tests for pyparse.

   - bpo-32837(6): Using the system and place-dependent default encoding
     for open() is a bad idea for IDLE’s system and location-independent
     files.

   - bpo-32826(7): Add “encoding=utf-8” to open() in IDLE’s
     test_help_about.  GUI test test_file_buttons() only looks at
     initial ascii-only lines, but failed on systems where open()
     defaults to ‘ascii’ because readline() internally reads and decodes
     far enough ahead to encounter a non-ascii character in CREDITS.txt.

   - bpo-32765(8): Update configdialog General tab docstring to add new
     widgets to the widget list.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32984

   (2) https://bugs.python.org/issue32940

   (3) https://bugs.python.org/issue32916

   (4) https://bugs.python.org/issue32905

   (5) https://bugs.python.org/issue32874

   (6) https://bugs.python.org/issue32837

   (7) https://bugs.python.org/issue32826

   (8) https://bugs.python.org/issue32765


File: python.info,  Node: Tools/Demos<19>,  Next: C API<29>,  Prev: IDLE<34>,  Up: Python 3 6 5 release candidate 1

1.19.46.10 Tools/Demos
......................

   - bpo-24960(1): 2to3 and lib2to3 can now read pickled grammar files
     using pkgutil.get_data() rather than probing the filesystem.  This
     lets 2to3 and lib2to3 work when run from a zipfile.

   - bpo-32222(2): Fix pygettext not extracting docstrings for functions
     with type annotated arguments.  Patch by Toby Harradine.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24960

   (2) https://bugs.python.org/issue32222


File: python.info,  Node: C API<29>,  Prev: Tools/Demos<19>,  Up: Python 3 6 5 release candidate 1

1.19.46.11 C API
................

   - bpo-29084(1): Undocumented C API for OrderedDict has been excluded
     from the limited C API. It was added by mistake and actually never
     worked in the limited C API.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29084


File: python.info,  Node: Python 3 6 4 final,  Next: Python 3 6 4 release candidate 1,  Prev: Python 3 6 5 release candidate 1,  Up: Changelog

1.19.47 Python 3.6.4 final
--------------------------

`Release date: 2017-12-18'

There were no new code changes in version 3.6.4 since v3.6.4rc1.


File: python.info,  Node: Python 3 6 4 release candidate 1,  Next: Python 3 6 3 final,  Prev: Python 3 6 4 final,  Up: Changelog

1.19.48 Python 3.6.4 release candidate 1
----------------------------------------

`Release date: 2017-12-05'

* Menu:

* Core and Builtins: Core and Builtins<41>.
* Library: Library<44>.
* Documentation: Documentation<38>.
* Tests: Tests<36>.
* Build: Build<36>.
* Windows: Windows<35>.
* macOS: macOS<29>.
* IDLE: IDLE<35>.
* Tools/Demos: Tools/Demos<20>.
* C API: C API<30>.


File: python.info,  Node: Core and Builtins<41>,  Next: Library<44>,  Up: Python 3 6 4 release candidate 1

1.19.48.1 Core and Builtins
...........................

   - bpo-32176(1): co_flags.CO_NOFREE is now always set correctly by the
     code object constructor based on freevars and cellvars, rather than
     needing to be set correctly by the caller.  This ensures it will be
     cleared automatically when additional cell references are injected
     into a modified code object and function.

   - bpo-31949(2): Fixed several issues in printing tracebacks
     (PyTraceBack_Print()).  Setting sys.tracebacklimit to 0 or less now
     suppresses printing tracebacks.  Setting sys.tracebacklimit to None
     now causes using the default limit.  Setting sys.tracebacklimit to
     an integer larger than LONG_MAX now means using the limit LONG_MAX
     rather than the default limit.  Fixed integer overflows in the case
     of more than ‘2**31’ traceback items on Windows.  Fixed output
     errors handling.

   - bpo-30696(3): Fix the interactive interpreter looping endlessly
     when no memory.

   - bpo-20047(4): Bytearray methods partition() and rpartition() now
     accept only bytes-like objects as separator, as documented.  In
     particular they now raise TypeError rather of returning a bogus
     result when an integer is passed as a separator.

   - bpo-31852(5): Fix a segmentation fault caused by a combination of
     the async soft keyword and continuation lines.

   - bpo-21720(6): BytesWarning no longer emitted when the `fromlist'
     argument of ‘__import__()’ or the ‘__all__’ attribute of the module
     contain bytes instances.

   - bpo-31825(7): Fixed OverflowError in the ‘unicode-escape’ codec and
     in codecs.escape_decode() when decode an escaped non-ascii byte.

   - bpo-28603(8): Print the full context/cause chain of exceptions on
     interpreter exit, even if an exception in the chain is unhashable
     or compares equal to later ones.  Patch by Zane Bitter.

   - bpo-31786(9): Fix timeout rounding in the select module to round
     correctly negative timeouts between -1.0 and 0.0.  The functions
     now block waiting for events as expected.  Previously, the call was
     incorrectly non-blocking.  Patch by Pablo Galindo.

   - bpo-31642(10): Restored blocking “from package import module” by
     setting sys.modules[“package.module”] to None.

   - bpo-31626(11): Fixed a bug in debug memory allocator.  There was a
     write to freed memory after shrinking a memory block.

   - bpo-31619(12): Fixed a ValueError when convert a string with large
     number of underscores to integer with binary base.

   - bpo-31592(13): Fixed an assertion failure in Python parser in case
     of a bad *note unicodedata.normalize(): 11e4.  Patch by Oren
     Milman.

   - bpo-31588(14): Raise a *note TypeError: 1fe. with a helpful error
     message when class creation fails due to a metaclass with a bad
     ‘__prepare__()’ method.  Patch by Oren Milman.

   - bpo-31566(15): Fix an assertion failure in ‘_warnings.warn()’ in
     case of a bad ‘__name__’ global.  Patch by Oren Milman.

   - bpo-31505(16): Fix an assertion failure in *note json: a4, in case
     ‘_json.make_encoder()’ received a bad ‘encoder()’ argument.  Patch
     by Oren Milman.

   - bpo-31492(17): Fix assertion failures in case of failing to import
     from a module with a bad ‘__name__’ attribute, and in case of
     failing to access an attribute of such a module.  Patch by Oren
     Milman.

   - bpo-31490(18): Fix an assertion failure in *note ctypes: 2a. class
     definition, in case the class has an attribute whose name is
     specified in ‘_anonymous_’ but not in ‘_fields_’.  Patch by Oren
     Milman.

   - bpo-31478(19): Fix an assertion failure in ‘_random.Random.seed()’
     in case the argument has a bad ‘__abs__()’ method.  Patch by Oren
     Milman.

   - bpo-31315(20): Fix an assertion failure in imp.create_dynamic(),
     when spec.name is not a string.  Patch by Oren Milman.

   - bpo-31311(21): Fix a crash in the ‘__setstate__()’ method of *note
     ctypes._CData: 11e5, in case of a bad ‘__dict__’.  Patch by Oren
     Milman.

   - bpo-31293(22): Fix crashes in true division and multiplication of a
     timedelta object by a float with a bad as_integer_ratio() method.
     Patch by Oren Milman.

   - bpo-31285(23): Fix an assertion failure in *note
     warnings.warn_explicit: 6a7, when the return value of the received
     loader’s get_source() has a bad splitlines() method.  Patch by Oren
     Milman.

   - bpo-30817(24): ‘PyErr_PrintEx()’ clears now the ignored exception
     that may be raised by ‘_PySys_SetObjectId()’, for example when no
     memory.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32176

   (2) https://bugs.python.org/issue31949

   (3) https://bugs.python.org/issue30696

   (4) https://bugs.python.org/issue20047

   (5) https://bugs.python.org/issue31852

   (6) https://bugs.python.org/issue21720

   (7) https://bugs.python.org/issue31825

   (8) https://bugs.python.org/issue28603

   (9) https://bugs.python.org/issue31786

   (10) https://bugs.python.org/issue31642

   (11) https://bugs.python.org/issue31626

   (12) https://bugs.python.org/issue31619

   (13) https://bugs.python.org/issue31592

   (14) https://bugs.python.org/issue31588

   (15) https://bugs.python.org/issue31566

   (16) https://bugs.python.org/issue31505

   (17) https://bugs.python.org/issue31492

   (18) https://bugs.python.org/issue31490

   (19) https://bugs.python.org/issue31478

   (20) https://bugs.python.org/issue31315

   (21) https://bugs.python.org/issue31311

   (22) https://bugs.python.org/issue31293

   (23) https://bugs.python.org/issue31285

   (24) https://bugs.python.org/issue30817


File: python.info,  Node: Library<44>,  Next: Documentation<38>,  Prev: Core and Builtins<41>,  Up: Python 3 6 4 release candidate 1

1.19.48.2 Library
.................

   - bpo-28556(1): Two minor fixes for ‘typing’ module: allow shallow
     copying instances of generic classes, improve interaction of
     ‘__init_subclass__’ with generics.  Original PRs by Ivan
     Levkivskyi.

   - bpo-27240(2): The header folding algorithm for the new email
     policies has been rewritten, which also fixes bpo-30788(3),
     bpo-31831(4), and bpo-32182(5).  In particular, RFC2231 folding is
     now done correctly.

   - bpo-32186(6): io.FileIO.readall() and io.FileIO.read() now release
     the GIL when getting the file size.  Fixed hang of all threads with
     inaccessible NFS server.  Patch by Nir Soffer.

   - bpo-12239(7): Make *note msilib.SummaryInformation.GetProperty():
     10fe. return ‘None’ when the value of property is ‘VT_EMPTY’.
     Initial patch by Mark Mc Mahon.

   - bpo-31325(8): Fix wrong usage of *note collections.namedtuple():
     1a1. in the *note RobotFileParser.parse(): 11d6. method.  Initial
     patch by Robin Wellner.

   - bpo-12382(9): *note msilib.OpenDatabase(): 1020. now raises a
     better exception message when it couldn’t open or create an MSI
     file.  Initial patch by William Tisäter.

   - bpo-32110(10): ‘codecs.StreamReader.read(n)’ now returns not more
     than `n' characters/bytes for non-negative `n'.  This makes it
     compatible with ‘read()’ methods of other file-like objects.

   - bpo-32072(11): Fixed issues with binary plists: Fixed saving
     bytearrays.  Identical objects will be saved only once.  Equal
     references will be load as identical objects.  Added support for
     saving and loading recursive data structures.

   - bpo-32034(12): Make asyncio.IncompleteReadError and
     LimitOverrunError pickleable.

   - bpo-32015(13): Fixed the looping of asyncio in the case of
     reconnection the socket during waiting async read/write from/to the
     socket.

   - bpo-32011(14): Restored support of loading marshal files with the
     TYPE_INT64 code.  These files can be produced in Python 2.7.

   - bpo-31970(15): Reduce performance overhead of asyncio debug mode.

   - bpo-9678(16): Fixed determining the MAC address in the uuid module:
     Using ifconfig on NetBSD and OpenBSD. Using arp on Linux, FreeBSD,
     NetBSD and OpenBSD. Based on patch by Takayuki Shimizukawa.

   - bpo-30057(17): Fix potential missed signal in signal.signal().

   - bpo-31933(18): Fix Blake2 params leaf_size and node_offset on big
     endian platforms.  Patch by Jack O’Connor.

   - bpo-31927(19): Fixed compilation of the socket module on NetBSD 8.
     Fixed assertion failure or reading arbitrary data when parse a
     AF_BLUETOOTH address on NetBSD and DragonFly BSD.

   - bpo-27666(20): Fixed stack corruption in curses.box() and
     curses.ungetmouse() when the size of types chtype or mmask_t is
     less than the size of C long.  curses.box() now accepts characters
     as arguments.  Based on patch by Steve Fink.

   - bpo-31897(21): plistlib now catches more errors when read binary
     plists and raises InvalidFileException instead of unexpected
     exceptions.

   - bpo-25720(22): Fix the method for checking pad state of curses
     WINDOW. Patch by Masayuki Yamamoto.

   - bpo-31893(23): Fixed the layout of the kqueue_event structure on
     OpenBSD and NetBSD. Fixed the comparison of the kqueue_event
     objects.

   - bpo-31891(24): Fixed building the curses module on NetBSD.

   - bpo-28416(25): Instances of pickle.Pickler subclass with the
     persistent_id() method and pickle.Unpickler subclass with the
     persistent_load() method no longer create reference cycles.

   - bpo-28326(26): Fix multiprocessing.Process when stdout and/or
     stderr is closed or None.

   - bpo-31457(27): If nested log adapters are used, the inner
     ‘process()’ methods are no longer omitted.

   - bpo-31457(28): The ‘manager’ property on LoggerAdapter objects is
     now properly settable.

   - bpo-31806(29): Fix timeout rounding in time.sleep(),
     threading.Lock.acquire() and socket.socket.settimeout() to round
     correctly negative timeouts between -1.0 and 0.0.  The functions
     now block waiting for events as expected.  Previously, the call was
     incorrectly non-blocking.  Patch by Pablo Galindo.

   - bpo-28603(30): traceback: Fix a TypeError that occurred during
     printing of exception tracebacks when either the current exception
     or an exception in its context/cause chain is unhashable.  Patch by
     Zane Bitter.

   - bpo-30058(31): Fixed buffer overflow in select.kqueue.control().

   - bpo-31770(32): Prevent a crash when calling the ‘__init__()’ method
     of a ‘sqlite3.Cursor’ object more than once.  Patch by Oren Milman.

   - bpo-31672(33): ‘idpattern’ in ‘string.Template’ matched some
     non-ASCII characters.  Now it uses ‘-i’ regular expression local
     flag to avoid non-ASCII characters.

   - bpo-31764(34): Prevent a crash in ‘sqlite3.Cursor.close()’ in case
     the ‘Cursor’ object is uninitialized.  Patch by Oren Milman.

   - bpo-31752(35): Fix possible crash in timedelta constructor called
     with custom integers.

   - bpo-31701(36): On Windows, faulthandler.enable() now ignores MSC
     and COM exceptions.

   - bpo-31728(37): Prevent crashes in ‘_elementtree’ due to unsafe
     cleanup of ‘Element.text’ and ‘Element.tail’.  Patch by Oren
     Milman.

   - bpo-31620(38): an empty asyncio.Queue now doesn’t leak memory when
     queue.get pollers timeout

   - bpo-31632(39): Fix method set_protocol() of class
     _SSLProtocolTransport in asyncio module.  This method was
     previously modifying a wrong reference to the protocol.

   - bpo-31675(40): Fixed memory leaks in Tkinter’s methods splitlist()
     and split() when pass a string larger than 2 GiB.

   - bpo-31673(41): Fixed typo in the name of Tkinter’s method
     adderrorinfo().

   - bpo-30806(42): Fix the string representation of a netrc object.

   - bpo-15037(43): Added a workaround for getkey() in curses for
     ncurses 5.7 and earlier.

   - bpo-25351(44): Avoid venv activate failures with undefined
     variables

   - bpo-25532(45): inspect.unwrap() will now only try to unwrap an
     object sys.getrecursionlimit() times, to protect against objects
     which create a new object on every attribute access.

   - bpo-30347(46): Stop crashes when concurrently iterate over
     itertools.groupby() iterators.

   - bpo-31516(47): ‘threading.current_thread()’ should not return a
     dummy thread at shutdown.

   - bpo-31351(48): python -m ensurepip now exits with non-zero exit
     code if pip bootstrapping has failed.

   - bpo-31482(49): ‘random.seed()’ now works with bytes in version=1

   - bpo-31334(50): Fix ‘poll.poll([timeout])’ in the ‘select’ module
     for arbitrary negative timeouts on all OSes where it can only be a
     non-negative integer or -1.  Patch by Riccardo Coccioli.

   - bpo-31310(51): multiprocessing’s semaphore tracker should be
     launched again if crashed.

   - bpo-31308(52): Make multiprocessing’s forkserver process immune to
     Ctrl-C and other user interruptions.  If it crashes, restart it
     when necessary.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28556

   (2) https://bugs.python.org/issue27240

   (3) https://bugs.python.org/issue30788

   (4) https://bugs.python.org/issue31831

   (5) https://bugs.python.org/issue32182

   (6) https://bugs.python.org/issue32186

   (7) https://bugs.python.org/issue12239

   (8) https://bugs.python.org/issue31325

   (9) https://bugs.python.org/issue12382

   (10) https://bugs.python.org/issue32110

   (11) https://bugs.python.org/issue32072

   (12) https://bugs.python.org/issue32034

   (13) https://bugs.python.org/issue32015

   (14) https://bugs.python.org/issue32011

   (15) https://bugs.python.org/issue31970

   (16) https://bugs.python.org/issue9678

   (17) https://bugs.python.org/issue30057

   (18) https://bugs.python.org/issue31933

   (19) https://bugs.python.org/issue31927

   (20) https://bugs.python.org/issue27666

   (21) https://bugs.python.org/issue31897

   (22) https://bugs.python.org/issue25720

   (23) https://bugs.python.org/issue31893

   (24) https://bugs.python.org/issue31891

   (25) https://bugs.python.org/issue28416

   (26) https://bugs.python.org/issue28326

   (27) https://bugs.python.org/issue31457

   (28) https://bugs.python.org/issue31457

   (29) https://bugs.python.org/issue31806

   (30) https://bugs.python.org/issue28603

   (31) https://bugs.python.org/issue30058

   (32) https://bugs.python.org/issue31770

   (33) https://bugs.python.org/issue31672

   (34) https://bugs.python.org/issue31764

   (35) https://bugs.python.org/issue31752

   (36) https://bugs.python.org/issue31701

   (37) https://bugs.python.org/issue31728

   (38) https://bugs.python.org/issue31620

   (39) https://bugs.python.org/issue31632

   (40) https://bugs.python.org/issue31675

   (41) https://bugs.python.org/issue31673

   (42) https://bugs.python.org/issue30806

   (43) https://bugs.python.org/issue15037

   (44) https://bugs.python.org/issue25351

   (45) https://bugs.python.org/issue25532

   (46) https://bugs.python.org/issue30347

   (47) https://bugs.python.org/issue31516

   (48) https://bugs.python.org/issue31351

   (49) https://bugs.python.org/issue31482

   (50) https://bugs.python.org/issue31334

   (51) https://bugs.python.org/issue31310

   (52) https://bugs.python.org/issue31308


File: python.info,  Node: Documentation<38>,  Next: Tests<36>,  Prev: Library<44>,  Up: Python 3 6 4 release candidate 1

1.19.48.3 Documentation
.......................

   - bpo-32105(1): Added asyncio.BaseEventLoop.connect_accepted_socket
     versionadded marker.

   - bpo-31537(2): Fix incorrect usage of ‘get_history_length’ in
     readline documentation example code.  Patch by Brad Smith.

   - bpo-30085(3): The operator functions without double underscores are
     preferred for clarity.  The one with underscores are only kept for
     back-compatibility.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32105

   (2) https://bugs.python.org/issue31537

   (3) https://bugs.python.org/issue30085


File: python.info,  Node: Tests<36>,  Next: Build<36>,  Prev: Documentation<38>,  Up: Python 3 6 4 release candidate 1

1.19.48.4 Tests
...............

   - bpo-31380(1): Skip test_httpservers test_undecodable_file on macOS:
     fails on APFS.

   - bpo-31705(2): Skip test_socket.test_sha256() on Linux kernel older
     than 4.5.  The test fails with ENOKEY on kernel 3.10 (on ppc64le).
     A fix was merged into the kernel 4.5.

   - bpo-31174(3): Fix test_tools.test_unparse: DirectoryTestCase now
     stores the names sample to always test the same files.  It prevents
     false alarms when hunting reference leaks.

   - bpo-30695(4): Add the ‘set_nomemory(start, stop)’ and
     ‘remove_mem_hooks()’ functions to the _testcapi module.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31380

   (2) https://bugs.python.org/issue31705

   (3) https://bugs.python.org/issue31174

   (4) https://bugs.python.org/issue30695


File: python.info,  Node: Build<36>,  Next: Windows<35>,  Prev: Tests<36>,  Up: Python 3 6 4 release candidate 1

1.19.48.5 Build
...............

   - bpo-32059(1): ‘detect_modules()’ in ‘setup.py’ now also searches
     the sysroot paths when cross-compiling.

   - bpo-31957(2): Fixes Windows SDK version detection when building for
     Windows.

   - bpo-31609(3): Fixes quotes in PCbuild/clean.bat

   - bpo-31934(4): Abort the build when building out of a not clean
     source tree.

   - bpo-31926(5): Fixed Argument Clinic sometimes causing compilation
     errors when there was more than one function and/or method in a .c
     file with the same name.

   - bpo-28791(6): Update Windows builds to use SQLite 3.21.0.

   - bpo-28791(7): Update OS X installer to use SQLite 3.21.0.

   - bpo-22140(8): Prevent double substitution of prefix in
     python-config.sh.

   - bpo-31536(9): Avoid wholesale rebuild after ‘make regen-all’ if
     nothing changed.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32059

   (2) https://bugs.python.org/issue31957

   (3) https://bugs.python.org/issue31609

   (4) https://bugs.python.org/issue31934

   (5) https://bugs.python.org/issue31926

   (6) https://bugs.python.org/issue28791

   (7) https://bugs.python.org/issue28791

   (8) https://bugs.python.org/issue22140

   (9) https://bugs.python.org/issue31536


File: python.info,  Node: Windows<35>,  Next: macOS<29>,  Prev: Build<36>,  Up: Python 3 6 4 release candidate 1

1.19.48.6 Windows
.................

   - bpo-1102(1): Return ‘None’ when ‘View.Fetch()’ returns
     ‘ERROR_NO_MORE_ITEMS’ instead of raising ‘MSIError’.  Initial patch
     by Anthony Tuininga.

   - bpo-31944(2): Fixes Modify button in Apps and Features dialog.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue1102

   (2) https://bugs.python.org/issue31944


File: python.info,  Node: macOS<29>,  Next: IDLE<35>,  Prev: Windows<35>,  Up: Python 3 6 4 release candidate 1

1.19.48.7 macOS
...............

   - bpo-31392(1): Update macOS installer to use OpenSSL 1.0.2m

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31392


File: python.info,  Node: IDLE<35>,  Next: Tools/Demos<20>,  Prev: macOS<29>,  Up: Python 3 6 4 release candidate 1

1.19.48.8 IDLE
..............

   - bpo-32207(1): Improve tk event exception tracebacks in IDLE. When
     tk event handling is driven by IDLE’s run loop, a confusing and
     distracting queue.EMPTY traceback context is no longer added to tk
     event exception tracebacks.  The traceback is now the same as when
     event handling is driven by user code.  Patch based on a suggestion
     by Serhiy Storchaka.

   - bpo-32164(2): Delete unused file idlelib/tabbedpages.py.  Use of
     TabbedPageSet in configdialog was replaced by ttk.Notebook.

   - bpo-32100(3): IDLE: Fix old and new bugs in pathbrowser; improve
     tests.  Patch mostly by Cheryl Sabella.

   - bpo-31858(4): IDLE – Restrict shell prompt manipulation to the
     shell.  Editor and output windows only see an empty last prompt
     line.  This simplifies the code and fixes a minor bug when newline
     is inserted.  Sys.ps1, if present, is read on Shell start-up, but
     is not set or changed.

   - bpo-31860(5): The font sample in the IDLE configuration dialog is
     now editable.  Changes persist while IDLE remains open

   - bpo-31836(6): Test_code_module now passes if run after test_idle,
     which sets ps1.  The code module uses sys.ps1 if present or sets it
     to ‘>>> ‘ if not.  Test_code_module now properly tests both
     behaviors.  Ditto for ps2.

   - bpo-28603(7): Fix a TypeError that caused a shell restart when
     printing a traceback that includes an exception that is unhashable.
     Patch by Zane Bitter.

   - bpo-13802(8): Use non-Latin characters in the IDLE’s Font settings
     sample.  Even if one selects a font that defines a limited subset
     of the unicode Basic Multilingual Plane, tcl/tk will use other
     fonts that define a character.  The expanded example give users of
     non-Latin characters a better idea of what they might see in IDLE’s
     shell and editors.  To make room for the expanded sample, frames on
     the Font tab are re-arranged.  The Font/Tabs help explains a bit
     about the additions.

   - bpo-31460(9): Simplify the API of IDLE’s Module Browser.  Passing a
     widget instead of an flist with a root widget opens the option of
     creating a browser frame that is only part of a window.  Passing a
     full file name instead of pieces assumed to come from a .py file
     opens the possibility of browsing python files that do not end in
     .py.

   - bpo-31649(10): IDLE - Make _htest, _utest parameters keyword only.

   - bpo-31559(11): Remove test order dependence in
     idle_test.test_browser.

   - bpo-31459(12): Rename IDLE’s module browser from Class Browser to
     Module Browser.  The original module-level class and method browser
     became a module browser, with the addition of module-level
     functions, years ago.  Nested classes and functions were added
     yesterday.  For back-compatibility, the virtual event
     <<open-class-browser>>, which appears on the Keys tab of the
     Settings dialog, is not changed.  Patch by Cheryl Sabella.

   - bpo-31500(13): Default fonts now are scaled on HiDPI displays.

   - bpo-1612262(14): IDLE module browser now shows nested classes and
     functions.  Original patches for code and tests by Guilherme Polo
     and Cheryl Sabella, respectively.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32207

   (2) https://bugs.python.org/issue32164

   (3) https://bugs.python.org/issue32100

   (4) https://bugs.python.org/issue31858

   (5) https://bugs.python.org/issue31860

   (6) https://bugs.python.org/issue31836

   (7) https://bugs.python.org/issue28603

   (8) https://bugs.python.org/issue13802

   (9) https://bugs.python.org/issue31460

   (10) https://bugs.python.org/issue31649

   (11) https://bugs.python.org/issue31559

   (12) https://bugs.python.org/issue31459

   (13) https://bugs.python.org/issue31500

   (14) https://bugs.python.org/issue1612262


File: python.info,  Node: Tools/Demos<20>,  Next: C API<30>,  Prev: IDLE<35>,  Up: Python 3 6 4 release candidate 1

1.19.48.9 Tools/Demos
.....................

   - bpo-30722(1): Make redemo work with Python 3.6 and newer versions.
     Also, remove the ‘LOCALE’ option since it doesn’t work with string
     patterns in Python 3.  Patch by Christoph Sarnowski.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30722


File: python.info,  Node: C API<30>,  Prev: Tools/Demos<20>,  Up: Python 3 6 4 release candidate 1

1.19.48.10 C API
................

   - bpo-20891(1): Fix PyGILState_Ensure().  When PyGILState_Ensure() is
     called in a non-Python thread before PyEval_InitThreads(), only
     call PyEval_InitThreads() after calling PyThreadState_New() to fix
     a crash.

   - bpo-31532(2): Fix memory corruption due to allocator mix in
     getpath.c between Py_GetPath() and Py_SetPath()

   - bpo-30697(3): The ‘PyExc_RecursionErrorInst’ singleton is removed
     and ‘PyErr_NormalizeException()’ does not use it anymore.  This
     singleton is persistent and its members being never cleared may
     cause a segfault during finalization of the interpreter.  See also
     bpo-22898(4).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20891

   (2) https://bugs.python.org/issue31532

   (3) https://bugs.python.org/issue30697

   (4) https://bugs.python.org/issue22898


File: python.info,  Node: Python 3 6 3 final,  Next: Python 3 6 3 release candidate 1,  Prev: Python 3 6 4 release candidate 1,  Up: Changelog

1.19.49 Python 3.6.3 final
--------------------------

`Release date: 2017-10-03'

* Menu:

* Library: Library<45>.
* Build: Build<37>.


File: python.info,  Node: Library<45>,  Next: Build<37>,  Up: Python 3 6 3 final

1.19.49.1 Library
.................

   - bpo-31641(1): Re-allow arbitrary iterables in *note
     concurrent.futures.as_completed(): 1223.  Fixes regression in
     3.6.3rc1.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31641


File: python.info,  Node: Build<37>,  Prev: Library<45>,  Up: Python 3 6 3 final

1.19.49.2 Build
...............

   - bpo-31662(1): Fix typos in Windows ‘uploadrelease.bat’ script.  Fix
     Windows Doc build issues in ‘Doc/make.bat’.

   - bpo-31423(2): Fix building the PDF documentation with newer
     versions of Sphinx.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31662

   (2) https://bugs.python.org/issue31423


File: python.info,  Node: Python 3 6 3 release candidate 1,  Next: Python 3 6 2 final,  Prev: Python 3 6 3 final,  Up: Changelog

1.19.50 Python 3.6.3 release candidate 1
----------------------------------------

`Release date: 2017-09-18'

* Menu:

* Security: Security<23>.
* Core and Builtins: Core and Builtins<42>.
* Library: Library<46>.
* Documentation: Documentation<39>.
* Tests: Tests<37>.
* Build: Build<38>.
* Windows: Windows<36>.
* IDLE: IDLE<36>.
* Tools/Demos: Tools/Demos<21>.


File: python.info,  Node: Security<23>,  Next: Core and Builtins<42>,  Up: Python 3 6 3 release candidate 1

1.19.50.1 Security
..................

   - bpo-29781(1): SSLObject.version() now correctly returns None when
     handshake over BIO has not been performed yet.

   - bpo-30947(2): Upgrade libexpat embedded copy from version 2.2.1 to
     2.2.3 to get security fixes.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29781

   (2) https://bugs.python.org/issue30947


File: python.info,  Node: Core and Builtins<42>,  Next: Library<46>,  Prev: Security<23>,  Up: Python 3 6 3 release candidate 1

1.19.50.2 Core and Builtins
...........................

   - bpo-31471(1): Fix an assertion failure in *note subprocess.Popen():
     3db. on Windows, in case the env argument has a bad keys() method.
     Patch by Oren Milman.

   - bpo-31418(2): Fix an assertion failure in ‘PyErr_WriteUnraisable()’
     in case of an exception with a bad ‘__module__’ attribute.  Patch
     by Oren Milman.

   - bpo-31416(3): Fix assertion failures in case of a bad
     warnings.filters or warnings.defaultaction.  Patch by Oren Milman.

   - bpo-31411(4): Raise a TypeError instead of SystemError in case
     warnings.onceregistry is not a dictionary.  Patch by Oren Milman.

   - bpo-31373(5): Fix several possible instances of undefined behavior
     due to floating-point demotions.

   - bpo-30465(6): Location information (‘lineno’ and ‘col_offset’) in
     f-strings is now (mostly) correct.  This fixes tools like flake8
     from showing warnings on the wrong line (typically the first line
     of the file).

   - bpo-31343(7): Include sys/sysmacros.h for major(), minor(), and
     makedev().  GNU C libray plans to remove the functions from
     sys/types.h.

   - bpo-31291(8): Fix an assertion failure in *note
     zipimport.zipimporter.get_data: 11ef. on Windows, when the return
     value of ‘pathname.replace('/','\\')’ isn’t a string.  Patch by
     Oren Milman.

   - bpo-31271(9): Fix an assertion failure in the write() method of
     *note io.TextIOWrapper: 6ea, when the encoder doesn’t return a
     bytes object.  Patch by Oren Milman.

   - bpo-31243(10): Fix a crash in some methods of *note
     io.TextIOWrapper: 6ea, when the decoder’s state is invalid.  Patch
     by Oren Milman.

   - bpo-30721(11): ‘print’ now shows correct usage hint for using
     Python 2 redirection syntax.  Patch by Sanyam Khurana.

   - bpo-31070(12): Fix a race condition in importlib
     _get_module_lock().

   - bpo-31095(13): Fix potential crash during GC caused by ‘tp_dealloc’
     which doesn’t call ‘PyObject_GC_UnTrack()’.

   - bpo-31071(14): Avoid masking original TypeError in call with *
     unpacking when other arguments are passed.

   - bpo-30978(15): str.format_map() now passes key lookup exceptions
     through.  Previously any exception was replaced with a KeyError
     exception.

   - bpo-30808(16): Use _Py_atomic API for concurrency-sensitive signal
     state.

   - bpo-30876(17): Relative import from unloaded package now reimports
     the package instead of failing with SystemError.  Relative import
     from non-package now fails with ImportError rather than
     SystemError.

   - bpo-30703(18): Improve signal delivery.  Avoid using
     Py_AddPendingCall from signal handler, to avoid calling
     signal-unsafe functions.  The tests I’m adding here fail without
     the rest of the patch, on Linux and OS X. This means our signal
     delivery logic had defects (some signals could be lost).

   - bpo-30765(19): Avoid blocking in pthread_mutex_lock() when
     PyThread_acquire_lock() is asked not to block.

   - bpo-31161(20): Make sure the ‘Missing parentheses’ syntax error
     message is only applied to SyntaxError, not to subclasses.  Patch
     by Martijn Pieters.

   - bpo-30814(21): Fixed a race condition when import a submodule from
     a package.

   - bpo-30597(22): ‘print’ now shows expected input in custom error
     message when used as a Python 2 statement.  Patch by Sanyam
     Khurana.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31471

   (2) https://bugs.python.org/issue31418

   (3) https://bugs.python.org/issue31416

   (4) https://bugs.python.org/issue31411

   (5) https://bugs.python.org/issue31373

   (6) https://bugs.python.org/issue30465

   (7) https://bugs.python.org/issue31343

   (8) https://bugs.python.org/issue31291

   (9) https://bugs.python.org/issue31271

   (10) https://bugs.python.org/issue31243

   (11) https://bugs.python.org/issue30721

   (12) https://bugs.python.org/issue31070

   (13) https://bugs.python.org/issue31095

   (14) https://bugs.python.org/issue31071

   (15) https://bugs.python.org/issue30978

   (16) https://bugs.python.org/issue30808

   (17) https://bugs.python.org/issue30876

   (18) https://bugs.python.org/issue30703

   (19) https://bugs.python.org/issue30765

   (20) https://bugs.python.org/issue31161

   (21) https://bugs.python.org/issue30814

   (22) https://bugs.python.org/issue30597


File: python.info,  Node: Library<46>,  Next: Documentation<39>,  Prev: Core and Builtins<42>,  Up: Python 3 6 3 release candidate 1

1.19.50.3 Library
.................

   - bpo-31499(1): xml.etree: Fix a crash when a parser is part of a
     reference cycle.

   - bpo-28556(2): typing.get_type_hints now finds the right globalns
     for classes and modules by default (when no ‘globalns’ was
     specified by the caller).

   - bpo-28556(3): Speed improvements to the ‘typing’ module.  Original
     PRs by Ivan Levkivskyi and Mitar.

   - bpo-31544(4): The C accelerator module of ElementTree ignored
     exceptions raised when looking up TreeBuilder target methods in
     XMLParser().

   - bpo-31234(5): socket.create_connection() now fixes manually a
     reference cycle: clear the variable storing the last exception on
     success.

   - bpo-31457(6): LoggerAdapter objects can now be nested.

   - bpo-31400(7): Improves SSL error handling to avoid losing error
     numbers.

   - bpo-28958(8): ssl.SSLContext() now uses OpenSSL error information
     when a context cannot be instantiated.

   - bpo-27340(9): SSLSocket.sendall() now uses memoryview to create
     slices of data.  This fixes support for all bytes-like object.  It
     is also more efficient and avoids costly copies.

   - bpo-31178(10): Fix string concatenation bug in rare error path in
     the subprocess module

   - bpo-31350(11): Micro-optimize ‘asyncio._get_running_loop()’ to
     become up to 10% faster.

   - bpo-31170(12): expat: Update libexpat from 2.2.3 to 2.2.4.  Fix
     copying of partial characters for UTF-8 input (libexpat bug 115):
     ‘https://github.com/libexpat/libexpat/issues/115’

   - bpo-29136(13): Add TLS 1.3 cipher suites and OP_NO_TLSv1_3.

   - bpo-29212(14): Fix concurrent.futures.thread.ThreadPoolExecutor
     threads to have a non repr() based thread name by default when no
     thread_name_prefix is supplied.  They will now identify themselves
     as “ThreadPoolExecutor-y_n”.

   - bpo-9146(15): Fix a segmentation fault in _hashopenssl when
     standard hash functions such as md5 are not available in the linked
     OpenSSL library.  As in some special FIPS-140 build environments.

   - bpo-27144(16): The ‘map()’ and ‘as_completed()’ iterators in
     ‘concurrent.futures’ now avoid keeping a reference to yielded
     objects.

   - bpo-10746(17): Fix ctypes producing wrong PEP 3118(18) type codes
     for integer types.

   - bpo-22536(19): The subprocess module now sets the filename when
     FileNotFoundError is raised on POSIX systems due to the executable
     or cwd not being found.

   - bpo-31249(20): concurrent.futures: WorkItem.run() used by
     ThreadPoolExecutor now breaks a reference cycle between an
     exception object and the WorkItem object.

   - bpo-31247(21): xmlrpc.server now explicitly breaks reference cycles
     when using sys.exc_info() in code handling exceptions.

   - bpo-30102(22): The ssl and hashlib modules now call
     OPENSSL_add_all_algorithms_noconf() on OpenSSL < 1.1.0.  The
     function detects CPU features and enables optimizations on some CPU
     architectures such as POWER8.  Patch is based on research from
     Gustavo Serra Scalet.

   - bpo-31185(23): Fixed miscellaneous errors in asyncio speedup
     module.

   - bpo-31135(24): ttk: fix the destroy() method of LabeledScale and
     OptionMenu classes.  Call the parent destroy() method even if the
     used attribute doesn’t exist.  The LabeledScale.destroy() method
     now also explicitly clears label and scale attributes to help the
     garbage collector to destroy all widgets.

   - bpo-31107(25): Fix ‘copyreg._slotnames()’ mangled attribute
     calculation for classes whose name begins with an underscore.
     Patch by Shane Harvey.

   - bpo-31061(26): Fixed a crash when using asyncio and threads.

   - bpo-30502(27): Fix handling of long oids in ssl.  Based on patch by
     Christian Heimes.

   - bpo-30119(28): ftplib.FTP.putline() now throws ValueError on
     commands that contains CR or LF. Patch by Dong-hee Na.

   - bpo-30595(29): multiprocessing.Queue.get() with a timeout now polls
     its reader in non-blocking mode if it succeeded to acquire the lock
     but the acquire took longer than the timeout.

   - bpo-29403(30): Fix ‘unittest.mock’’s autospec to not fail on
     method-bound builtin functions.  Patch by Aaron Gallagher.

   - bpo-30961(31): Fix decrementing a borrowed reference in
     tracemalloc.

   - bpo-25684(32): Change ‘ttk.OptionMenu’ radiobuttons to be unique
     across instances of ‘OptionMenu’.

   - bpo-30886(33): Fix multiprocessing.Queue.join_thread(): it now
     waits until the thread completes, even if the thread was started by
     the same process which created the queue.

   - bpo-29854(34): Fix segfault in readline when using readline’s
     history-size option.  Patch by Nir Soffer.

   - bpo-30319(35): socket.close() now ignores ECONNRESET error.

   - bpo-30828(36): Fix out of bounds write in
     ‘asyncio.CFuture.remove_done_callback()’.

   - bpo-30807(37): signal.setitimer() may disable the timer when passed
     a tiny value.  Tiny values (such as 1e-6) are valid non-zero values
     for setitimer(), which is specified as taking
     microsecond-resolution intervals.  However, on some platform, our
     conversion routine could convert 1e-6 into a zero interval,
     therefore disabling the timer instead of (re-)scheduling it.

   - bpo-30441(38): Fix bug when modifying os.environ while iterating
     over it

   - bpo-30532(39): Fix email header value parser dropping folding white
     space in certain cases.

   - bpo-30879(40): os.listdir() and os.scandir() now emit bytes names
     when called with bytes-like argument.

   - bpo-30746(41): Prohibited the ‘=’ character in environment variable
     names in ‘os.putenv()’ and ‘os.spawn*()’.

   - bpo-29755(42): Fixed the lgettext() family of functions in the
     gettext module.  They now always return bytes.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31499

   (2) https://bugs.python.org/issue28556

   (3) https://bugs.python.org/issue28556

   (4) https://bugs.python.org/issue31544

   (5) https://bugs.python.org/issue31234

   (6) https://bugs.python.org/issue31457

   (7) https://bugs.python.org/issue31400

   (8) https://bugs.python.org/issue28958

   (9) https://bugs.python.org/issue27340

   (10) https://bugs.python.org/issue31178

   (11) https://bugs.python.org/issue31350

   (12) https://bugs.python.org/issue31170

   (13) https://bugs.python.org/issue29136

   (14) https://bugs.python.org/issue29212

   (15) https://bugs.python.org/issue9146

   (16) https://bugs.python.org/issue27144

   (17) https://bugs.python.org/issue10746

   (18) https://www.python.org/dev/peps/pep-3118

   (19) https://bugs.python.org/issue22536

   (20) https://bugs.python.org/issue31249

   (21) https://bugs.python.org/issue31247

   (22) https://bugs.python.org/issue30102

   (23) https://bugs.python.org/issue31185

   (24) https://bugs.python.org/issue31135

   (25) https://bugs.python.org/issue31107

   (26) https://bugs.python.org/issue31061

   (27) https://bugs.python.org/issue30502

   (28) https://bugs.python.org/issue30119

   (29) https://bugs.python.org/issue30595

   (30) https://bugs.python.org/issue29403

   (31) https://bugs.python.org/issue30961

   (32) https://bugs.python.org/issue25684

   (33) https://bugs.python.org/issue30886

   (34) https://bugs.python.org/issue29854

   (35) https://bugs.python.org/issue30319

   (36) https://bugs.python.org/issue30828

   (37) https://bugs.python.org/issue30807

   (38) https://bugs.python.org/issue30441

   (39) https://bugs.python.org/issue30532

   (40) https://bugs.python.org/issue30879

   (41) https://bugs.python.org/issue30746

   (42) https://bugs.python.org/issue29755


File: python.info,  Node: Documentation<39>,  Next: Tests<37>,  Prev: Library<46>,  Up: Python 3 6 3 release candidate 1

1.19.50.4 Documentation
.......................

   - bpo-31294(1): Fix incomplete code snippet in the
     ZeroMQSocketListener and ZeroMQSocketHandler examples and adapt
     them to Python 3.

   - bpo-21649(2): Add RFC 7525 and Mozilla server side TLS links to SSL
     documentation.

   - bpo-30803(3): Clarify doc on truth value testing.  Original patch
     by Peter Thomassen.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31294

   (2) https://bugs.python.org/issue21649

   (3) https://bugs.python.org/issue30803


File: python.info,  Node: Tests<37>,  Next: Build<38>,  Prev: Documentation<39>,  Up: Python 3 6 3 release candidate 1

1.19.50.5 Tests
...............

   - bpo-31320(1): Silence traceback in test_ssl

   - bpo-25674(2): Remove sha256.tbs-internet.com ssl test

   - bpo-30715(3): Address ALPN callback changes for OpenSSL 1.1.0f.
     The latest version behaves like OpenSSL 1.0.2 and no longer aborts
     handshake.

   - bpo-30822(4): regrtest: Exclude tzdata from regrtest –all.  When
     running the test suite using –use=all / -u all, exclude tzdata
     since it makes test_datetime too slow (15-20 min on some buildbots)
     which then times out on some buildbots.  Fix also regrtest command
     line parser to allow passing -u extralargefile to run
     test_zipfile64.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31320

   (2) https://bugs.python.org/issue25674

   (3) https://bugs.python.org/issue30715

   (4) https://bugs.python.org/issue30822


File: python.info,  Node: Build<38>,  Next: Windows<36>,  Prev: Tests<37>,  Up: Python 3 6 3 release candidate 1

1.19.50.6 Build
...............

   - bpo-30854(1): Fix compile error when compiling –without-threads.
     Patch by Masayuki Yamamoto.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30854


File: python.info,  Node: Windows<36>,  Next: IDLE<36>,  Prev: Build<38>,  Up: Python 3 6 3 release candidate 1

1.19.50.7 Windows
.................

   - bpo-30389(1): Adds detection of Visual Studio 2017 to distutils on
     Windows.

   - bpo-31340(2): Change to building with MSVC v141 (included with
     Visual Studio 2017)

   - bpo-30581(3): os.cpu_count() now returns the correct number of
     processors on Windows when the number of logical processors is
     greater than 64.

   - bpo-30731(4): Add a missing xmlns to python.manifest so that it
     matches the schema.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30389

   (2) https://bugs.python.org/issue31340

   (3) https://bugs.python.org/issue30581

   (4) https://bugs.python.org/issue30731


File: python.info,  Node: IDLE<36>,  Next: Tools/Demos<21>,  Prev: Windows<36>,  Up: Python 3 6 3 release candidate 1

1.19.50.8 IDLE
..............

   - bpo-31493(1): IDLE code context – fix code update and font update
     timers.  Canceling timers prevents a warning message when test_idle
     completes.

   - bpo-31488(2): IDLE - Update non-key options in former extension
     classes.  When applying configdialog changes, call .reload for each
     feature class.  Change ParenMatch so updated options affect
     existing instances attached to existing editor windows.

   - bpo-31477(3): IDLE - Improve rstrip entry in doc.  Strip trailing
     whitespace strips more than blank spaces.  Multiline string
     literals are not skipped.

   - bpo-31480(4): IDLE - make tests pass with zzdummy extension
     disabled by default.

   - bpo-31421(5): Document how IDLE runs tkinter programs.  IDLE calls
     tcl/tk update in the background in order to make live interaction
     and experimentation with tkinter applications much easier.

   - bpo-31414(6): IDLE – fix tk entry box tests by deleting first.
     Adding to an int entry is not the same as deleting and inserting
     because int(‘’) will fail.

   - bpo-31051(7): Rearrange IDLE configdialog GenPage into Window,
     Editor, and Help sections.

   - bpo-30617(8): IDLE - Add docstrings and tests for outwin subclass
     of editor.  Move some data and functions from the class to module
     level.  Patch by Cheryl Sabella.

   - bpo-31287(9): IDLE - Do not modify tkinter.message in
     test_configdialog.

   - bpo-27099(10): Convert IDLE’s built-in ‘extensions’ to regular
     features.  About 10 IDLE features were implemented as supposedly
     optional extensions.  Their different behavior could be confusing
     or worse for users and not good for maintenance.  Hence the
     conversion.  The main difference for users is that user
     configurable key bindings for builtin features are now handled
     uniformly.  Now, editing a binding in a keyset only affects its
     value in the keyset.  All bindings are defined together in the
     system-specific default keysets in config-extensions.def.  All
     custom keysets are saved as a whole in config-extension.cfg.  All
     take effect as soon as one clicks Apply or Ok.  The affected events
     are ‘<<force-open-completions>>’, ‘<<expand-word>>’,
     ‘<<force-open-calltip>>’, ‘<<flash-paren>>’,
     ‘<<format-paragraph>>’, ‘<<run-module>>’, ‘<<check-module>>’, and
     ‘<<zoom-height>>’.  Any (global) customizations made before 3.6.3
     will not affect their keyset-specific customization after 3.6.3.
     and vice versa.  Initial patch by Charles Wohlganger.

   - bpo-31206(11): IDLE: Factor HighPage(Frame) class from
     ConfigDialog.  Patch by Cheryl Sabella.

   - bpo-31001(12): Add tests for configdialog highlight tab.  Patch by
     Cheryl Sabella.

   - bpo-31205(13): IDLE: Factor KeysPage(Frame) class from
     ConfigDialog.  The slightly modified tests continue to pass.  Patch
     by Cheryl Sabella.

   - bpo-31130(14): IDLE – stop leaks in test_configdialog.  Initial
     patch by Victor Stinner.

   - bpo-31002(15): Add tests for configdialog keys tab.  Patch by
     Cheryl Sabella.

   - bpo-19903(16): IDLE: Calltips use *note inspect.signature: 655.
     instead of *note inspect.getfullargspec: 657.  This improves
     calltips for builtins converted to use Argument Clinic.  Patch by
     Louie Lu.

   - bpo-31083(17): IDLE - Add an outline of a TabPage class in
     configdialog.  Update existing classes to match outline.  Initial
     patch by Cheryl Sabella.

   - bpo-31050(18): Factor GenPage(Frame) class from ConfigDialog.  The
     slightly modified tests continue to pass.  Patch by Cheryl Sabella.

   - bpo-31004(19): IDLE - Factor FontPage(Frame) class from
     ConfigDialog.  Slightly modified tests continue to pass.  Fix
     General tests.  Patch mostly by Cheryl Sabella.

   - bpo-30781(20): IDLE - Use ttk widgets in ConfigDialog.  Patches by
     Terry Jan Reedy and Cheryl Sabella.

   - bpo-31060(21): IDLE - Finish rearranging methods of ConfigDialog
     Grouping methods pertaining to each tab and the buttons will aid
     writing tests and improving the tabs and will enable splitting the
     groups into classes.

   - bpo-30853(22): IDLE – Factor a VarTrace class out of ConfigDialog.
     Instance tracers manages pairs consisting of a tk variable and a
     callback function.  When tracing is turned on, setting the variable
     calls the function.  Test coverage for the new class is 100%.

   - bpo-31003(23): IDLE: Add more tests for General tab.

   - bpo-30993(24): IDLE - Improve configdialog font page and tests.  In
     configdialog: Document causal pathways in create_font_tab
     docstring.  Simplify some attribute names.  Move set_samples calls
     to var_changed_font (idea from Cheryl Sabella).  Move related
     functions to positions after the create widgets function.  In
     test_configdialog: Fix test_font_set so not order dependent.  Fix
     renamed test_indent_scale so it tests the widget.  Adjust tests for
     movement of set_samples call.  Add tests for load functions.  Put
     all font tests in one class and tab indent tests in another.
     Except for two lines, these tests completely cover the related
     functions.

   - bpo-30981(25): IDLE – Add more configdialog font page tests.

   - bpo-28523(26): IDLE: replace ‘colour’ with ‘color’ in configdialog.

   - bpo-30917(27): Add tests for idlelib.config.IdleConf.  Increase
     coverage from 46% to 96%.  Patch by Louie Lu.

   - bpo-30934(28): Document coverage details for idlelib tests.  Add
     section to idlelib/idle-test/README.txt.  Include check that
     branches are taken both ways.  Exclude IDLE-specific code that does
     not run during unit tests.

   - bpo-30913(29): IDLE: Document ConfigDialog tk Vars, methods, and
     widgets in docstrings This will facilitate improving the dialog and
     splitting up the class.  Original patch by Cheryl Sabella.

   - bpo-30899(30): IDLE: Add tests for ConfigParser subclasses in
     config.  Patch by Louie Lu.

   - bpo-30881(31): IDLE: Add docstrings to browser.py.  Patch by Cheryl
     Sabella.

   - bpo-30851(32): IDLE: Remove unused variables in configdialog.  One
     is a duplicate, one is set but cannot be altered by users.  Patch
     by Cheryl Sabella.

   - bpo-30870(33): IDLE: In Settings dialog, select font with Up, Down
     keys as well as mouse.  Initial patch by Louie Lu.

   - bpo-8231(34): IDLE: call config.IdleConf.GetUserCfgDir only once.

   - bpo-30779(35): IDLE: Factor ConfigChanges class from configdialog,
     put in config; test.  * In config, put dump test code in a
     function; run it and unittest in ‘if __name__ == ‘__main__’.  * Add
     class config.ConfigChanges based on changes_class_v4.py on bpo
     issue.  * Add class test_config.ChangesTest, partly using
     configdialog_tests_v1.py.  * Revise configdialog to use
     ConfigChanges; see tracker msg297804.  * Revise test_configdialog
     to match configdialog changes.  * Remove configdialog functions
     unused or moved to ConfigChanges.  Cheryl Sabella contributed parts
     of the patch.

   - bpo-30777(36): IDLE: configdialog - Add docstrings and fix
     comments.  Patch by Cheryl Sabella.

   - bpo-30495(37): IDLE: Improve textview with docstrings, PEP8 names,
     and more tests.  Patch by Cheryl Sabella.

   - bpo-30723(38): IDLE: Make several improvements to parenmatch.  Add
     ‘parens’ style to highlight both opener and closer.  Make ‘default’
     style, which is not default, a synonym for ‘opener’.  Make
     time-delay work the same with all styles.  Add help for config
     dialog extensions tab, including help for parenmatch.  Add new
     tests.  Original patch by Charles Wohlganger.

   - bpo-30674(39): IDLE: add docstrings to grep module.  Patch by
     Cheryl Sabella

   - bpo-21519(40): IDLE’s basic custom key entry dialog now detects
     duplicates properly.  Original patch by Saimadhav Heblikar.

   - bpo-29910(41): IDLE no longer deletes a character after commenting
     out a region by a key shortcut.  Add ‘return 'break'’ for this and
     other potential conflicts between IDLE and default key bindings.

   - bpo-30728(42): Review and change idlelib.configdialog names.
     Lowercase method and attribute names.  Replace ‘colour’ with
     ‘color’, expand overly cryptic names, delete unneeded underscores.
     Replace ‘import *’ with specific imports.  Patches by Cheryl
     Sabella.

   - bpo-6739(43): IDLE: Verify user-entered key sequences by trying to
     bind them with tk.  Add tests for all 3 validation functions.
     Original patch by G Polo.  Tests added by Cheryl Sabella.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31493

   (2) https://bugs.python.org/issue31488

   (3) https://bugs.python.org/issue31477

   (4) https://bugs.python.org/issue31480

   (5) https://bugs.python.org/issue31421

   (6) https://bugs.python.org/issue31414

   (7) https://bugs.python.org/issue31051

   (8) https://bugs.python.org/issue30617

   (9) https://bugs.python.org/issue31287

   (10) https://bugs.python.org/issue27099

   (11) https://bugs.python.org/issue31206

   (12) https://bugs.python.org/issue31001

   (13) https://bugs.python.org/issue31205

   (14) https://bugs.python.org/issue31130

   (15) https://bugs.python.org/issue31002

   (16) https://bugs.python.org/issue19903

   (17) https://bugs.python.org/issue31083

   (18) https://bugs.python.org/issue31050

   (19) https://bugs.python.org/issue31004

   (20) https://bugs.python.org/issue30781

   (21) https://bugs.python.org/issue31060

   (22) https://bugs.python.org/issue30853

   (23) https://bugs.python.org/issue31003

   (24) https://bugs.python.org/issue30993

   (25) https://bugs.python.org/issue30981

   (26) https://bugs.python.org/issue28523

   (27) https://bugs.python.org/issue30917

   (28) https://bugs.python.org/issue30934

   (29) https://bugs.python.org/issue30913

   (30) https://bugs.python.org/issue30899

   (31) https://bugs.python.org/issue30881

   (32) https://bugs.python.org/issue30851

   (33) https://bugs.python.org/issue30870

   (34) https://bugs.python.org/issue8231

   (35) https://bugs.python.org/issue30779

   (36) https://bugs.python.org/issue30777

   (37) https://bugs.python.org/issue30495

   (38) https://bugs.python.org/issue30723

   (39) https://bugs.python.org/issue30674

   (40) https://bugs.python.org/issue21519

   (41) https://bugs.python.org/issue29910

   (42) https://bugs.python.org/issue30728

   (43) https://bugs.python.org/issue6739


File: python.info,  Node: Tools/Demos<21>,  Prev: IDLE<36>,  Up: Python 3 6 3 release candidate 1

1.19.50.9 Tools/Demos
.....................

   - bpo-30983(1): gdb integration commands (py-bt, etc.)  work on
     optimized shared builds now, too.  PEP 523(2) introduced
     _PyEval_EvalFrameDefault which inlines PyEval_EvalFrameEx on
     non-debug shared builds.  This broke the ability to use py-bt,
     py-up, and a few other Python-specific gdb integrations.  The
     problem is fixed by only looking for _PyEval_EvalFrameDefault
     frames in python-gdb.py.  Original patch by Bruno “Polaco”
     Penteado.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30983

   (2) https://www.python.org/dev/peps/pep-0523


File: python.info,  Node: Python 3 6 2 final,  Next: Python 3 6 2 release candidate 2,  Prev: Python 3 6 3 release candidate 1,  Up: Changelog

1.19.51 Python 3.6.2 final
--------------------------

`Release date: 2017-07-17'

No changes since release candidate 2


File: python.info,  Node: Python 3 6 2 release candidate 2,  Next: Python 3 6 2 release candidate 1,  Prev: Python 3 6 2 final,  Up: Changelog

1.19.52 Python 3.6.2 release candidate 2
----------------------------------------

`Release date: 2017-07-07'

* Menu:

* Security: Security<24>.


File: python.info,  Node: Security<24>,  Up: Python 3 6 2 release candidate 2

1.19.52.1 Security
..................

   - bpo-30730(1): Prevent environment variables injection in subprocess
     on Windows.  Prevent passing other environment variables and
     command arguments.

   - bpo-30694(2): Upgrade expat copy from 2.2.0 to 2.2.1 to get fixes
     of multiple security vulnerabilities including: CVE-2017-9233
     (External entity infinite loop DoS), CVE-2016-9063 (Integer
     overflow, re-fix), CVE-2016-0718 (Fix regression bugs from 2.2.0’s
     fix to CVE-2016-0718) and CVE-2012-0876 (Counter hash flooding with
     SipHash).  Note: the CVE-2016-5300 (Use os-specific entropy sources
     like getrandom) doesn’t impact Python, since Python already gets
     entropy from the OS to set the expat secret using
     ‘XML_SetHashSalt()’.

   - bpo-30500(3): Fix urllib.parse.splithost() to correctly parse
     fragments.  For example, ‘splithost('//127.0.0.1#@evil.com/')’ now
     correctly returns the ‘127.0.0.1’ host, instead of treating
     ‘@evil.com’ as the host in an authentication (‘login@host’).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30730

   (2) https://bugs.python.org/issue30694

   (3) https://bugs.python.org/issue30500


File: python.info,  Node: Python 3 6 2 release candidate 1,  Next: Python 3 6 1 final,  Prev: Python 3 6 2 release candidate 2,  Up: Changelog

1.19.53 Python 3.6.2 release candidate 1
----------------------------------------

`Release date: 2017-06-17'

* Menu:

* Core and Builtins: Core and Builtins<43>.
* Library: Library<47>.
* Security: Security<25>.
* Library: Library<48>.
* IDLE: IDLE<37>.
* C API: C API<31>.
* Build: Build<39>.
* Documentation: Documentation<40>.
* Tools/Demos: Tools/Demos<22>.
* Tests: Tests<38>.
* Windows: Windows<37>.


File: python.info,  Node: Core and Builtins<43>,  Next: Library<47>,  Up: Python 3 6 2 release candidate 1

1.19.53.1 Core and Builtins
...........................

   - bpo-30682(1): Removed a too-strict assertion that failed for
     certain f-strings, such as eval(“f’\n’”) and eval(“f’\r’”).

   - bpo-30604(2): Move co_extra_freefuncs to not be per-thread to avoid
     crashes

   - bpo-29104(3): Fixed parsing backslashes in f-strings.

   - bpo-27945(4): Fixed various segfaults with dict when input
     collections are mutated during searching, inserting or comparing.
     Based on patches by Duane Griffin and Tim Mitchell.

   - bpo-25794(5): Fixed type.__setattr__() and type.__delattr__() for
     non-interned attribute names.  Based on patch by Eryk Sun.

   - bpo-30039(6): If a KeyboardInterrupt happens when the interpreter
     is in the middle of resuming a chain of nested ‘yield from’ or
     ‘await’ calls, it’s now correctly delivered to the innermost frame.

   - bpo-12414(7): sys.getsizeof() on a code object now returns the
     sizes which includes the code struct and sizes of objects which it
     references.  Patch by Dong-hee Na.

   - bpo-29949(8): Fix memory usage regression of set and frozenset
     object.

   - bpo-29935(9): Fixed error messages in the index() method of tuple,
     list and deque when pass indices of wrong type.

   - bpo-29859(10): Show correct error messages when any of the
     pthread_* calls in thread_pthread.h fails.

   - bpo-28876(11): ‘bool(range)’ works even if ‘len(range)’ raises
     *note OverflowError: a41.

   - bpo-29600(12): Fix wrapping coroutine return values in
     StopIteration.

   - bpo-28856(13): Fix an oversight that %b format for bytes should
     support objects follow the buffer protocol.

   - bpo-29714(14): Fix a regression that bytes format may fail when
     containing zero bytes inside.

   - bpo-29478(15): If max_line_length=None is specified while using the
     Compat32 policy, it is no longer ignored.  Patch by Mircea Cosbuc.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30682

   (2) https://bugs.python.org/issue30604

   (3) https://bugs.python.org/issue29104

   (4) https://bugs.python.org/issue27945

   (5) https://bugs.python.org/issue25794

   (6) https://bugs.python.org/issue30039

   (7) https://bugs.python.org/issue12414

   (8) https://bugs.python.org/issue29949

   (9) https://bugs.python.org/issue29935

   (10) https://bugs.python.org/issue29859

   (11) https://bugs.python.org/issue28876

   (12) https://bugs.python.org/issue29600

   (13) https://bugs.python.org/issue28856

   (14) https://bugs.python.org/issue29714

   (15) https://bugs.python.org/issue29478


File: python.info,  Node: Library<47>,  Next: Security<25>,  Prev: Core and Builtins<43>,  Up: Python 3 6 2 release candidate 1

1.19.53.2 Library
.................

   - bpo-30616(1): Functional API of enum allows to create empty enums.
     Patched by Dong-hee Na

   - bpo-30038(2): Fix race condition between signal delivery and wakeup
     file descriptor.  Patch by Nathaniel Smith.

   - bpo-23894(3): lib2to3 now recognizes ‘rb'...'’ and ‘f'...'’
     strings.

   - bpo-23890(4): unittest.TestCase.assertRaises() now manually breaks
     a reference cycle to not keep objects alive longer than expected.

   - bpo-30149(5): inspect.signature() now supports callables with
     variable-argument parameters wrapped with partialmethod.  Patch by
     Dong-hee Na.

   - bpo-30645(6): Fix path calculation in imp.load_package(), fixing it
     for cases when a package is only shipped with bytecodes.  Patch by
     Alexandru Ardelean.

   - bpo-29931(7): Fixed comparison check for ipaddress.ip_interface
     objects.  Patch by Sanjay Sundaresan.

   - bpo-30605(8): re.compile() no longer raises a BytesWarning when
     compiling a bytes instance with misplaced inline modifier.  Patch
     by Roy Williams.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30616

   (2) https://bugs.python.org/issue30038

   (3) https://bugs.python.org/issue23894

   (4) https://bugs.python.org/issue23890

   (5) https://bugs.python.org/issue30149

   (6) https://bugs.python.org/issue30645

   (7) https://bugs.python.org/issue29931

   (8) https://bugs.python.org/issue30605


File: python.info,  Node: Security<25>,  Next: Library<48>,  Prev: Library<47>,  Up: Python 3 6 2 release candidate 1

1.19.53.3 Security
..................

   - bpo-29591(1): Update expat copy from 2.1.1 to 2.2.0 to get fixes of
     CVE-2016-0718 and CVE-2016-4472.  See
     ‘https://sourceforge.net/p/expat/bugs/537/’ for more information.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29591


File: python.info,  Node: Library<48>,  Next: IDLE<37>,  Prev: Security<25>,  Up: Python 3 6 2 release candidate 1

1.19.53.4 Library
.................

   - bpo-24484(1): Avoid race condition in multiprocessing cleanup
     (#2159)

   - bpo-28994(2): The traceback no longer displayed for SystemExit
     raised in a callback registered by atexit.

   - bpo-30508(3): Don’t log exceptions if Task/Future “cancel()” method
     was called.

   - bpo-28556(4): Updates to typing module: Add generic
     AsyncContextManager, add support for ContextManager on all
     versions.  Original PRs by Jelle Zijlstra and Ivan Levkivskyi

   - bpo-29870(5): Fix ssl sockets leaks when connection is aborted in
     asyncio/ssl implementation.  Patch by Michaël Sghaïer.

   - bpo-29743(6): Closing transport during handshake process leaks open
     socket.  Patch by Nikolay Kim

   - bpo-27585(7): Fix waiter cancellation in asyncio.Lock.  Patch by
     Mathieu Sornay.

   - bpo-30418(8): On Windows, subprocess.Popen.communicate() now also
     ignore EINVAL on stdin.write() if the child process is still
     running but closed the pipe.

   - bpo-29822(9): inspect.isabstract() now works during
     __init_subclass__.  Patch by Nate Soares.

   - bpo-29581(10): ABCMeta.__new__ now accepts ‘**kwargs’, allowing
     abstract base classes to use keyword parameters in
     __init_subclass__.  Patch by Nate Soares.

   - bpo-30557(11): faulthandler now correctly filters and displays
     exception codes on Windows

   - bpo-30378(12): Fix the problem that logging.handlers.SysLogHandler
     cannot handle IPv6 addresses.

   - bpo-29960(13): Preserve generator state when
     _random.Random.setstate() raises an exception.  Patch by Bryan
     Olson.

   - bpo-30414(14): multiprocessing.Queue._feed background running
     thread do not break from main loop on exception.

   - bpo-30003(15): Fix handling escape characters in HZ codec.  Based
     on patch by Ma Lin.

   - bpo-30301(16): Fix AttributeError when using SimpleQueue.empty()
     under `spawn' and `forkserver' start methods.

   - bpo-30329(17): imaplib and poplib now catch the Windows socket
     WSAEINVAL error (code 10022) on shutdown(SHUT_RDWR): An invalid
     operation was attempted.  This error occurs sometimes on SSL
     connections.

   - bpo-30375(18): Warnings emitted when compile a regular expression
     now always point to the line in the user code.  Previously they
     could point into inners of the re module if emitted from inside of
     groups or conditionals.

   - bpo-30048(19): Fixed ‘Task.cancel()’ can be ignored when the task
     is running coroutine and the coroutine returned without any more
     ‘await’.

   - bpo-30266(20): contextlib.AbstractContextManager now supports
     anti-registration by setting __enter__ = None or __exit__ = None,
     following the pattern introduced in bpo-25958(21).  Patch by Jelle
     Zijlstra.

   - bpo-30298(22): Weaken the condition of deprecation warnings for
     inline modifiers.  Now allowed several subsequential inline
     modifiers at the start of the pattern (e.g.  ‘'(?i)(?s)...'’).  In
     verbose mode whitespaces and comments now are allowed before and
     between inline modifiers (e.g.  ‘'(?x) (?i) (?s)...'’).

   - bpo-29990(23): Fix range checking in GB18030 decoder.  Original
     patch by Ma Lin.

   - bpo-26293(24): Change resulted because of zipfile breakage.  (See
     also: bpo-29094(25))

   - bpo-30243(26): Removed the __init__ methods of _json’s scanner and
     encoder.  Misusing them could cause memory leaks or crashes.  Now
     scanner and encoder objects are completely initialized in the
     __new__ methods.

   - bpo-30185(27): Avoid KeyboardInterrupt tracebacks in forkserver
     helper process when Ctrl-C is received.

   - bpo-28556(28): Various updates to typing module: add
     typing.NoReturn type, use WrapperDescriptorType, minor bug-fixes.
     Original PRs by Jim Fasarakis-Hilliard and Ivan Levkivskyi.

   - bpo-30205(29): Fix getsockname() for unbound AF_UNIX sockets on
     Linux.

   - bpo-30070(30): Fixed leaks and crashes in errors handling in the
     parser module.

   - bpo-30061(31): Fixed crashes in IOBase methods __next__() and
     readlines() when readline() or __next__() respectively return
     non-sizeable object.  Fixed possible other errors caused by not
     checking results of PyObject_Size(), PySequence_Size(), or
     PyMapping_Size().

   - bpo-30017(32): Allowed calling the close() method of the zip entry
     writer object multiple times.  Writing to a closed writer now
     always produces a ValueError.

   - bpo-30068(33): _io._IOBase.readlines will check if it’s closed
     first when hint is present.

   - bpo-29694(34): Fixed race condition in pathlib mkdir with flags
     parents=True.  Patch by Armin Rigo.

   - bpo-29692(35): Fixed arbitrary unchaining of RuntimeError
     exceptions in contextlib.contextmanager.  Patch by Siddharth
     Velankar.

   - bpo-29998(36): Pickling and copying ImportError now preserves name
     and path attributes.

   - bpo-29953(37): Fixed memory leaks in the replace() method of
     datetime and time objects when pass out of bound fold argument.

   - bpo-29942(38): Fix a crash in itertools.chain.from_iterable when
     encountering long runs of empty iterables.

   - bpo-27863(39): Fixed multiple crashes in ElementTree caused by race
     conditions and wrong types.

   - bpo-28699(40): Fixed a bug in pools in multiprocessing.pool that
     raising an exception at the very first of an iterable may swallow
     the exception or make the program hang.  Patch by Davin Potts and
     Xiang Zhang.

   - bpo-25803(41): Avoid incorrect errors raised by
     Path.mkdir(exist_ok=True) when the OS gives priority to errors such
     as EACCES over EEXIST.

   - bpo-29861(42): Release references to tasks, their arguments and
     their results as soon as they are finished in multiprocessing.Pool.

   - bpo-29884(43): faulthandler: Restore the old sigaltstack during
     teardown.  Patch by Christophe Zeitouny.

   - bpo-25455(44): Fixed crashes in repr of recursive buffered
     file-like objects.

   - bpo-29800(45): Fix crashes in partial.__repr__ if the keys of
     partial.keywords are not strings.  Patch by Michael Seifert.

   - bpo-29742(46): get_extra_info() raises exception if get called on
     closed ssl transport.  Patch by Nikolay Kim.

   - bpo-8256(47): Fixed possible failing or crashing input() if
     attributes “encoding” or “errors” of sys.stdin or sys.stdout are
     not set or are not strings.

   - bpo-28298(48): Fix a bug that prevented array ‘Q’, ‘L’ and ‘I’ from
     accepting big intables (objects that have __int__) as elements.
     Patch by Oren Milman.

   - bpo-28231(49): The zipfile module now accepts path-like objects for
     external paths.

   - bpo-26915(50): index() and count() methods of
     collections.abc.Sequence now check identity before checking
     equality when do comparisons.

   - bpo-29615(51): SimpleXMLRPCDispatcher no longer chains KeyError (or
     any other exception) to exception(s) raised in the dispatched
     methods.  Patch by Petr Motejlek.

   - bpo-30177(52): path.resolve(strict=False) no longer cuts the path
     after the first element not present in the filesystem.  Patch by
     Antoine Pietri.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24484

   (2) https://bugs.python.org/issue28994

   (3) https://bugs.python.org/issue30508

   (4) https://bugs.python.org/issue28556

   (5) https://bugs.python.org/issue29870

   (6) https://bugs.python.org/issue29743

   (7) https://bugs.python.org/issue27585

   (8) https://bugs.python.org/issue30418

   (9) https://bugs.python.org/issue29822

   (10) https://bugs.python.org/issue29581

   (11) https://bugs.python.org/issue30557

   (12) https://bugs.python.org/issue30378

   (13) https://bugs.python.org/issue29960

   (14) https://bugs.python.org/issue30414

   (15) https://bugs.python.org/issue30003

   (16) https://bugs.python.org/issue30301

   (17) https://bugs.python.org/issue30329

   (18) https://bugs.python.org/issue30375

   (19) https://bugs.python.org/issue30048

   (20) https://bugs.python.org/issue30266

   (21) https://bugs.python.org/issue25958

   (22) https://bugs.python.org/issue30298

   (23) https://bugs.python.org/issue29990

   (24) https://bugs.python.org/issue26293

   (25) https://bugs.python.org/issue29094

   (26) https://bugs.python.org/issue30243

   (27) https://bugs.python.org/issue30185

   (28) https://bugs.python.org/issue28556

   (29) https://bugs.python.org/issue30205

   (30) https://bugs.python.org/issue30070

   (31) https://bugs.python.org/issue30061

   (32) https://bugs.python.org/issue30017

   (33) https://bugs.python.org/issue30068

   (34) https://bugs.python.org/issue29694

   (35) https://bugs.python.org/issue29692

   (36) https://bugs.python.org/issue29998

   (37) https://bugs.python.org/issue29953

   (38) https://bugs.python.org/issue29942

   (39) https://bugs.python.org/issue27863

   (40) https://bugs.python.org/issue28699

   (41) https://bugs.python.org/issue25803

   (42) https://bugs.python.org/issue29861

   (43) https://bugs.python.org/issue29884

   (44) https://bugs.python.org/issue25455

   (45) https://bugs.python.org/issue29800

   (46) https://bugs.python.org/issue29742

   (47) https://bugs.python.org/issue8256

   (48) https://bugs.python.org/issue28298

   (49) https://bugs.python.org/issue28231

   (50) https://bugs.python.org/issue26915

   (51) https://bugs.python.org/issue29615

   (52) https://bugs.python.org/issue30177


File: python.info,  Node: IDLE<37>,  Next: C API<31>,  Prev: Library<48>,  Up: Python 3 6 2 release candidate 1

1.19.53.5 IDLE
..............

   - bpo-15786(1): Fix several problems with IDLE’s autocompletion box.
     The following should now work: clicking on selection box items;
     using the scrollbar; selecting an item by hitting Return.  Hangs on
     MacOSX should no longer happen.  Patch by Louie Lu.

   - bpo-25514(2): Add doc subsubsection about IDLE failure to start.
     Popup no-connection message directs users to this section.

   - bpo-30642(3): Fix reference leaks in IDLE tests.  Patches by Louie
     Lu and Terry Jan Reedy.

   - bpo-30495(4): Add docstrings for textview.py and use PEP8 names.
     Patches by Cheryl Sabella and Terry Jan Reedy.

   - bpo-30290(5): Help-about: use pep8 names and add tests.  Increase
     coverage to 100%.  Patches by Louie Lu, Cheryl Sabella, and Terry
     Jan Reedy.

   - bpo-30303(6): Add _utest option to textview; add new tests.
     Increase coverage to 100%.  Patches by Louie Lu and Terry Jan
     Reedy.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15786

   (2) https://bugs.python.org/issue25514

   (3) https://bugs.python.org/issue30642

   (4) https://bugs.python.org/issue30495

   (5) https://bugs.python.org/issue30290

   (6) https://bugs.python.org/issue30303


File: python.info,  Node: C API<31>,  Next: Build<39>,  Prev: IDLE<37>,  Up: Python 3 6 2 release candidate 1

1.19.53.6 C API
...............

   - bpo-27867(1): Function PySlice_GetIndicesEx() no longer replaced
     with a macro if Py_LIMITED_API is not set.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27867


File: python.info,  Node: Build<39>,  Next: Documentation<40>,  Prev: C API<31>,  Up: Python 3 6 2 release candidate 1

1.19.53.7 Build
...............

   - bpo-29941(1): Add ‘--with-assertions’ configure flag to explicitly
     enable C ‘assert()’ checks.  Defaults to off.  ‘--with-pydebug’
     implies ‘--with-assertions’.

   - bpo-28787(2): Fix out-of-tree builds of Python when configured with
     ‘--with--dtrace’.

   - bpo-29243(3): Prevent unnecessary rebuilding of Python during ‘make
     test’, ‘make install’ and some other make targets when configured
     with ‘--enable-optimizations’.

   - bpo-23404(4): Don’t regenerate generated files based on file
     modification time anymore: the action is now explicit.  Replace
     ‘make touch’ with ‘make regen-all’.

   - bpo-29643(5): Fix ‘--enable-optimization’ didn’t work.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29941

   (2) https://bugs.python.org/issue28787

   (3) https://bugs.python.org/issue29243

   (4) https://bugs.python.org/issue23404

   (5) https://bugs.python.org/issue29643


File: python.info,  Node: Documentation<40>,  Next: Tools/Demos<22>,  Prev: Build<39>,  Up: Python 3 6 2 release candidate 1

1.19.53.8 Documentation
.......................

   - bpo-30176(1): Add missing attribute related constants in curses
     documentation.

   - bpo-30052(2): the link targets for *note bytes(): 172. and *note
     bytearray(): 173. are now their respective type definitions, rather
     than the corresponding builtin function entries.  Use *note bytes:
     11f2. and *note bytearray: 11f3. to reference the latter.  In order
     to ensure this and future cross-reference updates are applied
     automatically, the daily documentation builds now disable the
     default output caching features in Sphinx.

   - bpo-26985(3): Add missing info of code object in inspect
     documentation.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30176

   (2) https://bugs.python.org/issue30052

   (3) https://bugs.python.org/issue26985


File: python.info,  Node: Tools/Demos<22>,  Next: Tests<38>,  Prev: Documentation<40>,  Up: Python 3 6 2 release candidate 1

1.19.53.9 Tools/Demos
.....................

   - bpo-29367(1): python-gdb.py now supports also ‘method-wrapper’
     (‘wrapperobject’) objects.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29367


File: python.info,  Node: Tests<38>,  Next: Windows<37>,  Prev: Tools/Demos<22>,  Up: Python 3 6 2 release candidate 1

1.19.53.10 Tests
................

   - bpo-30357(1): test_thread: setUp() now uses
     support.threading_setup() and support.threading_cleanup() to wait
     until threads complete to avoid random side effects on following
     tests.  Initial patch written by Grzegorz Grzywacz.

   - bpo-30197(2): Enhanced functions swap_attr() and swap_item() in the
     test.support module.  They now work when delete replaced attribute
     or item inside the with statement.  The old value of the attribute
     or item (or None if it doesn’t exist) now will be assigned to the
     target of the “as” clause, if there is one.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30357

   (2) https://bugs.python.org/issue30197


File: python.info,  Node: Windows<37>,  Prev: Tests<38>,  Up: Python 3 6 2 release candidate 1

1.19.53.11 Windows
..................

   - bpo-30687(1): Locate msbuild.exe on Windows when building rather
     than vcvarsall.bat

   - bpo-30450(2): The build process on Windows no longer depends on
     Subversion, instead pulling external code from GitHub via a Python
     script.  If Python 3.6 is not found on the system (via ‘py -3.6’),
     NuGet is used to download a copy of 32-bit Python.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30687

   (2) https://bugs.python.org/issue30450


File: python.info,  Node: Python 3 6 1 final,  Next: Python 3 6 1 release candidate 1,  Prev: Python 3 6 2 release candidate 1,  Up: Changelog

1.19.54 Python 3.6.1 final
--------------------------

`Release date: 2017-03-21'

* Menu:

* Core and Builtins: Core and Builtins<44>.
* Build: Build<40>.


File: python.info,  Node: Core and Builtins<44>,  Next: Build<40>,  Up: Python 3 6 1 final

1.19.54.1 Core and Builtins
...........................

   - bpo-29723(1): The ‘sys.path[0]’ initialization change for
     bpo-29139(2) caused a regression by revealing an inconsistency in
     how sys.path is initialized when executing ‘__main__’ from a
     zipfile, directory, or other import location.  The interpreter now
     consistently avoids ever adding the import location’s parent
     directory to ‘sys.path’, and ensures no other ‘sys.path’ entries
     are inadvertently modified when inserting the import location named
     on the command line.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29723

   (2) https://bugs.python.org/issue29139


File: python.info,  Node: Build<40>,  Prev: Core and Builtins<44>,  Up: Python 3 6 1 final

1.19.54.2 Build
...............

   - bpo-27593(1): fix format of git information used in sys.version

   - Fix incompatible comment in python.h

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27593


File: python.info,  Node: Python 3 6 1 release candidate 1,  Next: Python 3 6 0 final,  Prev: Python 3 6 1 final,  Up: Changelog

1.19.55 Python 3.6.1 release candidate 1
----------------------------------------

`Release date: 2017-03-04'

* Menu:

* Core and Builtins: Core and Builtins<45>.
* Library: Library<49>.
* IDLE: IDLE<38>.
* Windows: Windows<38>.
* C API: C API<32>.
* Documentation: Documentation<41>.
* Tests: Tests<39>.
* Build: Build<41>.


File: python.info,  Node: Core and Builtins<45>,  Next: Library<49>,  Up: Python 3 6 1 release candidate 1

1.19.55.1 Core and Builtins
...........................

   - bpo-28893(1): Set correct __cause__ for errors about invalid
     awaitables returned from __aiter__ and __anext__.

   - bpo-29683(2): Fixes to memory allocation in _PyCode_SetExtra.
     Patch by Brian Coleman.

   - bpo-29684(3): Fix minor regression of
     PyEval_CallObjectWithKeywords.  It should raise TypeError when
     kwargs is not a dict.  But it might cause segv when args=NULL and
     kwargs is not a dict.

   - bpo-28598(4): Support __rmod__ for subclasses of str being called
     before str.__mod__.  Patch by Martijn Pieters.

   - bpo-29607(5): Fix stack_effect computation for CALL_FUNCTION_EX.
     Patch by Matthieu Dartiailh.

   - bpo-29602(6): Fix incorrect handling of signed zeros in complex
     constructor for complex subclasses and for inputs having a
     __complex__ method.  Patch by Serhiy Storchaka.

   - bpo-29347(7): Fixed possibly dereferencing undefined pointers when
     creating weakref objects.

   - bpo-29438(8): Fixed use-after-free problem in key sharing dict.

   - bpo-29319(9): Prevent RunMainFromImporter overwriting sys.path[0].

   - bpo-29337(10): Fixed possible BytesWarning when compare the code
     objects.  Warnings could be emitted at compile time.

   - bpo-29327(11): Fixed a crash when pass the iterable keyword
     argument to sorted().

   - bpo-29034(12): Fix memory leak and use-after-free in os module
     (path_converter).

   - bpo-29159(13): Fix regression in bytes(x) when x.__index__() raises
     Exception.

   - bpo-28932(14): Do not include <sys/random.h> if it does not exist.

   - bpo-25677(15): Correct the positioning of the syntax error caret
     for indented blocks.  Based on patch by Michael Layzell.

   - bpo-29000(16): Fixed bytes formatting of octals with zero padding
     in alternate form.

   - bpo-26919(17): On Android, operating system data is now always
     encoded/decoded to/from UTF-8, instead of the locale encoding to
     avoid inconsistencies with os.fsencode() and os.fsdecode() which
     are already using UTF-8.

   - bpo-28991(18): functools.lru_cache() was susceptible to an obscure
     reentrancy bug triggerable by a monkey-patched len() function.

   - bpo-28739(19): f-string expressions are no longer accepted as
     docstrings and by ast.literal_eval() even if they do not include
     expressions.

   - bpo-28512(20): Fixed setting the offset attribute of SyntaxError by
     PyErr_SyntaxLocationEx() and PyErr_SyntaxLocationObject().

   - bpo-28918(21): Fix the cross compilation of xxlimited when Python
     has been built with Py_DEBUG defined.

   - bpo-28731(22): Optimize _PyDict_NewPresized() to create correct
     size dict.  Improve speed of dict literal with constant keys up to
     30%.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28893

   (2) https://bugs.python.org/issue29683

   (3) https://bugs.python.org/issue29684

   (4) https://bugs.python.org/issue28598

   (5) https://bugs.python.org/issue29607

   (6) https://bugs.python.org/issue29602

   (7) https://bugs.python.org/issue29347

   (8) https://bugs.python.org/issue29438

   (9) https://bugs.python.org/issue29319

   (10) https://bugs.python.org/issue29337

   (11) https://bugs.python.org/issue29327

   (12) https://bugs.python.org/issue29034

   (13) https://bugs.python.org/issue29159

   (14) https://bugs.python.org/issue28932

   (15) https://bugs.python.org/issue25677

   (16) https://bugs.python.org/issue29000

   (17) https://bugs.python.org/issue26919

   (18) https://bugs.python.org/issue28991

   (19) https://bugs.python.org/issue28739

   (20) https://bugs.python.org/issue28512

   (21) https://bugs.python.org/issue28918

   (22) https://bugs.python.org/issue28731


File: python.info,  Node: Library<49>,  Next: IDLE<38>,  Prev: Core and Builtins<45>,  Up: Python 3 6 1 release candidate 1

1.19.55.2 Library
.................

   - bpo-29169(1): Update zlib to 1.2.11.

   - bpo-29623(2): Allow use of path-like object as a single argument in
     ConfigParser.read().  Patch by David Ellis.

   - bpo-28963(3): Fix out of bound iteration in
     asyncio.Future.remove_done_callback implemented in C.

   - bpo-29704(4): asyncio.subprocess.SubprocessStreamProtocol no longer
     closes before all pipes are closed.

   - bpo-29271(5): Fix Task.current_task and Task.all_tasks implemented
     in C to accept None argument as their pure Python implementation.

   - bpo-29703(6): Fix asyncio to support instantiation of new event
     loops in child processes.

   - bpo-29376(7): Fix assertion error in
     threading._DummyThread.is_alive().

   - bpo-28624(8): Add a test that checks that cwd parameter of Popen()
     accepts PathLike objects.  Patch by Sayan Chowdhury.

   - bpo-28518(9): Start a transaction implicitly before a DML
     statement.  Patch by Aviv Palivoda.

   - bpo-29532(10): Altering a kwarg dictionary passed to
     functools.partial() no longer affects a partial object after
     creation.

   - bpo-29110(11): Fix file object leak in aifc.open() when file is
     given as a filesystem path and is not in valid AIFF format.  Patch
     by Anthony Zhang.

   - bpo-28556(12): Various updates to typing module: typing.Counter,
     typing.ChainMap, improved ABC caching, etc.  Original PRs by Jelle
     Zijlstra, Ivan Levkivskyi, Manuel Krebber, and Łukasz Langa.

   - bpo-29100(13): Fix datetime.fromtimestamp() regression introduced
     in Python 3.6.0: check minimum and maximum years.

   - bpo-29519(14): Fix weakref spewing exceptions during interpreter
     shutdown when used with a rare combination of multiprocessing and
     custom codecs.

   - bpo-29416(15): Prevent infinite loop in pathlib.Path.mkdir

   - bpo-29444(16): Fixed out-of-bounds buffer access in the group()
     method of the match object.  Based on patch by WGH.

   - bpo-29335(17): Fix subprocess.Popen.wait() when the child process
     has exited to a stopped instead of terminated state (ex: when under
     ptrace).

   - bpo-29290(18): Fix a regression in argparse that help messages
     would wrap at non-breaking spaces.

   - bpo-28735(19): Fixed the comparison of mock.MagickMock with
     mock.ANY.

   - bpo-29316(20): Restore the provisional status of typing module, add
     corresponding note to documentation.  Patch by Ivan L.

   - bpo-29219(21): Fixed infinite recursion in the repr of
     uninitialized ctypes.CDLL instances.

   - bpo-29011(22): Fix an important omission by adding Deque to the
     typing module.

   - bpo-28969(23): Fixed race condition in C implementation of
     functools.lru_cache.  KeyError could be raised when cached function
     with full cache was simultaneously called from different threads
     with the same uncached arguments.

   - bpo-29142(24): In urllib.request, suffixes in no_proxy environment
     variable with leading dots could match related hostnames again
     (e.g.  .b.c matches a.b.c).  Patch by Milan Oberkirch.

   - bpo-28961(25): Fix unittest.mock._Call helper: don’t ignore the
     name parameter anymore.  Patch written by Jiajun Huang.

   - bpo-29203(26): functools.lru_cache() now respects PEP 468(27) and
     preserves the order of keyword arguments.  f(a=1, b=2) is now
     cached separately from f(b=2, a=1) since both calls could
     potentially give different results.

   - bpo-15812(28): inspect.getframeinfo() now correctly shows the first
     line of a context.  Patch by Sam Breese.

   - bpo-29094(29): Offsets in a ZIP file created with extern file
     object and modes “w” and “x” now are relative to the start of the
     file.

   - bpo-29085(30): Allow random.Random.seed() to use high quality OS
     randomness rather than the pid and time.

   - bpo-29061(31): Fixed bug in secrets.randbelow() which would hang
     when given a negative input.  Patch by Brendan Donegan.

   - bpo-29079(32): Prevent infinite loop in pathlib.resolve() on
     Windows

   - bpo-13051(33): Fixed recursion errors in large or resized
     curses.textpad.Textbox.  Based on patch by Tycho Andersen.

   - bpo-29119(34): Fix weakrefs in the pure python version of
     collections.OrderedDict move_to_end() method.  Contributed by Andra
     Bogildea.

   - bpo-9770(35): curses.ascii predicates now work correctly with
     negative integers.

   - bpo-28427(36): old keys should not remove new values from
     WeakValueDictionary when collecting from another thread.

   - bpo-28923(37): Remove editor artifacts from Tix.py.

   - bpo-29055(38): Neaten-up empty population error on random.choice()
     by suppressing the upstream exception.

   - bpo-28871(39): Fixed a crash when deallocate deep ElementTree.

   - bpo-19542(40): Fix bugs in WeakValueDictionary.setdefault() and
     WeakValueDictionary.pop() when a GC collection happens in another
     thread.

   - bpo-20191(41): Fixed a crash in resource.prlimit() when passing a
     sequence that doesn’t own its elements as limits.

   - bpo-28779(42): multiprocessing.set_forkserver_preload() would crash
     the forkserver process if a preloaded module instantiated some
     multiprocessing objects such as locks.

   - bpo-28847(43): dbm.dumb now supports reading read-only files and no
     longer writes the index file when it is not changed.

   - bpo-26937(44): The chown() method of the tarfile.TarFile class does
     not fail now when the grp module cannot be imported, as for example
     on Android platforms.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29169

   (2) https://bugs.python.org/issue29623

   (3) https://bugs.python.org/issue28963

   (4) https://bugs.python.org/issue29704

   (5) https://bugs.python.org/issue29271

   (6) https://bugs.python.org/issue29703

   (7) https://bugs.python.org/issue29376

   (8) https://bugs.python.org/issue28624

   (9) https://bugs.python.org/issue28518

   (10) https://bugs.python.org/issue29532

   (11) https://bugs.python.org/issue29110

   (12) https://bugs.python.org/issue28556

   (13) https://bugs.python.org/issue29100

   (14) https://bugs.python.org/issue29519

   (15) https://bugs.python.org/issue29416

   (16) https://bugs.python.org/issue29444

   (17) https://bugs.python.org/issue29335

   (18) https://bugs.python.org/issue29290

   (19) https://bugs.python.org/issue28735

   (20) https://bugs.python.org/issue29316

   (21) https://bugs.python.org/issue29219

   (22) https://bugs.python.org/issue29011

   (23) https://bugs.python.org/issue28969

   (24) https://bugs.python.org/issue29142

   (25) https://bugs.python.org/issue28961

   (26) https://bugs.python.org/issue29203

   (27) https://www.python.org/dev/peps/pep-0468

   (28) https://bugs.python.org/issue15812

   (29) https://bugs.python.org/issue29094

   (30) https://bugs.python.org/issue29085

   (31) https://bugs.python.org/issue29061

   (32) https://bugs.python.org/issue29079

   (33) https://bugs.python.org/issue13051

   (34) https://bugs.python.org/issue29119

   (35) https://bugs.python.org/issue9770

   (36) https://bugs.python.org/issue28427

   (37) https://bugs.python.org/issue28923

   (38) https://bugs.python.org/issue29055

   (39) https://bugs.python.org/issue28871

   (40) https://bugs.python.org/issue19542

   (41) https://bugs.python.org/issue20191

   (42) https://bugs.python.org/issue28779

   (43) https://bugs.python.org/issue28847

   (44) https://bugs.python.org/issue26937


File: python.info,  Node: IDLE<38>,  Next: Windows<38>,  Prev: Library<49>,  Up: Python 3 6 1 release candidate 1

1.19.55.3 IDLE
..............

   - bpo-29071(1): IDLE colors f-string prefixes (but not invalid ur
     prefixes).

   - bpo-28572(2): Add 10% to coverage of IDLE’s test_configdialog.
     Update and augment description of the configuration system.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29071

   (2) https://bugs.python.org/issue28572


File: python.info,  Node: Windows<38>,  Next: C API<32>,  Prev: IDLE<38>,  Up: Python 3 6 1 release candidate 1

1.19.55.4 Windows
.................

   - bpo-29579(1): Removes readme.txt from the installer

   - bpo-29326(2): Ignores blank lines in ._pth files (Patch by Alexey
     Izbyshev)

   - bpo-28164(3): Correctly handle special console filenames (patch by
     Eryk Sun)

   - bpo-29409(4): Implement PEP 529(5) for io.FileIO (Patch by Eryk
     Sun)

   - bpo-29392(6): Prevent crash when passing invalid arguments into
     msvcrt module.

   - bpo-25778(7): winreg does not truncate string correctly (Patch by
     Eryk Sun)

   - bpo-28896(8): Deprecate WindowsRegistryFinder and disable it by
     default.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29579

   (2) https://bugs.python.org/issue29326

   (3) https://bugs.python.org/issue28164

   (4) https://bugs.python.org/issue29409

   (5) https://www.python.org/dev/peps/pep-0529

   (6) https://bugs.python.org/issue29392

   (7) https://bugs.python.org/issue25778

   (8) https://bugs.python.org/issue28896


File: python.info,  Node: C API<32>,  Next: Documentation<41>,  Prev: Windows<38>,  Up: Python 3 6 1 release candidate 1

1.19.55.5 C API
...............

   - bpo-27867(1): Function PySlice_GetIndicesEx() is replaced with a
     macro if Py_LIMITED_API is not set or set to the value between
     0x03050400 and 0x03060000 (not including) or 0x03060100 or higher.

   - bpo-29083(2): Fixed the declaration of some public API functions.
     PyArg_VaParse() and PyArg_VaParseTupleAndKeywords() were not
     available in limited API. PyArg_ValidateKeywordArguments(),
     PyArg_UnpackTuple() and Py_BuildValue() were not available in
     limited API of version < 3.3 when PY_SSIZE_T_CLEAN is defined.

   - bpo-29058(3): All stable API extensions added after Python 3.2 are
     now available only when Py_LIMITED_API is set to the PY_VERSION_HEX
     value of the minimum Python version supporting this API.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27867

   (2) https://bugs.python.org/issue29083

   (3) https://bugs.python.org/issue29058


File: python.info,  Node: Documentation<41>,  Next: Tests<39>,  Prev: C API<32>,  Up: Python 3 6 1 release candidate 1

1.19.55.6 Documentation
.......................

   - bpo-28929(1): Link the documentation to its source file on GitHub.

   - bpo-25008(2): Document smtpd.py as effectively deprecated and add a
     pointer to aiosmtpd, a third-party asyncio-based replacement.

   - bpo-26355(3): Add canonical header link on each page to
     corresponding major version of the documentation.  Patch by
     Matthias Bussonnier.

   - bpo-29349(4): Fix Python 2 syntax in code for building the
     documentation.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28929

   (2) https://bugs.python.org/issue25008

   (3) https://bugs.python.org/issue26355

   (4) https://bugs.python.org/issue29349


File: python.info,  Node: Tests<39>,  Next: Build<41>,  Prev: Documentation<41>,  Up: Python 3 6 1 release candidate 1

1.19.55.7 Tests
...............

   - bpo-28087(1): Skip test_asyncore and test_eintr poll failures on
     macOS. Skip some tests of select.poll when running on macOS due to
     unresolved issues with the underlying system poll function on some
     macOS versions.

   - bpo-29571(2): to match the behaviour of the ‘re.LOCALE’ flag,
     test_re.test_locale_flag now uses
     ‘locale.getpreferredencoding(False)’ to determine the candidate
     encoding for the test regex (allowing it to correctly skip the test
     when the default locale encoding is a multi-byte encoding)

   - bpo-28950(3): Disallow -j0 to be combined with -T/-l in regrtest
     command line arguments.

   - bpo-28683(4): Fix the tests that bind() a unix socket and raise
     PermissionError on Android for a non-root user.

   - bpo-26939(5): Add the support.setswitchinterval() function to fix
     test_functools hanging on the Android armv7 qemu emulator.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28087

   (2) https://bugs.python.org/issue29571

   (3) https://bugs.python.org/issue28950

   (4) https://bugs.python.org/issue28683

   (5) https://bugs.python.org/issue26939


File: python.info,  Node: Build<41>,  Prev: Tests<39>,  Up: Python 3 6 1 release candidate 1

1.19.55.8 Build
...............

   - bpo-27593(1): sys.version and the platform module python_build(),
     python_branch(), and python_revision() functions now use git
     information rather than hg when building from a repo.

   - bpo-29572(2): Update Windows build and OS X installers to use
     OpenSSL 1.0.2k.

   - bpo-26851(3): Set Android compilation and link flags.

   - bpo-28768(4): Fix implicit declaration of function _setmode.  Patch
     by Masayuki Yamamoto

   - bpo-29080(5): Removes hard dependency on hg.exe from
     PCBuild/build.bat

   - bpo-23903(6): Added missed names to PC/python3.def.

   - bpo-28762(7): lockf() is available on Android API level 24, but the
     F_LOCK macro is not defined in android-ndk-r13.

   - bpo-28538(8): Fix the compilation error that occurs because
     if_nameindex() is available on Android API level 24, but the
     if_nameindex structure is not defined.

   - bpo-20211(9): Do not add the directory for installing C header
     files and the directory for installing object code libraries to the
     cross compilation search paths.  Original patch by Thomas
     Petazzoni.

   - bpo-28849(10): Do not define sys.implementation._multiarch on
     Android.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27593

   (2) https://bugs.python.org/issue29572

   (3) https://bugs.python.org/issue26851

   (4) https://bugs.python.org/issue28768

   (5) https://bugs.python.org/issue29080

   (6) https://bugs.python.org/issue23903

   (7) https://bugs.python.org/issue28762

   (8) https://bugs.python.org/issue28538

   (9) https://bugs.python.org/issue20211

   (10) https://bugs.python.org/issue28849


File: python.info,  Node: Python 3 6 0 final,  Next: Python 3 6 0 release candidate 2,  Prev: Python 3 6 1 release candidate 1,  Up: Changelog

1.19.56 Python 3.6.0 final
--------------------------

`Release date: 2016-12-23'

No changes since release candidate 2


File: python.info,  Node: Python 3 6 0 release candidate 2,  Next: Python 3 6 0 release candidate 1,  Prev: Python 3 6 0 final,  Up: Changelog

1.19.57 Python 3.6.0 release candidate 2
----------------------------------------

`Release date: 2016-12-16'

* Menu:

* Core and Builtins: Core and Builtins<46>.
* Tools/Demos: Tools/Demos<23>.
* Windows: Windows<39>.
* Build: Build<42>.


File: python.info,  Node: Core and Builtins<46>,  Next: Tools/Demos<23>,  Up: Python 3 6 0 release candidate 2

1.19.57.1 Core and Builtins
...........................

   - bpo-28147(1): Fix a memory leak in split-table dictionaries:
     setattr() must not convert combined table into split table.  Patch
     written by INADA Naoki.

   - bpo-28990(2): Fix asyncio SSL hanging if connection is closed
     before handshake is completed.  (Patch by HoHo-Ho)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28147

   (2) https://bugs.python.org/issue28990


File: python.info,  Node: Tools/Demos<23>,  Next: Windows<39>,  Prev: Core and Builtins<46>,  Up: Python 3 6 0 release candidate 2

1.19.57.2 Tools/Demos
.....................

   - bpo-28770(1): Fix python-gdb.py for fastcalls.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28770


File: python.info,  Node: Windows<39>,  Next: Build<42>,  Prev: Tools/Demos<23>,  Up: Python 3 6 0 release candidate 2

1.19.57.3 Windows
.................

   - bpo-28896(1): Deprecate WindowsRegistryFinder.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28896


File: python.info,  Node: Build<42>,  Prev: Windows<39>,  Up: Python 3 6 0 release candidate 2

1.19.57.4 Build
...............

   - bpo-28898(1): Prevent gdb build errors due to HAVE_LONG_LONG
     redefinition.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28898


File: python.info,  Node: Python 3 6 0 release candidate 1,  Next: Python 3 6 0 beta 4,  Prev: Python 3 6 0 release candidate 2,  Up: Changelog

1.19.58 Python 3.6.0 release candidate 1
----------------------------------------

`Release date: 2016-12-06'

* Menu:

* Core and Builtins: Core and Builtins<47>.
* Library: Library<50>.
* C API: C API<33>.
* Documentation: Documentation<42>.
* Tools/Demos: Tools/Demos<24>.


File: python.info,  Node: Core and Builtins<47>,  Next: Library<50>,  Up: Python 3 6 0 release candidate 1

1.19.58.1 Core and Builtins
...........................

   - bpo-23722(1): Rather than silently producing a class that doesn’t
     support zero-argument ‘super()’ in methods, failing to pass the new
     ‘__classcell__’ namespace entry up to ‘type.__new__’ now results in
     a ‘DeprecationWarning’ and a class that supports zero-argument
     ‘super()’.

   - bpo-28797(2): Modifying the class __dict__ inside the __set_name__
     method of a descriptor that is used inside that class no longer
     prevents calling the __set_name__ method of other descriptors.

   - bpo-28782(3): Fix a bug in the implementation ‘yield from’ when
     checking if the next instruction is YIELD_FROM. Regression
     introduced by WORDCODE (bpo-26647(4)).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23722

   (2) https://bugs.python.org/issue28797

   (3) https://bugs.python.org/issue28782

   (4) https://bugs.python.org/issue26647


File: python.info,  Node: Library<50>,  Next: C API<33>,  Prev: Core and Builtins<47>,  Up: Python 3 6 0 release candidate 1

1.19.58.2 Library
.................

   - bpo-27030(1): Unknown escapes in re.sub() replacement template are
     allowed again.  But they still are deprecated and will be disabled
     in 3.7.

   - bpo-28835(2): Fix a regression introduced in
     warnings.catch_warnings(): call warnings.showwarning() if it was
     overridden inside the context manager.

   - bpo-27172(3): To assist with upgrades from 2.7, the previously
     documented deprecation of ‘inspect.getfullargspec()’ has been
     reversed.  This decision may be revisited again after the Python
     2.7 branch is no longer officially supported.

   - bpo-26273(4): Add new ‘socket.TCP_CONGESTION’ (Linux 2.6.13) and
     ‘socket.TCP_USER_TIMEOUT’ (Linux 2.6.37) constants.  Patch written
     by Omar Sandoval.

   - bpo-24142(5): Reading a corrupt config file left configparser in an
     invalid state.  Original patch by Florian Höch.

   - bpo-28843(6): Fix asyncio C Task to handle exceptions
     __traceback__.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27030

   (2) https://bugs.python.org/issue28835

   (3) https://bugs.python.org/issue27172

   (4) https://bugs.python.org/issue26273

   (5) https://bugs.python.org/issue24142

   (6) https://bugs.python.org/issue28843


File: python.info,  Node: C API<33>,  Next: Documentation<42>,  Prev: Library<50>,  Up: Python 3 6 0 release candidate 1

1.19.58.3 C API
...............

   - bpo-28808(1): PyUnicode_CompareWithASCIIString() now never raises
     exceptions.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28808


File: python.info,  Node: Documentation<42>,  Next: Tools/Demos<24>,  Prev: C API<33>,  Up: Python 3 6 0 release candidate 1

1.19.58.4 Documentation
.......................

   - bpo-23722(1): The data model reference and the porting section in
     the What’s New guide now cover the additional ‘__classcell__’
     handling needed for custom metaclasses to fully support PEP 487(2)
     and zero-argument ‘super()’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23722

   (2) https://www.python.org/dev/peps/pep-0487


File: python.info,  Node: Tools/Demos<24>,  Prev: Documentation<42>,  Up: Python 3 6 0 release candidate 1

1.19.58.5 Tools/Demos
.....................

   - bpo-28023(1): Fix python-gdb.py didn’t support new dict
     implementation.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28023


File: python.info,  Node: Python 3 6 0 beta 4,  Next: Python 3 6 0 beta 3,  Prev: Python 3 6 0 release candidate 1,  Up: Changelog

1.19.59 Python 3.6.0 beta 4
---------------------------

`Release date: 2016-11-21'

* Menu:

* Core and Builtins: Core and Builtins<48>.
* Library: Library<51>.
* Documentation: Documentation<43>.
* Tests: Tests<40>.
* Build: Build<43>.


File: python.info,  Node: Core and Builtins<48>,  Next: Library<51>,  Up: Python 3 6 0 beta 4

1.19.59.1 Core and Builtins
...........................

   - bpo-28532(1): Show sys.version when -V option is supplied twice.

   - bpo-27100(2): The with-statement now checks for __enter__ before it
     checks for __exit__.  This gives less confusing error messages when
     both methods are missing.  Patch by Jonathan Ellington.

   - bpo-28746(3): Fix the set_inheritable() file descriptor method on
     platforms that do not have the ioctl FIOCLEX and FIONCLEX commands.

   - bpo-26920(4): Fix not getting the locale’s charset upon
     initializing the interpreter, on platforms that do not have
     langinfo.

   - bpo-28648(5): Fixed crash in Py_DecodeLocale() in debug build on
     Mac OS X when decode astral characters.  Patch by Xiang Zhang.

   - bpo-19398(6): Extra slash no longer added to sys.path components in
     case of empty compile-time PYTHONPATH components.

   - bpo-28665(7): Improve speed of the STORE_DEREF opcode by 40%.

   - bpo-28583(8): PyDict_SetDefault didn’t combine split table when
     needed.  Patch by Xiang Zhang.

   - bpo-27243(9): Change PendingDeprecationWarning ->
     DeprecationWarning.  As it was agreed in the issue, __aiter__
     returning an awaitable should result in PendingDeprecationWarning
     in 3.5 and in DeprecationWarning in 3.6.

   - bpo-26182(10): Fix a refleak in code that raises
     DeprecationWarning.

   - bpo-28721(11): Fix asynchronous generators aclose() and athrow() to
     handle StopAsyncIteration propagation properly.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28532

   (2) https://bugs.python.org/issue27100

   (3) https://bugs.python.org/issue28746

   (4) https://bugs.python.org/issue26920

   (5) https://bugs.python.org/issue28648

   (6) https://bugs.python.org/issue19398

   (7) https://bugs.python.org/issue28665

   (8) https://bugs.python.org/issue28583

   (9) https://bugs.python.org/issue27243

   (10) https://bugs.python.org/issue26182

   (11) https://bugs.python.org/issue28721


File: python.info,  Node: Library<51>,  Next: Documentation<43>,  Prev: Core and Builtins<48>,  Up: Python 3 6 0 beta 4

1.19.59.2 Library
.................

   - bpo-28752(1): Restored the __reduce__() methods of datetime
     objects.

   - bpo-28727(2): Regular expression patterns, _sre.SRE_Pattern objects
     created by re.compile(), become comparable (only x==y and x!=y
     operators).  This change should fix the bpo-18383(3): don’t
     duplicate warning filters when the warnings module is reloaded
     (thing usually only done in unit tests).

   - bpo-20572(4): The subprocess.Popen.wait method’s undocumented
     endtime parameter now raises a DeprecationWarning.

   - bpo-25659(5): In ctypes, prevent a crash calling the from_buffer()
     and from_buffer_copy() methods on abstract classes like Array.

   - bpo-19717(6): Makes Path.resolve() succeed on paths that do not
     exist.  Patch by Vajrasky Kok

   - bpo-28563(7): Fixed possible DoS and arbitrary code execution when
     handle plural form selections in the gettext module.  The
     expression parser now supports exact syntax supported by GNU
     gettext.

   - bpo-28387(8): Fixed possible crash in _io.TextIOWrapper deallocator
     when the garbage collector is invoked in other thread.  Based on
     patch by Sebastian Cufre.

   - bpo-28600(9): Optimize loop.call_soon.

   - bpo-28613(10): Fix get_event_loop() return the current loop if
     called from coroutines/callbacks.

   - bpo-28634(11): Fix asyncio.isfuture() to support unittest.Mock.

   - bpo-26081(12): Fix refleak in _asyncio.Future.__iter__().throw.

   - bpo-28639(13): Fix inspect.isawaitable to always return bool Patch
     by Justin Mayfield.

   - bpo-28652(14): Make loop methods reject socket kinds they do not
     support.

   - bpo-28653(15): Fix a refleak in functools.lru_cache.

   - bpo-28703(16): Fix asyncio.iscoroutinefunction to handle Mock
     objects.

   - bpo-28704(17): Fix create_unix_server to support Path-like objects
     (PEP 519).

   - bpo-28720(18): Add collections.abc.AsyncGenerator.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28752

   (2) https://bugs.python.org/issue28727

   (3) https://bugs.python.org/issue18383

   (4) https://bugs.python.org/issue20572

   (5) https://bugs.python.org/issue25659

   (6) https://bugs.python.org/issue19717

   (7) https://bugs.python.org/issue28563

   (8) https://bugs.python.org/issue28387

   (9) https://bugs.python.org/issue28600

   (10) https://bugs.python.org/issue28613

   (11) https://bugs.python.org/issue28634

   (12) https://bugs.python.org/issue26081

   (13) https://bugs.python.org/issue28639

   (14) https://bugs.python.org/issue28652

   (15) https://bugs.python.org/issue28653

   (16) https://bugs.python.org/issue28703

   (17) https://bugs.python.org/issue28704

   (18) https://bugs.python.org/issue28720


File: python.info,  Node: Documentation<43>,  Next: Tests<40>,  Prev: Library<51>,  Up: Python 3 6 0 beta 4

1.19.59.3 Documentation
.......................

   - bpo-28513(1): Documented command-line interface of zipfile.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28513


File: python.info,  Node: Tests<40>,  Next: Build<43>,  Prev: Documentation<43>,  Up: Python 3 6 0 beta 4

1.19.59.4 Tests
...............

   - bpo-28666(1): Now test.support.rmtree is able to remove unwritable
     or unreadable directories.

   - bpo-23839(2): Various caches now are cleared before running every
     test file.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28666

   (2) https://bugs.python.org/issue23839


File: python.info,  Node: Build<43>,  Prev: Tests<40>,  Up: Python 3 6 0 beta 4

1.19.59.5 Build
...............

   - bpo-10656(1): Fix out-of-tree building on AIX. Patch by Tristan
     Carel and Michael Haubenwallner.

   - bpo-26359(2): Rename –with-optimiations to –enable-optimizations.

   - bpo-28676(3): Prevent missing ‘getentropy’ declaration warning on
     macOS. Patch by Gareth Rees.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue10656

   (2) https://bugs.python.org/issue26359

   (3) https://bugs.python.org/issue28676


File: python.info,  Node: Python 3 6 0 beta 3,  Next: Python 3 6 0 beta 2,  Prev: Python 3 6 0 beta 4,  Up: Changelog

1.19.60 Python 3.6.0 beta 3
---------------------------

`Release date: 2016-10-31'

* Menu:

* Core and Builtins: Core and Builtins<49>.
* Library: Library<52>.
* Windows: Windows<40>.
* Build: Build<44>.
* Tests: Tests<41>.


File: python.info,  Node: Core and Builtins<49>,  Next: Library<52>,  Up: Python 3 6 0 beta 3

1.19.60.1 Core and Builtins
...........................

   - bpo-28128(1): Deprecation warning for invalid str and byte escape
     sequences now prints better information about where the error
     occurs.  Patch by Serhiy Storchaka and Eric Smith.

   - bpo-28509(2): dict.update() no longer allocate unnecessary large
     memory.

   - bpo-28426(3): Fixed potential crash in PyUnicode_AsDecodedObject()
     in debug build.

   - bpo-28517(4): Fixed of-by-one error in the peephole optimizer that
     caused keeping unreachable code.

   - bpo-28214(5): Improved exception reporting for problematic
     __set_name__ attributes.

   - bpo-23782(6): Fixed possible memory leak in _PyTraceback_Add() and
     exception loss in PyTraceBack_Here().

   - bpo-28471(7): Fix “Python memory allocator called without holding
     the GIL” crash in socket.setblocking.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28128

   (2) https://bugs.python.org/issue28509

   (3) https://bugs.python.org/issue28426

   (4) https://bugs.python.org/issue28517

   (5) https://bugs.python.org/issue28214

   (6) https://bugs.python.org/issue23782

   (7) https://bugs.python.org/issue28471


File: python.info,  Node: Library<52>,  Next: Windows<40>,  Prev: Core and Builtins<49>,  Up: Python 3 6 0 beta 3

1.19.60.2 Library
.................

   - bpo-27517(1): LZMA compressor and decompressor no longer raise
     exceptions if given empty data twice.  Patch by Benjamin Fogle.

   - bpo-28549(2): Fixed segfault in curses’s addch() with ncurses6.

   - bpo-28449(3): tarfile.open() with mode “r” or “r:” now tries to
     open a tar file with compression before trying to open it without
     compression.  Otherwise it had 50% chance failed with
     ignore_zeros=True.

   - bpo-23262(4): The webbrowser module now supports Firefox 36+ and
     derived browsers.  Based on patch by Oleg Broytman.

   - bpo-27939(5): Fixed bugs in tkinter.ttk.LabeledScale and
     tkinter.Scale caused by representing the scale as float value
     internally in Tk.  tkinter.IntVar now works if float value is set
     to underlying Tk variable.

   - bpo-18844(6): The various ways of specifying weights for
     random.choices() now produce the same result sequences.

   - bpo-28255(7): calendar.TextCalendar().prmonth() no longer prints a
     space at the start of new line after printing a month’s calendar.
     Patch by Xiang Zhang.

   - bpo-20491(8): The textwrap.TextWrapper class now honors
     non-breaking spaces.  Based on patch by Kaarle Ritvanen.

   - bpo-28353(9): os.fwalk() no longer fails on broken links.

   - bpo-28430(10): Fix iterator of C implemented asyncio.Future doesn’t
     accept non-None value is passed to it.send(val).

   - bpo-27025(11): Generated names for Tkinter widgets now start by the
     “!” prefix for readability.

   - bpo-25464(12): Fixed HList.header_exists() in tkinter.tix module by
     addin a workaround to Tix library bug.

   - bpo-28488(13): shutil.make_archive() no longer adds entry “./” to
     ZIP archive.

   - bpo-25953(14): re.sub() now raises an error for invalid numerical
     group reference in replacement template even if the pattern is not
     found in the string.  Error message for invalid group reference now
     includes the group index and the position of the reference.  Based
     on patch by SilentGhost.

   - bpo-18219(15): Optimize csv.DictWriter for large number of columns.
     Patch by Mariatta Wijaya.

   - bpo-28448(16): Fix C implemented asyncio.Future didn’t work on
     Windows.

   - bpo-28480(17): Fix error building socket module when multithreading
     is disabled.

   - bpo-24452(18): Make webbrowser support Chrome on Mac OS X.

   - bpo-20766(19): Fix references leaked by pdb in the handling of
     SIGINT handlers.

   - bpo-28492(20): Fix how StopIteration exception is raised in
     _asyncio.Future.

   - bpo-28500(21): Fix asyncio to handle async gens GC from another
     thread.

   - bpo-26923(22): Fix asyncio.Gather to refuse being cancelled once
     all children are done.  Patch by Johannes Ebke.

   - bpo-26796(23): Don’t configure the number of workers for default
     threadpool executor.  Initial patch by Hans Lawrenz.

   - bpo-28544(24): Implement asyncio.Task in C.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27517

   (2) https://bugs.python.org/issue28549

   (3) https://bugs.python.org/issue28449

   (4) https://bugs.python.org/issue23262

   (5) https://bugs.python.org/issue27939

   (6) https://bugs.python.org/issue18844

   (7) https://bugs.python.org/issue28255

   (8) https://bugs.python.org/issue20491

   (9) https://bugs.python.org/issue28353

   (10) https://bugs.python.org/issue28430

   (11) https://bugs.python.org/issue27025

   (12) https://bugs.python.org/issue25464

   (13) https://bugs.python.org/issue28488

   (14) https://bugs.python.org/issue25953

   (15) https://bugs.python.org/issue18219

   (16) https://bugs.python.org/issue28448

   (17) https://bugs.python.org/issue28480

   (18) https://bugs.python.org/issue24452

   (19) https://bugs.python.org/issue20766

   (20) https://bugs.python.org/issue28492

   (21) https://bugs.python.org/issue28500

   (22) https://bugs.python.org/issue26923

   (23) https://bugs.python.org/issue26796

   (24) https://bugs.python.org/issue28544


File: python.info,  Node: Windows<40>,  Next: Build<44>,  Prev: Library<52>,  Up: Python 3 6 0 beta 3

1.19.60.3 Windows
.................

   - bpo-28522(1): Fixes mishandled buffer reallocation in getpathp.c

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28522


File: python.info,  Node: Build<44>,  Next: Tests<41>,  Prev: Windows<40>,  Up: Python 3 6 0 beta 3

1.19.60.4 Build
...............

   - bpo-28444(1): Fix missing extensions modules when cross compiling.

   - bpo-28208(2): Update Windows build and OS X installers to use
     SQLite 3.14.2.

   - bpo-28248(3): Update Windows build and OS X installers to use
     OpenSSL 1.0.2j.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28444

   (2) https://bugs.python.org/issue28208

   (3) https://bugs.python.org/issue28248


File: python.info,  Node: Tests<41>,  Prev: Build<44>,  Up: Python 3 6 0 beta 3

1.19.60.5 Tests
...............

   - bpo-26944(1): Fix test_posix for Android where ‘id -G’ is entirely
     wrong or missing the effective gid.

   - bpo-28409(2): regrtest: fix the parser of command line arguments.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26944

   (2) https://bugs.python.org/issue28409


File: python.info,  Node: Python 3 6 0 beta 2,  Next: Python 3 6 0 beta 1,  Prev: Python 3 6 0 beta 3,  Up: Changelog

1.19.61 Python 3.6.0 beta 2
---------------------------

`Release date: 2016-10-10'

* Menu:

* Core and Builtins: Core and Builtins<50>.
* Library: Library<53>.
* Windows: Windows<41>.
* C API: C API<34>.
* Build: Build<45>.
* Tests: Tests<42>.


File: python.info,  Node: Core and Builtins<50>,  Next: Library<53>,  Up: Python 3 6 0 beta 2

1.19.61.1 Core and Builtins
...........................

   - bpo-28183(1): Optimize and cleanup dict iteration.

   - bpo-26081(2): Added C implementation of asyncio.Future.  Original
     patch by Yury Selivanov.

   - bpo-28379(3): Added sanity checks and tests for
     PyUnicode_CopyCharacters().  Patch by Xiang Zhang.

   - bpo-28376(4): The type of long range iterator is now registered as
     Iterator.  Patch by Oren Milman.

   - bpo-28376(5): Creating instances of range_iterator by calling
     range_iterator type now is deprecated.  Patch by Oren Milman.

   - bpo-28376(6): The constructor of range_iterator now checks that
     step is not 0.  Patch by Oren Milman.

   - bpo-26906(7): Resolving special methods of uninitialized type now
     causes implicit initialization of the type instead of a fail.

   - bpo-18287(8): PyType_Ready() now checks that tp_name is not NULL.
     Original patch by Niklas Koep.

   - bpo-24098(9): Fixed possible crash when AST is changed in process
     of compiling it.

   - bpo-28201(10): Dict reduces possibility of 2nd conflict in hash
     table when hashes have same lower bits.

   - bpo-28350(11): String constants with null character no longer
     interned.

   - bpo-26617(12): Fix crash when GC runs during weakref callbacks.

   - bpo-27942(13): String constants now interned recursively in tuples
     and frozensets.

   - bpo-21578(14): Fixed misleading error message when ImportError
     called with invalid keyword args.

   - bpo-28203(15): Fix incorrect type in complex(1.0, {2:3}) error
     message.  Patch by Soumya Sharma.

   - bpo-28086(16): Single var-positional argument of tuple subtype was
     passed unscathed to the C-defined function.  Now it is converted to
     exact tuple.

   - bpo-28214(17): Now __set_name__ is looked up on the class instead
     of the instance.

   - bpo-27955(18): Fallback on reading /dev/urandom device when the
     getrandom() syscall fails with EPERM, for example when blocked by
     SECCOMP.

   - bpo-28192(19): Don’t import readline in isolated mode.

   - Upgrade internal unicode databases to Unicode version 9.0.0.

   - bpo-28131(20): Fix a regression in zipimport’s compile_source().
     zipimport should use the same optimization level as the
     interpreter.

   - bpo-28126(21): Replace Py_MEMCPY with memcpy().  Visual Studio can
     properly optimize memcpy().

   - bpo-28120(22): Fix dict.pop() for splitted dictionary when trying
     to remove a “pending key” (Not yet inserted in split-table).  Patch
     by Xiang Zhang.

   - bpo-26182(23): Raise DeprecationWarning when async and await
     keywords are used as variable/attribute/class/function name.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28183

   (2) https://bugs.python.org/issue26081

   (3) https://bugs.python.org/issue28379

   (4) https://bugs.python.org/issue28376

   (5) https://bugs.python.org/issue28376

   (6) https://bugs.python.org/issue28376

   (7) https://bugs.python.org/issue26906

   (8) https://bugs.python.org/issue18287

   (9) https://bugs.python.org/issue24098

   (10) https://bugs.python.org/issue28201

   (11) https://bugs.python.org/issue28350

   (12) https://bugs.python.org/issue26617

   (13) https://bugs.python.org/issue27942

   (14) https://bugs.python.org/issue21578

   (15) https://bugs.python.org/issue28203

   (16) https://bugs.python.org/issue28086

   (17) https://bugs.python.org/issue28214

   (18) https://bugs.python.org/issue27955

   (19) https://bugs.python.org/issue28192

   (20) https://bugs.python.org/issue28131

   (21) https://bugs.python.org/issue28126

   (22) https://bugs.python.org/issue28120

   (23) https://bugs.python.org/issue26182


File: python.info,  Node: Library<53>,  Next: Windows<41>,  Prev: Core and Builtins<50>,  Up: Python 3 6 0 beta 2

1.19.61.2 Library
.................

   - bpo-27998(1): Fixed bytes path support in os.scandir() on Windows.
     Patch by Eryk Sun.

   - bpo-28317(2): The disassembler now decodes FORMAT_VALUE argument.

   - bpo-26293(3): Fixed writing ZIP files that starts not from the
     start of the file.  Offsets in ZIP file now are relative to the
     start of the archive in conforming to the specification.

   - bpo-28380(4): unittest.mock Mock autospec functions now properly
     support assert_called, assert_not_called, and assert_called_once.

   - bpo-27181(5): remove statistics.geometric_mean and defer until 3.7.

   - bpo-28229(6): lzma module now supports pathlib.

   - bpo-28321(7): Fixed writing non-BMP characters with binary format
     in plistlib.

   - bpo-28225(8): bz2 module now supports pathlib.  Initial patch by
     Ethan Furman.

   - bpo-28227(9): gzip now supports pathlib.  Patch by Ethan Furman.

   - bpo-27358(10): Optimized merging var-keyword arguments and improved
     error message when passing a non-mapping as a var-keyword argument.

   - bpo-28257(11): Improved error message when passing a non-iterable
     as a var-positional argument.  Added opcode
     BUILD_TUPLE_UNPACK_WITH_CALL.

   - bpo-28322(12): Fixed possible crashes when unpickle itertools
     objects from incorrect pickle data.  Based on patch by John Leitch.

   - bpo-28228(13): imghdr now supports pathlib.

   - bpo-28226(14): compileall now supports pathlib.

   - bpo-28314(15): Fix function declaration (C flags) for the
     getiterator() method of xml.etree.ElementTree.Element.

   - bpo-28148(16): Stop using localtime() and gmtime() in the time
     module.  Introduced platform independent _PyTime_localtime API that
     is similar to POSIX localtime_r, but available on all platforms.
     Patch by Ed Schouten.

   - bpo-28253(17): Fixed calendar functions for extreme months: 0001-01
     and 9999-12.  Methods itermonthdays() and itermonthdays2() are
     reimplemented so that they don’t call itermonthdates() which can
     cause datetime.date under/overflow.

   - bpo-28275(18): Fixed possible use after free in the decompress()
     methods of the LZMADecompressor and BZ2Decompressor classes.
     Original patch by John Leitch.

   - bpo-27897(19): Fixed possible crash in
     sqlite3.Connection.create_collation() if pass invalid string-like
     object as a name.  Patch by Xiang Zhang.

   - bpo-18844(20): random.choices() now has k as a keyword-only
     argument to improve the readability of common cases and come into
     line with the signature used in other languages.

   - bpo-18893(21): Fix invalid exception handling in
     Lib/ctypes/macholib/dyld.py.  Patch by Madison May.

   - bpo-27611(22): Fixed support of default root window in the
     tkinter.tix module.  Added the master parameter in the DisplayStyle
     constructor.

   - bpo-27348(23): In the traceback module, restore the formatting of
     exception messages like “Exception: None”.  This fixes a regression
     introduced in 3.5a2.

   - bpo-25651(24): Allow falsy values to be used for msg parameter of
     subTest().

   - bpo-27778(25): Fix a memory leak in os.getrandom() when the
     getrandom() is interrupted by a signal and a signal handler raises
     a Python exception.

   - bpo-28200(26): Fix memory leak on Windows in the os module (fix
     path_converter() function).

   - bpo-25400(27): RobotFileParser now correctly returns default values
     for crawl_delay and request_rate.  Initial patch by Peter Wirtz.

   - bpo-27932(28): Prevent memory leak in win32_ver().

   - Fix UnboundLocalError in socket._sendfile_use_sendfile.

   - bpo-28075(29): Check for ERROR_ACCESS_DENIED in Windows
     implementation of os.stat().  Patch by Eryk Sun.

   - bpo-22493(30): Warning message emitted by using inline flags in the
     middle of regular expression now contains a (truncated) regex
     pattern.  Patch by Tim Graham.

   - bpo-25270(31): Prevent codecs.escape_encode() from raising
     SystemError when an empty bytestring is passed.

   - bpo-28181(32): Get antigravity over HTTPS. Patch by Kaartic
     Sivaraam.

   - bpo-25895(33): Enable WebSocket URL schemes in
     urllib.parse.urljoin.  Patch by Gergely Imreh and Markus
     Holtermann.

   - bpo-28114(34): Fix a crash in parse_envlist() when env contains
     byte strings.  Patch by Eryk Sun.

   - bpo-27599(35): Fixed buffer overrun in binascii.b2a_qp() and
     binascii.a2b_qp().

   - bpo-27906(36): Fix socket accept exhaustion during high TCP
     traffic.  Patch by Kevin Conway.

   - bpo-28174(37): Handle when SO_REUSEPORT isn’t properly supported.
     Patch by Seth Michael Larson.

   - bpo-26654(38): Inspect functools.partial in
     asyncio.Handle.__repr__.  Patch by iceboy.

   - bpo-26909(39): Fix slow pipes IO in asyncio.  Patch by INADA Naoki.

   - bpo-28176(40): Fix callbacks race in
     asyncio.SelectorLoop.sock_connect.

   - bpo-27759(41): Fix selectors incorrectly retain invalid file
     descriptors.  Patch by Mark Williams.

   - bpo-28368(42): Refuse monitoring processes if the child watcher has
     no loop attached.  Patch by Vincent Michel.

   - bpo-28369(43): Raise RuntimeError when transport’s FD is used with
     add_reader, add_writer, etc.

   - bpo-28370(44): Speedup asyncio.StreamReader.readexactly.  Patch by
     Коренберг Марк.

   - bpo-28371(45): Deprecate passing asyncio.Handles to
     run_in_executor.

   - bpo-28372(46): Fix asyncio to support formatting of non-python
     coroutines.

   - bpo-28399(47): Remove UNIX socket from FS before binding.  Patch by
     Коренберг Марк.

   - bpo-27972(48): Prohibit Tasks to await on themselves.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27998

   (2) https://bugs.python.org/issue28317

   (3) https://bugs.python.org/issue26293

   (4) https://bugs.python.org/issue28380

   (5) https://bugs.python.org/issue27181

   (6) https://bugs.python.org/issue28229

   (7) https://bugs.python.org/issue28321

   (8) https://bugs.python.org/issue28225

   (9) https://bugs.python.org/issue28227

   (10) https://bugs.python.org/issue27358

   (11) https://bugs.python.org/issue28257

   (12) https://bugs.python.org/issue28322

   (13) https://bugs.python.org/issue28228

   (14) https://bugs.python.org/issue28226

   (15) https://bugs.python.org/issue28314

   (16) https://bugs.python.org/issue28148

   (17) https://bugs.python.org/issue28253

   (18) https://bugs.python.org/issue28275

   (19) https://bugs.python.org/issue27897

   (20) https://bugs.python.org/issue18844

   (21) https://bugs.python.org/issue18893

   (22) https://bugs.python.org/issue27611

   (23) https://bugs.python.org/issue27348

   (24) https://bugs.python.org/issue25651

   (25) https://bugs.python.org/issue27778

   (26) https://bugs.python.org/issue28200

   (27) https://bugs.python.org/issue25400

   (28) https://bugs.python.org/issue27932

   (29) https://bugs.python.org/issue28075

   (30) https://bugs.python.org/issue22493

   (31) https://bugs.python.org/issue25270

   (32) https://bugs.python.org/issue28181

   (33) https://bugs.python.org/issue25895

   (34) https://bugs.python.org/issue28114

   (35) https://bugs.python.org/issue27599

   (36) https://bugs.python.org/issue27906

   (37) https://bugs.python.org/issue28174

   (38) https://bugs.python.org/issue26654

   (39) https://bugs.python.org/issue26909

   (40) https://bugs.python.org/issue28176

   (41) https://bugs.python.org/issue27759

   (42) https://bugs.python.org/issue28368

   (43) https://bugs.python.org/issue28369

   (44) https://bugs.python.org/issue28370

   (45) https://bugs.python.org/issue28371

   (46) https://bugs.python.org/issue28372

   (47) https://bugs.python.org/issue28399

   (48) https://bugs.python.org/issue27972


File: python.info,  Node: Windows<41>,  Next: C API<34>,  Prev: Library<53>,  Up: Python 3 6 0 beta 2

1.19.61.3 Windows
.................

   - bpo-28402(1): Adds signed catalog files for stdlib on Windows.

   - bpo-28333(2): Enables Unicode for ps1/ps2 and input() prompts.
     (Patch by Eryk Sun)

   - bpo-28251(3): Improvements to help manuals on Windows.

   - bpo-28110(4): launcher.msi has different product codes between
     32-bit and 64-bit

   - bpo-28161(5): Opening CON for write access fails

   - bpo-28162(6): WindowsConsoleIO readall() fails if first line starts
     with Ctrl+Z

   - bpo-28163(7): WindowsConsoleIO fileno() passes wrong flags to
     _open_osfhandle

   - bpo-28164(8): _PyIO_get_console_type fails for various paths

   - bpo-28137(9): Renames Windows path file to ._pth

   - bpo-28138(10): Windows ._pth file should allow import site

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28402

   (2) https://bugs.python.org/issue28333

   (3) https://bugs.python.org/issue28251

   (4) https://bugs.python.org/issue28110

   (5) https://bugs.python.org/issue28161

   (6) https://bugs.python.org/issue28162

   (7) https://bugs.python.org/issue28163

   (8) https://bugs.python.org/issue28164

   (9) https://bugs.python.org/issue28137

   (10) https://bugs.python.org/issue28138


File: python.info,  Node: C API<34>,  Next: Build<45>,  Prev: Windows<41>,  Up: Python 3 6 0 beta 2

1.19.61.4 C API
...............

   - bpo-28426(1): Deprecated undocumented functions
     PyUnicode_AsEncodedObject(), PyUnicode_AsDecodedObject(),
     PyUnicode_AsDecodedUnicode() and PyUnicode_AsEncodedUnicode().

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28426


File: python.info,  Node: Build<45>,  Next: Tests<42>,  Prev: C API<34>,  Up: Python 3 6 0 beta 2

1.19.61.5 Build
...............

   - bpo-28258(1): Fixed build with Estonian locale (python-config and
     distclean targets in Makefile).  Patch by Arfrever Frehtes
     Taifersar Arahesis.

   - bpo-26661(2): setup.py now detects system libffi with multiarch
     wrapper.

   - bpo-15819(3): Remove redundant include search directory option for
     building outside the source tree.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28258

   (2) https://bugs.python.org/issue26661

   (3) https://bugs.python.org/issue15819


File: python.info,  Node: Tests<42>,  Prev: Build<45>,  Up: Python 3 6 0 beta 2

1.19.61.6 Tests
...............

   - bpo-28217(1): Adds _testconsole module to test console input.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28217


File: python.info,  Node: Python 3 6 0 beta 1,  Next: Python 3 6 0 alpha 4,  Prev: Python 3 6 0 beta 2,  Up: Changelog

1.19.62 Python 3.6.0 beta 1
---------------------------

`Release date: 2016-09-12'

* Menu:

* Core and Builtins: Core and Builtins<51>.
* Library: Library<54>.
* IDLE: IDLE<39>.
* C API: C API<35>.
* Tests: Tests<43>.
* Build: Build<46>.
* Tools/Demos: Tools/Demos<25>.
* Windows: Windows<42>.


File: python.info,  Node: Core and Builtins<51>,  Next: Library<54>,  Up: Python 3 6 0 beta 1

1.19.62.1 Core and Builtins
...........................

   - bpo-23722(1): The __class__ cell used by zero-argument super() is
     now initialized from type.__new__ rather than __build_class__, so
     class methods relying on that will now work correctly when called
     from metaclass methods during class creation.  Patch by Martin
     Teichmann.

   - bpo-25221(2): Fix corrupted result from PyLong_FromLong(0) when
     Python is compiled with NSMALLPOSINTS = 0.

   - bpo-27080(3): Implement formatting support for PEP 515(4).  Initial
     patch by Chris Angelico.

   - bpo-27199(5): In tarfile, expose copyfileobj bufsize to improve
     throughput.  Patch by Jason Fried.

   - bpo-27948(6): In f-strings, only allow backslashes inside the
     braces (where the expressions are).  This is a breaking change from
     the 3.6 alpha releases, where backslashes are allowed anywhere in
     an f-string.  Also, require that expressions inside f-strings be
     enclosed within literal braces, and not escapes like
     ‘f'\x7b"hi"\x7d'’.

   - bpo-28046(7): Remove platform-specific directories from sys.path.

   - bpo-28071(8): Add early-out for differencing from an empty set.

   - bpo-25758(9): Prevents zipimport from unnecessarily encoding a
     filename (patch by Eryk Sun)

   - bpo-25856(10): The __module__ attribute of extension classes and
     functions now is interned.  This leads to more compact pickle data
     with protocol 4.

   - bpo-27213(11): Rework CALL_FUNCTION* opcodes to produce shorter and
     more efficient bytecode.  Patch by Demur Rumed, design by Serhiy
     Storchaka, reviewed by Serhiy Storchaka and Victor Stinner.

   - bpo-26331(12): Implement tokenizing support for PEP 515(13).  Patch
     by Georg Brandl.

   - bpo-27999(14): Make “global after use” a SyntaxError, and ditto for
     nonlocal.  Patch by Ivan Levkivskyi.

   - bpo-28003(15): Implement PEP 525(16) – Asynchronous Generators.

   - bpo-27985(17): Implement PEP 526(18) – Syntax for Variable
     Annotations.  Patch by Ivan Levkivskyi.

   - bpo-26058(19): Add a new private version to the builtin dict type,
     incremented at each dictionary creation and at each dictionary
     change.  Implementation of the PEP 509.

   - bpo-27364(20): A backslash-character pair that is not a valid
     escape sequence now generates a DeprecationWarning.  Patch by
     Emanuel Barry.

   - bpo-27350(21): *note dict: 164. implementation is changed like
     PyPy.  It is more compact and preserves insertion order.  (Concept
     developed by Raymond Hettinger and patch by Inada Naoki.)

   - bpo-27911(22): Remove unnecessary error checks in
     ‘exec_builtin_or_dynamic()’.

   - bpo-27078(23): Added BUILD_STRING opcode.  Optimized f-strings
     evaluation.

   - bpo-17884(24): Python now requires systems with inttypes.h and
     stdint.h

   - bpo-27961(25): Require platforms to support ‘long long’.  Python
     hasn’t compiled without ‘long long’ for years, so this is basically
     a formality.

   - bpo-27355(26): Removed support for Windows CE. It was never
     finished, and Windows CE is no longer a relevant platform for
     Python.

   - Implement PEP 523(27).

   - bpo-27870(28): A left shift of zero by a large integer no longer
     attempts to allocate large amounts of memory.

   - bpo-25402(29): In int-to-decimal-string conversion, improve the
     estimate of the intermediate memory required, and remove an
     unnecessarily strict overflow check.  Patch by Serhiy Storchaka.

   - bpo-27214(30): In long_invert, be more careful about modifying
     object returned by long_add, and remove an unnecessary check for
     small longs.  Thanks Oren Milman for analysis and patch.

   - bpo-27506(31): Support passing the bytes/bytearray.translate()
     “delete” argument by keyword.

   - bpo-27812(32): Properly clear out a generator’s frame’s
     backreference to the generator to prevent crashes in frame.clear().

   - bpo-27811(33): Fix a crash when a coroutine that has not been
     awaited is finalized with warnings-as-errors enabled.

   - bpo-27587(34): Fix another issue found by PVS-Studio: Null pointer
     check after use of ‘def’ in _PyState_AddModule().  Initial patch by
     Christian Heimes.

   - bpo-27792(35): The modulo operation applied to ‘bool’ and other
     ‘int’ subclasses now always returns an ‘int’.  Previously the
     return type depended on the input values.  Patch by Xiang Zhang.

   - bpo-26984(36): int() now always returns an instance of exact int.

   - bpo-25604(37): Fix a minor bug in integer true division; this bug
     could potentially have caused off-by-one-ulp results on platforms
     with unreliable ldexp implementations.

   - bpo-24254(38): Make class definition namespace ordered by default.

   - bpo-27662(39): Fix an overflow check in ‘List_New’: the original
     code was checking against ‘Py_SIZE_MAX’ instead of the correct
     upper bound of ‘Py_SSIZE_T_MAX’.  Patch by Xiang Zhang.

   - bpo-27782(40): Multi-phase extension module import now correctly
     allows the ‘m_methods’ field to be used to add module level
     functions to instances of non-module types returned from
     ‘Py_create_mod’.  Patch by Xiang Zhang.

   - bpo-27936(41): The round() function accepted a second None argument
     for some types but not for others.  Fixed the inconsistency by
     accepting None for all numeric types.

   - bpo-27487(42): Warn if a submodule argument to “python -m” or
     runpy.run_module() is found in sys.modules after parent packages
     are imported, but before the submodule is executed.

   - bpo-27157(43): Make only type() itself accept the one-argument
     form.  Patch by Eryk Sun and Emanuel Barry.

   - bpo-27558(44): Fix a SystemError in the implementation of “raise”
     statement.  In a brand new thread, raise a RuntimeError since there
     is no active exception to reraise.  Patch written by Xiang Zhang.

   - bpo-28008(45): Implement PEP 530(46) – asynchronous comprehensions.

   - bpo-27942(47): Fix memory leak in codeobject.c

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23722

   (2) https://bugs.python.org/issue25221

   (3) https://bugs.python.org/issue27080

   (4) https://www.python.org/dev/peps/pep-0515

   (5) https://bugs.python.org/issue27199

   (6) https://bugs.python.org/issue27948

   (7) https://bugs.python.org/issue28046

   (8) https://bugs.python.org/issue28071

   (9) https://bugs.python.org/issue25758

   (10) https://bugs.python.org/issue25856

   (11) https://bugs.python.org/issue27213

   (12) https://bugs.python.org/issue26331

   (13) https://www.python.org/dev/peps/pep-0515

   (14) https://bugs.python.org/issue27999

   (15) https://bugs.python.org/issue28003

   (16) https://www.python.org/dev/peps/pep-0525

   (17) https://bugs.python.org/issue27985

   (18) https://www.python.org/dev/peps/pep-0526

   (19) https://bugs.python.org/issue26058

   (20) https://bugs.python.org/issue27364

   (21) https://bugs.python.org/issue27350

   (22) https://bugs.python.org/issue27911

   (23) https://bugs.python.org/issue27078

   (24) https://bugs.python.org/issue17884

   (25) https://bugs.python.org/issue27961

   (26) https://bugs.python.org/issue27355

   (27) https://www.python.org/dev/peps/pep-0523

   (28) https://bugs.python.org/issue27870

   (29) https://bugs.python.org/issue25402

   (30) https://bugs.python.org/issue27214

   (31) https://bugs.python.org/issue27506

   (32) https://bugs.python.org/issue27812

   (33) https://bugs.python.org/issue27811

   (34) https://bugs.python.org/issue27587

   (35) https://bugs.python.org/issue27792

   (36) https://bugs.python.org/issue26984

   (37) https://bugs.python.org/issue25604

   (38) https://bugs.python.org/issue24254

   (39) https://bugs.python.org/issue27662

   (40) https://bugs.python.org/issue27782

   (41) https://bugs.python.org/issue27936

   (42) https://bugs.python.org/issue27487

   (43) https://bugs.python.org/issue27157

   (44) https://bugs.python.org/issue27558

   (45) https://bugs.python.org/issue28008

   (46) https://www.python.org/dev/peps/pep-0530

   (47) https://bugs.python.org/issue27942


File: python.info,  Node: Library<54>,  Next: IDLE<39>,  Prev: Core and Builtins<51>,  Up: Python 3 6 0 beta 1

1.19.62.2 Library
.................

   - bpo-28732(1): Fix crash in os.spawnv() with no elements in args

   - bpo-28485(2): Always raise ValueError for negative
     compileall.compile_dir(workers=…) parameter, even when
     multithreading is unavailable.

   - bpo-28037(3): Use sqlite3_get_autocommit() instead of setting
     Connection->inTransaction manually.

   - bpo-25283(4): Attributes tm_gmtoff and tm_zone are now available on
     all platforms in the return values of time.localtime() and
     time.gmtime().

   - bpo-24454(5): Regular expression match object groups are now
     accessible using __getitem__.  “mo[x]” is equivalent to
     “mo.group(x)”.

   - bpo-10740(6): sqlite3 no longer implicitly commit an open
     transaction before DDL statements.

   - bpo-17941(7): Add a `module' parameter to collections.namedtuple().

   - bpo-22493(8): Inline flags now should be used only at the start of
     the regular expression.  Deprecation warning is emitted if uses
     them in the middle of the regular expression.

   - bpo-26885(9): xmlrpc now supports unmarshalling additional data
     types used by Apache XML-RPC implementation for numerics and None.

   - bpo-28070(10): Fixed parsing inline verbose flag in regular
     expressions.

   - bpo-19500(11): Add client-side SSL session resumption to the ssl
     module.

   - bpo-28022(12): Deprecate ssl-related arguments in favor of
     SSLContext.  The deprecation include manual creation of SSLSocket
     and certfile/keyfile (or similar) in ftplib, httplib, imaplib,
     smtplib, poplib and urllib.

   - bpo-28043(13): SSLContext has improved default settings:
     OP_NO_SSLv2, OP_NO_SSLv3, OP_NO_COMPRESSION,
     OP_CIPHER_SERVER_PREFERENCE, OP_SINGLE_DH_USE, OP_SINGLE_ECDH_USE
     and HIGH ciphers without MD5.

   - bpo-24693(14): Changed some RuntimeError’s in the zipfile module to
     more appropriate types.  Improved some error messages and debugging
     output.

   - bpo-17909(15): ‘json.load’ and ‘json.loads’ now support binary
     input encoded as UTF-8, UTF-16 or UTF-32.  Patch by Serhiy
     Storchaka.

   - bpo-27137(16): the pure Python fallback implementation of
     ‘functools.partial’ now matches the behaviour of its accelerated C
     counterpart for subclassing, pickling and text representation
     purposes.  Patch by Emanuel Barry and Serhiy Storchaka.

   - Fix possible integer overflows and crashes in the mmap module with
     unusual usage patterns.

   - bpo-1703178(17): Fix the ability to pass the –link-objects option
     to the distutils build_ext command.

   - bpo-28019(18): itertools.count() no longer rounds non-integer step
     in range between 1.0 and 2.0 to 1.

   - bpo-18401(19): Pdb now supports the ‘readrc’ keyword argument to
     control whether .pdbrc files should be read.  Patch by Martin
     Matusiak and Sam Kimbrel.

   - bpo-25969(20): Update the lib2to3 grammar to handle the unpacking
     generalizations added in 3.5.

   - bpo-14977(21): mailcap now respects the order of the lines in the
     mailcap files (“first match”), as required by RFC 1542.  Patch by
     Michael Lazar.

   - bpo-28082(22): Convert re flag constants to IntFlag.

   - bpo-28025(23): Convert all ssl module constants to IntEnum and
     IntFlags.  SSLContext properties now return flags and enums.

   - bpo-23591(24): Add Flag, IntFlag, and auto() to enum module.

   - bpo-433028(25): Added support of modifier spans in regular
     expressions.

   - bpo-24594(26): Validates persist parameter when opening MSI
     database

   - bpo-17582(27): xml.etree.ElementTree nows preserves whitespaces in
     attributes (Patch by Duane Griffin.  Reviewed and approved by
     Stefan Behnel.)

   - bpo-28047(28): Fixed calculation of line length used for the base64
     CTE in the new email policies.

   - bpo-27576(29): Fix call order in OrderedDict.__init__().

   - email.generator.DecodedGenerator now supports the policy keyword.

   - bpo-28027(30): Remove undocumented modules from ‘Lib/plat-*’: IN,
     CDROM, DLFCN, TYPES, CDIO, and STROPTS.

   - bpo-27445(31): Don’t pass str(_charset) to MIMEText.set_payload().
     Patch by Claude Paroz.

   - bpo-24277(32): The new email API is no longer provisional, and the
     docs have been reorganized and rewritten to emphasize the new API.

   - bpo-22450(33): urllib now includes an ‘Accept: */*’ header among
     the default headers.  This makes the results of REST API requests
     more consistent and predictable especially when proxy servers are
     involved.

   - lib2to3.pgen3.driver.load_grammar() now creates a stable cache file
     between runs given the same Grammar.txt input regardless of the
     hash randomization setting.

   - bpo-28005(34): Allow ImportErrors in encoding implementation to
     propagate.

   - bpo-26667(35): Support path-like objects in importlib.util.

   - bpo-27570(36): Avoid zero-length memcpy() etc calls with null
     source pointers in the “ctypes” and “array” modules.

   - bpo-22233(37): Break email header lines `only' on the RFC specified
     CR and LF characters, not on arbitrary unicode line breaks.  This
     also fixes a bug in HTTP header parsing.

   - bpo-27331(38): The email.mime classes now all accept an optional
     policy keyword.

   - bpo-27988(39): Fix email iter_attachments incorrect mutation of
     payload list.

   - bpo-16113(40): Add SHA-3 and SHAKE support to hashlib module.

   - Eliminate a tautological-pointer-compare warning in _scproxy.c.

   - bpo-27776(41): The *note os.urandom(): 5cc. function does now block
     on Linux 3.17 and newer until the system urandom entropy pool is
     initialized to increase the security.  This change is part of the
     PEP 524(42).

   - bpo-27778(43): Expose the Linux ‘getrandom()’ syscall as a new
     *note os.getrandom(): 662. function.  This change is part of the
     PEP 524(44).

   - bpo-27691(45): Fix ssl module’s parsing of GEN_RID subject
     alternative name fields in X.509 certs.

   - bpo-18844(46): Add random.choices().

   - bpo-25761(47): Improved error reporting about truncated pickle data
     in C implementation of unpickler.  UnpicklingError is now raised
     instead of AttributeError and ValueError in some cases.

   - bpo-26798(48): Add BLAKE2 (blake2b and blake2s) to hashlib.

   - bpo-26032(49): Optimized globbing in pathlib by using os.scandir();
     it is now about 1.5–4 times faster.

   - bpo-25596(50): Optimized glob() and iglob() functions in the glob
     module; they are now about 3–6 times faster.

   - bpo-27928(51): Add scrypt (password-based key derivation function)
     to hashlib module (requires OpenSSL 1.1.0).

   - bpo-27850(52): Remove 3DES from ssl module’s default cipher list to
     counter measure sweet32 attack (CVE-2016-2183).

   - bpo-27766(53): Add ChaCha20 Poly1305 to ssl module’s default cipher
     list.  (Required OpenSSL 1.1.0 or LibreSSL).

   - bpo-25387(54): Check return value of winsound.MessageBeep.

   - bpo-27866(55): Add SSLContext.get_ciphers() method to get a list of
     all enabled ciphers.

   - bpo-27744(56): Add AF_ALG (Linux Kernel crypto) to socket module.

   - bpo-26470(57): Port ssl and hashlib module to OpenSSL 1.1.0.

   - bpo-11620(58): Fix support for SND_MEMORY in winsound.PlaySound.
     Based on a patch by Tim Lesher.

   - bpo-11734(59): Add support for IEEE 754 half-precision floats to
     the struct module.  Based on a patch by Eli Stevens.

   - bpo-27919(60): Deprecated ‘extra_path’ distribution option in
     distutils packaging.

   - bpo-23229(61): Add new ‘cmath’ constants: ‘cmath.inf’ and
     ‘cmath.nan’ to match ‘math.inf’ and ‘math.nan’, and also
     ‘cmath.infj’ and ‘cmath.nanj’ to match the format used by complex
     repr.

   - bpo-27842(62): The csv.DictReader now returns rows of type
     OrderedDict.  (Contributed by Steve Holden.)

   - Remove support for passing a file descriptor to os.access.  It
     never worked but previously didn’t raise.

   - bpo-12885(63): Fix error when distutils encounters symlink.

   - bpo-27881(64): Fixed possible bugs when setting
     sqlite3.Connection.isolation_level.  Based on patch by Xiang Zhang.

   - bpo-27861(65): Fixed a crash in sqlite3.Connection.cursor() when a
     factory creates not a cursor.  Patch by Xiang Zhang.

   - bpo-19884(66): Avoid spurious output on OS X with Gnu Readline.

   - bpo-27706(67): Restore deterministic behavior of
     random.Random().seed() for string seeds using seeding version 1.
     Allows sequences of calls to random() to exactly match those
     obtained in Python 2.  Patch by Nofar Schnider.

   - bpo-10513(68): Fix a regression in Connection.commit().  Statements
     should not be reset after a commit.

   - bpo-12319(69): Chunked transfer encoding support added to
     http.client.HTTPConnection requests.  The
     urllib.request.AbstractHTTPHandler class does not enforce a
     Content-Length header any more.  If a HTTP request has a file or
     iterable body, but no Content-Length header, the library now falls
     back to use chunked transfer-encoding.

   - A new version of typing.py from ‘https://github.com/python/typing’:
     - Collection (only for 3.6) (bpo-27598(70)) - Add FrozenSet to
     __all__ (upstream #261) - fix crash in _get_type_vars() (upstream
     #259) - Remove the dict constraint in ForwardRef._eval_type
     (upstream #252)

   - bpo-27832(71): Make ‘_normalize’ parameter to ‘Fraction’
     constructor keyword-only, so that ‘Fraction(2, 3, 4)’ now raises
     ‘TypeError’.

   - bpo-27539(72): Fix unnormalised ‘Fraction.__pow__’ result in the
     case of negative exponent and negative base.

   - bpo-21718(73): cursor.description is now available for queries
     using CTEs.

   - bpo-27819(74): In distutils sdists, simply produce the “gztar”
     (gzipped tar format) distributions on all platforms unless
     “formats” is supplied.

   - bpo-2466(75): posixpath.ismount now correctly recognizes mount
     points which the user does not have permission to access.

   - bpo-9998(76): On Linux, ctypes.util.find_library now looks in
     LD_LIBRARY_PATH for shared libraries.

   - bpo-27573(77): exit message for code.interact is now configurable.

   - bpo-27930(78): Improved behaviour of
     logging.handlers.QueueListener.  Thanks to Paulo Andrade and Petr
     Viktorin for the analysis and patch.

   - bpo-6766(79): Distributed reference counting added to
     multiprocessing to support nesting of shared values / proxy
     objects.

   - bpo-21201(80): Improves readability of multiprocessing error
     message.  Thanks to Wojciech Walczak for patch.

   - asyncio: Add set_protocol / get_protocol to Transports.

   - bpo-27456(81): asyncio: Set TCP_NODELAY by default.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28732

   (2) https://bugs.python.org/issue28485

   (3) https://bugs.python.org/issue28037

   (4) https://bugs.python.org/issue25283

   (5) https://bugs.python.org/issue24454

   (6) https://bugs.python.org/issue10740

   (7) https://bugs.python.org/issue17941

   (8) https://bugs.python.org/issue22493

   (9) https://bugs.python.org/issue26885

   (10) https://bugs.python.org/issue28070

   (11) https://bugs.python.org/issue19500

   (12) https://bugs.python.org/issue28022

   (13) https://bugs.python.org/issue28043

   (14) https://bugs.python.org/issue24693

   (15) https://bugs.python.org/issue17909

   (16) https://bugs.python.org/issue27137

   (17) https://bugs.python.org/issue1703178

   (18) https://bugs.python.org/issue28019

   (19) https://bugs.python.org/issue18401

   (20) https://bugs.python.org/issue25969

   (21) https://bugs.python.org/issue14977

   (22) https://bugs.python.org/issue28082

   (23) https://bugs.python.org/issue28025

   (24) https://bugs.python.org/issue23591

   (25) https://bugs.python.org/issue433028

   (26) https://bugs.python.org/issue24594

   (27) https://bugs.python.org/issue17582

   (28) https://bugs.python.org/issue28047

   (29) https://bugs.python.org/issue27576

   (30) https://bugs.python.org/issue28027

   (31) https://bugs.python.org/issue27445

   (32) https://bugs.python.org/issue24277

   (33) https://bugs.python.org/issue22450

   (34) https://bugs.python.org/issue28005

   (35) https://bugs.python.org/issue26667

   (36) https://bugs.python.org/issue27570

   (37) https://bugs.python.org/issue22233

   (38) https://bugs.python.org/issue27331

   (39) https://bugs.python.org/issue27988

   (40) https://bugs.python.org/issue16113

   (41) https://bugs.python.org/issue27776

   (42) https://www.python.org/dev/peps/pep-0524

   (43) https://bugs.python.org/issue27778

   (44) https://www.python.org/dev/peps/pep-0524

   (45) https://bugs.python.org/issue27691

   (46) https://bugs.python.org/issue18844

   (47) https://bugs.python.org/issue25761

   (48) https://bugs.python.org/issue26798

   (49) https://bugs.python.org/issue26032

   (50) https://bugs.python.org/issue25596

   (51) https://bugs.python.org/issue27928

   (52) https://bugs.python.org/issue27850

   (53) https://bugs.python.org/issue27766

   (54) https://bugs.python.org/issue25387

   (55) https://bugs.python.org/issue27866

   (56) https://bugs.python.org/issue27744

   (57) https://bugs.python.org/issue26470

   (58) https://bugs.python.org/issue11620

   (59) https://bugs.python.org/issue11734

   (60) https://bugs.python.org/issue27919

   (61) https://bugs.python.org/issue23229

   (62) https://bugs.python.org/issue27842

   (63) https://bugs.python.org/issue12885

   (64) https://bugs.python.org/issue27881

   (65) https://bugs.python.org/issue27861

   (66) https://bugs.python.org/issue19884

   (67) https://bugs.python.org/issue27706

   (68) https://bugs.python.org/issue10513

   (69) https://bugs.python.org/issue12319

   (70) https://bugs.python.org/issue27598

   (71) https://bugs.python.org/issue27832

   (72) https://bugs.python.org/issue27539

   (73) https://bugs.python.org/issue21718

   (74) https://bugs.python.org/issue27819

   (75) https://bugs.python.org/issue2466

   (76) https://bugs.python.org/issue9998

   (77) https://bugs.python.org/issue27573

   (78) https://bugs.python.org/issue27930

   (79) https://bugs.python.org/issue6766

   (80) https://bugs.python.org/issue21201

   (81) https://bugs.python.org/issue27456


File: python.info,  Node: IDLE<39>,  Next: C API<35>,  Prev: Library<54>,  Up: Python 3 6 0 beta 1

1.19.62.3 IDLE
..............

   - bpo-15308(1): Add ‘interrupt execution’ (^C) to Shell menu.  Patch
     by Roger Serwy, updated by Bayard Randel.

   - bpo-27922(2): Stop IDLE tests from ‘flashing’ gui widgets on the
     screen.

   - bpo-27891(3): Consistently group and sort imports within idlelib
     modules.

   - bpo-17642(4): add larger font sizes for classroom projection.

   - Add version to title of IDLE help window.

   - bpo-25564(5): In section on IDLE – console differences, mention
     that using exec means that __builtins__ is defined for each
     statement.

   - bpo-27821(6): Fix 3.6.0a3 regression that prevented custom key sets
     from being selected when no custom theme was defined.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15308

   (2) https://bugs.python.org/issue27922

   (3) https://bugs.python.org/issue27891

   (4) https://bugs.python.org/issue17642

   (5) https://bugs.python.org/issue25564

   (6) https://bugs.python.org/issue27821


File: python.info,  Node: C API<35>,  Next: Tests<43>,  Prev: IDLE<39>,  Up: Python 3 6 0 beta 1

1.19.62.4 C API
...............

   - bpo-26900(1): Excluded underscored names and other private API from
     limited API.

   - bpo-26027(2): Add support for path-like objects in
     PyUnicode_FSConverter() & PyUnicode_FSDecoder().

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26900

   (2) https://bugs.python.org/issue26027


File: python.info,  Node: Tests<43>,  Next: Build<46>,  Prev: C API<35>,  Up: Python 3 6 0 beta 1

1.19.62.5 Tests
...............

   - bpo-27427(1): Additional tests for the math module.  Patch by
     Francisco Couzo.

   - bpo-27953(2): Skip math and cmath tests that fail on OS X 10.4 due
     to a poor libm implementation of tan.

   - bpo-26040(3): Improve test_math and test_cmath coverage and rigour.
     Patch by Jeff Allen.

   - bpo-27787(4): Call gc.collect() before checking each test for
     “dangling threads”, since the dangling threads are weak references.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27427

   (2) https://bugs.python.org/issue27953

   (3) https://bugs.python.org/issue26040

   (4) https://bugs.python.org/issue27787


File: python.info,  Node: Build<46>,  Next: Tools/Demos<25>,  Prev: Tests<43>,  Up: Python 3 6 0 beta 1

1.19.62.6 Build
...............

   - bpo-27566(1): Fix clean target in freeze makefile (patch by Lisa
     Roach)

   - bpo-27705(2): Update message in validate_ucrtbase.py

   - bpo-27976(3): Deprecate building _ctypes with the bundled copy of
     libffi on non-OSX UNIX platforms.

   - bpo-27983(4): Cause lack of llvm-profdata tool when using clang as
     required for PGO linking to be a configure time error rather than
     make time when ‘--with-optimizations’ is enabled.  Also improve our
     ability to find the llvm-profdata tool on MacOS and some Linuxes.

   - bpo-21590(5): Support for DTrace and SystemTap probes.

   - bpo-26307(6): The profile-opt build now applies PGO to the built-in
     modules.

   - bpo-26359(7): Add the –with-optimizations flag to turn on LTO and
     PGO build support when available.

   - bpo-27917(8): Set platform triplets for Android builds.

   - bpo-25825(9): Update references to the $(LIBPL) installation path
     on AIX. This path was changed in 3.2a4.

   - Update OS X installer to use SQLite 3.14.1 and XZ 5.2.2.

   - bpo-21122(10): Fix LTO builds on OS X.

   - bpo-17128(11): Build OS X installer with a private copy of OpenSSL.
     Also provide a sample Install Certificates command script to
     install a set of root certificates from the third-party certifi
     module.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27566

   (2) https://bugs.python.org/issue27705

   (3) https://bugs.python.org/issue27976

   (4) https://bugs.python.org/issue27983

   (5) https://bugs.python.org/issue21590

   (6) https://bugs.python.org/issue26307

   (7) https://bugs.python.org/issue26359

   (8) https://bugs.python.org/issue27917

   (9) https://bugs.python.org/issue25825

   (10) https://bugs.python.org/issue21122

   (11) https://bugs.python.org/issue17128


File: python.info,  Node: Tools/Demos<25>,  Next: Windows<42>,  Prev: Build<46>,  Up: Python 3 6 0 beta 1

1.19.62.7 Tools/Demos
.....................

   - bpo-27952(1): Get Tools/scripts/fixcid.py working with Python 3 and
     the current “re” module, avoid invalid Python backslash escapes,
     and fix a bug parsing escaped C quote signs.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27952


File: python.info,  Node: Windows<42>,  Prev: Tools/Demos<25>,  Up: Python 3 6 0 beta 1

1.19.62.8 Windows
.................

   - bpo-28065(1): Update xz dependency to 5.2.2 and build it from
     source.

   - bpo-25144(2): Ensures TargetDir is set before continuing with
     custom install.

   - bpo-1602(3): Windows console doesn’t input or print Unicode (PEP
     528)

   - bpo-27781(4): Change file system encoding on Windows to UTF-8 (PEP
     529)

   - bpo-27731(5): Opt-out of MAX_PATH on Windows 10

   - bpo-6135(6): Adds encoding and errors parameters to subprocess.

   - bpo-27959(7): Adds oem encoding, alias ansi to mbcs, move aliasmbcs
     to codec lookup.

   - bpo-27982(8): The functions of the winsound module now accept
     keyword arguments.

   - bpo-20366(9): Build full text search support into SQLite on
     Windows.

   - bpo-27756(10): Adds new icons for Python files and processes on
     Windows.  Designs by Cherry Wang.

   - bpo-27883(11): Update sqlite to 3.14.1.0 on Windows.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28065

   (2) https://bugs.python.org/issue25144

   (3) https://bugs.python.org/issue1602

   (4) https://bugs.python.org/issue27781

   (5) https://bugs.python.org/issue27731

   (6) https://bugs.python.org/issue6135

   (7) https://bugs.python.org/issue27959

   (8) https://bugs.python.org/issue27982

   (9) https://bugs.python.org/issue20366

   (10) https://bugs.python.org/issue27756

   (11) https://bugs.python.org/issue27883


File: python.info,  Node: Python 3 6 0 alpha 4,  Next: Python 3 6 0 alpha 3,  Prev: Python 3 6 0 beta 1,  Up: Changelog

1.19.63 Python 3.6.0 alpha 4
----------------------------

`Release date: 2016-08-15'

* Menu:

* Core and Builtins: Core and Builtins<52>.
* Library: Library<55>.
* IDLE: IDLE<40>.
* Tests: Tests<44>.
* Windows: Windows<43>.
* Build: Build<47>.


File: python.info,  Node: Core and Builtins<52>,  Next: Library<55>,  Up: Python 3 6 0 alpha 4

1.19.63.1 Core and Builtins
...........................

   - bpo-27704(1): Optimized creating bytes and bytearray from byte-like
     objects and iterables.  Speed up to 3 times for short objects.
     Original patch by Naoki Inada.

   - bpo-26823(2): Large sections of repeated lines in tracebacks are
     now abbreviated as “[Previous line repeated {count} more times]” by
     the builtin traceback rendering.  Patch by Emanuel Barry.

   - bpo-27574(3): Decreased an overhead of parsing keyword arguments in
     functions implemented with using Argument Clinic.

   - bpo-22557(4): Now importing already imported modules is up to 2.5
     times faster.

   - bpo-17596(5): Include <wincrypt.h> to help with Min GW building.

   - bpo-17599(6): On Windows, rename the privately defined
     REPARSE_DATA_BUFFER structure to avoid conflicting with the
     definition from Min GW.

   - bpo-27507(7): Add integer overflow check in bytearray.extend().
     Patch by Xiang Zhang.

   - bpo-27581(8): Don’t rely on wrapping for overflow check in
     PySequence_Tuple().  Patch by Xiang Zhang.

   - bpo-1621(9): Avoid signed integer overflow in list and tuple
     operations.  Patch by Xiang Zhang.

   - bpo-27419(10): Standard __import__() no longer look up “__import__”
     in globals or builtins for importing submodules or “from import”.
     Fixed a crash if raise a warning about unabling to resolve package
     from __spec__ or __package__.

   - bpo-27083(11): Respect the PYTHONCASEOK environment variable under
     Windows.

   - bpo-27514(12): Make having too many statically nested blocks a
     SyntaxError instead of SystemError.

   - bpo-27366(13): Implemented PEP 487(14) (Simpler customization of
     class creation).  Upon subclassing, the __init_subclass__
     classmethod is called on the base class.  Descriptors are
     initialized with __set_name__ after class creation.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27704

   (2) https://bugs.python.org/issue26823

   (3) https://bugs.python.org/issue27574

   (4) https://bugs.python.org/issue22557

   (5) https://bugs.python.org/issue17596

   (6) https://bugs.python.org/issue17599

   (7) https://bugs.python.org/issue27507

   (8) https://bugs.python.org/issue27581

   (9) https://bugs.python.org/issue1621

   (10) https://bugs.python.org/issue27419

   (11) https://bugs.python.org/issue27083

   (12) https://bugs.python.org/issue27514

   (13) https://bugs.python.org/issue27366

   (14) https://www.python.org/dev/peps/pep-0487


File: python.info,  Node: Library<55>,  Next: IDLE<40>,  Prev: Core and Builtins<52>,  Up: Python 3 6 0 alpha 4

1.19.63.2 Library
.................

   - bpo-26027(1): Add PEP 519(2)/__fspath__() support to the os and
     os.path modules.  Includes code from Jelle Zijlstra.  (See also:
     bpo-27524(3))

   - bpo-27598(4): Add Collections to collections.abc.  Patch by Ivan
     Levkivskyi, docs by Neil Girdhar.

   - bpo-25958(5): Support “anti-registration” of special methods from
     various ABCs, like __hash__, __iter__ or __len__.  All these (and
     several more) can be set to None in an implementation class and the
     behavior will be as if the method is not defined at all.
     (Previously, this mechanism existed only for __hash__, to make
     mutable classes unhashable.)  Code contributed by Andrew Barnert
     and Ivan Levkivskyi.

   - bpo-16764(6): Support keyword arguments to zlib.decompress().
     Patch by Xiang Zhang.

   - bpo-27736(7): Prevent segfault after interpreter re-initialization
     due to ref count problem introduced in code for bpo-27038(8) in
     3.6.0a3.  Patch by Xiang Zhang.

   - bpo-25628(9): The `verbose' and `rename' parameters for
     collections.namedtuple are now keyword-only.

   - bpo-12345(10): Add mathematical constant tau to math and cmath.
     See also PEP 628(11).

   - bpo-26823(12): traceback.StackSummary.format now abbreviates large
     sections of repeated lines as “[Previous line repeated {count} more
     times]” (this change then further affects other traceback display
     operations in the module).  Patch by Emanuel Barry.

   - bpo-27664(13): Add to
     concurrent.futures.thread.ThreadPoolExecutor() the ability to
     specify a thread name prefix.

   - bpo-27181(14): Add geometric_mean and harmonic_mean to statistics
     module.

   - bpo-27573(15): code.interact now prints an message when exiting.

   - bpo-6422(16): Add autorange method to timeit.Timer objects.

   - bpo-27773(17): Correct some memory management errors
     server_hostname in _ssl.wrap_socket().

   - bpo-26750(18): unittest.mock.create_autospec() now works properly
     for subclasses of property() and other data descriptors.  Removes
     the never publicly used, never documented
     unittest.mock.DescriptorTypes tuple.

   - bpo-26754(19): Undocumented support of general bytes-like objects
     as path in compile() and similar functions is now deprecated.

   - bpo-26800(20): Undocumented support of general bytes-like objects
     as paths in os functions is now deprecated.

   - bpo-26981(21): Add _order_ compatibility shim to enum.Enum for
     Python 2/3 code bases.

   - bpo-27661(22): Added tzinfo keyword argument to datetime.combine.

   - In the curses module, raise an error if window.getstr() or
     window.instr() is passed a negative value.

   - bpo-27783(23): Fix possible usage of uninitialized memory in
     operator.methodcaller.

   - bpo-27774(24): Fix possible Py_DECREF on unowned object in _sre.

   - bpo-27760(25): Fix possible integer overflow in binascii.b2a_qp.

   - bpo-27758(26): Fix possible integer overflow in the _csv module for
     large record lengths.

   - bpo-27568(27): Prevent HTTPoxy attack (CVE-2016-1000110).  Ignore
     the HTTP_PROXY variable when REQUEST_METHOD environment is set,
     which indicates that the script is in CGI mode.

   - bpo-7063(28): Remove dead code from the “array” module’s slice
     handling.  Patch by Chuck.

   - bpo-27656(29): Do not assume sched.h defines any SCHED_* constants.

   - bpo-27130(30): In the “zlib” module, fix handling of large buffers
     (typically 4 GiB) when compressing and decompressing.  Previously,
     inputs were limited to 4 GiB, and compression and decompression
     operations did not properly handle results of 4 GiB.

   - bpo-24773(31): Implemented PEP 495(32) (Local Time Disambiguation).

   - Expose the EPOLLEXCLUSIVE constant (when it is defined) in the
     select module.

   - bpo-27567(33): Expose the EPOLLRDHUP and POLLRDHUP constants in the
     select module.

   - bpo-1621(34): Avoid signed int negation overflow in the “audioop”
     module.

   - bpo-27533(35): Release GIL in nt._isdir

   - bpo-17711(36): Fixed unpickling by the persistent ID with protocol
     0.  Original patch by Alexandre Vassalotti.

   - bpo-27522(37): Avoid an unintentional reference cycle in
     email.feedparser.

   - bpo-27512(38): Fix a segfault when os.fspath() called an
     __fspath__() method that raised an exception.  Patch by Xiang
     Zhang.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26027

   (2) https://www.python.org/dev/peps/pep-0519

   (3) https://bugs.python.org/issue27524

   (4) https://bugs.python.org/issue27598

   (5) https://bugs.python.org/issue25958

   (6) https://bugs.python.org/issue16764

   (7) https://bugs.python.org/issue27736

   (8) https://bugs.python.org/issue27038

   (9) https://bugs.python.org/issue25628

   (10) https://bugs.python.org/issue12345

   (11) https://www.python.org/dev/peps/pep-0628

   (12) https://bugs.python.org/issue26823

   (13) https://bugs.python.org/issue27664

   (14) https://bugs.python.org/issue27181

   (15) https://bugs.python.org/issue27573

   (16) https://bugs.python.org/issue6422

   (17) https://bugs.python.org/issue27773

   (18) https://bugs.python.org/issue26750

   (19) https://bugs.python.org/issue26754

   (20) https://bugs.python.org/issue26800

   (21) https://bugs.python.org/issue26981

   (22) https://bugs.python.org/issue27661

   (23) https://bugs.python.org/issue27783

   (24) https://bugs.python.org/issue27774

   (25) https://bugs.python.org/issue27760

   (26) https://bugs.python.org/issue27758

   (27) https://bugs.python.org/issue27568

   (28) https://bugs.python.org/issue7063

   (29) https://bugs.python.org/issue27656

   (30) https://bugs.python.org/issue27130

   (31) https://bugs.python.org/issue24773

   (32) https://www.python.org/dev/peps/pep-0495

   (33) https://bugs.python.org/issue27567

   (34) https://bugs.python.org/issue1621

   (35) https://bugs.python.org/issue27533

   (36) https://bugs.python.org/issue17711

   (37) https://bugs.python.org/issue27522

   (38) https://bugs.python.org/issue27512


File: python.info,  Node: IDLE<40>,  Next: Tests<44>,  Prev: Library<55>,  Up: Python 3 6 0 alpha 4

1.19.63.3 IDLE
..............

   - bpo-27714(1): text_textview and test_autocomplete now pass when
     re-run in the same process.  This occurs when test_idle fails when
     run with the -w option but without -jn.  Fix warning from
     test_config.

   - bpo-27621(2): Put query response validation error messages in the
     query box itself instead of in a separate messagebox.  Redo tests
     to match.  Add Mac OSX refinements.  Original patch by Mark
     Roseman.

   - bpo-27620(3): Escape key now closes Query box as cancelled.

   - bpo-27609(4): IDLE: tab after initial whitespace should tab, not
     autocomplete.  This fixes problem with writing docstrings at least
     twice indented.

   - bpo-27609(5): Explicitly return None when there are also non-None
     returns.  In a few cases, reverse a condition and eliminate a
     return.

   - bpo-25507(6): IDLE no longer runs buggy code because of its tkinter
     imports.  Users must include the same imports required to run
     directly in Python.

   - bpo-27173(7): Add ‘IDLE Modern Unix’ to the built-in key sets.
     Make the default key set depend on the platform.  Add tests for the
     changes to the config module.

   - bpo-27452(8): add line counter and crc to IDLE configHandler test
     dump.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27714

   (2) https://bugs.python.org/issue27621

   (3) https://bugs.python.org/issue27620

   (4) https://bugs.python.org/issue27609

   (5) https://bugs.python.org/issue27609

   (6) https://bugs.python.org/issue25507

   (7) https://bugs.python.org/issue27173

   (8) https://bugs.python.org/issue27452


File: python.info,  Node: Tests<44>,  Next: Windows<43>,  Prev: IDLE<40>,  Up: Python 3 6 0 alpha 4

1.19.63.4 Tests
...............

   - bpo-25805(1): Skip a test in test_pkgutil as needed that doesn’t
     work when ‘__name__ == __main__’.  Patch by SilentGhost.

   - bpo-27472(2): Add test.support.unix_shell as the path to the
     default shell.

   - bpo-27369(3): In test_pyexpat, avoid testing an error message
     detail that changed in Expat 2.2.0.

   - bpo-27594(4): Prevent assertion error when running test_ast with
     coverage enabled: ensure code object has a valid first line number.
     Patch suggested by Ivan Levkivskyi.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25805

   (2) https://bugs.python.org/issue27472

   (3) https://bugs.python.org/issue27369

   (4) https://bugs.python.org/issue27594


File: python.info,  Node: Windows<43>,  Next: Build<47>,  Prev: Tests<44>,  Up: Python 3 6 0 alpha 4

1.19.63.5 Windows
.................

   - bpo-27647(1): Update bundled Tcl/Tk to 8.6.6.

   - bpo-27610(2): Adds PEP 514(3) metadata to Windows installer

   - bpo-27469(4): Adds a shell extension to the launcher so that drag
     and drop works correctly.

   - bpo-27309(5): Enables proper Windows styles in python[w].exe
     manifest.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27647

   (2) https://bugs.python.org/issue27610

   (3) https://www.python.org/dev/peps/pep-0514

   (4) https://bugs.python.org/issue27469

   (5) https://bugs.python.org/issue27309


File: python.info,  Node: Build<47>,  Prev: Windows<43>,  Up: Python 3 6 0 alpha 4

1.19.63.6 Build
...............

   - bpo-27713(1): Suppress spurious build warnings when updating
     importlib’s bootstrap files.  Patch by Xiang Zhang

   - bpo-25825(2): Correct the references to Modules/python.exp, which
     is required on AIX. The references were accidentally changed in
     3.5.0a1.

   - bpo-27453(3): CPP invocation in configure must use CPPFLAGS. Patch
     by Chi Hsuan Yen.

   - bpo-27641(4): The configure script now inserts comments into the
     makefile to prevent the pgen and _freeze_importlib executables from
     being cross-compiled.

   - bpo-26662(5): Set PYTHON_FOR_GEN in configure as the Python program
     to be used for file generation during the build.

   - bpo-10910(6): Avoid C++ compilation errors on FreeBSD and OS X.
     Also update FreedBSD version checks for the original ctype UTF-8
     workaround.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27713

   (2) https://bugs.python.org/issue25825

   (3) https://bugs.python.org/issue27453

   (4) https://bugs.python.org/issue27641

   (5) https://bugs.python.org/issue26662

   (6) https://bugs.python.org/issue10910


File: python.info,  Node: Python 3 6 0 alpha 3,  Next: Python 3 6 0 alpha 2,  Prev: Python 3 6 0 alpha 4,  Up: Changelog

1.19.64 Python 3.6.0 alpha 3
----------------------------

`Release date: 2016-07-11'

* Menu:

* Core and Builtins: Core and Builtins<53>.
* Library: Library<56>.
* Security: Security<26>.
* Library: Library<57>.
* Security: Security<27>.
* Library: Library<58>.
* IDLE: IDLE<41>.
* C API: C API<36>.
* Build: Build<48>.
* Tools/Demos: Tools/Demos<26>.
* Documentation: Documentation<44>.
* Tests: Tests<45>.


File: python.info,  Node: Core and Builtins<53>,  Next: Library<56>,  Up: Python 3 6 0 alpha 3

1.19.64.1 Core and Builtins
...........................

   - bpo-27473(1): Fixed possible integer overflow in bytes and
     bytearray concatenations.  Patch by Xiang Zhang.

   - bpo-23034(2): The output of a special Python build with defined
     COUNT_ALLOCS, SHOW_ALLOC_COUNT or SHOW_TRACK_COUNT macros is now
     off by default.  It can be re-enabled using the “-X showalloccount”
     option.  It now outputs to stderr instead of stdout.

   - bpo-27443(3): __length_hint__() of bytearray iterators no longer
     return a negative integer for a resized bytearray.

   - bpo-27007(4): The fromhex() class methods of bytes and bytearray
     subclasses now return an instance of corresponding subclass.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27473

   (2) https://bugs.python.org/issue23034

   (3) https://bugs.python.org/issue27443

   (4) https://bugs.python.org/issue27007


File: python.info,  Node: Library<56>,  Next: Security<26>,  Prev: Core and Builtins<53>,  Up: Python 3 6 0 alpha 3

1.19.64.2 Library
.................

   - bpo-26844(1): Fix error message for imp.find_module() to refer to
     ‘path’ instead of ‘name’.  Patch by Lev Maximov.

   - bpo-23804(2): Fix SSL zero-length recv() calls to not block and not
     raise an error about unclean EOF.

   - bpo-27466(3): Change time format returned by
     http.cookie.time2netscape, confirming the netscape cookie format
     and making it consistent with documentation.

   - bpo-21708(4): Deprecated dbm.dumb behavior that differs from common
     dbm behavior: creating a database in ‘r’ and ‘w’ modes and
     modifying a database in ‘r’ mode.

   - bpo-26721(5): Change the socketserver.StreamRequestHandler.wfile
     attribute to implement BufferedIOBase.  In particular, the write()
     method no longer does partial writes.

   - bpo-22115(6): Added methods trace_add, trace_remove and trace_info
     in the tkinter.Variable class.  They replace old methods
     trace_variable, trace, trace_vdelete and trace_vinfo that use
     obsolete Tcl commands and might not work in future versions of Tcl.
     Fixed old tracing methods: trace_vdelete() with wrong mode no
     longer break tracing, trace_vinfo() now always returns a list of
     pairs of strings, tracing in the “u” mode now works.

   - bpo-26243(7): Only the level argument to zlib.compress() is keyword
     argument now.  The first argument is positional-only.

   - bpo-27038(8): Expose the DirEntry type as os.DirEntry.  Code patch
     by Jelle Zijlstra.

   - bpo-27186(9): Update os.fspath()/PyOS_FSPath() to check the return
     value of __fspath__() to be either str or bytes.

   - bpo-18726(10): All optional parameters of the dump(), dumps(),
     load() and loads() functions and JSONEncoder and JSONDecoder class
     constructors in the json module are now keyword-only.

   - bpo-27319(11): Methods selection_set(), selection_add(),
     selection_remove() and selection_toggle() of ttk.TreeView now allow
     passing multiple items as multiple arguments instead of passing
     them as a tuple.  Deprecated undocumented ability of calling the
     selection() method with arguments.

   - bpo-27079(12): Fixed curses.ascii functions isblank(), iscntrl()
     and ispunct().

   - bpo-27294(13): Numerical state in the repr for Tkinter event
     objects is now represented as a combination of known flags.

   - bpo-27177(14): Match objects in the re module now support
     index-like objects as group indices.  Based on patches by Jeroen
     Demeyer and Xiang Zhang.

   - bpo-26754(15): Some functions (compile() etc) accepted a filename
     argument encoded as an iterable of integers.  Now only strings and
     byte-like objects are accepted.

   - bpo-26536(16): socket.ioctl now supports SIO_LOOPBACK_FAST_PATH.
     Patch by Daniel Stokes.

   - bpo-27048(17): Prevents distutils failing on Windows when
     environment variables contain non-ASCII characters

   - bpo-27330(18): Fixed possible leaks in the ctypes module.

   - bpo-27238(19): Got rid of bare excepts in the turtle module.
     Original patch by Jelle Zijlstra.

   - bpo-27122(20): When an exception is raised within the context being
     managed by a contextlib.ExitStack() and one of the exit stack
     generators catches and raises it in a chain, do not re-raise the
     original exception when exiting, let the new chained one through.
     This avoids the PEP 479(21) bug described in issue25782.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26844

   (2) https://bugs.python.org/issue23804

   (3) https://bugs.python.org/issue27466

   (4) https://bugs.python.org/issue21708

   (5) https://bugs.python.org/issue26721

   (6) https://bugs.python.org/issue22115

   (7) https://bugs.python.org/issue26243

   (8) https://bugs.python.org/issue27038

   (9) https://bugs.python.org/issue27186

   (10) https://bugs.python.org/issue18726

   (11) https://bugs.python.org/issue27319

   (12) https://bugs.python.org/issue27079

   (13) https://bugs.python.org/issue27294

   (14) https://bugs.python.org/issue27177

   (15) https://bugs.python.org/issue26754

   (16) https://bugs.python.org/issue26536

   (17) https://bugs.python.org/issue27048

   (18) https://bugs.python.org/issue27330

   (19) https://bugs.python.org/issue27238

   (20) https://bugs.python.org/issue27122

   (21) https://www.python.org/dev/peps/pep-0479


File: python.info,  Node: Security<26>,  Next: Library<57>,  Prev: Library<56>,  Up: Python 3 6 0 alpha 3

1.19.64.3 Security
..................

   - bpo-27278(1): Fix os.urandom() implementation using getrandom() on
     Linux.  Truncate size to INT_MAX and loop until we collected enough
     random bytes, instead of casting a directly Py_ssize_t to int.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27278


File: python.info,  Node: Library<57>,  Next: Security<27>,  Prev: Security<26>,  Up: Python 3 6 0 alpha 3

1.19.64.4 Library
.................

   - bpo-16864(1): sqlite3.Cursor.lastrowid now supports REPLACE
     statement.  Initial patch by Alex LordThorsen.

   - bpo-26386(2): Fixed ttk.TreeView selection operations with item
     id’s containing spaces.

   - bpo-8637(3): Honor a pager set by the env var MANPAGER (in
     preference to one set by the env var PAGER).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16864

   (2) https://bugs.python.org/issue26386

   (3) https://bugs.python.org/issue8637


File: python.info,  Node: Security<27>,  Next: Library<58>,  Prev: Library<57>,  Up: Python 3 6 0 alpha 3

1.19.64.5 Security
..................

   - bpo-22636(1): Avoid shell injection problems with
     ctypes.util.find_library().

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22636


File: python.info,  Node: Library<58>,  Next: IDLE<41>,  Prev: Security<27>,  Up: Python 3 6 0 alpha 3

1.19.64.6 Library
.................

   - bpo-16182(1): Fix various functions in the “readline” module to use
     the locale encoding, and fix get_begidx() and get_endidx() to
     return code point indexes.

   - bpo-27392(2): Add loop.connect_accepted_socket().  Patch by Jim
     Fulton.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16182

   (2) https://bugs.python.org/issue27392


File: python.info,  Node: IDLE<41>,  Next: C API<36>,  Prev: Library<58>,  Up: Python 3 6 0 alpha 3

1.19.64.7 IDLE
..............

   - bpo-27477(1): IDLE search dialogs now use ttk widgets.

   - bpo-27173(2): Add ‘IDLE Modern Unix’ to the built-in key sets.
     Make the default key set depend on the platform.  Add tests for the
     changes to the config module.

   - bpo-27452(3): make command line “idle-test> python test_help.py”
     work.  __file__ is relative when python is started in the file’s
     directory.

   - bpo-27452(4): add line counter and crc to IDLE configHandler test
     dump.

   - bpo-27380(5): IDLE: add query.py with base Query dialog and ttk
     widgets.  Module had subclasses SectionName, ModuleName, and
     HelpSource, which are used to get information from users by
     configdialog and file =>Load Module.  Each subclass has itw own
     validity checks.  Using ModuleName allows users to edit bad module
     names instead of starting over.  Add tests and delete the two files
     combined into the new one.

   - bpo-27372(6): Test_idle no longer changes the locale.

   - bpo-27365(7): Allow non-ascii chars in IDLE NEWS.txt, for
     contributor names.

   - bpo-27245(8): IDLE: Cleanly delete custom themes and key bindings.
     Previously, when IDLE was started from a console or by import, a
     cascade of warnings was emitted.  Patch by Serhiy Storchaka.

   - bpo-24137(9): Run IDLE, test_idle, and htest with tkinter default
     root disabled.  Fix code and tests that fail with this restriction.
     Fix htests to not create a second and redundant root and mainloop.

   - bpo-27310(10): Fix IDLE.app failure to launch on OS X due to
     vestigial import.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27477

   (2) https://bugs.python.org/issue27173

   (3) https://bugs.python.org/issue27452

   (4) https://bugs.python.org/issue27452

   (5) https://bugs.python.org/issue27380

   (6) https://bugs.python.org/issue27372

   (7) https://bugs.python.org/issue27365

   (8) https://bugs.python.org/issue27245

   (9) https://bugs.python.org/issue24137

   (10) https://bugs.python.org/issue27310


File: python.info,  Node: C API<36>,  Next: Build<48>,  Prev: IDLE<41>,  Up: Python 3 6 0 alpha 3

1.19.64.8 C API
...............

   - bpo-26754(1): PyUnicode_FSDecoder() accepted a filename argument
     encoded as an iterable of integers.  Now only strings and byte-like
     objects are accepted.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26754


File: python.info,  Node: Build<48>,  Next: Tools/Demos<26>,  Prev: C API<36>,  Up: Python 3 6 0 alpha 3

1.19.64.9 Build
...............

   - bpo-28066(1): Fix the logic that searches build directories for
     generated include files when building outside the source tree.

   - bpo-27442(2): Expose the Android API level that python was built
     against, in sysconfig.get_config_vars() as ‘ANDROID_API_LEVEL’.

   - bpo-27434(3): The interpreter that runs the cross-build, found in
     PATH, must now be of the same feature version (e.g.  3.6) as the
     source being built.

   - bpo-26930(4): Update Windows builds to use OpenSSL 1.0.2h.

   - bpo-23968(5): Rename the platform directory from plat-$(MACHDEP) to
     plat-$(PLATFORM_TRIPLET). Rename the config directory (LIBPL) from
     config-$(LDVERSION) to config-$(LDVERSION)-$(PLATFORM_TRIPLET).
     Install the platform specific _sysconfigdata module into the
     platform directory and rename it to include the ABIFLAGS.

   - Don’t use largefile support for GNU/Hurd.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28066

   (2) https://bugs.python.org/issue27442

   (3) https://bugs.python.org/issue27434

   (4) https://bugs.python.org/issue26930

   (5) https://bugs.python.org/issue23968


File: python.info,  Node: Tools/Demos<26>,  Next: Documentation<44>,  Prev: Build<48>,  Up: Python 3 6 0 alpha 3

1.19.64.10 Tools/Demos
......................

   - bpo-27332(1): Fixed the type of the first argument of module-level
     functions generated by Argument Clinic.  Patch by Petr Viktorin.

   - bpo-27418(2): Fixed Tools/importbench/importbench.py.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27332

   (2) https://bugs.python.org/issue27418


File: python.info,  Node: Documentation<44>,  Next: Tests<45>,  Prev: Tools/Demos<26>,  Up: Python 3 6 0 alpha 3

1.19.64.11 Documentation
........................

   - bpo-19489(1): Moved the search box from the sidebar to the header
     and footer of each page.  Patch by Ammar Askar.

   - bpo-27285(2): Update documentation to reflect the deprecation of
     ‘pyvenv’ and normalize on the term “virtual environment”.  Patch by
     Steve Piercy.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19489

   (2) https://bugs.python.org/issue27285


File: python.info,  Node: Tests<45>,  Prev: Documentation<44>,  Up: Python 3 6 0 alpha 3

1.19.64.12 Tests
................

   - bpo-27027(1): Added test.support.is_android that is True when this
     is an Android build.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27027


File: python.info,  Node: Python 3 6 0 alpha 2,  Next: Python 3 6 0 alpha 1,  Prev: Python 3 6 0 alpha 3,  Up: Changelog

1.19.65 Python 3.6.0 alpha 2
----------------------------

`Release date: 2016-06-13'

* Menu:

* Core and Builtins: Core and Builtins<54>.
* Library: Library<59>.
* Security: Security<28>.
* Library: Library<60>.
* Security: Security<29>.
* Library: Library<61>.
* IDLE: IDLE<42>.
* Documentation: Documentation<45>.
* Tests: Tests<46>.
* Windows: Windows<44>.
* Build: Build<49>.
* Windows: Windows<45>.
* C API: C API<37>.
* Tools/Demos: Tools/Demos<27>.


File: python.info,  Node: Core and Builtins<54>,  Next: Library<59>,  Up: Python 3 6 0 alpha 2

1.19.65.1 Core and Builtins
...........................

   - bpo-27095(1): Simplified MAKE_FUNCTION and removed MAKE_CLOSURE
     opcodes.  Patch by Demur Rumed.

   - bpo-27190(2): Raise NotSupportedError if sqlite3 is older than
     3.3.1.  Patch by Dave Sawyer.

   - bpo-27286(3): Fixed compiling BUILD_MAP_UNPACK_WITH_CALL opcode.
     Calling function with generalized unpacking (PEP 448) and
     conflicting keyword names could cause undefined behavior.

   - bpo-27140(4): Added BUILD_CONST_KEY_MAP opcode.

   - bpo-27186(5): Add support for os.PathLike objects to open() (part
     of PEP 519(6)).

   - bpo-27066(7): Fixed SystemError if a custom opener (for open())
     returns a negative number without setting an exception.

   - bpo-26983(8): float() now always return an instance of exact float.
     The deprecation warning is emitted if __float__ returns an instance
     of a strict subclass of float.  In a future versions of Python this
     can be an error.

   - bpo-27097(9): Python interpreter is now about 7% faster due to
     optimized instruction decoding.  Based on patch by Demur Rumed.

   - bpo-26647(10): Python interpreter now uses 16-bit wordcode instead
     of bytecode.  Patch by Demur Rumed.

   - bpo-23275(11): Allow assigning to an empty target list in round
     brackets: () = iterable.

   - bpo-27243(12): Update the __aiter__ protocol: instead of returning
     an awaitable that resolves to an asynchronous iterator, the
     asynchronous iterator should be returned directly.  Doing the
     former will trigger a PendingDeprecationWarning.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27095

   (2) https://bugs.python.org/issue27190

   (3) https://bugs.python.org/issue27286

   (4) https://bugs.python.org/issue27140

   (5) https://bugs.python.org/issue27186

   (6) https://www.python.org/dev/peps/pep-0519

   (7) https://bugs.python.org/issue27066

   (8) https://bugs.python.org/issue26983

   (9) https://bugs.python.org/issue27097

   (10) https://bugs.python.org/issue26647

   (11) https://bugs.python.org/issue23275

   (12) https://bugs.python.org/issue27243


File: python.info,  Node: Library<59>,  Next: Security<28>,  Prev: Core and Builtins<54>,  Up: Python 3 6 0 alpha 2

1.19.65.2 Library
.................

   - Comment out socket (SO_REUSEPORT) and posix (O_SHLOCK, O_EXLOCK)
     constants exposed on the API which are not implemented on GNU/Hurd.
     They would not work at runtime anyway.

   - bpo-27025(1): Generated names for Tkinter widgets are now more
     meaningful and recognizable.

   - bpo-25455(2): Fixed crashes in repr of recursive
     ElementTree.Element and functools.partial objects.

   - bpo-27294(3): Improved repr for Tkinter event objects.

   - bpo-20508(4): Improve exception message of
     IPv{4,6}Network.__getitem__.  Patch by Gareth Rees.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27025

   (2) https://bugs.python.org/issue25455

   (3) https://bugs.python.org/issue27294

   (4) https://bugs.python.org/issue20508


File: python.info,  Node: Security<28>,  Next: Library<60>,  Prev: Library<59>,  Up: Python 3 6 0 alpha 2

1.19.65.3 Security
..................

   - bpo-26556(1): Update expat to 2.1.1, fixes CVE-2015-1283.

   - Fix TLS stripping vulnerability in smtplib, CVE-2016-0772.
     Reported by Team Oststrom.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26556


File: python.info,  Node: Library<60>,  Next: Security<29>,  Prev: Security<28>,  Up: Python 3 6 0 alpha 2

1.19.65.4 Library
.................

   - bpo-21386(1): Implement missing IPv4Address.is_global property.  It
     was documented since 07a5610bae9d.  Initial patch by Roger Luethi.

   - bpo-27029(2): Removed deprecated support of universal newlines mode
     from ZipFile.open().

   - bpo-27030(3): Unknown escapes consisting of ‘'\'’ and an ASCII
     letter in regular expressions now are errors.  The re.LOCALE flag
     now can be used only with bytes patterns.

   - bpo-27186(4): Add os.PathLike support to DirEntry (part of PEP
     519(5)).  Initial patch by Jelle Zijlstra.

   - bpo-20900(6): distutils register command now decodes HTTP responses
     correctly.  Initial patch by ingrid.

   - bpo-27186(7): Add os.PathLike support to pathlib, removing its
     provisional status (part of PEP 519).  Initial patch by Dusty
     Phillips.

   - bpo-27186(8): Add support for os.PathLike objects to os.fsencode()
     and os.fsdecode() (part of PEP 519(9)).

   - bpo-27186(10): Introduce os.PathLike and os.fspath() (part of PEP
     519(11)).

   - A new version of typing.py provides several new classes and
     features: @overload outside stubs, Reversible, DefaultDict, Text,
     ContextManager, Type[], NewType(), TYPE_CHECKING, and numerous bug
     fixes (note that some of the new features are not yet implemented
     in mypy or other static analyzers).  Also classes for PEP 492(12)
     (Awaitable, AsyncIterable, AsyncIterator) have been added (in fact
     they made it into 3.5.1 but were never mentioned).

   - bpo-25738(13): Stop http.server.BaseHTTPRequestHandler.send_error()
     from sending a message body for 205 Reset Content.  Also, don’t
     send Content header fields in responses that don’t have a body.
     Patch by Susumu Koshiba.

   - bpo-21313(14): Fix the “platform” module to tolerate when
     sys.version contains truncated build information.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21386

   (2) https://bugs.python.org/issue27029

   (3) https://bugs.python.org/issue27030

   (4) https://bugs.python.org/issue27186

   (5) https://www.python.org/dev/peps/pep-0519

   (6) https://bugs.python.org/issue20900

   (7) https://bugs.python.org/issue27186

   (8) https://bugs.python.org/issue27186

   (9) https://www.python.org/dev/peps/pep-0519

   (10) https://bugs.python.org/issue27186

   (11) https://www.python.org/dev/peps/pep-0519

   (12) https://www.python.org/dev/peps/pep-0492

   (13) https://bugs.python.org/issue25738

   (14) https://bugs.python.org/issue21313


File: python.info,  Node: Security<29>,  Next: Library<61>,  Prev: Library<60>,  Up: Python 3 6 0 alpha 2

1.19.65.5 Security
..................

   - bpo-26839(1): On Linux, *note os.urandom(): 5cc. now calls
     ‘getrandom()’ with ‘GRND_NONBLOCK’ to fall back on reading
     ‘/dev/urandom’ if the urandom entropy pool is not initialized yet.
     Patch written by Colm Buckley.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26839


File: python.info,  Node: Library<61>,  Next: IDLE<42>,  Prev: Security<29>,  Up: Python 3 6 0 alpha 2

1.19.65.6 Library
.................

   - bpo-23883(1): Added missing APIs to __all__ to match the documented
     APIs for the following modules: cgi, mailbox, mimetypes, plistlib
     and smtpd.  Patches by Jacek Kołodziej.

   - bpo-27164(2): In the zlib module, allow decompressing raw Deflate
     streams with a predefined zdict.  Based on patch by Xiang Zhang.

   - bpo-24291(3): Fix wsgiref.simple_server.WSGIRequestHandler to
     completely write data to the client.  Previously it could do
     partial writes and truncate data.  Also,
     wsgiref.handler.ServerHandler can now handle stdout doing partial
     writes, but this is deprecated.

   - bpo-21272(4): Use _sysconfigdata.py to initialize
     distutils.sysconfig.

   - bpo-19611(5): *note inspect: a0. now reports the implicit ‘.0’
     parameters generated by the compiler for comprehension and
     generator expression scopes as if they were positional-only
     parameters called ‘implicit0’.  Patch by Jelle Zijlstra.

   - bpo-26809(6): Add ‘__all__’ to *note string: f6.  Patch by Emanuel
     Barry.

   - bpo-26373(7): subprocess.Popen.communicate now correctly ignores
     BrokenPipeError when the child process dies before .communicate()
     is called in more/all circumstances.

   - signal, socket, and ssl module IntEnum constant name lookups now
     return a consistent name for values having multiple names.  Ex:
     signal.Signals(6) now refers to itself as signal.SIGALRM rather
     than flipping between that and signal.SIGIOT based on the
     interpreter’s hash randomization seed.

   - bpo-27167(8): Clarify the subprocess.CalledProcessError error
     message text when the child process died due to a signal.

   - bpo-25931(9): Don’t define socketserver.Forking* names on platforms
     such as Windows that do not support os.fork().

   - bpo-21776(10): distutils.upload now correctly handles HTTPError.
     Initial patch by Claudiu Popa.

   - bpo-26526(11): Replace custom parse tree validation in the parser
     module with a simple DFA validator.

   - bpo-27114(12): Fix SSLContext._load_windows_store_certs fails with
     PermissionError

   - bpo-18383(13): Avoid creating duplicate filters when using
     filterwarnings and simplefilter.  Based on patch by Alex Shkop.

   - bpo-23026(14): winreg.QueryValueEx() now return an integer for
     REG_QWORD type.

   - bpo-26741(15): subprocess.Popen destructor now emits a
     ResourceWarning warning if the child process is still running.

   - bpo-27056(16): Optimize pickle.load() and pickle.loads(), up to 10%
     faster to deserialize a lot of small objects.

   - bpo-21271(17): New keyword only parameters in reset_mock call.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23883

   (2) https://bugs.python.org/issue27164

   (3) https://bugs.python.org/issue24291

   (4) https://bugs.python.org/issue21272

   (5) https://bugs.python.org/issue19611

   (6) https://bugs.python.org/issue26809

   (7) https://bugs.python.org/issue26373

   (8) https://bugs.python.org/issue27167

   (9) https://bugs.python.org/issue25931

   (10) https://bugs.python.org/issue21776

   (11) https://bugs.python.org/issue26526

   (12) https://bugs.python.org/issue27114

   (13) https://bugs.python.org/issue18383

   (14) https://bugs.python.org/issue23026

   (15) https://bugs.python.org/issue26741

   (16) https://bugs.python.org/issue27056

   (17) https://bugs.python.org/issue21271


File: python.info,  Node: IDLE<42>,  Next: Documentation<45>,  Prev: Library<61>,  Up: Python 3 6 0 alpha 2

1.19.65.7 IDLE
..............

   - bpo-5124(1): Paste with text selected now replaces the selection on
     X11.  This matches how paste works on Windows, Mac, most modern
     Linux apps, and ttk widgets.  Original patch by Serhiy Storchaka.

   - bpo-24750(2): Switch all scrollbars in IDLE to ttk versions.  Where
     needed, minimal tests are added to cover changes.

   - bpo-24759(3): IDLE requires tk 8.5 and availability ttk widgets.
     Delete now unneeded tk version tests and code for older versions.
     Add test for IDLE syntax colorizer.

   - bpo-27239(4): idlelib.macosx.isXyzTk functions initialize as
     needed.

   - bpo-27262(5): move Aqua unbinding code, which enable context menus,
     to macosx.

   - bpo-24759(6): Make clear in idlelib.idle_test.__init__ that the
     directory is a private implementation of test.test_idle and tool
     for maintainers.

   - bpo-27196(7): Stop ‘ThemeChanged’ warnings when running IDLE tests.
     These persisted after other warnings were suppressed in #20567.
     Apply Serhiy Storchaka’s update_idletasks solution to four test
     files.  Record this additional advice in idle_test/README.txt

   - bpo-20567(8): Revise idle_test/README.txt with advice about
     avoiding tk warning messages from tests.  Apply advice to several
     IDLE tests.

   - bpo-24225(9): Update idlelib/README.txt with new file names and
     event handlers.

   - bpo-27156(10): Remove obsolete code not used by IDLE.

   - bpo-27117(11): Make colorizer htest and turtledemo work with dark
     themes.  Move code for configuring text widget colors to a new
     function.

   - bpo-24225(12): Rename many ‘idlelib/*.py’ and ‘idle_test/test_*.py’
     files.  Edit files to replace old names with new names when the old
     name referred to the module rather than the class it contained.
     See the issue and IDLE section in What’s New in 3.6 for more.

   - bpo-26673(13): When tk reports font size as 0, change to size 10.
     Such fonts on Linux prevented the configuration dialog from
     opening.

   - bpo-21939(14): Add test for IDLE’s percolator.  Original patch by
     Saimadhav Heblikar.

   - bpo-21676(15): Add test for IDLE’s replace dialog.  Original patch
     by Saimadhav Heblikar.

   - bpo-18410(16): Add test for IDLE’s search dialog.  Original patch
     by Westley Martínez.

   - bpo-21703(17): Add test for undo delegator.  Patch mostly by
     Saimadhav Heblikar .

   - bpo-27044(18): Add ConfigDialog.remove_var_callbacks to stop memory
     leaks.

   - bpo-23977(19): Add more asserts to test_delegator.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5124

   (2) https://bugs.python.org/issue24750

   (3) https://bugs.python.org/issue24759

   (4) https://bugs.python.org/issue27239

   (5) https://bugs.python.org/issue27262

   (6) https://bugs.python.org/issue24759

   (7) https://bugs.python.org/issue27196

   (8) https://bugs.python.org/issue20567

   (9) https://bugs.python.org/issue24225

   (10) https://bugs.python.org/issue27156

   (11) https://bugs.python.org/issue27117

   (12) https://bugs.python.org/issue24225

   (13) https://bugs.python.org/issue26673

   (14) https://bugs.python.org/issue21939

   (15) https://bugs.python.org/issue21676

   (16) https://bugs.python.org/issue18410

   (17) https://bugs.python.org/issue21703

   (18) https://bugs.python.org/issue27044

   (19) https://bugs.python.org/issue23977


File: python.info,  Node: Documentation<45>,  Next: Tests<46>,  Prev: IDLE<42>,  Up: Python 3 6 0 alpha 2

1.19.65.8 Documentation
.......................

   - bpo-16484(1): Change the default PYTHONDOCS URL to “https:”, and
     fix the resulting links to use lowercase.  Patch by Sean Rodman,
     test by Kaushik Nadikuditi.

   - bpo-24136(2): Document the new PEP 448(3) unpacking syntax of 3.5.

   - bpo-22558(4): Add remaining doc links to source code for
     Python-coded modules.  Patch by Yoni Lavi.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16484

   (2) https://bugs.python.org/issue24136

   (3) https://www.python.org/dev/peps/pep-0448

   (4) https://bugs.python.org/issue22558


File: python.info,  Node: Tests<46>,  Next: Windows<44>,  Prev: Documentation<45>,  Up: Python 3 6 0 alpha 2

1.19.65.9 Tests
...............

   - bpo-25285(1): regrtest now uses subprocesses when the -j1 command
     line option is used: each test file runs in a fresh child process.
     Before, the -j1 option was ignored.

   - bpo-25285(2): Tools/buildbot/test.bat script now uses -j1 by
     default to run each test file in fresh child process.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25285

   (2) https://bugs.python.org/issue25285


File: python.info,  Node: Windows<44>,  Next: Build<49>,  Prev: Tests<46>,  Up: Python 3 6 0 alpha 2

1.19.65.10 Windows
..................

   - bpo-27064(1): The py.exe launcher now defaults to Python 3.  The
     Windows launcher ‘py.exe’ no longer prefers an installed Python 2
     version over Python 3 by default when used interactively.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27064


File: python.info,  Node: Build<49>,  Next: Windows<45>,  Prev: Windows<44>,  Up: Python 3 6 0 alpha 2

1.19.65.11 Build
................

   - bpo-27229(1): Fix the cross-compiling pgen rule for in-tree builds.
     Patch by Xavier de Gaye.

   - bpo-26930(2): Update OS X 10.5+ 32-bit-only installer to build and
     link with OpenSSL 1.0.2h.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27229

   (2) https://bugs.python.org/issue26930


File: python.info,  Node: Windows<45>,  Next: C API<37>,  Prev: Build<49>,  Up: Python 3 6 0 alpha 2

1.19.65.12 Windows
..................

   - bpo-17500(1): Remove unused and outdated icons.  (See also:
     ‘https://github.com/python/pythondotorg/issues/945’)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17500


File: python.info,  Node: C API<37>,  Next: Tools/Demos<27>,  Prev: Windows<45>,  Up: Python 3 6 0 alpha 2

1.19.65.13 C API
................

   - bpo-27186(1): Add the PyOS_FSPath() function (part of PEP 519(2)).

   - bpo-26282(3): PyArg_ParseTupleAndKeywords() now supports
     positional-only parameters.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27186

   (2) https://www.python.org/dev/peps/pep-0519

   (3) https://bugs.python.org/issue26282


File: python.info,  Node: Tools/Demos<27>,  Prev: C API<37>,  Up: Python 3 6 0 alpha 2

1.19.65.14 Tools/Demos
......................

   - bpo-26282(1): Argument Clinic now supports positional-only and
     keyword parameters in the same function.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26282


File: python.info,  Node: Python 3 6 0 alpha 1,  Next: Python 3 5 5 final,  Prev: Python 3 6 0 alpha 2,  Up: Changelog

1.19.66 Python 3.6.0 alpha 1
----------------------------

`Release date: 2016-05-16'

* Menu:

* Core and Builtins: Core and Builtins<55>.
* Library: Library<62>.
* Security: Security<30>.
* Library: Library<63>.
* Security: Security<31>.
* Library: Library<64>.
* Security: Security<32>.
* Library: Library<65>.
* IDLE: IDLE<43>.
* Documentation: Documentation<46>.
* Tests: Tests<47>.
* Build: Build<50>.
* Windows: Windows<46>.
* Tools/Demos: Tools/Demos<28>.
* C API: C API<38>.


File: python.info,  Node: Core and Builtins<55>,  Next: Library<62>,  Up: Python 3 6 0 alpha 1

1.19.66.1 Core and Builtins
...........................

   - bpo-20041(1): Fixed TypeError when frame.f_trace is set to None.
     Patch by Xavier de Gaye.

   - bpo-26168(2): Fixed possible refleaks in failing Py_BuildValue()
     with the “N” format unit.

   - bpo-26991(3): Fix possible refleak when creating a function with
     annotations.

   - bpo-27039(4): Fixed bytearray.remove() for values greater than 127.
     Based on patch by Joe Jevnik.

   - bpo-23640(5): int.from_bytes() no longer bypasses constructors for
     subclasses.

   - bpo-27005(6): Optimized the float.fromhex() class method for exact
     float.  It is now 2 times faster.

   - bpo-18531(7): Single var-keyword argument of dict subtype was
     passed unscathed to the C-defined function.  Now it is converted to
     exact dict.

   - bpo-26811(8): gc.get_objects() no longer contains a broken tuple
     with NULL pointer.

   - bpo-20120(9): Use RawConfigParser for .pypirc parsing, removing
     support for interpolation unintentionally added with move to Python
     3.  Behavior no longer does any interpolation in .pypirc files,
     matching behavior in Python 2.7 and Setuptools 19.0.

   - bpo-26249(10): Memory functions of the *note PyMem_Malloc(): 5ff.
     domain (*note PYMEM_DOMAIN_MEM: 603.) now use the *note pymalloc
     allocator: 6b8. rather than system ‘malloc()’.  Applications
     calling *note PyMem_Malloc(): 5ff. without holding the GIL can now
     crash: use ‘PYTHONMALLOC=debug’ environment variable to validate
     the usage of memory allocators in your application.

   - bpo-26802(11): Optimize function calls only using unpacking like
     ‘func(*tuple)’ (no other positional argument, no keyword): avoid
     copying the tuple.  Patch written by Joe Jevnik.

   - bpo-26659(12): Make the builtin slice type support cycle
     collection.

   - bpo-26718(13): super.__init__ no longer leaks memory if called
     multiple times.  NOTE: A direct call of super.__init__ is not
     endorsed!

   - bpo-27138(14): Fix the doc comment for FileFinder.find_spec().

   - bpo-27147(15): Mention PEP 420(16) in the importlib docs.

   - bpo-25339(17): PYTHONIOENCODING now has priority over locale in
     setting the error handler for stdin and stdout.

   - bpo-26494(18): Fixed crash on iterating exhausting iterators.
     Affected classes are generic sequence iterators, iterators of str,
     bytes, bytearray, list, tuple, set, frozenset, dict, OrderedDict,
     corresponding views and os.scandir() iterator.

   - bpo-26574(19): Optimize ‘bytes.replace(b'', b'.')’ and
     ‘bytearray.replace(b'', b'.')’.  Patch written by Josh Snider.

   - bpo-26581(20): If coding cookie is specified multiple times on a
     line in Python source code file, only the first one is taken to
     account.

   - bpo-19711(21): Add tests for reloading namespace packages.

   - bpo-21099(22): Switch applicable importlib tests to use PEP 451(23)
     API.

   - bpo-26563(24): Debug hooks on Python memory allocators now raise a
     fatal error if functions of the *note PyMem_Malloc(): 5ff. family
     are called without holding the GIL.

   - bpo-26564(25): On error, the debug hooks on Python memory
     allocators now use the *note tracemalloc: 11d. module to get the
     traceback where a memory block was allocated.

   - bpo-26558(26): The debug hooks on Python memory allocator *note
     PyObject_Malloc(): 602. now detect when functions are called
     without holding the GIL.

   - bpo-26516(27): Add *note PYTHONMALLOC: 5fd. environment variable to
     set the Python memory allocators and/or install debug hooks.

   - bpo-26516(28): The *note PyMem_SetupDebugHooks(): 604. function can
     now also be used on Python compiled in release mode.

   - bpo-26516(29): The *note PYTHONMALLOCSTATS: 1297. environment
     variable can now also be used on Python compiled in release mode.
     It now has no effect if set to an empty string.

   - bpo-26516(30): In debug mode, debug hooks are now also installed on
     Python memory allocators when Python is configured without
     pymalloc.

   - bpo-26464(31): Fix str.translate() when string is ASCII and first
     replacements removes character, but next replacement uses a
     non-ASCII character or a string longer than 1 character.
     Regression introduced in Python 3.5.0.

   - bpo-22836(32): Ensure exception reports from PyErr_Display() and
     PyErr_WriteUnraisable() are sensible even when formatting them
     produces secondary errors.  This affects the reports produced by
     sys.__excepthook__() and when __del__() raises an exception.

   - bpo-26302(33): Correct behavior to reject comma as a legal
     character for cookie names.

   - bpo-26136(34): Upgrade the warning when a generator raises
     StopIteration from PendingDeprecationWarning to DeprecationWarning.
     Patch by Anish Shah.

   - bpo-26204(35): The compiler now ignores all constant statements:
     bytes, str, int, float, complex, name constants (None, False,
     True), Ellipsis and ast.Constant; not only str and int.  For
     example, ‘1.0’ is now ignored in ‘def f(): 1.0’.

   - bpo-4806(36): Avoid masking the original TypeError exception when
     using star (‘*’) unpacking in function calls.  Based on patch by
     Hagen Fürstenau and Daniel Urban.

   - bpo-26146(37): Add a new kind of AST node: ‘ast.Constant’.  It can
     be used by external AST optimizers, but the compiler does not emit
     directly such node.

   - bpo-23601(38): Sped-up allocation of dict key objects by using
     Python’s small object allocator.  (Contributed by Julian Taylor.)

   - bpo-18018(39): Import raises ImportError instead of SystemError if
     a relative import is attempted without a known parent package.

   - bpo-25843(40): When compiling code, don’t merge constants if they
     are equal but have a different types.  For example, ‘f1, f2 =
     lambda: 1, lambda: 1.0’ is now correctly compiled to two different
     functions: ‘f1()’ returns ‘1’ (‘int’) and ‘f2()’ returns ‘1.0’
     (‘float’), even if ‘1’ and ‘1.0’ are equal.

   - bpo-26107(41): The format of the ‘co_lnotab’ attribute of code
     objects changes to support negative line number delta.

   - bpo-26154(42): Add a new private _PyThreadState_UncheckedGet()
     function to get the current Python thread state, but don’t issue a
     fatal error if it is NULL. This new function must be used instead
     of accessing directly the _PyThreadState_Current variable.  The
     variable is no more exposed since Python 3.5.1 to hide the exact
     implementation of atomic C types, to avoid compiler issues.

   - bpo-25791(43): If __package__ != __spec__.parent or if neither
     __package__ or __spec__ are defined then ImportWarning is raised.

   - bpo-22995(44): [UPDATE] Comment out the one of the pickleability
     tests in _PyObject_GetState() due to regressions observed in
     Cython-based projects.

   - bpo-25961(45): Disallowed null characters in the type name.

   - bpo-25973(46): Fix segfault when an invalid nonlocal statement
     binds a name starting with two underscores.

   - bpo-22995(47): Instances of extension types with a state that
     aren’t subclasses of list or dict and haven’t implemented any
     pickle-related methods (__reduce__, __reduce_ex__, __getnewargs__,
     __getnewargs_ex__, or __getstate__), can no longer be pickled.
     Including memoryview.

   - bpo-20440(48): Massive replacing unsafe attribute setting code with
     special macro Py_SETREF.

   - bpo-25766(49): Special method __bytes__() now works in str
     subclasses.

   - bpo-25421(50): __sizeof__ methods of builtin types now use dynamic
     basic size.  This allows sys.getsize() to work correctly with their
     subclasses with __slots__ defined.

   - bpo-25709(51): Fixed problem with in-place string concatenation and
     utf-8 cache.

   - bpo-5319(52): New Py_FinalizeEx() API allowing Python to set an
     exit status of 120 on failure to flush buffered streams.

   - bpo-25485(53): telnetlib.Telnet is now a context manager.

   - bpo-24097(54): Fixed crash in object.__reduce__() if slot name is
     freed inside __getattr__.

   - bpo-24731(55): Fixed crash on converting objects with special
     methods __bytes__, __trunc__, and __float__ returning instances of
     subclasses of bytes, int, and float to subclasses of bytes, int,
     and float correspondingly.

   - bpo-25630(56): Fix a possible segfault during argument parsing in
     functions that accept filesystem paths.

   - bpo-23564(57): Fixed a partially broken sanity check in the
     _posixsubprocess internals regarding how fds_to_pass were passed to
     the child.  The bug had no actual impact as subprocess.py already
     avoided it.

   - bpo-25388(58): Fixed tokenizer crash when processing undecodable
     source code with a null byte.

   - bpo-25462(59): The hash of the key now is calculated only once in
     most operations in C implementation of OrderedDict.

   - bpo-22995(60): Default implementation of __reduce__ and
     __reduce_ex__ now rejects builtin types with not defined __new__.

   - bpo-24802(61): Avoid buffer overreads when int(), float(),
     compile(), exec() and eval() are passed bytes-like objects.  These
     objects are not necessarily terminated by a null byte, but the
     functions assumed they were.

   - bpo-25555(62): Fix parser and AST: fill lineno and col_offset of
     “arg” node when compiling AST from Python objects.

   - bpo-24726(63): Fixed a crash and leaking NULL in repr() of
     OrderedDict that was mutated by direct calls of dict methods.

   - bpo-25449(64): Iterating OrderedDict with keys with unstable hash
     now raises KeyError in C implementations as well as in Python
     implementation.

   - bpo-25395(65): Fixed crash when highly nested OrderedDict
     structures were garbage collected.

   - bpo-25401(66): Optimize bytes.fromhex() and bytearray.fromhex():
     they are now between 2x and 3.5x faster.

   - bpo-25399(67): Optimize bytearray % args using the new private
     _PyBytesWriter API. Formatting is now between 2.5 and 5 times
     faster.

   - bpo-25274(68): sys.setrecursionlimit() now raises a RecursionError
     if the new recursion limit is too low depending at the current
     recursion depth.  Modify also the “lower-water mark” formula to
     make it monotonic.  This mark is used to decide when the overflowed
     flag of the thread state is reset.

   - bpo-24402(69): Fix input() to prompt to the redirected stdout when
     sys.stdout.fileno() fails.

   - bpo-25349(70): Optimize bytes % args using the new private
     _PyBytesWriter API. Formatting is now up to 2 times faster.

   - bpo-24806(71): Prevent builtin types that are not allowed to be
     subclassed from being subclassed through multiple inheritance.

   - bpo-25301(72): The UTF-8 decoder is now up to 15 times as fast for
     error handlers: ‘ignore’, ‘replace’ and ‘surrogateescape’.

   - bpo-24848(73): Fixed a number of bugs in UTF-7 decoding of
     misformed data.

   - bpo-25267(74): The UTF-8 encoder is now up to 75 times as fast for
     error handlers: ‘ignore’, ‘replace’, ‘surrogateescape’,
     ‘surrogatepass’.  Patch co-written with Serhiy Storchaka.

   - bpo-25280(75): Import trace messages emitted in verbose (-v) mode
     are no longer formatted twice.

   - bpo-25227(76): Optimize ASCII and latin1 encoders with the
     ‘surrogateescape’ error handler: the encoders are now up to 3 times
     as fast.  Initial patch written by Serhiy Storchaka.

   - bpo-25003(77): On Solaris 11.3 or newer, os.urandom() now uses the
     getrandom() function instead of the getentropy() function.  The
     getentropy() function is blocking to generate very good quality
     entropy, os.urandom() doesn’t need such high-quality entropy.

   - bpo-9232(78): Modify Python’s grammar to allow trailing commas in
     the argument list of a function declaration.  For example, “def
     f(*, a = 3,): pass” is now legal.  Patch from Mark Dickinson.

   - bpo-24965(79): Implement PEP 498(80) “Literal String
     Interpolation”.  This allows you to embed expressions inside
     f-strings, which are converted to normal strings at run time.
     Given x=3, then f’value={x}’ == ‘value=3’.  Patch by Eric V. Smith.

   - bpo-26478(81): Fix semantic bugs when using binary operators with
     dictionary views and tuples.

   - bpo-26171(82): Fix possible integer overflow and heap corruption in
     zipimporter.get_data().

   - bpo-25660(83): Fix TAB key behaviour in REPL with readline.

   - bpo-26288(84): Optimize PyLong_AsDouble.

   - bpo-26289(85): Optimize floor and modulo division for single-digit
     longs.  Microbenchmarks show 2-2.5x improvement.  Built-in ‘divmod’
     function is now also ~10% faster.  (See also: bpo-26315(86))

   - bpo-25887(87): Raise a RuntimeError when a coroutine object is
     awaited more than once.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20041

   (2) https://bugs.python.org/issue26168

   (3) https://bugs.python.org/issue26991

   (4) https://bugs.python.org/issue27039

   (5) https://bugs.python.org/issue23640

   (6) https://bugs.python.org/issue27005

   (7) https://bugs.python.org/issue18531

   (8) https://bugs.python.org/issue26811

   (9) https://bugs.python.org/issue20120

   (10) https://bugs.python.org/issue26249

   (11) https://bugs.python.org/issue26802

   (12) https://bugs.python.org/issue26659

   (13) https://bugs.python.org/issue26718

   (14) https://bugs.python.org/issue27138

   (15) https://bugs.python.org/issue27147

   (16) https://www.python.org/dev/peps/pep-0420

   (17) https://bugs.python.org/issue25339

   (18) https://bugs.python.org/issue26494

   (19) https://bugs.python.org/issue26574

   (20) https://bugs.python.org/issue26581

   (21) https://bugs.python.org/issue19711

   (22) https://bugs.python.org/issue21099

   (23) https://www.python.org/dev/peps/pep-0451

   (24) https://bugs.python.org/issue26563

   (25) https://bugs.python.org/issue26564

   (26) https://bugs.python.org/issue26558

   (27) https://bugs.python.org/issue26516

   (28) https://bugs.python.org/issue26516

   (29) https://bugs.python.org/issue26516

   (30) https://bugs.python.org/issue26516

   (31) https://bugs.python.org/issue26464

   (32) https://bugs.python.org/issue22836

   (33) https://bugs.python.org/issue26302

   (34) https://bugs.python.org/issue26136

   (35) https://bugs.python.org/issue26204

   (36) https://bugs.python.org/issue4806

   (37) https://bugs.python.org/issue26146

   (38) https://bugs.python.org/issue23601

   (39) https://bugs.python.org/issue18018

   (40) https://bugs.python.org/issue25843

   (41) https://bugs.python.org/issue26107

   (42) https://bugs.python.org/issue26154

   (43) https://bugs.python.org/issue25791

   (44) https://bugs.python.org/issue22995

   (45) https://bugs.python.org/issue25961

   (46) https://bugs.python.org/issue25973

   (47) https://bugs.python.org/issue22995

   (48) https://bugs.python.org/issue20440

   (49) https://bugs.python.org/issue25766

   (50) https://bugs.python.org/issue25421

   (51) https://bugs.python.org/issue25709

   (52) https://bugs.python.org/issue5319

   (53) https://bugs.python.org/issue25485

   (54) https://bugs.python.org/issue24097

   (55) https://bugs.python.org/issue24731

   (56) https://bugs.python.org/issue25630

   (57) https://bugs.python.org/issue23564

   (58) https://bugs.python.org/issue25388

   (59) https://bugs.python.org/issue25462

   (60) https://bugs.python.org/issue22995

   (61) https://bugs.python.org/issue24802

   (62) https://bugs.python.org/issue25555

   (63) https://bugs.python.org/issue24726

   (64) https://bugs.python.org/issue25449

   (65) https://bugs.python.org/issue25395

   (66) https://bugs.python.org/issue25401

   (67) https://bugs.python.org/issue25399

   (68) https://bugs.python.org/issue25274

   (69) https://bugs.python.org/issue24402

   (70) https://bugs.python.org/issue25349

   (71) https://bugs.python.org/issue24806

   (72) https://bugs.python.org/issue25301

   (73) https://bugs.python.org/issue24848

   (74) https://bugs.python.org/issue25267

   (75) https://bugs.python.org/issue25280

   (76) https://bugs.python.org/issue25227

   (77) https://bugs.python.org/issue25003

   (78) https://bugs.python.org/issue9232

   (79) https://bugs.python.org/issue24965

   (80) https://www.python.org/dev/peps/pep-0498

   (81) https://bugs.python.org/issue26478

   (82) https://bugs.python.org/issue26171

   (83) https://bugs.python.org/issue25660

   (84) https://bugs.python.org/issue26288

   (85) https://bugs.python.org/issue26289

   (86) https://bugs.python.org/issue26315

   (87) https://bugs.python.org/issue25887


File: python.info,  Node: Library<62>,  Next: Security<30>,  Prev: Core and Builtins<55>,  Up: Python 3 6 0 alpha 1

1.19.66.2 Library
.................

   - bpo-27057(1): Fix os.set_inheritable() on Android, ioctl() is
     blocked by SELinux and fails with EACCESS. The function now falls
     back to fcntl().  Patch written by Michał Bednarski.

   - bpo-27014(2): Fix infinite recursion using typing.py.  Thanks to
     Kalle Tuure!

   - bpo-27031(3): Removed dummy methods in Tkinter widget classes:
     tk_menuBar() and tk_bindForTraversal().

   - bpo-14132(4): Fix urllib.request redirect handling when the target
     only has a query string.  Original fix by Ján Janech.

   - bpo-17214(5): The “urllib.request” module now percent-encodes
     non-ASCII bytes found in redirect target URLs.  Some servers send
     Location header fields with non-ASCII bytes, but “http.client”
     requires the request target to be ASCII-encodable, otherwise a
     UnicodeEncodeError is raised.  Based on patch by Christian Heimes.

   - bpo-27033(6): The default value of the decode_data parameter for
     smtpd.SMTPChannel and smtpd.SMTPServer constructors is changed to
     False.

   - bpo-27034(7): Removed deprecated class asynchat.fifo.

   - bpo-26870(8): Added readline.set_auto_history(), which can stop
     entries being automatically added to the history list.  Based on
     patch by Tyler Crompton.

   - bpo-26039(9): zipfile.ZipFile.open() can now be used to write data
     into a ZIP file, as well as for extracting data.  Patch by Thomas
     Kluyver.

   - bpo-26892(10): Honor debuglevel flag in urllib.request.HTTPHandler.
     Patch contributed by Chi Hsuan Yen.

   - bpo-22274(11): In the subprocess module, allow stderr to be
     redirected to stdout even when stdout is not redirected.  Patch by
     Akira Li.

   - bpo-26807(12): mock_open ‘files’ no longer error on readline at end
     of file.  Patch from Yolanda Robla.

   - bpo-25745(13): Fixed leaking a userptr in curses panel destructor.

   - bpo-26977(14): Removed unnecessary, and ignored, call to sum of
     squares helper in statistics.pvariance.

   - bpo-26002(15): Use bisect in statistics.median instead of a linear
     search.  Patch by Upendra Kuma.

   - bpo-25974(16): Make use of new Decimal.as_integer_ratio() method in
     statistics module.  Patch by Stefan Krah.

   - bpo-26996(17): Add secrets module as described in PEP 506(18).

   - bpo-26881(19): The modulefinder module now supports extended opcode
     arguments.

   - bpo-23815(20): Fixed crashes related to directly created instances
     of types in _tkinter and curses.panel modules.

   - bpo-17765(21): weakref.ref() no longer silently ignores keyword
     arguments.  Patch by Georg Brandl.

   - bpo-26873(22): xmlrpc now raises ResponseError on unsupported type
     tags instead of silently return incorrect result.

   - bpo-26915(23): The __contains__ methods in the collections ABCs now
     check for identity before checking equality.  This better matches
     the behavior of the concrete classes, allows sensible handling of
     NaNs, and makes it easier to reason about container invariants.

   - bpo-26711(24): Fixed the comparison of plistlib.Data with other
     types.

   - bpo-24114(25): Fix an uninitialized variable in ‘ctypes.util’.  The
     bug only occurs on SunOS when the ctypes implementation searches
     for the ‘crle’ program.  Patch by Xiang Zhang.  Tested on SunOS by
     Kees Bos.

   - bpo-26864(26): In urllib.request, change the proxy bypass host
     checking against no_proxy to be case-insensitive, and to not match
     unrelated host names that happen to have a bypassed hostname as a
     suffix.  Patch by Xiang Zhang.

   - bpo-24902(27): Print server URL on http.server startup.  Initial
     patch by Felix Kaiser.

   - bpo-25788(28): fileinput.hook_encoded() now supports an “errors”
     argument for passing to open.  Original patch by Joseph Hackman.

   - bpo-26634(29): recursive_repr() now sets __qualname__ of wrapper.
     Patch by Xiang Zhang.

   - bpo-26804(30): urllib.request will prefer lower_case proxy
     environment variables over UPPER_CASE or Mixed_Case ones.  Patch
     contributed by Hans-Peter Jansen.

   - bpo-26837(31): assertSequenceEqual() now correctly outputs
     non-stringified differing items (like bytes in the -b mode).  This
     affects assertListEqual() and assertTupleEqual().

   - bpo-26041(32): Remove “will be removed in Python 3.7” from
     deprecation messages of platform.dist() and
     platform.linux_distribution().  Patch by Kumaripaba Miyurusara
     Athukorala.

   - bpo-26822(33): itemgetter, attrgetter and methodcaller objects no
     longer silently ignore keyword arguments.

   - bpo-26733(34): Disassembling a class now disassembles class and
     static methods.  Patch by Xiang Zhang.

   - bpo-26801(35): Fix error handling in *note
     shutil.get_terminal_size(): b25, catch *note AttributeError: 4a2.
     instead of *note NameError: e40.  Patch written by Emanuel Barry.

   - bpo-24838(36): tarfile’s ustar and gnu formats now correctly
     calculate name and link field limits for multibyte character
     encodings like utf-8.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27057

   (2) https://bugs.python.org/issue27014

   (3) https://bugs.python.org/issue27031

   (4) https://bugs.python.org/issue14132

   (5) https://bugs.python.org/issue17214

   (6) https://bugs.python.org/issue27033

   (7) https://bugs.python.org/issue27034

   (8) https://bugs.python.org/issue26870

   (9) https://bugs.python.org/issue26039

   (10) https://bugs.python.org/issue26892

   (11) https://bugs.python.org/issue22274

   (12) https://bugs.python.org/issue26807

   (13) https://bugs.python.org/issue25745

   (14) https://bugs.python.org/issue26977

   (15) https://bugs.python.org/issue26002

   (16) https://bugs.python.org/issue25974

   (17) https://bugs.python.org/issue26996

   (18) https://www.python.org/dev/peps/pep-0506

   (19) https://bugs.python.org/issue26881

   (20) https://bugs.python.org/issue23815

   (21) https://bugs.python.org/issue17765

   (22) https://bugs.python.org/issue26873

   (23) https://bugs.python.org/issue26915

   (24) https://bugs.python.org/issue26711

   (25) https://bugs.python.org/issue24114

   (26) https://bugs.python.org/issue26864

   (27) https://bugs.python.org/issue24902

   (28) https://bugs.python.org/issue25788

   (29) https://bugs.python.org/issue26634

   (30) https://bugs.python.org/issue26804

   (31) https://bugs.python.org/issue26837

   (32) https://bugs.python.org/issue26041

   (33) https://bugs.python.org/issue26822

   (34) https://bugs.python.org/issue26733

   (35) https://bugs.python.org/issue26801

   (36) https://bugs.python.org/issue24838


File: python.info,  Node: Security<30>,  Next: Library<63>,  Prev: Library<62>,  Up: Python 3 6 0 alpha 1

1.19.66.3 Security
..................

   - bpo-26657(1): Fix directory traversal vulnerability with
     http.server on Windows.  This fixes a regression that was
     introduced in 3.3.4rc1 and 3.4.0rc1.  Based on patch by Philipp
     Hagemeister.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26657


File: python.info,  Node: Library<63>,  Next: Security<31>,  Prev: Security<30>,  Up: Python 3 6 0 alpha 1

1.19.66.4 Library
.................

   - bpo-26717(1): Stop encoding Latin-1-ized WSGI paths with UTF-8.
     Patch by Anthony Sottile.

   - bpo-26782(2): Add STARTUPINFO to subprocess.__all__ on Windows.

   - bpo-26404(3): Add context manager to socketserver.  Patch by Aviv
     Palivoda.

   - bpo-26735(4): Fix *note os.urandom(): 5cc. on Solaris 11.3 and
     newer when reading more than 1,024 bytes: call ‘getrandom()’
     multiple times with a limit of 1024 bytes per call.

   - bpo-26585(5): Eliminate http.server._quote_html() and use
     html.escape(quote=False).  Patch by Xiang Zhang.

   - bpo-26685(6): Raise OSError if closing a socket fails.

   - bpo-16329(7): Add .webm to mimetypes.types_map.  Patch by Giampaolo
     Rodola’.

   - bpo-13952(8): Add .csv to mimetypes.types_map.  Patch by Geoff
     Wilson.

   - bpo-26587(9): the site module now allows .pth files to specify
     files to be added to sys.path (e.g.  zip files).

   - bpo-25609(10): Introduce contextlib.AbstractContextManager and
     typing.ContextManager.

   - bpo-26709(11): Fixed Y2038 problem in loading binary PLists.

   - bpo-23735(12): Handle terminal resizing with Readline 6.3+ by
     installing our own SIGWINCH handler.  Patch by Eric Price.

   - bpo-25951(13): Change SSLSocket.sendall() to return None, as
     explicitly documented for plain socket objects.  Patch by Aviv
     Palivoda.

   - bpo-26586(14): In http.server, respond with “413 Request header
     fields too large” if there are too many header fields to parse,
     rather than killing the connection and raising an unhandled
     exception.  Patch by Xiang Zhang.

   - bpo-26676(15): Added missing XMLPullParser to ElementTree.__all__.

   - bpo-22854(16): Change BufferedReader.writable() and
     BufferedWriter.readable() to always return False.

   - bpo-26492(17): Exhausted iterator of array.array now conforms with
     the behavior of iterators of other mutable sequences: it lefts
     exhausted even if iterated array is extended.

   - bpo-26641(18): doctest.DocFileTest and doctest.testfile() now
     support packages (module splitted into multiple directories) for
     the package parameter.

   - bpo-25195(19): Fix a regression in mock.MagicMock.  _Call is a
     subclass of tuple (changeset 3603bae63c13 only works for classes)
     so we need to implement __ne__ ourselves.  Patch by Andrew Plummer.

   - bpo-26644(20): Raise ValueError rather than SystemError when a
     negative length is passed to SSLSocket.recv() or read().

   - bpo-23804(21): Fix SSL recv(0) and read(0) methods to return zero
     bytes instead of up to 1024.

   - bpo-26616(22): Fixed a bug in datetime.astimezone() method.

   - bpo-26637(23): The *note importlib: 9a. module now emits an *note
     ImportError: 16c. rather than a *note TypeError: 1fe. if *note
     __import__(): 16b. is tried during the Python shutdown process but
     *note sys.path: 260. is already cleared (set to ‘None’).

   - bpo-21925(24): *note warnings.formatwarning(): 112d. now catches
     exceptions when calling *note linecache.getline(): 7fa. and *note
     tracemalloc.get_object_traceback(): 129b. to be able to log *note
     ResourceWarning: 5cb. emitted late during the Python shutdown
     process.

   - bpo-23848(25): On Windows, faulthandler.enable() now also installs
     an exception handler to dump the traceback of all Python threads on
     any Windows exception, not only on UNIX signals (SIGSEGV, SIGFPE,
     SIGABRT).

   - bpo-26530(26): Add C functions ‘_PyTraceMalloc_Track()’ and
     ‘_PyTraceMalloc_Untrack()’ to track memory blocks using the *note
     tracemalloc: 11d. module.  Add ‘_PyTraceMalloc_GetTraceback()’ to
     get the traceback of an object.

   - bpo-26588(27): The _tracemalloc now supports tracing memory
     allocations of multiple address spaces (domains).

   - bpo-24266(28): Ctrl+C during Readline history search now cancels
     the search mode when compiled with Readline 7.

   - bpo-26590(29): Implement a safe finalizer for the _socket.socket
     type.  It now releases the GIL to close the socket.

   - bpo-18787(30): spwd.getspnam() now raises a PermissionError if the
     user doesn’t have privileges.

   - bpo-26560(31): Avoid potential ValueError in
     BaseHandler.start_response.  Initial patch by Peter Inglesby.

   - bpo-26567(32): Add a new function *note PyErr_ResourceWarning():
     6c3. function to pass the destroyed object.  Add a `source'
     attribute to ‘warnings.WarningMessage’.  Add
     warnings._showwarnmsg() which uses tracemalloc to get the traceback
     where source object was allocated.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26717

   (2) https://bugs.python.org/issue26782

   (3) https://bugs.python.org/issue26404

   (4) https://bugs.python.org/issue26735

   (5) https://bugs.python.org/issue26585

   (6) https://bugs.python.org/issue26685

   (7) https://bugs.python.org/issue16329

   (8) https://bugs.python.org/issue13952

   (9) https://bugs.python.org/issue26587

   (10) https://bugs.python.org/issue25609

   (11) https://bugs.python.org/issue26709

   (12) https://bugs.python.org/issue23735

   (13) https://bugs.python.org/issue25951

   (14) https://bugs.python.org/issue26586

   (15) https://bugs.python.org/issue26676

   (16) https://bugs.python.org/issue22854

   (17) https://bugs.python.org/issue26492

   (18) https://bugs.python.org/issue26641

   (19) https://bugs.python.org/issue25195

   (20) https://bugs.python.org/issue26644

   (21) https://bugs.python.org/issue23804

   (22) https://bugs.python.org/issue26616

   (23) https://bugs.python.org/issue26637

   (24) https://bugs.python.org/issue21925

   (25) https://bugs.python.org/issue23848

   (26) https://bugs.python.org/issue26530

   (27) https://bugs.python.org/issue26588

   (28) https://bugs.python.org/issue24266

   (29) https://bugs.python.org/issue26590

   (30) https://bugs.python.org/issue18787

   (31) https://bugs.python.org/issue26560

   (32) https://bugs.python.org/issue26567


File: python.info,  Node: Security<31>,  Next: Library<64>,  Prev: Library<63>,  Up: Python 3 6 0 alpha 1

1.19.66.5 Security
..................

   - bpo-26313(1): ssl.py _load_windows_store_certs fails if windows
     cert store is empty.  Patch by Baji.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26313


File: python.info,  Node: Library<64>,  Next: Security<32>,  Prev: Security<31>,  Up: Python 3 6 0 alpha 1

1.19.66.6 Library
.................

   - bpo-26569(1): Fix *note pyclbr.readmodule(): 129e. and *note
     pyclbr.readmodule_ex(): 129f. to support importing packages.

   - bpo-26499(2): Account for remaining Content-Length in
     HTTPResponse.readline() and read1().  Based on patch by Silent
     Ghost.  Also document that HTTPResponse now supports these methods.

   - bpo-25320(3): Handle sockets in directories unittest discovery is
     scanning.  Patch from Victor van den Elzen.

   - bpo-16181(4): cookiejar.http2time() now returns None if year is
     higher than datetime.MAXYEAR.

   - bpo-26513(5): Fixes platform module detection of Windows Server

   - bpo-23718(6): Fixed parsing time in week 0 before Jan 1.  Original
     patch by Tamás Bence Gedai.

   - bpo-26323(7): Add Mock.assert_called() and
     Mock.assert_called_once() methods to unittest.mock.  Patch written
     by Amit Saha.

   - bpo-20589(8): Invoking Path.owner() and Path.group() on Windows now
     raise NotImplementedError instead of ImportError.

   - bpo-26177(9): Fixed the keys() method for Canvas and Scrollbar
     widgets.

   - bpo-15068(10): Got rid of excessive buffering in fileinput.  The
     bufsize parameter is now deprecated and ignored.

   - bpo-19475(11): Added an optional argument timespec to the datetime
     isoformat() method to choose the precision of the time component.

   - bpo-2202(12): Fix UnboundLocalError in
     AbstractDigestAuthHandler.get_algorithm_impls.  Initial patch by
     Mathieu Dupuy.

   - bpo-26167(13): Minimized overhead in copy.copy() and
     copy.deepcopy().  Optimized copying and deepcopying bytearrays,
     NotImplemented, slices, short lists, tuples, dicts, sets.

   - bpo-25718(14): Fixed pickling and copying the accumulate() iterator
     with total is None.

   - bpo-26475(15): Fixed debugging output for regular expressions with
     the (?x) flag.

   - bpo-26482(16): Allowed pickling recursive dequeues.

   - bpo-26335(17): Make mmap.write() return the number of bytes written
     like other write methods.  Patch by Jakub Stasiak.

   - bpo-26457(18): Fixed the subnets() methods in IP network classes
     for the case when resulting prefix length is equal to maximal
     prefix length.  Based on patch by Xiang Zhang.

   - bpo-26385(19): Remove the file if the internal open() call in
     NamedTemporaryFile() fails.  Patch by Silent Ghost.

   - bpo-26402(20): Fix XML-RPC client to retry when the server shuts
     down a persistent connection.  This was a regression related to the
     new http.client.RemoteDisconnected exception in 3.5.0a4.

   - bpo-25913(21): Leading ‘<~’ is optional now in base64.a85decode()
     with adobe=True.  Patch by Swati Jaiswal.

   - bpo-26186(22): Remove an invalid type check in
     importlib.util.LazyLoader.

   - bpo-26367(23): importlib.__import__() raises ImportError like
     builtins.__import__() when ‘level’ is specified but without an
     accompanying package specified.

   - bpo-26309(24): In the “socketserver” module, shut down the request
     (closing the connected socket) when verify_request() returns false.
     Patch by Aviv Palivoda.

   - bpo-23430(25): Change the socketserver module to only catch
     exceptions raised from a request handler that are derived from
     Exception (instead of BaseException).  Therefore SystemExit and
     KeyboardInterrupt no longer trigger the handle_error() method, and
     will now to stop a single-threaded server.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26569

   (2) https://bugs.python.org/issue26499

   (3) https://bugs.python.org/issue25320

   (4) https://bugs.python.org/issue16181

   (5) https://bugs.python.org/issue26513

   (6) https://bugs.python.org/issue23718

   (7) https://bugs.python.org/issue26323

   (8) https://bugs.python.org/issue20589

   (9) https://bugs.python.org/issue26177

   (10) https://bugs.python.org/issue15068

   (11) https://bugs.python.org/issue19475

   (12) https://bugs.python.org/issue2202

   (13) https://bugs.python.org/issue26167

   (14) https://bugs.python.org/issue25718

   (15) https://bugs.python.org/issue26475

   (16) https://bugs.python.org/issue26482

   (17) https://bugs.python.org/issue26335

   (18) https://bugs.python.org/issue26457

   (19) https://bugs.python.org/issue26385

   (20) https://bugs.python.org/issue26402

   (21) https://bugs.python.org/issue25913

   (22) https://bugs.python.org/issue26186

   (23) https://bugs.python.org/issue26367

   (24) https://bugs.python.org/issue26309

   (25) https://bugs.python.org/issue23430


File: python.info,  Node: Security<32>,  Next: Library<65>,  Prev: Library<64>,  Up: Python 3 6 0 alpha 1

1.19.66.7 Security
..................

   - bpo-25939(1): On Windows open the cert store readonly in
     ssl.enum_certificates.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25939


File: python.info,  Node: Library<65>,  Next: IDLE<43>,  Prev: Security<32>,  Up: Python 3 6 0 alpha 1

1.19.66.8 Library
.................

   - bpo-25995(1): os.walk() no longer uses FDs proportional to the tree
     depth.

   - bpo-25994(2): Added the close() method and the support of the
     context manager protocol for the os.scandir() iterator.

   - bpo-23992(3): multiprocessing: make MapResult not fail-fast upon
     exception.

   - bpo-26243(4): Support keyword arguments to zlib.compress().  Patch
     by Aviv Palivoda.

   - bpo-26117(5): The os.scandir() iterator now closes file descriptor
     not only when the iteration is finished, but when it was failed
     with error.

   - bpo-25949(6): __dict__ for an OrderedDict instance is now created
     only when needed.

   - bpo-25911(7): Restored support of bytes paths in os.walk() on
     Windows.

   - bpo-26045(8): Add UTF-8 suggestion to error message when posting a
     non-Latin-1 string with http.client.

   - bpo-26039(9): Added zipfile.ZipInfo.from_file() and
     zipinfo.ZipInfo.is_dir().  Patch by Thomas Kluyver.

   - bpo-12923(10): Reset FancyURLopener’s redirect counter even if
     there is an exception.  Based on patches by Brian Brazil and Daniel
     Rocco.

   - bpo-25945(11): Fixed a crash when unpickle the functools.partial
     object with wrong state.  Fixed a leak in failed functools.partial
     constructor.  “args” and “keywords” attributes of functools.partial
     have now always types tuple and dict correspondingly.

   - bpo-26202(12): copy.deepcopy() now correctly copies range() objects
     with non-atomic attributes.

   - bpo-23076(13): Path.glob() now raises a ValueError if it’s called
     with an invalid pattern.  Patch by Thomas Nyberg.

   - bpo-19883(14): Fixed possible integer overflows in zipimport.

   - bpo-26227(15): On Windows, getnameinfo(), gethostbyaddr() and
     gethostbyname_ex() functions of the socket module now decode the
     hostname from the ANSI code page rather than UTF-8.

   - bpo-26099(16): The site module now writes an error into stderr if
     sitecustomize module can be imported but executing the module raise
     an ImportError.  Same change for usercustomize.

   - bpo-26147(17): xmlrpc now works with strings not encodable with
     used non-UTF-8 encoding.

   - bpo-25935(18): Garbage collector now breaks reference loops with
     OrderedDict.

   - bpo-16620(19): Fixed AttributeError in msilib.Directory.glob().

   - bpo-26013(20): Added compatibility with broken protocol 2 pickles
     created in old Python 3 versions (3.4.3 and lower).

   - bpo-26129(21): Deprecated accepting non-integers in grp.getgrgid().

   - bpo-25850(22): Use cross-compilation by default for 64-bit Windows.

   - bpo-25822(23): Add docstrings to the fields of urllib.parse
     results.  Patch contributed by Swati Jaiswal.

   - bpo-22642(24): Convert trace module option parsing mechanism to
     argparse.  Patch contributed by SilentGhost.

   - bpo-24705(25): Fix sysconfig._parse_makefile not expanding ${} vars
     appearing before $() vars.

   - bpo-26069(26): Remove the deprecated apis in the trace module.

   - bpo-22138(27): Fix mock.patch behavior when patching descriptors.
     Restore original values after patching.  Patch contributed by Sean
     McCully.

   - bpo-25672(28): In the ssl module, enable the
     SSL_MODE_RELEASE_BUFFERS mode option if it is safe to do so.

   - bpo-26012(29): Don’t traverse into symlinks for ‘**’ pattern in
     pathlib.Path.[r]glob().

   - bpo-24120(30): Ignore PermissionError when traversing a tree with
     pathlib.Path.[r]glob().  Patch by Ulrich Petri.

   - bpo-21815(31): Accept ] characters in the data portion of imap
     responses, in order to handle the flags with square brackets
     accepted and produced by servers such as gmail.

   - bpo-25447(32): fileinput now uses sys.stdin as-is if it does not
     have a buffer attribute (restores backward compatibility).

   - bpo-25971(33): Optimized creating Fractions from floats by 2 times
     and from Decimals by 3 times.

   - bpo-25802(34): Document as deprecated the remaining implementations
     of importlib.abc.Loader.load_module().

   - bpo-25928(35): Add Decimal.as_integer_ratio().

   - bpo-25447(36): Copying the lru_cache() wrapper object now always
     works, independently from the type of the wrapped object (by
     returning the original object unchanged).

   - bpo-25768(37): Have the functions in compileall return booleans
     instead of ints and add proper documentation and tests for the
     return values.

   - bpo-24103(38): Fixed possible use after free in
     ElementTree.XMLPullParser.

   - bpo-25860(39): os.fwalk() no longer skips remaining directories
     when error occurs.  Original patch by Samson Lee.

   - bpo-25914(40): Fixed and simplified OrderedDict.__sizeof__.

   - bpo-25869(41): Optimized deepcopying ElementTree; it is now 20
     times faster.

   - bpo-25873(42): Optimized iterating ElementTree.  Iterating elements
     Element.iter() is now 40% faster, iterating text Element.itertext()
     is now up to 2.5 times faster.

   - bpo-25902(43): Fixed various refcount issues in ElementTree
     iteration.

   - bpo-22227(44): The TarFile iterator is reimplemented using
     generator.  This implementation is simpler that using class.

   - bpo-25638(45): Optimized ElementTree.iterparse(); it is now 2x
     faster.  Optimized ElementTree parsing; it is now 10% faster.

   - bpo-25761(46): Improved detecting errors in broken pickle data.

   - bpo-25717(47): Restore the previous behaviour of tolerating most
     fstat() errors when opening files.  This was a regression in 3.5a1,
     and stopped anonymous temporary files from working in special
     cases.

   - bpo-24903(48): Fix regression in number of arguments compileall
     accepts when ‘-d’ is specified.  The check on the number of
     arguments has been dropped completely as it never worked correctly
     anyway.

   - bpo-25764(49): In the subprocess module, preserve any exception
     caused by fork() failure when preexec_fn is used.

   - bpo-25771(50): Tweak the exception message for
     importlib.util.resolve_name() when ‘package’ isn’t specified but
     necessary.

   - bpo-6478(51): _strptime’s regexp cache now is reset after changing
     timezone with time.tzset().

   - bpo-14285(52): When executing a package with the “python -m
     package” option, and package initialization fails, a proper
     traceback is now reported.  The “runpy” module now lets exceptions
     from package initialization pass back to the caller, rather than
     raising ImportError.

   - bpo-19771(53): Also in runpy and the “-m” option, omit the
     irrelevant message “… is a package and cannot be directly executed”
     if the package could not even be initialized (e.g.  due to a bad
     ‘*.pyc’ file).

   - bpo-25177(54): Fixed problem with the mean of very small and very
     large numbers.  As a side effect, statistics.mean and
     statistics.variance should be significantly faster.

   - bpo-25718(55): Fixed copying object with state with boolean value
     is false.

   - bpo-10131(56): Fixed deep copying of minidom documents.  Based on
     patch by Marian Ganisin.

   - bpo-7990(57): dir() on ElementTree.Element now lists properties:
     “tag”, “text”, “tail” and “attrib”.  Original patch by Santoso
     Wijaya.

   - bpo-25725(58): Fixed a reference leak in pickle.loads() when
     unpickling invalid data including tuple instructions.

   - bpo-25663(59): In the Readline completer, avoid listing duplicate
     global names, and search the global namespace before searching
     builtins.

   - bpo-25688(60): Fixed file leak in ElementTree.iterparse() raising
     an error.

   - bpo-23914(61): Fixed SystemError raised by unpickler on broken
     pickle data.

   - bpo-25691(62): Fixed crash on deleting ElementTree.Element
     attributes.

   - bpo-25624(63): ZipFile now always writes a ZIP_STORED header for
     directory entries.  Patch by Dingyuan Wang.

   - bpo-25626(64): Change three zlib functions to accept sizes that fit
     in Py_ssize_t, but internally cap those sizes to UINT_MAX. This
     resolves a regression in 3.5 where GzipFile.read() failed to read
     chunks larger than 2 or 4 GiB. The change affects the
     zlib.Decompress.decompress() max_length parameter, the
     zlib.decompress() bufsize parameter, and the
     zlib.Decompress.flush() length parameter.

   - bpo-25583(65): Avoid incorrect errors raised by
     os.makedirs(exist_ok=True) when the OS gives priority to errors
     such as EACCES over EEXIST.

   - bpo-25593(66): Change semantics of EventLoop.stop() in asyncio.

   - bpo-6973(67): When we know a subprocess.Popen process has died, do
     not allow the send_signal(), terminate(), or kill() methods to do
     anything as they could potentially signal a different process.

   - bpo-23883(68): Added missing APIs to __all__ to match the
     documented APIs for the following modules: calendar, csv, enum,
     fileinput, ftplib, logging, optparse, tarfile, threading and wave.
     Also added a test.support.check__all__() helper.  Patches by Jacek
     Kołodziej, Mauro S. M. Rodrigues and Joel Taddei.

   - bpo-25590(69): In the Readline completer, only call getattr() once
     per attribute.  Also complete names of attributes such as
     properties and slots which are listed by dir() but not yet created
     on an instance.

   - bpo-25498(70): Fix a crash when garbage-collecting ctypes objects
     created by wrapping a memoryview.  This was a regression made in
     3.5a1.  Based on patch by Eryksun.

   - bpo-25584(71): Added “escape” to the __all__ list in the glob
     module.

   - bpo-25584(72): Fixed recursive glob() with patterns starting with
     ‘**’.

   - bpo-25446(73): Fix regression in smtplib’s AUTH LOGIN support.

   - bpo-18010(74): Fix the pydoc web server’s module search function to
     handle exceptions from importing packages.

   - bpo-25554(75): Got rid of circular references in regular expression
     parsing.

   - bpo-18973(76): Command-line interface of the calendar module now
     uses argparse instead of optparse.

   - bpo-25510(77): fileinput.FileInput.readline() now returns b’’
     instead of ‘’ at the end if the FileInput was opened with binary
     mode.  Patch by Ryosuke Ito.

   - bpo-25503(78): Fixed inspect.getdoc() for inherited docstrings of
     properties.  Original patch by John Mark Vandenberg.

   - bpo-25515(79): Always use os.urandom as a source of randomness in
     uuid.uuid4.

   - bpo-21827(80): Fixed textwrap.dedent() for the case when largest
     common whitespace is a substring of smallest leading whitespace.
     Based on patch by Robert Li.

   - bpo-25447(81): The lru_cache() wrapper objects now can be copied
     and pickled (by returning the original object unchanged).

   - bpo-25390(82): typing: Don’t crash on Union[str, Pattern].

   - bpo-25441(83): asyncio: Raise error from drain() when socket is
     closed.

   - bpo-25410(84): Cleaned up and fixed minor bugs in C implementation
     of OrderedDict.

   - bpo-25411(85): Improved Unicode support in SMTPHandler through
     better use of the email package.  Thanks to user simon04 for the
     patch.

   - Move the imp module from a PendingDeprecationWarning to
     DeprecationWarning.

   - bpo-25407(86): Remove mentions of the formatter module being
     removed in Python 3.6.

   - bpo-25406(87): Fixed a bug in C implementation of
     OrderedDict.move_to_end() that caused segmentation fault or hang in
     iterating after moving several items to the start of ordered dict.

   - bpo-25382(88): pickletools.dis() now outputs implicit memo index
     for the MEMOIZE opcode.

   - bpo-25357(89): Add an optional newline parameter to
     binascii.b2a_base64().  base64.b64encode() uses it to avoid a
     memory copy.

   - bpo-24164(90): Objects that need calling ‘__new__’ with keyword
     arguments, can now be pickled using pickle protocols older than
     protocol version 4.

   - bpo-25364(91): zipfile now works in threads disabled builds.

   - bpo-25328(92): smtpd’s SMTPChannel now correctly raises a
     ValueError if both decode_data and enable_SMTPUTF8 are set to true.

   - bpo-16099(93): RobotFileParser now supports Crawl-delay and
     Request-rate extensions.  Patch by Nikolay Bogoychev.

   - bpo-25316(94): distutils raises OSError instead of
     DistutilsPlatformError when MSVC is not installed.

   - bpo-25380(95): Fixed protocol for the STACK_GLOBAL opcode in
     pickletools.opcodes.

   - bpo-23972(96): Updates asyncio datagram create method allowing
     reuseport and reuseaddr socket options to be set prior to binding
     the socket.  Mirroring the existing asyncio create_server method
     the reuseaddr option for datagram sockets defaults to True if the
     O/S is ‘posix’ (except if the platform is Cygwin).  Patch by Chris
     Laws.

   - bpo-25304(97): Add asyncio.run_coroutine_threadsafe().  This lets
     you submit a coroutine to a loop from another thread, returning a
     concurrent.futures.Future.  By Vincent Michel.

   - bpo-25232(98): Fix CGIRequestHandler to split the query from the
     URL at the first question mark (?)  rather than the last.  Patch
     from Xiang Zhang.

   - bpo-24657(99): Prevent CGIRequestHandler from collapsing slashes in
     the query part of the URL as if it were a path.  Patch from Xiang
     Zhang.

   - bpo-25287(100): Don’t add crypt.METHOD_CRYPT to crypt.methods if
     it’s not supported.  Check if it is supported, it may not be
     supported on OpenBSD for example.

   - bpo-23600(101): Default implementation of tzinfo.fromutc() was
     returning wrong results in some cases.

   - bpo-25203(102): Failed readline.set_completer_delims() no longer
     left the module in inconsistent state.

   - bpo-25011(103): rlcompleter now omits private and special attribute
     names unless the prefix starts with underscores.

   - bpo-25209(104): rlcompleter now can add a space or a colon after
     completed keyword.

   - bpo-22241(105): timezone.utc name is now plain ‘UTC’, not
     ‘UTC-00:00’.

   - bpo-23517(106): fromtimestamp() and utcfromtimestamp() methods of
     datetime.datetime now round microseconds to nearest with ties going
     to nearest even integer (ROUND_HALF_EVEN), as round(float), instead
     of rounding towards -Infinity (ROUND_FLOOR).

   - bpo-23552(107): Timeit now warns when there is substantial (4x)
     variance between best and worst times.  Patch from Serhiy
     Storchaka.

   - bpo-24633(108): site-packages/README -> README.txt.

   - bpo-24879(109): help() and pydoc can now list named tuple fields in
     the order they were defined rather than alphabetically.  The
     ordering is determined by the _fields attribute if present.

   - bpo-24874(110): Improve speed of itertools.cycle() and make its
     pickle more compact.

   - Fix crash in itertools.cycle.__setstate__() when the first argument
     wasn’t a list.

   - bpo-20059(111): urllib.parse raises ValueError on all invalid
     ports.  Patch by Martin Panter.

   - bpo-24360(112): Improve __repr__ of argparse.Namespace() for
     invalid identifiers.  Patch by Matthias Bussonnier.

   - bpo-23426(113): run_setup was broken in distutils.  Patch from
     Alexander Belopolsky.

   - bpo-13938(114): 2to3 converts StringTypes to a tuple.  Patch from
     Mark Hammond.

   - bpo-2091(115): open() accepted a ‘U’ mode string containing ‘+’,
     but ‘U’ can only be used with ‘r’.  Patch from Jeff Balogh and John
     O’Connor.

   - bpo-8585(116): improved tests for zipimporter2.  Patch from Mark
     Lawrence.

   - bpo-18622(117): unittest.mock.mock_open().reset_mock would recurse
     infinitely.  Patch from Nicola Palumbo and Laurent De Buyst.

   - bpo-24426(118): Fast searching optimization in regular expressions
     now works for patterns that starts with capturing groups.  Fast
     searching optimization now can’t be disabled at compile time.

   - bpo-23661(119): unittest.mock side_effects can now be exceptions
     again.  This was a regression vs Python 3.4.  Patch from Ignacio
     Rossi

   - bpo-13248(120): Remove deprecated inspect.getmoduleinfo function.

   - bpo-25578(121): Fix (another) memory leak in
     SSLSocket.getpeercer().

   - bpo-25530(122): Disable the vulnerable SSLv3 protocol by default
     when creating ssl.SSLContext.

   - bpo-25569(123): Fix memory leak in SSLSocket.getpeercert().

   - bpo-25471(124): Sockets returned from accept() shouldn’t appear to
     be nonblocking.

   - bpo-25319(125): When threading.Event is reinitialized, the
     underlying condition should use a regular lock rather than a
     recursive lock.

   - Skip getaddrinfo if host is already resolved.  Patch by A. Jesse
     Jiryu Davis.

   - bpo-26050(126): Add asyncio.StreamReader.readuntil() method.  Patch
     by Марк Коренберг.

   - bpo-25924(127): Avoid unnecessary serialization of getaddrinfo(3)
     calls on OS X versions 10.5 or higher.  Original patch by A. Jesse
     Jiryu Davis.

   - bpo-26406(128): Avoid unnecessary serialization of getaddrinfo(3)
     calls on current versions of OpenBSD and NetBSD. Patch by A. Jesse
     Jiryu Davis.

   - bpo-26848(129): Fix asyncio/subprocess.communicate() to handle
     empty input.  Patch by Jack O’Connor.

   - bpo-27040(130): Add loop.get_exception_handler method

   - bpo-27041(131): asyncio: Add loop.create_future method

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25995

   (2) https://bugs.python.org/issue25994

   (3) https://bugs.python.org/issue23992

   (4) https://bugs.python.org/issue26243

   (5) https://bugs.python.org/issue26117

   (6) https://bugs.python.org/issue25949

   (7) https://bugs.python.org/issue25911

   (8) https://bugs.python.org/issue26045

   (9) https://bugs.python.org/issue26039

   (10) https://bugs.python.org/issue12923

   (11) https://bugs.python.org/issue25945

   (12) https://bugs.python.org/issue26202

   (13) https://bugs.python.org/issue23076

   (14) https://bugs.python.org/issue19883

   (15) https://bugs.python.org/issue26227

   (16) https://bugs.python.org/issue26099

   (17) https://bugs.python.org/issue26147

   (18) https://bugs.python.org/issue25935

   (19) https://bugs.python.org/issue16620

   (20) https://bugs.python.org/issue26013

   (21) https://bugs.python.org/issue26129

   (22) https://bugs.python.org/issue25850

   (23) https://bugs.python.org/issue25822

   (24) https://bugs.python.org/issue22642

   (25) https://bugs.python.org/issue24705

   (26) https://bugs.python.org/issue26069

   (27) https://bugs.python.org/issue22138

   (28) https://bugs.python.org/issue25672

   (29) https://bugs.python.org/issue26012

   (30) https://bugs.python.org/issue24120

   (31) https://bugs.python.org/issue21815

   (32) https://bugs.python.org/issue25447

   (33) https://bugs.python.org/issue25971

   (34) https://bugs.python.org/issue25802

   (35) https://bugs.python.org/issue25928

   (36) https://bugs.python.org/issue25447

   (37) https://bugs.python.org/issue25768

   (38) https://bugs.python.org/issue24103

   (39) https://bugs.python.org/issue25860

   (40) https://bugs.python.org/issue25914

   (41) https://bugs.python.org/issue25869

   (42) https://bugs.python.org/issue25873

   (43) https://bugs.python.org/issue25902

   (44) https://bugs.python.org/issue22227

   (45) https://bugs.python.org/issue25638

   (46) https://bugs.python.org/issue25761

   (47) https://bugs.python.org/issue25717

   (48) https://bugs.python.org/issue24903

   (49) https://bugs.python.org/issue25764

   (50) https://bugs.python.org/issue25771

   (51) https://bugs.python.org/issue6478

   (52) https://bugs.python.org/issue14285

   (53) https://bugs.python.org/issue19771

   (54) https://bugs.python.org/issue25177

   (55) https://bugs.python.org/issue25718

   (56) https://bugs.python.org/issue10131

   (57) https://bugs.python.org/issue7990

   (58) https://bugs.python.org/issue25725

   (59) https://bugs.python.org/issue25663

   (60) https://bugs.python.org/issue25688

   (61) https://bugs.python.org/issue23914

   (62) https://bugs.python.org/issue25691

   (63) https://bugs.python.org/issue25624

   (64) https://bugs.python.org/issue25626

   (65) https://bugs.python.org/issue25583

   (66) https://bugs.python.org/issue25593

   (67) https://bugs.python.org/issue6973

   (68) https://bugs.python.org/issue23883

   (69) https://bugs.python.org/issue25590

   (70) https://bugs.python.org/issue25498

   (71) https://bugs.python.org/issue25584

   (72) https://bugs.python.org/issue25584

   (73) https://bugs.python.org/issue25446

   (74) https://bugs.python.org/issue18010

   (75) https://bugs.python.org/issue25554

   (76) https://bugs.python.org/issue18973

   (77) https://bugs.python.org/issue25510

   (78) https://bugs.python.org/issue25503

   (79) https://bugs.python.org/issue25515

   (80) https://bugs.python.org/issue21827

   (81) https://bugs.python.org/issue25447

   (82) https://bugs.python.org/issue25390

   (83) https://bugs.python.org/issue25441

   (84) https://bugs.python.org/issue25410

   (85) https://bugs.python.org/issue25411

   (86) https://bugs.python.org/issue25407

   (87) https://bugs.python.org/issue25406

   (88) https://bugs.python.org/issue25382

   (89) https://bugs.python.org/issue25357

   (90) https://bugs.python.org/issue24164

   (91) https://bugs.python.org/issue25364

   (92) https://bugs.python.org/issue25328

   (93) https://bugs.python.org/issue16099

   (94) https://bugs.python.org/issue25316

   (95) https://bugs.python.org/issue25380

   (96) https://bugs.python.org/issue23972

   (97) https://bugs.python.org/issue25304

   (98) https://bugs.python.org/issue25232

   (99) https://bugs.python.org/issue24657

   (100) https://bugs.python.org/issue25287

   (101) https://bugs.python.org/issue23600

   (102) https://bugs.python.org/issue25203

   (103) https://bugs.python.org/issue25011

   (104) https://bugs.python.org/issue25209

   (105) https://bugs.python.org/issue22241

   (106) https://bugs.python.org/issue23517

   (107) https://bugs.python.org/issue23552

   (108) https://bugs.python.org/issue24633

   (109) https://bugs.python.org/issue24879

   (110) https://bugs.python.org/issue24874

   (111) https://bugs.python.org/issue20059

   (112) https://bugs.python.org/issue24360

   (113) https://bugs.python.org/issue23426

   (114) https://bugs.python.org/issue13938

   (115) https://bugs.python.org/issue2091

   (116) https://bugs.python.org/issue8585

   (117) https://bugs.python.org/issue18622

   (118) https://bugs.python.org/issue24426

   (119) https://bugs.python.org/issue23661

   (120) https://bugs.python.org/issue13248

   (121) https://bugs.python.org/issue25578

   (122) https://bugs.python.org/issue25530

   (123) https://bugs.python.org/issue25569

   (124) https://bugs.python.org/issue25471

   (125) https://bugs.python.org/issue25319

   (126) https://bugs.python.org/issue26050

   (127) https://bugs.python.org/issue25924

   (128) https://bugs.python.org/issue26406

   (129) https://bugs.python.org/issue26848

   (130) https://bugs.python.org/issue27040

   (131) https://bugs.python.org/issue27041


File: python.info,  Node: IDLE<43>,  Next: Documentation<46>,  Prev: Library<65>,  Up: Python 3 6 0 alpha 1

1.19.66.9 IDLE
..............

   - bpo-20640(1): Add tests for idlelib.configHelpSourceEdit.  Patch by
     Saimadhav Heblikar.

   - In the ‘IDLE-console differences’ section of the IDLE doc, clarify
     how running with IDLE affects sys.modules and the standard streams.

   - bpo-25507(2): fix incorrect change in IOBinding that prevented
     printing.  Augment IOBinding htest to include all major IOBinding
     functions.

   - bpo-25905(3): Revert unwanted conversion of ‘ to ’ RIGHT SINGLE
     QUOTATION MARK in README.txt and open this and NEWS.txt with
     ‘ascii’.  Re-encode CREDITS.txt to utf-8 and open it with ‘utf-8’.

   - bpo-15348(4): Stop the debugger engine (normally in a user process)
     before closing the debugger window (running in the IDLE process).
     This prevents the RuntimeErrors that were being caught and ignored.

   - bpo-24455(5): Prevent IDLE from hanging when a) closing the shell
     while the debugger is active (15347); b) closing the debugger with
     the [X] button (15348); and c) activating the debugger when already
     active (24455).  The patch by Mark Roseman does this by making two
     changes.  1.  Suspend and resume the gui.interaction method with
     the tcl vwait mechanism intended for this purpose (instead of
     root.mainloop & .quit).  2.  In gui.run, allow any existing
     interaction to terminate first.

   - Change ‘The program’ to ‘Your program’ in an IDLE ‘kill program?’
     message to make it clearer that the program referred to is the
     currently running user program, not IDLE itself.

   - bpo-24750(6): Improve the appearance of the IDLE editor window
     status bar.  Patch by Mark Roseman.

   - bpo-25313(7): Change the handling of new built-in text color themes
     to better address the compatibility problem introduced by the
     addition of IDLE Dark.  Consistently use the revised
     idleConf.CurrentTheme everywhere in idlelib.

   - bpo-24782(8): Extension configuration is now a tab in the IDLE
     Preferences dialog rather than a separate dialog.  The former tabs
     are now a sorted list.  Patch by Mark Roseman.

   - bpo-22726(9): Re-activate the config dialog help button with some
     content about the other buttons and the new IDLE Dark theme.

   - bpo-24820(10): IDLE now has an ‘IDLE Dark’ built-in text color
     theme.  It is more or less IDLE Classic inverted, with a cobalt
     blue background.  Strings, comments, keywords, … are still green,
     red, orange, … .  To use it with IDLEs released before November
     2015, hit the ‘Save as New Custom Theme’ button and enter a new
     name, such as ‘Custom Dark’.  The custom theme will work with any
     IDLE release, and can be modified.

   - bpo-25224(11): README.txt is now an idlelib index for IDLE
     developers and curious users.  The previous user content is now in
     the IDLE doc chapter.  ‘IDLE’ now means ‘Integrated Development and
     Learning Environment’.

   - bpo-24820(12): Users can now set breakpoint colors in Settings ->
     Custom Highlighting.  Original patch by Mark Roseman.

   - bpo-24972(13): Inactive selection background now matches active
     selection background, as configured by users, on all systems.
     Found items are now always highlighted on Windows.  Initial patch
     by Mark Roseman.

   - bpo-24570(14): Idle: make calltip and completion boxes appear on
     Macs affected by a tk regression.  Initial patch by Mark Roseman.

   - bpo-24988(15): Idle ScrolledList context menus (used in debugger)
     now work on Mac Aqua.  Patch by Mark Roseman.

   - bpo-24801(16): Make right-click for context menu work on Mac Aqua.
     Patch by Mark Roseman.

   - bpo-25173(17): Associate tkinter messageboxes with a specific
     widget.  For Mac OSX, make them a ‘sheet’.  Patch by Mark Roseman.

   - bpo-25198(18): Enhance the initial html viewer now used for Idle
     Help.  Properly indent fixed-pitch text (patch by Mark Roseman).
     Give code snippet a very Sphinx-like light blueish-gray background.
     Re-use initial width and height set by users for shell and editor.
     When the Table of Contents (TOC) menu is used, put the section
     header at the top of the screen.

   - bpo-25225(19): Condense and rewrite Idle doc section on text
     colors.

   - bpo-21995(20): Explain some differences between IDLE and console
     Python.

   - bpo-22820(21): Explain need for `print' when running file from Idle
     editor.

   - bpo-25224(22): Doc: augment Idle feature list and no-subprocess
     section.

   - bpo-25219(23): Update doc for Idle command line options.  Some were
     missing and notes were not correct.

   - bpo-24861(24): Most of idlelib is private and subject to change.
     Use idleib.idle.* to start Idle.  See idlelib.__init__.__doc__.

   - bpo-25199(25): Idle: add synchronization comments for future
     maintainers.

   - bpo-16893(26): Replace help.txt with help.html for Idle doc
     display.  The new idlelib/help.html is rstripped
     Doc/build/html/library/idle.html.  It looks better than help.txt
     and will better document Idle as released.  The tkinter html viewer
     that works for this file was written by Rose Roseman.  The now
     unused EditorWindow.HelpDialog class and helt.txt file are
     deprecated.

   - bpo-24199(27): Deprecate unused idlelib.idlever with possible
     removal in 3.6.

   - bpo-24790(28): Remove extraneous code (which also create 2 & 3
     conflicts).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20640

   (2) https://bugs.python.org/issue25507

   (3) https://bugs.python.org/issue25905

   (4) https://bugs.python.org/issue15348

   (5) https://bugs.python.org/issue24455

   (6) https://bugs.python.org/issue24750

   (7) https://bugs.python.org/issue25313

   (8) https://bugs.python.org/issue24782

   (9) https://bugs.python.org/issue22726

   (10) https://bugs.python.org/issue24820

   (11) https://bugs.python.org/issue25224

   (12) https://bugs.python.org/issue24820

   (13) https://bugs.python.org/issue24972

   (14) https://bugs.python.org/issue24570

   (15) https://bugs.python.org/issue24988

   (16) https://bugs.python.org/issue24801

   (17) https://bugs.python.org/issue25173

   (18) https://bugs.python.org/issue25198

   (19) https://bugs.python.org/issue25225

   (20) https://bugs.python.org/issue21995

   (21) https://bugs.python.org/issue22820

   (22) https://bugs.python.org/issue25224

   (23) https://bugs.python.org/issue25219

   (24) https://bugs.python.org/issue24861

   (25) https://bugs.python.org/issue25199

   (26) https://bugs.python.org/issue16893

   (27) https://bugs.python.org/issue24199

   (28) https://bugs.python.org/issue24790


File: python.info,  Node: Documentation<46>,  Next: Tests<47>,  Prev: IDLE<43>,  Up: Python 3 6 0 alpha 1

1.19.66.10 Documentation
........................

   - bpo-26736(1): Used HTTPS for external links in the documentation if
     possible.

   - bpo-6953(2): Rework the Readline module documentation to group
     related functions together, and add more details such as what
     underlying Readline functions and variables are accessed.

   - bpo-23606(3): Adds note to ctypes documentation regarding
     cdll.msvcrt.

   - bpo-24952(4): Clarify the default size argument of stack_size() in
     the “threading” and “_thread” modules.  Patch from Mattip.

   - bpo-26014(5): Update 3.x packaging documentation: * “See also”
     links to the new docs are now provided in the legacy pages * links
     to setuptools documentation have been updated

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26736

   (2) https://bugs.python.org/issue6953

   (3) https://bugs.python.org/issue23606

   (4) https://bugs.python.org/issue24952

   (5) https://bugs.python.org/issue26014


File: python.info,  Node: Tests<47>,  Next: Build<50>,  Prev: Documentation<46>,  Up: Python 3 6 0 alpha 1

1.19.66.11 Tests
................

   - bpo-21916(1): Added tests for the turtle module.  Patch by ingrid,
     Gregory Loyse and Jelle Zijlstra.

   - bpo-26295(2): When using “python3 -m test –testdir=TESTDIR”,
     regrtest doesn’t add “test.” prefix to test module names.

   - bpo-26523(3): The multiprocessing thread pool
     (multiprocessing.dummy.Pool) was untested.

   - bpo-26015(4): Added new tests for pickling iterators of mutable
     sequences.

   - bpo-26325(5): Added test.support.check_no_resource_warning() to
     check that no ResourceWarning is emitted.

   - bpo-25940(6): Changed test_ssl to use its internal local server
     more.  This avoids relying on svn.python.org, which recently
     changed root certificate.

   - bpo-25616(7): Tests for OrderedDict are extracted from
     test_collections into separate file test_ordered_dict.

   - bpo-25449(8): Added tests for OrderedDict subclasses.

   - bpo-25188(9): Add -P/–pgo to test.regrtest to suppress error output
     when running the test suite for the purposes of a PGO build.
     Initial patch by Alecsandru Patrascu.

   - bpo-22806(10): Add ‘python -m test --list-tests’ command to list
     tests.

   - bpo-18174(11): ‘python -m test --huntrleaks ...’ now also checks
     for leak of file descriptors.  Patch written by Richard Oudkerk.

   - bpo-25260(12): Fix ‘python -m test --coverage’ on Windows.  Remove
     the list of ignored directories.

   - ‘PCbuild\rt.bat’ now accepts an unlimited number of arguments to
     pass along to regrtest.py.  Previously there was a limit of 9.

   - bpo-26583(13): Skip test_timestamp_overflow in test_import if
     bytecode files cannot be written.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21916

   (2) https://bugs.python.org/issue26295

   (3) https://bugs.python.org/issue26523

   (4) https://bugs.python.org/issue26015

   (5) https://bugs.python.org/issue26325

   (6) https://bugs.python.org/issue25940

   (7) https://bugs.python.org/issue25616

   (8) https://bugs.python.org/issue25449

   (9) https://bugs.python.org/issue25188

   (10) https://bugs.python.org/issue22806

   (11) https://bugs.python.org/issue18174

   (12) https://bugs.python.org/issue25260

   (13) https://bugs.python.org/issue26583


File: python.info,  Node: Build<50>,  Next: Windows<46>,  Prev: Tests<47>,  Up: Python 3 6 0 alpha 1

1.19.66.12 Build
................

   - bpo-21277(1): Don’t try to link _ctypes with a ffi_convenience
     library.

   - bpo-26884(2): Fix linking extension modules for cross builds.
     Patch by Xavier de Gaye.

   - bpo-26932(3): Fixed support of RTLD_* constants defined as enum
     values, not via macros (in particular on Android).  Patch by Chi
     Hsuan Yen.

   - bpo-22359(4): Disable the rules for running _freeze_importlib and
     pgen when cross-compiling.  The output of these programs is
     normally saved with the source code anyway, and is still
     regenerated when doing a native build.  Patch by Xavier de Gaye.

   - bpo-21668(5): Link audioop, _datetime, _ctypes_test modules to
     libm, except on Mac OS X. Patch written by Chi Hsuan Yen.

   - bpo-25702(6): A –with-lto configure option has been added that will
     enable link time optimizations at build time during a make
     profile-opt.  Some compilers and toolchains are known to not
     produce stable code when using LTO, be sure to test things
     thoroughly before relying on it.  It can provide a few % speed up
     over profile-opt alone.

   - bpo-26624(7): Adds validation of ucrtbase[d].dll version with
     warning for old versions.

   - bpo-17603(8): Avoid error about nonexistent fileblocks.o file by
     using a lower-level check for st_blocks in struct stat.

   - bpo-26079(9): Fixing the build output folder for tix-8.4.3.6.
     Patch by Bjoern Thiel.

   - bpo-26465(10): Update Windows builds to use OpenSSL 1.0.2g.

   - bpo-25348(11): Added ‘--pgo’ and ‘--pgo-job’ arguments to
     ‘PCbuild\build.bat’ for building with Profile-Guided Optimization.
     The old ‘PCbuild\build_pgo.bat’ script is removed.

   - bpo-25827(12): Add support for building with ICC to ‘configure’,
     including a new ‘--with-icc’ flag.

   - bpo-25696(13): Fix installation of Python on UNIX with make -j9.

   - bpo-24986(14): It is now possible to build Python on Windows
     without errors when external libraries are not available.

   - bpo-24421(15): Compile Modules/_math.c once, before building
     extensions.  Previously it could fail to compile properly if the
     math and cmath builds were concurrent.

   - bpo-26465(16): Update OS X 10.5+ 32-bit-only installer to build and
     link with OpenSSL 1.0.2g.

   - bpo-26268(17): Update Windows builds to use OpenSSL 1.0.2f.

   - bpo-25136(18): Support Apple Xcode 7’s new textual SDK stub
     libraries.

   - bpo-24324(19): Do not enable unreachable code warnings when using
     gcc as the option does not work correctly in older versions of gcc
     and has been silently removed as of gcc-4.5.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21277

   (2) https://bugs.python.org/issue26884

   (3) https://bugs.python.org/issue26932

   (4) https://bugs.python.org/issue22359

   (5) https://bugs.python.org/issue21668

   (6) https://bugs.python.org/issue25702

   (7) https://bugs.python.org/issue26624

   (8) https://bugs.python.org/issue17603

   (9) https://bugs.python.org/issue26079

   (10) https://bugs.python.org/issue26465

   (11) https://bugs.python.org/issue25348

   (12) https://bugs.python.org/issue25827

   (13) https://bugs.python.org/issue25696

   (14) https://bugs.python.org/issue24986

   (15) https://bugs.python.org/issue24421

   (16) https://bugs.python.org/issue26465

   (17) https://bugs.python.org/issue26268

   (18) https://bugs.python.org/issue25136

   (19) https://bugs.python.org/issue24324


File: python.info,  Node: Windows<46>,  Next: Tools/Demos<28>,  Prev: Build<50>,  Up: Python 3 6 0 alpha 1

1.19.66.13 Windows
..................

   - bpo-27053(1): Updates make_zip.py to correctly generate library ZIP
     file.

   - bpo-26268(2): Update the prepare_ssl.py script to handle OpenSSL
     releases that don’t include the contents of the include directory
     (that is, 1.0.2e and later).

   - bpo-26071(3): bdist_wininst created binaries fail to start and find
     32bit Python

   - bpo-26073(4): Update the list of magic numbers in launcher

   - bpo-26065(5): Excludes venv from library when generating embeddable
     distro.

   - bpo-25022(6): Removed very outdated PC/example_nt/ directory.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27053

   (2) https://bugs.python.org/issue26268

   (3) https://bugs.python.org/issue26071

   (4) https://bugs.python.org/issue26073

   (5) https://bugs.python.org/issue26065

   (6) https://bugs.python.org/issue25022


File: python.info,  Node: Tools/Demos<28>,  Next: C API<38>,  Prev: Windows<46>,  Up: Python 3 6 0 alpha 1

1.19.66.14 Tools/Demos
......................

   - bpo-26799(1): Fix python-gdb.py: don’t get C types once when the
     Python code is loaded, but get C types on demand.  The C types can
     change if python-gdb.py is loaded before the Python executable.
     Patch written by Thomas Ilsche.

   - bpo-26271(2): Fix the Freeze tool to properly use flags passed
     through configure.  Patch by Daniel Shaulov.

   - bpo-26489(3): Add dictionary unpacking support to
     Tools/parser/unparse.py.  Patch by Guo Ci Teo.

   - bpo-26316(4): Fix variable name typo in Argument Clinic.

   - bpo-25440(5): Fix output of python-config –extension-suffix.

   - bpo-25154(6): The pyvenv script has been deprecated in favour of
     ‘python3 -m venv’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26799

   (2) https://bugs.python.org/issue26271

   (3) https://bugs.python.org/issue26489

   (4) https://bugs.python.org/issue26316

   (5) https://bugs.python.org/issue25440

   (6) https://bugs.python.org/issue25154


File: python.info,  Node: C API<38>,  Prev: Tools/Demos<28>,  Up: Python 3 6 0 alpha 1

1.19.66.15 C API
................

   - bpo-26312(1): SystemError is now raised in all programming bugs
     with using PyArg_ParseTupleAndKeywords().  RuntimeError did raised
     before in some programming bugs.

   - bpo-26198(2): ValueError is now raised instead of TypeError on
     buffer overflow in parsing “es#” and “et#” format units.
     SystemError is now raised instead of TypeError on programmatical
     error in parsing format string.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26312

   (2) https://bugs.python.org/issue26198


File: python.info,  Node: Python 3 5 5 final,  Next: Python 3 5 5 release candidate 1,  Prev: Python 3 6 0 alpha 1,  Up: Changelog

1.19.67 Python 3.5.5 final
--------------------------

`Release date: 2018-02-04'

There were no new changes in version 3.5.5.


File: python.info,  Node: Python 3 5 5 release candidate 1,  Next: Python 3 5 4 final,  Prev: Python 3 5 5 final,  Up: Changelog

1.19.68 Python 3.5.5 release candidate 1
----------------------------------------

`Release date: 2018-01-23'

* Menu:

* Security: Security<33>.
* Core and Builtins: Core and Builtins<56>.
* Library: Library<66>.


File: python.info,  Node: Security<33>,  Next: Core and Builtins<56>,  Up: Python 3 5 5 release candidate 1

1.19.68.1 Security
..................

   - bpo-32551(1): The ‘sys.path[0]’ initialization change for
     bpo-29139(2) caused a regression by revealing an inconsistency in
     how sys.path is initialized when executing ‘__main__’ from a
     zipfile, directory, or other import location.  This is considered a
     potential security issue, as it may lead to privileged processes
     unexpectedly loading code from user controlled directories in
     situations where that was not previously the case.  The interpreter
     now consistently avoids ever adding the import location’s parent
     directory to ‘sys.path’, and ensures no other ‘sys.path’ entries
     are inadvertently modified when inserting the import location named
     on the command line.  (Originally reported as bpo-29723(3) against
     Python 3.6rc1, but it was missed at the time that the then upcoming
     Python 3.5.4 release would also be affected)

   - bpo-30657(4): Fixed possible integer overflow in
     PyBytes_DecodeEscape, CVE-2017-1000158.  Original patch by Jay
     Bosamiya; rebased to Python 3 by Miro Hrončok.

   - bpo-30947(5): Upgrade libexpat embedded copy from version 2.2.1 to
     2.2.3 to get security fixes.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32551

   (2) https://bugs.python.org/issue29139

   (3) https://bugs.python.org/issue29723

   (4) https://bugs.python.org/issue30657

   (5) https://bugs.python.org/issue30947


File: python.info,  Node: Core and Builtins<56>,  Next: Library<66>,  Prev: Security<33>,  Up: Python 3 5 5 release candidate 1

1.19.68.2 Core and Builtins
...........................

   - bpo-31095(1): Fix potential crash during GC caused by ‘tp_dealloc’
     which doesn’t call ‘PyObject_GC_UnTrack()’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue31095


File: python.info,  Node: Library<66>,  Prev: Core and Builtins<56>,  Up: Python 3 5 5 release candidate 1

1.19.68.3 Library
.................

   - bpo-32072(1): Fixed issues with binary plists: Fixed saving
     bytearrays.  Identical objects will be saved only once.  Equal
     references will be load as identical objects.  Added support for
     saving and loading recursive data structures.

   - bpo-31170(2): expat: Update libexpat from 2.2.3 to 2.2.4.  Fix
     copying of partial characters for UTF-8 input (libexpat bug 115):
     ‘https://github.com/libexpat/libexpat/issues/115’

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue32072

   (2) https://bugs.python.org/issue31170


File: python.info,  Node: Python 3 5 4 final,  Next: Python 3 5 4 release candidate 1,  Prev: Python 3 5 5 release candidate 1,  Up: Changelog

1.19.69 Python 3.5.4 final
--------------------------

`Release date: 2017-08-07'

* Menu:

* Library: Library<67>.


File: python.info,  Node: Library<67>,  Up: Python 3 5 4 final

1.19.69.1 Library
.................

   - bpo-30119(1): ftplib.FTP.putline() now throws ValueError on
     commands that contains CR or LF. Patch by Dong-hee Na.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30119


File: python.info,  Node: Python 3 5 4 release candidate 1,  Next: Python 3 5 3 final,  Prev: Python 3 5 4 final,  Up: Changelog

1.19.70 Python 3.5.4 release candidate 1
----------------------------------------

`Release date: 2017-07-23'

* Menu:

* Security: Security<34>.
* Core and Builtins: Core and Builtins<57>.
* Library: Library<68>.
* Documentation: Documentation<47>.
* Tests: Tests<48>.
* Build: Build<51>.
* Windows: Windows<47>.
* C API: C API<39>.


File: python.info,  Node: Security<34>,  Next: Core and Builtins<57>,  Up: Python 3 5 4 release candidate 1

1.19.70.1 Security
..................

   - bpo-30730(1): Prevent environment variables injection in subprocess
     on Windows.  Prevent passing other environment variables and
     command arguments.

   - bpo-30694(2): Upgrade expat copy from 2.2.0 to 2.2.1 to get fixes
     of multiple security vulnerabilities including: CVE-2017-9233
     (External entity infinite loop DoS), CVE-2016-9063 (Integer
     overflow, re-fix), CVE-2016-0718 (Fix regression bugs from 2.2.0’s
     fix to CVE-2016-0718) and CVE-2012-0876 (Counter hash flooding with
     SipHash).  Note: the CVE-2016-5300 (Use os-specific entropy sources
     like getrandom) doesn’t impact Python, since Python already gets
     entropy from the OS to set the expat secret using
     ‘XML_SetHashSalt()’.

   - bpo-30500(3): Fix urllib.parse.splithost() to correctly parse
     fragments.  For example, ‘splithost('//127.0.0.1#@evil.com/')’ now
     correctly returns the ‘127.0.0.1’ host, instead of treating
     ‘@evil.com’ as the host in an authentication (‘login@host’).

   - bpo-29591(4): Update expat copy from 2.1.1 to 2.2.0 to get fixes of
     CVE-2016-0718 and CVE-2016-4472.  See
     ‘https://sourceforge.net/p/expat/bugs/537/’ for more information.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30730

   (2) https://bugs.python.org/issue30694

   (3) https://bugs.python.org/issue30500

   (4) https://bugs.python.org/issue29591


File: python.info,  Node: Core and Builtins<57>,  Next: Library<68>,  Prev: Security<34>,  Up: Python 3 5 4 release candidate 1

1.19.70.2 Core and Builtins
...........................

   - bpo-30876(1): Relative import from unloaded package now reimports
     the package instead of failing with SystemError.  Relative import
     from non-package now fails with ImportError rather than
     SystemError.

   - bpo-30765(2): Avoid blocking in pthread_mutex_lock() when
     PyThread_acquire_lock() is asked not to block.

   - bpo-27945(3): Fixed various segfaults with dict when input
     collections are mutated during searching, inserting or comparing.
     Based on patches by Duane Griffin and Tim Mitchell.

   - bpo-25794(4): Fixed type.__setattr__() and type.__delattr__() for
     non-interned attribute names.  Based on patch by Eryk Sun.

   - bpo-29935(5): Fixed error messages in the index() method of tuple,
     list and deque when pass indices of wrong type.

   - bpo-28876(6): ‘bool(range)’ works even if ‘len(range)’ raises *note
     OverflowError: a41.

   - bpo-29600(7): Fix wrapping coroutine return values in
     StopIteration.

   - bpo-29537(8): Restore runtime compatibility with bytecode files
     generated by CPython 3.5.0 to 3.5.2, and adjust the eval loop to
     avoid the problems that could be caused by the malformed variant of
     the BUILD_MAP_UNPACK_WITH_CALL opcode that they may contain.  Patch
     by Petr Viktorin, Serhiy Storchaka, and Nick Coghlan.

   - bpo-28598(9): Support __rmod__ for subclasses of str being called
     before str.__mod__.  Patch by Martijn Pieters.

   - bpo-29602(10): Fix incorrect handling of signed zeros in complex
     constructor for complex subclasses and for inputs having a
     __complex__ method.  Patch by Serhiy Storchaka.

   - bpo-29347(11): Fixed possibly dereferencing undefined pointers when
     creating weakref objects.

   - bpo-29438(12): Fixed use-after-free problem in key sharing dict.

   - bpo-29319(13): Prevent RunMainFromImporter overwriting sys.path[0].

   - bpo-29337(14): Fixed possible BytesWarning when compare the code
     objects.  Warnings could be emitted at compile time.

   - bpo-29478(15): If max_line_length=None is specified while using the
     Compat32 policy, it is no longer ignored.  Patch by Mircea Cosbuc.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30876

   (2) https://bugs.python.org/issue30765

   (3) https://bugs.python.org/issue27945

   (4) https://bugs.python.org/issue25794

   (5) https://bugs.python.org/issue29935

   (6) https://bugs.python.org/issue28876

   (7) https://bugs.python.org/issue29600

   (8) https://bugs.python.org/issue29537

   (9) https://bugs.python.org/issue28598

   (10) https://bugs.python.org/issue29602

   (11) https://bugs.python.org/issue29347

   (12) https://bugs.python.org/issue29438

   (13) https://bugs.python.org/issue29319

   (14) https://bugs.python.org/issue29337

   (15) https://bugs.python.org/issue29478


File: python.info,  Node: Library<68>,  Next: Documentation<47>,  Prev: Core and Builtins<57>,  Up: Python 3 5 4 release candidate 1

1.19.70.3 Library
.................

   - bpo-29403(1): Fix ‘unittest.mock’’s autospec to not fail on
     method-bound builtin functions.  Patch by Aaron Gallagher.

   - bpo-30961(2): Fix decrementing a borrowed reference in tracemalloc.

   - bpo-30886(3): Fix multiprocessing.Queue.join_thread(): it now waits
     until the thread completes, even if the thread was started by the
     same process which created the queue.

   - bpo-29854(4): Fix segfault in readline when using readline’s
     history-size option.  Patch by Nir Soffer.

   - bpo-30807(5): signal.setitimer() may disable the timer when passed
     a tiny value.  Tiny values (such as 1e-6) are valid non-zero values
     for setitimer(), which is specified as taking
     microsecond-resolution intervals.  However, on some platform, our
     conversion routine could convert 1e-6 into a zero interval,
     therefore disabling the timer instead of (re-)scheduling it.

   - bpo-30441(6): Fix bug when modifying os.environ while iterating
     over it

   - bpo-30532(7): Fix email header value parser dropping folding white
     space in certain cases.

   - bpo-29169(8): Update zlib to 1.2.11.

   - bpo-30879(9): os.listdir() and os.scandir() now emit bytes names
     when called with bytes-like argument.

   - bpo-30746(10): Prohibited the ‘=’ character in environment variable
     names in ‘os.putenv()’ and ‘os.spawn*()’.

   - bpo-29755(11): Fixed the lgettext() family of functions in the
     gettext module.  They now always return bytes.

   - bpo-30645(12): Fix path calculation in imp.load_package(), fixing
     it for cases when a package is only shipped with bytecodes.  Patch
     by Alexandru Ardelean.

   - bpo-23890(13): unittest.TestCase.assertRaises() now manually breaks
     a reference cycle to not keep objects alive longer than expected.

   - bpo-30149(14): inspect.signature() now supports callables with
     variable-argument parameters wrapped with partialmethod.  Patch by
     Dong-hee Na.

   - bpo-29931(15): Fixed comparison check for ipaddress.ip_interface
     objects.  Patch by Sanjay Sundaresan.

   - bpo-24484(16): Avoid race condition in multiprocessing cleanup.

   - bpo-28994(17): The traceback no longer displayed for SystemExit
     raised in a callback registered by atexit.

   - bpo-30508(18): Don’t log exceptions if Task/Future “cancel()”
     method was called.

   - bpo-28556(19): Updates to typing module: Add generic
     AsyncContextManager, add support for ContextManager on all
     versions.  Original PRs by Jelle Zijlstra and Ivan Levkivskyi

   - bpo-29870(20): Fix ssl sockets leaks when connection is aborted in
     asyncio/ssl implementation.  Patch by Michaël Sghaïer.

   - bpo-29743(21): Closing transport during handshake process leaks
     open socket.  Patch by Nikolay Kim

   - bpo-27585(22): Fix waiter cancellation in asyncio.Lock.  Patch by
     Mathieu Sornay.

   - bpo-30418(23): On Windows, subprocess.Popen.communicate() now also
     ignore EINVAL on stdin.write() if the child process is still
     running but closed the pipe.

   - bpo-30378(24): Fix the problem that logging.handlers.SysLogHandler
     cannot handle IPv6 addresses.

   - bpo-29960(25): Preserve generator state when
     _random.Random.setstate() raises an exception.  Patch by Bryan
     Olson.

   - bpo-30414(26): multiprocessing.Queue._feed background running
     thread do not break from main loop on exception.

   - bpo-30003(27): Fix handling escape characters in HZ codec.  Based
     on patch by Ma Lin.

   - bpo-30301(28): Fix AttributeError when using SimpleQueue.empty()
     under `spawn' and `forkserver' start methods.

   - bpo-30329(29): imaplib and poplib now catch the Windows socket
     WSAEINVAL error (code 10022) on shutdown(SHUT_RDWR): An invalid
     operation was attempted.  This error occurs sometimes on SSL
     connections.

   - bpo-30375(30): Warnings emitted when compile a regular expression
     now always point to the line in the user code.  Previously they
     could point into inners of the re module if emitted from inside of
     groups or conditionals.

   - bpo-30048(31): Fixed ‘Task.cancel()’ can be ignored when the task
     is running coroutine and the coroutine returned without any more
     ‘await’.

   - bpo-29990(32): Fix range checking in GB18030 decoder.  Original
     patch by Ma Lin.

   - bpo-26293(33): Change resulted because of zipfile breakage.  (See
     also: bpo-29094(34))

   - bpo-30243(35): Removed the __init__ methods of _json’s scanner and
     encoder.  Misusing them could cause memory leaks or crashes.  Now
     scanner and encoder objects are completely initialized in the
     __new__ methods.

   - bpo-30185(36): Avoid KeyboardInterrupt tracebacks in forkserver
     helper process when Ctrl-C is received.

   - bpo-28556(37): Various updates to typing module: add
     typing.NoReturn type, use WrapperDescriptorType, minor bug-fixes.
     Original PRs by Jim Fasarakis-Hilliard and Ivan Levkivskyi.

   - bpo-30205(38): Fix getsockname() for unbound AF_UNIX sockets on
     Linux.

   - bpo-30070(39): Fixed leaks and crashes in errors handling in the
     parser module.

   - bpo-30061(40): Fixed crashes in IOBase methods __next__() and
     readlines() when readline() or __next__() respectively return
     non-sizeable object.  Fixed possible other errors caused by not
     checking results of PyObject_Size(), PySequence_Size(), or
     PyMapping_Size().

   - bpo-30068(41): _io._IOBase.readlines will check if it’s closed
     first when hint is present.

   - bpo-29694(42): Fixed race condition in pathlib mkdir with flags
     parents=True.  Patch by Armin Rigo.

   - bpo-29692(43): Fixed arbitrary unchaining of RuntimeError
     exceptions in contextlib.contextmanager.  Patch by Siddharth
     Velankar.

   - bpo-29998(44): Pickling and copying ImportError now preserves name
     and path attributes.

   - bpo-29942(45): Fix a crash in itertools.chain.from_iterable when
     encountering long runs of empty iterables.

   - bpo-27863(46): Fixed multiple crashes in ElementTree caused by race
     conditions and wrong types.

   - bpo-28699(47): Fixed a bug in pools in multiprocessing.pool that
     raising an exception at the very first of an iterable may swallow
     the exception or make the program hang.  Patch by Davin Potts and
     Xiang Zhang.

   - bpo-25803(48): Avoid incorrect errors raised by
     Path.mkdir(exist_ok=True) when the OS gives priority to errors such
     as EACCES over EEXIST.

   - bpo-29861(49): Release references to tasks, their arguments and
     their results as soon as they are finished in multiprocessing.Pool.

   - bpo-29884(50): faulthandler: Restore the old sigaltstack during
     teardown.  Patch by Christophe Zeitouny.

   - bpo-25455(51): Fixed crashes in repr of recursive buffered
     file-like objects.

   - bpo-29800(52): Fix crashes in partial.__repr__ if the keys of
     partial.keywords are not strings.  Patch by Michael Seifert.

   - bpo-29742(53): get_extra_info() raises exception if get called on
     closed ssl transport.  Patch by Nikolay Kim.

   - bpo-8256(54): Fixed possible failing or crashing input() if
     attributes “encoding” or “errors” of sys.stdin or sys.stdout are
     not set or are not strings.

   - bpo-28298(55): Fix a bug that prevented array ‘Q’, ‘L’ and ‘I’ from
     accepting big intables (objects that have __int__) as elements.
     Patch by Oren Milman.

   - bpo-29615(56): SimpleXMLRPCDispatcher no longer chains KeyError (or
     any other exception) to exception(s) raised in the dispatched
     methods.  Patch by Petr Motejlek.

   - bpo-29704(57): asyncio.subprocess.SubprocessStreamProtocol no
     longer closes before all pipes are closed.

   - bpo-29703(58): Fix asyncio to support instantiation of new event
     loops in child processes.

   - bpo-29376(59): Fix assertion error in
     threading._DummyThread.is_alive().

   - bpo-29110(60): Fix file object leak in aifc.open() when file is
     given as a filesystem path and is not in valid AIFF format.  Patch
     by Anthony Zhang.

   - bpo-28961(61): Fix unittest.mock._Call helper: don’t ignore the
     name parameter anymore.  Patch written by Jiajun Huang.

   - bpo-29532(62): Altering a kwarg dictionary passed to
     functools.partial() no longer affects a partial object after
     creation.

   - bpo-28556(63): Various updates to typing module: typing.Counter,
     typing.ChainMap, improved ABC caching, etc.  Original PRs by Jelle
     Zijlstra, Ivan Levkivskyi, Manuel Krebber, and Łukasz Langa.

   - bpo-29100(64): Fix datetime.fromtimestamp() regression introduced
     in Python 3.6.0: check minimum and maximum years.

   - bpo-29519(65): Fix weakref spewing exceptions during interpreter
     shutdown when used with a rare combination of multiprocessing and
     custom codecs.

   - bpo-29416(66): Prevent infinite loop in pathlib.Path.mkdir

   - bpo-29444(67): Fixed out-of-bounds buffer access in the group()
     method of the match object.  Based on patch by WGH.

   - bpo-29335(68): Fix subprocess.Popen.wait() when the child process
     has exited to a stopped instead of terminated state (ex: when under
     ptrace).

   - bpo-29290(69): Fix a regression in argparse that help messages
     would wrap at non-breaking spaces.

   - bpo-28735(70): Fixed the comparison of mock.MagickMock with
     mock.ANY.

   - bpo-29011(71): Fix an important omission by adding Deque to the
     typing module.

   - bpo-29219(72): Fixed infinite recursion in the repr of
     uninitialized ctypes.CDLL instances.

   - bpo-28969(73): Fixed race condition in C implementation of
     functools.lru_cache.  KeyError could be raised when cached function
     with full cache was simultaneously called from different threads
     with the same uncached arguments.

   - bpo-29142(74): In urllib.request, suffixes in no_proxy environment
     variable with leading dots could match related hostnames again
     (e.g.  .b.c matches a.b.c).  Patch by Milan Oberkirch.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29403

   (2) https://bugs.python.org/issue30961

   (3) https://bugs.python.org/issue30886

   (4) https://bugs.python.org/issue29854

   (5) https://bugs.python.org/issue30807

   (6) https://bugs.python.org/issue30441

   (7) https://bugs.python.org/issue30532

   (8) https://bugs.python.org/issue29169

   (9) https://bugs.python.org/issue30879

   (10) https://bugs.python.org/issue30746

   (11) https://bugs.python.org/issue29755

   (12) https://bugs.python.org/issue30645

   (13) https://bugs.python.org/issue23890

   (14) https://bugs.python.org/issue30149

   (15) https://bugs.python.org/issue29931

   (16) https://bugs.python.org/issue24484

   (17) https://bugs.python.org/issue28994

   (18) https://bugs.python.org/issue30508

   (19) https://bugs.python.org/issue28556

   (20) https://bugs.python.org/issue29870

   (21) https://bugs.python.org/issue29743

   (22) https://bugs.python.org/issue27585

   (23) https://bugs.python.org/issue30418

   (24) https://bugs.python.org/issue30378

   (25) https://bugs.python.org/issue29960

   (26) https://bugs.python.org/issue30414

   (27) https://bugs.python.org/issue30003

   (28) https://bugs.python.org/issue30301

   (29) https://bugs.python.org/issue30329

   (30) https://bugs.python.org/issue30375

   (31) https://bugs.python.org/issue30048

   (32) https://bugs.python.org/issue29990

   (33) https://bugs.python.org/issue26293

   (34) https://bugs.python.org/issue29094

   (35) https://bugs.python.org/issue30243

   (36) https://bugs.python.org/issue30185

   (37) https://bugs.python.org/issue28556

   (38) https://bugs.python.org/issue30205

   (39) https://bugs.python.org/issue30070

   (40) https://bugs.python.org/issue30061

   (41) https://bugs.python.org/issue30068

   (42) https://bugs.python.org/issue29694

   (43) https://bugs.python.org/issue29692

   (44) https://bugs.python.org/issue29998

   (45) https://bugs.python.org/issue29942

   (46) https://bugs.python.org/issue27863

   (47) https://bugs.python.org/issue28699

   (48) https://bugs.python.org/issue25803

   (49) https://bugs.python.org/issue29861

   (50) https://bugs.python.org/issue29884

   (51) https://bugs.python.org/issue25455

   (52) https://bugs.python.org/issue29800

   (53) https://bugs.python.org/issue29742

   (54) https://bugs.python.org/issue8256

   (55) https://bugs.python.org/issue28298

   (56) https://bugs.python.org/issue29615

   (57) https://bugs.python.org/issue29704

   (58) https://bugs.python.org/issue29703

   (59) https://bugs.python.org/issue29376

   (60) https://bugs.python.org/issue29110

   (61) https://bugs.python.org/issue28961

   (62) https://bugs.python.org/issue29532

   (63) https://bugs.python.org/issue28556

   (64) https://bugs.python.org/issue29100

   (65) https://bugs.python.org/issue29519

   (66) https://bugs.python.org/issue29416

   (67) https://bugs.python.org/issue29444

   (68) https://bugs.python.org/issue29335

   (69) https://bugs.python.org/issue29290

   (70) https://bugs.python.org/issue28735

   (71) https://bugs.python.org/issue29011

   (72) https://bugs.python.org/issue29219

   (73) https://bugs.python.org/issue28969

   (74) https://bugs.python.org/issue29142


File: python.info,  Node: Documentation<47>,  Next: Tests<48>,  Prev: Library<68>,  Up: Python 3 5 4 release candidate 1

1.19.70.4 Documentation
.......................

   - bpo-30176(1): Add missing attribute related constants in curses
     documentation.

   - bpo-26985(2): Add missing info of code object in inspect
     documentation.

   - bpo-28929(3): Link the documentation to its source file on GitHub.

   - bpo-25008(4): Document smtpd.py as effectively deprecated and add a
     pointer to aiosmtpd, a third-party asyncio-based replacement.

   - bpo-26355(5): Add canonical header link on each page to
     corresponding major version of the documentation.  Patch by
     Matthias Bussonnier.

   - bpo-29349(6): Fix Python 2 syntax in code for building the
     documentation.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30176

   (2) https://bugs.python.org/issue26985

   (3) https://bugs.python.org/issue28929

   (4) https://bugs.python.org/issue25008

   (5) https://bugs.python.org/issue26355

   (6) https://bugs.python.org/issue29349


File: python.info,  Node: Tests<48>,  Next: Build<51>,  Prev: Documentation<47>,  Up: Python 3 5 4 release candidate 1

1.19.70.5 Tests
...............

   - bpo-30822(1): Fix regrtest command line parser to allow passing -u
     extralargefile to run test_zipfile64.

   - bpo-30383(2): regrtest: Enhance regrtest and backport features from
     the master branch.  Add options: –coverage, –testdir, –list-tests
     (list test files, don’t run them), –list-cases (list test
     identifiers, don’t run them, bpo-30523(3)), –matchfile (load a list
     of test filters from a text file, bpo-30540(4)), –slowest (alias to
     –slow).  Enhance output: add timestamp, test result, currently
     running tests, “Tests result: xxx” summary with total duration,
     etc.  Fix reference leak hunting in regrtest, –huntrleaks: regrtest
     now warms up caches, create explicitly all internal singletons
     which are created on demand to prevent false positives when
     checking for reference leaks.  (bpo-30675(5)).

   - bpo-30357(6): test_thread: setUp() now uses
     support.threading_setup() and support.threading_cleanup() to wait
     until threads complete to avoid random side effects on following
     tests.  Initial patch written by Grzegorz Grzywacz.

   - bpo-28087(7): Skip test_asyncore and test_eintr poll failures on
     macOS. Skip some tests of select.poll when running on macOS due to
     unresolved issues with the underlying system poll function on some
     macOS versions.

   - bpo-30197(8): Enhanced functions swap_attr() and swap_item() in the
     test.support module.  They now work when delete replaced attribute
     or item inside the with statement.  The old value of the attribute
     or item (or None if it doesn’t exist) now will be assigned to the
     target of the “as” clause, if there is one.

   - bpo-29571(9): to match the behaviour of the ‘re.LOCALE’ flag,
     test_re.test_locale_flag now uses
     ‘locale.getpreferredencoding(False)’ to determine the candidate
     encoding for the test regex (allowing it to correctly skip the test
     when the default locale encoding is a multi-byte encoding)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30822

   (2) https://bugs.python.org/issue30383

   (3) https://bugs.python.org/issue30523

   (4) https://bugs.python.org/issue30540

   (5) https://bugs.python.org/issue30675

   (6) https://bugs.python.org/issue30357

   (7) https://bugs.python.org/issue28087

   (8) https://bugs.python.org/issue30197

   (9) https://bugs.python.org/issue29571


File: python.info,  Node: Build<51>,  Next: Windows<47>,  Prev: Tests<48>,  Up: Python 3 5 4 release candidate 1

1.19.70.6 Build
...............

   - bpo-29243(1): Prevent unnecessary rebuilding of Python during ‘make
     test’, ‘make install’ and some other make targets when configured
     with ‘--enable-optimizations’.

   - bpo-23404(2): Don’t regenerate generated files based on file
     modification time anymore: the action is now explicit.  Replace
     ‘make touch’ with ‘make regen-all’.

   - bpo-29643(3): Fix ‘--enable-optimization’ didn’t work.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29243

   (2) https://bugs.python.org/issue23404

   (3) https://bugs.python.org/issue29643


File: python.info,  Node: Windows<47>,  Next: C API<39>,  Prev: Build<51>,  Up: Python 3 5 4 release candidate 1

1.19.70.7 Windows
.................

   - bpo-30687(1): Locate msbuild.exe on Windows when building rather
     than vcvarsall.bat

   - bpo-29392(2): Prevent crash when passing invalid arguments into
     msvcrt module.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue30687

   (2) https://bugs.python.org/issue29392


File: python.info,  Node: C API<39>,  Prev: Windows<47>,  Up: Python 3 5 4 release candidate 1

1.19.70.8 C API
...............

   - bpo-27867(1): Function PySlice_GetIndicesEx() is replaced with a
     macro if Py_LIMITED_API is set to the value between 0x03050400 and
     0x03060000 (not including) or 0x03060100 or higher.

   - bpo-29083(2): Fixed the declaration of some public API functions.
     PyArg_VaParse() and PyArg_VaParseTupleAndKeywords() were not
     available in limited API. PyArg_ValidateKeywordArguments(),
     PyArg_UnpackTuple() and Py_BuildValue() were not available in
     limited API of version < 3.3 when PY_SSIZE_T_CLEAN is defined.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27867

   (2) https://bugs.python.org/issue29083


File: python.info,  Node: Python 3 5 3 final,  Next: Python 3 5 3 release candidate 1,  Prev: Python 3 5 4 release candidate 1,  Up: Changelog

1.19.71 Python 3.5.3 final
--------------------------

`Release date: 2017-01-17'

There were no code changes between 3.5.3rc1 and 3.5.3 final.


File: python.info,  Node: Python 3 5 3 release candidate 1,  Next: Python 3 5 2 final,  Prev: Python 3 5 3 final,  Up: Changelog

1.19.72 Python 3.5.3 release candidate 1
----------------------------------------

`Release date: 2017-01-02'

* Menu:

* Core and Builtins: Core and Builtins<58>.
* Library: Library<69>.
* Security: Security<35>.
* Library: Library<70>.
* Security: Security<36>.
* Library: Library<71>.
* IDLE: IDLE<44>.
* C API: C API<40>.
* Documentation: Documentation<48>.
* Tests: Tests<49>.
* Tools/Demos: Tools/Demos<29>.
* Windows: Windows<48>.
* Build: Build<52>.


File: python.info,  Node: Core and Builtins<58>,  Next: Library<69>,  Up: Python 3 5 3 release candidate 1

1.19.72.1 Core and Builtins
...........................

   - bpo-29073(1): bytearray formatting no longer truncates on first
     null byte.

   - bpo-28932(2): Do not include <sys/random.h> if it does not exist.

   - bpo-28147(3): Fix a memory leak in split-table dictionaries:
     setattr() must not convert combined table into split table.

   - bpo-25677(4): Correct the positioning of the syntax error caret for
     indented blocks.  Based on patch by Michael Layzell.

   - bpo-29000(5): Fixed bytes formatting of octals with zero padding in
     alternate form.

   - bpo-28512(6): Fixed setting the offset attribute of SyntaxError by
     PyErr_SyntaxLocationEx() and PyErr_SyntaxLocationObject().

   - bpo-28991(7): functools.lru_cache() was susceptible to an obscure
     reentrancy bug caused by a monkey-patched len() function.

   - bpo-28648(8): Fixed crash in Py_DecodeLocale() in debug build on
     Mac OS X when decode astral characters.  Patch by Xiang Zhang.

   - bpo-19398(9): Extra slash no longer added to sys.path components in
     case of empty compile-time PYTHONPATH components.

   - bpo-28426(10): Fixed potential crash in PyUnicode_AsDecodedObject()
     in debug build.

   - bpo-23782(11): Fixed possible memory leak in _PyTraceback_Add() and
     exception loss in PyTraceBack_Here().

   - bpo-28379(12): Added sanity checks and tests for
     PyUnicode_CopyCharacters().  Patch by Xiang Zhang.

   - bpo-28376(13): The type of long range iterator is now registered as
     Iterator.  Patch by Oren Milman.

   - bpo-28376(14): The constructor of range_iterator now checks that
     step is not 0.  Patch by Oren Milman.

   - bpo-26906(15): Resolving special methods of uninitialized type now
     causes implicit initialization of the type instead of a fail.

   - bpo-18287(16): PyType_Ready() now checks that tp_name is not NULL.
     Original patch by Niklas Koep.

   - bpo-24098(17): Fixed possible crash when AST is changed in process
     of compiling it.

   - bpo-28350(18): String constants with null character no longer
     interned.

   - bpo-26617(19): Fix crash when GC runs during weakref callbacks.

   - bpo-27942(20): String constants now interned recursively in tuples
     and frozensets.

   - bpo-21578(21): Fixed misleading error message when ImportError
     called with invalid keyword args.

   - bpo-28203(22): Fix incorrect type in error message from
     ‘complex(1.0, {2:3})’.  Patch by Soumya Sharma.

   - bpo-27955(23): Fallback on reading /dev/urandom device when the
     getrandom() syscall fails with EPERM, for example when blocked by
     SECCOMP.

   - bpo-28131(24): Fix a regression in zipimport’s compile_source().
     zipimport should use the same optimization level as the
     interpreter.

   - bpo-25221(25): Fix corrupted result from PyLong_FromLong(0) when
     Python is compiled with NSMALLPOSINTS = 0.

   - bpo-25758(26): Prevents zipimport from unnecessarily encoding a
     filename (patch by Eryk Sun)

   - bpo-28189(27): dictitems_contains no longer swallows compare
     errors.  (Patch by Xiang Zhang)

   - bpo-27812(28): Properly clear out a generator’s frame’s
     backreference to the generator to prevent crashes in frame.clear().

   - bpo-27811(29): Fix a crash when a coroutine that has not been
     awaited is finalized with warnings-as-errors enabled.

   - bpo-27587(30): Fix another issue found by PVS-Studio: Null pointer
     check after use of ‘def’ in _PyState_AddModule().  Initial patch by
     Christian Heimes.

   - bpo-26020(31): set literal evaluation order did not match
     documented behaviour.

   - bpo-27782(32): Multi-phase extension module import now correctly
     allows the ‘m_methods’ field to be used to add module level
     functions to instances of non-module types returned from
     ‘Py_create_mod’.  Patch by Xiang Zhang.

   - bpo-27936(33): The round() function accepted a second None argument
     for some types but not for others.  Fixed the inconsistency by
     accepting None for all numeric types.

   - bpo-27487(34): Warn if a submodule argument to “python -m” or
     runpy.run_module() is found in sys.modules after parent packages
     are imported, but before the submodule is executed.

   - bpo-27558(35): Fix a SystemError in the implementation of “raise”
     statement.  In a brand new thread, raise a RuntimeError since there
     is no active exception to reraise.  Patch written by Xiang Zhang.

   - bpo-27419(36): Standard __import__() no longer look up “__import__”
     in globals or builtins for importing submodules or “from import”.
     Fixed handling an error of non-string package name.

   - bpo-27083(37): Respect the PYTHONCASEOK environment variable under
     Windows.

   - bpo-27514(38): Make having too many statically nested blocks a
     SyntaxError instead of SystemError.

   - bpo-27473(39): Fixed possible integer overflow in bytes and
     bytearray concatenations.  Patch by Xiang Zhang.

   - bpo-27507(40): Add integer overflow check in bytearray.extend().
     Patch by Xiang Zhang.

   - bpo-27581(41): Don’t rely on wrapping for overflow check in
     PySequence_Tuple().  Patch by Xiang Zhang.

   - bpo-27443(42): __length_hint__() of bytearray iterators no longer
     return a negative integer for a resized bytearray.

   - bpo-27942(43): Fix memory leak in codeobject.c

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29073

   (2) https://bugs.python.org/issue28932

   (3) https://bugs.python.org/issue28147

   (4) https://bugs.python.org/issue25677

   (5) https://bugs.python.org/issue29000

   (6) https://bugs.python.org/issue28512

   (7) https://bugs.python.org/issue28991

   (8) https://bugs.python.org/issue28648

   (9) https://bugs.python.org/issue19398

   (10) https://bugs.python.org/issue28426

   (11) https://bugs.python.org/issue23782

   (12) https://bugs.python.org/issue28379

   (13) https://bugs.python.org/issue28376

   (14) https://bugs.python.org/issue28376

   (15) https://bugs.python.org/issue26906

   (16) https://bugs.python.org/issue18287

   (17) https://bugs.python.org/issue24098

   (18) https://bugs.python.org/issue28350

   (19) https://bugs.python.org/issue26617

   (20) https://bugs.python.org/issue27942

   (21) https://bugs.python.org/issue21578

   (22) https://bugs.python.org/issue28203

   (23) https://bugs.python.org/issue27955

   (24) https://bugs.python.org/issue28131

   (25) https://bugs.python.org/issue25221

   (26) https://bugs.python.org/issue25758

   (27) https://bugs.python.org/issue28189

   (28) https://bugs.python.org/issue27812

   (29) https://bugs.python.org/issue27811

   (30) https://bugs.python.org/issue27587

   (31) https://bugs.python.org/issue26020

   (32) https://bugs.python.org/issue27782

   (33) https://bugs.python.org/issue27936

   (34) https://bugs.python.org/issue27487

   (35) https://bugs.python.org/issue27558

   (36) https://bugs.python.org/issue27419

   (37) https://bugs.python.org/issue27083

   (38) https://bugs.python.org/issue27514

   (39) https://bugs.python.org/issue27473

   (40) https://bugs.python.org/issue27507

   (41) https://bugs.python.org/issue27581

   (42) https://bugs.python.org/issue27443

   (43) https://bugs.python.org/issue27942


File: python.info,  Node: Library<69>,  Next: Security<35>,  Prev: Core and Builtins<58>,  Up: Python 3 5 3 release candidate 1

1.19.72.2 Library
.................

   - bpo-15812(1): inspect.getframeinfo() now correctly shows the first
     line of a context.  Patch by Sam Breese.

   - bpo-29094(2): Offsets in a ZIP file created with extern file object
     and modes “w” and “x” now are relative to the start of the file.

   - bpo-13051(3): Fixed recursion errors in large or resized
     curses.textpad.Textbox.  Based on patch by Tycho Andersen.

   - bpo-29119(4): Fix weakrefs in the pure python version of
     collections.OrderedDict move_to_end() method.  Contributed by Andra
     Bogildea.

   - bpo-9770(5): curses.ascii predicates now work correctly with
     negative integers.

   - bpo-28427(6): old keys should not remove new values from
     WeakValueDictionary when collecting from another thread.

   - bpo-28923(7): Remove editor artifacts from Tix.py.

   - bpo-28871(8): Fixed a crash when deallocate deep ElementTree.

   - bpo-19542(9): Fix bugs in WeakValueDictionary.setdefault() and
     WeakValueDictionary.pop() when a GC collection happens in another
     thread.

   - bpo-20191(10): Fixed a crash in resource.prlimit() when pass a
     sequence that doesn’t own its elements as limits.

   - bpo-28779(11): multiprocessing.set_forkserver_preload() would crash
     the forkserver process if a preloaded module instantiated some
     multiprocessing objects such as locks.

   - bpo-28847(12): dbm.dumb now supports reading read-only files and no
     longer writes the index file when it is not changed.

   - bpo-25659(13): In ctypes, prevent a crash calling the from_buffer()
     and from_buffer_copy() methods on abstract classes like Array.

   - bpo-28732(14): Fix crash in os.spawnv() with no elements in args

   - bpo-28485(15): Always raise ValueError for negative
     compileall.compile_dir(workers=…) parameter, even when
     multithreading is unavailable.

   - bpo-28387(16): Fixed possible crash in _io.TextIOWrapper
     deallocator when the garbage collector is invoked in other thread.
     Based on patch by Sebastian Cufre.

   - bpo-27517(17): LZMA compressor and decompressor no longer raise
     exceptions if given empty data twice.  Patch by Benjamin Fogle.

   - bpo-28549(18): Fixed segfault in curses’s addch() with ncurses6.

   - bpo-28449(19): tarfile.open() with mode “r” or “r:” now tries to
     open a tar file with compression before trying to open it without
     compression.  Otherwise it had 50% chance failed with
     ignore_zeros=True.

   - bpo-23262(20): The webbrowser module now supports Firefox 36+ and
     derived browsers.  Based on patch by Oleg Broytman.

   - bpo-27939(21): Fixed bugs in tkinter.ttk.LabeledScale and
     tkinter.Scale caused by representing the scale as float value
     internally in Tk.  tkinter.IntVar now works if float value is set
     to underlying Tk variable.

   - bpo-28255(22): calendar.TextCalendar().prmonth() no longer prints a
     space at the start of new line after printing a month’s calendar.
     Patch by Xiang Zhang.

   - bpo-20491(23): The textwrap.TextWrapper class now honors
     non-breaking spaces.  Based on patch by Kaarle Ritvanen.

   - bpo-28353(24): os.fwalk() no longer fails on broken links.

   - bpo-25464(25): Fixed HList.header_exists() in tkinter.tix module by
     addin a workaround to Tix library bug.

   - bpo-28488(26): shutil.make_archive() no longer add entry “./” to
     ZIP archive.

   - bpo-24452(27): Make webbrowser support Chrome on Mac OS X.

   - bpo-20766(28): Fix references leaked by pdb in the handling of
     SIGINT handlers.

   - bpo-26293(29): Fixed writing ZIP files that starts not from the
     start of the file.  Offsets in ZIP file now are relative to the
     start of the archive in conforming to the specification.

   - bpo-28321(30): Fixed writing non-BMP characters with binary format
     in plistlib.

   - bpo-28322(31): Fixed possible crashes when unpickle itertools
     objects from incorrect pickle data.  Based on patch by John Leitch.

   - Fix possible integer overflows and crashes in the mmap module with
     unusual usage patterns.

   - bpo-1703178(32): Fix the ability to pass the –link-objects option
     to the distutils build_ext command.

   - bpo-28253(33): Fixed calendar functions for extreme months: 0001-01
     and 9999-12.  Methods itermonthdays() and itermonthdays2() are
     reimplemented so that they don’t call itermonthdates() which can
     cause datetime.date under/overflow.

   - bpo-28275(34): Fixed possible use after free in the decompress()
     methods of the LZMADecompressor and BZ2Decompressor classes.
     Original patch by John Leitch.

   - bpo-27897(35): Fixed possible crash in
     sqlite3.Connection.create_collation() if pass invalid string-like
     object as a name.  Patch by Xiang Zhang.

   - bpo-18893(36): Fix invalid exception handling in
     Lib/ctypes/macholib/dyld.py.  Patch by Madison May.

   - bpo-27611(37): Fixed support of default root window in the
     tkinter.tix module.

   - bpo-27348(38): In the traceback module, restore the formatting of
     exception messages like “Exception: None”.  This fixes a regression
     introduced in 3.5a2.

   - bpo-25651(39): Allow falsy values to be used for msg parameter of
     subTest().

   - bpo-27932(40): Prevent memory leak in win32_ver().

   - Fix UnboundLocalError in socket._sendfile_use_sendfile.

   - bpo-28075(41): Check for ERROR_ACCESS_DENIED in Windows
     implementation of os.stat().  Patch by Eryk Sun.

   - bpo-25270(42): Prevent codecs.escape_encode() from raising
     SystemError when an empty bytestring is passed.

   - bpo-28181(43): Get antigravity over HTTPS. Patch by Kaartic
     Sivaraam.

   - bpo-25895(44): Enable WebSocket URL schemes in
     urllib.parse.urljoin.  Patch by Gergely Imreh and Markus
     Holtermann.

   - bpo-27599(45): Fixed buffer overrun in binascii.b2a_qp() and
     binascii.a2b_qp().

   - bpo-19003(46): m email.generator now replaces only ‘\r’ and/or ‘\n’
     line endings, per the RFC, instead of all unicode line endings.

   - bpo-28019(47): itertools.count() no longer rounds non-integer step
     in range between 1.0 and 2.0 to 1.

   - bpo-25969(48): Update the lib2to3 grammar to handle the unpacking
     generalizations added in 3.5.

   - bpo-14977(49): mailcap now respects the order of the lines in the
     mailcap files (“first match”), as required by RFC 1542.  Patch by
     Michael Lazar.

   - bpo-24594(50): Validates persist parameter when opening MSI
     database

   - bpo-17582(51): xml.etree.ElementTree nows preserves whitespaces in
     attributes (Patch by Duane Griffin.  Reviewed and approved by
     Stefan Behnel.)

   - bpo-28047(52): Fixed calculation of line length used for the base64
     CTE in the new email policies.

   - bpo-27445(53): Don’t pass str(_charset) to MIMEText.set_payload().
     Patch by Claude Paroz.

   - bpo-22450(54): urllib now includes an ‘Accept: */*’ header among
     the default headers.  This makes the results of REST API requests
     more consistent and predictable especially when proxy servers are
     involved.

   - lib2to3.pgen3.driver.load_grammar() now creates a stable cache file
     between runs given the same Grammar.txt input regardless of the
     hash randomization setting.

   - bpo-27570(55): Avoid zero-length memcpy() etc calls with null
     source pointers in the “ctypes” and “array” modules.

   - bpo-22233(56): Break email header lines `only' on the RFC specified
     CR and LF characters, not on arbitrary unicode line breaks.  This
     also fixes a bug in HTTP header parsing.

   - bpo-27988(57): Fix email iter_attachments incorrect mutation of
     payload list.

   - bpo-27691(58): Fix ssl module’s parsing of GEN_RID subject
     alternative name fields in X.509 certs.

   - bpo-27850(59): Remove 3DES from ssl module’s default cipher list to
     counter measure sweet32 attack (CVE-2016-2183).

   - bpo-27766(60): Add ChaCha20 Poly1305 to ssl module’s default cipher
     list.  (Required OpenSSL 1.1.0 or LibreSSL).

   - bpo-26470(61): Port ssl and hashlib module to OpenSSL 1.1.0.

   - Remove support for passing a file descriptor to os.access.  It
     never worked but previously didn’t raise.

   - bpo-12885(62): Fix error when distutils encounters symlink.

   - bpo-27881(63): Fixed possible bugs when setting
     sqlite3.Connection.isolation_level.  Based on patch by Xiang Zhang.

   - bpo-27861(64): Fixed a crash in sqlite3.Connection.cursor() when a
     factory creates not a cursor.  Patch by Xiang Zhang.

   - bpo-19884(65): Avoid spurious output on OS X with Gnu Readline.

   - bpo-27706(66): Restore deterministic behavior of
     random.Random().seed() for string seeds using seeding version 1.
     Allows sequences of calls to random() to exactly match those
     obtained in Python 2.  Patch by Nofar Schnider.

   - bpo-10513(67): Fix a regression in Connection.commit().  Statements
     should not be reset after a commit.

   - A new version of typing.py from ‘https://github.com/python/typing’:
     Collection (only for 3.6) (bpo-27598(68)).  Add FrozenSet to
     __all__ (upstream #261).  Fix crash in _get_type_vars() (upstream
     #259).  Remove the dict constraint in ForwardRef._eval_type
     (upstream #252).

   - bpo-27539(69): Fix unnormalised ‘Fraction.__pow__’ result in the
     case of negative exponent and negative base.

   - bpo-21718(70): cursor.description is now available for queries
     using CTEs.

   - bpo-2466(71): posixpath.ismount now correctly recognizes mount
     points which the user does not have permission to access.

   - bpo-27773(72): Correct some memory management errors
     server_hostname in _ssl.wrap_socket().

   - bpo-26750(73): unittest.mock.create_autospec() now works properly
     for subclasses of property() and other data descriptors.

   - In the curses module, raise an error if window.getstr() or
     window.instr() is passed a negative value.

   - bpo-27783(74): Fix possible usage of uninitialized memory in
     operator.methodcaller.

   - bpo-27774(75): Fix possible Py_DECREF on unowned object in _sre.

   - bpo-27760(76): Fix possible integer overflow in binascii.b2a_qp.

   - bpo-27758(77): Fix possible integer overflow in the _csv module for
     large record lengths.

   - bpo-27568(78): Prevent HTTPoxy attack (CVE-2016-1000110).  Ignore
     the HTTP_PROXY variable when REQUEST_METHOD environment is set,
     which indicates that the script is in CGI mode.

   - bpo-27656(79): Do not assume sched.h defines any SCHED_* constants.

   - bpo-27130(80): In the “zlib” module, fix handling of large buffers
     (typically 4 GiB) when compressing and decompressing.  Previously,
     inputs were limited to 4 GiB, and compression and decompression
     operations did not properly handle results of 4 GiB.

   - bpo-27533(81): Release GIL in nt._isdir

   - bpo-17711(82): Fixed unpickling by the persistent ID with protocol
     0.  Original patch by Alexandre Vassalotti.

   - bpo-27522(83): Avoid an unintentional reference cycle in
     email.feedparser.

   - bpo-26844(84): Fix error message for imp.find_module() to refer to
     ‘path’ instead of ‘name’.  Patch by Lev Maximov.

   - bpo-23804(85): Fix SSL zero-length recv() calls to not block and
     not raise an error about unclean EOF.

   - bpo-27466(86): Change time format returned by
     http.cookie.time2netscape, confirming the netscape cookie format
     and making it consistent with documentation.

   - bpo-26664(87): Fix activate.fish by removing mis-use of ‘$’.

   - bpo-22115(88): Fixed tracing Tkinter variables: trace_vdelete()
     with wrong mode no longer break tracing, trace_vinfo() now always
     returns a list of pairs of strings, tracing in the “u” mode now
     works.

   - Fix a scoping issue in importlib.util.LazyLoader which triggered an
     UnboundLocalError when lazy-loading a module that was already put
     into sys.modules.

   - bpo-27079(89): Fixed curses.ascii functions isblank(), iscntrl()
     and ispunct().

   - bpo-26754(90): Some functions (compile() etc) accepted a filename
     argument encoded as an iterable of integers.  Now only strings and
     byte-like objects are accepted.

   - bpo-27048(91): Prevents distutils failing on Windows when
     environment variables contain non-ASCII characters

   - bpo-27330(92): Fixed possible leaks in the ctypes module.

   - bpo-27238(93): Got rid of bare excepts in the turtle module.
     Original patch by Jelle Zijlstra.

   - bpo-27122(94): When an exception is raised within the context being
     managed by a contextlib.ExitStack() and one of the exit stack
     generators catches and raises it in a chain, do not re-raise the
     original exception when exiting, let the new chained one through.
     This avoids the PEP 479(95) bug described in issue25782.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15812

   (2) https://bugs.python.org/issue29094

   (3) https://bugs.python.org/issue13051

   (4) https://bugs.python.org/issue29119

   (5) https://bugs.python.org/issue9770

   (6) https://bugs.python.org/issue28427

   (7) https://bugs.python.org/issue28923

   (8) https://bugs.python.org/issue28871

   (9) https://bugs.python.org/issue19542

   (10) https://bugs.python.org/issue20191

   (11) https://bugs.python.org/issue28779

   (12) https://bugs.python.org/issue28847

   (13) https://bugs.python.org/issue25659

   (14) https://bugs.python.org/issue28732

   (15) https://bugs.python.org/issue28485

   (16) https://bugs.python.org/issue28387

   (17) https://bugs.python.org/issue27517

   (18) https://bugs.python.org/issue28549

   (19) https://bugs.python.org/issue28449

   (20) https://bugs.python.org/issue23262

   (21) https://bugs.python.org/issue27939

   (22) https://bugs.python.org/issue28255

   (23) https://bugs.python.org/issue20491

   (24) https://bugs.python.org/issue28353

   (25) https://bugs.python.org/issue25464

   (26) https://bugs.python.org/issue28488

   (27) https://bugs.python.org/issue24452

   (28) https://bugs.python.org/issue20766

   (29) https://bugs.python.org/issue26293

   (30) https://bugs.python.org/issue28321

   (31) https://bugs.python.org/issue28322

   (32) https://bugs.python.org/issue1703178

   (33) https://bugs.python.org/issue28253

   (34) https://bugs.python.org/issue28275

   (35) https://bugs.python.org/issue27897

   (36) https://bugs.python.org/issue18893

   (37) https://bugs.python.org/issue27611

   (38) https://bugs.python.org/issue27348

   (39) https://bugs.python.org/issue25651

   (40) https://bugs.python.org/issue27932

   (41) https://bugs.python.org/issue28075

   (42) https://bugs.python.org/issue25270

   (43) https://bugs.python.org/issue28181

   (44) https://bugs.python.org/issue25895

   (45) https://bugs.python.org/issue27599

   (46) https://bugs.python.org/issue19003

   (47) https://bugs.python.org/issue28019

   (48) https://bugs.python.org/issue25969

   (49) https://bugs.python.org/issue14977

   (50) https://bugs.python.org/issue24594

   (51) https://bugs.python.org/issue17582

   (52) https://bugs.python.org/issue28047

   (53) https://bugs.python.org/issue27445

   (54) https://bugs.python.org/issue22450

   (55) https://bugs.python.org/issue27570

   (56) https://bugs.python.org/issue22233

   (57) https://bugs.python.org/issue27988

   (58) https://bugs.python.org/issue27691

   (59) https://bugs.python.org/issue27850

   (60) https://bugs.python.org/issue27766

   (61) https://bugs.python.org/issue26470

   (62) https://bugs.python.org/issue12885

   (63) https://bugs.python.org/issue27881

   (64) https://bugs.python.org/issue27861

   (65) https://bugs.python.org/issue19884

   (66) https://bugs.python.org/issue27706

   (67) https://bugs.python.org/issue10513

   (68) https://bugs.python.org/issue27598

   (69) https://bugs.python.org/issue27539

   (70) https://bugs.python.org/issue21718

   (71) https://bugs.python.org/issue2466

   (72) https://bugs.python.org/issue27773

   (73) https://bugs.python.org/issue26750

   (74) https://bugs.python.org/issue27783

   (75) https://bugs.python.org/issue27774

   (76) https://bugs.python.org/issue27760

   (77) https://bugs.python.org/issue27758

   (78) https://bugs.python.org/issue27568

   (79) https://bugs.python.org/issue27656

   (80) https://bugs.python.org/issue27130

   (81) https://bugs.python.org/issue27533

   (82) https://bugs.python.org/issue17711

   (83) https://bugs.python.org/issue27522

   (84) https://bugs.python.org/issue26844

   (85) https://bugs.python.org/issue23804

   (86) https://bugs.python.org/issue27466

   (87) https://bugs.python.org/issue26664

   (88) https://bugs.python.org/issue22115

   (89) https://bugs.python.org/issue27079

   (90) https://bugs.python.org/issue26754

   (91) https://bugs.python.org/issue27048

   (92) https://bugs.python.org/issue27330

   (93) https://bugs.python.org/issue27238

   (94) https://bugs.python.org/issue27122

   (95) https://www.python.org/dev/peps/pep-0479


File: python.info,  Node: Security<35>,  Next: Library<70>,  Prev: Library<69>,  Up: Python 3 5 3 release candidate 1

1.19.72.3 Security
..................

   - bpo-27278(1): Fix os.urandom() implementation using getrandom() on
     Linux.  Truncate size to INT_MAX and loop until we collected enough
     random bytes, instead of casting a directly Py_ssize_t to int.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27278


File: python.info,  Node: Library<70>,  Next: Security<36>,  Prev: Security<35>,  Up: Python 3 5 3 release candidate 1

1.19.72.4 Library
.................

   - bpo-26386(1): Fixed ttk.TreeView selection operations with item
     id’s containing spaces.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26386


File: python.info,  Node: Security<36>,  Next: Library<71>,  Prev: Library<70>,  Up: Python 3 5 3 release candidate 1

1.19.72.5 Security
..................

   - bpo-22636(1): Avoid shell injection problems with
     ctypes.util.find_library().

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22636


File: python.info,  Node: Library<71>,  Next: IDLE<44>,  Prev: Security<36>,  Up: Python 3 5 3 release candidate 1

1.19.72.6 Library
.................

   - bpo-16182(1): Fix various functions in the “readline” module to use
     the locale encoding, and fix get_begidx() and get_endidx() to
     return code point indexes.

   - bpo-27392(2): Add loop.connect_accepted_socket().  Patch by Jim
     Fulton.

   - bpo-27930(3): Improved behaviour of logging.handlers.QueueListener.
     Thanks to Paulo Andrade and Petr Viktorin for the analysis and
     patch.

   - bpo-21201(4): Improves readability of multiprocessing error
     message.  Thanks to Wojciech Walczak for patch.

   - bpo-27456(5): asyncio: Set TCP_NODELAY by default.

   - bpo-27906(6): Fix socket accept exhaustion during high TCP traffic.
     Patch by Kevin Conway.

   - bpo-28174(7): Handle when SO_REUSEPORT isn’t properly supported.
     Patch by Seth Michael Larson.

   - bpo-26654(8): Inspect functools.partial in asyncio.Handle.__repr__.
     Patch by iceboy.

   - bpo-26909(9): Fix slow pipes IO in asyncio.  Patch by INADA Naoki.

   - bpo-28176(10): Fix callbacks race in
     asyncio.SelectorLoop.sock_connect.

   - bpo-27759(11): Fix selectors incorrectly retain invalid file
     descriptors.  Patch by Mark Williams.

   - bpo-28368(12): Refuse monitoring processes if the child watcher has
     no loop attached.  Patch by Vincent Michel.

   - bpo-28369(13): Raise RuntimeError when transport’s FD is used with
     add_reader, add_writer, etc.

   - bpo-28370(14): Speedup asyncio.StreamReader.readexactly.  Patch by
     Коренберг Марк.

   - bpo-28371(15): Deprecate passing asyncio.Handles to
     run_in_executor.

   - bpo-28372(16): Fix asyncio to support formatting of non-python
     coroutines.

   - bpo-28399(17): Remove UNIX socket from FS before binding.  Patch by
     Коренберг Марк.

   - bpo-27972(18): Prohibit Tasks to await on themselves.

   - bpo-26923(19): Fix asyncio.Gather to refuse being cancelled once
     all children are done.  Patch by Johannes Ebke.

   - bpo-26796(20): Don’t configure the number of workers for default
     threadpool executor.  Initial patch by Hans Lawrenz.

   - bpo-28600(21): Optimize loop.call_soon().

   - bpo-28613(22): Fix get_event_loop() return the current loop if
     called from coroutines/callbacks.

   - bpo-28639(23): Fix inspect.isawaitable to always return bool Patch
     by Justin Mayfield.

   - bpo-28652(24): Make loop methods reject socket kinds they do not
     support.

   - bpo-28653(25): Fix a refleak in functools.lru_cache.

   - bpo-28703(26): Fix asyncio.iscoroutinefunction to handle Mock
     objects.

   - bpo-24142(27): Reading a corrupt config file left the parser in an
     invalid state.  Original patch by Florian Höch.

   - bpo-28990(28): Fix SSL hanging if connection is closed before
     handshake completed.  (Patch by HoHo-Ho)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue16182

   (2) https://bugs.python.org/issue27392

   (3) https://bugs.python.org/issue27930

   (4) https://bugs.python.org/issue21201

   (5) https://bugs.python.org/issue27456

   (6) https://bugs.python.org/issue27906

   (7) https://bugs.python.org/issue28174

   (8) https://bugs.python.org/issue26654

   (9) https://bugs.python.org/issue26909

   (10) https://bugs.python.org/issue28176

   (11) https://bugs.python.org/issue27759

   (12) https://bugs.python.org/issue28368

   (13) https://bugs.python.org/issue28369

   (14) https://bugs.python.org/issue28370

   (15) https://bugs.python.org/issue28371

   (16) https://bugs.python.org/issue28372

   (17) https://bugs.python.org/issue28399

   (18) https://bugs.python.org/issue27972

   (19) https://bugs.python.org/issue26923

   (20) https://bugs.python.org/issue26796

   (21) https://bugs.python.org/issue28600

   (22) https://bugs.python.org/issue28613

   (23) https://bugs.python.org/issue28639

   (24) https://bugs.python.org/issue28652

   (25) https://bugs.python.org/issue28653

   (26) https://bugs.python.org/issue28703

   (27) https://bugs.python.org/issue24142

   (28) https://bugs.python.org/issue28990


File: python.info,  Node: IDLE<44>,  Next: C API<40>,  Prev: Library<71>,  Up: Python 3 5 3 release candidate 1

1.19.72.7 IDLE
..............

   - bpo-15308(1): Add ‘interrupt execution’ (^C) to Shell menu.  Patch
     by Roger Serwy, updated by Bayard Randel.

   - bpo-27922(2): Stop IDLE tests from ‘flashing’ gui widgets on the
     screen.

   - Add version to title of IDLE help window.

   - bpo-25564(3): In section on IDLE – console differences, mention
     that using exec means that __builtins__ is defined for each
     statement.

   - bpo-27714(4): text_textview and test_autocomplete now pass when
     re-run in the same process.  This occurs when test_idle fails when
     run with the -w option but without -jn.  Fix warning from
     test_config.

   - bpo-25507(5): IDLE no longer runs buggy code because of its tkinter
     imports.  Users must include the same imports required to run
     directly in Python.

   - bpo-27452(6): add line counter and crc to IDLE configHandler test
     dump.

   - bpo-27365(7): Allow non-ascii chars in IDLE NEWS.txt, for
     contributor names.

   - bpo-27245(8): IDLE: Cleanly delete custom themes and key bindings.
     Previously, when IDLE was started from a console or by import, a
     cascade of warnings was emitted.  Patch by Serhiy Storchaka.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15308

   (2) https://bugs.python.org/issue27922

   (3) https://bugs.python.org/issue25564

   (4) https://bugs.python.org/issue27714

   (5) https://bugs.python.org/issue25507

   (6) https://bugs.python.org/issue27452

   (7) https://bugs.python.org/issue27365

   (8) https://bugs.python.org/issue27245


File: python.info,  Node: C API<40>,  Next: Documentation<48>,  Prev: IDLE<44>,  Up: Python 3 5 3 release candidate 1

1.19.72.8 C API
...............

   - bpo-28808(1): PyUnicode_CompareWithASCIIString() now never raises
     exceptions.

   - bpo-26754(2): PyUnicode_FSDecoder() accepted a filename argument
     encoded as an iterable of integers.  Now only strings and
     bytes-like objects are accepted.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28808

   (2) https://bugs.python.org/issue26754


File: python.info,  Node: Documentation<48>,  Next: Tests<49>,  Prev: C API<40>,  Up: Python 3 5 3 release candidate 1

1.19.72.9 Documentation
.......................

   - bpo-28513(1): Documented command-line interface of zipfile.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28513


File: python.info,  Node: Tests<49>,  Next: Tools/Demos<29>,  Prev: Documentation<48>,  Up: Python 3 5 3 release candidate 1

1.19.72.10 Tests
................

   - bpo-28950(1): Disallow -j0 to be combined with -T/-l/-M in regrtest
     command line arguments.

   - bpo-28666(2): Now test.support.rmtree is able to remove unwritable
     or unreadable directories.

   - bpo-23839(3): Various caches now are cleared before running every
     test file.

   - bpo-28409(4): regrtest: fix the parser of command line arguments.

   - bpo-27787(5): Call gc.collect() before checking each test for
     “dangling threads”, since the dangling threads are weak references.

   - bpo-27369(6): In test_pyexpat, avoid testing an error message
     detail that changed in Expat 2.2.0.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28950

   (2) https://bugs.python.org/issue28666

   (3) https://bugs.python.org/issue23839

   (4) https://bugs.python.org/issue28409

   (5) https://bugs.python.org/issue27787

   (6) https://bugs.python.org/issue27369


File: python.info,  Node: Tools/Demos<29>,  Next: Windows<48>,  Prev: Tests<49>,  Up: Python 3 5 3 release candidate 1

1.19.72.11 Tools/Demos
......................

   - bpo-27952(1): Get Tools/scripts/fixcid.py working with Python 3 and
     the current “re” module, avoid invalid Python backslash escapes,
     and fix a bug parsing escaped C quote signs.

   - bpo-27332(2): Fixed the type of the first argument of module-level
     functions generated by Argument Clinic.  Patch by Petr Viktorin.

   - bpo-27418(3): Fixed Tools/importbench/importbench.py.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27952

   (2) https://bugs.python.org/issue27332

   (3) https://bugs.python.org/issue27418


File: python.info,  Node: Windows<48>,  Next: Build<52>,  Prev: Tools/Demos<29>,  Up: Python 3 5 3 release candidate 1

1.19.72.12 Windows
..................

   - bpo-28251(1): Improvements to help manuals on Windows.

   - bpo-28110(2): launcher.msi has different product codes between
     32-bit and 64-bit

   - bpo-25144(3): Ensures TargetDir is set before continuing with
     custom install.

   - bpo-27469(4): Adds a shell extension to the launcher so that drag
     and drop works correctly.

   - bpo-27309(5): Enabled proper Windows styles in python[w].exe
     manifest.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28251

   (2) https://bugs.python.org/issue28110

   (3) https://bugs.python.org/issue25144

   (4) https://bugs.python.org/issue27469

   (5) https://bugs.python.org/issue27309


File: python.info,  Node: Build<52>,  Prev: Windows<48>,  Up: Python 3 5 3 release candidate 1

1.19.72.13 Build
................

   - bpo-29080(1): Removes hard dependency on hg.exe from
     PCBuild/build.bat

   - bpo-23903(2): Added missed names to PC/python3.def.

   - bpo-10656(3): Fix out-of-tree building on AIX. Patch by Tristan
     Carel and Michael Haubenwallner.

   - bpo-26359(4): Rename –with-optimiations to –enable-optimizations.

   - bpo-28444(5): Fix missing extensions modules when cross compiling.

   - bpo-28248(6): Update Windows build and OS X installers to use
     OpenSSL 1.0.2j.

   - bpo-28258(7): Fixed build with Estonian locale (python-config and
     distclean targets in Makefile).  Patch by Arfrever Frehtes
     Taifersar Arahesis.

   - bpo-26661(8): setup.py now detects system libffi with multiarch
     wrapper.

   - bpo-28066(9): Fix the logic that searches build directories for
     generated include files when building outside the source tree.

   - bpo-15819(10): Remove redundant include search directory option for
     building outside the source tree.

   - bpo-27566(11): Fix clean target in freeze makefile (patch by Lisa
     Roach)

   - bpo-27705(12): Update message in validate_ucrtbase.py

   - bpo-27983(13): Cause lack of llvm-profdata tool when using clang as
     required for PGO linking to be a configure time error rather than
     make time when –with-optimizations is enabled.  Also improve our
     ability to find the llvm-profdata tool on MacOS and some Linuxes.

   - bpo-26307(14): The profile-opt build now applies PGO to the
     built-in modules.

   - bpo-26359(15): Add the –with-optimizations configure flag.

   - bpo-27713(16): Suppress spurious build warnings when updating
     importlib’s bootstrap files.  Patch by Xiang Zhang

   - bpo-25825(17): Correct the references to Modules/python.exp and
     ld_so_aix, which are required on AIX. This updates references to an
     installation path that was changed in 3.2a4, and undoes changed
     references to the build tree that were made in 3.5.0a1.

   - bpo-27453(18): CPP invocation in configure must use CPPFLAGS. Patch
     by Chi Hsuan Yen.

   - bpo-27641(19): The configure script now inserts comments into the
     makefile to prevent the pgen and _freeze_importlib executables from
     being cross-compiled.

   - bpo-26662(20): Set PYTHON_FOR_GEN in configure as the Python
     program to be used for file generation during the build.

   - bpo-10910(21): Avoid C++ compilation errors on FreeBSD and OS X.
     Also update FreedBSD version checks for the original ctype UTF-8
     workaround.

   - bpo-28676(22): Prevent missing ‘getentropy’ declaration warning on
     macOS. Patch by Gareth Rees.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue29080

   (2) https://bugs.python.org/issue23903

   (3) https://bugs.python.org/issue10656

   (4) https://bugs.python.org/issue26359

   (5) https://bugs.python.org/issue28444

   (6) https://bugs.python.org/issue28248

   (7) https://bugs.python.org/issue28258

   (8) https://bugs.python.org/issue26661

   (9) https://bugs.python.org/issue28066

   (10) https://bugs.python.org/issue15819

   (11) https://bugs.python.org/issue27566

   (12) https://bugs.python.org/issue27705

   (13) https://bugs.python.org/issue27983

   (14) https://bugs.python.org/issue26307

   (15) https://bugs.python.org/issue26359

   (16) https://bugs.python.org/issue27713

   (17) https://bugs.python.org/issue25825

   (18) https://bugs.python.org/issue27453

   (19) https://bugs.python.org/issue27641

   (20) https://bugs.python.org/issue26662

   (21) https://bugs.python.org/issue10910

   (22) https://bugs.python.org/issue28676


File: python.info,  Node: Python 3 5 2 final,  Next: Python 3 5 2 release candidate 1,  Prev: Python 3 5 3 release candidate 1,  Up: Changelog

1.19.73 Python 3.5.2 final
--------------------------

`Release date: 2016-06-26'

* Menu:

* Core and Builtins: Core and Builtins<59>.
* Tests: Tests<50>.
* IDLE: IDLE<45>.


File: python.info,  Node: Core and Builtins<59>,  Next: Tests<50>,  Up: Python 3 5 2 final

1.19.73.1 Core and Builtins
...........................

   - bpo-26930(1): Update Windows builds to use OpenSSL 1.0.2h.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26930


File: python.info,  Node: Tests<50>,  Next: IDLE<45>,  Prev: Core and Builtins<59>,  Up: Python 3 5 2 final

1.19.73.2 Tests
...............

   - bpo-26867(1): Ubuntu’s openssl OP_NO_SSLv3 is forced on by default;
     fix test.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26867


File: python.info,  Node: IDLE<45>,  Prev: Tests<50>,  Up: Python 3 5 2 final

1.19.73.3 IDLE
..............

   - bpo-27365(1): Allow non-ascii in idlelib/NEWS.txt - minimal part
     for 3.5.2.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27365


File: python.info,  Node: Python 3 5 2 release candidate 1,  Next: Python 3 5 1 final,  Prev: Python 3 5 2 final,  Up: Changelog

1.19.74 Python 3.5.2 release candidate 1
----------------------------------------

`Release date: 2016-06-12'

* Menu:

* Core and Builtins: Core and Builtins<60>.
* Security: Security<37>.
* Library: Library<72>.
* Security: Security<38>.
* Library: Library<73>.
* Security: Security<39>.
* Library: Library<74>.
* Security: Security<40>.
* Library: Library<75>.
* Security: Security<41>.
* Library: Library<76>.
* IDLE: IDLE<46>.
* Documentation: Documentation<49>.
* Tests: Tests<51>.
* Build: Build<53>.
* Windows: Windows<49>.
* Tools/Demos: Tools/Demos<30>.
* Windows: Windows<50>.


File: python.info,  Node: Core and Builtins<60>,  Next: Security<37>,  Up: Python 3 5 2 release candidate 1

1.19.74.1 Core and Builtins
...........................

   - bpo-27066(1): Fixed SystemError if a custom opener (for open())
     returns a negative number without setting an exception.

   - bpo-20041(2): Fixed TypeError when frame.f_trace is set to None.
     Patch by Xavier de Gaye.

   - bpo-26168(3): Fixed possible refleaks in failing Py_BuildValue()
     with the “N” format unit.

   - bpo-26991(4): Fix possible refleak when creating a function with
     annotations.

   - bpo-27039(5): Fixed bytearray.remove() for values greater than 127.
     Patch by Joe Jevnik.

   - bpo-23640(6): int.from_bytes() no longer bypasses constructors for
     subclasses.

   - bpo-26811(7): gc.get_objects() no longer contains a broken tuple
     with NULL pointer.

   - bpo-20120(8): Use RawConfigParser for .pypirc parsing, removing
     support for interpolation unintentionally added with move to Python
     3.  Behavior no longer does any interpolation in .pypirc files,
     matching behavior in Python 2.7 and Setuptools 19.0.

   - bpo-26659(9): Make the builtin slice type support cycle collection.

   - bpo-26718(10): super.__init__ no longer leaks memory if called
     multiple times.  NOTE: A direct call of super.__init__ is not
     endorsed!

   - bpo-25339(11): PYTHONIOENCODING now has priority over locale in
     setting the error handler for stdin and stdout.

   - bpo-26494(12): Fixed crash on iterating exhausting iterators.
     Affected classes are generic sequence iterators, iterators of str,
     bytes, bytearray, list, tuple, set, frozenset, dict, OrderedDict,
     corresponding views and os.scandir() iterator.

   - bpo-26581(13): If coding cookie is specified multiple times on a
     line in Python source code file, only the first one is taken to
     account.

   - bpo-26464(14): Fix str.translate() when string is ASCII and first
     replacements removes character, but next replacement uses a
     non-ASCII character or a string longer than 1 character.
     Regression introduced in Python 3.5.0.

   - bpo-22836(15): Ensure exception reports from PyErr_Display() and
     PyErr_WriteUnraisable() are sensible even when formatting them
     produces secondary errors.  This affects the reports produced by
     sys.__excepthook__() and when __del__() raises an exception.

   - bpo-26302(16): Correct behavior to reject comma as a legal
     character for cookie names.

   - bpo-4806(17): Avoid masking the original TypeError exception when
     using star (‘*’) unpacking in function calls.  Based on patch by
     Hagen Fürstenau and Daniel Urban.

   - bpo-27138(18): Fix the doc comment for FileFinder.find_spec().

   - bpo-26154(19): Add a new private _PyThreadState_UncheckedGet()
     function to get the current Python thread state, but don’t issue a
     fatal error if it is NULL. This new function must be used instead
     of accessing directly the _PyThreadState_Current variable.  The
     variable is no more exposed since Python 3.5.1 to hide the exact
     implementation of atomic C types, to avoid compiler issues.

   - bpo-26194(20): Deque.insert() gave odd results for bounded deques
     that had reached their maximum size.  Now an IndexError will be
     raised when attempting to insert into a full deque.

   - bpo-25843(21): When compiling code, don’t merge constants if they
     are equal but have a different types.  For example, ‘f1, f2 =
     lambda: 1, lambda: 1.0’ is now correctly compiled to two different
     functions: ‘f1()’ returns ‘1’ (‘int’) and ‘f2()’ returns ‘1.0’
     (‘int’), even if ‘1’ and ‘1.0’ are equal.

   - bpo-22995(22): [UPDATE] Comment out the one of the pickleability
     tests in _PyObject_GetState() due to regressions observed in
     Cython-based projects.

   - bpo-25961(23): Disallowed null characters in the type name.

   - bpo-25973(24): Fix segfault when an invalid nonlocal statement
     binds a name starting with two underscores.

   - bpo-22995(25): Instances of extension types with a state that
     aren’t subclasses of list or dict and haven’t implemented any
     pickle-related methods (__reduce__, __reduce_ex__, __getnewargs__,
     __getnewargs_ex__, or __getstate__), can no longer be pickled.
     Including memoryview.

   - bpo-20440(26): Massive replacing unsafe attribute setting code with
     special macro Py_SETREF.

   - bpo-25766(27): Special method __bytes__() now works in str
     subclasses.

   - bpo-25421(28): __sizeof__ methods of builtin types now use dynamic
     basic size.  This allows sys.getsize() to work correctly with their
     subclasses with __slots__ defined.

   - bpo-25709(29): Fixed problem with in-place string concatenation and
     utf-8 cache.

   - bpo-27147(30): Mention PEP 420(31) in the importlib docs.

   - bpo-24097(32): Fixed crash in object.__reduce__() if slot name is
     freed inside __getattr__.

   - bpo-24731(33): Fixed crash on converting objects with special
     methods __bytes__, __trunc__, and __float__ returning instances of
     subclasses of bytes, int, and float to subclasses of bytes, int,
     and float correspondingly.

   - bpo-26478(34): Fix semantic bugs when using binary operators with
     dictionary views and tuples.

   - bpo-26171(35): Fix possible integer overflow and heap corruption in
     zipimporter.get_data().

   - bpo-25660(36): Fix TAB key behaviour in REPL with readline.

   - bpo-25887(37): Raise a RuntimeError when a coroutine object is
     awaited more than once.

   - bpo-27243(38): Update the __aiter__ protocol: instead of returning
     an awaitable that resolves to an asynchronous iterator, the
     asynchronous iterator should be returned directly.  Doing the
     former will trigger a PendingDeprecationWarning.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27066

   (2) https://bugs.python.org/issue20041

   (3) https://bugs.python.org/issue26168

   (4) https://bugs.python.org/issue26991

   (5) https://bugs.python.org/issue27039

   (6) https://bugs.python.org/issue23640

   (7) https://bugs.python.org/issue26811

   (8) https://bugs.python.org/issue20120

   (9) https://bugs.python.org/issue26659

   (10) https://bugs.python.org/issue26718

   (11) https://bugs.python.org/issue25339

   (12) https://bugs.python.org/issue26494

   (13) https://bugs.python.org/issue26581

   (14) https://bugs.python.org/issue26464

   (15) https://bugs.python.org/issue22836

   (16) https://bugs.python.org/issue26302

   (17) https://bugs.python.org/issue4806

   (18) https://bugs.python.org/issue27138

   (19) https://bugs.python.org/issue26154

   (20) https://bugs.python.org/issue26194

   (21) https://bugs.python.org/issue25843

   (22) https://bugs.python.org/issue22995

   (23) https://bugs.python.org/issue25961

   (24) https://bugs.python.org/issue25973

   (25) https://bugs.python.org/issue22995

   (26) https://bugs.python.org/issue20440

   (27) https://bugs.python.org/issue25766

   (28) https://bugs.python.org/issue25421

   (29) https://bugs.python.org/issue25709

   (30) https://bugs.python.org/issue27147

   (31) https://www.python.org/dev/peps/pep-0420

   (32) https://bugs.python.org/issue24097

   (33) https://bugs.python.org/issue24731

   (34) https://bugs.python.org/issue26478

   (35) https://bugs.python.org/issue26171

   (36) https://bugs.python.org/issue25660

   (37) https://bugs.python.org/issue25887

   (38) https://bugs.python.org/issue27243


File: python.info,  Node: Security<37>,  Next: Library<72>,  Prev: Core and Builtins<60>,  Up: Python 3 5 2 release candidate 1

1.19.74.2 Security
..................

   - bpo-26556(1): Update expat to 2.1.1, fixes CVE-2015-1283.

   - Fix TLS stripping vulnerability in smtplib, CVE-2016-0772.
     Reported by Team Oststrom

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26556


File: python.info,  Node: Library<72>,  Next: Security<38>,  Prev: Security<37>,  Up: Python 3 5 2 release candidate 1

1.19.74.3 Library
.................

   - bpo-21386(1): Implement missing IPv4Address.is_global property.  It
     was documented since 07a5610bae9d.  Initial patch by Roger Luethi.

   - bpo-20900(2): distutils register command now decodes HTTP responses
     correctly.  Initial patch by ingrid.

   - A new version of typing.py provides several new classes and
     features: @overload outside stubs, Reversible, DefaultDict, Text,
     ContextManager, Type[], NewType(), TYPE_CHECKING, and numerous bug
     fixes (note that some of the new features are not yet implemented
     in mypy or other static analyzers).  Also classes for PEP 492(3)
     (Awaitable, AsyncIterable, AsyncIterator) have been added (in fact
     they made it into 3.5.1 but were never mentioned).

   - bpo-25738(4): Stop http.server.BaseHTTPRequestHandler.send_error()
     from sending a message body for 205 Reset Content.  Also, don’t
     send Content header fields in responses that don’t have a body.
     Patch by Susumu Koshiba.

   - bpo-21313(5): Fix the “platform” module to tolerate when
     sys.version contains truncated build information.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21386

   (2) https://bugs.python.org/issue20900

   (3) https://www.python.org/dev/peps/pep-0492

   (4) https://bugs.python.org/issue25738

   (5) https://bugs.python.org/issue21313


File: python.info,  Node: Security<38>,  Next: Library<73>,  Prev: Library<72>,  Up: Python 3 5 2 release candidate 1

1.19.74.4 Security
..................

   - bpo-26839(1): On Linux, *note os.urandom(): 5cc. now calls
     ‘getrandom()’ with ‘GRND_NONBLOCK’ to fall back on reading
     ‘/dev/urandom’ if the urandom entropy pool is not initialized yet.
     Patch written by Colm Buckley.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26839


File: python.info,  Node: Library<73>,  Next: Security<39>,  Prev: Security<38>,  Up: Python 3 5 2 release candidate 1

1.19.74.5 Library
.................

   - bpo-27164(1): In the zlib module, allow decompressing raw Deflate
     streams with a predefined zdict.  Based on patch by Xiang Zhang.

   - bpo-24291(2): Fix wsgiref.simple_server.WSGIRequestHandler to
     completely write data to the client.  Previously it could do
     partial writes and truncate data.  Also,
     wsgiref.handler.ServerHandler can now handle stdout doing partial
     writes, but this is deprecated.

   - bpo-26809(3): Add ‘__all__’ to *note string: f6.  Patch by Emanuel
     Barry.

   - bpo-26373(4): subprocess.Popen.communicate now correctly ignores
     BrokenPipeError when the child process dies before .communicate()
     is called in more/all circumstances.

   - bpo-21776(5): distutils.upload now correctly handles HTTPError.
     Initial patch by Claudiu Popa.

   - bpo-27114(6): Fix SSLContext._load_windows_store_certs fails with
     PermissionError

   - bpo-18383(7): Avoid creating duplicate filters when using
     filterwarnings and simplefilter.  Based on patch by Alex Shkop.

   - bpo-27057(8): Fix os.set_inheritable() on Android, ioctl() is
     blocked by SELinux and fails with EACCESS. The function now falls
     back to fcntl().  Patch written by Michał Bednarski.

   - bpo-27014(9): Fix infinite recursion using typing.py.  Thanks to
     Kalle Tuure!

   - bpo-14132(10): Fix urllib.request redirect handling when the target
     only has a query string.  Original fix by Ján Janech.

   - bpo-17214(11): The “urllib.request” module now percent-encodes
     non-ASCII bytes found in redirect target URLs.  Some servers send
     Location header fields with non-ASCII bytes, but “http.client”
     requires the request target to be ASCII-encodable, otherwise a
     UnicodeEncodeError is raised.  Based on patch by Christian Heimes.

   - bpo-26892(12): Honor debuglevel flag in urllib.request.HTTPHandler.
     Patch contributed by Chi Hsuan Yen.

   - bpo-22274(13): In the subprocess module, allow stderr to be
     redirected to stdout even when stdout is not redirected.  Patch by
     Akira Li.

   - bpo-26807(14): mock_open ‘files’ no longer error on readline at end
     of file.  Patch from Yolanda Robla.

   - bpo-25745(15): Fixed leaking a userptr in curses panel destructor.

   - bpo-26977(16): Removed unnecessary, and ignored, call to sum of
     squares helper in statistics.pvariance.

   - bpo-26881(17): The modulefinder module now supports extended opcode
     arguments.

   - bpo-23815(18): Fixed crashes related to directly created instances
     of types in _tkinter and curses.panel modules.

   - bpo-17765(19): weakref.ref() no longer silently ignores keyword
     arguments.  Patch by Georg Brandl.

   - bpo-26873(20): xmlrpc now raises ResponseError on unsupported type
     tags instead of silently return incorrect result.

   - bpo-26711(21): Fixed the comparison of plistlib.Data with other
     types.

   - bpo-24114(22): Fix an uninitialized variable in ‘ctypes.util’.  The
     bug only occurs on SunOS when the ctypes implementation searches
     for the ‘crle’ program.  Patch by Xiang Zhang.  Tested on SunOS by
     Kees Bos.

   - bpo-26864(23): In urllib.request, change the proxy bypass host
     checking against no_proxy to be case-insensitive, and to not match
     unrelated host names that happen to have a bypassed hostname as a
     suffix.  Patch by Xiang Zhang.

   - bpo-26634(24): recursive_repr() now sets __qualname__ of wrapper.
     Patch by Xiang Zhang.

   - bpo-26804(25): urllib.request will prefer lower_case proxy
     environment variables over UPPER_CASE or Mixed_Case ones.  Patch
     contributed by Hans-Peter Jansen.

   - bpo-26837(26): assertSequenceEqual() now correctly outputs
     non-stringified differing items (like bytes in the -b mode).  This
     affects assertListEqual() and assertTupleEqual().

   - bpo-26041(27): Remove “will be removed in Python 3.7” from
     deprecation messages of platform.dist() and
     platform.linux_distribution().  Patch by Kumaripaba Miyurusara
     Athukorala.

   - bpo-26822(28): itemgetter, attrgetter and methodcaller objects no
     longer silently ignore keyword arguments.

   - bpo-26733(29): Disassembling a class now disassembles class and
     static methods.  Patch by Xiang Zhang.

   - bpo-26801(30): Fix error handling in *note
     shutil.get_terminal_size(): b25, catch *note AttributeError: 4a2.
     instead of *note NameError: e40.  Patch written by Emanuel Barry.

   - bpo-24838(31): tarfile’s ustar and gnu formats now correctly
     calculate name and link field limits for multibyte character
     encodings like utf-8.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27164

   (2) https://bugs.python.org/issue24291

   (3) https://bugs.python.org/issue26809

   (4) https://bugs.python.org/issue26373

   (5) https://bugs.python.org/issue21776

   (6) https://bugs.python.org/issue27114

   (7) https://bugs.python.org/issue18383

   (8) https://bugs.python.org/issue27057

   (9) https://bugs.python.org/issue27014

   (10) https://bugs.python.org/issue14132

   (11) https://bugs.python.org/issue17214

   (12) https://bugs.python.org/issue26892

   (13) https://bugs.python.org/issue22274

   (14) https://bugs.python.org/issue26807

   (15) https://bugs.python.org/issue25745

   (16) https://bugs.python.org/issue26977

   (17) https://bugs.python.org/issue26881

   (18) https://bugs.python.org/issue23815

   (19) https://bugs.python.org/issue17765

   (20) https://bugs.python.org/issue26873

   (21) https://bugs.python.org/issue26711

   (22) https://bugs.python.org/issue24114

   (23) https://bugs.python.org/issue26864

   (24) https://bugs.python.org/issue26634

   (25) https://bugs.python.org/issue26804

   (26) https://bugs.python.org/issue26837

   (27) https://bugs.python.org/issue26041

   (28) https://bugs.python.org/issue26822

   (29) https://bugs.python.org/issue26733

   (30) https://bugs.python.org/issue26801

   (31) https://bugs.python.org/issue24838


File: python.info,  Node: Security<39>,  Next: Library<74>,  Prev: Library<73>,  Up: Python 3 5 2 release candidate 1

1.19.74.6 Security
..................

   - bpo-26657(1): Fix directory traversal vulnerability with
     http.server on Windows.  This fixes a regression that was
     introduced in 3.3.4rc1 and 3.4.0rc1.  Based on patch by Philipp
     Hagemeister.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26657


File: python.info,  Node: Library<74>,  Next: Security<40>,  Prev: Security<39>,  Up: Python 3 5 2 release candidate 1

1.19.74.7 Library
.................

   - bpo-26717(1): Stop encoding Latin-1-ized WSGI paths with UTF-8.
     Patch by Anthony Sottile.

   - bpo-26735(2): Fix *note os.urandom(): 5cc. on Solaris 11.3 and
     newer when reading more than 1,024 bytes: call ‘getrandom()’
     multiple times with a limit of 1024 bytes per call.

   - bpo-16329(3): Add .webm to mimetypes.types_map.  Patch by Giampaolo
     Rodola’.

   - bpo-13952(4): Add .csv to mimetypes.types_map.  Patch by Geoff
     Wilson.

   - bpo-26709(5): Fixed Y2038 problem in loading binary PLists.

   - bpo-23735(6): Handle terminal resizing with Readline 6.3+ by
     installing our own SIGWINCH handler.  Patch by Eric Price.

   - bpo-26586(7): In http.server, respond with “413 Request header
     fields too large” if there are too many header fields to parse,
     rather than killing the connection and raising an unhandled
     exception.  Patch by Xiang Zhang.

   - bpo-22854(8): Change BufferedReader.writable() and
     BufferedWriter.readable() to always return False.

   - bpo-25195(9): Fix a regression in mock.MagicMock.  _Call is a
     subclass of tuple (changeset 3603bae63c13 only works for classes)
     so we need to implement __ne__ ourselves.  Patch by Andrew Plummer.

   - bpo-26644(10): Raise ValueError rather than SystemError when a
     negative length is passed to SSLSocket.recv() or read().

   - bpo-23804(11): Fix SSL recv(0) and read(0) methods to return zero
     bytes instead of up to 1024.

   - bpo-26616(12): Fixed a bug in datetime.astimezone() method.

   - bpo-21925(13): *note warnings.formatwarning(): 112d. now catches
     exceptions on ‘linecache.getline(...)’ to be able to log *note
     ResourceWarning: 5cb. emitted late during the Python shutdown
     process.

   - bpo-24266(14): Ctrl+C during Readline history search now cancels
     the search mode when compiled with Readline 7.

   - bpo-26560(15): Avoid potential ValueError in
     BaseHandler.start_response.  Initial patch by Peter Inglesby.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26717

   (2) https://bugs.python.org/issue26735

   (3) https://bugs.python.org/issue16329

   (4) https://bugs.python.org/issue13952

   (5) https://bugs.python.org/issue26709

   (6) https://bugs.python.org/issue23735

   (7) https://bugs.python.org/issue26586

   (8) https://bugs.python.org/issue22854

   (9) https://bugs.python.org/issue25195

   (10) https://bugs.python.org/issue26644

   (11) https://bugs.python.org/issue23804

   (12) https://bugs.python.org/issue26616

   (13) https://bugs.python.org/issue21925

   (14) https://bugs.python.org/issue24266

   (15) https://bugs.python.org/issue26560


File: python.info,  Node: Security<40>,  Next: Library<75>,  Prev: Library<74>,  Up: Python 3 5 2 release candidate 1

1.19.74.8 Security
..................

   - bpo-26313(1): ssl.py _load_windows_store_certs fails if windows
     cert store is empty.  Patch by Baji.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26313


File: python.info,  Node: Library<75>,  Next: Security<41>,  Prev: Security<40>,  Up: Python 3 5 2 release candidate 1

1.19.74.9 Library
.................

   - bpo-26569(1): Fix *note pyclbr.readmodule(): 129e. and *note
     pyclbr.readmodule_ex(): 129f. to support importing packages.

   - bpo-26499(2): Account for remaining Content-Length in
     HTTPResponse.readline() and read1().  Based on patch by Silent
     Ghost.  Also document that HTTPResponse now supports these methods.

   - bpo-25320(3): Handle sockets in directories unittest discovery is
     scanning.  Patch from Victor van den Elzen.

   - bpo-16181(4): cookiejar.http2time() now returns None if year is
     higher than datetime.MAXYEAR.

   - bpo-26513(5): Fixes platform module detection of Windows Server

   - bpo-23718(6): Fixed parsing time in week 0 before Jan 1.  Original
     patch by Tamás Bence Gedai.

   - bpo-20589(7): Invoking Path.owner() and Path.group() on Windows now
     raise NotImplementedError instead of ImportError.

   - bpo-26177(8): Fixed the keys() method for Canvas and Scrollbar
     widgets.

   - bpo-15068(9): Got rid of excessive buffering in the fileinput
     module.  The bufsize parameter is no longer used.

   - bpo-2202(10): Fix UnboundLocalError in
     AbstractDigestAuthHandler.get_algorithm_impls.  Initial patch by
     Mathieu Dupuy.

   - bpo-25718(11): Fixed pickling and copying the accumulate() iterator
     with total is None.

   - bpo-26475(12): Fixed debugging output for regular expressions with
     the (?x) flag.

   - bpo-26457(13): Fixed the subnets() methods in IP network classes
     for the case when resulting prefix length is equal to maximal
     prefix length.  Based on patch by Xiang Zhang.

   - bpo-26385(14): Remove the file if the internal open() call in
     NamedTemporaryFile() fails.  Patch by Silent Ghost.

   - bpo-26402(15): Fix XML-RPC client to retry when the server shuts
     down a persistent connection.  This was a regression related to the
     new http.client.RemoteDisconnected exception in 3.5.0a4.

   - bpo-25913(16): Leading ‘<~’ is optional now in base64.a85decode()
     with adobe=True.  Patch by Swati Jaiswal.

   - bpo-26186(17): Remove an invalid type check in
     importlib.util.LazyLoader.

   - bpo-26367(18): importlib.__import__() raises SystemError like
     builtins.__import__() when ‘level’ is specified but without an
     accompanying package specified.

   - bpo-26309(19): In the “socketserver” module, shut down the request
     (closing the connected socket) when verify_request() returns false.
     Patch by Aviv Palivoda.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26569

   (2) https://bugs.python.org/issue26499

   (3) https://bugs.python.org/issue25320

   (4) https://bugs.python.org/issue16181

   (5) https://bugs.python.org/issue26513

   (6) https://bugs.python.org/issue23718

   (7) https://bugs.python.org/issue20589

   (8) https://bugs.python.org/issue26177

   (9) https://bugs.python.org/issue15068

   (10) https://bugs.python.org/issue2202

   (11) https://bugs.python.org/issue25718

   (12) https://bugs.python.org/issue26475

   (13) https://bugs.python.org/issue26457

   (14) https://bugs.python.org/issue26385

   (15) https://bugs.python.org/issue26402

   (16) https://bugs.python.org/issue25913

   (17) https://bugs.python.org/issue26186

   (18) https://bugs.python.org/issue26367

   (19) https://bugs.python.org/issue26309


File: python.info,  Node: Security<41>,  Next: Library<76>,  Prev: Library<75>,  Up: Python 3 5 2 release candidate 1

1.19.74.10 Security
...................

   - bpo-25939(1): On Windows open the cert store readonly in
     ssl.enum_certificates.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25939


File: python.info,  Node: Library<76>,  Next: IDLE<46>,  Prev: Security<41>,  Up: Python 3 5 2 release candidate 1

1.19.74.11 Library
..................

   - bpo-25995(1): os.walk() no longer uses FDs proportional to the tree
     depth.

   - bpo-26117(2): The os.scandir() iterator now closes file descriptor
     not only when the iteration is finished, but when it was failed
     with error.

   - bpo-25911(3): Restored support of bytes paths in os.walk() on
     Windows.

   - bpo-26045(4): Add UTF-8 suggestion to error message when posting a
     non-Latin-1 string with http.client.

   - bpo-12923(5): Reset FancyURLopener’s redirect counter even if there
     is an exception.  Based on patches by Brian Brazil and Daniel
     Rocco.

   - bpo-25945(6): Fixed a crash when unpickle the functools.partial
     object with wrong state.  Fixed a leak in failed functools.partial
     constructor.  “args” and “keywords” attributes of functools.partial
     have now always types tuple and dict correspondingly.

   - bpo-26202(7): copy.deepcopy() now correctly copies range() objects
     with non-atomic attributes.

   - bpo-23076(8): Path.glob() now raises a ValueError if it’s called
     with an invalid pattern.  Patch by Thomas Nyberg.

   - bpo-19883(9): Fixed possible integer overflows in zipimport.

   - bpo-26227(10): On Windows, getnameinfo(), gethostbyaddr() and
     gethostbyname_ex() functions of the socket module now decode the
     hostname from the ANSI code page rather than UTF-8.

   - bpo-26147(11): xmlrpc now works with strings not encodable with
     used non-UTF-8 encoding.

   - bpo-25935(12): Garbage collector now breaks reference loops with
     OrderedDict.

   - bpo-16620(13): Fixed AttributeError in msilib.Directory.glob().

   - bpo-26013(14): Added compatibility with broken protocol 2 pickles
     created in old Python 3 versions (3.4.3 and lower).

   - bpo-25850(15): Use cross-compilation by default for 64-bit Windows.

   - bpo-17633(16): Improve zipimport’s support for namespace packages.

   - bpo-24705(17): Fix sysconfig._parse_makefile not expanding ${} vars
     appearing before $() vars.

   - bpo-22138(18): Fix mock.patch behavior when patching descriptors.
     Restore original values after patching.  Patch contributed by Sean
     McCully.

   - bpo-25672(19): In the ssl module, enable the
     SSL_MODE_RELEASE_BUFFERS mode option if it is safe to do so.

   - bpo-26012(20): Don’t traverse into symlinks for ‘**’ pattern in
     pathlib.Path.[r]glob().

   - bpo-24120(21): Ignore PermissionError when traversing a tree with
     pathlib.Path.[r]glob().  Patch by Ulrich Petri.

   - bpo-25447(22): fileinput now uses sys.stdin as-is if it does not
     have a buffer attribute (restores backward compatibility).

   - bpo-25447(23): Copying the lru_cache() wrapper object now always
     works, independently from the type of the wrapped object (by
     returning the original object unchanged).

   - bpo-24103(24): Fixed possible use after free in
     ElementTree.XMLPullParser.

   - bpo-25860(25): os.fwalk() no longer skips remaining directories
     when error occurs.  Original patch by Samson Lee.

   - bpo-25914(26): Fixed and simplified OrderedDict.__sizeof__.

   - bpo-25902(27): Fixed various refcount issues in ElementTree
     iteration.

   - bpo-25717(28): Restore the previous behaviour of tolerating most
     fstat() errors when opening files.  This was a regression in 3.5a1,
     and stopped anonymous temporary files from working in special
     cases.

   - bpo-24903(29): Fix regression in number of arguments compileall
     accepts when ‘-d’ is specified.  The check on the number of
     arguments has been dropped completely as it never worked correctly
     anyway.

   - bpo-25764(30): In the subprocess module, preserve any exception
     caused by fork() failure when preexec_fn is used.

   - bpo-6478(31): _strptime’s regexp cache now is reset after changing
     timezone with time.tzset().

   - bpo-14285(32): When executing a package with the “python -m
     package” option, and package initialization fails, a proper
     traceback is now reported.  The “runpy” module now lets exceptions
     from package initialization pass back to the caller, rather than
     raising ImportError.

   - bpo-19771(33): Also in runpy and the “-m” option, omit the
     irrelevant message “… is a package and cannot be directly executed”
     if the package could not even be initialized (e.g.  due to a bad
     ‘*.pyc’ file).

   - bpo-25177(34): Fixed problem with the mean of very small and very
     large numbers.  As a side effect, statistics.mean and
     statistics.variance should be significantly faster.

   - bpo-25718(35): Fixed copying object with state with boolean value
     is false.

   - bpo-10131(36): Fixed deep copying of minidom documents.  Based on
     patch by Marian Ganisin.

   - bpo-25725(37): Fixed a reference leak in pickle.loads() when
     unpickling invalid data including tuple instructions.

   - bpo-25663(38): In the Readline completer, avoid listing duplicate
     global names, and search the global namespace before searching
     builtins.

   - bpo-25688(39): Fixed file leak in ElementTree.iterparse() raising
     an error.

   - bpo-23914(40): Fixed SystemError raised by unpickler on broken
     pickle data.

   - bpo-25691(41): Fixed crash on deleting ElementTree.Element
     attributes.

   - bpo-25624(42): ZipFile now always writes a ZIP_STORED header for
     directory entries.  Patch by Dingyuan Wang.

   - Skip getaddrinfo if host is already resolved.  Patch by A. Jesse
     Jiryu Davis.

   - bpo-26050(43): Add asyncio.StreamReader.readuntil() method.  Patch
     by Марк Коренберг.

   - bpo-25924(44): Avoid unnecessary serialization of getaddrinfo(3)
     calls on OS X versions 10.5 or higher.  Original patch by A. Jesse
     Jiryu Davis.

   - bpo-26406(45): Avoid unnecessary serialization of getaddrinfo(3)
     calls on current versions of OpenBSD and NetBSD. Patch by A. Jesse
     Jiryu Davis.

   - bpo-26848(46): Fix asyncio/subprocess.communicate() to handle empty
     input.  Patch by Jack O’Connor.

   - bpo-27040(47): Add loop.get_exception_handler method

   - bpo-27041(48): asyncio: Add loop.create_future method

   - bpo-27223(49): asyncio: Fix _read_ready and _write_ready to respect
     _conn_lost.  Patch by Łukasz Langa.

   - bpo-22970(50): asyncio: Fix inconsistency cancelling
     Condition.wait.  Patch by David Coles.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25995

   (2) https://bugs.python.org/issue26117

   (3) https://bugs.python.org/issue25911

   (4) https://bugs.python.org/issue26045

   (5) https://bugs.python.org/issue12923

   (6) https://bugs.python.org/issue25945

   (7) https://bugs.python.org/issue26202

   (8) https://bugs.python.org/issue23076

   (9) https://bugs.python.org/issue19883

   (10) https://bugs.python.org/issue26227

   (11) https://bugs.python.org/issue26147

   (12) https://bugs.python.org/issue25935

   (13) https://bugs.python.org/issue16620

   (14) https://bugs.python.org/issue26013

   (15) https://bugs.python.org/issue25850

   (16) https://bugs.python.org/issue17633

   (17) https://bugs.python.org/issue24705

   (18) https://bugs.python.org/issue22138

   (19) https://bugs.python.org/issue25672

   (20) https://bugs.python.org/issue26012

   (21) https://bugs.python.org/issue24120

   (22) https://bugs.python.org/issue25447

   (23) https://bugs.python.org/issue25447

   (24) https://bugs.python.org/issue24103

   (25) https://bugs.python.org/issue25860

   (26) https://bugs.python.org/issue25914

   (27) https://bugs.python.org/issue25902

   (28) https://bugs.python.org/issue25717

   (29) https://bugs.python.org/issue24903

   (30) https://bugs.python.org/issue25764

   (31) https://bugs.python.org/issue6478

   (32) https://bugs.python.org/issue14285

   (33) https://bugs.python.org/issue19771

   (34) https://bugs.python.org/issue25177

   (35) https://bugs.python.org/issue25718

   (36) https://bugs.python.org/issue10131

   (37) https://bugs.python.org/issue25725

   (38) https://bugs.python.org/issue25663

   (39) https://bugs.python.org/issue25688

   (40) https://bugs.python.org/issue23914

   (41) https://bugs.python.org/issue25691

   (42) https://bugs.python.org/issue25624

   (43) https://bugs.python.org/issue26050

   (44) https://bugs.python.org/issue25924

   (45) https://bugs.python.org/issue26406

   (46) https://bugs.python.org/issue26848

   (47) https://bugs.python.org/issue27040

   (48) https://bugs.python.org/issue27041

   (49) https://bugs.python.org/issue27223

   (50) https://bugs.python.org/issue22970


File: python.info,  Node: IDLE<46>,  Next: Documentation<49>,  Prev: Library<76>,  Up: Python 3 5 2 release candidate 1

1.19.74.12 IDLE
...............

   - bpo-5124(1): Paste with text selected now replaces the selection on
     X11.  This matches how paste works on Windows, Mac, most modern
     Linux apps, and ttk widgets.  Original patch by Serhiy Storchaka.

   - bpo-24759(2): Make clear in idlelib.idle_test.__init__ that the
     directory is a private implementation of test.test_idle and tool
     for maintainers.

   - bpo-27196(3): Stop ‘ThemeChanged’ warnings when running IDLE tests.
     These persisted after other warnings were suppressed in #20567.
     Apply Serhiy Storchaka’s update_idletasks solution to four test
     files.  Record this additional advice in idle_test/README.txt

   - bpo-20567(4): Revise idle_test/README.txt with advice about
     avoiding tk warning messages from tests.  Apply advice to several
     IDLE tests.

   - bpo-27117(5): Make colorizer htest and turtledemo work with dark
     themes.  Move code for configuring text widget colors to a new
     function.

   - bpo-26673(6): When tk reports font size as 0, change to size 10.
     Such fonts on Linux prevented the configuration dialog from
     opening.

   - bpo-21939(7): Add test for IDLE’s percolator.  Original patch by
     Saimadhav Heblikar.

   - bpo-21676(8): Add test for IDLE’s replace dialog.  Original patch
     by Saimadhav Heblikar.

   - bpo-18410(9): Add test for IDLE’s search dialog.  Original patch by
     Westley Martínez.

   - bpo-21703(10): Add test for IDLE’s undo delegator.  Original patch
     by Saimadhav Heblikar .

   - bpo-27044(11): Add ConfigDialog.remove_var_callbacks to stop memory
     leaks.

   - bpo-23977(12): Add more asserts to test_delegator.

   - bpo-20640(13): Add tests for idlelib.configHelpSourceEdit.  Patch
     by Saimadhav Heblikar.

   - In the ‘IDLE-console differences’ section of the IDLE doc, clarify
     how running with IDLE affects sys.modules and the standard streams.

   - bpo-25507(14): fix incorrect change in IOBinding that prevented
     printing.  Augment IOBinding htest to include all major IOBinding
     functions.

   - bpo-25905(15): Revert unwanted conversion of ‘ to ’ RIGHT SINGLE
     QUOTATION MARK in README.txt and open this and NEWS.txt with
     ‘ascii’.  Re-encode CREDITS.txt to utf-8 and open it with ‘utf-8’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5124

   (2) https://bugs.python.org/issue24759

   (3) https://bugs.python.org/issue27196

   (4) https://bugs.python.org/issue20567

   (5) https://bugs.python.org/issue27117

   (6) https://bugs.python.org/issue26673

   (7) https://bugs.python.org/issue21939

   (8) https://bugs.python.org/issue21676

   (9) https://bugs.python.org/issue18410

   (10) https://bugs.python.org/issue21703

   (11) https://bugs.python.org/issue27044

   (12) https://bugs.python.org/issue23977

   (13) https://bugs.python.org/issue20640

   (14) https://bugs.python.org/issue25507

   (15) https://bugs.python.org/issue25905


File: python.info,  Node: Documentation<49>,  Next: Tests<51>,  Prev: IDLE<46>,  Up: Python 3 5 2 release candidate 1

1.19.74.13 Documentation
........................

   - bpo-19489(1): Moved the search box from the sidebar to the header
     and footer of each page.  Patch by Ammar Askar.

   - bpo-24136(2): Document the new PEP 448(3) unpacking syntax of 3.5.

   - bpo-26736(4): Used HTTPS for external links in the documentation if
     possible.

   - bpo-6953(5): Rework the Readline module documentation to group
     related functions together, and add more details such as what
     underlying Readline functions and variables are accessed.

   - bpo-23606(6): Adds note to ctypes documentation regarding
     cdll.msvcrt.

   - bpo-25500(7): Fix documentation to not claim that __import__ is
     searched for in the global scope.

   - bpo-26014(8): Update 3.x packaging documentation: * “See also”
     links to the new docs are now provided in the legacy pages * links
     to setuptools documentation have been updated

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19489

   (2) https://bugs.python.org/issue24136

   (3) https://www.python.org/dev/peps/pep-0448

   (4) https://bugs.python.org/issue26736

   (5) https://bugs.python.org/issue6953

   (6) https://bugs.python.org/issue23606

   (7) https://bugs.python.org/issue25500

   (8) https://bugs.python.org/issue26014


File: python.info,  Node: Tests<51>,  Next: Build<53>,  Prev: Documentation<49>,  Up: Python 3 5 2 release candidate 1

1.19.74.14 Tests
................

   - bpo-21916(1): Added tests for the turtle module.  Patch by ingrid,
     Gregory Loyse and Jelle Zijlstra.

   - bpo-26523(2): The multiprocessing thread pool
     (multiprocessing.dummy.Pool) was untested.

   - bpo-26015(3): Added new tests for pickling iterators of mutable
     sequences.

   - bpo-26325(4): Added test.support.check_no_resource_warning() to
     check that no ResourceWarning is emitted.

   - bpo-25940(5): Changed test_ssl to use self-signed.pythontest.net.
     This avoids relying on svn.python.org, which recently changed root
     certificate.

   - bpo-25616(6): Tests for OrderedDict are extracted from
     test_collections into separate file test_ordered_dict.

   - bpo-26583(7): Skip test_timestamp_overflow in test_import if
     bytecode files cannot be written.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21916

   (2) https://bugs.python.org/issue26523

   (3) https://bugs.python.org/issue26015

   (4) https://bugs.python.org/issue26325

   (5) https://bugs.python.org/issue25940

   (6) https://bugs.python.org/issue25616

   (7) https://bugs.python.org/issue26583


File: python.info,  Node: Build<53>,  Next: Windows<49>,  Prev: Tests<51>,  Up: Python 3 5 2 release candidate 1

1.19.74.15 Build
................

   - bpo-26884(1): Fix linking extension modules for cross builds.
     Patch by Xavier de Gaye.

   - bpo-22359(2): Disable the rules for running _freeze_importlib and
     pgen when cross-compiling.  The output of these programs is
     normally saved with the source code anyway, and is still
     regenerated when doing a native build.  Patch by Xavier de Gaye.

   - bpo-27229(3): Fix the cross-compiling pgen rule for in-tree builds.
     Patch by Xavier de Gaye.

   - bpo-21668(4): Link audioop, _datetime, _ctypes_test modules to
     libm, except on Mac OS X. Patch written by Xavier de Gaye.

   - bpo-25702(5): A –with-lto configure option has been added that will
     enable link time optimizations at build time during a make
     profile-opt.  Some compilers and toolchains are known to not
     produce stable code when using LTO, be sure to test things
     thoroughly before relying on it.  It can provide a few % speed up
     over profile-opt alone.

   - bpo-26624(6): Adds validation of ucrtbase[d].dll version with
     warning for old versions.

   - bpo-17603(7): Avoid error about nonexistent fileblocks.o file by
     using a lower-level check for st_blocks in struct stat.

   - bpo-26079(8): Fixing the build output folder for tix-8.4.3.6.
     Patch by Bjoern Thiel.

   - bpo-26465(9): Update Windows builds to use OpenSSL 1.0.2g.

   - bpo-24421(10): Compile Modules/_math.c once, before building
     extensions.  Previously it could fail to compile properly if the
     math and cmath builds were concurrent.

   - bpo-25348(11): Added ‘--pgo’ and ‘--pgo-job’ arguments to
     ‘PCbuild\build.bat’ for building with Profile-Guided Optimization.
     The old ‘PCbuild\build_pgo.bat’ script is now deprecated, and
     simply calls ‘PCbuild\build.bat --pgo %*’.

   - bpo-25827(12): Add support for building with ICC to ‘configure’,
     including a new ‘--with-icc’ flag.

   - bpo-25696(13): Fix installation of Python on UNIX with make -j9.

   - bpo-26930(14): Update OS X 10.5+ 32-bit-only installer to build and
     link with OpenSSL 1.0.2h.

   - bpo-26268(15): Update Windows builds to use OpenSSL 1.0.2f.

   - bpo-25136(16): Support Apple Xcode 7’s new textual SDK stub
     libraries.

   - bpo-24324(17): Do not enable unreachable code warnings when using
     gcc as the option does not work correctly in older versions of gcc
     and has been silently removed as of gcc-4.5.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26884

   (2) https://bugs.python.org/issue22359

   (3) https://bugs.python.org/issue27229

   (4) https://bugs.python.org/issue21668

   (5) https://bugs.python.org/issue25702

   (6) https://bugs.python.org/issue26624

   (7) https://bugs.python.org/issue17603

   (8) https://bugs.python.org/issue26079

   (9) https://bugs.python.org/issue26465

   (10) https://bugs.python.org/issue24421

   (11) https://bugs.python.org/issue25348

   (12) https://bugs.python.org/issue25827

   (13) https://bugs.python.org/issue25696

   (14) https://bugs.python.org/issue26930

   (15) https://bugs.python.org/issue26268

   (16) https://bugs.python.org/issue25136

   (17) https://bugs.python.org/issue24324


File: python.info,  Node: Windows<49>,  Next: Tools/Demos<30>,  Prev: Build<53>,  Up: Python 3 5 2 release candidate 1

1.19.74.16 Windows
..................

   - bpo-27053(1): Updates make_zip.py to correctly generate library ZIP
     file.

   - bpo-26268(2): Update the prepare_ssl.py script to handle OpenSSL
     releases that don’t include the contents of the include directory
     (that is, 1.0.2e and later).

   - bpo-26071(3): bdist_wininst created binaries fail to start and find
     32bit Python

   - bpo-26073(4): Update the list of magic numbers in launcher

   - bpo-26065(5): Excludes venv from library when generating embeddable
     distro.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue27053

   (2) https://bugs.python.org/issue26268

   (3) https://bugs.python.org/issue26071

   (4) https://bugs.python.org/issue26073

   (5) https://bugs.python.org/issue26065


File: python.info,  Node: Tools/Demos<30>,  Next: Windows<50>,  Prev: Windows<49>,  Up: Python 3 5 2 release candidate 1

1.19.74.17 Tools/Demos
......................

   - bpo-26799(1): Fix python-gdb.py: don’t get C types once when the
     Python code is loaded, but get C types on demand.  The C types can
     change if python-gdb.py is loaded before the Python executable.
     Patch written by Thomas Ilsche.

   - bpo-26271(2): Fix the Freeze tool to properly use flags passed
     through configure.  Patch by Daniel Shaulov.

   - bpo-26489(3): Add dictionary unpacking support to
     Tools/parser/unparse.py.  Patch by Guo Ci Teo.

   - bpo-26316(4): Fix variable name typo in Argument Clinic.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue26799

   (2) https://bugs.python.org/issue26271

   (3) https://bugs.python.org/issue26489

   (4) https://bugs.python.org/issue26316


File: python.info,  Node: Windows<50>,  Prev: Tools/Demos<30>,  Up: Python 3 5 2 release candidate 1

1.19.74.18 Windows
..................

   - bpo-17500(1): Remove unused and outdated icons.  (See also:
     ‘https://github.com/python/pythondotorg/issues/945’)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue17500


File: python.info,  Node: Python 3 5 1 final,  Next: Python 3 5 1 release candidate 1,  Prev: Python 3 5 2 release candidate 1,  Up: Changelog

1.19.75 Python 3.5.1 final
--------------------------

`Release date: 2015-12-06'

* Menu:

* Core and Builtins: Core and Builtins<61>.
* Windows: Windows<51>.


File: python.info,  Node: Core and Builtins<61>,  Next: Windows<51>,  Up: Python 3 5 1 final

1.19.75.1 Core and Builtins
...........................

   - bpo-25709(1): Fixed problem with in-place string concatenation and
     utf-8 cache.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25709


File: python.info,  Node: Windows<51>,  Prev: Core and Builtins<61>,  Up: Python 3 5 1 final

1.19.75.2 Windows
.................

   - bpo-25715(1): Python 3.5.1 installer shows wrong upgrade path and
     incorrect logic for launcher detection.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25715


File: python.info,  Node: Python 3 5 1 release candidate 1,  Next: Python 3 5 0 final,  Prev: Python 3 5 1 final,  Up: Changelog

1.19.76 Python 3.5.1 release candidate 1
----------------------------------------

`Release date: 2015-11-22'

* Menu:

* Core and Builtins: Core and Builtins<62>.
* Library: Library<77>.
* IDLE: IDLE<47>.
* Documentation: Documentation<50>.
* Tests: Tests<52>.
* Build: Build<54>.
* Windows: Windows<52>.
* Tools/Demos: Tools/Demos<31>.


File: python.info,  Node: Core and Builtins<62>,  Next: Library<77>,  Up: Python 3 5 1 release candidate 1

1.19.76.1 Core and Builtins
...........................

   - bpo-25630(1): Fix a possible segfault during argument parsing in
     functions that accept filesystem paths.

   - bpo-23564(2): Fixed a partially broken sanity check in the
     _posixsubprocess internals regarding how fds_to_pass were passed to
     the child.  The bug had no actual impact as subprocess.py already
     avoided it.

   - bpo-25388(3): Fixed tokenizer crash when processing undecodable
     source code with a null byte.

   - bpo-25462(4): The hash of the key now is calculated only once in
     most operations in C implementation of OrderedDict.

   - bpo-22995(5): Default implementation of __reduce__ and
     __reduce_ex__ now rejects builtin types with not defined __new__.

   - bpo-25555(6): Fix parser and AST: fill lineno and col_offset of
     “arg” node when compiling AST from Python objects.

   - bpo-24802(7): Avoid buffer overreads when int(), float(),
     compile(), exec() and eval() are passed bytes-like objects.  These
     objects are not necessarily terminated by a null byte, but the
     functions assumed they were.

   - bpo-24726(8): Fixed a crash and leaking NULL in repr() of
     OrderedDict that was mutated by direct calls of dict methods.

   - bpo-25449(9): Iterating OrderedDict with keys with unstable hash
     now raises KeyError in C implementations as well as in Python
     implementation.

   - bpo-25395(10): Fixed crash when highly nested OrderedDict
     structures were garbage collected.

   - bpo-25274(11): sys.setrecursionlimit() now raises a RecursionError
     if the new recursion limit is too low depending at the current
     recursion depth.  Modify also the “lower-water mark” formula to
     make it monotonic.  This mark is used to decide when the overflowed
     flag of the thread state is reset.

   - bpo-24402(12): Fix input() to prompt to the redirected stdout when
     sys.stdout.fileno() fails.

   - bpo-24806(13): Prevent builtin types that are not allowed to be
     subclassed from being subclassed through multiple inheritance.

   - bpo-24848(14): Fixed a number of bugs in UTF-7 decoding of
     misformed data.

   - bpo-25280(15): Import trace messages emitted in verbose (-v) mode
     are no longer formatted twice.

   - bpo-25003(16): On Solaris 11.3 or newer, os.urandom() now uses the
     getrandom() function instead of the getentropy() function.  The
     getentropy() function is blocking to generate very good quality
     entropy, os.urandom() doesn’t need such high-quality entropy.

   - bpo-25182(17): The stdprinter (used as sys.stderr before the io
     module is imported at startup) now uses the backslashreplace error
     handler.

   - bpo-25131(18): Make the line number and column offset of set/dict
     literals and comprehensions correspond to the opening brace.

   - bpo-25150(19): Hide the private _Py_atomic_xxx symbols from the
     public Python.h header to fix a compilation error with OpenMP.
     PyThreadState_GET() becomes an alias to PyThreadState_Get() to
     avoid ABI incompatibilities.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25630

   (2) https://bugs.python.org/issue23564

   (3) https://bugs.python.org/issue25388

   (4) https://bugs.python.org/issue25462

   (5) https://bugs.python.org/issue22995

   (6) https://bugs.python.org/issue25555

   (7) https://bugs.python.org/issue24802

   (8) https://bugs.python.org/issue24726

   (9) https://bugs.python.org/issue25449

   (10) https://bugs.python.org/issue25395

   (11) https://bugs.python.org/issue25274

   (12) https://bugs.python.org/issue24402

   (13) https://bugs.python.org/issue24806

   (14) https://bugs.python.org/issue24848

   (15) https://bugs.python.org/issue25280

   (16) https://bugs.python.org/issue25003

   (17) https://bugs.python.org/issue25182

   (18) https://bugs.python.org/issue25131

   (19) https://bugs.python.org/issue25150


File: python.info,  Node: Library<77>,  Next: IDLE<47>,  Prev: Core and Builtins<62>,  Up: Python 3 5 1 release candidate 1

1.19.76.2 Library
.................

   - bpo-25626(1): Change three zlib functions to accept sizes that fit
     in Py_ssize_t, but internally cap those sizes to UINT_MAX. This
     resolves a regression in 3.5 where GzipFile.read() failed to read
     chunks larger than 2 or 4 GiB. The change affects the
     zlib.Decompress.decompress() max_length parameter, the
     zlib.decompress() bufsize parameter, and the
     zlib.Decompress.flush() length parameter.

   - bpo-25583(2): Avoid incorrect errors raised by
     os.makedirs(exist_ok=True) when the OS gives priority to errors
     such as EACCES over EEXIST.

   - bpo-25593(3): Change semantics of EventLoop.stop() in asyncio.

   - bpo-6973(4): When we know a subprocess.Popen process has died, do
     not allow the send_signal(), terminate(), or kill() methods to do
     anything as they could potentially signal a different process.

   - bpo-25590(5): In the Readline completer, only call getattr() once
     per attribute.

   - bpo-25498(6): Fix a crash when garbage-collecting ctypes objects
     created by wrapping a memoryview.  This was a regression made in
     3.5a1.  Based on patch by Eryksun.

   - bpo-25584(7): Added “escape” to the __all__ list in the glob
     module.

   - bpo-25584(8): Fixed recursive glob() with patterns starting with
     ‘**’.

   - bpo-25446(9): Fix regression in smtplib’s AUTH LOGIN support.

   - bpo-18010(10): Fix the pydoc web server’s module search function to
     handle exceptions from importing packages.

   - bpo-25554(11): Got rid of circular references in regular expression
     parsing.

   - bpo-25510(12): fileinput.FileInput.readline() now returns b’’
     instead of ‘’ at the end if the FileInput was opened with binary
     mode.  Patch by Ryosuke Ito.

   - bpo-25503(13): Fixed inspect.getdoc() for inherited docstrings of
     properties.  Original patch by John Mark Vandenberg.

   - bpo-25515(14): Always use os.urandom as a source of randomness in
     uuid.uuid4.

   - bpo-21827(15): Fixed textwrap.dedent() for the case when largest
     common whitespace is a substring of smallest leading whitespace.
     Based on patch by Robert Li.

   - bpo-25447(16): The lru_cache() wrapper objects now can be copied
     and pickled (by returning the original object unchanged).

   - bpo-25390(17): typing: Don’t crash on Union[str, Pattern].

   - bpo-25441(18): asyncio: Raise error from drain() when socket is
     closed.

   - bpo-25410(19): Cleaned up and fixed minor bugs in C implementation
     of OrderedDict.

   - bpo-25411(20): Improved Unicode support in SMTPHandler through
     better use of the email package.  Thanks to user simon04 for the
     patch.

   - bpo-25407(21): Remove mentions of the formatter module being
     removed in Python 3.6.

   - bpo-25406(22): Fixed a bug in C implementation of
     OrderedDict.move_to_end() that caused segmentation fault or hang in
     iterating after moving several items to the start of ordered dict.

   - bpo-25364(23): zipfile now works in threads disabled builds.

   - bpo-25328(24): smtpd’s SMTPChannel now correctly raises a
     ValueError if both decode_data and enable_SMTPUTF8 are set to true.

   - bpo-25316(25): distutils raises OSError instead of
     DistutilsPlatformError when MSVC is not installed.

   - bpo-25380(26): Fixed protocol for the STACK_GLOBAL opcode in
     pickletools.opcodes.

   - bpo-23972(27): Updates asyncio datagram create method allowing
     reuseport and reuseaddr socket options to be set prior to binding
     the socket.  Mirroring the existing asyncio create_server method
     the reuseaddr option for datagram sockets defaults to True if the
     O/S is ‘posix’ (except if the platform is Cygwin).  Patch by Chris
     Laws.

   - bpo-25304(28): Add asyncio.run_coroutine_threadsafe().  This lets
     you submit a coroutine to a loop from another thread, returning a
     concurrent.futures.Future.  By Vincent Michel.

   - bpo-25232(29): Fix CGIRequestHandler to split the query from the
     URL at the first question mark (?)  rather than the last.  Patch
     from Xiang Zhang.

   - bpo-24657(30): Prevent CGIRequestHandler from collapsing slashes in
     the query part of the URL as if it were a path.  Patch from Xiang
     Zhang.

   - bpo-24483(31): C implementation of functools.lru_cache() now
     calculates key’s hash only once.

   - bpo-22958(32): Constructor and update method of
     weakref.WeakValueDictionary now accept the self and the dict
     keyword arguments.

   - bpo-22609(33): Constructor of collections.UserDict now accepts the
     self keyword argument.

   - bpo-25111(34): Fixed comparison of traceback.FrameSummary.

   - bpo-25262(35): Added support for BINBYTES8 opcode in Python
     implementation of unpickler.  Highest 32 bits of 64-bit size for
     BINUNICODE8 and BINBYTES8 opcodes no longer silently ignored on
     32-bit platforms in C implementation.

   - bpo-25034(36): Fix string.Formatter problem with auto-numbering and
     nested format_specs.  Patch by Anthon van der Neut.

   - bpo-25233(37): Rewrite the guts of asyncio.Queue and
     asyncio.Semaphore to be more understandable and correct.

   - bpo-25203(38): Failed readline.set_completer_delims() no longer
     left the module in inconsistent state.

   - bpo-23600(39): Default implementation of tzinfo.fromutc() was
     returning wrong results in some cases.

   - bpo-23329(40): Allow the ssl module to be built with older versions
     of LibreSSL.

   - Prevent overflow in _Unpickler_Read.

   - bpo-25047(41): The XML encoding declaration written by Element Tree
     now respects the letter case given by the user.  This restores the
     ability to write encoding names in uppercase like “UTF-8”, which
     worked in Python 2.

   - bpo-25135(42): Make deque_clear() safer by emptying the deque
     before clearing.  This helps avoid possible reentrancy issues.

   - bpo-19143(43): platform module now reads Windows version from
     kernel32.dll to avoid compatibility shims.

   - bpo-25092(44): Fix datetime.strftime() failure when errno was
     already set to EINVAL.

   - bpo-23517(45): Fix rounding in fromtimestamp() and
     utcfromtimestamp() methods of datetime.datetime: microseconds are
     now rounded to nearest with ties going to nearest even integer
     (ROUND_HALF_EVEN), instead of being rounding towards minus infinity
     (ROUND_FLOOR). It’s important that these methods use the same
     rounding mode than datetime.timedelta to keep the property:
     (datetime(1970,1,1) + timedelta(seconds=t)) ==
     datetime.utcfromtimestamp(t).  It also the rounding mode used by
     round(float) for example.

   - bpo-25155(46): Fix datetime.datetime.now() and
     datetime.datetime.utcnow() on Windows to support date after year
     2038.  It was a regression introduced in Python 3.5.0.

   - bpo-25108(47): Omitted internal frames in traceback functions
     print_stack(), format_stack(), and extract_stack() called without
     arguments.

   - bpo-25118(48): Fix a regression of Python 3.5.0 in os.waitpid() on
     Windows.

   - bpo-24684(49): socket.socket.getaddrinfo() now calls
     PyUnicode_AsEncodedString() instead of calling the encode() method
     of the host, to handle correctly custom string with an encode()
     method which doesn’t return a byte string.  The encoder of the IDNA
     codec is now called directly instead of calling the encode() method
     of the string.

   - bpo-25060(50): Correctly compute stack usage of the BUILD_MAP
     opcode.

   - bpo-24857(51): Comparing call_args to a long sequence now correctly
     returns a boolean result instead of raising an exception.  Patch by
     A Kaptur.

   - bpo-23144(52): Make sure that HTMLParser.feed() returns all the
     data, even when convert_charrefs is True.

   - bpo-24982(53): shutil.make_archive() with the “zip” format now adds
     entries for directories (including empty directories) in ZIP file.

   - bpo-25019(54): Fixed a crash caused by setting non-string key of
     expat parser.  Based on patch by John Leitch.

   - bpo-16180(55): Exit pdb if file has syntax error, instead of
     trapping user in an infinite loop.  Patch by Xavier de Gaye.

   - bpo-24891(56): Fix a race condition at Python startup if the file
     descriptor of stdin (0), stdout (1) or stderr (2) is closed while
     Python is creating sys.stdin, sys.stdout and sys.stderr objects.
     These attributes are now set to None if the creation of the object
     failed, instead of raising an OSError exception.  Initial patch
     written by Marco Paolini.

   - bpo-24992(57): Fix error handling and a race condition (related to
     garbage collection) in collections.OrderedDict constructor.

   - bpo-24881(58): Fixed setting binary mode in Python implementation
     of FileIO on Windows and Cygwin.  Patch from Akira Li.

   - bpo-25578(59): Fix (another) memory leak in SSLSocket.getpeercer().

   - bpo-25530(60): Disable the vulnerable SSLv3 protocol by default
     when creating ssl.SSLContext.

   - bpo-25569(61): Fix memory leak in SSLSocket.getpeercert().

   - bpo-25471(62): Sockets returned from accept() shouldn’t appear to
     be nonblocking.

   - bpo-25319(63): When threading.Event is reinitialized, the
     underlying condition should use a regular lock rather than a
     recursive lock.

   - bpo-21112(64): Fix regression in unittest.expectedFailure on
     subclasses.  Patch from Berker Peksag.

   - bpo-24764(65): cgi.FieldStorage.read_multi() now ignores the
     Content-Length header in part headers.  Patch written by Peter
     Landry and reviewed by Pierre Quentel.

   - bpo-24913(66): Fix overrun error in deque.index().  Found by John
     Leitch and Bryce Darling.

   - bpo-24774(67): Fix docstring in http.server.test.  Patch from
     Chiu-Hsiang Hsu.

   - bpo-21159(68): Improve message in
     configparser.InterpolationMissingOptionError.  Patch from Łukasz
     Langa.

   - bpo-20362(69): Honour TestCase.longMessage correctly in
     assertRegex.  Patch from Ilia Kurenkov.

   - bpo-23572(70): Fixed functools.singledispatch on classes with falsy
     metaclasses.  Patch by Ethan Furman.

   - asyncio: ensure_future() now accepts awaitable objects.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25626

   (2) https://bugs.python.org/issue25583

   (3) https://bugs.python.org/issue25593

   (4) https://bugs.python.org/issue6973

   (5) https://bugs.python.org/issue25590

   (6) https://bugs.python.org/issue25498

   (7) https://bugs.python.org/issue25584

   (8) https://bugs.python.org/issue25584

   (9) https://bugs.python.org/issue25446

   (10) https://bugs.python.org/issue18010

   (11) https://bugs.python.org/issue25554

   (12) https://bugs.python.org/issue25510

   (13) https://bugs.python.org/issue25503

   (14) https://bugs.python.org/issue25515

   (15) https://bugs.python.org/issue21827

   (16) https://bugs.python.org/issue25447

   (17) https://bugs.python.org/issue25390

   (18) https://bugs.python.org/issue25441

   (19) https://bugs.python.org/issue25410

   (20) https://bugs.python.org/issue25411

   (21) https://bugs.python.org/issue25407

   (22) https://bugs.python.org/issue25406

   (23) https://bugs.python.org/issue25364

   (24) https://bugs.python.org/issue25328

   (25) https://bugs.python.org/issue25316

   (26) https://bugs.python.org/issue25380

   (27) https://bugs.python.org/issue23972

   (28) https://bugs.python.org/issue25304

   (29) https://bugs.python.org/issue25232

   (30) https://bugs.python.org/issue24657

   (31) https://bugs.python.org/issue24483

   (32) https://bugs.python.org/issue22958

   (33) https://bugs.python.org/issue22609

   (34) https://bugs.python.org/issue25111

   (35) https://bugs.python.org/issue25262

   (36) https://bugs.python.org/issue25034

   (37) https://bugs.python.org/issue25233

   (38) https://bugs.python.org/issue25203

   (39) https://bugs.python.org/issue23600

   (40) https://bugs.python.org/issue23329

   (41) https://bugs.python.org/issue25047

   (42) https://bugs.python.org/issue25135

   (43) https://bugs.python.org/issue19143

   (44) https://bugs.python.org/issue25092

   (45) https://bugs.python.org/issue23517

   (46) https://bugs.python.org/issue25155

   (47) https://bugs.python.org/issue25108

   (48) https://bugs.python.org/issue25118

   (49) https://bugs.python.org/issue24684

   (50) https://bugs.python.org/issue25060

   (51) https://bugs.python.org/issue24857

   (52) https://bugs.python.org/issue23144

   (53) https://bugs.python.org/issue24982

   (54) https://bugs.python.org/issue25019

   (55) https://bugs.python.org/issue16180

   (56) https://bugs.python.org/issue24891

   (57) https://bugs.python.org/issue24992

   (58) https://bugs.python.org/issue24881

   (59) https://bugs.python.org/issue25578

   (60) https://bugs.python.org/issue25530

   (61) https://bugs.python.org/issue25569

   (62) https://bugs.python.org/issue25471

   (63) https://bugs.python.org/issue25319

   (64) https://bugs.python.org/issue21112

   (65) https://bugs.python.org/issue24764

   (66) https://bugs.python.org/issue24913

   (67) https://bugs.python.org/issue24774

   (68) https://bugs.python.org/issue21159

   (69) https://bugs.python.org/issue20362

   (70) https://bugs.python.org/issue23572


File: python.info,  Node: IDLE<47>,  Next: Documentation<50>,  Prev: Library<77>,  Up: Python 3 5 1 release candidate 1

1.19.76.3 IDLE
..............

   - bpo-15348(1): Stop the debugger engine (normally in a user process)
     before closing the debugger window (running in the IDLE process).
     This prevents the RuntimeErrors that were being caught and ignored.

   - bpo-24455(2): Prevent IDLE from hanging when a) closing the shell
     while the debugger is active (15347); b) closing the debugger with
     the [X] button (15348); and c) activating the debugger when already
     active (24455).  The patch by Mark Roseman does this by making two
     changes.  1.  Suspend and resume the gui.interaction method with
     the tcl vwait mechanism intended for this purpose (instead of
     root.mainloop & .quit).  2.  In gui.run, allow any existing
     interaction to terminate first.

   - Change ‘The program’ to ‘Your program’ in an IDLE ‘kill program?’
     message to make it clearer that the program referred to is the
     currently running user program, not IDLE itself.

   - bpo-24750(3): Improve the appearance of the IDLE editor window
     status bar.  Patch by Mark Roseman.

   - bpo-25313(4): Change the handling of new built-in text color themes
     to better address the compatibility problem introduced by the
     addition of IDLE Dark.  Consistently use the revised
     idleConf.CurrentTheme everywhere in idlelib.

   - bpo-24782(5): Extension configuration is now a tab in the IDLE
     Preferences dialog rather than a separate dialog.  The former tabs
     are now a sorted list.  Patch by Mark Roseman.

   - bpo-22726(6): Re-activate the config dialog help button with some
     content about the other buttons and the new IDLE Dark theme.

   - bpo-24820(7): IDLE now has an ‘IDLE Dark’ built-in text color
     theme.  It is more or less IDLE Classic inverted, with a cobalt
     blue background.  Strings, comments, keywords, … are still green,
     red, orange, … .  To use it with IDLEs released before November
     2015, hit the ‘Save as New Custom Theme’ button and enter a new
     name, such as ‘Custom Dark’.  The custom theme will work with any
     IDLE release, and can be modified.

   - bpo-25224(8): README.txt is now an idlelib index for IDLE
     developers and curious users.  The previous user content is now in
     the IDLE doc chapter.  ‘IDLE’ now means ‘Integrated Development and
     Learning Environment’.

   - bpo-24820(9): Users can now set breakpoint colors in Settings ->
     Custom Highlighting.  Original patch by Mark Roseman.

   - bpo-24972(10): Inactive selection background now matches active
     selection background, as configured by users, on all systems.
     Found items are now always highlighted on Windows.  Initial patch
     by Mark Roseman.

   - bpo-24570(11): Idle: make calltip and completion boxes appear on
     Macs affected by a tk regression.  Initial patch by Mark Roseman.

   - bpo-24988(12): Idle ScrolledList context menus (used in debugger)
     now work on Mac Aqua.  Patch by Mark Roseman.

   - bpo-24801(13): Make right-click for context menu work on Mac Aqua.
     Patch by Mark Roseman.

   - bpo-25173(14): Associate tkinter messageboxes with a specific
     widget.  For Mac OSX, make them a ‘sheet’.  Patch by Mark Roseman.

   - bpo-25198(15): Enhance the initial html viewer now used for Idle
     Help.  Properly indent fixed-pitch text (patch by Mark Roseman).
     Give code snippet a very Sphinx-like light blueish-gray background.
     Re-use initial width and height set by users for shell and editor.
     When the Table of Contents (TOC) menu is used, put the section
     header at the top of the screen.

   - bpo-25225(16): Condense and rewrite Idle doc section on text
     colors.

   - bpo-21995(17): Explain some differences between IDLE and console
     Python.

   - bpo-22820(18): Explain need for `print' when running file from Idle
     editor.

   - bpo-25224(19): Doc: augment Idle feature list and no-subprocess
     section.

   - bpo-25219(20): Update doc for Idle command line options.  Some were
     missing and notes were not correct.

   - bpo-24861(21): Most of idlelib is private and subject to change.
     Use idleib.idle.* to start Idle.  See idlelib.__init__.__doc__.

   - bpo-25199(22): Idle: add synchronization comments for future
     maintainers.

   - bpo-16893(23): Replace help.txt with help.html for Idle doc
     display.  The new idlelib/help.html is rstripped
     Doc/build/html/library/idle.html.  It looks better than help.txt
     and will better document Idle as released.  The tkinter html viewer
     that works for this file was written by Mark Roseman.  The now
     unused EditorWindow.HelpDialog class and helt.txt file are
     deprecated.

   - bpo-24199(24): Deprecate unused idlelib.idlever with possible
     removal in 3.6.

   - bpo-24790(25): Remove extraneous code (which also create 2 & 3
     conflicts).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15348

   (2) https://bugs.python.org/issue24455

   (3) https://bugs.python.org/issue24750

   (4) https://bugs.python.org/issue25313

   (5) https://bugs.python.org/issue24782

   (6) https://bugs.python.org/issue22726

   (7) https://bugs.python.org/issue24820

   (8) https://bugs.python.org/issue25224

   (9) https://bugs.python.org/issue24820

   (10) https://bugs.python.org/issue24972

   (11) https://bugs.python.org/issue24570

   (12) https://bugs.python.org/issue24988

   (13) https://bugs.python.org/issue24801

   (14) https://bugs.python.org/issue25173

   (15) https://bugs.python.org/issue25198

   (16) https://bugs.python.org/issue25225

   (17) https://bugs.python.org/issue21995

   (18) https://bugs.python.org/issue22820

   (19) https://bugs.python.org/issue25224

   (20) https://bugs.python.org/issue25219

   (21) https://bugs.python.org/issue24861

   (22) https://bugs.python.org/issue25199

   (23) https://bugs.python.org/issue16893

   (24) https://bugs.python.org/issue24199

   (25) https://bugs.python.org/issue24790


File: python.info,  Node: Documentation<50>,  Next: Tests<52>,  Prev: IDLE<47>,  Up: Python 3 5 1 release candidate 1

1.19.76.4 Documentation
.......................

   - bpo-22558(1): Add remaining doc links to source code for
     Python-coded modules.  Patch by Yoni Lavi.

   - bpo-12067(2): Rewrite Comparisons section in the Expressions
     chapter of the language reference.  Some of the details of
     comparing mixed types were incorrect or ambiguous.  NotImplemented
     is only relevant at a lower level than the Expressions chapter.
     Added details of comparing range() objects, and default behaviour
     and consistency suggestions for user-defined classes.  Patch from
     Andy Maier.

   - bpo-24952(3): Clarify the default size argument of stack_size() in
     the “threading” and “_thread” modules.  Patch from Mattip.

   - bpo-23725(4): Overhaul tempfile docs.  Note deprecated status of
     mktemp.  Patch from Zbigniew Jędrzejewski-Szmek.

   - bpo-24808(5): Update the types of some PyTypeObject fields.  Patch
     by Joseph Weston.

   - bpo-22812(6): Fix unittest discovery examples.  Patch from Pam
     McA’Nulty.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22558

   (2) https://bugs.python.org/issue12067

   (3) https://bugs.python.org/issue24952

   (4) https://bugs.python.org/issue23725

   (5) https://bugs.python.org/issue24808

   (6) https://bugs.python.org/issue22812


File: python.info,  Node: Tests<52>,  Next: Build<54>,  Prev: Documentation<50>,  Up: Python 3 5 1 release candidate 1

1.19.76.5 Tests
...............

   - bpo-25449(1): Added tests for OrderedDict subclasses.

   - bpo-25099(2): Make test_compileall not fail when an entry on
     sys.path cannot be written to (commonly seen in administrative
     installs on Windows).

   - bpo-23919(3): Prevents assert dialogs appearing in the test suite.

   - ‘PCbuild\rt.bat’ now accepts an unlimited number of arguments to
     pass along to regrtest.py.  Previously there was a limit of 9.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25449

   (2) https://bugs.python.org/issue25099

   (3) https://bugs.python.org/issue23919


File: python.info,  Node: Build<54>,  Next: Windows<52>,  Prev: Tests<52>,  Up: Python 3 5 1 release candidate 1

1.19.76.6 Build
...............

   - bpo-24915(1): Add LLVM support for PGO builds and use the test
     suite to generate the profile data.  Initial patch by Alecsandru
     Patrascu of Intel.

   - bpo-24910(2): Windows MSIs now have unique display names.

   - bpo-24986(3): It is now possible to build Python on Windows without
     errors when external libraries are not available.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24915

   (2) https://bugs.python.org/issue24910

   (3) https://bugs.python.org/issue24986


File: python.info,  Node: Windows<52>,  Next: Tools/Demos<31>,  Prev: Build<54>,  Up: Python 3 5 1 release candidate 1

1.19.76.7 Windows
.................

   - bpo-25450(1): Updates shortcuts to start Python in installation
     directory.

   - bpo-25164(2): Changes default all-users install directory to match
     per-user directory.

   - bpo-25143(3): Improves installer error messages for unsupported
     platforms.

   - bpo-25163(4): Display correct directory in installer when using
     non-default settings.

   - bpo-25361(5): Disables use of SSE2 instructions in Windows 32-bit
     build

   - bpo-25089(6): Adds logging to installer for case where launcher is
     not selected on upgrade.

   - bpo-25165(7): Windows uninstallation should not remove launcher if
     other versions remain

   - bpo-25112(8): py.exe launcher is missing icons

   - bpo-25102(9): Windows installer does not precompile for -O or -OO.

   - bpo-25081(10): Makes Back button in installer go back to upgrade
     page when upgrading.

   - bpo-25091(11): Increases font size of the installer.

   - bpo-25126(12): Clarifies that the non-web installer will download
     some components.

   - bpo-25213(13): Restores requestedExecutionLevel to manifest to
     disable UAC virtualization.

   - bpo-25022(14): Removed very outdated PC/example_nt/ directory.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25450

   (2) https://bugs.python.org/issue25164

   (3) https://bugs.python.org/issue25143

   (4) https://bugs.python.org/issue25163

   (5) https://bugs.python.org/issue25361

   (6) https://bugs.python.org/issue25089

   (7) https://bugs.python.org/issue25165

   (8) https://bugs.python.org/issue25112

   (9) https://bugs.python.org/issue25102

   (10) https://bugs.python.org/issue25081

   (11) https://bugs.python.org/issue25091

   (12) https://bugs.python.org/issue25126

   (13) https://bugs.python.org/issue25213

   (14) https://bugs.python.org/issue25022


File: python.info,  Node: Tools/Demos<31>,  Prev: Windows<52>,  Up: Python 3 5 1 release candidate 1

1.19.76.8 Tools/Demos
.....................

   - bpo-25440(1): Fix output of python-config –extension-suffix.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25440


File: python.info,  Node: Python 3 5 0 final,  Next: Python 3 5 0 release candidate 4,  Prev: Python 3 5 1 release candidate 1,  Up: Changelog

1.19.77 Python 3.5.0 final
--------------------------

`Release date: 2015-09-13'

* Menu:

* Build: Build<55>.


File: python.info,  Node: Build<55>,  Up: Python 3 5 0 final

1.19.77.1 Build
...............

   - bpo-25071(1): Windows installer should not require TargetDir
     parameter when installing quietly.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25071


File: python.info,  Node: Python 3 5 0 release candidate 4,  Next: Python 3 5 0 release candidate 3,  Prev: Python 3 5 0 final,  Up: Changelog

1.19.78 Python 3.5.0 release candidate 4
----------------------------------------

`Release date: 2015-09-09'

* Menu:

* Library: Library<78>.
* Build: Build<56>.


File: python.info,  Node: Library<78>,  Next: Build<56>,  Up: Python 3 5 0 release candidate 4

1.19.78.1 Library
.................

   - bpo-25029(1): Fixes MemoryError in test_strptime.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25029


File: python.info,  Node: Build<56>,  Prev: Library<78>,  Up: Python 3 5 0 release candidate 4

1.19.78.2 Build
...............

   - bpo-25027(1): Reverts partial-static build options and adds
     vcruntime140.dll to Windows installation.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue25027


File: python.info,  Node: Python 3 5 0 release candidate 3,  Next: Python 3 5 0 release candidate 2,  Prev: Python 3 5 0 release candidate 4,  Up: Changelog

1.19.79 Python 3.5.0 release candidate 3
----------------------------------------

`Release date: 2015-09-07'

* Menu:

* Core and Builtins: Core and Builtins<63>.
* Library: Library<79>.


File: python.info,  Node: Core and Builtins<63>,  Next: Library<79>,  Up: Python 3 5 0 release candidate 3

1.19.79.1 Core and Builtins
...........................

   - bpo-24305(1): Prevent import subsystem stack frames from being
     counted by the warnings.warn(stacklevel=) parameter.

   - bpo-24912(2): Prevent __class__ assignment to immutable built-in
     objects.

   - bpo-24975(3): Fix AST compilation for PEP 448(4) syntax.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24305

   (2) https://bugs.python.org/issue24912

   (3) https://bugs.python.org/issue24975

   (4) https://www.python.org/dev/peps/pep-0448


File: python.info,  Node: Library<79>,  Prev: Core and Builtins<63>,  Up: Python 3 5 0 release candidate 3

1.19.79.2 Library
.................

   - bpo-24917(1): time_strftime() buffer over-read.

   - bpo-24748(2): To resolve a compatibility problem found with py2exe
     and pywin32, imp.load_dynamic() once again ignores previously
     loaded modules to support Python modules replacing themselves with
     extension modules.  Patch by Petr Viktorin.

   - bpo-24635(3): Fixed a bug in typing.py where isinstance([],
     typing.Iterable) would return True once, then False on subsequent
     calls.

   - bpo-24989(4): Fixed buffer overread in BytesIO.readline() if a
     position is set beyond size.  Based on patch by John Leitch.

   - bpo-24913(5): Fix overrun error in deque.index().  Found by John
     Leitch and Bryce Darling.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24917

   (2) https://bugs.python.org/issue24748

   (3) https://bugs.python.org/issue24635

   (4) https://bugs.python.org/issue24989

   (5) https://bugs.python.org/issue24913


File: python.info,  Node: Python 3 5 0 release candidate 2,  Next: Python 3 5 0 release candidate 1,  Prev: Python 3 5 0 release candidate 3,  Up: Changelog

1.19.80 Python 3.5.0 release candidate 2
----------------------------------------

`Release date: 2015-08-25'

* Menu:

* Core and Builtins: Core and Builtins<64>.
* Library: Library<80>.


File: python.info,  Node: Core and Builtins<64>,  Next: Library<80>,  Up: Python 3 5 0 release candidate 2

1.19.80.1 Core and Builtins
...........................

   - bpo-24769(1): Interpreter now starts properly when dynamic loading
     is disabled.  Patch by Petr Viktorin.

   - bpo-21167(2): NAN operations are now handled correctly when python
     is compiled with ICC even if -fp-model strict is not specified.

   - bpo-24492(3): A “package” lacking a __name__ attribute when trying
     to perform a ‘from .. import ...’ statement will trigger an
     ImportError instead of an AttributeError.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24769

   (2) https://bugs.python.org/issue21167

   (3) https://bugs.python.org/issue24492


File: python.info,  Node: Library<80>,  Prev: Core and Builtins<64>,  Up: Python 3 5 0 release candidate 2

1.19.80.2 Library
.................

   - bpo-24847(1): Removes vcruntime140.dll dependency from Tcl/Tk.

   - bpo-24839(2): platform._syscmd_ver raises DeprecationWarning

   - bpo-24867(3): Fix Task.get_stack() for ‘async def’ coroutines

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24847

   (2) https://bugs.python.org/issue24839

   (3) https://bugs.python.org/issue24867


File: python.info,  Node: Python 3 5 0 release candidate 1,  Next: Python 3 5 0 beta 4,  Prev: Python 3 5 0 release candidate 2,  Up: Changelog

1.19.81 Python 3.5.0 release candidate 1
----------------------------------------

`Release date: 2015-08-09'

* Menu:

* Core and Builtins: Core and Builtins<65>.
* Library: Library<81>.
* IDLE: IDLE<48>.
* Documentation: Documentation<51>.
* Tests: Tests<53>.


File: python.info,  Node: Core and Builtins<65>,  Next: Library<81>,  Up: Python 3 5 0 release candidate 1

1.19.81.1 Core and Builtins
...........................

   - bpo-24667(1): Resize odict in all cases that the underlying dict
     resizes.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24667


File: python.info,  Node: Library<81>,  Next: IDLE<48>,  Prev: Core and Builtins<65>,  Up: Python 3 5 0 release candidate 1

1.19.81.2 Library
.................

   - bpo-24824(1): Signatures of codecs.encode() and codecs.decode() now
     are compatible with pydoc.

   - bpo-24634(2): Importing uuid should not try to load libc on Windows

   - bpo-24798(3): _msvccompiler.py doesn’t properly support manifests

   - bpo-4395(4): Better testing and documentation of binary operators.
     Patch by Martin Panter.

   - bpo-23973(5): Update typing.py from GitHub repo.

   - bpo-23004(6): mock_open() now reads binary data correctly when the
     type of read_data is bytes.  Initial patch by Aaron Hill.

   - bpo-23888(7): Handle fractional time in cookie expiry.  Patch by
     ssh.

   - bpo-23652(8): Make it possible to compile the select module against
     the libc headers from the Linux Standard Base, which do not include
     some EPOLL macros.  Patch by Matt Frank.

   - bpo-22932(9): Fix timezones in email.utils.formatdate.  Patch from
     Dmitry Shachnev.

   - bpo-23779(10): imaplib raises TypeError if authenticator tries to
     abort.  Patch from Craig Holmquist.

   - bpo-23319(11): Fix ctypes.BigEndianStructure, swap correctly bytes.
     Patch written by Matthieu Gautier.

   - bpo-23254(12): Document how to close the TCPServer listening
     socket.  Patch from Martin Panter.

   - bpo-19450(13): Update Windows and OS X installer builds to use
     SQLite 3.8.11.

   - bpo-17527(14): Add PATCH to wsgiref.validator.  Patch from Luca
     Sbardella.

   - bpo-24791(15): Fix grammar regression for call syntax: ‘g(*a or
     b)’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24824

   (2) https://bugs.python.org/issue24634

   (3) https://bugs.python.org/issue24798

   (4) https://bugs.python.org/issue4395

   (5) https://bugs.python.org/issue23973

   (6) https://bugs.python.org/issue23004

   (7) https://bugs.python.org/issue23888

   (8) https://bugs.python.org/issue23652

   (9) https://bugs.python.org/issue22932

   (10) https://bugs.python.org/issue23779

   (11) https://bugs.python.org/issue23319

   (12) https://bugs.python.org/issue23254

   (13) https://bugs.python.org/issue19450

   (14) https://bugs.python.org/issue17527

   (15) https://bugs.python.org/issue24791


File: python.info,  Node: IDLE<48>,  Next: Documentation<51>,  Prev: Library<81>,  Up: Python 3 5 0 release candidate 1

1.19.81.3 IDLE
..............

   - bpo-23672(1): Allow Idle to edit and run files with astral chars in
     name.  Patch by Mohd Sanad Zaki Rizvi.

   - bpo-24745(2): Idle editor default font.  Switch from Courier to
     platform-sensitive TkFixedFont.  This should not affect current
     customized font selections.  If there is a problem, edit
     $HOME/.idlerc/config-main.cfg and remove ‘fontxxx’ entries from
     [Editor Window].  Patch by Mark Roseman.

   - bpo-21192(3): Idle editor.  When a file is run, put its name in the
     restart bar.  Do not print false prompts.  Original patch by Adnan
     Umer.

   - bpo-13884(4): Idle menus.  Remove tearoff lines.  Patch by Roger
     Serwy.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23672

   (2) https://bugs.python.org/issue24745

   (3) https://bugs.python.org/issue21192

   (4) https://bugs.python.org/issue13884


File: python.info,  Node: Documentation<51>,  Next: Tests<53>,  Prev: IDLE<48>,  Up: Python 3 5 0 release candidate 1

1.19.81.4 Documentation
.......................

   - bpo-24129(1): Clarify the reference documentation for name
     resolution.  This includes removing the assumption that readers
     will be familiar with the name resolution scheme Python used prior
     to the introduction of lexical scoping for function namespaces.
     Patch by Ivan Levkivskyi.

   - bpo-20769(2): Improve reload() docs.  Patch by Dorian Pula.

   - bpo-23589(3): Remove duplicate sentence from the FAQ. Patch by
     Yongzhi Pan.

   - bpo-24729(4): Correct IO tutorial to match implementation regarding
     encoding parameter to open function.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24129

   (2) https://bugs.python.org/issue20769

   (3) https://bugs.python.org/issue23589

   (4) https://bugs.python.org/issue24729


File: python.info,  Node: Tests<53>,  Prev: Documentation<51>,  Up: Python 3 5 0 release candidate 1

1.19.81.5 Tests
...............

   - bpo-24751(1): When running regrtest with the ‘-w’ command line
     option, a test run is no longer marked as a failure if all tests
     succeed when re-run.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24751


File: python.info,  Node: Python 3 5 0 beta 4,  Next: Python 3 5 0 beta 3,  Prev: Python 3 5 0 release candidate 1,  Up: Changelog

1.19.82 Python 3.5.0 beta 4
---------------------------

`Release date: 2015-07-26'

* Menu:

* Core and Builtins: Core and Builtins<66>.
* Library: Library<82>.
* Build: Build<57>.


File: python.info,  Node: Core and Builtins<66>,  Next: Library<82>,  Up: Python 3 5 0 beta 4

1.19.82.1 Core and Builtins
...........................

   - bpo-23573(1): Restored optimization of bytes.rfind() and
     bytearray.rfind() for single-byte argument on Linux.

   - bpo-24569(2): Make PEP 448(3) dictionary evaluation more
     consistent.

   - bpo-24583(4): Fix crash when set is mutated while being updated.

   - bpo-24407(5): Fix crash when dict is mutated while being updated.

   - bpo-24619(6): New approach for tokenizing async/await.  As a
     consequence, it is now possible to have one-line ‘async def foo():
     await ..’ functions.

   - bpo-24687(7): Plug refleak on SyntaxError in function parameters
     annotations.

   - bpo-15944(8): memoryview: Allow arbitrary formats when casting to
     bytes.  Patch by Martin Panter.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23573

   (2) https://bugs.python.org/issue24569

   (3) https://www.python.org/dev/peps/pep-0448

   (4) https://bugs.python.org/issue24583

   (5) https://bugs.python.org/issue24407

   (6) https://bugs.python.org/issue24619

   (7) https://bugs.python.org/issue24687

   (8) https://bugs.python.org/issue15944


File: python.info,  Node: Library<82>,  Next: Build<57>,  Prev: Core and Builtins<66>,  Up: Python 3 5 0 beta 4

1.19.82.2 Library
.................

   - bpo-23441(1): rcompleter now prints a tab character instead of
     displaying possible completions for an empty word.  Initial patch
     by Martin Sekera.

   - bpo-24683(2): Fixed crashes in _json functions called with
     arguments of inappropriate type.

   - bpo-21697(3): shutil.copytree() now correctly handles symbolic
     links that point to directories.  Patch by Eduardo Seabra and
     Thomas Kluyver.

   - bpo-14373(4): Fixed segmentation fault when gc.collect() is called
     during constructing lru_cache (C implementation).

   - bpo-24695(5): Fix a regression in traceback.print_exception().  If
     exc_traceback is None we shouldn’t print a traceback header like
     described in the documentation.

   - bpo-24620(6): Random.setstate() now validates the value of state
     last element.

   - bpo-22485(7): Fixed an issue that caused *note inspect.getsource:
     fda. to return incorrect results on nested functions.

   - bpo-22153(8): Improve unittest docs.  Patch from Martin Panter and
     evilzero.

   - bpo-24580(9): Symbolic group references to open group in re
     patterns now are explicitly forbidden as well as numeric group
     references.

   - bpo-24206(10): Fixed __eq__ and __ne__ methods of inspect classes.

   - bpo-24631(11): Fixed regression in the timeit module with multiline
     setup.

   - bpo-18622(12): unittest.mock.mock_open().reset_mock would recurse
     infinitely.  Patch from Nicola Palumbo and Laurent De Buyst.

   - bpo-23661(13): unittest.mock side_effects can now be exceptions
     again.  This was a regression vs Python 3.4.  Patch from Ignacio
     Rossi

   - bpo-24608(14): chunk.Chunk.read() now always returns bytes, not
     str.

   - bpo-18684(15): Fixed reading out of the buffer in the re module.

   - bpo-24259(16): tarfile now raises a ReadError if an archive is
     truncated inside a data segment.

   - bpo-15014(17): SMTP.auth() and SMTP.login() now support RFC 4954’s
     optional initial-response argument to the SMTP AUTH command.

   - bpo-24669(18): Fix inspect.getsource() for ‘async def’ functions.
     Patch by Kai Groner.

   - bpo-24688(19): ast.get_docstring() for ‘async def’ functions.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23441

   (2) https://bugs.python.org/issue24683

   (3) https://bugs.python.org/issue21697

   (4) https://bugs.python.org/issue14373

   (5) https://bugs.python.org/issue24695

   (6) https://bugs.python.org/issue24620

   (7) https://bugs.python.org/issue22485

   (8) https://bugs.python.org/issue22153

   (9) https://bugs.python.org/issue24580

   (10) https://bugs.python.org/issue24206

   (11) https://bugs.python.org/issue24631

   (12) https://bugs.python.org/issue18622

   (13) https://bugs.python.org/issue23661

   (14) https://bugs.python.org/issue24608

   (15) https://bugs.python.org/issue18684

   (16) https://bugs.python.org/issue24259

   (17) https://bugs.python.org/issue15014

   (18) https://bugs.python.org/issue24669

   (19) https://bugs.python.org/issue24688


File: python.info,  Node: Build<57>,  Prev: Library<82>,  Up: Python 3 5 0 beta 4

1.19.82.3 Build
...............

   - bpo-24603(1): Update Windows builds and OS X 10.5 installer to use
     OpenSSL 1.0.2d.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24603


File: python.info,  Node: Python 3 5 0 beta 3,  Next: Python 3 5 0 beta 2,  Prev: Python 3 5 0 beta 4,  Up: Changelog

1.19.83 Python 3.5.0 beta 3
---------------------------

`Release date: 2015-07-05'

* Menu:

* Core and Builtins: Core and Builtins<67>.
* Library: Library<83>.
* Tests: Tests<54>.
* Documentation: Documentation<52>.
* Build: Build<58>.


File: python.info,  Node: Core and Builtins<67>,  Next: Library<83>,  Up: Python 3 5 0 beta 3

1.19.83.1 Core and Builtins
...........................

   - bpo-24467(1): Fixed possible buffer over-read in bytearray.  The
     bytearray object now always allocates place for trailing null byte
     and it’s buffer now is always null-terminated.

   - Upgrade to Unicode 8.0.0.

   - bpo-24345(2): Add Py_tp_finalize slot for the stable ABI.

   - bpo-24400(3): Introduce a distinct type for PEP 492(4) coroutines;
     add types.CoroutineType, inspect.getcoroutinestate,
     inspect.getcoroutinelocals; coroutines no longer use CO_GENERATOR
     flag; sys.set_coroutine_wrapper works only for ‘async def’
     coroutines; inspect.iscoroutine no longer uses
     collections.abc.Coroutine, it’s intended to test for pure ‘async
     def’ coroutines only; add new opcode: GET_YIELD_FROM_ITER; fix
     generators wrapper used in types.coroutine to be instance of
     collections.abc.Generator; collections.abc.Awaitable and
     collections.abc.Coroutine can no longer be used to detect
     generator-based coroutines–use inspect.isawaitable instead.

   - bpo-24450(5): Add gi_yieldfrom to generators and cr_await to
     coroutines.  Contributed by Benno Leslie and Yury Selivanov.

   - bpo-19235(6): Add new RecursionError exception.  Patch by Georg
     Brandl.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24467

   (2) https://bugs.python.org/issue24345

   (3) https://bugs.python.org/issue24400

   (4) https://www.python.org/dev/peps/pep-0492

   (5) https://bugs.python.org/issue24450

   (6) https://bugs.python.org/issue19235


File: python.info,  Node: Library<83>,  Next: Tests<54>,  Prev: Core and Builtins<67>,  Up: Python 3 5 0 beta 3

1.19.83.2 Library
.................

   - bpo-21750(1): mock_open.read_data can now be read from each
     instance, as it could in Python 3.3.

   - bpo-24552(2): Fix use after free in an error case of the _pickle
     module.

   - bpo-24514(3): tarfile now tolerates number fields consisting of
     only whitespace.

   - bpo-19176(4): Fixed doctype() related bugs in C implementation of
     ElementTree.  A deprecation warning no longer issued by XMLParser
     subclass with default doctype() method.  Direct call of doctype()
     now issues a warning.  Parser’s doctype() now is not called if
     target’s doctype() is called.  Based on patch by Martin Panter.

   - bpo-20387(5): Restore semantic round-trip correctness in
     tokenize/untokenize for tab-indented blocks.

   - bpo-24456(6): Fixed possible buffer over-read in adpcm2lin() and
     lin2adpcm() functions of the audioop module.

   - bpo-24336(7): The contextmanager decorator now works with functions
     with keyword arguments called “func” and “self”.  Patch by Martin
     Panter.

   - bpo-24522(8): Fix possible integer overflow in json accelerator
     module.

   - bpo-24489(9): ensure a previously set C errno doesn’t disturb
     cmath.polar().

   - bpo-24408(10): Fixed AttributeError in measure() and metrics()
     methods of tkinter.Font.

   - bpo-14373(11): C implementation of functools.lru_cache() now can be
     used with methods.

   - bpo-24347(12): Set KeyError if PyDict_GetItemWithError returns
     NULL.

   - bpo-24348(13): Drop superfluous incref/decref.

   - bpo-24359(14): Check for changed OrderedDict size during iteration.

   - bpo-24368(15): Support keyword arguments in OrderedDict methods.

   - bpo-24362(16): Simplify the C OrderedDict fast nodes resize logic.

   - bpo-24377(17): Fix a ref leak in OrderedDict.__repr__.

   - bpo-24369(18): Defend against key-changes during iteration.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21750

   (2) https://bugs.python.org/issue24552

   (3) https://bugs.python.org/issue24514

   (4) https://bugs.python.org/issue19176

   (5) https://bugs.python.org/issue20387

   (6) https://bugs.python.org/issue24456

   (7) https://bugs.python.org/issue24336

   (8) https://bugs.python.org/issue24522

   (9) https://bugs.python.org/issue24489

   (10) https://bugs.python.org/issue24408

   (11) https://bugs.python.org/issue14373

   (12) https://bugs.python.org/issue24347

   (13) https://bugs.python.org/issue24348

   (14) https://bugs.python.org/issue24359

   (15) https://bugs.python.org/issue24368

   (16) https://bugs.python.org/issue24362

   (17) https://bugs.python.org/issue24377

   (18) https://bugs.python.org/issue24369


File: python.info,  Node: Tests<54>,  Next: Documentation<52>,  Prev: Library<83>,  Up: Python 3 5 0 beta 3

1.19.83.3 Tests
...............

   - bpo-24373(1): _testmultiphase and xxlimited now use tp_traverse and
     tp_finalize to avoid reference leaks encountered when combining
     tp_dealloc with PyType_FromSpec (see bpo-16690(2) for details)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24373

   (2) https://bugs.python.org/issue16690


File: python.info,  Node: Documentation<52>,  Next: Build<58>,  Prev: Tests<54>,  Up: Python 3 5 0 beta 3

1.19.83.4 Documentation
.......................

   - bpo-24458(1): Update documentation to cover multi-phase
     initialization for extension modules (PEP 489).  Patch by Petr
     Viktorin.

   - bpo-24351(2): Clarify what is meant by “identifier” in the context
     of string.Template instances.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24458

   (2) https://bugs.python.org/issue24351


File: python.info,  Node: Build<58>,  Prev: Documentation<52>,  Up: Python 3 5 0 beta 3

1.19.83.5 Build
...............

   - bpo-24432(1): Update Windows builds and OS X 10.5 installer to use
     OpenSSL 1.0.2c.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24432


File: python.info,  Node: Python 3 5 0 beta 2,  Next: Python 3 5 0 beta 1,  Prev: Python 3 5 0 beta 3,  Up: Changelog

1.19.84 Python 3.5.0 beta 2
---------------------------

`Release date: 2015-05-31'

* Menu:

* Core and Builtins: Core and Builtins<68>.
* Library: Library<84>.


File: python.info,  Node: Core and Builtins<68>,  Next: Library<84>,  Up: Python 3 5 0 beta 2

1.19.84.1 Core and Builtins
...........................

   - bpo-24284(1): The startswith and endswith methods of the str class
     no longer return True when finding the empty string and the indexes
     are completely out of range.

   - bpo-24115(2): Update uses of PyObject_IsTrue(), PyObject_Not(),
     PyObject_IsInstance(), PyObject_RichCompareBool() and
     _PyDict_Contains() to check for and handle errors correctly.

   - bpo-24328(3): Fix importing one character extension modules.

   - bpo-11205(4): In dictionary displays, evaluate the key before the
     value.

   - bpo-24285(5): Fixed regression that prevented importing extension
     modules from inside packages.  Patch by Petr Viktorin.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24284

   (2) https://bugs.python.org/issue24115

   (3) https://bugs.python.org/issue24328

   (4) https://bugs.python.org/issue11205

   (5) https://bugs.python.org/issue24285


File: python.info,  Node: Library<84>,  Prev: Core and Builtins<68>,  Up: Python 3 5 0 beta 2

1.19.84.2 Library
.................

   - bpo-23247(1): Fix a crash in the StreamWriter.reset() of CJK
     codecs.

   - bpo-24270(2): Add math.isclose() and cmath.isclose() functions as
     per PEP 485(3).  Contributed by Chris Barker and Tal Einat.

   - bpo-5633(4): Fixed timeit when the statement is a string and the
     setup is not.

   - bpo-24326(5): Fixed audioop.ratecv() with non-default weightB
     argument.  Original patch by David Moore.

   - bpo-16991(6): Add a C implementation of OrderedDict.

   - bpo-23934(7): Fix inspect.signature to fail correctly for builtin
     types lacking signature information.  Initial patch by James
     Powell.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23247

   (2) https://bugs.python.org/issue24270

   (3) https://www.python.org/dev/peps/pep-0485

   (4) https://bugs.python.org/issue5633

   (5) https://bugs.python.org/issue24326

   (6) https://bugs.python.org/issue16991

   (7) https://bugs.python.org/issue23934


File: python.info,  Node: Python 3 5 0 beta 1,  Next: Python 3 5 0 alpha 4,  Prev: Python 3 5 0 beta 2,  Up: Changelog

1.19.85 Python 3.5.0 beta 1
---------------------------

`Release date: 2015-05-24'

* Menu:

* Core and Builtins: Core and Builtins<69>.
* Library: Library<85>.
* IDLE: IDLE<49>.
* Tests: Tests<55>.
* Documentation: Documentation<53>.
* Tools/Demos: Tools/Demos<32>.


File: python.info,  Node: Core and Builtins<69>,  Next: Library<85>,  Up: Python 3 5 0 beta 1

1.19.85.1 Core and Builtins
...........................

   - bpo-24276(1): Fixed optimization of property descriptor getter.

   - bpo-24268(2): PEP 489: Multi-phase extension module initialization.
     Patch by Petr Viktorin.

   - bpo-23955(3): Add pyvenv.cfg option to suppress
     registry/environment lookup for generating sys.path on Windows.

   - bpo-24257(4): Fixed system error in the comparison of faked
     types.SimpleNamespace.

   - bpo-22939(5): Fixed integer overflow in iterator object.  Patch by
     Clement Rouault.

   - bpo-23985(6): Fix a possible buffer overrun when deleting a slice
     from the front of a bytearray and then appending some other bytes
     data.

   - bpo-24102(7): Fixed exception type checking in standard error
     handlers.

   - bpo-15027(8): The UTF-32 encoder is now 3x to 7x faster.

   - bpo-23290(9): Optimize set_merge() for cases where the target is
     empty.  (Contributed by Serhiy Storchaka.)

   - bpo-2292(10): PEP 448: Additional Unpacking Generalizations.

   - bpo-24096(11): Make warnings.warn_explicit more robust against
     mutation of the warnings.filters list.

   - bpo-23996(12): Avoid a crash when a delegated generator raises an
     unnormalized StopIteration exception.  Patch by Stefan Behnel.

   - bpo-23910(13): Optimize property() getter calls.  Patch by Joe
     Jevnik.

   - bpo-23911(14): Move path-based importlib bootstrap code to a
     separate frozen module.

   - bpo-24192(15): Fix namespace package imports.

   - bpo-24022(16): Fix tokenizer crash when processing undecodable
     source code.

   - bpo-9951(17): Added a hex() method to bytes, bytearray, and
     memoryview.

   - bpo-22906(18): PEP 479: Change StopIteration handling inside
     generators.

   - bpo-24017(19): PEP 492: Coroutines with async and await syntax.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24276

   (2) https://bugs.python.org/issue24268

   (3) https://bugs.python.org/issue23955

   (4) https://bugs.python.org/issue24257

   (5) https://bugs.python.org/issue22939

   (6) https://bugs.python.org/issue23985

   (7) https://bugs.python.org/issue24102

   (8) https://bugs.python.org/issue15027

   (9) https://bugs.python.org/issue23290

   (10) https://bugs.python.org/issue2292

   (11) https://bugs.python.org/issue24096

   (12) https://bugs.python.org/issue23996

   (13) https://bugs.python.org/issue23910

   (14) https://bugs.python.org/issue23911

   (15) https://bugs.python.org/issue24192

   (16) https://bugs.python.org/issue24022

   (17) https://bugs.python.org/issue9951

   (18) https://bugs.python.org/issue22906

   (19) https://bugs.python.org/issue24017


File: python.info,  Node: Library<85>,  Next: IDLE<49>,  Prev: Core and Builtins<69>,  Up: Python 3 5 0 beta 1

1.19.85.2 Library
.................

   - bpo-14373(1): Added C implementation of functools.lru_cache().
     Based on patches by Matt Joiner and Alexey Kachayev.

   - bpo-24230(2): The tempfile module now accepts bytes for prefix,
     suffix and dir parameters and returns bytes in such situations
     (matching the os module APIs).

   - bpo-22189(3): collections.UserString now supports __getnewargs__(),
     __rmod__(), casefold(), format_map(), isprintable(), and
     maketrans().  Patch by Joe Jevnik.

   - bpo-24244(4): Prevents termination when an invalid format string is
     encountered on Windows in strftime.

   - bpo-23973(5): PEP 484: Add the typing module.

   - bpo-23086(6): The collections.abc.Sequence() abstract base class
     added `start' and `stop' parameters to the index() mixin.  Patch by
     Devin Jeanpierre.

   - bpo-20035(7): Replaced the ‘tkinter._fix’ module used for setting
     up the Tcl/Tk environment on Windows with a private function in the
     ‘_tkinter’ module that makes no permanent changes to the
     environment.

   - bpo-24257(8): Fixed segmentation fault in sqlite3.Row constructor
     with faked cursor type.

   - bpo-15836(9): assertRaises(), assertRaisesRegex(), assertWarns()
     and assertWarnsRegex() assertments now check the type of the first
     argument to prevent possible user error.  Based on patch by Daniel
     Wagner-Hall.

   - bpo-9858(10): Add missing method stubs to _io.RawIOBase.  Patch by
     Laura Rupprecht.

   - bpo-22955(11): attrgetter, itemgetter and methodcaller objects in
     the operator module now support pickling.  Added readable and
     evaluable repr for these objects.  Based on patch by Josh
     Rosenberg.

   - bpo-22107(12): tempfile.gettempdir() and tempfile.mkdtemp() now try
     again when a directory with the chosen name already exists on
     Windows as well as on Unix.  tempfile.mkstemp() now fails early if
     parent directory is not valid (not exists or is a file) on Windows.

   - bpo-23780(13): Improved error message in os.path.join() with single
     argument.

   - bpo-6598(14): Increased time precision and random number range in
     email.utils.make_msgid() to strengthen the uniqueness of the
     message ID.

   - bpo-24091(15): Fixed various crashes in corner cases in C
     implementation of ElementTree.

   - bpo-21931(16): msilib.FCICreate() now raises TypeError in the case
     of a bad argument instead of a ValueError with a bogus FCI error
     number.  Patch by Jeffrey Armstrong.

   - bpo-13866(17): `quote_via' argument added to
     urllib.parse.urlencode.

   - bpo-20098(18): New mangle_from policy option for email, default
     True for compat32, but False for all other policies.

   - bpo-24211(19): The email library now supports RFC 6532: it can
     generate headers using utf-8 instead of encoded words.

   - bpo-16314(20): Added support for the LZMA compression in distutils.

   - bpo-21804(21): poplib now supports RFC 6856 (UTF8).

   - bpo-18682(22): Optimized pprint functions for builtin scalar types.

   - bpo-22027(23): smtplib now supports RFC 6531 (SMTPUTF8).

   - bpo-23488(24): Random generator objects now consume 2x less memory
     on 64-bit.

   - bpo-1322(25): platform.dist() and platform.linux_distribution()
     functions are now deprecated.  Initial patch by Vajrasky Kok.

   - bpo-22486(26): Added the math.gcd() function.  The fractions.gcd()
     function now is deprecated.  Based on patch by Mark Dickinson.

   - bpo-24064(27): Property() docstrings are now writeable.  (Patch by
     Berker Peksag.)

   - bpo-22681(28): Added support for the koi8_t encoding.

   - bpo-22682(29): Added support for the kz1048 encoding.

   - bpo-23796(30): peek and read1 methods of BufferedReader now raise
     ValueError if they called on a closed object.  Patch by John
     Hergenroeder.

   - bpo-21795(31): smtpd now supports the 8BITMIME extension whenever
     the new `decode_data' constructor argument is set to False.

   - bpo-24155(32): optimize heapq.heapify() for better cache
     performance when heapifying large lists.

   - bpo-21800(33): imaplib now supports RFC 5161 (enable), RFC 6855
     (utf8/internationalized email) and automatically encodes non-ASCII
     usernames and passwords to UTF8.

   - bpo-20274(34): When calling a _sqlite.Connection, it now complains
     if passed any keyword arguments.  Previously it silently ignored
     them.

   - bpo-20274(35): Remove ignored and erroneous “kwargs” parameters
     from three METH_VARARGS methods on _sqlite.Connection.

   - bpo-24134(36): assertRaises(), assertRaisesRegex(), assertWarns()
     and assertWarnsRegex() checks now emits a deprecation warning when
     callable is None or keyword arguments except msg is passed in the
     context manager mode.

   - bpo-24018(37): Add a collections.abc.Generator abstract base class.
     Contributed by Stefan Behnel.

   - bpo-23880(38): Tkinter’s getint() and getdouble() now support
     Tcl_Obj.  Tkinter’s getdouble() now supports any numbers (in
     particular int).

   - bpo-22619(39): Added negative limit support in the traceback
     module.  Based on patch by Dmitry Kazakov.

   - bpo-24094(40): Fix possible crash in json.encode with poorly
     behaved dict subclasses.

   - bpo-9246(41): On POSIX, os.getcwd() now supports paths longer than
     1025 bytes.  Patch written by William Orr.

   - bpo-17445(42): add difflib.diff_bytes() to support comparison of
     byte strings (fixes a regression from Python 2).

   - bpo-23917(43): Fall back to sequential compilation when
     ProcessPoolExecutor doesn’t exist.  Patch by Claudiu Popa.

   - bpo-23008(44): Fixed resolving attributes with boolean value is
     False in pydoc.

   - Fix asyncio issue 235: LifoQueue and PriorityQueue’s put didn’t
     increment unfinished tasks (this bug was introduced when
     JoinableQueue was merged with Queue).

   - bpo-23908(45): os functions now reject paths with embedded null
     character on Windows instead of silently truncating them.

   - bpo-23728(46): binascii.crc_hqx() could return an integer outside
     of the range 0-0xffff for empty data.

   - bpo-23887(47): urllib.error.HTTPError now has a proper repr()
     representation.  Patch by Berker Peksag.

   - asyncio: New event loop APIs: set_task_factory() and
     get_task_factory().

   - asyncio: async() function is deprecated in favour of
     ensure_future().

   - bpo-24178(48): asyncio.Lock, Condition, Semaphore, and
     BoundedSemaphore support new ‘async with’ syntax.  Contributed by
     Yury Selivanov.

   - bpo-24179(49): Support ‘async for’ for asyncio.StreamReader.
     Contributed by Yury Selivanov.

   - bpo-24184(50): Add AsyncIterator and AsyncIterable ABCs to
     collections.abc.  Contributed by Yury Selivanov.

   - bpo-22547(51): Implement informative __repr__ for
     inspect.BoundArguments.  Contributed by Yury Selivanov.

   - bpo-24190(52): Implement inspect.BoundArgument.apply_defaults()
     method.  Contributed by Yury Selivanov.

   - bpo-20691(53): Add ‘follow_wrapped’ argument to
     inspect.Signature.from_callable() and inspect.signature().
     Contributed by Yury Selivanov.

   - bpo-24248(54): Deprecate inspect.Signature.from_function() and
     inspect.Signature.from_builtin().

   - bpo-23898(55): Fix inspect.classify_class_attrs() to support
     attributes with overloaded __eq__ and __bool__.  Patch by Mike
     Bayer.

   - bpo-24298(56): Fix inspect.signature() to correctly unwrap wrappers
     around bound methods.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14373

   (2) https://bugs.python.org/issue24230

   (3) https://bugs.python.org/issue22189

   (4) https://bugs.python.org/issue24244

   (5) https://bugs.python.org/issue23973

   (6) https://bugs.python.org/issue23086

   (7) https://bugs.python.org/issue20035

   (8) https://bugs.python.org/issue24257

   (9) https://bugs.python.org/issue15836

   (10) https://bugs.python.org/issue9858

   (11) https://bugs.python.org/issue22955

   (12) https://bugs.python.org/issue22107

   (13) https://bugs.python.org/issue23780

   (14) https://bugs.python.org/issue6598

   (15) https://bugs.python.org/issue24091

   (16) https://bugs.python.org/issue21931

   (17) https://bugs.python.org/issue13866

   (18) https://bugs.python.org/issue20098

   (19) https://bugs.python.org/issue24211

   (20) https://bugs.python.org/issue16314

   (21) https://bugs.python.org/issue21804

   (22) https://bugs.python.org/issue18682

   (23) https://bugs.python.org/issue22027

   (24) https://bugs.python.org/issue23488

   (25) https://bugs.python.org/issue1322

   (26) https://bugs.python.org/issue22486

   (27) https://bugs.python.org/issue24064

   (28) https://bugs.python.org/issue22681

   (29) https://bugs.python.org/issue22682

   (30) https://bugs.python.org/issue23796

   (31) https://bugs.python.org/issue21795

   (32) https://bugs.python.org/issue24155

   (33) https://bugs.python.org/issue21800

   (34) https://bugs.python.org/issue20274

   (35) https://bugs.python.org/issue20274

   (36) https://bugs.python.org/issue24134

   (37) https://bugs.python.org/issue24018

   (38) https://bugs.python.org/issue23880

   (39) https://bugs.python.org/issue22619

   (40) https://bugs.python.org/issue24094

   (41) https://bugs.python.org/issue9246

   (42) https://bugs.python.org/issue17445

   (43) https://bugs.python.org/issue23917

   (44) https://bugs.python.org/issue23008

   (45) https://bugs.python.org/issue23908

   (46) https://bugs.python.org/issue23728

   (47) https://bugs.python.org/issue23887

   (48) https://bugs.python.org/issue24178

   (49) https://bugs.python.org/issue24179

   (50) https://bugs.python.org/issue24184

   (51) https://bugs.python.org/issue22547

   (52) https://bugs.python.org/issue24190

   (53) https://bugs.python.org/issue20691

   (54) https://bugs.python.org/issue24248

   (55) https://bugs.python.org/issue23898

   (56) https://bugs.python.org/issue24298


File: python.info,  Node: IDLE<49>,  Next: Tests<55>,  Prev: Library<85>,  Up: Python 3 5 0 beta 1

1.19.85.3 IDLE
..............

   - bpo-23184(1): remove unused names and imports in idlelib.  Initial
     patch by Al Sweigart.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23184


File: python.info,  Node: Tests<55>,  Next: Documentation<53>,  Prev: IDLE<49>,  Up: Python 3 5 0 beta 1

1.19.85.4 Tests
...............

   - bpo-21520(1): test_zipfile no longer fails if the word ‘bad’
     appears anywhere in the name of the current directory.

   - bpo-9517(2): Move script_helper into the support package.  Patch by
     Christie Wilson.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue21520

   (2) https://bugs.python.org/issue9517


File: python.info,  Node: Documentation<53>,  Next: Tools/Demos<32>,  Prev: Tests<55>,  Up: Python 3 5 0 beta 1

1.19.85.5 Documentation
.......................

   - bpo-22155(1): Add File Handlers subsection with createfilehandler
     to tkinter doc.  Remove obsolete example from FAQ. Patch by Martin
     Panter.

   - bpo-24029(2): Document the name binding behavior for submodule
     imports.

   - bpo-24077(3): Fix typo in man page for -I command option: -s, not
     -S

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22155

   (2) https://bugs.python.org/issue24029

   (3) https://bugs.python.org/issue24077


File: python.info,  Node: Tools/Demos<32>,  Prev: Documentation<53>,  Up: Python 3 5 0 beta 1

1.19.85.6 Tools/Demos
.....................

   - bpo-24000(1): Improved Argument Clinic’s mapping of converters to
     legacy “format units”.  Updated the documentation to match.

   - bpo-24001(2): Argument Clinic converters now use accept={type}
     instead of types={‘type’} to specify the types the converter
     accepts.

   - bpo-23330(3): h2py now supports arbitrary filenames in #include.

   - bpo-24031(4): make patchcheck now supports git checkouts, too.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue24000

   (2) https://bugs.python.org/issue24001

   (3) https://bugs.python.org/issue23330

   (4) https://bugs.python.org/issue24031


File: python.info,  Node: Python 3 5 0 alpha 4,  Next: Python 3 5 0 alpha 3,  Prev: Python 3 5 0 beta 1,  Up: Changelog

1.19.86 Python 3.5.0 alpha 4
----------------------------

`Release date: 2015-04-19'

* Menu:

* Core and Builtins: Core and Builtins<70>.
* Library: Library<86>.
* Build: Build<59>.
* Tests: Tests<56>.
* Tools/Demos: Tools/Demos<33>.
* C API: C API<41>.


File: python.info,  Node: Core and Builtins<70>,  Next: Library<86>,  Up: Python 3 5 0 alpha 4

1.19.86.1 Core and Builtins
...........................

   - bpo-22980(1): Under Linux, GNU/KFreeBSD and the Hurd, C extensions
     now include the architecture triplet in the extension name, to make
     it easy to test builds for different ABIs in the same working tree.
     Under OS X, the extension name now includes PEP 3149(2)-style
     information.

   - bpo-22631(3): Added Linux-specific socket constant
     CAN_RAW_FD_FRAMES. Patch courtesy of Joe Jevnik.

   - bpo-23731(4): Implement PEP 488(5): removal of .pyo files.

   - bpo-23726(6): Don’t enable GC for user subclasses of non-GC types
     that don’t add any new fields.  Patch by Eugene Toder.

   - bpo-23309(7): Avoid a deadlock at shutdown if a daemon thread is
     aborted while it is holding a lock to a buffered I/O object, and
     the main thread tries to use the same I/O object (typically stdout
     or stderr).  A fatal error is emitted instead.

   - bpo-22977(8): Fixed formatting Windows error messages on Wine.
     Patch by Martin Panter.

   - bpo-23466(9): %c, %o, %x, and %X in bytes formatting now raise
     TypeError on non-integer input.

   - bpo-24044(10): Fix possible null pointer dereference in list.sort
     in out of memory conditions.

   - bpo-21354(11): PyCFunction_New function is exposed by python DLL
     again.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22980

   (2) https://www.python.org/dev/peps/pep-3149

   (3) https://bugs.python.org/issue22631

   (4) https://bugs.python.org/issue23731

   (5) https://www.python.org/dev/peps/pep-0488

   (6) https://bugs.python.org/issue23726

   (7) https://bugs.python.org/issue23309

   (8) https://bugs.python.org/issue22977

   (9) https://bugs.python.org/issue23466

   (10) https://bugs.python.org/issue24044

   (11) https://bugs.python.org/issue21354


File: python.info,  Node: Library<86>,  Next: Build<59>,  Prev: Core and Builtins<70>,  Up: Python 3 5 0 alpha 4

1.19.86.2 Library
.................

   - bpo-23840(1): tokenize.open() now closes the temporary binary file
     on error to fix a resource warning.

   - bpo-16914(2): new debuglevel 2 in smtplib adds timestamps to debug
     output.

   - bpo-7159(3): urllib.request now supports sending auth credentials
     automatically after the first 401.  This enhancement is a superset
     of the enhancement from bpo-19494(4) and supersedes that change.

   - bpo-23703(5): Fix a regression in urljoin() introduced in
     901e4e52b20a.  Patch by Demian Brecht.

   - bpo-4254(6): Adds _curses.update_lines_cols().  Patch by Arnon
     Yaari

   - bpo-19933(7): Provide default argument for ndigits in round.  Patch
     by Vajrasky Kok.

   - bpo-23193(8): Add a numeric_owner parameter to
     tarfile.TarFile.extract and tarfile.TarFile.extractall.  Patch by
     Michael Vogt and Eric Smith.

   - bpo-23342(9): Add a subprocess.run() function than returns a
     CalledProcess instance for a more consistent API than the existing
     call* functions.

   - bpo-21217(10): inspect.getsourcelines() now tries to compute the
     start and end lines from the code object, fixing an issue when a
     lambda function is used as decorator argument.  Patch by Thomas
     Ballinger and Allison Kaptur.

   - bpo-24521(11): Fix possible integer overflows in the pickle module.

   - bpo-22931(12): Allow ‘[’ and ‘]’ in cookie values.

   - The keywords attribute of functools.partial is now always a
     dictionary.

   - bpo-23811(13): Add missing newline to the PyCompileError error
     message.  Patch by Alex Shkop.

   - bpo-21116(14): Avoid blowing memory when allocating a
     multiprocessing shared array that’s larger than 50% of the
     available RAM. Patch by Médéric Boquien.

   - bpo-22982(15): Improve BOM handling when seeking to multiple
     positions of a writable text file.

   - bpo-23464(16): Removed deprecated asyncio JoinableQueue.

   - bpo-23529(17): Limit the size of decompressed data when reading
     from GzipFile, BZ2File or LZMAFile.  This defeats denial of service
     attacks using compressed bombs (i.e.  compressed payloads which
     decompress to a huge size).  Patch by Martin Panter and Nikolaus
     Rath.

   - bpo-21859(18): Added Python implementation of io.FileIO.

   - bpo-23865(19): close() methods in multiple modules now are
     idempotent and more robust at shutdown.  If they need to release
     multiple resources, all are released even if errors occur.

   - bpo-23400(20): Raise same exception on both Python 2 and 3 if
     sem_open is not available.  Patch by Davin Potts.

   - bpo-10838(21): The subprocess now module includes SubprocessError
     and TimeoutError in its list of exported names for the users wild
     enough to use ‘from subprocess import *’.

   - bpo-23411(22): Added DefragResult, ParseResult, SplitResult,
     DefragResultBytes, ParseResultBytes, and SplitResultBytes to
     urllib.parse.__all__.  Patch by Martin Panter.

   - bpo-23881(23): urllib.request.ftpwrapper constructor now closes the
     socket if the FTP connection failed to fix a ResourceWarning.

   - bpo-23853(24): *note socket.socket.sendall(): 76e. does no more
     reset the socket timeout each time data is sent successfully.  The
     socket timeout is now the maximum total duration to send all data.

   - bpo-22721(25): An order of multiline pprint output of set or dict
     containing orderable and non-orderable elements no longer depends
     on iteration order of set or dict.

   - bpo-15133(26): _tkinter.tkapp.getboolean() now supports Tcl_Obj and
     always returns bool.  tkinter.BooleanVar now validates input values
     (accepted bool, int, str, and Tcl_Obj).  tkinter.BooleanVar.get()
     now always returns bool.

   - bpo-10590(27): xml.sax.parseString() now supports string argument.

   - bpo-23338(28): Fixed formatting ctypes error messages on Cygwin.
     Patch by Makoto Kato.

   - bpo-15582(29): inspect.getdoc() now follows inheritance chains.

   - bpo-2175(30): SAX parsers now support a character stream of
     InputSource object.

   - bpo-16840(31): Tkinter now supports 64-bit integers added in Tcl
     8.4 and arbitrary precision integers added in Tcl 8.5.

   - bpo-23834(32): Fix socket.sendto(), use the C Py_ssize_t type to
     store the result of sendto() instead of the C int type.

   - bpo-23618(33): *note socket.socket.connect(): 769. now waits until
     the connection completes instead of raising *note InterruptedError:
     74c. if the connection is interrupted by signals, signal handlers
     don’t raise an exception and the socket is blocking or has a
     timeout.  *note socket.socket.connect(): 769. still raise *note
     InterruptedError: 74c. for non-blocking sockets.

   - bpo-21526(34): Tkinter now supports new boolean type in Tcl 8.5.

   - bpo-23836(35): Fix the faulthandler module to handle reentrant
     calls to its signal handlers.

   - bpo-23838(36): linecache now clears the cache and returns an empty
     result on MemoryError.

   - bpo-10395(37): Added os.path.commonpath().  Implemented in
     posixpath and ntpath.  Based on patch by Rafik Draoui.

   - bpo-23611(38): Serializing more “lookupable” objects (such as
     unbound methods or nested classes) now are supported with pickle
     protocols < 4.

   - bpo-13583(39): sqlite3.Row now supports slice indexing.

   - bpo-18473(40): Fixed 2to3 and 3to2 compatible pickle mappings.
     Fixed ambiguous reverse mappings.  Added many new mappings.  Import
     mapping is no longer applied to modules already mapped with full
     name mapping.

   - bpo-23485(41): select.select() is now retried automatically with
     the recomputed timeout when interrupted by a signal, except if the
     signal handler raises an exception.  This change is part of the PEP
     475(42).

   - bpo-23752(43): When built from an existing file descriptor,
     io.FileIO() now only calls fstat() once.  Before fstat() was called
     twice, which was not necessary.

   - bpo-23704(44): collections.deque() objects now support __add__,
     __mul__, and __imul__().

   - bpo-23171(45): csv.Writer.writerow() now supports arbitrary
     iterables.

   - bpo-23745(46): The new email header parser now handles duplicate
     MIME parameter names without error, similar to how get_param
     behaves.

   - bpo-22117(47): Fix os.utime(), it now rounds the timestamp towards
     minus infinity (-inf) instead of rounding towards zero.

   - bpo-23310(48): Fix MagicMock’s initializer to work with
     __methods__, just like configure_mock().  Patch by Kasia Jachim.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23840

   (2) https://bugs.python.org/issue16914

   (3) https://bugs.python.org/issue7159

   (4) https://bugs.python.org/issue19494

   (5) https://bugs.python.org/issue23703

   (6) https://bugs.python.org/issue4254

   (7) https://bugs.python.org/issue19933

   (8) https://bugs.python.org/issue23193

   (9) https://bugs.python.org/issue23342

   (10) https://bugs.python.org/issue21217

   (11) https://bugs.python.org/issue24521

   (12) https://bugs.python.org/issue22931

   (13) https://bugs.python.org/issue23811

   (14) https://bugs.python.org/issue21116

   (15) https://bugs.python.org/issue22982

   (16) https://bugs.python.org/issue23464

   (17) https://bugs.python.org/issue23529

   (18) https://bugs.python.org/issue21859

   (19) https://bugs.python.org/issue23865

   (20) https://bugs.python.org/issue23400

   (21) https://bugs.python.org/issue10838

   (22) https://bugs.python.org/issue23411

   (23) https://bugs.python.org/issue23881

   (24) https://bugs.python.org/issue23853

   (25) https://bugs.python.org/issue22721

   (26) https://bugs.python.org/issue15133

   (27) https://bugs.python.org/issue10590

   (28) https://bugs.python.org/issue23338

   (29) https://bugs.python.org/issue15582

   (30) https://bugs.python.org/issue2175

   (31) https://bugs.python.org/issue16840

   (32) https://bugs.python.org/issue23834

   (33) https://bugs.python.org/issue23618

   (34) https://bugs.python.org/issue21526

   (35) https://bugs.python.org/issue23836

   (36) https://bugs.python.org/issue23838

   (37) https://bugs.python.org/issue10395

   (38) https://bugs.python.org/issue23611

   (39) https://bugs.python.org/issue13583

   (40) https://bugs.python.org/issue18473

   (41) https://bugs.python.org/issue23485

   (42) https://www.python.org/dev/peps/pep-0475

   (43) https://bugs.python.org/issue23752

   (44) https://bugs.python.org/issue23704

   (45) https://bugs.python.org/issue23171

   (46) https://bugs.python.org/issue23745

   (47) https://bugs.python.org/issue22117

   (48) https://bugs.python.org/issue23310


File: python.info,  Node: Build<59>,  Next: Tests<56>,  Prev: Library<86>,  Up: Python 3 5 0 alpha 4

1.19.86.3 Build
...............

   - bpo-23817(1): FreeBSD now uses “1.0” in the SOVERSION as other
     operating systems, instead of just “1”.

   - bpo-23501(2): Argument Clinic now generates code into separate
     files by default.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23817

   (2) https://bugs.python.org/issue23501


File: python.info,  Node: Tests<56>,  Next: Tools/Demos<33>,  Prev: Build<59>,  Up: Python 3 5 0 alpha 4

1.19.86.4 Tests
...............

   - bpo-23799(1): Added test.support.start_threads() for running and
     cleaning up multiple threads.

   - bpo-22390(2): test.regrtest now emits a warning if temporary files
     or directories are left after running a test.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23799

   (2) https://bugs.python.org/issue22390


File: python.info,  Node: Tools/Demos<33>,  Next: C API<41>,  Prev: Tests<56>,  Up: Python 3 5 0 alpha 4

1.19.86.5 Tools/Demos
.....................

   - bpo-18128(1): pygettext now uses standard +NNNN format in the
     POT-Creation-Date header.

   - bpo-23935(2): Argument Clinic’s understanding of format units
     accepting bytes, bytearrays, and buffers is now consistent with
     both the documentation and the implementation.

   - bpo-23944(3): Argument Clinic now wraps long impl prototypes at
     column 78.

   - bpo-20586(4): Argument Clinic now ensures that functions without
     docstrings have signatures.

   - bpo-23492(5): Argument Clinic now generates argument parsing code
     with PyArg_Parse instead of PyArg_ParseTuple if possible.

   - bpo-23500(6): Argument Clinic is now smarter about generating the
     “#ifndef” (empty) definition of the methoddef macro: it’s only
     generated once, even if Argument Clinic processes the same symbol
     multiple times, and it’s emitted at the end of all processing
     rather than immediately after the first use.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18128

   (2) https://bugs.python.org/issue23935

   (3) https://bugs.python.org/issue23944

   (4) https://bugs.python.org/issue20586

   (5) https://bugs.python.org/issue23492

   (6) https://bugs.python.org/issue23500


File: python.info,  Node: C API<41>,  Prev: Tools/Demos<33>,  Up: Python 3 5 0 alpha 4

1.19.86.6 C API
...............

   - bpo-23998(1): PyImport_ReInitLock() now checks for lock allocation
     error

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23998


File: python.info,  Node: Python 3 5 0 alpha 3,  Next: Python 3 5 0 alpha 2,  Prev: Python 3 5 0 alpha 4,  Up: Changelog

1.19.87 Python 3.5.0 alpha 3
----------------------------

`Release date: 2015-03-28'

* Menu:

* Core and Builtins: Core and Builtins<71>.
* Library: Library<87>.
* Build: Build<60>.
* Tests: Tests<57>.
* Tools/Demos: Tools/Demos<34>.


File: python.info,  Node: Core and Builtins<71>,  Next: Library<87>,  Up: Python 3 5 0 alpha 3

1.19.87.1 Core and Builtins
...........................

   - bpo-23573(1): Increased performance of string search operations
     (str.find, str.index, str.count, the in operator, str.split,
     str.partition) with arguments of different kinds (UCS1, UCS2,
     UCS4).

   - bpo-23753(2): Python doesn’t support anymore platforms without
     stat() or fstat(), these functions are always required.

   - bpo-23681(3): The -b option now affects comparisons of bytes with
     int.

   - bpo-23632(4): Memoryviews now allow tuple indexing (including for
     multi-dimensional memoryviews).

   - bpo-23192(5): Fixed generator lambdas.  Patch by Bruno Cauet.

   - bpo-23629(6): Fix the default __sizeof__ implementation for
     variable-sized objects.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23573

   (2) https://bugs.python.org/issue23753

   (3) https://bugs.python.org/issue23681

   (4) https://bugs.python.org/issue23632

   (5) https://bugs.python.org/issue23192

   (6) https://bugs.python.org/issue23629


File: python.info,  Node: Library<87>,  Next: Build<60>,  Prev: Core and Builtins<71>,  Up: Python 3 5 0 alpha 3

1.19.87.2 Library
.................

   - bpo-14260(1): The groupindex attribute of regular expression
     pattern object now is non-modifiable mapping.

   - bpo-23792(2): Ignore KeyboardInterrupt when the pydoc pager is
     active.  This mimics the behavior of the standard unix pagers, and
     prevents pipepager from shutting down while the pager itself is
     still running.

   - bpo-23775(3): pprint() of OrderedDict now outputs the same
     representation as repr().

   - bpo-23765(4): Removed IsBadStringPtr calls in ctypes

   - bpo-22364(5): Improved some re error messages using regex for
     hints.

   - bpo-23742(6): ntpath.expandvars() no longer loses unbalanced single
     quotes.

   - bpo-21717(7): The zipfile.ZipFile.open function now supports ‘x’
     (exclusive creation) mode.

   - bpo-21802(8): The reader in BufferedRWPair now is closed even when
     closing writer failed in BufferedRWPair.close().

   - bpo-23622(9): Unknown escapes in regular expressions that consist
     of ‘'\'’ and ASCII letter now raise a deprecation warning and will
     be forbidden in Python 3.6.

   - bpo-23671(10): string.Template now allows specifying the “self”
     parameter as a keyword argument.  string.Formatter now allows
     specifying the “self” and the “format_string” parameters as keyword
     arguments.

   - bpo-23502(11): The pprint module now supports mapping proxies.

   - bpo-17530(12): pprint now wraps long bytes objects and bytearrays.

   - bpo-22687(13): Fixed some corner cases in breaking words in
     tetxtwrap.  Got rid of quadratic complexity in breaking long words.

   - bpo-4727(14): The copy module now uses pickle protocol 4 (PEP 3154)
     and supports copying of instances of classes whose __new__ method
     takes keyword-only arguments.

   - bpo-23491(15): Added a zipapp module to support creating executable
     zip file archives of Python code.  Registered “.pyz” and “.pyzw”
     extensions on Windows for these archives (PEP 441).

   - bpo-23657(16): Avoid explicit checks for str in zipapp, adding
     support for pathlib.Path objects as arguments.

   - bpo-23688(17): Added support of arbitrary bytes-like objects and
     avoided unnecessary copying of memoryview in gzip.GzipFile.write().
     Original patch by Wolfgang Maier.

   - bpo-23252(18): Added support for writing ZIP files to unseekable
     streams.

   - bpo-23647(19): Increase imaplib’s MAXLINE to accommodate modern
     mailbox sizes.

   - bpo-23539(20): If body is None, http.client.HTTPConnection.request
     now sets Content-Length to 0 for PUT, POST, and PATCH headers to
     avoid 411 errors from some web servers.

   - bpo-22351(21): The nntplib.NNTP constructor no longer leaves the
     connection and socket open until the garbage collector cleans them
     up.  Patch by Martin Panter.

   - bpo-23704(22): collections.deque() objects now support methods for
     index(), insert(), and copy().  This allows deques to be registered
     as a MutableSequence and it improves their substitutability for
     lists.

   - bpo-23715(23): *note signal.sigwaitinfo(): 772. and *note
     signal.sigtimedwait(): 771. are now retried when interrupted by a
     signal not in the `sigset' parameter, if the signal handler does
     not raise an exception.  signal.sigtimedwait() recomputes the
     timeout with a monotonic clock when it is retried.

   - bpo-23001(24): Few functions in modules mmap, ossaudiodev, socket,
     ssl, and codecs, that accepted only read-only bytes-like object now
     accept writable bytes-like object too.

   - bpo-23646(25): If time.sleep() is interrupted by a signal, the
     sleep is now retried with the recomputed delay, except if the
     signal handler raises an exception (PEP 475).

   - bpo-23136(26): _strptime now uniformly handles all days in week 0,
     including Dec 30 of previous year.  Based on patch by Jim Carroll.

   - bpo-23700(27): Iterator of NamedTemporaryFile now keeps a reference
     to NamedTemporaryFile instance.  Patch by Bohuslav Kabrda.

   - bpo-22903(28): The fake test case created by unittest.loader when
     it fails importing a test module is now picklable.

   - bpo-22181(29): On Linux, os.urandom() now uses the new getrandom()
     syscall if available, syscall introduced in the Linux kernel 3.17.
     It is more reliable and more secure, because it avoids the need of
     a file descriptor and waits until the kernel has enough entropy.

   - bpo-2211(30): Updated the implementation of the http.cookies.Morsel
     class.  Setting attributes key, value and coded_value directly now
     is deprecated.  update() and setdefault() now transform and check
     keys.  Comparing for equality now takes into account attributes
     key, value and coded_value.  copy() now returns a Morsel, not a
     dict.  repr() now contains all attributes.  Optimized checking keys
     and quoting values.  Added new tests.  Original patch by Demian
     Brecht.

   - bpo-18983(31): Allow selection of output units in timeit.  Patch by
     Julian Gindi.

   - bpo-23631(32): Fix traceback.format_list when a traceback has been
     mutated.

   - bpo-23568(33): Add rdivmod support to MagicMock() objects.  Patch
     by Håkan Lövdahl.

   - bpo-2052(34): Add charset parameter to HtmlDiff.make_file().

   - bpo-23668(35): Support os.truncate and os.ftruncate on Windows.

   - bpo-23138(36): Fixed parsing cookies with absent keys or values in
     cookiejar.  Patch by Demian Brecht.

   - bpo-23051(37): multiprocessing.Pool methods imap() and
     imap_unordered() now handle exceptions raised by an iterator.
     Patch by Alon Diamant and Davin Potts.

   - bpo-23581(38): Add matmul support to MagicMock.  Patch by Håkan
     Lövdahl.

   - bpo-23566(39): enable(), register(), dump_traceback() and
     dump_traceback_later() functions of faulthandler now accept file
     descriptors.  Patch by Wei Wu.

   - bpo-22928(40): Disabled HTTP header injections in http.client.
     Original patch by Demian Brecht.

   - bpo-23615(41): Modules bz2, tarfile and tokenize now can be
     reloaded with imp.reload().  Patch by Thomas Kluyver.

   - bpo-23605(42): os.walk() now calls os.scandir() instead of
     os.listdir().  The usage of os.scandir() reduces the number of
     calls to os.stat().  Initial patch written by Ben Hoyt.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14260

   (2) https://bugs.python.org/issue23792

   (3) https://bugs.python.org/issue23775

   (4) https://bugs.python.org/issue23765

   (5) https://bugs.python.org/issue22364

   (6) https://bugs.python.org/issue23742

   (7) https://bugs.python.org/issue21717

   (8) https://bugs.python.org/issue21802

   (9) https://bugs.python.org/issue23622

   (10) https://bugs.python.org/issue23671

   (11) https://bugs.python.org/issue23502

   (12) https://bugs.python.org/issue17530

   (13) https://bugs.python.org/issue22687

   (14) https://bugs.python.org/issue4727

   (15) https://bugs.python.org/issue23491

   (16) https://bugs.python.org/issue23657

   (17) https://bugs.python.org/issue23688

   (18) https://bugs.python.org/issue23252

   (19) https://bugs.python.org/issue23647

   (20) https://bugs.python.org/issue23539

   (21) https://bugs.python.org/issue22351

   (22) https://bugs.python.org/issue23704

   (23) https://bugs.python.org/issue23715

   (24) https://bugs.python.org/issue23001

   (25) https://bugs.python.org/issue23646

   (26) https://bugs.python.org/issue23136

   (27) https://bugs.python.org/issue23700

   (28) https://bugs.python.org/issue22903

   (29) https://bugs.python.org/issue22181

   (30) https://bugs.python.org/issue2211

   (31) https://bugs.python.org/issue18983

   (32) https://bugs.python.org/issue23631

   (33) https://bugs.python.org/issue23568

   (34) https://bugs.python.org/issue2052

   (35) https://bugs.python.org/issue23668

   (36) https://bugs.python.org/issue23138

   (37) https://bugs.python.org/issue23051

   (38) https://bugs.python.org/issue23581

   (39) https://bugs.python.org/issue23566

   (40) https://bugs.python.org/issue22928

   (41) https://bugs.python.org/issue23615

   (42) https://bugs.python.org/issue23605


File: python.info,  Node: Build<60>,  Next: Tests<57>,  Prev: Library<87>,  Up: Python 3 5 0 alpha 3

1.19.87.3 Build
...............

   - bpo-23585(1): make patchcheck will ensure the interpreter is built.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23585


File: python.info,  Node: Tests<57>,  Next: Tools/Demos<34>,  Prev: Build<60>,  Up: Python 3 5 0 alpha 3

1.19.87.4 Tests
...............

   - bpo-23583(1): Added tests for standard IO streams in IDLE.

   - bpo-22289(2): Prevent test_urllib2net failures due to ftp
     connection timeout.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23583

   (2) https://bugs.python.org/issue22289


File: python.info,  Node: Tools/Demos<34>,  Prev: Tests<57>,  Up: Python 3 5 0 alpha 3

1.19.87.5 Tools/Demos
.....................

   - bpo-22826(1): The result of open() in Tools/freeze/bkfile.py is now
     better compatible with regular files (in particular it now supports
     the context management protocol).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22826


File: python.info,  Node: Python 3 5 0 alpha 2,  Next: Python 3 5 0 alpha 1,  Prev: Python 3 5 0 alpha 3,  Up: Changelog

1.19.88 Python 3.5.0 alpha 2
----------------------------

`Release date: 2015-03-09'

* Menu:

* Core and Builtins: Core and Builtins<72>.
* Library: Library<88>.
* Build: Build<61>.
* C API: C API<42>.
* Windows: Windows<53>.


File: python.info,  Node: Core and Builtins<72>,  Next: Library<88>,  Up: Python 3 5 0 alpha 2

1.19.88.1 Core and Builtins
...........................

   - bpo-23571(1): PyObject_Call() and PyCFunction_Call() now raise a
     SystemError if a function returns a result and raises an exception.
     The SystemError is chained to the previous exception.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23571


File: python.info,  Node: Library<88>,  Next: Build<61>,  Prev: Core and Builtins<72>,  Up: Python 3 5 0 alpha 2

1.19.88.2 Library
.................

   - bpo-22524(1): New os.scandir() function, part of the PEP 471(2):
     “os.scandir() function – a better and faster directory iterator”.
     Patch written by Ben Hoyt.

   - bpo-23103(3): Reduced the memory consumption of IPv4Address and
     IPv6Address.

   - bpo-21793(4): BaseHTTPRequestHandler again logs response code as
     numeric, not as stringified enum.  Patch by Demian Brecht.

   - bpo-23476(5): In the ssl module, enable OpenSSL’s
     X509_V_FLAG_TRUSTED_FIRST flag on certificate stores when it is
     available.

   - bpo-23576(6): Avoid stalling in SSL reads when EOF has been reached
     in the SSL layer but the underlying connection hasn’t been closed.

   - bpo-23504(7): Added an __all__ to the types module.

   - bpo-23563(8): Optimized utility functions in urllib.parse.

   - bpo-7830(9): Flatten nested functools.partial.

   - bpo-20204(10): Added the __module__ attribute to _tkinter classes.

   - bpo-19980(11): Improved help() for non-recognized strings.
     help(‘’) now shows the help on str.  help(‘help’) now shows the
     help on help().  Original patch by Mark Lawrence.

   - bpo-23521(12): Corrected pure python implementation of timedelta
     division.  Eliminated OverflowError from ‘timedelta * float’ for
     some floats; Corrected rounding in timedelta true division.

   - bpo-21619(13): Popen objects no longer leave a zombie after exit in
     the with statement if the pipe was broken.  Patch by Martin Panter.

   - bpo-22936(14): Make it possible to show local variables in
     tracebacks for both the traceback module and unittest.

   - bpo-15955(15): Add an option to limit the output size in
     bz2.decompress().  Patch by Nikolaus Rath.

   - bpo-6639(16): Module-level turtle functions no longer raise
     TclError after closing the window.

   - bpo-814253(17): Group references and conditional group references
     now work in lookbehind assertions in regular expressions.  (See
     also: bpo-9179(18))

   - bpo-23215(19): Multibyte codecs with custom error handlers that
     ignores errors consumed too much memory and raised SystemError or
     MemoryError.  Original patch by Aleksi Torhamo.

   - bpo-5700(20): io.FileIO() called flush() after closing the file.
     flush() was not called in close() if closefd=False.

   - bpo-23374(21): Fixed pydoc failure with non-ASCII files when stdout
     encoding differs from file system encoding (e.g.  on Mac OS).

   - bpo-23481(22): Remove RC4 from the SSL module’s default cipher
     list.

   - bpo-21548(23): Fix pydoc.synopsis() and pydoc.apropos() on modules
     with empty docstrings.

   - bpo-22885(24): Fixed arbitrary code execution vulnerability in the
     dbm.dumb module.  Original patch by Claudiu Popa.

   - bpo-23239(25): ssl.match_hostname() now supports matching of IP
     addresses.

   - bpo-23146(26): Fix mishandling of absolute Windows paths with
     forward slashes in pathlib.

   - bpo-23096(27): Pickle representation of floats with protocol 0 now
     is the same for both Python and C implementations.

   - bpo-19105(28): pprint now more efficiently uses free space at the
     right.

   - bpo-14910(29): Add allow_abbrev parameter to
     argparse.ArgumentParser.  Patch by Jonathan Paugh, Steven Bethard,
     paul j3 and Daniel Eriksson.

   - bpo-21717(30): tarfile.open() now supports ‘x’ (exclusive creation)
     mode.

   - bpo-23344(31): marshal.dumps() is now 20-25% faster on average.

   - bpo-20416(32): marshal.dumps() with protocols 3 and 4 is now 40-50%
     faster on average.

   - bpo-23421(33): Fixed compression in tarfile CLI. Patch by wdv4758h.

   - bpo-23367(34): Fix possible overflows in the unicodedata module.

   - bpo-23361(35): Fix possible overflow in Windows subprocess creation
     code.

   - logging.handlers.QueueListener now takes a respect_handler_level
     keyword argument which, if set to True, will pass messages to
     handlers taking handler levels into account.

   - bpo-19705(36): turtledemo now has a visual sorting algorithm demo.
     Original patch from Jason Yeo.

   - bpo-23801(37): Fix issue where cgi.FieldStorage did not always
     ignore the entire preamble to a multipart body.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22524

   (2) https://www.python.org/dev/peps/pep-0471

   (3) https://bugs.python.org/issue23103

   (4) https://bugs.python.org/issue21793

   (5) https://bugs.python.org/issue23476

   (6) https://bugs.python.org/issue23576

   (7) https://bugs.python.org/issue23504

   (8) https://bugs.python.org/issue23563

   (9) https://bugs.python.org/issue7830

   (10) https://bugs.python.org/issue20204

   (11) https://bugs.python.org/issue19980

   (12) https://bugs.python.org/issue23521

   (13) https://bugs.python.org/issue21619

   (14) https://bugs.python.org/issue22936

   (15) https://bugs.python.org/issue15955

   (16) https://bugs.python.org/issue6639

   (17) https://bugs.python.org/issue814253

   (18) https://bugs.python.org/issue9179

   (19) https://bugs.python.org/issue23215

   (20) https://bugs.python.org/issue5700

   (21) https://bugs.python.org/issue23374

   (22) https://bugs.python.org/issue23481

   (23) https://bugs.python.org/issue21548

   (24) https://bugs.python.org/issue22885

   (25) https://bugs.python.org/issue23239

   (26) https://bugs.python.org/issue23146

   (27) https://bugs.python.org/issue23096

   (28) https://bugs.python.org/issue19105

   (29) https://bugs.python.org/issue14910

   (30) https://bugs.python.org/issue21717

   (31) https://bugs.python.org/issue23344

   (32) https://bugs.python.org/issue20416

   (33) https://bugs.python.org/issue23421

   (34) https://bugs.python.org/issue23367

   (35) https://bugs.python.org/issue23361

   (36) https://bugs.python.org/issue19705

   (37) https://bugs.python.org/issue23801


File: python.info,  Node: Build<61>,  Next: C API<42>,  Prev: Library<88>,  Up: Python 3 5 0 alpha 2

1.19.88.3 Build
...............

   - bpo-23445(1): pydebug builds now use “gcc -Og” where possible, to
     make the resulting executable faster.

   - bpo-23686(2): Update OS X 10.5 installer build to use OpenSSL
     1.0.2a.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23445

   (2) https://bugs.python.org/issue23686


File: python.info,  Node: C API<42>,  Next: Windows<53>,  Prev: Build<61>,  Up: Python 3 5 0 alpha 2

1.19.88.4 C API
...............

   - bpo-20204(1): Deprecation warning is now raised for builtin types
     without the __module__ attribute.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20204


File: python.info,  Node: Windows<53>,  Prev: C API<42>,  Up: Python 3 5 0 alpha 2

1.19.88.5 Windows
.................

   - bpo-23465(1): Implement PEP 486(2) - Make the Python Launcher aware
     of virtual environments.  Patch by Paul Moore.

   - bpo-23437(3): Make user scripts directory versioned on Windows.
     Patch by Paul Moore.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23465

   (2) https://www.python.org/dev/peps/pep-0486

   (3) https://bugs.python.org/issue23437


File: python.info,  Node: Python 3 5 0 alpha 1,  Prev: Python 3 5 0 alpha 2,  Up: Changelog

1.19.89 Python 3.5.0 alpha 1
----------------------------

`Release date: 2015-02-08'

* Menu:

* Core and Builtins: Core and Builtins<73>.
* Library: Library<89>.
* IDLE: IDLE<50>.
* Build: Build<62>.
* C API: C API<43>.
* Documentation: Documentation<54>.
* Tests: Tests<58>.
* Tools/Demos: Tools/Demos<35>.
* Windows: Windows<54>.


File: python.info,  Node: Core and Builtins<73>,  Next: Library<89>,  Up: Python 3 5 0 alpha 1

1.19.89.1 Core and Builtins
...........................

   - bpo-23285(1): PEP 475 - EINTR handling.

   - bpo-22735(2): Fix many edge cases (including crashes) involving
     custom mro() implementations.

   - bpo-22896(3): Avoid using PyObject_AsCharBuffer(),
     PyObject_AsReadBuffer() and PyObject_AsWriteBuffer().

   - bpo-21295(4): Revert some changes (bpo-16795(5)) to AST line
     numbers and column offsets that constituted a regression.

   - bpo-22986(6): Allow changing an object’s __class__ between a
     dynamic type and static type in some cases.

   - bpo-15859(7): PyUnicode_EncodeFSDefault(), PyUnicode_EncodeMBCS()
     and PyUnicode_EncodeCodePage() now raise an exception if the object
     is not a Unicode object.  For PyUnicode_EncodeFSDefault(), it was
     already the case on platforms other than Windows.  Patch written by
     Campbell Barton.

   - bpo-21408(8): The default __ne__() now returns NotImplemented if
     __eq__() returned NotImplemented.  Original patch by Martin Panter.

   - bpo-23321(9): Fixed a crash in str.decode() when error handler
     returned replacement string longer than malformed input data.

   - bpo-22286(10): The “backslashreplace” error handlers now works with
     decoding and translating.

   - bpo-23253(11): Delay-load ShellExecute[AW] in os.startfile for
     reduced startup overhead on Windows.

   - bpo-22038(12): pyatomic.h now uses stdatomic.h or GCC built-in
     functions for atomic memory access if available.  Patch written by
     Vitor de Lima and Gustavo Temple.

   - bpo-20284(13): %-interpolation (aka printf) formatting added for
     bytes and bytearray.

   - bpo-23048(14): Fix jumping out of an infinite while loop in the
     pdb.

   - bpo-20335(15): bytes constructor now raises TypeError when encoding
     or errors is specified with non-string argument.  Based on patch by
     Renaud Blanch.

   - bpo-22834(16): If the current working directory ends up being set
     to a non-existent directory then import will no longer raise
     FileNotFoundError.

   - bpo-22869(17): Move the interpreter startup & shutdown code to a
     new dedicated pylifecycle.c module

   - bpo-22847(18): Improve method cache efficiency.

   - bpo-22335(19): Fix crash when trying to enlarge a bytearray to
     0x7fffffff bytes on a 32-bit platform.

   - bpo-22653(20): Fix an assertion failure in debug mode when doing a
     reentrant dict insertion in debug mode.

   - bpo-22643(21): Fix integer overflow in Unicode case operations
     (upper, lower, title, swapcase, casefold).

   - bpo-17636(22): Circular imports involving relative imports are now
     supported.

   - bpo-22604(23): Fix assertion error in debug mode when dividing a
     complex number by (nan+0j).

   - bpo-21052(24): Do not raise ImportWarning when sys.path_hooks or
     sys.meta_path are set to None.

   - bpo-16518(25): Use ‘bytes-like object required’ in error messages
     that previously used the far more cryptic “‘x’ does not support the
     buffer protocol.

   - bpo-22470(26): Fixed integer overflow issues in “backslashreplace”,
     “xmlcharrefreplace”, and “surrogatepass” error handlers.

   - bpo-22540(27): speed up ‘PyObject_IsInstance’ and
     ‘PyObject_IsSubclass’ in the common case that the second argument
     has metaclass *note type: 6ff.

   - bpo-18711(28): Add a new ‘PyErr_FormatV’ function, similar to
     ‘PyErr_Format’ but accepting a ‘va_list’ argument.

   - bpo-22520(29): Fix overflow checking when generating the repr of a
     unicode object.

   - bpo-22519(30): Fix overflow checking in PyBytes_Repr.

   - bpo-22518(31): Fix integer overflow issues in latin-1 encoding.

   - bpo-16324(32): _charset parameter of MIMEText now also accepts
     email.charset.Charset instances.  Initial patch by Claude Paroz.

   - bpo-1764286(33): Fix inspect.getsource() to support decorated
     functions.  Patch by Claudiu Popa.

   - bpo-18554(34): os.__all__ includes posix functions.

   - bpo-21391(35): Use os.path.abspath in the shutil module.

   - bpo-11471(36): avoid generating a JUMP_FORWARD instruction at the
     end of an if-block if there is no else-clause.  Original patch by
     Eugene Toder.

   - bpo-22215(37): Now ValueError is raised instead of TypeError when
     str or bytes argument contains not permitted null character or
     byte.

   - bpo-22258(38): Fix the internal function set_inheritable() on
     Illumos.  This platform exposes the function ‘ioctl(FIOCLEX)’, but
     calling it fails with errno is ENOTTY: “Inappropriate ioctl for
     device”.  set_inheritable() now falls back to the slower ‘fcntl()’
     (‘F_GETFD’ and then ‘F_SETFD’).

   - bpo-21389(39): Displaying the __qualname__ of the underlying
     function in the repr of a bound method.

   - bpo-22206(40): Using pthread, PyThread_create_key() now sets errno
     to ENOMEM and returns -1 (error) on integer overflow.

   - bpo-20184(41): Argument Clinic based signature introspection added
     for 30 of the builtin functions.

   - bpo-22116(42): C functions and methods (of the
     ‘builtin_function_or_method’ type) can now be weakref’ed.  Patch by
     Wei Wu.

   - bpo-22077(43): Improve index error messages for bytearrays, bytes,
     lists, and tuples by adding ‘or slices’.  Added ‘, not <typename>’
     for bytearrays.  Original patch by Claudiu Popa.

   - bpo-20179(44): Apply Argument Clinic to bytes and bytearray.  Patch
     by Tal Einat.

   - bpo-22082(45): Clear interned strings in slotdefs.

   - Upgrade Unicode database to Unicode 7.0.0.

   - bpo-21897(46): Fix a crash with the f_locals attribute with closure
     variables when frame.clear() has been called.

   - bpo-21205(47): Add a new ‘__qualname__’ attribute to generator, the
     qualified name, and use it in the representation of a generator
     (‘repr(gen)’).  The default name of the generator (‘__name__’
     attribute) is now get from the function instead of the code.  Use
     ‘gen.gi_code.co_name’ to get the name of the code.

   - bpo-21669(48): With the aid of heuristics in SyntaxError.__init__,
     the parser now attempts to generate more meaningful (or at least
     more search engine friendly) error messages when “exec” and “print”
     are used as statements.

   - bpo-21642(49): In the conditional if-else expression, allow an
     integer written with no space between itself and the ‘else’ keyword
     (e.g.  ‘True if 42else False’) to be valid syntax.

   - bpo-21523(50): Fix over-pessimistic computation of the stack effect
     of some opcodes in the compiler.  This also fixes a quadratic
     compilation time issue noticeable when compiling code with a large
     number of “and” and “or” operators.

   - bpo-21418(51): Fix a crash in the builtin function super() when
     called without argument and without current frame (ex: embedded
     Python).

   - bpo-21425(52): Fix flushing of standard streams in the interactive
     interpreter.

   - bpo-21435(53): In rare cases, when running finalizers on objects in
     cyclic trash a bad pointer dereference could occur due to a subtle
     flaw in internal iteration logic.

   - bpo-21377(54): PyBytes_Concat() now tries to concatenate in-place
     when the first argument has a reference count of 1.  Patch by
     Nikolaus Rath.

   - bpo-20355(55): -W command line options now have higher priority
     than the PYTHONWARNINGS environment variable.  Patch by Arfrever.

   - bpo-21274(56): Define PATH_MAX for GNU/Hurd in Python/pythonrun.c.

   - bpo-20904(57): Support setting FPU precision on m68k.

   - bpo-21209(58): Fix sending tuples to custom generator objects with
     the yield from syntax.

   - bpo-21193(59): pow(a, b, c) now raises ValueError rather than
     TypeError when b is negative.  Patch by Josh Rosenberg.

   - bpo-21176(60): PEP 465: Add the ‘@’ operator for matrix
     multiplication.

   - bpo-21134(61): Fix segfault when str is called on an uninitialized
     UnicodeEncodeError, UnicodeDecodeError, or UnicodeTranslateError
     object.

   - bpo-19537(62): Fix PyUnicode_DATA() alignment under m68k.  Patch by
     Andreas Schwab.

   - bpo-20929(63): Add a type cast to avoid shifting a negative number.

   - bpo-20731(64): Properly position in source code files even if they
     are opened in text mode.  Patch by Serhiy Storchaka.

   - bpo-20637(65): Key-sharing now also works for instance dictionaries
     of subclasses.  Patch by Peter Ingebretson.

   - bpo-8297(66): Attributes missing from modules now include the
     module name in the error text.  Original patch by ysj.ray.

   - bpo-19995(67): %c, %o, %x, and %X now raise TypeError on
     non-integer input.

   - bpo-19655(68): The ASDL parser - used by the build process to
     generate code for managing the Python AST in C - was rewritten.
     The new parser is self contained and does not require to carry long
     the spark.py parser-generator library; spark.py was removed from
     the source base.

   - bpo-12546(69): Allow ‘\x00’ to be used as a fill character when
     using str, int, float, and complex __format__ methods.

   - bpo-20480(70): Add ipaddress.reverse_pointer.  Patch by Leon Weber.

   - bpo-13598(71): Modify string.Formatter to support auto-numbering of
     replacement fields.  It now matches the behavior of str.format() in
     this regard.  Patches by Phil Elson and Ramchandra Apte.

   - bpo-8931(72): Make alternate formatting (‘#’) for type ‘c’ raise an
     exception.  In versions prior to 3.5, ‘#’ with ‘c’ had no effect.
     Now specifying it is an error.  Patch by Torsten Landschoff.

   - bpo-23165(73): Perform overflow checks before allocating memory in
     the _Py_char2wchar function.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23285

   (2) https://bugs.python.org/issue22735

   (3) https://bugs.python.org/issue22896

   (4) https://bugs.python.org/issue21295

   (5) https://bugs.python.org/issue16795

   (6) https://bugs.python.org/issue22986

   (7) https://bugs.python.org/issue15859

   (8) https://bugs.python.org/issue21408

   (9) https://bugs.python.org/issue23321

   (10) https://bugs.python.org/issue22286

   (11) https://bugs.python.org/issue23253

   (12) https://bugs.python.org/issue22038

   (13) https://bugs.python.org/issue20284

   (14) https://bugs.python.org/issue23048

   (15) https://bugs.python.org/issue20335

   (16) https://bugs.python.org/issue22834

   (17) https://bugs.python.org/issue22869

   (18) https://bugs.python.org/issue22847

   (19) https://bugs.python.org/issue22335

   (20) https://bugs.python.org/issue22653

   (21) https://bugs.python.org/issue22643

   (22) https://bugs.python.org/issue17636

   (23) https://bugs.python.org/issue22604

   (24) https://bugs.python.org/issue21052

   (25) https://bugs.python.org/issue16518

   (26) https://bugs.python.org/issue22470

   (27) https://bugs.python.org/issue22540

   (28) https://bugs.python.org/issue18711

   (29) https://bugs.python.org/issue22520

   (30) https://bugs.python.org/issue22519

   (31) https://bugs.python.org/issue22518

   (32) https://bugs.python.org/issue16324

   (33) https://bugs.python.org/issue1764286

   (34) https://bugs.python.org/issue18554

   (35) https://bugs.python.org/issue21391

   (36) https://bugs.python.org/issue11471

   (37) https://bugs.python.org/issue22215

   (38) https://bugs.python.org/issue22258

   (39) https://bugs.python.org/issue21389

   (40) https://bugs.python.org/issue22206

   (41) https://bugs.python.org/issue20184

   (42) https://bugs.python.org/issue22116

   (43) https://bugs.python.org/issue22077

   (44) https://bugs.python.org/issue20179

   (45) https://bugs.python.org/issue22082

   (46) https://bugs.python.org/issue21897

   (47) https://bugs.python.org/issue21205

   (48) https://bugs.python.org/issue21669

   (49) https://bugs.python.org/issue21642

   (50) https://bugs.python.org/issue21523

   (51) https://bugs.python.org/issue21418

   (52) https://bugs.python.org/issue21425

   (53) https://bugs.python.org/issue21435

   (54) https://bugs.python.org/issue21377

   (55) https://bugs.python.org/issue20355

   (56) https://bugs.python.org/issue21274

   (57) https://bugs.python.org/issue20904

   (58) https://bugs.python.org/issue21209

   (59) https://bugs.python.org/issue21193

   (60) https://bugs.python.org/issue21176

   (61) https://bugs.python.org/issue21134

   (62) https://bugs.python.org/issue19537

   (63) https://bugs.python.org/issue20929

   (64) https://bugs.python.org/issue20731

   (65) https://bugs.python.org/issue20637

   (66) https://bugs.python.org/issue8297

   (67) https://bugs.python.org/issue19995

   (68) https://bugs.python.org/issue19655

   (69) https://bugs.python.org/issue12546

   (70) https://bugs.python.org/issue20480

   (71) https://bugs.python.org/issue13598

   (72) https://bugs.python.org/issue8931

   (73) https://bugs.python.org/issue23165


File: python.info,  Node: Library<89>,  Next: IDLE<50>,  Prev: Core and Builtins<73>,  Up: Python 3 5 0 alpha 1

1.19.89.2 Library
.................

   - bpo-23399(1): pyvenv creates relative symlinks where possible.

   - bpo-20289(2): cgi.FieldStorage() now supports the context
     management protocol.

   - bpo-13128(3): Print response headers for CONNECT requests when
     debuglevel > 0.  Patch by Demian Brecht.

   - bpo-15381(4): Optimized io.BytesIO to make less allocations and
     copyings.

   - bpo-22818(5): Splitting on a pattern that could match an empty
     string now raises a warning.  Patterns that can only match empty
     strings are now rejected.

   - bpo-23099(6): Closing io.BytesIO with exported buffer is rejected
     now to prevent corrupting exported buffer.

   - bpo-23326(7): Removed __ne__ implementations.  Since fixing default
     __ne__ implementation in bpo-21408(8) they are redundant.

   - bpo-23363(9): Fix possible overflow in itertools.permutations.

   - bpo-23364(10): Fix possible overflow in itertools.product.

   - bpo-23366(11): Fixed possible integer overflow in
     itertools.combinations.

   - bpo-23369(12): Fixed possible integer overflow in
     _json.encode_basestring_ascii.

   - bpo-23353(13): Fix the exception handling of generators in
     PyEval_EvalFrameEx().  At entry, save or swap the exception state
     even if PyEval_EvalFrameEx() is called with throwflag=0.  At exit,
     the exception state is now always restored or swapped, not only if
     why is WHY_YIELD or WHY_RETURN. Patch co-written with Antoine
     Pitrou.

   - bpo-14099(14): Restored support of writing ZIP files to tellable
     but non-seekable streams.

   - bpo-14099(15): Writing to ZipFile and reading multiple ZipExtFiles
     is threadsafe now.

   - bpo-19361(16): JSON decoder now raises JSONDecodeError instead of
     ValueError.

   - bpo-18518(17): timeit now rejects statements which can’t be
     compiled outside a function or a loop (e.g.  “return” or “break”).

   - bpo-23094(18): Fixed readline with frames in Python implementation
     of pickle.

   - bpo-23268(19): Fixed bugs in the comparison of ipaddress classes.

   - bpo-21408(20): Removed incorrect implementations of __ne__() which
     didn’t returned NotImplemented if __eq__() returned NotImplemented.
     The default __ne__() now works correctly.

   - bpo-19996(21): ‘email.feedparser.FeedParser’ now handles
     (malformed) headers with no key rather than assuming the body has
     started.

   - bpo-20188(22): Support Application-Layer Protocol Negotiation
     (ALPN) in the ssl module.

   - bpo-23133(23): Pickling of ipaddress objects now produces more
     compact and portable representation.

   - bpo-23248(24): Update ssl error codes from latest OpenSSL git
     master.

   - bpo-23266(25): Much faster implementation of
     ipaddress.collapse_addresses() when there are many non-consecutive
     addresses.

   - bpo-23098(26): 64-bit dev_t is now supported in the os module.

   - bpo-21817(27): When an exception is raised in a task submitted to a
     ProcessPoolExecutor, the remote traceback is now displayed in the
     parent process.  Patch by Claudiu Popa.

   - bpo-15955(28): Add an option to limit output size when
     decompressing LZMA data.  Patch by Nikolaus Rath and Martin Panter.

   - bpo-23250(29): In the http.cookies module, capitalize “HttpOnly”
     and “Secure” as they are written in the standard.

   - bpo-23063(30): In the distutils’ check command, fix parsing of reST
     with code or code-block directives.

   - bpo-23209(31): selectors.BaseSelector.get_key() now raises a
     RuntimeError if the selector is closed.  And
     selectors.BaseSelector.close() now clears its internal reference to
     the selector mapping to break a reference cycle.  Initial patch
     written by Martin Richard.  (See also: bpo-23225(32))

   - bpo-17911(33): Provide a way to seed the linecache for a PEP-302
     module without actually loading the code.

   - bpo-17911(34): Provide a new object API for traceback, including
     the ability to not lookup lines at all until the traceback is
     actually rendered, without any trace of the original objects being
     kept alive.

   - bpo-19777(35): Provide a home() classmethod on Path objects.
     Contributed by Victor Salgado and Mayank Tripathi.

   - bpo-23206(36): Make ‘json.dumps(..., ensure_ascii=False)’ as fast
     as the default case of ‘ensure_ascii=True’.  Patch by Naoki Inada.

   - bpo-23185(37): Add math.inf and math.nan constants.

   - bpo-23186(38): Add ssl.SSLObject.shared_ciphers() and
     ssl.SSLSocket.shared_ciphers() to fetch the client’s list ciphers
     sent at handshake.

   - bpo-23143(39): Remove compatibility with OpenSSLs older than 0.9.8.

   - bpo-23132(40): Improve performance and introspection support of
     comparison methods created by functool.total_ordering.

   - bpo-19776(41): Add an expanduser() method on Path objects.

   - bpo-23112(42): Fix SimpleHTTPServer to correctly carry the query
     string and fragment when it redirects to add a trailing slash.

   - bpo-21793(43): Added http.HTTPStatus enums (i.e.  HTTPStatus.OK,
     HTTPStatus.NOT_FOUND). Patch by Demian Brecht.

   - bpo-23093(44): In the io, module allow more operations to work on
     detached streams.

   - bpo-23111(45): In the ftplib, make ssl.PROTOCOL_SSLv23 the default
     protocol version.

   - bpo-22585(46): On OpenBSD 5.6 and newer, os.urandom() now calls
     getentropy(), instead of reading /dev/urandom, to get pseudo-random
     bytes.

   - bpo-19104(47): pprint now produces evaluable output for wrapped
     strings.

   - bpo-23071(48): Added missing names to codecs.__all__.  Patch by
     Martin Panter.

   - bpo-22783(49): Pickling now uses the NEWOBJ opcode instead of the
     NEWOBJ_EX opcode if possible.

   - bpo-15513(50): Added a __sizeof__ implementation for pickle
     classes.

   - bpo-19858(51): pickletools.optimize() now aware of the MEMOIZE
     opcode, can produce more compact result and no longer produces
     invalid output if input data contains MEMOIZE opcodes together with
     PUT or BINPUT opcodes.

   - bpo-22095(52): Fixed HTTPConnection.set_tunnel with default port.
     The port value in the host header was set to “None”.  Patch by
     Demian Brecht.

   - bpo-23016(53): A warning no longer produces an AttributeError when
     the program is run with pythonw.exe.

   - bpo-21775(54): shutil.copytree(): fix crash when copying to VFAT.
     An exception handler assumed that OSError objects always have a
     ‘winerror’ attribute.  That is not the case, so the exception
     handler itself raised AttributeError when run on Linux (and,
     presumably, any other non-Windows OS). Patch by Greg Ward.

   - bpo-1218234(55): Fix inspect.getsource() to load updated source of
     reloaded module.  Initial patch by Berker Peksag.

   - bpo-21740(56): Support wrapped callables in doctest.  Patch by
     Claudiu Popa.

   - bpo-23009(57): Make sure selectors.EpollSelector.select() works
     when no FD is registered.

   - bpo-22959(58): In the constructor of http.client.HTTPSConnection,
     prefer the context’s check_hostname attribute over the
     `check_hostname' parameter.

   - bpo-22696(59): Add function *note sys.is_finalizing(): 851. to know
     about interpreter shutdown.

   - bpo-16043(60): Add a default limit for the amount of data
     xmlrpclib.gzip_decode will return.  This resolves CVE-2013-1753.

   - bpo-14099(61): ZipFile.open() no longer reopen the underlying file.
     Objects returned by ZipFile.open() can now operate independently of
     the ZipFile even if the ZipFile was created by passing in a
     file-like object as the first argument to the constructor.

   - bpo-22966(62): Fix __pycache__ pyc file name clobber when
     pyc_compile is asked to compile a source file containing multiple
     dots in the source file name.

   - bpo-21971(63): Update turtledemo doc and add module to the index.

   - bpo-21032(64): Fixed socket leak if HTTPConnection.getresponse()
     fails.  Original patch by Martin Panter.

   - bpo-22407(65): Deprecated the use of re.LOCALE flag with str
     patterns or re.ASCII. It was newer worked.

   - bpo-22902(66): The “ip” command is now used on Linux to determine
     MAC address in uuid.getnode().  Pach by Bruno Cauet.

   - bpo-22960(67): Add a context argument to xmlrpclib.ServerProxy
     constructor.

   - bpo-22389(68): Add contextlib.redirect_stderr().

   - bpo-21356(69): Make ssl.RAND_egd() optional to support LibreSSL.
     The availability of the function is checked during the compilation.
     Patch written by Bernard Spil.

   - bpo-22915(70): SAX parser now supports files opened with file
     descriptor or bytes path.

   - bpo-22609(71): Constructors and update methods of mapping classes
     in the collections module now accept the self keyword argument.

   - bpo-22940(72): Add readline.append_history_file.

   - bpo-19676(73): Added the “namereplace” error handler.

   - bpo-22788(74): Add `context' parameter to
     logging.handlers.HTTPHandler.

   - bpo-22921(75): Allow SSLContext to take the `hostname' parameter
     even if OpenSSL doesn’t support SNI.

   - bpo-22894(76): TestCase.subTest() would cause the test suite to be
     stopped when in failfast mode, even in the absence of failures.

   - bpo-22796(77): HTTP cookie parsing is now stricter, in order to
     protect against potential injection attacks.

   - bpo-22370(78): Windows detection in pathlib is now more robust.

   - bpo-22841(79): Reject coroutines in asyncio add_signal_handler().
     Patch by Ludovic.Gasc.

   - bpo-19494(80): Added urllib.request.HTTPBasicPriorAuthHandler.
     Patch by Matej Cepl.

   - bpo-22578(81): Added attributes to the re.error class.

   - bpo-22849(82): Fix possible double free in the io.TextIOWrapper
     constructor.

   - bpo-12728(83): Different Unicode characters having the same
     uppercase but different lowercase are now matched in
     case-insensitive regular expressions.

   - bpo-22821(84): Fixed fcntl() with integer argument on 64-bit
     big-endian platforms.

   - bpo-21650(85): Add an ‘--sort-keys’ option to json.tool CLI.

   - bpo-22824(86): Updated reprlib output format for sets to use set
     literals.  Patch contributed by Berker Peksag.

   - bpo-22824(87): Updated reprlib output format for arrays to display
     empty arrays without an unnecessary empty list.  Suggested by
     Serhiy Storchaka.

   - bpo-22406(88): Fixed the uu_codec codec incorrectly ported to 3.x.
     Based on patch by Martin Panter.

   - bpo-17293(89): uuid.getnode() now determines MAC address on AIX
     using netstat.  Based on patch by Aivars Kalvāns.

   - bpo-22769(90): Fixed ttk.Treeview.tag_has() when called without
     arguments.

   - bpo-22417(91): Verify certificates by default in httplib (PEP 476).

   - bpo-22775(92): Fixed unpickling of http.cookies.SimpleCookie with
     protocol 2 and above.  Patch by Tim Graham.

   - bpo-22776(93): Brought excluded code into the scope of a try block
     in SysLogHandler.emit().

   - bpo-22665(94): Add missing get_terminal_size and SameFileError to
     shutil.__all__.

   - bpo-6623(95): Remove deprecated Netrc class in the ftplib module.
     Patch by Matt Chaput.

   - bpo-17381(96): Fixed handling of case-insensitive ranges in regular
     expressions.

   - bpo-22410(97): Module level functions in the re module now cache
     compiled locale-dependent regular expressions taking into account
     the locale.

   - bpo-22759(98): Query methods on pathlib.Path() (exists(), is_dir(),
     etc.)  now return False when the underlying stat call raises
     NotADirectoryError.

   - bpo-8876(99): distutils now falls back to copying files when hard
     linking doesn’t work.  This allows use with special filesystems
     such as VirtualBox shared folders.

   - bpo-22217(100): Implemented reprs of classes in the zipfile module.

   - bpo-22457(101): Honour load_tests in the start_dir of discovery.

   - bpo-18216(102): gettext now raises an error when a .mo file has an
     unsupported major version number.  Patch by Aaron Hill.

   - bpo-13918(103): Provide a locale.delocalize() function which can
     remove locale-specific number formatting from a string representing
     a number, without then converting it to a specific type.  Patch by
     Cédric Krier.

   - bpo-22676(104): Make the pickling of global objects which don’t
     have a __module__ attribute less slow.

   - bpo-18853(105): Fixed ResourceWarning in shlex.__nain__.

   - bpo-9351(106): Defaults set with set_defaults on an argparse
     subparser are no longer ignored when also set on the parent parser.

   - bpo-7559(107): unittest test loading ImportErrors are reported as
     import errors with their import exception rather than as attribute
     errors after the import has already failed.

   - bpo-19746(108): Make it possible to examine the errors from
     unittest discovery without executing the test suite.  The new
     ‘errors’ attribute on TestLoader exposes these non-fatal errors
     encountered during discovery.

   - bpo-21991(109): Make email.headerregistry’s header ‘params’
     attributes be read-only (MappingProxyType).  Previously the
     dictionary was modifiable but a new one was created on each access
     of the attribute.

   - bpo-22638(110): SSLv3 is now disabled throughout the standard
     library.  It can still be enabled by instantiating a SSLContext
     manually.

   - bpo-22641(111): In asyncio, the default SSL context for client
     connections is now created using ssl.create_default_context(), for
     stronger security.

   - bpo-17401(112): Include closefd in io.FileIO repr.

   - bpo-21338(113): Add silent mode for compileall.  quiet parameters
     of compile_{dir, file, path} functions now have a multilevel value.
     Also, -q option of the CLI now have a multilevel value.  Patch by
     Thomas Kluyver.

   - bpo-20152(114): Convert the array and cmath modules to Argument
     Clinic.

   - bpo-18643(115): Add socket.socketpair() on Windows.

   - bpo-22435(116): Fix a file descriptor leak when socketserver bind
     fails.

   - bpo-13096(117): Fixed segfault in CTypes POINTER handling of large
     values.

   - bpo-11694(118): Raise ConversionError in xdrlib as documented.
     Patch by Filip Gruszczyński and Claudiu Popa.

   - bpo-19380(119): Optimized parsing of regular expressions.

   - bpo-1519638(120): Now unmatched groups are replaced with empty
     strings in re.sub() and re.subn().

   - bpo-18615(121): sndhdr.what/whathdr now return a namedtuple.

   - bpo-22462(122): Fix pyexpat’s creation of a dummy frame to make it
     appear in exception tracebacks.

   - bpo-21965(123): Add support for in-memory SSL to the ssl module.
     Patch by Geert Jansen.

   - bpo-21173(124): Fix len() on a WeakKeyDictionary when .clear() was
     called with an iterator alive.

   - bpo-11866(125): Eliminated race condition in the computation of
     names for new threads.

   - bpo-21905(126): Avoid RuntimeError in pickle.whichmodule() when
     sys.modules is mutated while iterating.  Patch by Olivier Grisel.

   - bpo-11271(127): concurrent.futures.Executor.map() now takes a
     `chunksize' argument to allow batching of tasks in child processes
     and improve performance of ProcessPoolExecutor.  Patch by Dan
     O’Reilly.

   - bpo-21883(128): os.path.join() and os.path.relpath() now raise a
     TypeError with more helpful error message for unsupported or
     mismatched types of arguments.

   - bpo-22219(129): The zipfile module CLI now adds entries for
     directories (including empty directories) in ZIP file.

   - bpo-22449(130): In the ssl.SSLContext.load_default_certs, consult
     the environmental variables SSL_CERT_DIR and SSL_CERT_FILE on
     Windows.

   - bpo-22508(131): The email.__version__ variable has been removed;
     the email code is no longer shipped separately from the stdlib, and
     __version__ hasn’t been updated in several releases.

   - bpo-20076(132): Added non derived UTF-8 aliases to locale aliases
     table.

   - bpo-20079(133): Added locales supported in glibc 2.18 to locale
     alias table.

   - bpo-20218(134): Added convenience methods read_text/write_text and
     read_bytes/ write_bytes to pathlib.Path objects.

   - bpo-22396(135): On 32-bit AIX platform, don’t expose
     os.posix_fadvise() nor os.posix_fallocate() because their
     prototypes in system headers are wrong.

   - bpo-22517(136): When an io.BufferedRWPair object is deallocated,
     clear its weakrefs.

   - bpo-22437(137): Number of capturing groups in regular expression is
     no longer limited by 100.

   - bpo-17442(138): InteractiveInterpreter now displays the full
     chained traceback in its showtraceback method, to match the built
     in interactive interpreter.

   - bpo-23392(139): Added tests for marshal C API that works with
     FILE*.

   - bpo-10510(140): distutils register and upload methods now use HTML
     standards compliant CRLF line endings.

   - bpo-9850(141): Fixed macpath.join() for empty first component.
     Patch by Oleg Oshmyan.

   - bpo-5309(142): distutils’ build and build_ext commands now accept a
     ‘-j’ option to enable parallel building of extension modules.

   - bpo-22448(143): Improve canceled timer handles cleanup to prevent
     unbound memory usage.  Patch by Joshua Moore-Oliva.

   - bpo-22427(144): TemporaryDirectory no longer attempts to clean up
     twice when used in the with statement in generator.

   - bpo-22362(145): Forbidden ambiguous octal escapes out of range
     0-0o377 in regular expressions.

   - bpo-20912(146): Now directories added to ZIP file have correct Unix
     and MS-DOS directory attributes.

   - bpo-21866(147): ZipFile.close() no longer writes ZIP64 central
     directory records if allowZip64 is false.

   - bpo-22278(148): Fix urljoin problem with relative urls, a
     regression observed after changes to issue22118 were submitted.

   - bpo-22415(149): Fixed debugging output of the GROUPREF_EXISTS
     opcode in the re module.  Removed trailing spaces in debugging
     output.

   - bpo-22423(150): Unhandled exception in thread no longer causes
     unhandled AttributeError when sys.stderr is None.

   - bpo-21332(151): Ensure that ‘bufsize=1’ in subprocess.Popen()
     selects line buffering, rather than block buffering.  Patch by
     Akira Li.

   - bpo-21091(152): Fix API bug:
     email.message.EmailMessage.is_attachment is now a method.

   - bpo-21079(153): Fix email.message.EmailMessage.is_attachment to
     return the correct result when the header has parameters as well as
     a value.

   - bpo-22247(154): Add NNTPError to nntplib.__all__.

   - bpo-22366(155): urllib.request.urlopen will accept a context object
     (SSLContext) as an argument which will then be used for HTTPS
     connection.  Patch by Alex Gaynor.

   - bpo-4180(156): The warnings registries are now reset when the
     filters are modified.

   - bpo-22419(157): Limit the length of incoming HTTP request in
     wsgiref server to 65536 bytes and send a 414 error code for higher
     lengths.  Patch contributed by Devin Cook.

   - Lax cookie parsing in http.cookies could be a security issue when
     combined with non-standard cookie handling in some Web browsers.
     Reported by Sergey Bobrov.

   - bpo-20537(158): logging methods now accept an exception instance as
     well as a Boolean value or exception tuple.  Thanks to Yury
     Selivanov for the patch.

   - bpo-22384(159): An exception in Tkinter callback no longer crashes
     the program when it is run with pythonw.exe.

   - bpo-22168(160): Prevent turtle AttributeError with non-default
     Canvas on OS X.

   - bpo-21147(161): sqlite3 now raises an exception if the request
     contains a null character instead of truncating it.  Based on patch
     by Victor Stinner.

   - bpo-13968(162): The glob module now supports recursive search in
     subdirectories using the ‘**’ pattern.

   - bpo-21951(163): Fixed a crash in Tkinter on AIX when called Tcl
     command with empty string or tuple argument.

   - bpo-21951(164): Tkinter now most likely raises MemoryError instead
     of crash if the memory allocation fails.

   - bpo-22338(165): Fix a crash in the json module on memory allocation
     failure.

   - bpo-12410(166): imaplib.IMAP4 now supports the context management
     protocol.  Original patch by Tarek Ziadé.

   - bpo-21270(167): We now override tuple methods in mock.call objects
     so that they can be used as normal call attributes.

   - bpo-16662(168): load_tests() is now unconditionally run when it is
     present in a package’s __init__.py.
     TestLoader.loadTestsFromModule() still accepts use_load_tests, but
     it is deprecated and ignored.  A new keyword-only attribute
     ‘pattern’ is added and documented.  Patch given by Robert Collins,
     tweaked by Barry Warsaw.

   - bpo-22226(169): First letter no longer is stripped from the
     “status” key in the result of Treeview.heading().

   - bpo-19524(170): Fixed resource leak in the HTTP connection when an
     invalid response is received.  Patch by Martin Panter.

   - bpo-20421(171): Add a .version() method to SSL sockets exposing the
     actual protocol version in use.

   - bpo-19546(172): configparser exceptions no longer expose
     implementation details.  Chained KeyErrors are removed, which leads
     to cleaner tracebacks.  Patch by Claudiu Popa.

   - bpo-22051(173): turtledemo no longer reloads examples to re-run
     them.  Initialization of variables and gui setup should be done in
     main(), which is called each time a demo is run, but not on import.

   - bpo-21933(174): Turtledemo users can change the code font size with
     a menu selection or control(command) ‘-’ or ‘+’ or
     control-mousewheel.  Original patch by Lita Cho.

   - bpo-21597(175): The separator between the turtledemo text pane and
     the drawing canvas can now be grabbed and dragged with a mouse.
     The code text pane can be widened to easily view or copy the full
     width of the text.  The canvas can be widened on small screens.
     Original patches by Jan Kanis and Lita Cho.

   - bpo-18132(176): Turtledemo buttons no longer disappear when the
     window is shrunk.  Original patches by Jan Kanis and Lita Cho.

   - bpo-22043(177): time.monotonic() is now always available.
     ‘threading.Lock.acquire()’, ‘threading.RLock.acquire()’ and socket
     operations now use a monotonic clock, instead of the system clock,
     when a timeout is used.

   - bpo-21527(178): Add a default number of workers to
     ThreadPoolExecutor equal to 5 times the number of CPUs.  Patch by
     Claudiu Popa.

   - bpo-22216(179): smtplib now resets its state more completely after
     a quit.  The most obvious consequence of the previous behavior was
     a STARTTLS failure during a connect/starttls/quit/connect/starttls
     sequence.

   - bpo-22098(180): ctypes’ BigEndianStructure and
     LittleEndianStructure now define an empty __slots__ so that
     subclasses don’t always get an instance dict.  Patch by Claudiu
     Popa.

   - bpo-22185(181): Fix an occasional RuntimeError in
     threading.Condition.wait() caused by mutation of the waiters queue
     without holding the lock.  Patch by Doug Zongker.

   - bpo-22287(182): On UNIX, _PyTime_gettimeofday() now uses
     clock_gettime(CLOCK_REALTIME) if available.  As a side effect,
     Python now depends on the librt library on Solaris and on Linux
     (only with glibc older than 2.17).

   - bpo-22182(183): Use e.args to unpack exceptions correctly in
     distutils.file_util.move_file.  Patch by Claudiu Popa.

   - The webbrowser module now uses subprocess’s start_new_session=True
     rather than a potentially risky preexec_fn=os.setsid call.

   - bpo-22042(184): signal.set_wakeup_fd(fd) now raises an exception if
     the file descriptor is in blocking mode.

   - bpo-16808(185): inspect.stack() now returns a named tuple instead
     of a tuple.  Patch by Daniel Shahaf.

   - bpo-22236(186): Fixed Tkinter images copying operations in
     NoDefaultRoot mode.

   - bpo-2527(187): Add a `globals' argument to timeit functions, in
     order to override the globals namespace in which the timed code is
     executed.  Patch by Ben Roberts.

   - bpo-22118(188): Switch urllib.parse to use RFC 3986 semantics for
     the resolution of relative URLs, rather than RFCs 1808 and 2396.
     Patch by Demian Brecht.

   - bpo-21549(189): Added the “members” parameter to TarFile.list().

   - bpo-19628(190): Allow compileall recursion depth to be specified
     with a -r option.

   - bpo-15696(191): Add a __sizeof__ implementation for mmap objects on
     Windows.

   - bpo-22068(192): Avoided reference loops with Variables and Fonts in
     Tkinter.

   - bpo-22165(193): SimpleHTTPRequestHandler now supports undecodable
     file names.

   - bpo-15381(194): Optimized line reading in io.BytesIO.

   - bpo-8797(195): Raise HTTPError on failed Basic Authentication
     immediately.  Initial patch by Sam Bull.

   - bpo-20729(196): Restored the use of lazy
     iterkeys()/itervalues()/iteritems() in the mailbox module.

   - bpo-21448(197): Changed FeedParser feed() to avoid O(N^2) behavior
     when parsing long line.  Original patch by Raymond Hettinger.

   - bpo-22184(198): The functools LRU Cache decorator factory now gives
     an earlier and clearer error message when the user forgets the
     required parameters.

   - bpo-17923(199): glob() patterns ending with a slash no longer match
     non-dirs on AIX. Based on patch by Delhallt.

   - bpo-21725(200): Added support for RFC 6531 (SMTPUTF8) in smtpd.

   - bpo-22176(201): Update the ctypes module’s libffi to v3.1.  This
     release adds support for the Linux AArch64 and POWERPC ELF ABIv2
     little endian architectures.

   - bpo-5411(202): Added support for the “xztar” format in the shutil
     module.

   - bpo-21121(203): Don’t force 3rd party C extensions to be built with
     -Werror=declaration-after-statement.

   - bpo-21975(204): Fixed crash when using uninitialized sqlite3.Row
     (in particular when unpickling pickled sqlite3.Row).  sqlite3.Row
     is now initialized in the __new__() method.

   - bpo-20170(205): Convert posixmodule to use Argument Clinic.

   - bpo-21539(206): Add an `exists_ok' argument to ‘Pathlib.mkdir()’ to
     mimic ‘mkdir -p’ and *note os.makedirs(): 4c4. functionality.  When
     true, ignore FileExistsErrors.  Patch by Berker Peksag.

   - bpo-22127(207): Bypass IDNA for pure-ASCII host names in the socket
     module (in particular for numeric IPs).

   - bpo-21047(208): set the default value for the `convert_charrefs'
     argument of HTMLParser to True.  Patch by Berker Peksag.

   - Add an __all__ to html.entities.

   - bpo-15114(209): the strict mode and argument of HTMLParser,
     HTMLParser.error, and the HTMLParserError exception have been
     removed.

   - bpo-22085(210): Dropped support of Tk 8.3 in Tkinter.

   - bpo-21580(211): Now Tkinter correctly handles bytes arguments
     passed to Tk.  In particular this allows initializing images from
     binary data.

   - bpo-22003(212): When initialized from a bytes object, io.BytesIO()
     now defers making a copy until it is mutated, improving performance
     and memory use on some use cases.  Patch by David Wilson.

   - bpo-22018(213): On Windows, signal.set_wakeup_fd() now also
     supports sockets.  A side effect is that Python depends to the
     WinSock library.

   - bpo-22054(214): Add os.get_blocking() and os.set_blocking()
     functions to get and set the blocking mode of a file descriptor
     (False if the O_NONBLOCK flag is set, True otherwise).  These
     functions are not available on Windows.

   - bpo-17172(215): Make turtledemo start as active on OS X even when
     run with subprocess.  Patch by Lita Cho.

   - bpo-21704(216): Fix build error for _multiprocessing when
     semaphores are not available.  Patch by Arfrever Frehtes Taifersar
     Arahesis.

   - bpo-20173(217): Convert sha1, sha256, sha512 and md5 to
     ArgumentClinic.  Patch by Vajrasky Kok.

   - Fix repr(_socket.socket) on Windows 64-bit: don’t fail with
     OverflowError on closed socket.  repr(socket.socket) already works
     fine.

   - bpo-22033(218): Reprs of most Python implemented classes now
     contain actual class name instead of hardcoded one.

   - bpo-21947(219): The dis module can now disassemble
     generator-iterator objects based on their gi_code attribute.  Patch
     by Clement Rouault.

   - bpo-16133(220): The asynchat.async_chat.handle_read() method now
     ignores BlockingIOError exceptions.

   - bpo-22044(221): Fixed premature DECREF in call_tzinfo_method.
     Patch by Tom Flanagan.

   - bpo-19884(222): readline: Disable the meta modifier key if stdout
     is not a terminal to not write the ANSI sequence ‘"\033[1034h"’
     into stdout.  This sequence is used on some terminal (ex:
     TERM=xterm-256color”) to enable support of 8 bit characters.

   - bpo-4350(223): Removed a number of out-of-dated and non-working for
     a long time Tkinter methods.

   - bpo-6167(224): Scrollbar.activate() now returns the name of active
     element if the argument is not specified.  Scrollbar.set() now
     always accepts only 2 arguments.

   - bpo-15275(225): Clean up and speed up the ntpath module.

   - bpo-21888(226): plistlib’s load() and loads() now work if the fmt
     parameter is specified.

   - bpo-22032(227): __qualname__ instead of __name__ is now always used
     to format fully qualified class names of Python implemented
     classes.

   - bpo-22031(228): Reprs now always use hexadecimal format with the
     “0x” prefix when contain an id in form ” at 0x…”.

   - bpo-22018(229): signal.set_wakeup_fd() now raises an OSError
     instead of a ValueError on ‘fstat()’ failure.

   - bpo-21044(230): tarfile.open() now handles fileobj with an integer
     ‘name’ attribute.  Based on patch by Antoine Pietri.

   - bpo-21966(231): Respect -q command-line option when code module is
     ran.

   - bpo-19076(232): Don’t pass the redundant ‘file’ argument to
     self.error().

   - bpo-16382(233): Improve exception message of warnings.warn() for
     bad category.  Initial patch by Phil Elson.

   - bpo-21932(234): os.read() now uses a ‘Py_ssize_t()’ type instead of
     ‘int’ for the size to support reading more than 2 GB at once.  On
     Windows, the size is truncated to INT_MAX. As any call to
     os.read(), the OS may read less bytes than the number of requested
     bytes.

   - bpo-21942(235): Fixed source file viewing in pydoc’s server mode on
     Windows.

   - bpo-11259(236): asynchat.async_chat().set_terminator() now raises a
     ValueError if the number of received bytes is negative.

   - bpo-12523(237): asynchat.async_chat.push() now raises a TypeError
     if it doesn’t get a bytes string

   - bpo-21707(238): Add missing kwonlyargcount argument to
     ModuleFinder.replace_paths_in_code().

   - bpo-20639(239): calling Path.with_suffix(‘’) allows removing the
     suffix again.  Patch by July Tikhonov.

   - bpo-21714(240): Disallow the construction of invalid paths using
     Path.with_name().  Original patch by Antony Lee.

   - bpo-15014(241): Added ‘auth’ method to smtplib to make implementing
     auth mechanisms simpler, and used it internally in the login
     method.

   - bpo-21151(242): Fixed a segfault in the winreg module when ‘None’
     is passed as a ‘REG_BINARY’ value to SetValueEx.  Patch by John
     Ehresman.

   - bpo-21090(243): io.FileIO.readall() does not ignore I/O errors
     anymore.  Before, it ignored I/O errors if at least the first C
     call read() succeed.

   - bpo-5800(244): headers parameter of wsgiref.headers.Headers is now
     optional.  Initial patch by Pablo Torres Navarrete and SilentGhost.

   - bpo-21781(245): ssl.RAND_add() now supports strings longer than 2
     GB.

   - bpo-21679(246): Prevent extraneous fstat() calls during open().
     Patch by Bohuslav Kabrda.

   - bpo-21863(247): cProfile now displays the module name of C
     extension functions, in addition to their own name.

   - bpo-11453(248): asyncore: emit a ResourceWarning when an unclosed
     file_wrapper object is destroyed.  The destructor now closes the
     file if needed.  The close() method can now be called twice: the
     second call does nothing.

   - bpo-21858(249): Better handling of Python exceptions in the sqlite3
     module.

   - bpo-21476(250): Make sure the email.parser.BytesParser
     TextIOWrapper is discarded after parsing, so the input file isn’t
     unexpectedly closed.

   - bpo-20295(251): imghdr now recognizes OpenEXR format images.

   - bpo-21729(252): Used the “with” statement in the dbm.dumb module to
     ensure files closing.  Patch by Claudiu Popa.

   - bpo-21491(253): socketserver: Fix a race condition in child
     processes reaping.

   - bpo-21719(254): Added the ‘st_file_attributes’ field to
     os.stat_result on Windows.

   - bpo-21832(255): Require named tuple inputs to be exact strings.

   - bpo-21722(256): The distutils “upload” command now exits with a
     non-zero return code when uploading fails.  Patch by Martin
     Dengler.

   - bpo-21723(257): asyncio.Queue: support any type of number (ex:
     float) for the maximum size.  Patch written by Vajrasky Kok.

   - bpo-21711(258): support for “site-python” directories has now been
     removed from the site module (it was deprecated in 3.4).

   - bpo-17552(259): new socket.sendfile() method allowing a file to be
     sent over a socket by using high-performance os.sendfile() on UNIX.
     Patch by Giampaolo Rodola’.

   - bpo-18039(260): dbm.dump.open() now always creates a new database
     when the flag has the value ‘n’.  Patch by Claudiu Popa.

   - bpo-21326(261): Add a new is_closed() method to
     asyncio.BaseEventLoop.  run_forever() and run_until_complete()
     methods of asyncio.BaseEventLoop now raise an exception if the
     event loop was closed.

   - bpo-21766(262): Prevent a security hole in CGIHTTPServer by URL
     unquoting paths before checking for a CGI script at that path.

   - bpo-21310(263): Fixed possible resource leak in failed open().

   - bpo-21256(264): Printout of keyword args should be in deterministic
     order in a mock function call.  This will help to write better
     doctests.

   - bpo-21677(265): Fixed chaining nonnormalized exceptions in io
     close() methods.

   - bpo-11709(266): Fix the pydoc.help function to not fail when
     sys.stdin is not a valid file.

   - bpo-21515(267): tempfile.TemporaryFile now uses os.O_TMPFILE flag
     is available.

   - bpo-13223(268): Fix pydoc.writedoc so that the HTML documentation
     for methods that use ‘self’ in the example code is generated
     correctly.

   - bpo-21463(269): In urllib.request, fix pruning of the FTP cache.

   - bpo-21618(270): The subprocess module could fail to close open fds
     that were inherited by the calling process and already higher than
     POSIX resource limits would otherwise allow.  On systems with a
     functioning /proc/self/fd or /dev/fd interface the max is now
     ignored and all fds are closed.

   - bpo-20383(271): Introduce importlib.util.module_from_spec() as the
     preferred way to create a new module.

   - bpo-21552(272): Fixed possible integer overflow of too long string
     lengths in the tkinter module on 64-bit platforms.

   - bpo-14315(273): The zipfile module now ignores extra fields in the
     central directory that are too short to be parsed instead of
     letting a struct.unpack error bubble up as this “bad data” appears
     in many real world zip files in the wild and is ignored by other
     zip tools.

   - bpo-13742(274): Added “key” and “reverse” parameters to
     heapq.merge().  (First draft of patch contributed by Simon Sapin.)

   - bpo-21402(275): tkinter.ttk now works when default root window is
     not set.

   - bpo-3015(276): _tkinter.create() now creates tkapp object with
     wantobject=1 by default.

   - bpo-10203(277): sqlite3.Row now truly supports sequence protocol.
     In particular it supports reverse() and negative indices.  Original
     patch by Claudiu Popa.

   - bpo-18807(278): If copying (no symlinks) specified for a venv, then
     the python interpreter aliases (python, python3) are now created by
     copying rather than symlinking.

   - bpo-20197(279): Added support for the WebP image type in the imghdr
     module.  Patch by Fabrice Aneche and Claudiu Popa.

   - bpo-21513(280): Speedup some properties of IP addresses
     (IPv4Address, IPv6Address) such as .is_private or .is_multicast.

   - bpo-21137(281): Improve the repr for threading.Lock() and its
     variants by showing the “locked” or “unlocked” status.  Patch by
     Berker Peksag.

   - bpo-21538(282): The plistlib module now supports loading of binary
     plist files when reference or offset size is not a power of two.

   - bpo-21455(283): Add a default backlog to socket.listen().

   - bpo-21525(284): Most Tkinter methods which accepted tuples now
     accept lists too.

   - bpo-22166(285): With the assistance of a new internal
     _codecs._forget_codec helping function, test_codecs now clears the
     encoding caches to avoid the appearance of a reference leak

   - bpo-22236(286): Tkinter tests now don’t reuse default root window.
     New root window is created for every test class.

   - bpo-10744(287): Fix PEP 3118(288) format strings on ctypes objects
     with a nontrivial shape.

   - bpo-20826(289): Optimize ipaddress.collapse_addresses().

   - bpo-21487(290): Optimize ipaddress.summarize_address_range() and
     ipaddress.{IPv4Network,IPv6Network}.subnets().

   - bpo-21486(291): Optimize parsing of netmasks in
     ipaddress.IPv4Network and ipaddress.IPv6Network.

   - bpo-13916(292): Disallowed the surrogatepass error handler for non
     UTF-* encodings.

   - bpo-20998(293): Fixed re.fullmatch() of repeated single character
     pattern with ignore case.  Original patch by Matthew Barnett.

   - bpo-21075(294): fileinput.FileInput now reads bytes from standard
     stream if binary mode is specified.  Patch by Sam Kimbrel.

   - bpo-19775(295): Add a samefile() method to pathlib Path objects.
     Initial patch by Vajrasky Kok.

   - bpo-21226(296): Set up modules properly in
     PyImport_ExecCodeModuleObject (and friends).

   - bpo-21398(297): Fix a unicode error in the pydoc pager when the
     documentation contains characters not encodable to the stdout
     encoding.

   - bpo-16531(298): ipaddress.IPv4Network and ipaddress.IPv6Network now
     accept an (address, netmask) tuple argument, so as to easily
     construct network objects from existing addresses.

   - bpo-21156(299): importlib.abc.InspectLoader.source_to_code() is now
     a staticmethod.

   - bpo-21424(300): Simplified and optimized heaqp.nlargest() and
     nmsmallest() to make fewer tuple comparisons.

   - bpo-21396(301): Fix TextIOWrapper(…, write_through=True) to not
     force a flush() on the underlying binary stream.  Patch by akira.

   - bpo-18314(302): Unlink now removes junctions on Windows.  Patch by
     Kim Gräsman

   - bpo-21088(303): Bugfix for curses.window.addch() regression in
     3.4.0.  In porting to Argument Clinic, the first two arguments were
     reversed.

   - bpo-21407(304): _decimal: The module now supports function
     signatures.

   - bpo-10650(305): Remove the non-standard ‘watchexp’ parameter from
     the Decimal.quantize() method in the Python version.  It had never
     been present in the C version.

   - bpo-21469(306): Reduced the risk of false positives in robotparser
     by checking to make sure that robots.txt has been read or does not
     exist prior to returning True in can_fetch().

   - bpo-19414(307): Have the OrderedDict mark deleted links as
     unusable.  This gives an early failure if the link is deleted
     during iteration.

   - bpo-21421(308): Add __slots__ to the MappingViews ABC. Patch by
     Josh Rosenberg.

   - bpo-21101(309): Eliminate double hashing in the C speed-up code for
     collections.Counter().

   - bpo-21321(310): itertools.islice() now releases the reference to
     the source iterator when the slice is exhausted.  Patch by Anton
     Afanasyev.

   - bpo-21057(311): TextIOWrapper now allows the underlying binary
     stream’s read() or read1() method to return an arbitrary bytes-like
     object (such as a memoryview).  Patch by Nikolaus Rath.

   - bpo-20951(312): SSLSocket.send() now raises either SSLWantReadError
     or SSLWantWriteError on a non-blocking socket if the operation
     would block.  Previously, it would return 0.  Patch by Nikolaus
     Rath.

   - bpo-13248(313): removed previously deprecated asyncore.dispatcher
     __getattr__ cheap inheritance hack.

   - bpo-9815(314): assertRaises now tries to clear references to local
     variables in the exception’s traceback.

   - bpo-19940(315): ssl.cert_time_to_seconds() now interprets the given
     time string in the UTC timezone (as specified in RFC 5280), not the
     local timezone.

   - bpo-13204(316): Calling sys.flags.__new__ would crash the
     interpreter, now it raises a TypeError.

   - bpo-19385(317): Make operations on a closed dbm.dumb database
     always raise the same exception.

   - bpo-21207(318): Detect when the os.urandom cached fd has been
     closed or replaced, and open it anew.

   - bpo-21291(319): subprocess’s Popen.wait() is now thread safe so
     that multiple threads may be calling wait() or poll() on a Popen
     instance at the same time without losing the Popen.returncode
     value.

   - bpo-21127(320): Path objects can now be instantiated from str
     subclass instances (such as ‘numpy.str_’).

   - bpo-15002(321): urllib.response object to use _TemporaryFileWrapper
     (and _TemporaryFileCloser) facility.  Provides a better way to
     handle file descriptor close.  Patch contributed by Christian
     Theune.

   - bpo-12220(322): mindom now raises a custom ValueError indicating it
     doesn’t support spaces in URIs instead of letting a ‘split’
     ValueError bubble up.

   - bpo-21068(323): The ssl.PROTOCOL* constants are now enum members.

   - bpo-21276(324): posixmodule: Don’t define USE_XATTRS on KFreeBSD
     and the Hurd.

   - bpo-21262(325): New method assert_not_called for Mock.  It raises
     AssertionError if the mock has been called.

   - bpo-21238(326): New keyword argument ‘unsafe’ to Mock.  It raises
     *note AttributeError: 4a2. incase of an attribute startswith assert
     or assret.

   - bpo-20896(327): ssl.get_server_certificate() now uses
     PROTOCOL_SSLv23, not PROTOCOL_SSLv3, for maximum compatibility.

   - bpo-21239(328): patch.stopall() didn’t work deterministically when
     the same name was patched more than once.

   - bpo-21203(329): Updated fileConfig and dictConfig to remove
     inconsistencies.  Thanks to Jure Koren for the patch.

   - bpo-21222(330): Passing name keyword argument to
     mock.create_autospec now works.

   - bpo-21197(331): Add lib64 -> lib symlink in venvs on 64-bit non-OS
     X POSIX.

   - bpo-17498(332): Some SMTP servers disconnect after certain errors,
     violating strict RFC conformance.  Instead of losing the error code
     when we issue the subsequent RSET, smtplib now returns the error
     code and defers raising the SMTPServerDisconnected error until the
     next command is issued.

   - bpo-17826(333): setting an iterable side_effect on a mock function
     created by create_autospec now works.  Patch by Kushal Das.

   - bpo-7776(334): Fix ‘Host:’ header and reconnection when using
     http.client.HTTPConnection.set_tunnel().  Patch by Nikolaus Rath.

   - bpo-20968(335): unittest.mock.MagicMock now supports division.
     Patch by Johannes Baiter.

   - bpo-21529(336): Fix arbitrary memory access in
     JSONDecoder.raw_decode with a negative second parameter.  Bug
     reported by Guido Vranken.  (See also: CVE-2014-4616)

   - bpo-21169(337): getpass now handles non-ascii characters that the
     input stream encoding cannot encode by re-encoding using the
     replace error handler.

   - bpo-21171(338): Fixed undocumented filter API of the rot13 codec.
     Patch by Berker Peksag.

   - bpo-20539(339): Improved math.factorial error message for large
     positive inputs and changed exception type (OverflowError ->
     ValueError) for large negative inputs.

   - bpo-21172(340): isinstance check relaxed from dict to
     collections.Mapping.

   - bpo-21155(341): asyncio.EventLoop.create_unix_server() now raises a
     ValueError if path and sock are specified at the same time.

   - bpo-21136(342): Avoid unnecessary normalization of Fractions
     resulting from power and other operations.  Patch by Raymond
     Hettinger.

   - bpo-17621(343): Introduce importlib.util.LazyLoader.

   - bpo-21076(344): signal module constants were turned into enums.
     Patch by Giampaolo Rodola’.

   - bpo-20636(345): Improved the repr of Tkinter widgets.

   - bpo-19505(346): The items, keys, and values views of OrderedDict
     now support reverse iteration using reversed().

   - bpo-21149(347): Improved thread-safety in logging cleanup during
     interpreter shutdown.  Thanks to Devin Jeanpierre for the patch.

   - bpo-21058(348): Fix a leak of file descriptor in *note
     tempfile.NamedTemporaryFile(): e0e, close the file descriptor if
     *note io.open(): 74d. fails

   - bpo-21200(349): Return None from pkgutil.get_loader() when __spec__
     is missing.

   - bpo-21013(350): Enhance ssl.create_default_context() when used for
     server side sockets to provide better security by default.

   - bpo-20145(351): ‘assertRaisesRegex’ and ‘assertWarnsRegex’ now
     raise a TypeError if the second argument is not a string or
     compiled regex.

   - bpo-20633(352): Replace relative import by absolute import.

   - bpo-20980(353): Stop wrapping exception when using ThreadPool.

   - bpo-21082(354): In os.makedirs, do not set the process-wide umask.
     Note this changes behavior of makedirs when exist_ok=True.

   - bpo-20990(355): Fix issues found by pyflakes for multiprocessing.

   - bpo-21015(356): SSL contexts will now automatically select an
     elliptic curve for ECDH key exchange on OpenSSL 1.0.2 and later,
     and otherwise default to “prime256v1”.

   - bpo-21000(357): Improve the command-line interface of json.tool.

   - bpo-20995(358): Enhance default ciphers used by the ssl module to
     enable better security and prioritize perfect forward secrecy.

   - bpo-20884(359): Don’t assume that __file__ is defined on
     importlib.__init__.

   - bpo-21499(360): Ignore __builtins__ in several
     test_importlib.test_api tests.

   - bpo-20627(361): xmlrpc.client.ServerProxy is now a context manager.

   - bpo-19165(362): The formatter module now raises DeprecationWarning
     instead of PendingDeprecationWarning.

   - bpo-13936(363): Remove the ability of datetime.time instances to be
     considered false in boolean contexts.

   - bpo-18931(364): selectors module now supports /dev/poll on Solaris.
     Patch by Giampaolo Rodola’.

   - bpo-19977(365): When the ‘LC_TYPE’ locale is the POSIX locale (‘C’
     locale), *note sys.stdin: 41e. and *note sys.stdout: 41f. are now
     using the ‘surrogateescape’ error handler, instead of the ‘strict’
     error handler.

   - bpo-20574(366): Implement incremental decoder for cp65001 code
     (Windows code page 65001, Microsoft UTF-8).

   - bpo-20879(367): Delay the initialization of encoding and decoding
     tables for base32, ascii85 and base85 codecs in the base64 module,
     and delay the initialization of the unquote_to_bytes() table of the
     urllib.parse module, to not waste memory if these modules are not
     used.

   - bpo-19157(368): Include the broadcast address in the usuable hosts
     for IPv6 in ipaddress.

   - bpo-11599(369): When an external command (e.g.  compiler) fails,
     distutils now prints out the whole command line (instead of just
     the command name) if the environment variable DISTUTILS_DEBUG is
     set.

   - bpo-4931(370): distutils should not produce unhelpful “error: None”
     messages anymore.  distutils.util.grok_environment_error is kept
     but doc-deprecated.

   - bpo-20875(371): Prevent possible gzip “‘read’ is not defined”
     NameError.  Patch by Claudiu Popa.

   - bpo-11558(372): ‘email.message.Message.attach’ now returns a more
     useful error message if ‘attach’ is called on a message for which
     ‘is_multipart’ is False.

   - bpo-20283(373): RE pattern methods now accept the string keyword
     parameters as documented.  The pattern and source keyword
     parameters are left as deprecated aliases.

   - bpo-20778(374): Fix modulefinder to work with bytecode-only
     modules.

   - bpo-20791(375): copy.copy() now doesn’t make a copy when the input
     is a bytes object.  Initial patch by Peter Otten.

   - bpo-19748(376): On AIX, time.mktime() now raises an OverflowError
     for year outsize range [1902; 2037].

   - bpo-19573(377): inspect.signature: Use enum for parameter kind
     constants.

   - bpo-20726(378): inspect.signature: Make Signature and Parameter
     picklable.

   - bpo-17373(379): Add inspect.Signature.from_callable method.

   - bpo-20378(380): Improve repr of inspect.Signature and
     inspect.Parameter.

   - bpo-20816(381): Fix inspect.getcallargs() to raise correct
     TypeError for missing keyword-only arguments.  Patch by Jeremiah
     Lowin.

   - bpo-20817(382): Fix inspect.getcallargs() to fail correctly if more
     than 3 arguments are missing.  Patch by Jeremiah Lowin.

   - bpo-6676(383): Ensure a meaningful exception is raised when
     attempting to parse more than one XML document per pyexpat
     xmlparser instance.  (Original patches by Hirokazu Yamamoto and
     Amaury Forgeot d’Arc, with suggested wording by David Gutteridge)

   - bpo-21117(384): Fix inspect.signature to better support
     functools.partial.  Due to the specifics of functools.partial
     implementation, positional-or-keyword arguments passed as keyword
     arguments become keyword-only.

   - bpo-20334(385): inspect.Signature and inspect.Parameter are now
     hashable.  Thanks to Antony Lee for bug reports and suggestions.

   - bpo-15916(386): doctest.DocTestSuite returns an empty
     unittest.TestSuite instead of raising ValueError if it finds no
     tests

   - bpo-21209(387): Fix asyncio.tasks.CoroWrapper to workaround a bug
     in yield-from implementation in CPythons prior to 3.4.1.

   - asyncio: Add gi_{frame,running,code} properties to CoroWrapper
     (upstream bpo-163(388)).

   - bpo-21311(389): Avoid exception in _osx_support with non-standard
     compiler configurations.  Patch by John Szakmeister.

   - bpo-11571(390): Ensure that the turtle window becomes the topmost
     window when launched on OS X.

   - bpo-21801(391): Validate that __signature__ is None or an instance
     of Signature.

   - bpo-21923(392): Prevent AttributeError in
     distutils.sysconfig.customize_compiler due to possible
     uninitialized _config_vars.

   - bpo-21323(393): Fix http.server to again handle scripts in CGI
     subdirectories, broken by the fix for security bpo-19435(394).
     Patch by Zach Byrne.

   - bpo-22733(395): Fix ffi_prep_args not zero-extending argument
     values correctly on 64-bit Windows.

   - bpo-23302(396): Default to TCP_NODELAY=1 upon establishing an
     HTTPConnection.  Removed use of hard-coded MSS as it’s an
     optimization that’s no longer needed with Nagle disabled.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23399

   (2) https://bugs.python.org/issue20289

   (3) https://bugs.python.org/issue13128

   (4) https://bugs.python.org/issue15381

   (5) https://bugs.python.org/issue22818

   (6) https://bugs.python.org/issue23099

   (7) https://bugs.python.org/issue23326

   (8) https://bugs.python.org/issue21408

   (9) https://bugs.python.org/issue23363

   (10) https://bugs.python.org/issue23364

   (11) https://bugs.python.org/issue23366

   (12) https://bugs.python.org/issue23369

   (13) https://bugs.python.org/issue23353

   (14) https://bugs.python.org/issue14099

   (15) https://bugs.python.org/issue14099

   (16) https://bugs.python.org/issue19361

   (17) https://bugs.python.org/issue18518

   (18) https://bugs.python.org/issue23094

   (19) https://bugs.python.org/issue23268

   (20) https://bugs.python.org/issue21408

   (21) https://bugs.python.org/issue19996

   (22) https://bugs.python.org/issue20188

   (23) https://bugs.python.org/issue23133

   (24) https://bugs.python.org/issue23248

   (25) https://bugs.python.org/issue23266

   (26) https://bugs.python.org/issue23098

   (27) https://bugs.python.org/issue21817

   (28) https://bugs.python.org/issue15955

   (29) https://bugs.python.org/issue23250

   (30) https://bugs.python.org/issue23063

   (31) https://bugs.python.org/issue23209

   (32) https://bugs.python.org/issue23225

   (33) https://bugs.python.org/issue17911

   (34) https://bugs.python.org/issue17911

   (35) https://bugs.python.org/issue19777

   (36) https://bugs.python.org/issue23206

   (37) https://bugs.python.org/issue23185

   (38) https://bugs.python.org/issue23186

   (39) https://bugs.python.org/issue23143

   (40) https://bugs.python.org/issue23132

   (41) https://bugs.python.org/issue19776

   (42) https://bugs.python.org/issue23112

   (43) https://bugs.python.org/issue21793

   (44) https://bugs.python.org/issue23093

   (45) https://bugs.python.org/issue23111

   (46) https://bugs.python.org/issue22585

   (47) https://bugs.python.org/issue19104

   (48) https://bugs.python.org/issue23071

   (49) https://bugs.python.org/issue22783

   (50) https://bugs.python.org/issue15513

   (51) https://bugs.python.org/issue19858

   (52) https://bugs.python.org/issue22095

   (53) https://bugs.python.org/issue23016

   (54) https://bugs.python.org/issue21775

   (55) https://bugs.python.org/issue1218234

   (56) https://bugs.python.org/issue21740

   (57) https://bugs.python.org/issue23009

   (58) https://bugs.python.org/issue22959

   (59) https://bugs.python.org/issue22696

   (60) https://bugs.python.org/issue16043

   (61) https://bugs.python.org/issue14099

   (62) https://bugs.python.org/issue22966

   (63) https://bugs.python.org/issue21971

   (64) https://bugs.python.org/issue21032

   (65) https://bugs.python.org/issue22407

   (66) https://bugs.python.org/issue22902

   (67) https://bugs.python.org/issue22960

   (68) https://bugs.python.org/issue22389

   (69) https://bugs.python.org/issue21356

   (70) https://bugs.python.org/issue22915

   (71) https://bugs.python.org/issue22609

   (72) https://bugs.python.org/issue22940

   (73) https://bugs.python.org/issue19676

   (74) https://bugs.python.org/issue22788

   (75) https://bugs.python.org/issue22921

   (76) https://bugs.python.org/issue22894

   (77) https://bugs.python.org/issue22796

   (78) https://bugs.python.org/issue22370

   (79) https://bugs.python.org/issue22841

   (80) https://bugs.python.org/issue19494

   (81) https://bugs.python.org/issue22578

   (82) https://bugs.python.org/issue22849

   (83) https://bugs.python.org/issue12728

   (84) https://bugs.python.org/issue22821

   (85) https://bugs.python.org/issue21650

   (86) https://bugs.python.org/issue22824

   (87) https://bugs.python.org/issue22824

   (88) https://bugs.python.org/issue22406

   (89) https://bugs.python.org/issue17293

   (90) https://bugs.python.org/issue22769

   (91) https://bugs.python.org/issue22417

   (92) https://bugs.python.org/issue22775

   (93) https://bugs.python.org/issue22776

   (94) https://bugs.python.org/issue22665

   (95) https://bugs.python.org/issue6623

   (96) https://bugs.python.org/issue17381

   (97) https://bugs.python.org/issue22410

   (98) https://bugs.python.org/issue22759

   (99) https://bugs.python.org/issue8876

   (100) https://bugs.python.org/issue22217

   (101) https://bugs.python.org/issue22457

   (102) https://bugs.python.org/issue18216

   (103) https://bugs.python.org/issue13918

   (104) https://bugs.python.org/issue22676

   (105) https://bugs.python.org/issue18853

   (106) https://bugs.python.org/issue9351

   (107) https://bugs.python.org/issue7559

   (108) https://bugs.python.org/issue19746

   (109) https://bugs.python.org/issue21991

   (110) https://bugs.python.org/issue22638

   (111) https://bugs.python.org/issue22641

   (112) https://bugs.python.org/issue17401

   (113) https://bugs.python.org/issue21338

   (114) https://bugs.python.org/issue20152

   (115) https://bugs.python.org/issue18643

   (116) https://bugs.python.org/issue22435

   (117) https://bugs.python.org/issue13096

   (118) https://bugs.python.org/issue11694

   (119) https://bugs.python.org/issue19380

   (120) https://bugs.python.org/issue1519638

   (121) https://bugs.python.org/issue18615

   (122) https://bugs.python.org/issue22462

   (123) https://bugs.python.org/issue21965

   (124) https://bugs.python.org/issue21173

   (125) https://bugs.python.org/issue11866

   (126) https://bugs.python.org/issue21905

   (127) https://bugs.python.org/issue11271

   (128) https://bugs.python.org/issue21883

   (129) https://bugs.python.org/issue22219

   (130) https://bugs.python.org/issue22449

   (131) https://bugs.python.org/issue22508

   (132) https://bugs.python.org/issue20076

   (133) https://bugs.python.org/issue20079

   (134) https://bugs.python.org/issue20218

   (135) https://bugs.python.org/issue22396

   (136) https://bugs.python.org/issue22517

   (137) https://bugs.python.org/issue22437

   (138) https://bugs.python.org/issue17442

   (139) https://bugs.python.org/issue23392

   (140) https://bugs.python.org/issue10510

   (141) https://bugs.python.org/issue9850

   (142) https://bugs.python.org/issue5309

   (143) https://bugs.python.org/issue22448

   (144) https://bugs.python.org/issue22427

   (145) https://bugs.python.org/issue22362

   (146) https://bugs.python.org/issue20912

   (147) https://bugs.python.org/issue21866

   (148) https://bugs.python.org/issue22278

   (149) https://bugs.python.org/issue22415

   (150) https://bugs.python.org/issue22423

   (151) https://bugs.python.org/issue21332

   (152) https://bugs.python.org/issue21091

   (153) https://bugs.python.org/issue21079

   (154) https://bugs.python.org/issue22247

   (155) https://bugs.python.org/issue22366

   (156) https://bugs.python.org/issue4180

   (157) https://bugs.python.org/issue22419

   (158) https://bugs.python.org/issue20537

   (159) https://bugs.python.org/issue22384

   (160) https://bugs.python.org/issue22168

   (161) https://bugs.python.org/issue21147

   (162) https://bugs.python.org/issue13968

   (163) https://bugs.python.org/issue21951

   (164) https://bugs.python.org/issue21951

   (165) https://bugs.python.org/issue22338

   (166) https://bugs.python.org/issue12410

   (167) https://bugs.python.org/issue21270

   (168) https://bugs.python.org/issue16662

   (169) https://bugs.python.org/issue22226

   (170) https://bugs.python.org/issue19524

   (171) https://bugs.python.org/issue20421

   (172) https://bugs.python.org/issue19546

   (173) https://bugs.python.org/issue22051

   (174) https://bugs.python.org/issue21933

   (175) https://bugs.python.org/issue21597

   (176) https://bugs.python.org/issue18132

   (177) https://bugs.python.org/issue22043

   (178) https://bugs.python.org/issue21527

   (179) https://bugs.python.org/issue22216

   (180) https://bugs.python.org/issue22098

   (181) https://bugs.python.org/issue22185

   (182) https://bugs.python.org/issue22287

   (183) https://bugs.python.org/issue22182

   (184) https://bugs.python.org/issue22042

   (185) https://bugs.python.org/issue16808

   (186) https://bugs.python.org/issue22236

   (187) https://bugs.python.org/issue2527

   (188) https://bugs.python.org/issue22118

   (189) https://bugs.python.org/issue21549

   (190) https://bugs.python.org/issue19628

   (191) https://bugs.python.org/issue15696

   (192) https://bugs.python.org/issue22068

   (193) https://bugs.python.org/issue22165

   (194) https://bugs.python.org/issue15381

   (195) https://bugs.python.org/issue8797

   (196) https://bugs.python.org/issue20729

   (197) https://bugs.python.org/issue21448

   (198) https://bugs.python.org/issue22184

   (199) https://bugs.python.org/issue17923

   (200) https://bugs.python.org/issue21725

   (201) https://bugs.python.org/issue22176

   (202) https://bugs.python.org/issue5411

   (203) https://bugs.python.org/issue21121

   (204) https://bugs.python.org/issue21975

   (205) https://bugs.python.org/issue20170

   (206) https://bugs.python.org/issue21539

   (207) https://bugs.python.org/issue22127

   (208) https://bugs.python.org/issue21047

   (209) https://bugs.python.org/issue15114

   (210) https://bugs.python.org/issue22085

   (211) https://bugs.python.org/issue21580

   (212) https://bugs.python.org/issue22003

   (213) https://bugs.python.org/issue22018

   (214) https://bugs.python.org/issue22054

   (215) https://bugs.python.org/issue17172

   (216) https://bugs.python.org/issue21704

   (217) https://bugs.python.org/issue20173

   (218) https://bugs.python.org/issue22033

   (219) https://bugs.python.org/issue21947

   (220) https://bugs.python.org/issue16133

   (221) https://bugs.python.org/issue22044

   (222) https://bugs.python.org/issue19884

   (223) https://bugs.python.org/issue4350

   (224) https://bugs.python.org/issue6167

   (225) https://bugs.python.org/issue15275

   (226) https://bugs.python.org/issue21888

   (227) https://bugs.python.org/issue22032

   (228) https://bugs.python.org/issue22031

   (229) https://bugs.python.org/issue22018

   (230) https://bugs.python.org/issue21044

   (231) https://bugs.python.org/issue21966

   (232) https://bugs.python.org/issue19076

   (233) https://bugs.python.org/issue16382

   (234) https://bugs.python.org/issue21932

   (235) https://bugs.python.org/issue21942

   (236) https://bugs.python.org/issue11259

   (237) https://bugs.python.org/issue12523

   (238) https://bugs.python.org/issue21707

   (239) https://bugs.python.org/issue20639

   (240) https://bugs.python.org/issue21714

   (241) https://bugs.python.org/issue15014

   (242) https://bugs.python.org/issue21151

   (243) https://bugs.python.org/issue21090

   (244) https://bugs.python.org/issue5800

   (245) https://bugs.python.org/issue21781

   (246) https://bugs.python.org/issue21679

   (247) https://bugs.python.org/issue21863

   (248) https://bugs.python.org/issue11453

   (249) https://bugs.python.org/issue21858

   (250) https://bugs.python.org/issue21476

   (251) https://bugs.python.org/issue20295

   (252) https://bugs.python.org/issue21729

   (253) https://bugs.python.org/issue21491

   (254) https://bugs.python.org/issue21719

   (255) https://bugs.python.org/issue21832

   (256) https://bugs.python.org/issue21722

   (257) https://bugs.python.org/issue21723

   (258) https://bugs.python.org/issue21711

   (259) https://bugs.python.org/issue17552

   (260) https://bugs.python.org/issue18039

   (261) https://bugs.python.org/issue21326

   (262) https://bugs.python.org/issue21766

   (263) https://bugs.python.org/issue21310

   (264) https://bugs.python.org/issue21256

   (265) https://bugs.python.org/issue21677

   (266) https://bugs.python.org/issue11709

   (267) https://bugs.python.org/issue21515

   (268) https://bugs.python.org/issue13223

   (269) https://bugs.python.org/issue21463

   (270) https://bugs.python.org/issue21618

   (271) https://bugs.python.org/issue20383

   (272) https://bugs.python.org/issue21552

   (273) https://bugs.python.org/issue14315

   (274) https://bugs.python.org/issue13742

   (275) https://bugs.python.org/issue21402

   (276) https://bugs.python.org/issue3015

   (277) https://bugs.python.org/issue10203

   (278) https://bugs.python.org/issue18807

   (279) https://bugs.python.org/issue20197

   (280) https://bugs.python.org/issue21513

   (281) https://bugs.python.org/issue21137

   (282) https://bugs.python.org/issue21538

   (283) https://bugs.python.org/issue21455

   (284) https://bugs.python.org/issue21525

   (285) https://bugs.python.org/issue22166

   (286) https://bugs.python.org/issue22236

   (287) https://bugs.python.org/issue10744

   (288) https://www.python.org/dev/peps/pep-3118

   (289) https://bugs.python.org/issue20826

   (290) https://bugs.python.org/issue21487

   (291) https://bugs.python.org/issue21486

   (292) https://bugs.python.org/issue13916

   (293) https://bugs.python.org/issue20998

   (294) https://bugs.python.org/issue21075

   (295) https://bugs.python.org/issue19775

   (296) https://bugs.python.org/issue21226

   (297) https://bugs.python.org/issue21398

   (298) https://bugs.python.org/issue16531

   (299) https://bugs.python.org/issue21156

   (300) https://bugs.python.org/issue21424

   (301) https://bugs.python.org/issue21396

   (302) https://bugs.python.org/issue18314

   (303) https://bugs.python.org/issue21088

   (304) https://bugs.python.org/issue21407

   (305) https://bugs.python.org/issue10650

   (306) https://bugs.python.org/issue21469

   (307) https://bugs.python.org/issue19414

   (308) https://bugs.python.org/issue21421

   (309) https://bugs.python.org/issue21101

   (310) https://bugs.python.org/issue21321

   (311) https://bugs.python.org/issue21057

   (312) https://bugs.python.org/issue20951

   (313) https://bugs.python.org/issue13248

   (314) https://bugs.python.org/issue9815

   (315) https://bugs.python.org/issue19940

   (316) https://bugs.python.org/issue13204

   (317) https://bugs.python.org/issue19385

   (318) https://bugs.python.org/issue21207

   (319) https://bugs.python.org/issue21291

   (320) https://bugs.python.org/issue21127

   (321) https://bugs.python.org/issue15002

   (322) https://bugs.python.org/issue12220

   (323) https://bugs.python.org/issue21068

   (324) https://bugs.python.org/issue21276

   (325) https://bugs.python.org/issue21262

   (326) https://bugs.python.org/issue21238

   (327) https://bugs.python.org/issue20896

   (328) https://bugs.python.org/issue21239

   (329) https://bugs.python.org/issue21203

   (330) https://bugs.python.org/issue21222

   (331) https://bugs.python.org/issue21197

   (332) https://bugs.python.org/issue17498

   (333) https://bugs.python.org/issue17826

   (334) https://bugs.python.org/issue7776

   (335) https://bugs.python.org/issue20968

   (336) https://bugs.python.org/issue21529

   (337) https://bugs.python.org/issue21169

   (338) https://bugs.python.org/issue21171

   (339) https://bugs.python.org/issue20539

   (340) https://bugs.python.org/issue21172

   (341) https://bugs.python.org/issue21155

   (342) https://bugs.python.org/issue21136

   (343) https://bugs.python.org/issue17621

   (344) https://bugs.python.org/issue21076

   (345) https://bugs.python.org/issue20636

   (346) https://bugs.python.org/issue19505

   (347) https://bugs.python.org/issue21149

   (348) https://bugs.python.org/issue21058

   (349) https://bugs.python.org/issue21200

   (350) https://bugs.python.org/issue21013

   (351) https://bugs.python.org/issue20145

   (352) https://bugs.python.org/issue20633

   (353) https://bugs.python.org/issue20980

   (354) https://bugs.python.org/issue21082

   (355) https://bugs.python.org/issue20990

   (356) https://bugs.python.org/issue21015

   (357) https://bugs.python.org/issue21000

   (358) https://bugs.python.org/issue20995

   (359) https://bugs.python.org/issue20884

   (360) https://bugs.python.org/issue21499

   (361) https://bugs.python.org/issue20627

   (362) https://bugs.python.org/issue19165

   (363) https://bugs.python.org/issue13936

   (364) https://bugs.python.org/issue18931

   (365) https://bugs.python.org/issue19977

   (366) https://bugs.python.org/issue20574

   (367) https://bugs.python.org/issue20879

   (368) https://bugs.python.org/issue19157

   (369) https://bugs.python.org/issue11599

   (370) https://bugs.python.org/issue4931

   (371) https://bugs.python.org/issue20875

   (372) https://bugs.python.org/issue11558

   (373) https://bugs.python.org/issue20283

   (374) https://bugs.python.org/issue20778

   (375) https://bugs.python.org/issue20791

   (376) https://bugs.python.org/issue19748

   (377) https://bugs.python.org/issue19573

   (378) https://bugs.python.org/issue20726

   (379) https://bugs.python.org/issue17373

   (380) https://bugs.python.org/issue20378

   (381) https://bugs.python.org/issue20816

   (382) https://bugs.python.org/issue20817

   (383) https://bugs.python.org/issue6676

   (384) https://bugs.python.org/issue21117

   (385) https://bugs.python.org/issue20334

   (386) https://bugs.python.org/issue15916

   (387) https://bugs.python.org/issue21209

   (388) https://bugs.python.org/issue163

   (389) https://bugs.python.org/issue21311

   (390) https://bugs.python.org/issue11571

   (391) https://bugs.python.org/issue21801

   (392) https://bugs.python.org/issue21923

   (393) https://bugs.python.org/issue21323

   (394) https://bugs.python.org/issue19435

   (395) https://bugs.python.org/issue22733

   (396) https://bugs.python.org/issue23302


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1.19.89.3 IDLE
..............

   - bpo-20577(1): Configuration of the max line length for the
     FormatParagraph extension has been moved from the General tab of
     the Idle preferences dialog to the FormatParagraph tab of the
     Config Extensions dialog.  Patch by Tal Einat.

   - bpo-16893(2): Update Idle doc chapter to match current Idle and add
     new information.

   - bpo-3068(3): Add Idle extension configuration dialog to Options
     menu.  Changes are written to HOME/.idlerc/config-extensions.cfg.
     Original patch by Tal Einat.

   - bpo-16233(4): A module browser (File : Class Browser, Alt+C)
     requires an editor window with a filename.  When Class Browser is
     requested otherwise, from a shell, output window, or ‘Untitled’
     editor, Idle no longer displays an error box.  It now pops up an
     Open Module box (Alt+M). If a valid name is entered and a module is
     opened, a corresponding browser is also opened.

   - bpo-4832(5): Save As to type Python files automatically adds .py to
     the name you enter (even if your system does not display it).  Some
     systems automatically add .txt when type is Text files.

   - bpo-21986(6): Code objects are not normally pickled by the pickle
     module.  To match this, they are no longer pickled when running
     under Idle.

   - bpo-17390(7): Adjust Editor window title; remove ‘Python’, move
     version to end.

   - bpo-14105(8): Idle debugger breakpoints no longer disappear when
     inserting or deleting lines.

   - bpo-17172(9): Turtledemo can now be run from Idle.  Currently, the
     entry is on the Help menu, but it may move to Run.  Patch by
     Ramchandra Apt and Lita Cho.

   - bpo-21765(10): Add support for non-ascii identifiers to
     HyperParser.

   - bpo-21940(11): Add unittest for WidgetRedirector.  Initial patch by
     Saimadhav Heblikar.

   - bpo-18592(12): Add unittest for SearchDialogBase.  Patch by Phil
     Webster.

   - bpo-21694(13): Add unittest for ParenMatch.  Patch by Saimadhav
     Heblikar.

   - bpo-21686(14): add unittest for HyperParser.  Original patch by
     Saimadhav Heblikar.

   - bpo-12387(15): Add missing upper(lower)case versions of default
     Windows key bindings for Idle so Caps Lock does not disable them.
     Patch by Roger Serwy.

   - bpo-21695(16): Closing a Find-in-files output window while the
     search is still in progress no longer closes Idle.

   - bpo-18910(17): Add unittest for textView.  Patch by Phil Webster.

   - bpo-18292(18): Add unittest for AutoExpand.  Patch by Saihadhav
     Heblikar.

   - bpo-18409(19): Add unittest for AutoComplete.  Patch by Phil
     Webster.

   - bpo-21477(20): htest.py - Improve framework, complete set of tests.
     Patches by Saimadhav Heblikar

   - bpo-18104(21): Add idlelib/idle_test/htest.py with a few sample
     tests to begin consolidating and improving human-validated tests of
     Idle.  Change other files as needed to work with htest.  Running
     the module as __main__ runs all tests.

   - bpo-21139(22): Change default paragraph width to 72, the PEP 8(23)
     recommendation.

   - bpo-21284(24): Paragraph reformat test passes after user changes
     reformat width.

   - bpo-17654(25): Ensure IDLE menus are customized properly on OS X
     for non-framework builds and for all variants of Tk.

   - bpo-23180(26): Rename IDLE “Windows” menu item to “Window”.  Patch
     by Al Sweigart.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue20577

   (2) https://bugs.python.org/issue16893

   (3) https://bugs.python.org/issue3068

   (4) https://bugs.python.org/issue16233

   (5) https://bugs.python.org/issue4832

   (6) https://bugs.python.org/issue21986

   (7) https://bugs.python.org/issue17390

   (8) https://bugs.python.org/issue14105

   (9) https://bugs.python.org/issue17172

   (10) https://bugs.python.org/issue21765

   (11) https://bugs.python.org/issue21940

   (12) https://bugs.python.org/issue18592

   (13) https://bugs.python.org/issue21694

   (14) https://bugs.python.org/issue21686

   (15) https://bugs.python.org/issue12387

   (16) https://bugs.python.org/issue21695

   (17) https://bugs.python.org/issue18910

   (18) https://bugs.python.org/issue18292

   (19) https://bugs.python.org/issue18409

   (20) https://bugs.python.org/issue21477

   (21) https://bugs.python.org/issue18104

   (22) https://bugs.python.org/issue21139

   (23) https://www.python.org/dev/peps/pep-0008

   (24) https://bugs.python.org/issue21284

   (25) https://bugs.python.org/issue17654

   (26) https://bugs.python.org/issue23180


File: python.info,  Node: Build<62>,  Next: C API<43>,  Prev: IDLE<50>,  Up: Python 3 5 0 alpha 1

1.19.89.4 Build
...............

   - bpo-15506(1): Use standard PKG_PROG_PKG_CONFIG autoconf macro in
     the configure script.

   - bpo-22935(2): Allow the ssl module to be compiled if openssl
     doesn’t support SSL 3.

   - bpo-22592(3): Drop support of the Borland C compiler to build
     Python.  The distutils module still supports it to build
     extensions.

   - bpo-22591(4): Drop support of MS-DOS, especially of the DJGPP
     compiler (MS-DOS port of GCC).

   - bpo-16537(5): Check whether self.extensions is empty in setup.py.
     Patch by Jonathan Hosmer.

   - bpo-22359(6): Remove incorrect uses of recursive make.  Patch by
     Jonas Wagner.

   - bpo-21958(7): Define HAVE_ROUND when building with Visual Studio
     2013 and above.  Patch by Zachary Turner.

   - bpo-18093(8): the programs that embed the CPython runtime are now
     in a separate “Programs” directory, rather than being kept in the
     Modules directory.

   - bpo-15759(9): “make suspicious”, “make linkcheck” and “make
     doctest” in Doc/ now display special message when and only when
     there are failures.

   - bpo-21141(10): The Windows build process no longer attempts to find
     Perl, instead relying on OpenSSL source being configured and ready
     to build.  The ‘PCbuild\build_ssl.py’ script has been re-written
     and re-named to ‘PCbuild\prepare_ssl.py’, and takes care of
     configuring OpenSSL source for both 32 and 64 bit platforms.
     OpenSSL sources obtained from svn.python.org will always be
     pre-configured and ready to build.

   - bpo-21037(11): Add a build option to enable AddressSanitizer
     support.

   - bpo-19962(12): The Windows build process now creates “python.bat”
     in the root of the source tree, which passes all arguments through
     to the most recently built interpreter.

   - bpo-21285(13): Refactor and fix curses configure check to always
     search in a ncursesw directory.

   - bpo-15234(14): For BerkeleyDB and Sqlite, only add the found
     library and include directories if they aren’t already being
     searched.  This avoids an explicit runtime library dependency.

   - bpo-17861(15): Tools/scripts/generate_opcode_h.py automatically
     regenerates Include/opcode.h from Lib/opcode.py if the latter gets
     any change.

   - bpo-20644(16): OS X installer build support for documentation build
     changes in 3.4.1: assume externally supplied sphinx-build is
     available in /usr/bin.

   - bpo-20022(17): Eliminate use of deprecated bundlebuilder in OS X
     builds.

   - bpo-15968(18): Incorporated Tcl, Tk, and Tix builds into the
     Windows build solution.

   - bpo-17095(19): Fix Modules/Setup `shared' support.

   - bpo-21811(20): Anticipated fixes to support OS X versions > 10.9.

   - bpo-21166(21): Prevent possible segfaults and other random failures
     of python –generate-posix-vars in pybuilddir.txt build target.

   - bpo-18096(22): Fix library order returned by python-config.

   - bpo-17219(23): Add library build dir for Python extension
     cross-builds.

   - bpo-22919(24): Windows build updated to support VC 14.0 (Visual
     Studio 2015), which will be used for the official release.

   - bpo-21236(25): Build _msi.pyd with cabinet.lib instead of fci.lib

   - bpo-17128(26): Use private version of OpenSSL for OS X 10.5+
     installer.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue15506

   (2) https://bugs.python.org/issue22935

   (3) https://bugs.python.org/issue22592

   (4) https://bugs.python.org/issue22591

   (5) https://bugs.python.org/issue16537

   (6) https://bugs.python.org/issue22359

   (7) https://bugs.python.org/issue21958

   (8) https://bugs.python.org/issue18093

   (9) https://bugs.python.org/issue15759

   (10) https://bugs.python.org/issue21141

   (11) https://bugs.python.org/issue21037

   (12) https://bugs.python.org/issue19962

   (13) https://bugs.python.org/issue21285

   (14) https://bugs.python.org/issue15234

   (15) https://bugs.python.org/issue17861

   (16) https://bugs.python.org/issue20644

   (17) https://bugs.python.org/issue20022

   (18) https://bugs.python.org/issue15968

   (19) https://bugs.python.org/issue17095

   (20) https://bugs.python.org/issue21811

   (21) https://bugs.python.org/issue21166

   (22) https://bugs.python.org/issue18096

   (23) https://bugs.python.org/issue17219

   (24) https://bugs.python.org/issue22919

   (25) https://bugs.python.org/issue21236

   (26) https://bugs.python.org/issue17128


File: python.info,  Node: C API<43>,  Next: Documentation<54>,  Prev: Build<62>,  Up: Python 3 5 0 alpha 1

1.19.89.5 C API
...............

   - bpo-14203(1): Remove obsolete support for view==NULL in
     PyBuffer_FillInfo(), bytearray_getbuffer(), bytesiobuf_getbuffer()
     and array_buffer_getbuf().  All functions now raise BufferError in
     that case.

   - bpo-22445(2): PyBuffer_IsContiguous() now implements precise
     contiguity tests, compatible with NumPy’s
     NPY_RELAXED_STRIDES_CHECKING compilation flag.  Previously the
     function reported false negatives for corner cases.

   - bpo-22079(3): PyType_Ready() now checks that statically allocated
     type has no dynamically allocated bases.

   - bpo-22453(4): Removed non-documented macro PyObject_REPR().

   - bpo-18395(5): Rename ‘_Py_char2wchar()’ to *note Py_DecodeLocale():
     53f, rename ‘_Py_wchar2char()’ to *note Py_EncodeLocale(): 540, and
     document these functions.

   - bpo-21233(6): Add new C functions: PyMem_RawCalloc(),
     PyMem_Calloc(), PyObject_Calloc(), _PyObject_GC_Calloc().
     bytes(int) is now using ‘calloc()’ instead of ‘malloc()’ for large
     objects which is faster and use less memory.

   - bpo-20942(7): PyImport_ImportFrozenModuleObject() no longer sets
     __file__ to match what importlib does; this affects
     _frozen_importlib as well as any module loaded using
     imp.init_frozen().

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue14203

   (2) https://bugs.python.org/issue22445

   (3) https://bugs.python.org/issue22079

   (4) https://bugs.python.org/issue22453

   (5) https://bugs.python.org/issue18395

   (6) https://bugs.python.org/issue21233

   (7) https://bugs.python.org/issue20942


File: python.info,  Node: Documentation<54>,  Next: Tests<58>,  Prev: C API<43>,  Up: Python 3 5 0 alpha 1

1.19.89.6 Documentation
.......................

   - bpo-19548(1): Update the codecs module documentation to better
     cover the distinction between text encodings and other codecs,
     together with other clarifications.  Patch by Martin Panter.

   - bpo-22394(2): Doc/Makefile now supports ‘make venv
     PYTHON=../python’ to create a venv for generating the
     documentation, e.g., ‘make html PYTHON=venv/bin/python3’.

   - bpo-21514(3): The documentation of the json module now refers to
     new JSON RFC 7159 instead of obsoleted RFC 4627.

   - bpo-21777(4): The binary sequence methods on bytes and bytearray
     are now documented explicitly, rather than assuming users will be
     able to derive the expected behaviour from the behaviour of the
     corresponding str methods.

   - bpo-6916(5): undocument deprecated asynchat.fifo class.

   - bpo-17386(6): Expanded functionality of the ‘Doc/make.bat’ script
     to make it much more comparable to ‘Doc/Makefile’.

   - bpo-21312(7): Update the thread_foobar.h template file to include
     newer threading APIs.  Patch by Jack McCracken.

   - bpo-21043(8): Remove the recommendation for specific CA
     organizations and to mention the ability to load the OS
     certificates.

   - bpo-20765(9): Add missing documentation for PurePath.with_name()
     and PurePath.with_suffix().

   - bpo-19407(10): New package installation and distribution guides
     based on the Python Packaging Authority tools.  Existing guides
     have been retained as legacy links from the distutils docs, as they
     still contain some required reference material for tool developers
     that isn’t recorded anywhere else.

   - bpo-19697(11): Document cases where __main__.__spec__ is None.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue19548

   (2) https://bugs.python.org/issue22394

   (3) https://bugs.python.org/issue21514

   (4) https://bugs.python.org/issue21777

   (5) https://bugs.python.org/issue6916

   (6) https://bugs.python.org/issue17386

   (7) https://bugs.python.org/issue21312

   (8) https://bugs.python.org/issue21043

   (9) https://bugs.python.org/issue20765

   (10) https://bugs.python.org/issue19407

   (11) https://bugs.python.org/issue19697


File: python.info,  Node: Tests<58>,  Next: Tools/Demos<35>,  Prev: Documentation<54>,  Up: Python 3 5 0 alpha 1

1.19.89.7 Tests
...............

   - bpo-18982(1): Add tests for CLI of the calendar module.

   - bpo-19548(2): Added some additional checks to test_codecs to ensure
     that statements in the updated documentation remain accurate.
     Patch by Martin Panter.

   - bpo-22838(3): All test_re tests now work with unittest test
     discovery.

   - bpo-22173(4): Update lib2to3 tests to use unittest test discovery.

   - bpo-16000(5): Convert test_curses to use unittest.

   - bpo-21456(6): Skip two tests in test_urllib2net.py if _ssl module
     not present.  Patch by Remi Pointel.

   - bpo-20746(7): Fix test_pdb to run in refleak mode (-R). Patch by
     Xavier de Gaye.

   - bpo-22060(8): test_ctypes has been somewhat cleaned up and
     simplified; it now uses unittest test discovery to find its tests.

   - bpo-22104(9): regrtest.py no longer holds a reference to the suite
     of tests loaded from test modules that don’t define test_main().

   - bpo-22111(10): Assorted cleanups in test_imaplib.  Patch by Milan
     Oberkirch.

   - bpo-22002(11): Added ‘load_package_tests’ function to test.support
     and used it to implement/augment test discovery in test_asyncio,
     test_email, test_importlib, test_json, and test_tools.

   - bpo-21976(12): Fix test_ssl to accept LibreSSL version strings.
     Thanks to William Orr.

   - bpo-21918(13): Converted test_tools from a module to a package
     containing separate test files for each tested script.

   - bpo-9554(14): Use modern unittest features in test_argparse.
     Initial patch by Denver Coneybeare and Radu Voicilas.

   - bpo-20155(15): Changed HTTP method names in failing tests in
     test_httpservers so that packet filtering software (specifically
     Windows Base Filtering Engine) does not interfere with the
     transaction semantics expected by the tests.

   - bpo-19493(16): Refactored the ctypes test package to skip tests
     explicitly rather than silently.

   - bpo-18492(17): All resources are now allowed when tests are not run
     by regrtest.py.

   - bpo-21634(18): Fix pystone micro-benchmark: use floor division
     instead of true division to benchmark integers instead of floating
     point numbers.  Set pystone version to 1.2.  Patch written by
     Lennart Regebro.

   - bpo-21605(19): Added tests for Tkinter images.

   - bpo-21493(20): Added test for ntpath.expanduser().  Original patch
     by Claudiu Popa.

   - bpo-19925(21): Added tests for the spwd module.  Original patch by
     Vajrasky Kok.

   - bpo-21522(22): Added Tkinter tests for Listbox.itemconfigure(),
     PanedWindow.paneconfigure(), and Menu.entryconfigure().

   - bpo-17756(23): Fix test_code test when run from the installed
     location.

   - bpo-17752(24): Fix distutils tests when run from the installed
     location.

   - bpo-18604(25): Consolidated checks for GUI availability.  All
     platforms now at least check whether Tk can be instantiated when
     the GUI resource is requested.

   - bpo-21275(26): Fix a socket test on KFreeBSD.

   - bpo-21223(27): Pass test_site/test_startup_imports when some of the
     extensions are built as builtins.

   - bpo-20635(28): Added tests for Tk geometry managers.

   - Add test case for freeze.

   - bpo-20743(29): Fix a reference leak in test_tcl.

   - bpo-21097(30): Move test_namespace_pkgs into test_importlib.

   - bpo-21503(31): Use test_both() consistently in test_importlib.

   - bpo-20939(32): Avoid various network test failures due to new
     redirect of ‘http://www.python.org/’ to ‘https://www.python.org’:
     use ‘http://www.example.com’ instead.

   - bpo-20668(33): asyncio tests no longer rely on tests.txt file.
     (Patch by Vajrasky Kok)

   - bpo-21093(34): Prevent failures of ctypes test_macholib on OS X if
     a copy of libz exists in $HOME/lib or /usr/local/lib.

   - bpo-22770(35): Prevent some Tk segfaults on OS X when running gui
     tests.

   - bpo-23211(36): Workaround test_logging failure on some OS X 10.6
     systems.

   - bpo-23345(37): Prevent test_ssl failures with large OpenSSL patch
     level values (like 0.9.8zc).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18982

   (2) https://bugs.python.org/issue19548

   (3) https://bugs.python.org/issue22838

   (4) https://bugs.python.org/issue22173

   (5) https://bugs.python.org/issue16000

   (6) https://bugs.python.org/issue21456

   (7) https://bugs.python.org/issue20746

   (8) https://bugs.python.org/issue22060

   (9) https://bugs.python.org/issue22104

   (10) https://bugs.python.org/issue22111

   (11) https://bugs.python.org/issue22002

   (12) https://bugs.python.org/issue21976

   (13) https://bugs.python.org/issue21918

   (14) https://bugs.python.org/issue9554

   (15) https://bugs.python.org/issue20155

   (16) https://bugs.python.org/issue19493

   (17) https://bugs.python.org/issue18492

   (18) https://bugs.python.org/issue21634

   (19) https://bugs.python.org/issue21605

   (20) https://bugs.python.org/issue21493

   (21) https://bugs.python.org/issue19925

   (22) https://bugs.python.org/issue21522

   (23) https://bugs.python.org/issue17756

   (24) https://bugs.python.org/issue17752

   (25) https://bugs.python.org/issue18604

   (26) https://bugs.python.org/issue21275

   (27) https://bugs.python.org/issue21223

   (28) https://bugs.python.org/issue20635

   (29) https://bugs.python.org/issue20743

   (30) https://bugs.python.org/issue21097

   (31) https://bugs.python.org/issue21503

   (32) https://bugs.python.org/issue20939

   (33) https://bugs.python.org/issue20668

   (34) https://bugs.python.org/issue21093

   (35) https://bugs.python.org/issue22770

   (36) https://bugs.python.org/issue23211

   (37) https://bugs.python.org/issue23345


File: python.info,  Node: Tools/Demos<35>,  Next: Windows<54>,  Prev: Tests<58>,  Up: Python 3 5 0 alpha 1

1.19.89.8 Tools/Demos
.....................

   - bpo-22314(1): pydoc now works when the LINES environment variable
     is set.

   - bpo-22615(2): Argument Clinic now supports the “type” argument for
     the int converter.  This permits using the int converter with enums
     and typedefs.

   - bpo-20076(3): The makelocalealias.py script no longer ignores UTF-8
     mapping.

   - bpo-20079(4): The makelocalealias.py script now can parse the
     SUPPORTED file from glibc sources and supports command line options
     for source paths.

   - bpo-22201(5): Command-line interface of the zipfile module now
     correctly extracts ZIP files with directory entries.  Patch by Ryan
     Wilson.

   - bpo-22120(6): For functions using an unsigned integer return
     converter, Argument Clinic now generates a cast to that type for
     the comparison to -1 in the generated code.  (This suppresses a
     compilation warning.)

   - bpo-18974(7): Tools/scripts/diff.py now uses argparse instead of
     optparse.

   - bpo-21906(8): Make Tools/scripts/md5sum.py work in Python 3.  Patch
     by Zachary Ware.

   - bpo-21629(9): Fix Argument Clinic’s “–converters” feature.

   - Add support for ‘yield from’ to 2to3.

   - Add support for the PEP 465(10) matrix multiplication operator to
     2to3.

   - bpo-16047(11): Fix module exception list and __file__ handling in
     freeze.  Patch by Meador Inge.

   - bpo-11824(12): Consider ABI tags in freeze.  Patch by Meador Inge.

   - bpo-20535(13): PYTHONWARNING no longer affects the run_tests.py
     script.  Patch by Arfrever Frehtes Taifersar Arahesis.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue22314

   (2) https://bugs.python.org/issue22615

   (3) https://bugs.python.org/issue20076

   (4) https://bugs.python.org/issue20079

   (5) https://bugs.python.org/issue22201

   (6) https://bugs.python.org/issue22120

   (7) https://bugs.python.org/issue18974

   (8) https://bugs.python.org/issue21906

   (9) https://bugs.python.org/issue21629

   (10) https://www.python.org/dev/peps/pep-0465

   (11) https://bugs.python.org/issue16047

   (12) https://bugs.python.org/issue11824

   (13) https://bugs.python.org/issue20535


File: python.info,  Node: Windows<54>,  Prev: Tools/Demos<35>,  Up: Python 3 5 0 alpha 1

1.19.89.9 Windows
.................

   - bpo-23260(1): Update Windows installer

   - The bundled version of Tcl/Tk has been updated to 8.6.3.  The most
     visible result of this change is the addition of new native file
     dialogs when running on Windows Vista or newer.  See Tcl/Tk’s TIP
     432 for more information.  Also, this version of Tcl/Tk includes
     support for Windows 10.

   - bpo-17896(2): The Windows build scripts now expect external library
     sources to be in ‘PCbuild\..\externals’ rather than
     ‘PCbuild\..\..’.

   - bpo-17717(3): The Windows build scripts now use a copy of NASM
     pulled from svn.python.org to build OpenSSL.

   - bpo-21907(4): Improved the batch scripts provided for building
     Python.

   - bpo-22644(5): The bundled version of OpenSSL has been updated to
     1.0.1j.

   - bpo-10747(6): Use versioned labels in the Windows start menu.
     Patch by Olive Kilburn.

   - bpo-22980(7): .pyd files with a version and platform tag (for
     example, “.cp35-win32.pyd”) will now be loaded in preference to
     those without tags.

`(For information about older versions, consult the HISTORY file.)'

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue23260

   (2) https://bugs.python.org/issue17896

   (3) https://bugs.python.org/issue17717

   (4) https://bugs.python.org/issue21907

   (5) https://bugs.python.org/issue22644

   (6) https://bugs.python.org/issue10747

   (7) https://bugs.python.org/issue22980


File: python.info,  Node: The Python Tutorial,  Next: Python Setup and Usage,  Prev: What’s New in Python,  Up: Top

2 The Python Tutorial
*********************

Python is an easy to learn, powerful programming language.  It has
efficient high-level data structures and a simple but effective approach
to object-oriented programming.  Python’s elegant syntax and dynamic
typing, together with its interpreted nature, make it an ideal language
for scripting and rapid application development in many areas on most
platforms.

The Python interpreter and the extensive standard library are freely
available in source or binary form for all major platforms from the
Python Web site, ‘https://www.python.org/’, and may be freely
distributed.  The same site also contains distributions of and pointers
to many free third party Python modules, programs and tools, and
additional documentation.

The Python interpreter is easily extended with new functions and data
types implemented in C or C++ (or other languages callable from C).
Python is also suitable as an extension language for customizable
applications.

This tutorial introduces the reader informally to the basic concepts and
features of the Python language and system.  It helps to have a Python
interpreter handy for hands-on experience, but all examples are
self-contained, so the tutorial can be read off-line as well.

For a description of standard objects and modules, see *note The Python
Standard Library: 1330.  *note The Python Language Reference: 1331.
gives a more formal definition of the language.  To write extensions in
C or C++, read *note Extending and Embedding the Python Interpreter:
1332. and *note Python/C API Reference Manual: 1333.  There are also
several books covering Python in depth.

This tutorial does not attempt to be comprehensive and cover every
single feature, or even every commonly used feature.  Instead, it
introduces many of Python’s most noteworthy features, and will give you
a good idea of the language’s flavor and style.  After reading it, you
will be able to read and write Python modules and programs, and you will
be ready to learn more about the various Python library modules
described in *note The Python Standard Library: 1330.

The *note Glossary: 1334. is also worth going through.

* Menu:

* Whetting Your Appetite::
* Using the Python Interpreter::
* An Informal Introduction to Python::
* More Control Flow Tools::
* Data Structures::
* Modules::
* Input and Output::
* Errors and Exceptions::
* Classes::
* Brief Tour of the Standard Library::
* Brief Tour of the Standard Library — Part II::
* Virtual Environments and Packages::
* What Now?::
* Interactive Input Editing and History Substitution::
* Floating Point Arithmetic; Issues and Limitations: Floating Point Arithmetic Issues and Limitations.
* Appendix::


File: python.info,  Node: Whetting Your Appetite,  Next: Using the Python Interpreter,  Up: The Python Tutorial

2.1 Whetting Your Appetite
==========================

If you do much work on computers, eventually you find that there’s some
task you’d like to automate.  For example, you may wish to perform a
search-and-replace over a large number of text files, or rename and
rearrange a bunch of photo files in a complicated way.  Perhaps you’d
like to write a small custom database, or a specialized GUI application,
or a simple game.

If you’re a professional software developer, you may have to work with
several C/C++/Java libraries but find the usual
write/compile/test/re-compile cycle is too slow.  Perhaps you’re writing
a test suite for such a library and find writing the testing code a
tedious task.  Or maybe you’ve written a program that could use an
extension language, and you don’t want to design and implement a whole
new language for your application.

Python is just the language for you.

You could write a Unix shell script or Windows batch files for some of
these tasks, but shell scripts are best at moving around files and
changing text data, not well-suited for GUI applications or games.  You
could write a C/C++/Java program, but it can take a lot of development
time to get even a first-draft program.  Python is simpler to use,
available on Windows, macOS, and Unix operating systems, and will help
you get the job done more quickly.

Python is simple to use, but it is a real programming language, offering
much more structure and support for large programs than shell scripts or
batch files can offer.  On the other hand, Python also offers much more
error checking than C, and, being a `very-high-level language', it has
high-level data types built in, such as flexible arrays and
dictionaries.  Because of its more general data types Python is
applicable to a much larger problem domain than Awk or even Perl, yet
many things are at least as easy in Python as in those languages.

Python allows you to split your program into modules that can be reused
in other Python programs.  It comes with a large collection of standard
modules that you can use as the basis of your programs — or as examples
to start learning to program in Python.  Some of these modules provide
things like file I/O, system calls, sockets, and even interfaces to
graphical user interface toolkits like Tk.

Python is an interpreted language, which can save you considerable time
during program development because no compilation and linking is
necessary.  The interpreter can be used interactively, which makes it
easy to experiment with features of the language, to write throw-away
programs, or to test functions during bottom-up program development.  It
is also a handy desk calculator.

Python enables programs to be written compactly and readably.  Programs
written in Python are typically much shorter than equivalent C, C++, or
Java programs, for several reasons:

   * the high-level data types allow you to express complex operations
     in a single statement;

   * statement grouping is done by indentation instead of beginning and
     ending brackets;

   * no variable or argument declarations are necessary.

Python is `extensible': if you know how to program in C it is easy to
add a new built-in function or module to the interpreter, either to
perform critical operations at maximum speed, or to link Python programs
to libraries that may only be available in binary form (such as a
vendor-specific graphics library).  Once you are really hooked, you can
link the Python interpreter into an application written in C and use it
as an extension or command language for that application.

By the way, the language is named after the BBC show “Monty Python’s
Flying Circus” and has nothing to do with reptiles.  Making references
to Monty Python skits in documentation is not only allowed, it is
encouraged!

Now that you are all excited about Python, you’ll want to examine it in
some more detail.  Since the best way to learn a language is to use it,
the tutorial invites you to play with the Python interpreter as you
read.

In the next chapter, the mechanics of using the interpreter are
explained.  This is rather mundane information, but essential for trying
out the examples shown later.

The rest of the tutorial introduces various features of the Python
language and system through examples, beginning with simple expressions,
statements and data types, through functions and modules, and finally
touching upon advanced concepts like exceptions and user-defined
classes.


File: python.info,  Node: Using the Python Interpreter,  Next: An Informal Introduction to Python,  Prev: Whetting Your Appetite,  Up: The Python Tutorial

2.2 Using the Python Interpreter
================================

* Menu:

* Invoking the Interpreter::
* The Interpreter and Its Environment::


File: python.info,  Node: Invoking the Interpreter,  Next: The Interpreter and Its Environment,  Up: Using the Python Interpreter

2.2.1 Invoking the Interpreter
------------------------------

The Python interpreter is usually installed as
‘/usr/local/bin/python3.9’ on those machines where it is available;
putting ‘/usr/local/bin’ in your Unix shell’s search path makes it
possible to start it by typing the command:

     python3.9

to the shell.  (1) Since the choice of the directory where the
interpreter lives is an installation option, other places are possible;
check with your local Python guru or system administrator.  (E.g.,
‘/usr/local/python’ is a popular alternative location.)

On Windows machines where you have installed Python from the *note
Microsoft Store: 133d, the ‘python3.9’ command will be available.  If
you have the *note py.exe launcher: a70. installed, you can use the ‘py’
command.  See *note Excursus; Setting environment variables: 133e. for
other ways to launch Python.

Typing an end-of-file character (‘Control-D’ on Unix, ‘Control-Z’ on
Windows) at the primary prompt causes the interpreter to exit with a
zero exit status.  If that doesn’t work, you can exit the interpreter by
typing the following command: ‘quit()’.

The interpreter’s line-editing features include interactive editing,
history substitution and code completion on systems that support the GNU
Readline(2) library.  Perhaps the quickest check to see whether command
line editing is supported is typing ‘Control-P’ to the first Python
prompt you get.  If it beeps, you have command line editing; see
Appendix *note Interactive Input Editing and History Substitution: 133f.
for an introduction to the keys.  If nothing appears to happen, or if
‘^P’ is echoed, command line editing isn’t available; you’ll only be
able to use backspace to remove characters from the current line.

The interpreter operates somewhat like the Unix shell: when called with
standard input connected to a tty device, it reads and executes commands
interactively; when called with a file name argument or with a file as
standard input, it reads and executes a `script' from that file.

A second way of starting the interpreter is ‘python -c command [arg]
...’, which executes the statement(s) in `command', analogous to the
shell’s *note -c: 1340. option.  Since Python statements often contain
spaces or other characters that are special to the shell, it is usually
advised to quote `command' in its entirety with single quotes.

Some Python modules are also useful as scripts.  These can be invoked
using ‘python -m module [arg] ...’, which executes the source file for
`module' as if you had spelled out its full name on the command line.

When a script file is used, it is sometimes useful to be able to run the
script and enter interactive mode afterwards.  This can be done by
passing *note -i: ee1. before the script.

All command line options are described in *note Command line and
environment: 10bd.

* Menu:

* Argument Passing::
* Interactive Mode::

   ---------- Footnotes ----------

   (1) (1) On Unix, the Python 3.x interpreter is by default not
installed with the executable named ‘python’, so that it does not
conflict with a simultaneously installed Python 2.x executable.

   (2) https://tiswww.case.edu/php/chet/readline/rltop.html


File: python.info,  Node: Argument Passing,  Next: Interactive Mode,  Up: Invoking the Interpreter

2.2.1.1 Argument Passing
........................

When known to the interpreter, the script name and additional arguments
thereafter are turned into a list of strings and assigned to the ‘argv’
variable in the ‘sys’ module.  You can access this list by executing
‘import sys’.  The length of the list is at least one; when no script
and no arguments are given, ‘sys.argv[0]’ is an empty string.  When the
script name is given as ‘'-'’ (meaning standard input), ‘sys.argv[0]’ is
set to ‘'-'’.  When *note -c: 1340. `command' is used, ‘sys.argv[0]’ is
set to ‘'-c'’.  When *note -m: 443. `module' is used, ‘sys.argv[0]’ is
set to the full name of the located module.  Options found after *note
-c: 1340. `command' or *note -m: 443. `module' are not consumed by the
Python interpreter’s option processing but left in ‘sys.argv’ for the
command or module to handle.


File: python.info,  Node: Interactive Mode,  Prev: Argument Passing,  Up: Invoking the Interpreter

2.2.1.2 Interactive Mode
........................

When commands are read from a tty, the interpreter is said to be in
`interactive mode'.  In this mode it prompts for the next command with
the `primary prompt', usually three greater-than signs (‘>>>’); for
continuation lines it prompts with the `secondary prompt', by default
three dots (‘...’).  The interpreter prints a welcome message stating
its version number and a copyright notice before printing the first
prompt:

     $ python3.9
     Python 3.9 (default, June 4 2019, 09:25:04)
     [GCC 4.8.2] on linux
     Type "help", "copyright", "credits" or "license" for more information.
     >>>

Continuation lines are needed when entering a multi-line construct.  As
an example, take a look at this *note if: eab. statement:

     >>> the_world_is_flat = True
     >>> if the_world_is_flat:
     ...     print("Be careful not to fall off!")
     ...
     Be careful not to fall off!

For more on interactive mode, see *note Interactive Mode: 1344.


File: python.info,  Node: The Interpreter and Its Environment,  Prev: Invoking the Interpreter,  Up: Using the Python Interpreter

2.2.2 The Interpreter and Its Environment
-----------------------------------------

* Menu:

* Source Code Encoding::


File: python.info,  Node: Source Code Encoding,  Up: The Interpreter and Its Environment

2.2.2.1 Source Code Encoding
............................

By default, Python source files are treated as encoded in UTF-8.  In
that encoding, characters of most languages in the world can be used
simultaneously in string literals, identifiers and comments — although
the standard library only uses ASCII characters for identifiers, a
convention that any portable code should follow.  To display all these
characters properly, your editor must recognize that the file is UTF-8,
and it must use a font that supports all the characters in the file.

To declare an encoding other than the default one, a special comment
line should be added as the `first' line of the file.  The syntax is as
follows:

     # -*- coding: encoding -*-

where `encoding' is one of the valid *note codecs: 1b. supported by
Python.

For example, to declare that Windows-1252 encoding is to be used, the
first line of your source code file should be:

     # -*- coding: cp1252 -*-

One exception to the `first line' rule is when the source code starts
with a *note UNIX “shebang” line: 1349.  In this case, the encoding
declaration should be added as the second line of the file.  For
example:

     #!/usr/bin/env python3
     # -*- coding: cp1252 -*-


File: python.info,  Node: An Informal Introduction to Python,  Next: More Control Flow Tools,  Prev: Using the Python Interpreter,  Up: The Python Tutorial

2.3 An Informal Introduction to Python
======================================

In the following examples, input and output are distinguished by the
presence or absence of prompts (*note >>>: 134d. and *note …: 134e.): to
repeat the example, you must type everything after the prompt, when the
prompt appears; lines that do not begin with a prompt are output from
the interpreter.  Note that a secondary prompt on a line by itself in an
example means you must type a blank line; this is used to end a
multi-line command.

Many of the examples in this manual, even those entered at the
interactive prompt, include comments.  Comments in Python start with the
hash character, ‘#’, and extend to the end of the physical line.  A
comment may appear at the start of a line or following whitespace or
code, but not within a string literal.  A hash character within a string
literal is just a hash character.  Since comments are to clarify code
and are not interpreted by Python, they may be omitted when typing in
examples.

Some examples:

     # this is the first comment
     spam = 1  # and this is the second comment
               # ... and now a third!
     text = "# This is not a comment because it's inside quotes."

* Menu:

* Using Python as a Calculator::
* First Steps Towards Programming::


File: python.info,  Node: Using Python as a Calculator,  Next: First Steps Towards Programming,  Up: An Informal Introduction to Python

2.3.1 Using Python as a Calculator
----------------------------------

Let’s try some simple Python commands.  Start the interpreter and wait
for the primary prompt, ‘>>>’.  (It shouldn’t take long.)

* Menu:

* Numbers::
* Strings::
* Lists::


File: python.info,  Node: Numbers,  Next: Strings,  Up: Using Python as a Calculator

2.3.1.1 Numbers
...............

The interpreter acts as a simple calculator: you can type an expression
at it and it will write the value.  Expression syntax is
straightforward: the operators ‘+’, ‘-’, ‘*’ and ‘/’ work just like in
most other languages (for example, Pascal or C); parentheses (‘()’) can
be used for grouping.  For example:

     >>> 2 + 2
     4
     >>> 50 - 5*6
     20
     >>> (50 - 5*6) / 4
     5.0
     >>> 8 / 5  # division always returns a floating point number
     1.6

The integer numbers (e.g.  ‘2’, ‘4’, ‘20’) have type *note int: 204, the
ones with a fractional part (e.g.  ‘5.0’, ‘1.6’) have type *note float:
1fd.  We will see more about numeric types later in the tutorial.

Division (‘/’) always returns a float.  To do *note floor division: 1f9.
and get an integer result (discarding any fractional result) you can use
the ‘//’ operator; to calculate the remainder you can use ‘%’:

     >>> 17 / 3  # classic division returns a float
     5.666666666666667
     >>>
     >>> 17 // 3  # floor division discards the fractional part
     5
     >>> 17 % 3  # the % operator returns the remainder of the division
     2
     >>> 5 * 3 + 2  # floored quotient * divisor + remainder
     17

With Python, it is possible to use the ‘**’ operator to calculate powers
(1):

     >>> 5 ** 2  # 5 squared
     25
     >>> 2 ** 7  # 2 to the power of 7
     128

The equal sign (‘=’) is used to assign a value to a variable.
Afterwards, no result is displayed before the next interactive prompt:

     >>> width = 20
     >>> height = 5 * 9
     >>> width * height
     900

If a variable is not “defined” (assigned a value), trying to use it will
give you an error:

     >>> n  # try to access an undefined variable
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     NameError: name 'n' is not defined

There is full support for floating point; operators with mixed type
operands convert the integer operand to floating point:

     >>> 4 * 3.75 - 1
     14.0

In interactive mode, the last printed expression is assigned to the
variable ‘_’.  This means that when you are using Python as a desk
calculator, it is somewhat easier to continue calculations, for example:

     >>> tax = 12.5 / 100
     >>> price = 100.50
     >>> price * tax
     12.5625
     >>> price + _
     113.0625
     >>> round(_, 2)
     113.06

This variable should be treated as read-only by the user.  Don’t
explicitly assign a value to it — you would create an independent local
variable with the same name masking the built-in variable with its magic
behavior.

In addition to *note int: 204. and *note float: 1fd, Python supports
other types of numbers, such as *note Decimal: 2c0. and *note Fraction:
2be.  Python also has built-in support for *note complex numbers: 1353,
and uses the ‘j’ or ‘J’ suffix to indicate the imaginary part (e.g.
‘3+5j’).

   ---------- Footnotes ----------

   (1) (1) Since ‘**’ has higher precedence than ‘-’, ‘-3**2’ will be
interpreted as ‘-(3**2)’ and thus result in ‘-9’.  To avoid this and get
‘9’, you can use ‘(-3)**2’.


File: python.info,  Node: Strings,  Next: Lists,  Prev: Numbers,  Up: Using Python as a Calculator

2.3.1.2 Strings
...............

Besides numbers, Python can also manipulate strings, which can be
expressed in several ways.  They can be enclosed in single quotes
(‘'...'’) or double quotes (‘"..."’) with the same result (1).  ‘\’ can
be used to escape quotes:

     >>> 'spam eggs'  # single quotes
     'spam eggs'
     >>> 'doesn\'t'  # use \' to escape the single quote...
     "doesn't"
     >>> "doesn't"  # ...or use double quotes instead
     "doesn't"
     >>> '"Yes," they said.'
     '"Yes," they said.'
     >>> "\"Yes,\" they said."
     '"Yes," they said.'
     >>> '"Isn\'t," they said.'
     '"Isn\'t," they said.'

In the interactive interpreter, the output string is enclosed in quotes
and special characters are escaped with backslashes.  While this might
sometimes look different from the input (the enclosing quotes could
change), the two strings are equivalent.  The string is enclosed in
double quotes if the string contains a single quote and no double
quotes, otherwise it is enclosed in single quotes.  The *note print():
971. function produces a more readable output, by omitting the enclosing
quotes and by printing escaped and special characters:

     >>> '"Isn\'t," they said.'
     '"Isn\'t," they said.'
     >>> print('"Isn\'t," they said.')
     "Isn't," they said.
     >>> s = 'First line.\nSecond line.'  # \n means newline
     >>> s  # without print(), \n is included in the output
     'First line.\nSecond line.'
     >>> print(s)  # with print(), \n produces a new line
     First line.
     Second line.

If you don’t want characters prefaced by ‘\’ to be interpreted as
special characters, you can use `raw strings' by adding an ‘r’ before
the first quote:

     >>> print('C:\some\name')  # here \n means newline!
     C:\some
     ame
     >>> print(r'C:\some\name')  # note the r before the quote
     C:\some\name

String literals can span multiple lines.  One way is using
triple-quotes: ‘"""..."""’ or ‘'''...'''’.  End of lines are
automatically included in the string, but it’s possible to prevent this
by adding a ‘\’ at the end of the line.  The following example:

     print("""\
     Usage: thingy [OPTIONS]
          -h                        Display this usage message
          -H hostname               Hostname to connect to
     """)

produces the following output (note that the initial newline is not
included):

     Usage: thingy [OPTIONS]
          -h                        Display this usage message
          -H hostname               Hostname to connect to

Strings can be concatenated (glued together) with the ‘+’ operator, and
repeated with ‘*’:

     >>> # 3 times 'un', followed by 'ium'
     >>> 3 * 'un' + 'ium'
     'unununium'

Two or more `string literals' (i.e.  the ones enclosed between quotes)
next to each other are automatically concatenated.

     >>> 'Py' 'thon'
     'Python'

This feature is particularly useful when you want to break long strings:

     >>> text = ('Put several strings within parentheses '
     ...         'to have them joined together.')
     >>> text
     'Put several strings within parentheses to have them joined together.'

This only works with two literals though, not with variables or
expressions:

     >>> prefix = 'Py'
     >>> prefix 'thon'  # can't concatenate a variable and a string literal
       File "<stdin>", line 1
         prefix 'thon'
                     ^
     SyntaxError: invalid syntax
     >>> ('un' * 3) 'ium'
       File "<stdin>", line 1
         ('un' * 3) 'ium'
                        ^
     SyntaxError: invalid syntax

If you want to concatenate variables or a variable and a literal, use
‘+’:

     >>> prefix + 'thon'
     'Python'

Strings can be `indexed' (subscripted), with the first character having
index 0.  There is no separate character type; a character is simply a
string of size one:

     >>> word = 'Python'
     >>> word[0]  # character in position 0
     'P'
     >>> word[5]  # character in position 5
     'n'

Indices may also be negative numbers, to start counting from the right:

     >>> word[-1]  # last character
     'n'
     >>> word[-2]  # second-last character
     'o'
     >>> word[-6]
     'P'

Note that since -0 is the same as 0, negative indices start from -1.

In addition to indexing, `slicing' is also supported.  While indexing is
used to obtain individual characters, `slicing' allows you to obtain
substring:

     >>> word[0:2]  # characters from position 0 (included) to 2 (excluded)
     'Py'
     >>> word[2:5]  # characters from position 2 (included) to 5 (excluded)
     'tho'

Slice indices have useful defaults; an omitted first index defaults to
zero, an omitted second index defaults to the size of the string being
sliced.

     >>> word[:2]   # character from the beginning to position 2 (excluded)
     'Py'
     >>> word[4:]   # characters from position 4 (included) to the end
     'on'
     >>> word[-2:]  # characters from the second-last (included) to the end
     'on'

Note how the start is always included, and the end always excluded.
This makes sure that ‘s[:i] + s[i:]’ is always equal to ‘s’:

     >>> word[:2] + word[2:]
     'Python'
     >>> word[:4] + word[4:]
     'Python'

One way to remember how slices work is to think of the indices as
pointing `between' characters, with the left edge of the first character
numbered 0.  Then the right edge of the last character of a string of
`n' characters has index `n', for example:

      +---+---+---+---+---+---+
      | P | y | t | h | o | n |
      +---+---+---+---+---+---+
      0   1   2   3   4   5   6
     -6  -5  -4  -3  -2  -1

The first row of numbers gives the position of the indices 0…6 in the
string; the second row gives the corresponding negative indices.  The
slice from `i' to `j' consists of all characters between the edges
labeled `i' and `j', respectively.

For non-negative indices, the length of a slice is the difference of the
indices, if both are within bounds.  For example, the length of
‘word[1:3]’ is 2.

Attempting to use an index that is too large will result in an error:

     >>> word[42]  # the word only has 6 characters
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     IndexError: string index out of range

However, out of range slice indexes are handled gracefully when used for
slicing:

     >>> word[4:42]
     'on'
     >>> word[42:]
     ''

Python strings cannot be changed — they are *note immutable: 1356.
Therefore, assigning to an indexed position in the string results in an
error:

     >>> word[0] = 'J'
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: 'str' object does not support item assignment
     >>> word[2:] = 'py'
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: 'str' object does not support item assignment

If you need a different string, you should create a new one:

     >>> 'J' + word[1:]
     'Jython'
     >>> word[:2] + 'py'
     'Pypy'

The built-in function *note len(): 28b. returns the length of a string:

     >>> s = 'supercalifragilisticexpialidocious'
     >>> len(s)
     34

See also
........

*note Text Sequence Type — str: 1357.

     Strings are examples of `sequence types', and support the common
     operations supported by such types.

*note String Methods: 1358.

     Strings support a large number of methods for basic transformations
     and searching.

*note Formatted string literals: 296.

     String literals that have embedded expressions.

*note Format String Syntax: de0.

     Information about string formatting with *note str.format(): 5d5.

*note printf-style String Formatting: 1359.

     The old formatting operations invoked when strings are the left
     operand of the ‘%’ operator are described in more detail here.

   ---------- Footnotes ----------

   (1) (2) Unlike other languages, special characters such as ‘\n’ have
the same meaning with both single (‘'...'’) and double (‘"..."’) quotes.
The only difference between the two is that within single quotes you
don’t need to escape ‘"’ (but you have to escape ‘\'’) and vice versa.


File: python.info,  Node: Lists,  Prev: Strings,  Up: Using Python as a Calculator

2.3.1.3 Lists
.............

Python knows a number of `compound' data types, used to group together
other values.  The most versatile is the `list', which can be written as
a list of comma-separated values (items) between square brackets.  Lists
might contain items of different types, but usually the items all have
the same type.

     >>> squares = [1, 4, 9, 16, 25]
     >>> squares
     [1, 4, 9, 16, 25]

Like strings (and all other built-in *note sequence: 135c. types), lists
can be indexed and sliced:

     >>> squares[0]  # indexing returns the item
     1
     >>> squares[-1]
     25
     >>> squares[-3:]  # slicing returns a new list
     [9, 16, 25]

All slice operations return a new list containing the requested
elements.  This means that the following slice returns a *note shallow
copy: 135d. of the list:

     >>> squares[:]
     [1, 4, 9, 16, 25]

Lists also support operations like concatenation:

     >>> squares + [36, 49, 64, 81, 100]
     [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

Unlike strings, which are *note immutable: 1356, lists are a *note
mutable: 135e. type, i.e.  it is possible to change their content:

     >>> cubes = [1, 8, 27, 65, 125]  # something's wrong here
     >>> 4 ** 3  # the cube of 4 is 64, not 65!
     64
     >>> cubes[3] = 64  # replace the wrong value
     >>> cubes
     [1, 8, 27, 64, 125]

You can also add new items at the end of the list, by using the
‘append()’ `method' (we will see more about methods later):

     >>> cubes.append(216)  # add the cube of 6
     >>> cubes.append(7 ** 3)  # and the cube of 7
     >>> cubes
     [1, 8, 27, 64, 125, 216, 343]

Assignment to slices is also possible, and this can even change the size
of the list or clear it entirely:

     >>> letters = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
     >>> letters
     ['a', 'b', 'c', 'd', 'e', 'f', 'g']
     >>> # replace some values
     >>> letters[2:5] = ['C', 'D', 'E']
     >>> letters
     ['a', 'b', 'C', 'D', 'E', 'f', 'g']
     >>> # now remove them
     >>> letters[2:5] = []
     >>> letters
     ['a', 'b', 'f', 'g']
     >>> # clear the list by replacing all the elements with an empty list
     >>> letters[:] = []
     >>> letters
     []

The built-in function *note len(): 28b. also applies to lists:

     >>> letters = ['a', 'b', 'c', 'd']
     >>> len(letters)
     4

It is possible to nest lists (create lists containing other lists), for
example:

     >>> a = ['a', 'b', 'c']
     >>> n = [1, 2, 3]
     >>> x = [a, n]
     >>> x
     [['a', 'b', 'c'], [1, 2, 3]]
     >>> x[0]
     ['a', 'b', 'c']
     >>> x[0][1]
     'b'


File: python.info,  Node: First Steps Towards Programming,  Prev: Using Python as a Calculator,  Up: An Informal Introduction to Python

2.3.2 First Steps Towards Programming
-------------------------------------

Of course, we can use Python for more complicated tasks than adding two
and two together.  For instance, we can write an initial sub-sequence of
the Fibonacci series(1) as follows:

     >>> # Fibonacci series:
     ... # the sum of two elements defines the next
     ... a, b = 0, 1
     >>> while a < 10:
     ...     print(a)
     ...     a, b = b, a+b
     ...
     0
     1
     1
     2
     3
     5
     8

This example introduces several new features.

   * The first line contains a `multiple assignment': the variables ‘a’
     and ‘b’ simultaneously get the new values 0 and 1.  On the last
     line this is used again, demonstrating that the expressions on the
     right-hand side are all evaluated first before any of the
     assignments take place.  The right-hand side expressions are
     evaluated from the left to the right.

   * The *note while: 1361. loop executes as long as the condition
     (here: ‘a < 10’) remains true.  In Python, like in C, any non-zero
     integer value is true; zero is false.  The condition may also be a
     string or list value, in fact any sequence; anything with a
     non-zero length is true, empty sequences are false.  The test used
     in the example is a simple comparison.  The standard comparison
     operators are written the same as in C: ‘<’ (less than), ‘>’
     (greater than), ‘==’ (equal to), ‘<=’ (less than or equal to), ‘>=’
     (greater than or equal to) and ‘!=’ (not equal to).

   * The `body' of the loop is `indented': indentation is Python’s way
     of grouping statements.  At the interactive prompt, you have to
     type a tab or space(s) for each indented line.  In practice you
     will prepare more complicated input for Python with a text editor;
     all decent text editors have an auto-indent facility.  When a
     compound statement is entered interactively, it must be followed by
     a blank line to indicate completion (since the parser cannot guess
     when you have typed the last line).  Note that each line within a
     basic block must be indented by the same amount.

   * The *note print(): 971. function writes the value of the
     argument(s) it is given.  It differs from just writing the
     expression you want to write (as we did earlier in the calculator
     examples) in the way it handles multiple arguments, floating point
     quantities, and strings.  Strings are printed without quotes, and a
     space is inserted between items, so you can format things nicely,
     like this:

          >>> i = 256*256
          >>> print('The value of i is', i)
          The value of i is 65536

     The keyword argument `end' can be used to avoid the newline after
     the output, or end the output with a different string:

          >>> a, b = 0, 1
          >>> while a < 1000:
          ...     print(a, end=',')
          ...     a, b = b, a+b
          ...
          0,1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Fibonacci_number


File: python.info,  Node: More Control Flow Tools,  Next: Data Structures,  Prev: An Informal Introduction to Python,  Up: The Python Tutorial

2.4 More Control Flow Tools
===========================

Besides the *note while: 1361. statement just introduced, Python uses
the usual flow control statements known from other languages, with some
twists.

* Menu:

* if Statements::
* for Statements::
* The range() Function: The range Function.
* break and continue Statements, and else Clauses on Loops: break and continue Statements and else Clauses on Loops.
* pass Statements::
* Defining Functions::
* More on Defining Functions::
* Intermezzo; Coding Style: Intermezzo Coding Style.


File: python.info,  Node: if Statements,  Next: for Statements,  Up: More Control Flow Tools

2.4.1 ‘if’ Statements
---------------------

Perhaps the most well-known statement type is the *note if: eab.
statement.  For example:

     >>> x = int(input("Please enter an integer: "))
     Please enter an integer: 42
     >>> if x < 0:
     ...     x = 0
     ...     print('Negative changed to zero')
     ... elif x == 0:
     ...     print('Zero')
     ... elif x == 1:
     ...     print('Single')
     ... else:
     ...     print('More')
     ...
     More

There can be zero or more *note elif: 1367. parts, and the *note else:
1368. part is optional.  The keyword ‘‘elif’’ is short for ‘else if’,
and is useful to avoid excessive indentation.  An ‘if’ … ‘elif’ … ‘elif’
… sequence is a substitute for the ‘switch’ or ‘case’ statements found
in other languages.


File: python.info,  Node: for Statements,  Next: The range Function,  Prev: if Statements,  Up: More Control Flow Tools

2.4.2 ‘for’ Statements
----------------------

The *note for: cfa. statement in Python differs a bit from what you may
be used to in C or Pascal.  Rather than always iterating over an
arithmetic progression of numbers (like in Pascal), or giving the user
the ability to define both the iteration step and halting condition (as
C), Python’s ‘for’ statement iterates over the items of any sequence (a
list or a string), in the order that they appear in the sequence.  For
example (no pun intended):

     >>> # Measure some strings:
     ... words = ['cat', 'window', 'defenestrate']
     >>> for w in words:
     ...     print(w, len(w))
     ...
     cat 3
     window 6
     defenestrate 12

Code that modifies a collection while iterating over that same
collection can be tricky to get right.  Instead, it is usually more
straight-forward to loop over a copy of the collection or to create a
new collection:

     # Strategy:  Iterate over a copy
     for user, status in users.copy().items():
         if status == 'inactive':
             del users[user]

     # Strategy:  Create a new collection
     active_users = {}
     for user, status in users.items():
         if status == 'active':
             active_users[user] = status


File: python.info,  Node: The range Function,  Next: break and continue Statements and else Clauses on Loops,  Prev: for Statements,  Up: More Control Flow Tools

2.4.3 The ‘range()’ Function
----------------------------

If you do need to iterate over a sequence of numbers, the built-in
function *note range(): 1f5. comes in handy.  It generates arithmetic
progressions:

     >>> for i in range(5):
     ...     print(i)
     ...
     0
     1
     2
     3
     4

The given end point is never part of the generated sequence; ‘range(10)’
generates 10 values, the legal indices for items of a sequence of length
10.  It is possible to let the range start at another number, or to
specify a different increment (even negative; sometimes this is called
the ‘step’):

     >>> list(range(5, 10))
     [5, 6, 7, 8, 9]

     >>> list(range(0, 10, 3))
     [0, 3, 6, 9]

     >>> list(range(-10, -100, -30))
     [-10, -40, -70]

To iterate over the indices of a sequence, you can combine *note
range(): 1f5. and *note len(): 28b. as follows:

     >>> a = ['Mary', 'had', 'a', 'little', 'lamb']
     >>> for i in range(len(a)):
     ...     print(i, a[i])
     ...
     0 Mary
     1 had
     2 a
     3 little
     4 lamb

In most such cases, however, it is convenient to use the *note
enumerate(): ea7. function, see *note Looping Techniques: 136d.

A strange thing happens if you just print a range:

     >>> range(10)
     range(0, 10)

In many ways the object returned by *note range(): 1f5. behaves as if it
is a list, but in fact it isn’t.  It is an object which returns the
successive items of the desired sequence when you iterate over it, but
it doesn’t really make the list, thus saving space.

We say such an object is *note iterable: c7c, that is, suitable as a
target for functions and constructs that expect something from which
they can obtain successive items until the supply is exhausted.  We have
seen that the *note for: cfa. statement is such a construct, while an
example of a function that takes an iterable is *note sum(): 316.:

     >>> sum(range(4))  # 0 + 1 + 2 + 3
     6

Later we will see more functions that return iterables and take
iterables as arguments.  In chapter *note Data Structures: 136e, we will
discuss in more detail about *note list(): 1f8.


File: python.info,  Node: break and continue Statements and else Clauses on Loops,  Next: pass Statements,  Prev: The range Function,  Up: More Control Flow Tools

2.4.4 ‘break’ and ‘continue’ Statements, and ‘else’ Clauses on Loops
--------------------------------------------------------------------

The *note break: 3fa. statement, like in C, breaks out of the innermost
enclosing *note for: cfa. or *note while: 1361. loop.

Loop statements may have an ‘else’ clause; it is executed when the loop
terminates through exhaustion of the iterable (with *note for: cfa.) or
when the condition becomes false (with *note while: 1361.), but not when
the loop is terminated by a *note break: 3fa. statement.  This is
exemplified by the following loop, which searches for prime numbers:

     >>> for n in range(2, 10):
     ...     for x in range(2, n):
     ...         if n % x == 0:
     ...             print(n, 'equals', x, '*', n//x)
     ...             break
     ...     else:
     ...         # loop fell through without finding a factor
     ...         print(n, 'is a prime number')
     ...
     2 is a prime number
     3 is a prime number
     4 equals 2 * 2
     5 is a prime number
     6 equals 2 * 3
     7 is a prime number
     8 equals 2 * 4
     9 equals 3 * 3

(Yes, this is the correct code.  Look closely: the ‘else’ clause belongs
to the *note for: cfa. loop, `not' the *note if: eab. statement.)

When used with a loop, the ‘else’ clause has more in common with the
‘else’ clause of a *note try: e37. statement than it does with that of
*note if: eab. statements: a *note try: e37. statement’s ‘else’ clause
runs when no exception occurs, and a loop’s ‘else’ clause runs when no
‘break’ occurs.  For more on the ‘try’ statement and exceptions, see
*note Handling Exceptions: 1371.

The *note continue: 2bb. statement, also borrowed from C, continues with
the next iteration of the loop:

     >>> for num in range(2, 10):
     ...     if num % 2 == 0:
     ...         print("Found an even number", num)
     ...         continue
     ...     print("Found an odd number", num)
     ...
     Found an even number 2
     Found an odd number 3
     Found an even number 4
     Found an odd number 5
     Found an even number 6
     Found an odd number 7
     Found an even number 8
     Found an odd number 9


File: python.info,  Node: pass Statements,  Next: Defining Functions,  Prev: break and continue Statements and else Clauses on Loops,  Up: More Control Flow Tools

2.4.5 ‘pass’ Statements
-----------------------

The *note pass: 1374. statement does nothing.  It can be used when a
statement is required syntactically but the program requires no action.
For example:

     >>> while True:
     ...     pass  # Busy-wait for keyboard interrupt (Ctrl+C)
     ...

This is commonly used for creating minimal classes:

     >>> class MyEmptyClass:
     ...     pass
     ...

Another place *note pass: 1374. can be used is as a place-holder for a
function or conditional body when you are working on new code, allowing
you to keep thinking at a more abstract level.  The ‘pass’ is silently
ignored:

     >>> def initlog(*args):
     ...     pass   # Remember to implement this!
     ...


File: python.info,  Node: Defining Functions,  Next: More on Defining Functions,  Prev: pass Statements,  Up: More Control Flow Tools

2.4.6 Defining Functions
------------------------

We can create a function that writes the Fibonacci series to an
arbitrary boundary:

     >>> def fib(n):    # write Fibonacci series up to n
     ...     """Print a Fibonacci series up to n."""
     ...     a, b = 0, 1
     ...     while a < n:
     ...         print(a, end=' ')
     ...         a, b = b, a+b
     ...     print()
     ...
     >>> # Now call the function we just defined:
     ... fib(2000)
     0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597

The keyword *note def: e83. introduces a function `definition'.  It must
be followed by the function name and the parenthesized list of formal
parameters.  The statements that form the body of the function start at
the next line, and must be indented.

The first statement of the function body can optionally be a string
literal; this string literal is the function’s documentation string, or
`docstring'.  (More about docstrings can be found in the section *note
Documentation Strings: 1377.)  There are tools which use docstrings to
automatically produce online or printed documentation, or to let the
user interactively browse through code; it’s good practice to include
docstrings in code that you write, so make a habit of it.

The `execution' of a function introduces a new symbol table used for the
local variables of the function.  More precisely, all variable
assignments in a function store the value in the local symbol table;
whereas variable references first look in the local symbol table, then
in the local symbol tables of enclosing functions, then in the global
symbol table, and finally in the table of built-in names.  Thus, global
variables and variables of enclosing functions cannot be directly
assigned a value within a function (unless, for global variables, named
in a *note global: 1378. statement, or, for variables of enclosing
functions, named in a *note nonlocal: d07. statement), although they may
be referenced.

The actual parameters (arguments) to a function call are introduced in
the local symbol table of the called function when it is called; thus,
arguments are passed using `call by value' (where the `value' is always
an object `reference', not the value of the object).  (1) When a
function calls another function, or calls itself recursively, a new
local symbol table is created for that call.

A function definition associates the function name with the function
object in the current symbol table.  The interpreter recognizes the
object pointed to by that name as a user-defined function.  Other names
can also point to that same function object and can also be used to
access the function:

     >>> fib
     <function fib at 10042ed0>
     >>> f = fib
     >>> f(100)
     0 1 1 2 3 5 8 13 21 34 55 89

Coming from other languages, you might object that ‘fib’ is not a
function but a procedure since it doesn’t return a value.  In fact, even
functions without a *note return: 2c8. statement do return a value,
albeit a rather boring one.  This value is called ‘None’ (it’s a
built-in name).  Writing the value ‘None’ is normally suppressed by the
interpreter if it would be the only value written.  You can see it if
you really want to using *note print(): 971.:

     >>> fib(0)
     >>> print(fib(0))
     None

It is simple to write a function that returns a list of the numbers of
the Fibonacci series, instead of printing it:

     >>> def fib2(n):  # return Fibonacci series up to n
     ...     """Return a list containing the Fibonacci series up to n."""
     ...     result = []
     ...     a, b = 0, 1
     ...     while a < n:
     ...         result.append(a)    # see below
     ...         a, b = b, a+b
     ...     return result
     ...
     >>> f100 = fib2(100)    # call it
     >>> f100                # write the result
     [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]

This example, as usual, demonstrates some new Python features:

   * The *note return: 2c8. statement returns with a value from a
     function.  ‘return’ without an expression argument returns ‘None’.
     Falling off the end of a function also returns ‘None’.

   * The statement ‘result.append(a)’ calls a `method' of the list
     object ‘result’.  A method is a function that ‘belongs’ to an
     object and is named ‘obj.methodname’, where ‘obj’ is some object
     (this may be an expression), and ‘methodname’ is the name of a
     method that is defined by the object’s type.  Different types
     define different methods.  Methods of different types may have the
     same name without causing ambiguity.  (It is possible to define
     your own object types and methods, using `classes', see *note
     Classes: 1379.) The method ‘append()’ shown in the example is
     defined for list objects; it adds a new element at the end of the
     list.  In this example it is equivalent to ‘result = result + [a]’,
     but more efficient.

   ---------- Footnotes ----------

   (1) (1) Actually, `call by object reference' would be a better
description, since if a mutable object is passed, the caller will see
any changes the callee makes to it (items inserted into a list).


File: python.info,  Node: More on Defining Functions,  Next: Intermezzo Coding Style,  Prev: Defining Functions,  Up: More Control Flow Tools

2.4.7 More on Defining Functions
--------------------------------

It is also possible to define functions with a variable number of
arguments.  There are three forms, which can be combined.

* Menu:

* Default Argument Values::
* Keyword Arguments::
* Special parameters::
* Arbitrary Argument Lists::
* Unpacking Argument Lists::
* Lambda Expressions::
* Documentation Strings::
* Function Annotations::


File: python.info,  Node: Default Argument Values,  Next: Keyword Arguments,  Up: More on Defining Functions

2.4.7.1 Default Argument Values
...............................

The most useful form is to specify a default value for one or more
arguments.  This creates a function that can be called with fewer
arguments than it is defined to allow.  For example:

     def ask_ok(prompt, retries=4, reminder='Please try again!'):
         while True:
             ok = input(prompt)
             if ok in ('y', 'ye', 'yes'):
                 return True
             if ok in ('n', 'no', 'nop', 'nope'):
                 return False
             retries = retries - 1
             if retries < 0:
                 raise ValueError('invalid user response')
             print(reminder)

This function can be called in several ways:

   * giving only the mandatory argument: ‘ask_ok('Do you really want to
     quit?')’

   * giving one of the optional arguments: ‘ask_ok('OK to overwrite the
     file?', 2)’

   * or even giving all arguments: ‘ask_ok('OK to overwrite the file?',
     2, 'Come on, only yes or no!')’

This example also introduces the *note in: 179. keyword.  This tests
whether or not a sequence contains a certain value.

The default values are evaluated at the point of function definition in
the `defining' scope, so that

     i = 5

     def f(arg=i):
         print(arg)

     i = 6
     f()

will print ‘5’.

`Important warning:' The default value is evaluated only once.  This
makes a difference when the default is a mutable object such as a list,
dictionary, or instances of most classes.  For example, the following
function accumulates the arguments passed to it on subsequent calls:

     def f(a, L=[]):
         L.append(a)
         return L

     print(f(1))
     print(f(2))
     print(f(3))

This will print

     [1]
     [1, 2]
     [1, 2, 3]

If you don’t want the default to be shared between subsequent calls, you
can write the function like this instead:

     def f(a, L=None):
         if L is None:
             L = []
         L.append(a)
         return L


File: python.info,  Node: Keyword Arguments,  Next: Special parameters,  Prev: Default Argument Values,  Up: More on Defining Functions

2.4.7.2 Keyword Arguments
.........................

Functions can also be called using *note keyword arguments: 6bb. of the
form ‘kwarg=value’.  For instance, the following function:

     def parrot(voltage, state='a stiff', action='voom', type='Norwegian Blue'):
         print("-- This parrot wouldn't", action, end=' ')
         print("if you put", voltage, "volts through it.")
         print("-- Lovely plumage, the", type)
         print("-- It's", state, "!")

accepts one required argument (‘voltage’) and three optional arguments
(‘state’, ‘action’, and ‘type’).  This function can be called in any of
the following ways:

     parrot(1000)                                          # 1 positional argument
     parrot(voltage=1000)                                  # 1 keyword argument
     parrot(voltage=1000000, action='VOOOOOM')             # 2 keyword arguments
     parrot(action='VOOOOOM', voltage=1000000)             # 2 keyword arguments
     parrot('a million', 'bereft of life', 'jump')         # 3 positional arguments
     parrot('a thousand', state='pushing up the daisies')  # 1 positional, 1 keyword

but all the following calls would be invalid:

     parrot()                     # required argument missing
     parrot(voltage=5.0, 'dead')  # non-keyword argument after a keyword argument
     parrot(110, voltage=220)     # duplicate value for the same argument
     parrot(actor='John Cleese')  # unknown keyword argument

In a function call, keyword arguments must follow positional arguments.
All the keyword arguments passed must match one of the arguments
accepted by the function (e.g.  ‘actor’ is not a valid argument for the
‘parrot’ function), and their order is not important.  This also
includes non-optional arguments (e.g.  ‘parrot(voltage=1000)’ is valid
too).  No argument may receive a value more than once.  Here’s an
example that fails due to this restriction:

     >>> def function(a):
     ...     pass
     ...
     >>> function(0, a=0)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: function() got multiple values for argument 'a'

When a final formal parameter of the form ‘**name’ is present, it
receives a dictionary (see *note Mapping Types — dict: 40e.) containing
all keyword arguments except for those corresponding to a formal
parameter.  This may be combined with a formal parameter of the form
‘*name’ (described in the next subsection) which receives a *note tuple:
1380. containing the positional arguments beyond the formal parameter
list.  (‘*name’ must occur before ‘**name’.)  For example, if we define
a function like this:

     def cheeseshop(kind, *arguments, **keywords):
         print("-- Do you have any", kind, "?")
         print("-- I'm sorry, we're all out of", kind)
         for arg in arguments:
             print(arg)
         print("-" * 40)
         for kw in keywords:
             print(kw, ":", keywords[kw])

It could be called like this:

     cheeseshop("Limburger", "It's very runny, sir.",
                "It's really very, VERY runny, sir.",
                shopkeeper="Michael Palin",
                client="John Cleese",
                sketch="Cheese Shop Sketch")

and of course it would print:

     -- Do you have any Limburger ?
     -- I'm sorry, we're all out of Limburger
     It's very runny, sir.
     It's really very, VERY runny, sir.
     ----------------------------------------
     shopkeeper : Michael Palin
     client : John Cleese
     sketch : Cheese Shop Sketch

Note that the order in which the keyword arguments are printed is
guaranteed to match the order in which they were provided in the
function call.


File: python.info,  Node: Special parameters,  Next: Arbitrary Argument Lists,  Prev: Keyword Arguments,  Up: More on Defining Functions

2.4.7.3 Special parameters
..........................

By default, arguments may be passed to a Python function either by
position or explicitly by keyword.  For readability and performance, it
makes sense to restrict the way arguments can be passed so that a
developer need only look at the function definition to determine if
items are passed by position, by position or keyword, or by keyword.

A function definition may look like:

     def f(pos1, pos2, /, pos_or_kwd, *, kwd1, kwd2):
           -----------    ----------     ----------
             |             |                  |
             |        Positional or keyword   |
             |                                - Keyword only
              -- Positional only

where ‘/’ and ‘*’ are optional.  If used, these symbols indicate the
kind of parameter by how the arguments may be passed to the function:
positional-only, positional-or-keyword, and keyword-only.  Keyword
parameters are also referred to as named parameters.

* Menu:

* Positional-or-Keyword Arguments::
* Positional-Only Parameters::
* Keyword-Only Arguments::
* Function Examples::
* Recap::


File: python.info,  Node: Positional-or-Keyword Arguments,  Next: Positional-Only Parameters,  Up: Special parameters

2.4.7.4 Positional-or-Keyword Arguments
.......................................

If ‘/’ and ‘*’ are not present in the function definition, arguments may
be passed to a function by position or by keyword.


File: python.info,  Node: Positional-Only Parameters,  Next: Keyword-Only Arguments,  Prev: Positional-or-Keyword Arguments,  Up: Special parameters

2.4.7.5 Positional-Only Parameters
..................................

Looking at this in a bit more detail, it is possible to mark certain
parameters as `positional-only'.  If `positional-only', the parameters’
order matters, and the parameters cannot be passed by keyword.
Positional-only parameters are placed before a ‘/’ (forward-slash).  The
‘/’ is used to logically separate the positional-only parameters from
the rest of the parameters.  If there is no ‘/’ in the function
definition, there are no positional-only parameters.

Parameters following the ‘/’ may be `positional-or-keyword' or
`keyword-only'.


File: python.info,  Node: Keyword-Only Arguments,  Next: Function Examples,  Prev: Positional-Only Parameters,  Up: Special parameters

2.4.7.6 Keyword-Only Arguments
..............................

To mark parameters as `keyword-only', indicating the parameters must be
passed by keyword argument, place an ‘*’ in the arguments list just
before the first `keyword-only' parameter.


File: python.info,  Node: Function Examples,  Next: Recap,  Prev: Keyword-Only Arguments,  Up: Special parameters

2.4.7.7 Function Examples
.........................

Consider the following example function definitions paying close
attention to the markers ‘/’ and ‘*’:

     >>> def standard_arg(arg):
     ...     print(arg)
     ...
     >>> def pos_only_arg(arg, /):
     ...     print(arg)
     ...
     >>> def kwd_only_arg(*, arg):
     ...     print(arg)
     ...
     >>> def combined_example(pos_only, /, standard, *, kwd_only):
     ...     print(pos_only, standard, kwd_only)

The first function definition, ‘standard_arg’, the most familiar form,
places no restrictions on the calling convention and arguments may be
passed by position or keyword:

     >>> standard_arg(2)
     2

     >>> standard_arg(arg=2)
     2

The second function ‘pos_only_arg’ is restricted to only use positional
parameters as there is a ‘/’ in the function definition:

     >>> pos_only_arg(1)
     1

     >>> pos_only_arg(arg=1)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: pos_only_arg() got some positional-only arguments passed as keyword arguments: 'arg'

The third function ‘kwd_only_args’ only allows keyword arguments as
indicated by a ‘*’ in the function definition:

     >>> kwd_only_arg(3)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: kwd_only_arg() takes 0 positional arguments but 1 was given

     >>> kwd_only_arg(arg=3)
     3

And the last uses all three calling conventions in the same function
definition:

     >>> combined_example(1, 2, 3)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: combined_example() takes 2 positional arguments but 3 were given

     >>> combined_example(1, 2, kwd_only=3)
     1 2 3

     >>> combined_example(1, standard=2, kwd_only=3)
     1 2 3

     >>> combined_example(pos_only=1, standard=2, kwd_only=3)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: combined_example() got some positional-only arguments passed as keyword arguments: 'pos_only'

Finally, consider this function definition which has a potential
collision between the positional argument ‘name’ and ‘**kwds’ which has
‘name’ as a key:

     def foo(name, **kwds):
         return 'name' in kwds

There is no possible call that will make it return ‘True’ as the keyword
‘'name'’ will always bind to the first parameter.  For example:

     >>> foo(1, **{'name': 2})
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: foo() got multiple values for argument 'name'
     >>>

But using ‘/’ (positional only arguments), it is possible since it
allows ‘name’ as a positional argument and ‘'name'’ as a key in the
keyword arguments:

     def foo(name, /, **kwds):
         return 'name' in kwds
     >>> foo(1, **{'name': 2})
     True

In other words, the names of positional-only parameters can be used in
‘**kwds’ without ambiguity.


File: python.info,  Node: Recap,  Prev: Function Examples,  Up: Special parameters

2.4.7.8 Recap
.............

The use case will determine which parameters to use in the function
definition:

     def f(pos1, pos2, /, pos_or_kwd, *, kwd1, kwd2):

As guidance:

   * Use positional-only if you want the name of the parameters to not
     be available to the user.  This is useful when parameter names have
     no real meaning, if you want to enforce the order of the arguments
     when the function is called or if you need to take some positional
     parameters and arbitrary keywords.

   * Use keyword-only when names have meaning and the function
     definition is more understandable by being explicit with names or
     you want to prevent users relying on the position of the argument
     being passed.

   * For an API, use positional-only to prevent breaking API changes if
     the parameter’s name is modified in the future.


File: python.info,  Node: Arbitrary Argument Lists,  Next: Unpacking Argument Lists,  Prev: Special parameters,  Up: More on Defining Functions

2.4.7.9 Arbitrary Argument Lists
................................

Finally, the least frequently used option is to specify that a function
can be called with an arbitrary number of arguments.  These arguments
will be wrapped up in a tuple (see *note Tuples and Sequences: 1380.).
Before the variable number of arguments, zero or more normal arguments
may occur.

     def write_multiple_items(file, separator, *args):
         file.write(separator.join(args))

Normally, these ‘variadic’ arguments will be last in the list of formal
parameters, because they scoop up all remaining input arguments that are
passed to the function.  Any formal parameters which occur after the
‘*args’ parameter are ‘keyword-only’ arguments, meaning that they can
only be used as keywords rather than positional arguments.

     >>> def concat(*args, sep="/"):
     ...     return sep.join(args)
     ...
     >>> concat("earth", "mars", "venus")
     'earth/mars/venus'
     >>> concat("earth", "mars", "venus", sep=".")
     'earth.mars.venus'


File: python.info,  Node: Unpacking Argument Lists,  Next: Lambda Expressions,  Prev: Arbitrary Argument Lists,  Up: More on Defining Functions

2.4.7.10 Unpacking Argument Lists
.................................

The reverse situation occurs when the arguments are already in a list or
tuple but need to be unpacked for a function call requiring separate
positional arguments.  For instance, the built-in *note range(): 1f5.
function expects separate `start' and `stop' arguments.  If they are not
available separately, write the function call with the ‘*’-operator to
unpack the arguments out of a list or tuple:

     >>> list(range(3, 6))            # normal call with separate arguments
     [3, 4, 5]
     >>> args = [3, 6]
     >>> list(range(*args))            # call with arguments unpacked from a list
     [3, 4, 5]

In the same fashion, dictionaries can deliver keyword arguments with the
‘**’-operator:

     >>> def parrot(voltage, state='a stiff', action='voom'):
     ...     print("-- This parrot wouldn't", action, end=' ')
     ...     print("if you put", voltage, "volts through it.", end=' ')
     ...     print("E's", state, "!")
     ...
     >>> d = {"voltage": "four million", "state": "bleedin' demised", "action": "VOOM"}
     >>> parrot(**d)
     -- This parrot wouldn't VOOM if you put four million volts through it. E's bleedin' demised !


File: python.info,  Node: Lambda Expressions,  Next: Documentation Strings,  Prev: Unpacking Argument Lists,  Up: More on Defining Functions

2.4.7.11 Lambda Expressions
...........................

Small anonymous functions can be created with the *note lambda: cf9.
keyword.  This function returns the sum of its two arguments: ‘lambda a,
b: a+b’.  Lambda functions can be used wherever function objects are
required.  They are syntactically restricted to a single expression.
Semantically, they are just syntactic sugar for a normal function
definition.  Like nested function definitions, lambda functions can
reference variables from the containing scope:

     >>> def make_incrementor(n):
     ...     return lambda x: x + n
     ...
     >>> f = make_incrementor(42)
     >>> f(0)
     42
     >>> f(1)
     43

The above example uses a lambda expression to return a function.
Another use is to pass a small function as an argument:

     >>> pairs = [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]
     >>> pairs.sort(key=lambda pair: pair[1])
     >>> pairs
     [(4, 'four'), (1, 'one'), (3, 'three'), (2, 'two')]


File: python.info,  Node: Documentation Strings,  Next: Function Annotations,  Prev: Lambda Expressions,  Up: More on Defining Functions

2.4.7.12 Documentation Strings
..............................

Here are some conventions about the content and formatting of
documentation strings.

The first line should always be a short, concise summary of the object’s
purpose.  For brevity, it should not explicitly state the object’s name
or type, since these are available by other means (except if the name
happens to be a verb describing a function’s operation).  This line
should begin with a capital letter and end with a period.

If there are more lines in the documentation string, the second line
should be blank, visually separating the summary from the rest of the
description.  The following lines should be one or more paragraphs
describing the object’s calling conventions, its side effects, etc.

The Python parser does not strip indentation from multi-line string
literals in Python, so tools that process documentation have to strip
indentation if desired.  This is done using the following convention.
The first non-blank line `after' the first line of the string determines
the amount of indentation for the entire documentation string.  (We
can’t use the first line since it is generally adjacent to the string’s
opening quotes so its indentation is not apparent in the string
literal.)  Whitespace “equivalent” to this indentation is then stripped
from the start of all lines of the string.  Lines that are indented less
should not occur, but if they occur all their leading whitespace should
be stripped.  Equivalence of whitespace should be tested after expansion
of tabs (to 8 spaces, normally).

Here is an example of a multi-line docstring:

     >>> def my_function():
     ...     """Do nothing, but document it.
     ...
     ...     No, really, it doesn't do anything.
     ...     """
     ...     pass
     ...
     >>> print(my_function.__doc__)
     Do nothing, but document it.

         No, really, it doesn't do anything.


File: python.info,  Node: Function Annotations,  Prev: Documentation Strings,  Up: More on Defining Functions

2.4.7.13 Function Annotations
.............................

*note Function annotations: 1390. are completely optional metadata
information about the types used by user-defined functions (see PEP
3107(1) and PEP 484(2) for more information).

*note Annotations: 1391. are stored in the ‘__annotations__’ attribute
of the function as a dictionary and have no effect on any other part of
the function.  Parameter annotations are defined by a colon after the
parameter name, followed by an expression evaluating to the value of the
annotation.  Return annotations are defined by a literal ‘->’, followed
by an expression, between the parameter list and the colon denoting the
end of the *note def: e83. statement.  The following example has a
required argument, an optional argument, and the return value annotated:

     >>> def f(ham: str, eggs: str = 'eggs') -> str:
     ...     print("Annotations:", f.__annotations__)
     ...     print("Arguments:", ham, eggs)
     ...     return ham + ' and ' + eggs
     ...
     >>> f('spam')
     Annotations: {'ham': <class 'str'>, 'return': <class 'str'>, 'eggs': <class 'str'>}
     Arguments: spam eggs
     'spam and eggs'

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3107

   (2) https://www.python.org/dev/peps/pep-0484


File: python.info,  Node: Intermezzo Coding Style,  Prev: More on Defining Functions,  Up: More Control Flow Tools

2.4.8 Intermezzo: Coding Style
------------------------------

Now that you are about to write longer, more complex pieces of Python,
it is a good time to talk about `coding style'.  Most languages can be
written (or more concise, `formatted') in different styles; some are
more readable than others.  Making it easy for others to read your code
is always a good idea, and adopting a nice coding style helps
tremendously for that.

For Python, PEP 8(1) has emerged as the style guide that most projects
adhere to; it promotes a very readable and eye-pleasing coding style.
Every Python developer should read it at some point; here are the most
important points extracted for you:

   * Use 4-space indentation, and no tabs.

     4 spaces are a good compromise between small indentation (allows
     greater nesting depth) and large indentation (easier to read).
     Tabs introduce confusion, and are best left out.

   * Wrap lines so that they don’t exceed 79 characters.

     This helps users with small displays and makes it possible to have
     several code files side-by-side on larger displays.

   * Use blank lines to separate functions and classes, and larger
     blocks of code inside functions.

   * When possible, put comments on a line of their own.

   * Use docstrings.

   * Use spaces around operators and after commas, but not directly
     inside bracketing constructs: ‘a = f(1, 2) + g(3, 4)’.

   * Name your classes and functions consistently; the convention is to
     use ‘UpperCamelCase’ for classes and ‘lowercase_with_underscores’
     for functions and methods.  Always use ‘self’ as the name for the
     first method argument (see *note A First Look at Classes: 1394. for
     more on classes and methods).

   * Don’t use fancy encodings if your code is meant to be used in
     international environments.  Python’s default, UTF-8, or even plain
     ASCII work best in any case.

   * Likewise, don’t use non-ASCII characters in identifiers if there is
     only the slightest chance people speaking a different language will
     read or maintain the code.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0008


File: python.info,  Node: Data Structures,  Next: Modules,  Prev: More Control Flow Tools,  Up: The Python Tutorial

2.5 Data Structures
===================

This chapter describes some things you’ve learned about already in more
detail, and adds some new things as well.

* Menu:

* More on Lists::
* The del statement::
* Tuples and Sequences::
* Sets::
* Dictionaries::
* Looping Techniques::
* More on Conditions::
* Comparing Sequences and Other Types::


File: python.info,  Node: More on Lists,  Next: The del statement,  Up: Data Structures

2.5.1 More on Lists
-------------------

The list data type has some more methods.  Here are all of the methods
of list objects:

 -- Method: list.append (x)

     Add an item to the end of the list.  Equivalent to ‘a[len(a):] =
     [x]’.

 -- Method: list.extend (iterable)

     Extend the list by appending all the items from the iterable.
     Equivalent to ‘a[len(a):] = iterable’.

 -- Method: list.insert (i, x)

     Insert an item at a given position.  The first argument is the
     index of the element before which to insert, so ‘a.insert(0, x)’
     inserts at the front of the list, and ‘a.insert(len(a), x)’ is
     equivalent to ‘a.append(x)’.

 -- Method: list.remove (x)

     Remove the first item from the list whose value is equal to `x'.
     It raises a *note ValueError: 16d. if there is no such item.

 -- Method: list.pop ([i])

     Remove the item at the given position in the list, and return it.
     If no index is specified, ‘a.pop()’ removes and returns the last
     item in the list.  (The square brackets around the `i' in the
     method signature denote that the parameter is optional, not that
     you should type square brackets at that position.  You will see
     this notation frequently in the Python Library Reference.)

 -- Method: list.clear ()

     Remove all items from the list.  Equivalent to ‘del a[:]’.

 -- Method: list.index (x[, start[, end]])

     Return zero-based index in the list of the first item whose value
     is equal to `x'.  Raises a *note ValueError: 16d. if there is no
     such item.

     The optional arguments `start' and `end' are interpreted as in the
     slice notation and are used to limit the search to a particular
     subsequence of the list.  The returned index is computed relative
     to the beginning of the full sequence rather than the `start'
     argument.

 -- Method: list.count (x)

     Return the number of times `x' appears in the list.

 -- Method: list.sort (*, key=None, reverse=False)

     Sort the items of the list in place (the arguments can be used for
     sort customization, see *note sorted(): 547. for their
     explanation).

 -- Method: list.reverse ()

     Reverse the elements of the list in place.

 -- Method: list.copy ()

     Return a shallow copy of the list.  Equivalent to ‘a[:]’.

An example that uses most of the list methods:

     >>> fruits = ['orange', 'apple', 'pear', 'banana', 'kiwi', 'apple', 'banana']
     >>> fruits.count('apple')
     2
     >>> fruits.count('tangerine')
     0
     >>> fruits.index('banana')
     3
     >>> fruits.index('banana', 4)  # Find next banana starting a position 4
     6
     >>> fruits.reverse()
     >>> fruits
     ['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange']
     >>> fruits.append('grape')
     >>> fruits
     ['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange', 'grape']
     >>> fruits.sort()
     >>> fruits
     ['apple', 'apple', 'banana', 'banana', 'grape', 'kiwi', 'orange', 'pear']
     >>> fruits.pop()
     'pear'

You might have noticed that methods like ‘insert’, ‘remove’ or ‘sort’
that only modify the list have no return value printed – they return the
default ‘None’.  (1) This is a design principle for all mutable data
structures in Python.

Another thing you might notice is that not all data can be sorted or
compared.  For instance, ‘[None, 'hello', 10]’ doesn’t sort because
integers can’t be compared to strings and `None' can’t be compared to
other types.  Also, there are some types that don’t have a defined
ordering relation.  For example, ‘3+4j < 5+7j’ isn’t a valid comparison.

* Menu:

* Using Lists as Stacks::
* Using Lists as Queues::
* List Comprehensions: List Comprehensions<2>.
* Nested List Comprehensions::

   ---------- Footnotes ----------

   (1) (1) Other languages may return the mutated object, which allows
method chaining, such as ‘d->insert("a")->remove("b")->sort();’.


File: python.info,  Node: Using Lists as Stacks,  Next: Using Lists as Queues,  Up: More on Lists

2.5.1.1 Using Lists as Stacks
.............................

The list methods make it very easy to use a list as a stack, where the
last element added is the first element retrieved (“last-in,
first-out”).  To add an item to the top of the stack, use ‘append()’.
To retrieve an item from the top of the stack, use ‘pop()’ without an
explicit index.  For example:

     >>> stack = [3, 4, 5]
     >>> stack.append(6)
     >>> stack.append(7)
     >>> stack
     [3, 4, 5, 6, 7]
     >>> stack.pop()
     7
     >>> stack
     [3, 4, 5, 6]
     >>> stack.pop()
     6
     >>> stack.pop()
     5
     >>> stack
     [3, 4]


File: python.info,  Node: Using Lists as Queues,  Next: List Comprehensions<2>,  Prev: Using Lists as Stacks,  Up: More on Lists

2.5.1.2 Using Lists as Queues
.............................

It is also possible to use a list as a queue, where the first element
added is the first element retrieved (“first-in, first-out”); however,
lists are not efficient for this purpose.  While appends and pops from
the end of list are fast, doing inserts or pops from the beginning of a
list is slow (because all of the other elements have to be shifted by
one).

To implement a queue, use *note collections.deque: 62b. which was
designed to have fast appends and pops from both ends.  For example:

     >>> from collections import deque
     >>> queue = deque(["Eric", "John", "Michael"])
     >>> queue.append("Terry")           # Terry arrives
     >>> queue.append("Graham")          # Graham arrives
     >>> queue.popleft()                 # The first to arrive now leaves
     'Eric'
     >>> queue.popleft()                 # The second to arrive now leaves
     'John'
     >>> queue                           # Remaining queue in order of arrival
     deque(['Michael', 'Terry', 'Graham'])


File: python.info,  Node: List Comprehensions<2>,  Next: Nested List Comprehensions,  Prev: Using Lists as Queues,  Up: More on Lists

2.5.1.3 List Comprehensions
...........................

List comprehensions provide a concise way to create lists.  Common
applications are to make new lists where each element is the result of
some operations applied to each member of another sequence or iterable,
or to create a subsequence of those elements that satisfy a certain
condition.

For example, assume we want to create a list of squares, like:

     >>> squares = []
     >>> for x in range(10):
     ...     squares.append(x**2)
     ...
     >>> squares
     [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

Note that this creates (or overwrites) a variable named ‘x’ that still
exists after the loop completes.  We can calculate the list of squares
without any side effects using:

     squares = list(map(lambda x: x**2, range(10)))

or, equivalently:

     squares = [x**2 for x in range(10)]

which is more concise and readable.

A list comprehension consists of brackets containing an expression
followed by a ‘for’ clause, then zero or more ‘for’ or ‘if’ clauses.
The result will be a new list resulting from evaluating the expression
in the context of the ‘for’ and ‘if’ clauses which follow it.  For
example, this listcomp combines the elements of two lists if they are
not equal:

     >>> [(x, y) for x in [1,2,3] for y in [3,1,4] if x != y]
     [(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]

and it’s equivalent to:

     >>> combs = []
     >>> for x in [1,2,3]:
     ...     for y in [3,1,4]:
     ...         if x != y:
     ...             combs.append((x, y))
     ...
     >>> combs
     [(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]

Note how the order of the *note for: cfa. and *note if: eab. statements
is the same in both these snippets.

If the expression is a tuple (e.g.  the ‘(x, y)’ in the previous
example), it must be parenthesized.

     >>> vec = [-4, -2, 0, 2, 4]
     >>> # create a new list with the values doubled
     >>> [x*2 for x in vec]
     [-8, -4, 0, 4, 8]
     >>> # filter the list to exclude negative numbers
     >>> [x for x in vec if x >= 0]
     [0, 2, 4]
     >>> # apply a function to all the elements
     >>> [abs(x) for x in vec]
     [4, 2, 0, 2, 4]
     >>> # call a method on each element
     >>> freshfruit = ['  banana', '  loganberry ', 'passion fruit  ']
     >>> [weapon.strip() for weapon in freshfruit]
     ['banana', 'loganberry', 'passion fruit']
     >>> # create a list of 2-tuples like (number, square)
     >>> [(x, x**2) for x in range(6)]
     [(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25)]
     >>> # the tuple must be parenthesized, otherwise an error is raised
     >>> [x, x**2 for x in range(6)]
       File "<stdin>", line 1, in <module>
         [x, x**2 for x in range(6)]
                    ^
     SyntaxError: invalid syntax
     >>> # flatten a list using a listcomp with two 'for'
     >>> vec = [[1,2,3], [4,5,6], [7,8,9]]
     >>> [num for elem in vec for num in elem]
     [1, 2, 3, 4, 5, 6, 7, 8, 9]

List comprehensions can contain complex expressions and nested
functions:

     >>> from math import pi
     >>> [str(round(pi, i)) for i in range(1, 6)]
     ['3.1', '3.14', '3.142', '3.1416', '3.14159']


File: python.info,  Node: Nested List Comprehensions,  Prev: List Comprehensions<2>,  Up: More on Lists

2.5.1.4 Nested List Comprehensions
..................................

The initial expression in a list comprehension can be any arbitrary
expression, including another list comprehension.

Consider the following example of a 3x4 matrix implemented as a list of
3 lists of length 4:

     >>> matrix = [
     ...     [1, 2, 3, 4],
     ...     [5, 6, 7, 8],
     ...     [9, 10, 11, 12],
     ... ]

The following list comprehension will transpose rows and columns:

     >>> [[row[i] for row in matrix] for i in range(4)]
     [[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]

As we saw in the previous section, the nested listcomp is evaluated in
the context of the *note for: cfa. that follows it, so this example is
equivalent to:

     >>> transposed = []
     >>> for i in range(4):
     ...     transposed.append([row[i] for row in matrix])
     ...
     >>> transposed
     [[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]

which, in turn, is the same as:

     >>> transposed = []
     >>> for i in range(4):
     ...     # the following 3 lines implement the nested listcomp
     ...     transposed_row = []
     ...     for row in matrix:
     ...         transposed_row.append(row[i])
     ...     transposed.append(transposed_row)
     ...
     >>> transposed
     [[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]

In the real world, you should prefer built-in functions to complex flow
statements.  The *note zip(): cfc. function would do a great job for
this use case:

     >>> list(zip(*matrix))
     [(1, 5, 9), (2, 6, 10), (3, 7, 11), (4, 8, 12)]

See *note Unpacking Argument Lists: 1389. for details on the asterisk in
this line.


File: python.info,  Node: The del statement,  Next: Tuples and Sequences,  Prev: More on Lists,  Up: Data Structures

2.5.2 The ‘del’ statement
-------------------------

There is a way to remove an item from a list given its index instead of
its value: the *note del: 13a2. statement.  This differs from the
‘pop()’ method which returns a value.  The ‘del’ statement can also be
used to remove slices from a list or clear the entire list (which we did
earlier by assignment of an empty list to the slice).  For example:

     >>> a = [-1, 1, 66.25, 333, 333, 1234.5]
     >>> del a[0]
     >>> a
     [1, 66.25, 333, 333, 1234.5]
     >>> del a[2:4]
     >>> a
     [1, 66.25, 1234.5]
     >>> del a[:]
     >>> a
     []

*note del: 13a2. can also be used to delete entire variables:

     >>> del a

Referencing the name ‘a’ hereafter is an error (at least until another
value is assigned to it).  We’ll find other uses for *note del: 13a2.
later.


File: python.info,  Node: Tuples and Sequences,  Next: Sets,  Prev: The del statement,  Up: Data Structures

2.5.3 Tuples and Sequences
--------------------------

We saw that lists and strings have many common properties, such as
indexing and slicing operations.  They are two examples of `sequence'
data types (see *note Sequence Types — list, tuple, range: 13a4.).
Since Python is an evolving language, other sequence data types may be
added.  There is also another standard sequence data type: the `tuple'.

A tuple consists of a number of values separated by commas, for
instance:

     >>> t = 12345, 54321, 'hello!'
     >>> t[0]
     12345
     >>> t
     (12345, 54321, 'hello!')
     >>> # Tuples may be nested:
     ... u = t, (1, 2, 3, 4, 5)
     >>> u
     ((12345, 54321, 'hello!'), (1, 2, 3, 4, 5))
     >>> # Tuples are immutable:
     ... t[0] = 88888
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: 'tuple' object does not support item assignment
     >>> # but they can contain mutable objects:
     ... v = ([1, 2, 3], [3, 2, 1])
     >>> v
     ([1, 2, 3], [3, 2, 1])

As you see, on output tuples are always enclosed in parentheses, so that
nested tuples are interpreted correctly; they may be input with or
without surrounding parentheses, although often parentheses are
necessary anyway (if the tuple is part of a larger expression).  It is
not possible to assign to the individual items of a tuple, however it is
possible to create tuples which contain mutable objects, such as lists.

Though tuples may seem similar to lists, they are often used in
different situations and for different purposes.  Tuples are *note
immutable: 1356, and usually contain a heterogeneous sequence of
elements that are accessed via unpacking (see later in this section) or
indexing (or even by attribute in the case of *note namedtuples: 1a1.).
Lists are *note mutable: 135e, and their elements are usually
homogeneous and are accessed by iterating over the list.

A special problem is the construction of tuples containing 0 or 1 items:
the syntax has some extra quirks to accommodate these.  Empty tuples are
constructed by an empty pair of parentheses; a tuple with one item is
constructed by following a value with a comma (it is not sufficient to
enclose a single value in parentheses).  Ugly, but effective.  For
example:

     >>> empty = ()
     >>> singleton = 'hello',    # <-- note trailing comma
     >>> len(empty)
     0
     >>> len(singleton)
     1
     >>> singleton
     ('hello',)

The statement ‘t = 12345, 54321, 'hello!'’ is an example of `tuple
packing': the values ‘12345’, ‘54321’ and ‘'hello!'’ are packed together
in a tuple.  The reverse operation is also possible:

     >>> x, y, z = t

This is called, appropriately enough, `sequence unpacking' and works for
any sequence on the right-hand side.  Sequence unpacking requires that
there are as many variables on the left side of the equals sign as there
are elements in the sequence.  Note that multiple assignment is really
just a combination of tuple packing and sequence unpacking.


File: python.info,  Node: Sets,  Next: Dictionaries,  Prev: Tuples and Sequences,  Up: Data Structures

2.5.4 Sets
----------

Python also includes a data type for `sets'.  A set is an unordered
collection with no duplicate elements.  Basic uses include membership
testing and eliminating duplicate entries.  Set objects also support
mathematical operations like union, intersection, difference, and
symmetric difference.

Curly braces or the *note set(): 1f6. function can be used to create
sets.  Note: to create an empty set you have to use ‘set()’, not ‘{}’;
the latter creates an empty dictionary, a data structure that we discuss
in the next section.

Here is a brief demonstration:

     >>> basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
     >>> print(basket)                      # show that duplicates have been removed
     {'orange', 'banana', 'pear', 'apple'}
     >>> 'orange' in basket                 # fast membership testing
     True
     >>> 'crabgrass' in basket
     False

     >>> # Demonstrate set operations on unique letters from two words
     ...
     >>> a = set('abracadabra')
     >>> b = set('alacazam')
     >>> a                                  # unique letters in a
     {'a', 'r', 'b', 'c', 'd'}
     >>> a - b                              # letters in a but not in b
     {'r', 'd', 'b'}
     >>> a | b                              # letters in a or b or both
     {'a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'}
     >>> a & b                              # letters in both a and b
     {'a', 'c'}
     >>> a ^ b                              # letters in a or b but not both
     {'r', 'd', 'b', 'm', 'z', 'l'}

Similarly to *note list comprehensions: 139e, set comprehensions are
also supported:

     >>> a = {x for x in 'abracadabra' if x not in 'abc'}
     >>> a
     {'r', 'd'}


File: python.info,  Node: Dictionaries,  Next: Looping Techniques,  Prev: Sets,  Up: Data Structures

2.5.5 Dictionaries
------------------

Another useful data type built into Python is the `dictionary' (see
*note Mapping Types — dict: 40e.).  Dictionaries are sometimes found in
other languages as “associative memories” or “associative arrays”.
Unlike sequences, which are indexed by a range of numbers, dictionaries
are indexed by `keys', which can be any immutable type; strings and
numbers can always be keys.  Tuples can be used as keys if they contain
only strings, numbers, or tuples; if a tuple contains any mutable object
either directly or indirectly, it cannot be used as a key.  You can’t
use lists as keys, since lists can be modified in place using index
assignments, slice assignments, or methods like ‘append()’ and
‘extend()’.

It is best to think of a dictionary as a set of `key: value' pairs, with
the requirement that the keys are unique (within one dictionary).  A
pair of braces creates an empty dictionary: ‘{}’.  Placing a
comma-separated list of key:value pairs within the braces adds initial
key:value pairs to the dictionary; this is also the way dictionaries are
written on output.

The main operations on a dictionary are storing a value with some key
and extracting the value given the key.  It is also possible to delete a
key:value pair with ‘del’.  If you store using a key that is already in
use, the old value associated with that key is forgotten.  It is an
error to extract a value using a non-existent key.

Performing ‘list(d)’ on a dictionary returns a list of all the keys used
in the dictionary, in insertion order (if you want it sorted, just use
‘sorted(d)’ instead).  To check whether a single key is in the
dictionary, use the *note in: 179. keyword.

Here is a small example using a dictionary:

     >>> tel = {'jack': 4098, 'sape': 4139}
     >>> tel['guido'] = 4127
     >>> tel
     {'jack': 4098, 'sape': 4139, 'guido': 4127}
     >>> tel['jack']
     4098
     >>> del tel['sape']
     >>> tel['irv'] = 4127
     >>> tel
     {'jack': 4098, 'guido': 4127, 'irv': 4127}
     >>> list(tel)
     ['jack', 'guido', 'irv']
     >>> sorted(tel)
     ['guido', 'irv', 'jack']
     >>> 'guido' in tel
     True
     >>> 'jack' not in tel
     False

The *note dict(): 164. constructor builds dictionaries directly from
sequences of key-value pairs:

     >>> dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])
     {'sape': 4139, 'guido': 4127, 'jack': 4098}

In addition, dict comprehensions can be used to create dictionaries from
arbitrary key and value expressions:

     >>> {x: x**2 for x in (2, 4, 6)}
     {2: 4, 4: 16, 6: 36}

When the keys are simple strings, it is sometimes easier to specify
pairs using keyword arguments:

     >>> dict(sape=4139, guido=4127, jack=4098)
     {'sape': 4139, 'guido': 4127, 'jack': 4098}


File: python.info,  Node: Looping Techniques,  Next: More on Conditions,  Prev: Dictionaries,  Up: Data Structures

2.5.6 Looping Techniques
------------------------

When looping through dictionaries, the key and corresponding value can
be retrieved at the same time using the ‘items()’ method.

     >>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}
     >>> for k, v in knights.items():
     ...     print(k, v)
     ...
     gallahad the pure
     robin the brave

When looping through a sequence, the position index and corresponding
value can be retrieved at the same time using the *note enumerate():
ea7. function.

     >>> for i, v in enumerate(['tic', 'tac', 'toe']):
     ...     print(i, v)
     ...
     0 tic
     1 tac
     2 toe

To loop over two or more sequences at the same time, the entries can be
paired with the *note zip(): cfc. function.

     >>> questions = ['name', 'quest', 'favorite color']
     >>> answers = ['lancelot', 'the holy grail', 'blue']
     >>> for q, a in zip(questions, answers):
     ...     print('What is your {0}?  It is {1}.'.format(q, a))
     ...
     What is your name?  It is lancelot.
     What is your quest?  It is the holy grail.
     What is your favorite color?  It is blue.

To loop over a sequence in reverse, first specify the sequence in a
forward direction and then call the *note reversed(): 2c6. function.

     >>> for i in reversed(range(1, 10, 2)):
     ...     print(i)
     ...
     9
     7
     5
     3
     1

To loop over a sequence in sorted order, use the *note sorted(): 547.
function which returns a new sorted list while leaving the source
unaltered.

     >>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
     >>> for i in sorted(basket):
     ...     print(i)
     ...
     apple
     apple
     banana
     orange
     orange
     pear

Using *note set(): 1f6. on a sequence eliminates duplicate elements.
The use of *note sorted(): 547. in combination with *note set(): 1f6.
over a sequence is an idiomatic way to loop over unique elements of the
sequence in sorted order.

     >>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
     >>> for f in sorted(set(basket)):
     ...     print(f)
     ...
     apple
     banana
     orange
     pear

It is sometimes tempting to change a list while you are looping over it;
however, it is often simpler and safer to create a new list instead.

     >>> import math
     >>> raw_data = [56.2, float('NaN'), 51.7, 55.3, 52.5, float('NaN'), 47.8]
     >>> filtered_data = []
     >>> for value in raw_data:
     ...     if not math.isnan(value):
     ...         filtered_data.append(value)
     ...
     >>> filtered_data
     [56.2, 51.7, 55.3, 52.5, 47.8]


File: python.info,  Node: More on Conditions,  Next: Comparing Sequences and Other Types,  Prev: Looping Techniques,  Up: Data Structures

2.5.7 More on Conditions
------------------------

The conditions used in ‘while’ and ‘if’ statements can contain any
operators, not just comparisons.

The comparison operators ‘in’ and ‘not in’ check whether a value occurs
(does not occur) in a sequence.  The operators ‘is’ and ‘is not’ compare
whether two objects are really the same object.  All comparison
operators have the same priority, which is lower than that of all
numerical operators.

Comparisons can be chained.  For example, ‘a < b == c’ tests whether ‘a’
is less than ‘b’ and moreover ‘b’ equals ‘c’.

Comparisons may be combined using the Boolean operators ‘and’ and ‘or’,
and the outcome of a comparison (or of any other Boolean expression) may
be negated with ‘not’.  These have lower priorities than comparison
operators; between them, ‘not’ has the highest priority and ‘or’ the
lowest, so that ‘A and not B or C’ is equivalent to ‘(A and (not B)) or
C’.  As always, parentheses can be used to express the desired
composition.

The Boolean operators ‘and’ and ‘or’ are so-called `short-circuit'
operators: their arguments are evaluated from left to right, and
evaluation stops as soon as the outcome is determined.  For example, if
‘A’ and ‘C’ are true but ‘B’ is false, ‘A and B and C’ does not evaluate
the expression ‘C’.  When used as a general value and not as a Boolean,
the return value of a short-circuit operator is the last evaluated
argument.

It is possible to assign the result of a comparison or other Boolean
expression to a variable.  For example,

     >>> string1, string2, string3 = '', 'Trondheim', 'Hammer Dance'
     >>> non_null = string1 or string2 or string3
     >>> non_null
     'Trondheim'

Note that in Python, unlike C, assignment inside expressions must be
done explicitly with the *note walrus operator: 13ac. ‘:=’.  This avoids
a common class of problems encountered in C programs: typing ‘=’ in an
expression when ‘==’ was intended.


File: python.info,  Node: Comparing Sequences and Other Types,  Prev: More on Conditions,  Up: Data Structures

2.5.8 Comparing Sequences and Other Types
-----------------------------------------

Sequence objects typically may be compared to other objects with the
same sequence type.  The comparison uses `lexicographical' ordering:
first the first two items are compared, and if they differ this
determines the outcome of the comparison; if they are equal, the next
two items are compared, and so on, until either sequence is exhausted.
If two items to be compared are themselves sequences of the same type,
the lexicographical comparison is carried out recursively.  If all items
of two sequences compare equal, the sequences are considered equal.  If
one sequence is an initial sub-sequence of the other, the shorter
sequence is the smaller (lesser) one.  Lexicographical ordering for
strings uses the Unicode code point number to order individual
characters.  Some examples of comparisons between sequences of the same
type:

     (1, 2, 3)              < (1, 2, 4)
     [1, 2, 3]              < [1, 2, 4]
     'ABC' < 'C' < 'Pascal' < 'Python'
     (1, 2, 3, 4)           < (1, 2, 4)
     (1, 2)                 < (1, 2, -1)
     (1, 2, 3)             == (1.0, 2.0, 3.0)
     (1, 2, ('aa', 'ab'))   < (1, 2, ('abc', 'a'), 4)

Note that comparing objects of different types with ‘<’ or ‘>’ is legal
provided that the objects have appropriate comparison methods.  For
example, mixed numeric types are compared according to their numeric
value, so 0 equals 0.0, etc.  Otherwise, rather than providing an
arbitrary ordering, the interpreter will raise a *note TypeError: 1fe.
exception.


File: python.info,  Node: Modules,  Next: Input and Output,  Prev: Data Structures,  Up: The Python Tutorial

2.6 Modules
===========

If you quit from the Python interpreter and enter it again, the
definitions you have made (functions and variables) are lost.
Therefore, if you want to write a somewhat longer program, you are
better off using a text editor to prepare the input for the interpreter
and running it with that file as input instead.  This is known as
creating a `script'.  As your program gets longer, you may want to split
it into several files for easier maintenance.  You may also want to use
a handy function that you’ve written in several programs without copying
its definition into each program.

To support this, Python has a way to put definitions in a file and use
them in a script or in an interactive instance of the interpreter.  Such
a file is called a `module'; definitions from a module can be `imported'
into other modules or into the `main' module (the collection of
variables that you have access to in a script executed at the top level
and in calculator mode).

A module is a file containing Python definitions and statements.  The
file name is the module name with the suffix ‘.py’ appended.  Within a
module, the module’s name (as a string) is available as the value of the
global variable ‘__name__’.  For instance, use your favorite text editor
to create a file called ‘fibo.py’ in the current directory with the
following contents:

     # Fibonacci numbers module

     def fib(n):    # write Fibonacci series up to n
         a, b = 0, 1
         while a < n:
             print(a, end=' ')
             a, b = b, a+b
         print()

     def fib2(n):   # return Fibonacci series up to n
         result = []
         a, b = 0, 1
         while a < n:
             result.append(a)
             a, b = b, a+b
         return result

Now enter the Python interpreter and import this module with the
following command:

     >>> import fibo

This does not enter the names of the functions defined in ‘fibo’
directly in the current symbol table; it only enters the module name
‘fibo’ there.  Using the module name you can access the functions:

     >>> fibo.fib(1000)
     0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987
     >>> fibo.fib2(100)
     [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
     >>> fibo.__name__
     'fibo'

If you intend to use a function often you can assign it to a local name:

     >>> fib = fibo.fib
     >>> fib(500)
     0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

* Menu:

* More on Modules::
* Standard Modules::
* The dir() Function: The dir Function.
* Packages::


File: python.info,  Node: More on Modules,  Next: Standard Modules,  Up: Modules

2.6.1 More on Modules
---------------------

A module can contain executable statements as well as function
definitions.  These statements are intended to initialize the module.
They are executed only the `first' time the module name is encountered
in an import statement.  (1) (They are also run if the file is executed
as a script.)

Each module has its own private symbol table, which is used as the
global symbol table by all functions defined in the module.  Thus, the
author of a module can use global variables in the module without
worrying about accidental clashes with a user’s global variables.  On
the other hand, if you know what you are doing you can touch a module’s
global variables with the same notation used to refer to its functions,
‘modname.itemname’.

Modules can import other modules.  It is customary but not required to
place all *note import: ce7. statements at the beginning of a module (or
script, for that matter).  The imported module names are placed in the
importing module’s global symbol table.

There is a variant of the *note import: ce7. statement that imports
names from a module directly into the importing module’s symbol table.
For example:

     >>> from fibo import fib, fib2
     >>> fib(500)
     0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

This does not introduce the module name from which the imports are taken
in the local symbol table (so in the example, ‘fibo’ is not defined).

There is even a variant to import all names that a module defines:

     >>> from fibo import *
     >>> fib(500)
     0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

This imports all names except those beginning with an underscore (‘_’).
In most cases Python programmers do not use this facility since it
introduces an unknown set of names into the interpreter, possibly hiding
some things you have already defined.

Note that in general the practice of importing ‘*’ from a module or
package is frowned upon, since it often causes poorly readable code.
However, it is okay to use it to save typing in interactive sessions.

If the module name is followed by ‘as’, then the name following ‘as’ is
bound directly to the imported module.

     >>> import fibo as fib
     >>> fib.fib(500)
     0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

This is effectively importing the module in the same way that ‘import
fibo’ will do, with the only difference of it being available as ‘fib’.

It can also be used when utilising *note from: d0d. with similar
effects:

     >>> from fibo import fib as fibonacci
     >>> fibonacci(500)
     0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

     Note: For efficiency reasons, each module is only imported once per
     interpreter session.  Therefore, if you change your modules, you
     must restart the interpreter – or, if it’s just one module you want
     to test interactively, use *note importlib.reload(): 4a0, e.g.
     ‘import importlib; importlib.reload(modulename)’.

* Menu:

* Executing modules as scripts::
* The Module Search Path::
* “Compiled” Python files::

   ---------- Footnotes ----------

   (1) (1) In fact function definitions are also ‘statements’ that are
‘executed’; the execution of a module-level function definition enters
the function name in the module’s global symbol table.


File: python.info,  Node: Executing modules as scripts,  Next: The Module Search Path,  Up: More on Modules

2.6.1.1 Executing modules as scripts
....................................

When you run a Python module with

     python fibo.py <arguments>

the code in the module will be executed, just as if you imported it, but
with the ‘__name__’ set to ‘"__main__"’.  That means that by adding this
code at the end of your module:

     if __name__ == "__main__":
         import sys
         fib(int(sys.argv[1]))

you can make the file usable as a script as well as an importable
module, because the code that parses the command line only runs if the
module is executed as the “main” file:

     $ python fibo.py 50
     0 1 1 2 3 5 8 13 21 34

If the module is imported, the code is not run:

     >>> import fibo
     >>>

This is often used either to provide a convenient user interface to a
module, or for testing purposes (running the module as a script executes
a test suite).


File: python.info,  Node: The Module Search Path,  Next: “Compiled” Python files,  Prev: Executing modules as scripts,  Up: More on Modules

2.6.1.2 The Module Search Path
..............................

When a module named ‘spam’ is imported, the interpreter first searches
for a built-in module with that name.  If not found, it then searches
for a file named ‘spam.py’ in a list of directories given by the
variable *note sys.path: 260.  *note sys.path: 260. is initialized from
these locations:

   * The directory containing the input script (or the current directory
     when no file is specified).

   * *note PYTHONPATH: a34. (a list of directory names, with the same
     syntax as the shell variable ‘PATH’).

   * The installation-dependent default (by convention including a
     ‘site-packages’ directory, handled by the *note site: eb. module).

     Note: On file systems which support symlinks, the directory
     containing the input script is calculated after the symlink is
     followed.  In other words the directory containing the symlink is
     `not' added to the module search path.

After initialization, Python programs can modify *note sys.path: 260.
The directory containing the script being run is placed at the beginning
of the search path, ahead of the standard library path.  This means that
scripts in that directory will be loaded instead of modules of the same
name in the library directory.  This is an error unless the replacement
is intended.  See section *note Standard Modules: 13b8. for more
information.


File: python.info,  Node: “Compiled” Python files,  Prev: The Module Search Path,  Up: More on Modules

2.6.1.3 “Compiled” Python files
...............................

To speed up loading modules, Python caches the compiled version of each
module in the ‘__pycache__’ directory under the name
‘module.`version'.pyc’, where the version encodes the format of the
compiled file; it generally contains the Python version number.  For
example, in CPython release 3.3 the compiled version of spam.py would be
cached as ‘__pycache__/spam.cpython-33.pyc’.  This naming convention
allows compiled modules from different releases and different versions
of Python to coexist.

Python checks the modification date of the source against the compiled
version to see if it’s out of date and needs to be recompiled.  This is
a completely automatic process.  Also, the compiled modules are
platform-independent, so the same library can be shared among systems
with different architectures.

Python does not check the cache in two circumstances.  First, it always
recompiles and does not store the result for the module that’s loaded
directly from the command line.  Second, it does not check the cache if
there is no source module.  To support a non-source (compiled only)
distribution, the compiled module must be in the source directory, and
there must not be a source module.

Some tips for experts:

   * You can use the *note -O: 77e. or *note -OO: 77f. switches on the
     Python command to reduce the size of a compiled module.  The ‘-O’
     switch removes assert statements, the ‘-OO’ switch removes both
     assert statements and __doc__ strings.  Since some programs may
     rely on having these available, you should only use this option if
     you know what you’re doing.  “Optimized” modules have an ‘opt-’ tag
     and are usually smaller.  Future releases may change the effects of
     optimization.

   * A program doesn’t run any faster when it is read from a ‘.pyc’ file
     than when it is read from a ‘.py’ file; the only thing that’s
     faster about ‘.pyc’ files is the speed with which they are loaded.

   * The module *note compileall: 20. can create .pyc files for all
     modules in a directory.

   * There is more detail on this process, including a flow chart of the
     decisions, in PEP 3147(1).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3147


File: python.info,  Node: Standard Modules,  Next: The dir Function,  Prev: More on Modules,  Up: Modules

2.6.2 Standard Modules
----------------------

Python comes with a library of standard modules, described in a separate
document, the Python Library Reference (“Library Reference” hereafter).
Some modules are built into the interpreter; these provide access to
operations that are not part of the core of the language but are
nevertheless built in, either for efficiency or to provide access to
operating system primitives such as system calls.  The set of such
modules is a configuration option which also depends on the underlying
platform.  For example, the *note winreg: 133. module is only provided
on Windows systems.  One particular module deserves some attention:
*note sys: fd, which is built into every Python interpreter.  The
variables ‘sys.ps1’ and ‘sys.ps2’ define the strings used as primary and
secondary prompts:

     >>> import sys
     >>> sys.ps1
     '>>> '
     >>> sys.ps2
     '... '
     >>> sys.ps1 = 'C> '
     C> print('Yuck!')
     Yuck!
     C>

These two variables are only defined if the interpreter is in
interactive mode.

The variable ‘sys.path’ is a list of strings that determines the
interpreter’s search path for modules.  It is initialized to a default
path taken from the environment variable *note PYTHONPATH: a34, or from
a built-in default if *note PYTHONPATH: a34. is not set.  You can modify
it using standard list operations:

     >>> import sys
     >>> sys.path.append('/ufs/guido/lib/python')


File: python.info,  Node: The dir Function,  Next: Packages,  Prev: Standard Modules,  Up: Modules

2.6.3 The ‘dir()’ Function
--------------------------

The built-in function *note dir(): df9. is used to find out which names
a module defines.  It returns a sorted list of strings:

     >>> import fibo, sys
     >>> dir(fibo)
     ['__name__', 'fib', 'fib2']
     >>> dir(sys)
     ['__breakpointhook__', '__displayhook__', '__doc__', '__excepthook__',
      '__interactivehook__', '__loader__', '__name__', '__package__', '__spec__',
      '__stderr__', '__stdin__', '__stdout__', '__unraisablehook__',
      '_clear_type_cache', '_current_frames', '_debugmallocstats', '_framework',
      '_getframe', '_git', '_home', '_xoptions', 'abiflags', 'addaudithook',
      'api_version', 'argv', 'audit', 'base_exec_prefix', 'base_prefix',
      'breakpointhook', 'builtin_module_names', 'byteorder', 'call_tracing',
      'callstats', 'copyright', 'displayhook', 'dont_write_bytecode', 'exc_info',
      'excepthook', 'exec_prefix', 'executable', 'exit', 'flags', 'float_info',
      'float_repr_style', 'get_asyncgen_hooks', 'get_coroutine_origin_tracking_depth',
      'getallocatedblocks', 'getdefaultencoding', 'getdlopenflags',
      'getfilesystemencodeerrors', 'getfilesystemencoding', 'getprofile',
      'getrecursionlimit', 'getrefcount', 'getsizeof', 'getswitchinterval',
      'gettrace', 'hash_info', 'hexversion', 'implementation', 'int_info',
      'intern', 'is_finalizing', 'last_traceback', 'last_type', 'last_value',
      'maxsize', 'maxunicode', 'meta_path', 'modules', 'path', 'path_hooks',
      'path_importer_cache', 'platform', 'prefix', 'ps1', 'ps2', 'pycache_prefix',
      'set_asyncgen_hooks', 'set_coroutine_origin_tracking_depth', 'setdlopenflags',
      'setprofile', 'setrecursionlimit', 'setswitchinterval', 'settrace', 'stderr',
      'stdin', 'stdout', 'thread_info', 'unraisablehook', 'version', 'version_info',
      'warnoptions']

Without arguments, *note dir(): df9. lists the names you have defined
currently:

     >>> a = [1, 2, 3, 4, 5]
     >>> import fibo
     >>> fib = fibo.fib
     >>> dir()
     ['__builtins__', '__name__', 'a', 'fib', 'fibo', 'sys']

Note that it lists all types of names: variables, modules, functions,
etc.

*note dir(): df9. does not list the names of built-in functions and
variables.  If you want a list of those, they are defined in the
standard module *note builtins: 12.:

     >>> import builtins
     >>> dir(builtins)
     ['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException',
      'BlockingIOError', 'BrokenPipeError', 'BufferError', 'BytesWarning',
      'ChildProcessError', 'ConnectionAbortedError', 'ConnectionError',
      'ConnectionRefusedError', 'ConnectionResetError', 'DeprecationWarning',
      'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False',
      'FileExistsError', 'FileNotFoundError', 'FloatingPointError',
      'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError',
      'ImportWarning', 'IndentationError', 'IndexError', 'InterruptedError',
      'IsADirectoryError', 'KeyError', 'KeyboardInterrupt', 'LookupError',
      'MemoryError', 'NameError', 'None', 'NotADirectoryError', 'NotImplemented',
      'NotImplementedError', 'OSError', 'OverflowError',
      'PendingDeprecationWarning', 'PermissionError', 'ProcessLookupError',
      'ReferenceError', 'ResourceWarning', 'RuntimeError', 'RuntimeWarning',
      'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError',
      'SystemExit', 'TabError', 'TimeoutError', 'True', 'TypeError',
      'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError',
      'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning',
      'ValueError', 'Warning', 'ZeroDivisionError', '_', '__build_class__',
      '__debug__', '__doc__', '__import__', '__name__', '__package__', 'abs',
      'all', 'any', 'ascii', 'bin', 'bool', 'bytearray', 'bytes', 'callable',
      'chr', 'classmethod', 'compile', 'complex', 'copyright', 'credits',
      'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'exec', 'exit',
      'filter', 'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr',
      'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass',
      'iter', 'len', 'license', 'list', 'locals', 'map', 'max', 'memoryview',
      'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property',
      'quit', 'range', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice',
      'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'vars',
      'zip']


File: python.info,  Node: Packages,  Prev: The dir Function,  Up: Modules

2.6.4 Packages
--------------

Packages are a way of structuring Python’s module namespace by using
“dotted module names”.  For example, the module name ‘A.B’ designates a
submodule named ‘B’ in a package named ‘A’.  Just like the use of
modules saves the authors of different modules from having to worry
about each other’s global variable names, the use of dotted module names
saves the authors of multi-module packages like NumPy or Pillow from
having to worry about each other’s module names.

Suppose you want to design a collection of modules (a “package”) for the
uniform handling of sound files and sound data.  There are many
different sound file formats (usually recognized by their extension, for
example: ‘.wav’, ‘.aiff’, ‘.au’), so you may need to create and maintain
a growing collection of modules for the conversion between the various
file formats.  There are also many different operations you might want
to perform on sound data (such as mixing, adding echo, applying an
equalizer function, creating an artificial stereo effect), so in
addition you will be writing a never-ending stream of modules to perform
these operations.  Here’s a possible structure for your package
(expressed in terms of a hierarchical filesystem):

     sound/                          Top-level package
           __init__.py               Initialize the sound package
           formats/                  Subpackage for file format conversions
                   __init__.py
                   wavread.py
                   wavwrite.py
                   aiffread.py
                   aiffwrite.py
                   auread.py
                   auwrite.py
                   ...
           effects/                  Subpackage for sound effects
                   __init__.py
                   echo.py
                   surround.py
                   reverse.py
                   ...
           filters/                  Subpackage for filters
                   __init__.py
                   equalizer.py
                   vocoder.py
                   karaoke.py
                   ...

When importing the package, Python searches through the directories on
‘sys.path’ looking for the package subdirectory.

The ‘__init__.py’ files are required to make Python treat directories
containing the file as packages.  This prevents directories with a
common name, such as ‘string’, unintentionally hiding valid modules that
occur later on the module search path.  In the simplest case,
‘__init__.py’ can just be an empty file, but it can also execute
initialization code for the package or set the ‘__all__’ variable,
described later.

Users of the package can import individual modules from the package, for
example:

     import sound.effects.echo

This loads the submodule ‘sound.effects.echo’.  It must be referenced
with its full name.

     sound.effects.echo.echofilter(input, output, delay=0.7, atten=4)

An alternative way of importing the submodule is:

     from sound.effects import echo

This also loads the submodule ‘echo’, and makes it available without its
package prefix, so it can be used as follows:

     echo.echofilter(input, output, delay=0.7, atten=4)

Yet another variation is to import the desired function or variable
directly:

     from sound.effects.echo import echofilter

Again, this loads the submodule ‘echo’, but this makes its function
‘echofilter()’ directly available:

     echofilter(input, output, delay=0.7, atten=4)

Note that when using ‘from package import item’, the item can be either
a submodule (or subpackage) of the package, or some other name defined
in the package, like a function, class or variable.  The ‘import’
statement first tests whether the item is defined in the package; if
not, it assumes it is a module and attempts to load it.  If it fails to
find it, an *note ImportError: 16c. exception is raised.

Contrarily, when using syntax like ‘import item.subitem.subsubitem’,
each item except for the last must be a package; the last item can be a
module or a package but can’t be a class or function or variable defined
in the previous item.

* Menu:

* Importing * From a Package::
* Intra-package References::
* Packages in Multiple Directories::


File: python.info,  Node: Importing * From a Package,  Next: Intra-package References,  Up: Packages

2.6.4.1 Importing * From a Package
..................................

Now what happens when the user writes ‘from sound.effects import *’?
Ideally, one would hope that this somehow goes out to the filesystem,
finds which submodules are present in the package, and imports them all.
This could take a long time and importing sub-modules might have
unwanted side-effects that should only happen when the sub-module is
explicitly imported.

The only solution is for the package author to provide an explicit index
of the package.  The *note import: ce7. statement uses the following
convention: if a package’s ‘__init__.py’ code defines a list named
‘__all__’, it is taken to be the list of module names that should be
imported when ‘from package import *’ is encountered.  It is up to the
package author to keep this list up-to-date when a new version of the
package is released.  Package authors may also decide not to support it,
if they don’t see a use for importing * from their package.  For
example, the file ‘sound/effects/__init__.py’ could contain the
following code:

     __all__ = ["echo", "surround", "reverse"]

This would mean that ‘from sound.effects import *’ would import the
three named submodules of the ‘sound’ package.

If ‘__all__’ is not defined, the statement ‘from sound.effects import *’
does `not' import all submodules from the package ‘sound.effects’ into
the current namespace; it only ensures that the package ‘sound.effects’
has been imported (possibly running any initialization code in
‘__init__.py’) and then imports whatever names are defined in the
package.  This includes any names defined (and submodules explicitly
loaded) by ‘__init__.py’.  It also includes any submodules of the
package that were explicitly loaded by previous *note import: ce7.
statements.  Consider this code:

     import sound.effects.echo
     import sound.effects.surround
     from sound.effects import *

In this example, the ‘echo’ and ‘surround’ modules are imported in the
current namespace because they are defined in the ‘sound.effects’
package when the ‘from...import’ statement is executed.  (This also
works when ‘__all__’ is defined.)

Although certain modules are designed to export only names that follow
certain patterns when you use ‘import *’, it is still considered bad
practice in production code.

Remember, there is nothing wrong with using ‘from package import
specific_submodule’!  In fact, this is the recommended notation unless
the importing module needs to use submodules with the same name from
different packages.


File: python.info,  Node: Intra-package References,  Next: Packages in Multiple Directories,  Prev: Importing * From a Package,  Up: Packages

2.6.4.2 Intra-package References
................................

When packages are structured into subpackages (as with the ‘sound’
package in the example), you can use absolute imports to refer to
submodules of siblings packages.  For example, if the module
‘sound.filters.vocoder’ needs to use the ‘echo’ module in the
‘sound.effects’ package, it can use ‘from sound.effects import echo’.

You can also write relative imports, with the ‘from module import name’
form of import statement.  These imports use leading dots to indicate
the current and parent packages involved in the relative import.  From
the ‘surround’ module for example, you might use:

     from . import echo
     from .. import formats
     from ..filters import equalizer

Note that relative imports are based on the name of the current module.
Since the name of the main module is always ‘"__main__"’, modules
intended for use as the main module of a Python application must always
use absolute imports.


File: python.info,  Node: Packages in Multiple Directories,  Prev: Intra-package References,  Up: Packages

2.6.4.3 Packages in Multiple Directories
........................................

Packages support one more special attribute, *note __path__: 13c3.  This
is initialized to be a list containing the name of the directory holding
the package’s ‘__init__.py’ before the code in that file is executed.
This variable can be modified; doing so affects future searches for
modules and subpackages contained in the package.

While this feature is not often needed, it can be used to extend the set
of modules found in a package.


File: python.info,  Node: Input and Output,  Next: Errors and Exceptions,  Prev: Modules,  Up: The Python Tutorial

2.7 Input and Output
====================

There are several ways to present the output of a program; data can be
printed in a human-readable form, or written to a file for future use.
This chapter will discuss some of the possibilities.

* Menu:

* Fancier Output Formatting::
* Reading and Writing Files::


File: python.info,  Node: Fancier Output Formatting,  Next: Reading and Writing Files,  Up: Input and Output

2.7.1 Fancier Output Formatting
-------------------------------

So far we’ve encountered two ways of writing values: `expression
statements' and the *note print(): 971. function.  (A third way is using
the ‘write()’ method of file objects; the standard output file can be
referenced as ‘sys.stdout’.  See the Library Reference for more
information on this.)

Often you’ll want more control over the formatting of your output than
simply printing space-separated values.  There are several ways to
format output.

   * To use *note formatted string literals: 13c9, begin a string with
     ‘f’ or ‘F’ before the opening quotation mark or triple quotation
     mark.  Inside this string, you can write a Python expression
     between ‘{’ and ‘}’ characters that can refer to variables or
     literal values.

          >>> year = 2016
          >>> event = 'Referendum'
          >>> f'Results of the {year} {event}'
          'Results of the 2016 Referendum'

   * The *note str.format(): 5d5. method of strings requires more manual
     effort.  You’ll still use ‘{’ and ‘}’ to mark where a variable will
     be substituted and can provide detailed formatting directives, but
     you’ll also need to provide the information to be formatted.

          >>> yes_votes = 42_572_654
          >>> no_votes = 43_132_495
          >>> percentage = yes_votes / (yes_votes + no_votes)
          >>> '{:-9} YES votes  {:2.2%}'.format(yes_votes, percentage)
          ' 42572654 YES votes  49.67%'

   * Finally, you can do all the string handling yourself by using
     string slicing and concatenation operations to create any layout
     you can imagine.  The string type has some methods that perform
     useful operations for padding strings to a given column width.

When you don’t need fancy output but just want a quick display of some
variables for debugging purposes, you can convert any value to a string
with the *note repr(): 8b9. or *note str(): 205. functions.

The *note str(): 205. function is meant to return representations of
values which are fairly human-readable, while *note repr(): 8b9. is
meant to generate representations which can be read by the interpreter
(or will force a *note SyntaxError: 55a. if there is no equivalent
syntax).  For objects which don’t have a particular representation for
human consumption, *note str(): 205. will return the same value as *note
repr(): 8b9.  Many values, such as numbers or structures like lists and
dictionaries, have the same representation using either function.
Strings, in particular, have two distinct representations.

Some examples:

     >>> s = 'Hello, world.'
     >>> str(s)
     'Hello, world.'
     >>> repr(s)
     "'Hello, world.'"
     >>> str(1/7)
     '0.14285714285714285'
     >>> x = 10 * 3.25
     >>> y = 200 * 200
     >>> s = 'The value of x is ' + repr(x) + ', and y is ' + repr(y) + '...'
     >>> print(s)
     The value of x is 32.5, and y is 40000...
     >>> # The repr() of a string adds string quotes and backslashes:
     ... hello = 'hello, world\n'
     >>> hellos = repr(hello)
     >>> print(hellos)
     'hello, world\n'
     >>> # The argument to repr() may be any Python object:
     ... repr((x, y, ('spam', 'eggs')))
     "(32.5, 40000, ('spam', 'eggs'))"

The *note string: f6. module contains a *note Template: 4f1. class that
offers yet another way to substitute values into strings, using
placeholders like ‘$x’ and replacing them with values from a dictionary,
but offers much less control of the formatting.

* Menu:

* Formatted String Literals::
* The String format() Method: The String format Method.
* Manual String Formatting::
* Old string formatting::


File: python.info,  Node: Formatted String Literals,  Next: The String format Method,  Up: Fancier Output Formatting

2.7.1.1 Formatted String Literals
.................................

*note Formatted string literals: 296. (also called f-strings for short)
let you include the value of Python expressions inside a string by
prefixing the string with ‘f’ or ‘F’ and writing expressions as
‘{expression}’.

An optional format specifier can follow the expression.  This allows
greater control over how the value is formatted.  The following example
rounds pi to three places after the decimal:

     >>> import math
     >>> print(f'The value of pi is approximately {math.pi:.3f}.')
     The value of pi is approximately 3.142.

Passing an integer after the ‘':'’ will cause that field to be a minimum
number of characters wide.  This is useful for making columns line up.

     >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 7678}
     >>> for name, phone in table.items():
     ...     print(f'{name:10} ==> {phone:10d}')
     ...
     Sjoerd     ==>       4127
     Jack       ==>       4098
     Dcab       ==>       7678

Other modifiers can be used to convert the value before it is formatted.
‘'!a'’ applies *note ascii(): e11, ‘'!s'’ applies *note str(): 205, and
‘'!r'’ applies *note repr(): 8b9.:

     >>> animals = 'eels'
     >>> print(f'My hovercraft is full of {animals}.')
     My hovercraft is full of eels.
     >>> print(f'My hovercraft is full of {animals!r}.')
     My hovercraft is full of 'eels'.

For a reference on these format specifications, see the reference guide
for the *note Format Specification Mini-Language: 5d9.


File: python.info,  Node: The String format Method,  Next: Manual String Formatting,  Prev: Formatted String Literals,  Up: Fancier Output Formatting

2.7.1.2 The String format() Method
..................................

Basic usage of the *note str.format(): 5d5. method looks like this:

     >>> print('We are the {} who say "{}!"'.format('knights', 'Ni'))
     We are the knights who say "Ni!"

The brackets and characters within them (called format fields) are
replaced with the objects passed into the *note str.format(): 5d5.
method.  A number in the brackets can be used to refer to the position
of the object passed into the *note str.format(): 5d5. method.

     >>> print('{0} and {1}'.format('spam', 'eggs'))
     spam and eggs
     >>> print('{1} and {0}'.format('spam', 'eggs'))
     eggs and spam

If keyword arguments are used in the *note str.format(): 5d5. method,
their values are referred to by using the name of the argument.

     >>> print('This {food} is {adjective}.'.format(
     ...       food='spam', adjective='absolutely horrible'))
     This spam is absolutely horrible.

Positional and keyword arguments can be arbitrarily combined:

     >>> print('The story of {0}, {1}, and {other}.'.format('Bill', 'Manfred',
                                                            other='Georg'))
     The story of Bill, Manfred, and Georg.

If you have a really long format string that you don’t want to split up,
it would be nice if you could reference the variables to be formatted by
name instead of by position.  This can be done by simply passing the
dict and using square brackets ‘'[]'’ to access the keys.

     >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
     >>> print('Jack: {0[Jack]:d}; Sjoerd: {0[Sjoerd]:d}; '
     ...       'Dcab: {0[Dcab]:d}'.format(table))
     Jack: 4098; Sjoerd: 4127; Dcab: 8637678

This could also be done by passing the table as keyword arguments with
the ‘**’ notation.

     >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}
     >>> print('Jack: {Jack:d}; Sjoerd: {Sjoerd:d}; Dcab: {Dcab:d}'.format(**table))
     Jack: 4098; Sjoerd: 4127; Dcab: 8637678

This is particularly useful in combination with the built-in function
*note vars(): 116d, which returns a dictionary containing all local
variables.

As an example, the following lines produce a tidily-aligned set of
columns giving integers and their squares and cubes:

     >>> for x in range(1, 11):
     ...     print('{0:2d} {1:3d} {2:4d}'.format(x, x*x, x*x*x))
     ...
      1   1    1
      2   4    8
      3   9   27
      4  16   64
      5  25  125
      6  36  216
      7  49  343
      8  64  512
      9  81  729
     10 100 1000

For a complete overview of string formatting with *note str.format():
5d5, see *note Format String Syntax: de0.


File: python.info,  Node: Manual String Formatting,  Next: Old string formatting,  Prev: The String format Method,  Up: Fancier Output Formatting

2.7.1.3 Manual String Formatting
................................

Here’s the same table of squares and cubes, formatted manually:

     >>> for x in range(1, 11):
     ...     print(repr(x).rjust(2), repr(x*x).rjust(3), end=' ')
     ...     # Note use of 'end' on previous line
     ...     print(repr(x*x*x).rjust(4))
     ...
      1   1    1
      2   4    8
      3   9   27
      4  16   64
      5  25  125
      6  36  216
      7  49  343
      8  64  512
      9  81  729
     10 100 1000

(Note that the one space between each column was added by the way *note
print(): 971. works: it always adds spaces between its arguments.)

The *note str.rjust(): 13ce. method of string objects right-justifies a
string in a field of a given width by padding it with spaces on the
left.  There are similar methods *note str.ljust(): 13cf. and *note
str.center(): 13d0.  These methods do not write anything, they just
return a new string.  If the input string is too long, they don’t
truncate it, but return it unchanged; this will mess up your column
lay-out but that’s usually better than the alternative, which would be
lying about a value.  (If you really want truncation you can always add
a slice operation, as in ‘x.ljust(n)[:n]’.)

There is another method, *note str.zfill(): 13d1, which pads a numeric
string on the left with zeros.  It understands about plus and minus
signs:

     >>> '12'.zfill(5)
     '00012'
     >>> '-3.14'.zfill(7)
     '-003.14'
     >>> '3.14159265359'.zfill(5)
     '3.14159265359'


File: python.info,  Node: Old string formatting,  Prev: Manual String Formatting,  Up: Fancier Output Formatting

2.7.1.4 Old string formatting
.............................

The % operator (modulo) can also be used for string formatting.  Given
‘'string' % values’, instances of ‘%’ in ‘string’ are replaced with zero
or more elements of ‘values’.  This operation is commonly known as
string interpolation.  For example:

     >>> import math
     >>> print('The value of pi is approximately %5.3f.' % math.pi)
     The value of pi is approximately 3.142.

More information can be found in the *note printf-style String
Formatting: 1359. section.


File: python.info,  Node: Reading and Writing Files,  Prev: Fancier Output Formatting,  Up: Input and Output

2.7.2 Reading and Writing Files
-------------------------------

*note open(): 16f. returns a *note file object: c14, and is most
commonly used with two arguments: ‘open(filename, mode)’.

     >>> f = open('workfile', 'w')

The first argument is a string containing the filename.  The second
argument is another string containing a few characters describing the
way in which the file will be used.  `mode' can be ‘'r'’ when the file
will only be read, ‘'w'’ for only writing (an existing file with the
same name will be erased), and ‘'a'’ opens the file for appending; any
data written to the file is automatically added to the end.  ‘'r+'’
opens the file for both reading and writing.  The `mode' argument is
optional; ‘'r'’ will be assumed if it’s omitted.

Normally, files are opened in `text mode', that means, you read and
write strings from and to the file, which are encoded in a specific
encoding.  If encoding is not specified, the default is platform
dependent (see *note open(): 16f.).  ‘'b'’ appended to the mode opens
the file in `binary mode': now the data is read and written in the form
of bytes objects.  This mode should be used for all files that don’t
contain text.

In text mode, the default when reading is to convert platform-specific
line endings (‘\n’ on Unix, ‘\r\n’ on Windows) to just ‘\n’.  When
writing in text mode, the default is to convert occurrences of ‘\n’ back
to platform-specific line endings.  This behind-the-scenes modification
to file data is fine for text files, but will corrupt binary data like
that in ‘JPEG’ or ‘EXE’ files.  Be very careful to use binary mode when
reading and writing such files.

It is good practice to use the *note with: 7da. keyword when dealing
with file objects.  The advantage is that the file is properly closed
after its suite finishes, even if an exception is raised at some point.
Using ‘with’ is also much shorter than writing equivalent *note try:
e37.-*note finally: 2bc. blocks:

     >>> with open('workfile') as f:
     ...     read_data = f.read()

     >>> # We can check that the file has been automatically closed.
     >>> f.closed
     True

If you’re not using the *note with: 7da. keyword, then you should call
‘f.close()’ to close the file and immediately free up any system
resources used by it.

     Warning: Calling ‘f.write()’ without using the ‘with’ keyword or
     calling ‘f.close()’ `might' result in the arguments of ‘f.write()’
     not being completely written to the disk, even if the program exits
     successfully.

After a file object is closed, either by a *note with: 7da. statement or
by calling ‘f.close()’, attempts to use the file object will
automatically fail.

     >>> f.close()
     >>> f.read()
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ValueError: I/O operation on closed file.

* Menu:

* Methods of File Objects::
* Saving structured data with json::


File: python.info,  Node: Methods of File Objects,  Next: Saving structured data with json,  Up: Reading and Writing Files

2.7.2.1 Methods of File Objects
...............................

The rest of the examples in this section will assume that a file object
called ‘f’ has already been created.

To read a file’s contents, call ‘f.read(size)’, which reads some
quantity of data and returns it as a string (in text mode) or bytes
object (in binary mode).  `size' is an optional numeric argument.  When
`size' is omitted or negative, the entire contents of the file will be
read and returned; it’s your problem if the file is twice as large as
your machine’s memory.  Otherwise, at most `size' characters (in text
mode) or `size' bytes (in binary mode) are read and returned.  If the
end of the file has been reached, ‘f.read()’ will return an empty string
(‘''’).

     >>> f.read()
     'This is the entire file.\n'
     >>> f.read()
     ''

‘f.readline()’ reads a single line from the file; a newline character
(‘\n’) is left at the end of the string, and is only omitted on the last
line of the file if the file doesn’t end in a newline.  This makes the
return value unambiguous; if ‘f.readline()’ returns an empty string, the
end of the file has been reached, while a blank line is represented by
‘'\n'’, a string containing only a single newline.

     >>> f.readline()
     'This is the first line of the file.\n'
     >>> f.readline()
     'Second line of the file\n'
     >>> f.readline()
     ''

For reading lines from a file, you can loop over the file object.  This
is memory efficient, fast, and leads to simple code:

     >>> for line in f:
     ...     print(line, end='')
     ...
     This is the first line of the file.
     Second line of the file

If you want to read all the lines of a file in a list you can also use
‘list(f)’ or ‘f.readlines()’.

‘f.write(string)’ writes the contents of `string' to the file, returning
the number of characters written.

     >>> f.write('This is a test\n')
     15

Other types of objects need to be converted – either to a string (in
text mode) or a bytes object (in binary mode) – before writing them:

     >>> value = ('the answer', 42)
     >>> s = str(value)  # convert the tuple to string
     >>> f.write(s)
     18

‘f.tell()’ returns an integer giving the file object’s current position
in the file represented as number of bytes from the beginning of the
file when in binary mode and an opaque number when in text mode.

To change the file object’s position, use ‘f.seek(offset, whence)’.  The
position is computed from adding `offset' to a reference point; the
reference point is selected by the `whence' argument.  A `whence' value
of 0 measures from the beginning of the file, 1 uses the current file
position, and 2 uses the end of the file as the reference point.
`whence' can be omitted and defaults to 0, using the beginning of the
file as the reference point.

     >>> f = open('workfile', 'rb+')
     >>> f.write(b'0123456789abcdef')
     16
     >>> f.seek(5)      # Go to the 6th byte in the file
     5
     >>> f.read(1)
     b'5'
     >>> f.seek(-3, 2)  # Go to the 3rd byte before the end
     13
     >>> f.read(1)
     b'd'

In text files (those opened without a ‘b’ in the mode string), only
seeks relative to the beginning of the file are allowed (the exception
being seeking to the very file end with ‘seek(0, 2)’) and the only valid
`offset' values are those returned from the ‘f.tell()’, or zero.  Any
other `offset' value produces undefined behaviour.

File objects have some additional methods, such as ‘isatty()’ and
‘truncate()’ which are less frequently used; consult the Library
Reference for a complete guide to file objects.


File: python.info,  Node: Saving structured data with json,  Prev: Methods of File Objects,  Up: Reading and Writing Files

2.7.2.2 Saving structured data with ‘json’
..........................................

Strings can easily be written to and read from a file.  Numbers take a
bit more effort, since the ‘read()’ method only returns strings, which
will have to be passed to a function like *note int(): 204, which takes
a string like ‘'123'’ and returns its numeric value 123.  When you want
to save more complex data types like nested lists and dictionaries,
parsing and serializing by hand becomes complicated.

Rather than having users constantly writing and debugging code to save
complicated data types to files, Python allows you to use the popular
data interchange format called JSON (JavaScript Object Notation)(1).
The standard module called *note json: a4. can take Python data
hierarchies, and convert them to string representations; this process is
called `serializing'.  Reconstructing the data from the string
representation is called `deserializing'.  Between serializing and
deserializing, the string representing the object may have been stored
in a file or data, or sent over a network connection to some distant
machine.

     Note: The JSON format is commonly used by modern applications to
     allow for data exchange.  Many programmers are already familiar
     with it, which makes it a good choice for interoperability.

If you have an object ‘x’, you can view its JSON string representation
with a simple line of code:

     >>> import json
     >>> x = [1, 'simple', 'list']
     >>> json.dumps(x)
     '[1, "simple", "list"]'

Another variant of the *note dumps(): 6fc. function, called *note
dump(): 6fb, simply serializes the object to a *note text file: 13d9.
So if ‘f’ is a *note text file: 13d9. object opened for writing, we can
do this:

     json.dump(x, f)

To decode the object again, if ‘f’ is a *note text file: 13d9. object
which has been opened for reading:

     x = json.load(f)

This simple serialization technique can handle lists and dictionaries,
but serializing arbitrary class instances in JSON requires a bit of
extra effort.  The reference for the *note json: a4. module contains an
explanation of this.

See also
........

*note pickle: ca. - the pickle module

Contrary to *note JSON: 13d8, `pickle' is a protocol which allows the
serialization of arbitrarily complex Python objects.  As such, it is
specific to Python and cannot be used to communicate with applications
written in other languages.  It is also insecure by default:
deserializing pickle data coming from an untrusted source can execute
arbitrary code, if the data was crafted by a skilled attacker.

   ---------- Footnotes ----------

   (1) http://json.org


File: python.info,  Node: Errors and Exceptions,  Next: Classes,  Prev: Input and Output,  Up: The Python Tutorial

2.8 Errors and Exceptions
=========================

Until now error messages haven’t been more than mentioned, but if you
have tried out the examples you have probably seen some.  There are (at
least) two distinguishable kinds of errors: `syntax errors' and
`exceptions'.

* Menu:

* Syntax Errors::
* Exceptions::
* Handling Exceptions::
* Raising Exceptions::
* Exception Chaining::
* User-defined Exceptions::
* Defining Clean-up Actions::
* Predefined Clean-up Actions::


File: python.info,  Node: Syntax Errors,  Next: Exceptions,  Up: Errors and Exceptions

2.8.1 Syntax Errors
-------------------

Syntax errors, also known as parsing errors, are perhaps the most common
kind of complaint you get while you are still learning Python:

     >>> while True print('Hello world')
       File "<stdin>", line 1
         while True print('Hello world')
                        ^
     SyntaxError: invalid syntax

The parser repeats the offending line and displays a little ‘arrow’
pointing at the earliest point in the line where the error was detected.
The error is caused by (or at least detected at) the token `preceding'
the arrow: in the example, the error is detected at the function *note
print(): 971, since a colon (‘':'’) is missing before it.  File name and
line number are printed so you know where to look in case the input came
from a script.


File: python.info,  Node: Exceptions,  Next: Handling Exceptions,  Prev: Syntax Errors,  Up: Errors and Exceptions

2.8.2 Exceptions
----------------

Even if a statement or expression is syntactically correct, it may cause
an error when an attempt is made to execute it.  Errors detected during
execution are called `exceptions' and are not unconditionally fatal: you
will soon learn how to handle them in Python programs.  Most exceptions
are not handled by programs, however, and result in error messages as
shown here:

     >>> 10 * (1/0)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ZeroDivisionError: division by zero
     >>> 4 + spam*3
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     NameError: name 'spam' is not defined
     >>> '2' + 2
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: can only concatenate str (not "int") to str

The last line of the error message indicates what happened.  Exceptions
come in different types, and the type is printed as part of the message:
the types in the example are *note ZeroDivisionError: 1fa, *note
NameError: e40. and *note TypeError: 1fe.  The string printed as the
exception type is the name of the built-in exception that occurred.
This is true for all built-in exceptions, but need not be true for
user-defined exceptions (although it is a useful convention).  Standard
exception names are built-in identifiers (not reserved keywords).

The rest of the line provides detail based on the type of exception and
what caused it.

The preceding part of the error message shows the context where the
exception occurred, in the form of a stack traceback.  In general it
contains a stack traceback listing source lines; however, it will not
display lines read from standard input.

*note Built-in Exceptions: f73. lists the built-in exceptions and their
meanings.


File: python.info,  Node: Handling Exceptions,  Next: Raising Exceptions,  Prev: Exceptions,  Up: Errors and Exceptions

2.8.3 Handling Exceptions
-------------------------

It is possible to write programs that handle selected exceptions.  Look
at the following example, which asks the user for input until a valid
integer has been entered, but allows the user to interrupt the program
(using ‘Control-C’ or whatever the operating system supports); note that
a user-generated interruption is signalled by raising the *note
KeyboardInterrupt: 2cc. exception.

     >>> while True:
     ...     try:
     ...         x = int(input("Please enter a number: "))
     ...         break
     ...     except ValueError:
     ...         print("Oops!  That was no valid number.  Try again...")
     ...

The *note try: e37. statement works as follows.

   * First, the `try clause' (the statement(s) between the *note try:
     e37. and *note except: c10. keywords) is executed.

   * If no exception occurs, the `except clause' is skipped and
     execution of the *note try: e37. statement is finished.

   * If an exception occurs during execution of the try clause, the rest
     of the clause is skipped.  Then if its type matches the exception
     named after the *note except: c10. keyword, the except clause is
     executed, and then execution continues after the *note try: e37.
     statement.

   * If an exception occurs which does not match the exception named in
     the except clause, it is passed on to outer *note try: e37.
     statements; if no handler is found, it is an `unhandled exception'
     and execution stops with a message as shown above.

A *note try: e37. statement may have more than one except clause, to
specify handlers for different exceptions.  At most one handler will be
executed.  Handlers only handle exceptions that occur in the
corresponding try clause, not in other handlers of the same ‘try’
statement.  An except clause may name multiple exceptions as a
parenthesized tuple, for example:

     ... except (RuntimeError, TypeError, NameError):
     ...     pass

A class in an *note except: c10. clause is compatible with an exception
if it is the same class or a base class thereof (but not the other way
around — an except clause listing a derived class is not compatible with
a base class).  For example, the following code will print B, C, D in
that order:

     class B(Exception):
         pass

     class C(B):
         pass

     class D(C):
         pass

     for cls in [B, C, D]:
         try:
             raise cls()
         except D:
             print("D")
         except C:
             print("C")
         except B:
             print("B")

Note that if the except clauses were reversed (with ‘except B’ first),
it would have printed B, B, B — the first matching except clause is
triggered.

The last except clause may omit the exception name(s), to serve as a
wildcard.  Use this with extreme caution, since it is easy to mask a
real programming error in this way!  It can also be used to print an
error message and then re-raise the exception (allowing a caller to
handle the exception as well):

     import sys

     try:
         f = open('myfile.txt')
         s = f.readline()
         i = int(s.strip())
     except OSError as err:
         print("OS error: {0}".format(err))
     except ValueError:
         print("Could not convert data to an integer.")
     except:
         print("Unexpected error:", sys.exc_info()[0])
         raise

The *note try: e37. … *note except: c10. statement has an optional `else
clause', which, when present, must follow all except clauses.  It is
useful for code that must be executed if the try clause does not raise
an exception.  For example:

     for arg in sys.argv[1:]:
         try:
             f = open(arg, 'r')
         except OSError:
             print('cannot open', arg)
         else:
             print(arg, 'has', len(f.readlines()), 'lines')
             f.close()

The use of the ‘else’ clause is better than adding additional code to
the *note try: e37. clause because it avoids accidentally catching an
exception that wasn’t raised by the code being protected by the ‘try’ …
‘except’ statement.

When an exception occurs, it may have an associated value, also known as
the exception’s `argument'.  The presence and type of the argument
depend on the exception type.

The except clause may specify a variable after the exception name.  The
variable is bound to an exception instance with the arguments stored in
‘instance.args’.  For convenience, the exception instance defines *note
__str__(): ef9. so the arguments can be printed directly without having
to reference ‘.args’.  One may also instantiate an exception first
before raising it and add any attributes to it as desired.

     >>> try:
     ...     raise Exception('spam', 'eggs')
     ... except Exception as inst:
     ...     print(type(inst))    # the exception instance
     ...     print(inst.args)     # arguments stored in .args
     ...     print(inst)          # __str__ allows args to be printed directly,
     ...                          # but may be overridden in exception subclasses
     ...     x, y = inst.args     # unpack args
     ...     print('x =', x)
     ...     print('y =', y)
     ...
     <class 'Exception'>
     ('spam', 'eggs')
     ('spam', 'eggs')
     x = spam
     y = eggs

If an exception has arguments, they are printed as the last part
(‘detail’) of the message for unhandled exceptions.

Exception handlers don’t just handle exceptions if they occur
immediately in the try clause, but also if they occur inside functions
that are called (even indirectly) in the try clause.  For example:

     >>> def this_fails():
     ...     x = 1/0
     ...
     >>> try:
     ...     this_fails()
     ... except ZeroDivisionError as err:
     ...     print('Handling run-time error:', err)
     ...
     Handling run-time error: division by zero


File: python.info,  Node: Raising Exceptions,  Next: Exception Chaining,  Prev: Handling Exceptions,  Up: Errors and Exceptions

2.8.4 Raising Exceptions
------------------------

The *note raise: d0a. statement allows the programmer to force a
specified exception to occur.  For example:

     >>> raise NameError('HiThere')
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     NameError: HiThere

The sole argument to *note raise: d0a. indicates the exception to be
raised.  This must be either an exception instance or an exception class
(a class that derives from *note Exception: 2dc.).  If an exception
class is passed, it will be implicitly instantiated by calling its
constructor with no arguments:

     raise ValueError  # shorthand for 'raise ValueError()'

If you need to determine whether an exception was raised but don’t
intend to handle it, a simpler form of the *note raise: d0a. statement
allows you to re-raise the exception:

     >>> try:
     ...     raise NameError('HiThere')
     ... except NameError:
     ...     print('An exception flew by!')
     ...     raise
     ...
     An exception flew by!
     Traceback (most recent call last):
       File "<stdin>", line 2, in <module>
     NameError: HiThere


File: python.info,  Node: Exception Chaining,  Next: User-defined Exceptions,  Prev: Raising Exceptions,  Up: Errors and Exceptions

2.8.5 Exception Chaining
------------------------

The *note raise: d0a. statement allows an optional *note from: d0a.
which enables chaining exceptions.  For example:

     # exc must be exception instance or None.
     raise RuntimeError from exc

This can be useful when you are transforming exceptions.  For example:

     >>> def func():
     ...     raise IOError
     ...
     >>> try:
     ...     func()
     ... except IOError as exc:
     ...     raise RuntimeError('Failed to open database') from exc
     ...
     Traceback (most recent call last):
       File "<stdin>", line 2, in <module>
       File "<stdin>", line 2, in func
     OSError

     The above exception was the direct cause of the following exception:

     Traceback (most recent call last):
       File "<stdin>", line 4, in <module>
     RuntimeError: Failed to open database

Exception chaining happens automatically when an exception is raised
inside an *note except: c10. or *note finally: 2bc. section.  Exception
chaining can be disabled by using ‘from None’ idiom:

     >>> try:
     ...     open('database.sqlite')
     ... except OSError:
     ...     raise RuntimeError from None
     ...
     Traceback (most recent call last):
       File "<stdin>", line 4, in <module>
     RuntimeError

For more information about chaining mechanics, see *note Built-in
Exceptions: f73.


File: python.info,  Node: User-defined Exceptions,  Next: Defining Clean-up Actions,  Prev: Exception Chaining,  Up: Errors and Exceptions

2.8.6 User-defined Exceptions
-----------------------------

Programs may name their own exceptions by creating a new exception class
(see *note Classes: 1379. for more about Python classes).  Exceptions
should typically be derived from the *note Exception: 2dc. class, either
directly or indirectly.

Exception classes can be defined which do anything any other class can
do, but are usually kept simple, often only offering a number of
attributes that allow information about the error to be extracted by
handlers for the exception.

Most exceptions are defined with names that end in “Error”, similar to
the naming of the standard exceptions.

Many standard modules define their own exceptions to report errors that
may occur in functions they define.  More information on classes is
presented in chapter *note Classes: 1379.


File: python.info,  Node: Defining Clean-up Actions,  Next: Predefined Clean-up Actions,  Prev: User-defined Exceptions,  Up: Errors and Exceptions

2.8.7 Defining Clean-up Actions
-------------------------------

The *note try: e37. statement has another optional clause which is
intended to define clean-up actions that must be executed under all
circumstances.  For example:

     >>> try:
     ...     raise KeyboardInterrupt
     ... finally:
     ...     print('Goodbye, world!')
     ...
     Goodbye, world!
     Traceback (most recent call last):
       File "<stdin>", line 2, in <module>
     KeyboardInterrupt

If a *note finally: 2bc. clause is present, the ‘finally’ clause will
execute as the last task before the *note try: e37. statement completes.
The ‘finally’ clause runs whether or not the ‘try’ statement produces an
exception.  The following points discuss more complex cases when an
exception occurs:

   * If an exception occurs during execution of the ‘try’ clause, the
     exception may be handled by an *note except: c10. clause.  If the
     exception is not handled by an ‘except’ clause, the exception is
     re-raised after the ‘finally’ clause has been executed.

   * An exception could occur during execution of an ‘except’ or ‘else’
     clause.  Again, the exception is re-raised after the ‘finally’
     clause has been executed.

   * If the ‘finally’ clause executes a *note break: 3fa, *note
     continue: 2bb. or *note return: 2c8. statement, exceptions are not
     re-raised.

   * If the ‘try’ statement reaches a *note break: 3fa, *note continue:
     2bb. or *note return: 2c8. statement, the ‘finally’ clause will
     execute just prior to the ‘break’, ‘continue’ or ‘return’
     statement’s execution.

   * If a ‘finally’ clause includes a ‘return’ statement, the returned
     value will be the one from the ‘finally’ clause’s ‘return’
     statement, not the value from the ‘try’ clause’s ‘return’
     statement.

For example:

     >>> def bool_return():
     ...     try:
     ...         return True
     ...     finally:
     ...         return False
     ...
     >>> bool_return()
     False

A more complicated example:

     >>> def divide(x, y):
     ...     try:
     ...         result = x / y
     ...     except ZeroDivisionError:
     ...         print("division by zero!")
     ...     else:
     ...         print("result is", result)
     ...     finally:
     ...         print("executing finally clause")
     ...
     >>> divide(2, 1)
     result is 2.0
     executing finally clause
     >>> divide(2, 0)
     division by zero!
     executing finally clause
     >>> divide("2", "1")
     executing finally clause
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
       File "<stdin>", line 3, in divide
     TypeError: unsupported operand type(s) for /: 'str' and 'str'

As you can see, the *note finally: 2bc. clause is executed in any event.
The *note TypeError: 1fe. raised by dividing two strings is not handled
by the *note except: c10. clause and therefore re-raised after the
‘finally’ clause has been executed.

In real world applications, the *note finally: 2bc. clause is useful for
releasing external resources (such as files or network connections),
regardless of whether the use of the resource was successful.


File: python.info,  Node: Predefined Clean-up Actions,  Prev: Defining Clean-up Actions,  Up: Errors and Exceptions

2.8.8 Predefined Clean-up Actions
---------------------------------

Some objects define standard clean-up actions to be undertaken when the
object is no longer needed, regardless of whether or not the operation
using the object succeeded or failed.  Look at the following example,
which tries to open a file and print its contents to the screen.

     for line in open("myfile.txt"):
         print(line, end="")

The problem with this code is that it leaves the file open for an
indeterminate amount of time after this part of the code has finished
executing.  This is not an issue in simple scripts, but can be a problem
for larger applications.  The *note with: 7da. statement allows objects
like files to be used in a way that ensures they are always cleaned up
promptly and correctly.

     with open("myfile.txt") as f:
         for line in f:
             print(line, end="")

After the statement is executed, the file `f' is always closed, even if
a problem was encountered while processing the lines.  Objects which,
like files, provide predefined clean-up actions will indicate this in
their documentation.


File: python.info,  Node: Classes,  Next: Brief Tour of the Standard Library,  Prev: Errors and Exceptions,  Up: The Python Tutorial

2.9 Classes
===========

Classes provide a means of bundling data and functionality together.
Creating a new class creates a new `type' of object, allowing new
`instances' of that type to be made.  Each class instance can have
attributes attached to it for maintaining its state.  Class instances
can also have methods (defined by its class) for modifying its state.

Compared with other programming languages, Python’s class mechanism adds
classes with a minimum of new syntax and semantics.  It is a mixture of
the class mechanisms found in C++ and Modula-3.  Python classes provide
all the standard features of Object Oriented Programming: the class
inheritance mechanism allows multiple base classes, a derived class can
override any methods of its base class or classes, and a method can call
the method of a base class with the same name.  Objects can contain
arbitrary amounts and kinds of data.  As is true for modules, classes
partake of the dynamic nature of Python: they are created at runtime,
and can be modified further after creation.

In C++ terminology, normally class members (including the data members)
are `public' (except see below *note Private Variables: 13ee.), and all
member functions are `virtual'.  As in Modula-3, there are no shorthands
for referencing the object’s members from its methods: the method
function is declared with an explicit first argument representing the
object, which is provided implicitly by the call.  As in Smalltalk,
classes themselves are objects.  This provides semantics for importing
and renaming.  Unlike C++ and Modula-3, built-in types can be used as
base classes for extension by the user.  Also, like in C++, most
built-in operators with special syntax (arithmetic operators,
subscripting etc.)  can be redefined for class instances.

(Lacking universally accepted terminology to talk about classes, I will
make occasional use of Smalltalk and C++ terms.  I would use Modula-3
terms, since its object-oriented semantics are closer to those of Python
than C++, but I expect that few readers have heard of it.)

* Menu:

* A Word About Names and Objects::
* Python Scopes and Namespaces::
* A First Look at Classes::
* Random Remarks::
* Inheritance::
* Private Variables::
* Odds and Ends::
* Iterators::
* Generators::
* Generator Expressions::


File: python.info,  Node: A Word About Names and Objects,  Next: Python Scopes and Namespaces,  Up: Classes

2.9.1 A Word About Names and Objects
------------------------------------

Objects have individuality, and multiple names (in multiple scopes) can
be bound to the same object.  This is known as aliasing in other
languages.  This is usually not appreciated on a first glance at Python,
and can be safely ignored when dealing with immutable basic types
(numbers, strings, tuples).  However, aliasing has a possibly surprising
effect on the semantics of Python code involving mutable objects such as
lists, dictionaries, and most other types.  This is usually used to the
benefit of the program, since aliases behave like pointers in some
respects.  For example, passing an object is cheap since only a pointer
is passed by the implementation; and if a function modifies an object
passed as an argument, the caller will see the change — this eliminates
the need for two different argument passing mechanisms as in Pascal.


File: python.info,  Node: Python Scopes and Namespaces,  Next: A First Look at Classes,  Prev: A Word About Names and Objects,  Up: Classes

2.9.2 Python Scopes and Namespaces
----------------------------------

Before introducing classes, I first have to tell you something about
Python’s scope rules.  Class definitions play some neat tricks with
namespaces, and you need to know how scopes and namespaces work to fully
understand what’s going on.  Incidentally, knowledge about this subject
is useful for any advanced Python programmer.

Let’s begin with some definitions.

A `namespace' is a mapping from names to objects.  Most namespaces are
currently implemented as Python dictionaries, but that’s normally not
noticeable in any way (except for performance), and it may change in the
future.  Examples of namespaces are: the set of built-in names
(containing functions such as *note abs(): 13f3, and built-in exception
names); the global names in a module; and the local names in a function
invocation.  In a sense the set of attributes of an object also form a
namespace.  The important thing to know about namespaces is that there
is absolutely no relation between names in different namespaces; for
instance, two different modules may both define a function ‘maximize’
without confusion — users of the modules must prefix it with the module
name.

By the way, I use the word `attribute' for any name following a dot —
for example, in the expression ‘z.real’, ‘real’ is an attribute of the
object ‘z’.  Strictly speaking, references to names in modules are
attribute references: in the expression ‘modname.funcname’, ‘modname’ is
a module object and ‘funcname’ is an attribute of it.  In this case
there happens to be a straightforward mapping between the module’s
attributes and the global names defined in the module: they share the
same namespace!  (1)

Attributes may be read-only or writable.  In the latter case, assignment
to attributes is possible.  Module attributes are writable: you can
write ‘modname.the_answer = 42’.  Writable attributes may also be
deleted with the *note del: 13a2. statement.  For example, ‘del
modname.the_answer’ will remove the attribute ‘the_answer’ from the
object named by ‘modname’.

Namespaces are created at different moments and have different
lifetimes.  The namespace containing the built-in names is created when
the Python interpreter starts up, and is never deleted.  The global
namespace for a module is created when the module definition is read in;
normally, module namespaces also last until the interpreter quits.  The
statements executed by the top-level invocation of the interpreter,
either read from a script file or interactively, are considered part of
a module called *note __main__: 1, so they have their own global
namespace.  (The built-in names actually also live in a module; this is
called *note builtins: 12.)

The local namespace for a function is created when the function is
called, and deleted when the function returns or raises an exception
that is not handled within the function.  (Actually, forgetting would be
a better way to describe what actually happens.)  Of course, recursive
invocations each have their own local namespace.

A `scope' is a textual region of a Python program where a namespace is
directly accessible.  “Directly accessible” here means that an
unqualified reference to a name attempts to find the name in the
namespace.

Although scopes are determined statically, they are used dynamically.
At any time during execution, there are 3 or 4 nested scopes whose
namespaces are directly accessible:

   * the innermost scope, which is searched first, contains the local
     names

   * the scopes of any enclosing functions, which are searched starting
     with the nearest enclosing scope, contains non-local, but also
     non-global names

   * the next-to-last scope contains the current module’s global names

   * the outermost scope (searched last) is the namespace containing
     built-in names

If a name is declared global, then all references and assignments go
directly to the middle scope containing the module’s global names.  To
rebind variables found outside of the innermost scope, the *note
nonlocal: d07. statement can be used; if not declared nonlocal, those
variables are read-only (an attempt to write to such a variable will
simply create a `new' local variable in the innermost scope, leaving the
identically named outer variable unchanged).

Usually, the local scope references the local names of the (textually)
current function.  Outside functions, the local scope references the
same namespace as the global scope: the module’s namespace.  Class
definitions place yet another namespace in the local scope.

It is important to realize that scopes are determined textually: the
global scope of a function defined in a module is that module’s
namespace, no matter from where or by what alias the function is called.
On the other hand, the actual search for names is done dynamically, at
run time — however, the language definition is evolving towards static
name resolution, at “compile” time, so don’t rely on dynamic name
resolution!  (In fact, local variables are already determined
statically.)

A special quirk of Python is that – if no *note global: 1378. or *note
nonlocal: d07. statement is in effect – assignments to names always go
into the innermost scope.  Assignments do not copy data — they just bind
names to objects.  The same is true for deletions: the statement ‘del x’
removes the binding of ‘x’ from the namespace referenced by the local
scope.  In fact, all operations that introduce new names use the local
scope: in particular, *note import: ce7. statements and function
definitions bind the module or function name in the local scope.

The *note global: 1378. statement can be used to indicate that
particular variables live in the global scope and should be rebound
there; the *note nonlocal: d07. statement indicates that particular
variables live in an enclosing scope and should be rebound there.

* Menu:

* Scopes and Namespaces Example::

   ---------- Footnotes ----------

   (1) (1) Except for one thing.  Module objects have a secret read-only
attribute called *note __dict__: 5f6. which returns the dictionary used
to implement the module’s namespace; the name *note __dict__: 5f6. is an
attribute but not a global name.  Obviously, using this violates the
abstraction of namespace implementation, and should be restricted to
things like post-mortem debuggers.


File: python.info,  Node: Scopes and Namespaces Example,  Up: Python Scopes and Namespaces

2.9.2.1 Scopes and Namespaces Example
.....................................

This is an example demonstrating how to reference the different scopes
and namespaces, and how *note global: 1378. and *note nonlocal: d07.
affect variable binding:

     def scope_test():
         def do_local():
             spam = "local spam"

         def do_nonlocal():
             nonlocal spam
             spam = "nonlocal spam"

         def do_global():
             global spam
             spam = "global spam"

         spam = "test spam"
         do_local()
         print("After local assignment:", spam)
         do_nonlocal()
         print("After nonlocal assignment:", spam)
         do_global()
         print("After global assignment:", spam)

     scope_test()
     print("In global scope:", spam)

The output of the example code is:

     After local assignment: test spam
     After nonlocal assignment: nonlocal spam
     After global assignment: nonlocal spam
     In global scope: global spam

Note how the `local' assignment (which is default) didn’t change
`scope_test'’s binding of `spam'.  The *note nonlocal: d07. assignment
changed `scope_test'’s binding of `spam', and the *note global: 1378.
assignment changed the module-level binding.

You can also see that there was no previous binding for `spam' before
the *note global: 1378. assignment.


File: python.info,  Node: A First Look at Classes,  Next: Random Remarks,  Prev: Python Scopes and Namespaces,  Up: Classes

2.9.3 A First Look at Classes
-----------------------------

Classes introduce a little bit of new syntax, three new object types,
and some new semantics.

* Menu:

* Class Definition Syntax::
* Class Objects::
* Instance Objects::
* Method Objects::
* Class and Instance Variables::


File: python.info,  Node: Class Definition Syntax,  Next: Class Objects,  Up: A First Look at Classes

2.9.3.1 Class Definition Syntax
...............................

The simplest form of class definition looks like this:

     class ClassName:
         <statement-1>
         .
         .
         .
         <statement-N>

Class definitions, like function definitions (*note def: e83.
statements) must be executed before they have any effect.  (You could
conceivably place a class definition in a branch of an *note if: eab.
statement, or inside a function.)

In practice, the statements inside a class definition will usually be
function definitions, but other statements are allowed, and sometimes
useful — we’ll come back to this later.  The function definitions inside
a class normally have a peculiar form of argument list, dictated by the
calling conventions for methods — again, this is explained later.

When a class definition is entered, a new namespace is created, and used
as the local scope — thus, all assignments to local variables go into
this new namespace.  In particular, function definitions bind the name
of the new function here.

When a class definition is left normally (via the end), a `class object'
is created.  This is basically a wrapper around the contents of the
namespace created by the class definition; we’ll learn more about class
objects in the next section.  The original local scope (the one in
effect just before the class definition was entered) is reinstated, and
the class object is bound here to the class name given in the class
definition header (‘ClassName’ in the example).


File: python.info,  Node: Class Objects,  Next: Instance Objects,  Prev: Class Definition Syntax,  Up: A First Look at Classes

2.9.3.2 Class Objects
.....................

Class objects support two kinds of operations: attribute references and
instantiation.

`Attribute references' use the standard syntax used for all attribute
references in Python: ‘obj.name’.  Valid attribute names are all the
names that were in the class’s namespace when the class object was
created.  So, if the class definition looked like this:

     class MyClass:
         """A simple example class"""
         i = 12345

         def f(self):
             return 'hello world'

then ‘MyClass.i’ and ‘MyClass.f’ are valid attribute references,
returning an integer and a function object, respectively.  Class
attributes can also be assigned to, so you can change the value of
‘MyClass.i’ by assignment.  ‘__doc__’ is also a valid attribute,
returning the docstring belonging to the class: ‘"A simple example
class"’.

Class `instantiation' uses function notation.  Just pretend that the
class object is a parameterless function that returns a new instance of
the class.  For example (assuming the above class):

     x = MyClass()

creates a new `instance' of the class and assigns this object to the
local variable ‘x’.

The instantiation operation (“calling” a class object) creates an empty
object.  Many classes like to create objects with instances customized
to a specific initial state.  Therefore a class may define a special
method named *note __init__(): e23, like this:

     def __init__(self):
         self.data = []

When a class defines an *note __init__(): e23. method, class
instantiation automatically invokes *note __init__(): e23. for the
newly-created class instance.  So in this example, a new, initialized
instance can be obtained by:

     x = MyClass()

Of course, the *note __init__(): e23. method may have arguments for
greater flexibility.  In that case, arguments given to the class
instantiation operator are passed on to *note __init__(): e23.  For
example,

     >>> class Complex:
     ...     def __init__(self, realpart, imagpart):
     ...         self.r = realpart
     ...         self.i = imagpart
     ...
     >>> x = Complex(3.0, -4.5)
     >>> x.r, x.i
     (3.0, -4.5)


File: python.info,  Node: Instance Objects,  Next: Method Objects,  Prev: Class Objects,  Up: A First Look at Classes

2.9.3.3 Instance Objects
........................

Now what can we do with instance objects?  The only operations
understood by instance objects are attribute references.  There are two
kinds of valid attribute names: data attributes and methods.

`data attributes' correspond to “instance variables” in Smalltalk, and
to “data members” in C++.  Data attributes need not be declared; like
local variables, they spring into existence when they are first assigned
to.  For example, if ‘x’ is the instance of ‘MyClass’ created above, the
following piece of code will print the value ‘16’, without leaving a
trace:

     x.counter = 1
     while x.counter < 10:
         x.counter = x.counter * 2
     print(x.counter)
     del x.counter

The other kind of instance attribute reference is a `method'.  A method
is a function that “belongs to” an object.  (In Python, the term method
is not unique to class instances: other object types can have methods as
well.  For example, list objects have methods called append, insert,
remove, sort, and so on.  However, in the following discussion, we’ll
use the term method exclusively to mean methods of class instance
objects, unless explicitly stated otherwise.)

Valid method names of an instance object depend on its class.  By
definition, all attributes of a class that are function objects define
corresponding methods of its instances.  So in our example, ‘x.f’ is a
valid method reference, since ‘MyClass.f’ is a function, but ‘x.i’ is
not, since ‘MyClass.i’ is not.  But ‘x.f’ is not the same thing as
‘MyClass.f’ — it is a `method object', not a function object.


File: python.info,  Node: Method Objects,  Next: Class and Instance Variables,  Prev: Instance Objects,  Up: A First Look at Classes

2.9.3.4 Method Objects
......................

Usually, a method is called right after it is bound:

     x.f()

In the ‘MyClass’ example, this will return the string ‘'hello world'’.
However, it is not necessary to call a method right away: ‘x.f’ is a
method object, and can be stored away and called at a later time.  For
example:

     xf = x.f
     while True:
         print(xf())

will continue to print ‘hello world’ until the end of time.

What exactly happens when a method is called?  You may have noticed that
‘x.f()’ was called without an argument above, even though the function
definition for ‘f()’ specified an argument.  What happened to the
argument?  Surely Python raises an exception when a function that
requires an argument is called without any — even if the argument isn’t
actually used…

Actually, you may have guessed the answer: the special thing about
methods is that the instance object is passed as the first argument of
the function.  In our example, the call ‘x.f()’ is exactly equivalent to
‘MyClass.f(x)’.  In general, calling a method with a list of `n'
arguments is equivalent to calling the corresponding function with an
argument list that is created by inserting the method’s instance object
before the first argument.

If you still don’t understand how methods work, a look at the
implementation can perhaps clarify matters.  When a non-data attribute
of an instance is referenced, the instance’s class is searched.  If the
name denotes a valid class attribute that is a function object, a method
object is created by packing (pointers to) the instance object and the
function object just found together in an abstract object: this is the
method object.  When the method object is called with an argument list,
a new argument list is constructed from the instance object and the
argument list, and the function object is called with this new argument
list.


File: python.info,  Node: Class and Instance Variables,  Prev: Method Objects,  Up: A First Look at Classes

2.9.3.5 Class and Instance Variables
....................................

Generally speaking, instance variables are for data unique to each
instance and class variables are for attributes and methods shared by
all instances of the class:

     class Dog:

         kind = 'canine'         # class variable shared by all instances

         def __init__(self, name):
             self.name = name    # instance variable unique to each instance

     >>> d = Dog('Fido')
     >>> e = Dog('Buddy')
     >>> d.kind                  # shared by all dogs
     'canine'
     >>> e.kind                  # shared by all dogs
     'canine'
     >>> d.name                  # unique to d
     'Fido'
     >>> e.name                  # unique to e
     'Buddy'

As discussed in *note A Word About Names and Objects: 13f0, shared data
can have possibly surprising effects with involving *note mutable: 135e.
objects such as lists and dictionaries.  For example, the `tricks' list
in the following code should not be used as a class variable because
just a single list would be shared by all `Dog' instances:

     class Dog:

         tricks = []             # mistaken use of a class variable

         def __init__(self, name):
             self.name = name

         def add_trick(self, trick):
             self.tricks.append(trick)

     >>> d = Dog('Fido')
     >>> e = Dog('Buddy')
     >>> d.add_trick('roll over')
     >>> e.add_trick('play dead')
     >>> d.tricks                # unexpectedly shared by all dogs
     ['roll over', 'play dead']

Correct design of the class should use an instance variable instead:

     class Dog:

         def __init__(self, name):
             self.name = name
             self.tricks = []    # creates a new empty list for each dog

         def add_trick(self, trick):
             self.tricks.append(trick)

     >>> d = Dog('Fido')
     >>> e = Dog('Buddy')
     >>> d.add_trick('roll over')
     >>> e.add_trick('play dead')
     >>> d.tricks
     ['roll over']
     >>> e.tricks
     ['play dead']


File: python.info,  Node: Random Remarks,  Next: Inheritance,  Prev: A First Look at Classes,  Up: Classes

2.9.4 Random Remarks
--------------------

If the same attribute name occurs in both an instance and in a class,
then attribute lookup prioritizes the instance:

     >>> class Warehouse:
             purpose = 'storage'
             region = 'west'

     >>> w1 = Warehouse()
     >>> print(w1.purpose, w1.region)
     storage west
     >>> w2 = Warehouse()
     >>> w2.region = 'east'
     >>> print(w2.purpose, w2.region)
     storage east

Data attributes may be referenced by methods as well as by ordinary
users (“clients”) of an object.  In other words, classes are not usable
to implement pure abstract data types.  In fact, nothing in Python makes
it possible to enforce data hiding — it is all based upon convention.
(On the other hand, the Python implementation, written in C, can
completely hide implementation details and control access to an object
if necessary; this can be used by extensions to Python written in C.)

Clients should use data attributes with care — clients may mess up
invariants maintained by the methods by stamping on their data
attributes.  Note that clients may add data attributes of their own to
an instance object without affecting the validity of the methods, as
long as name conflicts are avoided — again, a naming convention can save
a lot of headaches here.

There is no shorthand for referencing data attributes (or other
methods!)  from within methods.  I find that this actually increases the
readability of methods: there is no chance of confusing local variables
and instance variables when glancing through a method.

Often, the first argument of a method is called ‘self’.  This is nothing
more than a convention: the name ‘self’ has absolutely no special
meaning to Python.  Note, however, that by not following the convention
your code may be less readable to other Python programmers, and it is
also conceivable that a `class browser' program might be written that
relies upon such a convention.

Any function object that is a class attribute defines a method for
instances of that class.  It is not necessary that the function
definition is textually enclosed in the class definition: assigning a
function object to a local variable in the class is also ok.  For
example:

     # Function defined outside the class
     def f1(self, x, y):
         return min(x, x+y)

     class C:
         f = f1

         def g(self):
             return 'hello world'

         h = g

Now ‘f’, ‘g’ and ‘h’ are all attributes of class ‘C’ that refer to
function objects, and consequently they are all methods of instances of
‘C’ — ‘h’ being exactly equivalent to ‘g’.  Note that this practice
usually only serves to confuse the reader of a program.

Methods may call other methods by using method attributes of the ‘self’
argument:

     class Bag:
         def __init__(self):
             self.data = []

         def add(self, x):
             self.data.append(x)

         def addtwice(self, x):
             self.add(x)
             self.add(x)

Methods may reference global names in the same way as ordinary
functions.  The global scope associated with a method is the module
containing its definition.  (A class is never used as a global scope.)
While one rarely encounters a good reason for using global data in a
method, there are many legitimate uses of the global scope: for one
thing, functions and modules imported into the global scope can be used
by methods, as well as functions and classes defined in it.  Usually,
the class containing the method is itself defined in this global scope,
and in the next section we’ll find some good reasons why a method would
want to reference its own class.

Each value is an object, and therefore has a `class' (also called its
`type').  It is stored as ‘object.__class__’.


File: python.info,  Node: Inheritance,  Next: Private Variables,  Prev: Random Remarks,  Up: Classes

2.9.5 Inheritance
-----------------

Of course, a language feature would not be worthy of the name “class”
without supporting inheritance.  The syntax for a derived class
definition looks like this:

     class DerivedClassName(BaseClassName):
         <statement-1>
         .
         .
         .
         <statement-N>

The name ‘BaseClassName’ must be defined in a scope containing the
derived class definition.  In place of a base class name, other
arbitrary expressions are also allowed.  This can be useful, for
example, when the base class is defined in another module:

     class DerivedClassName(modname.BaseClassName):

Execution of a derived class definition proceeds the same as for a base
class.  When the class object is constructed, the base class is
remembered.  This is used for resolving attribute references: if a
requested attribute is not found in the class, the search proceeds to
look in the base class.  This rule is applied recursively if the base
class itself is derived from some other class.

There’s nothing special about instantiation of derived classes:
‘DerivedClassName()’ creates a new instance of the class.  Method
references are resolved as follows: the corresponding class attribute is
searched, descending down the chain of base classes if necessary, and
the method reference is valid if this yields a function object.

Derived classes may override methods of their base classes.  Because
methods have no special privileges when calling other methods of the
same object, a method of a base class that calls another method defined
in the same base class may end up calling a method of a derived class
that overrides it.  (For C++ programmers: all methods in Python are
effectively ‘virtual’.)

An overriding method in a derived class may in fact want to extend
rather than simply replace the base class method of the same name.
There is a simple way to call the base class method directly: just call
‘BaseClassName.methodname(self, arguments)’.  This is occasionally
useful to clients as well.  (Note that this only works if the base class
is accessible as ‘BaseClassName’ in the global scope.)

Python has two built-in functions that work with inheritance:

   * Use *note isinstance(): 552. to check an instance’s type:
     ‘isinstance(obj, int)’ will be ‘True’ only if ‘obj.__class__’ is
     *note int: 204. or some class derived from *note int: 204.

   * Use *note issubclass(): 553. to check class inheritance:
     ‘issubclass(bool, int)’ is ‘True’ since *note bool: 2bd. is a
     subclass of *note int: 204.  However, ‘issubclass(float, int)’ is
     ‘False’ since *note float: 1fd. is not a subclass of *note int:
     204.

* Menu:

* Multiple Inheritance::


File: python.info,  Node: Multiple Inheritance,  Up: Inheritance

2.9.5.1 Multiple Inheritance
............................

Python supports a form of multiple inheritance as well.  A class
definition with multiple base classes looks like this:

     class DerivedClassName(Base1, Base2, Base3):
         <statement-1>
         .
         .
         .
         <statement-N>

For most purposes, in the simplest cases, you can think of the search
for attributes inherited from a parent class as depth-first,
left-to-right, not searching twice in the same class where there is an
overlap in the hierarchy.  Thus, if an attribute is not found in
‘DerivedClassName’, it is searched for in ‘Base1’, then (recursively) in
the base classes of ‘Base1’, and if it was not found there, it was
searched for in ‘Base2’, and so on.

In fact, it is slightly more complex than that; the method resolution
order changes dynamically to support cooperative calls to *note super():
5dd.  This approach is known in some other multiple-inheritance
languages as call-next-method and is more powerful than the super call
found in single-inheritance languages.

Dynamic ordering is necessary because all cases of multiple inheritance
exhibit one or more diamond relationships (where at least one of the
parent classes can be accessed through multiple paths from the
bottommost class).  For example, all classes inherit from *note object:
3d2, so any case of multiple inheritance provides more than one path to
reach *note object: 3d2.  To keep the base classes from being accessed
more than once, the dynamic algorithm linearizes the search order in a
way that preserves the left-to-right ordering specified in each class,
that calls each parent only once, and that is monotonic (meaning that a
class can be subclassed without affecting the precedence order of its
parents).  Taken together, these properties make it possible to design
reliable and extensible classes with multiple inheritance.  For more
detail, see ‘https://www.python.org/download/releases/2.3/mro/’.


File: python.info,  Node: Private Variables,  Next: Odds and Ends,  Prev: Inheritance,  Up: Classes

2.9.6 Private Variables
-----------------------

“Private” instance variables that cannot be accessed except from inside
an object don’t exist in Python.  However, there is a convention that is
followed by most Python code: a name prefixed with an underscore (e.g.
‘_spam’) should be treated as a non-public part of the API (whether it
is a function, a method or a data member).  It should be considered an
implementation detail and subject to change without notice.

Since there is a valid use-case for class-private members (namely to
avoid name clashes of names with names defined by subclasses), there is
limited support for such a mechanism, called `name mangling'.  Any
identifier of the form ‘__spam’ (at least two leading underscores, at
most one trailing underscore) is textually replaced with
‘_classname__spam’, where ‘classname’ is the current class name with
leading underscore(s) stripped.  This mangling is done without regard to
the syntactic position of the identifier, as long as it occurs within
the definition of a class.

Name mangling is helpful for letting subclasses override methods without
breaking intraclass method calls.  For example:

     class Mapping:
         def __init__(self, iterable):
             self.items_list = []
             self.__update(iterable)

         def update(self, iterable):
             for item in iterable:
                 self.items_list.append(item)

         __update = update   # private copy of original update() method

     class MappingSubclass(Mapping):

         def update(self, keys, values):
             # provides new signature for update()
             # but does not break __init__()
             for item in zip(keys, values):
                 self.items_list.append(item)

The above example would work even if ‘MappingSubclass’ were to introduce
a ‘__update’ identifier since it is replaced with ‘_Mapping__update’ in
the ‘Mapping’ class and ‘_MappingSubclass__update’ in the
‘MappingSubclass’ class respectively.

Note that the mangling rules are designed mostly to avoid accidents; it
still is possible to access or modify a variable that is considered
private.  This can even be useful in special circumstances, such as in
the debugger.

Notice that code passed to ‘exec()’ or ‘eval()’ does not consider the
classname of the invoking class to be the current class; this is similar
to the effect of the ‘global’ statement, the effect of which is likewise
restricted to code that is byte-compiled together.  The same restriction
applies to ‘getattr()’, ‘setattr()’ and ‘delattr()’, as well as when
referencing ‘__dict__’ directly.


File: python.info,  Node: Odds and Ends,  Next: Iterators,  Prev: Private Variables,  Up: Classes

2.9.7 Odds and Ends
-------------------

Sometimes it is useful to have a data type similar to the Pascal
“record” or C “struct”, bundling together a few named data items.  An
empty class definition will do nicely:

     class Employee:
         pass

     john = Employee()  # Create an empty employee record

     # Fill the fields of the record
     john.name = 'John Doe'
     john.dept = 'computer lab'
     john.salary = 1000

A piece of Python code that expects a particular abstract data type can
often be passed a class that emulates the methods of that data type
instead.  For instance, if you have a function that formats some data
from a file object, you can define a class with methods ‘read()’ and
‘readline()’ that get the data from a string buffer instead, and pass it
as an argument.

Instance method objects have attributes, too: ‘m.__self__’ is the
instance object with the method ‘m()’, and ‘m.__func__’ is the function
object corresponding to the method.


File: python.info,  Node: Iterators,  Next: Generators,  Prev: Odds and Ends,  Up: Classes

2.9.8 Iterators
---------------

By now you have probably noticed that most container objects can be
looped over using a *note for: cfa. statement:

     for element in [1, 2, 3]:
         print(element)
     for element in (1, 2, 3):
         print(element)
     for key in {'one':1, 'two':2}:
         print(key)
     for char in "123":
         print(char)
     for line in open("myfile.txt"):
         print(line, end='')

This style of access is clear, concise, and convenient.  The use of
iterators pervades and unifies Python.  Behind the scenes, the *note
for: cfa. statement calls *note iter(): ded. on the container object.
The function returns an iterator object that defines the method *note
__next__(): d2c. which accesses elements in the container one at a time.
When there are no more elements, *note __next__(): d2c. raises a *note
StopIteration: 582. exception which tells the ‘for’ loop to terminate.
You can call the *note __next__(): d2c. method using the *note next():
775. built-in function; this example shows how it all works:

     >>> s = 'abc'
     >>> it = iter(s)
     >>> it
     <str_iterator object at 0x10c90e650>
     >>> next(it)
     'a'
     >>> next(it)
     'b'
     >>> next(it)
     'c'
     >>> next(it)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
         next(it)
     StopIteration

Having seen the mechanics behind the iterator protocol, it is easy to
add iterator behavior to your classes.  Define an *note __iter__(): 609.
method which returns an object with a *note __next__(): d2c. method.  If
the class defines ‘__next__()’, then *note __iter__(): 609. can just
return ‘self’:

     class Reverse:
         """Iterator for looping over a sequence backwards."""
         def __init__(self, data):
             self.data = data
             self.index = len(data)

         def __iter__(self):
             return self

         def __next__(self):
             if self.index == 0:
                 raise StopIteration
             self.index = self.index - 1
             return self.data[self.index]

     >>> rev = Reverse('spam')
     >>> iter(rev)
     <__main__.Reverse object at 0x00A1DB50>
     >>> for char in rev:
     ...     print(char)
     ...
     m
     a
     p
     s


File: python.info,  Node: Generators,  Next: Generator Expressions,  Prev: Iterators,  Up: Classes

2.9.9 Generators
----------------

*note Generators: a83. are a simple and powerful tool for creating
iterators.  They are written like regular functions but use the *note
yield: 2c7. statement whenever they want to return data.  Each time
*note next(): 775. is called on it, the generator resumes where it left
off (it remembers all the data values and which statement was last
executed).  An example shows that generators can be trivially easy to
create:

     def reverse(data):
         for index in range(len(data)-1, -1, -1):
             yield data[index]

     >>> for char in reverse('golf'):
     ...     print(char)
     ...
     f
     l
     o
     g

Anything that can be done with generators can also be done with
class-based iterators as described in the previous section.  What makes
generators so compact is that the *note __iter__(): 609. and *note
__next__(): 140e. methods are created automatically.

Another key feature is that the local variables and execution state are
automatically saved between calls.  This made the function easier to
write and much more clear than an approach using instance variables like
‘self.index’ and ‘self.data’.

In addition to automatic method creation and saving program state, when
generators terminate, they automatically raise *note StopIteration: 582.
In combination, these features make it easy to create iterators with no
more effort than writing a regular function.


File: python.info,  Node: Generator Expressions,  Prev: Generators,  Up: Classes

2.9.10 Generator Expressions
----------------------------

Some simple generators can be coded succinctly as expressions using a
syntax similar to list comprehensions but with parentheses instead of
square brackets.  These expressions are designed for situations where
the generator is used right away by an enclosing function.  Generator
expressions are more compact but less versatile than full generator
definitions and tend to be more memory friendly than equivalent list
comprehensions.

Examples:

     >>> sum(i*i for i in range(10))                 # sum of squares
     285

     >>> xvec = [10, 20, 30]
     >>> yvec = [7, 5, 3]
     >>> sum(x*y for x,y in zip(xvec, yvec))         # dot product
     260

     >>> unique_words = set(word for line in page  for word in line.split())

     >>> valedictorian = max((student.gpa, student.name) for student in graduates)

     >>> data = 'golf'
     >>> list(data[i] for i in range(len(data)-1, -1, -1))
     ['f', 'l', 'o', 'g']


File: python.info,  Node: Brief Tour of the Standard Library,  Next: Brief Tour of the Standard Library — Part II,  Prev: Classes,  Up: The Python Tutorial

2.10 Brief Tour of the Standard Library
=======================================

* Menu:

* Operating System Interface::
* File Wildcards::
* Command Line Arguments::
* Error Output Redirection and Program Termination::
* String Pattern Matching::
* Mathematics::
* Internet Access::
* Dates and Times::
* Data Compression::
* Performance Measurement::
* Quality Control::
* Batteries Included::


File: python.info,  Node: Operating System Interface,  Next: File Wildcards,  Up: Brief Tour of the Standard Library

2.10.1 Operating System Interface
---------------------------------

The *note os: c4. module provides dozens of functions for interacting
with the operating system:

     >>> import os
     >>> os.getcwd()      # Return the current working directory
     'C:\\Python39'
     >>> os.chdir('/server/accesslogs')   # Change current working directory
     >>> os.system('mkdir today')   # Run the command mkdir in the system shell
     0

Be sure to use the ‘import os’ style instead of ‘from os import *’.
This will keep *note os.open(): 758. from shadowing the built-in *note
open(): 16f. function which operates much differently.

The built-in *note dir(): df9. and *note help(): 175. functions are
useful as interactive aids for working with large modules like *note os:
c4.:

     >>> import os
     >>> dir(os)
     <returns a list of all module functions>
     >>> help(os)
     <returns an extensive manual page created from the module's docstrings>

For daily file and directory management tasks, the *note shutil: e9.
module provides a higher level interface that is easier to use:

     >>> import shutil
     >>> shutil.copyfile('data.db', 'archive.db')
     'archive.db'
     >>> shutil.move('/build/executables', 'installdir')
     'installdir'


File: python.info,  Node: File Wildcards,  Next: Command Line Arguments,  Prev: Operating System Interface,  Up: Brief Tour of the Standard Library

2.10.2 File Wildcards
---------------------

The *note glob: 88. module provides a function for making file lists
from directory wildcard searches:

     >>> import glob
     >>> glob.glob('*.py')
     ['primes.py', 'random.py', 'quote.py']


File: python.info,  Node: Command Line Arguments,  Next: Error Output Redirection and Program Termination,  Prev: File Wildcards,  Up: Brief Tour of the Standard Library

2.10.3 Command Line Arguments
-----------------------------

Common utility scripts often need to process command line arguments.
These arguments are stored in the *note sys: fd. module’s `argv'
attribute as a list.  For instance the following output results from
running ‘python demo.py one two three’ at the command line:

     >>> import sys
     >>> print(sys.argv)
     ['demo.py', 'one', 'two', 'three']

The *note argparse: 5. module provides a more sophisticated mechanism to
process command line arguments.  The following script extracts one or
more filenames and an optional number of lines to be displayed:

     import argparse

     parser = argparse.ArgumentParser(prog = 'top',
         description = 'Show top lines from each file')
     parser.add_argument('filenames', nargs='+')
     parser.add_argument('-l', '--lines', type=int, default=10)
     args = parser.parse_args()
     print(args)

When run at the command line with ‘python top.py --lines=5 alpha.txt
beta.txt’, the script sets ‘args.lines’ to ‘5’ and ‘args.filenames’ to
‘['alpha.txt', 'beta.txt']’.


File: python.info,  Node: Error Output Redirection and Program Termination,  Next: String Pattern Matching,  Prev: Command Line Arguments,  Up: Brief Tour of the Standard Library

2.10.4 Error Output Redirection and Program Termination
-------------------------------------------------------

The *note sys: fd. module also has attributes for `stdin', `stdout', and
`stderr'.  The latter is useful for emitting warnings and error messages
to make them visible even when `stdout' has been redirected:

     >>> sys.stderr.write('Warning, log file not found starting a new one\n')
     Warning, log file not found starting a new one

The most direct way to terminate a script is to use ‘sys.exit()’.


File: python.info,  Node: String Pattern Matching,  Next: Mathematics,  Prev: Error Output Redirection and Program Termination,  Up: Brief Tour of the Standard Library

2.10.5 String Pattern Matching
------------------------------

The *note re: dd. module provides regular expression tools for advanced
string processing.  For complex matching and manipulation, regular
expressions offer succinct, optimized solutions:

     >>> import re
     >>> re.findall(r'\bf[a-z]*', 'which foot or hand fell fastest')
     ['foot', 'fell', 'fastest']
     >>> re.sub(r'(\b[a-z]+) \1', r'\1', 'cat in the the hat')
     'cat in the hat'

When only simple capabilities are needed, string methods are preferred
because they are easier to read and debug:

     >>> 'tea for too'.replace('too', 'two')
     'tea for two'


File: python.info,  Node: Mathematics,  Next: Internet Access,  Prev: String Pattern Matching,  Up: Brief Tour of the Standard Library

2.10.6 Mathematics
------------------

The *note math: b1. module gives access to the underlying C library
functions for floating point math:

     >>> import math
     >>> math.cos(math.pi / 4)
     0.70710678118654757
     >>> math.log(1024, 2)
     10.0

The *note random: dc. module provides tools for making random
selections:

     >>> import random
     >>> random.choice(['apple', 'pear', 'banana'])
     'apple'
     >>> random.sample(range(100), 10)   # sampling without replacement
     [30, 83, 16, 4, 8, 81, 41, 50, 18, 33]
     >>> random.random()    # random float
     0.17970987693706186
     >>> random.randrange(6)    # random integer chosen from range(6)
     4

The *note statistics: f5. module calculates basic statistical properties
(the mean, median, variance, etc.)  of numeric data:

     >>> import statistics
     >>> data = [2.75, 1.75, 1.25, 0.25, 0.5, 1.25, 3.5]
     >>> statistics.mean(data)
     1.6071428571428572
     >>> statistics.median(data)
     1.25
     >>> statistics.variance(data)
     1.3720238095238095

The SciPy project <‘https://scipy.org’> has many other modules for
numerical computations.


File: python.info,  Node: Internet Access,  Next: Dates and Times,  Prev: Mathematics,  Up: Brief Tour of the Standard Library

2.10.7 Internet Access
----------------------

There are a number of modules for accessing the internet and processing
internet protocols.  Two of the simplest are *note urllib.request: 129.
for retrieving data from URLs and *note smtplib: ed. for sending mail:

     >>> from urllib.request import urlopen
     >>> with urlopen('http://worldtimeapi.org/api/timezone/etc/UTC.txt') as response:
     ...     for line in response:
     ...         line = line.decode()             # Convert bytes to a str
     ...         if line.startswith('datetime'):
     ...             print(line.rstrip())         # Remove trailing newline
     ...
     datetime: 2022-01-01T01:36:47.689215+00:00

     >>> import smtplib
     >>> server = smtplib.SMTP('localhost')
     >>> server.sendmail('soothsayer@example.org', 'jcaesar@example.org',
     ... """To: jcaesar@example.org
     ... From: soothsayer@example.org
     ...
     ... Beware the Ides of March.
     ... """)
     >>> server.quit()

(Note that the second example needs a mailserver running on localhost.)


File: python.info,  Node: Dates and Times,  Next: Data Compression,  Prev: Internet Access,  Up: Brief Tour of the Standard Library

2.10.8 Dates and Times
----------------------

The *note datetime: 30. module supplies classes for manipulating dates
and times in both simple and complex ways.  While date and time
arithmetic is supported, the focus of the implementation is on efficient
member extraction for output formatting and manipulation.  The module
also supports objects that are timezone aware.

     >>> # dates are easily constructed and formatted
     >>> from datetime import date
     >>> now = date.today()
     >>> now
     datetime.date(2003, 12, 2)
     >>> now.strftime("%m-%d-%y. %d %b %Y is a %A on the %d day of %B.")
     '12-02-03. 02 Dec 2003 is a Tuesday on the 02 day of December.'

     >>> # dates support calendar arithmetic
     >>> birthday = date(1964, 7, 31)
     >>> age = now - birthday
     >>> age.days
     14368


File: python.info,  Node: Data Compression,  Next: Performance Measurement,  Prev: Dates and Times,  Up: Brief Tour of the Standard Library

2.10.9 Data Compression
-----------------------

Common data archiving and compression formats are directly supported by
modules including: *note zlib: 14d, *note gzip: 8b, *note bz2: 13, *note
lzma: ad, *note zipfile: 14b. and *note tarfile: 101.

     >>> import zlib
     >>> s = b'witch which has which witches wrist watch'
     >>> len(s)
     41
     >>> t = zlib.compress(s)
     >>> len(t)
     37
     >>> zlib.decompress(t)
     b'witch which has which witches wrist watch'
     >>> zlib.crc32(s)
     226805979


File: python.info,  Node: Performance Measurement,  Next: Quality Control,  Prev: Data Compression,  Up: Brief Tour of the Standard Library

2.10.10 Performance Measurement
-------------------------------

Some Python users develop a deep interest in knowing the relative
performance of different approaches to the same problem.  Python
provides a measurement tool that answers those questions immediately.

For example, it may be tempting to use the tuple packing and unpacking
feature instead of the traditional approach to swapping arguments.  The
*note timeit: 10d. module quickly demonstrates a modest performance
advantage:

     >>> from timeit import Timer
     >>> Timer('t=a; a=b; b=t', 'a=1; b=2').timeit()
     0.57535828626024577
     >>> Timer('a,b = b,a', 'a=1; b=2').timeit()
     0.54962537085770791

In contrast to *note timeit: 10d.’s fine level of granularity, the *note
profile: d3. and *note pstats: d4. modules provide tools for identifying
time critical sections in larger blocks of code.


File: python.info,  Node: Quality Control,  Next: Batteries Included,  Prev: Performance Measurement,  Up: Brief Tour of the Standard Library

2.10.11 Quality Control
-----------------------

One approach for developing high quality software is to write tests for
each function as it is developed and to run those tests frequently
during the development process.

The *note doctest: 66. module provides a tool for scanning a module and
validating tests embedded in a program’s docstrings.  Test construction
is as simple as cutting-and-pasting a typical call along with its
results into the docstring.  This improves the documentation by
providing the user with an example and it allows the doctest module to
make sure the code remains true to the documentation:

     def average(values):
         """Computes the arithmetic mean of a list of numbers.

         >>> print(average([20, 30, 70]))
         40.0
         """
         return sum(values) / len(values)

     import doctest
     doctest.testmod()   # automatically validate the embedded tests

The *note unittest: 124. module is not as effortless as the *note
doctest: 66. module, but it allows a more comprehensive set of tests to
be maintained in a separate file:

     import unittest

     class TestStatisticalFunctions(unittest.TestCase):

         def test_average(self):
             self.assertEqual(average([20, 30, 70]), 40.0)
             self.assertEqual(round(average([1, 5, 7]), 1), 4.3)
             with self.assertRaises(ZeroDivisionError):
                 average([])
             with self.assertRaises(TypeError):
                 average(20, 30, 70)

     unittest.main()  # Calling from the command line invokes all tests


File: python.info,  Node: Batteries Included,  Prev: Quality Control,  Up: Brief Tour of the Standard Library

2.10.12 Batteries Included
--------------------------

Python has a “batteries included” philosophy.  This is best seen through
the sophisticated and robust capabilities of its larger packages.  For
example:

   * The *note xmlrpc.client: 148. and *note xmlrpc.server: 149. modules
     make implementing remote procedure calls into an almost trivial
     task.  Despite the modules names, no direct knowledge or handling
     of XML is needed.

   * The *note email: 67. package is a library for managing email
     messages, including MIME and other RFC 2822(1)-based message
     documents.  Unlike *note smtplib: ed. and *note poplib: d0. which
     actually send and receive messages, the email package has a
     complete toolset for building or decoding complex message
     structures (including attachments) and for implementing internet
     encoding and header protocols.

   * The *note json: a4. package provides robust support for parsing
     this popular data interchange format.  The *note csv: 29. module
     supports direct reading and writing of files in Comma-Separated
     Value format, commonly supported by databases and spreadsheets.
     XML processing is supported by the *note xml.etree.ElementTree:
     140, *note xml.dom: 13d. and *note xml.sax: 144. packages.
     Together, these modules and packages greatly simplify data
     interchange between Python applications and other tools.

   * The *note sqlite3: f2. module is a wrapper for the SQLite database
     library, providing a persistent database that can be updated and
     accessed using slightly nonstandard SQL syntax.

   * Internationalization is supported by a number of modules including
     *note gettext: 87, *note locale: a9, and the *note codecs: 1b.
     package.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2822.html


File: python.info,  Node: Brief Tour of the Standard Library — Part II,  Next: Virtual Environments and Packages,  Prev: Brief Tour of the Standard Library,  Up: The Python Tutorial

2.11 Brief Tour of the Standard Library — Part II
=================================================

This second tour covers more advanced modules that support professional
programming needs.  These modules rarely occur in small scripts.

* Menu:

* Output Formatting::
* Templating::
* Working with Binary Data Record Layouts::
* Multi-threading: Multi-threading<2>.
* Logging::
* Weak References::
* Tools for Working with Lists::
* Decimal Floating Point Arithmetic::


File: python.info,  Node: Output Formatting,  Next: Templating,  Up: Brief Tour of the Standard Library — Part II

2.11.1 Output Formatting
------------------------

The *note reprlib: df. module provides a version of *note repr(): 8b9.
customized for abbreviated displays of large or deeply nested
containers:

     >>> import reprlib
     >>> reprlib.repr(set('supercalifragilisticexpialidocious'))
     "{'a', 'c', 'd', 'e', 'f', 'g', ...}"

The *note pprint: d2. module offers more sophisticated control over
printing both built-in and user defined objects in a way that is
readable by the interpreter.  When the result is longer than one line,
the “pretty printer” adds line breaks and indentation to more clearly
reveal data structure:

     >>> import pprint
     >>> t = [[[['black', 'cyan'], 'white', ['green', 'red']], [['magenta',
     ...     'yellow'], 'blue']]]
     ...
     >>> pprint.pprint(t, width=30)
     [[[['black', 'cyan'],
        'white',
        ['green', 'red']],
       [['magenta', 'yellow'],
        'blue']]]

The *note textwrap: 10a. module formats paragraphs of text to fit a
given screen width:

     >>> import textwrap
     >>> doc = """The wrap() method is just like fill() except that it returns
     ... a list of strings instead of one big string with newlines to separate
     ... the wrapped lines."""
     ...
     >>> print(textwrap.fill(doc, width=40))
     The wrap() method is just like fill()
     except that it returns a list of strings
     instead of one big string with newlines
     to separate the wrapped lines.

The *note locale: a9. module accesses a database of culture specific
data formats.  The grouping attribute of locale’s format function
provides a direct way of formatting numbers with group separators:

     >>> import locale
     >>> locale.setlocale(locale.LC_ALL, 'English_United States.1252')
     'English_United States.1252'
     >>> conv = locale.localeconv()          # get a mapping of conventions
     >>> x = 1234567.8
     >>> locale.format("%d", x, grouping=True)
     '1,234,567'
     >>> locale.format_string("%s%.*f", (conv['currency_symbol'],
     ...                      conv['frac_digits'], x), grouping=True)
     '$1,234,567.80'


File: python.info,  Node: Templating,  Next: Working with Binary Data Record Layouts,  Prev: Output Formatting,  Up: Brief Tour of the Standard Library — Part II

2.11.2 Templating
-----------------

The *note string: f6. module includes a versatile *note Template: 4f1.
class with a simplified syntax suitable for editing by end-users.  This
allows users to customize their applications without having to alter the
application.

The format uses placeholder names formed by ‘$’ with valid Python
identifiers (alphanumeric characters and underscores).  Surrounding the
placeholder with braces allows it to be followed by more alphanumeric
letters with no intervening spaces.  Writing ‘$$’ creates a single
escaped ‘$’:

     >>> from string import Template
     >>> t = Template('${village}folk send $$10 to $cause.')
     >>> t.substitute(village='Nottingham', cause='the ditch fund')
     'Nottinghamfolk send $10 to the ditch fund.'

The *note substitute(): 1433. method raises a *note KeyError: 3e9. when
a placeholder is not supplied in a dictionary or a keyword argument.
For mail-merge style applications, user supplied data may be incomplete
and the *note safe_substitute(): 1434. method may be more appropriate —
it will leave placeholders unchanged if data is missing:

     >>> t = Template('Return the $item to $owner.')
     >>> d = dict(item='unladen swallow')
     >>> t.substitute(d)
     Traceback (most recent call last):
       ...
     KeyError: 'owner'
     >>> t.safe_substitute(d)
     'Return the unladen swallow to $owner.'

Template subclasses can specify a custom delimiter.  For example, a
batch renaming utility for a photo browser may elect to use percent
signs for placeholders such as the current date, image sequence number,
or file format:

     >>> import time, os.path
     >>> photofiles = ['img_1074.jpg', 'img_1076.jpg', 'img_1077.jpg']
     >>> class BatchRename(Template):
     ...     delimiter = '%'
     >>> fmt = input('Enter rename style (%d-date %n-seqnum %f-format):  ')
     Enter rename style (%d-date %n-seqnum %f-format):  Ashley_%n%f

     >>> t = BatchRename(fmt)
     >>> date = time.strftime('%d%b%y')
     >>> for i, filename in enumerate(photofiles):
     ...     base, ext = os.path.splitext(filename)
     ...     newname = t.substitute(d=date, n=i, f=ext)
     ...     print('{0} --> {1}'.format(filename, newname))

     img_1074.jpg --> Ashley_0.jpg
     img_1076.jpg --> Ashley_1.jpg
     img_1077.jpg --> Ashley_2.jpg

Another application for templating is separating program logic from the
details of multiple output formats.  This makes it possible to
substitute custom templates for XML files, plain text reports, and HTML
web reports.


File: python.info,  Node: Working with Binary Data Record Layouts,  Next: Multi-threading<2>,  Prev: Templating,  Up: Brief Tour of the Standard Library — Part II

2.11.3 Working with Binary Data Record Layouts
----------------------------------------------

The *note struct: f8. module provides *note pack(): cd6. and *note
unpack(): 1437. functions for working with variable length binary record
formats.  The following example shows how to loop through header
information in a ZIP file without using the *note zipfile: 14b. module.
Pack codes ‘"H"’ and ‘"I"’ represent two and four byte unsigned numbers
respectively.  The ‘"<"’ indicates that they are standard size and in
little-endian byte order:

     import struct

     with open('myfile.zip', 'rb') as f:
         data = f.read()

     start = 0
     for i in range(3):                      # show the first 3 file headers
         start += 14
         fields = struct.unpack('<IIIHH', data[start:start+16])
         crc32, comp_size, uncomp_size, filenamesize, extra_size = fields

         start += 16
         filename = data[start:start+filenamesize]
         start += filenamesize
         extra = data[start:start+extra_size]
         print(filename, hex(crc32), comp_size, uncomp_size)

         start += extra_size + comp_size     # skip to the next header


File: python.info,  Node: Multi-threading<2>,  Next: Logging,  Prev: Working with Binary Data Record Layouts,  Up: Brief Tour of the Standard Library — Part II

2.11.4 Multi-threading
----------------------

Threading is a technique for decoupling tasks which are not sequentially
dependent.  Threads can be used to improve the responsiveness of
applications that accept user input while other tasks run in the
background.  A related use case is running I/O in parallel with
computations in another thread.

The following code shows how the high level *note threading: 10b. module
can run tasks in background while the main program continues to run:

     import threading, zipfile

     class AsyncZip(threading.Thread):
         def __init__(self, infile, outfile):
             threading.Thread.__init__(self)
             self.infile = infile
             self.outfile = outfile

         def run(self):
             f = zipfile.ZipFile(self.outfile, 'w', zipfile.ZIP_DEFLATED)
             f.write(self.infile)
             f.close()
             print('Finished background zip of:', self.infile)

     background = AsyncZip('mydata.txt', 'myarchive.zip')
     background.start()
     print('The main program continues to run in foreground.')

     background.join()    # Wait for the background task to finish
     print('Main program waited until background was done.')

The principal challenge of multi-threaded applications is coordinating
threads that share data or other resources.  To that end, the threading
module provides a number of synchronization primitives including locks,
events, condition variables, and semaphores.

While those tools are powerful, minor design errors can result in
problems that are difficult to reproduce.  So, the preferred approach to
task coordination is to concentrate all access to a resource in a single
thread and then use the *note queue: da. module to feed that thread with
requests from other threads.  Applications using *note Queue: dde.
objects for inter-thread communication and coordination are easier to
design, more readable, and more reliable.


File: python.info,  Node: Logging,  Next: Weak References,  Prev: Multi-threading<2>,  Up: Brief Tour of the Standard Library — Part II

2.11.5 Logging
--------------

The *note logging: aa. module offers a full featured and flexible
logging system.  At its simplest, log messages are sent to a file or to
‘sys.stderr’:

     import logging
     logging.debug('Debugging information')
     logging.info('Informational message')
     logging.warning('Warning:config file %s not found', 'server.conf')
     logging.error('Error occurred')
     logging.critical('Critical error -- shutting down')

This produces the following output:

     WARNING:root:Warning:config file server.conf not found
     ERROR:root:Error occurred
     CRITICAL:root:Critical error -- shutting down

By default, informational and debugging messages are suppressed and the
output is sent to standard error.  Other output options include routing
messages through email, datagrams, sockets, or to an HTTP Server.  New
filters can select different routing based on message priority: ‘DEBUG’,
‘INFO’, ‘WARNING’, ‘ERROR’, and ‘CRITICAL’.

The logging system can be configured directly from Python or can be
loaded from a user editable configuration file for customized logging
without altering the application.


File: python.info,  Node: Weak References,  Next: Tools for Working with Lists,  Prev: Logging,  Up: Brief Tour of the Standard Library — Part II

2.11.6 Weak References
----------------------

Python does automatic memory management (reference counting for most
objects and *note garbage collection: fc8. to eliminate cycles).  The
memory is freed shortly after the last reference to it has been
eliminated.

This approach works fine for most applications but occasionally there is
a need to track objects only as long as they are being used by something
else.  Unfortunately, just tracking them creates a reference that makes
them permanent.  The *note weakref: 131. module provides tools for
tracking objects without creating a reference.  When the object is no
longer needed, it is automatically removed from a weakref table and a
callback is triggered for weakref objects.  Typical applications include
caching objects that are expensive to create:

     >>> import weakref, gc
     >>> class A:
     ...     def __init__(self, value):
     ...         self.value = value
     ...     def __repr__(self):
     ...         return str(self.value)
     ...
     >>> a = A(10)                   # create a reference
     >>> d = weakref.WeakValueDictionary()
     >>> d['primary'] = a            # does not create a reference
     >>> d['primary']                # fetch the object if it is still alive
     10
     >>> del a                       # remove the one reference
     >>> gc.collect()                # run garbage collection right away
     0
     >>> d['primary']                # entry was automatically removed
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
         d['primary']                # entry was automatically removed
       File "C:/python39/lib/weakref.py", line 46, in __getitem__
         o = self.data[key]()
     KeyError: 'primary'


File: python.info,  Node: Tools for Working with Lists,  Next: Decimal Floating Point Arithmetic,  Prev: Weak References,  Up: Brief Tour of the Standard Library — Part II

2.11.7 Tools for Working with Lists
-----------------------------------

Many data structure needs can be met with the built-in list type.
However, sometimes there is a need for alternative implementations with
different performance trade-offs.

The *note array: 6. module provides an *note array(): 216. object that
is like a list that stores only homogeneous data and stores it more
compactly.  The following example shows an array of numbers stored as
two byte unsigned binary numbers (typecode ‘"H"’) rather than the usual
16 bytes per entry for regular lists of Python int objects:

     >>> from array import array
     >>> a = array('H', [4000, 10, 700, 22222])
     >>> sum(a)
     26932
     >>> a[1:3]
     array('H', [10, 700])

The *note collections: 1d. module provides a *note deque(): 62b. object
that is like a list with faster appends and pops from the left side but
slower lookups in the middle.  These objects are well suited for
implementing queues and breadth first tree searches:

     >>> from collections import deque
     >>> d = deque(["task1", "task2", "task3"])
     >>> d.append("task4")
     >>> print("Handling", d.popleft())
     Handling task1

     unsearched = deque([starting_node])
     def breadth_first_search(unsearched):
         node = unsearched.popleft()
         for m in gen_moves(node):
             if is_goal(m):
                 return m
             unsearched.append(m)

In addition to alternative list implementations, the library also offers
other tools such as the *note bisect: 11. module with functions for
manipulating sorted lists:

     >>> import bisect
     >>> scores = [(100, 'perl'), (200, 'tcl'), (400, 'lua'), (500, 'python')]
     >>> bisect.insort(scores, (300, 'ruby'))
     >>> scores
     [(100, 'perl'), (200, 'tcl'), (300, 'ruby'), (400, 'lua'), (500, 'python')]

The *note heapq: 8d. module provides functions for implementing heaps
based on regular lists.  The lowest valued entry is always kept at
position zero.  This is useful for applications which repeatedly access
the smallest element but do not want to run a full list sort:

     >>> from heapq import heapify, heappop, heappush
     >>> data = [1, 3, 5, 7, 9, 2, 4, 6, 8, 0]
     >>> heapify(data)                      # rearrange the list into heap order
     >>> heappush(data, -5)                 # add a new entry
     >>> [heappop(data) for i in range(3)]  # fetch the three smallest entries
     [-5, 0, 1]


File: python.info,  Node: Decimal Floating Point Arithmetic,  Prev: Tools for Working with Lists,  Up: Brief Tour of the Standard Library — Part II

2.11.8 Decimal Floating Point Arithmetic
----------------------------------------

The *note decimal: 35. module offers a *note Decimal: 2c0. datatype for
decimal floating point arithmetic.  Compared to the built-in *note
float: 1fd. implementation of binary floating point, the class is
especially helpful for

   * financial applications and other uses which require exact decimal
     representation,

   * control over precision,

   * control over rounding to meet legal or regulatory requirements,

   * tracking of significant decimal places, or

   * applications where the user expects the results to match
     calculations done by hand.

For example, calculating a 5% tax on a 70 cent phone charge gives
different results in decimal floating point and binary floating point.
The difference becomes significant if the results are rounded to the
nearest cent:

     >>> from decimal import *
     >>> round(Decimal('0.70') * Decimal('1.05'), 2)
     Decimal('0.74')
     >>> round(.70 * 1.05, 2)
     0.73

The *note Decimal: 2c0. result keeps a trailing zero, automatically
inferring four place significance from multiplicands with two place
significance.  Decimal reproduces mathematics as done by hand and avoids
issues that can arise when binary floating point cannot exactly
represent decimal quantities.

Exact representation enables the *note Decimal: 2c0. class to perform
modulo calculations and equality tests that are unsuitable for binary
floating point:

     >>> Decimal('1.00') % Decimal('.10')
     Decimal('0.00')
     >>> 1.00 % 0.10
     0.09999999999999995

     >>> sum([Decimal('0.1')]*10) == Decimal('1.0')
     True
     >>> sum([0.1]*10) == 1.0
     False

The *note decimal: 35. module provides arithmetic with as much precision
as needed:

     >>> getcontext().prec = 36
     >>> Decimal(1) / Decimal(7)
     Decimal('0.142857142857142857142857142857142857')


File: python.info,  Node: Virtual Environments and Packages,  Next: What Now?,  Prev: Brief Tour of the Standard Library — Part II,  Up: The Python Tutorial

2.12 Virtual Environments and Packages
======================================

* Menu:

* Introduction: Introduction<4>.
* Creating Virtual Environments::
* Managing Packages with pip::


File: python.info,  Node: Introduction<4>,  Next: Creating Virtual Environments,  Up: Virtual Environments and Packages

2.12.1 Introduction
-------------------

Python applications will often use packages and modules that don’t come
as part of the standard library.  Applications will sometimes need a
specific version of a library, because the application may require that
a particular bug has been fixed or the application may be written using
an obsolete version of the library’s interface.

This means it may not be possible for one Python installation to meet
the requirements of every application.  If application A needs version
1.0 of a particular module but application B needs version 2.0, then the
requirements are in conflict and installing either version 1.0 or 2.0
will leave one application unable to run.

The solution for this problem is to create a *note virtual environment:
1446, a self-contained directory tree that contains a Python
installation for a particular version of Python, plus a number of
additional packages.

Different applications can then use different virtual environments.  To
resolve the earlier example of conflicting requirements, application A
can have its own virtual environment with version 1.0 installed while
application B has another virtual environment with version 2.0.  If
application B requires a library be upgraded to version 3.0, this will
not affect application A’s environment.


File: python.info,  Node: Creating Virtual Environments,  Next: Managing Packages with pip,  Prev: Introduction<4>,  Up: Virtual Environments and Packages

2.12.2 Creating Virtual Environments
------------------------------------

The module used to create and manage virtual environments is called
*note venv: 12e.  *note venv: 12e. will usually install the most recent
version of Python that you have available.  If you have multiple
versions of Python on your system, you can select a specific Python
version by running ‘python3’ or whichever version you want.

To create a virtual environment, decide upon a directory where you want
to place it, and run the *note venv: 12e. module as a script with the
directory path:

     python3 -m venv tutorial-env

This will create the ‘tutorial-env’ directory if it doesn’t exist, and
also create directories inside it containing a copy of the Python
interpreter, the standard library, and various supporting files.

A common directory location for a virtual environment is ‘.venv’.  This
name keeps the directory typically hidden in your shell and thus out of
the way while giving it a name that explains why the directory exists.
It also prevents clashing with ‘.env’ environment variable definition
files that some tooling supports.

Once you’ve created a virtual environment, you may activate it.

On Windows, run:

     tutorial-env\Scripts\activate.bat

On Unix or MacOS, run:

     source tutorial-env/bin/activate

(This script is written for the bash shell.  If you use the ‘csh’ or
‘fish’ shells, there are alternate ‘activate.csh’ and ‘activate.fish’
scripts you should use instead.)

Activating the virtual environment will change your shell’s prompt to
show what virtual environment you’re using, and modify the environment
so that running ‘python’ will get you that particular version and
installation of Python.  For example:

     $ source ~/envs/tutorial-env/bin/activate
     (tutorial-env) $ python
     Python 3.5.1 (default, May  6 2016, 10:59:36)
       ...
     >>> import sys
     >>> sys.path
     ['', '/usr/local/lib/python35.zip', ...,
     '~/envs/tutorial-env/lib/python3.5/site-packages']
     >>>


File: python.info,  Node: Managing Packages with pip,  Prev: Creating Virtual Environments,  Up: Virtual Environments and Packages

2.12.3 Managing Packages with pip
---------------------------------

You can install, upgrade, and remove packages using a program called
‘pip’.  By default ‘pip’ will install packages from the Python Package
Index, <‘https://pypi.org’>.  You can browse the Python Package Index by
going to it in your web browser.

‘pip’ has a number of subcommands: “install”, “uninstall”, “freeze”,
etc.  (Consult the *note Installing Python Modules: 8e2. guide for
complete documentation for ‘pip’.)

You can install the latest version of a package by specifying a
package’s name:

     (tutorial-env) $ python -m pip install novas
     Collecting novas
       Downloading novas-3.1.1.3.tar.gz (136kB)
     Installing collected packages: novas
       Running setup.py install for novas
     Successfully installed novas-3.1.1.3

You can also install a specific version of a package by giving the
package name followed by ‘==’ and the version number:

     (tutorial-env) $ python -m pip install requests==2.6.0
     Collecting requests==2.6.0
       Using cached requests-2.6.0-py2.py3-none-any.whl
     Installing collected packages: requests
     Successfully installed requests-2.6.0

If you re-run this command, ‘pip’ will notice that the requested version
is already installed and do nothing.  You can supply a different version
number to get that version, or you can run ‘pip install --upgrade’ to
upgrade the package to the latest version:

     (tutorial-env) $ python -m pip install --upgrade requests
     Collecting requests
     Installing collected packages: requests
       Found existing installation: requests 2.6.0
         Uninstalling requests-2.6.0:
           Successfully uninstalled requests-2.6.0
     Successfully installed requests-2.7.0

‘pip uninstall’ followed by one or more package names will remove the
packages from the virtual environment.

‘pip show’ will display information about a particular package:

     (tutorial-env) $ pip show requests
     ---
     Metadata-Version: 2.0
     Name: requests
     Version: 2.7.0
     Summary: Python HTTP for Humans.
     Home-page: http://python-requests.org
     Author: Kenneth Reitz
     Author-email: me@kennethreitz.com
     License: Apache 2.0
     Location: /Users/akuchling/envs/tutorial-env/lib/python3.4/site-packages
     Requires:

‘pip list’ will display all of the packages installed in the virtual
environment:

     (tutorial-env) $ pip list
     novas (3.1.1.3)
     numpy (1.9.2)
     pip (7.0.3)
     requests (2.7.0)
     setuptools (16.0)

‘pip freeze’ will produce a similar list of the installed packages, but
the output uses the format that ‘pip install’ expects.  A common
convention is to put this list in a ‘requirements.txt’ file:

     (tutorial-env) $ pip freeze > requirements.txt
     (tutorial-env) $ cat requirements.txt
     novas==3.1.1.3
     numpy==1.9.2
     requests==2.7.0

The ‘requirements.txt’ can then be committed to version control and
shipped as part of an application.  Users can then install all the
necessary packages with ‘install -r’:

     (tutorial-env) $ python -m pip install -r requirements.txt
     Collecting novas==3.1.1.3 (from -r requirements.txt (line 1))
       ...
     Collecting numpy==1.9.2 (from -r requirements.txt (line 2))
       ...
     Collecting requests==2.7.0 (from -r requirements.txt (line 3))
       ...
     Installing collected packages: novas, numpy, requests
       Running setup.py install for novas
     Successfully installed novas-3.1.1.3 numpy-1.9.2 requests-2.7.0

‘pip’ has many more options.  Consult the *note Installing Python
Modules: 8e2. guide for complete documentation for ‘pip’.  When you’ve
written a package and want to make it available on the Python Package
Index, consult the *note Distributing Python Modules: 8e3. guide.


File: python.info,  Node: What Now?,  Next: Interactive Input Editing and History Substitution,  Prev: Virtual Environments and Packages,  Up: The Python Tutorial

2.13 What Now?
==============

Reading this tutorial has probably reinforced your interest in using
Python — you should be eager to apply Python to solving your real-world
problems.  Where should you go to learn more?

This tutorial is part of Python’s documentation set.  Some other
documents in the set are:

   * *note The Python Standard Library: 1330.:

     You should browse through this manual, which gives complete (though
     terse) reference material about types, functions, and the modules
     in the standard library.  The standard Python distribution includes
     a `lot' of additional code.  There are modules to read Unix
     mailboxes, retrieve documents via HTTP, generate random numbers,
     parse command-line options, write CGI programs, compress data, and
     many other tasks.  Skimming through the Library Reference will give
     you an idea of what’s available.

   * *note Installing Python Modules: 8e2. explains how to install
     additional modules written by other Python users.

   * *note The Python Language Reference: 1331.: A detailed explanation
     of Python’s syntax and semantics.  It’s heavy reading, but is
     useful as a complete guide to the language itself.

More Python resources:

   * ‘https://www.python.org’: The major Python Web site.  It contains
     code, documentation, and pointers to Python-related pages around
     the Web.  This Web site is mirrored in various places around the
     world, such as Europe, Japan, and Australia; a mirror may be faster
     than the main site, depending on your geographical location.

   * ‘https://docs.python.org’: Fast access to Python’s documentation.

   * ‘https://pypi.org’: The Python Package Index, previously also
     nicknamed the Cheese Shop (1), is an index of user-created Python
     modules that are available for download.  Once you begin releasing
     code, you can register it here so that others can find it.

   * ‘https://code.activestate.com/recipes/langs/python/’: The Python
     Cookbook is a sizable collection of code examples, larger modules,
     and useful scripts.  Particularly notable contributions are
     collected in a book also titled Python Cookbook (O’Reilly &
     Associates, ISBN 0-596-00797-3.)

   * ‘http://www.pyvideo.org’ collects links to Python-related videos
     from conferences and user-group meetings.

   * ‘https://scipy.org’: The Scientific Python project includes modules
     for fast array computations and manipulations plus a host of
     packages for such things as linear algebra, Fourier transforms,
     non-linear solvers, random number distributions, statistical
     analysis and the like.

For Python-related questions and problem reports, you can post to the
newsgroup ‘comp.lang.python’, or send them to the mailing list at
<python-list@python.org>.  The newsgroup and mailing list are gatewayed,
so messages posted to one will automatically be forwarded to the other.
There are hundreds of postings a day, asking (and answering) questions,
suggesting new features, and announcing new modules.  Mailing list
archives are available at ‘https://mail.python.org/pipermail/’.

Before posting, be sure to check the list of *note Frequently Asked
Questions: 144c. (also called the FAQ). The FAQ answers many of the
questions that come up again and again, and may already contain the
solution for your problem.

   ---------- Footnotes ----------

   (1) (1) “Cheese Shop” is a Monty Python’s sketch: a customer enters a
cheese shop, but whatever cheese he asks for, the clerk says it’s
missing.


File: python.info,  Node: Interactive Input Editing and History Substitution,  Next: Floating Point Arithmetic Issues and Limitations,  Prev: What Now?,  Up: The Python Tutorial

2.14 Interactive Input Editing and History Substitution
=======================================================

Some versions of the Python interpreter support editing of the current
input line and history substitution, similar to facilities found in the
Korn shell and the GNU Bash shell.  This is implemented using the GNU
Readline(1) library, which supports various styles of editing.  This
library has its own documentation which we won’t duplicate here.

* Menu:

* Tab Completion and History Editing::
* Alternatives to the Interactive Interpreter::

   ---------- Footnotes ----------

   (1) https://tiswww.case.edu/php/chet/readline/rltop.html


File: python.info,  Node: Tab Completion and History Editing,  Next: Alternatives to the Interactive Interpreter,  Up: Interactive Input Editing and History Substitution

2.14.1 Tab Completion and History Editing
-----------------------------------------

Completion of variable and module names is *note automatically enabled:
9cc. at interpreter startup so that the ‘Tab’ key invokes the completion
function; it looks at Python statement names, the current local
variables, and the available module names.  For dotted expressions such
as ‘string.a’, it will evaluate the expression up to the final ‘'.'’ and
then suggest completions from the attributes of the resulting object.
Note that this may execute application-defined code if an object with a
*note __getattr__(): 42a. method is part of the expression.  The default
configuration also saves your history into a file named
‘.python_history’ in your user directory.  The history will be available
again during the next interactive interpreter session.


File: python.info,  Node: Alternatives to the Interactive Interpreter,  Prev: Tab Completion and History Editing,  Up: Interactive Input Editing and History Substitution

2.14.2 Alternatives to the Interactive Interpreter
--------------------------------------------------

This facility is an enormous step forward compared to earlier versions
of the interpreter; however, some wishes are left: It would be nice if
the proper indentation were suggested on continuation lines (the parser
knows if an indent token is required next).  The completion mechanism
might use the interpreter’s symbol table.  A command to check (or even
suggest) matching parentheses, quotes, etc., would also be useful.

One alternative enhanced interactive interpreter that has been around
for quite some time is IPython(1), which features tab completion, object
exploration and advanced history management.  It can also be thoroughly
customized and embedded into other applications.  Another similar
enhanced interactive environment is bpython(2).

   ---------- Footnotes ----------

   (1) https://ipython.org/

   (2) https://www.bpython-interpreter.org/


File: python.info,  Node: Floating Point Arithmetic Issues and Limitations,  Next: Appendix,  Prev: Interactive Input Editing and History Substitution,  Up: The Python Tutorial

2.15 Floating Point Arithmetic: Issues and Limitations
======================================================

Floating-point numbers are represented in computer hardware as base 2
(binary) fractions.  For example, the decimal fraction

     0.125

has value 1/10 + 2/100 + 5/1000, and in the same way the binary fraction

     0.001

has value 0/2 + 0/4 + 1/8.  These two fractions have identical values,
the only real difference being that the first is written in base 10
fractional notation, and the second in base 2.

Unfortunately, most decimal fractions cannot be represented exactly as
binary fractions.  A consequence is that, in general, the decimal
floating-point numbers you enter are only approximated by the binary
floating-point numbers actually stored in the machine.

The problem is easier to understand at first in base 10.  Consider the
fraction 1/3.  You can approximate that as a base 10 fraction:

     0.3

or, better,

     0.33

or, better,

     0.333

and so on.  No matter how many digits you’re willing to write down, the
result will never be exactly 1/3, but will be an increasingly better
approximation of 1/3.

In the same way, no matter how many base 2 digits you’re willing to use,
the decimal value 0.1 cannot be represented exactly as a base 2
fraction.  In base 2, 1/10 is the infinitely repeating fraction

     0.0001100110011001100110011001100110011001100110011...

Stop at any finite number of bits, and you get an approximation.  On
most machines today, floats are approximated using a binary fraction
with the numerator using the first 53 bits starting with the most
significant bit and with the denominator as a power of two.  In the case
of 1/10, the binary fraction is ‘3602879701896397 / 2 ** 55’ which is
close to but not exactly equal to the true value of 1/10.

Many users are not aware of the approximation because of the way values
are displayed.  Python only prints a decimal approximation to the true
decimal value of the binary approximation stored by the machine.  On
most machines, if Python were to print the true decimal value of the
binary approximation stored for 0.1, it would have to display

     >>> 0.1
     0.1000000000000000055511151231257827021181583404541015625

That is more digits than most people find useful, so Python keeps the
number of digits manageable by displaying a rounded value instead

     >>> 1 / 10
     0.1

Just remember, even though the printed result looks like the exact value
of 1/10, the actual stored value is the nearest representable binary
fraction.

Interestingly, there are many different decimal numbers that share the
same nearest approximate binary fraction.  For example, the numbers
‘0.1’ and ‘0.10000000000000001’ and
‘0.1000000000000000055511151231257827021181583404541015625’ are all
approximated by ‘3602879701896397 / 2 ** 55’.  Since all of these
decimal values share the same approximation, any one of them could be
displayed while still preserving the invariant ‘eval(repr(x)) == x’.

Historically, the Python prompt and built-in *note repr(): 8b9. function
would choose the one with 17 significant digits, ‘0.10000000000000001’.
Starting with Python 3.1, Python (on most systems) is now able to choose
the shortest of these and simply display ‘0.1’.

Note that this is in the very nature of binary floating-point: this is
not a bug in Python, and it is not a bug in your code either.  You’ll
see the same kind of thing in all languages that support your hardware’s
floating-point arithmetic (although some languages may not `display' the
difference by default, or in all output modes).

For more pleasant output, you may wish to use string formatting to
produce a limited number of significant digits:

     >>> format(math.pi, '.12g')  # give 12 significant digits
     '3.14159265359'

     >>> format(math.pi, '.2f')   # give 2 digits after the point
     '3.14'

     >>> repr(math.pi)
     '3.141592653589793'

It’s important to realize that this is, in a real sense, an illusion:
you’re simply rounding the `display' of the true machine value.

One illusion may beget another.  For example, since 0.1 is not exactly
1/10, summing three values of 0.1 may not yield exactly 0.3, either:

     >>> .1 + .1 + .1 == .3
     False

Also, since the 0.1 cannot get any closer to the exact value of 1/10 and
0.3 cannot get any closer to the exact value of 3/10, then pre-rounding
with *note round(): d35. function cannot help:

     >>> round(.1, 1) + round(.1, 1) + round(.1, 1) == round(.3, 1)
     False

Though the numbers cannot be made closer to their intended exact values,
the *note round(): d35. function can be useful for post-rounding so that
results with inexact values become comparable to one another:

     >>> round(.1 + .1 + .1, 10) == round(.3, 10)
     True

Binary floating-point arithmetic holds many surprises like this.  The
problem with “0.1” is explained in precise detail below, in the
“Representation Error” section.  See The Perils of Floating Point(1) for
a more complete account of other common surprises.

As that says near the end, “there are no easy answers.” Still, don’t be
unduly wary of floating-point!  The errors in Python float operations
are inherited from the floating-point hardware, and on most machines are
on the order of no more than 1 part in 2**53 per operation.  That’s more
than adequate for most tasks, but you do need to keep in mind that it’s
not decimal arithmetic and that every float operation can suffer a new
rounding error.

While pathological cases do exist, for most casual use of floating-point
arithmetic you’ll see the result you expect in the end if you simply
round the display of your final results to the number of decimal digits
you expect.  *note str(): 205. usually suffices, and for finer control
see the *note str.format(): 5d5. method’s format specifiers in *note
Format String Syntax: de0.

For use cases which require exact decimal representation, try using the
*note decimal: 35. module which implements decimal arithmetic suitable
for accounting applications and high-precision applications.

Another form of exact arithmetic is supported by the *note fractions:
81. module which implements arithmetic based on rational numbers (so the
numbers like 1/3 can be represented exactly).

If you are a heavy user of floating point operations you should take a
look at the NumPy package and many other packages for mathematical and
statistical operations supplied by the SciPy project.  See
<‘https://scipy.org’>.

Python provides tools that may help on those rare occasions when you
really `do' want to know the exact value of a float.  The *note
float.as_integer_ratio(): 1457. method expresses the value of a float as
a fraction:

     >>> x = 3.14159
     >>> x.as_integer_ratio()
     (3537115888337719, 1125899906842624)

Since the ratio is exact, it can be used to losslessly recreate the
original value:

     >>> x == 3537115888337719 / 1125899906842624
     True

The *note float.hex(): 1458. method expresses a float in hexadecimal
(base 16), again giving the exact value stored by your computer:

     >>> x.hex()
     '0x1.921f9f01b866ep+1'

This precise hexadecimal representation can be used to reconstruct the
float value exactly:

     >>> x == float.fromhex('0x1.921f9f01b866ep+1')
     True

Since the representation is exact, it is useful for reliably porting
values across different versions of Python (platform independence) and
exchanging data with other languages that support the same format (such
as Java and C99).

Another helpful tool is the *note math.fsum(): e04. function which helps
mitigate loss-of-precision during summation.  It tracks “lost digits” as
values are added onto a running total.  That can make a difference in
overall accuracy so that the errors do not accumulate to the point where
they affect the final total:

     >>> sum([0.1] * 10) == 1.0
     False
     >>> math.fsum([0.1] * 10) == 1.0
     True

* Menu:

* Representation Error::

   ---------- Footnotes ----------

   (1) https://www.lahey.com/float.htm


File: python.info,  Node: Representation Error,  Up: Floating Point Arithmetic Issues and Limitations

2.15.1 Representation Error
---------------------------

This section explains the “0.1” example in detail, and shows how you can
perform an exact analysis of cases like this yourself.  Basic
familiarity with binary floating-point representation is assumed.

`Representation error' refers to the fact that some (most, actually)
decimal fractions cannot be represented exactly as binary (base 2)
fractions.  This is the chief reason why Python (or Perl, C, C++, Java,
Fortran, and many others) often won’t display the exact decimal number
you expect.

Why is that?  1/10 is not exactly representable as a binary fraction.
Almost all machines today (November 2000) use IEEE-754 floating point
arithmetic, and almost all platforms map Python floats to IEEE-754
“double precision”.  754 doubles contain 53 bits of precision, so on
input the computer strives to convert 0.1 to the closest fraction it can
of the form `J'/2**`N' where `J' is an integer containing exactly 53
bits.  Rewriting

     1 / 10 ~= J / (2**N)

as

     J ~= 2**N / 10

and recalling that `J' has exactly 53 bits (is ‘>= 2**52’ but ‘<
2**53’), the best value for `N' is 56:

     >>> 2**52 <=  2**56 // 10  < 2**53
     True

That is, 56 is the only value for `N' that leaves `J' with exactly 53
bits.  The best possible value for `J' is then that quotient rounded:

     >>> q, r = divmod(2**56, 10)
     >>> r
     6

Since the remainder is more than half of 10, the best approximation is
obtained by rounding up:

     >>> q+1
     7205759403792794

Therefore the best possible approximation to 1/10 in 754 double
precision is:

     7205759403792794 / 2 ** 56

Dividing both the numerator and denominator by two reduces the fraction
to:

     3602879701896397 / 2 ** 55

Note that since we rounded up, this is actually a little bit larger than
1/10; if we had not rounded up, the quotient would have been a little
bit smaller than 1/10.  But in no case can it be `exactly' 1/10!

So the computer never “sees” 1/10: what it sees is the exact fraction
given above, the best 754 double approximation it can get:

     >>> 0.1 * 2 ** 55
     3602879701896397.0

If we multiply that fraction by 10**55, we can see the value out to 55
decimal digits:

     >>> 3602879701896397 * 10 ** 55 // 2 ** 55
     1000000000000000055511151231257827021181583404541015625

meaning that the exact number stored in the computer is equal to the
decimal value 0.1000000000000000055511151231257827021181583404541015625.
Instead of displaying the full decimal value, many languages (including
older versions of Python), round the result to 17 significant digits:

     >>> format(0.1, '.17f')
     '0.10000000000000001'

The *note fractions: 81. and *note decimal: 35. modules make these
calculations easy:

     >>> from decimal import Decimal
     >>> from fractions import Fraction

     >>> Fraction.from_float(0.1)
     Fraction(3602879701896397, 36028797018963968)

     >>> (0.1).as_integer_ratio()
     (3602879701896397, 36028797018963968)

     >>> Decimal.from_float(0.1)
     Decimal('0.1000000000000000055511151231257827021181583404541015625')

     >>> format(Decimal.from_float(0.1), '.17')
     '0.10000000000000001'


File: python.info,  Node: Appendix,  Prev: Floating Point Arithmetic Issues and Limitations,  Up: The Python Tutorial

2.16 Appendix
=============

* Menu:

* Interactive Mode: Interactive Mode<2>.


File: python.info,  Node: Interactive Mode<2>,  Up: Appendix

2.16.1 Interactive Mode
-----------------------

* Menu:

* Error Handling::
* Executable Python Scripts::
* The Interactive Startup File::
* The Customization Modules::


File: python.info,  Node: Error Handling,  Next: Executable Python Scripts,  Up: Interactive Mode<2>

2.16.1.1 Error Handling
.......................

When an error occurs, the interpreter prints an error message and a
stack trace.  In interactive mode, it then returns to the primary
prompt; when input came from a file, it exits with a nonzero exit status
after printing the stack trace.  (Exceptions handled by an *note except:
c10. clause in a *note try: e37. statement are not errors in this
context.)  Some errors are unconditionally fatal and cause an exit with
a nonzero exit; this applies to internal inconsistencies and some cases
of running out of memory.  All error messages are written to the
standard error stream; normal output from executed commands is written
to standard output.

Typing the interrupt character (usually ‘Control-C’ or ‘Delete’) to the
primary or secondary prompt cancels the input and returns to the primary
prompt.  (1) Typing an interrupt while a command is executing raises the
*note KeyboardInterrupt: 2cc. exception, which may be handled by a *note
try: e37. statement.

   ---------- Footnotes ----------

   (1) (1) A problem with the GNU Readline package may prevent this.


File: python.info,  Node: Executable Python Scripts,  Next: The Interactive Startup File,  Prev: Error Handling,  Up: Interactive Mode<2>

2.16.1.2 Executable Python Scripts
..................................

On BSD’ish Unix systems, Python scripts can be made directly executable,
like shell scripts, by putting the line

     #!/usr/bin/env python3.5

(assuming that the interpreter is on the user’s ‘PATH’) at the beginning
of the script and giving the file an executable mode.  The ‘#!’ must be
the first two characters of the file.  On some platforms, this first
line must end with a Unix-style line ending (‘'\n'’), not a Windows
(‘'\r\n'’) line ending.  Note that the hash, or pound, character, ‘'#'’,
is used to start a comment in Python.

The script can be given an executable mode, or permission, using the
‘chmod’ command.

     $ chmod +x myscript.py

On Windows systems, there is no notion of an “executable mode”.  The
Python installer automatically associates ‘.py’ files with ‘python.exe’
so that a double-click on a Python file will run it as a script.  The
extension can also be ‘.pyw’, in that case, the console window that
normally appears is suppressed.


File: python.info,  Node: The Interactive Startup File,  Next: The Customization Modules,  Prev: Executable Python Scripts,  Up: Interactive Mode<2>

2.16.1.3 The Interactive Startup File
.....................................

When you use Python interactively, it is frequently handy to have some
standard commands executed every time the interpreter is started.  You
can do this by setting an environment variable named *note
PYTHONSTARTUP: 9cb. to the name of a file containing your start-up
commands.  This is similar to the ‘.profile’ feature of the Unix shells.

This file is only read in interactive sessions, not when Python reads
commands from a script, and not when ‘/dev/tty’ is given as the explicit
source of commands (which otherwise behaves like an interactive
session).  It is executed in the same namespace where interactive
commands are executed, so that objects that it defines or imports can be
used without qualification in the interactive session.  You can also
change the prompts ‘sys.ps1’ and ‘sys.ps2’ in this file.

If you want to read an additional start-up file from the current
directory, you can program this in the global start-up file using code
like ‘if os.path.isfile('.pythonrc.py'):
exec(open('.pythonrc.py').read())’.  If you want to use the startup file
in a script, you must do this explicitly in the script:

     import os
     filename = os.environ.get('PYTHONSTARTUP')
     if filename and os.path.isfile(filename):
         with open(filename) as fobj:
             startup_file = fobj.read()
         exec(startup_file)


File: python.info,  Node: The Customization Modules,  Prev: The Interactive Startup File,  Up: Interactive Mode<2>

2.16.1.4 The Customization Modules
..................................

Python provides two hooks to let you customize it: ‘sitecustomize’ and
‘usercustomize’.  To see how it works, you need first to find the
location of your user site-packages directory.  Start Python and run
this code:

     >>> import site
     >>> site.getusersitepackages()
     '/home/user/.local/lib/python3.5/site-packages'

Now you can create a file named ‘usercustomize.py’ in that directory and
put anything you want in it.  It will affect every invocation of Python,
unless it is started with the *note -s: ddb. option to disable the
automatic import.

‘sitecustomize’ works in the same way, but is typically created by an
administrator of the computer in the global site-packages directory, and
is imported before ‘usercustomize’.  See the documentation of the *note
site: eb. module for more details.


File: python.info,  Node: Python Setup and Usage,  Next: The Python Language Reference,  Prev: The Python Tutorial,  Up: Top

3 Python Setup and Usage
************************

This part of the documentation is devoted to general information on the
setup of the Python environment on different platforms, the invocation
of the interpreter and things that make working with Python easier.

* Menu:

* Command line and environment::
* Using Python on Unix platforms::
* Using Python on Windows::
* Using Python on a Mac::
* Editors and IDEs::


File: python.info,  Node: Command line and environment,  Next: Using Python on Unix platforms,  Up: Python Setup and Usage

3.1 Command line and environment
================================

The CPython interpreter scans the command line and the environment for
various settings.

`CPython implementation detail:' Other implementations’ command line
schemes may differ.  See *note Alternate Implementations: 146b. for
further resources.

* Menu:

* Command line::
* Environment variables::


File: python.info,  Node: Command line,  Next: Environment variables,  Up: Command line and environment

3.1.1 Command line
------------------

When invoking Python, you may specify any of these options:

     python [-bBdEhiIOqsSuvVWx?] [-c command | -m module-name | script | - ] [args]

The most common use case is, of course, a simple invocation of a script:

     python myscript.py

* Menu:

* Interface options::
* Generic options::
* Miscellaneous options::
* Options you shouldn’t use::


File: python.info,  Node: Interface options,  Next: Generic options,  Up: Command line

3.1.1.1 Interface options
.........................

The interpreter interface resembles that of the UNIX shell, but provides
some additional methods of invocation:

   * When called with standard input connected to a tty device, it
     prompts for commands and executes them until an EOF (an end-of-file
     character, you can produce that with ‘Ctrl-D’ on UNIX or ‘Ctrl-Z,
     Enter’ on Windows) is read.

   * When called with a file name argument or with a file as standard
     input, it reads and executes a script from that file.

   * When called with a directory name argument, it reads and executes
     an appropriately named script from that directory.

   * When called with ‘-c command’, it executes the Python statement(s)
     given as `command'.  Here `command' may contain multiple statements
     separated by newlines.  Leading whitespace is significant in Python
     statements!

   * When called with ‘-m module-name’, the given module is located on
     the Python module path and executed as a script.

In non-interactive mode, the entire input is parsed before it is
executed.

An interface option terminates the list of options consumed by the
interpreter, all consecutive arguments will end up in *note sys.argv:
cc6. – note that the first element, subscript zero (‘sys.argv[0]’), is a
string reflecting the program’s source.

 -- Program Option: -c <command>

     Execute the Python code in `command'.  `command' can be one or more
     statements separated by newlines, with significant leading
     whitespace as in normal module code.

     If this option is given, the first element of *note sys.argv: cc6.
     will be ‘"-c"’ and the current directory will be added to the start
     of *note sys.path: 260. (allowing modules in that directory to be
     imported as top level modules).

     Raises an *note auditing event: fa1. ‘cpython.run_command’ with
     argument ‘command’.

 -- Program Option: -m <module-name>

     Search *note sys.path: 260. for the named module and execute its
     contents as the *note __main__: 1. module.

     Since the argument is a `module' name, you must not give a file
     extension (‘.py’).  The module name should be a valid absolute
     Python module name, but the implementation may not always enforce
     this (e.g.  it may allow you to use a name that includes a hyphen).

     Package names (including namespace packages) are also permitted.
     When a package name is supplied instead of a normal module, the
     interpreter will execute ‘<pkg>.__main__’ as the main module.  This
     behaviour is deliberately similar to the handling of directories
     and zipfiles that are passed to the interpreter as the script
     argument.

          Note: This option cannot be used with built-in modules and
          extension modules written in C, since they do not have Python
          module files.  However, it can still be used for precompiled
          modules, even if the original source file is not available.

     If this option is given, the first element of *note sys.argv: cc6.
     will be the full path to the module file (while the module file is
     being located, the first element will be set to ‘"-m"’).  As with
     the *note -c: 1340. option, the current directory will be added to
     the start of *note sys.path: 260.

     *note -I: 232. option can be used to run the script in isolated
     mode where *note sys.path: 260. contains neither the current
     directory nor the user’s site-packages directory.  All ‘PYTHON*’
     environment variables are ignored, too.

     Many standard library modules contain code that is invoked on their
     execution as a script.  An example is the *note timeit: 10d.
     module:

          python -m timeit -s 'setup here' 'benchmarked code here'
          python -m timeit -h # for details

     Raises an *note auditing event: fa1. ‘cpython.run_module’ with
     argument ‘module-name’.

     See also
     ........

     *note runpy.run_module(): 146f.

          Equivalent functionality directly available to Python code

     PEP 338(1) – Executing modules as scripts

     Changed in version 3.1: Supply the package name to run a ‘__main__’
     submodule.

     Changed in version 3.4: namespace packages are also supported

 -- Describe: -

     Read commands from standard input (*note sys.stdin: 41e.).  If
     standard input is a terminal, *note -i: ee1. is implied.

     If this option is given, the first element of *note sys.argv: cc6.
     will be ‘"-"’ and the current directory will be added to the start
     of *note sys.path: 260.

     Raises an *note auditing event: fa1. ‘cpython.run_stdin’ with no
     arguments.

 -- Describe: <script>

     Execute the Python code contained in `script', which must be a
     filesystem path (absolute or relative) referring to either a Python
     file, a directory containing a ‘__main__.py’ file, or a zipfile
     containing a ‘__main__.py’ file.

     If this option is given, the first element of *note sys.argv: cc6.
     will be the script name as given on the command line.

     If the script name refers directly to a Python file, the directory
     containing that file is added to the start of *note sys.path: 260,
     and the file is executed as the *note __main__: 1. module.

     If the script name refers to a directory or zipfile, the script
     name is added to the start of *note sys.path: 260. and the
     ‘__main__.py’ file in that location is executed as the *note
     __main__: 1. module.

     *note -I: 232. option can be used to run the script in isolated
     mode where *note sys.path: 260. contains neither the script’s
     directory nor the user’s site-packages directory.  All ‘PYTHON*’
     environment variables are ignored, too.

     Raises an *note auditing event: fa1. ‘cpython.run_file’ with
     argument ‘filename’.

     See also
     ........

     *note runpy.run_path(): d79.

          Equivalent functionality directly available to Python code

If no interface option is given, *note -i: ee1. is implied,
‘sys.argv[0]’ is an empty string (‘""’) and the current directory will
be added to the start of *note sys.path: 260.  Also, tab-completion and
history editing is automatically enabled, if available on your platform
(see *note Readline configuration: 9cc.).

See also
........

*note Invoking the Interpreter: 133c.

Changed in version 3.4: Automatic enabling of tab-completion and history
editing.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0338


File: python.info,  Node: Generic options,  Next: Miscellaneous options,  Prev: Interface options,  Up: Command line

3.1.1.2 Generic options
.......................

 -- Program Option: -?
 -- Program Option: -h
 -- Program Option: --help

     Print a short description of all command line options.

 -- Program Option: -V
 -- Program Option: --version

     Print the Python version number and exit.  Example output could be:

          Python 3.8.0b2+

     When given twice, print more information about the build, like:

          Python 3.8.0b2+ (3.8:0c076caaa8, Apr 20 2019, 21:55:00)
          [GCC 6.2.0 20161005]

     New in version 3.6: The ‘-VV’ option.


File: python.info,  Node: Miscellaneous options,  Next: Options you shouldn’t use,  Prev: Generic options,  Up: Command line

3.1.1.3 Miscellaneous options
.............................

 -- Program Option: -b

     Issue a warning when comparing *note bytes: 172. or *note
     bytearray: 173. with *note str: 205. or *note bytes: 172. with
     *note int: 204.  Issue an error when the option is given twice
     (‘-bb’).

     Changed in version 3.5: Affects comparisons of *note bytes: 172.
     with *note int: 204.

 -- Program Option: -B

     If given, Python won’t try to write ‘.pyc’ files on the import of
     source modules.  See also *note PYTHONDONTWRITEBYTECODE: dff.

 -- Program Option: --check-hash-based-pycs default|always|never

     Control the validation behavior of hash-based ‘.pyc’ files.  See
     *note Cached bytecode invalidation: 439.  When set to ‘default’,
     checked and unchecked hash-based bytecode cache files are validated
     according to their default semantics.  When set to ‘always’, all
     hash-based ‘.pyc’ files, whether checked or unchecked, are
     validated against their corresponding source file.  When set to
     ‘never’, hash-based ‘.pyc’ files are not validated against their
     corresponding source files.

     The semantics of timestamp-based ‘.pyc’ files are unaffected by
     this option.

 -- Program Option: -d

     Turn on parser debugging output (for expert only, depending on
     compilation options).  See also *note PYTHONDEBUG: 1477.

 -- Program Option: -E

     Ignore all ‘PYTHON*’ environment variables, e.g.  *note PYTHONPATH:
     a34. and *note PYTHONHOME: 5d1, that might be set.

 -- Program Option: -i

     When a script is passed as first argument or the *note -c: 1340.
     option is used, enter interactive mode after executing the script
     or the command, even when *note sys.stdin: 41e. does not appear to
     be a terminal.  The *note PYTHONSTARTUP: 9cb. file is not read.

     This can be useful to inspect global variables or a stack trace
     when a script raises an exception.  See also *note PYTHONINSPECT:
     ee0.

 -- Program Option: -I

     Run Python in isolated mode.  This also implies -E and -s.  In
     isolated mode *note sys.path: 260. contains neither the script’s
     directory nor the user’s site-packages directory.  All ‘PYTHON*’
     environment variables are ignored, too.  Further restrictions may
     be imposed to prevent the user from injecting malicious code.

     New in version 3.4.

 -- Program Option: -O

     Remove assert statements and any code conditional on the value of
     *note __debug__: 1137.  Augment the filename for compiled (*note
     bytecode: 709.) files by adding ‘.opt-1’ before the ‘.pyc’
     extension (see PEP 488(1)).  See also *note PYTHONOPTIMIZE: 1478.

     Changed in version 3.5: Modify ‘.pyc’ filenames according to PEP
     488(2).

 -- Program Option: -OO

     Do *note -O: 77e. and also discard docstrings.  Augment the
     filename for compiled (*note bytecode: 709.) files by adding
     ‘.opt-2’ before the ‘.pyc’ extension (see PEP 488(3)).

     Changed in version 3.5: Modify ‘.pyc’ filenames according to PEP
     488(4).

 -- Program Option: -q

     Don’t display the copyright and version messages even in
     interactive mode.

     New in version 3.2.

 -- Program Option: -R

     Turn on hash randomization.  This option only has an effect if the
     *note PYTHONHASHSEED: aa4. environment variable is set to ‘0’,
     since hash randomization is enabled by default.

     On previous versions of Python, this option turns on hash
     randomization, so that the *note __hash__(): 44c. values of str and
     bytes objects are “salted” with an unpredictable random value.
     Although they remain constant within an individual Python process,
     they are not predictable between repeated invocations of Python.

     Hash randomization is intended to provide protection against a
     denial-of-service caused by carefully-chosen inputs that exploit
     the worst case performance of a dict construction, O(n^2)
     complexity.  See
     ‘http://www.ocert.org/advisories/ocert-2011-003.html’ for details.

     *note PYTHONHASHSEED: aa4. allows you to set a fixed value for the
     hash seed secret.

     Changed in version 3.7: The option is no longer ignored.

     New in version 3.2.3.

 -- Program Option: -s

     Don’t add the *note user site-packages directory: 147a. to *note
     sys.path: 260.

     See also
     ........

     PEP 370(5) – Per user site-packages directory

 -- Program Option: -S

     Disable the import of the module *note site: eb. and the
     site-dependent manipulations of *note sys.path: 260. that it
     entails.  Also disable these manipulations if *note site: eb. is
     explicitly imported later (call *note site.main(): 147b. if you
     want them to be triggered).

 -- Program Option: -u

     Force the stdout and stderr streams to be unbuffered.  This option
     has no effect on the stdin stream.

     See also *note PYTHONUNBUFFERED: 109e.

     Changed in version 3.7: The text layer of the stdout and stderr
     streams now is unbuffered.

 -- Program Option: -v

     Print a message each time a module is initialized, showing the
     place (filename or built-in module) from which it is loaded.  When
     given twice (‘-vv’), print a message for each file that is checked
     for when searching for a module.  Also provides information on
     module cleanup at exit.  See also *note PYTHONVERBOSE: 147c.
 -- Program Option: -W arg

     Warning control.  Python’s warning machinery by default prints
     warning messages to *note sys.stderr: 1ea.  A typical warning
     message has the following form:

          file:line: category: message

     By default, each warning is printed once for each source line where
     it occurs.  This option controls how often warnings are printed.

     Multiple *note -W: 15b. options may be given; when a warning
     matches more than one option, the action for the last matching
     option is performed.  Invalid *note -W: 15b. options are ignored
     (though, a warning message is printed about invalid options when
     the first warning is issued).

     Warnings can also be controlled using the *note PYTHONWARNINGS:
     51c. environment variable and from within a Python program using
     the *note warnings: 12f. module.

     The simplest settings apply a particular action unconditionally to
     all warnings emitted by a process (even those that are otherwise
     ignored by default):

          -Wdefault  # Warn once per call location
          -Werror    # Convert to exceptions
          -Walways   # Warn every time
          -Wmodule   # Warn once per calling module
          -Wonce     # Warn once per Python process
          -Wignore   # Never warn

     The action names can be abbreviated as desired (e.g.  ‘-Wi’, ‘-Wd’,
     ‘-Wa’, ‘-We’) and the interpreter will resolve them to the
     appropriate action name.

     See *note The Warnings Filter: 15d. and *note Describing Warning
     Filters: 147e. for more details.

 -- Program Option: -x

     Skip the first line of the source, allowing use of non-Unix forms
     of ‘#!cmd’.  This is intended for a DOS specific hack only.

 -- Program Option: -X

     Reserved for various implementation-specific options.  CPython
     currently defines the following possible values:

        * ‘-X faulthandler’ to enable *note faulthandler: 7b.;

        * ‘-X oldparser’: enable the traditional LL(1) parser.  See also
          *note PYTHONOLDPARSER: 1480. and PEP 617(6).

        * ‘-X showrefcount’ to output the total reference count and
          number of used memory blocks when the program finishes or
          after each statement in the interactive interpreter.  This
          only works on debug builds.

        * ‘-X tracemalloc’ to start tracing Python memory allocations
          using the *note tracemalloc: 11d. module.  By default, only
          the most recent frame is stored in a traceback of a trace.
          Use ‘-X tracemalloc=NFRAME’ to start tracing with a traceback
          limit of `NFRAME' frames.  See the *note tracemalloc.start():
          1481. for more information.

        * ‘-X importtime’ to show how long each import takes.  It shows
          module name, cumulative time (including nested imports) and
          self time (excluding nested imports).  Note that its output
          may be broken in multi-threaded application.  Typical usage is
          ‘python3 -X importtime -c 'import asyncio'’.  See also *note
          PYTHONPROFILEIMPORTTIME: 444.

        * ‘-X dev’: enable *note Python Development Mode: 160,
          introducing additional runtime checks that are too expensive
          to be enabled by default.

        * ‘-X utf8’ enables UTF-8 mode for operating system interfaces,
          overriding the default locale-aware mode.  ‘-X utf8=0’
          explicitly disables UTF-8 mode (even when it would otherwise
          activate automatically).  See *note PYTHONUTF8: 421. for more
          details.

        * ‘-X pycache_prefix=PATH’ enables writing ‘.pyc’ files to a
          parallel tree rooted at the given directory instead of to the
          code tree.  See also *note PYTHONPYCACHEPREFIX: 28f.

     It also allows passing arbitrary values and retrieving them through
     the *note sys._xoptions: 1482. dictionary.

     Changed in version 3.2: The *note -X: 290. option was added.

     New in version 3.3: The ‘-X faulthandler’ option.

     New in version 3.4: The ‘-X showrefcount’ and ‘-X tracemalloc’
     options.

     New in version 3.6: The ‘-X showalloccount’ option.

     New in version 3.7: The ‘-X importtime’, ‘-X dev’ and ‘-X utf8’
     options.

     New in version 3.8: The ‘-X pycache_prefix’ option.  The ‘-X dev’
     option now logs ‘close()’ exceptions in *note io.IOBase: 30c.
     destructor.

     Changed in version 3.9: Using ‘-X dev’ option, check `encoding' and
     `errors' arguments on string encoding and decoding operations.

     The ‘-X showalloccount’ option has been removed.

     Deprecated since version 3.9, will be removed in version 3.10: The
     ‘-X oldparser’ option.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0488

   (2) https://www.python.org/dev/peps/pep-0488

   (3) https://www.python.org/dev/peps/pep-0488

   (4) https://www.python.org/dev/peps/pep-0488

   (5) https://www.python.org/dev/peps/pep-0370

   (6) https://www.python.org/dev/peps/pep-0617


File: python.info,  Node: Options you shouldn’t use,  Prev: Miscellaneous options,  Up: Command line

3.1.1.4 Options you shouldn’t use
.................................

 -- Program Option: -J

     Reserved for use by Jython(1).

   ---------- Footnotes ----------

   (1) http://www.jython.org/


File: python.info,  Node: Environment variables,  Prev: Command line,  Up: Command line and environment

3.1.2 Environment variables
---------------------------

These environment variables influence Python’s behavior, they are
processed before the command-line switches other than -E or -I. It is
customary that command-line switches override environmental variables
where there is a conflict.

 -- Environment Variable: PYTHONHOME

     Change the location of the standard Python libraries.  By default,
     the libraries are searched in ‘`prefix'/lib/python`version'’ and
     ‘`exec_prefix'/lib/python`version'’, where ‘`prefix'’ and
     ‘`exec_prefix'’ are installation-dependent directories, both
     defaulting to ‘/usr/local’.

     When *note PYTHONHOME: 5d1. is set to a single directory, its value
     replaces both ‘`prefix'’ and ‘`exec_prefix'’.  To specify different
     values for these, set *note PYTHONHOME: 5d1. to
     ‘`prefix':`exec_prefix'’.

 -- Environment Variable: PYTHONPATH

     Augment the default search path for module files.  The format is
     the same as the shell’s ‘PATH’: one or more directory pathnames
     separated by *note os.pathsep: 1486. (e.g.  colons on Unix or
     semicolons on Windows).  Non-existent directories are silently
     ignored.

     In addition to normal directories, individual *note PYTHONPATH:
     a34. entries may refer to zipfiles containing pure Python modules
     (in either source or compiled form).  Extension modules cannot be
     imported from zipfiles.

     The default search path is installation dependent, but generally
     begins with ‘`prefix'/lib/python`version'’ (see *note PYTHONHOME:
     5d1. above).  It is `always' appended to *note PYTHONPATH: a34.

     An additional directory will be inserted in the search path in
     front of *note PYTHONPATH: a34. as described above under *note
     Interface options: 146e.  The search path can be manipulated from
     within a Python program as the variable *note sys.path: 260.

 -- Environment Variable: PYTHONPLATLIBDIR

     If this is set to a non-empty string, it overrides the *note
     sys.platlibdir: 1e9. value.

     New in version 3.9.

 -- Environment Variable: PYTHONSTARTUP

     If this is the name of a readable file, the Python commands in that
     file are executed before the first prompt is displayed in
     interactive mode.  The file is executed in the same namespace where
     interactive commands are executed so that objects defined or
     imported in it can be used without qualification in the interactive
     session.  You can also change the prompts *note sys.ps1: 1487. and
     *note sys.ps2: 1488. and the hook *note sys.__interactivehook__:
     9ca. in this file.

     Raises an *note auditing event: fa1. ‘cpython.run_startup’ with the
     filename as the argument when called on startup.

 -- Environment Variable: PYTHONOPTIMIZE

     If this is set to a non-empty string it is equivalent to specifying
     the *note -O: 77e. option.  If set to an integer, it is equivalent
     to specifying *note -O: 77e. multiple times.

 -- Environment Variable: PYTHONBREAKPOINT

     If this is set, it names a callable using dotted-path notation.
     The module containing the callable will be imported and then the
     callable will be run by the default implementation of *note
     sys.breakpointhook(): 423. which itself is called by built-in *note
     breakpoint(): 40b.  If not set, or set to the empty string, it is
     equivalent to the value “pdb.set_trace”.  Setting this to the
     string “0” causes the default implementation of *note
     sys.breakpointhook(): 423. to do nothing but return immediately.

     New in version 3.7.

 -- Environment Variable: PYTHONDEBUG

     If this is set to a non-empty string it is equivalent to specifying
     the *note -d: 1476. option.  If set to an integer, it is equivalent
     to specifying *note -d: 1476. multiple times.

 -- Environment Variable: PYTHONOLDPARSER

     If this is set to a non-empty string, enable the traditional LL(1)
     parser.

     See also the *note -X: 290. ‘oldparser’ option and PEP 617(1).

     Deprecated since version 3.9, will be removed in version 3.10.

 -- Environment Variable: PYTHONINSPECT

     If this is set to a non-empty string it is equivalent to specifying
     the *note -i: ee1. option.

     This variable can also be modified by Python code using *note
     os.environ: c09. to force inspect mode on program termination.

 -- Environment Variable: PYTHONUNBUFFERED

     If this is set to a non-empty string it is equivalent to specifying
     the *note -u: 109d. option.

 -- Environment Variable: PYTHONVERBOSE

     If this is set to a non-empty string it is equivalent to specifying
     the *note -v: e4d. option.  If set to an integer, it is equivalent
     to specifying *note -v: e4d. multiple times.

 -- Environment Variable: PYTHONCASEOK

     If this is set, Python ignores case in *note import: ce7.
     statements.  This only works on Windows and macOS.

 -- Environment Variable: PYTHONDONTWRITEBYTECODE

     If this is set to a non-empty string, Python won’t try to write
     ‘.pyc’ files on the import of source modules.  This is equivalent
     to specifying the *note -B: dfe. option.

 -- Environment Variable: PYTHONPYCACHEPREFIX

     If this is set, Python will write ‘.pyc’ files in a mirror
     directory tree at this path, instead of in ‘__pycache__’
     directories within the source tree.  This is equivalent to
     specifying the *note -X: 290. ‘pycache_prefix=PATH’ option.

     New in version 3.8.

 -- Environment Variable: PYTHONHASHSEED

     If this variable is not set or set to ‘random’, a random value is
     used to seed the hashes of str and bytes objects.

     If *note PYTHONHASHSEED: aa4. is set to an integer value, it is
     used as a fixed seed for generating the hash() of the types covered
     by the hash randomization.

     Its purpose is to allow repeatable hashing, such as for selftests
     for the interpreter itself, or to allow a cluster of python
     processes to share hash values.

     The integer must be a decimal number in the range [0,4294967295].
     Specifying the value 0 will disable hash randomization.

     New in version 3.2.3.

 -- Environment Variable: PYTHONIOENCODING

     If this is set before running the interpreter, it overrides the
     encoding used for stdin/stdout/stderr, in the syntax
     ‘encodingname:errorhandler’.  Both the ‘encodingname’ and the
     ‘:errorhandler’ parts are optional and have the same meaning as in
     *note str.encode(): 170.

     For stderr, the ‘:errorhandler’ part is ignored; the handler will
     always be ‘'backslashreplace'’.

     Changed in version 3.4: The ‘encodingname’ part is now optional.

     Changed in version 3.6: On Windows, the encoding specified by this
     variable is ignored for interactive console buffers unless *note
     PYTHONLEGACYWINDOWSSTDIO: 5f4. is also specified.  Files and pipes
     redirected through the standard streams are not affected.

 -- Environment Variable: PYTHONNOUSERSITE

     If this is set, Python won’t add the *note user site-packages
     directory: 147a. to *note sys.path: 260.

     See also
     ........

     PEP 370(2) – Per user site-packages directory

 -- Environment Variable: PYTHONUSERBASE

     Defines the *note user base directory: 1489, which is used to
     compute the path of the *note user site-packages directory: 147a.
     and *note Distutils installation paths: 148a. for ‘python setup.py
     install --user’.

     See also
     ........

     PEP 370(3) – Per user site-packages directory

 -- Environment Variable: PYTHONEXECUTABLE

     If this environment variable is set, ‘sys.argv[0]’ will be set to
     its value instead of the value got through the C runtime.  Only
     works on macOS.

 -- Environment Variable: PYTHONWARNINGS

     This is equivalent to the *note -W: 15b. option.  If set to a comma
     separated string, it is equivalent to specifying *note -W: 15b.
     multiple times, with filters later in the list taking precedence
     over those earlier in the list.

     The simplest settings apply a particular action unconditionally to
     all warnings emitted by a process (even those that are otherwise
     ignored by default):

          PYTHONWARNINGS=default  # Warn once per call location
          PYTHONWARNINGS=error    # Convert to exceptions
          PYTHONWARNINGS=always   # Warn every time
          PYTHONWARNINGS=module   # Warn once per calling module
          PYTHONWARNINGS=once     # Warn once per Python process
          PYTHONWARNINGS=ignore   # Never warn

     See *note The Warnings Filter: 15d. and *note Describing Warning
     Filters: 147e. for more details.

 -- Environment Variable: PYTHONFAULTHANDLER

     If this environment variable is set to a non-empty string, *note
     faulthandler.enable(): 642. is called at startup: install a handler
     for ‘SIGSEGV’, ‘SIGFPE’, ‘SIGABRT’, ‘SIGBUS’ and ‘SIGILL’ signals
     to dump the Python traceback.  This is equivalent to *note -X: 290.
     ‘faulthandler’ option.

     New in version 3.3.

 -- Environment Variable: PYTHONTRACEMALLOC

     If this environment variable is set to a non-empty string, start
     tracing Python memory allocations using the *note tracemalloc: 11d.
     module.  The value of the variable is the maximum number of frames
     stored in a traceback of a trace.  For example,
     ‘PYTHONTRACEMALLOC=1’ stores only the most recent frame.  See the
     *note tracemalloc.start(): 1481. for more information.

     New in version 3.4.

 -- Environment Variable: PYTHONPROFILEIMPORTTIME

     If this environment variable is set to a non-empty string, Python
     will show how long each import takes.  This is exactly equivalent
     to setting ‘-X importtime’ on the command line.

     New in version 3.7.

 -- Environment Variable: PYTHONASYNCIODEBUG

     If this environment variable is set to a non-empty string, enable
     the *note debug mode: 148e. of the *note asyncio: 9. module.

     New in version 3.4.

 -- Environment Variable: PYTHONMALLOC

     Set the Python memory allocators and/or install debug hooks.

     Set the family of memory allocators used by Python:

        * ‘default’: use the *note default memory allocators: 148f.

        * ‘malloc’: use the ‘malloc()’ function of the C library for all
          domains (*note PYMEM_DOMAIN_RAW: 1490, *note PYMEM_DOMAIN_MEM:
          603, *note PYMEM_DOMAIN_OBJ: 601.).

        * ‘pymalloc’: use the *note pymalloc allocator: 6b8. for *note
          PYMEM_DOMAIN_MEM: 603. and *note PYMEM_DOMAIN_OBJ: 601.
          domains and use the ‘malloc()’ function for the *note
          PYMEM_DOMAIN_RAW: 1490. domain.

     Install debug hooks:

        * ‘debug’: install debug hooks on top of the *note default
          memory allocators: 148f.

        * ‘malloc_debug’: same as ‘malloc’ but also install debug hooks.

        * ‘pymalloc_debug’: same as ‘pymalloc’ but also install debug
          hooks.

     See the *note default memory allocators: 148f. and the *note
     PyMem_SetupDebugHooks(): 604. function (install debug hooks on
     Python memory allocators).

     Changed in version 3.7: Added the ‘"default"’ allocator.

     New in version 3.6.

 -- Environment Variable: PYTHONMALLOCSTATS

     If set to a non-empty string, Python will print statistics of the
     *note pymalloc memory allocator: 6b8. every time a new pymalloc
     object arena is created, and on shutdown.

     This variable is ignored if the *note PYTHONMALLOC: 5fd.
     environment variable is used to force the ‘malloc()’ allocator of
     the C library, or if Python is configured without ‘pymalloc’
     support.

     Changed in version 3.6: This variable can now also be used on
     Python compiled in release mode.  It now has no effect if set to an
     empty string.

 -- Environment Variable: PYTHONLEGACYWINDOWSFSENCODING

     If set to a non-empty string, the default filesystem encoding and
     errors mode will revert to their pre-3.6 values of ‘mbcs’ and
     ‘replace’, respectively.  Otherwise, the new defaults ‘utf-8’ and
     ‘surrogatepass’ are used.

     This may also be enabled at runtime with *note
     sys._enablelegacywindowsfsencoding(): 5f2.

     *note Availability: 1491.: Windows.

     New in version 3.6: See PEP 529(4) for more details.

 -- Environment Variable: PYTHONLEGACYWINDOWSSTDIO

     If set to a non-empty string, does not use the new console reader
     and writer.  This means that Unicode characters will be encoded
     according to the active console code page, rather than using utf-8.

     This variable is ignored if the standard streams are redirected (to
     files or pipes) rather than referring to console buffers.

     *note Availability: 1491.: Windows.

     New in version 3.6.

 -- Environment Variable: PYTHONCOERCECLOCALE

     If set to the value ‘0’, causes the main Python command line
     application to skip coercing the legacy ASCII-based C and POSIX
     locales to a more capable UTF-8 based alternative.

     If this variable is `not' set (or is set to a value other than
     ‘0’), the ‘LC_ALL’ locale override environment variable is also not
     set, and the current locale reported for the ‘LC_CTYPE’ category is
     either the default ‘C’ locale, or else the explicitly ASCII-based
     ‘POSIX’ locale, then the Python CLI will attempt to configure the
     following locales for the ‘LC_CTYPE’ category in the order listed
     before loading the interpreter runtime:

        * ‘C.UTF-8’

        * ‘C.utf8’

        * ‘UTF-8’

     If setting one of these locale categories succeeds, then the
     ‘LC_CTYPE’ environment variable will also be set accordingly in the
     current process environment before the Python runtime is
     initialized.  This ensures that in addition to being seen by both
     the interpreter itself and other locale-aware components running in
     the same process (such as the GNU ‘readline’ library), the updated
     setting is also seen in subprocesses (regardless of whether or not
     those processes are running a Python interpreter), as well as in
     operations that query the environment rather than the current C
     locale (such as Python’s own *note locale.getdefaultlocale():
     1492.).

     Configuring one of these locales (either explicitly or via the
     above implicit locale coercion) automatically enables the
     ‘surrogateescape’ *note error handler: 1493. for *note sys.stdin:
     41e. and *note sys.stdout: 41f. (*note sys.stderr: 1ea. continues
     to use ‘backslashreplace’ as it does in any other locale).  This
     stream handling behavior can be overridden using *note
     PYTHONIOENCODING: a14. as usual.

     For debugging purposes, setting ‘PYTHONCOERCECLOCALE=warn’ will
     cause Python to emit warning messages on ‘stderr’ if either the
     locale coercion activates, or else if a locale that `would' have
     triggered coercion is still active when the Python runtime is
     initialized.

     Also note that even when locale coercion is disabled, or when it
     fails to find a suitable target locale, *note PYTHONUTF8: 421. will
     still activate by default in legacy ASCII-based locales.  Both
     features must be disabled in order to force the interpreter to use
     ‘ASCII’ instead of ‘UTF-8’ for system interfaces.

     *note Availability: 1491.: *nix.

     New in version 3.7: See PEP 538(5) for more details.

 -- Environment Variable: PYTHONDEVMODE

     If this environment variable is set to a non-empty string, enable
     *note Python Development Mode: 160, introducing additional runtime
     checks that are too expensive to be enabled by default.

     New in version 3.7.

 -- Environment Variable: PYTHONUTF8

     If set to ‘1’, enables the interpreter’s UTF-8 mode, where ‘UTF-8’
     is used as the text encoding for system interfaces, regardless of
     the current locale setting.

     This means that:

             * *note sys.getfilesystemencoding(): 5f0. returns ‘'UTF-8'’
               (the locale encoding is ignored).

             * *note locale.getpreferredencoding(): 4ac. returns
               ‘'UTF-8'’ (the locale encoding is ignored, and the
               function’s ‘do_setlocale’ parameter has no effect).

             * *note sys.stdin: 41e, *note sys.stdout: 41f, and *note
               sys.stderr: 1ea. all use UTF-8 as their text encoding,
               with the ‘surrogateescape’ *note error handler: 1493.
               being enabled for *note sys.stdin: 41e. and *note
               sys.stdout: 41f. (*note sys.stderr: 1ea. continues to use
               ‘backslashreplace’ as it does in the default locale-aware
               mode)

     As a consequence of the changes in those lower level APIs, other
     higher level APIs also exhibit different default behaviours:

             * Command line arguments, environment variables and
               filenames are decoded to text using the UTF-8 encoding.

             * *note os.fsdecode(): 5e9. and *note os.fsencode(): 5ea.
               use the UTF-8 encoding.

             * *note open(): 16f, *note io.open(): 74d, and *note
               codecs.open(): 10c3. use the UTF-8 encoding by default.
               However, they still use the strict error handler by
               default so that attempting to open a binary file in text
               mode is likely to raise an exception rather than
               producing nonsense data.

     Note that the standard stream settings in UTF-8 mode can be
     overridden by *note PYTHONIOENCODING: a14. (just as they can be in
     the default locale-aware mode).

     If set to ‘0’, the interpreter runs in its default locale-aware
     mode.

     Setting any other non-empty string causes an error during
     interpreter initialisation.

     If this environment variable is not set at all, then the
     interpreter defaults to using the current locale settings, `unless'
     the current locale is identified as a legacy ASCII-based locale (as
     described for *note PYTHONCOERCECLOCALE: 41d.), and locale coercion
     is either disabled or fails.  In such legacy locales, the
     interpreter will default to enabling UTF-8 mode unless explicitly
     instructed not to do so.

     Also available as the *note -X: 290. ‘utf8’ option.

     New in version 3.7: See PEP 540(6) for more details.

* Menu:

* Debug-mode variables::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0617

   (2) https://www.python.org/dev/peps/pep-0370

   (3) https://www.python.org/dev/peps/pep-0370

   (4) https://www.python.org/dev/peps/pep-0529

   (5) https://www.python.org/dev/peps/pep-0538

   (6) https://www.python.org/dev/peps/pep-0540


File: python.info,  Node: Debug-mode variables,  Up: Environment variables

3.1.2.1 Debug-mode variables
............................

Setting these variables only has an effect in a debug build of Python.

 -- Environment Variable: PYTHONTHREADDEBUG

     If set, Python will print threading debug info.

     Need Python configured with the ‘--with-pydebug’ build option.

 -- Environment Variable: PYTHONDUMPREFS

     If set, Python will dump objects and reference counts still alive
     after shutting down the interpreter.

     Need Python configured with the ‘--with-trace-refs’ build option.


File: python.info,  Node: Using Python on Unix platforms,  Next: Using Python on Windows,  Prev: Command line and environment,  Up: Python Setup and Usage

3.2 Using Python on Unix platforms
==================================

* Menu:

* Getting and installing the latest version of Python::
* Building Python::
* Python-related paths and files::
* Miscellaneous::


File: python.info,  Node: Getting and installing the latest version of Python,  Next: Building Python,  Up: Using Python on Unix platforms

3.2.1 Getting and installing the latest version of Python
---------------------------------------------------------

* Menu:

* On Linux::
* On FreeBSD and OpenBSD::
* On OpenSolaris::


File: python.info,  Node: On Linux,  Next: On FreeBSD and OpenBSD,  Up: Getting and installing the latest version of Python

3.2.1.1 On Linux
................

Python comes preinstalled on most Linux distributions, and is available
as a package on all others.  However there are certain features you
might want to use that are not available on your distro’s package.  You
can easily compile the latest version of Python from source.

In the event that Python doesn’t come preinstalled and isn’t in the
repositories as well, you can easily make packages for your own distro.
Have a look at the following links:

See also
........

‘https://www.debian.org/doc/manuals/maint-guide/first.en.html’

     for Debian users

‘https://en.opensuse.org/Portal:Packaging’

     for OpenSuse users

‘https://docs-old.fedoraproject.org/en-US/Fedora_Draft_Documentation/0.1/html/RPM_Guide/ch-creating-rpms.html’

     for Fedora users

‘http://www.slackbook.org/html/package-management-making-packages.html’

     for Slackware users


File: python.info,  Node: On FreeBSD and OpenBSD,  Next: On OpenSolaris,  Prev: On Linux,  Up: Getting and installing the latest version of Python

3.2.1.2 On FreeBSD and OpenBSD
..............................

   * FreeBSD users, to add the package use:

          pkg install python3

   * OpenBSD users, to add the package use:

          pkg_add -r python

          pkg_add ftp://ftp.openbsd.org/pub/OpenBSD/4.2/packages/<insert your architecture here>/python-<version>.tgz

     For example i386 users get the 2.5.1 version of Python using:

          pkg_add ftp://ftp.openbsd.org/pub/OpenBSD/4.2/packages/i386/python-2.5.1p2.tgz


File: python.info,  Node: On OpenSolaris,  Prev: On FreeBSD and OpenBSD,  Up: Getting and installing the latest version of Python

3.2.1.3 On OpenSolaris
......................

You can get Python from OpenCSW(1). Various versions of Python are
available and can be installed with e.g.  ‘pkgutil -i python27’.

   ---------- Footnotes ----------

   (1) https://www.opencsw.org/


File: python.info,  Node: Building Python,  Next: Python-related paths and files,  Prev: Getting and installing the latest version of Python,  Up: Using Python on Unix platforms

3.2.2 Building Python
---------------------

If you want to compile CPython yourself, first thing you should do is
get the source(1).  You can download either the latest release’s source
or just grab a fresh clone(2).  (If you want to contribute patches, you
will need a clone.)

The build process consists of the usual commands:

     ./configure
     make
     make install

Configuration options and caveats for specific Unix platforms are
extensively documented in the README.rst(3) file in the root of the
Python source tree.

     Warning: ‘make install’ can overwrite or masquerade the ‘python3’
     binary.  ‘make altinstall’ is therefore recommended instead of
     ‘make install’ since it only installs
     ‘`exec_prefix'/bin/python`version'’.

   ---------- Footnotes ----------

   (1) https://www.python.org/downloads/source/

   (2) https://devguide.python.org/setup/#getting-the-source-code

   (3) https://github.com/python/cpython/tree/3.9/README.rst


File: python.info,  Node: Python-related paths and files,  Next: Miscellaneous,  Prev: Building Python,  Up: Using Python on Unix platforms

3.2.3 Python-related paths and files
------------------------------------

These are subject to difference depending on local installation
conventions; ‘prefix’ (‘${prefix}’) and ‘exec_prefix’ (‘${exec_prefix}’)
are installation-dependent and should be interpreted as for GNU
software; they may be the same.

For example, on most Linux systems, the default for both is ‘/usr’.

File/directory                                      Meaning
                                                    
---------------------------------------------------------------------------------------------------
                                                    
‘`exec_prefix'/bin/python3’                         Recommended location of the interpreter.
                                                    
                                                    
‘`prefix'/lib/python`version'’,                     Recommended locations of the directories
‘`exec_prefix'/lib/python`version'’                 containing the standard modules.
                                                    
                                                    
‘`prefix'/include/python`version'’,                 Recommended locations of the directories
‘`exec_prefix'/include/python`version'’             containing the include files needed for
                                                    developing Python extensions and embedding
                                                    the interpreter.
                                                    


File: python.info,  Node: Miscellaneous,  Prev: Python-related paths and files,  Up: Using Python on Unix platforms

3.2.4 Miscellaneous
-------------------

To easily use Python scripts on Unix, you need to make them executable,
e.g.  with

     $ chmod +x script

and put an appropriate Shebang line at the top of the script.  A good
choice is usually

     #!/usr/bin/env python3

which searches for the Python interpreter in the whole ‘PATH’.  However,
some Unices may not have the ‘env’ command, so you may need to hardcode
‘/usr/bin/python3’ as the interpreter path.

To use shell commands in your Python scripts, look at the *note
subprocess: f9. module.


File: python.info,  Node: Using Python on Windows,  Next: Using Python on a Mac,  Prev: Using Python on Unix platforms,  Up: Python Setup and Usage

3.3 Using Python on Windows
===========================

This document aims to give an overview of Windows-specific behaviour you
should know about when using Python on Microsoft Windows.

Unlike most Unix systems and services, Windows does not include a system
supported installation of Python.  To make Python available, the CPython
team has compiled Windows installers (MSI packages) with every
release(1) for many years.  These installers are primarily intended to
add a per-user installation of Python, with the core interpreter and
library being used by a single user.  The installer is also able to
install for all users of a single machine, and a separate ZIP file is
available for application-local distributions.

As specified in PEP 11(2), a Python release only supports a Windows
platform while Microsoft considers the platform under extended support.
This means that Python 3.9 supports Windows 8.1 and newer.  If you
require Windows 7 support, please install Python 3.8.

There are a number of different installers available for Windows, each
with certain benefits and downsides.

*note The full installer: 14a2. contains all components and is the best
option for developers using Python for any kind of project.

*note The Microsoft Store package: 133d. is a simple installation of
Python that is suitable for running scripts and packages, and using IDLE
or other development environments.  It requires Windows 10, but can be
safely installed without corrupting other programs.  It also provides
many convenient commands for launching Python and its tools.

*note The nuget.org packages: 14a3. are lightweight installations
intended for continuous integration systems.  It can be used to build
Python packages or run scripts, but is not updateable and has no user
interface tools.

*note The embeddable package: 14a4. is a minimal package of Python
suitable for embedding into a larger application.

* Menu:

* The full installer::
* The Microsoft Store package::
* The nuget.org packages: The nuget org packages.
* The embeddable package::
* Alternative bundles::
* Configuring Python::
* UTF-8 mode::
* Python Launcher for Windows::
* Finding modules::
* Additional modules::
* Compiling Python on Windows::
* Other Platforms::

   ---------- Footnotes ----------

   (1) https://www.python.org/download/releases/

   (2) https://www.python.org/dev/peps/pep-0011


File: python.info,  Node: The full installer,  Next: The Microsoft Store package,  Up: Using Python on Windows

3.3.1 The full installer
------------------------

* Menu:

* Installation steps::
* Removing the MAX_PATH Limitation::
* Installing Without UI::
* Installing Without Downloading::
* Modifying an install::


File: python.info,  Node: Installation steps,  Next: Removing the MAX_PATH Limitation,  Up: The full installer

3.3.1.1 Installation steps
..........................

Four Python 3.9 installers are available for download - two each for the
32-bit and 64-bit versions of the interpreter.  The `web installer' is a
small initial download, and it will automatically download the required
components as necessary.  The `offline installer' includes the
components necessary for a default installation and only requires an
internet connection for optional features.  See *note Installing Without
Downloading: 14a7. for other ways to avoid downloading during
installation.

After starting the installer, one of two options may be selected:

[python-figures/win_installer]
If you select “Install Now”:

   * You will `not' need to be an administrator (unless a system update
     for the C Runtime Library is required or you install the *note
     Python Launcher for Windows: a70. for all users)

   * Python will be installed into your user directory

   * The *note Python Launcher for Windows: a70. will be installed
     according to the option at the bottom of the first page

   * The standard library, test suite, launcher and pip will be
     installed

   * If selected, the install directory will be added to your ‘PATH’

   * Shortcuts will only be visible for the current user

Selecting “Customize installation” will allow you to select the features
to install, the installation location and other options or post-install
actions.  To install debugging symbols or binaries, you will need to use
this option.

To perform an all-users installation, you should select “Customize
installation”.  In this case:

   * You may be required to provide administrative credentials or
     approval

   * Python will be installed into the Program Files directory

   * The *note Python Launcher for Windows: a70. will be installed into
     the Windows directory

   * Optional features may be selected during installation

   * The standard library can be pre-compiled to bytecode

   * If selected, the install directory will be added to the system
     ‘PATH’

   * Shortcuts are available for all users


File: python.info,  Node: Removing the MAX_PATH Limitation,  Next: Installing Without UI,  Prev: Installation steps,  Up: The full installer

3.3.1.2 Removing the MAX_PATH Limitation
........................................

Windows historically has limited path lengths to 260 characters.  This
meant that paths longer than this would not resolve and errors would
result.

In the latest versions of Windows, this limitation can be expanded to
approximately 32,000 characters.  Your administrator will need to
activate the “Enable Win32 long paths” group policy, or set
‘LongPathsEnabled’ to ‘1’ in the registry key
‘HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem’.

This allows the *note open(): 16f. function, the *note os: c4. module
and most other path functionality to accept and return paths longer than
260 characters.

After changing the above option, no further configuration is required.

Changed in version 3.6: Support for long paths was enabled in Python.


File: python.info,  Node: Installing Without UI,  Next: Installing Without Downloading,  Prev: Removing the MAX_PATH Limitation,  Up: The full installer

3.3.1.3 Installing Without UI
.............................

All of the options available in the installer UI can also be specified
from the command line, allowing scripted installers to replicate an
installation on many machines without user interaction.  These options
may also be set without suppressing the UI in order to change some of
the defaults.

To completely hide the installer UI and install Python silently, pass
the ‘/quiet’ option.  To skip past the user interaction but still
display progress and errors, pass the ‘/passive’ option.  The
‘/uninstall’ option may be passed to immediately begin removing Python -
no prompt will be displayed.

All other options are passed as ‘name=value’, where the value is usually
‘0’ to disable a feature, ‘1’ to enable a feature, or a path.  The full
list of available options is shown below.

Name                            Description                                Default
                                                                           
----------------------------------------------------------------------------------------------------------
                                                                           
InstallAllUsers                 Perform a system-wide installation.        0
                                                                           
                                                                           
TargetDir                       The installation directory                 Selected based on
                                                                           InstallAllUsers
                                                                           
                                                                           
DefaultAllUsersTargetDir        The default installation directory for     ‘%ProgramFiles%\Python X.Y’
                                all-user installs                          or
                                                                           ‘%ProgramFiles(x86)%\Python
                                                                           X.Y’
                                                                           
                                                                           
DefaultJustForMeTargetDir       The default install directory for          ‘%LocalAppData%\Programs\PythonXY’
                                just-for-me installs                       or
                                                                           ‘%LocalAppData%\Programs\PythonXY-32’
                                                                           or
                                                                           ‘%LocalAppData%\Programs\PythonXY-64’
                                                                           
                                                                           
DefaultCustomTargetDir          The default custom install directory       (empty)
                                displayed in the UI                        
                                
                                                                           
AssociateFiles                  Create file associations if the launcher   1
                                is also installed.                         
                                
                                                                           
CompileAll                      Compile all ‘.py’ files to ‘.pyc’.         0
                                                                           
                                                                           
PrependPath                     Add install and Scripts directories to     0
                                ‘PATH’ and ‘.PY’ to ‘PATHEXT’              
                                
                                                                           
Shortcuts                       Create shortcuts for the interpreter,      1
                                documentation and IDLE if installed.       
                                
                                                                           
Include_doc                     Install Python manual                      1
                                                                           
                                                                           
Include_debug                   Install debug binaries                     0
                                                                           
                                                                           
Include_dev                     Install developer headers and libraries    1
                                                                           
                                                                           
Include_exe                     Install ‘python.exe’ and related files     1
                                                                           
                                                                           
Include_launcher                Install                                    1
                                *note Python Launcher for Windows: a70.    
                                
                                                                           
InstallLauncherAllUsers         Installs                                   1
                                *note Python Launcher for Windows: a70.    
                                for all users.
                                
                                                                           
Include_lib                     Install standard library and extension     1
                                modules                                    
                                
                                                                           
Include_pip                     Install bundled pip and setuptools         1
                                                                           
                                                                           
Include_symbols                 Install debugging symbols (‘*’.pdb)        0
                                                                           
                                                                           
Include_tcltk                   Install Tcl/Tk support and IDLE            1
                                                                           
                                                                           
Include_test                    Install standard library test suite        1
                                                                           
                                                                           
Include_tools                   Install utility scripts                    1
                                                                           
                                                                           
LauncherOnly                    Only installs the launcher.  This will     0
                                override most other options.               
                                
                                                                           
SimpleInstall                   Disable most install UI                    0
                                                                           
                                                                           
SimpleInstallDescription        A custom message to display when the       (empty)
                                simplified install UI is used.             
                                

For example, to silently install a default, system-wide Python
installation, you could use the following command (from an elevated
command prompt):

     python-3.9.0.exe /quiet InstallAllUsers=1 PrependPath=1 Include_test=0

To allow users to easily install a personal copy of Python without the
test suite, you could provide a shortcut with the following command.
This will display a simplified initial page and disallow customization:

     python-3.9.0.exe InstallAllUsers=0 Include_launcher=0 Include_test=0
         SimpleInstall=1 SimpleInstallDescription="Just for me, no test suite."

(Note that omitting the launcher also omits file associations, and is
only recommended for per-user installs when there is also a system-wide
installation that included the launcher.)

The options listed above can also be provided in a file named
‘unattend.xml’ alongside the executable.  This file specifies a list of
options and values.  When a value is provided as an attribute, it will
be converted to a number if possible.  Values provided as element text
are always left as strings.  This example file sets the same options as
the previous example:

     <Options>
         <Option Name="InstallAllUsers" Value="no" />
         <Option Name="Include_launcher" Value="0" />
         <Option Name="Include_test" Value="no" />
         <Option Name="SimpleInstall" Value="yes" />
         <Option Name="SimpleInstallDescription">Just for me, no test suite</Option>
     </Options>


File: python.info,  Node: Installing Without Downloading,  Next: Modifying an install,  Prev: Installing Without UI,  Up: The full installer

3.3.1.4 Installing Without Downloading
......................................

As some features of Python are not included in the initial installer
download, selecting those features may require an internet connection.
To avoid this need, all possible components may be downloaded on-demand
to create a complete `layout' that will no longer require an internet
connection regardless of the selected features.  Note that this download
may be bigger than required, but where a large number of installations
are going to be performed it is very useful to have a locally cached
copy.

Execute the following command from Command Prompt to download all
possible required files.  Remember to substitute ‘python-3.9.0.exe’ for
the actual name of your installer, and to create layouts in their own
directories to avoid collisions between files with the same name.

     python-3.9.0.exe /layout [optional target directory]

You may also specify the ‘/quiet’ option to hide the progress display.


File: python.info,  Node: Modifying an install,  Prev: Installing Without Downloading,  Up: The full installer

3.3.1.5 Modifying an install
............................

Once Python has been installed, you can add or remove features through
the Programs and Features tool that is part of Windows.  Select the
Python entry and choose “Uninstall/Change” to open the installer in
maintenance mode.

“Modify” allows you to add or remove features by modifying the
checkboxes - unchanged checkboxes will not install or remove anything.
Some options cannot be changed in this mode, such as the install
directory; to modify these, you will need to remove and then reinstall
Python completely.

“Repair” will verify all the files that should be installed using the
current settings and replace any that have been removed or modified.

“Uninstall” will remove Python entirely, with the exception of the *note
Python Launcher for Windows: a70, which has its own entry in Programs
and Features.


File: python.info,  Node: The Microsoft Store package,  Next: The nuget org packages,  Prev: The full installer,  Up: Using Python on Windows

3.3.2 The Microsoft Store package
---------------------------------

New in version 3.7.2.

The Microsoft Store package is an easily installable Python interpreter
that is intended mainly for interactive use, for example, by students.

To install the package, ensure you have the latest Windows 10 updates
and search the Microsoft Store app for “Python 3.9”.  Ensure that the
app you select is published by the Python Software Foundation, and
install it.

     Warning: Python will always be available for free on the Microsoft
     Store.  If you are asked to pay for it, you have not selected the
     correct package.

After installation, Python may be launched by finding it in Start.
Alternatively, it will be available from any Command Prompt or
PowerShell session by typing ‘python’.  Further, pip and IDLE may be
used by typing ‘pip’ or ‘idle’.  IDLE can also be found in Start.

All three commands are also available with version number suffixes, for
example, as ‘python3.exe’ and ‘python3.x.exe’ as well as ‘python.exe’
(where ‘3.x’ is the specific version you want to launch, such as 3.9).
Open “Manage App Execution Aliases” through Start to select which
version of Python is associated with each command.  It is recommended to
make sure that ‘pip’ and ‘idle’ are consistent with whichever version of
‘python’ is selected.

Virtual environments can be created with ‘python -m venv’ and activated
and used as normal.

If you have installed another version of Python and added it to your
‘PATH’ variable, it will be available as ‘python.exe’ rather than the
one from the Microsoft Store.  To access the new installation, use
‘python3.exe’ or ‘python3.x.exe’.

The ‘py.exe’ launcher will detect this Python installation, but will
prefer installations from the traditional installer.

To remove Python, open Settings and use Apps and Features, or else find
Python in Start and right-click to select Uninstall.  Uninstalling will
remove all packages you installed directly into this Python
installation, but will not remove any virtual environments

* Menu:

* Known Issues::


File: python.info,  Node: Known Issues,  Up: The Microsoft Store package

3.3.2.1 Known Issues
....................

Because of restrictions on Microsoft Store apps, Python scripts may not
have full write access to shared locations such as ‘TEMP’ and the
registry.  Instead, it will write to a private copy.  If your scripts
must modify the shared locations, you will need to install the full
installer.

For more detail on the technical basis for these limitations, please
consult Microsoft’s documentation on packaged full-trust apps, currently
available at
docs.microsoft.com/en-us/windows/msix/desktop/desktop-to-uwp-behind-the-scenes(1)

   ---------- Footnotes ----------

   (1) 
https://docs.microsoft.com/en-us/windows/msix/desktop/desktop-to-uwp-behind-the-scenes


File: python.info,  Node: The nuget org packages,  Next: The embeddable package,  Prev: The Microsoft Store package,  Up: Using Python on Windows

3.3.3 The nuget.org packages
----------------------------

New in version 3.5.2.

The nuget.org package is a reduced size Python environment intended for
use on continuous integration and build systems that do not have a
system-wide install of Python.  While nuget is “the package manager for
.NET”, it also works perfectly fine for packages containing build-time
tools.

Visit nuget.org(1) for the most up-to-date information on using nuget.
What follows is a summary that is sufficient for Python developers.

The ‘nuget.exe’ command line tool may be downloaded directly from
‘https://aka.ms/nugetclidl’, for example, using curl or PowerShell.
With the tool, the latest version of Python for 64-bit or 32-bit
machines is installed using:

     nuget.exe install python -ExcludeVersion -OutputDirectory .
     nuget.exe install pythonx86 -ExcludeVersion -OutputDirectory .

To select a particular version, add a ‘-Version 3.x.y’.  The output
directory may be changed from ‘.’, and the package will be installed
into a subdirectory.  By default, the subdirectory is named the same as
the package, and without the ‘-ExcludeVersion’ option this name will
include the specific version installed.  Inside the subdirectory is a
‘tools’ directory that contains the Python installation:

     # Without -ExcludeVersion
     > .\python.3.5.2\tools\python.exe -V
     Python 3.5.2

     # With -ExcludeVersion
     > .\python\tools\python.exe -V
     Python 3.5.2

In general, nuget packages are not upgradeable, and newer versions
should be installed side-by-side and referenced using the full path.
Alternatively, delete the package directory manually and install it
again.  Many CI systems will do this automatically if they do not
preserve files between builds.

Alongside the ‘tools’ directory is a ‘build\native’ directory.  This
contains a MSBuild properties file ‘python.props’ that can be used in a
C++ project to reference the Python install.  Including the settings
will automatically use the headers and import libraries in your build.

The package information pages on nuget.org are
www.nuget.org/packages/python(2) for the 64-bit version and
www.nuget.org/packages/pythonx86(3) for the 32-bit version.

   ---------- Footnotes ----------

   (1) https://www.nuget.org/

   (2) https://www.nuget.org/packages/python

   (3) https://www.nuget.org/packages/pythonx86


File: python.info,  Node: The embeddable package,  Next: Alternative bundles,  Prev: The nuget org packages,  Up: Using Python on Windows

3.3.4 The embeddable package
----------------------------

New in version 3.5.

The embedded distribution is a ZIP file containing a minimal Python
environment.  It is intended for acting as part of another application,
rather than being directly accessed by end-users.

When extracted, the embedded distribution is (almost) fully isolated
from the user’s system, including environment variables, system registry
settings, and installed packages.  The standard library is included as
pre-compiled and optimized ‘.pyc’ files in a ZIP, and ‘python3.dll’,
‘python37.dll’, ‘python.exe’ and ‘pythonw.exe’ are all provided.  Tcl/tk
(including all dependants, such as Idle), pip and the Python
documentation are not included.

     Note: The embedded distribution does not include the Microsoft C
     Runtime(1) and it is the responsibility of the application
     installer to provide this.  The runtime may have already been
     installed on a user’s system previously or automatically via
     Windows Update, and can be detected by finding ‘ucrtbase.dll’ in
     the system directory.

Third-party packages should be installed by the application installer
alongside the embedded distribution.  Using pip to manage dependencies
as for a regular Python installation is not supported with this
distribution, though with some care it may be possible to include and
use pip for automatic updates.  In general, third-party packages should
be treated as part of the application (“vendoring”) so that the
developer can ensure compatibility with newer versions before providing
updates to users.

The two recommended use cases for this distribution are described below.

* Menu:

* Python Application::
* Embedding Python::

   ---------- Footnotes ----------

   (1) https://www.microsoft.com/en-us/download/details.aspx?id=48145


File: python.info,  Node: Python Application,  Next: Embedding Python,  Up: The embeddable package

3.3.4.1 Python Application
..........................

An application written in Python does not necessarily require users to
be aware of that fact.  The embedded distribution may be used in this
case to include a private version of Python in an install package.
Depending on how transparent it should be (or conversely, how
professional it should appear), there are two options.

Using a specialized executable as a launcher requires some coding, but
provides the most transparent experience for users.  With a customized
launcher, there are no obvious indications that the program is running
on Python: icons can be customized, company and version information can
be specified, and file associations behave properly.  In most cases, a
custom launcher should simply be able to call ‘Py_Main’ with a
hard-coded command line.

The simpler approach is to provide a batch file or generated shortcut
that directly calls the ‘python.exe’ or ‘pythonw.exe’ with the required
command-line arguments.  In this case, the application will appear to be
Python and not its actual name, and users may have trouble
distinguishing it from other running Python processes or file
associations.

With the latter approach, packages should be installed as directories
alongside the Python executable to ensure they are available on the
path.  With the specialized launcher, packages can be located in other
locations as there is an opportunity to specify the search path before
launching the application.


File: python.info,  Node: Embedding Python,  Prev: Python Application,  Up: The embeddable package

3.3.4.2 Embedding Python
........................

Applications written in native code often require some form of scripting
language, and the embedded Python distribution can be used for this
purpose.  In general, the majority of the application is in native code,
and some part will either invoke ‘python.exe’ or directly use
‘python3.dll’.  For either case, extracting the embedded distribution to
a subdirectory of the application installation is sufficient to provide
a loadable Python interpreter.

As with the application use, packages can be installed to any location
as there is an opportunity to specify search paths before initializing
the interpreter.  Otherwise, there is no fundamental differences between
using the embedded distribution and a regular installation.


File: python.info,  Node: Alternative bundles,  Next: Configuring Python,  Prev: The embeddable package,  Up: Using Python on Windows

3.3.5 Alternative bundles
-------------------------

Besides the standard CPython distribution, there are modified packages
including additional functionality.  The following is a list of popular
versions and their key features:

ActivePython(1)

     Installer with multi-platform compatibility, documentation, PyWin32

Anaconda(2)

     Popular scientific modules (such as numpy, scipy and pandas) and
     the ‘conda’ package manager.

Canopy(3)

     A “comprehensive Python analysis environment” with editors and
     other development tools.

WinPython(4)

     Windows-specific distribution with prebuilt scientific packages and
     tools for building packages.

Note that these packages may not include the latest versions of Python
or other libraries, and are not maintained or supported by the core
Python team.

   ---------- Footnotes ----------

   (1) https://www.activestate.com/activepython/

   (2) https://www.anaconda.com/download/

   (3) https://www.enthought.com/product/canopy/

   (4) https://winpython.github.io/


File: python.info,  Node: Configuring Python,  Next: UTF-8 mode,  Prev: Alternative bundles,  Up: Using Python on Windows

3.3.6 Configuring Python
------------------------

To run Python conveniently from a command prompt, you might consider
changing some default environment variables in Windows.  While the
installer provides an option to configure the PATH and PATHEXT variables
for you, this is only reliable for a single, system-wide installation.
If you regularly use multiple versions of Python, consider using the
*note Python Launcher for Windows: a70.

* Menu:

* Excursus; Setting environment variables: Excursus Setting environment variables.
* Finding the Python executable::


File: python.info,  Node: Excursus Setting environment variables,  Next: Finding the Python executable,  Up: Configuring Python

3.3.6.1 Excursus: Setting environment variables
...............................................

Windows allows environment variables to be configured permanently at
both the User level and the System level, or temporarily in a command
prompt.

To temporarily set environment variables, open Command Prompt and use
the ‘set’ command:

     C:\>set PATH=C:\Program Files\Python 3.9;%PATH%
     C:\>set PYTHONPATH=%PYTHONPATH%;C:\My_python_lib
     C:\>python

These changes will apply to any further commands executed in that
console, and will be inherited by any applications started from the
console.

Including the variable name within percent signs will expand to the
existing value, allowing you to add your new value at either the start
or the end.  Modifying ‘PATH’ by adding the directory containing
‘python.exe’ to the start is a common way to ensure the correct version
of Python is launched.

To permanently modify the default environment variables, click Start and
search for ‘edit environment variables’, or open System properties,
Advanced system settings and click the Environment Variables button.  In
this dialog, you can add or modify User and System variables.  To change
System variables, you need non-restricted access to your machine (i.e.
Administrator rights).

     Note: Windows will concatenate User variables `after' System
     variables, which may cause unexpected results when modifying
     ‘PATH’.

     The *note PYTHONPATH: a34. variable is used by all versions of
     Python 2 and Python 3, so you should not permanently configure this
     variable unless it only includes code that is compatible with all
     of your installed Python versions.

See also
........

‘https://www.microsoft.com/en-us/wdsi/help/folder-variables’

     Environment variables in Windows NT

‘https://technet.microsoft.com/en-us/library/cc754250.aspx’

     The SET command, for temporarily modifying environment variables

‘https://technet.microsoft.com/en-us/library/cc755104.aspx’

     The SETX command, for permanently modifying environment variables

‘https://support.microsoft.com/en-us/help/310519/how-to-manage-environment-variables-in-windows-xp’

     How To Manage Environment Variables in Windows XP

‘https://www.chem.gla.ac.uk/~louis/software/faq/q1.html’

     Setting Environment variables, Louis J. Farrugia


File: python.info,  Node: Finding the Python executable,  Prev: Excursus Setting environment variables,  Up: Configuring Python

3.3.6.2 Finding the Python executable
.....................................

Changed in version 3.5.

Besides using the automatically created start menu entry for the Python
interpreter, you might want to start Python in the command prompt.  The
installer has an option to set that up for you.

On the first page of the installer, an option labelled “Add Python to
PATH” may be selected to have the installer add the install location
into the ‘PATH’.  The location of the ‘Scripts\’ folder is also added.
This allows you to type ‘python’ to run the interpreter, and ‘pip’ for
the package installer.  Thus, you can also execute your scripts with
command line options, see *note Command line: a10. documentation.

If you don’t enable this option at install time, you can always re-run
the installer, select Modify, and enable it.  Alternatively, you can
manually modify the ‘PATH’ using the directions in *note Excursus;
Setting environment variables: 133e.  You need to set your ‘PATH’
environment variable to include the directory of your Python
installation, delimited by a semicolon from other entries.  An example
variable could look like this (assuming the first two entries already
existed):

     C:\WINDOWS\system32;C:\WINDOWS;C:\Program Files\Python 3.9


File: python.info,  Node: UTF-8 mode,  Next: Python Launcher for Windows,  Prev: Configuring Python,  Up: Using Python on Windows

3.3.7 UTF-8 mode
----------------

New in version 3.7.

Windows still uses legacy encodings for the system encoding (the ANSI
Code Page).  Python uses it for the default encoding of text files (e.g.
*note locale.getpreferredencoding(): 4ac.).

This may cause issues because UTF-8 is widely used on the internet and
most Unix systems, including WSL (Windows Subsystem for Linux).

You can use UTF-8 mode to change the default text encoding to UTF-8.
You can enable UTF-8 mode via the ‘-X utf8’ command line option, or the
‘PYTHONUTF8=1’ environment variable.  See *note PYTHONUTF8: 421. for
enabling UTF-8 mode, and *note Excursus; Setting environment variables:
133e. for how to modify environment variables.

When UTF-8 mode is enabled:

   * *note locale.getpreferredencoding(): 4ac. returns ‘'UTF-8'’ instead
     of the system encoding.  This function is used for the default text
     encoding in many places, including *note open(): 16f, ‘Popen’,
     ‘Path.read_text()’, etc.

   * *note sys.stdin: 41e, *note sys.stdout: 41f, and *note sys.stderr:
     1ea. all use UTF-8 as their text encoding.

   * You can still use the system encoding via the “mbcs” codec.

Note that adding ‘PYTHONUTF8=1’ to the default environment variables
will affect all Python 3.7+ applications on your system.  If you have
any Python 3.7+ applications which rely on the legacy system encoding,
it is recommended to set the environment variable temporarily or use the
‘-X utf8’ command line option.

     Note: Even when UTF-8 mode is disabled, Python uses UTF-8 by
     default on Windows for:

        * Console I/O including standard I/O (see PEP 528(1) for
          details).

        * The filesystem encoding (see PEP 529(2) for details).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0528

   (2) https://www.python.org/dev/peps/pep-0529


File: python.info,  Node: Python Launcher for Windows,  Next: Finding modules,  Prev: UTF-8 mode,  Up: Using Python on Windows

3.3.8 Python Launcher for Windows
---------------------------------

New in version 3.3.

The Python launcher for Windows is a utility which aids in locating and
executing of different Python versions.  It allows scripts (or the
command-line) to indicate a preference for a specific Python version,
and will locate and execute that version.

Unlike the ‘PATH’ variable, the launcher will correctly select the most
appropriate version of Python.  It will prefer per-user installations
over system-wide ones, and orders by language version rather than using
the most recently installed version.

The launcher was originally specified in PEP 397(1).

* Menu:

* Getting started::
* Shebang Lines::
* Arguments in shebang lines::
* Customization::
* Diagnostics::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0397


File: python.info,  Node: Getting started,  Next: Shebang Lines,  Up: Python Launcher for Windows

3.3.8.1 Getting started
.......................

* Menu:

* From the command-line::
* Virtual environments::
* From a script::
* From file associations::


File: python.info,  Node: From the command-line,  Next: Virtual environments,  Up: Getting started

3.3.8.2 From the command-line
.............................

Changed in version 3.6.

System-wide installations of Python 3.3 and later will put the launcher
on your ‘PATH’.  The launcher is compatible with all available versions
of Python, so it does not matter which version is installed.  To check
that the launcher is available, execute the following command in Command
Prompt:

     py

You should find that the latest version of Python you have installed is
started - it can be exited as normal, and any additional command-line
arguments specified will be sent directly to Python.

If you have multiple versions of Python installed (e.g., 2.7 and 3.9)
you will have noticed that Python 3.9 was started - to launch Python
2.7, try the command:

     py -2.7

If you want the latest version of Python 2.x you have installed, try the
command:

     py -2

You should find the latest version of Python 2.x starts.

If you see the following error, you do not have the launcher installed:

     'py' is not recognized as an internal or external command,
     operable program or batch file.

Per-user installations of Python do not add the launcher to ‘PATH’
unless the option was selected on installation.


File: python.info,  Node: Virtual environments,  Next: From a script,  Prev: From the command-line,  Up: Getting started

3.3.8.3 Virtual environments
............................

New in version 3.5.

If the launcher is run with no explicit Python version specification,
and a virtual environment (created with the standard library *note venv:
12e. module or the external ‘virtualenv’ tool) active, the launcher will
run the virtual environment’s interpreter rather than the global one.
To run the global interpreter, either deactivate the virtual
environment, or explicitly specify the global Python version.


File: python.info,  Node: From a script,  Next: From file associations,  Prev: Virtual environments,  Up: Getting started

3.3.8.4 From a script
.....................

Let’s create a test Python script - create a file called ‘hello.py’ with
the following contents

     #! python
     import sys
     sys.stdout.write("hello from Python %s\n" % (sys.version,))

From the directory in which hello.py lives, execute the command:

     py hello.py

You should notice the version number of your latest Python 2.x
installation is printed.  Now try changing the first line to be:

     #! python3

Re-executing the command should now print the latest Python 3.x
information.  As with the above command-line examples, you can specify a
more explicit version qualifier.  Assuming you have Python 2.6
installed, try changing the first line to ‘#! python2.6’ and you should
find the 2.6 version information printed.

Note that unlike interactive use, a bare “python” will use the latest
version of Python 2.x that you have installed.  This is for backward
compatibility and for compatibility with Unix, where the command
‘python’ typically refers to Python 2.


File: python.info,  Node: From file associations,  Prev: From a script,  Up: Getting started

3.3.8.5 From file associations
..............................

The launcher should have been associated with Python files (i.e.  ‘.py’,
‘.pyw’, ‘.pyc’ files) when it was installed.  This means that when you
double-click on one of these files from Windows explorer the launcher
will be used, and therefore you can use the same facilities described
above to have the script specify the version which should be used.

The key benefit of this is that a single launcher can support multiple
Python versions at the same time depending on the contents of the first
line.


File: python.info,  Node: Shebang Lines,  Next: Arguments in shebang lines,  Prev: Getting started,  Up: Python Launcher for Windows

3.3.8.6 Shebang Lines
.....................

If the first line of a script file starts with ‘#!’, it is known as a
“shebang” line.  Linux and other Unix like operating systems have native
support for such lines and they are commonly used on such systems to
indicate how a script should be executed.  This launcher allows the same
facilities to be used with Python scripts on Windows and the examples
above demonstrate their use.

To allow shebang lines in Python scripts to be portable between Unix and
Windows, this launcher supports a number of ‘virtual’ commands to
specify which interpreter to use.  The supported virtual commands are:

   * ‘/usr/bin/env python’

   * ‘/usr/bin/python’

   * ‘/usr/local/bin/python’

   * ‘python’

For example, if the first line of your script starts with

     #! /usr/bin/python

The default Python will be located and used.  As many Python scripts
written to work on Unix will already have this line, you should find
these scripts can be used by the launcher without modification.  If you
are writing a new script on Windows which you hope will be useful on
Unix, you should use one of the shebang lines starting with ‘/usr’.

Any of the above virtual commands can be suffixed with an explicit
version (either just the major version, or the major and minor version).
Furthermore the 32-bit version can be requested by adding “-32” after
the minor version.  I.e.  ‘/usr/bin/python2.7-32’ will request usage of
the 32-bit python 2.7.

New in version 3.7: Beginning with python launcher 3.7 it is possible to
request 64-bit version by the “-64” suffix.  Furthermore it is possible
to specify a major and architecture without minor (i.e.
‘/usr/bin/python3-64’).

The ‘/usr/bin/env’ form of shebang line has one further special
property.  Before looking for installed Python interpreters, this form
will search the executable ‘PATH’ for a Python executable.  This
corresponds to the behaviour of the Unix ‘env’ program, which performs a
‘PATH’ search.


File: python.info,  Node: Arguments in shebang lines,  Next: Customization,  Prev: Shebang Lines,  Up: Python Launcher for Windows

3.3.8.7 Arguments in shebang lines
..................................

The shebang lines can also specify additional options to be passed to
the Python interpreter.  For example, if you have a shebang line:

     #! /usr/bin/python -v

Then Python will be started with the ‘-v’ option


File: python.info,  Node: Customization,  Next: Diagnostics,  Prev: Arguments in shebang lines,  Up: Python Launcher for Windows

3.3.8.8 Customization
.....................

* Menu:

* Customization via INI files::
* Customizing default Python versions::


File: python.info,  Node: Customization via INI files,  Next: Customizing default Python versions,  Up: Customization

3.3.8.9 Customization via INI files
...................................

Two .ini files will be searched by the launcher - ‘py.ini’ in the
current user’s “application data” directory (i.e.  the directory
returned by calling the Windows function ‘SHGetFolderPath’ with
‘CSIDL_LOCAL_APPDATA’) and ‘py.ini’ in the same directory as the
launcher.  The same .ini files are used for both the ‘console’ version
of the launcher (i.e.  py.exe) and for the ‘windows’ version (i.e.
pyw.exe).

Customization specified in the “application directory” will have
precedence over the one next to the executable, so a user, who may not
have write access to the .ini file next to the launcher, can override
commands in that global .ini file.


File: python.info,  Node: Customizing default Python versions,  Prev: Customization via INI files,  Up: Customization

3.3.8.10 Customizing default Python versions
............................................

In some cases, a version qualifier can be included in a command to
dictate which version of Python will be used by the command.  A version
qualifier starts with a major version number and can optionally be
followed by a period (‘.’) and a minor version specifier.  Furthermore
it is possible to specify if a 32 or 64 bit implementation shall be
requested by adding “-32” or “-64”.

For example, a shebang line of ‘#!python’ has no version qualifier,
while ‘#!python3’ has a version qualifier which specifies only a major
version.

If no version qualifiers are found in a command, the environment
variable ‘PY_PYTHON’ can be set to specify the default version
qualifier.  If it is not set, the default is “3”.  The variable can
specify any value that may be passed on the command line, such as “3”,
“3.7”, “3.7-32” or “3.7-64”.  (Note that the “-64” option is only
available with the launcher included with Python 3.7 or newer.)

If no minor version qualifiers are found, the environment variable
‘PY_PYTHON{major}’ (where ‘{major}’ is the current major version
qualifier as determined above) can be set to specify the full version.
If no such option is found, the launcher will enumerate the installed
Python versions and use the latest minor release found for the major
version, which is likely, although not guaranteed, to be the most
recently installed version in that family.

On 64-bit Windows with both 32-bit and 64-bit implementations of the
same (major.minor) Python version installed, the 64-bit version will
always be preferred.  This will be true for both 32-bit and 64-bit
implementations of the launcher - a 32-bit launcher will prefer to
execute a 64-bit Python installation of the specified version if
available.  This is so the behavior of the launcher can be predicted
knowing only what versions are installed on the PC and without regard to
the order in which they were installed (i.e., without knowing whether a
32 or 64-bit version of Python and corresponding launcher was installed
last).  As noted above, an optional “-32” or “-64” suffix can be used on
a version specifier to change this behaviour.

Examples:

   * If no relevant options are set, the commands ‘python’ and ‘python2’
     will use the latest Python 2.x version installed and the command
     ‘python3’ will use the latest Python 3.x installed.

   * The commands ‘python3.1’ and ‘python2.7’ will not consult any
     options at all as the versions are fully specified.

   * If ‘PY_PYTHON=3’, the commands ‘python’ and ‘python3’ will both use
     the latest installed Python 3 version.

   * If ‘PY_PYTHON=3.1-32’, the command ‘python’ will use the 32-bit
     implementation of 3.1 whereas the command ‘python3’ will use the
     latest installed Python (PY_PYTHON was not considered at all as a
     major version was specified.)

   * If ‘PY_PYTHON=3’ and ‘PY_PYTHON3=3.1’, the commands ‘python’ and
     ‘python3’ will both use specifically 3.1

In addition to environment variables, the same settings can be
configured in the .INI file used by the launcher.  The section in the
INI file is called ‘[defaults]’ and the key name will be the same as the
environment variables without the leading ‘PY_’ prefix (and note that
the key names in the INI file are case insensitive.)  The contents of an
environment variable will override things specified in the INI file.

For example:

   * Setting ‘PY_PYTHON=3.1’ is equivalent to the INI file containing:

     [defaults]
     python=3.1

   * Setting ‘PY_PYTHON=3’ and ‘PY_PYTHON3=3.1’ is equivalent to the INI
     file containing:

     [defaults]
     python=3
     python3=3.1


File: python.info,  Node: Diagnostics,  Prev: Customization,  Up: Python Launcher for Windows

3.3.8.11 Diagnostics
....................

If an environment variable ‘PYLAUNCH_DEBUG’ is set (to any value), the
launcher will print diagnostic information to stderr (i.e.  to the
console).  While this information manages to be simultaneously verbose
`and' terse, it should allow you to see what versions of Python were
located, why a particular version was chosen and the exact command-line
used to execute the target Python.


File: python.info,  Node: Finding modules,  Next: Additional modules,  Prev: Python Launcher for Windows,  Up: Using Python on Windows

3.3.9 Finding modules
---------------------

Python usually stores its library (and thereby your site-packages
folder) in the installation directory.  So, if you had installed Python
to ‘C:\Python\’, the default library would reside in ‘C:\Python\Lib\’
and third-party modules should be stored in
‘C:\Python\Lib\site-packages\’.

To completely override *note sys.path: 260, create a ‘._pth’ file with
the same name as the DLL (‘python37._pth’) or the executable
(‘python._pth’) and specify one line for each path to add to *note
sys.path: 260.  The file based on the DLL name overrides the one based
on the executable, which allows paths to be restricted for any program
loading the runtime if desired.

When the file exists, all registry and environment variables are
ignored, isolated mode is enabled, and *note site: eb. is not imported
unless one line in the file specifies ‘import site’.  Blank paths and
lines starting with ‘#’ are ignored.  Each path may be absolute or
relative to the location of the file.  Import statements other than to
‘site’ are not permitted, and arbitrary code cannot be specified.

Note that ‘.pth’ files (without leading underscore) will be processed
normally by the *note site: eb. module when ‘import site’ has been
specified.

When no ‘._pth’ file is found, this is how *note sys.path: 260. is
populated on Windows:

   * An empty entry is added at the start, which corresponds to the
     current directory.

   * If the environment variable *note PYTHONPATH: a34. exists, as
     described in *note Environment variables: 1485, its entries are
     added next.  Note that on Windows, paths in this variable must be
     separated by semicolons, to distinguish them from the colon used in
     drive identifiers (‘C:\’ etc.).

   * Additional “application paths” can be added in the registry as
     subkeys of ‘\SOFTWARE\Python\PythonCore{version}\PythonPath’ under
     both the ‘HKEY_CURRENT_USER’ and ‘HKEY_LOCAL_MACHINE’ hives.
     Subkeys which have semicolon-delimited path strings as their
     default value will cause each path to be added to *note sys.path:
     260.  (Note that all known installers only use HKLM, so HKCU is
     typically empty.)

   * If the environment variable *note PYTHONHOME: 5d1. is set, it is
     assumed as “Python Home”.  Otherwise, the path of the main Python
     executable is used to locate a “landmark file” (either ‘Lib\os.py’
     or ‘pythonXY.zip’) to deduce the “Python Home”.  If a Python home
     is found, the relevant sub-directories added to *note sys.path:
     260. (‘Lib’, ‘plat-win’, etc) are based on that folder.  Otherwise,
     the core Python path is constructed from the PythonPath stored in
     the registry.

   * If the Python Home cannot be located, no *note PYTHONPATH: a34. is
     specified in the environment, and no registry entries can be found,
     a default path with relative entries is used (e.g.
     ‘.\Lib;.\plat-win’, etc).

If a ‘pyvenv.cfg’ file is found alongside the main executable or in the
directory one level above the executable, the following variations
apply:

   * If ‘home’ is an absolute path and *note PYTHONHOME: 5d1. is not
     set, this path is used instead of the path to the main executable
     when deducing the home location.

The end result of all this is:

   * When running ‘python.exe’, or any other .exe in the main Python
     directory (either an installed version, or directly from the
     PCbuild directory), the core path is deduced, and the core paths in
     the registry are ignored.  Other “application paths” in the
     registry are always read.

   * When Python is hosted in another .exe (different directory,
     embedded via COM, etc), the “Python Home” will not be deduced, so
     the core path from the registry is used.  Other “application paths”
     in the registry are always read.

   * If Python can’t find its home and there are no registry value
     (frozen .exe, some very strange installation setup) you get a path
     with some default, but relative, paths.

For those who want to bundle Python into their application or
distribution, the following advice will prevent conflicts with other
installations:

   * Include a ‘._pth’ file alongside your executable containing the
     directories to include.  This will ignore paths listed in the
     registry and environment variables, and also ignore *note site: eb.
     unless ‘import site’ is listed.

   * If you are loading ‘python3.dll’ or ‘python37.dll’ in your own
     executable, explicitly call *note Py_SetPath(): 39c. or (at least)
     *note Py_SetProgramName(): 10f2. before *note Py_Initialize(): 20f.

   * Clear and/or overwrite *note PYTHONPATH: a34. and set *note
     PYTHONHOME: 5d1. before launching ‘python.exe’ from your
     application.

   * If you cannot use the previous suggestions (for example, you are a
     distribution that allows people to run ‘python.exe’ directly),
     ensure that the landmark file (‘Lib\os.py’) exists in your install
     directory.  (Note that it will not be detected inside a ZIP file,
     but a correctly named ZIP file will be detected instead.)

These will ensure that the files in a system-wide installation will not
take precedence over the copy of the standard library bundled with your
application.  Otherwise, your users may experience problems using your
application.  Note that the first suggestion is the best, as the others
may still be susceptible to non-standard paths in the registry and user
site-packages.

     Changed in version 3.6:

        * Adds ‘._pth’ file support and removes ‘applocal’ option from
          ‘pyvenv.cfg’.

        * Adds ‘pythonXX.zip’ as a potential landmark when directly
          adjacent to the executable.

     Deprecated since version 3.6: Modules specified in the registry
     under ‘Modules’ (not ‘PythonPath’) may be imported by *note
     importlib.machinery.WindowsRegistryFinder: 6dc.  This finder is
     enabled on Windows in 3.6.0 and earlier, but may need to be
     explicitly added to *note sys.meta_path: 6dd. in the future.


File: python.info,  Node: Additional modules,  Next: Compiling Python on Windows,  Prev: Finding modules,  Up: Using Python on Windows

3.3.10 Additional modules
-------------------------

Even though Python aims to be portable among all platforms, there are
features that are unique to Windows.  A couple of modules, both in the
standard library and external, and snippets exist to use these features.

The Windows-specific standard modules are documented in *note MS Windows
Specific Services: 14c7.

* Menu:

* PyWin32::
* cx_Freeze::
* WConio::


File: python.info,  Node: PyWin32,  Next: cx_Freeze,  Up: Additional modules

3.3.10.1 PyWin32
................

The PyWin32(1) module by Mark Hammond is a collection of modules for
advanced Windows-specific support.  This includes utilities for:

   * Component Object Model(2) (COM)

   * Win32 API calls

   * Registry

   * Event log

   * Microsoft Foundation Classes(3) (MFC) user interfaces

PythonWin(4) is a sample MFC application shipped with PyWin32.  It is an
embeddable IDE with a built-in debugger.

See also
........

Win32 How Do I...?(5)

     by Tim Golden

Python and COM(6)

     by David and Paul Boddie

   ---------- Footnotes ----------

   (1) https://pypi.org/project/pywin32

   (2) 
https://docs.microsoft.com/en-us/windows/desktop/com/component-object-model–com–portal

   (3) https://msdn.microsoft.com/en-us/library/fe1cf721%28VS.80%29.aspx

   (4) 
https://web.archive.org/web/20060524042422/https://www.python.org/windows/pythonwin/

   (5) http://timgolden.me.uk/python/win32_how_do_i.html

   (6) http://www.boddie.org.uk/python/COM.html


File: python.info,  Node: cx_Freeze,  Next: WConio,  Prev: PyWin32,  Up: Additional modules

3.3.10.2 cx_Freeze
..................

cx_Freeze(1) is a *note distutils: 38. extension (see *note Extending
Distutils: 14ca.) which wraps Python scripts into executable Windows
programs (‘`*'.exe’ files).  When you have done this, you can distribute
your application without requiring your users to install Python.

   ---------- Footnotes ----------

   (1) https://cx-freeze.readthedocs.io/en/latest/


File: python.info,  Node: WConio,  Prev: cx_Freeze,  Up: Additional modules

3.3.10.3 WConio
...............

Since Python’s advanced terminal handling layer, *note curses: 2b, is
restricted to Unix-like systems, there is a library exclusive to Windows
as well: Windows Console I/O for Python.

WConio(1) is a wrapper for Turbo-C’s ‘CONIO.H’, used to create text user
interfaces.

   ---------- Footnotes ----------

   (1) http://newcenturycomputers.net/projects/wconio.html


File: python.info,  Node: Compiling Python on Windows,  Next: Other Platforms,  Prev: Additional modules,  Up: Using Python on Windows

3.3.11 Compiling Python on Windows
----------------------------------

If you want to compile CPython yourself, first thing you should do is
get the source(1).  You can download either the latest release’s source
or just grab a fresh checkout(2).

The source tree contains a build solution and project files for
Microsoft Visual Studio 2015, which is the compiler used to build the
official Python releases.  These files are in the ‘PCbuild’ directory.

Check ‘PCbuild/readme.txt’ for general information on the build process.

For extension modules, consult *note Building C and C++ Extensions on
Windows: 14cd.

See also
........

Python + Windows + distutils + SWIG + gcc MinGW(3)

     or “Creating Python extensions in C/C++ with SWIG and compiling
     them with MinGW gcc under Windows” or “Installing Python extension
     with distutils and without Microsoft Visual C++” by Sébastien
     Sauvage, 2003

   ---------- Footnotes ----------

   (1) https://www.python.org/downloads/source/

   (2) https://devguide.python.org/setup/#getting-the-source-code

   (3) http://sebsauvage.net/python/mingw.html


File: python.info,  Node: Other Platforms,  Prev: Compiling Python on Windows,  Up: Using Python on Windows

3.3.12 Other Platforms
----------------------

With ongoing development of Python, some platforms that used to be
supported earlier are no longer supported (due to the lack of users or
developers).  Check PEP 11(1) for details on all unsupported platforms.

   * Windows CE(2) is still supported.

   * The Cygwin(3) installer offers to install the Python interpreter as
     well (cf.  Cygwin package source(4), Maintainer releases(5))

See Python for Windows(6) for detailed information about platforms with
pre-compiled installers.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0011

   (2) http://pythonce.sourceforge.net/

   (3) https://cygwin.com/

   (4) 
ftp://ftp.uni-erlangen.de/pub/pc/gnuwin32/cygwin/mirrors/cygnus/release/python

   (5) http://www.tishler.net/jason/software/python/

   (6) https://www.python.org/downloads/windows/


File: python.info,  Node: Using Python on a Mac,  Next: Editors and IDEs,  Prev: Using Python on Windows,  Up: Python Setup and Usage

3.4 Using Python on a Mac
=========================


Author: Bob Savage <<bobsavage@mac.com>>

Python on a Mac running macOS is in principle very similar to Python on
any other Unix platform, but there are a number of additional features
such as the IDE and the Package Manager that are worth pointing out.

* Menu:

* Getting and Installing MacPython::
* The IDE::
* Installing Additional Python Packages::
* GUI Programming on the Mac::
* Distributing Python Applications on the Mac::
* Other Resources::


File: python.info,  Node: Getting and Installing MacPython,  Next: The IDE,  Up: Using Python on a Mac

3.4.1 Getting and Installing MacPython
--------------------------------------

macOS since version 10.8 comes with Python 2.7 pre-installed by Apple.
If you wish, you are invited to install the most recent version of
Python 3 from the Python website (‘https://www.python.org’).  A current
“universal binary” build of Python, which runs natively on the Mac’s new
Intel and legacy PPC CPU’s, is available there.

What you get after installing is a number of things:

   * A ‘Python 3.9’ folder in your ‘Applications’ folder.  In here you
     find IDLE, the development environment that is a standard part of
     official Python distributions; and PythonLauncher, which handles
     double-clicking Python scripts from the Finder.

   * A framework ‘/Library/Frameworks/Python.framework’, which includes
     the Python executable and libraries.  The installer adds this
     location to your shell path.  To uninstall MacPython, you can
     simply remove these three things.  A symlink to the Python
     executable is placed in /usr/local/bin/.

The Apple-provided build of Python is installed in
‘/System/Library/Frameworks/Python.framework’ and ‘/usr/bin/python’,
respectively.  You should never modify or delete these, as they are
Apple-controlled and are used by Apple- or third-party software.
Remember that if you choose to install a newer Python version from
python.org, you will have two different but functional Python
installations on your computer, so it will be important that your paths
and usages are consistent with what you want to do.

IDLE includes a help menu that allows you to access Python
documentation.  If you are completely new to Python you should start
reading the tutorial introduction in that document.

If you are familiar with Python on other Unix platforms you should read
the section on running Python scripts from the Unix shell.

* Menu:

* How to run a Python script::
* Running scripts with a GUI::
* Configuration::


File: python.info,  Node: How to run a Python script,  Next: Running scripts with a GUI,  Up: Getting and Installing MacPython

3.4.1.1 How to run a Python script
..................................

Your best way to get started with Python on macOS is through the IDLE
integrated development environment, see section *note The IDE: 14d5. and
use the Help menu when the IDE is running.

If you want to run Python scripts from the Terminal window command line
or from the Finder you first need an editor to create your script.
macOS comes with a number of standard Unix command line editors, ‘vim’
and ‘emacs’ among them.  If you want a more Mac-like editor, ‘BBEdit’ or
‘TextWrangler’ from Bare Bones Software (see
‘http://www.barebones.com/products/bbedit/index.html’) are good choices,
as is ‘TextMate’ (see ‘https://macromates.com/’).  Other editors include
‘Gvim’ (‘http://macvim-dev.github.io/macvim/’) and ‘Aquamacs’
(‘http://aquamacs.org/’).

To run your script from the Terminal window you must make sure that
‘/usr/local/bin’ is in your shell search path.

To run your script from the Finder you have two options:

   * Drag it to ‘PythonLauncher’

   * Select ‘PythonLauncher’ as the default application to open your
     script (or any .py script) through the finder Info window and
     double-click it.  ‘PythonLauncher’ has various preferences to
     control how your script is launched.  Option-dragging allows you to
     change these for one invocation, or use its Preferences menu to
     change things globally.


File: python.info,  Node: Running scripts with a GUI,  Next: Configuration,  Prev: How to run a Python script,  Up: Getting and Installing MacPython

3.4.1.2 Running scripts with a GUI
..................................

With older versions of Python, there is one macOS quirk that you need to
be aware of: programs that talk to the Aqua window manager (in other
words, anything that has a GUI) need to be run in a special way.  Use
‘pythonw’ instead of ‘python’ to start such scripts.

With Python 3.9, you can use either ‘python’ or ‘pythonw’.


File: python.info,  Node: Configuration,  Prev: Running scripts with a GUI,  Up: Getting and Installing MacPython

3.4.1.3 Configuration
.....................

Python on macOS honors all standard Unix environment variables such as
*note PYTHONPATH: a34, but setting these variables for programs started
from the Finder is non-standard as the Finder does not read your
‘.profile’ or ‘.cshrc’ at startup.  You need to create a file
‘~/.MacOSX/environment.plist’.  See Apple’s Technical Document QA1067
for details.

For more information on installation Python packages in MacPython, see
section *note Installing Additional Python Packages: 14d9.


File: python.info,  Node: The IDE,  Next: Installing Additional Python Packages,  Prev: Getting and Installing MacPython,  Up: Using Python on a Mac

3.4.2 The IDE
-------------

MacPython ships with the standard IDLE development environment.  A good
introduction to using IDLE can be found at
‘http://www.hashcollision.org/hkn/python/idle_intro/index.html’.


File: python.info,  Node: Installing Additional Python Packages,  Next: GUI Programming on the Mac,  Prev: The IDE,  Up: Using Python on a Mac

3.4.3 Installing Additional Python Packages
-------------------------------------------

There are several methods to install additional Python packages:

   * Packages can be installed via the standard Python distutils mode
     (‘python setup.py install’).

   * Many packages can also be installed via the ‘setuptools’ extension
     or ‘pip’ wrapper, see ‘https://pip.pypa.io/’.


File: python.info,  Node: GUI Programming on the Mac,  Next: Distributing Python Applications on the Mac,  Prev: Installing Additional Python Packages,  Up: Using Python on a Mac

3.4.4 GUI Programming on the Mac
--------------------------------

There are several options for building GUI applications on the Mac with
Python.

`PyObjC' is a Python binding to Apple’s Objective-C/Cocoa framework,
which is the foundation of most modern Mac development.  Information on
PyObjC is available from ‘https://pypi.org/project/pyobjc/’.

The standard Python GUI toolkit is *note tkinter: 10e, based on the
cross-platform Tk toolkit (‘https://www.tcl.tk’).  An Aqua-native
version of Tk is bundled with OS X by Apple, and the latest version can
be downloaded and installed from ‘https://www.activestate.com’; it can
also be built from source.

`wxPython' is another popular cross-platform GUI toolkit that runs
natively on macOS. Packages and documentation are available from
‘https://www.wxpython.org’.

`PyQt' is another popular cross-platform GUI toolkit that runs natively
on macOS. More information can be found at
‘https://riverbankcomputing.com/software/pyqt/intro’.


File: python.info,  Node: Distributing Python Applications on the Mac,  Next: Other Resources,  Prev: GUI Programming on the Mac,  Up: Using Python on a Mac

3.4.5 Distributing Python Applications on the Mac
-------------------------------------------------

The standard tool for deploying standalone Python applications on the
Mac is ‘py2app’.  More information on installing and using py2app can be
found at ‘http://undefined.org/python/#py2app’.


File: python.info,  Node: Other Resources,  Prev: Distributing Python Applications on the Mac,  Up: Using Python on a Mac

3.4.6 Other Resources
---------------------

The MacPython mailing list is an excellent support resource for Python
users and developers on the Mac:

‘https://www.python.org/community/sigs/current/pythonmac-sig/’

Another useful resource is the MacPython wiki:

‘https://wiki.python.org/moin/MacPython’


File: python.info,  Node: Editors and IDEs,  Prev: Using Python on a Mac,  Up: Python Setup and Usage

3.5 Editors and IDEs
====================

There are a number of IDEs that support Python programming language.
Many editors and IDEs provide syntax highlighting, debugging tools, and
PEP 8(1) checks.

Please go to Python Editors(2) and Integrated Development
Environments(3) for a comprehensive list.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0008

   (2) https://wiki.python.org/moin/PythonEditors

   (3) https://wiki.python.org/moin/IntegratedDevelopmentEnvironments


File: python.info,  Node: The Python Language Reference,  Next: The Python Standard Library,  Prev: Python Setup and Usage,  Up: Top

4 The Python Language Reference
*******************************

This reference manual describes the syntax and “core semantics” of the
language.  It is terse, but attempts to be exact and complete.  The
semantics of non-essential built-in object types and of the built-in
functions and modules are described in *note The Python Standard
Library: 1330.  For an informal introduction to the language, see *note
The Python Tutorial: 132f.  For C or C++ programmers, two additional
manuals exist: *note Extending and Embedding the Python Interpreter:
1332. describes the high-level picture of how to write a Python
extension module, and the *note Python/C API Reference Manual: 1333.
describes the interfaces available to C/C++ programmers in detail.

* Menu:

* Introduction: Introduction<5>.
* Lexical analysis::
* Data model::
* Execution model::
* The import system::
* Expressions::
* Simple statements::
* Compound statements::
* Top-level components::
* Full Grammar specification::


File: python.info,  Node: Introduction<5>,  Next: Lexical analysis,  Up: The Python Language Reference

4.1 Introduction
================

This reference manual describes the Python programming language.  It is
not intended as a tutorial.

While I am trying to be as precise as possible, I chose to use English
rather than formal specifications for everything except syntax and
lexical analysis.  This should make the document more understandable to
the average reader, but will leave room for ambiguities.  Consequently,
if you were coming from Mars and tried to re-implement Python from this
document alone, you might have to guess things and in fact you would
probably end up implementing quite a different language.  On the other
hand, if you are using Python and wonder what the precise rules about a
particular area of the language are, you should definitely be able to
find them here.  If you would like to see a more formal definition of
the language, maybe you could volunteer your time — or invent a cloning
machine :-).

It is dangerous to add too many implementation details to a language
reference document — the implementation may change, and other
implementations of the same language may work differently.  On the other
hand, CPython is the one Python implementation in widespread use
(although alternate implementations continue to gain support), and its
particular quirks are sometimes worth being mentioned, especially where
the implementation imposes additional limitations.  Therefore, you’ll
find short “implementation notes” sprinkled throughout the text.

Every Python implementation comes with a number of built-in and standard
modules.  These are documented in *note The Python Standard Library:
1330.  A few built-in modules are mentioned when they interact in a
significant way with the language definition.

* Menu:

* Alternate Implementations::
* Notation::


File: python.info,  Node: Alternate Implementations,  Next: Notation,  Up: Introduction<5>

4.1.1 Alternate Implementations
-------------------------------

Though there is one Python implementation which is by far the most
popular, there are some alternate implementations which are of
particular interest to different audiences.

Known implementations include:

CPython

     This is the original and most-maintained implementation of Python,
     written in C. New language features generally appear here first.

Jython

     Python implemented in Java.  This implementation can be used as a
     scripting language for Java applications, or can be used to create
     applications using the Java class libraries.  It is also often used
     to create tests for Java libraries.  More information can be found
     at the Jython website(1).

Python for .NET

     This implementation actually uses the CPython implementation, but
     is a managed .NET application and makes .NET libraries available.
     It was created by Brian Lloyd.  For more information, see the
     Python for .NET home page(2).

IronPython

     An alternate Python for .NET. Unlike Python.NET, this is a complete
     Python implementation that generates IL, and compiles Python code
     directly to .NET assemblies.  It was created by Jim Hugunin, the
     original creator of Jython.  For more information, see the
     IronPython website(3).

PyPy

     An implementation of Python written completely in Python.  It
     supports several advanced features not found in other
     implementations like stackless support and a Just in Time compiler.
     One of the goals of the project is to encourage experimentation
     with the language itself by making it easier to modify the
     interpreter (since it is written in Python).  Additional
     information is available on the PyPy project’s home page(4).

Each of these implementations varies in some way from the language as
documented in this manual, or introduces specific information beyond
what’s covered in the standard Python documentation.  Please refer to
the implementation-specific documentation to determine what else you
need to know about the specific implementation you’re using.

   ---------- Footnotes ----------

   (1) http://www.jython.org/

   (2) https://pythonnet.github.io/

   (3) http://ironpython.net/

   (4) http://pypy.org/


File: python.info,  Node: Notation,  Prev: Alternate Implementations,  Up: Introduction<5>

4.1.2 Notation
--------------

The descriptions of lexical analysis and syntax use a modified BNF
grammar notation.  This uses the following style of definition:

     name      ::= lc_letter (lc_letter | "_")*
     lc_letter ::= "a"..."z"

The first line says that a ‘name’ is an ‘lc_letter’ followed by a
sequence of zero or more ‘lc_letter’s and underscores.  An ‘lc_letter’
in turn is any of the single characters ‘'a'’ through ‘'z'’.  (This rule
is actually adhered to for the names defined in lexical and grammar
rules in this document.)

Each rule begins with a name (which is the name defined by the rule) and
‘::=’.  A vertical bar (‘|’) is used to separate alternatives; it is the
least binding operator in this notation.  A star (‘*’) means zero or
more repetitions of the preceding item; likewise, a plus (‘+’) means one
or more repetitions, and a phrase enclosed in square brackets (‘[ ]’)
means zero or one occurrences (in other words, the enclosed phrase is
optional).  The ‘*’ and ‘+’ operators bind as tightly as possible;
parentheses are used for grouping.  Literal strings are enclosed in
quotes.  White space is only meaningful to separate tokens.  Rules are
normally contained on a single line; rules with many alternatives may be
formatted alternatively with each line after the first beginning with a
vertical bar.

In lexical definitions (as the example above), two more conventions are
used: Two literal characters separated by three dots mean a choice of
any single character in the given (inclusive) range of ASCII characters.
A phrase between angular brackets (‘<...>’) gives an informal
description of the symbol defined; e.g., this could be used to describe
the notion of ‘control character’ if needed.

Even though the notation used is almost the same, there is a big
difference between the meaning of lexical and syntactic definitions: a
lexical definition operates on the individual characters of the input
source, while a syntax definition operates on the stream of tokens
generated by the lexical analysis.  All uses of BNF in the next chapter
(“Lexical Analysis”) are lexical definitions; uses in subsequent
chapters are syntactic definitions.


File: python.info,  Node: Lexical analysis,  Next: Data model,  Prev: Introduction<5>,  Up: The Python Language Reference

4.2 Lexical analysis
====================

A Python program is read by a `parser'.  Input to the parser is a stream
of `tokens', generated by the `lexical analyzer'.  This chapter
describes how the lexical analyzer breaks a file into tokens.

Python reads program text as Unicode code points; the encoding of a
source file can be given by an encoding declaration and defaults to
UTF-8, see PEP 3120(1) for details.  If the source file cannot be
decoded, a *note SyntaxError: 55a. is raised.

* Menu:

* Line structure::
* Other tokens::
* Identifiers and keywords::
* Literals::
* Operators::
* Delimiters::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3120


File: python.info,  Node: Line structure,  Next: Other tokens,  Up: Lexical analysis

4.2.1 Line structure
--------------------

A Python program is divided into a number of `logical lines'.

* Menu:

* Logical lines::
* Physical lines::
* Comments::
* Encoding declarations::
* Explicit line joining::
* Implicit line joining::
* Blank lines::
* Indentation::
* Whitespace between tokens::


File: python.info,  Node: Logical lines,  Next: Physical lines,  Up: Line structure

4.2.1.1 Logical lines
.....................

The end of a logical line is represented by the token NEWLINE.
Statements cannot cross logical line boundaries except where NEWLINE is
allowed by the syntax (e.g., between statements in compound statements).
A logical line is constructed from one or more `physical lines' by
following the explicit or implicit `line joining' rules.


File: python.info,  Node: Physical lines,  Next: Comments,  Prev: Logical lines,  Up: Line structure

4.2.1.2 Physical lines
......................

A physical line is a sequence of characters terminated by an end-of-line
sequence.  In source files and strings, any of the standard platform
line termination sequences can be used - the Unix form using ASCII LF
(linefeed), the Windows form using the ASCII sequence CR LF (return
followed by linefeed), or the old Macintosh form using the ASCII CR
(return) character.  All of these forms can be used equally, regardless
of platform.  The end of input also serves as an implicit terminator for
the final physical line.

When embedding Python, source code strings should be passed to Python
APIs using the standard C conventions for newline characters (the ‘\n’
character, representing ASCII LF, is the line terminator).


File: python.info,  Node: Comments,  Next: Encoding declarations,  Prev: Physical lines,  Up: Line structure

4.2.1.3 Comments
................

A comment starts with a hash character (‘#’) that is not part of a
string literal, and ends at the end of the physical line.  A comment
signifies the end of the logical line unless the implicit line joining
rules are invoked.  Comments are ignored by the syntax.


File: python.info,  Node: Encoding declarations,  Next: Explicit line joining,  Prev: Comments,  Up: Line structure

4.2.1.4 Encoding declarations
.............................

If a comment in the first or second line of the Python script matches
the regular expression ‘coding[=:]\s*([-\w.]+)’, this comment is
processed as an encoding declaration; the first group of this expression
names the encoding of the source code file.  The encoding declaration
must appear on a line of its own.  If it is the second line, the first
line must also be a comment-only line.  The recommended forms of an
encoding expression are

     # -*- coding: <encoding-name> -*-

which is recognized also by GNU Emacs, and

     # vim:fileencoding=<encoding-name>

which is recognized by Bram Moolenaar’s VIM.

If no encoding declaration is found, the default encoding is UTF-8.  In
addition, if the first bytes of the file are the UTF-8 byte-order mark
(‘b'\xef\xbb\xbf'’), the declared file encoding is UTF-8 (this is
supported, among others, by Microsoft’s ‘notepad’).

If an encoding is declared, the encoding name must be recognized by
Python.  The encoding is used for all lexical analysis, including string
literals, comments and identifiers.


File: python.info,  Node: Explicit line joining,  Next: Implicit line joining,  Prev: Encoding declarations,  Up: Line structure

4.2.1.5 Explicit line joining
.............................

Two or more physical lines may be joined into logical lines using
backslash characters (‘\’), as follows: when a physical line ends in a
backslash that is not part of a string literal or comment, it is joined
with the following forming a single logical line, deleting the backslash
and the following end-of-line character.  For example:

     if 1900 < year < 2100 and 1 <= month <= 12 \
        and 1 <= day <= 31 and 0 <= hour < 24 \
        and 0 <= minute < 60 and 0 <= second < 60:   # Looks like a valid date
             return 1

A line ending in a backslash cannot carry a comment.  A backslash does
not continue a comment.  A backslash does not continue a token except
for string literals (i.e., tokens other than string literals cannot be
split across physical lines using a backslash).  A backslash is illegal
elsewhere on a line outside a string literal.


File: python.info,  Node: Implicit line joining,  Next: Blank lines,  Prev: Explicit line joining,  Up: Line structure

4.2.1.6 Implicit line joining
.............................

Expressions in parentheses, square brackets or curly braces can be split
over more than one physical line without using backslashes.  For
example:

     month_names = ['Januari', 'Februari', 'Maart',      # These are the
                    'April',   'Mei',      'Juni',       # Dutch names
                    'Juli',    'Augustus', 'September',  # for the months
                    'Oktober', 'November', 'December']   # of the year

Implicitly continued lines can carry comments.  The indentation of the
continuation lines is not important.  Blank continuation lines are
allowed.  There is no NEWLINE token between implicit continuation lines.
Implicitly continued lines can also occur within triple-quoted strings
(see below); in that case they cannot carry comments.


File: python.info,  Node: Blank lines,  Next: Indentation,  Prev: Implicit line joining,  Up: Line structure

4.2.1.7 Blank lines
...................

A logical line that contains only spaces, tabs, formfeeds and possibly a
comment, is ignored (i.e., no NEWLINE token is generated).  During
interactive input of statements, handling of a blank line may differ
depending on the implementation of the read-eval-print loop.  In the
standard interactive interpreter, an entirely blank logical line (i.e.
one containing not even whitespace or a comment) terminates a multi-line
statement.


File: python.info,  Node: Indentation,  Next: Whitespace between tokens,  Prev: Blank lines,  Up: Line structure

4.2.1.8 Indentation
...................

Leading whitespace (spaces and tabs) at the beginning of a logical line
is used to compute the indentation level of the line, which in turn is
used to determine the grouping of statements.

Tabs are replaced (from left to right) by one to eight spaces such that
the total number of characters up to and including the replacement is a
multiple of eight (this is intended to be the same rule as used by
Unix).  The total number of spaces preceding the first non-blank
character then determines the line’s indentation.  Indentation cannot be
split over multiple physical lines using backslashes; the whitespace up
to the first backslash determines the indentation.

Indentation is rejected as inconsistent if a source file mixes tabs and
spaces in a way that makes the meaning dependent on the worth of a tab
in spaces; a *note TabError: f38. is raised in that case.

`Cross-platform compatibility note:' because of the nature of text
editors on non-UNIX platforms, it is unwise to use a mixture of spaces
and tabs for the indentation in a single source file.  It should also be
noted that different platforms may explicitly limit the maximum
indentation level.

A formfeed character may be present at the start of the line; it will be
ignored for the indentation calculations above.  Formfeed characters
occurring elsewhere in the leading whitespace have an undefined effect
(for instance, they may reset the space count to zero).

The indentation levels of consecutive lines are used to generate INDENT
and DEDENT tokens, using a stack, as follows.

Before the first line of the file is read, a single zero is pushed on
the stack; this will never be popped off again.  The numbers pushed on
the stack will always be strictly increasing from bottom to top.  At the
beginning of each logical line, the line’s indentation level is compared
to the top of the stack.  If it is equal, nothing happens.  If it is
larger, it is pushed on the stack, and one INDENT token is generated.
If it is smaller, it `must' be one of the numbers occurring on the
stack; all numbers on the stack that are larger are popped off, and for
each number popped off a DEDENT token is generated.  At the end of the
file, a DEDENT token is generated for each number remaining on the stack
that is larger than zero.

Here is an example of a correctly (though confusingly) indented piece of
Python code:

     def perm(l):
             # Compute the list of all permutations of l
         if len(l) <= 1:
                       return [l]
         r = []
         for i in range(len(l)):
                  s = l[:i] + l[i+1:]
                  p = perm(s)
                  for x in p:
                   r.append(l[i:i+1] + x)
         return r

The following example shows various indentation errors:

      def perm(l):                       # error: first line indented
     for i in range(len(l)):             # error: not indented
         s = l[:i] + l[i+1:]
             p = perm(l[:i] + l[i+1:])   # error: unexpected indent
             for x in p:
                     r.append(l[i:i+1] + x)
                 return r                # error: inconsistent dedent

(Actually, the first three errors are detected by the parser; only the
last error is found by the lexical analyzer — the indentation of ‘return
r’ does not match a level popped off the stack.)


File: python.info,  Node: Whitespace between tokens,  Prev: Indentation,  Up: Line structure

4.2.1.9 Whitespace between tokens
.................................

Except at the beginning of a logical line or in string literals, the
whitespace characters space, tab and formfeed can be used
interchangeably to separate tokens.  Whitespace is needed between two
tokens only if their concatenation could otherwise be interpreted as a
different token (e.g., ab is one token, but a b is two tokens).


File: python.info,  Node: Other tokens,  Next: Identifiers and keywords,  Prev: Line structure,  Up: Lexical analysis

4.2.2 Other tokens
------------------

Besides NEWLINE, INDENT and DEDENT, the following categories of tokens
exist: `identifiers', `keywords', `literals', `operators', and
`delimiters'.  Whitespace characters (other than line terminators,
discussed earlier) are not tokens, but serve to delimit tokens.  Where
ambiguity exists, a token comprises the longest possible string that
forms a legal token, when read from left to right.


File: python.info,  Node: Identifiers and keywords,  Next: Literals,  Prev: Other tokens,  Up: Lexical analysis

4.2.3 Identifiers and keywords
------------------------------

Identifiers (also referred to as `names') are described by the following
lexical definitions.

The syntax of identifiers in Python is based on the Unicode standard
annex UAX-31, with elaboration and changes as defined below; see also
PEP 3131(1) for further details.

Within the ASCII range (U+0001..U+007F), the valid characters for
identifiers are the same as in Python 2.x: the uppercase and lowercase
letters ‘A’ through ‘Z’, the underscore ‘_’ and, except for the first
character, the digits ‘0’ through ‘9’.

Python 3.0 introduces additional characters from outside the ASCII range
(see PEP 3131(2)).  For these characters, the classification uses the
version of the Unicode Character Database as included in the *note
unicodedata: 123. module.

Identifiers are unlimited in length.  Case is significant.

     identifier   ::= xid_start xid_continue*
     id_start     ::= <all characters in general categories Lu, Ll, Lt, Lm, Lo, Nl, the underscore, and characters with the Other_ID_Start property>
     id_continue  ::= <all characters in id_start, plus characters in the categories Mn, Mc, Nd, Pc and others with the Other_ID_Continue property>
     xid_start    ::= <all characters in id_start whose NFKC normalization is in "id_start xid_continue*">
     xid_continue ::= <all characters in id_continue whose NFKC normalization is in "id_continue*">

The Unicode category codes mentioned above stand for:

   * `Lu' - uppercase letters

   * `Ll' - lowercase letters

   * `Lt' - titlecase letters

   * `Lm' - modifier letters

   * `Lo' - other letters

   * `Nl' - letter numbers

   * `Mn' - nonspacing marks

   * `Mc' - spacing combining marks

   * `Nd' - decimal numbers

   * `Pc' - connector punctuations

   * `Other_ID_Start' - explicit list of characters in PropList.txt(3)
     to support backwards compatibility

   * `Other_ID_Continue' - likewise

All identifiers are converted into the normal form NFKC while parsing;
comparison of identifiers is based on NFKC.

A non-normative HTML file listing all valid identifier characters for
Unicode 4.1 can be found at
‘https://www.unicode.org/Public/13.0.0/ucd/DerivedCoreProperties.txt’

* Menu:

* Keywords::
* Reserved classes of identifiers::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3131

   (2) https://www.python.org/dev/peps/pep-3131

   (3) https://www.unicode.org/Public/13.0.0/ucd/PropList.txt


File: python.info,  Node: Keywords,  Next: Reserved classes of identifiers,  Up: Identifiers and keywords

4.2.3.1 Keywords
................

The following identifiers are used as reserved words, or `keywords' of
the language, and cannot be used as ordinary identifiers.  They must be
spelled exactly as written here:

     False      await      else       import     pass
     None       break      except     in         raise
     True       class      finally    is         return
     and        continue   for        lambda     try
     as         def        from       nonlocal   while
     assert     del        global     not        with
     async      elif       if         or         yield


File: python.info,  Node: Reserved classes of identifiers,  Prev: Keywords,  Up: Identifiers and keywords

4.2.3.2 Reserved classes of identifiers
.......................................

Certain classes of identifiers (besides keywords) have special meanings.
These classes are identified by the patterns of leading and trailing
underscore characters:

‘_*’

     Not imported by ‘from module import *’.  The special identifier ‘_’
     is used in the interactive interpreter to store the result of the
     last evaluation; it is stored in the *note builtins: 12. module.
     When not in interactive mode, ‘_’ has no special meaning and is not
     defined.  See section *note The import statement: ce7.

          Note: The name ‘_’ is often used in conjunction with
          internationalization; refer to the documentation for the *note
          gettext: 87. module for more information on this convention.

‘__*__’

     System-defined names, informally known as “dunder” names.  These
     names are defined by the interpreter and its implementation
     (including the standard library).  Current system names are
     discussed in the *note Special method names: 608. section and
     elsewhere.  More will likely be defined in future versions of
     Python.  `Any' use of ‘__*__’ names, in any context, that does not
     follow explicitly documented use, is subject to breakage without
     warning.

‘__*’

     Class-private names.  Names in this category, when used within the
     context of a class definition, are re-written to use a mangled form
     to help avoid name clashes between “private” attributes of base and
     derived classes.  See section *note Identifiers (Names): 1510.


File: python.info,  Node: Literals,  Next: Operators,  Prev: Identifiers and keywords,  Up: Lexical analysis

4.2.4 Literals
--------------

Literals are notations for constant values of some built-in types.

* Menu:

* String and Bytes literals::
* String literal concatenation::
* Formatted string literals::
* Numeric literals::
* Integer literals::
* Floating point literals::
* Imaginary literals::


File: python.info,  Node: String and Bytes literals,  Next: String literal concatenation,  Up: Literals

4.2.4.1 String and Bytes literals
.................................

String literals are described by the following lexical definitions:

     stringliteral   ::= [stringprefix](shortstring | longstring)
     stringprefix    ::= "r" | "u" | "R" | "U" | "f" | "F"
                         | "fr" | "Fr" | "fR" | "FR" | "rf" | "rF" | "Rf" | "RF"
     shortstring     ::= "'" shortstringitem* "'" | '"' shortstringitem* '"'
     longstring      ::= "'''" longstringitem* "'''" | '"""' longstringitem* '"""'
     shortstringitem ::= shortstringchar | stringescapeseq
     longstringitem  ::= longstringchar | stringescapeseq
     shortstringchar ::= <any source character except "\" or newline or the quote>
     longstringchar  ::= <any source character except "\">
     stringescapeseq ::= "\" <any source character>

     bytesliteral   ::= bytesprefix(shortbytes | longbytes)
     bytesprefix    ::= "b" | "B" | "br" | "Br" | "bR" | "BR" | "rb" | "rB" | "Rb" | "RB"
     shortbytes     ::= "'" shortbytesitem* "'" | '"' shortbytesitem* '"'
     longbytes      ::= "'''" longbytesitem* "'''" | '"""' longbytesitem* '"""'
     shortbytesitem ::= shortbyteschar | bytesescapeseq
     longbytesitem  ::= longbyteschar | bytesescapeseq
     shortbyteschar ::= <any ASCII character except "\" or newline or the quote>
     longbyteschar  ::= <any ASCII character except "\">
     bytesescapeseq ::= "\" <any ASCII character>

One syntactic restriction not indicated by these productions is that
whitespace is not allowed between the *note stringprefix: 1516. or *note
bytesprefix: 151f. and the rest of the literal.  The source character
set is defined by the encoding declaration; it is UTF-8 if no encoding
declaration is given in the source file; see section *note Encoding
declarations: 14f8.

In plain English: Both types of literals can be enclosed in matching
single quotes (‘'’) or double quotes (‘"’).  They can also be enclosed
in matching groups of three single or double quotes (these are generally
referred to as `triple-quoted strings').  The backslash (‘\’) character
is used to escape characters that otherwise have a special meaning, such
as newline, backslash itself, or the quote character.

Bytes literals are always prefixed with ‘'b'’ or ‘'B'’; they produce an
instance of the *note bytes: 172. type instead of the *note str: 205.
type.  They may only contain ASCII characters; bytes with a numeric
value of 128 or greater must be expressed with escapes.

Both string and bytes literals may optionally be prefixed with a letter
‘'r'’ or ‘'R'’; such strings are called `raw strings' and treat
backslashes as literal characters.  As a result, in string literals,
‘'\U'’ and ‘'\u'’ escapes in raw strings are not treated specially.
Given that Python 2.x’s raw unicode literals behave differently than
Python 3.x’s the ‘'ur'’ syntax is not supported.

New in version 3.3: The ‘'rb'’ prefix of raw bytes literals has been
added as a synonym of ‘'br'’.

New in version 3.3: Support for the unicode legacy literal (‘u'value'’)
was reintroduced to simplify the maintenance of dual Python 2.x and 3.x
codebases.  See PEP 414(1) for more information.

A string literal with ‘'f'’ or ‘'F'’ in its prefix is a `formatted
string literal'; see *note Formatted string literals: 296.  The ‘'f'’
may be combined with ‘'r'’, but not with ‘'b'’ or ‘'u'’, therefore raw
formatted strings are possible, but formatted bytes literals are not.

In triple-quoted literals, unescaped newlines and quotes are allowed
(and are retained), except that three unescaped quotes in a row
terminate the literal.  (A “quote” is the character used to open the
literal, i.e.  either ‘'’ or ‘"’.)

Unless an ‘'r'’ or ‘'R'’ prefix is present, escape sequences in string
and bytes literals are interpreted according to rules similar to those
used by Standard C. The recognized escape sequences are:

Escape Sequence       Meaning                               Notes
                                                            
------------------------------------------------------------------------
                                                            
‘\newline’            Backslash and newline ignored
                      
                                                            
‘\\’                  Backslash (‘\’)
                      
                                                            
‘\'’                  Single quote (‘'’)
                      
                                                            
‘\"’                  Double quote (‘"’)
                      
                                                            
‘\a’                  ASCII Bell (BEL)
                      
                                                            
‘\b’                  ASCII Backspace (BS)
                      
                                                            
‘\f’                  ASCII Formfeed (FF)
                      
                                                            
‘\n’                  ASCII Linefeed (LF)
                      
                                                            
‘\r’                  ASCII Carriage Return (CR)
                      
                                                            
‘\t’                  ASCII Horizontal Tab (TAB)
                      
                                                            
‘\v’                  ASCII Vertical Tab (VT)
                      
                                                            
‘\ooo’                Character with octal value `ooo'      (1,3)
                                                            
                                                            
‘\xhh’                Character with hex value `hh'         (2,3)
                                                            

Escape sequences only recognized in string literals are:

Escape Sequence       Meaning                               Notes
                                                            
------------------------------------------------------------------------
                                                            
‘\N{name}’            Character named `name' in the         (4)
                      Unicode database                      
                      
                                                            
‘\uxxxx’              Character with 16-bit hex value       (5)
                      `xxxx'                                
                      
                                                            
‘\Uxxxxxxxx’          Character with 32-bit hex value       (6)
                      `xxxxxxxx'                            
                      

Notes:

  1. As in Standard C, up to three octal digits are accepted.

  2. Unlike in Standard C, exactly two hex digits are required.

  3. In a bytes literal, hexadecimal and octal escapes denote the byte
     with the given value.  In a string literal, these escapes denote a
     Unicode character with the given value.

  4. 
     Changed in version 3.3: Support for name aliases (2) has been
     added.

  5. Exactly four hex digits are required.

  6. Any Unicode character can be encoded this way.  Exactly eight hex
     digits are required.

Unlike Standard C, all unrecognized escape sequences are left in the
string unchanged, i.e., `the backslash is left in the result'.  (This
behavior is useful when debugging: if an escape sequence is mistyped,
the resulting output is more easily recognized as broken.)  It is also
important to note that the escape sequences only recognized in string
literals fall into the category of unrecognized escapes for bytes
literals.

     Changed in version 3.6: Unrecognized escape sequences produce a
     *note DeprecationWarning: 15a.  In a future Python version they
     will be a *note SyntaxWarning: 2c9. and eventually a *note
     SyntaxError: 55a.

Even in a raw literal, quotes can be escaped with a backslash, but the
backslash remains in the result; for example, ‘r"\""’ is a valid string
literal consisting of two characters: a backslash and a double quote;
‘r"\"’ is not a valid string literal (even a raw string cannot end in an
odd number of backslashes).  Specifically, `a raw literal cannot end in
a single backslash' (since the backslash would escape the following
quote character).  Note also that a single backslash followed by a
newline is interpreted as those two characters as part of the literal,
`not' as a line continuation.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0414

   (2) (1) ‘https://www.unicode.org/Public/11.0.0/ucd/NameAliases.txt’


File: python.info,  Node: String literal concatenation,  Next: Formatted string literals,  Prev: String and Bytes literals,  Up: Literals

4.2.4.2 String literal concatenation
....................................

Multiple adjacent string or bytes literals (delimited by whitespace),
possibly using different quoting conventions, are allowed, and their
meaning is the same as their concatenation.  Thus, ‘"hello" 'world'’ is
equivalent to ‘"helloworld"’.  This feature can be used to reduce the
number of backslashes needed, to split long strings conveniently across
long lines, or even to add comments to parts of strings, for example:

     re.compile("[A-Za-z_]"       # letter or underscore
                "[A-Za-z0-9_]*"   # letter, digit or underscore
               )

Note that this feature is defined at the syntactical level, but
implemented at compile time.  The ‘+’ operator must be used to
concatenate string expressions at run time.  Also note that literal
concatenation can use different quoting styles for each component (even
mixing raw strings and triple quoted strings), and formatted string
literals may be concatenated with plain string literals.


File: python.info,  Node: Formatted string literals,  Next: Numeric literals,  Prev: String literal concatenation,  Up: Literals

4.2.4.3 Formatted string literals
.................................

New in version 3.6.

A `formatted string literal' or `f-string' is a string literal that is
prefixed with ‘'f'’ or ‘'F'’.  These strings may contain replacement
fields, which are expressions delimited by curly braces ‘{}’.  While
other string literals always have a constant value, formatted strings
are really expressions evaluated at run time.

Escape sequences are decoded like in ordinary string literals (except
when a literal is also marked as a raw string).  After decoding, the
grammar for the contents of the string is:

     f_string          ::= (literal_char | "{{" | "}}" | replacement_field)*
     replacement_field ::= "{" f_expression ["="] ["!" conversion] [":" format_spec] "}"
     f_expression      ::= (conditional_expression | "*" or_expr)
                             ("," conditional_expression | "," "*" or_expr)* [","]
                           | yield_expression
     conversion        ::= "s" | "r" | "a"
     format_spec       ::= (literal_char | NULL | replacement_field)*
     literal_char      ::= <any code point except "{", "}" or NULL>

The parts of the string outside curly braces are treated literally,
except that any doubled curly braces ‘'{{'’ or ‘'}}'’ are replaced with
the corresponding single curly brace.  A single opening curly bracket
‘'{'’ marks a replacement field, which starts with a Python expression.
To display both the expression text and its value after evaluation,
(useful in debugging), an equal sign ‘'='’ may be added after the
expression.  A conversion field, introduced by an exclamation point
‘'!'’ may follow.  A format specifier may also be appended, introduced
by a colon ‘':'’.  A replacement field ends with a closing curly bracket
‘'}'’.

Expressions in formatted string literals are treated like regular Python
expressions surrounded by parentheses, with a few exceptions.  An empty
expression is not allowed, and both *note lambda: cf9. and assignment
expressions ‘:=’ must be surrounded by explicit parentheses.
Replacement expressions can contain line breaks (e.g.  in triple-quoted
strings), but they cannot contain comments.  Each expression is
evaluated in the context where the formatted string literal appears, in
order from left to right.

Changed in version 3.7: Prior to Python 3.7, an *note await: 2d8.
expression and comprehensions containing an *note async for: 3fd. clause
were illegal in the expressions in formatted string literals due to a
problem with the implementation.

When the equal sign ‘'='’ is provided, the output will have the
expression text, the ‘'='’ and the evaluated value.  Spaces after the
opening brace ‘'{'’, within the expression and after the ‘'='’ are all
retained in the output.  By default, the ‘'='’ causes the *note repr():
8b9. of the expression to be provided, unless there is a format
specified.  When a format is specified it defaults to the *note str():
205. of the expression unless a conversion ‘'!r'’ is declared.

New in version 3.8: The equal sign ‘'='’.

If a conversion is specified, the result of evaluating the expression is
converted before formatting.  Conversion ‘'!s'’ calls *note str(): 205.
on the result, ‘'!r'’ calls *note repr(): 8b9, and ‘'!a'’ calls *note
ascii(): e11.

The result is then formatted using the *note format(): 5d6. protocol.
The format specifier is passed to the *note __format__(): a2f. method of
the expression or conversion result.  An empty string is passed when the
format specifier is omitted.  The formatted result is then included in
the final value of the whole string.

Top-level format specifiers may include nested replacement fields.
These nested fields may include their own conversion fields and *note
format specifiers: 5d9, but may not include more deeply-nested
replacement fields.  The *note format specifier mini-language: 5d9. is
the same as that used by the *note str.format(): 5d5. method.

Formatted string literals may be concatenated, but replacement fields
cannot be split across literals.

Some examples of formatted string literals:

     >>> name = "Fred"
     >>> f"He said his name is {name!r}."
     "He said his name is 'Fred'."
     >>> f"He said his name is {repr(name)}."  # repr() is equivalent to !r
     "He said his name is 'Fred'."
     >>> width = 10
     >>> precision = 4
     >>> value = decimal.Decimal("12.34567")
     >>> f"result: {value:{width}.{precision}}"  # nested fields
     'result:      12.35'
     >>> today = datetime(year=2017, month=1, day=27)
     >>> f"{today:%B %d, %Y}"  # using date format specifier
     'January 27, 2017'
     >>> f"{today=:%B %d, %Y}" # using date format specifier and debugging
     'today=January 27, 2017'
     >>> number = 1024
     >>> f"{number:#0x}"  # using integer format specifier
     '0x400'
     >>> foo = "bar"
     >>> f"{ foo = }" # preserves whitespace
     " foo = 'bar'"
     >>> line = "The mill's closed"
     >>> f"{line = }"
     'line = "The mill\'s closed"'
     >>> f"{line = :20}"
     "line = The mill's closed   "
     >>> f"{line = !r:20}"
     'line = "The mill\'s closed" '

A consequence of sharing the same syntax as regular string literals is
that characters in the replacement fields must not conflict with the
quoting used in the outer formatted string literal:

     f"abc {a["x"]} def"    # error: outer string literal ended prematurely
     f"abc {a['x']} def"    # workaround: use different quoting

Backslashes are not allowed in format expressions and will raise an
error:

     f"newline: {ord('\n')}"  # raises SyntaxError

To include a value in which a backslash escape is required, create a
temporary variable.

     >>> newline = ord('\n')
     >>> f"newline: {newline}"
     'newline: 10'

Formatted string literals cannot be used as docstrings, even if they do
not include expressions.

     >>> def foo():
     ...     f"Not a docstring"
     ...
     >>> foo.__doc__ is None
     True

See also PEP 498(1) for the proposal that added formatted string
literals, and *note str.format(): 5d5, which uses a related format
string mechanism.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0498


File: python.info,  Node: Numeric literals,  Next: Integer literals,  Prev: Formatted string literals,  Up: Literals

4.2.4.4 Numeric literals
........................

There are three types of numeric literals: integers, floating point
numbers, and imaginary numbers.  There are no complex literals (complex
numbers can be formed by adding a real number and an imaginary number).

Note that numeric literals do not include a sign; a phrase like ‘-1’ is
actually an expression composed of the unary operator ‘‘-’’ and the
literal ‘1’.


File: python.info,  Node: Integer literals,  Next: Floating point literals,  Prev: Numeric literals,  Up: Literals

4.2.4.5 Integer literals
........................

Integer literals are described by the following lexical definitions:

     integer      ::= decinteger | bininteger | octinteger | hexinteger
     decinteger   ::= nonzerodigit (["_"] digit)* | "0"+ (["_"] "0")*
     bininteger   ::= "0" ("b" | "B") (["_"] bindigit)+
     octinteger   ::= "0" ("o" | "O") (["_"] octdigit)+
     hexinteger   ::= "0" ("x" | "X") (["_"] hexdigit)+
     nonzerodigit ::= "1"..."9"
     digit        ::= "0"..."9"
     bindigit     ::= "0" | "1"
     octdigit     ::= "0"..."7"
     hexdigit     ::= digit | "a"..."f" | "A"..."F"

There is no limit for the length of integer literals apart from what can
be stored in available memory.

Underscores are ignored for determining the numeric value of the
literal.  They can be used to group digits for enhanced readability.
One underscore can occur between digits, and after base specifiers like
‘0x’.

Note that leading zeros in a non-zero decimal number are not allowed.
This is for disambiguation with C-style octal literals, which Python
used before version 3.0.

Some examples of integer literals:

     7     2147483647                        0o177    0b100110111
     3     79228162514264337593543950336     0o377    0xdeadbeef
           100_000_000_000                   0b_1110_0101

Changed in version 3.6: Underscores are now allowed for grouping
purposes in literals.


File: python.info,  Node: Floating point literals,  Next: Imaginary literals,  Prev: Integer literals,  Up: Literals

4.2.4.6 Floating point literals
...............................

Floating point literals are described by the following lexical
definitions:

     floatnumber   ::= pointfloat | exponentfloat
     pointfloat    ::= [digitpart] fraction | digitpart "."
     exponentfloat ::= (digitpart | pointfloat) exponent
     digitpart     ::= digit (["_"] digit)*
     fraction      ::= "." digitpart
     exponent      ::= ("e" | "E") ["+" | "-"] digitpart

Note that the integer and exponent parts are always interpreted using
radix 10.  For example, ‘077e010’ is legal, and denotes the same number
as ‘77e10’.  The allowed range of floating point literals is
implementation-dependent.  As in integer literals, underscores are
supported for digit grouping.

Some examples of floating point literals:

     3.14    10.    .001    1e100    3.14e-10    0e0    3.14_15_93

Changed in version 3.6: Underscores are now allowed for grouping
purposes in literals.


File: python.info,  Node: Imaginary literals,  Prev: Floating point literals,  Up: Literals

4.2.4.7 Imaginary literals
..........................

Imaginary literals are described by the following lexical definitions:

     imagnumber ::= (floatnumber | digitpart) ("j" | "J")

An imaginary literal yields a complex number with a real part of 0.0.
Complex numbers are represented as a pair of floating point numbers and
have the same restrictions on their range.  To create a complex number
with a nonzero real part, add a floating point number to it, e.g.,
‘(3+4j)’.  Some examples of imaginary literals:

     3.14j   10.j    10j     .001j   1e100j   3.14e-10j   3.14_15_93j


File: python.info,  Node: Operators,  Next: Delimiters,  Prev: Literals,  Up: Lexical analysis

4.2.5 Operators
---------------

The following tokens are operators:

     +       -       *       **      /       //      %      @
     <<      >>      &       |       ^       ~       :=
     <       >       <=      >=      ==      !=


File: python.info,  Node: Delimiters,  Prev: Operators,  Up: Lexical analysis

4.2.6 Delimiters
----------------

The following tokens serve as delimiters in the grammar:

     (       )       [       ]       {       }
     ,       :       .       ;       @       =       ->
     +=      -=      *=      /=      //=     %=      @=
     &=      |=      ^=      >>=     <<=     **=

The period can also occur in floating-point and imaginary literals.  A
sequence of three periods has a special meaning as an ellipsis literal.
The second half of the list, the augmented assignment operators, serve
lexically as delimiters, but also perform an operation.

The following printing ASCII characters have special meaning as part of
other tokens or are otherwise significant to the lexical analyzer:

     '       "       #       \

The following printing ASCII characters are not used in Python.  Their
occurrence outside string literals and comments is an unconditional
error:

     $       ?       `


File: python.info,  Node: Data model,  Next: Execution model,  Prev: Lexical analysis,  Up: The Python Language Reference

4.3 Data model
==============

* Menu:

* Objects, values and types: Objects values and types.
* The standard type hierarchy::
* Special method names::
* Coroutines::


File: python.info,  Node: Objects values and types,  Next: The standard type hierarchy,  Up: Data model

4.3.1 Objects, values and types
-------------------------------

`Objects' are Python’s abstraction for data.  All data in a Python
program is represented by objects or by relations between objects.  (In
a sense, and in conformance to Von Neumann’s model of a “stored program
computer”, code is also represented by objects.)

Every object has an identity, a type and a value.  An object’s
`identity' never changes once it has been created; you may think of it
as the object’s address in memory.  The ‘*note is: 1551.’ operator
compares the identity of two objects; the *note id(): e4b. function
returns an integer representing its identity.

`CPython implementation detail:' For CPython, ‘id(x)’ is the memory
address where ‘x’ is stored.

An object’s type determines the operations that the object supports
(e.g., “does it have a length?”) and also defines the possible values
for objects of that type.  The *note type(): 6ff. function returns an
object’s type (which is an object itself).  Like its identity, an
object’s `type' is also unchangeable.  (1)

The `value' of some objects can change.  Objects whose value can change
are said to be `mutable'; objects whose value is unchangeable once they
are created are called `immutable'.  (The value of an immutable
container object that contains a reference to a mutable object can
change when the latter’s value is changed; however the container is
still considered immutable, because the collection of objects it
contains cannot be changed.  So, immutability is not strictly the same
as having an unchangeable value, it is more subtle.)  An object’s
mutability is determined by its type; for instance, numbers, strings and
tuples are immutable, while dictionaries and lists are mutable.

Objects are never explicitly destroyed; however, when they become
unreachable they may be garbage-collected.  An implementation is allowed
to postpone garbage collection or omit it altogether — it is a matter of
implementation quality how garbage collection is implemented, as long as
no objects are collected that are still reachable.

`CPython implementation detail:' CPython currently uses a
reference-counting scheme with (optional) delayed detection of
cyclically linked garbage, which collects most objects as soon as they
become unreachable, but is not guaranteed to collect garbage containing
circular references.  See the documentation of the *note gc: 84. module
for information on controlling the collection of cyclic garbage.  Other
implementations act differently and CPython may change.  Do not depend
on immediate finalization of objects when they become unreachable (so
you should always close files explicitly).

Note that the use of the implementation’s tracing or debugging
facilities may keep objects alive that would normally be collectable.
Also note that catching an exception with a ‘*note try: e37.…*note
except: c10.’ statement may keep objects alive.

Some objects contain references to “external” resources such as open
files or windows.  It is understood that these resources are freed when
the object is garbage-collected, but since garbage collection is not
guaranteed to happen, such objects also provide an explicit way to
release the external resource, usually a ‘close()’ method.  Programs are
strongly recommended to explicitly close such objects.  The ‘*note try:
e37.…*note finally: 2bc.’ statement and the ‘*note with: 7da.’ statement
provide convenient ways to do this.

Some objects contain references to other objects; these are called
`containers'.  Examples of containers are tuples, lists and
dictionaries.  The references are part of a container’s value.  In most
cases, when we talk about the value of a container, we imply the values,
not the identities of the contained objects; however, when we talk about
the mutability of a container, only the identities of the immediately
contained objects are implied.  So, if an immutable container (like a
tuple) contains a reference to a mutable object, its value changes if
that mutable object is changed.

Types affect almost all aspects of object behavior.  Even the importance
of object identity is affected in some sense: for immutable types,
operations that compute new values may actually return a reference to
any existing object with the same type and value, while for mutable
objects this is not allowed.  E.g., after ‘a = 1; b = 1’, ‘a’ and ‘b’
may or may not refer to the same object with the value one, depending on
the implementation, but after ‘c = []; d = []’, ‘c’ and ‘d’ are
guaranteed to refer to two different, unique, newly created empty lists.
(Note that ‘c = d = []’ assigns the same object to both ‘c’ and ‘d’.)

   ---------- Footnotes ----------

   (1) (1) It `is' possible in some cases to change an object’s type,
under certain controlled conditions.  It generally isn’t a good idea
though, since it can lead to some very strange behaviour if it is
handled incorrectly.


File: python.info,  Node: The standard type hierarchy,  Next: Special method names,  Prev: Objects values and types,  Up: Data model

4.3.2 The standard type hierarchy
---------------------------------

Below is a list of the types that are built into Python.  Extension
modules (written in C, Java, or other languages, depending on the
implementation) can define additional types.  Future versions of Python
may add types to the type hierarchy (e.g., rational numbers, efficiently
stored arrays of integers, etc.), although such additions will often be
provided via the standard library instead.

Some of the type descriptions below contain a paragraph listing ‘special
attributes.’ These are attributes that provide access to the
implementation and are not intended for general use.  Their definition
may change in the future.

None

     This type has a single value.  There is a single object with this
     value.  This object is accessed through the built-in name ‘None’.
     It is used to signify the absence of a value in many situations,
     e.g., it is returned from functions that don’t explicitly return
     anything.  Its truth value is false.

NotImplemented

     This type has a single value.  There is a single object with this
     value.  This object is accessed through the built-in name
     ‘NotImplemented’.  Numeric methods and rich comparison methods
     should return this value if they do not implement the operation for
     the operands provided.  (The interpreter will then try the
     reflected operation, or some other fallback, depending on the
     operator.)  It should not be evaluated in a boolean context.

     See *note Implementing the arithmetic operations: 1554. for more
     details.

     Changed in version 3.9: Evaluating ‘NotImplemented’ in a boolean
     context is deprecated.  While it currently evaluates as true, it
     will emit a *note DeprecationWarning: 15a.  It will raise a *note
     TypeError: 1fe. in a future version of Python.

Ellipsis

     This type has a single value.  There is a single object with this
     value.  This object is accessed through the literal ‘...’ or the
     built-in name ‘Ellipsis’.  Its truth value is true.

*note numbers.Number: 1555.

     These are created by numeric literals and returned as results by
     arithmetic operators and arithmetic built-in functions.  Numeric
     objects are immutable; once created their value never changes.
     Python numbers are of course strongly related to mathematical
     numbers, but subject to the limitations of numerical representation
     in computers.

     The string representations of the numeric classes, computed by
     *note __repr__(): 44a. and *note __str__(): ef9, have the following
     properties:

        * They are valid numeric literals which, when passed to their
          class constructor, produce an object having the value of the
          original numeric.

        * The representation is in base 10, when possible.

        * Leading zeros, possibly excepting a single zero before a
          decimal point, are not shown.

        * Trailing zeros, possibly excepting a single zero after a
          decimal point, are not shown.

        * A sign is shown only when the number is negative.

     Python distinguishes between integers, floating point numbers, and
     complex numbers:

     *note numbers.Integral: 1556.

          These represent elements from the mathematical set of integers
          (positive and negative).

          There are two types of integers:

          Integers (*note int: 204.)

               These represent numbers in an unlimited range, subject to
               available (virtual) memory only.  For the purpose of
               shift and mask operations, a binary representation is
               assumed, and negative numbers are represented in a
               variant of 2’s complement which gives the illusion of an
               infinite string of sign bits extending to the left.

          Booleans (*note bool: 2bd.)

               These represent the truth values False and True.  The two
               objects representing the values ‘False’ and ‘True’ are
               the only Boolean objects.  The Boolean type is a subtype
               of the integer type, and Boolean values behave like the
               values 0 and 1, respectively, in almost all contexts, the
               exception being that when converted to a string, the
               strings ‘"False"’ or ‘"True"’ are returned, respectively.

          The rules for integer representation are intended to give the
          most meaningful interpretation of shift and mask operations
          involving negative integers.

     *note numbers.Real: 1557. (*note float: 1fd.)

          These represent machine-level double precision floating point
          numbers.  You are at the mercy of the underlying machine
          architecture (and C or Java implementation) for the accepted
          range and handling of overflow.  Python does not support
          single-precision floating point numbers; the savings in
          processor and memory usage that are usually the reason for
          using these are dwarfed by the overhead of using objects in
          Python, so there is no reason to complicate the language with
          two kinds of floating point numbers.

     *note numbers.Complex: 1558. (*note complex: 2c1.)

          These represent complex numbers as a pair of machine-level
          double precision floating point numbers.  The same caveats
          apply as for floating point numbers.  The real and imaginary
          parts of a complex number ‘z’ can be retrieved through the
          read-only attributes ‘z.real’ and ‘z.imag’.

Sequences

     These represent finite ordered sets indexed by non-negative
     numbers.  The built-in function *note len(): 28b. returns the
     number of items of a sequence.  When the length of a sequence is
     `n', the index set contains the numbers 0, 1, …, `n'-1.  Item `i'
     of sequence `a' is selected by ‘a[i]’.

     Sequences also support slicing: ‘a[i:j]’ selects all items with
     index `k' such that `i' ‘<=’ `k' ‘<’ `j'.  When used as an
     expression, a slice is a sequence of the same type.  This implies
     that the index set is renumbered so that it starts at 0.

     Some sequences also support “extended slicing” with a third “step”
     parameter: ‘a[i:j:k]’ selects all items of `a' with index `x' where
     ‘x = i + n*k’, `n' ‘>=’ ‘0’ and `i' ‘<=’ `x' ‘<’ `j'.

     Sequences are distinguished according to their mutability:

     Immutable sequences

          An object of an immutable sequence type cannot change once it
          is created.  (If the object contains references to other
          objects, these other objects may be mutable and may be
          changed; however, the collection of objects directly
          referenced by an immutable object cannot change.)

          The following types are immutable sequences:

          Strings

               A string is a sequence of values that represent Unicode
               code points.  All the code points in the range ‘U+0000 -
               U+10FFFF’ can be represented in a string.  Python doesn’t
               have a ‘char’ type; instead, every code point in the
               string is represented as a string object with length ‘1’.
               The built-in function *note ord(): 1559. converts a code
               point from its string form to an integer in the range ‘0
               - 10FFFF’; *note chr(): 155a. converts an integer in the
               range ‘0 - 10FFFF’ to the corresponding length ‘1’ string
               object.  *note str.encode(): 170. can be used to convert
               a *note str: 205. to *note bytes: 172. using the given
               text encoding, and *note bytes.decode(): 171. can be used
               to achieve the opposite.

          Tuples

               The items of a tuple are arbitrary Python objects.
               Tuples of two or more items are formed by comma-separated
               lists of expressions.  A tuple of one item (a
               ‘singleton’) can be formed by affixing a comma to an
               expression (an expression by itself does not create a
               tuple, since parentheses must be usable for grouping of
               expressions).  An empty tuple can be formed by an empty
               pair of parentheses.

          Bytes

               A bytes object is an immutable array.  The items are
               8-bit bytes, represented by integers in the range 0 <= x
               < 256.  Bytes literals (like ‘b'abc'’) and the built-in
               *note bytes(): 172. constructor can be used to create
               bytes objects.  Also, bytes objects can be decoded to
               strings via the *note decode(): 171. method.

     Mutable sequences

          Mutable sequences can be changed after they are created.  The
          subscription and slicing notations can be used as the target
          of assignment and *note del: 13a2. (delete) statements.

          There are currently two intrinsic mutable sequence types:

          Lists

               The items of a list are arbitrary Python objects.  Lists
               are formed by placing a comma-separated list of
               expressions in square brackets.  (Note that there are no
               special cases needed to form lists of length 0 or 1.)

          Byte Arrays

               A bytearray object is a mutable array.  They are created
               by the built-in *note bytearray(): 173. constructor.
               Aside from being mutable (and hence unhashable), byte
               arrays otherwise provide the same interface and
               functionality as immutable *note bytes: 172. objects.

          The extension module *note array: 6. provides an additional
          example of a mutable sequence type, as does the *note
          collections: 1d. module.

Set types

     These represent unordered, finite sets of unique, immutable
     objects.  As such, they cannot be indexed by any subscript.
     However, they can be iterated over, and the built-in function *note
     len(): 28b. returns the number of items in a set.  Common uses for
     sets are fast membership testing, removing duplicates from a
     sequence, and computing mathematical operations such as
     intersection, union, difference, and symmetric difference.

     For set elements, the same immutability rules apply as for
     dictionary keys.  Note that numeric types obey the normal rules for
     numeric comparison: if two numbers compare equal (e.g., ‘1’ and
     ‘1.0’), only one of them can be contained in a set.

     There are currently two intrinsic set types:

     Sets

          These represent a mutable set.  They are created by the
          built-in *note set(): 1f6. constructor and can be modified
          afterwards by several methods, such as ‘add()’.

     Frozen sets

          These represent an immutable set.  They are created by the
          built-in *note frozenset(): 1f7. constructor.  As a frozenset
          is immutable and *note hashable: 276, it can be used again as
          an element of another set, or as a dictionary key.

Mappings

     These represent finite sets of objects indexed by arbitrary index
     sets.  The subscript notation ‘a[k]’ selects the item indexed by
     ‘k’ from the mapping ‘a’; this can be used in expressions and as
     the target of assignments or *note del: 13a2. statements.  The
     built-in function *note len(): 28b. returns the number of items in
     a mapping.

     There is currently a single intrinsic mapping type:

     Dictionaries

          These represent finite sets of objects indexed by nearly
          arbitrary values.  The only types of values not acceptable as
          keys are values containing lists or dictionaries or other
          mutable types that are compared by value rather than by object
          identity, the reason being that the efficient implementation
          of dictionaries requires a key’s hash value to remain
          constant.  Numeric types used for keys obey the normal rules
          for numeric comparison: if two numbers compare equal (e.g.,
          ‘1’ and ‘1.0’) then they can be used interchangeably to index
          the same dictionary entry.

          Dictionaries preserve insertion order, meaning that keys will
          be produced in the same order they were added sequentially
          over the dictionary.  Replacing an existing key does not
          change the order, however removing a key and re-inserting it
          will add it to the end instead of keeping its old place.

          Dictionaries are mutable; they can be created by the ‘{...}’
          notation (see section *note Dictionary displays: 741.).

          The extension modules *note dbm.ndbm: 34. and *note dbm.gnu:
          33. provide additional examples of mapping types, as does the
          *note collections: 1d. module.

          Changed in version 3.7: Dictionaries did not preserve
          insertion order in versions of Python before 3.6.  In CPython
          3.6, insertion order was preserved, but it was considered an
          implementation detail at that time rather than a language
          guarantee.

Callable types

     These are the types to which the function call operation (see
     section *note Calls: 73f.) can be applied:

     User-defined functions

          A user-defined function object is created by a function
          definition (see section *note Function definitions: 1390.).
          It should be called with an argument list containing the same
          number of items as the function’s formal parameter list.

          Special attributes:

          Attribute                     Meaning
                                        
          ----------------------------------------------------------------------------------
                                                                            
          ‘__doc__’                     The function’s documentation        Writable
                                        string, or ‘None’ if unavailable;   
                                        not inherited by subclasses.
                                        
                                                                            
          *note __name__: d2f.          The function’s name.                Writable
                                                                            
                                                                            
          *note __qualname__: 155b.     The function’s                      Writable
                                        *note qualified name: 155c.         
                                        
                                        New in version 3.3.
                                        
                                                                            
          ‘__module__’                  The name of the module the          Writable
                                        function was defined in, or         
                                        ‘None’ if unavailable.
                                        
                                                                            
          ‘__defaults__’                A tuple containing default          Writable
                                        argument values for those           
                                        arguments that have defaults, or
                                        ‘None’ if no arguments have a
                                        default value.
                                        
                                                                            
          ‘__code__’                    The code object representing the    Writable
                                        compiled function body.             
                                        
                                                                            
          ‘__globals__’                 A reference to the dictionary       Read-only
                                        that holds the function’s global    
                                        variables — the global namespace
                                        of the module in which the
                                        function was defined.
                                        
                                                                            
          *note __dict__: 5f6.          The namespace supporting            Writable
                                        arbitrary function attributes.      
                                        
                                                                            
          ‘__closure__’                 ‘None’ or a tuple of cells that     Read-only
                                        contain bindings for the            
                                        function’s free variables.  See
                                        below for information on the
                                        ‘cell_contents’ attribute.
                                        
                                                                            
          ‘__annotations__’             A dict containing annotations of    Writable
                                        parameters.  The keys of the dict   
                                        are the parameter names, and
                                        ‘'return'’ for the return
                                        annotation, if provided.
                                        
                                                                            
          ‘__kwdefaults__’              A dict containing defaults for      Writable
                                        keyword-only parameters.            
                                        

          Most of the attributes labelled “Writable” check the type of
          the assigned value.

          Function objects also support getting and setting arbitrary
          attributes, which can be used, for example, to attach metadata
          to functions.  Regular attribute dot-notation is used to get
          and set such attributes.  `Note that the current
          implementation only supports function attributes on
          user-defined functions.  Function attributes on built-in
          functions may be supported in the future.'

          A cell object has the attribute ‘cell_contents’.  This can be
          used to get the value of the cell, as well as set the value.

          Additional information about a function’s definition can be
          retrieved from its code object; see the description of
          internal types below.  The *note cell: 155d. type can be
          accessed in the *note types: 121. module.

     Instance methods

          An instance method object combines a class, a class instance
          and any callable object (normally a user-defined function).

          Special read-only attributes: ‘__self__’ is the class instance
          object, ‘__func__’ is the function object; ‘__doc__’ is the
          method’s documentation (same as ‘__func__.__doc__’); *note
          __name__: d2f. is the method name (same as
          ‘__func__.__name__’); ‘__module__’ is the name of the module
          the method was defined in, or ‘None’ if unavailable.

          Methods also support accessing (but not setting) the arbitrary
          function attributes on the underlying function object.

          User-defined method objects may be created when getting an
          attribute of a class (perhaps via an instance of that class),
          if that attribute is a user-defined function object or a class
          method object.

          When an instance method object is created by retrieving a
          user-defined function object from a class via one of its
          instances, its ‘__self__’ attribute is the instance, and the
          method object is said to be bound.  The new method’s
          ‘__func__’ attribute is the original function object.

          When an instance method object is created by retrieving a
          class method object from a class or instance, its ‘__self__’
          attribute is the class itself, and its ‘__func__’ attribute is
          the function object underlying the class method.

          When an instance method object is called, the underlying
          function (‘__func__’) is called, inserting the class instance
          (‘__self__’) in front of the argument list.  For instance,
          when ‘C’ is a class which contains a definition for a function
          ‘f()’, and ‘x’ is an instance of ‘C’, calling ‘x.f(1)’ is
          equivalent to calling ‘C.f(x, 1)’.

          When an instance method object is derived from a class method
          object, the “class instance” stored in ‘__self__’ will
          actually be the class itself, so that calling either ‘x.f(1)’
          or ‘C.f(1)’ is equivalent to calling ‘f(C,1)’ where ‘f’ is the
          underlying function.

          Note that the transformation from function object to instance
          method object happens each time the attribute is retrieved
          from the instance.  In some cases, a fruitful optimization is
          to assign the attribute to a local variable and call that
          local variable.  Also notice that this transformation only
          happens for user-defined functions; other callable objects
          (and all non-callable objects) are retrieved without
          transformation.  It is also important to note that
          user-defined functions which are attributes of a class
          instance are not converted to bound methods; this `only'
          happens when the function is an attribute of the class.

     Generator functions

          A function or method which uses the *note yield: 2c7.
          statement (see section *note The yield statement: 2c7.) is
          called a `generator function'.  Such a function, when called,
          always returns an iterator object which can be used to execute
          the body of the function: calling the iterator’s *note
          iterator.__next__(): d2c. method will cause the function to
          execute until it provides a value using the ‘yield’ statement.
          When the function executes a *note return: 2c8. statement or
          falls off the end, a *note StopIteration: 582. exception is
          raised and the iterator will have reached the end of the set
          of values to be returned.

     Coroutine functions

          A function or method which is defined using *note async def:
          3a9. is called a `coroutine function'.  Such a function, when
          called, returns a *note coroutine: 18a. object.  It may
          contain *note await: 2d8. expressions, as well as *note async
          with: 736. and *note async for: 3fd. statements.  See also the
          *note Coroutine Objects: 155e. section.

     Asynchronous generator functions

          A function or method which is defined using *note async def:
          3a9. and which uses the *note yield: 2c7. statement is called
          a `asynchronous generator function'.  Such a function, when
          called, returns an asynchronous iterator object which can be
          used in an *note async for: 3fd. statement to execute the body
          of the function.

          Calling the asynchronous iterator’s *note aiterator.__anext__:
          155f. method will return an *note awaitable: 613. which when
          awaited will execute until it provides a value using the *note
          yield: 2c7. expression.  When the function executes an empty
          *note return: 2c8. statement or falls off the end, a *note
          StopAsyncIteration: 114a. exception is raised and the
          asynchronous iterator will have reached the end of the set of
          values to be yielded.

     Built-in functions

          A built-in function object is a wrapper around a C function.
          Examples of built-in functions are *note len(): 28b. and *note
          math.sin(): ed1. (*note math: b1. is a standard built-in
          module).  The number and type of the arguments are determined
          by the C function.  Special read-only attributes: ‘__doc__’ is
          the function’s documentation string, or ‘None’ if unavailable;
          *note __name__: d2f. is the function’s name; ‘__self__’ is set
          to ‘None’ (but see the next item); ‘__module__’ is the name of
          the module the function was defined in or ‘None’ if
          unavailable.

     Built-in methods

          This is really a different disguise of a built-in function,
          this time containing an object passed to the C function as an
          implicit extra argument.  An example of a built-in method is
          ‘alist.append()’, assuming `alist' is a list object.  In this
          case, the special read-only attribute ‘__self__’ is set to the
          object denoted by `alist'.

     Classes

          Classes are callable.  These objects normally act as factories
          for new instances of themselves, but variations are possible
          for class types that override *note __new__(): 974.  The
          arguments of the call are passed to *note __new__(): 974. and,
          in the typical case, to *note __init__(): e23. to initialize
          the new instance.

     Class Instances

          Instances of arbitrary classes can be made callable by
          defining a *note __call__(): 1560. method in their class.

Modules

     Modules are a basic organizational unit of Python code, and are
     created by the *note import system: 1561. as invoked either by the
     *note import: ce7. statement, or by calling functions such as *note
     importlib.import_module(): be6. and built-in *note __import__():
     16b.  A module object has a namespace implemented by a dictionary
     object (this is the dictionary referenced by the ‘__globals__’
     attribute of functions defined in the module).  Attribute
     references are translated to lookups in this dictionary, e.g.,
     ‘m.x’ is equivalent to ‘m.__dict__["x"]’.  A module object does not
     contain the code object used to initialize the module (since it
     isn’t needed once the initialization is done).

     Attribute assignment updates the module’s namespace dictionary,
     e.g., ‘m.x = 1’ is equivalent to ‘m.__dict__["x"] = 1’.

     Predefined (writable) attributes: *note __name__: dd8. is the
     module’s name; ‘__doc__’ is the module’s documentation string, or
     ‘None’ if unavailable; ‘__annotations__’ (optional) is a dictionary
     containing *note variable annotations: 712. collected during module
     body execution; *note __file__: 1562. is the pathname of the file
     from which the module was loaded, if it was loaded from a file.
     The *note __file__: 1562. attribute may be missing for certain
     types of modules, such as C modules that are statically linked into
     the interpreter; for extension modules loaded dynamically from a
     shared library, it is the pathname of the shared library file.

     Special read-only attribute: *note __dict__: 5f6. is the module’s
     namespace as a dictionary object.

     `CPython implementation detail:' Because of the way CPython clears
     module dictionaries, the module dictionary will be cleared when the
     module falls out of scope even if the dictionary still has live
     references.  To avoid this, copy the dictionary or keep the module
     around while using its dictionary directly.

Custom classes

     Custom class types are typically created by class definitions (see
     section *note Class definitions: d32.).  A class has a namespace
     implemented by a dictionary object.  Class attribute references are
     translated to lookups in this dictionary, e.g., ‘C.x’ is translated
     to ‘C.__dict__["x"]’ (although there are a number of hooks which
     allow for other means of locating attributes).  When the attribute
     name is not found there, the attribute search continues in the base
     classes.  This search of the base classes uses the C3 method
     resolution order which behaves correctly even in the presence of
     ‘diamond’ inheritance structures where there are multiple
     inheritance paths leading back to a common ancestor.  Additional
     details on the C3 MRO used by Python can be found in the
     documentation accompanying the 2.3 release at
     ‘https://www.python.org/download/releases/2.3/mro/’.

     When a class attribute reference (for class ‘C’, say) would yield a
     class method object, it is transformed into an instance method
     object whose ‘__self__’ attribute is ‘C’.  When it would yield a
     static method object, it is transformed into the object wrapped by
     the static method object.  See section *note Implementing
     Descriptors: 5e4. for another way in which attributes retrieved
     from a class may differ from those actually contained in its *note
     __dict__: 5f6.

     Class attribute assignments update the class’s dictionary, never
     the dictionary of a base class.

     A class object can be called (see above) to yield a class instance
     (see below).

     Special attributes: *note __name__: d2f. is the class name;
     ‘__module__’ is the module name in which the class was defined;
     *note __dict__: 5f6. is the dictionary containing the class’s
     namespace; *note __bases__: ecb. is a tuple containing the base
     classes, in the order of their occurrence in the base class list;
     ‘__doc__’ is the class’s documentation string, or ‘None’ if
     undefined; ‘__annotations__’ (optional) is a dictionary containing
     *note variable annotations: 712. collected during class body
     execution.

Class instances

     A class instance is created by calling a class object (see above).
     A class instance has a namespace implemented as a dictionary which
     is the first place in which attribute references are searched.
     When an attribute is not found there, and the instance’s class has
     an attribute by that name, the search continues with the class
     attributes.  If a class attribute is found that is a user-defined
     function object, it is transformed into an instance method object
     whose ‘__self__’ attribute is the instance.  Static method and
     class method objects are also transformed; see above under
     “Classes”.  See section *note Implementing Descriptors: 5e4. for
     another way in which attributes of a class retrieved via its
     instances may differ from the objects actually stored in the
     class’s *note __dict__: 5f6.  If no class attribute is found, and
     the object’s class has a *note __getattr__(): 42a. method, that is
     called to satisfy the lookup.

     Attribute assignments and deletions update the instance’s
     dictionary, never a class’s dictionary.  If the class has a *note
     __setattr__(): eee. or *note __delattr__(): 1563. method, this is
     called instead of updating the instance dictionary directly.

     Class instances can pretend to be numbers, sequences, or mappings
     if they have methods with certain special names.  See section *note
     Special method names: 608.

     Special attributes: *note __dict__: 5f6. is the attribute
     dictionary; *note __class__: ecc. is the instance’s class.

I/O objects (also known as file objects)

     A *note file object: c14. represents an open file.  Various
     shortcuts are available to create file objects: the *note open():
     16f. built-in function, and also *note os.popen(): 3cb, *note
     os.fdopen(): 1564, and the *note makefile(): bec. method of socket
     objects (and perhaps by other functions or methods provided by
     extension modules).

     The objects ‘sys.stdin’, ‘sys.stdout’ and ‘sys.stderr’ are
     initialized to file objects corresponding to the interpreter’s
     standard input, output and error streams; they are all open in text
     mode and therefore follow the interface defined by the *note
     io.TextIOBase: d01. abstract class.

Internal types

     A few types used internally by the interpreter are exposed to the
     user.  Their definitions may change with future versions of the
     interpreter, but they are mentioned here for completeness.

     Code objects

          Code objects represent `byte-compiled' executable Python code,
          or *note bytecode: 709.  The difference between a code object
          and a function object is that the function object contains an
          explicit reference to the function’s globals (the module in
          which it was defined), while a code object contains no
          context; also the default argument values are stored in the
          function object, not in the code object (because they
          represent values calculated at run-time).  Unlike function
          objects, code objects are immutable and contain no references
          (directly or indirectly) to mutable objects.

          Special read-only attributes: ‘co_name’ gives the function
          name; ‘co_argcount’ is the total number of positional
          arguments (including positional-only arguments and arguments
          with default values); ‘co_posonlyargcount’ is the number of
          positional-only arguments (including arguments with default
          values); ‘co_kwonlyargcount’ is the number of keyword-only
          arguments (including arguments with default values);
          ‘co_nlocals’ is the number of local variables used by the
          function (including arguments); ‘co_varnames’ is a tuple
          containing the names of the local variables (starting with the
          argument names); ‘co_cellvars’ is a tuple containing the names
          of local variables that are referenced by nested functions;
          ‘co_freevars’ is a tuple containing the names of free
          variables; ‘co_code’ is a string representing the sequence of
          bytecode instructions; ‘co_consts’ is a tuple containing the
          literals used by the bytecode; ‘co_names’ is a tuple
          containing the names used by the bytecode; ‘co_filename’ is
          the filename from which the code was compiled;
          ‘co_firstlineno’ is the first line number of the function;
          ‘co_lnotab’ is a string encoding the mapping from bytecode
          offsets to line numbers (for details see the source code of
          the interpreter); ‘co_stacksize’ is the required stack size;
          ‘co_flags’ is an integer encoding a number of flags for the
          interpreter.

          The following flag bits are defined for ‘co_flags’: bit ‘0x04’
          is set if the function uses the ‘*arguments’ syntax to accept
          an arbitrary number of positional arguments; bit ‘0x08’ is set
          if the function uses the ‘**keywords’ syntax to accept
          arbitrary keyword arguments; bit ‘0x20’ is set if the function
          is a generator.

          Future feature declarations (‘from __future__ import
          division’) also use bits in ‘co_flags’ to indicate whether a
          code object was compiled with a particular feature enabled:
          bit ‘0x2000’ is set if the function was compiled with future
          division enabled; bits ‘0x10’ and ‘0x1000’ were used in
          earlier versions of Python.

          Other bits in ‘co_flags’ are reserved for internal use.

          If a code object represents a function, the first item in
          ‘co_consts’ is the documentation string of the function, or
          ‘None’ if undefined.

     Frame objects

          Frame objects represent execution frames.  They may occur in
          traceback objects (see below), and are also passed to
          registered trace functions.

          Special read-only attributes: ‘f_back’ is to the previous
          stack frame (towards the caller), or ‘None’ if this is the
          bottom stack frame; ‘f_code’ is the code object being executed
          in this frame; ‘f_locals’ is the dictionary used to look up
          local variables; ‘f_globals’ is used for global variables;
          ‘f_builtins’ is used for built-in (intrinsic) names; ‘f_lasti’
          gives the precise instruction (this is an index into the
          bytecode string of the code object).

          Accessing ‘f_code’ raises an *note auditing event: fa1.
          ‘object.__getattr__’ with arguments ‘obj’ and ‘"f_code"’.

          Special writable attributes: ‘f_trace’, if not ‘None’, is a
          function called for various events during code execution (this
          is used by the debugger).  Normally an event is triggered for
          each new source line - this can be disabled by setting
          ‘f_trace_lines’ to *note False: 48f.

          Implementations `may' allow per-opcode events to be requested
          by setting ‘f_trace_opcodes’ to *note True: 594.  Note that
          this may lead to undefined interpreter behaviour if exceptions
          raised by the trace function escape to the function being
          traced.

          ‘f_lineno’ is the current line number of the frame — writing
          to this from within a trace function jumps to the given line
          (only for the bottom-most frame).  A debugger can implement a
          Jump command (aka Set Next Statement) by writing to f_lineno.

          Frame objects support one method:

           -- Method: frame.clear ()

               This method clears all references to local variables held
               by the frame.  Also, if the frame belonged to a
               generator, the generator is finalized.  This helps break
               reference cycles involving frame objects (for example
               when catching an exception and storing its traceback for
               later use).

               *note RuntimeError: 3dc. is raised if the frame is
               currently executing.

               New in version 3.4.

     Traceback objects

          Traceback objects represent a stack trace of an exception.  A
          traceback object is implicitly created when an exception
          occurs, and may also be explicitly created by calling *note
          types.TracebackType: 441.

          For implicitly created tracebacks, when the search for an
          exception handler unwinds the execution stack, at each unwound
          level a traceback object is inserted in front of the current
          traceback.  When an exception handler is entered, the stack
          trace is made available to the program.  (See section *note
          The try statement: e37.)  It is accessible as the third item
          of the tuple returned by ‘sys.exc_info()’, and as the
          ‘__traceback__’ attribute of the caught exception.

          When the program contains no suitable handler, the stack trace
          is written (nicely formatted) to the standard error stream; if
          the interpreter is interactive, it is also made available to
          the user as ‘sys.last_traceback’.

          For explicitly created tracebacks, it is up to the creator of
          the traceback to determine how the ‘tb_next’ attributes should
          be linked to form a full stack trace.

          Special read-only attributes: ‘tb_frame’ points to the
          execution frame of the current level; ‘tb_lineno’ gives the
          line number where the exception occurred; ‘tb_lasti’ indicates
          the precise instruction.  The line number and last instruction
          in the traceback may differ from the line number of its frame
          object if the exception occurred in a *note try: e37.
          statement with no matching except clause or with a finally
          clause.

          Accessing ‘tb_frame’ raises an *note auditing event: fa1.
          ‘object.__getattr__’ with arguments ‘obj’ and ‘"tb_frame"’.

          Special writable attribute: ‘tb_next’ is the next level in the
          stack trace (towards the frame where the exception occurred),
          or ‘None’ if there is no next level.

          Changed in version 3.7: Traceback objects can now be
          explicitly instantiated from Python code, and the ‘tb_next’
          attribute of existing instances can be updated.

     Slice objects

          Slice objects are used to represent slices for *note
          __getitem__(): 3a2. methods.  They are also created by the
          built-in *note slice(): ec8. function.

          Special read-only attributes: ‘start’ is the lower bound;
          ‘stop’ is the upper bound; ‘step’ is the step value; each is
          ‘None’ if omitted.  These attributes can have any type.

          Slice objects support one method:

           -- Method: slice.indices (self, length)

               This method takes a single integer argument `length' and
               computes information about the slice that the slice
               object would describe if applied to a sequence of
               `length' items.  It returns a tuple of three integers;
               respectively these are the `start' and `stop' indices and
               the `step' or stride length of the slice.  Missing or
               out-of-bounds indices are handled in a manner consistent
               with regular slices.

     Static method objects

          Static method objects provide a way of defeating the
          transformation of function objects to method objects described
          above.  A static method object is a wrapper around any other
          object, usually a user-defined method object.  When a static
          method object is retrieved from a class or a class instance,
          the object actually returned is the wrapped object, which is
          not subject to any further transformation.  Static method
          objects are not themselves callable, although the objects they
          wrap usually are.  Static method objects are created by the
          built-in *note staticmethod(): 30a. constructor.

     Class method objects

          A class method object, like a static method object, is a
          wrapper around another object that alters the way in which
          that object is retrieved from classes and class instances.
          The behaviour of class method objects upon such retrieval is
          described above, under “User-defined methods”.  Class method
          objects are created by the built-in *note classmethod(): 309.
          constructor.


File: python.info,  Node: Special method names,  Next: Coroutines,  Prev: The standard type hierarchy,  Up: Data model

4.3.3 Special method names
--------------------------

A class can implement certain operations that are invoked by special
syntax (such as arithmetic operations or subscripting and slicing) by
defining methods with special names.  This is Python’s approach to
`operator overloading', allowing classes to define their own behavior
with respect to language operators.  For instance, if a class defines a
method named *note __getitem__(): 3a2, and ‘x’ is an instance of this
class, then ‘x[i]’ is roughly equivalent to ‘type(x).__getitem__(x, i)’.
Except where mentioned, attempts to execute an operation raise an
exception when no appropriate method is defined (typically *note
AttributeError: 4a2. or *note TypeError: 1fe.).

Setting a special method to ‘None’ indicates that the corresponding
operation is not available.  For example, if a class sets *note
__iter__(): 609. to ‘None’, the class is not iterable, so calling *note
iter(): ded. on its instances will raise a *note TypeError: 1fe.
(without falling back to *note __getitem__(): 3a2.).  (1)

When implementing a class that emulates any built-in type, it is
important that the emulation only be implemented to the degree that it
makes sense for the object being modelled.  For example, some sequences
may work well with retrieval of individual elements, but extracting a
slice may not make sense.  (One example of this is the ‘NodeList’
interface in the W3C’s Document Object Model.)

* Menu:

* Basic customization::
* Customizing attribute access::
* Customizing class creation::
* Customizing instance and subclass checks::
* Emulating generic types::
* Emulating callable objects::
* Emulating container types::
* Emulating numeric types::
* With Statement Context Managers::
* Special method lookup::

   ---------- Footnotes ----------

   (1) (2) The *note __hash__(): 44c, *note __iter__(): 609, *note
__reversed__(): 629, and *note __contains__(): dee. methods have special
handling for this; others will still raise a *note TypeError: 1fe, but
may do so by relying on the behavior that ‘None’ is not callable.


File: python.info,  Node: Basic customization,  Next: Customizing attribute access,  Up: Special method names

4.3.3.1 Basic customization
...........................

 -- Method: object.__new__ (cls[, ...])

     Called to create a new instance of class `cls'.  *note __new__():
     974. is a static method (special-cased so you need not declare it
     as such) that takes the class of which an instance was requested as
     its first argument.  The remaining arguments are those passed to
     the object constructor expression (the call to the class).  The
     return value of *note __new__(): 974. should be the new object
     instance (usually an instance of `cls').

     Typical implementations create a new instance of the class by
     invoking the superclass’s *note __new__(): 974. method using
     ‘super().__new__(cls[, ...])’ with appropriate arguments and then
     modifying the newly-created instance as necessary before returning
     it.

     If *note __new__(): 974. is invoked during object construction and
     it returns an instance of `cls', then the new instance’s *note
     __init__(): e23. method will be invoked like ‘__init__(self[,
     ...])’, where `self' is the new instance and the remaining
     arguments are the same as were passed to the object constructor.

     If *note __new__(): 974. does not return an instance of `cls', then
     the new instance’s *note __init__(): e23. method will not be
     invoked.

     *note __new__(): 974. is intended mainly to allow subclasses of
     immutable types (like int, str, or tuple) to customize instance
     creation.  It is also commonly overridden in custom metaclasses in
     order to customize class creation.

 -- Method: object.__init__ (self[, ...])

     Called after the instance has been created (by *note __new__():
     974.), but before it is returned to the caller.  The arguments are
     those passed to the class constructor expression.  If a base class
     has an *note __init__(): e23. method, the derived class’s *note
     __init__(): e23. method, if any, must explicitly call it to ensure
     proper initialization of the base class part of the instance; for
     example: ‘super().__init__([args...])’.

     Because *note __new__(): 974. and *note __init__(): e23. work
     together in constructing objects (*note __new__(): 974. to create
     it, and *note __init__(): e23. to customize it), no non-‘None’
     value may be returned by *note __init__(): e23.; doing so will
     cause a *note TypeError: 1fe. to be raised at runtime.

 -- Method: object.__del__ (self)

     Called when the instance is about to be destroyed.  This is also
     called a finalizer or (improperly) a destructor.  If a base class
     has a *note __del__(): a04. method, the derived class’s *note
     __del__(): a04. method, if any, must explicitly call it to ensure
     proper deletion of the base class part of the instance.

     It is possible (though not recommended!)  for the *note __del__():
     a04. method to postpone destruction of the instance by creating a
     new reference to it.  This is called object `resurrection'.  It is
     implementation-dependent whether *note __del__(): a04. is called a
     second time when a resurrected object is about to be destroyed; the
     current *note CPython: 1569. implementation only calls it once.

     It is not guaranteed that *note __del__(): a04. methods are called
     for objects that still exist when the interpreter exits.

          Note: ‘del x’ doesn’t directly call ‘x.__del__()’ — the former
          decrements the reference count for ‘x’ by one, and the latter
          is only called when ‘x’’s reference count reaches zero.

     `CPython implementation detail:' It is possible for a reference
     cycle to prevent the reference count of an object from going to
     zero.  In this case, the cycle will be later detected and deleted
     by the *note cyclic garbage collector: fc8.  A common cause of
     reference cycles is when an exception has been caught in a local
     variable.  The frame’s locals then reference the exception, which
     references its own traceback, which references the locals of all
     frames caught in the traceback.

     See also
     ........

     Documentation for the *note gc: 84. module.

          Warning: Due to the precarious circumstances under which *note
          __del__(): a04. methods are invoked, exceptions that occur
          during their execution are ignored, and a warning is printed
          to ‘sys.stderr’ instead.  In particular:

             * *note __del__(): a04. can be invoked when arbitrary code
               is being executed, including from any arbitrary thread.
               If *note __del__(): a04. needs to take a lock or invoke
               any other blocking resource, it may deadlock as the
               resource may already be taken by the code that gets
               interrupted to execute *note __del__(): a04.

             * *note __del__(): a04. can be executed during interpreter
               shutdown.  As a consequence, the global variables it
               needs to access (including other modules) may already
               have been deleted or set to ‘None’.  Python guarantees
               that globals whose name begins with a single underscore
               are deleted from their module before other globals are
               deleted; if no other references to such globals exist,
               this may help in assuring that imported modules are still
               available at the time when the *note __del__(): a04.
               method is called.

 -- Method: object.__repr__ (self)

     Called by the *note repr(): 8b9. built-in function to compute the
     “official” string representation of an object.  If at all possible,
     this should look like a valid Python expression that could be used
     to recreate an object with the same value (given an appropriate
     environment).  If this is not possible, a string of the form
     ‘<...some useful description...>’ should be returned.  The return
     value must be a string object.  If a class defines *note
     __repr__(): 44a. but not *note __str__(): ef9, then *note
     __repr__(): 44a. is also used when an “informal” string
     representation of instances of that class is required.

     This is typically used for debugging, so it is important that the
     representation is information-rich and unambiguous.

 -- Method: object.__str__ (self)

     Called by *note str(object): 205. and the built-in functions *note
     format(): 5d6. and *note print(): 971. to compute the “informal” or
     nicely printable string representation of an object.  The return
     value must be a *note string: 1357. object.

     This method differs from *note object.__repr__(): 44a. in that
     there is no expectation that *note __str__(): ef9. return a valid
     Python expression: a more convenient or concise representation can
     be used.

     The default implementation defined by the built-in type *note
     object: 3d2. calls *note object.__repr__(): 44a.

 -- Method: object.__bytes__ (self)

     Called by *note bytes: 11f2. to compute a byte-string
     representation of an object.  This should return a *note bytes:
     172. object.

 -- Method: object.__format__ (self, format_spec)

     Called by the *note format(): 5d6. built-in function, and by
     extension, evaluation of *note formatted string literals: 296. and
     the *note str.format(): 5d5. method, to produce a “formatted”
     string representation of an object.  The `format_spec' argument is
     a string that contains a description of the formatting options
     desired.  The interpretation of the `format_spec' argument is up to
     the type implementing *note __format__(): a2f, however most classes
     will either delegate formatting to one of the built-in types, or
     use a similar formatting option syntax.

     See *note Format Specification Mini-Language: 5d9. for a
     description of the standard formatting syntax.

     The return value must be a string object.

     Changed in version 3.4: The __format__ method of ‘object’ itself
     raises a *note TypeError: 1fe. if passed any non-empty string.

     Changed in version 3.7: ‘object.__format__(x, '')’ is now
     equivalent to ‘str(x)’ rather than ‘format(str(x), '')’.

 -- Method: object.__lt__ (self, other)
 -- Method: object.__le__ (self, other)
 -- Method: object.__eq__ (self, other)
 -- Method: object.__ne__ (self, other)
 -- Method: object.__gt__ (self, other)
 -- Method: object.__ge__ (self, other)

     These are the so-called “rich comparison” methods.  The
     correspondence between operator symbols and method names is as
     follows: ‘x<y’ calls ‘x.__lt__(y)’, ‘x<=y’ calls ‘x.__le__(y)’,
     ‘x==y’ calls ‘x.__eq__(y)’, ‘x!=y’ calls ‘x.__ne__(y)’, ‘x>y’ calls
     ‘x.__gt__(y)’, and ‘x>=y’ calls ‘x.__ge__(y)’.

     A rich comparison method may return the singleton ‘NotImplemented’
     if it does not implement the operation for a given pair of
     arguments.  By convention, ‘False’ and ‘True’ are returned for a
     successful comparison.  However, these methods can return any
     value, so if the comparison operator is used in a Boolean context
     (e.g., in the condition of an ‘if’ statement), Python will call
     *note bool(): 2bd. on the value to determine if the result is true
     or false.

     By default, ‘object’ implements *note __eq__(): 44b. by using ‘is’,
     returning ‘NotImplemented’ in the case of a false comparison: ‘True
     if x is y else NotImplemented’.  For *note __ne__(): f18, by
     default it delegates to *note __eq__(): 44b. and inverts the result
     unless it is ‘NotImplemented’.  There are no other implied
     relationships among the comparison operators or default
     implementations; for example, the truth of ‘(x<y or x==y)’ does not
     imply ‘x<=y’.  To automatically generate ordering operations from a
     single root operation, see *note functools.total_ordering(): 938.

     See the paragraph on *note __hash__(): 44c. for some important
     notes on creating *note hashable: 276. objects which support custom
     comparison operations and are usable as dictionary keys.

     There are no swapped-argument versions of these methods (to be used
     when the left argument does not support the operation but the right
     argument does); rather, *note __lt__(): cfe. and *note __gt__():
     d69. are each other’s reflection, *note __le__(): d68. and *note
     __ge__(): d6a. are each other’s reflection, and *note __eq__():
     44b. and *note __ne__(): f18. are their own reflection.  If the
     operands are of different types, and right operand’s type is a
     direct or indirect subclass of the left operand’s type, the
     reflected method of the right operand has priority, otherwise the
     left operand’s method has priority.  Virtual subclassing is not
     considered.

 -- Method: object.__hash__ (self)

     Called by built-in function *note hash(): aa3. and for operations
     on members of hashed collections including *note set: 1f6, *note
     frozenset: 1f7, and *note dict: 164.  *note __hash__(): 44c. should
     return an integer.  The only required property is that objects
     which compare equal have the same hash value; it is advised to mix
     together the hash values of the components of the object that also
     play a part in comparison of objects by packing them into a tuple
     and hashing the tuple.  Example:

          def __hash__(self):
              return hash((self.name, self.nick, self.color))

          Note: *note hash(): aa3. truncates the value returned from an
          object’s custom *note __hash__(): 44c. method to the size of a
          ‘Py_ssize_t’.  This is typically 8 bytes on 64-bit builds and
          4 bytes on 32-bit builds.  If an object’s *note __hash__():
          44c. must interoperate on builds of different bit sizes, be
          sure to check the width on all supported builds.  An easy way
          to do this is with ‘python -c "import sys;
          print(sys.hash_info.width)"’.

     If a class does not define an *note __eq__(): 44b. method it should
     not define a *note __hash__(): 44c. operation either; if it defines
     *note __eq__(): 44b. but not *note __hash__(): 44c, its instances
     will not be usable as items in hashable collections.  If a class
     defines mutable objects and implements an *note __eq__(): 44b.
     method, it should not implement *note __hash__(): 44c, since the
     implementation of hashable collections requires that a key’s hash
     value is immutable (if the object’s hash value changes, it will be
     in the wrong hash bucket).

     User-defined classes have *note __eq__(): 44b. and *note
     __hash__(): 44c. methods by default; with them, all objects compare
     unequal (except with themselves) and ‘x.__hash__()’ returns an
     appropriate value such that ‘x == y’ implies both that ‘x is y’ and
     ‘hash(x) == hash(y)’.

     A class that overrides *note __eq__(): 44b. and does not define
     *note __hash__(): 44c. will have its *note __hash__(): 44c.
     implicitly set to ‘None’.  When the *note __hash__(): 44c. method
     of a class is ‘None’, instances of the class will raise an
     appropriate *note TypeError: 1fe. when a program attempts to
     retrieve their hash value, and will also be correctly identified as
     unhashable when checking ‘isinstance(obj,
     collections.abc.Hashable)’.

     If a class that overrides *note __eq__(): 44b. needs to retain the
     implementation of *note __hash__(): 44c. from a parent class, the
     interpreter must be told this explicitly by setting ‘__hash__ =
     <ParentClass>.__hash__’.

     If a class that does not override *note __eq__(): 44b. wishes to
     suppress hash support, it should include ‘__hash__ = None’ in the
     class definition.  A class which defines its own *note __hash__():
     44c. that explicitly raises a *note TypeError: 1fe. would be
     incorrectly identified as hashable by an ‘isinstance(obj,
     collections.abc.Hashable)’ call.

          Note: By default, the *note __hash__(): 44c. values of str and
          bytes objects are “salted” with an unpredictable random value.
          Although they remain constant within an individual Python
          process, they are not predictable between repeated invocations
          of Python.

          This is intended to provide protection against a
          denial-of-service caused by carefully-chosen inputs that
          exploit the worst case performance of a dict insertion, O(n^2)
          complexity.  See
          ‘http://www.ocert.org/advisories/ocert-2011-003.html’ for
          details.

          Changing hash values affects the iteration order of sets.
          Python has never made guarantees about this ordering (and it
          typically varies between 32-bit and 64-bit builds).

          See also *note PYTHONHASHSEED: aa4.

     Changed in version 3.3: Hash randomization is enabled by default.

 -- Method: object.__bool__ (self)

     Called to implement truth value testing and the built-in operation
     ‘bool()’; should return ‘False’ or ‘True’.  When this method is not
     defined, *note __len__(): e90. is called, if it is defined, and the
     object is considered true if its result is nonzero.  If a class
     defines neither *note __len__(): e90. nor *note __bool__(): d30,
     all its instances are considered true.


File: python.info,  Node: Customizing attribute access,  Next: Customizing class creation,  Prev: Basic customization,  Up: Special method names

4.3.3.2 Customizing attribute access
....................................

The following methods can be defined to customize the meaning of
attribute access (use of, assignment to, or deletion of ‘x.name’) for
class instances.

 -- Method: object.__getattr__ (self, name)

     Called when the default attribute access fails with an *note
     AttributeError: 4a2. (either *note __getattribute__(): 54c. raises
     an *note AttributeError: 4a2. because `name' is not an instance
     attribute or an attribute in the class tree for ‘self’; or *note
     __get__(): 156e. of a `name' property raises *note AttributeError:
     4a2.).  This method should either return the (computed) attribute
     value or raise an *note AttributeError: 4a2. exception.

     Note that if the attribute is found through the normal mechanism,
     *note __getattr__(): 42a. is not called.  (This is an intentional
     asymmetry between *note __getattr__(): 42a. and *note
     __setattr__(): eee.)  This is done both for efficiency reasons and
     because otherwise *note __getattr__(): 42a. would have no way to
     access other attributes of the instance.  Note that at least for
     instance variables, you can fake total control by not inserting any
     values in the instance attribute dictionary (but instead inserting
     them in another object).  See the *note __getattribute__(): 54c.
     method below for a way to actually get total control over attribute
     access.

 -- Method: object.__getattribute__ (self, name)

     Called unconditionally to implement attribute accesses for
     instances of the class.  If the class also defines *note
     __getattr__(): 42a, the latter will not be called unless *note
     __getattribute__(): 54c. either calls it explicitly or raises an
     *note AttributeError: 4a2.  This method should return the
     (computed) attribute value or raise an *note AttributeError: 4a2.
     exception.  In order to avoid infinite recursion in this method,
     its implementation should always call the base class method with
     the same name to access any attributes it needs, for example,
     ‘object.__getattribute__(self, name)’.

          Note: This method may still be bypassed when looking up
          special methods as the result of implicit invocation via
          language syntax or built-in functions.  See *note Special
          method lookup: 156f.

     For certain sensitive attribute accesses, raises an *note auditing
     event: fa1. ‘object.__getattr__’ with arguments ‘obj’ and ‘name’.

 -- Method: object.__setattr__ (self, name, value)

     Called when an attribute assignment is attempted.  This is called
     instead of the normal mechanism (i.e.  store the value in the
     instance dictionary).  `name' is the attribute name, `value' is the
     value to be assigned to it.

     If *note __setattr__(): eee. wants to assign to an instance
     attribute, it should call the base class method with the same name,
     for example, ‘object.__setattr__(self, name, value)’.

     For certain sensitive attribute assignments, raises an *note
     auditing event: fa1. ‘object.__setattr__’ with arguments ‘obj’,
     ‘name’, ‘value’.

 -- Method: object.__delattr__ (self, name)

     Like *note __setattr__(): eee. but for attribute deletion instead
     of assignment.  This should only be implemented if ‘del obj.name’
     is meaningful for the object.

     For certain sensitive attribute deletions, raises an *note auditing
     event: fa1. ‘object.__delattr__’ with arguments ‘obj’ and ‘name’.

 -- Method: object.__dir__ (self)

     Called when *note dir(): df9. is called on the object.  A sequence
     must be returned.  *note dir(): df9. converts the returned sequence
     to a list and sorts it.

* Menu:

* Customizing module attribute access::
* Implementing Descriptors::
* Invoking Descriptors::
* __slots__::


File: python.info,  Node: Customizing module attribute access,  Next: Implementing Descriptors,  Up: Customizing attribute access

4.3.3.3 Customizing module attribute access
...........................................

Special names ‘__getattr__’ and ‘__dir__’ can be also used to customize
access to module attributes.  The ‘__getattr__’ function at the module
level should accept one argument which is the name of an attribute and
return the computed value or raise an *note AttributeError: 4a2.  If an
attribute is not found on a module object through the normal lookup,
i.e.  *note object.__getattribute__(): 54c, then ‘__getattr__’ is
searched in the module ‘__dict__’ before raising an *note
AttributeError: 4a2.  If found, it is called with the attribute name and
the result is returned.

The ‘__dir__’ function should accept no arguments, and return a sequence
of strings that represents the names accessible on module.  If present,
this function overrides the standard *note dir(): df9. search on a
module.

For a more fine grained customization of the module behavior (setting
attributes, properties, etc.), one can set the ‘__class__’ attribute of
a module object to a subclass of *note types.ModuleType: 7e2.  For
example:

     import sys
     from types import ModuleType

     class VerboseModule(ModuleType):
         def __repr__(self):
             return f'Verbose {self.__name__}'

         def __setattr__(self, attr, value):
             print(f'Setting {attr}...')
             super().__setattr__(attr, value)

     sys.modules[__name__].__class__ = VerboseModule

     Note: Defining module ‘__getattr__’ and setting module ‘__class__’
     only affect lookups made using the attribute access syntax –
     directly accessing the module globals (whether by code within the
     module, or via a reference to the module’s globals dictionary) is
     unaffected.

Changed in version 3.5: ‘__class__’ module attribute is now writable.

New in version 3.7: ‘__getattr__’ and ‘__dir__’ module attributes.

See also
........

PEP 562(1) - Module __getattr__ and __dir__

     Describes the ‘__getattr__’ and ‘__dir__’ functions on modules.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0562


File: python.info,  Node: Implementing Descriptors,  Next: Invoking Descriptors,  Prev: Customizing module attribute access,  Up: Customizing attribute access

4.3.3.4 Implementing Descriptors
................................

The following methods only apply when an instance of the class
containing the method (a so-called `descriptor' class) appears in an
`owner' class (the descriptor must be in either the owner’s class
dictionary or in the class dictionary for one of its parents).  In the
examples below, “the attribute” refers to the attribute whose name is
the key of the property in the owner class’ *note __dict__: 5f6.

 -- Method: object.__get__ (self, instance, owner=None)

     Called to get the attribute of the owner class (class attribute
     access) or of an instance of that class (instance attribute
     access).  The optional `owner' argument is the owner class, while
     `instance' is the instance that the attribute was accessed through,
     or ‘None’ when the attribute is accessed through the `owner'.

     This method should return the computed attribute value or raise an
     *note AttributeError: 4a2. exception.

     PEP 252(1) specifies that *note __get__(): 156e. is callable with
     one or two arguments.  Python’s own built-in descriptors support
     this specification; however, it is likely that some third-party
     tools have descriptors that require both arguments.  Python’s own
     *note __getattribute__(): 54c. implementation always passes in both
     arguments whether they are required or not.

 -- Method: object.__set__ (self, instance, value)

     Called to set the attribute on an instance `instance' of the owner
     class to a new value, `value'.

     Note, adding *note __set__(): 1572. or *note __delete__(): 1573.
     changes the kind of descriptor to a “data descriptor”.  See *note
     Invoking Descriptors: 1574. for more details.

 -- Method: object.__delete__ (self, instance)

     Called to delete the attribute on an instance `instance' of the
     owner class.

 -- Method: object.__set_name__ (self, owner, name)

     Called at the time the owning class `owner' is created.  The
     descriptor has been assigned to `name'.

          Note: *note __set_name__(): 5e3. is only called implicitly as
          part of the *note type: 6ff. constructor, so it will need to
          be called explicitly with the appropriate parameters when a
          descriptor is added to a class after initial creation:

               class A:
                  pass
               descr = custom_descriptor()
               A.attr = descr
               descr.__set_name__(A, 'attr')

          See *note Creating the class object: 5df. for more details.

     New in version 3.6.

The attribute ‘__objclass__’ is interpreted by the *note inspect: a0.
module as specifying the class where this object was defined (setting
this appropriately can assist in runtime introspection of dynamic class
attributes).  For callables, it may indicate that an instance of the
given type (or a subclass) is expected or required as the first
positional argument (for example, CPython sets this attribute for
unbound methods that are implemented in C).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0252


File: python.info,  Node: Invoking Descriptors,  Next: __slots__,  Prev: Implementing Descriptors,  Up: Customizing attribute access

4.3.3.5 Invoking Descriptors
............................

In general, a descriptor is an object attribute with “binding behavior”,
one whose attribute access has been overridden by methods in the
descriptor protocol: *note __get__(): 156e, *note __set__(): 1572, and
*note __delete__(): 1573.  If any of those methods are defined for an
object, it is said to be a descriptor.

The default behavior for attribute access is to get, set, or delete the
attribute from an object’s dictionary.  For instance, ‘a.x’ has a lookup
chain starting with ‘a.__dict__['x']’, then ‘type(a).__dict__['x']’, and
continuing through the base classes of ‘type(a)’ excluding metaclasses.

However, if the looked-up value is an object defining one of the
descriptor methods, then Python may override the default behavior and
invoke the descriptor method instead.  Where this occurs in the
precedence chain depends on which descriptor methods were defined and
how they were called.

The starting point for descriptor invocation is a binding, ‘a.x’.  How
the arguments are assembled depends on ‘a’:

Direct Call

     The simplest and least common call is when user code directly
     invokes a descriptor method: ‘x.__get__(a)’.

Instance Binding

     If binding to an object instance, ‘a.x’ is transformed into the
     call: ‘type(a).__dict__['x'].__get__(a, type(a))’.

Class Binding

     If binding to a class, ‘A.x’ is transformed into the call:
     ‘A.__dict__['x'].__get__(None, A)’.

Super Binding

     If ‘a’ is an instance of *note super: 5dd, then the binding
     ‘super(B, obj).m()’ searches ‘obj.__class__.__mro__’ for the base
     class ‘A’ immediately following ‘B’ and then invokes the descriptor
     with the call: ‘A.__dict__['m'].__get__(obj, obj.__class__)’.

For instance bindings, the precedence of descriptor invocation depends
on which descriptor methods are defined.  A descriptor can define any
combination of *note __get__(): 156e, *note __set__(): 1572. and *note
__delete__(): 1573.  If it does not define *note __get__(): 156e, then
accessing the attribute will return the descriptor object itself unless
there is a value in the object’s instance dictionary.  If the descriptor
defines *note __set__(): 1572. and/or *note __delete__(): 1573, it is a
data descriptor; if it defines neither, it is a non-data descriptor.
Normally, data descriptors define both *note __get__(): 156e. and *note
__set__(): 1572, while non-data descriptors have just the *note
__get__(): 156e. method.  Data descriptors with *note __get__(): 156e.
and *note __set__(): 1572. (and/or *note __delete__(): 1573.) defined
always override a redefinition in an instance dictionary.  In contrast,
non-data descriptors can be overridden by instances.

Python methods (including those decorated with *note @staticmethod: 30a.
and *note @classmethod: 309.) are implemented as non-data descriptors.
Accordingly, instances can redefine and override methods.  This allows
individual instances to acquire behaviors that differ from other
instances of the same class.

The *note property(): 308. function is implemented as a data descriptor.
Accordingly, instances cannot override the behavior of a property.


File: python.info,  Node: __slots__,  Prev: Invoking Descriptors,  Up: Customizing attribute access

4.3.3.6 __slots__
.................

`__slots__' allow us to explicitly declare data members (like
properties) and deny the creation of *note __dict__: 5f6. and
`__weakref__' (unless explicitly declared in `__slots__' or available in
a parent.)

The space saved over using *note __dict__: 5f6. can be significant.
Attribute lookup speed can be significantly improved as well.

 -- Data: object.__slots__

     This class variable can be assigned a string, iterable, or sequence
     of strings with variable names used by instances.  `__slots__'
     reserves space for the declared variables and prevents the
     automatic creation of *note __dict__: 5f6. and `__weakref__' for
     each instance.

* Menu:

* Notes on using __slots__::


File: python.info,  Node: Notes on using __slots__,  Up: __slots__

4.3.3.7 Notes on using `__slots__'
..................................

   * When inheriting from a class without `__slots__', the *note
     __dict__: 5f6. and `__weakref__' attribute of the instances will
     always be accessible.

   * Without a *note __dict__: 5f6. variable, instances cannot be
     assigned new variables not listed in the `__slots__' definition.
     Attempts to assign to an unlisted variable name raises *note
     AttributeError: 4a2.  If dynamic assignment of new variables is
     desired, then add ‘'__dict__'’ to the sequence of strings in the
     `__slots__' declaration.

   * Without a `__weakref__' variable for each instance, classes
     defining `__slots__' do not support *note weak references: 131. to
     its instances.  If weak reference support is needed, then add
     ‘'__weakref__'’ to the sequence of strings in the `__slots__'
     declaration.

   * `__slots__' are implemented at the class level by creating *note
     descriptors: 5e4. for each variable name.  As a result, class
     attributes cannot be used to set default values for instance
     variables defined by `__slots__'; otherwise, the class attribute
     would overwrite the descriptor assignment.

   * The action of a `__slots__' declaration is not limited to the class
     where it is defined.  `__slots__' declared in parents are available
     in child classes.  However, child subclasses will get a *note
     __dict__: 5f6. and `__weakref__' unless they also define
     `__slots__' (which should only contain names of any `additional'
     slots).

   * If a class defines a slot also defined in a base class, the
     instance variable defined by the base class slot is inaccessible
     (except by retrieving its descriptor directly from the base class).
     This renders the meaning of the program undefined.  In the future,
     a check may be added to prevent this.

   * Nonempty `__slots__' does not work for classes derived from
     “variable-length” built-in types such as *note int: 204, *note
     bytes: 172. and *note tuple: 1a2.

   * Any non-string *note iterable: c7c. may be assigned to `__slots__'.

   * If a *note dictionary: 164. is used to assign `__slots__', the
     dictionary keys will be used as the slot names.  The values of the
     dictionary can be used to provide per-attribute docstrings that
     will be recognised by *note inspect.getdoc(): 307. and displayed in
     the output of *note help(): 175.

   * *note __class__: ecc. assignment works only if both classes have
     the same `__slots__'.

   * *note Multiple inheritance: 1406. with multiple slotted parent
     classes can be used, but only one parent is allowed to have
     attributes created by slots (the other bases must have empty slot
     layouts) - violations raise *note TypeError: 1fe.

   * If an *note iterator: 1171. is used for `__slots__' then a *note
     descriptor: 1579. is created for each of the iterator’s values.
     However, the `__slots__' attribute will be an empty iterator.


File: python.info,  Node: Customizing class creation,  Next: Customizing instance and subclass checks,  Prev: Customizing attribute access,  Up: Special method names

4.3.3.8 Customizing class creation
..................................

Whenever a class inherits from another class, *note __init_subclass__():
5de. is called on that class.  This way, it is possible to write classes
which change the behavior of subclasses.  This is closely related to
class decorators, but where class decorators only affect the specific
class they’re applied to, ‘__init_subclass__’ solely applies to future
subclasses of the class defining the method.

 -- Method: classmethod object.__init_subclass__ (cls)

     This method is called whenever the containing class is subclassed.
     `cls' is then the new subclass.  If defined as a normal instance
     method, this method is implicitly converted to a class method.

     Keyword arguments which are given to a new class are passed to the
     parent’s class ‘__init_subclass__’.  For compatibility with other
     classes using ‘__init_subclass__’, one should take out the needed
     keyword arguments and pass the others over to the base class, as
     in:

          class Philosopher:
              def __init_subclass__(cls, /, default_name, **kwargs):
                  super().__init_subclass__(**kwargs)
                  cls.default_name = default_name

          class AustralianPhilosopher(Philosopher, default_name="Bruce"):
              pass

     The default implementation ‘object.__init_subclass__’ does nothing,
     but raises an error if it is called with any arguments.

          Note: The metaclass hint ‘metaclass’ is consumed by the rest
          of the type machinery, and is never passed to
          ‘__init_subclass__’ implementations.  The actual metaclass
          (rather than the explicit hint) can be accessed as
          ‘type(cls)’.

     New in version 3.6.

* Menu:

* Metaclasses::
* Resolving MRO entries::
* Determining the appropriate metaclass::
* Preparing the class namespace::
* Executing the class body::
* Creating the class object::
* Uses for metaclasses::


File: python.info,  Node: Metaclasses,  Next: Resolving MRO entries,  Up: Customizing class creation

4.3.3.9 Metaclasses
...................

By default, classes are constructed using *note type(): 6ff.  The class
body is executed in a new namespace and the class name is bound locally
to the result of ‘type(name, bases, namespace)’.

The class creation process can be customized by passing the ‘metaclass’
keyword argument in the class definition line, or by inheriting from an
existing class that included such an argument.  In the following
example, both ‘MyClass’ and ‘MySubclass’ are instances of ‘Meta’:

     class Meta(type):
         pass

     class MyClass(metaclass=Meta):
         pass

     class MySubclass(MyClass):
         pass

Any other keyword arguments that are specified in the class definition
are passed through to all metaclass operations described below.

When a class definition is executed, the following steps occur:

   * MRO entries are resolved;

   * the appropriate metaclass is determined;

   * the class namespace is prepared;

   * the class body is executed;

   * the class object is created.


File: python.info,  Node: Resolving MRO entries,  Next: Determining the appropriate metaclass,  Prev: Metaclasses,  Up: Customizing class creation

4.3.3.10 Resolving MRO entries
..............................

If a base that appears in class definition is not an instance of *note
type: 6ff, then an ‘__mro_entries__’ method is searched on it.  If
found, it is called with the original bases tuple.  This method must
return a tuple of classes that will be used instead of this base.  The
tuple may be empty, in such case the original base is ignored.

See also
........

PEP 560(1) - Core support for typing module and generic types

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0560


File: python.info,  Node: Determining the appropriate metaclass,  Next: Preparing the class namespace,  Prev: Resolving MRO entries,  Up: Customizing class creation

4.3.3.11 Determining the appropriate metaclass
..............................................

The appropriate metaclass for a class definition is determined as
follows:

   * if no bases and no explicit metaclass are given, then *note type():
     6ff. is used;

   * if an explicit metaclass is given and it is `not' an instance of
     *note type(): 6ff, then it is used directly as the metaclass;

   * if an instance of *note type(): 6ff. is given as the explicit
     metaclass, or bases are defined, then the most derived metaclass is
     used.

The most derived metaclass is selected from the explicitly specified
metaclass (if any) and the metaclasses (i.e.  ‘type(cls)’) of all
specified base classes.  The most derived metaclass is one which is a
subtype of `all' of these candidate metaclasses.  If none of the
candidate metaclasses meets that criterion, then the class definition
will fail with ‘TypeError’.


File: python.info,  Node: Preparing the class namespace,  Next: Executing the class body,  Prev: Determining the appropriate metaclass,  Up: Customizing class creation

4.3.3.12 Preparing the class namespace
......................................

Once the appropriate metaclass has been identified, then the class
namespace is prepared.  If the metaclass has a ‘__prepare__’ attribute,
it is called as ‘namespace = metaclass.__prepare__(name, bases, **kwds)’
(where the additional keyword arguments, if any, come from the class
definition).  The ‘__prepare__’ method should be implemented as a *note
classmethod: 309.  The namespace returned by ‘__prepare__’ is passed in
to ‘__new__’, but when the final class object is created the namespace
is copied into a new ‘dict’.

If the metaclass has no ‘__prepare__’ attribute, then the class
namespace is initialised as an empty ordered mapping.

See also
........

PEP 3115(1) - Metaclasses in Python 3000

     Introduced the ‘__prepare__’ namespace hook

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3115


File: python.info,  Node: Executing the class body,  Next: Creating the class object,  Prev: Preparing the class namespace,  Up: Customizing class creation

4.3.3.13 Executing the class body
.................................

The class body is executed (approximately) as ‘exec(body, globals(),
namespace)’.  The key difference from a normal call to *note exec():
d0c. is that lexical scoping allows the class body (including any
methods) to reference names from the current and outer scopes when the
class definition occurs inside a function.

However, even when the class definition occurs inside the function,
methods defined inside the class still cannot see names defined at the
class scope.  Class variables must be accessed through the first
parameter of instance or class methods, or through the implicit
lexically scoped ‘__class__’ reference described in the next section.


File: python.info,  Node: Creating the class object,  Next: Uses for metaclasses,  Prev: Executing the class body,  Up: Customizing class creation

4.3.3.14 Creating the class object
..................................

Once the class namespace has been populated by executing the class body,
the class object is created by calling ‘metaclass(name, bases,
namespace, **kwds)’ (the additional keywords passed here are the same as
those passed to ‘__prepare__’).

This class object is the one that will be referenced by the
zero-argument form of *note super(): 5dd.  ‘__class__’ is an implicit
closure reference created by the compiler if any methods in a class body
refer to either ‘__class__’ or ‘super’.  This allows the zero argument
form of *note super(): 5dd. to correctly identify the class being
defined based on lexical scoping, while the class or instance that was
used to make the current call is identified based on the first argument
passed to the method.

`CPython implementation detail:' In CPython 3.6 and later, the
‘__class__’ cell is passed to the metaclass as a ‘__classcell__’ entry
in the class namespace.  If present, this must be propagated up to the
‘type.__new__’ call in order for the class to be initialised correctly.
Failing to do so will result in a *note RuntimeError: 3dc. in Python
3.8.

When using the default metaclass *note type: 6ff, or any metaclass that
ultimately calls ‘type.__new__’, the following additional customisation
steps are invoked after creating the class object:

   * first, ‘type.__new__’ collects all of the descriptors in the class
     namespace that define a *note __set_name__(): 5e3. method;

   * second, all of these ‘__set_name__’ methods are called with the
     class being defined and the assigned name of that particular
     descriptor;

   * finally, the *note __init_subclass__(): 5de. hook is called on the
     immediate parent of the new class in its method resolution order.

After the class object is created, it is passed to the class decorators
included in the class definition (if any) and the resulting object is
bound in the local namespace as the defined class.

When a new class is created by ‘type.__new__’, the object provided as
the namespace parameter is copied to a new ordered mapping and the
original object is discarded.  The new copy is wrapped in a read-only
proxy, which becomes the *note __dict__: 5f6. attribute of the class
object.

See also
........

PEP 3135(1) - New super

     Describes the implicit ‘__class__’ closure reference

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3135


File: python.info,  Node: Uses for metaclasses,  Prev: Creating the class object,  Up: Customizing class creation

4.3.3.15 Uses for metaclasses
.............................

The potential uses for metaclasses are boundless.  Some ideas that have
been explored include enum, logging, interface checking, automatic
delegation, automatic property creation, proxies, frameworks, and
automatic resource locking/synchronization.


File: python.info,  Node: Customizing instance and subclass checks,  Next: Emulating generic types,  Prev: Customizing class creation,  Up: Special method names

4.3.3.16 Customizing instance and subclass checks
.................................................

The following methods are used to override the default behavior of the
*note isinstance(): 552. and *note issubclass(): 553. built-in
functions.

In particular, the metaclass *note abc.ABCMeta: 906. implements these
methods in order to allow the addition of Abstract Base Classes (ABCs)
as “virtual base classes” to any class or type (including built-in
types), including other ABCs.

 -- Method: class.__instancecheck__ (self, instance)

     Return true if `instance' should be considered a (direct or
     indirect) instance of `class'.  If defined, called to implement
     ‘isinstance(instance, class)’.

 -- Method: class.__subclasscheck__ (self, subclass)

     Return true if `subclass' should be considered a (direct or
     indirect) subclass of `class'.  If defined, called to implement
     ‘issubclass(subclass, class)’.

Note that these methods are looked up on the type (metaclass) of a
class.  They cannot be defined as class methods in the actual class.
This is consistent with the lookup of special methods that are called on
instances, only in this case the instance is itself a class.

See also
........

PEP 3119(1) - Introducing Abstract Base Classes

     Includes the specification for customizing *note isinstance(): 552.
     and *note issubclass(): 553. behavior through *note
     __instancecheck__(): 1584. and *note __subclasscheck__(): 1585,
     with motivation for this functionality in the context of adding
     Abstract Base Classes (see the *note abc: 3. module) to the
     language.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3119


File: python.info,  Node: Emulating generic types,  Next: Emulating callable objects,  Prev: Customizing instance and subclass checks,  Up: Special method names

4.3.3.17 Emulating generic types
................................

When using *note type annotations: 1587, it is often useful to
`parameterize' a *note generic type: fea. using Python’s square-brackets
notation.  For example, the annotation ‘list[int]’ might be used to
signify a *note list: 1f8. in which all the elements are of type *note
int: 204.

See also
........

PEP 484(1) - Type Hints

     Introducing Python’s framework for type annotations

*note Generic Alias Types: fe5.

     Documentation for objects representing parameterized generic
     classes

*note Generics: 1588, *note user-defined generics: 1589. and *note typing.Generic: 100b.

     Documentation on how to implement generic classes that can be
     parameterized at runtime and understood by static type-checkers.

A class can `generally' only be parameterized if it defines the special
class method ‘__class_getitem__()’.

 -- Method: classmethod object.__class_getitem__ (cls, key)

     Return an object representing the specialization of a generic class
     by type arguments found in `key'.

     When defined on a class, ‘__class_getitem__()’ is automatically a
     class method.  As such, there is no need for it to be decorated
     with *note @classmethod: 309. when it is defined.

* Menu:

* The purpose of __class_getitem__::
* __class_getitem__ versus __getitem__::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0484


File: python.info,  Node: The purpose of __class_getitem__,  Next: __class_getitem__ versus __getitem__,  Up: Emulating generic types

4.3.3.18 The purpose of `__class_getitem__'
...........................................

The purpose of *note __class_getitem__(): 437. is to allow runtime
parameterization of standard-library generic classes in order to more
easily apply *note type hints: 158b. to these classes.

To implement custom generic classes that can be parameterized at runtime
and understood by static type-checkers, users should either inherit from
a standard library class that already implements *note
__class_getitem__(): 437, or inherit from *note typing.Generic: 100b,
which has its own implementation of ‘__class_getitem__()’.

Custom implementations of *note __class_getitem__(): 437. on classes
defined outside of the standard library may not be understood by
third-party type-checkers such as mypy.  Using ‘__class_getitem__()’ on
any class for purposes other than type hinting is discouraged.


File: python.info,  Node: __class_getitem__ versus __getitem__,  Prev: The purpose of __class_getitem__,  Up: Emulating generic types

4.3.3.19 `__class_getitem__' versus `__getitem__'
.................................................

Usually, the *note subscription: 158e. of an object using square
brackets will call the *note __getitem__(): 3a2. instance method defined
on the object’s class.  However, if the object being subscribed is
itself a class, the class method *note __class_getitem__(): 437. may be
called instead.  ‘__class_getitem__()’ should return a *note
GenericAlias: fe5. object if it is properly defined.

Presented with the *note expression: 158f. ‘obj[x]’, the Python
interpreter follows something like the following process to decide
whether *note __getitem__(): 3a2. or *note __class_getitem__(): 437.
should be called:

     from inspect import isclass

     def subscribe(obj, x):
         """Return the result of the expression `obj[x]`"""

         class_of_obj = type(obj)

         # If the class of obj defines __getitem__,
         # call class_of_obj.__getitem__(obj, x)
         if hasattr(class_of_obj, '__getitem__'):
             return class_of_obj.__getitem__(obj, x)

         # Else, if obj is a class and defines __class_getitem__,
         # call obj.__class_getitem__(x)
         elif isclass(obj) and hasattr(obj, '__class_getitem__'):
             return obj.__class_getitem__(x)

         # Else, raise an exception
         else:
             raise TypeError(
                 f"'{class_of_obj.__name__}' object is not subscriptable"
             )

In Python, all classes are themselves instances of other classes.  The
class of a class is known as that class’s *note metaclass: 1590, and
most classes have the *note type: 6ff. class as their metaclass.  *note
type: 6ff. does not define *note __getitem__(): 3a2, meaning that
expressions such as ‘list[int]’, ‘dict[str, float]’ and ‘tuple[str,
bytes]’ all result in *note __class_getitem__(): 437. being called:

     >>> # list has class "type" as its metaclass, like most classes:
     >>> type(list)
     <class 'type'>
     >>> type(dict) == type(list) == type(tuple) == type(str) == type(bytes)
     True
     >>> # "list[int]" calls "list.__class_getitem__(int)"
     >>> list[int]
     list[int]
     >>> # list.__class_getitem__ returns a GenericAlias object:
     >>> type(list[int])
     <class 'types.GenericAlias'>

However, if a class has a custom metaclass that defines *note
__getitem__(): 3a2, subscribing the class may result in different
behaviour.  An example of this can be found in the *note enum: 79.
module:

     >>> from enum import Enum
     >>> class Menu(Enum):
     ...     """A breakfast menu"""
     ...     SPAM = 'spam'
     ...     BACON = 'bacon'
     ...
     >>> # Enum classes have a custom metaclass:
     >>> type(Menu)
     <class 'enum.EnumMeta'>
     >>> # EnumMeta defines __getitem__,
     >>> # so __class_getitem__ is not called,
     >>> # and the result is not a GenericAlias object:
     >>> Menu['SPAM']
     <Menu.SPAM: 'spam'>
     >>> type(Menu['SPAM'])
     <enum 'Menu'>

See also
........

PEP 560(1) - Core Support for typing module and generic types

     Introducing *note __class_getitem__(): 437, and outlining when a
     *note subscription: 158e. results in ‘__class_getitem__()’ being
     called instead of *note __getitem__(): 3a2.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0560


File: python.info,  Node: Emulating callable objects,  Next: Emulating container types,  Prev: Emulating generic types,  Up: Special method names

4.3.3.20 Emulating callable objects
...................................

 -- Method: object.__call__ (self[, args...])

     Called when the instance is “called” as a function; if this method
     is defined, ‘x(arg1, arg2, ...)’ roughly translates to
     ‘type(x).__call__(x, arg1, ...)’.


File: python.info,  Node: Emulating container types,  Next: Emulating numeric types,  Prev: Emulating callable objects,  Up: Special method names

4.3.3.21 Emulating container types
..................................

The following methods can be defined to implement container objects.
Containers usually are *note sequences: 135c. (such as *note lists: 1f8.
or *note tuples: 1a2.) or *note mappings: c0b. (like *note dictionaries:
164.), but can represent other containers as well.  The first set of
methods is used either to emulate a sequence or to emulate a mapping;
the difference is that for a sequence, the allowable keys should be the
integers `k' for which ‘0 <= k < N’ where `N' is the length of the
sequence, or *note slice: ec8. objects, which define a range of items.
It is also recommended that mappings provide the methods ‘keys()’,
‘values()’, ‘items()’, ‘get()’, ‘clear()’, ‘setdefault()’, ‘pop()’,
‘popitem()’, ‘copy()’, and ‘update()’ behaving similar to those for
Python’s standard *note dictionary: 164. objects.  The *note
collections.abc: 1e. module provides a *note MutableMapping: ace. *note
abstract base class: c05. to help create those methods from a base set
of *note __getitem__(): 3a2, *note __setitem__(): d2a, *note
__delitem__(): d2b, and ‘keys()’.  Mutable sequences should provide
methods ‘append()’, ‘count()’, ‘index()’, ‘extend()’, ‘insert()’,
‘pop()’, ‘remove()’, ‘reverse()’ and ‘sort()’, like Python standard
*note list: 1f8. objects.  Finally, sequence types should implement
addition (meaning concatenation) and multiplication (meaning repetition)
by defining the methods *note __add__(): 1595, *note __radd__(): 1596,
*note __iadd__(): f30, *note __mul__(): 1597, *note __rmul__(): 1598.
and *note __imul__(): 1599. described below; they should not define
other numerical operators.  It is recommended that both mappings and
sequences implement the *note __contains__(): dee. method to allow
efficient use of the ‘in’ operator; for mappings, ‘in’ should search the
mapping’s keys; for sequences, it should search through the values.  It
is further recommended that both mappings and sequences implement the
*note __iter__(): 609. method to allow efficient iteration through the
container; for mappings, *note __iter__(): 609. should iterate through
the object’s keys; for sequences, it should iterate through the values.

 -- Method: object.__len__ (self)

     Called to implement the built-in function *note len(): 28b.  Should
     return the length of the object, an integer ‘>=’ 0.  Also, an
     object that doesn’t define a *note __bool__(): d30. method and
     whose *note __len__(): e90. method returns zero is considered to be
     false in a Boolean context.

     `CPython implementation detail:' In CPython, the length is required
     to be at most *note sys.maxsize: c15.  If the length is larger than
     ‘sys.maxsize’ some features (such as *note len(): 28b.) may raise
     *note OverflowError: a41.  To prevent raising ‘OverflowError’ by
     truth value testing, an object must define a *note __bool__(): d30.
     method.

 -- Method: object.__length_hint__ (self)

     Called to implement *note operator.length_hint(): 968.  Should
     return an estimated length for the object (which may be greater or
     less than the actual length).  The length must be an integer ‘>=’
     0.  The return value may also be *note NotImplemented: 202, which
     is treated the same as if the ‘__length_hint__’ method didn’t exist
     at all.  This method is purely an optimization and is never
     required for correctness.

     New in version 3.4.

     Note: Slicing is done exclusively with the following three methods.
     A call like

          a[1:2] = b

     is translated to

          a[slice(1, 2, None)] = b

     and so forth.  Missing slice items are always filled in with
     ‘None’.

 -- Method: object.__getitem__ (self, key)

     Called to implement evaluation of ‘self[key]’.  For *note sequence:
     135c. types, the accepted keys should be integers and slice
     objects.  Note that the special interpretation of negative indexes
     (if the class wishes to emulate a *note sequence: 135c. type) is up
     to the *note __getitem__(): 3a2. method.  If `key' is of an
     inappropriate type, *note TypeError: 1fe. may be raised; if of a
     value outside the set of indexes for the sequence (after any
     special interpretation of negative values), *note IndexError: f36.
     should be raised.  For *note mapping: c0b. types, if `key' is
     missing (not in the container), *note KeyError: 3e9. should be
     raised.

          Note: *note for: cfa. loops expect that an *note IndexError:
          f36. will be raised for illegal indexes to allow proper
          detection of the end of the sequence.

          Note: When *note subscripting: 158e. a `class', the special
          class method *note __class_getitem__(): 437. may be called
          instead of ‘__getitem__()’.  See *note __class_getitem__
          versus __getitem__: 158d. for more details.

 -- Method: object.__setitem__ (self, key, value)

     Called to implement assignment to ‘self[key]’.  Same note as for
     *note __getitem__(): 3a2.  This should only be implemented for
     mappings if the objects support changes to the values for keys, or
     if new keys can be added, or for sequences if elements can be
     replaced.  The same exceptions should be raised for improper `key'
     values as for the *note __getitem__(): 3a2. method.

 -- Method: object.__delitem__ (self, key)

     Called to implement deletion of ‘self[key]’.  Same note as for
     *note __getitem__(): 3a2.  This should only be implemented for
     mappings if the objects support removal of keys, or for sequences
     if elements can be removed from the sequence.  The same exceptions
     should be raised for improper `key' values as for the *note
     __getitem__(): 3a2. method.

 -- Method: object.__missing__ (self, key)

     Called by *note dict: 164.*note __getitem__(): 3a2. to implement
     ‘self[key]’ for dict subclasses when key is not in the dictionary.

 -- Method: object.__iter__ (self)

     This method is called when an iterator is required for a container.
     This method should return a new iterator object that can iterate
     over all the objects in the container.  For mappings, it should
     iterate over the keys of the container.

     Iterator objects also need to implement this method; they are
     required to return themselves.  For more information on iterator
     objects, see *note Iterator Types: 159a.

 -- Method: object.__reversed__ (self)

     Called (if present) by the *note reversed(): 2c6. built-in to
     implement reverse iteration.  It should return a new iterator
     object that iterates over all the objects in the container in
     reverse order.

     If the *note __reversed__(): 629. method is not provided, the *note
     reversed(): 2c6. built-in will fall back to using the sequence
     protocol (*note __len__(): e90. and *note __getitem__(): 3a2.).
     Objects that support the sequence protocol should only provide
     *note __reversed__(): 629. if they can provide an implementation
     that is more efficient than the one provided by *note reversed():
     2c6.

The membership test operators (*note in: 179. and *note not in: 159b.)
are normally implemented as an iteration through a container.  However,
container objects can supply the following special method with a more
efficient implementation, which also does not require the object be
iterable.

 -- Method: object.__contains__ (self, item)

     Called to implement membership test operators.  Should return true
     if `item' is in `self', false otherwise.  For mapping objects, this
     should consider the keys of the mapping rather than the values or
     the key-item pairs.

     For objects that don’t define *note __contains__(): dee, the
     membership test first tries iteration via *note __iter__(): 609,
     then the old sequence iteration protocol via *note __getitem__():
     3a2, see *note this section in the language reference: 159c.


File: python.info,  Node: Emulating numeric types,  Next: With Statement Context Managers,  Prev: Emulating container types,  Up: Special method names

4.3.3.22 Emulating numeric types
................................

The following methods can be defined to emulate numeric objects.
Methods corresponding to operations that are not supported by the
particular kind of number implemented (e.g., bitwise operations for
non-integral numbers) should be left undefined.

 -- Method: object.__add__ (self, other)
 -- Method: object.__sub__ (self, other)
 -- Method: object.__mul__ (self, other)
 -- Method: object.__matmul__ (self, other)
 -- Method: object.__truediv__ (self, other)
 -- Method: object.__floordiv__ (self, other)
 -- Method: object.__mod__ (self, other)
 -- Method: object.__divmod__ (self, other)
 -- Method: object.__pow__ (self, other[, modulo])
 -- Method: object.__lshift__ (self, other)
 -- Method: object.__rshift__ (self, other)
 -- Method: object.__and__ (self, other)
 -- Method: object.__xor__ (self, other)
 -- Method: object.__or__ (self, other)

     These methods are called to implement the binary arithmetic
     operations (‘+’, ‘-’, ‘*’, ‘@’, ‘/’, ‘//’, ‘%’, *note divmod():
     28d, *note pow(): 2cf, ‘**’, ‘<<’, ‘>>’, ‘&’, ‘^’, ‘|’).  For
     instance, to evaluate the expression ‘x + y’, where `x' is an
     instance of a class that has an *note __add__(): 1595. method,
     ‘x.__add__(y)’ is called.  The *note __divmod__(): 876. method
     should be the equivalent to using *note __floordiv__(): ef7. and
     *note __mod__(): 15a0.; it should not be related to *note
     __truediv__(): 875.  Note that *note __pow__(): 15a1. should be
     defined to accept an optional third argument if the ternary version
     of the built-in *note pow(): 2cf. function is to be supported.

     If one of those methods does not support the operation with the
     supplied arguments, it should return ‘NotImplemented’.

 -- Method: object.__radd__ (self, other)
 -- Method: object.__rsub__ (self, other)
 -- Method: object.__rmul__ (self, other)
 -- Method: object.__rmatmul__ (self, other)
 -- Method: object.__rtruediv__ (self, other)
 -- Method: object.__rfloordiv__ (self, other)
 -- Method: object.__rmod__ (self, other)
 -- Method: object.__rdivmod__ (self, other)
 -- Method: object.__rpow__ (self, other[, modulo])
 -- Method: object.__rlshift__ (self, other)
 -- Method: object.__rrshift__ (self, other)
 -- Method: object.__rand__ (self, other)
 -- Method: object.__rxor__ (self, other)
 -- Method: object.__ror__ (self, other)

     These methods are called to implement the binary arithmetic
     operations (‘+’, ‘-’, ‘*’, ‘@’, ‘/’, ‘//’, ‘%’, *note divmod():
     28d, *note pow(): 2cf, ‘**’, ‘<<’, ‘>>’, ‘&’, ‘^’, ‘|’) with
     reflected (swapped) operands.  These functions are only called if
     the left operand does not support the corresponding operation (1)
     and the operands are of different types.  (2) For instance, to
     evaluate the expression ‘x - y’, where `y' is an instance of a
     class that has an *note __rsub__(): 15a7. method, ‘y.__rsub__(x)’
     is called if ‘x.__sub__(y)’ returns `NotImplemented'.

     Note that ternary *note pow(): 2cf. will not try calling *note
     __rpow__(): 15ab. (the coercion rules would become too
     complicated).

          Note: If the right operand’s type is a subclass of the left
          operand’s type and that subclass provides a different
          implementation of the reflected method for the operation, this
          method will be called before the left operand’s non-reflected
          method.  This behavior allows subclasses to override their
          ancestors’ operations.

 -- Method: object.__iadd__ (self, other)
 -- Method: object.__isub__ (self, other)
 -- Method: object.__imul__ (self, other)
 -- Method: object.__imatmul__ (self, other)
 -- Method: object.__itruediv__ (self, other)
 -- Method: object.__ifloordiv__ (self, other)
 -- Method: object.__imod__ (self, other)
 -- Method: object.__ipow__ (self, other[, modulo])
 -- Method: object.__ilshift__ (self, other)
 -- Method: object.__irshift__ (self, other)
 -- Method: object.__iand__ (self, other)
 -- Method: object.__ixor__ (self, other)
 -- Method: object.__ior__ (self, other)

     These methods are called to implement the augmented arithmetic
     assignments (‘+=’, ‘-=’, ‘*=’, ‘@=’, ‘/=’, ‘//=’, ‘%=’, ‘**=’,
     ‘<<=’, ‘>>=’, ‘&=’, ‘^=’, ‘|=’).  These methods should attempt to
     do the operation in-place (modifying `self') and return the result
     (which could be, but does not have to be, `self').  If a specific
     method is not defined, the augmented assignment falls back to the
     normal methods.  For instance, if `x' is an instance of a class
     with an *note __iadd__(): f30. method, ‘x += y’ is equivalent to ‘x
     = x.__iadd__(y)’ .  Otherwise, ‘x.__add__(y)’ and ‘y.__radd__(x)’
     are considered, as with the evaluation of ‘x + y’.  In certain
     situations, augmented assignment can result in unexpected errors
     (see *note Why does a_tuple[i] += [‘item’] raise an exception when
     the addition works?: 15ba.), but this behavior is in fact part of
     the data model.

          Note: Due to a bug in the dispatching mechanism for ‘**=’, a
          class that defines *note __ipow__(): 15b4. but returns
          ‘NotImplemented’ would fail to fall back to ‘x.__pow__(y)’ and
          ‘y.__rpow__(x)’.  This bug is fixed in Python 3.10.

 -- Method: object.__neg__ (self)
 -- Method: object.__pos__ (self)
 -- Method: object.__abs__ (self)
 -- Method: object.__invert__ (self)

     Called to implement the unary arithmetic operations (‘-’, ‘+’,
     *note abs(): 13f3. and ‘~’).

 -- Method: object.__complex__ (self)
 -- Method: object.__int__ (self)
 -- Method: object.__float__ (self)

     Called to implement the built-in functions *note complex(): 2c1,
     *note int(): 204. and *note float(): 1fd.  Should return a value of
     the appropriate type.

 -- Method: object.__index__ (self)

     Called to implement *note operator.index(): 15bf, and whenever
     Python needs to losslessly convert the numeric object to an integer
     object (such as in slicing, or in the built-in *note bin(): d08,
     *note hex(): d2e. and *note oct(): d2d. functions).  Presence of
     this method indicates that the numeric object is an integer type.
     Must return an integer.

     If *note __int__(): 2c3, *note __float__(): 2c4. and *note
     __complex__(): 2c5. are not defined then corresponding built-in
     functions *note int(): 204, *note float(): 1fd. and *note
     complex(): 2c1. fall back to *note __index__(): 2c2.

 -- Method: object.__round__ (self[, ndigits])
 -- Method: object.__trunc__ (self)
 -- Method: object.__floor__ (self)
 -- Method: object.__ceil__ (self)

     Called to implement the built-in function *note round(): d35. and
     *note math: b1. functions *note trunc(): df4, *note floor(): df2.
     and *note ceil(): df3.  Unless `ndigits' is passed to ‘__round__()’
     all these methods should return the value of the object truncated
     to an *note Integral: 1556. (typically an *note int: 204.).

     The built-in function *note int(): 204. falls back to *note
     __trunc__(): 15c1. if neither *note __int__(): 2c3. nor *note
     __index__(): 2c2. is defined.

   ---------- Footnotes ----------

   (1) (3) “Does not support” here means that the class has no such
method, or the method returns ‘NotImplemented’.  Do not set the method
to ‘None’ if you want to force fallback to the right operand’s reflected
method—that will instead have the opposite effect of explicitly
`blocking' such fallback.

   (2) (4) For operands of the same type, it is assumed that if the
non-reflected method – such as *note __add__(): 1595. – fails then the
overall operation is not supported, which is why the reflected method is
not called.


File: python.info,  Node: With Statement Context Managers,  Next: Special method lookup,  Prev: Emulating numeric types,  Up: Special method names

4.3.3.23 With Statement Context Managers
........................................

A `context manager' is an object that defines the runtime context to be
established when executing a *note with: 7da. statement.  The context
manager handles the entry into, and the exit from, the desired runtime
context for the execution of the block of code.  Context managers are
normally invoked using the ‘with’ statement (described in section *note
The with statement: 7da.), but can also be used by directly invoking
their methods.

Typical uses of context managers include saving and restoring various
kinds of global state, locking and unlocking resources, closing opened
files, etc.

For more information on context managers, see *note Context Manager
Types: 15c6.

 -- Method: object.__enter__ (self)

     Enter the runtime context related to this object.  The *note with:
     7da. statement will bind this method’s return value to the
     target(s) specified in the ‘as’ clause of the statement, if any.

 -- Method: object.__exit__ (self, exc_type, exc_value, traceback)

     Exit the runtime context related to this object.  The parameters
     describe the exception that caused the context to be exited.  If
     the context was exited without an exception, all three arguments
     will be *note None: 203.

     If an exception is supplied, and the method wishes to suppress the
     exception (i.e., prevent it from being propagated), it should
     return a true value.  Otherwise, the exception will be processed
     normally upon exit from this method.

     Note that *note __exit__(): d5e. methods should not reraise the
     passed-in exception; this is the caller’s responsibility.

See also
........

PEP 343(1) - The “with” statement

     The specification, background, and examples for the Python *note
     with: 7da. statement.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0343


File: python.info,  Node: Special method lookup,  Prev: With Statement Context Managers,  Up: Special method names

4.3.3.24 Special method lookup
..............................

For custom classes, implicit invocations of special methods are only
guaranteed to work correctly if defined on an object’s type, not in the
object’s instance dictionary.  That behaviour is the reason why the
following code raises an exception:

     >>> class C:
     ...     pass
     ...
     >>> c = C()
     >>> c.__len__ = lambda: 5
     >>> len(c)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: object of type 'C' has no len()

The rationale behind this behaviour lies with a number of special
methods such as *note __hash__(): 44c. and *note __repr__(): 44a. that
are implemented by all objects, including type objects.  If the implicit
lookup of these methods used the conventional lookup process, they would
fail when invoked on the type object itself:

     >>> 1 .__hash__() == hash(1)
     True
     >>> int.__hash__() == hash(int)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: descriptor '__hash__' of 'int' object needs an argument

Incorrectly attempting to invoke an unbound method of a class in this
way is sometimes referred to as ‘metaclass confusion’, and is avoided by
bypassing the instance when looking up special methods:

     >>> type(1).__hash__(1) == hash(1)
     True
     >>> type(int).__hash__(int) == hash(int)
     True

In addition to bypassing any instance attributes in the interest of
correctness, implicit special method lookup generally also bypasses the
*note __getattribute__(): 54c. method even of the object’s metaclass:

     >>> class Meta(type):
     ...     def __getattribute__(*args):
     ...         print("Metaclass getattribute invoked")
     ...         return type.__getattribute__(*args)
     ...
     >>> class C(object, metaclass=Meta):
     ...     def __len__(self):
     ...         return 10
     ...     def __getattribute__(*args):
     ...         print("Class getattribute invoked")
     ...         return object.__getattribute__(*args)
     ...
     >>> c = C()
     >>> c.__len__()                 # Explicit lookup via instance
     Class getattribute invoked
     10
     >>> type(c).__len__(c)          # Explicit lookup via type
     Metaclass getattribute invoked
     10
     >>> len(c)                      # Implicit lookup
     10

Bypassing the *note __getattribute__(): 54c. machinery in this fashion
provides significant scope for speed optimisations within the
interpreter, at the cost of some flexibility in the handling of special
methods (the special method `must' be set on the class object itself in
order to be consistently invoked by the interpreter).


File: python.info,  Node: Coroutines,  Prev: Special method names,  Up: Data model

4.3.4 Coroutines
----------------

* Menu:

* Awaitable Objects::
* Coroutine Objects::
* Asynchronous Iterators::
* Asynchronous Context Managers::


File: python.info,  Node: Awaitable Objects,  Next: Coroutine Objects,  Up: Coroutines

4.3.4.1 Awaitable Objects
.........................

An *note awaitable: 613. object generally implements an *note
__await__(): 735. method.  *note Coroutine objects: 18a. returned from
*note async def: 3a9. functions are awaitable.

     Note: The *note generator iterator: 559. objects returned from
     generators decorated with *note types.coroutine(): 86b. or *note
     asyncio.coroutine(): 3a8. are also awaitable, but they do not
     implement *note __await__(): 735.

 -- Method: object.__await__ (self)

     Must return an *note iterator: 1171.  Should be used to implement
     *note awaitable: 613. objects.  For instance, *note asyncio.Future:
     546. implements this method to be compatible with the *note await:
     2d8. expression.

New in version 3.5.

See also
........

PEP 492(1) for additional information about awaitable objects.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0492


File: python.info,  Node: Coroutine Objects,  Next: Asynchronous Iterators,  Prev: Awaitable Objects,  Up: Coroutines

4.3.4.2 Coroutine Objects
.........................

*note Coroutine objects: 18a. are *note awaitable: 613. objects.  A
coroutine’s execution can be controlled by calling *note __await__():
735. and iterating over the result.  When the coroutine has finished
executing and returns, the iterator raises *note StopIteration: 582, and
the exception’s ‘value’ attribute holds the return value.  If the
coroutine raises an exception, it is propagated by the iterator.
Coroutines should not directly raise unhandled *note StopIteration: 582.
exceptions.

Coroutines also have the methods listed below, which are analogous to
those of generators (see *note Generator-iterator methods: 15cb.).
However, unlike generators, coroutines do not directly support
iteration.

Changed in version 3.5.2: It is a *note RuntimeError: 3dc. to await on a
coroutine more than once.

 -- Method: coroutine.send (value)

     Starts or resumes execution of the coroutine.  If `value' is
     ‘None’, this is equivalent to advancing the iterator returned by
     *note __await__(): 735.  If `value' is not ‘None’, this method
     delegates to the *note send(): 15cd. method of the iterator that
     caused the coroutine to suspend.  The result (return value, *note
     StopIteration: 582, or other exception) is the same as when
     iterating over the *note __await__(): 735. return value, described
     above.

 -- Method: coroutine.throw (type[, value[, traceback]])

     Raises the specified exception in the coroutine.  This method
     delegates to the *note throw(): ff8. method of the iterator that
     caused the coroutine to suspend, if it has such a method.
     Otherwise, the exception is raised at the suspension point.  The
     result (return value, *note StopIteration: 582, or other exception)
     is the same as when iterating over the *note __await__(): 735.
     return value, described above.  If the exception is not caught in
     the coroutine, it propagates back to the caller.

 -- Method: coroutine.close ()

     Causes the coroutine to clean itself up and exit.  If the coroutine
     is suspended, this method first delegates to the *note close():
     15d0. method of the iterator that caused the coroutine to suspend,
     if it has such a method.  Then it raises *note GeneratorExit: df8.
     at the suspension point, causing the coroutine to immediately clean
     itself up.  Finally, the coroutine is marked as having finished
     executing, even if it was never started.

     Coroutine objects are automatically closed using the above process
     when they are about to be destroyed.


File: python.info,  Node: Asynchronous Iterators,  Next: Asynchronous Context Managers,  Prev: Coroutine Objects,  Up: Coroutines

4.3.4.3 Asynchronous Iterators
..............................

An `asynchronous iterator' can call asynchronous code in its ‘__anext__’
method.

Asynchronous iterators can be used in an *note async for: 3fd.
statement.

 -- Method: object.__aiter__ (self)

     Must return an `asynchronous iterator' object.

 -- Method: object.__anext__ (self)

     Must return an `awaitable' resulting in a next value of the
     iterator.  Should raise a *note StopAsyncIteration: 114a. error
     when the iteration is over.

An example of an asynchronous iterable object:

     class Reader:
         async def readline(self):
             ...

         def __aiter__(self):
             return self

         async def __anext__(self):
             val = await self.readline()
             if val == b'':
                 raise StopAsyncIteration
             return val

New in version 3.5.

Changed in version 3.7: Prior to Python 3.7, *note __aiter__(): 583.
could return an `awaitable' that would resolve to an *note asynchronous
iterator: 738.

Starting with Python 3.7, *note __aiter__(): 583. must return an
asynchronous iterator object.  Returning anything else will result in a
*note TypeError: 1fe. error.


File: python.info,  Node: Asynchronous Context Managers,  Prev: Asynchronous Iterators,  Up: Coroutines

4.3.4.4 Asynchronous Context Managers
.....................................

An `asynchronous context manager' is a `context manager' that is able to
suspend execution in its ‘__aenter__’ and ‘__aexit__’ methods.

Asynchronous context managers can be used in an *note async with: 736.
statement.

 -- Method: object.__aenter__ (self)

     Semantically similar to *note __enter__(): d5d, the only difference
     being that it must return an `awaitable'.

 -- Method: object.__aexit__ (self, exc_type, exc_value, traceback)

     Semantically similar to *note __exit__(): d5e, the only difference
     being that it must return an `awaitable'.

An example of an asynchronous context manager class:

     class AsyncContextManager:
         async def __aenter__(self):
             await log('entering context')

         async def __aexit__(self, exc_type, exc, tb):
             await log('exiting context')

New in version 3.5.


File: python.info,  Node: Execution model,  Next: The import system,  Prev: Data model,  Up: The Python Language Reference

4.4 Execution model
===================

* Menu:

* Structure of a program::
* Naming and binding::
* Exceptions: Exceptions<2>.


File: python.info,  Node: Structure of a program,  Next: Naming and binding,  Up: Execution model

4.4.1 Structure of a program
----------------------------

A Python program is constructed from code blocks.  A `block' is a piece
of Python program text that is executed as a unit.  The following are
blocks: a module, a function body, and a class definition.  Each command
typed interactively is a block.  A script file (a file given as standard
input to the interpreter or specified as a command line argument to the
interpreter) is a code block.  A script command (a command specified on
the interpreter command line with the *note -c: 1340. option) is a code
block.  A module run as a top level script (as module ‘__main__’) from
the command line using a *note -m: 443. argument is also a code block.
The string argument passed to the built-in functions *note eval(): c61.
and *note exec(): d0c. is a code block.

A code block is executed in an `execution frame'.  A frame contains some
administrative information (used for debugging) and determines where and
how execution continues after the code block’s execution has completed.


File: python.info,  Node: Naming and binding,  Next: Exceptions<2>,  Prev: Structure of a program,  Up: Execution model

4.4.2 Naming and binding
------------------------

* Menu:

* Binding of names::
* Resolution of names::
* Builtins and restricted execution::
* Interaction with dynamic features::


File: python.info,  Node: Binding of names,  Next: Resolution of names,  Up: Naming and binding

4.4.2.1 Binding of names
........................

`Names' refer to objects.  Names are introduced by name binding
operations.

The following constructs bind names: formal parameters to functions,
*note import: ce7. statements, class and function definitions (these
bind the class or function name in the defining block), and targets that
are identifiers if occurring in an assignment, *note for: cfa. loop
header, or after ‘as’ in a *note with: 7da. statement or *note except:
c10. clause.  The ‘import’ statement of the form ‘from ... import *’
binds all names defined in the imported module, except those beginning
with an underscore.  This form may only be used at the module level.

A target occurring in a *note del: 13a2. statement is also considered
bound for this purpose (though the actual semantics are to unbind the
name).

Each assignment or import statement occurs within a block defined by a
class or function definition or at the module level (the top-level code
block).

If a name is bound in a block, it is a local variable of that block,
unless declared as *note nonlocal: d07. or *note global: 1378.  If a
name is bound at the module level, it is a global variable.  (The
variables of the module code block are local and global.)  If a variable
is used in a code block but not defined there, it is a `free variable'.

Each occurrence of a name in the program text refers to the `binding' of
that name established by the following name resolution rules.


File: python.info,  Node: Resolution of names,  Next: Builtins and restricted execution,  Prev: Binding of names,  Up: Naming and binding

4.4.2.2 Resolution of names
...........................

A `scope' defines the visibility of a name within a block.  If a local
variable is defined in a block, its scope includes that block.  If the
definition occurs in a function block, the scope extends to any blocks
contained within the defining one, unless a contained block introduces a
different binding for the name.

When a name is used in a code block, it is resolved using the nearest
enclosing scope.  The set of all such scopes visible to a code block is
called the block’s `environment'.

When a name is not found at all, a *note NameError: e40. exception is
raised.  If the current scope is a function scope, and the name refers
to a local variable that has not yet been bound to a value at the point
where the name is used, an *note UnboundLocalError: f37. exception is
raised.  *note UnboundLocalError: f37. is a subclass of *note NameError:
e40.

If a name binding operation occurs anywhere within a code block, all
uses of the name within the block are treated as references to the
current block.  This can lead to errors when a name is used within a
block before it is bound.  This rule is subtle.  Python lacks
declarations and allows name binding operations to occur anywhere within
a code block.  The local variables of a code block can be determined by
scanning the entire text of the block for name binding operations.

If the *note global: 1378. statement occurs within a block, all uses of
the names specified in the statement refer to the bindings of those
names in the top-level namespace.  Names are resolved in the top-level
namespace by searching the global namespace, i.e.  the namespace of the
module containing the code block, and the builtins namespace, the
namespace of the module *note builtins: 12.  The global namespace is
searched first.  If the names are not found there, the builtins
namespace is searched.  The ‘global’ statement must precede all uses of
the listed names.

The *note global: 1378. statement has the same scope as a name binding
operation in the same block.  If the nearest enclosing scope for a free
variable contains a global statement, the free variable is treated as a
global.

The *note nonlocal: d07. statement causes corresponding names to refer
to previously bound variables in the nearest enclosing function scope.
*note SyntaxError: 55a. is raised at compile time if the given name does
not exist in any enclosing function scope.

The namespace for a module is automatically created the first time a
module is imported.  The main module for a script is always called *note
__main__: 1.

Class definition blocks and arguments to *note exec(): d0c. and *note
eval(): c61. are special in the context of name resolution.  A class
definition is an executable statement that may use and define names.
These references follow the normal rules for name resolution with an
exception that unbound local variables are looked up in the global
namespace.  The namespace of the class definition becomes the attribute
dictionary of the class.  The scope of names defined in a class block is
limited to the class block; it does not extend to the code blocks of
methods – this includes comprehensions and generator expressions since
they are implemented using a function scope.  This means that the
following will fail:

     class A:
         a = 42
         b = list(a + i for i in range(10))


File: python.info,  Node: Builtins and restricted execution,  Next: Interaction with dynamic features,  Prev: Resolution of names,  Up: Naming and binding

4.4.2.3 Builtins and restricted execution
.........................................

`CPython implementation detail:' Users should not touch ‘__builtins__’;
it is strictly an implementation detail.  Users wanting to override
values in the builtins namespace should *note import: ce7. the *note
builtins: 12. module and modify its attributes appropriately.

The builtins namespace associated with the execution of a code block is
actually found by looking up the name ‘__builtins__’ in its global
namespace; this should be a dictionary or a module (in the latter case
the module’s dictionary is used).  By default, when in the *note
__main__: 1. module, ‘__builtins__’ is the built-in module *note
builtins: 12.; when in any other module, ‘__builtins__’ is an alias for
the dictionary of the *note builtins: 12. module itself.


File: python.info,  Node: Interaction with dynamic features,  Prev: Builtins and restricted execution,  Up: Naming and binding

4.4.2.4 Interaction with dynamic features
.........................................

Name resolution of free variables occurs at runtime, not at compile
time.  This means that the following code will print 42:

     i = 10
     def f():
         print(i)
     i = 42
     f()

The *note eval(): c61. and *note exec(): d0c. functions do not have
access to the full environment for resolving names.  Names may be
resolved in the local and global namespaces of the caller.  Free
variables are not resolved in the nearest enclosing namespace, but in
the global namespace.  (1) The *note exec(): d0c. and *note eval(): c61.
functions have optional arguments to override the global and local
namespace.  If only one namespace is specified, it is used for both.

   ---------- Footnotes ----------

   (1) (1) This limitation occurs because the code that is executed by
these operations is not available at the time the module is compiled.


File: python.info,  Node: Exceptions<2>,  Prev: Naming and binding,  Up: Execution model

4.4.3 Exceptions
----------------

Exceptions are a means of breaking out of the normal flow of control of
a code block in order to handle errors or other exceptional conditions.
An exception is `raised' at the point where the error is detected; it
may be `handled' by the surrounding code block or by any code block that
directly or indirectly invoked the code block where the error occurred.

The Python interpreter raises an exception when it detects a run-time
error (such as division by zero).  A Python program can also explicitly
raise an exception with the *note raise: d0a. statement.  Exception
handlers are specified with the *note try: e37. … *note except: c10.
statement.  The *note finally: 2bc. clause of such a statement can be
used to specify cleanup code which does not handle the exception, but is
executed whether an exception occurred or not in the preceding code.

Python uses the “termination” model of error handling: an exception
handler can find out what happened and continue execution at an outer
level, but it cannot repair the cause of the error and retry the failing
operation (except by re-entering the offending piece of code from the
top).

When an exception is not handled at all, the interpreter terminates
execution of the program, or returns to its interactive main loop.  In
either case, it prints a stack traceback, except when the exception is
*note SystemExit: 6f3.

Exceptions are identified by class instances.  The *note except: c10.
clause is selected depending on the class of the instance: it must
reference the class of the instance or a base class thereof.  The
instance can be received by the handler and can carry additional
information about the exceptional condition.

     Note: Exception messages are not part of the Python API. Their
     contents may change from one version of Python to the next without
     warning and should not be relied on by code which will run under
     multiple versions of the interpreter.

See also the description of the *note try: e37. statement in section
*note The try statement: e37. and *note raise: d0a. statement in section
*note The raise statement: d0a.


File: python.info,  Node: The import system,  Next: Expressions,  Prev: Execution model,  Up: The Python Language Reference

4.5 The import system
=====================

Python code in one *note module: 15e7. gains access to the code in
another module by the process of *note importing: 15e8. it.  The *note
import: ce7. statement is the most common way of invoking the import
machinery, but it is not the only way.  Functions such as *note
importlib.import_module(): be6. and built-in *note __import__(): 16b.
can also be used to invoke the import machinery.

The *note import: ce7. statement combines two operations; it searches
for the named module, then it binds the results of that search to a name
in the local scope.  The search operation of the ‘import’ statement is
defined as a call to the *note __import__(): 16b. function, with the
appropriate arguments.  The return value of *note __import__(): 16b. is
used to perform the name binding operation of the ‘import’ statement.
See the ‘import’ statement for the exact details of that name binding
operation.

A direct call to *note __import__(): 16b. performs only the module
search and, if found, the module creation operation.  While certain
side-effects may occur, such as the importing of parent packages, and
the updating of various caches (including *note sys.modules: 1051.),
only the *note import: ce7. statement performs a name binding operation.

When an *note import: ce7. statement is executed, the standard builtin
*note __import__(): 16b. function is called.  Other mechanisms for
invoking the import system (such as *note importlib.import_module():
be6.) may choose to bypass *note __import__(): 16b. and use their own
solutions to implement import semantics.

When a module is first imported, Python searches for the module and if
found, it creates a module object (1), initializing it.  If the named
module cannot be found, a *note ModuleNotFoundError: 4a1. is raised.
Python implements various strategies to search for the named module when
the import machinery is invoked.  These strategies can be modified and
extended by using various hooks described in the sections below.

Changed in version 3.3: The import system has been updated to fully
implement the second phase of PEP 302(2).  There is no longer any
implicit import machinery - the full import system is exposed through
*note sys.meta_path: 6dd.  In addition, native namespace package support
has been implemented (see PEP 420(3)).

* Menu:

* importlib: importlib<8>.
* Packages: Packages<2>.
* Searching::
* Loading::
* The Path Based Finder::
* Replacing the standard import system::
* Package Relative Imports::
* Special considerations for __main__::
* Open issues::
* References::

   ---------- Footnotes ----------

   (1) (1) See *note types.ModuleType: 7e2.

   (2) https://www.python.org/dev/peps/pep-0302

   (3) https://www.python.org/dev/peps/pep-0420


File: python.info,  Node: importlib<8>,  Next: Packages<2>,  Up: The import system

4.5.1 ‘importlib’
-----------------

The *note importlib: 9a. module provides a rich API for interacting with
the import system.  For example *note importlib.import_module(): be6.
provides a recommended, simpler API than built-in *note __import__():
16b. for invoking the import machinery.  Refer to the *note importlib:
9a. library documentation for additional detail.


File: python.info,  Node: Packages<2>,  Next: Searching,  Prev: importlib<8>,  Up: The import system

4.5.2 Packages
--------------

Python has only one type of module object, and all modules are of this
type, regardless of whether the module is implemented in Python, C, or
something else.  To help organize modules and provide a naming
hierarchy, Python has a concept of *note packages: 15eb.

You can think of packages as the directories on a file system and
modules as files within directories, but don’t take this analogy too
literally since packages and modules need not originate from the file
system.  For the purposes of this documentation, we’ll use this
convenient analogy of directories and files.  Like file system
directories, packages are organized hierarchically, and packages may
themselves contain subpackages, as well as regular modules.

It’s important to keep in mind that all packages are modules, but not
all modules are packages.  Or put another way, packages are just a
special kind of module.  Specifically, any module that contains a
‘__path__’ attribute is considered a package.

All modules have a name.  Subpackage names are separated from their
parent package name by a dot, akin to Python’s standard attribute access
syntax.  Thus you might have a module called *note sys: fd. and a
package called *note email: 67, which in turn has a subpackage called
*note email.mime: 71. and a module within that subpackage called
‘email.mime.text’.

* Menu:

* Regular packages::
* Namespace packages::


File: python.info,  Node: Regular packages,  Next: Namespace packages,  Up: Packages<2>

4.5.2.1 Regular packages
........................

Python defines two types of packages, *note regular packages: 15ed. and
*note namespace packages: 15ee.  Regular packages are traditional
packages as they existed in Python 3.2 and earlier.  A regular package
is typically implemented as a directory containing an ‘__init__.py’
file.  When a regular package is imported, this ‘__init__.py’ file is
implicitly executed, and the objects it defines are bound to names in
the package’s namespace.  The ‘__init__.py’ file can contain the same
Python code that any other module can contain, and Python will add some
additional attributes to the module when it is imported.

For example, the following file system layout defines a top level
‘parent’ package with three subpackages:

     parent/
         __init__.py
         one/
             __init__.py
         two/
             __init__.py
         three/
             __init__.py

Importing ‘parent.one’ will implicitly execute ‘parent/__init__.py’ and
‘parent/one/__init__.py’.  Subsequent imports of ‘parent.two’ or
‘parent.three’ will execute ‘parent/two/__init__.py’ and
‘parent/three/__init__.py’ respectively.


File: python.info,  Node: Namespace packages,  Prev: Regular packages,  Up: Packages<2>

4.5.2.2 Namespace packages
..........................

A namespace package is a composite of various *note portions: 15f0,
where each portion contributes a subpackage to the parent package.
Portions may reside in different locations on the file system.  Portions
may also be found in zip files, on the network, or anywhere else that
Python searches during import.  Namespace packages may or may not
correspond directly to objects on the file system; they may be virtual
modules that have no concrete representation.

Namespace packages do not use an ordinary list for their ‘__path__’
attribute.  They instead use a custom iterable type which will
automatically perform a new search for package portions on the next
import attempt within that package if the path of their parent package
(or *note sys.path: 260. for a top level package) changes.

With namespace packages, there is no ‘parent/__init__.py’ file.  In
fact, there may be multiple ‘parent’ directories found during import
search, where each one is provided by a different portion.  Thus
‘parent/one’ may not be physically located next to ‘parent/two’.  In
this case, Python will create a namespace package for the top-level
‘parent’ package whenever it or one of its subpackages is imported.

See also PEP 420(1) for the namespace package specification.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0420


File: python.info,  Node: Searching,  Next: Loading,  Prev: Packages<2>,  Up: The import system

4.5.3 Searching
---------------

To begin the search, Python needs the *note fully qualified: 155c. name
of the module (or package, but for the purposes of this discussion, the
difference is immaterial) being imported.  This name may come from
various arguments to the *note import: ce7. statement, or from the
parameters to the *note importlib.import_module(): be6. or *note
__import__(): 16b. functions.

This name will be used in various phases of the import search, and it
may be the dotted path to a submodule, e.g.  ‘foo.bar.baz’.  In this
case, Python first tries to import ‘foo’, then ‘foo.bar’, and finally
‘foo.bar.baz’.  If any of the intermediate imports fail, a *note
ModuleNotFoundError: 4a1. is raised.

* Menu:

* The module cache::
* Finders and loaders::
* Import hooks::
* The meta path::


File: python.info,  Node: The module cache,  Next: Finders and loaders,  Up: Searching

4.5.3.1 The module cache
........................

The first place checked during import search is *note sys.modules: 1051.
This mapping serves as a cache of all modules that have been previously
imported, including the intermediate paths.  So if ‘foo.bar.baz’ was
previously imported, *note sys.modules: 1051. will contain entries for
‘foo’, ‘foo.bar’, and ‘foo.bar.baz’.  Each key will have as its value
the corresponding module object.

During import, the module name is looked up in *note sys.modules: 1051.
and if present, the associated value is the module satisfying the
import, and the process completes.  However, if the value is ‘None’,
then a *note ModuleNotFoundError: 4a1. is raised.  If the module name is
missing, Python will continue searching for the module.

*note sys.modules: 1051. is writable.  Deleting a key may not destroy
the associated module (as other modules may hold references to it), but
it will invalidate the cache entry for the named module, causing Python
to search anew for the named module upon its next import.  The key can
also be assigned to ‘None’, forcing the next import of the module to
result in a *note ModuleNotFoundError: 4a1.

Beware though, as if you keep a reference to the module object,
invalidate its cache entry in *note sys.modules: 1051, and then
re-import the named module, the two module objects will `not' be the
same.  By contrast, *note importlib.reload(): 4a0. will reuse the `same'
module object, and simply reinitialise the module contents by rerunning
the module’s code.


File: python.info,  Node: Finders and loaders,  Next: Import hooks,  Prev: The module cache,  Up: Searching

4.5.3.2 Finders and loaders
...........................

If the named module is not found in *note sys.modules: 1051, then
Python’s import protocol is invoked to find and load the module.  This
protocol consists of two conceptual objects, *note finders: 15f5. and
*note loaders: 15f6.  A finder’s job is to determine whether it can find
the named module using whatever strategy it knows about.  Objects that
implement both of these interfaces are referred to as *note importers:
15f7. - they return themselves when they find that they can load the
requested module.

Python includes a number of default finders and importers.  The first
one knows how to locate built-in modules, and the second knows how to
locate frozen modules.  A third default finder searches an *note import
path: 15f8. for modules.  The *note import path: 15f8. is a list of
locations that may name file system paths or zip files.  It can also be
extended to search for any locatable resource, such as those identified
by URLs.

The import machinery is extensible, so new finders can be added to
extend the range and scope of module searching.

Finders do not actually load modules.  If they can find the named
module, they return a `module spec', an encapsulation of the module’s
import-related information, which the import machinery then uses when
loading the module.

The following sections describe the protocol for finders and loaders in
more detail, including how you can create and register new ones to
extend the import machinery.

Changed in version 3.4: In previous versions of Python, finders returned
*note loaders: 15f6. directly, whereas now they return module specs
which `contain' loaders.  Loaders are still used during import but have
fewer responsibilities.


File: python.info,  Node: Import hooks,  Next: The meta path,  Prev: Finders and loaders,  Up: Searching

4.5.3.3 Import hooks
....................

The import machinery is designed to be extensible; the primary mechanism
for this are the `import hooks'.  There are two types of import hooks:
`meta hooks' and `import path hooks'.

Meta hooks are called at the start of import processing, before any
other import processing has occurred, other than *note sys.modules:
1051. cache look up.  This allows meta hooks to override *note sys.path:
260. processing, frozen modules, or even built-in modules.  Meta hooks
are registered by adding new finder objects to *note sys.meta_path: 6dd,
as described below.

Import path hooks are called as part of *note sys.path: 260. (or
‘package.__path__’) processing, at the point where their associated path
item is encountered.  Import path hooks are registered by adding new
callables to *note sys.path_hooks: a3d. as described below.


File: python.info,  Node: The meta path,  Prev: Import hooks,  Up: Searching

4.5.3.4 The meta path
.....................

When the named module is not found in *note sys.modules: 1051, Python
next searches *note sys.meta_path: 6dd, which contains a list of meta
path finder objects.  These finders are queried in order to see if they
know how to handle the named module.  Meta path finders must implement a
method called *note find_spec(): 565. which takes three arguments: a
name, an import path, and (optionally) a target module.  The meta path
finder can use any strategy it wants to determine whether it can handle
the named module or not.

If the meta path finder knows how to handle the named module, it returns
a spec object.  If it cannot handle the named module, it returns ‘None’.
If *note sys.meta_path: 6dd. processing reaches the end of its list
without returning a spec, then a *note ModuleNotFoundError: 4a1. is
raised.  Any other exceptions raised are simply propagated up, aborting
the import process.

The *note find_spec(): 565. method of meta path finders is called with
two or three arguments.  The first is the fully qualified name of the
module being imported, for example ‘foo.bar.baz’.  The second argument
is the path entries to use for the module search.  For top-level
modules, the second argument is ‘None’, but for submodules or
subpackages, the second argument is the value of the parent package’s
‘__path__’ attribute.  If the appropriate ‘__path__’ attribute cannot be
accessed, a *note ModuleNotFoundError: 4a1. is raised.  The third
argument is an existing module object that will be the target of loading
later.  The import system passes in a target module only during reload.

The meta path may be traversed multiple times for a single import
request.  For example, assuming none of the modules involved has already
been cached, importing ‘foo.bar.baz’ will first perform a top level
import, calling ‘mpf.find_spec("foo", None, None)’ on each meta path
finder (‘mpf’).  After ‘foo’ has been imported, ‘foo.bar’ will be
imported by traversing the meta path a second time, calling
‘mpf.find_spec("foo.bar", foo.__path__, None)’.  Once ‘foo.bar’ has been
imported, the final traversal will call ‘mpf.find_spec("foo.bar.baz",
foo.bar.__path__, None)’.

Some meta path finders only support top level imports.  These importers
will always return ‘None’ when anything other than ‘None’ is passed as
the second argument.

Python’s default *note sys.meta_path: 6dd. has three meta path finders,
one that knows how to import built-in modules, one that knows how to
import frozen modules, and one that knows how to import modules from an
*note import path: 15f8. (i.e.  the *note path based finder: 15fb.).

Changed in version 3.4: The *note find_spec(): 565. method of meta path
finders replaced *note find_module(): 564, which is now deprecated.
While it will continue to work without change, the import machinery will
try it only if the finder does not implement ‘find_spec()’.


File: python.info,  Node: Loading,  Next: The Path Based Finder,  Prev: Searching,  Up: The import system

4.5.4 Loading
-------------

If and when a module spec is found, the import machinery will use it
(and the loader it contains) when loading the module.  Here is an
approximation of what happens during the loading portion of import:

     module = None
     if spec.loader is not None and hasattr(spec.loader, 'create_module'):
         # It is assumed 'exec_module' will also be defined on the loader.
         module = spec.loader.create_module(spec)
     if module is None:
         module = ModuleType(spec.name)
     # The import-related module attributes get set here:
     _init_module_attrs(spec, module)

     if spec.loader is None:
         # unsupported
         raise ImportError
     if spec.origin is None and spec.submodule_search_locations is not None:
         # namespace package
         sys.modules[spec.name] = module
     elif not hasattr(spec.loader, 'exec_module'):
         module = spec.loader.load_module(spec.name)
         # Set __loader__ and __package__ if missing.
     else:
         sys.modules[spec.name] = module
         try:
             spec.loader.exec_module(module)
         except BaseException:
             try:
                 del sys.modules[spec.name]
             except KeyError:
                 pass
             raise
     return sys.modules[spec.name]

Note the following details:

        * If there is an existing module object with the given name in
          *note sys.modules: 1051, import will have already returned it.

        * The module will exist in *note sys.modules: 1051. before the
          loader executes the module code.  This is crucial because the
          module code may (directly or indirectly) import itself; adding
          it to *note sys.modules: 1051. beforehand prevents unbounded
          recursion in the worst case and multiple loading in the best.

        * If loading fails, the failing module – and only the failing
          module – gets removed from *note sys.modules: 1051.  Any
          module already in the *note sys.modules: 1051. cache, and any
          module that was successfully loaded as a side-effect, must
          remain in the cache.  This contrasts with reloading where even
          the failing module is left in *note sys.modules: 1051.

        * After the module is created but before execution, the import
          machinery sets the import-related module attributes
          (“_init_module_attrs” in the pseudo-code example above), as
          summarized in a *note later section: 15fd.

        * Module execution is the key moment of loading in which the
          module’s namespace gets populated.  Execution is entirely
          delegated to the loader, which gets to decide what gets
          populated and how.

        * The module created during loading and passed to exec_module()
          may not be the one returned at the end of import (1).

Changed in version 3.4: The import system has taken over the boilerplate
responsibilities of loaders.  These were previously performed by the
*note importlib.abc.Loader.load_module(): 6da. method.

* Menu:

* Loaders::
* Submodules::
* Module spec::
* Import-related module attributes::
* module.__path__: module __path__.
* Module reprs::
* Cached bytecode invalidation::

   ---------- Footnotes ----------

   (1) (2) The importlib implementation avoids using the return value
directly.  Instead, it gets the module object by looking the module name
up in *note sys.modules: 1051.  The indirect effect of this is that an
imported module may replace itself in *note sys.modules: 1051.  This is
implementation-specific behavior that is not guaranteed to work in other
Python implementations.


File: python.info,  Node: Loaders,  Next: Submodules,  Up: Loading

4.5.4.1 Loaders
...............

Module loaders provide the critical function of loading: module
execution.  The import machinery calls the *note
importlib.abc.Loader.exec_module(): 6db. method with a single argument,
the module object to execute.  Any value returned from *note
exec_module(): 6db. is ignored.

Loaders must satisfy the following requirements:

        * If the module is a Python module (as opposed to a built-in
          module or a dynamically loaded extension), the loader should
          execute the module’s code in the module’s global name space
          (‘module.__dict__’).

        * If the loader cannot execute the module, it should raise an
          *note ImportError: 16c, although any other exception raised
          during *note exec_module(): 6db. will be propagated.

In many cases, the finder and loader can be the same object; in such
cases the *note find_spec(): 565. method would just return a spec with
the loader set to ‘self’.

Module loaders may opt in to creating the module object during loading
by implementing a *note create_module(): 64e. method.  It takes one
argument, the module spec, and returns the new module object to use
during loading.  ‘create_module()’ does not need to set any attributes
on the module object.  If the method returns ‘None’, the import
machinery will create the new module itself.

New in version 3.4: The *note create_module(): 64e. method of loaders.

Changed in version 3.4: The *note load_module(): 6da. method was
replaced by *note exec_module(): 6db. and the import machinery assumed
all the boilerplate responsibilities of loading.

For compatibility with existing loaders, the import machinery will use
the ‘load_module()’ method of loaders if it exists and the loader does
not also implement ‘exec_module()’.  However, ‘load_module()’ has been
deprecated and loaders should implement ‘exec_module()’ instead.

The ‘load_module()’ method must implement all the boilerplate loading
functionality described above in addition to executing the module.  All
the same constraints apply, with some additional clarification:

        * If there is an existing module object with the given name in
          *note sys.modules: 1051, the loader must use that existing
          module.  (Otherwise, *note importlib.reload(): 4a0. will not
          work correctly.)  If the named module does not exist in *note
          sys.modules: 1051, the loader must create a new module object
          and add it to *note sys.modules: 1051.

        * The module `must' exist in *note sys.modules: 1051. before the
          loader executes the module code, to prevent unbounded
          recursion or multiple loading.

        * If loading fails, the loader must remove any modules it has
          inserted into *note sys.modules: 1051, but it must remove
          `only' the failing module(s), and only if the loader itself
          has loaded the module(s) explicitly.

Changed in version 3.5: A *note DeprecationWarning: 15a. is raised when
‘exec_module()’ is defined but ‘create_module()’ is not.

Changed in version 3.6: An *note ImportError: 16c. is raised when
‘exec_module()’ is defined but ‘create_module()’ is not.


File: python.info,  Node: Submodules,  Next: Module spec,  Prev: Loaders,  Up: Loading

4.5.4.2 Submodules
..................

When a submodule is loaded using any mechanism (e.g.  ‘importlib’ APIs,
the ‘import’ or ‘import-from’ statements, or built-in ‘__import__()’) a
binding is placed in the parent module’s namespace to the submodule
object.  For example, if package ‘spam’ has a submodule ‘foo’, after
importing ‘spam.foo’, ‘spam’ will have an attribute ‘foo’ which is bound
to the submodule.  Let’s say you have the following directory structure:

     spam/
         __init__.py
         foo.py
         bar.py

and ‘spam/__init__.py’ has the following lines in it:

     from .foo import Foo
     from .bar import Bar

then executing the following puts a name binding to ‘foo’ and ‘bar’ in
the ‘spam’ module:

     >>> import spam
     >>> spam.foo
     <module 'spam.foo' from '/tmp/imports/spam/foo.py'>
     >>> spam.bar
     <module 'spam.bar' from '/tmp/imports/spam/bar.py'>

Given Python’s familiar name binding rules this might seem surprising,
but it’s actually a fundamental feature of the import system.  The
invariant holding is that if you have ‘sys.modules['spam']’ and
‘sys.modules['spam.foo']’ (as you would after the above import), the
latter must appear as the ‘foo’ attribute of the former.


File: python.info,  Node: Module spec,  Next: Import-related module attributes,  Prev: Submodules,  Up: Loading

4.5.4.3 Module spec
...................

The import machinery uses a variety of information about each module
during import, especially before loading.  Most of the information is
common to all modules.  The purpose of a module’s spec is to encapsulate
this import-related information on a per-module basis.

Using a spec during import allows state to be transferred between import
system components, e.g.  between the finder that creates the module spec
and the loader that executes it.  Most importantly, it allows the import
machinery to perform the boilerplate operations of loading, whereas
without a module spec the loader had that responsibility.

The module’s spec is exposed as the ‘__spec__’ attribute on a module
object.  See *note ModuleSpec: 1601. for details on the contents of the
module spec.

New in version 3.4.


File: python.info,  Node: Import-related module attributes,  Next: module __path__,  Prev: Module spec,  Up: Loading

4.5.4.4 Import-related module attributes
........................................

The import machinery fills in these attributes on each module object
during loading, based on the module’s spec, before the loader executes
the module.

 -- Attribute: __name__

     The ‘__name__’ attribute must be set to the fully-qualified name of
     the module.  This name is used to uniquely identify the module in
     the import system.

 -- Attribute: __loader__

     The ‘__loader__’ attribute must be set to the loader object that
     the import machinery used when loading the module.  This is mostly
     for introspection, but can be used for additional loader-specific
     functionality, for example getting data associated with a loader.

 -- Attribute: __package__

     The module’s ‘__package__’ attribute must be set.  Its value must
     be a string, but it can be the same value as its ‘__name__’.  When
     the module is a package, its ‘__package__’ value should be set to
     its ‘__name__’.  When the module is not a package, ‘__package__’
     should be set to the empty string for top-level modules, or for
     submodules, to the parent package’s name.  See PEP 366(1) for
     further details.

     This attribute is used instead of ‘__name__’ to calculate explicit
     relative imports for main modules, as defined in PEP 366(2).  It is
     expected to have the same value as ‘__spec__.parent’.

     Changed in version 3.6: The value of ‘__package__’ is expected to
     be the same as ‘__spec__.parent’.

 -- Attribute: __spec__

     The ‘__spec__’ attribute must be set to the module spec that was
     used when importing the module.  Setting ‘__spec__’ appropriately
     applies equally to *note modules initialized during interpreter
     startup: 1604.  The one exception is ‘__main__’, where ‘__spec__’
     is *note set to None in some cases: 1605.

     When ‘__package__’ is not defined, ‘__spec__.parent’ is used as a
     fallback.

     New in version 3.4.

     Changed in version 3.6: ‘__spec__.parent’ is used as a fallback
     when ‘__package__’ is not defined.

 -- Attribute: __path__

     If the module is a package (either regular or namespace), the
     module object’s ‘__path__’ attribute must be set.  The value must
     be iterable, but may be empty if ‘__path__’ has no further
     significance.  If ‘__path__’ is not empty, it must produce strings
     when iterated over.  More details on the semantics of ‘__path__’
     are given *note below: 1606.

     Non-package modules should not have a ‘__path__’ attribute.

 -- Attribute: __file__

 -- Attribute: __cached__

     ‘__file__’ is optional.  If set, this attribute’s value must be a
     string.  The import system may opt to leave ‘__file__’ unset if it
     has no semantic meaning (e.g.  a module loaded from a database).

     If ‘__file__’ is set, it may also be appropriate to set the
     ‘__cached__’ attribute which is the path to any compiled version of
     the code (e.g.  byte-compiled file).  The file does not need to
     exist to set this attribute; the path can simply point to where the
     compiled file would exist (see PEP 3147(3)).

     It is also appropriate to set ‘__cached__’ when ‘__file__’ is not
     set.  However, that scenario is quite atypical.  Ultimately, the
     loader is what makes use of ‘__file__’ and/or ‘__cached__’.  So if
     a loader can load from a cached module but otherwise does not load
     from a file, that atypical scenario may be appropriate.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0366

   (2) https://www.python.org/dev/peps/pep-0366

   (3) https://www.python.org/dev/peps/pep-3147


File: python.info,  Node: module __path__,  Next: Module reprs,  Prev: Import-related module attributes,  Up: Loading

4.5.4.5 module.__path__
.......................

By definition, if a module has a ‘__path__’ attribute, it is a package.

A package’s ‘__path__’ attribute is used during imports of its
subpackages.  Within the import machinery, it functions much the same as
*note sys.path: 260, i.e.  providing a list of locations to search for
modules during import.  However, ‘__path__’ is typically much more
constrained than *note sys.path: 260.

‘__path__’ must be an iterable of strings, but it may be empty.  The
same rules used for *note sys.path: 260. also apply to a package’s
‘__path__’, and *note sys.path_hooks: a3d. (described below) are
consulted when traversing a package’s ‘__path__’.

A package’s ‘__init__.py’ file may set or alter the package’s ‘__path__’
attribute, and this was typically the way namespace packages were
implemented prior to PEP 420(1).  With the adoption of PEP 420(2),
namespace packages no longer need to supply ‘__init__.py’ files
containing only ‘__path__’ manipulation code; the import machinery
automatically sets ‘__path__’ correctly for the namespace package.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0420

   (2) https://www.python.org/dev/peps/pep-0420


File: python.info,  Node: Module reprs,  Next: Cached bytecode invalidation,  Prev: module __path__,  Up: Loading

4.5.4.6 Module reprs
....................

By default, all modules have a usable repr, however depending on the
attributes set above, and in the module’s spec, you can more explicitly
control the repr of module objects.

If the module has a spec (‘__spec__’), the import machinery will try to
generate a repr from it.  If that fails or there is no spec, the import
system will craft a default repr using whatever information is available
on the module.  It will try to use the ‘module.__name__’,
‘module.__file__’, and ‘module.__loader__’ as input into the repr, with
defaults for whatever information is missing.

Here are the exact rules used:

        * If the module has a ‘__spec__’ attribute, the information in
          the spec is used to generate the repr.  The “name”, “loader”,
          “origin”, and “has_location” attributes are consulted.

        * If the module has a ‘__file__’ attribute, this is used as part
          of the module’s repr.

        * If the module has no ‘__file__’ but does have a ‘__loader__’
          that is not ‘None’, then the loader’s repr is used as part of
          the module’s repr.

        * Otherwise, just use the module’s ‘__name__’ in the repr.

Changed in version 3.4: Use of *note loader.module_repr(): a25. has been
deprecated and the module spec is now used by the import machinery to
generate a module repr.

For backward compatibility with Python 3.3, the module repr will be
generated by calling the loader’s *note module_repr(): a25. method, if
defined, before trying either approach described above.  However, the
method is deprecated.


File: python.info,  Node: Cached bytecode invalidation,  Prev: Module reprs,  Up: Loading

4.5.4.7 Cached bytecode invalidation
....................................

Before Python loads cached bytecode from a ‘.pyc’ file, it checks
whether the cache is up-to-date with the source ‘.py’ file.  By default,
Python does this by storing the source’s last-modified timestamp and
size in the cache file when writing it.  At runtime, the import system
then validates the cache file by checking the stored metadata in the
cache file against the source’s metadata.

Python also supports “hash-based” cache files, which store a hash of the
source file’s contents rather than its metadata.  There are two variants
of hash-based ‘.pyc’ files: checked and unchecked.  For checked
hash-based ‘.pyc’ files, Python validates the cache file by hashing the
source file and comparing the resulting hash with the hash in the cache
file.  If a checked hash-based cache file is found to be invalid, Python
regenerates it and writes a new checked hash-based cache file.  For
unchecked hash-based ‘.pyc’ files, Python simply assumes the cache file
is valid if it exists.  Hash-based ‘.pyc’ files validation behavior may
be overridden with the *note –check-hash-based-pycs: 1475. flag.

Changed in version 3.7: Added hash-based ‘.pyc’ files.  Previously,
Python only supported timestamp-based invalidation of bytecode caches.


File: python.info,  Node: The Path Based Finder,  Next: Replacing the standard import system,  Prev: Loading,  Up: The import system

4.5.5 The Path Based Finder
---------------------------

As mentioned previously, Python comes with several default meta path
finders.  One of these, called the *note path based finder: 15fb. (*note
PathFinder: a3c.), searches an *note import path: 15f8, which contains a
list of *note path entries: 160b.  Each path entry names a location to
search for modules.

The path based finder itself doesn’t know how to import anything.
Instead, it traverses the individual path entries, associating each of
them with a path entry finder that knows how to handle that particular
kind of path.

The default set of path entry finders implement all the semantics for
finding modules on the file system, handling special file types such as
Python source code (‘.py’ files), Python byte code (‘.pyc’ files) and
shared libraries (e.g.  ‘.so’ files).  When supported by the *note
zipimport: 14c. module in the standard library, the default path entry
finders also handle loading all of these file types (other than shared
libraries) from zipfiles.

Path entries need not be limited to file system locations.  They can
refer to URLs, database queries, or any other location that can be
specified as a string.

The path based finder provides additional hooks and protocols so that
you can extend and customize the types of searchable path entries.  For
example, if you wanted to support path entries as network URLs, you
could write a hook that implements HTTP semantics to find modules on the
web.  This hook (a callable) would return a *note path entry finder:
a92. supporting the protocol described below, which was then used to get
a loader for the module from the web.

A word of warning: this section and the previous both use the term
`finder', distinguishing between them by using the terms *note meta path
finder: a91. and *note path entry finder: a92.  These two types of
finders are very similar, support similar protocols, and function in
similar ways during the import process, but it’s important to keep in
mind that they are subtly different.  In particular, meta path finders
operate at the beginning of the import process, as keyed off the *note
sys.meta_path: 6dd. traversal.

By contrast, path entry finders are in a sense an implementation detail
of the path based finder, and in fact, if the path based finder were to
be removed from *note sys.meta_path: 6dd, none of the path entry finder
semantics would be invoked.

* Menu:

* Path entry finders::
* Path entry finder protocol::


File: python.info,  Node: Path entry finders,  Next: Path entry finder protocol,  Up: The Path Based Finder

4.5.5.1 Path entry finders
..........................

The *note path based finder: 15fb. is responsible for finding and
loading Python modules and packages whose location is specified with a
string *note path entry: 160b.  Most path entries name locations in the
file system, but they need not be limited to this.

As a meta path finder, the *note path based finder: 15fb. implements the
*note find_spec(): 565. protocol previously described, however it
exposes additional hooks that can be used to customize how modules are
found and loaded from the *note import path: 15f8.

Three variables are used by the *note path based finder: 15fb, *note
sys.path: 260, *note sys.path_hooks: a3d. and *note
sys.path_importer_cache: 598.  The ‘__path__’ attributes on package
objects are also used.  These provide additional ways that the import
machinery can be customized.

*note sys.path: 260. contains a list of strings providing search
locations for modules and packages.  It is initialized from the
‘PYTHONPATH’ environment variable and various other installation- and
implementation-specific defaults.  Entries in *note sys.path: 260. can
name directories on the file system, zip files, and potentially other
“locations” (see the *note site: eb. module) that should be searched for
modules, such as URLs, or database queries.  Only strings and bytes
should be present on *note sys.path: 260.; all other data types are
ignored.  The encoding of bytes entries is determined by the individual
*note path entry finders: a92.

The *note path based finder: 15fb. is a *note meta path finder: a91, so
the import machinery begins the *note import path: 15f8. search by
calling the path based finder’s *note find_spec(): a1e. method as
described previously.  When the ‘path’ argument to *note find_spec():
a1e. is given, it will be a list of string paths to traverse - typically
a package’s ‘__path__’ attribute for an import within that package.  If
the ‘path’ argument is ‘None’, this indicates a top level import and
*note sys.path: 260. is used.

The path based finder iterates over every entry in the search path, and
for each of these, looks for an appropriate *note path entry finder:
a92. (*note PathEntryFinder: a94.) for the path entry.  Because this can
be an expensive operation (e.g.  there may be ‘stat()’ call overheads
for this search), the path based finder maintains a cache mapping path
entries to path entry finders.  This cache is maintained in *note
sys.path_importer_cache: 598. (despite the name, this cache actually
stores finder objects rather than being limited to *note importer: 15f7.
objects).  In this way, the expensive search for a particular *note path
entry: 160b. location’s *note path entry finder: a92. need only be done
once.  User code is free to remove cache entries from *note
sys.path_importer_cache: 598. forcing the path based finder to perform
the path entry search again (1).

If the path entry is not present in the cache, the path based finder
iterates over every callable in *note sys.path_hooks: a3d.  Each of the
*note path entry hooks: 160d. in this list is called with a single
argument, the path entry to be searched.  This callable may either
return a *note path entry finder: a92. that can handle the path entry,
or it may raise *note ImportError: 16c.  An *note ImportError: 16c. is
used by the path based finder to signal that the hook cannot find a
*note path entry finder: a92. for that *note path entry: 160b.  The
exception is ignored and *note import path: 15f8. iteration continues.
The hook should expect either a string or bytes object; the encoding of
bytes objects is up to the hook (e.g.  it may be a file system encoding,
UTF-8, or something else), and if the hook cannot decode the argument,
it should raise *note ImportError: 16c.

If *note sys.path_hooks: a3d. iteration ends with no *note path entry
finder: a92. being returned, then the path based finder’s *note
find_spec(): a1e. method will store ‘None’ in *note
sys.path_importer_cache: 598. (to indicate that there is no finder for
this path entry) and return ‘None’, indicating that this *note meta path
finder: a91. could not find the module.

If a *note path entry finder: a92. `is' returned by one of the *note
path entry hook: 160d. callables on *note sys.path_hooks: a3d, then the
following protocol is used to ask the finder for a module spec, which is
then used when loading the module.

The current working directory – denoted by an empty string – is handled
slightly differently from other entries on *note sys.path: 260.  First,
if the current working directory is found to not exist, no value is
stored in *note sys.path_importer_cache: 598.  Second, the value for the
current working directory is looked up fresh for each module lookup.
Third, the path used for *note sys.path_importer_cache: 598. and
returned by *note importlib.machinery.PathFinder.find_spec(): a1e. will
be the actual current working directory and not the empty string.

   ---------- Footnotes ----------

   (1) (3) In legacy code, it is possible to find instances of *note
imp.NullImporter: a9b. in the *note sys.path_importer_cache: 598.  It is
recommended that code be changed to use ‘None’ instead.  See *note
Porting Python code: be5. for more details.


File: python.info,  Node: Path entry finder protocol,  Prev: Path entry finders,  Up: The Path Based Finder

4.5.5.2 Path entry finder protocol
..................................

In order to support imports of modules and initialized packages and also
to contribute portions to namespace packages, path entry finders must
implement the *note find_spec(): 567. method.

*note find_spec(): 567. takes two arguments: the fully qualified name of
the module being imported, and the (optional) target module.
‘find_spec()’ returns a fully populated spec for the module.  This spec
will always have “loader” set (with one exception).

To indicate to the import machinery that the spec represents a namespace
*note portion: 15f0, the path entry finder sets
“submodule_search_locations” to a list containing the portion.

Changed in version 3.4: *note find_spec(): 567. replaced *note
find_loader(): 566. and *note find_module(): a1f, both of which are now
deprecated, but will be used if ‘find_spec()’ is not defined.

Older path entry finders may implement one of these two deprecated
methods instead of ‘find_spec()’.  The methods are still respected for
the sake of backward compatibility.  However, if ‘find_spec()’ is
implemented on the path entry finder, the legacy methods are ignored.

*note find_loader(): 566. takes one argument, the fully qualified name
of the module being imported.  ‘find_loader()’ returns a 2-tuple where
the first item is the loader and the second item is a namespace *note
portion: 15f0.

For backwards compatibility with other implementations of the import
protocol, many path entry finders also support the same, traditional
‘find_module()’ method that meta path finders support.  However path
entry finder ‘find_module()’ methods are never called with a ‘path’
argument (they are expected to record the appropriate path information
from the initial call to the path hook).

The ‘find_module()’ method on path entry finders is deprecated, as it
does not allow the path entry finder to contribute portions to namespace
packages.  If both ‘find_loader()’ and ‘find_module()’ exist on a path
entry finder, the import system will always call ‘find_loader()’ in
preference to ‘find_module()’.


File: python.info,  Node: Replacing the standard import system,  Next: Package Relative Imports,  Prev: The Path Based Finder,  Up: The import system

4.5.6 Replacing the standard import system
------------------------------------------

The most reliable mechanism for replacing the entire import system is to
delete the default contents of *note sys.meta_path: 6dd, replacing them
entirely with a custom meta path hook.

If it is acceptable to only alter the behaviour of import statements
without affecting other APIs that access the import system, then
replacing the builtin *note __import__(): 16b. function may be
sufficient.  This technique may also be employed at the module level to
only alter the behaviour of import statements within that module.

To selectively prevent the import of some modules from a hook early on
the meta path (rather than disabling the standard import system
entirely), it is sufficient to raise *note ModuleNotFoundError: 4a1.
directly from *note find_spec(): 565. instead of returning ‘None’.  The
latter indicates that the meta path search should continue, while
raising an exception terminates it immediately.


File: python.info,  Node: Package Relative Imports,  Next: Special considerations for __main__,  Prev: Replacing the standard import system,  Up: The import system

4.5.7 Package Relative Imports
------------------------------

Relative imports use leading dots.  A single leading dot indicates a
relative import, starting with the current package.  Two or more leading
dots indicate a relative import to the parent(s) of the current package,
one level per dot after the first.  For example, given the following
package layout:

     package/
         __init__.py
         subpackage1/
             __init__.py
             moduleX.py
             moduleY.py
         subpackage2/
             __init__.py
             moduleZ.py
         moduleA.py

In either ‘subpackage1/moduleX.py’ or ‘subpackage1/__init__.py’, the
following are valid relative imports:

     from .moduleY import spam
     from .moduleY import spam as ham
     from . import moduleY
     from ..subpackage1 import moduleY
     from ..subpackage2.moduleZ import eggs
     from ..moduleA import foo

Absolute imports may use either the ‘import <>’ or ‘from <> import <>’
syntax, but relative imports may only use the second form; the reason
for this is that:

     import XXX.YYY.ZZZ

should expose ‘XXX.YYY.ZZZ’ as a usable expression, but .moduleY is not
a valid expression.


File: python.info,  Node: Special considerations for __main__,  Next: Open issues,  Prev: Package Relative Imports,  Up: The import system

4.5.8 Special considerations for __main__
-----------------------------------------

The *note __main__: 1. module is a special case relative to Python’s
import system.  As noted *note elsewhere: 1604, the ‘__main__’ module is
directly initialized at interpreter startup, much like *note sys: fd.
and *note builtins: 12.  However, unlike those two, it doesn’t strictly
qualify as a built-in module.  This is because the manner in which
‘__main__’ is initialized depends on the flags and other options with
which the interpreter is invoked.

* Menu:

* __main__.__spec__: __main__ __spec__.


File: python.info,  Node: __main__ __spec__,  Up: Special considerations for __main__

4.5.8.1 __main__.__spec__
.........................

Depending on how *note __main__: 1. is initialized, ‘__main__.__spec__’
gets set appropriately or to ‘None’.

When Python is started with the *note -m: 443. option, ‘__spec__’ is set
to the module spec of the corresponding module or package.  ‘__spec__’
is also populated when the ‘__main__’ module is loaded as part of
executing a directory, zipfile or other *note sys.path: 260. entry.

In *note the remaining cases: 146e. ‘__main__.__spec__’ is set to
‘None’, as the code used to populate the *note __main__: 1. does not
correspond directly with an importable module:

   - interactive prompt

   - *note -c: 1340. option

   - running from stdin

   - running directly from a source or bytecode file

Note that ‘__main__.__spec__’ is always ‘None’ in the last case, `even
if' the file could technically be imported directly as a module instead.
Use the *note -m: 443. switch if valid module metadata is desired in
*note __main__: 1.

Note also that even when ‘__main__’ corresponds with an importable
module and ‘__main__.__spec__’ is set accordingly, they’re still
considered `distinct' modules.  This is due to the fact that blocks
guarded by ‘if __name__ == "__main__":’ checks only execute when the
module is used to populate the ‘__main__’ namespace, and not during
normal import.


File: python.info,  Node: Open issues,  Next: References,  Prev: Special considerations for __main__,  Up: The import system

4.5.9 Open issues
-----------------

XXX It would be really nice to have a diagram.

XXX * (import_machinery.rst) how about a section devoted just to the
attributes of modules and packages, perhaps expanding upon or
supplanting the related entries in the data model reference page?

XXX runpy, pkgutil, et al in the library manual should all get “See
Also” links at the top pointing to the new import system section.

XXX Add more explanation regarding the different ways in which
‘__main__’ is initialized?

XXX Add more info on ‘__main__’ quirks/pitfalls (i.e.  copy from PEP
395(1)).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0395


File: python.info,  Node: References,  Prev: Open issues,  Up: The import system

4.5.10 References
-----------------

The import machinery has evolved considerably since Python’s early days.
The original specification for packages(1) is still available to read,
although some details have changed since the writing of that document.

The original specification for *note sys.meta_path: 6dd. was PEP 302(2),
with subsequent extension in PEP 420(3).

PEP 420(4) introduced *note namespace packages: 15ee. for Python 3.3.
PEP 420(5) also introduced the ‘find_loader()’ protocol as an
alternative to ‘find_module()’.

PEP 366(6) describes the addition of the ‘__package__’ attribute for
explicit relative imports in main modules.

PEP 328(7) introduced absolute and explicit relative imports and
initially proposed ‘__name__’ for semantics PEP 366(8) would eventually
specify for ‘__package__’.

PEP 338(9) defines executing modules as scripts.

PEP 451(10) adds the encapsulation of per-module import state in spec
objects.  It also off-loads most of the boilerplate responsibilities of
loaders back onto the import machinery.  These changes allow the
deprecation of several APIs in the import system and also addition of
new methods to finders and loaders.

   ---------- Footnotes ----------

   (1) https://www.python.org/doc/essays/packages/

   (2) https://www.python.org/dev/peps/pep-0302

   (3) https://www.python.org/dev/peps/pep-0420

   (4) https://www.python.org/dev/peps/pep-0420

   (5) https://www.python.org/dev/peps/pep-0420

   (6) https://www.python.org/dev/peps/pep-0366

   (7) https://www.python.org/dev/peps/pep-0328

   (8) https://www.python.org/dev/peps/pep-0366

   (9) https://www.python.org/dev/peps/pep-0338

   (10) https://www.python.org/dev/peps/pep-0451


File: python.info,  Node: Expressions,  Next: Simple statements,  Prev: The import system,  Up: The Python Language Reference

4.6 Expressions
===============

This chapter explains the meaning of the elements of expressions in
Python.

`Syntax Notes:' In this and the following chapters, extended BNF
notation will be used to describe syntax, not lexical analysis.  When
(one alternative of) a syntax rule has the form

     name ::= othername

and no semantics are given, the semantics of this form of ‘name’ are the
same as for ‘othername’.

* Menu:

* Arithmetic conversions::
* Atoms::
* Primaries::
* Await expression::
* The power operator::
* Unary arithmetic and bitwise operations::
* Binary arithmetic operations::
* Shifting operations::
* Binary bitwise operations::
* Comparisons::
* Boolean operations::
* Assignment expressions: Assignment expressions<2>.
* Conditional expressions::
* Lambdas::
* Expression lists::
* Evaluation order::
* Operator precedence::


File: python.info,  Node: Arithmetic conversions,  Next: Atoms,  Up: Expressions

4.6.1 Arithmetic conversions
----------------------------

When a description of an arithmetic operator below uses the phrase “the
numeric arguments are converted to a common type”, this means that the
operator implementation for built-in types works as follows:

   * If either argument is a complex number, the other is converted to
     complex;

   * otherwise, if either argument is a floating point number, the other
     is converted to floating point;

   * otherwise, both must be integers and no conversion is necessary.

Some additional rules apply for certain operators (e.g., a string as a
left argument to the ‘%’ operator).  Extensions must define their own
conversion behavior.


File: python.info,  Node: Atoms,  Next: Primaries,  Prev: Arithmetic conversions,  Up: Expressions

4.6.2 Atoms
-----------

Atoms are the most basic elements of expressions.  The simplest atoms
are identifiers or literals.  Forms enclosed in parentheses, brackets or
braces are also categorized syntactically as atoms.  The syntax for
atoms is:

     atom      ::= identifier | literal | enclosure
     enclosure ::= parenth_form | list_display | dict_display | set_display
                   | generator_expression | yield_atom

* Menu:

* Identifiers (Names): Identifiers Names.
* Literals: Literals<2>.
* Parenthesized forms::
* Displays for lists, sets and dictionaries: Displays for lists sets and dictionaries.
* List displays::
* Set displays::
* Dictionary displays::
* Generator expressions::
* Yield expressions::


File: python.info,  Node: Identifiers Names,  Next: Literals<2>,  Up: Atoms

4.6.2.1 Identifiers (Names)
...........................

An identifier occurring as an atom is a name.  See section *note
Identifiers and keywords: 1505. for lexical definition and section *note
Naming and binding: 15d9. for documentation of naming and binding.

When the name is bound to an object, evaluation of the atom yields that
object.  When a name is not bound, an attempt to evaluate it raises a
*note NameError: e40. exception.

`Private name mangling:' When an identifier that textually occurs in a
class definition begins with two or more underscore characters and does
not end in two or more underscores, it is considered a `private name' of
that class.  Private names are transformed to a longer form before code
is generated for them.  The transformation inserts the class name, with
leading underscores removed and a single underscore inserted, in front
of the name.  For example, the identifier ‘__spam’ occurring in a class
named ‘Ham’ will be transformed to ‘_Ham__spam’.  This transformation is
independent of the syntactical context in which the identifier is used.
If the transformed name is extremely long (longer than 255 characters),
implementation defined truncation may happen.  If the class name
consists only of underscores, no transformation is done.


File: python.info,  Node: Literals<2>,  Next: Parenthesized forms,  Prev: Identifiers Names,  Up: Atoms

4.6.2.2 Literals
................

Python supports string and bytes literals and various numeric literals:

     literal ::= stringliteral | bytesliteral
                 | integer | floatnumber | imagnumber

Evaluation of a literal yields an object of the given type (string,
bytes, integer, floating point number, complex number) with the given
value.  The value may be approximated in the case of floating point and
imaginary (complex) literals.  See section *note Literals: 1512. for
details.

All literals correspond to immutable data types, and hence the object’s
identity is less important than its value.  Multiple evaluations of
literals with the same value (either the same occurrence in the program
text or a different occurrence) may obtain the same object or a
different object with the same value.


File: python.info,  Node: Parenthesized forms,  Next: Displays for lists sets and dictionaries,  Prev: Literals<2>,  Up: Atoms

4.6.2.3 Parenthesized forms
...........................

A parenthesized form is an optional expression list enclosed in
parentheses:

     parenth_form ::= "(" [starred_expression] ")"

A parenthesized expression list yields whatever that expression list
yields: if the list contains at least one comma, it yields a tuple;
otherwise, it yields the single expression that makes up the expression
list.

An empty pair of parentheses yields an empty tuple object.  Since tuples
are immutable, the same rules as for literals apply (i.e., two
occurrences of the empty tuple may or may not yield the same object).

Note that tuples are not formed by the parentheses, but rather by use of
the comma operator.  The exception is the empty tuple, for which
parentheses `are' required — allowing unparenthesized “nothing” in
expressions would cause ambiguities and allow common typos to pass
uncaught.


File: python.info,  Node: Displays for lists sets and dictionaries,  Next: List displays,  Prev: Parenthesized forms,  Up: Atoms

4.6.2.4 Displays for lists, sets and dictionaries
.................................................

For constructing a list, a set or a dictionary Python provides special
syntax called “displays”, each of them in two flavors:

   * either the container contents are listed explicitly, or

   * they are computed via a set of looping and filtering instructions,
     called a `comprehension'.

Common syntax elements for comprehensions are:

     comprehension ::= assignment_expression comp_for
     comp_for      ::= ["async"] "for" target_list "in" or_test [comp_iter]
     comp_iter     ::= comp_for | comp_if
     comp_if       ::= "if" or_test [comp_iter]

The comprehension consists of a single expression followed by at least
one ‘for’ clause and zero or more ‘for’ or ‘if’ clauses.  In this case,
the elements of the new container are those that would be produced by
considering each of the ‘for’ or ‘if’ clauses a block, nesting from left
to right, and evaluating the expression to produce an element each time
the innermost block is reached.

However, aside from the iterable expression in the leftmost ‘for’
clause, the comprehension is executed in a separate implicitly nested
scope.  This ensures that names assigned to in the target list don’t
“leak” into the enclosing scope.

The iterable expression in the leftmost ‘for’ clause is evaluated
directly in the enclosing scope and then passed as an argument to the
implicitly nested scope.  Subsequent ‘for’ clauses and any filter
condition in the leftmost ‘for’ clause cannot be evaluated in the
enclosing scope as they may depend on the values obtained from the
leftmost iterable.  For example: ‘[x*y for x in range(10) for y in
range(x, x+10)]’.

To ensure the comprehension always results in a container of the
appropriate type, ‘yield’ and ‘yield from’ expressions are prohibited in
the implicitly nested scope.

Since Python 3.6, in an *note async def: 3a9. function, an ‘async for’
clause may be used to iterate over a *note asynchronous iterator: 738.
A comprehension in an ‘async def’ function may consist of either a ‘for’
or ‘async for’ clause following the leading expression, may contain
additional ‘for’ or ‘async for’ clauses, and may also use *note await:
2d8. expressions.  If a comprehension contains either ‘async for’
clauses or ‘await’ expressions it is called an `asynchronous
comprehension'.  An asynchronous comprehension may suspend the execution
of the coroutine function in which it appears.  See also PEP 530(1).

New in version 3.6: Asynchronous comprehensions were introduced.

Changed in version 3.8: ‘yield’ and ‘yield from’ prohibited in the
implicitly nested scope.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0530


File: python.info,  Node: List displays,  Next: Set displays,  Prev: Displays for lists sets and dictionaries,  Up: Atoms

4.6.2.5 List displays
.....................

A list display is a possibly empty series of expressions enclosed in
square brackets:

     list_display ::= "[" [starred_list | comprehension] "]"

A list display yields a new list object, the contents being specified by
either a list of expressions or a comprehension.  When a comma-separated
list of expressions is supplied, its elements are evaluated from left to
right and placed into the list object in that order.  When a
comprehension is supplied, the list is constructed from the elements
resulting from the comprehension.


File: python.info,  Node: Set displays,  Next: Dictionary displays,  Prev: List displays,  Up: Atoms

4.6.2.6 Set displays
....................

A set display is denoted by curly braces and distinguishable from
dictionary displays by the lack of colons separating keys and values:

     set_display ::= "{" (starred_list | comprehension) "}"

A set display yields a new mutable set object, the contents being
specified by either a sequence of expressions or a comprehension.  When
a comma-separated list of expressions is supplied, its elements are
evaluated from left to right and added to the set object.  When a
comprehension is supplied, the set is constructed from the elements
resulting from the comprehension.

An empty set cannot be constructed with ‘{}’; this literal constructs an
empty dictionary.


File: python.info,  Node: Dictionary displays,  Next: Generator expressions,  Prev: Set displays,  Up: Atoms

4.6.2.7 Dictionary displays
...........................

A dictionary display is a possibly empty series of key/datum pairs
enclosed in curly braces:

     dict_display       ::= "{" [key_datum_list | dict_comprehension] "}"
     key_datum_list     ::= key_datum ("," key_datum)* [","]
     key_datum          ::= expression ":" expression | "**" or_expr
     dict_comprehension ::= expression ":" expression comp_for

A dictionary display yields a new dictionary object.

If a comma-separated sequence of key/datum pairs is given, they are
evaluated from left to right to define the entries of the dictionary:
each key object is used as a key into the dictionary to store the
corresponding datum.  This means that you can specify the same key
multiple times in the key/datum list, and the final dictionary’s value
for that key will be the last one given.

A double asterisk ‘**’ denotes `dictionary unpacking'.  Its operand must
be a *note mapping: c0b.  Each mapping item is added to the new
dictionary.  Later values replace values already set by earlier
key/datum pairs and earlier dictionary unpackings.

New in version 3.5: Unpacking into dictionary displays, originally
proposed by PEP 448(1).

A dict comprehension, in contrast to list and set comprehensions, needs
two expressions separated with a colon followed by the usual “for” and
“if” clauses.  When the comprehension is run, the resulting key and
value elements are inserted in the new dictionary in the order they are
produced.

Restrictions on the types of the key values are listed earlier in
section *note The standard type hierarchy: 1553.  (To summarize, the key
type should be *note hashable: 276, which excludes all mutable objects.)
Clashes between duplicate keys are not detected; the last datum
(textually rightmost in the display) stored for a given key value
prevails.

Changed in version 3.8: Prior to Python 3.8, in dict comprehensions, the
evaluation order of key and value was not well-defined.  In CPython, the
value was evaluated before the key.  Starting with 3.8, the key is
evaluated before the value, as proposed by PEP 572(2).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0448

   (2) https://www.python.org/dev/peps/pep-0572


File: python.info,  Node: Generator expressions,  Next: Yield expressions,  Prev: Dictionary displays,  Up: Atoms

4.6.2.8 Generator expressions
.............................

A generator expression is a compact generator notation in parentheses:

     generator_expression ::= "(" expression comp_for ")"

A generator expression yields a new generator object.  Its syntax is the
same as for comprehensions, except that it is enclosed in parentheses
instead of brackets or curly braces.

Variables used in the generator expression are evaluated lazily when the
*note __next__(): 140e. method is called for the generator object (in
the same fashion as normal generators).  However, the iterable
expression in the leftmost ‘for’ clause is immediately evaluated, so
that an error produced by it will be emitted at the point where the
generator expression is defined, rather than at the point where the
first value is retrieved.  Subsequent ‘for’ clauses and any filter
condition in the leftmost ‘for’ clause cannot be evaluated in the
enclosing scope as they may depend on the values obtained from the
leftmost iterable.  For example: ‘(x*y for x in range(10) for y in
range(x, x+10))’.

The parentheses can be omitted on calls with only one argument.  See
section *note Calls: 73f. for details.

To avoid interfering with the expected operation of the generator
expression itself, ‘yield’ and ‘yield from’ expressions are prohibited
in the implicitly defined generator.

If a generator expression contains either ‘async for’ clauses or *note
await: 2d8. expressions it is called an `asynchronous generator
expression'.  An asynchronous generator expression returns a new
asynchronous generator object, which is an asynchronous iterator (see
*note Asynchronous Iterators: 739.).

New in version 3.6: Asynchronous generator expressions were introduced.

Changed in version 3.7: Prior to Python 3.7, asynchronous generator
expressions could only appear in *note async def: 3a9. coroutines.
Starting with 3.7, any function can use asynchronous generator
expressions.

Changed in version 3.8: ‘yield’ and ‘yield from’ prohibited in the
implicitly nested scope.


File: python.info,  Node: Yield expressions,  Prev: Generator expressions,  Up: Atoms

4.6.2.9 Yield expressions
.........................

     yield_atom       ::= "(" yield_expression ")"
     yield_expression ::= "yield" [expression_list | "from" expression]

The yield expression is used when defining a *note generator: a83.
function or an *note asynchronous generator: 1640. function and thus can
only be used in the body of a function definition.  Using a yield
expression in a function’s body causes that function to be a generator
function, and using it in an *note async def: 3a9. function’s body
causes that coroutine function to be an asynchronous generator function.
For example:

     def gen():  # defines a generator function
         yield 123

     async def agen(): # defines an asynchronous generator function
         yield 123

Due to their side effects on the containing scope, ‘yield’ expressions
are not permitted as part of the implicitly defined scopes used to
implement comprehensions and generator expressions.

Changed in version 3.8: Yield expressions prohibited in the implicitly
nested scopes used to implement comprehensions and generator
expressions.

Generator functions are described below, while asynchronous generator
functions are described separately in section *note Asynchronous
generator functions: 1641.

When a generator function is called, it returns an iterator known as a
generator.  That generator then controls the execution of the generator
function.  The execution starts when one of the generator’s methods is
called.  At that time, the execution proceeds to the first yield
expression, where it is suspended again, returning the value of *note
expression_list: 1642. to the generator’s caller.  By suspended, we mean
that all local state is retained, including the current bindings of
local variables, the instruction pointer, the internal evaluation stack,
and the state of any exception handling.  When the execution is resumed
by calling one of the generator’s methods, the function can proceed
exactly as if the yield expression were just another external call.  The
value of the yield expression after resuming depends on the method which
resumed the execution.  If *note __next__(): 140e. is used (typically
via either a *note for: cfa. or the *note next(): 775. builtin) then the
result is *note None: 203.  Otherwise, if *note send(): 15cd. is used,
then the result will be the value passed in to that method.

All of this makes generator functions quite similar to coroutines; they
yield multiple times, they have more than one entry point and their
execution can be suspended.  The only difference is that a generator
function cannot control where the execution should continue after it
yields; the control is always transferred to the generator’s caller.

Yield expressions are allowed anywhere in a *note try: e37. construct.
If the generator is not resumed before it is finalized (by reaching a
zero reference count or by being garbage collected), the
generator-iterator’s *note close(): 15d0. method will be called,
allowing any pending *note finally: 2bc. clauses to execute.

When ‘yield from <expr>’ is used, the supplied expression must be an
iterable.  The values produced by iterating that iterable are passed
directly to the caller of the current generator’s methods.  Any values
passed in with *note send(): 15cd. and any exceptions passed in with
*note throw(): ff8. are passed to the underlying iterator if it has the
appropriate methods.  If this is not the case, then *note send(): 15cd.
will raise *note AttributeError: 4a2. or *note TypeError: 1fe, while
*note throw(): ff8. will just raise the passed in exception immediately.

When the underlying iterator is complete, the ‘value’ attribute of the
raised *note StopIteration: 582. instance becomes the value of the yield
expression.  It can be either set explicitly when raising *note
StopIteration: 582, or automatically when the subiterator is a generator
(by returning a value from the subgenerator).

     Changed in version 3.3: Added ‘yield from <expr>’ to delegate
     control flow to a subiterator.

The parentheses may be omitted when the yield expression is the sole
expression on the right hand side of an assignment statement.

See also
........

PEP 255(1) - Simple Generators

     The proposal for adding generators and the *note yield: 2c7.
     statement to Python.

PEP 342(2) - Coroutines via Enhanced Generators

     The proposal to enhance the API and syntax of generators, making
     them usable as simple coroutines.

PEP 380(3) - Syntax for Delegating to a Subgenerator

     The proposal to introduce the ‘yield_from’ syntax, making
     delegation to subgenerators easy.

PEP 525(4) - Asynchronous Generators

     The proposal that expanded on PEP 492(5) by adding generator
     capabilities to coroutine functions.

* Menu:

* Generator-iterator methods::
* Examples::
* Asynchronous generator functions::
* Asynchronous generator-iterator methods::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0255

   (2) https://www.python.org/dev/peps/pep-0342

   (3) https://www.python.org/dev/peps/pep-0380

   (4) https://www.python.org/dev/peps/pep-0525

   (5) https://www.python.org/dev/peps/pep-0492


File: python.info,  Node: Generator-iterator methods,  Next: Examples,  Up: Yield expressions

4.6.2.10 Generator-iterator methods
...................................

This subsection describes the methods of a generator iterator.  They can
be used to control the execution of a generator function.

Note that calling any of the generator methods below when the generator
is already executing raises a *note ValueError: 16d. exception.

 -- Method: generator.__next__ ()

     Starts the execution of a generator function or resumes it at the
     last executed yield expression.  When a generator function is
     resumed with a *note __next__(): 140e. method, the current yield
     expression always evaluates to *note None: 203.  The execution then
     continues to the next yield expression, where the generator is
     suspended again, and the value of the *note expression_list: 1642.
     is returned to *note __next__(): 140e.’s caller.  If the generator
     exits without yielding another value, a *note StopIteration: 582.
     exception is raised.

     This method is normally called implicitly, e.g.  by a *note for:
     cfa. loop, or by the built-in *note next(): 775. function.

 -- Method: generator.send (value)

     Resumes the execution and “sends” a value into the generator
     function.  The `value' argument becomes the result of the current
     yield expression.  The *note send(): 15cd. method returns the next
     value yielded by the generator, or raises *note StopIteration: 582.
     if the generator exits without yielding another value.  When *note
     send(): 15cd. is called to start the generator, it must be called
     with *note None: 203. as the argument, because there is no yield
     expression that could receive the value.

 -- Method: generator.throw (type[, value[, traceback]])

     Raises an exception of type ‘type’ at the point where the generator
     was paused, and returns the next value yielded by the generator
     function.  If the generator exits without yielding another value, a
     *note StopIteration: 582. exception is raised.  If the generator
     function does not catch the passed-in exception, or raises a
     different exception, then that exception propagates to the caller.

 -- Method: generator.close ()

     Raises a *note GeneratorExit: df8. at the point where the generator
     function was paused.  If the generator function then exits
     gracefully, is already closed, or raises *note GeneratorExit: df8.
     (by not catching the exception), close returns to its caller.  If
     the generator yields a value, a *note RuntimeError: 3dc. is raised.
     If the generator raises any other exception, it is propagated to
     the caller.  *note close(): 15d0. does nothing if the generator has
     already exited due to an exception or normal exit.


File: python.info,  Node: Examples,  Next: Asynchronous generator functions,  Prev: Generator-iterator methods,  Up: Yield expressions

4.6.2.11 Examples
.................

Here is a simple example that demonstrates the behavior of generators
and generator functions:

     >>> def echo(value=None):
     ...     print("Execution starts when 'next()' is called for the first time.")
     ...     try:
     ...         while True:
     ...             try:
     ...                 value = (yield value)
     ...             except Exception as e:
     ...                 value = e
     ...     finally:
     ...         print("Don't forget to clean up when 'close()' is called.")
     ...
     >>> generator = echo(1)
     >>> print(next(generator))
     Execution starts when 'next()' is called for the first time.
     1
     >>> print(next(generator))
     None
     >>> print(generator.send(2))
     2
     >>> generator.throw(TypeError, "spam")
     TypeError('spam',)
     >>> generator.close()
     Don't forget to clean up when 'close()' is called.

For examples using ‘yield from’, see *note PEP 380; Syntax for
Delegating to a Subgenerator: a59. in “What’s New in Python.”


File: python.info,  Node: Asynchronous generator functions,  Next: Asynchronous generator-iterator methods,  Prev: Examples,  Up: Yield expressions

4.6.2.12 Asynchronous generator functions
.........................................

The presence of a yield expression in a function or method defined using
*note async def: 3a9. further defines the function as an *note
asynchronous generator: 1640. function.

When an asynchronous generator function is called, it returns an
asynchronous iterator known as an asynchronous generator object.  That
object then controls the execution of the generator function.  An
asynchronous generator object is typically used in an *note async for:
3fd. statement in a coroutine function analogously to how a generator
object would be used in a *note for: cfa. statement.

Calling one of the asynchronous generator’s methods returns an *note
awaitable: 613. object, and the execution starts when this object is
awaited on.  At that time, the execution proceeds to the first yield
expression, where it is suspended again, returning the value of *note
expression_list: 1642. to the awaiting coroutine.  As with a generator,
suspension means that all local state is retained, including the current
bindings of local variables, the instruction pointer, the internal
evaluation stack, and the state of any exception handling.  When the
execution is resumed by awaiting on the next object returned by the
asynchronous generator’s methods, the function can proceed exactly as if
the yield expression were just another external call.  The value of the
yield expression after resuming depends on the method which resumed the
execution.  If *note __anext__(): 1646. is used then the result is *note
None: 203.  Otherwise, if *note asend(): 177. is used, then the result
will be the value passed in to that method.

In an asynchronous generator function, yield expressions are allowed
anywhere in a *note try: e37. construct.  However, if an asynchronous
generator is not resumed before it is finalized (by reaching a zero
reference count or by being garbage collected), then a yield expression
within a ‘try’ construct could result in a failure to execute pending
*note finally: 2bc. clauses.  In this case, it is the responsibility of
the event loop or scheduler running the asynchronous generator to call
the asynchronous generator-iterator’s *note aclose(): 176. method and
run the resulting coroutine object, thus allowing any pending ‘finally’
clauses to execute.

To take care of finalization, an event loop should define a `finalizer'
function which takes an asynchronous generator-iterator and presumably
calls *note aclose(): 176. and executes the coroutine.  This `finalizer'
may be registered by calling *note sys.set_asyncgen_hooks(): 1057.  When
first iterated over, an asynchronous generator-iterator will store the
registered `finalizer' to be called upon finalization.  For a reference
example of a `finalizer' method see the implementation of
‘asyncio.Loop.shutdown_asyncgens’ in Lib/asyncio/base_events.py(1).

The expression ‘yield from <expr>’ is a syntax error when used in an
asynchronous generator function.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/asyncio/base_events.py


File: python.info,  Node: Asynchronous generator-iterator methods,  Prev: Asynchronous generator functions,  Up: Yield expressions

4.6.2.13 Asynchronous generator-iterator methods
................................................

This subsection describes the methods of an asynchronous generator
iterator, which are used to control the execution of a generator
function.

 -- Method: coroutine agen.__anext__ ()

     Returns an awaitable which when run starts to execute the
     asynchronous generator or resumes it at the last executed yield
     expression.  When an asynchronous generator function is resumed
     with an *note __anext__(): 1646. method, the current yield
     expression always evaluates to *note None: 203. in the returned
     awaitable, which when run will continue to the next yield
     expression.  The value of the *note expression_list: 1642. of the
     yield expression is the value of the *note StopIteration: 582.
     exception raised by the completing coroutine.  If the asynchronous
     generator exits without yielding another value, the awaitable
     instead raises a *note StopAsyncIteration: 114a. exception,
     signalling that the asynchronous iteration has completed.

     This method is normally called implicitly by a *note async for:
     3fd. loop.

 -- Method: coroutine agen.asend (value)

     Returns an awaitable which when run resumes the execution of the
     asynchronous generator.  As with the *note send(): 15cd. method for
     a generator, this “sends” a value into the asynchronous generator
     function, and the `value' argument becomes the result of the
     current yield expression.  The awaitable returned by the *note
     asend(): 177. method will return the next value yielded by the
     generator as the value of the raised *note StopIteration: 582, or
     raises *note StopAsyncIteration: 114a. if the asynchronous
     generator exits without yielding another value.  When *note
     asend(): 177. is called to start the asynchronous generator, it
     must be called with *note None: 203. as the argument, because there
     is no yield expression that could receive the value.

 -- Method: coroutine agen.athrow (type[, value[, traceback]])

     Returns an awaitable that raises an exception of type ‘type’ at the
     point where the asynchronous generator was paused, and returns the
     next value yielded by the generator function as the value of the
     raised *note StopIteration: 582. exception.  If the asynchronous
     generator exits without yielding another value, a *note
     StopAsyncIteration: 114a. exception is raised by the awaitable.  If
     the generator function does not catch the passed-in exception, or
     raises a different exception, then when the awaitable is run that
     exception propagates to the caller of the awaitable.

 -- Method: coroutine agen.aclose ()

     Returns an awaitable that when run will throw a *note
     GeneratorExit: df8. into the asynchronous generator function at the
     point where it was paused.  If the asynchronous generator function
     then exits gracefully, is already closed, or raises *note
     GeneratorExit: df8. (by not catching the exception), then the
     returned awaitable will raise a *note StopIteration: 582.
     exception.  Any further awaitables returned by subsequent calls to
     the asynchronous generator will raise a *note StopAsyncIteration:
     114a. exception.  If the asynchronous generator yields a value, a
     *note RuntimeError: 3dc. is raised by the awaitable.  If the
     asynchronous generator raises any other exception, it is propagated
     to the caller of the awaitable.  If the asynchronous generator has
     already exited due to an exception or normal exit, then further
     calls to *note aclose(): 176. will return an awaitable that does
     nothing.


File: python.info,  Node: Primaries,  Next: Await expression,  Prev: Atoms,  Up: Expressions

4.6.3 Primaries
---------------

Primaries represent the most tightly bound operations of the language.
Their syntax is:

     primary ::= atom | attributeref | subscription | slicing | call

* Menu:

* Attribute references::
* Subscriptions::
* Slicings::
* Calls::


File: python.info,  Node: Attribute references,  Next: Subscriptions,  Up: Primaries

4.6.3.1 Attribute references
............................

An attribute reference is a primary followed by a period and a name:

     attributeref ::= primary "." identifier

The primary must evaluate to an object of a type that supports attribute
references, which most objects do.  This object is then asked to produce
the attribute whose name is the identifier.  This production can be
customized by overriding the *note __getattr__(): 42a. method.  If this
attribute is not available, the exception *note AttributeError: 4a2. is
raised.  Otherwise, the type and value of the object produced is
determined by the object.  Multiple evaluations of the same attribute
reference may yield different objects.


File: python.info,  Node: Subscriptions,  Next: Slicings,  Prev: Attribute references,  Up: Primaries

4.6.3.2 Subscriptions
.....................

Subscription of a sequence (string, tuple or list) or mapping
(dictionary) object usually selects an item from the collection:

     subscription ::= primary "[" expression_list "]"

The primary must evaluate to an object that supports subscription (lists
or dictionaries for example).  User-defined objects can support
subscription by defining a *note __getitem__(): 3a2. method.

For built-in objects, there are two types of objects that support
subscription:

If the primary is a mapping, the expression list must evaluate to an
object whose value is one of the keys of the mapping, and the
subscription selects the value in the mapping that corresponds to that
key.  (The expression list is a tuple except if it has exactly one
item.)

If the primary is a sequence, the expression list must evaluate to an
integer or a slice (as discussed in the following section).

The formal syntax makes no special provision for negative indices in
sequences; however, built-in sequences all provide a *note
__getitem__(): 3a2. method that interprets negative indices by adding
the length of the sequence to the index (so that ‘x[-1]’ selects the
last item of ‘x’).  The resulting value must be a nonnegative integer
less than the number of items in the sequence, and the subscription
selects the item whose index is that value (counting from zero).  Since
the support for negative indices and slicing occurs in the object’s
*note __getitem__(): 3a2. method, subclasses overriding this method will
need to explicitly add that support.

A string’s items are characters.  A character is not a separate data
type but a string of exactly one character.

Subscription of certain *note classes: fe8. or *note types: fe9. creates
a *note generic alias: fe5.  In this case, user-defined classes can
support subscription by providing a *note __class_getitem__(): 437.
classmethod.


File: python.info,  Node: Slicings,  Next: Calls,  Prev: Subscriptions,  Up: Primaries

4.6.3.3 Slicings
................

A slicing selects a range of items in a sequence object (e.g., a string,
tuple or list).  Slicings may be used as expressions or as targets in
assignment or *note del: 13a2. statements.  The syntax for a slicing:

     slicing      ::= primary "[" slice_list "]"
     slice_list   ::= slice_item ("," slice_item)* [","]
     slice_item   ::= expression | proper_slice
     proper_slice ::= [lower_bound] ":" [upper_bound] [ ":" [stride] ]
     lower_bound  ::= expression
     upper_bound  ::= expression
     stride       ::= expression

There is ambiguity in the formal syntax here: anything that looks like
an expression list also looks like a slice list, so any subscription can
be interpreted as a slicing.  Rather than further complicating the
syntax, this is disambiguated by defining that in this case the
interpretation as a subscription takes priority over the interpretation
as a slicing (this is the case if the slice list contains no proper
slice).

The semantics for a slicing are as follows.  The primary is indexed
(using the same *note __getitem__(): 3a2. method as normal subscription)
with a key that is constructed from the slice list, as follows.  If the
slice list contains at least one comma, the key is a tuple containing
the conversion of the slice items; otherwise, the conversion of the lone
slice item is the key.  The conversion of a slice item that is an
expression is that expression.  The conversion of a proper slice is a
slice object (see section *note The standard type hierarchy: 1553.)
whose ‘start’, ‘stop’ and ‘step’ attributes are the values of the
expressions given as lower bound, upper bound and stride, respectively,
substituting ‘None’ for missing expressions.


File: python.info,  Node: Calls,  Prev: Slicings,  Up: Primaries

4.6.3.4 Calls
.............

A call calls a callable object (e.g., a *note function: 165b.) with a
possibly empty series of *note arguments: 165c.:

     call                 ::= primary "(" [argument_list [","] | comprehension] ")"
     argument_list        ::= positional_arguments ["," starred_and_keywords]
                                ["," keywords_arguments]
                              | starred_and_keywords ["," keywords_arguments]
                              | keywords_arguments
     positional_arguments ::= positional_item ("," positional_item)*
     positional_item      ::= assignment_expression | "*" expression
     starred_and_keywords ::= ("*" expression | keyword_item)
                              ("," "*" expression | "," keyword_item)*
     keywords_arguments   ::= (keyword_item | "**" expression)
                              ("," keyword_item | "," "**" expression)*
     keyword_item         ::= identifier "=" expression

An optional trailing comma may be present after the positional and
keyword arguments but does not affect the semantics.

The primary must evaluate to a callable object (user-defined functions,
built-in functions, methods of built-in objects, class objects, methods
of class instances, and all objects having a *note __call__(): 1560.
method are callable).  All argument expressions are evaluated before the
call is attempted.  Please refer to section *note Function definitions:
1390. for the syntax of formal *note parameter: 1664. lists.

If keyword arguments are present, they are first converted to positional
arguments, as follows.  First, a list of unfilled slots is created for
the formal parameters.  If there are N positional arguments, they are
placed in the first N slots.  Next, for each keyword argument, the
identifier is used to determine the corresponding slot (if the
identifier is the same as the first formal parameter name, the first
slot is used, and so on).  If the slot is already filled, a *note
TypeError: 1fe. exception is raised.  Otherwise, the value of the
argument is placed in the slot, filling it (even if the expression is
‘None’, it fills the slot).  When all arguments have been processed, the
slots that are still unfilled are filled with the corresponding default
value from the function definition.  (Default values are calculated,
once, when the function is defined; thus, a mutable object such as a
list or dictionary used as default value will be shared by all calls
that don’t specify an argument value for the corresponding slot; this
should usually be avoided.)  If there are any unfilled slots for which
no default value is specified, a *note TypeError: 1fe. exception is
raised.  Otherwise, the list of filled slots is used as the argument
list for the call.

`CPython implementation detail:' An implementation may provide built-in
functions whose positional parameters do not have names, even if they
are ‘named’ for the purpose of documentation, and which therefore cannot
be supplied by keyword.  In CPython, this is the case for functions
implemented in C that use *note PyArg_ParseTuple(): 393. to parse their
arguments.

If there are more positional arguments than there are formal parameter
slots, a *note TypeError: 1fe. exception is raised, unless a formal
parameter using the syntax ‘*identifier’ is present; in this case, that
formal parameter receives a tuple containing the excess positional
arguments (or an empty tuple if there were no excess positional
arguments).

If any keyword argument does not correspond to a formal parameter name,
a *note TypeError: 1fe. exception is raised, unless a formal parameter
using the syntax ‘**identifier’ is present; in this case, that formal
parameter receives a dictionary containing the excess keyword arguments
(using the keywords as keys and the argument values as corresponding
values), or a (new) empty dictionary if there were no excess keyword
arguments.

If the syntax ‘*expression’ appears in the function call, ‘expression’
must evaluate to an *note iterable: c7c.  Elements from these iterables
are treated as if they were additional positional arguments.  For the
call ‘f(x1, x2, *y, x3, x4)’, if `y' evaluates to a sequence `y1', …,
`yM', this is equivalent to a call with M+4 positional arguments `x1',
`x2', `y1', …, `yM', `x3', `x4'.

A consequence of this is that although the ‘*expression’ syntax may
appear `after' explicit keyword arguments, it is processed `before' the
keyword arguments (and any ‘**expression’ arguments – see below).  So:

     >>> def f(a, b):
     ...     print(a, b)
     ...
     >>> f(b=1, *(2,))
     2 1
     >>> f(a=1, *(2,))
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: f() got multiple values for keyword argument 'a'
     >>> f(1, *(2,))
     1 2

It is unusual for both keyword arguments and the ‘*expression’ syntax to
be used in the same call, so in practice this confusion does not arise.

If the syntax ‘**expression’ appears in the function call, ‘expression’
must evaluate to a *note mapping: c0b, the contents of which are treated
as additional keyword arguments.  If a keyword is already present (as an
explicit keyword argument, or from another unpacking), a *note
TypeError: 1fe. exception is raised.

Formal parameters using the syntax ‘*identifier’ or ‘**identifier’
cannot be used as positional argument slots or as keyword argument
names.

Changed in version 3.5: Function calls accept any number of ‘*’ and ‘**’
unpackings, positional arguments may follow iterable unpackings (‘*’),
and keyword arguments may follow dictionary unpackings (‘**’).
Originally proposed by PEP 448(1).

A call always returns some value, possibly ‘None’, unless it raises an
exception.  How this value is computed depends on the type of the
callable object.

If it is—

a user-defined function:

     The code block for the function is executed, passing it the
     argument list.  The first thing the code block will do is bind the
     formal parameters to the arguments; this is described in section
     *note Function definitions: 1390.  When the code block executes a
     *note return: 2c8. statement, this specifies the return value of
     the function call.

a built-in function or method:

     The result is up to the interpreter; see *note Built-in Functions:
     cbe. for the descriptions of built-in functions and methods.

a class object:

     A new instance of that class is returned.

a class instance method:

     The corresponding user-defined function is called, with an argument
     list that is one longer than the argument list of the call: the
     instance becomes the first argument.

a class instance:

     The class must define a *note __call__(): 1560. method; the effect
     is then the same as if that method was called.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0448


File: python.info,  Node: Await expression,  Next: The power operator,  Prev: Primaries,  Up: Expressions

4.6.4 Await expression
----------------------

Suspend the execution of *note coroutine: 18a. on an *note awaitable:
613. object.  Can only be used inside a *note coroutine function: 732.

     await_expr ::= "await" primary

New in version 3.5.


File: python.info,  Node: The power operator,  Next: Unary arithmetic and bitwise operations,  Prev: Await expression,  Up: Expressions

4.6.5 The power operator
------------------------

The power operator binds more tightly than unary operators on its left;
it binds less tightly than unary operators on its right.  The syntax is:

     power ::= (await_expr | primary) ["**" u_expr]

Thus, in an unparenthesized sequence of power and unary operators, the
operators are evaluated from right to left (this does not constrain the
evaluation order for the operands): ‘-1**2’ results in ‘-1’.

The power operator has the same semantics as the built-in *note pow():
2cf. function, when called with two arguments: it yields its left
argument raised to the power of its right argument.  The numeric
arguments are first converted to a common type, and the result is of
that type.

For int operands, the result has the same type as the operands unless
the second argument is negative; in that case, all arguments are
converted to float and a float result is delivered.  For example,
‘10**2’ returns ‘100’, but ‘10**-2’ returns ‘0.01’.

Raising ‘0.0’ to a negative power results in a *note ZeroDivisionError:
1fa.  Raising a negative number to a fractional power results in a *note
complex: 2c1. number.  (In earlier versions it raised a *note
ValueError: 16d.)

This operation can be customized using the special *note __pow__():
15a1. method.


File: python.info,  Node: Unary arithmetic and bitwise operations,  Next: Binary arithmetic operations,  Prev: The power operator,  Up: Expressions

4.6.6 Unary arithmetic and bitwise operations
---------------------------------------------

All unary arithmetic and bitwise operations have the same priority:

     u_expr ::= power | "-" u_expr | "+" u_expr | "~" u_expr

The unary ‘-’ (minus) operator yields the negation of its numeric
argument; the operation can be overridden with the *note __neg__():
15bb. special method.

The unary ‘+’ (plus) operator yields its numeric argument unchanged; the
operation can be overridden with the *note __pos__(): 15bc. special
method.

The unary ‘~’ (invert) operator yields the bitwise inversion of its
integer argument.  The bitwise inversion of ‘x’ is defined as ‘-(x+1)’.
It only applies to integral numbers or to custom objects that override
the *note __invert__(): 15be. special method.

In all three cases, if the argument does not have the proper type, a
*note TypeError: 1fe. exception is raised.


File: python.info,  Node: Binary arithmetic operations,  Next: Shifting operations,  Prev: Unary arithmetic and bitwise operations,  Up: Expressions

4.6.7 Binary arithmetic operations
----------------------------------

The binary arithmetic operations have the conventional priority levels.
Note that some of these operations also apply to certain non-numeric
types.  Apart from the power operator, there are only two levels, one
for multiplicative operators and one for additive operators:

     m_expr ::= u_expr | m_expr "*" u_expr | m_expr "@" m_expr |
                m_expr "//" u_expr | m_expr "/" u_expr |
                m_expr "%" u_expr
     a_expr ::= m_expr | a_expr "+" m_expr | a_expr "-" m_expr

The ‘*’ (multiplication) operator yields the product of its arguments.
The arguments must either both be numbers, or one argument must be an
integer and the other must be a sequence.  In the former case, the
numbers are converted to a common type and then multiplied together.  In
the latter case, sequence repetition is performed; a negative repetition
factor yields an empty sequence.

This operation can be customized using the special *note __mul__():
1597. and *note __rmul__(): 1598. methods.

The ‘@’ (at) operator is intended to be used for matrix multiplication.
No builtin Python types implement this operator.

New in version 3.5.

The ‘/’ (division) and ‘//’ (floor division) operators yield the
quotient of their arguments.  The numeric arguments are first converted
to a common type.  Division of integers yields a float, while floor
division of integers results in an integer; the result is that of
mathematical division with the ‘floor’ function applied to the result.
Division by zero raises the *note ZeroDivisionError: 1fa. exception.

This operation can be customized using the special *note __truediv__():
875. and *note __floordiv__(): ef7. methods.

The ‘%’ (modulo) operator yields the remainder from the division of the
first argument by the second.  The numeric arguments are first converted
to a common type.  A zero right argument raises the *note
ZeroDivisionError: 1fa. exception.  The arguments may be floating point
numbers, e.g., ‘3.14%0.7’ equals ‘0.34’ (since ‘3.14’ equals ‘4*0.7 +
0.34’.)  The modulo operator always yields a result with the same sign
as its second operand (or zero); the absolute value of the result is
strictly smaller than the absolute value of the second operand (1).

The floor division and modulo operators are connected by the following
identity: ‘x == (x//y)*y + (x%y)’.  Floor division and modulo are also
connected with the built-in function *note divmod(): 28d.: ‘divmod(x, y)
== (x//y, x%y)’.  (2).

In addition to performing the modulo operation on numbers, the ‘%’
operator is also overloaded by string objects to perform old-style
string formatting (also known as interpolation).  The syntax for string
formatting is described in the Python Library Reference, section *note
printf-style String Formatting: 1359.

The `modulo' operation can be customized using the special *note
__mod__(): 15a0. method.

The floor division operator, the modulo operator, and the *note
divmod(): 28d. function are not defined for complex numbers.  Instead,
convert to a floating point number using the *note abs(): 13f3. function
if appropriate.

The ‘+’ (addition) operator yields the sum of its arguments.  The
arguments must either both be numbers or both be sequences of the same
type.  In the former case, the numbers are converted to a common type
and then added together.  In the latter case, the sequences are
concatenated.

This operation can be customized using the special *note __add__():
1595. and *note __radd__(): 1596. methods.

The ‘-’ (subtraction) operator yields the difference of its arguments.
The numeric arguments are first converted to a common type.

This operation can be customized using the special *note __sub__():
159f. method.

   ---------- Footnotes ----------

   (1) (1) While ‘abs(x%y) < abs(y)’ is true mathematically, for floats
it may not be true numerically due to roundoff.  For example, and
assuming a platform on which a Python float is an IEEE 754
double-precision number, in order that ‘-1e-100 % 1e100’ have the same
sign as ‘1e100’, the computed result is ‘-1e-100 + 1e100’, which is
numerically exactly equal to ‘1e100’.  The function *note math.fmod():
1671. returns a result whose sign matches the sign of the first argument
instead, and so returns ‘-1e-100’ in this case.  Which approach is more
appropriate depends on the application.

   (2) (2) If x is very close to an exact integer multiple of y, it’s
possible for ‘x//y’ to be one larger than ‘(x-x%y)//y’ due to rounding.
In such cases, Python returns the latter result, in order to preserve
that ‘divmod(x,y)[0] * y + x % y’ be very close to ‘x’.


File: python.info,  Node: Shifting operations,  Next: Binary bitwise operations,  Prev: Binary arithmetic operations,  Up: Expressions

4.6.8 Shifting operations
-------------------------

The shifting operations have lower priority than the arithmetic
operations:

     shift_expr ::= a_expr | shift_expr ("<<" | ">>") a_expr

These operators accept integers as arguments.  They shift the first
argument to the left or right by the number of bits given by the second
argument.

This operation can be customized using the special *note __lshift__():
15a2. and *note __rshift__(): 15a3. methods.

A right shift by `n' bits is defined as floor division by ‘pow(2,n)’.  A
left shift by `n' bits is defined as multiplication with ‘pow(2,n)’.


File: python.info,  Node: Binary bitwise operations,  Next: Comparisons,  Prev: Shifting operations,  Up: Expressions

4.6.9 Binary bitwise operations
-------------------------------

Each of the three bitwise operations has a different priority level:

     and_expr ::= shift_expr | and_expr "&" shift_expr
     xor_expr ::= and_expr | xor_expr "^" and_expr
     or_expr  ::= xor_expr | or_expr "|" xor_expr

The ‘&’ operator yields the bitwise AND of its arguments, which must be
integers or one of them must be a custom object overriding *note
__and__(): 15a4. or *note __rand__(): 15ae. special methods.

The ‘^’ operator yields the bitwise XOR (exclusive OR) of its arguments,
which must be integers or one of them must be a custom object overriding
*note __xor__(): 15a5. or *note __rxor__(): 15af. special methods.

The ‘|’ operator yields the bitwise (inclusive) OR of its arguments,
which must be integers or one of them must be a custom object overriding
*note __or__(): 15a6. or *note __ror__(): 15b0. special methods.


File: python.info,  Node: Comparisons,  Next: Boolean operations,  Prev: Binary bitwise operations,  Up: Expressions

4.6.10 Comparisons
------------------

Unlike C, all comparison operations in Python have the same priority,
which is lower than that of any arithmetic, shifting or bitwise
operation.  Also unlike C, expressions like ‘a < b < c’ have the
interpretation that is conventional in mathematics:

     comparison    ::= or_expr (comp_operator or_expr)*
     comp_operator ::= "<" | ">" | "==" | ">=" | "<=" | "!="
                       | "is" ["not"] | ["not"] "in"

Comparisons yield boolean values: ‘True’ or ‘False’.  Custom `rich
comparison methods' may return non-boolean values.  In this case Python
will call *note bool(): 2bd. on such value in boolean contexts.

Comparisons can be chained arbitrarily, e.g., ‘x < y <= z’ is equivalent
to ‘x < y and y <= z’, except that ‘y’ is evaluated only once (but in
both cases ‘z’ is not evaluated at all when ‘x < y’ is found to be
false).

Formally, if `a', `b', `c', …, `y', `z' are expressions and `op1',
`op2', …, `opN' are comparison operators, then ‘a op1 b op2 c ... y opN
z’ is equivalent to ‘a op1 b and b op2 c and ... y opN z’, except that
each expression is evaluated at most once.

Note that ‘a op1 b op2 c’ doesn’t imply any kind of comparison between
`a' and `c', so that, e.g., ‘x < y > z’ is perfectly legal (though
perhaps not pretty).

* Menu:

* Value comparisons::
* Membership test operations::
* Identity comparisons::


File: python.info,  Node: Value comparisons,  Next: Membership test operations,  Up: Comparisons

4.6.10.1 Value comparisons
..........................

The operators ‘<’, ‘>’, ‘==’, ‘>=’, ‘<=’, and ‘!=’ compare the values of
two objects.  The objects do not need to have the same type.

Chapter *note Objects, values and types: 154f. states that objects have
a value (in addition to type and identity).  The value of an object is a
rather abstract notion in Python: For example, there is no canonical
access method for an object’s value.  Also, there is no requirement that
the value of an object should be constructed in a particular way, e.g.
comprised of all its data attributes.  Comparison operators implement a
particular notion of what the value of an object is.  One can think of
them as defining the value of an object indirectly, by means of their
comparison implementation.

Because all types are (direct or indirect) subtypes of *note object:
3d2, they inherit the default comparison behavior from *note object:
3d2.  Types can customize their comparison behavior by implementing
`rich comparison methods' like *note __lt__(): cfe, described in *note
Basic customization: 1568.

The default behavior for equality comparison (‘==’ and ‘!=’) is based on
the identity of the objects.  Hence, equality comparison of instances
with the same identity results in equality, and equality comparison of
instances with different identities results in inequality.  A motivation
for this default behavior is the desire that all objects should be
reflexive (i.e.  ‘x is y’ implies ‘x == y’).

A default order comparison (‘<’, ‘>’, ‘<=’, and ‘>=’) is not provided;
an attempt raises *note TypeError: 1fe.  A motivation for this default
behavior is the lack of a similar invariant as for equality.

The behavior of the default equality comparison, that instances with
different identities are always unequal, may be in contrast to what
types will need that have a sensible definition of object value and
value-based equality.  Such types will need to customize their
comparison behavior, and in fact, a number of built-in types have done
that.

The following list describes the comparison behavior of the most
important built-in types.

   * Numbers of built-in numeric types (*note Numeric Types — int,
     float, complex: 1353.) and of the standard library types *note
     fractions.Fraction: 2be. and *note decimal.Decimal: 2c0. can be
     compared within and across their types, with the restriction that
     complex numbers do not support order comparison.  Within the limits
     of the types involved, they compare mathematically
     (algorithmically) correct without loss of precision.

     The not-a-number values ‘float('NaN')’ and ‘decimal.Decimal('NaN')’
     are special.  Any ordered comparison of a number to a not-a-number
     value is false.  A counter-intuitive implication is that
     not-a-number values are not equal to themselves.  For example, if
     ‘x = float('NaN')’, ‘3 < x’, ‘x < 3’ and ‘x == x’ are all false,
     while ‘x != x’ is true.  This behavior is compliant with IEEE 754.

   * ‘None’ and ‘NotImplemented’ are singletons.  PEP 8(1) advises that
     comparisons for singletons should always be done with ‘is’ or ‘is
     not’, never the equality operators.

   * Binary sequences (instances of *note bytes: 172. or *note
     bytearray: 173.) can be compared within and across their types.
     They compare lexicographically using the numeric values of their
     elements.

   * Strings (instances of *note str: 205.) compare lexicographically
     using the numerical Unicode code points (the result of the built-in
     function *note ord(): 1559.) of their characters.  (2)

     Strings and binary sequences cannot be directly compared.

   * Sequences (instances of *note tuple: 1a2, *note list: 1f8, or *note
     range: 1f5.) can be compared only within each of their types, with
     the restriction that ranges do not support order comparison.
     Equality comparison across these types results in inequality, and
     ordering comparison across these types raises *note TypeError: 1fe.

     Sequences compare lexicographically using comparison of
     corresponding elements.  The built-in containers typically assume
     identical objects are equal to themselves.  That lets them bypass
     equality tests for identical objects to improve performance and to
     maintain their internal invariants.

     Lexicographical comparison between built-in collections works as
     follows:

        - For two collections to compare equal, they must be of the same
          type, have the same length, and each pair of corresponding
          elements must compare equal (for example, ‘[1,2] == (1,2)’ is
          false because the type is not the same).

        - Collections that support order comparison are ordered the same
          as their first unequal elements (for example, ‘[1,2,x] <=
          [1,2,y]’ has the same value as ‘x <= y’).  If a corresponding
          element does not exist, the shorter collection is ordered
          first (for example, ‘[1,2] < [1,2,3]’ is true).

   * Mappings (instances of *note dict: 164.) compare equal if and only
     if they have equal ‘(key, value)’ pairs.  Equality comparison of
     the keys and values enforces reflexivity.

     Order comparisons (‘<’, ‘>’, ‘<=’, and ‘>=’) raise *note TypeError:
     1fe.

   * Sets (instances of *note set: 1f6. or *note frozenset: 1f7.) can be
     compared within and across their types.

     They define order comparison operators to mean subset and superset
     tests.  Those relations do not define total orderings (for example,
     the two sets ‘{1,2}’ and ‘{2,3}’ are not equal, nor subsets of one
     another, nor supersets of one another).  Accordingly, sets are not
     appropriate arguments for functions which depend on total ordering
     (for example, *note min(): 8f6, *note max(): 8f7, and *note
     sorted(): 547. produce undefined results given a list of sets as
     inputs).

     Comparison of sets enforces reflexivity of its elements.

   * Most other built-in types have no comparison methods implemented,
     so they inherit the default comparison behavior.

User-defined classes that customize their comparison behavior should
follow some consistency rules, if possible:

   * Equality comparison should be reflexive.  In other words, identical
     objects should compare equal:

          ‘x is y’ implies ‘x == y’

   * Comparison should be symmetric.  In other words, the following
     expressions should have the same result:

          ‘x == y’ and ‘y == x’

          ‘x != y’ and ‘y != x’

          ‘x < y’ and ‘y > x’

          ‘x <= y’ and ‘y >= x’

   * Comparison should be transitive.  The following (non-exhaustive)
     examples illustrate that:

          ‘x > y and y > z’ implies ‘x > z’

          ‘x < y and y <= z’ implies ‘x < z’

   * Inverse comparison should result in the boolean negation.  In other
     words, the following expressions should have the same result:

          ‘x == y’ and ‘not x != y’

          ‘x < y’ and ‘not x >= y’ (for total ordering)

          ‘x > y’ and ‘not x <= y’ (for total ordering)

     The last two expressions apply to totally ordered collections (e.g.
     to sequences, but not to sets or mappings).  See also the *note
     total_ordering(): 938. decorator.

   * The *note hash(): aa3. result should be consistent with equality.
     Objects that are equal should either have the same hash value, or
     be marked as unhashable.

Python does not enforce these consistency rules.  In fact, the
not-a-number values are an example for not following these rules.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0008

   (2) (3) The Unicode standard distinguishes between `code points'
(e.g.  U+0041) and `abstract characters' (e.g.  “LATIN CAPITAL LETTER
A”).  While most abstract characters in Unicode are only represented
using one code point, there is a number of abstract characters that can
in addition be represented using a sequence of more than one code point.
For example, the abstract character “LATIN CAPITAL LETTER C WITH
CEDILLA” can be represented as a single `precomposed character' at code
position U+00C7, or as a sequence of a `base character' at code position
U+0043 (LATIN CAPITAL LETTER C), followed by a `combining character' at
code position U+0327 (COMBINING CEDILLA).

The comparison operators on strings compare at the level of Unicode code
points.  This may be counter-intuitive to humans.  For example,
‘"\u00C7" == "\u0043\u0327"’ is ‘False’, even though both strings
represent the same abstract character “LATIN CAPITAL LETTER C WITH
CEDILLA”.

To compare strings at the level of abstract characters (that is, in a
way intuitive to humans), use *note unicodedata.normalize(): 11e4.


File: python.info,  Node: Membership test operations,  Next: Identity comparisons,  Prev: Value comparisons,  Up: Comparisons

4.6.10.2 Membership test operations
...................................

The operators *note in: 179. and *note not in: 159b. test for
membership.  ‘x in s’ evaluates to ‘True’ if `x' is a member of `s', and
‘False’ otherwise.  ‘x not in s’ returns the negation of ‘x in s’.  All
built-in sequences and set types support this as well as dictionary, for
which ‘in’ tests whether the dictionary has a given key.  For container
types such as list, tuple, set, frozenset, dict, or collections.deque,
the expression ‘x in y’ is equivalent to ‘any(x is e or x == e for e in
y)’.

For the string and bytes types, ‘x in y’ is ‘True’ if and only if `x' is
a substring of `y'.  An equivalent test is ‘y.find(x) != -1’.  Empty
strings are always considered to be a substring of any other string, so
‘"" in "abc"’ will return ‘True’.

For user-defined classes which define the *note __contains__(): dee.
method, ‘x in y’ returns ‘True’ if ‘y.__contains__(x)’ returns a true
value, and ‘False’ otherwise.

For user-defined classes which do not define *note __contains__(): dee.
but do define *note __iter__(): 609, ‘x in y’ is ‘True’ if some value
‘z’, for which the expression ‘x is z or x == z’ is true, is produced
while iterating over ‘y’.  If an exception is raised during the
iteration, it is as if *note in: 179. raised that exception.

Lastly, the old-style iteration protocol is tried: if a class defines
*note __getitem__(): 3a2, ‘x in y’ is ‘True’ if and only if there is a
non-negative integer index `i' such that ‘x is y[i] or x == y[i]’, and
no lower integer index raises the *note IndexError: f36. exception.  (If
any other exception is raised, it is as if *note in: 179. raised that
exception).

The operator *note not in: 159b. is defined to have the inverse truth
value of *note in: 179.


File: python.info,  Node: Identity comparisons,  Prev: Membership test operations,  Up: Comparisons

4.6.10.3 Identity comparisons
.............................

The operators *note is: 1551. and *note is not: 1681. test for an
object’s identity: ‘x is y’ is true if and only if `x' and `y' are the
same object.  An Object’s identity is determined using the *note id():
e4b. function.  ‘x is not y’ yields the inverse truth value.  (1)

   ---------- Footnotes ----------

   (1) (4) Due to automatic garbage-collection, free lists, and the
dynamic nature of descriptors, you may notice seemingly unusual
behaviour in certain uses of the *note is: 1551. operator, like those
involving comparisons between instance methods, or constants.  Check
their documentation for more info.


File: python.info,  Node: Boolean operations,  Next: Assignment expressions<2>,  Prev: Comparisons,  Up: Expressions

4.6.11 Boolean operations
-------------------------

     or_test  ::= and_test | or_test "or" and_test
     and_test ::= not_test | and_test "and" not_test
     not_test ::= comparison | "not" not_test

In the context of Boolean operations, and also when expressions are used
by control flow statements, the following values are interpreted as
false: ‘False’, ‘None’, numeric zero of all types, and empty strings and
containers (including strings, tuples, lists, dictionaries, sets and
frozensets).  All other values are interpreted as true.  User-defined
objects can customize their truth value by providing a *note __bool__():
d30. method.

The operator *note not: 1686. yields ‘True’ if its argument is false,
‘False’ otherwise.

The expression ‘x and y’ first evaluates `x'; if `x' is false, its value
is returned; otherwise, `y' is evaluated and the resulting value is
returned.

The expression ‘x or y’ first evaluates `x'; if `x' is true, its value
is returned; otherwise, `y' is evaluated and the resulting value is
returned.

Note that neither *note and: 1683. nor *note or: 1684. restrict the
value and type they return to ‘False’ and ‘True’, but rather return the
last evaluated argument.  This is sometimes useful, e.g., if ‘s’ is a
string that should be replaced by a default value if it is empty, the
expression ‘s or 'foo'’ yields the desired value.  Because *note not:
1686. has to create a new value, it returns a boolean value regardless
of the type of its argument (for example, ‘not 'foo'’ produces ‘False’
rather than ‘''’.)


File: python.info,  Node: Assignment expressions<2>,  Next: Conditional expressions,  Prev: Boolean operations,  Up: Expressions

4.6.12 Assignment expressions
-----------------------------

     assignment_expression ::= [identifier ":="] expression

An assignment expression (sometimes also called a “named expression” or
“walrus”) assigns an *note expression: 168c. to an *note identifier:
1507, while also returning the value of the *note expression: 168c.

One common use case is when handling matched regular expressions:

     if matching := pattern.search(data):
         do_something(matching)

Or, when processing a file stream in chunks:

     while chunk := file.read(9000):
         process(chunk)

New in version 3.8: See PEP 572(1) for more details about assignment
expressions.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0572


File: python.info,  Node: Conditional expressions,  Next: Lambdas,  Prev: Assignment expressions<2>,  Up: Expressions

4.6.13 Conditional expressions
------------------------------

     conditional_expression ::= or_test ["if" or_test "else" expression]
     expression             ::= conditional_expression | lambda_expr

Conditional expressions (sometimes called a “ternary operator”) have the
lowest priority of all Python operations.

The expression ‘x if C else y’ first evaluates the condition, `C' rather
than `x'.  If `C' is true, `x' is evaluated and its value is returned;
otherwise, `y' is evaluated and its value is returned.

See PEP 308(1) for more details about conditional expressions.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0308


File: python.info,  Node: Lambdas,  Next: Expression lists,  Prev: Conditional expressions,  Up: Expressions

4.6.14 Lambdas
--------------

     lambda_expr ::= "lambda" [parameter_list] ":" expression

Lambda expressions (sometimes called lambda forms) are used to create
anonymous functions.  The expression ‘lambda parameters: expression’
yields a function object.  The unnamed object behaves like a function
object defined with:

     def <lambda>(parameters):
         return expression

See section *note Function definitions: 1390. for the syntax of
parameter lists.  Note that functions created with lambda expressions
cannot contain statements or annotations.


File: python.info,  Node: Expression lists,  Next: Evaluation order,  Prev: Lambdas,  Up: Expressions

4.6.15 Expression lists
-----------------------

     expression_list    ::= expression ("," expression)* [","]
     starred_list       ::= starred_item ("," starred_item)* [","]
     starred_expression ::= expression | (starred_item ",")* [starred_item]
     starred_item       ::= assignment_expression | "*" or_expr

Except when part of a list or set display, an expression list containing
at least one comma yields a tuple.  The length of the tuple is the
number of expressions in the list.  The expressions are evaluated from
left to right.

An asterisk ‘*’ denotes `iterable unpacking'.  Its operand must be an
*note iterable: c7c.  The iterable is expanded into a sequence of items,
which are included in the new tuple, list, or set, at the site of the
unpacking.

New in version 3.5: Iterable unpacking in expression lists, originally
proposed by PEP 448(1).

The trailing comma is required only to create a single tuple (a.k.a.  a
`singleton'); it is optional in all other cases.  A single expression
without a trailing comma doesn’t create a tuple, but rather yields the
value of that expression.  (To create an empty tuple, use an empty pair
of parentheses: ‘()’.)

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0448


File: python.info,  Node: Evaluation order,  Next: Operator precedence,  Prev: Expression lists,  Up: Expressions

4.6.16 Evaluation order
-----------------------

Python evaluates expressions from left to right.  Notice that while
evaluating an assignment, the right-hand side is evaluated before the
left-hand side.

In the following lines, expressions will be evaluated in the arithmetic
order of their suffixes:

     expr1, expr2, expr3, expr4
     (expr1, expr2, expr3, expr4)
     {expr1: expr2, expr3: expr4}
     expr1 + expr2 * (expr3 - expr4)
     expr1(expr2, expr3, *expr4, **expr5)
     expr3, expr4 = expr1, expr2


File: python.info,  Node: Operator precedence,  Prev: Evaluation order,  Up: Expressions

4.6.17 Operator precedence
--------------------------

The following table summarizes the operator precedence in Python, from
highest precedence (most binding) to lowest precedence (least binding).
Operators in the same box have the same precedence.  Unless the syntax
is explicitly given, operators are binary.  Operators in the same box
group left to right (except for exponentiation, which groups from right
to left).

Note that comparisons, membership tests, and identity tests, all have
the same precedence and have a left-to-right chaining feature as
described in the *note Comparisons: 167a. section.

Operator                                            Description
                                                    
----------------------------------------------------------------------------------------------
                                                    
‘(expressions...)’,                                 Binding or parenthesized expression,
                                                    list display, dictionary display, set
‘[expressions...]’, ‘{key: value...}’,              display
‘{expressions...}’                                  

‘x[index]’, ‘x[index:index]’, ‘x(arguments...)’,    Subscription, slicing, call, attribute
‘x.attribute’                                       reference
                                                    
                                                    
*note await: 2d8. ‘x’                               Await expression
                                                    
                                                    
‘**’                                                Exponentiation (1)
                                                    
                                                    
‘+x’, ‘-x’, ‘~x’                                    Positive, negative, bitwise NOT
                                                    
                                                    
‘*’, ‘@’, ‘/’, ‘//’, ‘%’                            Multiplication, matrix multiplication,
                                                    division, floor division, remainder (2)
                                                    
                                                    
‘+’, ‘-’                                            Addition and subtraction
                                                    
                                                    
‘<<’, ‘>>’                                          Shifts
                                                    
                                                    
‘&’                                                 Bitwise AND
                                                    
                                                    
‘^’                                                 Bitwise XOR
                                                    
                                                    
‘|’                                                 Bitwise OR
                                                    
                                                    
*note in: 179, *note not in: 159b,                  Comparisons, including membership tests
*note is: 1551, *note is not: 1681, ‘<’, ‘<=’,      and identity tests
‘>’, ‘>=’, ‘!=’, ‘==’                               

*note not: 1686. ‘x’                                Boolean NOT
                                                    
                                                    
*note and: 1683.                                    Boolean AND
                                                    
                                                    
*note or: 1684.                                     Boolean OR
                                                    
                                                    
*note if: 168e. – ‘else’                            Conditional expression
                                                    
                                                    
*note lambda: cf9.                                  Lambda expression
                                                    
                                                    
‘:=’                                                Assignment expression
                                                    

   ---------- Footnotes ----------

   (1) (5) The power operator ‘**’ binds less tightly than an arithmetic
or bitwise unary operator on its right, that is, ‘2**-1’ is ‘0.5’.

   (2) (6) The ‘%’ operator is also used for string formatting; the same
precedence applies.


File: python.info,  Node: Simple statements,  Next: Compound statements,  Prev: Expressions,  Up: The Python Language Reference

4.7 Simple statements
=====================

A simple statement is comprised within a single logical line.  Several
simple statements may occur on a single line separated by semicolons.
The syntax for simple statements is:

     simple_stmt ::= expression_stmt
                     | assert_stmt
                     | assignment_stmt
                     | augmented_assignment_stmt
                     | annotated_assignment_stmt
                     | pass_stmt
                     | del_stmt
                     | return_stmt
                     | yield_stmt
                     | raise_stmt
                     | break_stmt
                     | continue_stmt
                     | import_stmt
                     | future_stmt
                     | global_stmt
                     | nonlocal_stmt

* Menu:

* Expression statements::
* Assignment statements::
* The assert statement::
* The pass statement::
* The del statement: The del statement<2>.
* The return statement::
* The yield statement::
* The raise statement::
* The break statement::
* The continue statement::
* The import statement::
* The global statement::
* The nonlocal statement::


File: python.info,  Node: Expression statements,  Next: Assignment statements,  Up: Simple statements

4.7.1 Expression statements
---------------------------

Expression statements are used (mostly interactively) to compute and
write a value, or (usually) to call a procedure (a function that returns
no meaningful result; in Python, procedures return the value ‘None’).
Other uses of expression statements are allowed and occasionally useful.
The syntax for an expression statement is:

     expression_stmt ::= starred_expression

An expression statement evaluates the expression list (which may be a
single expression).

In interactive mode, if the value is not ‘None’, it is converted to a
string using the built-in *note repr(): 8b9. function and the resulting
string is written to standard output on a line by itself (except if the
result is ‘None’, so that procedure calls do not cause any output.)


File: python.info,  Node: Assignment statements,  Next: The assert statement,  Prev: Expression statements,  Up: Simple statements

4.7.2 Assignment statements
---------------------------

Assignment statements are used to (re)bind names to values and to modify
attributes or items of mutable objects:

     assignment_stmt ::= (target_list "=")+ (starred_expression | yield_expression)
     target_list     ::= target ("," target)* [","]
     target          ::= identifier
                         | "(" [target_list] ")"
                         | "[" [target_list] "]"
                         | attributeref
                         | subscription
                         | slicing
                         | "*" target

(See section *note Primaries: 164a. for the syntax definitions for
`attributeref', `subscription', and `slicing'.)

An assignment statement evaluates the expression list (remember that
this can be a single expression or a comma-separated list, the latter
yielding a tuple) and assigns the single resulting object to each of the
target lists, from left to right.

Assignment is defined recursively depending on the form of the target
(list).  When a target is part of a mutable object (an attribute
reference, subscription or slicing), the mutable object must ultimately
perform the assignment and decide about its validity, and may raise an
exception if the assignment is unacceptable.  The rules observed by
various types and the exceptions raised are given with the definition of
the object types (see section *note The standard type hierarchy: 1553.).

Assignment of an object to a target list, optionally enclosed in
parentheses or square brackets, is recursively defined as follows.

   * If the target list is a single target with no trailing comma,
     optionally in parentheses, the object is assigned to that target.

   * Else: The object must be an iterable with the same number of items
     as there are targets in the target list, and the items are
     assigned, from left to right, to the corresponding targets.

        * If the target list contains one target prefixed with an
          asterisk, called a “starred” target: The object must be an
          iterable with at least as many items as there are targets in
          the target list, minus one.  The first items of the iterable
          are assigned, from left to right, to the targets before the
          starred target.  The final items of the iterable are assigned
          to the targets after the starred target.  A list of the
          remaining items in the iterable is then assigned to the
          starred target (the list can be empty).

        * Else: The object must be an iterable with the same number of
          items as there are targets in the target list, and the items
          are assigned, from left to right, to the corresponding
          targets.

Assignment of an object to a single target is recursively defined as
follows.

   * If the target is an identifier (name):

        * If the name does not occur in a *note global: 1378. or *note
          nonlocal: d07. statement in the current code block: the name
          is bound to the object in the current local namespace.

        * Otherwise: the name is bound to the object in the global
          namespace or the outer namespace determined by *note nonlocal:
          d07, respectively.

     The name is rebound if it was already bound.  This may cause the
     reference count for the object previously bound to the name to
     reach zero, causing the object to be deallocated and its destructor
     (if it has one) to be called.

   * If the target is an attribute reference: The primary expression in
     the reference is evaluated.  It should yield an object with
     assignable attributes; if this is not the case, *note TypeError:
     1fe. is raised.  That object is then asked to assign the assigned
     object to the given attribute; if it cannot perform the assignment,
     it raises an exception (usually but not necessarily *note
     AttributeError: 4a2.).  Note: If the object is a class instance and
     the attribute reference occurs on both sides of the assignment
     operator, the right-hand side expression, ‘a.x’ can access either
     an instance attribute or (if no instance attribute exists) a class
     attribute.  The left-hand side target ‘a.x’ is always set as an
     instance attribute, creating it if necessary.  Thus, the two
     occurrences of ‘a.x’ do not necessarily refer to the same
     attribute: if the right-hand side expression refers to a class
     attribute, the left-hand side creates a new instance attribute as
     the target of the assignment:

          class Cls:
              x = 3             # class variable
          inst = Cls()
          inst.x = inst.x + 1   # writes inst.x as 4 leaving Cls.x as 3

     This description does not necessarily apply to descriptor
     attributes, such as properties created with *note property(): 308.

   * If the target is a subscription: The primary expression in the
     reference is evaluated.  It should yield either a mutable sequence
     object (such as a list) or a mapping object (such as a dictionary).
     Next, the subscript expression is evaluated.

     If the primary is a mutable sequence object (such as a list), the
     subscript must yield an integer.  If it is negative, the sequence’s
     length is added to it.  The resulting value must be a nonnegative
     integer less than the sequence’s length, and the sequence is asked
     to assign the assigned object to its item with that index.  If the
     index is out of range, *note IndexError: f36. is raised (assignment
     to a subscripted sequence cannot add new items to a list).

     If the primary is a mapping object (such as a dictionary), the
     subscript must have a type compatible with the mapping’s key type,
     and the mapping is then asked to create a key/datum pair which maps
     the subscript to the assigned object.  This can either replace an
     existing key/value pair with the same key value, or insert a new
     key/value pair (if no key with the same value existed).

     For user-defined objects, the *note __setitem__(): d2a. method is
     called with appropriate arguments.

   * If the target is a slicing: The primary expression in the reference
     is evaluated.  It should yield a mutable sequence object (such as a
     list).  The assigned object should be a sequence object of the same
     type.  Next, the lower and upper bound expressions are evaluated,
     insofar they are present; defaults are zero and the sequence’s
     length.  The bounds should evaluate to integers.  If either bound
     is negative, the sequence’s length is added to it.  The resulting
     bounds are clipped to lie between zero and the sequence’s length,
     inclusive.  Finally, the sequence object is asked to replace the
     slice with the items of the assigned sequence.  The length of the
     slice may be different from the length of the assigned sequence,
     thus changing the length of the target sequence, if the target
     sequence allows it.

`CPython implementation detail:' In the current implementation, the
syntax for targets is taken to be the same as for expressions, and
invalid syntax is rejected during the code generation phase, causing
less detailed error messages.

Although the definition of assignment implies that overlaps between the
left-hand side and the right-hand side are ‘simultaneous’ (for example
‘a, b = b, a’ swaps two variables), overlaps `within' the collection of
assigned-to variables occur left-to-right, sometimes resulting in
confusion.  For instance, the following program prints ‘[0, 2]’:

     x = [0, 1]
     i = 0
     i, x[i] = 1, 2         # i is updated, then x[i] is updated
     print(x)

See also
........

PEP 3132(1) - Extended Iterable Unpacking

     The specification for the ‘*target’ feature.

* Menu:

* Augmented assignment statements::
* Annotated assignment statements::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3132


File: python.info,  Node: Augmented assignment statements,  Next: Annotated assignment statements,  Up: Assignment statements

4.7.2.1 Augmented assignment statements
.......................................

Augmented assignment is the combination, in a single statement, of a
binary operation and an assignment statement:

     augmented_assignment_stmt ::= augtarget augop (expression_list | yield_expression)
     augtarget                 ::= identifier | attributeref | subscription | slicing
     augop                     ::= "+=" | "-=" | "*=" | "@=" | "/=" | "//=" | "%=" | "**="
                                   | ">>=" | "<<=" | "&=" | "^=" | "|="

(See section *note Primaries: 164a. for the syntax definitions of the
last three symbols.)

An augmented assignment evaluates the target (which, unlike normal
assignment statements, cannot be an unpacking) and the expression list,
performs the binary operation specific to the type of assignment on the
two operands, and assigns the result to the original target.  The target
is only evaluated once.

An augmented assignment expression like ‘x += 1’ can be rewritten as ‘x
= x + 1’ to achieve a similar, but not exactly equal effect.  In the
augmented version, ‘x’ is only evaluated once.  Also, when possible, the
actual operation is performed `in-place', meaning that rather than
creating a new object and assigning that to the target, the old object
is modified instead.

Unlike normal assignments, augmented assignments evaluate the left-hand
side `before' evaluating the right-hand side.  For example, ‘a[i] +=
f(x)’ first looks-up ‘a[i]’, then it evaluates ‘f(x)’ and performs the
addition, and lastly, it writes the result back to ‘a[i]’.

With the exception of assigning to tuples and multiple targets in a
single statement, the assignment done by augmented assignment statements
is handled the same way as normal assignments.  Similarly, with the
exception of the possible `in-place' behavior, the binary operation
performed by augmented assignment is the same as the normal binary
operations.

For targets which are attribute references, the same *note caveat about
class and instance attributes: 16a7. applies as for regular assignments.


File: python.info,  Node: Annotated assignment statements,  Prev: Augmented assignment statements,  Up: Assignment statements

4.7.2.2 Annotated assignment statements
.......................................

*note Annotation: 712. assignment is the combination, in a single
statement, of a variable or attribute annotation and an optional
assignment statement:

     annotated_assignment_stmt ::= augtarget ":" expression
                                   ["=" (starred_expression | yield_expression)]

The difference from normal *note Assignment statements: 16a2. is that
only single target is allowed.

For simple names as assignment targets, if in class or module scope, the
annotations are evaluated and stored in a special class or module
attribute ‘__annotations__’ that is a dictionary mapping from variable
names (mangled if private) to evaluated annotations.  This attribute is
writable and is automatically created at the start of class or module
body execution, if annotations are found statically.

For expressions as assignment targets, the annotations are evaluated if
in class or module scope, but not stored.

If a name is annotated in a function scope, then this name is local for
that scope.  Annotations are never evaluated and stored in function
scopes.

If the right hand side is present, an annotated assignment performs the
actual assignment before evaluating annotations (where applicable).  If
the right hand side is not present for an expression target, then the
interpreter evaluates the target except for the last *note
__setitem__(): d2a. or *note __setattr__(): eee. call.

See also
........

PEP 526(1) - Syntax for Variable Annotations

     The proposal that added syntax for annotating the types of
     variables (including class variables and instance variables),
     instead of expressing them through comments.

PEP 484(2) - Type hints

     The proposal that added the *note typing: 122. module to provide a
     standard syntax for type annotations that can be used in static
     analysis tools and IDEs.

Changed in version 3.8: Now annotated assignments allow same expressions
in the right hand side as the regular assignments.  Previously, some
expressions (like un-parenthesized tuple expressions) caused a syntax
error.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0526

   (2) https://www.python.org/dev/peps/pep-0484


File: python.info,  Node: The assert statement,  Next: The pass statement,  Prev: Assignment statements,  Up: Simple statements

4.7.3 The ‘assert’ statement
----------------------------

Assert statements are a convenient way to insert debugging assertions
into a program:

     assert_stmt ::= "assert" expression ["," expression]

The simple form, ‘assert expression’, is equivalent to

     if __debug__:
         if not expression: raise AssertionError

The extended form, ‘assert expression1, expression2’, is equivalent to

     if __debug__:
         if not expression1: raise AssertionError(expression2)

These equivalences assume that *note __debug__: 1137. and *note
AssertionError: 240. refer to the built-in variables with those names.
In the current implementation, the built-in variable *note __debug__:
1137. is ‘True’ under normal circumstances, ‘False’ when optimization is
requested (command line option *note -O: 77e.).  The current code
generator emits no code for an assert statement when optimization is
requested at compile time.  Note that it is unnecessary to include the
source code for the expression that failed in the error message; it will
be displayed as part of the stack trace.

Assignments to *note __debug__: 1137. are illegal.  The value for the
built-in variable is determined when the interpreter starts.


File: python.info,  Node: The pass statement,  Next: The del statement<2>,  Prev: The assert statement,  Up: Simple statements

4.7.4 The ‘pass’ statement
--------------------------

     pass_stmt ::= "pass"

*note pass: 1374. is a null operation — when it is executed, nothing
happens.  It is useful as a placeholder when a statement is required
syntactically, but no code needs to be executed, for example:

     def f(arg): pass    # a function that does nothing (yet)

     class C: pass       # a class with no methods (yet)


File: python.info,  Node: The del statement<2>,  Next: The return statement,  Prev: The pass statement,  Up: Simple statements

4.7.5 The ‘del’ statement
-------------------------

     del_stmt ::= "del" target_list

Deletion is recursively defined very similar to the way assignment is
defined.  Rather than spelling it out in full details, here are some
hints.

Deletion of a target list recursively deletes each target, from left to
right.

Deletion of a name removes the binding of that name from the local or
global namespace, depending on whether the name occurs in a *note
global: 1378. statement in the same code block.  If the name is unbound,
a *note NameError: e40. exception will be raised.

Deletion of attribute references, subscriptions and slicings is passed
to the primary object involved; deletion of a slicing is in general
equivalent to assignment of an empty slice of the right type (but even
this is determined by the sliced object).

Changed in version 3.2: Previously it was illegal to delete a name from
the local namespace if it occurs as a free variable in a nested block.


File: python.info,  Node: The return statement,  Next: The yield statement,  Prev: The del statement<2>,  Up: Simple statements

4.7.6 The ‘return’ statement
----------------------------

     return_stmt ::= "return" [expression_list]

*note return: 2c8. may only occur syntactically nested in a function
definition, not within a nested class definition.

If an expression list is present, it is evaluated, else ‘None’ is
substituted.

*note return: 2c8. leaves the current function call with the expression
list (or ‘None’) as return value.

When *note return: 2c8. passes control out of a *note try: e37.
statement with a *note finally: 2bc. clause, that ‘finally’ clause is
executed before really leaving the function.

In a generator function, the *note return: 2c8. statement indicates that
the generator is done and will cause *note StopIteration: 582. to be
raised.  The returned value (if any) is used as an argument to construct
*note StopIteration: 582. and becomes the ‘StopIteration.value’
attribute.

In an asynchronous generator function, an empty *note return: 2c8.
statement indicates that the asynchronous generator is done and will
cause *note StopAsyncIteration: 114a. to be raised.  A non-empty
‘return’ statement is a syntax error in an asynchronous generator
function.


File: python.info,  Node: The yield statement,  Next: The raise statement,  Prev: The return statement,  Up: Simple statements

4.7.7 The ‘yield’ statement
---------------------------

     yield_stmt ::= yield_expression

A *note yield: 2c7. statement is semantically equivalent to a *note
yield expression: 163d.  The yield statement can be used to omit the
parentheses that would otherwise be required in the equivalent yield
expression statement.  For example, the yield statements

     yield <expr>
     yield from <expr>

are equivalent to the yield expression statements

     (yield <expr>)
     (yield from <expr>)

Yield expressions and statements are only used when defining a *note
generator: a83. function, and are only used in the body of the generator
function.  Using yield in a function definition is sufficient to cause
that definition to create a generator function instead of a normal
function.

For full details of *note yield: 2c7. semantics, refer to the *note
Yield expressions: 163d. section.


File: python.info,  Node: The raise statement,  Next: The break statement,  Prev: The yield statement,  Up: Simple statements

4.7.8 The ‘raise’ statement
---------------------------

     raise_stmt ::= "raise" [expression ["from" expression]]

If no expressions are present, *note raise: d0a. re-raises the last
exception that was active in the current scope.  If no exception is
active in the current scope, a *note RuntimeError: 3dc. exception is
raised indicating that this is an error.

Otherwise, *note raise: d0a. evaluates the first expression as the
exception object.  It must be either a subclass or an instance of *note
BaseException: 2db.  If it is a class, the exception instance will be
obtained when needed by instantiating the class with no arguments.

The `type' of the exception is the exception instance’s class, the
`value' is the instance itself.

A traceback object is normally created automatically when an exception
is raised and attached to it as the ‘__traceback__’ attribute, which is
writable.  You can create an exception and set your own traceback in one
step using the ‘with_traceback()’ exception method (which returns the
same exception instance, with its traceback set to its argument), like
so:

     raise Exception("foo occurred").with_traceback(tracebackobj)

The ‘from’ clause is used for exception chaining: if given, the second
`expression' must be another exception class or instance.  If the second
expression is an exception instance, it will be attached to the raised
exception as the ‘__cause__’ attribute (which is writable).  If the
expression is an exception class, the class will be instantiated and the
resulting exception instance will be attached to the raised exception as
the ‘__cause__’ attribute.  If the raised exception is not handled, both
exceptions will be printed:

     >>> try:
     ...     print(1 / 0)
     ... except Exception as exc:
     ...     raise RuntimeError("Something bad happened") from exc
     ...
     Traceback (most recent call last):
       File "<stdin>", line 2, in <module>
     ZeroDivisionError: division by zero

     The above exception was the direct cause of the following exception:

     Traceback (most recent call last):
       File "<stdin>", line 4, in <module>
     RuntimeError: Something bad happened

A similar mechanism works implicitly if an exception is raised inside an
exception handler or a *note finally: 2bc. clause: the previous
exception is then attached as the new exception’s ‘__context__’
attribute:

     >>> try:
     ...     print(1 / 0)
     ... except:
     ...     raise RuntimeError("Something bad happened")
     ...
     Traceback (most recent call last):
       File "<stdin>", line 2, in <module>
     ZeroDivisionError: division by zero

     During handling of the above exception, another exception occurred:

     Traceback (most recent call last):
       File "<stdin>", line 4, in <module>
     RuntimeError: Something bad happened

Exception chaining can be explicitly suppressed by specifying *note
None: 203. in the ‘from’ clause:

     >>> try:
     ...     print(1 / 0)
     ... except:
     ...     raise RuntimeError("Something bad happened") from None
     ...
     Traceback (most recent call last):
       File "<stdin>", line 4, in <module>
     RuntimeError: Something bad happened

Additional information on exceptions can be found in section *note
Exceptions: 15e3, and information about handling exceptions is in
section *note The try statement: e37.

Changed in version 3.3: *note None: 203. is now permitted as ‘Y’ in
‘raise X from Y’.

New in version 3.3: The ‘__suppress_context__’ attribute to suppress
automatic display of the exception context.


File: python.info,  Node: The break statement,  Next: The continue statement,  Prev: The raise statement,  Up: Simple statements

4.7.9 The ‘break’ statement
---------------------------

     break_stmt ::= "break"

*note break: 3fa. may only occur syntactically nested in a *note for:
cfa. or *note while: 1361. loop, but not nested in a function or class
definition within that loop.

It terminates the nearest enclosing loop, skipping the optional ‘else’
clause if the loop has one.

If a *note for: cfa. loop is terminated by *note break: 3fa, the loop
control target keeps its current value.

When *note break: 3fa. passes control out of a *note try: e37. statement
with a *note finally: 2bc. clause, that ‘finally’ clause is executed
before really leaving the loop.


File: python.info,  Node: The continue statement,  Next: The import statement,  Prev: The break statement,  Up: Simple statements

4.7.10 The ‘continue’ statement
-------------------------------

     continue_stmt ::= "continue"

*note continue: 2bb. may only occur syntactically nested in a *note for:
cfa. or *note while: 1361. loop, but not nested in a function or class
definition within that loop.  It continues with the next cycle of the
nearest enclosing loop.

When *note continue: 2bb. passes control out of a *note try: e37.
statement with a *note finally: 2bc. clause, that ‘finally’ clause is
executed before really starting the next loop cycle.


File: python.info,  Node: The import statement,  Next: The global statement,  Prev: The continue statement,  Up: Simple statements

4.7.11 The ‘import’ statement
-----------------------------

     import_stmt     ::= "import" module ["as" identifier] ("," module ["as" identifier])*
                         | "from" relative_module "import" identifier ["as" identifier]
                         ("," identifier ["as" identifier])*
                         | "from" relative_module "import" "(" identifier ["as" identifier]
                         ("," identifier ["as" identifier])* [","] ")"
                         | "from" relative_module "import" "*"
     module          ::= (identifier ".")* identifier
     relative_module ::= "."* module | "."+

The basic import statement (no *note from: d0d. clause) is executed in
two steps:

  1. find a module, loading and initializing it if necessary

  2. define a name or names in the local namespace for the scope where
     the *note import: ce7. statement occurs.

When the statement contains multiple clauses (separated by commas) the
two steps are carried out separately for each clause, just as though the
clauses had been separated out into individual import statements.

The details of the first step, finding and loading modules are described
in greater detail in the section on the *note import system: 1561, which
also describes the various types of packages and modules that can be
imported, as well as all the hooks that can be used to customize the
import system.  Note that failures in this step may indicate either that
the module could not be located, `or' that an error occurred while
initializing the module, which includes execution of the module’s code.

If the requested module is retrieved successfully, it will be made
available in the local namespace in one of three ways:

   * If the module name is followed by ‘as’, then the name following
     ‘as’ is bound directly to the imported module.

   * If no other name is specified, and the module being imported is a
     top level module, the module’s name is bound in the local namespace
     as a reference to the imported module

   * If the module being imported is `not' a top level module, then the
     name of the top level package that contains the module is bound in
     the local namespace as a reference to the top level package.  The
     imported module must be accessed using its full qualified name
     rather than directly

The *note from: d0d. form uses a slightly more complex process:

  1. find the module specified in the *note from: d0d. clause, loading
     and initializing it if necessary;

  2. for each of the identifiers specified in the *note import: ce7.
     clauses:

       1. check if the imported module has an attribute by that name

       2. if not, attempt to import a submodule with that name and then
          check the imported module again for that attribute

       3. if the attribute is not found, *note ImportError: 16c. is
          raised.

       4. otherwise, a reference to that value is stored in the local
          namespace, using the name in the ‘as’ clause if it is present,
          otherwise using the attribute name

Examples:

     import foo                 # foo imported and bound locally
     import foo.bar.baz         # foo.bar.baz imported, foo bound locally
     import foo.bar.baz as fbb  # foo.bar.baz imported and bound as fbb
     from foo.bar import baz    # foo.bar.baz imported and bound as baz
     from foo import attr       # foo imported and foo.attr bound as attr

If the list of identifiers is replaced by a star (‘'*'’), all public
names defined in the module are bound in the local namespace for the
scope where the *note import: ce7. statement occurs.

The `public names' defined by a module are determined by checking the
module’s namespace for a variable named ‘__all__’; if defined, it must
be a sequence of strings which are names defined or imported by that
module.  The names given in ‘__all__’ are all considered public and are
required to exist.  If ‘__all__’ is not defined, the set of public names
includes all names found in the module’s namespace which do not begin
with an underscore character (‘'_'’).  ‘__all__’ should contain the
entire public API. It is intended to avoid accidentally exporting items
that are not part of the API (such as library modules which were
imported and used within the module).

The wild card form of import — ‘from module import *’ — is only allowed
at the module level.  Attempting to use it in class or function
definitions will raise a *note SyntaxError: 55a.

When specifying what module to import you do not have to specify the
absolute name of the module.  When a module or package is contained
within another package it is possible to make a relative import within
the same top package without having to mention the package name.  By
using leading dots in the specified module or package after *note from:
d0d. you can specify how high to traverse up the current package
hierarchy without specifying exact names.  One leading dot means the
current package where the module making the import exists.  Two dots
means up one package level.  Three dots is up two levels, etc.  So if
you execute ‘from . import mod’ from a module in the ‘pkg’ package then
you will end up importing ‘pkg.mod’.  If you execute ‘from ..subpkg2
import mod’ from within ‘pkg.subpkg1’ you will import ‘pkg.subpkg2.mod’.
The specification for relative imports is contained in the *note Package
Relative Imports: 1611. section.

*note importlib.import_module(): be6. is provided to support
applications that determine dynamically the modules to be loaded.

Raises an *note auditing event: fa1. ‘import’ with arguments ‘module’,
‘filename’, ‘sys.path’, ‘sys.meta_path’, ‘sys.path_hooks’.

* Menu:

* Future statements::


File: python.info,  Node: Future statements,  Up: The import statement

4.7.11.1 Future statements
..........................

A `future statement' is a directive to the compiler that a particular
module should be compiled using syntax or semantics that will be
available in a specified future release of Python where the feature
becomes standard.

The future statement is intended to ease migration to future versions of
Python that introduce incompatible changes to the language.  It allows
use of the new features on a per-module basis before the release in
which the feature becomes standard.

     future_stmt ::= "from" "__future__" "import" feature ["as" identifier]
                     ("," feature ["as" identifier])*
                     | "from" "__future__" "import" "(" feature ["as" identifier]
                     ("," feature ["as" identifier])* [","] ")"
     feature     ::= identifier

A future statement must appear near the top of the module.  The only
lines that can appear before a future statement are:

   * the module docstring (if any),

   * comments,

   * blank lines, and

   * other future statements.

The only feature that requires using the future statement is
‘annotations’ (see PEP 563(1)).

All historical features enabled by the future statement are still
recognized by Python 3.  The list includes ‘absolute_import’,
‘division’, ‘generators’, ‘generator_stop’, ‘unicode_literals’,
‘print_function’, ‘nested_scopes’ and ‘with_statement’.  They are all
redundant because they are always enabled, and only kept for backwards
compatibility.

A future statement is recognized and treated specially at compile time:
Changes to the semantics of core constructs are often implemented by
generating different code.  It may even be the case that a new feature
introduces new incompatible syntax (such as a new reserved word), in
which case the compiler may need to parse the module differently.  Such
decisions cannot be pushed off until runtime.

For any given release, the compiler knows which feature names have been
defined, and raises a compile-time error if a future statement contains
a feature not known to it.

The direct runtime semantics are the same as for any import statement:
there is a standard module *note __future__: 0, described later, and it
will be imported in the usual way at the time the future statement is
executed.

The interesting runtime semantics depend on the specific feature enabled
by the future statement.

Note that there is nothing special about the statement:

     import __future__ [as name]

That is not a future statement; it’s an ordinary import statement with
no special semantics or syntax restrictions.

Code compiled by calls to the built-in functions *note exec(): d0c. and
*note compile(): 2e7. that occur in a module ‘M’ containing a future
statement will, by default, use the new syntax or semantics associated
with the future statement.  This can be controlled by optional arguments
to *note compile(): 2e7. — see the documentation of that function for
details.

A future statement typed at an interactive interpreter prompt will take
effect for the rest of the interpreter session.  If an interpreter is
started with the *note -i: ee1. option, is passed a script name to
execute, and the script includes a future statement, it will be in
effect in the interactive session started after the script is executed.

See also
........

PEP 236(2) - Back to the __future__

     The original proposal for the __future__ mechanism.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0563

   (2) https://www.python.org/dev/peps/pep-0236


File: python.info,  Node: The global statement,  Next: The nonlocal statement,  Prev: The import statement,  Up: Simple statements

4.7.12 The ‘global’ statement
-----------------------------

     global_stmt ::= "global" identifier ("," identifier)*

The *note global: 1378. statement is a declaration which holds for the
entire current code block.  It means that the listed identifiers are to
be interpreted as globals.  It would be impossible to assign to a global
variable without ‘global’, although free variables may refer to globals
without being declared global.

Names listed in a *note global: 1378. statement must not be used in the
same code block textually preceding that ‘global’ statement.

Names listed in a *note global: 1378. statement must not be defined as
formal parameters or in a *note for: cfa. loop control target, *note
class: d32. definition, function definition, *note import: ce7.
statement, or variable annotation.

`CPython implementation detail:' The current implementation does not
enforce some of these restrictions, but programs should not abuse this
freedom, as future implementations may enforce them or silently change
the meaning of the program.

`Programmer’s note:' *note global: 1378. is a directive to the parser.
It applies only to code parsed at the same time as the ‘global’
statement.  In particular, a ‘global’ statement contained in a string or
code object supplied to the built-in *note exec(): d0c. function does
not affect the code block `containing' the function call, and code
contained in such a string is unaffected by ‘global’ statements in the
code containing the function call.  The same applies to the *note
eval(): c61. and *note compile(): 2e7. functions.


File: python.info,  Node: The nonlocal statement,  Prev: The global statement,  Up: Simple statements

4.7.13 The ‘nonlocal’ statement
-------------------------------

     nonlocal_stmt ::= "nonlocal" identifier ("," identifier)*

The *note nonlocal: d07. statement causes the listed identifiers to
refer to previously bound variables in the nearest enclosing scope
excluding globals.  This is important because the default behavior for
binding is to search the local namespace first.  The statement allows
encapsulated code to rebind variables outside of the local scope besides
the global (module) scope.

Names listed in a *note nonlocal: d07. statement, unlike those listed in
a *note global: 1378. statement, must refer to pre-existing bindings in
an enclosing scope (the scope in which a new binding should be created
cannot be determined unambiguously).

Names listed in a *note nonlocal: d07. statement must not collide with
pre-existing bindings in the local scope.

See also
........

PEP 3104(1) - Access to Names in Outer Scopes

     The specification for the *note nonlocal: d07. statement.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3104


File: python.info,  Node: Compound statements,  Next: Top-level components,  Prev: Simple statements,  Up: The Python Language Reference

4.8 Compound statements
=======================

Compound statements contain (groups of) other statements; they affect or
control the execution of those other statements in some way.  In
general, compound statements span multiple lines, although in simple
incarnations a whole compound statement may be contained in one line.

The *note if: eab, *note while: 1361. and *note for: cfa. statements
implement traditional control flow constructs.  *note try: e37.
specifies exception handlers and/or cleanup code for a group of
statements, while the *note with: 7da. statement allows the execution of
initialization and finalization code around a block of code.  Function
and class definitions are also syntactically compound statements.

A compound statement consists of one or more ‘clauses.’ A clause
consists of a header and a ‘suite.’ The clause headers of a particular
compound statement are all at the same indentation level.  Each clause
header begins with a uniquely identifying keyword and ends with a colon.
A suite is a group of statements controlled by a clause.  A suite can be
one or more semicolon-separated simple statements on the same line as
the header, following the header’s colon, or it can be one or more
indented statements on subsequent lines.  Only the latter form of a
suite can contain nested compound statements; the following is illegal,
mostly because it wouldn’t be clear to which *note if: eab. clause a
following *note else: 1368. clause would belong:

     if test1: if test2: print(x)

Also note that the semicolon binds tighter than the colon in this
context, so that in the following example, either all or none of the
*note print(): 971. calls are executed:

     if x < y < z: print(x); print(y); print(z)

Summarizing:

     compound_stmt ::= if_stmt
                       | while_stmt
                       | for_stmt
                       | try_stmt
                       | with_stmt
                       | funcdef
                       | classdef
                       | async_with_stmt
                       | async_for_stmt
                       | async_funcdef
     suite         ::= stmt_list NEWLINE | NEWLINE INDENT statement+ DEDENT
     statement     ::= stmt_list NEWLINE | compound_stmt
     stmt_list     ::= simple_stmt (";" simple_stmt)* [";"]

Note that statements always end in a ‘NEWLINE’ possibly followed by a
‘DEDENT’.  Also note that optional continuation clauses always begin
with a keyword that cannot start a statement, thus there are no
ambiguities (the ‘dangling *note else: 1368.’ problem is solved in
Python by requiring nested *note if: eab. statements to be indented).

The formatting of the grammar rules in the following sections places
each clause on a separate line for clarity.
* Menu:

* The if statement::
* The while statement::
* The for statement::
* The try statement::
* The with statement::
* Function definitions::
* Class definitions::
* Coroutines: Coroutines<2>.


File: python.info,  Node: The if statement,  Next: The while statement,  Up: Compound statements

4.8.1 The ‘if’ statement
------------------------

The *note if: eab. statement is used for conditional execution:

     if_stmt ::= "if" assignment_expression ":" suite
                 ("elif" assignment_expression ":" suite)*
                 ["else" ":" suite]

It selects exactly one of the suites by evaluating the expressions one
by one until one is found to be true (see section *note Boolean
operations: 1682. for the definition of true and false); then that suite
is executed (and no other part of the *note if: eab. statement is
executed or evaluated).  If all expressions are false, the suite of the
*note else: 1368. clause, if present, is executed.


File: python.info,  Node: The while statement,  Next: The for statement,  Prev: The if statement,  Up: Compound statements

4.8.2 The ‘while’ statement
---------------------------

The *note while: 1361. statement is used for repeated execution as long
as an expression is true:

     while_stmt ::= "while" assignment_expression ":" suite
                    ["else" ":" suite]

This repeatedly tests the expression and, if it is true, executes the
first suite; if the expression is false (which may be the first time it
is tested) the suite of the ‘else’ clause, if present, is executed and
the loop terminates.

A *note break: 3fa. statement executed in the first suite terminates the
loop without executing the ‘else’ clause’s suite.  A *note continue:
2bb. statement executed in the first suite skips the rest of the suite
and goes back to testing the expression.


File: python.info,  Node: The for statement,  Next: The try statement,  Prev: The while statement,  Up: Compound statements

4.8.3 The ‘for’ statement
-------------------------

The *note for: cfa. statement is used to iterate over the elements of a
sequence (such as a string, tuple or list) or other iterable object:

     for_stmt ::= "for" target_list "in" expression_list ":" suite
                  ["else" ":" suite]

The expression list is evaluated once; it should yield an iterable
object.  An iterator is created for the result of the ‘expression_list’.
The suite is then executed once for each item provided by the iterator,
in the order returned by the iterator.  Each item in turn is assigned to
the target list using the standard rules for assignments (see *note
Assignment statements: 16a2.), and then the suite is executed.  When the
items are exhausted (which is immediately when the sequence is empty or
an iterator raises a *note StopIteration: 582. exception), the suite in
the ‘else’ clause, if present, is executed, and the loop terminates.

A *note break: 3fa. statement executed in the first suite terminates the
loop without executing the ‘else’ clause’s suite.  A *note continue:
2bb. statement executed in the first suite skips the rest of the suite
and continues with the next item, or with the ‘else’ clause if there is
no next item.

The for-loop makes assignments to the variables in the target list.
This overwrites all previous assignments to those variables including
those made in the suite of the for-loop:

     for i in range(10):
         print(i)
         i = 5             # this will not affect the for-loop
                           # because i will be overwritten with the next
                           # index in the range

Names in the target list are not deleted when the loop is finished, but
if the sequence is empty, they will not have been assigned to at all by
the loop.  Hint: the built-in function *note range(): 1f5. returns an
iterator of integers suitable to emulate the effect of Pascal’s ‘for i
:= a to b do’; e.g., ‘list(range(3))’ returns the list ‘[0, 1, 2]’.

     Note: 
     There is a subtlety when the sequence is being modified by the loop
     (this can only occur for mutable sequences, e.g.  lists).  An
     internal counter is used to keep track of which item is used next,
     and this is incremented on each iteration.  When this counter has
     reached the length of the sequence the loop terminates.  This means
     that if the suite deletes the current (or a previous) item from the
     sequence, the next item will be skipped (since it gets the index of
     the current item which has already been treated).  Likewise, if the
     suite inserts an item in the sequence before the current item, the
     current item will be treated again the next time through the loop.
     This can lead to nasty bugs that can be avoided by making a
     temporary copy using a slice of the whole sequence, e.g.,

          for x in a[:]:
              if x < 0: a.remove(x)


File: python.info,  Node: The try statement,  Next: The with statement,  Prev: The for statement,  Up: Compound statements

4.8.4 The ‘try’ statement
-------------------------

The *note try: e37. statement specifies exception handlers and/or
cleanup code for a group of statements:

     try_stmt  ::= try1_stmt | try2_stmt
     try1_stmt ::= "try" ":" suite
                   ("except" [expression ["as" identifier]] ":" suite)+
                   ["else" ":" suite]
                   ["finally" ":" suite]
     try2_stmt ::= "try" ":" suite
                   "finally" ":" suite

The *note except: c10. clause(s) specify one or more exception handlers.
When no exception occurs in the *note try: e37. clause, no exception
handler is executed.  When an exception occurs in the ‘try’ suite, a
search for an exception handler is started.  This search inspects the
except clauses in turn until one is found that matches the exception.
An expression-less except clause, if present, must be last; it matches
any exception.  For an except clause with an expression, that expression
is evaluated, and the clause matches the exception if the resulting
object is “compatible” with the exception.  An object is compatible with
an exception if it is the class or a base class of the exception object,
or a tuple containing an item that is the class or a base class of the
exception object.

If no except clause matches the exception, the search for an exception
handler continues in the surrounding code and on the invocation stack.
(1)

If the evaluation of an expression in the header of an except clause
raises an exception, the original search for a handler is canceled and a
search starts for the new exception in the surrounding code and on the
call stack (it is treated as if the entire *note try: e37. statement
raised the exception).

When a matching except clause is found, the exception is assigned to the
target specified after the ‘as’ keyword in that except clause, if
present, and the except clause’s suite is executed.  All except clauses
must have an executable block.  When the end of this block is reached,
execution continues normally after the entire try statement.  (This
means that if two nested handlers exist for the same exception, and the
exception occurs in the try clause of the inner handler, the outer
handler will not handle the exception.)

When an exception has been assigned using ‘as target’, it is cleared at
the end of the except clause.  This is as if

     except E as N:
         foo

was translated to

     except E as N:
         try:
             foo
         finally:
             del N

This means the exception must be assigned to a different name to be able
to refer to it after the except clause.  Exceptions are cleared because
with the traceback attached to them, they form a reference cycle with
the stack frame, keeping all locals in that frame alive until the next
garbage collection occurs.

Before an except clause’s suite is executed, details about the exception
are stored in the *note sys: fd. module and can be accessed via *note
sys.exc_info(): d27.  *note sys.exc_info(): d27. returns a 3-tuple
consisting of the exception class, the exception instance and a
traceback object (see section *note The standard type hierarchy: 1553.)
identifying the point in the program where the exception occurred.
*note sys.exc_info(): d27. values are restored to their previous values
(before the call) when returning from a function that handled an
exception.

The optional ‘else’ clause is executed if the control flow leaves the
*note try: e37. suite, no exception was raised, and no *note return:
2c8, *note continue: 2bb, or *note break: 3fa. statement was executed.
Exceptions in the ‘else’ clause are not handled by the preceding *note
except: c10. clauses.

If *note finally: 2bc. is present, it specifies a ‘cleanup’ handler.
The *note try: e37. clause is executed, including any *note except: c10.
and ‘else’ clauses.  If an exception occurs in any of the clauses and is
not handled, the exception is temporarily saved.  The ‘finally’ clause
is executed.  If there is a saved exception it is re-raised at the end
of the ‘finally’ clause.  If the ‘finally’ clause raises another
exception, the saved exception is set as the context of the new
exception.  If the ‘finally’ clause executes a *note return: 2c8, *note
break: 3fa. or *note continue: 2bb. statement, the saved exception is
discarded:

     >>> def f():
     ...     try:
     ...         1/0
     ...     finally:
     ...         return 42
     ...
     >>> f()
     42

The exception information is not available to the program during
execution of the *note finally: 2bc. clause.

When a *note return: 2c8, *note break: 3fa. or *note continue: 2bb.
statement is executed in the *note try: e37. suite of a ‘try’…‘finally’
statement, the *note finally: 2bc. clause is also executed ‘on the way
out.’

The return value of a function is determined by the last *note return:
2c8. statement executed.  Since the *note finally: 2bc. clause always
executes, a ‘return’ statement executed in the ‘finally’ clause will
always be the last one executed:

     >>> def foo():
     ...     try:
     ...         return 'try'
     ...     finally:
     ...         return 'finally'
     ...
     >>> foo()
     'finally'

Additional information on exceptions can be found in section *note
Exceptions: 15e3, and information on using the *note raise: d0a.
statement to generate exceptions may be found in section *note The raise
statement: d0a.

Changed in version 3.8: Prior to Python 3.8, a *note continue: 2bb.
statement was illegal in the *note finally: 2bc. clause due to a problem
with the implementation.

   ---------- Footnotes ----------

   (1) (1) The exception is propagated to the invocation stack unless
there is a *note finally: 2bc. clause which happens to raise another
exception.  That new exception causes the old one to be lost.


File: python.info,  Node: The with statement,  Next: Function definitions,  Prev: The try statement,  Up: Compound statements

4.8.5 The ‘with’ statement
--------------------------

The *note with: 7da. statement is used to wrap the execution of a block
with methods defined by a context manager (see section *note With
Statement Context Managers: 15c4.).  This allows common *note try:
e37.…*note except: c10.…*note finally: 2bc. usage patterns to be
encapsulated for convenient reuse.

     with_stmt ::= "with" with_item ("," with_item)* ":" suite
     with_item ::= expression ["as" target]

The execution of the *note with: 7da. statement with one “item” proceeds
as follows:

  1. The context expression (the expression given in the *note
     with_item: 16e0.) is evaluated to obtain a context manager.

  2. The context manager’s *note __enter__(): d5d. is loaded for later
     use.

  3. The context manager’s *note __exit__(): d5e. is loaded for later
     use.

  4. The context manager’s *note __enter__(): d5d. method is invoked.

  5. If a target was included in the *note with: 7da. statement, the
     return value from *note __enter__(): d5d. is assigned to it.

          Note: The *note with: 7da. statement guarantees that if the
          *note __enter__(): d5d. method returns without an error, then
          *note __exit__(): d5e. will always be called.  Thus, if an
          error occurs during the assignment to the target list, it will
          be treated the same as an error occurring within the suite
          would be.  See step 6 below.

  6. The suite is executed.

  7. The context manager’s *note __exit__(): d5e. method is invoked.  If
     an exception caused the suite to be exited, its type, value, and
     traceback are passed as arguments to *note __exit__(): d5e.
     Otherwise, three *note None: 203. arguments are supplied.

     If the suite was exited due to an exception, and the return value
     from the *note __exit__(): d5e. method was false, the exception is
     reraised.  If the return value was true, the exception is
     suppressed, and execution continues with the statement following
     the *note with: 7da. statement.

     If the suite was exited for any reason other than an exception, the
     return value from *note __exit__(): d5e. is ignored, and execution
     proceeds at the normal location for the kind of exit that was
     taken.

The following code:

     with EXPRESSION as TARGET:
         SUITE

is semantically equivalent to:

     manager = (EXPRESSION)
     enter = type(manager).__enter__
     exit = type(manager).__exit__
     value = enter(manager)
     hit_except = False

     try:
         TARGET = value
         SUITE
     except:
         hit_except = True
         if not exit(manager, *sys.exc_info()):
             raise
     finally:
         if not hit_except:
             exit(manager, None, None, None)

With more than one item, the context managers are processed as if
multiple *note with: 7da. statements were nested:

     with A() as a, B() as b:
         SUITE

is semantically equivalent to:

     with A() as a:
         with B() as b:
             SUITE

Changed in version 3.1: Support for multiple context expressions.

See also
........

PEP 343(1) - The “with” statement

     The specification, background, and examples for the Python *note
     with: 7da. statement.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0343


File: python.info,  Node: Function definitions,  Next: Class definitions,  Prev: The with statement,  Up: Compound statements

4.8.6 Function definitions
--------------------------

A function definition defines a user-defined function object (see
section *note The standard type hierarchy: 1553.):

     funcdef                   ::= [decorators] "def" funcname "(" [parameter_list] ")"
                                   ["->" expression] ":" suite
     decorators                ::= decorator+
     decorator                 ::= "@" assignment_expression NEWLINE
     parameter_list            ::= defparameter ("," defparameter)* "," "/" ["," [parameter_list_no_posonly]]
                                     | parameter_list_no_posonly
     parameter_list_no_posonly ::= defparameter ("," defparameter)* ["," [parameter_list_starargs]]
                                   | parameter_list_starargs
     parameter_list_starargs   ::= "*" [parameter] ("," defparameter)* ["," ["**" parameter [","]]]
                                   | "**" parameter [","]
     parameter                 ::= identifier [":" expression]
     defparameter              ::= parameter ["=" expression]
     funcname                  ::= identifier

A function definition is an executable statement.  Its execution binds
the function name in the current local namespace to a function object (a
wrapper around the executable code for the function).  This function
object contains a reference to the current global namespace as the
global namespace to be used when the function is called.

The function definition does not execute the function body; this gets
executed only when the function is called.  (1)

A function definition may be wrapped by one or more *note decorator:
174. expressions.  Decorator expressions are evaluated when the function
is defined, in the scope that contains the function definition.  The
result must be a callable, which is invoked with the function object as
the only argument.  The returned value is bound to the function name
instead of the function object.  Multiple decorators are applied in
nested fashion.  For example, the following code

     @f1(arg)
     @f2
     def func(): pass

is roughly equivalent to

     def func(): pass
     func = f1(arg)(f2(func))

except that the original function is not temporarily bound to the name
‘func’.

Changed in version 3.9: Functions may be decorated with any valid *note
assignment_expression: 168b.  Previously, the grammar was much more
restrictive; see PEP 614(2) for details.

When one or more *note parameters: 1664. have the form `parameter' ‘=’
`expression', the function is said to have “default parameter values.”
For a parameter with a default value, the corresponding *note argument:
165c. may be omitted from a call, in which case the parameter’s default
value is substituted.  If a parameter has a default value, all following
parameters up until the “‘*’” must also have a default value — this is a
syntactic restriction that is not expressed by the grammar.

`Default parameter values are evaluated from left to right when the
function definition is executed.'  This means that the expression is
evaluated once, when the function is defined, and that the same
“pre-computed” value is used for each call.  This is especially
important to understand when a default parameter is a mutable object,
such as a list or a dictionary: if the function modifies the object
(e.g.  by appending an item to a list), the default value is in effect
modified.  This is generally not what was intended.  A way around this
is to use ‘None’ as the default, and explicitly test for it in the body
of the function, e.g.:

     def whats_on_the_telly(penguin=None):
         if penguin is None:
             penguin = []
         penguin.append("property of the zoo")
         return penguin

Function call semantics are described in more detail in section *note
Calls: 73f.  A function call always assigns values to all parameters
mentioned in the parameter list, either from positional arguments, from
keyword arguments, or from default values.  If the form “‘*identifier’”
is present, it is initialized to a tuple receiving any excess positional
parameters, defaulting to the empty tuple.  If the form “‘**identifier’”
is present, it is initialized to a new ordered mapping receiving any
excess keyword arguments, defaulting to a new empty mapping of the same
type.  Parameters after “‘*’” or “‘*identifier’” are keyword-only
parameters and may only be passed by keyword arguments.  Parameters
before “‘/’” are positional-only parameters and may only be passed by
positional arguments.

Changed in version 3.8: The ‘/’ function parameter syntax may be used to
indicate positional-only parameters.  See PEP 570(3) for details.

Parameters may have an *note annotation: 1391. of the form “‘:
expression’” following the parameter name.  Any parameter may have an
annotation, even those of the form ‘*identifier’ or ‘**identifier’.
Functions may have “return” annotation of the form “‘-> expression’”
after the parameter list.  These annotations can be any valid Python
expression.  The presence of annotations does not change the semantics
of a function.  The annotation values are available as values of a
dictionary keyed by the parameters’ names in the ‘__annotations__’
attribute of the function object.  If the ‘annotations’ import from
*note __future__: 0. is used, annotations are preserved as strings at
runtime which enables postponed evaluation.  Otherwise, they are
evaluated when the function definition is executed.  In this case
annotations may be evaluated in a different order than they appear in
the source code.

It is also possible to create anonymous functions (functions not bound
to a name), for immediate use in expressions.  This uses lambda
expressions, described in section *note Lambdas: cf9.  Note that the
lambda expression is merely a shorthand for a simplified function
definition; a function defined in a “*note def: e83.” statement can be
passed around or assigned to another name just like a function defined
by a lambda expression.  The “‘def’” form is actually more powerful
since it allows the execution of multiple statements and annotations.

`Programmer’s note:' Functions are first-class objects.  A “‘def’”
statement executed inside a function definition defines a local function
that can be returned or passed around.  Free variables used in the
nested function can access the local variables of the function
containing the def.  See section *note Naming and binding: 15d9. for
details.

See also
........

PEP 3107(4) - Function Annotations

     The original specification for function annotations.

PEP 484(5) - Type Hints

     Definition of a standard meaning for annotations: type hints.

PEP 526(6) - Syntax for Variable Annotations

     Ability to type hint variable declarations, including class
     variables and instance variables

PEP 563(7) - Postponed Evaluation of Annotations

     Support for forward references within annotations by preserving
     annotations in a string form at runtime instead of eager
     evaluation.

   ---------- Footnotes ----------

   (1) (2) A string literal appearing as the first statement in the
function body is transformed into the function’s ‘__doc__’ attribute and
therefore the function’s *note docstring: 16eb.

   (2) https://www.python.org/dev/peps/pep-0614

   (3) https://www.python.org/dev/peps/pep-0570

   (4) https://www.python.org/dev/peps/pep-3107

   (5) https://www.python.org/dev/peps/pep-0484

   (6) https://www.python.org/dev/peps/pep-0526

   (7) https://www.python.org/dev/peps/pep-0563


File: python.info,  Node: Class definitions,  Next: Coroutines<2>,  Prev: Function definitions,  Up: Compound statements

4.8.7 Class definitions
-----------------------

A class definition defines a class object (see section *note The
standard type hierarchy: 1553.):

     classdef    ::= [decorators] "class" classname [inheritance] ":" suite
     inheritance ::= "(" [argument_list] ")"
     classname   ::= identifier

A class definition is an executable statement.  The inheritance list
usually gives a list of base classes (see *note Metaclasses: 157c. for
more advanced uses), so each item in the list should evaluate to a class
object which allows subclassing.  Classes without an inheritance list
inherit, by default, from the base class *note object: 3d2.; hence,

     class Foo:
         pass

is equivalent to

     class Foo(object):
         pass

The class’s suite is then executed in a new execution frame (see *note
Naming and binding: 15d9.), using a newly created local namespace and
the original global namespace.  (Usually, the suite contains mostly
function definitions.)  When the class’s suite finishes execution, its
execution frame is discarded but its local namespace is saved.  (1) A
class object is then created using the inheritance list for the base
classes and the saved local namespace for the attribute dictionary.  The
class name is bound to this class object in the original local
namespace.

The order in which attributes are defined in the class body is preserved
in the new class’s ‘__dict__’.  Note that this is reliable only right
after the class is created and only for classes that were defined using
the definition syntax.

Class creation can be customized heavily using *note metaclasses: 157c.

Classes can also be decorated: just like when decorating functions,

     @f1(arg)
     @f2
     class Foo: pass

is roughly equivalent to

     class Foo: pass
     Foo = f1(arg)(f2(Foo))

The evaluation rules for the decorator expressions are the same as for
function decorators.  The result is then bound to the class name.

Changed in version 3.9: Classes may be decorated with any valid *note
assignment_expression: 168b.  Previously, the grammar was much more
restrictive; see PEP 614(2) for details.

`Programmer’s note:' Variables defined in the class definition are class
attributes; they are shared by instances.  Instance attributes can be
set in a method with ‘self.name = value’.  Both class and instance
attributes are accessible through the notation “‘self.name’”, and an
instance attribute hides a class attribute with the same name when
accessed in this way.  Class attributes can be used as defaults for
instance attributes, but using mutable values there can lead to
unexpected results.  *note Descriptors: 5e4. can be used to create
instance variables with different implementation details.

See also
........

PEP 3115(3) - Metaclasses in Python 3000

     The proposal that changed the declaration of metaclasses to the
     current syntax, and the semantics for how classes with metaclasses
     are constructed.

PEP 3129(4) - Class Decorators

     The proposal that added class decorators.  Function and method
     decorators were introduced in PEP 318(5).

   ---------- Footnotes ----------

   (1) (3) A string literal appearing as the first statement in the
class body is transformed into the namespace’s ‘__doc__’ item and
therefore the class’s *note docstring: 16eb.

   (2) https://www.python.org/dev/peps/pep-0614

   (3) https://www.python.org/dev/peps/pep-3115

   (4) https://www.python.org/dev/peps/pep-3129

   (5) https://www.python.org/dev/peps/pep-0318


File: python.info,  Node: Coroutines<2>,  Prev: Class definitions,  Up: Compound statements

4.8.8 Coroutines
----------------

New in version 3.5.

* Menu:

* Coroutine function definition::
* The async for statement::
* The async with statement::


File: python.info,  Node: Coroutine function definition,  Next: The async for statement,  Up: Coroutines<2>

4.8.8.1 Coroutine function definition
.....................................

     async_funcdef ::= [decorators] "async" "def" funcname "(" [parameter_list] ")"
                       ["->" expression] ":" suite

Execution of Python coroutines can be suspended and resumed at many
points (see *note coroutine: 18a.).  Inside the body of a coroutine
function, ‘await’ and ‘async’ identifiers become reserved keywords;
*note await: 2d8. expressions, *note async for: 3fd. and *note async
with: 736. can only be used in coroutine function bodies.

Functions defined with ‘async def’ syntax are always coroutine
functions, even if they do not contain ‘await’ or ‘async’ keywords.

It is a *note SyntaxError: 55a. to use a ‘yield from’ expression inside
the body of a coroutine function.

An example of a coroutine function:

     async def func(param1, param2):
         do_stuff()
         await some_coroutine()


File: python.info,  Node: The async for statement,  Next: The async with statement,  Prev: Coroutine function definition,  Up: Coroutines<2>

4.8.8.2 The ‘async for’ statement
.................................

     async_for_stmt ::= "async" for_stmt

An *note asynchronous iterable: 733. provides an ‘__aiter__’ method that
directly returns an *note asynchronous iterator: 738, which can call
asynchronous code in its ‘__anext__’ method.

The ‘async for’ statement allows convenient iteration over asynchronous
iterables.

The following code:

     async for TARGET in ITER:
         SUITE
     else:
         SUITE2

Is semantically equivalent to:

     iter = (ITER)
     iter = type(iter).__aiter__(iter)
     running = True

     while running:
         try:
             TARGET = await type(iter).__anext__(iter)
         except StopAsyncIteration:
             running = False
         else:
             SUITE
     else:
         SUITE2

See also *note __aiter__(): 583. and *note __anext__(): 155f. for
details.

It is a *note SyntaxError: 55a. to use an ‘async for’ statement outside
the body of a coroutine function.


File: python.info,  Node: The async with statement,  Prev: The async for statement,  Up: Coroutines<2>

4.8.8.3 The ‘async with’ statement
..................................

     async_with_stmt ::= "async" with_stmt

An *note asynchronous context manager: 734. is a *note context manager:
661. that is able to suspend execution in its `enter' and `exit'
methods.

The following code:

     async with EXPRESSION as TARGET:
         SUITE

is semantically equivalent to:

     manager = (EXPRESSION)
     aenter = type(manager).__aenter__
     aexit = type(manager).__aexit__
     value = await aenter(manager)
     hit_except = False

     try:
         TARGET = value
         SUITE
     except:
         hit_except = True
         if not await aexit(manager, *sys.exc_info()):
             raise
     finally:
         if not hit_except:
             await aexit(manager, None, None, None)

See also *note __aenter__(): 109a. and *note __aexit__(): 109b. for
details.

It is a *note SyntaxError: 55a. to use an ‘async with’ statement outside
the body of a coroutine function.

See also
........

PEP 492(1) - Coroutines with async and await syntax

     The proposal that made coroutines a proper standalone concept in
     Python, and added supporting syntax.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0492


File: python.info,  Node: Top-level components,  Next: Full Grammar specification,  Prev: Compound statements,  Up: The Python Language Reference

4.9 Top-level components
========================

The Python interpreter can get its input from a number of sources: from
a script passed to it as standard input or as program argument, typed in
interactively, from a module source file, etc.  This chapter gives the
syntax used in these cases.

* Menu:

* Complete Python programs::
* File input::
* Interactive input::
* Expression input::


File: python.info,  Node: Complete Python programs,  Next: File input,  Up: Top-level components

4.9.1 Complete Python programs
------------------------------

While a language specification need not prescribe how the language
interpreter is invoked, it is useful to have a notion of a complete
Python program.  A complete Python program is executed in a minimally
initialized environment: all built-in and standard modules are
available, but none have been initialized, except for *note sys: fd.
(various system services), *note builtins: 12. (built-in functions,
exceptions and ‘None’) and *note __main__: 1.  The latter is used to
provide the local and global namespace for execution of the complete
program.

The syntax for a complete Python program is that for file input,
described in the next section.

The interpreter may also be invoked in interactive mode; in this case,
it does not read and execute a complete program but reads and executes
one statement (possibly compound) at a time.  The initial environment is
identical to that of a complete program; each statement is executed in
the namespace of *note __main__: 1.

A complete program can be passed to the interpreter in three forms: with
the *note -c: 1340. `string' command line option, as a file passed as
the first command line argument, or as standard input.  If the file or
standard input is a tty device, the interpreter enters interactive mode;
otherwise, it executes the file as a complete program.


File: python.info,  Node: File input,  Next: Interactive input,  Prev: Complete Python programs,  Up: Top-level components

4.9.2 File input
----------------

All input read from non-interactive files has the same form:

     file_input ::= (NEWLINE | statement)*

This syntax is used in the following situations:

   * when parsing a complete Python program (from a file or from a
     string);

   * when parsing a module;

   * when parsing a string passed to the *note exec(): d0c. function;


File: python.info,  Node: Interactive input,  Next: Expression input,  Prev: File input,  Up: Top-level components

4.9.3 Interactive input
-----------------------

Input in interactive mode is parsed using the following grammar:

     interactive_input ::= [stmt_list] NEWLINE | compound_stmt NEWLINE

Note that a (top-level) compound statement must be followed by a blank
line in interactive mode; this is needed to help the parser detect the
end of the input.


File: python.info,  Node: Expression input,  Prev: Interactive input,  Up: Top-level components

4.9.4 Expression input
----------------------

*note eval(): c61. is used for expression input.  It ignores leading
whitespace.  The string argument to *note eval(): c61. must have the
following form:

     eval_input ::= expression_list NEWLINE*


File: python.info,  Node: Full Grammar specification,  Prev: Top-level components,  Up: The Python Language Reference

4.10 Full Grammar specification
===============================

This is the full Python grammar, derived directly from the grammar used
to generate the CPython parser (see Grammar/python.gram(1)).  The
version here omits details related to code generation and error
recovery.

The notation is a mixture of EBNF(2) and PEG(3). In particular, ‘&’
followed by a symbol, token or parenthesized group indicates a positive
lookahead (i.e., is required to match but not consumed), while ‘!’
indicates a negative lookahead (i.e., is required _not_ to match).  We
use the ‘|’ separator to mean PEG’s “ordered choice” (written as ‘/’ in
traditional PEG grammars).

     # PEG grammar for Python

     @trailer '''
     void *
     _PyPegen_parse(Parser *p)
     {
         // Initialize keywords
         p->keywords = reserved_keywords;
         p->n_keyword_lists = n_keyword_lists;

         // Run parser
         void *result = NULL;
         if (p->start_rule == Py_file_input) {
             result = file_rule(p);
         } else if (p->start_rule == Py_single_input) {
             result = interactive_rule(p);
         } else if (p->start_rule == Py_eval_input) {
             result = eval_rule(p);
         } else if (p->start_rule == Py_func_type_input) {
             result = func_type_rule(p);
         } else if (p->start_rule == Py_fstring_input) {
             result = fstring_rule(p);
         }

         return result;
     }

     // The end
     '''
     file[mod_ty]: a=[statements] ENDMARKER { _PyPegen_make_module(p, a) }
     interactive[mod_ty]: a=statement_newline { Interactive(a, p->arena) }
     eval[mod_ty]: a=expressions NEWLINE* ENDMARKER { Expression(a, p->arena) }
     func_type[mod_ty]: '(' a=[type_expressions] ')' '->' b=expression NEWLINE* ENDMARKER { FunctionType(a, b, p->arena) }
     fstring[expr_ty]: star_expressions

     # type_expressions allow */** but ignore them
     type_expressions[asdl_seq*]:
         | a=','.expression+ ',' '*' b=expression ',' '**' c=expression {
             _PyPegen_seq_append_to_end(p, CHECK(_PyPegen_seq_append_to_end(p, a, b)), c) }
         | a=','.expression+ ',' '*' b=expression { _PyPegen_seq_append_to_end(p, a, b) }
         | a=','.expression+ ',' '**' b=expression { _PyPegen_seq_append_to_end(p, a, b) }
         | '*' a=expression ',' '**' b=expression {
             _PyPegen_seq_append_to_end(p, CHECK(_PyPegen_singleton_seq(p, a)), b) }
         | '*' a=expression { _PyPegen_singleton_seq(p, a) }
         | '**' a=expression { _PyPegen_singleton_seq(p, a) }
         | ','.expression+

     statements[asdl_seq*]: a=statement+ { _PyPegen_seq_flatten(p, a) }
     statement[asdl_seq*]: a=compound_stmt { _PyPegen_singleton_seq(p, a) } | simple_stmt
     statement_newline[asdl_seq*]:
         | a=compound_stmt NEWLINE { _PyPegen_singleton_seq(p, a) }
         | simple_stmt
         | NEWLINE { _PyPegen_singleton_seq(p, CHECK(_Py_Pass(EXTRA))) }
         | ENDMARKER { _PyPegen_interactive_exit(p) }
     simple_stmt[asdl_seq*]:
         | a=small_stmt !';' NEWLINE { _PyPegen_singleton_seq(p, a) } # Not needed, there for speedup
         | a=';'.small_stmt+ [';'] NEWLINE { a }
     # NOTE: assignment MUST precede expression, else parsing a simple assignment
     # will throw a SyntaxError.
     small_stmt[stmt_ty] (memo):
         | assignment
         | e=star_expressions { _Py_Expr(e, EXTRA) }
         | &'return' return_stmt
         | &('import' | 'from') import_stmt
         | &'raise' raise_stmt
         | 'pass' { _Py_Pass(EXTRA) }
         | &'del' del_stmt
         | &'yield' yield_stmt
         | &'assert' assert_stmt
         | 'break' { _Py_Break(EXTRA) }
         | 'continue' { _Py_Continue(EXTRA) }
         | &'global' global_stmt
         | &'nonlocal' nonlocal_stmt
     compound_stmt[stmt_ty]:
         | &('def' | '@' | ASYNC) function_def
         | &'if' if_stmt
         | &('class' | '@') class_def
         | &('with' | ASYNC) with_stmt
         | &('for' | ASYNC) for_stmt
         | &'try' try_stmt
         | &'while' while_stmt

     # NOTE: annotated_rhs may start with 'yield'; yield_expr must start with 'yield'
     assignment[stmt_ty]:
         | a=NAME ':' b=expression c=['=' d=annotated_rhs { d }] {
             CHECK_VERSION(
                 6,
                 "Variable annotation syntax is",
                 _Py_AnnAssign(CHECK(_PyPegen_set_expr_context(p, a, Store)), b, c, 1, EXTRA)
             ) }
         | a=('(' b=single_target ')' { b }
              | single_subscript_attribute_target) ':' b=expression c=['=' d=annotated_rhs { d }] {
             CHECK_VERSION(6, "Variable annotations syntax is", _Py_AnnAssign(a, b, c, 0, EXTRA)) }
         | a=(z=star_targets '=' { z })+ b=(yield_expr | star_expressions) !'=' tc=[TYPE_COMMENT] {
              _Py_Assign(a, b, NEW_TYPE_COMMENT(p, tc), EXTRA) }
         | a=single_target b=augassign ~ c=(yield_expr | star_expressions) {
              _Py_AugAssign(a, b->kind, c, EXTRA) }
         | invalid_assignment

     augassign[AugOperator*]:
         | '+=' { _PyPegen_augoperator(p, Add) }
         | '-=' { _PyPegen_augoperator(p, Sub) }
         | '*=' { _PyPegen_augoperator(p, Mult) }
         | '@=' { CHECK_VERSION(5, "The '@' operator is", _PyPegen_augoperator(p, MatMult)) }
         | '/=' { _PyPegen_augoperator(p, Div) }
         | '%=' { _PyPegen_augoperator(p, Mod) }
         | '&=' { _PyPegen_augoperator(p, BitAnd) }
         | '|=' { _PyPegen_augoperator(p, BitOr) }
         | '^=' { _PyPegen_augoperator(p, BitXor) }
         | '<<=' { _PyPegen_augoperator(p, LShift) }
         | '>>=' { _PyPegen_augoperator(p, RShift) }
         | '**=' { _PyPegen_augoperator(p, Pow) }
         | '//=' { _PyPegen_augoperator(p, FloorDiv) }

     global_stmt[stmt_ty]: 'global' a=','.NAME+ {
         _Py_Global(CHECK(_PyPegen_map_names_to_ids(p, a)), EXTRA) }
     nonlocal_stmt[stmt_ty]: 'nonlocal' a=','.NAME+ {
         _Py_Nonlocal(CHECK(_PyPegen_map_names_to_ids(p, a)), EXTRA) }

     yield_stmt[stmt_ty]: y=yield_expr { _Py_Expr(y, EXTRA) }

     assert_stmt[stmt_ty]: 'assert' a=expression b=[',' z=expression { z }] { _Py_Assert(a, b, EXTRA) }

     del_stmt[stmt_ty]:
         | 'del' a=del_targets &(';' | NEWLINE) { _Py_Delete(a, EXTRA) }
         | invalid_del_stmt

     import_stmt[stmt_ty]: import_name | import_from
     import_name[stmt_ty]: 'import' a=dotted_as_names { _Py_Import(a, EXTRA) }
     # note below: the ('.' | '...') is necessary because '...' is tokenized as ELLIPSIS
     import_from[stmt_ty]:
         | 'from' a=('.' | '...')* b=dotted_name 'import' c=import_from_targets {
             _Py_ImportFrom(b->v.Name.id, c, _PyPegen_seq_count_dots(a), EXTRA) }
         | 'from' a=('.' | '...')+ 'import' b=import_from_targets {
             _Py_ImportFrom(NULL, b, _PyPegen_seq_count_dots(a), EXTRA) }
     import_from_targets[asdl_seq*]:
         | '(' a=import_from_as_names [','] ')' { a }
         | import_from_as_names !','
         | '*' { _PyPegen_singleton_seq(p, CHECK(_PyPegen_alias_for_star(p))) }
         | invalid_import_from_targets
     import_from_as_names[asdl_seq*]:
         | a=','.import_from_as_name+ { a }
     import_from_as_name[alias_ty]:
         | a=NAME b=['as' z=NAME { z }] { _Py_alias(a->v.Name.id,
                                                    (b) ? ((expr_ty) b)->v.Name.id : NULL,
                                                    p->arena) }
     dotted_as_names[asdl_seq*]:
         | a=','.dotted_as_name+ { a }
     dotted_as_name[alias_ty]:
         | a=dotted_name b=['as' z=NAME { z }] { _Py_alias(a->v.Name.id,
                                                           (b) ? ((expr_ty) b)->v.Name.id : NULL,
                                                           p->arena) }
     dotted_name[expr_ty]:
         | a=dotted_name '.' b=NAME { _PyPegen_join_names_with_dot(p, a, b) }
         | NAME

     if_stmt[stmt_ty]:
         | 'if' a=named_expression ':' b=block c=elif_stmt { _Py_If(a, b, CHECK(_PyPegen_singleton_seq(p, c)), EXTRA) }
         | 'if' a=named_expression ':' b=block c=[else_block] { _Py_If(a, b, c, EXTRA) }
     elif_stmt[stmt_ty]:
         | 'elif' a=named_expression ':' b=block c=elif_stmt { _Py_If(a, b, CHECK(_PyPegen_singleton_seq(p, c)), EXTRA) }
         | 'elif' a=named_expression ':' b=block c=[else_block] { _Py_If(a, b, c, EXTRA) }
     else_block[asdl_seq*]: 'else' ':' b=block { b }

     while_stmt[stmt_ty]:
         | 'while' a=named_expression ':' b=block c=[else_block] { _Py_While(a, b, c, EXTRA) }

     for_stmt[stmt_ty]:
         | 'for' t=star_targets 'in' ~ ex=star_expressions ':' tc=[TYPE_COMMENT] b=block el=[else_block] {
             _Py_For(t, ex, b, el, NEW_TYPE_COMMENT(p, tc), EXTRA) }
         | ASYNC 'for' t=star_targets 'in' ~ ex=star_expressions ':' tc=[TYPE_COMMENT] b=block el=[else_block] {
             CHECK_VERSION(5, "Async for loops are", _Py_AsyncFor(t, ex, b, el, NEW_TYPE_COMMENT(p, tc), EXTRA)) }
         | invalid_for_target

     with_stmt[stmt_ty]:
         | 'with' '(' a=','.with_item+ ','? ')' ':' b=block {
             _Py_With(a, b, NULL, EXTRA) }
         | 'with' a=','.with_item+ ':' tc=[TYPE_COMMENT] b=block {
             _Py_With(a, b, NEW_TYPE_COMMENT(p, tc), EXTRA) }
         | ASYNC 'with' '(' a=','.with_item+ ','? ')' ':' b=block {
            CHECK_VERSION(5, "Async with statements are", _Py_AsyncWith(a, b, NULL, EXTRA)) }
         | ASYNC 'with' a=','.with_item+ ':' tc=[TYPE_COMMENT] b=block {
            CHECK_VERSION(5, "Async with statements are", _Py_AsyncWith(a, b, NEW_TYPE_COMMENT(p, tc), EXTRA)) }
     with_item[withitem_ty]:
         | e=expression 'as' t=star_target &(',' | ')' | ':') { _Py_withitem(e, t, p->arena) }
         | invalid_with_item
         | e=expression { _Py_withitem(e, NULL, p->arena) }

     try_stmt[stmt_ty]:
         | 'try' ':' b=block f=finally_block { _Py_Try(b, NULL, NULL, f, EXTRA) }
         | 'try' ':' b=block ex=except_block+ el=[else_block] f=[finally_block] { _Py_Try(b, ex, el, f, EXTRA) }
     except_block[excepthandler_ty]:
         | 'except' e=expression t=['as' z=NAME { z }] ':' b=block {
             _Py_ExceptHandler(e, (t) ? ((expr_ty) t)->v.Name.id : NULL, b, EXTRA) }
         | 'except' ':' b=block { _Py_ExceptHandler(NULL, NULL, b, EXTRA) }
     finally_block[asdl_seq*]: 'finally' ':' a=block { a }

     return_stmt[stmt_ty]:
         | 'return' a=[star_expressions] { _Py_Return(a, EXTRA) }

     raise_stmt[stmt_ty]:
         | 'raise' a=expression b=['from' z=expression { z }] { _Py_Raise(a, b, EXTRA) }
         | 'raise' { _Py_Raise(NULL, NULL, EXTRA) }

     function_def[stmt_ty]:
         | d=decorators f=function_def_raw { _PyPegen_function_def_decorators(p, d, f) }
         | function_def_raw

     function_def_raw[stmt_ty]:
         | 'def' n=NAME '(' params=[params] ')' a=['->' z=expression { z }] ':' tc=[func_type_comment] b=block {
             _Py_FunctionDef(n->v.Name.id,
                             (params) ? params : CHECK(_PyPegen_empty_arguments(p)),
                             b, NULL, a, NEW_TYPE_COMMENT(p, tc), EXTRA) }
         | ASYNC 'def' n=NAME '(' params=[params] ')' a=['->' z=expression { z }] ':' tc=[func_type_comment] b=block {
             CHECK_VERSION(
                 5,
                 "Async functions are",
                 _Py_AsyncFunctionDef(n->v.Name.id,
                                 (params) ? params : CHECK(_PyPegen_empty_arguments(p)),
                                 b, NULL, a, NEW_TYPE_COMMENT(p, tc), EXTRA)
             ) }
     func_type_comment[Token*]:
         | NEWLINE t=TYPE_COMMENT &(NEWLINE INDENT) { t }  # Must be followed by indented block
         | invalid_double_type_comments
         | TYPE_COMMENT

     params[arguments_ty]:
         | invalid_parameters
         | parameters

     parameters[arguments_ty]:
         | a=slash_no_default b=param_no_default* c=param_with_default* d=[star_etc] {
             _PyPegen_make_arguments(p, a, NULL, b, c, d) }
         | a=slash_with_default b=param_with_default* c=[star_etc] {
             _PyPegen_make_arguments(p, NULL, a, NULL, b, c) }
         | a=param_no_default+ b=param_with_default* c=[star_etc] {
             _PyPegen_make_arguments(p, NULL, NULL, a, b, c) }
         | a=param_with_default+ b=[star_etc] { _PyPegen_make_arguments(p, NULL, NULL, NULL, a, b)}
         | a=star_etc { _PyPegen_make_arguments(p, NULL, NULL, NULL, NULL, a) }

     # Some duplication here because we can't write (',' | &')'),
     # which is because we don't support empty alternatives (yet).
     #
     slash_no_default[asdl_seq*]:
         | a=param_no_default+ '/' ',' { a }
         | a=param_no_default+ '/' &')' { a }
     slash_with_default[SlashWithDefault*]:
         | a=param_no_default* b=param_with_default+ '/' ',' { _PyPegen_slash_with_default(p, a, b) }
         | a=param_no_default* b=param_with_default+ '/' &')' { _PyPegen_slash_with_default(p, a, b) }

     star_etc[StarEtc*]:
         | '*' a=param_no_default b=param_maybe_default* c=[kwds] {
             _PyPegen_star_etc(p, a, b, c) }
         | '*' ',' b=param_maybe_default+ c=[kwds] {
             _PyPegen_star_etc(p, NULL, b, c) }
         | a=kwds { _PyPegen_star_etc(p, NULL, NULL, a) }
         | invalid_star_etc

     kwds[arg_ty]: '**' a=param_no_default { a }

     # One parameter.  This *includes* a following comma and type comment.
     #
     # There are three styles:
     # - No default
     # - With default
     # - Maybe with default
     #
     # There are two alternative forms of each, to deal with type comments:
     # - Ends in a comma followed by an optional type comment
     # - No comma, optional type comment, must be followed by close paren
     # The latter form is for a final parameter without trailing comma.
     #
     param_no_default[arg_ty]:
         | a=param ',' tc=TYPE_COMMENT? { _PyPegen_add_type_comment_to_arg(p, a, tc) }
         | a=param tc=TYPE_COMMENT? &')' { _PyPegen_add_type_comment_to_arg(p, a, tc) }
     param_with_default[NameDefaultPair*]:
         | a=param c=default ',' tc=TYPE_COMMENT? { _PyPegen_name_default_pair(p, a, c, tc) }
         | a=param c=default tc=TYPE_COMMENT? &')' { _PyPegen_name_default_pair(p, a, c, tc) }
     param_maybe_default[NameDefaultPair*]:
         | a=param c=default? ',' tc=TYPE_COMMENT? { _PyPegen_name_default_pair(p, a, c, tc) }
         | a=param c=default? tc=TYPE_COMMENT? &')' { _PyPegen_name_default_pair(p, a, c, tc) }
     param[arg_ty]: a=NAME b=annotation? { _Py_arg(a->v.Name.id, b, NULL, EXTRA) }

     annotation[expr_ty]: ':' a=expression { a }
     default[expr_ty]: '=' a=expression { a }

     decorators[asdl_seq*]: a=('@' f=named_expression NEWLINE { f })+ { a }

     class_def[stmt_ty]:
         | a=decorators b=class_def_raw { _PyPegen_class_def_decorators(p, a, b) }
         | class_def_raw
     class_def_raw[stmt_ty]:
         | 'class' a=NAME b=['(' z=[arguments] ')' { z }] ':' c=block {
             _Py_ClassDef(a->v.Name.id,
                          (b) ? ((expr_ty) b)->v.Call.args : NULL,
                          (b) ? ((expr_ty) b)->v.Call.keywords : NULL,
                          c, NULL, EXTRA) }

     block[asdl_seq*] (memo):
         | NEWLINE INDENT a=statements DEDENT { a }
         | simple_stmt
         | invalid_block

     star_expressions[expr_ty]:
         | a=star_expression b=(',' c=star_expression { c })+ [','] {
             _Py_Tuple(CHECK(_PyPegen_seq_insert_in_front(p, a, b)), Load, EXTRA) }
         | a=star_expression ',' { _Py_Tuple(CHECK(_PyPegen_singleton_seq(p, a)), Load, EXTRA) }
         | star_expression
     star_expression[expr_ty] (memo):
         | '*' a=bitwise_or { _Py_Starred(a, Load, EXTRA) }
         | expression

     star_named_expressions[asdl_seq*]: a=','.star_named_expression+ [','] { a }
     star_named_expression[expr_ty]:
         | '*' a=bitwise_or { _Py_Starred(a, Load, EXTRA) }
         | named_expression
     named_expression[expr_ty]:
         | a=NAME ':=' ~ b=expression { _Py_NamedExpr(CHECK(_PyPegen_set_expr_context(p, a, Store)), b, EXTRA) }
         | expression !':='
         | invalid_named_expression

     annotated_rhs[expr_ty]: yield_expr | star_expressions

     expressions[expr_ty]:
         | a=expression b=(',' c=expression { c })+ [','] {
             _Py_Tuple(CHECK(_PyPegen_seq_insert_in_front(p, a, b)), Load, EXTRA) }
         | a=expression ',' { _Py_Tuple(CHECK(_PyPegen_singleton_seq(p, a)), Load, EXTRA) }
         | expression
     expression[expr_ty] (memo):
         | a=disjunction 'if' b=disjunction 'else' c=expression { _Py_IfExp(b, a, c, EXTRA) }
         | disjunction
         | lambdef

     lambdef[expr_ty]:
         | 'lambda' a=[lambda_params] ':' b=expression { _Py_Lambda((a) ? a : CHECK(_PyPegen_empty_arguments(p)), b, EXTRA) }

     lambda_params[arguments_ty]:
         | invalid_lambda_parameters
         | lambda_parameters

     # lambda_parameters etc. duplicates parameters but without annotations
     # or type comments, and if there's no comma after a parameter, we expect
     # a colon, not a close parenthesis.  (For more, see parameters above.)
     #
     lambda_parameters[arguments_ty]:
         | a=lambda_slash_no_default b=lambda_param_no_default* c=lambda_param_with_default* d=[lambda_star_etc] {
             _PyPegen_make_arguments(p, a, NULL, b, c, d) }
         | a=lambda_slash_with_default b=lambda_param_with_default* c=[lambda_star_etc] {
             _PyPegen_make_arguments(p, NULL, a, NULL, b, c) }
         | a=lambda_param_no_default+ b=lambda_param_with_default* c=[lambda_star_etc] {
             _PyPegen_make_arguments(p, NULL, NULL, a, b, c) }
         | a=lambda_param_with_default+ b=[lambda_star_etc] { _PyPegen_make_arguments(p, NULL, NULL, NULL, a, b)}
         | a=lambda_star_etc { _PyPegen_make_arguments(p, NULL, NULL, NULL, NULL, a) }

     lambda_slash_no_default[asdl_seq*]:
         | a=lambda_param_no_default+ '/' ',' { a }
         | a=lambda_param_no_default+ '/' &':' { a }
     lambda_slash_with_default[SlashWithDefault*]:
         | a=lambda_param_no_default* b=lambda_param_with_default+ '/' ',' { _PyPegen_slash_with_default(p, a, b) }
         | a=lambda_param_no_default* b=lambda_param_with_default+ '/' &':' { _PyPegen_slash_with_default(p, a, b) }

     lambda_star_etc[StarEtc*]:
         | '*' a=lambda_param_no_default b=lambda_param_maybe_default* c=[lambda_kwds] {
             _PyPegen_star_etc(p, a, b, c) }
         | '*' ',' b=lambda_param_maybe_default+ c=[lambda_kwds] {
             _PyPegen_star_etc(p, NULL, b, c) }
         | a=lambda_kwds { _PyPegen_star_etc(p, NULL, NULL, a) }
         | invalid_lambda_star_etc

     lambda_kwds[arg_ty]: '**' a=lambda_param_no_default { a }

     lambda_param_no_default[arg_ty]:
         | a=lambda_param ',' { a }
         | a=lambda_param &':' { a }
     lambda_param_with_default[NameDefaultPair*]:
         | a=lambda_param c=default ',' { _PyPegen_name_default_pair(p, a, c, NULL) }
         | a=lambda_param c=default &':' { _PyPegen_name_default_pair(p, a, c, NULL) }
     lambda_param_maybe_default[NameDefaultPair*]:
         | a=lambda_param c=default? ',' { _PyPegen_name_default_pair(p, a, c, NULL) }
         | a=lambda_param c=default? &':' { _PyPegen_name_default_pair(p, a, c, NULL) }
     lambda_param[arg_ty]: a=NAME { _Py_arg(a->v.Name.id, NULL, NULL, EXTRA) }

     disjunction[expr_ty] (memo):
         | a=conjunction b=('or' c=conjunction { c })+ { _Py_BoolOp(
             Or,
             CHECK(_PyPegen_seq_insert_in_front(p, a, b)),
             EXTRA) }
         | conjunction
     conjunction[expr_ty] (memo):
         | a=inversion b=('and' c=inversion { c })+ { _Py_BoolOp(
             And,
             CHECK(_PyPegen_seq_insert_in_front(p, a, b)),
             EXTRA) }
         | inversion
     inversion[expr_ty] (memo):
         | 'not' a=inversion { _Py_UnaryOp(Not, a, EXTRA) }
         | comparison
     comparison[expr_ty]:
         | a=bitwise_or b=compare_op_bitwise_or_pair+ {
             _Py_Compare(a, CHECK(_PyPegen_get_cmpops(p, b)), CHECK(_PyPegen_get_exprs(p, b)), EXTRA) }
         | bitwise_or
     compare_op_bitwise_or_pair[CmpopExprPair*]:
         | eq_bitwise_or
         | noteq_bitwise_or
         | lte_bitwise_or
         | lt_bitwise_or
         | gte_bitwise_or
         | gt_bitwise_or
         | notin_bitwise_or
         | in_bitwise_or
         | isnot_bitwise_or
         | is_bitwise_or
     eq_bitwise_or[CmpopExprPair*]: '==' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, Eq, a) }
     noteq_bitwise_or[CmpopExprPair*]:
         | (tok='!=' { _PyPegen_check_barry_as_flufl(p, tok) ? NULL : tok}) a=bitwise_or {_PyPegen_cmpop_expr_pair(p, NotEq, a) }
     lte_bitwise_or[CmpopExprPair*]: '<=' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, LtE, a) }
     lt_bitwise_or[CmpopExprPair*]: '<' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, Lt, a) }
     gte_bitwise_or[CmpopExprPair*]: '>=' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, GtE, a) }
     gt_bitwise_or[CmpopExprPair*]: '>' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, Gt, a) }
     notin_bitwise_or[CmpopExprPair*]: 'not' 'in' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, NotIn, a) }
     in_bitwise_or[CmpopExprPair*]: 'in' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, In, a) }
     isnot_bitwise_or[CmpopExprPair*]: 'is' 'not' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, IsNot, a) }
     is_bitwise_or[CmpopExprPair*]: 'is' a=bitwise_or { _PyPegen_cmpop_expr_pair(p, Is, a) }

     bitwise_or[expr_ty]:
         | a=bitwise_or '|' b=bitwise_xor { _Py_BinOp(a, BitOr, b, EXTRA) }
         | bitwise_xor
     bitwise_xor[expr_ty]:
         | a=bitwise_xor '^' b=bitwise_and { _Py_BinOp(a, BitXor, b, EXTRA) }
         | bitwise_and
     bitwise_and[expr_ty]:
         | a=bitwise_and '&' b=shift_expr { _Py_BinOp(a, BitAnd, b, EXTRA) }
         | shift_expr
     shift_expr[expr_ty]:
         | a=shift_expr '<<' b=sum { _Py_BinOp(a, LShift, b, EXTRA) }
         | a=shift_expr '>>' b=sum { _Py_BinOp(a, RShift, b, EXTRA) }
         | sum

     sum[expr_ty]:
         | a=sum '+' b=term { _Py_BinOp(a, Add, b, EXTRA) }
         | a=sum '-' b=term { _Py_BinOp(a, Sub, b, EXTRA) }
         | term
     term[expr_ty]:
         | a=term '*' b=factor { _Py_BinOp(a, Mult, b, EXTRA) }
         | a=term '/' b=factor { _Py_BinOp(a, Div, b, EXTRA) }
         | a=term '//' b=factor { _Py_BinOp(a, FloorDiv, b, EXTRA) }
         | a=term '%' b=factor { _Py_BinOp(a, Mod, b, EXTRA) }
         | a=term '@' b=factor { CHECK_VERSION(5, "The '@' operator is", _Py_BinOp(a, MatMult, b, EXTRA)) }
         | factor
     factor[expr_ty] (memo):
         | '+' a=factor { _Py_UnaryOp(UAdd, a, EXTRA) }
         | '-' a=factor { _Py_UnaryOp(USub, a, EXTRA) }
         | '~' a=factor { _Py_UnaryOp(Invert, a, EXTRA) }
         | power
     power[expr_ty]:
         | a=await_primary '**' b=factor { _Py_BinOp(a, Pow, b, EXTRA) }
         | await_primary
     await_primary[expr_ty] (memo):
         | AWAIT a=primary { CHECK_VERSION(5, "Await expressions are", _Py_Await(a, EXTRA)) }
         | primary
     primary[expr_ty]:
         | invalid_primary  # must be before 'primay genexp' because of invalid_genexp
         | a=primary '.' b=NAME { _Py_Attribute(a, b->v.Name.id, Load, EXTRA) }
         | a=primary b=genexp { _Py_Call(a, CHECK(_PyPegen_singleton_seq(p, b)), NULL, EXTRA) }
         | a=primary '(' b=[arguments] ')' {
             _Py_Call(a,
                      (b) ? ((expr_ty) b)->v.Call.args : NULL,
                      (b) ? ((expr_ty) b)->v.Call.keywords : NULL,
                      EXTRA) }
         | a=primary '[' b=slices ']' { _Py_Subscript(a, b, Load, EXTRA) }
         | atom

     slices[expr_ty]:
         | a=slice !',' { a }
         | a=','.slice+ [','] { _Py_Tuple(a, Load, EXTRA) }
     slice[expr_ty]:
         | a=[expression] ':' b=[expression] c=[':' d=[expression] { d }] { _Py_Slice(a, b, c, EXTRA) }
         | a=expression { a }
     atom[expr_ty]:
         | NAME
         | 'True' { _Py_Constant(Py_True, NULL, EXTRA) }
         | 'False' { _Py_Constant(Py_False, NULL, EXTRA) }
         | 'None' { _Py_Constant(Py_None, NULL, EXTRA) }
         | '__peg_parser__' { RAISE_SYNTAX_ERROR("You found it!") }
         | &STRING strings
         | NUMBER
         | &'(' (tuple | group | genexp)
         | &'[' (list | listcomp)
         | &'{' (dict | set | dictcomp | setcomp)
         | '...' { _Py_Constant(Py_Ellipsis, NULL, EXTRA) }

     strings[expr_ty] (memo): a=STRING+ { _PyPegen_concatenate_strings(p, a) }
     list[expr_ty]:
         | '[' a=[star_named_expressions] ']' { _Py_List(a, Load, EXTRA) }
     listcomp[expr_ty]:
         | '[' a=named_expression ~ b=for_if_clauses ']' { _Py_ListComp(a, b, EXTRA) }
         | invalid_comprehension
     tuple[expr_ty]:
         | '(' a=[y=star_named_expression ',' z=[star_named_expressions] { _PyPegen_seq_insert_in_front(p, y, z) } ] ')' {
             _Py_Tuple(a, Load, EXTRA) }
     group[expr_ty]:
         | '(' a=(yield_expr | named_expression) ')' { a }
         | invalid_group
     genexp[expr_ty]:
         | '(' a=named_expression ~ b=for_if_clauses ')' { _Py_GeneratorExp(a, b, EXTRA) }
         | invalid_comprehension
     set[expr_ty]: '{' a=star_named_expressions '}' { _Py_Set(a, EXTRA) }
     setcomp[expr_ty]:
         | '{' a=named_expression ~ b=for_if_clauses '}' { _Py_SetComp(a, b, EXTRA) }
         | invalid_comprehension
     dict[expr_ty]:
         | '{' a=[double_starred_kvpairs] '}' {
             _Py_Dict(CHECK(_PyPegen_get_keys(p, a)), CHECK(_PyPegen_get_values(p, a)), EXTRA) }
     dictcomp[expr_ty]:
         | '{' a=kvpair b=for_if_clauses '}' { _Py_DictComp(a->key, a->value, b, EXTRA) }
         | invalid_dict_comprehension
     double_starred_kvpairs[asdl_seq*]: a=','.double_starred_kvpair+ [','] { a }
     double_starred_kvpair[KeyValuePair*]:
         | '**' a=bitwise_or { _PyPegen_key_value_pair(p, NULL, a) }
         | kvpair
     kvpair[KeyValuePair*]: a=expression ':' b=expression { _PyPegen_key_value_pair(p, a, b) }
     for_if_clauses[asdl_seq*]:
         | for_if_clause+
     for_if_clause[comprehension_ty]:
         | ASYNC 'for' a=star_targets 'in' ~ b=disjunction c=('if' z=disjunction { z })* {
             CHECK_VERSION(6, "Async comprehensions are", _Py_comprehension(a, b, c, 1, p->arena)) }
         | 'for' a=star_targets 'in' ~ b=disjunction c=('if' z=disjunction { z })* {
             _Py_comprehension(a, b, c, 0, p->arena) }
         | invalid_for_target

     yield_expr[expr_ty]:
         | 'yield' 'from' a=expression { _Py_YieldFrom(a, EXTRA) }
         | 'yield' a=[star_expressions] { _Py_Yield(a, EXTRA) }

     arguments[expr_ty] (memo):
         | a=args [','] &')' { a }
         | invalid_arguments
     args[expr_ty]:
         | a=','.(starred_expression | named_expression !'=')+ b=[',' k=kwargs {k}] { _PyPegen_collect_call_seqs(p, a, b, EXTRA) }
         | a=kwargs { _Py_Call(_PyPegen_dummy_name(p),
                               CHECK_NULL_ALLOWED(_PyPegen_seq_extract_starred_exprs(p, a)),
                               CHECK_NULL_ALLOWED(_PyPegen_seq_delete_starred_exprs(p, a)),
                               EXTRA) }
     kwargs[asdl_seq*]:
         | a=','.kwarg_or_starred+ ',' b=','.kwarg_or_double_starred+ { _PyPegen_join_sequences(p, a, b) }
         | ','.kwarg_or_starred+
         | ','.kwarg_or_double_starred+
     starred_expression[expr_ty]:
         | '*' a=expression { _Py_Starred(a, Load, EXTRA) }
     kwarg_or_starred[KeywordOrStarred*]:
         | a=NAME '=' b=expression {
             _PyPegen_keyword_or_starred(p, CHECK(_Py_keyword(a->v.Name.id, b, EXTRA)), 1) }
         | a=starred_expression { _PyPegen_keyword_or_starred(p, a, 0) }
         | invalid_kwarg
     kwarg_or_double_starred[KeywordOrStarred*]:
         | a=NAME '=' b=expression {
             _PyPegen_keyword_or_starred(p, CHECK(_Py_keyword(a->v.Name.id, b, EXTRA)), 1) }
         | '**' a=expression { _PyPegen_keyword_or_starred(p, CHECK(_Py_keyword(NULL, a, EXTRA)), 1) }
         | invalid_kwarg

     # NOTE: star_targets may contain *bitwise_or, targets may not.
     star_targets[expr_ty]:
         | a=star_target !',' { a }
         | a=star_target b=(',' c=star_target { c })* [','] {
             _Py_Tuple(CHECK(_PyPegen_seq_insert_in_front(p, a, b)), Store, EXTRA) }
     star_targets_list_seq[asdl_seq*]: a=','.star_target+ [','] { a }
     star_targets_tuple_seq[asdl_seq*]:
         | a=star_target b=(',' c=star_target { c })+ [','] { _PyPegen_seq_insert_in_front(p, a, b) }
         | a=star_target ',' { _PyPegen_singleton_seq(p, a) }
     star_target[expr_ty] (memo):
         | '*' a=(!'*' star_target) {
             _Py_Starred(CHECK(_PyPegen_set_expr_context(p, a, Store)), Store, EXTRA) }
         | target_with_star_atom
     target_with_star_atom[expr_ty] (memo):
         | a=t_primary '.' b=NAME !t_lookahead { _Py_Attribute(a, b->v.Name.id, Store, EXTRA) }
         | a=t_primary '[' b=slices ']' !t_lookahead { _Py_Subscript(a, b, Store, EXTRA) }
         | star_atom
     star_atom[expr_ty]:
         | a=NAME { _PyPegen_set_expr_context(p, a, Store) }
         | '(' a=target_with_star_atom ')' { _PyPegen_set_expr_context(p, a, Store) }
         | '(' a=[star_targets_tuple_seq] ')' { _Py_Tuple(a, Store, EXTRA) }
         | '[' a=[star_targets_list_seq] ']' { _Py_List(a, Store, EXTRA) }

     single_target[expr_ty]:
         | single_subscript_attribute_target
         | a=NAME { _PyPegen_set_expr_context(p, a, Store) }
         | '(' a=single_target ')' { a }
     single_subscript_attribute_target[expr_ty]:
         | a=t_primary '.' b=NAME !t_lookahead { _Py_Attribute(a, b->v.Name.id, Store, EXTRA) }
         | a=t_primary '[' b=slices ']' !t_lookahead { _Py_Subscript(a, b, Store, EXTRA) }

     del_targets[asdl_seq*]: a=','.del_target+ [','] { a }
     del_target[expr_ty] (memo):
         | a=t_primary '.' b=NAME !t_lookahead { _Py_Attribute(a, b->v.Name.id, Del, EXTRA) }
         | a=t_primary '[' b=slices ']' !t_lookahead { _Py_Subscript(a, b, Del, EXTRA) }
         | del_t_atom
     del_t_atom[expr_ty]:
         | a=NAME { _PyPegen_set_expr_context(p, a, Del) }
         | '(' a=del_target ')' { _PyPegen_set_expr_context(p, a, Del) }
         | '(' a=[del_targets] ')' { _Py_Tuple(a, Del, EXTRA) }
         | '[' a=[del_targets] ']' { _Py_List(a, Del, EXTRA) }

     t_primary[expr_ty]:
         | a=t_primary '.' b=NAME &t_lookahead { _Py_Attribute(a, b->v.Name.id, Load, EXTRA) }
         | a=t_primary '[' b=slices ']' &t_lookahead { _Py_Subscript(a, b, Load, EXTRA) }
         | a=t_primary b=genexp &t_lookahead { _Py_Call(a, CHECK(_PyPegen_singleton_seq(p, b)), NULL, EXTRA) }
         | a=t_primary '(' b=[arguments] ')' &t_lookahead {
             _Py_Call(a,
                      (b) ? ((expr_ty) b)->v.Call.args : NULL,
                      (b) ? ((expr_ty) b)->v.Call.keywords : NULL,
                      EXTRA) }
         | a=atom &t_lookahead { a }
     t_lookahead: '(' | '[' | '.'

     # From here on, there are rules for invalid syntax with specialised error messages
     invalid_arguments:
         | args ',' '*' { RAISE_SYNTAX_ERROR("iterable argument unpacking follows keyword argument unpacking") }
         | a=expression for_if_clauses ',' [args | expression for_if_clauses] {
             RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "Generator expression must be parenthesized") }
         | a=args for_if_clauses { _PyPegen_nonparen_genexp_in_call(p, a) }
         | args ',' a=expression for_if_clauses {
             RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "Generator expression must be parenthesized") }
         | a=args ',' args { _PyPegen_arguments_parsing_error(p, a) }
     invalid_kwarg:
         | !(NAME '=') a=expression b='=' {
             RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
                 a, "expression cannot contain assignment, perhaps you meant \"==\"?") }
     invalid_named_expression:
         | a=expression ':=' expression {
             RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
                 a, "cannot use assignment expressions with %s", _PyPegen_get_expr_name(a)) }
     invalid_assignment:
         | a=invalid_ann_assign_target ':' expression {
             RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
                 a,
                 "only single target (not %s) can be annotated",
                 _PyPegen_get_expr_name(a)
             )}
         | a=star_named_expression ',' star_named_expressions* ':' expression {
             RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "only single target (not tuple) can be annotated") }
         | a=expression ':' expression {
             RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "illegal target for annotation") }
         | (star_targets '=')* a=star_expressions '=' {
             RAISE_SYNTAX_ERROR_INVALID_TARGET(STAR_TARGETS, a) }
         | (star_targets '=')* a=yield_expr '=' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "assignment to yield expression not possible") }
         | a=star_expressions augassign (yield_expr | star_expressions) {
             RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
                 a,
                 "'%s' is an illegal expression for augmented assignment",
                 _PyPegen_get_expr_name(a)
             )}
     invalid_ann_assign_target[expr_ty]:
         | list
         | tuple
         | '(' a=invalid_ann_assign_target ')' { a }
     invalid_del_stmt:
         | 'del' a=star_expressions {
             RAISE_SYNTAX_ERROR_INVALID_TARGET(DEL_TARGETS, a) }
     invalid_block:
         | NEWLINE !INDENT { RAISE_INDENTATION_ERROR("expected an indented block") }
     invalid_primary:
         | primary a='{' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "invalid syntax") }
     invalid_comprehension:
         | ('[' | '(' | '{') a=starred_expression for_if_clauses {
             RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "iterable unpacking cannot be used in comprehension") }
     invalid_dict_comprehension:
         | '{' a='**' bitwise_or for_if_clauses '}' {
             RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "dict unpacking cannot be used in dict comprehension") }
     invalid_parameters:
         | param_no_default* (slash_with_default | param_with_default+) param_no_default {
             RAISE_SYNTAX_ERROR("non-default argument follows default argument") }
     invalid_lambda_parameters:
         | lambda_param_no_default* (lambda_slash_with_default | lambda_param_with_default+) lambda_param_no_default {
             RAISE_SYNTAX_ERROR("non-default argument follows default argument") }
     invalid_star_etc:
         | '*' (')' | ',' (')' | '**')) { RAISE_SYNTAX_ERROR("named arguments must follow bare *") }
         | '*' ',' TYPE_COMMENT { RAISE_SYNTAX_ERROR("bare * has associated type comment") }
     invalid_lambda_star_etc:
         | '*' (':' | ',' (':' | '**')) { RAISE_SYNTAX_ERROR("named arguments must follow bare *") }
     invalid_double_type_comments:
         | TYPE_COMMENT NEWLINE TYPE_COMMENT NEWLINE INDENT {
             RAISE_SYNTAX_ERROR("Cannot have two type comments on def") }
     invalid_with_item:
         | expression 'as' a=expression {
             RAISE_SYNTAX_ERROR_INVALID_TARGET(STAR_TARGETS, a) }

     invalid_for_target:
         | ASYNC? 'for' a=star_expressions {
             RAISE_SYNTAX_ERROR_INVALID_TARGET(FOR_TARGETS, a) }

     invalid_group:
         | '(' a=starred_expression ')' {
             RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "can't use starred expression here") }
     invalid_import_from_targets:
         | import_from_as_names ',' NEWLINE {
             RAISE_SYNTAX_ERROR("trailing comma not allowed without surrounding parentheses") }

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Grammar/python.gram

   (2) https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form

   (3) https://en.wikipedia.org/wiki/Parsing_expression_grammar


File: python.info,  Node: The Python Standard Library,  Next: Extending and Embedding the Python Interpreter,  Prev: The Python Language Reference,  Up: Top

5 The Python Standard Library
*****************************

While *note The Python Language Reference: 1331. describes the exact
syntax and semantics of the Python language, this library reference
manual describes the standard library that is distributed with Python.
It also describes some of the optional components that are commonly
included in Python distributions.

Python’s standard library is very extensive, offering a wide range of
facilities as indicated by the long table of contents listed below.  The
library contains built-in modules (written in C) that provide access to
system functionality such as file I/O that would otherwise be
inaccessible to Python programmers, as well as modules written in Python
that provide standardized solutions for many problems that occur in
everyday programming.  Some of these modules are explicitly designed to
encourage and enhance the portability of Python programs by abstracting
away platform-specifics into platform-neutral APIs.

The Python installers for the Windows platform usually include the
entire standard library and often also include many additional
components.  For Unix-like operating systems Python is normally provided
as a collection of packages, so it may be necessary to use the packaging
tools provided with the operating system to obtain some or all of the
optional components.

In addition to the standard library, there is a growing collection of
several thousand components (from individual programs and modules to
packages and entire application development frameworks), available from
the Python Package Index(1).

* Menu:

* Introduction: Introduction<6>.
* Built-in Functions::
* Built-in Constants::
* Built-in Types::
* Built-in Exceptions::
* Text Processing Services::
* Binary Data Services::
* Data Types::
* Numeric and Mathematical Modules::
* Functional Programming Modules::
* File and Directory Access::
* Data Persistence::
* Data Compression and Archiving::
* File Formats::
* Cryptographic Services::
* Generic Operating System Services::
* Concurrent Execution::
* Networking and Interprocess Communication::
* Internet Data Handling::
* Structured Markup Processing Tools::
* Internet Protocols and Support::
* Multimedia Services::
* Internationalization::
* Program Frameworks::
* Graphical User Interfaces with Tk::
* Development Tools::
* Debugging and Profiling::
* Software Packaging and Distribution::
* Python Runtime Services::
* Custom Python Interpreters::
* Importing Modules::
* Python Language Services::
* Miscellaneous Services::
* MS Windows Specific Services::
* Unix Specific Services::
* Superseded Modules::
* Undocumented Modules::
* Security Considerations: Security Considerations<2>.

   ---------- Footnotes ----------

   (1) https://pypi.org


File: python.info,  Node: Introduction<6>,  Next: Built-in Functions,  Up: The Python Standard Library

5.1 Introduction
================

The “Python library” contains several different kinds of components.

It contains data types that would normally be considered part of the
“core” of a language, such as numbers and lists.  For these types, the
Python language core defines the form of literals and places some
constraints on their semantics, but does not fully define the semantics.
(On the other hand, the language core does define syntactic properties
like the spelling and priorities of operators.)

The library also contains built-in functions and exceptions — objects
that can be used by all Python code without the need of an *note import:
ce7. statement.  Some of these are defined by the core language, but
many are not essential for the core semantics and are only described
here.

The bulk of the library, however, consists of a collection of modules.
There are many ways to dissect this collection.  Some modules are
written in C and built in to the Python interpreter; others are written
in Python and imported in source form.  Some modules provide interfaces
that are highly specific to Python, like printing a stack trace; some
provide interfaces that are specific to particular operating systems,
such as access to specific hardware; others provide interfaces that are
specific to a particular application domain, like the World Wide Web.
Some modules are available in all versions and ports of Python; others
are only available when the underlying system supports or requires them;
yet others are available only when a particular configuration option was
chosen at the time when Python was compiled and installed.

This manual is organized “from the inside out:” it first describes the
built-in functions, data types and exceptions, and finally the modules,
grouped in chapters of related modules.

This means that if you start reading this manual from the start, and
skip to the next chapter when you get bored, you will get a reasonable
overview of the available modules and application areas that are
supported by the Python library.  Of course, you don’t `have' to read it
like a novel — you can also browse the table of contents (in front of
the manual), or look for a specific function, module or term in the
index (in the back).  And finally, if you enjoy learning about random
subjects, you choose a random page number (see module *note random: dc.)
and read a section or two.  Regardless of the order in which you read
the sections of this manual, it helps to start with chapter *note
Built-in Functions: cbe, as the remainder of the manual assumes
familiarity with this material.

Let the show begin!

* Menu:

* Notes on availability::


File: python.info,  Node: Notes on availability,  Up: Introduction<6>

5.1.1 Notes on availability
---------------------------

   * An “Availability: Unix” note means that this function is commonly
     found on Unix systems.  It does not make any claims about its
     existence on a specific operating system.

   * If not separately noted, all functions that claim “Availability:
     Unix” are supported on macOS, which builds on a Unix core.


File: python.info,  Node: Built-in Functions,  Next: Built-in Constants,  Prev: Introduction<6>,  Up: The Python Standard Library

5.2 Built-in Functions
======================

The Python interpreter has a number of functions and types built into it
that are always available.  They are listed here in alphabetical order.

                                              Built-in Functions
                                              
---------------------------------------------------------------------------------------------------------------------
                                                                                            
*note abs(): 13f3.      *note delattr(): 170e.*note hash(): aa3.     *note memoryview(): 170f.*note set(): 1710.
                                                                                            
                                                                                            
*note all(): e4a.       *note dict(): 1711.   *note help(): 175.     *note min(): 8f6.      *note setattr(): 1712.
                                                                                            
                                                                                            
*note any(): e49.       *note dir(): df9.     *note hex(): d2e.      *note next(): 775.     *note slice(): ec8.
                                                                                            
                                                                                            
*note ascii(): e11.     *note divmod(): 28d.  *note id(): e4b.       *note object(): 3d2.   *note sorted(): 547.
                                                                                            
                                                                                            
*note bin(): d08.       *note enumerate(): ea7.*note input(): d33.   *note oct(): d2d.      *note staticmethod(): 30a.
                                                                                            
                                                                                            
*note bool(): 2bd.      *note eval(): c61.    *note int(): 204.      *note open(): 16f.     *note str(): 1713.
                                                                                            
                                                                                            
*note breakpoint(): 40b.*note exec(): d0c.    *note isinstance(): 552.*note ord(): 1559.    *note sum(): 316.
                                                                                            
                                                                                            
*note bytearray(): 11f3.*note filter(): cf8.  *note issubclass(): 553.*note pow(): 2cf.     *note super(): 5dd.
                                                                                            
                                                                                            
*note bytes(): 11f2.    *note float(): 1fd.   *note iter(): ded.     *note print(): 971.    *note tuple(): 1714.
                                                                                            
                                                                                            
*note callable(): c16.  *note format(): 5d6.  *note len(): 28b.      *note property(): 308. *note type(): 6ff.
                                                                                            
                                                                                            
*note chr(): 155a.      *note frozenset(): 1715.*note list(): 1716.  *note range(): 1717.   *note vars(): 116d.
                                                                                            
                                                                                            
*note classmethod(): 309.*note getattr(): 54b.*note locals(): 557.   *note repr(): 8b9.     *note zip(): cfc.
                                                                                            
                                                                                            
*note compile(): 2e7.   *note globals(): f55. *note map(): cf7.      *note reversed(): 2c6. *note __import__(): 16b.
                                                                                            
                                                                                            
*note complex(): 2c1.   *note hasattr(): 54a. *note max(): 8f7.      *note round(): d35.
                                                                     

 -- Function: abs (x)

     Return the absolute value of a number.  The argument may be an
     integer, a floating point number, or an object implementing *note
     __abs__(): 15bd.  If the argument is a complex number, its
     magnitude is returned.

 -- Function: all (iterable)

     Return ‘True’ if all elements of the `iterable' are true (or if the
     iterable is empty).  Equivalent to:

          def all(iterable):
              for element in iterable:
                  if not element:
                      return False
              return True

 -- Function: any (iterable)

     Return ‘True’ if any element of the `iterable' is true.  If the
     iterable is empty, return ‘False’.  Equivalent to:

          def any(iterable):
              for element in iterable:
                  if element:
                      return True
              return False

 -- Function: ascii (object)

     As *note repr(): 8b9, return a string containing a printable
     representation of an object, but escape the non-ASCII characters in
     the string returned by *note repr(): 8b9. using ‘\x’, ‘\u’ or ‘\U’
     escapes.  This generates a string similar to that returned by *note
     repr(): 8b9. in Python 2.

 -- Function: bin (x)

     Convert an integer number to a binary string prefixed with “0b”.
     The result is a valid Python expression.  If `x' is not a Python
     *note int: 204. object, it has to define an *note __index__(): 2c2.
     method that returns an integer.  Some examples:

          >>> bin(3)
          '0b11'
          >>> bin(-10)
          '-0b1010'

     If prefix “0b” is desired or not, you can use either of the
     following ways.

          >>> format(14, '#b'), format(14, 'b')
          ('0b1110', '1110')
          >>> f'{14:#b}', f'{14:b}'
          ('0b1110', '1110')

     See also *note format(): 5d6. for more information.

 -- Class: bool ([x])

     Return a Boolean value, i.e.  one of ‘True’ or ‘False’.  `x' is
     converted using the standard *note truth testing procedure: 1718.
     If `x' is false or omitted, this returns ‘False’; otherwise it
     returns ‘True’.  The *note bool: 2bd. class is a subclass of *note
     int: 204. (see *note Numeric Types — int, float, complex: 1353.).
     It cannot be subclassed further.  Its only instances are ‘False’
     and ‘True’ (see *note Boolean Values: 1719.).

     Changed in version 3.7: `x' is now a positional-only parameter.

 -- Function: breakpoint (*args, **kws)

     This function drops you into the debugger at the call site.
     Specifically, it calls *note sys.breakpointhook(): 423, passing
     ‘args’ and ‘kws’ straight through.  By default,
     ‘sys.breakpointhook()’ calls *note pdb.set_trace(): 4c9. expecting
     no arguments.  In this case, it is purely a convenience function so
     you don’t have to explicitly import *note pdb: c9. or type as much
     code to enter the debugger.  However, *note sys.breakpointhook():
     423. can be set to some other function and *note breakpoint(): 40b.
     will automatically call that, allowing you to drop into the
     debugger of choice.

     Raises an *note auditing event: fa1. ‘builtins.breakpoint’ with
     argument ‘breakpointhook’.

     New in version 3.7.

 -- Class: bytearray ([source[, encoding[, errors]]])

     Return a new array of bytes.  The *note bytearray: 173. class is a
     mutable sequence of integers in the range 0 <= x < 256.  It has
     most of the usual methods of mutable sequences, described in *note
     Mutable Sequence Types: 171a, as well as most methods that the
     *note bytes: 172. type has, see *note Bytes and Bytearray
     Operations: 171b.

     The optional `source' parameter can be used to initialize the array
     in a few different ways:

        * If it is a `string', you must also give the `encoding' (and
          optionally, `errors') parameters; *note bytearray(): 173. then
          converts the string to bytes using *note str.encode(): 170.

        * If it is an `integer', the array will have that size and will
          be initialized with null bytes.

        * If it is an object conforming to the *note buffer interface:
          171c, a read-only buffer of the object will be used to
          initialize the bytes array.

        * If it is an `iterable', it must be an iterable of integers in
          the range ‘0 <= x < 256’, which are used as the initial
          contents of the array.

     Without an argument, an array of size 0 is created.

     See also *note Binary Sequence Types — bytes, bytearray,
     memoryview: 171d. and *note Bytearray Objects: 171e.

 -- Class: bytes ([source[, encoding[, errors]]])

     Return a new “bytes” object, which is an immutable sequence of
     integers in the range ‘0 <= x < 256’.  *note bytes: 172. is an
     immutable version of *note bytearray: 173. – it has the same
     non-mutating methods and the same indexing and slicing behavior.

     Accordingly, constructor arguments are interpreted as for *note
     bytearray(): 173.

     Bytes objects can also be created with literals, see *note String
     and Bytes literals: 1514.

     See also *note Binary Sequence Types — bytes, bytearray,
     memoryview: 171d, *note Bytes Objects: 171f, and *note Bytes and
     Bytearray Operations: 171b.

 -- Function: callable (object)

     Return *note True: 594. if the `object' argument appears callable,
     *note False: 48f. if not.  If this returns ‘True’, it is still
     possible that a call fails, but if it is ‘False’, calling `object'
     will never succeed.  Note that classes are callable (calling a
     class returns a new instance); instances are callable if their
     class has a *note __call__(): 1560. method.

     New in version 3.2: This function was first removed in Python 3.0
     and then brought back in Python 3.2.

 -- Function: chr (i)

     Return the string representing a character whose Unicode code point
     is the integer `i'.  For example, ‘chr(97)’ returns the string
     ‘'a'’, while ‘chr(8364)’ returns the string ‘'€'’.  This is the
     inverse of *note ord(): 1559.

     The valid range for the argument is from 0 through 1,114,111
     (0x10FFFF in base 16).  *note ValueError: 16d. will be raised if
     `i' is outside that range.

 -- Function: @classmethod

     Transform a method into a class method.

     A class method receives the class as implicit first argument, just
     like an instance method receives the instance.  To declare a class
     method, use this idiom:

          class C:
              @classmethod
              def f(cls, arg1, arg2, ...): ...

     The ‘@classmethod’ form is a function *note decorator: 174. – see
     *note Function definitions: 1390. for details.

     A class method can be called either on the class (such as ‘C.f()’)
     or on an instance (such as ‘C().f()’).  The instance is ignored
     except for its class.  If a class method is called for a derived
     class, the derived class object is passed as the implied first
     argument.

     Class methods are different than C++ or Java static methods.  If
     you want those, see *note staticmethod(): 30a. in this section.
     For more information on class methods, see *note The standard type
     hierarchy: 1553.

     Changed in version 3.9: Class methods can now wrap other *note
     descriptors: 1579. such as *note property(): 308.

 -- Function: compile (source, filename, mode, flags=0,
          dont_inherit=False, optimize=-1)

     Compile the `source' into a code or AST object.  Code objects can
     be executed by *note exec(): d0c. or *note eval(): c61.  `source'
     can either be a normal string, a byte string, or an AST object.
     Refer to the *note ast: 7. module documentation for information on
     how to work with AST objects.

     The `filename' argument should give the file from which the code
     was read; pass some recognizable value if it wasn’t read from a
     file (‘'<string>'’ is commonly used).

     The `mode' argument specifies what kind of code must be compiled;
     it can be ‘'exec'’ if `source' consists of a sequence of
     statements, ‘'eval'’ if it consists of a single expression, or
     ‘'single'’ if it consists of a single interactive statement (in the
     latter case, expression statements that evaluate to something other
     than ‘None’ will be printed).

     The optional arguments `flags' and `dont_inherit' control which
     *note compiler options: 1720. should be activated and which *note
     future features: 16c4. should be allowed.  If neither is present
     (or both are zero) the code is compiled with the same flags that
     affect the code that is calling *note compile(): 2e7.  If the
     `flags' argument is given and `dont_inherit' is not (or is zero)
     then the compiler options and the future statements specified by
     the `flags' argument are used in addition to those that would be
     used anyway.  If `dont_inherit' is a non-zero integer then the
     `flags' argument is it – the flags (future features and compiler
     options) in the surrounding code are ignored.

     Compiler options and future statements are specified by bits which
     can be bitwise ORed together to specify multiple options.  The
     bitfield required to specify a given future feature can be found as
     the ‘compiler_flag’ attribute on the ‘_Feature’ instance in the
     *note __future__: 0. module.  *note Compiler flags: 1720. can be
     found in *note ast: 7. module, with ‘PyCF_’ prefix.

     The argument `optimize' specifies the optimization level of the
     compiler; the default value of ‘-1’ selects the optimization level
     of the interpreter as given by *note -O: 77e. options.  Explicit
     levels are ‘0’ (no optimization; ‘__debug__’ is true), ‘1’ (asserts
     are removed, ‘__debug__’ is false) or ‘2’ (docstrings are removed
     too).

     This function raises *note SyntaxError: 55a. if the compiled source
     is invalid, and *note ValueError: 16d. if the source contains null
     bytes.

     If you want to parse Python code into its AST representation, see
     *note ast.parse(): 2d6.

     Raises an *note auditing event: fa1. ‘compile’ with arguments
     ‘source’ and ‘filename’.  This event may also be raised by implicit
     compilation.

          Note: When compiling a string with multi-line code in
          ‘'single'’ or ‘'eval'’ mode, input must be terminated by at
          least one newline character.  This is to facilitate detection
          of incomplete and complete statements in the *note code: 1a.
          module.

          Warning: It is possible to crash the Python interpreter with a
          sufficiently large/complex string when compiling to an AST
          object due to stack depth limitations in Python’s AST
          compiler.

     Changed in version 3.2: Allowed use of Windows and Mac newlines.
     Also input in ‘'exec'’ mode does not have to end in a newline
     anymore.  Added the `optimize' parameter.

     Changed in version 3.5: Previously, *note TypeError: 1fe. was
     raised when null bytes were encountered in `source'.

     New in version 3.8: ‘ast.PyCF_ALLOW_TOP_LEVEL_AWAIT’ can now be
     passed in flags to enable support for top-level ‘await’, ‘async
     for’, and ‘async with’.

 -- Class: complex ([real[, imag]])

     Return a complex number with the value `real' + `imag'*1j or
     convert a string or number to a complex number.  If the first
     parameter is a string, it will be interpreted as a complex number
     and the function must be called without a second parameter.  The
     second parameter can never be a string.  Each argument may be any
     numeric type (including complex).  If `imag' is omitted, it
     defaults to zero and the constructor serves as a numeric conversion
     like *note int: 204. and *note float: 1fd.  If both arguments are
     omitted, returns ‘0j’.

     For a general Python object ‘x’, ‘complex(x)’ delegates to
     ‘x.__complex__()’.  If ‘__complex__()’ is not defined then it falls
     back to *note __float__(): 2c4.  If ‘__float__()’ is not defined
     then it falls back to *note __index__(): 2c2.

          Note: When converting from a string, the string must not
          contain whitespace around the central ‘+’ or ‘-’ operator.
          For example, ‘complex('1+2j')’ is fine, but ‘complex('1 +
          2j')’ raises *note ValueError: 16d.

     The complex type is described in *note Numeric Types — int, float,
     complex: 1353.

     Changed in version 3.6: Grouping digits with underscores as in code
     literals is allowed.

     Changed in version 3.8: Falls back to *note __index__(): 2c2. if
     *note __complex__(): 2c5. and *note __float__(): 2c4. are not
     defined.

 -- Function: delattr (object, name)

     This is a relative of *note setattr(): 1712.  The arguments are an
     object and a string.  The string must be the name of one of the
     object’s attributes.  The function deletes the named attribute,
     provided the object allows it.  For example, ‘delattr(x, 'foobar')’
     is equivalent to ‘del x.foobar’.

 -- Class: dict (**kwarg)

 -- Class: dict (mapping, **kwarg)

 -- Class: dict (iterable, **kwarg)

     Create a new dictionary.  The *note dict: 164. object is the
     dictionary class.  See *note dict: 164. and *note Mapping Types —
     dict: 40e. for documentation about this class.

     For other containers see the built-in *note list: 1f8, *note set:
     1f6, and *note tuple: 1a2. classes, as well as the *note
     collections: 1d. module.

 -- Function: dir ([object])

     Without arguments, return the list of names in the current local
     scope.  With an argument, attempt to return a list of valid
     attributes for that object.

     If the object has a method named *note __dir__(): 42b, this method
     will be called and must return the list of attributes.  This allows
     objects that implement a custom *note __getattr__(): 42a. or *note
     __getattribute__(): 54c. function to customize the way *note dir():
     df9. reports their attributes.

     If the object does not provide *note __dir__(): 42b, the function
     tries its best to gather information from the object’s *note
     __dict__: 5f6. attribute, if defined, and from its type object.
     The resulting list is not necessarily complete, and may be
     inaccurate when the object has a custom *note __getattr__(): 42a.

     The default *note dir(): df9. mechanism behaves differently with
     different types of objects, as it attempts to produce the most
     relevant, rather than complete, information:

        * If the object is a module object, the list contains the names
          of the module’s attributes.

        * If the object is a type or class object, the list contains the
          names of its attributes, and recursively of the attributes of
          its bases.

        * Otherwise, the list contains the object’s attributes’ names,
          the names of its class’s attributes, and recursively of the
          attributes of its class’s base classes.

     The resulting list is sorted alphabetically.  For example:

          >>> import struct
          >>> dir()   # show the names in the module namespace
          ['__builtins__', '__name__', 'struct']
          >>> dir(struct)   # show the names in the struct module
          ['Struct', '__all__', '__builtins__', '__cached__', '__doc__', '__file__',
           '__initializing__', '__loader__', '__name__', '__package__',
           '_clearcache', 'calcsize', 'error', 'pack', 'pack_into',
           'unpack', 'unpack_from']
          >>> class Shape:
          ...     def __dir__(self):
          ...         return ['area', 'perimeter', 'location']
          >>> s = Shape()
          >>> dir(s)
          ['area', 'location', 'perimeter']

          Note: Because *note dir(): df9. is supplied primarily as a
          convenience for use at an interactive prompt, it tries to
          supply an interesting set of names more than it tries to
          supply a rigorously or consistently defined set of names, and
          its detailed behavior may change across releases.  For
          example, metaclass attributes are not in the result list when
          the argument is a class.

 -- Function: divmod (a, b)

     Take two (non complex) numbers as arguments and return a pair of
     numbers consisting of their quotient and remainder when using
     integer division.  With mixed operand types, the rules for binary
     arithmetic operators apply.  For integers, the result is the same
     as ‘(a // b, a % b)’.  For floating point numbers the result is
     ‘(q, a % b)’, where `q' is usually ‘math.floor(a / b)’ but may be 1
     less than that.  In any case ‘q * b + a % b’ is very close to `a',
     if ‘a % b’ is non-zero it has the same sign as `b', and ‘0 <= abs(a
     % b) < abs(b)’.

 -- Function: enumerate (iterable, start=0)

     Return an enumerate object.  `iterable' must be a sequence, an
     *note iterator: 1171, or some other object which supports
     iteration.  The *note __next__(): d2c. method of the iterator
     returned by *note enumerate(): ea7. returns a tuple containing a
     count (from `start' which defaults to 0) and the values obtained
     from iterating over `iterable'.

          >>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']
          >>> list(enumerate(seasons))
          [(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]
          >>> list(enumerate(seasons, start=1))
          [(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]

     Equivalent to:

          def enumerate(sequence, start=0):
              n = start
              for elem in sequence:
                  yield n, elem
                  n += 1

 -- Function: eval (expression[, globals[, locals]])

     The arguments are a string and optional globals and locals.  If
     provided, `globals' must be a dictionary.  If provided, `locals'
     can be any mapping object.

     The `expression' argument is parsed and evaluated as a Python
     expression (technically speaking, a condition list) using the
     `globals' and `locals' dictionaries as global and local namespace.
     If the `globals' dictionary is present and does not contain a value
     for the key ‘__builtins__’, a reference to the dictionary of the
     built-in module *note builtins: 12. is inserted under that key
     before `expression' is parsed.  This means that `expression'
     normally has full access to the standard *note builtins: 12. module
     and restricted environments are propagated.  If the `locals'
     dictionary is omitted it defaults to the `globals' dictionary.  If
     both dictionaries are omitted, the expression is executed with the
     `globals' and `locals' in the environment where *note eval(): c61.
     is called.  Note, `eval()' does not have access to the *note nested
     scopes: 1721. (non-locals) in the enclosing environment.

     The return value is the result of the evaluated expression.  Syntax
     errors are reported as exceptions.  Example:

          >>> x = 1
          >>> eval('x+1')
          2

     This function can also be used to execute arbitrary code objects
     (such as those created by *note compile(): 2e7.).  In this case
     pass a code object instead of a string.  If the code object has
     been compiled with ‘'exec'’ as the `mode' argument, *note eval():
     c61.’s return value will be ‘None’.

     Hints: dynamic execution of statements is supported by the *note
     exec(): d0c. function.  The *note globals(): f55. and *note
     locals(): 557. functions returns the current global and local
     dictionary, respectively, which may be useful to pass around for
     use by *note eval(): c61. or *note exec(): d0c.

     See *note ast.literal_eval(): 5a0. for a function that can safely
     evaluate strings with expressions containing only literals.

     Raises an *note auditing event: fa1. ‘exec’ with the code object as
     the argument.  Code compilation events may also be raised.

 -- Function: exec (object[, globals[, locals]])

     This function supports dynamic execution of Python code.  `object'
     must be either a string or a code object.  If it is a string, the
     string is parsed as a suite of Python statements which is then
     executed (unless a syntax error occurs).  (1) If it is a code
     object, it is simply executed.  In all cases, the code that’s
     executed is expected to be valid as file input (see the section
     *note File input: 16fb. in the Reference Manual).  Be aware that
     the *note nonlocal: d07, *note yield: 2c7, and *note return: 2c8.
     statements may not be used outside of function definitions even
     within the context of code passed to the *note exec(): d0c.
     function.  The return value is ‘None’.

     In all cases, if the optional parts are omitted, the code is
     executed in the current scope.  If only `globals' is provided, it
     must be a dictionary (and not a subclass of dictionary), which will
     be used for both the global and the local variables.  If `globals'
     and `locals' are given, they are used for the global and local
     variables, respectively.  If provided, `locals' can be any mapping
     object.  Remember that at module level, globals and locals are the
     same dictionary.  If exec gets two separate objects as `globals'
     and `locals', the code will be executed as if it were embedded in a
     class definition.

     If the `globals' dictionary does not contain a value for the key
     ‘__builtins__’, a reference to the dictionary of the built-in
     module *note builtins: 12. is inserted under that key.  That way
     you can control what builtins are available to the executed code by
     inserting your own ‘__builtins__’ dictionary into `globals' before
     passing it to *note exec(): d0c.

     Raises an *note auditing event: fa1. ‘exec’ with the code object as
     the argument.  Code compilation events may also be raised.

          Note: The built-in functions *note globals(): f55. and *note
          locals(): 557. return the current global and local dictionary,
          respectively, which may be useful to pass around for use as
          the second and third argument to *note exec(): d0c.

          Note: The default `locals' act as described for function *note
          locals(): 557. below: modifications to the default `locals'
          dictionary should not be attempted.  Pass an explicit `locals'
          dictionary if you need to see effects of the code on `locals'
          after function *note exec(): d0c. returns.

 -- Function: filter (function, iterable)

     Construct an iterator from those elements of `iterable' for which
     `function' returns true.  `iterable' may be either a sequence, a
     container which supports iteration, or an iterator.  If `function'
     is ‘None’, the identity function is assumed, that is, all elements
     of `iterable' that are false are removed.

     Note that ‘filter(function, iterable)’ is equivalent to the
     generator expression ‘(item for item in iterable if
     function(item))’ if function is not ‘None’ and ‘(item for item in
     iterable if item)’ if function is ‘None’.

     See *note itertools.filterfalse(): 1722. for the complementary
     function that returns elements of `iterable' for which `function'
     returns false.

 -- Class: float ([x])

     Return a floating point number constructed from a number or string
     `x'.

     If the argument is a string, it should contain a decimal number,
     optionally preceded by a sign, and optionally embedded in
     whitespace.  The optional sign may be ‘'+'’ or ‘'-'’; a ‘'+'’ sign
     has no effect on the value produced.  The argument may also be a
     string representing a NaN (not-a-number), or a positive or negative
     infinity.  More precisely, the input must conform to the following
     grammar after leading and trailing whitespace characters are
     removed:

          sign           ::= "+" | "-"
          infinity       ::= "Infinity" | "inf"
          nan            ::= "nan"
          numeric_value  ::= floatnumber | infinity | nan
          numeric_string ::= [sign] numeric_value

     Here ‘floatnumber’ is the form of a Python floating-point literal,
     described in *note Floating point literals: 153e.  Case is not
     significant, so, for example, “inf”, “Inf”, “INFINITY” and
     “iNfINity” are all acceptable spellings for positive infinity.

     Otherwise, if the argument is an integer or a floating point
     number, a floating point number with the same value (within
     Python’s floating point precision) is returned.  If the argument is
     outside the range of a Python float, an *note OverflowError: a41.
     will be raised.

     For a general Python object ‘x’, ‘float(x)’ delegates to
     ‘x.__float__()’.  If ‘__float__()’ is not defined then it falls
     back to *note __index__(): 2c2.

     If no argument is given, ‘0.0’ is returned.

     Examples:

          >>> float('+1.23')
          1.23
          >>> float('   -12345\n')
          -12345.0
          >>> float('1e-003')
          0.001
          >>> float('+1E6')
          1000000.0
          >>> float('-Infinity')
          -inf

     The float type is described in *note Numeric Types — int, float,
     complex: 1353.

     Changed in version 3.6: Grouping digits with underscores as in code
     literals is allowed.

     Changed in version 3.7: `x' is now a positional-only parameter.

     Changed in version 3.8: Falls back to *note __index__(): 2c2. if
     *note __float__(): 2c4. is not defined.

 -- Function: format (value[, format_spec])

     Convert a `value' to a “formatted” representation, as controlled by
     `format_spec'.  The interpretation of `format_spec' will depend on
     the type of the `value' argument, however there is a standard
     formatting syntax that is used by most built-in types: *note Format
     Specification Mini-Language: 5d9.

     The default `format_spec' is an empty string which usually gives
     the same effect as calling *note str(value): 205.

     A call to ‘format(value, format_spec)’ is translated to
     ‘type(value).__format__(value, format_spec)’ which bypasses the
     instance dictionary when searching for the value’s *note
     __format__(): a2f. method.  A *note TypeError: 1fe. exception is
     raised if the method search reaches *note object: 3d2. and the
     `format_spec' is non-empty, or if either the `format_spec' or the
     return value are not strings.

     Changed in version 3.4: ‘object().__format__(format_spec)’ raises
     *note TypeError: 1fe. if `format_spec' is not an empty string.

 -- Class: frozenset ([iterable])

     Return a new *note frozenset: 1f7. object, optionally with elements
     taken from `iterable'.  ‘frozenset’ is a built-in class.  See *note
     frozenset: 1f7. and *note Set Types — set, frozenset: 1728. for
     documentation about this class.

     For other containers see the built-in *note set: 1f6, *note list:
     1f8, *note tuple: 1a2, and *note dict: 164. classes, as well as the
     *note collections: 1d. module.

 -- Function: getattr (object, name[, default])

     Return the value of the named attribute of `object'.  `name' must
     be a string.  If the string is the name of one of the object’s
     attributes, the result is the value of that attribute.  For
     example, ‘getattr(x, 'foobar')’ is equivalent to ‘x.foobar’.  If
     the named attribute does not exist, `default' is returned if
     provided, otherwise *note AttributeError: 4a2. is raised.

          Note: Since *note private name mangling: 1621. happens at
          compilation time, one must manually mangle a private
          attribute’s (attributes with two leading underscores) name in
          order to retrieve it with *note getattr(): 54b.

 -- Function: globals ()

     Return the dictionary implementing the current module namespace.
     For code within functions, this is set when the function is defined
     and remains the same regardless of where the function is called.

 -- Function: hasattr (object, name)

     The arguments are an object and a string.  The result is ‘True’ if
     the string is the name of one of the object’s attributes, ‘False’
     if not.  (This is implemented by calling ‘getattr(object, name)’
     and seeing whether it raises an *note AttributeError: 4a2. or not.)

 -- Function: hash (object)

     Return the hash value of the object (if it has one).  Hash values
     are integers.  They are used to quickly compare dictionary keys
     during a dictionary lookup.  Numeric values that compare equal have
     the same hash value (even if they are of different types, as is the
     case for 1 and 1.0).

          Note: For objects with custom *note __hash__(): 44c. methods,
          note that *note hash(): aa3. truncates the return value based
          on the bit width of the host machine.  See *note __hash__():
          44c. for details.

 -- Function: help ([object])

     Invoke the built-in help system.  (This function is intended for
     interactive use.)  If no argument is given, the interactive help
     system starts on the interpreter console.  If the argument is a
     string, then the string is looked up as the name of a module,
     function, class, method, keyword, or documentation topic, and a
     help page is printed on the console.  If the argument is any other
     kind of object, a help page on the object is generated.

     Note that if a slash(/) appears in the parameter list of a
     function, when invoking *note help(): 175, it means that the
     parameters prior to the slash are positional-only.  For more info,
     see *note the FAQ entry on positional-only parameters: 1729.

     This function is added to the built-in namespace by the *note site:
     eb. module.

     Changed in version 3.4: Changes to *note pydoc: d9. and *note
     inspect: a0. mean that the reported signatures for callables are
     now more comprehensive and consistent.

 -- Function: hex (x)

     Convert an integer number to a lowercase hexadecimal string
     prefixed with “0x”.  If `x' is not a Python *note int: 204. object,
     it has to define an *note __index__(): 2c2. method that returns an
     integer.  Some examples:

          >>> hex(255)
          '0xff'
          >>> hex(-42)
          '-0x2a'

     If you want to convert an integer number to an uppercase or lower
     hexadecimal string with prefix or not, you can use either of the
     following ways:

          >>> '%#x' % 255, '%x' % 255, '%X' % 255
          ('0xff', 'ff', 'FF')
          >>> format(255, '#x'), format(255, 'x'), format(255, 'X')
          ('0xff', 'ff', 'FF')
          >>> f'{255:#x}', f'{255:x}', f'{255:X}'
          ('0xff', 'ff', 'FF')

     See also *note format(): 5d6. for more information.

     See also *note int(): 204. for converting a hexadecimal string to
     an integer using a base of 16.

          Note: To obtain a hexadecimal string representation for a
          float, use the *note float.hex(): 1458. method.

 -- Function: id (object)

     Return the “identity” of an object.  This is an integer which is
     guaranteed to be unique and constant for this object during its
     lifetime.  Two objects with non-overlapping lifetimes may have the
     same *note id(): e4b. value.

     `CPython implementation detail:' This is the address of the object
     in memory.

     Raises an *note auditing event: fa1. ‘builtins.id’ with argument
     ‘id’.

 -- Function: input ([prompt])

     If the `prompt' argument is present, it is written to standard
     output without a trailing newline.  The function then reads a line
     from input, converts it to a string (stripping a trailing newline),
     and returns that.  When EOF is read, *note EOFError: d34. is
     raised.  Example:

          >>> s = input('--> ')
          --> Monty Python's Flying Circus
          >>> s
          "Monty Python's Flying Circus"

     If the *note readline: de. module was loaded, then *note input():
     d33. will use it to provide elaborate line editing and history
     features.

     Raises an *note auditing event: fa1. ‘builtins.input’ with argument
     ‘prompt’ before reading input

     Raises an auditing event ‘builtins.input/result’ with the result
     after successfully reading input.

 -- Class: int ([x])

 -- Class: int (x, base=10)

     Return an integer object constructed from a number or string `x',
     or return ‘0’ if no arguments are given.  If `x' defines *note
     __int__(): 2c3, ‘int(x)’ returns ‘x.__int__()’.  If `x' defines
     *note __index__(): 2c2, it returns ‘x.__index__()’.  If `x' defines
     *note __trunc__(): 15c1, it returns ‘x.__trunc__()’.  For floating
     point numbers, this truncates towards zero.

     If `x' is not a number or if `base' is given, then `x' must be a
     string, *note bytes: 172, or *note bytearray: 173. instance
     representing an *note integer literal: 1533. in radix `base'.
     Optionally, the literal can be preceded by ‘+’ or ‘-’ (with no
     space in between) and surrounded by whitespace.  A base-n literal
     consists of the digits 0 to n-1, with ‘a’ to ‘z’ (or ‘A’ to ‘Z’)
     having values 10 to 35.  The default `base' is 10.  The allowed
     values are 0 and 2–36.  Base-2, -8, and -16 literals can be
     optionally prefixed with ‘0b’/‘0B’, ‘0o’/‘0O’, or ‘0x’/‘0X’, as
     with integer literals in code.  Base 0 means to interpret exactly
     as a code literal, so that the actual base is 2, 8, 10, or 16, and
     so that ‘int('010', 0)’ is not legal, while ‘int('010')’ is, as
     well as ‘int('010', 8)’.

     The integer type is described in *note Numeric Types — int, float,
     complex: 1353.

     Changed in version 3.4: If `base' is not an instance of *note int:
     204. and the `base' object has a *note base.__index__: 2c2. method,
     that method is called to obtain an integer for the base.  Previous
     versions used *note base.__int__: 2c3. instead of *note
     base.__index__: 2c2.

     Changed in version 3.6: Grouping digits with underscores as in code
     literals is allowed.

     Changed in version 3.7: `x' is now a positional-only parameter.

     Changed in version 3.8: Falls back to *note __index__(): 2c2. if
     *note __int__(): 2c3. is not defined.

 -- Function: isinstance (object, classinfo)

     Return ‘True’ if the `object' argument is an instance of the
     `classinfo' argument, or of a (direct, indirect or *note virtual:
     c05.) subclass thereof.  If `object' is not an object of the given
     type, the function always returns ‘False’.  If `classinfo' is a
     tuple of type objects (or recursively, other such tuples), return
     ‘True’ if `object' is an instance of any of the types.  If
     `classinfo' is not a type or tuple of types and such tuples, a
     *note TypeError: 1fe. exception is raised.

 -- Function: issubclass (class, classinfo)

     Return ‘True’ if `class' is a subclass (direct, indirect or *note
     virtual: c05.) of `classinfo'.  A class is considered a subclass of
     itself.  `classinfo' may be a tuple of class objects, in which case
     return ‘True’ if `class' is a subclass of any entry in `classinfo'.
     In any other case, a *note TypeError: 1fe. exception is raised.

 -- Function: iter (object[, sentinel])

     Return an *note iterator: 1171. object.  The first argument is
     interpreted very differently depending on the presence of the
     second argument.  Without a second argument, `object' must be a
     collection object which supports the iteration protocol (the *note
     __iter__(): 609. method), or it must support the sequence protocol
     (the *note __getitem__(): 3a2. method with integer arguments
     starting at ‘0’).  If it does not support either of those
     protocols, *note TypeError: 1fe. is raised.  If the second
     argument, `sentinel', is given, then `object' must be a callable
     object.  The iterator created in this case will call `object' with
     no arguments for each call to its *note __next__(): d2c. method; if
     the value returned is equal to `sentinel', *note StopIteration:
     582. will be raised, otherwise the value will be returned.

     See also *note Iterator Types: 159a.

     One useful application of the second form of *note iter(): ded. is
     to build a block-reader.  For example, reading fixed-width blocks
     from a binary database file until the end of file is reached:

          from functools import partial
          with open('mydata.db', 'rb') as f:
              for block in iter(partial(f.read, 64), b''):
                  process_block(block)

 -- Function: len (s)

     Return the length (the number of items) of an object.  The argument
     may be a sequence (such as a string, bytes, tuple, list, or range)
     or a collection (such as a dictionary, set, or frozen set).

     `CPython implementation detail:' ‘len’ raises *note OverflowError:
     a41. on lengths larger than *note sys.maxsize: c15, such as *note
     range(2 ** 100): 1f5.

 -- Class: list ([iterable])

     Rather than being a function, *note list: 1f8. is actually a
     mutable sequence type, as documented in *note Lists: 172a. and
     *note Sequence Types — list, tuple, range: 13a4.

 -- Function: locals ()

     Update and return a dictionary representing the current local
     symbol table.  Free variables are returned by *note locals(): 557.
     when it is called in function blocks, but not in class blocks.
     Note that at the module level, *note locals(): 557. and *note
     globals(): f55. are the same dictionary.

          Note: The contents of this dictionary should not be modified;
          changes may not affect the values of local and free variables
          used by the interpreter.

 -- Function: map (function, iterable, ...)

     Return an iterator that applies `function' to every item of
     `iterable', yielding the results.  If additional `iterable'
     arguments are passed, `function' must take that many arguments and
     is applied to the items from all iterables in parallel.  With
     multiple iterables, the iterator stops when the shortest iterable
     is exhausted.  For cases where the function inputs are already
     arranged into argument tuples, see *note itertools.starmap(): b05.

 -- Function: max (iterable, *[, key, default])

 -- Function: max (arg1, arg2, *args[, key])

     Return the largest item in an iterable or the largest of two or
     more arguments.

     If one positional argument is provided, it should be an *note
     iterable: c7c.  The largest item in the iterable is returned.  If
     two or more positional arguments are provided, the largest of the
     positional arguments is returned.

     There are two optional keyword-only arguments.  The `key' argument
     specifies a one-argument ordering function like that used for *note
     list.sort(): 548.  The `default' argument specifies an object to
     return if the provided iterable is empty.  If the iterable is empty
     and `default' is not provided, a *note ValueError: 16d. is raised.

     If multiple items are maximal, the function returns the first one
     encountered.  This is consistent with other sort-stability
     preserving tools such as ‘sorted(iterable, key=keyfunc,
     reverse=True)[0]’ and ‘heapq.nlargest(1, iterable, key=keyfunc)’.

     New in version 3.4: The `default' keyword-only argument.

     Changed in version 3.8: The `key' can be ‘None’.

 -- Class: memoryview (object)

     Return a “memory view” object created from the given argument.  See
     *note Memory Views: 172b. for more information.

 -- Function: min (iterable, *[, key, default])

 -- Function: min (arg1, arg2, *args[, key])

     Return the smallest item in an iterable or the smallest of two or
     more arguments.

     If one positional argument is provided, it should be an *note
     iterable: c7c.  The smallest item in the iterable is returned.  If
     two or more positional arguments are provided, the smallest of the
     positional arguments is returned.

     There are two optional keyword-only arguments.  The `key' argument
     specifies a one-argument ordering function like that used for *note
     list.sort(): 548.  The `default' argument specifies an object to
     return if the provided iterable is empty.  If the iterable is empty
     and `default' is not provided, a *note ValueError: 16d. is raised.

     If multiple items are minimal, the function returns the first one
     encountered.  This is consistent with other sort-stability
     preserving tools such as ‘sorted(iterable, key=keyfunc)[0]’ and
     ‘heapq.nsmallest(1, iterable, key=keyfunc)’.

     New in version 3.4: The `default' keyword-only argument.

     Changed in version 3.8: The `key' can be ‘None’.

 -- Function: next (iterator[, default])

     Retrieve the next item from the `iterator' by calling its *note
     __next__(): d2c. method.  If `default' is given, it is returned if
     the iterator is exhausted, otherwise *note StopIteration: 582. is
     raised.

 -- Class: object

     Return a new featureless object.  *note object: 3d2. is a base for
     all classes.  It has the methods that are common to all instances
     of Python classes.  This function does not accept any arguments.

          Note: *note object: 3d2. does `not' have a *note __dict__:
          5f6, so you can’t assign arbitrary attributes to an instance
          of the *note object: 3d2. class.

 -- Function: oct (x)

     Convert an integer number to an octal string prefixed with “0o”.
     The result is a valid Python expression.  If `x' is not a Python
     *note int: 204. object, it has to define an *note __index__(): 2c2.
     method that returns an integer.  For example:

          >>> oct(8)
          '0o10'
          >>> oct(-56)
          '-0o70'

     If you want to convert an integer number to octal string either
     with prefix “0o” or not, you can use either of the following ways.

          >>> '%#o' % 10, '%o' % 10
          ('0o12', '12')
          >>> format(10, '#o'), format(10, 'o')
          ('0o12', '12')
          >>> f'{10:#o}', f'{10:o}'
          ('0o12', '12')

     See also *note format(): 5d6. for more information.

 -- Function: open (file, mode='r', buffering=-1, encoding=None,
          errors=None, newline=None, closefd=True, opener=None)

     Open `file' and return a corresponding *note file object: c14.  If
     the file cannot be opened, an *note OSError: 304. is raised.  See
     *note Reading and Writing Files: 13d4. for more examples of how to
     use this function.

     `file' is a *note path-like object: 472. giving the pathname
     (absolute or relative to the current working directory) of the file
     to be opened or an integer file descriptor of the file to be
     wrapped.  (If a file descriptor is given, it is closed when the
     returned I/O object is closed, unless `closefd' is set to ‘False’.)

     `mode' is an optional string that specifies the mode in which the
     file is opened.  It defaults to ‘'r'’ which means open for reading
     in text mode.  Other common values are ‘'w'’ for writing
     (truncating the file if it already exists), ‘'x'’ for exclusive
     creation and ‘'a'’ for appending (which on `some' Unix systems,
     means that `all' writes append to the end of the file regardless of
     the current seek position).  In text mode, if `encoding' is not
     specified the encoding used is platform dependent:
     ‘locale.getpreferredencoding(False)’ is called to get the current
     locale encoding.  (For reading and writing raw bytes use binary
     mode and leave `encoding' unspecified.)  The available modes are:

     Character     Meaning
                   
     ----------------------------------------------------------------------------------
                   
     ‘'r'’         open for reading (default)
                   
                   
     ‘'w'’         open for writing, truncating the file first
                   
                   
     ‘'x'’         open for exclusive creation, failing if the file already exists
                   
                   
     ‘'a'’         open for writing, appending to the end of the file if it exists
                   
                   
     ‘'b'’         binary mode
                   
                   
     ‘'t'’         text mode (default)
                   
                   
     ‘'+'’         open for updating (reading and writing)
                   

     The default mode is ‘'r'’ (open for reading text, synonym of
     ‘'rt'’).  Modes ‘'w+'’ and ‘'w+b'’ open and truncate the file.
     Modes ‘'r+'’ and ‘'r+b'’ open the file with no truncation.

     As mentioned in the *note Overview: 172d, Python distinguishes
     between binary and text I/O. Files opened in binary mode (including
     ‘'b'’ in the `mode' argument) return contents as *note bytes: 172.
     objects without any decoding.  In text mode (the default, or when
     ‘'t'’ is included in the `mode' argument), the contents of the file
     are returned as *note str: 205, the bytes having been first decoded
     using a platform-dependent encoding or using the specified
     `encoding' if given.

     There is an additional mode character permitted, ‘'U'’, which no
     longer has any effect, and is considered deprecated.  It previously
     enabled *note universal newlines: 6eb. in text mode, which became
     the default behaviour in Python 3.0.  Refer to the documentation of
     the *note newline: 172e. parameter for further details.

          Note: Python doesn’t depend on the underlying operating
          system’s notion of text files; all the processing is done by
          Python itself, and is therefore platform-independent.

     `buffering' is an optional integer used to set the buffering
     policy.  Pass 0 to switch buffering off (only allowed in binary
     mode), 1 to select line buffering (only usable in text mode), and
     an integer > 1 to indicate the size in bytes of a fixed-size chunk
     buffer.  When no `buffering' argument is given, the default
     buffering policy works as follows:

        * Binary files are buffered in fixed-size chunks; the size of
          the buffer is chosen using a heuristic trying to determine the
          underlying device’s “block size” and falling back on *note
          io.DEFAULT_BUFFER_SIZE: 172f.  On many systems, the buffer
          will typically be 4096 or 8192 bytes long.

        * “Interactive” text files (files for which *note isatty():
          1730. returns ‘True’) use line buffering.  Other text files
          use the policy described above for binary files.

     `encoding' is the name of the encoding used to decode or encode the
     file.  This should only be used in text mode.  The default encoding
     is platform dependent (whatever *note
     locale.getpreferredencoding(): 4ac. returns), but any *note text
     encoding: 1731. supported by Python can be used.  See the *note
     codecs: 1b. module for the list of supported encodings.

     `errors' is an optional string that specifies how encoding and
     decoding errors are to be handled—this cannot be used in binary
     mode.  A variety of standard error handlers are available (listed
     under *note Error Handlers: 1493.), though any error handling name
     that has been registered with *note codecs.register_error(): eb9.
     is also valid.  The standard names include:

        * ‘'strict'’ to raise a *note ValueError: 16d. exception if
          there is an encoding error.  The default value of ‘None’ has
          the same effect.

        * ‘'ignore'’ ignores errors.  Note that ignoring encoding errors
          can lead to data loss.

        * ‘'replace'’ causes a replacement marker (such as ‘'?'’) to be
          inserted where there is malformed data.

        * ‘'surrogateescape'’ will represent any incorrect bytes as low
          surrogate code units ranging from U+DC80 to U+DCFF. These
          surrogate code units will then be turned back into the same
          bytes when the ‘surrogateescape’ error handler is used when
          writing data.  This is useful for processing files in an
          unknown encoding.

        * ‘'xmlcharrefreplace'’ is only supported when writing to a
          file.  Characters not supported by the encoding are replaced
          with the appropriate XML character reference ‘&#nnn;’.

        * ‘'backslashreplace'’ replaces malformed data by Python’s
          backslashed escape sequences.

        * ‘'namereplace'’ (also only supported when writing) replaces
          unsupported characters with ‘\N{...}’ escape sequences.

     `newline' controls how *note universal newlines: 6eb. mode works
     (it only applies to text mode).  It can be ‘None’, ‘''’, ‘'\n'’,
     ‘'\r'’, and ‘'\r\n'’.  It works as follows:

        * When reading input from the stream, if `newline' is ‘None’,
          universal newlines mode is enabled.  Lines in the input can
          end in ‘'\n'’, ‘'\r'’, or ‘'\r\n'’, and these are translated
          into ‘'\n'’ before being returned to the caller.  If it is
          ‘''’, universal newlines mode is enabled, but line endings are
          returned to the caller untranslated.  If it has any of the
          other legal values, input lines are only terminated by the
          given string, and the line ending is returned to the caller
          untranslated.

        * When writing output to the stream, if `newline' is ‘None’, any
          ‘'\n'’ characters written are translated to the system default
          line separator, *note os.linesep: 1732.  If `newline' is ‘''’
          or ‘'\n'’, no translation takes place.  If `newline' is any of
          the other legal values, any ‘'\n'’ characters written are
          translated to the given string.

     If `closefd' is ‘False’ and a file descriptor rather than a
     filename was given, the underlying file descriptor will be kept
     open when the file is closed.  If a filename is given `closefd'
     must be ‘True’ (the default) otherwise an error will be raised.

     A custom opener can be used by passing a callable as `opener'.  The
     underlying file descriptor for the file object is then obtained by
     calling `opener' with (`file', `flags').  `opener' must return an
     open file descriptor (passing *note os.open: 758. as `opener'
     results in functionality similar to passing ‘None’).

     The newly created file is *note non-inheritable: 8e7.

     The following example uses the *note dir_fd: b0b. parameter of the
     *note os.open(): 758. function to open a file relative to a given
     directory:

          >>> import os
          >>> dir_fd = os.open('somedir', os.O_RDONLY)
          >>> def opener(path, flags):
          ...     return os.open(path, flags, dir_fd=dir_fd)
          ...
          >>> with open('spamspam.txt', 'w', opener=opener) as f:
          ...     print('This will be written to somedir/spamspam.txt', file=f)
          ...
          >>> os.close(dir_fd)  # don't leak a file descriptor

     The type of *note file object: c14. returned by the *note open():
     16f. function depends on the mode.  When *note open(): 16f. is used
     to open a file in a text mode (‘'w'’, ‘'r'’, ‘'wt'’, ‘'rt'’, etc.),
     it returns a subclass of *note io.TextIOBase: d01. (specifically
     *note io.TextIOWrapper: 6ea.).  When used to open a file in a
     binary mode with buffering, the returned class is a subclass of
     *note io.BufferedIOBase: 67f.  The exact class varies: in read
     binary mode, it returns an *note io.BufferedReader: c5b.; in write
     binary and append binary modes, it returns an *note
     io.BufferedWriter: 1733, and in read/write mode, it returns an
     *note io.BufferedRandom: 1734.  When buffering is disabled, the raw
     stream, a subclass of *note io.RawIOBase: af1, *note io.FileIO:
     d6c, is returned.

     See also the file handling modules, such as, *note fileinput: 7e,
     *note io: a1. (where *note open(): 16f. is declared), *note os: c4,
     *note os.path: c5, *note tempfile: 103, and *note shutil: e9.

     Raises an *note auditing event: fa1. ‘open’ with arguments ‘file’,
     ‘mode’, ‘flags’.

     The ‘mode’ and ‘flags’ arguments may have been modified or inferred
     from the original call.

          Changed in version 3.3:

             * The `opener' parameter was added.

             * The ‘'x'’ mode was added.

             * *note IOError: a73. used to be raised, it is now an alias
               of *note OSError: 304.

             * *note FileExistsError: a39. is now raised if the file
               opened in exclusive creation mode (‘'x'’) already exists.

          Changed in version 3.4:

             * The file is now non-inheritable.

     Deprecated since version 3.4, will be removed in version 3.10: The
     ‘'U'’ mode.

          Changed in version 3.5:

             * If the system call is interrupted and the signal handler
               does not raise an exception, the function now retries the
               system call instead of raising an *note InterruptedError:
               74c. exception (see PEP 475(2) for the rationale).

             * The ‘'namereplace'’ error handler was added.

          Changed in version 3.6:

             * Support added to accept objects implementing *note
               os.PathLike: 5e6.

             * On Windows, opening a console buffer may return a
               subclass of *note io.RawIOBase: af1. other than *note
               io.FileIO: d6c.

 -- Function: ord (c)

     Given a string representing one Unicode character, return an
     integer representing the Unicode code point of that character.  For
     example, ‘ord('a')’ returns the integer ‘97’ and ‘ord('€')’ (Euro
     sign) returns ‘8364’.  This is the inverse of *note chr(): 155a.

 -- Function: pow (base, exp[, mod])

     Return `base' to the power `exp'; if `mod' is present, return
     `base' to the power `exp', modulo `mod' (computed more efficiently
     than ‘pow(base, exp) % mod’).  The two-argument form ‘pow(base,
     exp)’ is equivalent to using the power operator: ‘base**exp’.

     The arguments must have numeric types.  With mixed operand types,
     the coercion rules for binary arithmetic operators apply.  For
     *note int: 204. operands, the result has the same type as the
     operands (after coercion) unless the second argument is negative;
     in that case, all arguments are converted to float and a float
     result is delivered.  For example, ‘pow(10, 2)’ returns ‘100’, but
     ‘pow(10, -2)’ returns ‘0.01’.  For a negative base of type *note
     int: 204. or *note float: 1fd. and a non-integral exponent, a
     complex result is delivered.  For example, ‘pow(-9, 0.5)’ returns a
     value close to ‘3j’.

     For *note int: 204. operands `base' and `exp', if `mod' is present,
     `mod' must also be of integer type and `mod' must be nonzero.  If
     `mod' is present and `exp' is negative, `base' must be relatively
     prime to `mod'.  In that case, ‘pow(inv_base, -exp, mod)’ is
     returned, where `inv_base' is an inverse to `base' modulo `mod'.

     Here’s an example of computing an inverse for ‘38’ modulo ‘97’:

          >>> pow(38, -1, mod=97)
          23
          >>> 23 * 38 % 97 == 1
          True

     Changed in version 3.8: For *note int: 204. operands, the
     three-argument form of ‘pow’ now allows the second argument to be
     negative, permitting computation of modular inverses.

     Changed in version 3.8: Allow keyword arguments.  Formerly, only
     positional arguments were supported.

 -- Function: print (*objects, sep=' ', end='\n', file=sys.stdout,
          flush=False)

     Print `objects' to the text stream `file', separated by `sep' and
     followed by `end'.  `sep', `end', `file' and `flush', if present,
     must be given as keyword arguments.

     All non-keyword arguments are converted to strings like *note
     str(): 205. does and written to the stream, separated by `sep' and
     followed by `end'.  Both `sep' and `end' must be strings; they can
     also be ‘None’, which means to use the default values.  If no
     `objects' are given, *note print(): 971. will just write `end'.

     The `file' argument must be an object with a ‘write(string)’
     method; if it is not present or ‘None’, *note sys.stdout: 41f. will
     be used.  Since printed arguments are converted to text strings,
     *note print(): 971. cannot be used with binary mode file objects.
     For these, use ‘file.write(...)’ instead.

     Whether output is buffered is usually determined by `file', but if
     the `flush' keyword argument is true, the stream is forcibly
     flushed.

     Changed in version 3.3: Added the `flush' keyword argument.

 -- Class: property (fget=None, fset=None, fdel=None, doc=None)

     Return a property attribute.

     `fget' is a function for getting an attribute value.  `fset' is a
     function for setting an attribute value.  `fdel' is a function for
     deleting an attribute value.  And `doc' creates a docstring for the
     attribute.

     A typical use is to define a managed attribute ‘x’:

          class C:
              def __init__(self):
                  self._x = None

              def getx(self):
                  return self._x

              def setx(self, value):
                  self._x = value

              def delx(self):
                  del self._x

              x = property(getx, setx, delx, "I'm the 'x' property.")

     If `c' is an instance of `C', ‘c.x’ will invoke the getter, ‘c.x =
     value’ will invoke the setter and ‘del c.x’ the deleter.

     If given, `doc' will be the docstring of the property attribute.
     Otherwise, the property will copy `fget'’s docstring (if it
     exists).  This makes it possible to create read-only properties
     easily using *note property(): 308. as a *note decorator: 174.:

          class Parrot:
              def __init__(self):
                  self._voltage = 100000

              @property
              def voltage(self):
                  """Get the current voltage."""
                  return self._voltage

     The ‘@property’ decorator turns the ‘voltage()’ method into a
     “getter” for a read-only attribute with the same name, and it sets
     the docstring for `voltage' to “Get the current voltage.”

     A property object has ‘getter’, ‘setter’, and ‘deleter’ methods
     usable as decorators that create a copy of the property with the
     corresponding accessor function set to the decorated function.
     This is best explained with an example:

          class C:
              def __init__(self):
                  self._x = None

              @property
              def x(self):
                  """I'm the 'x' property."""
                  return self._x

              @x.setter
              def x(self, value):
                  self._x = value

              @x.deleter
              def x(self):
                  del self._x

     This code is exactly equivalent to the first example.  Be sure to
     give the additional functions the same name as the original
     property (‘x’ in this case.)

     The returned property object also has the attributes ‘fget’,
     ‘fset’, and ‘fdel’ corresponding to the constructor arguments.

     Changed in version 3.5: The docstrings of property objects are now
     writeable.

 -- Class: range (stop)

 -- Class: range (start, stop[, step])

     Rather than being a function, *note range: 1f5. is actually an
     immutable sequence type, as documented in *note Ranges: 1735. and
     *note Sequence Types — list, tuple, range: 13a4.

 -- Function: repr (object)

     Return a string containing a printable representation of an object.
     For many types, this function makes an attempt to return a string
     that would yield an object with the same value when passed to *note
     eval(): c61, otherwise the representation is a string enclosed in
     angle brackets that contains the name of the type of the object
     together with additional information often including the name and
     address of the object.  A class can control what this function
     returns for its instances by defining a *note __repr__(): 44a.
     method.

 -- Function: reversed (seq)

     Return a reverse *note iterator: 1171.  `seq' must be an object
     which has a *note __reversed__(): 629. method or supports the
     sequence protocol (the *note __len__(): e90. method and the *note
     __getitem__(): 3a2. method with integer arguments starting at ‘0’).

 -- Function: round (number[, ndigits])

     Return `number' rounded to `ndigits' precision after the decimal
     point.  If `ndigits' is omitted or is ‘None’, it returns the
     nearest integer to its input.

     For the built-in types supporting *note round(): d35, values are
     rounded to the closest multiple of 10 to the power minus `ndigits';
     if two multiples are equally close, rounding is done toward the
     even choice (so, for example, both ‘round(0.5)’ and ‘round(-0.5)’
     are ‘0’, and ‘round(1.5)’ is ‘2’).  Any integer value is valid for
     `ndigits' (positive, zero, or negative).  The return value is an
     integer if `ndigits' is omitted or ‘None’.  Otherwise the return
     value has the same type as `number'.

     For a general Python object ‘number’, ‘round’ delegates to
     ‘number.__round__’.

          Note: The behavior of *note round(): d35. for floats can be
          surprising: for example, ‘round(2.675, 2)’ gives ‘2.67’
          instead of the expected ‘2.68’.  This is not a bug: it’s a
          result of the fact that most decimal fractions can’t be
          represented exactly as a float.  See *note Floating Point
          Arithmetic; Issues and Limitations: 1456. for more
          information.

 -- Class: set ([iterable])

     Return a new *note set: 1f6. object, optionally with elements taken
     from `iterable'.  ‘set’ is a built-in class.  See *note set: 1f6.
     and *note Set Types — set, frozenset: 1728. for documentation about
     this class.

     For other containers see the built-in *note frozenset: 1f7, *note
     list: 1f8, *note tuple: 1a2, and *note dict: 164. classes, as well
     as the *note collections: 1d. module.

 -- Function: setattr (object, name, value)

     This is the counterpart of *note getattr(): 54b.  The arguments are
     an object, a string and an arbitrary value.  The string may name an
     existing attribute or a new attribute.  The function assigns the
     value to the attribute, provided the object allows it.  For
     example, ‘setattr(x, 'foobar', 123)’ is equivalent to ‘x.foobar =
     123’.

          Note: Since *note private name mangling: 1621. happens at
          compilation time, one must manually mangle a private
          attribute’s (attributes with two leading underscores) name in
          order to set it with *note setattr(): 1712.

 -- Class: slice (stop)

 -- Class: slice (start, stop[, step])

     Return a *note slice: 1736. object representing the set of indices
     specified by ‘range(start, stop, step)’.  The `start' and `step'
     arguments default to ‘None’.  Slice objects have read-only data
     attributes ‘start’, ‘stop’ and ‘step’ which merely return the
     argument values (or their default).  They have no other explicit
     functionality; however they are used by NumPy and other third party
     packages.  Slice objects are also generated when extended indexing
     syntax is used.  For example: ‘a[start:stop:step]’ or
     ‘a[start:stop, i]’.  See *note itertools.islice(): 4a9. for an
     alternate version that returns an iterator.

 -- Function: sorted (iterable, /, *, key=None, reverse=False)

     Return a new sorted list from the items in `iterable'.

     Has two optional arguments which must be specified as keyword
     arguments.

     `key' specifies a function of one argument that is used to extract
     a comparison key from each element in `iterable' (for example,
     ‘key=str.lower’).  The default value is ‘None’ (compare the
     elements directly).

     `reverse' is a boolean value.  If set to ‘True’, then the list
     elements are sorted as if each comparison were reversed.

     Use *note functools.cmp_to_key(): c28. to convert an old-style
     `cmp' function to a `key' function.

     The built-in *note sorted(): 547. function is guaranteed to be
     stable.  A sort is stable if it guarantees not to change the
     relative order of elements that compare equal — this is helpful for
     sorting in multiple passes (for example, sort by department, then
     by salary grade).

     The sort algorithm uses only ‘<’ comparisons between items.  While
     defining an *note __lt__(): cfe. method will suffice for sorting,
     PEP 8(3) recommends that all six *note rich comparisons: 167a. be
     implemented.  This will help avoid bugs when using the same data
     with other ordering tools such as *note max(): 8f7. that rely on a
     different underlying method.  Implementing all six comparisons also
     helps avoid confusion for mixed type comparisons which can call
     reflected the *note __gt__(): d69. method.

     For sorting examples and a brief sorting tutorial, see *note
     Sorting HOW TO: 1737.

 -- Function: @staticmethod

     Transform a method into a static method.

     A static method does not receive an implicit first argument.  To
     declare a static method, use this idiom:

          class C:
              @staticmethod
              def f(arg1, arg2, ...): ...

     The ‘@staticmethod’ form is a function *note decorator: 174. – see
     *note Function definitions: 1390. for details.

     A static method can be called either on the class (such as ‘C.f()’)
     or on an instance (such as ‘C().f()’).

     Static methods in Python are similar to those found in Java or C++.
     Also see *note classmethod(): 309. for a variant that is useful for
     creating alternate class constructors.

     Like all decorators, it is also possible to call ‘staticmethod’ as
     a regular function and do something with its result.  This is
     needed in some cases where you need a reference to a function from
     a class body and you want to avoid the automatic transformation to
     instance method.  For these cases, use this idiom:

          class C:
              builtin_open = staticmethod(open)

     For more information on static methods, see *note The standard type
     hierarchy: 1553.

 -- Class: str (object='')

 -- Class: str (object=b'', encoding='utf-8', errors='strict')

     Return a *note str: 205. version of `object'.  See *note str():
     205. for details.

     ‘str’ is the built-in string *note class: fe8.  For general
     information about strings, see *note Text Sequence Type — str:
     1357.

 -- Function: sum (iterable, /, start=0)

     Sums `start' and the items of an `iterable' from left to right and
     returns the total.  The `iterable'’s items are normally numbers,
     and the start value is not allowed to be a string.

     For some use cases, there are good alternatives to *note sum():
     316.  The preferred, fast way to concatenate a sequence of strings
     is by calling ‘''.join(sequence)’.  To add floating point values
     with extended precision, see *note math.fsum(): e04.  To
     concatenate a series of iterables, consider using *note
     itertools.chain(): 1738.

     Changed in version 3.8: The `start' parameter can be specified as a
     keyword argument.

 -- Function: super ([type[, object-or-type]])

     Return a proxy object that delegates method calls to a parent or
     sibling class of `type'.  This is useful for accessing inherited
     methods that have been overridden in a class.

     The `object-or-type' determines the *note method resolution order:
     1739. to be searched.  The search starts from the class right after
     the `type'.

     For example, if *note __mro__: 173a. of `object-or-type' is ‘D -> B
     -> C -> A -> object’ and the value of `type' is ‘B’, then *note
     super(): 5dd. searches ‘C -> A -> object’.

     The *note __mro__: 173a. attribute of the `object-or-type' lists
     the method resolution search order used by both *note getattr():
     54b. and *note super(): 5dd.  The attribute is dynamic and can
     change whenever the inheritance hierarchy is updated.

     If the second argument is omitted, the super object returned is
     unbound.  If the second argument is an object, ‘isinstance(obj,
     type)’ must be true.  If the second argument is a type,
     ‘issubclass(type2, type)’ must be true (this is useful for
     classmethods).

     There are two typical use cases for `super'.  In a class hierarchy
     with single inheritance, `super' can be used to refer to parent
     classes without naming them explicitly, thus making the code more
     maintainable.  This use closely parallels the use of `super' in
     other programming languages.

     The second use case is to support cooperative multiple inheritance
     in a dynamic execution environment.  This use case is unique to
     Python and is not found in statically compiled languages or
     languages that only support single inheritance.  This makes it
     possible to implement “diamond diagrams” where multiple base
     classes implement the same method.  Good design dictates that such
     implementations have the same calling signature in every case
     (because the order of calls is determined at runtime, because that
     order adapts to changes in the class hierarchy, and because that
     order can include sibling classes that are unknown prior to
     runtime).

     For both use cases, a typical superclass call looks like this:

          class C(B):
              def method(self, arg):
                  super().method(arg)    # This does the same thing as:
                                         # super(C, self).method(arg)

     In addition to method lookups, *note super(): 5dd. also works for
     attribute lookups.  One possible use case for this is calling *note
     descriptors: 1579. in a parent or sibling class.

     Note that *note super(): 5dd. is implemented as part of the binding
     process for explicit dotted attribute lookups such as
     ‘super().__getitem__(name)’.  It does so by implementing its own
     *note __getattribute__(): 54c. method for searching classes in a
     predictable order that supports cooperative multiple inheritance.
     Accordingly, *note super(): 5dd. is undefined for implicit lookups
     using statements or operators such as ‘super()[name]’.

     Also note that, aside from the zero argument form, *note super():
     5dd. is not limited to use inside methods.  The two argument form
     specifies the arguments exactly and makes the appropriate
     references.  The zero argument form only works inside a class
     definition, as the compiler fills in the necessary details to
     correctly retrieve the class being defined, as well as accessing
     the current instance for ordinary methods.

     For practical suggestions on how to design cooperative classes
     using *note super(): 5dd, see guide to using super()(4).

 -- Class: tuple ([iterable])

     Rather than being a function, *note tuple: 1a2. is actually an
     immutable sequence type, as documented in *note Tuples: 173b. and
     *note Sequence Types — list, tuple, range: 13a4.

 -- Class: type (object)

 -- Class: type (name, bases, dict, **kwds)

     With one argument, return the type of an `object'.  The return
     value is a type object and generally the same object as returned by
     *note object.__class__: ecc.

     The *note isinstance(): 552. built-in function is recommended for
     testing the type of an object, because it takes subclasses into
     account.

     With three arguments, return a new type object.  This is
     essentially a dynamic form of the *note class: d32. statement.  The
     `name' string is the class name and becomes the *note __name__:
     d2f. attribute.  The `bases' tuple contains the base classes and
     becomes the *note __bases__: ecb. attribute; if empty, *note
     object: 3d2, the ultimate base of all classes, is added.  The
     `dict' dictionary contains attribute and method definitions for the
     class body; it may be copied or wrapped before becoming the *note
     __dict__: 5f6. attribute.  The following two statements create
     identical *note type: 6ff. objects:

          >>> class X:
          ...     a = 1
          ...
          >>> X = type('X', (), dict(a=1))

     See also *note Type Objects: 173c.

     Keyword arguments provided to the three argument form are passed to
     the appropriate metaclass machinery (usually *note
     __init_subclass__(): 5de.) in the same way that keywords in a class
     definition (besides `metaclass') would.

     See also *note Customizing class creation: 5e0.

     Changed in version 3.6: Subclasses of *note type: 6ff. which don’t
     override ‘type.__new__’ may no longer use the one-argument form to
     get the type of an object.

 -- Function: vars ([object])

     Return the *note __dict__: 5f6. attribute for a module, class,
     instance, or any other object with a *note __dict__: 5f6.
     attribute.

     Objects such as modules and instances have an updateable *note
     __dict__: 5f6. attribute; however, other objects may have write
     restrictions on their *note __dict__: 5f6. attributes (for example,
     classes use a *note types.MappingProxyType: b8e. to prevent direct
     dictionary updates).

     Without an argument, *note vars(): 116d. acts like *note locals():
     557.  Note, the locals dictionary is only useful for reads since
     updates to the locals dictionary are ignored.

     A *note TypeError: 1fe. exception is raised if an object is
     specified but it doesn’t have a *note __dict__: 5f6. attribute (for
     example, if its class defines the *note __slots__: eef. attribute).

 -- Function: zip (*iterables)

     Make an iterator that aggregates elements from each of the
     iterables.

     Returns an iterator of tuples, where the `i'-th tuple contains the
     `i'-th element from each of the argument sequences or iterables.
     The iterator stops when the shortest input iterable is exhausted.
     With a single iterable argument, it returns an iterator of
     1-tuples.  With no arguments, it returns an empty iterator.
     Equivalent to:

          def zip(*iterables):
              # zip('ABCD', 'xy') --> Ax By
              sentinel = object()
              iterators = [iter(it) for it in iterables]
              while iterators:
                  result = []
                  for it in iterators:
                      elem = next(it, sentinel)
                      if elem is sentinel:
                          return
                      result.append(elem)
                  yield tuple(result)

     The left-to-right evaluation order of the iterables is guaranteed.
     This makes possible an idiom for clustering a data series into
     n-length groups using ‘zip(*[iter(s)]*n)’.  This repeats the `same'
     iterator ‘n’ times so that each output tuple has the result of ‘n’
     calls to the iterator.  This has the effect of dividing the input
     into n-length chunks.

     *note zip(): cfc. should only be used with unequal length inputs
     when you don’t care about trailing, unmatched values from the
     longer iterables.  If those values are important, use *note
     itertools.zip_longest(): cfb. instead.

     *note zip(): cfc. in conjunction with the ‘*’ operator can be used
     to unzip a list:

          >>> x = [1, 2, 3]
          >>> y = [4, 5, 6]
          >>> zipped = zip(x, y)
          >>> list(zipped)
          [(1, 4), (2, 5), (3, 6)]
          >>> x2, y2 = zip(*zip(x, y))
          >>> x == list(x2) and y == list(y2)
          True

 -- Function: __import__ (name, globals=None, locals=None, fromlist=(),
          level=0)

          Note: This is an advanced function that is not needed in
          everyday Python programming, unlike *note
          importlib.import_module(): be6.

     This function is invoked by the *note import: ce7. statement.  It
     can be replaced (by importing the *note builtins: 12. module and
     assigning to ‘builtins.__import__’) in order to change semantics of
     the ‘import’ statement, but doing so is `strongly' discouraged as
     it is usually simpler to use import hooks (see PEP 302(5)) to
     attain the same goals and does not cause issues with code which
     assumes the default import implementation is in use.  Direct use of
     *note __import__(): 16b. is also discouraged in favor of *note
     importlib.import_module(): be6.

     The function imports the module `name', potentially using the given
     `globals' and `locals' to determine how to interpret the name in a
     package context.  The `fromlist' gives the names of objects or
     submodules that should be imported from the module given by `name'.
     The standard implementation does not use its `locals' argument at
     all, and uses its `globals' only to determine the package context
     of the *note import: ce7. statement.

     `level' specifies whether to use absolute or relative imports.  ‘0’
     (the default) means only perform absolute imports.  Positive values
     for `level' indicate the number of parent directories to search
     relative to the directory of the module calling *note __import__():
     16b. (see PEP 328(6) for the details).

     When the `name' variable is of the form ‘package.module’, normally,
     the top-level package (the name up till the first dot) is returned,
     `not' the module named by `name'.  However, when a non-empty
     `fromlist' argument is given, the module named by `name' is
     returned.

     For example, the statement ‘import spam’ results in bytecode
     resembling the following code:

          spam = __import__('spam', globals(), locals(), [], 0)

     The statement ‘import spam.ham’ results in this call:

          spam = __import__('spam.ham', globals(), locals(), [], 0)

     Note how *note __import__(): 16b. returns the toplevel module here
     because this is the object that is bound to a name by the *note
     import: ce7. statement.

     On the other hand, the statement ‘from spam.ham import eggs,
     sausage as saus’ results in

          _temp = __import__('spam.ham', globals(), locals(), ['eggs', 'sausage'], 0)
          eggs = _temp.eggs
          saus = _temp.sausage

     Here, the ‘spam.ham’ module is returned from *note __import__():
     16b.  From this object, the names to import are retrieved and
     assigned to their respective names.

     If you simply want to import a module (potentially within a
     package) by name, use *note importlib.import_module(): be6.

     Changed in version 3.3: Negative values for `level' are no longer
     supported (which also changes the default value to 0).

     Changed in version 3.9: When the command line options *note -E:
     231. or *note -I: 232. are being used, the environment variable
     *note PYTHONCASEOK: 230. is now ignored.

   ---------- Footnotes ----------

   (1) (1) Note that the parser only accepts the Unix-style end of line
convention.  If you are reading the code from a file, make sure to use
newline conversion mode to convert Windows or Mac-style newlines.

   (2) https://www.python.org/dev/peps/pep-0475

   (3) https://www.python.org/dev/peps/pep-0008

   (4) 
https://rhettinger.wordpress.com/2011/05/26/super-considered-super/

   (5) https://www.python.org/dev/peps/pep-0302

   (6) https://www.python.org/dev/peps/pep-0328


File: python.info,  Node: Built-in Constants,  Next: Built-in Types,  Prev: Built-in Functions,  Up: The Python Standard Library

5.3 Built-in Constants
======================

A small number of constants live in the built-in namespace.  They are:

 -- Data: False

     The false value of the *note bool: 2bd. type.  Assignments to
     ‘False’ are illegal and raise a *note SyntaxError: 55a.

 -- Data: True

     The true value of the *note bool: 2bd. type.  Assignments to ‘True’
     are illegal and raise a *note SyntaxError: 55a.

 -- Data: None

     The sole value of the type ‘NoneType’.  ‘None’ is frequently used
     to represent the absence of a value, as when default arguments are
     not passed to a function.  Assignments to ‘None’ are illegal and
     raise a *note SyntaxError: 55a.

 -- Data: NotImplemented

     Special value which should be returned by the binary special
     methods (e.g.  *note __eq__(): 44b, *note __lt__(): cfe, *note
     __add__(): 1595, *note __rsub__(): 15a7, etc.)  to indicate that
     the operation is not implemented with respect to the other type;
     may be returned by the in-place binary special methods (e.g.  *note
     __imul__(): 1599, *note __iand__(): 15b7, etc.)  for the same
     purpose.  It should not be evaluated in a boolean context.

          Note: When a binary (or in-place) method returns
          ‘NotImplemented’ the interpreter will try the reflected
          operation on the other type (or some other fallback, depending
          on the operator).  If all attempts return ‘NotImplemented’,
          the interpreter will raise an appropriate exception.
          Incorrectly returning ‘NotImplemented’ will result in a
          misleading error message or the ‘NotImplemented’ value being
          returned to Python code.

          See *note Implementing the arithmetic operations: 1554. for
          examples.

          Note: ‘NotImplementedError’ and ‘NotImplemented’ are not
          interchangeable, even though they have similar names and
          purposes.  See *note NotImplementedError: 704. for details on
          when to use it.

     Changed in version 3.9: Evaluating ‘NotImplemented’ in a boolean
     context is deprecated.  While it currently evaluates as true, it
     will emit a *note DeprecationWarning: 15a.  It will raise a *note
     TypeError: 1fe. in a future version of Python.

 -- Data: Ellipsis

     The same as the ellipsis literal “‘...’”.  Special value used
     mostly in conjunction with extended slicing syntax for user-defined
     container data types.

 -- Data: __debug__

     This constant is true if Python was not started with an *note -O:
     77e. option.  See also the *note assert: 23f. statement.

     Note: The names *note None: 203, *note False: 48f, *note True: 594.
     and *note __debug__: 1137. cannot be reassigned (assignments to
     them, even as an attribute name, raise *note SyntaxError: 55a.), so
     they can be considered “true” constants.

* Menu:

* Constants added by the site module::


File: python.info,  Node: Constants added by the site module,  Up: Built-in Constants

5.3.1 Constants added by the ‘site’ module
------------------------------------------

The *note site: eb. module (which is imported automatically during
startup, except if the *note -S: bf7. command-line option is given) adds
several constants to the built-in namespace.  They are useful for the
interactive interpreter shell and should not be used in programs.

 -- Data: quit (code=None)
 -- Data: exit (code=None)

     Objects that when printed, print a message like “Use quit() or
     Ctrl-D (i.e.  EOF) to exit”, and when called, raise *note
     SystemExit: 6f3. with the specified exit code.

 -- Data: copyright
 -- Data: credits

     Objects that when printed or called, print the text of copyright or
     credits, respectively.

 -- Data: license

     Object that when printed, prints the message “Type license() to see
     the full license text”, and when called, displays the full license
     text in a pager-like fashion (one screen at a time).


File: python.info,  Node: Built-in Types,  Next: Built-in Exceptions,  Prev: Built-in Constants,  Up: The Python Standard Library

5.4 Built-in Types
==================

The following sections describe the standard types that are built into
the interpreter.

The principal built-in types are numerics, sequences, mappings, classes,
instances and exceptions.

Some collection classes are mutable.  The methods that add, subtract, or
rearrange their members in place, and don’t return a specific item,
never return the collection instance itself but ‘None’.

Some operations are supported by several object types; in particular,
practically all objects can be compared for equality, tested for truth
value, and converted to a string (with the *note repr(): 8b9. function
or the slightly different *note str(): 205. function).  The latter
function is implicitly used when an object is written by the *note
print(): 971. function.

* Menu:

* Truth Value Testing::
* Boolean Operations — and, or, not: Boolean Operations — and or not.
* Comparisons: Comparisons<2>.
* Numeric Types — int, float, complex: Numeric Types — int float complex.
* Iterator Types::
* Sequence Types — list, tuple, range: Sequence Types — list tuple range.
* Text Sequence Type — str::
* Binary Sequence Types — bytes, bytearray, memoryview: Binary Sequence Types — bytes bytearray memoryview.
* Set Types — set, frozenset: Set Types — set frozenset.
* Mapping Types — dict::
* Context Manager Types::
* Generic Alias Type::
* Other Built-in Types::
* Special Attributes::


File: python.info,  Node: Truth Value Testing,  Next: Boolean Operations — and or not,  Up: Built-in Types

5.4.1 Truth Value Testing
-------------------------

Any object can be tested for truth value, for use in an *note if: eab.
or *note while: 1361. condition or as operand of the Boolean operations
below.

By default, an object is considered true unless its class defines either
a *note __bool__(): d30. method that returns ‘False’ or a *note
__len__(): e90. method that returns zero, when called with the object.
(1) Here are most of the built-in objects considered false:

   * constants defined to be false: ‘None’ and ‘False’.

   * zero of any numeric type: ‘0’, ‘0.0’, ‘0j’, ‘Decimal(0)’,
     ‘Fraction(0, 1)’

   * empty sequences and collections: ‘''’, ‘()’, ‘[]’, ‘{}’, ‘set()’,
     ‘range(0)’

Operations and built-in functions that have a Boolean result always
return ‘0’ or ‘False’ for false and ‘1’ or ‘True’ for true, unless
otherwise stated.  (Important exception: the Boolean operations ‘or’ and
‘and’ always return one of their operands.)

   ---------- Footnotes ----------

   (1) (1) Additional information on these special methods may be found
in the Python Reference Manual (*note Basic customization: 1568.).


File: python.info,  Node: Boolean Operations — and or not,  Next: Comparisons<2>,  Prev: Truth Value Testing,  Up: Built-in Types

5.4.2 Boolean Operations — ‘and’, ‘or’, ‘not’
---------------------------------------------

These are the Boolean operations, ordered by ascending priority:

Operation         Result                                Notes
                                                        
--------------------------------------------------------------------
                                                        
‘x or y’          if `x' is false, then `y', else `x'   (1)
                                                        
                                                        
‘x and y’         if `x' is false, then `x', else `y'   (2)
                                                        
                                                        
‘not x’           if `x' is false, then ‘True’, else    (3)
                  ‘False’                               
                  

Notes:

  1. This is a short-circuit operator, so it only evaluates the second
     argument if the first one is false.

  2. This is a short-circuit operator, so it only evaluates the second
     argument if the first one is true.

  3. ‘not’ has a lower priority than non-Boolean operators, so ‘not a ==
     b’ is interpreted as ‘not (a == b)’, and ‘a == not b’ is a syntax
     error.


File: python.info,  Node: Comparisons<2>,  Next: Numeric Types — int float complex,  Prev: Boolean Operations — and or not,  Up: Built-in Types

5.4.3 Comparisons
-----------------

There are eight comparison operations in Python.  They all have the same
priority (which is higher than that of the Boolean operations).
Comparisons can be chained arbitrarily; for example, ‘x < y <= z’ is
equivalent to ‘x < y and y <= z’, except that `y' is evaluated only once
(but in both cases `z' is not evaluated at all when ‘x < y’ is found to
be false).

This table summarizes the comparison operations:

Operation        Meaning
                 
-----------------------------------------------
                 
‘<’              strictly less than
                 
                 
‘<=’             less than or equal
                 
                 
‘>’              strictly greater than
                 
                 
‘>=’             greater than or equal
                 
                 
‘==’             equal
                 
                 
‘!=’             not equal
                 
                 
‘is’             object identity
                 
                 
‘is not’         negated object identity
                 

Objects of different types, except different numeric types, never
compare equal.  The ‘==’ operator is always defined but for some object
types (for example, class objects) is equivalent to *note is: 1551.  The
‘<’, ‘<=’, ‘>’ and ‘>=’ operators are only defined where they make
sense; for example, they raise a *note TypeError: 1fe. exception when
one of the arguments is a complex number.

Non-identical instances of a class normally compare as non-equal unless
the class defines the *note __eq__(): 44b. method.

Instances of a class cannot be ordered with respect to other instances
of the same class, or other types of object, unless the class defines
enough of the methods *note __lt__(): cfe, *note __le__(): d68, *note
__gt__(): d69, and *note __ge__(): d6a. (in general, *note __lt__():
cfe. and *note __eq__(): 44b. are sufficient, if you want the
conventional meanings of the comparison operators).

The behavior of the *note is: 1551. and *note is not: 1681. operators
cannot be customized; also they can be applied to any two objects and
never raise an exception.

Two more operations with the same syntactic priority, *note in: 179. and
*note not in: 159b, are supported by types that are *note iterable: c7c.
or implement the *note __contains__(): dee. method.


File: python.info,  Node: Numeric Types — int float complex,  Next: Iterator Types,  Prev: Comparisons<2>,  Up: Built-in Types

5.4.4 Numeric Types — ‘int’, ‘float’, ‘complex’
-----------------------------------------------

There are three distinct numeric types: `integers', `floating point
numbers', and `complex numbers'.  In addition, Booleans are a subtype of
integers.  Integers have unlimited precision.  Floating point numbers
are usually implemented using ‘double’ in C; information about the
precision and internal representation of floating point numbers for the
machine on which your program is running is available in *note
sys.float_info: 10fc.  Complex numbers have a real and imaginary part,
which are each a floating point number.  To extract these parts from a
complex number `z', use ‘z.real’ and ‘z.imag’.  (The standard library
includes the additional numeric types *note fractions.Fraction: 2be, for
rationals, and *note decimal.Decimal: 2c0, for floating-point numbers
with user-definable precision.)

Numbers are created by numeric literals or as the result of built-in
functions and operators.  Unadorned integer literals (including hex,
octal and binary numbers) yield integers.  Numeric literals containing a
decimal point or an exponent sign yield floating point numbers.
Appending ‘'j'’ or ‘'J'’ to a numeric literal yields an imaginary number
(a complex number with a zero real part) which you can add to an integer
or float to get a complex number with real and imaginary parts.

Python fully supports mixed arithmetic: when a binary arithmetic
operator has operands of different numeric types, the operand with the
“narrower” type is widened to that of the other, where integer is
narrower than floating point, which is narrower than complex.  A
comparison between numbers of different types behaves as though the
exact values of those numbers were being compared.  (1)

The constructors *note int(): 204, *note float(): 1fd, and *note
complex(): 2c1. can be used to produce numbers of a specific type.

All numeric types (except complex) support the following operations (for
priorities of the operations, see *note Operator precedence: 169a.):

Operation                 Result                                Notes         Full documentation
                                                                              
-------------------------------------------------------------------------------------------------------
                                                                              
‘x + y’                   sum of `x' and `y'
                          
                                                                              
‘x - y’                   difference of `x' and `y'
                          
                                                                              
‘x * y’                   product of `x' and `y'
                          
                                                                              
‘x / y’                   quotient of `x' and `y'
                          
                                                                              
‘x // y’                  floored quotient of `x' and `y'       (1)
                                                                
                                                                              
‘x % y’                   remainder of ‘x / y’                  (2)
                                                                
                                                                              
‘-x’                      `x' negated
                          
                                                                              
‘+x’                      `x' unchanged
                          
                                                                              
‘abs(x)’                  absolute value or magnitude of `x'                  *note abs(): 13f3.
                                                                              
                                                                              
‘int(x)’                  `x' converted to integer              (3)(6)        *note int(): 204.
                                                                              
                                                                              
‘float(x)’                `x' converted to floating point       (4)(6)        *note float(): 1fd.
                                                                              
                                                                              
‘complex(re, im)’         a complex number with real part       (6)           *note complex(): 2c1.
                          `re', imaginary part `im'.  `im'                    
                          defaults to zero.
                          
                                                                              
‘c.conjugate()’           conjugate of the complex number `c'
                          
                                                                              
‘divmod(x, y)’            the pair ‘(x // y, x % y)’            (2)           *note divmod(): 28d.
                                                                              
                                                                              
‘pow(x, y)’               `x' to the power `y'                  (5)           *note pow(): 2cf.
                                                                              
                                                                              
‘x ** y’                  `x' to the power `y'                  (5)
                                                                

Notes:

  1. Also referred to as integer division.  The resultant value is a
     whole integer, though the result’s type is not necessarily int.
     The result is always rounded towards minus infinity: ‘1//2’ is ‘0’,
     ‘(-1)//2’ is ‘-1’, ‘1//(-2)’ is ‘-1’, and ‘(-1)//(-2)’ is ‘0’.

  2. Not for complex numbers.  Instead convert to floats using *note
     abs(): 13f3. if appropriate.

  3. 
     Conversion from floating point to integer may round or truncate as
     in C; see functions *note math.floor(): df2. and *note math.ceil():
     df3. for well-defined conversions.

  4. float also accepts the strings “nan” and “inf” with an optional
     prefix “+” or “-” for Not a Number (NaN) and positive or negative
     infinity.

  5. Python defines ‘pow(0, 0)’ and ‘0 ** 0’ to be ‘1’, as is common for
     programming languages.

  6. The numeric literals accepted include the digits ‘0’ to ‘9’ or any
     Unicode equivalent (code points with the ‘Nd’ property).

     See
     ‘https://www.unicode.org/Public/13.0.0/ucd/extracted/DerivedNumericType.txt’
     for a complete list of code points with the ‘Nd’ property.

All *note numbers.Real: 1557. types (*note int: 204. and *note float:
1fd.) also include the following operations:

Operation                Result
                         
---------------------------------------------------------------------------
                         
*note math.trunc(x): df4.`x' truncated to *note Integral: 1556.
                         
                         
*note round(x[, n]): d35.`x' rounded to `n' digits, rounding half to
                         even.  If `n' is omitted, it defaults to 0.
                         
                         
*note math.floor(x): df2.the greatest *note Integral: 1556. <= `x'
                         
                         
*note math.ceil(x): df3. the least *note Integral: 1556. >= `x'
                         

For additional numeric operations see the *note math: b1. and *note
cmath: 18. modules.

* Menu:

* Bitwise Operations on Integer Types::
* Additional Methods on Integer Types::
* Additional Methods on Float::
* Hashing of numeric types::

   ---------- Footnotes ----------

   (1) (2) As a consequence, the list ‘[1, 2]’ is considered equal to
‘[1.0, 2.0]’, and similarly for tuples.


File: python.info,  Node: Bitwise Operations on Integer Types,  Next: Additional Methods on Integer Types,  Up: Numeric Types — int float complex

5.4.4.1 Bitwise Operations on Integer Types
...........................................

Bitwise operations only make sense for integers.  The result of bitwise
operations is calculated as though carried out in two’s complement with
an infinite number of sign bits.

The priorities of the binary bitwise operations are all lower than the
numeric operations and higher than the comparisons; the unary operation
‘~’ has the same priority as the other unary numeric operations (‘+’ and
‘-’).

This table lists the bitwise operations sorted in ascending priority:

Operation        Result                               Notes
                                                      
---------------------------------------------------------------------
                                                      
‘x | y’          bitwise `or' of `x' and `y'          (4)
                                                      
                                                      
‘x ^ y’          bitwise `exclusive or' of `x' and    (4)
                 `y'                                  
                 
                                                      
‘x & y’          bitwise `and' of `x' and `y'         (4)
                                                      
                                                      
‘x << n’         `x' shifted left by `n' bits         (1)(2)
                                                      
                                                      
‘x >> n’         `x' shifted right by `n' bits        (1)(3)
                                                      
                                                      
‘~x’             the bits of `x' inverted
                 

Notes:

  1. Negative shift counts are illegal and cause a *note ValueError:
     16d. to be raised.

  2. A left shift by `n' bits is equivalent to multiplication by ‘pow(2,
     n)’.

  3. A right shift by `n' bits is equivalent to floor division by
     ‘pow(2, n)’.

  4. Performing these calculations with at least one extra sign
     extension bit in a finite two’s complement representation (a
     working bit-width of ‘1 + max(x.bit_length(), y.bit_length())’ or
     more) is sufficient to get the same result as if there were an
     infinite number of sign bits.


File: python.info,  Node: Additional Methods on Integer Types,  Next: Additional Methods on Float,  Prev: Bitwise Operations on Integer Types,  Up: Numeric Types — int float complex

5.4.4.2 Additional Methods on Integer Types
...........................................

The int type implements the *note numbers.Integral: 1556. *note abstract
base class: c05.  In addition, it provides a few more methods:

 -- Method: int.bit_length ()

     Return the number of bits necessary to represent an integer in
     binary, excluding the sign and leading zeros:

          >>> n = -37
          >>> bin(n)
          '-0b100101'
          >>> n.bit_length()
          6

     More precisely, if ‘x’ is nonzero, then ‘x.bit_length()’ is the
     unique positive integer ‘k’ such that ‘2**(k-1) <= abs(x) < 2**k’.
     Equivalently, when ‘abs(x)’ is small enough to have a correctly
     rounded logarithm, then ‘k = 1 + int(log(abs(x), 2))’.  If ‘x’ is
     zero, then ‘x.bit_length()’ returns ‘0’.

     Equivalent to:

          def bit_length(self):
              s = bin(self)       # binary representation:  bin(-37) --> '-0b100101'
              s = s.lstrip('-0b') # remove leading zeros and minus sign
              return len(s)       # len('100101') --> 6

     New in version 3.1.

 -- Method: int.to_bytes (length, byteorder, *, signed=False)

     Return an array of bytes representing an integer.

          >>> (1024).to_bytes(2, byteorder='big')
          b'\x04\x00'
          >>> (1024).to_bytes(10, byteorder='big')
          b'\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00'
          >>> (-1024).to_bytes(10, byteorder='big', signed=True)
          b'\xff\xff\xff\xff\xff\xff\xff\xff\xfc\x00'
          >>> x = 1000
          >>> x.to_bytes((x.bit_length() + 7) // 8, byteorder='little')
          b'\xe8\x03'

     The integer is represented using `length' bytes.  An *note
     OverflowError: a41. is raised if the integer is not representable
     with the given number of bytes.

     The `byteorder' argument determines the byte order used to
     represent the integer.  If `byteorder' is ‘"big"’, the most
     significant byte is at the beginning of the byte array.  If
     `byteorder' is ‘"little"’, the most significant byte is at the end
     of the byte array.  To request the native byte order of the host
     system, use *note sys.byteorder: 1755. as the byte order value.

     The `signed' argument determines whether two’s complement is used
     to represent the integer.  If `signed' is ‘False’ and a negative
     integer is given, an *note OverflowError: a41. is raised.  The
     default value for `signed' is ‘False’.

     New in version 3.2.

 -- Method: classmethod int.from_bytes (bytes, byteorder, *,
          signed=False)

     Return the integer represented by the given array of bytes.

          >>> int.from_bytes(b'\x00\x10', byteorder='big')
          16
          >>> int.from_bytes(b'\x00\x10', byteorder='little')
          4096
          >>> int.from_bytes(b'\xfc\x00', byteorder='big', signed=True)
          -1024
          >>> int.from_bytes(b'\xfc\x00', byteorder='big', signed=False)
          64512
          >>> int.from_bytes([255, 0, 0], byteorder='big')
          16711680

     The argument `bytes' must either be a *note bytes-like object: 6df.
     or an iterable producing bytes.

     The `byteorder' argument determines the byte order used to
     represent the integer.  If `byteorder' is ‘"big"’, the most
     significant byte is at the beginning of the byte array.  If
     `byteorder' is ‘"little"’, the most significant byte is at the end
     of the byte array.  To request the native byte order of the host
     system, use *note sys.byteorder: 1755. as the byte order value.

     The `signed' argument indicates whether two’s complement is used to
     represent the integer.

     New in version 3.2.

 -- Method: int.as_integer_ratio ()

     Return a pair of integers whose ratio is exactly equal to the
     original integer and with a positive denominator.  The integer
     ratio of integers (whole numbers) is always the integer as the
     numerator and ‘1’ as the denominator.

     New in version 3.8.


File: python.info,  Node: Additional Methods on Float,  Next: Hashing of numeric types,  Prev: Additional Methods on Integer Types,  Up: Numeric Types — int float complex

5.4.4.3 Additional Methods on Float
...................................

The float type implements the *note numbers.Real: 1557. *note abstract
base class: c05.  float also has the following additional methods.

 -- Method: float.as_integer_ratio ()

     Return a pair of integers whose ratio is exactly equal to the
     original float and with a positive denominator.  Raises *note
     OverflowError: a41. on infinities and a *note ValueError: 16d. on
     NaNs.

 -- Method: float.is_integer ()

     Return ‘True’ if the float instance is finite with integral value,
     and ‘False’ otherwise:

          >>> (-2.0).is_integer()
          True
          >>> (3.2).is_integer()
          False

Two methods support conversion to and from hexadecimal strings.  Since
Python’s floats are stored internally as binary numbers, converting a
float to or from a `decimal' string usually involves a small rounding
error.  In contrast, hexadecimal strings allow exact representation and
specification of floating-point numbers.  This can be useful when
debugging, and in numerical work.

 -- Method: float.hex ()

     Return a representation of a floating-point number as a hexadecimal
     string.  For finite floating-point numbers, this representation
     will always include a leading ‘0x’ and a trailing ‘p’ and exponent.

 -- Method: classmethod float.fromhex (s)

     Class method to return the float represented by a hexadecimal
     string `s'.  The string `s' may have leading and trailing
     whitespace.

Note that *note float.hex(): 1458. is an instance method, while *note
float.fromhex(): 1759. is a class method.

A hexadecimal string takes the form:

     [sign] ['0x'] integer ['.' fraction] ['p' exponent]

where the optional ‘sign’ may by either ‘+’ or ‘-’, ‘integer’ and
‘fraction’ are strings of hexadecimal digits, and ‘exponent’ is a
decimal integer with an optional leading sign.  Case is not significant,
and there must be at least one hexadecimal digit in either the integer
or the fraction.  This syntax is similar to the syntax specified in
section 6.4.4.2 of the C99 standard, and also to the syntax used in Java
1.5 onwards.  In particular, the output of *note float.hex(): 1458. is
usable as a hexadecimal floating-point literal in C or Java code, and
hexadecimal strings produced by C’s ‘%a’ format character or Java’s
‘Double.toHexString’ are accepted by *note float.fromhex(): 1759.

Note that the exponent is written in decimal rather than hexadecimal,
and that it gives the power of 2 by which to multiply the coefficient.
For example, the hexadecimal string ‘0x3.a7p10’ represents the
floating-point number ‘(3 + 10./16 + 7./16**2) * 2.0**10’, or ‘3740.0’:

     >>> float.fromhex('0x3.a7p10')
     3740.0

Applying the reverse conversion to ‘3740.0’ gives a different
hexadecimal string representing the same number:

     >>> float.hex(3740.0)
     '0x1.d380000000000p+11'


File: python.info,  Node: Hashing of numeric types,  Prev: Additional Methods on Float,  Up: Numeric Types — int float complex

5.4.4.4 Hashing of numeric types
................................

For numbers ‘x’ and ‘y’, possibly of different types, it’s a requirement
that ‘hash(x) == hash(y)’ whenever ‘x == y’ (see the *note __hash__():
44c. method documentation for more details).  For ease of implementation
and efficiency across a variety of numeric types (including *note int:
204, *note float: 1fd, *note decimal.Decimal: 2c0. and *note
fractions.Fraction: 2be.) Python’s hash for numeric types is based on a
single mathematical function that’s defined for any rational number, and
hence applies to all instances of *note int: 204. and *note
fractions.Fraction: 2be, and all finite instances of *note float: 1fd.
and *note decimal.Decimal: 2c0.  Essentially, this function is given by
reduction modulo ‘P’ for a fixed prime ‘P’.  The value of ‘P’ is made
available to Python as the ‘modulus’ attribute of *note sys.hash_info:
a06.

`CPython implementation detail:' Currently, the prime used is ‘P = 2**31
- 1’ on machines with 32-bit C longs and ‘P = 2**61 - 1’ on machines
with 64-bit C longs.

Here are the rules in detail:

   - If ‘x = m / n’ is a nonnegative rational number and ‘n’ is not
     divisible by ‘P’, define ‘hash(x)’ as ‘m * invmod(n, P) % P’, where
     ‘invmod(n, P)’ gives the inverse of ‘n’ modulo ‘P’.

   - If ‘x = m / n’ is a nonnegative rational number and ‘n’ is
     divisible by ‘P’ (but ‘m’ is not) then ‘n’ has no inverse modulo
     ‘P’ and the rule above doesn’t apply; in this case define ‘hash(x)’
     to be the constant value ‘sys.hash_info.inf’.

   - If ‘x = m / n’ is a negative rational number define ‘hash(x)’ as
     ‘-hash(-x)’.  If the resulting hash is ‘-1’, replace it with ‘-2’.

   - The particular values ‘sys.hash_info.inf’, ‘-sys.hash_info.inf’ and
     ‘sys.hash_info.nan’ are used as hash values for positive infinity,
     negative infinity, or nans (respectively).  (All hashable nans have
     the same hash value.)

   - For a *note complex: 2c1. number ‘z’, the hash values of the real
     and imaginary parts are combined by computing ‘hash(z.real) +
     sys.hash_info.imag * hash(z.imag)’, reduced modulo
     ‘2**sys.hash_info.width’ so that it lies in
     ‘range(-2**(sys.hash_info.width - 1), 2**(sys.hash_info.width -
     1))’.  Again, if the result is ‘-1’, it’s replaced with ‘-2’.

To clarify the above rules, here’s some example Python code, equivalent
to the built-in hash, for computing the hash of a rational number, *note
float: 1fd, or *note complex: 2c1.:

     import sys, math

     def hash_fraction(m, n):
         """Compute the hash of a rational number m / n.

         Assumes m and n are integers, with n positive.
         Equivalent to hash(fractions.Fraction(m, n)).

         """
         P = sys.hash_info.modulus
         # Remove common factors of P.  (Unnecessary if m and n already coprime.)
         while m % P == n % P == 0:
             m, n = m // P, n // P

         if n % P == 0:
             hash_value = sys.hash_info.inf
         else:
             # Fermat's Little Theorem: pow(n, P-1, P) is 1, so
             # pow(n, P-2, P) gives the inverse of n modulo P.
             hash_value = (abs(m) % P) * pow(n, P - 2, P) % P
         if m < 0:
             hash_value = -hash_value
         if hash_value == -1:
             hash_value = -2
         return hash_value

     def hash_float(x):
         """Compute the hash of a float x."""

         if math.isnan(x):
             return sys.hash_info.nan
         elif math.isinf(x):
             return sys.hash_info.inf if x > 0 else -sys.hash_info.inf
         else:
             return hash_fraction(*x.as_integer_ratio())

     def hash_complex(z):
         """Compute the hash of a complex number z."""

         hash_value = hash_float(z.real) + sys.hash_info.imag * hash_float(z.imag)
         # do a signed reduction modulo 2**sys.hash_info.width
         M = 2**(sys.hash_info.width - 1)
         hash_value = (hash_value & (M - 1)) - (hash_value & M)
         if hash_value == -1:
             hash_value = -2
         return hash_value


File: python.info,  Node: Iterator Types,  Next: Sequence Types — list tuple range,  Prev: Numeric Types — int float complex,  Up: Built-in Types

5.4.5 Iterator Types
--------------------

Python supports a concept of iteration over containers.  This is
implemented using two distinct methods; these are used to allow
user-defined classes to support iteration.  Sequences, described below
in more detail, always support the iteration methods.

One method needs to be defined for container objects to provide
iteration support:

 -- Method: container.__iter__ ()

     Return an iterator object.  The object is required to support the
     iterator protocol described below.  If a container supports
     different types of iteration, additional methods can be provided to
     specifically request iterators for those iteration types.  (An
     example of an object supporting multiple forms of iteration would
     be a tree structure which supports both breadth-first and
     depth-first traversal.)  This method corresponds to the *note
     tp_iter: ef2. slot of the type structure for Python objects in the
     Python/C API.

The iterator objects themselves are required to support the following
two methods, which together form the `iterator protocol':

 -- Method: iterator.__iter__ ()

     Return the iterator object itself.  This is required to allow both
     containers and iterators to be used with the *note for: cfa. and
     *note in: 179. statements.  This method corresponds to the *note
     tp_iter: ef2. slot of the type structure for Python objects in the
     Python/C API.

 -- Method: iterator.__next__ ()

     Return the next item from the container.  If there are no further
     items, raise the *note StopIteration: 582. exception.  This method
     corresponds to the *note tp_iternext: ef3. slot of the type
     structure for Python objects in the Python/C API.

Python defines several iterator objects to support iteration over
general and specific sequence types, dictionaries, and other more
specialized forms.  The specific types are not important beyond their
implementation of the iterator protocol.

Once an iterator’s *note __next__(): d2c. method raises *note
StopIteration: 582, it must continue to do so on subsequent calls.
Implementations that do not obey this property are deemed broken.

* Menu:

* Generator Types::


File: python.info,  Node: Generator Types,  Up: Iterator Types

5.4.5.1 Generator Types
.......................

Python’s *note generator: a83.s provide a convenient way to implement
the iterator protocol.  If a container object’s *note __iter__(): 609.
method is implemented as a generator, it will automatically return an
iterator object (technically, a generator object) supplying the *note
__iter__(): 609. and *note __next__(): 140e. methods.  More information
about generators can be found in *note the documentation for the yield
expression: 163d.


File: python.info,  Node: Sequence Types — list tuple range,  Next: Text Sequence Type — str,  Prev: Iterator Types,  Up: Built-in Types

5.4.6 Sequence Types — ‘list’, ‘tuple’, ‘range’
-----------------------------------------------

There are three basic sequence types: lists, tuples, and range objects.
Additional sequence types tailored for processing of *note binary data:
171d. and *note text strings: 1357. are described in dedicated sections.

* Menu:

* Common Sequence Operations::
* Immutable Sequence Types::
* Mutable Sequence Types::
* Lists: Lists<2>.
* Tuples::
* Ranges::


File: python.info,  Node: Common Sequence Operations,  Next: Immutable Sequence Types,  Up: Sequence Types — list tuple range

5.4.6.1 Common Sequence Operations
..................................

The operations in the following table are supported by most sequence
types, both mutable and immutable.  The *note collections.abc.Sequence:
1764. ABC is provided to make it easier to correctly implement these
operations on custom sequence types.

This table lists the sequence operations sorted in ascending priority.
In the table, `s' and `t' are sequences of the same type, `n', `i', `j'
and `k' are integers and `x' is an arbitrary object that meets any type
and value restrictions imposed by `s'.

The ‘in’ and ‘not in’ operations have the same priorities as the
comparison operations.  The ‘+’ (concatenation) and ‘*’ (repetition)
operations have the same priority as the corresponding numeric
operations.  (1)

Operation                      Result                               Notes
                                                                    
-----------------------------------------------------------------------------------
                                                                    
‘x in s’                       ‘True’ if an item of `s' is equal    (1)
                               to `x', else ‘False’                 
                               
                                                                    
‘x not in s’                   ‘False’ if an item of `s' is equal   (1)
                               to `x', else ‘True’                  
                               
                                                                    
‘s + t’                        the concatenation of `s' and `t'     (6)(7)
                                                                    
                                                                    
‘s * n’ or ‘n * s’             equivalent to adding `s' to itself   (2)(7)
                               `n' times                            
                               
                                                                    
‘s[i]’                         `i'th item of `s', origin 0          (3)
                                                                    
                                                                    
‘s[i:j]’                       slice of `s' from `i' to `j'         (3)(4)
                                                                    
                                                                    
‘s[i:j:k]’                     slice of `s' from `i' to `j' with    (3)(5)
                               step `k'                             
                               
                                                                    
‘len(s)’                       length of `s'
                               
                                                                    
‘min(s)’                       smallest item of `s'
                               
                                                                    
‘max(s)’                       largest item of `s'
                               
                                                                    
‘s.index(x[, i[, j]])’         index of the first occurrence of     (8)
                               `x' in `s' (at or after index `i'    
                               and before index `j')
                               
                                                                    
‘s.count(x)’                   total number of occurrences of `x'
                               in `s'
                               

Sequences of the same type also support comparisons.  In particular,
tuples and lists are compared lexicographically by comparing
corresponding elements.  This means that to compare equal, every element
must compare equal and the two sequences must be of the same type and
have the same length.  (For full details see *note Comparisons: 167a. in
the language reference.)

Notes:

  1. While the ‘in’ and ‘not in’ operations are used only for simple
     containment testing in the general case, some specialised sequences
     (such as *note str: 205, *note bytes: 172. and *note bytearray:
     173.) also use them for subsequence testing:

          >>> "gg" in "eggs"
          True

  2. Values of `n' less than ‘0’ are treated as ‘0’ (which yields an
     empty sequence of the same type as `s').  Note that items in the
     sequence `s' are not copied; they are referenced multiple times.
     This often haunts new Python programmers; consider:

          >>> lists = [[]] * 3
          >>> lists
          [[], [], []]
          >>> lists[0].append(3)
          >>> lists
          [[3], [3], [3]]

     What has happened is that ‘[[]]’ is a one-element list containing
     an empty list, so all three elements of ‘[[]] * 3’ are references
     to this single empty list.  Modifying any of the elements of
     ‘lists’ modifies this single list.  You can create a list of
     different lists this way:

          >>> lists = [[] for i in range(3)]
          >>> lists[0].append(3)
          >>> lists[1].append(5)
          >>> lists[2].append(7)
          >>> lists
          [[3], [5], [7]]

     Further explanation is available in the FAQ entry *note How do I
     create a multidimensional list?: 1765.

  3. If `i' or `j' is negative, the index is relative to the end of
     sequence `s': ‘len(s) + i’ or ‘len(s) + j’ is substituted.  But
     note that ‘-0’ is still ‘0’.

  4. The slice of `s' from `i' to `j' is defined as the sequence of
     items with index `k' such that ‘i <= k < j’.  If `i' or `j' is
     greater than ‘len(s)’, use ‘len(s)’.  If `i' is omitted or ‘None’,
     use ‘0’.  If `j' is omitted or ‘None’, use ‘len(s)’.  If `i' is
     greater than or equal to `j', the slice is empty.

  5. The slice of `s' from `i' to `j' with step `k' is defined as the
     sequence of items with index ‘x = i + n*k’ such that ‘0 <= n <
     (j-i)/k’.  In other words, the indices are ‘i’, ‘i+k’, ‘i+2*k’,
     ‘i+3*k’ and so on, stopping when `j' is reached (but never
     including `j').  When `k' is positive, `i' and `j' are reduced to
     ‘len(s)’ if they are greater.  When `k' is negative, `i' and `j'
     are reduced to ‘len(s) - 1’ if they are greater.  If `i' or `j' are
     omitted or ‘None’, they become “end” values (which end depends on
     the sign of `k').  Note, `k' cannot be zero.  If `k' is ‘None’, it
     is treated like ‘1’.

  6. Concatenating immutable sequences always results in a new object.
     This means that building up a sequence by repeated concatenation
     will have a quadratic runtime cost in the total sequence length.
     To get a linear runtime cost, you must switch to one of the
     alternatives below:

        * if concatenating *note str: 205. objects, you can build a list
          and use *note str.join(): 1766. at the end or else write to an
          *note io.StringIO: 91a. instance and retrieve its value when
          complete

        * if concatenating *note bytes: 172. objects, you can similarly
          use *note bytes.join(): 1767. or *note io.BytesIO: 88a, or you
          can do in-place concatenation with a *note bytearray: 173.
          object.  *note bytearray: 173. objects are mutable and have an
          efficient overallocation mechanism

        * if concatenating *note tuple: 1a2. objects, extend a *note
          list: 1f8. instead

        * for other types, investigate the relevant class documentation

  7. Some sequence types (such as *note range: 1f5.) only support item
     sequences that follow specific patterns, and hence don’t support
     sequence concatenation or repetition.

  8. ‘index’ raises *note ValueError: 16d. when `x' is not found in `s'.
     Not all implementations support passing the additional arguments
     `i' and `j'.  These arguments allow efficient searching of
     subsections of the sequence.  Passing the extra arguments is
     roughly equivalent to using ‘s[i:j].index(x)’, only without copying
     any data and with the returned index being relative to the start of
     the sequence rather than the start of the slice.

   ---------- Footnotes ----------

   (1) (3) They must have since the parser can’t tell the type of the
operands.


File: python.info,  Node: Immutable Sequence Types,  Next: Mutable Sequence Types,  Prev: Common Sequence Operations,  Up: Sequence Types — list tuple range

5.4.6.2 Immutable Sequence Types
................................

The only operation that immutable sequence types generally implement
that is not also implemented by mutable sequence types is support for
the *note hash(): aa3. built-in.

This support allows immutable sequences, such as *note tuple: 1a2.
instances, to be used as *note dict: 164. keys and stored in *note set:
1f6. and *note frozenset: 1f7. instances.

Attempting to hash an immutable sequence that contains unhashable values
will result in *note TypeError: 1fe.


File: python.info,  Node: Mutable Sequence Types,  Next: Lists<2>,  Prev: Immutable Sequence Types,  Up: Sequence Types — list tuple range

5.4.6.3 Mutable Sequence Types
..............................

The operations in the following table are defined on mutable sequence
types.  The *note collections.abc.MutableSequence: 79f. ABC is provided
to make it easier to correctly implement these operations on custom
sequence types.

In the table `s' is an instance of a mutable sequence type, `t' is any
iterable object and `x' is an arbitrary object that meets any type and
value restrictions imposed by `s' (for example, *note bytearray: 173.
only accepts integers that meet the value restriction ‘0 <= x <= 255’).

Operation                          Result                               Notes
                                                                        
--------------------------------------------------------------------------------------------------
                                                                        
‘s[i] = x’                         item `i' of `s' is replaced by `x'
                                   
                                                                        
‘s[i:j] = t’                       slice of `s' from `i' to `j' is
                                   replaced by the contents of the
                                   iterable `t'
                                   
                                                                        
‘del s[i:j]’                       same as ‘s[i:j] = []’
                                   
                                                                        
‘s[i:j:k] = t’                     the elements of ‘s[i:j:k]’ are       (1)
                                   replaced by those of `t'             
                                   
                                                                        
‘del s[i:j:k]’                     removes the elements of ‘s[i:j:k]’
                                   from the list
                                   
                                                                        
‘s.append(x)’                      appends `x' to the end of the
                                   sequence (same as
                                   ‘s[len(s):len(s)] = [x]’)
                                   
                                                                        
‘s.clear()’                        removes all items from `s' (same     (5)
                                   as ‘del s[:]’)                       
                                   
                                                                        
‘s.copy()’                         creates a shallow copy of `s'        (5)
                                   (same as ‘s[:]’)                     
                                   
                                                                        
‘s.extend(t)’ or ‘s += t’          extends `s' with the contents of
                                   `t' (for the most part the same as
                                   ‘s[len(s):len(s)] = t’)
                                   
                                                                        
‘s *= n’                           updates `s' with its contents        (6)
                                   repeated `n' times                   
                                   
                                                                        
‘s.insert(i, x)’                   inserts `x' into `s' at the index
                                   given by `i' (same as ‘s[i:i] =
                                   [x]’)
                                   
                                                                        
‘s.pop()’ or ‘s.pop(i)’            retrieves the item at `i' and also   (2)
                                   removes it from `s'                  
                                   
                                                                        
‘s.remove(x)’                      remove the first item from `s'       (3)
                                   where ‘s[i]’ is equal to `x'         
                                   
                                                                        
‘s.reverse()’                      reverses the items of `s' in place   (4)
                                                                        

Notes:

  1. `t' must have the same length as the slice it is replacing.

  2. The optional argument `i' defaults to ‘-1’, so that by default the
     last item is removed and returned.

  3. ‘remove()’ raises *note ValueError: 16d. when `x' is not found in
     `s'.

  4. The ‘reverse()’ method modifies the sequence in place for economy
     of space when reversing a large sequence.  To remind users that it
     operates by side effect, it does not return the reversed sequence.

  5. ‘clear()’ and ‘copy()’ are included for consistency with the
     interfaces of mutable containers that don’t support slicing
     operations (such as *note dict: 164. and *note set: 1f6.).
     ‘copy()’ is not part of the *note collections.abc.MutableSequence:
     79f. ABC, but most concrete mutable sequence classes provide it.

     New in version 3.3: ‘clear()’ and ‘copy()’ methods.

  6. The value `n' is an integer, or an object implementing *note
     __index__(): 2c2.  Zero and negative values of `n' clear the
     sequence.  Items in the sequence are not copied; they are
     referenced multiple times, as explained for ‘s * n’ under *note
     Common Sequence Operations: 1763.


File: python.info,  Node: Lists<2>,  Next: Tuples,  Prev: Mutable Sequence Types,  Up: Sequence Types — list tuple range

5.4.6.4 Lists
.............

Lists are mutable sequences, typically used to store collections of
homogeneous items (where the precise degree of similarity will vary by
application).

 -- Class: list ([iterable])

     Lists may be constructed in several ways:

        * Using a pair of square brackets to denote the empty list: ‘[]’

        * Using square brackets, separating items with commas: ‘[a]’,
          ‘[a, b, c]’

        * Using a list comprehension: ‘[x for x in iterable]’

        * Using the type constructor: ‘list()’ or ‘list(iterable)’

     The constructor builds a list whose items are the same and in the
     same order as `iterable'’s items.  `iterable' may be either a
     sequence, a container that supports iteration, or an iterator
     object.  If `iterable' is already a list, a copy is made and
     returned, similar to ‘iterable[:]’.  For example, ‘list('abc')’
     returns ‘['a', 'b', 'c']’ and ‘list( (1, 2, 3) )’ returns ‘[1, 2,
     3]’.  If no argument is given, the constructor creates a new empty
     list, ‘[]’.

     Many other operations also produce lists, including the *note
     sorted(): 547. built-in.

     Lists implement all of the *note common: 1763. and *note mutable:
     171a. sequence operations.  Lists also provide the following
     additional method:

      -- Method: sort (*, key=None, reverse=False)

          This method sorts the list in place, using only ‘<’
          comparisons between items.  Exceptions are not suppressed - if
          any comparison operations fail, the entire sort operation will
          fail (and the list will likely be left in a partially modified
          state).

          *note sort(): 548. accepts two arguments that can only be
          passed by keyword (*note keyword-only arguments: 3ce.):

          `key' specifies a function of one argument that is used to
          extract a comparison key from each list element (for example,
          ‘key=str.lower’).  The key corresponding to each item in the
          list is calculated once and then used for the entire sorting
          process.  The default value of ‘None’ means that list items
          are sorted directly without calculating a separate key value.

          The *note functools.cmp_to_key(): c28. utility is available to
          convert a 2.x style `cmp' function to a `key' function.

          `reverse' is a boolean value.  If set to ‘True’, then the list
          elements are sorted as if each comparison were reversed.

          This method modifies the sequence in place for economy of
          space when sorting a large sequence.  To remind users that it
          operates by side effect, it does not return the sorted
          sequence (use *note sorted(): 547. to explicitly request a new
          sorted list instance).

          The *note sort(): 548. method is guaranteed to be stable.  A
          sort is stable if it guarantees not to change the relative
          order of elements that compare equal — this is helpful for
          sorting in multiple passes (for example, sort by department,
          then by salary grade).

          For sorting examples and a brief sorting tutorial, see *note
          Sorting HOW TO: 1737.

          `CPython implementation detail:' While a list is being sorted,
          the effect of attempting to mutate, or even inspect, the list
          is undefined.  The C implementation of Python makes the list
          appear empty for the duration, and raises *note ValueError:
          16d. if it can detect that the list has been mutated during a
          sort.


File: python.info,  Node: Tuples,  Next: Ranges,  Prev: Lists<2>,  Up: Sequence Types — list tuple range

5.4.6.5 Tuples
..............

Tuples are immutable sequences, typically used to store collections of
heterogeneous data (such as the 2-tuples produced by the *note
enumerate(): ea7. built-in).  Tuples are also used for cases where an
immutable sequence of homogeneous data is needed (such as allowing
storage in a *note set: 1f6. or *note dict: 164. instance).

 -- Class: tuple ([iterable])

     Tuples may be constructed in a number of ways:

        * Using a pair of parentheses to denote the empty tuple: ‘()’

        * Using a trailing comma for a singleton tuple: ‘a,’ or ‘(a,)’

        * Separating items with commas: ‘a, b, c’ or ‘(a, b, c)’

        * Using the *note tuple(): 1a2. built-in: ‘tuple()’ or
          ‘tuple(iterable)’

     The constructor builds a tuple whose items are the same and in the
     same order as `iterable'’s items.  `iterable' may be either a
     sequence, a container that supports iteration, or an iterator
     object.  If `iterable' is already a tuple, it is returned
     unchanged.  For example, ‘tuple('abc')’ returns ‘('a', 'b', 'c')’
     and ‘tuple( [1, 2, 3] )’ returns ‘(1, 2, 3)’.  If no argument is
     given, the constructor creates a new empty tuple, ‘()’.

     Note that it is actually the comma which makes a tuple, not the
     parentheses.  The parentheses are optional, except in the empty
     tuple case, or when they are needed to avoid syntactic ambiguity.
     For example, ‘f(a, b, c)’ is a function call with three arguments,
     while ‘f((a, b, c))’ is a function call with a 3-tuple as the sole
     argument.

     Tuples implement all of the *note common: 1763. sequence
     operations.

For heterogeneous collections of data where access by name is clearer
than access by index, *note collections.namedtuple(): 1a1. may be a more
appropriate choice than a simple tuple object.


File: python.info,  Node: Ranges,  Prev: Tuples,  Up: Sequence Types — list tuple range

5.4.6.6 Ranges
..............

The *note range: 1f5. type represents an immutable sequence of numbers
and is commonly used for looping a specific number of times in *note
for: cfa. loops.

 -- Class: range (stop)

 -- Class: range (start, stop[, step])

     The arguments to the range constructor must be integers (either
     built-in *note int: 204. or any object that implements the *note
     __index__(): 2c2. special method).  If the `step' argument is
     omitted, it defaults to ‘1’.  If the `start' argument is omitted,
     it defaults to ‘0’.  If `step' is zero, *note ValueError: 16d. is
     raised.

     For a positive `step', the contents of a range ‘r’ are determined
     by the formula ‘r[i] = start + step*i’ where ‘i >= 0’ and ‘r[i] <
     stop’.

     For a negative `step', the contents of the range are still
     determined by the formula ‘r[i] = start + step*i’, but the
     constraints are ‘i >= 0’ and ‘r[i] > stop’.

     A range object will be empty if ‘r[0]’ does not meet the value
     constraint.  Ranges do support negative indices, but these are
     interpreted as indexing from the end of the sequence determined by
     the positive indices.

     Ranges containing absolute values larger than *note sys.maxsize:
     c15. are permitted but some features (such as *note len(): 28b.)
     may raise *note OverflowError: a41.

     Range examples:

          >>> list(range(10))
          [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
          >>> list(range(1, 11))
          [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
          >>> list(range(0, 30, 5))
          [0, 5, 10, 15, 20, 25]
          >>> list(range(0, 10, 3))
          [0, 3, 6, 9]
          >>> list(range(0, -10, -1))
          [0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
          >>> list(range(0))
          []
          >>> list(range(1, 0))
          []

     Ranges implement all of the *note common: 1763. sequence operations
     except concatenation and repetition (due to the fact that range
     objects can only represent sequences that follow a strict pattern
     and repetition and concatenation will usually violate that
     pattern).

      -- Attribute: start

          The value of the `start' parameter (or ‘0’ if the parameter
          was not supplied)

      -- Attribute: stop

          The value of the `stop' parameter

      -- Attribute: step

          The value of the `step' parameter (or ‘1’ if the parameter was
          not supplied)

The advantage of the *note range: 1f5. type over a regular *note list:
1f8. or *note tuple: 1a2. is that a *note range: 1f5. object will always
take the same (small) amount of memory, no matter the size of the range
it represents (as it only stores the ‘start’, ‘stop’ and ‘step’ values,
calculating individual items and subranges as needed).

Range objects implement the *note collections.abc.Sequence: 1764. ABC,
and provide features such as containment tests, element index lookup,
slicing and support for negative indices (see *note Sequence Types —
list, tuple, range: 13a4.):

     >>> r = range(0, 20, 2)
     >>> r
     range(0, 20, 2)
     >>> 11 in r
     False
     >>> 10 in r
     True
     >>> r.index(10)
     5
     >>> r[5]
     10
     >>> r[:5]
     range(0, 10, 2)
     >>> r[-1]
     18

Testing range objects for equality with ‘==’ and ‘!=’ compares them as
sequences.  That is, two range objects are considered equal if they
represent the same sequence of values.  (Note that two range objects
that compare equal might have different *note start: 176e, *note stop:
176f. and *note step: 1770. attributes, for example ‘range(0) ==
range(2, 1, 3)’ or ‘range(0, 3, 2) == range(0, 4, 2)’.)

Changed in version 3.2: Implement the Sequence ABC. Support slicing and
negative indices.  Test *note int: 204. objects for membership in
constant time instead of iterating through all items.

Changed in version 3.3: Define ‘==’ and ‘!=’ to compare range objects
based on the sequence of values they define (instead of comparing based
on object identity).

New in version 3.3: The *note start: 176e, *note stop: 176f. and *note
step: 1770. attributes.

See also
........

   * The linspace recipe(1) shows how to implement a lazy version of
     range suitable for floating point applications.

   ---------- Footnotes ----------

   (1) http://code.activestate.com/recipes/579000/


File: python.info,  Node: Text Sequence Type — str,  Next: Binary Sequence Types — bytes bytearray memoryview,  Prev: Sequence Types — list tuple range,  Up: Built-in Types

5.4.7 Text Sequence Type — ‘str’
--------------------------------

Textual data in Python is handled with *note str: 205. objects, or
`strings'.  Strings are immutable *note sequences: 13a4. of Unicode code
points.  String literals are written in a variety of ways:

   * Single quotes: ‘'allows embedded "double" quotes'’

   * Double quotes: ‘"allows embedded 'single' quotes"’

   * Triple quoted: ‘'''Three single quotes'''’, ‘"""Three double
     quotes"""’

Triple quoted strings may span multiple lines - all associated
whitespace will be included in the string literal.

String literals that are part of a single expression and have only
whitespace between them will be implicitly converted to a single string
literal.  That is, ‘("spam " "eggs") == "spam eggs"’.

See *note String and Bytes literals: 1514. for more about the various
forms of string literal, including supported escape sequences, and the
‘r’ (“raw”) prefix that disables most escape sequence processing.

Strings may also be created from other objects using the *note str: 205.
constructor.

Since there is no separate “character” type, indexing a string produces
strings of length 1.  That is, for a non-empty string `s', ‘s[0] ==
s[0:1]’.

There is also no mutable string type, but *note str.join(): 1766. or
*note io.StringIO: 91a. can be used to efficiently construct strings
from multiple fragments.

Changed in version 3.3: For backwards compatibility with the Python 2
series, the ‘u’ prefix is once again permitted on string literals.  It
has no effect on the meaning of string literals and cannot be combined
with the ‘r’ prefix.

 -- Class: str (object='')

 -- Class: str (object=b'', encoding='utf-8', errors='strict')

     Return a *note string: 1357. version of `object'.  If `object' is
     not provided, returns the empty string.  Otherwise, the behavior of
     ‘str()’ depends on whether `encoding' or `errors' is given, as
     follows.

     If neither `encoding' nor `errors' is given, ‘str(object)’ returns
     *note object.__str__(): ef9, which is the “informal” or nicely
     printable string representation of `object'.  For string objects,
     this is the string itself.  If `object' does not have a *note
     __str__(): ef9. method, then *note str(): 205. falls back to
     returning *note repr(object): 8b9.

     If at least one of `encoding' or `errors' is given, `object' should
     be a *note bytes-like object: 6df. (e.g.  *note bytes: 172. or
     *note bytearray: 173.).  In this case, if `object' is a *note
     bytes: 172. (or *note bytearray: 173.) object, then ‘str(bytes,
     encoding, errors)’ is equivalent to *note bytes.decode(encoding,
     errors): 171.  Otherwise, the bytes object underlying the buffer
     object is obtained before calling *note bytes.decode(): 171.  See
     *note Binary Sequence Types — bytes, bytearray, memoryview: 171d.
     and *note Buffer Protocol: 171c. for information on buffer objects.

     Passing a *note bytes: 172. object to *note str(): 205. without the
     `encoding' or `errors' arguments falls under the first case of
     returning the informal string representation (see also the *note
     -b: 51a. command-line option to Python).  For example:

          >>> str(b'Zoot!')
          "b'Zoot!'"

     For more information on the ‘str’ class and its methods, see *note
     Text Sequence Type — str: 1357. and the *note String Methods: 1358.
     section below.  To output formatted strings, see the *note
     Formatted string literals: 296. and *note Format String Syntax:
     de0. sections.  In addition, see the *note Text Processing
     Services: 1772. section.

* Menu:

* String Methods: String Methods<2>.
* printf-style String Formatting::


File: python.info,  Node: String Methods<2>,  Next: printf-style String Formatting,  Up: Text Sequence Type — str

5.4.7.1 String Methods
......................

Strings implement all of the *note common: 1763. sequence operations,
along with the additional methods described below.

Strings also support two styles of string formatting, one providing a
large degree of flexibility and customization (see *note str.format():
5d5, *note Format String Syntax: de0. and *note Custom String
Formatting: 1774.) and the other based on C ‘printf’ style formatting
that handles a narrower range of types and is slightly harder to use
correctly, but is often faster for the cases it can handle (*note
printf-style String Formatting: 1359.).

The *note Text Processing Services: 1775. section of the standard
library covers a number of other modules that provide various text
related utilities (including regular expression support in the *note re:
dd. module).

 -- Method: str.capitalize ()

     Return a copy of the string with its first character capitalized
     and the rest lowercased.

     Changed in version 3.8: The first character is now put into
     titlecase rather than uppercase.  This means that characters like
     digraphs will only have their first letter capitalized, instead of
     the full character.

 -- Method: str.casefold ()

     Return a casefolded copy of the string.  Casefolded strings may be
     used for caseless matching.

     Casefolding is similar to lowercasing but more aggressive because
     it is intended to remove all case distinctions in a string.  For
     example, the German lowercase letter ‘'ß'’ is equivalent to ‘"ss"’.
     Since it is already lowercase, *note lower(): 1777. would do
     nothing to ‘'ß'’; *note casefold(): 7a3. converts it to ‘"ss"’.

     The casefolding algorithm is described in section 3.13 of the
     Unicode Standard.

     New in version 3.3.

 -- Method: str.center (width[, fillchar])

     Return centered in a string of length `width'.  Padding is done
     using the specified `fillchar' (default is an ASCII space).  The
     original string is returned if `width' is less than or equal to
     ‘len(s)’.

 -- Method: str.count (sub[, start[, end]])

     Return the number of non-overlapping occurrences of substring `sub'
     in the range [`start', `end'].  Optional arguments `start' and
     `end' are interpreted as in slice notation.

 -- Method: str.encode (encoding="utf-8", errors="strict")

     Return an encoded version of the string as a bytes object.  Default
     encoding is ‘'utf-8'’.  `errors' may be given to set a different
     error handling scheme.  The default for `errors' is ‘'strict'’,
     meaning that encoding errors raise a *note UnicodeError: d03.
     Other possible values are ‘'ignore'’, ‘'replace'’,
     ‘'xmlcharrefreplace'’, ‘'backslashreplace'’ and any other name
     registered via *note codecs.register_error(): eb9, see section
     *note Error Handlers: 1493.  For a list of possible encodings, see
     section *note Standard Encodings: 782.

     By default, the `errors' argument is not checked for best
     performances, but only used at the first encoding error.  Enable
     the *note Python Development Mode: 160, or use a debug build to
     check `errors'.

     Changed in version 3.1: Support for keyword arguments added.

     Changed in version 3.9: The `errors' is now checked in development
     mode and in debug mode.

 -- Method: str.endswith (suffix[, start[, end]])

     Return ‘True’ if the string ends with the specified `suffix',
     otherwise return ‘False’.  `suffix' can also be a tuple of suffixes
     to look for.  With optional `start', test beginning at that
     position.  With optional `end', stop comparing at that position.

 -- Method: str.expandtabs (tabsize=8)

     Return a copy of the string where all tab characters are replaced
     by one or more spaces, depending on the current column and the
     given tab size.  Tab positions occur every `tabsize' characters
     (default is 8, giving tab positions at columns 0, 8, 16 and so on).
     To expand the string, the current column is set to zero and the
     string is examined character by character.  If the character is a
     tab (‘\t’), one or more space characters are inserted in the result
     until the current column is equal to the next tab position.  (The
     tab character itself is not copied.)  If the character is a newline
     (‘\n’) or return (‘\r’), it is copied and the current column is
     reset to zero.  Any other character is copied unchanged and the
     current column is incremented by one regardless of how the
     character is represented when printed.

          >>> '01\t012\t0123\t01234'.expandtabs()
          '01      012     0123    01234'
          >>> '01\t012\t0123\t01234'.expandtabs(4)
          '01  012 0123    01234'

 -- Method: str.find (sub[, start[, end]])

     Return the lowest index in the string where substring `sub' is
     found within the slice ‘s[start:end]’.  Optional arguments `start'
     and `end' are interpreted as in slice notation.  Return ‘-1’ if
     `sub' is not found.

          Note: The *note find(): 88e. method should be used only if you
          need to know the position of `sub'.  To check if `sub' is a
          substring or not, use the *note in: 179. operator:

               >>> 'Py' in 'Python'
               True

 -- Method: str.format (*args, **kwargs)

     Perform a string formatting operation.  The string on which this
     method is called can contain literal text or replacement fields
     delimited by braces ‘{}’.  Each replacement field contains either
     the numeric index of a positional argument, or the name of a
     keyword argument.  Returns a copy of the string where each
     replacement field is replaced with the string value of the
     corresponding argument.

          >>> "The sum of 1 + 2 is {0}".format(1+2)
          'The sum of 1 + 2 is 3'

     See *note Format String Syntax: de0. for a description of the
     various formatting options that can be specified in format strings.

          Note: When formatting a number (*note int: 204, *note float:
          1fd, *note complex: 2c1, *note decimal.Decimal: 2c0. and
          subclasses) with the ‘n’ type (ex: ‘'{:n}'.format(1234)’), the
          function temporarily sets the ‘LC_CTYPE’ locale to the
          ‘LC_NUMERIC’ locale to decode ‘decimal_point’ and
          ‘thousands_sep’ fields of ‘localeconv()’ if they are non-ASCII
          or longer than 1 byte, and the ‘LC_NUMERIC’ locale is
          different than the ‘LC_CTYPE’ locale.  This temporary change
          affects other threads.

     Changed in version 3.7: When formatting a number with the ‘n’ type,
     the function sets temporarily the ‘LC_CTYPE’ locale to the
     ‘LC_NUMERIC’ locale in some cases.

 -- Method: str.format_map (mapping)

     Similar to ‘str.format(**mapping)’, except that ‘mapping’ is used
     directly and not copied to a *note dict: 164.  This is useful if
     for example ‘mapping’ is a dict subclass:

          >>> class Default(dict):
          ...     def __missing__(self, key):
          ...         return key
          ...
          >>> '{name} was born in {country}'.format_map(Default(name='Guido'))
          'Guido was born in country'

     New in version 3.2.

 -- Method: str.index (sub[, start[, end]])

     Like *note find(): 88e, but raise *note ValueError: 16d. when the
     substring is not found.

 -- Method: str.isalnum ()

     Return ‘True’ if all characters in the string are alphanumeric and
     there is at least one character, ‘False’ otherwise.  A character
     ‘c’ is alphanumeric if one of the following returns ‘True’:
     ‘c.isalpha()’, ‘c.isdecimal()’, ‘c.isdigit()’, or ‘c.isnumeric()’.

 -- Method: str.isalpha ()

     Return ‘True’ if all characters in the string are alphabetic and
     there is at least one character, ‘False’ otherwise.  Alphabetic
     characters are those characters defined in the Unicode character
     database as “Letter”, i.e., those with general category property
     being one of “Lm”, “Lt”, “Lu”, “Ll”, or “Lo”.  Note that this is
     different from the “Alphabetic” property defined in the Unicode
     Standard.

 -- Method: str.isascii ()

     Return ‘True’ if the string is empty or all characters in the
     string are ASCII, ‘False’ otherwise.  ASCII characters have code
     points in the range U+0000-U+007F.

     New in version 3.7.

 -- Method: str.isdecimal ()

     Return ‘True’ if all characters in the string are decimal
     characters and there is at least one character, ‘False’ otherwise.
     Decimal characters are those that can be used to form numbers in
     base 10, e.g.  U+0660, ARABIC-INDIC DIGIT ZERO. Formally a decimal
     character is a character in the Unicode General Category “Nd”.

 -- Method: str.isdigit ()

     Return ‘True’ if all characters in the string are digits and there
     is at least one character, ‘False’ otherwise.  Digits include
     decimal characters and digits that need special handling, such as
     the compatibility superscript digits.  This covers digits which
     cannot be used to form numbers in base 10, like the Kharosthi
     numbers.  Formally, a digit is a character that has the property
     value Numeric_Type=Digit or Numeric_Type=Decimal.

 -- Method: str.isidentifier ()

     Return ‘True’ if the string is a valid identifier according to the
     language definition, section *note Identifiers and keywords: 1505.

     Call *note keyword.iskeyword(): 177f. to test whether string ‘s’ is
     a reserved identifier, such as *note def: e83. and *note class:
     d32.

     Example:

          >>> from keyword import iskeyword

          >>> 'hello'.isidentifier(), iskeyword('hello')
          (True, False)
          >>> 'def'.isidentifier(), iskeyword('def')
          (True, True)

 -- Method: str.islower ()

     Return ‘True’ if all cased characters (1) in the string are
     lowercase and there is at least one cased character, ‘False’
     otherwise.

 -- Method: str.isnumeric ()

     Return ‘True’ if all characters in the string are numeric
     characters, and there is at least one character, ‘False’ otherwise.
     Numeric characters include digit characters, and all characters
     that have the Unicode numeric value property, e.g.  U+2155, VULGAR
     FRACTION ONE FIFTH. Formally, numeric characters are those with the
     property value Numeric_Type=Digit, Numeric_Type=Decimal or
     Numeric_Type=Numeric.

 -- Method: str.isprintable ()

     Return ‘True’ if all characters in the string are printable or the
     string is empty, ‘False’ otherwise.  Nonprintable characters are
     those characters defined in the Unicode character database as
     “Other” or “Separator”, excepting the ASCII space (0x20) which is
     considered printable.  (Note that printable characters in this
     context are those which should not be escaped when *note repr():
     8b9. is invoked on a string.  It has no bearing on the handling of
     strings written to *note sys.stdout: 41f. or *note sys.stderr:
     1ea.)

 -- Method: str.isspace ()

     Return ‘True’ if there are only whitespace characters in the string
     and there is at least one character, ‘False’ otherwise.

     A character is `whitespace' if in the Unicode character database
     (see *note unicodedata: 123.), either its general category is ‘Zs’
     (“Separator, space”), or its bidirectional class is one of ‘WS’,
     ‘B’, or ‘S’.

 -- Method: str.istitle ()

     Return ‘True’ if the string is a titlecased string and there is at
     least one character, for example uppercase characters may only
     follow uncased characters and lowercase characters only cased ones.
     Return ‘False’ otherwise.

 -- Method: str.isupper ()

     Return ‘True’ if all cased characters (2) in the string are
     uppercase and there is at least one cased character, ‘False’
     otherwise.

          >>> 'BANANA'.isupper()
          True
          >>> 'banana'.isupper()
          False
          >>> 'baNana'.isupper()
          False
          >>> ' '.isupper()
          False

 -- Method: str.join (iterable)

     Return a string which is the concatenation of the strings in
     `iterable'.  A *note TypeError: 1fe. will be raised if there are
     any non-string values in `iterable', including *note bytes: 172.
     objects.  The separator between elements is the string providing
     this method.

 -- Method: str.ljust (width[, fillchar])

     Return the string left justified in a string of length `width'.
     Padding is done using the specified `fillchar' (default is an ASCII
     space).  The original string is returned if `width' is less than or
     equal to ‘len(s)’.

 -- Method: str.lower ()

     Return a copy of the string with all the cased characters (3)
     converted to lowercase.

     The lowercasing algorithm used is described in section 3.13 of the
     Unicode Standard.

 -- Method: str.lstrip ([chars])

     Return a copy of the string with leading characters removed.  The
     `chars' argument is a string specifying the set of characters to be
     removed.  If omitted or ‘None’, the `chars' argument defaults to
     removing whitespace.  The `chars' argument is not a prefix; rather,
     all combinations of its values are stripped:

          >>> '   spacious   '.lstrip()
          'spacious   '
          >>> 'www.example.com'.lstrip('cmowz.')
          'example.com'

     See *note str.removeprefix(): 166. for a method that will remove a
     single prefix string rather than all of a set of characters.  For
     example:

          >>> 'Arthur: three!'.lstrip('Arthur: ')
          'ee!'
          >>> 'Arthur: three!'.removeprefix('Arthur: ')
          'three!'

 -- Method: static str.maketrans (x[, y[, z]])

     This static method returns a translation table usable for *note
     str.translate(): 1786.

     If there is only one argument, it must be a dictionary mapping
     Unicode ordinals (integers) or characters (strings of length 1) to
     Unicode ordinals, strings (of arbitrary lengths) or ‘None’.
     Character keys will then be converted to ordinals.

     If there are two arguments, they must be strings of equal length,
     and in the resulting dictionary, each character in x will be mapped
     to the character at the same position in y.  If there is a third
     argument, it must be a string, whose characters will be mapped to
     ‘None’ in the result.

 -- Method: str.partition (sep)

     Split the string at the first occurrence of `sep', and return a
     3-tuple containing the part before the separator, the separator
     itself, and the part after the separator.  If the separator is not
     found, return a 3-tuple containing the string itself, followed by
     two empty strings.

 -- Method: str.removeprefix (prefix, /)

     If the string starts with the `prefix' string, return
     ‘string[len(prefix):]’.  Otherwise, return a copy of the original
     string:

          >>> 'TestHook'.removeprefix('Test')
          'Hook'
          >>> 'BaseTestCase'.removeprefix('Test')
          'BaseTestCase'

     New in version 3.9.

 -- Method: str.removesuffix (suffix, /)

     If the string ends with the `suffix' string and that `suffix' is
     not empty, return ‘string[:-len(suffix)]’.  Otherwise, return a
     copy of the original string:

          >>> 'MiscTests'.removesuffix('Tests')
          'Misc'
          >>> 'TmpDirMixin'.removesuffix('Tests')
          'TmpDirMixin'

     New in version 3.9.

 -- Method: str.replace (old, new[, count])

     Return a copy of the string with all occurrences of substring `old'
     replaced by `new'.  If the optional argument `count' is given, only
     the first `count' occurrences are replaced.

 -- Method: str.rfind (sub[, start[, end]])

     Return the highest index in the string where substring `sub' is
     found, such that `sub' is contained within ‘s[start:end]’.
     Optional arguments `start' and `end' are interpreted as in slice
     notation.  Return ‘-1’ on failure.

 -- Method: str.rindex (sub[, start[, end]])

     Like *note rfind(): 88f. but raises *note ValueError: 16d. when the
     substring `sub' is not found.

 -- Method: str.rjust (width[, fillchar])

     Return the string right justified in a string of length `width'.
     Padding is done using the specified `fillchar' (default is an ASCII
     space).  The original string is returned if `width' is less than or
     equal to ‘len(s)’.

 -- Method: str.rpartition (sep)

     Split the string at the last occurrence of `sep', and return a
     3-tuple containing the part before the separator, the separator
     itself, and the part after the separator.  If the separator is not
     found, return a 3-tuple containing two empty strings, followed by
     the string itself.

 -- Method: str.rsplit (sep=None, maxsplit=-1)

     Return a list of the words in the string, using `sep' as the
     delimiter string.  If `maxsplit' is given, at most `maxsplit'
     splits are done, the `rightmost' ones.  If `sep' is not specified
     or ‘None’, any whitespace string is a separator.  Except for
     splitting from the right, *note rsplit(): 178a. behaves like *note
     split(): 890. which is described in detail below.

 -- Method: str.rstrip ([chars])

     Return a copy of the string with trailing characters removed.  The
     `chars' argument is a string specifying the set of characters to be
     removed.  If omitted or ‘None’, the `chars' argument defaults to
     removing whitespace.  The `chars' argument is not a suffix; rather,
     all combinations of its values are stripped:

          >>> '   spacious   '.rstrip()
          '   spacious'
          >>> 'mississippi'.rstrip('ipz')
          'mississ'

     See *note str.removesuffix(): 167. for a method that will remove a
     single suffix string rather than all of a set of characters.  For
     example:

          >>> 'Monty Python'.rstrip(' Python')
          'M'
          >>> 'Monty Python'.removesuffix(' Python')
          'Monty'

 -- Method: str.split (sep=None, maxsplit=-1)

     Return a list of the words in the string, using `sep' as the
     delimiter string.  If `maxsplit' is given, at most `maxsplit'
     splits are done (thus, the list will have at most ‘maxsplit+1’
     elements).  If `maxsplit' is not specified or ‘-1’, then there is
     no limit on the number of splits (all possible splits are made).

     If `sep' is given, consecutive delimiters are not grouped together
     and are deemed to delimit empty strings (for example,
     ‘'1,,2'.split(',')’ returns ‘['1', '', '2']’).  The `sep' argument
     may consist of multiple characters (for example,
     ‘'1<>2<>3'.split('<>')’ returns ‘['1', '2', '3']’).  Splitting an
     empty string with a specified separator returns ‘['']’.

     For example:

          >>> '1,2,3'.split(',')
          ['1', '2', '3']
          >>> '1,2,3'.split(',', maxsplit=1)
          ['1', '2,3']
          >>> '1,2,,3,'.split(',')
          ['1', '2', '', '3', '']

     If `sep' is not specified or is ‘None’, a different splitting
     algorithm is applied: runs of consecutive whitespace are regarded
     as a single separator, and the result will contain no empty strings
     at the start or end if the string has leading or trailing
     whitespace.  Consequently, splitting an empty string or a string
     consisting of just whitespace with a ‘None’ separator returns ‘[]’.

     For example:

          >>> '1 2 3'.split()
          ['1', '2', '3']
          >>> '1 2 3'.split(maxsplit=1)
          ['1', '2 3']
          >>> '   1   2   3   '.split()
          ['1', '2', '3']

 -- Method: str.splitlines (keepends=False)

     Return a list of the lines in the string, breaking at line
     boundaries.  Line breaks are not included in the resulting list
     unless `keepends' is given and true.

     This method splits on the following line boundaries.  In
     particular, the boundaries are a superset of *note universal
     newlines: 6eb.

     Representation              Description
                                 
     --------------------------------------------------------------
                                 
     ‘\n’                        Line Feed
                                 
                                 
     ‘\r’                        Carriage Return
                                 
                                 
     ‘\r\n’                      Carriage Return + Line Feed
                                 
                                 
     ‘\v’ or ‘\x0b’              Line Tabulation
                                 
                                 
     ‘\f’ or ‘\x0c’              Form Feed
                                 
                                 
     ‘\x1c’                      File Separator
                                 
                                 
     ‘\x1d’                      Group Separator
                                 
                                 
     ‘\x1e’                      Record Separator
                                 
                                 
     ‘\x85’                      Next Line (C1 Control Code)
                                 
                                 
     ‘\u2028’                    Line Separator
                                 
                                 
     ‘\u2029’                    Paragraph Separator
                                 

     Changed in version 3.2: ‘\v’ and ‘\f’ added to list of line
     boundaries.

     For example:

          >>> 'ab c\n\nde fg\rkl\r\n'.splitlines()
          ['ab c', '', 'de fg', 'kl']
          >>> 'ab c\n\nde fg\rkl\r\n'.splitlines(keepends=True)
          ['ab c\n', '\n', 'de fg\r', 'kl\r\n']

     Unlike *note split(): 890. when a delimiter string `sep' is given,
     this method returns an empty list for the empty string, and a
     terminal line break does not result in an extra line:

          >>> "".splitlines()
          []
          >>> "One line\n".splitlines()
          ['One line']

     For comparison, ‘split('\n')’ gives:

          >>> ''.split('\n')
          ['']
          >>> 'Two lines\n'.split('\n')
          ['Two lines', '']

 -- Method: str.startswith (prefix[, start[, end]])

     Return ‘True’ if string starts with the `prefix', otherwise return
     ‘False’.  `prefix' can also be a tuple of prefixes to look for.
     With optional `start', test string beginning at that position.
     With optional `end', stop comparing string at that position.

 -- Method: str.strip ([chars])

     Return a copy of the string with the leading and trailing
     characters removed.  The `chars' argument is a string specifying
     the set of characters to be removed.  If omitted or ‘None’, the
     `chars' argument defaults to removing whitespace.  The `chars'
     argument is not a prefix or suffix; rather, all combinations of its
     values are stripped:

          >>> '   spacious   '.strip()
          'spacious'
          >>> 'www.example.com'.strip('cmowz.')
          'example'

     The outermost leading and trailing `chars' argument values are
     stripped from the string.  Characters are removed from the leading
     end until reaching a string character that is not contained in the
     set of characters in `chars'.  A similar action takes place on the
     trailing end.  For example:

          >>> comment_string = '#....... Section 3.2.1 Issue #32 .......'
          >>> comment_string.strip('.#! ')
          'Section 3.2.1 Issue #32'

 -- Method: str.swapcase ()

     Return a copy of the string with uppercase characters converted to
     lowercase and vice versa.  Note that it is not necessarily true
     that ‘s.swapcase().swapcase() == s’.

 -- Method: str.title ()

     Return a titlecased version of the string where words start with an
     uppercase character and the remaining characters are lowercase.

     For example:

          >>> 'Hello world'.title()
          'Hello World'

     The algorithm uses a simple language-independent definition of a
     word as groups of consecutive letters.  The definition works in
     many contexts but it means that apostrophes in contractions and
     possessives form word boundaries, which may not be the desired
     result:

          >>> "they're bill's friends from the UK".title()
          "They'Re Bill'S Friends From The Uk"

     A workaround for apostrophes can be constructed using regular
     expressions:

          >>> import re
          >>> def titlecase(s):
          ...     return re.sub(r"[A-Za-z]+('[A-Za-z]+)?",
          ...                   lambda mo: mo.group(0).capitalize(),
          ...                   s)
          ...
          >>> titlecase("they're bill's friends.")
          "They're Bill's Friends."

 -- Method: str.translate (table)

     Return a copy of the string in which each character has been mapped
     through the given translation table.  The table must be an object
     that implements indexing via *note __getitem__(): 3a2, typically a
     *note mapping: c0b. or *note sequence: 135c.  When indexed by a
     Unicode ordinal (an integer), the table object can do any of the
     following: return a Unicode ordinal or a string, to map the
     character to one or more other characters; return ‘None’, to delete
     the character from the return string; or raise a *note LookupError:
     1790. exception, to map the character to itself.

     You can use *note str.maketrans(): 7a6. to create a translation map
     from character-to-character mappings in different formats.

     See also the *note codecs: 1b. module for a more flexible approach
     to custom character mappings.

 -- Method: str.upper ()

     Return a copy of the string with all the cased characters (4)
     converted to uppercase.  Note that ‘s.upper().isupper()’ might be
     ‘False’ if ‘s’ contains uncased characters or if the Unicode
     category of the resulting character(s) is not “Lu” (Letter,
     uppercase), but e.g.  “Lt” (Letter, titlecase).

     The uppercasing algorithm used is described in section 3.13 of the
     Unicode Standard.

 -- Method: str.zfill (width)

     Return a copy of the string left filled with ASCII ‘'0'’ digits to
     make a string of length `width'.  A leading sign prefix
     (‘'+'’/‘'-'’) is handled by inserting the padding `after' the sign
     character rather than before.  The original string is returned if
     `width' is less than or equal to ‘len(s)’.

     For example:

          >>> "42".zfill(5)
          '00042'
          >>> "-42".zfill(5)
          '-0042'

   ---------- Footnotes ----------

   (1) (4) Cased characters are those with general category property
being one of “Lu” (Letter, uppercase), “Ll” (Letter, lowercase), or “Lt”
(Letter, titlecase).

   (2) (4) Cased characters are those with general category property
being one of “Lu” (Letter, uppercase), “Ll” (Letter, lowercase), or “Lt”
(Letter, titlecase).

   (3) (4) Cased characters are those with general category property
being one of “Lu” (Letter, uppercase), “Ll” (Letter, lowercase), or “Lt”
(Letter, titlecase).

   (4) (4) Cased characters are those with general category property
being one of “Lu” (Letter, uppercase), “Ll” (Letter, lowercase), or “Lt”
(Letter, titlecase).


File: python.info,  Node: printf-style String Formatting,  Prev: String Methods<2>,  Up: Text Sequence Type — str

5.4.7.2 ‘printf’-style String Formatting
........................................

     Note: The formatting operations described here exhibit a variety of
     quirks that lead to a number of common errors (such as failing to
     display tuples and dictionaries correctly).  Using the newer *note
     formatted string literals: 296, the *note str.format(): 5d5.
     interface, or *note template strings: 1793. may help avoid these
     errors.  Each of these alternatives provides their own trade-offs
     and benefits of simplicity, flexibility, and/or extensibility.

String objects have one unique built-in operation: the ‘%’ operator
(modulo).  This is also known as the string `formatting' or
`interpolation' operator.  Given ‘format % values’ (where `format' is a
string), ‘%’ conversion specifications in `format' are replaced with
zero or more elements of `values'.  The effect is similar to using the
‘sprintf()’ in the C language.

If `format' requires a single argument, `values' may be a single
non-tuple object.  (1) Otherwise, `values' must be a tuple with exactly
the number of items specified by the format string, or a single mapping
object (for example, a dictionary).

A conversion specifier contains two or more characters and has the
following components, which must occur in this order:

  1. The ‘'%'’ character, which marks the start of the specifier.

  2. Mapping key (optional), consisting of a parenthesised sequence of
     characters (for example, ‘(somename)’).

  3. Conversion flags (optional), which affect the result of some
     conversion types.

  4. Minimum field width (optional).  If specified as an ‘'*'’
     (asterisk), the actual width is read from the next element of the
     tuple in `values', and the object to convert comes after the
     minimum field width and optional precision.

  5. Precision (optional), given as a ‘'.'’ (dot) followed by the
     precision.  If specified as ‘'*'’ (an asterisk), the actual
     precision is read from the next element of the tuple in `values',
     and the value to convert comes after the precision.

  6. Length modifier (optional).

  7. Conversion type.

When the right argument is a dictionary (or other mapping type), then
the formats in the string `must' include a parenthesised mapping key
into that dictionary inserted immediately after the ‘'%'’ character.
The mapping key selects the value to be formatted from the mapping.  For
example:

     >>> print('%(language)s has %(number)03d quote types.' %
     ...       {'language': "Python", "number": 2})
     Python has 002 quote types.

In this case no ‘*’ specifiers may occur in a format (since they require
a sequential parameter list).

The conversion flag characters are:

Flag          Meaning
              
----------------------------------------------------------------------------------------
              
‘'#'’         The value conversion will use the “alternate form” (where defined
              below).
              
              
‘'0'’         The conversion will be zero padded for numeric values.
              
              
‘'-'’         The converted value is left adjusted (overrides the ‘'0'’ conversion if
              both are given).
              
              
‘' '’         (a space) A blank should be left before a positive number (or empty
              string) produced by a signed conversion.
              
              
‘'+'’         A sign character (‘'+'’ or ‘'-'’) will precede the conversion
              (overrides a “space” flag).
              

A length modifier (‘h’, ‘l’, or ‘L’) may be present, but is ignored as
it is not necessary for Python – so e.g.  ‘%ld’ is identical to ‘%d’.

The conversion types are:

Conversion       Meaning                                                   Notes
                                                                           
---------------------------------------------------------------------------------------
                                                                           
‘'d'’            Signed integer decimal.
                 
                                                                           
‘'i'’            Signed integer decimal.
                 
                                                                           
‘'o'’            Signed octal value.                                       (1)
                                                                           
                                                                           
‘'u'’            Obsolete type – it is identical to ‘'d'’.                 (6)
                                                                           
                                                                           
‘'x'’            Signed hexadecimal (lowercase).                           (2)
                                                                           
                                                                           
‘'X'’            Signed hexadecimal (uppercase).                           (2)
                                                                           
                                                                           
‘'e'’            Floating point exponential format (lowercase).            (3)
                                                                           
                                                                           
‘'E'’            Floating point exponential format (uppercase).            (3)
                                                                           
                                                                           
‘'f'’            Floating point decimal format.                            (3)
                                                                           
                                                                           
‘'F'’            Floating point decimal format.                            (3)
                                                                           
                                                                           
‘'g'’            Floating point format.  Uses lowercase exponential        (4)
                 format if exponent is less than -4 or not less than       
                 precision, decimal format otherwise.
                 
                                                                           
‘'G'’            Floating point format.  Uses uppercase exponential        (4)
                 format if exponent is less than -4 or not less than       
                 precision, decimal format otherwise.
                 
                                                                           
‘'c'’            Single character (accepts integer or single character
                 string).
                 
                                                                           
‘'r'’            String (converts any Python object using                  (5)
                 *note repr(): 8b9.).                                      
                 
                                                                           
‘'s'’            String (converts any Python object using                  (5)
                 *note str(): 205.).                                       
                 
                                                                           
‘'a'’            String (converts any Python object using                  (5)
                 *note ascii(): e11.).                                     
                 
                                                                           
‘'%'’            No argument is converted, results in a ‘'%'’ character
                 in the result.
                 

Notes:

  1. The alternate form causes a leading octal specifier (‘'0o'’) to be
     inserted before the first digit.

  2. The alternate form causes a leading ‘'0x'’ or ‘'0X'’ (depending on
     whether the ‘'x'’ or ‘'X'’ format was used) to be inserted before
     the first digit.

  3. The alternate form causes the result to always contain a decimal
     point, even if no digits follow it.

     The precision determines the number of digits after the decimal
     point and defaults to 6.

  4. The alternate form causes the result to always contain a decimal
     point, and trailing zeroes are not removed as they would otherwise
     be.

     The precision determines the number of significant digits before
     and after the decimal point and defaults to 6.

  5. If precision is ‘N’, the output is truncated to ‘N’ characters.

  6. See PEP 237(2).

Since Python strings have an explicit length, ‘%s’ conversions do not
assume that ‘'\0'’ is the end of the string.

Changed in version 3.1: ‘%f’ conversions for numbers whose absolute
value is over 1e50 are no longer replaced by ‘%g’ conversions.

   ---------- Footnotes ----------

   (1) (5) To format only a tuple you should therefore provide a
singleton tuple whose only element is the tuple to be formatted.

   (2) https://www.python.org/dev/peps/pep-0237


File: python.info,  Node: Binary Sequence Types — bytes bytearray memoryview,  Next: Set Types — set frozenset,  Prev: Text Sequence Type — str,  Up: Built-in Types

5.4.8 Binary Sequence Types — ‘bytes’, ‘bytearray’, ‘memoryview’
----------------------------------------------------------------

The core built-in types for manipulating binary data are *note bytes:
172. and *note bytearray: 173.  They are supported by *note memoryview:
386. which uses the *note buffer protocol: 171c. to access the memory of
other binary objects without needing to make a copy.

The *note array: 6. module supports efficient storage of basic data
types like 32-bit integers and IEEE754 double-precision floating values.

* Menu:

* Bytes Objects::
* Bytearray Objects::
* Bytes and Bytearray Operations::
* printf-style Bytes Formatting::
* Memory Views::


File: python.info,  Node: Bytes Objects,  Next: Bytearray Objects,  Up: Binary Sequence Types — bytes bytearray memoryview

5.4.8.1 Bytes Objects
.....................

Bytes objects are immutable sequences of single bytes.  Since many major
binary protocols are based on the ASCII text encoding, bytes objects
offer several methods that are only valid when working with ASCII
compatible data and are closely related to string objects in a variety
of other ways.

 -- Class: bytes ([source[, encoding[, errors]]])

     Firstly, the syntax for bytes literals is largely the same as that
     for string literals, except that a ‘b’ prefix is added:

        * Single quotes: ‘b'still allows embedded "double" quotes'’

        * Double quotes: ‘b"still allows embedded 'single' quotes"’

        * Triple quoted: ‘b'''3 single quotes'''’, ‘b"""3 double
          quotes"""’

     Only ASCII characters are permitted in bytes literals (regardless
     of the declared source code encoding).  Any binary values over 127
     must be entered into bytes literals using the appropriate escape
     sequence.

     As with string literals, bytes literals may also use a ‘r’ prefix
     to disable processing of escape sequences.  See *note String and
     Bytes literals: 1514. for more about the various forms of bytes
     literal, including supported escape sequences.

     While bytes literals and representations are based on ASCII text,
     bytes objects actually behave like immutable sequences of integers,
     with each value in the sequence restricted such that ‘0 <= x < 256’
     (attempts to violate this restriction will trigger *note
     ValueError: 16d.).  This is done deliberately to emphasise that
     while many binary formats include ASCII based elements and can be
     usefully manipulated with some text-oriented algorithms, this is
     not generally the case for arbitrary binary data (blindly applying
     text processing algorithms to binary data formats that are not
     ASCII compatible will usually lead to data corruption).

     In addition to the literal forms, bytes objects can be created in a
     number of other ways:

        * A zero-filled bytes object of a specified length: ‘bytes(10)’

        * From an iterable of integers: ‘bytes(range(20))’

        * Copying existing binary data via the buffer protocol:
          ‘bytes(obj)’

     Also see the *note bytes: 11f2. built-in.

     Since 2 hexadecimal digits correspond precisely to a single byte,
     hexadecimal numbers are a commonly used format for describing
     binary data.  Accordingly, the bytes type has an additional class
     method to read data in that format:

      -- Method: classmethod fromhex (string)

          This *note bytes: 172. class method returns a bytes object,
          decoding the given string object.  The string must contain two
          hexadecimal digits per byte, with ASCII whitespace being
          ignored.

               >>> bytes.fromhex('2Ef0 F1f2  ')
               b'.\xf0\xf1\xf2'

          Changed in version 3.7: *note bytes.fromhex(): 43e. now skips
          all ASCII whitespace in the string, not just spaces.

     A reverse conversion function exists to transform a bytes object
     into its hexadecimal representation.

      -- Method: hex ([sep[, bytes_per_sep]])

          Return a string object containing two hexadecimal digits for
          each byte in the instance.

               >>> b'\xf0\xf1\xf2'.hex()
               'f0f1f2'

          If you want to make the hex string easier to read, you can
          specify a single character separator `sep' parameter to
          include in the output.  By default between each byte.  A
          second optional `bytes_per_sep' parameter controls the
          spacing.  Positive values calculate the separator position
          from the right, negative values from the left.

               >>> value = b'\xf0\xf1\xf2'
               >>> value.hex('-')
               'f0-f1-f2'
               >>> value.hex('_', 2)
               'f0_f1f2'
               >>> b'UUDDLRLRAB'.hex(' ', -4)
               '55554444 4c524c52 4142'

          New in version 3.5.

          Changed in version 3.8: *note bytes.hex(): 724. now supports
          optional `sep' and `bytes_per_sep' parameters to insert
          separators between bytes in the hex output.

Since bytes objects are sequences of integers (akin to a tuple), for a
bytes object `b', ‘b[0]’ will be an integer, while ‘b[0:1]’ will be a
bytes object of length 1.  (This contrasts with text strings, where both
indexing and slicing will produce a string of length 1)

The representation of bytes objects uses the literal format (‘b'...'’)
since it is often more useful than e.g.  ‘bytes([46, 46, 46])’.  You can
always convert a bytes object into a list of integers using ‘list(b)’.

     Note: For Python 2.x users: In the Python 2.x series, a variety of
     implicit conversions between 8-bit strings (the closest thing 2.x
     offers to a built-in binary data type) and Unicode strings were
     permitted.  This was a backwards compatibility workaround to
     account for the fact that Python originally only supported 8-bit
     text, and Unicode text was a later addition.  In Python 3.x, those
     implicit conversions are gone - conversions between 8-bit binary
     data and Unicode text must be explicit, and bytes and string
     objects will always compare unequal.


File: python.info,  Node: Bytearray Objects,  Next: Bytes and Bytearray Operations,  Prev: Bytes Objects,  Up: Binary Sequence Types — bytes bytearray memoryview

5.4.8.2 Bytearray Objects
.........................

*note bytearray: 173. objects are a mutable counterpart to *note bytes:
172. objects.

 -- Class: bytearray ([source[, encoding[, errors]]])

     There is no dedicated literal syntax for bytearray objects, instead
     they are always created by calling the constructor:

        * Creating an empty instance: ‘bytearray()’

        * Creating a zero-filled instance with a given length:
          ‘bytearray(10)’

        * From an iterable of integers: ‘bytearray(range(20))’

        * Copying existing binary data via the buffer protocol:
          ‘bytearray(b'Hi!')’

     As bytearray objects are mutable, they support the *note mutable:
     171a. sequence operations in addition to the common bytes and
     bytearray operations described in *note Bytes and Bytearray
     Operations: 171b.

     Also see the *note bytearray: 11f3. built-in.

     Since 2 hexadecimal digits correspond precisely to a single byte,
     hexadecimal numbers are a commonly used format for describing
     binary data.  Accordingly, the bytearray type has an additional
     class method to read data in that format:

      -- Method: classmethod fromhex (string)

          This *note bytearray: 173. class method returns bytearray
          object, decoding the given string object.  The string must
          contain two hexadecimal digits per byte, with ASCII whitespace
          being ignored.

               >>> bytearray.fromhex('2Ef0 F1f2  ')
               bytearray(b'.\xf0\xf1\xf2')

          Changed in version 3.7: *note bytearray.fromhex(): 43f. now
          skips all ASCII whitespace in the string, not just spaces.

     A reverse conversion function exists to transform a bytearray
     object into its hexadecimal representation.

      -- Method: hex ([sep[, bytes_per_sep]])

          Return a string object containing two hexadecimal digits for
          each byte in the instance.

               >>> bytearray(b'\xf0\xf1\xf2').hex()
               'f0f1f2'

          New in version 3.5.

          Changed in version 3.8: Similar to *note bytes.hex(): 724,
          *note bytearray.hex(): 725. now supports optional `sep' and
          `bytes_per_sep' parameters to insert separators between bytes
          in the hex output.

Since bytearray objects are sequences of integers (akin to a list), for
a bytearray object `b', ‘b[0]’ will be an integer, while ‘b[0:1]’ will
be a bytearray object of length 1.  (This contrasts with text strings,
where both indexing and slicing will produce a string of length 1)

The representation of bytearray objects uses the bytes literal format
(‘bytearray(b'...')’) since it is often more useful than e.g.
‘bytearray([46, 46, 46])’.  You can always convert a bytearray object
into a list of integers using ‘list(b)’.


File: python.info,  Node: Bytes and Bytearray Operations,  Next: printf-style Bytes Formatting,  Prev: Bytearray Objects,  Up: Binary Sequence Types — bytes bytearray memoryview

5.4.8.3 Bytes and Bytearray Operations
......................................

Both bytes and bytearray objects support the *note common: 1763.
sequence operations.  They interoperate not just with operands of the
same type, but with any *note bytes-like object: 6df.  Due to this
flexibility, they can be freely mixed in operations without causing
errors.  However, the return type of the result may depend on the order
of operands.

     Note: The methods on bytes and bytearray objects don’t accept
     strings as their arguments, just as the methods on strings don’t
     accept bytes as their arguments.  For example, you have to write:

          a = "abc"
          b = a.replace("a", "f")

     and:

          a = b"abc"
          b = a.replace(b"a", b"f")

Some bytes and bytearray operations assume the use of ASCII compatible
binary formats, and hence should be avoided when working with arbitrary
binary data.  These restrictions are covered below.

     Note: Using these ASCII based operations to manipulate binary data
     that is not stored in an ASCII based format may lead to data
     corruption.

The following methods on bytes and bytearray objects can be used with
arbitrary binary data.

 -- Method: bytes.count (sub[, start[, end]])
 -- Method: bytearray.count (sub[, start[, end]])

     Return the number of non-overlapping occurrences of subsequence
     `sub' in the range [`start', `end'].  Optional arguments `start'
     and `end' are interpreted as in slice notation.

     The subsequence to search for may be any *note bytes-like object:
     6df. or an integer in the range 0 to 255.

     Changed in version 3.3: Also accept an integer in the range 0 to
     255 as the subsequence.

 -- Method: bytes.removeprefix (prefix, /)
 -- Method: bytearray.removeprefix (prefix, /)

     If the binary data starts with the `prefix' string, return
     ‘bytes[len(prefix):]’.  Otherwise, return a copy of the original
     binary data:

          >>> b'TestHook'.removeprefix(b'Test')
          b'Hook'
          >>> b'BaseTestCase'.removeprefix(b'Test')
          b'BaseTestCase'

     The `prefix' may be any *note bytes-like object: 6df.

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

     New in version 3.9.

 -- Method: bytes.removesuffix (suffix, /)
 -- Method: bytearray.removesuffix (suffix, /)

     If the binary data ends with the `suffix' string and that `suffix'
     is not empty, return ‘bytes[:-len(suffix)]’.  Otherwise, return a
     copy of the original binary data:

          >>> b'MiscTests'.removesuffix(b'Tests')
          b'Misc'
          >>> b'TmpDirMixin'.removesuffix(b'Tests')
          b'TmpDirMixin'

     The `suffix' may be any *note bytes-like object: 6df.

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

     New in version 3.9.

 -- Method: bytes.decode (encoding="utf-8", errors="strict")
 -- Method: bytearray.decode (encoding="utf-8", errors="strict")

     Return a string decoded from the given bytes.  Default encoding is
     ‘'utf-8'’.  `errors' may be given to set a different error handling
     scheme.  The default for `errors' is ‘'strict'’, meaning that
     encoding errors raise a *note UnicodeError: d03.  Other possible
     values are ‘'ignore'’, ‘'replace'’ and any other name registered
     via *note codecs.register_error(): eb9, see section *note Error
     Handlers: 1493.  For a list of possible encodings, see section
     *note Standard Encodings: 782.

     By default, the `errors' argument is not checked for best
     performances, but only used at the first decoding error.  Enable
     the *note Python Development Mode: 160, or use a debug build to
     check `errors'.

          Note: Passing the `encoding' argument to *note str: 205.
          allows decoding any *note bytes-like object: 6df. directly,
          without needing to make a temporary bytes or bytearray object.

     Changed in version 3.1: Added support for keyword arguments.

     Changed in version 3.9: The `errors' is now checked in development
     mode and in debug mode.

 -- Method: bytes.endswith (suffix[, start[, end]])
 -- Method: bytearray.endswith (suffix[, start[, end]])

     Return ‘True’ if the binary data ends with the specified `suffix',
     otherwise return ‘False’.  `suffix' can also be a tuple of suffixes
     to look for.  With optional `start', test beginning at that
     position.  With optional `end', stop comparing at that position.

     The suffix(es) to search for may be any *note bytes-like object:
     6df.

 -- Method: bytes.find (sub[, start[, end]])
 -- Method: bytearray.find (sub[, start[, end]])

     Return the lowest index in the data where the subsequence `sub' is
     found, such that `sub' is contained in the slice ‘s[start:end]’.
     Optional arguments `start' and `end' are interpreted as in slice
     notation.  Return ‘-1’ if `sub' is not found.

     The subsequence to search for may be any *note bytes-like object:
     6df. or an integer in the range 0 to 255.

          Note: The *note find(): 17a1. method should be used only if
          you need to know the position of `sub'.  To check if `sub' is
          a substring or not, use the *note in: 179. operator:

               >>> b'Py' in b'Python'
               True

     Changed in version 3.3: Also accept an integer in the range 0 to
     255 as the subsequence.

 -- Method: bytes.index (sub[, start[, end]])
 -- Method: bytearray.index (sub[, start[, end]])

     Like *note find(): 17a1, but raise *note ValueError: 16d. when the
     subsequence is not found.

     The subsequence to search for may be any *note bytes-like object:
     6df. or an integer in the range 0 to 255.

     Changed in version 3.3: Also accept an integer in the range 0 to
     255 as the subsequence.

 -- Method: bytes.join (iterable)
 -- Method: bytearray.join (iterable)

     Return a bytes or bytearray object which is the concatenation of
     the binary data sequences in `iterable'.  A *note TypeError: 1fe.
     will be raised if there are any values in `iterable' that are not
     *note bytes-like objects: 6df, including *note str: 205. objects.
     The separator between elements is the contents of the bytes or
     bytearray object providing this method.

 -- Method: static bytes.maketrans (from, to)
 -- Method: static bytearray.maketrans (from, to)

     This static method returns a translation table usable for *note
     bytes.translate(): 17a6. that will map each character in `from'
     into the character at the same position in `to'; `from' and `to'
     must both be *note bytes-like objects: 6df. and have the same
     length.

     New in version 3.1.

 -- Method: bytes.partition (sep)
 -- Method: bytearray.partition (sep)

     Split the sequence at the first occurrence of `sep', and return a
     3-tuple containing the part before the separator, the separator
     itself or its bytearray copy, and the part after the separator.  If
     the separator is not found, return a 3-tuple containing a copy of
     the original sequence, followed by two empty bytes or bytearray
     objects.

     The separator to search for may be any *note bytes-like object:
     6df.

 -- Method: bytes.replace (old, new[, count])
 -- Method: bytearray.replace (old, new[, count])

     Return a copy of the sequence with all occurrences of subsequence
     `old' replaced by `new'.  If the optional argument `count' is
     given, only the first `count' occurrences are replaced.

     The subsequence to search for and its replacement may be any *note
     bytes-like object: 6df.

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

 -- Method: bytes.rfind (sub[, start[, end]])
 -- Method: bytearray.rfind (sub[, start[, end]])

     Return the highest index in the sequence where the subsequence
     `sub' is found, such that `sub' is contained within ‘s[start:end]’.
     Optional arguments `start' and `end' are interpreted as in slice
     notation.  Return ‘-1’ on failure.

     The subsequence to search for may be any *note bytes-like object:
     6df. or an integer in the range 0 to 255.

     Changed in version 3.3: Also accept an integer in the range 0 to
     255 as the subsequence.

 -- Method: bytes.rindex (sub[, start[, end]])
 -- Method: bytearray.rindex (sub[, start[, end]])

     Like *note rfind(): 17ab. but raises *note ValueError: 16d. when
     the subsequence `sub' is not found.

     The subsequence to search for may be any *note bytes-like object:
     6df. or an integer in the range 0 to 255.

     Changed in version 3.3: Also accept an integer in the range 0 to
     255 as the subsequence.

 -- Method: bytes.rpartition (sep)
 -- Method: bytearray.rpartition (sep)

     Split the sequence at the last occurrence of `sep', and return a
     3-tuple containing the part before the separator, the separator
     itself or its bytearray copy, and the part after the separator.  If
     the separator is not found, return a 3-tuple containing two empty
     bytes or bytearray objects, followed by a copy of the original
     sequence.

     The separator to search for may be any *note bytes-like object:
     6df.

 -- Method: bytes.startswith (prefix[, start[, end]])
 -- Method: bytearray.startswith (prefix[, start[, end]])

     Return ‘True’ if the binary data starts with the specified
     `prefix', otherwise return ‘False’.  `prefix' can also be a tuple
     of prefixes to look for.  With optional `start', test beginning at
     that position.  With optional `end', stop comparing at that
     position.

     The prefix(es) to search for may be any *note bytes-like object:
     6df.

 -- Method: bytes.translate (table, /, delete=b'')
 -- Method: bytearray.translate (table, /, delete=b'')

     Return a copy of the bytes or bytearray object where all bytes
     occurring in the optional argument `delete' are removed, and the
     remaining bytes have been mapped through the given translation
     table, which must be a bytes object of length 256.

     You can use the *note bytes.maketrans(): cd4. method to create a
     translation table.

     Set the `table' argument to ‘None’ for translations that only
     delete characters:

          >>> b'read this short text'.translate(None, b'aeiou')
          b'rd ths shrt txt'

     Changed in version 3.6: `delete' is now supported as a keyword
     argument.

The following methods on bytes and bytearray objects have default
behaviours that assume the use of ASCII compatible binary formats, but
can still be used with arbitrary binary data by passing appropriate
arguments.  Note that all of the bytearray methods in this section do
`not' operate in place, and instead produce new objects.

 -- Method: bytes.center (width[, fillbyte])
 -- Method: bytearray.center (width[, fillbyte])

     Return a copy of the object centered in a sequence of length
     `width'.  Padding is done using the specified `fillbyte' (default
     is an ASCII space).  For *note bytes: 172. objects, the original
     sequence is returned if `width' is less than or equal to ‘len(s)’.

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

 -- Method: bytes.ljust (width[, fillbyte])
 -- Method: bytearray.ljust (width[, fillbyte])

     Return a copy of the object left justified in a sequence of length
     `width'.  Padding is done using the specified `fillbyte' (default
     is an ASCII space).  For *note bytes: 172. objects, the original
     sequence is returned if `width' is less than or equal to ‘len(s)’.

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

 -- Method: bytes.lstrip ([chars])
 -- Method: bytearray.lstrip ([chars])

     Return a copy of the sequence with specified leading bytes removed.
     The `chars' argument is a binary sequence specifying the set of
     byte values to be removed - the name refers to the fact this method
     is usually used with ASCII characters.  If omitted or ‘None’, the
     `chars' argument defaults to removing ASCII whitespace.  The
     `chars' argument is not a prefix; rather, all combinations of its
     values are stripped:

          >>> b'   spacious   '.lstrip()
          b'spacious   '
          >>> b'www.example.com'.lstrip(b'cmowz.')
          b'example.com'

     The binary sequence of byte values to remove may be any *note
     bytes-like object: 6df.  See *note removeprefix(): 179a. for a
     method that will remove a single prefix string rather than all of a
     set of characters.  For example:

          >>> b'Arthur: three!'.lstrip(b'Arthur: ')
          b'ee!'
          >>> b'Arthur: three!'.removeprefix(b'Arthur: ')
          b'three!'

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

 -- Method: bytes.rjust (width[, fillbyte])
 -- Method: bytearray.rjust (width[, fillbyte])

     Return a copy of the object right justified in a sequence of length
     `width'.  Padding is done using the specified `fillbyte' (default
     is an ASCII space).  For *note bytes: 172. objects, the original
     sequence is returned if `width' is less than or equal to ‘len(s)’.

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

 -- Method: bytes.rsplit (sep=None, maxsplit=-1)
 -- Method: bytearray.rsplit (sep=None, maxsplit=-1)

     Split the binary sequence into subsequences of the same type, using
     `sep' as the delimiter string.  If `maxsplit' is given, at most
     `maxsplit' splits are done, the `rightmost' ones.  If `sep' is not
     specified or ‘None’, any subsequence consisting solely of ASCII
     whitespace is a separator.  Except for splitting from the right,
     *note rsplit(): 17bc. behaves like *note split(): 17bd. which is
     described in detail below.

 -- Method: bytes.rstrip ([chars])
 -- Method: bytearray.rstrip ([chars])

     Return a copy of the sequence with specified trailing bytes
     removed.  The `chars' argument is a binary sequence specifying the
     set of byte values to be removed - the name refers to the fact this
     method is usually used with ASCII characters.  If omitted or
     ‘None’, the `chars' argument defaults to removing ASCII whitespace.
     The `chars' argument is not a suffix; rather, all combinations of
     its values are stripped:

          >>> b'   spacious   '.rstrip()
          b'   spacious'
          >>> b'mississippi'.rstrip(b'ipz')
          b'mississ'

     The binary sequence of byte values to remove may be any *note
     bytes-like object: 6df.  See *note removesuffix(): 179c. for a
     method that will remove a single suffix string rather than all of a
     set of characters.  For example:

          >>> b'Monty Python'.rstrip(b' Python')
          b'M'
          >>> b'Monty Python'.removesuffix(b' Python')
          b'Monty'

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

 -- Method: bytes.split (sep=None, maxsplit=-1)
 -- Method: bytearray.split (sep=None, maxsplit=-1)

     Split the binary sequence into subsequences of the same type, using
     `sep' as the delimiter string.  If `maxsplit' is given and
     non-negative, at most `maxsplit' splits are done (thus, the list
     will have at most ‘maxsplit+1’ elements).  If `maxsplit' is not
     specified or is ‘-1’, then there is no limit on the number of
     splits (all possible splits are made).

     If `sep' is given, consecutive delimiters are not grouped together
     and are deemed to delimit empty subsequences (for example,
     ‘b'1,,2'.split(b',')’ returns ‘[b'1', b'', b'2']’).  The `sep'
     argument may consist of a multibyte sequence (for example,
     ‘b'1<>2<>3'.split(b'<>')’ returns ‘[b'1', b'2', b'3']’).  Splitting
     an empty sequence with a specified separator returns ‘[b'']’ or
     ‘[bytearray(b'')]’ depending on the type of object being split.
     The `sep' argument may be any *note bytes-like object: 6df.

     For example:

          >>> b'1,2,3'.split(b',')
          [b'1', b'2', b'3']
          >>> b'1,2,3'.split(b',', maxsplit=1)
          [b'1', b'2,3']
          >>> b'1,2,,3,'.split(b',')
          [b'1', b'2', b'', b'3', b'']

     If `sep' is not specified or is ‘None’, a different splitting
     algorithm is applied: runs of consecutive ASCII whitespace are
     regarded as a single separator, and the result will contain no
     empty strings at the start or end if the sequence has leading or
     trailing whitespace.  Consequently, splitting an empty sequence or
     a sequence consisting solely of ASCII whitespace without a
     specified separator returns ‘[]’.

     For example:

          >>> b'1 2 3'.split()
          [b'1', b'2', b'3']
          >>> b'1 2 3'.split(maxsplit=1)
          [b'1', b'2 3']
          >>> b'   1   2   3   '.split()
          [b'1', b'2', b'3']

 -- Method: bytes.strip ([chars])
 -- Method: bytearray.strip ([chars])

     Return a copy of the sequence with specified leading and trailing
     bytes removed.  The `chars' argument is a binary sequence
     specifying the set of byte values to be removed - the name refers
     to the fact this method is usually used with ASCII characters.  If
     omitted or ‘None’, the `chars' argument defaults to removing ASCII
     whitespace.  The `chars' argument is not a prefix or suffix;
     rather, all combinations of its values are stripped:

          >>> b'   spacious   '.strip()
          b'spacious'
          >>> b'www.example.com'.strip(b'cmowz.')
          b'example'

     The binary sequence of byte values to remove may be any *note
     bytes-like object: 6df.

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

The following methods on bytes and bytearray objects assume the use of
ASCII compatible binary formats and should not be applied to arbitrary
binary data.  Note that all of the bytearray methods in this section do
`not' operate in place, and instead produce new objects.

 -- Method: bytes.capitalize ()
 -- Method: bytearray.capitalize ()

     Return a copy of the sequence with each byte interpreted as an
     ASCII character, and the first byte capitalized and the rest
     lowercased.  Non-ASCII byte values are passed through unchanged.

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

 -- Method: bytes.expandtabs (tabsize=8)
 -- Method: bytearray.expandtabs (tabsize=8)

     Return a copy of the sequence where all ASCII tab characters are
     replaced by one or more ASCII spaces, depending on the current
     column and the given tab size.  Tab positions occur every `tabsize'
     bytes (default is 8, giving tab positions at columns 0, 8, 16 and
     so on).  To expand the sequence, the current column is set to zero
     and the sequence is examined byte by byte.  If the byte is an ASCII
     tab character (‘b'\t'’), one or more space characters are inserted
     in the result until the current column is equal to the next tab
     position.  (The tab character itself is not copied.)  If the
     current byte is an ASCII newline (‘b'\n'’) or carriage return
     (‘b'\r'’), it is copied and the current column is reset to zero.
     Any other byte value is copied unchanged and the current column is
     incremented by one regardless of how the byte value is represented
     when printed:

          >>> b'01\t012\t0123\t01234'.expandtabs()
          b'01      012     0123    01234'
          >>> b'01\t012\t0123\t01234'.expandtabs(4)
          b'01  012 0123    01234'

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

 -- Method: bytes.isalnum ()
 -- Method: bytearray.isalnum ()

     Return ‘True’ if all bytes in the sequence are alphabetical ASCII
     characters or ASCII decimal digits and the sequence is not empty,
     ‘False’ otherwise.  Alphabetic ASCII characters are those byte
     values in the sequence
     ‘b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'’.  ASCII
     decimal digits are those byte values in the sequence
     ‘b'0123456789'’.

     For example:

          >>> b'ABCabc1'.isalnum()
          True
          >>> b'ABC abc1'.isalnum()
          False

 -- Method: bytes.isalpha ()
 -- Method: bytearray.isalpha ()

     Return ‘True’ if all bytes in the sequence are alphabetic ASCII
     characters and the sequence is not empty, ‘False’ otherwise.
     Alphabetic ASCII characters are those byte values in the sequence
     ‘b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'’.

     For example:

          >>> b'ABCabc'.isalpha()
          True
          >>> b'ABCabc1'.isalpha()
          False

 -- Method: bytes.isascii ()
 -- Method: bytearray.isascii ()

     Return ‘True’ if the sequence is empty or all bytes in the sequence
     are ASCII, ‘False’ otherwise.  ASCII bytes are in the range 0-0x7F.

     New in version 3.7.

 -- Method: bytes.isdigit ()
 -- Method: bytearray.isdigit ()

     Return ‘True’ if all bytes in the sequence are ASCII decimal digits
     and the sequence is not empty, ‘False’ otherwise.  ASCII decimal
     digits are those byte values in the sequence ‘b'0123456789'’.

     For example:

          >>> b'1234'.isdigit()
          True
          >>> b'1.23'.isdigit()
          False

 -- Method: bytes.islower ()
 -- Method: bytearray.islower ()

     Return ‘True’ if there is at least one lowercase ASCII character in
     the sequence and no uppercase ASCII characters, ‘False’ otherwise.

     For example:

          >>> b'hello world'.islower()
          True
          >>> b'Hello world'.islower()
          False

     Lowercase ASCII characters are those byte values in the sequence
     ‘b'abcdefghijklmnopqrstuvwxyz'’.  Uppercase ASCII characters are
     those byte values in the sequence ‘b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'’.

 -- Method: bytes.isspace ()
 -- Method: bytearray.isspace ()

     Return ‘True’ if all bytes in the sequence are ASCII whitespace and
     the sequence is not empty, ‘False’ otherwise.  ASCII whitespace
     characters are those byte values in the sequence ‘b' \t\n\r\x0b\f'’
     (space, tab, newline, carriage return, vertical tab, form feed).

 -- Method: bytes.istitle ()
 -- Method: bytearray.istitle ()

     Return ‘True’ if the sequence is ASCII titlecase and the sequence
     is not empty, ‘False’ otherwise.  See *note bytes.title(): 17d5.
     for more details on the definition of “titlecase”.

     For example:

          >>> b'Hello World'.istitle()
          True
          >>> b'Hello world'.istitle()
          False

 -- Method: bytes.isupper ()
 -- Method: bytearray.isupper ()

     Return ‘True’ if there is at least one uppercase alphabetic ASCII
     character in the sequence and no lowercase ASCII characters,
     ‘False’ otherwise.

     For example:

          >>> b'HELLO WORLD'.isupper()
          True
          >>> b'Hello world'.isupper()
          False

     Lowercase ASCII characters are those byte values in the sequence
     ‘b'abcdefghijklmnopqrstuvwxyz'’.  Uppercase ASCII characters are
     those byte values in the sequence ‘b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'’.

 -- Method: bytes.lower ()
 -- Method: bytearray.lower ()

     Return a copy of the sequence with all the uppercase ASCII
     characters converted to their corresponding lowercase counterpart.

     For example:

          >>> b'Hello World'.lower()
          b'hello world'

     Lowercase ASCII characters are those byte values in the sequence
     ‘b'abcdefghijklmnopqrstuvwxyz'’.  Uppercase ASCII characters are
     those byte values in the sequence ‘b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'’.

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

 -- Method: bytes.splitlines (keepends=False)
 -- Method: bytearray.splitlines (keepends=False)

     Return a list of the lines in the binary sequence, breaking at
     ASCII line boundaries.  This method uses the *note universal
     newlines: 6eb. approach to splitting lines.  Line breaks are not
     included in the resulting list unless `keepends' is given and true.

     For example:

          >>> b'ab c\n\nde fg\rkl\r\n'.splitlines()
          [b'ab c', b'', b'de fg', b'kl']
          >>> b'ab c\n\nde fg\rkl\r\n'.splitlines(keepends=True)
          [b'ab c\n', b'\n', b'de fg\r', b'kl\r\n']

     Unlike *note split(): 17c0. when a delimiter string `sep' is given,
     this method returns an empty list for the empty string, and a
     terminal line break does not result in an extra line:

          >>> b"".split(b'\n'), b"Two lines\n".split(b'\n')
          ([b''], [b'Two lines', b''])
          >>> b"".splitlines(), b"One line\n".splitlines()
          ([], [b'One line'])

 -- Method: bytes.swapcase ()
 -- Method: bytearray.swapcase ()

     Return a copy of the sequence with all the lowercase ASCII
     characters converted to their corresponding uppercase counterpart
     and vice-versa.

     For example:

          >>> b'Hello World'.swapcase()
          b'hELLO wORLD'

     Lowercase ASCII characters are those byte values in the sequence
     ‘b'abcdefghijklmnopqrstuvwxyz'’.  Uppercase ASCII characters are
     those byte values in the sequence ‘b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'’.

     Unlike *note str.swapcase(): 178e, it is always the case that
     ‘bin.swapcase().swapcase() == bin’ for the binary versions.  Case
     conversions are symmetrical in ASCII, even though that is not
     generally true for arbitrary Unicode code points.

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

 -- Method: bytes.title ()
 -- Method: bytearray.title ()

     Return a titlecased version of the binary sequence where words
     start with an uppercase ASCII character and the remaining
     characters are lowercase.  Uncased byte values are left unmodified.

     For example:

          >>> b'Hello world'.title()
          b'Hello World'

     Lowercase ASCII characters are those byte values in the sequence
     ‘b'abcdefghijklmnopqrstuvwxyz'’.  Uppercase ASCII characters are
     those byte values in the sequence ‘b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'’.
     All other byte values are uncased.

     The algorithm uses a simple language-independent definition of a
     word as groups of consecutive letters.  The definition works in
     many contexts but it means that apostrophes in contractions and
     possessives form word boundaries, which may not be the desired
     result:

          >>> b"they're bill's friends from the UK".title()
          b"They'Re Bill'S Friends From The Uk"

     A workaround for apostrophes can be constructed using regular
     expressions:

          >>> import re
          >>> def titlecase(s):
          ...     return re.sub(rb"[A-Za-z]+('[A-Za-z]+)?",
          ...                   lambda mo: mo.group(0)[0:1].upper() +
          ...                              mo.group(0)[1:].lower(),
          ...                   s)
          ...
          >>> titlecase(b"they're bill's friends.")
          b"They're Bill's Friends."

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

 -- Method: bytes.upper ()
 -- Method: bytearray.upper ()

     Return a copy of the sequence with all the lowercase ASCII
     characters converted to their corresponding uppercase counterpart.

     For example:

          >>> b'Hello World'.upper()
          b'HELLO WORLD'

     Lowercase ASCII characters are those byte values in the sequence
     ‘b'abcdefghijklmnopqrstuvwxyz'’.  Uppercase ASCII characters are
     those byte values in the sequence ‘b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'’.

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.

 -- Method: bytes.zfill (width)
 -- Method: bytearray.zfill (width)

     Return a copy of the sequence left filled with ASCII ‘b'0'’ digits
     to make a sequence of length `width'.  A leading sign prefix
     (‘b'+'’/ ‘b'-'’) is handled by inserting the padding `after' the
     sign character rather than before.  For *note bytes: 172. objects,
     the original sequence is returned if `width' is less than or equal
     to ‘len(seq)’.

     For example:

          >>> b"42".zfill(5)
          b'00042'
          >>> b"-42".zfill(5)
          b'-0042'

          Note: The bytearray version of this method does `not' operate
          in place - it always produces a new object, even if no changes
          were made.


File: python.info,  Node: printf-style Bytes Formatting,  Next: Memory Views,  Prev: Bytes and Bytearray Operations,  Up: Binary Sequence Types — bytes bytearray memoryview

5.4.8.4 ‘printf’-style Bytes Formatting
.......................................

     Note: The formatting operations described here exhibit a variety of
     quirks that lead to a number of common errors (such as failing to
     display tuples and dictionaries correctly).  If the value being
     printed may be a tuple or dictionary, wrap it in a tuple.

Bytes objects (‘bytes’/‘bytearray’) have one unique built-in operation:
the ‘%’ operator (modulo).  This is also known as the bytes `formatting'
or `interpolation' operator.  Given ‘format % values’ (where `format' is
a bytes object), ‘%’ conversion specifications in `format' are replaced
with zero or more elements of `values'.  The effect is similar to using
the ‘sprintf()’ in the C language.

If `format' requires a single argument, `values' may be a single
non-tuple object.  (1) Otherwise, `values' must be a tuple with exactly
the number of items specified by the format bytes object, or a single
mapping object (for example, a dictionary).

A conversion specifier contains two or more characters and has the
following components, which must occur in this order:

  1. The ‘'%'’ character, which marks the start of the specifier.

  2. Mapping key (optional), consisting of a parenthesised sequence of
     characters (for example, ‘(somename)’).

  3. Conversion flags (optional), which affect the result of some
     conversion types.

  4. Minimum field width (optional).  If specified as an ‘'*'’
     (asterisk), the actual width is read from the next element of the
     tuple in `values', and the object to convert comes after the
     minimum field width and optional precision.

  5. Precision (optional), given as a ‘'.'’ (dot) followed by the
     precision.  If specified as ‘'*'’ (an asterisk), the actual
     precision is read from the next element of the tuple in `values',
     and the value to convert comes after the precision.

  6. Length modifier (optional).

  7. Conversion type.

When the right argument is a dictionary (or other mapping type), then
the formats in the bytes object `must' include a parenthesised mapping
key into that dictionary inserted immediately after the ‘'%'’ character.
The mapping key selects the value to be formatted from the mapping.  For
example:

     >>> print(b'%(language)s has %(number)03d quote types.' %
     ...       {b'language': b"Python", b"number": 2})
     b'Python has 002 quote types.'

In this case no ‘*’ specifiers may occur in a format (since they require
a sequential parameter list).

The conversion flag characters are:

Flag          Meaning
              
----------------------------------------------------------------------------------------
              
‘'#'’         The value conversion will use the “alternate form” (where defined
              below).
              
              
‘'0'’         The conversion will be zero padded for numeric values.
              
              
‘'-'’         The converted value is left adjusted (overrides the ‘'0'’ conversion if
              both are given).
              
              
‘' '’         (a space) A blank should be left before a positive number (or empty
              string) produced by a signed conversion.
              
              
‘'+'’         A sign character (‘'+'’ or ‘'-'’) will precede the conversion
              (overrides a “space” flag).
              

A length modifier (‘h’, ‘l’, or ‘L’) may be present, but is ignored as
it is not necessary for Python – so e.g.  ‘%ld’ is identical to ‘%d’.

The conversion types are:

Conversion       Meaning                                                   Notes
                                                                           
---------------------------------------------------------------------------------------
                                                                           
‘'d'’            Signed integer decimal.
                 
                                                                           
‘'i'’            Signed integer decimal.
                 
                                                                           
‘'o'’            Signed octal value.                                       (1)
                                                                           
                                                                           
‘'u'’            Obsolete type – it is identical to ‘'d'’.                 (8)
                                                                           
                                                                           
‘'x'’            Signed hexadecimal (lowercase).                           (2)
                                                                           
                                                                           
‘'X'’            Signed hexadecimal (uppercase).                           (2)
                                                                           
                                                                           
‘'e'’            Floating point exponential format (lowercase).            (3)
                                                                           
                                                                           
‘'E'’            Floating point exponential format (uppercase).            (3)
                                                                           
                                                                           
‘'f'’            Floating point decimal format.                            (3)
                                                                           
                                                                           
‘'F'’            Floating point decimal format.                            (3)
                                                                           
                                                                           
‘'g'’            Floating point format.  Uses lowercase exponential        (4)
                 format if exponent is less than -4 or not less than       
                 precision, decimal format otherwise.
                 
                                                                           
‘'G'’            Floating point format.  Uses uppercase exponential        (4)
                 format if exponent is less than -4 or not less than       
                 precision, decimal format otherwise.
                 
                                                                           
‘'c'’            Single byte (accepts integer or single byte objects).
                 
                                                                           
‘'b'’            Bytes (any object that follows the                        (5)
                 *note buffer protocol: 171c. or has                       
                 *note __bytes__(): 156a.).
                 
                                                                           
‘'s'’            ‘'s'’ is an alias for ‘'b'’ and should only be used for   (6)
                 Python2/3 code bases.                                     
                 
                                                                           
‘'a'’            Bytes (converts any Python object using                   (5)
                 ‘repr(obj).encode('ascii','backslashreplace)’).           
                 
                                                                           
‘'r'’            ‘'r'’ is an alias for ‘'a'’ and should only be used for   (7)
                 Python2/3 code bases.                                     
                 
                                                                           
‘'%'’            No argument is converted, results in a ‘'%'’ character
                 in the result.
                 

Notes:

  1. The alternate form causes a leading octal specifier (‘'0o'’) to be
     inserted before the first digit.

  2. The alternate form causes a leading ‘'0x'’ or ‘'0X'’ (depending on
     whether the ‘'x'’ or ‘'X'’ format was used) to be inserted before
     the first digit.

  3. The alternate form causes the result to always contain a decimal
     point, even if no digits follow it.

     The precision determines the number of digits after the decimal
     point and defaults to 6.

  4. The alternate form causes the result to always contain a decimal
     point, and trailing zeroes are not removed as they would otherwise
     be.

     The precision determines the number of significant digits before
     and after the decimal point and defaults to 6.

  5. If precision is ‘N’, the output is truncated to ‘N’ characters.

  6. ‘b'%s'’ is deprecated, but will not be removed during the 3.x
     series.

  7. ‘b'%r'’ is deprecated, but will not be removed during the 3.x
     series.

  8. See PEP 237(2).

     Note: The bytearray version of this method does `not' operate in
     place - it always produces a new object, even if no changes were
     made.

See also
........

PEP 461(3) - Adding % formatting to bytes and bytearray

New in version 3.5.

   ---------- Footnotes ----------

   (1) (5) To format only a tuple you should therefore provide a
singleton tuple whose only element is the tuple to be formatted.

   (2) https://www.python.org/dev/peps/pep-0237

   (3) https://www.python.org/dev/peps/pep-0461


File: python.info,  Node: Memory Views,  Prev: printf-style Bytes Formatting,  Up: Binary Sequence Types — bytes bytearray memoryview

5.4.8.5 Memory Views
....................

*note memoryview: 386. objects allow Python code to access the internal
data of an object that supports the *note buffer protocol: 171c. without
copying.

 -- Class: memoryview (object)

     Create a *note memoryview: 386. that references `object'.  `object'
     must support the buffer protocol.  Built-in objects that support
     the buffer protocol include *note bytes: 172. and *note bytearray:
     173.

     A *note memoryview: 386. has the notion of an `element', which is
     the atomic memory unit handled by the originating `object'.  For
     many simple types such as *note bytes: 172. and *note bytearray:
     173, an element is a single byte, but other types such as *note
     array.array: 216. may have bigger elements.

     ‘len(view)’ is equal to the length of *note tolist: 17e5.  If
     ‘view.ndim = 0’, the length is 1.  If ‘view.ndim = 1’, the length
     is equal to the number of elements in the view.  For higher
     dimensions, the length is equal to the length of the nested list
     representation of the view.  The *note itemsize: 17e6. attribute
     will give you the number of bytes in a single element.

     A *note memoryview: 386. supports slicing and indexing to expose
     its data.  One-dimensional slicing will result in a subview:

          >>> v = memoryview(b'abcefg')
          >>> v[1]
          98
          >>> v[-1]
          103
          >>> v[1:4]
          <memory at 0x7f3ddc9f4350>
          >>> bytes(v[1:4])
          b'bce'

     If *note format: 17e7. is one of the native format specifiers from
     the *note struct: f8. module, indexing with an integer or a tuple
     of integers is also supported and returns a single `element' with
     the correct type.  One-dimensional memoryviews can be indexed with
     an integer or a one-integer tuple.  Multi-dimensional memoryviews
     can be indexed with tuples of exactly `ndim' integers where `ndim'
     is the number of dimensions.  Zero-dimensional memoryviews can be
     indexed with the empty tuple.

     Here is an example with a non-byte format:

          >>> import array
          >>> a = array.array('l', [-11111111, 22222222, -33333333, 44444444])
          >>> m = memoryview(a)
          >>> m[0]
          -11111111
          >>> m[-1]
          44444444
          >>> m[::2].tolist()
          [-11111111, -33333333]

     If the underlying object is writable, the memoryview supports
     one-dimensional slice assignment.  Resizing is not allowed:

          >>> data = bytearray(b'abcefg')
          >>> v = memoryview(data)
          >>> v.readonly
          False
          >>> v[0] = ord(b'z')
          >>> data
          bytearray(b'zbcefg')
          >>> v[1:4] = b'123'
          >>> data
          bytearray(b'z123fg')
          >>> v[2:3] = b'spam'
          Traceback (most recent call last):
            File "<stdin>", line 1, in <module>
          ValueError: memoryview assignment: lvalue and rvalue have different structures
          >>> v[2:6] = b'spam'
          >>> data
          bytearray(b'z1spam')

     One-dimensional memoryviews of hashable (read-only) types with
     formats ‘B’, ‘b’ or ‘c’ are also hashable.  The hash is defined as
     ‘hash(m) == hash(m.tobytes())’:

          >>> v = memoryview(b'abcefg')
          >>> hash(v) == hash(b'abcefg')
          True
          >>> hash(v[2:4]) == hash(b'ce')
          True
          >>> hash(v[::-2]) == hash(b'abcefg'[::-2])
          True

     Changed in version 3.3: One-dimensional memoryviews can now be
     sliced.  One-dimensional memoryviews with formats ‘B’, ‘b’ or ‘c’
     are now hashable.

     Changed in version 3.4: memoryview is now registered automatically
     with *note collections.abc.Sequence: 1764.

     Changed in version 3.5: memoryviews can now be indexed with tuple
     of integers.

     *note memoryview: 386. has several methods:

      -- Method: __eq__ (exporter)

          A memoryview and a PEP 3118(1) exporter are equal if their
          shapes are equivalent and if all corresponding values are
          equal when the operands’ respective format codes are
          interpreted using *note struct: f8. syntax.

          For the subset of *note struct: f8. format strings currently
          supported by *note tolist(): 17e5, ‘v’ and ‘w’ are equal if
          ‘v.tolist() == w.tolist()’:

               >>> import array
               >>> a = array.array('I', [1, 2, 3, 4, 5])
               >>> b = array.array('d', [1.0, 2.0, 3.0, 4.0, 5.0])
               >>> c = array.array('b', [5, 3, 1])
               >>> x = memoryview(a)
               >>> y = memoryview(b)
               >>> x == a == y == b
               True
               >>> x.tolist() == a.tolist() == y.tolist() == b.tolist()
               True
               >>> z = y[::-2]
               >>> z == c
               True
               >>> z.tolist() == c.tolist()
               True

          If either format string is not supported by the *note struct:
          f8. module, then the objects will always compare as unequal
          (even if the format strings and buffer contents are
          identical):

               >>> from ctypes import BigEndianStructure, c_long
               >>> class BEPoint(BigEndianStructure):
               ...     _fields_ = [("x", c_long), ("y", c_long)]
               ...
               >>> point = BEPoint(100, 200)
               >>> a = memoryview(point)
               >>> b = memoryview(point)
               >>> a == point
               False
               >>> a == b
               False

          Note that, as with floating point numbers, ‘v is w’ does `not'
          imply ‘v == w’ for memoryview objects.

          Changed in version 3.3: Previous versions compared the raw
          memory disregarding the item format and the logical array
          structure.

      -- Method: tobytes (order=None)

          Return the data in the buffer as a bytestring.  This is
          equivalent to calling the *note bytes: 172. constructor on the
          memoryview.

               >>> m = memoryview(b"abc")
               >>> m.tobytes()
               b'abc'
               >>> bytes(m)
               b'abc'

          For non-contiguous arrays the result is equal to the flattened
          list representation with all elements converted to bytes.
          *note tobytes(): 17e9. supports all format strings, including
          those that are not in *note struct: f8. module syntax.

          New in version 3.8: `order' can be {‘C’, ‘F’, ‘A’}.  When
          `order' is ‘C’ or ‘F’, the data of the original array is
          converted to C or Fortran order.  For contiguous views, ‘A’
          returns an exact copy of the physical memory.  In particular,
          in-memory Fortran order is preserved.  For non-contiguous
          views, the data is converted to C first.  `order=None' is the
          same as `order=’C’'.

      -- Method: hex ([sep[, bytes_per_sep]])

          Return a string object containing two hexadecimal digits for
          each byte in the buffer.

               >>> m = memoryview(b"abc")
               >>> m.hex()
               '616263'

          New in version 3.5.

          Changed in version 3.8: Similar to *note bytes.hex(): 724,
          *note memoryview.hex(): 726. now supports optional `sep' and
          `bytes_per_sep' parameters to insert separators between bytes
          in the hex output.

      -- Method: tolist ()

          Return the data in the buffer as a list of elements.

               >>> memoryview(b'abc').tolist()
               [97, 98, 99]
               >>> import array
               >>> a = array.array('d', [1.1, 2.2, 3.3])
               >>> m = memoryview(a)
               >>> m.tolist()
               [1.1, 2.2, 3.3]

          Changed in version 3.3: *note tolist(): 17e5. now supports all
          single character native formats in *note struct: f8. module
          syntax as well as multi-dimensional representations.

      -- Method: toreadonly ()

          Return a readonly version of the memoryview object.  The
          original memoryview object is unchanged.

               >>> m = memoryview(bytearray(b'abc'))
               >>> mm = m.toreadonly()
               >>> mm.tolist()
               [89, 98, 99]
               >>> mm[0] = 42
               Traceback (most recent call last):
                 File "<stdin>", line 1, in <module>
               TypeError: cannot modify read-only memory
               >>> m[0] = 43
               >>> mm.tolist()
               [43, 98, 99]

          New in version 3.8.

      -- Method: release ()

          Release the underlying buffer exposed by the memoryview
          object.  Many objects take special actions when a view is held
          on them (for example, a *note bytearray: 173. would
          temporarily forbid resizing); therefore, calling release() is
          handy to remove these restrictions (and free any dangling
          resources) as soon as possible.

          After this method has been called, any further operation on
          the view raises a *note ValueError: 16d. (except *note
          release(): c0f. itself which can be called multiple times):

               >>> m = memoryview(b'abc')
               >>> m.release()
               >>> m[0]
               Traceback (most recent call last):
                 File "<stdin>", line 1, in <module>
               ValueError: operation forbidden on released memoryview object

          The context management protocol can be used for a similar
          effect, using the ‘with’ statement:

               >>> with memoryview(b'abc') as m:
               ...     m[0]
               ...
               97
               >>> m[0]
               Traceback (most recent call last):
                 File "<stdin>", line 1, in <module>
               ValueError: operation forbidden on released memoryview object

          New in version 3.2.

      -- Method: cast (format[, shape])

          Cast a memoryview to a new format or shape.  `shape' defaults
          to ‘[byte_length//new_itemsize]’, which means that the result
          view will be one-dimensional.  The return value is a new
          memoryview, but the buffer itself is not copied.  Supported
          casts are 1D -> C-*note contiguous: 17ec. and C-contiguous ->
          1D.

          The destination format is restricted to a single element
          native format in *note struct: f8. syntax.  One of the formats
          must be a byte format (‘B’, ‘b’ or ‘c’).  The byte length of
          the result must be the same as the original length.

          Cast 1D/long to 1D/unsigned bytes:

               >>> import array
               >>> a = array.array('l', [1,2,3])
               >>> x = memoryview(a)
               >>> x.format
               'l'
               >>> x.itemsize
               8
               >>> len(x)
               3
               >>> x.nbytes
               24
               >>> y = x.cast('B')
               >>> y.format
               'B'
               >>> y.itemsize
               1
               >>> len(y)
               24
               >>> y.nbytes
               24

          Cast 1D/unsigned bytes to 1D/char:

               >>> b = bytearray(b'zyz')
               >>> x = memoryview(b)
               >>> x[0] = b'a'
               Traceback (most recent call last):
                 File "<stdin>", line 1, in <module>
               ValueError: memoryview: invalid value for format "B"
               >>> y = x.cast('c')
               >>> y[0] = b'a'
               >>> b
               bytearray(b'ayz')

          Cast 1D/bytes to 3D/ints to 1D/signed char:

               >>> import struct
               >>> buf = struct.pack("i"*12, *list(range(12)))
               >>> x = memoryview(buf)
               >>> y = x.cast('i', shape=[2,2,3])
               >>> y.tolist()
               [[[0, 1, 2], [3, 4, 5]], [[6, 7, 8], [9, 10, 11]]]
               >>> y.format
               'i'
               >>> y.itemsize
               4
               >>> len(y)
               2
               >>> y.nbytes
               48
               >>> z = y.cast('b')
               >>> z.format
               'b'
               >>> z.itemsize
               1
               >>> len(z)
               48
               >>> z.nbytes
               48

          Cast 1D/unsigned long to 2D/unsigned long:

               >>> buf = struct.pack("L"*6, *list(range(6)))
               >>> x = memoryview(buf)
               >>> y = x.cast('L', shape=[2,3])
               >>> len(y)
               2
               >>> y.nbytes
               48
               >>> y.tolist()
               [[0, 1, 2], [3, 4, 5]]

          New in version 3.3.

          Changed in version 3.5: The source format is no longer
          restricted when casting to a byte view.

     There are also several readonly attributes available:

      -- Attribute: obj

          The underlying object of the memoryview:

               >>> b  = bytearray(b'xyz')
               >>> m = memoryview(b)
               >>> m.obj is b
               True

          New in version 3.3.

      -- Attribute: nbytes

          ‘nbytes == product(shape) * itemsize == len(m.tobytes())’.
          This is the amount of space in bytes that the array would use
          in a contiguous representation.  It is not necessarily equal
          to ‘len(m)’:

               >>> import array
               >>> a = array.array('i', [1,2,3,4,5])
               >>> m = memoryview(a)
               >>> len(m)
               5
               >>> m.nbytes
               20
               >>> y = m[::2]
               >>> len(y)
               3
               >>> y.nbytes
               12
               >>> len(y.tobytes())
               12

          Multi-dimensional arrays:

               >>> import struct
               >>> buf = struct.pack("d"*12, *[1.5*x for x in range(12)])
               >>> x = memoryview(buf)
               >>> y = x.cast('d', shape=[3,4])
               >>> y.tolist()
               [[0.0, 1.5, 3.0, 4.5], [6.0, 7.5, 9.0, 10.5], [12.0, 13.5, 15.0, 16.5]]
               >>> len(y)
               3
               >>> y.nbytes
               96

          New in version 3.3.

      -- Attribute: readonly

          A bool indicating whether the memory is read only.

      -- Attribute: format

          A string containing the format (in *note struct: f8. module
          style) for each element in the view.  A memoryview can be
          created from exporters with arbitrary format strings, but some
          methods (e.g.  *note tolist(): 17e5.) are restricted to native
          single element formats.

          Changed in version 3.3: format ‘'B'’ is now handled according
          to the struct module syntax.  This means that
          ‘memoryview(b'abc')[0] == b'abc'[0] == 97’.

      -- Attribute: itemsize

          The size in bytes of each element of the memoryview:

               >>> import array, struct
               >>> m = memoryview(array.array('H', [32000, 32001, 32002]))
               >>> m.itemsize
               2
               >>> m[0]
               32000
               >>> struct.calcsize('H') == m.itemsize
               True

      -- Attribute: ndim

          An integer indicating how many dimensions of a
          multi-dimensional array the memory represents.

      -- Attribute: shape

          A tuple of integers the length of *note ndim: 17f0. giving the
          shape of the memory as an N-dimensional array.

          Changed in version 3.3: An empty tuple instead of ‘None’ when
          ndim = 0.

      -- Attribute: strides

          A tuple of integers the length of *note ndim: 17f0. giving the
          size in bytes to access each element for each dimension of the
          array.

          Changed in version 3.3: An empty tuple instead of ‘None’ when
          ndim = 0.

      -- Attribute: suboffsets

          Used internally for PIL-style arrays.  The value is
          informational only.

      -- Attribute: c_contiguous

          A bool indicating whether the memory is C-*note contiguous:
          17ec.

          New in version 3.3.

      -- Attribute: f_contiguous

          A bool indicating whether the memory is Fortran *note
          contiguous: 17ec.

          New in version 3.3.

      -- Attribute: contiguous

          A bool indicating whether the memory is *note contiguous:
          17ec.

          New in version 3.3.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3118


File: python.info,  Node: Set Types — set frozenset,  Next: Mapping Types — dict,  Prev: Binary Sequence Types — bytes bytearray memoryview,  Up: Built-in Types

5.4.9 Set Types — ‘set’, ‘frozenset’
------------------------------------

A `set' object is an unordered collection of distinct *note hashable:
276. objects.  Common uses include membership testing, removing
duplicates from a sequence, and computing mathematical operations such
as intersection, union, difference, and symmetric difference.  (For
other containers see the built-in *note dict: 164, *note list: 1f8, and
*note tuple: 1a2. classes, and the *note collections: 1d. module.)

Like other collections, sets support ‘x in set’, ‘len(set)’, and ‘for x
in set’.  Being an unordered collection, sets do not record element
position or order of insertion.  Accordingly, sets do not support
indexing, slicing, or other sequence-like behavior.

There are currently two built-in set types, *note set: 1f6. and *note
frozenset: 1f7.  The *note set: 1f6. type is mutable — the contents can
be changed using methods like ‘add()’ and ‘remove()’.  Since it is
mutable, it has no hash value and cannot be used as either a dictionary
key or as an element of another set.  The *note frozenset: 1f7. type is
immutable and *note hashable: 276. — its contents cannot be altered
after it is created; it can therefore be used as a dictionary key or as
an element of another set.

Non-empty sets (not frozensets) can be created by placing a
comma-separated list of elements within braces, for example: ‘{'jack',
'sjoerd'}’, in addition to the *note set: 1f6. constructor.

The constructors for both classes work the same:

 -- Class: set ([iterable])
 -- Class: frozenset ([iterable])

     Return a new set or frozenset object whose elements are taken from
     `iterable'.  The elements of a set must be *note hashable: 276.  To
     represent sets of sets, the inner sets must be *note frozenset:
     1f7. objects.  If `iterable' is not specified, a new empty set is
     returned.

     Sets can be created by several means:

        * Use a comma-separated list of elements within braces:
          ‘{'jack', 'sjoerd'}’

        * Use a set comprehension: ‘{c for c in 'abracadabra' if c not
          in 'abc'}’

        * Use the type constructor: ‘set()’, ‘set('foobar')’, ‘set(['a',
          'b', 'foo'])’

     Instances of *note set: 1f6. and *note frozenset: 1f7. provide the
     following operations:

      -- Describe: len(s)

          Return the number of elements in set `s' (cardinality of `s').

      -- Describe: x in s

          Test `x' for membership in `s'.

      -- Describe: x not in s

          Test `x' for non-membership in `s'.

      -- Method: isdisjoint (other)

          Return ‘True’ if the set has no elements in common with
          `other'.  Sets are disjoint if and only if their intersection
          is the empty set.

      -- Method: issubset (other)

      -- Method: set <= other

          Test whether every element in the set is in `other'.

      -- Method: set < other

          Test whether the set is a proper subset of `other', that is,
          ‘set <= other and set != other’.

      -- Method: issuperset (other)

      -- Method: set >= other

          Test whether every element in `other' is in the set.

      -- Method: set > other

          Test whether the set is a proper superset of `other', that is,
          ‘set >= other and set != other’.

      -- Method: union (*others)

      -- Method: set | other | ...

          Return a new set with elements from the set and all others.

      -- Method: intersection (*others)

      -- Method: set & other & ...

          Return a new set with elements common to the set and all
          others.

      -- Method: difference (*others)

      -- Method: set - other - ...

          Return a new set with elements in the set that are not in the
          others.

      -- Method: symmetric_difference (other)

      -- Method: set ^ other

          Return a new set with elements in either the set or `other'
          but not both.

      -- Method: copy ()

          Return a shallow copy of the set.

     Note, the non-operator versions of *note union(): 17fb, *note
     intersection(): 17fc, *note difference(): 17fd, and *note
     symmetric_difference(): 17fe, *note issubset(): 17f9, and *note
     issuperset(): 17fa. methods will accept any iterable as an
     argument.  In contrast, their operator based counterparts require
     their arguments to be sets.  This precludes error-prone
     constructions like ‘set('abc') & 'cbs'’ in favor of the more
     readable ‘set('abc').intersection('cbs')’.

     Both *note set: 1f6. and *note frozenset: 1f7. support set to set
     comparisons.  Two sets are equal if and only if every element of
     each set is contained in the other (each is a subset of the other).
     A set is less than another set if and only if the first set is a
     proper subset of the second set (is a subset, but is not equal).  A
     set is greater than another set if and only if the first set is a
     proper superset of the second set (is a superset, but is not
     equal).

     Instances of *note set: 1f6. are compared to instances of *note
     frozenset: 1f7. based on their members.  For example, ‘set('abc')
     == frozenset('abc')’ returns ‘True’ and so does ‘set('abc') in
     set([frozenset('abc')])’.

     The subset and equality comparisons do not generalize to a total
     ordering function.  For example, any two nonempty disjoint sets are
     not equal and are not subsets of each other, so `all' of the
     following return ‘False’: ‘a<b’, ‘a==b’, or ‘a>b’.

     Since sets only define partial ordering (subset relationships), the
     output of the *note list.sort(): 548. method is undefined for lists
     of sets.

     Set elements, like dictionary keys, must be *note hashable: 276.

     Binary operations that mix *note set: 1f6. instances with *note
     frozenset: 1f7. return the type of the first operand.  For example:
     ‘frozenset('ab') | set('bc')’ returns an instance of *note
     frozenset: 1f7.

     The following table lists operations available for *note set: 1f6.
     that do not apply to immutable instances of *note frozenset: 1f7.:

      -- Method: update (*others)

      -- Method: set |= other | ...

          Update the set, adding elements from all others.

      -- Method: intersection_update (*others)

      -- Method: set &= other & ...

          Update the set, keeping only elements found in it and all
          others.

      -- Method: difference_update (*others)

      -- Method: set -= other | ...

          Update the set, removing elements found in others.

      -- Method: symmetric_difference_update (other)

      -- Method: set ^= other

          Update the set, keeping only elements found in either set, but
          not in both.

      -- Method: add (elem)

          Add element `elem' to the set.

      -- Method: remove (elem)

          Remove element `elem' from the set.  Raises *note KeyError:
          3e9. if `elem' is not contained in the set.

      -- Method: discard (elem)

          Remove element `elem' from the set if it is present.

      -- Method: pop ()

          Remove and return an arbitrary element from the set.  Raises
          *note KeyError: 3e9. if the set is empty.

      -- Method: clear ()

          Remove all elements from the set.

     Note, the non-operator versions of the *note update(): 1800, *note
     intersection_update(): 1801, *note difference_update(): 1802, and
     *note symmetric_difference_update(): 1803. methods will accept any
     iterable as an argument.

     Note, the `elem' argument to the *note __contains__(): dee, *note
     remove(): 1805, and *note discard(): 1806. methods may be a set.
     To support searching for an equivalent frozenset, a temporary one
     is created from `elem'.


File: python.info,  Node: Mapping Types — dict,  Next: Context Manager Types,  Prev: Set Types — set frozenset,  Up: Built-in Types

5.4.10 Mapping Types — ‘dict’
-----------------------------

A *note mapping: c0b. object maps *note hashable: 276. values to
arbitrary objects.  Mappings are mutable objects.  There is currently
only one standard mapping type, the `dictionary'.  (For other containers
see the built-in *note list: 1f8, *note set: 1f6, and *note tuple: 1a2.
classes, and the *note collections: 1d. module.)

A dictionary’s keys are `almost' arbitrary values.  Values that are not
*note hashable: 276, that is, values containing lists, dictionaries or
other mutable types (that are compared by value rather than by object
identity) may not be used as keys.  Numeric types used for keys obey the
normal rules for numeric comparison: if two numbers compare equal (such
as ‘1’ and ‘1.0’) then they can be used interchangeably to index the
same dictionary entry.  (Note however, that since computers store
floating-point numbers as approximations it is usually unwise to use
them as dictionary keys.)

Dictionaries can be created by placing a comma-separated list of ‘key:
value’ pairs within braces, for example: ‘{'jack': 4098, 'sjoerd':
4127}’ or ‘{4098: 'jack', 4127: 'sjoerd'}’, or by the *note dict: 164.
constructor.

 -- Class: dict (**kwargs)

 -- Class: dict (mapping, **kwargs)

 -- Class: dict (iterable, **kwargs)

     Return a new dictionary initialized from an optional positional
     argument and a possibly empty set of keyword arguments.

     Dictionaries can be created by several means:

        * Use a comma-separated list of ‘key: value’ pairs within
          braces: ‘{'jack': 4098, 'sjoerd': 4127}’ or ‘{4098: 'jack',
          4127: 'sjoerd'}’

        * Use a dict comprehension: ‘{}’, ‘{x: x ** 2 for x in
          range(10)}’

        * Use the type constructor: ‘dict()’, ‘dict([('foo', 100),
          ('bar', 200)])’, ‘dict(foo=100, bar=200)’

     If no positional argument is given, an empty dictionary is created.
     If a positional argument is given and it is a mapping object, a
     dictionary is created with the same key-value pairs as the mapping
     object.  Otherwise, the positional argument must be an *note
     iterable: c7c. object.  Each item in the iterable must itself be an
     iterable with exactly two objects.  The first object of each item
     becomes a key in the new dictionary, and the second object the
     corresponding value.  If a key occurs more than once, the last
     value for that key becomes the corresponding value in the new
     dictionary.

     If keyword arguments are given, the keyword arguments and their
     values are added to the dictionary created from the positional
     argument.  If a key being added is already present, the value from
     the keyword argument replaces the value from the positional
     argument.

     To illustrate, the following examples all return a dictionary equal
     to ‘{"one": 1, "two": 2, "three": 3}’:

          >>> a = dict(one=1, two=2, three=3)
          >>> b = {'one': 1, 'two': 2, 'three': 3}
          >>> c = dict(zip(['one', 'two', 'three'], [1, 2, 3]))
          >>> d = dict([('two', 2), ('one', 1), ('three', 3)])
          >>> e = dict({'three': 3, 'one': 1, 'two': 2})
          >>> f = dict({'one': 1, 'three': 3}, two=2)
          >>> a == b == c == d == e == f
          True

     Providing keyword arguments as in the first example only works for
     keys that are valid Python identifiers.  Otherwise, any valid keys
     can be used.

     These are the operations that dictionaries support (and therefore,
     custom mapping types should support too):

      -- Describe: list(d)

          Return a list of all the keys used in the dictionary `d'.

      -- Describe: len(d)

          Return the number of items in the dictionary `d'.

      -- Describe: d[key]

          Return the item of `d' with key `key'.  Raises a *note
          KeyError: 3e9. if `key' is not in the map.

          If a subclass of dict defines a method *note __missing__():
          c0d. and `key' is not present, the ‘d[key]’ operation calls
          that method with the key `key' as argument.  The ‘d[key]’
          operation then returns or raises whatever is returned or
          raised by the ‘__missing__(key)’ call.  No other operations or
          methods invoke *note __missing__(): c0d.  If *note
          __missing__(): c0d. is not defined, *note KeyError: 3e9. is
          raised.  *note __missing__(): c0d. must be a method; it cannot
          be an instance variable:

               >>> class Counter(dict):
               ...     def __missing__(self, key):
               ...         return 0
               >>> c = Counter()
               >>> c['red']
               0
               >>> c['red'] += 1
               >>> c['red']
               1

          The example above shows part of the implementation of *note
          collections.Counter: ab9.  A different ‘__missing__’ method is
          used by *note collections.defaultdict: c0c.

      -- Describe: d[key] = value

          Set ‘d[key]’ to `value'.

      -- Describe: del d[key]

          Remove ‘d[key]’ from `d'.  Raises a *note KeyError: 3e9. if
          `key' is not in the map.

      -- Describe: key in d

          Return ‘True’ if `d' has a key `key', else ‘False’.

      -- Describe: key not in d

          Equivalent to ‘not key in d’.

      -- Describe: iter(d)

          Return an iterator over the keys of the dictionary.  This is a
          shortcut for ‘iter(d.keys())’.

      -- Method: clear ()

          Remove all items from the dictionary.

      -- Method: copy ()

          Return a shallow copy of the dictionary.

      -- Method: classmethod fromkeys (iterable[, value])

          Create a new dictionary with keys from `iterable' and values
          set to `value'.

          *note fromkeys(): 180a. is a class method that returns a new
          dictionary.  `value' defaults to ‘None’.  All of the values
          refer to just a single instance, so it generally doesn’t make
          sense for `value' to be a mutable object such as an empty
          list.  To get distinct values, use a *note dict comprehension:
          741. instead.

      -- Method: get (key[, default])

          Return the value for `key' if `key' is in the dictionary, else
          `default'.  If `default' is not given, it defaults to ‘None’,
          so that this method never raises a *note KeyError: 3e9.

      -- Method: items ()

          Return a new view of the dictionary’s items (‘(key, value)’
          pairs).  See the *note documentation of view objects: 180c.

      -- Method: keys ()

          Return a new view of the dictionary’s keys.  See the *note
          documentation of view objects: 180c.

      -- Method: pop (key[, default])

          If `key' is in the dictionary, remove it and return its value,
          else return `default'.  If `default' is not given and `key' is
          not in the dictionary, a *note KeyError: 3e9. is raised.

      -- Method: popitem ()

          Remove and return a ‘(key, value)’ pair from the dictionary.
          Pairs are returned in LIFO (last-in, first-out) order.

          *note popitem(): 180e. is useful to destructively iterate over
          a dictionary, as often used in set algorithms.  If the
          dictionary is empty, calling *note popitem(): 180e. raises a
          *note KeyError: 3e9.

          Changed in version 3.7: LIFO order is now guaranteed.  In
          prior versions, *note popitem(): 180e. would return an
          arbitrary key/value pair.

      -- Describe: reversed(d)

          Return a reverse iterator over the keys of the dictionary.
          This is a shortcut for ‘reversed(d.keys())’.

          New in version 3.8.

      -- Method: setdefault (key[, default])

          If `key' is in the dictionary, return its value.  If not,
          insert `key' with a value of `default' and return `default'.
          `default' defaults to ‘None’.

      -- Method: update ([other])

          Update the dictionary with the key/value pairs from `other',
          overwriting existing keys.  Return ‘None’.

          *note update(): e8e. accepts either another dictionary object
          or an iterable of key/value pairs (as tuples or other
          iterables of length two).  If keyword arguments are specified,
          the dictionary is then updated with those key/value pairs:
          ‘d.update(red=1, blue=2)’.

      -- Method: values ()

          Return a new view of the dictionary’s values.  See the *note
          documentation of view objects: 180c.

          An equality comparison between one ‘dict.values()’ view and
          another will always return ‘False’.  This also applies when
          comparing ‘dict.values()’ to itself:

               >>> d = {'a': 1}
               >>> d.values() == d.values()
               False

      -- Describe: d | other

          Create a new dictionary with the merged keys and values of `d'
          and `other', which must both be dictionaries.  The values of
          `other' take priority when `d' and `other' share keys.

          New in version 3.9.

      -- Describe: d |= other

          Update the dictionary `d' with keys and values from `other',
          which may be either a *note mapping: c0b. or an *note
          iterable: c7c. of key/value pairs.  The values of `other' take
          priority when `d' and `other' share keys.

          New in version 3.9.

     Dictionaries compare equal if and only if they have the same ‘(key,
     value)’ pairs (regardless of ordering).  Order comparisons (‘<’,
     ‘<=’, ‘>=’, ‘>’) raise *note TypeError: 1fe.

     Dictionaries preserve insertion order.  Note that updating a key
     does not affect the order.  Keys added after deletion are inserted
     at the end.

          >>> d = {"one": 1, "two": 2, "three": 3, "four": 4}
          >>> d
          {'one': 1, 'two': 2, 'three': 3, 'four': 4}
          >>> list(d)
          ['one', 'two', 'three', 'four']
          >>> list(d.values())
          [1, 2, 3, 4]
          >>> d["one"] = 42
          >>> d
          {'one': 42, 'two': 2, 'three': 3, 'four': 4}
          >>> del d["two"]
          >>> d["two"] = None
          >>> d
          {'one': 42, 'three': 3, 'four': 4, 'two': None}

     Changed in version 3.7: Dictionary order is guaranteed to be
     insertion order.  This behavior was an implementation detail of
     CPython from 3.6.

     Dictionaries and dictionary views are reversible.

          >>> d = {"one": 1, "two": 2, "three": 3, "four": 4}
          >>> d
          {'one': 1, 'two': 2, 'three': 3, 'four': 4}
          >>> list(reversed(d))
          ['four', 'three', 'two', 'one']
          >>> list(reversed(d.values()))
          [4, 3, 2, 1]
          >>> list(reversed(d.items()))
          [('four', 4), ('three', 3), ('two', 2), ('one', 1)]

     Changed in version 3.8: Dictionaries are now reversible.

See also
........

*note types.MappingProxyType: b8e. can be used to create a read-only
view of a *note dict: 164.

* Menu:

* Dictionary view objects::


File: python.info,  Node: Dictionary view objects,  Up: Mapping Types — dict

5.4.10.1 Dictionary view objects
................................

The objects returned by *note dict.keys(): cf4, *note dict.values():
cf6. and *note dict.items(): cf5. are `view objects'.  They provide a
dynamic view on the dictionary’s entries, which means that when the
dictionary changes, the view reflects these changes.

Dictionary views can be iterated over to yield their respective data,
and support membership tests:

 -- Describe: len(dictview)

     Return the number of entries in the dictionary.

 -- Describe: iter(dictview)

     Return an iterator over the keys, values or items (represented as
     tuples of ‘(key, value)’) in the dictionary.

     Keys and values are iterated over in insertion order.  This allows
     the creation of ‘(value, key)’ pairs using *note zip(): cfc.:
     ‘pairs = zip(d.values(), d.keys())’.  Another way to create the
     same list is ‘pairs = [(v, k) for (k, v) in d.items()]’.

     Iterating views while adding or deleting entries in the dictionary
     may raise a *note RuntimeError: 3dc. or fail to iterate over all
     entries.

     Changed in version 3.7: Dictionary order is guaranteed to be
     insertion order.

 -- Describe: x in dictview

     Return ‘True’ if `x' is in the underlying dictionary’s keys, values
     or items (in the latter case, `x' should be a ‘(key, value)’
     tuple).

 -- Describe: reversed(dictview)

     Return a reverse iterator over the keys, values or items of the
     dictionary.  The view will be iterated in reverse order of the
     insertion.

     Changed in version 3.8: Dictionary views are now reversible.

Keys views are set-like since their entries are unique and hashable.  If
all values are hashable, so that ‘(key, value)’ pairs are unique and
hashable, then the items view is also set-like.  (Values views are not
treated as set-like since the entries are generally not unique.)  For
set-like views, all of the operations defined for the abstract base
class *note collections.abc.Set: 1810. are available (for example, ‘==’,
‘<’, or ‘^’).

An example of dictionary view usage:

     >>> dishes = {'eggs': 2, 'sausage': 1, 'bacon': 1, 'spam': 500}
     >>> keys = dishes.keys()
     >>> values = dishes.values()

     >>> # iteration
     >>> n = 0
     >>> for val in values:
     ...     n += val
     >>> print(n)
     504

     >>> # keys and values are iterated over in the same order (insertion order)
     >>> list(keys)
     ['eggs', 'sausage', 'bacon', 'spam']
     >>> list(values)
     [2, 1, 1, 500]

     >>> # view objects are dynamic and reflect dict changes
     >>> del dishes['eggs']
     >>> del dishes['sausage']
     >>> list(keys)
     ['bacon', 'spam']

     >>> # set operations
     >>> keys & {'eggs', 'bacon', 'salad'}
     {'bacon'}
     >>> keys ^ {'sausage', 'juice'}
     {'juice', 'sausage', 'bacon', 'spam'}


File: python.info,  Node: Context Manager Types,  Next: Generic Alias Type,  Prev: Mapping Types — dict,  Up: Built-in Types

5.4.11 Context Manager Types
----------------------------

Python’s *note with: 7da. statement supports the concept of a runtime
context defined by a context manager.  This is implemented using a pair
of methods that allow user-defined classes to define a runtime context
that is entered before the statement body is executed and exited when
the statement ends:

 -- Method: contextmanager.__enter__ ()

     Enter the runtime context and return either this object or another
     object related to the runtime context.  The value returned by this
     method is bound to the identifier in the ‘as’ clause of *note with:
     7da. statements using this context manager.

     An example of a context manager that returns itself is a *note file
     object: c14.  File objects return themselves from __enter__() to
     allow *note open(): 16f. to be used as the context expression in a
     *note with: 7da. statement.

     An example of a context manager that returns a related object is
     the one returned by *note decimal.localcontext(): 1813.  These
     managers set the active decimal context to a copy of the original
     decimal context and then return the copy.  This allows changes to
     be made to the current decimal context in the body of the *note
     with: 7da. statement without affecting code outside the ‘with’
     statement.

 -- Method: contextmanager.__exit__ (exc_type, exc_val, exc_tb)

     Exit the runtime context and return a Boolean flag indicating if
     any exception that occurred should be suppressed.  If an exception
     occurred while executing the body of the *note with: 7da.
     statement, the arguments contain the exception type, value and
     traceback information.  Otherwise, all three arguments are ‘None’.

     Returning a true value from this method will cause the *note with:
     7da. statement to suppress the exception and continue execution
     with the statement immediately following the ‘with’ statement.
     Otherwise the exception continues propagating after this method has
     finished executing.  Exceptions that occur during execution of this
     method will replace any exception that occurred in the body of the
     ‘with’ statement.

     The exception passed in should never be reraised explicitly -
     instead, this method should return a false value to indicate that
     the method completed successfully and does not want to suppress the
     raised exception.  This allows context management code to easily
     detect whether or not an *note __exit__(): 1814. method has
     actually failed.

Python defines several context managers to support easy thread
synchronisation, prompt closure of files or other objects, and simpler
manipulation of the active decimal arithmetic context.  The specific
types are not treated specially beyond their implementation of the
context management protocol.  See the *note contextlib: 23. module for
some examples.

Python’s *note generator: a83.s and the *note contextlib.contextmanager:
c4f. decorator provide a convenient way to implement these protocols.
If a generator function is decorated with the *note
contextlib.contextmanager: c4f. decorator, it will return a context
manager implementing the necessary *note __enter__(): 1812. and *note
__exit__(): 1814. methods, rather than the iterator produced by an
undecorated generator function.

Note that there is no specific slot for any of these methods in the type
structure for Python objects in the Python/C API. Extension types
wanting to define these methods must provide them as a normal Python
accessible method.  Compared to the overhead of setting up the runtime
context, the overhead of a single class dictionary lookup is negligible.


File: python.info,  Node: Generic Alias Type,  Next: Other Built-in Types,  Prev: Context Manager Types,  Up: Built-in Types

5.4.12 Generic Alias Type
-------------------------

‘GenericAlias’ objects are created by subscripting a class (usually a
container), such as ‘list[int]’.  They are intended primarily for *note
type annotations: 1587.

Usually, the *note subscription: 158e. of container objects calls the
method *note __getitem__(): 3a2. of the object.  However, the
subscription of some containers’ classes may call the classmethod *note
__class_getitem__(): 437. of the class instead.  The classmethod *note
__class_getitem__(): 437. should return a ‘GenericAlias’ object.

     Note: If the *note __getitem__(): 3a2. of the class’ metaclass is
     present, it will take precedence over the *note
     __class_getitem__(): 437. defined in the class (see PEP 560(1) for
     more details).

The ‘GenericAlias’ object acts as a proxy for *note generic types: fea,
implementing `parameterized generics' - a specific instance of a generic
which provides the types for container elements.

The user-exposed type for the ‘GenericAlias’ object can be accessed from
*note types.GenericAlias: 27c. and used for *note isinstance(): 552.
checks.  It can also be used to create ‘GenericAlias’ objects directly.

 -- Describe: T[X, Y, ...]

     Creates a ‘GenericAlias’ representing a type ‘T’ containing
     elements of types `X', `Y', and more depending on the ‘T’ used.
     For example, a function expecting a *note list: 1f8. containing
     *note float: 1fd. elements:

          def average(values: list[float]) -> float:
              return sum(values) / len(values)

     Another example for *note mapping: c0b. objects, using a *note
     dict: 164, which is a generic type expecting two type parameters
     representing the key type and the value type.  In this example, the
     function expects a ‘dict’ with keys of type *note str: 205. and
     values of type *note int: 204.:

          def send_post_request(url: str, body: dict[str, int]) -> None:
              ...

The builtin functions *note isinstance(): 552. and *note issubclass():
553. do not accept ‘GenericAlias’ types for their second argument:

     >>> isinstance([1, 2], list[str])
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: isinstance() argument 2 cannot be a parameterized generic

The Python runtime does not enforce *note type annotations: 1587.  This
extends to generic types and their type parameters.  When creating an
object from a ‘GenericAlias’, container elements are not checked against
their type.  For example, the following code is discouraged, but will
run without errors:

     >>> t = list[str]
     >>> t([1, 2, 3])
     [1, 2, 3]

Furthermore, parameterized generics erase type parameters during object
creation:

     >>> t = list[str]
     >>> type(t)
     <class 'types.GenericAlias'>

     >>> l = t()
     >>> type(l)
     <class 'list'>

Calling *note repr(): 8b9. or *note str(): 205. on a generic shows the
parameterized type:

     >>> repr(list[int])
     'list[int]'

     >>> str(list[int])
     'list[int]'

The *note __getitem__(): 3a2. method of generics will raise an exception
to disallow mistakes like ‘dict[str][str]’:

     >>> dict[str][str]
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: There are no type variables left in dict[str]

However, such expressions are valid when *note type variables: 1588. are
used.  The index must have as many elements as there are type variable
items in the ‘GenericAlias’ object’s *note __args__: 1816.

     >>> from typing import TypeVar
     >>> Y = TypeVar('Y')
     >>> dict[str, Y][int]
     dict[str, int]

* Menu:

* Standard Generic Collections::
* Special Attributes of Generic Alias::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0560


File: python.info,  Node: Standard Generic Collections,  Next: Special Attributes of Generic Alias,  Up: Generic Alias Type

5.4.12.1 Standard Generic Collections
.....................................

These standard library collections support parameterized generics.

   * *note tuple: 1a2.

   * *note list: 1f8.

   * *note dict: 164.

   * *note set: 1f6.

   * *note frozenset: 1f7.

   * *note type: 6ff.

   * *note collections.deque: 62b.

   * *note collections.defaultdict: c0c.

   * *note collections.OrderedDict: 2ea.

   * *note collections.Counter: ab9.

   * *note collections.ChainMap: 5a4.

   * *note collections.abc.Awaitable: 7a9.

   * *note collections.abc.Coroutine: 7aa.

   * *note collections.abc.AsyncIterable: 7ac.

   * *note collections.abc.AsyncIterator: 7ab.

   * *note collections.abc.AsyncGenerator: 62a.

   * *note collections.abc.Iterable: 1818.

   * *note collections.abc.Iterator: 1819.

   * *note collections.abc.Generator: 7a8.

   * *note collections.abc.Reversible: 628.

   * *note collections.abc.Container: 181a.

   * *note collections.abc.Collection: 627.

   * *note collections.abc.Callable: 27a.

   * *note collections.abc.Set: 1810.

   * *note collections.abc.MutableSet: 181b.

   * *note collections.abc.Mapping: 15f.

   * *note collections.abc.MutableMapping: ace.

   * *note collections.abc.Sequence: 1764.

   * *note collections.abc.MutableSequence: 79f.

   * *note collections.abc.ByteString: 181c.

   * *note collections.abc.MappingView: 181d.

   * *note collections.abc.KeysView: 181e.

   * *note collections.abc.ItemsView: 181f.

   * *note collections.abc.ValuesView: 1820.

   * *note contextlib.AbstractContextManager: 62e.

   * *note contextlib.AbstractAsyncContextManager: 480.

   * *note re.Pattern: 983.

   * *note re.Match: 984.


File: python.info,  Node: Special Attributes of Generic Alias,  Prev: Standard Generic Collections,  Up: Generic Alias Type

5.4.12.2 Special Attributes of Generic Alias
............................................

All parameterized generics implement special read-only attributes.

 -- Attribute: genericalias.__origin__

     This attribute points at the non-parameterized generic class:

          >>> list[int].__origin__
          <class 'list'>

 -- Attribute: genericalias.__args__

     This attribute is a *note tuple: 1a2. (possibly of length 1) of
     generic types passed to the original *note __class_getitem__():
     437. of the generic container:

          >>> dict[str, list[int]].__args__
          (<class 'str'>, list[int])

 -- Attribute: genericalias.__parameters__

     This attribute is a lazily computed tuple (possibly empty) of
     unique type variables found in ‘__args__’:

          >>> from typing import TypeVar

          >>> T = TypeVar('T')
          >>> list[T].__parameters__
          (~T,)

See also
........

   * PEP 585(1) – “Type Hinting Generics In Standard Collections”

   * *note __class_getitem__(): 437. – Used to implement parameterized
     generics.

   * *note Generics: 1588. – Generics in the *note typing: 122. module.

New in version 3.9.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0585


File: python.info,  Node: Other Built-in Types,  Next: Special Attributes,  Prev: Generic Alias Type,  Up: Built-in Types

5.4.13 Other Built-in Types
---------------------------

The interpreter supports several other kinds of objects.  Most of these
support only one or two operations.

* Menu:

* Modules: Modules<2>.
* Classes and Class Instances::
* Functions::
* Methods::
* Code Objects::
* Type Objects::
* The Null Object::
* The Ellipsis Object::
* The NotImplemented Object::
* Boolean Values::
* Internal Objects::


File: python.info,  Node: Modules<2>,  Next: Classes and Class Instances,  Up: Other Built-in Types

5.4.13.1 Modules
................

The only special operation on a module is attribute access: ‘m.name’,
where `m' is a module and `name' accesses a name defined in `m'’s symbol
table.  Module attributes can be assigned to.  (Note that the *note
import: ce7. statement is not, strictly speaking, an operation on a
module object; ‘import foo’ does not require a module object named `foo'
to exist, rather it requires an (external) `definition' for a module
named `foo' somewhere.)

A special attribute of every module is *note __dict__: 5f6.  This is the
dictionary containing the module’s symbol table.  Modifying this
dictionary will actually change the module’s symbol table, but direct
assignment to the *note __dict__: 5f6. attribute is not possible (you
can write ‘m.__dict__['a'] = 1’, which defines ‘m.a’ to be ‘1’, but you
can’t write ‘m.__dict__ = {}’).  Modifying *note __dict__: 5f6. directly
is not recommended.

Modules built into the interpreter are written like this: ‘<module 'sys'
(built-in)>’.  If loaded from a file, they are written as ‘<module 'os'
from '/usr/local/lib/pythonX.Y/os.pyc'>’.


File: python.info,  Node: Classes and Class Instances,  Next: Functions,  Prev: Modules<2>,  Up: Other Built-in Types

5.4.13.2 Classes and Class Instances
....................................

See *note Objects, values and types: 154f. and *note Class definitions:
d32. for these.


File: python.info,  Node: Functions,  Next: Methods,  Prev: Classes and Class Instances,  Up: Other Built-in Types

5.4.13.3 Functions
..................

Function objects are created by function definitions.  The only
operation on a function object is to call it: ‘func(argument-list)’.

There are really two flavors of function objects: built-in functions and
user-defined functions.  Both support the same operation (to call the
function), but the implementation is different, hence the different
object types.

See *note Function definitions: 1390. for more information.


File: python.info,  Node: Methods,  Next: Code Objects,  Prev: Functions,  Up: Other Built-in Types

5.4.13.4 Methods
................

Methods are functions that are called using the attribute notation.
There are two flavors: built-in methods (such as ‘append()’ on lists)
and class instance methods.  Built-in methods are described with the
types that support them.

If you access a method (a function defined in a class namespace) through
an instance, you get a special object: a `bound method' (also called
`instance method') object.  When called, it will add the ‘self’ argument
to the argument list.  Bound methods have two special read-only
attributes: ‘m.__self__’ is the object on which the method operates, and
‘m.__func__’ is the function implementing the method.  Calling ‘m(arg-1,
arg-2, ..., arg-n)’ is completely equivalent to calling
‘m.__func__(m.__self__, arg-1, arg-2, ..., arg-n)’.

Like function objects, bound method objects support getting arbitrary
attributes.  However, since method attributes are actually stored on the
underlying function object (‘meth.__func__’), setting method attributes
on bound methods is disallowed.  Attempting to set an attribute on a
method results in an *note AttributeError: 4a2. being raised.  In order
to set a method attribute, you need to explicitly set it on the
underlying function object:

     >>> class C:
     ...     def method(self):
     ...         pass
     ...
     >>> c = C()
     >>> c.method.whoami = 'my name is method'  # can't set on the method
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     AttributeError: 'method' object has no attribute 'whoami'
     >>> c.method.__func__.whoami = 'my name is method'
     >>> c.method.whoami
     'my name is method'

See *note The standard type hierarchy: 1553. for more information.


File: python.info,  Node: Code Objects,  Next: Type Objects,  Prev: Methods,  Up: Other Built-in Types

5.4.13.5 Code Objects
.....................

Code objects are used by the implementation to represent
“pseudo-compiled” executable Python code such as a function body.  They
differ from function objects because they don’t contain a reference to
their global execution environment.  Code objects are returned by the
built-in *note compile(): 2e7. function and can be extracted from
function objects through their ‘__code__’ attribute.  See also the *note
code: 1a. module.

Accessing ‘__code__’ raises an *note auditing event: fa1.
‘object.__getattr__’ with arguments ‘obj’ and ‘"__code__"’.

A code object can be executed or evaluated by passing it (instead of a
source string) to the *note exec(): d0c. or *note eval(): c61. built-in
functions.

See *note The standard type hierarchy: 1553. for more information.


File: python.info,  Node: Type Objects,  Next: The Null Object,  Prev: Code Objects,  Up: Other Built-in Types

5.4.13.6 Type Objects
.....................

Type objects represent the various object types.  An object’s type is
accessed by the built-in function *note type(): 6ff.  There are no
special operations on types.  The standard module *note types: 121.
defines names for all standard built-in types.

Types are written like this: ‘<class 'int'>’.


File: python.info,  Node: The Null Object,  Next: The Ellipsis Object,  Prev: Type Objects,  Up: Other Built-in Types

5.4.13.7 The Null Object
........................

This object is returned by functions that don’t explicitly return a
value.  It supports no special operations.  There is exactly one null
object, named ‘None’ (a built-in name).  ‘type(None)()’ produces the
same singleton.

It is written as ‘None’.


File: python.info,  Node: The Ellipsis Object,  Next: The NotImplemented Object,  Prev: The Null Object,  Up: Other Built-in Types

5.4.13.8 The Ellipsis Object
............................

This object is commonly used by slicing (see *note Slicings: 1652.).  It
supports no special operations.  There is exactly one ellipsis object,
named *note Ellipsis: 1740. (a built-in name).  ‘type(Ellipsis)()’
produces the *note Ellipsis: 1740. singleton.

It is written as ‘Ellipsis’ or ‘...’.


File: python.info,  Node: The NotImplemented Object,  Next: Boolean Values,  Prev: The Ellipsis Object,  Up: Other Built-in Types

5.4.13.9 The NotImplemented Object
..................................

This object is returned from comparisons and binary operations when they
are asked to operate on types they don’t support.  See *note
Comparisons: 167a. for more information.  There is exactly one
‘NotImplemented’ object.  ‘type(NotImplemented)()’ produces the
singleton instance.

It is written as ‘NotImplemented’.


File: python.info,  Node: Boolean Values,  Next: Internal Objects,  Prev: The NotImplemented Object,  Up: Other Built-in Types

5.4.13.10 Boolean Values
........................

Boolean values are the two constant objects ‘False’ and ‘True’.  They
are used to represent truth values (although other values can also be
considered false or true).  In numeric contexts (for example when used
as the argument to an arithmetic operator), they behave like the
integers 0 and 1, respectively.  The built-in function *note bool():
2bd. can be used to convert any value to a Boolean, if the value can be
interpreted as a truth value (see section *note Truth Value Testing:
1718. above).

They are written as ‘False’ and ‘True’, respectively.


File: python.info,  Node: Internal Objects,  Prev: Boolean Values,  Up: Other Built-in Types

5.4.13.11 Internal Objects
..........................

See *note The standard type hierarchy: 1553. for this information.  It
describes stack frame objects, traceback objects, and slice objects.


File: python.info,  Node: Special Attributes,  Prev: Other Built-in Types,  Up: Built-in Types

5.4.14 Special Attributes
-------------------------

The implementation adds a few special read-only attributes to several
object types, where they are relevant.  Some of these are not reported
by the *note dir(): df9. built-in function.

 -- Attribute: object.__dict__

     A dictionary or other mapping object used to store an object’s
     (writable) attributes.

 -- Attribute: instance.__class__

     The class to which a class instance belongs.

 -- Attribute: class.__bases__

     The tuple of base classes of a class object.

 -- Attribute: definition.__name__

     The name of the class, function, method, descriptor, or generator
     instance.

 -- Attribute: definition.__qualname__

     The *note qualified name: 155c. of the class, function, method,
     descriptor, or generator instance.

     New in version 3.3.

 -- Attribute: class.__mro__

     This attribute is a tuple of classes that are considered when
     looking for base classes during method resolution.

 -- Method: class.mro ()

     This method can be overridden by a metaclass to customize the
     method resolution order for its instances.  It is called at class
     instantiation, and its result is stored in *note __mro__: 173a.

 -- Method: class.__subclasses__ ()

     Each class keeps a list of weak references to its immediate
     subclasses.  This method returns a list of all those references
     still alive.  The list is in definition order.  Example:

          >>> int.__subclasses__()
          [<class 'bool'>]


File: python.info,  Node: Built-in Exceptions,  Next: Text Processing Services,  Prev: Built-in Types,  Up: The Python Standard Library

5.5 Built-in Exceptions
=======================

In Python, all exceptions must be instances of a class that derives from
*note BaseException: 2db.  In a *note try: e37. statement with an *note
except: c10. clause that mentions a particular class, that clause also
handles any exception classes derived from that class (but not exception
classes from which `it' is derived).  Two exception classes that are not
related via subclassing are never equivalent, even if they have the same
name.

The built-in exceptions listed below can be generated by the interpreter
or built-in functions.  Except where mentioned, they have an “associated
value” indicating the detailed cause of the error.  This may be a string
or a tuple of several items of information (e.g., an error code and a
string explaining the code).  The associated value is usually passed as
arguments to the exception class’s constructor.

User code can raise built-in exceptions.  This can be used to test an
exception handler or to report an error condition “just like” the
situation in which the interpreter raises the same exception; but beware
that there is nothing to prevent user code from raising an inappropriate
error.

The built-in exception classes can be subclassed to define new
exceptions; programmers are encouraged to derive new exceptions from the
*note Exception: 2dc. class or one of its subclasses, and not from *note
BaseException: 2db.  More information on defining exceptions is
available in the Python Tutorial under *note User-defined Exceptions:
13e6.

* Menu:

* Exception context::
* Inheriting from built-in exceptions::
* Base classes::
* Concrete exceptions::
* Warnings::
* Exception hierarchy::


File: python.info,  Node: Exception context,  Next: Inheriting from built-in exceptions,  Up: Built-in Exceptions

5.5.1 Exception context
-----------------------

When raising (or re-raising) an exception in an *note except: c10. or
*note finally: 2bc. clause ‘__context__’ is automatically set to the
last exception caught; if the new exception is not handled the traceback
that is eventually displayed will include the originating exception(s)
and the final exception.

When raising a new exception (rather than using a bare ‘raise’ to
re-raise the exception currently being handled), the implicit exception
context can be supplemented with an explicit cause by using *note from:
d0a. with *note raise: d0a.:

     raise new_exc from original_exc

The expression following *note from: d0a. must be an exception or
‘None’.  It will be set as ‘__cause__’ on the raised exception.  Setting
‘__cause__’ also implicitly sets the ‘__suppress_context__’ attribute to
‘True’, so that using ‘raise new_exc from None’ effectively replaces the
old exception with the new one for display purposes (e.g.  converting
*note KeyError: 3e9. to *note AttributeError: 4a2.), while leaving the
old exception available in ‘__context__’ for introspection when
debugging.

The default traceback display code shows these chained exceptions in
addition to the traceback for the exception itself.  An explicitly
chained exception in ‘__cause__’ is always shown when present.  An
implicitly chained exception in ‘__context__’ is shown only if
‘__cause__’ is *note None: 203. and ‘__suppress_context__’ is false.

In either case, the exception itself is always shown after any chained
exceptions so that the final line of the traceback always shows the last
exception that was raised.


File: python.info,  Node: Inheriting from built-in exceptions,  Next: Base classes,  Prev: Exception context,  Up: Built-in Exceptions

5.5.2 Inheriting from built-in exceptions
-----------------------------------------

User code can create subclasses that inherit from an exception type.
It’s recommended to only subclass one exception type at a time to avoid
any possible conflicts between how the bases handle the ‘args’
attribute, as well as due to possible memory layout incompatibilities.

`CPython implementation detail:' Most built-in exceptions are
implemented in C for efficiency, see: Objects/exceptions.c(1).  Some
have custom memory layouts which makes it impossible to create a
subclass that inherits from multiple exception types.  The memory layout
of a type is an implementation detail and might change between Python
versions, leading to new conflicts in the future.  Therefore, it’s
recommended to avoid subclassing multiple exception types altogether.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Objects/exceptions.c


File: python.info,  Node: Base classes,  Next: Concrete exceptions,  Prev: Inheriting from built-in exceptions,  Up: Built-in Exceptions

5.5.3 Base classes
------------------

The following exceptions are used mostly as base classes for other
exceptions.

 -- Exception: BaseException

     The base class for all built-in exceptions.  It is not meant to be
     directly inherited by user-defined classes (for that, use *note
     Exception: 2dc.).  If *note str(): 205. is called on an instance of
     this class, the representation of the argument(s) to the instance
     are returned, or the empty string when there were no arguments.

      -- Attribute: args

          The tuple of arguments given to the exception constructor.
          Some built-in exceptions (like *note OSError: 304.) expect a
          certain number of arguments and assign a special meaning to
          the elements of this tuple, while others are usually called
          only with a single string giving an error message.

      -- Method: with_traceback (tb)

          This method sets `tb' as the new traceback for the exception
          and returns the exception object.  It is usually used in
          exception handling code like this:

               try:
                   ...
               except SomeException:
                   tb = sys.exc_info()[2]
                   raise OtherException(...).with_traceback(tb)

 -- Exception: Exception

     All built-in, non-system-exiting exceptions are derived from this
     class.  All user-defined exceptions should also be derived from
     this class.

 -- Exception: ArithmeticError

     The base class for those built-in exceptions that are raised for
     various arithmetic errors: *note OverflowError: a41, *note
     ZeroDivisionError: 1fa, *note FloatingPointError: 1846.

 -- Exception: BufferError

     Raised when a *note buffer: 171c. related operation cannot be
     performed.

 -- Exception: LookupError

     The base class for the exceptions that are raised when a key or
     index used on a mapping or sequence is invalid: *note IndexError:
     f36, *note KeyError: 3e9.  This can be raised directly by *note
     codecs.lookup(): 238.


File: python.info,  Node: Concrete exceptions,  Next: Warnings,  Prev: Base classes,  Up: Built-in Exceptions

5.5.4 Concrete exceptions
-------------------------

The following exceptions are the exceptions that are usually raised.

 -- Exception: AssertionError

     Raised when an *note assert: 23f. statement fails.

 -- Exception: AttributeError

     Raised when an attribute reference (see *note Attribute references:
     164c.) or assignment fails.  (When an object does not support
     attribute references or attribute assignments at all, *note
     TypeError: 1fe. is raised.)

 -- Exception: EOFError

     Raised when the *note input(): d33. function hits an end-of-file
     condition (EOF) without reading any data.  (N.B.: the
     ‘io.IOBase.read()’ and *note io.IOBase.readline(): 1849. methods
     return an empty string when they hit EOF.)

 -- Exception: FloatingPointError

     Not currently used.

 -- Exception: GeneratorExit

     Raised when a *note generator: a83. or *note coroutine: 18a. is
     closed; see *note generator.close(): 15d0. and *note
     coroutine.close(): 15cf.  It directly inherits from *note
     BaseException: 2db. instead of *note Exception: 2dc. since it is
     technically not an error.

 -- Exception: ImportError

     Raised when the *note import: ce7. statement has troubles trying to
     load a module.  Also raised when the “from list” in ‘from ...
     import’ has a name that cannot be found.

     The ‘name’ and ‘path’ attributes can be set using keyword-only
     arguments to the constructor.  When set they represent the name of
     the module that was attempted to be imported and the path to any
     file which triggered the exception, respectively.

     Changed in version 3.3: Added the ‘name’ and ‘path’ attributes.

 -- Exception: ModuleNotFoundError

     A subclass of *note ImportError: 16c. which is raised by *note
     import: ce7. when a module could not be located.  It is also raised
     when ‘None’ is found in *note sys.modules: 1051.

     New in version 3.6.

 -- Exception: IndexError

     Raised when a sequence subscript is out of range.  (Slice indices
     are silently truncated to fall in the allowed range; if an index is
     not an integer, *note TypeError: 1fe. is raised.)

 -- Exception: KeyError

     Raised when a mapping (dictionary) key is not found in the set of
     existing keys.

 -- Exception: KeyboardInterrupt

     Raised when the user hits the interrupt key (normally ‘Control-C’
     or ‘Delete’).  During execution, a check for interrupts is made
     regularly.  The exception inherits from *note BaseException: 2db.
     so as to not be accidentally caught by code that catches *note
     Exception: 2dc. and thus prevent the interpreter from exiting.

 -- Exception: MemoryError

     Raised when an operation runs out of memory but the situation may
     still be rescued (by deleting some objects).  The associated value
     is a string indicating what kind of (internal) operation ran out of
     memory.  Note that because of the underlying memory management
     architecture (C’s ‘malloc()’ function), the interpreter may not
     always be able to completely recover from this situation; it
     nevertheless raises an exception so that a stack traceback can be
     printed, in case a run-away program was the cause.

 -- Exception: NameError

     Raised when a local or global name is not found.  This applies only
     to unqualified names.  The associated value is an error message
     that includes the name that could not be found.

 -- Exception: NotImplementedError

     This exception is derived from *note RuntimeError: 3dc.  In user
     defined base classes, abstract methods should raise this exception
     when they require derived classes to override the method, or while
     the class is being developed to indicate that the real
     implementation still needs to be added.

          Note: It should not be used to indicate that an operator or
          method is not meant to be supported at all – in that case
          either leave the operator / method undefined or, if a
          subclass, set it to *note None: 203.

          Note: ‘NotImplementedError’ and ‘NotImplemented’ are not
          interchangeable, even though they have similar names and
          purposes.  See *note NotImplemented: 202. for details on when
          to use it.

 -- Exception: OSError ([arg])

 -- Exception: OSError (errno, strerror[, filename[, winerror[,
          filename2]]])

     This exception is raised when a system function returns a
     system-related error, including I/O failures such as “file not
     found” or “disk full” (not for illegal argument types or other
     incidental errors).

     The second form of the constructor sets the corresponding
     attributes, described below.  The attributes default to *note None:
     203. if not specified.  For backwards compatibility, if three
     arguments are passed, the *note args: 1843. attribute contains only
     a 2-tuple of the first two constructor arguments.

     The constructor often actually returns a subclass of *note OSError:
     304, as described in *note OS exceptions: 184a. below.  The
     particular subclass depends on the final *note errno: 184b. value.
     This behaviour only occurs when constructing *note OSError: 304.
     directly or via an alias, and is not inherited when subclassing.

      -- Attribute: errno

          A numeric error code from the C variable ‘errno’.

      -- Attribute: winerror

          Under Windows, this gives you the native Windows error code.
          The *note errno: 184b. attribute is then an approximate
          translation, in POSIX terms, of that native error code.

          Under Windows, if the `winerror' constructor argument is an
          integer, the *note errno: 184b. attribute is determined from
          the Windows error code, and the `errno' argument is ignored.
          On other platforms, the `winerror' argument is ignored, and
          the *note winerror: 184c. attribute does not exist.

      -- Attribute: strerror

          The corresponding error message, as provided by the operating
          system.  It is formatted by the C functions ‘perror()’ under
          POSIX, and ‘FormatMessage()’ under Windows.

      -- Attribute: filename
      -- Attribute: filename2

          For exceptions that involve a file system path (such as *note
          open(): 16f. or *note os.unlink(): b18.), *note filename:
          184e. is the file name passed to the function.  For functions
          that involve two file system paths (such as *note os.rename():
          b14.), *note filename2: 184f. corresponds to the second file
          name passed to the function.

     Changed in version 3.3: *note EnvironmentError: a74, *note IOError:
     a73, *note WindowsError: a75, *note socket.error: a76, *note
     select.error: a77. and ‘mmap.error’ have been merged into *note
     OSError: 304, and the constructor may return a subclass.

     Changed in version 3.4: The *note filename: 184e. attribute is now
     the original file name passed to the function, instead of the name
     encoded to or decoded from the filesystem encoding.  Also, the
     `filename2' constructor argument and attribute was added.

 -- Exception: OverflowError

     Raised when the result of an arithmetic operation is too large to
     be represented.  This cannot occur for integers (which would rather
     raise *note MemoryError: f69. than give up).  However, for
     historical reasons, OverflowError is sometimes raised for integers
     that are outside a required range.  Because of the lack of
     standardization of floating point exception handling in C, most
     floating point operations are not checked.

 -- Exception: RecursionError

     This exception is derived from *note RuntimeError: 3dc.  It is
     raised when the interpreter detects that the maximum recursion
     depth (see *note sys.getrecursionlimit(): f3b.) is exceeded.

     New in version 3.5: Previously, a plain *note RuntimeError: 3dc.
     was raised.

 -- Exception: ReferenceError

     This exception is raised when a weak reference proxy, created by
     the *note weakref.proxy(): 37a. function, is used to access an
     attribute of the referent after it has been garbage collected.  For
     more information on weak references, see the *note weakref: 131.
     module.

 -- Exception: RuntimeError

     Raised when an error is detected that doesn’t fall in any of the
     other categories.  The associated value is a string indicating what
     precisely went wrong.

 -- Exception: StopIteration

     Raised by built-in function *note next(): 775. and an *note
     iterator: 1171.’s *note __next__(): d2c. method to signal that
     there are no further items produced by the iterator.

     The exception object has a single attribute ‘value’, which is given
     as an argument when constructing the exception, and defaults to
     *note None: 203.

     When a *note generator: a83. or *note coroutine: 18a. function
     returns, a new *note StopIteration: 582. instance is raised, and
     the value returned by the function is used as the ‘value’ parameter
     to the constructor of the exception.

     If a generator code directly or indirectly raises *note
     StopIteration: 582, it is converted into a *note RuntimeError: 3dc.
     (retaining the *note StopIteration: 582. as the new exception’s
     cause).

     Changed in version 3.3: Added ‘value’ attribute and the ability for
     generator functions to use it to return a value.

     Changed in version 3.5: Introduced the RuntimeError transformation
     via ‘from __future__ import generator_stop’, see PEP 479(1).

     Changed in version 3.7: Enable PEP 479(2) for all code by default:
     a *note StopIteration: 582. error raised in a generator is
     transformed into a *note RuntimeError: 3dc.

 -- Exception: StopAsyncIteration

     Must be raised by *note __anext__(): 155f. method of an *note
     asynchronous iterator: 738. object to stop the iteration.

     New in version 3.5.

 -- Exception: SyntaxError (message, details)

     Raised when the parser encounters a syntax error.  This may occur
     in an *note import: ce7. statement, in a call to the built-in
     functions *note compile(): 2e7, *note exec(): d0c, or *note eval():
     c61, or when reading the initial script or standard input (also
     interactively).

     The *note str(): 205. of the exception instance returns only the
     error message.  Details is a tuple whose members are also available
     as separate attributes.

      -- Attribute: filename

          The name of the file the syntax error occurred in.

      -- Attribute: lineno

          Which line number in the file the error occurred in.  This is
          1-indexed: the first line in the file has a ‘lineno’ of 1.

      -- Attribute: offset

          The column in the line where the error occurred.  This is
          1-indexed: the first character in the line has an ‘offset’ of
          1.

      -- Attribute: text

          The source code text involved in the error.

     For errors in f-string fields, the message is prefixed by
     “f-string: ” and the offsets are offsets in a text constructed from
     the replacement expression.  For example, compiling f’Bad {a b}
     field’ results in this args attribute: (‘f-string: …’, (‘’, 1, 4,
     ‘(a b)n’)).

 -- Exception: IndentationError

     Base class for syntax errors related to incorrect indentation.
     This is a subclass of *note SyntaxError: 55a.

 -- Exception: TabError

     Raised when indentation contains an inconsistent use of tabs and
     spaces.  This is a subclass of *note IndentationError: f39.

 -- Exception: SystemError

     Raised when the interpreter finds an internal error, but the
     situation does not look so serious to cause it to abandon all hope.
     The associated value is a string indicating what went wrong (in
     low-level terms).

     You should report this to the author or maintainer of your Python
     interpreter.  Be sure to report the version of the Python
     interpreter (‘sys.version’; it is also printed at the start of an
     interactive Python session), the exact error message (the
     exception’s associated value) and if possible the source of the
     program that triggered the error.

 -- Exception: SystemExit

     This exception is raised by the *note sys.exit(): daa. function.
     It inherits from *note BaseException: 2db. instead of *note
     Exception: 2dc. so that it is not accidentally caught by code that
     catches *note Exception: 2dc.  This allows the exception to
     properly propagate up and cause the interpreter to exit.  When it
     is not handled, the Python interpreter exits; no stack traceback is
     printed.  The constructor accepts the same optional argument passed
     to *note sys.exit(): daa.  If the value is an integer, it specifies
     the system exit status (passed to C’s ‘exit()’ function); if it is
     ‘None’, the exit status is zero; if it has another type (such as a
     string), the object’s value is printed and the exit status is one.

     A call to *note sys.exit(): daa. is translated into an exception so
     that clean-up handlers (*note finally: 2bc. clauses of *note try:
     e37. statements) can be executed, and so that a debugger can
     execute a script without running the risk of losing control.  The
     *note os._exit(): 1854. function can be used if it is absolutely
     positively necessary to exit immediately (for example, in the child
     process after a call to *note os.fork(): a42.).

      -- Attribute: code

          The exit status or error message that is passed to the
          constructor.  (Defaults to ‘None’.)

 -- Exception: TypeError

     Raised when an operation or function is applied to an object of
     inappropriate type.  The associated value is a string giving
     details about the type mismatch.

     This exception may be raised by user code to indicate that an
     attempted operation on an object is not supported, and is not meant
     to be.  If an object is meant to support a given operation but has
     not yet provided an implementation, *note NotImplementedError: 704.
     is the proper exception to raise.

     Passing arguments of the wrong type (e.g.  passing a *note list:
     1f8. when an *note int: 204. is expected) should result in a *note
     TypeError: 1fe, but passing arguments with the wrong value (e.g.  a
     number outside expected boundaries) should result in a *note
     ValueError: 16d.

 -- Exception: UnboundLocalError

     Raised when a reference is made to a local variable in a function
     or method, but no value has been bound to that variable.  This is a
     subclass of *note NameError: e40.

 -- Exception: UnicodeError

     Raised when a Unicode-related encoding or decoding error occurs.
     It is a subclass of *note ValueError: 16d.

     *note UnicodeError: d03. has attributes that describe the encoding
     or decoding error.  For example, ‘err.object[err.start:err.end]’
     gives the particular invalid input that the codec failed on.

      -- Attribute: encoding

          The name of the encoding that raised the error.

      -- Attribute: reason

          A string describing the specific codec error.

      -- Attribute: object

          The object the codec was attempting to encode or decode.

      -- Attribute: start

          The first index of invalid data in *note object: 3d2.

      -- Attribute: end

          The index after the last invalid data in *note object: 3d2.

 -- Exception: UnicodeEncodeError

     Raised when a Unicode-related error occurs during encoding.  It is
     a subclass of *note UnicodeError: d03.

 -- Exception: UnicodeDecodeError

     Raised when a Unicode-related error occurs during decoding.  It is
     a subclass of *note UnicodeError: d03.

 -- Exception: UnicodeTranslateError

     Raised when a Unicode-related error occurs during translating.  It
     is a subclass of *note UnicodeError: d03.

 -- Exception: ValueError

     Raised when an operation or function receives an argument that has
     the right type but an inappropriate value, and the situation is not
     described by a more precise exception such as *note IndexError:
     f36.

 -- Exception: ZeroDivisionError

     Raised when the second argument of a division or modulo operation
     is zero.  The associated value is a string indicating the type of
     the operands and the operation.

The following exceptions are kept for compatibility with previous
versions; starting from Python 3.3, they are aliases of *note OSError:
304.

 -- Exception: EnvironmentError

 -- Exception: IOError

 -- Exception: WindowsError

     Only available on Windows.

* Menu:

* OS exceptions::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0479

   (2) https://www.python.org/dev/peps/pep-0479


File: python.info,  Node: OS exceptions,  Up: Concrete exceptions

5.5.4.1 OS exceptions
.....................

The following exceptions are subclasses of *note OSError: 304, they get
raised depending on the system error code.

 -- Exception: BlockingIOError

     Raised when an operation would block on an object (e.g.  socket)
     set for non-blocking operation.  Corresponds to ‘errno’ ‘EAGAIN’,
     ‘EALREADY’, ‘EWOULDBLOCK’ and ‘EINPROGRESS’.

     In addition to those of *note OSError: 304, *note BlockingIOError:
     a78. can have one more attribute:

      -- Attribute: characters_written

          An integer containing the number of characters written to the
          stream before it blocked.  This attribute is available when
          using the buffered I/O classes from the *note io: a1. module.

 -- Exception: ChildProcessError

     Raised when an operation on a child process failed.  Corresponds to
     ‘errno’ ‘ECHILD’.

 -- Exception: ConnectionError

     A base class for connection-related issues.

     Subclasses are *note BrokenPipeError: a7e, *note
     ConnectionAbortedError: a7f, *note ConnectionRefusedError: a80. and
     *note ConnectionResetError: a81.

 -- Exception: BrokenPipeError

     A subclass of *note ConnectionError: 7d7, raised when trying to
     write on a pipe while the other end has been closed, or trying to
     write on a socket which has been shutdown for writing.  Corresponds
     to ‘errno’ ‘EPIPE’ and ‘ESHUTDOWN’.

 -- Exception: ConnectionAbortedError

     A subclass of *note ConnectionError: 7d7, raised when a connection
     attempt is aborted by the peer.  Corresponds to ‘errno’
     ‘ECONNABORTED’.

 -- Exception: ConnectionRefusedError

     A subclass of *note ConnectionError: 7d7, raised when a connection
     attempt is refused by the peer.  Corresponds to ‘errno’
     ‘ECONNREFUSED’.

 -- Exception: ConnectionResetError

     A subclass of *note ConnectionError: 7d7, raised when a connection
     is reset by the peer.  Corresponds to ‘errno’ ‘ECONNRESET’.

 -- Exception: FileExistsError

     Raised when trying to create a file or directory which already
     exists.  Corresponds to ‘errno’ ‘EEXIST’.

 -- Exception: FileNotFoundError

     Raised when a file or directory is requested but doesn’t exist.
     Corresponds to ‘errno’ ‘ENOENT’.

 -- Exception: InterruptedError

     Raised when a system call is interrupted by an incoming signal.
     Corresponds to ‘errno’ *note EINTR: 74b.

     Changed in version 3.5: Python now retries system calls when a
     syscall is interrupted by a signal, except if the signal handler
     raises an exception (see PEP 475(1) for the rationale), instead of
     raising *note InterruptedError: 74c.

 -- Exception: IsADirectoryError

     Raised when a file operation (such as *note os.remove(): b13.) is
     requested on a directory.  Corresponds to ‘errno’ ‘EISDIR’.

 -- Exception: NotADirectoryError

     Raised when a directory operation (such as *note os.listdir():
     b1c.) is requested on something which is not a directory.  On most
     POSIX platforms, it may also be raised if an operation attempts to
     open or traverse a non-directory file as if it were a directory.
     Corresponds to ‘errno’ ‘ENOTDIR’.

 -- Exception: PermissionError

     Raised when trying to run an operation without the adequate access
     rights - for example filesystem permissions.  Corresponds to
     ‘errno’ ‘EACCES’ and ‘EPERM’.

 -- Exception: ProcessLookupError

     Raised when a given process doesn’t exist.  Corresponds to ‘errno’
     ‘ESRCH’.

 -- Exception: TimeoutError

     Raised when a system function timed out at the system level.
     Corresponds to ‘errno’ ‘ETIMEDOUT’.

New in version 3.3: All the above *note OSError: 304. subclasses were
added.

See also
........

PEP 3151(2) - Reworking the OS and IO exception hierarchy

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0475

   (2) https://www.python.org/dev/peps/pep-3151


File: python.info,  Node: Warnings,  Next: Exception hierarchy,  Prev: Concrete exceptions,  Up: Built-in Exceptions

5.5.5 Warnings
--------------

The following exceptions are used as warning categories; see the *note
Warning Categories: 185f. documentation for more details.

 -- Exception: Warning

     Base class for warning categories.

 -- Exception: UserWarning

     Base class for warnings generated by user code.

 -- Exception: DeprecationWarning

     Base class for warnings about deprecated features when those
     warnings are intended for other Python developers.

     Ignored by the default warning filters, except in the ‘__main__’
     module ( PEP 565(1)).  Enabling the *note Python Development Mode:
     160. shows this warning.

     The deprecation policy is described in PEP 387(2).

 -- Exception: PendingDeprecationWarning

     Base class for warnings about features which are obsolete and
     expected to be deprecated in the future, but are not deprecated at
     the moment.

     This class is rarely used as emitting a warning about a possible
     upcoming deprecation is unusual, and *note DeprecationWarning: 15a.
     is preferred for already active deprecations.

     Ignored by the default warning filters.  Enabling the *note Python
     Development Mode: 160. shows this warning.

     The deprecation policy is described in PEP 387(3).

 -- Exception: SyntaxWarning

     Base class for warnings about dubious syntax.

 -- Exception: RuntimeWarning

     Base class for warnings about dubious runtime behavior.

 -- Exception: FutureWarning

     Base class for warnings about deprecated features when those
     warnings are intended for end users of applications that are
     written in Python.

 -- Exception: ImportWarning

     Base class for warnings about probable mistakes in module imports.

     Ignored by the default warning filters.  Enabling the *note Python
     Development Mode: 160. shows this warning.

 -- Exception: UnicodeWarning

     Base class for warnings related to Unicode.

 -- Exception: BytesWarning

     Base class for warnings related to *note bytes: 172. and *note
     bytearray: 173.

 -- Exception: ResourceWarning

     Base class for warnings related to resource usage.

     Ignored by the default warning filters.  Enabling the *note Python
     Development Mode: 160. shows this warning.

     New in version 3.2.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0565

   (2) https://www.python.org/dev/peps/pep-0387

   (3) https://www.python.org/dev/peps/pep-0387


File: python.info,  Node: Exception hierarchy,  Prev: Warnings,  Up: Built-in Exceptions

5.5.6 Exception hierarchy
-------------------------

The class hierarchy for built-in exceptions is:

     BaseException
      +-- SystemExit
      +-- KeyboardInterrupt
      +-- GeneratorExit
      +-- Exception
           +-- StopIteration
           +-- StopAsyncIteration
           +-- ArithmeticError
           |    +-- FloatingPointError
           |    +-- OverflowError
           |    +-- ZeroDivisionError
           +-- AssertionError
           +-- AttributeError
           +-- BufferError
           +-- EOFError
           +-- ImportError
           |    +-- ModuleNotFoundError
           +-- LookupError
           |    +-- IndexError
           |    +-- KeyError
           +-- MemoryError
           +-- NameError
           |    +-- UnboundLocalError
           +-- OSError
           |    +-- BlockingIOError
           |    +-- ChildProcessError
           |    +-- ConnectionError
           |    |    +-- BrokenPipeError
           |    |    +-- ConnectionAbortedError
           |    |    +-- ConnectionRefusedError
           |    |    +-- ConnectionResetError
           |    +-- FileExistsError
           |    +-- FileNotFoundError
           |    +-- InterruptedError
           |    +-- IsADirectoryError
           |    +-- NotADirectoryError
           |    +-- PermissionError
           |    +-- ProcessLookupError
           |    +-- TimeoutError
           +-- ReferenceError
           +-- RuntimeError
           |    +-- NotImplementedError
           |    +-- RecursionError
           +-- SyntaxError
           |    +-- IndentationError
           |         +-- TabError
           +-- SystemError
           +-- TypeError
           +-- ValueError
           |    +-- UnicodeError
           |         +-- UnicodeDecodeError
           |         +-- UnicodeEncodeError
           |         +-- UnicodeTranslateError
           +-- Warning
                +-- DeprecationWarning
                +-- PendingDeprecationWarning
                +-- RuntimeWarning
                +-- SyntaxWarning
                +-- UserWarning
                +-- FutureWarning
                +-- ImportWarning
                +-- UnicodeWarning
                +-- BytesWarning
                +-- ResourceWarning


File: python.info,  Node: Text Processing Services,  Next: Binary Data Services,  Prev: Built-in Exceptions,  Up: The Python Standard Library

5.6 Text Processing Services
============================

The modules described in this chapter provide a wide range of string
manipulation operations and other text processing services.

The *note codecs: 1b. module described under *note Binary Data Services:
1865. is also highly relevant to text processing.  In addition, see the
documentation for Python’s built-in string type in *note Text Sequence
Type — str: 1357.

* Menu:

* string — Common string operations::
* re — Regular expression operations::
* difflib — Helpers for computing deltas::
* textwrap — Text wrapping and filling::
* unicodedata — Unicode Database::
* stringprep — Internet String Preparation::
* readline — GNU readline interface::
* rlcompleter — Completion function for GNU readline::


File: python.info,  Node: string — Common string operations,  Next: re — Regular expression operations,  Up: Text Processing Services

5.6.1 ‘string’ — Common string operations
-----------------------------------------

`Source code:' Lib/string.py(1)

__________________________________________________________________

See also
........

*note Text Sequence Type — str: 1357.

*note String Methods: 1358.

* Menu:

* String constants::
* Custom String Formatting::
* Format String Syntax::
* Template strings::
* Helper functions::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/string.py


File: python.info,  Node: String constants,  Next: Custom String Formatting,  Up: string — Common string operations

5.6.1.1 String constants
........................

The constants defined in this module are:

 -- Data: string.ascii_letters

     The concatenation of the *note ascii_lowercase: 1869. and *note
     ascii_uppercase: 186a. constants described below.  This value is
     not locale-dependent.

 -- Data: string.ascii_lowercase

     The lowercase letters ‘'abcdefghijklmnopqrstuvwxyz'’.  This value
     is not locale-dependent and will not change.

 -- Data: string.ascii_uppercase

     The uppercase letters ‘'ABCDEFGHIJKLMNOPQRSTUVWXYZ'’.  This value
     is not locale-dependent and will not change.

 -- Data: string.digits

     The string ‘'0123456789'’.

 -- Data: string.hexdigits

     The string ‘'0123456789abcdefABCDEF'’.

 -- Data: string.octdigits

     The string ‘'01234567'’.

 -- Data: string.punctuation

     String of ASCII characters which are considered punctuation
     characters in the ‘C’ locale: ‘!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~’.

 -- Data: string.printable

     String of ASCII characters which are considered printable.  This is
     a combination of *note digits: 186b, *note ascii_letters: d24,
     *note punctuation: 186e, and *note whitespace: 1870.

 -- Data: string.whitespace

     A string containing all ASCII characters that are considered
     whitespace.  This includes the characters space, tab, linefeed,
     return, formfeed, and vertical tab.


File: python.info,  Node: Custom String Formatting,  Next: Format String Syntax,  Prev: String constants,  Up: string — Common string operations

5.6.1.2 Custom String Formatting
................................

The built-in string class provides the ability to do complex variable
substitutions and value formatting via the *note format(): 5d5. method
described in PEP 3101(1).  The *note Formatter: 8a3. class in the *note
string: f6. module allows you to create and customize your own string
formatting behaviors using the same implementation as the built-in *note
format(): 5d5. method.

 -- Class: string.Formatter

     The *note Formatter: 8a3. class has the following public methods:

      -- Method: format (format_string, /, *args, **kwargs)

          The primary API method.  It takes a format string and an
          arbitrary set of positional and keyword arguments.  It is just
          a wrapper that calls *note vformat(): 1872.

          Changed in version 3.7: A format string argument is now *note
          positional-only: 3c9.

      -- Method: vformat (format_string, args, kwargs)

          This function does the actual work of formatting.  It is
          exposed as a separate function for cases where you want to
          pass in a predefined dictionary of arguments, rather than
          unpacking and repacking the dictionary as individual arguments
          using the ‘*args’ and ‘**kwargs’ syntax.  *note vformat():
          1872. does the work of breaking up the format string into
          character data and replacement fields.  It calls the various
          methods described below.

     In addition, the *note Formatter: 8a3. defines a number of methods
     that are intended to be replaced by subclasses:

      -- Method: parse (format_string)

          Loop over the format_string and return an iterable of tuples
          (`literal_text', `field_name', `format_spec', `conversion').
          This is used by *note vformat(): 1872. to break the string
          into either literal text, or replacement fields.

          The values in the tuple conceptually represent a span of
          literal text followed by a single replacement field.  If there
          is no literal text (which can happen if two replacement fields
          occur consecutively), then `literal_text' will be a
          zero-length string.  If there is no replacement field, then
          the values of `field_name', `format_spec' and `conversion'
          will be ‘None’.

      -- Method: get_field (field_name, args, kwargs)

          Given `field_name' as returned by *note parse(): 1873. (see
          above), convert it to an object to be formatted.  Returns a
          tuple (obj, used_key).  The default version takes strings of
          the form defined in PEP 3101(2), such as “0[name]” or
          “label.title”.  `args' and `kwargs' are as passed in to *note
          vformat(): 1872.  The return value `used_key' has the same
          meaning as the `key' parameter to *note get_value(): 1875.

      -- Method: get_value (key, args, kwargs)

          Retrieve a given field value.  The `key' argument will be
          either an integer or a string.  If it is an integer, it
          represents the index of the positional argument in `args'; if
          it is a string, then it represents a named argument in
          `kwargs'.

          The `args' parameter is set to the list of positional
          arguments to *note vformat(): 1872, and the `kwargs' parameter
          is set to the dictionary of keyword arguments.

          For compound field names, these functions are only called for
          the first component of the field name; subsequent components
          are handled through normal attribute and indexing operations.

          So for example, the field expression ‘0.name’ would cause
          *note get_value(): 1875. to be called with a `key' argument of
          0.  The ‘name’ attribute will be looked up after *note
          get_value(): 1875. returns by calling the built-in *note
          getattr(): 54b. function.

          If the index or keyword refers to an item that does not exist,
          then an *note IndexError: f36. or *note KeyError: 3e9. should
          be raised.

      -- Method: check_unused_args (used_args, args, kwargs)

          Implement checking for unused arguments if desired.  The
          arguments to this function is the set of all argument keys
          that were actually referred to in the format string (integers
          for positional arguments, and strings for named arguments),
          and a reference to the `args' and `kwargs' that was passed to
          vformat.  The set of unused args can be calculated from these
          parameters.  *note check_unused_args(): 1876. is assumed to
          raise an exception if the check fails.

      -- Method: format_field (value, format_spec)

          *note format_field(): 1877. simply calls the global *note
          format(): 5d6. built-in.  The method is provided so that
          subclasses can override it.

      -- Method: convert_field (value, conversion)

          Converts the value (returned by *note get_field(): 1874.)
          given a conversion type (as in the tuple returned by the *note
          parse(): 1873. method).  The default version understands ‘s’
          (str), ‘r’ (repr) and ‘a’ (ascii) conversion types.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3101

   (2) https://www.python.org/dev/peps/pep-3101


File: python.info,  Node: Format String Syntax,  Next: Template strings,  Prev: Custom String Formatting,  Up: string — Common string operations

5.6.1.3 Format String Syntax
............................

The *note str.format(): 5d5. method and the *note Formatter: 8a3. class
share the same syntax for format strings (although in the case of *note
Formatter: 8a3, subclasses can define their own format string syntax).
The syntax is related to that of *note formatted string literals: 296,
but it is less sophisticated and, in particular, does not support
arbitrary expressions.

Format strings contain “replacement fields” surrounded by curly braces
‘{}’.  Anything that is not contained in braces is considered literal
text, which is copied unchanged to the output.  If you need to include a
brace character in the literal text, it can be escaped by doubling: ‘{{’
and ‘}}’.

The grammar for a replacement field is as follows:

          replacement_field ::= "{" [field_name] ["!" conversion] [":" format_spec] "}"
          field_name        ::= arg_name ("." attribute_name | "[" element_index "]")*
          arg_name          ::= [identifier | digit+]
          attribute_name    ::= identifier
          element_index     ::= digit+ | index_string
          index_string      ::= <any source character except "]"> +
          conversion        ::= "r" | "s" | "a"
          format_spec       ::= <described in the next section>

In less formal terms, the replacement field can start with a
`field_name' that specifies the object whose value is to be formatted
and inserted into the output instead of the replacement field.  The
`field_name' is optionally followed by a `conversion' field, which is
preceded by an exclamation point ‘'!'’, and a `format_spec', which is
preceded by a colon ‘':'’.  These specify a non-default format for the
replacement value.

See also the *note Format Specification Mini-Language: 5d9. section.

The `field_name' itself begins with an `arg_name' that is either a
number or a keyword.  If it’s a number, it refers to a positional
argument, and if it’s a keyword, it refers to a named keyword argument.
If the numerical arg_names in a format string are 0, 1, 2, … in
sequence, they can all be omitted (not just some) and the numbers 0, 1,
2, … will be automatically inserted in that order.  Because `arg_name'
is not quote-delimited, it is not possible to specify arbitrary
dictionary keys (e.g., the strings ‘'10'’ or ‘':-]'’) within a format
string.  The `arg_name' can be followed by any number of index or
attribute expressions.  An expression of the form ‘'.name'’ selects the
named attribute using *note getattr(): 54b, while an expression of the
form ‘'[index]'’ does an index lookup using *note __getitem__(): 3a2.

Changed in version 3.1: The positional argument specifiers can be
omitted for *note str.format(): 5d5, so ‘'{} {}'.format(a, b)’ is
equivalent to ‘'{0} {1}'.format(a, b)’.

Changed in version 3.4: The positional argument specifiers can be
omitted for *note Formatter: 8a3.

Some simple format string examples:

     "First, thou shalt count to {0}"  # References first positional argument
     "Bring me a {}"                   # Implicitly references the first positional argument
     "From {} to {}"                   # Same as "From {0} to {1}"
     "My quest is {name}"              # References keyword argument 'name'
     "Weight in tons {0.weight}"       # 'weight' attribute of first positional arg
     "Units destroyed: {players[0]}"   # First element of keyword argument 'players'.

The `conversion' field causes a type coercion before formatting.
Normally, the job of formatting a value is done by the *note
__format__(): a2f. method of the value itself.  However, in some cases
it is desirable to force a type to be formatted as a string, overriding
its own definition of formatting.  By converting the value to a string
before calling *note __format__(): a2f, the normal formatting logic is
bypassed.

Three conversion flags are currently supported: ‘'!s'’ which calls *note
str(): 205. on the value, ‘'!r'’ which calls *note repr(): 8b9. and
‘'!a'’ which calls *note ascii(): e11.

Some examples:

     "Harold's a clever {0!s}"        # Calls str() on the argument first
     "Bring out the holy {name!r}"    # Calls repr() on the argument first
     "More {!a}"                      # Calls ascii() on the argument first

The `format_spec' field contains a specification of how the value should
be presented, including such details as field width, alignment, padding,
decimal precision and so on.  Each value type can define its own
“formatting mini-language” or interpretation of the `format_spec'.

Most built-in types support a common formatting mini-language, which is
described in the next section.

A `format_spec' field can also include nested replacement fields within
it.  These nested replacement fields may contain a field name,
conversion flag and format specification, but deeper nesting is not
allowed.  The replacement fields within the format_spec are substituted
before the `format_spec' string is interpreted.  This allows the
formatting of a value to be dynamically specified.

See the *note Format examples: 1882. section for some examples.

* Menu:

* Format Specification Mini-Language::
* Format examples::


File: python.info,  Node: Format Specification Mini-Language,  Next: Format examples,  Up: Format String Syntax

5.6.1.4 Format Specification Mini-Language
..........................................

“Format specifications” are used within replacement fields contained
within a format string to define how individual values are presented
(see *note Format String Syntax: de0. and *note Formatted string
literals: 296.).  They can also be passed directly to the built-in *note
format(): 5d6. function.  Each formattable type may define how the
format specification is to be interpreted.

Most built-in types implement the following options for format
specifications, although some of the formatting options are only
supported by the numeric types.

A general convention is that an empty format specification produces the
same result as if you had called *note str(): 205. on the value.  A
non-empty format specification typically modifies the result.

The general form of a `standard format specifier' is:

     format_spec     ::= [[fill]align][sign][#][0][width][grouping_option][.precision][type]
     fill            ::= <any character>
     align           ::= "<" | ">" | "=" | "^"
     sign            ::= "+" | "-" | " "
     width           ::= digit+
     grouping_option ::= "_" | ","
     precision       ::= digit+
     type            ::= "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"

If a valid `align' value is specified, it can be preceded by a `fill'
character that can be any character and defaults to a space if omitted.
It is not possible to use a literal curly brace (”‘{’” or “‘}’”) as the
`fill' character in a *note formatted string literal: 296. or when using
the *note str.format(): 5d5. method.  However, it is possible to insert
a curly brace with a nested replacement field.  This limitation doesn’t
affect the *note format(): 5d6. function.

The meaning of the various alignment options is as follows:

     Option        Meaning
                   
     -----------------------------------------------------------------------------
                   
     ‘'<'’         Forces the field to be left-aligned within the available
                   space (this is the default for most objects).
                   
                   
     ‘'>'’         Forces the field to be right-aligned within the available
                   space (this is the default for numbers).
                   
                   
     ‘'='’         Forces the padding to be placed after the sign (if any) but
                   before the digits.  This is used for printing fields in the
                   form ‘+000000120’.  This alignment option is only valid for
                   numeric types.  It becomes the default when ‘0’ immediately
                   precedes the field width.
                   
                   
     ‘'^'’         Forces the field to be centered within the available space.
                   

Note that unless a minimum field width is defined, the field width will
always be the same size as the data to fill it, so that the alignment
option has no meaning in this case.

The `sign' option is only valid for number types, and can be one of the
following:

     Option        Meaning
                   
     -----------------------------------------------------------------------------
                   
     ‘'+'’         indicates that a sign should be used for both positive as
                   well as negative numbers.
                   
                   
     ‘'-'’         indicates that a sign should be used only for negative
                   numbers (this is the default behavior).
                   
                   
     space         indicates that a leading space should be used on positive
                   numbers, and a minus sign on negative numbers.
                   

The ‘'#'’ option causes the “alternate form” to be used for the
conversion.  The alternate form is defined differently for different
types.  This option is only valid for integer, float and complex types.
For integers, when binary, octal, or hexadecimal output is used, this
option adds the respective prefix ‘'0b'’, ‘'0o'’, ‘'0x'’, or ‘'0X'’ to
the output value.  For float and complex the alternate form causes the
result of the conversion to always contain a decimal-point character,
even if no digits follow it.  Normally, a decimal-point character
appears in the result of these conversions only if a digit follows it.
In addition, for ‘'g'’ and ‘'G'’ conversions, trailing zeros are not
removed from the result.

The ‘','’ option signals the use of a comma for a thousands separator.
For a locale aware separator, use the ‘'n'’ integer presentation type
instead.

Changed in version 3.1: Added the ‘','’ option (see also PEP 378(1)).

The ‘'_'’ option signals the use of an underscore for a thousands
separator for floating point presentation types and for integer
presentation type ‘'d'’.  For integer presentation types ‘'b'’, ‘'o'’,
‘'x'’, and ‘'X'’, underscores will be inserted every 4 digits.  For
other presentation types, specifying this option is an error.

Changed in version 3.6: Added the ‘'_'’ option (see also PEP 515(2)).

`width' is a decimal integer defining the minimum total field width,
including any prefixes, separators, and other formatting characters.  If
not specified, then the field width will be determined by the content.

When no explicit alignment is given, preceding the `width' field by a
zero (‘'0'’) character enables sign-aware zero-padding for numeric
types.  This is equivalent to a `fill' character of ‘'0'’ with an
`alignment' type of ‘'='’.

The `precision' is a decimal number indicating how many digits should be
displayed after the decimal point for a floating point value formatted
with ‘'f'’ and ‘'F'’, or before and after the decimal point for a
floating point value formatted with ‘'g'’ or ‘'G'’.  For non-number
types the field indicates the maximum field size - in other words, how
many characters will be used from the field content.  The `precision' is
not allowed for integer values.

Finally, the `type' determines how the data should be presented.

The available string presentation types are:

     Type          Meaning
                   
     -----------------------------------------------------------------------------
                   
     ‘'s'’         String format.  This is the default type for strings and may
                   be omitted.
                   
                   
     None          The same as ‘'s'’.
                   

The available integer presentation types are:

     Type          Meaning
                   
     -----------------------------------------------------------------------------
                   
     ‘'b'’         Binary format.  Outputs the number in base 2.
                   
                   
     ‘'c'’         Character.  Converts the integer to the corresponding
                   unicode character before printing.
                   
                   
     ‘'d'’         Decimal Integer.  Outputs the number in base 10.
                   
                   
     ‘'o'’         Octal format.  Outputs the number in base 8.
                   
                   
     ‘'x'’         Hex format.  Outputs the number in base 16, using lower-case
                   letters for the digits above 9.
                   
                   
     ‘'X'’         Hex format.  Outputs the number in base 16, using upper-case
                   letters for the digits above 9.  In case ‘'#'’ is specified,
                   the prefix ‘'0x'’ will be upper-cased to ‘'0X'’ as well.
                   
                   
     ‘'n'’         Number.  This is the same as ‘'d'’, except that it uses the
                   current locale setting to insert the appropriate number
                   separator characters.
                   
                   
     None          The same as ‘'d'’.
                   

In addition to the above presentation types, integers can be formatted
with the floating point presentation types listed below (except ‘'n'’
and ‘None’).  When doing so, *note float(): 1fd. is used to convert the
integer to a floating point number before formatting.

The available presentation types for *note float: 1fd. and *note
Decimal: 2c0. values are:

     Type          Meaning
                   
     -----------------------------------------------------------------------------
                   
     ‘'e'’         Scientific notation.  For a given precision ‘p’, formats the
                   number in scientific notation with the letter ‘e’ separating
                   the coefficient from the exponent.  The coefficient has one
                   digit before and ‘p’ digits after the decimal point, for a
                   total of ‘p + 1’ significant digits.  With no precision
                   given, uses a precision of ‘6’ digits after the decimal
                   point for *note float: 1fd, and shows all coefficient digits
                   for *note Decimal: 2c0.  If no digits follow the decimal
                   point, the decimal point is also removed unless the ‘#’
                   option is used.
                   
                   
     ‘'E'’         Scientific notation.  Same as ‘'e'’ except it uses an upper
                   case ‘E’ as the separator character.
                   
                   
     ‘'f'’         Fixed-point notation.  For a given precision ‘p’, formats
                   the number as a decimal number with exactly ‘p’ digits
                   following the decimal point.  With no precision given, uses
                   a precision of ‘6’ digits after the decimal point for
                   *note float: 1fd, and uses a precision large enough to show
                   all coefficient digits for *note Decimal: 2c0.  If no digits
                   follow the decimal point, the decimal point is also removed
                   unless the ‘#’ option is used.
                   
                   
     ‘'F'’         Fixed-point notation.  Same as ‘'f'’, but converts ‘nan’ to
                   ‘NAN’ and ‘inf’ to ‘INF’.
                   
                   
     ‘'g'’         General format.  For a given precision ‘p >= 1’, this rounds
                   the number to ‘p’ significant digits and then formats the
                   result in either fixed-point format or in scientific
                   notation, depending on its magnitude.  A precision of ‘0’ is
                   treated as equivalent to a precision of ‘1’.
                   
                   The precise rules are as follows: suppose that the result
                   formatted with presentation type ‘'e'’ and precision ‘p-1’
                   would have exponent ‘exp’.  Then, if ‘m <= exp < p’, where
                   ‘m’ is -4 for floats and -6 for *note Decimals: 2c0, the
                   number is formatted with presentation type ‘'f'’ and
                   precision ‘p-1-exp’.  Otherwise, the number is formatted
                   with presentation type ‘'e'’ and precision ‘p-1’.  In both
                   cases insignificant trailing zeros are removed from the
                   significand, and the decimal point is also removed if there
                   are no remaining digits following it, unless the ‘'#'’
                   option is used.
                   
                   With no precision given, uses a precision of ‘6’ significant
                   digits for *note float: 1fd.  For *note Decimal: 2c0, the
                   coefficient of the result is formed from the coefficient
                   digits of the value; scientific notation is used for values
                   smaller than ‘1e-6’ in absolute value and values where the
                   place value of the least significant digit is larger than 1,
                   and fixed-point notation is used otherwise.
                   
                   Positive and negative infinity, positive and negative zero,
                   and nans, are formatted as ‘inf’, ‘-inf’, ‘0’, ‘-0’ and
                   ‘nan’ respectively, regardless of the precision.
                   
                   
     ‘'G'’         General format.  Same as ‘'g'’ except switches to ‘'E'’ if
                   the number gets too large.  The representations of infinity
                   and NaN are uppercased, too.
                   
                   
     ‘'n'’         Number.  This is the same as ‘'g'’, except that it uses the
                   current locale setting to insert the appropriate number
                   separator characters.
                   
                   
     ‘'%'’         Percentage.  Multiplies the number by 100 and displays in
                   fixed (‘'f'’) format, followed by a percent sign.
                   
                   
     None          For *note float: 1fd. this is the same as ‘'g'’, except that
                   when fixed-point notation is used to format the result, it
                   always includes at least one digit past the decimal point.
                   The precision used is as large as needed to represent the
                   given value faithfully.
                   
                   For *note Decimal: 2c0, this is the same as either ‘'g'’ or
                   ‘'G'’ depending on the value of ‘context.capitals’ for the
                   current decimal context.
                   
                   The overall effect is to match the output of
                   *note str(): 205. as altered by the other format modifiers.
                   

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0378

   (2) https://www.python.org/dev/peps/pep-0515


File: python.info,  Node: Format examples,  Prev: Format Specification Mini-Language,  Up: Format String Syntax

5.6.1.5 Format examples
.......................

This section contains examples of the *note str.format(): 5d5. syntax
and comparison with the old ‘%’-formatting.

In most of the cases the syntax is similar to the old ‘%’-formatting,
with the addition of the ‘{}’ and with ‘:’ used instead of ‘%’.  For
example, ‘'%03.2f'’ can be translated to ‘'{:03.2f}'’.

The new format syntax also supports new and different options, shown in
the following examples.

Accessing arguments by position:

     >>> '{0}, {1}, {2}'.format('a', 'b', 'c')
     'a, b, c'
     >>> '{}, {}, {}'.format('a', 'b', 'c')  # 3.1+ only
     'a, b, c'
     >>> '{2}, {1}, {0}'.format('a', 'b', 'c')
     'c, b, a'
     >>> '{2}, {1}, {0}'.format(*'abc')      # unpacking argument sequence
     'c, b, a'
     >>> '{0}{1}{0}'.format('abra', 'cad')   # arguments' indices can be repeated
     'abracadabra'

Accessing arguments by name:

     >>> 'Coordinates: {latitude}, {longitude}'.format(latitude='37.24N', longitude='-115.81W')
     'Coordinates: 37.24N, -115.81W'
     >>> coord = {'latitude': '37.24N', 'longitude': '-115.81W'}
     >>> 'Coordinates: {latitude}, {longitude}'.format(**coord)
     'Coordinates: 37.24N, -115.81W'

Accessing arguments’ attributes:

     >>> c = 3-5j
     >>> ('The complex number {0} is formed from the real part {0.real} '
     ...  'and the imaginary part {0.imag}.').format(c)
     'The complex number (3-5j) is formed from the real part 3.0 and the imaginary part -5.0.'
     >>> class Point:
     ...     def __init__(self, x, y):
     ...         self.x, self.y = x, y
     ...     def __str__(self):
     ...         return 'Point({self.x}, {self.y})'.format(self=self)
     ...
     >>> str(Point(4, 2))
     'Point(4, 2)'

Accessing arguments’ items:

     >>> coord = (3, 5)
     >>> 'X: {0[0]};  Y: {0[1]}'.format(coord)
     'X: 3;  Y: 5'

Replacing ‘%s’ and ‘%r’:

     >>> "repr() shows quotes: {!r}; str() doesn't: {!s}".format('test1', 'test2')
     "repr() shows quotes: 'test1'; str() doesn't: test2"

Aligning the text and specifying a width:

     >>> '{:<30}'.format('left aligned')
     'left aligned                  '
     >>> '{:>30}'.format('right aligned')
     '                 right aligned'
     >>> '{:^30}'.format('centered')
     '           centered           '
     >>> '{:*^30}'.format('centered')  # use '*' as a fill char
     '***********centered***********'

Replacing ‘%+f’, ‘%-f’, and ‘% f’ and specifying a sign:

     >>> '{:+f}; {:+f}'.format(3.14, -3.14)  # show it always
     '+3.140000; -3.140000'
     >>> '{: f}; {: f}'.format(3.14, -3.14)  # show a space for positive numbers
     ' 3.140000; -3.140000'
     >>> '{:-f}; {:-f}'.format(3.14, -3.14)  # show only the minus -- same as '{:f}; {:f}'
     '3.140000; -3.140000'

Replacing ‘%x’ and ‘%o’ and converting the value to different bases:

     >>> # format also supports binary numbers
     >>> "int: {0:d};  hex: {0:x};  oct: {0:o};  bin: {0:b}".format(42)
     'int: 42;  hex: 2a;  oct: 52;  bin: 101010'
     >>> # with 0x, 0o, or 0b as prefix:
     >>> "int: {0:d};  hex: {0:#x};  oct: {0:#o};  bin: {0:#b}".format(42)
     'int: 42;  hex: 0x2a;  oct: 0o52;  bin: 0b101010'

Using the comma as a thousands separator:

     >>> '{:,}'.format(1234567890)
     '1,234,567,890'

Expressing a percentage:

     >>> points = 19
     >>> total = 22
     >>> 'Correct answers: {:.2%}'.format(points/total)
     'Correct answers: 86.36%'

Using type-specific formatting:

     >>> import datetime
     >>> d = datetime.datetime(2010, 7, 4, 12, 15, 58)
     >>> '{:%Y-%m-%d %H:%M:%S}'.format(d)
     '2010-07-04 12:15:58'

Nesting arguments and more complex examples:

     >>> for align, text in zip('<^>', ['left', 'center', 'right']):
     ...     '{0:{fill}{align}16}'.format(text, fill=align, align=align)
     ...
     'left<<<<<<<<<<<<'
     '^^^^^center^^^^^'
     '>>>>>>>>>>>right'
     >>>
     >>> octets = [192, 168, 0, 1]
     >>> '{:02X}{:02X}{:02X}{:02X}'.format(*octets)
     'C0A80001'
     >>> int(_, 16)
     3232235521
     >>>
     >>> width = 5
     >>> for num in range(5,12):
     ...     for base in 'dXob':
     ...         print('{0:{width}{base}}'.format(num, base=base, width=width), end=' ')
     ...     print()
     ...
         5     5     5   101
         6     6     6   110
         7     7     7   111
         8     8    10  1000
         9     9    11  1001
        10     A    12  1010
        11     B    13  1011


File: python.info,  Node: Template strings,  Next: Helper functions,  Prev: Format String Syntax,  Up: string — Common string operations

5.6.1.6 Template strings
........................

Template strings provide simpler string substitutions as described in
PEP 292(1).  A primary use case for template strings is for
internationalization (i18n) since in that context, the simpler syntax
and functionality makes it easier to translate than other built-in
string formatting facilities in Python.  As an example of a library
built on template strings for i18n, see the flufl.i18n(2) package.

Template strings support ‘$’-based substitutions, using the following
rules:

   * ‘$$’ is an escape; it is replaced with a single ‘$’.

   * ‘$identifier’ names a substitution placeholder matching a mapping
     key of ‘"identifier"’.  By default, ‘"identifier"’ is restricted to
     any case-insensitive ASCII alphanumeric string (including
     underscores) that starts with an underscore or ASCII letter.  The
     first non-identifier character after the ‘$’ character terminates
     this placeholder specification.

   * ‘${identifier}’ is equivalent to ‘$identifier’.  It is required
     when valid identifier characters follow the placeholder but are not
     part of the placeholder, such as ‘"${noun}ification"’.

Any other appearance of ‘$’ in the string will result in a *note
ValueError: 16d. being raised.

The *note string: f6. module provides a *note Template: 4f1. class that
implements these rules.  The methods of *note Template: 4f1. are:

 -- Class: string.Template (template)

     The constructor takes a single argument which is the template
     string.

      -- Method: substitute (mapping={}, /, **kwds)

          Performs the template substitution, returning a new string.
          `mapping' is any dictionary-like object with keys that match
          the placeholders in the template.  Alternatively, you can
          provide keyword arguments, where the keywords are the
          placeholders.  When both `mapping' and `kwds' are given and
          there are duplicates, the placeholders from `kwds' take
          precedence.

      -- Method: safe_substitute (mapping={}, /, **kwds)

          Like *note substitute(): 1433, except that if placeholders are
          missing from `mapping' and `kwds', instead of raising a *note
          KeyError: 3e9. exception, the original placeholder will appear
          in the resulting string intact.  Also, unlike with *note
          substitute(): 1433, any other appearances of the ‘$’ will
          simply return ‘$’ instead of raising *note ValueError: 16d.

          While other exceptions may still occur, this method is called
          “safe” because it always tries to return a usable string
          instead of raising an exception.  In another sense, *note
          safe_substitute(): 1434. may be anything other than safe,
          since it will silently ignore malformed templates containing
          dangling delimiters, unmatched braces, or placeholders that
          are not valid Python identifiers.

     *note Template: 4f1. instances also provide one public data
     attribute:

      -- Attribute: template

          This is the object passed to the constructor’s `template'
          argument.  In general, you shouldn’t change it, but read-only
          access is not enforced.

Here is an example of how to use a Template:

     >>> from string import Template
     >>> s = Template('$who likes $what')
     >>> s.substitute(who='tim', what='kung pao')
     'tim likes kung pao'
     >>> d = dict(who='tim')
     >>> Template('Give $who $100').substitute(d)
     Traceback (most recent call last):
     ...
     ValueError: Invalid placeholder in string: line 1, col 11
     >>> Template('$who likes $what').substitute(d)
     Traceback (most recent call last):
     ...
     KeyError: 'what'
     >>> Template('$who likes $what').safe_substitute(d)
     'tim likes $what'

Advanced usage: you can derive subclasses of *note Template: 4f1. to
customize the placeholder syntax, delimiter character, or the entire
regular expression used to parse template strings.  To do this, you can
override these class attributes:

   * `delimiter' – This is the literal string describing a placeholder
     introducing delimiter.  The default value is ‘$’.  Note that this
     should `not' be a regular expression, as the implementation will
     call *note re.escape(): 590. on this string as needed.  Note
     further that you cannot change the delimiter after class creation
     (i.e.  a different delimiter must be set in the subclass’s class
     namespace).

   * `idpattern' – This is the regular expression describing the pattern
     for non-braced placeholders.  The default value is the regular
     expression ‘(?a:[_a-z][_a-z0-9]*)’.  If this is given and
     `braceidpattern' is ‘None’ this pattern will also apply to braced
     placeholders.

          Note: Since default `flags' is ‘re.IGNORECASE’, pattern
          ‘[a-z]’ can match with some non-ASCII characters.  That’s why
          we use the local ‘a’ flag here.

     Changed in version 3.7: `braceidpattern' can be used to define
     separate patterns used inside and outside the braces.

   * `braceidpattern' – This is like `idpattern' but describes the
     pattern for braced placeholders.  Defaults to ‘None’ which means to
     fall back to `idpattern' (i.e.  the same pattern is used both
     inside and outside braces).  If given, this allows you to define
     different patterns for braced and unbraced placeholders.

     New in version 3.7.

   * `flags' – The regular expression flags that will be applied when
     compiling the regular expression used for recognizing
     substitutions.  The default value is ‘re.IGNORECASE’.  Note that
     ‘re.VERBOSE’ will always be added to the flags, so custom
     `idpattern's must follow conventions for verbose regular
     expressions.

     New in version 3.2.

Alternatively, you can provide the entire regular expression pattern by
overriding the class attribute `pattern'.  If you do this, the value
must be a regular expression object with four named capturing groups.
The capturing groups correspond to the rules given above, along with the
invalid placeholder rule:

   * `escaped' – This group matches the escape sequence, e.g.  ‘$$’, in
     the default pattern.

   * `named' – This group matches the unbraced placeholder name; it
     should not include the delimiter in capturing group.

   * `braced' – This group matches the brace enclosed placeholder name;
     it should not include either the delimiter or braces in the
     capturing group.

   * `invalid' – This group matches any other delimiter pattern (usually
     a single delimiter), and it should appear last in the regular
     expression.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0292

   (2) http://flufli18n.readthedocs.io/en/latest/


File: python.info,  Node: Helper functions,  Prev: Template strings,  Up: string — Common string operations

5.6.1.7 Helper functions
........................

 -- Function: string.capwords (s, sep=None)

     Split the argument into words using *note str.split(): 890,
     capitalize each word using *note str.capitalize(): 1776, and join
     the capitalized words using *note str.join(): 1766.  If the
     optional second argument `sep' is absent or ‘None’, runs of
     whitespace characters are replaced by a single space and leading
     and trailing whitespace are removed, otherwise `sep' is used to
     split and join the words.


File: python.info,  Node: re — Regular expression operations,  Next: difflib — Helpers for computing deltas,  Prev: string — Common string operations,  Up: Text Processing Services

5.6.2 ‘re’ — Regular expression operations
------------------------------------------

`Source code:' Lib/re.py(1)

__________________________________________________________________

This module provides regular expression matching operations similar to
those found in Perl.

Both patterns and strings to be searched can be Unicode strings (*note
str: 205.) as well as 8-bit strings (*note bytes: 172.).  However,
Unicode strings and 8-bit strings cannot be mixed: that is, you cannot
match a Unicode string with a byte pattern or vice-versa; similarly,
when asking for a substitution, the replacement string must be of the
same type as both the pattern and the search string.

Regular expressions use the backslash character (‘'\'’) to indicate
special forms or to allow special characters to be used without invoking
their special meaning.  This collides with Python’s usage of the same
character for the same purpose in string literals; for example, to match
a literal backslash, one might have to write ‘'\\\\'’ as the pattern
string, because the regular expression must be ‘\\’, and each backslash
must be expressed as ‘\\’ inside a regular Python string literal.  Also,
please note that any invalid escape sequences in Python’s usage of the
backslash in string literals now generate a *note DeprecationWarning:
15a. and in the future this will become a *note SyntaxError: 55a.  This
behaviour will happen even if it is a valid escape sequence for a
regular expression.

The solution is to use Python’s raw string notation for regular
expression patterns; backslashes are not handled in any special way in a
string literal prefixed with ‘'r'’.  So ‘r"\n"’ is a two-character
string containing ‘'\'’ and ‘'n'’, while ‘"\n"’ is a one-character
string containing a newline.  Usually patterns will be expressed in
Python code using this raw string notation.

It is important to note that most regular expression operations are
available as module-level functions and methods on *note compiled
regular expressions: 983.  The functions are shortcuts that don’t
require you to compile a regex object first, but miss some fine-tuning
parameters.

See also
........

The third-party regex(2) module, which has an API compatible with the
standard library *note re: dd. module, but offers additional
functionality and a more thorough Unicode support.

* Menu:

* Regular Expression Syntax::
* Module Contents::
* Regular Expression Objects::
* Match Objects::
* Regular Expression Examples::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/re.py

   (2) https://pypi.org/project/regex/


File: python.info,  Node: Regular Expression Syntax,  Next: Module Contents,  Up: re — Regular expression operations

5.6.2.1 Regular Expression Syntax
.................................

A regular expression (or RE) specifies a set of strings that matches it;
the functions in this module let you check if a particular string
matches a given regular expression (or if a given regular expression
matches a particular string, which comes down to the same thing).

Regular expressions can be concatenated to form new regular expressions;
if `A' and `B' are both regular expressions, then `AB' is also a regular
expression.  In general, if a string `p' matches `A' and another string
`q' matches `B', the string `pq' will match AB. This holds unless `A' or
`B' contain low precedence operations; boundary conditions between `A'
and `B'; or have numbered group references.  Thus, complex expressions
can easily be constructed from simpler primitive expressions like the
ones described here.  For details of the theory and implementation of
regular expressions, consult the Friedl book *note [Frie09]: 1895, or
almost any textbook about compiler construction.

A brief explanation of the format of regular expressions follows.  For
further information and a gentler presentation, consult the *note
Regular Expression HOWTO: 1896.

Regular expressions can contain both special and ordinary characters.
Most ordinary characters, like ‘'A'’, ‘'a'’, or ‘'0'’, are the simplest
regular expressions; they simply match themselves.  You can concatenate
ordinary characters, so ‘last’ matches the string ‘'last'’.  (In the
rest of this section, we’ll write RE’s in ‘this special style’, usually
without quotes, and strings to be matched ‘'in single quotes'’.)

Some characters, like ‘'|'’ or ‘'('’, are special.  Special characters
either stand for classes of ordinary characters, or affect how the
regular expressions around them are interpreted.

Repetition qualifiers (‘*’, ‘+’, ‘?’, ‘{m,n}’, etc) cannot be directly
nested.  This avoids ambiguity with the non-greedy modifier suffix ‘?’,
and with other modifiers in other implementations.  To apply a second
repetition to an inner repetition, parentheses may be used.  For
example, the expression ‘(?:a{6})*’ matches any multiple of six ‘'a'’
characters.

The special characters are:

‘.’

     (Dot.)  In the default mode, this matches any character except a
     newline.  If the *note DOTALL: 1897. flag has been specified, this
     matches any character including a newline.

‘^’

     (Caret.)  Matches the start of the string, and in *note MULTILINE:
     1898. mode also matches immediately after each newline.

‘$’

     Matches the end of the string or just before the newline at the end
     of the string, and in *note MULTILINE: 1898. mode also matches
     before a newline.  ‘foo’ matches both ‘foo’ and ‘foobar’, while the
     regular expression ‘foo$’ matches only ‘foo’.  More interestingly,
     searching for ‘foo.$’ in ‘'foo1\nfoo2\n'’ matches ‘foo2’ normally,
     but ‘foo1’ in *note MULTILINE: 1898. mode; searching for a single
     ‘$’ in ‘'foo\n'’ will find two (empty) matches: one just before the
     newline, and one at the end of the string.

‘*’

     Causes the resulting RE to match 0 or more repetitions of the
     preceding RE, as many repetitions as are possible.  ‘ab*’ will
     match ‘a’, ‘ab’, or ‘a’ followed by any number of ‘b’s.

‘+’

     Causes the resulting RE to match 1 or more repetitions of the
     preceding RE. ‘ab+’ will match ‘a’ followed by any non-zero number
     of ‘b’s; it will not match just ‘a’.

‘?’

     Causes the resulting RE to match 0 or 1 repetitions of the
     preceding RE. ‘ab?’ will match either ‘a’ or ‘ab’.

‘*?’, ‘+?’, ‘??’

     The ‘'*'’, ‘'+'’, and ‘'?'’ qualifiers are all `greedy'; they match
     as much text as possible.  Sometimes this behaviour isn’t desired;
     if the RE ‘<.*>’ is matched against ‘'<a> b <c>'’, it will match
     the entire string, and not just ‘'<a>'’.  Adding ‘?’ after the
     qualifier makes it perform the match in `non-greedy' or `minimal'
     fashion; as `few' characters as possible will be matched.  Using
     the RE ‘<.*?>’ will match only ‘'<a>'’.

‘{m}’

     Specifies that exactly `m' copies of the previous RE should be
     matched; fewer matches cause the entire RE not to match.  For
     example, ‘a{6}’ will match exactly six ‘'a'’ characters, but not
     five.

‘{m,n}’

     Causes the resulting RE to match from `m' to `n' repetitions of the
     preceding RE, attempting to match as many repetitions as possible.
     For example, ‘a{3,5}’ will match from 3 to 5 ‘'a'’ characters.
     Omitting `m' specifies a lower bound of zero, and omitting `n'
     specifies an infinite upper bound.  As an example, ‘a{4,}b’ will
     match ‘'aaaab'’ or a thousand ‘'a'’ characters followed by a ‘'b'’,
     but not ‘'aaab'’.  The comma may not be omitted or the modifier
     would be confused with the previously described form.

‘{m,n}?’

     Causes the resulting RE to match from `m' to `n' repetitions of the
     preceding RE, attempting to match as `few' repetitions as possible.
     This is the non-greedy version of the previous qualifier.  For
     example, on the 6-character string ‘'aaaaaa'’, ‘a{3,5}’ will match
     5 ‘'a'’ characters, while ‘a{3,5}?’ will only match 3 characters.

‘\’

     Either escapes special characters (permitting you to match
     characters like ‘'*'’, ‘'?'’, and so forth), or signals a special
     sequence; special sequences are discussed below.

     If you’re not using a raw string to express the pattern, remember
     that Python also uses the backslash as an escape sequence in string
     literals; if the escape sequence isn’t recognized by Python’s
     parser, the backslash and subsequent character are included in the
     resulting string.  However, if Python would recognize the resulting
     sequence, the backslash should be repeated twice.  This is
     complicated and hard to understand, so it’s highly recommended that
     you use raw strings for all but the simplest expressions.

‘[]’

     Used to indicate a set of characters.  In a set:

        * Characters can be listed individually, e.g.  ‘[amk]’ will
          match ‘'a'’, ‘'m'’, or ‘'k'’.

        * Ranges of characters can be indicated by giving two characters
          and separating them by a ‘'-'’, for example ‘[a-z]’ will match
          any lowercase ASCII letter, ‘[0-5][0-9]’ will match all the
          two-digits numbers from ‘00’ to ‘59’, and ‘[0-9A-Fa-f]’ will
          match any hexadecimal digit.  If ‘-’ is escaped (e.g.
          ‘[a\-z]’) or if it’s placed as the first or last character
          (e.g.  ‘[-a]’ or ‘[a-]’), it will match a literal ‘'-'’.

        * Special characters lose their special meaning inside sets.
          For example, ‘[(+*)]’ will match any of the literal characters
          ‘'('’, ‘'+'’, ‘'*'’, or ‘')'’.

        * Character classes such as ‘\w’ or ‘\S’ (defined below) are
          also accepted inside a set, although the characters they match
          depends on whether *note ASCII: 4cf. or *note LOCALE: 4d0.
          mode is in force.

        * Characters that are not within a range can be matched by
          `complementing' the set.  If the first character of the set is
          ‘'^'’, all the characters that are `not' in the set will be
          matched.  For example, ‘[^5]’ will match any character except
          ‘'5'’, and ‘[^^]’ will match any character except ‘'^'’.  ‘^’
          has no special meaning if it’s not the first character in the
          set.

        * To match a literal ‘']'’ inside a set, precede it with a
          backslash, or place it at the beginning of the set.  For
          example, both ‘[()[\]{}]’ and ‘[]()[{}]’ will both match a
          parenthesis.

        * Support of nested sets and set operations as in Unicode
          Technical Standard #18(1) might be added in the future.  This
          would change the syntax, so to facilitate this change a *note
          FutureWarning: 435. will be raised in ambiguous cases for the
          time being.  That includes sets starting with a literal ‘'['’
          or containing literal character sequences ‘'--'’, ‘'&&'’,
          ‘'~~'’, and ‘'||'’.  To avoid a warning escape them with a
          backslash.

     Changed in version 3.7: *note FutureWarning: 435. is raised if a
     character set contains constructs that will change semantically in
     the future.

‘|’

     ‘A|B’, where `A' and `B' can be arbitrary REs, creates a regular
     expression that will match either `A' or `B'. An arbitrary number
     of REs can be separated by the ‘'|'’ in this way.  This can be used
     inside groups (see below) as well.  As the target string is
     scanned, REs separated by ‘'|'’ are tried from left to right.  When
     one pattern completely matches, that branch is accepted.  This
     means that once `A' matches, `B' will not be tested further, even
     if it would produce a longer overall match.  In other words, the
     ‘'|'’ operator is never greedy.  To match a literal ‘'|'’, use
     ‘\|’, or enclose it inside a character class, as in ‘[|]’.

‘(...)’

     Matches whatever regular expression is inside the parentheses, and
     indicates the start and end of a group; the contents of a group can
     be retrieved after a match has been performed, and can be matched
     later in the string with the ‘\number’ special sequence, described
     below.  To match the literals ‘'('’ or ‘')'’, use ‘\(’ or ‘\)’, or
     enclose them inside a character class: ‘[(]’, ‘[)]’.

‘(?...)’

     This is an extension notation (a ‘'?'’ following a ‘'('’ is not
     meaningful otherwise).  The first character after the ‘'?'’
     determines what the meaning and further syntax of the construct is.
     Extensions usually do not create a new group; ‘(?P<name>...)’ is
     the only exception to this rule.  Following are the currently
     supported extensions.

‘(?aiLmsux)’

     (One or more letters from the set ‘'a'’, ‘'i'’, ‘'L'’, ‘'m'’,
     ‘'s'’, ‘'u'’, ‘'x'’.)  The group matches the empty string; the
     letters set the corresponding flags: *note re.A: 1899. (ASCII-only
     matching), *note re.I: 189a. (ignore case), *note re.L: 189b.
     (locale dependent), *note re.M: 189c. (multi-line), *note re.S:
     189d. (dot matches all), ‘re.U’ (Unicode matching), and *note re.X:
     189e. (verbose), for the entire regular expression.  (The flags are
     described in *note Module Contents: 189f.)  This is useful if you
     wish to include the flags as part of the regular expression,
     instead of passing a `flag' argument to the *note re.compile():
     54d. function.  Flags should be used first in the expression
     string.

‘(?:...)’

     A non-capturing version of regular parentheses.  Matches whatever
     regular expression is inside the parentheses, but the substring
     matched by the group `cannot' be retrieved after performing a match
     or referenced later in the pattern.

‘(?aiLmsux-imsx:...)’

     (Zero or more letters from the set ‘'a'’, ‘'i'’, ‘'L'’, ‘'m'’,
     ‘'s'’, ‘'u'’, ‘'x'’, optionally followed by ‘'-'’ followed by one
     or more letters from the ‘'i'’, ‘'m'’, ‘'s'’, ‘'x'’.)  The letters
     set or remove the corresponding flags: *note re.A: 1899.
     (ASCII-only matching), *note re.I: 189a. (ignore case), *note re.L:
     189b. (locale dependent), *note re.M: 189c. (multi-line), *note
     re.S: 189d. (dot matches all), ‘re.U’ (Unicode matching), and *note
     re.X: 189e. (verbose), for the part of the expression.  (The flags
     are described in *note Module Contents: 189f.)

     The letters ‘'a'’, ‘'L'’ and ‘'u'’ are mutually exclusive when used
     as inline flags, so they can’t be combined or follow ‘'-'’.
     Instead, when one of them appears in an inline group, it overrides
     the matching mode in the enclosing group.  In Unicode patterns
     ‘(?a:...)’ switches to ASCII-only matching, and ‘(?u:...)’ switches
     to Unicode matching (default).  In byte pattern ‘(?L:...)’ switches
     to locale depending matching, and ‘(?a:...)’ switches to ASCII-only
     matching (default).  This override is only in effect for the narrow
     inline group, and the original matching mode is restored outside of
     the group.

     New in version 3.6.

     Changed in version 3.7: The letters ‘'a'’, ‘'L'’ and ‘'u'’ also can
     be used in a group.

‘(?P<name>...)’

     Similar to regular parentheses, but the substring matched by the
     group is accessible via the symbolic group name `name'.  Group
     names must be valid Python identifiers, and each group name must be
     defined only once within a regular expression.  A symbolic group is
     also a numbered group, just as if the group were not named.

     Named groups can be referenced in three contexts.  If the pattern
     is ‘(?P<quote>['"]).*?(?P=quote)’ (i.e.  matching a string quoted
     with either single or double quotes):

     Context of reference to group “quote”       Ways to reference it
                                                 
     -----------------------------------------------------------------------------------
                                                 
     in the same pattern itself                     * ‘(?P=quote)’ (as shown)
                                                 
                                                    * ‘\1’
                                                 
                                                 
     when processing match object `m'               * ‘m.group('quote')’
                                                 
                                                    * ‘m.end('quote')’ (etc.)
                                                 
                                                 
     in a string passed to the `repl' argument      * ‘\g<quote>’
     of ‘re.sub()’                               
                                                    * ‘\g<1>’
                                                 
                                                    * ‘\1’
                                                 

‘(?P=name)’

     A backreference to a named group; it matches whatever text was
     matched by the earlier group named `name'.

‘(?#...)’

     A comment; the contents of the parentheses are simply ignored.

‘(?=...)’

     Matches if ‘...’ matches next, but doesn’t consume any of the
     string.  This is called a `lookahead assertion'.  For example,
     ‘Isaac (?=Asimov)’ will match ‘'Isaac '’ only if it’s followed by
     ‘'Asimov'’.

‘(?!...)’

     Matches if ‘...’ doesn’t match next.  This is a `negative lookahead
     assertion'.  For example, ‘Isaac (?!Asimov)’ will match ‘'Isaac '’
     only if it’s `not' followed by ‘'Asimov'’.

‘(?<=...)’

     Matches if the current position in the string is preceded by a
     match for ‘...’ that ends at the current position.  This is called
     a `positive lookbehind assertion'.  ‘(?<=abc)def’ will find a match
     in ‘'abcdef'’, since the lookbehind will back up 3 characters and
     check if the contained pattern matches.  The contained pattern must
     only match strings of some fixed length, meaning that ‘abc’ or
     ‘a|b’ are allowed, but ‘a*’ and ‘a{3,4}’ are not.  Note that
     patterns which start with positive lookbehind assertions will not
     match at the beginning of the string being searched; you will most
     likely want to use the *note search(): c82. function rather than
     the *note match(): c83. function:

          >>> import re
          >>> m = re.search('(?<=abc)def', 'abcdef')
          >>> m.group(0)
          'def'

     This example looks for a word following a hyphen:

          >>> m = re.search(r'(?<=-)\w+', 'spam-egg')
          >>> m.group(0)
          'egg'

     Changed in version 3.5: Added support for group references of fixed
     length.

‘(?<!...)’

     Matches if the current position in the string is not preceded by a
     match for ‘...’.  This is called a `negative lookbehind assertion'.
     Similar to positive lookbehind assertions, the contained pattern
     must only match strings of some fixed length.  Patterns which start
     with negative lookbehind assertions may match at the beginning of
     the string being searched.

‘(?(id/name)yes-pattern|no-pattern)’

     Will try to match with ‘yes-pattern’ if the group with given `id'
     or `name' exists, and with ‘no-pattern’ if it doesn’t.
     ‘no-pattern’ is optional and can be omitted.  For example,
     ‘(<)?(\w+@\w+(?:\.\w+)+)(?(1)>|$)’ is a poor email matching
     pattern, which will match with ‘'<user@host.com>'’ as well as
     ‘'user@host.com'’, but not with ‘'<user@host.com'’ nor
     ‘'user@host.com>'’.

The special sequences consist of ‘'\'’ and a character from the list
below.  If the ordinary character is not an ASCII digit or an ASCII
letter, then the resulting RE will match the second character.  For
example, ‘\$’ matches the character ‘'$'’.

‘\number’

     Matches the contents of the group of the same number.  Groups are
     numbered starting from 1.  For example, ‘(.+) \1’ matches ‘'the
     the'’ or ‘'55 55'’, but not ‘'thethe'’ (note the space after the
     group).  This special sequence can only be used to match one of the
     first 99 groups.  If the first digit of `number' is 0, or `number'
     is 3 octal digits long, it will not be interpreted as a group
     match, but as the character with octal value `number'.  Inside the
     ‘'['’ and ‘']'’ of a character class, all numeric escapes are
     treated as characters.

‘\A’

     Matches only at the start of the string.

‘\b’

     Matches the empty string, but only at the beginning or end of a
     word.  A word is defined as a sequence of word characters.  Note
     that formally, ‘\b’ is defined as the boundary between a ‘\w’ and a
     ‘\W’ character (or vice versa), or between ‘\w’ and the
     beginning/end of the string.  This means that ‘r'\bfoo\b'’ matches
     ‘'foo'’, ‘'foo.'’, ‘'(foo)'’, ‘'bar foo baz'’ but not ‘'foobar'’ or
     ‘'foo3'’.

     By default Unicode alphanumerics are the ones used in Unicode
     patterns, but this can be changed by using the *note ASCII: 4cf.
     flag.  Word boundaries are determined by the current locale if the
     *note LOCALE: 4d0. flag is used.  Inside a character range, ‘\b’
     represents the backspace character, for compatibility with Python’s
     string literals.

‘\B’

     Matches the empty string, but only when it is `not' at the
     beginning or end of a word.  This means that ‘r'py\B'’ matches
     ‘'python'’, ‘'py3'’, ‘'py2'’, but not ‘'py'’, ‘'py.'’, or ‘'py!'’.
     ‘\B’ is just the opposite of ‘\b’, so word characters in Unicode
     patterns are Unicode alphanumerics or the underscore, although this
     can be changed by using the *note ASCII: 4cf. flag.  Word
     boundaries are determined by the current locale if the *note
     LOCALE: 4d0. flag is used.

‘\d’

     For Unicode (str) patterns:

          Matches any Unicode decimal digit (that is, any character in
          Unicode character category [Nd]).  This includes ‘[0-9]’, and
          also many other digit characters.  If the *note ASCII: 4cf.
          flag is used only ‘[0-9]’ is matched.

     For 8-bit (bytes) patterns:

          Matches any decimal digit; this is equivalent to ‘[0-9]’.

‘\D’

     Matches any character which is not a decimal digit.  This is the
     opposite of ‘\d’.  If the *note ASCII: 4cf. flag is used this
     becomes the equivalent of ‘[^0-9]’.

‘\s’

     For Unicode (str) patterns:

          Matches Unicode whitespace characters (which includes ‘[
          \t\n\r\f\v]’, and also many other characters, for example the
          non-breaking spaces mandated by typography rules in many
          languages).  If the *note ASCII: 4cf. flag is used, only ‘[
          \t\n\r\f\v]’ is matched.

     For 8-bit (bytes) patterns:

          Matches characters considered whitespace in the ASCII
          character set; this is equivalent to ‘[ \t\n\r\f\v]’.

‘\S’

     Matches any character which is not a whitespace character.  This is
     the opposite of ‘\s’.  If the *note ASCII: 4cf. flag is used this
     becomes the equivalent of ‘[^ \t\n\r\f\v]’.

‘\w’

     For Unicode (str) patterns:

          Matches Unicode word characters; this includes most characters
          that can be part of a word in any language, as well as numbers
          and the underscore.  If the *note ASCII: 4cf. flag is used,
          only ‘[a-zA-Z0-9_]’ is matched.

     For 8-bit (bytes) patterns:

          Matches characters considered alphanumeric in the ASCII
          character set; this is equivalent to ‘[a-zA-Z0-9_]’.  If the
          *note LOCALE: 4d0. flag is used, matches characters considered
          alphanumeric in the current locale and the underscore.

‘\W’

     Matches any character which is not a word character.  This is the
     opposite of ‘\w’.  If the *note ASCII: 4cf. flag is used this
     becomes the equivalent of ‘[^a-zA-Z0-9_]’.  If the *note LOCALE:
     4d0. flag is used, matches characters which are neither
     alphanumeric in the current locale nor the underscore.

‘\Z’

     Matches only at the end of the string.

Most of the standard escapes supported by Python string literals are
also accepted by the regular expression parser:

     \a      \b      \f      \n
     \N      \r      \t      \u
     \U      \v      \x      \\

(Note that ‘\b’ is used to represent word boundaries, and means
“backspace” only inside character classes.)

‘'\u'’, ‘'\U'’, and ‘'\N'’ escape sequences are only recognized in
Unicode patterns.  In bytes patterns they are errors.  Unknown escapes
of ASCII letters are reserved for future use and treated as errors.

Octal escapes are included in a limited form.  If the first digit is a
0, or if there are three octal digits, it is considered an octal escape.
Otherwise, it is a group reference.  As for string literals, octal
escapes are always at most three digits in length.

Changed in version 3.3: The ‘'\u'’ and ‘'\U'’ escape sequences have been
added.

Changed in version 3.6: Unknown escapes consisting of ‘'\'’ and an ASCII
letter now are errors.

Changed in version 3.8: The ‘'\N{name}'’ escape sequence has been added.
As in string literals, it expands to the named Unicode character (e.g.
‘'\N{EM DASH}'’).

   ---------- Footnotes ----------

   (1) https://unicode.org/reports/tr18/


File: python.info,  Node: Module Contents,  Next: Regular Expression Objects,  Prev: Regular Expression Syntax,  Up: re — Regular expression operations

5.6.2.2 Module Contents
.......................

The module defines several functions, constants, and an exception.  Some
of the functions are simplified versions of the full featured methods
for compiled regular expressions.  Most non-trivial applications always
use the compiled form.

Changed in version 3.6: Flag constants are now instances of ‘RegexFlag’,
which is a subclass of *note enum.IntFlag: 18a1.

 -- Function: re.compile (pattern, flags=0)

     Compile a regular expression pattern into a *note regular
     expression object: 983, which can be used for matching using its
     *note match(): 18a2, *note search(): 18a3. and other methods,
     described below.

     The expression’s behaviour can be modified by specifying a `flags'
     value.  Values can be any of the following variables, combined
     using bitwise OR (the ‘|’ operator).

     The sequence

          prog = re.compile(pattern)
          result = prog.match(string)

     is equivalent to

          result = re.match(pattern, string)

     but using *note re.compile(): 54d. and saving the resulting regular
     expression object for reuse is more efficient when the expression
     will be used several times in a single program.

          Note: The compiled versions of the most recent patterns passed
          to *note re.compile(): 54d. and the module-level matching
          functions are cached, so programs that use only a few regular
          expressions at a time needn’t worry about compiling regular
          expressions.

 -- Data: re.A
 -- Data: re.ASCII

     Make ‘\w’, ‘\W’, ‘\b’, ‘\B’, ‘\d’, ‘\D’, ‘\s’ and ‘\S’ perform
     ASCII-only matching instead of full Unicode matching.  This is only
     meaningful for Unicode patterns, and is ignored for byte patterns.
     Corresponds to the inline flag ‘(?a)’.

     Note that for backward compatibility, the ‘re.U’ flag still exists
     (as well as its synonym ‘re.UNICODE’ and its embedded counterpart
     ‘(?u)’), but these are redundant in Python 3 since matches are
     Unicode by default for strings (and Unicode matching isn’t allowed
     for bytes).

 -- Data: re.DEBUG

     Display debug information about compiled expression.  No
     corresponding inline flag.

 -- Data: re.I
 -- Data: re.IGNORECASE

     Perform case-insensitive matching; expressions like ‘[A-Z]’ will
     also match lowercase letters.  Full Unicode matching (such as ‘Ü’
     matching ‘ü’) also works unless the *note re.ASCII: 4cf. flag is
     used to disable non-ASCII matches.  The current locale does not
     change the effect of this flag unless the *note re.LOCALE: 4d0.
     flag is also used.  Corresponds to the inline flag ‘(?i)’.

     Note that when the Unicode patterns ‘[a-z]’ or ‘[A-Z]’ are used in
     combination with the *note IGNORECASE: 18a5. flag, they will match
     the 52 ASCII letters and 4 additional non-ASCII letters: ‘İ’
     (U+0130, Latin capital letter I with dot above), ‘ı’ (U+0131, Latin
     small letter dotless i), ‘ſ’ (U+017F, Latin small letter long s)
     and ‘K’ (U+212A, Kelvin sign).  If the *note ASCII: 4cf. flag is
     used, only letters ‘a’ to ‘z’ and ‘A’ to ‘Z’ are matched.

 -- Data: re.L
 -- Data: re.LOCALE

     Make ‘\w’, ‘\W’, ‘\b’, ‘\B’ and case-insensitive matching dependent
     on the current locale.  This flag can be used only with bytes
     patterns.  The use of this flag is discouraged as the locale
     mechanism is very unreliable, it only handles one “culture” at a
     time, and it only works with 8-bit locales.  Unicode matching is
     already enabled by default in Python 3 for Unicode (str) patterns,
     and it is able to handle different locales/languages.  Corresponds
     to the inline flag ‘(?L)’.

     Changed in version 3.6: *note re.LOCALE: 4d0. can be used only with
     bytes patterns and is not compatible with *note re.ASCII: 4cf.

     Changed in version 3.7: Compiled regular expression objects with
     the *note re.LOCALE: 4d0. flag no longer depend on the locale at
     compile time.  Only the locale at matching time affects the result
     of matching.

 -- Data: re.M
 -- Data: re.MULTILINE

     When specified, the pattern character ‘'^'’ matches at the
     beginning of the string and at the beginning of each line
     (immediately following each newline); and the pattern character
     ‘'$'’ matches at the end of the string and at the end of each line
     (immediately preceding each newline).  By default, ‘'^'’ matches
     only at the beginning of the string, and ‘'$'’ only at the end of
     the string and immediately before the newline (if any) at the end
     of the string.  Corresponds to the inline flag ‘(?m)’.

 -- Data: re.S
 -- Data: re.DOTALL

     Make the ‘'.'’ special character match any character at all,
     including a newline; without this flag, ‘'.'’ will match anything
     `except' a newline.  Corresponds to the inline flag ‘(?s)’.

 -- Data: re.X
 -- Data: re.VERBOSE

     This flag allows you to write regular expressions that look nicer
     and are more readable by allowing you to visually separate logical
     sections of the pattern and add comments.  Whitespace within the
     pattern is ignored, except when in a character class, or when
     preceded by an unescaped backslash, or within tokens like ‘*?’,
     ‘(?:’ or ‘(?P<...>’.  When a line contains a ‘#’ that is not in a
     character class and is not preceded by an unescaped backslash, all
     characters from the leftmost such ‘#’ through the end of the line
     are ignored.

     This means that the two following regular expression objects that
     match a decimal number are functionally equal:

          a = re.compile(r"""\d +  # the integral part
                             \.    # the decimal point
                             \d *  # some fractional digits""", re.X)
          b = re.compile(r"\d+\.\d*")

     Corresponds to the inline flag ‘(?x)’.

 -- Function: re.search (pattern, string, flags=0)

     Scan through `string' looking for the first location where the
     regular expression `pattern' produces a match, and return a
     corresponding *note match object: 984.  Return ‘None’ if no
     position in the string matches the pattern; note that this is
     different from finding a zero-length match at some point in the
     string.

 -- Function: re.match (pattern, string, flags=0)

     If zero or more characters at the beginning of `string' match the
     regular expression `pattern', return a corresponding *note match
     object: 984.  Return ‘None’ if the string does not match the
     pattern; note that this is different from a zero-length match.

     Note that even in *note MULTILINE: 1898. mode, *note re.match():
     c83. will only match at the beginning of the string and not at the
     beginning of each line.

     If you want to locate a match anywhere in `string', use *note
     search(): c82. instead (see also *note search() vs.  match():
     18a7.).

 -- Function: re.fullmatch (pattern, string, flags=0)

     If the whole `string' matches the regular expression `pattern',
     return a corresponding *note match object: 984.  Return ‘None’ if
     the string does not match the pattern; note that this is different
     from a zero-length match.

     New in version 3.4.

 -- Function: re.split (pattern, string, maxsplit=0, flags=0)

     Split `string' by the occurrences of `pattern'.  If capturing
     parentheses are used in `pattern', then the text of all groups in
     the pattern are also returned as part of the resulting list.  If
     `maxsplit' is nonzero, at most `maxsplit' splits occur, and the
     remainder of the string is returned as the final element of the
     list.

          >>> re.split(r'\W+', 'Words, words, words.')
          ['Words', 'words', 'words', '']
          >>> re.split(r'(\W+)', 'Words, words, words.')
          ['Words', ', ', 'words', ', ', 'words', '.', '']
          >>> re.split(r'\W+', 'Words, words, words.', 1)
          ['Words', 'words, words.']
          >>> re.split('[a-f]+', '0a3B9', flags=re.IGNORECASE)
          ['0', '3', '9']

     If there are capturing groups in the separator and it matches at
     the start of the string, the result will start with an empty
     string.  The same holds for the end of the string:

          >>> re.split(r'(\W+)', '...words, words...')
          ['', '...', 'words', ', ', 'words', '...', '']

     That way, separator components are always found at the same
     relative indices within the result list.

     Empty matches for the pattern split the string only when not
     adjacent to a previous empty match.

          >>> re.split(r'\b', 'Words, words, words.')
          ['', 'Words', ', ', 'words', ', ', 'words', '.']
          >>> re.split(r'\W*', '...words...')
          ['', '', 'w', 'o', 'r', 'd', 's', '', '']
          >>> re.split(r'(\W*)', '...words...')
          ['', '...', '', '', 'w', '', 'o', '', 'r', '', 'd', '', 's', '...', '', '', '']

     Changed in version 3.1: Added the optional flags argument.

     Changed in version 3.7: Added support of splitting on a pattern
     that could match an empty string.

 -- Function: re.findall (pattern, string, flags=0)

     Return all non-overlapping matches of `pattern' in `string', as a
     list of strings or tuples.  The `string' is scanned left-to-right,
     and matches are returned in the order found.  Empty matches are
     included in the result.

     The result depends on the number of capturing groups in the
     pattern.  If there are no groups, return a list of strings matching
     the whole pattern.  If there is exactly one group, return a list of
     strings matching that group.  If multiple groups are present,
     return a list of tuples of strings matching the groups.
     Non-capturing groups do not affect the form of the result.

          >>> re.findall(r'\bf[a-z]*', 'which foot or hand fell fastest')
          ['foot', 'fell', 'fastest']
          >>> re.findall(r'(\w+)=(\d+)', 'set width=20 and height=10')
          [('width', '20'), ('height', '10')]

     Changed in version 3.7: Non-empty matches can now start just after
     a previous empty match.

 -- Function: re.finditer (pattern, string, flags=0)

     Return an *note iterator: 1171. yielding *note match objects: 984.
     over all non-overlapping matches for the RE `pattern' in `string'.
     The `string' is scanned left-to-right, and matches are returned in
     the order found.  Empty matches are included in the result.

     Changed in version 3.7: Non-empty matches can now start just after
     a previous empty match.

 -- Function: re.sub (pattern, repl, string, count=0, flags=0)

     Return the string obtained by replacing the leftmost
     non-overlapping occurrences of `pattern' in `string' by the
     replacement `repl'.  If the pattern isn’t found, `string' is
     returned unchanged.  `repl' can be a string or a function; if it is
     a string, any backslash escapes in it are processed.  That is, ‘\n’
     is converted to a single newline character, ‘\r’ is converted to a
     carriage return, and so forth.  Unknown escapes of ASCII letters
     are reserved for future use and treated as errors.  Other unknown
     escapes such as ‘\&’ are left alone.  Backreferences, such as ‘\6’,
     are replaced with the substring matched by group 6 in the pattern.
     For example:

          >>> re.sub(r'def\s+([a-zA-Z_][a-zA-Z_0-9]*)\s*\(\s*\):',
          ...        r'static PyObject*\npy_\1(void)\n{',
          ...        'def myfunc():')
          'static PyObject*\npy_myfunc(void)\n{'

     If `repl' is a function, it is called for every non-overlapping
     occurrence of `pattern'.  The function takes a single *note match
     object: 984. argument, and returns the replacement string.  For
     example:

          >>> def dashrepl(matchobj):
          ...     if matchobj.group(0) == '-': return ' '
          ...     else: return '-'
          >>> re.sub('-{1,2}', dashrepl, 'pro----gram-files')
          'pro--gram files'
          >>> re.sub(r'\sAND\s', ' & ', 'Baked Beans And Spam', flags=re.IGNORECASE)
          'Baked Beans & Spam'

     The pattern may be a string or a *note pattern object: 983.

     The optional argument `count' is the maximum number of pattern
     occurrences to be replaced; `count' must be a non-negative integer.
     If omitted or zero, all occurrences will be replaced.  Empty
     matches for the pattern are replaced only when not adjacent to a
     previous empty match, so ‘sub('x*', '-', 'abxd')’ returns
     ‘'-a-b--d-'’.

     In string-type `repl' arguments, in addition to the character
     escapes and backreferences described above, ‘\g<name>’ will use the
     substring matched by the group named ‘name’, as defined by the
     ‘(?P<name>...)’ syntax.  ‘\g<number>’ uses the corresponding group
     number; ‘\g<2>’ is therefore equivalent to ‘\2’, but isn’t
     ambiguous in a replacement such as ‘\g<2>0’.  ‘\20’ would be
     interpreted as a reference to group 20, not a reference to group 2
     followed by the literal character ‘'0'’.  The backreference ‘\g<0>’
     substitutes in the entire substring matched by the RE.

     Changed in version 3.1: Added the optional flags argument.

     Changed in version 3.5: Unmatched groups are replaced with an empty
     string.

     Changed in version 3.6: Unknown escapes in `pattern' consisting of
     ‘'\'’ and an ASCII letter now are errors.

     Changed in version 3.7: Unknown escapes in `repl' consisting of
     ‘'\'’ and an ASCII letter now are errors.

     Changed in version 3.7: Empty matches for the pattern are replaced
     when adjacent to a previous non-empty match.

 -- Function: re.subn (pattern, repl, string, count=0, flags=0)

     Perform the same operation as *note sub(): 57a, but return a tuple
     ‘(new_string, number_of_subs_made)’.

     Changed in version 3.1: Added the optional flags argument.

     Changed in version 3.5: Unmatched groups are replaced with an empty
     string.

 -- Function: re.escape (pattern)

     Escape special characters in `pattern'.  This is useful if you want
     to match an arbitrary literal string that may have regular
     expression metacharacters in it.  For example:

          >>> print(re.escape('https://www.python.org'))
          https://www\.python\.org

          >>> legal_chars = string.ascii_lowercase + string.digits + "!#$%&'*+-.^_`|~:"
          >>> print('[%s]+' % re.escape(legal_chars))
          [abcdefghijklmnopqrstuvwxyz0123456789!\#\$%\&'\*\+\-\.\^_`\|\~:]+

          >>> operators = ['+', '-', '*', '/', '**']
          >>> print('|'.join(map(re.escape, sorted(operators, reverse=True))))
          /|\-|\+|\*\*|\*

     This function must not be used for the replacement string in *note
     sub(): 57a. and *note subn(): 823, only backslashes should be
     escaped.  For example:

          >>> digits_re = r'\d+'
          >>> sample = '/usr/sbin/sendmail - 0 errors, 12 warnings'
          >>> print(re.sub(digits_re, digits_re.replace('\\', r'\\'), sample))
          /usr/sbin/sendmail - \d+ errors, \d+ warnings

     Changed in version 3.3: The ‘'_'’ character is no longer escaped.

     Changed in version 3.7: Only characters that can have special
     meaning in a regular expression are escaped.  As a result, ‘'!'’,
     ‘'"'’, ‘'%'’, ‘"'"’, ‘','’, ‘'/'’, ‘':'’, ‘';'’, ‘'<'’, ‘'='’,
     ‘'>'’, ‘'@'’, and ‘"`"’ are no longer escaped.

 -- Function: re.purge ()

     Clear the regular expression cache.

 -- Exception: re.error (msg, pattern=None, pos=None)

     Exception raised when a string passed to one of the functions here
     is not a valid regular expression (for example, it might contain
     unmatched parentheses) or when some other error occurs during
     compilation or matching.  It is never an error if a string contains
     no match for a pattern.  The error instance has the following
     additional attributes:

      -- Attribute: msg

          The unformatted error message.

      -- Attribute: pattern

          The regular expression pattern.

      -- Attribute: pos

          The index in `pattern' where compilation failed (may be
          ‘None’).

      -- Attribute: lineno

          The line corresponding to `pos' (may be ‘None’).

      -- Attribute: colno

          The column corresponding to `pos' (may be ‘None’).

     Changed in version 3.5: Added additional attributes.


File: python.info,  Node: Regular Expression Objects,  Next: Match Objects,  Prev: Module Contents,  Up: re — Regular expression operations

5.6.2.3 Regular Expression Objects
..................................

Compiled regular expression objects support the following methods and
attributes:

 -- Method: Pattern.search (string[, pos[, endpos]])

     Scan through `string' looking for the first location where this
     regular expression produces a match, and return a corresponding
     *note match object: 984.  Return ‘None’ if no position in the
     string matches the pattern; note that this is different from
     finding a zero-length match at some point in the string.

     The optional second parameter `pos' gives an index in the string
     where the search is to start; it defaults to ‘0’.  This is not
     completely equivalent to slicing the string; the ‘'^'’ pattern
     character matches at the real beginning of the string and at
     positions just after a newline, but not necessarily at the index
     where the search is to start.

     The optional parameter `endpos' limits how far the string will be
     searched; it will be as if the string is `endpos' characters long,
     so only the characters from `pos' to ‘endpos - 1’ will be searched
     for a match.  If `endpos' is less than `pos', no match will be
     found; otherwise, if `rx' is a compiled regular expression object,
     ‘rx.search(string, 0, 50)’ is equivalent to ‘rx.search(string[:50],
     0)’.

          >>> pattern = re.compile("d")
          >>> pattern.search("dog")     # Match at index 0
          <re.Match object; span=(0, 1), match='d'>
          >>> pattern.search("dog", 1)  # No match; search doesn't include the "d"

 -- Method: Pattern.match (string[, pos[, endpos]])

     If zero or more characters at the `beginning' of `string' match
     this regular expression, return a corresponding *note match object:
     984.  Return ‘None’ if the string does not match the pattern; note
     that this is different from a zero-length match.

     The optional `pos' and `endpos' parameters have the same meaning as
     for the *note search(): 18a3. method.

          >>> pattern = re.compile("o")
          >>> pattern.match("dog")      # No match as "o" is not at the start of "dog".
          >>> pattern.match("dog", 1)   # Match as "o" is the 2nd character of "dog".
          <re.Match object; span=(1, 2), match='o'>

     If you want to locate a match anywhere in `string', use *note
     search(): 18a3. instead (see also *note search() vs.  match():
     18a7.).

 -- Method: Pattern.fullmatch (string[, pos[, endpos]])

     If the whole `string' matches this regular expression, return a
     corresponding *note match object: 984.  Return ‘None’ if the string
     does not match the pattern; note that this is different from a
     zero-length match.

     The optional `pos' and `endpos' parameters have the same meaning as
     for the *note search(): 18a3. method.

          >>> pattern = re.compile("o[gh]")
          >>> pattern.fullmatch("dog")      # No match as "o" is not at the start of "dog".
          >>> pattern.fullmatch("ogre")     # No match as not the full string matches.
          >>> pattern.fullmatch("doggie", 1, 3)   # Matches within given limits.
          <re.Match object; span=(1, 3), match='og'>

     New in version 3.4.

 -- Method: Pattern.split (string, maxsplit=0)

     Identical to the *note split(): 4d1. function, using the compiled
     pattern.

 -- Method: Pattern.findall (string[, pos[, endpos]])

     Similar to the *note findall(): a44. function, using the compiled
     pattern, but also accepts optional `pos' and `endpos' parameters
     that limit the search region like for *note search(): c82.

 -- Method: Pattern.finditer (string[, pos[, endpos]])

     Similar to the *note finditer(): 18a8. function, using the compiled
     pattern, but also accepts optional `pos' and `endpos' parameters
     that limit the search region like for *note search(): c82.

 -- Method: Pattern.sub (repl, string, count=0)

     Identical to the *note sub(): 57a. function, using the compiled
     pattern.

 -- Method: Pattern.subn (repl, string, count=0)

     Identical to the *note subn(): 823. function, using the compiled
     pattern.

 -- Attribute: Pattern.flags

     The regex matching flags.  This is a combination of the flags given
     to *note compile(): 54d, any ‘(?...)’ inline flags in the pattern,
     and implicit flags such as ‘UNICODE’ if the pattern is a Unicode
     string.

 -- Attribute: Pattern.groups

     The number of capturing groups in the pattern.

 -- Attribute: Pattern.groupindex

     A dictionary mapping any symbolic group names defined by ‘(?P<id>)’
     to group numbers.  The dictionary is empty if no symbolic groups
     were used in the pattern.

 -- Attribute: Pattern.pattern

     The pattern string from which the pattern object was compiled.

Changed in version 3.7: Added support of *note copy.copy(): 4d2. and
*note copy.deepcopy(): 4d3.  Compiled regular expression objects are
considered atomic.


File: python.info,  Node: Match Objects,  Next: Regular Expression Examples,  Prev: Regular Expression Objects,  Up: re — Regular expression operations

5.6.2.4 Match Objects
.....................

Match objects always have a boolean value of ‘True’.  Since *note
match(): 18a2. and *note search(): 18a3. return ‘None’ when there is no
match, you can test whether there was a match with a simple ‘if’
statement:

     match = re.search(pattern, string)
     if match:
         process(match)

Match objects support the following methods and attributes:

 -- Method: Match.expand (template)

     Return the string obtained by doing backslash substitution on the
     template string `template', as done by the *note sub(): 18af.
     method.  Escapes such as ‘\n’ are converted to the appropriate
     characters, and numeric backreferences (‘\1’, ‘\2’) and named
     backreferences (‘\g<1>’, ‘\g<name>’) are replaced by the contents
     of the corresponding group.

     Changed in version 3.5: Unmatched groups are replaced with an empty
     string.

 -- Method: Match.group ([group1, ...])

     Returns one or more subgroups of the match.  If there is a single
     argument, the result is a single string; if there are multiple
     arguments, the result is a tuple with one item per argument.
     Without arguments, `group1' defaults to zero (the whole match is
     returned).  If a `groupN' argument is zero, the corresponding
     return value is the entire matching string; if it is in the
     inclusive range [1..99], it is the string matching the
     corresponding parenthesized group.  If a group number is negative
     or larger than the number of groups defined in the pattern, an
     *note IndexError: f36. exception is raised.  If a group is
     contained in a part of the pattern that did not match, the
     corresponding result is ‘None’.  If a group is contained in a part
     of the pattern that matched multiple times, the last match is
     returned.

          >>> m = re.match(r"(\w+) (\w+)", "Isaac Newton, physicist")
          >>> m.group(0)       # The entire match
          'Isaac Newton'
          >>> m.group(1)       # The first parenthesized subgroup.
          'Isaac'
          >>> m.group(2)       # The second parenthesized subgroup.
          'Newton'
          >>> m.group(1, 2)    # Multiple arguments give us a tuple.
          ('Isaac', 'Newton')

     If the regular expression uses the ‘(?P<name>...)’ syntax, the
     `groupN' arguments may also be strings identifying groups by their
     group name.  If a string argument is not used as a group name in
     the pattern, an *note IndexError: f36. exception is raised.

     A moderately complicated example:

          >>> m = re.match(r"(?P<first_name>\w+) (?P<last_name>\w+)", "Malcolm Reynolds")
          >>> m.group('first_name')
          'Malcolm'
          >>> m.group('last_name')
          'Reynolds'

     Named groups can also be referred to by their index:

          >>> m.group(1)
          'Malcolm'
          >>> m.group(2)
          'Reynolds'

     If a group matches multiple times, only the last match is
     accessible:

          >>> m = re.match(r"(..)+", "a1b2c3")  # Matches 3 times.
          >>> m.group(1)                        # Returns only the last match.
          'c3'

 -- Method: Match.__getitem__ (g)

     This is identical to ‘m.group(g)’.  This allows easier access to an
     individual group from a match:

          >>> m = re.match(r"(\w+) (\w+)", "Isaac Newton, physicist")
          >>> m[0]       # The entire match
          'Isaac Newton'
          >>> m[1]       # The first parenthesized subgroup.
          'Isaac'
          >>> m[2]       # The second parenthesized subgroup.
          'Newton'

     New in version 3.6.

 -- Method: Match.groups (default=None)

     Return a tuple containing all the subgroups of the match, from 1 up
     to however many groups are in the pattern.  The `default' argument
     is used for groups that did not participate in the match; it
     defaults to ‘None’.

     For example:

          >>> m = re.match(r"(\d+)\.(\d+)", "24.1632")
          >>> m.groups()
          ('24', '1632')

     If we make the decimal place and everything after it optional, not
     all groups might participate in the match.  These groups will
     default to ‘None’ unless the `default' argument is given:

          >>> m = re.match(r"(\d+)\.?(\d+)?", "24")
          >>> m.groups()      # Second group defaults to None.
          ('24', None)
          >>> m.groups('0')   # Now, the second group defaults to '0'.
          ('24', '0')

 -- Method: Match.groupdict (default=None)

     Return a dictionary containing all the `named' subgroups of the
     match, keyed by the subgroup name.  The `default' argument is used
     for groups that did not participate in the match; it defaults to
     ‘None’.  For example:

          >>> m = re.match(r"(?P<first_name>\w+) (?P<last_name>\w+)", "Malcolm Reynolds")
          >>> m.groupdict()
          {'first_name': 'Malcolm', 'last_name': 'Reynolds'}

 -- Method: Match.start ([group])
 -- Method: Match.end ([group])

     Return the indices of the start and end of the substring matched by
     `group'; `group' defaults to zero (meaning the whole matched
     substring).  Return ‘-1’ if `group' exists but did not contribute
     to the match.  For a match object `m', and a group `g' that did
     contribute to the match, the substring matched by group `g'
     (equivalent to ‘m.group(g)’) is

          m.string[m.start(g):m.end(g)]

     Note that ‘m.start(group)’ will equal ‘m.end(group)’ if `group'
     matched a null string.  For example, after ‘m = re.search('b(c?)',
     'cba')’, ‘m.start(0)’ is 1, ‘m.end(0)’ is 2, ‘m.start(1)’ and
     ‘m.end(1)’ are both 2, and ‘m.start(2)’ raises an *note IndexError:
     f36. exception.

     An example that will remove `remove_this' from email addresses:

          >>> email = "tony@tiremove_thisger.net"
          >>> m = re.search("remove_this", email)
          >>> email[:m.start()] + email[m.end():]
          'tony@tiger.net'

 -- Method: Match.span ([group])

     For a match `m', return the 2-tuple ‘(m.start(group),
     m.end(group))’.  Note that if `group' did not contribute to the
     match, this is ‘(-1, -1)’.  `group' defaults to zero, the entire
     match.

 -- Attribute: Match.pos

     The value of `pos' which was passed to the *note search(): 18a3. or
     *note match(): 18a2. method of a *note regex object: 983.  This is
     the index into the string at which the RE engine started looking
     for a match.

 -- Attribute: Match.endpos

     The value of `endpos' which was passed to the *note search(): 18a3.
     or *note match(): 18a2. method of a *note regex object: 983.  This
     is the index into the string beyond which the RE engine will not
     go.

 -- Attribute: Match.lastindex

     The integer index of the last matched capturing group, or ‘None’ if
     no group was matched at all.  For example, the expressions ‘(a)b’,
     ‘((a)(b))’, and ‘((ab))’ will have ‘lastindex == 1’ if applied to
     the string ‘'ab'’, while the expression ‘(a)(b)’ will have
     ‘lastindex == 2’, if applied to the same string.

 -- Attribute: Match.lastgroup

     The name of the last matched capturing group, or ‘None’ if the
     group didn’t have a name, or if no group was matched at all.

 -- Attribute: Match.re

     The *note regular expression object: 983. whose *note match():
     18a2. or *note search(): 18a3. method produced this match instance.

 -- Attribute: Match.string

     The string passed to *note match(): 18a2. or *note search(): 18a3.

Changed in version 3.7: Added support of *note copy.copy(): 4d2. and
*note copy.deepcopy(): 4d3.  Match objects are considered atomic.


File: python.info,  Node: Regular Expression Examples,  Prev: Match Objects,  Up: re — Regular expression operations

5.6.2.5 Regular Expression Examples
...................................

* Menu:

* Checking for a Pair::
* Simulating scanf(): Simulating scanf.
* search() vs. match(): search vs match.
* Making a Phonebook::
* Text Munging::
* Finding all Adverbs::
* Finding all Adverbs and their Positions::
* Raw String Notation::
* Writing a Tokenizer::


File: python.info,  Node: Checking for a Pair,  Next: Simulating scanf,  Up: Regular Expression Examples

5.6.2.6 Checking for a Pair
...........................

In this example, we’ll use the following helper function to display
match objects a little more gracefully:

     def displaymatch(match):
         if match is None:
             return None
         return '<Match: %r, groups=%r>' % (match.group(), match.groups())

Suppose you are writing a poker program where a player’s hand is
represented as a 5-character string with each character representing a
card, “a” for ace, “k” for king, “q” for queen, “j” for jack, “t” for
10, and “2” through “9” representing the card with that value.

To see if a given string is a valid hand, one could do the following:

     >>> valid = re.compile(r"^[a2-9tjqk]{5}$")
     >>> displaymatch(valid.match("akt5q"))  # Valid.
     "<Match: 'akt5q', groups=()>"
     >>> displaymatch(valid.match("akt5e"))  # Invalid.
     >>> displaymatch(valid.match("akt"))    # Invalid.
     >>> displaymatch(valid.match("727ak"))  # Valid.
     "<Match: '727ak', groups=()>"

That last hand, ‘"727ak"’, contained a pair, or two of the same valued
cards.  To match this with a regular expression, one could use
backreferences as such:

     >>> pair = re.compile(r".*(.).*\1")
     >>> displaymatch(pair.match("717ak"))     # Pair of 7s.
     "<Match: '717', groups=('7',)>"
     >>> displaymatch(pair.match("718ak"))     # No pairs.
     >>> displaymatch(pair.match("354aa"))     # Pair of aces.
     "<Match: '354aa', groups=('a',)>"

To find out what card the pair consists of, one could use the *note
group(): 18b7. method of the match object in the following manner:

     >>> pair = re.compile(r".*(.).*\1")
     >>> pair.match("717ak").group(1)
     '7'

     # Error because re.match() returns None, which doesn't have a group() method:
     >>> pair.match("718ak").group(1)
     Traceback (most recent call last):
       File "<pyshell#23>", line 1, in <module>
         re.match(r".*(.).*\1", "718ak").group(1)
     AttributeError: 'NoneType' object has no attribute 'group'

     >>> pair.match("354aa").group(1)
     'a'


File: python.info,  Node: Simulating scanf,  Next: search vs match,  Prev: Checking for a Pair,  Up: Regular Expression Examples

5.6.2.7 Simulating scanf()
..........................

Python does not currently have an equivalent to ‘scanf()’.  Regular
expressions are generally more powerful, though also more verbose, than
‘scanf()’ format strings.  The table below offers some more-or-less
equivalent mappings between ‘scanf()’ format tokens and regular
expressions.

‘scanf()’ Token                      Regular Expression
                                     
---------------------------------------------------------------------------------------
                                     
‘%c’                                 ‘.’
                                     
                                     
‘%5c’                                ‘.{5}’
                                     
                                     
‘%d’                                 ‘[-+]?\d+’
                                     
                                     
‘%e’, ‘%E’, ‘%f’, ‘%g’               ‘[-+]?(\d+(\.\d*)?|\.\d+)([eE][-+]?\d+)?’
                                     
                                     
‘%i’                                 ‘[-+]?(0[xX][\dA-Fa-f]+|0[0-7]*|\d+)’
                                     
                                     
‘%o’                                 ‘[-+]?[0-7]+’
                                     
                                     
‘%s’                                 ‘\S+’
                                     
                                     
‘%u’                                 ‘\d+’
                                     
                                     
‘%x’, ‘%X’                           ‘[-+]?(0[xX])?[\dA-Fa-f]+’
                                     

To extract the filename and numbers from a string like

     /usr/sbin/sendmail - 0 errors, 4 warnings

you would use a ‘scanf()’ format like

     %s - %d errors, %d warnings

The equivalent regular expression would be

     (\S+) - (\d+) errors, (\d+) warnings


File: python.info,  Node: search vs match,  Next: Making a Phonebook,  Prev: Simulating scanf,  Up: Regular Expression Examples

5.6.2.8 search() vs. match()
............................

Python offers two different primitive operations based on regular
expressions: *note re.match(): c83. checks for a match only at the
beginning of the string, while *note re.search(): c82. checks for a
match anywhere in the string (this is what Perl does by default).

For example:

     >>> re.match("c", "abcdef")    # No match
     >>> re.search("c", "abcdef")   # Match
     <re.Match object; span=(2, 3), match='c'>

Regular expressions beginning with ‘'^'’ can be used with *note
search(): c82. to restrict the match at the beginning of the string:

     >>> re.match("c", "abcdef")    # No match
     >>> re.search("^c", "abcdef")  # No match
     >>> re.search("^a", "abcdef")  # Match
     <re.Match object; span=(0, 1), match='a'>

Note however that in *note MULTILINE: 1898. mode *note match(): c83.
only matches at the beginning of the string, whereas using *note
search(): c82. with a regular expression beginning with ‘'^'’ will match
at the beginning of each line.

     >>> re.match('X', 'A\nB\nX', re.MULTILINE)  # No match
     >>> re.search('^X', 'A\nB\nX', re.MULTILINE)  # Match
     <re.Match object; span=(4, 5), match='X'>


File: python.info,  Node: Making a Phonebook,  Next: Text Munging,  Prev: search vs match,  Up: Regular Expression Examples

5.6.2.9 Making a Phonebook
..........................

*note split(): 4d1. splits a string into a list delimited by the passed
pattern.  The method is invaluable for converting textual data into data
structures that can be easily read and modified by Python as
demonstrated in the following example that creates a phonebook.

First, here is the input.  Normally it may come from a file, here we are
using triple-quoted string syntax

     >>> text = """Ross McFluff: 834.345.1254 155 Elm Street
     ...
     ... Ronald Heathmore: 892.345.3428 436 Finley Avenue
     ... Frank Burger: 925.541.7625 662 South Dogwood Way
     ...
     ...
     ... Heather Albrecht: 548.326.4584 919 Park Place"""

The entries are separated by one or more newlines.  Now we convert the
string into a list with each nonempty line having its own entry:

     >>> entries = re.split("\n+", text)
     >>> entries
     ['Ross McFluff: 834.345.1254 155 Elm Street',
     'Ronald Heathmore: 892.345.3428 436 Finley Avenue',
     'Frank Burger: 925.541.7625 662 South Dogwood Way',
     'Heather Albrecht: 548.326.4584 919 Park Place']

Finally, split each entry into a list with first name, last name,
telephone number, and address.  We use the ‘maxsplit’ parameter of *note
split(): 4d1. because the address has spaces, our splitting pattern, in
it:

     >>> [re.split(":? ", entry, 3) for entry in entries]
     [['Ross', 'McFluff', '834.345.1254', '155 Elm Street'],
     ['Ronald', 'Heathmore', '892.345.3428', '436 Finley Avenue'],
     ['Frank', 'Burger', '925.541.7625', '662 South Dogwood Way'],
     ['Heather', 'Albrecht', '548.326.4584', '919 Park Place']]

The ‘:?’ pattern matches the colon after the last name, so that it does
not occur in the result list.  With a ‘maxsplit’ of ‘4’, we could
separate the house number from the street name:

     >>> [re.split(":? ", entry, 4) for entry in entries]
     [['Ross', 'McFluff', '834.345.1254', '155', 'Elm Street'],
     ['Ronald', 'Heathmore', '892.345.3428', '436', 'Finley Avenue'],
     ['Frank', 'Burger', '925.541.7625', '662', 'South Dogwood Way'],
     ['Heather', 'Albrecht', '548.326.4584', '919', 'Park Place']]


File: python.info,  Node: Text Munging,  Next: Finding all Adverbs,  Prev: Making a Phonebook,  Up: Regular Expression Examples

5.6.2.10 Text Munging
.....................

*note sub(): 57a. replaces every occurrence of a pattern with a string
or the result of a function.  This example demonstrates using *note
sub(): 57a. with a function to “munge” text, or randomize the order of
all the characters in each word of a sentence except for the first and
last characters:

     >>> def repl(m):
     ...     inner_word = list(m.group(2))
     ...     random.shuffle(inner_word)
     ...     return m.group(1) + "".join(inner_word) + m.group(3)
     >>> text = "Professor Abdolmalek, please report your absences promptly."
     >>> re.sub(r"(\w)(\w+)(\w)", repl, text)
     'Poefsrosr Aealmlobdk, pslaee reorpt your abnseces plmrptoy.'
     >>> re.sub(r"(\w)(\w+)(\w)", repl, text)
     'Pofsroser Aodlambelk, plasee reoprt yuor asnebces potlmrpy.'


File: python.info,  Node: Finding all Adverbs,  Next: Finding all Adverbs and their Positions,  Prev: Text Munging,  Up: Regular Expression Examples

5.6.2.11 Finding all Adverbs
............................

*note findall(): a44. matches `all' occurrences of a pattern, not just
the first one as *note search(): c82. does.  For example, if a writer
wanted to find all of the adverbs in some text, they might use *note
findall(): a44. in the following manner:

     >>> text = "He was carefully disguised but captured quickly by police."
     >>> re.findall(r"\w+ly\b", text)
     ['carefully', 'quickly']


File: python.info,  Node: Finding all Adverbs and their Positions,  Next: Raw String Notation,  Prev: Finding all Adverbs,  Up: Regular Expression Examples

5.6.2.12 Finding all Adverbs and their Positions
................................................

If one wants more information about all matches of a pattern than the
matched text, *note finditer(): 18a8. is useful as it provides *note
match objects: 984. instead of strings.  Continuing with the previous
example, if a writer wanted to find all of the adverbs `and their
positions' in some text, they would use *note finditer(): 18a8. in the
following manner:

     >>> text = "He was carefully disguised but captured quickly by police."
     >>> for m in re.finditer(r"\w+ly\b", text):
     ...     print('%02d-%02d: %s' % (m.start(), m.end(), m.group(0)))
     07-16: carefully
     40-47: quickly


File: python.info,  Node: Raw String Notation,  Next: Writing a Tokenizer,  Prev: Finding all Adverbs and their Positions,  Up: Regular Expression Examples

5.6.2.13 Raw String Notation
............................

Raw string notation (‘r"text"’) keeps regular expressions sane.  Without
it, every backslash (‘'\'’) in a regular expression would have to be
prefixed with another one to escape it.  For example, the two following
lines of code are functionally identical:

     >>> re.match(r"\W(.)\1\W", " ff ")
     <re.Match object; span=(0, 4), match=' ff '>
     >>> re.match("\\W(.)\\1\\W", " ff ")
     <re.Match object; span=(0, 4), match=' ff '>

When one wants to match a literal backslash, it must be escaped in the
regular expression.  With raw string notation, this means ‘r"\\"’.
Without raw string notation, one must use ‘"\\\\"’, making the following
lines of code functionally identical:

     >>> re.match(r"\\", r"\\")
     <re.Match object; span=(0, 1), match='\\'>
     >>> re.match("\\\\", r"\\")
     <re.Match object; span=(0, 1), match='\\'>


File: python.info,  Node: Writing a Tokenizer,  Prev: Raw String Notation,  Up: Regular Expression Examples

5.6.2.14 Writing a Tokenizer
............................

A tokenizer or scanner(1) analyzes a string to categorize groups of
characters.  This is a useful first step in writing a compiler or
interpreter.

The text categories are specified with regular expressions.  The
technique is to combine those into a single master regular expression
and to loop over successive matches:

     from typing import NamedTuple
     import re

     class Token(NamedTuple):
         type: str
         value: str
         line: int
         column: int

     def tokenize(code):
         keywords = {'IF', 'THEN', 'ENDIF', 'FOR', 'NEXT', 'GOSUB', 'RETURN'}
         token_specification = [
             ('NUMBER',   r'\d+(\.\d*)?'),  # Integer or decimal number
             ('ASSIGN',   r':='),           # Assignment operator
             ('END',      r';'),            # Statement terminator
             ('ID',       r'[A-Za-z]+'),    # Identifiers
             ('OP',       r'[+\-*/]'),      # Arithmetic operators
             ('NEWLINE',  r'\n'),           # Line endings
             ('SKIP',     r'[ \t]+'),       # Skip over spaces and tabs
             ('MISMATCH', r'.'),            # Any other character
         ]
         tok_regex = '|'.join('(?P<%s>%s)' % pair for pair in token_specification)
         line_num = 1
         line_start = 0
         for mo in re.finditer(tok_regex, code):
             kind = mo.lastgroup
             value = mo.group()
             column = mo.start() - line_start
             if kind == 'NUMBER':
                 value = float(value) if '.' in value else int(value)
             elif kind == 'ID' and value in keywords:
                 kind = value
             elif kind == 'NEWLINE':
                 line_start = mo.end()
                 line_num += 1
                 continue
             elif kind == 'SKIP':
                 continue
             elif kind == 'MISMATCH':
                 raise RuntimeError(f'{value!r} unexpected on line {line_num}')
             yield Token(kind, value, line_num, column)

     statements = '''
         IF quantity THEN
             total := total + price * quantity;
             tax := price * 0.05;
         ENDIF;
     '''

     for token in tokenize(statements):
         print(token)

The tokenizer produces the following output:

     Token(type='IF', value='IF', line=2, column=4)
     Token(type='ID', value='quantity', line=2, column=7)
     Token(type='THEN', value='THEN', line=2, column=16)
     Token(type='ID', value='total', line=3, column=8)
     Token(type='ASSIGN', value=':=', line=3, column=14)
     Token(type='ID', value='total', line=3, column=17)
     Token(type='OP', value='+', line=3, column=23)
     Token(type='ID', value='price', line=3, column=25)
     Token(type='OP', value='*', line=3, column=31)
     Token(type='ID', value='quantity', line=3, column=33)
     Token(type='END', value=';', line=3, column=41)
     Token(type='ID', value='tax', line=4, column=8)
     Token(type='ASSIGN', value=':=', line=4, column=12)
     Token(type='ID', value='price', line=4, column=15)
     Token(type='OP', value='*', line=4, column=21)
     Token(type='NUMBER', value=0.05, line=4, column=23)
     Token(type='END', value=';', line=4, column=27)
     Token(type='ENDIF', value='ENDIF', line=5, column=4)
     Token(type='END', value=';', line=5, column=9)

(Frie09) Friedl, Jeffrey.  Mastering Regular Expressions.  3rd ed.,
O’Reilly Media, 2009.  The third edition of the book no longer covers
Python at all, but the first edition covered writing good regular
expression patterns in great detail.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Lexical_analysis


File: python.info,  Node: difflib — Helpers for computing deltas,  Next: textwrap — Text wrapping and filling,  Prev: re — Regular expression operations,  Up: Text Processing Services

5.6.3 ‘difflib’ — Helpers for computing deltas
----------------------------------------------

`Source code:' Lib/difflib.py(1)

__________________________________________________________________

This module provides classes and functions for comparing sequences.  It
can be used for example, for comparing files, and can produce
information about file differences in various formats, including HTML
and context and unified diffs.  For comparing directories and files, see
also, the *note filecmp: 7d. module.

 -- Class: difflib.SequenceMatcher

     This is a flexible class for comparing pairs of sequences of any
     type, so long as the sequence elements are *note hashable: 276.
     The basic algorithm predates, and is a little fancier than, an
     algorithm published in the late 1980’s by Ratcliff and Obershelp
     under the hyperbolic name “gestalt pattern matching.” The idea is
     to find the longest contiguous matching subsequence that contains
     no “junk” elements; these “junk” elements are ones that are
     uninteresting in some sense, such as blank lines or whitespace.
     (Handling junk is an extension to the Ratcliff and Obershelp
     algorithm.)  The same idea is then applied recursively to the
     pieces of the sequences to the left and to the right of the
     matching subsequence.  This does not yield minimal edit sequences,
     but does tend to yield matches that “look right” to people.

     `Timing:' The basic Ratcliff-Obershelp algorithm is cubic time in
     the worst case and quadratic time in the expected case.  *note
     SequenceMatcher: a30. is quadratic time for the worst case and has
     expected-case behavior dependent in a complicated way on how many
     elements the sequences have in common; best case time is linear.

     `Automatic junk heuristic:' *note SequenceMatcher: a30. supports a
     heuristic that automatically treats certain sequence items as junk.
     The heuristic counts how many times each individual item appears in
     the sequence.  If an item’s duplicates (after the first one)
     account for more than 1% of the sequence and the sequence is at
     least 200 items long, this item is marked as “popular” and is
     treated as junk for the purpose of sequence matching.  This
     heuristic can be turned off by setting the ‘autojunk’ argument to
     ‘False’ when creating the *note SequenceMatcher: a30.

     New in version 3.2: The `autojunk' parameter.

 -- Class: difflib.Differ

     This is a class for comparing sequences of lines of text, and
     producing human-readable differences or deltas.  Differ uses *note
     SequenceMatcher: a30. both to compare sequences of lines, and to
     compare sequences of characters within similar (near-matching)
     lines.

     Each line of a *note Differ: 18d0. delta begins with a two-letter
     code:

     Code           Meaning
                    
     ---------------------------------------------------------------
                    
     ‘'- '’         line unique to sequence 1
                    
                    
     ‘'+ '’         line unique to sequence 2
                    
                    
     ‘' '’          line common to both sequences
                    
                    
     ‘'? '’         line not present in either input sequence
                    

     Lines beginning with ‘‘?’’ attempt to guide the eye to intraline
     differences, and were not present in either input sequence.  These
     lines can be confusing if the sequences contain tab characters.

 -- Class: difflib.HtmlDiff

     This class can be used to create an HTML table (or a complete HTML
     file containing the table) showing a side by side, line by line
     comparison of text with inter-line and intra-line change
     highlights.  The table can be generated in either full or
     contextual difference mode.

     The constructor for this class is:

      -- Method: __init__ (tabsize=8, wrapcolumn=None, linejunk=None,
               charjunk=IS_CHARACTER_JUNK)

          Initializes instance of *note HtmlDiff: 18d1.

          `tabsize' is an optional keyword argument to specify tab stop
          spacing and defaults to ‘8’.

          `wrapcolumn' is an optional keyword to specify column number
          where lines are broken and wrapped, defaults to ‘None’ where
          lines are not wrapped.

          `linejunk' and `charjunk' are optional keyword arguments
          passed into *note ndiff(): 18d3. (used by *note HtmlDiff:
          18d1. to generate the side by side HTML differences).  See
          *note ndiff(): 18d3. documentation for argument default values
          and descriptions.

     The following methods are public:

      -- Method: make_file (fromlines, tolines, fromdesc='', todesc='',
               context=False, numlines=5, *, charset='utf-8')

          Compares `fromlines' and `tolines' (lists of strings) and
          returns a string which is a complete HTML file containing a
          table showing line by line differences with inter-line and
          intra-line changes highlighted.

          `fromdesc' and `todesc' are optional keyword arguments to
          specify from/to file column header strings (both default to an
          empty string).

          `context' and `numlines' are both optional keyword arguments.
          Set `context' to ‘True’ when contextual differences are to be
          shown, else the default is ‘False’ to show the full files.
          `numlines' defaults to ‘5’.  When `context' is ‘True’
          `numlines' controls the number of context lines which surround
          the difference highlights.  When `context' is ‘False’
          `numlines' controls the number of lines which are shown before
          a difference highlight when using the “next” hyperlinks
          (setting to zero would cause the “next” hyperlinks to place
          the next difference highlight at the top of the browser
          without any leading context).

               Note: `fromdesc' and `todesc' are interpreted as
               unescaped HTML and should be properly escaped while
               receiving input from untrusted sources.

          Changed in version 3.5: `charset' keyword-only argument was
          added.  The default charset of HTML document changed from
          ‘'ISO-8859-1'’ to ‘'utf-8'’.

      -- Method: make_table (fromlines, tolines, fromdesc='', todesc='',
               context=False, numlines=5)

          Compares `fromlines' and `tolines' (lists of strings) and
          returns a string which is a complete HTML table showing line
          by line differences with inter-line and intra-line changes
          highlighted.

          The arguments for this method are the same as those for the
          *note make_file(): 7bc. method.

     ‘Tools/scripts/diff.py’ is a command-line front-end to this class
     and contains a good example of its use.

 -- Function: difflib.context_diff (a, b, fromfile='', tofile='',
          fromfiledate='', tofiledate='', n=3, lineterm='\n')

     Compare `a' and `b' (lists of strings); return a delta (a *note
     generator: a83. generating the delta lines) in context diff format.

     Context diffs are a compact way of showing just the lines that have
     changed plus a few lines of context.  The changes are shown in a
     before/after style.  The number of context lines is set by `n'
     which defaults to three.

     By default, the diff control lines (those with ‘***’ or ‘---’) are
     created with a trailing newline.  This is helpful so that inputs
     created from *note io.IOBase.readlines(): 18d6. result in diffs
     that are suitable for use with *note io.IOBase.writelines(): 18d7.
     since both the inputs and outputs have trailing newlines.

     For inputs that do not have trailing newlines, set the `lineterm'
     argument to ‘""’ so that the output will be uniformly newline free.

     The context diff format normally has a header for filenames and
     modification times.  Any or all of these may be specified using
     strings for `fromfile', `tofile', `fromfiledate', and `tofiledate'.
     The modification times are normally expressed in the ISO 8601
     format.  If not specified, the strings default to blanks.

          >>> s1 = ['bacon\n', 'eggs\n', 'ham\n', 'guido\n']
          >>> s2 = ['python\n', 'eggy\n', 'hamster\n', 'guido\n']
          >>> sys.stdout.writelines(context_diff(s1, s2, fromfile='before.py', tofile='after.py'))
          *** before.py
          --- after.py
          ***************
          *** 1,4 ****
          ! bacon
          ! eggs
          ! ham
            guido
          --- 1,4 ----
          ! python
          ! eggy
          ! hamster
            guido

     See *note A command-line interface to difflib: 18d8. for a more
     detailed example.

 -- Function: difflib.get_close_matches (word, possibilities, n=3,
          cutoff=0.6)

     Return a list of the best “good enough” matches.  `word' is a
     sequence for which close matches are desired (typically a string),
     and `possibilities' is a list of sequences against which to match
     `word' (typically a list of strings).

     Optional argument `n' (default ‘3’) is the maximum number of close
     matches to return; `n' must be greater than ‘0’.

     Optional argument `cutoff' (default ‘0.6’) is a float in the range
     [0, 1].  Possibilities that don’t score at least that similar to
     `word' are ignored.

     The best (no more than `n') matches among the possibilities are
     returned in a list, sorted by similarity score, most similar first.

          >>> get_close_matches('appel', ['ape', 'apple', 'peach', 'puppy'])
          ['apple', 'ape']
          >>> import keyword
          >>> get_close_matches('wheel', keyword.kwlist)
          ['while']
          >>> get_close_matches('pineapple', keyword.kwlist)
          []
          >>> get_close_matches('accept', keyword.kwlist)
          ['except']

 -- Function: difflib.ndiff (a, b, linejunk=None,
          charjunk=IS_CHARACTER_JUNK)

     Compare `a' and `b' (lists of strings); return a *note Differ:
     18d0.-style delta (a *note generator: a83. generating the delta
     lines).

     Optional keyword parameters `linejunk' and `charjunk' are filtering
     functions (or ‘None’):

     `linejunk': A function that accepts a single string argument, and
     returns true if the string is junk, or false if not.  The default
     is ‘None’.  There is also a module-level function *note
     IS_LINE_JUNK(): 18da, which filters out lines without visible
     characters, except for at most one pound character (‘'#'’) –
     however the underlying *note SequenceMatcher: a30. class does a
     dynamic analysis of which lines are so frequent as to constitute
     noise, and this usually works better than using this function.

     `charjunk': A function that accepts a character (a string of length
     1), and returns if the character is junk, or false if not.  The
     default is module-level function *note IS_CHARACTER_JUNK(): 18db,
     which filters out whitespace characters (a blank or tab; it’s a bad
     idea to include newline in this!).

     ‘Tools/scripts/ndiff.py’ is a command-line front-end to this
     function.

          >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(keepends=True),
          ...              'ore\ntree\nemu\n'.splitlines(keepends=True))
          >>> print(''.join(diff), end="")
          - one
          ?  ^
          + ore
          ?  ^
          - two
          - three
          ?  -
          + tree
          + emu

 -- Function: difflib.restore (sequence, which)

     Return one of the two sequences that generated a delta.

     Given a `sequence' produced by *note Differ.compare(): 18dd. or
     *note ndiff(): 18d3, extract lines originating from file 1 or 2
     (parameter `which'), stripping off line prefixes.

     Example:

          >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(keepends=True),
          ...              'ore\ntree\nemu\n'.splitlines(keepends=True))
          >>> diff = list(diff) # materialize the generated delta into a list
          >>> print(''.join(restore(diff, 1)), end="")
          one
          two
          three
          >>> print(''.join(restore(diff, 2)), end="")
          ore
          tree
          emu

 -- Function: difflib.unified_diff (a, b, fromfile='', tofile='',
          fromfiledate='', tofiledate='', n=3, lineterm='\n')

     Compare `a' and `b' (lists of strings); return a delta (a *note
     generator: a83. generating the delta lines) in unified diff format.

     Unified diffs are a compact way of showing just the lines that have
     changed plus a few lines of context.  The changes are shown in an
     inline style (instead of separate before/after blocks).  The number
     of context lines is set by `n' which defaults to three.

     By default, the diff control lines (those with ‘---’, ‘+++’, or
     ‘@@’) are created with a trailing newline.  This is helpful so that
     inputs created from *note io.IOBase.readlines(): 18d6. result in
     diffs that are suitable for use with *note io.IOBase.writelines():
     18d7. since both the inputs and outputs have trailing newlines.

     For inputs that do not have trailing newlines, set the `lineterm'
     argument to ‘""’ so that the output will be uniformly newline free.

     The context diff format normally has a header for filenames and
     modification times.  Any or all of these may be specified using
     strings for `fromfile', `tofile', `fromfiledate', and `tofiledate'.
     The modification times are normally expressed in the ISO 8601
     format.  If not specified, the strings default to blanks.

          >>> s1 = ['bacon\n', 'eggs\n', 'ham\n', 'guido\n']
          >>> s2 = ['python\n', 'eggy\n', 'hamster\n', 'guido\n']
          >>> sys.stdout.writelines(unified_diff(s1, s2, fromfile='before.py', tofile='after.py'))
          --- before.py
          +++ after.py
          @@ -1,4 +1,4 @@
          -bacon
          -eggs
          -ham
          +python
          +eggy
          +hamster
           guido

     See *note A command-line interface to difflib: 18d8. for a more
     detailed example.

 -- Function: difflib.diff_bytes (dfunc, a, b, fromfile=b'', tofile=b'',
          fromfiledate=b'', tofiledate=b'', n=3, lineterm=b'\n')

     Compare `a' and `b' (lists of bytes objects) using `dfunc'; yield a
     sequence of delta lines (also bytes) in the format returned by
     `dfunc'.  `dfunc' must be a callable, typically either *note
     unified_diff(): 18de. or *note context_diff(): 18d5.

     Allows you to compare data with unknown or inconsistent encoding.
     All inputs except `n' must be bytes objects, not str.  Works by
     losslessly converting all inputs (except `n') to str, and calling
     ‘dfunc(a, b, fromfile, tofile, fromfiledate, tofiledate, n,
     lineterm)’.  The output of `dfunc' is then converted back to bytes,
     so the delta lines that you receive have the same
     unknown/inconsistent encodings as `a' and `b'.

     New in version 3.5.

 -- Function: difflib.IS_LINE_JUNK (line)

     Return ‘True’ for ignorable lines.  The line `line' is ignorable if
     `line' is blank or contains a single ‘'#'’, otherwise it is not
     ignorable.  Used as a default for parameter `linejunk' in *note
     ndiff(): 18d3. in older versions.

 -- Function: difflib.IS_CHARACTER_JUNK (ch)

     Return ‘True’ for ignorable characters.  The character `ch' is
     ignorable if `ch' is a space or tab, otherwise it is not ignorable.
     Used as a default for parameter `charjunk' in *note ndiff(): 18d3.

See also
........

Pattern Matching: The Gestalt Approach(2)

     Discussion of a similar algorithm by John W. Ratcliff and D. E.
     Metzener.  This was published in Dr.  Dobb’s Journal(3) in July,
     1988.

* Menu:

* SequenceMatcher Objects::
* SequenceMatcher Examples::
* Differ Objects::
* Differ Example::
* A command-line interface to difflib::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/difflib.py

   (2) 
http://www.drdobbs.com/database/pattern-matching-the-gestalt-approach/184407970

   (3) http://www.drdobbs.com/


File: python.info,  Node: SequenceMatcher Objects,  Next: SequenceMatcher Examples,  Up: difflib — Helpers for computing deltas

5.6.3.1 SequenceMatcher Objects
...............................

The *note SequenceMatcher: a30. class has this constructor:

 -- Class: difflib.SequenceMatcher (isjunk=None, a='', b='',
          autojunk=True)

     Optional argument `isjunk' must be ‘None’ (the default) or a
     one-argument function that takes a sequence element and returns
     true if and only if the element is “junk” and should be ignored.
     Passing ‘None’ for `isjunk' is equivalent to passing ‘lambda x:
     False’; in other words, no elements are ignored.  For example,
     pass:

          lambda x: x in " \t"

     if you’re comparing lines as sequences of characters, and don’t
     want to synch up on blanks or hard tabs.

     The optional arguments `a' and `b' are sequences to be compared;
     both default to empty strings.  The elements of both sequences must
     be *note hashable: 276.

     The optional argument `autojunk' can be used to disable the
     automatic junk heuristic.

     New in version 3.2: The `autojunk' parameter.

     SequenceMatcher objects get three data attributes: `bjunk' is the
     set of elements of `b' for which `isjunk' is ‘True’; `bpopular' is
     the set of non-junk elements considered popular by the heuristic
     (if it is not disabled); `b2j' is a dict mapping the remaining
     elements of `b' to a list of positions where they occur.  All three
     are reset whenever `b' is reset with *note set_seqs(): 18e1. or
     *note set_seq2(): 18e2.

     New in version 3.2: The `bjunk' and `bpopular' attributes.

     *note SequenceMatcher: a30. objects have the following methods:

      -- Method: set_seqs (a, b)

          Set the two sequences to be compared.

     *note SequenceMatcher: a30. computes and caches detailed
     information about the second sequence, so if you want to compare
     one sequence against many sequences, use *note set_seq2(): 18e2. to
     set the commonly used sequence once and call *note set_seq1():
     18e3. repeatedly, once for each of the other sequences.

      -- Method: set_seq1 (a)

          Set the first sequence to be compared.  The second sequence to
          be compared is not changed.

      -- Method: set_seq2 (b)

          Set the second sequence to be compared.  The first sequence to
          be compared is not changed.

      -- Method: find_longest_match (alo=0, ahi=None, blo=0, bhi=None)

          Find longest matching block in ‘a[alo:ahi]’ and ‘b[blo:bhi]’.

          If `isjunk' was omitted or ‘None’, *note find_longest_match():
          1041. returns ‘(i, j, k)’ such that ‘a[i:i+k]’ is equal to
          ‘b[j:j+k]’, where ‘alo <= i <= i+k <= ahi’ and ‘blo <= j <=
          j+k <= bhi’.  For all ‘(i', j', k')’ meeting those conditions,
          the additional conditions ‘k >= k'’, ‘i <= i'’, and if ‘i ==
          i'’, ‘j <= j'’ are also met.  In other words, of all maximal
          matching blocks, return one that starts earliest in `a', and
          of all those maximal matching blocks that start earliest in
          `a', return the one that starts earliest in `b'.

               >>> s = SequenceMatcher(None, " abcd", "abcd abcd")
               >>> s.find_longest_match(0, 5, 0, 9)
               Match(a=0, b=4, size=5)

          If `isjunk' was provided, first the longest matching block is
          determined as above, but with the additional restriction that
          no junk element appears in the block.  Then that block is
          extended as far as possible by matching (only) junk elements
          on both sides.  So the resulting block never matches on junk
          except as identical junk happens to be adjacent to an
          interesting match.

          Here’s the same example as before, but considering blanks to
          be junk.  That prevents ‘' abcd'’ from matching the ‘' abcd'’
          at the tail end of the second sequence directly.  Instead only
          the ‘'abcd'’ can match, and matches the leftmost ‘'abcd'’ in
          the second sequence:

               >>> s = SequenceMatcher(lambda x: x==" ", " abcd", "abcd abcd")
               >>> s.find_longest_match(0, 5, 0, 9)
               Match(a=1, b=0, size=4)

          If no blocks match, this returns ‘(alo, blo, 0)’.

          This method returns a *note named tuple: b7b. ‘Match(a, b,
          size)’.

          Changed in version 3.9: Added default arguments.

      -- Method: get_matching_blocks ()

          Return list of triples describing non-overlapping matching
          subsequences.  Each triple is of the form ‘(i, j, n)’, and
          means that ‘a[i:i+n] == b[j:j+n]’.  The triples are
          monotonically increasing in `i' and `j'.

          The last triple is a dummy, and has the value ‘(len(a),
          len(b), 0)’.  It is the only triple with ‘n == 0’.  If ‘(i, j,
          n)’ and ‘(i', j', n')’ are adjacent triples in the list, and
          the second is not the last triple in the list, then ‘i+n < i'’
          or ‘j+n < j'’; in other words, adjacent triples always
          describe non-adjacent equal blocks.

               >>> s = SequenceMatcher(None, "abxcd", "abcd")
               >>> s.get_matching_blocks()
               [Match(a=0, b=0, size=2), Match(a=3, b=2, size=2), Match(a=5, b=4, size=0)]

      -- Method: get_opcodes ()

          Return list of 5-tuples describing how to turn `a' into `b'.
          Each tuple is of the form ‘(tag, i1, i2, j1, j2)’.  The first
          tuple has ‘i1 == j1 == 0’, and remaining tuples have `i1'
          equal to the `i2' from the preceding tuple, and, likewise,
          `j1' equal to the previous `j2'.

          The `tag' values are strings, with these meanings:

          Value               Meaning
                              
          ----------------------------------------------------------------------
                              
          ‘'replace'’         ‘a[i1:i2]’ should be replaced by ‘b[j1:j2]’.
                              
                              
          ‘'delete'’          ‘a[i1:i2]’ should be deleted.  Note that ‘j1 ==
                              j2’ in this case.
                              
                              
          ‘'insert'’          ‘b[j1:j2]’ should be inserted at ‘a[i1:i1]’.
                              Note that ‘i1 == i2’ in this case.
                              
                              
          ‘'equal'’           ‘a[i1:i2] == b[j1:j2]’ (the sub-sequences are
                              equal).
                              

          For example:

               >>> a = "qabxcd"
               >>> b = "abycdf"
               >>> s = SequenceMatcher(None, a, b)
               >>> for tag, i1, i2, j1, j2 in s.get_opcodes():
               ...     print('{:7}   a[{}:{}] --> b[{}:{}] {!r:>8} --> {!r}'.format(
               ...         tag, i1, i2, j1, j2, a[i1:i2], b[j1:j2]))
               delete    a[0:1] --> b[0:0]      'q' --> ''
               equal     a[1:3] --> b[0:2]     'ab' --> 'ab'
               replace   a[3:4] --> b[2:3]      'x' --> 'y'
               equal     a[4:6] --> b[3:5]     'cd' --> 'cd'
               insert    a[6:6] --> b[5:6]       '' --> 'f'

      -- Method: get_grouped_opcodes (n=3)

          Return a *note generator: a83. of groups with up to `n' lines
          of context.

          Starting with the groups returned by *note get_opcodes():
          18e5, this method splits out smaller change clusters and
          eliminates intervening ranges which have no changes.

          The groups are returned in the same format as *note
          get_opcodes(): 18e5.

      -- Method: ratio ()

          Return a measure of the sequences’ similarity as a float in
          the range [0, 1].

          Where T is the total number of elements in both sequences, and
          M is the number of matches, this is 2.0*M / T. Note that this
          is ‘1.0’ if the sequences are identical, and ‘0.0’ if they
          have nothing in common.

          This is expensive to compute if *note get_matching_blocks():
          18e4. or *note get_opcodes(): 18e5. hasn’t already been
          called, in which case you may want to try *note quick_ratio():
          18e8. or *note real_quick_ratio(): 18e9. first to get an upper
          bound.

               Note: Caution: The result of a *note ratio(): 18e7. call
               may depend on the order of the arguments.  For instance:

                    >>> SequenceMatcher(None, 'tide', 'diet').ratio()
                    0.25
                    >>> SequenceMatcher(None, 'diet', 'tide').ratio()
                    0.5

      -- Method: quick_ratio ()

          Return an upper bound on *note ratio(): 18e7. relatively
          quickly.

      -- Method: real_quick_ratio ()

          Return an upper bound on *note ratio(): 18e7. very quickly.

The three methods that return the ratio of matching to total characters
can give different results due to differing levels of approximation,
although ‘quick_ratio()’ and ‘real_quick_ratio()’ are always at least as
large as ‘ratio()’:

     >>> s = SequenceMatcher(None, "abcd", "bcde")
     >>> s.ratio()
     0.75
     >>> s.quick_ratio()
     0.75
     >>> s.real_quick_ratio()
     1.0


File: python.info,  Node: SequenceMatcher Examples,  Next: Differ Objects,  Prev: SequenceMatcher Objects,  Up: difflib — Helpers for computing deltas

5.6.3.2 SequenceMatcher Examples
................................

This example compares two strings, considering blanks to be “junk”:

     >>> s = SequenceMatcher(lambda x: x == " ",
     ...                     "private Thread currentThread;",
     ...                     "private volatile Thread currentThread;")

‘ratio()’ returns a float in [0, 1], measuring the similarity of the
sequences.  As a rule of thumb, a ‘ratio()’ value over 0.6 means the
sequences are close matches:

     >>> print(round(s.ratio(), 3))
     0.866

If you’re only interested in where the sequences match,
‘get_matching_blocks()’ is handy:

     >>> for block in s.get_matching_blocks():
     ...     print("a[%d] and b[%d] match for %d elements" % block)
     a[0] and b[0] match for 8 elements
     a[8] and b[17] match for 21 elements
     a[29] and b[38] match for 0 elements

Note that the last tuple returned by ‘get_matching_blocks()’ is always a
dummy, ‘(len(a), len(b), 0)’, and this is the only case in which the
last tuple element (number of elements matched) is ‘0’.

If you want to know how to change the first sequence into the second,
use ‘get_opcodes()’:

     >>> for opcode in s.get_opcodes():
     ...     print("%6s a[%d:%d] b[%d:%d]" % opcode)
      equal a[0:8] b[0:8]
     insert a[8:8] b[8:17]
      equal a[8:29] b[17:38]

See also
........

   * The *note get_close_matches(): 18d9. function in this module which
     shows how simple code building on *note SequenceMatcher: a30. can
     be used to do useful work.

   * Simple version control recipe(1) for a small application built with
     *note SequenceMatcher: a30.

   ---------- Footnotes ----------

   (1) https://code.activestate.com/recipes/576729/


File: python.info,  Node: Differ Objects,  Next: Differ Example,  Prev: SequenceMatcher Examples,  Up: difflib — Helpers for computing deltas

5.6.3.3 Differ Objects
......................

Note that *note Differ: 18d0.-generated deltas make no claim to be
`minimal' diffs.  To the contrary, minimal diffs are often
counter-intuitive, because they synch up anywhere possible, sometimes
accidental matches 100 pages apart.  Restricting synch points to
contiguous matches preserves some notion of locality, at the occasional
cost of producing a longer diff.

The *note Differ: 18d0. class has this constructor:

 -- Class: difflib.Differ (linejunk=None, charjunk=None)

     Optional keyword parameters `linejunk' and `charjunk' are for
     filter functions (or ‘None’):

     `linejunk': A function that accepts a single string argument, and
     returns true if the string is junk.  The default is ‘None’, meaning
     that no line is considered junk.

     `charjunk': A function that accepts a single character argument (a
     string of length 1), and returns true if the character is junk.
     The default is ‘None’, meaning that no character is considered
     junk.

     These junk-filtering functions speed up matching to find
     differences and do not cause any differing lines or characters to
     be ignored.  Read the description of the *note
     find_longest_match(): 1041. method’s `isjunk' parameter for an
     explanation.

     *note Differ: 18d0. objects are used (deltas generated) via a
     single method:

      -- Method: compare (a, b)

          Compare two sequences of lines, and generate the delta (a
          sequence of lines).

          Each sequence must contain individual single-line strings
          ending with newlines.  Such sequences can be obtained from the
          *note readlines(): 18d6. method of file-like objects.  The
          delta generated also consists of newline-terminated strings,
          ready to be printed as-is via the *note writelines(): 18d7.
          method of a file-like object.


File: python.info,  Node: Differ Example,  Next: A command-line interface to difflib,  Prev: Differ Objects,  Up: difflib — Helpers for computing deltas

5.6.3.4 Differ Example
......................

This example compares two texts.  First we set up the texts, sequences
of individual single-line strings ending with newlines (such sequences
can also be obtained from the ‘readlines()’ method of file-like
objects):

     >>> text1 = '''  1. Beautiful is better than ugly.
     ...   2. Explicit is better than implicit.
     ...   3. Simple is better than complex.
     ...   4. Complex is better than complicated.
     ... '''.splitlines(keepends=True)
     >>> len(text1)
     4
     >>> text1[0][-1]
     '\n'
     >>> text2 = '''  1. Beautiful is better than ugly.
     ...   3.   Simple is better than complex.
     ...   4. Complicated is better than complex.
     ...   5. Flat is better than nested.
     ... '''.splitlines(keepends=True)

Next we instantiate a Differ object:

     >>> d = Differ()

Note that when instantiating a *note Differ: 18d0. object we may pass
functions to filter out line and character “junk.” See the *note
Differ(): 18d0. constructor for details.

Finally, we compare the two:

     >>> result = list(d.compare(text1, text2))

‘result’ is a list of strings, so let’s pretty-print it:

     >>> from pprint import pprint
     >>> pprint(result)
     ['    1. Beautiful is better than ugly.\n',
      '-   2. Explicit is better than implicit.\n',
      '-   3. Simple is better than complex.\n',
      '+   3.   Simple is better than complex.\n',
      '?     ++\n',
      '-   4. Complex is better than complicated.\n',
      '?            ^                     ---- ^\n',
      '+   4. Complicated is better than complex.\n',
      '?           ++++ ^                      ^\n',
      '+   5. Flat is better than nested.\n']

As a single multi-line string it looks like this:

     >>> import sys
     >>> sys.stdout.writelines(result)
         1. Beautiful is better than ugly.
     -   2. Explicit is better than implicit.
     -   3. Simple is better than complex.
     +   3.   Simple is better than complex.
     ?     ++
     -   4. Complex is better than complicated.
     ?            ^                     ---- ^
     +   4. Complicated is better than complex.
     ?           ++++ ^                      ^
     +   5. Flat is better than nested.


File: python.info,  Node: A command-line interface to difflib,  Prev: Differ Example,  Up: difflib — Helpers for computing deltas

5.6.3.5 A command-line interface to difflib
...........................................

This example shows how to use difflib to create a ‘diff’-like utility.
It is also contained in the Python source distribution, as
‘Tools/scripts/diff.py’.

     #!/usr/bin/env python3
     """ Command line interface to difflib.py providing diffs in four formats:

     * ndiff:    lists every line and highlights interline changes.
     * context:  highlights clusters of changes in a before/after format.
     * unified:  highlights clusters of changes in an inline format.
     * html:     generates side by side comparison with change highlights.

     """

     import sys, os, difflib, argparse
     from datetime import datetime, timezone

     def file_mtime(path):
         t = datetime.fromtimestamp(os.stat(path).st_mtime,
                                    timezone.utc)
         return t.astimezone().isoformat()

     def main():

         parser = argparse.ArgumentParser()
         parser.add_argument('-c', action='store_true', default=False,
                             help='Produce a context format diff (default)')
         parser.add_argument('-u', action='store_true', default=False,
                             help='Produce a unified format diff')
         parser.add_argument('-m', action='store_true', default=False,
                             help='Produce HTML side by side diff '
                                  '(can use -c and -l in conjunction)')
         parser.add_argument('-n', action='store_true', default=False,
                             help='Produce a ndiff format diff')
         parser.add_argument('-l', '--lines', type=int, default=3,
                             help='Set number of context lines (default 3)')
         parser.add_argument('fromfile')
         parser.add_argument('tofile')
         options = parser.parse_args()

         n = options.lines
         fromfile = options.fromfile
         tofile = options.tofile

         fromdate = file_mtime(fromfile)
         todate = file_mtime(tofile)
         with open(fromfile) as ff:
             fromlines = ff.readlines()
         with open(tofile) as tf:
             tolines = tf.readlines()

         if options.u:
             diff = difflib.unified_diff(fromlines, tolines, fromfile, tofile, fromdate, todate, n=n)
         elif options.n:
             diff = difflib.ndiff(fromlines, tolines)
         elif options.m:
             diff = difflib.HtmlDiff().make_file(fromlines,tolines,fromfile,tofile,context=options.c,numlines=n)
         else:
             diff = difflib.context_diff(fromlines, tolines, fromfile, tofile, fromdate, todate, n=n)

         sys.stdout.writelines(diff)

     if __name__ == '__main__':
         main()


File: python.info,  Node: textwrap — Text wrapping and filling,  Next: unicodedata — Unicode Database,  Prev: difflib — Helpers for computing deltas,  Up: Text Processing Services

5.6.4 ‘textwrap’ — Text wrapping and filling
--------------------------------------------

`Source code:' Lib/textwrap.py(1)

__________________________________________________________________

The *note textwrap: 10a. module provides some convenience functions, as
well as *note TextWrapper: 9d0, the class that does all the work.  If
you’re just wrapping or filling one or two text strings, the convenience
functions should be good enough; otherwise, you should use an instance
of *note TextWrapper: 9d0. for efficiency.

 -- Function: textwrap.wrap (text, width=70, *, initial_indent="",
          subsequent_indent="", expand_tabs=True,
          replace_whitespace=True, fix_sentence_endings=False,
          break_long_words=True, drop_whitespace=True,
          break_on_hyphens=True, tabsize=8, max_lines=None)

     Wraps the single paragraph in `text' (a string) so every line is at
     most `width' characters long.  Returns a list of output lines,
     without final newlines.

     Optional keyword arguments correspond to the instance attributes of
     *note TextWrapper: 9d0, documented below.

     See the *note TextWrapper.wrap(): 18f3. method for additional
     details on how *note wrap(): f86. behaves.

 -- Function: textwrap.fill (text, width=70, *, initial_indent="",
          subsequent_indent="", expand_tabs=True,
          replace_whitespace=True, fix_sentence_endings=False,
          break_long_words=True, drop_whitespace=True,
          break_on_hyphens=True, tabsize=8, max_lines=None)

     Wraps the single paragraph in `text', and returns a single string
     containing the wrapped paragraph.  *note fill(): f87. is shorthand
     for

          "\n".join(wrap(text, ...))

     In particular, *note fill(): f87. accepts exactly the same keyword
     arguments as *note wrap(): f86.

 -- Function: textwrap.shorten (text, width, *,
          fix_sentence_endings=False, break_long_words=True,
          break_on_hyphens=True, placeholder=' [...]')

     Collapse and truncate the given `text' to fit in the given `width'.

     First the whitespace in `text' is collapsed (all whitespace is
     replaced by single spaces).  If the result fits in the `width', it
     is returned.  Otherwise, enough words are dropped from the end so
     that the remaining words plus the ‘placeholder’ fit within ‘width’:

          >>> textwrap.shorten("Hello  world!", width=12)
          'Hello world!'
          >>> textwrap.shorten("Hello  world!", width=11)
          'Hello [...]'
          >>> textwrap.shorten("Hello world", width=10, placeholder="...")
          'Hello...'

     Optional keyword arguments correspond to the instance attributes of
     *note TextWrapper: 9d0, documented below.  Note that the whitespace
     is collapsed before the text is passed to the *note TextWrapper:
     9d0. *note fill(): f87. function, so changing the value of *note
     tabsize: 18f4, *note expand_tabs: 18f5, *note drop_whitespace:
     18f6, and *note replace_whitespace: 18f7. will have no effect.

     New in version 3.4.

 -- Function: textwrap.dedent (text)

     Remove any common leading whitespace from every line in `text'.

     This can be used to make triple-quoted strings line up with the
     left edge of the display, while still presenting them in the source
     code in indented form.

     Note that tabs and spaces are both treated as whitespace, but they
     are not equal: the lines ‘" hello"’ and ‘"\thello"’ are considered
     to have no common leading whitespace.

     Lines containing only whitespace are ignored in the input and
     normalized to a single newline character in the output.

     For example:

          def test():
              # end first line with \ to avoid the empty line!
              s = '''\
              hello
                world
              '''
              print(repr(s))          # prints '    hello\n      world\n    '
              print(repr(dedent(s)))  # prints 'hello\n  world\n'

 -- Function: textwrap.indent (text, prefix, predicate=None)

     Add `prefix' to the beginning of selected lines in `text'.

     Lines are separated by calling ‘text.splitlines(True)’.

     By default, `prefix' is added to all lines that do not consist
     solely of whitespace (including any line endings).

     For example:

          >>> s = 'hello\n\n \nworld'
          >>> indent(s, '  ')
          '  hello\n\n \n  world'

     The optional `predicate' argument can be used to control which
     lines are indented.  For example, it is easy to add `prefix' to
     even empty and whitespace-only lines:

          >>> print(indent(s, '+ ', lambda line: True))
          + hello
          +
          +
          + world

     New in version 3.3.

*note wrap(): f86, *note fill(): f87. and *note shorten(): 9d3. work by
creating a *note TextWrapper: 9d0. instance and calling a single method
on it.  That instance is not reused, so for applications that process
many text strings using *note wrap(): f86. and/or *note fill(): f87, it
may be more efficient to create your own *note TextWrapper: 9d0. object.

Text is preferably wrapped on whitespaces and right after the hyphens in
hyphenated words; only then will long words be broken if necessary,
unless *note TextWrapper.break_long_words: 18f9. is set to false.

 -- Class: textwrap.TextWrapper (**kwargs)

     The *note TextWrapper: 9d0. constructor accepts a number of
     optional keyword arguments.  Each keyword argument corresponds to
     an instance attribute, so for example

          wrapper = TextWrapper(initial_indent="* ")

     is the same as

          wrapper = TextWrapper()
          wrapper.initial_indent = "* "

     You can re-use the same *note TextWrapper: 9d0. object many times,
     and you can change any of its options through direct assignment to
     instance attributes between uses.

     The *note TextWrapper: 9d0. instance attributes (and keyword
     arguments to the constructor) are as follows:

      -- Attribute: width

          (default: ‘70’) The maximum length of wrapped lines.  As long
          as there are no individual words in the input text longer than
          *note width: 18fa, *note TextWrapper: 9d0. guarantees that no
          output line will be longer than *note width: 18fa. characters.

      -- Attribute: expand_tabs

          (default: ‘True’) If true, then all tab characters in `text'
          will be expanded to spaces using the ‘expandtabs()’ method of
          `text'.

      -- Attribute: tabsize

          (default: ‘8’) If *note expand_tabs: 18f5. is true, then all
          tab characters in `text' will be expanded to zero or more
          spaces, depending on the current column and the given tab
          size.

          New in version 3.3.

      -- Attribute: replace_whitespace

          (default: ‘True’) If true, after tab expansion but before
          wrapping, the *note wrap(): f86. method will replace each
          whitespace character with a single space.  The whitespace
          characters replaced are as follows: tab, newline, vertical
          tab, formfeed, and carriage return (‘'\t\n\v\f\r'’).

               Note: If *note expand_tabs: 18f5. is false and *note
               replace_whitespace: 18f7. is true, each tab character
               will be replaced by a single space, which is `not' the
               same as tab expansion.

               Note: If *note replace_whitespace: 18f7. is false,
               newlines may appear in the middle of a line and cause
               strange output.  For this reason, text should be split
               into paragraphs (using *note str.splitlines(): 178c. or
               similar) which are wrapped separately.

      -- Attribute: drop_whitespace

          (default: ‘True’) If true, whitespace at the beginning and
          ending of every line (after wrapping but before indenting) is
          dropped.  Whitespace at the beginning of the paragraph,
          however, is not dropped if non-whitespace follows it.  If
          whitespace being dropped takes up an entire line, the whole
          line is dropped.

      -- Attribute: initial_indent

          (default: ‘''’) String that will be prepended to the first
          line of wrapped output.  Counts towards the length of the
          first line.  The empty string is not indented.

      -- Attribute: subsequent_indent

          (default: ‘''’) String that will be prepended to all lines of
          wrapped output except the first.  Counts towards the length of
          each line except the first.

      -- Attribute: fix_sentence_endings

          (default: ‘False’) If true, *note TextWrapper: 9d0. attempts
          to detect sentence endings and ensure that sentences are
          always separated by exactly two spaces.  This is generally
          desired for text in a monospaced font.  However, the sentence
          detection algorithm is imperfect: it assumes that a sentence
          ending consists of a lowercase letter followed by one of
          ‘'.'’, ‘'!'’, or ‘'?'’, possibly followed by one of ‘'"'’ or
          ‘"'"’, followed by a space.  One problem with this is
          algorithm is that it is unable to detect the difference
          between “Dr.” in

               [...] Dr. Frankenstein's monster [...]

          and “Spot.” in

               [...] See Spot. See Spot run [...]

          *note fix_sentence_endings: 18fd. is false by default.

          Since the sentence detection algorithm relies on
          ‘string.lowercase’ for the definition of “lowercase letter”,
          and a convention of using two spaces after a period to
          separate sentences on the same line, it is specific to
          English-language texts.

      -- Attribute: break_long_words

          (default: ‘True’) If true, then words longer than *note width:
          18fa. will be broken in order to ensure that no lines are
          longer than *note width: 18fa.  If it is false, long words
          will not be broken, and some lines may be longer than *note
          width: 18fa.  (Long words will be put on a line by themselves,
          in order to minimize the amount by which *note width: 18fa. is
          exceeded.)

      -- Attribute: break_on_hyphens

          (default: ‘True’) If true, wrapping will occur preferably on
          whitespaces and right after hyphens in compound words, as it
          is customary in English.  If false, only whitespaces will be
          considered as potentially good places for line breaks, but you
          need to set *note break_long_words: 18f9. to false if you want
          truly insecable words.  Default behaviour in previous versions
          was to always allow breaking hyphenated words.

      -- Attribute: max_lines

          (default: ‘None’) If not ‘None’, then the output will contain
          at most `max_lines' lines, with `placeholder' appearing at the
          end of the output.

          New in version 3.4.

      -- Attribute: placeholder

          (default: ‘' [...]'’) String that will appear at the end of
          the output text if it has been truncated.

          New in version 3.4.

     *note TextWrapper: 9d0. also provides some public methods,
     analogous to the module-level convenience functions:

      -- Method: wrap (text)

          Wraps the single paragraph in `text' (a string) so every line
          is at most *note width: 18fa. characters long.  All wrapping
          options are taken from instance attributes of the *note
          TextWrapper: 9d0. instance.  Returns a list of output lines,
          without final newlines.  If the wrapped output has no content,
          the returned list is empty.

      -- Method: fill (text)

          Wraps the single paragraph in `text', and returns a single
          string containing the wrapped paragraph.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/textwrap.py


File: python.info,  Node: unicodedata — Unicode Database,  Next: stringprep — Internet String Preparation,  Prev: textwrap — Text wrapping and filling,  Up: Text Processing Services

5.6.5 ‘unicodedata’ — Unicode Database
--------------------------------------

__________________________________________________________________

This module provides access to the Unicode Character Database (UCD)
which defines character properties for all Unicode characters.  The data
contained in this database is compiled from the UCD version 13.0.0(1).

The module uses the same names and symbols as defined by Unicode
Standard Annex #44, "Unicode Character Database"(2).  It defines the
following functions:

 -- Function: unicodedata.lookup (name)

     Look up character by name.  If a character with the given name is
     found, return the corresponding character.  If not found, *note
     KeyError: 3e9. is raised.

     Changed in version 3.3: Support for name aliases (3) and named
     sequences (4) has been added.

 -- Function: unicodedata.name (chr[, default])

     Returns the name assigned to the character `chr' as a string.  If
     no name is defined, `default' is returned, or, if not given, *note
     ValueError: 16d. is raised.

 -- Function: unicodedata.decimal (chr[, default])

     Returns the decimal value assigned to the character `chr' as
     integer.  If no such value is defined, `default' is returned, or,
     if not given, *note ValueError: 16d. is raised.

 -- Function: unicodedata.digit (chr[, default])

     Returns the digit value assigned to the character `chr' as integer.
     If no such value is defined, `default' is returned, or, if not
     given, *note ValueError: 16d. is raised.

 -- Function: unicodedata.numeric (chr[, default])

     Returns the numeric value assigned to the character `chr' as float.
     If no such value is defined, `default' is returned, or, if not
     given, *note ValueError: 16d. is raised.

 -- Function: unicodedata.category (chr)

     Returns the general category assigned to the character `chr' as
     string.

 -- Function: unicodedata.bidirectional (chr)

     Returns the bidirectional class assigned to the character `chr' as
     string.  If no such value is defined, an empty string is returned.

 -- Function: unicodedata.combining (chr)

     Returns the canonical combining class assigned to the character
     `chr' as integer.  Returns ‘0’ if no combining class is defined.

 -- Function: unicodedata.east_asian_width (chr)

     Returns the east asian width assigned to the character `chr' as
     string.

 -- Function: unicodedata.mirrored (chr)

     Returns the mirrored property assigned to the character `chr' as
     integer.  Returns ‘1’ if the character has been identified as a
     “mirrored” character in bidirectional text, ‘0’ otherwise.

 -- Function: unicodedata.decomposition (chr)

     Returns the character decomposition mapping assigned to the
     character `chr' as string.  An empty string is returned in case no
     such mapping is defined.

 -- Function: unicodedata.normalize (form, unistr)

     Return the normal form `form' for the Unicode string `unistr'.
     Valid values for `form' are ‘NFC’, ‘NFKC’, ‘NFD’, and ‘NFKD’.

     The Unicode standard defines various normalization forms of a
     Unicode string, based on the definition of canonical equivalence
     and compatibility equivalence.  In Unicode, several characters can
     be expressed in various way.  For example, the character U+00C7
     (LATIN CAPITAL LETTER C WITH CEDILLA) can also be expressed as the
     sequence U+0043 (LATIN CAPITAL LETTER C) U+0327 (COMBINING
     CEDILLA).

     For each character, there are two normal forms: normal form C and
     normal form D. Normal form D (NFD) is also known as canonical
     decomposition, and translates each character into its decomposed
     form.  Normal form C (NFC) first applies a canonical decomposition,
     then composes pre-combined characters again.

     In addition to these two forms, there are two additional normal
     forms based on compatibility equivalence.  In Unicode, certain
     characters are supported which normally would be unified with other
     characters.  For example, U+2160 (ROMAN NUMERAL ONE) is really the
     same thing as U+0049 (LATIN CAPITAL LETTER I). However, it is
     supported in Unicode for compatibility with existing character sets
     (e.g.  gb2312).

     The normal form KD (NFKD) will apply the compatibility
     decomposition, i.e.  replace all compatibility characters with
     their equivalents.  The normal form KC (NFKC) first applies the
     compatibility decomposition, followed by the canonical composition.

     Even if two unicode strings are normalized and look the same to a
     human reader, if one has combining characters and the other
     doesn’t, they may not compare equal.

 -- Function: unicodedata.is_normalized (form, unistr)

     Return whether the Unicode string `unistr' is in the normal form
     `form'.  Valid values for `form' are ‘NFC’, ‘NFKC’, ‘NFD’, and
     ‘NFKD’.

     New in version 3.8.

In addition, the module exposes the following constant:

 -- Data: unicodedata.unidata_version

     The version of the Unicode database used in this module.

 -- Data: unicodedata.ucd_3_2_0

     This is an object that has the same methods as the entire module,
     but uses the Unicode database version 3.2 instead, for applications
     that require this specific version of the Unicode database (such as
     IDNA).

Examples:

     >>> import unicodedata
     >>> unicodedata.lookup('LEFT CURLY BRACKET')
     '{'
     >>> unicodedata.name('/')
     'SOLIDUS'
     >>> unicodedata.decimal('9')
     9
     >>> unicodedata.decimal('a')
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ValueError: not a decimal
     >>> unicodedata.category('A')  # 'L'etter, 'u'ppercase
     'Lu'
     >>> unicodedata.bidirectional('\u0660') # 'A'rabic, 'N'umber
     'AN'

   ---------- Footnotes ----------

   (1) https://www.unicode.org/Public/13.0.0/ucd

   (2) https://www.unicode.org/reports/tr44/

   (3) (1) ‘https://www.unicode.org/Public/13.0.0/ucd/NameAliases.txt’

   (4) (2)
‘https://www.unicode.org/Public/13.0.0/ucd/NamedSequences.txt’


File: python.info,  Node: stringprep — Internet String Preparation,  Next: readline — GNU readline interface,  Prev: unicodedata — Unicode Database,  Up: Text Processing Services

5.6.6 ‘stringprep’ — Internet String Preparation
------------------------------------------------

`Source code:' Lib/stringprep.py(1)

__________________________________________________________________

When identifying things (such as host names) in the internet, it is
often necessary to compare such identifications for “equality”.  Exactly
how this comparison is executed may depend on the application domain,
e.g.  whether it should be case-insensitive or not.  It may be also
necessary to restrict the possible identifications, to allow only
identifications consisting of “printable” characters.

RFC 3454(2) defines a procedure for “preparing” Unicode strings in
internet protocols.  Before passing strings onto the wire, they are
processed with the preparation procedure, after which they have a
certain normalized form.  The RFC defines a set of tables, which can be
combined into profiles.  Each profile must define which tables it uses,
and what other optional parts of the ‘stringprep’ procedure are part of
the profile.  One example of a ‘stringprep’ profile is ‘nameprep’, which
is used for internationalized domain names.

The module *note stringprep: f7. only exposes the tables from RFC
3454(3).  As these tables would be very large to represent them as
dictionaries or lists, the module uses the Unicode character database
internally.  The module source code itself was generated using the
‘mkstringprep.py’ utility.

As a result, these tables are exposed as functions, not as data
structures.  There are two kinds of tables in the RFC: sets and
mappings.  For a set, *note stringprep: f7. provides the “characteristic
function”, i.e.  a function that returns ‘True’ if the parameter is part
of the set.  For mappings, it provides the mapping function: given the
key, it returns the associated value.  Below is a list of all functions
available in the module.

 -- Function: stringprep.in_table_a1 (code)

     Determine whether `code' is in tableA.1 (Unassigned code points in
     Unicode 3.2).

 -- Function: stringprep.in_table_b1 (code)

     Determine whether `code' is in tableB.1 (Commonly mapped to
     nothing).

 -- Function: stringprep.map_table_b2 (code)

     Return the mapped value for `code' according to tableB.2 (Mapping
     for case-folding used with NFKC).

 -- Function: stringprep.map_table_b3 (code)

     Return the mapped value for `code' according to tableB.3 (Mapping
     for case-folding used with no normalization).

 -- Function: stringprep.in_table_c11 (code)

     Determine whether `code' is in tableC.1.1 (ASCII space characters).

 -- Function: stringprep.in_table_c12 (code)

     Determine whether `code' is in tableC.1.2 (Non-ASCII space
     characters).

 -- Function: stringprep.in_table_c11_c12 (code)

     Determine whether `code' is in tableC.1 (Space characters, union of
     C.1.1 and C.1.2).

 -- Function: stringprep.in_table_c21 (code)

     Determine whether `code' is in tableC.2.1 (ASCII control
     characters).

 -- Function: stringprep.in_table_c22 (code)

     Determine whether `code' is in tableC.2.2 (Non-ASCII control
     characters).

 -- Function: stringprep.in_table_c21_c22 (code)

     Determine whether `code' is in tableC.2 (Control characters, union
     of C.2.1 and C.2.2).

 -- Function: stringprep.in_table_c3 (code)

     Determine whether `code' is in tableC.3 (Private use).

 -- Function: stringprep.in_table_c4 (code)

     Determine whether `code' is in tableC.4 (Non-character code
     points).

 -- Function: stringprep.in_table_c5 (code)

     Determine whether `code' is in tableC.5 (Surrogate codes).

 -- Function: stringprep.in_table_c6 (code)

     Determine whether `code' is in tableC.6 (Inappropriate for plain
     text).

 -- Function: stringprep.in_table_c7 (code)

     Determine whether `code' is in tableC.7 (Inappropriate for
     canonical representation).

 -- Function: stringprep.in_table_c8 (code)

     Determine whether `code' is in tableC.8 (Change display properties
     or are deprecated).

 -- Function: stringprep.in_table_c9 (code)

     Determine whether `code' is in tableC.9 (Tagging characters).

 -- Function: stringprep.in_table_d1 (code)

     Determine whether `code' is in tableD.1 (Characters with
     bidirectional property “R” or “AL”).

 -- Function: stringprep.in_table_d2 (code)

     Determine whether `code' is in tableD.2 (Characters with
     bidirectional property “L”).

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/stringprep.py

   (2) https://tools.ietf.org/html/rfc3454.html

   (3) https://tools.ietf.org/html/rfc3454.html


File: python.info,  Node: readline — GNU readline interface,  Next: rlcompleter — Completion function for GNU readline,  Prev: stringprep — Internet String Preparation,  Up: Text Processing Services

5.6.7 ‘readline’ — GNU readline interface
-----------------------------------------

__________________________________________________________________

The *note readline: de. module defines a number of functions to
facilitate completion and reading/writing of history files from the
Python interpreter.  This module can be used directly, or via the *note
rlcompleter: e1. module, which supports completion of Python identifiers
at the interactive prompt.  Settings made using this module affect the
behaviour of both the interpreter’s interactive prompt and the prompts
offered by the built-in *note input(): d33. function.

Readline keybindings may be configured via an initialization file,
typically ‘.inputrc’ in your home directory.  See Readline Init File(1)
in the GNU Readline manual for information about the format and
allowable constructs of that file, and the capabilities of the Readline
library in general.

     Note: The underlying Readline library API may be implemented by the
     ‘libedit’ library instead of GNU readline.  On macOS the *note
     readline: de. module detects which library is being used at run
     time.

     The configuration file for ‘libedit’ is different from that of GNU
     readline.  If you programmatically load configuration strings you
     can check for the text “libedit” in ‘readline.__doc__’ to
     differentiate between GNU readline and libedit.

     If you use `editline'/‘libedit’ readline emulation on macOS, the
     initialization file located in your home directory is named
     ‘.editrc’.  For example, the following content in ‘~/.editrc’ will
     turn ON `vi' keybindings and TAB completion:

          python:bind -v
          python:bind ^I rl_complete

* Menu:

* Init file::
* Line buffer::
* History file::
* History list::
* Startup hooks::
* Completion::
* Example::

   ---------- Footnotes ----------

   (1) https://tiswww.cwru.edu/php/chet/readline/rluserman.html#SEC9


File: python.info,  Node: Init file,  Next: Line buffer,  Up: readline — GNU readline interface

5.6.7.1 Init file
.................

The following functions relate to the init file and user configuration:

 -- Function: readline.parse_and_bind (string)

     Execute the init line provided in the `string' argument.  This
     calls ‘rl_parse_and_bind()’ in the underlying library.

 -- Function: readline.read_init_file ([filename])

     Execute a readline initialization file.  The default filename is
     the last filename used.  This calls ‘rl_read_init_file()’ in the
     underlying library.


File: python.info,  Node: Line buffer,  Next: History file,  Prev: Init file,  Up: readline — GNU readline interface

5.6.7.2 Line buffer
...................

The following functions operate on the line buffer:

 -- Function: readline.get_line_buffer ()

     Return the current contents of the line buffer (‘rl_line_buffer’ in
     the underlying library).

 -- Function: readline.insert_text (string)

     Insert text into the line buffer at the cursor position.  This
     calls ‘rl_insert_text()’ in the underlying library, but ignores the
     return value.

 -- Function: readline.redisplay ()

     Change what’s displayed on the screen to reflect the current
     contents of the line buffer.  This calls ‘rl_redisplay()’ in the
     underlying library.


File: python.info,  Node: History file,  Next: History list,  Prev: Line buffer,  Up: readline — GNU readline interface

5.6.7.3 History file
....................

The following functions operate on a history file:

 -- Function: readline.read_history_file ([filename])

     Load a readline history file, and append it to the history list.
     The default filename is ‘~/.history’.  This calls ‘read_history()’
     in the underlying library.

 -- Function: readline.write_history_file ([filename])

     Save the history list to a readline history file, overwriting any
     existing file.  The default filename is ‘~/.history’.  This calls
     ‘write_history()’ in the underlying library.

 -- Function: readline.append_history_file (nelements[, filename])

     Append the last `nelements' items of history to a file.  The
     default filename is ‘~/.history’.  The file must already exist.
     This calls ‘append_history()’ in the underlying library.  This
     function only exists if Python was compiled for a version of the
     library that supports it.

     New in version 3.5.

 -- Function: readline.get_history_length ()
 -- Function: readline.set_history_length (length)

     Set or return the desired number of lines to save in the history
     file.  The *note write_history_file(): 192c. function uses this
     value to truncate the history file, by calling
     ‘history_truncate_file()’ in the underlying library.  Negative
     values imply unlimited history file size.


File: python.info,  Node: History list,  Next: Startup hooks,  Prev: History file,  Up: readline — GNU readline interface

5.6.7.4 History list
....................

The following functions operate on a global history list:

 -- Function: readline.clear_history ()

     Clear the current history.  This calls ‘clear_history()’ in the
     underlying library.  The Python function only exists if Python was
     compiled for a version of the library that supports it.

 -- Function: readline.get_current_history_length ()

     Return the number of items currently in the history.  (This is
     different from *note get_history_length(): 192d, which returns the
     maximum number of lines that will be written to a history file.)

 -- Function: readline.get_history_item (index)

     Return the current contents of history item at `index'.  The item
     index is one-based.  This calls ‘history_get()’ in the underlying
     library.

 -- Function: readline.remove_history_item (pos)

     Remove history item specified by its position from the history.
     The position is zero-based.  This calls ‘remove_history()’ in the
     underlying library.

 -- Function: readline.replace_history_item (pos, line)

     Replace history item specified by its position with `line'.  The
     position is zero-based.  This calls ‘replace_history_entry()’ in
     the underlying library.

 -- Function: readline.add_history (line)

     Append `line' to the history buffer, as if it was the last line
     typed.  This calls ‘add_history()’ in the underlying library.

 -- Function: readline.set_auto_history (enabled)

     Enable or disable automatic calls to ‘add_history()’ when reading
     input via readline.  The `enabled' argument should be a Boolean
     value that when true, enables auto history, and that when false,
     disables auto history.

     New in version 3.6.

     `CPython implementation detail:' Auto history is enabled by
     default, and changes to this do not persist across multiple
     sessions.


File: python.info,  Node: Startup hooks,  Next: Completion,  Prev: History list,  Up: readline — GNU readline interface

5.6.7.5 Startup hooks
.....................

 -- Function: readline.set_startup_hook ([function])

     Set or remove the function invoked by the ‘rl_startup_hook’
     callback of the underlying library.  If `function' is specified, it
     will be used as the new hook function; if omitted or ‘None’, any
     function already installed is removed.  The hook is called with no
     arguments just before readline prints the first prompt.

 -- Function: readline.set_pre_input_hook ([function])

     Set or remove the function invoked by the ‘rl_pre_input_hook’
     callback of the underlying library.  If `function' is specified, it
     will be used as the new hook function; if omitted or ‘None’, any
     function already installed is removed.  The hook is called with no
     arguments after the first prompt has been printed and just before
     readline starts reading input characters.  This function only
     exists if Python was compiled for a version of the library that
     supports it.


File: python.info,  Node: Completion,  Next: Example,  Prev: Startup hooks,  Up: readline — GNU readline interface

5.6.7.6 Completion
..................

The following functions relate to implementing a custom word completion
function.  This is typically operated by the Tab key, and can suggest
and automatically complete a word being typed.  By default, Readline is
set up to be used by *note rlcompleter: e1. to complete Python
identifiers for the interactive interpreter.  If the *note readline: de.
module is to be used with a custom completer, a different set of word
delimiters should be set.

 -- Function: readline.set_completer ([function])

     Set or remove the completer function.  If `function' is specified,
     it will be used as the new completer function; if omitted or
     ‘None’, any completer function already installed is removed.  The
     completer function is called as ‘function(text, state)’, for
     `state' in ‘0’, ‘1’, ‘2’, …, until it returns a non-string value.
     It should return the next possible completion starting with `text'.

     The installed completer function is invoked by the `entry_func'
     callback passed to ‘rl_completion_matches()’ in the underlying
     library.  The `text' string comes from the first parameter to the
     ‘rl_attempted_completion_function’ callback of the underlying
     library.

 -- Function: readline.get_completer ()

     Get the completer function, or ‘None’ if no completer function has
     been set.

 -- Function: readline.get_completion_type ()

     Get the type of completion being attempted.  This returns the
     ‘rl_completion_type’ variable in the underlying library as an
     integer.

 -- Function: readline.get_begidx ()
 -- Function: readline.get_endidx ()

     Get the beginning or ending index of the completion scope.  These
     indexes are the `start' and `end' arguments passed to the
     ‘rl_attempted_completion_function’ callback of the underlying
     library.

 -- Function: readline.set_completer_delims (string)
 -- Function: readline.get_completer_delims ()

     Set or get the word delimiters for completion.  These determine the
     start of the word to be considered for completion (the completion
     scope).  These functions access the
     ‘rl_completer_word_break_characters’ variable in the underlying
     library.

 -- Function: readline.set_completion_display_matches_hook ([function])

     Set or remove the completion display function.  If `function' is
     specified, it will be used as the new completion display function;
     if omitted or ‘None’, any completion display function already
     installed is removed.  This sets or clears the
     ‘rl_completion_display_matches_hook’ callback in the underlying
     library.  The completion display function is called as
     ‘function(substitution, [matches], longest_match_length)’ once each
     time matches need to be displayed.


File: python.info,  Node: Example,  Prev: Completion,  Up: readline — GNU readline interface

5.6.7.7 Example
...............

The following example demonstrates how to use the *note readline: de.
module’s history reading and writing functions to automatically load and
save a history file named ‘.python_history’ from the user’s home
directory.  The code below would normally be executed automatically
during interactive sessions from the user’s *note PYTHONSTARTUP: 9cb.
file.

     import atexit
     import os
     import readline

     histfile = os.path.join(os.path.expanduser("~"), ".python_history")
     try:
         readline.read_history_file(histfile)
         # default history len is -1 (infinite), which may grow unruly
         readline.set_history_length(1000)
     except FileNotFoundError:
         pass

     atexit.register(readline.write_history_file, histfile)

This code is actually automatically run when Python is run in *note
interactive mode: 9c9. (see *note Readline configuration: 9cc.).

The following example achieves the same goal but supports concurrent
interactive sessions, by only appending the new history.

     import atexit
     import os
     import readline
     histfile = os.path.join(os.path.expanduser("~"), ".python_history")

     try:
         readline.read_history_file(histfile)
         h_len = readline.get_current_history_length()
     except FileNotFoundError:
         open(histfile, 'wb').close()
         h_len = 0

     def save(prev_h_len, histfile):
         new_h_len = readline.get_current_history_length()
         readline.set_history_length(1000)
         readline.append_history_file(new_h_len - prev_h_len, histfile)
     atexit.register(save, h_len, histfile)

The following example extends the *note code.InteractiveConsole: 1944.
class to support history save/restore.

     import atexit
     import code
     import os
     import readline

     class HistoryConsole(code.InteractiveConsole):
         def __init__(self, locals=None, filename="<console>",
                      histfile=os.path.expanduser("~/.console-history")):
             code.InteractiveConsole.__init__(self, locals, filename)
             self.init_history(histfile)

         def init_history(self, histfile):
             readline.parse_and_bind("tab: complete")
             if hasattr(readline, "read_history_file"):
                 try:
                     readline.read_history_file(histfile)
                 except FileNotFoundError:
                     pass
                 atexit.register(self.save_history, histfile)

         def save_history(self, histfile):
             readline.set_history_length(1000)
             readline.write_history_file(histfile)


File: python.info,  Node: rlcompleter — Completion function for GNU readline,  Prev: readline — GNU readline interface,  Up: Text Processing Services

5.6.8 ‘rlcompleter’ — Completion function for GNU readline
----------------------------------------------------------

`Source code:' Lib/rlcompleter.py(1)

__________________________________________________________________

The *note rlcompleter: e1. module defines a completion function suitable
for the *note readline: de. module by completing valid Python
identifiers and keywords.

When this module is imported on a Unix platform with the *note readline:
de. module available, an instance of the ‘Completer’ class is
automatically created and its ‘complete()’ method is set as the *note
readline: de. completer.

Example:

     >>> import rlcompleter
     >>> import readline
     >>> readline.parse_and_bind("tab: complete")
     >>> readline. <TAB PRESSED>
     readline.__doc__          readline.get_line_buffer(  readline.read_init_file(
     readline.__file__         readline.insert_text(      readline.set_completer(
     readline.__name__         readline.parse_and_bind(
     >>> readline.

The *note rlcompleter: e1. module is designed for use with Python’s
*note interactive mode: 9c9.  Unless Python is run with the *note -S:
bf7. option, the module is automatically imported and configured (see
*note Readline configuration: 9cc.).

On platforms without *note readline: de, the ‘Completer’ class defined
by this module can still be used for custom purposes.

* Menu:

* Completer Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/rlcompleter.py


File: python.info,  Node: Completer Objects,  Up: rlcompleter — Completion function for GNU readline

5.6.8.1 Completer Objects
.........................

Completer objects have the following method:

 -- Method: Completer.complete (text, state)

     Return the `state'th completion for `text'.

     If called for `text' that doesn’t include a period character
     (‘'.'’), it will complete from names currently defined in *note
     __main__: 1, *note builtins: 12. and keywords (as defined by the
     *note keyword: a6. module).

     If called for a dotted name, it will try to evaluate anything
     without obvious side-effects (functions will not be evaluated, but
     it can generate calls to *note __getattr__(): 42a.) up to the last
     part, and find matches for the rest via the *note dir(): df9.
     function.  Any exception raised during the evaluation of the
     expression is caught, silenced and *note None: 203. is returned.


File: python.info,  Node: Binary Data Services,  Next: Data Types,  Prev: Text Processing Services,  Up: The Python Standard Library

5.7 Binary Data Services
========================

The modules described in this chapter provide some basic services
operations for manipulation of binary data.  Other operations on binary
data, specifically in relation to file formats and network protocols,
are described in the relevant sections.

Some libraries described under *note Text Processing Services: 1775.
also work with either ASCII-compatible binary formats (for example,
*note re: dd.) or all binary data (for example, *note difflib: 36.).

In addition, see the documentation for Python’s built-in binary data
types in *note Binary Sequence Types — bytes, bytearray, memoryview:
171d.

* Menu:

* struct — Interpret bytes as packed binary data::
* codecs — Codec registry and base classes::


File: python.info,  Node: struct — Interpret bytes as packed binary data,  Next: codecs — Codec registry and base classes,  Up: Binary Data Services

5.7.1 ‘struct’ — Interpret bytes as packed binary data
------------------------------------------------------

`Source code:' Lib/struct.py(1)

__________________________________________________________________

This module performs conversions between Python values and C structs
represented as Python *note bytes: 172. objects.  This can be used in
handling binary data stored in files or from network connections, among
other sources.  It uses *note Format Strings: 194e. as compact
descriptions of the layout of the C structs and the intended conversion
to/from Python values.

     Note: By default, the result of packing a given C struct includes
     pad bytes in order to maintain proper alignment for the C types
     involved; similarly, alignment is taken into account when
     unpacking.  This behavior is chosen so that the bytes of a packed
     struct correspond exactly to the layout in memory of the
     corresponding C struct.  To handle platform-independent data
     formats or omit implicit pad bytes, use ‘standard’ size and
     alignment instead of ‘native’ size and alignment: see *note Byte
     Order, Size, and Alignment: 194f. for details.

Several *note struct: f8. functions (and methods of *note Struct: 1950.)
take a `buffer' argument.  This refers to objects that implement the
*note Buffer Protocol: 171c. and provide either a readable or
read-writable buffer.  The most common types used for that purpose are
*note bytes: 172. and *note bytearray: 173, but many other types that
can be viewed as an array of bytes implement the buffer protocol, so
that they can be read/filled without additional copying from a *note
bytes: 172. object.

* Menu:

* Functions and Exceptions::
* Format Strings::
* Classes: Classes<2>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/struct.py


File: python.info,  Node: Functions and Exceptions,  Next: Format Strings,  Up: struct — Interpret bytes as packed binary data

5.7.1.1 Functions and Exceptions
................................

The module defines the following exception and functions:

 -- Exception: struct.error

     Exception raised on various occasions; argument is a string
     describing what is wrong.

 -- Function: struct.pack (format, v1, v2, ...)

     Return a bytes object containing the values `v1', `v2', … packed
     according to the format string `format'.  The arguments must match
     the values required by the format exactly.

 -- Function: struct.pack_into (format, buffer, offset, v1, v2, ...)

     Pack the values `v1', `v2', … according to the format string
     `format' and write the packed bytes into the writable buffer
     `buffer' starting at position `offset'.  Note that `offset' is a
     required argument.

 -- Function: struct.unpack (format, buffer)

     Unpack from the buffer `buffer' (presumably packed by ‘pack(format,
     ...)’) according to the format string `format'.  The result is a
     tuple even if it contains exactly one item.  The buffer’s size in
     bytes must match the size required by the format, as reflected by
     *note calcsize(): 10c5.

 -- Function: struct.unpack_from (format, /, buffer, offset=0)

     Unpack from `buffer' starting at position `offset', according to
     the format string `format'.  The result is a tuple even if it
     contains exactly one item.  The buffer’s size in bytes, starting at
     position `offset', must be at least the size required by the
     format, as reflected by *note calcsize(): 10c5.

 -- Function: struct.iter_unpack (format, buffer)

     Iteratively unpack from the buffer `buffer' according to the format
     string `format'.  This function returns an iterator which will read
     equally-sized chunks from the buffer until all its contents have
     been consumed.  The buffer’s size in bytes must be a multiple of
     the size required by the format, as reflected by *note calcsize():
     10c5.

     Each iteration yields a tuple as specified by the format string.

     New in version 3.4.

 -- Function: struct.calcsize (format)

     Return the size of the struct (and hence of the bytes object
     produced by ‘pack(format, ...)’) corresponding to the format string
     `format'.


File: python.info,  Node: Format Strings,  Next: Classes<2>,  Prev: Functions and Exceptions,  Up: struct — Interpret bytes as packed binary data

5.7.1.2 Format Strings
......................

Format strings are the mechanism used to specify the expected layout
when packing and unpacking data.  They are built up from *note Format
Characters: 1955, which specify the type of data being packed/unpacked.
In addition, there are special characters for controlling the *note Byte
Order, Size, and Alignment: 194f.

* Menu:

* Byte Order, Size, and Alignment: Byte Order Size and Alignment.
* Format Characters::
* Examples: Examples<2>.


File: python.info,  Node: Byte Order Size and Alignment,  Next: Format Characters,  Up: Format Strings

5.7.1.3 Byte Order, Size, and Alignment
.......................................

By default, C types are represented in the machine’s native format and
byte order, and properly aligned by skipping pad bytes if necessary
(according to the rules used by the C compiler).

Alternatively, the first character of the format string can be used to
indicate the byte order, size and alignment of the packed data,
according to the following table:

Character       Byte order                   Size           Alignment
                                                            
----------------------------------------------------------------------------
                                                            
‘@’             native                       native         native
                                                            
                                                            
‘=’             native                       standard       none
                                                            
                                                            
‘<’             little-endian                standard       none
                                                            
                                                            
‘>’             big-endian                   standard       none
                                                            
                                                            
‘!’             network (= big-endian)       standard       none
                                                            

If the first character is not one of these, ‘'@'’ is assumed.

Native byte order is big-endian or little-endian, depending on the host
system.  For example, Intel x86 and AMD64 (x86-64) are little-endian;
Motorola 68000 and PowerPC G5 are big-endian; ARM and Intel Itanium
feature switchable endianness (bi-endian).  Use ‘sys.byteorder’ to check
the endianness of your system.

Native size and alignment are determined using the C compiler’s ‘sizeof’
expression.  This is always combined with native byte order.

Standard size depends only on the format character; see the table in the
*note Format Characters: 1955. section.

Note the difference between ‘'@'’ and ‘'='’: both use native byte order,
but the size and alignment of the latter is standardized.

The form ‘'!'’ represents the network byte order which is always
big-endian as defined in IETF RFC 1700(1).

There is no way to indicate non-native byte order (force byte-swapping);
use the appropriate choice of ‘'<'’ or ‘'>'’.

Notes:

  1. Padding is only automatically added between successive structure
     members.  No padding is added at the beginning or the end of the
     encoded struct.

  2. No padding is added when using non-native size and alignment, e.g.
     with ‘<’, ‘>’, ‘=’, and ‘!’.

  3. To align the end of a structure to the alignment requirement of a
     particular type, end the format with the code for that type with a
     repeat count of zero.  See *note Examples: 1957.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc1700


File: python.info,  Node: Format Characters,  Next: Examples<2>,  Prev: Byte Order Size and Alignment,  Up: Format Strings

5.7.1.4 Format Characters
.........................

Format characters have the following meaning; the conversion between C
and Python values should be obvious given their types.  The ‘Standard
size’ column refers to the size of the packed value in bytes when using
standard size; that is, when the format string starts with one of ‘'<'’,
‘'>'’, ‘'!'’ or ‘'='’.  When using native size, the size of the packed
value is platform-dependent.

Format       C Type                         Python type              Standard size        Notes
                                                                                          
-----------------------------------------------------------------------------------------------------------
                                                                                          
‘x’          pad byte                       no value
                                            
                                                                                          
‘c’          ‘char’                         bytes of length 1        1
                                                                     
                                                                                          
‘b’          ‘signed char’                  integer                  1                    (1), (2)
                                                                                          
                                                                                          
‘B’          ‘unsigned char’                integer                  1                    (2)
                                                                                          
                                                                                          
‘?’          ‘_Bool’                        bool                     1                    (1)
                                                                                          
                                                                                          
‘h’          ‘short’                        integer                  2                    (2)
                                                                                          
                                                                                          
‘H’          ‘unsigned short’               integer                  2                    (2)
                                                                                          
                                                                                          
‘i’          ‘int’                          integer                  4                    (2)
                                                                                          
                                                                                          
‘I’          ‘unsigned int’                 integer                  4                    (2)
                                                                                          
                                                                                          
‘l’          ‘long’                         integer                  4                    (2)
                                                                                          
                                                                                          
‘L’          ‘unsigned long’                integer                  4                    (2)
                                                                                          
                                                                                          
‘q’          ‘long long’                    integer                  8                    (2)
                                                                                          
                                                                                          
‘Q’          ‘unsigned long long’           integer                  8                    (2)
                                                                                          
                                                                                          
‘n’          ‘ssize_t’                      integer                                       (3)
                                                                                          
                                                                                          
‘N’          ‘size_t’                       integer                                       (3)
                                                                                          
                                                                                          
‘e’          (6)                            float                    2                    (4)
                                                                                          
                                                                                          
‘f’          ‘float’                        float                    4                    (4)
                                                                                          
                                                                                          
‘d’          ‘double’                       float                    8                    (4)
                                                                                          
                                                                                          
‘s’          ‘char[]’                       bytes
                                            
                                                                                          
‘p’          ‘char[]’                       bytes
                                            
                                                                                          
‘P’          ‘void *’                       integer                                       (5)
                                                                                          

Changed in version 3.3: Added support for the ‘'n'’ and ‘'N'’ formats.

Changed in version 3.6: Added support for the ‘'e'’ format.

Notes:

  1. 
     The ‘'?'’ conversion code corresponds to the ‘_Bool’ type defined
     by C99.  If this type is not available, it is simulated using a
     ‘char’.  In standard mode, it is always represented by one byte.

  2. When attempting to pack a non-integer using any of the integer
     conversion codes, if the non-integer has a *note __index__(): 2c2.
     method then that method is called to convert the argument to an
     integer before packing.

     Changed in version 3.2: Added use of the *note __index__(): 2c2.
     method for non-integers.

  3. The ‘'n'’ and ‘'N'’ conversion codes are only available for the
     native size (selected as the default or with the ‘'@'’ byte order
     character).  For the standard size, you can use whichever of the
     other integer formats fits your application.

  4. For the ‘'f'’, ‘'d'’ and ‘'e'’ conversion codes, the packed
     representation uses the IEEE 754 binary32, binary64 or binary16
     format (for ‘'f'’, ‘'d'’ or ‘'e'’ respectively), regardless of the
     floating-point format used by the platform.

  5. The ‘'P'’ format character is only available for the native byte
     ordering (selected as the default or with the ‘'@'’ byte order
     character).  The byte order character ‘'='’ chooses to use little-
     or big-endian ordering based on the host system.  The struct module
     does not interpret this as native ordering, so the ‘'P'’ format is
     not available.

  6. The IEEE 754 binary16 “half precision” type was introduced in the
     2008 revision of the IEEE 754 standard(1).  It has a sign bit, a
     5-bit exponent and 11-bit precision (with 10 bits explicitly
     stored), and can represent numbers between approximately ‘6.1e-05’
     and ‘6.5e+04’ at full precision.  This type is not widely supported
     by C compilers: on a typical machine, an unsigned short can be used
     for storage, but not for math operations.  See the Wikipedia page
     on the half-precision floating-point format(2) for more
     information.

A format character may be preceded by an integral repeat count.  For
example, the format string ‘'4h'’ means exactly the same as ‘'hhhh'’.

Whitespace characters between formats are ignored; a count and its
format must not contain whitespace though.

For the ‘'s'’ format character, the count is interpreted as the length
of the bytes, not a repeat count like for the other format characters;
for example, ‘'10s'’ means a single 10-byte string, while ‘'10c'’ means
10 characters.  If a count is not given, it defaults to 1.  For packing,
the string is truncated or padded with null bytes as appropriate to make
it fit.  For unpacking, the resulting bytes object always has exactly
the specified number of bytes.  As a special case, ‘'0s'’ means a
single, empty string (while ‘'0c'’ means 0 characters).

When packing a value ‘x’ using one of the integer formats (‘'b'’, ‘'B'’,
‘'h'’, ‘'H'’, ‘'i'’, ‘'I'’, ‘'l'’, ‘'L'’, ‘'q'’, ‘'Q'’), if ‘x’ is
outside the valid range for that format then *note struct.error: d7c. is
raised.

Changed in version 3.1: Previously, some of the integer formats wrapped
out-of-range values and raised *note DeprecationWarning: 15a. instead of
*note struct.error: d7c.

The ‘'p'’ format character encodes a “Pascal string”, meaning a short
variable-length string stored in a `fixed number of bytes', given by the
count.  The first byte stored is the length of the string, or 255,
whichever is smaller.  The bytes of the string follow.  If the string
passed in to *note pack(): cd6. is too long (longer than the count minus
1), only the leading ‘count-1’ bytes of the string are stored.  If the
string is shorter than ‘count-1’, it is padded with null bytes so that
exactly count bytes in all are used.  Note that for *note unpack():
1437, the ‘'p'’ format character consumes ‘count’ bytes, but that the
string returned can never contain more than 255 bytes.

For the ‘'?'’ format character, the return value is either *note True:
594. or *note False: 48f.  When packing, the truth value of the argument
object is used.  Either 0 or 1 in the native or standard bool
representation will be packed, and any non-zero value will be ‘True’
when unpacking.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/IEEE_floating_point#IEEE_754-2008

   (2) 
https://en.wikipedia.org/wiki/Half-precision_floating-point_format


File: python.info,  Node: Examples<2>,  Prev: Format Characters,  Up: Format Strings

5.7.1.5 Examples
................

     Note: All examples assume a native byte order, size, and alignment
     with a big-endian machine.

A basic example of packing/unpacking three integers:

     >>> from struct import *
     >>> pack('hhl', 1, 2, 3)
     b'\x00\x01\x00\x02\x00\x00\x00\x03'
     >>> unpack('hhl', b'\x00\x01\x00\x02\x00\x00\x00\x03')
     (1, 2, 3)
     >>> calcsize('hhl')
     8

Unpacked fields can be named by assigning them to variables or by
wrapping the result in a named tuple:

     >>> record = b'raymond   \x32\x12\x08\x01\x08'
     >>> name, serialnum, school, gradelevel = unpack('<10sHHb', record)

     >>> from collections import namedtuple
     >>> Student = namedtuple('Student', 'name serialnum school gradelevel')
     >>> Student._make(unpack('<10sHHb', record))
     Student(name=b'raymond   ', serialnum=4658, school=264, gradelevel=8)

The ordering of format characters may have an impact on size since the
padding needed to satisfy alignment requirements is different:

     >>> pack('ci', b'*', 0x12131415)
     b'*\x00\x00\x00\x12\x13\x14\x15'
     >>> pack('ic', 0x12131415, b'*')
     b'\x12\x13\x14\x15*'
     >>> calcsize('ci')
     8
     >>> calcsize('ic')
     5

The following format ‘'llh0l'’ specifies two pad bytes at the end,
assuming longs are aligned on 4-byte boundaries:

     >>> pack('llh0l', 1, 2, 3)
     b'\x00\x00\x00\x01\x00\x00\x00\x02\x00\x03\x00\x00'

This only works when native size and alignment are in effect; standard
size and alignment does not enforce any alignment.

See also
........

Module *note array: 6.

     Packed binary storage of homogeneous data.

Module *note xdrlib: 13b.

     Packing and unpacking of XDR data.


File: python.info,  Node: Classes<2>,  Prev: Format Strings,  Up: struct — Interpret bytes as packed binary data

5.7.1.6 Classes
...............

The *note struct: f8. module also defines the following type:

 -- Class: struct.Struct (format)

     Return a new Struct object which writes and reads binary data
     according to the format string `format'.  Creating a Struct object
     once and calling its methods is more efficient than calling the
     *note struct: f8. functions with the same format since the format
     string only needs to be compiled once.

          Note: The compiled versions of the most recent format strings
          passed to *note Struct: 1950. and the module-level functions
          are cached, so programs that use only a few format strings
          needn’t worry about reusing a single *note Struct: 1950.
          instance.

     Compiled Struct objects support the following methods and
     attributes:

      -- Method: pack (v1, v2, ...)

          Identical to the *note pack(): cd6. function, using the
          compiled format.  (‘len(result)’ will equal *note size: 195d.)

      -- Method: pack_into (buffer, offset, v1, v2, ...)

          Identical to the *note pack_into(): 1952. function, using the
          compiled format.

      -- Method: unpack (buffer)

          Identical to the *note unpack(): 1437. function, using the
          compiled format.  The buffer’s size in bytes must equal *note
          size: 195d.

      -- Method: unpack_from (buffer, offset=0)

          Identical to the *note unpack_from(): 1953. function, using
          the compiled format.  The buffer’s size in bytes, starting at
          position `offset', must be at least *note size: 195d.

      -- Method: iter_unpack (buffer)

          Identical to the *note iter_unpack(): 9be. function, using the
          compiled format.  The buffer’s size in bytes must be a
          multiple of *note size: 195d.

          New in version 3.4.

      -- Attribute: format

          The format string used to construct this Struct object.

          Changed in version 3.7: The format string type is now *note
          str: 205. instead of *note bytes: 172.

      -- Attribute: size

          The calculated size of the struct (and hence of the bytes
          object produced by the *note pack(): cd6. method)
          corresponding to *note format: 5d6.


File: python.info,  Node: codecs — Codec registry and base classes,  Prev: struct — Interpret bytes as packed binary data,  Up: Binary Data Services

5.7.2 ‘codecs’ — Codec registry and base classes
------------------------------------------------

`Source code:' Lib/codecs.py(1)

__________________________________________________________________

This module defines base classes for standard Python codecs (encoders
and decoders) and provides access to the internal Python codec registry,
which manages the codec and error handling lookup process.  Most
standard codecs are *note text encodings: 1731, which encode text to
bytes, but there are also codecs provided that encode text to text, and
bytes to bytes.  Custom codecs may encode and decode between arbitrary
types, but some module features are restricted to use specifically with
*note text encodings: 1731, or with codecs that encode to *note bytes:
172.

The module defines the following functions for encoding and decoding
with any codec:

 -- Function: codecs.encode (obj, encoding='utf-8', errors='strict')

     Encodes `obj' using the codec registered for `encoding'.

     `Errors' may be given to set the desired error handling scheme.
     The default error handler is ‘'strict'’ meaning that encoding
     errors raise *note ValueError: 16d. (or a more codec specific
     subclass, such as *note UnicodeEncodeError: 32a.).  Refer to *note
     Codec Base Classes: 1964. for more information on codec error
     handling.

 -- Function: codecs.decode (obj, encoding='utf-8', errors='strict')

     Decodes `obj' using the codec registered for `encoding'.

     `Errors' may be given to set the desired error handling scheme.
     The default error handler is ‘'strict'’ meaning that decoding
     errors raise *note ValueError: 16d. (or a more codec specific
     subclass, such as *note UnicodeDecodeError: 32b.).  Refer to *note
     Codec Base Classes: 1964. for more information on codec error
     handling.

The full details for each codec can also be looked up directly:

 -- Function: codecs.lookup (encoding)

     Looks up the codec info in the Python codec registry and returns a
     *note CodecInfo: 1965. object as defined below.

     Encodings are first looked up in the registry’s cache.  If not
     found, the list of registered search functions is scanned.  If no
     *note CodecInfo: 1965. object is found, a *note LookupError: 1790.
     is raised.  Otherwise, the *note CodecInfo: 1965. object is stored
     in the cache and returned to the caller.

 -- Class: codecs.CodecInfo (encode, decode, streamreader=None,
          streamwriter=None, incrementalencoder=None,
          incrementaldecoder=None, name=None)

     Codec details when looking up the codec registry.  The constructor
     arguments are stored in attributes of the same name:

      -- Attribute: name

          The name of the encoding.

      -- Attribute: encode
      -- Attribute: decode

          The stateless encoding and decoding functions.  These must be
          functions or methods which have the same interface as the
          *note encode(): 1969. and *note decode(): 196a. methods of
          Codec instances (see *note Codec Interface: 196b.).  The
          functions or methods are expected to work in a stateless mode.

      -- Attribute: incrementalencoder
      -- Attribute: incrementaldecoder

          Incremental encoder and decoder classes or factory functions.
          These have to provide the interface defined by the base
          classes *note IncrementalEncoder: 196e. and *note
          IncrementalDecoder: 196f, respectively.  Incremental codecs
          can maintain state.

      -- Attribute: streamwriter
      -- Attribute: streamreader

          Stream writer and reader classes or factory functions.  These
          have to provide the interface defined by the base classes
          *note StreamWriter: 1972. and *note StreamReader: 1973,
          respectively.  Stream codecs can maintain state.

To simplify access to the various codec components, the module provides
these additional functions which use *note lookup(): 238. for the codec
lookup:

 -- Function: codecs.getencoder (encoding)

     Look up the codec for the given encoding and return its encoder
     function.

     Raises a *note LookupError: 1790. in case the encoding cannot be
     found.

 -- Function: codecs.getdecoder (encoding)

     Look up the codec for the given encoding and return its decoder
     function.

     Raises a *note LookupError: 1790. in case the encoding cannot be
     found.

 -- Function: codecs.getincrementalencoder (encoding)

     Look up the codec for the given encoding and return its incremental
     encoder class or factory function.

     Raises a *note LookupError: 1790. in case the encoding cannot be
     found or the codec doesn’t support an incremental encoder.

 -- Function: codecs.getincrementaldecoder (encoding)

     Look up the codec for the given encoding and return its incremental
     decoder class or factory function.

     Raises a *note LookupError: 1790. in case the encoding cannot be
     found or the codec doesn’t support an incremental decoder.

 -- Function: codecs.getreader (encoding)

     Look up the codec for the given encoding and return its *note
     StreamReader: 1973. class or factory function.

     Raises a *note LookupError: 1790. in case the encoding cannot be
     found.

 -- Function: codecs.getwriter (encoding)

     Look up the codec for the given encoding and return its *note
     StreamWriter: 1972. class or factory function.

     Raises a *note LookupError: 1790. in case the encoding cannot be
     found.

Custom codecs are made available by registering a suitable codec search
function:

 -- Function: codecs.register (search_function)

     Register a codec search function.  Search functions are expected to
     take one argument, being the encoding name in all lower case
     letters with hyphens and spaces converted to underscores, and
     return a *note CodecInfo: 1965. object.  In case a search function
     cannot find a given encoding, it should return ‘None’.

     Changed in version 3.9: Hyphens and spaces are converted to
     underscore.

          Note: Search function registration is not currently
          reversible, which may cause problems in some cases, such as
          unit testing or module reloading.

While the builtin *note open(): 16f. and the associated *note io: a1.
module are the recommended approach for working with encoded text files,
this module provides additional utility functions and classes that allow
the use of a wider range of codecs when working with binary files:

 -- Function: codecs.open (filename, mode='r', encoding=None,
          errors='strict', buffering=-1)

     Open an encoded file using the given `mode' and return an instance
     of *note StreamReaderWriter: 197b, providing transparent
     encoding/decoding.  The default file mode is ‘'r'’, meaning to open
     the file in read mode.

          Note: Underlying encoded files are always opened in binary
          mode.  No automatic conversion of ‘'\n'’ is done on reading
          and writing.  The `mode' argument may be any binary mode
          acceptable to the built-in *note open(): 16f. function; the
          ‘'b'’ is automatically added.

     `encoding' specifies the encoding which is to be used for the file.
     Any encoding that encodes to and decodes from bytes is allowed, and
     the data types supported by the file methods depend on the codec
     used.

     `errors' may be given to define the error handling.  It defaults to
     ‘'strict'’ which causes a *note ValueError: 16d. to be raised in
     case an encoding error occurs.

     `buffering' has the same meaning as for the built-in *note open():
     16f. function.  It defaults to -1 which means that the default
     buffer size will be used.

 -- Function: codecs.EncodedFile (file, data_encoding,
          file_encoding=None, errors='strict')

     Return a *note StreamRecoder: 1108. instance, a wrapped version of
     `file' which provides transparent transcoding.  The original file
     is closed when the wrapped version is closed.

     Data written to the wrapped file is decoded according to the given
     `data_encoding' and then written to the original file as bytes
     using `file_encoding'.  Bytes read from the original file are
     decoded according to `file_encoding', and the result is encoded
     using `data_encoding'.

     If `file_encoding' is not given, it defaults to `data_encoding'.

     `errors' may be given to define the error handling.  It defaults to
     ‘'strict'’, which causes *note ValueError: 16d. to be raised in
     case an encoding error occurs.

 -- Function: codecs.iterencode (iterator, encoding, errors='strict',
          **kwargs)

     Uses an incremental encoder to iteratively encode the input
     provided by `iterator'.  This function is a *note generator: a83.
     The `errors' argument (as well as any other keyword argument) is
     passed through to the incremental encoder.

     This function requires that the codec accept text *note str: 205.
     objects to encode.  Therefore it does not support bytes-to-bytes
     encoders such as ‘base64_codec’.

 -- Function: codecs.iterdecode (iterator, encoding, errors='strict',
          **kwargs)

     Uses an incremental decoder to iteratively decode the input
     provided by `iterator'.  This function is a *note generator: a83.
     The `errors' argument (as well as any other keyword argument) is
     passed through to the incremental decoder.

     This function requires that the codec accept *note bytes: 172.
     objects to decode.  Therefore it does not support text-to-text
     encoders such as ‘rot_13’, although ‘rot_13’ may be used
     equivalently with *note iterencode(): 197d.

The module also provides the following constants which are useful for
reading and writing to platform dependent files:

 -- Data: codecs.BOM
 -- Data: codecs.BOM_BE
 -- Data: codecs.BOM_LE
 -- Data: codecs.BOM_UTF8
 -- Data: codecs.BOM_UTF16
 -- Data: codecs.BOM_UTF16_BE
 -- Data: codecs.BOM_UTF16_LE
 -- Data: codecs.BOM_UTF32
 -- Data: codecs.BOM_UTF32_BE
 -- Data: codecs.BOM_UTF32_LE

     These constants define various byte sequences, being Unicode byte
     order marks (BOMs) for several encodings.  They are used in UTF-16
     and UTF-32 data streams to indicate the byte order used, and in
     UTF-8 as a Unicode signature.  *note BOM_UTF16: 1983. is either
     *note BOM_UTF16_BE: 1984. or *note BOM_UTF16_LE: 1985. depending on
     the platform’s native byte order, *note BOM: 197f. is an alias for
     *note BOM_UTF16: 1983, *note BOM_LE: 1981. for *note BOM_UTF16_LE:
     1985. and *note BOM_BE: 1980. for *note BOM_UTF16_BE: 1984.  The
     others represent the BOM in UTF-8 and UTF-32 encodings.

* Menu:

* Codec Base Classes::
* Encodings and Unicode::
* Standard Encodings::
* Python Specific Encodings::
* encodings.idna — Internationalized Domain Names in Applications: encodings idna — Internationalized Domain Names in Applications.
* encodings.mbcs — Windows ANSI codepage: encodings mbcs — Windows ANSI codepage.
* encodings.utf_8_sig — UTF-8 codec with BOM signature: encodings utf_8_sig — UTF-8 codec with BOM signature.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/codecs.py


File: python.info,  Node: Codec Base Classes,  Next: Encodings and Unicode,  Up: codecs — Codec registry and base classes

5.7.2.1 Codec Base Classes
..........................

The *note codecs: 1b. module defines a set of base classes which define
the interfaces for working with codec objects, and can also be used as
the basis for custom codec implementations.

Each codec has to define four interfaces to make it usable as codec in
Python: stateless encoder, stateless decoder, stream reader and stream
writer.  The stream reader and writers typically reuse the stateless
encoder/decoder to implement the file protocols.  Codec authors also
need to define how the codec will handle encoding and decoding errors.
* Menu:

* Error Handlers::
* Stateless Encoding and Decoding::
* Incremental Encoding and Decoding::
* Stream Encoding and Decoding::


File: python.info,  Node: Error Handlers,  Next: Stateless Encoding and Decoding,  Up: Codec Base Classes

5.7.2.2 Error Handlers
......................

To simplify and standardize error handling, codecs may implement
different error handling schemes by accepting the `errors' string
argument.  The following string values are defined and implemented by
all standard Python codecs:

Value                         Meaning
                              
----------------------------------------------------------------------------------
                              
‘'strict'’                    Raise *note UnicodeError: d03. (or a subclass);
                              this is the default.  Implemented in
                              *note strict_errors(): 198c.
                              
                              
‘'ignore'’                    Ignore the malformed data and continue without
                              further notice.  Implemented in
                              *note ignore_errors(): 198d.
                              

The following error handlers are only applicable to *note text
encodings: 1731.:

Value                         Meaning
                              
----------------------------------------------------------------------------------
                              
‘'replace'’                   Replace with a suitable replacement marker;
                              Python will use the official ‘U+FFFD’ REPLACEMENT
                              CHARACTER for the built-in codecs on decoding,
                              and ‘?’ on encoding.  Implemented in
                              *note replace_errors(): 198e.
                              
                              
‘'xmlcharrefreplace'’         Replace with the appropriate XML character
                              reference (only for encoding).  Implemented in
                              *note xmlcharrefreplace_errors(): 198f.
                              
                              
‘'backslashreplace'’          Replace with backslashed escape sequences.
                              Implemented in
                              *note backslashreplace_errors(): 1990.
                              
                              
‘'namereplace'’               Replace with ‘\N{...}’ escape sequences (only for
                              encoding).  Implemented in
                              *note namereplace_errors(): 1991.
                              
                              
‘'surrogateescape'’           On decoding, replace byte with individual
                              surrogate code ranging from ‘U+DC80’ to ‘U+DCFF’.
                              This code will then be turned back into the same
                              byte when the ‘'surrogateescape'’ error handler
                              is used when encoding the data.  (See PEP 383(1)
                              for more.)
                              

In addition, the following error handler is specific to the given
codecs:

Value                   Codecs                       Meaning
                                                     
-----------------------------------------------------------------------------------------------------
                                                     
‘'surrogatepass'’       utf-8, utf-16, utf-32,       Allow encoding and decoding of surrogate
                        utf-16-be, utf-16-le,        codes.  These codecs normally treat the
                        utf-32-be, utf-32-le         presence of surrogates as an error.
                                                     

New in version 3.1: The ‘'surrogateescape'’ and ‘'surrogatepass'’ error
handlers.

Changed in version 3.4: The ‘'surrogatepass'’ error handlers now works
with utf-16* and utf-32* codecs.

New in version 3.5: The ‘'namereplace'’ error handler.

Changed in version 3.5: The ‘'backslashreplace'’ error handlers now
works with decoding and translating.

The set of allowed values can be extended by registering a new named
error handler:

 -- Function: codecs.register_error (name, error_handler)

     Register the error handling function `error_handler' under the name
     `name'.  The `error_handler' argument will be called during
     encoding and decoding in case of an error, when `name' is specified
     as the errors parameter.

     For encoding, `error_handler' will be called with a *note
     UnicodeEncodeError: 32a. instance, which contains information about
     the location of the error.  The error handler must either raise
     this or a different exception, or return a tuple with a replacement
     for the unencodable part of the input and a position where encoding
     should continue.  The replacement may be either *note str: 205. or
     *note bytes: 172.  If the replacement is bytes, the encoder will
     simply copy them into the output buffer.  If the replacement is a
     string, the encoder will encode the replacement.  Encoding
     continues on original input at the specified position.  Negative
     position values will be treated as being relative to the end of the
     input string.  If the resulting position is out of bound an *note
     IndexError: f36. will be raised.

     Decoding and translating works similarly, except *note
     UnicodeDecodeError: 32b. or *note UnicodeTranslateError: 185b. will
     be passed to the handler and that the replacement from the error
     handler will be put into the output directly.

Previously registered error handlers (including the standard error
handlers) can be looked up by name:

 -- Function: codecs.lookup_error (name)

     Return the error handler previously registered under the name
     `name'.

     Raises a *note LookupError: 1790. in case the handler cannot be
     found.

The following standard error handlers are also made available as module
level functions:

 -- Function: codecs.strict_errors (exception)

     Implements the ‘'strict'’ error handling: each encoding or decoding
     error raises a *note UnicodeError: d03.

 -- Function: codecs.replace_errors (exception)

     Implements the ‘'replace'’ error handling (for *note text
     encodings: 1731. only): substitutes ‘'?'’ for encoding errors (to
     be encoded by the codec), and ‘'\ufffd'’ (the Unicode replacement
     character) for decoding errors.

 -- Function: codecs.ignore_errors (exception)

     Implements the ‘'ignore'’ error handling: malformed data is ignored
     and encoding or decoding is continued without further notice.

 -- Function: codecs.xmlcharrefreplace_errors (exception)

     Implements the ‘'xmlcharrefreplace'’ error handling (for encoding
     with *note text encodings: 1731. only): the unencodable character
     is replaced by an appropriate XML character reference.

 -- Function: codecs.backslashreplace_errors (exception)

     Implements the ‘'backslashreplace'’ error handling (for *note text
     encodings: 1731. only): malformed data is replaced by a backslashed
     escape sequence.

 -- Function: codecs.namereplace_errors (exception)

     Implements the ‘'namereplace'’ error handling (for encoding with
     *note text encodings: 1731. only): the unencodable character is
     replaced by a ‘\N{...}’ escape sequence.

     New in version 3.5.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0383


File: python.info,  Node: Stateless Encoding and Decoding,  Next: Incremental Encoding and Decoding,  Prev: Error Handlers,  Up: Codec Base Classes

5.7.2.3 Stateless Encoding and Decoding
.......................................

The base ‘Codec’ class defines these methods which also define the
function interfaces of the stateless encoder and decoder:

 -- Method: Codec.encode (input[, errors])

     Encodes the object `input' and returns a tuple (output object,
     length consumed).  For instance, *note text encoding: 1731.
     converts a string object to a bytes object using a particular
     character set encoding (e.g., ‘cp1252’ or ‘iso-8859-1’).

     The `errors' argument defines the error handling to apply.  It
     defaults to ‘'strict'’ handling.

     The method may not store state in the ‘Codec’ instance.  Use *note
     StreamWriter: 1972. for codecs which have to keep state in order to
     make encoding efficient.

     The encoder must be able to handle zero length input and return an
     empty object of the output object type in this situation.

 -- Method: Codec.decode (input[, errors])

     Decodes the object `input' and returns a tuple (output object,
     length consumed).  For instance, for a *note text encoding: 1731,
     decoding converts a bytes object encoded using a particular
     character set encoding to a string object.

     For text encodings and bytes-to-bytes codecs, `input' must be a
     bytes object or one which provides the read-only buffer interface –
     for example, buffer objects and memory mapped files.

     The `errors' argument defines the error handling to apply.  It
     defaults to ‘'strict'’ handling.

     The method may not store state in the ‘Codec’ instance.  Use *note
     StreamReader: 1973. for codecs which have to keep state in order to
     make decoding efficient.

     The decoder must be able to handle zero length input and return an
     empty object of the output object type in this situation.


File: python.info,  Node: Incremental Encoding and Decoding,  Next: Stream Encoding and Decoding,  Prev: Stateless Encoding and Decoding,  Up: Codec Base Classes

5.7.2.4 Incremental Encoding and Decoding
.........................................

The *note IncrementalEncoder: 196e. and *note IncrementalDecoder: 196f.
classes provide the basic interface for incremental encoding and
decoding.  Encoding/decoding the input isn’t done with one call to the
stateless encoder/decoder function, but with multiple calls to the *note
encode(): 1994./*note decode(): 1995. method of the incremental
encoder/decoder.  The incremental encoder/decoder keeps track of the
encoding/decoding process during method calls.

The joined output of calls to the *note encode(): 1994./*note decode():
1995. method is the same as if all the single inputs were joined into
one, and this input was encoded/decoded with the stateless
encoder/decoder.

* Menu:

* IncrementalEncoder Objects::
* IncrementalDecoder Objects::


File: python.info,  Node: IncrementalEncoder Objects,  Next: IncrementalDecoder Objects,  Up: Incremental Encoding and Decoding

5.7.2.5 IncrementalEncoder Objects
..................................

The *note IncrementalEncoder: 196e. class is used for encoding an input
in multiple steps.  It defines the following methods which every
incremental encoder must define in order to be compatible with the
Python codec registry.

 -- Class: codecs.IncrementalEncoder (errors='strict')

     Constructor for an *note IncrementalEncoder: 196e. instance.

     All incremental encoders must provide this constructor interface.
     They are free to add additional keyword arguments, but only the
     ones defined here are used by the Python codec registry.

     The *note IncrementalEncoder: 196e. may implement different error
     handling schemes by providing the `errors' keyword argument.  See
     *note Error Handlers: 1493. for possible values.

     The `errors' argument will be assigned to an attribute of the same
     name.  Assigning to this attribute makes it possible to switch
     between different error handling strategies during the lifetime of
     the *note IncrementalEncoder: 196e. object.

      -- Method: encode (object[, final])

          Encodes `object' (taking the current state of the encoder into
          account) and returns the resulting encoded object.  If this is
          the last call to *note encode(): 8ef. `final' must be true
          (the default is false).

      -- Method: reset ()

          Reset the encoder to the initial state.  The output is
          discarded: call ‘.encode(object, final=True)’, passing an
          empty byte or text string if necessary, to reset the encoder
          and to get the output.

      -- Method: getstate ()

          Return the current state of the encoder which must be an
          integer.  The implementation should make sure that ‘0’ is the
          most common state.  (States that are more complicated than
          integers can be converted into an integer by
          marshaling/pickling the state and encoding the bytes of the
          resulting string into an integer.)

      -- Method: setstate (state)

          Set the state of the encoder to `state'.  `state' must be an
          encoder state returned by *note getstate(): 1999.


File: python.info,  Node: IncrementalDecoder Objects,  Prev: IncrementalEncoder Objects,  Up: Incremental Encoding and Decoding

5.7.2.6 IncrementalDecoder Objects
..................................

The *note IncrementalDecoder: 196f. class is used for decoding an input
in multiple steps.  It defines the following methods which every
incremental decoder must define in order to be compatible with the
Python codec registry.

 -- Class: codecs.IncrementalDecoder (errors='strict')

     Constructor for an *note IncrementalDecoder: 196f. instance.

     All incremental decoders must provide this constructor interface.
     They are free to add additional keyword arguments, but only the
     ones defined here are used by the Python codec registry.

     The *note IncrementalDecoder: 196f. may implement different error
     handling schemes by providing the `errors' keyword argument.  See
     *note Error Handlers: 1493. for possible values.

     The `errors' argument will be assigned to an attribute of the same
     name.  Assigning to this attribute makes it possible to switch
     between different error handling strategies during the lifetime of
     the *note IncrementalDecoder: 196f. object.

      -- Method: decode (object[, final])

          Decodes `object' (taking the current state of the decoder into
          account) and returns the resulting decoded object.  If this is
          the last call to *note decode(): 8f0. `final' must be true
          (the default is false).  If `final' is true the decoder must
          decode the input completely and must flush all buffers.  If
          this isn’t possible (e.g.  because of incomplete byte
          sequences at the end of the input) it must initiate error
          handling just like in the stateless case (which might raise an
          exception).

      -- Method: reset ()

          Reset the decoder to the initial state.

      -- Method: getstate ()

          Return the current state of the decoder.  This must be a tuple
          with two items, the first must be the buffer containing the
          still undecoded input.  The second must be an integer and can
          be additional state info.  (The implementation should make
          sure that ‘0’ is the most common additional state info.)  If
          this additional state info is ‘0’ it must be possible to set
          the decoder to the state which has no input buffered and ‘0’
          as the additional state info, so that feeding the previously
          buffered input to the decoder returns it to the previous state
          without producing any output.  (Additional state info that is
          more complicated than integers can be converted into an
          integer by marshaling/pickling the info and encoding the bytes
          of the resulting string into an integer.)

      -- Method: setstate (state)

          Set the state of the decoder to `state'.  `state' must be a
          decoder state returned by *note getstate(): 199e.


File: python.info,  Node: Stream Encoding and Decoding,  Prev: Incremental Encoding and Decoding,  Up: Codec Base Classes

5.7.2.7 Stream Encoding and Decoding
....................................

The *note StreamWriter: 1972. and *note StreamReader: 1973. classes
provide generic working interfaces which can be used to implement new
encoding submodules very easily.  See ‘encodings.utf_8’ for an example
of how this is done.

* Menu:

* StreamWriter Objects::
* StreamReader Objects::
* StreamReaderWriter Objects::
* StreamRecoder Objects::


File: python.info,  Node: StreamWriter Objects,  Next: StreamReader Objects,  Up: Stream Encoding and Decoding

5.7.2.8 StreamWriter Objects
............................

The *note StreamWriter: 1972. class is a subclass of ‘Codec’ and defines
the following methods which every stream writer must define in order to
be compatible with the Python codec registry.

 -- Class: codecs.StreamWriter (stream, errors='strict')

     Constructor for a *note StreamWriter: 1972. instance.

     All stream writers must provide this constructor interface.  They
     are free to add additional keyword arguments, but only the ones
     defined here are used by the Python codec registry.

     The `stream' argument must be a file-like object open for writing
     text or binary data, as appropriate for the specific codec.

     The *note StreamWriter: 1972. may implement different error
     handling schemes by providing the `errors' keyword argument.  See
     *note Error Handlers: 1493. for the standard error handlers the
     underlying stream codec may support.

     The `errors' argument will be assigned to an attribute of the same
     name.  Assigning to this attribute makes it possible to switch
     between different error handling strategies during the lifetime of
     the *note StreamWriter: 1972. object.

      -- Method: write (object)

          Writes the object’s contents encoded to the stream.

      -- Method: writelines (list)

          Writes the concatenated list of strings to the stream
          (possibly by reusing the *note write(): 19a3. method).  The
          standard bytes-to-bytes codecs do not support this method.

      -- Method: reset ()

          Resets the codec buffers used for keeping internal state.

          Calling this method should ensure that the data on the output
          is put into a clean state that allows appending of new fresh
          data without having to rescan the whole stream to recover
          state.

In addition to the above methods, the *note StreamWriter: 1972. must
also inherit all other methods and attributes from the underlying
stream.


File: python.info,  Node: StreamReader Objects,  Next: StreamReaderWriter Objects,  Prev: StreamWriter Objects,  Up: Stream Encoding and Decoding

5.7.2.9 StreamReader Objects
............................

The *note StreamReader: 1973. class is a subclass of ‘Codec’ and defines
the following methods which every stream reader must define in order to
be compatible with the Python codec registry.

 -- Class: codecs.StreamReader (stream, errors='strict')

     Constructor for a *note StreamReader: 1973. instance.

     All stream readers must provide this constructor interface.  They
     are free to add additional keyword arguments, but only the ones
     defined here are used by the Python codec registry.

     The `stream' argument must be a file-like object open for reading
     text or binary data, as appropriate for the specific codec.

     The *note StreamReader: 1973. may implement different error
     handling schemes by providing the `errors' keyword argument.  See
     *note Error Handlers: 1493. for the standard error handlers the
     underlying stream codec may support.

     The `errors' argument will be assigned to an attribute of the same
     name.  Assigning to this attribute makes it possible to switch
     between different error handling strategies during the lifetime of
     the *note StreamReader: 1973. object.

     The set of allowed values for the `errors' argument can be extended
     with *note register_error(): eb9.

      -- Method: read ([size[, chars[, firstline]]])

          Decodes data from the stream and returns the resulting object.

          The `chars' argument indicates the number of decoded code
          points or bytes to return.  The *note read(): 19a8. method
          will never return more data than requested, but it might
          return less, if there is not enough available.

          The `size' argument indicates the approximate maximum number
          of encoded bytes or code points to read for decoding.  The
          decoder can modify this setting as appropriate.  The default
          value -1 indicates to read and decode as much as possible.
          This parameter is intended to prevent having to decode huge
          files in one step.

          The `firstline' flag indicates that it would be sufficient to
          only return the first line, if there are decoding errors on
          later lines.

          The method should use a greedy read strategy meaning that it
          should read as much data as is allowed within the definition
          of the encoding and the given size, e.g.  if optional encoding
          endings or state markers are available on the stream, these
          should be read too.

      -- Method: readline ([size[, keepends]])

          Read one line from the input stream and return the decoded
          data.

          `size', if given, is passed as size argument to the stream’s
          *note read(): 19a8. method.

          If `keepends' is false line-endings will be stripped from the
          lines returned.

      -- Method: readlines ([sizehint[, keepends]])

          Read all lines available on the input stream and return them
          as a list of lines.

          Line-endings are implemented using the codec’s *note decode():
          8f0. method and are included in the list entries if `keepends'
          is true.

          `sizehint', if given, is passed as the `size' argument to the
          stream’s *note read(): 19a8. method.

      -- Method: reset ()

          Resets the codec buffers used for keeping internal state.

          Note that no stream repositioning should take place.  This
          method is primarily intended to be able to recover from
          decoding errors.

In addition to the above methods, the *note StreamReader: 1973. must
also inherit all other methods and attributes from the underlying
stream.


File: python.info,  Node: StreamReaderWriter Objects,  Next: StreamRecoder Objects,  Prev: StreamReader Objects,  Up: Stream Encoding and Decoding

5.7.2.10 StreamReaderWriter Objects
...................................

The *note StreamReaderWriter: 197b. is a convenience class that allows
wrapping streams which work in both read and write modes.

The design is such that one can use the factory functions returned by
the *note lookup(): 238. function to construct the instance.

 -- Class: codecs.StreamReaderWriter (stream, Reader, Writer,
          errors='strict')

     Creates a *note StreamReaderWriter: 197b. instance.  `stream' must
     be a file-like object.  `Reader' and `Writer' must be factory
     functions or classes providing the *note StreamReader: 1973. and
     *note StreamWriter: 1972. interface resp.  Error handling is done
     in the same way as defined for the stream readers and writers.

*note StreamReaderWriter: 197b. instances define the combined interfaces
of *note StreamReader: 1973. and *note StreamWriter: 1972. classes.
They inherit all other methods and attributes from the underlying
stream.


File: python.info,  Node: StreamRecoder Objects,  Prev: StreamReaderWriter Objects,  Up: Stream Encoding and Decoding

5.7.2.11 StreamRecoder Objects
..............................

The *note StreamRecoder: 1108. translates data from one encoding to
another, which is sometimes useful when dealing with different encoding
environments.

The design is such that one can use the factory functions returned by
the *note lookup(): 238. function to construct the instance.

 -- Class: codecs.StreamRecoder (stream, encode, decode, Reader, Writer,
          errors='strict')

     Creates a *note StreamRecoder: 1108. instance which implements a
     two-way conversion: `encode' and `decode' work on the frontend —
     the data visible to code calling ‘read()’ and ‘write()’, while
     `Reader' and `Writer' work on the backend — the data in `stream'.

     You can use these objects to do transparent transcodings, e.g.,
     from Latin-1 to UTF-8 and back.

     The `stream' argument must be a file-like object.

     The `encode' and `decode' arguments must adhere to the ‘Codec’
     interface.  `Reader' and `Writer' must be factory functions or
     classes providing objects of the *note StreamReader: 1973. and
     *note StreamWriter: 1972. interface respectively.

     Error handling is done in the same way as defined for the stream
     readers and writers.

*note StreamRecoder: 1108. instances define the combined interfaces of
*note StreamReader: 1973. and *note StreamWriter: 1972. classes.  They
inherit all other methods and attributes from the underlying stream.


File: python.info,  Node: Encodings and Unicode,  Next: Standard Encodings,  Prev: Codec Base Classes,  Up: codecs — Codec registry and base classes

5.7.2.12 Encodings and Unicode
..............................

Strings are stored internally as sequences of code points in range
‘0x0’–‘0x10FFFF’.  (See PEP 393(1) for more details about the
implementation.)  Once a string object is used outside of CPU and
memory, endianness and how these arrays are stored as bytes become an
issue.  As with other codecs, serialising a string into a sequence of
bytes is known as `encoding', and recreating the string from the
sequence of bytes is known as `decoding'.  There are a variety of
different text serialisation codecs, which are collectivity referred to
as *note text encodings: 1731.

The simplest text encoding (called ‘'latin-1'’ or ‘'iso-8859-1'’) maps
the code points 0–255 to the bytes ‘0x0’–‘0xff’, which means that a
string object that contains code points above ‘U+00FF’ can’t be encoded
with this codec.  Doing so will raise a *note UnicodeEncodeError: 32a.
that looks like the following (although the details of the error message
may differ): ‘UnicodeEncodeError: 'latin-1' codec can't encode character
'\u1234' in position 3: ordinal not in range(256)’.

There’s another group of encodings (the so called charmap encodings)
that choose a different subset of all Unicode code points and how these
code points are mapped to the bytes ‘0x0’–‘0xff’.  To see how this is
done simply open e.g.  ‘encodings/cp1252.py’ (which is an encoding that
is used primarily on Windows).  There’s a string constant with 256
characters that shows you which character is mapped to which byte value.

All of these encodings can only encode 256 of the 1114112 code points
defined in Unicode.  A simple and straightforward way that can store
each Unicode code point, is to store each code point as four consecutive
bytes.  There are two possibilities: store the bytes in big endian or in
little endian order.  These two encodings are called ‘UTF-32-BE’ and
‘UTF-32-LE’ respectively.  Their disadvantage is that if e.g.  you use
‘UTF-32-BE’ on a little endian machine you will always have to swap
bytes on encoding and decoding.  ‘UTF-32’ avoids this problem: bytes
will always be in natural endianness.  When these bytes are read by a
CPU with a different endianness, then bytes have to be swapped though.
To be able to detect the endianness of a ‘UTF-16’ or ‘UTF-32’ byte
sequence, there’s the so called BOM (“Byte Order Mark”).  This is the
Unicode character ‘U+FEFF’.  This character can be prepended to every
‘UTF-16’ or ‘UTF-32’ byte sequence.  The byte swapped version of this
character (‘0xFFFE’) is an illegal character that may not appear in a
Unicode text.  So when the first character in an ‘UTF-16’ or ‘UTF-32’
byte sequence appears to be a ‘U+FFFE’ the bytes have to be swapped on
decoding.  Unfortunately the character ‘U+FEFF’ had a second purpose as
a ‘ZERO WIDTH NO-BREAK SPACE’: a character that has no width and doesn’t
allow a word to be split.  It can e.g.  be used to give hints to a
ligature algorithm.  With Unicode 4.0 using ‘U+FEFF’ as a ‘ZERO WIDTH
NO-BREAK SPACE’ has been deprecated (with ‘U+2060’ (‘WORD JOINER’)
assuming this role).  Nevertheless Unicode software still must be able
to handle ‘U+FEFF’ in both roles: as a BOM it’s a device to determine
the storage layout of the encoded bytes, and vanishes once the byte
sequence has been decoded into a string; as a ‘ZERO WIDTH NO-BREAK
SPACE’ it’s a normal character that will be decoded like any other.

There’s another encoding that is able to encode the full range of
Unicode characters: UTF-8.  UTF-8 is an 8-bit encoding, which means
there are no issues with byte order in UTF-8.  Each byte in a UTF-8 byte
sequence consists of two parts: marker bits (the most significant bits)
and payload bits.  The marker bits are a sequence of zero to four ‘1’
bits followed by a ‘0’ bit.  Unicode characters are encoded like this
(with x being payload bits, which when concatenated give the Unicode
character):

Range                                   Encoding
                                        
-------------------------------------------------------------------------------------------
                                        
‘U-00000000’ … ‘U-0000007F’             0xxxxxxx
                                        
                                        
‘U-00000080’ … ‘U-000007FF’             110xxxxx 10xxxxxx
                                        
                                        
‘U-00000800’ … ‘U-0000FFFF’             1110xxxx 10xxxxxx 10xxxxxx
                                        
                                        
‘U-00010000’ … ‘U-0010FFFF’             11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
                                        

The least significant bit of the Unicode character is the rightmost x
bit.

As UTF-8 is an 8-bit encoding no BOM is required and any ‘U+FEFF’
character in the decoded string (even if it’s the first character) is
treated as a ‘ZERO WIDTH NO-BREAK SPACE’.

Without external information it’s impossible to reliably determine which
encoding was used for encoding a string.  Each charmap encoding can
decode any random byte sequence.  However that’s not possible with
UTF-8, as UTF-8 byte sequences have a structure that doesn’t allow
arbitrary byte sequences.  To increase the reliability with which a
UTF-8 encoding can be detected, Microsoft invented a variant of UTF-8
(that Python 2.5 calls ‘"utf-8-sig"’) for its Notepad program: Before
any of the Unicode characters is written to the file, a UTF-8 encoded
BOM (which looks like this as a byte sequence: ‘0xef’, ‘0xbb’, ‘0xbf’)
is written.  As it’s rather improbable that any charmap encoded file
starts with these byte values (which would e.g.  map to

          LATIN SMALL LETTER I WITH DIAERESIS 
          RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK 
          INVERTED QUESTION MARK 

in iso-8859-1), this increases the probability that a ‘utf-8-sig’
encoding can be correctly guessed from the byte sequence.  So here the
BOM is not used to be able to determine the byte order used for
generating the byte sequence, but as a signature that helps in guessing
the encoding.  On encoding the utf-8-sig codec will write ‘0xef’,
‘0xbb’, ‘0xbf’ as the first three bytes to the file.  On decoding
‘utf-8-sig’ will skip those three bytes if they appear as the first
three bytes in the file.  In UTF-8, the use of the BOM is discouraged
and should generally be avoided.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0393


File: python.info,  Node: Standard Encodings,  Next: Python Specific Encodings,  Prev: Encodings and Unicode,  Up: codecs — Codec registry and base classes

5.7.2.13 Standard Encodings
...........................

Python comes with a number of codecs built-in, either implemented as C
functions or with dictionaries as mapping tables.  The following table
lists the codecs by name, together with a few common aliases, and the
languages for which the encoding is likely used.  Neither the list of
aliases nor the list of languages is meant to be exhaustive.  Notice
that spelling alternatives that only differ in case or use a hyphen
instead of an underscore are also valid aliases; therefore, e.g.
‘'utf-8'’ is a valid alias for the ‘'utf_8'’ codec.

`CPython implementation detail:' Some common encodings can bypass the
codecs lookup machinery to improve performance.  These optimization
opportunities are only recognized by CPython for a limited set of (case
insensitive) aliases: utf-8, utf8, latin-1, latin1, iso-8859-1,
iso8859-1, mbcs (Windows only), ascii, us-ascii, utf-16, utf16, utf-32,
utf32, and the same using underscores instead of dashes.  Using
alternative aliases for these encodings may result in slower execution.

Changed in version 3.6: Optimization opportunity recognized for
us-ascii.

Many of the character sets support the same languages.  They vary in
individual characters (e.g.  whether the EURO SIGN is supported or not),
and in the assignment of characters to code positions.  For the European
languages in particular, the following variants typically exist:

   * an ISO 8859 codeset

   * a Microsoft Windows code page, which is typically derived from an
     8859 codeset, but replaces control characters with additional
     graphic characters

   * an IBM EBCDIC code page

   * an IBM PC code page, which is ASCII compatible

Codec                 Aliases                              Languages
                                                           
------------------------------------------------------------------------------------------------
                                                           
ascii                 646, us-ascii                        English
                                                           
                                                           
big5                  big5-tw, csbig5                      Traditional Chinese
                                                           
                                                           
big5hkscs             big5-hkscs, hkscs                    Traditional Chinese
                                                           
                                                           
cp037                 IBM037, IBM039                       English
                                                           
                                                           
cp273                 273, IBM273, csIBM273                German
                                                           
                                                           New in version 3.4.
                                                           
                                                           
cp424                 EBCDIC-CP-HE, IBM424                 Hebrew
                                                           
                                                           
cp437                 437, IBM437                          English
                                                           
                                                           
cp500                 EBCDIC-CP-BE, EBCDIC-CP-CH, IBM500   Western Europe
                                                           
                                                           
cp720                                                      Arabic
                                                           
                                                           
cp737                                                      Greek
                                                           
                                                           
cp775                 IBM775                               Baltic languages
                                                           
                                                           
cp850                 850, IBM850                          Western Europe
                                                           
                                                           
cp852                 852, IBM852                          Central and Eastern Europe
                                                           
                                                           
cp855                 855, IBM855                          Bulgarian, Byelorussian,
                                                           Macedonian, Russian, Serbian
                                                           
                                                           
cp856                                                      Hebrew
                                                           
                                                           
cp857                 857, IBM857                          Turkish
                                                           
                                                           
cp858                 858, IBM858                          Western Europe
                                                           
                                                           
cp860                 860, IBM860                          Portuguese
                                                           
                                                           
cp861                 861, CP-IS, IBM861                   Icelandic
                                                           
                                                           
cp862                 862, IBM862                          Hebrew
                                                           
                                                           
cp863                 863, IBM863                          Canadian
                                                           
                                                           
cp864                 IBM864                               Arabic
                                                           
                                                           
cp865                 865, IBM865                          Danish, Norwegian
                                                           
                                                           
cp866                 866, IBM866                          Russian
                                                           
                                                           
cp869                 869, CP-GR, IBM869                   Greek
                                                           
                                                           
cp874                                                      Thai
                                                           
                                                           
cp875                                                      Greek
                                                           
                                                           
cp932                 932, ms932, mskanji, ms-kanji        Japanese
                                                           
                                                           
cp949                 949, ms949, uhc                      Korean
                                                           
                                                           
cp950                 950, ms950                           Traditional Chinese
                                                           
                                                           
cp1006                                                     Urdu
                                                           
                                                           
cp1026                ibm1026                              Turkish
                                                           
                                                           
cp1125                1125, ibm1125, cp866u, ruscii        Ukrainian
                                                           
                                                           New in version 3.4.
                                                           
                                                           
cp1140                ibm1140                              Western Europe
                                                           
                                                           
cp1250                windows-1250                         Central and Eastern Europe
                                                           
                                                           
cp1251                windows-1251                         Bulgarian, Byelorussian,
                                                           Macedonian, Russian, Serbian
                                                           
                                                           
cp1252                windows-1252                         Western Europe
                                                           
                                                           
cp1253                windows-1253                         Greek
                                                           
                                                           
cp1254                windows-1254                         Turkish
                                                           
                                                           
cp1255                windows-1255                         Hebrew
                                                           
                                                           
cp1256                windows-1256                         Arabic
                                                           
                                                           
cp1257                windows-1257                         Baltic languages
                                                           
                                                           
cp1258                windows-1258                         Vietnamese
                                                           
                                                           
euc_jp                eucjp, ujis, u-jis                   Japanese
                                                           
                                                           
euc_jis_2004          jisx0213, eucjis2004                 Japanese
                                                           
                                                           
euc_jisx0213          eucjisx0213                          Japanese
                                                           
                                                           
euc_kr                euckr, korean, ksc5601, ks_c-5601,   Korean
                      ks_c-5601-1987, ksx1001, ks_x-1001   
                      
                                                           
gb2312                chinese, csiso58gb231280, euc-cn,    Simplified Chinese
                      euccn, eucgb2312-cn, gb2312-1980,    
                      gb2312-80, iso-ir-58
                      
                                                           
gbk                   936, cp936, ms936                    Unified Chinese
                                                           
                                                           
gb18030               gb18030-2000                         Unified Chinese
                                                           
                                                           
hz                    hzgb, hz-gb, hz-gb-2312              Simplified Chinese
                                                           
                                                           
iso2022_jp            csiso2022jp, iso2022jp,              Japanese
                      iso-2022-jp                          
                      
                                                           
iso2022_jp_1          iso2022jp-1, iso-2022-jp-1           Japanese
                                                           
                                                           
iso2022_jp_2          iso2022jp-2, iso-2022-jp-2           Japanese, Korean, Simplified
                                                           Chinese, Western Europe, Greek
                                                           
                                                           
iso2022_jp_2004       iso2022jp-2004, iso-2022-jp-2004     Japanese
                                                           
                                                           
iso2022_jp_3          iso2022jp-3, iso-2022-jp-3           Japanese
                                                           
                                                           
iso2022_jp_ext        iso2022jp-ext, iso-2022-jp-ext       Japanese
                                                           
                                                           
iso2022_kr            csiso2022kr, iso2022kr,              Korean
                      iso-2022-kr                          
                      
                                                           
latin_1               iso-8859-1, iso8859-1, 8859,         Western Europe
                      cp819, latin, latin1, L1             
                      
                                                           
iso8859_2             iso-8859-2, latin2, L2               Central and Eastern Europe
                                                           
                                                           
iso8859_3             iso-8859-3, latin3, L3               Esperanto, Maltese
                                                           
                                                           
iso8859_4             iso-8859-4, latin4, L4               Baltic languages
                                                           
                                                           
iso8859_5             iso-8859-5, cyrillic                 Bulgarian, Byelorussian,
                                                           Macedonian, Russian, Serbian
                                                           
                                                           
iso8859_6             iso-8859-6, arabic                   Arabic
                                                           
                                                           
iso8859_7             iso-8859-7, greek, greek8            Greek
                                                           
                                                           
iso8859_8             iso-8859-8, hebrew                   Hebrew
                                                           
                                                           
iso8859_9             iso-8859-9, latin5, L5               Turkish
                                                           
                                                           
iso8859_10            iso-8859-10, latin6, L6              Nordic languages
                                                           
                                                           
iso8859_11            iso-8859-11, thai                    Thai languages
                                                           
                                                           
iso8859_13            iso-8859-13, latin7, L7              Baltic languages
                                                           
                                                           
iso8859_14            iso-8859-14, latin8, L8              Celtic languages
                                                           
                                                           
iso8859_15            iso-8859-15, latin9, L9              Western Europe
                                                           
                                                           
iso8859_16            iso-8859-16, latin10, L10            South-Eastern Europe
                                                           
                                                           
johab                 cp1361, ms1361                       Korean
                                                           
                                                           
koi8_r                                                     Russian
                                                           
                                                           
koi8_t                                                     Tajik
                                                           
                                                           New in version 3.5.
                                                           
                                                           
koi8_u                                                     Ukrainian
                                                           
                                                           
kz1048                kz_1048, strk1048_2002, rk1048       Kazakh
                                                           
                                                           New in version 3.5.
                                                           
                                                           
mac_cyrillic          maccyrillic                          Bulgarian, Byelorussian,
                                                           Macedonian, Russian, Serbian
                                                           
                                                           
mac_greek             macgreek                             Greek
                                                           
                                                           
mac_iceland           maciceland                           Icelandic
                                                           
                                                           
mac_latin2            maclatin2, maccentraleurope,         Central and Eastern Europe
                      mac_centeuro                         
                      
                                                           
mac_roman             macroman, macintosh                  Western Europe
                                                           
                                                           
mac_turkish           macturkish                           Turkish
                                                           
                                                           
ptcp154               csptcp154, pt154, cp154,             Kazakh
                      cyrillic-asian                       
                      
                                                           
shift_jis             csshiftjis, shiftjis, sjis, s_jis    Japanese
                                                           
                                                           
shift_jis_2004        shiftjis2004, sjis_2004, sjis2004    Japanese
                                                           
                                                           
shift_jisx0213        shiftjisx0213, sjisx0213,            Japanese
                      s_jisx0213                           
                      
                                                           
utf_32                U32, utf32                           all languages
                                                           
                                                           
utf_32_be             UTF-32BE                             all languages
                                                           
                                                           
utf_32_le             UTF-32LE                             all languages
                                                           
                                                           
utf_16                U16, utf16                           all languages
                                                           
                                                           
utf_16_be             UTF-16BE                             all languages
                                                           
                                                           
utf_16_le             UTF-16LE                             all languages
                                                           
                                                           
utf_7                 U7, unicode-1-1-utf-7                all languages
                                                           
                                                           
utf_8                 U8, UTF, utf8, cp65001               all languages
                                                           
                                                           
utf_8_sig                                                  all languages
                                                           

Changed in version 3.4: The utf-16* and utf-32* encoders no longer allow
surrogate code points (‘U+D800’–‘U+DFFF’) to be encoded.  The utf-32*
decoders no longer decode byte sequences that correspond to surrogate
code points.

Changed in version 3.8: ‘cp65001’ is now an alias to ‘utf_8’.


File: python.info,  Node: Python Specific Encodings,  Next: encodings idna — Internationalized Domain Names in Applications,  Prev: Standard Encodings,  Up: codecs — Codec registry and base classes

5.7.2.14 Python Specific Encodings
..................................

A number of predefined codecs are specific to Python, so their codec
names have no meaning outside Python.  These are listed in the tables
below based on the expected input and output types (note that while text
encodings are the most common use case for codecs, the underlying codec
infrastructure supports arbitrary data transforms rather than just text
encodings).  For asymmetric codecs, the stated meaning describes the
encoding direction.

* Menu:

* Text Encodings::
* Binary Transforms::
* Text Transforms::


File: python.info,  Node: Text Encodings,  Next: Binary Transforms,  Up: Python Specific Encodings

5.7.2.15 Text Encodings
.......................

The following codecs provide *note str: 205. to *note bytes: 172.
encoding and *note bytes-like object: 6df. to *note str: 205. decoding,
similar to the Unicode text encodings.

Codec                    Aliases       Meaning
                                       
-----------------------------------------------------------------------
                                       
idna                                   Implement RFC 3490(1), see
                                       also
                                       *note encodings.idna: 75.
                                       Only ‘errors='strict'’ is
                                       supported.
                                       
                                       
mbcs                     ansi, dbcs    Windows only: Encode the
                                       operand according to the ANSI
                                       codepage (CP_ACP).
                                       
                                       
oem                                    Windows only: Encode the
                                       operand according to the OEM
                                       codepage (CP_OEMCP).
                                       
                                       New in version 3.6.
                                       
                                       
palmos                                 Encoding of PalmOS 3.5.
                                       
                                       
punycode                               Implement RFC 3492(2).
                                       Stateful codecs are not
                                       supported.
                                       
                                       
raw_unicode_escape                     Latin-1 encoding with
                                       ‘\uXXXX’ and ‘\UXXXXXXXX’ for
                                       other code points.  Existing
                                       backslashes are not escaped
                                       in any way.  It is used in
                                       the Python pickle protocol.
                                       
                                       
undefined                              Raise an exception for all
                                       conversions, even empty
                                       strings.  The error handler
                                       is ignored.
                                       
                                       
unicode_escape                         Encoding suitable as the
                                       contents of a Unicode literal
                                       in ASCII-encoded Python
                                       source code, except that
                                       quotes are not escaped.
                                       Decode from Latin-1 source
                                       code.  Beware that Python
                                       source code actually uses
                                       UTF-8 by default.
                                       

Changed in version 3.8: “unicode_internal” codec is removed.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3490.html

   (2) https://tools.ietf.org/html/rfc3492.html


File: python.info,  Node: Binary Transforms,  Next: Text Transforms,  Prev: Text Encodings,  Up: Python Specific Encodings

5.7.2.16 Binary Transforms
..........................

The following codecs provide binary transforms: *note bytes-like object:
6df. to *note bytes: 172. mappings.  They are not supported by *note
bytes.decode(): 171. (which only produces *note str: 205. output).

Codec                      Aliases                Meaning                            Encoder / decoder
                                                                                     
------------------------------------------------------------------------------------------------------------------------
                                                                                     
base64_codec (1)           base64, base_64        Convert the operand to multiline   *note base64.encodebytes(): 222.
                                                  MIME base64 (the result always     /
                                                  includes a trailing ‘'\n'’).       *note base64.decodebytes(): 223.
                                                                                     
                                                  Changed in version 3.4: accepts
                                                  any
                                                  *note bytes-like object: 6df. as
                                                  input for encoding and decoding
                                                  
                                                                                     
bz2_codec                  bz2                    Compress the operand using bz2.    *note bz2.compress(): 19b6. /
                                                                                     *note bz2.decompress(): ab6.
                                                                                     
                                                                                     
hex_codec                  hex                    Convert the operand to             *note binascii.b2a_hex(): 19b7.
                                                  hexadecimal representation, with   /
                                                  two digits per byte.               *note binascii.a2b_hex(): 19b8.
                                                                                     
                                                                                     
quopri_codec               quopri,                Convert the operand to MIME        *note quopri.encode(): 19b9.
                           quotedprintable,       quoted printable.                  with ‘quotetabs=True’ /
                           quoted_printable                                          *note quopri.decode(): 19ba.
                                                                                     
                                                                                     
uu_codec                   uu                     Convert the operand using          *note uu.encode(): 514. /
                                                  uuencode.                          *note uu.decode(): 19bb.
                                                                                     
                                                                                     
zlib_codec                 zip, zlib              Compress the operand using gzip.   *note zlib.compress(): 6b5. /
                                                                                     *note zlib.decompress(): 6b6.
                                                                                     

New in version 3.2: Restoration of the binary transforms.

Changed in version 3.4: Restoration of the aliases for the binary
transforms.

   ---------- Footnotes ----------

   (1) (1) In addition to *note bytes-like objects: 6df,
‘'base64_codec'’ also accepts ASCII-only instances of *note str: 205.
for decoding


File: python.info,  Node: Text Transforms,  Prev: Binary Transforms,  Up: Python Specific Encodings

5.7.2.17 Text Transforms
........................

The following codec provides a text transform: a *note str: 205. to
*note str: 205. mapping.  It is not supported by *note str.encode():
170. (which only produces *note bytes: 172. output).

Codec                    Aliases       Meaning
                                       
-----------------------------------------------------------------------
                                       
rot_13                   rot13         Return the Caesar-cypher
                                       encryption of the operand.
                                       

New in version 3.2: Restoration of the ‘rot_13’ text transform.

Changed in version 3.4: Restoration of the ‘rot13’ alias.


File: python.info,  Node: encodings idna — Internationalized Domain Names in Applications,  Next: encodings mbcs — Windows ANSI codepage,  Prev: Python Specific Encodings,  Up: codecs — Codec registry and base classes

5.7.2.18 ‘encodings.idna’ — Internationalized Domain Names in Applications
..........................................................................

This module implements RFC 3490(1) (Internationalized Domain Names in
Applications) and RFC 3492(2) (Nameprep: A Stringprep Profile for
Internationalized Domain Names (IDN)). It builds upon the ‘punycode’
encoding and *note stringprep: f7.

If you need the IDNA 2008 standard from RFC 5891(3) and RFC 5895(4), use
the third-party ‘idna module <https://pypi.org/project/idna/>_’.

These RFCs together define a protocol to support non-ASCII characters in
domain names.  A domain name containing non-ASCII characters (such as
‘www.Alliancefrançaise.nu’) is converted into an ASCII-compatible
encoding (ACE, such as ‘www.xn--alliancefranaise-npb.nu’).  The ACE form
of the domain name is then used in all places where arbitrary characters
are not allowed by the protocol, such as DNS queries, HTTP ‘Host’
fields, and so on.  This conversion is carried out in the application;
if possible invisible to the user: The application should transparently
convert Unicode domain labels to IDNA on the wire, and convert back ACE
labels to Unicode before presenting them to the user.

Python supports this conversion in several ways: the ‘idna’ codec
performs conversion between Unicode and ACE, separating an input string
into labels based on the separator characters defined in section 3.1 of
RFC 3490(5) and converting each label to ACE as required, and conversely
separating an input byte string into labels based on the ‘.’ separator
and converting any ACE labels found into unicode.  Furthermore, the
*note socket: ef. module transparently converts Unicode host names to
ACE, so that applications need not be concerned about converting host
names themselves when they pass them to the socket module.  On top of
that, modules that have host names as function parameters, such as *note
http.client: 93. and *note ftplib: 82, accept Unicode host names (*note
http.client: 93. then also transparently sends an IDNA hostname in the
‘Host’ field if it sends that field at all).

When receiving host names from the wire (such as in reverse name
lookup), no automatic conversion to Unicode is performed: applications
wishing to present such host names to the user should decode them to
Unicode.

The module *note encodings.idna: 75. also implements the nameprep
procedure, which performs certain normalizations on host names, to
achieve case-insensitivity of international domain names, and to unify
similar characters.  The nameprep functions can be used directly if
desired.

 -- Function: encodings.idna.nameprep (label)

     Return the nameprepped version of `label'.  The implementation
     currently assumes query strings, so ‘AllowUnassigned’ is true.

 -- Function: encodings.idna.ToASCII (label)

     Convert a label to ASCII, as specified in RFC 3490(6).
     ‘UseSTD3ASCIIRules’ is assumed to be false.

 -- Function: encodings.idna.ToUnicode (label)

     Convert a label to Unicode, as specified in RFC 3490(7).

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3490.html

   (2) https://tools.ietf.org/html/rfc3492.html

   (3) https://tools.ietf.org/html/rfc5891.html

   (4) https://tools.ietf.org/html/rfc5895.html

   (5) https://tools.ietf.org/html/rfc3490.html#section-3.1

   (6) https://tools.ietf.org/html/rfc3490.html

   (7) https://tools.ietf.org/html/rfc3490.html


File: python.info,  Node: encodings mbcs — Windows ANSI codepage,  Next: encodings utf_8_sig — UTF-8 codec with BOM signature,  Prev: encodings idna — Internationalized Domain Names in Applications,  Up: codecs — Codec registry and base classes

5.7.2.19 ‘encodings.mbcs’ — Windows ANSI codepage
.................................................

This module implements the ANSI codepage (CP_ACP).

*note Availability: 1491.: Windows only.

Changed in version 3.3: Support any error handler.

Changed in version 3.2: Before 3.2, the `errors' argument was ignored;
‘'replace'’ was always used to encode, and ‘'ignore'’ to decode.


File: python.info,  Node: encodings utf_8_sig — UTF-8 codec with BOM signature,  Prev: encodings mbcs — Windows ANSI codepage,  Up: codecs — Codec registry and base classes

5.7.2.20 ‘encodings.utf_8_sig’ — UTF-8 codec with BOM signature
...............................................................

This module implements a variant of the UTF-8 codec.  On encoding, a
UTF-8 encoded BOM will be prepended to the UTF-8 encoded bytes.  For the
stateful encoder this is only done once (on the first write to the byte
stream).  On decoding, an optional UTF-8 encoded BOM at the start of the
data will be skipped.


File: python.info,  Node: Data Types,  Next: Numeric and Mathematical Modules,  Prev: Binary Data Services,  Up: The Python Standard Library

5.8 Data Types
==============

The modules described in this chapter provide a variety of specialized
data types such as dates and times, fixed-type arrays, heap queues,
double-ended queues, and enumerations.

Python also provides some built-in data types, in particular, *note
dict: 164, *note list: 1f8, *note set: 1f6. and *note frozenset: 1f7,
and *note tuple: 1a2.  The *note str: 205. class is used to hold Unicode
strings, and the *note bytes: 172. and *note bytearray: 173. classes are
used to hold binary data.

The following modules are documented in this chapter:

* Menu:

* datetime — Basic date and time types::
* zoneinfo — IANA time zone support::
* calendar — General calendar-related functions::
* collections — Container datatypes::
* collections.abc — Abstract Base Classes for Containers: collections abc — Abstract Base Classes for Containers.
* heapq — Heap queue algorithm::
* bisect — Array bisection algorithm::
* array — Efficient arrays of numeric values::
* weakref — Weak references::
* types — Dynamic type creation and names for built-in types::
* copy — Shallow and deep copy operations::
* pprint — Data pretty printer::
* reprlib — Alternate repr() implementation: reprlib — Alternate repr implementation.
* enum — Support for enumerations::
* graphlib — Functionality to operate with graph-like structures::


File: python.info,  Node: datetime — Basic date and time types,  Next: zoneinfo — IANA time zone support,  Up: Data Types

5.8.1 ‘datetime’ — Basic date and time types
--------------------------------------------

`Source code:' Lib/datetime.py(1)

__________________________________________________________________

The *note datetime: 30. module supplies classes for manipulating dates
and times.

While date and time arithmetic is supported, the focus of the
implementation is on efficient attribute extraction for output
formatting and manipulation.

See also
........

Module *note calendar: 14.

     General calendar related functions.

Module *note time: 10c.

     Time access and conversions.

Module *note zoneinfo: 14e.

     Concrete time zones representing the IANA time zone database.

Package dateutil(2)

     Third-party library with expanded time zone and parsing support.

* Menu:

* Aware and Naive Objects::
* Constants::
* Available Types::
* timedelta Objects::
* date Objects::
* datetime Objects::
* time Objects::
* tzinfo Objects::
* timezone Objects::
* strftime() and strptime() Behavior: strftime and strptime Behavior.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/datetime.py

   (2) https://dateutil.readthedocs.io/en/stable/


File: python.info,  Node: Aware and Naive Objects,  Next: Constants,  Up: datetime — Basic date and time types

5.8.1.1 Aware and Naive Objects
...............................

Date and time objects may be categorized as “aware” or “naive” depending
on whether or not they include timezone information.

With sufficient knowledge of applicable algorithmic and political time
adjustments, such as time zone and daylight saving time information, an
`aware' object can locate itself relative to other aware objects.  An
aware object represents a specific moment in time that is not open to
interpretation.  (1)

A `naive' object does not contain enough information to unambiguously
locate itself relative to other date/time objects.  Whether a naive
object represents Coordinated Universal Time (UTC), local time, or time
in some other timezone is purely up to the program, just like it is up
to the program whether a particular number represents metres, miles, or
mass.  Naive objects are easy to understand and to work with, at the
cost of ignoring some aspects of reality.

For applications requiring aware objects, *note datetime: 1a0. and *note
time: 5ed. objects have an optional time zone information attribute,
‘tzinfo’, that can be set to an instance of a subclass of the abstract
*note tzinfo: 180. class.  These *note tzinfo: 180. objects capture
information about the offset from UTC time, the time zone name, and
whether daylight saving time is in effect.

Only one concrete *note tzinfo: 180. class, the *note timezone: ae0.
class, is supplied by the *note datetime: 30. module.  The *note
timezone: ae0. class can represent simple timezones with fixed offsets
from UTC, such as UTC itself or North American EST and EDT timezones.
Supporting timezones at deeper levels of detail is up to the
application.  The rules for time adjustment across the world are more
political than rational, change frequently, and there is no standard
suitable for every application aside from UTC.

   ---------- Footnotes ----------

   (1) (1) If, that is, we ignore the effects of Relativity


File: python.info,  Node: Constants,  Next: Available Types,  Prev: Aware and Naive Objects,  Up: datetime — Basic date and time types

5.8.1.2 Constants
.................

The *note datetime: 30. module exports the following constants:

 -- Data: datetime.MINYEAR

     The smallest year number allowed in a *note date: 19e. or *note
     datetime: 1a0. object.  *note MINYEAR: 19cb. is ‘1’.

 -- Data: datetime.MAXYEAR

     The largest year number allowed in a *note date: 19e. or *note
     datetime: 1a0. object.  *note MAXYEAR: 19cc. is ‘9999’.


File: python.info,  Node: Available Types,  Next: timedelta Objects,  Prev: Constants,  Up: datetime — Basic date and time types

5.8.1.3 Available Types
.......................

 -- Class: datetime.date

     An idealized naive date, assuming the current Gregorian calendar
     always was, and always will be, in effect.  Attributes: *note year:
     19ce, *note month: 19cf, and *note day: 19d0.

 -- Class: datetime.time

     An idealized time, independent of any particular day, assuming that
     every day has exactly 24*60*60 seconds.  (There is no notion of
     “leap seconds” here.)  Attributes: *note hour: 19d1, *note minute:
     19d2, *note second: 19d3, *note microsecond: 19d4, and *note
     tzinfo: 19d5.

 -- Class: datetime.datetime

     A combination of a date and a time.  Attributes: *note year: 19d6,
     *note month: 19d7, *note day: 19d8, *note hour: 19d9, *note minute:
     19da, *note second: 19db, *note microsecond: 19dc, and *note
     tzinfo: 19dd.

 -- Class: datetime.timedelta

     A duration expressing the difference between two *note date: 19e,
     *note time: 5ed, or *note datetime: 1a0. instances to microsecond
     resolution.

 -- Class: datetime.tzinfo

     An abstract base class for time zone information objects.  These
     are used by the *note datetime: 1a0. and *note time: 5ed. classes
     to provide a customizable notion of time adjustment (for example,
     to account for time zone and/or daylight saving time).

 -- Class: datetime.timezone

     A class that implements the *note tzinfo: 180. abstract base class
     as a fixed offset from the UTC.

     New in version 3.2.

Objects of these types are immutable.

Subclass relationships:

     object
         timedelta
         tzinfo
             timezone
         time
         date
             datetime

* Menu:

* Common Properties::
* Determining if an Object is Aware or Naive::


File: python.info,  Node: Common Properties,  Next: Determining if an Object is Aware or Naive,  Up: Available Types

5.8.1.4 Common Properties
.........................

The *note date: 19e, *note datetime: 1a0, *note time: 5ed, and *note
timezone: ae0. types share these common features:

   - Objects of these types are immutable.

   - Objects of these types are hashable, meaning that they can be used
     as dictionary keys.

   - Objects of these types support efficient pickling via the *note
     pickle: ca. module.


File: python.info,  Node: Determining if an Object is Aware or Naive,  Prev: Common Properties,  Up: Available Types

5.8.1.5 Determining if an Object is Aware or Naive
..................................................

Objects of the *note date: 19e. type are always naive.

An object of type *note time: 5ed. or *note datetime: 1a0. may be aware
or naive.

A *note datetime: 1a0. object `d' is aware if both of the following
hold:

  1. ‘d.tzinfo’ is not ‘None’

  2. ‘d.tzinfo.utcoffset(d)’ does not return ‘None’

Otherwise, `d' is naive.

A *note time: 5ed. object `t' is aware if both of the following hold:

  1. ‘t.tzinfo’ is not ‘None’

  2. ‘t.tzinfo.utcoffset(None)’ does not return ‘None’.

Otherwise, `t' is naive.

The distinction between aware and naive doesn’t apply to *note
timedelta: 2ca. objects.


File: python.info,  Node: timedelta Objects,  Next: date Objects,  Prev: Available Types,  Up: datetime — Basic date and time types

5.8.1.6 ‘timedelta’ Objects
...........................

A *note timedelta: 2ca. object represents a duration, the difference
between two dates or times.

 -- Class: datetime.timedelta (days=0, seconds=0, microseconds=0,
          milliseconds=0, minutes=0, hours=0, weeks=0)

     All arguments are optional and default to ‘0’.  Arguments may be
     integers or floats, and may be positive or negative.

     Only `days', `seconds' and `microseconds' are stored internally.
     Arguments are converted to those units:

        * A millisecond is converted to 1000 microseconds.

        * A minute is converted to 60 seconds.

        * An hour is converted to 3600 seconds.

        * A week is converted to 7 days.

     and days, seconds and microseconds are then normalized so that the
     representation is unique, with

        * ‘0 <= microseconds < 1000000’

        * ‘0 <= seconds < 3600*24’ (the number of seconds in one day)

        * ‘-999999999 <= days <= 999999999’

     The following example illustrates how any arguments besides `days',
     `seconds' and `microseconds' are “merged” and normalized into those
     three resulting attributes:

          >>> from datetime import timedelta
          >>> delta = timedelta(
          ...     days=50,
          ...     seconds=27,
          ...     microseconds=10,
          ...     milliseconds=29000,
          ...     minutes=5,
          ...     hours=8,
          ...     weeks=2
          ... )
          >>> # Only days, seconds, and microseconds remain
          >>> delta
          datetime.timedelta(days=64, seconds=29156, microseconds=10)

     If any argument is a float and there are fractional microseconds,
     the fractional microseconds left over from all arguments are
     combined and their sum is rounded to the nearest microsecond using
     round-half-to-even tiebreaker.  If no argument is a float, the
     conversion and normalization processes are exact (no information is
     lost).

     If the normalized value of days lies outside the indicated range,
     *note OverflowError: a41. is raised.

     Note that normalization of negative values may be surprising at
     first.  For example:

          >>> from datetime import timedelta
          >>> d = timedelta(microseconds=-1)
          >>> (d.days, d.seconds, d.microseconds)
          (-1, 86399, 999999)

Class attributes:

 -- Attribute: timedelta.min

     The most negative *note timedelta: 2ca. object,
     ‘timedelta(-999999999)’.

 -- Attribute: timedelta.max

     The most positive *note timedelta: 2ca. object,
     ‘timedelta(days=999999999, hours=23, minutes=59, seconds=59,
     microseconds=999999)’.

 -- Attribute: timedelta.resolution

     The smallest possible difference between non-equal *note timedelta:
     2ca. objects, ‘timedelta(microseconds=1)’.

Note that, because of normalization, ‘timedelta.max’ > ‘-timedelta.min’.
‘-timedelta.max’ is not representable as a *note timedelta: 2ca. object.

Instance attributes (read-only):

Attribute              Value
                       
------------------------------------------------------------------------
                       
‘days’                 Between -999999999 and 999999999 inclusive
                       
                       
‘seconds’              Between 0 and 86399 inclusive
                       
                       
‘microseconds’         Between 0 and 999999 inclusive
                       

Supported operations:

Operation                            Result
                                     
-----------------------------------------------------------------------------------------
                                     
‘t1 = t2 + t3’                       Sum of `t2' and `t3'.  Afterwards `t1'-`t2' ==
                                     `t3' and `t1'-`t3' == `t2' are true.  (1)
                                     
                                     
‘t1 = t2 - t3’                       Difference of `t2' and `t3'.  Afterwards `t1' ==
                                     `t2' - `t3' and `t2' == `t1' + `t3' are true.
                                     (1)(6)
                                     
                                     
‘t1 = t2 * i or t1 = i * t2’         Delta multiplied by an integer.  Afterwards `t1'
                                     // i == `t2' is true, provided ‘i != 0’.
                                     
                                     
                                     In general, `t1' * i == `t1' * (i-1) + `t1' is
                                     true.  (1)
                                     
                                     
‘t1 = t2 * f or t1 = f * t2’         Delta multiplied by a float.  The result is
                                     rounded to the nearest multiple of
                                     timedelta.resolution using round-half-to-even.
                                     
                                     
‘f = t2 / t3’                        Division (3) of overall duration `t2' by interval
                                     unit `t3'.  Returns a *note float: 1fd. object.
                                     
                                     
‘t1 = t2 / f or t1 = t2 / i’         Delta divided by a float or an int.  The result
                                     is rounded to the nearest multiple of
                                     timedelta.resolution using round-half-to-even.
                                     
                                     
‘t1 = t2 // i’ or ‘t1 = t2 // t3’    The floor is computed and the remainder (if any)
                                     is thrown away.  In the second case, an integer
                                     is returned.  (3)
                                     
                                     
‘t1 = t2 % t3’                       The remainder is computed as a
                                     *note timedelta: 2ca. object.  (3)
                                     
                                     
‘q, r = divmod(t1, t2)’              Computes the quotient and the remainder: ‘q = t1
                                     // t2’ (3) and ‘r = t1 % t2’.  q is an integer
                                     and r is a *note timedelta: 2ca. object.
                                     
                                     
‘+t1’                                Returns a *note timedelta: 2ca. object with the
                                     same value.  (2)
                                     
                                     
‘-t1’                                equivalent to *note timedelta: 2ca.(-`t1.days',
                                     -`t1.seconds', -`t1.microseconds'), and to `t1'*
                                     -1.  (1)(4)
                                     
                                     
‘abs(t)’                             equivalent to +`t' when ‘t.days >= 0’, and to
                                     -`t' when ‘t.days < 0’.  (2)
                                     
                                     
‘str(t)’                             Returns a string in the form ‘[D day[s],
                                     ][H]H:MM:SS[.UUUUUU]’, where D is negative for
                                     negative ‘t’.  (5)
                                     
                                     
‘repr(t)’                            Returns a string representation of the
                                     *note timedelta: 2ca. object as a constructor
                                     call with canonical attribute values.
                                     

Notes:

  1. This is exact but may overflow.

  2. This is exact and cannot overflow.

  3. Division by 0 raises *note ZeroDivisionError: 1fa.

  4. -`timedelta.max' is not representable as a *note timedelta: 2ca.
     object.

  5. String representations of *note timedelta: 2ca. objects are
     normalized similarly to their internal representation.  This leads
     to somewhat unusual results for negative timedeltas.  For example:

          >>> timedelta(hours=-5)
          datetime.timedelta(days=-1, seconds=68400)
          >>> print(_)
          -1 day, 19:00:00

  6. The expression ‘t2 - t3’ will always be equal to the expression ‘t2
     + (-t3)’ except when t3 is equal to ‘timedelta.max’; in that case
     the former will produce a result while the latter will overflow.

In addition to the operations listed above, *note timedelta: 2ca.
objects support certain additions and subtractions with *note date: 19e.
and *note datetime: 1a0. objects (see below).

Changed in version 3.2: Floor division and true division of a *note
timedelta: 2ca. object by another *note timedelta: 2ca. object are now
supported, as are remainder operations and the *note divmod(): 28d.
function.  True division and multiplication of a *note timedelta: 2ca.
object by a *note float: 1fd. object are now supported.

Comparisons of *note timedelta: 2ca. objects are supported, with some
caveats.

The comparisons ‘==’ or ‘!=’ `always' return a *note bool: 2bd, no
matter the type of the compared object:

     >>> from datetime import timedelta
     >>> delta1 = timedelta(seconds=57)
     >>> delta2 = timedelta(hours=25, seconds=2)
     >>> delta2 != delta1
     True
     >>> delta2 == 5
     False

For all other comparisons (such as ‘<’ and ‘>’), when a *note timedelta:
2ca. object is compared to an object of a different type, *note
TypeError: 1fe. is raised:

     >>> delta2 > delta1
     True
     >>> delta2 > 5
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: '>' not supported between instances of 'datetime.timedelta' and 'int'

In Boolean contexts, a *note timedelta: 2ca. object is considered to be
true if and only if it isn’t equal to ‘timedelta(0)’.

Instance methods:

 -- Method: timedelta.total_seconds ()

     Return the total number of seconds contained in the duration.
     Equivalent to ‘td / timedelta(seconds=1)’.  For interval units
     other than seconds, use the division form directly (e.g.  ‘td /
     timedelta(microseconds=1)’).

     Note that for very large time intervals (greater than 270 years on
     most platforms) this method will lose microsecond accuracy.

     New in version 3.2.

* Menu:

* Examples of usage; timedelta: Examples of usage timedelta.


File: python.info,  Node: Examples of usage timedelta,  Up: timedelta Objects

5.8.1.7 Examples of usage: ‘timedelta’
......................................

An additional example of normalization:

     >>> # Components of another_year add up to exactly 365 days
     >>> from datetime import timedelta
     >>> year = timedelta(days=365)
     >>> another_year = timedelta(weeks=40, days=84, hours=23,
     ...                          minutes=50, seconds=600)
     >>> year == another_year
     True
     >>> year.total_seconds()
     31536000.0

Examples of *note timedelta: 2ca. arithmetic:

     >>> from datetime import timedelta
     >>> year = timedelta(days=365)
     >>> ten_years = 10 * year
     >>> ten_years
     datetime.timedelta(days=3650)
     >>> ten_years.days // 365
     10
     >>> nine_years = ten_years - year
     >>> nine_years
     datetime.timedelta(days=3285)
     >>> three_years = nine_years // 3
     >>> three_years, three_years.days // 365
     (datetime.timedelta(days=1095), 3)


File: python.info,  Node: date Objects,  Next: datetime Objects,  Prev: timedelta Objects,  Up: datetime — Basic date and time types

5.8.1.8 ‘date’ Objects
......................

A *note date: 19e. object represents a date (year, month and day) in an
idealized calendar, the current Gregorian calendar indefinitely extended
in both directions.

January 1 of year 1 is called day number 1, January 2 of year 1 is
called day number 2, and so on.  (1)

 -- Class: datetime.date (year, month, day)

     All arguments are required.  Arguments must be integers, in the
     following ranges:

        * ‘MINYEAR <= year <= MAXYEAR’

        * ‘1 <= month <= 12’

        * ‘1 <= day <= number of days in the given month and year’

     If an argument outside those ranges is given, *note ValueError:
     16d. is raised.

Other constructors, all class methods:

 -- Method: classmethod date.today ()

     Return the current local date.

     This is equivalent to ‘date.fromtimestamp(time.time())’.

 -- Method: classmethod date.fromtimestamp (timestamp)

     Return the local date corresponding to the POSIX timestamp, such as
     is returned by *note time.time(): 42d.

     This may raise *note OverflowError: a41, if the timestamp is out of
     the range of values supported by the platform C ‘localtime()’
     function, and *note OSError: 304. on ‘localtime()’ failure.  It’s
     common for this to be restricted to years from 1970 through 2038.
     Note that on non-POSIX systems that include leap seconds in their
     notion of a timestamp, leap seconds are ignored by *note
     fromtimestamp(): 19e9.

     Changed in version 3.3: Raise *note OverflowError: a41. instead of
     *note ValueError: 16d. if the timestamp is out of the range of
     values supported by the platform C ‘localtime()’ function.  Raise
     *note OSError: 304. instead of *note ValueError: 16d. on
     ‘localtime()’ failure.

 -- Method: classmethod date.fromordinal (ordinal)

     Return the date corresponding to the proleptic Gregorian ordinal,
     where January 1 of year 1 has ordinal 1.

     *note ValueError: 16d. is raised unless ‘1 <= ordinal <=
     date.max.toordinal()’.  For any date `d',
     ‘date.fromordinal(d.toordinal()) == d’.

 -- Method: classmethod date.fromisoformat (date_string)

     Return a *note date: 19e. corresponding to a `date_string' given in
     the format ‘YYYY-MM-DD’:

          >>> from datetime import date
          >>> date.fromisoformat('2019-12-04')
          datetime.date(2019, 12, 4)

     This is the inverse of *note date.isoformat(): 19eb.  It only
     supports the format ‘YYYY-MM-DD’.

     New in version 3.7.

 -- Method: classmethod date.fromisocalendar (year, week, day)

     Return a *note date: 19e. corresponding to the ISO calendar date
     specified by year, week and day.  This is the inverse of the
     function *note date.isocalendar(): 19d.

     New in version 3.8.

Class attributes:

 -- Attribute: date.min

     The earliest representable date, ‘date(MINYEAR, 1, 1)’.

 -- Attribute: date.max

     The latest representable date, ‘date(MAXYEAR, 12, 31)’.

 -- Attribute: date.resolution

     The smallest possible difference between non-equal date objects,
     ‘timedelta(days=1)’.

Instance attributes (read-only):

 -- Attribute: date.year

     Between *note MINYEAR: 19cb. and *note MAXYEAR: 19cc. inclusive.

 -- Attribute: date.month

     Between 1 and 12 inclusive.

 -- Attribute: date.day

     Between 1 and the number of days in the given month of the given
     year.

Supported operations:

Operation                           Result
                                    
---------------------------------------------------------------------------------------
                                    
‘date2 = date1 + timedelta’         `date2' is ‘timedelta.days’ days removed from
                                    `date1'.  (1)
                                    
                                    
‘date2 = date1 - timedelta’         Computes `date2' such that ‘date2 + timedelta ==
                                    date1’.  (2)
                                    
                                    
‘timedelta = date1 - date2’         (3)
                                    
                                    
‘date1 < date2’                     `date1' is considered less than `date2' when
                                    `date1' precedes `date2' in time.  (4)
                                    

Notes:

  1. `date2' is moved forward in time if ‘timedelta.days > 0’, or
     backward if ‘timedelta.days < 0’.  Afterward ‘date2 - date1 ==
     timedelta.days’.  ‘timedelta.seconds’ and ‘timedelta.microseconds’
     are ignored.  *note OverflowError: a41. is raised if ‘date2.year’
     would be smaller than *note MINYEAR: 19cb. or larger than *note
     MAXYEAR: 19cc.

  2. ‘timedelta.seconds’ and ‘timedelta.microseconds’ are ignored.

  3. This is exact, and cannot overflow.  timedelta.seconds and
     timedelta.microseconds are 0, and date2 + timedelta == date1 after.

  4. In other words, ‘date1 < date2’ if and only if ‘date1.toordinal() <
     date2.toordinal()’.  Date comparison raises *note TypeError: 1fe.
     if the other comparand isn’t also a *note date: 19e. object.
     However, ‘NotImplemented’ is returned instead if the other
     comparand has a ‘timetuple()’ attribute.  This hook gives other
     kinds of date objects a chance at implementing mixed-type
     comparison.  If not, when a *note date: 19e. object is compared to
     an object of a different type, *note TypeError: 1fe. is raised
     unless the comparison is ‘==’ or ‘!=’.  The latter cases return
     *note False: 48f. or *note True: 594, respectively.

In Boolean contexts, all *note date: 19e. objects are considered to be
true.

Instance methods:

 -- Method: date.replace (year=self.year, month=self.month,
          day=self.day)

     Return a date with the same value, except for those parameters
     given new values by whichever keyword arguments are specified.

     Example:

          >>> from datetime import date
          >>> d = date(2002, 12, 31)
          >>> d.replace(day=26)
          datetime.date(2002, 12, 26)

 -- Method: date.timetuple ()

     Return a *note time.struct_time: 690. such as returned by *note
     time.localtime(): 1080.

     The hours, minutes and seconds are 0, and the DST flag is -1.

     ‘d.timetuple()’ is equivalent to:

          time.struct_time((d.year, d.month, d.day, 0, 0, 0, d.weekday(), yday, -1))

     where ‘yday = d.toordinal() - date(d.year, 1, 1).toordinal() + 1’
     is the day number within the current year starting with ‘1’ for
     January 1st.

 -- Method: date.toordinal ()

     Return the proleptic Gregorian ordinal of the date, where January 1
     of year 1 has ordinal 1.  For any *note date: 19e. object `d',
     ‘date.fromordinal(d.toordinal()) == d’.

 -- Method: date.weekday ()

     Return the day of the week as an integer, where Monday is 0 and
     Sunday is 6.  For example, ‘date(2002, 12, 4).weekday() == 2’, a
     Wednesday.  See also *note isoweekday(): 19f3.

 -- Method: date.isoweekday ()

     Return the day of the week as an integer, where Monday is 1 and
     Sunday is 7.  For example, ‘date(2002, 12, 4).isoweekday() == 3’, a
     Wednesday.  See also *note weekday(): 19f2, *note isocalendar():
     19d.

 -- Method: date.isocalendar ()

     Return a *note named tuple: b7b. object with three components:
     ‘year’, ‘week’ and ‘weekday’.

     The ISO calendar is a widely used variant of the Gregorian
     calendar.  (2)

     The ISO year consists of 52 or 53 full weeks, and where a week
     starts on a Monday and ends on a Sunday.  The first week of an ISO
     year is the first (Gregorian) calendar week of a year containing a
     Thursday.  This is called week number 1, and the ISO year of that
     Thursday is the same as its Gregorian year.

     For example, 2004 begins on a Thursday, so the first week of ISO
     year 2004 begins on Monday, 29 Dec 2003 and ends on Sunday, 4 Jan
     2004:

          >>> from datetime import date
          >>> date(2003, 12, 29).isocalendar()
          datetime.IsoCalendarDate(year=2004, week=1, weekday=1)
          >>> date(2004, 1, 4).isocalendar()
          datetime.IsoCalendarDate(year=2004, week=1, weekday=7)

     Changed in version 3.9: Result changed from a tuple to a *note
     named tuple: b7b.

 -- Method: date.isoformat ()

     Return a string representing the date in ISO 8601 format,
     ‘YYYY-MM-DD’:

          >>> from datetime import date
          >>> date(2002, 12, 4).isoformat()
          '2002-12-04'

     This is the inverse of *note date.fromisoformat(): 11cc.

 -- Method: date.__str__ ()

     For a date `d', ‘str(d)’ is equivalent to ‘d.isoformat()’.

 -- Method: date.ctime ()

     Return a string representing the date:

          >>> from datetime import date
          >>> date(2002, 12, 4).ctime()
          'Wed Dec  4 00:00:00 2002'

     ‘d.ctime()’ is equivalent to:

          time.ctime(time.mktime(d.timetuple()))

     on platforms where the native C ‘ctime()’ function (which *note
     time.ctime(): 19f6. invokes, but which *note date.ctime(): 19f5.
     does not invoke) conforms to the C standard.

 -- Method: date.strftime (format)

     Return a string representing the date, controlled by an explicit
     format string.  Format codes referring to hours, minutes or seconds
     will see 0 values.  For a complete list of formatting directives,
     see *note strftime() and strptime() Behavior: 19f7.

 -- Method: date.__format__ (format)

     Same as *note date.strftime(): 632.  This makes it possible to
     specify a format string for a *note date: 19e. object in *note
     formatted string literals: 296. and when using *note str.format():
     5d5.  For a complete list of formatting directives, see *note
     strftime() and strptime() Behavior: 19f7.

* Menu:

* Examples of Usage; date: Examples of Usage date.

   ---------- Footnotes ----------

   (1) (2) This matches the definition of the “proleptic Gregorian”
calendar in Dershowitz and Reingold’s book `Calendrical Calculations',
where it’s the base calendar for all computations.  See the book for
algorithms for converting between proleptic Gregorian ordinals and many
other calendar systems.

   (2) (3) See R. H. van Gent’s guide to the mathematics of the ISO 8601
calendar
(https://www.staff.science.uu.nl/~gent0113/calendar/isocalendar.htm) for
a good explanation.


File: python.info,  Node: Examples of Usage date,  Up: date Objects

5.8.1.9 Examples of Usage: ‘date’
.................................

Example of counting days to an event:

     >>> import time
     >>> from datetime import date
     >>> today = date.today()
     >>> today
     datetime.date(2007, 12, 5)
     >>> today == date.fromtimestamp(time.time())
     True
     >>> my_birthday = date(today.year, 6, 24)
     >>> if my_birthday < today:
     ...     my_birthday = my_birthday.replace(year=today.year + 1)
     >>> my_birthday
     datetime.date(2008, 6, 24)
     >>> time_to_birthday = abs(my_birthday - today)
     >>> time_to_birthday.days
     202

More examples of working with *note date: 19e.:

     >>> from datetime import date
     >>> d = date.fromordinal(730920) # 730920th day after 1. 1. 0001
     >>> d
     datetime.date(2002, 3, 11)

     >>> # Methods related to formatting string output
     >>> d.isoformat()
     '2002-03-11'
     >>> d.strftime("%d/%m/%y")
     '11/03/02'
     >>> d.strftime("%A %d. %B %Y")
     'Monday 11. March 2002'
     >>> d.ctime()
     'Mon Mar 11 00:00:00 2002'
     >>> 'The {1} is {0:%d}, the {2} is {0:%B}.'.format(d, "day", "month")
     'The day is 11, the month is March.'

     >>> # Methods for to extracting 'components' under different calendars
     >>> t = d.timetuple()
     >>> for i in t:
     ...     print(i)
     2002                # year
     3                   # month
     11                  # day
     0
     0
     0
     0                   # weekday (0 = Monday)
     70                  # 70th day in the year
     -1
     >>> ic = d.isocalendar()
     >>> for i in ic:
     ...     print(i)
     2002                # ISO year
     11                  # ISO week number
     1                   # ISO day number ( 1 = Monday )

     >>> # A date object is immutable; all operations produce a new object
     >>> d.replace(year=2005)
     datetime.date(2005, 3, 11)


File: python.info,  Node: datetime Objects,  Next: time Objects,  Prev: date Objects,  Up: datetime — Basic date and time types

5.8.1.10 ‘datetime’ Objects
...........................

A *note datetime: 1a0. object is a single object containing all the
information from a *note date: 19e. object and a *note time: 5ed.
object.

Like a *note date: 19e. object, *note datetime: 1a0. assumes the current
Gregorian calendar extended in both directions; like a *note time: 5ed.
object, *note datetime: 1a0. assumes there are exactly 3600*24 seconds
in every day.

Constructor:

 -- Class: datetime.datetime (year, month, day, hour=0, minute=0,
          second=0, microsecond=0, tzinfo=None, *, fold=0)

     The `year', `month' and `day' arguments are required.  `tzinfo' may
     be ‘None’, or an instance of a *note tzinfo: 180. subclass.  The
     remaining arguments must be integers in the following ranges:

        * ‘MINYEAR <= year <= MAXYEAR’,

        * ‘1 <= month <= 12’,

        * ‘1 <= day <= number of days in the given month and year’,

        * ‘0 <= hour < 24’,

        * ‘0 <= minute < 60’,

        * ‘0 <= second < 60’,

        * ‘0 <= microsecond < 1000000’,

        * ‘fold in [0, 1]’.

     If an argument outside those ranges is given, *note ValueError:
     16d. is raised.

     New in version 3.6: Added the ‘fold’ argument.

Other constructors, all class methods:

 -- Method: classmethod datetime.today ()

     Return the current local datetime, with *note tzinfo: 19dd. ‘None’.

     Equivalent to:

          datetime.fromtimestamp(time.time())

     See also *note now(): 113b, *note fromtimestamp(): 11c0.

     This method is functionally equivalent to *note now(): 113b, but
     without a ‘tz’ parameter.

 -- Method: classmethod datetime.now (tz=None)

     Return the current local date and time.

     If optional argument `tz' is ‘None’ or not specified, this is like
     *note today(): 19fc, but, if possible, supplies more precision than
     can be gotten from going through a *note time.time(): 42d.
     timestamp (for example, this may be possible on platforms supplying
     the C ‘gettimeofday()’ function).

     If `tz' is not ‘None’, it must be an instance of a *note tzinfo:
     180. subclass, and the current date and time are converted to
     `tz'’s time zone.

     This function is preferred over *note today(): 19fc. and *note
     utcnow(): 19fd.

 -- Method: classmethod datetime.utcnow ()

     Return the current UTC date and time, with *note tzinfo: 19dd.
     ‘None’.

     This is like *note now(): 113b, but returns the current UTC date
     and time, as a naive *note datetime: 1a0. object.  An aware current
     UTC datetime can be obtained by calling
     ‘datetime.now(timezone.utc)’.  See also *note now(): 113b.

          Warning: Because naive ‘datetime’ objects are treated by many
          ‘datetime’ methods as local times, it is preferred to use
          aware datetimes to represent times in UTC. As such, the
          recommended way to create an object representing the current
          time in UTC is by calling ‘datetime.now(timezone.utc)’.

 -- Method: classmethod datetime.fromtimestamp (timestamp, tz=None)

     Return the local date and time corresponding to the POSIX
     timestamp, such as is returned by *note time.time(): 42d.  If
     optional argument `tz' is ‘None’ or not specified, the timestamp is
     converted to the platform’s local date and time, and the returned
     *note datetime: 1a0. object is naive.

     If `tz' is not ‘None’, it must be an instance of a *note tzinfo:
     180. subclass, and the timestamp is converted to `tz'’s time zone.

     *note fromtimestamp(): 11c0. may raise *note OverflowError: a41, if
     the timestamp is out of the range of values supported by the
     platform C ‘localtime()’ or ‘gmtime()’ functions, and *note
     OSError: 304. on ‘localtime()’ or ‘gmtime()’ failure.  It’s common
     for this to be restricted to years in 1970 through 2038.  Note that
     on non-POSIX systems that include leap seconds in their notion of a
     timestamp, leap seconds are ignored by *note fromtimestamp(): 11c0,
     and then it’s possible to have two timestamps differing by a second
     that yield identical *note datetime: 1a0. objects.  This method is
     preferred over *note utcfromtimestamp(): 19fe.

     Changed in version 3.3: Raise *note OverflowError: a41. instead of
     *note ValueError: 16d. if the timestamp is out of the range of
     values supported by the platform C ‘localtime()’ or ‘gmtime()’
     functions.  Raise *note OSError: 304. instead of *note ValueError:
     16d. on ‘localtime()’ or ‘gmtime()’ failure.

     Changed in version 3.6: *note fromtimestamp(): 11c0. may return
     instances with *note fold: 5ee. set to 1.

 -- Method: classmethod datetime.utcfromtimestamp (timestamp)

     Return the UTC *note datetime: 1a0. corresponding to the POSIX
     timestamp, with *note tzinfo: 19dd. ‘None’.  (The resulting object
     is naive.)

     This may raise *note OverflowError: a41, if the timestamp is out of
     the range of values supported by the platform C ‘gmtime()’
     function, and *note OSError: 304. on ‘gmtime()’ failure.  It’s
     common for this to be restricted to years in 1970 through 2038.

     To get an aware *note datetime: 1a0. object, call *note
     fromtimestamp(): 11c0.:

          datetime.fromtimestamp(timestamp, timezone.utc)

     On the POSIX compliant platforms, it is equivalent to the following
     expression:

          datetime(1970, 1, 1, tzinfo=timezone.utc) + timedelta(seconds=timestamp)

     except the latter formula always supports the full years range:
     between *note MINYEAR: 19cb. and *note MAXYEAR: 19cc. inclusive.

          Warning: Because naive ‘datetime’ objects are treated by many
          ‘datetime’ methods as local times, it is preferred to use
          aware datetimes to represent times in UTC. As such, the
          recommended way to create an object representing a specific
          timestamp in UTC is by calling
          ‘datetime.fromtimestamp(timestamp, tz=timezone.utc)’.

     Changed in version 3.3: Raise *note OverflowError: a41. instead of
     *note ValueError: 16d. if the timestamp is out of the range of
     values supported by the platform C ‘gmtime()’ function.  Raise
     *note OSError: 304. instead of *note ValueError: 16d. on ‘gmtime()’
     failure.

 -- Method: classmethod datetime.fromordinal (ordinal)

     Return the *note datetime: 1a0. corresponding to the proleptic
     Gregorian ordinal, where January 1 of year 1 has ordinal 1.  *note
     ValueError: 16d. is raised unless ‘1 <= ordinal <=
     datetime.max.toordinal()’.  The hour, minute, second and
     microsecond of the result are all 0, and *note tzinfo: 19dd. is
     ‘None’.

 -- Method: classmethod datetime.combine (date, time,
          tzinfo=self.tzinfo)

     Return a new *note datetime: 1a0. object whose date components are
     equal to the given *note date: 19e. object’s, and whose time
     components are equal to the given *note time: 5ed. object’s.  If
     the `tzinfo' argument is provided, its value is used to set the
     *note tzinfo: 19dd. attribute of the result, otherwise the *note
     tzinfo: 19d5. attribute of the `time' argument is used.

     For any *note datetime: 1a0. object `d', ‘d ==
     datetime.combine(d.date(), d.time(), d.tzinfo)’.  If date is a
     *note datetime: 1a0. object, its time components and *note tzinfo:
     19dd. attributes are ignored.

     Changed in version 3.6: Added the `tzinfo' argument.

 -- Method: classmethod datetime.fromisoformat (date_string)

     Return a *note datetime: 1a0. corresponding to a `date_string' in
     one of the formats emitted by *note date.isoformat(): 19eb. and
     *note datetime.isoformat(): 487.

     Specifically, this function supports strings in the format:

          YYYY-MM-DD[*HH[:MM[:SS[.fff[fff]]]][+HH:MM[:SS[.ffffff]]]]

     where ‘*’ can match any single character.

          Caution: This does `not' support parsing arbitrary ISO 8601
          strings - it is only intended as the inverse operation of
          *note datetime.isoformat(): 487.  A more full-featured ISO
          8601 parser, ‘dateutil.parser.isoparse’ is available in the
          third-party package dateutil(1).

     Examples:

          >>> from datetime import datetime
          >>> datetime.fromisoformat('2011-11-04')
          datetime.datetime(2011, 11, 4, 0, 0)
          >>> datetime.fromisoformat('2011-11-04T00:05:23')
          datetime.datetime(2011, 11, 4, 0, 5, 23)
          >>> datetime.fromisoformat('2011-11-04 00:05:23.283')
          datetime.datetime(2011, 11, 4, 0, 5, 23, 283000)
          >>> datetime.fromisoformat('2011-11-04 00:05:23.283+00:00')
          datetime.datetime(2011, 11, 4, 0, 5, 23, 283000, tzinfo=datetime.timezone.utc)
          >>> datetime.fromisoformat('2011-11-04T00:05:23+04:00')
          datetime.datetime(2011, 11, 4, 0, 5, 23,
              tzinfo=datetime.timezone(datetime.timedelta(seconds=14400)))

     New in version 3.7.

 -- Method: classmethod datetime.fromisocalendar (year, week, day)

     Return a *note datetime: 1a0. corresponding to the ISO calendar
     date specified by year, week and day.  The non-date components of
     the datetime are populated with their normal default values.  This
     is the inverse of the function *note datetime.isocalendar(): 19f.

     New in version 3.8.

 -- Method: classmethod datetime.strptime (date_string, format)

     Return a *note datetime: 1a0. corresponding to `date_string',
     parsed according to `format'.

     This is equivalent to:

          datetime(*(time.strptime(date_string, format)[0:6]))

     *note ValueError: 16d. is raised if the date_string and format
     can’t be parsed by *note time.strptime(): e56. or if it returns a
     value which isn’t a time tuple.  For a complete list of formatting
     directives, see *note strftime() and strptime() Behavior: 19f7.

Class attributes:

 -- Attribute: datetime.min

     The earliest representable *note datetime: 1a0, ‘datetime(MINYEAR,
     1, 1, tzinfo=None)’.

 -- Attribute: datetime.max

     The latest representable *note datetime: 1a0, ‘datetime(MAXYEAR,
     12, 31, 23, 59, 59, 999999, tzinfo=None)’.

 -- Attribute: datetime.resolution

     The smallest possible difference between non-equal *note datetime:
     1a0. objects, ‘timedelta(microseconds=1)’.

Instance attributes (read-only):

 -- Attribute: datetime.year

     Between *note MINYEAR: 19cb. and *note MAXYEAR: 19cc. inclusive.

 -- Attribute: datetime.month

     Between 1 and 12 inclusive.

 -- Attribute: datetime.day

     Between 1 and the number of days in the given month of the given
     year.

 -- Attribute: datetime.hour

     In ‘range(24)’.

 -- Attribute: datetime.minute

     In ‘range(60)’.

 -- Attribute: datetime.second

     In ‘range(60)’.

 -- Attribute: datetime.microsecond

     In ‘range(1000000)’.

 -- Attribute: datetime.tzinfo

     The object passed as the `tzinfo' argument to the *note datetime:
     1a0. constructor, or ‘None’ if none was passed.

 -- Attribute: datetime.fold

     In ‘[0, 1]’.  Used to disambiguate wall times during a repeated
     interval.  (A repeated interval occurs when clocks are rolled back
     at the end of daylight saving time or when the UTC offset for the
     current zone is decreased for political reasons.)  The value 0 (1)
     represents the earlier (later) of the two moments with the same
     wall time representation.

     New in version 3.6.

Supported operations:

Operation                                   Result
                                            
---------------------------------------------------------------------------------
                                            
‘datetime2 = datetime1 + timedelta’         (1)
                                            
                                            
‘datetime2 = datetime1 - timedelta’         (2)
                                            
                                            
‘timedelta = datetime1 - datetime2’         (3)
                                            
                                            
‘datetime1 < datetime2’                     Compares *note datetime: 1a0. to
                                            *note datetime: 1a0.  (4)
                                            

  1. datetime2 is a duration of timedelta removed from datetime1, moving
     forward in time if ‘timedelta.days’ > 0, or backward if
     ‘timedelta.days’ < 0.  The result has the same *note tzinfo: 19dd.
     attribute as the input datetime, and datetime2 - datetime1 ==
     timedelta after.  *note OverflowError: a41. is raised if
     datetime2.year would be smaller than *note MINYEAR: 19cb. or larger
     than *note MAXYEAR: 19cc.  Note that no time zone adjustments are
     done even if the input is an aware object.

  2. Computes the datetime2 such that datetime2 + timedelta ==
     datetime1.  As for addition, the result has the same *note tzinfo:
     19dd. attribute as the input datetime, and no time zone adjustments
     are done even if the input is aware.

  3. Subtraction of a *note datetime: 1a0. from a *note datetime: 1a0.
     is defined only if both operands are naive, or if both are aware.
     If one is aware and the other is naive, *note TypeError: 1fe. is
     raised.

     If both are naive, or both are aware and have the same *note
     tzinfo: 19dd. attribute, the *note tzinfo: 19dd. attributes are
     ignored, and the result is a *note timedelta: 2ca. object `t' such
     that ‘datetime2 + t == datetime1’.  No time zone adjustments are
     done in this case.

     If both are aware and have different *note tzinfo: 19dd.
     attributes, ‘a-b’ acts as if `a' and `b' were first converted to
     naive UTC datetimes first.  The result is ‘(a.replace(tzinfo=None)
     - a.utcoffset()) - (b.replace(tzinfo=None) - b.utcoffset())’ except
     that the implementation never overflows.

  4. `datetime1' is considered less than `datetime2' when `datetime1'
     precedes `datetime2' in time.

     If one comparand is naive and the other is aware, *note TypeError:
     1fe. is raised if an order comparison is attempted.  For equality
     comparisons, naive instances are never equal to aware instances.

     If both comparands are aware, and have the same *note tzinfo: 19dd.
     attribute, the common *note tzinfo: 19dd. attribute is ignored and
     the base datetimes are compared.  If both comparands are aware and
     have different *note tzinfo: 19dd. attributes, the comparands are
     first adjusted by subtracting their UTC offsets (obtained from
     ‘self.utcoffset()’).

     Changed in version 3.3: Equality comparisons between aware and
     naive *note datetime: 1a0. instances don’t raise *note TypeError:
     1fe.

          Note: In order to stop comparison from falling back to the
          default scheme of comparing object addresses, datetime
          comparison normally raises *note TypeError: 1fe. if the other
          comparand isn’t also a *note datetime: 1a0. object.  However,
          ‘NotImplemented’ is returned instead if the other comparand
          has a ‘timetuple()’ attribute.  This hook gives other kinds of
          date objects a chance at implementing mixed-type comparison.
          If not, when a *note datetime: 1a0. object is compared to an
          object of a different type, *note TypeError: 1fe. is raised
          unless the comparison is ‘==’ or ‘!=’.  The latter cases
          return *note False: 48f. or *note True: 594, respectively.

Instance methods:

 -- Method: datetime.date ()

     Return *note date: 19e. object with same year, month and day.

 -- Method: datetime.time ()

     Return *note time: 5ed. object with same hour, minute, second,
     microsecond and fold.  *note tzinfo: 19dd. is ‘None’.  See also
     method *note timetz(): 1a05.

     Changed in version 3.6: The fold value is copied to the returned
     *note time: 5ed. object.

 -- Method: datetime.timetz ()

     Return *note time: 5ed. object with same hour, minute, second,
     microsecond, fold, and tzinfo attributes.  See also method *note
     time(): 10c.

     Changed in version 3.6: The fold value is copied to the returned
     *note time: 5ed. object.

 -- Method: datetime.replace (year=self.year, month=self.month,
          day=self.day, hour=self.hour, minute=self.minute,
          second=self.second, microsecond=self.microsecond,
          tzinfo=self.tzinfo, *, fold=0)

     Return a datetime with the same attributes, except for those
     attributes given new values by whichever keyword arguments are
     specified.  Note that ‘tzinfo=None’ can be specified to create a
     naive datetime from an aware datetime with no conversion of date
     and time data.

     New in version 3.6: Added the ‘fold’ argument.

 -- Method: datetime.astimezone (tz=None)

     Return a *note datetime: 1a0. object with new *note tzinfo: 19dd.
     attribute `tz', adjusting the date and time data so the result is
     the same UTC time as `self', but in `tz'’s local time.

     If provided, `tz' must be an instance of a *note tzinfo: 180.
     subclass, and its *note utcoffset(): 1a07. and *note dst(): 1a08.
     methods must not return ‘None’.  If `self' is naive, it is presumed
     to represent time in the system timezone.

     If called without arguments (or with ‘tz=None’) the system local
     timezone is assumed for the target timezone.  The ‘.tzinfo’
     attribute of the converted datetime instance will be set to an
     instance of *note timezone: ae0. with the zone name and offset
     obtained from the OS.

     If ‘self.tzinfo’ is `tz', ‘self.astimezone(tz)’ is equal to `self':
     no adjustment of date or time data is performed.  Else the result
     is local time in the timezone `tz', representing the same UTC time
     as `self': after ‘astz = dt.astimezone(tz)’, ‘astz -
     astz.utcoffset()’ will have the same date and time data as ‘dt -
     dt.utcoffset()’.

     If you merely want to attach a time zone object `tz' to a datetime
     `dt' without adjustment of date and time data, use
     ‘dt.replace(tzinfo=tz)’.  If you merely want to remove the time
     zone object from an aware datetime `dt' without conversion of date
     and time data, use ‘dt.replace(tzinfo=None)’.

     Note that the default *note tzinfo.fromutc(): 1a09. method can be
     overridden in a *note tzinfo: 180. subclass to affect the result
     returned by *note astimezone(): 2cb.  Ignoring error cases, *note
     astimezone(): 2cb. acts like:

          def astimezone(self, tz):
              if self.tzinfo is tz:
                  return self
              # Convert self to UTC, and attach the new time zone object.
              utc = (self - self.utcoffset()).replace(tzinfo=tz)
              # Convert from UTC to tz's local time.
              return tz.fromutc(utc)

     Changed in version 3.3: `tz' now can be omitted.

     Changed in version 3.6: The *note astimezone(): 2cb. method can now
     be called on naive instances that are presumed to represent system
     local time.

 -- Method: datetime.utcoffset ()

     If *note tzinfo: 19dd. is ‘None’, returns ‘None’, else returns
     ‘self.tzinfo.utcoffset(self)’, and raises an exception if the
     latter doesn’t return ‘None’ or a *note timedelta: 2ca. object with
     magnitude less than one day.

     Changed in version 3.7: The UTC offset is not restricted to a whole
     number of minutes.

 -- Method: datetime.dst ()

     If *note tzinfo: 19dd. is ‘None’, returns ‘None’, else returns
     ‘self.tzinfo.dst(self)’, and raises an exception if the latter
     doesn’t return ‘None’ or a *note timedelta: 2ca. object with
     magnitude less than one day.

     Changed in version 3.7: The DST offset is not restricted to a whole
     number of minutes.

 -- Method: datetime.tzname ()

     If *note tzinfo: 19dd. is ‘None’, returns ‘None’, else returns
     ‘self.tzinfo.tzname(self)’, raises an exception if the latter
     doesn’t return ‘None’ or a string object,

 -- Method: datetime.timetuple ()

     Return a *note time.struct_time: 690. such as returned by *note
     time.localtime(): 1080.

     ‘d.timetuple()’ is equivalent to:

          time.struct_time((d.year, d.month, d.day,
                            d.hour, d.minute, d.second,
                            d.weekday(), yday, dst))

     where ‘yday = d.toordinal() - date(d.year, 1, 1).toordinal() + 1’
     is the day number within the current year starting with ‘1’ for
     January 1st.  The ‘tm_isdst’ flag of the result is set according to
     the *note dst(): 1a08. method: *note tzinfo: 19dd. is ‘None’ or
     *note dst(): 1a08. returns ‘None’, ‘tm_isdst’ is set to ‘-1’; else
     if *note dst(): 1a08. returns a non-zero value, ‘tm_isdst’ is set
     to ‘1’; else ‘tm_isdst’ is set to ‘0’.

 -- Method: datetime.utctimetuple ()

     If *note datetime: 1a0. instance `d' is naive, this is the same as
     ‘d.timetuple()’ except that ‘tm_isdst’ is forced to 0 regardless of
     what ‘d.dst()’ returns.  DST is never in effect for a UTC time.

     If `d' is aware, `d' is normalized to UTC time, by subtracting
     ‘d.utcoffset()’, and a *note time.struct_time: 690. for the
     normalized time is returned.  ‘tm_isdst’ is forced to 0.  Note that
     an *note OverflowError: a41. may be raised if `d'.year was
     ‘MINYEAR’ or ‘MAXYEAR’ and UTC adjustment spills over a year
     boundary.

          Warning: Because naive ‘datetime’ objects are treated by many
          ‘datetime’ methods as local times, it is preferred to use
          aware datetimes to represent times in UTC; as a result, using
          ‘utcfromtimetuple’ may give misleading results.  If you have a
          naive ‘datetime’ representing UTC, use
          ‘datetime.replace(tzinfo=timezone.utc)’ to make it aware, at
          which point you can use *note datetime.timetuple(): 1a0b.

 -- Method: datetime.toordinal ()

     Return the proleptic Gregorian ordinal of the date.  The same as
     ‘self.date().toordinal()’.

 -- Method: datetime.timestamp ()

     Return POSIX timestamp corresponding to the *note datetime: 1a0.
     instance.  The return value is a *note float: 1fd. similar to that
     returned by *note time.time(): 42d.

     Naive *note datetime: 1a0. instances are assumed to represent local
     time and this method relies on the platform C ‘mktime()’ function
     to perform the conversion.  Since *note datetime: 1a0. supports
     wider range of values than ‘mktime()’ on many platforms, this
     method may raise *note OverflowError: a41. for times far in the
     past or far in the future.

     For aware *note datetime: 1a0. instances, the return value is
     computed as:

          (dt - datetime(1970, 1, 1, tzinfo=timezone.utc)).total_seconds()

     New in version 3.3.

     Changed in version 3.6: The *note timestamp(): ac1. method uses the
     *note fold: 5ee. attribute to disambiguate the times during a
     repeated interval.

          Note: There is no method to obtain the POSIX timestamp
          directly from a naive *note datetime: 1a0. instance
          representing UTC time.  If your application uses this
          convention and your system timezone is not set to UTC, you can
          obtain the POSIX timestamp by supplying ‘tzinfo=timezone.utc’:

               timestamp = dt.replace(tzinfo=timezone.utc).timestamp()

          or by calculating the timestamp directly:

               timestamp = (dt - datetime(1970, 1, 1)) / timedelta(seconds=1)

 -- Method: datetime.weekday ()

     Return the day of the week as an integer, where Monday is 0 and
     Sunday is 6.  The same as ‘self.date().weekday()’.  See also *note
     isoweekday(): 1a0f.

 -- Method: datetime.isoweekday ()

     Return the day of the week as an integer, where Monday is 1 and
     Sunday is 7.  The same as ‘self.date().isoweekday()’.  See also
     *note weekday(): 1a0e, *note isocalendar(): 19f.

 -- Method: datetime.isocalendar ()

     Return a *note named tuple: b7b. with three components: ‘year’,
     ‘week’ and ‘weekday’.  The same as ‘self.date().isocalendar()’.

 -- Method: datetime.isoformat (sep='T', timespec='auto')

     Return a string representing the date and time in ISO 8601 format:

        - ‘YYYY-MM-DDTHH:MM:SS.ffffff’, if *note microsecond: 19dc. is
          not 0

        - ‘YYYY-MM-DDTHH:MM:SS’, if *note microsecond: 19dc. is 0

     If *note utcoffset(): 1a07. does not return ‘None’, a string is
     appended, giving the UTC offset:

        - ‘YYYY-MM-DDTHH:MM:SS.ffffff+HH:MM[:SS[.ffffff]]’, if *note
          microsecond: 19dc. is not 0

        - ‘YYYY-MM-DDTHH:MM:SS+HH:MM[:SS[.ffffff]]’, if *note
          microsecond: 19dc. is 0

     Examples:

          >>> from datetime import datetime, timezone
          >>> datetime(2019, 5, 18, 15, 17, 8, 132263).isoformat()
          '2019-05-18T15:17:08.132263'
          >>> datetime(2019, 5, 18, 15, 17, tzinfo=timezone.utc).isoformat()
          '2019-05-18T15:17:00+00:00'

     The optional argument `sep' (default ‘'T'’) is a one-character
     separator, placed between the date and time portions of the result.
     For example:

          >>> from datetime import tzinfo, timedelta, datetime
          >>> class TZ(tzinfo):
          ...     """A time zone with an arbitrary, constant -06:39 offset."""
          ...     def utcoffset(self, dt):
          ...         return timedelta(hours=-6, minutes=-39)
          ...
          >>> datetime(2002, 12, 25, tzinfo=TZ()).isoformat(' ')
          '2002-12-25 00:00:00-06:39'
          >>> datetime(2009, 11, 27, microsecond=100, tzinfo=TZ()).isoformat()
          '2009-11-27T00:00:00.000100-06:39'

     The optional argument `timespec' specifies the number of additional
     components of the time to include (the default is ‘'auto'’).  It
     can be one of the following:

        - ‘'auto'’: Same as ‘'seconds'’ if *note microsecond: 19dc. is
          0, same as ‘'microseconds'’ otherwise.

        - ‘'hours'’: Include the *note hour: 19d9. in the two-digit ‘HH’
          format.

        - ‘'minutes'’: Include *note hour: 19d9. and *note minute: 19da.
          in ‘HH:MM’ format.

        - ‘'seconds'’: Include *note hour: 19d9, *note minute: 19da, and
          *note second: 19db. in ‘HH:MM:SS’ format.

        - ‘'milliseconds'’: Include full time, but truncate fractional
          second part to milliseconds.  ‘HH:MM:SS.sss’ format.

        - ‘'microseconds'’: Include full time in ‘HH:MM:SS.ffffff’
          format.

          Note: Excluded time components are truncated, not rounded.

     *note ValueError: 16d. will be raised on an invalid `timespec'
     argument:

          >>> from datetime import datetime
          >>> datetime.now().isoformat(timespec='minutes')
          '2002-12-25T00:00'
          >>> dt = datetime(2015, 1, 1, 12, 30, 59, 0)
          >>> dt.isoformat(timespec='microseconds')
          '2015-01-01T12:30:59.000000'

     New in version 3.6: Added the `timespec' argument.

 -- Method: datetime.__str__ ()

     For a *note datetime: 1a0. instance `d', ‘str(d)’ is equivalent to
     ‘d.isoformat(' ')’.

 -- Method: datetime.ctime ()

     Return a string representing the date and time:

          >>> from datetime import datetime
          >>> datetime(2002, 12, 4, 20, 30, 40).ctime()
          'Wed Dec  4 20:30:40 2002'

     The output string will `not' include time zone information,
     regardless of whether the input is aware or naive.

     ‘d.ctime()’ is equivalent to:

          time.ctime(time.mktime(d.timetuple()))

     on platforms where the native C ‘ctime()’ function (which *note
     time.ctime(): 19f6. invokes, but which *note datetime.ctime():
     1a11. does not invoke) conforms to the C standard.

 -- Method: datetime.strftime (format)

     Return a string representing the date and time, controlled by an
     explicit format string.  For a complete list of formatting
     directives, see *note strftime() and strptime() Behavior: 19f7.

 -- Method: datetime.__format__ (format)

     Same as *note datetime.strftime(): 631.  This makes it possible to
     specify a format string for a *note datetime: 1a0. object in *note
     formatted string literals: 296. and when using *note str.format():
     5d5.  For a complete list of formatting directives, see *note
     strftime() and strptime() Behavior: 19f7.

* Menu:

* Examples of Usage; datetime: Examples of Usage datetime.

   ---------- Footnotes ----------

   (1) 
https://dateutil.readthedocs.io/en/stable/parser.html#dateutil.parser.isoparse


File: python.info,  Node: Examples of Usage datetime,  Up: datetime Objects

5.8.1.11 Examples of Usage: ‘datetime’
......................................

Examples of working with *note datetime: 1a0. objects:

     >>> from datetime import datetime, date, time, timezone

     >>> # Using datetime.combine()
     >>> d = date(2005, 7, 14)
     >>> t = time(12, 30)
     >>> datetime.combine(d, t)
     datetime.datetime(2005, 7, 14, 12, 30)

     >>> # Using datetime.now()
     >>> datetime.now()
     datetime.datetime(2007, 12, 6, 16, 29, 43, 79043)   # GMT +1
     >>> datetime.now(timezone.utc)
     datetime.datetime(2007, 12, 6, 15, 29, 43, 79060, tzinfo=datetime.timezone.utc)

     >>> # Using datetime.strptime()
     >>> dt = datetime.strptime("21/11/06 16:30", "%d/%m/%y %H:%M")
     >>> dt
     datetime.datetime(2006, 11, 21, 16, 30)

     >>> # Using datetime.timetuple() to get tuple of all attributes
     >>> tt = dt.timetuple()
     >>> for it in tt:
     ...     print(it)
     ...
     2006    # year
     11      # month
     21      # day
     16      # hour
     30      # minute
     0       # second
     1       # weekday (0 = Monday)
     325     # number of days since 1st January
     -1      # dst - method tzinfo.dst() returned None

     >>> # Date in ISO format
     >>> ic = dt.isocalendar()
     >>> for it in ic:
     ...     print(it)
     ...
     2006    # ISO year
     47      # ISO week
     2       # ISO weekday

     >>> # Formatting a datetime
     >>> dt.strftime("%A, %d. %B %Y %I:%M%p")
     'Tuesday, 21. November 2006 04:30PM'
     >>> 'The {1} is {0:%d}, the {2} is {0:%B}, the {3} is {0:%I:%M%p}.'.format(dt, "day", "month", "time")
     'The day is 21, the month is November, the time is 04:30PM.'

The example below defines a *note tzinfo: 180. subclass capturing time
zone information for Kabul, Afghanistan, which used +4 UTC until 1945
and then +4:30 UTC thereafter:

     from datetime import timedelta, datetime, tzinfo, timezone

     class KabulTz(tzinfo):
         # Kabul used +4 until 1945, when they moved to +4:30
         UTC_MOVE_DATE = datetime(1944, 12, 31, 20, tzinfo=timezone.utc)

         def utcoffset(self, dt):
             if dt.year < 1945:
                 return timedelta(hours=4)
             elif (1945, 1, 1, 0, 0) <= dt.timetuple()[:5] < (1945, 1, 1, 0, 30):
                 # An ambiguous ("imaginary") half-hour range representing
                 # a 'fold' in time due to the shift from +4 to +4:30.
                 # If dt falls in the imaginary range, use fold to decide how
                 # to resolve. See PEP495.
                 return timedelta(hours=4, minutes=(30 if dt.fold else 0))
             else:
                 return timedelta(hours=4, minutes=30)

         def fromutc(self, dt):
             # Follow same validations as in datetime.tzinfo
             if not isinstance(dt, datetime):
                 raise TypeError("fromutc() requires a datetime argument")
             if dt.tzinfo is not self:
                 raise ValueError("dt.tzinfo is not self")

             # A custom implementation is required for fromutc as
             # the input to this function is a datetime with utc values
             # but with a tzinfo set to self.
             # See datetime.astimezone or fromtimestamp.
             if dt.replace(tzinfo=timezone.utc) >= self.UTC_MOVE_DATE:
                 return dt + timedelta(hours=4, minutes=30)
             else:
                 return dt + timedelta(hours=4)

         def dst(self, dt):
             # Kabul does not observe daylight saving time.
             return timedelta(0)

         def tzname(self, dt):
             if dt >= self.UTC_MOVE_DATE:
                 return "+04:30"
             return "+04"

Usage of ‘KabulTz’ from above:

     >>> tz1 = KabulTz()

     >>> # Datetime before the change
     >>> dt1 = datetime(1900, 11, 21, 16, 30, tzinfo=tz1)
     >>> print(dt1.utcoffset())
     4:00:00

     >>> # Datetime after the change
     >>> dt2 = datetime(2006, 6, 14, 13, 0, tzinfo=tz1)
     >>> print(dt2.utcoffset())
     4:30:00

     >>> # Convert datetime to another time zone
     >>> dt3 = dt2.astimezone(timezone.utc)
     >>> dt3
     datetime.datetime(2006, 6, 14, 8, 30, tzinfo=datetime.timezone.utc)
     >>> dt2
     datetime.datetime(2006, 6, 14, 13, 0, tzinfo=KabulTz())
     >>> dt2 == dt3
     True


File: python.info,  Node: time Objects,  Next: tzinfo Objects,  Prev: datetime Objects,  Up: datetime — Basic date and time types

5.8.1.12 ‘time’ Objects
.......................

A *note time: 10c. object represents a (local) time of day, independent
of any particular day, and subject to adjustment via a *note tzinfo:
180. object.

 -- Class: datetime.time (hour=0, minute=0, second=0, microsecond=0,
          tzinfo=None, *, fold=0)

     All arguments are optional.  `tzinfo' may be ‘None’, or an instance
     of a *note tzinfo: 180. subclass.  The remaining arguments must be
     integers in the following ranges:

        * ‘0 <= hour < 24’,

        * ‘0 <= minute < 60’,

        * ‘0 <= second < 60’,

        * ‘0 <= microsecond < 1000000’,

        * ‘fold in [0, 1]’.

     If an argument outside those ranges is given, *note ValueError:
     16d. is raised.  All default to ‘0’ except `tzinfo', which defaults
     to *note None: 203.

Class attributes:

 -- Attribute: time.min

     The earliest representable *note time: 5ed, ‘time(0, 0, 0, 0)’.

 -- Attribute: time.max

     The latest representable *note time: 5ed, ‘time(23, 59, 59,
     999999)’.

 -- Attribute: time.resolution

     The smallest possible difference between non-equal *note time: 5ed.
     objects, ‘timedelta(microseconds=1)’, although note that arithmetic
     on *note time: 5ed. objects is not supported.

Instance attributes (read-only):

 -- Attribute: time.hour

     In ‘range(24)’.

 -- Attribute: time.minute

     In ‘range(60)’.

 -- Attribute: time.second

     In ‘range(60)’.

 -- Attribute: time.microsecond

     In ‘range(1000000)’.

 -- Attribute: time.tzinfo

     The object passed as the tzinfo argument to the *note time: 5ed.
     constructor, or ‘None’ if none was passed.

 -- Attribute: time.fold

     In ‘[0, 1]’.  Used to disambiguate wall times during a repeated
     interval.  (A repeated interval occurs when clocks are rolled back
     at the end of daylight saving time or when the UTC offset for the
     current zone is decreased for political reasons.)  The value 0 (1)
     represents the earlier (later) of the two moments with the same
     wall time representation.

     New in version 3.6.

*note time: 5ed. objects support comparison of *note time: 5ed. to *note
time: 5ed, where `a' is considered less than `b' when `a' precedes `b'
in time.  If one comparand is naive and the other is aware, *note
TypeError: 1fe. is raised if an order comparison is attempted.  For
equality comparisons, naive instances are never equal to aware
instances.

If both comparands are aware, and have the same *note tzinfo: 19d5.
attribute, the common *note tzinfo: 19d5. attribute is ignored and the
base times are compared.  If both comparands are aware and have
different *note tzinfo: 19d5. attributes, the comparands are first
adjusted by subtracting their UTC offsets (obtained from
‘self.utcoffset()’).  In order to stop mixed-type comparisons from
falling back to the default comparison by object address, when a *note
time: 5ed. object is compared to an object of a different type, *note
TypeError: 1fe. is raised unless the comparison is ‘==’ or ‘!=’.  The
latter cases return *note False: 48f. or *note True: 594, respectively.

Changed in version 3.3: Equality comparisons between aware and naive
*note time: 5ed. instances don’t raise *note TypeError: 1fe.

In Boolean contexts, a *note time: 5ed. object is always considered to
be true.

Changed in version 3.5: Before Python 3.5, a *note time: 5ed. object was
considered to be false if it represented midnight in UTC. This behavior
was considered obscure and error-prone and has been removed in Python
3.5.  See bpo-13936(1) for full details.

Other constructor:

 -- Method: classmethod time.fromisoformat (time_string)

     Return a *note time: 5ed. corresponding to a `time_string' in one
     of the formats emitted by *note time.isoformat(): 1a1a.
     Specifically, this function supports strings in the format:

          HH[:MM[:SS[.fff[fff]]]][+HH:MM[:SS[.ffffff]]]

          Caution: This does `not' support parsing arbitrary ISO 8601
          strings.  It is only intended as the inverse operation of
          *note time.isoformat(): 1a1a.

     Examples:

          >>> from datetime import time
          >>> time.fromisoformat('04:23:01')
          datetime.time(4, 23, 1)
          >>> time.fromisoformat('04:23:01.000384')
          datetime.time(4, 23, 1, 384)
          >>> time.fromisoformat('04:23:01+04:00')
          datetime.time(4, 23, 1, tzinfo=datetime.timezone(datetime.timedelta(seconds=14400)))

     New in version 3.7.

Instance methods:

 -- Method: time.replace (hour=self.hour, minute=self.minute,
          second=self.second, microsecond=self.microsecond,
          tzinfo=self.tzinfo, *, fold=0)

     Return a *note time: 5ed. with the same value, except for those
     attributes given new values by whichever keyword arguments are
     specified.  Note that ‘tzinfo=None’ can be specified to create a
     naive *note time: 5ed. from an aware *note time: 5ed, without
     conversion of the time data.

     New in version 3.6: Added the ‘fold’ argument.

 -- Method: time.isoformat (timespec='auto')

     Return a string representing the time in ISO 8601 format, one of:

        - ‘HH:MM:SS.ffffff’, if *note microsecond: 19d4. is not 0

        - ‘HH:MM:SS’, if *note microsecond: 19d4. is 0

        - ‘HH:MM:SS.ffffff+HH:MM[:SS[.ffffff]]’, if *note utcoffset():
          1a1c. does not return ‘None’

        - ‘HH:MM:SS+HH:MM[:SS[.ffffff]]’, if *note microsecond: 19d4. is
          0 and *note utcoffset(): 1a1c. does not return ‘None’

     The optional argument `timespec' specifies the number of additional
     components of the time to include (the default is ‘'auto'’).  It
     can be one of the following:

        - ‘'auto'’: Same as ‘'seconds'’ if *note microsecond: 19d4. is
          0, same as ‘'microseconds'’ otherwise.

        - ‘'hours'’: Include the *note hour: 19d1. in the two-digit ‘HH’
          format.

        - ‘'minutes'’: Include *note hour: 19d1. and *note minute: 19d2.
          in ‘HH:MM’ format.

        - ‘'seconds'’: Include *note hour: 19d1, *note minute: 19d2, and
          *note second: 19d3. in ‘HH:MM:SS’ format.

        - ‘'milliseconds'’: Include full time, but truncate fractional
          second part to milliseconds.  ‘HH:MM:SS.sss’ format.

        - ‘'microseconds'’: Include full time in ‘HH:MM:SS.ffffff’
          format.

          Note: Excluded time components are truncated, not rounded.

     *note ValueError: 16d. will be raised on an invalid `timespec'
     argument.

     Example:

          >>> from datetime import time
          >>> time(hour=12, minute=34, second=56, microsecond=123456).isoformat(timespec='minutes')
          '12:34'
          >>> dt = time(hour=12, minute=34, second=56, microsecond=0)
          >>> dt.isoformat(timespec='microseconds')
          '12:34:56.000000'
          >>> dt.isoformat(timespec='auto')
          '12:34:56'

     New in version 3.6: Added the `timespec' argument.

 -- Method: time.__str__ ()

     For a time `t', ‘str(t)’ is equivalent to ‘t.isoformat()’.

 -- Method: time.strftime (format)

     Return a string representing the time, controlled by an explicit
     format string.  For a complete list of formatting directives, see
     *note strftime() and strptime() Behavior: 19f7.

 -- Method: time.__format__ (format)

     Same as *note time.strftime(): 1a1e.  This makes it possible to
     specify a format string for a *note time: 5ed. object in *note
     formatted string literals: 296. and when using *note str.format():
     5d5.  For a complete list of formatting directives, see *note
     strftime() and strptime() Behavior: 19f7.

 -- Method: time.utcoffset ()

     If *note tzinfo: 19d5. is ‘None’, returns ‘None’, else returns
     ‘self.tzinfo.utcoffset(None)’, and raises an exception if the
     latter doesn’t return ‘None’ or a *note timedelta: 2ca. object with
     magnitude less than one day.

     Changed in version 3.7: The UTC offset is not restricted to a whole
     number of minutes.

 -- Method: time.dst ()

     If *note tzinfo: 19d5. is ‘None’, returns ‘None’, else returns
     ‘self.tzinfo.dst(None)’, and raises an exception if the latter
     doesn’t return ‘None’, or a *note timedelta: 2ca. object with
     magnitude less than one day.

     Changed in version 3.7: The DST offset is not restricted to a whole
     number of minutes.

 -- Method: time.tzname ()

     If *note tzinfo: 19d5. is ‘None’, returns ‘None’, else returns
     ‘self.tzinfo.tzname(None)’, or raises an exception if the latter
     doesn’t return ‘None’ or a string object.

* Menu:

* Examples of Usage; time: Examples of Usage time.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue13936


File: python.info,  Node: Examples of Usage time,  Up: time Objects

5.8.1.13 Examples of Usage: ‘time’
..................................

Examples of working with a *note time: 5ed. object:

     >>> from datetime import time, tzinfo, timedelta
     >>> class TZ1(tzinfo):
     ...     def utcoffset(self, dt):
     ...         return timedelta(hours=1)
     ...     def dst(self, dt):
     ...         return timedelta(0)
     ...     def tzname(self,dt):
     ...         return "+01:00"
     ...     def  __repr__(self):
     ...         return f"{self.__class__.__name__}()"
     ...
     >>> t = time(12, 10, 30, tzinfo=TZ1())
     >>> t
     datetime.time(12, 10, 30, tzinfo=TZ1())
     >>> t.isoformat()
     '12:10:30+01:00'
     >>> t.dst()
     datetime.timedelta(0)
     >>> t.tzname()
     '+01:00'
     >>> t.strftime("%H:%M:%S %Z")
     '12:10:30 +01:00'
     >>> 'The {} is {:%H:%M}.'.format("time", t)
     'The time is 12:10.'


File: python.info,  Node: tzinfo Objects,  Next: timezone Objects,  Prev: time Objects,  Up: datetime — Basic date and time types

5.8.1.14 ‘tzinfo’ Objects
.........................

 -- Class: datetime.tzinfo

     This is an abstract base class, meaning that this class should not
     be instantiated directly.  Define a subclass of *note tzinfo: 180.
     to capture information about a particular time zone.

     An instance of (a concrete subclass of) *note tzinfo: 180. can be
     passed to the constructors for *note datetime: 1a0. and *note time:
     5ed. objects.  The latter objects view their attributes as being in
     local time, and the *note tzinfo: 180. object supports methods
     revealing offset of local time from UTC, the name of the time zone,
     and DST offset, all relative to a date or time object passed to
     them.

     You need to derive a concrete subclass, and (at least) supply
     implementations of the standard *note tzinfo: 180. methods needed
     by the *note datetime: 1a0. methods you use.  The *note datetime:
     30. module provides *note timezone: ae0, a simple concrete subclass
     of *note tzinfo: 180. which can represent timezones with fixed
     offset from UTC such as UTC itself or North American EST and EDT.

     Special requirement for pickling: A *note tzinfo: 180. subclass
     must have an *note __init__(): e23. method that can be called with
     no arguments, otherwise it can be pickled but possibly not
     unpickled again.  This is a technical requirement that may be
     relaxed in the future.

     A concrete subclass of *note tzinfo: 180. may need to implement the
     following methods.  Exactly which methods are needed depends on the
     uses made of aware *note datetime: 30. objects.  If in doubt,
     simply implement all of them.

 -- Method: tzinfo.utcoffset (dt)

     Return offset of local time from UTC, as a *note timedelta: 2ca.
     object that is positive east of UTC. If local time is west of UTC,
     this should be negative.

     This represents the `total' offset from UTC; for example, if a
     *note tzinfo: 180. object represents both time zone and DST
     adjustments, *note utcoffset(): 1a25. should return their sum.  If
     the UTC offset isn’t known, return ‘None’.  Else the value returned
     must be a *note timedelta: 2ca. object strictly between
     ‘-timedelta(hours=24)’ and ‘timedelta(hours=24)’ (the magnitude of
     the offset must be less than one day).  Most implementations of
     *note utcoffset(): 1a25. will probably look like one of these two:

          return CONSTANT                 # fixed-offset class
          return CONSTANT + self.dst(dt)  # daylight-aware class

     If *note utcoffset(): 1a25. does not return ‘None’, *note dst():
     1a26. should not return ‘None’ either.

     The default implementation of *note utcoffset(): 1a25. raises *note
     NotImplementedError: 704.

     Changed in version 3.7: The UTC offset is not restricted to a whole
     number of minutes.

 -- Method: tzinfo.dst (dt)

     Return the daylight saving time (DST) adjustment, as a *note
     timedelta: 2ca. object or ‘None’ if DST information isn’t known.

     Return ‘timedelta(0)’ if DST is not in effect.  If DST is in
     effect, return the offset as a *note timedelta: 2ca. object (see
     *note utcoffset(): 1a25. for details).  Note that DST offset, if
     applicable, has already been added to the UTC offset returned by
     *note utcoffset(): 1a25, so there’s no need to consult *note dst():
     1a26. unless you’re interested in obtaining DST info separately.
     For example, *note datetime.timetuple(): 1a0b. calls its *note
     tzinfo: 19dd. attribute’s *note dst(): 1a26. method to determine
     how the ‘tm_isdst’ flag should be set, and *note tzinfo.fromutc():
     1a09. calls *note dst(): 1a26. to account for DST changes when
     crossing time zones.

     An instance `tz' of a *note tzinfo: 180. subclass that models both
     standard and daylight times must be consistent in this sense:

     ‘tz.utcoffset(dt) - tz.dst(dt)’

     must return the same result for every *note datetime: 1a0. `dt'
     with ‘dt.tzinfo == tz’ For sane *note tzinfo: 180. subclasses, this
     expression yields the time zone’s “standard offset”, which should
     not depend on the date or the time, but only on geographic
     location.  The implementation of *note datetime.astimezone(): 2cb.
     relies on this, but cannot detect violations; it’s the programmer’s
     responsibility to ensure it.  If a *note tzinfo: 180. subclass
     cannot guarantee this, it may be able to override the default
     implementation of *note tzinfo.fromutc(): 1a09. to work correctly
     with ‘astimezone()’ regardless.

     Most implementations of *note dst(): 1a26. will probably look like
     one of these two:

          def dst(self, dt):
              # a fixed-offset class:  doesn't account for DST
              return timedelta(0)

     or:

          def dst(self, dt):
              # Code to set dston and dstoff to the time zone's DST
              # transition times based on the input dt.year, and expressed
              # in standard local time.

              if dston <= dt.replace(tzinfo=None) < dstoff:
                  return timedelta(hours=1)
              else:
                  return timedelta(0)

     The default implementation of *note dst(): 1a26. raises *note
     NotImplementedError: 704.

     Changed in version 3.7: The DST offset is not restricted to a whole
     number of minutes.

 -- Method: tzinfo.tzname (dt)

     Return the time zone name corresponding to the *note datetime: 1a0.
     object `dt', as a string.  Nothing about string names is defined by
     the *note datetime: 30. module, and there’s no requirement that it
     mean anything in particular.  For example, “GMT”, “UTC”, “-500”,
     “-5:00”, “EDT”, “US/Eastern”, “America/New York” are all valid
     replies.  Return ‘None’ if a string name isn’t known.  Note that
     this is a method rather than a fixed string primarily because some
     *note tzinfo: 180. subclasses will wish to return different names
     depending on the specific value of `dt' passed, especially if the
     *note tzinfo: 180. class is accounting for daylight time.

     The default implementation of *note tzname(): 1a27. raises *note
     NotImplementedError: 704.

These methods are called by a *note datetime: 1a0. or *note time: 5ed.
object, in response to their methods of the same names.  A *note
datetime: 1a0. object passes itself as the argument, and a *note time:
5ed. object passes ‘None’ as the argument.  A *note tzinfo: 180.
subclass’s methods should therefore be prepared to accept a `dt'
argument of ‘None’, or of class *note datetime: 1a0.

When ‘None’ is passed, it’s up to the class designer to decide the best
response.  For example, returning ‘None’ is appropriate if the class
wishes to say that time objects don’t participate in the *note tzinfo:
180. protocols.  It may be more useful for ‘utcoffset(None)’ to return
the standard UTC offset, as there is no other convention for discovering
the standard offset.

When a *note datetime: 1a0. object is passed in response to a *note
datetime: 1a0. method, ‘dt.tzinfo’ is the same object as `self'.  *note
tzinfo: 180. methods can rely on this, unless user code calls *note
tzinfo: 180. methods directly.  The intent is that the *note tzinfo:
180. methods interpret `dt' as being in local time, and not need worry
about objects in other timezones.

There is one more *note tzinfo: 180. method that a subclass may wish to
override:

 -- Method: tzinfo.fromutc (dt)

     This is called from the default *note datetime.astimezone(): 2cb.
     implementation.  When called from that, ‘dt.tzinfo’ is `self', and
     `dt'’s date and time data are to be viewed as expressing a UTC
     time.  The purpose of *note fromutc(): 1a09. is to adjust the date
     and time data, returning an equivalent datetime in `self'’s local
     time.

     Most *note tzinfo: 180. subclasses should be able to inherit the
     default *note fromutc(): 1a09. implementation without problems.
     It’s strong enough to handle fixed-offset time zones, and time
     zones accounting for both standard and daylight time, and the
     latter even if the DST transition times differ in different years.
     An example of a time zone the default *note fromutc(): 1a09.
     implementation may not handle correctly in all cases is one where
     the standard offset (from UTC) depends on the specific date and
     time passed, which can happen for political reasons.  The default
     implementations of ‘astimezone()’ and *note fromutc(): 1a09. may
     not produce the result you want if the result is one of the hours
     straddling the moment the standard offset changes.

     Skipping code for error cases, the default *note fromutc(): 1a09.
     implementation acts like:

          def fromutc(self, dt):
              # raise ValueError error if dt.tzinfo is not self
              dtoff = dt.utcoffset()
              dtdst = dt.dst()
              # raise ValueError if dtoff is None or dtdst is None
              delta = dtoff - dtdst  # this is self's standard offset
              if delta:
                  dt += delta   # convert to standard local time
                  dtdst = dt.dst()
                  # raise ValueError if dtdst is None
              if dtdst:
                  return dt + dtdst
              else:
                  return dt

In the following ‘tzinfo_examples.py’ file there are some examples of
*note tzinfo: 180. classes:

     from datetime import tzinfo, timedelta, datetime

     ZERO = timedelta(0)
     HOUR = timedelta(hours=1)
     SECOND = timedelta(seconds=1)

     # A class capturing the platform's idea of local time.
     # (May result in wrong values on historical times in
     #  timezones where UTC offset and/or the DST rules had
     #  changed in the past.)
     import time as _time

     STDOFFSET = timedelta(seconds = -_time.timezone)
     if _time.daylight:
         DSTOFFSET = timedelta(seconds = -_time.altzone)
     else:
         DSTOFFSET = STDOFFSET

     DSTDIFF = DSTOFFSET - STDOFFSET

     class LocalTimezone(tzinfo):

         def fromutc(self, dt):
             assert dt.tzinfo is self
             stamp = (dt - datetime(1970, 1, 1, tzinfo=self)) // SECOND
             args = _time.localtime(stamp)[:6]
             dst_diff = DSTDIFF // SECOND
             # Detect fold
             fold = (args == _time.localtime(stamp - dst_diff))
             return datetime(*args, microsecond=dt.microsecond,
                             tzinfo=self, fold=fold)

         def utcoffset(self, dt):
             if self._isdst(dt):
                 return DSTOFFSET
             else:
                 return STDOFFSET

         def dst(self, dt):
             if self._isdst(dt):
                 return DSTDIFF
             else:
                 return ZERO

         def tzname(self, dt):
             return _time.tzname[self._isdst(dt)]

         def _isdst(self, dt):
             tt = (dt.year, dt.month, dt.day,
                   dt.hour, dt.minute, dt.second,
                   dt.weekday(), 0, 0)
             stamp = _time.mktime(tt)
             tt = _time.localtime(stamp)
             return tt.tm_isdst > 0

     Local = LocalTimezone()


     # A complete implementation of current DST rules for major US time zones.

     def first_sunday_on_or_after(dt):
         days_to_go = 6 - dt.weekday()
         if days_to_go:
             dt += timedelta(days_to_go)
         return dt


     # US DST Rules
     #
     # This is a simplified (i.e., wrong for a few cases) set of rules for US
     # DST start and end times. For a complete and up-to-date set of DST rules
     # and timezone definitions, visit the Olson Database (or try pytz):
     # http://www.twinsun.com/tz/tz-link.htm
     # http://sourceforge.net/projects/pytz/ (might not be up-to-date)
     #
     # In the US, since 2007, DST starts at 2am (standard time) on the second
     # Sunday in March, which is the first Sunday on or after Mar 8.
     DSTSTART_2007 = datetime(1, 3, 8, 2)
     # and ends at 2am (DST time) on the first Sunday of Nov.
     DSTEND_2007 = datetime(1, 11, 1, 2)
     # From 1987 to 2006, DST used to start at 2am (standard time) on the first
     # Sunday in April and to end at 2am (DST time) on the last
     # Sunday of October, which is the first Sunday on or after Oct 25.
     DSTSTART_1987_2006 = datetime(1, 4, 1, 2)
     DSTEND_1987_2006 = datetime(1, 10, 25, 2)
     # From 1967 to 1986, DST used to start at 2am (standard time) on the last
     # Sunday in April (the one on or after April 24) and to end at 2am (DST time)
     # on the last Sunday of October, which is the first Sunday
     # on or after Oct 25.
     DSTSTART_1967_1986 = datetime(1, 4, 24, 2)
     DSTEND_1967_1986 = DSTEND_1987_2006

     def us_dst_range(year):
         # Find start and end times for US DST. For years before 1967, return
         # start = end for no DST.
         if 2006 < year:
             dststart, dstend = DSTSTART_2007, DSTEND_2007
         elif 1986 < year < 2007:
             dststart, dstend = DSTSTART_1987_2006, DSTEND_1987_2006
         elif 1966 < year < 1987:
             dststart, dstend = DSTSTART_1967_1986, DSTEND_1967_1986
         else:
             return (datetime(year, 1, 1), ) * 2

         start = first_sunday_on_or_after(dststart.replace(year=year))
         end = first_sunday_on_or_after(dstend.replace(year=year))
         return start, end


     class USTimeZone(tzinfo):

         def __init__(self, hours, reprname, stdname, dstname):
             self.stdoffset = timedelta(hours=hours)
             self.reprname = reprname
             self.stdname = stdname
             self.dstname = dstname

         def __repr__(self):
             return self.reprname

         def tzname(self, dt):
             if self.dst(dt):
                 return self.dstname
             else:
                 return self.stdname

         def utcoffset(self, dt):
             return self.stdoffset + self.dst(dt)

         def dst(self, dt):
             if dt is None or dt.tzinfo is None:
                 # An exception may be sensible here, in one or both cases.
                 # It depends on how you want to treat them.  The default
                 # fromutc() implementation (called by the default astimezone()
                 # implementation) passes a datetime with dt.tzinfo is self.
                 return ZERO
             assert dt.tzinfo is self
             start, end = us_dst_range(dt.year)
             # Can't compare naive to aware objects, so strip the timezone from
             # dt first.
             dt = dt.replace(tzinfo=None)
             if start + HOUR <= dt < end - HOUR:
                 # DST is in effect.
                 return HOUR
             if end - HOUR <= dt < end:
                 # Fold (an ambiguous hour): use dt.fold to disambiguate.
                 return ZERO if dt.fold else HOUR
             if start <= dt < start + HOUR:
                 # Gap (a non-existent hour): reverse the fold rule.
                 return HOUR if dt.fold else ZERO
             # DST is off.
             return ZERO

         def fromutc(self, dt):
             assert dt.tzinfo is self
             start, end = us_dst_range(dt.year)
             start = start.replace(tzinfo=self)
             end = end.replace(tzinfo=self)
             std_time = dt + self.stdoffset
             dst_time = std_time + HOUR
             if end <= dst_time < end + HOUR:
                 # Repeated hour
                 return std_time.replace(fold=1)
             if std_time < start or dst_time >= end:
                 # Standard time
                 return std_time
             if start <= std_time < end - HOUR:
                 # Daylight saving time
                 return dst_time


     Eastern  = USTimeZone(-5, "Eastern",  "EST", "EDT")
     Central  = USTimeZone(-6, "Central",  "CST", "CDT")
     Mountain = USTimeZone(-7, "Mountain", "MST", "MDT")
     Pacific  = USTimeZone(-8, "Pacific",  "PST", "PDT")

Note that there are unavoidable subtleties twice per year in a *note
tzinfo: 180. subclass accounting for both standard and daylight time, at
the DST transition points.  For concreteness, consider US Eastern (UTC
-0500), where EDT begins the minute after 1:59 (EST) on the second
Sunday in March, and ends the minute after 1:59 (EDT) on the first
Sunday in November:

       UTC   3:MM  4:MM  5:MM  6:MM  7:MM  8:MM
       EST  22:MM 23:MM  0:MM  1:MM  2:MM  3:MM
       EDT  23:MM  0:MM  1:MM  2:MM  3:MM  4:MM

     start  22:MM 23:MM  0:MM  1:MM  3:MM  4:MM

       end  23:MM  0:MM  1:MM  1:MM  2:MM  3:MM

When DST starts (the “start” line), the local wall clock leaps from 1:59
to 3:00.  A wall time of the form 2:MM doesn’t really make sense on that
day, so ‘astimezone(Eastern)’ won’t deliver a result with ‘hour == 2’ on
the day DST begins.  For example, at the Spring forward transition of
2016, we get:

     >>> from datetime import datetime, timezone
     >>> from tzinfo_examples import HOUR, Eastern
     >>> u0 = datetime(2016, 3, 13, 5, tzinfo=timezone.utc)
     >>> for i in range(4):
     ...     u = u0 + i*HOUR
     ...     t = u.astimezone(Eastern)
     ...     print(u.time(), 'UTC =', t.time(), t.tzname())
     ...
     05:00:00 UTC = 00:00:00 EST
     06:00:00 UTC = 01:00:00 EST
     07:00:00 UTC = 03:00:00 EDT
     08:00:00 UTC = 04:00:00 EDT

When DST ends (the “end” line), there’s a potentially worse problem:
there’s an hour that can’t be spelled unambiguously in local wall time:
the last hour of daylight time.  In Eastern, that’s times of the form
5:MM UTC on the day daylight time ends.  The local wall clock leaps from
1:59 (daylight time) back to 1:00 (standard time) again.  Local times of
the form 1:MM are ambiguous.  ‘astimezone()’ mimics the local clock’s
behavior by mapping two adjacent UTC hours into the same local hour
then.  In the Eastern example, UTC times of the form 5:MM and 6:MM both
map to 1:MM when converted to Eastern, but earlier times have the *note
fold: 5ee. attribute set to 0 and the later times have it set to 1.  For
example, at the Fall back transition of 2016, we get:

     >>> u0 = datetime(2016, 11, 6, 4, tzinfo=timezone.utc)
     >>> for i in range(4):
     ...     u = u0 + i*HOUR
     ...     t = u.astimezone(Eastern)
     ...     print(u.time(), 'UTC =', t.time(), t.tzname(), t.fold)
     ...
     04:00:00 UTC = 00:00:00 EDT 0
     05:00:00 UTC = 01:00:00 EDT 0
     06:00:00 UTC = 01:00:00 EST 1
     07:00:00 UTC = 02:00:00 EST 0

Note that the *note datetime: 1a0. instances that differ only by the
value of the *note fold: 5ee. attribute are considered equal in
comparisons.

Applications that can’t bear wall-time ambiguities should explicitly
check the value of the *note fold: 5ee. attribute or avoid using hybrid
*note tzinfo: 180. subclasses; there are no ambiguities when using *note
timezone: ae0, or any other fixed-offset *note tzinfo: 180. subclass
(such as a class representing only EST (fixed offset -5 hours), or only
EDT (fixed offset -4 hours)).

See also
........

     *note zoneinfo: 14e.

          The *note datetime: 30. module has a basic *note timezone:
          ae0. class (for handling arbitrary fixed offsets from UTC) and
          its *note timezone.utc: 1a28. attribute (a UTC timezone
          instance).

          ‘zoneinfo’ brings the `IANA timezone database' (also known as
          the Olson database) to Python, and its usage is recommended.

IANA timezone database(1)

     The Time Zone Database (often called tz, tzdata or zoneinfo)
     contains code and data that represent the history of local time for
     many representative locations around the globe.  It is updated
     periodically to reflect changes made by political bodies to time
     zone boundaries, UTC offsets, and daylight-saving rules.

   ---------- Footnotes ----------

   (1) https://www.iana.org/time-zones


File: python.info,  Node: timezone Objects,  Next: strftime and strptime Behavior,  Prev: tzinfo Objects,  Up: datetime — Basic date and time types

5.8.1.15 ‘timezone’ Objects
...........................

The *note timezone: ae0. class is a subclass of *note tzinfo: 180, each
instance of which represents a timezone defined by a fixed offset from
UTC.

Objects of this class cannot be used to represent timezone information
in the locations where different offsets are used in different days of
the year or where historical changes have been made to civil time.

 -- Class: datetime.timezone (offset, name=None)

     The `offset' argument must be specified as a *note timedelta: 2ca.
     object representing the difference between the local time and UTC.
     It must be strictly between ‘-timedelta(hours=24)’ and
     ‘timedelta(hours=24)’, otherwise *note ValueError: 16d. is raised.

     The `name' argument is optional.  If specified it must be a string
     that will be used as the value returned by the *note
     datetime.tzname(): 1a0a. method.

     New in version 3.2.

     Changed in version 3.7: The UTC offset is not restricted to a whole
     number of minutes.

 -- Method: timezone.utcoffset (dt)

     Return the fixed value specified when the *note timezone: ae0.
     instance is constructed.

     The `dt' argument is ignored.  The return value is a *note
     timedelta: 2ca. instance equal to the difference between the local
     time and UTC.

     Changed in version 3.7: The UTC offset is not restricted to a whole
     number of minutes.

 -- Method: timezone.tzname (dt)

     Return the fixed value specified when the *note timezone: ae0.
     instance is constructed.

     If `name' is not provided in the constructor, the name returned by
     ‘tzname(dt)’ is generated from the value of the ‘offset’ as
     follows.  If `offset' is ‘timedelta(0)’, the name is “UTC”,
     otherwise it is a string in the format ‘UTC±HH:MM’, where ± is the
     sign of ‘offset’, HH and MM are two digits of ‘offset.hours’ and
     ‘offset.minutes’ respectively.

     Changed in version 3.6: Name generated from ‘offset=timedelta(0)’
     is now plain ‘‘UTC’’, not ‘'UTC+00:00'’.

 -- Method: timezone.dst (dt)

     Always returns ‘None’.

 -- Method: timezone.fromutc (dt)

     Return ‘dt + offset’.  The `dt' argument must be an aware *note
     datetime: 1a0. instance, with ‘tzinfo’ set to ‘self’.

Class attributes:

 -- Attribute: timezone.utc

     The UTC timezone, ‘timezone(timedelta(0))’.


File: python.info,  Node: strftime and strptime Behavior,  Prev: timezone Objects,  Up: datetime — Basic date and time types

5.8.1.16 ‘strftime()’ and ‘strptime()’ Behavior
...............................................

*note date: 19e, *note datetime: 1a0, and *note time: 5ed. objects all
support a ‘strftime(format)’ method, to create a string representing the
time under the control of an explicit format string.

Conversely, the *note datetime.strptime(): f91. class method creates a
*note datetime: 1a0. object from a string representing a date and time
and a corresponding format string.

The table below provides a high-level comparison of ‘strftime()’ versus
‘strptime()’:

                     ‘strftime’                                                   ‘strptime’
                                                                                  
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                  
Usage                Convert object to a string according to a given format       Parse a string into a *note datetime: 1a0. object given a corresponding format
                                                                                  
                                                                                  
Type of method       Instance method                                              Class method
                                                                                  
                                                                                  
Method of            *note date: 19e.; *note datetime: 1a0.; *note time: 5ed.     *note datetime: 1a0.
                                                                                  
                                                                                  
Signature            ‘strftime(format)’                                           ‘strptime(date_string, format)’
                                                                                  

* Menu:

* strftime() and strptime() Format Codes: strftime and strptime Format Codes.
* Technical Detail::


File: python.info,  Node: strftime and strptime Format Codes,  Next: Technical Detail,  Up: strftime and strptime Behavior

5.8.1.17 ‘strftime()’ and ‘strptime()’ Format Codes
...................................................

The following is a list of all the format codes that the 1989 C standard
requires, and these work on all platforms with a standard C
implementation.

Directive       Meaning                              Example                      Notes
                                                                                  
----------------------------------------------------------------------------------------------
                                                                                  
‘%a’            Weekday as locale’s abbreviated           Sun, Mon, …, Sat (en_US); (1)
                name.                                     So, Mo, …, Sa (de_DE)   
                                                     
                                                                                  
‘%A’            Weekday as locale’s full name.            Sunday, Monday, …, Saturday (en_US); (1)
                                                          Sonntag, Montag, …, Samstag (de_DE) 
                                                     
                                                                                  
‘%w’            Weekday as a decimal number, where   0, 1, …, 6
                0 is Sunday and 6 is Saturday.       
                
                                                                                  
‘%d’            Day of the month as a zero-padded    01, 02, …, 31                (9)
                decimal number.                                                   
                
                                                                                  
‘%b’            Month as locale’s abbreviated             Jan, Feb, …, Dec (en_US); (1)
                name.                                     Jan, Feb, …, Dez (de_DE) 
                                                     
                                                                                  
‘%B’            Month as locale’s full name.              January, February, …, December (en_US); (1)
                                                          Januar, Februar, …, Dezember (de_DE) 
                                                     
                                                                                  
‘%m’            Month as a zero-padded decimal       01, 02, …, 12                (9)
                number.                                                           
                
                                                                                  
‘%y’            Year without century as a            00, 01, …, 99                (9)
                zero-padded decimal number.                                       
                
                                                                                  
‘%Y’            Year with century as a decimal       0001, 0002, …, 2013, 2014,   (2)
                number.                              …, 9998, 9999                
                                                     
                                                                                  
‘%H’            Hour (24-hour clock) as a            00, 01, …, 23                (9)
                zero-padded decimal number.                                       
                
                                                                                  
‘%I’            Hour (12-hour clock) as a            01, 02, …, 12                (9)
                zero-padded decimal number.                                       
                
                                                                                  
‘%p’            Locale’s equivalent of either AM          AM, PM (en_US);         (1), (3)
                or PM.                                    am, pm (de_DE)          
                                                     
                                                                                  
‘%M’            Minute as a zero-padded decimal      00, 01, …, 59                (9)
                number.                                                           
                
                                                                                  
‘%S’            Second as a zero-padded decimal      00, 01, …, 59                (4), (9)
                number.                                                           
                
                                                                                  
‘%f’            Microsecond as a decimal number,     000000, 000001, …, 999999    (5)
                zero-padded to 6 digits.                                          
                
                                                                                  
‘%z’            UTC offset in the form               (empty), +0000, -0400,       (6)
                ‘±HHMM[SS[.ffffff]]’ (empty string   +1030, +063415,              
                if the object is naive).             -030712.345216
                                                     
                                                                                  
‘%Z’            Time zone name (empty string if      (empty), UTC, GMT            (6)
                the object is naive).                                             
                
                                                                                  
‘%j’            Day of the year as a zero-padded     001, 002, …, 366             (9)
                decimal number.                                                   
                
                                                                                  
‘%U’            Week number of the year (Sunday as   00, 01, …, 53                (7), (9)
                the first day of the week) as a                                   
                zero padded decimal number.  All
                days in a new year preceding the
                first Sunday are considered to be
                in week 0.
                
                                                                                  
‘%W’            Week number of the year (Monday as   00, 01, …, 53                (7), (9)
                the first day of the week) as a                                   
                decimal number.  All days in a new
                year preceding the first Monday
                are considered to be in week 0.
                
                                                                                  
‘%c’            Locale’s appropriate date and time        Tue Aug 16 21:30:00 1988 (en_US); (1)
                representation.                           Di 16 Aug 21:30:00 1988 (de_DE) 
                                                     
                                                                                  
‘%x’            Locale’s appropriate date                 08/16/88 (None);        (1)
                representation.                           08/16/1988 (en_US);     
                                                          16.08.1988 (de_DE) 
                                                     
                                                                                  
‘%X’            Locale’s appropriate time                 21:30:00 (en_US);       (1)
                representation.                           21:30:00 (de_DE)        
                                                     
                                                                                  
‘%%’            A literal ‘'%'’ character.           %
                                                     

Several additional directives not required by the C89 standard are
included for convenience.  These parameters all correspond to ISO 8601
date values.

Directive       Meaning                              Example                      Notes
                                                                                  
----------------------------------------------------------------------------------------------
                                                                                  
‘%G’            ISO 8601 year with century           0001, 0002, …, 2013, 2014,   (8)
                representing the year that           …, 9998, 9999                
                contains the greater part of the     
                ISO week (‘%V’).
                
                                                                                  
‘%u’            ISO 8601 weekday as a decimal        1, 2, …, 7
                number where 1 is Monday.            
                
                                                                                  
‘%V’            ISO 8601 week as a decimal number    01, 02, …, 53                (8), (9)
                with Monday as the first day of                                   
                the week.  Week 01 is the week
                containing Jan 4.
                

These may not be available on all platforms when used with the
‘strftime()’ method.  The ISO 8601 year and ISO 8601 week directives are
not interchangeable with the year and week number directives above.
Calling ‘strptime()’ with incomplete or ambiguous ISO 8601 directives
will raise a *note ValueError: 16d.

The full set of format codes supported varies across platforms, because
Python calls the platform C library’s ‘strftime()’ function, and
platform variations are common.  To see the full set of format codes
supported on your platform, consult the ‘strftime(3)’ documentation.
There are also differences between platforms in handling of unsupported
format specifiers.

New in version 3.6: ‘%G’, ‘%u’ and ‘%V’ were added.


File: python.info,  Node: Technical Detail,  Prev: strftime and strptime Format Codes,  Up: strftime and strptime Behavior

5.8.1.18 Technical Detail
.........................

Broadly speaking, ‘d.strftime(fmt)’ acts like the *note time: 10c.
module’s ‘time.strftime(fmt, d.timetuple())’ although not all objects
support a ‘timetuple()’ method.

For the *note datetime.strptime(): f91. class method, the default value
is ‘1900-01-01T00:00:00.000’: any components not specified in the format
string will be pulled from the default value.  (1)

Using ‘datetime.strptime(date_string, format)’ is equivalent to:

     datetime(*(time.strptime(date_string, format)[0:6]))

except when the format includes sub-second components or timezone offset
information, which are supported in ‘datetime.strptime’ but are
discarded by ‘time.strptime’.

For *note time: 5ed. objects, the format codes for year, month, and day
should not be used, as *note time: 10c. objects have no such values.  If
they’re used anyway, ‘1900’ is substituted for the year, and ‘1’ for the
month and day.

For *note date: 19e. objects, the format codes for hours, minutes,
seconds, and microseconds should not be used, as *note date: 19e.
objects have no such values.  If they’re used anyway, ‘0’ is substituted
for them.

For the same reason, handling of format strings containing Unicode code
points that can’t be represented in the charset of the current locale is
also platform-dependent.  On some platforms such code points are
preserved intact in the output, while on others ‘strftime’ may raise
*note UnicodeError: d03. or return an empty string instead.

Notes:

  1. Because the format depends on the current locale, care should be
     taken when making assumptions about the output value.  Field
     orderings will vary (for example, “month/day/year” versus
     “day/month/year”), and the output may contain Unicode characters
     encoded using the locale’s default encoding (for example, if the
     current locale is ‘ja_JP’, the default encoding could be any one of
     ‘eucJP’, ‘SJIS’, or ‘utf-8’; use *note locale.getlocale(): 1a32. to
     determine the current locale’s encoding).

  2. The ‘strptime()’ method can parse years in the full [1, 9999]
     range, but years < 1000 must be zero-filled to 4-digit width.

     Changed in version 3.2: In previous versions, ‘strftime()’ method
     was restricted to years >= 1900.

     Changed in version 3.3: In version 3.2, ‘strftime()’ method was
     restricted to years >= 1000.

  3. When used with the ‘strptime()’ method, the ‘%p’ directive only
     affects the output hour field if the ‘%I’ directive is used to
     parse the hour.

  4. Unlike the *note time: 10c. module, the *note datetime: 30. module
     does not support leap seconds.

  5. When used with the ‘strptime()’ method, the ‘%f’ directive accepts
     from one to six digits and zero pads on the right.  ‘%f’ is an
     extension to the set of format characters in the C standard (but
     implemented separately in datetime objects, and therefore always
     available).

  6. For a naive object, the ‘%z’ and ‘%Z’ format codes are replaced by
     empty strings.

     For an aware object:

     ‘%z’

          ‘utcoffset()’ is transformed into a string of the form
          ‘±HHMM[SS[.ffffff]]’, where ‘HH’ is a 2-digit string giving
          the number of UTC offset hours, ‘MM’ is a 2-digit string
          giving the number of UTC offset minutes, ‘SS’ is a 2-digit
          string giving the number of UTC offset seconds and ‘ffffff’ is
          a 6-digit string giving the number of UTC offset microseconds.
          The ‘ffffff’ part is omitted when the offset is a whole number
          of seconds and both the ‘ffffff’ and the ‘SS’ part is omitted
          when the offset is a whole number of minutes.  For example, if
          ‘utcoffset()’ returns ‘timedelta(hours=-3, minutes=-30)’, ‘%z’
          is replaced with the string ‘'-0330'’.

     Changed in version 3.7: The UTC offset is not restricted to a whole
     number of minutes.

     Changed in version 3.7: When the ‘%z’ directive is provided to the
     ‘strptime()’ method, the UTC offsets can have a colon as a
     separator between hours, minutes and seconds.  For example,
     ‘'+01:00:00'’ will be parsed as an offset of one hour.  In
     addition, providing ‘'Z'’ is identical to ‘'+00:00'’.

     ‘%Z’

          In ‘strftime()’, ‘%Z’ is replaced by an empty string if
          ‘tzname()’ returns ‘None’; otherwise ‘%Z’ is replaced by the
          returned value, which must be a string.

          ‘strptime()’ only accepts certain values for ‘%Z’:

            1. any value in ‘time.tzname’ for your machine’s locale

            2. the hard-coded values ‘UTC’ and ‘GMT’

          So someone living in Japan may have ‘JST’, ‘UTC’, and ‘GMT’ as
          valid values, but probably not ‘EST’.  It will raise
          ‘ValueError’ for invalid values.

     Changed in version 3.2: When the ‘%z’ directive is provided to the
     ‘strptime()’ method, an aware *note datetime: 1a0. object will be
     produced.  The ‘tzinfo’ of the result will be set to a *note
     timezone: ae0. instance.

  7. When used with the ‘strptime()’ method, ‘%U’ and ‘%W’ are only used
     in calculations when the day of the week and the calendar year
     (‘%Y’) are specified.

  8. Similar to ‘%U’ and ‘%W’, ‘%V’ is only used in calculations when
     the day of the week and the ISO year (‘%G’) are specified in a
     ‘strptime()’ format string.  Also note that ‘%G’ and ‘%Y’ are not
     interchangeable.

  9. When used with the ‘strptime()’ method, the leading zero is
     optional for formats ‘%d’, ‘%m’, ‘%H’, ‘%I’, ‘%M’, ‘%S’, ‘%J’,
     ‘%U’, ‘%W’, and ‘%V’.  Format ‘%y’ does require a leading zero.

   ---------- Footnotes ----------

   (1) (4) Passing ‘datetime.strptime('Feb 29', '%b %d')’ will fail
since ‘1900’ is not a leap year.


File: python.info,  Node: zoneinfo — IANA time zone support,  Next: calendar — General calendar-related functions,  Prev: datetime — Basic date and time types,  Up: Data Types

5.8.2 ‘zoneinfo’ — IANA time zone support
-----------------------------------------

New in version 3.9.

__________________________________________________________________

The *note zoneinfo: 14e. module provides a concrete time zone
implementation to support the IANA time zone database as originally
specified in PEP 615(1).  By default, *note zoneinfo: 14e. uses the
system’s time zone data if available; if no system time zone data is
available, the library will fall back to using the first-party tzdata(2)
package available on PyPI.

See also
........

Module: *note datetime: 30.

     Provides the *note time: 5ed. and *note datetime: 1a0. types with
     which the *note ZoneInfo: 17f. class is designed to be used.

Package tzdata(3)

     First-party package maintained by the CPython core developers to
     supply time zone data via PyPI.

* Menu:

* Using ZoneInfo::
* Data sources::
* The ZoneInfo class::
* Functions: Functions<2>.
* Globals::
* Exceptions and warnings::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0615

   (2) https://pypi.org/project/tzdata/

   (3) https://pypi.org/project/tzdata/


File: python.info,  Node: Using ZoneInfo,  Next: Data sources,  Up: zoneinfo — IANA time zone support

5.8.2.1 Using ‘ZoneInfo’
........................

*note ZoneInfo: 17f. is a concrete implementation of the *note
datetime.tzinfo: 180. abstract base class, and is intended to be
attached to ‘tzinfo’, either via the constructor, the *note
datetime.replace: 1a06. method or *note datetime.astimezone: 2cb.:

     >>> from zoneinfo import ZoneInfo
     >>> from datetime import datetime, timedelta

     >>> dt = datetime(2020, 10, 31, 12, tzinfo=ZoneInfo("America/Los_Angeles"))
     >>> print(dt)
     2020-10-31 12:00:00-07:00

     >>> dt.tzname()
     'PDT'

Datetimes constructed in this way are compatible with datetime
arithmetic and handle daylight saving time transitions with no further
intervention:

     >>> dt_add = dt + timedelta(days=1)

     >>> print(dt_add)
     2020-11-01 12:00:00-08:00

     >>> dt_add.tzname()
     'PST'

These time zones also support the *note fold: 5ee. attribute introduced
in PEP 495(1).  During offset transitions which induce ambiguous times
(such as a daylight saving time to standard time transition), the offset
from `before' the transition is used when ‘fold=0’, and the offset
`after' the transition is used when ‘fold=1’, for example:

     >>> dt = datetime(2020, 11, 1, 1, tzinfo=ZoneInfo("America/Los_Angeles"))
     >>> print(dt)
     2020-11-01 01:00:00-07:00

     >>> print(dt.replace(fold=1))
     2020-11-01 01:00:00-08:00

When converting from another time zone, the fold will be set to the
correct value:

     >>> from datetime import timezone
     >>> LOS_ANGELES = ZoneInfo("America/Los_Angeles")
     >>> dt_utc = datetime(2020, 11, 1, 8, tzinfo=timezone.utc)

     >>> # Before the PDT -> PST transition
     >>> print(dt_utc.astimezone(LOS_ANGELES))
     2020-11-01 01:00:00-07:00

     >>> # After the PDT -> PST transition
     >>> print((dt_utc + timedelta(hours=1)).astimezone(LOS_ANGELES))
     2020-11-01 01:00:00-08:00

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0495


File: python.info,  Node: Data sources,  Next: The ZoneInfo class,  Prev: Using ZoneInfo,  Up: zoneinfo — IANA time zone support

5.8.2.2 Data sources
....................

The ‘zoneinfo’ module does not directly provide time zone data, and
instead pulls time zone information from the system time zone database
or the first-party PyPI package tzdata(1), if available.  Some systems,
including notably Windows systems, do not have an IANA database
available, and so for projects targeting cross-platform compatibility
that require time zone data, it is recommended to declare a dependency
on tzdata.  If neither system data nor tzdata are available, all calls
to *note ZoneInfo: 17f. will raise *note ZoneInfoNotFoundError: 1a37.

* Menu:

* Configuring the data sources::

   ---------- Footnotes ----------

   (1) https://pypi.org/project/tzdata/


File: python.info,  Node: Configuring the data sources,  Up: Data sources

5.8.2.3 Configuring the data sources
....................................

When ‘ZoneInfo(key)’ is called, the constructor first searches the
directories specified in *note TZPATH: 1a3a. for a file matching ‘key’,
and on failure looks for a match in the tzdata package.  This behavior
can be configured in three ways:

  1. The default *note TZPATH: 1a3a. when not otherwise specified can be
     configured at *note compile time: 1a3b.

  2. *note TZPATH: 1a3a. can be configured using *note an environment
     variable: 1a3c.

  3. At *note runtime: 1a3d, the search path can be manipulated using
     the *note reset_tzpath(): 1a3e. function.

* Menu:

* Compile-time configuration::
* Environment configuration::
* Runtime configuration::


File: python.info,  Node: Compile-time configuration,  Next: Environment configuration,  Up: Configuring the data sources

5.8.2.4 Compile-time configuration
..................................

The default *note TZPATH: 1a3a. includes several common deployment
locations for the time zone database (except on Windows, where there are
no “well-known” locations for time zone data).  On POSIX systems,
downstream distributors and those building Python from source who know
where their system time zone data is deployed may change the default
time zone path by specifying the compile-time option ‘TZPATH’ (or, more
likely, the ‘configure’ flag ‘--with-tzpath’), which should be a string
delimited by *note os.pathsep: 1486.

On all platforms, the configured value is available as the ‘TZPATH’ key
in *note sysconfig.get_config_var(): a45.


File: python.info,  Node: Environment configuration,  Next: Runtime configuration,  Prev: Compile-time configuration,  Up: Configuring the data sources

5.8.2.5 Environment configuration
.................................

When initializing *note TZPATH: 1a3a. (either at import time or whenever
*note reset_tzpath(): 1a3e. is called with no arguments), the ‘zoneinfo’
module will use the environment variable ‘PYTHONTZPATH’, if it exists,
to set the search path.

 -- Environment Variable: PYTHONTZPATH

     This is an *note os.pathsep: 1486.-separated string containing the
     time zone search path to use.  It must consist of only absolute
     rather than relative paths.  Relative components specified in
     ‘PYTHONTZPATH’ will not be used, but otherwise the behavior when a
     relative path is specified is implementation-defined; CPython will
     raise *note InvalidTZPathWarning: 1a42, but other implementations
     are free to silently ignore the erroneous component or raise an
     exception.

To set the system to ignore the system data and use the tzdata package
instead, set ‘PYTHONTZPATH=""’.


File: python.info,  Node: Runtime configuration,  Prev: Environment configuration,  Up: Configuring the data sources

5.8.2.6 Runtime configuration
.............................

The TZ search path can also be configured at runtime using the *note
reset_tzpath(): 1a3e. function.  This is generally not an advisable
operation, though it is reasonable to use it in test functions that
require the use of a specific time zone path (or require disabling
access to the system time zones).


File: python.info,  Node: The ZoneInfo class,  Next: Functions<2>,  Prev: Data sources,  Up: zoneinfo — IANA time zone support

5.8.2.7 The ‘ZoneInfo’ class
............................

 -- Class: zoneinfo.ZoneInfo (key)

     A concrete *note datetime.tzinfo: 180. subclass that represents an
     IANA time zone specified by the string ‘key’.  Calls to the primary
     constructor will always return objects that compare identically;
     put another way, barring cache invalidation via *note
     ZoneInfo.clear_cache(): 1a45, for all values of ‘key’, the
     following assertion will always be true:

          a = ZoneInfo(key)
          b = ZoneInfo(key)
          assert a is b

     ‘key’ must be in the form of a relative, normalized POSIX path,
     with no up-level references.  The constructor will raise *note
     ValueError: 16d. if a non-conforming key is passed.

     If no file matching ‘key’ is found, the constructor will raise
     *note ZoneInfoNotFoundError: 1a37.

The ‘ZoneInfo’ class has two alternate constructors:

 -- Method: classmethod ZoneInfo.from_file (fobj, /, key=None)

     Constructs a ‘ZoneInfo’ object from a file-like object returning
     bytes (e.g.  a file opened in binary mode or an *note io.BytesIO:
     88a. object).  Unlike the primary constructor, this always
     constructs a new object.

     The ‘key’ parameter sets the name of the zone for the purposes of
     *note __str__(): ef9. and *note __repr__(): 44a.

     Objects created via this constructor cannot be pickled (see *note
     pickling: 1a47.).

 -- Method: classmethod ZoneInfo.no_cache (key)

     An alternate constructor that bypasses the constructor’s cache.  It
     is identical to the primary constructor, but returns a new object
     on each call.  This is most likely to be useful for testing or
     demonstration purposes, but it can also be used to create a system
     with a different cache invalidation strategy.

     Objects created via this constructor will also bypass the cache of
     a deserializing process when unpickled.

          Caution: Using this constructor may change the semantics of
          your datetimes in surprising ways, only use it if you know
          that you need to.

The following class methods are also available:

 -- Method: classmethod ZoneInfo.clear_cache (*, only_keys=None)

     A method for invalidating the cache on the ‘ZoneInfo’ class.  If no
     arguments are passed, all caches are invalidated and the next call
     to the primary constructor for each key will return a new instance.

     If an iterable of key names is passed to the ‘only_keys’ parameter,
     only the specified keys will be removed from the cache.  Keys
     passed to ‘only_keys’ but not found in the cache are ignored.

          Warning: Invoking this function may change the semantics of
          datetimes using ‘ZoneInfo’ in surprising ways; this modifies
          process-wide global state and thus may have wide-ranging
          effects.  Only use it if you know that you need to.

The class has one attribute:

 -- Attribute: ZoneInfo.key

     This is a read-only *note attribute: 1a4a. that returns the value
     of ‘key’ passed to the constructor, which should be a lookup key in
     the IANA time zone database (e.g.  ‘America/New_York’,
     ‘Europe/Paris’ or ‘Asia/Tokyo’).

     For zones constructed from file without specifying a ‘key’
     parameter, this will be set to ‘None’.

          Note: Although it is a somewhat common practice to expose
          these to end users, these values are designed to be primary
          keys for representing the relevant zones and not necessarily
          user-facing elements.  Projects like CLDR (the Unicode Common
          Locale Data Repository) can be used to get more user-friendly
          strings from these keys.

* Menu:

* String representations::
* Pickle serialization::


File: python.info,  Node: String representations,  Next: Pickle serialization,  Up: The ZoneInfo class

5.8.2.8 String representations
..............................

The string representation returned when calling *note str: 205. on a
*note ZoneInfo: 17f. object defaults to using the *note ZoneInfo.key:
1a49. attribute (see the note on usage in the attribute documentation):

     >>> zone = ZoneInfo("Pacific/Kwajalein")
     >>> str(zone)
     'Pacific/Kwajalein'

     >>> dt = datetime(2020, 4, 1, 3, 15, tzinfo=zone)
     >>> f"{dt.isoformat()} [{dt.tzinfo}]"
     '2020-04-01T03:15:00+12:00 [Pacific/Kwajalein]'

For objects constructed from a file without specifying a ‘key’
parameter, ‘str’ falls back to calling *note repr(): 8b9.  ‘ZoneInfo’’s
‘repr’ is implementation-defined and not necessarily stable between
versions, but it is guaranteed not to be a valid ‘ZoneInfo’ key.


File: python.info,  Node: Pickle serialization,  Prev: String representations,  Up: The ZoneInfo class

5.8.2.9 Pickle serialization
............................

Rather than serializing all transition data, ‘ZoneInfo’ objects are
serialized by key, and ‘ZoneInfo’ objects constructed from files (even
those with a value for ‘key’ specified) cannot be pickled.

The behavior of a ‘ZoneInfo’ file depends on how it was constructed:

  1. ‘ZoneInfo(key)’: When constructed with the primary constructor, a
     ‘ZoneInfo’ object is serialized by key, and when deserialized, the
     deserializing process uses the primary and thus it is expected that
     these are expected to be the same object as other references to the
     same time zone.  For example, if ‘europe_berlin_pkl’ is a string
     containing a pickle constructed from ‘ZoneInfo("Europe/Berlin")’,
     one would expect the following behavior:

          >>> a = ZoneInfo("Europe/Berlin")
          >>> b = pickle.loads(europe_berlin_pkl)
          >>> a is b
          True

  2. ‘ZoneInfo.no_cache(key)’: When constructed from the cache-bypassing
     constructor, the ‘ZoneInfo’ object is also serialized by key, but
     when deserialized, the deserializing process uses the cache
     bypassing constructor.  If ‘europe_berlin_pkl_nc’ is a string
     containing a pickle constructed from
     ‘ZoneInfo.no_cache("Europe/Berlin")’, one would expect the
     following behavior:

          >>> a = ZoneInfo("Europe/Berlin")
          >>> b = pickle.loads(europe_berlin_pkl_nc)
          >>> a is b
          False

  3. ‘ZoneInfo.from_file(fobj, /, key=None)’: When constructed from a
     file, the ‘ZoneInfo’ object raises an exception on pickling.  If an
     end user wants to pickle a ‘ZoneInfo’ constructed from a file, it
     is recommended that they use a wrapper type or a custom
     serialization function: either serializing by key or storing the
     contents of the file object and serializing that.

This method of serialization requires that the time zone data for the
required key be available on both the serializing and deserializing
side, similar to the way that references to classes and functions are
expected to exist in both the serializing and deserializing
environments.  It also means that no guarantees are made about the
consistency of results when unpickling a ‘ZoneInfo’ pickled in an
environment with a different version of the time zone data.


File: python.info,  Node: Functions<2>,  Next: Globals,  Prev: The ZoneInfo class,  Up: zoneinfo — IANA time zone support

5.8.2.10 Functions
..................

 -- Function: zoneinfo.available_timezones ()

     Get a set containing all the valid keys for IANA time zones
     available anywhere on the time zone path.  This is recalculated on
     every call to the function.

     This function only includes canonical zone names and does not
     include “special” zones such as those under the ‘posix/’ and
     ‘right/’ directories, or the ‘posixrules’ zone.

          Caution: This function may open a large number of files, as
          the best way to determine if a file on the time zone path is a
          valid time zone is to read the “magic string” at the
          beginning.

          Note: These values are not designed to be exposed to
          end-users; for user facing elements, applications should use
          something like CLDR (the Unicode Common Locale Data
          Repository) to get more user-friendly strings.  See also the
          cautionary note on *note ZoneInfo.key: 1a49.

 -- Function: zoneinfo.reset_tzpath (to=None)

     Sets or resets the time zone search path (*note TZPATH: 1a3a.) for
     the module.  When called with no arguments, *note TZPATH: 1a3a. is
     set to the default value.

     Calling ‘reset_tzpath’ will not invalidate the *note ZoneInfo: 17f.
     cache, and so calls to the primary ‘ZoneInfo’ constructor will only
     use the new ‘TZPATH’ in the case of a cache miss.

     The ‘to’ parameter must be a *note sequence: 135c. of strings or
     *note os.PathLike: 5e6. and not a string, all of which must be
     absolute paths.  *note ValueError: 16d. will be raised if something
     other than an absolute path is passed.


File: python.info,  Node: Globals,  Next: Exceptions and warnings,  Prev: Functions<2>,  Up: zoneinfo — IANA time zone support

5.8.2.11 Globals
................

 -- Data: zoneinfo.TZPATH

     A read-only sequence representing the time zone search path – when
     constructing a ‘ZoneInfo’ from a key, the key is joined to each
     entry in the ‘TZPATH’, and the first file found is used.

     ‘TZPATH’ may contain only absolute paths, never relative paths,
     regardless of how it is configured.

     The object that ‘zoneinfo.TZPATH’ points to may change in response
     to a call to *note reset_tzpath(): 1a3e, so it is recommended to
     use ‘zoneinfo.TZPATH’ rather than importing ‘TZPATH’ from
     ‘zoneinfo’ or assigning a long-lived variable to ‘zoneinfo.TZPATH’.

     For more information on configuring the time zone search path, see
     *note Configuring the data sources: 1a39.


File: python.info,  Node: Exceptions and warnings,  Prev: Globals,  Up: zoneinfo — IANA time zone support

5.8.2.12 Exceptions and warnings
................................

 -- Exception: zoneinfo.ZoneInfoNotFoundError

     Raised when construction of a *note ZoneInfo: 17f. object fails
     because the specified key could not be found on the system.  This
     is a subclass of *note KeyError: 3e9.

 -- Exception: zoneinfo.InvalidTZPathWarning

     Raised when *note PYTHONTZPATH: 1a41. contains an invalid component
     that will be filtered out, such as a relative path.


File: python.info,  Node: calendar — General calendar-related functions,  Next: collections — Container datatypes,  Prev: zoneinfo — IANA time zone support,  Up: Data Types

5.8.3 ‘calendar’ — General calendar-related functions
-----------------------------------------------------

`Source code:' Lib/calendar.py(1)

__________________________________________________________________

This module allows you to output calendars like the Unix ‘cal’ program,
and provides additional useful functions related to the calendar.  By
default, these calendars have Monday as the first day of the week, and
Sunday as the last (the European convention).  Use *note
setfirstweekday(): 1a53. to set the first day of the week to Sunday (6)
or to any other weekday.  Parameters that specify dates are given as
integers.  For related functionality, see also the *note datetime: 30.
and *note time: 10c. modules.

The functions and classes defined in this module use an idealized
calendar, the current Gregorian calendar extended indefinitely in both
directions.  This matches the definition of the “proleptic Gregorian”
calendar in Dershowitz and Reingold’s book “Calendrical Calculations”,
where it’s the base calendar for all computations.  Zero and negative
years are interpreted as prescribed by the ISO 8601 standard.  Year 0 is
1 BC, year -1 is 2 BC, and so on.

 -- Class: calendar.Calendar (firstweekday=0)

     Creates a *note Calendar: 1a54. object.  `firstweekday' is an
     integer specifying the first day of the week.  ‘0’ is Monday (the
     default), ‘6’ is Sunday.

     A *note Calendar: 1a54. object provides several methods that can be
     used for preparing the calendar data for formatting.  This class
     doesn’t do any formatting itself.  This is the job of subclasses.

     *note Calendar: 1a54. instances have the following methods:

      -- Method: iterweekdays ()

          Return an iterator for the week day numbers that will be used
          for one week.  The first value from the iterator will be the
          same as the value of the *note firstweekday: 1a56. property.

      -- Method: itermonthdates (year, month)

          Return an iterator for the month `month' (1–12) in the year
          `year'.  This iterator will return all days (as *note
          datetime.date: 19e. objects) for the month and all days before
          the start of the month or after the end of the month that are
          required to get a complete week.

      -- Method: itermonthdays (year, month)

          Return an iterator for the month `month' in the year `year'
          similar to *note itermonthdates(): 5a1, but not restricted by
          the *note datetime.date: 19e. range.  Days returned will
          simply be day of the month numbers.  For the days outside of
          the specified month, the day number is ‘0’.

      -- Method: itermonthdays2 (year, month)

          Return an iterator for the month `month' in the year `year'
          similar to *note itermonthdates(): 5a1, but not restricted by
          the *note datetime.date: 19e. range.  Days returned will be
          tuples consisting of a day of the month number and a week day
          number.

      -- Method: itermonthdays3 (year, month)

          Return an iterator for the month `month' in the year `year'
          similar to *note itermonthdates(): 5a1, but not restricted by
          the *note datetime.date: 19e. range.  Days returned will be
          tuples consisting of a year, a month and a day of the month
          numbers.

          New in version 3.7.

      -- Method: itermonthdays4 (year, month)

          Return an iterator for the month `month' in the year `year'
          similar to *note itermonthdates(): 5a1, but not restricted by
          the *note datetime.date: 19e. range.  Days returned will be
          tuples consisting of a year, a month, a day of the month, and
          a day of the week numbers.

          New in version 3.7.

      -- Method: monthdatescalendar (year, month)

          Return a list of the weeks in the month `month' of the `year'
          as full weeks.  Weeks are lists of seven *note datetime.date:
          19e. objects.

      -- Method: monthdays2calendar (year, month)

          Return a list of the weeks in the month `month' of the `year'
          as full weeks.  Weeks are lists of seven tuples of day numbers
          and weekday numbers.

      -- Method: monthdayscalendar (year, month)

          Return a list of the weeks in the month `month' of the `year'
          as full weeks.  Weeks are lists of seven day numbers.

      -- Method: yeardatescalendar (year, width=3)

          Return the data for the specified year ready for formatting.
          The return value is a list of month rows.  Each month row
          contains up to `width' months (defaulting to 3).  Each month
          contains between 4 and 6 weeks and each week contains 1–7
          days.  Days are *note datetime.date: 19e. objects.

      -- Method: yeardays2calendar (year, width=3)

          Return the data for the specified year ready for formatting
          (similar to *note yeardatescalendar(): 1a5c.).  Entries in the
          week lists are tuples of day numbers and weekday numbers.  Day
          numbers outside this month are zero.

      -- Method: yeardayscalendar (year, width=3)

          Return the data for the specified year ready for formatting
          (similar to *note yeardatescalendar(): 1a5c.).  Entries in the
          week lists are day numbers.  Day numbers outside this month
          are zero.

 -- Class: calendar.TextCalendar (firstweekday=0)

     This class can be used to generate plain text calendars.

     *note TextCalendar: 1a5f. instances have the following methods:

      -- Method: formatmonth (theyear, themonth, w=0, l=0)

          Return a month’s calendar in a multi-line string.  If `w' is
          provided, it specifies the width of the date columns, which
          are centered.  If `l' is given, it specifies the number of
          lines that each week will use.  Depends on the first weekday
          as specified in the constructor or set by the *note
          setfirstweekday(): 1a53. method.

      -- Method: prmonth (theyear, themonth, w=0, l=0)

          Print a month’s calendar as returned by *note formatmonth():
          1a60.

      -- Method: formatyear (theyear, w=2, l=1, c=6, m=3)

          Return a `m'-column calendar for an entire year as a
          multi-line string.  Optional parameters `w', `l', and `c' are
          for date column width, lines per week, and number of spaces
          between month columns, respectively.  Depends on the first
          weekday as specified in the constructor or set by the *note
          setfirstweekday(): 1a53. method.  The earliest year for which
          a calendar can be generated is platform-dependent.

      -- Method: pryear (theyear, w=2, l=1, c=6, m=3)

          Print the calendar for an entire year as returned by *note
          formatyear(): 1a62.

 -- Class: calendar.HTMLCalendar (firstweekday=0)

     This class can be used to generate HTML calendars.

     ‘HTMLCalendar’ instances have the following methods:

      -- Method: formatmonth (theyear, themonth, withyear=True)

          Return a month’s calendar as an HTML table.  If `withyear' is
          true the year will be included in the header, otherwise just
          the month name will be used.

      -- Method: formatyear (theyear, width=3)

          Return a year’s calendar as an HTML table.  `width'
          (defaulting to 3) specifies the number of months per row.

      -- Method: formatyearpage (theyear, width=3, css='calendar.css',
               encoding=None)

          Return a year’s calendar as a complete HTML page.  `width'
          (defaulting to 3) specifies the number of months per row.
          `css' is the name for the cascading style sheet to be used.
          *note None: 203. can be passed if no style sheet should be
          used.  `encoding' specifies the encoding to be used for the
          output (defaulting to the system default encoding).

     ‘HTMLCalendar’ has the following attributes you can override to
     customize the CSS classes used by the calendar:

      -- Attribute: cssclasses

          A list of CSS classes used for each weekday.  The default
          class list is:

               cssclasses = ["mon", "tue", "wed", "thu", "fri", "sat", "sun"]

          more styles can be added for each day:

               cssclasses = ["mon text-bold", "tue", "wed", "thu", "fri", "sat", "sun red"]

          Note that the length of this list must be seven items.

      -- Attribute: cssclass_noday

          The CSS class for a weekday occurring in the previous or
          coming month.

          New in version 3.7.

      -- Attribute: cssclasses_weekday_head

          A list of CSS classes used for weekday names in the header
          row.  The default is the same as *note cssclasses: 1a67.

          New in version 3.7.

      -- Attribute: cssclass_month_head

          The month’s head CSS class (used by ‘formatmonthname()’).  The
          default value is ‘"month"’.

          New in version 3.7.

      -- Attribute: cssclass_month

          The CSS class for the whole month’s table (used by *note
          formatmonth(): 1a64.).  The default value is ‘"month"’.

          New in version 3.7.

      -- Attribute: cssclass_year

          The CSS class for the whole year’s table of tables (used by
          *note formatyear(): 1a65.).  The default value is ‘"year"’.

          New in version 3.7.

      -- Attribute: cssclass_year_head

          The CSS class for the table head for the whole year (used by
          *note formatyear(): 1a65.).  The default value is ‘"year"’.

          New in version 3.7.

     Note that although the naming for the above described class
     attributes is singular (e.g.  ‘cssclass_month’ ‘cssclass_noday’),
     one can replace the single CSS class with a space separated list of
     CSS classes, for example:

          "text-bold text-red"

     Here is an example how ‘HTMLCalendar’ can be customized:

          class CustomHTMLCal(calendar.HTMLCalendar):
              cssclasses = [style + " text-nowrap" for style in
                            calendar.HTMLCalendar.cssclasses]
              cssclass_month_head = "text-center month-head"
              cssclass_month = "text-center month"
              cssclass_year = "text-italic lead"

 -- Class: calendar.LocaleTextCalendar (firstweekday=0, locale=None)

     This subclass of *note TextCalendar: 1a5f. can be passed a locale
     name in the constructor and will return month and weekday names in
     the specified locale.  If this locale includes an encoding all
     strings containing month and weekday names will be returned as
     unicode.

 -- Class: calendar.LocaleHTMLCalendar (firstweekday=0, locale=None)

     This subclass of *note HTMLCalendar: 477. can be passed a locale
     name in the constructor and will return month and weekday names in
     the specified locale.  If this locale includes an encoding all
     strings containing month and weekday names will be returned as
     unicode.

     Note: The ‘formatweekday()’ and ‘formatmonthname()’ methods of
     these two classes temporarily change the current locale to the
     given `locale'.  Because the current locale is a process-wide
     setting, they are not thread-safe.

For simple text calendars this module provides the following functions.

 -- Function: calendar.setfirstweekday (weekday)

     Sets the weekday (‘0’ is Monday, ‘6’ is Sunday) to start each week.
     The values ‘MONDAY’, ‘TUESDAY’, ‘WEDNESDAY’, ‘THURSDAY’, ‘FRIDAY’,
     ‘SATURDAY’, and ‘SUNDAY’ are provided for convenience.  For
     example, to set the first weekday to Sunday:

          import calendar
          calendar.setfirstweekday(calendar.SUNDAY)

 -- Function: calendar.firstweekday ()

     Returns the current setting for the weekday to start each week.

 -- Function: calendar.isleap (year)

     Returns *note True: 594. if `year' is a leap year, otherwise *note
     False: 48f.

 -- Function: calendar.leapdays (y1, y2)

     Returns the number of leap years in the range from `y1' to `y2'
     (exclusive), where `y1' and `y2' are years.

     This function works for ranges spanning a century change.

 -- Function: calendar.weekday (year, month, day)

     Returns the day of the week (‘0’ is Monday) for `year' (‘1970’–…),
     `month' (‘1’–‘12’), `day' (‘1’–‘31’).

 -- Function: calendar.weekheader (n)

     Return a header containing abbreviated weekday names.  `n'
     specifies the width in characters for one weekday.

 -- Function: calendar.monthrange (year, month)

     Returns weekday of first day of the month and number of days in
     month, for the specified `year' and `month'.

 -- Function: calendar.monthcalendar (year, month)

     Returns a matrix representing a month’s calendar.  Each row
     represents a week; days outside of the month are represented by
     zeros.  Each week begins with Monday unless set by *note
     setfirstweekday(): 1a53.

 -- Function: calendar.prmonth (theyear, themonth, w=0, l=0)

     Prints a month’s calendar as returned by *note month(): 1a77.

 -- Function: calendar.month (theyear, themonth, w=0, l=0)

     Returns a month’s calendar in a multi-line string using the
     ‘formatmonth()’ of the *note TextCalendar: 1a5f. class.

 -- Function: calendar.prcal (year, w=0, l=0, c=6, m=3)

     Prints the calendar for an entire year as returned by *note
     calendar(): 14.

 -- Function: calendar.calendar (year, w=2, l=1, c=6, m=3)

     Returns a 3-column calendar for an entire year as a multi-line
     string using the ‘formatyear()’ of the *note TextCalendar: 1a5f.
     class.

 -- Function: calendar.timegm (tuple)

     An unrelated but handy function that takes a time tuple such as
     returned by the *note gmtime(): c11. function in the *note time:
     10c. module, and returns the corresponding Unix timestamp value,
     assuming an epoch of 1970, and the POSIX encoding.  In fact, *note
     time.gmtime(): c11. and *note timegm(): 1a7a. are each others’
     inverse.

The *note calendar: 14. module exports the following data attributes:

 -- Data: calendar.day_name

     An array that represents the days of the week in the current
     locale.

 -- Data: calendar.day_abbr

     An array that represents the abbreviated days of the week in the
     current locale.

 -- Data: calendar.month_name

     An array that represents the months of the year in the current
     locale.  This follows normal convention of January being month
     number 1, so it has a length of 13 and ‘month_name[0]’ is the empty
     string.

 -- Data: calendar.month_abbr

     An array that represents the abbreviated months of the year in the
     current locale.  This follows normal convention of January being
     month number 1, so it has a length of 13 and ‘month_abbr[0]’ is the
     empty string.

See also
........

Module *note datetime: 30.

     Object-oriented interface to dates and times with similar
     functionality to the *note time: 10c. module.

Module *note time: 10c.

     Low-level time related functions.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/calendar.py


File: python.info,  Node: collections — Container datatypes,  Next: collections abc — Abstract Base Classes for Containers,  Prev: calendar — General calendar-related functions,  Up: Data Types

5.8.4 ‘collections’ — Container datatypes
-----------------------------------------

`Source code:' Lib/collections/__init__.py(1)

__________________________________________________________________

This module implements specialized container datatypes providing
alternatives to Python’s general purpose built-in containers, *note
dict: 164, *note list: 1f8, *note set: 1f6, and *note tuple: 1a2.

*note namedtuple(): 1a1.  factory function for creating tuple subclasses with named fields
                          
                          
*note deque: 62b.         list-like container with fast appends and pops on either end
                          
                          
*note ChainMap: 5a4.      dict-like class for creating a single view of multiple mappings
                          
                          
*note Counter: ab9.       dict subclass for counting hashable objects
                          
                          
*note OrderedDict: 2ea.   dict subclass that remembers the order entries were added
                          
                          
*note defaultdict: c0c.   dict subclass that calls a factory function to supply missing values
                          
                          
*note UserDict: 1081.     wrapper around dictionary objects for easier dict subclassing
                          
                          
*note UserList: 1a81.     wrapper around list objects for easier list subclassing
                          
                          
*note UserString: 7a0.    wrapper around string objects for easier string subclassing
                          

Deprecated since version 3.3, will be removed in version 3.10: Moved
*note Collections Abstract Base Classes: 15e. to the *note
collections.abc: 1e. module.  For backwards compatibility, they continue
to be visible in this module through Python 3.9.

* Menu:

* ChainMap objects::
* Counter objects::
* deque objects::
* defaultdict objects::
* namedtuple() Factory Function for Tuples with Named Fields: namedtuple Factory Function for Tuples with Named Fields.
* OrderedDict objects::
* UserDict objects::
* UserList objects::
* UserString objects::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/collections/__init__.py


File: python.info,  Node: ChainMap objects,  Next: Counter objects,  Up: collections — Container datatypes

5.8.4.1 ‘ChainMap’ objects
..........................

New in version 3.3.

A *note ChainMap: 5a4. class is provided for quickly linking a number of
mappings so they can be treated as a single unit.  It is often much
faster than creating a new dictionary and running multiple *note
update(): e8e. calls.

The class can be used to simulate nested scopes and is useful in
templating.

 -- Class: collections.ChainMap (*maps)

     A *note ChainMap: 5a4. groups multiple dicts or other mappings
     together to create a single, updateable view.  If no `maps' are
     specified, a single empty dictionary is provided so that a new
     chain always has at least one mapping.

     The underlying mappings are stored in a list.  That list is public
     and can be accessed or updated using the `maps' attribute.  There
     is no other state.

     Lookups search the underlying mappings successively until a key is
     found.  In contrast, writes, updates, and deletions only operate on
     the first mapping.

     A *note ChainMap: 5a4. incorporates the underlying mappings by
     reference.  So, if one of the underlying mappings gets updated,
     those changes will be reflected in *note ChainMap: 5a4.

     All of the usual dictionary methods are supported.  In addition,
     there is a `maps' attribute, a method for creating new subcontexts,
     and a property for accessing all but the first mapping:

      -- Attribute: maps

          A user updateable list of mappings.  The list is ordered from
          first-searched to last-searched.  It is the only stored state
          and can be modified to change which mappings are searched.
          The list should always contain at least one mapping.

      -- Method: new_child (m=None)

          Returns a new *note ChainMap: 5a4. containing a new map
          followed by all of the maps in the current instance.  If ‘m’
          is specified, it becomes the new map at the front of the list
          of mappings; if not specified, an empty dict is used, so that
          a call to ‘d.new_child()’ is equivalent to: ‘ChainMap({},
          *d.maps)’.  This method is used for creating subcontexts that
          can be updated without altering values in any of the parent
          mappings.

          Changed in version 3.4: The optional ‘m’ parameter was added.

      -- Attribute: parents

          Property returning a new *note ChainMap: 5a4. containing all
          of the maps in the current instance except the first one.
          This is useful for skipping the first map in the search.  Use
          cases are similar to those for the *note nonlocal: d07.
          keyword used in *note nested scopes: 1721.  The use cases also
          parallel those for the built-in *note super(): 5dd. function.
          A reference to ‘d.parents’ is equivalent to:
          ‘ChainMap(*d.maps[1:])’.

     Note, the iteration order of a *note ChainMap(): 5a4. is determined
     by scanning the mappings last to first:

          >>> baseline = {'music': 'bach', 'art': 'rembrandt'}
          >>> adjustments = {'art': 'van gogh', 'opera': 'carmen'}
          >>> list(ChainMap(adjustments, baseline))
          ['music', 'art', 'opera']

     This gives the same ordering as a series of *note dict.update():
     e8e. calls starting with the last mapping:

          >>> combined = baseline.copy()
          >>> combined.update(adjustments)
          >>> list(combined)
          ['music', 'art', 'opera']

     Changed in version 3.9: Added support for ‘|’ and ‘|=’ operators,
     specified in PEP 584(1).

See also
........

   * The MultiContext class(2) in the Enthought CodeTools package(3) has
     options to support writing to any mapping in the chain.

   * Django’s Context class(4) for templating is a read-only chain of
     mappings.  It also features pushing and popping of contexts similar
     to the *note new_child(): 916. method and the *note parents: 1a84.
     property.

   * The Nested Contexts recipe(5) has options to control whether writes
     and other mutations apply only to the first mapping or to any
     mapping in the chain.

   * A greatly simplified read-only version of Chainmap(6).

* Menu:

* ChainMap Examples and Recipes::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0584

   (2) 
https://github.com/enthought/codetools/blob/4.0.0/codetools/contexts/multi_context.py

   (3) https://github.com/enthought/codetools

   (4) 
https://github.com/django/django/blob/main/django/template/context.py

   (5) https://code.activestate.com/recipes/577434/

   (6) https://code.activestate.com/recipes/305268/


File: python.info,  Node: ChainMap Examples and Recipes,  Up: ChainMap objects

5.8.4.2 ‘ChainMap’ Examples and Recipes
.......................................

This section shows various approaches to working with chained maps.

Example of simulating Python’s internal lookup chain:

     import builtins
     pylookup = ChainMap(locals(), globals(), vars(builtins))

Example of letting user specified command-line arguments take precedence
over environment variables which in turn take precedence over default
values:

     import os, argparse

     defaults = {'color': 'red', 'user': 'guest'}

     parser = argparse.ArgumentParser()
     parser.add_argument('-u', '--user')
     parser.add_argument('-c', '--color')
     namespace = parser.parse_args()
     command_line_args = {k: v for k, v in vars(namespace).items() if v is not None}

     combined = ChainMap(command_line_args, os.environ, defaults)
     print(combined['color'])
     print(combined['user'])

Example patterns for using the *note ChainMap: 5a4. class to simulate
nested contexts:

     c = ChainMap()        # Create root context
     d = c.new_child()     # Create nested child context
     e = c.new_child()     # Child of c, independent from d
     e.maps[0]             # Current context dictionary -- like Python's locals()
     e.maps[-1]            # Root context -- like Python's globals()
     e.parents             # Enclosing context chain -- like Python's nonlocals

     d['x'] = 1            # Set value in current context
     d['x']                # Get first key in the chain of contexts
     del d['x']            # Delete from current context
     list(d)               # All nested values
     k in d                # Check all nested values
     len(d)                # Number of nested values
     d.items()             # All nested items
     dict(d)               # Flatten into a regular dictionary

The *note ChainMap: 5a4. class only makes updates (writes and deletions)
to the first mapping in the chain while lookups will search the full
chain.  However, if deep writes and deletions are desired, it is easy to
make a subclass that updates keys found deeper in the chain:

     class DeepChainMap(ChainMap):
         'Variant of ChainMap that allows direct updates to inner scopes'

         def __setitem__(self, key, value):
             for mapping in self.maps:
                 if key in mapping:
                     mapping[key] = value
                     return
             self.maps[0][key] = value

         def __delitem__(self, key):
             for mapping in self.maps:
                 if key in mapping:
                     del mapping[key]
                     return
             raise KeyError(key)

     >>> d = DeepChainMap({'zebra': 'black'}, {'elephant': 'blue'}, {'lion': 'yellow'})
     >>> d['lion'] = 'orange'         # update an existing key two levels down
     >>> d['snake'] = 'red'           # new keys get added to the topmost dict
     >>> del d['elephant']            # remove an existing key one level down
     >>> d                            # display result
     DeepChainMap({'zebra': 'black', 'snake': 'red'}, {}, {'lion': 'orange'})


File: python.info,  Node: Counter objects,  Next: deque objects,  Prev: ChainMap objects,  Up: collections — Container datatypes

5.8.4.3 ‘Counter’ objects
.........................

A counter tool is provided to support convenient and rapid tallies.  For
example:

     >>> # Tally occurrences of words in a list
     >>> cnt = Counter()
     >>> for word in ['red', 'blue', 'red', 'green', 'blue', 'blue']:
     ...     cnt[word] += 1
     >>> cnt
     Counter({'blue': 3, 'red': 2, 'green': 1})

     >>> # Find the ten most common words in Hamlet
     >>> import re
     >>> words = re.findall(r'\w+', open('hamlet.txt').read().lower())
     >>> Counter(words).most_common(10)
     [('the', 1143), ('and', 966), ('to', 762), ('of', 669), ('i', 631),
      ('you', 554),  ('a', 546), ('my', 514), ('hamlet', 471), ('in', 451)]

 -- Class: collections.Counter ([iterable-or-mapping])

     A *note Counter: ab9. is a *note dict: 164. subclass for counting
     hashable objects.  It is a collection where elements are stored as
     dictionary keys and their counts are stored as dictionary values.
     Counts are allowed to be any integer value including zero or
     negative counts.  The *note Counter: ab9. class is similar to bags
     or multisets in other languages.

     Elements are counted from an `iterable' or initialized from another
     `mapping' (or counter):

          >>> c = Counter()                           # a new, empty counter
          >>> c = Counter('gallahad')                 # a new counter from an iterable
          >>> c = Counter({'red': 4, 'blue': 2})      # a new counter from a mapping
          >>> c = Counter(cats=4, dogs=8)             # a new counter from keyword args

     Counter objects have a dictionary interface except that they return
     a zero count for missing items instead of raising a *note KeyError:
     3e9.:

          >>> c = Counter(['eggs', 'ham'])
          >>> c['bacon']                              # count of a missing element is zero
          0

     Setting a count to zero does not remove an element from a counter.
     Use ‘del’ to remove it entirely:

          >>> c['sausage'] = 0                        # counter entry with a zero count
          >>> del c['sausage']                        # del actually removes the entry

     New in version 3.1.

     Changed in version 3.7: As a *note dict: 164. subclass, *note
     Counter: ab9. Inherited the capability to remember insertion order.
     Math operations on `Counter' objects also preserve order.  Results
     are ordered according to when an element is first encountered in
     the left operand and then by the order encountered in the right
     operand.

     Counter objects support three methods beyond those available for
     all dictionaries:

      -- Method: elements ()

          Return an iterator over elements repeating each as many times
          as its count.  Elements are returned in the order first
          encountered.  If an element’s count is less than one, *note
          elements(): d62. will ignore it.

               >>> c = Counter(a=4, b=2, c=0, d=-2)
               >>> sorted(c.elements())
               ['a', 'a', 'a', 'a', 'b', 'b']

      -- Method: most_common ([n])

          Return a list of the `n' most common elements and their counts
          from the most common to the least.  If `n' is omitted or
          ‘None’, *note most_common(): d61. returns `all' elements in
          the counter.  Elements with equal counts are ordered in the
          order first encountered:

               >>> Counter('abracadabra').most_common(3)
               [('a', 5), ('b', 2), ('r', 2)]

      -- Method: subtract ([iterable-or-mapping])

          Elements are subtracted from an `iterable' or from another
          `mapping' (or counter).  Like *note dict.update(): e8e. but
          subtracts counts instead of replacing them.  Both inputs and
          outputs may be zero or negative.

               >>> c = Counter(a=4, b=2, c=0, d=-2)
               >>> d = Counter(a=1, b=2, c=3, d=4)
               >>> c.subtract(d)
               >>> c
               Counter({'a': 3, 'b': 0, 'c': -3, 'd': -6})

          New in version 3.2.

     The usual dictionary methods are available for *note Counter: ab9.
     objects except for two which work differently for counters.

      -- Method: fromkeys (iterable)

          This class method is not implemented for *note Counter: ab9.
          objects.

      -- Method: update ([iterable-or-mapping])

          Elements are counted from an `iterable' or added-in from
          another `mapping' (or counter).  Like *note dict.update():
          e8e. but adds counts instead of replacing them.  Also, the
          `iterable' is expected to be a sequence of elements, not a
          sequence of ‘(key, value)’ pairs.

Common patterns for working with *note Counter: ab9. objects:

     sum(c.values())                 # total of all counts
     c.clear()                       # reset all counts
     list(c)                         # list unique elements
     set(c)                          # convert to a set
     dict(c)                         # convert to a regular dictionary
     c.items()                       # convert to a list of (elem, cnt) pairs
     Counter(dict(list_of_pairs))    # convert from a list of (elem, cnt) pairs
     c.most_common()[:-n-1:-1]       # n least common elements
     +c                              # remove zero and negative counts

Several mathematical operations are provided for combining *note
Counter: ab9. objects to produce multisets (counters that have counts
greater than zero).  Addition and subtraction combine counters by adding
or subtracting the counts of corresponding elements.  Intersection and
union return the minimum and maximum of corresponding counts.  Each
operation can accept inputs with signed counts, but the output will
exclude results with counts of zero or less.

     >>> c = Counter(a=3, b=1)
     >>> d = Counter(a=1, b=2)
     >>> c + d                       # add two counters together:  c[x] + d[x]
     Counter({'a': 4, 'b': 3})
     >>> c - d                       # subtract (keeping only positive counts)
     Counter({'a': 2})
     >>> c & d                       # intersection:  min(c[x], d[x])
     Counter({'a': 1, 'b': 1})
     >>> c | d                       # union:  max(c[x], d[x])
     Counter({'a': 3, 'b': 2})

Unary addition and subtraction are shortcuts for adding an empty counter
or subtracting from an empty counter.

     >>> c = Counter(a=2, b=-4)
     >>> +c
     Counter({'a': 2})
     >>> -c
     Counter({'b': 4})

New in version 3.3: Added support for unary plus, unary minus, and
in-place multiset operations.

     Note: Counters were primarily designed to work with positive
     integers to represent running counts; however, care was taken to
     not unnecessarily preclude use cases needing other types or
     negative values.  To help with those use cases, this section
     documents the minimum range and type restrictions.

        * The *note Counter: ab9. class itself is a dictionary subclass
          with no restrictions on its keys and values.  The values are
          intended to be numbers representing counts, but you `could'
          store anything in the value field.

        * The *note most_common(): d61. method requires only that the
          values be orderable.

        * For in-place operations such as ‘c[key] += 1’, the value type
          need only support addition and subtraction.  So fractions,
          floats, and decimals would work and negative values are
          supported.  The same is also true for *note update(): 1a88.
          and *note subtract(): c2c. which allow negative and zero
          values for both inputs and outputs.

        * The multiset methods are designed only for use cases with
          positive values.  The inputs may be negative or zero, but only
          outputs with positive values are created.  There are no type
          restrictions, but the value type needs to support addition,
          subtraction, and comparison.

        * The *note elements(): d62. method requires integer counts.  It
          ignores zero and negative counts.

See also
........

   * Bag class(1) in Smalltalk.

   * Wikipedia entry for Multisets(2).

   * C++ multisets(3) tutorial with examples.

   * For mathematical operations on multisets and their use cases, see
     `Knuth, Donald.  The Art of Computer Programming Volume II, Section
     4.6.3, Exercise 19'.

   * To enumerate all distinct multisets of a given size over a given
     set of elements, see *note
     itertools.combinations_with_replacement(): ce3.:

          map(Counter, combinations_with_replacement('ABC', 2)) # --> AA AB AC BB BC CC

   ---------- Footnotes ----------

   (1) 
https://www.gnu.org/software/smalltalk/manual-base/html_node/Bag.html

   (2) https://en.wikipedia.org/wiki/Multiset

   (3) 
http://www.java2s.com/Tutorial/Cpp/0380__set-multiset/Catalog0380__set-multiset.htm


File: python.info,  Node: deque objects,  Next: defaultdict objects,  Prev: Counter objects,  Up: collections — Container datatypes

5.8.4.4 ‘deque’ objects
.......................

 -- Class: collections.deque ([iterable[, maxlen]])

     Returns a new deque object initialized left-to-right (using *note
     append(): 1a8a.) with data from `iterable'.  If `iterable' is not
     specified, the new deque is empty.

     Deques are a generalization of stacks and queues (the name is
     pronounced “deck” and is short for “double-ended queue”).  Deques
     support thread-safe, memory efficient appends and pops from either
     side of the deque with approximately the same O(1) performance in
     either direction.

     Though *note list: 1f8. objects support similar operations, they
     are optimized for fast fixed-length operations and incur O(n)
     memory movement costs for ‘pop(0)’ and ‘insert(0, v)’ operations
     which change both the size and position of the underlying data
     representation.

     If `maxlen' is not specified or is ‘None’, deques may grow to an
     arbitrary length.  Otherwise, the deque is bounded to the specified
     maximum length.  Once a bounded length deque is full, when new
     items are added, a corresponding number of items are discarded from
     the opposite end.  Bounded length deques provide functionality
     similar to the ‘tail’ filter in Unix.  They are also useful for
     tracking transactions and other pools of data where only the most
     recent activity is of interest.

     Deque objects support the following methods:

      -- Method: append (x)

          Add `x' to the right side of the deque.

      -- Method: appendleft (x)

          Add `x' to the left side of the deque.

      -- Method: clear ()

          Remove all elements from the deque leaving it with length 0.

      -- Method: copy ()

          Create a shallow copy of the deque.

          New in version 3.5.

      -- Method: count (x)

          Count the number of deque elements equal to `x'.

          New in version 3.2.

      -- Method: extend (iterable)

          Extend the right side of the deque by appending elements from
          the iterable argument.

      -- Method: extendleft (iterable)

          Extend the left side of the deque by appending elements from
          `iterable'.  Note, the series of left appends results in
          reversing the order of elements in the iterable argument.

      -- Method: index (x[, start[, stop]])

          Return the position of `x' in the deque (at or after index
          `start' and before index `stop').  Returns the first match or
          raises *note ValueError: 16d. if not found.

          New in version 3.5.

      -- Method: insert (i, x)

          Insert `x' into the deque at position `i'.

          If the insertion would cause a bounded deque to grow beyond
          `maxlen', an *note IndexError: f36. is raised.

          New in version 3.5.

      -- Method: pop ()

          Remove and return an element from the right side of the deque.
          If no elements are present, raises an *note IndexError: f36.

      -- Method: popleft ()

          Remove and return an element from the left side of the deque.
          If no elements are present, raises an *note IndexError: f36.

      -- Method: remove (value)

          Remove the first occurrence of `value'.  If not found, raises
          a *note ValueError: 16d.

      -- Method: reverse ()

          Reverse the elements of the deque in-place and then return
          ‘None’.

          New in version 3.2.

      -- Method: rotate (n=1)

          Rotate the deque `n' steps to the right.  If `n' is negative,
          rotate to the left.

          When the deque is not empty, rotating one step to the right is
          equivalent to ‘d.appendleft(d.pop())’, and rotating one step
          to the left is equivalent to ‘d.append(d.popleft())’.

     Deque objects also provide one read-only attribute:

      -- Attribute: maxlen

          Maximum size of a deque or ‘None’ if unbounded.

          New in version 3.1.

In addition to the above, deques support iteration, pickling, ‘len(d)’,
‘reversed(d)’, ‘copy.copy(d)’, ‘copy.deepcopy(d)’, membership testing
with the *note in: 179. operator, and subscript references such as
‘d[0]’ to access the first element.  Indexed access is O(1) at both ends
but slows to O(n) in the middle.  For fast random access, use lists
instead.

Starting in version 3.5, deques support ‘__add__()’, ‘__mul__()’, and
‘__imul__()’.

Example:

     >>> from collections import deque
     >>> d = deque('ghi')                 # make a new deque with three items
     >>> for elem in d:                   # iterate over the deque's elements
     ...     print(elem.upper())
     G
     H
     I

     >>> d.append('j')                    # add a new entry to the right side
     >>> d.appendleft('f')                # add a new entry to the left side
     >>> d                                # show the representation of the deque
     deque(['f', 'g', 'h', 'i', 'j'])

     >>> d.pop()                          # return and remove the rightmost item
     'j'
     >>> d.popleft()                      # return and remove the leftmost item
     'f'
     >>> list(d)                          # list the contents of the deque
     ['g', 'h', 'i']
     >>> d[0]                             # peek at leftmost item
     'g'
     >>> d[-1]                            # peek at rightmost item
     'i'

     >>> list(reversed(d))                # list the contents of a deque in reverse
     ['i', 'h', 'g']
     >>> 'h' in d                         # search the deque
     True
     >>> d.extend('jkl')                  # add multiple elements at once
     >>> d
     deque(['g', 'h', 'i', 'j', 'k', 'l'])
     >>> d.rotate(1)                      # right rotation
     >>> d
     deque(['l', 'g', 'h', 'i', 'j', 'k'])
     >>> d.rotate(-1)                     # left rotation
     >>> d
     deque(['g', 'h', 'i', 'j', 'k', 'l'])

     >>> deque(reversed(d))               # make a new deque in reverse order
     deque(['l', 'k', 'j', 'i', 'h', 'g'])
     >>> d.clear()                        # empty the deque
     >>> d.pop()                          # cannot pop from an empty deque
     Traceback (most recent call last):
         File "<pyshell#6>", line 1, in -toplevel-
             d.pop()
     IndexError: pop from an empty deque

     >>> d.extendleft('abc')              # extendleft() reverses the input order
     >>> d
     deque(['c', 'b', 'a'])

* Menu:

* deque Recipes::


File: python.info,  Node: deque Recipes,  Up: deque objects

5.8.4.5 ‘deque’ Recipes
.......................

This section shows various approaches to working with deques.

Bounded length deques provide functionality similar to the ‘tail’ filter
in Unix:

     def tail(filename, n=10):
         'Return the last n lines of a file'
         with open(filename) as f:
             return deque(f, n)

Another approach to using deques is to maintain a sequence of recently
added elements by appending to the right and popping to the left:

     def moving_average(iterable, n=3):
         # moving_average([40, 30, 50, 46, 39, 44]) --> 40.0 42.0 45.0 43.0
         # http://en.wikipedia.org/wiki/Moving_average
         it = iter(iterable)
         d = deque(itertools.islice(it, n-1))
         d.appendleft(0)
         s = sum(d)
         for elem in it:
             s += elem - d.popleft()
             d.append(elem)
             yield s / n

A round-robin scheduler(1) can be implemented with input iterators
stored in a *note deque: 62b.  Values are yielded from the active
iterator in position zero.  If that iterator is exhausted, it can be
removed with *note popleft(): 1a90.; otherwise, it can be cycled back to
the end with the *note rotate(): 1a92. method:

     def roundrobin(*iterables):
         "roundrobin('ABC', 'D', 'EF') --> A D E B F C"
         iterators = deque(map(iter, iterables))
         while iterators:
             try:
                 while True:
                     yield next(iterators[0])
                     iterators.rotate(-1)
             except StopIteration:
                 # Remove an exhausted iterator.
                 iterators.popleft()

The *note rotate(): 1a92. method provides a way to implement *note
deque: 62b. slicing and deletion.  For example, a pure Python
implementation of ‘del d[n]’ relies on the ‘rotate()’ method to position
elements to be popped:

     def delete_nth(d, n):
         d.rotate(-n)
         d.popleft()
         d.rotate(n)

To implement *note deque: 62b. slicing, use a similar approach applying
*note rotate(): 1a92. to bring a target element to the left side of the
deque.  Remove old entries with *note popleft(): 1a90, add new entries
with *note extend(): 1a8d, and then reverse the rotation.  With minor
variations on that approach, it is easy to implement Forth style stack
manipulations such as ‘dup’, ‘drop’, ‘swap’, ‘over’, ‘pick’, ‘rot’, and
‘roll’.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Round-robin_scheduling


File: python.info,  Node: defaultdict objects,  Next: namedtuple Factory Function for Tuples with Named Fields,  Prev: deque objects,  Up: collections — Container datatypes

5.8.4.6 ‘defaultdict’ objects
.............................

 -- Class: collections.defaultdict (default_factory=None, /[, ...])

     Return a new dictionary-like object.  *note defaultdict: c0c. is a
     subclass of the built-in *note dict: 164. class.  It overrides one
     method and adds one writable instance variable.  The remaining
     functionality is the same as for the *note dict: 164. class and is
     not documented here.

     The first argument provides the initial value for the *note
     default_factory: 1a95. attribute; it defaults to ‘None’.  All
     remaining arguments are treated the same as if they were passed to
     the *note dict: 164. constructor, including keyword arguments.

     *note defaultdict: c0c. objects support the following method in
     addition to the standard *note dict: 164. operations:

      -- Method: __missing__ (key)

          If the *note default_factory: 1a95. attribute is ‘None’, this
          raises a *note KeyError: 3e9. exception with the `key' as
          argument.

          If *note default_factory: 1a95. is not ‘None’, it is called
          without arguments to provide a default value for the given
          `key', this value is inserted in the dictionary for the `key',
          and returned.

          If calling *note default_factory: 1a95. raises an exception
          this exception is propagated unchanged.

          This method is called by the *note __getitem__(): 3a2. method
          of the *note dict: 164. class when the requested key is not
          found; whatever it returns or raises is then returned or
          raised by *note __getitem__(): 3a2.

          Note that *note __missing__(): 1a96. is `not' called for any
          operations besides *note __getitem__(): 3a2.  This means that
          ‘get()’ will, like normal dictionaries, return ‘None’ as a
          default rather than using *note default_factory: 1a95.

     *note defaultdict: c0c. objects support the following instance
     variable:

      -- Attribute: default_factory

          This attribute is used by the *note __missing__(): 1a96.
          method; it is initialized from the first argument to the
          constructor, if present, or to ‘None’, if absent.

     Changed in version 3.9: Added merge (‘|’) and update (‘|=’)
     operators, specified in PEP 584(1).

* Menu:

* defaultdict Examples::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0584


File: python.info,  Node: defaultdict Examples,  Up: defaultdict objects

5.8.4.7 ‘defaultdict’ Examples
..............................

Using *note list: 1f8. as the *note default_factory: 1a95, it is easy to
group a sequence of key-value pairs into a dictionary of lists:

     >>> s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]
     >>> d = defaultdict(list)
     >>> for k, v in s:
     ...     d[k].append(v)
     ...
     >>> sorted(d.items())
     [('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])]

When each key is encountered for the first time, it is not already in
the mapping; so an entry is automatically created using the *note
default_factory: 1a95. function which returns an empty *note list: 1f8.
The ‘list.append()’ operation then attaches the value to the new list.
When keys are encountered again, the look-up proceeds normally
(returning the list for that key) and the ‘list.append()’ operation adds
another value to the list.  This technique is simpler and faster than an
equivalent technique using *note dict.setdefault(): a9e.:

     >>> d = {}
     >>> for k, v in s:
     ...     d.setdefault(k, []).append(v)
     ...
     >>> sorted(d.items())
     [('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])]

Setting the *note default_factory: 1a95. to *note int: 204. makes the
*note defaultdict: c0c. useful for counting (like a bag or multiset in
other languages):

     >>> s = 'mississippi'
     >>> d = defaultdict(int)
     >>> for k in s:
     ...     d[k] += 1
     ...
     >>> sorted(d.items())
     [('i', 4), ('m', 1), ('p', 2), ('s', 4)]

When a letter is first encountered, it is missing from the mapping, so
the *note default_factory: 1a95. function calls *note int(): 204. to
supply a default count of zero.  The increment operation then builds up
the count for each letter.

The function *note int(): 204. which always returns zero is just a
special case of constant functions.  A faster and more flexible way to
create constant functions is to use a lambda function which can supply
any constant value (not just zero):

     >>> def constant_factory(value):
     ...     return lambda: value
     >>> d = defaultdict(constant_factory('<missing>'))
     >>> d.update(name='John', action='ran')
     >>> '%(name)s %(action)s to %(object)s' % d
     'John ran to <missing>'

Setting the *note default_factory: 1a95. to *note set: 1f6. makes the
*note defaultdict: c0c. useful for building a dictionary of sets:

     >>> s = [('red', 1), ('blue', 2), ('red', 3), ('blue', 4), ('red', 1), ('blue', 4)]
     >>> d = defaultdict(set)
     >>> for k, v in s:
     ...     d[k].add(v)
     ...
     >>> sorted(d.items())
     [('blue', {2, 4}), ('red', {1, 3})]


File: python.info,  Node: namedtuple Factory Function for Tuples with Named Fields,  Next: OrderedDict objects,  Prev: defaultdict objects,  Up: collections — Container datatypes

5.8.4.8 ‘namedtuple()’ Factory Function for Tuples with Named Fields
....................................................................

Named tuples assign meaning to each position in a tuple and allow for
more readable, self-documenting code.  They can be used wherever regular
tuples are used, and they add the ability to access fields by name
instead of position index.

 -- Function: collections.namedtuple (typename, field_names, *,
          rename=False, defaults=None, module=None)

     Returns a new tuple subclass named `typename'.  The new subclass is
     used to create tuple-like objects that have fields accessible by
     attribute lookup as well as being indexable and iterable.
     Instances of the subclass also have a helpful docstring (with
     typename and field_names) and a helpful *note __repr__(): 44a.
     method which lists the tuple contents in a ‘name=value’ format.

     The `field_names' are a sequence of strings such as ‘['x', 'y']’.
     Alternatively, `field_names' can be a single string with each
     fieldname separated by whitespace and/or commas, for example ‘'x
     y'’ or ‘'x, y'’.

     Any valid Python identifier may be used for a fieldname except for
     names starting with an underscore.  Valid identifiers consist of
     letters, digits, and underscores but do not start with a digit or
     underscore and cannot be a *note keyword: a6. such as `class',
     `for', `return', `global', `pass', or `raise'.

     If `rename' is true, invalid fieldnames are automatically replaced
     with positional names.  For example, ‘['abc', 'def', 'ghi', 'abc']’
     is converted to ‘['abc', '_1', 'ghi', '_3']’, eliminating the
     keyword ‘def’ and the duplicate fieldname ‘abc’.

     `defaults' can be ‘None’ or an *note iterable: c7c. of default
     values.  Since fields with a default value must come after any
     fields without a default, the `defaults' are applied to the
     rightmost parameters.  For example, if the fieldnames are ‘['x',
     'y', 'z']’ and the defaults are ‘(1, 2)’, then ‘x’ will be a
     required argument, ‘y’ will default to ‘1’, and ‘z’ will default to
     ‘2’.

     If `module' is defined, the ‘__module__’ attribute of the named
     tuple is set to that value.

     Named tuple instances do not have per-instance dictionaries, so
     they are lightweight and require no more memory than regular
     tuples.

     To support pickling, the named tuple class should be assigned to a
     variable that matches `typename'.

     Changed in version 3.1: Added support for `rename'.

     Changed in version 3.6: The `verbose' and `rename' parameters
     became *note keyword-only arguments: 3ce.

     Changed in version 3.6: Added the `module' parameter.

     Changed in version 3.7: Removed the `verbose' parameter and the
     ‘_source’ attribute.

     Changed in version 3.7: Added the `defaults' parameter and the
     ‘_field_defaults’ attribute.

     >>> # Basic example
     >>> Point = namedtuple('Point', ['x', 'y'])
     >>> p = Point(11, y=22)     # instantiate with positional or keyword arguments
     >>> p[0] + p[1]             # indexable like the plain tuple (11, 22)
     33
     >>> x, y = p                # unpack like a regular tuple
     >>> x, y
     (11, 22)
     >>> p.x + p.y               # fields also accessible by name
     33
     >>> p                       # readable __repr__ with a name=value style
     Point(x=11, y=22)

Named tuples are especially useful for assigning field names to result
tuples returned by the *note csv: 29. or *note sqlite3: f2. modules:

     EmployeeRecord = namedtuple('EmployeeRecord', 'name, age, title, department, paygrade')

     import csv
     for emp in map(EmployeeRecord._make, csv.reader(open("employees.csv", "rb"))):
         print(emp.name, emp.title)

     import sqlite3
     conn = sqlite3.connect('/companydata')
     cursor = conn.cursor()
     cursor.execute('SELECT name, age, title, department, paygrade FROM employees')
     for emp in map(EmployeeRecord._make, cursor.fetchall()):
         print(emp.name, emp.title)

In addition to the methods inherited from tuples, named tuples support
three additional methods and two attributes.  To prevent conflicts with
field names, the method and attribute names start with an underscore.

 -- Method: classmethod somenamedtuple._make (iterable)

     Class method that makes a new instance from an existing sequence or
     iterable.

          >>> t = [11, 22]
          >>> Point._make(t)
          Point(x=11, y=22)

 -- Method: somenamedtuple._asdict ()

     Return a new *note dict: 164. which maps field names to their
     corresponding values:

          >>> p = Point(x=11, y=22)
          >>> p._asdict()
          {'x': 11, 'y': 22}

     Changed in version 3.1: Returns an *note OrderedDict: 2ea. instead
     of a regular *note dict: 164.

     Changed in version 3.8: Returns a regular *note dict: 164. instead
     of an *note OrderedDict: 2ea.  As of Python 3.7, regular dicts are
     guaranteed to be ordered.  If the extra features of *note
     OrderedDict: 2ea. are required, the suggested remediation is to
     cast the result to the desired type: ‘OrderedDict(nt._asdict())’.

 -- Method: somenamedtuple._replace (**kwargs)

     Return a new instance of the named tuple replacing specified fields
     with new values:

          >>> p = Point(x=11, y=22)
          >>> p._replace(x=33)
          Point(x=33, y=22)

          >>> for partnum, record in inventory.items():
          ...     inventory[partnum] = record._replace(price=newprices[partnum], timestamp=time.now())

 -- Attribute: somenamedtuple._fields

     Tuple of strings listing the field names.  Useful for introspection
     and for creating new named tuple types from existing named tuples.

          >>> p._fields            # view the field names
          ('x', 'y')

          >>> Color = namedtuple('Color', 'red green blue')
          >>> Pixel = namedtuple('Pixel', Point._fields + Color._fields)
          >>> Pixel(11, 22, 128, 255, 0)
          Pixel(x=11, y=22, red=128, green=255, blue=0)

 -- Attribute: somenamedtuple._field_defaults

     Dictionary mapping field names to default values.

          >>> Account = namedtuple('Account', ['type', 'balance'], defaults=[0])
          >>> Account._field_defaults
          {'balance': 0}
          >>> Account('premium')
          Account(type='premium', balance=0)

To retrieve a field whose name is stored in a string, use the *note
getattr(): 54b. function:

     >>> getattr(p, 'x')
     11

To convert a dictionary to a named tuple, use the double-star-operator
(as described in *note Unpacking Argument Lists: 1389.):

     >>> d = {'x': 11, 'y': 22}
     >>> Point(**d)
     Point(x=11, y=22)

Since a named tuple is a regular Python class, it is easy to add or
change functionality with a subclass.  Here is how to add a calculated
field and a fixed-width print format:

     >>> class Point(namedtuple('Point', ['x', 'y'])):
     ...     __slots__ = ()
     ...     @property
     ...     def hypot(self):
     ...         return (self.x ** 2 + self.y ** 2) ** 0.5
     ...     def __str__(self):
     ...         return 'Point: x=%6.3f  y=%6.3f  hypot=%6.3f' % (self.x, self.y, self.hypot)

     >>> for p in Point(3, 4), Point(14, 5/7):
     ...     print(p)
     Point: x= 3.000  y= 4.000  hypot= 5.000
     Point: x=14.000  y= 0.714  hypot=14.018

The subclass shown above sets ‘__slots__’ to an empty tuple.  This helps
keep memory requirements low by preventing the creation of instance
dictionaries.

Subclassing is not useful for adding new, stored fields.  Instead,
simply create a new named tuple type from the *note _fields: 1a9b.
attribute:

     >>> Point3D = namedtuple('Point3D', Point._fields + ('z',))

Docstrings can be customized by making direct assignments to the
‘__doc__’ fields:

     >>> Book = namedtuple('Book', ['id', 'title', 'authors'])
     >>> Book.__doc__ += ': Hardcover book in active collection'
     >>> Book.id.__doc__ = '13-digit ISBN'
     >>> Book.title.__doc__ = 'Title of first printing'
     >>> Book.authors.__doc__ = 'List of authors sorted by last name'

Changed in version 3.5: Property docstrings became writeable.

See also
........

   * See *note typing.NamedTuple: 227. for a way to add type hints for
     named tuples.  It also provides an elegant notation using the *note
     class: d32. keyword:

          class Component(NamedTuple):
              part_number: int
              weight: float
              description: Optional[str] = None

   * See *note types.SimpleNamespace(): 1d8. for a mutable namespace
     based on an underlying dictionary instead of a tuple.

   * The *note dataclasses: 2f. module provides a decorator and
     functions for automatically adding generated special methods to
     user-defined classes.


File: python.info,  Node: OrderedDict objects,  Next: UserDict objects,  Prev: namedtuple Factory Function for Tuples with Named Fields,  Up: collections — Container datatypes

5.8.4.9 ‘OrderedDict’ objects
.............................

Ordered dictionaries are just like regular dictionaries but have some
extra capabilities relating to ordering operations.  They have become
less important now that the built-in *note dict: 164. class gained the
ability to remember insertion order (this new behavior became guaranteed
in Python 3.7).

Some differences from *note dict: 164. still remain:

   * The regular *note dict: 164. was designed to be very good at
     mapping operations.  Tracking insertion order was secondary.

   * The *note OrderedDict: 2ea. was designed to be good at reordering
     operations.  Space efficiency, iteration speed, and the performance
     of update operations were secondary.

   * Algorithmically, *note OrderedDict: 2ea. can handle frequent
     reordering operations better than *note dict: 164.  This makes it
     suitable for tracking recent accesses (for example in an LRU
     cache(1)).

   * The equality operation for *note OrderedDict: 2ea. checks for
     matching order.

   * The ‘popitem()’ method of *note OrderedDict: 2ea. has a different
     signature.  It accepts an optional argument to specify which item
     is popped.

   * *note OrderedDict: 2ea. has a ‘move_to_end()’ method to efficiently
     reposition an element to an endpoint.

   * Until Python 3.8, *note dict: 164. lacked a *note __reversed__():
     629. method.

 -- Class: collections.OrderedDict ([items])

     Return an instance of a *note dict: 164. subclass that has methods
     specialized for rearranging dictionary order.

     New in version 3.1.

      -- Method: popitem (last=True)

          The *note popitem(): d4c. method for ordered dictionaries
          returns and removes a (key, value) pair.  The pairs are
          returned in LIFO order if `last' is true or FIFO (first-in,
          first-out) order if false.

      -- Method: move_to_end (key, last=True)

          Move an existing `key' to either end of an ordered dictionary.
          The item is moved to the right end if `last' is true (the
          default) or to the beginning if `last' is false.  Raises *note
          KeyError: 3e9. if the `key' does not exist:

               >>> d = OrderedDict.fromkeys('abcde')
               >>> d.move_to_end('b')
               >>> ''.join(d.keys())
               'acdeb'
               >>> d.move_to_end('b', last=False)
               >>> ''.join(d.keys())
               'bacde'

          New in version 3.2.

In addition to the usual mapping methods, ordered dictionaries also
support reverse iteration using *note reversed(): 2c6.

Equality tests between *note OrderedDict: 2ea. objects are
order-sensitive and are implemented as
‘list(od1.items())==list(od2.items())’.  Equality tests between *note
OrderedDict: 2ea. objects and other *note Mapping: 15f. objects are
order-insensitive like regular dictionaries.  This allows *note
OrderedDict: 2ea. objects to be substituted anywhere a regular
dictionary is used.

Changed in version 3.5: The items, keys, and values *note views: 1a9e.
of *note OrderedDict: 2ea. now support reverse iteration using *note
reversed(): 2c6.

Changed in version 3.6: With the acceptance of PEP 468(2), order is
retained for keyword arguments passed to the *note OrderedDict: 2ea.
constructor and its ‘update()’ method.

Changed in version 3.9: Added merge (‘|’) and update (‘|=’) operators,
specified in PEP 584(3).

* Menu:

* OrderedDict Examples and Recipes::

   ---------- Footnotes ----------

   (1) 
https://medium.com/@krishankantsinghal/my-first-blog-on-medium-583159139237

   (2) https://www.python.org/dev/peps/pep-0468

   (3) https://www.python.org/dev/peps/pep-0584


File: python.info,  Node: OrderedDict Examples and Recipes,  Up: OrderedDict objects

5.8.4.10 ‘OrderedDict’ Examples and Recipes
...........................................

It is straightforward to create an ordered dictionary variant that
remembers the order the keys were `last' inserted.  If a new entry
overwrites an existing entry, the original insertion position is changed
and moved to the end:

     class LastUpdatedOrderedDict(OrderedDict):
         'Store items in the order the keys were last added'

         def __setitem__(self, key, value):
             super().__setitem__(key, value)
             self.move_to_end(key)

An *note OrderedDict: 2ea. would also be useful for implementing
variants of *note functools.lru_cache(): 2f8.:

     class LRU:

         def __init__(self, func, maxsize=128):
             self.func = func
             self.maxsize = maxsize
             self.cache = OrderedDict()

         def __call__(self, *args):
             if args in self.cache:
                 value = self.cache[args]
                 self.cache.move_to_end(args)
                 return value
             value = self.func(*args)
             if len(self.cache) >= self.maxsize:
                 self.cache.popitem(False)
             self.cache[args] = value
             return value


File: python.info,  Node: UserDict objects,  Next: UserList objects,  Prev: OrderedDict objects,  Up: collections — Container datatypes

5.8.4.11 ‘UserDict’ objects
...........................

The class, *note UserDict: 1081. acts as a wrapper around dictionary
objects.  The need for this class has been partially supplanted by the
ability to subclass directly from *note dict: 164.; however, this class
can be easier to work with because the underlying dictionary is
accessible as an attribute.

 -- Class: collections.UserDict ([initialdata])

     Class that simulates a dictionary.  The instance’s contents are
     kept in a regular dictionary, which is accessible via the *note
     data: 1aa1. attribute of *note UserDict: 1081. instances.  If
     `initialdata' is provided, *note data: 1aa1. is initialized with
     its contents; note that a reference to `initialdata' will not be
     kept, allowing it to be used for other purposes.

     In addition to supporting the methods and operations of mappings,
     *note UserDict: 1081. instances provide the following attribute:

      -- Attribute: data

          A real dictionary used to store the contents of the *note
          UserDict: 1081. class.


File: python.info,  Node: UserList objects,  Next: UserString objects,  Prev: UserDict objects,  Up: collections — Container datatypes

5.8.4.12 ‘UserList’ objects
...........................

This class acts as a wrapper around list objects.  It is a useful base
class for your own list-like classes which can inherit from them and
override existing methods or add new ones.  In this way, one can add new
behaviors to lists.

The need for this class has been partially supplanted by the ability to
subclass directly from *note list: 1f8.; however, this class can be
easier to work with because the underlying list is accessible as an
attribute.

 -- Class: collections.UserList ([list])

     Class that simulates a list.  The instance’s contents are kept in a
     regular list, which is accessible via the *note data: 1aa3.
     attribute of *note UserList: 1a81. instances.  The instance’s
     contents are initially set to a copy of `list', defaulting to the
     empty list ‘[]’.  `list' can be any iterable, for example a real
     Python list or a *note UserList: 1a81. object.

     In addition to supporting the methods and operations of mutable
     sequences, *note UserList: 1a81. instances provide the following
     attribute:

      -- Attribute: data

          A real *note list: 1f8. object used to store the contents of
          the *note UserList: 1a81. class.

`Subclassing requirements:' Subclasses of *note UserList: 1a81. are
expected to offer a constructor which can be called with either no
arguments or one argument.  List operations which return a new sequence
attempt to create an instance of the actual implementation class.  To do
so, it assumes that the constructor can be called with a single
parameter, which is a sequence object used as a data source.

If a derived class does not wish to comply with this requirement, all of
the special methods supported by this class will need to be overridden;
please consult the sources for information about the methods which need
to be provided in that case.


File: python.info,  Node: UserString objects,  Prev: UserList objects,  Up: collections — Container datatypes

5.8.4.13 ‘UserString’ objects
.............................

The class, *note UserString: 7a0. acts as a wrapper around string
objects.  The need for this class has been partially supplanted by the
ability to subclass directly from *note str: 205.; however, this class
can be easier to work with because the underlying string is accessible
as an attribute.

 -- Class: collections.UserString (seq)

     Class that simulates a string object.  The instance’s content is
     kept in a regular string object, which is accessible via the *note
     data: 1aa5. attribute of *note UserString: 7a0. instances.  The
     instance’s contents are initially set to a copy of `seq'.  The
     `seq' argument can be any object which can be converted into a
     string using the built-in *note str(): 205. function.

     In addition to supporting the methods and operations of strings,
     *note UserString: 7a0. instances provide the following attribute:

      -- Attribute: data

          A real *note str: 205. object used to store the contents of
          the *note UserString: 7a0. class.

     Changed in version 3.5: New methods ‘__getnewargs__’, ‘__rmod__’,
     ‘casefold’, ‘format_map’, ‘isprintable’, and ‘maketrans’.


File: python.info,  Node: collections abc — Abstract Base Classes for Containers,  Next: heapq — Heap queue algorithm,  Prev: collections — Container datatypes,  Up: Data Types

5.8.5 ‘collections.abc’ — Abstract Base Classes for Containers
--------------------------------------------------------------

New in version 3.3: Formerly, this module was part of the *note
collections: 1d. module.

`Source code:' Lib/_collections_abc.py(1)

__________________________________________________________________

This module provides *note abstract base classes: c05. that can be used
to test whether a class provides a particular interface; for example,
whether it is hashable or whether it is a mapping.

New in version 3.9: These abstract classes now support ‘[]’.  See *note
Generic Alias Type: fe5. and PEP 585(2).

* Menu:

* Collections Abstract Base Classes::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/_collections_abc.py

   (2) https://www.python.org/dev/peps/pep-0585


File: python.info,  Node: Collections Abstract Base Classes,  Up: collections abc — Abstract Base Classes for Containers

5.8.5.1 Collections Abstract Base Classes
.........................................

The collections module offers the following *note ABCs: c05.:

ABC                            Inherits from              Abstract Methods            Mixin Methods
                                                                                      
-----------------------------------------------------------------------------------------------------------------------------------------------
                                                                                      
*note Container: 181a.                                    ‘__contains__’
                                                          
                                                                                      
*note Hashable: 1aa9.                                     ‘__hash__’
                                                          
                                                                                      
*note Iterable: 1818.                                     ‘__iter__’
                                                          
                                                                                      
*note Iterator: 1819.          *note Iterable: 1818.      ‘__next__’                  ‘__iter__’
                                                                                      
                                                                                      
*note Reversible: 628.         *note Iterable: 1818.      ‘__reversed__’
                                                          
                                                                                      
*note Generator: 7a8.          *note Iterator: 1819.      ‘send’, ‘throw’             ‘close’, ‘__iter__’, ‘__next__’
                                                                                      
                                                                                      
*note Sized: 1aaa.                                        ‘__len__’
                                                          
                                                                                      
*note Callable: 27a.                                      ‘__call__’
                                                          
                                                                                      
*note Collection: 627.         *note Sized: 1aaa,         ‘__contains__’,
                               *note Iterable: 1818,      ‘__iter__’, ‘__len__’
                               *note Container: 181a.     
                               
                                                                                      
*note Sequence: 1764.          *note Reversible: 628,     ‘__getitem__’, ‘__len__’    ‘__contains__’, ‘__iter__’, ‘__reversed__’, ‘index’,
                               *note Collection: 627.                                 and ‘count’
                                                                                      
                                                                                      
*note MutableSequence: 79f.    *note Sequence: 1764.      ‘__getitem__’,              Inherited *note Sequence: 1764. methods and ‘append’,
                                                          ‘__setitem__’,              ‘reverse’, ‘extend’, ‘pop’, ‘remove’, and ‘__iadd__’
                                                          ‘__delitem__’, ‘__len__’,   
                                                          ‘insert’
                                                          
                                                                                      
*note ByteString: 181c.        *note Sequence: 1764.      ‘__getitem__’, ‘__len__’    Inherited *note Sequence: 1764. methods
                                                                                      
                                                                                      
*note Set: 1810.               *note Collection: 627.     ‘__contains__’,             ‘__le__’, ‘__lt__’, ‘__eq__’, ‘__ne__’, ‘__gt__’,
                                                          ‘__iter__’, ‘__len__’       ‘__ge__’, ‘__and__’, ‘__or__’, ‘__sub__’, ‘__xor__’,
                                                                                      and ‘isdisjoint’
                                                                                      
                                                                                      
*note MutableSet: 181b.        *note Set: 1810.           ‘__contains__’,             Inherited *note Set: 1810. methods and ‘clear’, ‘pop’,
                                                          ‘__iter__’, ‘__len__’,      ‘remove’, ‘__ior__’, ‘__iand__’, ‘__ixor__’, and
                                                          ‘add’, ‘discard’            ‘__isub__’
                                                                                      
                                                                                      
*note Mapping: 15f.            *note Collection: 627.     ‘__getitem__’,              ‘__contains__’, ‘keys’, ‘items’, ‘values’, ‘get’,
                                                          ‘__iter__’, ‘__len__’       ‘__eq__’, and ‘__ne__’
                                                                                      
                                                                                      
*note MutableMapping: ace.     *note Mapping: 15f.        ‘__getitem__’,              Inherited *note Mapping: 15f. methods and ‘pop’,
                                                          ‘__setitem__’,              ‘popitem’, ‘clear’, ‘update’, and ‘setdefault’
                                                          ‘__delitem__’,              
                                                          ‘__iter__’, ‘__len__’
                                                          
                                                                                      
*note MappingView: 181d.       *note Sized: 1aaa.                                     ‘__len__’
                                                                                      
                                                                                      
*note ItemsView: 181f.         *note MappingView: 181d,                               ‘__contains__’, ‘__iter__’
                               *note Set: 1810.                                       
                               
                                                                                      
*note KeysView: 181e.          *note MappingView: 181d,                               ‘__contains__’, ‘__iter__’
                               *note Set: 1810.                                       
                               
                                                                                      
*note ValuesView: 1820.        *note MappingView: 181d,                               ‘__contains__’, ‘__iter__’
                               *note Collection: 627.                                 
                               
                                                                                      
*note Awaitable: 7a9.                                     ‘__await__’
                                                          
                                                                                      
*note Coroutine: 7aa.          *note Awaitable: 7a9.      ‘send’, ‘throw’             ‘close’
                                                                                      
                                                                                      
*note AsyncIterable: 7ac.                                 ‘__aiter__’
                                                          
                                                                                      
*note AsyncIterator: 7ab.      *note AsyncIterable: 7ac.  ‘__anext__’                 ‘__aiter__’
                                                                                      
                                                                                      
*note AsyncGenerator: 62a.     *note AsyncIterator: 7ab.  ‘asend’, ‘athrow’           ‘aclose’, ‘__aiter__’, ‘__anext__’
                                                                                      

 -- Class: collections.abc.Container

     ABC for classes that provide the *note __contains__(): dee. method.

 -- Class: collections.abc.Hashable

     ABC for classes that provide the *note __hash__(): 44c. method.

 -- Class: collections.abc.Sized

     ABC for classes that provide the *note __len__(): e90. method.

 -- Class: collections.abc.Callable

     ABC for classes that provide the *note __call__(): 1560. method.

 -- Class: collections.abc.Iterable

     ABC for classes that provide the *note __iter__(): 609. method.

     Checking ‘isinstance(obj, Iterable)’ detects classes that are
     registered as *note Iterable: 1818. or that have an *note
     __iter__(): 609. method, but it does not detect classes that
     iterate with the *note __getitem__(): 3a2. method.  The only
     reliable way to determine whether an object is *note iterable: c7c.
     is to call ‘iter(obj)’.

 -- Class: collections.abc.Collection

     ABC for sized iterable container classes.

     New in version 3.6.

 -- Class: collections.abc.Iterator

     ABC for classes that provide the *note __iter__(): 175e. and *note
     __next__(): d2c. methods.  See also the definition of *note
     iterator: 1171.

 -- Class: collections.abc.Reversible

     ABC for iterable classes that also provide the *note
     __reversed__(): 629. method.

     New in version 3.6.

 -- Class: collections.abc.Generator

     ABC for generator classes that implement the protocol defined in
     PEP 342(1) that extends iterators with the *note send(): 15cd,
     *note throw(): ff8. and *note close(): 15d0. methods.  See also the
     definition of *note generator: a83.

     New in version 3.5.

 -- Class: collections.abc.Sequence
 -- Class: collections.abc.MutableSequence
 -- Class: collections.abc.ByteString

     ABCs for read-only and mutable *note sequences: 135c.

     Implementation note: Some of the mixin methods, such as *note
     __iter__(): 609, *note __reversed__(): 629. and ‘index()’, make
     repeated calls to the underlying *note __getitem__(): 3a2. method.
     Consequently, if *note __getitem__(): 3a2. is implemented with
     constant access speed, the mixin methods will have linear
     performance; however, if the underlying method is linear (as it
     would be with a linked list), the mixins will have quadratic
     performance and will likely need to be overridden.

     Changed in version 3.5: The index() method added support for `stop'
     and `start' arguments.

 -- Class: collections.abc.Set
 -- Class: collections.abc.MutableSet

     ABCs for read-only and mutable sets.

 -- Class: collections.abc.Mapping
 -- Class: collections.abc.MutableMapping

     ABCs for read-only and mutable *note mappings: c0b.

 -- Class: collections.abc.MappingView
 -- Class: collections.abc.ItemsView
 -- Class: collections.abc.KeysView
 -- Class: collections.abc.ValuesView

     ABCs for mapping, items, keys, and values *note views: 1a9e.

 -- Class: collections.abc.Awaitable

     ABC for *note awaitable: 613. objects, which can be used in *note
     await: 2d8. expressions.  Custom implementations must provide the
     *note __await__(): 735. method.

     *note Coroutine: 18a. objects and instances of the *note Coroutine:
     7aa. ABC are all instances of this ABC.

          Note: In CPython, generator-based coroutines (generators
          decorated with *note types.coroutine(): 86b. or *note
          asyncio.coroutine(): 3a8.) are `awaitables', even though they
          do not have an *note __await__(): 735. method.  Using
          ‘isinstance(gencoro, Awaitable)’ for them will return ‘False’.
          Use *note inspect.isawaitable(): 7ea. to detect them.

     New in version 3.5.

 -- Class: collections.abc.Coroutine

     ABC for coroutine compatible classes.  These implement the
     following methods, defined in *note Coroutine Objects: 155e.: *note
     send(): 15cc, *note throw(): 15ce, and *note close(): 15cf.  Custom
     implementations must also implement *note __await__(): 735.  All
     *note Coroutine: 7aa. instances are also instances of *note
     Awaitable: 7a9.  See also the definition of *note coroutine: 18a.

          Note: In CPython, generator-based coroutines (generators
          decorated with *note types.coroutine(): 86b. or *note
          asyncio.coroutine(): 3a8.) are `awaitables', even though they
          do not have an *note __await__(): 735. method.  Using
          ‘isinstance(gencoro, Coroutine)’ for them will return ‘False’.
          Use *note inspect.isawaitable(): 7ea. to detect them.

     New in version 3.5.

 -- Class: collections.abc.AsyncIterable

     ABC for classes that provide ‘__aiter__’ method.  See also the
     definition of *note asynchronous iterable: 733.

     New in version 3.5.

 -- Class: collections.abc.AsyncIterator

     ABC for classes that provide ‘__aiter__’ and ‘__anext__’ methods.
     See also the definition of *note asynchronous iterator: 738.

     New in version 3.5.

 -- Class: collections.abc.AsyncGenerator

     ABC for asynchronous generator classes that implement the protocol
     defined in PEP 525(2) and PEP 492(3).

     New in version 3.6.

These ABCs allow us to ask classes or instances if they provide
particular functionality, for example:

     size = None
     if isinstance(myvar, collections.abc.Sized):
         size = len(myvar)

Several of the ABCs are also useful as mixins that make it easier to
develop classes supporting container APIs.  For example, to write a
class supporting the full *note Set: 1810. API, it is only necessary to
supply the three underlying abstract methods: *note __contains__(): dee,
*note __iter__(): 609, and *note __len__(): e90.  The ABC supplies the
remaining methods such as *note __and__(): 15a4. and ‘isdisjoint()’:

     class ListBasedSet(collections.abc.Set):
         ''' Alternate set implementation favoring space over speed
             and not requiring the set elements to be hashable. '''
         def __init__(self, iterable):
             self.elements = lst = []
             for value in iterable:
                 if value not in lst:
                     lst.append(value)

         def __iter__(self):
             return iter(self.elements)

         def __contains__(self, value):
             return value in self.elements

         def __len__(self):
             return len(self.elements)

     s1 = ListBasedSet('abcdef')
     s2 = ListBasedSet('defghi')
     overlap = s1 & s2            # The __and__() method is supported automatically

Notes on using *note Set: 1810. and *note MutableSet: 181b. as a mixin:

  1. Since some set operations create new sets, the default mixin
     methods need a way to create new instances from an iterable.  The
     class constructor is assumed to have a signature in the form
     ‘ClassName(iterable)’.  That assumption is factored-out to an
     internal classmethod called ‘_from_iterable()’ which calls
     ‘cls(iterable)’ to produce a new set.  If the *note Set: 1810.
     mixin is being used in a class with a different constructor
     signature, you will need to override ‘_from_iterable()’ with a
     classmethod or regular method that can construct new instances from
     an iterable argument.

  2. To override the comparisons (presumably for speed, as the semantics
     are fixed), redefine *note __le__(): d68. and *note __ge__(): d6a,
     then the other operations will automatically follow suit.

  3. The *note Set: 1810. mixin provides a ‘_hash()’ method to compute a
     hash value for the set; however, *note __hash__(): 44c. is not
     defined because not all sets are hashable or immutable.  To add set
     hashability using mixins, inherit from both *note Set(): 1810. and
     *note Hashable(): 1aa9, then define ‘__hash__ = Set._hash’.

See also
........

   * OrderedSet recipe(4) for an example built on *note MutableSet:
     181b.

   * For more about ABCs, see the *note abc: 3. module and PEP 3119(5).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0342

   (2) https://www.python.org/dev/peps/pep-0525

   (3) https://www.python.org/dev/peps/pep-0492

   (4) https://code.activestate.com/recipes/576694/

   (5) https://www.python.org/dev/peps/pep-3119


File: python.info,  Node: heapq — Heap queue algorithm,  Next: bisect — Array bisection algorithm,  Prev: collections abc — Abstract Base Classes for Containers,  Up: Data Types

5.8.6 ‘heapq’ — Heap queue algorithm
------------------------------------

`Source code:' Lib/heapq.py(1)

__________________________________________________________________

This module provides an implementation of the heap queue algorithm, also
known as the priority queue algorithm.

Heaps are binary trees for which every parent node has a value less than
or equal to any of its children.  This implementation uses arrays for
which ‘heap[k] <= heap[2*k+1]’ and ‘heap[k] <= heap[2*k+2]’ for all `k',
counting elements from zero.  For the sake of comparison, non-existing
elements are considered to be infinite.  The interesting property of a
heap is that its smallest element is always the root, ‘heap[0]’.

The API below differs from textbook heap algorithms in two aspects: (a)
We use zero-based indexing.  This makes the relationship between the
index for a node and the indexes for its children slightly less obvious,
but is more suitable since Python uses zero-based indexing.  (b) Our pop
method returns the smallest item, not the largest (called a “min heap”
in textbooks; a “max heap” is more common in texts because of its
suitability for in-place sorting).

These two make it possible to view the heap as a regular Python list
without surprises: ‘heap[0]’ is the smallest item, and ‘heap.sort()’
maintains the heap invariant!

To create a heap, use a list initialized to ‘[]’, or you can transform a
populated list into a heap via function *note heapify(): 1aad.

The following functions are provided:

 -- Function: heapq.heappush (heap, item)

     Push the value `item' onto the `heap', maintaining the heap
     invariant.

 -- Function: heapq.heappop (heap)

     Pop and return the smallest item from the `heap', maintaining the
     heap invariant.  If the heap is empty, *note IndexError: f36. is
     raised.  To access the smallest item without popping it, use
     ‘heap[0]’.

 -- Function: heapq.heappushpop (heap, item)

     Push `item' on the heap, then pop and return the smallest item from
     the `heap'.  The combined action runs more efficiently than *note
     heappush(): 1aae. followed by a separate call to *note heappop():
     1aaf.

 -- Function: heapq.heapify (x)

     Transform list `x' into a heap, in-place, in linear time.

 -- Function: heapq.heapreplace (heap, item)

     Pop and return the smallest item from the `heap', and also push the
     new `item'.  The heap size doesn’t change.  If the heap is empty,
     *note IndexError: f36. is raised.

     This one step operation is more efficient than a *note heappop():
     1aaf. followed by *note heappush(): 1aae. and can be more
     appropriate when using a fixed-size heap.  The pop/push combination
     always returns an element from the heap and replaces it with
     `item'.

     The value returned may be larger than the `item' added.  If that
     isn’t desired, consider using *note heappushpop(): 1ab0. instead.
     Its push/pop combination returns the smaller of the two values,
     leaving the larger value on the heap.

The module also offers three general purpose functions based on heaps.

 -- Function: heapq.merge (*iterables, key=None, reverse=False)

     Merge multiple sorted inputs into a single sorted output (for
     example, merge timestamped entries from multiple log files).
     Returns an *note iterator: 1171. over the sorted values.

     Similar to ‘sorted(itertools.chain(*iterables))’ but returns an
     iterable, does not pull the data into memory all at once, and
     assumes that each of the input streams is already sorted (smallest
     to largest).

     Has two optional arguments which must be specified as keyword
     arguments.

     `key' specifies a *note key function: 7d2. of one argument that is
     used to extract a comparison key from each input element.  The
     default value is ‘None’ (compare the elements directly).

     `reverse' is a boolean value.  If set to ‘True’, then the input
     elements are merged as if each comparison were reversed.  To
     achieve behavior similar to ‘sorted(itertools.chain(*iterables),
     reverse=True)’, all iterables must be sorted from largest to
     smallest.

     Changed in version 3.5: Added the optional `key' and `reverse'
     parameters.

 -- Function: heapq.nlargest (n, iterable, key=None)

     Return a list with the `n' largest elements from the dataset
     defined by `iterable'.  `key', if provided, specifies a function of
     one argument that is used to extract a comparison key from each
     element in `iterable' (for example, ‘key=str.lower’).  Equivalent
     to: ‘sorted(iterable, key=key, reverse=True)[:n]’.

 -- Function: heapq.nsmallest (n, iterable, key=None)

     Return a list with the `n' smallest elements from the dataset
     defined by `iterable'.  `key', if provided, specifies a function of
     one argument that is used to extract a comparison key from each
     element in `iterable' (for example, ‘key=str.lower’).  Equivalent
     to: ‘sorted(iterable, key=key)[:n]’.

The latter two functions perform best for smaller values of `n'.  For
larger values, it is more efficient to use the *note sorted(): 547.
function.  Also, when ‘n==1’, it is more efficient to use the built-in
*note min(): 8f6. and *note max(): 8f7. functions.  If repeated usage of
these functions is required, consider turning the iterable into an
actual heap.

* Menu:

* Basic Examples::
* Priority Queue Implementation Notes::
* Theory::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/heapq.py


File: python.info,  Node: Basic Examples,  Next: Priority Queue Implementation Notes,  Up: heapq — Heap queue algorithm

5.8.6.1 Basic Examples
......................

A heapsort(1) can be implemented by pushing all values onto a heap and
then popping off the smallest values one at a time:

     >>> def heapsort(iterable):
     ...     h = []
     ...     for value in iterable:
     ...         heappush(h, value)
     ...     return [heappop(h) for i in range(len(h))]
     ...
     >>> heapsort([1, 3, 5, 7, 9, 2, 4, 6, 8, 0])
     [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

This is similar to ‘sorted(iterable)’, but unlike *note sorted(): 547,
this implementation is not stable.

Heap elements can be tuples.  This is useful for assigning comparison
values (such as task priorities) alongside the main record being
tracked:

     >>> h = []
     >>> heappush(h, (5, 'write code'))
     >>> heappush(h, (7, 'release product'))
     >>> heappush(h, (1, 'write spec'))
     >>> heappush(h, (3, 'create tests'))
     >>> heappop(h)
     (1, 'write spec')

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Heapsort


File: python.info,  Node: Priority Queue Implementation Notes,  Next: Theory,  Prev: Basic Examples,  Up: heapq — Heap queue algorithm

5.8.6.2 Priority Queue Implementation Notes
...........................................

A priority queue(1) is common use for a heap, and it presents several
implementation challenges:

   * Sort stability: how do you get two tasks with equal priorities to
     be returned in the order they were originally added?

   * Tuple comparison breaks for (priority, task) pairs if the
     priorities are equal and the tasks do not have a default comparison
     order.

   * If the priority of a task changes, how do you move it to a new
     position in the heap?

   * Or if a pending task needs to be deleted, how do you find it and
     remove it from the queue?

A solution to the first two challenges is to store entries as 3-element
list including the priority, an entry count, and the task.  The entry
count serves as a tie-breaker so that two tasks with the same priority
are returned in the order they were added.  And since no two entry
counts are the same, the tuple comparison will never attempt to directly
compare two tasks.

Another solution to the problem of non-comparable tasks is to create a
wrapper class that ignores the task item and only compares the priority
field:

     from dataclasses import dataclass, field
     from typing import Any

     @dataclass(order=True)
     class PrioritizedItem:
         priority: int
         item: Any=field(compare=False)

The remaining challenges revolve around finding a pending task and
making changes to its priority or removing it entirely.  Finding a task
can be done with a dictionary pointing to an entry in the queue.

Removing the entry or changing its priority is more difficult because it
would break the heap structure invariants.  So, a possible solution is
to mark the entry as removed and add a new entry with the revised
priority:

     pq = []                         # list of entries arranged in a heap
     entry_finder = {}               # mapping of tasks to entries
     REMOVED = '<removed-task>'      # placeholder for a removed task
     counter = itertools.count()     # unique sequence count

     def add_task(task, priority=0):
         'Add a new task or update the priority of an existing task'
         if task in entry_finder:
             remove_task(task)
         count = next(counter)
         entry = [priority, count, task]
         entry_finder[task] = entry
         heappush(pq, entry)

     def remove_task(task):
         'Mark an existing task as REMOVED.  Raise KeyError if not found.'
         entry = entry_finder.pop(task)
         entry[-1] = REMOVED

     def pop_task():
         'Remove and return the lowest priority task. Raise KeyError if empty.'
         while pq:
             priority, count, task = heappop(pq)
             if task is not REMOVED:
                 del entry_finder[task]
                 return task
         raise KeyError('pop from an empty priority queue')

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Priority_queue


File: python.info,  Node: Theory,  Prev: Priority Queue Implementation Notes,  Up: heapq — Heap queue algorithm

5.8.6.3 Theory
..............

Heaps are arrays for which ‘a[k] <= a[2*k+1]’ and ‘a[k] <= a[2*k+2]’ for
all `k', counting elements from 0.  For the sake of comparison,
non-existing elements are considered to be infinite.  The interesting
property of a heap is that ‘a[0]’ is always its smallest element.

The strange invariant above is meant to be an efficient memory
representation for a tournament.  The numbers below are `k', not ‘a[k]’:

                                    0

                   1                                 2

           3               4                5               6

       7       8       9       10      11      12      13      14

     15 16   17 18   19 20   21 22   23 24   25 26   27 28   29 30

In the tree above, each cell `k' is topping ‘2*k+1’ and ‘2*k+2’.  In a
usual binary tournament we see in sports, each cell is the winner over
the two cells it tops, and we can trace the winner down the tree to see
all opponents s/he had.  However, in many computer applications of such
tournaments, we do not need to trace the history of a winner.  To be
more memory efficient, when a winner is promoted, we try to replace it
by something else at a lower level, and the rule becomes that a cell and
the two cells it tops contain three different items, but the top cell
“wins” over the two topped cells.

If this heap invariant is protected at all time, index 0 is clearly the
overall winner.  The simplest algorithmic way to remove it and find the
“next” winner is to move some loser (let’s say cell 30 in the diagram
above) into the 0 position, and then percolate this new 0 down the tree,
exchanging values, until the invariant is re-established.  This is
clearly logarithmic on the total number of items in the tree.  By
iterating over all items, you get an O(n log n) sort.

A nice feature of this sort is that you can efficiently insert new items
while the sort is going on, provided that the inserted items are not
“better” than the last 0’th element you extracted.  This is especially
useful in simulation contexts, where the tree holds all incoming events,
and the “win” condition means the smallest scheduled time.  When an
event schedules other events for execution, they are scheduled into the
future, so they can easily go into the heap.  So, a heap is a good
structure for implementing schedulers (this is what I used for my MIDI
sequencer :-).

Various structures for implementing schedulers have been extensively
studied, and heaps are good for this, as they are reasonably speedy, the
speed is almost constant, and the worst case is not much different than
the average case.  However, there are other representations which are
more efficient overall, yet the worst cases might be terrible.

Heaps are also very useful in big disk sorts.  You most probably all
know that a big sort implies producing “runs” (which are pre-sorted
sequences, whose size is usually related to the amount of CPU memory),
followed by a merging passes for these runs, which merging is often very
cleverly organised (1).  It is very important that the initial sort
produces the longest runs possible.  Tournaments are a good way to
achieve that.  If, using all the memory available to hold a tournament,
you replace and percolate items that happen to fit the current run,
you’ll produce runs which are twice the size of the memory for random
input, and much better for input fuzzily ordered.

Moreover, if you output the 0’th item on disk and get an input which may
not fit in the current tournament (because the value “wins” over the
last output value), it cannot fit in the heap, so the size of the heap
decreases.  The freed memory could be cleverly reused immediately for
progressively building a second heap, which grows at exactly the same
rate the first heap is melting.  When the first heap completely
vanishes, you switch heaps and start a new run.  Clever and quite
effective!

In a word, heaps are useful memory structures to know.  I use them in a
few applications, and I think it is good to keep a ‘heap’ module around.
:-)

   ---------- Footnotes ----------

   (1) (1) The disk balancing algorithms which are current, nowadays,
are more annoying than clever, and this is a consequence of the seeking
capabilities of the disks.  On devices which cannot seek, like big tape
drives, the story was quite different, and one had to be very clever to
ensure (far in advance) that each tape movement will be the most
effective possible (that is, will best participate at “progressing” the
merge).  Some tapes were even able to read backwards, and this was also
used to avoid the rewinding time.  Believe me, real good tape sorts were
quite spectacular to watch!  From all times, sorting has always been a
Great Art!  :-)


File: python.info,  Node: bisect — Array bisection algorithm,  Next: array — Efficient arrays of numeric values,  Prev: heapq — Heap queue algorithm,  Up: Data Types

5.8.7 ‘bisect’ — Array bisection algorithm
------------------------------------------

`Source code:' Lib/bisect.py(1)

__________________________________________________________________

This module provides support for maintaining a list in sorted order
without having to sort the list after each insertion.  For long lists of
items with expensive comparison operations, this can be an improvement
over the more common approach.  The module is called *note bisect: 11.
because it uses a basic bisection algorithm to do its work.  The source
code may be most useful as a working example of the algorithm (the
boundary conditions are already right!).

The following functions are provided:

 -- Function: bisect.bisect_left (a, x, lo=0, hi=len(a))

     Locate the insertion point for `x' in `a' to maintain sorted order.
     The parameters `lo' and `hi' may be used to specify a subset of the
     list which should be considered; by default the entire list is
     used.  If `x' is already present in `a', the insertion point will
     be before (to the left of) any existing entries.  The return value
     is suitable for use as the first parameter to ‘list.insert()’
     assuming that `a' is already sorted.

     The returned insertion point `i' partitions the array `a' into two
     halves so that ‘all(val < x for val in a[lo:i])’ for the left side
     and ‘all(val >= x for val in a[i:hi])’ for the right side.

 -- Function: bisect.bisect_right (a, x, lo=0, hi=len(a))
 -- Function: bisect.bisect (a, x, lo=0, hi=len(a))

     Similar to *note bisect_left(): 1ab9, but returns an insertion
     point which comes after (to the right of) any existing entries of
     `x' in `a'.

     The returned insertion point `i' partitions the array `a' into two
     halves so that ‘all(val <= x for val in a[lo:i])’ for the left side
     and ‘all(val > x for val in a[i:hi])’ for the right side.

 -- Function: bisect.insort_left (a, x, lo=0, hi=len(a))

     Insert `x' in `a' in sorted order.  This is equivalent to
     ‘a.insert(bisect.bisect_left(a, x, lo, hi), x)’ assuming that `a'
     is already sorted.  Keep in mind that the O(log n) search is
     dominated by the slow O(n) insertion step.

 -- Function: bisect.insort_right (a, x, lo=0, hi=len(a))
 -- Function: bisect.insort (a, x, lo=0, hi=len(a))

     Similar to *note insort_left(): 1abc, but inserting `x' in `a'
     after any existing entries of `x'.

See also
........

SortedCollection recipe(2) that uses bisect to build a full-featured
collection class with straight-forward search methods and support for a
key-function.  The keys are precomputed to save unnecessary calls to the
key function during searches.

* Menu:

* Searching Sorted Lists::
* Other Examples::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/bisect.py

   (2) https://code.activestate.com/recipes/577197-sortedcollection/


File: python.info,  Node: Searching Sorted Lists,  Next: Other Examples,  Up: bisect — Array bisection algorithm

5.8.7.1 Searching Sorted Lists
..............................

The above *note bisect(): 11. functions are useful for finding insertion
points but can be tricky or awkward to use for common searching tasks.
The following five functions show how to transform them into the
standard lookups for sorted lists:

     def index(a, x):
         'Locate the leftmost value exactly equal to x'
         i = bisect_left(a, x)
         if i != len(a) and a[i] == x:
             return i
         raise ValueError

     def find_lt(a, x):
         'Find rightmost value less than x'
         i = bisect_left(a, x)
         if i:
             return a[i-1]
         raise ValueError

     def find_le(a, x):
         'Find rightmost value less than or equal to x'
         i = bisect_right(a, x)
         if i:
             return a[i-1]
         raise ValueError

     def find_gt(a, x):
         'Find leftmost value greater than x'
         i = bisect_right(a, x)
         if i != len(a):
             return a[i]
         raise ValueError

     def find_ge(a, x):
         'Find leftmost item greater than or equal to x'
         i = bisect_left(a, x)
         if i != len(a):
             return a[i]
         raise ValueError


File: python.info,  Node: Other Examples,  Prev: Searching Sorted Lists,  Up: bisect — Array bisection algorithm

5.8.7.2 Other Examples
......................

The *note bisect(): 11. function can be useful for numeric table
lookups.  This example uses *note bisect(): 11. to look up a letter
grade for an exam score (say) based on a set of ordered numeric
breakpoints: 90 and up is an ‘A’, 80 to 89 is a ‘B’, and so on:

     >>> def grade(score, breakpoints=[60, 70, 80, 90], grades='FDCBA'):
     ...     i = bisect(breakpoints, score)
     ...     return grades[i]
     ...
     >>> [grade(score) for score in [33, 99, 77, 70, 89, 90, 100]]
     ['F', 'A', 'C', 'C', 'B', 'A', 'A']

Unlike the *note sorted(): 547. function, it does not make sense for the
*note bisect(): 11. functions to have `key' or `reversed' arguments
because that would lead to an inefficient design (successive calls to
bisect functions would not “remember” all of the previous key lookups).

Instead, it is better to search a list of precomputed keys to find the
index of the record in question:

     >>> data = [('red', 5), ('blue', 1), ('yellow', 8), ('black', 0)]
     >>> data.sort(key=lambda r: r[1])
     >>> keys = [r[1] for r in data]         # precomputed list of keys
     >>> data[bisect_left(keys, 0)]
     ('black', 0)
     >>> data[bisect_left(keys, 1)]
     ('blue', 1)
     >>> data[bisect_left(keys, 5)]
     ('red', 5)
     >>> data[bisect_left(keys, 8)]
     ('yellow', 8)


File: python.info,  Node: array — Efficient arrays of numeric values,  Next: weakref — Weak references,  Prev: bisect — Array bisection algorithm,  Up: Data Types

5.8.8 ‘array’ — Efficient arrays of numeric values
--------------------------------------------------

__________________________________________________________________

This module defines an object type which can compactly represent an
array of basic values: characters, integers, floating point numbers.
Arrays are sequence types and behave very much like lists, except that
the type of objects stored in them is constrained.  The type is
specified at object creation time by using a `type code', which is a
single character.  The following type codes are defined:

Type code       C Type                   Python Type             Minimum size in bytes       Notes
                                                                                             
---------------------------------------------------------------------------------------------------------
                                                                                             
‘'b'’           signed char              int                     1
                                                                 
                                                                                             
‘'B'’           unsigned char            int                     1
                                                                 
                                                                                             
‘'u'’           wchar_t                  Unicode character       2                           (1)
                                                                                             
                                                                                             
‘'h'’           signed short             int                     2
                                                                 
                                                                                             
‘'H'’           unsigned short           int                     2
                                                                 
                                                                                             
‘'i'’           signed int               int                     2
                                                                 
                                                                                             
‘'I'’           unsigned int             int                     2
                                                                 
                                                                                             
‘'l'’           signed long              int                     4
                                                                 
                                                                                             
‘'L'’           unsigned long            int                     4
                                                                 
                                                                                             
‘'q'’           signed long long         int                     8
                                                                 
                                                                                             
‘'Q'’           unsigned long long       int                     8
                                                                 
                                                                                             
‘'f'’           float                    float                   4
                                                                 
                                                                                             
‘'d'’           double                   float                   8
                                                                 

Notes:

  1. It can be 16 bits or 32 bits depending on the platform.

     Changed in version 3.9: ‘array('u')’ now uses ‘wchar_t’ as C type
     instead of deprecated ‘Py_UNICODE’.  This change doesn’t affect to
     its behavior because ‘Py_UNICODE’ is alias of ‘wchar_t’ since
     Python 3.3.

     Deprecated since version 3.3, will be removed in version 4.0.

The actual representation of values is determined by the machine
architecture (strictly speaking, by the C implementation).  The actual
size can be accessed through the ‘itemsize’ attribute.

The module defines the following type:

 -- Class: array.array (typecode[, initializer])

     A new array whose items are restricted by `typecode', and
     initialized from the optional `initializer' value, which must be a
     list, a *note bytes-like object: 6df, or iterable over elements of
     the appropriate type.

     If given a list or string, the initializer is passed to the new
     array’s *note fromlist(): 1ac4, *note frombytes(): 1ac5, or *note
     fromunicode(): 1ac6. method (see below) to add initial items to the
     array.  Otherwise, the iterable initializer is passed to the *note
     extend(): 1ac7. method.

     Raises an *note auditing event: fa1. ‘array.__new__’ with arguments
     ‘typecode’, ‘initializer’.

 -- Data: array.typecodes

     A string with all available type codes.

Array objects support the ordinary sequence operations of indexing,
slicing, concatenation, and multiplication.  When using slice
assignment, the assigned value must be an array object with the same
type code; in all other cases, *note TypeError: 1fe. is raised.  Array
objects also implement the buffer interface, and may be used wherever
*note bytes-like objects: 6df. are supported.

The following data items and methods are also supported:

 -- Attribute: array.typecode

     The typecode character used to create the array.

 -- Attribute: array.itemsize

     The length in bytes of one array item in the internal
     representation.

 -- Method: array.append (x)

     Append a new item with value `x' to the end of the array.

 -- Method: array.buffer_info ()

     Return a tuple ‘(address, length)’ giving the current memory
     address and the length in elements of the buffer used to hold
     array’s contents.  The size of the memory buffer in bytes can be
     computed as ‘array.buffer_info()[1] * array.itemsize’.  This is
     occasionally useful when working with low-level (and inherently
     unsafe) I/O interfaces that require memory addresses, such as
     certain ‘ioctl()’ operations.  The returned numbers are valid as
     long as the array exists and no length-changing operations are
     applied to it.

          Note: When using array objects from code written in C or C++
          (the only way to effectively make use of this information), it
          makes more sense to use the buffer interface supported by
          array objects.  This method is maintained for backward
          compatibility and should be avoided in new code.  The buffer
          interface is documented in *note Buffer Protocol: 171c.

 -- Method: array.byteswap ()

     “Byteswap” all items of the array.  This is only supported for
     values which are 1, 2, 4, or 8 bytes in size; for other types of
     values, *note RuntimeError: 3dc. is raised.  It is useful when
     reading data from a file written on a machine with a different byte
     order.

 -- Method: array.count (x)

     Return the number of occurrences of `x' in the array.

 -- Method: array.extend (iterable)

     Append items from `iterable' to the end of the array.  If
     `iterable' is another array, it must have `exactly' the same type
     code; if not, *note TypeError: 1fe. will be raised.  If `iterable'
     is not an array, it must be iterable and its elements must be the
     right type to be appended to the array.

 -- Method: array.frombytes (s)

     Appends items from the string, interpreting the string as an array
     of machine values (as if it had been read from a file using the
     *note fromfile(): 1acf. method).

     New in version 3.2: ‘fromstring()’ is renamed to *note frombytes():
     1ac5. for clarity.

 -- Method: array.fromfile (f, n)

     Read `n' items (as machine values) from the *note file object: c14.
     `f' and append them to the end of the array.  If less than `n'
     items are available, *note EOFError: d34. is raised, but the items
     that were available are still inserted into the array.

 -- Method: array.fromlist (list)

     Append items from the list.  This is equivalent to ‘for x in list:
     a.append(x)’ except that if there is a type error, the array is
     unchanged.

 -- Method: array.fromunicode (s)

     Extends this array with data from the given unicode string.  The
     array must be a type ‘'u'’ array; otherwise a *note ValueError:
     16d. is raised.  Use ‘array.frombytes(unicodestring.encode(enc))’
     to append Unicode data to an array of some other type.

 -- Method: array.index (x)

     Return the smallest `i' such that `i' is the index of the first
     occurrence of `x' in the array.

 -- Method: array.insert (i, x)

     Insert a new item with value `x' in the array before position `i'.
     Negative values are treated as being relative to the end of the
     array.

 -- Method: array.pop ([i])

     Removes the item with the index `i' from the array and returns it.
     The optional argument defaults to ‘-1’, so that by default the last
     item is removed and returned.

 -- Method: array.remove (x)

     Remove the first occurrence of `x' from the array.

 -- Method: array.reverse ()

     Reverse the order of the items in the array.

 -- Method: array.tobytes ()

     Convert the array to an array of machine values and return the
     bytes representation (the same sequence of bytes that would be
     written to a file by the *note tofile(): 1ad5. method.)

     New in version 3.2: ‘tostring()’ is renamed to *note tobytes():
     1ad4. for clarity.

 -- Method: array.tofile (f)

     Write all items (as machine values) to the *note file object: c14.
     `f'.

 -- Method: array.tolist ()

     Convert the array to an ordinary list with the same items.

 -- Method: array.tounicode ()

     Convert the array to a unicode string.  The array must be a type
     ‘'u'’ array; otherwise a *note ValueError: 16d. is raised.  Use
     ‘array.tobytes().decode(enc)’ to obtain a unicode string from an
     array of some other type.

When an array object is printed or converted to a string, it is
represented as ‘array(typecode, initializer)’.  The `initializer' is
omitted if the array is empty, otherwise it is a string if the
`typecode' is ‘'u'’, otherwise it is a list of numbers.  The string is
guaranteed to be able to be converted back to an array with the same
type and value using *note eval(): c61, so long as the *note array: 216.
class has been imported using ‘from array import array’.  Examples:

     array('l')
     array('u', 'hello \u2641')
     array('l', [1, 2, 3, 4, 5])
     array('d', [1.0, 2.0, 3.14])

See also
........

Module *note struct: f8.

     Packing and unpacking of heterogeneous binary data.

Module *note xdrlib: 13b.

     Packing and unpacking of External Data Representation (XDR) data as
     used in some remote procedure call systems.

NumPy(1)

     The NumPy package defines another array type.

   ---------- Footnotes ----------

   (1) https://numpy.org/


File: python.info,  Node: weakref — Weak references,  Next: types — Dynamic type creation and names for built-in types,  Prev: array — Efficient arrays of numeric values,  Up: Data Types

5.8.9 ‘weakref’ — Weak references
---------------------------------

`Source code:' Lib/weakref.py(1)

__________________________________________________________________

The *note weakref: 131. module allows the Python programmer to create
`weak references' to objects.

In the following, the term `referent' means the object which is referred
to by a weak reference.

A weak reference to an object is not enough to keep the object alive:
when the only remaining references to a referent are weak references,
*note garbage collection: fc8. is free to destroy the referent and reuse
its memory for something else.  However, until the object is actually
destroyed the weak reference may return the object even if there are no
strong references to it.

A primary use for weak references is to implement caches or mappings
holding large objects, where it’s desired that a large object not be
kept alive solely because it appears in a cache or mapping.

For example, if you have a number of large binary image objects, you may
wish to associate a name with each.  If you used a Python dictionary to
map names to images, or images to names, the image objects would remain
alive just because they appeared as values or keys in the dictionaries.
The *note WeakKeyDictionary: 1054. and *note WeakValueDictionary: 1053.
classes supplied by the *note weakref: 131. module are an alternative,
using weak references to construct mappings that don’t keep objects
alive solely because they appear in the mapping objects.  If, for
example, an image object is a value in a *note WeakValueDictionary:
1053, then when the last remaining references to that image object are
the weak references held by weak mappings, garbage collection can
reclaim the object, and its corresponding entries in weak mappings are
simply deleted.

*note WeakKeyDictionary: 1054. and *note WeakValueDictionary: 1053. use
weak references in their implementation, setting up callback functions
on the weak references that notify the weak dictionaries when a key or
value has been reclaimed by garbage collection.  *note WeakSet: d80.
implements the *note set: 1f6. interface, but keeps weak references to
its elements, just like a *note WeakKeyDictionary: 1054. does.

*note finalize: 3c0. provides a straight forward way to register a
cleanup function to be called when an object is garbage collected.  This
is simpler to use than setting up a callback function on a raw weak
reference, since the module automatically ensures that the finalizer
remains alive until the object is collected.

Most programs should find that using one of these weak container types
or *note finalize: 3c0. is all they need – it’s not usually necessary to
create your own weak references directly.  The low-level machinery is
exposed by the *note weakref: 131. module for the benefit of advanced
uses.

Not all objects can be weakly referenced; those objects which can
include class instances, functions written in Python (but not in C),
instance methods, sets, frozensets, some *note file objects: c14, *note
generators: a83, type objects, sockets, arrays, deques, regular
expression pattern objects, and code objects.

Changed in version 3.2: Added support for thread.lock, threading.Lock,
and code objects.

Several built-in types such as *note list: 1f8. and *note dict: 164. do
not directly support weak references but can add support through
subclassing:

     class Dict(dict):
         pass

     obj = Dict(red=1, green=2, blue=3)   # this object is weak referenceable

`CPython implementation detail:' Other built-in types such as *note
tuple: 1a2. and *note int: 204. do not support weak references even when
subclassed.

Extension types can easily be made to support weak references; see *note
Weak Reference Support: 1ada.

When ‘__slots__’ are defined for a given type, weak reference support is
disabled unless a ‘'__weakref__'’ string is also present in the sequence
of strings in the ‘__slots__’ declaration.  See *note __slots__
documentation: 1577. for details.

 -- Class: weakref.ref (object[, callback])

     Return a weak reference to `object'.  The original object can be
     retrieved by calling the reference object if the referent is still
     alive; if the referent is no longer alive, calling the reference
     object will cause *note None: 203. to be returned.  If `callback'
     is provided and not *note None: 203, and the returned weakref
     object is still alive, the callback will be called when the object
     is about to be finalized; the weak reference object will be passed
     as the only parameter to the callback; the referent will no longer
     be available.

     It is allowable for many weak references to be constructed for the
     same object.  Callbacks registered for each weak reference will be
     called from the most recently registered callback to the oldest
     registered callback.

     Exceptions raised by the callback will be noted on the standard
     error output, but cannot be propagated; they are handled in exactly
     the same way as exceptions raised from an object’s *note __del__():
     a04. method.

     Weak references are *note hashable: 276. if the `object' is
     hashable.  They will maintain their hash value even after the
     `object' was deleted.  If *note hash(): aa3. is called the first
     time only after the `object' was deleted, the call will raise *note
     TypeError: 1fe.

     Weak references support tests for equality, but not ordering.  If
     the referents are still alive, two references have the same
     equality relationship as their referents (regardless of the
     `callback').  If either referent has been deleted, the references
     are equal only if the reference objects are the same object.

     This is a subclassable type rather than a factory function.

      -- Attribute: __callback__

          This read-only attribute returns the callback currently
          associated to the weakref.  If there is no callback or if the
          referent of the weakref is no longer alive then this attribute
          will have value ‘None’.

     Changed in version 3.4: Added the *note __callback__: 9f7.
     attribute.

 -- Function: weakref.proxy (object[, callback])

     Return a proxy to `object' which uses a weak reference.  This
     supports use of the proxy in most contexts instead of requiring the
     explicit dereferencing used with weak reference objects.  The
     returned object will have a type of either ‘ProxyType’ or
     ‘CallableProxyType’, depending on whether `object' is callable.
     Proxy objects are not *note hashable: 276. regardless of the
     referent; this avoids a number of problems related to their
     fundamentally mutable nature, and prevent their use as dictionary
     keys.  `callback' is the same as the parameter of the same name to
     the *note ref(): 9f6. function.

     Changed in version 3.8: Extended the operator support on proxy
     objects to include the matrix multiplication operators ‘@’ and
     ‘@=’.

 -- Function: weakref.getweakrefcount (object)

     Return the number of weak references and proxies which refer to
     `object'.

 -- Function: weakref.getweakrefs (object)

     Return a list of all weak reference and proxy objects which refer
     to `object'.

 -- Class: weakref.WeakKeyDictionary ([dict])

     Mapping class that references keys weakly.  Entries in the
     dictionary will be discarded when there is no longer a strong
     reference to the key.  This can be used to associate additional
     data with an object owned by other parts of an application without
     adding attributes to those objects.  This can be especially useful
     with objects that override attribute accesses.

     Changed in version 3.9: Added support for ‘|’ and ‘|=’ operators,
     specified in PEP 584(2).

*note WeakKeyDictionary: 1054. objects have an additional method that
exposes the internal references directly.  The references are not
guaranteed to be “live” at the time they are used, so the result of
calling the references needs to be checked before being used.  This can
be used to avoid creating references that will cause the garbage
collector to keep the keys around longer than needed.

 -- Method: WeakKeyDictionary.keyrefs ()

     Return an iterable of the weak references to the keys.

 -- Class: weakref.WeakValueDictionary ([dict])

     Mapping class that references values weakly.  Entries in the
     dictionary will be discarded when no strong reference to the value
     exists any more.

     Changed in version 3.9: Added support for ‘|’ and ‘|=’ operators,
     as specified in PEP 584(3).

*note WeakValueDictionary: 1053. objects have an additional method that
has the same issues as the ‘keyrefs()’ method of *note
WeakKeyDictionary: 1054. objects.

 -- Method: WeakValueDictionary.valuerefs ()

     Return an iterable of the weak references to the values.

 -- Class: weakref.WeakSet ([elements])

     Set class that keeps weak references to its elements.  An element
     will be discarded when no strong reference to it exists any more.

 -- Class: weakref.WeakMethod (method)

     A custom *note ref: 9f6. subclass which simulates a weak reference
     to a bound method (i.e., a method defined on a class and looked up
     on an instance).  Since a bound method is ephemeral, a standard
     weak reference cannot keep hold of it.  *note WeakMethod: 9f5. has
     special code to recreate the bound method until either the object
     or the original function dies:

          >>> class C:
          ...     def method(self):
          ...         print("method called!")
          ...
          >>> c = C()
          >>> r = weakref.ref(c.method)
          >>> r()
          >>> r = weakref.WeakMethod(c.method)
          >>> r()
          <bound method C.method of <__main__.C object at 0x7fc859830220>>
          >>> r()()
          method called!
          >>> del c
          >>> gc.collect()
          0
          >>> r()
          >>>

     New in version 3.4.

 -- Class: weakref.finalize (obj, func, /, *args, **kwargs)

     Return a callable finalizer object which will be called when `obj'
     is garbage collected.  Unlike an ordinary weak reference, a
     finalizer will always survive until the reference object is
     collected, greatly simplifying lifecycle management.

     A finalizer is considered `alive' until it is called (either
     explicitly or at garbage collection), and after that it is `dead'.
     Calling a live finalizer returns the result of evaluating
     ‘func(*arg, **kwargs)’, whereas calling a dead finalizer returns
     *note None: 203.

     Exceptions raised by finalizer callbacks during garbage collection
     will be shown on the standard error output, but cannot be
     propagated.  They are handled in the same way as exceptions raised
     from an object’s *note __del__(): a04. method or a weak reference’s
     callback.

     When the program exits, each remaining live finalizer is called
     unless its *note atexit: b. attribute has been set to false.  They
     are called in reverse order of creation.

     A finalizer will never invoke its callback during the later part of
     the *note interpreter shutdown: 852. when module globals are liable
     to have been replaced by *note None: 203.

      -- Method: __call__ ()

          If `self' is alive then mark it as dead and return the result
          of calling ‘func(*args, **kwargs)’.  If `self' is dead then
          return *note None: 203.

      -- Method: detach ()

          If `self' is alive then mark it as dead and return the tuple
          ‘(obj, func, args, kwargs)’.  If `self' is dead then return
          *note None: 203.

      -- Method: peek ()

          If `self' is alive then return the tuple ‘(obj, func, args,
          kwargs)’.  If `self' is dead then return *note None: 203.

      -- Attribute: alive

          Property which is true if the finalizer is alive, false
          otherwise.

      -- Attribute: atexit

          A writable boolean property which by default is true.  When
          the program exits, it calls all remaining live finalizers for
          which *note atexit: 1ae3. is true.  They are called in reverse
          order of creation.

          Note: It is important to ensure that `func', `args' and
          `kwargs' do not own any references to `obj', either directly
          or indirectly, since otherwise `obj' will never be garbage
          collected.  In particular, `func' should not be a bound method
          of `obj'.

     New in version 3.4.

 -- Data: weakref.ReferenceType

     The type object for weak references objects.

 -- Data: weakref.ProxyType

     The type object for proxies of objects which are not callable.

 -- Data: weakref.CallableProxyType

     The type object for proxies of callable objects.

 -- Data: weakref.ProxyTypes

     Sequence containing all the type objects for proxies.  This can
     make it simpler to test if an object is a proxy without being
     dependent on naming both proxy types.

See also
........

PEP 205(4) - Weak References

     The proposal and rationale for this feature, including links to
     earlier implementations and information about similar features in
     other languages.

* Menu:

* Weak Reference Objects::
* Example: Example<2>.
* Finalizer Objects::
* Comparing finalizers with __del__() methods: Comparing finalizers with __del__ methods.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/weakref.py

   (2) https://www.python.org/dev/peps/pep-0584

   (3) https://www.python.org/dev/peps/pep-0584

   (4) https://www.python.org/dev/peps/pep-0205


File: python.info,  Node: Weak Reference Objects,  Next: Example<2>,  Up: weakref — Weak references

5.8.9.1 Weak Reference Objects
..............................

Weak reference objects have no methods and no attributes besides *note
ref.__callback__: 9f7.  A weak reference object allows the referent to
be obtained, if it still exists, by calling it:

     >>> import weakref
     >>> class Object:
     ...     pass
     ...
     >>> o = Object()
     >>> r = weakref.ref(o)
     >>> o2 = r()
     >>> o is o2
     True

If the referent no longer exists, calling the reference object returns
*note None: 203.:

     >>> del o, o2
     >>> print(r())
     None

Testing that a weak reference object is still live should be done using
the expression ‘ref() is not None’.  Normally, application code that
needs to use a reference object should follow this pattern:

     # r is a weak reference object
     o = r()
     if o is None:
         # referent has been garbage collected
         print("Object has been deallocated; can't frobnicate.")
     else:
         print("Object is still live!")
         o.do_something_useful()

Using a separate test for “liveness” creates race conditions in threaded
applications; another thread can cause a weak reference to become
invalidated before the weak reference is called; the idiom shown above
is safe in threaded applications as well as single-threaded
applications.

Specialized versions of *note ref: 9f6. objects can be created through
subclassing.  This is used in the implementation of the *note
WeakValueDictionary: 1053. to reduce the memory overhead for each entry
in the mapping.  This may be most useful to associate additional
information with a reference, but could also be used to insert
additional processing on calls to retrieve the referent.

This example shows how a subclass of *note ref: 9f6. can be used to
store additional information about an object and affect the value that’s
returned when the referent is accessed:

     import weakref

     class ExtendedRef(weakref.ref):
         def __init__(self, ob, callback=None, /, **annotations):
             super().__init__(ob, callback)
             self.__counter = 0
             for k, v in annotations.items():
                 setattr(self, k, v)

         def __call__(self):
             """Return a pair containing the referent and the number of
             times the reference has been called.
             """
             ob = super().__call__()
             if ob is not None:
                 self.__counter += 1
                 ob = (ob, self.__counter)
             return ob


File: python.info,  Node: Example<2>,  Next: Finalizer Objects,  Prev: Weak Reference Objects,  Up: weakref — Weak references

5.8.9.2 Example
...............

This simple example shows how an application can use object IDs to
retrieve objects that it has seen before.  The IDs of the objects can
then be used in other data structures without forcing the objects to
remain alive, but the objects can still be retrieved by ID if they do.

     import weakref

     _id2obj_dict = weakref.WeakValueDictionary()

     def remember(obj):
         oid = id(obj)
         _id2obj_dict[oid] = obj
         return oid

     def id2obj(oid):
         return _id2obj_dict[oid]


File: python.info,  Node: Finalizer Objects,  Next: Comparing finalizers with __del__ methods,  Prev: Example<2>,  Up: weakref — Weak references

5.8.9.3 Finalizer Objects
.........................

The main benefit of using *note finalize: 3c0. is that it makes it
simple to register a callback without needing to preserve the returned
finalizer object.  For instance

     >>> import weakref
     >>> class Object:
     ...     pass
     ...
     >>> kenny = Object()
     >>> weakref.finalize(kenny, print, "You killed Kenny!")
     <finalize object at ...; for 'Object' at ...>
     >>> del kenny
     You killed Kenny!

The finalizer can be called directly as well.  However the finalizer
will invoke the callback at most once.

     >>> def callback(x, y, z):
     ...     print("CALLBACK")
     ...     return x + y + z
     ...
     >>> obj = Object()
     >>> f = weakref.finalize(obj, callback, 1, 2, z=3)
     >>> assert f.alive
     >>> assert f() == 6
     CALLBACK
     >>> assert not f.alive
     >>> f()                     # callback not called because finalizer dead
     >>> del obj                 # callback not called because finalizer dead

You can unregister a finalizer using its *note detach(): 1ae0. method.
This kills the finalizer and returns the arguments passed to the
constructor when it was created.

     >>> obj = Object()
     >>> f = weakref.finalize(obj, callback, 1, 2, z=3)
     >>> f.detach()
     (<...Object object ...>, <function callback ...>, (1, 2), {'z': 3})
     >>> newobj, func, args, kwargs = _
     >>> assert not f.alive
     >>> assert newobj is obj
     >>> assert func(*args, **kwargs) == 6
     CALLBACK

Unless you set the *note atexit: 1ae3. attribute to *note False: 48f, a
finalizer will be called when the program exits if it is still alive.
For instance

     >>> obj = Object()
     >>> weakref.finalize(obj, print, "obj dead or exiting")
     <finalize object at ...; for 'Object' at ...>
     >>> exit()
     obj dead or exiting


File: python.info,  Node: Comparing finalizers with __del__ methods,  Prev: Finalizer Objects,  Up: weakref — Weak references

5.8.9.4 Comparing finalizers with ‘__del__()’ methods
.....................................................

Suppose we want to create a class whose instances represent temporary
directories.  The directories should be deleted with their contents when
the first of the following events occurs:

   * the object is garbage collected,

   * the object’s ‘remove()’ method is called, or

   * the program exits.

We might try to implement the class using a *note __del__(): a04. method
as follows:

     class TempDir:
         def __init__(self):
             self.name = tempfile.mkdtemp()

         def remove(self):
             if self.name is not None:
                 shutil.rmtree(self.name)
                 self.name = None

         @property
         def removed(self):
             return self.name is None

         def __del__(self):
             self.remove()

Starting with Python 3.4, *note __del__(): a04. methods no longer
prevent reference cycles from being garbage collected, and module
globals are no longer forced to *note None: 203. during *note
interpreter shutdown: 852.  So this code should work without any issues
on CPython.

However, handling of *note __del__(): a04. methods is notoriously
implementation specific, since it depends on internal details of the
interpreter’s garbage collector implementation.

A more robust alternative can be to define a finalizer which only
references the specific functions and objects that it needs, rather than
having access to the full state of the object:

     class TempDir:
         def __init__(self):
             self.name = tempfile.mkdtemp()
             self._finalizer = weakref.finalize(self, shutil.rmtree, self.name)

         def remove(self):
             self._finalizer()

         @property
         def removed(self):
             return not self._finalizer.alive

Defined like this, our finalizer only receives a reference to the
details it needs to clean up the directory appropriately.  If the object
never gets garbage collected the finalizer will still be called at exit.

The other advantage of weakref based finalizers is that they can be used
to register finalizers for classes where the definition is controlled by
a third party, such as running code when a module is unloaded:

     import weakref, sys
     def unloading_module():
         # implicit reference to the module globals from the function body
     weakref.finalize(sys.modules[__name__], unloading_module)

     Note: If you create a finalizer object in a daemonic thread just as
     the program exits then there is the possibility that the finalizer
     does not get called at exit.  However, in a daemonic thread *note
     atexit.register(): f46, ‘try: ... finally: ...’ and ‘with: ...’ do
     not guarantee that cleanup occurs either.


File: python.info,  Node: types — Dynamic type creation and names for built-in types,  Next: copy — Shallow and deep copy operations,  Prev: weakref — Weak references,  Up: Data Types

5.8.10 ‘types’ — Dynamic type creation and names for built-in types
-------------------------------------------------------------------

`Source code:' Lib/types.py(1)

__________________________________________________________________

This module defines utility functions to assist in dynamic creation of
new types.

It also defines names for some object types that are used by the
standard Python interpreter, but not exposed as builtins like *note int:
204. or *note str: 205. are.

Finally, it provides some additional type-related utility classes and
functions that are not fundamental enough to be builtins.

* Menu:

* Dynamic Type Creation::
* Standard Interpreter Types::
* Additional Utility Classes and Functions::
* Coroutine Utility Functions::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/types.py


File: python.info,  Node: Dynamic Type Creation,  Next: Standard Interpreter Types,  Up: types — Dynamic type creation and names for built-in types

5.8.10.1 Dynamic Type Creation
..............................

 -- Function: types.new_class (name, bases=(), kwds=None,
          exec_body=None)

     Creates a class object dynamically using the appropriate metaclass.

     The first three arguments are the components that make up a class
     definition header: the class name, the base classes (in order), the
     keyword arguments (such as ‘metaclass’).

     The `exec_body' argument is a callback that is used to populate the
     freshly created class namespace.  It should accept the class
     namespace as its sole argument and update the namespace directly
     with the class contents.  If no callback is provided, it has the
     same effect as passing in ‘lambda ns: None’.

     New in version 3.3.

 -- Function: types.prepare_class (name, bases=(), kwds=None)

     Calculates the appropriate metaclass and creates the class
     namespace.

     The arguments are the components that make up a class definition
     header: the class name, the base classes (in order) and the keyword
     arguments (such as ‘metaclass’).

     The return value is a 3-tuple: ‘metaclass, namespace, kwds’

     `metaclass' is the appropriate metaclass, `namespace' is the
     prepared class namespace and `kwds' is an updated copy of the
     passed in `kwds' argument with any ‘'metaclass'’ entry removed.  If
     no `kwds' argument is passed in, this will be an empty dict.

     New in version 3.3.

     Changed in version 3.6: The default value for the ‘namespace’
     element of the returned tuple has changed.  Now an
     insertion-order-preserving mapping is used when the metaclass does
     not have a ‘__prepare__’ method.

See also
........

*note Metaclasses: 157c.

     Full details of the class creation process supported by these
     functions

PEP 3115(1) - Metaclasses in Python 3000

     Introduced the ‘__prepare__’ namespace hook

 -- Function: types.resolve_bases (bases)

     Resolve MRO entries dynamically as specified by PEP 560(2).

     This function looks for items in `bases' that are not instances of
     *note type: 6ff, and returns a tuple where each such object that
     has an ‘__mro_entries__’ method is replaced with an unpacked result
     of calling this method.  If a `bases' item is an instance of *note
     type: 6ff, or it doesn’t have an ‘__mro_entries__’ method, then it
     is included in the return tuple unchanged.

     New in version 3.7.

See also
........

PEP 560(3) - Core support for typing module and generic types

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3115

   (2) https://www.python.org/dev/peps/pep-0560

   (3) https://www.python.org/dev/peps/pep-0560


File: python.info,  Node: Standard Interpreter Types,  Next: Additional Utility Classes and Functions,  Prev: Dynamic Type Creation,  Up: types — Dynamic type creation and names for built-in types

5.8.10.2 Standard Interpreter Types
...................................

This module provides names for many of the types that are required to
implement a Python interpreter.  It deliberately avoids including some
of the types that arise only incidentally during processing such as the
‘listiterator’ type.

Typical use of these names is for *note isinstance(): 552. or *note
issubclass(): 553. checks.

If you instantiate any of these types, note that signatures may vary
between Python versions.

Standard names are defined for the following types:

 -- Data: types.FunctionType
 -- Data: types.LambdaType

     The type of user-defined functions and functions created by *note
     lambda: cf9. expressions.

     Raises an *note auditing event: fa1. ‘function.__new__’ with
     argument ‘code’.

     The audit event only occurs for direct instantiation of function
     objects, and is not raised for normal compilation.

 -- Data: types.GeneratorType

     The type of *note generator: a83.-iterator objects, created by
     generator functions.

 -- Data: types.CoroutineType

     The type of *note coroutine: 18a. objects, created by *note async
     def: 3a9. functions.

     New in version 3.5.

 -- Data: types.AsyncGeneratorType

     The type of *note asynchronous generator: 1640.-iterator objects,
     created by asynchronous generator functions.

     New in version 3.6.

 -- Class: types.CodeType (**kwargs)

     The type for code objects such as returned by *note compile(): 2e7.

     Raises an *note auditing event: fa1. ‘code.__new__’ with arguments
     ‘code’, ‘filename’, ‘name’, ‘argcount’, ‘posonlyargcount’,
     ‘kwonlyargcount’, ‘nlocals’, ‘stacksize’, ‘flags’.

     Note that the audited arguments may not match the names or
     positions required by the initializer.  The audit event only occurs
     for direct instantiation of code objects, and is not raised for
     normal compilation.

      -- Method: replace (**kwargs)

          Return a copy of the code object with new values for the
          specified fields.

          New in version 3.8.

 -- Data: types.CellType

     The type for cell objects: such objects are used as containers for
     a function’s free variables.

     New in version 3.8.

 -- Data: types.MethodType

     The type of methods of user-defined class instances.

 -- Data: types.BuiltinFunctionType
 -- Data: types.BuiltinMethodType

     The type of built-in functions like *note len(): 28b. or *note
     sys.exit(): daa, and methods of built-in classes.  (Here, the term
     “built-in” means “written in C”.)

 -- Data: types.WrapperDescriptorType

     The type of methods of some built-in data types and base classes
     such as *note object.__init__(): e23. or *note object.__lt__():
     cfe.

     New in version 3.7.

 -- Data: types.MethodWrapperType

     The type of `bound' methods of some built-in data types and base
     classes.  For example it is the type of ‘object().__str__’.

     New in version 3.7.

 -- Data: types.MethodDescriptorType

     The type of methods of some built-in data types such as *note
     str.join(): 1766.

     New in version 3.7.

 -- Data: types.ClassMethodDescriptorType

     The type of `unbound' class methods of some built-in data types
     such as ‘dict.__dict__['fromkeys']’.

     New in version 3.7.

 -- Class: types.ModuleType (name, doc=None)

     The type of *note modules: 15e7.  The constructor takes the name of
     the module to be created and optionally its *note docstring: 16eb.

          Note: Use *note importlib.util.module_from_spec(): 7e1. to
          create a new module if you wish to set the various
          import-controlled attributes.

      -- Attribute: __doc__

          The *note docstring: 16eb. of the module.  Defaults to ‘None’.

      -- Attribute: __loader__

          The *note loader: 15f6. which loaded the module.  Defaults to
          ‘None’.

          This attribute is to match *note
          importlib.machinery.ModuleSpec.loader: 1afd. as stored in the
          attr:‘__spec__’ object.

               Note: A future version of Python may stop setting this
               attribute by default.  To guard against this potential
               change, preferably read from the *note __spec__: 1603.
               attribute instead or use ‘getattr(module, "__loader__",
               None)’ if you explicitly need to use this attribute.

          Changed in version 3.4: Defaults to ‘None’.  Previously the
          attribute was optional.

      -- Attribute: __name__

          The name of the module.  Expected to match *note
          importlib.machinery.ModuleSpec.name: 1aff.

      -- Attribute: __package__

          Which *note package: 15eb. a module belongs to.  If the module
          is top-level (i.e.  not a part of any specific package) then
          the attribute should be set to ‘''’, else it should be set to
          the name of the package (which can be *note __name__: dd8. if
          the module is a package itself).  Defaults to ‘None’.

          This attribute is to match *note
          importlib.machinery.ModuleSpec.parent: 1b01. as stored in the
          attr:‘__spec__’ object.

               Note: A future version of Python may stop setting this
               attribute by default.  To guard against this potential
               change, preferably read from the *note __spec__: 1603.
               attribute instead or use ‘getattr(module, "__package__",
               None)’ if you explicitly need to use this attribute.

          Changed in version 3.4: Defaults to ‘None’.  Previously the
          attribute was optional.

      -- Attribute: __spec__

          A record of the module’s import-system-related state.
          Expected to be an instance of *note
          importlib.machinery.ModuleSpec: 1601.

          New in version 3.4.

 -- Class: types.GenericAlias (t_origin, t_args)

     The type of *note parameterized generics: fe5. such as ‘list[int]’.

     ‘t_origin’ should be a non-parameterized generic class, such as
     ‘list’, ‘tuple’ or ‘dict’.  ‘t_args’ should be a *note tuple: 1a2.
     (possibly of length 1) of types which parameterize ‘t_origin’:

          >>> from types import GenericAlias

          >>> list[int] == GenericAlias(list, (int,))
          True
          >>> dict[str, int] == GenericAlias(dict, (str, int))
          True

     New in version 3.9.

     Changed in version 3.9.2: This type can now be subclassed.

 -- Class: types.TracebackType (tb_next, tb_frame, tb_lasti, tb_lineno)

     The type of traceback objects such as found in ‘sys.exc_info()[2]’.

     See *note the language reference: 442. for details of the available
     attributes and operations, and guidance on creating tracebacks
     dynamically.

 -- Data: types.FrameType

     The type of frame objects such as found in ‘tb.tb_frame’ if ‘tb’ is
     a traceback object.

     See *note the language reference: 1565. for details of the
     available attributes and operations.

 -- Data: types.GetSetDescriptorType

     The type of objects defined in extension modules with
     ‘PyGetSetDef’, such as ‘FrameType.f_locals’ or
     ‘array.array.typecode’.  This type is used as descriptor for object
     attributes; it has the same purpose as the *note property: 308.
     type, but for classes defined in extension modules.

 -- Data: types.MemberDescriptorType

     The type of objects defined in extension modules with
     ‘PyMemberDef’, such as ‘datetime.timedelta.days’.  This type is
     used as descriptor for simple C data members which use standard
     conversion functions; it has the same purpose as the *note
     property: 308. type, but for classes defined in extension modules.

     `CPython implementation detail:' In other implementations of
     Python, this type may be identical to ‘GetSetDescriptorType’.

 -- Class: types.MappingProxyType (mapping)

     Read-only proxy of a mapping.  It provides a dynamic view on the
     mapping’s entries, which means that when the mapping changes, the
     view reflects these changes.

     New in version 3.3.

     Changed in version 3.9: Updated to support the new union (‘|’)
     operator from PEP 584(1), which simply delegates to the underlying
     mapping.

      -- Describe: key in proxy

          Return ‘True’ if the underlying mapping has a key `key', else
          ‘False’.

      -- Describe: proxy[key]

          Return the item of the underlying mapping with key `key'.
          Raises a *note KeyError: 3e9. if `key' is not in the
          underlying mapping.

      -- Describe: iter(proxy)

          Return an iterator over the keys of the underlying mapping.
          This is a shortcut for ‘iter(proxy.keys())’.

      -- Describe: len(proxy)

          Return the number of items in the underlying mapping.

      -- Method: copy ()

          Return a shallow copy of the underlying mapping.

      -- Method: get (key[, default])

          Return the value for `key' if `key' is in the underlying
          mapping, else `default'.  If `default' is not given, it
          defaults to ‘None’, so that this method never raises a *note
          KeyError: 3e9.

      -- Method: items ()

          Return a new view of the underlying mapping’s items (‘(key,
          value)’ pairs).

      -- Method: keys ()

          Return a new view of the underlying mapping’s keys.

      -- Method: values ()

          Return a new view of the underlying mapping’s values.

      -- Describe: reversed(proxy)

          Return a reverse iterator over the keys of the underlying
          mapping.

          New in version 3.9.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0584


File: python.info,  Node: Additional Utility Classes and Functions,  Next: Coroutine Utility Functions,  Prev: Standard Interpreter Types,  Up: types — Dynamic type creation and names for built-in types

5.8.10.3 Additional Utility Classes and Functions
.................................................

 -- Class: types.SimpleNamespace

     A simple *note object: 3d2. subclass that provides attribute access
     to its namespace, as well as a meaningful repr.

     Unlike *note object: 3d2, with ‘SimpleNamespace’ you can add and
     remove attributes.  If a ‘SimpleNamespace’ object is initialized
     with keyword arguments, those are directly added to the underlying
     namespace.

     The type is roughly equivalent to the following code:

          class SimpleNamespace:
              def __init__(self, /, **kwargs):
                  self.__dict__.update(kwargs)

              def __repr__(self):
                  items = (f"{k}={v!r}" for k, v in self.__dict__.items())
                  return "{}({})".format(type(self).__name__, ", ".join(items))

              def __eq__(self, other):
                  if isinstance(self, SimpleNamespace) and isinstance(other, SimpleNamespace):
                     return self.__dict__ == other.__dict__
                  return NotImplemented

     ‘SimpleNamespace’ may be useful as a replacement for ‘class NS:
     pass’.  However, for a structured record type use *note
     namedtuple(): 1a1. instead.

     New in version 3.3.

     Changed in version 3.9: Attribute order in the repr changed from
     alphabetical to insertion (like ‘dict’).

 -- Function: types.DynamicClassAttribute (fget=None, fset=None,
          fdel=None, doc=None)

     Route attribute access on a class to __getattr__.

     This is a descriptor, used to define attributes that act
     differently when accessed through an instance and through a class.
     Instance access remains normal, but access to an attribute through
     a class will be routed to the class’s __getattr__ method; this is
     done by raising AttributeError.

     This allows one to have properties active on an instance, and have
     virtual attributes on the class with the same name (see *note
     enum.Enum: 48e. for an example).

     New in version 3.4.


File: python.info,  Node: Coroutine Utility Functions,  Prev: Additional Utility Classes and Functions,  Up: types — Dynamic type creation and names for built-in types

5.8.10.4 Coroutine Utility Functions
....................................

 -- Function: types.coroutine (gen_func)

     This function transforms a *note generator: a83. function into a
     *note coroutine function: 732. which returns a generator-based
     coroutine.  The generator-based coroutine is still a *note
     generator iterator: 559, but is also considered to be a *note
     coroutine: 18a. object and is *note awaitable: 613.  However, it
     may not necessarily implement the *note __await__(): 735. method.

     If `gen_func' is a generator function, it will be modified
     in-place.

     If `gen_func' is not a generator function, it will be wrapped.  If
     it returns an instance of *note collections.abc.Generator: 7a8, the
     instance will be wrapped in an `awaitable' proxy object.  All other
     types of objects will be returned as is.

     New in version 3.5.


File: python.info,  Node: copy — Shallow and deep copy operations,  Next: pprint — Data pretty printer,  Prev: types — Dynamic type creation and names for built-in types,  Up: Data Types

5.8.11 ‘copy’ — Shallow and deep copy operations
------------------------------------------------

`Source code:' Lib/copy.py(1)

__________________________________________________________________

Assignment statements in Python do not copy objects, they create
bindings between a target and an object.  For collections that are
mutable or contain mutable items, a copy is sometimes needed so one can
change one copy without changing the other.  This module provides
generic shallow and deep copy operations (explained below).

Interface summary:

 -- Function: copy.copy (x)

     Return a shallow copy of `x'.

 -- Function: copy.deepcopy (x[, memo])

     Return a deep copy of `x'.

 -- Exception: copy.Error

     Raised for module specific errors.
The difference between shallow and deep copying is only relevant for
compound objects (objects that contain other objects, like lists or
class instances):

   * A `shallow copy' constructs a new compound object and then (to the
     extent possible) inserts `references' into it to the objects found
     in the original.

   * A `deep copy' constructs a new compound object and then,
     recursively, inserts `copies' into it of the objects found in the
     original.

Two problems often exist with deep copy operations that don’t exist with
shallow copy operations:

   * Recursive objects (compound objects that, directly or indirectly,
     contain a reference to themselves) may cause a recursive loop.

   * Because deep copy copies everything it may copy too much, such as
     data which is intended to be shared between copies.

The *note deepcopy(): 4d3. function avoids these problems by:

   * keeping a ‘memo’ dictionary of objects already copied during the
     current copying pass; and

   * letting user-defined classes override the copying operation or the
     set of components copied.

This module does not copy types like module, method, stack trace, stack
frame, file, socket, window, or any similar types.  It does “copy”
functions and classes (shallow and deeply), by returning the original
object unchanged; this is compatible with the way these are treated by
the *note pickle: ca. module.

Shallow copies of dictionaries can be made using *note dict.copy(): 549,
and of lists by assigning a slice of the entire list, for example,
‘copied_list = original_list[:]’.

Classes can use the same interfaces to control copying that they use to
control pickling.  See the description of module *note pickle: ca. for
information on these methods.  In fact, the *note copy: 25. module uses
the registered pickle functions from the *note copyreg: 26. module.

In order for a class to define its own copy implementation, it can
define special methods ‘__copy__()’ and ‘__deepcopy__()’.  The former is
called to implement the shallow copy operation; no additional arguments
are passed.  The latter is called to implement the deep copy operation;
it is passed one argument, the ‘memo’ dictionary.  If the
‘__deepcopy__()’ implementation needs to make a deep copy of a
component, it should call the *note deepcopy(): 4d3. function with the
component as first argument and the memo dictionary as second argument.

See also
........

Module *note pickle: ca.

     Discussion of the special methods used to support object state
     retrieval and restoration.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/copy.py


File: python.info,  Node: pprint — Data pretty printer,  Next: reprlib — Alternate repr implementation,  Prev: copy — Shallow and deep copy operations,  Up: Data Types

5.8.12 ‘pprint’ — Data pretty printer
-------------------------------------

`Source code:' Lib/pprint.py(1)

__________________________________________________________________

The *note pprint: d2. module provides a capability to “pretty-print”
arbitrary Python data structures in a form which can be used as input to
the interpreter.  If the formatted structures include objects which are
not fundamental Python types, the representation may not be loadable.
This may be the case if objects such as files, sockets or classes are
included, as well as many other objects which are not representable as
Python literals.

The formatted representation keeps objects on a single line if it can,
and breaks them onto multiple lines if they don’t fit within the allowed
width.  Construct *note PrettyPrinter: 97c. objects explicitly if you
need to adjust the width constraint.

Dictionaries are sorted by key before the display is computed.

Changed in version 3.9: Added support for pretty-printing *note
types.SimpleNamespace: 1d8.

The *note pprint: d2. module defines one class:

 -- Class: pprint.PrettyPrinter (indent=1, width=80, depth=None,
          stream=None, *, compact=False, sort_dicts=True)

     Construct a *note PrettyPrinter: 97c. instance.  This constructor
     understands several keyword parameters.  An output stream may be
     set using the `stream' keyword; the only method used on the stream
     object is the file protocol’s ‘write()’ method.  If not specified,
     the *note PrettyPrinter: 97c. adopts ‘sys.stdout’.  The amount of
     indentation added for each recursive level is specified by
     `indent'; the default is one.  Other values can cause output to
     look a little odd, but can make nesting easier to spot.  The number
     of levels which may be printed is controlled by `depth'; if the
     data structure being printed is too deep, the next contained level
     is replaced by ‘...’.  By default, there is no constraint on the
     depth of the objects being formatted.  The desired output width is
     constrained using the `width' parameter; the default is 80
     characters.  If a structure cannot be formatted within the
     constrained width, a best effort will be made.  If `compact' is
     false (the default) each item of a long sequence will be formatted
     on a separate line.  If `compact' is true, as many items as will
     fit within the `width' will be formatted on each output line.  If
     `sort_dicts' is true (the default), dictionaries will be formatted
     with their keys sorted, otherwise they will display in insertion
     order.

     Changed in version 3.4: Added the `compact' parameter.

     Changed in version 3.8: Added the `sort_dicts' parameter.

          >>> import pprint
          >>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
          >>> stuff.insert(0, stuff[:])
          >>> pp = pprint.PrettyPrinter(indent=4)
          >>> pp.pprint(stuff)
          [   ['spam', 'eggs', 'lumberjack', 'knights', 'ni'],
              'spam',
              'eggs',
              'lumberjack',
              'knights',
              'ni']
          >>> pp = pprint.PrettyPrinter(width=41, compact=True)
          >>> pp.pprint(stuff)
          [['spam', 'eggs', 'lumberjack',
            'knights', 'ni'],
           'spam', 'eggs', 'lumberjack', 'knights',
           'ni']
          >>> tup = ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead',
          ... ('parrot', ('fresh fruit',))))))))
          >>> pp = pprint.PrettyPrinter(depth=6)
          >>> pp.pprint(tup)
          ('spam', ('eggs', ('lumberjack', ('knights', ('ni', ('dead', (...)))))))

The *note pprint: d2. module also provides several shortcut functions:

 -- Function: pprint.pformat (object, indent=1, width=80, depth=None, *,
          compact=False, sort_dicts=True)

     Return the formatted representation of `object' as a string.
     `indent', `width', `depth', `compact' and `sort_dicts' will be
     passed to the *note PrettyPrinter: 97c. constructor as formatting
     parameters.

     Changed in version 3.4: Added the `compact' parameter.

     Changed in version 3.8: Added the `sort_dicts' parameter.

 -- Function: pprint.pp (object, *args, sort_dicts=False, **kwargs)

     Prints the formatted representation of `object' followed by a
     newline.  If `sort_dicts' is false (the default), dictionaries will
     be displayed with their keys in insertion order, otherwise the dict
     keys will be sorted.  `args' and `kwargs' will be passed to *note
     pprint(): d2. as formatting parameters.

     New in version 3.8.

 -- Function: pprint.pprint (object, stream=None, indent=1, width=80,
          depth=None, *, compact=False, sort_dicts=True)

     Prints the formatted representation of `object' on `stream',
     followed by a newline.  If `stream' is ‘None’, ‘sys.stdout’ is
     used.  This may be used in the interactive interpreter instead of
     the *note print(): 971. function for inspecting values (you can
     even reassign ‘print = pprint.pprint’ for use within a scope).
     `indent', `width', `depth', `compact' and `sort_dicts' will be
     passed to the *note PrettyPrinter: 97c. constructor as formatting
     parameters.

     Changed in version 3.4: Added the `compact' parameter.

     Changed in version 3.8: Added the `sort_dicts' parameter.

          >>> import pprint
          >>> stuff = ['spam', 'eggs', 'lumberjack', 'knights', 'ni']
          >>> stuff.insert(0, stuff)
          >>> pprint.pprint(stuff)
          [<Recursion on list with id=...>,
           'spam',
           'eggs',
           'lumberjack',
           'knights',
           'ni']

 -- Function: pprint.isreadable (object)

     Determine if the formatted representation of `object' is
     “readable”, or can be used to reconstruct the value using *note
     eval(): c61.  This always returns ‘False’ for recursive objects.

          >>> pprint.isreadable(stuff)
          False

 -- Function: pprint.isrecursive (object)

     Determine if `object' requires a recursive representation.

One more support function is also defined:

 -- Function: pprint.saferepr (object)

     Return a string representation of `object', protected against
     recursive data structures.  If the representation of `object'
     exposes a recursive entry, the recursive reference will be
     represented as ‘<Recursion on typename with id=number>’.  The
     representation is not otherwise formatted.

          >>> pprint.saferepr(stuff)
          "[<Recursion on list with id=...>, 'spam', 'eggs', 'lumberjack', 'knights', 'ni']"

* Menu:

* PrettyPrinter Objects::
* Example: Example<3>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/pprint.py


File: python.info,  Node: PrettyPrinter Objects,  Next: Example<3>,  Up: pprint — Data pretty printer

5.8.12.1 PrettyPrinter Objects
..............................

*note PrettyPrinter: 97c. instances have the following methods:

 -- Method: PrettyPrinter.pformat (object)

     Return the formatted representation of `object'.  This takes into
     account the options passed to the *note PrettyPrinter: 97c.
     constructor.

 -- Method: PrettyPrinter.pprint (object)

     Print the formatted representation of `object' on the configured
     stream, followed by a newline.

The following methods provide the implementations for the corresponding
functions of the same names.  Using these methods on an instance is
slightly more efficient since new *note PrettyPrinter: 97c. objects
don’t need to be created.

 -- Method: PrettyPrinter.isreadable (object)

     Determine if the formatted representation of the object is
     “readable,” or can be used to reconstruct the value using *note
     eval(): c61.  Note that this returns ‘False’ for recursive objects.
     If the `depth' parameter of the *note PrettyPrinter: 97c. is set
     and the object is deeper than allowed, this returns ‘False’.

 -- Method: PrettyPrinter.isrecursive (object)

     Determine if the object requires a recursive representation.

This method is provided as a hook to allow subclasses to modify the way
objects are converted to strings.  The default implementation uses the
internals of the *note saferepr(): 1b14. implementation.

 -- Method: PrettyPrinter.format (object, context, maxlevels, level)

     Returns three values: the formatted version of `object' as a
     string, a flag indicating whether the result is readable, and a
     flag indicating whether recursion was detected.  The first argument
     is the object to be presented.  The second is a dictionary which
     contains the *note id(): e4b. of objects that are part of the
     current presentation context (direct and indirect containers for
     `object' that are affecting the presentation) as the keys; if an
     object needs to be presented which is already represented in
     `context', the third return value should be ‘True’.  Recursive
     calls to the *note format(): 1b1b. method should add additional
     entries for containers to this dictionary.  The third argument,
     `maxlevels', gives the requested limit to recursion; this will be
     ‘0’ if there is no requested limit.  This argument should be passed
     unmodified to recursive calls.  The fourth argument, `level', gives
     the current level; recursive calls should be passed a value less
     than that of the current call.


File: python.info,  Node: Example<3>,  Prev: PrettyPrinter Objects,  Up: pprint — Data pretty printer

5.8.12.2 Example
................

To demonstrate several uses of the *note pprint(): d2. function and its
parameters, let’s fetch information about a project from PyPI(1):

     >>> import json
     >>> import pprint
     >>> from urllib.request import urlopen
     >>> with urlopen('https://pypi.org/pypi/sampleproject/json') as resp:
     ...     project_info = json.load(resp)['info']

In its basic form, *note pprint(): d2. shows the whole object:

     >>> pprint.pprint(project_info)
     {'author': 'The Python Packaging Authority',
      'author_email': 'pypa-dev@googlegroups.com',
      'bugtrack_url': None,
      'classifiers': ['Development Status :: 3 - Alpha',
                      'Intended Audience :: Developers',
                      'License :: OSI Approved :: MIT License',
                      'Programming Language :: Python :: 2',
                      'Programming Language :: Python :: 2.6',
                      'Programming Language :: Python :: 2.7',
                      'Programming Language :: Python :: 3',
                      'Programming Language :: Python :: 3.2',
                      'Programming Language :: Python :: 3.3',
                      'Programming Language :: Python :: 3.4',
                      'Topic :: Software Development :: Build Tools'],
      'description': 'A sample Python project\n'
                     '=======================\n'
                     '\n'
                     'This is the description file for the project.\n'
                     '\n'
                     'The file should use UTF-8 encoding and be written using '
                     'ReStructured Text. It\n'
                     'will be used to generate the project webpage on PyPI, and '
                     'should be written for\n'
                     'that purpose.\n'
                     '\n'
                     'Typical contents for this file would include an overview of '
                     'the project, basic\n'
                     'usage examples, etc. Generally, including the project '
                     'changelog in here is not\n'
                     'a good idea, although a simple "What\'s New" section for the '
                     'most recent version\n'
                     'may be appropriate.',
      'description_content_type': None,
      'docs_url': None,
      'download_url': 'UNKNOWN',
      'downloads': {'last_day': -1, 'last_month': -1, 'last_week': -1},
      'home_page': 'https://github.com/pypa/sampleproject',
      'keywords': 'sample setuptools development',
      'license': 'MIT',
      'maintainer': None,
      'maintainer_email': None,
      'name': 'sampleproject',
      'package_url': 'https://pypi.org/project/sampleproject/',
      'platform': 'UNKNOWN',
      'project_url': 'https://pypi.org/project/sampleproject/',
      'project_urls': {'Download': 'UNKNOWN',
                       'Homepage': 'https://github.com/pypa/sampleproject'},
      'release_url': 'https://pypi.org/project/sampleproject/1.2.0/',
      'requires_dist': None,
      'requires_python': None,
      'summary': 'A sample Python project',
      'version': '1.2.0'}

The result can be limited to a certain `depth' (ellipsis is used for
deeper contents):

     >>> pprint.pprint(project_info, depth=1)
     {'author': 'The Python Packaging Authority',
      'author_email': 'pypa-dev@googlegroups.com',
      'bugtrack_url': None,
      'classifiers': [...],
      'description': 'A sample Python project\n'
                     '=======================\n'
                     '\n'
                     'This is the description file for the project.\n'
                     '\n'
                     'The file should use UTF-8 encoding and be written using '
                     'ReStructured Text. It\n'
                     'will be used to generate the project webpage on PyPI, and '
                     'should be written for\n'
                     'that purpose.\n'
                     '\n'
                     'Typical contents for this file would include an overview of '
                     'the project, basic\n'
                     'usage examples, etc. Generally, including the project '
                     'changelog in here is not\n'
                     'a good idea, although a simple "What\'s New" section for the '
                     'most recent version\n'
                     'may be appropriate.',
      'description_content_type': None,
      'docs_url': None,
      'download_url': 'UNKNOWN',
      'downloads': {...},
      'home_page': 'https://github.com/pypa/sampleproject',
      'keywords': 'sample setuptools development',
      'license': 'MIT',
      'maintainer': None,
      'maintainer_email': None,
      'name': 'sampleproject',
      'package_url': 'https://pypi.org/project/sampleproject/',
      'platform': 'UNKNOWN',
      'project_url': 'https://pypi.org/project/sampleproject/',
      'project_urls': {...},
      'release_url': 'https://pypi.org/project/sampleproject/1.2.0/',
      'requires_dist': None,
      'requires_python': None,
      'summary': 'A sample Python project',
      'version': '1.2.0'}

Additionally, maximum character `width' can be suggested.  If a long
object cannot be split, the specified width will be exceeded:

     >>> pprint.pprint(project_info, depth=1, width=60)
     {'author': 'The Python Packaging Authority',
      'author_email': 'pypa-dev@googlegroups.com',
      'bugtrack_url': None,
      'classifiers': [...],
      'description': 'A sample Python project\n'
                     '=======================\n'
                     '\n'
                     'This is the description file for the '
                     'project.\n'
                     '\n'
                     'The file should use UTF-8 encoding and be '
                     'written using ReStructured Text. It\n'
                     'will be used to generate the project '
                     'webpage on PyPI, and should be written '
                     'for\n'
                     'that purpose.\n'
                     '\n'
                     'Typical contents for this file would '
                     'include an overview of the project, '
                     'basic\n'
                     'usage examples, etc. Generally, including '
                     'the project changelog in here is not\n'
                     'a good idea, although a simple "What\'s '
                     'New" section for the most recent version\n'
                     'may be appropriate.',
      'description_content_type': None,
      'docs_url': None,
      'download_url': 'UNKNOWN',
      'downloads': {...},
      'home_page': 'https://github.com/pypa/sampleproject',
      'keywords': 'sample setuptools development',
      'license': 'MIT',
      'maintainer': None,
      'maintainer_email': None,
      'name': 'sampleproject',
      'package_url': 'https://pypi.org/project/sampleproject/',
      'platform': 'UNKNOWN',
      'project_url': 'https://pypi.org/project/sampleproject/',
      'project_urls': {...},
      'release_url': 'https://pypi.org/project/sampleproject/1.2.0/',
      'requires_dist': None,
      'requires_python': None,
      'summary': 'A sample Python project',
      'version': '1.2.0'}

   ---------- Footnotes ----------

   (1) https://pypi.org


File: python.info,  Node: reprlib — Alternate repr implementation,  Next: enum — Support for enumerations,  Prev: pprint — Data pretty printer,  Up: Data Types

5.8.13 ‘reprlib’ — Alternate ‘repr()’ implementation
----------------------------------------------------

`Source code:' Lib/reprlib.py(1)

__________________________________________________________________

The *note reprlib: df. module provides a means for producing object
representations with limits on the size of the resulting strings.  This
is used in the Python debugger and may be useful in other contexts as
well.

This module provides a class, an instance, and a function:

 -- Class: reprlib.Repr

     Class which provides formatting services useful in implementing
     functions similar to the built-in *note repr(): 8b9.; size limits
     for different object types are added to avoid the generation of
     representations which are excessively long.

 -- Data: reprlib.aRepr

     This is an instance of *note Repr: 1b20. which is used to provide
     the *note repr(): 1b22. function described below.  Changing the
     attributes of this object will affect the size limits used by *note
     repr(): 1b22. and the Python debugger.

 -- Function: reprlib.repr (obj)

     This is the *note repr(): 1b23. method of ‘aRepr’.  It returns a
     string similar to that returned by the built-in function of the
     same name, but with limits on most sizes.

In addition to size-limiting tools, the module also provides a decorator
for detecting recursive calls to *note __repr__(): 44a. and substituting
a placeholder string instead.

 -- Function: @reprlib.recursive_repr (fillvalue="...")

     Decorator for *note __repr__(): 44a. methods to detect recursive
     calls within the same thread.  If a recursive call is made, the
     `fillvalue' is returned, otherwise, the usual *note __repr__():
     44a. call is made.  For example:

          >>> from reprlib import recursive_repr
          >>> class MyList(list):
          ...     @recursive_repr()
          ...     def __repr__(self):
          ...         return '<' + '|'.join(map(repr, self)) + '>'
          ...
          >>> m = MyList('abc')
          >>> m.append(m)
          >>> m.append('x')
          >>> print(m)
          <'a'|'b'|'c'|...|'x'>

     New in version 3.2.

* Menu:

* Repr Objects::
* Subclassing Repr Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/reprlib.py


File: python.info,  Node: Repr Objects,  Next: Subclassing Repr Objects,  Up: reprlib — Alternate repr implementation

5.8.13.1 Repr Objects
.....................

*note Repr: 1b20. instances provide several attributes which can be used
to provide size limits for the representations of different object
types, and methods which format specific object types.

 -- Attribute: Repr.maxlevel

     Depth limit on the creation of recursive representations.  The
     default is ‘6’.

 -- Attribute: Repr.maxdict
 -- Attribute: Repr.maxlist
 -- Attribute: Repr.maxtuple
 -- Attribute: Repr.maxset
 -- Attribute: Repr.maxfrozenset
 -- Attribute: Repr.maxdeque
 -- Attribute: Repr.maxarray

     Limits on the number of entries represented for the named object
     type.  The default is ‘4’ for *note maxdict: 1b27, ‘5’ for *note
     maxarray: 1b2d, and ‘6’ for the others.

 -- Attribute: Repr.maxlong

     Maximum number of characters in the representation for an integer.
     Digits are dropped from the middle.  The default is ‘40’.

 -- Attribute: Repr.maxstring

     Limit on the number of characters in the representation of the
     string.  Note that the “normal” representation of the string is
     used as the character source: if escape sequences are needed in the
     representation, these may be mangled when the representation is
     shortened.  The default is ‘30’.

 -- Attribute: Repr.maxother

     This limit is used to control the size of object types for which no
     specific formatting method is available on the *note Repr: 1b20.
     object.  It is applied in a similar manner as *note maxstring:
     1b2f.  The default is ‘20’.

 -- Method: Repr.repr (obj)

     The equivalent to the built-in *note repr(): 8b9. that uses the
     formatting imposed by the instance.

 -- Method: Repr.repr1 (obj, level)

     Recursive implementation used by *note repr(): 1b23.  This uses the
     type of `obj' to determine which formatting method to call, passing
     it `obj' and `level'.  The type-specific methods should call *note
     repr1(): 1b31. to perform recursive formatting, with ‘level - 1’
     for the value of `level' in the recursive call.

 -- Method: Repr.repr_TYPE (obj, level)

     Formatting methods for specific types are implemented as methods
     with a name based on the type name.  In the method name, `TYPE' is
     replaced by ‘'_'.join(type(obj).__name__.split())’.  Dispatch to
     these methods is handled by *note repr1(): 1b31.  Type-specific
     methods which need to recursively format a value should call
     ‘self.repr1(subobj, level - 1)’.


File: python.info,  Node: Subclassing Repr Objects,  Prev: Repr Objects,  Up: reprlib — Alternate repr implementation

5.8.13.2 Subclassing Repr Objects
.................................

The use of dynamic dispatching by *note Repr.repr1(): 1b31. allows
subclasses of *note Repr: 1b20. to add support for additional built-in
object types or to modify the handling of types already supported.  This
example shows how special support for file objects could be added:

     import reprlib
     import sys

     class MyRepr(reprlib.Repr):

         def repr_TextIOWrapper(self, obj, level):
             if obj.name in {'<stdin>', '<stdout>', '<stderr>'}:
                 return obj.name
             return repr(obj)

     aRepr = MyRepr()
     print(aRepr.repr(sys.stdin))         # prints '<stdin>'


File: python.info,  Node: enum — Support for enumerations,  Next: graphlib — Functionality to operate with graph-like structures,  Prev: reprlib — Alternate repr implementation,  Up: Data Types

5.8.14 ‘enum’ — Support for enumerations
----------------------------------------

New in version 3.4.

`Source code:' Lib/enum.py(1)

__________________________________________________________________

An enumeration is a set of symbolic names (members) bound to unique,
constant values.  Within an enumeration, the members can be compared by
identity, and the enumeration itself can be iterated over.

     Note: Case of Enum Members

     Because Enums are used to represent constants we recommend using
     UPPER_CASE names for enum members, and will be using that style in
     our examples.

* Menu:

* Module Contents: Module Contents<2>.
* Creating an Enum::
* Programmatic access to enumeration members and their attributes::
* Duplicating enum members and values::
* Ensuring unique enumeration values::
* Using automatic values::
* Iteration::
* Comparisons: Comparisons<3>.
* Allowed members and attributes of enumerations::
* Restricted Enum subclassing::
* Pickling::
* Functional API::
* Derived Enumerations::
* When to use __new__() vs. __init__(): When to use __new__ vs __init__.
* Interesting examples::
* How are Enums different?::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/enum.py


File: python.info,  Node: Module Contents<2>,  Next: Creating an Enum,  Up: enum — Support for enumerations

5.8.14.1 Module Contents
........................

This module defines four enumeration classes that can be used to define
unique sets of names and values: *note Enum: 48e, *note IntEnum: 684,
*note Flag: 63f, and *note IntFlag: 18a1.  It also defines one
decorator, *note unique(): 1b37, and one helper, *note auto: 640.

 -- Class: enum.Enum

     Base class for creating enumerated constants.  See section *note
     Functional API: 1b38. for an alternate construction syntax.

 -- Class: enum.IntEnum

     Base class for creating enumerated constants that are also
     subclasses of *note int: 204.

 -- Class: enum.IntFlag

     Base class for creating enumerated constants that can be combined
     using the bitwise operators without losing their *note IntFlag:
     18a1. membership.  *note IntFlag: 18a1. members are also subclasses
     of *note int: 204.

 -- Class: enum.Flag

     Base class for creating enumerated constants that can be combined
     using the bitwise operations without losing their *note Flag: 63f.
     membership.

 -- Function: enum.unique ()

     Enum class decorator that ensures only one name is bound to any one
     value.

 -- Class: enum.auto

     Instances are replaced with an appropriate value for Enum members.
     By default, the initial value starts at 1.

New in version 3.6: ‘Flag’, ‘IntFlag’, ‘auto’


File: python.info,  Node: Creating an Enum,  Next: Programmatic access to enumeration members and their attributes,  Prev: Module Contents<2>,  Up: enum — Support for enumerations

5.8.14.2 Creating an Enum
.........................

Enumerations are created using the *note class: d32. syntax, which makes
them easy to read and write.  An alternative creation method is
described in *note Functional API: 1b38.  To define an enumeration,
subclass *note Enum: 48e. as follows:

     >>> from enum import Enum
     >>> class Color(Enum):
     ...     RED = 1
     ...     GREEN = 2
     ...     BLUE = 3
     ...

     Note: Enum member values

     Member values can be anything: *note int: 204, *note str: 205,
     etc..  If the exact value is unimportant you may use *note auto:
     640. instances and an appropriate value will be chosen for you.
     Care must be taken if you mix *note auto: 640. with other values.

     Note: Nomenclature

        - The class ‘Color’ is an `enumeration' (or `enum')

        - The attributes ‘Color.RED’, ‘Color.GREEN’, etc., are
          `enumeration members' (or `enum members') and are functionally
          constants.

        - The enum members have `names' and `values' (the name of
          ‘Color.RED’ is ‘RED’, the value of ‘Color.BLUE’ is ‘3’, etc.)

     Note: Even though we use the *note class: d32. syntax to create
     Enums, Enums are not normal Python classes.  See *note How are
     Enums different?: 1b3a. for more details.

Enumeration members have human readable string representations:

     >>> print(Color.RED)
     Color.RED

…while their ‘repr’ has more information:

     >>> print(repr(Color.RED))
     <Color.RED: 1>

The `type' of an enumeration member is the enumeration it belongs to:

     >>> type(Color.RED)
     <enum 'Color'>
     >>> isinstance(Color.GREEN, Color)
     True
     >>>

Enum members also have a property that contains just their item name:

     >>> print(Color.RED.name)
     RED

Enumerations support iteration, in definition order:

     >>> class Shake(Enum):
     ...     VANILLA = 7
     ...     CHOCOLATE = 4
     ...     COOKIES = 9
     ...     MINT = 3
     ...
     >>> for shake in Shake:
     ...     print(shake)
     ...
     Shake.VANILLA
     Shake.CHOCOLATE
     Shake.COOKIES
     Shake.MINT

Enumeration members are hashable, so they can be used in dictionaries
and sets:

     >>> apples = {}
     >>> apples[Color.RED] = 'red delicious'
     >>> apples[Color.GREEN] = 'granny smith'
     >>> apples == {Color.RED: 'red delicious', Color.GREEN: 'granny smith'}
     True


File: python.info,  Node: Programmatic access to enumeration members and their attributes,  Next: Duplicating enum members and values,  Prev: Creating an Enum,  Up: enum — Support for enumerations

5.8.14.3 Programmatic access to enumeration members and their attributes
........................................................................

Sometimes it’s useful to access members in enumerations programmatically
(i.e.  situations where ‘Color.RED’ won’t do because the exact color is
not known at program-writing time).  ‘Enum’ allows such access:

     >>> Color(1)
     <Color.RED: 1>
     >>> Color(3)
     <Color.BLUE: 3>

If you want to access enum members by `name', use item access:

     >>> Color['RED']
     <Color.RED: 1>
     >>> Color['GREEN']
     <Color.GREEN: 2>

If you have an enum member and need its ‘name’ or ‘value’:

     >>> member = Color.RED
     >>> member.name
     'RED'
     >>> member.value
     1


File: python.info,  Node: Duplicating enum members and values,  Next: Ensuring unique enumeration values,  Prev: Programmatic access to enumeration members and their attributes,  Up: enum — Support for enumerations

5.8.14.4 Duplicating enum members and values
............................................

Having two enum members with the same name is invalid:

     >>> class Shape(Enum):
     ...     SQUARE = 2
     ...     SQUARE = 3
     ...
     Traceback (most recent call last):
     ...
     TypeError: Attempted to reuse key: 'SQUARE'

However, two enum members are allowed to have the same value.  Given two
members A and B with the same value (and A defined first), B is an alias
to A. By-value lookup of the value of A and B will return A. By-name
lookup of B will also return A:

     >>> class Shape(Enum):
     ...     SQUARE = 2
     ...     DIAMOND = 1
     ...     CIRCLE = 3
     ...     ALIAS_FOR_SQUARE = 2
     ...
     >>> Shape.SQUARE
     <Shape.SQUARE: 2>
     >>> Shape.ALIAS_FOR_SQUARE
     <Shape.SQUARE: 2>
     >>> Shape(2)
     <Shape.SQUARE: 2>

     Note: Attempting to create a member with the same name as an
     already defined attribute (another member, a method, etc.)  or
     attempting to create an attribute with the same name as a member is
     not allowed.


File: python.info,  Node: Ensuring unique enumeration values,  Next: Using automatic values,  Prev: Duplicating enum members and values,  Up: enum — Support for enumerations

5.8.14.5 Ensuring unique enumeration values
...........................................

By default, enumerations allow multiple names as aliases for the same
value.  When this behavior isn’t desired, the following decorator can be
used to ensure each value is used only once in the enumeration:

 -- Function: @enum.unique

A *note class: d32. decorator specifically for enumerations.  It
searches an enumeration’s ‘__members__’ gathering any aliases it finds;
if any are found *note ValueError: 16d. is raised with the details:

     >>> from enum import Enum, unique
     >>> @unique
     ... class Mistake(Enum):
     ...     ONE = 1
     ...     TWO = 2
     ...     THREE = 3
     ...     FOUR = 3
     ...
     Traceback (most recent call last):
     ...
     ValueError: duplicate values found in <enum 'Mistake'>: FOUR -> THREE


File: python.info,  Node: Using automatic values,  Next: Iteration,  Prev: Ensuring unique enumeration values,  Up: enum — Support for enumerations

5.8.14.6 Using automatic values
...............................

If the exact value is unimportant you can use *note auto: 640.:

     >>> from enum import Enum, auto
     >>> class Color(Enum):
     ...     RED = auto()
     ...     BLUE = auto()
     ...     GREEN = auto()
     ...
     >>> list(Color)
     [<Color.RED: 1>, <Color.BLUE: 2>, <Color.GREEN: 3>]

The values are chosen by ‘_generate_next_value_()’, which can be
overridden:

     >>> class AutoName(Enum):
     ...     def _generate_next_value_(name, start, count, last_values):
     ...         return name
     ...
     >>> class Ordinal(AutoName):
     ...     NORTH = auto()
     ...     SOUTH = auto()
     ...     EAST = auto()
     ...     WEST = auto()
     ...
     >>> list(Ordinal)
     [<Ordinal.NORTH: 'NORTH'>, <Ordinal.SOUTH: 'SOUTH'>, <Ordinal.EAST: 'EAST'>, <Ordinal.WEST: 'WEST'>]

     Note: The goal of the default ‘_generate_next_value_()’ method is
     to provide the next *note int: 204. in sequence with the last *note
     int: 204. provided, but the way it does this is an implementation
     detail and may change.

     Note: The ‘_generate_next_value_()’ method must be defined before
     any members.


File: python.info,  Node: Iteration,  Next: Comparisons<3>,  Prev: Using automatic values,  Up: enum — Support for enumerations

5.8.14.7 Iteration
..................

Iterating over the members of an enum does not provide the aliases:

     >>> list(Shape)
     [<Shape.SQUARE: 2>, <Shape.DIAMOND: 1>, <Shape.CIRCLE: 3>]

The special attribute ‘__members__’ is a read-only ordered mapping of
names to members.  It includes all names defined in the enumeration,
including the aliases:

     >>> for name, member in Shape.__members__.items():
     ...     name, member
     ...
     ('SQUARE', <Shape.SQUARE: 2>)
     ('DIAMOND', <Shape.DIAMOND: 1>)
     ('CIRCLE', <Shape.CIRCLE: 3>)
     ('ALIAS_FOR_SQUARE', <Shape.SQUARE: 2>)

The ‘__members__’ attribute can be used for detailed programmatic access
to the enumeration members.  For example, finding all the aliases:

     >>> [name for name, member in Shape.__members__.items() if member.name != name]
     ['ALIAS_FOR_SQUARE']


File: python.info,  Node: Comparisons<3>,  Next: Allowed members and attributes of enumerations,  Prev: Iteration,  Up: enum — Support for enumerations

5.8.14.8 Comparisons
....................

Enumeration members are compared by identity:

     >>> Color.RED is Color.RED
     True
     >>> Color.RED is Color.BLUE
     False
     >>> Color.RED is not Color.BLUE
     True

Ordered comparisons between enumeration values are `not' supported.
Enum members are not integers (but see *note IntEnum: 1b41. below):

     >>> Color.RED < Color.BLUE
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: '<' not supported between instances of 'Color' and 'Color'

Equality comparisons are defined though:

     >>> Color.BLUE == Color.RED
     False
     >>> Color.BLUE != Color.RED
     True
     >>> Color.BLUE == Color.BLUE
     True

Comparisons against non-enumeration values will always compare not equal
(again, *note IntEnum: 684. was explicitly designed to behave
differently, see below):

     >>> Color.BLUE == 2
     False


File: python.info,  Node: Allowed members and attributes of enumerations,  Next: Restricted Enum subclassing,  Prev: Comparisons<3>,  Up: enum — Support for enumerations

5.8.14.9 Allowed members and attributes of enumerations
.......................................................

The examples above use integers for enumeration values.  Using integers
is short and handy (and provided by default by the *note Functional API:
1b38.), but not strictly enforced.  In the vast majority of use-cases,
one doesn’t care what the actual value of an enumeration is.  But if the
value `is' important, enumerations can have arbitrary values.

Enumerations are Python classes, and can have methods and special
methods as usual.  If we have this enumeration:

     >>> class Mood(Enum):
     ...     FUNKY = 1
     ...     HAPPY = 3
     ...
     ...     def describe(self):
     ...         # self is the member here
     ...         return self.name, self.value
     ...
     ...     def __str__(self):
     ...         return 'my custom str! {0}'.format(self.value)
     ...
     ...     @classmethod
     ...     def favorite_mood(cls):
     ...         # cls here is the enumeration
     ...         return cls.HAPPY
     ...

Then:

     >>> Mood.favorite_mood()
     <Mood.HAPPY: 3>
     >>> Mood.HAPPY.describe()
     ('HAPPY', 3)
     >>> str(Mood.FUNKY)
     'my custom str! 1'

The rules for what is allowed are as follows: names that start and end
with a single underscore are reserved by enum and cannot be used; all
other attributes defined within an enumeration will become members of
this enumeration, with the exception of special methods (*note
__str__(): ef9, *note __add__(): 1595, etc.), descriptors (methods are
also descriptors), and variable names listed in ‘_ignore_’.

Note: if your enumeration defines *note __new__(): 974. and/or *note
__init__(): e23. then any value(s) given to the enum member will be
passed into those methods.  See *note Planet: 1b43. for an example.


File: python.info,  Node: Restricted Enum subclassing,  Next: Pickling,  Prev: Allowed members and attributes of enumerations,  Up: enum — Support for enumerations

5.8.14.10 Restricted Enum subclassing
.....................................

A new *note Enum: 48e. class must have one base Enum class, up to one
concrete data type, and as many *note object: 3d2.-based mixin classes
as needed.  The order of these base classes is:

     class EnumName([mix-in, ...,] [data-type,] base-enum):
         pass

Also, subclassing an enumeration is allowed only if the enumeration does
not define any members.  So this is forbidden:

     >>> class MoreColor(Color):
     ...     PINK = 17
     ...
     Traceback (most recent call last):
     ...
     TypeError: Cannot extend enumerations

But this is allowed:

     >>> class Foo(Enum):
     ...     def some_behavior(self):
     ...         pass
     ...
     >>> class Bar(Foo):
     ...     HAPPY = 1
     ...     SAD = 2
     ...

Allowing subclassing of enums that define members would lead to a
violation of some important invariants of types and instances.  On the
other hand, it makes sense to allow sharing some common behavior between
a group of enumerations.  (See *note OrderedEnum: 1b45. for an example.)


File: python.info,  Node: Pickling,  Next: Functional API,  Prev: Restricted Enum subclassing,  Up: enum — Support for enumerations

5.8.14.11 Pickling
..................

Enumerations can be pickled and unpickled:

     >>> from test.test_enum import Fruit
     >>> from pickle import dumps, loads
     >>> Fruit.TOMATO is loads(dumps(Fruit.TOMATO))
     True

The usual restrictions for pickling apply: picklable enums must be
defined in the top level of a module, since unpickling requires them to
be importable from that module.

     Note: With pickle protocol version 4 it is possible to easily
     pickle enums nested in other classes.

It is possible to modify how Enum members are pickled/unpickled by
defining *note __reduce_ex__(): 1b47. in the enumeration class.


File: python.info,  Node: Functional API,  Next: Derived Enumerations,  Prev: Pickling,  Up: enum — Support for enumerations

5.8.14.12 Functional API
........................

The *note Enum: 48e. class is callable, providing the following
functional API:

     >>> Animal = Enum('Animal', 'ANT BEE CAT DOG')
     >>> Animal
     <enum 'Animal'>
     >>> Animal.ANT
     <Animal.ANT: 1>
     >>> Animal.ANT.value
     1
     >>> list(Animal)
     [<Animal.ANT: 1>, <Animal.BEE: 2>, <Animal.CAT: 3>, <Animal.DOG: 4>]

The semantics of this API resemble *note namedtuple: 1a1.  The first
argument of the call to *note Enum: 48e. is the name of the enumeration.

The second argument is the `source' of enumeration member names.  It can
be a whitespace-separated string of names, a sequence of names, a
sequence of 2-tuples with key/value pairs, or a mapping (e.g.
dictionary) of names to values.  The last two options enable assigning
arbitrary values to enumerations; the others auto-assign increasing
integers starting with 1 (use the ‘start’ parameter to specify a
different starting value).  A new class derived from *note Enum: 48e. is
returned.  In other words, the above assignment to ‘Animal’ is
equivalent to:

     >>> class Animal(Enum):
     ...     ANT = 1
     ...     BEE = 2
     ...     CAT = 3
     ...     DOG = 4
     ...

The reason for defaulting to ‘1’ as the starting number and not ‘0’ is
that ‘0’ is ‘False’ in a boolean sense, but enum members all evaluate to
‘True’.

Pickling enums created with the functional API can be tricky as frame
stack implementation details are used to try and figure out which module
the enumeration is being created in (e.g.  it will fail if you use a
utility function in separate module, and also may not work on IronPython
or Jython).  The solution is to specify the module name explicitly as
follows:

     >>> Animal = Enum('Animal', 'ANT BEE CAT DOG', module=__name__)

     Warning: If ‘module’ is not supplied, and Enum cannot determine
     what it is, the new Enum members will not be unpicklable; to keep
     errors closer to the source, pickling will be disabled.

The new pickle protocol 4 also, in some circumstances, relies on *note
__qualname__: 155b. being set to the location where pickle will be able
to find the class.  For example, if the class was made available in
class SomeData in the global scope:

     >>> Animal = Enum('Animal', 'ANT BEE CAT DOG', qualname='SomeData.Animal')

The complete signature is:

     Enum(value='NewEnumName', names=<...>, *, module='...', qualname='...', type=<mixed-in class>, start=1)


value: What the new Enum class will record as its name.


names: The Enum members.  This can be a whitespace or comma separated
string (values will start at 1 unless otherwise specified):

     'RED GREEN BLUE' | 'RED,GREEN,BLUE' | 'RED, GREEN, BLUE'

or an iterator of names:

     ['RED', 'GREEN', 'BLUE']

or an iterator of (name, value) pairs:

     [('CYAN', 4), ('MAGENTA', 5), ('YELLOW', 6)]

or a mapping:

     {'CHARTREUSE': 7, 'SEA_GREEN': 11, 'ROSEMARY': 42}


module: name of module where new Enum class can be found.


qualname: where in module new Enum class can be found.


type: type to mix in to new Enum class.


start: number to start counting at if only names are passed in.

Changed in version 3.5: The `start' parameter was added.


File: python.info,  Node: Derived Enumerations,  Next: When to use __new__ vs __init__,  Prev: Functional API,  Up: enum — Support for enumerations

5.8.14.13 Derived Enumerations
..............................

* Menu:

* IntEnum::
* IntFlag::
* Flag::
* Others::


File: python.info,  Node: IntEnum,  Next: IntFlag,  Up: Derived Enumerations

5.8.14.14 IntEnum
.................

The first variation of *note Enum: 48e. that is provided is also a
subclass of *note int: 204.  Members of an *note IntEnum: 684. can be
compared to integers; by extension, integer enumerations of different
types can also be compared to each other:

     >>> from enum import IntEnum
     >>> class Shape(IntEnum):
     ...     CIRCLE = 1
     ...     SQUARE = 2
     ...
     >>> class Request(IntEnum):
     ...     POST = 1
     ...     GET = 2
     ...
     >>> Shape == 1
     False
     >>> Shape.CIRCLE == 1
     True
     >>> Shape.CIRCLE == Request.POST
     True

However, they still can’t be compared to standard *note Enum: 48e.
enumerations:

     >>> class Shape(IntEnum):
     ...     CIRCLE = 1
     ...     SQUARE = 2
     ...
     >>> class Color(Enum):
     ...     RED = 1
     ...     GREEN = 2
     ...
     >>> Shape.CIRCLE == Color.RED
     False

*note IntEnum: 684. values behave like integers in other ways you’d
expect:

     >>> int(Shape.CIRCLE)
     1
     >>> ['a', 'b', 'c'][Shape.CIRCLE]
     'b'
     >>> [i for i in range(Shape.SQUARE)]
     [0, 1]


File: python.info,  Node: IntFlag,  Next: Flag,  Prev: IntEnum,  Up: Derived Enumerations

5.8.14.15 IntFlag
.................

The next variation of *note Enum: 48e. provided, *note IntFlag: 18a1, is
also based on *note int: 204.  The difference being *note IntFlag: 18a1.
members can be combined using the bitwise operators (&, |, ^, ~) and the
result is still an *note IntFlag: 18a1. member.  However, as the name
implies, *note IntFlag: 18a1. members also subclass *note int: 204. and
can be used wherever an *note int: 204. is used.  Any operation on an
*note IntFlag: 18a1. member besides the bit-wise operations will lose
the *note IntFlag: 18a1. membership.

New in version 3.6.

Sample *note IntFlag: 18a1. class:

     >>> from enum import IntFlag
     >>> class Perm(IntFlag):
     ...     R = 4
     ...     W = 2
     ...     X = 1
     ...
     >>> Perm.R | Perm.W
     <Perm.R|W: 6>
     >>> Perm.R + Perm.W
     6
     >>> RW = Perm.R | Perm.W
     >>> Perm.R in RW
     True

It is also possible to name the combinations:

     >>> class Perm(IntFlag):
     ...     R = 4
     ...     W = 2
     ...     X = 1
     ...     RWX = 7
     >>> Perm.RWX
     <Perm.RWX: 7>
     >>> ~Perm.RWX
     <Perm.-8: -8>

Another important difference between *note IntFlag: 18a1. and *note
Enum: 48e. is that if no flags are set (the value is 0), its boolean
evaluation is *note False: 48f.:

     >>> Perm.R & Perm.X
     <Perm.0: 0>
     >>> bool(Perm.R & Perm.X)
     False

Because *note IntFlag: 18a1. members are also subclasses of *note int:
204. they can be combined with them:

     >>> Perm.X | 8
     <Perm.8|X: 9>


File: python.info,  Node: Flag,  Next: Others,  Prev: IntFlag,  Up: Derived Enumerations

5.8.14.16 Flag
..............

The last variation is *note Flag: 63f.  Like *note IntFlag: 18a1, *note
Flag: 63f. members can be combined using the bitwise operators (&, |, ^,
~).  Unlike *note IntFlag: 18a1, they cannot be combined with, nor
compared against, any other *note Flag: 63f. enumeration, nor *note int:
204.  While it is possible to specify the values directly it is
recommended to use *note auto: 640. as the value and let *note Flag:
63f. select an appropriate value.

New in version 3.6.

Like *note IntFlag: 18a1, if a combination of *note Flag: 63f. members
results in no flags being set, the boolean evaluation is *note False:
48f.:

     >>> from enum import Flag, auto
     >>> class Color(Flag):
     ...     RED = auto()
     ...     BLUE = auto()
     ...     GREEN = auto()
     ...
     >>> Color.RED & Color.GREEN
     <Color.0: 0>
     >>> bool(Color.RED & Color.GREEN)
     False

Individual flags should have values that are powers of two (1, 2, 4, 8,
…), while combinations of flags won’t:

     >>> class Color(Flag):
     ...     RED = auto()
     ...     BLUE = auto()
     ...     GREEN = auto()
     ...     WHITE = RED | BLUE | GREEN
     ...
     >>> Color.WHITE
     <Color.WHITE: 7>

Giving a name to the “no flags set” condition does not change its
boolean value:

     >>> class Color(Flag):
     ...     BLACK = 0
     ...     RED = auto()
     ...     BLUE = auto()
     ...     GREEN = auto()
     ...
     >>> Color.BLACK
     <Color.BLACK: 0>
     >>> bool(Color.BLACK)
     False

     Note: For the majority of new code, *note Enum: 48e. and *note
     Flag: 63f. are strongly recommended, since *note IntEnum: 684. and
     *note IntFlag: 18a1. break some semantic promises of an enumeration
     (by being comparable to integers, and thus by transitivity to other
     unrelated enumerations).  *note IntEnum: 684. and *note IntFlag:
     18a1. should be used only in cases where *note Enum: 48e. and *note
     Flag: 63f. will not do; for example, when integer constants are
     replaced with enumerations, or for interoperability with other
     systems.


File: python.info,  Node: Others,  Prev: Flag,  Up: Derived Enumerations

5.8.14.17 Others
................

While *note IntEnum: 684. is part of the *note enum: 79. module, it
would be very simple to implement independently:

     class IntEnum(int, Enum):
         pass

This demonstrates how similar derived enumerations can be defined; for
example a ‘StrEnum’ that mixes in *note str: 205. instead of *note int:
204.

Some rules:

  1. When subclassing *note Enum: 48e, mix-in types must appear before
     *note Enum: 48e. itself in the sequence of bases, as in the *note
     IntEnum: 684. example above.

  2. While *note Enum: 48e. can have members of any type, once you mix
     in an additional type, all the members must have values of that
     type, e.g.  *note int: 204. above.  This restriction does not apply
     to mix-ins which only add methods and don’t specify another type.

  3. When another data type is mixed in, the ‘value’ attribute is `not
     the same' as the enum member itself, although it is equivalent and
     will compare equal.

  4. %-style formatting: ‘%s’ and ‘%r’ call the *note Enum: 48e. class’s
     *note __str__(): ef9. and *note __repr__(): 44a. respectively;
     other codes (such as ‘%i’ or ‘%h’ for IntEnum) treat the enum
     member as its mixed-in type.

  5. *note Formatted string literals: 296, *note str.format(): 5d5, and
     *note format(): 5d6. will use the mixed-in type’s *note
     __format__(): a2f. unless *note __str__(): ef9. or *note
     __format__(): a2f. is overridden in the subclass, in which case the
     overridden methods or *note Enum: 48e. methods will be used.  Use
     the !s and !r format codes to force usage of the *note Enum: 48e.
     class’s *note __str__(): ef9. and *note __repr__(): 44a. methods.


File: python.info,  Node: When to use __new__ vs __init__,  Next: Interesting examples,  Prev: Derived Enumerations,  Up: enum — Support for enumerations

5.8.14.18 When to use ‘__new__()’ vs. ‘__init__()’
..................................................

*note __new__(): 974. must be used whenever you want to customize the
actual value of the *note Enum: 48e. member.  Any other modifications
may go in either *note __new__(): 974. or *note __init__(): e23, with
*note __init__(): e23. being preferred.

For example, if you want to pass several items to the constructor, but
only want one of them to be the value:

     >>> class Coordinate(bytes, Enum):
     ...     """
     ...     Coordinate with binary codes that can be indexed by the int code.
     ...     """
     ...     def __new__(cls, value, label, unit):
     ...         obj = bytes.__new__(cls, [value])
     ...         obj._value_ = value
     ...         obj.label = label
     ...         obj.unit = unit
     ...         return obj
     ...     PX = (0, 'P.X', 'km')
     ...     PY = (1, 'P.Y', 'km')
     ...     VX = (2, 'V.X', 'km/s')
     ...     VY = (3, 'V.Y', 'km/s')
     ...

     >>> print(Coordinate['PY'])
     Coordinate.PY

     >>> print(Coordinate(3))
     Coordinate.VY


File: python.info,  Node: Interesting examples,  Next: How are Enums different?,  Prev: When to use __new__ vs __init__,  Up: enum — Support for enumerations

5.8.14.19 Interesting examples
..............................

While *note Enum: 48e, *note IntEnum: 684, *note IntFlag: 18a1, and
*note Flag: 63f. are expected to cover the majority of use-cases, they
cannot cover them all.  Here are recipes for some different types of
enumerations that can be used directly, or as examples for creating
one’s own.

* Menu:

* Omitting values::
* OrderedEnum::
* DuplicateFreeEnum::
* Planet::
* TimePeriod::


File: python.info,  Node: Omitting values,  Next: OrderedEnum,  Up: Interesting examples

5.8.14.20 Omitting values
.........................

In many use-cases one doesn’t care what the actual value of an
enumeration is.  There are several ways to define this type of simple
enumeration:

   - use instances of *note auto: 640. for the value

   - use instances of *note object: 3d2. as the value

   - use a descriptive string as the value

   - use a tuple as the value and a custom *note __new__(): 974. to
     replace the tuple with an *note int: 204. value

Using any of these methods signifies to the user that these values are
not important, and also enables one to add, remove, or reorder members
without having to renumber the remaining members.

Whichever method you choose, you should provide a *note repr(): 8b9.
that also hides the (unimportant) value:

     >>> class NoValue(Enum):
     ...     def __repr__(self):
     ...         return '<%s.%s>' % (self.__class__.__name__, self.name)
     ...

* Menu:

* Using auto::
* Using object::
* Using a descriptive string::
* Using a custom __new__(): Using a custom __new__.


File: python.info,  Node: Using auto,  Next: Using object,  Up: Omitting values

5.8.14.21 Using ‘auto’
......................

Using *note auto: 640. would look like:

     >>> class Color(NoValue):
     ...     RED = auto()
     ...     BLUE = auto()
     ...     GREEN = auto()
     ...
     >>> Color.GREEN
     <Color.GREEN>


File: python.info,  Node: Using object,  Next: Using a descriptive string,  Prev: Using auto,  Up: Omitting values

5.8.14.22 Using ‘object’
........................

Using *note object: 3d2. would look like:

     >>> class Color(NoValue):
     ...     RED = object()
     ...     GREEN = object()
     ...     BLUE = object()
     ...
     >>> Color.GREEN
     <Color.GREEN>


File: python.info,  Node: Using a descriptive string,  Next: Using a custom __new__,  Prev: Using object,  Up: Omitting values

5.8.14.23 Using a descriptive string
....................................

Using a string as the value would look like:

     >>> class Color(NoValue):
     ...     RED = 'stop'
     ...     GREEN = 'go'
     ...     BLUE = 'too fast!'
     ...
     >>> Color.GREEN
     <Color.GREEN>
     >>> Color.GREEN.value
     'go'


File: python.info,  Node: Using a custom __new__,  Prev: Using a descriptive string,  Up: Omitting values

5.8.14.24 Using a custom ‘__new__()’
....................................

Using an auto-numbering *note __new__(): 974. would look like:

     >>> class AutoNumber(NoValue):
     ...     def __new__(cls):
     ...         value = len(cls.__members__) + 1
     ...         obj = object.__new__(cls)
     ...         obj._value_ = value
     ...         return obj
     ...
     >>> class Color(AutoNumber):
     ...     RED = ()
     ...     GREEN = ()
     ...     BLUE = ()
     ...
     >>> Color.GREEN
     <Color.GREEN>
     >>> Color.GREEN.value
     2

To make a more general purpose ‘AutoNumber’, add ‘*args’ to the
signature:

     >>> class AutoNumber(NoValue):
     ...     def __new__(cls, *args):      # this is the only change from above
     ...         value = len(cls.__members__) + 1
     ...         obj = object.__new__(cls)
     ...         obj._value_ = value
     ...         return obj
     ...

Then when you inherit from ‘AutoNumber’ you can write your own
‘__init__’ to handle any extra arguments:

     >>> class Swatch(AutoNumber):
     ...     def __init__(self, pantone='unknown'):
     ...         self.pantone = pantone
     ...     AUBURN = '3497'
     ...     SEA_GREEN = '1246'
     ...     BLEACHED_CORAL = () # New color, no Pantone code yet!
     ...
     >>> Swatch.SEA_GREEN
     <Swatch.SEA_GREEN: 2>
     >>> Swatch.SEA_GREEN.pantone
     '1246'
     >>> Swatch.BLEACHED_CORAL.pantone
     'unknown'

     Note: The *note __new__(): 974. method, if defined, is used during
     creation of the Enum members; it is then replaced by Enum’s *note
     __new__(): 974. which is used after class creation for lookup of
     existing members.


File: python.info,  Node: OrderedEnum,  Next: DuplicateFreeEnum,  Prev: Omitting values,  Up: Interesting examples

5.8.14.25 OrderedEnum
.....................

An ordered enumeration that is not based on *note IntEnum: 684. and so
maintains the normal *note Enum: 48e. invariants (such as not being
comparable to other enumerations):

     >>> class OrderedEnum(Enum):
     ...     def __ge__(self, other):
     ...         if self.__class__ is other.__class__:
     ...             return self.value >= other.value
     ...         return NotImplemented
     ...     def __gt__(self, other):
     ...         if self.__class__ is other.__class__:
     ...             return self.value > other.value
     ...         return NotImplemented
     ...     def __le__(self, other):
     ...         if self.__class__ is other.__class__:
     ...             return self.value <= other.value
     ...         return NotImplemented
     ...     def __lt__(self, other):
     ...         if self.__class__ is other.__class__:
     ...             return self.value < other.value
     ...         return NotImplemented
     ...
     >>> class Grade(OrderedEnum):
     ...     A = 5
     ...     B = 4
     ...     C = 3
     ...     D = 2
     ...     F = 1
     ...
     >>> Grade.C < Grade.A
     True


File: python.info,  Node: DuplicateFreeEnum,  Next: Planet,  Prev: OrderedEnum,  Up: Interesting examples

5.8.14.26 DuplicateFreeEnum
...........................

Raises an error if a duplicate member name is found instead of creating
an alias:

     >>> class DuplicateFreeEnum(Enum):
     ...     def __init__(self, *args):
     ...         cls = self.__class__
     ...         if any(self.value == e.value for e in cls):
     ...             a = self.name
     ...             e = cls(self.value).name
     ...             raise ValueError(
     ...                 "aliases not allowed in DuplicateFreeEnum:  %r --> %r"
     ...                 % (a, e))
     ...
     >>> class Color(DuplicateFreeEnum):
     ...     RED = 1
     ...     GREEN = 2
     ...     BLUE = 3
     ...     GRENE = 2
     ...
     Traceback (most recent call last):
     ...
     ValueError: aliases not allowed in DuplicateFreeEnum:  'GRENE' --> 'GREEN'

     Note: This is a useful example for subclassing Enum to add or
     change other behaviors as well as disallowing aliases.  If the only
     desired change is disallowing aliases, the *note unique(): 1b37.
     decorator can be used instead.


File: python.info,  Node: Planet,  Next: TimePeriod,  Prev: DuplicateFreeEnum,  Up: Interesting examples

5.8.14.27 Planet
................

If *note __new__(): 974. or *note __init__(): e23. is defined the value
of the enum member will be passed to those methods:

     >>> class Planet(Enum):
     ...     MERCURY = (3.303e+23, 2.4397e6)
     ...     VENUS   = (4.869e+24, 6.0518e6)
     ...     EARTH   = (5.976e+24, 6.37814e6)
     ...     MARS    = (6.421e+23, 3.3972e6)
     ...     JUPITER = (1.9e+27,   7.1492e7)
     ...     SATURN  = (5.688e+26, 6.0268e7)
     ...     URANUS  = (8.686e+25, 2.5559e7)
     ...     NEPTUNE = (1.024e+26, 2.4746e7)
     ...     def __init__(self, mass, radius):
     ...         self.mass = mass       # in kilograms
     ...         self.radius = radius   # in meters
     ...     @property
     ...     def surface_gravity(self):
     ...         # universal gravitational constant  (m3 kg-1 s-2)
     ...         G = 6.67300E-11
     ...         return G * self.mass / (self.radius * self.radius)
     ...
     >>> Planet.EARTH.value
     (5.976e+24, 6378140.0)
     >>> Planet.EARTH.surface_gravity
     9.802652743337129


File: python.info,  Node: TimePeriod,  Prev: Planet,  Up: Interesting examples

5.8.14.28 TimePeriod
....................

An example to show the ‘_ignore_’ attribute in use:

     >>> from datetime import timedelta
     >>> class Period(timedelta, Enum):
     ...     "different lengths of time"
     ...     _ignore_ = 'Period i'
     ...     Period = vars()
     ...     for i in range(367):
     ...         Period['day_%d' % i] = i
     ...
     >>> list(Period)[:2]
     [<Period.day_0: datetime.timedelta(0)>, <Period.day_1: datetime.timedelta(days=1)>]
     >>> list(Period)[-2:]
     [<Period.day_365: datetime.timedelta(days=365)>, <Period.day_366: datetime.timedelta(days=366)>]


File: python.info,  Node: How are Enums different?,  Prev: Interesting examples,  Up: enum — Support for enumerations

5.8.14.29 How are Enums different?
..................................

Enums have a custom metaclass that affects many aspects of both derived
Enum classes and their instances (members).

* Menu:

* Enum Classes::
* Enum Members (aka instances): Enum Members aka instances.
* Finer Points::


File: python.info,  Node: Enum Classes,  Next: Enum Members aka instances,  Up: How are Enums different?

5.8.14.30 Enum Classes
......................

The ‘EnumMeta’ metaclass is responsible for providing the *note
__contains__(): dee, *note __dir__(): 42b, *note __iter__(): 609. and
other methods that allow one to do things with an *note Enum: 48e. class
that fail on a typical class, such as ‘list(Color)’ or ‘some_enum_var in
Color’.  ‘EnumMeta’ is responsible for ensuring that various other
methods on the final *note Enum: 48e. class are correct (such as *note
__new__(): 974, *note __getnewargs__(): 7a1, *note __str__(): ef9. and
*note __repr__(): 44a.).


File: python.info,  Node: Enum Members aka instances,  Next: Finer Points,  Prev: Enum Classes,  Up: How are Enums different?

5.8.14.31 Enum Members (aka instances)
......................................

The most interesting thing about Enum members is that they are
singletons.  ‘EnumMeta’ creates them all while it is creating the *note
Enum: 48e. class itself, and then puts a custom *note __new__(): 974. in
place to ensure that no new ones are ever instantiated by returning only
the existing member instances.


File: python.info,  Node: Finer Points,  Prev: Enum Members aka instances,  Up: How are Enums different?

5.8.14.32 Finer Points
......................

* Menu:

* Supported __dunder__ names::
* Supported _sunder_ names::
* _Private__names::
* Enum member type::
* Boolean value of Enum classes and members::
* Enum classes with methods::
* Combining members of Flag::


File: python.info,  Node: Supported __dunder__ names,  Next: Supported _sunder_ names,  Up: Finer Points

5.8.14.33 Supported ‘__dunder__’ names
......................................

‘__members__’ is a read-only ordered mapping of ‘member_name’:‘member’
items.  It is only available on the class.

*note __new__(): 974, if specified, must create and return the enum
members; it is also a very good idea to set the member’s ‘_value_’
appropriately.  Once all the members are created it is no longer used.


File: python.info,  Node: Supported _sunder_ names,  Next: _Private__names,  Prev: Supported __dunder__ names,  Up: Finer Points

5.8.14.34 Supported ‘_sunder_’ names
....................................

   - ‘_name_’ – name of the member

   - ‘_value_’ – value of the member; can be set / modified in ‘__new__’

   - ‘_missing_’ – a lookup function used when a value is not found; may
     be overridden

   - ‘_ignore_’ – a list of names, either as a *note list: 1f8. or a
     *note str: 205, that will not be transformed into members, and will
     be removed from the final class

   - ‘_order_’ – used in Python 2/3 code to ensure member order is
     consistent (class attribute, removed during class creation)

   - ‘_generate_next_value_’ – used by the *note Functional API: 1b38.
     and by *note auto: 640. to get an appropriate value for an enum
     member; may be overridden

New in version 3.6: ‘_missing_’, ‘_order_’, ‘_generate_next_value_’

New in version 3.7: ‘_ignore_’

To help keep Python 2 / Python 3 code in sync an ‘_order_’ attribute can
be provided.  It will be checked against the actual order of the
enumeration and raise an error if the two do not match:

     >>> class Color(Enum):
     ...     _order_ = 'RED GREEN BLUE'
     ...     RED = 1
     ...     BLUE = 3
     ...     GREEN = 2
     ...
     Traceback (most recent call last):
     ...
     TypeError: member order does not match _order_

     Note: In Python 2 code the ‘_order_’ attribute is necessary as
     definition order is lost before it can be recorded.


File: python.info,  Node: _Private__names,  Next: Enum member type,  Prev: Supported _sunder_ names,  Up: Finer Points

5.8.14.35 _Private__names
.........................

*note Private names: 1621. will be normal attributes in Python 3.11
instead of either an error or a member (depending on if the name ends
with an underscore).  Using these names in 3.9 and 3.10 will issue a
*note DeprecationWarning: 15a.


File: python.info,  Node: Enum member type,  Next: Boolean value of Enum classes and members,  Prev: _Private__names,  Up: Finer Points

5.8.14.36 ‘Enum’ member type
............................

*note Enum: 48e. members are instances of their *note Enum: 48e. class,
and are normally accessed as ‘EnumClass.member’.  Under certain
circumstances they can also be accessed as ‘EnumClass.member.member’,
but you should never do this as that lookup may fail or, worse, return
something besides the *note Enum: 48e. member you are looking for (this
is another good reason to use all-uppercase names for members):

     >>> class FieldTypes(Enum):
     ...     name = 0
     ...     value = 1
     ...     size = 2
     ...
     >>> FieldTypes.value.size
     <FieldTypes.size: 2>
     >>> FieldTypes.size.value
     2

     Note: This behavior is deprecated and will be removed in 3.11.

Changed in version 3.5.


File: python.info,  Node: Boolean value of Enum classes and members,  Next: Enum classes with methods,  Prev: Enum member type,  Up: Finer Points

5.8.14.37 Boolean value of ‘Enum’ classes and members
.....................................................

*note Enum: 48e. members that are mixed with non-*note Enum: 48e. types
(such as *note int: 204, *note str: 205, etc.)  are evaluated according
to the mixed-in type’s rules; otherwise, all members evaluate as *note
True: 594.  To make your own Enum’s boolean evaluation depend on the
member’s value add the following to your class:

     def __bool__(self):
         return bool(self.value)

*note Enum: 48e. classes always evaluate as *note True: 594.


File: python.info,  Node: Enum classes with methods,  Next: Combining members of Flag,  Prev: Boolean value of Enum classes and members,  Up: Finer Points

5.8.14.38 ‘Enum’ classes with methods
.....................................

If you give your *note Enum: 48e. subclass extra methods, like the *note
Planet: 1b43. class above, those methods will show up in a *note dir():
df9. of the member, but not of the class:

     >>> dir(Planet)
     ['EARTH', 'JUPITER', 'MARS', 'MERCURY', 'NEPTUNE', 'SATURN', 'URANUS', 'VENUS', '__class__', '__doc__', '__members__', '__module__']
     >>> dir(Planet.EARTH)
     ['__class__', '__doc__', '__module__', 'name', 'surface_gravity', 'value']


File: python.info,  Node: Combining members of Flag,  Prev: Enum classes with methods,  Up: Finer Points

5.8.14.39 Combining members of ‘Flag’
.....................................

If a combination of Flag members is not named, the *note repr(): 8b9.
will include all named flags and all named combinations of flags that
are in the value:

     >>> class Color(Flag):
     ...     RED = auto()
     ...     GREEN = auto()
     ...     BLUE = auto()
     ...     MAGENTA = RED | BLUE
     ...     YELLOW = RED | GREEN
     ...     CYAN = GREEN | BLUE
     ...
     >>> Color(3)  # named combination
     <Color.YELLOW: 3>
     >>> Color(7)      # not named combination
     <Color.CYAN|MAGENTA|BLUE|YELLOW|GREEN|RED: 7>

     Note: In 3.11 unnamed combinations of flags will only produce the
     canonical flag members (aka single-value flags).  So ‘Color(7)’
     would produce something like ‘<Color.BLUE|GREEN|RED: 7>’.


File: python.info,  Node: graphlib — Functionality to operate with graph-like structures,  Prev: enum — Support for enumerations,  Up: Data Types

5.8.15 ‘graphlib’ — Functionality to operate with graph-like structures
-----------------------------------------------------------------------

`Source code:' Lib/graphlib.py(1)

__________________________________________________________________

 -- Class: graphlib.TopologicalSorter (graph=None)

     Provides functionality to topologically sort a graph of hashable
     nodes.

     A topological order is a linear ordering of the vertices in a graph
     such that for every directed edge u -> v from vertex u to vertex v,
     vertex u comes before vertex v in the ordering.  For instance, the
     vertices of the graph may represent tasks to be performed, and the
     edges may represent constraints that one task must be performed
     before another; in this example, a topological ordering is just a
     valid sequence for the tasks.  A complete topological ordering is
     possible if and only if the graph has no directed cycles, that is,
     if it is a directed acyclic graph.

     If the optional `graph' argument is provided it must be a
     dictionary representing a directed acyclic graph where the keys are
     nodes and the values are iterables of all predecessors of that node
     in the graph (the nodes that have edges that point to the value in
     the key).  Additional nodes can be added to the graph using the
     *note add(): 1b61. method.

     In the general case, the steps required to perform the sorting of a
     given graph are as follows:

             * Create an instance of the *note TopologicalSorter: 182.
               with an optional initial graph.

             * Add additional nodes to the graph.

             * Call *note prepare(): 1b62. on the graph.

             * While *note is_active(): 1b63. is ‘True’, iterate over
               the nodes returned by *note get_ready(): 1b64. and
               process them.  Call *note done(): 1b65. on each node as
               it finishes processing.

     In case just an immediate sorting of the nodes in the graph is
     required and no parallelism is involved, the convenience method
     *note TopologicalSorter.static_order(): 1b66. can be used directly:

          >>> graph = {"D": {"B", "C"}, "C": {"A"}, "B": {"A"}}
          >>> ts = TopologicalSorter(graph)
          >>> tuple(ts.static_order())
          ('A', 'C', 'B', 'D')

     The class is designed to easily support parallel processing of the
     nodes as they become ready.  For instance:

          topological_sorter = TopologicalSorter()

          # Add nodes to 'topological_sorter'...

          topological_sorter.prepare()
          while topological_sorter.is_active():
              for node in topological_sorter.get_ready():
                  # Worker threads or processes take nodes to work on off the
                  # 'task_queue' queue.
                  task_queue.put(node)

              # When the work for a node is done, workers put the node in
              # 'finalized_tasks_queue' so we can get more nodes to work on.
              # The definition of 'is_active()' guarantees that, at this point, at
              # least one node has been placed on 'task_queue' that hasn't yet
              # been passed to 'done()', so this blocking 'get()' must (eventually)
              # succeed.  After calling 'done()', we loop back to call 'get_ready()'
              # again, so put newly freed nodes on 'task_queue' as soon as
              # logically possible.
              node = finalized_tasks_queue.get()
              topological_sorter.done(node)

      -- Method: add (node, *predecessors)

          Add a new node and its predecessors to the graph.  Both the
          `node' and all elements in `predecessors' must be hashable.

          If called multiple times with the same node argument, the set
          of dependencies will be the union of all dependencies passed
          in.

          It is possible to add a node with no dependencies
          (`predecessors' is not provided) or to provide a dependency
          twice.  If a node that has not been provided before is
          included among `predecessors' it will be automatically added
          to the graph with no predecessors of its own.

          Raises *note ValueError: 16d. if called after *note prepare():
          1b62.

      -- Method: prepare ()

          Mark the graph as finished and check for cycles in the graph.
          If any cycle is detected, *note CycleError: 1b67. will be
          raised, but *note get_ready(): 1b64. can still be used to
          obtain as many nodes as possible until cycles block more
          progress.  After a call to this function, the graph cannot be
          modified, and therefore no more nodes can be added using *note
          add(): 1b61.

      -- Method: is_active ()

          Returns ‘True’ if more progress can be made and ‘False’
          otherwise.  Progress can be made if cycles do not block the
          resolution and either there are still nodes ready that haven’t
          yet been returned by *note TopologicalSorter.get_ready():
          1b64. or the number of nodes marked *note
          TopologicalSorter.done(): 1b65. is less than the number that
          have been returned by *note TopologicalSorter.get_ready():
          1b64.

          The ‘__bool__()’ method of this class defers to this function,
          so instead of:

               if ts.is_active():
                   ...

          it is possible to simply do:

               if ts:
                   ...

          Raises *note ValueError: 16d. if called without calling *note
          prepare(): 1b62. previously.

      -- Method: done (*nodes)

          Marks a set of nodes returned by *note
          TopologicalSorter.get_ready(): 1b64. as processed, unblocking
          any successor of each node in `nodes' for being returned in
          the future by a call to *note TopologicalSorter.get_ready():
          1b64.

          Raises *note ValueError: 16d. if any node in `nodes' has
          already been marked as processed by a previous call to this
          method or if a node was not added to the graph by using *note
          TopologicalSorter.add(): 1b61, if called without calling *note
          prepare(): 1b62. or if node has not yet been returned by *note
          get_ready(): 1b64.

      -- Method: get_ready ()

          Returns a ‘tuple’ with all the nodes that are ready.
          Initially it returns all nodes with no predecessors, and once
          those are marked as processed by calling *note
          TopologicalSorter.done(): 1b65, further calls will return all
          new nodes that have all their predecessors already processed.
          Once no more progress can be made, empty tuples are returned.

          Raises *note ValueError: 16d. if called without calling *note
          prepare(): 1b62. previously.

      -- Method: static_order ()

          Returns an iterator object which will iterate over nodes in a
          topological order.  When using this method, *note prepare():
          1b62. and *note done(): 1b65. should not be called.  This
          method is equivalent to:

               def static_order(self):
                   self.prepare()
                   while self.is_active():
                       node_group = self.get_ready()
                       yield from node_group
                       self.done(*node_group)

          The particular order that is returned may depend on the
          specific order in which the items were inserted in the graph.
          For example:

               >>> ts = TopologicalSorter()
               >>> ts.add(3, 2, 1)
               >>> ts.add(1, 0)
               >>> print([*ts.static_order()])
               [2, 0, 1, 3]

               >>> ts2 = TopologicalSorter()
               >>> ts2.add(1, 0)
               >>> ts2.add(3, 2, 1)
               >>> print([*ts2.static_order()])
               [0, 2, 1, 3]

          This is due to the fact that “0” and “2” are in the same level
          in the graph (they would have been returned in the same call
          to *note get_ready(): 1b64.) and the order between them is
          determined by the order of insertion.

          If any cycle is detected, *note CycleError: 1b67. will be
          raised.

     New in version 3.9.

* Menu:

* Exceptions: Exceptions<3>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/graphlib.py


File: python.info,  Node: Exceptions<3>,  Up: graphlib — Functionality to operate with graph-like structures

5.8.15.1 Exceptions
...................

The *note graphlib: 89. module defines the following exception classes:

 -- Exception: graphlib.CycleError

     Subclass of *note ValueError: 16d. raised by *note
     TopologicalSorter.prepare(): 1b62. if cycles exist in the working
     graph.  If multiple cycles exist, only one undefined choice among
     them will be reported and included in the exception.

     The detected cycle can be accessed via the second element in the
     ‘args’ attribute of the exception instance and consists in a list
     of nodes, such that each node is, in the graph, an immediate
     predecessor of the next node in the list.  In the reported list,
     the first and the last node will be the same, to make it clear that
     it is cyclic.


File: python.info,  Node: Numeric and Mathematical Modules,  Next: Functional Programming Modules,  Prev: Data Types,  Up: The Python Standard Library

5.9 Numeric and Mathematical Modules
====================================

The modules described in this chapter provide numeric and math-related
functions and data types.  The *note numbers: c1. module defines an
abstract hierarchy of numeric types.  The *note math: b1. and *note
cmath: 18. modules contain various mathematical functions for
floating-point and complex numbers.  The *note decimal: 35. module
supports exact representations of decimal numbers, using arbitrary
precision arithmetic.

The following modules are documented in this chapter:

* Menu:

* numbers — Numeric abstract base classes::
* math — Mathematical functions::
* cmath — Mathematical functions for complex numbers::
* decimal — Decimal fixed point and floating point arithmetic::
* fractions — Rational numbers::
* random — Generate pseudo-random numbers::
* statistics — Mathematical statistics functions::


File: python.info,  Node: numbers — Numeric abstract base classes,  Next: math — Mathematical functions,  Up: Numeric and Mathematical Modules

5.9.1 ‘numbers’ — Numeric abstract base classes
-----------------------------------------------

`Source code:' Lib/numbers.py(1)

__________________________________________________________________

The *note numbers: c1. module ( PEP 3141(2)) defines a hierarchy of
numeric *note abstract base classes: c05. which progressively define
more operations.  None of the types defined in this module are intended
to be instantiated.

 -- Class: numbers.Number

     The root of the numeric hierarchy.  If you just want to check if an
     argument `x' is a number, without caring what kind, use
     ‘isinstance(x, Number)’.

* Menu:

* The numeric tower::
* Notes for type implementors::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/numbers.py

   (2) https://www.python.org/dev/peps/pep-3141


File: python.info,  Node: The numeric tower,  Next: Notes for type implementors,  Up: numbers — Numeric abstract base classes

5.9.1.1 The numeric tower
.........................

 -- Class: numbers.Complex

     Subclasses of this type describe complex numbers and include the
     operations that work on the built-in *note complex: 2c1. type.
     These are: conversions to *note complex: 2c1. and *note bool: 2bd,
     *note real: 1b6f, *note imag: 1b70, ‘+’, ‘-’, ‘*’, ‘/’, ‘**’, *note
     abs(): 13f3, *note conjugate(): 1b71, ‘==’, and ‘!=’.  All except
     ‘-’ and ‘!=’ are abstract.

      -- Attribute: real

          Abstract.  Retrieves the real component of this number.

      -- Attribute: imag

          Abstract.  Retrieves the imaginary component of this number.

      -- Method: abstractmethod conjugate ()

          Abstract.  Returns the complex conjugate.  For example,
          ‘(1+3j).conjugate() == (1-3j)’.

 -- Class: numbers.Real

     To *note Complex: 1558, *note Real: 1557. adds the operations that
     work on real numbers.

     In short, those are: a conversion to *note float: 1fd, *note
     math.trunc(): df4, *note round(): d35, *note math.floor(): df2,
     *note math.ceil(): df3, *note divmod(): 28d, ‘//’, ‘%’, ‘<’, ‘<=’,
     ‘>’, and ‘>=’.

     Real also provides defaults for *note complex(): 2c1, *note real:
     1b6f, *note imag: 1b70, and *note conjugate(): 1b71.

 -- Class: numbers.Rational

     Subtypes *note Real: 1557. and adds *note numerator: 1b72. and
     *note denominator: 1b73. properties, which should be in lowest
     terms.  With these, it provides a default for *note float(): 1fd.

      -- Attribute: numerator

          Abstract.

      -- Attribute: denominator

          Abstract.

 -- Class: numbers.Integral

     Subtypes *note Rational: d20. and adds a conversion to *note int:
     204.  Provides defaults for *note float(): 1fd, *note numerator:
     1b72, and *note denominator: 1b73.  Adds abstract methods for *note
     pow(): 2cf. with modulus and bit-string operations: ‘<<’, ‘>>’,
     ‘&’, ‘^’, ‘|’, ‘~’.


File: python.info,  Node: Notes for type implementors,  Prev: The numeric tower,  Up: numbers — Numeric abstract base classes

5.9.1.2 Notes for type implementors
...................................

Implementors should be careful to make equal numbers equal and hash them
to the same values.  This may be subtle if there are two different
extensions of the real numbers.  For example, *note fractions.Fraction:
2be. implements *note hash(): aa3. as follows:

     def __hash__(self):
         if self.denominator == 1:
             # Get integers right.
             return hash(self.numerator)
         # Expensive check, but definitely correct.
         if self == float(self):
             return hash(float(self))
         else:
             # Use tuple's hash to avoid a high collision rate on
             # simple fractions.
             return hash((self.numerator, self.denominator))

* Menu:

* Adding More Numeric ABCs::
* Implementing the arithmetic operations::


File: python.info,  Node: Adding More Numeric ABCs,  Next: Implementing the arithmetic operations,  Up: Notes for type implementors

5.9.1.3 Adding More Numeric ABCs
................................

There are, of course, more possible ABCs for numbers, and this would be
a poor hierarchy if it precluded the possibility of adding those.  You
can add ‘MyFoo’ between *note Complex: 1558. and *note Real: 1557. with:

     class MyFoo(Complex): ...
     MyFoo.register(Real)


File: python.info,  Node: Implementing the arithmetic operations,  Prev: Adding More Numeric ABCs,  Up: Notes for type implementors

5.9.1.4 Implementing the arithmetic operations
..............................................

We want to implement the arithmetic operations so that mixed-mode
operations either call an implementation whose author knew about the
types of both arguments, or convert both to the nearest built in type
and do the operation there.  For subtypes of *note Integral: 1556, this
means that *note __add__(): 1595. and *note __radd__(): 1596. should be
defined as:

     class MyIntegral(Integral):

         def __add__(self, other):
             if isinstance(other, MyIntegral):
                 return do_my_adding_stuff(self, other)
             elif isinstance(other, OtherTypeIKnowAbout):
                 return do_my_other_adding_stuff(self, other)
             else:
                 return NotImplemented

         def __radd__(self, other):
             if isinstance(other, MyIntegral):
                 return do_my_adding_stuff(other, self)
             elif isinstance(other, OtherTypeIKnowAbout):
                 return do_my_other_adding_stuff(other, self)
             elif isinstance(other, Integral):
                 return int(other) + int(self)
             elif isinstance(other, Real):
                 return float(other) + float(self)
             elif isinstance(other, Complex):
                 return complex(other) + complex(self)
             else:
                 return NotImplemented

There are 5 different cases for a mixed-type operation on subclasses of
*note Complex: 1558.  I’ll refer to all of the above code that doesn’t
refer to ‘MyIntegral’ and ‘OtherTypeIKnowAbout’ as “boilerplate”.  ‘a’
will be an instance of ‘A’, which is a subtype of *note Complex: 1558.
(‘a : A <: Complex’), and ‘b : B <: Complex’.  I’ll consider ‘a + b’:

       1. If ‘A’ defines an *note __add__(): 1595. which accepts ‘b’,
          all is well.

       2. If ‘A’ falls back to the boilerplate code, and it were to
          return a value from *note __add__(): 1595, we’d miss the
          possibility that ‘B’ defines a more intelligent *note
          __radd__(): 1596, so the boilerplate should return *note
          NotImplemented: 202. from *note __add__(): 1595.  (Or ‘A’ may
          not implement *note __add__(): 1595. at all.)

       3. Then ‘B’’s *note __radd__(): 1596. gets a chance.  If it
          accepts ‘a’, all is well.

       4. If it falls back to the boilerplate, there are no more
          possible methods to try, so this is where the default
          implementation should live.

       5. If ‘B <: A’, Python tries ‘B.__radd__’ before ‘A.__add__’.
          This is ok, because it was implemented with knowledge of ‘A’,
          so it can handle those instances before delegating to *note
          Complex: 1558.

If ‘A <: Complex’ and ‘B <: Real’ without sharing any other knowledge,
then the appropriate shared operation is the one involving the built in
*note complex: 2c1, and both *note __radd__(): 1596. s land there, so
‘a+b == b+a’.

Because most of the operations on any given type will be very similar,
it can be useful to define a helper function which generates the forward
and reverse instances of any given operator.  For example, *note
fractions.Fraction: 2be. uses:

     def _operator_fallbacks(monomorphic_operator, fallback_operator):
         def forward(a, b):
             if isinstance(b, (int, Fraction)):
                 return monomorphic_operator(a, b)
             elif isinstance(b, float):
                 return fallback_operator(float(a), b)
             elif isinstance(b, complex):
                 return fallback_operator(complex(a), b)
             else:
                 return NotImplemented
         forward.__name__ = '__' + fallback_operator.__name__ + '__'
         forward.__doc__ = monomorphic_operator.__doc__

         def reverse(b, a):
             if isinstance(a, Rational):
                 # Includes ints.
                 return monomorphic_operator(a, b)
             elif isinstance(a, numbers.Real):
                 return fallback_operator(float(a), float(b))
             elif isinstance(a, numbers.Complex):
                 return fallback_operator(complex(a), complex(b))
             else:
                 return NotImplemented
         reverse.__name__ = '__r' + fallback_operator.__name__ + '__'
         reverse.__doc__ = monomorphic_operator.__doc__

         return forward, reverse

     def _add(a, b):
         """a + b"""
         return Fraction(a.numerator * b.denominator +
                         b.numerator * a.denominator,
                         a.denominator * b.denominator)

     __add__, __radd__ = _operator_fallbacks(_add, operator.add)

     # ...


File: python.info,  Node: math — Mathematical functions,  Next: cmath — Mathematical functions for complex numbers,  Prev: numbers — Numeric abstract base classes,  Up: Numeric and Mathematical Modules

5.9.2 ‘math’ — Mathematical functions
-------------------------------------

__________________________________________________________________

This module provides access to the mathematical functions defined by the
C standard.

These functions cannot be used with complex numbers; use the functions
of the same name from the *note cmath: 18. module if you require support
for complex numbers.  The distinction between functions which support
complex numbers and those which don’t is made since most users do not
want to learn quite as much mathematics as required to understand
complex numbers.  Receiving an exception instead of a complex result
allows earlier detection of the unexpected complex number used as a
parameter, so that the programmer can determine how and why it was
generated in the first place.

The following functions are provided by this module.  Except when
explicitly noted otherwise, all return values are floats.

* Menu:

* Number-theoretic and representation functions::
* Power and logarithmic functions::
* Trigonometric functions::
* Angular conversion::
* Hyperbolic functions::
* Special functions::
* Constants: Constants<2>.


File: python.info,  Node: Number-theoretic and representation functions,  Next: Power and logarithmic functions,  Up: math — Mathematical functions

5.9.2.1 Number-theoretic and representation functions
.....................................................

 -- Function: math.ceil (x)

     Return the ceiling of `x', the smallest integer greater than or
     equal to `x'.  If `x' is not a float, delegates to ‘x.__ceil__()’,
     which should return an *note Integral: 1556. value.

 -- Function: math.comb (n, k)

     Return the number of ways to choose `k' items from `n' items
     without repetition and without order.

     Evaluates to ‘n! / (k! * (n - k)!)’ when ‘k <= n’ and evaluates to
     zero when ‘k > n’.

     Also called the binomial coefficient because it is equivalent to
     the coefficient of k-th term in polynomial expansion of the
     expression ‘(1 + x) ** n’.

     Raises *note TypeError: 1fe. if either of the arguments are not
     integers.  Raises *note ValueError: 16d. if either of the arguments
     are negative.

     New in version 3.8.

 -- Function: math.copysign (x, y)

     Return a float with the magnitude (absolute value) of `x' but the
     sign of `y'.  On platforms that support signed zeros,
     ‘copysign(1.0, -0.0)’ returns `-1.0'.

 -- Function: math.fabs (x)

     Return the absolute value of `x'.

 -- Function: math.factorial (x)

     Return `x' factorial as an integer.  Raises *note ValueError: 16d.
     if `x' is not integral or is negative.

     Deprecated since version 3.9: Accepting floats with integral values
     (like ‘5.0’) is deprecated.

 -- Function: math.floor (x)

     Return the floor of `x', the largest integer less than or equal to
     `x'.  If `x' is not a float, delegates to ‘x.__floor__()’, which
     should return an *note Integral: 1556. value.

 -- Function: math.fmod (x, y)

     Return ‘fmod(x, y)’, as defined by the platform C library.  Note
     that the Python expression ‘x % y’ may not return the same result.
     The intent of the C standard is that ‘fmod(x, y)’ be exactly
     (mathematically; to infinite precision) equal to ‘x - n*y’ for some
     integer `n' such that the result has the same sign as `x' and
     magnitude less than ‘abs(y)’.  Python’s ‘x % y’ returns a result
     with the sign of `y' instead, and may not be exactly computable for
     float arguments.  For example, ‘fmod(-1e-100, 1e100)’ is ‘-1e-100’,
     but the result of Python’s ‘-1e-100 % 1e100’ is ‘1e100-1e-100’,
     which cannot be represented exactly as a float, and rounds to the
     surprising ‘1e100’.  For this reason, function *note fmod(): 1671.
     is generally preferred when working with floats, while Python’s ‘x
     % y’ is preferred when working with integers.

 -- Function: math.frexp (x)

     Return the mantissa and exponent of `x' as the pair ‘(m, e)’.  `m'
     is a float and `e' is an integer such that ‘x == m * 2**e’ exactly.
     If `x' is zero, returns ‘(0.0, 0)’, otherwise ‘0.5 <= abs(m) < 1’.
     This is used to “pick apart” the internal representation of a float
     in a portable way.

 -- Function: math.fsum (iterable)

     Return an accurate floating point sum of values in the iterable.
     Avoids loss of precision by tracking multiple intermediate partial
     sums:

          >>> sum([.1, .1, .1, .1, .1, .1, .1, .1, .1, .1])
          0.9999999999999999
          >>> fsum([.1, .1, .1, .1, .1, .1, .1, .1, .1, .1])
          1.0

     The algorithm’s accuracy depends on IEEE-754 arithmetic guarantees
     and the typical case where the rounding mode is half-even.  On some
     non-Windows builds, the underlying C library uses extended
     precision addition and may occasionally double-round an
     intermediate sum causing it to be off in its least significant bit.

     For further discussion and two alternative approaches, see the ASPN
     cookbook recipes for accurate floating point summation(1).

 -- Function: math.gcd (*integers)

     Return the greatest common divisor of the specified integer
     arguments.  If any of the arguments is nonzero, then the returned
     value is the largest positive integer that is a divisor of all
     arguments.  If all arguments are zero, then the returned value is
     ‘0’.  ‘gcd()’ without arguments returns ‘0’.

     New in version 3.5.

     Changed in version 3.9: Added support for an arbitrary number of
     arguments.  Formerly, only two arguments were supported.

 -- Function: math.isclose (a, b, *, rel_tol=1e-09, abs_tol=0.0)

     Return ‘True’ if the values `a' and `b' are close to each other and
     ‘False’ otherwise.

     Whether or not two values are considered close is determined
     according to given absolute and relative tolerances.

     `rel_tol' is the relative tolerance – it is the maximum allowed
     difference between `a' and `b', relative to the larger absolute
     value of `a' or `b'.  For example, to set a tolerance of 5%, pass
     ‘rel_tol=0.05’.  The default tolerance is ‘1e-09’, which assures
     that the two values are the same within about 9 decimal digits.
     `rel_tol' must be greater than zero.

     `abs_tol' is the minimum absolute tolerance – useful for
     comparisons near zero.  `abs_tol' must be at least zero.

     If no errors occur, the result will be: ‘abs(a-b) <= max(rel_tol *
     max(abs(a), abs(b)), abs_tol)’.

     The IEEE 754 special values of ‘NaN’, ‘inf’, and ‘-inf’ will be
     handled according to IEEE rules.  Specifically, ‘NaN’ is not
     considered close to any other value, including ‘NaN’.  ‘inf’ and
     ‘-inf’ are only considered close to themselves.

     New in version 3.5.

     See also
     ........

     PEP 485(2) – A function for testing approximate equality

 -- Function: math.isfinite (x)

     Return ‘True’ if `x' is neither an infinity nor a NaN, and ‘False’
     otherwise.  (Note that ‘0.0’ `is' considered finite.)

     New in version 3.2.

 -- Function: math.isinf (x)

     Return ‘True’ if `x' is a positive or negative infinity, and
     ‘False’ otherwise.

 -- Function: math.isnan (x)

     Return ‘True’ if `x' is a NaN (not a number), and ‘False’
     otherwise.

 -- Function: math.isqrt (n)

     Return the integer square root of the nonnegative integer `n'.
     This is the floor of the exact square root of `n', or equivalently
     the greatest integer `a' such that `a'² ≤ `n'.

     For some applications, it may be more convenient to have the least
     integer `a' such that `n' ≤ `a'², or in other words the ceiling of
     the exact square root of `n'.  For positive `n', this can be
     computed using ‘a = 1 + isqrt(n - 1)’.

     New in version 3.8.

 -- Function: math.lcm (*integers)

     Return the least common multiple of the specified integer
     arguments.  If all arguments are nonzero, then the returned value
     is the smallest positive integer that is a multiple of all
     arguments.  If any of the arguments is zero, then the returned
     value is ‘0’.  ‘lcm()’ without arguments returns ‘1’.

     New in version 3.9.

 -- Function: math.ldexp (x, i)

     Return ‘x * (2**i)’.  This is essentially the inverse of function
     *note frexp(): 1b7b.

 -- Function: math.modf (x)

     Return the fractional and integer parts of `x'.  Both results carry
     the sign of `x' and are floats.

 -- Function: math.nextafter (x, y)

     Return the next floating-point value after `x' towards `y'.

     If `x' is equal to `y', return `y'.

     Examples:

        * ‘math.nextafter(x, math.inf)’ goes up: towards positive
          infinity.

        * ‘math.nextafter(x, -math.inf)’ goes down: towards minus
          infinity.

        * ‘math.nextafter(x, 0.0)’ goes towards zero.

        * ‘math.nextafter(x, math.copysign(math.inf, x))’ goes away from
          zero.

     See also *note math.ulp(): 1c1.

     New in version 3.9.

 -- Function: math.perm (n, k=None)

     Return the number of ways to choose `k' items from `n' items
     without repetition and with order.

     Evaluates to ‘n! / (n - k)!’ when ‘k <= n’ and evaluates to zero
     when ‘k > n’.

     If `k' is not specified or is None, then `k' defaults to `n' and
     the function returns ‘n!’.

     Raises *note TypeError: 1fe. if either of the arguments are not
     integers.  Raises *note ValueError: 16d. if either of the arguments
     are negative.

     New in version 3.8.

 -- Function: math.prod (iterable, *, start=1)

     Calculate the product of all the elements in the input `iterable'.
     The default `start' value for the product is ‘1’.

     When the iterable is empty, return the start value.  This function
     is intended specifically for use with numeric values and may reject
     non-numeric types.

     New in version 3.8.

 -- Function: math.remainder (x, y)

     Return the IEEE 754-style remainder of `x' with respect to `y'.
     For finite `x' and finite nonzero `y', this is the difference ‘x -
     n*y’, where ‘n’ is the closest integer to the exact value of the
     quotient ‘x / y’.  If ‘x / y’ is exactly halfway between two
     consecutive integers, the nearest `even' integer is used for ‘n’.
     The remainder ‘r = remainder(x, y)’ thus always satisfies ‘abs(r)
     <= 0.5 * abs(y)’.

     Special cases follow IEEE 754: in particular, ‘remainder(x,
     math.inf)’ is `x' for any finite `x', and ‘remainder(x, 0)’ and
     ‘remainder(math.inf, x)’ raise *note ValueError: 16d. for any
     non-NaN `x'.  If the result of the remainder operation is zero,
     that zero will have the same sign as `x'.

     On platforms using IEEE 754 binary floating-point, the result of
     this operation is always exactly representable: no rounding error
     is introduced.

     New in version 3.7.

 -- Function: math.trunc (x)

     Return the *note Real: 1557. value `x' truncated to an *note
     Integral: 1556. (usually an integer).  Delegates to *note
     x.__trunc__(): 15c1.

 -- Function: math.ulp (x)

     Return the value of the least significant bit of the float `x':

        * If `x' is a NaN (not a number), return `x'.

        * If `x' is negative, return ‘ulp(-x)’.

        * If `x' is a positive infinity, return `x'.

        * If `x' is equal to zero, return the smallest positive
          `denormalized' representable float (smaller than the minimum
          positive `normalized' float, *note sys.float_info.min: 10fc.).

        * If `x' is equal to the largest positive representable float,
          return the value of the least significant bit of `x', such
          that the first float smaller than `x' is ‘x - ulp(x)’.

        * Otherwise (`x' is a positive finite number), return the value
          of the least significant bit of `x', such that the first float
          bigger than `x' is ‘x + ulp(x)’.

     ULP stands for “Unit in the Last Place”.

     See also *note math.nextafter(): 1c0. and *note
     sys.float_info.epsilon: 10fc.

     New in version 3.9.

Note that *note frexp(): 1b7b. and *note modf(): 1b7d. have a different
call/return pattern than their C equivalents: they take a single
argument and return a pair of values, rather than returning their second
return value through an ‘output parameter’ (there is no such thing in
Python).

For the *note ceil(): df3, *note floor(): df2, and *note modf(): 1b7d.
functions, note that `all' floating-point numbers of sufficiently large
magnitude are exact integers.  Python floats typically carry no more
than 53 bits of precision (the same as the platform C double type), in
which case any float `x' with ‘abs(x) >= 2**52’ necessarily has no
fractional bits.

   ---------- Footnotes ----------

   (1) https://code.activestate.com/recipes/393090/

   (2) https://www.python.org/dev/peps/pep-0485


File: python.info,  Node: Power and logarithmic functions,  Next: Trigonometric functions,  Prev: Number-theoretic and representation functions,  Up: math — Mathematical functions

5.9.2.2 Power and logarithmic functions
.......................................

 -- Function: math.exp (x)

     Return `e' raised to the power `x', where `e' = 2.718281… is the
     base of natural logarithms.  This is usually more accurate than
     ‘math.e ** x’ or ‘pow(math.e, x)’.

 -- Function: math.expm1 (x)

     Return `e' raised to the power `x', minus 1.  Here `e' is the base
     of natural logarithms.  For small floats `x', the subtraction in
     ‘exp(x) - 1’ can result in a significant loss of precision(1); the
     *note expm1(): c3a. function provides a way to compute this
     quantity to full precision:

          >>> from math import exp, expm1
          >>> exp(1e-5) - 1  # gives result accurate to 11 places
          1.0000050000069649e-05
          >>> expm1(1e-5)    # result accurate to full precision
          1.0000050000166668e-05

     New in version 3.2.

 -- Function: math.log (x[, base])

     With one argument, return the natural logarithm of `x' (to base
     `e').

     With two arguments, return the logarithm of `x' to the given
     `base', calculated as ‘log(x)/log(base)’.

 -- Function: math.log1p (x)

     Return the natural logarithm of `1+x' (base `e').  The result is
     calculated in a way which is accurate for `x' near zero.

 -- Function: math.log2 (x)

     Return the base-2 logarithm of `x'.  This is usually more accurate
     than ‘log(x, 2)’.

     New in version 3.3.

     See also
     ........

     *note int.bit_length(): 1753. returns the number of bits necessary
     to represent an integer in binary, excluding the sign and leading
     zeros.

 -- Function: math.log10 (x)

     Return the base-10 logarithm of `x'.  This is usually more accurate
     than ‘log(x, 10)’.

 -- Function: math.pow (x, y)

     Return ‘x’ raised to the power ‘y’.  Exceptional cases follow Annex
     ‘F’ of the C99 standard as far as possible.  In particular,
     ‘pow(1.0, x)’ and ‘pow(x, 0.0)’ always return ‘1.0’, even when ‘x’
     is a zero or a NaN. If both ‘x’ and ‘y’ are finite, ‘x’ is
     negative, and ‘y’ is not an integer then ‘pow(x, y)’ is undefined,
     and raises *note ValueError: 16d.

     Unlike the built-in ‘**’ operator, *note math.pow(): 1b80. converts
     both its arguments to type *note float: 1fd.  Use ‘**’ or the
     built-in *note pow(): 2cf. function for computing exact integer
     powers.

 -- Function: math.sqrt (x)

     Return the square root of `x'.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Loss_of_significance


File: python.info,  Node: Trigonometric functions,  Next: Angular conversion,  Prev: Power and logarithmic functions,  Up: math — Mathematical functions

5.9.2.3 Trigonometric functions
...............................

 -- Function: math.acos (x)

     Return the arc cosine of `x', in radians.  The result is between
     ‘0’ and ‘pi’.

 -- Function: math.asin (x)

     Return the arc sine of `x', in radians.  The result is between
     ‘-pi/2’ and ‘pi/2’.

 -- Function: math.atan (x)

     Return the arc tangent of `x', in radians.  The result is between
     ‘-pi/2’ and ‘pi/2’.

 -- Function: math.atan2 (y, x)

     Return ‘atan(y / x)’, in radians.  The result is between ‘-pi’ and
     ‘pi’.  The vector in the plane from the origin to point ‘(x, y)’
     makes this angle with the positive X axis.  The point of *note
     atan2(): 1b85. is that the signs of both inputs are known to it, so
     it can compute the correct quadrant for the angle.  For example,
     ‘atan(1)’ and ‘atan2(1, 1)’ are both ‘pi/4’, but ‘atan2(-1, -1)’ is
     ‘-3*pi/4’.

 -- Function: math.cos (x)

     Return the cosine of `x' radians.

 -- Function: math.dist (p, q)

     Return the Euclidean distance between two points `p' and `q', each
     given as a sequence (or iterable) of coordinates.  The two points
     must have the same dimension.

     Roughly equivalent to:

          sqrt(sum((px - qx) ** 2.0 for px, qx in zip(p, q)))

     New in version 3.8.

 -- Function: math.hypot (*coordinates)

     Return the Euclidean norm, ‘sqrt(sum(x**2 for x in coordinates))’.
     This is the length of the vector from the origin to the point given
     by the coordinates.

     For a two dimensional point ‘(x, y)’, this is equivalent to
     computing the hypotenuse of a right triangle using the Pythagorean
     theorem, ‘sqrt(x*x + y*y)’.

     Changed in version 3.8: Added support for n-dimensional points.
     Formerly, only the two dimensional case was supported.

 -- Function: math.sin (x)

     Return the sine of `x' radians.

 -- Function: math.tan (x)

     Return the tangent of `x' radians.


File: python.info,  Node: Angular conversion,  Next: Hyperbolic functions,  Prev: Trigonometric functions,  Up: math — Mathematical functions

5.9.2.4 Angular conversion
..........................

 -- Function: math.degrees (x)

     Convert angle `x' from radians to degrees.

 -- Function: math.radians (x)

     Convert angle `x' from degrees to radians.


File: python.info,  Node: Hyperbolic functions,  Next: Special functions,  Prev: Angular conversion,  Up: math — Mathematical functions

5.9.2.5 Hyperbolic functions
............................

Hyperbolic functions(1) are analogs of trigonometric functions that are
based on hyperbolas instead of circles.

 -- Function: math.acosh (x)

     Return the inverse hyperbolic cosine of `x'.

 -- Function: math.asinh (x)

     Return the inverse hyperbolic sine of `x'.

 -- Function: math.atanh (x)

     Return the inverse hyperbolic tangent of `x'.

 -- Function: math.cosh (x)

     Return the hyperbolic cosine of `x'.

 -- Function: math.sinh (x)

     Return the hyperbolic sine of `x'.

 -- Function: math.tanh (x)

     Return the hyperbolic tangent of `x'.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Hyperbolic_function


File: python.info,  Node: Special functions,  Next: Constants<2>,  Prev: Hyperbolic functions,  Up: math — Mathematical functions

5.9.2.6 Special functions
.........................

 -- Function: math.erf (x)

     Return the error function(1) at `x'.

     The *note erf(): 554. function can be used to compute traditional
     statistical functions such as the cumulative standard normal
     distribution(2):

          def phi(x):
              'Cumulative distribution function for the standard normal distribution'
              return (1.0 + erf(x / sqrt(2.0))) / 2.0

     New in version 3.2.

 -- Function: math.erfc (x)

     Return the complementary error function at `x'.  The complementary
     error function(3) is defined as ‘1.0 - erf(x)’.  It is used for
     large values of `x' where a subtraction from one would cause a loss
     of significance(4).

     New in version 3.2.

 -- Function: math.gamma (x)

     Return the Gamma function(5) at `x'.

     New in version 3.2.

 -- Function: math.lgamma (x)

     Return the natural logarithm of the absolute value of the Gamma
     function at `x'.

     New in version 3.2.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Error_function

   (2) 
https://en.wikipedia.org/wiki/Normal_distribution#Cumulative_distribution_function

   (3) https://en.wikipedia.org/wiki/Error_function

   (4) https://en.wikipedia.org/wiki/Loss_of_significance

   (5) https://en.wikipedia.org/wiki/Gamma_function


File: python.info,  Node: Constants<2>,  Prev: Special functions,  Up: math — Mathematical functions

5.9.2.7 Constants
.................

 -- Data: math.pi

     The mathematical constant `π' = 3.141592…, to available precision.

 -- Data: math.e

     The mathematical constant `e' = 2.718281…, to available precision.

 -- Data: math.tau

     The mathematical constant `τ' = 6.283185…, to available precision.
     Tau is a circle constant equal to 2`π', the ratio of a circle’s
     circumference to its radius.  To learn more about Tau, check out Vi
     Hart’s video Pi is (still) Wrong(1), and start celebrating Tau
     day(2) by eating twice as much pie!

     New in version 3.6.

 -- Data: math.inf

     A floating-point positive infinity.  (For negative infinity, use
     ‘-math.inf’.)  Equivalent to the output of ‘float('inf')’.

     New in version 3.5.

 -- Data: math.nan

     A floating-point “not a number” (NaN) value.  Equivalent to the
     output of ‘float('nan')’.

     New in version 3.5.

`CPython implementation detail:' The *note math: b1. module consists
mostly of thin wrappers around the platform C math library functions.
Behavior in exceptional cases follows Annex F of the C99 standard where
appropriate.  The current implementation will raise *note ValueError:
16d. for invalid operations like ‘sqrt(-1.0)’ or ‘log(0.0)’ (where C99
Annex F recommends signaling invalid operation or divide-by-zero), and
*note OverflowError: a41. for results that overflow (for example,
‘exp(1000.0)’).  A NaN will not be returned from any of the functions
above unless one or more of the input arguments was a NaN; in that case,
most functions will return a NaN, but (again following C99 Annex F)
there are some exceptions to this rule, for example ‘pow(float('nan'),
0.0)’ or ‘hypot(float('nan'), float('inf'))’.

Note that Python makes no effort to distinguish signaling NaNs from
quiet NaNs, and behavior for signaling NaNs remains unspecified.
Typical behavior is to treat all NaNs as though they were quiet.

See also
........

Module *note cmath: 18.

     Complex number versions of many of these functions.

   ---------- Footnotes ----------

   (1) https://www.youtube.com/watch?v=jG7vhMMXagQ

   (2) https://tauday.com/


File: python.info,  Node: cmath — Mathematical functions for complex numbers,  Next: decimal — Decimal fixed point and floating point arithmetic,  Prev: math — Mathematical functions,  Up: Numeric and Mathematical Modules

5.9.3 ‘cmath’ — Mathematical functions for complex numbers
----------------------------------------------------------

__________________________________________________________________

This module provides access to mathematical functions for complex
numbers.  The functions in this module accept integers, floating-point
numbers or complex numbers as arguments.  They will also accept any
Python object that has either a *note __complex__(): 2c5. or a *note
__float__(): 2c4. method: these methods are used to convert the object
to a complex or floating-point number, respectively, and the function is
then applied to the result of the conversion.

     Note: On platforms with hardware and system-level support for
     signed zeros, functions involving branch cuts are continuous on
     `both' sides of the branch cut: the sign of the zero distinguishes
     one side of the branch cut from the other.  On platforms that do
     not support signed zeros the continuity is as specified below.

* Menu:

* Conversions to and from polar coordinates::
* Power and logarithmic functions: Power and logarithmic functions<2>.
* Trigonometric functions: Trigonometric functions<2>.
* Hyperbolic functions: Hyperbolic functions<2>.
* Classification functions::
* Constants: Constants<3>.


File: python.info,  Node: Conversions to and from polar coordinates,  Next: Power and logarithmic functions<2>,  Up: cmath — Mathematical functions for complex numbers

5.9.3.1 Conversions to and from polar coordinates
.................................................

A Python complex number ‘z’ is stored internally using `rectangular' or
`Cartesian' coordinates.  It is completely determined by its `real part'
‘z.real’ and its `imaginary part' ‘z.imag’.  In other words:

     z == z.real + z.imag*1j

`Polar coordinates' give an alternative way to represent a complex
number.  In polar coordinates, a complex number `z' is defined by the
modulus `r' and the phase angle `phi'.  The modulus `r' is the distance
from `z' to the origin, while the phase `phi' is the counterclockwise
angle, measured in radians, from the positive x-axis to the line segment
that joins the origin to `z'.

The following functions can be used to convert from the native
rectangular coordinates to polar coordinates and back.

 -- Function: cmath.phase (x)

     Return the phase of `x' (also known as the `argument' of `x'), as a
     float.  ‘phase(x)’ is equivalent to ‘math.atan2(x.imag, x.real)’.
     The result lies in the range [-`π', `π'], and the branch cut for
     this operation lies along the negative real axis, continuous from
     above.  On systems with support for signed zeros (which includes
     most systems in current use), this means that the sign of the
     result is the same as the sign of ‘x.imag’, even when ‘x.imag’ is
     zero:

          >>> phase(complex(-1.0, 0.0))
          3.141592653589793
          >>> phase(complex(-1.0, -0.0))
          -3.141592653589793

     Note: The modulus (absolute value) of a complex number `x' can be
     computed using the built-in *note abs(): 13f3. function.  There is
     no separate *note cmath: 18. module function for this operation.

 -- Function: cmath.polar (x)

     Return the representation of `x' in polar coordinates.  Returns a
     pair ‘(r, phi)’ where `r' is the modulus of `x' and phi is the
     phase of `x'.  ‘polar(x)’ is equivalent to ‘(abs(x), phase(x))’.

 -- Function: cmath.rect (r, phi)

     Return the complex number `x' with polar coordinates `r' and `phi'.
     Equivalent to ‘r * (math.cos(phi) + math.sin(phi)*1j)’.


File: python.info,  Node: Power and logarithmic functions<2>,  Next: Trigonometric functions<2>,  Prev: Conversions to and from polar coordinates,  Up: cmath — Mathematical functions for complex numbers

5.9.3.2 Power and logarithmic functions
.......................................

 -- Function: cmath.exp (x)

     Return `e' raised to the power `x', where `e' is the base of
     natural logarithms.

 -- Function: cmath.log (x[, base])

     Returns the logarithm of `x' to the given `base'.  If the `base' is
     not specified, returns the natural logarithm of `x'.  There is one
     branch cut, from 0 along the negative real axis to -∞, continuous
     from above.

 -- Function: cmath.log10 (x)

     Return the base-10 logarithm of `x'.  This has the same branch cut
     as *note log(): 1b9b.

 -- Function: cmath.sqrt (x)

     Return the square root of `x'.  This has the same branch cut as
     *note log(): 1b9b.


File: python.info,  Node: Trigonometric functions<2>,  Next: Hyperbolic functions<2>,  Prev: Power and logarithmic functions<2>,  Up: cmath — Mathematical functions for complex numbers

5.9.3.3 Trigonometric functions
...............................

 -- Function: cmath.acos (x)

     Return the arc cosine of `x'.  There are two branch cuts: One
     extends right from 1 along the real axis to ∞, continuous from
     below.  The other extends left from -1 along the real axis to -∞,
     continuous from above.

 -- Function: cmath.asin (x)

     Return the arc sine of `x'.  This has the same branch cuts as *note
     acos(): 1b9f.

 -- Function: cmath.atan (x)

     Return the arc tangent of `x'.  There are two branch cuts: One
     extends from ‘1j’ along the imaginary axis to ‘∞j’, continuous from
     the right.  The other extends from ‘-1j’ along the imaginary axis
     to ‘-∞j’, continuous from the left.

 -- Function: cmath.cos (x)

     Return the cosine of `x'.

 -- Function: cmath.sin (x)

     Return the sine of `x'.

 -- Function: cmath.tan (x)

     Return the tangent of `x'.


File: python.info,  Node: Hyperbolic functions<2>,  Next: Classification functions,  Prev: Trigonometric functions<2>,  Up: cmath — Mathematical functions for complex numbers

5.9.3.4 Hyperbolic functions
............................

 -- Function: cmath.acosh (x)

     Return the inverse hyperbolic cosine of `x'.  There is one branch
     cut, extending left from 1 along the real axis to -∞, continuous
     from above.

 -- Function: cmath.asinh (x)

     Return the inverse hyperbolic sine of `x'.  There are two branch
     cuts: One extends from ‘1j’ along the imaginary axis to ‘∞j’,
     continuous from the right.  The other extends from ‘-1j’ along the
     imaginary axis to ‘-∞j’, continuous from the left.

 -- Function: cmath.atanh (x)

     Return the inverse hyperbolic tangent of `x'.  There are two branch
     cuts: One extends from ‘1’ along the real axis to ‘∞’, continuous
     from below.  The other extends from ‘-1’ along the real axis to
     ‘-∞’, continuous from above.

 -- Function: cmath.cosh (x)

     Return the hyperbolic cosine of `x'.

 -- Function: cmath.sinh (x)

     Return the hyperbolic sine of `x'.

 -- Function: cmath.tanh (x)

     Return the hyperbolic tangent of `x'.


File: python.info,  Node: Classification functions,  Next: Constants<3>,  Prev: Hyperbolic functions<2>,  Up: cmath — Mathematical functions for complex numbers

5.9.3.5 Classification functions
................................

 -- Function: cmath.isfinite (x)

     Return ‘True’ if both the real and imaginary parts of `x' are
     finite, and ‘False’ otherwise.

     New in version 3.2.

 -- Function: cmath.isinf (x)

     Return ‘True’ if either the real or the imaginary part of `x' is an
     infinity, and ‘False’ otherwise.

 -- Function: cmath.isnan (x)

     Return ‘True’ if either the real or the imaginary part of `x' is a
     NaN, and ‘False’ otherwise.

 -- Function: cmath.isclose (a, b, *, rel_tol=1e-09, abs_tol=0.0)

     Return ‘True’ if the values `a' and `b' are close to each other and
     ‘False’ otherwise.

     Whether or not two values are considered close is determined
     according to given absolute and relative tolerances.

     `rel_tol' is the relative tolerance – it is the maximum allowed
     difference between `a' and `b', relative to the larger absolute
     value of `a' or `b'.  For example, to set a tolerance of 5%, pass
     ‘rel_tol=0.05’.  The default tolerance is ‘1e-09’, which assures
     that the two values are the same within about 9 decimal digits.
     `rel_tol' must be greater than zero.

     `abs_tol' is the minimum absolute tolerance – useful for
     comparisons near zero.  `abs_tol' must be at least zero.

     If no errors occur, the result will be: ‘abs(a-b) <= max(rel_tol *
     max(abs(a), abs(b)), abs_tol)’.

     The IEEE 754 special values of ‘NaN’, ‘inf’, and ‘-inf’ will be
     handled according to IEEE rules.  Specifically, ‘NaN’ is not
     considered close to any other value, including ‘NaN’.  ‘inf’ and
     ‘-inf’ are only considered close to themselves.

     New in version 3.5.

     See also
     ........

     PEP 485(1) – A function for testing approximate equality

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0485


File: python.info,  Node: Constants<3>,  Prev: Classification functions,  Up: cmath — Mathematical functions for complex numbers

5.9.3.6 Constants
.................

 -- Data: cmath.pi

     The mathematical constant `π', as a float.

 -- Data: cmath.e

     The mathematical constant `e', as a float.

 -- Data: cmath.tau

     The mathematical constant `τ', as a float.

     New in version 3.6.

 -- Data: cmath.inf

     Floating-point positive infinity.  Equivalent to ‘float('inf')’.

     New in version 3.6.

 -- Data: cmath.infj

     Complex number with zero real part and positive infinity imaginary
     part.  Equivalent to ‘complex(0.0, float('inf'))’.

     New in version 3.6.

 -- Data: cmath.nan

     A floating-point “not a number” (NaN) value.  Equivalent to
     ‘float('nan')’.

     New in version 3.6.

 -- Data: cmath.nanj

     Complex number with zero real part and NaN imaginary part.
     Equivalent to ‘complex(0.0, float('nan'))’.

     New in version 3.6.

Note that the selection of functions is similar, but not identical, to
that in module *note math: b1.  The reason for having two modules is
that some users aren’t interested in complex numbers, and perhaps don’t
even know what they are.  They would rather have ‘math.sqrt(-1)’ raise
an exception than return a complex number.  Also note that the functions
defined in *note cmath: 18. always return a complex number, even if the
answer can be expressed as a real number (in which case the complex
number has an imaginary part of zero).

A note on branch cuts: They are curves along which the given function
fails to be continuous.  They are a necessary feature of many complex
functions.  It is assumed that if you need to compute with complex
functions, you will understand about branch cuts.  Consult almost any
(not too elementary) book on complex variables for enlightenment.  For
information of the proper choice of branch cuts for numerical purposes,
a good reference should be the following:

See also
........

Kahan, W: Branch cuts for complex elementary functions; or, Much ado
about nothing’s sign bit.  In Iserles, A., and Powell, M. (eds.), The
state of the art in numerical analysis.  Clarendon Press (1987)
pp165–211.


File: python.info,  Node: decimal — Decimal fixed point and floating point arithmetic,  Next: fractions — Rational numbers,  Prev: cmath — Mathematical functions for complex numbers,  Up: Numeric and Mathematical Modules

5.9.4 ‘decimal’ — Decimal fixed point and floating point arithmetic
-------------------------------------------------------------------

`Source code:' Lib/decimal.py(1)

__________________________________________________________________

The *note decimal: 35. module provides support for fast
correctly-rounded decimal floating point arithmetic.  It offers several
advantages over the *note float: 1fd. datatype:

   * Decimal “is based on a floating-point model which was designed with
     people in mind, and necessarily has a paramount guiding principle –
     computers must provide an arithmetic that works in the same way as
     the arithmetic that people learn at school.” – excerpt from the
     decimal arithmetic specification.

   * Decimal numbers can be represented exactly.  In contrast, numbers
     like ‘1.1’ and ‘2.2’ do not have exact representations in binary
     floating point.  End users typically would not expect ‘1.1 + 2.2’
     to display as ‘3.3000000000000003’ as it does with binary floating
     point.

   * The exactness carries over into arithmetic.  In decimal floating
     point, ‘0.1 + 0.1 + 0.1 - 0.3’ is exactly equal to zero.  In binary
     floating point, the result is ‘5.5511151231257827e-017’.  While
     near to zero, the differences prevent reliable equality testing and
     differences can accumulate.  For this reason, decimal is preferred
     in accounting applications which have strict equality invariants.

   * The decimal module incorporates a notion of significant places so
     that ‘1.30 + 1.20’ is ‘2.50’.  The trailing zero is kept to
     indicate significance.  This is the customary presentation for
     monetary applications.  For multiplication, the “schoolbook”
     approach uses all the figures in the multiplicands.  For instance,
     ‘1.3 * 1.2’ gives ‘1.56’ while ‘1.30 * 1.20’ gives ‘1.5600’.

   * Unlike hardware based binary floating point, the decimal module has
     a user alterable precision (defaulting to 28 places) which can be
     as large as needed for a given problem:

          >>> from decimal import *
          >>> getcontext().prec = 6
          >>> Decimal(1) / Decimal(7)
          Decimal('0.142857')
          >>> getcontext().prec = 28
          >>> Decimal(1) / Decimal(7)
          Decimal('0.1428571428571428571428571429')

   * Both binary and decimal floating point are implemented in terms of
     published standards.  While the built-in float type exposes only a
     modest portion of its capabilities, the decimal module exposes all
     required parts of the standard.  When needed, the programmer has
     full control over rounding and signal handling.  This includes an
     option to enforce exact arithmetic by using exceptions to block any
     inexact operations.

   * The decimal module was designed to support “without prejudice, both
     exact unrounded decimal arithmetic (sometimes called fixed-point
     arithmetic) and rounded floating-point arithmetic.” – excerpt from
     the decimal arithmetic specification.

The module design is centered around three concepts: the decimal number,
the context for arithmetic, and signals.

A decimal number is immutable.  It has a sign, coefficient digits, and
an exponent.  To preserve significance, the coefficient digits do not
truncate trailing zeros.  Decimals also include special values such as
‘Infinity’, ‘-Infinity’, and ‘NaN’.  The standard also differentiates
‘-0’ from ‘+0’.

The context for arithmetic is an environment specifying precision,
rounding rules, limits on exponents, flags indicating the results of
operations, and trap enablers which determine whether signals are
treated as exceptions.  Rounding options include *note ROUND_CEILING:
1bb5, *note ROUND_DOWN: 1bb6, *note ROUND_FLOOR: 1bb7, *note
ROUND_HALF_DOWN: 1bb8, *note ROUND_HALF_EVEN: 1bb9, *note ROUND_HALF_UP:
1bba, *note ROUND_UP: 1bbb, and *note ROUND_05UP: 1bbc.

Signals are groups of exceptional conditions arising during the course
of computation.  Depending on the needs of the application, signals may
be ignored, considered as informational, or treated as exceptions.  The
signals in the decimal module are: *note Clamped: 1bbd, *note
InvalidOperation: aca, *note DivisionByZero: 1bbe, *note Inexact: 1bbf,
*note Rounded: 1bc0, *note Subnormal: 1bc1, *note Overflow: 1bc2, *note
Underflow: 1bc3. and *note FloatOperation: ac4.

For each signal there is a flag and a trap enabler.  When a signal is
encountered, its flag is set to one, then, if the trap enabler is set to
one, an exception is raised.  Flags are sticky, so the user needs to
reset them before monitoring a calculation.

See also
........

   * IBM’s General Decimal Arithmetic Specification, The General Decimal
     Arithmetic Specification(2).

* Menu:

* Quick-start Tutorial::
* Decimal objects::
* Context objects::
* Constants: Constants<4>.
* Rounding modes::
* Signals::
* Floating Point Notes::
* Working with threads::
* Recipes::
* Decimal FAQ::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/decimal.py

   (2) http://speleotrove.com/decimal/decarith.html


File: python.info,  Node: Quick-start Tutorial,  Next: Decimal objects,  Up: decimal — Decimal fixed point and floating point arithmetic

5.9.4.1 Quick-start Tutorial
............................

The usual start to using decimals is importing the module, viewing the
current context with *note getcontext(): 1bc6. and, if necessary,
setting new values for precision, rounding, or enabled traps:

     >>> from decimal import *
     >>> getcontext()
     Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999,
             capitals=1, clamp=0, flags=[], traps=[Overflow, DivisionByZero,
             InvalidOperation])

     >>> getcontext().prec = 7       # Set a new precision

Decimal instances can be constructed from integers, strings, floats, or
tuples.  Construction from an integer or a float performs an exact
conversion of the value of that integer or float.  Decimal numbers
include special values such as ‘NaN’ which stands for “Not a number”,
positive and negative ‘Infinity’, and ‘-0’:

     >>> getcontext().prec = 28
     >>> Decimal(10)
     Decimal('10')
     >>> Decimal('3.14')
     Decimal('3.14')
     >>> Decimal(3.14)
     Decimal('3.140000000000000124344978758017532527446746826171875')
     >>> Decimal((0, (3, 1, 4), -2))
     Decimal('3.14')
     >>> Decimal(str(2.0 ** 0.5))
     Decimal('1.4142135623730951')
     >>> Decimal(2) ** Decimal('0.5')
     Decimal('1.414213562373095048801688724')
     >>> Decimal('NaN')
     Decimal('NaN')
     >>> Decimal('-Infinity')
     Decimal('-Infinity')

If the *note FloatOperation: ac4. signal is trapped, accidental mixing
of decimals and floats in constructors or ordering comparisons raises an
exception:

     >>> c = getcontext()
     >>> c.traps[FloatOperation] = True
     >>> Decimal(3.14)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     decimal.FloatOperation: [<class 'decimal.FloatOperation'>]
     >>> Decimal('3.5') < 3.7
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     decimal.FloatOperation: [<class 'decimal.FloatOperation'>]
     >>> Decimal('3.5') == 3.5
     True

New in version 3.3.

The significance of a new Decimal is determined solely by the number of
digits input.  Context precision and rounding only come into play during
arithmetic operations.

     >>> getcontext().prec = 6
     >>> Decimal('3.0')
     Decimal('3.0')
     >>> Decimal('3.1415926535')
     Decimal('3.1415926535')
     >>> Decimal('3.1415926535') + Decimal('2.7182818285')
     Decimal('5.85987')
     >>> getcontext().rounding = ROUND_UP
     >>> Decimal('3.1415926535') + Decimal('2.7182818285')
     Decimal('5.85988')

If the internal limits of the C version are exceeded, constructing a
decimal raises *note InvalidOperation: aca.:

     >>> Decimal("1e9999999999999999999")
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     decimal.InvalidOperation: [<class 'decimal.InvalidOperation'>]

Changed in version 3.3.

Decimals interact well with much of the rest of Python.  Here is a small
decimal floating point flying circus:

     >>> data = list(map(Decimal, '1.34 1.87 3.45 2.35 1.00 0.03 9.25'.split()))
     >>> max(data)
     Decimal('9.25')
     >>> min(data)
     Decimal('0.03')
     >>> sorted(data)
     [Decimal('0.03'), Decimal('1.00'), Decimal('1.34'), Decimal('1.87'),
      Decimal('2.35'), Decimal('3.45'), Decimal('9.25')]
     >>> sum(data)
     Decimal('19.29')
     >>> a,b,c = data[:3]
     >>> str(a)
     '1.34'
     >>> float(a)
     1.34
     >>> round(a, 1)
     Decimal('1.3')
     >>> int(a)
     1
     >>> a * 5
     Decimal('6.70')
     >>> a * b
     Decimal('2.5058')
     >>> c % a
     Decimal('0.77')

And some mathematical functions are also available to Decimal:

     >>> getcontext().prec = 28
     >>> Decimal(2).sqrt()
     Decimal('1.414213562373095048801688724')
     >>> Decimal(1).exp()
     Decimal('2.718281828459045235360287471')
     >>> Decimal('10').ln()
     Decimal('2.302585092994045684017991455')
     >>> Decimal('10').log10()
     Decimal('1')

The ‘quantize()’ method rounds a number to a fixed exponent.  This
method is useful for monetary applications that often round results to a
fixed number of places:

     >>> Decimal('7.325').quantize(Decimal('.01'), rounding=ROUND_DOWN)
     Decimal('7.32')
     >>> Decimal('7.325').quantize(Decimal('1.'), rounding=ROUND_UP)
     Decimal('8')

As shown above, the *note getcontext(): 1bc6. function accesses the
current context and allows the settings to be changed.  This approach
meets the needs of most applications.

For more advanced work, it may be useful to create alternate contexts
using the Context() constructor.  To make an alternate active, use the
*note setcontext(): 1bc7. function.

In accordance with the standard, the *note decimal: 35. module provides
two ready to use standard contexts, *note BasicContext: ac8. and *note
ExtendedContext: ac9.  The former is especially useful for debugging
because many of the traps are enabled:

     >>> myothercontext = Context(prec=60, rounding=ROUND_HALF_DOWN)
     >>> setcontext(myothercontext)
     >>> Decimal(1) / Decimal(7)
     Decimal('0.142857142857142857142857142857142857142857142857142857142857')

     >>> ExtendedContext
     Context(prec=9, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999,
             capitals=1, clamp=0, flags=[], traps=[])
     >>> setcontext(ExtendedContext)
     >>> Decimal(1) / Decimal(7)
     Decimal('0.142857143')
     >>> Decimal(42) / Decimal(0)
     Decimal('Infinity')

     >>> setcontext(BasicContext)
     >>> Decimal(42) / Decimal(0)
     Traceback (most recent call last):
       File "<pyshell#143>", line 1, in -toplevel-
         Decimal(42) / Decimal(0)
     DivisionByZero: x / 0

Contexts also have signal flags for monitoring exceptional conditions
encountered during computations.  The flags remain set until explicitly
cleared, so it is best to clear the flags before each set of monitored
computations by using the ‘clear_flags()’ method.

     >>> setcontext(ExtendedContext)
     >>> getcontext().clear_flags()
     >>> Decimal(355) / Decimal(113)
     Decimal('3.14159292')
     >>> getcontext()
     Context(prec=9, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999,
             capitals=1, clamp=0, flags=[Inexact, Rounded], traps=[])

The `flags' entry shows that the rational approximation to ‘Pi’ was
rounded (digits beyond the context precision were thrown away) and that
the result is inexact (some of the discarded digits were non-zero).

Individual traps are set using the dictionary in the ‘traps’ field of a
context:

     >>> setcontext(ExtendedContext)
     >>> Decimal(1) / Decimal(0)
     Decimal('Infinity')
     >>> getcontext().traps[DivisionByZero] = 1
     >>> Decimal(1) / Decimal(0)
     Traceback (most recent call last):
       File "<pyshell#112>", line 1, in -toplevel-
         Decimal(1) / Decimal(0)
     DivisionByZero: x / 0

Most programs adjust the current context only once, at the beginning of
the program.  And, in many applications, data is converted to *note
Decimal: 2c0. with a single cast inside a loop.  With context set and
decimals created, the bulk of the program manipulates the data no
differently than with other Python numeric types.


File: python.info,  Node: Decimal objects,  Next: Context objects,  Prev: Quick-start Tutorial,  Up: decimal — Decimal fixed point and floating point arithmetic

5.9.4.2 Decimal objects
.......................

 -- Class: decimal.Decimal (value="0", context=None)

     Construct a new *note Decimal: 2c0. object based from `value'.

     `value' can be an integer, string, tuple, *note float: 1fd, or
     another *note Decimal: 2c0. object.  If no `value' is given,
     returns ‘Decimal('0')’.  If `value' is a string, it should conform
     to the decimal numeric string syntax after leading and trailing
     whitespace characters, as well as underscores throughout, are
     removed:

          sign           ::=  '+' | '-'
          digit          ::=  '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9'
          indicator      ::=  'e' | 'E'
          digits         ::=  digit [digit]...
          decimal-part   ::=  digits '.' [digits] | ['.'] digits
          exponent-part  ::=  indicator [sign] digits
          infinity       ::=  'Infinity' | 'Inf'
          nan            ::=  'NaN' [digits] | 'sNaN' [digits]
          numeric-value  ::=  decimal-part [exponent-part] | infinity
          numeric-string ::=  [sign] numeric-value | [sign] nan

     Other Unicode decimal digits are also permitted where ‘digit’
     appears above.  These include decimal digits from various other
     alphabets (for example, Arabic-Indic and Devanāgarī digits) along
     with the fullwidth digits ‘'\uff10'’ through ‘'\uff19'’.

     If `value' is a *note tuple: 1a2, it should have three components,
     a sign (‘0’ for positive or ‘1’ for negative), a *note tuple: 1a2.
     of digits, and an integer exponent.  For example, ‘Decimal((0, (1,
     4, 1, 4), -3))’ returns ‘Decimal('1.414')’.

     If `value' is a *note float: 1fd, the binary floating point value
     is losslessly converted to its exact decimal equivalent.  This
     conversion can often require 53 or more digits of precision.  For
     example, ‘Decimal(float('1.1'))’ converts to
     ‘Decimal('1.100000000000000088817841970012523233890533447265625')’.

     The `context' precision does not affect how many digits are stored.
     That is determined exclusively by the number of digits in `value'.
     For example, ‘Decimal('3.00000')’ records all five zeros even if
     the context precision is only three.

     The purpose of the `context' argument is determining what to do if
     `value' is a malformed string.  If the context traps *note
     InvalidOperation: aca, an exception is raised; otherwise, the
     constructor returns a new Decimal with the value of ‘NaN’.

     Once constructed, *note Decimal: 2c0. objects are immutable.

     Changed in version 3.2: The argument to the constructor is now
     permitted to be a *note float: 1fd. instance.

     Changed in version 3.3: *note float: 1fd. arguments raise an
     exception if the *note FloatOperation: ac4. trap is set.  By
     default the trap is off.

     Changed in version 3.6: Underscores are allowed for grouping, as
     with integral and floating-point literals in code.

     Decimal floating point objects share many properties with the other
     built-in numeric types such as *note float: 1fd. and *note int:
     204.  All of the usual math operations and special methods apply.
     Likewise, decimal objects can be copied, pickled, printed, used as
     dictionary keys, used as set elements, compared, sorted, and
     coerced to another type (such as *note float: 1fd. or *note int:
     204.).

     There are some small differences between arithmetic on Decimal
     objects and arithmetic on integers and floats.  When the remainder
     operator ‘%’ is applied to Decimal objects, the sign of the result
     is the sign of the `dividend' rather than the sign of the divisor:

          >>> (-7) % 4
          1
          >>> Decimal(-7) % Decimal(4)
          Decimal('-3')

     The integer division operator ‘//’ behaves analogously, returning
     the integer part of the true quotient (truncating towards zero)
     rather than its floor, so as to preserve the usual identity ‘x ==
     (x // y) * y + x % y’:

          >>> -7 // 4
          -2
          >>> Decimal(-7) // Decimal(4)
          Decimal('-1')

     The ‘%’ and ‘//’ operators implement the ‘remainder’ and
     ‘divide-integer’ operations (respectively) as described in the
     specification.

     Decimal objects cannot generally be combined with floats or
     instances of *note fractions.Fraction: 2be. in arithmetic
     operations: an attempt to add a *note Decimal: 2c0. to a *note
     float: 1fd, for example, will raise a *note TypeError: 1fe.
     However, it is possible to use Python’s comparison operators to
     compare a *note Decimal: 2c0. instance ‘x’ with another number ‘y’.
     This avoids confusing results when doing equality comparisons
     between numbers of different types.

     Changed in version 3.2: Mixed-type comparisons between *note
     Decimal: 2c0. instances and other numeric types are now fully
     supported.

     In addition to the standard numeric properties, decimal floating
     point objects also have a number of specialized methods:

      -- Method: adjusted ()

          Return the adjusted exponent after shifting out the
          coefficient’s rightmost digits until only the lead digit
          remains: ‘Decimal('321e+5').adjusted()’ returns seven.  Used
          for determining the position of the most significant digit
          with respect to the decimal point.

      -- Method: as_integer_ratio ()

          Return a pair ‘(n, d)’ of integers that represent the given
          *note Decimal: 2c0. instance as a fraction, in lowest terms
          and with a positive denominator:

               >>> Decimal('-3.14').as_integer_ratio()
               (-157, 50)

          The conversion is exact.  Raise OverflowError on infinities
          and ValueError on NaNs.

     New in version 3.6.

      -- Method: as_tuple ()

          Return a *note named tuple: b7b. representation of the number:
          ‘DecimalTuple(sign, digits, exponent)’.

      -- Method: canonical ()

          Return the canonical encoding of the argument.  Currently, the
          encoding of a *note Decimal: 2c0. instance is always
          canonical, so this operation returns its argument unchanged.

      -- Method: compare (other, context=None)

          Compare the values of two Decimal instances.  *note compare():
          1bcd. returns a Decimal instance, and if either operand is a
          NaN then the result is a NaN:

               a or b is a NaN  ==> Decimal('NaN')
               a < b            ==> Decimal('-1')
               a == b           ==> Decimal('0')
               a > b            ==> Decimal('1')

      -- Method: compare_signal (other, context=None)

          This operation is identical to the *note compare(): 1bcd.
          method, except that all NaNs signal.  That is, if neither
          operand is a signaling NaN then any quiet NaN operand is
          treated as though it were a signaling NaN.

      -- Method: compare_total (other, context=None)

          Compare two operands using their abstract representation
          rather than their numerical value.  Similar to the *note
          compare(): 1bcd. method, but the result gives a total ordering
          on *note Decimal: 2c0. instances.  Two *note Decimal: 2c0.
          instances with the same numeric value but different
          representations compare unequal in this ordering:

               >>> Decimal('12.0').compare_total(Decimal('12'))
               Decimal('-1')

          Quiet and signaling NaNs are also included in the total
          ordering.  The result of this function is ‘Decimal('0')’ if
          both operands have the same representation, ‘Decimal('-1')’ if
          the first operand is lower in the total order than the second,
          and ‘Decimal('1')’ if the first operand is higher in the total
          order than the second operand.  See the specification for
          details of the total order.

          This operation is unaffected by context and is quiet: no flags
          are changed and no rounding is performed.  As an exception,
          the C version may raise InvalidOperation if the second operand
          cannot be converted exactly.

      -- Method: compare_total_mag (other, context=None)

          Compare two operands using their abstract representation
          rather than their value as in *note compare_total(): 1bcf, but
          ignoring the sign of each operand.  ‘x.compare_total_mag(y)’
          is equivalent to ‘x.copy_abs().compare_total(y.copy_abs())’.

          This operation is unaffected by context and is quiet: no flags
          are changed and no rounding is performed.  As an exception,
          the C version may raise InvalidOperation if the second operand
          cannot be converted exactly.

      -- Method: conjugate ()

          Just returns self, this method is only to comply with the
          Decimal Specification.

      -- Method: copy_abs ()

          Return the absolute value of the argument.  This operation is
          unaffected by the context and is quiet: no flags are changed
          and no rounding is performed.

      -- Method: copy_negate ()

          Return the negation of the argument.  This operation is
          unaffected by the context and is quiet: no flags are changed
          and no rounding is performed.

      -- Method: copy_sign (other, context=None)

          Return a copy of the first operand with the sign set to be the
          same as the sign of the second operand.  For example:

               >>> Decimal('2.3').copy_sign(Decimal('-1.5'))
               Decimal('-2.3')

          This operation is unaffected by context and is quiet: no flags
          are changed and no rounding is performed.  As an exception,
          the C version may raise InvalidOperation if the second operand
          cannot be converted exactly.

      -- Method: exp (context=None)

          Return the value of the (natural) exponential function ‘e**x’
          at the given number.  The result is correctly rounded using
          the *note ROUND_HALF_EVEN: 1bb9. rounding mode.

               >>> Decimal(1).exp()
               Decimal('2.718281828459045235360287471')
               >>> Decimal(321).exp()
               Decimal('2.561702493119680037517373933E+139')

      -- Method: from_float (f)

          Classmethod that converts a float to a decimal number,
          exactly.

          Note ‘Decimal.from_float(0.1)’ is not the same as
          ‘Decimal(‘0.1’)’.  Since 0.1 is not exactly representable in
          binary floating point, the value is stored as the nearest
          representable value which is ‘0x1.999999999999ap-4’.  That
          equivalent value in decimal is
          ‘0.1000000000000000055511151231257827021181583404541015625’.

               Note: From Python 3.2 onwards, a *note Decimal: 2c0.
               instance can also be constructed directly from a *note
               float: 1fd.

               >>> Decimal.from_float(0.1)
               Decimal('0.1000000000000000055511151231257827021181583404541015625')
               >>> Decimal.from_float(float('nan'))
               Decimal('NaN')
               >>> Decimal.from_float(float('inf'))
               Decimal('Infinity')
               >>> Decimal.from_float(float('-inf'))
               Decimal('-Infinity')

          New in version 3.1.

      -- Method: fma (other, third, context=None)

          Fused multiply-add.  Return self*other+third with no rounding
          of the intermediate product self*other.

               >>> Decimal(2).fma(3, 5)
               Decimal('11')

      -- Method: is_canonical ()

          Return *note True: 594. if the argument is canonical and *note
          False: 48f. otherwise.  Currently, a *note Decimal: 2c0.
          instance is always canonical, so this operation always returns
          *note True: 594.

      -- Method: is_finite ()

          Return *note True: 594. if the argument is a finite number,
          and *note False: 48f. if the argument is an infinity or a NaN.

      -- Method: is_infinite ()

          Return *note True: 594. if the argument is either positive or
          negative infinity and *note False: 48f. otherwise.

      -- Method: is_nan ()

          Return *note True: 594. if the argument is a (quiet or
          signaling) NaN and *note False: 48f. otherwise.

      -- Method: is_normal (context=None)

          Return *note True: 594. if the argument is a `normal' finite
          number.  Return *note False: 48f. if the argument is zero,
          subnormal, infinite or a NaN.

      -- Method: is_qnan ()

          Return *note True: 594. if the argument is a quiet NaN, and
          *note False: 48f. otherwise.

      -- Method: is_signed ()

          Return *note True: 594. if the argument has a negative sign
          and *note False: 48f. otherwise.  Note that zeros and NaNs can
          both carry signs.

      -- Method: is_snan ()

          Return *note True: 594. if the argument is a signaling NaN and
          *note False: 48f. otherwise.

      -- Method: is_subnormal (context=None)

          Return *note True: 594. if the argument is subnormal, and
          *note False: 48f. otherwise.

      -- Method: is_zero ()

          Return *note True: 594. if the argument is a (positive or
          negative) zero and *note False: 48f. otherwise.

      -- Method: ln (context=None)

          Return the natural (base e) logarithm of the operand.  The
          result is correctly rounded using the *note ROUND_HALF_EVEN:
          1bb9. rounding mode.

      -- Method: log10 (context=None)

          Return the base ten logarithm of the operand.  The result is
          correctly rounded using the *note ROUND_HALF_EVEN: 1bb9.
          rounding mode.

      -- Method: logb (context=None)

          For a nonzero number, return the adjusted exponent of its
          operand as a *note Decimal: 2c0. instance.  If the operand is
          a zero then ‘Decimal('-Infinity')’ is returned and the *note
          DivisionByZero: 1bbe. flag is raised.  If the operand is an
          infinity then ‘Decimal('Infinity')’ is returned.

      -- Method: logical_and (other, context=None)

          *note logical_and(): 1be2. is a logical operation which takes
          two `logical operands' (see *note Logical operands: 1be3.).
          The result is the digit-wise ‘and’ of the two operands.

      -- Method: logical_invert (context=None)

          *note logical_invert(): 1be4. is a logical operation.  The
          result is the digit-wise inversion of the operand.

      -- Method: logical_or (other, context=None)

          *note logical_or(): 1be5. is a logical operation which takes
          two `logical operands' (see *note Logical operands: 1be3.).
          The result is the digit-wise ‘or’ of the two operands.

      -- Method: logical_xor (other, context=None)

          *note logical_xor(): 1be6. is a logical operation which takes
          two `logical operands' (see *note Logical operands: 1be3.).
          The result is the digit-wise exclusive or of the two operands.

      -- Method: max (other, context=None)

          Like ‘max(self, other)’ except that the context rounding rule
          is applied before returning and that ‘NaN’ values are either
          signaled or ignored (depending on the context and whether they
          are signaling or quiet).

      -- Method: max_mag (other, context=None)

          Similar to the *note max(): 1be7. method, but the comparison
          is done using the absolute values of the operands.

      -- Method: min (other, context=None)

          Like ‘min(self, other)’ except that the context rounding rule
          is applied before returning and that ‘NaN’ values are either
          signaled or ignored (depending on the context and whether they
          are signaling or quiet).

      -- Method: min_mag (other, context=None)

          Similar to the *note min(): 1be9. method, but the comparison
          is done using the absolute values of the operands.

      -- Method: next_minus (context=None)

          Return the largest number representable in the given context
          (or in the current thread’s context if no context is given)
          that is smaller than the given operand.

      -- Method: next_plus (context=None)

          Return the smallest number representable in the given context
          (or in the current thread’s context if no context is given)
          that is larger than the given operand.

      -- Method: next_toward (other, context=None)

          If the two operands are unequal, return the number closest to
          the first operand in the direction of the second operand.  If
          both operands are numerically equal, return a copy of the
          first operand with the sign set to be the same as the sign of
          the second operand.

      -- Method: normalize (context=None)

          Normalize the number by stripping the rightmost trailing zeros
          and converting any result equal to ‘Decimal('0')’ to
          ‘Decimal('0e0')’.  Used for producing canonical values for
          attributes of an equivalence class.  For example,
          ‘Decimal('32.100')’ and ‘Decimal('0.321000e+2')’ both
          normalize to the equivalent value ‘Decimal('32.1')’.

      -- Method: number_class (context=None)

          Return a string describing the `class' of the operand.  The
          returned value is one of the following ten strings.

             * ‘"-Infinity"’, indicating that the operand is negative
               infinity.

             * ‘"-Normal"’, indicating that the operand is a negative
               normal number.

             * ‘"-Subnormal"’, indicating that the operand is negative
               and subnormal.

             * ‘"-Zero"’, indicating that the operand is a negative
               zero.

             * ‘"+Zero"’, indicating that the operand is a positive
               zero.

             * ‘"+Subnormal"’, indicating that the operand is positive
               and subnormal.

             * ‘"+Normal"’, indicating that the operand is a positive
               normal number.

             * ‘"+Infinity"’, indicating that the operand is positive
               infinity.

             * ‘"NaN"’, indicating that the operand is a quiet NaN (Not
               a Number).

             * ‘"sNaN"’, indicating that the operand is a signaling NaN.

      -- Method: quantize (exp, rounding=None, context=None)

          Return a value equal to the first operand after rounding and
          having the exponent of the second operand.

               >>> Decimal('1.41421356').quantize(Decimal('1.000'))
               Decimal('1.414')

          Unlike other operations, if the length of the coefficient
          after the quantize operation would be greater than precision,
          then an *note InvalidOperation: aca. is signaled.  This
          guarantees that, unless there is an error condition, the
          quantized exponent is always equal to that of the right-hand
          operand.

          Also unlike other operations, quantize never signals
          Underflow, even if the result is subnormal and inexact.

          If the exponent of the second operand is larger than that of
          the first then rounding may be necessary.  In this case, the
          rounding mode is determined by the ‘rounding’ argument if
          given, else by the given ‘context’ argument; if neither
          argument is given the rounding mode of the current thread’s
          context is used.

          An error is returned whenever the resulting exponent is
          greater than ‘Emax’ or less than ‘Etiny’.

      -- Method: radix ()

          Return ‘Decimal(10)’, the radix (base) in which the *note
          Decimal: 2c0. class does all its arithmetic.  Included for
          compatibility with the specification.

      -- Method: remainder_near (other, context=None)

          Return the remainder from dividing `self' by `other'.  This
          differs from ‘self % other’ in that the sign of the remainder
          is chosen so as to minimize its absolute value.  More
          precisely, the return value is ‘self - n * other’ where ‘n’ is
          the integer nearest to the exact value of ‘self / other’, and
          if two integers are equally near then the even one is chosen.

          If the result is zero then its sign will be the sign of
          `self'.

               >>> Decimal(18).remainder_near(Decimal(10))
               Decimal('-2')
               >>> Decimal(25).remainder_near(Decimal(10))
               Decimal('5')
               >>> Decimal(35).remainder_near(Decimal(10))
               Decimal('-5')

      -- Method: rotate (other, context=None)

          Return the result of rotating the digits of the first operand
          by an amount specified by the second operand.  The second
          operand must be an integer in the range -precision through
          precision.  The absolute value of the second operand gives the
          number of places to rotate.  If the second operand is positive
          then rotation is to the left; otherwise rotation is to the
          right.  The coefficient of the first operand is padded on the
          left with zeros to length precision if necessary.  The sign
          and exponent of the first operand are unchanged.

      -- Method: same_quantum (other, context=None)

          Test whether self and other have the same exponent or whether
          both are ‘NaN’.

          This operation is unaffected by context and is quiet: no flags
          are changed and no rounding is performed.  As an exception,
          the C version may raise InvalidOperation if the second operand
          cannot be converted exactly.

      -- Method: scaleb (other, context=None)

          Return the first operand with exponent adjusted by the second.
          Equivalently, return the first operand multiplied by
          ‘10**other’.  The second operand must be an integer.

      -- Method: shift (other, context=None)

          Return the result of shifting the digits of the first operand
          by an amount specified by the second operand.  The second
          operand must be an integer in the range -precision through
          precision.  The absolute value of the second operand gives the
          number of places to shift.  If the second operand is positive
          then the shift is to the left; otherwise the shift is to the
          right.  Digits shifted into the coefficient are zeros.  The
          sign and exponent of the first operand are unchanged.

      -- Method: sqrt (context=None)

          Return the square root of the argument to full precision.

      -- Method: to_eng_string (context=None)

          Convert to a string, using engineering notation if an exponent
          is needed.

          Engineering notation has an exponent which is a multiple of 3.
          This can leave up to 3 digits to the left of the decimal place
          and may require the addition of either one or two trailing
          zeros.

          For example, this converts ‘Decimal('123E+1')’ to
          ‘Decimal('1.23E+3')’.

      -- Method: to_integral (rounding=None, context=None)

          Identical to the *note to_integral_value(): 1bf9. method.  The
          ‘to_integral’ name has been kept for compatibility with older
          versions.

      -- Method: to_integral_exact (rounding=None, context=None)

          Round to the nearest integer, signaling *note Inexact: 1bbf.
          or *note Rounded: 1bc0. as appropriate if rounding occurs.
          The rounding mode is determined by the ‘rounding’ parameter if
          given, else by the given ‘context’.  If neither parameter is
          given then the rounding mode of the current context is used.

      -- Method: to_integral_value (rounding=None, context=None)

          Round to the nearest integer without signaling *note Inexact:
          1bbf. or *note Rounded: 1bc0.  If given, applies `rounding';
          otherwise, uses the rounding method in either the supplied
          `context' or the current context.

* Menu:

* Logical operands::


File: python.info,  Node: Logical operands,  Up: Decimal objects

5.9.4.3 Logical operands
........................

The ‘logical_and()’, ‘logical_invert()’, ‘logical_or()’, and
‘logical_xor()’ methods expect their arguments to be `logical operands'.
A `logical operand' is a *note Decimal: 2c0. instance whose exponent and
sign are both zero, and whose digits are all either ‘0’ or ‘1’.


File: python.info,  Node: Context objects,  Next: Constants<4>,  Prev: Decimal objects,  Up: decimal — Decimal fixed point and floating point arithmetic

5.9.4.4 Context objects
.......................

Contexts are environments for arithmetic operations.  They govern
precision, set rules for rounding, determine which signals are treated
as exceptions, and limit the range for exponents.

Each thread has its own current context which is accessed or changed
using the *note getcontext(): 1bc6. and *note setcontext(): 1bc7.
functions:

 -- Function: decimal.getcontext ()

     Return the current context for the active thread.

 -- Function: decimal.setcontext (c)

     Set the current context for the active thread to `c'.

You can also use the *note with: 7da. statement and the *note
localcontext(): 1813. function to temporarily change the active context.

 -- Function: decimal.localcontext (ctx=None)

     Return a context manager that will set the current context for the
     active thread to a copy of `ctx' on entry to the with-statement and
     restore the previous context when exiting the with-statement.  If
     no context is specified, a copy of the current context is used.

     For example, the following code sets the current decimal precision
     to 42 places, performs a calculation, and then automatically
     restores the previous context:

          from decimal import localcontext

          with localcontext() as ctx:
              ctx.prec = 42   # Perform a high precision calculation
              s = calculate_something()
          s = +s  # Round the final result back to the default precision

New contexts can also be created using the *note Context: acf.
constructor described below.  In addition, the module provides three
pre-made contexts:

 -- Class: decimal.BasicContext

     This is a standard context defined by the General Decimal
     Arithmetic Specification.  Precision is set to nine.  Rounding is
     set to *note ROUND_HALF_UP: 1bba.  All flags are cleared.  All
     traps are enabled (treated as exceptions) except *note Inexact:
     1bbf, *note Rounded: 1bc0, and *note Subnormal: 1bc1.

     Because many of the traps are enabled, this context is useful for
     debugging.

 -- Class: decimal.ExtendedContext

     This is a standard context defined by the General Decimal
     Arithmetic Specification.  Precision is set to nine.  Rounding is
     set to *note ROUND_HALF_EVEN: 1bb9.  All flags are cleared.  No
     traps are enabled (so that exceptions are not raised during
     computations).

     Because the traps are disabled, this context is useful for
     applications that prefer to have result value of ‘NaN’ or
     ‘Infinity’ instead of raising exceptions.  This allows an
     application to complete a run in the presence of conditions that
     would otherwise halt the program.

 -- Class: decimal.DefaultContext

     This context is used by the *note Context: acf. constructor as a
     prototype for new contexts.  Changing a field (such a precision)
     has the effect of changing the default for new contexts created by
     the *note Context: acf. constructor.

     This context is most useful in multi-threaded environments.
     Changing one of the fields before threads are started has the
     effect of setting system-wide defaults.  Changing the fields after
     threads have started is not recommended as it would require thread
     synchronization to prevent race conditions.

     In single threaded environments, it is preferable to not use this
     context at all.  Instead, simply create contexts explicitly as
     described below.

     The default values are ‘prec’=‘28’, ‘rounding’=*note
     ROUND_HALF_EVEN: 1bb9, and enabled traps for *note Overflow: 1bc2,
     *note InvalidOperation: aca, and *note DivisionByZero: 1bbe.

In addition to the three supplied contexts, new contexts can be created
with the *note Context: acf. constructor.

 -- Class: decimal.Context (prec=None, rounding=None, Emin=None,
          Emax=None, capitals=None, clamp=None, flags=None, traps=None)

     Creates a new context.  If a field is not specified or is *note
     None: 203, the default values are copied from the *note
     DefaultContext: ac7.  If the `flags' field is not specified or is
     *note None: 203, all flags are cleared.

     `prec' is an integer in the range [‘1’, *note MAX_PREC: 1bfe.] that
     sets the precision for arithmetic operations in the context.

     The `rounding' option is one of the constants listed in the section
     *note Rounding Modes: 1bff.

     The `traps' and `flags' fields list any signals to be set.
     Generally, new contexts should only set traps and leave the flags
     clear.

     The `Emin' and `Emax' fields are integers specifying the outer
     limits allowable for exponents.  `Emin' must be in the range [*note
     MIN_EMIN: 1c00, ‘0’], `Emax' in the range [‘0’, *note MAX_EMAX:
     1c01.].

     The `capitals' field is either ‘0’ or ‘1’ (the default).  If set to
     ‘1’, exponents are printed with a capital ‘E’; otherwise, a
     lowercase ‘e’ is used: ‘Decimal('6.02e+23')’.

     The `clamp' field is either ‘0’ (the default) or ‘1’.  If set to
     ‘1’, the exponent ‘e’ of a *note Decimal: 2c0. instance
     representable in this context is strictly limited to the range
     ‘Emin - prec + 1 <= e <= Emax - prec + 1’.  If `clamp' is ‘0’ then
     a weaker condition holds: the adjusted exponent of the *note
     Decimal: 2c0. instance is at most ‘Emax’.  When `clamp' is ‘1’, a
     large normal number will, where possible, have its exponent reduced
     and a corresponding number of zeros added to its coefficient, in
     order to fit the exponent constraints; this preserves the value of
     the number but loses information about significant trailing zeros.
     For example:

          >>> Context(prec=6, Emax=999, clamp=1).create_decimal('1.23e999')
          Decimal('1.23000E+999')

     A `clamp' value of ‘1’ allows compatibility with the fixed-width
     decimal interchange formats specified in IEEE 754.

     The *note Context: acf. class defines several general purpose
     methods as well as a large number of methods for doing arithmetic
     directly in a given context.  In addition, for each of the *note
     Decimal: 2c0. methods described above (with the exception of the
     ‘adjusted()’ and ‘as_tuple()’ methods) there is a corresponding
     *note Context: acf. method.  For example, for a *note Context: acf.
     instance ‘C’ and *note Decimal: 2c0. instance ‘x’, ‘C.exp(x)’ is
     equivalent to ‘x.exp(context=C)’.  Each *note Context: acf. method
     accepts a Python integer (an instance of *note int: 204.) anywhere
     that a Decimal instance is accepted.

      -- Method: clear_flags ()

          Resets all of the flags to ‘0’.

      -- Method: clear_traps ()

          Resets all of the traps to ‘0’.

          New in version 3.3.

      -- Method: copy ()

          Return a duplicate of the context.

      -- Method: copy_decimal (num)

          Return a copy of the Decimal instance num.

      -- Method: create_decimal (num)

          Creates a new Decimal instance from `num' but using `self' as
          context.  Unlike the *note Decimal: 2c0. constructor, the
          context precision, rounding method, flags, and traps are
          applied to the conversion.

          This is useful because constants are often given to a greater
          precision than is needed by the application.  Another benefit
          is that rounding immediately eliminates unintended effects
          from digits beyond the current precision.  In the following
          example, using unrounded inputs means that adding zero to a
          sum can change the result:

               >>> getcontext().prec = 3
               >>> Decimal('3.4445') + Decimal('1.0023')
               Decimal('4.45')
               >>> Decimal('3.4445') + Decimal(0) + Decimal('1.0023')
               Decimal('4.44')

          This method implements the to-number operation of the IBM
          specification.  If the argument is a string, no leading or
          trailing whitespace or underscores are permitted.

      -- Method: create_decimal_from_float (f)

          Creates a new Decimal instance from a float `f' but rounding
          using `self' as the context.  Unlike the *note
          Decimal.from_float(): c51. class method, the context
          precision, rounding method, flags, and traps are applied to
          the conversion.

               >>> context = Context(prec=5, rounding=ROUND_DOWN)
               >>> context.create_decimal_from_float(math.pi)
               Decimal('3.1415')
               >>> context = Context(prec=5, traps=[Inexact])
               >>> context.create_decimal_from_float(math.pi)
               Traceback (most recent call last):
                   ...
               decimal.Inexact: None

          New in version 3.1.

      -- Method: Etiny ()

          Returns a value equal to ‘Emin - prec + 1’ which is the
          minimum exponent value for subnormal results.  When underflow
          occurs, the exponent is set to *note Etiny: 1c07.

      -- Method: Etop ()

          Returns a value equal to ‘Emax - prec + 1’.

     The usual approach to working with decimals is to create *note
     Decimal: 2c0. instances and then apply arithmetic operations which
     take place within the current context for the active thread.  An
     alternative approach is to use context methods for calculating
     within a specific context.  The methods are similar to those for
     the *note Decimal: 2c0. class and are only briefly recounted here.

      -- Method: abs (x)

          Returns the absolute value of `x'.

      -- Method: add (x, y)

          Return the sum of `x' and `y'.

      -- Method: canonical (x)

          Returns the same Decimal object `x'.

      -- Method: compare (x, y)

          Compares `x' and `y' numerically.

      -- Method: compare_signal (x, y)

          Compares the values of the two operands numerically.

      -- Method: compare_total (x, y)

          Compares two operands using their abstract representation.

      -- Method: compare_total_mag (x, y)

          Compares two operands using their abstract representation,
          ignoring sign.

      -- Method: copy_abs (x)

          Returns a copy of `x' with the sign set to 0.

      -- Method: copy_negate (x)

          Returns a copy of `x' with the sign inverted.

      -- Method: copy_sign (x, y)

          Copies the sign from `y' to `x'.

      -- Method: divide (x, y)

          Return `x' divided by `y'.

      -- Method: divide_int (x, y)

          Return `x' divided by `y', truncated to an integer.

      -- Method: divmod (x, y)

          Divides two numbers and returns the integer part of the
          result.

      -- Method: exp (x)

          Returns ‘e ** x’.

      -- Method: fma (x, y, z)

          Returns `x' multiplied by `y', plus `z'.

      -- Method: is_canonical (x)

          Returns ‘True’ if `x' is canonical; otherwise returns ‘False’.

      -- Method: is_finite (x)

          Returns ‘True’ if `x' is finite; otherwise returns ‘False’.

      -- Method: is_infinite (x)

          Returns ‘True’ if `x' is infinite; otherwise returns ‘False’.

      -- Method: is_nan (x)

          Returns ‘True’ if `x' is a qNaN or sNaN; otherwise returns
          ‘False’.

      -- Method: is_normal (x)

          Returns ‘True’ if `x' is a normal number; otherwise returns
          ‘False’.

      -- Method: is_qnan (x)

          Returns ‘True’ if `x' is a quiet NaN; otherwise returns
          ‘False’.

      -- Method: is_signed (x)

          Returns ‘True’ if `x' is negative; otherwise returns ‘False’.

      -- Method: is_snan (x)

          Returns ‘True’ if `x' is a signaling NaN; otherwise returns
          ‘False’.

      -- Method: is_subnormal (x)

          Returns ‘True’ if `x' is subnormal; otherwise returns ‘False’.

      -- Method: is_zero (x)

          Returns ‘True’ if `x' is a zero; otherwise returns ‘False’.

      -- Method: ln (x)

          Returns the natural (base e) logarithm of `x'.

      -- Method: log10 (x)

          Returns the base 10 logarithm of `x'.

      -- Method: logb (x)

          Returns the exponent of the magnitude of the operand’s MSD.

      -- Method: logical_and (x, y)

          Applies the logical operation `and' between each operand’s
          digits.

      -- Method: logical_invert (x)

          Invert all the digits in `x'.

      -- Method: logical_or (x, y)

          Applies the logical operation `or' between each operand’s
          digits.

      -- Method: logical_xor (x, y)

          Applies the logical operation `xor' between each operand’s
          digits.

      -- Method: max (x, y)

          Compares two values numerically and returns the maximum.

      -- Method: max_mag (x, y)

          Compares the values numerically with their sign ignored.

      -- Method: min (x, y)

          Compares two values numerically and returns the minimum.

      -- Method: min_mag (x, y)

          Compares the values numerically with their sign ignored.

      -- Method: minus (x)

          Minus corresponds to the unary prefix minus operator in
          Python.

      -- Method: multiply (x, y)

          Return the product of `x' and `y'.

      -- Method: next_minus (x)

          Returns the largest representable number smaller than `x'.

      -- Method: next_plus (x)

          Returns the smallest representable number larger than `x'.

      -- Method: next_toward (x, y)

          Returns the number closest to `x', in direction towards `y'.

      -- Method: normalize (x)

          Reduces `x' to its simplest form.

      -- Method: number_class (x)

          Returns an indication of the class of `x'.

      -- Method: plus (x)

          Plus corresponds to the unary prefix plus operator in Python.
          This operation applies the context precision and rounding, so
          it is `not' an identity operation.

      -- Method: power (x, y, modulo=None)

          Return ‘x’ to the power of ‘y’, reduced modulo ‘modulo’ if
          given.

          With two arguments, compute ‘x**y’.  If ‘x’ is negative then
          ‘y’ must be integral.  The result will be inexact unless ‘y’
          is integral and the result is finite and can be expressed
          exactly in ‘precision’ digits.  The rounding mode of the
          context is used.  Results are always correctly-rounded in the
          Python version.

          ‘Decimal(0) ** Decimal(0)’ results in ‘InvalidOperation’, and
          if ‘InvalidOperation’ is not trapped, then results in
          ‘Decimal('NaN')’.

          Changed in version 3.3: The C module computes *note power():
          1c33. in terms of the correctly-rounded *note exp(): 1c15. and
          *note ln(): 1c20. functions.  The result is well-defined but
          only “almost always correctly-rounded”.

          With three arguments, compute ‘(x**y) % modulo’.  For the
          three argument form, the following restrictions on the
          arguments hold:

                  - all three arguments must be integral

                  - ‘y’ must be nonnegative

                  - at least one of ‘x’ or ‘y’ must be nonzero

                  - ‘modulo’ must be nonzero and have at most
                    ‘precision’ digits

          The value resulting from ‘Context.power(x, y, modulo)’ is
          equal to the value that would be obtained by computing ‘(x**y)
          % modulo’ with unbounded precision, but is computed more
          efficiently.  The exponent of the result is zero, regardless
          of the exponents of ‘x’, ‘y’ and ‘modulo’.  The result is
          always exact.

      -- Method: quantize (x, y)

          Returns a value equal to `x' (rounded), having the exponent of
          `y'.

      -- Method: radix ()

          Just returns 10, as this is Decimal, :)

      -- Method: remainder (x, y)

          Returns the remainder from integer division.

          The sign of the result, if non-zero, is the same as that of
          the original dividend.

      -- Method: remainder_near (x, y)

          Returns ‘x - y * n’, where `n' is the integer nearest the
          exact value of ‘x / y’ (if the result is 0 then its sign will
          be the sign of `x').

      -- Method: rotate (x, y)

          Returns a rotated copy of `x', `y' times.

      -- Method: same_quantum (x, y)

          Returns ‘True’ if the two operands have the same exponent.

      -- Method: scaleb (x, y)

          Returns the first operand after adding the second value its
          exp.

      -- Method: shift (x, y)

          Returns a shifted copy of `x', `y' times.

      -- Method: sqrt (x)

          Square root of a non-negative number to context precision.

      -- Method: subtract (x, y)

          Return the difference between `x' and `y'.

      -- Method: to_eng_string (x)

          Convert to a string, using engineering notation if an exponent
          is needed.

          Engineering notation has an exponent which is a multiple of 3.
          This can leave up to 3 digits to the left of the decimal place
          and may require the addition of either one or two trailing
          zeros.

      -- Method: to_integral_exact (x)

          Rounds to an integer.

      -- Method: to_sci_string (x)

          Converts a number to a string using scientific notation.


File: python.info,  Node: Constants<4>,  Next: Rounding modes,  Prev: Context objects,  Up: decimal — Decimal fixed point and floating point arithmetic

5.9.4.5 Constants
.................

The constants in this section are only relevant for the C module.  They
are also included in the pure Python version for compatibility.

                          32-bit                    64-bit
                                                    
----------------------------------------------------------------------------------------
                                                    
 -- Data:                 ‘425000000’               ‘999999999999999999’
          decimal.MAX_PREC                          

 -- Data:                 ‘425000000’               ‘999999999999999999’
          decimal.MAX_EMAX                          

 -- Data:                 ‘-425000000’              ‘-999999999999999999’
          decimal.MIN_EMIN                          

 -- Data:                 ‘-849999999’              ‘-1999999999999999997’
          decimal.MIN_ETINY                         

 -- Data: decimal.HAVE_THREADS

     The value is ‘True’.  Deprecated, because Python now always has
     threads.

Deprecated since version 3.9.

 -- Data: decimal.HAVE_CONTEXTVAR

     The default value is ‘True’.  If Python is compiled
     ‘--without-decimal-contextvar’, the C version uses a thread-local
     rather than a coroutine-local context and the value is ‘False’.
     This is slightly faster in some nested context scenarios.

New in version 3.9: backported to 3.7 and 3.8.


File: python.info,  Node: Rounding modes,  Next: Signals,  Prev: Constants<4>,  Up: decimal — Decimal fixed point and floating point arithmetic

5.9.4.6 Rounding modes
......................

 -- Data: decimal.ROUND_CEILING

     Round towards ‘Infinity’.

 -- Data: decimal.ROUND_DOWN

     Round towards zero.

 -- Data: decimal.ROUND_FLOOR

     Round towards ‘-Infinity’.

 -- Data: decimal.ROUND_HALF_DOWN

     Round to nearest with ties going towards zero.

 -- Data: decimal.ROUND_HALF_EVEN

     Round to nearest with ties going to nearest even integer.

 -- Data: decimal.ROUND_HALF_UP

     Round to nearest with ties going away from zero.

 -- Data: decimal.ROUND_UP

     Round away from zero.

 -- Data: decimal.ROUND_05UP

     Round away from zero if last digit after rounding towards zero
     would have been 0 or 5; otherwise round towards zero.


File: python.info,  Node: Signals,  Next: Floating Point Notes,  Prev: Rounding modes,  Up: decimal — Decimal fixed point and floating point arithmetic

5.9.4.7 Signals
...............

Signals represent conditions that arise during computation.  Each
corresponds to one context flag and one context trap enabler.

The context flag is set whenever the condition is encountered.  After
the computation, flags may be checked for informational purposes (for
instance, to determine whether a computation was exact).  After checking
the flags, be sure to clear all flags before starting the next
computation.

If the context’s trap enabler is set for the signal, then the condition
causes a Python exception to be raised.  For example, if the *note
DivisionByZero: 1bbe. trap is set, then a *note DivisionByZero: 1bbe.
exception is raised upon encountering the condition.

 -- Class: decimal.Clamped

     Altered an exponent to fit representation constraints.

     Typically, clamping occurs when an exponent falls outside the
     context’s ‘Emin’ and ‘Emax’ limits.  If possible, the exponent is
     reduced to fit by adding zeros to the coefficient.

 -- Class: decimal.DecimalException

     Base class for other signals and a subclass of *note
     ArithmeticError: 1845.

 -- Class: decimal.DivisionByZero

     Signals the division of a non-infinite number by zero.

     Can occur with division, modulo division, or when raising a number
     to a negative power.  If this signal is not trapped, returns
     ‘Infinity’ or ‘-Infinity’ with the sign determined by the inputs to
     the calculation.

 -- Class: decimal.Inexact

     Indicates that rounding occurred and the result is not exact.

     Signals when non-zero digits were discarded during rounding.  The
     rounded result is returned.  The signal flag or trap is used to
     detect when results are inexact.

 -- Class: decimal.InvalidOperation

     An invalid operation was performed.

     Indicates that an operation was requested that does not make sense.
     If not trapped, returns ‘NaN’.  Possible causes include:

          Infinity - Infinity
          0 * Infinity
          Infinity / Infinity
          x % 0
          Infinity % x
          sqrt(-x) and x > 0
          0 ** 0
          x ** (non-integer)
          x ** Infinity

 -- Class: decimal.Overflow

     Numerical overflow.

     Indicates the exponent is larger than ‘Emax’ after rounding has
     occurred.  If not trapped, the result depends on the rounding mode,
     either pulling inward to the largest representable finite number or
     rounding outward to ‘Infinity’.  In either case, *note Inexact:
     1bbf. and *note Rounded: 1bc0. are also signaled.

 -- Class: decimal.Rounded

     Rounding occurred though possibly no information was lost.

     Signaled whenever rounding discards digits; even if those digits
     are zero (such as rounding ‘5.00’ to ‘5.0’).  If not trapped,
     returns the result unchanged.  This signal is used to detect loss
     of significant digits.

 -- Class: decimal.Subnormal

     Exponent was lower than ‘Emin’ prior to rounding.

     Occurs when an operation result is subnormal (the exponent is too
     small).  If not trapped, returns the result unchanged.

 -- Class: decimal.Underflow

     Numerical underflow with result rounded to zero.

     Occurs when a subnormal result is pushed to zero by rounding.
     *note Inexact: 1bbf. and *note Subnormal: 1bc1. are also signaled.

 -- Class: decimal.FloatOperation

     Enable stricter semantics for mixing floats and Decimals.

     If the signal is not trapped (default), mixing floats and Decimals
     is permitted in the *note Decimal: 2c0. constructor, *note
     create_decimal(): acb. and all comparison operators.  Both
     conversion and comparisons are exact.  Any occurrence of a mixed
     operation is silently recorded by setting *note FloatOperation:
     ac4. in the context flags.  Explicit conversions with *note
     from_float(): c51. or *note create_decimal_from_float(): 1c06. do
     not set the flag.

     Otherwise (the signal is trapped), only equality comparisons and
     explicit conversions are silent.  All other mixed operations raise
     *note FloatOperation: ac4.

The following table summarizes the hierarchy of signals:

     exceptions.ArithmeticError(exceptions.Exception)
         DecimalException
             Clamped
             DivisionByZero(DecimalException, exceptions.ZeroDivisionError)
             Inexact
                 Overflow(Inexact, Rounded)
                 Underflow(Inexact, Rounded, Subnormal)
             InvalidOperation
             Rounded
             Subnormal
             FloatOperation(DecimalException, exceptions.TypeError)


File: python.info,  Node: Floating Point Notes,  Next: Working with threads,  Prev: Signals,  Up: decimal — Decimal fixed point and floating point arithmetic

5.9.4.8 Floating Point Notes
............................

* Menu:

* Mitigating round-off error with increased precision::
* Special values::


File: python.info,  Node: Mitigating round-off error with increased precision,  Next: Special values,  Up: Floating Point Notes

5.9.4.9 Mitigating round-off error with increased precision
...........................................................

The use of decimal floating point eliminates decimal representation
error (making it possible to represent ‘0.1’ exactly); however, some
operations can still incur round-off error when non-zero digits exceed
the fixed precision.

The effects of round-off error can be amplified by the addition or
subtraction of nearly offsetting quantities resulting in loss of
significance.  Knuth provides two instructive examples where rounded
floating point arithmetic with insufficient precision causes the
breakdown of the associative and distributive properties of addition:

     # Examples from Seminumerical Algorithms, Section 4.2.2.
     >>> from decimal import Decimal, getcontext
     >>> getcontext().prec = 8

     >>> u, v, w = Decimal(11111113), Decimal(-11111111), Decimal('7.51111111')
     >>> (u + v) + w
     Decimal('9.5111111')
     >>> u + (v + w)
     Decimal('10')

     >>> u, v, w = Decimal(20000), Decimal(-6), Decimal('6.0000003')
     >>> (u*v) + (u*w)
     Decimal('0.01')
     >>> u * (v+w)
     Decimal('0.0060000')

The *note decimal: 35. module makes it possible to restore the
identities by expanding the precision sufficiently to avoid loss of
significance:

     >>> getcontext().prec = 20
     >>> u, v, w = Decimal(11111113), Decimal(-11111111), Decimal('7.51111111')
     >>> (u + v) + w
     Decimal('9.51111111')
     >>> u + (v + w)
     Decimal('9.51111111')
     >>>
     >>> u, v, w = Decimal(20000), Decimal(-6), Decimal('6.0000003')
     >>> (u*v) + (u*w)
     Decimal('0.0060000')
     >>> u * (v+w)
     Decimal('0.0060000')


File: python.info,  Node: Special values,  Prev: Mitigating round-off error with increased precision,  Up: Floating Point Notes

5.9.4.10 Special values
.......................

The number system for the *note decimal: 35. module provides special
values including ‘NaN’, ‘sNaN’, ‘-Infinity’, ‘Infinity’, and two zeros,
‘+0’ and ‘-0’.

Infinities can be constructed directly with: ‘Decimal('Infinity')’.
Also, they can arise from dividing by zero when the *note
DivisionByZero: 1bbe. signal is not trapped.  Likewise, when the *note
Overflow: 1bc2. signal is not trapped, infinity can result from rounding
beyond the limits of the largest representable number.

The infinities are signed (affine) and can be used in arithmetic
operations where they get treated as very large, indeterminate numbers.
For instance, adding a constant to infinity gives another infinite
result.

Some operations are indeterminate and return ‘NaN’, or if the *note
InvalidOperation: aca. signal is trapped, raise an exception.  For
example, ‘0/0’ returns ‘NaN’ which means “not a number”.  This variety
of ‘NaN’ is quiet and, once created, will flow through other
computations always resulting in another ‘NaN’.  This behavior can be
useful for a series of computations that occasionally have missing
inputs — it allows the calculation to proceed while flagging specific
results as invalid.

A variant is ‘sNaN’ which signals rather than remaining quiet after
every operation.  This is a useful return value when an invalid result
needs to interrupt a calculation for special handling.

The behavior of Python’s comparison operators can be a little surprising
where a ‘NaN’ is involved.  A test for equality where one of the
operands is a quiet or signaling ‘NaN’ always returns *note False: 48f.
(even when doing ‘Decimal('NaN')==Decimal('NaN')’), while a test for
inequality always returns *note True: 594.  An attempt to compare two
Decimals using any of the ‘<’, ‘<=’, ‘>’ or ‘>=’ operators will raise
the *note InvalidOperation: aca. signal if either operand is a ‘NaN’,
and return *note False: 48f. if this signal is not trapped.  Note that
the General Decimal Arithmetic specification does not specify the
behavior of direct comparisons; these rules for comparisons involving a
‘NaN’ were taken from the IEEE 854 standard (see Table 3 in section
5.7).  To ensure strict standards-compliance, use the ‘compare()’ and
‘compare-signal()’ methods instead.

The signed zeros can result from calculations that underflow.  They keep
the sign that would have resulted if the calculation had been carried
out to greater precision.  Since their magnitude is zero, both positive
and negative zeros are treated as equal and their sign is informational.

In addition to the two signed zeros which are distinct yet equal, there
are various representations of zero with differing precisions yet
equivalent in value.  This takes a bit of getting used to.  For an eye
accustomed to normalized floating point representations, it is not
immediately obvious that the following calculation returns a value equal
to zero:

     >>> 1 / Decimal('Infinity')
     Decimal('0E-1000026')


File: python.info,  Node: Working with threads,  Next: Recipes,  Prev: Floating Point Notes,  Up: decimal — Decimal fixed point and floating point arithmetic

5.9.4.11 Working with threads
.............................

The *note getcontext(): 1bc6. function accesses a different *note
Context: acf. object for each thread.  Having separate thread contexts
means that threads may make changes (such as ‘getcontext().prec=10’)
without interfering with other threads.

Likewise, the *note setcontext(): 1bc7. function automatically assigns
its target to the current thread.

If *note setcontext(): 1bc7. has not been called before *note
getcontext(): 1bc6, then *note getcontext(): 1bc6. will automatically
create a new context for use in the current thread.

The new context is copied from a prototype context called
`DefaultContext'.  To control the defaults so that each thread will use
the same values throughout the application, directly modify the
`DefaultContext' object.  This should be done `before' any threads are
started so that there won’t be a race condition between threads calling
*note getcontext(): 1bc6.  For example:

     # Set applicationwide defaults for all threads about to be launched
     DefaultContext.prec = 12
     DefaultContext.rounding = ROUND_DOWN
     DefaultContext.traps = ExtendedContext.traps.copy()
     DefaultContext.traps[InvalidOperation] = 1
     setcontext(DefaultContext)

     # Afterwards, the threads can be started
     t1.start()
     t2.start()
     t3.start()
      . . .


File: python.info,  Node: Recipes,  Next: Decimal FAQ,  Prev: Working with threads,  Up: decimal — Decimal fixed point and floating point arithmetic

5.9.4.12 Recipes
................

Here are a few recipes that serve as utility functions and that
demonstrate ways to work with the *note Decimal: 2c0. class:

     def moneyfmt(value, places=2, curr='', sep=',', dp='.',
                  pos='', neg='-', trailneg=''):
         """Convert Decimal to a money formatted string.

         places:  required number of places after the decimal point
         curr:    optional currency symbol before the sign (may be blank)
         sep:     optional grouping separator (comma, period, space, or blank)
         dp:      decimal point indicator (comma or period)
                  only specify as blank when places is zero
         pos:     optional sign for positive numbers: '+', space or blank
         neg:     optional sign for negative numbers: '-', '(', space or blank
         trailneg:optional trailing minus indicator:  '-', ')', space or blank

         >>> d = Decimal('-1234567.8901')
         >>> moneyfmt(d, curr='$')
         '-$1,234,567.89'
         >>> moneyfmt(d, places=0, sep='.', dp='', neg='', trailneg='-')
         '1.234.568-'
         >>> moneyfmt(d, curr='$', neg='(', trailneg=')')
         '($1,234,567.89)'
         >>> moneyfmt(Decimal(123456789), sep=' ')
         '123 456 789.00'
         >>> moneyfmt(Decimal('-0.02'), neg='<', trailneg='>')
         '<0.02>'

         """
         q = Decimal(10) ** -places      # 2 places --> '0.01'
         sign, digits, exp = value.quantize(q).as_tuple()
         result = []
         digits = list(map(str, digits))
         build, next = result.append, digits.pop
         if sign:
             build(trailneg)
         for i in range(places):
             build(next() if digits else '0')
         if places:
             build(dp)
         if not digits:
             build('0')
         i = 0
         while digits:
             build(next())
             i += 1
             if i == 3 and digits:
                 i = 0
                 build(sep)
         build(curr)
         build(neg if sign else pos)
         return ''.join(reversed(result))

     def pi():
         """Compute Pi to the current precision.

         >>> print(pi())
         3.141592653589793238462643383

         """
         getcontext().prec += 2  # extra digits for intermediate steps
         three = Decimal(3)      # substitute "three=3.0" for regular floats
         lasts, t, s, n, na, d, da = 0, three, 3, 1, 0, 0, 24
         while s != lasts:
             lasts = s
             n, na = n+na, na+8
             d, da = d+da, da+32
             t = (t * n) / d
             s += t
         getcontext().prec -= 2
         return +s               # unary plus applies the new precision

     def exp(x):
         """Return e raised to the power of x.  Result type matches input type.

         >>> print(exp(Decimal(1)))
         2.718281828459045235360287471
         >>> print(exp(Decimal(2)))
         7.389056098930650227230427461
         >>> print(exp(2.0))
         7.38905609893
         >>> print(exp(2+0j))
         (7.38905609893+0j)

         """
         getcontext().prec += 2
         i, lasts, s, fact, num = 0, 0, 1, 1, 1
         while s != lasts:
             lasts = s
             i += 1
             fact *= i
             num *= x
             s += num / fact
         getcontext().prec -= 2
         return +s

     def cos(x):
         """Return the cosine of x as measured in radians.

         The Taylor series approximation works best for a small value of x.
         For larger values, first compute x = x % (2 * pi).

         >>> print(cos(Decimal('0.5')))
         0.8775825618903727161162815826
         >>> print(cos(0.5))
         0.87758256189
         >>> print(cos(0.5+0j))
         (0.87758256189+0j)

         """
         getcontext().prec += 2
         i, lasts, s, fact, num, sign = 0, 0, 1, 1, 1, 1
         while s != lasts:
             lasts = s
             i += 2
             fact *= i * (i-1)
             num *= x * x
             sign *= -1
             s += num / fact * sign
         getcontext().prec -= 2
         return +s

     def sin(x):
         """Return the sine of x as measured in radians.

         The Taylor series approximation works best for a small value of x.
         For larger values, first compute x = x % (2 * pi).

         >>> print(sin(Decimal('0.5')))
         0.4794255386042030002732879352
         >>> print(sin(0.5))
         0.479425538604
         >>> print(sin(0.5+0j))
         (0.479425538604+0j)

         """
         getcontext().prec += 2
         i, lasts, s, fact, num, sign = 1, 0, x, 1, x, 1
         while s != lasts:
             lasts = s
             i += 2
             fact *= i * (i-1)
             num *= x * x
             sign *= -1
             s += num / fact * sign
         getcontext().prec -= 2
         return +s


File: python.info,  Node: Decimal FAQ,  Prev: Recipes,  Up: decimal — Decimal fixed point and floating point arithmetic

5.9.4.13 Decimal FAQ
....................

Q. It is cumbersome to type ‘decimal.Decimal('1234.5')’.  Is there a way
to minimize typing when using the interactive interpreter?

A. Some users abbreviate the constructor to just a single letter:

     >>> D = decimal.Decimal
     >>> D('1.23') + D('3.45')
     Decimal('4.68')

Q. In a fixed-point application with two decimal places, some inputs
have many places and need to be rounded.  Others are not supposed to
have excess digits and need to be validated.  What methods should be
used?

A. The ‘quantize()’ method rounds to a fixed number of decimal places.
If the *note Inexact: 1bbf. trap is set, it is also useful for
validation:

     >>> TWOPLACES = Decimal(10) ** -2       # same as Decimal('0.01')

     >>> # Round to two places
     >>> Decimal('3.214').quantize(TWOPLACES)
     Decimal('3.21')

     >>> # Validate that a number does not exceed two places
     >>> Decimal('3.21').quantize(TWOPLACES, context=Context(traps=[Inexact]))
     Decimal('3.21')

     >>> Decimal('3.214').quantize(TWOPLACES, context=Context(traps=[Inexact]))
     Traceback (most recent call last):
        ...
     Inexact: None

Q. Once I have valid two place inputs, how do I maintain that invariant
throughout an application?

A. Some operations like addition, subtraction, and multiplication by an
integer will automatically preserve fixed point.  Others operations,
like division and non-integer multiplication, will change the number of
decimal places and need to be followed-up with a ‘quantize()’ step:

     >>> a = Decimal('102.72')           # Initial fixed-point values
     >>> b = Decimal('3.17')
     >>> a + b                           # Addition preserves fixed-point
     Decimal('105.89')
     >>> a - b
     Decimal('99.55')
     >>> a * 42                          # So does integer multiplication
     Decimal('4314.24')
     >>> (a * b).quantize(TWOPLACES)     # Must quantize non-integer multiplication
     Decimal('325.62')
     >>> (b / a).quantize(TWOPLACES)     # And quantize division
     Decimal('0.03')

In developing fixed-point applications, it is convenient to define
functions to handle the ‘quantize()’ step:

     >>> def mul(x, y, fp=TWOPLACES):
     ...     return (x * y).quantize(fp)
     >>> def div(x, y, fp=TWOPLACES):
     ...     return (x / y).quantize(fp)

     >>> mul(a, b)                       # Automatically preserve fixed-point
     Decimal('325.62')
     >>> div(b, a)
     Decimal('0.03')

Q. There are many ways to express the same value.  The numbers ‘200’,
‘200.000’, ‘2E2’, and ‘02E+4’ all have the same value at various
precisions.  Is there a way to transform them to a single recognizable
canonical value?

A. The ‘normalize()’ method maps all equivalent values to a single
representative:

     >>> values = map(Decimal, '200 200.000 2E2 .02E+4'.split())
     >>> [v.normalize() for v in values]
     [Decimal('2E+2'), Decimal('2E+2'), Decimal('2E+2'), Decimal('2E+2')]

Q. Some decimal values always print with exponential notation.  Is there
a way to get a non-exponential representation?

A. For some values, exponential notation is the only way to express the
number of significant places in the coefficient.  For example,
expressing ‘5.0E+3’ as ‘5000’ keeps the value constant but cannot show
the original’s two-place significance.

If an application does not care about tracking significance, it is easy
to remove the exponent and trailing zeroes, losing significance, but
keeping the value unchanged:

     >>> def remove_exponent(d):
     ...     return d.quantize(Decimal(1)) if d == d.to_integral() else d.normalize()

     >>> remove_exponent(Decimal('5E+3'))
     Decimal('5000')

Q. Is there a way to convert a regular float to a *note Decimal: 2c0.?

A. Yes, any binary floating point number can be exactly expressed as a
Decimal though an exact conversion may take more precision than
intuition would suggest:

     >>> Decimal(math.pi)
     Decimal('3.141592653589793115997963468544185161590576171875')

Q. Within a complex calculation, how can I make sure that I haven’t
gotten a spurious result because of insufficient precision or rounding
anomalies.

A. The decimal module makes it easy to test results.  A best practice is
to re-run calculations using greater precision and with various rounding
modes.  Widely differing results indicate insufficient precision,
rounding mode issues, ill-conditioned inputs, or a numerically unstable
algorithm.

Q. I noticed that context precision is applied to the results of
operations but not to the inputs.  Is there anything to watch out for
when mixing values of different precisions?

A. Yes.  The principle is that all values are considered to be exact and
so is the arithmetic on those values.  Only the results are rounded.
The advantage for inputs is that “what you type is what you get”.  A
disadvantage is that the results can look odd if you forget that the
inputs haven’t been rounded:

     >>> getcontext().prec = 3
     >>> Decimal('3.104') + Decimal('2.104')
     Decimal('5.21')
     >>> Decimal('3.104') + Decimal('0.000') + Decimal('2.104')
     Decimal('5.20')

The solution is either to increase precision or to force rounding of
inputs using the unary plus operation:

     >>> getcontext().prec = 3
     >>> +Decimal('1.23456789')      # unary plus triggers rounding
     Decimal('1.23')

Alternatively, inputs can be rounded upon creation using the *note
Context.create_decimal(): acb. method:

     >>> Context(prec=5, rounding=ROUND_DOWN).create_decimal('1.2345678')
     Decimal('1.2345')

Q. Is the CPython implementation fast for large numbers?

A. Yes.  In the CPython and PyPy3 implementations, the C/CFFI versions
of the decimal module integrate the high speed libmpdec(1) library for
arbitrary precision correctly-rounded decimal floating point arithmetic
(2).  ‘libmpdec’ uses Karatsuba multiplication(3) for medium-sized
numbers and the Number Theoretic Transform(4) for very large numbers.

The context must be adapted for exact arbitrary precision arithmetic.
‘Emin’ and ‘Emax’ should always be set to the maximum values, ‘clamp’
should always be 0 (the default).  Setting ‘prec’ requires some care.

The easiest approach for trying out bignum arithmetic is to use the
maximum value for ‘prec’ as well (5):

     >>> setcontext(Context(prec=MAX_PREC, Emax=MAX_EMAX, Emin=MIN_EMIN))
     >>> x = Decimal(2) ** 256
     >>> x / 128
     Decimal('904625697166532776746648320380374280103671755200316906558262375061821325312')

For inexact results, *note MAX_PREC: 1bfe. is far too large on 64-bit
platforms and the available memory will be insufficient:

     >>> Decimal(1) / 3
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     MemoryError

On systems with overallocation (e.g.  Linux), a more sophisticated
approach is to adjust ‘prec’ to the amount of available RAM. Suppose
that you have 8GB of RAM and expect 10 simultaneous operands using a
maximum of 500MB each:

     >>> import sys
     >>>
     >>> # Maximum number of digits for a single operand using 500MB in 8-byte words
     >>> # with 19 digits per word (4-byte and 9 digits for the 32-bit build):
     >>> maxdigits = 19 * ((500 * 1024**2) // 8)
     >>>
     >>> # Check that this works:
     >>> c = Context(prec=maxdigits, Emax=MAX_EMAX, Emin=MIN_EMIN)
     >>> c.traps[Inexact] = True
     >>> setcontext(c)
     >>>
     >>> # Fill the available precision with nines:
     >>> x = Decimal(0).logical_invert() * 9
     >>> sys.getsizeof(x)
     524288112
     >>> x + 2
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
       decimal.Inexact: [<class 'decimal.Inexact'>]

In general (and especially on systems without overallocation), it is
recommended to estimate even tighter bounds and set the *note Inexact:
1bbf. trap if all calculations are expected to be exact.

   ---------- Footnotes ----------

   (1) https://www.bytereef.org/mpdecimal/doc/libmpdec/index.html

   (2) (1)

New in version 3.3.

   (3) https://en.wikipedia.org/wiki/Karatsuba_algorithm

   (4) 
https://en.wikipedia.org/wiki/Discrete_Fourier_transform_(general)#Number-theoretic_transform

   (5) (2)

Changed in version 3.9: This approach now works for all exact results
except for non-integer powers.


File: python.info,  Node: fractions — Rational numbers,  Next: random — Generate pseudo-random numbers,  Prev: decimal — Decimal fixed point and floating point arithmetic,  Up: Numeric and Mathematical Modules

5.9.5 ‘fractions’ — Rational numbers
------------------------------------

`Source code:' Lib/fractions.py(1)

__________________________________________________________________

The *note fractions: 81. module provides support for rational number
arithmetic.

A Fraction instance can be constructed from a pair of integers, from
another rational number, or from a string.

 -- Class: fractions.Fraction (numerator=0, denominator=1)

 -- Class: fractions.Fraction (other_fraction)

 -- Class: fractions.Fraction (float)

 -- Class: fractions.Fraction (decimal)

 -- Class: fractions.Fraction (string)

     The first version requires that `numerator' and `denominator' are
     instances of *note numbers.Rational: d20. and returns a new *note
     Fraction: 2be. instance with value ‘numerator/denominator’.  If
     `denominator' is ‘0’, it raises a *note ZeroDivisionError: 1fa.
     The second version requires that `other_fraction' is an instance of
     *note numbers.Rational: d20. and returns a *note Fraction: 2be.
     instance with the same value.  The next two versions accept either
     a *note float: 1fd. or a *note decimal.Decimal: 2c0. instance, and
     return a *note Fraction: 2be. instance with exactly the same value.
     Note that due to the usual issues with binary floating-point (see
     *note Floating Point Arithmetic; Issues and Limitations: 1456.),
     the argument to ‘Fraction(1.1)’ is not exactly equal to 11/10, and
     so ‘Fraction(1.1)’ does `not' return ‘Fraction(11, 10)’ as one
     might expect.  (But see the documentation for the *note
     limit_denominator(): 1c54. method below.)  The last version of the
     constructor expects a string or unicode instance.  The usual form
     for this instance is:

          [sign] numerator ['/' denominator]

     where the optional ‘sign’ may be either ‘+’ or ‘-’ and ‘numerator’
     and ‘denominator’ (if present) are strings of decimal digits.  In
     addition, any string that represents a finite value and is accepted
     by the *note float: 1fd. constructor is also accepted by the *note
     Fraction: 2be. constructor.  In either form the input string may
     also have leading and/or trailing whitespace.  Here are some
     examples:

          >>> from fractions import Fraction
          >>> Fraction(16, -10)
          Fraction(-8, 5)
          >>> Fraction(123)
          Fraction(123, 1)
          >>> Fraction()
          Fraction(0, 1)
          >>> Fraction('3/7')
          Fraction(3, 7)
          >>> Fraction(' -3/7 ')
          Fraction(-3, 7)
          >>> Fraction('1.414213 \t\n')
          Fraction(1414213, 1000000)
          >>> Fraction('-.125')
          Fraction(-1, 8)
          >>> Fraction('7e-6')
          Fraction(7, 1000000)
          >>> Fraction(2.25)
          Fraction(9, 4)
          >>> Fraction(1.1)
          Fraction(2476979795053773, 2251799813685248)
          >>> from decimal import Decimal
          >>> Fraction(Decimal('1.1'))
          Fraction(11, 10)

     The *note Fraction: 2be. class inherits from the abstract base
     class *note numbers.Rational: d20, and implements all of the
     methods and operations from that class.  *note Fraction: 2be.
     instances are hashable, and should be treated as immutable.  In
     addition, *note Fraction: 2be. has the following properties and
     methods:

     Changed in version 3.2: The *note Fraction: 2be. constructor now
     accepts *note float: 1fd. and *note decimal.Decimal: 2c0.
     instances.

     Changed in version 3.9: The *note math.gcd(): 1be. function is now
     used to normalize the `numerator' and `denominator'.  *note
     math.gcd(): 1be. always return a *note int: 204. type.  Previously,
     the GCD type depended on `numerator' and `denominator'.

      -- Attribute: numerator

          Numerator of the Fraction in lowest term.

      -- Attribute: denominator

          Denominator of the Fraction in lowest term.

      -- Method: as_integer_ratio ()

          Return a tuple of two integers, whose ratio is equal to the
          Fraction and with a positive denominator.

          New in version 3.8.

      -- Method: from_float (flt)

          This class method constructs a *note Fraction: 2be.
          representing the exact value of `flt', which must be a *note
          float: 1fd.  Beware that ‘Fraction.from_float(0.3)’ is not the
          same value as ‘Fraction(3, 10)’.

               Note: From Python 3.2 onwards, you can also construct a
               *note Fraction: 2be. instance directly from a *note
               float: 1fd.

      -- Method: from_decimal (dec)

          This class method constructs a *note Fraction: 2be.
          representing the exact value of `dec', which must be a *note
          decimal.Decimal: 2c0. instance.

               Note: From Python 3.2 onwards, you can also construct a
               *note Fraction: 2be. instance directly from a *note
               decimal.Decimal: 2c0. instance.

      -- Method: limit_denominator (max_denominator=1000000)

          Finds and returns the closest *note Fraction: 2be. to ‘self’
          that has denominator at most max_denominator.  This method is
          useful for finding rational approximations to a given
          floating-point number:

               >>> from fractions import Fraction
               >>> Fraction('3.1415926535897932').limit_denominator(1000)
               Fraction(355, 113)

          or for recovering a rational number that’s represented as a
          float:

               >>> from math import pi, cos
               >>> Fraction(cos(pi/3))
               Fraction(4503599627370497, 9007199254740992)
               >>> Fraction(cos(pi/3)).limit_denominator()
               Fraction(1, 2)
               >>> Fraction(1.1).limit_denominator()
               Fraction(11, 10)

      -- Method: __floor__ ()

          Returns the greatest *note int: 204. ‘<= self’.  This method
          can also be accessed through the *note math.floor(): df2.
          function:

               >>> from math import floor
               >>> floor(Fraction(355, 113))
               3

      -- Method: __ceil__ ()

          Returns the least *note int: 204. ‘>= self’.  This method can
          also be accessed through the *note math.ceil(): df3. function.

      -- Method: __round__ ()

      -- Method: __round__ (ndigits)

          The first version returns the nearest *note int: 204. to
          ‘self’, rounding half to even.  The second version rounds
          ‘self’ to the nearest multiple of ‘Fraction(1, 10**ndigits)’
          (logically, if ‘ndigits’ is negative), again rounding half
          toward even.  This method can also be accessed through the
          *note round(): d35. function.

See also
........

Module *note numbers: c1.

     The abstract base classes making up the numeric tower.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/fractions.py


File: python.info,  Node: random — Generate pseudo-random numbers,  Next: statistics — Mathematical statistics functions,  Prev: fractions — Rational numbers,  Up: Numeric and Mathematical Modules

5.9.6 ‘random’ — Generate pseudo-random numbers
-----------------------------------------------

`Source code:' Lib/random.py(1)

__________________________________________________________________

This module implements pseudo-random number generators for various
distributions.

For integers, there is uniform selection from a range.  For sequences,
there is uniform selection of a random element, a function to generate a
random permutation of a list in-place, and a function for random
sampling without replacement.

On the real line, there are functions to compute uniform, normal
(Gaussian), lognormal, negative exponential, gamma, and beta
distributions.  For generating distributions of angles, the von Mises
distribution is available.

Almost all module functions depend on the basic function *note random():
1c5d, which generates a random float uniformly in the semi-open range
[0.0, 1.0).  Python uses the Mersenne Twister as the core generator.  It
produces 53-bit precision floats and has a period of 2**19937-1.  The
underlying implementation in C is both fast and threadsafe.  The
Mersenne Twister is one of the most extensively tested random number
generators in existence.  However, being completely deterministic, it is
not suitable for all purposes, and is completely unsuitable for
cryptographic purposes.

The functions supplied by this module are actually bound methods of a
hidden instance of the *note random.Random: 1c5e. class.  You can
instantiate your own instances of *note Random: 1c5e. to get generators
that don’t share state.

Class *note Random: 1c5e. can also be subclassed if you want to use a
different basic generator of your own devising: in that case, override
the ‘random()’, ‘seed()’, ‘getstate()’, and ‘setstate()’ methods.
Optionally, a new generator can supply a ‘getrandbits()’ method — this
allows *note randrange(): c8b. to produce selections over an arbitrarily
large range.

The *note random: dc. module also provides the *note SystemRandom: 1c5f.
class which uses the system function *note os.urandom(): 5cc. to
generate random numbers from sources provided by the operating system.

     Warning: The pseudo-random generators of this module should not be
     used for security purposes.  For security or cryptographic uses,
     see the *note secrets: e4. module.

See also
........

M. Matsumoto and T. Nishimura, “Mersenne Twister: A 623-dimensionally
equidistributed uniform pseudorandom number generator”, ACM Transactions
on Modeling and Computer Simulation Vol.  8, No.  1, January pp.3–30
1998.

Complementary-Multiply-with-Carry recipe(2) for a compatible alternative
random number generator with a long period and comparatively simple
update operations.

* Menu:

* Bookkeeping functions::
* Functions for bytes::
* Functions for integers::
* Functions for sequences::
* Real-valued distributions::
* Alternative Generator::
* Notes on Reproducibility::
* Examples: Examples<3>.
* Recipes: Recipes<2>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/random.py

   (2) https://code.activestate.com/recipes/576707/


File: python.info,  Node: Bookkeeping functions,  Next: Functions for bytes,  Up: random — Generate pseudo-random numbers

5.9.6.1 Bookkeeping functions
.............................

 -- Function: random.seed (a=None, version=2)

     Initialize the random number generator.

     If `a' is omitted or ‘None’, the current system time is used.  If
     randomness sources are provided by the operating system, they are
     used instead of the system time (see the *note os.urandom(): 5cc.
     function for details on availability).

     If `a' is an int, it is used directly.

     With version 2 (the default), a *note str: 205, *note bytes: 172,
     or *note bytearray: 173. object gets converted to an *note int:
     204. and all of its bits are used.

     With version 1 (provided for reproducing random sequences from
     older versions of Python), the algorithm for *note str: 205. and
     *note bytes: 172. generates a narrower range of seeds.

     Changed in version 3.2: Moved to the version 2 scheme which uses
     all of the bits in a string seed.

     Deprecated since version 3.9: In the future, the `seed' must be one
     of the following types: `NoneType', *note int: 204, *note float:
     1fd, *note str: 205, *note bytes: 172, or *note bytearray: 173.

 -- Function: random.getstate ()

     Return an object capturing the current internal state of the
     generator.  This object can be passed to *note setstate(): 1c62. to
     restore the state.

 -- Function: random.setstate (state)

     `state' should have been obtained from a previous call to *note
     getstate(): 1c61, and *note setstate(): 1c62. restores the internal
     state of the generator to what it was at the time *note getstate():
     1c61. was called.


File: python.info,  Node: Functions for bytes,  Next: Functions for integers,  Prev: Bookkeeping functions,  Up: random — Generate pseudo-random numbers

5.9.6.2 Functions for bytes
...........................

 -- Function: random.randbytes (n)

     Generate `n' random bytes.

     This method should not be used for generating security tokens.  Use
     *note secrets.token_bytes(): 1c64. instead.

     New in version 3.9.


File: python.info,  Node: Functions for integers,  Next: Functions for sequences,  Prev: Functions for bytes,  Up: random — Generate pseudo-random numbers

5.9.6.3 Functions for integers
..............................

 -- Function: random.randrange (stop)

 -- Function: random.randrange (start, stop[, step])

     Return a randomly selected element from ‘range(start, stop, step)’.
     This is equivalent to ‘choice(range(start, stop, step))’, but
     doesn’t actually build a range object.

     The positional argument pattern matches that of *note range(): 1f5.
     Keyword arguments should not be used because the function may use
     them in unexpected ways.

     Changed in version 3.2: *note randrange(): c8b. is more
     sophisticated about producing equally distributed values.  Formerly
     it used a style like ‘int(random()*n)’ which could produce slightly
     uneven distributions.

 -- Function: random.randint (a, b)

     Return a random integer `N' such that ‘a <= N <= b’.  Alias for
     ‘randrange(a, b+1)’.

 -- Function: random.getrandbits (k)

     Returns a non-negative Python integer with `k' random bits.  This
     method is supplied with the MersenneTwister generator and some
     other generators may also provide it as an optional part of the
     API. When available, *note getrandbits(): a17. enables *note
     randrange(): c8b. to handle arbitrarily large ranges.

     Changed in version 3.9: This method now accepts zero for `k'.


File: python.info,  Node: Functions for sequences,  Next: Real-valued distributions,  Prev: Functions for integers,  Up: random — Generate pseudo-random numbers

5.9.6.4 Functions for sequences
...............................

 -- Function: random.choice (seq)

     Return a random element from the non-empty sequence `seq'.  If
     `seq' is empty, raises *note IndexError: f36.

 -- Function: random.choices (population, weights=None, *,
          cum_weights=None, k=1)

     Return a `k' sized list of elements chosen from the `population'
     with replacement.  If the `population' is empty, raises *note
     IndexError: f36.

     If a `weights' sequence is specified, selections are made according
     to the relative weights.  Alternatively, if a `cum_weights'
     sequence is given, the selections are made according to the
     cumulative weights (perhaps computed using *note
     itertools.accumulate(): 30e.).  For example, the relative weights
     ‘[10, 5, 30, 5]’ are equivalent to the cumulative weights ‘[10, 15,
     45, 50]’.  Internally, the relative weights are converted to
     cumulative weights before making selections, so supplying the
     cumulative weights saves work.

     If neither `weights' nor `cum_weights' are specified, selections
     are made with equal probability.  If a weights sequence is
     supplied, it must be the same length as the `population' sequence.
     It is a *note TypeError: 1fe. to specify both `weights' and
     `cum_weights'.

     The `weights' or `cum_weights' can use any numeric type that
     interoperates with the *note float: 1fd. values returned by *note
     random(): dc. (that includes integers, floats, and fractions but
     excludes decimals).  Behavior is undefined if any weight is
     negative.  A *note ValueError: 16d. is raised if all weights are
     zero.

     For a given seed, the *note choices(): 66b. function with equal
     weighting typically produces a different sequence than repeated
     calls to *note choice(): c8d.  The algorithm used by *note
     choices(): 66b. uses floating point arithmetic for internal
     consistency and speed.  The algorithm used by *note choice(): c8d.
     defaults to integer arithmetic with repeated selections to avoid
     small biases from round-off error.

     New in version 3.6.

     Changed in version 3.9: Raises a *note ValueError: 16d. if all
     weights are zero.

 -- Function: random.shuffle (x[, random])

     Shuffle the sequence `x' in place.

     The optional argument `random' is a 0-argument function returning a
     random float in [0.0, 1.0); by default, this is the function *note
     random(): 1c5d.

     To shuffle an immutable sequence and return a new shuffled list,
     use ‘sample(x, k=len(x))’ instead.

     Note that even for small ‘len(x)’, the total number of permutations
     of `x' can quickly grow larger than the period of most random
     number generators.  This implies that most permutations of a long
     sequence can never be generated.  For example, a sequence of length
     2080 is the largest that can fit within the period of the Mersenne
     Twister random number generator.

     Deprecated since version 3.9, will be removed in version 3.11: The
     optional parameter `random'.

 -- Function: random.sample (population, k, *, counts=None)

     Return a `k' length list of unique elements chosen from the
     population sequence or set.  Used for random sampling without
     replacement.

     Returns a new list containing elements from the population while
     leaving the original population unchanged.  The resulting list is
     in selection order so that all sub-slices will also be valid random
     samples.  This allows raffle winners (the sample) to be partitioned
     into grand prize and second place winners (the subslices).

     Members of the population need not be *note hashable: 276. or
     unique.  If the population contains repeats, then each occurrence
     is a possible selection in the sample.

     Repeated elements can be specified one at a time or with the
     optional keyword-only `counts' parameter.  For example,
     ‘sample(['red', 'blue'], counts=[4, 2], k=5)’ is equivalent to
     ‘sample(['red', 'red', 'red', 'red', 'blue', 'blue'], k=5)’.

     To choose a sample from a range of integers, use a *note range():
     1f5. object as an argument.  This is especially fast and space
     efficient for sampling from a large population:
     ‘sample(range(10000000), k=60)’.

     If the sample size is larger than the population size, a *note
     ValueError: 16d. is raised.

     Changed in version 3.9: Added the `counts' parameter.

     Deprecated since version 3.9: In the future, the `population' must
     be a sequence.  Instances of *note set: 1f6. are no longer
     supported.  The set must first be converted to a *note list: 1f8.
     or *note tuple: 1a2, preferably in a deterministic order so that
     the sample is reproducible.


File: python.info,  Node: Real-valued distributions,  Next: Alternative Generator,  Prev: Functions for sequences,  Up: random — Generate pseudo-random numbers

5.9.6.5 Real-valued distributions
.................................

The following functions generate specific real-valued distributions.
Function parameters are named after the corresponding variables in the
distribution’s equation, as used in common mathematical practice; most
of these equations can be found in any statistics text.

 -- Function: random.random ()

     Return the next random floating point number in the range [0.0,
     1.0).

 -- Function: random.uniform (a, b)

     Return a random floating point number `N' such that ‘a <= N <= b’
     for ‘a <= b’ and ‘b <= N <= a’ for ‘b < a’.

     The end-point value ‘b’ may or may not be included in the range
     depending on floating-point rounding in the equation ‘a + (b-a) *
     random()’.

 -- Function: random.triangular (low, high, mode)

     Return a random floating point number `N' such that ‘low <= N <=
     high’ and with the specified `mode' between those bounds.  The
     `low' and `high' bounds default to zero and one.  The `mode'
     argument defaults to the midpoint between the bounds, giving a
     symmetric distribution.

 -- Function: random.betavariate (alpha, beta)

     Beta distribution.  Conditions on the parameters are ‘alpha > 0’
     and ‘beta > 0’.  Returned values range between 0 and 1.

 -- Function: random.expovariate (lambd)

     Exponential distribution.  `lambd' is 1.0 divided by the desired
     mean.  It should be nonzero.  (The parameter would be called
     “lambda”, but that is a reserved word in Python.)  Returned values
     range from 0 to positive infinity if `lambd' is positive, and from
     negative infinity to 0 if `lambd' is negative.

 -- Function: random.gammavariate (alpha, beta)

     Gamma distribution.  (`Not' the gamma function!)  Conditions on the
     parameters are ‘alpha > 0’ and ‘beta > 0’.

     The probability distribution function is:

                    x ** (alpha - 1) * math.exp(-x / beta)
          pdf(x) =  --------------------------------------
                      math.gamma(alpha) * beta ** alpha

 -- Function: random.gauss (mu, sigma)

     Gaussian distribution.  `mu' is the mean, and `sigma' is the
     standard deviation.  This is slightly faster than the *note
     normalvariate(): 1c6f. function defined below.

     Multithreading note: When two threads call this function
     simultaneously, it is possible that they will receive the same
     return value.  This can be avoided in three ways.  1) Have each
     thread use a different instance of the random number generator.  2)
     Put locks around all calls.  3) Use the slower, but thread-safe
     *note normalvariate(): 1c6f. function instead.

 -- Function: random.lognormvariate (mu, sigma)

     Log normal distribution.  If you take the natural logarithm of this
     distribution, you’ll get a normal distribution with mean `mu' and
     standard deviation `sigma'.  `mu' can have any value, and `sigma'
     must be greater than zero.

 -- Function: random.normalvariate (mu, sigma)

     Normal distribution.  `mu' is the mean, and `sigma' is the standard
     deviation.

 -- Function: random.vonmisesvariate (mu, kappa)

     `mu' is the mean angle, expressed in radians between 0 and 2*`pi',
     and `kappa' is the concentration parameter, which must be greater
     than or equal to zero.  If `kappa' is equal to zero, this
     distribution reduces to a uniform random angle over the range 0 to
     2*`pi'.

 -- Function: random.paretovariate (alpha)

     Pareto distribution.  `alpha' is the shape parameter.

 -- Function: random.weibullvariate (alpha, beta)

     Weibull distribution.  `alpha' is the scale parameter and `beta' is
     the shape parameter.


File: python.info,  Node: Alternative Generator,  Next: Notes on Reproducibility,  Prev: Real-valued distributions,  Up: random — Generate pseudo-random numbers

5.9.6.6 Alternative Generator
.............................

 -- Class: random.Random ([seed])

     Class that implements the default pseudo-random number generator
     used by the *note random: dc. module.

     Deprecated since version 3.9: In the future, the `seed' must be one
     of the following types: ‘NoneType’, *note int: 204, *note float:
     1fd, *note str: 205, *note bytes: 172, or *note bytearray: 173.

 -- Class: random.SystemRandom ([seed])

     Class that uses the *note os.urandom(): 5cc. function for
     generating random numbers from sources provided by the operating
     system.  Not available on all systems.  Does not rely on software
     state, and sequences are not reproducible.  Accordingly, the *note
     seed(): cd3. method has no effect and is ignored.  The *note
     getstate(): 1c61. and *note setstate(): 1c62. methods raise *note
     NotImplementedError: 704. if called.


File: python.info,  Node: Notes on Reproducibility,  Next: Examples<3>,  Prev: Alternative Generator,  Up: random — Generate pseudo-random numbers

5.9.6.7 Notes on Reproducibility
................................

Sometimes it is useful to be able to reproduce the sequences given by a
pseudo-random number generator.  By re-using a seed value, the same
sequence should be reproducible from run to run as long as multiple
threads are not running.

Most of the random module’s algorithms and seeding functions are subject
to change across Python versions, but two aspects are guaranteed not to
change:

   * If a new seeding method is added, then a backward compatible seeder
     will be offered.

   * The generator’s ‘random()’ method will continue to produce the same
     sequence when the compatible seeder is given the same seed.


File: python.info,  Node: Examples<3>,  Next: Recipes<2>,  Prev: Notes on Reproducibility,  Up: random — Generate pseudo-random numbers

5.9.6.8 Examples
................

Basic examples:

     >>> random()                             # Random float:  0.0 <= x < 1.0
     0.37444887175646646

     >>> uniform(2.5, 10.0)                   # Random float:  2.5 <= x <= 10.0
     3.1800146073117523

     >>> expovariate(1 / 5)                   # Interval between arrivals averaging 5 seconds
     5.148957571865031

     >>> randrange(10)                        # Integer from 0 to 9 inclusive
     7

     >>> randrange(0, 101, 2)                 # Even integer from 0 to 100 inclusive
     26

     >>> choice(['win', 'lose', 'draw'])      # Single random element from a sequence
     'draw'

     >>> deck = 'ace two three four'.split()
     >>> shuffle(deck)                        # Shuffle a list
     >>> deck
     ['four', 'two', 'ace', 'three']

     >>> sample([10, 20, 30, 40, 50], k=4)    # Four samples without replacement
     [40, 10, 50, 30]

Simulations:

     >>> # Six roulette wheel spins (weighted sampling with replacement)
     >>> choices(['red', 'black', 'green'], [18, 18, 2], k=6)
     ['red', 'green', 'black', 'black', 'red', 'black']

     >>> # Deal 20 cards without replacement from a deck
     >>> # of 52 playing cards, and determine the proportion of cards
     >>> # with a ten-value:  ten, jack, queen, or king.
     >>> dealt = sample(['tens', 'low cards'], counts=[16, 36], k=20)
     >>> dealt.count('tens') / 20
     0.15

     >>> # Estimate the probability of getting 5 or more heads from 7 spins
     >>> # of a biased coin that settles on heads 60% of the time.
     >>> def trial():
     ...     return choices('HT', cum_weights=(0.60, 1.00), k=7).count('H') >= 5
     ...
     >>> sum(trial() for i in range(10_000)) / 10_000
     0.4169

     >>> # Probability of the median of 5 samples being in middle two quartiles
     >>> def trial():
     ...     return 2_500 <= sorted(choices(range(10_000), k=5))[2] < 7_500
     ...
     >>> sum(trial() for i in range(10_000)) / 10_000
     0.7958

Example of statistical bootstrapping(1) using resampling with
replacement to estimate a confidence interval for the mean of a sample:

     # http://statistics.about.com/od/Applications/a/Example-Of-Bootstrapping.htm
     from statistics import fmean as mean
     from random import choices

     data = [41, 50, 29, 37, 81, 30, 73, 63, 20, 35, 68, 22, 60, 31, 95]
     means = sorted(mean(choices(data, k=len(data))) for i in range(100))
     print(f'The sample mean of {mean(data):.1f} has a 90% confidence '
           f'interval from {means[5]:.1f} to {means[94]:.1f}')

Example of a resampling permutation test(2) to determine the statistical
significance or p-value(3) of an observed difference between the effects
of a drug versus a placebo:

     # Example from "Statistics is Easy" by Dennis Shasha and Manda Wilson
     from statistics import fmean as mean
     from random import shuffle

     drug = [54, 73, 53, 70, 73, 68, 52, 65, 65]
     placebo = [54, 51, 58, 44, 55, 52, 42, 47, 58, 46]
     observed_diff = mean(drug) - mean(placebo)

     n = 10_000
     count = 0
     combined = drug + placebo
     for i in range(n):
         shuffle(combined)
         new_diff = mean(combined[:len(drug)]) - mean(combined[len(drug):])
         count += (new_diff >= observed_diff)

     print(f'{n} label reshufflings produced only {count} instances with a difference')
     print(f'at least as extreme as the observed difference of {observed_diff:.1f}.')
     print(f'The one-sided p-value of {count / n:.4f} leads us to reject the null')
     print(f'hypothesis that there is no difference between the drug and the placebo.')

Simulation of arrival times and service deliveries for a multiserver
queue:

     from heapq import heapify, heapreplace
     from random import expovariate, gauss
     from statistics import mean, median, stdev

     average_arrival_interval = 5.6
     average_service_time = 15.0
     stdev_service_time = 3.5
     num_servers = 3

     waits = []
     arrival_time = 0.0
     servers = [0.0] * num_servers  # time when each server becomes available
     heapify(servers)
     for i in range(1_000_000):
         arrival_time += expovariate(1.0 / average_arrival_interval)
         next_server_available = servers[0]
         wait = max(0.0, next_server_available - arrival_time)
         waits.append(wait)
         service_duration = max(0.0, gauss(average_service_time, stdev_service_time))
         service_completed = arrival_time + wait + service_duration
         heapreplace(servers, service_completed)

     print(f'Mean wait: {mean(waits):.1f}.  Stdev wait: {stdev(waits):.1f}.')
     print(f'Median wait: {median(waits):.1f}.  Max wait: {max(waits):.1f}.')

See also
........

Statistics for Hackers(4) a video tutorial by Jake Vanderplas(5) on
statistical analysis using just a few fundamental concepts including
simulation, sampling, shuffling, and cross-validation.

Economics Simulation(6) a simulation of a marketplace by Peter Norvig(7)
that shows effective use of many of the tools and distributions provided
by this module (gauss, uniform, sample, betavariate, choice, triangular,
and randrange).

A Concrete Introduction to Probability (using Python)(8) a tutorial by
Peter Norvig(9) covering the basics of probability theory, how to write
simulations, and how to perform data analysis using Python.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Bootstrapping_(statistics)

   (2) 
https://en.wikipedia.org/wiki/Resampling_(statistics)#Permutation_tests

   (3) https://en.wikipedia.org/wiki/P-value

   (4) https://www.youtube.com/watch?v=Iq9DzN6mvYA

   (5) https://us.pycon.org/2016/speaker/profile/295/

   (6) 
http://nbviewer.jupyter.org/url/norvig.com/ipython/Economics.ipynb

   (7) http://norvig.com/bio.html

   (8) 
http://nbviewer.jupyter.org/url/norvig.com/ipython/Probability.ipynb

   (9) http://norvig.com/bio.html


File: python.info,  Node: Recipes<2>,  Prev: Examples<3>,  Up: random — Generate pseudo-random numbers

5.9.6.9 Recipes
...............

The default *note random(): 1c5d. returns multiples of 2⁻⁵³ in the range
`0.0 ≤ x < 1.0'.  All such numbers are evenly spaced and are exactly
representable as Python floats.  However, many other representable
floats in that interval are not possible selections.  For example,
‘0.05954861408025609’ isn’t an integer multiple of 2⁻⁵³.

The following recipe takes a different approach.  All floats in the
interval are possible selections.  The mantissa comes from a uniform
distribution of integers in the range `2⁵² ≤ mantissa < 2⁵³'.  The
exponent comes from a geometric distribution where exponents smaller
than `-53' occur half as often as the next larger exponent.

     from random import Random
     from math import ldexp

     class FullRandom(Random):

         def random(self):
             mantissa = 0x10_0000_0000_0000 | self.getrandbits(52)
             exponent = -53
             x = 0
             while not x:
                 x = self.getrandbits(32)
                 exponent += x.bit_length() - 32
             return ldexp(mantissa, exponent)

All *note real valued distributions: 1c68. in the class will use the new
method:

     >>> fr = FullRandom()
     >>> fr.random()
     0.05954861408025609
     >>> fr.expovariate(0.25)
     8.87925541791544

The recipe is conceptually equivalent to an algorithm that chooses from
all the multiples of 2⁻¹⁰⁷⁴ in the range `0.0 ≤ x < 1.0'.  All such
numbers are evenly spaced, but most have to be rounded down to the
nearest representable Python float.  (The value 2⁻¹⁰⁷⁴ is the smallest
positive unnormalized float and is equal to ‘math.ulp(0.0)’.)

See also
........

Generating Pseudo-random Floating-Point Values(1) a paper by Allen B.
Downey describing ways to generate more fine-grained floats than
normally generated by *note random(): 1c5d.

   ---------- Footnotes ----------

   (1) https://allendowney.com/research/rand/downey07randfloat.pdf


File: python.info,  Node: statistics — Mathematical statistics functions,  Prev: random — Generate pseudo-random numbers,  Up: Numeric and Mathematical Modules

5.9.7 ‘statistics’ — Mathematical statistics functions
------------------------------------------------------

New in version 3.4.

`Source code:' Lib/statistics.py(1)

__________________________________________________________________

This module provides functions for calculating mathematical statistics
of numeric (*note Real: 1557.-valued) data.

The module is not intended to be a competitor to third-party libraries
such as NumPy(2), SciPy(3), or proprietary full-featured statistics
packages aimed at professional statisticians such as Minitab, SAS and
Matlab.  It is aimed at the level of graphing and scientific
calculators.

Unless explicitly noted, these functions support *note int: 204, *note
float: 1fd, *note Decimal: 2c0. and *note Fraction: 2be.  Behaviour with
other types (whether in the numeric tower or not) is currently
unsupported.  Collections with a mix of types are also undefined and
implementation-dependent.  If your input data consists of mixed types,
you may be able to use *note map(): cf7. to ensure a consistent result,
for example: ‘map(float, input_data)’.

* Menu:

* Averages and measures of central location::
* Measures of spread::
* Function details::
* Exceptions: Exceptions<4>.
* NormalDist objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/statistics.py

   (2) https://numpy.org

   (3) https://www.scipy.org/


File: python.info,  Node: Averages and measures of central location,  Next: Measures of spread,  Up: statistics — Mathematical statistics functions

5.9.7.1 Averages and measures of central location
.................................................

These functions calculate an average or typical value from a population
or sample.

*note mean(): 2ce.          Arithmetic mean (“average”) of data.
                            
                            
*note fmean(): 354.         Fast, floating point arithmetic mean.
                            
                            
*note geometric_mean(): 355.Geometric mean of data.
                            
                            
*note harmonic_mean(): 686. Harmonic mean of data.
                            
                            
*note median(): 1c7b.       Median (middle value) of data.
                            
                            
*note median_low(): 1c7c.   Low median of data.
                            
                            
*note median_high(): 1c7d.  High median of data.
                            
                            
*note median_grouped(): 1c7e.Median, or 50th percentile, of grouped data.
                            
                            
*note mode(): 3dd.          Single mode (most common value) of discrete or nominal data.
                            
                            
*note multimode(): 356.     List of modes (most common values) of discrete or nomimal data.
                            
                            
*note quantiles(): 357.     Divide data into intervals with equal probability.
                            


File: python.info,  Node: Measures of spread,  Next: Function details,  Prev: Averages and measures of central location,  Up: statistics — Mathematical statistics functions

5.9.7.2 Measures of spread
..........................

These functions calculate a measure of how much the population or sample
tends to deviate from the typical or average values.

*note pstdev(): 1c80.       Population standard deviation of data.
                            
                            
*note pvariance(): 1c81.    Population variance of data.
                            
                            
*note stdev(): 1c82.        Sample standard deviation of data.
                            
                            
*note variance(): 1c83.     Sample variance of data.
                            


File: python.info,  Node: Function details,  Next: Exceptions<4>,  Prev: Measures of spread,  Up: statistics — Mathematical statistics functions

5.9.7.3 Function details
........................

Note: The functions do not require the data given to them to be sorted.
However, for reading convenience, most of the examples show sorted
sequences.

 -- Function: statistics.mean (data)

     Return the sample arithmetic mean of `data' which can be a sequence
     or iterable.

     The arithmetic mean is the sum of the data divided by the number of
     data points.  It is commonly called “the average”, although it is
     only one of many different mathematical averages.  It is a measure
     of the central location of the data.

     If `data' is empty, *note StatisticsError: 1c85. will be raised.

     Some examples of use:

          >>> mean([1, 2, 3, 4, 4])
          2.8
          >>> mean([-1.0, 2.5, 3.25, 5.75])
          2.625

          >>> from fractions import Fraction as F
          >>> mean([F(3, 7), F(1, 21), F(5, 3), F(1, 3)])
          Fraction(13, 21)

          >>> from decimal import Decimal as D
          >>> mean([D("0.5"), D("0.75"), D("0.625"), D("0.375")])
          Decimal('0.5625')

          Note: The mean is strongly affected by outliers(1) and is not
          necessarily a typical example of the data points.  For a more
          robust, although less efficient, measure of central
          tendency(2), see *note median(): 1c7b.

          The sample mean gives an unbiased estimate of the true
          population mean, so that when taken on average over all the
          possible samples, ‘mean(sample)’ converges on the true mean of
          the entire population.  If `data' represents the entire
          population rather than a sample, then ‘mean(data)’ is
          equivalent to calculating the true population mean μ.

 -- Function: statistics.fmean (data)

     Convert `data' to floats and compute the arithmetic mean.

     This runs faster than the *note mean(): 2ce. function and it always
     returns a *note float: 1fd.  The `data' may be a sequence or
     iterable.  If the input dataset is empty, raises a *note
     StatisticsError: 1c85.

          >>> fmean([3.5, 4.0, 5.25])
          4.25

     New in version 3.8.

 -- Function: statistics.geometric_mean (data)

     Convert `data' to floats and compute the geometric mean.

     The geometric mean indicates the central tendency or typical value
     of the `data' using the product of the values (as opposed to the
     arithmetic mean which uses their sum).

     Raises a *note StatisticsError: 1c85. if the input dataset is
     empty, if it contains a zero, or if it contains a negative value.
     The `data' may be a sequence or iterable.

     No special efforts are made to achieve exact results.  (However,
     this may change in the future.)

          >>> round(geometric_mean([54, 24, 36]), 1)
          36.0

     New in version 3.8.

 -- Function: statistics.harmonic_mean (data)

     Return the harmonic mean of `data', a sequence or iterable of
     real-valued numbers.

     The harmonic mean, sometimes called the subcontrary mean, is the
     reciprocal of the arithmetic *note mean(): 2ce. of the reciprocals
     of the data.  For example, the harmonic mean of three values `a',
     `b' and `c' will be equivalent to ‘3/(1/a + 1/b + 1/c)’.  If one of
     the values is zero, the result will be zero.

     The harmonic mean is a type of average, a measure of the central
     location of the data.  It is often appropriate when averaging rates
     or ratios, for example speeds.

     Suppose a car travels 10 km at 40 km/hr, then another 10 km at 60
     km/hr.  What is the average speed?

          >>> harmonic_mean([40, 60])
          48.0

     Suppose an investor purchases an equal value of shares in each of
     three companies, with P/E (price/earning) ratios of 2.5, 3 and 10.
     What is the average P/E ratio for the investor’s portfolio?

          >>> harmonic_mean([2.5, 3, 10])  # For an equal investment portfolio.
          3.6

     *note StatisticsError: 1c85. is raised if `data' is empty, or any
     element is less than zero.

     The current algorithm has an early-out when it encounters a zero in
     the input.  This means that the subsequent inputs are not tested
     for validity.  (This behavior may change in the future.)

     New in version 3.6.

 -- Function: statistics.median (data)

     Return the median (middle value) of numeric data, using the common
     “mean of middle two” method.  If `data' is empty, *note
     StatisticsError: 1c85. is raised.  `data' can be a sequence or
     iterable.

     The median is a robust measure of central location and is less
     affected by the presence of outliers.  When the number of data
     points is odd, the middle data point is returned:

          >>> median([1, 3, 5])
          3

     When the number of data points is even, the median is interpolated
     by taking the average of the two middle values:

          >>> median([1, 3, 5, 7])
          4.0

     This is suited for when your data is discrete, and you don’t mind
     that the median may not be an actual data point.

     If the data is ordinal (supports order operations) but not numeric
     (doesn’t support addition), consider using *note median_low():
     1c7c. or *note median_high(): 1c7d. instead.

 -- Function: statistics.median_low (data)

     Return the low median of numeric data.  If `data' is empty, *note
     StatisticsError: 1c85. is raised.  `data' can be a sequence or
     iterable.

     The low median is always a member of the data set.  When the number
     of data points is odd, the middle value is returned.  When it is
     even, the smaller of the two middle values is returned.

          >>> median_low([1, 3, 5])
          3
          >>> median_low([1, 3, 5, 7])
          3

     Use the low median when your data are discrete and you prefer the
     median to be an actual data point rather than interpolated.

 -- Function: statistics.median_high (data)

     Return the high median of data.  If `data' is empty, *note
     StatisticsError: 1c85. is raised.  `data' can be a sequence or
     iterable.

     The high median is always a member of the data set.  When the
     number of data points is odd, the middle value is returned.  When
     it is even, the larger of the two middle values is returned.

          >>> median_high([1, 3, 5])
          3
          >>> median_high([1, 3, 5, 7])
          5

     Use the high median when your data are discrete and you prefer the
     median to be an actual data point rather than interpolated.

 -- Function: statistics.median_grouped (data, interval=1)

     Return the median of grouped continuous data, calculated as the
     50th percentile, using interpolation.  If `data' is empty, *note
     StatisticsError: 1c85. is raised.  `data' can be a sequence or
     iterable.

          >>> median_grouped([52, 52, 53, 54])
          52.5

     In the following example, the data are rounded, so that each value
     represents the midpoint of data classes, e.g.  1 is the midpoint of
     the class 0.5–1.5, 2 is the midpoint of 1.5–2.5, 3 is the midpoint
     of 2.5–3.5, etc.  With the data given, the middle value falls
     somewhere in the class 3.5–4.5, and interpolation is used to
     estimate it:

          >>> median_grouped([1, 2, 2, 3, 4, 4, 4, 4, 4, 5])
          3.7

     Optional argument `interval' represents the class interval, and
     defaults to 1.  Changing the class interval naturally will change
     the interpolation:

          >>> median_grouped([1, 3, 3, 5, 7], interval=1)
          3.25
          >>> median_grouped([1, 3, 3, 5, 7], interval=2)
          3.5

     This function does not check whether the data points are at least
     `interval' apart.

     `CPython implementation detail:' Under some circumstances, *note
     median_grouped(): 1c7e. may coerce data points to floats.  This
     behaviour is likely to change in the future.

     See also
     ........

        * “Statistics for the Behavioral Sciences”, Frederick J
          Gravetter and Larry B Wallnau (8th Edition).

        * The SSMEDIAN(3) function in the Gnome Gnumeric spreadsheet,
          including this discussion(4).

 -- Function: statistics.mode (data)

     Return the single most common data point from discrete or nominal
     `data'.  The mode (when it exists) is the most typical value and
     serves as a measure of central location.

     If there are multiple modes with the same frequency, returns the
     first one encountered in the `data'.  If the smallest or largest of
     those is desired instead, use ‘min(multimode(data))’ or
     ‘max(multimode(data))’.  If the input `data' is empty, *note
     StatisticsError: 1c85. is raised.

     ‘mode’ assumes discrete data and returns a single value.  This is
     the standard treatment of the mode as commonly taught in schools:

          >>> mode([1, 1, 2, 3, 3, 3, 3, 4])
          3

     The mode is unique in that it is the only statistic in this package
     that also applies to nominal (non-numeric) data:

          >>> mode(["red", "blue", "blue", "red", "green", "red", "red"])
          'red'

     Changed in version 3.8: Now handles multimodal datasets by
     returning the first mode encountered.  Formerly, it raised *note
     StatisticsError: 1c85. when more than one mode was found.

 -- Function: statistics.multimode (data)

     Return a list of the most frequently occurring values in the order
     they were first encountered in the `data'.  Will return more than
     one result if there are multiple modes or an empty list if the
     `data' is empty:

          >>> multimode('aabbbbccddddeeffffgg')
          ['b', 'd', 'f']
          >>> multimode('')
          []

     New in version 3.8.

 -- Function: statistics.pstdev (data, mu=None)

     Return the population standard deviation (the square root of the
     population variance).  See *note pvariance(): 1c81. for arguments
     and other details.

          >>> pstdev([1.5, 2.5, 2.5, 2.75, 3.25, 4.75])
          0.986893273527251

 -- Function: statistics.pvariance (data, mu=None)

     Return the population variance of `data', a non-empty sequence or
     iterable of real-valued numbers.  Variance, or second moment about
     the mean, is a measure of the variability (spread or dispersion) of
     data.  A large variance indicates that the data is spread out; a
     small variance indicates it is clustered closely around the mean.

     If the optional second argument `mu' is given, it is typically the
     mean of the `data'.  It can also be used to compute the second
     moment around a point that is not the mean.  If it is missing or
     ‘None’ (the default), the arithmetic mean is automatically
     calculated.

     Use this function to calculate the variance from the entire
     population.  To estimate the variance from a sample, the *note
     variance(): 1c83. function is usually a better choice.

     Raises *note StatisticsError: 1c85. if `data' is empty.

     Examples:

          >>> data = [0.0, 0.25, 0.25, 1.25, 1.5, 1.75, 2.75, 3.25]
          >>> pvariance(data)
          1.25

     If you have already calculated the mean of your data, you can pass
     it as the optional second argument `mu' to avoid recalculation:

          >>> mu = mean(data)
          >>> pvariance(data, mu)
          1.25

     Decimals and Fractions are supported:

          >>> from decimal import Decimal as D
          >>> pvariance([D("27.5"), D("30.25"), D("30.25"), D("34.5"), D("41.75")])
          Decimal('24.815')

          >>> from fractions import Fraction as F
          >>> pvariance([F(1, 4), F(5, 4), F(1, 2)])
          Fraction(13, 72)

          Note: When called with the entire population, this gives the
          population variance σ².  When called on a sample instead, this
          is the biased sample variance s², also known as variance with
          N degrees of freedom.

          If you somehow know the true population mean μ, you may use
          this function to calculate the variance of a sample, giving
          the known population mean as the second argument.  Provided
          the data points are a random sample of the population, the
          result will be an unbiased estimate of the population
          variance.

 -- Function: statistics.stdev (data, xbar=None)

     Return the sample standard deviation (the square root of the sample
     variance).  See *note variance(): 1c83. for arguments and other
     details.

          >>> stdev([1.5, 2.5, 2.5, 2.75, 3.25, 4.75])
          1.0810874155219827

 -- Function: statistics.variance (data, xbar=None)

     Return the sample variance of `data', an iterable of at least two
     real-valued numbers.  Variance, or second moment about the mean, is
     a measure of the variability (spread or dispersion) of data.  A
     large variance indicates that the data is spread out; a small
     variance indicates it is clustered closely around the mean.

     If the optional second argument `xbar' is given, it should be the
     mean of `data'.  If it is missing or ‘None’ (the default), the mean
     is automatically calculated.

     Use this function when your data is a sample from a population.  To
     calculate the variance from the entire population, see *note
     pvariance(): 1c81.

     Raises *note StatisticsError: 1c85. if `data' has fewer than two
     values.

     Examples:

          >>> data = [2.75, 1.75, 1.25, 0.25, 0.5, 1.25, 3.5]
          >>> variance(data)
          1.3720238095238095

     If you have already calculated the mean of your data, you can pass
     it as the optional second argument `xbar' to avoid recalculation:

          >>> m = mean(data)
          >>> variance(data, m)
          1.3720238095238095

     This function does not attempt to verify that you have passed the
     actual mean as `xbar'.  Using arbitrary values for `xbar' can lead
     to invalid or impossible results.

     Decimal and Fraction values are supported:

          >>> from decimal import Decimal as D
          >>> variance([D("27.5"), D("30.25"), D("30.25"), D("34.5"), D("41.75")])
          Decimal('31.01875')

          >>> from fractions import Fraction as F
          >>> variance([F(1, 6), F(1, 2), F(5, 3)])
          Fraction(67, 108)

          Note: This is the sample variance s² with Bessel’s correction,
          also known as variance with N-1 degrees of freedom.  Provided
          that the data points are representative (e.g.  independent and
          identically distributed), the result should be an unbiased
          estimate of the true population variance.

          If you somehow know the actual population mean μ you should
          pass it to the *note pvariance(): 1c81. function as the `mu'
          parameter to get the variance of a sample.

 -- Function: statistics.quantiles (data, *, n=4, method='exclusive')

     Divide `data' into `n' continuous intervals with equal probability.
     Returns a list of ‘n - 1’ cut points separating the intervals.

     Set `n' to 4 for quartiles (the default).  Set `n' to 10 for
     deciles.  Set `n' to 100 for percentiles which gives the 99 cuts
     points that separate `data' into 100 equal sized groups.  Raises
     *note StatisticsError: 1c85. if `n' is not least 1.

     The `data' can be any iterable containing sample data.  For
     meaningful results, the number of data points in `data' should be
     larger than `n'.  Raises *note StatisticsError: 1c85. if there are
     not at least two data points.

     The cut points are linearly interpolated from the two nearest data
     points.  For example, if a cut point falls one-third of the
     distance between two sample values, ‘100’ and ‘112’, the cut-point
     will evaluate to ‘104’.

     The `method' for computing quantiles can be varied depending on
     whether the `data' includes or excludes the lowest and highest
     possible values from the population.

     The default `method' is “exclusive” and is used for data sampled
     from a population that can have more extreme values than found in
     the samples.  The portion of the population falling below the
     `i-th' of `m' sorted data points is computed as ‘i / (m + 1)’.
     Given nine sample values, the method sorts them and assigns the
     following percentiles: 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%.

     Setting the `method' to “inclusive” is used for describing
     population data or for samples that are known to include the most
     extreme values from the population.  The minimum value in `data' is
     treated as the 0th percentile and the maximum value is treated as
     the 100th percentile.  The portion of the population falling below
     the `i-th' of `m' sorted data points is computed as ‘(i - 1) / (m -
     1)’.  Given 11 sample values, the method sorts them and assigns the
     following percentiles: 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%,
     90%, 100%.

          # Decile cut points for empirically sampled data
          >>> data = [105, 129, 87, 86, 111, 111, 89, 81, 108, 92, 110,
          ...         100, 75, 105, 103, 109, 76, 119, 99, 91, 103, 129,
          ...         106, 101, 84, 111, 74, 87, 86, 103, 103, 106, 86,
          ...         111, 75, 87, 102, 121, 111, 88, 89, 101, 106, 95,
          ...         103, 107, 101, 81, 109, 104]
          >>> [round(q, 1) for q in quantiles(data, n=10)]
          [81.0, 86.2, 89.0, 99.4, 102.5, 103.6, 106.0, 109.8, 111.0]

     New in version 3.8.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Outlier

   (2) https://en.wikipedia.org/wiki/Central_tendency

   (3) 
https://help.gnome.org/users/gnumeric/stable/gnumeric.html#gnumeric-function-SSMEDIAN

   (4) 
https://mail.gnome.org/archives/gnumeric-list/2011-April/msg00018.html


File: python.info,  Node: Exceptions<4>,  Next: NormalDist objects,  Prev: Function details,  Up: statistics — Mathematical statistics functions

5.9.7.4 Exceptions
..................

A single exception is defined:

 -- Exception: statistics.StatisticsError

     Subclass of *note ValueError: 16d. for statistics-related
     exceptions.


File: python.info,  Node: NormalDist objects,  Prev: Exceptions<4>,  Up: statistics — Mathematical statistics functions

5.9.7.5 ‘NormalDist’ objects
............................

*note NormalDist: 358. is a tool for creating and manipulating normal
distributions of a random variable(1).  It is a class that treats the
mean and standard deviation of data measurements as a single entity.

Normal distributions arise from the Central Limit Theorem(2) and have a
wide range of applications in statistics.

 -- Class: statistics.NormalDist (mu=0.0, sigma=1.0)

     Returns a new `NormalDist' object where `mu' represents the
     arithmetic mean(3) and `sigma' represents the standard
     deviation(4).

     If `sigma' is negative, raises *note StatisticsError: 1c85.

      -- Attribute: mean

          A read-only property for the arithmetic mean(5) of a normal
          distribution.

      -- Attribute: median

          A read-only property for the median(6) of a normal
          distribution.

      -- Attribute: mode

          A read-only property for the mode(7) of a normal distribution.

      -- Attribute: stdev

          A read-only property for the standard deviation(8) of a normal
          distribution.

      -- Attribute: variance

          A read-only property for the variance(9) of a normal
          distribution.  Equal to the square of the standard deviation.

      -- Method: classmethod from_samples (data)

          Makes a normal distribution instance with `mu' and `sigma'
          parameters estimated from the `data' using *note fmean(): 354.
          and *note stdev(): 1c82.

          The `data' can be any *note iterable: c7c. and should consist
          of values that can be converted to type *note float: 1fd.  If
          `data' does not contain at least two elements, raises *note
          StatisticsError: 1c85. because it takes at least one point to
          estimate a central value and at least two points to estimate
          dispersion.

      -- Method: samples (n, *, seed=None)

          Generates `n' random samples for a given mean and standard
          deviation.  Returns a *note list: 1f8. of *note float: 1fd.
          values.

          If `seed' is given, creates a new instance of the underlying
          random number generator.  This is useful for creating
          reproducible results, even in a multi-threading context.

      -- Method: pdf (x)

          Using a probability density function (pdf)(10), compute the
          relative likelihood that a random variable `X' will be near
          the given value `x'.  Mathematically, it is the limit of the
          ratio ‘P(x <= X < x+dx) / dx’ as `dx' approaches zero.

          The relative likelihood is computed as the probability of a
          sample occurring in a narrow range divided by the width of the
          range (hence the word “density”).  Since the likelihood is
          relative to other points, its value can be greater than ‘1.0’.

      -- Method: cdf (x)

          Using a cumulative distribution function (cdf)(11), compute
          the probability that a random variable `X' will be less than
          or equal to `x'.  Mathematically, it is written ‘P(X <= x)’.

      -- Method: inv_cdf (p)

          Compute the inverse cumulative distribution function, also
          known as the quantile function(12) or the percent-point(13)
          function.  Mathematically, it is written ‘x : P(X <= x) = p’.

          Finds the value `x' of the random variable `X' such that the
          probability of the variable being less than or equal to that
          value equals the given probability `p'.

      -- Method: overlap (other)

          Measures the agreement between two normal probability
          distributions.  Returns a value between 0.0 and 1.0 giving the
          overlapping area for the two probability density
          functions(14).

      -- Method: quantiles (n=4)

          Divide the normal distribution into `n' continuous intervals
          with equal probability.  Returns a list of (n - 1) cut points
          separating the intervals.

          Set `n' to 4 for quartiles (the default).  Set `n' to 10 for
          deciles.  Set `n' to 100 for percentiles which gives the 99
          cuts points that separate the normal distribution into 100
          equal sized groups.

      -- Method: zscore (x)

          Compute the Standard Score(15) describing `x' in terms of the
          number of standard deviations above or below the mean of the
          normal distribution: ‘(x - mean) / stdev’.

          New in version 3.9.

     Instances of *note NormalDist: 358. support addition, subtraction,
     multiplication and division by a constant.  These operations are
     used for translation and scaling.  For example:

          >>> temperature_february = NormalDist(5, 2.5)             # Celsius
          >>> temperature_february * (9/5) + 32                     # Fahrenheit
          NormalDist(mu=41.0, sigma=4.5)

     Dividing a constant by an instance of *note NormalDist: 358. is not
     supported because the result wouldn’t be normally distributed.

     Since normal distributions arise from additive effects of
     independent variables, it is possible to add and subtract two
     independent normally distributed random variables(16) represented
     as instances of *note NormalDist: 358.  For example:

          >>> birth_weights = NormalDist.from_samples([2.5, 3.1, 2.1, 2.4, 2.7, 3.5])
          >>> drug_effects = NormalDist(0.4, 0.15)
          >>> combined = birth_weights + drug_effects
          >>> round(combined.mean, 1)
          3.1
          >>> round(combined.stdev, 1)
          0.5

     New in version 3.8.

* Menu:

* NormalDist Examples and Recipes::

   ---------- Footnotes ----------

   (1) http://www.stat.yale.edu/Courses/1997-98/101/ranvar.htm

   (2) https://en.wikipedia.org/wiki/Central_limit_theorem

   (3) https://en.wikipedia.org/wiki/Arithmetic_mean

   (4) https://en.wikipedia.org/wiki/Standard_deviation

   (5) https://en.wikipedia.org/wiki/Arithmetic_mean

   (6) https://en.wikipedia.org/wiki/Median

   (7) https://en.wikipedia.org/wiki/Mode_(statistics)

   (8) https://en.wikipedia.org/wiki/Standard_deviation

   (9) https://en.wikipedia.org/wiki/Variance

   (10) https://en.wikipedia.org/wiki/Probability_density_function

   (11) https://en.wikipedia.org/wiki/Cumulative_distribution_function

   (12) https://en.wikipedia.org/wiki/Quantile_function

   (13) 
https://www.statisticshowto.datasciencecentral.com/inverse-distribution-function/

   (14) https://www.rasch.org/rmt/rmt101r.htm

   (15) 
https://www.statisticshowto.com/probability-and-statistics/z-score/

   (16) 
https://en.wikipedia.org/wiki/Sum_of_normally_distributed_random_variables


File: python.info,  Node: NormalDist Examples and Recipes,  Up: NormalDist objects

5.9.7.6 ‘NormalDist’ Examples and Recipes
.........................................

*note NormalDist: 358. readily solves classic probability problems.

For example, given historical data for SAT exams(1) showing that scores
are normally distributed with a mean of 1060 and a standard deviation of
195, determine the percentage of students with test scores between 1100
and 1200, after rounding to the nearest whole number:

     >>> sat = NormalDist(1060, 195)
     >>> fraction = sat.cdf(1200 + 0.5) - sat.cdf(1100 - 0.5)
     >>> round(fraction * 100.0, 1)
     18.4

Find the quartiles(2) and deciles(3) for the SAT scores:

     >>> list(map(round, sat.quantiles()))
     [928, 1060, 1192]
     >>> list(map(round, sat.quantiles(n=10)))
     [810, 896, 958, 1011, 1060, 1109, 1162, 1224, 1310]

To estimate the distribution for a model than isn’t easy to solve
analytically, *note NormalDist: 358. can generate input samples for a
Monte Carlo simulation(4):

     >>> def model(x, y, z):
     ...     return (3*x + 7*x*y - 5*y) / (11 * z)
     ...
     >>> n = 100_000
     >>> X = NormalDist(10, 2.5).samples(n, seed=3652260728)
     >>> Y = NormalDist(15, 1.75).samples(n, seed=4582495471)
     >>> Z = NormalDist(50, 1.25).samples(n, seed=6582483453)
     >>> quantiles(map(model, X, Y, Z))
     [1.4591308524824727, 1.8035946855390597, 2.175091447274739]

Normal distributions can be used to approximate Binomial
distributions(5) when the sample size is large and when the probability
of a successful trial is near 50%.

For example, an open source conference has 750 attendees and two rooms
with a 500 person capacity.  There is a talk about Python and another
about Ruby.  In previous conferences, 65% of the attendees preferred to
listen to Python talks.  Assuming the population preferences haven’t
changed, what is the probability that the Python room will stay within
its capacity limits?

     >>> n = 750             # Sample size
     >>> p = 0.65            # Preference for Python
     >>> q = 1.0 - p         # Preference for Ruby
     >>> k = 500             # Room capacity

     >>> # Approximation using the cumulative normal distribution
     >>> from math import sqrt
     >>> round(NormalDist(mu=n*p, sigma=sqrt(n*p*q)).cdf(k + 0.5), 4)
     0.8402

     >>> # Solution using the cumulative binomial distribution
     >>> from math import comb, fsum
     >>> round(fsum(comb(n, r) * p**r * q**(n-r) for r in range(k+1)), 4)
     0.8402

     >>> # Approximation using a simulation
     >>> from random import seed, choices
     >>> seed(8675309)
     >>> def trial():
     ...     return choices(('Python', 'Ruby'), (p, q), k=n).count('Python')
     >>> mean(trial() <= k for i in range(10_000))
     0.8398

Normal distributions commonly arise in machine learning problems.

Wikipedia has a nice example of a Naive Bayesian Classifier(6).  The
challenge is to predict a person’s gender from measurements of normally
distributed features including height, weight, and foot size.

We’re given a training dataset with measurements for eight people.  The
measurements are assumed to be normally distributed, so we summarize the
data with *note NormalDist: 358.:

     >>> height_male = NormalDist.from_samples([6, 5.92, 5.58, 5.92])
     >>> height_female = NormalDist.from_samples([5, 5.5, 5.42, 5.75])
     >>> weight_male = NormalDist.from_samples([180, 190, 170, 165])
     >>> weight_female = NormalDist.from_samples([100, 150, 130, 150])
     >>> foot_size_male = NormalDist.from_samples([12, 11, 12, 10])
     >>> foot_size_female = NormalDist.from_samples([6, 8, 7, 9])

Next, we encounter a new person whose feature measurements are known but
whose gender is unknown:

     >>> ht = 6.0        # height
     >>> wt = 130        # weight
     >>> fs = 8          # foot size

Starting with a 50% prior probability(7) of being male or female, we
compute the posterior as the prior times the product of likelihoods for
the feature measurements given the gender:

     >>> prior_male = 0.5
     >>> prior_female = 0.5
     >>> posterior_male = (prior_male * height_male.pdf(ht) *
     ...                   weight_male.pdf(wt) * foot_size_male.pdf(fs))

     >>> posterior_female = (prior_female * height_female.pdf(ht) *
     ...                     weight_female.pdf(wt) * foot_size_female.pdf(fs))

The final prediction goes to the largest posterior.  This is known as
the maximum a posteriori(8) or MAP:

     >>> 'male' if posterior_male > posterior_female else 'female'
     'female'

   ---------- Footnotes ----------

   (1) https://nces.ed.gov/programs/digest/d17/tables/dt17_226.40.asp

   (2) https://en.wikipedia.org/wiki/Quartile

   (3) https://en.wikipedia.org/wiki/Decile

   (4) https://en.wikipedia.org/wiki/Monte_Carlo_method

   (5) http://mathworld.wolfram.com/BinomialDistribution.html

   (6) 
https://en.wikipedia.org/wiki/Naive_Bayes_classifier#Sex_classification

   (7) https://en.wikipedia.org/wiki/Prior_probability

   (8) https://en.wikipedia.org/wiki/Maximum_a_posteriori_estimation


File: python.info,  Node: Functional Programming Modules,  Next: File and Directory Access,  Prev: Numeric and Mathematical Modules,  Up: The Python Standard Library

5.10 Functional Programming Modules
===================================

The modules described in this chapter provide functions and classes that
support a functional programming style, and general operations on
callables.

The following modules are documented in this chapter:

* Menu:

* itertools — Functions creating iterators for efficient looping::
* functools — Higher-order functions and operations on callable objects::
* operator — Standard operators as functions::


File: python.info,  Node: itertools — Functions creating iterators for efficient looping,  Next: functools — Higher-order functions and operations on callable objects,  Up: Functional Programming Modules

5.10.1 ‘itertools’ — Functions creating iterators for efficient looping
-----------------------------------------------------------------------

__________________________________________________________________

This module implements a number of *note iterator: 1171. building blocks
inspired by constructs from APL, Haskell, and SML. Each has been recast
in a form suitable for Python.

The module standardizes a core set of fast, memory efficient tools that
are useful by themselves or in combination.  Together, they form an
“iterator algebra” making it possible to construct specialized tools
succinctly and efficiently in pure Python.

For instance, SML provides a tabulation tool: ‘tabulate(f)’ which
produces a sequence ‘f(0), f(1), ...’.  The same effect can be achieved
in Python by combining *note map(): cf7. and *note count(): ce5. to form
‘map(f, count())’.

These tools and their built-in counterparts also work well with the
high-speed functions in the *note operator: c2. module.  For example,
the multiplication operator can be mapped across two vectors to form an
efficient dot-product: ‘sum(map(operator.mul, vector1, vector2))’.

`Infinite iterators:'

Iterator               Arguments             Results                                               Example
                                                                                                   
-------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                   
*note count(): ce5.    start, [step]         start, start+step, start+2*step, …                    ‘count(10) --> 10 11 12 13 14 ...’
                                                                                                   
                                                                                                   
*note cycle(): 1c9a.   p                     p0, p1, … plast, p0, p1, …                            ‘cycle('ABCD') --> A B C D A B C D ...’
                                                                                                   
                                                                                                   
*note repeat(): 11e7.  elem [,n]             elem, elem, elem, … endlessly or up to n times        ‘repeat(10, 3) --> 10 10 10’
                                                                                                   

`Iterators terminating on the shortest input sequence:'

Iterator                         Arguments                        Results                                               Example
                                                                                                                        
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                        
*note accumulate(): 30e.         p [,func]                        p0, p0+p1, p0+p1+p2, …                                ‘accumulate([1,2,3,4,5]) --> 1 3 6 10 15’
                                                                                                                        
                                                                                                                        
*note chain(): 1738.             p, q, …                          p0, p1, … plast, q0, q1, …                            ‘chain('ABC', 'DEF') --> A B C D E F’
                                                                                                                        
                                                                                                                        
*note chain.from_iterable(): 1c9b.iterable                        p0, p1, … plast, q0, q1, …                            ‘chain.from_iterable(['ABC', 'DEF']) --> A B C D E F’
                                                                                                                        
                                                                                                                        
*note compress(): ce4.           data, selectors                  (d[0] if s[0]), (d[1] if s[1]), …                     ‘compress('ABCDEF', [1,0,1,0,1,1]) --> A C E F’
                                                                                                                        
                                                                                                                        
*note dropwhile(): 1c9c.         pred, seq                        seq[n], seq[n+1], starting when pred fails            ‘dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1’
                                                                                                                        
                                                                                                                        
*note filterfalse(): 1722.       pred, seq                        elements of seq where pred(elem) is false             ‘filterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8’
                                                                                                                        
                                                                                                                        
*note groupby(): 1c9d.           iterable[, key]                  sub-iterators grouped by value of key(v)
                                                                  
                                                                                                                        
*note islice(): 4a9.             seq, [start,] stop [, step]      elements from seq[start:stop:step]                    ‘islice('ABCDEFG', 2, None) --> C D E F G’
                                                                                                                        
                                                                                                                        
*note starmap(): b05.            func, seq                        func(*seq[0]), func(*seq[1]), …                       ‘starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000’
                                                                                                                        
                                                                                                                        
*note takewhile(): 1c9e.         pred, seq                        seq[0], seq[1], until pred fails                      ‘takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4’
                                                                                                                        
                                                                                                                        
*note tee(): 1c9f.               it, n                            it1, it2, … itn splits one iterator into n
                                                                  
                                                                                                                        
*note zip_longest(): cfb.        p, q, …                          (p[0], q[0]), (p[1], q[1]), …                         ‘zip_longest('ABCD', 'xy', fillvalue='-') --> Ax By C- D-’
                                                                                                                        

`Combinatoric iterators:'

Iterator                                           Arguments                Results
                                                                            
----------------------------------------------------------------------------------------------------------------------------------------------
                                                                            
*note product(): d6f.                              p, q, … [repeat=1]       cartesian product, equivalent to a nested for-loop
                                                                            
                                                                            
*note permutations(): fc9.                         p[, r]                   r-length tuples, all possible orderings, no repeated elements
                                                                            
                                                                            
*note combinations(): d6e.                         p, r                     r-length tuples, in sorted order, no repeated elements
                                                                            
                                                                            
*note combinations_with_replacement(): ce3.        p, r                     r-length tuples, in sorted order, with repeated elements
                                                                            

Examples                                           Results
                                                   
---------------------------------------------------------------------------------------------------------------------
                                                   
‘product('ABCD', repeat=2)’                        ‘AA AB AC AD BA BB BC BD CA CB CC CD DA DB DC DD’
                                                   
                                                   
‘permutations('ABCD', 2)’                          ‘AB AC AD BA BC BD CA CB CD DA DB DC’
                                                   
                                                   
‘combinations('ABCD', 2)’                          ‘AB AC AD BC BD CD’
                                                   
                                                   
‘combinations_with_replacement('ABCD', 2)’         ‘AA AB AC AD BB BC BD CC CD DD’
                                                   

* Menu:

* Itertool functions::
* Itertools Recipes::


File: python.info,  Node: Itertool functions,  Next: Itertools Recipes,  Up: itertools — Functions creating iterators for efficient looping

5.10.1.1 Itertool functions
...........................

The following module functions all construct and return iterators.  Some
provide streams of infinite length, so they should only be accessed by
functions or loops that truncate the stream.

 -- Function: itertools.accumulate (iterable[, func, *, initial=None])

     Make an iterator that returns accumulated sums, or accumulated
     results of other binary functions (specified via the optional
     `func' argument).

     If `func' is supplied, it should be a function of two arguments.
     Elements of the input `iterable' may be any type that can be
     accepted as arguments to `func'.  (For example, with the default
     operation of addition, elements may be any addable type including
     *note Decimal: 2c0. or *note Fraction: 2be.)

     Usually, the number of elements output matches the input iterable.
     However, if the keyword argument `initial' is provided, the
     accumulation leads off with the `initial' value so that the output
     has one more element than the input iterable.

     Roughly equivalent to:

          def accumulate(iterable, func=operator.add, *, initial=None):
              'Return running totals'
              # accumulate([1,2,3,4,5]) --> 1 3 6 10 15
              # accumulate([1,2,3,4,5], initial=100) --> 100 101 103 106 110 115
              # accumulate([1,2,3,4,5], operator.mul) --> 1 2 6 24 120
              it = iter(iterable)
              total = initial
              if initial is None:
                  try:
                      total = next(it)
                  except StopIteration:
                      return
              yield total
              for element in it:
                  total = func(total, element)
                  yield total

     There are a number of uses for the `func' argument.  It can be set
     to *note min(): 8f6. for a running minimum, *note max(): 8f7. for a
     running maximum, or *note operator.mul(): 1ca2. for a running
     product.  Amortization tables can be built by accumulating interest
     and applying payments.  First-order recurrence relations(1) can be
     modeled by supplying the initial value in the iterable and using
     only the accumulated total in `func' argument:

          >>> data = [3, 4, 6, 2, 1, 9, 0, 7, 5, 8]
          >>> list(accumulate(data, operator.mul))     # running product
          [3, 12, 72, 144, 144, 1296, 0, 0, 0, 0]
          >>> list(accumulate(data, max))              # running maximum
          [3, 4, 6, 6, 6, 9, 9, 9, 9, 9]

          # Amortize a 5% loan of 1000 with 4 annual payments of 90
          >>> cashflows = [1000, -90, -90, -90, -90]
          >>> list(accumulate(cashflows, lambda bal, pmt: bal*1.05 + pmt))
          [1000, 960.0, 918.0, 873.9000000000001, 827.5950000000001]

          # Chaotic recurrence relation https://en.wikipedia.org/wiki/Logistic_map
          >>> logistic_map = lambda x, _:  r * x * (1 - x)
          >>> r = 3.8
          >>> x0 = 0.4
          >>> inputs = repeat(x0, 36)     # only the initial value is used
          >>> [format(x, '.2f') for x in accumulate(inputs, logistic_map)]
          ['0.40', '0.91', '0.30', '0.81', '0.60', '0.92', '0.29', '0.79', '0.63',
           '0.88', '0.39', '0.90', '0.33', '0.84', '0.52', '0.95', '0.18', '0.57',
           '0.93', '0.25', '0.71', '0.79', '0.63', '0.88', '0.39', '0.91', '0.32',
           '0.83', '0.54', '0.95', '0.20', '0.60', '0.91', '0.30', '0.80', '0.60']

     See *note functools.reduce(): d37. for a similar function that
     returns only the final accumulated value.

     New in version 3.2.

     Changed in version 3.3: Added the optional `func' parameter.

     Changed in version 3.8: Added the optional `initial' parameter.

 -- Function: itertools.chain (*iterables)

     Make an iterator that returns elements from the first iterable
     until it is exhausted, then proceeds to the next iterable, until
     all of the iterables are exhausted.  Used for treating consecutive
     sequences as a single sequence.  Roughly equivalent to:

          def chain(*iterables):
              # chain('ABC', 'DEF') --> A B C D E F
              for it in iterables:
                  for element in it:
                      yield element

 -- Method: classmethod chain.from_iterable (iterable)

     Alternate constructor for *note chain(): 1738.  Gets chained inputs
     from a single iterable argument that is evaluated lazily.  Roughly
     equivalent to:

          def from_iterable(iterables):
              # chain.from_iterable(['ABC', 'DEF']) --> A B C D E F
              for it in iterables:
                  for element in it:
                      yield element

 -- Function: itertools.combinations (iterable, r)

     Return `r' length subsequences of elements from the input
     `iterable'.

     The combination tuples are emitted in lexicographic ordering
     according to the order of the input `iterable'.  So, if the input
     `iterable' is sorted, the combination tuples will be produced in
     sorted order.

     Elements are treated as unique based on their position, not on
     their value.  So if the input elements are unique, there will be no
     repeat values in each combination.

     Roughly equivalent to:

          def combinations(iterable, r):
              # combinations('ABCD', 2) --> AB AC AD BC BD CD
              # combinations(range(4), 3) --> 012 013 023 123
              pool = tuple(iterable)
              n = len(pool)
              if r > n:
                  return
              indices = list(range(r))
              yield tuple(pool[i] for i in indices)
              while True:
                  for i in reversed(range(r)):
                      if indices[i] != i + n - r:
                          break
                  else:
                      return
                  indices[i] += 1
                  for j in range(i+1, r):
                      indices[j] = indices[j-1] + 1
                  yield tuple(pool[i] for i in indices)

     The code for *note combinations(): d6e. can be also expressed as a
     subsequence of *note permutations(): fc9. after filtering entries
     where the elements are not in sorted order (according to their
     position in the input pool):

          def combinations(iterable, r):
              pool = tuple(iterable)
              n = len(pool)
              for indices in permutations(range(n), r):
                  if sorted(indices) == list(indices):
                      yield tuple(pool[i] for i in indices)

     The number of items returned is ‘n! / r! / (n-r)!’ when ‘0 <= r <=
     n’ or zero when ‘r > n’.

 -- Function: itertools.combinations_with_replacement (iterable, r)

     Return `r' length subsequences of elements from the input
     `iterable' allowing individual elements to be repeated more than
     once.

     The combination tuples are emitted in lexicographic ordering
     according to the order of the input `iterable'.  So, if the input
     `iterable' is sorted, the combination tuples will be produced in
     sorted order.

     Elements are treated as unique based on their position, not on
     their value.  So if the input elements are unique, the generated
     combinations will also be unique.

     Roughly equivalent to:

          def combinations_with_replacement(iterable, r):
              # combinations_with_replacement('ABC', 2) --> AA AB AC BB BC CC
              pool = tuple(iterable)
              n = len(pool)
              if not n and r:
                  return
              indices = [0] * r
              yield tuple(pool[i] for i in indices)
              while True:
                  for i in reversed(range(r)):
                      if indices[i] != n - 1:
                          break
                  else:
                      return
                  indices[i:] = [indices[i] + 1] * (r - i)
                  yield tuple(pool[i] for i in indices)

     The code for *note combinations_with_replacement(): ce3. can be
     also expressed as a subsequence of *note product(): d6f. after
     filtering entries where the elements are not in sorted order
     (according to their position in the input pool):

          def combinations_with_replacement(iterable, r):
              pool = tuple(iterable)
              n = len(pool)
              for indices in product(range(n), repeat=r):
                  if sorted(indices) == list(indices):
                      yield tuple(pool[i] for i in indices)

     The number of items returned is ‘(n+r-1)! / r! / (n-1)!’ when ‘n >
     0’.

     New in version 3.1.

 -- Function: itertools.compress (data, selectors)

     Make an iterator that filters elements from `data' returning only
     those that have a corresponding element in `selectors' that
     evaluates to ‘True’.  Stops when either the `data' or `selectors'
     iterables has been exhausted.  Roughly equivalent to:

          def compress(data, selectors):
              # compress('ABCDEF', [1,0,1,0,1,1]) --> A C E F
              return (d for d, s in zip(data, selectors) if s)

     New in version 3.1.

 -- Function: itertools.count (start=0, step=1)

     Make an iterator that returns evenly spaced values starting with
     number `start'.  Often used as an argument to *note map(): cf7. to
     generate consecutive data points.  Also, used with *note zip():
     cfc. to add sequence numbers.  Roughly equivalent to:

          def count(start=0, step=1):
              # count(10) --> 10 11 12 13 14 ...
              # count(2.5, 0.5) -> 2.5 3.0 3.5 ...
              n = start
              while True:
                  yield n
                  n += step

     When counting with floating point numbers, better accuracy can
     sometimes be achieved by substituting multiplicative code such as:
     ‘(start + step * i for i in count())’.

     Changed in version 3.1: Added `step' argument and allowed
     non-integer arguments.

 -- Function: itertools.cycle (iterable)

     Make an iterator returning elements from the iterable and saving a
     copy of each.  When the iterable is exhausted, return elements from
     the saved copy.  Repeats indefinitely.  Roughly equivalent to:

          def cycle(iterable):
              # cycle('ABCD') --> A B C D A B C D A B C D ...
              saved = []
              for element in iterable:
                  yield element
                  saved.append(element)
              while saved:
                  for element in saved:
                        yield element

     Note, this member of the toolkit may require significant auxiliary
     storage (depending on the length of the iterable).

 -- Function: itertools.dropwhile (predicate, iterable)

     Make an iterator that drops elements from the iterable as long as
     the predicate is true; afterwards, returns every element.  Note,
     the iterator does not produce `any' output until the predicate
     first becomes false, so it may have a lengthy start-up time.
     Roughly equivalent to:

          def dropwhile(predicate, iterable):
              # dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1
              iterable = iter(iterable)
              for x in iterable:
                  if not predicate(x):
                      yield x
                      break
              for x in iterable:
                  yield x

 -- Function: itertools.filterfalse (predicate, iterable)

     Make an iterator that filters elements from iterable returning only
     those for which the predicate is ‘False’.  If `predicate' is
     ‘None’, return the items that are false.  Roughly equivalent to:

          def filterfalse(predicate, iterable):
              # filterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8
              if predicate is None:
                  predicate = bool
              for x in iterable:
                  if not predicate(x):
                      yield x

 -- Function: itertools.groupby (iterable, key=None)

     Make an iterator that returns consecutive keys and groups from the
     `iterable'.  The `key' is a function computing a key value for each
     element.  If not specified or is ‘None’, `key' defaults to an
     identity function and returns the element unchanged.  Generally,
     the iterable needs to already be sorted on the same key function.

     The operation of *note groupby(): 1c9d. is similar to the ‘uniq’
     filter in Unix.  It generates a break or new group every time the
     value of the key function changes (which is why it is usually
     necessary to have sorted the data using the same key function).
     That behavior differs from SQL’s GROUP BY which aggregates common
     elements regardless of their input order.

     The returned group is itself an iterator that shares the underlying
     iterable with *note groupby(): 1c9d.  Because the source is shared,
     when the *note groupby(): 1c9d. object is advanced, the previous
     group is no longer visible.  So, if that data is needed later, it
     should be stored as a list:

          groups = []
          uniquekeys = []
          data = sorted(data, key=keyfunc)
          for k, g in groupby(data, keyfunc):
              groups.append(list(g))      # Store group iterator as a list
              uniquekeys.append(k)

     *note groupby(): 1c9d. is roughly equivalent to:

          class groupby:
              # [k for k, g in groupby('AAAABBBCCDAABBB')] --> A B C D A B
              # [list(g) for k, g in groupby('AAAABBBCCD')] --> AAAA BBB CC D
              def __init__(self, iterable, key=None):
                  if key is None:
                      key = lambda x: x
                  self.keyfunc = key
                  self.it = iter(iterable)
                  self.tgtkey = self.currkey = self.currvalue = object()
              def __iter__(self):
                  return self
              def __next__(self):
                  self.id = object()
                  while self.currkey == self.tgtkey:
                      self.currvalue = next(self.it)    # Exit on StopIteration
                      self.currkey = self.keyfunc(self.currvalue)
                  self.tgtkey = self.currkey
                  return (self.currkey, self._grouper(self.tgtkey, self.id))
              def _grouper(self, tgtkey, id):
                  while self.id is id and self.currkey == tgtkey:
                      yield self.currvalue
                      try:
                          self.currvalue = next(self.it)
                      except StopIteration:
                          return
                      self.currkey = self.keyfunc(self.currvalue)

 -- Function: itertools.islice (iterable, stop)

 -- Function: itertools.islice (iterable, start, stop[, step])

     Make an iterator that returns selected elements from the iterable.
     If `start' is non-zero, then elements from the iterable are skipped
     until start is reached.  Afterward, elements are returned
     consecutively unless `step' is set higher than one which results in
     items being skipped.  If `stop' is ‘None’, then iteration continues
     until the iterator is exhausted, if at all; otherwise, it stops at
     the specified position.  Unlike regular slicing, *note islice():
     4a9. does not support negative values for `start', `stop', or
     `step'.  Can be used to extract related fields from data where the
     internal structure has been flattened (for example, a multi-line
     report may list a name field on every third line).  Roughly
     equivalent to:

          def islice(iterable, *args):
              # islice('ABCDEFG', 2) --> A B
              # islice('ABCDEFG', 2, 4) --> C D
              # islice('ABCDEFG', 2, None) --> C D E F G
              # islice('ABCDEFG', 0, None, 2) --> A C E G
              s = slice(*args)
              start, stop, step = s.start or 0, s.stop or sys.maxsize, s.step or 1
              it = iter(range(start, stop, step))
              try:
                  nexti = next(it)
              except StopIteration:
                  # Consume *iterable* up to the *start* position.
                  for i, element in zip(range(start), iterable):
                      pass
                  return
              try:
                  for i, element in enumerate(iterable):
                      if i == nexti:
                          yield element
                          nexti = next(it)
              except StopIteration:
                  # Consume to *stop*.
                  for i, element in zip(range(i + 1, stop), iterable):
                      pass

     If `start' is ‘None’, then iteration starts at zero.  If `step' is
     ‘None’, then the step defaults to one.

 -- Function: itertools.permutations (iterable, r=None)

     Return successive `r' length permutations of elements in the
     `iterable'.

     If `r' is not specified or is ‘None’, then `r' defaults to the
     length of the `iterable' and all possible full-length permutations
     are generated.

     The permutation tuples are emitted in lexicographic ordering
     according to the order of the input `iterable'.  So, if the input
     `iterable' is sorted, the combination tuples will be produced in
     sorted order.

     Elements are treated as unique based on their position, not on
     their value.  So if the input elements are unique, there will be no
     repeat values in each permutation.

     Roughly equivalent to:

          def permutations(iterable, r=None):
              # permutations('ABCD', 2) --> AB AC AD BA BC BD CA CB CD DA DB DC
              # permutations(range(3)) --> 012 021 102 120 201 210
              pool = tuple(iterable)
              n = len(pool)
              r = n if r is None else r
              if r > n:
                  return
              indices = list(range(n))
              cycles = list(range(n, n-r, -1))
              yield tuple(pool[i] for i in indices[:r])
              while n:
                  for i in reversed(range(r)):
                      cycles[i] -= 1
                      if cycles[i] == 0:
                          indices[i:] = indices[i+1:] + indices[i:i+1]
                          cycles[i] = n - i
                      else:
                          j = cycles[i]
                          indices[i], indices[-j] = indices[-j], indices[i]
                          yield tuple(pool[i] for i in indices[:r])
                          break
                  else:
                      return

     The code for *note permutations(): fc9. can be also expressed as a
     subsequence of *note product(): d6f, filtered to exclude entries
     with repeated elements (those from the same position in the input
     pool):

          def permutations(iterable, r=None):
              pool = tuple(iterable)
              n = len(pool)
              r = n if r is None else r
              for indices in product(range(n), repeat=r):
                  if len(set(indices)) == r:
                      yield tuple(pool[i] for i in indices)

     The number of items returned is ‘n! / (n-r)!’ when ‘0 <= r <= n’ or
     zero when ‘r > n’.

 -- Function: itertools.product (*iterables, repeat=1)

     Cartesian product of input iterables.

     Roughly equivalent to nested for-loops in a generator expression.
     For example, ‘product(A, B)’ returns the same as ‘((x,y) for x in A
     for y in B)’.

     The nested loops cycle like an odometer with the rightmost element
     advancing on every iteration.  This pattern creates a lexicographic
     ordering so that if the input’s iterables are sorted, the product
     tuples are emitted in sorted order.

     To compute the product of an iterable with itself, specify the
     number of repetitions with the optional `repeat' keyword argument.
     For example, ‘product(A, repeat=4)’ means the same as ‘product(A,
     A, A, A)’.

     This function is roughly equivalent to the following code, except
     that the actual implementation does not build up intermediate
     results in memory:

          def product(*args, repeat=1):
              # product('ABCD', 'xy') --> Ax Ay Bx By Cx Cy Dx Dy
              # product(range(2), repeat=3) --> 000 001 010 011 100 101 110 111
              pools = [tuple(pool) for pool in args] * repeat
              result = [[]]
              for pool in pools:
                  result = [x+[y] for x in result for y in pool]
              for prod in result:
                  yield tuple(prod)

     Before *note product(): d6f. runs, it completely consumes the input
     iterables, keeping pools of values in memory to generate the
     products.  Accordingly, it is only useful with finite inputs.

 -- Function: itertools.repeat (object[, times])

     Make an iterator that returns `object' over and over again.  Runs
     indefinitely unless the `times' argument is specified.  Used as
     argument to *note map(): cf7. for invariant parameters to the
     called function.  Also used with *note zip(): cfc. to create an
     invariant part of a tuple record.

     Roughly equivalent to:

          def repeat(object, times=None):
              # repeat(10, 3) --> 10 10 10
              if times is None:
                  while True:
                      yield object
              else:
                  for i in range(times):
                      yield object

     A common use for `repeat' is to supply a stream of constant values
     to `map' or `zip':

          >>> list(map(pow, range(10), repeat(2)))
          [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

 -- Function: itertools.starmap (function, iterable)

     Make an iterator that computes the function using arguments
     obtained from the iterable.  Used instead of *note map(): cf7. when
     argument parameters are already grouped in tuples from a single
     iterable (the data has been “pre-zipped”).  The difference between
     *note map(): cf7. and *note starmap(): b05. parallels the
     distinction between ‘function(a,b)’ and ‘function(*c)’.  Roughly
     equivalent to:

          def starmap(function, iterable):
              # starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000
              for args in iterable:
                  yield function(*args)

 -- Function: itertools.takewhile (predicate, iterable)

     Make an iterator that returns elements from the iterable as long as
     the predicate is true.  Roughly equivalent to:

          def takewhile(predicate, iterable):
              # takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4
              for x in iterable:
                  if predicate(x):
                      yield x
                  else:
                      break

 -- Function: itertools.tee (iterable, n=2)

     Return `n' independent iterators from a single iterable.

     The following Python code helps explain what `tee' does (although
     the actual implementation is more complex and uses only a single
     underlying FIFO queue).

     Roughly equivalent to:

          def tee(iterable, n=2):
              it = iter(iterable)
              deques = [collections.deque() for i in range(n)]
              def gen(mydeque):
                  while True:
                      if not mydeque:             # when the local deque is empty
                          try:
                              newval = next(it)   # fetch a new value and
                          except StopIteration:
                              return
                          for d in deques:        # load it to all the deques
                              d.append(newval)
                      yield mydeque.popleft()
              return tuple(gen(d) for d in deques)

     Once *note tee(): 1c9f. has made a split, the original `iterable'
     should not be used anywhere else; otherwise, the `iterable' could
     get advanced without the tee objects being informed.

     ‘tee’ iterators are not threadsafe.  A *note RuntimeError: 3dc. may
     be raised when using simultaneously iterators returned by the same
     *note tee(): 1c9f. call, even if the original `iterable' is
     threadsafe.

     This itertool may require significant auxiliary storage (depending
     on how much temporary data needs to be stored).  In general, if one
     iterator uses most or all of the data before another iterator
     starts, it is faster to use *note list(): 1f8. instead of *note
     tee(): 1c9f.

 -- Function: itertools.zip_longest (*iterables, fillvalue=None)

     Make an iterator that aggregates elements from each of the
     iterables.  If the iterables are of uneven length, missing values
     are filled-in with `fillvalue'.  Iteration continues until the
     longest iterable is exhausted.  Roughly equivalent to:

          def zip_longest(*args, fillvalue=None):
              # zip_longest('ABCD', 'xy', fillvalue='-') --> Ax By C- D-
              iterators = [iter(it) for it in args]
              num_active = len(iterators)
              if not num_active:
                  return
              while True:
                  values = []
                  for i, it in enumerate(iterators):
                      try:
                          value = next(it)
                      except StopIteration:
                          num_active -= 1
                          if not num_active:
                              return
                          iterators[i] = repeat(fillvalue)
                          value = fillvalue
                      values.append(value)
                  yield tuple(values)

     If one of the iterables is potentially infinite, then the *note
     zip_longest(): cfb. function should be wrapped with something that
     limits the number of calls (for example *note islice(): 4a9. or
     *note takewhile(): 1c9e.).  If not specified, `fillvalue' defaults
     to ‘None’.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Recurrence_relation


File: python.info,  Node: Itertools Recipes,  Prev: Itertool functions,  Up: itertools — Functions creating iterators for efficient looping

5.10.1.2 Itertools Recipes
..........................

This section shows recipes for creating an extended toolset using the
existing itertools as building blocks.

Substantially all of these recipes and many, many others can be
installed from the more-itertools project(1) found on the Python Package
Index:

     pip install more-itertools

The extended tools offer the same high performance as the underlying
toolset.  The superior memory performance is kept by processing elements
one at a time rather than bringing the whole iterable into memory all at
once.  Code volume is kept small by linking the tools together in a
functional style which helps eliminate temporary variables.  High speed
is retained by preferring “vectorized” building blocks over the use of
for-loops and *note generator: a83.s which incur interpreter overhead.

     def take(n, iterable):
         "Return first n items of the iterable as a list"
         return list(islice(iterable, n))

     def prepend(value, iterator):
         "Prepend a single value in front of an iterator"
         # prepend(1, [2, 3, 4]) -> 1 2 3 4
         return chain([value], iterator)

     def tabulate(function, start=0):
         "Return function(0), function(1), ..."
         return map(function, count(start))

     def tail(n, iterable):
         "Return an iterator over the last n items"
         # tail(3, 'ABCDEFG') --> E F G
         return iter(collections.deque(iterable, maxlen=n))

     def consume(iterator, n=None):
         "Advance the iterator n-steps ahead. If n is None, consume entirely."
         # Use functions that consume iterators at C speed.
         if n is None:
             # feed the entire iterator into a zero-length deque
             collections.deque(iterator, maxlen=0)
         else:
             # advance to the empty slice starting at position n
             next(islice(iterator, n, n), None)

     def nth(iterable, n, default=None):
         "Returns the nth item or a default value"
         return next(islice(iterable, n, None), default)

     def all_equal(iterable):
         "Returns True if all the elements are equal to each other"
         g = groupby(iterable)
         return next(g, True) and not next(g, False)

     def quantify(iterable, pred=bool):
         "Count how many times the predicate is true"
         return sum(map(pred, iterable))

     def pad_none(iterable):
         """Returns the sequence elements and then returns None indefinitely.

         Useful for emulating the behavior of the built-in map() function.
         """
         return chain(iterable, repeat(None))

     def ncycles(iterable, n):
         "Returns the sequence elements n times"
         return chain.from_iterable(repeat(tuple(iterable), n))

     def dotproduct(vec1, vec2):
         return sum(map(operator.mul, vec1, vec2))

     def convolve(signal, kernel):
         # See:  https://betterexplained.com/articles/intuitive-convolution/
         # convolve(data, [0.25, 0.25, 0.25, 0.25]) --> Moving average (blur)
         # convolve(data, [1, -1]) --> 1st finite difference (1st derivative)
         # convolve(data, [1, -2, 1]) --> 2nd finite difference (2nd derivative)
         kernel = tuple(kernel)[::-1]
         n = len(kernel)
         window = collections.deque([0], maxlen=n) * n
         for x in chain(signal, repeat(0, n-1)):
             window.append(x)
             yield sum(map(operator.mul, kernel, window))

     def flatten(list_of_lists):
         "Flatten one level of nesting"
         return chain.from_iterable(list_of_lists)

     def repeatfunc(func, times=None, *args):
         """Repeat calls to func with specified arguments.

         Example:  repeatfunc(random.random)
         """
         if times is None:
             return starmap(func, repeat(args))
         return starmap(func, repeat(args, times))

     def pairwise(iterable):
         "s -> (s0,s1), (s1,s2), (s2, s3), ..."
         a, b = tee(iterable)
         next(b, None)
         return zip(a, b)

     def grouper(iterable, n, fillvalue=None):
         "Collect data into fixed-length chunks or blocks"
         # grouper('ABCDEFG', 3, 'x') --> ABC DEF Gxx"
         args = [iter(iterable)] * n
         return zip_longest(*args, fillvalue=fillvalue)

     def roundrobin(*iterables):
         "roundrobin('ABC', 'D', 'EF') --> A D E B F C"
         # Recipe credited to George Sakkis
         num_active = len(iterables)
         nexts = cycle(iter(it).__next__ for it in iterables)
         while num_active:
             try:
                 for next in nexts:
                     yield next()
             except StopIteration:
                 # Remove the iterator we just exhausted from the cycle.
                 num_active -= 1
                 nexts = cycle(islice(nexts, num_active))

     def partition(pred, iterable):
         "Use a predicate to partition entries into false entries and true entries"
         # partition(is_odd, range(10)) --> 0 2 4 6 8   and  1 3 5 7 9
         t1, t2 = tee(iterable)
         return filterfalse(pred, t1), filter(pred, t2)

     def powerset(iterable):
         "powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)"
         s = list(iterable)
         return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))

     def unique_everseen(iterable, key=None):
         "List unique elements, preserving order. Remember all elements ever seen."
         # unique_everseen('AAAABBBCCDAABBB') --> A B C D
         # unique_everseen('ABBCcAD', str.lower) --> A B C D
         seen = set()
         seen_add = seen.add
         if key is None:
             for element in filterfalse(seen.__contains__, iterable):
                 seen_add(element)
                 yield element
         else:
             for element in iterable:
                 k = key(element)
                 if k not in seen:
                     seen_add(k)
                     yield element

     def unique_justseen(iterable, key=None):
         "List unique elements, preserving order. Remember only the element just seen."
         # unique_justseen('AAAABBBCCDAABBB') --> A B C D A B
         # unique_justseen('ABBCcAD', str.lower) --> A B C A D
         return map(next, map(operator.itemgetter(1), groupby(iterable, key)))

     def iter_except(func, exception, first=None):
         """ Call a function repeatedly until an exception is raised.

         Converts a call-until-exception interface to an iterator interface.
         Like builtins.iter(func, sentinel) but uses an exception instead
         of a sentinel to end the loop.

         Examples:
             iter_except(functools.partial(heappop, h), IndexError)   # priority queue iterator
             iter_except(d.popitem, KeyError)                         # non-blocking dict iterator
             iter_except(d.popleft, IndexError)                       # non-blocking deque iterator
             iter_except(q.get_nowait, Queue.Empty)                   # loop over a producer Queue
             iter_except(s.pop, KeyError)                             # non-blocking set iterator

         """
         try:
             if first is not None:
                 yield first()            # For database APIs needing an initial cast to db.first()
             while True:
                 yield func()
         except exception:
             pass

     def first_true(iterable, default=False, pred=None):
         """Returns the first true value in the iterable.

         If no true value is found, returns *default*

         If *pred* is not None, returns the first item
         for which pred(item) is true.

         """
         # first_true([a,b,c], x) --> a or b or c or x
         # first_true([a,b], x, f) --> a if f(a) else b if f(b) else x
         return next(filter(pred, iterable), default)

     def random_product(*args, repeat=1):
         "Random selection from itertools.product(*args, **kwds)"
         pools = [tuple(pool) for pool in args] * repeat
         return tuple(map(random.choice, pools))

     def random_permutation(iterable, r=None):
         "Random selection from itertools.permutations(iterable, r)"
         pool = tuple(iterable)
         r = len(pool) if r is None else r
         return tuple(random.sample(pool, r))

     def random_combination(iterable, r):
         "Random selection from itertools.combinations(iterable, r)"
         pool = tuple(iterable)
         n = len(pool)
         indices = sorted(random.sample(range(n), r))
         return tuple(pool[i] for i in indices)

     def random_combination_with_replacement(iterable, r):
         "Random selection from itertools.combinations_with_replacement(iterable, r)"
         pool = tuple(iterable)
         n = len(pool)
         indices = sorted(random.choices(range(n), k=r))
         return tuple(pool[i] for i in indices)

     def nth_combination(iterable, r, index):
         "Equivalent to list(combinations(iterable, r))[index]"
         pool = tuple(iterable)
         n = len(pool)
         if r < 0 or r > n:
             raise ValueError
         c = 1
         k = min(r, n-r)
         for i in range(1, k+1):
             c = c * (n - k + i) // i
         if index < 0:
             index += c
         if index < 0 or index >= c:
             raise IndexError
         result = []
         while r:
             c, n, r = c*r//n, n-1, r-1
             while index >= c:
                 index -= c
                 c, n = c*(n-r)//n, n-1
             result.append(pool[-1-n])
         return tuple(result)

   ---------- Footnotes ----------

   (1) https://pypi.org/project/more-itertools/


File: python.info,  Node: functools — Higher-order functions and operations on callable objects,  Next: operator — Standard operators as functions,  Prev: itertools — Functions creating iterators for efficient looping,  Up: Functional Programming Modules

5.10.2 ‘functools’ — Higher-order functions and operations on callable objects
------------------------------------------------------------------------------

`Source code:' Lib/functools.py(1)

__________________________________________________________________

The *note functools: 83. module is for higher-order functions: functions
that act on or return other functions.  In general, any callable object
can be treated as a function for the purposes of this module.

The *note functools: 83. module defines the following functions:

 -- Function: @functools.cache (user_function)

     Simple lightweight unbounded function cache.  Sometimes called
     "memoize"(2).

     Returns the same as ‘lru_cache(maxsize=None)’, creating a thin
     wrapper around a dictionary lookup for the function arguments.
     Because it never needs to evict old values, this is smaller and
     faster than *note lru_cache(): 2f8. with a size limit.

     For example:

          @cache
          def factorial(n):
              return n * factorial(n-1) if n else 1

          >>> factorial(10)      # no previously cached result, makes 11 recursive calls
          3628800
          >>> factorial(5)       # just looks up cached value result
          120
          >>> factorial(12)      # makes two new recursive calls, the other 10 are cached
          479001600

     New in version 3.9.

 -- Function: @functools.cached_property (func)

     Transform a method of a class into a property whose value is
     computed once and then cached as a normal attribute for the life of
     the instance.  Similar to *note property(): 308, with the addition
     of caching.  Useful for expensive computed properties of instances
     that are otherwise effectively immutable.

     Example:

          class DataSet:

              def __init__(self, sequence_of_numbers):
                  self._data = tuple(sequence_of_numbers)

              @cached_property
              def stdev(self):
                  return statistics.stdev(self._data)

     The mechanics of *note cached_property(): 2f9. are somewhat
     different from *note property(): 308.  A regular property blocks
     attribute writes unless a setter is defined.  In contrast, a
     `cached_property' allows writes.

     The `cached_property' decorator only runs on lookups and only when
     an attribute of the same name doesn’t exist.  When it does run, the
     `cached_property' writes to the attribute with the same name.
     Subsequent attribute reads and writes take precedence over the
     `cached_property' method and it works like a normal attribute.

     The cached value can be cleared by deleting the attribute.  This
     allows the `cached_property' method to run again.

     Note, this decorator interferes with the operation of PEP 412(3)
     key-sharing dictionaries.  This means that instance dictionaries
     can take more space than usual.

     Also, this decorator requires that the ‘__dict__’ attribute on each
     instance be a mutable mapping.  This means it will not work with
     some types, such as metaclasses (since the ‘__dict__’ attributes on
     type instances are read-only proxies for the class namespace), and
     those that specify ‘__slots__’ without including ‘__dict__’ as one
     of the defined slots (as such classes don’t provide a ‘__dict__’
     attribute at all).

     If a mutable mapping is not available or if space-efficient key
     sharing is desired, an effect similar to *note cached_property():
     2f9. can be achieved by a stacking *note property(): 308. on top of
     *note cache(): 1ca6.:

          class DataSet:
              def __init__(self, sequence_of_numbers):
                  self._data = sequence_of_numbers

              @property
              @cache
              def stdev(self):
                  return statistics.stdev(self._data)

     New in version 3.8.

 -- Function: functools.cmp_to_key (func)

     Transform an old-style comparison function to a *note key function:
     7d2.  Used with tools that accept key functions (such as *note
     sorted(): 547, *note min(): 8f6, *note max(): 8f7, *note
     heapq.nlargest(): 1ab2, *note heapq.nsmallest(): 1ab3, *note
     itertools.groupby(): 1c9d.).  This function is primarily used as a
     transition tool for programs being converted from Python 2 which
     supported the use of comparison functions.

     A comparison function is any callable that accept two arguments,
     compares them, and returns a negative number for less-than, zero
     for equality, or a positive number for greater-than.  A key
     function is a callable that accepts one argument and returns
     another value to be used as the sort key.

     Example:

          sorted(iterable, key=cmp_to_key(locale.strcoll))  # locale-aware sort order

     For sorting examples and a brief sorting tutorial, see *note
     Sorting HOW TO: 1737.

     New in version 3.2.

 -- Function: @functools.lru_cache (user_function)

 -- Function: @functools.lru_cache (maxsize=128, typed=False)

     Decorator to wrap a function with a memoizing callable that saves
     up to the `maxsize' most recent calls.  It can save time when an
     expensive or I/O bound function is periodically called with the
     same arguments.

     Since a dictionary is used to cache results, the positional and
     keyword arguments to the function must be hashable.

     Distinct argument patterns may be considered to be distinct calls
     with separate cache entries.  For example, ‘f(a=1, b=2)’ and
     ‘f(b=2, a=1)’ differ in their keyword argument order and may have
     two separate cache entries.

     If `user_function' is specified, it must be a callable.  This
     allows the `lru_cache' decorator to be applied directly to a user
     function, leaving the `maxsize' at its default value of 128:

          @lru_cache
          def count_vowels(sentence):
              sentence = sentence.casefold()
              return sum(sentence.count(vowel) for vowel in 'aeiou')

     If `maxsize' is set to ‘None’, the LRU feature is disabled and the
     cache can grow without bound.

     If `typed' is set to true, function arguments of different types
     will be cached separately.  For example, ‘f(3)’ and ‘f(3.0)’ will
     be treated as distinct calls with distinct results.

     The wrapped function is instrumented with a ‘cache_parameters()’
     function that returns a new *note dict: 164. showing the values for
     `maxsize' and `typed'.  This is for information purposes only.
     Mutating the values has no effect.

     To help measure the effectiveness of the cache and tune the
     `maxsize' parameter, the wrapped function is instrumented with a
     ‘cache_info()’ function that returns a *note named tuple: b7b.
     showing `hits', `misses', `maxsize' and `currsize'.  In a
     multi-threaded environment, the hits and misses are approximate.

     The decorator also provides a ‘cache_clear()’ function for clearing
     or invalidating the cache.

     The original underlying function is accessible through the
     ‘__wrapped__’ attribute.  This is useful for introspection, for
     bypassing the cache, or for rewrapping the function with a
     different cache.

     An LRU (least recently used) cache(4) works best when the most
     recent calls are the best predictors of upcoming calls (for
     example, the most popular articles on a news server tend to change
     each day).  The cache’s size limit assures that the cache does not
     grow without bound on long-running processes such as web servers.

     In general, the LRU cache should only be used when you want to
     reuse previously computed values.  Accordingly, it doesn’t make
     sense to cache functions with side-effects, functions that need to
     create distinct mutable objects on each call, or impure functions
     such as time() or random().

     Example of an LRU cache for static web content:

          @lru_cache(maxsize=32)
          def get_pep(num):
              'Retrieve text of a Python Enhancement Proposal'
              resource = 'https://www.python.org/dev/peps/pep-%04d/' % num
              try:
                  with urllib.request.urlopen(resource) as s:
                      return s.read()
              except urllib.error.HTTPError:
                  return 'Not Found'

          >>> for n in 8, 290, 308, 320, 8, 218, 320, 279, 289, 320, 9991:
          ...     pep = get_pep(n)
          ...     print(n, len(pep))

          >>> get_pep.cache_info()
          CacheInfo(hits=3, misses=8, maxsize=32, currsize=8)

     Example of efficiently computing Fibonacci numbers(5) using a cache
     to implement a dynamic programming(6) technique:

          @lru_cache(maxsize=None)
          def fib(n):
              if n < 2:
                  return n
              return fib(n-1) + fib(n-2)

          >>> [fib(n) for n in range(16)]
          [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610]

          >>> fib.cache_info()
          CacheInfo(hits=28, misses=16, maxsize=None, currsize=16)

     New in version 3.2.

     Changed in version 3.3: Added the `typed' option.

     Changed in version 3.8: Added the `user_function' option.

     New in version 3.9: Added the function ‘cache_parameters()’

 -- Function: @functools.total_ordering

     Given a class defining one or more rich comparison ordering
     methods, this class decorator supplies the rest.  This simplifies
     the effort involved in specifying all of the possible rich
     comparison operations:

     The class must define one of *note __lt__(): cfe, *note __le__():
     d68, *note __gt__(): d69, or *note __ge__(): d6a.  In addition, the
     class should supply an *note __eq__(): 44b. method.

     For example:

          @total_ordering
          class Student:
              def _is_valid_operand(self, other):
                  return (hasattr(other, "lastname") and
                          hasattr(other, "firstname"))
              def __eq__(self, other):
                  if not self._is_valid_operand(other):
                      return NotImplemented
                  return ((self.lastname.lower(), self.firstname.lower()) ==
                          (other.lastname.lower(), other.firstname.lower()))
              def __lt__(self, other):
                  if not self._is_valid_operand(other):
                      return NotImplemented
                  return ((self.lastname.lower(), self.firstname.lower()) <
                          (other.lastname.lower(), other.firstname.lower()))

          Note: While this decorator makes it easy to create well
          behaved totally ordered types, it `does' come at the cost of
          slower execution and more complex stack traces for the derived
          comparison methods.  If performance benchmarking indicates
          this is a bottleneck for a given application, implementing all
          six rich comparison methods instead is likely to provide an
          easy speed boost.

     New in version 3.2.

     Changed in version 3.4: Returning NotImplemented from the
     underlying comparison function for unrecognised types is now
     supported.

 -- Function: functools.partial (func, /, *args, **keywords)

     Return a new *note partial object: 1ca7. which when called will
     behave like `func' called with the positional arguments `args' and
     keyword arguments `keywords'.  If more arguments are supplied to
     the call, they are appended to `args'.  If additional keyword
     arguments are supplied, they extend and override `keywords'.
     Roughly equivalent to:

          def partial(func, /, *args, **keywords):
              def newfunc(*fargs, **fkeywords):
                  newkeywords = {**keywords, **fkeywords}
                  return func(*args, *fargs, **newkeywords)
              newfunc.func = func
              newfunc.args = args
              newfunc.keywords = keywords
              return newfunc

     The *note partial(): 8b5. is used for partial function application
     which “freezes” some portion of a function’s arguments and/or
     keywords resulting in a new object with a simplified signature.
     For example, *note partial(): 8b5. can be used to create a callable
     that behaves like the *note int(): 204. function where the `base'
     argument defaults to two:

          >>> from functools import partial
          >>> basetwo = partial(int, base=2)
          >>> basetwo.__doc__ = 'Convert base 2 string to an int.'
          >>> basetwo('10010')
          18

 -- Class: functools.partialmethod (func, /, *args, **keywords)

     Return a new *note partialmethod: 3bf. descriptor which behaves
     like *note partial: 8b5. except that it is designed to be used as a
     method definition rather than being directly callable.

     `func' must be a *note descriptor: 1579. or a callable (objects
     which are both, like normal functions, are handled as descriptors).

     When `func' is a descriptor (such as a normal Python function,
     *note classmethod(): 309, *note staticmethod(): 30a,
     ‘abstractmethod()’ or another instance of *note partialmethod:
     3bf.), calls to ‘__get__’ are delegated to the underlying
     descriptor, and an appropriate *note partial object: 1ca7. returned
     as the result.

     When `func' is a non-descriptor callable, an appropriate bound
     method is created dynamically.  This behaves like a normal Python
     function when used as a method: the `self' argument will be
     inserted as the first positional argument, even before the `args'
     and `keywords' supplied to the *note partialmethod: 3bf.
     constructor.

     Example:

          >>> class Cell:
          ...     def __init__(self):
          ...         self._alive = False
          ...     @property
          ...     def alive(self):
          ...         return self._alive
          ...     def set_state(self, state):
          ...         self._alive = bool(state)
          ...     set_alive = partialmethod(set_state, True)
          ...     set_dead = partialmethod(set_state, False)
          ...
          >>> c = Cell()
          >>> c.alive
          False
          >>> c.set_alive()
          >>> c.alive
          True

     New in version 3.4.

 -- Function: functools.reduce (function, iterable[, initializer])

     Apply `function' of two arguments cumulatively to the items of
     `iterable', from left to right, so as to reduce the iterable to a
     single value.  For example, ‘reduce(lambda x, y: x+y, [1, 2, 3, 4,
     5])’ calculates ‘((((1+2)+3)+4)+5)’.  The left argument, `x', is
     the accumulated value and the right argument, `y', is the update
     value from the `iterable'.  If the optional `initializer' is
     present, it is placed before the items of the iterable in the
     calculation, and serves as a default when the iterable is empty.
     If `initializer' is not given and `iterable' contains only one
     item, the first item is returned.

     Roughly equivalent to:

          def reduce(function, iterable, initializer=None):
              it = iter(iterable)
              if initializer is None:
                  value = next(it)
              else:
                  value = initializer
              for element in it:
                  value = function(value, element)
              return value

     See *note itertools.accumulate(): 30e. for an iterator that yields
     all intermediate values.

 -- Function: @functools.singledispatch

     Transform a function into a *note single-dispatch: 2fc. *note
     generic function: 2fb.

     To define a generic function, decorate it with the
     ‘@singledispatch’ decorator.  When defining a function using
     ‘@singledispatch’, note that the dispatch happens on the type of
     the first argument:

          >>> from functools import singledispatch
          >>> @singledispatch
          ... def fun(arg, verbose=False):
          ...     if verbose:
          ...         print("Let me just say,", end=" ")
          ...     print(arg)

     To add overloaded implementations to the function, use the
     ‘register()’ attribute of the generic function, which can be used
     as a decorator.  For functions annotated with types, the decorator
     will infer the type of the first argument automatically:

          >>> @fun.register
          ... def _(arg: int, verbose=False):
          ...     if verbose:
          ...         print("Strength in numbers, eh?", end=" ")
          ...     print(arg)
          ...
          >>> @fun.register
          ... def _(arg: list, verbose=False):
          ...     if verbose:
          ...         print("Enumerate this:")
          ...     for i, elem in enumerate(arg):
          ...         print(i, elem)

     For code which doesn’t use type annotations, the appropriate type
     argument can be passed explicitly to the decorator itself:

          >>> @fun.register(complex)
          ... def _(arg, verbose=False):
          ...     if verbose:
          ...         print("Better than complicated.", end=" ")
          ...     print(arg.real, arg.imag)
          ...

     To enable registering *note lambdas: 1ca8. and pre-existing
     functions, the ‘register()’ attribute can also be used in a
     functional form:

          >>> def nothing(arg, verbose=False):
          ...     print("Nothing.")
          ...
          >>> fun.register(type(None), nothing)

     The ‘register()’ attribute returns the undecorated function.  This
     enables decorator stacking, *note pickling: ca, and the creation of
     unit tests for each variant independently:

          >>> @fun.register(float)
          ... @fun.register(Decimal)
          ... def fun_num(arg, verbose=False):
          ...     if verbose:
          ...         print("Half of your number:", end=" ")
          ...     print(arg / 2)
          ...
          >>> fun_num is fun
          False

     When called, the generic function dispatches on the type of the
     first argument:

          >>> fun("Hello, world.")
          Hello, world.
          >>> fun("test.", verbose=True)
          Let me just say, test.
          >>> fun(42, verbose=True)
          Strength in numbers, eh? 42
          >>> fun(['spam', 'spam', 'eggs', 'spam'], verbose=True)
          Enumerate this:
          0 spam
          1 spam
          2 eggs
          3 spam
          >>> fun(None)
          Nothing.
          >>> fun(1.23)
          0.615

     Where there is no registered implementation for a specific type,
     its method resolution order is used to find a more generic
     implementation.  The original function decorated with
     ‘@singledispatch’ is registered for the base *note object: 3d2.
     type, which means it is used if no better implementation is found.

     If an implementation is registered to an *note abstract base class:
     c05, virtual subclasses of the base class will be dispatched to
     that implementation:

          >>> from collections.abc import Mapping
          >>> @fun.register
          ... def _(arg: Mapping, verbose=False):
          ...     if verbose:
          ...         print("Keys & Values")
          ...     for key, value in arg.items():
          ...         print(key, "=>", value)
          ...
          >>> fun({"a": "b"})
          a => b

     To check which implementation the generic function will choose for
     a given type, use the ‘dispatch()’ attribute:

          >>> fun.dispatch(float)
          <function fun_num at 0x1035a2840>
          >>> fun.dispatch(dict)    # note: default implementation
          <function fun at 0x103fe0000>

     To access all registered implementations, use the read-only
     ‘registry’ attribute:

          >>> fun.registry.keys()
          dict_keys([<class 'NoneType'>, <class 'int'>, <class 'object'>,
                    <class 'decimal.Decimal'>, <class 'list'>,
                    <class 'float'>])
          >>> fun.registry[float]
          <function fun_num at 0x1035a2840>
          >>> fun.registry[object]
          <function fun at 0x103fe0000>

     New in version 3.4.

     Changed in version 3.7: The ‘register()’ attribute now supports
     using type annotations.

 -- Class: functools.singledispatchmethod (func)

     Transform a method into a *note single-dispatch: 2fc. *note generic
     function: 2fb.

     To define a generic method, decorate it with the
     ‘@singledispatchmethod’ decorator.  When defining a function using
     ‘@singledispatchmethod’, note that the dispatch happens on the type
     of the first non-`self' or non-`cls' argument:

          class Negator:
              @singledispatchmethod
              def neg(self, arg):
                  raise NotImplementedError("Cannot negate a")

              @neg.register
              def _(self, arg: int):
                  return -arg

              @neg.register
              def _(self, arg: bool):
                  return not arg

     ‘@singledispatchmethod’ supports nesting with other decorators such
     as *note @classmethod: 309.  Note that to allow for
     ‘dispatcher.register’, ‘singledispatchmethod’ must be the `outer
     most' decorator.  Here is the ‘Negator’ class with the ‘neg’
     methods bound to the class, rather than an instance of the class:

          class Negator:
              @singledispatchmethod
              @classmethod
              def neg(cls, arg):
                  raise NotImplementedError("Cannot negate a")

              @neg.register
              @classmethod
              def _(cls, arg: int):
                  return -arg

              @neg.register
              @classmethod
              def _(cls, arg: bool):
                  return not arg

     The same pattern can be used for other similar decorators: *note
     @staticmethod: 30a, *note @abstractmethod: aad, and others.

     New in version 3.8.

 -- Function: functools.update_wrapper (wrapper, wrapped,
          assigned=WRAPPER_ASSIGNMENTS, updated=WRAPPER_UPDATES)

     Update a `wrapper' function to look like the `wrapped' function.
     The optional arguments are tuples to specify which attributes of
     the original function are assigned directly to the matching
     attributes on the wrapper function and which attributes of the
     wrapper function are updated with the corresponding attributes from
     the original function.  The default values for these arguments are
     the module level constants ‘WRAPPER_ASSIGNMENTS’ (which assigns to
     the wrapper function’s ‘__module__’, ‘__name__’, ‘__qualname__’,
     ‘__annotations__’ and ‘__doc__’, the documentation string) and
     ‘WRAPPER_UPDATES’ (which updates the wrapper function’s ‘__dict__’,
     i.e.  the instance dictionary).

     To allow access to the original function for introspection and
     other purposes (e.g.  bypassing a caching decorator such as *note
     lru_cache(): 2f8.), this function automatically adds a
     ‘__wrapped__’ attribute to the wrapper that refers to the function
     being wrapped.

     The main intended use for this function is in *note decorator: 174.
     functions which wrap the decorated function and return the wrapper.
     If the wrapper function is not updated, the metadata of the
     returned function will reflect the wrapper definition rather than
     the original function definition, which is typically less than
     helpful.

     *note update_wrapper(): a3b. may be used with callables other than
     functions.  Any attributes named in `assigned' or `updated' that
     are missing from the object being wrapped are ignored (i.e.  this
     function will not attempt to set them on the wrapper function).
     *note AttributeError: 4a2. is still raised if the wrapper function
     itself is missing any attributes named in `updated'.

     New in version 3.2: Automatic addition of the ‘__wrapped__’
     attribute.

     New in version 3.2: Copying of the ‘__annotations__’ attribute by
     default.

     Changed in version 3.2: Missing attributes no longer trigger an
     *note AttributeError: 4a2.

     Changed in version 3.4: The ‘__wrapped__’ attribute now always
     refers to the wrapped function, even if that function defined a
     ‘__wrapped__’ attribute.  (see bpo-17482(7))

 -- Function: @functools.wraps (wrapped, assigned=WRAPPER_ASSIGNMENTS,
          updated=WRAPPER_UPDATES)

     This is a convenience function for invoking *note update_wrapper():
     a3b. as a function decorator when defining a wrapper function.  It
     is equivalent to ‘partial(update_wrapper, wrapped=wrapped,
     assigned=assigned, updated=updated)’.  For example:

          >>> from functools import wraps
          >>> def my_decorator(f):
          ...     @wraps(f)
          ...     def wrapper(*args, **kwds):
          ...         print('Calling decorated function')
          ...         return f(*args, **kwds)
          ...     return wrapper
          ...
          >>> @my_decorator
          ... def example():
          ...     """Docstring"""
          ...     print('Called example function')
          ...
          >>> example()
          Calling decorated function
          Called example function
          >>> example.__name__
          'example'
          >>> example.__doc__
          'Docstring'

     Without the use of this decorator factory, the name of the example
     function would have been ‘'wrapper'’, and the docstring of the
     original ‘example()’ would have been lost.

* Menu:

* partial Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/functools.py

   (2) https://en.wikipedia.org/wiki/Memoization

   (3) https://www.python.org/dev/peps/pep-0412

   (4) 
https://en.wikipedia.org/wiki/Cache_replacement_policies#Least_recently_used_(LRU)

   (5) https://en.wikipedia.org/wiki/Fibonacci_number

   (6) https://en.wikipedia.org/wiki/Dynamic_programming

   (7) https://bugs.python.org/issue17482


File: python.info,  Node: partial Objects,  Up: functools — Higher-order functions and operations on callable objects

5.10.2.1 ‘partial’ Objects
..........................

*note partial: 8b5. objects are callable objects created by *note
partial(): 8b5.  They have three read-only attributes:

 -- Attribute: partial.func

     A callable object or function.  Calls to the *note partial: 8b5.
     object will be forwarded to *note func: 1caa. with new arguments
     and keywords.

 -- Attribute: partial.args

     The leftmost positional arguments that will be prepended to the
     positional arguments provided to a *note partial: 8b5. object call.

 -- Attribute: partial.keywords

     The keyword arguments that will be supplied when the *note partial:
     8b5. object is called.

*note partial: 8b5. objects are like ‘function’ objects in that they are
callable, weak referencable, and can have attributes.  There are some
important differences.  For instance, the *note __name__: d2f. and
‘__doc__’ attributes are not created automatically.  Also, *note
partial: 8b5. objects defined in classes behave like static methods and
do not transform into bound methods during instance attribute look-up.


File: python.info,  Node: operator — Standard operators as functions,  Prev: functools — Higher-order functions and operations on callable objects,  Up: Functional Programming Modules

5.10.3 ‘operator’ — Standard operators as functions
---------------------------------------------------

`Source code:' Lib/operator.py(1)

__________________________________________________________________

The *note operator: c2. module exports a set of efficient functions
corresponding to the intrinsic operators of Python.  For example,
‘operator.add(x, y)’ is equivalent to the expression ‘x+y’.  Many
function names are those used for special methods, without the double
underscores.  For backward compatibility, many of these have a variant
with the double underscores kept.  The variants without the double
underscores are preferred for clarity.

The functions fall into categories that perform object comparisons,
logical operations, mathematical operations and sequence operations.

The object comparison functions are useful for all objects, and are
named after the rich comparison operators they support:

 -- Function: operator.lt (a, b)
 -- Function: operator.le (a, b)
 -- Function: operator.eq (a, b)
 -- Function: operator.ne (a, b)
 -- Function: operator.ge (a, b)
 -- Function: operator.gt (a, b)
 -- Function: operator.__lt__ (a, b)
 -- Function: operator.__le__ (a, b)
 -- Function: operator.__eq__ (a, b)
 -- Function: operator.__ne__ (a, b)
 -- Function: operator.__ge__ (a, b)
 -- Function: operator.__gt__ (a, b)

     Perform “rich comparisons” between `a' and `b'.  Specifically,
     ‘lt(a, b)’ is equivalent to ‘a < b’, ‘le(a, b)’ is equivalent to ‘a
     <= b’, ‘eq(a, b)’ is equivalent to ‘a == b’, ‘ne(a, b)’ is
     equivalent to ‘a != b’, ‘gt(a, b)’ is equivalent to ‘a > b’ and
     ‘ge(a, b)’ is equivalent to ‘a >= b’.  Note that these functions
     can return any value, which may or may not be interpretable as a
     Boolean value.  See *note Comparisons: 167a. for more information
     about rich comparisons.

The logical operations are also generally applicable to all objects, and
support truth tests, identity tests, and boolean operations:

 -- Function: operator.not_ (obj)
 -- Function: operator.__not__ (obj)

     Return the outcome of *note not: 1686. `obj'.  (Note that there is
     no *note __not__(): 1cbc. method for object instances; only the
     interpreter core defines this operation.  The result is affected by
     the *note __bool__(): d30. and *note __len__(): e90. methods.)

 -- Function: operator.truth (obj)

     Return *note True: 594. if `obj' is true, and *note False: 48f.
     otherwise.  This is equivalent to using the *note bool: 2bd.
     constructor.

 -- Function: operator.is_ (a, b)

     Return ‘a is b’.  Tests object identity.

 -- Function: operator.is_not (a, b)

     Return ‘a is not b’.  Tests object identity.

The mathematical and bitwise operations are the most numerous:

 -- Function: operator.abs (obj)
 -- Function: operator.__abs__ (obj)

     Return the absolute value of `obj'.

 -- Function: operator.add (a, b)
 -- Function: operator.__add__ (a, b)

     Return ‘a + b’, for `a' and `b' numbers.

 -- Function: operator.and_ (a, b)
 -- Function: operator.__and__ (a, b)

     Return the bitwise and of `a' and `b'.

 -- Function: operator.floordiv (a, b)
 -- Function: operator.__floordiv__ (a, b)

     Return ‘a // b’.

 -- Function: operator.index (a)
 -- Function: operator.__index__ (a)

     Return `a' converted to an integer.  Equivalent to ‘a.__index__()’.

 -- Function: operator.inv (obj)
 -- Function: operator.invert (obj)
 -- Function: operator.__inv__ (obj)
 -- Function: operator.__invert__ (obj)

     Return the bitwise inverse of the number `obj'.  This is equivalent
     to ‘~obj’.

 -- Function: operator.lshift (a, b)
 -- Function: operator.__lshift__ (a, b)

     Return `a' shifted left by `b'.

 -- Function: operator.mod (a, b)
 -- Function: operator.__mod__ (a, b)

     Return ‘a % b’.

 -- Function: operator.mul (a, b)
 -- Function: operator.__mul__ (a, b)

     Return ‘a * b’, for `a' and `b' numbers.

 -- Function: operator.matmul (a, b)
 -- Function: operator.__matmul__ (a, b)

     Return ‘a @ b’.

     New in version 3.5.

 -- Function: operator.neg (obj)
 -- Function: operator.__neg__ (obj)

     Return `obj' negated (‘-obj’).

 -- Function: operator.or_ (a, b)
 -- Function: operator.__or__ (a, b)

     Return the bitwise or of `a' and `b'.

 -- Function: operator.pos (obj)
 -- Function: operator.__pos__ (obj)

     Return `obj' positive (‘+obj’).

 -- Function: operator.pow (a, b)
 -- Function: operator.__pow__ (a, b)

     Return ‘a ** b’, for `a' and `b' numbers.

 -- Function: operator.rshift (a, b)
 -- Function: operator.__rshift__ (a, b)

     Return `a' shifted right by `b'.

 -- Function: operator.sub (a, b)
 -- Function: operator.__sub__ (a, b)

     Return ‘a - b’.

 -- Function: operator.truediv (a, b)
 -- Function: operator.__truediv__ (a, b)

     Return ‘a / b’ where 2/3 is .66 rather than 0.  This is also known
     as “true” division.

 -- Function: operator.xor (a, b)
 -- Function: operator.__xor__ (a, b)

     Return the bitwise exclusive or of `a' and `b'.

Operations which work with sequences (some of them with mappings too)
include:

 -- Function: operator.concat (a, b)
 -- Function: operator.__concat__ (a, b)

     Return ‘a + b’ for `a' and `b' sequences.

 -- Function: operator.contains (a, b)
 -- Function: operator.__contains__ (a, b)

     Return the outcome of the test ‘b in a’.  Note the reversed
     operands.

 -- Function: operator.countOf (a, b)

     Return the number of occurrences of `b' in `a'.

 -- Function: operator.delitem (a, b)
 -- Function: operator.__delitem__ (a, b)

     Remove the value of `a' at index `b'.

 -- Function: operator.getitem (a, b)
 -- Function: operator.__getitem__ (a, b)

     Return the value of `a' at index `b'.

 -- Function: operator.indexOf (a, b)

     Return the index of the first of occurrence of `b' in `a'.

 -- Function: operator.setitem (a, b, c)
 -- Function: operator.__setitem__ (a, b, c)

     Set the value of `a' at index `b' to `c'.

 -- Function: operator.length_hint (obj, default=0)

     Return an estimated length for the object `o'.  First try to return
     its actual length, then an estimate using *note
     object.__length_hint__(): 8f9, and finally return the default
     value.

     New in version 3.4.

The *note operator: c2. module also defines tools for generalized
attribute and item lookups.  These are useful for making fast field
extractors as arguments for *note map(): cf7, *note sorted(): 547, *note
itertools.groupby(): 1c9d, or other functions that expect a function
argument.

 -- Function: operator.attrgetter (attr)

 -- Function: operator.attrgetter (*attrs)

     Return a callable object that fetches `attr' from its operand.  If
     more than one attribute is requested, returns a tuple of
     attributes.  The attribute names can also contain dots.  For
     example:

        * After ‘f = attrgetter('name')’, the call ‘f(b)’ returns
          ‘b.name’.

        * After ‘f = attrgetter('name', 'date')’, the call ‘f(b)’
          returns ‘(b.name, b.date)’.

        * After ‘f = attrgetter('name.first', 'name.last')’, the call
          ‘f(b)’ returns ‘(b.name.first, b.name.last)’.

     Equivalent to:

          def attrgetter(*items):
              if any(not isinstance(item, str) for item in items):
                  raise TypeError('attribute name must be a string')
              if len(items) == 1:
                  attr = items[0]
                  def g(obj):
                      return resolve_attr(obj, attr)
              else:
                  def g(obj):
                      return tuple(resolve_attr(obj, attr) for attr in items)
              return g

          def resolve_attr(obj, attr):
              for name in attr.split("."):
                  obj = getattr(obj, name)
              return obj

 -- Function: operator.itemgetter (item)

 -- Function: operator.itemgetter (*items)

     Return a callable object that fetches `item' from its operand using
     the operand’s *note __getitem__(): 1ce9. method.  If multiple items
     are specified, returns a tuple of lookup values.  For example:

        * After ‘f = itemgetter(2)’, the call ‘f(r)’ returns ‘r[2]’.

        * After ‘g = itemgetter(2, 5, 3)’, the call ‘g(r)’ returns
          ‘(r[2], r[5], r[3])’.

     Equivalent to:

          def itemgetter(*items):
              if len(items) == 1:
                  item = items[0]
                  def g(obj):
                      return obj[item]
              else:
                  def g(obj):
                      return tuple(obj[item] for item in items)
              return g

     The items can be any type accepted by the operand’s *note
     __getitem__(): 1ce9. method.  Dictionaries accept any hashable
     value.  Lists, tuples, and strings accept an index or a slice:

          >>> itemgetter(1)('ABCDEFG')
          'B'
          >>> itemgetter(1, 3, 5)('ABCDEFG')
          ('B', 'D', 'F')
          >>> itemgetter(slice(2, None))('ABCDEFG')
          'CDEFG'
          >>> soldier = dict(rank='captain', name='dotterbart')
          >>> itemgetter('rank')(soldier)
          'captain'

     Example of using *note itemgetter(): 38b. to retrieve specific
     fields from a tuple record:

          >>> inventory = [('apple', 3), ('banana', 2), ('pear', 5), ('orange', 1)]
          >>> getcount = itemgetter(1)
          >>> list(map(getcount, inventory))
          [3, 2, 5, 1]
          >>> sorted(inventory, key=getcount)
          [('orange', 1), ('banana', 2), ('apple', 3), ('pear', 5)]

 -- Function: operator.methodcaller (name, /, *args, **kwargs)

     Return a callable object that calls the method `name' on its
     operand.  If additional arguments and/or keyword arguments are
     given, they will be given to the method as well.  For example:

        * After ‘f = methodcaller('name')’, the call ‘f(b)’ returns
          ‘b.name()’.

        * After ‘f = methodcaller('name', 'foo', bar=1)’, the call
          ‘f(b)’ returns ‘b.name('foo', bar=1)’.

     Equivalent to:

          def methodcaller(name, /, *args, **kwargs):
              def caller(obj):
                  return getattr(obj, name)(*args, **kwargs)
              return caller

* Menu:

* Mapping Operators to Functions::
* In-place Operators::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/operator.py


File: python.info,  Node: Mapping Operators to Functions,  Next: In-place Operators,  Up: operator — Standard operators as functions

5.10.3.1 Mapping Operators to Functions
.......................................

This table shows how abstract operations correspond to operator symbols
in the Python syntax and the functions in the *note operator: c2.
module.

Operation                   Syntax                        Function
                                                          
------------------------------------------------------------------------------------------------------
                                                          
Addition                    ‘a + b’                       ‘add(a, b)’
                                                          
                                                          
Concatenation               ‘seq1 + seq2’                 ‘concat(seq1, seq2)’
                                                          
                                                          
Containment Test            ‘obj in seq’                  ‘contains(seq, obj)’
                                                          
                                                          
Division                    ‘a / b’                       ‘truediv(a, b)’
                                                          
                                                          
Division                    ‘a // b’                      ‘floordiv(a, b)’
                                                          
                                                          
Bitwise And                 ‘a & b’                       ‘and_(a, b)’
                                                          
                                                          
Bitwise Exclusive Or        ‘a ^ b’                       ‘xor(a, b)’
                                                          
                                                          
Bitwise Inversion           ‘~ a’                         ‘invert(a)’
                                                          
                                                          
Bitwise Or                  ‘a | b’                       ‘or_(a, b)’
                                                          
                                                          
Exponentiation              ‘a ** b’                      ‘pow(a, b)’
                                                          
                                                          
Identity                    ‘a is b’                      ‘is_(a, b)’
                                                          
                                                          
Identity                    ‘a is not b’                  ‘is_not(a, b)’
                                                          
                                                          
Indexed Assignment          ‘obj[k] = v’                  ‘setitem(obj, k, v)’
                                                          
                                                          
Indexed Deletion            ‘del obj[k]’                  ‘delitem(obj, k)’
                                                          
                                                          
Indexing                    ‘obj[k]’                      ‘getitem(obj, k)’
                                                          
                                                          
Left Shift                  ‘a << b’                      ‘lshift(a, b)’
                                                          
                                                          
Modulo                      ‘a % b’                       ‘mod(a, b)’
                                                          
                                                          
Multiplication              ‘a * b’                       ‘mul(a, b)’
                                                          
                                                          
Matrix Multiplication       ‘a @ b’                       ‘matmul(a, b)’
                                                          
                                                          
Negation (Arithmetic)       ‘- a’                         ‘neg(a)’
                                                          
                                                          
Negation (Logical)          ‘not a’                       ‘not_(a)’
                                                          
                                                          
Positive                    ‘+ a’                         ‘pos(a)’
                                                          
                                                          
Right Shift                 ‘a >> b’                      ‘rshift(a, b)’
                                                          
                                                          
Slice Assignment            ‘seq[i:j] = values’           ‘setitem(seq, slice(i, j), values)’
                                                          
                                                          
Slice Deletion              ‘del seq[i:j]’                ‘delitem(seq, slice(i, j))’
                                                          
                                                          
Slicing                     ‘seq[i:j]’                    ‘getitem(seq, slice(i, j))’
                                                          
                                                          
String Formatting           ‘s % obj’                     ‘mod(s, obj)’
                                                          
                                                          
Subtraction                 ‘a - b’                       ‘sub(a, b)’
                                                          
                                                          
Truth Test                  ‘obj’                         ‘truth(obj)’
                                                          
                                                          
Ordering                    ‘a < b’                       ‘lt(a, b)’
                                                          
                                                          
Ordering                    ‘a <= b’                      ‘le(a, b)’
                                                          
                                                          
Equality                    ‘a == b’                      ‘eq(a, b)’
                                                          
                                                          
Difference                  ‘a != b’                      ‘ne(a, b)’
                                                          
                                                          
Ordering                    ‘a >= b’                      ‘ge(a, b)’
                                                          
                                                          
Ordering                    ‘a > b’                       ‘gt(a, b)’
                                                          


File: python.info,  Node: In-place Operators,  Prev: Mapping Operators to Functions,  Up: operator — Standard operators as functions

5.10.3.2 In-place Operators
...........................

Many operations have an “in-place” version.  Listed below are functions
providing a more primitive access to in-place operators than the usual
syntax does; for example, the *note statement: 1cef. ‘x += y’ is
equivalent to ‘x = operator.iadd(x, y)’.  Another way to put it is to
say that ‘z = operator.iadd(x, y)’ is equivalent to the compound
statement ‘z = x; z += y’.

In those examples, note that when an in-place method is called, the
computation and assignment are performed in two separate steps.  The
in-place functions listed below only do the first step, calling the
in-place method.  The second step, assignment, is not handled.

For immutable targets such as strings, numbers, and tuples, the updated
value is computed, but not assigned back to the input variable:

     >>> a = 'hello'
     >>> iadd(a, ' world')
     'hello world'
     >>> a
     'hello'

For mutable targets such as lists and dictionaries, the in-place method
will perform the update, so no subsequent assignment is necessary:

     >>> s = ['h', 'e', 'l', 'l', 'o']
     >>> iadd(s, [' ', 'w', 'o', 'r', 'l', 'd'])
     ['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd']
     >>> s
     ['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd']

 -- Function: operator.iadd (a, b)
 -- Function: operator.__iadd__ (a, b)

     ‘a = iadd(a, b)’ is equivalent to ‘a += b’.

 -- Function: operator.iand (a, b)
 -- Function: operator.__iand__ (a, b)

     ‘a = iand(a, b)’ is equivalent to ‘a &= b’.

 -- Function: operator.iconcat (a, b)
 -- Function: operator.__iconcat__ (a, b)

     ‘a = iconcat(a, b)’ is equivalent to ‘a += b’ for `a' and `b'
     sequences.

 -- Function: operator.ifloordiv (a, b)
 -- Function: operator.__ifloordiv__ (a, b)

     ‘a = ifloordiv(a, b)’ is equivalent to ‘a //= b’.

 -- Function: operator.ilshift (a, b)
 -- Function: operator.__ilshift__ (a, b)

     ‘a = ilshift(a, b)’ is equivalent to ‘a <<= b’.

 -- Function: operator.imod (a, b)
 -- Function: operator.__imod__ (a, b)

     ‘a = imod(a, b)’ is equivalent to ‘a %= b’.

 -- Function: operator.imul (a, b)
 -- Function: operator.__imul__ (a, b)

     ‘a = imul(a, b)’ is equivalent to ‘a *= b’.

 -- Function: operator.imatmul (a, b)
 -- Function: operator.__imatmul__ (a, b)

     ‘a = imatmul(a, b)’ is equivalent to ‘a @= b’.

     New in version 3.5.

 -- Function: operator.ior (a, b)
 -- Function: operator.__ior__ (a, b)

     ‘a = ior(a, b)’ is equivalent to ‘a |= b’.

 -- Function: operator.ipow (a, b)
 -- Function: operator.__ipow__ (a, b)

     ‘a = ipow(a, b)’ is equivalent to ‘a **= b’.

 -- Function: operator.irshift (a, b)
 -- Function: operator.__irshift__ (a, b)

     ‘a = irshift(a, b)’ is equivalent to ‘a >>= b’.

 -- Function: operator.isub (a, b)
 -- Function: operator.__isub__ (a, b)

     ‘a = isub(a, b)’ is equivalent to ‘a -= b’.

 -- Function: operator.itruediv (a, b)
 -- Function: operator.__itruediv__ (a, b)

     ‘a = itruediv(a, b)’ is equivalent to ‘a /= b’.

 -- Function: operator.ixor (a, b)
 -- Function: operator.__ixor__ (a, b)

     ‘a = ixor(a, b)’ is equivalent to ‘a ^= b’.


File: python.info,  Node: File and Directory Access,  Next: Data Persistence,  Prev: Functional Programming Modules,  Up: The Python Standard Library

5.11 File and Directory Access
==============================

The modules described in this chapter deal with disk files and
directories.  For example, there are modules for reading the properties
of files, manipulating paths in a portable way, and creating temporary
files.  The full list of modules in this chapter is:

* Menu:

* pathlib — Object-oriented filesystem paths::
* os.path — Common pathname manipulations: os path — Common pathname manipulations.
* fileinput — Iterate over lines from multiple input streams::
* stat — Interpreting stat() results: stat — Interpreting stat results.
* filecmp — File and Directory Comparisons::
* tempfile — Generate temporary files and directories::
* glob — Unix style pathname pattern expansion::
* fnmatch — Unix filename pattern matching::
* linecache — Random access to text lines::
* shutil — High-level file operations::


File: python.info,  Node: pathlib — Object-oriented filesystem paths,  Next: os path — Common pathname manipulations,  Up: File and Directory Access

5.11.1 ‘pathlib’ — Object-oriented filesystem paths
---------------------------------------------------

New in version 3.4.

`Source code:' Lib/pathlib.py(1)

__________________________________________________________________

This module offers classes representing filesystem paths with semantics
appropriate for different operating systems.  Path classes are divided
between *note pure paths: 1d10, which provide purely computational
operations without I/O, and *note concrete paths: 1d11, which inherit
from pure paths but also provide I/O operations.

[python-figures/pathlib-inheritance]
If you’ve never used this module before or just aren’t sure which class
is right for your task, *note Path: 32f. is most likely what you need.
It instantiates a *note concrete path: 1d11. for the platform the code
is running on.

Pure paths are useful in some special cases; for example:

  1. If you want to manipulate Windows paths on a Unix machine (or vice
     versa).  You cannot instantiate a *note WindowsPath: 1d12. when
     running on Unix, but you can instantiate *note PureWindowsPath:
     1d13.

  2. You want to make sure that your code only manipulates paths without
     actually accessing the OS. In this case, instantiating one of the
     pure classes may be useful since those simply don’t have any
     OS-accessing operations.

See also
........

PEP 428(2): The pathlib module – object-oriented filesystem paths.

See also
........

For low-level path manipulation on strings, you can also use the *note
os.path: c5. module.

* Menu:

* Basic use::
* Pure paths::
* Concrete paths::
* Correspondence to tools in the os module::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/pathlib.py

   (2) https://www.python.org/dev/peps/pep-0428


File: python.info,  Node: Basic use,  Next: Pure paths,  Up: pathlib — Object-oriented filesystem paths

5.11.1.1 Basic use
..................

Importing the main class:

     >>> from pathlib import Path

Listing subdirectories:

     >>> p = Path('.')
     >>> [x for x in p.iterdir() if x.is_dir()]
     [PosixPath('.hg'), PosixPath('docs'), PosixPath('dist'),
      PosixPath('__pycache__'), PosixPath('build')]

Listing Python source files in this directory tree:

     >>> list(p.glob('**/*.py'))
     [PosixPath('test_pathlib.py'), PosixPath('setup.py'),
      PosixPath('pathlib.py'), PosixPath('docs/conf.py'),
      PosixPath('build/lib/pathlib.py')]

Navigating inside a directory tree:

     >>> p = Path('/etc')
     >>> q = p / 'init.d' / 'reboot'
     >>> q
     PosixPath('/etc/init.d/reboot')
     >>> q.resolve()
     PosixPath('/etc/rc.d/init.d/halt')

Querying path properties:

     >>> q.exists()
     True
     >>> q.is_dir()
     False

Opening a file:

     >>> with q.open() as f: f.readline()
     ...
     '#!/bin/bash\n'


File: python.info,  Node: Pure paths,  Next: Concrete paths,  Prev: Basic use,  Up: pathlib — Object-oriented filesystem paths

5.11.1.2 Pure paths
...................

Pure path objects provide path-handling operations which don’t actually
access a filesystem.  There are three ways to access these classes,
which we also call `flavours':

 -- Class: pathlib.PurePath (*pathsegments)

     A generic class that represents the system’s path flavour
     (instantiating it creates either a *note PurePosixPath: 1d16. or a
     *note PureWindowsPath: 1d13.):

          >>> PurePath('setup.py')      # Running on a Unix machine
          PurePosixPath('setup.py')

     Each element of `pathsegments' can be either a string representing
     a path segment, an object implementing the *note os.PathLike: 5e6.
     interface which returns a string, or another path object:

          >>> PurePath('foo', 'some/path', 'bar')
          PurePosixPath('foo/some/path/bar')
          >>> PurePath(Path('foo'), Path('bar'))
          PurePosixPath('foo/bar')

     When `pathsegments' is empty, the current directory is assumed:

          >>> PurePath()
          PurePosixPath('.')

     When several absolute paths are given, the last is taken as an
     anchor (mimicking *note os.path.join(): 10c7.’s behaviour):

          >>> PurePath('/etc', '/usr', 'lib64')
          PurePosixPath('/usr/lib64')
          >>> PureWindowsPath('c:/Windows', 'd:bar')
          PureWindowsPath('d:bar')

     However, in a Windows path, changing the local root doesn’t discard
     the previous drive setting:

          >>> PureWindowsPath('c:/Windows', '/Program Files')
          PureWindowsPath('c:/Program Files')

     Spurious slashes and single dots are collapsed, but double dots
     (‘'..'’) are not, since this would change the meaning of a path in
     the face of symbolic links:

          >>> PurePath('foo//bar')
          PurePosixPath('foo/bar')
          >>> PurePath('foo/./bar')
          PurePosixPath('foo/bar')
          >>> PurePath('foo/../bar')
          PurePosixPath('foo/../bar')

     (a naïve approach would make ‘PurePosixPath('foo/../bar')’
     equivalent to ‘PurePosixPath('bar')’, which is wrong if ‘foo’ is a
     symbolic link to another directory)

     Pure path objects implement the *note os.PathLike: 5e6. interface,
     allowing them to be used anywhere the interface is accepted.

     Changed in version 3.6: Added support for the *note os.PathLike:
     5e6. interface.

 -- Class: pathlib.PurePosixPath (*pathsegments)

     A subclass of *note PurePath: 235, this path flavour represents
     non-Windows filesystem paths:

          >>> PurePosixPath('/etc')
          PurePosixPath('/etc')

     `pathsegments' is specified similarly to *note PurePath: 235.

 -- Class: pathlib.PureWindowsPath (*pathsegments)

     A subclass of *note PurePath: 235, this path flavour represents
     Windows filesystem paths:

          >>> PureWindowsPath('c:/Program Files/')
          PureWindowsPath('c:/Program Files')

     `pathsegments' is specified similarly to *note PurePath: 235.

Regardless of the system you’re running on, you can instantiate all of
these classes, since they don’t provide any operation that does system
calls.

* Menu:

* General properties::
* Operators: Operators<2>.
* Accessing individual parts::
* Methods and properties::


File: python.info,  Node: General properties,  Next: Operators<2>,  Up: Pure paths

5.11.1.3 General properties
...........................

Paths are immutable and hashable.  Paths of a same flavour are
comparable and orderable.  These properties respect the flavour’s
case-folding semantics:

     >>> PurePosixPath('foo') == PurePosixPath('FOO')
     False
     >>> PureWindowsPath('foo') == PureWindowsPath('FOO')
     True
     >>> PureWindowsPath('FOO') in { PureWindowsPath('foo') }
     True
     >>> PureWindowsPath('C:') < PureWindowsPath('d:')
     True

Paths of a different flavour compare unequal and cannot be ordered:

     >>> PureWindowsPath('foo') == PurePosixPath('foo')
     False
     >>> PureWindowsPath('foo') < PurePosixPath('foo')
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: '<' not supported between instances of 'PureWindowsPath' and 'PurePosixPath'


File: python.info,  Node: Operators<2>,  Next: Accessing individual parts,  Prev: General properties,  Up: Pure paths

5.11.1.4 Operators
..................

The slash operator helps create child paths, similarly to *note
os.path.join(): 10c7.:

     >>> p = PurePath('/etc')
     >>> p
     PurePosixPath('/etc')
     >>> p / 'init.d' / 'apache2'
     PurePosixPath('/etc/init.d/apache2')
     >>> q = PurePath('bin')
     >>> '/usr' / q
     PurePosixPath('/usr/bin')

A path object can be used anywhere an object implementing *note
os.PathLike: 5e6. is accepted:

     >>> import os
     >>> p = PurePath('/etc')
     >>> os.fspath(p)
     '/etc'

The string representation of a path is the raw filesystem path itself
(in native form, e.g.  with backslashes under Windows), which you can
pass to any function taking a file path as a string:

     >>> p = PurePath('/etc')
     >>> str(p)
     '/etc'
     >>> p = PureWindowsPath('c:/Program Files')
     >>> str(p)
     'c:\\Program Files'

Similarly, calling *note bytes: 172. on a path gives the raw filesystem
path as a bytes object, as encoded by *note os.fsencode(): 5ea.:

     >>> bytes(p)
     b'/etc'

     Note: Calling *note bytes: 172. is only recommended under Unix.
     Under Windows, the unicode form is the canonical representation of
     filesystem paths.


File: python.info,  Node: Accessing individual parts,  Next: Methods and properties,  Prev: Operators<2>,  Up: Pure paths

5.11.1.5 Accessing individual parts
...................................

To access the individual “parts” (components) of a path, use the
following property:

 -- Data: PurePath.parts

     A tuple giving access to the path’s various components:

          >>> p = PurePath('/usr/bin/python3')
          >>> p.parts
          ('/', 'usr', 'bin', 'python3')

          >>> p = PureWindowsPath('c:/Program Files/PSF')
          >>> p.parts
          ('c:\\', 'Program Files', 'PSF')

     (note how the drive and local root are regrouped in a single part)


File: python.info,  Node: Methods and properties,  Prev: Accessing individual parts,  Up: Pure paths

5.11.1.6 Methods and properties
...............................

Pure paths provide the following methods and properties:

 -- Data: PurePath.drive

     A string representing the drive letter or name, if any:

          >>> PureWindowsPath('c:/Program Files/').drive
          'c:'
          >>> PureWindowsPath('/Program Files/').drive
          ''
          >>> PurePosixPath('/etc').drive
          ''

     UNC shares are also considered drives:

          >>> PureWindowsPath('//host/share/foo.txt').drive
          '\\\\host\\share'

 -- Data: PurePath.root

     A string representing the (local or global) root, if any:

          >>> PureWindowsPath('c:/Program Files/').root
          '\\'
          >>> PureWindowsPath('c:Program Files/').root
          ''
          >>> PurePosixPath('/etc').root
          '/'

     UNC shares always have a root:

          >>> PureWindowsPath('//host/share').root
          '\\'

 -- Data: PurePath.anchor

     The concatenation of the drive and root:

          >>> PureWindowsPath('c:/Program Files/').anchor
          'c:\\'
          >>> PureWindowsPath('c:Program Files/').anchor
          'c:'
          >>> PurePosixPath('/etc').anchor
          '/'
          >>> PureWindowsPath('//host/share').anchor
          '\\\\host\\share\\'

 -- Data: PurePath.parents

     An immutable sequence providing access to the logical ancestors of
     the path:

          >>> p = PureWindowsPath('c:/foo/bar/setup.py')
          >>> p.parents[0]
          PureWindowsPath('c:/foo/bar')
          >>> p.parents[1]
          PureWindowsPath('c:/foo')
          >>> p.parents[2]
          PureWindowsPath('c:/')

 -- Data: PurePath.parent

     The logical parent of the path:

          >>> p = PurePosixPath('/a/b/c/d')
          >>> p.parent
          PurePosixPath('/a/b/c')

     You cannot go past an anchor, or empty path:

          >>> p = PurePosixPath('/')
          >>> p.parent
          PurePosixPath('/')
          >>> p = PurePosixPath('.')
          >>> p.parent
          PurePosixPath('.')

          Note: This is a purely lexical operation, hence the following
          behaviour:

               >>> p = PurePosixPath('foo/..')
               >>> p.parent
               PurePosixPath('foo')

          If you want to walk an arbitrary filesystem path upwards, it
          is recommended to first call *note Path.resolve(): 1d21. so as
          to resolve symlinks and eliminate ‘“..”’ components.

 -- Data: PurePath.name

     A string representing the final path component, excluding the drive
     and root, if any:

          >>> PurePosixPath('my/library/setup.py').name
          'setup.py'

     UNC drive names are not considered:

          >>> PureWindowsPath('//some/share/setup.py').name
          'setup.py'
          >>> PureWindowsPath('//some/share').name
          ''

 -- Data: PurePath.suffix

     The file extension of the final component, if any:

          >>> PurePosixPath('my/library/setup.py').suffix
          '.py'
          >>> PurePosixPath('my/library.tar.gz').suffix
          '.gz'
          >>> PurePosixPath('my/library').suffix
          ''

 -- Data: PurePath.suffixes

     A list of the path’s file extensions:

          >>> PurePosixPath('my/library.tar.gar').suffixes
          ['.tar', '.gar']
          >>> PurePosixPath('my/library.tar.gz').suffixes
          ['.tar', '.gz']
          >>> PurePosixPath('my/library').suffixes
          []

 -- Data: PurePath.stem

     The final path component, without its suffix:

          >>> PurePosixPath('my/library.tar.gz').stem
          'library.tar'
          >>> PurePosixPath('my/library.tar').stem
          'library'
          >>> PurePosixPath('my/library').stem
          'library'

 -- Method: PurePath.as_posix ()

     Return a string representation of the path with forward slashes
     (‘/’):

          >>> p = PureWindowsPath('c:\\windows')
          >>> str(p)
          'c:\\windows'
          >>> p.as_posix()
          'c:/windows'

 -- Method: PurePath.as_uri ()

     Represent the path as a ‘file’ URI. *note ValueError: 16d. is
     raised if the path isn’t absolute.

          >>> p = PurePosixPath('/etc/passwd')
          >>> p.as_uri()
          'file:///etc/passwd'
          >>> p = PureWindowsPath('c:/Windows')
          >>> p.as_uri()
          'file:///c:/Windows'

 -- Method: PurePath.is_absolute ()

     Return whether the path is absolute or not.  A path is considered
     absolute if it has both a root and (if the flavour allows) a drive:

          >>> PurePosixPath('/a/b').is_absolute()
          True
          >>> PurePosixPath('a/b').is_absolute()
          False

          >>> PureWindowsPath('c:/a/b').is_absolute()
          True
          >>> PureWindowsPath('/a/b').is_absolute()
          False
          >>> PureWindowsPath('c:').is_absolute()
          False
          >>> PureWindowsPath('//some/share').is_absolute()
          True

 -- Method: PurePath.is_relative_to (*other)

     Return whether or not this path is relative to the `other' path.

          >>> p = PurePath('/etc/passwd')
          >>> p.is_relative_to('/etc')
          True
          >>> p.is_relative_to('/usr')
          False

     New in version 3.9.

 -- Method: PurePath.is_reserved ()

     With *note PureWindowsPath: 1d13, return ‘True’ if the path is
     considered reserved under Windows, ‘False’ otherwise.  With *note
     PurePosixPath: 1d16, ‘False’ is always returned.

          >>> PureWindowsPath('nul').is_reserved()
          True
          >>> PurePosixPath('nul').is_reserved()
          False

     File system calls on reserved paths can fail mysteriously or have
     unintended effects.

 -- Method: PurePath.joinpath (*other)

     Calling this method is equivalent to combining the path with each
     of the `other' arguments in turn:

          >>> PurePosixPath('/etc').joinpath('passwd')
          PurePosixPath('/etc/passwd')
          >>> PurePosixPath('/etc').joinpath(PurePosixPath('passwd'))
          PurePosixPath('/etc/passwd')
          >>> PurePosixPath('/etc').joinpath('init.d', 'apache2')
          PurePosixPath('/etc/init.d/apache2')
          >>> PureWindowsPath('c:').joinpath('/Program Files')
          PureWindowsPath('c:/Program Files')

 -- Method: PurePath.match (pattern)

     Match this path against the provided glob-style pattern.  Return
     ‘True’ if matching is successful, ‘False’ otherwise.

     If `pattern' is relative, the path can be either relative or
     absolute, and matching is done from the right:

          >>> PurePath('a/b.py').match('*.py')
          True
          >>> PurePath('/a/b/c.py').match('b/*.py')
          True
          >>> PurePath('/a/b/c.py').match('a/*.py')
          False

     If `pattern' is absolute, the path must be absolute, and the whole
     path must match:

          >>> PurePath('/a.py').match('/*.py')
          True
          >>> PurePath('a/b.py').match('/*.py')
          False

     As with other methods, case-sensitivity follows platform defaults:

          >>> PurePosixPath('b.py').match('*.PY')
          False
          >>> PureWindowsPath('b.py').match('*.PY')
          True

 -- Method: PurePath.relative_to (*other)

     Compute a version of this path relative to the path represented by
     `other'.  If it’s impossible, ValueError is raised:

          >>> p = PurePosixPath('/etc/passwd')
          >>> p.relative_to('/')
          PurePosixPath('etc/passwd')
          >>> p.relative_to('/etc')
          PurePosixPath('passwd')
          >>> p.relative_to('/usr')
          Traceback (most recent call last):
            File "<stdin>", line 1, in <module>
            File "pathlib.py", line 694, in relative_to
              .format(str(self), str(formatted)))
          ValueError: '/etc/passwd' is not in the subpath of '/usr' OR one path is relative and the other absolute.

     NOTE: This function is part of *note PurePath: 235. and works with
     strings.  It does not check or access the underlying file
     structure.

 -- Method: PurePath.with_name (name)

     Return a new path with the *note name: 1d22. changed.  If the
     original path doesn’t have a name, ValueError is raised:

          >>> p = PureWindowsPath('c:/Downloads/pathlib.tar.gz')
          >>> p.with_name('setup.py')
          PureWindowsPath('c:/Downloads/setup.py')
          >>> p = PureWindowsPath('c:/')
          >>> p.with_name('setup.py')
          Traceback (most recent call last):
            File "<stdin>", line 1, in <module>
            File "/home/antoine/cpython/default/Lib/pathlib.py", line 751, in with_name
              raise ValueError("%r has an empty name" % (self,))
          ValueError: PureWindowsPath('c:/') has an empty name

 -- Method: PurePath.with_stem (stem)

     Return a new path with the *note stem: 1d25. changed.  If the
     original path doesn’t have a name, ValueError is raised:

          >>> p = PureWindowsPath('c:/Downloads/draft.txt')
          >>> p.with_stem('final')
          PureWindowsPath('c:/Downloads/final.txt')
          >>> p = PureWindowsPath('c:/Downloads/pathlib.tar.gz')
          >>> p.with_stem('lib')
          PureWindowsPath('c:/Downloads/lib.gz')
          >>> p = PureWindowsPath('c:/')
          >>> p.with_stem('')
          Traceback (most recent call last):
            File "<stdin>", line 1, in <module>
            File "/home/antoine/cpython/default/Lib/pathlib.py", line 861, in with_stem
              return self.with_name(stem + self.suffix)
            File "/home/antoine/cpython/default/Lib/pathlib.py", line 851, in with_name
              raise ValueError("%r has an empty name" % (self,))
          ValueError: PureWindowsPath('c:/') has an empty name

     New in version 3.9.

 -- Method: PurePath.with_suffix (suffix)

     Return a new path with the *note suffix: 1d23. changed.  If the
     original path doesn’t have a suffix, the new `suffix' is appended
     instead.  If the `suffix' is an empty string, the original suffix
     is removed:

          >>> p = PureWindowsPath('c:/Downloads/pathlib.tar.gz')
          >>> p.with_suffix('.bz2')
          PureWindowsPath('c:/Downloads/pathlib.tar.bz2')
          >>> p = PureWindowsPath('README')
          >>> p.with_suffix('.txt')
          PureWindowsPath('README.txt')
          >>> p = PureWindowsPath('README.txt')
          >>> p.with_suffix('')
          PureWindowsPath('README')


File: python.info,  Node: Concrete paths,  Next: Correspondence to tools in the os module,  Prev: Pure paths,  Up: pathlib — Object-oriented filesystem paths

5.11.1.7 Concrete paths
.......................

Concrete paths are subclasses of the pure path classes.  In addition to
operations provided by the latter, they also provide methods to do
system calls on path objects.  There are three ways to instantiate
concrete paths:

 -- Class: pathlib.Path (*pathsegments)

     A subclass of *note PurePath: 235, this class represents concrete
     paths of the system’s path flavour (instantiating it creates either
     a *note PosixPath: 1d31. or a *note WindowsPath: 1d12.):

          >>> Path('setup.py')
          PosixPath('setup.py')

     `pathsegments' is specified similarly to *note PurePath: 235.

 -- Class: pathlib.PosixPath (*pathsegments)

     A subclass of *note Path: 32f. and *note PurePosixPath: 1d16, this
     class represents concrete non-Windows filesystem paths:

          >>> PosixPath('/etc')
          PosixPath('/etc')

     `pathsegments' is specified similarly to *note PurePath: 235.

 -- Class: pathlib.WindowsPath (*pathsegments)

     A subclass of *note Path: 32f. and *note PureWindowsPath: 1d13,
     this class represents concrete Windows filesystem paths:

          >>> WindowsPath('c:/Program Files/')
          WindowsPath('c:/Program Files')

     `pathsegments' is specified similarly to *note PurePath: 235.

You can only instantiate the class flavour that corresponds to your
system (allowing system calls on non-compatible path flavours could lead
to bugs or failures in your application):

     >>> import os
     >>> os.name
     'posix'
     >>> Path('setup.py')
     PosixPath('setup.py')
     >>> PosixPath('setup.py')
     PosixPath('setup.py')
     >>> WindowsPath('setup.py')
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
       File "pathlib.py", line 798, in __new__
         % (cls.__name__,))
     NotImplementedError: cannot instantiate 'WindowsPath' on your system

* Menu:

* Methods: Methods<2>.


File: python.info,  Node: Methods<2>,  Up: Concrete paths

5.11.1.8 Methods
................

Concrete paths provide the following methods in addition to pure paths
methods.  Many of these methods can raise an *note OSError: 304. if a
system call fails (for example because the path doesn’t exist).

Changed in version 3.8: *note exists(): 330, *note is_dir(): 331, *note
is_file(): 332, *note is_mount(): 333, *note is_symlink(): 334, *note
is_block_device(): 335, *note is_char_device(): 336, *note is_fifo():
337, *note is_socket(): 338. now return ‘False’ instead of raising an
exception for paths that contain characters unrepresentable at the OS
level.

 -- Method: classmethod Path.cwd ()

     Return a new path object representing the current directory (as
     returned by *note os.getcwd(): 1119.):

          >>> Path.cwd()
          PosixPath('/home/antoine/pathlib')

 -- Method: classmethod Path.home ()

     Return a new path object representing the user’s home directory (as
     returned by *note os.path.expanduser(): 32c. with ‘~’ construct):

          >>> Path.home()
          PosixPath('/home/antoine')

     Note that unlike *note os.path.expanduser(): 32c, on POSIX systems
     a *note KeyError: 3e9. or *note RuntimeError: 3dc. will be raised,
     and on Windows systems a *note RuntimeError: 3dc. will be raised if
     home directory can’t be resolved.

     New in version 3.5.

 -- Method: Path.stat ()

     Return a *note os.stat_result: 11bf. object containing information
     about this path, like *note os.stat(): 321.  The result is looked
     up at each call to this method.

          >>> p = Path('setup.py')
          >>> p.stat().st_size
          956
          >>> p.stat().st_mtime
          1327883547.852554

 -- Method: Path.chmod (mode)

     Change the file mode and permissions, like *note os.chmod(): b0f.:

          >>> p = Path('setup.py')
          >>> p.stat().st_mode
          33277
          >>> p.chmod(0o444)
          >>> p.stat().st_mode
          33060

 -- Method: Path.exists ()

     Whether the path points to an existing file or directory:

          >>> Path('.').exists()
          True
          >>> Path('setup.py').exists()
          True
          >>> Path('/etc').exists()
          True
          >>> Path('nonexistentfile').exists()
          False

          Note: If the path points to a symlink, *note exists(): 330.
          returns whether the symlink `points to' an existing file or
          directory.

 -- Method: Path.expanduser ()

     Return a new path with expanded ‘~’ and ‘~user’ constructs, as
     returned by *note os.path.expanduser(): 32c.:

          >>> p = PosixPath('~/films/Monty Python')
          >>> p.expanduser()
          PosixPath('/home/eric/films/Monty Python')

     Note that unlike *note os.path.expanduser(): 32c, on POSIX systems
     a *note KeyError: 3e9. or *note RuntimeError: 3dc. will be raised,
     and on Windows systems a *note RuntimeError: 3dc. will be raised if
     home directory can’t be resolved.

     New in version 3.5.

 -- Method: Path.glob (pattern)

     Glob the given relative `pattern' in the directory represented by
     this path, yielding all matching files (of any kind):

          >>> sorted(Path('.').glob('*.py'))
          [PosixPath('pathlib.py'), PosixPath('setup.py'), PosixPath('test_pathlib.py')]
          >>> sorted(Path('.').glob('*/*.py'))
          [PosixPath('docs/conf.py')]

     The “‘**’” pattern means “this directory and all subdirectories,
     recursively”.  In other words, it enables recursive globbing:

          >>> sorted(Path('.').glob('**/*.py'))
          [PosixPath('build/lib/pathlib.py'),
           PosixPath('docs/conf.py'),
           PosixPath('pathlib.py'),
           PosixPath('setup.py'),
           PosixPath('test_pathlib.py')]

          Note: Using the “‘**’” pattern in large directory trees may
          consume an inordinate amount of time.

     Raises an *note auditing event: fa1. ‘pathlib.Path.glob’ with
     arguments ‘self’, ‘pattern’.

 -- Method: Path.group ()

     Return the name of the group owning the file.  *note KeyError: 3e9.
     is raised if the file’s gid isn’t found in the system database.

 -- Method: Path.is_dir ()

     Return ‘True’ if the path points to a directory (or a symbolic link
     pointing to a directory), ‘False’ if it points to another kind of
     file.

     ‘False’ is also returned if the path doesn’t exist or is a broken
     symlink; other errors (such as permission errors) are propagated.

 -- Method: Path.is_file ()

     Return ‘True’ if the path points to a regular file (or a symbolic
     link pointing to a regular file), ‘False’ if it points to another
     kind of file.

     ‘False’ is also returned if the path doesn’t exist or is a broken
     symlink; other errors (such as permission errors) are propagated.

 -- Method: Path.is_mount ()

     Return ‘True’ if the path is a `mount point': a point in a file
     system where a different file system has been mounted.  On POSIX,
     the function checks whether `path'’s parent, ‘path/..’, is on a
     different device than `path', or whether ‘path/..’ and `path' point
     to the same i-node on the same device — this should detect mount
     points for all Unix and POSIX variants.  Not implemented on
     Windows.

     New in version 3.7.

 -- Method: Path.is_symlink ()

     Return ‘True’ if the path points to a symbolic link, ‘False’
     otherwise.

     ‘False’ is also returned if the path doesn’t exist; other errors
     (such as permission errors) are propagated.

 -- Method: Path.is_socket ()

     Return ‘True’ if the path points to a Unix socket (or a symbolic
     link pointing to a Unix socket), ‘False’ if it points to another
     kind of file.

     ‘False’ is also returned if the path doesn’t exist or is a broken
     symlink; other errors (such as permission errors) are propagated.

 -- Method: Path.is_fifo ()

     Return ‘True’ if the path points to a FIFO (or a symbolic link
     pointing to a FIFO), ‘False’ if it points to another kind of file.

     ‘False’ is also returned if the path doesn’t exist or is a broken
     symlink; other errors (such as permission errors) are propagated.

 -- Method: Path.is_block_device ()

     Return ‘True’ if the path points to a block device (or a symbolic
     link pointing to a block device), ‘False’ if it points to another
     kind of file.

     ‘False’ is also returned if the path doesn’t exist or is a broken
     symlink; other errors (such as permission errors) are propagated.

 -- Method: Path.is_char_device ()

     Return ‘True’ if the path points to a character device (or a
     symbolic link pointing to a character device), ‘False’ if it points
     to another kind of file.

     ‘False’ is also returned if the path doesn’t exist or is a broken
     symlink; other errors (such as permission errors) are propagated.

 -- Method: Path.iterdir ()

     When the path points to a directory, yield path objects of the
     directory contents:

          >>> p = Path('docs')
          >>> for child in p.iterdir(): child
          ...
          PosixPath('docs/conf.py')
          PosixPath('docs/_templates')
          PosixPath('docs/make.bat')
          PosixPath('docs/index.rst')
          PosixPath('docs/_build')
          PosixPath('docs/_static')
          PosixPath('docs/Makefile')

     The children are yielded in arbitrary order, and the special
     entries ‘'.'’ and ‘'..'’ are not included.  If a file is removed
     from or added to the directory after creating the iterator, whether
     an path object for that file be included is unspecified.

 -- Method: Path.lchmod (mode)

     Like *note Path.chmod(): 1d35. but, if the path points to a
     symbolic link, the symbolic link’s mode is changed rather than its
     target’s.

 -- Method: Path.lstat ()

     Like *note Path.stat(): 1d34. but, if the path points to a symbolic
     link, return the symbolic link’s information rather than its
     target’s.

 -- Method: Path.mkdir (mode=0o777, parents=False, exist_ok=False)

     Create a new directory at this given path.  If `mode' is given, it
     is combined with the process’ ‘umask’ value to determine the file
     mode and access flags.  If the path already exists, *note
     FileExistsError: a39. is raised.

     If `parents' is true, any missing parents of this path are created
     as needed; they are created with the default permissions without
     taking `mode' into account (mimicking the POSIX ‘mkdir -p’
     command).

     If `parents' is false (the default), a missing parent raises *note
     FileNotFoundError: 8ad.

     If `exist_ok' is false (the default), *note FileExistsError: a39.
     is raised if the target directory already exists.

     If `exist_ok' is true, *note FileExistsError: a39. exceptions will
     be ignored (same behavior as the POSIX ‘mkdir -p’ command), but
     only if the last path component is not an existing non-directory
     file.

     Changed in version 3.5: The `exist_ok' parameter was added.

 -- Method: Path.open (mode='r', buffering=-1, encoding=None,
          errors=None, newline=None)

     Open the file pointed to by the path, like the built-in *note
     open(): 16f. function does:

          >>> p = Path('setup.py')
          >>> with p.open() as f:
          ...     f.readline()
          ...
          '#!/usr/bin/env python3\n'

 -- Method: Path.owner ()

     Return the name of the user owning the file.  *note KeyError: 3e9.
     is raised if the file’s uid isn’t found in the system database.

 -- Method: Path.read_bytes ()

     Return the binary contents of the pointed-to file as a bytes
     object:

          >>> p = Path('my_binary_file')
          >>> p.write_bytes(b'Binary file contents')
          20
          >>> p.read_bytes()
          b'Binary file contents'

     New in version 3.5.

 -- Method: Path.read_text (encoding=None, errors=None)

     Return the decoded contents of the pointed-to file as a string:

          >>> p = Path('my_text_file')
          >>> p.write_text('Text file contents')
          18
          >>> p.read_text()
          'Text file contents'

     The file is opened and then closed.  The optional parameters have
     the same meaning as in *note open(): 16f.

     New in version 3.5.

 -- Method: Path.readlink ()

     Return the path to which the symbolic link points (as returned by
     *note os.readlink(): 1d1.):

          >>> p = Path('mylink')
          >>> p.symlink_to('setup.py')
          >>> p.readlink()
          PosixPath('setup.py')

     New in version 3.9.

 -- Method: Path.rename (target)

     Rename this file or directory to the given `target', and return a
     new Path instance pointing to `target'.  On Unix, if `target'
     exists and is a file, it will be replaced silently if the user has
     permission.  `target' can be either a string or another path
     object:

          >>> p = Path('foo')
          >>> p.open('w').write('some text')
          9
          >>> target = Path('bar')
          >>> p.rename(target)
          PosixPath('bar')
          >>> target.open().read()
          'some text'

     The target path may be absolute or relative.  Relative paths are
     interpreted relative to the current working directory, `not' the
     directory of the Path object.

     Changed in version 3.8: Added return value, return the new Path
     instance.

 -- Method: Path.replace (target)

     Rename this file or directory to the given `target', and return a
     new Path instance pointing to `target'.  If `target' points to an
     existing file or directory, it will be unconditionally replaced.

     The target path may be absolute or relative.  Relative paths are
     interpreted relative to the current working directory, `not' the
     directory of the Path object.

     Changed in version 3.8: Added return value, return the new Path
     instance.

 -- Method: Path.resolve (strict=False)

     Make the path absolute, resolving any symlinks.  A new path object
     is returned:

          >>> p = Path()
          >>> p
          PosixPath('.')
          >>> p.resolve()
          PosixPath('/home/antoine/pathlib')

     “‘..’” components are also eliminated (this is the only method to
     do so):

          >>> p = Path('docs/../setup.py')
          >>> p.resolve()
          PosixPath('/home/antoine/pathlib/setup.py')

     If the path doesn’t exist and `strict' is ‘True’, *note
     FileNotFoundError: 8ad. is raised.  If `strict' is ‘False’, the
     path is resolved as far as possible and any remainder is appended
     without checking whether it exists.  If an infinite loop is
     encountered along the resolution path, *note RuntimeError: 3dc. is
     raised.

     New in version 3.6: The `strict' argument (pre-3.6 behavior is
     strict).

 -- Method: Path.rglob (pattern)

     This is like calling *note Path.glob(): 1084. with “‘**/’” added in
     front of the given relative `pattern':

          >>> sorted(Path().rglob("*.py"))
          [PosixPath('build/lib/pathlib.py'),
           PosixPath('docs/conf.py'),
           PosixPath('pathlib.py'),
           PosixPath('setup.py'),
           PosixPath('test_pathlib.py')]

     Raises an *note auditing event: fa1. ‘pathlib.Path.rglob’ with
     arguments ‘self’, ‘pattern’.

 -- Method: Path.rmdir ()

     Remove this directory.  The directory must be empty.

 -- Method: Path.samefile (other_path)

     Return whether this path points to the same file as `other_path',
     which can be either a Path object, or a string.  The semantics are
     similar to *note os.path.samefile(): 96d. and *note
     os.path.samestat(): 96c.

     An *note OSError: 304. can be raised if either file cannot be
     accessed for some reason.

          >>> p = Path('spam')
          >>> q = Path('eggs')
          >>> p.samefile(q)
          False
          >>> p.samefile('spam')
          True

     New in version 3.5.

 -- Method: Path.symlink_to (target, target_is_directory=False)

     Make this path a symbolic link to `target'.  Under Windows,
     `target_is_directory' must be true (default ‘False’) if the link’s
     target is a directory.  Under POSIX, `target_is_directory'’s value
     is ignored.

          >>> p = Path('mylink')
          >>> p.symlink_to('setup.py')
          >>> p.resolve()
          PosixPath('/home/antoine/pathlib/setup.py')
          >>> p.stat().st_size
          956
          >>> p.lstat().st_size
          8

          Note: The order of arguments (link, target) is the reverse of
          *note os.symlink(): b17.’s.

 -- Method: Path.link_to (target)

     Make `target' a hard link to this path.

          Warning: This function does not make this path a hard link to
          `target', despite the implication of the function and argument
          names.  The argument order (target, link) is the reverse of
          *note Path.symlink_to(): 1d3f, but matches that of *note
          os.link(): b11.

     New in version 3.8.

 -- Method: Path.touch (mode=0o666, exist_ok=True)

     Create a file at this given path.  If `mode' is given, it is
     combined with the process’ ‘umask’ value to determine the file mode
     and access flags.  If the file already exists, the function
     succeeds if `exist_ok' is true (and its modification time is
     updated to the current time), otherwise *note FileExistsError: a39.
     is raised.

 -- Method: Path.unlink (missing_ok=False)

     Remove this file or symbolic link.  If the path points to a
     directory, use *note Path.rmdir(): 1d3e. instead.

     If `missing_ok' is false (the default), *note FileNotFoundError:
     8ad. is raised if the path does not exist.

     If `missing_ok' is true, *note FileNotFoundError: 8ad. exceptions
     will be ignored (same behavior as the POSIX ‘rm -f’ command).

     Changed in version 3.8: The `missing_ok' parameter was added.

 -- Method: Path.write_bytes (data)

     Open the file pointed to in bytes mode, write `data' to it, and
     close the file:

          >>> p = Path('my_binary_file')
          >>> p.write_bytes(b'Binary file contents')
          20
          >>> p.read_bytes()
          b'Binary file contents'

     An existing file of the same name is overwritten.

     New in version 3.5.

 -- Method: Path.write_text (data, encoding=None, errors=None)

     Open the file pointed to in text mode, write `data' to it, and
     close the file:

          >>> p = Path('my_text_file')
          >>> p.write_text('Text file contents')
          18
          >>> p.read_text()
          'Text file contents'

     An existing file of the same name is overwritten.  The optional
     parameters have the same meaning as in *note open(): 16f.

     New in version 3.5.


File: python.info,  Node: Correspondence to tools in the os module,  Prev: Concrete paths,  Up: pathlib — Object-oriented filesystem paths

5.11.1.9 Correspondence to tools in the ‘os’ module
...................................................

Below is a table mapping various *note os: c4. functions to their
corresponding *note PurePath: 235./*note Path: 32f. equivalent.

     Note: Although *note os.path.relpath(): 1d42. and *note
     PurePath.relative_to(): 1d2d. have some overlapping use-cases,
     their semantics differ enough to warrant not considering them
     equivalent.

os and os.path                           pathlib
                                         
----------------------------------------------------------------------------
                                         
*note os.path.abspath(): d78.            *note Path.resolve(): 1d21.
                                         
                                         
*note os.chmod(): b0f.                   *note Path.chmod(): 1d35.
                                         
                                         
*note os.mkdir(): b12.                   *note Path.mkdir(): 818.
                                         
                                         
*note os.makedirs(): 4c4.                *note Path.mkdir(): 818.
                                         
                                         
*note os.rename(): b14.                  *note Path.rename(): 1d3c.
                                         
                                         
*note os.replace(): b15.                 *note Path.replace(): 1d3d.
                                         
                                         
*note os.rmdir(): b16.                   *note Path.rmdir(): 1d3e.
                                         
                                         
*note os.remove(): b13,                  *note Path.unlink(): 1109.
*note os.unlink(): b18.                  

*note os.getcwd(): 1119.                 *note Path.cwd(): 1d33.
                                         
                                         
*note os.path.exists(): 325.             *note Path.exists(): 330.
                                         
                                         
*note os.path.expanduser(): 32c.         *note Path.expanduser(): 819.
                                         and *note Path.home(): 81a.
                                         
                                         
*note os.listdir(): b1c.                 *note Path.iterdir(): 1d37.
                                         
                                         
*note os.path.isdir(): 327.              *note Path.is_dir(): 331.
                                         
                                         
*note os.path.isfile(): 328.             *note Path.is_file(): 332.
                                         
                                         
*note os.path.islink(): 323.             *note Path.is_symlink(): 334.
                                         
                                         
*note os.link(): b11.                    *note Path.link_to(): 339.
                                         
                                         
*note os.symlink(): b17.                 *note Path.symlink_to(): 1d3f.
                                         
                                         
*note os.readlink(): 1d1.                *note Path.readlink(): 1d0.
                                         
                                         
*note os.stat(): 321.                    *note Path.stat(): 1d34,
                                         *note Path.owner(): 1d3b,
                                         *note Path.group(): 1d36.
                                         
                                         
*note os.path.isabs(): 1d43.             *note PurePath.is_absolute(): 1d28.
                                         
                                         
*note os.path.join(): 10c7.              *note PurePath.joinpath(): 1d2b.
                                         
                                         
*note os.path.basename(): 1d44.          *note PurePath.name: 1d22.
                                         
                                         
*note os.path.dirname(): 1d45.           *note PurePath.parent: 1d20.
                                         
                                         
*note os.path.samefile(): 96d.           *note Path.samefile(): 817.
                                         
                                         
*note os.path.splitext(): 1d46.          *note PurePath.suffix: 1d23.
                                         


File: python.info,  Node: os path — Common pathname manipulations,  Next: fileinput — Iterate over lines from multiple input streams,  Prev: pathlib — Object-oriented filesystem paths,  Up: File and Directory Access

5.11.2 ‘os.path’ — Common pathname manipulations
------------------------------------------------

`Source code:' Lib/posixpath.py(1) (for POSIX) and Lib/ntpath.py(2) (for
Windows NT).

__________________________________________________________________

This module implements some useful functions on pathnames.  To read or
write files see *note open(): 16f, and for accessing the filesystem see
the *note os: c4. module.  The path parameters can be passed as either
strings, or bytes.  Applications are encouraged to represent file names
as (Unicode) character strings.  Unfortunately, some file names may not
be representable as strings on Unix, so applications that need to
support arbitrary file names on Unix should use bytes objects to
represent path names.  Vice versa, using bytes objects cannot represent
all file names on Windows (in the standard ‘mbcs’ encoding), hence
Windows applications should use string objects to access all files.

Unlike a unix shell, Python does not do any `automatic' path expansions.
Functions such as *note expanduser(): 32c. and *note expandvars(): e09.
can be invoked explicitly when an application desires shell-like path
expansion.  (See also the *note glob: 88. module.)

See also
........

The *note pathlib: c8. module offers high-level path objects.

     Note: All of these functions accept either only bytes or only
     string objects as their parameters.  The result is an object of the
     same type, if a path or file name is returned.

     Note: Since different operating systems have different path name
     conventions, there are several versions of this module in the
     standard library.  The *note os.path: c5. module is always the path
     module suitable for the operating system Python is running on, and
     therefore usable for local paths.  However, you can also import and
     use the individual modules if you want to manipulate a path that is
     `always' in one of the different formats.  They all have the same
     interface:

        * ‘posixpath’ for UNIX-style paths

        * ‘ntpath’ for Windows paths

Changed in version 3.8: *note exists(): 325, *note lexists(): 326, *note
isdir(): 327, *note isfile(): 328, *note islink(): 323, and *note
ismount(): 329. now return ‘False’ instead of raising an exception for
paths that contain characters or bytes unrepresentable at the OS level.

 -- Function: os.path.abspath (path)

     Return a normalized absolutized version of the pathname `path'.  On
     most platforms, this is equivalent to calling the function *note
     normpath(): d77. as follows: ‘normpath(join(os.getcwd(), path))’.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.basename (path)

     Return the base name of pathname `path'.  This is the second
     element of the pair returned by passing `path' to the function
     *note split(): 1d49.  Note that the result of this function is
     different from the Unix ‘basename’ program; where ‘basename’ for
     ‘'/foo/bar/'’ returns ‘'bar'’, the *note basename(): 1d44. function
     returns an empty string (‘''’).

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.commonpath (paths)

     Return the longest common sub-path of each pathname in the sequence
     `paths'.  Raise *note ValueError: 16d. if `paths' contain both
     absolute and relative pathnames, the `paths' are on the different
     drives or if `paths' is empty.  Unlike *note commonprefix(): 815,
     this returns a valid path.

     *note Availability: 1491.: Unix, Windows.

     New in version 3.5.

     Changed in version 3.6: Accepts a sequence of *note path-like
     objects: 472.

 -- Function: os.path.commonprefix (list)

     Return the longest path prefix (taken character-by-character) that
     is a prefix of all paths in `list'.  If `list' is empty, return the
     empty string (‘''’).

          Note: This function may return invalid paths because it works
          a character at a time.  To obtain a valid path, see *note
          commonpath(): 814.

               >>> os.path.commonprefix(['/usr/lib', '/usr/local/lib'])
               '/usr/l'

               >>> os.path.commonpath(['/usr/lib', '/usr/local/lib'])
               '/usr'

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.dirname (path)

     Return the directory name of pathname `path'.  This is the first
     element of the pair returned by passing `path' to the function
     *note split(): 1d49.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.exists (path)

     Return ‘True’ if `path' refers to an existing path or an open file
     descriptor.  Returns ‘False’ for broken symbolic links.  On some
     platforms, this function may return ‘False’ if permission is not
     granted to execute *note os.stat(): 321. on the requested file,
     even if the `path' physically exists.

     Changed in version 3.3: `path' can now be an integer: ‘True’ is
     returned if it is an open file descriptor, ‘False’ otherwise.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.lexists (path)

     Return ‘True’ if `path' refers to an existing path.  Returns ‘True’
     for broken symbolic links.  Equivalent to *note exists(): 325. on
     platforms lacking *note os.lstat(): 322.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.expanduser (path)

     On Unix and Windows, return the argument with an initial component
     of ‘~’ or ‘~user’ replaced by that `user'’s home directory.

     On Unix, an initial ‘~’ is replaced by the environment variable
     ‘HOME’ if it is set; otherwise the current user’s home directory is
     looked up in the password directory through the built-in module
     *note pwd: d6.  An initial ‘~user’ is looked up directly in the
     password directory.

     On Windows, ‘USERPROFILE’ will be used if set, otherwise a
     combination of ‘HOMEPATH’ and ‘HOMEDRIVE’ will be used.  An initial
     ‘~user’ is handled by stripping the last directory component from
     the created user path derived above.

     If the expansion fails or if the path does not begin with a tilde,
     the path is returned unchanged.

     Changed in version 3.6: Accepts a *note path-like object: 472.

     Changed in version 3.8: No longer uses ‘HOME’ on Windows.

 -- Function: os.path.expandvars (path)

     Return the argument with environment variables expanded.
     Substrings of the form ‘$name’ or ‘${name}’ are replaced by the
     value of environment variable `name'.  Malformed variable names and
     references to non-existing variables are left unchanged.

     On Windows, ‘%name%’ expansions are supported in addition to
     ‘$name’ and ‘${name}’.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.getatime (path)

     Return the time of last access of `path'.  The return value is a
     floating point number giving the number of seconds since the epoch
     (see the *note time: 10c. module).  Raise *note OSError: 304. if
     the file does not exist or is inaccessible.

 -- Function: os.path.getmtime (path)

     Return the time of last modification of `path'.  The return value
     is a floating point number giving the number of seconds since the
     epoch (see the *note time: 10c. module).  Raise *note OSError: 304.
     if the file does not exist or is inaccessible.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.getctime (path)

     Return the system’s ctime which, on some systems (like Unix) is the
     time of the last metadata change, and, on others (like Windows), is
     the creation time for `path'.  The return value is a number giving
     the number of seconds since the epoch (see the *note time: 10c.
     module).  Raise *note OSError: 304. if the file does not exist or
     is inaccessible.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.getsize (path)

     Return the size, in bytes, of `path'.  Raise *note OSError: 304. if
     the file does not exist or is inaccessible.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.isabs (path)

     Return ‘True’ if `path' is an absolute pathname.  On Unix, that
     means it begins with a slash, on Windows that it begins with a
     (back)slash after chopping off a potential drive letter.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.isfile (path)

     Return ‘True’ if `path' is an *note existing: 325. regular file.
     This follows symbolic links, so both *note islink(): 323. and *note
     isfile(): 328. can be true for the same path.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.isdir (path)

     Return ‘True’ if `path' is an *note existing: 325. directory.  This
     follows symbolic links, so both *note islink(): 323. and *note
     isdir(): 327. can be true for the same path.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.islink (path)

     Return ‘True’ if `path' refers to an *note existing: 325. directory
     entry that is a symbolic link.  Always ‘False’ if symbolic links
     are not supported by the Python runtime.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.ismount (path)

     Return ‘True’ if pathname `path' is a `mount point': a point in a
     file system where a different file system has been mounted.  On
     POSIX, the function checks whether `path'’s parent, ‘`path'/..’, is
     on a different device than `path', or whether ‘`path'/..’ and
     `path' point to the same i-node on the same device — this should
     detect mount points for all Unix and POSIX variants.  It is not
     able to reliably detect bind mounts on the same filesystem.  On
     Windows, a drive letter root and a share UNC are always mount
     points, and for any other path ‘GetVolumePathName’ is called to see
     if it is different from the input path.

     New in version 3.4: Support for detecting non-root mount points on
     Windows.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.join (path, *paths)

     Join one or more path components intelligently.  The return value
     is the concatenation of `path' and any members of `*paths' with
     exactly one directory separator following each non-empty part
     except the last, meaning that the result will only end in a
     separator if the last part is empty.  If a component is an absolute
     path, all previous components are thrown away and joining continues
     from the absolute path component.

     On Windows, the drive letter is not reset when an absolute path
     component (e.g., ‘r'\foo'’) is encountered.  If a component
     contains a drive letter, all previous components are thrown away
     and the drive letter is reset.  Note that since there is a current
     directory for each drive, ‘os.path.join("c:", "foo")’ represents a
     path relative to the current directory on drive ‘C:’ (‘c:foo’), not
     ‘c:\foo’.

     Changed in version 3.6: Accepts a *note path-like object: 472. for
     `path' and `paths'.

 -- Function: os.path.normcase (path)

     Normalize the case of a pathname.  On Windows, convert all
     characters in the pathname to lowercase, and also convert forward
     slashes to backward slashes.  On other operating systems, return
     the path unchanged.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.normpath (path)

          Normalize a pathname by collapsing redundant separators and
          up-level references so that ‘A//B’, ‘A/B/’, ‘A/./B’ and
          ‘A/foo/../B’ all become ‘A/B’.  This string manipulation may
          change the meaning of a path that contains symbolic links.  On
          Windows, it converts forward slashes to backward slashes.  To
          normalize case, use *note normcase(): 1d4e.

          Note: 
               On POSIX systems, in accordance with IEEE Std 1003.1 2013
               Edition; 4.13 Pathname Resolution(3), if a pathname
               begins with exactly two slashes, the first component
               following the leading characters may be interpreted in an
               implementation-defined manner, although more than two
               leading characters shall be treated as a single
               character.

          Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.realpath (path)

     Return the canonical path of the specified filename, eliminating
     any symbolic links encountered in the path (if they are supported
     by the operating system).

          Note: When symbolic link cycles occur, the returned path will
          be one member of the cycle, but no guarantee is made about
          which member that will be.

     Changed in version 3.6: Accepts a *note path-like object: 472.

     Changed in version 3.8: Symbolic links and junctions are now
     resolved on Windows.

 -- Function: os.path.relpath (path, start=os.curdir)

     Return a relative filepath to `path' either from the current
     directory or from an optional `start' directory.  This is a path
     computation: the filesystem is not accessed to confirm the
     existence or nature of `path' or `start'.  On Windows, *note
     ValueError: 16d. is raised when `path' and `start' are on different
     drives.

     `start' defaults to *note os.curdir: 1d4f.

     *note Availability: 1491.: Unix, Windows.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.samefile (path1, path2)

     Return ‘True’ if both pathname arguments refer to the same file or
     directory.  This is determined by the device number and i-node
     number and raises an exception if an *note os.stat(): 321. call on
     either pathname fails.

     *note Availability: 1491.: Unix, Windows.

     Changed in version 3.2: Added Windows support.

     Changed in version 3.4: Windows now uses the same implementation as
     all other platforms.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.sameopenfile (fp1, fp2)

     Return ‘True’ if the file descriptors `fp1' and `fp2' refer to the
     same file.

     *note Availability: 1491.: Unix, Windows.

     Changed in version 3.2: Added Windows support.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.samestat (stat1, stat2)

     Return ‘True’ if the stat tuples `stat1' and `stat2' refer to the
     same file.  These structures may have been returned by *note
     os.fstat(): 752, *note os.lstat(): 322, or *note os.stat(): 321.
     This function implements the underlying comparison used by *note
     samefile(): 96d. and *note sameopenfile(): 1d50.

     *note Availability: 1491.: Unix, Windows.

     Changed in version 3.4: Added Windows support.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.split (path)

     Split the pathname `path' into a pair, ‘(head, tail)’ where `tail'
     is the last pathname component and `head' is everything leading up
     to that.  The `tail' part will never contain a slash; if `path'
     ends in a slash, `tail' will be empty.  If there is no slash in
     `path', `head' will be empty.  If `path' is empty, both `head' and
     `tail' are empty.  Trailing slashes are stripped from `head' unless
     it is the root (one or more slashes only).  In all cases,
     ‘join(head, tail)’ returns a path to the same location as `path'
     (but the strings may differ).  Also see the functions *note
     dirname(): 1d45. and *note basename(): 1d44.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.splitdrive (path)

     Split the pathname `path' into a pair ‘(drive, tail)’ where `drive'
     is either a mount point or the empty string.  On systems which do
     not use drive specifications, `drive' will always be the empty
     string.  In all cases, ‘drive + tail’ will be the same as `path'.

     On Windows, splits a pathname into drive/UNC sharepoint and
     relative path.

     If the path contains a drive letter, drive will contain everything
     up to and including the colon:

          >>> splitdrive("c:/dir")
          ("c:", "/dir")

     If the path contains a UNC path, drive will contain the host name
     and share, up to but not including the fourth separator:

          >>> splitdrive("//host/computer/dir")
          ("//host/computer", "/dir")

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.path.splitext (path)

     Split the pathname `path' into a pair ‘(root, ext)’ such that ‘root
     + ext == path’, and the extension, `ext', is empty or begins with a
     period and contains at most one period.

     If the path contains no extension, `ext' will be ‘''’:

          >>> splitext('bar')
          ('bar', '')

     If the path contains an extension, then `ext' will be set to this
     extension, including the leading period.  Note that previous
     periods will be ignored:

          >>> splitext('foo.bar.exe')
          ('foo.bar', '.exe')
          >>> splitext('/foo/bar.exe')
          ('/foo/bar', '.exe')

     Leading periods of the last component of the path are considered to
     be part of the root:

          >>> splitext('.cshrc')
          ('.cshrc', '')
          >>> splitext('/foo/....jpg')
          ('/foo/....jpg', '')

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Data: os.path.supports_unicode_filenames

     ‘True’ if arbitrary Unicode strings can be used as file names
     (within limitations imposed by the file system).

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/posixpath.py

   (2) https://github.com/python/cpython/tree/3.9/Lib/ntpath.py

   (3) 
http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13


File: python.info,  Node: fileinput — Iterate over lines from multiple input streams,  Next: stat — Interpreting stat results,  Prev: os path — Common pathname manipulations,  Up: File and Directory Access

5.11.3 ‘fileinput’ — Iterate over lines from multiple input streams
-------------------------------------------------------------------

`Source code:' Lib/fileinput.py(1)

__________________________________________________________________

This module implements a helper class and functions to quickly write a
loop over standard input or a list of files.  If you just want to read
or write one file see *note open(): 16f.

The typical use is:

     import fileinput
     for line in fileinput.input():
         process(line)

This iterates over the lines of all files listed in ‘sys.argv[1:]’,
defaulting to ‘sys.stdin’ if the list is empty.  If a filename is ‘'-'’,
it is also replaced by ‘sys.stdin’ and the optional arguments `mode' and
`openhook' are ignored.  To specify an alternative list of filenames,
pass it as the first argument to *note input(): 3cf.  A single file name
is also allowed.

All files are opened in text mode by default, but you can override this
by specifying the `mode' parameter in the call to *note input(): 3cf. or
*note FileInput: 3a5.  If an I/O error occurs during opening or reading
a file, *note OSError: 304. is raised.

Changed in version 3.3: *note IOError: a73. used to be raised; it is now
an alias of *note OSError: 304.

If ‘sys.stdin’ is used more than once, the second and further use will
return no lines, except perhaps for interactive use, or if it has been
explicitly reset (e.g.  using ‘sys.stdin.seek(0)’).

Empty files are opened and immediately closed; the only time their
presence in the list of filenames is noticeable at all is when the last
file opened is empty.

Lines are returned with any newlines intact, which means that the last
line in a file may not have one.

You can control how files are opened by providing an opening hook via
the `openhook' parameter to *note fileinput.input(): 3cf. or *note
FileInput(): 3a5.  The hook must be a function that takes two arguments,
`filename' and `mode', and returns an accordingly opened file-like
object.  Two useful hooks are already provided by this module.

The following function is the primary interface of this module:

 -- Function: fileinput.input (files=None, inplace=False, backup='', *,
          mode='r', openhook=None)

     Create an instance of the *note FileInput: 3a5. class.  The
     instance will be used as global state for the functions of this
     module, and is also returned to use during iteration.  The
     parameters to this function will be passed along to the constructor
     of the *note FileInput: 3a5. class.

     The *note FileInput: 3a5. instance can be used as a context manager
     in the *note with: 7da. statement.  In this example, `input' is
     closed after the ‘with’ statement is exited, even if an exception
     occurs:

          with fileinput.input(files=('spam.txt', 'eggs.txt')) as f:
              for line in f:
                  process(line)

     Changed in version 3.2: Can be used as a context manager.

     Changed in version 3.8: The keyword parameters `mode' and
     `openhook' are now keyword-only.

The following functions use the global state created by *note
fileinput.input(): 3cf.; if there is no active state, *note
RuntimeError: 3dc. is raised.

 -- Function: fileinput.filename ()

     Return the name of the file currently being read.  Before the first
     line has been read, returns ‘None’.

 -- Function: fileinput.fileno ()

     Return the integer “file descriptor” for the current file.  When no
     file is opened (before the first line and between files), returns
     ‘-1’.

 -- Function: fileinput.lineno ()

     Return the cumulative line number of the line that has just been
     read.  Before the first line has been read, returns ‘0’.  After the
     last line of the last file has been read, returns the line number
     of that line.

 -- Function: fileinput.filelineno ()

     Return the line number in the current file.  Before the first line
     has been read, returns ‘0’.  After the last line of the last file
     has been read, returns the line number of that line within the
     file.

 -- Function: fileinput.isfirstline ()

     Return ‘True’ if the line just read is the first line of its file,
     otherwise return ‘False’.

 -- Function: fileinput.isstdin ()

     Return ‘True’ if the last line was read from ‘sys.stdin’, otherwise
     return ‘False’.

 -- Function: fileinput.nextfile ()

     Close the current file so that the next iteration will read the
     first line from the next file (if any); lines not read from the
     file will not count towards the cumulative line count.  The
     filename is not changed until after the first line of the next file
     has been read.  Before the first line has been read, this function
     has no effect; it cannot be used to skip the first file.  After the
     last line of the last file has been read, this function has no
     effect.

 -- Function: fileinput.close ()

     Close the sequence.

The class which implements the sequence behavior provided by the module
is available for subclassing as well:

 -- Class: fileinput.FileInput (files=None, inplace=False, backup='', *,
          mode='r', openhook=None)

     Class *note FileInput: 3a5. is the implementation; its methods
     *note filename(): 1d53, *note fileno(): 1d54, *note lineno(): 1d55,
     *note filelineno(): 1d56, *note isfirstline(): 1d57, *note
     isstdin(): 1d58, *note nextfile(): 1d59. and *note close(): 1d5a.
     correspond to the functions of the same name in the module.  In
     addition it has a *note readline(): 1d5b. method which returns the
     next input line, and a *note __getitem__(): 3a2. method which
     implements the sequence behavior.  The sequence must be accessed in
     strictly sequential order; random access and *note readline():
     1d5b. cannot be mixed.

     With `mode' you can specify which file mode will be passed to *note
     open(): 16f.  It must be one of ‘'r'’, ‘'rU'’, ‘'U'’ and ‘'rb'’.

     The `openhook', when given, must be a function that takes two
     arguments, `filename' and `mode', and returns an accordingly opened
     file-like object.  You cannot use `inplace' and `openhook'
     together.

     A *note FileInput: 3a5. instance can be used as a context manager
     in the *note with: 7da. statement.  In this example, `input' is
     closed after the ‘with’ statement is exited, even if an exception
     occurs:

          with FileInput(files=('spam.txt', 'eggs.txt')) as input:
              process(input)

     Changed in version 3.2: Can be used as a context manager.

     Deprecated since version 3.4: The ‘'rU'’ and ‘'U'’ modes.

     Deprecated since version 3.8: Support for *note __getitem__(): 3a2.
     method is deprecated.

     Changed in version 3.8: The keyword parameter `mode' and `openhook'
     are now keyword-only.

`Optional in-place filtering:' if the keyword argument ‘inplace=True’ is
passed to *note fileinput.input(): 3cf. or to the *note FileInput: 3a5.
constructor, the file is moved to a backup file and standard output is
directed to the input file (if a file of the same name as the backup
file already exists, it will be replaced silently).  This makes it
possible to write a filter that rewrites its input file in place.  If
the `backup' parameter is given (typically as ‘backup='.<some
extension>'’), it specifies the extension for the backup file, and the
backup file remains around; by default, the extension is ‘'.bak'’ and it
is deleted when the output file is closed.  In-place filtering is
disabled when standard input is read.

The two following opening hooks are provided by this module:

 -- Function: fileinput.hook_compressed (filename, mode)

     Transparently opens files compressed with gzip and bzip2
     (recognized by the extensions ‘'.gz'’ and ‘'.bz2'’) using the *note
     gzip: 8b. and *note bz2: 13. modules.  If the filename extension is
     not ‘'.gz'’ or ‘'.bz2'’, the file is opened normally (ie, using
     *note open(): 16f. without any decompression).

     Usage example: ‘fi =
     fileinput.FileInput(openhook=fileinput.hook_compressed)’

 -- Function: fileinput.hook_encoded (encoding, errors=None)

     Returns a hook which opens each file with *note open(): 16f, using
     the given `encoding' and `errors' to read the file.

     Usage example: ‘fi =
     fileinput.FileInput(openhook=fileinput.hook_encoded("utf-8",
     "surrogateescape"))’

     Changed in version 3.6: Added the optional `errors' parameter.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/fileinput.py


File: python.info,  Node: stat — Interpreting stat results,  Next: filecmp — File and Directory Comparisons,  Prev: fileinput — Iterate over lines from multiple input streams,  Up: File and Directory Access

5.11.4 ‘stat’ — Interpreting ‘stat()’ results
---------------------------------------------

`Source code:' Lib/stat.py(1)

__________________________________________________________________

The *note stat: f4. module defines constants and functions for
interpreting the results of *note os.stat(): 321, *note os.fstat(): 752.
and *note os.lstat(): 322. (if they exist).  For complete details about
the ‘stat()’, ‘fstat()’ and ‘lstat()’ calls, consult the documentation
for your system.

Changed in version 3.4: The stat module is backed by a C implementation.

The *note stat: f4. module defines the following functions to test for
specific file types:

 -- Function: stat.S_ISDIR (mode)

     Return non-zero if the mode is from a directory.

 -- Function: stat.S_ISCHR (mode)

     Return non-zero if the mode is from a character special device
     file.

 -- Function: stat.S_ISBLK (mode)

     Return non-zero if the mode is from a block special device file.

 -- Function: stat.S_ISREG (mode)

     Return non-zero if the mode is from a regular file.

 -- Function: stat.S_ISFIFO (mode)

     Return non-zero if the mode is from a FIFO (named pipe).

 -- Function: stat.S_ISLNK (mode)

     Return non-zero if the mode is from a symbolic link.

 -- Function: stat.S_ISSOCK (mode)

     Return non-zero if the mode is from a socket.

 -- Function: stat.S_ISDOOR (mode)

     Return non-zero if the mode is from a door.

     New in version 3.4.

 -- Function: stat.S_ISPORT (mode)

     Return non-zero if the mode is from an event port.

     New in version 3.4.

 -- Function: stat.S_ISWHT (mode)

     Return non-zero if the mode is from a whiteout.

     New in version 3.4.

Two additional functions are defined for more general manipulation of
the file’s mode:

 -- Function: stat.S_IMODE (mode)

     Return the portion of the file’s mode that can be set by *note
     os.chmod(): b0f.—that is, the file’s permission bits, plus the
     sticky bit, set-group-id, and set-user-id bits (on systems that
     support them).

 -- Function: stat.S_IFMT (mode)

     Return the portion of the file’s mode that describes the file type
     (used by the ‘S_IS*()’ functions above).

Normally, you would use the ‘os.path.is*()’ functions for testing the
type of a file; the functions here are useful when you are doing
multiple tests of the same file and wish to avoid the overhead of the
‘stat()’ system call for each test.  These are also useful when checking
for information about a file that isn’t handled by *note os.path: c5,
like the tests for block and character devices.

Example:

     import os, sys
     from stat import *

     def walktree(top, callback):
         '''recursively descend the directory tree rooted at top,
            calling the callback function for each regular file'''

         for f in os.listdir(top):
             pathname = os.path.join(top, f)
             mode = os.stat(pathname).st_mode
             if S_ISDIR(mode):
                 # It's a directory, recurse into it
                 walktree(pathname, callback)
             elif S_ISREG(mode):
                 # It's a file, call the callback function
                 callback(pathname)
             else:
                 # Unknown file type, print a message
                 print('Skipping %s' % pathname)

     def visitfile(file):
         print('visiting', file)

     if __name__ == '__main__':
         walktree(sys.argv[1], visitfile)

An additional utility function is provided to convert a file’s mode in a
human readable string:

 -- Function: stat.filemode (mode)

     Convert a file’s mode to a string of the form ‘-rwxrwxrwx’.

     New in version 3.3.

     Changed in version 3.4: The function supports *note S_IFDOOR: 9ba,
     *note S_IFPORT: 9bb. and *note S_IFWHT: 9bc.

All the variables below are simply symbolic indexes into the 10-tuple
returned by *note os.stat(): 321, *note os.fstat(): 752. or *note
os.lstat(): 322.

 -- Data: stat.ST_MODE

     Inode protection mode.

 -- Data: stat.ST_INO

     Inode number.

 -- Data: stat.ST_DEV

     Device inode resides on.

 -- Data: stat.ST_NLINK

     Number of links to the inode.

 -- Data: stat.ST_UID

     User id of the owner.

 -- Data: stat.ST_GID

     Group id of the owner.

 -- Data: stat.ST_SIZE

     Size in bytes of a plain file; amount of data waiting on some
     special files.

 -- Data: stat.ST_ATIME

     Time of last access.

 -- Data: stat.ST_MTIME

     Time of last modification.

 -- Data: stat.ST_CTIME

     The “ctime” as reported by the operating system.  On some systems
     (like Unix) is the time of the last metadata change, and, on others
     (like Windows), is the creation time (see platform documentation
     for details).

The interpretation of “file size” changes according to the file type.
For plain files this is the size of the file in bytes.  For FIFOs and
sockets under most flavors of Unix (including Linux in particular), the
“size” is the number of bytes waiting to be read at the time of the call
to *note os.stat(): 321, *note os.fstat(): 752, or *note os.lstat():
322.; this can sometimes be useful, especially for polling one of these
special files after a non-blocking open.  The meaning of the size field
for other character and block devices varies more, depending on the
implementation of the underlying system call.

The variables below define the flags used in the *note ST_MODE: 9b9.
field.

Use of the functions above is more portable than use of the first set of
flags:

 -- Data: stat.S_IFSOCK

     Socket.

 -- Data: stat.S_IFLNK

     Symbolic link.

 -- Data: stat.S_IFREG

     Regular file.

 -- Data: stat.S_IFBLK

     Block device.

 -- Data: stat.S_IFDIR

     Directory.

 -- Data: stat.S_IFCHR

     Character device.

 -- Data: stat.S_IFIFO

     FIFO.

 -- Data: stat.S_IFDOOR

     Door.

     New in version 3.4.

 -- Data: stat.S_IFPORT

     Event port.

     New in version 3.4.

 -- Data: stat.S_IFWHT

     Whiteout.

     New in version 3.4.

     Note: *note S_IFDOOR: 9ba, *note S_IFPORT: 9bb. or *note S_IFWHT:
     9bc. are defined as 0 when the platform does not have support for
     the file types.

The following flags can also be used in the `mode' argument of *note
os.chmod(): b0f.:

 -- Data: stat.S_ISUID

     Set UID bit.

 -- Data: stat.S_ISGID

     Set-group-ID bit.  This bit has several special uses.  For a
     directory it indicates that BSD semantics is to be used for that
     directory: files created there inherit their group ID from the
     directory, not from the effective group ID of the creating process,
     and directories created there will also get the *note S_ISGID:
     1d79. bit set.  For a file that does not have the group execution
     bit (*note S_IXGRP: 1d7a.) set, the set-group-ID bit indicates
     mandatory file/record locking (see also *note S_ENFMT: 1d7b.).

 -- Data: stat.S_ISVTX

     Sticky bit.  When this bit is set on a directory it means that a
     file in that directory can be renamed or deleted only by the owner
     of the file, by the owner of the directory, or by a privileged
     process.

 -- Data: stat.S_IRWXU

     Mask for file owner permissions.

 -- Data: stat.S_IRUSR

     Owner has read permission.

 -- Data: stat.S_IWUSR

     Owner has write permission.

 -- Data: stat.S_IXUSR

     Owner has execute permission.

 -- Data: stat.S_IRWXG

     Mask for group permissions.

 -- Data: stat.S_IRGRP

     Group has read permission.

 -- Data: stat.S_IWGRP

     Group has write permission.

 -- Data: stat.S_IXGRP

     Group has execute permission.

 -- Data: stat.S_IRWXO

     Mask for permissions for others (not in group).

 -- Data: stat.S_IROTH

     Others have read permission.

 -- Data: stat.S_IWOTH

     Others have write permission.

 -- Data: stat.S_IXOTH

     Others have execute permission.

 -- Data: stat.S_ENFMT

     System V file locking enforcement.  This flag is shared with *note
     S_ISGID: 1d79.: file/record locking is enforced on files that do
     not have the group execution bit (*note S_IXGRP: 1d7a.) set.

 -- Data: stat.S_IREAD

     Unix V7 synonym for *note S_IRUSR: 1d7e.

 -- Data: stat.S_IWRITE

     Unix V7 synonym for *note S_IWUSR: 1d7f.

 -- Data: stat.S_IEXEC

     Unix V7 synonym for *note S_IXUSR: 1d80.

The following flags can be used in the `flags' argument of *note
os.chflags(): b0e.:

 -- Data: stat.UF_NODUMP

     Do not dump the file.

 -- Data: stat.UF_IMMUTABLE

     The file may not be changed.

 -- Data: stat.UF_APPEND

     The file may only be appended to.

 -- Data: stat.UF_OPAQUE

     The directory is opaque when viewed through a union stack.

 -- Data: stat.UF_NOUNLINK

     The file may not be renamed or deleted.

 -- Data: stat.UF_COMPRESSED

     The file is stored compressed (macOS 10.6+).

 -- Data: stat.UF_HIDDEN

     The file should not be displayed in a GUI (macOS 10.5+).

 -- Data: stat.SF_ARCHIVED

     The file may be archived.

 -- Data: stat.SF_IMMUTABLE

     The file may not be changed.

 -- Data: stat.SF_APPEND

     The file may only be appended to.

 -- Data: stat.SF_NOUNLINK

     The file may not be renamed or deleted.

 -- Data: stat.SF_SNAPSHOT

     The file is a snapshot file.

See the *BSD or macOS systems man page ‘chflags(2)’ for more
information.

On Windows, the following file attribute constants are available for use
when testing bits in the ‘st_file_attributes’ member returned by *note
os.stat(): 321.  See the Windows API documentation(2) for more detail on
the meaning of these constants.

 -- Data: stat.FILE_ATTRIBUTE_ARCHIVE
 -- Data: stat.FILE_ATTRIBUTE_COMPRESSED
 -- Data: stat.FILE_ATTRIBUTE_DEVICE
 -- Data: stat.FILE_ATTRIBUTE_DIRECTORY
 -- Data: stat.FILE_ATTRIBUTE_ENCRYPTED
 -- Data: stat.FILE_ATTRIBUTE_HIDDEN
 -- Data: stat.FILE_ATTRIBUTE_INTEGRITY_STREAM
 -- Data: stat.FILE_ATTRIBUTE_NORMAL
 -- Data: stat.FILE_ATTRIBUTE_NOT_CONTENT_INDEXED
 -- Data: stat.FILE_ATTRIBUTE_NO_SCRUB_DATA
 -- Data: stat.FILE_ATTRIBUTE_OFFLINE
 -- Data: stat.FILE_ATTRIBUTE_READONLY
 -- Data: stat.FILE_ATTRIBUTE_REPARSE_POINT
 -- Data: stat.FILE_ATTRIBUTE_SPARSE_FILE
 -- Data: stat.FILE_ATTRIBUTE_SYSTEM
 -- Data: stat.FILE_ATTRIBUTE_TEMPORARY
 -- Data: stat.FILE_ATTRIBUTE_VIRTUAL

     New in version 3.5.

On Windows, the following constants are available for comparing against
the ‘st_reparse_tag’ member returned by *note os.lstat(): 322.  These
are well-known constants, but are not an exhaustive list.

 -- Data: stat.IO_REPARSE_TAG_SYMLINK
 -- Data: stat.IO_REPARSE_TAG_MOUNT_POINT
 -- Data: stat.IO_REPARSE_TAG_APPEXECLINK

     New in version 3.8.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/stat.py

   (2) 
https://msdn.microsoft.com/en-us/library/windows/desktop/gg258117.aspx


File: python.info,  Node: filecmp — File and Directory Comparisons,  Next: tempfile — Generate temporary files and directories,  Prev: stat — Interpreting stat results,  Up: File and Directory Access

5.11.5 ‘filecmp’ — File and Directory Comparisons
-------------------------------------------------

`Source code:' Lib/filecmp.py(1)

__________________________________________________________________

The *note filecmp: 7d. module defines functions to compare files and
directories, with various optional time/correctness trade-offs.  For
comparing files, see also the *note difflib: 36. module.

The *note filecmp: 7d. module defines the following functions:

 -- Function: filecmp.cmp (f1, f2, shallow=True)

     Compare the files named `f1' and `f2', returning ‘True’ if they
     seem equal, ‘False’ otherwise.

     If `shallow' is true and the *note os.stat(): 321. signatures (file
     type, size, and modification time) of both files are identical, the
     files are taken to be equal.

     Otherwise, the files are treated as different if their sizes or
     contents differ.

     Note that no external programs are called from this function,
     giving it portability and efficiency.

     This function uses a cache for past comparisons and the results,
     with cache entries invalidated if the *note os.stat(): 321.
     information for the file changes.  The entire cache may be cleared
     using *note clear_cache(): 934.

 -- Function: filecmp.cmpfiles (dir1, dir2, common, shallow=True)

     Compare the files in the two directories `dir1' and `dir2' whose
     names are given by `common'.

     Returns three lists of file names: `match', `mismatch', `errors'.
     `match' contains the list of files that match, `mismatch' contains
     the names of those that don’t, and `errors' lists the names of
     files which could not be compared.  Files are listed in `errors' if
     they don’t exist in one of the directories, the user lacks
     permission to read them or if the comparison could not be done for
     some other reason.

     The `shallow' parameter has the same meaning and default value as
     for *note filecmp.cmp(): f85.

     For example, ‘cmpfiles('a', 'b', ['c', 'd/e'])’ will compare ‘a/c’
     with ‘b/c’ and ‘a/d/e’ with ‘b/d/e’.  ‘'c'’ and ‘'d/e'’ will each
     be in one of the three returned lists.

 -- Function: filecmp.clear_cache ()

     Clear the filecmp cache.  This may be useful if a file is compared
     so quickly after it is modified that it is within the mtime
     resolution of the underlying filesystem.

     New in version 3.4.

* Menu:

* The dircmp class::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/filecmp.py


File: python.info,  Node: The dircmp class,  Up: filecmp — File and Directory Comparisons

5.11.5.1 The ‘dircmp’ class
...........................

 -- Class: filecmp.dircmp (a, b, ignore=None, hide=None)

     Construct a new directory comparison object, to compare the
     directories `a' and `b'.  `ignore' is a list of names to ignore,
     and defaults to *note filecmp.DEFAULT_IGNORES: 935.  `hide' is a
     list of names to hide, and defaults to ‘[os.curdir, os.pardir]’.

     The *note dircmp: 936. class compares files by doing `shallow'
     comparisons as described for *note filecmp.cmp(): f85.

     The *note dircmp: 936. class provides the following methods:

      -- Method: report ()

          Print (to *note sys.stdout: 41f.) a comparison between `a' and
          `b'.

      -- Method: report_partial_closure ()

          Print a comparison between `a' and `b' and common immediate
          subdirectories.

      -- Method: report_full_closure ()

          Print a comparison between `a' and `b' and common
          subdirectories (recursively).

     The *note dircmp: 936. class offers a number of interesting
     attributes that may be used to get various bits of information
     about the directory trees being compared.

     Note that via *note __getattr__(): 42a. hooks, all attributes are
     computed lazily, so there is no speed penalty if only those
     attributes which are lightweight to compute are used.

      -- Attribute: left

          The directory `a'.

      -- Attribute: right

          The directory `b'.

      -- Attribute: left_list

          Files and subdirectories in `a', filtered by `hide' and
          `ignore'.

      -- Attribute: right_list

          Files and subdirectories in `b', filtered by `hide' and
          `ignore'.

      -- Attribute: common

          Files and subdirectories in both `a' and `b'.

      -- Attribute: left_only

          Files and subdirectories only in `a'.

      -- Attribute: right_only

          Files and subdirectories only in `b'.

      -- Attribute: common_dirs

          Subdirectories in both `a' and `b'.

      -- Attribute: common_files

          Files in both `a' and `b'.

      -- Attribute: common_funny

          Names in both `a' and `b', such that the type differs between
          the directories, or names for which *note os.stat(): 321.
          reports an error.

      -- Attribute: same_files

          Files which are identical in both `a' and `b', using the
          class’s file comparison operator.

      -- Attribute: diff_files

          Files which are in both `a' and `b', whose contents differ
          according to the class’s file comparison operator.

      -- Attribute: funny_files

          Files which are in both `a' and `b', but could not be
          compared.

      -- Attribute: subdirs

          A dictionary mapping names in *note common_dirs: 1dba. to
          *note dircmp: 936. objects.

 -- Attribute: filecmp.DEFAULT_IGNORES

     New in version 3.4.

     List of directories ignored by *note dircmp: 936. by default.

Here is a simplified example of using the ‘subdirs’ attribute to search
recursively through two directories to show common different files:

     >>> from filecmp import dircmp
     >>> def print_diff_files(dcmp):
     ...     for name in dcmp.diff_files:
     ...         print("diff_file %s found in %s and %s" % (name, dcmp.left,
     ...               dcmp.right))
     ...     for sub_dcmp in dcmp.subdirs.values():
     ...         print_diff_files(sub_dcmp)
     ...
     >>> dcmp = dircmp('dir1', 'dir2')
     >>> print_diff_files(dcmp)


File: python.info,  Node: tempfile — Generate temporary files and directories,  Next: glob — Unix style pathname pattern expansion,  Prev: filecmp — File and Directory Comparisons,  Up: File and Directory Access

5.11.6 ‘tempfile’ — Generate temporary files and directories
------------------------------------------------------------

`Source code:' Lib/tempfile.py(1)

__________________________________________________________________

This module creates temporary files and directories.  It works on all
supported platforms.  *note TemporaryFile: 1dc3, *note
NamedTemporaryFile: e0e, *note TemporaryDirectory: c96, and *note
SpooledTemporaryFile: b7e. are high-level interfaces which provide
automatic cleanup and can be used as context managers.  *note mkstemp():
1dc4. and *note mkdtemp(): 1dc5. are lower-level functions which require
manual cleanup.

All the user-callable functions and constructors take additional
arguments which allow direct control over the location and name of
temporary files and directories.  Files names used by this module
include a string of random characters which allows those files to be
securely created in shared temporary directories.  To maintain backward
compatibility, the argument order is somewhat odd; it is recommended to
use keyword arguments for clarity.

The module defines the following user-callable items:

 -- Function: tempfile.TemporaryFile (mode='w+b', buffering=-1,
          encoding=None, newline=None, suffix=None, prefix=None,
          dir=None, *, errors=None)

     Return a *note file-like object: 1dc6. that can be used as a
     temporary storage area.  The file is created securely, using the
     same rules as *note mkstemp(): 1dc4.  It will be destroyed as soon
     as it is closed (including an implicit close when the object is
     garbage collected).  Under Unix, the directory entry for the file
     is either not created at all or is removed immediately after the
     file is created.  Other platforms do not support this; your code
     should not rely on a temporary file created using this function
     having or not having a visible name in the file system.

     The resulting object can be used as a context manager (see *note
     Examples: 1dc7.).  On completion of the context or destruction of
     the file object the temporary file will be removed from the
     filesystem.

     The `mode' parameter defaults to ‘'w+b'’ so that the file created
     can be read and written without being closed.  Binary mode is used
     so that it behaves consistently on all platforms without regard for
     the data that is stored.  `buffering', `encoding', `errors' and
     `newline' are interpreted as for *note open(): 16f.

     The `dir', `prefix' and `suffix' parameters have the same meaning
     and defaults as with *note mkstemp(): 1dc4.

     The returned object is a true file object on POSIX platforms.  On
     other platforms, it is a file-like object whose ‘file’ attribute is
     the underlying true file object.

     The *note os.O_TMPFILE: 96f. flag is used if it is available and
     works (Linux-specific, requires Linux kernel 3.11 or later).

     Raises an *note auditing event: fa1. ‘tempfile.mkstemp’ with
     argument ‘fullpath’.

     Changed in version 3.5: The *note os.O_TMPFILE: 96f. flag is now
     used if available.

     Changed in version 3.8: Added `errors' parameter.

 -- Function: tempfile.NamedTemporaryFile (mode='w+b', buffering=-1,
          encoding=None, newline=None, suffix=None, prefix=None,
          dir=None, delete=True, *, errors=None)

     This function operates exactly as *note TemporaryFile(): 1dc3.
     does, except that the file is guaranteed to have a visible name in
     the file system (on Unix, the directory entry is not unlinked).
     That name can be retrieved from the ‘name’ attribute of the
     returned file-like object.  Whether the name can be used to open
     the file a second time, while the named temporary file is still
     open, varies across platforms (it can be so used on Unix; it cannot
     on Windows NT or later).  If `delete' is true (the default), the
     file is deleted as soon as it is closed.  The returned object is
     always a file-like object whose ‘file’ attribute is the underlying
     true file object.  This file-like object can be used in a *note
     with: 7da. statement, just like a normal file.

     Raises an *note auditing event: fa1. ‘tempfile.mkstemp’ with
     argument ‘fullpath’.

     Changed in version 3.8: Added `errors' parameter.

 -- Function: tempfile.SpooledTemporaryFile (max_size=0, mode='w+b',
          buffering=-1, encoding=None, newline=None, suffix=None,
          prefix=None, dir=None, *, errors=None)

     This function operates exactly as *note TemporaryFile(): 1dc3.
     does, except that data is spooled in memory until the file size
     exceeds `max_size', or until the file’s ‘fileno()’ method is
     called, at which point the contents are written to disk and
     operation proceeds as with *note TemporaryFile(): 1dc3.

     The resulting file has one additional method, ‘rollover()’, which
     causes the file to roll over to an on-disk file regardless of its
     size.

     The returned object is a file-like object whose ‘_file’ attribute
     is either an *note io.BytesIO: 88a. or *note io.TextIOWrapper: 6ea.
     object (depending on whether binary or text `mode' was specified)
     or a true file object, depending on whether ‘rollover()’ has been
     called.  This file-like object can be used in a *note with: 7da.
     statement, just like a normal file.

     Changed in version 3.3: the truncate method now accepts a ‘size’
     argument.

     Changed in version 3.8: Added `errors' parameter.

 -- Function: tempfile.TemporaryDirectory (suffix=None, prefix=None,
          dir=None)

     This function securely creates a temporary directory using the same
     rules as *note mkdtemp(): 1dc5.  The resulting object can be used
     as a context manager (see *note Examples: 1dc7.).  On completion of
     the context or destruction of the temporary directory object the
     newly created temporary directory and all its contents are removed
     from the filesystem.

     The directory name can be retrieved from the ‘name’ attribute of
     the returned object.  When the returned object is used as a context
     manager, the ‘name’ will be assigned to the target of the ‘as’
     clause in the *note with: 7da. statement, if there is one.

     The directory can be explicitly cleaned up by calling the
     ‘cleanup()’ method.

     Raises an *note auditing event: fa1. ‘tempfile.mkdtemp’ with
     argument ‘fullpath’.

     New in version 3.2.

 -- Function: tempfile.mkstemp (suffix=None, prefix=None, dir=None,
          text=False)

     Creates a temporary file in the most secure manner possible.  There
     are no race conditions in the file’s creation, assuming that the
     platform properly implements the *note os.O_EXCL: 1dc8. flag for
     *note os.open(): 758.  The file is readable and writable only by
     the creating user ID. If the platform uses permission bits to
     indicate whether a file is executable, the file is executable by no
     one.  The file descriptor is not inherited by child processes.

     Unlike *note TemporaryFile(): 1dc3, the user of *note mkstemp():
     1dc4. is responsible for deleting the temporary file when done with
     it.

     If `suffix' is not ‘None’, the file name will end with that suffix,
     otherwise there will be no suffix.  *note mkstemp(): 1dc4. does not
     put a dot between the file name and the suffix; if you need one,
     put it at the beginning of `suffix'.

     If `prefix' is not ‘None’, the file name will begin with that
     prefix; otherwise, a default prefix is used.  The default is the
     return value of *note gettempprefix(): 1dc9. or *note
     gettempprefixb(): 1dca, as appropriate.

     If `dir' is not ‘None’, the file will be created in that directory;
     otherwise, a default directory is used.  The default directory is
     chosen from a platform-dependent list, but the user of the
     application can control the directory location by setting the
     `TMPDIR', `TEMP' or `TMP' environment variables.  There is thus no
     guarantee that the generated filename will have any nice
     properties, such as not requiring quoting when passed to external
     commands via ‘os.popen()’.

     If any of `suffix', `prefix', and `dir' are not ‘None’, they must
     be the same type.  If they are bytes, the returned name will be
     bytes instead of str.  If you want to force a bytes return value
     with otherwise default behavior, pass ‘suffix=b''’.

     If `text' is specified and true, the file is opened in text mode.
     Otherwise, (the default) the file is opened in binary mode.

     *note mkstemp(): 1dc4. returns a tuple containing an OS-level
     handle to an open file (as would be returned by *note os.open():
     758.) and the absolute pathname of that file, in that order.

     Raises an *note auditing event: fa1. ‘tempfile.mkstemp’ with
     argument ‘fullpath’.

     Changed in version 3.5: `suffix', `prefix', and `dir' may now be
     supplied in bytes in order to obtain a bytes return value.  Prior
     to this, only str was allowed.  `suffix' and `prefix' now accept
     and default to ‘None’ to cause an appropriate default value to be
     used.

     Changed in version 3.6: The `dir' parameter now accepts a *note
     path-like object: 472.

 -- Function: tempfile.mkdtemp (suffix=None, prefix=None, dir=None)

     Creates a temporary directory in the most secure manner possible.
     There are no race conditions in the directory’s creation.  The
     directory is readable, writable, and searchable only by the
     creating user ID.

     The user of *note mkdtemp(): 1dc5. is responsible for deleting the
     temporary directory and its contents when done with it.

     The `prefix', `suffix', and `dir' arguments are the same as for
     *note mkstemp(): 1dc4.

     *note mkdtemp(): 1dc5. returns the absolute pathname of the new
     directory.

     Raises an *note auditing event: fa1. ‘tempfile.mkdtemp’ with
     argument ‘fullpath’.

     Changed in version 3.5: `suffix', `prefix', and `dir' may now be
     supplied in bytes in order to obtain a bytes return value.  Prior
     to this, only str was allowed.  `suffix' and `prefix' now accept
     and default to ‘None’ to cause an appropriate default value to be
     used.

     Changed in version 3.6: The `dir' parameter now accepts a *note
     path-like object: 472.

 -- Function: tempfile.gettempdir ()

     Return the name of the directory used for temporary files.  This
     defines the default value for the `dir' argument to all functions
     in this module.

     Python searches a standard list of directories to find one which
     the calling user can create files in.  The list is:

       1. The directory named by the ‘TMPDIR’ environment variable.

       2. The directory named by the ‘TEMP’ environment variable.

       3. The directory named by the ‘TMP’ environment variable.

       4. A platform-specific location:

             * On Windows, the directories ‘C:\TEMP’, ‘C:\TMP’, ‘\TEMP’,
               and ‘\TMP’, in that order.

             * On all other platforms, the directories ‘/tmp’,
               ‘/var/tmp’, and ‘/usr/tmp’, in that order.

       5. As a last resort, the current working directory.

     The result of this search is cached, see the description of *note
     tempdir: 1dcc. below.

 -- Function: tempfile.gettempdirb ()

     Same as *note gettempdir(): 1dcb. but the return value is in bytes.

     New in version 3.5.

 -- Function: tempfile.gettempprefix ()

     Return the filename prefix used to create temporary files.  This
     does not contain the directory component.

 -- Function: tempfile.gettempprefixb ()

     Same as *note gettempprefix(): 1dc9. but the return value is in
     bytes.

     New in version 3.5.

The module uses a global variable to store the name of the directory
used for temporary files returned by *note gettempdir(): 1dcb.  It can
be set directly to override the selection process, but this is
discouraged.  All functions in this module take a `dir' argument which
can be used to specify the directory and this is the recommended
approach.

 -- Data: tempfile.tempdir

     When set to a value other than ‘None’, this variable defines the
     default value for the `dir' argument to the functions defined in
     this module.

     If ‘tempdir’ is ‘None’ (the default) at any call to any of the
     above functions except *note gettempprefix(): 1dc9. it is
     initialized following the algorithm described in *note
     gettempdir(): 1dcb.

* Menu:

* Examples: Examples<4>.
* Deprecated functions and variables::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/tempfile.py


File: python.info,  Node: Examples<4>,  Next: Deprecated functions and variables,  Up: tempfile — Generate temporary files and directories

5.11.6.1 Examples
.................

Here are some examples of typical usage of the *note tempfile: 103.
module:

     >>> import tempfile

     # create a temporary file and write some data to it
     >>> fp = tempfile.TemporaryFile()
     >>> fp.write(b'Hello world!')
     # read data from file
     >>> fp.seek(0)
     >>> fp.read()
     b'Hello world!'
     # close the file, it will be removed
     >>> fp.close()

     # create a temporary file using a context manager
     >>> with tempfile.TemporaryFile() as fp:
     ...     fp.write(b'Hello world!')
     ...     fp.seek(0)
     ...     fp.read()
     b'Hello world!'
     >>>
     # file is now closed and removed

     # create a temporary directory using the context manager
     >>> with tempfile.TemporaryDirectory() as tmpdirname:
     ...     print('created temporary directory', tmpdirname)
     >>>
     # directory and contents have been removed


File: python.info,  Node: Deprecated functions and variables,  Prev: Examples<4>,  Up: tempfile — Generate temporary files and directories

5.11.6.2 Deprecated functions and variables
...........................................

A historical way to create temporary files was to first generate a file
name with the *note mktemp(): f7d. function and then create a file using
this name.  Unfortunately this is not secure, because a different
process may create a file with this name in the time between the call to
*note mktemp(): f7d. and the subsequent attempt to create the file by
the first process.  The solution is to combine the two steps and create
the file immediately.  This approach is used by *note mkstemp(): 1dc4.
and the other functions described above.

 -- Function: tempfile.mktemp (suffix='', prefix='tmp', dir=None)

     Deprecated since version 2.3: Use *note mkstemp(): 1dc4. instead.

     Return an absolute pathname of a file that did not exist at the
     time the call is made.  The `prefix', `suffix', and `dir' arguments
     are similar to those of *note mkstemp(): 1dc4, except that bytes
     file names, ‘suffix=None’ and ‘prefix=None’ are not supported.

          Warning: Use of this function may introduce a security hole in
          your program.  By the time you get around to doing anything
          with the file name it returns, someone else may have beaten
          you to the punch.  *note mktemp(): f7d. usage can be replaced
          easily with *note NamedTemporaryFile(): e0e, passing it the
          ‘delete=False’ parameter:

               >>> f = NamedTemporaryFile(delete=False)
               >>> f.name
               '/tmp/tmptjujjt'
               >>> f.write(b"Hello World!\n")
               13
               >>> f.close()
               >>> os.unlink(f.name)
               >>> os.path.exists(f.name)
               False


File: python.info,  Node: glob — Unix style pathname pattern expansion,  Next: fnmatch — Unix filename pattern matching,  Prev: tempfile — Generate temporary files and directories,  Up: File and Directory Access

5.11.7 ‘glob’ — Unix style pathname pattern expansion
-----------------------------------------------------

`Source code:' Lib/glob.py(1)

__________________________________________________________________

The *note glob: 88. module finds all the pathnames matching a specified
pattern according to the rules used by the Unix shell, although results
are returned in arbitrary order.  No tilde expansion is done, but ‘*’,
‘?’, and character ranges expressed with ‘[]’ will be correctly matched.
This is done by using the *note os.scandir(): 389. and *note
fnmatch.fnmatch(): 1dd3. functions in concert, and not by actually
invoking a subshell.  Note that unlike *note fnmatch.fnmatch(): 1dd3,
*note glob: 88. treats filenames beginning with a dot (‘.’) as special
cases.  (For tilde and shell variable expansion, use *note
os.path.expanduser(): 32c. and *note os.path.expandvars(): e09.)

For a literal match, wrap the meta-characters in brackets.  For example,
‘'[?]'’ matches the character ‘'?'’.

See also
........

The *note pathlib: c8. module offers high-level path objects.

 -- Function: glob.glob (pathname, *, recursive=False)

     Return a possibly-empty list of path names that match `pathname',
     which must be a string containing a path specification.  `pathname'
     can be either absolute (like ‘/usr/src/Python-1.5/Makefile’) or
     relative (like ‘../../Tools/*/*.gif’), and can contain shell-style
     wildcards.  Broken symlinks are included in the results (as in the
     shell).  Whether or not the results are sorted depends on the file
     system.  If a file that satisfies conditions is removed or added
     during the call of this function, whether a path name for that file
     be included is unspecified.

     If `recursive' is true, the pattern “‘**’” will match any files and
     zero or more directories, subdirectories and symbolic links to
     directories.  If the pattern is followed by an *note os.sep: 1dd4.
     or *note os.altsep: 1dd5. then files will not match.

     Raises an *note auditing event: fa1. ‘glob.glob’ with arguments
     ‘pathname’, ‘recursive’.

          Note: Using the “‘**’” pattern in large directory trees may
          consume an inordinate amount of time.

     Changed in version 3.5: Support for recursive globs using “‘**’”.

 -- Function: glob.iglob (pathname, *, recursive=False)

     Return an *note iterator: 1171. which yields the same values as
     *note glob(): 88. without actually storing them all simultaneously.

     Raises an *note auditing event: fa1. ‘glob.glob’ with arguments
     ‘pathname’, ‘recursive’.

 -- Function: glob.escape (pathname)

     Escape all special characters (‘'?'’, ‘'*'’ and ‘'['’).  This is
     useful if you want to match an arbitrary literal string that may
     have special characters in it.  Special characters in drive/UNC
     sharepoints are not escaped, e.g.  on Windows ‘escape('//?/c:/Quo
     vadis?.txt')’ returns ‘'//?/c:/Quo vadis[?].txt'’.

     New in version 3.4.

For example, consider a directory containing the following files:
‘1.gif’, ‘2.txt’, ‘card.gif’ and a subdirectory ‘sub’ which contains
only the file ‘3.txt’.  *note glob(): 88. will produce the following
results.  Notice how any leading components of the path are preserved.

     >>> import glob
     >>> glob.glob('./[0-9].*')
     ['./1.gif', './2.txt']
     >>> glob.glob('*.gif')
     ['1.gif', 'card.gif']
     >>> glob.glob('?.gif')
     ['1.gif']
     >>> glob.glob('**/*.txt', recursive=True)
     ['2.txt', 'sub/3.txt']
     >>> glob.glob('./**/', recursive=True)
     ['./', './sub/']

If the directory contains files starting with ‘.’ they won’t be matched
by default.  For example, consider a directory containing ‘card.gif’ and
‘.card.gif’:

     >>> import glob
     >>> glob.glob('*.gif')
     ['card.gif']
     >>> glob.glob('.c*')
     ['.card.gif']

See also
........

Module *note fnmatch: 7f.

     Shell-style filename (not path) expansion

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/glob.py


File: python.info,  Node: fnmatch — Unix filename pattern matching,  Next: linecache — Random access to text lines,  Prev: glob — Unix style pathname pattern expansion,  Up: File and Directory Access

5.11.8 ‘fnmatch’ — Unix filename pattern matching
-------------------------------------------------

`Source code:' Lib/fnmatch.py(1)

__________________________________________________________________

This module provides support for Unix shell-style wildcards, which are
`not' the same as regular expressions (which are documented in the *note
re: dd. module).  The special characters used in shell-style wildcards
are:

Pattern          Meaning
                 
----------------------------------------------------------
                 
‘*’              matches everything
                 
                 
‘?’              matches any single character
                 
                 
‘[seq]’          matches any character in `seq'
                 
                 
‘[!seq]’         matches any character not in `seq'
                 

For a literal match, wrap the meta-characters in brackets.  For example,
‘'[?]'’ matches the character ‘'?'’.

Note that the filename separator (‘'/'’ on Unix) is `not' special to
this module.  See module *note glob: 88. for pathname expansion (*note
glob: 88. uses *note filter(): 1dd8. to match pathname segments).
Similarly, filenames starting with a period are not special for this
module, and are matched by the ‘*’ and ‘?’ patterns.

 -- Function: fnmatch.fnmatch (filename, pattern)

     Test whether the `filename' string matches the `pattern' string,
     returning *note True: 594. or *note False: 48f.  Both parameters
     are case-normalized using *note os.path.normcase(): 1d4e.  *note
     fnmatchcase(): 1dd9. can be used to perform a case-sensitive
     comparison, regardless of whether that’s standard for the operating
     system.

     This example will print all file names in the current directory
     with the extension ‘.txt’:

          import fnmatch
          import os

          for file in os.listdir('.'):
              if fnmatch.fnmatch(file, '*.txt'):
                  print(file)

 -- Function: fnmatch.fnmatchcase (filename, pattern)

     Test whether `filename' matches `pattern', returning *note True:
     594. or *note False: 48f.; the comparison is case-sensitive and
     does not apply *note os.path.normcase(): 1d4e.

 -- Function: fnmatch.filter (names, pattern)

     Construct a list from those elements of the iterable `names' that
     match `pattern'.  It is the same as ‘[n for n in names if
     fnmatch(n, pattern)]’, but implemented more efficiently.

 -- Function: fnmatch.translate (pattern)

     Return the shell-style `pattern' converted to a regular expression
     for using with *note re.match(): c83.

     Example:

          >>> import fnmatch, re
          >>>
          >>> regex = fnmatch.translate('*.txt')
          >>> regex
          '(?s:.*\\.txt)\\Z'
          >>> reobj = re.compile(regex)
          >>> reobj.match('foobar.txt')
          <re.Match object; span=(0, 10), match='foobar.txt'>

See also
........

Module *note glob: 88.

     Unix shell-style path expansion.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/fnmatch.py


File: python.info,  Node: linecache — Random access to text lines,  Next: shutil — High-level file operations,  Prev: fnmatch — Unix filename pattern matching,  Up: File and Directory Access

5.11.9 ‘linecache’ — Random access to text lines
------------------------------------------------

`Source code:' Lib/linecache.py(1)

__________________________________________________________________

The *note linecache: a8. module allows one to get any line from a Python
source file, while attempting to optimize internally, using a cache, the
common case where many lines are read from a single file.  This is used
by the *note traceback: 11c. module to retrieve source lines for
inclusion in the formatted traceback.

The *note tokenize.open(): 1ddc. function is used to open files.  This
function uses *note tokenize.detect_encoding(): 1ddd. to get the
encoding of the file; in the absence of an encoding token, the file
encoding defaults to UTF-8.

The *note linecache: a8. module defines the following functions:

 -- Function: linecache.getline (filename, lineno, module_globals=None)

     Get line `lineno' from file named `filename'.  This function will
     never raise an exception — it will return ‘''’ on errors (the
     terminating newline character will be included for lines that are
     found).

     If a file named `filename' is not found, the function first checks
     for a PEP 302(2) ‘__loader__’ in `module_globals'.  If there is
     such a loader and it defines a ‘get_source’ method, then that
     determines the source lines (if ‘get_source()’ returns ‘None’, then
     ‘''’ is returned).  Finally, if `filename' is a relative filename,
     it is looked up relative to the entries in the module search path,
     ‘sys.path’.

 -- Function: linecache.clearcache ()

     Clear the cache.  Use this function if you no longer need lines
     from files previously read using *note getline(): 7fa.

 -- Function: linecache.checkcache (filename=None)

     Check the cache for validity.  Use this function if files in the
     cache may have changed on disk, and you require the updated
     version.  If `filename' is omitted, it will check all the entries
     in the cache.

 -- Function: linecache.lazycache (filename, module_globals)

     Capture enough detail about a non-file-based module to permit
     getting its lines later via *note getline(): 7fa. even if
     `module_globals' is ‘None’ in the later call.  This avoids doing
     I/O until a line is actually needed, without having to carry the
     module globals around indefinitely.

     New in version 3.5.

Example:

     >>> import linecache
     >>> linecache.getline(linecache.__file__, 8)
     'import sys\n'

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/linecache.py

   (2) https://www.python.org/dev/peps/pep-0302


File: python.info,  Node: shutil — High-level file operations,  Prev: linecache — Random access to text lines,  Up: File and Directory Access

5.11.10 ‘shutil’ — High-level file operations
---------------------------------------------

`Source code:' Lib/shutil.py(1)

__________________________________________________________________

The *note shutil: e9. module offers a number of high-level operations on
files and collections of files.  In particular, functions are provided
which support file copying and removal.  For operations on individual
files, see also the *note os: c4. module.

     Warning: Even the higher-level file copying functions (*note
     shutil.copy(): 383, *note shutil.copy2(): 384.) cannot copy all
     file metadata.

     On POSIX platforms, this means that file owner and group are lost
     as well as ACLs.  On Mac OS, the resource fork and other metadata
     are not used.  This means that resources will be lost and file type
     and creator codes will not be correct.  On Windows, file owners,
     ACLs and alternate data streams are not copied.

* Menu:

* Directory and files operations::
* Archiving operations::
* Querying the size of the output terminal::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/shutil.py


File: python.info,  Node: Directory and files operations,  Next: Archiving operations,  Up: shutil — High-level file operations

5.11.10.1 Directory and files operations
........................................

 -- Function: shutil.copyfileobj (fsrc, fdst[, length])

     Copy the contents of the file-like object `fsrc' to the file-like
     object `fdst'.  The integer `length', if given, is the buffer size.
     In particular, a negative `length' value means to copy the data
     without looping over the source data in chunks; by default the data
     is read in chunks to avoid uncontrolled memory consumption.  Note
     that if the current file position of the `fsrc' object is not 0,
     only the contents from the current file position to the end of the
     file will be copied.

 -- Function: shutil.copyfile (src, dst, *, follow_symlinks=True)

     Copy the contents (no metadata) of the file named `src' to a file
     named `dst' and return `dst' in the most efficient way possible.
     `src' and `dst' are path-like objects or path names given as
     strings.

     `dst' must be the complete target file name; look at *note copy():
     383. for a copy that accepts a target directory path.  If `src' and
     `dst' specify the same file, *note SameFileError: 99a. is raised.

     The destination location must be writable; otherwise, an *note
     OSError: 304. exception will be raised.  If `dst' already exists,
     it will be replaced.  Special files such as character or block
     devices and pipes cannot be copied with this function.

     If `follow_symlinks' is false and `src' is a symbolic link, a new
     symbolic link will be created instead of copying the file `src'
     points to.

     Raises an *note auditing event: fa1. ‘shutil.copyfile’ with
     arguments ‘src’, ‘dst’.

     Changed in version 3.3: *note IOError: a73. used to be raised
     instead of *note OSError: 304.  Added `follow_symlinks' argument.
     Now returns `dst'.

     Changed in version 3.4: Raise *note SameFileError: 99a. instead of
     *note Error: 999.  Since the former is a subclass of the latter,
     this change is backward compatible.

     Changed in version 3.8: Platform-specific fast-copy syscalls may be
     used internally in order to copy the file more efficiently.  See
     *note Platform-dependent efficient copy operations: 388. section.

 -- Exception: shutil.SameFileError

     This exception is raised if source and destination in *note
     copyfile(): 382. are the same file.

     New in version 3.4.

 -- Function: shutil.copymode (src, dst, *, follow_symlinks=True)

     Copy the permission bits from `src' to `dst'.  The file contents,
     owner, and group are unaffected.  `src' and `dst' are path-like
     objects or path names given as strings.  If `follow_symlinks' is
     false, and both `src' and `dst' are symbolic links, *note
     copymode(): 1de4. will attempt to modify the mode of `dst' itself
     (rather than the file it points to).  This functionality is not
     available on every platform; please see *note copystat(): b52. for
     more information.  If *note copymode(): 1de4. cannot modify
     symbolic links on the local platform, and it is asked to do so, it
     will do nothing and return.

     Raises an *note auditing event: fa1. ‘shutil.copymode’ with
     arguments ‘src’, ‘dst’.

     Changed in version 3.3: Added `follow_symlinks' argument.

 -- Function: shutil.copystat (src, dst, *, follow_symlinks=True)

     Copy the permission bits, last access time, last modification time,
     and flags from `src' to `dst'.  On Linux, *note copystat(): b52.
     also copies the “extended attributes” where possible.  The file
     contents, owner, and group are unaffected.  `src' and `dst' are
     path-like objects or path names given as strings.

     If `follow_symlinks' is false, and `src' and `dst' both refer to
     symbolic links, *note copystat(): b52. will operate on the symbolic
     links themselves rather than the files the symbolic links refer
     to—reading the information from the `src' symbolic link, and
     writing the information to the `dst' symbolic link.

          Note: Not all platforms provide the ability to examine and
          modify symbolic links.  Python itself can tell you what
          functionality is locally available.

             * If ‘os.chmod in os.supports_follow_symlinks’ is ‘True’,
               *note copystat(): b52. can modify the permission bits of
               a symbolic link.

             * If ‘os.utime in os.supports_follow_symlinks’ is ‘True’,
               *note copystat(): b52. can modify the last access and
               modification times of a symbolic link.

             * If ‘os.chflags in os.supports_follow_symlinks’ is ‘True’,
               *note copystat(): b52. can modify the flags of a symbolic
               link.  (‘os.chflags’ is not available on all platforms.)

          On platforms where some or all of this functionality is
          unavailable, when asked to modify a symbolic link, *note
          copystat(): b52. will copy everything it can.  *note
          copystat(): b52. never returns failure.

          Please see *note os.supports_follow_symlinks: 1de5. for more
          information.

     Raises an *note auditing event: fa1. ‘shutil.copystat’ with
     arguments ‘src’, ‘dst’.

     Changed in version 3.3: Added `follow_symlinks' argument and
     support for Linux extended attributes.

 -- Function: shutil.copy (src, dst, *, follow_symlinks=True)

     Copies the file `src' to the file or directory `dst'.  `src' and
     `dst' should be *note path-like objects: 472. or strings.  If `dst'
     specifies a directory, the file will be copied into `dst' using the
     base filename from `src'.  Returns the path to the newly created
     file.

     If `follow_symlinks' is false, and `src' is a symbolic link, `dst'
     will be created as a symbolic link.  If `follow_symlinks' is true
     and `src' is a symbolic link, `dst' will be a copy of the file
     `src' refers to.

     *note copy(): 383. copies the file data and the file’s permission
     mode (see *note os.chmod(): b0f.).  Other metadata, like the file’s
     creation and modification times, is not preserved.  To preserve all
     file metadata from the original, use *note copy2(): 384. instead.

     Raises an *note auditing event: fa1. ‘shutil.copyfile’ with
     arguments ‘src’, ‘dst’.

     Raises an *note auditing event: fa1. ‘shutil.copymode’ with
     arguments ‘src’, ‘dst’.

     Changed in version 3.3: Added `follow_symlinks' argument.  Now
     returns path to the newly created file.

     Changed in version 3.8: Platform-specific fast-copy syscalls may be
     used internally in order to copy the file more efficiently.  See
     *note Platform-dependent efficient copy operations: 388. section.

 -- Function: shutil.copy2 (src, dst, *, follow_symlinks=True)

     Identical to *note copy(): 383. except that *note copy2(): 384.
     also attempts to preserve file metadata.

     When `follow_symlinks' is false, and `src' is a symbolic link,
     *note copy2(): 384. attempts to copy all metadata from the `src'
     symbolic link to the newly-created `dst' symbolic link.  However,
     this functionality is not available on all platforms.  On platforms
     where some or all of this functionality is unavailable, *note
     copy2(): 384. will preserve all the metadata it can; *note copy2():
     384. never raises an exception because it cannot preserve file
     metadata.

     *note copy2(): 384. uses *note copystat(): b52. to copy the file
     metadata.  Please see *note copystat(): b52. for more information
     about platform support for modifying symbolic link metadata.

     Raises an *note auditing event: fa1. ‘shutil.copyfile’ with
     arguments ‘src’, ‘dst’.

     Raises an *note auditing event: fa1. ‘shutil.copystat’ with
     arguments ‘src’, ‘dst’.

     Changed in version 3.3: Added `follow_symlinks' argument, try to
     copy extended file system attributes too (currently Linux only).
     Now returns path to the newly created file.

     Changed in version 3.8: Platform-specific fast-copy syscalls may be
     used internally in order to copy the file more efficiently.  See
     *note Platform-dependent efficient copy operations: 388. section.

 -- Function: shutil.ignore_patterns (*patterns)

     This factory function creates a function that can be used as a
     callable for *note copytree(): 347.’s `ignore' argument, ignoring
     files and directories that match one of the glob-style `patterns'
     provided.  See the example below.

 -- Function: shutil.copytree (src, dst, symlinks=False, ignore=None,
          copy_function=copy2, ignore_dangling_symlinks=False,
          dirs_exist_ok=False)

     Recursively copy an entire directory tree rooted at `src' to a
     directory named `dst' and return the destination directory.
     `dirs_exist_ok' dictates whether to raise an exception in case
     `dst' or any missing parent directory already exists.

     Permissions and times of directories are copied with *note
     copystat(): b52, individual files are copied using *note copy2():
     384.

     If `symlinks' is true, symbolic links in the source tree are
     represented as symbolic links in the new tree and the metadata of
     the original links will be copied as far as the platform allows; if
     false or omitted, the contents and metadata of the linked files are
     copied to the new tree.

     When `symlinks' is false, if the file pointed by the symlink
     doesn’t exist, an exception will be added in the list of errors
     raised in an *note Error: 999. exception at the end of the copy
     process.  You can set the optional `ignore_dangling_symlinks' flag
     to true if you want to silence this exception.  Notice that this
     option has no effect on platforms that don’t support *note
     os.symlink(): b17.

     If `ignore' is given, it must be a callable that will receive as
     its arguments the directory being visited by *note copytree(): 347,
     and a list of its contents, as returned by *note os.listdir(): b1c.
     Since *note copytree(): 347. is called recursively, the `ignore'
     callable will be called once for each directory that is copied.
     The callable must return a sequence of directory and file names
     relative to the current directory (i.e.  a subset of the items in
     its second argument); these names will then be ignored in the copy
     process.  *note ignore_patterns(): 1de6. can be used to create such
     a callable that ignores names based on glob-style patterns.

     If exception(s) occur, an *note Error: 999. is raised with a list
     of reasons.

     If `copy_function' is given, it must be a callable that will be
     used to copy each file.  It will be called with the source path and
     the destination path as arguments.  By default, *note copy2(): 384.
     is used, but any function that supports the same signature (like
     *note copy(): 383.) can be used.

     Raises an *note auditing event: fa1. ‘shutil.copytree’ with
     arguments ‘src’, ‘dst’.

     Changed in version 3.3: Copy metadata when `symlinks' is false.
     Now returns `dst'.

     Changed in version 3.2: Added the `copy_function' argument to be
     able to provide a custom copy function.  Added the
     `ignore_dangling_symlinks' argument to silent dangling symlinks
     errors when `symlinks' is false.

     Changed in version 3.8: Platform-specific fast-copy syscalls may be
     used internally in order to copy the file more efficiently.  See
     *note Platform-dependent efficient copy operations: 388. section.

     New in version 3.8: The `dirs_exist_ok' parameter.

 -- Function: shutil.rmtree (path, ignore_errors=False, onerror=None)

     Delete an entire directory tree; `path' must point to a directory
     (but not a symbolic link to a directory).  If `ignore_errors' is
     true, errors resulting from failed removals will be ignored; if
     false or omitted, such errors are handled by calling a handler
     specified by `onerror' or, if that is omitted, they raise an
     exception.

          Note: On platforms that support the necessary fd-based
          functions a symlink attack resistant version of *note
          rmtree(): 349. is used by default.  On other platforms, the
          *note rmtree(): 349. implementation is susceptible to a
          symlink attack: given proper timing and circumstances,
          attackers can manipulate symlinks on the filesystem to delete
          files they wouldn’t be able to access otherwise.  Applications
          can use the *note rmtree.avoids_symlink_attacks: 1de7.
          function attribute to determine which case applies.

     If `onerror' is provided, it must be a callable that accepts three
     parameters: `function', `path', and `excinfo'.

     The first parameter, `function', is the function which raised the
     exception; it depends on the platform and implementation.  The
     second parameter, `path', will be the path name passed to
     `function'.  The third parameter, `excinfo', will be the exception
     information returned by *note sys.exc_info(): d27.  Exceptions
     raised by `onerror' will not be caught.

     Raises an *note auditing event: fa1. ‘shutil.rmtree’ with argument
     ‘path’.

     Changed in version 3.3: Added a symlink attack resistant version
     that is used automatically if platform supports fd-based functions.

     Changed in version 3.8: On Windows, will no longer delete the
     contents of a directory junction before removing the junction.

      -- Attribute: rmtree.avoids_symlink_attacks

          Indicates whether the current platform and implementation
          provides a symlink attack resistant version of *note rmtree():
          349.  Currently this is only true for platforms supporting
          fd-based directory access functions.

          New in version 3.3.

 -- Function: shutil.move (src, dst, copy_function=copy2)

     Recursively move a file or directory (`src') to another location
     (`dst') and return the destination.

     If the destination is an existing directory, then `src' is moved
     inside that directory.  If the destination already exists but is
     not a directory, it may be overwritten depending on *note
     os.rename(): b14. semantics.

     If the destination is on the current filesystem, then *note
     os.rename(): b14. is used.  Otherwise, `src' is copied to `dst'
     using `copy_function' and then removed.  In case of symlinks, a new
     symlink pointing to the target of `src' will be created in or as
     `dst' and `src' will be removed.

     If `copy_function' is given, it must be a callable that takes two
     arguments `src' and `dst', and will be used to copy `src' to `dst'
     if *note os.rename(): b14. cannot be used.  If the source is a
     directory, *note copytree(): 347. is called, passing it the
     ‘copy_function()’.  The default `copy_function' is *note copy2():
     384.  Using *note copy(): 383. as the `copy_function' allows the
     move to succeed when it is not possible to also copy the metadata,
     at the expense of not copying any of the metadata.

     Raises an *note auditing event: fa1. ‘shutil.move’ with arguments
     ‘src’, ‘dst’.

     Changed in version 3.3: Added explicit symlink handling for foreign
     filesystems, thus adapting it to the behavior of GNU’s ‘mv’.  Now
     returns `dst'.

     Changed in version 3.5: Added the `copy_function' keyword argument.

     Changed in version 3.8: Platform-specific fast-copy syscalls may be
     used internally in order to copy the file more efficiently.  See
     *note Platform-dependent efficient copy operations: 388. section.

     Changed in version 3.9: Accepts a *note path-like object: 472. for
     both `src' and `dst'.

 -- Function: shutil.disk_usage (path)

     Return disk usage statistics about the given path as a *note named
     tuple: b7b. with the attributes `total', `used' and `free', which
     are the amount of total, used and free space, in bytes.  `path' may
     be a file or a directory.

     New in version 3.3.

     Changed in version 3.8: On Windows, `path' can now be a file or
     directory.

     *note Availability: 1491.: Unix, Windows.

 -- Function: shutil.chown (path, user=None, group=None)

     Change owner `user' and/or `group' of the given `path'.

     `user' can be a system user name or a uid; the same applies to
     `group'.  At least one argument is required.

     See also *note os.chown(): b10, the underlying function.

     Raises an *note auditing event: fa1. ‘shutil.chown’ with arguments
     ‘path’, ‘user’, ‘group’.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: shutil.which (cmd, mode=os.F_OK | os.X_OK, path=None)

     Return the path to an executable which would be run if the given
     `cmd' was called.  If no `cmd' would be called, return ‘None’.

     `mode' is a permission mask passed to *note os.access(): b0d, by
     default determining if the file exists and executable.

     When no `path' is specified, the results of *note os.environ():
     c09. are used, returning either the “PATH” value or a fallback of
     *note os.defpath: 111a.

     On Windows, the current directory is always prepended to the `path'
     whether or not you use the default or provide your own, which is
     the behavior the command shell uses when finding executables.
     Additionally, when finding the `cmd' in the `path', the ‘PATHEXT’
     environment variable is checked.  For example, if you call
     ‘shutil.which("python")’, *note which(): fe6. will search ‘PATHEXT’
     to know that it should look for ‘python.exe’ within the `path'
     directories.  For example, on Windows:

          >>> shutil.which("python")
          'C:\\Python33\\python.EXE'

     New in version 3.3.

     Changed in version 3.8: The *note bytes: 172. type is now accepted.
     If `cmd' type is *note bytes: 172, the result type is also *note
     bytes: 172.

 -- Exception: shutil.Error

     This exception collects exceptions that are raised during a
     multi-file operation.  For *note copytree(): 347, the exception
     argument is a list of 3-tuples (`srcname', `dstname', `exception').

* Menu:

* Platform-dependent efficient copy operations::
* copytree example::
* rmtree example::


File: python.info,  Node: Platform-dependent efficient copy operations,  Next: copytree example,  Up: Directory and files operations

5.11.10.2 Platform-dependent efficient copy operations
......................................................

Starting from Python 3.8, all functions involving a file copy (*note
copyfile(): 382, *note copy(): 383, *note copy2(): 384, *note
copytree(): 347, and *note move(): 385.) may use platform-specific
“fast-copy” syscalls in order to copy the file more efficiently (see
bpo-33671(1)).  “fast-copy” means that the copying operation occurs
within the kernel, avoiding the use of userspace buffers in Python as in
“‘outfd.write(infd.read())’”.

On macOS fcopyfile(2) is used to copy the file content (not metadata).

On Linux *note os.sendfile(): 461. is used.

On Windows *note shutil.copyfile(): 382. uses a bigger default buffer
size (1 MiB instead of 64 KiB) and a *note memoryview(): 386.-based
variant of *note shutil.copyfileobj(): 387. is used.

If the fast-copy operation fails and no data was written in the
destination file then shutil will silently fallback on using less
efficient *note copyfileobj(): 387. function internally.

Changed in version 3.8.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33671

   (2) http://www.manpagez.com/man/3/copyfile/


File: python.info,  Node: copytree example,  Next: rmtree example,  Prev: Platform-dependent efficient copy operations,  Up: Directory and files operations

5.11.10.3 copytree example
..........................

This example is the implementation of the *note copytree(): 347.
function, described above, with the docstring omitted.  It demonstrates
many of the other functions provided by this module.

     def copytree(src, dst, symlinks=False):
         names = os.listdir(src)
         os.makedirs(dst)
         errors = []
         for name in names:
             srcname = os.path.join(src, name)
             dstname = os.path.join(dst, name)
             try:
                 if symlinks and os.path.islink(srcname):
                     linkto = os.readlink(srcname)
                     os.symlink(linkto, dstname)
                 elif os.path.isdir(srcname):
                     copytree(srcname, dstname, symlinks)
                 else:
                     copy2(srcname, dstname)
                 # XXX What about devices, sockets etc.?
             except OSError as why:
                 errors.append((srcname, dstname, str(why)))
             # catch the Error from the recursive copytree so that we can
             # continue with other files
             except Error as err:
                 errors.extend(err.args[0])
         try:
             copystat(src, dst)
         except OSError as why:
             # can't copy file access times on Windows
             if why.winerror is None:
                 errors.extend((src, dst, str(why)))
         if errors:
             raise Error(errors)

Another example that uses the *note ignore_patterns(): 1de6. helper:

     from shutil import copytree, ignore_patterns

     copytree(source, destination, ignore=ignore_patterns('*.pyc', 'tmp*'))

This will copy everything except ‘.pyc’ files and files or directories
whose name starts with ‘tmp’.

Another example that uses the `ignore' argument to add a logging call:

     from shutil import copytree
     import logging

     def _logpath(path, names):
         logging.info('Working in %s', path)
         return []   # nothing will be ignored

     copytree(source, destination, ignore=_logpath)


File: python.info,  Node: rmtree example,  Prev: copytree example,  Up: Directory and files operations

5.11.10.4 rmtree example
........................

This example shows how to remove a directory tree on Windows where some
of the files have their read-only bit set.  It uses the onerror callback
to clear the readonly bit and reattempt the remove.  Any subsequent
failure will propagate.

     import os, stat
     import shutil

     def remove_readonly(func, path, _):
         "Clear the readonly bit and reattempt the removal"
         os.chmod(path, stat.S_IWRITE)
         func(path)

     shutil.rmtree(directory, onerror=remove_readonly)


File: python.info,  Node: Archiving operations,  Next: Querying the size of the output terminal,  Prev: Directory and files operations,  Up: shutil — High-level file operations

5.11.10.5 Archiving operations
..............................

New in version 3.2.

Changed in version 3.5: Added support for the `xztar' format.

High-level utilities to create and read compressed and archived files
are also provided.  They rely on the *note zipfile: 14b. and *note
tarfile: 101. modules.

 -- Function: shutil.make_archive (base_name, format[, root_dir[,
          base_dir[, verbose[, dry_run[, owner[, group[, logger]]]]]]])

     Create an archive file (such as zip or tar) and return its name.

     `base_name' is the name of the file to create, including the path,
     minus any format-specific extension.  `format' is the archive
     format: one of “zip” (if the *note zlib: 14d. module is available),
     “tar”, “gztar” (if the *note zlib: 14d. module is available),
     “bztar” (if the *note bz2: 13. module is available), or “xztar” (if
     the *note lzma: ad. module is available).

     `root_dir' is a directory that will be the root directory of the
     archive, all paths in the archive will be relative to it; for
     example, we typically chdir into `root_dir' before creating the
     archive.

     `base_dir' is the directory where we start archiving from; i.e.
     `base_dir' will be the common prefix of all files and directories
     in the archive.  `base_dir' must be given relative to `root_dir'.
     See *note Archiving example with base_dir: 1dee. for how to use
     `base_dir' and `root_dir' together.

     `root_dir' and `base_dir' both default to the current directory.

     If `dry_run' is true, no archive is created, but the operations
     that would be executed are logged to `logger'.

     `owner' and `group' are used when creating a tar archive.  By
     default, uses the current owner and group.

     `logger' must be an object compatible with PEP 282(1), usually an
     instance of *note logging.Logger: 4ae.

     The `verbose' argument is unused and deprecated.

     Raises an *note auditing event: fa1. ‘shutil.make_archive’ with
     arguments ‘base_name’, ‘format’, ‘root_dir’, ‘base_dir’.

          Note: This function is not thread-safe.

     Changed in version 3.8: The modern pax (POSIX.1-2001) format is now
     used instead of the legacy GNU format for archives created with
     ‘format="tar"’.

 -- Function: shutil.get_archive_formats ()

     Return a list of supported formats for archiving.  Each element of
     the returned sequence is a tuple ‘(name, description)’.

     By default *note shutil: e9. provides these formats:

        - `zip': ZIP file (if the *note zlib: 14d. module is available).

        - `tar': Uncompressed tar file.  Uses POSIX.1-2001 pax format
          for new archives.

        - `gztar': gzip’ed tar-file (if the *note zlib: 14d. module is
          available).

        - `bztar': bzip2’ed tar-file (if the *note bz2: 13. module is
          available).

        - `xztar': xz’ed tar-file (if the *note lzma: ad. module is
          available).

     You can register new formats or provide your own archiver for any
     existing formats, by using *note register_archive_format(): 1df0.

 -- Function: shutil.register_archive_format (name, function[,
          extra_args[, description]])

     Register an archiver for the format `name'.

     `function' is the callable that will be used to unpack archives.
     The callable will receive the `base_name' of the file to create,
     followed by the `base_dir' (which defaults to *note os.curdir:
     1d4f.) to start archiving from.  Further arguments are passed as
     keyword arguments: `owner', `group', `dry_run' and `logger' (as
     passed in *note make_archive(): 348.).

     If given, `extra_args' is a sequence of ‘(name, value)’ pairs that
     will be used as extra keywords arguments when the archiver callable
     is used.

     `description' is used by *note get_archive_formats(): 1def. which
     returns the list of archivers.  Defaults to an empty string.

 -- Function: shutil.unregister_archive_format (name)

     Remove the archive format `name' from the list of supported
     formats.

 -- Function: shutil.unpack_archive (filename[, extract_dir[, format]])

     Unpack an archive.  `filename' is the full path of the archive.

     `extract_dir' is the name of the target directory where the archive
     is unpacked.  If not provided, the current working directory is
     used.

     `format' is the archive format: one of “zip”, “tar”, “gztar”,
     “bztar”, or “xztar”.  Or any other format registered with *note
     register_unpack_format(): 1df2.  If not provided, *note
     unpack_archive(): c68. will use the archive file name extension and
     see if an unpacker was registered for that extension.  In case none
     is found, a *note ValueError: 16d. is raised.

     Raises an *note auditing event: fa1. ‘shutil.unpack_archive’ with
     arguments ‘filename’, ‘extract_dir’, ‘format’.

     Changed in version 3.7: Accepts a *note path-like object: 472. for
     `filename' and `extract_dir'.

 -- Function: shutil.register_unpack_format (name, extensions,
          function[, extra_args[, description]])

     Registers an unpack format.  `name' is the name of the format and
     `extensions' is a list of extensions corresponding to the format,
     like ‘.zip’ for Zip files.

     `function' is the callable that will be used to unpack archives.
     The callable will receive the path of the archive, followed by the
     directory the archive must be extracted to.

     When provided, `extra_args' is a sequence of ‘(name, value)’ tuples
     that will be passed as keywords arguments to the callable.

     `description' can be provided to describe the format, and will be
     returned by the *note get_unpack_formats(): 1df3. function.

 -- Function: shutil.unregister_unpack_format (name)

     Unregister an unpack format.  `name' is the name of the format.

 -- Function: shutil.get_unpack_formats ()

     Return a list of all registered formats for unpacking.  Each
     element of the returned sequence is a tuple ‘(name, extensions,
     description)’.

     By default *note shutil: e9. provides these formats:

        - `zip': ZIP file (unpacking compressed files works only if the
          corresponding module is available).

        - `tar': uncompressed tar file.

        - `gztar': gzip’ed tar-file (if the *note zlib: 14d. module is
          available).

        - `bztar': bzip2’ed tar-file (if the *note bz2: 13. module is
          available).

        - `xztar': xz’ed tar-file (if the *note lzma: ad. module is
          available).

     You can register new formats or provide your own unpacker for any
     existing formats, by using *note register_unpack_format(): 1df2.

* Menu:

* Archiving example::
* Archiving example with base_dir::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0282


File: python.info,  Node: Archiving example,  Next: Archiving example with base_dir,  Up: Archiving operations

5.11.10.6 Archiving example
...........................

In this example, we create a gzip’ed tar-file archive containing all
files found in the ‘.ssh’ directory of the user:

     >>> from shutil import make_archive
     >>> import os
     >>> archive_name = os.path.expanduser(os.path.join('~', 'myarchive'))
     >>> root_dir = os.path.expanduser(os.path.join('~', '.ssh'))
     >>> make_archive(archive_name, 'gztar', root_dir)
     '/Users/tarek/myarchive.tar.gz'

The resulting archive contains:

     $ tar -tzvf /Users/tarek/myarchive.tar.gz
     drwx------ tarek/staff       0 2010-02-01 16:23:40 ./
     -rw-r--r-- tarek/staff     609 2008-06-09 13:26:54 ./authorized_keys
     -rwxr-xr-x tarek/staff      65 2008-06-09 13:26:54 ./config
     -rwx------ tarek/staff     668 2008-06-09 13:26:54 ./id_dsa
     -rwxr-xr-x tarek/staff     609 2008-06-09 13:26:54 ./id_dsa.pub
     -rw------- tarek/staff    1675 2008-06-09 13:26:54 ./id_rsa
     -rw-r--r-- tarek/staff     397 2008-06-09 13:26:54 ./id_rsa.pub
     -rw-r--r-- tarek/staff   37192 2010-02-06 18:23:10 ./known_hosts


File: python.info,  Node: Archiving example with base_dir,  Prev: Archiving example,  Up: Archiving operations

5.11.10.7 Archiving example with `base_dir'
...........................................

In this example, similar to the *note one above: 1df6, we show how to
use *note make_archive(): 348, but this time with the usage of
`base_dir'.  We now have the following directory structure:

     $ tree tmp
     tmp
     └── root
         └── structure
             ├── content
                 └── please_add.txt
             └── do_not_add.txt

In the final archive, ‘please_add.txt’ should be included, but
‘do_not_add.txt’ should not.  Therefore we use the following:

     >>> from shutil import make_archive
     >>> import os
     >>> archive_name = os.path.expanduser(os.path.join('~', 'myarchive'))
     >>> make_archive(
     ...     archive_name,
     ...     'tar',
     ...     root_dir='tmp/root',
     ...     base_dir='structure/content',
     ... )
     '/Users/tarek/my_archive.tar'

Listing the files in the resulting archive gives us:

     $ python -m tarfile -l /Users/tarek/myarchive.tar
     structure/content/
     structure/content/please_add.txt


File: python.info,  Node: Querying the size of the output terminal,  Prev: Archiving operations,  Up: shutil — High-level file operations

5.11.10.8 Querying the size of the output terminal
..................................................

 -- Function: shutil.get_terminal_size (fallback=(columns, lines))

     Get the size of the terminal window.

     For each of the two dimensions, the environment variable, ‘COLUMNS’
     and ‘LINES’ respectively, is checked.  If the variable is defined
     and the value is a positive integer, it is used.

     When ‘COLUMNS’ or ‘LINES’ is not defined, which is the common case,
     the terminal connected to *note sys.__stdout__: 1df9. is queried by
     invoking *note os.get_terminal_size(): b24.

     If the terminal size cannot be successfully queried, either because
     the system doesn’t support querying, or because we are not
     connected to a terminal, the value given in ‘fallback’ parameter is
     used.  ‘fallback’ defaults to ‘(80, 24)’ which is the default size
     used by many terminal emulators.

     The value returned is a named tuple of type *note os.terminal_size:
     1dfa.

     See also: The Single UNIX Specification, Version 2, Other
     Environment Variables(1).

     New in version 3.3.

See also
........

Module *note os: c4.

     Operating system interfaces, including functions to work with files
     at a lower level than Python *note file objects: c14.

Module *note io: a1.

     Python’s built-in I/O library, including both abstract classes and
     some concrete classes such as file I/O.

Built-in function *note open(): 16f.

     The standard way to open files for reading and writing with Python.

   ---------- Footnotes ----------

   (1) 
http://pubs.opengroup.org/onlinepubs/7908799/xbd/envvar.html#tag_002_003


File: python.info,  Node: Data Persistence,  Next: Data Compression and Archiving,  Prev: File and Directory Access,  Up: The Python Standard Library

5.12 Data Persistence
=====================

The modules described in this chapter support storing Python data in a
persistent form on disk.  The *note pickle: ca. and *note marshal: b0.
modules can turn many Python data types into a stream of bytes and then
recreate the objects from the bytes.  The various DBM-related modules
support a family of hash-based file formats that store a mapping of
strings to other strings.

The list of modules described in this chapter is:

* Menu:

* pickle — Python object serialization::
* copyreg — Register pickle support functions::
* shelve — Python object persistence::
* marshal — Internal Python object serialization::
* dbm — Interfaces to Unix “databases”::
* sqlite3 — DB-API 2.0 interface for SQLite databases: sqlite3 — DB-API 2 0 interface for SQLite databases.


File: python.info,  Node: pickle — Python object serialization,  Next: copyreg — Register pickle support functions,  Up: Data Persistence

5.12.1 ‘pickle’ — Python object serialization
---------------------------------------------

`Source code:' Lib/pickle.py(1)

__________________________________________________________________

The *note pickle: ca. module implements binary protocols for serializing
and de-serializing a Python object structure.  `“Pickling”' is the
process whereby a Python object hierarchy is converted into a byte
stream, and `“unpickling”' is the inverse operation, whereby a byte
stream (from a *note binary file: 1e01. or *note bytes-like object:
6df.) is converted back into an object hierarchy.  Pickling (and
unpickling) is alternatively known as “serialization”, “marshalling,”
(2) or “flattening”; however, to avoid confusion, the terms used here
are “pickling” and “unpickling”.

     Warning: The ‘pickle’ module `is not secure'.  Only unpickle data
     you trust.

     It is possible to construct malicious pickle data which will
     `execute arbitrary code during unpickling'.  Never unpickle data
     that could have come from an untrusted source, or that could have
     been tampered with.

     Consider signing data with *note hmac: 8e. if you need to ensure
     that it has not been tampered with.

     Safer serialization formats such as *note json: a4. may be more
     appropriate if you are processing untrusted data.  See *note
     Comparison with json: 1e02.

* Menu:

* Relationship to other Python modules::
* Data stream format::
* Module Interface::
* What can be pickled and unpickled?::
* Pickling Class Instances::
* Custom Reduction for Types, Functions, and Other Objects: Custom Reduction for Types Functions and Other Objects.
* Out-of-band Buffers::
* Restricting Globals::
* Performance: Performance<2>.
* Examples: Examples<5>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/pickle.py

   (2) (1) Don’t confuse this with the *note marshal: b0. module


File: python.info,  Node: Relationship to other Python modules,  Next: Data stream format,  Up: pickle — Python object serialization

5.12.1.1 Relationship to other Python modules
.............................................

* Menu:

* Comparison with marshal::
* Comparison with json::


File: python.info,  Node: Comparison with marshal,  Next: Comparison with json,  Up: Relationship to other Python modules

5.12.1.2 Comparison with ‘marshal’
..................................

Python has a more primitive serialization module called *note marshal:
b0, but in general *note pickle: ca. should always be the preferred way
to serialize Python objects.  *note marshal: b0. exists primarily to
support Python’s ‘.pyc’ files.

The *note pickle: ca. module differs from *note marshal: b0. in several
significant ways:

   * The *note pickle: ca. module keeps track of the objects it has
     already serialized, so that later references to the same object
     won’t be serialized again.  *note marshal: b0. doesn’t do this.

     This has implications both for recursive objects and object
     sharing.  Recursive objects are objects that contain references to
     themselves.  These are not handled by marshal, and in fact,
     attempting to marshal recursive objects will crash your Python
     interpreter.  Object sharing happens when there are multiple
     references to the same object in different places in the object
     hierarchy being serialized.  *note pickle: ca. stores such objects
     only once, and ensures that all other references point to the
     master copy.  Shared objects remain shared, which can be very
     important for mutable objects.

   * *note marshal: b0. cannot be used to serialize user-defined classes
     and their instances.  *note pickle: ca. can save and restore class
     instances transparently, however the class definition must be
     importable and live in the same module as when the object was
     stored.

   * The *note marshal: b0. serialization format is not guaranteed to be
     portable across Python versions.  Because its primary job in life
     is to support ‘.pyc’ files, the Python implementers reserve the
     right to change the serialization format in non-backwards
     compatible ways should the need arise.  The *note pickle: ca.
     serialization format is guaranteed to be backwards compatible
     across Python releases provided a compatible pickle protocol is
     chosen and pickling and unpickling code deals with Python 2 to
     Python 3 type differences if your data is crossing that unique
     breaking change language boundary.


File: python.info,  Node: Comparison with json,  Prev: Comparison with marshal,  Up: Relationship to other Python modules

5.12.1.3 Comparison with ‘json’
...............................

There are fundamental differences between the pickle protocols and JSON
(JavaScript Object Notation)(1):

   * JSON is a text serialization format (it outputs unicode text,
     although most of the time it is then encoded to ‘utf-8’), while
     pickle is a binary serialization format;

   * JSON is human-readable, while pickle is not;

   * JSON is interoperable and widely used outside of the Python
     ecosystem, while pickle is Python-specific;

   * JSON, by default, can only represent a subset of the Python
     built-in types, and no custom classes; pickle can represent an
     extremely large number of Python types (many of them automatically,
     by clever usage of Python’s introspection facilities; complex cases
     can be tackled by implementing *note specific object APIs: 1e06.);

   * Unlike pickle, deserializing untrusted JSON does not in itself
     create an arbitrary code execution vulnerability.

See also
........

The *note json: a4. module: a standard library module allowing JSON
serialization and deserialization.

   ---------- Footnotes ----------

   (1) http://json.org


File: python.info,  Node: Data stream format,  Next: Module Interface,  Prev: Relationship to other Python modules,  Up: pickle — Python object serialization

5.12.1.4 Data stream format
...........................

The data format used by *note pickle: ca. is Python-specific.  This has
the advantage that there are no restrictions imposed by external
standards such as JSON or XDR (which can’t represent pointer sharing);
however it means that non-Python programs may not be able to reconstruct
pickled Python objects.

By default, the *note pickle: ca. data format uses a relatively compact
binary representation.  If you need optimal size characteristics, you
can efficiently *note compress: 1e08. pickled data.

The module *note pickletools: cb. contains tools for analyzing data
streams generated by *note pickle: ca.  *note pickletools: cb. source
code has extensive comments about opcodes used by pickle protocols.

There are currently 6 different protocols which can be used for
pickling.  The higher the protocol used, the more recent the version of
Python needed to read the pickle produced.

   * Protocol version 0 is the original “human-readable” protocol and is
     backwards compatible with earlier versions of Python.

   * Protocol version 1 is an old binary format which is also compatible
     with earlier versions of Python.

   * Protocol version 2 was introduced in Python 2.3.  It provides much
     more efficient pickling of *note new-style class: 1e09.es.  Refer
     to PEP 307(1) for information about improvements brought by
     protocol 2.

   * Protocol version 3 was added in Python 3.0.  It has explicit
     support for *note bytes: 172. objects and cannot be unpickled by
     Python 2.x.  This was the default protocol in Python 3.0–3.7.

   * Protocol version 4 was added in Python 3.4.  It adds support for
     very large objects, pickling more kinds of objects, and some data
     format optimizations.  It is the default protocol starting with
     Python 3.8.  Refer to PEP 3154(2) for information about
     improvements brought by protocol 4.

   * Protocol version 5 was added in Python 3.8.  It adds support for
     out-of-band data and speedup for in-band data.  Refer to PEP 574(3)
     for information about improvements brought by protocol 5.

     Note: Serialization is a more primitive notion than persistence;
     although *note pickle: ca. reads and writes file objects, it does
     not handle the issue of naming persistent objects, nor the (even
     more complicated) issue of concurrent access to persistent objects.
     The *note pickle: ca. module can transform a complex object into a
     byte stream and it can transform the byte stream into an object
     with the same internal structure.  Perhaps the most obvious thing
     to do with these byte streams is to write them onto a file, but it
     is also conceivable to send them across a network or store them in
     a database.  The *note shelve: e7. module provides a simple
     interface to pickle and unpickle objects on DBM-style database
     files.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0307

   (2) https://www.python.org/dev/peps/pep-3154

   (3) https://www.python.org/dev/peps/pep-0574


File: python.info,  Node: Module Interface,  Next: What can be pickled and unpickled?,  Prev: Data stream format,  Up: pickle — Python object serialization

5.12.1.5 Module Interface
.........................

To serialize an object hierarchy, you simply call the *note dumps():
ec3. function.  Similarly, to de-serialize a data stream, you call the
*note loads(): 6ba. function.  However, if you want more control over
serialization and de-serialization, you can create a *note Pickler: 33b.
or an *note Unpickler: 1e0b. object, respectively.

The *note pickle: ca. module provides the following constants:

 -- Data: pickle.HIGHEST_PROTOCOL

     An integer, the highest *note protocol version: 666. available.
     This value can be passed as a `protocol' value to functions *note
     dump(): 1e0c. and *note dumps(): ec3. as well as the *note Pickler:
     33b. constructor.

 -- Data: pickle.DEFAULT_PROTOCOL

     An integer, the default *note protocol version: 666. used for
     pickling.  May be less than *note HIGHEST_PROTOCOL: ec4.  Currently
     the default protocol is 4, first introduced in Python 3.4 and
     incompatible with previous versions.

     Changed in version 3.0: The default protocol is 3.

     Changed in version 3.8: The default protocol is 4.

The *note pickle: ca. module provides the following functions to make
the pickling process more convenient:

 -- Function: pickle.dump (obj, file, protocol=None, *,
          fix_imports=True, buffer_callback=None)

     Write the pickled representation of the object `obj' to the open
     *note file object: c14. `file'.  This is equivalent to
     ‘Pickler(file, protocol).dump(obj)’.

     Arguments `file', `protocol', `fix_imports' and `buffer_callback'
     have the same meaning as in the *note Pickler: 33b. constructor.

     Changed in version 3.8: The `buffer_callback' argument was added.

 -- Function: pickle.dumps (obj, protocol=None, *, fix_imports=True,
          buffer_callback=None)

     Return the pickled representation of the object `obj' as a *note
     bytes: 172. object, instead of writing it to a file.

     Arguments `protocol', `fix_imports' and `buffer_callback' have the
     same meaning as in the *note Pickler: 33b. constructor.

     Changed in version 3.8: The `buffer_callback' argument was added.

 -- Function: pickle.load (file, *, fix_imports=True, encoding="ASCII",
          errors="strict", buffers=None)

     Read the pickled representation of an object from the open *note
     file object: c14. `file' and return the reconstituted object
     hierarchy specified therein.  This is equivalent to
     ‘Unpickler(file).load()’.

     The protocol version of the pickle is detected automatically, so no
     protocol argument is needed.  Bytes past the pickled representation
     of the object are ignored.

     Arguments `file', `fix_imports', `encoding', `errors', `strict' and
     `buffers' have the same meaning as in the *note Unpickler: 1e0b.
     constructor.

     Changed in version 3.8: The `buffers' argument was added.

 -- Function: pickle.loads (data, /, *, fix_imports=True,
          encoding="ASCII", errors="strict", buffers=None)

     Return the reconstituted object hierarchy of the pickled
     representation `data' of an object.  `data' must be a *note
     bytes-like object: 6df.

     The protocol version of the pickle is detected automatically, so no
     protocol argument is needed.  Bytes past the pickled representation
     of the object are ignored.

     Arguments `file', `fix_imports', `encoding', `errors', `strict' and
     `buffers' have the same meaning as in the *note Unpickler: 1e0b.
     constructor.

     Changed in version 3.8: The `buffers' argument was added.

The *note pickle: ca. module defines three exceptions:

 -- Exception: pickle.PickleError

     Common base class for the other pickling exceptions.  It inherits
     *note Exception: 2dc.

 -- Exception: pickle.PicklingError

     Error raised when an unpicklable object is encountered by *note
     Pickler: 33b.  It inherits *note PickleError: 1e0e.

     Refer to *note What can be pickled and unpickled?: 1e10. to learn
     what kinds of objects can be pickled.

 -- Exception: pickle.UnpicklingError

     Error raised when there is a problem unpickling an object, such as
     a data corruption or a security violation.  It inherits *note
     PickleError: 1e0e.

     Note that other exceptions may also be raised during unpickling,
     including (but not necessarily limited to) AttributeError,
     EOFError, ImportError, and IndexError.

The *note pickle: ca. module exports three classes, *note Pickler: 33b,
*note Unpickler: 1e0b. and *note PickleBuffer: 1e12.:

 -- Class: pickle.Pickler (file, protocol=None, *, fix_imports=True,
          buffer_callback=None)

     This takes a binary file for writing a pickle data stream.

     The optional `protocol' argument, an integer, tells the pickler to
     use the given protocol; supported protocols are 0 to *note
     HIGHEST_PROTOCOL: ec4.  If not specified, the default is *note
     DEFAULT_PROTOCOL: 1e0d.  If a negative number is specified, *note
     HIGHEST_PROTOCOL: ec4. is selected.

     The `file' argument must have a write() method that accepts a
     single bytes argument.  It can thus be an on-disk file opened for
     binary writing, an *note io.BytesIO: 88a. instance, or any other
     custom object that meets this interface.

     If `fix_imports' is true and `protocol' is less than 3, pickle will
     try to map the new Python 3 names to the old module names used in
     Python 2, so that the pickle data stream is readable with Python 2.

     If `buffer_callback' is None (the default), buffer views are
     serialized into `file' as part of the pickle stream.

     If `buffer_callback' is not None, then it can be called any number
     of times with a buffer view.  If the callback returns a false value
     (such as None), the given buffer is *note out-of-band: 1e13.;
     otherwise the buffer is serialized in-band, i.e.  inside the pickle
     stream.

     It is an error if `buffer_callback' is not None and `protocol' is
     None or smaller than 5.

     Changed in version 3.8: The `buffer_callback' argument was added.

      -- Method: dump (obj)

          Write the pickled representation of `obj' to the open file
          object given in the constructor.

      -- Method: persistent_id (obj)

          Do nothing by default.  This exists so a subclass can override
          it.

          If *note persistent_id(): 1e14. returns ‘None’, `obj' is
          pickled as usual.  Any other value causes *note Pickler: 33b.
          to emit the returned value as a persistent ID for `obj'.  The
          meaning of this persistent ID should be defined by *note
          Unpickler.persistent_load(): 1e15.  Note that the value
          returned by *note persistent_id(): 1e14. cannot itself have a
          persistent ID.

          See *note Persistence of External Objects: 1e16. for details
          and examples of uses.

      -- Attribute: dispatch_table

          A pickler object’s dispatch table is a registry of `reduction
          functions' of the kind which can be declared using *note
          copyreg.pickle(): 1e17.  It is a mapping whose keys are
          classes and whose values are reduction functions.  A reduction
          function takes a single argument of the associated class and
          should conform to the same interface as a *note __reduce__():
          2d0. method.

          By default, a pickler object will not have a *note
          dispatch_table: b44. attribute, and it will instead use the
          global dispatch table managed by the *note copyreg: 26.
          module.  However, to customize the pickling for a specific
          pickler object one can set the *note dispatch_table: b44.
          attribute to a dict-like object.  Alternatively, if a subclass
          of *note Pickler: 33b. has a *note dispatch_table: b44.
          attribute then this will be used as the default dispatch table
          for instances of that class.

          See *note Dispatch Tables: 1e18. for usage examples.

          New in version 3.3.

      -- Method: reducer_override (self, obj)

          Special reducer that can be defined in *note Pickler: 33b.
          subclasses.  This method has priority over any reducer in the
          *note dispatch_table: b44.  It should conform to the same
          interface as a *note __reduce__(): 2d0. method, and can
          optionally return ‘NotImplemented’ to fallback on *note
          dispatch_table: b44.-registered reducers to pickle ‘obj’.

          For a detailed example, see *note Custom Reduction for Types,
          Functions, and Other Objects: 1e19.

          New in version 3.8.

      -- Attribute: fast

          Deprecated.  Enable fast mode if set to a true value.  The
          fast mode disables the usage of memo, therefore speeding the
          pickling process by not generating superfluous PUT opcodes.
          It should not be used with self-referential objects, doing
          otherwise will cause *note Pickler: 33b. to recurse
          infinitely.

          Use *note pickletools.optimize(): 1e1b. if you need more
          compact pickles.

 -- Class: pickle.Unpickler (file, *, fix_imports=True,
          encoding="ASCII", errors="strict", buffers=None)

     This takes a binary file for reading a pickle data stream.

     The protocol version of the pickle is detected automatically, so no
     protocol argument is needed.

     The argument `file' must have three methods, a read() method that
     takes an integer argument, a readinto() method that takes a buffer
     argument and a readline() method that requires no arguments, as in
     the *note io.BufferedIOBase: 67f. interface.  Thus `file' can be an
     on-disk file opened for binary reading, an *note io.BytesIO: 88a.
     object, or any other custom object that meets this interface.

     The optional arguments `fix_imports', `encoding' and `errors' are
     used to control compatibility support for pickle stream generated
     by Python 2.  If `fix_imports' is true, pickle will try to map the
     old Python 2 names to the new names used in Python 3.  The
     `encoding' and `errors' tell pickle how to decode 8-bit string
     instances pickled by Python 2; these default to ‘ASCII’ and
     ‘strict’, respectively.  The `encoding' can be ‘bytes’ to read
     these 8-bit string instances as bytes objects.  Using
     ‘encoding='latin1'’ is required for unpickling NumPy arrays and
     instances of *note datetime: 1a0, *note date: 19e. and *note time:
     5ed. pickled by Python 2.

     If `buffers' is None (the default), then all data necessary for
     deserialization must be contained in the pickle stream.  This means
     that the `buffer_callback' argument was None when a *note Pickler:
     33b. was instantiated (or when *note dump(): 1e0c. or *note
     dumps(): ec3. was called).

     If `buffers' is not None, it should be an iterable of
     buffer-enabled objects that is consumed each time the pickle stream
     references an *note out-of-band: 1e13. buffer view.  Such buffers
     have been given in order to the `buffer_callback' of a Pickler
     object.

     Changed in version 3.8: The `buffers' argument was added.

      -- Method: load ()

          Read the pickled representation of an object from the open
          file object given in the constructor, and return the
          reconstituted object hierarchy specified therein.  Bytes past
          the pickled representation of the object are ignored.

      -- Method: persistent_load (pid)

          Raise an *note UnpicklingError: 1e11. by default.

          If defined, *note persistent_load(): 1e15. should return the
          object specified by the persistent ID `pid'.  If an invalid
          persistent ID is encountered, an *note UnpicklingError: 1e11.
          should be raised.

          See *note Persistence of External Objects: 1e16. for details
          and examples of uses.

      -- Method: find_class (module, name)

          Import `module' if necessary and return the object called
          `name' from it, where the `module' and `name' arguments are
          *note str: 205. objects.  Note, unlike its name suggests,
          *note find_class(): 1e1d. is also used for finding functions.

          Subclasses may override this to gain control over what type of
          objects and how they can be loaded, potentially reducing
          security risks.  Refer to *note Restricting Globals: 1e1e. for
          details.

          Raises an *note auditing event: fa1. ‘pickle.find_class’ with
          arguments ‘module’, ‘name’.

 -- Class: pickle.PickleBuffer (buffer)

     A wrapper for a buffer representing picklable data.  `buffer' must
     be a *note buffer-providing: 171c. object, such as a *note
     bytes-like object: 6df. or a N-dimensional array.

     *note PickleBuffer: 1e12. is itself a buffer provider, therefore it
     is possible to pass it to other APIs expecting a buffer-providing
     object, such as *note memoryview: 386.

     *note PickleBuffer: 1e12. objects can only be serialized using
     pickle protocol 5 or higher.  They are eligible for *note
     out-of-band serialization: 1e13.

     New in version 3.8.

      -- Method: raw ()

          Return a *note memoryview: 386. of the memory area underlying
          this buffer.  The returned object is a one-dimensional,
          C-contiguous memoryview with format ‘B’ (unsigned bytes).
          *note BufferError: 1847. is raised if the buffer is neither C-
          nor Fortran-contiguous.

      -- Method: release ()

          Release the underlying buffer exposed by the PickleBuffer
          object.


File: python.info,  Node: What can be pickled and unpickled?,  Next: Pickling Class Instances,  Prev: Module Interface,  Up: pickle — Python object serialization

5.12.1.6 What can be pickled and unpickled?
...........................................

The following types can be pickled:

   * ‘None’, ‘True’, and ‘False’

   * integers, floating point numbers, complex numbers

   * strings, bytes, bytearrays

   * tuples, lists, sets, and dictionaries containing only picklable
     objects

   * functions defined at the top level of a module (using *note def:
     e83, not *note lambda: cf9.)

   * built-in functions defined at the top level of a module

   * classes that are defined at the top level of a module

   * instances of such classes whose *note __dict__: 5f6. or the result
     of calling *note __getstate__(): ec5. is picklable (see section
     *note Pickling Class Instances: 1e06. for details).

Attempts to pickle unpicklable objects will raise the *note
PicklingError: 1e0f. exception; when this happens, an unspecified number
of bytes may have already been written to the underlying file.  Trying
to pickle a highly recursive data structure may exceed the maximum
recursion depth, a *note RecursionError: 727. will be raised in this
case.  You can carefully raise this limit with *note
sys.setrecursionlimit(): f3c.

Note that functions (built-in and user-defined) are pickled by “fully
qualified” name reference, not by value.  (1) This means that only the
function name is pickled, along with the name of the module the function
is defined in.  Neither the function’s code, nor any of its function
attributes are pickled.  Thus the defining module must be importable in
the unpickling environment, and the module must contain the named
object, otherwise an exception will be raised.  (2)

Similarly, classes are pickled by named reference, so the same
restrictions in the unpickling environment apply.  Note that none of the
class’s code or data is pickled, so in the following example the class
attribute ‘attr’ is not restored in the unpickling environment:

     class Foo:
         attr = 'A class attribute'

     picklestring = pickle.dumps(Foo)

These restrictions are why picklable functions and classes must be
defined in the top level of a module.

Similarly, when class instances are pickled, their class’s code and data
are not pickled along with them.  Only the instance data are pickled.
This is done on purpose, so you can fix bugs in a class or add methods
to the class and still load objects that were created with an earlier
version of the class.  If you plan to have long-lived objects that will
see many versions of a class, it may be worthwhile to put a version
number in the objects so that suitable conversions can be made by the
class’s *note __setstate__(): 2d1. method.

   ---------- Footnotes ----------

   (1) (2) This is why *note lambda: cf9. functions cannot be pickled:
all ‘lambda’ functions share the same name: ‘<lambda>’.

   (2) (3) The exception raised will likely be an *note ImportError:
16c. or an *note AttributeError: 4a2. but it could be something else.


File: python.info,  Node: Pickling Class Instances,  Next: Custom Reduction for Types Functions and Other Objects,  Prev: What can be pickled and unpickled?,  Up: pickle — Python object serialization

5.12.1.7 Pickling Class Instances
.................................

In this section, we describe the general mechanisms available to you to
define, customize, and control how class instances are pickled and
unpickled.

In most cases, no additional code is needed to make instances picklable.
By default, pickle will retrieve the class and the attributes of an
instance via introspection.  When a class instance is unpickled, its
*note __init__(): e23. method is usually `not' invoked.  The default
behaviour first creates an uninitialized instance and then restores the
saved attributes.  The following code shows an implementation of this
behaviour:

     def save(obj):
         return (obj.__class__, obj.__dict__)

     def load(cls, attributes):
         obj = cls.__new__(cls)
         obj.__dict__.update(attributes)
         return obj

Classes can alter the default behaviour by providing one or several
special methods:

 -- Method: object.__getnewargs_ex__ ()

     In protocols 2 and newer, classes that implements the *note
     __getnewargs_ex__(): 1e23. method can dictate the values passed to
     the *note __new__(): 974. method upon unpickling.  The method must
     return a pair ‘(args, kwargs)’ where `args' is a tuple of
     positional arguments and `kwargs' a dictionary of named arguments
     for constructing the object.  Those will be passed to the *note
     __new__(): 974. method upon unpickling.

     You should implement this method if the *note __new__(): 974.
     method of your class requires keyword-only arguments.  Otherwise,
     it is recommended for compatibility to implement *note
     __getnewargs__(): 7a1.

     Changed in version 3.6: *note __getnewargs_ex__(): 1e23. is now
     used in protocols 2 and 3.

 -- Method: object.__getnewargs__ ()

     This method serves a similar purpose as *note __getnewargs_ex__():
     1e23, but supports only positional arguments.  It must return a
     tuple of arguments ‘args’ which will be passed to the *note
     __new__(): 974. method upon unpickling.

     *note __getnewargs__(): 7a1. will not be called if *note
     __getnewargs_ex__(): 1e23. is defined.

     Changed in version 3.6: Before Python 3.6, *note __getnewargs__():
     7a1. was called instead of *note __getnewargs_ex__(): 1e23. in
     protocols 2 and 3.

 -- Method: object.__getstate__ ()

     Classes can further influence how their instances are pickled; if
     the class defines the method *note __getstate__(): ec5, it is
     called and the returned object is pickled as the contents for the
     instance, instead of the contents of the instance’s dictionary.  If
     the *note __getstate__(): ec5. method is absent, the instance’s
     *note __dict__: 5f6. is pickled as usual.

 -- Method: object.__setstate__ (state)

     Upon unpickling, if the class defines *note __setstate__(): 2d1, it
     is called with the unpickled state.  In that case, there is no
     requirement for the state object to be a dictionary.  Otherwise,
     the pickled state must be a dictionary and its items are assigned
     to the new instance’s dictionary.

          Note: If *note __getstate__(): ec5. returns a false value, the
          *note __setstate__(): 2d1. method will not be called upon
          unpickling.

Refer to the section *note Handling Stateful Objects: 1e24. for more
information about how to use the methods *note __getstate__(): ec5. and
*note __setstate__(): 2d1.

     Note: At unpickling time, some methods like *note __getattr__():
     42a, *note __getattribute__(): 54c, or *note __setattr__(): eee.
     may be called upon the instance.  In case those methods rely on
     some internal invariant being true, the type should implement *note
     __new__(): 974. to establish such an invariant, as *note
     __init__(): e23. is not called when unpickling an instance.

As we shall see, pickle does not use directly the methods described
above.  In fact, these methods are part of the copy protocol which
implements the *note __reduce__(): 2d0. special method.  The copy
protocol provides a unified interface for retrieving the data necessary
for pickling and copying objects.  (1)

Although powerful, implementing *note __reduce__(): 2d0. directly in
your classes is error prone.  For this reason, class designers should
use the high-level interface (i.e., *note __getnewargs_ex__(): 1e23,
*note __getstate__(): ec5. and *note __setstate__(): 2d1.) whenever
possible.  We will show, however, cases where using *note __reduce__():
2d0. is the only option or leads to more efficient pickling or both.

 -- Method: object.__reduce__ ()

     The interface is currently defined as follows.  The *note
     __reduce__(): 2d0. method takes no argument and shall return either
     a string or preferably a tuple (the returned object is often
     referred to as the “reduce value”).

     If a string is returned, the string should be interpreted as the
     name of a global variable.  It should be the object’s local name
     relative to its module; the pickle module searches the module
     namespace to determine the object’s module.  This behaviour is
     typically useful for singletons.

     When a tuple is returned, it must be between two and six items
     long.  Optional items can either be omitted, or ‘None’ can be
     provided as their value.  The semantics of each item are in order:

        * A callable object that will be called to create the initial
          version of the object.

        * A tuple of arguments for the callable object.  An empty tuple
          must be given if the callable does not accept any argument.

        * Optionally, the object’s state, which will be passed to the
          object’s *note __setstate__(): 2d1. method as previously
          described.  If the object has no such method then, the value
          must be a dictionary and it will be added to the object’s
          *note __dict__: 5f6. attribute.

        * Optionally, an iterator (and not a sequence) yielding
          successive items.  These items will be appended to the object
          either using ‘obj.append(item)’ or, in batch, using
          ‘obj.extend(list_of_items)’.  This is primarily used for list
          subclasses, but may be used by other classes as long as they
          have ‘append()’ and ‘extend()’ methods with the appropriate
          signature.  (Whether ‘append()’ or ‘extend()’ is used depends
          on which pickle protocol version is used as well as the number
          of items to append, so both must be supported.)

        * Optionally, an iterator (not a sequence) yielding successive
          key-value pairs.  These items will be stored to the object
          using ‘obj[key] = value’.  This is primarily used for
          dictionary subclasses, but may be used by other classes as
          long as they implement *note __setitem__(): d2a.

        * Optionally, a callable with a ‘(obj, state)’ signature.  This
          callable allows the user to programmatically control the
          state-updating behavior of a specific object, instead of using
          ‘obj’’s static *note __setstate__(): 2d1. method.  If not
          ‘None’, this callable will have priority over ‘obj’’s *note
          __setstate__(): 2d1.

          New in version 3.8: The optional sixth tuple item, ‘(obj,
          state)’, was added.

 -- Method: object.__reduce_ex__ (protocol)

     Alternatively, a *note __reduce_ex__(): 1b47. method may be
     defined.  The only difference is this method should take a single
     integer argument, the protocol version.  When defined, pickle will
     prefer it over the *note __reduce__(): 2d0. method.  In addition,
     *note __reduce__(): 2d0. automatically becomes a synonym for the
     extended version.  The main use for this method is to provide
     backwards-compatible reduce values for older Python releases.

* Menu:

* Persistence of External Objects::
* Dispatch Tables::
* Handling Stateful Objects::

   ---------- Footnotes ----------

   (1) (4) The *note copy: 25. module uses this protocol for shallow and
deep copying operations.


File: python.info,  Node: Persistence of External Objects,  Next: Dispatch Tables,  Up: Pickling Class Instances

5.12.1.8 Persistence of External Objects
........................................

For the benefit of object persistence, the *note pickle: ca. module
supports the notion of a reference to an object outside the pickled data
stream.  Such objects are referenced by a persistent ID, which should be
either a string of alphanumeric characters (for protocol 0) (1) or just
an arbitrary object (for any newer protocol).

The resolution of such persistent IDs is not defined by the *note
pickle: ca. module; it will delegate this resolution to the user-defined
methods on the pickler and unpickler, *note persistent_id(): 1e14. and
*note persistent_load(): 1e15. respectively.

To pickle objects that have an external persistent ID, the pickler must
have a custom *note persistent_id(): 1e14. method that takes an object
as an argument and returns either ‘None’ or the persistent ID for that
object.  When ‘None’ is returned, the pickler simply pickles the object
as normal.  When a persistent ID string is returned, the pickler will
pickle that object, along with a marker so that the unpickler will
recognize it as a persistent ID.

To unpickle external objects, the unpickler must have a custom *note
persistent_load(): 1e15. method that takes a persistent ID object and
returns the referenced object.

Here is a comprehensive example presenting how persistent ID can be used
to pickle external objects by reference.

     # Simple example presenting how persistent ID can be used to pickle
     # external objects by reference.

     import pickle
     import sqlite3
     from collections import namedtuple

     # Simple class representing a record in our database.
     MemoRecord = namedtuple("MemoRecord", "key, task")

     class DBPickler(pickle.Pickler):

         def persistent_id(self, obj):
             # Instead of pickling MemoRecord as a regular class instance, we emit a
             # persistent ID.
             if isinstance(obj, MemoRecord):
                 # Here, our persistent ID is simply a tuple, containing a tag and a
                 # key, which refers to a specific record in the database.
                 return ("MemoRecord", obj.key)
             else:
                 # If obj does not have a persistent ID, return None. This means obj
                 # needs to be pickled as usual.
                 return None


     class DBUnpickler(pickle.Unpickler):

         def __init__(self, file, connection):
             super().__init__(file)
             self.connection = connection

         def persistent_load(self, pid):
             # This method is invoked whenever a persistent ID is encountered.
             # Here, pid is the tuple returned by DBPickler.
             cursor = self.connection.cursor()
             type_tag, key_id = pid
             if type_tag == "MemoRecord":
                 # Fetch the referenced record from the database and return it.
                 cursor.execute("SELECT * FROM memos WHERE key=?", (str(key_id),))
                 key, task = cursor.fetchone()
                 return MemoRecord(key, task)
             else:
                 # Always raises an error if you cannot return the correct object.
                 # Otherwise, the unpickler will think None is the object referenced
                 # by the persistent ID.
                 raise pickle.UnpicklingError("unsupported persistent object")


     def main():
         import io
         import pprint

         # Initialize and populate our database.
         conn = sqlite3.connect(":memory:")
         cursor = conn.cursor()
         cursor.execute("CREATE TABLE memos(key INTEGER PRIMARY KEY, task TEXT)")
         tasks = (
             'give food to fish',
             'prepare group meeting',
             'fight with a zebra',
             )
         for task in tasks:
             cursor.execute("INSERT INTO memos VALUES(NULL, ?)", (task,))

         # Fetch the records to be pickled.
         cursor.execute("SELECT * FROM memos")
         memos = [MemoRecord(key, task) for key, task in cursor]
         # Save the records using our custom DBPickler.
         file = io.BytesIO()
         DBPickler(file).dump(memos)

         print("Pickled records:")
         pprint.pprint(memos)

         # Update a record, just for good measure.
         cursor.execute("UPDATE memos SET task='learn italian' WHERE key=1")

         # Load the records from the pickle data stream.
         file.seek(0)
         memos = DBUnpickler(file, conn).load()

         print("Unpickled records:")
         pprint.pprint(memos)


     if __name__ == '__main__':
         main()

   ---------- Footnotes ----------

   (1) (5) The limitation on alphanumeric characters is due to the fact
the persistent IDs, in protocol 0, are delimited by the newline
character.  Therefore if any kind of newline characters occurs in
persistent IDs, the resulting pickle will become unreadable.


File: python.info,  Node: Dispatch Tables,  Next: Handling Stateful Objects,  Prev: Persistence of External Objects,  Up: Pickling Class Instances

5.12.1.9 Dispatch Tables
........................

If one wants to customize pickling of some classes without disturbing
any other code which depends on pickling, then one can create a pickler
with a private dispatch table.

The global dispatch table managed by the *note copyreg: 26. module is
available as ‘copyreg.dispatch_table’.  Therefore, one may choose to use
a modified copy of ‘copyreg.dispatch_table’ as a private dispatch table.

For example

     f = io.BytesIO()
     p = pickle.Pickler(f)
     p.dispatch_table = copyreg.dispatch_table.copy()
     p.dispatch_table[SomeClass] = reduce_SomeClass

creates an instance of *note pickle.Pickler: 33b. with a private
dispatch table which handles the ‘SomeClass’ class specially.
Alternatively, the code

     class MyPickler(pickle.Pickler):
         dispatch_table = copyreg.dispatch_table.copy()
         dispatch_table[SomeClass] = reduce_SomeClass
     f = io.BytesIO()
     p = MyPickler(f)

does the same, but all instances of ‘MyPickler’ will by default share
the same dispatch table.  The equivalent code using the *note copyreg:
26. module is

     copyreg.pickle(SomeClass, reduce_SomeClass)
     f = io.BytesIO()
     p = pickle.Pickler(f)


File: python.info,  Node: Handling Stateful Objects,  Prev: Dispatch Tables,  Up: Pickling Class Instances

5.12.1.10 Handling Stateful Objects
...................................

Here’s an example that shows how to modify pickling behavior for a
class.  The ‘TextReader’ class opens a text file, and returns the line
number and line contents each time its ‘readline()’ method is called.
If a ‘TextReader’ instance is pickled, all attributes `except' the file
object member are saved.  When the instance is unpickled, the file is
reopened, and reading resumes from the last location.  The *note
__setstate__(): 2d1. and *note __getstate__(): ec5. methods are used to
implement this behavior.

     class TextReader:
         """Print and number lines in a text file."""

         def __init__(self, filename):
             self.filename = filename
             self.file = open(filename)
             self.lineno = 0

         def readline(self):
             self.lineno += 1
             line = self.file.readline()
             if not line:
                 return None
             if line.endswith('\n'):
                 line = line[:-1]
             return "%i: %s" % (self.lineno, line)

         def __getstate__(self):
             # Copy the object's state from self.__dict__ which contains
             # all our instance attributes. Always use the dict.copy()
             # method to avoid modifying the original state.
             state = self.__dict__.copy()
             # Remove the unpicklable entries.
             del state['file']
             return state

         def __setstate__(self, state):
             # Restore instance attributes (i.e., filename and lineno).
             self.__dict__.update(state)
             # Restore the previously opened file's state. To do so, we need to
             # reopen it and read from it until the line count is restored.
             file = open(self.filename)
             for _ in range(self.lineno):
                 file.readline()
             # Finally, save the file.
             self.file = file

A sample usage might be something like this:

     >>> reader = TextReader("hello.txt")
     >>> reader.readline()
     '1: Hello world!'
     >>> reader.readline()
     '2: I am line number two.'
     >>> new_reader = pickle.loads(pickle.dumps(reader))
     >>> new_reader.readline()
     '3: Goodbye!'


File: python.info,  Node: Custom Reduction for Types Functions and Other Objects,  Next: Out-of-band Buffers,  Prev: Pickling Class Instances,  Up: pickle — Python object serialization

5.12.1.11 Custom Reduction for Types, Functions, and Other Objects
..................................................................

New in version 3.8.

Sometimes, *note dispatch_table: b44. may not be flexible enough.  In
particular we may want to customize pickling based on another criterion
than the object’s type, or we may want to customize the pickling of
functions and classes.

For those cases, it is possible to subclass from the *note Pickler: 33b.
class and implement a *note reducer_override(): 33c. method.  This
method can return an arbitrary reduction tuple (see *note __reduce__():
2d0.).  It can alternatively return ‘NotImplemented’ to fallback to the
traditional behavior.

If both the *note dispatch_table: b44. and *note reducer_override():
33c. are defined, then *note reducer_override(): 33c. method takes
priority.

     Note: For performance reasons, *note reducer_override(): 33c. may
     not be called for the following objects: ‘None’, ‘True’, ‘False’,
     and exact instances of *note int: 204, *note float: 1fd, *note
     bytes: 172, *note str: 205, *note dict: 164, *note set: 1f6, *note
     frozenset: 1f7, *note list: 1f8. and *note tuple: 1a2.

Here is a simple example where we allow pickling and reconstructing a
given class:

     import io
     import pickle

     class MyClass:
         my_attribute = 1

     class MyPickler(pickle.Pickler):
         def reducer_override(self, obj):
             """Custom reducer for MyClass."""
             if getattr(obj, "__name__", None) == "MyClass":
                 return type, (obj.__name__, obj.__bases__,
                               {'my_attribute': obj.my_attribute})
             else:
                 # For any other object, fallback to usual reduction
                 return NotImplemented

     f = io.BytesIO()
     p = MyPickler(f)
     p.dump(MyClass)

     del MyClass

     unpickled_class = pickle.loads(f.getvalue())

     assert isinstance(unpickled_class, type)
     assert unpickled_class.__name__ == "MyClass"
     assert unpickled_class.my_attribute == 1


File: python.info,  Node: Out-of-band Buffers,  Next: Restricting Globals,  Prev: Custom Reduction for Types Functions and Other Objects,  Up: pickle — Python object serialization

5.12.1.12 Out-of-band Buffers
.............................

New in version 3.8.

In some contexts, the *note pickle: ca. module is used to transfer
massive amounts of data.  Therefore, it can be important to minimize the
number of memory copies, to preserve performance and resource
consumption.  However, normal operation of the *note pickle: ca. module,
as it transforms a graph-like structure of objects into a sequential
stream of bytes, intrinsically involves copying data to and from the
pickle stream.

This constraint can be eschewed if both the `provider' (the
implementation of the object types to be transferred) and the `consumer'
(the implementation of the communications system) support the
out-of-band transfer facilities provided by pickle protocol 5 and
higher.

* Menu:

* Provider API::
* Consumer API::
* Example: Example<4>.


File: python.info,  Node: Provider API,  Next: Consumer API,  Up: Out-of-band Buffers

5.12.1.13 Provider API
......................

The large data objects to be pickled must implement a *note
__reduce_ex__(): 1b47. method specialized for protocol 5 and higher,
which returns a *note PickleBuffer: 1e12. instance (instead of e.g.  a
*note bytes: 172. object) for any large data.

A *note PickleBuffer: 1e12. object `signals' that the underlying buffer
is eligible for out-of-band data transfer.  Those objects remain
compatible with normal usage of the *note pickle: ca. module.  However,
consumers can also opt-in to tell *note pickle: ca. that they will
handle those buffers by themselves.


File: python.info,  Node: Consumer API,  Next: Example<4>,  Prev: Provider API,  Up: Out-of-band Buffers

5.12.1.14 Consumer API
......................

A communications system can enable custom handling of the *note
PickleBuffer: 1e12. objects generated when serializing an object graph.

On the sending side, it needs to pass a `buffer_callback' argument to
*note Pickler: 33b. (or to the *note dump(): 1e0c. or *note dumps():
ec3. function), which will be called with each *note PickleBuffer: 1e12.
generated while pickling the object graph.  Buffers accumulated by the
`buffer_callback' will not see their data copied into the pickle stream,
only a cheap marker will be inserted.

On the receiving side, it needs to pass a `buffers' argument to *note
Unpickler: 1e0b. (or to the *note load(): 6b9. or *note loads(): 6ba.
function), which is an iterable of the buffers which were passed to
`buffer_callback'.  That iterable should produce buffers in the same
order as they were passed to `buffer_callback'.  Those buffers will
provide the data expected by the reconstructors of the objects whose
pickling produced the original *note PickleBuffer: 1e12. objects.

Between the sending side and the receiving side, the communications
system is free to implement its own transfer mechanism for out-of-band
buffers.  Potential optimizations include the use of shared memory or
datatype-dependent compression.


File: python.info,  Node: Example<4>,  Prev: Consumer API,  Up: Out-of-band Buffers

5.12.1.15 Example
.................

Here is a trivial example where we implement a *note bytearray: 173.
subclass able to participate in out-of-band buffer pickling:

     class ZeroCopyByteArray(bytearray):

         def __reduce_ex__(self, protocol):
             if protocol >= 5:
                 return type(self)._reconstruct, (PickleBuffer(self),), None
             else:
                 # PickleBuffer is forbidden with pickle protocols <= 4.
                 return type(self)._reconstruct, (bytearray(self),)

         @classmethod
         def _reconstruct(cls, obj):
             with memoryview(obj) as m:
                 # Get a handle over the original buffer object
                 obj = m.obj
                 if type(obj) is cls:
                     # Original buffer object is a ZeroCopyByteArray, return it
                     # as-is.
                     return obj
                 else:
                     return cls(obj)

The reconstructor (the ‘_reconstruct’ class method) returns the buffer’s
providing object if it has the right type.  This is an easy way to
simulate zero-copy behaviour on this toy example.

On the consumer side, we can pickle those objects the usual way, which
when unserialized will give us a copy of the original object:

     b = ZeroCopyByteArray(b"abc")
     data = pickle.dumps(b, protocol=5)
     new_b = pickle.loads(data)
     print(b == new_b)  # True
     print(b is new_b)  # False: a copy was made

But if we pass a `buffer_callback' and then give back the accumulated
buffers when unserializing, we are able to get back the original object:

     b = ZeroCopyByteArray(b"abc")
     buffers = []
     data = pickle.dumps(b, protocol=5, buffer_callback=buffers.append)
     new_b = pickle.loads(data, buffers=buffers)
     print(b == new_b)  # True
     print(b is new_b)  # True: no copy was made

This example is limited by the fact that *note bytearray: 173. allocates
its own memory: you cannot create a *note bytearray: 173. instance that
is backed by another object’s memory.  However, third-party datatypes
such as NumPy arrays do not have this limitation, and allow use of
zero-copy pickling (or making as few copies as possible) when
transferring between distinct processes or systems.

See also
........

PEP 574(1) – Pickle protocol 5 with out-of-band data

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0574


File: python.info,  Node: Restricting Globals,  Next: Performance<2>,  Prev: Out-of-band Buffers,  Up: pickle — Python object serialization

5.12.1.16 Restricting Globals
.............................

By default, unpickling will import any class or function that it finds
in the pickle data.  For many applications, this behaviour is
unacceptable as it permits the unpickler to import and invoke arbitrary
code.  Just consider what this hand-crafted pickle data stream does when
loaded:

     >>> import pickle
     >>> pickle.loads(b"cos\nsystem\n(S'echo hello world'\ntR.")
     hello world
     0

In this example, the unpickler imports the *note os.system(): e86.
function and then apply the string argument “echo hello world”.
Although this example is inoffensive, it is not difficult to imagine one
that could damage your system.

For this reason, you may want to control what gets unpickled by
customizing *note Unpickler.find_class(): 1e1d.  Unlike its name
suggests, *note Unpickler.find_class(): 1e1d. is called whenever a
global (i.e., a class or a function) is requested.  Thus it is possible
to either completely forbid globals or restrict them to a safe subset.

Here is an example of an unpickler allowing only few safe classes from
the *note builtins: 12. module to be loaded:

     import builtins
     import io
     import pickle

     safe_builtins = {
         'range',
         'complex',
         'set',
         'frozenset',
         'slice',
     }

     class RestrictedUnpickler(pickle.Unpickler):

         def find_class(self, module, name):
             # Only allow safe classes from builtins.
             if module == "builtins" and name in safe_builtins:
                 return getattr(builtins, name)
             # Forbid everything else.
             raise pickle.UnpicklingError("global '%s.%s' is forbidden" %
                                          (module, name))

     def restricted_loads(s):
         """Helper function analogous to pickle.loads()."""
         return RestrictedUnpickler(io.BytesIO(s)).load()

A sample usage of our unpickler working has intended:

     >>> restricted_loads(pickle.dumps([1, 2, range(15)]))
     [1, 2, range(0, 15)]
     >>> restricted_loads(b"cos\nsystem\n(S'echo hello world'\ntR.")
     Traceback (most recent call last):
       ...
     pickle.UnpicklingError: global 'os.system' is forbidden
     >>> restricted_loads(b'cbuiltins\neval\n'
     ...                  b'(S\'getattr(__import__("os"), "system")'
     ...                  b'("echo hello world")\'\ntR.')
     Traceback (most recent call last):
       ...
     pickle.UnpicklingError: global 'builtins.eval' is forbidden

As our examples shows, you have to be careful with what you allow to be
unpickled.  Therefore if security is a concern, you may want to consider
alternatives such as the marshalling API in *note xmlrpc.client: 148. or
third-party solutions.


File: python.info,  Node: Performance<2>,  Next: Examples<5>,  Prev: Restricting Globals,  Up: pickle — Python object serialization

5.12.1.17 Performance
.....................

Recent versions of the pickle protocol (from protocol 2 and upwards)
feature efficient binary encodings for several common features and
built-in types.  Also, the *note pickle: ca. module has a transparent
optimizer written in C.


File: python.info,  Node: Examples<5>,  Prev: Performance<2>,  Up: pickle — Python object serialization

5.12.1.18 Examples
..................

For the simplest code, use the *note dump(): 1e0c. and *note load():
6b9. functions.

     import pickle

     # An arbitrary collection of objects supported by pickle.
     data = {
         'a': [1, 2.0, 3, 4+6j],
         'b': ("character string", b"byte string"),
         'c': {None, True, False}
     }

     with open('data.pickle', 'wb') as f:
         # Pickle the 'data' dictionary using the highest protocol available.
         pickle.dump(data, f, pickle.HIGHEST_PROTOCOL)

The following example reads the resulting pickled data.

     import pickle

     with open('data.pickle', 'rb') as f:
         # The protocol version used is detected automatically, so we do not
         # have to specify it.
         data = pickle.load(f)

See also
........

Module *note copyreg: 26.

     Pickle interface constructor registration for extension types.

Module *note pickletools: cb.

     Tools for working with and analyzing pickled data.

Module *note shelve: e7.

     Indexed databases of objects; uses *note pickle: ca.

Module *note copy: 25.

     Shallow and deep object copying.

Module *note marshal: b0.

     High-performance serialization of built-in types.


File: python.info,  Node: copyreg — Register pickle support functions,  Next: shelve — Python object persistence,  Prev: pickle — Python object serialization,  Up: Data Persistence

5.12.2 ‘copyreg’ — Register ‘pickle’ support functions
------------------------------------------------------

`Source code:' Lib/copyreg.py(1)

__________________________________________________________________

The *note copyreg: 26. module offers a way to define functions used
while pickling specific objects.  The *note pickle: ca. and *note copy:
25. modules use those functions when pickling/copying those objects.
The module provides configuration information about object constructors
which are not classes.  Such constructors may be factory functions or
class instances.

 -- Function: copyreg.constructor (object)

     Declares `object' to be a valid constructor.  If `object' is not
     callable (and hence not valid as a constructor), raises *note
     TypeError: 1fe.

 -- Function: copyreg.pickle (type, function, constructor=None)

     Declares that `function' should be used as a “reduction” function
     for objects of type `type'.  `function' should return either a
     string or a tuple containing two or three elements.

     The optional `constructor' parameter, if provided, is a callable
     object which can be used to reconstruct the object when called with
     the tuple of arguments returned by `function' at pickling time.
     *note TypeError: 1fe. will be raised if `object' is a class or
     `constructor' is not callable.

     See the *note pickle: ca. module for more details on the interface
     expected of `function' and `constructor'.  Note that the *note
     dispatch_table: b44. attribute of a pickler object or subclass of
     *note pickle.Pickler: 33b. can also be used for declaring reduction
     functions.

* Menu:

* Example: Example<5>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/copyreg.py


File: python.info,  Node: Example<5>,  Up: copyreg — Register pickle support functions

5.12.2.1 Example
................

The example below would like to show how to register a pickle function
and how it will be used:

     >>> import copyreg, copy, pickle
     >>> class C:
     ...     def __init__(self, a):
     ...         self.a = a
     ...
     >>> def pickle_c(c):
     ...     print("pickling a C instance...")
     ...     return C, (c.a,)
     ...
     >>> copyreg.pickle(C, pickle_c)
     >>> c = C(1)
     >>> d = copy.copy(c)
     pickling a C instance...
     >>> p = pickle.dumps(c)
     pickling a C instance...


File: python.info,  Node: shelve — Python object persistence,  Next: marshal — Internal Python object serialization,  Prev: copyreg — Register pickle support functions,  Up: Data Persistence

5.12.3 ‘shelve’ — Python object persistence
-------------------------------------------

`Source code:' Lib/shelve.py(1)

__________________________________________________________________

A “shelf” is a persistent, dictionary-like object.  The difference with
“dbm” databases is that the values (not the keys!)  in a shelf can be
essentially arbitrary Python objects — anything that the *note pickle:
ca. module can handle.  This includes most class instances, recursive
data types, and objects containing lots of shared sub-objects.  The keys
are ordinary strings.

 -- Function: shelve.open (filename, flag='c', protocol=None,
          writeback=False)

     Open a persistent dictionary.  The filename specified is the base
     filename for the underlying database.  As a side-effect, an
     extension may be added to the filename and more than one file may
     be created.  By default, the underlying database file is opened for
     reading and writing.  The optional `flag' parameter has the same
     interpretation as the `flag' parameter of *note dbm.open(): 91d.

     By default, version 3 pickles are used to serialize values.  The
     version of the pickle protocol can be specified with the `protocol'
     parameter.

     Because of Python semantics, a shelf cannot know when a mutable
     persistent-dictionary entry is modified.  By default modified
     objects are written `only' when assigned to the shelf (see *note
     Example: 1e38.).  If the optional `writeback' parameter is set to
     ‘True’, all entries accessed are also cached in memory, and written
     back on *note sync(): 1e39. and *note close(): 1e3a.; this can make
     it handier to mutate mutable entries in the persistent dictionary,
     but, if many entries are accessed, it can consume vast amounts of
     memory for the cache, and it can make the close operation very slow
     since all accessed entries are written back (there is no way to
     determine which accessed entries are mutable, nor which ones were
     actually mutated).

          Note: Do not rely on the shelf being closed automatically;
          always call *note close(): 1e3a. explicitly when you don’t
          need it any more, or use *note shelve.open(): 1e37. as a
          context manager:

               with shelve.open('spam') as db:
                   db['eggs'] = 'eggs'
     Warning: Because the *note shelve: e7. module is backed by *note
     pickle: ca, it is insecure to load a shelf from an untrusted
     source.  Like with pickle, loading a shelf can execute arbitrary
     code.

Shelf objects support most of methods and operations supported by
dictionaries (except copying, constructors and operators ‘|’ and ‘|=’).
This eases the transition from dictionary based scripts to those
requiring persistent storage.

Two additional methods are supported:

 -- Method: Shelf.sync ()

     Write back all entries in the cache if the shelf was opened with
     `writeback' set to *note True: 594.  Also empty the cache and
     synchronize the persistent dictionary on disk, if feasible.  This
     is called automatically when the shelf is closed with *note
     close(): 1e3a.

 -- Method: Shelf.close ()

     Synchronize and close the persistent `dict' object.  Operations on
     a closed shelf will fail with a *note ValueError: 16d.

See also
........

Persistent dictionary recipe(2) with widely supported storage formats
and having the speed of native dictionaries.

* Menu:

* Restrictions::
* Example: Example<6>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/shelve.py

   (2) https://code.activestate.com/recipes/576642/


File: python.info,  Node: Restrictions,  Next: Example<6>,  Up: shelve — Python object persistence

5.12.3.1 Restrictions
.....................

   * The choice of which database package will be used (such as *note
     dbm.ndbm: 34. or *note dbm.gnu: 33.) depends on which interface is
     available.  Therefore it is not safe to open the database directly
     using *note dbm: 31.  The database is also (unfortunately) subject
     to the limitations of *note dbm: 31, if it is used — this means
     that (the pickled representation of) the objects stored in the
     database should be fairly small, and in rare cases key collisions
     may cause the database to refuse updates.

   * The *note shelve: e7. module does not support `concurrent'
     read/write access to shelved objects.  (Multiple simultaneous read
     accesses are safe.)  When a program has a shelf open for writing,
     no other program should have it open for reading or writing.  Unix
     file locking can be used to solve this, but this differs across
     Unix versions and requires knowledge about the database
     implementation used.

 -- Class: shelve.Shelf (dict, protocol=None, writeback=False,
          keyencoding='utf-8')

     A subclass of *note collections.abc.MutableMapping: ace. which
     stores pickled values in the `dict' object.

     By default, version 3 pickles are used to serialize values.  The
     version of the pickle protocol can be specified with the `protocol'
     parameter.  See the *note pickle: ca. documentation for a
     discussion of the pickle protocols.

     If the `writeback' parameter is ‘True’, the object will hold a
     cache of all entries accessed and write them back to the `dict' at
     sync and close times.  This allows natural operations on mutable
     entries, but can consume much more memory and make sync and close
     take a long time.

     The `keyencoding' parameter is the encoding used to encode keys
     before they are used with the underlying dict.

     A *note Shelf: 997. object can also be used as a context manager,
     in which case it will be automatically closed when the *note with:
     7da. block ends.

     Changed in version 3.2: Added the `keyencoding' parameter;
     previously, keys were always encoded in UTF-8.

     Changed in version 3.4: Added context manager support.

 -- Class: shelve.BsdDbShelf (dict, protocol=None, writeback=False,
          keyencoding='utf-8')

     A subclass of *note Shelf: 997. which exposes ‘first()’, ‘next()’,
     ‘previous()’, ‘last()’ and ‘set_location()’ which are available in
     the third-party ‘bsddb’ module from pybsddb(1) but not in other
     database modules.  The `dict' object passed to the constructor must
     support those methods.  This is generally accomplished by calling
     one of ‘bsddb.hashopen()’, ‘bsddb.btopen()’ or ‘bsddb.rnopen()’.
     The optional `protocol', `writeback', and `keyencoding' parameters
     have the same interpretation as for the *note Shelf: 997. class.

 -- Class: shelve.DbfilenameShelf (filename, flag='c', protocol=None,
          writeback=False)

     A subclass of *note Shelf: 997. which accepts a `filename' instead
     of a dict-like object.  The underlying file will be opened using
     *note dbm.open(): 91d.  By default, the file will be created and
     opened for both read and write.  The optional `flag' parameter has
     the same interpretation as for the *note open(): 1e37. function.
     The optional `protocol' and `writeback' parameters have the same
     interpretation as for the *note Shelf: 997. class.

   ---------- Footnotes ----------

   (1) https://www.jcea.es/programacion/pybsddb.htm


File: python.info,  Node: Example<6>,  Prev: Restrictions,  Up: shelve — Python object persistence

5.12.3.2 Example
................

To summarize the interface (‘key’ is a string, ‘data’ is an arbitrary
object):

     import shelve

     d = shelve.open(filename)  # open -- file may get suffix added by low-level
                                # library

     d[key] = data              # store data at key (overwrites old data if
                                # using an existing key)
     data = d[key]              # retrieve a COPY of data at key (raise KeyError
                                # if no such key)
     del d[key]                 # delete data stored at key (raises KeyError
                                # if no such key)

     flag = key in d            # true if the key exists
     klist = list(d.keys())     # a list of all existing keys (slow!)

     # as d was opened WITHOUT writeback=True, beware:
     d['xx'] = [0, 1, 2]        # this works as expected, but...
     d['xx'].append(3)          # *this doesn't!* -- d['xx'] is STILL [0, 1, 2]!

     # having opened d without writeback=True, you need to code carefully:
     temp = d['xx']             # extracts the copy
     temp.append(5)             # mutates the copy
     d['xx'] = temp             # stores the copy right back, to persist it

     # or, d=shelve.open(filename,writeback=True) would let you just code
     # d['xx'].append(5) and have it work as expected, BUT it would also
     # consume more memory and make the d.close() operation slower.

     d.close()                  # close it

See also
........

Module *note dbm: 31.

     Generic interface to ‘dbm’-style databases.

Module *note pickle: ca.

     Object serialization used by *note shelve: e7.


File: python.info,  Node: marshal — Internal Python object serialization,  Next: dbm — Interfaces to Unix “databases”,  Prev: shelve — Python object persistence,  Up: Data Persistence

5.12.4 ‘marshal’ — Internal Python object serialization
-------------------------------------------------------

__________________________________________________________________

This module contains functions that can read and write Python values in
a binary format.  The format is specific to Python, but independent of
machine architecture issues (e.g., you can write a Python value to a
file on a PC, transport the file to a Sun, and read it back there).
Details of the format are undocumented on purpose; it may change between
Python versions (although it rarely does).  (1)

This is not a general “persistence” module.  For general persistence and
transfer of Python objects through RPC calls, see the modules *note
pickle: ca. and *note shelve: e7.  The *note marshal: b0. module exists
mainly to support reading and writing the “pseudo-compiled” code for
Python modules of ‘.pyc’ files.  Therefore, the Python maintainers
reserve the right to modify the marshal format in backward incompatible
ways should the need arise.  If you’re serializing and de-serializing
Python objects, use the *note pickle: ca. module instead – the
performance is comparable, version independence is guaranteed, and
pickle supports a substantially wider range of objects than marshal.

     Warning: The *note marshal: b0. module is not intended to be secure
     against erroneous or maliciously constructed data.  Never unmarshal
     data received from an untrusted or unauthenticated source.

Not all Python object types are supported; in general, only objects
whose value is independent from a particular invocation of Python can be
written and read by this module.  The following types are supported:
booleans, integers, floating point numbers, complex numbers, strings,
bytes, bytearrays, tuples, lists, sets, frozensets, dictionaries, and
code objects, where it should be understood that tuples, lists, sets,
frozensets and dictionaries are only supported as long as the values
contained therein are themselves supported.  The singletons *note None:
203, *note Ellipsis: 1740. and *note StopIteration: 582. can also be
marshalled and unmarshalled.  For format `version' lower than 3,
recursive lists, sets and dictionaries cannot be written (see below).

There are functions that read/write files as well as functions operating
on bytes-like objects.

The module defines these functions:

 -- Function: marshal.dump (value, file[, version])

     Write the value on the open file.  The value must be a supported
     type.  The file must be a writeable *note binary file: 1e01.

     If the value has (or contains an object that has) an unsupported
     type, a *note ValueError: 16d. exception is raised — but garbage
     data will also be written to the file.  The object will not be
     properly read back by *note load(): 112b.

     The `version' argument indicates the data format that ‘dump’ should
     use (see below).

     Raises an *note auditing event: fa1. ‘marshal.dumps’ with arguments
     ‘value’, ‘version’.

 -- Function: marshal.load (file)

     Read one value from the open file and return it.  If no valid value
     is read (e.g.  because the data has a different Python version’s
     incompatible marshal format), raise *note EOFError: d34, *note
     ValueError: 16d. or *note TypeError: 1fe.  The file must be a
     readable *note binary file: 1e01.

     Raises an *note auditing event: fa1. ‘marshal.load’ with no
     arguments.

          Note: If an object containing an unsupported type was
          marshalled with *note dump(): 1e42, *note load(): 112b. will
          substitute ‘None’ for the unmarshallable type.

     Changed in version 3.9.7: This call used to raise a ‘code.__new__’
     audit event for each code object.  Now it raises a single
     ‘marshal.load’ event for the entire load operation.

 -- Function: marshal.dumps (value[, version])

     Return the bytes object that would be written to a file by
     ‘dump(value, file)’.  The value must be a supported type.  Raise a
     *note ValueError: 16d. exception if value has (or contains an
     object that has) an unsupported type.

     The `version' argument indicates the data format that ‘dumps’
     should use (see below).

     Raises an *note auditing event: fa1. ‘marshal.dumps’ with arguments
     ‘value’, ‘version’.

 -- Function: marshal.loads (bytes)

     Convert the *note bytes-like object: 6df. to a value.  If no valid
     value is found, raise *note EOFError: d34, *note ValueError: 16d.
     or *note TypeError: 1fe.  Extra bytes in the input are ignored.

     Raises an *note auditing event: fa1. ‘marshal.loads’ with argument
     ‘bytes’.

     Changed in version 3.9.7: This call used to raise a ‘code.__new__’
     audit event for each code object.  Now it raises a single
     ‘marshal.loads’ event for the entire load operation.

In addition, the following constants are defined:

 -- Data: marshal.version

     Indicates the format that the module uses.  Version 0 is the
     historical format, version 1 shares interned strings and version 2
     uses a binary format for floating point numbers.  Version 3 adds
     support for object instancing and recursion.  The current version
     is 4.

   ---------- Footnotes ----------

   (1) (1) The name of this module stems from a bit of terminology used
by the designers of Modula-3 (amongst others), who use the term
“marshalling” for shipping of data around in a self-contained form.
Strictly speaking, “to marshal” means to convert some data from internal
to external form (in an RPC buffer for instance) and “unmarshalling” for
the reverse process.


File: python.info,  Node: dbm — Interfaces to Unix “databases”,  Next: sqlite3 — DB-API 2 0 interface for SQLite databases,  Prev: marshal — Internal Python object serialization,  Up: Data Persistence

5.12.5 ‘dbm’ — Interfaces to Unix “databases”
---------------------------------------------

`Source code:' Lib/dbm/__init__.py(1)

__________________________________________________________________

*note dbm: 31. is a generic interface to variants of the DBM database —
*note dbm.gnu: 33. or *note dbm.ndbm: 34.  If none of these modules is
installed, the slow-but-simple implementation in module *note dbm.dumb:
32. will be used.  There is a third party interface(2) to the Oracle
Berkeley DB.

 -- Exception: dbm.error

     A tuple containing the exceptions that can be raised by each of the
     supported modules, with a unique exception also named *note
     dbm.error: 1e47. as the first item — the latter is used when *note
     dbm.error: 1e47. is raised.

 -- Function: dbm.whichdb (filename)

     This function attempts to guess which of the several simple
     database modules available — *note dbm.gnu: 33, *note dbm.ndbm: 34.
     or *note dbm.dumb: 32. — should be used to open a given file.

     Returns one of the following values: ‘None’ if the file can’t be
     opened because it’s unreadable or doesn’t exist; the empty string
     (‘''’) if the file’s format can’t be guessed; or a string
     containing the required module name, such as ‘'dbm.ndbm'’ or
     ‘'dbm.gnu'’.

 -- Function: dbm.open (file, flag='r', mode=0o666)

     Open the database file `file' and return a corresponding object.

     If the database file already exists, the *note whichdb(): 1e48.
     function is used to determine its type and the appropriate module
     is used; if it does not exist, the first module listed above that
     can be imported is used.

     The optional `flag' argument can be:

     Value         Meaning
                   
     --------------------------------------------------------------
                   
     ‘'r'’         Open existing database for reading only
                   (default)
                   
                   
     ‘'w'’         Open existing database for reading and
                   writing
                   
                   
     ‘'c'’         Open database for reading and writing,
                   creating it if it doesn’t exist
                   
                   
     ‘'n'’         Always create a new, empty database, open for
                   reading and writing
                   

     The optional `mode' argument is the Unix mode of the file, used
     only when the database has to be created.  It defaults to octal
     ‘0o666’ (and will be modified by the prevailing umask).

The object returned by *note open(): 91d. supports the same basic
functionality as dictionaries; keys and their corresponding values can
be stored, retrieved, and deleted, and the *note in: 179. operator and
the ‘keys()’ method are available, as well as ‘get()’ and
‘setdefault()’.

Changed in version 3.2: ‘get()’ and ‘setdefault()’ are now available in
all database modules.

Changed in version 3.8: Deleting a key from a read-only database raises
database module specific error instead of *note KeyError: 3e9.

Key and values are always stored as bytes.  This means that when strings
are used they are implicitly converted to the default encoding before
being stored.

These objects also support being used in a *note with: 7da. statement,
which will automatically close them when done.

Changed in version 3.4: Added native support for the context management
protocol to the objects returned by *note open(): 91d.

The following example records some hostnames and a corresponding title,
and then prints out the contents of the database:

     import dbm

     # Open database, creating it if necessary.
     with dbm.open('cache', 'c') as db:

         # Record some values
         db[b'hello'] = b'there'
         db['www.python.org'] = 'Python Website'
         db['www.cnn.com'] = 'Cable News Network'

         # Note that the keys are considered bytes now.
         assert db[b'www.python.org'] == b'Python Website'
         # Notice how the value is now in bytes.
         assert db['www.cnn.com'] == b'Cable News Network'

         # Often-used methods of the dict interface work too.
         print(db.get('python.org', b'not present'))

         # Storing a non-string key or value will raise an exception (most
         # likely a TypeError).
         db['www.yahoo.com'] = 4

     # db is automatically closed when leaving the with statement.

See also
........

Module *note shelve: e7.

     Persistence module which stores non-string data.

The individual submodules are described in the following sections.

* Menu:

* dbm.gnu — GNU’s reinterpretation of dbm: dbm gnu — GNU’s reinterpretation of dbm.
* dbm.ndbm — Interface based on ndbm: dbm ndbm — Interface based on ndbm.
* dbm.dumb — Portable DBM implementation: dbm dumb — Portable DBM implementation.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/dbm/__init__.py

   (2) https://www.jcea.es/programacion/pybsddb.htm


File: python.info,  Node: dbm gnu — GNU’s reinterpretation of dbm,  Next: dbm ndbm — Interface based on ndbm,  Up: dbm — Interfaces to Unix “databases”

5.12.5.1 ‘dbm.gnu’ — GNU’s reinterpretation of dbm
..................................................

`Source code:' Lib/dbm/gnu.py(1)

__________________________________________________________________

This module is quite similar to the *note dbm: 31. module, but uses the
GNU library ‘gdbm’ instead to provide some additional functionality.
Please note that the file formats created by *note dbm.gnu: 33. and
*note dbm.ndbm: 34. are incompatible.

The *note dbm.gnu: 33. module provides an interface to the GNU DBM
library.  ‘dbm.gnu.gdbm’ objects behave like mappings (dictionaries),
except that keys and values are always converted to bytes before
storing.  Printing a ‘gdbm’ object doesn’t print the keys and values,
and the ‘items()’ and ‘values()’ methods are not supported.

 -- Exception: dbm.gnu.error

     Raised on *note dbm.gnu: 33.-specific errors, such as I/O errors.
     *note KeyError: 3e9. is raised for general mapping errors like
     specifying an incorrect key.

 -- Function: dbm.gnu.open (filename[, flag[, mode]])

     Open a ‘gdbm’ database and return a ‘gdbm’ object.  The `filename'
     argument is the name of the database file.

     The optional `flag' argument can be:

     Value         Meaning
                   
     --------------------------------------------------------------
                   
     ‘'r'’         Open existing database for reading only
                   (default)
                   
                   
     ‘'w'’         Open existing database for reading and
                   writing
                   
                   
     ‘'c'’         Open database for reading and writing,
                   creating it if it doesn’t exist
                   
                   
     ‘'n'’         Always create a new, empty database, open for
                   reading and writing
                   

     The following additional characters may be appended to the flag to
     control how the database is opened:

     Value         Meaning
                   
     ---------------------------------------------------------------
                   
     ‘'f'’         Open the database in fast mode.  Writes to the
                   database will not be synchronized.
                   
                   
     ‘'s'’         Synchronized mode.  This will cause changes to
                   the database to be immediately written to the
                   file.
                   
                   
     ‘'u'’         Do not lock database.
                   

     Not all flags are valid for all versions of ‘gdbm’.  The module
     constant ‘open_flags’ is a string of supported flag characters.
     The exception *note error: 3e7. is raised if an invalid flag is
     specified.

     The optional `mode' argument is the Unix mode of the file, used
     only when the database has to be created.  It defaults to octal
     ‘0o666’.

     In addition to the dictionary-like methods, ‘gdbm’ objects have the
     following methods:

      -- Method: gdbm.firstkey ()

          It’s possible to loop over every key in the database using
          this method and the *note nextkey(): 1e4b. method.  The
          traversal is ordered by ‘gdbm’’s internal hash values, and
          won’t be sorted by the key values.  This method returns the
          starting key.

      -- Method: gdbm.nextkey (key)

          Returns the key that follows `key' in the traversal.  The
          following code prints every key in the database ‘db’, without
          having to create a list in memory that contains them all:

               k = db.firstkey()
               while k is not None:
                   print(k)
                   k = db.nextkey(k)

      -- Method: gdbm.reorganize ()

          If you have carried out a lot of deletions and would like to
          shrink the space used by the ‘gdbm’ file, this routine will
          reorganize the database.  ‘gdbm’ objects will not shorten the
          length of a database file except by using this reorganization;
          otherwise, deleted file space will be kept and reused as new
          (key, value) pairs are added.

      -- Method: gdbm.sync ()

          When the database has been opened in fast mode, this method
          forces any unwritten data to be written to the disk.

      -- Method: gdbm.close ()

          Close the ‘gdbm’ database.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/dbm/gnu.py


File: python.info,  Node: dbm ndbm — Interface based on ndbm,  Next: dbm dumb — Portable DBM implementation,  Prev: dbm gnu — GNU’s reinterpretation of dbm,  Up: dbm — Interfaces to Unix “databases”

5.12.5.2 ‘dbm.ndbm’ — Interface based on ndbm
.............................................

`Source code:' Lib/dbm/ndbm.py(1)

__________________________________________________________________

The *note dbm.ndbm: 34. module provides an interface to the Unix
“(n)dbm” library.  Dbm objects behave like mappings (dictionaries),
except that keys and values are always stored as bytes.  Printing a
‘dbm’ object doesn’t print the keys and values, and the ‘items()’ and
‘values()’ methods are not supported.

This module can be used with the “classic” ndbm interface or the GNU
GDBM compatibility interface.  On Unix, the ‘configure’ script will
attempt to locate the appropriate header file to simplify building this
module.

 -- Exception: dbm.ndbm.error

     Raised on *note dbm.ndbm: 34.-specific errors, such as I/O errors.
     *note KeyError: 3e9. is raised for general mapping errors like
     specifying an incorrect key.

 -- Data: dbm.ndbm.library

     Name of the ‘ndbm’ implementation library used.

 -- Function: dbm.ndbm.open (filename[, flag[, mode]])

     Open a dbm database and return a ‘ndbm’ object.  The `filename'
     argument is the name of the database file (without the ‘.dir’ or
     ‘.pag’ extensions).

     The optional `flag' argument must be one of these values:

     Value         Meaning
                   
     --------------------------------------------------------------
                   
     ‘'r'’         Open existing database for reading only
                   (default)
                   
                   
     ‘'w'’         Open existing database for reading and
                   writing
                   
                   
     ‘'c'’         Open database for reading and writing,
                   creating it if it doesn’t exist
                   
                   
     ‘'n'’         Always create a new, empty database, open for
                   reading and writing
                   

     The optional `mode' argument is the Unix mode of the file, used
     only when the database has to be created.  It defaults to octal
     ‘0o666’ (and will be modified by the prevailing umask).

     In addition to the dictionary-like methods, ‘ndbm’ objects provide
     the following method:

      -- Method: ndbm.close ()

          Close the ‘ndbm’ database.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/dbm/ndbm.py


File: python.info,  Node: dbm dumb — Portable DBM implementation,  Prev: dbm ndbm — Interface based on ndbm,  Up: dbm — Interfaces to Unix “databases”

5.12.5.3 ‘dbm.dumb’ — Portable DBM implementation
.................................................

`Source code:' Lib/dbm/dumb.py(1)

     Note: The *note dbm.dumb: 32. module is intended as a last resort
     fallback for the *note dbm: 31. module when a more robust module is
     not available.  The *note dbm.dumb: 32. module is not written for
     speed and is not nearly as heavily used as the other database
     modules.

__________________________________________________________________

The *note dbm.dumb: 32. module provides a persistent dictionary-like
interface which is written entirely in Python.  Unlike other modules
such as *note dbm.gnu: 33. no external library is required.  As with
other persistent mappings, the keys and values are always stored as
bytes.

The module defines the following:

 -- Exception: dbm.dumb.error

     Raised on *note dbm.dumb: 32.-specific errors, such as I/O errors.
     *note KeyError: 3e9. is raised for general mapping errors like
     specifying an incorrect key.

 -- Function: dbm.dumb.open (filename[, flag[, mode]])

     Open a ‘dumbdbm’ database and return a dumbdbm object.  The
     `filename' argument is the basename of the database file (without
     any specific extensions).  When a dumbdbm database is created,
     files with ‘.dat’ and ‘.dir’ extensions are created.

     The optional `flag' argument can be:

     Value         Meaning
                   
     --------------------------------------------------------------
                   
     ‘'r'’         Open existing database for reading only
                   (default)
                   
                   
     ‘'w'’         Open existing database for reading and
                   writing
                   
                   
     ‘'c'’         Open database for reading and writing,
                   creating it if it doesn’t exist
                   
                   
     ‘'n'’         Always create a new, empty database, open for
                   reading and writing
                   

     The optional `mode' argument is the Unix mode of the file, used
     only when the database has to be created.  It defaults to octal
     ‘0o666’ (and will be modified by the prevailing umask).

          Warning: It is possible to crash the Python interpreter when
          loading a database with a sufficiently large/complex entry due
          to stack depth limitations in Python’s AST compiler.

     Changed in version 3.5: *note open(): 3e1. always creates a new
     database when the flag has the value ‘'n'’.

     Changed in version 3.8: A database opened with flags ‘'r'’ is now
     read-only.  Opening with flags ‘'r'’ and ‘'w'’ no longer creates a
     database if it does not exist.

     In addition to the methods provided by the *note
     collections.abc.MutableMapping: ace. class, ‘dumbdbm’ objects
     provide the following methods:

      -- Method: dumbdbm.sync ()

          Synchronize the on-disk directory and data files.  This method
          is called by the ‘Shelve.sync()’ method.

      -- Method: dumbdbm.close ()

          Close the ‘dumbdbm’ database.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/dbm/dumb.py


File: python.info,  Node: sqlite3 — DB-API 2 0 interface for SQLite databases,  Prev: dbm — Interfaces to Unix “databases”,  Up: Data Persistence

5.12.6 ‘sqlite3’ — DB-API 2.0 interface for SQLite databases
------------------------------------------------------------

`Source code:' Lib/sqlite3/(1)

__________________________________________________________________

SQLite is a C library that provides a lightweight disk-based database
that doesn’t require a separate server process and allows accessing the
database using a nonstandard variant of the SQL query language.  Some
applications can use SQLite for internal data storage.  It’s also
possible to prototype an application using SQLite and then port the code
to a larger database such as PostgreSQL or Oracle.

The sqlite3 module was written by Gerhard Häring.  It provides a SQL
interface compliant with the DB-API 2.0 specification described by PEP
249(2).

To use the module, start by creating a *note Connection: 4df. object
that represents the database.  Here the data will be stored in the
‘example.db’ file:

     import sqlite3
     con = sqlite3.connect('example.db')

The special path name ‘:memory:’ can be provided to create a temporary
database in RAM.

Once a *note Connection: 4df. has been established, create a *note
Cursor: 1e57. object and call its *note execute(): 1e58. method to
perform SQL commands:

     cur = con.cursor()

     # Create table
     cur.execute('''CREATE TABLE stocks
                    (date text, trans text, symbol text, qty real, price real)''')

     # Insert a row of data
     cur.execute("INSERT INTO stocks VALUES ('2006-01-05','BUY','RHAT',100,35.14)")

     # Save (commit) the changes
     con.commit()

     # We can also close the connection if we are done with it.
     # Just be sure any changes have been committed or they will be lost.
     con.close()

The saved data is persistent: it can be reloaded in a subsequent session
even after restarting the Python interpreter:

     import sqlite3
     con = sqlite3.connect('example.db')
     cur = con.cursor()

To retrieve data after executing a SELECT statement, either treat the
cursor as an *note iterator: 1171, call the cursor’s *note fetchone():
1e59. method to retrieve a single matching row, or call *note
fetchall(): 1e5a. to get a list of the matching rows.

This example uses the iterator form:

     >>> for row in cur.execute('SELECT * FROM stocks ORDER BY price'):
             print(row)

     ('2006-01-05', 'BUY', 'RHAT', 100, 35.14)
     ('2006-03-28', 'BUY', 'IBM', 1000, 45.0)
     ('2006-04-06', 'SELL', 'IBM', 500, 53.0)
     ('2006-04-05', 'BUY', 'MSFT', 1000, 72.0)
SQL operations usually need to use values from Python variables.
However, beware of using Python’s string operations to assemble queries,
as they are vulnerable to SQL injection attacks (see the xkcd
webcomic(3) for a humorous example of what can go wrong):

     # Never do this -- insecure!
     symbol = 'RHAT'
     cur.execute("SELECT * FROM stocks WHERE symbol = '%s'" % symbol)

Instead, use the DB-API’s parameter substitution.  To insert a variable
into a query string, use a placeholder in the string, and substitute the
actual values into the query by providing them as a *note tuple: 1a2. of
values to the second argument of the cursor’s *note execute(): 1e58.
method.  An SQL statement may use one of two kinds of placeholders:
question marks (qmark style) or named placeholders (named style).  For
the qmark style, ‘parameters’ must be a *note sequence: 135c.  For the
named style, it can be either a *note sequence: 135c. or *note dict:
164. instance.  The length of the *note sequence: 135c. must match the
number of placeholders, or a *note ProgrammingError: ff3. is raised.  If
a *note dict: 164. is given, it must contain keys for all named
parameters.  Any extra items are ignored.  Here’s an example of both
styles:

     import sqlite3

     con = sqlite3.connect(":memory:")
     cur = con.cursor()
     cur.execute("create table lang (name, first_appeared)")

     # This is the qmark style:
     cur.execute("insert into lang values (?, ?)", ("C", 1972))

     # The qmark style used with executemany():
     lang_list = [
         ("Fortran", 1957),
         ("Python", 1991),
         ("Go", 2009),
     ]
     cur.executemany("insert into lang values (?, ?)", lang_list)

     # And this is the named style:
     cur.execute("select * from lang where first_appeared=:year", {"year": 1972})
     print(cur.fetchall())

     con.close()

See also
........

‘https://www.sqlite.org’

     The SQLite web page; the documentation describes the syntax and the
     available data types for the supported SQL dialect.

‘https://www.w3schools.com/sql/’

     Tutorial, reference and examples for learning SQL syntax.

PEP 249(4) - Database API Specification 2.0

     PEP written by Marc-André Lemburg.

* Menu:

* Module functions and constants::
* Connection Objects::
* Cursor Objects::
* Row Objects::
* Exceptions: Exceptions<5>.
* SQLite and Python types::
* Controlling Transactions::
* Using sqlite3 efficiently::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/sqlite3/

   (2) https://www.python.org/dev/peps/pep-0249

   (3) https://xkcd.com/327/

   (4) https://www.python.org/dev/peps/pep-0249


File: python.info,  Node: Module functions and constants,  Next: Connection Objects,  Up: sqlite3 — DB-API 2 0 interface for SQLite databases

5.12.6.1 Module functions and constants
.......................................

 -- Data: sqlite3.apilevel

     String constant stating the supported DB-API level.  Required by
     the DB-API. Hard-coded to ‘"2.0"’.

 -- Data: sqlite3.paramstyle

     String constant stating the type of parameter marker formatting
     expected by the *note sqlite3: f2. module.  Required by the DB-API.
     Hard-coded to ‘"qmark"’.

          Note: The *note sqlite3: f2. module supports both ‘qmark’ and
          ‘numeric’ DB-API parameter styles, because that is what the
          underlying SQLite library supports.  However, the DB-API does
          not allow multiple values for the ‘paramstyle’ attribute.

 -- Data: sqlite3.version

     The version number of this module, as a string.  This is not the
     version of the SQLite library.

 -- Data: sqlite3.version_info

     The version number of this module, as a tuple of integers.  This is
     not the version of the SQLite library.

 -- Data: sqlite3.sqlite_version

     The version number of the run-time SQLite library, as a string.

 -- Data: sqlite3.sqlite_version_info

     The version number of the run-time SQLite library, as a tuple of
     integers.

 -- Data: sqlite3.threadsafety

     Integer constant required by the DB-API, stating the level of
     thread safety the *note sqlite3: f2. module supports.  Currently
     hard-coded to ‘1’, meaning `“Threads may share the module, but not
     connections.”' However, this may not always be true.  You can check
     the underlying SQLite library’s compile-time threaded mode using
     the following query:

          import sqlite3
          con = sqlite3.connect(":memory:")
          con.execute("""
              select * from pragma_compile_options
              where compile_options like 'THREADSAFE=%'
          """).fetchall()

     Note that the SQLITE_THREADSAFE levels(1) do not match the DB-API
     2.0 ‘threadsafety’ levels.

 -- Data: sqlite3.PARSE_DECLTYPES

     This constant is meant to be used with the `detect_types' parameter
     of the *note connect(): 4e1. function.

     Setting it makes the *note sqlite3: f2. module parse the declared
     type for each column it returns.  It will parse out the first word
     of the declared type, i.  e.  for “integer primary key”, it will
     parse out “integer”, or for “number(10)” it will parse out
     “number”.  Then for that column, it will look into the converters
     dictionary and use the converter function registered for that type
     there.

 -- Data: sqlite3.PARSE_COLNAMES

     This constant is meant to be used with the `detect_types' parameter
     of the *note connect(): 4e1. function.

     Setting this makes the SQLite interface parse the column name for
     each column it returns.  It will look for a string formed [mytype]
     in there, and then decide that ‘mytype’ is the type of the column.
     It will try to find an entry of ‘mytype’ in the converters
     dictionary and then use the converter function found there to
     return the value.  The column name found in *note
     Cursor.description: 1e67. does not include the type, i.  e.  if you
     use something like ‘'as "Expiration date [datetime]"'’ in your SQL,
     then we will parse out everything until the first ‘'['’ for the
     column name and strip the preceding space: the column name would
     simply be “Expiration date”.

 -- Function: sqlite3.connect (database[, timeout, detect_types,
          isolation_level, check_same_thread, factory,
          cached_statements, uri])

     Opens a connection to the SQLite database file `database'.  By
     default returns a *note Connection: 4df. object, unless a custom
     `factory' is given.

     `database' is a *note path-like object: 472. giving the pathname
     (absolute or relative to the current working directory) of the
     database file to be opened.  You can use ‘":memory:"’ to open a
     database connection to a database that resides in RAM instead of on
     disk.

     When a database is accessed by multiple connections, and one of the
     processes modifies the database, the SQLite database is locked
     until that transaction is committed.  The `timeout' parameter
     specifies how long the connection should wait for the lock to go
     away until raising an exception.  The default for the timeout
     parameter is 5.0 (five seconds).

     For the `isolation_level' parameter, please see the *note
     isolation_level: 1e68. property of *note Connection: 4df. objects.

     SQLite natively supports only the types TEXT, INTEGER, REAL, BLOB
     and NULL. If you want to use other types you must add support for
     them yourself.  The `detect_types' parameter and the using custom
     `converters' registered with the module-level *note
     register_converter(): 1e69. function allow you to easily do that.

     `detect_types' defaults to 0 (i.  e.  off, no type detection), you
     can set it to any combination of *note PARSE_DECLTYPES: 1e65. and
     *note PARSE_COLNAMES: 1e66. to turn type detection on.  Due to
     SQLite behaviour, types can’t be detected for generated fields (for
     example ‘max(data)’), even when `detect_types' parameter is set.
     In such case, the returned type is *note str: 205.

     By default, `check_same_thread' is *note True: 594. and only the
     creating thread may use the connection.  If set *note False: 48f,
     the returned connection may be shared across multiple threads.
     When using multiple threads with the same connection writing
     operations should be serialized by the user to avoid data
     corruption.

     By default, the *note sqlite3: f2. module uses its *note
     Connection: 4df. class for the connect call.  You can, however,
     subclass the *note Connection: 4df. class and make *note connect():
     4e1. use your class instead by providing your class for the
     `factory' parameter.

     Consult the section *note SQLite and Python types: 1e6a. of this
     manual for details.

     The *note sqlite3: f2. module internally uses a statement cache to
     avoid SQL parsing overhead.  If you want to explicitly set the
     number of statements that are cached for the connection, you can
     set the `cached_statements' parameter.  The currently implemented
     default is to cache 100 statements.

     If `uri' is true, `database' is interpreted as a URI. This allows
     you to specify options.  For example, to open a database in
     read-only mode you can use:

          db = sqlite3.connect('file:path/to/database?mode=ro', uri=True)

     More information about this feature, including a list of recognized
     options, can be found in the SQLite URI documentation(2).

     Raises an *note auditing event: fa1. ‘sqlite3.connect’ with
     argument ‘database’.

     Changed in version 3.4: Added the `uri' parameter.

     Changed in version 3.7: `database' can now also be a *note
     path-like object: 472, not only a string.

 -- Function: sqlite3.register_converter (typename, callable)

     Registers a callable to convert a bytestring from the database into
     a custom Python type.  The callable will be invoked for all
     database values that are of the type `typename'.  Confer the
     parameter `detect_types' of the *note connect(): 4e1. function for
     how the type detection works.  Note that `typename' and the name of
     the type in your query are matched in case-insensitive manner.

 -- Function: sqlite3.register_adapter (type, callable)

     Registers a callable to convert the custom Python type `type' into
     one of SQLite’s supported types.  The callable `callable' accepts
     as single parameter the Python value, and must return a value of
     the following types: int, float, str or bytes.

 -- Function: sqlite3.complete_statement (sql)

     Returns *note True: 594. if the string `sql' contains one or more
     complete SQL statements terminated by semicolons.  It does not
     verify that the SQL is syntactically correct, only that there are
     no unclosed string literals and the statement is terminated by a
     semicolon.

     This can be used to build a shell for SQLite, as in the following
     example:

          # A minimal SQLite shell for experiments

          import sqlite3

          con = sqlite3.connect(":memory:")
          con.isolation_level = None
          cur = con.cursor()

          buffer = ""

          print("Enter your SQL commands to execute in sqlite3.")
          print("Enter a blank line to exit.")

          while True:
              line = input()
              if line == "":
                  break
              buffer += line
              if sqlite3.complete_statement(buffer):
                  try:
                      buffer = buffer.strip()
                      cur.execute(buffer)

                      if buffer.lstrip().upper().startswith("SELECT"):
                          print(cur.fetchall())
                  except sqlite3.Error as e:
                      print("An error occurred:", e.args[0])
                  buffer = ""

          con.close()

 -- Function: sqlite3.enable_callback_tracebacks (flag)

     By default you will not get any tracebacks in user-defined
     functions, aggregates, converters, authorizer callbacks etc.  If
     you want to debug them, you can call this function with `flag' set
     to ‘True’.  Afterwards, you will get tracebacks from callbacks on
     ‘sys.stderr’.  Use *note False: 48f. to disable the feature again.

   ---------- Footnotes ----------

   (1) https://sqlite.org/compile.html#threadsafe

   (2) https://www.sqlite.org/uri.html


File: python.info,  Node: Connection Objects,  Next: Cursor Objects,  Prev: Module functions and constants,  Up: sqlite3 — DB-API 2 0 interface for SQLite databases

5.12.6.2 Connection Objects
...........................

 -- Class: sqlite3.Connection

     A SQLite database connection has the following attributes and
     methods:

      -- Attribute: isolation_level

          Get or set the current default isolation level.  *note None:
          203. for autocommit mode or one of “DEFERRED”, “IMMEDIATE” or
          “EXCLUSIVE”.  See section *note Controlling Transactions:
          1e70. for a more detailed explanation.

      -- Attribute: in_transaction

          *note True: 594. if a transaction is active (there are
          uncommitted changes), *note False: 48f. otherwise.  Read-only
          attribute.

          New in version 3.2.

      -- Method: cursor (factory=Cursor)

          The cursor method accepts a single optional parameter
          `factory'.  If supplied, this must be a callable returning an
          instance of *note Cursor: 1e57. or its subclasses.

      -- Method: commit ()

          This method commits the current transaction.  If you don’t
          call this method, anything you did since the last call to
          ‘commit()’ is not visible from other database connections.  If
          you wonder why you don’t see the data you’ve written to the
          database, please check you didn’t forget to call this method.

      -- Method: rollback ()

          This method rolls back any changes to the database since the
          last call to *note commit(): 1e73.

      -- Method: close ()

          This closes the database connection.  Note that this does not
          automatically call *note commit(): 1e73.  If you just close
          your database connection without calling *note commit(): 1e73.
          first, your changes will be lost!

      -- Method: execute (sql[, parameters])

          This is a nonstandard shortcut that creates a cursor object by
          calling the *note cursor(): 1e72. method, calls the cursor’s
          *note execute(): 1e58. method with the `parameters' given, and
          returns the cursor.

      -- Method: executemany (sql[, parameters])

          This is a nonstandard shortcut that creates a cursor object by
          calling the *note cursor(): 1e72. method, calls the cursor’s
          *note executemany(): 1e78. method with the `parameters' given,
          and returns the cursor.

      -- Method: executescript (sql_script)

          This is a nonstandard shortcut that creates a cursor object by
          calling the *note cursor(): 1e72. method, calls the cursor’s
          *note executescript(): 1e7a. method with the given
          `sql_script', and returns the cursor.

      -- Method: create_function (name, num_params, func, *,
               deterministic=False)

          Creates a user-defined function that you can later use from
          within SQL statements under the function name `name'.
          `num_params' is the number of parameters the function accepts
          (if `num_params' is -1, the function may take any number of
          arguments), and `func' is a Python callable that is called as
          the SQL function.  If `deterministic' is true, the created
          function is marked as deterministic(1), which allows SQLite to
          perform additional optimizations.  This flag is supported by
          SQLite 3.8.3 or higher, *note NotSupportedError: 1e7b. will be
          raised if used with older versions.

          The function can return any of the types supported by SQLite:
          bytes, str, int, float and ‘None’.

          Changed in version 3.8: The `deterministic' parameter was
          added.

          Example:

               import sqlite3
               import hashlib

               def md5sum(t):
                   return hashlib.md5(t).hexdigest()

               con = sqlite3.connect(":memory:")
               con.create_function("md5", 1, md5sum)
               cur = con.cursor()
               cur.execute("select md5(?)", (b"foo",))
               print(cur.fetchone()[0])

               con.close()

      -- Method: create_aggregate (name, num_params, aggregate_class)

          Creates a user-defined aggregate function.

          The aggregate class must implement a ‘step’ method, which
          accepts the number of parameters `num_params' (if `num_params'
          is -1, the function may take any number of arguments), and a
          ‘finalize’ method which will return the final result of the
          aggregate.

          The ‘finalize’ method can return any of the types supported by
          SQLite: bytes, str, int, float and ‘None’.

          Example:

               import sqlite3

               class MySum:
                   def __init__(self):
                       self.count = 0

                   def step(self, value):
                       self.count += value

                   def finalize(self):
                       return self.count

               con = sqlite3.connect(":memory:")
               con.create_aggregate("mysum", 1, MySum)
               cur = con.cursor()
               cur.execute("create table test(i)")
               cur.execute("insert into test(i) values (1)")
               cur.execute("insert into test(i) values (2)")
               cur.execute("select mysum(i) from test")
               print(cur.fetchone()[0])

               con.close()

      -- Method: create_collation (name, callable)

          Creates a collation with the specified `name' and `callable'.
          The callable will be passed two string arguments.  It should
          return -1 if the first is ordered lower than the second, 0 if
          they are ordered equal and 1 if the first is ordered higher
          than the second.  Note that this controls sorting (ORDER BY in
          SQL) so your comparisons don’t affect other SQL operations.

          Note that the callable will get its parameters as Python
          bytestrings, which will normally be encoded in UTF-8.

          The following example shows a custom collation that sorts “the
          wrong way”:

               import sqlite3

               def collate_reverse(string1, string2):
                   if string1 == string2:
                       return 0
                   elif string1 < string2:
                       return 1
                   else:
                       return -1

               con = sqlite3.connect(":memory:")
               con.create_collation("reverse", collate_reverse)

               cur = con.cursor()
               cur.execute("create table test(x)")
               cur.executemany("insert into test(x) values (?)", [("a",), ("b",)])
               cur.execute("select x from test order by x collate reverse")
               for row in cur:
                   print(row)
               con.close()

          To remove a collation, call ‘create_collation’ with ‘None’ as
          callable:

               con.create_collation("reverse", None)

      -- Method: interrupt ()

          You can call this method from a different thread to abort any
          queries that might be executing on the connection.  The query
          will then abort and the caller will get an exception.

      -- Method: set_authorizer (authorizer_callback)

          This routine registers a callback.  The callback is invoked
          for each attempt to access a column of a table in the
          database.  The callback should return ‘SQLITE_OK’ if access is
          allowed, ‘SQLITE_DENY’ if the entire SQL statement should be
          aborted with an error and ‘SQLITE_IGNORE’ if the column should
          be treated as a NULL value.  These constants are available in
          the *note sqlite3: f2. module.

          The first argument to the callback signifies what kind of
          operation is to be authorized.  The second and third argument
          will be arguments or *note None: 203. depending on the first
          argument.  The 4th argument is the name of the database
          (“main”, “temp”, etc.)  if applicable.  The 5th argument is
          the name of the inner-most trigger or view that is responsible
          for the access attempt or *note None: 203. if this access
          attempt is directly from input SQL code.

          Please consult the SQLite documentation about the possible
          values for the first argument and the meaning of the second
          and third argument depending on the first one.  All necessary
          constants are available in the *note sqlite3: f2. module.

      -- Method: set_progress_handler (handler, n)

          This routine registers a callback.  The callback is invoked
          for every `n' instructions of the SQLite virtual machine.
          This is useful if you want to get called from SQLite during
          long-running operations, for example to update a GUI.

          If you want to clear any previously installed progress
          handler, call the method with *note None: 203. for `handler'.

          Returning a non-zero value from the handler function will
          terminate the currently executing query and cause it to raise
          an *note OperationalError: 1e7e. exception.

      -- Method: set_trace_callback (trace_callback)

          Registers `trace_callback' to be called for each SQL statement
          that is actually executed by the SQLite backend.

          The only argument passed to the callback is the statement (as
          *note str: 205.) that is being executed.  The return value of
          the callback is ignored.  Note that the backend does not only
          run statements passed to the *note Cursor.execute(): 1e58.
          methods.  Other sources include the *note transaction
          management: 1e70. of the sqlite3 module and the execution of
          triggers defined in the current database.

          Passing *note None: 203. as `trace_callback' will disable the
          trace callback.

               Note: Exceptions raised in the trace callback are not
               propagated.  As a development and debugging aid, use
               *note enable_callback_tracebacks(): 1e6d. to enable
               printing tracebacks from exceptions raised in the trace
               callback.

          New in version 3.3.

      -- Method: enable_load_extension (enabled)

          This routine allows/disallows the SQLite engine to load SQLite
          extensions from shared libraries.  SQLite extensions can
          define new functions, aggregates or whole new virtual table
          implementations.  One well-known extension is the
          fulltext-search extension distributed with SQLite.

          Loadable extensions are disabled by default.  See (2).

          New in version 3.2.

               import sqlite3

               con = sqlite3.connect(":memory:")

               # enable extension loading
               con.enable_load_extension(True)

               # Load the fulltext search extension
               con.execute("select load_extension('./fts3.so')")

               # alternatively you can load the extension using an API call:
               # con.load_extension("./fts3.so")

               # disable extension loading again
               con.enable_load_extension(False)

               # example from SQLite wiki
               con.execute("create virtual table recipe using fts3(name, ingredients)")
               con.executescript("""
                   insert into recipe (name, ingredients) values ('broccoli stew', 'broccoli peppers cheese tomatoes');
                   insert into recipe (name, ingredients) values ('pumpkin stew', 'pumpkin onions garlic celery');
                   insert into recipe (name, ingredients) values ('broccoli pie', 'broccoli cheese onions flour');
                   insert into recipe (name, ingredients) values ('pumpkin pie', 'pumpkin sugar flour butter');
                   """)
               for row in con.execute("select rowid, name, ingredients from recipe where name match 'pie'"):
                   print(row)

               con.close()

      -- Method: load_extension (path)

          This routine loads a SQLite extension from a shared library.
          You have to enable extension loading with *note
          enable_load_extension(): c6a. before you can use this routine.

          Loadable extensions are disabled by default.  See (3).

          New in version 3.2.

      -- Attribute: row_factory

          You can change this attribute to a callable that accepts the
          cursor and the original row as a tuple and will return the
          real result row.  This way, you can implement more advanced
          ways of returning results, such as returning an object that
          can also access columns by name.

          Example:

               import sqlite3

               def dict_factory(cursor, row):
                   d = {}
                   for idx, col in enumerate(cursor.description):
                       d[col[0]] = row[idx]
                   return d

               con = sqlite3.connect(":memory:")
               con.row_factory = dict_factory
               cur = con.cursor()
               cur.execute("select 1 as a")
               print(cur.fetchone()["a"])

               con.close()

          If returning a tuple doesn’t suffice and you want name-based
          access to columns, you should consider setting *note
          row_factory: 1e7f. to the highly-optimized *note sqlite3.Row:
          84d. type.  *note Row: 84d. provides both index-based and
          case-insensitive name-based access to columns with almost no
          memory overhead.  It will probably be better than your own
          custom dictionary-based approach or even a db_row based
          solution.

      -- Attribute: text_factory

          Using this attribute you can control what objects are returned
          for the ‘TEXT’ data type.  By default, this attribute is set
          to *note str: 205. and the *note sqlite3: f2. module will
          return *note str: 205. objects for ‘TEXT’.  If you want to
          return *note bytes: 172. instead, you can set it to *note
          bytes: 172.

          You can also set it to any other callable that accepts a
          single bytestring parameter and returns the resulting object.

          See the following example code for illustration:

               import sqlite3

               con = sqlite3.connect(":memory:")
               cur = con.cursor()

               AUSTRIA = "Österreich"

               # by default, rows are returned as str
               cur.execute("select ?", (AUSTRIA,))
               row = cur.fetchone()
               assert row[0] == AUSTRIA

               # but we can make sqlite3 always return bytestrings ...
               con.text_factory = bytes
               cur.execute("select ?", (AUSTRIA,))
               row = cur.fetchone()
               assert type(row[0]) is bytes
               # the bytestrings will be encoded in UTF-8, unless you stored garbage in the
               # database ...
               assert row[0] == AUSTRIA.encode("utf-8")

               # we can also implement a custom text_factory ...
               # here we implement one that appends "foo" to all strings
               con.text_factory = lambda x: x.decode("utf-8") + "foo"
               cur.execute("select ?", ("bar",))
               row = cur.fetchone()
               assert row[0] == "barfoo"

               con.close()

      -- Attribute: total_changes

          Returns the total number of database rows that have been
          modified, inserted, or deleted since the database connection
          was opened.

      -- Method: iterdump ()

          Returns an iterator to dump the database in an SQL text
          format.  Useful when saving an in-memory database for later
          restoration.  This function provides the same capabilities as
          the ‘.dump’ command in the ‘sqlite3’ shell.

          Example:

               # Convert file existing_db.db to SQL dump file dump.sql
               import sqlite3

               con = sqlite3.connect('existing_db.db')
               with open('dump.sql', 'w') as f:
                   for line in con.iterdump():
                       f.write('%s\n' % line)
               con.close()

      -- Method: backup (target, *, pages=-1, progress=None,
               name="main", sleep=0.250)

          This method makes a backup of a SQLite database even while
          it’s being accessed by other clients, or concurrently by the
          same connection.  The copy will be written into the mandatory
          argument `target', that must be another *note Connection: 4df.
          instance.

          By default, or when `pages' is either ‘0’ or a negative
          integer, the entire database is copied in a single step;
          otherwise the method performs a loop copying up to `pages'
          pages at a time.

          If `progress' is specified, it must either be ‘None’ or a
          callable object that will be executed at each iteration with
          three integer arguments, respectively the `status' of the last
          iteration, the `remaining' number of pages still to be copied
          and the `total' number of pages.

          The `name' argument specifies the database name that will be
          copied: it must be a string containing either ‘"main"’, the
          default, to indicate the main database, ‘"temp"’ to indicate
          the temporary database or the name specified after the ‘AS’
          keyword in an ‘ATTACH DATABASE’ statement for an attached
          database.

          The `sleep' argument specifies the number of seconds to sleep
          by between successive attempts to backup remaining pages, can
          be specified either as an integer or a floating point value.

          Example 1, copy an existing database into another:

               import sqlite3

               def progress(status, remaining, total):
                   print(f'Copied {total-remaining} of {total} pages...')

               con = sqlite3.connect('existing_db.db')
               bck = sqlite3.connect('backup.db')
               with bck:
                   con.backup(bck, pages=1, progress=progress)
               bck.close()
               con.close()

          Example 2, copy an existing database into a transient copy:

               import sqlite3

               source = sqlite3.connect('existing_db.db')
               dest = sqlite3.connect(':memory:')
               source.backup(dest)

          Availability: SQLite 3.6.11 or higher

          New in version 3.7.

   ---------- Footnotes ----------

   (1) https://sqlite.org/deterministic.html

   (2) (1) The sqlite3 module is not built with loadable extension
support by default, because some platforms (notably macOS) have SQLite
libraries which are compiled without this feature.  To get loadable
extension support, you must pass ‘--enable-loadable-sqlite-extensions’
to configure.

   (3) (1) The sqlite3 module is not built with loadable extension
support by default, because some platforms (notably macOS) have SQLite
libraries which are compiled without this feature.  To get loadable
extension support, you must pass ‘--enable-loadable-sqlite-extensions’
to configure.


File: python.info,  Node: Cursor Objects,  Next: Row Objects,  Prev: Connection Objects,  Up: sqlite3 — DB-API 2 0 interface for SQLite databases

5.12.6.3 Cursor Objects
.......................

 -- Class: sqlite3.Cursor

     A *note Cursor: 1e57. instance has the following attributes and
     methods.

      -- Method: execute (sql[, parameters])

          Executes an SQL statement.  Values may be bound to the
          statement using *note placeholders: 1e5b.

          *note execute(): 1e58. will only execute a single SQL
          statement.  If you try to execute more than one statement with
          it, it will raise a *note Warning: 1e85.  Use *note
          executescript(): 1e7a. if you want to execute multiple SQL
          statements with one call.

      -- Method: executemany (sql, seq_of_parameters)

          Executes a *note parameterized: 1e5b. SQL command against all
          parameter sequences or mappings found in the sequence
          `seq_of_parameters'.  The *note sqlite3: f2. module also
          allows using an *note iterator: 1171. yielding parameters
          instead of a sequence.

               import sqlite3

               class IterChars:
                   def __init__(self):
                       self.count = ord('a')

                   def __iter__(self):
                       return self

                   def __next__(self):
                       if self.count > ord('z'):
                           raise StopIteration
                       self.count += 1
                       return (chr(self.count - 1),) # this is a 1-tuple

               con = sqlite3.connect(":memory:")
               cur = con.cursor()
               cur.execute("create table characters(c)")

               theIter = IterChars()
               cur.executemany("insert into characters(c) values (?)", theIter)

               cur.execute("select c from characters")
               print(cur.fetchall())

               con.close()

          Here’s a shorter example using a *note generator: a83.:

               import sqlite3
               import string

               def char_generator():
                   for c in string.ascii_lowercase:
                       yield (c,)

               con = sqlite3.connect(":memory:")
               cur = con.cursor()
               cur.execute("create table characters(c)")

               cur.executemany("insert into characters(c) values (?)", char_generator())

               cur.execute("select c from characters")
               print(cur.fetchall())

               con.close()

      -- Method: executescript (sql_script)

          This is a nonstandard convenience method for executing
          multiple SQL statements at once.  It issues a ‘COMMIT’
          statement first, then executes the SQL script it gets as a
          parameter.  This method disregards ‘isolation_level’; any
          transaction control must be added to `sql_script'.

          `sql_script' can be an instance of *note str: 205.

          Example:

               import sqlite3

               con = sqlite3.connect(":memory:")
               cur = con.cursor()
               cur.executescript("""
                   create table person(
                       firstname,
                       lastname,
                       age
                   );

                   create table book(
                       title,
                       author,
                       published
                   );

                   insert into book(title, author, published)
                   values (
                       'Dirk Gently''s Holistic Detective Agency',
                       'Douglas Adams',
                       1987
                   );
                   """)
               con.close()

      -- Method: fetchone ()

          Fetches the next row of a query result set, returning a single
          sequence, or *note None: 203. when no more data is available.

      -- Method: fetchmany (size=cursor.arraysize)

          Fetches the next set of rows of a query result, returning a
          list.  An empty list is returned when no more rows are
          available.

          The number of rows to fetch per call is specified by the
          `size' parameter.  If it is not given, the cursor’s arraysize
          determines the number of rows to be fetched.  The method
          should try to fetch as many rows as indicated by the size
          parameter.  If this is not possible due to the specified
          number of rows not being available, fewer rows may be
          returned.

          Note there are performance considerations involved with the
          `size' parameter.  For optimal performance, it is usually best
          to use the arraysize attribute.  If the `size' parameter is
          used, then it is best for it to retain the same value from one
          *note fetchmany(): 1e86. call to the next.

      -- Method: fetchall ()

          Fetches all (remaining) rows of a query result, returning a
          list.  Note that the cursor’s arraysize attribute can affect
          the performance of this operation.  An empty list is returned
          when no rows are available.

      -- Method: close ()

          Close the cursor now (rather than whenever ‘__del__’ is
          called).

          The cursor will be unusable from this point forward; a *note
          ProgrammingError: ff3. exception will be raised if any
          operation is attempted with the cursor.

      -- Method: setinputsizes (sizes)

          Required by the DB-API. Is a no-op in *note sqlite3: f2.

      -- Method: setoutputsize (size[, column])

          Required by the DB-API. Is a no-op in *note sqlite3: f2.

      -- Attribute: rowcount

          Although the *note Cursor: 1e57. class of the *note sqlite3:
          f2. module implements this attribute, the database engine’s
          own support for the determination of “rows affected”/”rows
          selected” is quirky.

          For *note executemany(): 1e78. statements, the number of
          modifications are summed up into *note rowcount: 1e8a.

          As required by the Python DB API Spec, the *note rowcount:
          1e8a. attribute “is -1 in case no ‘executeXX()’ has been
          performed on the cursor or the rowcount of the last operation
          is not determinable by the interface”.  This includes ‘SELECT’
          statements because we cannot determine the number of rows a
          query produced until all rows were fetched.

          With SQLite versions before 3.6.5, *note rowcount: 1e8a. is
          set to 0 if you make a ‘DELETE FROM table’ without any
          condition.

      -- Attribute: lastrowid

          This read-only attribute provides the row id of the last
          inserted row.  It is only updated after successful ‘INSERT’ or
          ‘REPLACE’ statements using the *note execute(): 1e58. method.
          For other statements, after *note executemany(): 1e78. or
          *note executescript(): 1e7a, or if the insertion failed, the
          value of ‘lastrowid’ is left unchanged.  The initial value of
          ‘lastrowid’ is *note None: 203.

               Note: Inserts into ‘WITHOUT ROWID’ tables are not
               recorded.

          Changed in version 3.6: Added support for the ‘REPLACE’
          statement.

      -- Attribute: arraysize

          Read/write attribute that controls the number of rows returned
          by *note fetchmany(): 1e86.  The default value is 1 which
          means a single row would be fetched per call.

      -- Attribute: description

          This read-only attribute provides the column names of the last
          query.  To remain compatible with the Python DB API, it
          returns a 7-tuple for each column where the last six items of
          each tuple are *note None: 203.

          It is set for ‘SELECT’ statements without any matching rows as
          well.

      -- Attribute: connection

          This read-only attribute provides the SQLite database *note
          Connection: 4df. used by the *note Cursor: 1e57. object.  A
          *note Cursor: 1e57. object created by calling *note
          con.cursor(): 1e72. will have a *note connection: 1e8c.
          attribute that refers to `con':

               >>> con = sqlite3.connect(":memory:")
               >>> cur = con.cursor()
               >>> cur.connection == con
               True


File: python.info,  Node: Row Objects,  Next: Exceptions<5>,  Prev: Cursor Objects,  Up: sqlite3 — DB-API 2 0 interface for SQLite databases

5.12.6.4 Row Objects
....................

 -- Class: sqlite3.Row

     A *note Row: 84d. instance serves as a highly optimized *note
     row_factory: 1e7f. for *note Connection: 4df. objects.  It tries to
     mimic a tuple in most of its features.

     It supports mapping access by column name and index, iteration,
     representation, equality testing and *note len(): 28b.

     If two *note Row: 84d. objects have exactly the same columns and
     their members are equal, they compare equal.

      -- Method: keys ()

          This method returns a list of column names.  Immediately after
          a query, it is the first member of each tuple in *note
          Cursor.description: 1e67.

     Changed in version 3.5: Added support of slicing.

Let’s assume we initialize a table as in the example given above:

     con = sqlite3.connect(":memory:")
     cur = con.cursor()
     cur.execute('''create table stocks
     (date text, trans text, symbol text,
      qty real, price real)''')
     cur.execute("""insert into stocks
                 values ('2006-01-05','BUY','RHAT',100,35.14)""")
     con.commit()
     cur.close()

Now we plug *note Row: 84d. in:

     >>> con.row_factory = sqlite3.Row
     >>> cur = con.cursor()
     >>> cur.execute('select * from stocks')
     <sqlite3.Cursor object at 0x7f4e7dd8fa80>
     >>> r = cur.fetchone()
     >>> type(r)
     <class 'sqlite3.Row'>
     >>> tuple(r)
     ('2006-01-05', 'BUY', 'RHAT', 100.0, 35.14)
     >>> len(r)
     5
     >>> r[2]
     'RHAT'
     >>> r.keys()
     ['date', 'trans', 'symbol', 'qty', 'price']
     >>> r['qty']
     100.0
     >>> for member in r:
     ...     print(member)
     ...
     2006-01-05
     BUY
     RHAT
     100.0
     35.14


File: python.info,  Node: Exceptions<5>,  Next: SQLite and Python types,  Prev: Row Objects,  Up: sqlite3 — DB-API 2 0 interface for SQLite databases

5.12.6.5 Exceptions
...................

 -- Exception: sqlite3.Warning

     A subclass of *note Exception: 2dc.

 -- Exception: sqlite3.Error

     The base class of the other exceptions in this module.  It is a
     subclass of *note Exception: 2dc.

 -- Exception: sqlite3.DatabaseError

     Exception raised for errors that are related to the database.

 -- Exception: sqlite3.IntegrityError

     Exception raised when the relational integrity of the database is
     affected, e.g.  a foreign key check fails.  It is a subclass of
     *note DatabaseError: 1e93.

 -- Exception: sqlite3.ProgrammingError

     Exception raised for programming errors, e.g.  table not found or
     already exists, syntax error in the SQL statement, wrong number of
     parameters specified, etc.  It is a subclass of *note
     DatabaseError: 1e93.

 -- Exception: sqlite3.OperationalError

     Exception raised for errors that are related to the database’s
     operation and not necessarily under the control of the programmer,
     e.g.  an unexpected disconnect occurs, the data source name is not
     found, a transaction could not be processed, etc.  It is a subclass
     of *note DatabaseError: 1e93.

 -- Exception: sqlite3.NotSupportedError

     Exception raised in case a method or database API was used which is
     not supported by the database, e.g.  calling the *note rollback():
     1e74. method on a connection that does not support transaction or
     has transactions turned off.  It is a subclass of *note
     DatabaseError: 1e93.


File: python.info,  Node: SQLite and Python types,  Next: Controlling Transactions,  Prev: Exceptions<5>,  Up: sqlite3 — DB-API 2 0 interface for SQLite databases

5.12.6.6 SQLite and Python types
................................

* Menu:

* Introduction: Introduction<7>.
* Using adapters to store additional Python types in SQLite databases::
* Converting SQLite values to custom Python types::
* Default adapters and converters::


File: python.info,  Node: Introduction<7>,  Next: Using adapters to store additional Python types in SQLite databases,  Up: SQLite and Python types

5.12.6.7 Introduction
.....................

SQLite natively supports the following types: ‘NULL’, ‘INTEGER’, ‘REAL’,
‘TEXT’, ‘BLOB’.

The following Python types can thus be sent to SQLite without any
problem:

Python type                         SQLite type
                                    
------------------------------------------------------
                                    
*note None: 203.                    ‘NULL’
                                    
                                    
*note int: 204.                     ‘INTEGER’
                                    
                                    
*note float: 1fd.                   ‘REAL’
                                    
                                    
*note str: 205.                     ‘TEXT’
                                    
                                    
*note bytes: 172.                   ‘BLOB’
                                    

This is how SQLite types are converted to Python types by default:

SQLite type       Python type
                  
---------------------------------------------------------------------
                  
‘NULL’            *note None: 203.
                  
                  
‘INTEGER’         *note int: 204.
                  
                  
‘REAL’            *note float: 1fd.
                  
                  
‘TEXT’            depends on *note text_factory: 1e80,
                  *note str: 205. by default
                  
                  
‘BLOB’            *note bytes: 172.
                  

The type system of the *note sqlite3: f2. module is extensible in two
ways: you can store additional Python types in a SQLite database via
object adaptation, and you can let the *note sqlite3: f2. module convert
SQLite types to different Python types via converters.


File: python.info,  Node: Using adapters to store additional Python types in SQLite databases,  Next: Converting SQLite values to custom Python types,  Prev: Introduction<7>,  Up: SQLite and Python types

5.12.6.8 Using adapters to store additional Python types in SQLite databases
............................................................................

As described before, SQLite supports only a limited set of types
natively.  To use other Python types with SQLite, you must `adapt' them
to one of the sqlite3 module’s supported types for SQLite: one of
NoneType, int, float, str, bytes.

There are two ways to enable the *note sqlite3: f2. module to adapt a
custom Python type to one of the supported ones.

* Menu:

* Letting your object adapt itself::
* Registering an adapter callable::


File: python.info,  Node: Letting your object adapt itself,  Next: Registering an adapter callable,  Up: Using adapters to store additional Python types in SQLite databases

5.12.6.9 Letting your object adapt itself
.........................................

This is a good approach if you write the class yourself.  Let’s suppose
you have a class like this:

     class Point:
         def __init__(self, x, y):
             self.x, self.y = x, y

Now you want to store the point in a single SQLite column.  First you’ll
have to choose one of the supported types to be used for representing
the point.  Let’s just use str and separate the coordinates using a
semicolon.  Then you need to give your class a method ‘__conform__(self,
protocol)’ which must return the converted value.  The parameter
`protocol' will be ‘PrepareProtocol’.

     import sqlite3

     class Point:
         def __init__(self, x, y):
             self.x, self.y = x, y

         def __conform__(self, protocol):
             if protocol is sqlite3.PrepareProtocol:
                 return "%f;%f" % (self.x, self.y)

     con = sqlite3.connect(":memory:")
     cur = con.cursor()

     p = Point(4.0, -3.2)
     cur.execute("select ?", (p,))
     print(cur.fetchone()[0])

     con.close()


File: python.info,  Node: Registering an adapter callable,  Prev: Letting your object adapt itself,  Up: Using adapters to store additional Python types in SQLite databases

5.12.6.10 Registering an adapter callable
.........................................

The other possibility is to create a function that converts the type to
the string representation and register the function with *note
register_adapter(): 1e6b.

     import sqlite3

     class Point:
         def __init__(self, x, y):
             self.x, self.y = x, y

     def adapt_point(point):
         return "%f;%f" % (point.x, point.y)

     sqlite3.register_adapter(Point, adapt_point)

     con = sqlite3.connect(":memory:")
     cur = con.cursor()

     p = Point(4.0, -3.2)
     cur.execute("select ?", (p,))
     print(cur.fetchone()[0])

     con.close()

The *note sqlite3: f2. module has two default adapters for Python’s
built-in *note datetime.date: 19e. and *note datetime.datetime: 1a0.
types.  Now let’s suppose we want to store *note datetime.datetime: 1a0.
objects not in ISO representation, but as a Unix timestamp.

     import sqlite3
     import datetime
     import time

     def adapt_datetime(ts):
         return time.mktime(ts.timetuple())

     sqlite3.register_adapter(datetime.datetime, adapt_datetime)

     con = sqlite3.connect(":memory:")
     cur = con.cursor()

     now = datetime.datetime.now()
     cur.execute("select ?", (now,))
     print(cur.fetchone()[0])

     con.close()


File: python.info,  Node: Converting SQLite values to custom Python types,  Next: Default adapters and converters,  Prev: Using adapters to store additional Python types in SQLite databases,  Up: SQLite and Python types

5.12.6.11 Converting SQLite values to custom Python types
.........................................................

Writing an adapter lets you send custom Python types to SQLite.  But to
make it really useful we need to make the Python to SQLite to Python
roundtrip work.

Enter converters.

Let’s go back to the ‘Point’ class.  We stored the x and y coordinates
separated via semicolons as strings in SQLite.

First, we’ll define a converter function that accepts the string as a
parameter and constructs a ‘Point’ object from it.

     Note: Converter functions `always' get called with a *note bytes:
     172. object, no matter under which data type you sent the value to
     SQLite.

     def convert_point(s):
         x, y = map(float, s.split(b";"))
         return Point(x, y)

Now you need to make the *note sqlite3: f2. module know that what you
select from the database is actually a point.  There are two ways of
doing this:

   * Implicitly via the declared type

   * Explicitly via the column name

Both ways are described in section *note Module functions and constants:
1e5d, in the entries for the constants *note PARSE_DECLTYPES: 1e65. and
*note PARSE_COLNAMES: 1e66.

The following example illustrates both approaches.

     import sqlite3

     class Point:
         def __init__(self, x, y):
             self.x, self.y = x, y

         def __repr__(self):
             return "(%f;%f)" % (self.x, self.y)

     def adapt_point(point):
         return ("%f;%f" % (point.x, point.y)).encode('ascii')

     def convert_point(s):
         x, y = list(map(float, s.split(b";")))
         return Point(x, y)

     # Register the adapter
     sqlite3.register_adapter(Point, adapt_point)

     # Register the converter
     sqlite3.register_converter("point", convert_point)

     p = Point(4.0, -3.2)

     #########################
     # 1) Using declared types
     con = sqlite3.connect(":memory:", detect_types=sqlite3.PARSE_DECLTYPES)
     cur = con.cursor()
     cur.execute("create table test(p point)")

     cur.execute("insert into test(p) values (?)", (p,))
     cur.execute("select p from test")
     print("with declared types:", cur.fetchone()[0])
     cur.close()
     con.close()

     #######################
     # 1) Using column names
     con = sqlite3.connect(":memory:", detect_types=sqlite3.PARSE_COLNAMES)
     cur = con.cursor()
     cur.execute("create table test(p)")

     cur.execute("insert into test(p) values (?)", (p,))
     cur.execute('select p as "p [point]" from test')
     print("with column names:", cur.fetchone()[0])
     cur.close()
     con.close()


File: python.info,  Node: Default adapters and converters,  Prev: Converting SQLite values to custom Python types,  Up: SQLite and Python types

5.12.6.12 Default adapters and converters
.........................................

There are default adapters for the date and datetime types in the
datetime module.  They will be sent as ISO dates/ISO timestamps to
SQLite.

The default converters are registered under the name “date” for *note
datetime.date: 19e. and under the name “timestamp” for *note
datetime.datetime: 1a0.

This way, you can use date/timestamps from Python without any additional
fiddling in most cases.  The format of the adapters is also compatible
with the experimental SQLite date/time functions.

The following example demonstrates this.

     import sqlite3
     import datetime

     con = sqlite3.connect(":memory:", detect_types=sqlite3.PARSE_DECLTYPES|sqlite3.PARSE_COLNAMES)
     cur = con.cursor()
     cur.execute("create table test(d date, ts timestamp)")

     today = datetime.date.today()
     now = datetime.datetime.now()

     cur.execute("insert into test(d, ts) values (?, ?)", (today, now))
     cur.execute("select d, ts from test")
     row = cur.fetchone()
     print(today, "=>", row[0], type(row[0]))
     print(now, "=>", row[1], type(row[1]))

     cur.execute('select current_date as "d [date]", current_timestamp as "ts [timestamp]"')
     row = cur.fetchone()
     print("current_date", row[0], type(row[0]))
     print("current_timestamp", row[1], type(row[1]))

     con.close()

If a timestamp stored in SQLite has a fractional part longer than 6
numbers, its value will be truncated to microsecond precision by the
timestamp converter.

     Note: The default “timestamp” converter ignores UTC offsets in the
     database and always returns a naive *note datetime.datetime: 1a0.
     object.  To preserve UTC offsets in timestamps, either leave
     converters disabled, or register an offset-aware converter with
     *note register_converter(): 1e69.


File: python.info,  Node: Controlling Transactions,  Next: Using sqlite3 efficiently,  Prev: SQLite and Python types,  Up: sqlite3 — DB-API 2 0 interface for SQLite databases

5.12.6.13 Controlling Transactions
..................................

The underlying ‘sqlite3’ library operates in ‘autocommit’ mode by
default, but the Python *note sqlite3: f2. module by default does not.

‘autocommit’ mode means that statements that modify the database take
effect immediately.  A ‘BEGIN’ or ‘SAVEPOINT’ statement disables
‘autocommit’ mode, and a ‘COMMIT’, a ‘ROLLBACK’, or a ‘RELEASE’ that
ends the outermost transaction, turns ‘autocommit’ mode back on.

The Python *note sqlite3: f2. module by default issues a ‘BEGIN’
statement implicitly before a Data Modification Language (DML) statement
(i.e.  ‘INSERT’/‘UPDATE’/‘DELETE’/‘REPLACE’).

You can control which kind of ‘BEGIN’ statements *note sqlite3: f2.
implicitly executes via the `isolation_level' parameter to the *note
connect(): 4e1. call, or via the ‘isolation_level’ property of
connections.  If you specify no `isolation_level', a plain ‘BEGIN’ is
used, which is equivalent to specifying ‘DEFERRED’.  Other possible
values are ‘IMMEDIATE’ and ‘EXCLUSIVE’.

You can disable the *note sqlite3: f2. module’s implicit transaction
management by setting ‘isolation_level’ to ‘None’.  This will leave the
underlying ‘sqlite3’ library operating in ‘autocommit’ mode.  You can
then completely control the transaction state by explicitly issuing
‘BEGIN’, ‘ROLLBACK’, ‘SAVEPOINT’, and ‘RELEASE’ statements in your code.

Note that *note executescript(): 1e7a. disregards ‘isolation_level’; any
transaction control must be added explicitly.

Changed in version 3.6: *note sqlite3: f2. used to implicitly commit an
open transaction before DDL statements.  This is no longer the case.


File: python.info,  Node: Using sqlite3 efficiently,  Prev: Controlling Transactions,  Up: sqlite3 — DB-API 2 0 interface for SQLite databases

5.12.6.14 Using ‘sqlite3’ efficiently
.....................................

* Menu:

* Using shortcut methods::
* Accessing columns by name instead of by index::
* Using the connection as a context manager::


File: python.info,  Node: Using shortcut methods,  Next: Accessing columns by name instead of by index,  Up: Using sqlite3 efficiently

5.12.6.15 Using shortcut methods
................................

Using the nonstandard ‘execute()’, ‘executemany()’ and ‘executescript()’
methods of the *note Connection: 4df. object, your code can be written
more concisely because you don’t have to create the (often superfluous)
*note Cursor: 1e57. objects explicitly.  Instead, the *note Cursor:
1e57. objects are created implicitly and these shortcut methods return
the cursor objects.  This way, you can execute a ‘SELECT’ statement and
iterate over it directly using only a single call on the *note
Connection: 4df. object.

     import sqlite3

     langs = [
         ("C++", 1985),
         ("Objective-C", 1984),
     ]

     con = sqlite3.connect(":memory:")

     # Create the table
     con.execute("create table lang(name, first_appeared)")

     # Fill the table
     con.executemany("insert into lang(name, first_appeared) values (?, ?)", langs)

     # Print the table contents
     for row in con.execute("select name, first_appeared from lang"):
         print(row)

     print("I just deleted", con.execute("delete from lang").rowcount, "rows")

     # close is not a shortcut method and it's not called automatically,
     # so the connection object should be closed manually
     con.close()


File: python.info,  Node: Accessing columns by name instead of by index,  Next: Using the connection as a context manager,  Prev: Using shortcut methods,  Up: Using sqlite3 efficiently

5.12.6.16 Accessing columns by name instead of by index
.......................................................

One useful feature of the *note sqlite3: f2. module is the built-in
*note sqlite3.Row: 84d. class designed to be used as a row factory.

Rows wrapped with this class can be accessed both by index (like tuples)
and case-insensitively by name:

     import sqlite3

     con = sqlite3.connect(":memory:")
     con.row_factory = sqlite3.Row

     cur = con.cursor()
     cur.execute("select 'John' as name, 42 as age")
     for row in cur:
         assert row[0] == row["name"]
         assert row["name"] == row["nAmE"]
         assert row[1] == row["age"]
         assert row[1] == row["AgE"]

     con.close()


File: python.info,  Node: Using the connection as a context manager,  Prev: Accessing columns by name instead of by index,  Up: Using sqlite3 efficiently

5.12.6.17 Using the connection as a context manager
...................................................

Connection objects can be used as context managers that automatically
commit or rollback transactions.  In the event of an exception, the
transaction is rolled back; otherwise, the transaction is committed:

     import sqlite3

     con = sqlite3.connect(":memory:")
     con.execute("create table lang (id integer primary key, name varchar unique)")

     # Successful, con.commit() is called automatically afterwards
     with con:
         con.execute("insert into lang(name) values (?)", ("Python",))

     # con.rollback() is called after the with block finishes with an exception, the
     # exception is still raised and must be caught
     try:
         with con:
             con.execute("insert into lang(name) values (?)", ("Python",))
     except sqlite3.IntegrityError:
         print("couldn't add Python twice")

     # Connection object used as context manager only commits or rollbacks transactions,
     # so the connection object should be closed manually
     con.close()


File: python.info,  Node: Data Compression and Archiving,  Next: File Formats,  Prev: Data Persistence,  Up: The Python Standard Library

5.13 Data Compression and Archiving
===================================

The modules described in this chapter support data compression with the
zlib, gzip, bzip2 and lzma algorithms, and the creation of ZIP- and
tar-format archives.  See also *note Archiving operations: c67. provided
by the *note shutil: e9. module.

* Menu:

* zlib — Compression compatible with gzip::
* gzip — Support for gzip files::
* bz2 — Support for bzip2 compression::
* lzma — Compression using the LZMA algorithm::
* zipfile — Work with ZIP archives::
* tarfile — Read and write tar archive files::


File: python.info,  Node: zlib — Compression compatible with gzip,  Next: gzip — Support for gzip files,  Up: Data Compression and Archiving

5.13.1 ‘zlib’ — Compression compatible with ‘gzip’
--------------------------------------------------

__________________________________________________________________

For applications that require data compression, the functions in this
module allow compression and decompression, using the zlib library.  The
zlib library has its own home page at ‘https://www.zlib.net’.  There are
known incompatibilities between the Python module and versions of the
zlib library earlier than 1.1.3; 1.1.3 has a security vulnerability(1),
so we recommend using 1.1.4 or later.

zlib’s functions have many options and often need to be used in a
particular order.  This documentation doesn’t attempt to cover all of
the permutations; consult the zlib manual at
‘http://www.zlib.net/manual.html’ for authoritative information.

For reading and writing ‘.gz’ files see the *note gzip: 8b. module.

The available exception and functions in this module are:

 -- Exception: zlib.error

     Exception raised on compression and decompression errors.

 -- Function: zlib.adler32 (data[, value])

     Computes an Adler-32 checksum of `data'.  (An Adler-32 checksum is
     almost as reliable as a CRC32 but can be computed much more
     quickly.)  The result is an unsigned 32-bit integer.  If `value' is
     present, it is used as the starting value of the checksum;
     otherwise, a default value of 1 is used.  Passing in `value' allows
     computing a running checksum over the concatenation of several
     inputs.  The algorithm is not cryptographically strong, and should
     not be used for authentication or digital signatures.  Since the
     algorithm is designed for use as a checksum algorithm, it is not
     suitable for use as a general hash algorithm.

     Changed in version 3.0: Always returns an unsigned value.  To
     generate the same numeric value across all Python versions and
     platforms, use ‘adler32(data) & 0xffffffff’.

 -- Function: zlib.compress (data, /, level=-1)

     Compresses the bytes in `data', returning a bytes object containing
     compressed data.  `level' is an integer from ‘0’ to ‘9’ or ‘-1’
     controlling the level of compression; ‘1’ (Z_BEST_SPEED) is fastest
     and produces the least compression, ‘9’ (Z_BEST_COMPRESSION) is
     slowest and produces the most.  ‘0’ (Z_NO_COMPRESSION) is no
     compression.  The default value is ‘-1’ (Z_DEFAULT_COMPRESSION).
     Z_DEFAULT_COMPRESSION represents a default compromise between speed
     and compression (currently equivalent to level 6).  Raises the
     *note error: 1ea5. exception if any error occurs.

     Changed in version 3.6: `level' can now be used as a keyword
     parameter.

 -- Function: zlib.compressobj (level=-1, method=DEFLATED,
          wbits=MAX_WBITS, memLevel=DEF_MEM_LEVEL,
          strategy=Z_DEFAULT_STRATEGY[, zdict])

     Returns a compression object, to be used for compressing data
     streams that won’t fit into memory at once.

     `level' is the compression level – an integer from ‘0’ to ‘9’ or
     ‘-1’.  A value of ‘1’ (Z_BEST_SPEED) is fastest and produces the
     least compression, while a value of ‘9’ (Z_BEST_COMPRESSION) is
     slowest and produces the most.  ‘0’ (Z_NO_COMPRESSION) is no
     compression.  The default value is ‘-1’ (Z_DEFAULT_COMPRESSION).
     Z_DEFAULT_COMPRESSION represents a default compromise between speed
     and compression (currently equivalent to level 6).

     `method' is the compression algorithm.  Currently, the only
     supported value is ‘DEFLATED’.

     The `wbits' argument controls the size of the history buffer (or
     the “window size”) used when compressing data, and whether a header
     and trailer is included in the output.  It can take several ranges
     of values, defaulting to ‘15’ (MAX_WBITS):

        * +9 to +15: The base-two logarithm of the window size, which
          therefore ranges between 512 and 32768.  Larger values produce
          better compression at the expense of greater memory usage.
          The resulting output will include a zlib-specific header and
          trailer.

        * −9 to −15: Uses the absolute value of `wbits' as the window
          size logarithm, while producing a raw output stream with no
          header or trailing checksum.

        * +25 to +31 = 16 + (9 to 15): Uses the low 4 bits of the value
          as the window size logarithm, while including a basic ‘gzip’
          header and trailing checksum in the output.

     The `memLevel' argument controls the amount of memory used for the
     internal compression state.  Valid values range from ‘1’ to ‘9’.
     Higher values use more memory, but are faster and produce smaller
     output.

     `strategy' is used to tune the compression algorithm.  Possible
     values are ‘Z_DEFAULT_STRATEGY’, ‘Z_FILTERED’, ‘Z_HUFFMAN_ONLY’,
     ‘Z_RLE’ (zlib 1.2.0.1) and ‘Z_FIXED’ (zlib 1.2.2.2).

     `zdict' is a predefined compression dictionary.  This is a sequence
     of bytes (such as a *note bytes: 172. object) containing
     subsequences that are expected to occur frequently in the data that
     is to be compressed.  Those subsequences that are expected to be
     most common should come at the end of the dictionary.

     Changed in version 3.3: Added the `zdict' parameter and keyword
     argument support.

 -- Function: zlib.crc32 (data[, value])

     Computes a CRC (Cyclic Redundancy Check) checksum of `data'.  The
     result is an unsigned 32-bit integer.  If `value' is present, it is
     used as the starting value of the checksum; otherwise, a default
     value of 0 is used.  Passing in `value' allows computing a running
     checksum over the concatenation of several inputs.  The algorithm
     is not cryptographically strong, and should not be used for
     authentication or digital signatures.  Since the algorithm is
     designed for use as a checksum algorithm, it is not suitable for
     use as a general hash algorithm.

     Changed in version 3.0: Always returns an unsigned value.  To
     generate the same numeric value across all Python versions and
     platforms, use ‘crc32(data) & 0xffffffff’.

 -- Function: zlib.decompress (data, /, wbits=MAX_WBITS,
          bufsize=DEF_BUF_SIZE)

     Decompresses the bytes in `data', returning a bytes object
     containing the uncompressed data.  The `wbits' parameter depends on
     the format of `data', and is discussed further below.  If `bufsize'
     is given, it is used as the initial size of the output buffer.
     Raises the *note error: 1ea5. exception if any error occurs.  The
     `wbits' parameter controls the size of the history buffer (or
     “window size”), and what header and trailer format is expected.  It
     is similar to the parameter for *note compressobj(): 1ea7, but
     accepts more ranges of values:

        * +8 to +15: The base-two logarithm of the window size.  The
          input must include a zlib header and trailer.

        * 0: Automatically determine the window size from the zlib
          header.  Only supported since zlib 1.2.3.5.

        * −8 to −15: Uses the absolute value of `wbits' as the window
          size logarithm.  The input must be a raw stream with no header
          or trailer.

        * +24 to +31 = 16 + (8 to 15): Uses the low 4 bits of the value
          as the window size logarithm.  The input must include a gzip
          header and trailer.

        * +40 to +47 = 32 + (8 to 15): Uses the low 4 bits of the value
          as the window size logarithm, and automatically accepts either
          the zlib or gzip format.

     When decompressing a stream, the window size must not be smaller
     than the size originally used to compress the stream; using a
     too-small value may result in an *note error: 1ea5. exception.  The
     default `wbits' value corresponds to the largest window size and
     requires a zlib header and trailer to be included.

     `bufsize' is the initial size of the buffer used to hold
     decompressed data.  If more space is required, the buffer size will
     be increased as needed, so you don’t have to get this value exactly
     right; tuning it will only save a few calls to ‘malloc()’.

     Changed in version 3.6: `wbits' and `bufsize' can be used as
     keyword arguments.

 -- Function: zlib.decompressobj (wbits=MAX_WBITS[, zdict])

     Returns a decompression object, to be used for decompressing data
     streams that won’t fit into memory at once.

     The `wbits' parameter controls the size of the history buffer (or
     the “window size”), and what header and trailer format is expected.
     It has the same meaning as *note described for decompress(): 1ea9.

     The `zdict' parameter specifies a predefined compression
     dictionary.  If provided, this must be the same dictionary as was
     used by the compressor that produced the data that is to be
     decompressed.

          Note: If `zdict' is a mutable object (such as a *note
          bytearray: 173.), you must not modify its contents between the
          call to *note decompressobj(): 1eaa. and the first call to the
          decompressor’s ‘decompress()’ method.

     Changed in version 3.3: Added the `zdict' parameter.

Compression objects support the following methods:

 -- Method: Compress.compress (data)

     Compress `data', returning a bytes object containing compressed
     data for at least part of the data in `data'.  This data should be
     concatenated to the output produced by any preceding calls to the
     *note compress(): 6b5. method.  Some input may be kept in internal
     buffers for later processing.

 -- Method: Compress.flush ([mode])

     All pending input is processed, and a bytes object containing the
     remaining compressed output is returned.  `mode' can be selected
     from the constants ‘Z_NO_FLUSH’, ‘Z_PARTIAL_FLUSH’, ‘Z_SYNC_FLUSH’,
     ‘Z_FULL_FLUSH’, ‘Z_BLOCK’ (zlib 1.2.3.4), or ‘Z_FINISH’, defaulting
     to ‘Z_FINISH’.  Except ‘Z_FINISH’, all constants allow compressing
     further bytestrings of data, while ‘Z_FINISH’ finishes the
     compressed stream and prevents compressing any more data.  After
     calling *note flush(): 1eac. with `mode' set to ‘Z_FINISH’, the
     *note compress(): 6b5. method cannot be called again; the only
     realistic action is to delete the object.

 -- Method: Compress.copy ()

     Returns a copy of the compression object.  This can be used to
     efficiently compress a set of data that share a common initial
     prefix.

Changed in version 3.8: Added *note copy.copy(): 4d2. and *note
copy.deepcopy(): 4d3. support to compression objects.

Decompression objects support the following methods and attributes:

 -- Attribute: Decompress.unused_data

     A bytes object which contains any bytes past the end of the
     compressed data.  That is, this remains ‘b""’ until the last byte
     that contains compression data is available.  If the whole
     bytestring turned out to contain compressed data, this is ‘b""’, an
     empty bytes object.

 -- Attribute: Decompress.unconsumed_tail

     A bytes object that contains any data that was not consumed by the
     last *note decompress(): 6b6. call because it exceeded the limit
     for the uncompressed data buffer.  This data has not yet been seen
     by the zlib machinery, so you must feed it (possibly with further
     data concatenated to it) back to a subsequent *note decompress():
     6b6. method call in order to get correct output.

 -- Attribute: Decompress.eof

     A boolean indicating whether the end of the compressed data stream
     has been reached.

     This makes it possible to distinguish between a properly-formed
     compressed stream, and an incomplete or truncated one.

     New in version 3.3.

 -- Method: Decompress.decompress (data, max_length=0)

     Decompress `data', returning a bytes object containing the
     uncompressed data corresponding to at least part of the data in
     `string'.  This data should be concatenated to the output produced
     by any preceding calls to the *note decompress(): 6b6. method.
     Some of the input data may be preserved in internal buffers for
     later processing.

     If the optional parameter `max_length' is non-zero then the return
     value will be no longer than `max_length'.  This may mean that not
     all of the compressed input can be processed; and unconsumed data
     will be stored in the attribute *note unconsumed_tail: 1eaf.  This
     bytestring must be passed to a subsequent call to *note
     decompress(): 6b6. if decompression is to continue.  If
     `max_length' is zero then the whole input is decompressed, and
     *note unconsumed_tail: 1eaf. is empty.

     Changed in version 3.6: `max_length' can be used as a keyword
     argument.

 -- Method: Decompress.flush ([length])

     All pending input is processed, and a bytes object containing the
     remaining uncompressed output is returned.  After calling *note
     flush(): 1eb1, the *note decompress(): 6b6. method cannot be called
     again; the only realistic action is to delete the object.

     The optional parameter `length' sets the initial size of the output
     buffer.

 -- Method: Decompress.copy ()

     Returns a copy of the decompression object.  This can be used to
     save the state of the decompressor midway through the data stream
     in order to speed up random seeks into the stream at a future
     point.

Changed in version 3.8: Added *note copy.copy(): 4d2. and *note
copy.deepcopy(): 4d3. support to decompression objects.

Information about the version of the zlib library in use is available
through the following constants:

 -- Data: zlib.ZLIB_VERSION

     The version string of the zlib library that was used for building
     the module.  This may be different from the zlib library actually
     used at runtime, which is available as *note ZLIB_RUNTIME_VERSION:
     b9e.

 -- Data: zlib.ZLIB_RUNTIME_VERSION

     The version string of the zlib library actually loaded by the
     interpreter.

     New in version 3.3.

See also
........

Module *note gzip: 8b.

     Reading and writing ‘gzip’-format files.

‘http://www.zlib.net’

     The zlib library home page.

‘http://www.zlib.net/manual.html’

     The zlib manual explains the semantics and usage of the library’s
     many functions.

   ---------- Footnotes ----------

   (1) https://zlib.net/zlib_faq.html#faq33


File: python.info,  Node: gzip — Support for gzip files,  Next: bz2 — Support for bzip2 compression,  Prev: zlib — Compression compatible with gzip,  Up: Data Compression and Archiving

5.13.2 ‘gzip’ — Support for ‘gzip’ files
----------------------------------------

`Source code:' Lib/gzip.py(1)

__________________________________________________________________

This module provides a simple interface to compress and decompress files
just like the GNU programs ‘gzip’ and ‘gunzip’ would.

The data compression is provided by the *note zlib: 14d. module.

The *note gzip: 8b. module provides the *note GzipFile: 206. class, as
well as the *note open(): 1eb6, *note compress(): 302. and *note
decompress(): c5a. convenience functions.  The *note GzipFile: 206.
class reads and writes ‘gzip’-format files, automatically compressing or
decompressing the data so that it looks like an ordinary *note file
object: c14.

Note that additional file formats which can be decompressed by the
‘gzip’ and ‘gunzip’ programs, such as those produced by ‘compress’ and
‘pack’, are not supported by this module.

The module defines the following items:

 -- Function: gzip.open (filename, mode='rb', compresslevel=9,
          encoding=None, errors=None, newline=None)

     Open a gzip-compressed file in binary or text mode, returning a
     *note file object: c14.

     The `filename' argument can be an actual filename (a *note str:
     205. or *note bytes: 172. object), or an existing file object to
     read from or write to.

     The `mode' argument can be any of ‘'r'’, ‘'rb'’, ‘'a'’, ‘'ab'’,
     ‘'w'’, ‘'wb'’, ‘'x'’ or ‘'xb'’ for binary mode, or ‘'rt'’, ‘'at'’,
     ‘'wt'’, or ‘'xt'’ for text mode.  The default is ‘'rb'’.

     The `compresslevel' argument is an integer from 0 to 9, as for the
     *note GzipFile: 206. constructor.

     For binary mode, this function is equivalent to the *note GzipFile:
     206. constructor: ‘GzipFile(filename, mode, compresslevel)’.  In
     this case, the `encoding', `errors' and `newline' arguments must
     not be provided.

     For text mode, a *note GzipFile: 206. object is created, and
     wrapped in an *note io.TextIOWrapper: 6ea. instance with the
     specified encoding, error handling behavior, and line ending(s).

     Changed in version 3.3: Added support for `filename' being a file
     object, support for text mode, and the `encoding', `errors' and
     `newline' arguments.

     Changed in version 3.4: Added support for the ‘'x'’, ‘'xb'’ and
     ‘'xt'’ modes.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Exception: gzip.BadGzipFile

     An exception raised for invalid gzip files.  It inherits *note
     OSError: 304.  *note EOFError: d34. and *note zlib.error: 1ea5. can
     also be raised for invalid gzip files.

     New in version 3.8.

 -- Class: gzip.GzipFile (filename=None, mode=None, compresslevel=9,
          fileobj=None, mtime=None)

     Constructor for the *note GzipFile: 206. class, which simulates
     most of the methods of a *note file object: c14, with the exception
     of the ‘truncate()’ method.  At least one of `fileobj' and
     `filename' must be given a non-trivial value.

     The new class instance is based on `fileobj', which can be a
     regular file, an *note io.BytesIO: 88a. object, or any other object
     which simulates a file.  It defaults to ‘None’, in which case
     `filename' is opened to provide a file object.

     When `fileobj' is not ‘None’, the `filename' argument is only used
     to be included in the ‘gzip’ file header, which may include the
     original filename of the uncompressed file.  It defaults to the
     filename of `fileobj', if discernible; otherwise, it defaults to
     the empty string, and in this case the original filename is not
     included in the header.

     The `mode' argument can be any of ‘'r'’, ‘'rb'’, ‘'a'’, ‘'ab'’,
     ‘'w'’, ‘'wb'’, ‘'x'’, or ‘'xb'’, depending on whether the file will
     be read or written.  The default is the mode of `fileobj' if
     discernible; otherwise, the default is ‘'rb'’.  In future Python
     releases the mode of `fileobj' will not be used.  It is better to
     always specify `mode' for writing.

     Note that the file is always opened in binary mode.  To open a
     compressed file in text mode, use *note open(): 1eb6. (or wrap your
     *note GzipFile: 206. with an *note io.TextIOWrapper: 6ea.).

     The `compresslevel' argument is an integer from ‘0’ to ‘9’
     controlling the level of compression; ‘1’ is fastest and produces
     the least compression, and ‘9’ is slowest and produces the most
     compression.  ‘0’ is no compression.  The default is ‘9’.

     The `mtime' argument is an optional numeric timestamp to be written
     to the last modification time field in the stream when compressing.
     It should only be provided in compression mode.  If omitted or
     ‘None’, the current time is used.  See the *note mtime: 1eb7.
     attribute for more details.

     Calling a *note GzipFile: 206. object’s ‘close()’ method does not
     close `fileobj', since you might wish to append more material after
     the compressed data.  This also allows you to pass an *note
     io.BytesIO: 88a. object opened for writing as `fileobj', and
     retrieve the resulting memory buffer using the *note io.BytesIO:
     88a. object’s *note getvalue(): 1eb8. method.

     *note GzipFile: 206. supports the *note io.BufferedIOBase: 67f.
     interface, including iteration and the *note with: 7da. statement.
     Only the ‘truncate()’ method isn’t implemented.

     *note GzipFile: 206. also provides the following method and
     attribute:

      -- Method: peek (n)

          Read `n' uncompressed bytes without advancing the file
          position.  At most one single read on the compressed stream is
          done to satisfy the call.  The number of bytes returned may be
          more or less than requested.

               Note: While calling *note peek(): c59. does not change
               the file position of the *note GzipFile: 206, it may
               change the position of the underlying file object (e.g.
               if the *note GzipFile: 206. was constructed with the
               `fileobj' parameter).

          New in version 3.2.

      -- Attribute: mtime

          When decompressing, the value of the last modification time
          field in the most recently read header may be read from this
          attribute, as an integer.  The initial value before reading
          any headers is ‘None’.

          All ‘gzip’ compressed streams are required to contain this
          timestamp field.  Some programs, such as ‘gunzip’, make use of
          the timestamp.  The format is the same as the return value of
          *note time.time(): 42d. and the *note st_mtime: 1eb9.
          attribute of the object returned by *note os.stat(): 321.

     Changed in version 3.1: Support for the *note with: 7da. statement
     was added, along with the `mtime' constructor argument and *note
     mtime: 1eb7. attribute.

     Changed in version 3.2: Support for zero-padded and unseekable
     files was added.

     Changed in version 3.3: The *note io.BufferedIOBase.read1(): 1eba.
     method is now implemented.

     Changed in version 3.4: Added support for the ‘'x'’ and ‘'xb'’
     modes.

     Changed in version 3.5: Added support for writing arbitrary *note
     bytes-like objects: 6df.  The *note read(): 1ebb. method now
     accepts an argument of ‘None’.

     Changed in version 3.6: Accepts a *note path-like object: 472.

     Deprecated since version 3.9: Opening *note GzipFile: 206. for
     writing without specifying the `mode' argument is deprecated.

 -- Function: gzip.compress (data, compresslevel=9, *, mtime=None)

     Compress the `data', returning a *note bytes: 172. object
     containing the compressed data.  `compresslevel' and `mtime' have
     the same meaning as in the *note GzipFile: 206. constructor above.

     New in version 3.2.

     Changed in version 3.8: Added the `mtime' parameter for
     reproducible output.

 -- Function: gzip.decompress (data)

     Decompress the `data', returning a *note bytes: 172. object
     containing the uncompressed data.

     New in version 3.2.

* Menu:

* Examples of usage::
* Command Line Interface::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/gzip.py


File: python.info,  Node: Examples of usage,  Next: Command Line Interface,  Up: gzip — Support for gzip files

5.13.2.1 Examples of usage
..........................

Example of how to read a compressed file:

     import gzip
     with gzip.open('/home/joe/file.txt.gz', 'rb') as f:
         file_content = f.read()

Example of how to create a compressed GZIP file:

     import gzip
     content = b"Lots of content here"
     with gzip.open('/home/joe/file.txt.gz', 'wb') as f:
         f.write(content)

Example of how to GZIP compress an existing file:

     import gzip
     import shutil
     with open('/home/joe/file.txt', 'rb') as f_in:
         with gzip.open('/home/joe/file.txt.gz', 'wb') as f_out:
             shutil.copyfileobj(f_in, f_out)

Example of how to GZIP compress a binary string:

     import gzip
     s_in = b"Lots of content here"
     s_out = gzip.compress(s_in)

See also
........

Module *note zlib: 14d.

     The basic data compression module needed to support the ‘gzip’ file
     format.


File: python.info,  Node: Command Line Interface,  Prev: Examples of usage,  Up: gzip — Support for gzip files

5.13.2.2 Command Line Interface
...............................

The *note gzip: 8b. module provides a simple command line interface to
compress or decompress files.

Once executed the *note gzip: 8b. module keeps the input file(s).

Changed in version 3.8: Add a new command line interface with a usage.
By default, when you will execute the CLI, the default compression level
is 6.

* Menu:

* Command line options::


File: python.info,  Node: Command line options,  Up: Command Line Interface

5.13.2.3 Command line options
.............................

 -- Program Option: file

     If `file' is not specified, read from *note sys.stdin: 41e.

 -- Program Option: --fast

     Indicates the fastest compression method (less compression).

 -- Program Option: --best

     Indicates the slowest compression method (best compression).

 -- Program Option: -d, --decompress

     Decompress the given file.

 -- Program Option: -h, --help

     Show the help message.


File: python.info,  Node: bz2 — Support for bzip2 compression,  Next: lzma — Compression using the LZMA algorithm,  Prev: gzip — Support for gzip files,  Up: Data Compression and Archiving

5.13.3 ‘bz2’ — Support for ‘bzip2’ compression
----------------------------------------------

`Source code:' Lib/bz2.py(1)

__________________________________________________________________

This module provides a comprehensive interface for compressing and
decompressing data using the bzip2 compression algorithm.

The *note bz2: 13. module contains:

   * The *note open(): ab5. function and *note BZ2File: 224. class for
     reading and writing compressed files.

   * The *note BZ2Compressor: 1ec7. and *note BZ2Decompressor: 1ec8.
     classes for incremental (de)compression.

   * The *note compress(): 19b6. and *note decompress(): ab6. functions
     for one-shot (de)compression.

All of the classes in this module may safely be accessed from multiple
threads.

* Menu:

* (De)compression of files: De compression of files.
* Incremental (de)compression: Incremental de compression.
* One-shot (de)compression: One-shot de compression.
* Examples of usage: Examples of usage<2>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/bz2.py


File: python.info,  Node: De compression of files,  Next: Incremental de compression,  Up: bz2 — Support for bzip2 compression

5.13.3.1 (De)compression of files
.................................

 -- Function: bz2.open (filename, mode='rb', compresslevel=9,
          encoding=None, errors=None, newline=None)

     Open a bzip2-compressed file in binary or text mode, returning a
     *note file object: c14.

     As with the constructor for *note BZ2File: 224, the `filename'
     argument can be an actual filename (a *note str: 205. or *note
     bytes: 172. object), or an existing file object to read from or
     write to.

     The `mode' argument can be any of ‘'r'’, ‘'rb'’, ‘'w'’, ‘'wb'’,
     ‘'x'’, ‘'xb'’, ‘'a'’ or ‘'ab'’ for binary mode, or ‘'rt'’, ‘'wt'’,
     ‘'xt'’, or ‘'at'’ for text mode.  The default is ‘'rb'’.

     The `compresslevel' argument is an integer from 1 to 9, as for the
     *note BZ2File: 224. constructor.

     For binary mode, this function is equivalent to the *note BZ2File:
     224. constructor: ‘BZ2File(filename, mode,
     compresslevel=compresslevel)’.  In this case, the `encoding',
     `errors' and `newline' arguments must not be provided.

     For text mode, a *note BZ2File: 224. object is created, and wrapped
     in an *note io.TextIOWrapper: 6ea. instance with the specified
     encoding, error handling behavior, and line ending(s).

     New in version 3.3.

     Changed in version 3.4: The ‘'x'’ (exclusive creation) mode was
     added.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Class: bz2.BZ2File (filename, mode='r', *, compresslevel=9)

     Open a bzip2-compressed file in binary mode.

     If `filename' is a *note str: 205. or *note bytes: 172. object,
     open the named file directly.  Otherwise, `filename' should be a
     *note file object: c14, which will be used to read or write the
     compressed data.

     The `mode' argument can be either ‘'r'’ for reading (default),
     ‘'w'’ for overwriting, ‘'x'’ for exclusive creation, or ‘'a'’ for
     appending.  These can equivalently be given as ‘'rb'’, ‘'wb'’,
     ‘'xb'’ and ‘'ab'’ respectively.

     If `filename' is a file object (rather than an actual file name), a
     mode of ‘'w'’ does not truncate the file, and is instead equivalent
     to ‘'a'’.

     If `mode' is ‘'w'’ or ‘'a'’, `compresslevel' can be an integer
     between ‘1’ and ‘9’ specifying the level of compression: ‘1’
     produces the least compression, and ‘9’ (default) produces the most
     compression.

     If `mode' is ‘'r'’, the input file may be the concatenation of
     multiple compressed streams.

     *note BZ2File: 224. provides all of the members specified by the
     *note io.BufferedIOBase: 67f, except for ‘detach()’ and
     ‘truncate()’.  Iteration and the *note with: 7da. statement are
     supported.

     *note BZ2File: 224. also provides the following method:

      -- Method: peek ([n])

          Return buffered data without advancing the file position.  At
          least one byte of data will be returned (unless at EOF). The
          exact number of bytes returned is unspecified.

               Note: While calling *note peek(): 1eca. does not change
               the file position of the *note BZ2File: 224, it may
               change the position of the underlying file object (e.g.
               if the *note BZ2File: 224. was constructed by passing a
               file object for `filename').

          New in version 3.3.

     Changed in version 3.1: Support for the *note with: 7da. statement
     was added.

     Changed in version 3.3: The ‘fileno()’, ‘readable()’, ‘seekable()’,
     ‘writable()’, ‘read1()’ and ‘readinto()’ methods were added.

     Changed in version 3.3: Support was added for `filename' being a
     *note file object: c14. instead of an actual filename.

     Changed in version 3.3: The ‘'a'’ (append) mode was added, along
     with support for reading multi-stream files.

     Changed in version 3.4: The ‘'x'’ (exclusive creation) mode was
     added.

     Changed in version 3.5: The *note read(): 1ebb. method now accepts
     an argument of ‘None’.

     Changed in version 3.6: Accepts a *note path-like object: 472.

     Changed in version 3.9: The `buffering' parameter has been removed.
     It was ignored and deprecated since Python 3.0.  Pass an open file
     object to control how the file is opened.

     The `compresslevel' parameter became keyword-only.


File: python.info,  Node: Incremental de compression,  Next: One-shot de compression,  Prev: De compression of files,  Up: bz2 — Support for bzip2 compression

5.13.3.2 Incremental (de)compression
....................................

 -- Class: bz2.BZ2Compressor (compresslevel=9)

     Create a new compressor object.  This object may be used to
     compress data incrementally.  For one-shot compression, use the
     *note compress(): 19b6. function instead.

     `compresslevel', if given, must be an integer between ‘1’ and ‘9’.
     The default is ‘9’.

      -- Method: compress (data)

          Provide data to the compressor object.  Returns a chunk of
          compressed data if possible, or an empty byte string
          otherwise.

          When you have finished providing data to the compressor, call
          the *note flush(): 1ecd. method to finish the compression
          process.

      -- Method: flush ()

          Finish the compression process.  Returns the compressed data
          left in internal buffers.

          The compressor object may not be used after this method has
          been called.

 -- Class: bz2.BZ2Decompressor

     Create a new decompressor object.  This object may be used to
     decompress data incrementally.  For one-shot compression, use the
     *note decompress(): ab6. function instead.

          Note: This class does not transparently handle inputs
          containing multiple compressed streams, unlike *note
          decompress(): ab6. and *note BZ2File: 224.  If you need to
          decompress a multi-stream input with *note BZ2Decompressor:
          1ec8, you must use a new decompressor for each stream.

      -- Method: decompress (data, max_length=-1)

          Decompress `data' (a *note bytes-like object: 6df.), returning
          uncompressed data as bytes.  Some of `data' may be buffered
          internally, for use in later calls to *note decompress(): ab6.
          The returned data should be concatenated with the output of
          any previous calls to *note decompress(): ab6.

          If `max_length' is nonnegative, returns at most `max_length'
          bytes of decompressed data.  If this limit is reached and
          further output can be produced, the *note needs_input: 1ece.
          attribute will be set to ‘False’.  In this case, the next call
          to *note decompress(): 796. may provide `data' as ‘b''’ to
          obtain more of the output.

          If all of the input data was decompressed and returned (either
          because this was less than `max_length' bytes, or because
          `max_length' was negative), the *note needs_input: 1ece.
          attribute will be set to ‘True’.

          Attempting to decompress data after the end of stream is
          reached raises an ‘EOFError’.  Any data found after the end of
          the stream is ignored and saved in the *note unused_data:
          1ecf. attribute.

          Changed in version 3.5: Added the `max_length' parameter.

      -- Attribute: eof

          ‘True’ if the end-of-stream marker has been reached.

          New in version 3.3.

      -- Attribute: unused_data

          Data found after the end of the compressed stream.

          If this attribute is accessed before the end of the stream has
          been reached, its value will be ‘b''’.

      -- Attribute: needs_input

          ‘False’ if the *note decompress(): 796. method can provide
          more decompressed data before requiring new uncompressed
          input.

          New in version 3.5.


File: python.info,  Node: One-shot de compression,  Next: Examples of usage<2>,  Prev: Incremental de compression,  Up: bz2 — Support for bzip2 compression

5.13.3.3 One-shot (de)compression
.................................

 -- Function: bz2.compress (data, compresslevel=9)

     Compress `data', a *note bytes-like object: 6df.

     `compresslevel', if given, must be an integer between ‘1’ and ‘9’.
     The default is ‘9’.

     For incremental compression, use a *note BZ2Compressor: 1ec7.
     instead.

 -- Function: bz2.decompress (data)

     Decompress `data', a *note bytes-like object: 6df.

     If `data' is the concatenation of multiple compressed streams,
     decompress all of the streams.

     For incremental decompression, use a *note BZ2Decompressor: 1ec8.
     instead.

     Changed in version 3.3: Support for multi-stream inputs was added.


File: python.info,  Node: Examples of usage<2>,  Prev: One-shot de compression,  Up: bz2 — Support for bzip2 compression

5.13.3.4 Examples of usage
..........................

Below are some examples of typical usage of the *note bz2: 13. module.

Using *note compress(): 19b6. and *note decompress(): ab6. to
demonstrate round-trip compression:

     >>> import bz2
     >>> data = b"""\
     ... Donec rhoncus quis sapien sit amet molestie. Fusce scelerisque vel augue
     ... nec ullamcorper. Nam rutrum pretium placerat. Aliquam vel tristique lorem,
     ... sit amet cursus ante. In interdum laoreet mi, sit amet ultrices purus
     ... pulvinar a. Nam gravida euismod magna, non varius justo tincidunt feugiat.
     ... Aliquam pharetra lacus non risus vehicula rutrum. Maecenas aliquam leo
     ... felis. Pellentesque semper nunc sit amet nibh ullamcorper, ac elementum
     ... dolor luctus. Curabitur lacinia mi ornare consectetur vestibulum."""
     >>> c = bz2.compress(data)
     >>> len(data) / len(c)  # Data compression ratio
     1.513595166163142
     >>> d = bz2.decompress(c)
     >>> data == d  # Check equality to original object after round-trip
     True

Using *note BZ2Compressor: 1ec7. for incremental compression:

     >>> import bz2
     >>> def gen_data(chunks=10, chunksize=1000):
     ...     """Yield incremental blocks of chunksize bytes."""
     ...     for _ in range(chunks):
     ...         yield b"z" * chunksize
     ...
     >>> comp = bz2.BZ2Compressor()
     >>> out = b""
     >>> for chunk in gen_data():
     ...     # Provide data to the compressor object
     ...     out = out + comp.compress(chunk)
     ...
     >>> # Finish the compression process.  Call this once you have
     >>> # finished providing data to the compressor.
     >>> out = out + comp.flush()

The example above uses a very “nonrandom” stream of data (a stream of
‘b”z”’ chunks).  Random data tends to compress poorly, while ordered,
repetitive data usually yields a high compression ratio.

Writing and reading a bzip2-compressed file in binary mode:

     >>> import bz2
     >>> data = b"""\
     ... Donec rhoncus quis sapien sit amet molestie. Fusce scelerisque vel augue
     ... nec ullamcorper. Nam rutrum pretium placerat. Aliquam vel tristique lorem,
     ... sit amet cursus ante. In interdum laoreet mi, sit amet ultrices purus
     ... pulvinar a. Nam gravida euismod magna, non varius justo tincidunt feugiat.
     ... Aliquam pharetra lacus non risus vehicula rutrum. Maecenas aliquam leo
     ... felis. Pellentesque semper nunc sit amet nibh ullamcorper, ac elementum
     ... dolor luctus. Curabitur lacinia mi ornare consectetur vestibulum."""
     >>> with bz2.open("myfile.bz2", "wb") as f:
     ...     # Write compressed data to file
     ...     unused = f.write(data)
     >>> with bz2.open("myfile.bz2", "rb") as f:
     ...     # Decompress data from file
     ...     content = f.read()
     >>> content == data  # Check equality to original object after round-trip
     True


File: python.info,  Node: lzma — Compression using the LZMA algorithm,  Next: zipfile — Work with ZIP archives,  Prev: bz2 — Support for bzip2 compression,  Up: Data Compression and Archiving

5.13.4 ‘lzma’ — Compression using the LZMA algorithm
----------------------------------------------------

New in version 3.3.

`Source code:' Lib/lzma.py(1)

__________________________________________________________________

This module provides classes and convenience functions for compressing
and decompressing data using the LZMA compression algorithm.  Also
included is a file interface supporting the ‘.xz’ and legacy ‘.lzma’
file formats used by the ‘xz’ utility, as well as raw compressed
streams.

The interface provided by this module is very similar to that of the
*note bz2: 13. module.  However, note that *note LZMAFile: a16. is `not'
thread-safe, unlike *note bz2.BZ2File: 224, so if you need to use a
single *note LZMAFile: a16. instance from multiple threads, it is
necessary to protect it with a lock.

 -- Exception: lzma.LZMAError

     This exception is raised when an error occurs during compression or
     decompression, or while initializing the compressor/decompressor
     state.

* Menu:

* Reading and writing compressed files::
* Compressing and decompressing data in memory::
* Miscellaneous: Miscellaneous<2>.
* Specifying custom filter chains::
* Examples: Examples<6>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/lzma.py


File: python.info,  Node: Reading and writing compressed files,  Next: Compressing and decompressing data in memory,  Up: lzma — Compression using the LZMA algorithm

5.13.4.1 Reading and writing compressed files
.............................................

 -- Function: lzma.open (filename, mode="rb", *, format=None, check=-1,
          preset=None, filters=None, encoding=None, errors=None,
          newline=None)

     Open an LZMA-compressed file in binary or text mode, returning a
     *note file object: c14.

     The `filename' argument can be either an actual file name (given as
     a *note str: 205, *note bytes: 172. or *note path-like: 472.
     object), in which case the named file is opened, or it can be an
     existing file object to read from or write to.

     The `mode' argument can be any of ‘"r"’, ‘"rb"’, ‘"w"’, ‘"wb"’,
     ‘"x"’, ‘"xb"’, ‘"a"’ or ‘"ab"’ for binary mode, or ‘"rt"’, ‘"wt"’,
     ‘"xt"’, or ‘"at"’ for text mode.  The default is ‘"rb"’.

     When opening a file for reading, the `format' and `filters'
     arguments have the same meanings as for *note LZMADecompressor:
     1ed9.  In this case, the `check' and `preset' arguments should not
     be used.

     When opening a file for writing, the `format', `check', `preset'
     and `filters' arguments have the same meanings as for *note
     LZMACompressor: 1eda.

     For binary mode, this function is equivalent to the *note LZMAFile:
     a16. constructor: ‘LZMAFile(filename, mode, ...)’.  In this case,
     the `encoding', `errors' and `newline' arguments must not be
     provided.

     For text mode, a *note LZMAFile: a16. object is created, and
     wrapped in an *note io.TextIOWrapper: 6ea. instance with the
     specified encoding, error handling behavior, and line ending(s).

     Changed in version 3.4: Added support for the ‘"x"’, ‘"xb"’ and
     ‘"xt"’ modes.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Class: lzma.LZMAFile (filename=None, mode="r", *, format=None,
          check=-1, preset=None, filters=None)

     Open an LZMA-compressed file in binary mode.

     An *note LZMAFile: a16. can wrap an already-open *note file object:
     c14, or operate directly on a named file.  The `filename' argument
     specifies either the file object to wrap, or the name of the file
     to open (as a *note str: 205, *note bytes: 172. or *note path-like:
     472. object).  When wrapping an existing file object, the wrapped
     file will not be closed when the *note LZMAFile: a16. is closed.

     The `mode' argument can be either ‘"r"’ for reading (default),
     ‘"w"’ for overwriting, ‘"x"’ for exclusive creation, or ‘"a"’ for
     appending.  These can equivalently be given as ‘"rb"’, ‘"wb"’,
     ‘"xb"’ and ‘"ab"’ respectively.

     If `filename' is a file object (rather than an actual file name), a
     mode of ‘"w"’ does not truncate the file, and is instead equivalent
     to ‘"a"’.

     When opening a file for reading, the input file may be the
     concatenation of multiple separate compressed streams.  These are
     transparently decoded as a single logical stream.

     When opening a file for reading, the `format' and `filters'
     arguments have the same meanings as for *note LZMADecompressor:
     1ed9.  In this case, the `check' and `preset' arguments should not
     be used.

     When opening a file for writing, the `format', `check', `preset'
     and `filters' arguments have the same meanings as for *note
     LZMACompressor: 1eda.

     *note LZMAFile: a16. supports all the members specified by *note
     io.BufferedIOBase: 67f, except for ‘detach()’ and ‘truncate()’.
     Iteration and the *note with: 7da. statement are supported.

     The following method is also provided:

      -- Method: peek (size=-1)

          Return buffered data without advancing the file position.  At
          least one byte of data will be returned, unless EOF has been
          reached.  The exact number of bytes returned is unspecified
          (the `size' argument is ignored).

               Note: While calling *note peek(): 1edb. does not change
               the file position of the *note LZMAFile: a16, it may
               change the position of the underlying file object (e.g.
               if the *note LZMAFile: a16. was constructed by passing a
               file object for `filename').

     Changed in version 3.4: Added support for the ‘"x"’ and ‘"xb"’
     modes.

     Changed in version 3.5: The *note read(): 1ebb. method now accepts
     an argument of ‘None’.

     Changed in version 3.6: Accepts a *note path-like object: 472.


File: python.info,  Node: Compressing and decompressing data in memory,  Next: Miscellaneous<2>,  Prev: Reading and writing compressed files,  Up: lzma — Compression using the LZMA algorithm

5.13.4.2 Compressing and decompressing data in memory
.....................................................

 -- Class: lzma.LZMACompressor (format=FORMAT_XZ, check=-1, preset=None,
          filters=None)

     Create a compressor object, which can be used to compress data
     incrementally.

     For a more convenient way of compressing a single chunk of data,
     see *note compress(): 1edd.

     The `format' argument specifies what container format should be
     used.  Possible values are:

        * 
          ‘FORMAT_XZ’: The ‘.xz’ container format.

               This is the default format.

        * 
          ‘FORMAT_ALONE’: The legacy ‘.lzma’ container format.

               This format is more limited than ‘.xz’ – it does not
               support integrity checks or multiple filters.

        * 
          ‘FORMAT_RAW’: A raw data stream, not using any container format.

               This format specifier does not support integrity checks,
               and requires that you always specify a custom filter
               chain (for both compression and decompression).
               Additionally, data compressed in this manner cannot be
               decompressed using ‘FORMAT_AUTO’ (see *note
               LZMADecompressor: 1ed9.).

     The `check' argument specifies the type of integrity check to
     include in the compressed data.  This check is used when
     decompressing, to ensure that the data has not been corrupted.
     Possible values are:

        * ‘CHECK_NONE’: No integrity check.  This is the default (and
          the only acceptable value) for ‘FORMAT_ALONE’ and
          ‘FORMAT_RAW’.

        * ‘CHECK_CRC32’: 32-bit Cyclic Redundancy Check.

        * ‘CHECK_CRC64’: 64-bit Cyclic Redundancy Check.  This is the
          default for ‘FORMAT_XZ’.

        * ‘CHECK_SHA256’: 256-bit Secure Hash Algorithm.

     If the specified check is not supported, an *note LZMAError: 1ed6.
     is raised.

     The compression settings can be specified either as a preset
     compression level (with the `preset' argument), or in detail as a
     custom filter chain (with the `filters' argument).

     The `preset' argument (if provided) should be an integer between
     ‘0’ and ‘9’ (inclusive), optionally OR-ed with the constant
     ‘PRESET_EXTREME’.  If neither `preset' nor `filters' are given, the
     default behavior is to use ‘PRESET_DEFAULT’ (preset level ‘6’).
     Higher presets produce smaller output, but make the compression
     process slower.

          Note: In addition to being more CPU-intensive, compression
          with higher presets also requires much more memory (and
          produces output that needs more memory to decompress).  With
          preset ‘9’ for example, the overhead for an *note
          LZMACompressor: 1eda. object can be as high as 800 MiB. For
          this reason, it is generally best to stick with the default
          preset.

     The `filters' argument (if provided) should be a filter chain
     specifier.  See *note Specifying custom filter chains: 1ede. for
     details.

      -- Method: compress (data)

          Compress `data' (a *note bytes: 172. object), returning a
          *note bytes: 172. object containing compressed data for at
          least part of the input.  Some of `data' may be buffered
          internally, for use in later calls to *note compress(): 1edd.
          and *note flush(): 1ee0.  The returned data should be
          concatenated with the output of any previous calls to *note
          compress(): 1edd.

      -- Method: flush ()

          Finish the compression process, returning a *note bytes: 172.
          object containing any data stored in the compressor’s internal
          buffers.

          The compressor cannot be used after this method has been
          called.

 -- Class: lzma.LZMADecompressor (format=FORMAT_AUTO, memlimit=None,
          filters=None)

     Create a decompressor object, which can be used to decompress data
     incrementally.

     For a more convenient way of decompressing an entire compressed
     stream at once, see *note decompress(): 1ee1.

     The `format' argument specifies the container format that should be
     used.  The default is ‘FORMAT_AUTO’, which can decompress both
     ‘.xz’ and ‘.lzma’ files.  Other possible values are ‘FORMAT_XZ’,
     ‘FORMAT_ALONE’, and ‘FORMAT_RAW’.

     The `memlimit' argument specifies a limit (in bytes) on the amount
     of memory that the decompressor can use.  When this argument is
     used, decompression will fail with an *note LZMAError: 1ed6. if it
     is not possible to decompress the input within the given memory
     limit.

     The `filters' argument specifies the filter chain that was used to
     create the stream being decompressed.  This argument is required if
     `format' is ‘FORMAT_RAW’, but should not be used for other formats.
     See *note Specifying custom filter chains: 1ede. for more
     information about filter chains.

          Note: This class does not transparently handle inputs
          containing multiple compressed streams, unlike *note
          decompress(): 1ee1. and *note LZMAFile: a16.  To decompress a
          multi-stream input with *note LZMADecompressor: 1ed9, you must
          create a new decompressor for each stream.

      -- Method: decompress (data, max_length=-1)

          Decompress `data' (a *note bytes-like object: 6df.), returning
          uncompressed data as bytes.  Some of `data' may be buffered
          internally, for use in later calls to *note decompress():
          1ee1.  The returned data should be concatenated with the
          output of any previous calls to *note decompress(): 1ee1.

          If `max_length' is nonnegative, returns at most `max_length'
          bytes of decompressed data.  If this limit is reached and
          further output can be produced, the *note needs_input: 1ee2.
          attribute will be set to ‘False’.  In this case, the next call
          to *note decompress(): 805. may provide `data' as ‘b''’ to
          obtain more of the output.

          If all of the input data was decompressed and returned (either
          because this was less than `max_length' bytes, or because
          `max_length' was negative), the *note needs_input: 1ee2.
          attribute will be set to ‘True’.

          Attempting to decompress data after the end of stream is
          reached raises an ‘EOFError’.  Any data found after the end of
          the stream is ignored and saved in the *note unused_data:
          1ee3. attribute.

          Changed in version 3.5: Added the `max_length' parameter.

      -- Attribute: check

          The ID of the integrity check used by the input stream.  This
          may be ‘CHECK_UNKNOWN’ until enough of the input has been
          decoded to determine what integrity check it uses.

      -- Attribute: eof

          ‘True’ if the end-of-stream marker has been reached.

      -- Attribute: unused_data

          Data found after the end of the compressed stream.

          Before the end of the stream is reached, this will be ‘b""’.

      -- Attribute: needs_input

          ‘False’ if the *note decompress(): 805. method can provide
          more decompressed data before requiring new uncompressed
          input.

          New in version 3.5.

 -- Function: lzma.compress (data, format=FORMAT_XZ, check=-1,
          preset=None, filters=None)

     Compress `data' (a *note bytes: 172. object), returning the
     compressed data as a *note bytes: 172. object.

     See *note LZMACompressor: 1eda. above for a description of the
     `format', `check', `preset' and `filters' arguments.

 -- Function: lzma.decompress (data, format=FORMAT_AUTO, memlimit=None,
          filters=None)

     Decompress `data' (a *note bytes: 172. object), returning the
     uncompressed data as a *note bytes: 172. object.

     If `data' is the concatenation of multiple distinct compressed
     streams, decompress all of these streams, and return the
     concatenation of the results.

     See *note LZMADecompressor: 1ed9. above for a description of the
     `format', `memlimit' and `filters' arguments.


File: python.info,  Node: Miscellaneous<2>,  Next: Specifying custom filter chains,  Prev: Compressing and decompressing data in memory,  Up: lzma — Compression using the LZMA algorithm

5.13.4.3 Miscellaneous
......................

 -- Function: lzma.is_check_supported (check)

     Return ‘True’ if the given integrity check is supported on this
     system.

     ‘CHECK_NONE’ and ‘CHECK_CRC32’ are always supported.  ‘CHECK_CRC64’
     and ‘CHECK_SHA256’ may be unavailable if you are using a version of
     ‘liblzma’ that was compiled with a limited feature set.


File: python.info,  Node: Specifying custom filter chains,  Next: Examples<6>,  Prev: Miscellaneous<2>,  Up: lzma — Compression using the LZMA algorithm

5.13.4.4 Specifying custom filter chains
........................................

A filter chain specifier is a sequence of dictionaries, where each
dictionary contains the ID and options for a single filter.  Each
dictionary must contain the key ‘"id"’, and may contain additional keys
to specify filter-dependent options.  Valid filter IDs are as follows:

   * 
     Compression filters:

             * ‘FILTER_LZMA1’ (for use with ‘FORMAT_ALONE’)

             * ‘FILTER_LZMA2’ (for use with ‘FORMAT_XZ’ and
               ‘FORMAT_RAW’)

   * 
     Delta filter:

             * ‘FILTER_DELTA’

   * 
     Branch-Call-Jump (BCJ) filters:

             * ‘FILTER_X86’

             * ‘FILTER_IA64’

             * ‘FILTER_ARM’

             * ‘FILTER_ARMTHUMB’

             * ‘FILTER_POWERPC’

             * ‘FILTER_SPARC’

A filter chain can consist of up to 4 filters, and cannot be empty.  The
last filter in the chain must be a compression filter, and any other
filters must be delta or BCJ filters.

Compression filters support the following options (specified as
additional entries in the dictionary representing the filter):

        * ‘preset’: A compression preset to use as a source of default
          values for options that are not specified explicitly.

        * ‘dict_size’: Dictionary size in bytes.  This should be between
          4 KiB and 1.5 GiB (inclusive).

        * ‘lc’: Number of literal context bits.

        * ‘lp’: Number of literal position bits.  The sum ‘lc + lp’ must
          be at most 4.

        * ‘pb’: Number of position bits; must be at most 4.

        * ‘mode’: ‘MODE_FAST’ or ‘MODE_NORMAL’.

        * ‘nice_len’: What should be considered a “nice length” for a
          match.  This should be 273 or less.

        * ‘mf’: What match finder to use – ‘MF_HC3’, ‘MF_HC4’, ‘MF_BT2’,
          ‘MF_BT3’, or ‘MF_BT4’.

        * ‘depth’: Maximum search depth used by match finder.  0
          (default) means to select automatically based on other filter
          options.

The delta filter stores the differences between bytes, producing more
repetitive input for the compressor in certain circumstances.  It
supports one option, ‘dist’.  This indicates the distance between bytes
to be subtracted.  The default is 1, i.e.  take the differences between
adjacent bytes.

The BCJ filters are intended to be applied to machine code.  They
convert relative branches, calls and jumps in the code to use absolute
addressing, with the aim of increasing the redundancy that can be
exploited by the compressor.  These filters support one option,
‘start_offset’.  This specifies the address that should be mapped to the
beginning of the input data.  The default is 0.


File: python.info,  Node: Examples<6>,  Prev: Specifying custom filter chains,  Up: lzma — Compression using the LZMA algorithm

5.13.4.5 Examples
.................

Reading in a compressed file:

     import lzma
     with lzma.open("file.xz") as f:
         file_content = f.read()

Creating a compressed file:

     import lzma
     data = b"Insert Data Here"
     with lzma.open("file.xz", "w") as f:
         f.write(data)

Compressing data in memory:

     import lzma
     data_in = b"Insert Data Here"
     data_out = lzma.compress(data_in)

Incremental compression:

     import lzma
     lzc = lzma.LZMACompressor()
     out1 = lzc.compress(b"Some data\n")
     out2 = lzc.compress(b"Another piece of data\n")
     out3 = lzc.compress(b"Even more data\n")
     out4 = lzc.flush()
     # Concatenate all the partial results:
     result = b"".join([out1, out2, out3, out4])

Writing compressed data to an already-open file:

     import lzma
     with open("file.xz", "wb") as f:
         f.write(b"This data will not be compressed\n")
         with lzma.open(f, "w") as lzf:
             lzf.write(b"This *will* be compressed\n")
         f.write(b"Not compressed\n")

Creating a compressed file using a custom filter chain:

     import lzma
     my_filters = [
         {"id": lzma.FILTER_DELTA, "dist": 5},
         {"id": lzma.FILTER_LZMA2, "preset": 7 | lzma.PRESET_EXTREME},
     ]
     with lzma.open("file.xz", "w", filters=my_filters) as f:
         f.write(b"blah blah blah")


File: python.info,  Node: zipfile — Work with ZIP archives,  Next: tarfile — Read and write tar archive files,  Prev: lzma — Compression using the LZMA algorithm,  Up: Data Compression and Archiving

5.13.5 ‘zipfile’ — Work with ZIP archives
-----------------------------------------

`Source code:' Lib/zipfile.py(1)

__________________________________________________________________

The ZIP file format is a common archive and compression standard.  This
module provides tools to create, read, write, append, and list a ZIP
file.  Any advanced use of this module will require an understanding of
the format, as defined in PKZIP Application Note(2).

This module does not currently handle multi-disk ZIP files.  It can
handle ZIP files that use the ZIP64 extensions (that is ZIP files that
are more than 4 GiB in size).  It supports decryption of encrypted files
in ZIP archives, but it currently cannot create an encrypted file.
Decryption is extremely slow as it is implemented in native Python
rather than C.

The module defines the following items:

 -- Exception: zipfile.BadZipFile

     The error raised for bad ZIP files.

     New in version 3.2.

 -- Exception: zipfile.BadZipfile

     Alias of *note BadZipFile: 1eec, for compatibility with older
     Python versions.

     Deprecated since version 3.2.

 -- Exception: zipfile.LargeZipFile

     The error raised when a ZIP file would require ZIP64 functionality
     but that has not been enabled.

 -- Class: zipfile.ZipFile

     The class for reading and writing ZIP files.  See section *note
     ZipFile Objects: 1eef. for constructor details.

 -- Class: zipfile.Path

     A pathlib-compatible wrapper for zip files.  See section *note Path
     Objects: 1ef0. for details.

     New in version 3.8.

 -- Class: zipfile.PyZipFile

     Class for creating ZIP archives containing Python libraries.

 -- Class: zipfile.ZipInfo (filename='NoName', date_time=(1980, 1, 1, 0,
          0, 0))

     Class used to represent information about a member of an archive.
     Instances of this class are returned by the *note getinfo(): 1ef1.
     and *note infolist(): 1ef2. methods of *note ZipFile: 523. objects.
     Most users of the *note zipfile: 14b. module will not need to
     create these, but only use those created by this module.
     `filename' should be the full name of the archive member, and
     `date_time' should be a tuple containing six fields which describe
     the time of the last modification to the file; the fields are
     described in section *note ZipInfo Objects: 1ef3.

 -- Function: zipfile.is_zipfile (filename)

     Returns ‘True’ if `filename' is a valid ZIP file based on its magic
     number, otherwise returns ‘False’.  `filename' may be a file or
     file-like object too.

     Changed in version 3.1: Support for file and file-like objects.

 -- Data: zipfile.ZIP_STORED

     The numeric constant for an uncompressed archive member.

 -- Data: zipfile.ZIP_DEFLATED

     The numeric constant for the usual ZIP compression method.  This
     requires the *note zlib: 14d. module.

 -- Data: zipfile.ZIP_BZIP2

     The numeric constant for the BZIP2 compression method.  This
     requires the *note bz2: 13. module.

     New in version 3.3.

 -- Data: zipfile.ZIP_LZMA

     The numeric constant for the LZMA compression method.  This
     requires the *note lzma: ad. module.

     New in version 3.3.

          Note: The ZIP file format specification has included support
          for bzip2 compression since 2001, and for LZMA compression
          since 2006.  However, some tools (including older Python
          releases) do not support these compression methods, and may
          either refuse to process the ZIP file altogether, or fail to
          extract individual files.

See also
........

PKZIP Application Note(3)

     Documentation on the ZIP file format by Phil Katz, the creator of
     the format and algorithms used.

Info-ZIP Home Page(4)

     Information about the Info-ZIP project’s ZIP archive programs and
     development libraries.

* Menu:

* ZipFile Objects::
* Path Objects::
* PyZipFile Objects::
* ZipInfo Objects::
* Command-Line Interface::
* Decompression pitfalls::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/zipfile.py

   (2) https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT

   (3) https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT

   (4) http://www.info-zip.org/


File: python.info,  Node: ZipFile Objects,  Next: Path Objects,  Up: zipfile — Work with ZIP archives

5.13.5.1 ZipFile Objects
........................

 -- Class: zipfile.ZipFile (file, mode='r', compression=ZIP_STORED,
          allowZip64=True, compresslevel=None, *,
          strict_timestamps=True)

     Open a ZIP file, where `file' can be a path to a file (a string), a
     file-like object or a *note path-like object: 472.

     The `mode' parameter should be ‘'r'’ to read an existing file,
     ‘'w'’ to truncate and write a new file, ‘'a'’ to append to an
     existing file, or ‘'x'’ to exclusively create and write a new file.
     If `mode' is ‘'x'’ and `file' refers to an existing file, a *note
     FileExistsError: a39. will be raised.  If `mode' is ‘'a'’ and
     `file' refers to an existing ZIP file, then additional files are
     added to it.  If `file' does not refer to a ZIP file, then a new
     ZIP archive is appended to the file.  This is meant for adding a
     ZIP archive to another file (such as ‘python.exe’).  If `mode' is
     ‘'a'’ and the file does not exist at all, it is created.  If `mode'
     is ‘'r'’ or ‘'a'’, the file should be seekable.

     `compression' is the ZIP compression method to use when writing the
     archive, and should be *note ZIP_STORED: 1ef4, *note ZIP_DEFLATED:
     1ef5, *note ZIP_BZIP2: 1ef6. or *note ZIP_LZMA: 1ef7.; unrecognized
     values will cause *note NotImplementedError: 704. to be raised.  If
     *note ZIP_DEFLATED: 1ef5, *note ZIP_BZIP2: 1ef6. or *note ZIP_LZMA:
     1ef7. is specified but the corresponding module (*note zlib: 14d,
     *note bz2: 13. or *note lzma: ad.) is not available, *note
     RuntimeError: 3dc. is raised.  The default is *note ZIP_STORED:
     1ef4.

     If `allowZip64' is ‘True’ (the default) zipfile will create ZIP
     files that use the ZIP64 extensions when the zipfile is larger than
     4 GiB. If it is ‘false’ *note zipfile: 14b. will raise an exception
     when the ZIP file would require ZIP64 extensions.

     The `compresslevel' parameter controls the compression level to use
     when writing files to the archive.  When using *note ZIP_STORED:
     1ef4. or *note ZIP_LZMA: 1ef7. it has no effect.  When using *note
     ZIP_DEFLATED: 1ef5. integers ‘0’ through ‘9’ are accepted (see
     *note zlib: 1ea7. for more information).  When using *note
     ZIP_BZIP2: 1ef6. integers ‘1’ through ‘9’ are accepted (see *note
     bz2: 224. for more information).

     The `strict_timestamps' argument, when set to ‘False’, allows to
     zip files older than 1980-01-01 at the cost of setting the
     timestamp to 1980-01-01.  Similar behavior occurs with files newer
     than 2107-12-31, the timestamp is also set to the limit.

     If the file is created with mode ‘'w'’, ‘'x'’ or ‘'a'’ and then
     *note closed: 1ef9. without adding any files to the archive, the
     appropriate ZIP structures for an empty archive will be written to
     the file.

     ZipFile is also a context manager and therefore supports the *note
     with: 7da. statement.  In the example, `myzip' is closed after the
     ‘with’ statement’s suite is finished—even if an exception occurs:

          with ZipFile('spam.zip', 'w') as myzip:
              myzip.write('eggs.txt')

     New in version 3.2: Added the ability to use *note ZipFile: 523. as
     a context manager.

     Changed in version 3.3: Added support for *note bzip2: 13. and
     *note lzma: ad. compression.

     Changed in version 3.4: ZIP64 extensions are enabled by default.

     Changed in version 3.5: Added support for writing to unseekable
     streams.  Added support for the ‘'x'’ mode.

     Changed in version 3.6: Previously, a plain *note RuntimeError:
     3dc. was raised for unrecognized compression values.

     Changed in version 3.6.2: The `file' parameter accepts a *note
     path-like object: 472.

     Changed in version 3.7: Add the `compresslevel' parameter.

     New in version 3.8: The `strict_timestamps' keyword-only argument

 -- Method: ZipFile.close ()

     Close the archive file.  You must call *note close(): 1ef9. before
     exiting your program or essential records will not be written.

 -- Method: ZipFile.getinfo (name)

     Return a *note ZipInfo: 6b1. object with information about the
     archive member `name'.  Calling *note getinfo(): 1ef1. for a name
     not currently contained in the archive will raise a *note KeyError:
     3e9.

 -- Method: ZipFile.infolist ()

     Return a list containing a *note ZipInfo: 6b1. object for each
     member of the archive.  The objects are in the same order as their
     entries in the actual ZIP file on disk if an existing archive was
     opened.

 -- Method: ZipFile.namelist ()

     Return a list of archive members by name.

 -- Method: ZipFile.open (name, mode='r', pwd=None, *,
          force_zip64=False)

     Access a member of the archive as a binary file-like object.
     `name' can be either the name of a file within the archive or a
     *note ZipInfo: 6b1. object.  The `mode' parameter, if included,
     must be ‘'r'’ (the default) or ‘'w'’.  `pwd' is the password used
     to decrypt encrypted ZIP files.

     *note open(): 6b3. is also a context manager and therefore supports
     the *note with: 7da. statement:

          with ZipFile('spam.zip') as myzip:
              with myzip.open('eggs.txt') as myfile:
                  print(myfile.read())

     With `mode' ‘'r'’ the file-like object (‘ZipExtFile’) is read-only
     and provides the following methods: *note read(): 1ebb, *note
     readline(): 1849, *note readlines(): 18d6, *note seek(): 1efb,
     *note tell(): 1efc, *note __iter__(): 609, *note __next__(): d2c.
     These objects can operate independently of the ZipFile.

     With ‘mode='w'’, a writable file handle is returned, which supports
     the *note write(): 680. method.  While a writable file handle is
     open, attempting to read or write other files in the ZIP file will
     raise a *note ValueError: 16d.

     When writing a file, if the file size is not known in advance but
     may exceed 2 GiB, pass ‘force_zip64=True’ to ensure that the header
     format is capable of supporting large files.  If the file size is
     known in advance, construct a *note ZipInfo: 6b1. object with *note
     file_size: 1efd. set, and use that as the `name' parameter.

          Note: The *note open(): 6b3, *note read(): d81. and *note
          extract(): 1efe. methods can take a filename or a *note
          ZipInfo: 6b1. object.  You will appreciate this when trying to
          read a ZIP file that contains members with duplicate names.

     Changed in version 3.6: Removed support of ‘mode='U'’.  Use *note
     io.TextIOWrapper: 6ea. for reading compressed text files in *note
     universal newlines: 6eb. mode.

     Changed in version 3.6: *note open(): 16f. can now be used to write
     files into the archive with the ‘mode='w'’ option.

     Changed in version 3.6: Calling *note open(): 6b3. on a closed
     ZipFile will raise a *note ValueError: 16d.  Previously, a *note
     RuntimeError: 3dc. was raised.

 -- Method: ZipFile.extract (member, path=None, pwd=None)

     Extract a member from the archive to the current working directory;
     `member' must be its full name or a *note ZipInfo: 6b1. object.
     Its file information is extracted as accurately as possible.
     `path' specifies a different directory to extract to.  `member' can
     be a filename or a *note ZipInfo: 6b1. object.  `pwd' is the
     password used for encrypted files.

     Returns the normalized path created (a directory or new file).

          Note: If a member filename is an absolute path, a drive/UNC
          sharepoint and leading (back)slashes will be stripped, e.g.:
          ‘///foo/bar’ becomes ‘foo/bar’ on Unix, and ‘C:\foo\bar’
          becomes ‘foo\bar’ on Windows.  And all ‘".."’ components in a
          member filename will be removed, e.g.: ‘../../foo../../ba..r’
          becomes ‘foo../ba..r’.  On Windows illegal characters (‘:’,
          ‘<’, ‘>’, ‘|’, ‘"’, ‘?’, and ‘*’) replaced by underscore
          (‘_’).

     Changed in version 3.6: Calling *note extract(): 1efe. on a closed
     ZipFile will raise a *note ValueError: 16d.  Previously, a *note
     RuntimeError: 3dc. was raised.

     Changed in version 3.6.2: The `path' parameter accepts a *note
     path-like object: 472.

 -- Method: ZipFile.extractall (path=None, members=None, pwd=None)

     Extract all members from the archive to the current working
     directory.  `path' specifies a different directory to extract to.
     `members' is optional and must be a subset of the list returned by
     *note namelist(): 1efa.  `pwd' is the password used for encrypted
     files.

          Warning: Never extract archives from untrusted sources without
          prior inspection.  It is possible that files are created
          outside of `path', e.g.  members that have absolute filenames
          starting with ‘"/"’ or filenames with two dots ‘".."’.  This
          module attempts to prevent that.  See *note extract(): 1efe.
          note.

     Changed in version 3.6: Calling *note extractall(): 1eff. on a
     closed ZipFile will raise a *note ValueError: 16d.  Previously, a
     *note RuntimeError: 3dc. was raised.

     Changed in version 3.6.2: The `path' parameter accepts a *note
     path-like object: 472.

 -- Method: ZipFile.printdir ()

     Print a table of contents for the archive to ‘sys.stdout’.

 -- Method: ZipFile.setpassword (pwd)

     Set `pwd' as default password to extract encrypted files.

 -- Method: ZipFile.read (name, pwd=None)

     Return the bytes of the file `name' in the archive.  `name' is the
     name of the file in the archive, or a *note ZipInfo: 6b1. object.
     The archive must be open for read or append.  `pwd' is the password
     used for encrypted files and, if specified, it will override the
     default password set with *note setpassword(): 1f01.  Calling *note
     read(): d81. on a ZipFile that uses a compression method other than
     *note ZIP_STORED: 1ef4, *note ZIP_DEFLATED: 1ef5, *note ZIP_BZIP2:
     1ef6. or *note ZIP_LZMA: 1ef7. will raise a *note
     NotImplementedError: 704.  An error will also be raised if the
     corresponding compression module is not available.

     Changed in version 3.6: Calling *note read(): d81. on a closed
     ZipFile will raise a *note ValueError: 16d.  Previously, a *note
     RuntimeError: 3dc. was raised.

 -- Method: ZipFile.testzip ()

     Read all the files in the archive and check their CRC’s and file
     headers.  Return the name of the first bad file, or else return
     ‘None’.

     Changed in version 3.6: Calling *note testzip(): 1f02. on a closed
     ZipFile will raise a *note ValueError: 16d.  Previously, a *note
     RuntimeError: 3dc. was raised.

 -- Method: ZipFile.write (filename, arcname=None, compress_type=None,
          compresslevel=None)

     Write the file named `filename' to the archive, giving it the
     archive name `arcname' (by default, this will be the same as
     `filename', but without a drive letter and with leading path
     separators removed).  If given, `compress_type' overrides the value
     given for the `compression' parameter to the constructor for the
     new entry.  Similarly, `compresslevel' will override the
     constructor if given.  The archive must be open with mode ‘'w'’,
     ‘'x'’ or ‘'a'’.

          Note: Archive names should be relative to the archive root,
          that is, they should not start with a path separator.

          Note: If ‘arcname’ (or ‘filename’, if ‘arcname’ is not given)
          contains a null byte, the name of the file in the archive will
          be truncated at the null byte.

          Note: A leading slash in the filename may lead to the archive
          being impossible to open in some zip programs on Windows
          systems.

     Changed in version 3.6: Calling *note write(): 705. on a ZipFile
     created with mode ‘'r'’ or a closed ZipFile will raise a *note
     ValueError: 16d.  Previously, a *note RuntimeError: 3dc. was
     raised.

 -- Method: ZipFile.writestr (zinfo_or_arcname, data,
          compress_type=None, compresslevel=None)

     Write a file into the archive.  The contents is `data', which may
     be either a *note str: 205. or a *note bytes: 172. instance; if it
     is a *note str: 205, it is encoded as UTF-8 first.
     `zinfo_or_arcname' is either the file name it will be given in the
     archive, or a *note ZipInfo: 6b1. instance.  If it’s an instance,
     at least the filename, date, and time must be given.  If it’s a
     name, the date and time is set to the current date and time.  The
     archive must be opened with mode ‘'w'’, ‘'x'’ or ‘'a'’.

     If given, `compress_type' overrides the value given for the
     `compression' parameter to the constructor for the new entry, or in
     the `zinfo_or_arcname' (if that is a *note ZipInfo: 6b1. instance).
     Similarly, `compresslevel' will override the constructor if given.

          Note: When passing a *note ZipInfo: 6b1. instance as the
          `zinfo_or_arcname' parameter, the compression method used will
          be that specified in the `compress_type' member of the given
          *note ZipInfo: 6b1. instance.  By default, the *note ZipInfo:
          6b1. constructor sets this member to *note ZIP_STORED: 1ef4.

     Changed in version 3.2: The `compress_type' argument.

     Changed in version 3.6: Calling *note writestr(): d83. on a ZipFile
     created with mode ‘'r'’ or a closed ZipFile will raise a *note
     ValueError: 16d.  Previously, a *note RuntimeError: 3dc. was
     raised.

The following data attributes are also available:

 -- Attribute: ZipFile.filename

     Name of the ZIP file.

 -- Attribute: ZipFile.debug

     The level of debug output to use.  This may be set from ‘0’ (the
     default, no output) to ‘3’ (the most output).  Debugging
     information is written to ‘sys.stdout’.

 -- Attribute: ZipFile.comment

     The comment associated with the ZIP file as a *note bytes: 172.
     object.  If assigning a comment to a *note ZipFile: 523. instance
     created with mode ‘'w'’, ‘'x'’ or ‘'a'’, it should be no longer
     than 65535 bytes.  Comments longer than this will be truncated.


File: python.info,  Node: Path Objects,  Next: PyZipFile Objects,  Prev: ZipFile Objects,  Up: zipfile — Work with ZIP archives

5.13.5.2 Path Objects
.....................

 -- Class: zipfile.Path (root, at='')

     Construct a Path object from a ‘root’ zipfile (which may be a *note
     ZipFile: 523. instance or ‘file’ suitable for passing to the *note
     ZipFile: 523. constructor).

     ‘at’ specifies the location of this Path within the zipfile, e.g.
     ‘dir/file.txt’, ‘dir/’, or ‘’.  Defaults to the empty string,
     indicating the root.

Path objects expose the following features of *note pathlib.Path: 32f.
objects:

Path objects are traversable using the ‘/’ operator.

 -- Attribute: Path.name

     The final path component.

 -- Method: Path.open (mode='r', *, pwd, **)

     Invoke *note ZipFile.open(): 6b3. on the current path.  Allows
     opening for read or write, text or binary through supported modes:
     ‘r’, ‘w’, ‘rb’, ‘wb’.  Positional and keyword arguments are passed
     through to *note io.TextIOWrapper: 6ea. when opened as text and
     ignored otherwise.  ‘pwd’ is the ‘pwd’ parameter to *note
     ZipFile.open(): 6b3.

     Changed in version 3.9: Added support for text and binary modes for
     open.  Default mode is now text.

 -- Method: Path.iterdir ()

     Enumerate the children of the current directory.

 -- Method: Path.is_dir ()

     Return ‘True’ if the current context references a directory.

 -- Method: Path.is_file ()

     Return ‘True’ if the current context references a file.

 -- Method: Path.exists ()

     Return ‘True’ if the current context references a file or directory
     in the zip file.

 -- Method: Path.read_text (*, **)

     Read the current file as unicode text.  Positional and keyword
     arguments are passed through to *note io.TextIOWrapper: 6ea.
     (except ‘buffer’, which is implied by the context).

 -- Method: Path.read_bytes ()

     Read the current file as bytes.


File: python.info,  Node: PyZipFile Objects,  Next: ZipInfo Objects,  Prev: Path Objects,  Up: zipfile — Work with ZIP archives

5.13.5.3 PyZipFile Objects
..........................

The *note PyZipFile: a00. constructor takes the same parameters as the
*note ZipFile: 523. constructor, and one additional parameter,
`optimize'.

 -- Class: zipfile.PyZipFile (file, mode='r', compression=ZIP_STORED,
          allowZip64=True, optimize=-1)

     New in version 3.2: The `optimize' parameter.

     Changed in version 3.4: ZIP64 extensions are enabled by default.

     Instances have one method in addition to those of *note ZipFile:
     523. objects:

      -- Method: writepy (pathname, basename='', filterfunc=None)

          Search for files ‘*.py’ and add the corresponding file to the
          archive.

          If the `optimize' parameter to *note PyZipFile: a00. was not
          given or ‘-1’, the corresponding file is a ‘*.pyc’ file,
          compiling if necessary.

          If the `optimize' parameter to *note PyZipFile: a00. was ‘0’,
          ‘1’ or ‘2’, only files with that optimization level (see *note
          compile(): 2e7.) are added to the archive, compiling if
          necessary.

          If `pathname' is a file, the filename must end with ‘.py’, and
          just the (corresponding ‘*.pyc’) file is added at the top
          level (no path information).  If `pathname' is a file that
          does not end with ‘.py’, a *note RuntimeError: 3dc. will be
          raised.  If it is a directory, and the directory is not a
          package directory, then all the files ‘*.pyc’ are added at the
          top level.  If the directory is a package directory, then all
          ‘*.pyc’ are added under the package name as a file path, and
          if any subdirectories are package directories, all of these
          are added recursively in sorted order.

          `basename' is intended for internal use only.

          `filterfunc', if given, must be a function taking a single
          string argument.  It will be passed each path (including each
          individual full file path) before it is added to the archive.
          If `filterfunc' returns a false value, the path will not be
          added, and if it is a directory its contents will be ignored.
          For example, if our test files are all either in ‘test’
          directories or start with the string ‘test_’, we can use a
          `filterfunc' to exclude them:

               >>> zf = PyZipFile('myprog.zip')
               >>> def notests(s):
               ...     fn = os.path.basename(s)
               ...     return (not (fn == 'test' or fn.startswith('test_')))
               >>> zf.writepy('myprog', filterfunc=notests)

          The *note writepy(): 9ff. method makes archives with file
          names like this:

               string.pyc                   # Top level name
               test/__init__.pyc            # Package directory
               test/testall.pyc             # Module test.testall
               test/bogus/__init__.pyc      # Subpackage directory
               test/bogus/myfile.pyc        # Submodule test.bogus.myfile

          New in version 3.4: The `filterfunc' parameter.

          Changed in version 3.6.2: The `pathname' parameter accepts a
          *note path-like object: 472.

          Changed in version 3.7: Recursion sorts directory entries.


File: python.info,  Node: ZipInfo Objects,  Next: Command-Line Interface,  Prev: PyZipFile Objects,  Up: zipfile — Work with ZIP archives

5.13.5.4 ZipInfo Objects
........................

Instances of the *note ZipInfo: 6b1. class are returned by the *note
getinfo(): 1ef1. and *note infolist(): 1ef2. methods of *note ZipFile:
523. objects.  Each object stores information about a single member of
the ZIP archive.

There is one classmethod to make a *note ZipInfo: 6b1. instance for a
filesystem file:

 -- Method: classmethod ZipInfo.from_file (filename, arcname=None, *,
          strict_timestamps=True)

     Construct a *note ZipInfo: 6b1. instance for a file on the
     filesystem, in preparation for adding it to a zip file.

     `filename' should be the path to a file or directory on the
     filesystem.

     If `arcname' is specified, it is used as the name within the
     archive.  If `arcname' is not specified, the name will be the same
     as `filename', but with any drive letter and leading path
     separators removed.

     The `strict_timestamps' argument, when set to ‘False’, allows to
     zip files older than 1980-01-01 at the cost of setting the
     timestamp to 1980-01-01.  Similar behavior occurs with files newer
     than 2107-12-31, the timestamp is also set to the limit.

     New in version 3.6.

     Changed in version 3.6.2: The `filename' parameter accepts a *note
     path-like object: 472.

     New in version 3.8: The `strict_timestamps' keyword-only argument

Instances have the following methods and attributes:

 -- Method: ZipInfo.is_dir ()

     Return ‘True’ if this archive member is a directory.

     This uses the entry’s name: directories should always end with ‘/’.

     New in version 3.6.

 -- Attribute: ZipInfo.filename

     Name of the file in the archive.

 -- Attribute: ZipInfo.date_time

     The time and date of the last modification to the archive member.
     This is a tuple of six values:

     Index       Value
                 
     -------------------------------------------
                 
     ‘0’         Year (>= 1980)
                 
                 
     ‘1’         Month (one-based)
                 
                 
     ‘2’         Day of month (one-based)
                 
                 
     ‘3’         Hours (zero-based)
                 
                 
     ‘4’         Minutes (zero-based)
                 
                 
     ‘5’         Seconds (zero-based)
                 

          Note: The ZIP file format does not support timestamps before
          1980.

 -- Attribute: ZipInfo.compress_type

     Type of compression for the archive member.

 -- Attribute: ZipInfo.comment

     Comment for the individual archive member as a *note bytes: 172.
     object.

 -- Attribute: ZipInfo.extra

     Expansion field data.  The PKZIP Application Note(1) contains some
     comments on the internal structure of the data contained in this
     *note bytes: 172. object.

 -- Attribute: ZipInfo.create_system

     System which created ZIP archive.

 -- Attribute: ZipInfo.create_version

     PKZIP version which created ZIP archive.

 -- Attribute: ZipInfo.extract_version

     PKZIP version needed to extract archive.

 -- Attribute: ZipInfo.reserved

     Must be zero.

 -- Attribute: ZipInfo.flag_bits

     ZIP flag bits.

 -- Attribute: ZipInfo.volume

     Volume number of file header.

 -- Attribute: ZipInfo.internal_attr

     Internal attributes.

 -- Attribute: ZipInfo.external_attr

     External file attributes.

 -- Attribute: ZipInfo.header_offset

     Byte offset to the file header.

 -- Attribute: ZipInfo.CRC

     CRC-32 of the uncompressed file.

 -- Attribute: ZipInfo.compress_size

     Size of the compressed data.

 -- Attribute: ZipInfo.file_size

     Size of the uncompressed file.

   ---------- Footnotes ----------

   (1) https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT


File: python.info,  Node: Command-Line Interface,  Next: Decompression pitfalls,  Prev: ZipInfo Objects,  Up: zipfile — Work with ZIP archives

5.13.5.5 Command-Line Interface
...............................

The *note zipfile: 14b. module provides a simple command-line interface
to interact with ZIP archives.

If you want to create a new ZIP archive, specify its name after the
*note -c: 1f24. option and then list the filename(s) that should be
included:

     $ python -m zipfile -c monty.zip spam.txt eggs.txt

Passing a directory is also acceptable:

     $ python -m zipfile -c monty.zip life-of-brian_1979/

If you want to extract a ZIP archive into the specified directory, use
the *note -e: 1f25. option:

     $ python -m zipfile -e monty.zip target-dir/

For a list of the files in a ZIP archive, use the *note -l: 1f26.
option:

     $ python -m zipfile -l monty.zip

* Menu:

* Command-line options::


File: python.info,  Node: Command-line options,  Up: Command-Line Interface

5.13.5.6 Command-line options
.............................

 -- Program Option: -l <zipfile>
 -- Program Option: --list <zipfile>

     List files in a zipfile.

 -- Program Option: -c <zipfile> <source1> ... <sourceN>
 -- Program Option: --create <zipfile> <source1> ... <sourceN>

     Create zipfile from source files.

 -- Program Option: -e <zipfile> <output_dir>
 -- Program Option: --extract <zipfile> <output_dir>

     Extract zipfile into target directory.

 -- Program Option: -t <zipfile>
 -- Program Option: --test <zipfile>

     Test whether the zipfile is valid or not.


File: python.info,  Node: Decompression pitfalls,  Prev: Command-Line Interface,  Up: zipfile — Work with ZIP archives

5.13.5.7 Decompression pitfalls
...............................

The extraction in zipfile module might fail due to some pitfalls listed
below.

* Menu:

* From file itself::
* File System limitations::
* Resources limitations::
* Interruption::
* Default behaviors of extraction::


File: python.info,  Node: From file itself,  Next: File System limitations,  Up: Decompression pitfalls

5.13.5.8 From file itself
.........................

Decompression may fail due to incorrect password / CRC checksum / ZIP
format or unsupported compression method / decryption.


File: python.info,  Node: File System limitations,  Next: Resources limitations,  Prev: From file itself,  Up: Decompression pitfalls

5.13.5.9 File System limitations
................................

Exceeding limitations on different file systems can cause decompression
failed.  Such as allowable characters in the directory entries, length
of the file name, length of the pathname, size of a single file, and
number of files, etc.


File: python.info,  Node: Resources limitations,  Next: Interruption,  Prev: File System limitations,  Up: Decompression pitfalls

5.13.5.10 Resources limitations
...............................

The lack of memory or disk volume would lead to decompression failed.
For example, decompression bombs (aka ZIP bomb(1)) apply to zipfile
library that can cause disk volume exhaustion.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Zip_bomb


File: python.info,  Node: Interruption,  Next: Default behaviors of extraction,  Prev: Resources limitations,  Up: Decompression pitfalls

5.13.5.11 Interruption
......................

Interruption during the decompression, such as pressing control-C or
killing the decompression process may result in incomplete decompression
of the archive.


File: python.info,  Node: Default behaviors of extraction,  Prev: Interruption,  Up: Decompression pitfalls

5.13.5.12 Default behaviors of extraction
.........................................

Not knowing the default extraction behaviors can cause unexpected
decompression results.  For example, when extracting the same archive
twice, it overwrites files without asking.


File: python.info,  Node: tarfile — Read and write tar archive files,  Prev: zipfile — Work with ZIP archives,  Up: Data Compression and Archiving

5.13.6 ‘tarfile’ — Read and write tar archive files
---------------------------------------------------

`Source code:' Lib/tarfile.py(1)

__________________________________________________________________

The *note tarfile: 101. module makes it possible to read and write tar
archives, including those using gzip, bz2 and lzma compression.  Use the
*note zipfile: 14b. module to read or write ‘.zip’ files, or the
higher-level functions in *note shutil: c67.

Some facts and figures:

   * reads and writes *note gzip: 8b, *note bz2: 13. and *note lzma: ad.
     compressed archives if the respective modules are available.

   * read/write support for the POSIX.1-1988 (ustar) format.

   * read/write support for the GNU tar format including `longname' and
     `longlink' extensions, read-only support for all variants of the
     `sparse' extension including restoration of sparse files.

   * read/write support for the POSIX.1-2001 (pax) format.

   * handles directories, regular files, hardlinks, symbolic links,
     fifos, character devices and block devices and is able to acquire
     and restore file information like timestamp, access permissions and
     owner.

Changed in version 3.3: Added support for *note lzma: ad. compression.

 -- Function: tarfile.open (name=None, mode='r', fileobj=None,
          bufsize=10240, **kwargs)

     Return a *note TarFile: c5d. object for the pathname `name'.  For
     detailed information on *note TarFile: c5d. objects and the keyword
     arguments that are allowed, see *note TarFile Objects: 1f37.

     `mode' has to be a string of the form ‘'filemode[:compression]'’,
     it defaults to ‘'r'’.  Here is a full list of mode combinations:

     mode                   action
                            
     -------------------------------------------------------------------------
                            
     ‘'r' or 'r:*'’         Open for reading with transparent compression
                            (recommended).
                            
                            
     ‘'r:'’                 Open for reading exclusively without
                            compression.
                            
                            
     ‘'r:gz'’               Open for reading with gzip compression.
                            
                            
     ‘'r:bz2'’              Open for reading with bzip2 compression.
                            
                            
     ‘'r:xz'’               Open for reading with lzma compression.
                            
                            
     ‘'x'’ or ‘'x:'’        Create a tarfile exclusively without
                            compression.  Raise an
                            *note FileExistsError: a39. exception if it
                            already exists.
                            
                            
     ‘'x:gz'’               Create a tarfile with gzip compression.  Raise
                            an *note FileExistsError: a39. exception if it
                            already exists.
                            
                            
     ‘'x:bz2'’              Create a tarfile with bzip2 compression.  Raise
                            an *note FileExistsError: a39. exception if it
                            already exists.
                            
                            
     ‘'x:xz'’               Create a tarfile with lzma compression.  Raise
                            an *note FileExistsError: a39. exception if it
                            already exists.
                            
                            
     ‘'a' or 'a:'’          Open for appending with no compression.  The
                            file is created if it does not exist.
                            
                            
     ‘'w' or 'w:'’          Open for uncompressed writing.
                            
                            
     ‘'w:gz'’               Open for gzip compressed writing.
                            
                            
     ‘'w:bz2'’              Open for bzip2 compressed writing.
                            
                            
     ‘'w:xz'’               Open for lzma compressed writing.
                            

     Note that ‘'a:gz'’, ‘'a:bz2'’ or ‘'a:xz'’ is not possible.  If
     `mode' is not suitable to open a certain (compressed) file for
     reading, *note ReadError: f71. is raised.  Use `mode' ‘'r'’ to
     avoid this.  If a compression method is not supported, *note
     CompressionError: 1f38. is raised.

     If `fileobj' is specified, it is used as an alternative to a *note
     file object: c14. opened in binary mode for `name'.  It is supposed
     to be at position 0.

     For modes ‘'w:gz'’, ‘'r:gz'’, ‘'w:bz2'’, ‘'r:bz2'’, ‘'x:gz'’,
     ‘'x:bz2'’, *note tarfile.open(): 855. accepts the keyword argument
     `compresslevel' (default ‘9’) to specify the compression level of
     the file.

     For modes ‘'w:xz'’ and ‘'x:xz'’, *note tarfile.open(): 855. accepts
     the keyword argument `preset' to specify the compression level of
     the file.

     For special purposes, there is a second format for `mode':
     ‘'filemode|[compression]'’.  *note tarfile.open(): 855. will return
     a *note TarFile: c5d. object that processes its data as a stream of
     blocks.  No random seeking will be done on the file.  If given,
     `fileobj' may be any object that has a ‘read()’ or ‘write()’ method
     (depending on the `mode').  `bufsize' specifies the blocksize and
     defaults to ‘20 * 512’ bytes.  Use this variant in combination with
     e.g.  ‘sys.stdin’, a socket *note file object: c14. or a tape
     device.  However, such a *note TarFile: c5d. object is limited in
     that it does not allow random access, see *note Examples: 1f39.
     The currently possible modes:

     Mode              Action
                       
     -------------------------------------------------------------------
                       
     ‘'r|*'’           Open a `stream' of tar blocks for reading with
                       transparent compression.
                       
                       
     ‘'r|'’            Open a `stream' of uncompressed tar blocks for
                       reading.
                       
                       
     ‘'r|gz'’          Open a gzip compressed `stream' for reading.
                       
                       
     ‘'r|bz2'’         Open a bzip2 compressed `stream' for reading.
                       
                       
     ‘'r|xz'’          Open an lzma compressed `stream' for reading.
                       
                       
     ‘'w|'’            Open an uncompressed `stream' for writing.
                       
                       
     ‘'w|gz'’          Open a gzip compressed `stream' for writing.
                       
                       
     ‘'w|bz2'’         Open a bzip2 compressed `stream' for writing.
                       
                       
     ‘'w|xz'’          Open an lzma compressed `stream' for writing.
                       

     Changed in version 3.5: The ‘'x'’ (exclusive creation) mode was
     added.

     Changed in version 3.6: The `name' parameter accepts a *note
     path-like object: 472.

 -- Class: tarfile.TarFile

     Class for reading and writing tar archives.  Do not use this class
     directly: use *note tarfile.open(): 855. instead.  See *note
     TarFile Objects: 1f37.

 -- Function: tarfile.is_tarfile (name)

     Return *note True: 594. if `name' is a tar archive file, that the
     *note tarfile: 101. module can read.  `name' may be a *note str:
     205, file, or file-like object.

     Changed in version 3.9: Support for file and file-like objects.

The *note tarfile: 101. module defines the following exceptions:

 -- Exception: tarfile.TarError

     Base class for all *note tarfile: 101. exceptions.

 -- Exception: tarfile.ReadError

     Is raised when a tar archive is opened, that either cannot be
     handled by the *note tarfile: 101. module or is somehow invalid.

 -- Exception: tarfile.CompressionError

     Is raised when a compression method is not supported or when the
     data cannot be decoded properly.

 -- Exception: tarfile.StreamError

     Is raised for the limitations that are typical for stream-like
     *note TarFile: c5d. objects.

 -- Exception: tarfile.ExtractError

     Is raised for `non-fatal' errors when using *note
     TarFile.extract(): 857, but only if ‘TarFile.errorlevel’‘== 2’.

 -- Exception: tarfile.HeaderError

     Is raised by *note TarInfo.frombuf(): 1f3e. if the buffer it gets
     is invalid.

The following constants are available at the module level:

 -- Data: tarfile.ENCODING

     The default character encoding: ‘'utf-8'’ on Windows, the value
     returned by *note sys.getfilesystemencoding(): 5f0. otherwise.

Each of the following constants defines a tar archive format that the
*note tarfile: 101. module is able to create.  See section *note
Supported tar formats: 1f40. for details.

 -- Data: tarfile.USTAR_FORMAT

     POSIX.1-1988 (ustar) format.

 -- Data: tarfile.GNU_FORMAT

     GNU tar format.

 -- Data: tarfile.PAX_FORMAT

     POSIX.1-2001 (pax) format.

 -- Data: tarfile.DEFAULT_FORMAT

     The default format for creating archives.  This is currently *note
     PAX_FORMAT: 1f43.

     Changed in version 3.8: The default format for new archives was
     changed to *note PAX_FORMAT: 1f43. from *note GNU_FORMAT: 1f42.

See also
........

Module *note zipfile: 14b.

     Documentation of the *note zipfile: 14b. standard module.

*note Archiving operations: c67.

     Documentation of the higher-level archiving facilities provided by
     the standard *note shutil: e9. module.

GNU tar manual, Basic Tar Format(2)

     Documentation for tar archive files, including GNU tar extensions.

* Menu:

* TarFile Objects::
* TarInfo Objects::
* Command-Line Interface: Command-Line Interface<2>.
* Examples: Examples<7>.
* Supported tar formats::
* Unicode issues::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/tarfile.py

   (2) https://www.gnu.org/software/tar/manual/html_node/Standard.html


File: python.info,  Node: TarFile Objects,  Next: TarInfo Objects,  Up: tarfile — Read and write tar archive files

5.13.6.1 TarFile Objects
........................

The *note TarFile: c5d. object provides an interface to a tar archive.
A tar archive is a sequence of blocks.  An archive member (a stored
file) is made up of a header block followed by data blocks.  It is
possible to store a file in a tar archive several times.  Each archive
member is represented by a *note TarInfo: c5e. object, see *note TarInfo
Objects: 1f46. for details.

A *note TarFile: c5d. object can be used as a context manager in a *note
with: 7da. statement.  It will automatically be closed when the block is
completed.  Please note that in the event of an exception an archive
opened for writing will not be finalized; only the internally used file
object will be closed.  See the *note Examples: 1f39. section for a use
case.

New in version 3.2: Added support for the context management protocol.

 -- Class: tarfile.TarFile (name=None, mode='r', fileobj=None,
          format=DEFAULT_FORMAT, tarinfo=TarInfo, dereference=False,
          ignore_zeros=False, encoding=ENCODING,
          errors='surrogateescape', pax_headers=None, debug=0,
          errorlevel=0)

     All following arguments are optional and can be accessed as
     instance attributes as well.

     `name' is the pathname of the archive.  `name' may be a *note
     path-like object: 472.  It can be omitted if `fileobj' is given.
     In this case, the file object’s ‘name’ attribute is used if it
     exists.

     `mode' is either ‘'r'’ to read from an existing archive, ‘'a'’ to
     append data to an existing file, ‘'w'’ to create a new file
     overwriting an existing one, or ‘'x'’ to create a new file only if
     it does not already exist.

     If `fileobj' is given, it is used for reading or writing data.  If
     it can be determined, `mode' is overridden by `fileobj'’s mode.
     `fileobj' will be used from position 0.

          Note: `fileobj' is not closed, when *note TarFile: c5d. is
          closed.

     `format' controls the archive format for writing.  It must be one
     of the constants *note USTAR_FORMAT: 1f41, *note GNU_FORMAT: 1f42.
     or *note PAX_FORMAT: 1f43. that are defined at module level.  When
     reading, format will be automatically detected, even if different
     formats are present in a single archive.

     The `tarinfo' argument can be used to replace the default *note
     TarInfo: c5e. class with a different one.

     If `dereference' is *note False: 48f, add symbolic and hard links
     to the archive.  If it is *note True: 594, add the content of the
     target files to the archive.  This has no effect on systems that do
     not support symbolic links.

     If `ignore_zeros' is *note False: 48f, treat an empty block as the
     end of the archive.  If it is *note True: 594, skip empty (and
     invalid) blocks and try to get as many members as possible.  This
     is only useful for reading concatenated or damaged archives.

     `debug' can be set from ‘0’ (no debug messages) up to ‘3’ (all
     debug messages).  The messages are written to ‘sys.stderr’.

     If `errorlevel' is ‘0’, all errors are ignored when using *note
     TarFile.extract(): 857.  Nevertheless, they appear as error
     messages in the debug output, when debugging is enabled.  If ‘1’,
     all `fatal' errors are raised as *note OSError: 304. exceptions.
     If ‘2’, all `non-fatal' errors are raised as *note TarError: 1f3a.
     exceptions as well.

     The `encoding' and `errors' arguments define the character encoding
     to be used for reading or writing the archive and how conversion
     errors are going to be handled.  The default settings will work for
     most users.  See section *note Unicode issues: 1f47. for in-depth
     information.

     The `pax_headers' argument is an optional dictionary of strings
     which will be added as a pax global header if `format' is *note
     PAX_FORMAT: 1f43.

     Changed in version 3.2: Use ‘'surrogateescape'’ as the default for
     the `errors' argument.

     Changed in version 3.5: The ‘'x'’ (exclusive creation) mode was
     added.

     Changed in version 3.6: The `name' parameter accepts a *note
     path-like object: 472.

 -- Method: classmethod TarFile.open (...)

     Alternative constructor.  The *note tarfile.open(): 855. function
     is actually a shortcut to this classmethod.

 -- Method: TarFile.getmember (name)

     Return a *note TarInfo: c5e. object for member `name'.  If `name'
     can not be found in the archive, *note KeyError: 3e9. is raised.

          Note: If a member occurs more than once in the archive, its
          last occurrence is assumed to be the most up-to-date version.

 -- Method: TarFile.getmembers ()

     Return the members of the archive as a list of *note TarInfo: c5e.
     objects.  The list has the same order as the members in the
     archive.

 -- Method: TarFile.getnames ()

     Return the members as a list of their names.  It has the same order
     as the list returned by *note getmembers(): 859.

 -- Method: TarFile.list (verbose=True, *, members=None)

     Print a table of contents to ‘sys.stdout’.  If `verbose' is *note
     False: 48f, only the names of the members are printed.  If it is
     *note True: 594, output similar to that of ‘ls -l’ is produced.  If
     optional `members' is given, it must be a subset of the list
     returned by *note getmembers(): 859.

     Changed in version 3.5: Added the `members' parameter.

 -- Method: TarFile.next ()

     Return the next member of the archive as a *note TarInfo: c5e.
     object, when *note TarFile: c5d. is opened for reading.  Return
     *note None: 203. if there is no more available.

 -- Method: TarFile.extractall (path=".", members=None, *,
          numeric_owner=False)

     Extract all members from the archive to the current working
     directory or directory `path'.  If optional `members' is given, it
     must be a subset of the list returned by *note getmembers(): 859.
     Directory information like owner, modification time and permissions
     are set after all members have been extracted.  This is done to
     work around two problems: A directory’s modification time is reset
     each time a file is created in it.  And, if a directory’s
     permissions do not allow writing, extracting files to it will fail.

     If `numeric_owner' is *note True: 594, the uid and gid numbers from
     the tarfile are used to set the owner/group for the extracted
     files.  Otherwise, the named values from the tarfile are used.

          Warning: Never extract archives from untrusted sources without
          prior inspection.  It is possible that files are created
          outside of `path', e.g.  members that have absolute filenames
          starting with ‘"/"’ or filenames with two dots ‘".."’.

     Changed in version 3.5: Added the `numeric_owner' parameter.

     Changed in version 3.6: The `path' parameter accepts a *note
     path-like object: 472.

 -- Method: TarFile.extract (member, path="", set_attrs=True, *,
          numeric_owner=False)

     Extract a member from the archive to the current working directory,
     using its full name.  Its file information is extracted as
     accurately as possible.  `member' may be a filename or a *note
     TarInfo: c5e. object.  You can specify a different directory using
     `path'.  `path' may be a *note path-like object: 472.  File
     attributes (owner, mtime, mode) are set unless `set_attrs' is
     false.

     If `numeric_owner' is *note True: 594, the uid and gid numbers from
     the tarfile are used to set the owner/group for the extracted
     files.  Otherwise, the named values from the tarfile are used.

          Note: The *note extract(): 857. method does not take care of
          several extraction issues.  In most cases you should consider
          using the *note extractall(): 856. method.

          Warning: See the warning for *note extractall(): 856.

     Changed in version 3.2: Added the `set_attrs' parameter.

     Changed in version 3.5: Added the `numeric_owner' parameter.

     Changed in version 3.6: The `path' parameter accepts a *note
     path-like object: 472.

 -- Method: TarFile.extractfile (member)

     Extract a member from the archive as a file object.  `member' may
     be a filename or a *note TarInfo: c5e. object.  If `member' is a
     regular file or a link, an *note io.BufferedReader: c5b. object is
     returned.  For all other existing members, *note None: 203. is
     returned.  If `member' does not appear in the archive, *note
     KeyError: 3e9. is raised.

     Changed in version 3.3: Return an *note io.BufferedReader: c5b.
     object.

 -- Method: TarFile.add (name, arcname=None, recursive=True, *,
          filter=None)

     Add the file `name' to the archive.  `name' may be any type of file
     (directory, fifo, symbolic link, etc.).  If given, `arcname'
     specifies an alternative name for the file in the archive.
     Directories are added recursively by default.  This can be avoided
     by setting `recursive' to *note False: 48f.  Recursion adds entries
     in sorted order.  If `filter' is given, it should be a function
     that takes a *note TarInfo: c5e. object argument and returns the
     changed *note TarInfo: c5e. object.  If it instead returns *note
     None: 203. the *note TarInfo: c5e. object will be excluded from the
     archive.  See *note Examples: 1f39. for an example.

     Changed in version 3.2: Added the `filter' parameter.

     Changed in version 3.7: Recursion adds entries in sorted order.

 -- Method: TarFile.addfile (tarinfo, fileobj=None)

     Add the *note TarInfo: c5e. object `tarinfo' to the archive.  If
     `fileobj' is given, it should be a *note binary file: 1e01, and
     ‘tarinfo.size’ bytes are read from it and added to the archive.
     You can create *note TarInfo: c5e. objects directly, or by using
     *note gettarinfo(): 1f4e.

 -- Method: TarFile.gettarinfo (name=None, arcname=None, fileobj=None)

     Create a *note TarInfo: c5e. object from the result of *note
     os.stat(): 321. or equivalent on an existing file.  The file is
     either named by `name', or specified as a *note file object: c14.
     `fileobj' with a file descriptor.  `name' may be a *note path-like
     object: 472.  If given, `arcname' specifies an alternative name for
     the file in the archive, otherwise, the name is taken from
     `fileobj'’s *note name: 1f4f. attribute, or the `name' argument.
     The name should be a text string.

     You can modify some of the *note TarInfo: c5e.’s attributes before
     you add it using *note addfile(): 1f4d.  If the file object is not
     an ordinary file object positioned at the beginning of the file,
     attributes such as *note size: 1f50. may need modifying.  This is
     the case for objects such as *note GzipFile: 206.  The *note name:
     1f51. may also be modified, in which case `arcname' could be a
     dummy string.

     Changed in version 3.6: The `name' parameter accepts a *note
     path-like object: 472.

 -- Method: TarFile.close ()

     Close the *note TarFile: c5d.  In write mode, two finishing zero
     blocks are appended to the archive.

 -- Attribute: TarFile.pax_headers

     A dictionary containing key-value pairs of pax global headers.


File: python.info,  Node: TarInfo Objects,  Next: Command-Line Interface<2>,  Prev: TarFile Objects,  Up: tarfile — Read and write tar archive files

5.13.6.2 TarInfo Objects
........................

A *note TarInfo: c5e. object represents one member in a *note TarFile:
c5d.  Aside from storing all required attributes of a file (like file
type, size, time, permissions, owner etc.), it provides some useful
methods to determine its type.  It does `not' contain the file’s data
itself.

*note TarInfo: c5e. objects are returned by *note TarFile: c5d.’s
methods ‘getmember()’, ‘getmembers()’ and ‘gettarinfo()’.

 -- Class: tarfile.TarInfo (name="")

     Create a *note TarInfo: c5e. object.

 -- Method: classmethod TarInfo.frombuf (buf, encoding, errors)

     Create and return a *note TarInfo: c5e. object from string buffer
     `buf'.

     Raises *note HeaderError: 1f3d. if the buffer is invalid.

 -- Method: classmethod TarInfo.fromtarfile (tarfile)

     Read the next member from the *note TarFile: c5d. object `tarfile'
     and return it as a *note TarInfo: c5e. object.

 -- Method: TarInfo.tobuf (format=DEFAULT_FORMAT, encoding=ENCODING,
          errors='surrogateescape')

     Create a string buffer from a *note TarInfo: c5e. object.  For
     information on the arguments see the constructor of the *note
     TarFile: c5d. class.

     Changed in version 3.2: Use ‘'surrogateescape'’ as the default for
     the `errors' argument.

A ‘TarInfo’ object has the following public data attributes:

 -- Attribute: TarInfo.name

     Name of the archive member.

 -- Attribute: TarInfo.size

     Size in bytes.

 -- Attribute: TarInfo.mtime

     Time of last modification.

 -- Attribute: TarInfo.mode

     Permission bits.

 -- Attribute: TarInfo.type

     File type.  `type' is usually one of these constants: ‘REGTYPE’,
     ‘AREGTYPE’, ‘LNKTYPE’, ‘SYMTYPE’, ‘DIRTYPE’, ‘FIFOTYPE’,
     ‘CONTTYPE’, ‘CHRTYPE’, ‘BLKTYPE’, ‘GNUTYPE_SPARSE’.  To determine
     the type of a *note TarInfo: c5e. object more conveniently, use the
     ‘is*()’ methods below.

 -- Attribute: TarInfo.linkname

     Name of the target file name, which is only present in *note
     TarInfo: c5e. objects of type ‘LNKTYPE’ and ‘SYMTYPE’.

 -- Attribute: TarInfo.uid

     User ID of the user who originally stored this member.

 -- Attribute: TarInfo.gid

     Group ID of the user who originally stored this member.

 -- Attribute: TarInfo.uname

     User name.

 -- Attribute: TarInfo.gname

     Group name.

 -- Attribute: TarInfo.pax_headers

     A dictionary containing key-value pairs of an associated pax
     extended header.

A *note TarInfo: c5e. object also provides some convenient query
methods:

 -- Method: TarInfo.isfile ()

     Return *note True: 594. if the ‘Tarinfo’ object is a regular file.

 -- Method: TarInfo.isreg ()

     Same as *note isfile(): 1f60.

 -- Method: TarInfo.isdir ()

     Return *note True: 594. if it is a directory.

 -- Method: TarInfo.issym ()

     Return *note True: 594. if it is a symbolic link.

 -- Method: TarInfo.islnk ()

     Return *note True: 594. if it is a hard link.

 -- Method: TarInfo.ischr ()

     Return *note True: 594. if it is a character device.

 -- Method: TarInfo.isblk ()

     Return *note True: 594. if it is a block device.

 -- Method: TarInfo.isfifo ()

     Return *note True: 594. if it is a FIFO.

 -- Method: TarInfo.isdev ()

     Return *note True: 594. if it is one of character device, block
     device or FIFO.


File: python.info,  Node: Command-Line Interface<2>,  Next: Examples<7>,  Prev: TarInfo Objects,  Up: tarfile — Read and write tar archive files

5.13.6.3 Command-Line Interface
...............................

New in version 3.4.

The *note tarfile: 101. module provides a simple command-line interface
to interact with tar archives.

If you want to create a new tar archive, specify its name after the
*note -c: 1f6a. option and then list the filename(s) that should be
included:

     $ python -m tarfile -c monty.tar  spam.txt eggs.txt

Passing a directory is also acceptable:

     $ python -m tarfile -c monty.tar life-of-brian_1979/

If you want to extract a tar archive into the current directory, use the
*note -e: 1f6b. option:

     $ python -m tarfile -e monty.tar

You can also extract a tar archive into a different directory by passing
the directory’s name:

     $ python -m tarfile -e monty.tar  other-dir/

For a list of the files in a tar archive, use the *note -l: 1f6c.
option:

     $ python -m tarfile -l monty.tar

* Menu:

* Command-line options: Command-line options<2>.


File: python.info,  Node: Command-line options<2>,  Up: Command-Line Interface<2>

5.13.6.4 Command-line options
.............................

 -- Program Option: -l <tarfile>
 -- Program Option: --list <tarfile>

     List files in a tarfile.

 -- Program Option: -c <tarfile> <source1> ... <sourceN>
 -- Program Option: --create <tarfile> <source1> ... <sourceN>

     Create tarfile from source files.

 -- Program Option: -e <tarfile> [<output_dir>]
 -- Program Option: --extract <tarfile> [<output_dir>]

     Extract tarfile into the current directory if `output_dir' is not
     specified.

 -- Program Option: -t <tarfile>
 -- Program Option: --test <tarfile>

     Test whether the tarfile is valid or not.

 -- Program Option: -v, --verbose

     Verbose output.


File: python.info,  Node: Examples<7>,  Next: Supported tar formats,  Prev: Command-Line Interface<2>,  Up: tarfile — Read and write tar archive files

5.13.6.5 Examples
.................

How to extract an entire tar archive to the current working directory:

     import tarfile
     tar = tarfile.open("sample.tar.gz")
     tar.extractall()
     tar.close()

How to extract a subset of a tar archive with *note
TarFile.extractall(): 856. using a generator function instead of a list:

     import os
     import tarfile

     def py_files(members):
         for tarinfo in members:
             if os.path.splitext(tarinfo.name)[1] == ".py":
                 yield tarinfo

     tar = tarfile.open("sample.tar.gz")
     tar.extractall(members=py_files(tar))
     tar.close()

How to create an uncompressed tar archive from a list of filenames:

     import tarfile
     tar = tarfile.open("sample.tar", "w")
     for name in ["foo", "bar", "quux"]:
         tar.add(name)
     tar.close()

The same example using the *note with: 7da. statement:

     import tarfile
     with tarfile.open("sample.tar", "w") as tar:
         for name in ["foo", "bar", "quux"]:
             tar.add(name)

How to read a gzip compressed tar archive and display some member
information:

     import tarfile
     tar = tarfile.open("sample.tar.gz", "r:gz")
     for tarinfo in tar:
         print(tarinfo.name, "is", tarinfo.size, "bytes in size and is ", end="")
         if tarinfo.isreg():
             print("a regular file.")
         elif tarinfo.isdir():
             print("a directory.")
         else:
             print("something else.")
     tar.close()

How to create an archive and reset the user information using the
`filter' parameter in *note TarFile.add(): 57b.:

     import tarfile
     def reset(tarinfo):
         tarinfo.uid = tarinfo.gid = 0
         tarinfo.uname = tarinfo.gname = "root"
         return tarinfo
     tar = tarfile.open("sample.tar.gz", "w:gz")
     tar.add("foo", filter=reset)
     tar.close()


File: python.info,  Node: Supported tar formats,  Next: Unicode issues,  Prev: Examples<7>,  Up: tarfile — Read and write tar archive files

5.13.6.6 Supported tar formats
..............................

There are three tar formats that can be created with the *note tarfile:
101. module:

   * The POSIX.1-1988 ustar format (*note USTAR_FORMAT: 1f41.).  It
     supports filenames up to a length of at best 256 characters and
     linknames up to 100 characters.  The maximum file size is 8 GiB.
     This is an old and limited but widely supported format.

   * The GNU tar format (*note GNU_FORMAT: 1f42.).  It supports long
     filenames and linknames, files bigger than 8 GiB and sparse files.
     It is the de facto standard on GNU/Linux systems.  *note tarfile:
     101. fully supports the GNU tar extensions for long names, sparse
     file support is read-only.

   * The POSIX.1-2001 pax format (*note PAX_FORMAT: 1f43.).  It is the
     most flexible format with virtually no limits.  It supports long
     filenames and linknames, large files and stores pathnames in a
     portable way.  Modern tar implementations, including GNU tar,
     bsdtar/libarchive and star, fully support extended `pax' features;
     some old or unmaintained libraries may not, but should treat `pax'
     archives as if they were in the universally-supported `ustar'
     format.  It is the current default format for new archives.

     It extends the existing `ustar' format with extra headers for
     information that cannot be stored otherwise.  There are two
     flavours of pax headers: Extended headers only affect the
     subsequent file header, global headers are valid for the complete
     archive and affect all following files.  All the data in a pax
     header is encoded in `UTF-8' for portability reasons.

There are some more variants of the tar format which can be read, but
not created:

   * The ancient V7 format.  This is the first tar format from Unix
     Seventh Edition, storing only regular files and directories.  Names
     must not be longer than 100 characters, there is no user/group name
     information.  Some archives have miscalculated header checksums in
     case of fields with non-ASCII characters.

   * The SunOS tar extended format.  This format is a variant of the
     POSIX.1-2001 pax format, but is not compatible.


File: python.info,  Node: Unicode issues,  Prev: Supported tar formats,  Up: tarfile — Read and write tar archive files

5.13.6.7 Unicode issues
.......................

The tar format was originally conceived to make backups on tape drives
with the main focus on preserving file system information.  Nowadays tar
archives are commonly used for file distribution and exchanging archives
over networks.  One problem of the original format (which is the basis
of all other formats) is that there is no concept of supporting
different character encodings.  For example, an ordinary tar archive
created on a `UTF-8' system cannot be read correctly on a `Latin-1'
system if it contains non-`ASCII' characters.  Textual metadata (like
filenames, linknames, user/group names) will appear damaged.
Unfortunately, there is no way to autodetect the encoding of an archive.
The pax format was designed to solve this problem.  It stores non-ASCII
metadata using the universal character encoding `UTF-8'.

The details of character conversion in *note tarfile: 101. are
controlled by the `encoding' and `errors' keyword arguments of the *note
TarFile: c5d. class.

`encoding' defines the character encoding to use for the metadata in the
archive.  The default value is *note sys.getfilesystemencoding(): 5f0.
or ‘'ascii'’ as a fallback.  Depending on whether the archive is read or
written, the metadata must be either decoded or encoded.  If `encoding'
is not set appropriately, this conversion may fail.

The `errors' argument defines how characters are treated that cannot be
converted.  Possible values are listed in section *note Error Handlers:
1493.  The default scheme is ‘'surrogateescape'’ which Python also uses
for its file system calls, see *note File Names, Command Line Arguments,
and Environment Variables: 1f77.

For *note PAX_FORMAT: 1f43. archives (the default), `encoding' is
generally not needed because all the metadata is stored using `UTF-8'.
`encoding' is only used in the rare cases when binary pax headers are
decoded or when strings with surrogate characters are stored.


File: python.info,  Node: File Formats,  Next: Cryptographic Services,  Prev: Data Compression and Archiving,  Up: The Python Standard Library

5.14 File Formats
=================

The modules described in this chapter parse various miscellaneous file
formats that aren’t markup languages and are not related to e-mail.

* Menu:

* csv — CSV File Reading and Writing::
* configparser — Configuration file parser::
* netrc — netrc file processing::
* xdrlib — Encode and decode XDR data::
* plistlib — Generate and parse Apple .plist files: plistlib — Generate and parse Apple plist files.


File: python.info,  Node: csv — CSV File Reading and Writing,  Next: configparser — Configuration file parser,  Up: File Formats

5.14.1 ‘csv’ — CSV File Reading and Writing
-------------------------------------------

`Source code:' Lib/csv.py(1)

__________________________________________________________________

The so-called CSV (Comma Separated Values) format is the most common
import and export format for spreadsheets and databases.  CSV format was
used for many years prior to attempts to describe the format in a
standardized way in RFC 4180(2).  The lack of a well-defined standard
means that subtle differences often exist in the data produced and
consumed by different applications.  These differences can make it
annoying to process CSV files from multiple sources.  Still, while the
delimiters and quoting characters vary, the overall format is similar
enough that it is possible to write a single module which can
efficiently manipulate such data, hiding the details of reading and
writing the data from the programmer.

The *note csv: 29. module implements classes to read and write tabular
data in CSV format.  It allows programmers to say, “write this data in
the format preferred by Excel,” or “read data from this file which was
generated by Excel,” without knowing the precise details of the CSV
format used by Excel.  Programmers can also describe the CSV formats
understood by other applications or define their own special-purpose CSV
formats.

The *note csv: 29. module’s *note reader: 101a. and *note writer: ec0.
objects read and write sequences.  Programmers can also read and write
data in dictionary form using the *note DictReader: 2ee. and *note
DictWriter: c4b. classes.

See also
........

PEP 305(3) - CSV File API

     The Python Enhancement Proposal which proposed this addition to
     Python.

* Menu:

* Module Contents: Module Contents<3>.
* Dialects and Formatting Parameters::
* Reader Objects::
* Writer Objects::
* Examples: Examples<8>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/csv.py

   (2) https://tools.ietf.org/html/rfc4180.html

   (3) https://www.python.org/dev/peps/pep-0305


File: python.info,  Node: Module Contents<3>,  Next: Dialects and Formatting Parameters,  Up: csv — CSV File Reading and Writing

5.14.1.1 Module Contents
........................

The *note csv: 29. module defines the following functions:

 -- Function: csv.reader (csvfile, dialect='excel', **fmtparams)

     Return a reader object which will iterate over lines in the given
     `csvfile'.  `csvfile' can be any object which supports the *note
     iterator: 1171. protocol and returns a string each time its
     ‘__next__()’ method is called — *note file objects: c14. and list
     objects are both suitable.  If `csvfile' is a file object, it
     should be opened with ‘newline=''’.  (1) An optional `dialect'
     parameter can be given which is used to define a set of parameters
     specific to a particular CSV dialect.  It may be an instance of a
     subclass of the *note Dialect: f6c. class or one of the strings
     returned by the *note list_dialects(): 1f7f. function.  The other
     optional `fmtparams' keyword arguments can be given to override
     individual formatting parameters in the current dialect.  For full
     details about the dialect and formatting parameters, see section
     *note Dialects and Formatting Parameters: 1f80.

     Each row read from the csv file is returned as a list of strings.
     No automatic data type conversion is performed unless the
     ‘QUOTE_NONNUMERIC’ format option is specified (in which case
     unquoted fields are transformed into floats).

     A short usage example:

          >>> import csv
          >>> with open('eggs.csv', newline='') as csvfile:
          ...     spamreader = csv.reader(csvfile, delimiter=' ', quotechar='|')
          ...     for row in spamreader:
          ...         print(', '.join(row))
          Spam, Spam, Spam, Spam, Spam, Baked Beans
          Spam, Lovely Spam, Wonderful Spam

 -- Function: csv.writer (csvfile, dialect='excel', **fmtparams)

     Return a writer object responsible for converting the user’s data
     into delimited strings on the given file-like object.  `csvfile'
     can be any object with a ‘write()’ method.  If `csvfile' is a file
     object, it should be opened with ‘newline=''’ (2).  An optional
     `dialect' parameter can be given which is used to define a set of
     parameters specific to a particular CSV dialect.  It may be an
     instance of a subclass of the *note Dialect: f6c. class or one of
     the strings returned by the *note list_dialects(): 1f7f. function.
     The other optional `fmtparams' keyword arguments can be given to
     override individual formatting parameters in the current dialect.
     For full details about dialects and formatting parameters, see the
     *note Dialects and Formatting Parameters: 1f80. section.  To make
     it as easy as possible to interface with modules which implement
     the DB API, the value *note None: 203. is written as the empty
     string.  While this isn’t a reversible transformation, it makes it
     easier to dump SQL NULL data values to CSV files without
     preprocessing the data returned from a ‘cursor.fetch*’ call.  All
     other non-string data are stringified with *note str(): 205. before
     being written.

     A short usage example:

          import csv
          with open('eggs.csv', 'w', newline='') as csvfile:
              spamwriter = csv.writer(csvfile, delimiter=' ',
                                      quotechar='|', quoting=csv.QUOTE_MINIMAL)
              spamwriter.writerow(['Spam'] * 5 + ['Baked Beans'])
              spamwriter.writerow(['Spam', 'Lovely Spam', 'Wonderful Spam'])

 -- Function: csv.register_dialect (name[, dialect[, **fmtparams]])

     Associate `dialect' with `name'.  `name' must be a string.  The
     dialect can be specified either by passing a sub-class of *note
     Dialect: f6c, or by `fmtparams' keyword arguments, or both, with
     keyword arguments overriding parameters of the dialect.  For full
     details about dialects and formatting parameters, see section *note
     Dialects and Formatting Parameters: 1f80.

 -- Function: csv.unregister_dialect (name)

     Delete the dialect associated with `name' from the dialect
     registry.  An *note Error: 1f83. is raised if `name' is not a
     registered dialect name.

 -- Function: csv.get_dialect (name)

     Return the dialect associated with `name'.  An *note Error: 1f83.
     is raised if `name' is not a registered dialect name.  This
     function returns an immutable *note Dialect: f6c.

 -- Function: csv.list_dialects ()

     Return the names of all registered dialects.

 -- Function: csv.field_size_limit ([new_limit])

     Returns the current maximum field size allowed by the parser.  If
     `new_limit' is given, this becomes the new limit.

The *note csv: 29. module defines the following classes:

 -- Class: csv.DictReader (f, fieldnames=None, restkey=None,
          restval=None, dialect='excel', *args, **kwds)

     Create an object that operates like a regular reader but maps the
     information in each row to a *note dict: 164. whose keys are given
     by the optional `fieldnames' parameter.

     The `fieldnames' parameter is a *note sequence: 135c.  If
     `fieldnames' is omitted, the values in the first row of file `f'
     will be used as the fieldnames.  Regardless of how the fieldnames
     are determined, the dictionary preserves their original ordering.

     If a row has more fields than fieldnames, the remaining data is put
     in a list and stored with the fieldname specified by `restkey'
     (which defaults to ‘None’).  If a non-blank row has fewer fields
     than fieldnames, the missing values are filled-in with the value of
     `restval' (which defaults to ‘None’).

     All other optional or keyword arguments are passed to the
     underlying *note reader: 101a. instance.

     Changed in version 3.6: Returned rows are now of type
     ‘OrderedDict’.

     Changed in version 3.8: Returned rows are now of type *note dict:
     164.

     A short usage example:

          >>> import csv
          >>> with open('names.csv', newline='') as csvfile:
          ...     reader = csv.DictReader(csvfile)
          ...     for row in reader:
          ...         print(row['first_name'], row['last_name'])
          ...
          Eric Idle
          John Cleese

          >>> print(row)
          {'first_name': 'John', 'last_name': 'Cleese'}

 -- Class: csv.DictWriter (f, fieldnames, restval='',
          extrasaction='raise', dialect='excel', *args, **kwds)

     Create an object which operates like a regular writer but maps
     dictionaries onto output rows.  The `fieldnames' parameter is a
     *note sequence: 1e. of keys that identify the order in which values
     in the dictionary passed to the ‘writerow()’ method are written to
     file `f'.  The optional `restval' parameter specifies the value to
     be written if the dictionary is missing a key in `fieldnames'.  If
     the dictionary passed to the ‘writerow()’ method contains a key not
     found in `fieldnames', the optional `extrasaction' parameter
     indicates what action to take.  If it is set to ‘'raise'’, the
     default value, a *note ValueError: 16d. is raised.  If it is set to
     ‘'ignore'’, extra values in the dictionary are ignored.  Any other
     optional or keyword arguments are passed to the underlying *note
     writer: ec0. instance.

     Note that unlike the *note DictReader: 2ee. class, the `fieldnames'
     parameter of the *note DictWriter: c4b. class is not optional.

     A short usage example:

          import csv

          with open('names.csv', 'w', newline='') as csvfile:
              fieldnames = ['first_name', 'last_name']
              writer = csv.DictWriter(csvfile, fieldnames=fieldnames)

              writer.writeheader()
              writer.writerow({'first_name': 'Baked', 'last_name': 'Beans'})
              writer.writerow({'first_name': 'Lovely', 'last_name': 'Spam'})
              writer.writerow({'first_name': 'Wonderful', 'last_name': 'Spam'})

 -- Class: csv.Dialect

     The *note Dialect: f6c. class is a container class whose attributes
     contain information for how to handle doublequotes, whitespace,
     delimiters, etc.  Due to the lack of a strict CSV specification,
     different applications produce subtly different CSV data.  *note
     Dialect: f6c. instances define how *note reader: 101a. and *note
     writer: ec0. instances behave.

     All available *note Dialect: f6c. names are returned by *note
     list_dialects(): 1f7f, and they can be registered with specific
     *note reader: 101a. and *note writer: ec0. classes through their
     initializer (‘__init__’) functions like this:

          import csv

          with open('students.csv', 'w', newline='') as csvfile:
              writer = csv.writer(csvfile, dialect='unix')
                                           ^^^^^^^^^^^^^^

 -- Class: csv.excel

     The *note excel: 1f86. class defines the usual properties of an
     Excel-generated CSV file.  It is registered with the dialect name
     ‘'excel'’.

 -- Class: csv.excel_tab

     The *note excel_tab: 1f87. class defines the usual properties of an
     Excel-generated TAB-delimited file.  It is registered with the
     dialect name ‘'excel-tab'’.

 -- Class: csv.unix_dialect

     The *note unix_dialect: c4a. class defines the usual properties of
     a CSV file generated on UNIX systems, i.e.  using ‘'\n'’ as line
     terminator and quoting all fields.  It is registered with the
     dialect name ‘'unix'’.

     New in version 3.2.

 -- Class: csv.Sniffer

     The *note Sniffer: 1f88. class is used to deduce the format of a
     CSV file.

     The *note Sniffer: 1f88. class provides two methods:

      -- Method: sniff (sample, delimiters=None)

          Analyze the given `sample' and return a *note Dialect: f6c.
          subclass reflecting the parameters found.  If the optional
          `delimiters' parameter is given, it is interpreted as a string
          containing possible valid delimiter characters.

      -- Method: has_header (sample)

          Analyze the sample text (presumed to be in CSV format) and
          return *note True: 594. if the first row appears to be a
          series of column headers.

An example for *note Sniffer: 1f88. use:

     with open('example.csv', newline='') as csvfile:
         dialect = csv.Sniffer().sniff(csvfile.read(1024))
         csvfile.seek(0)
         reader = csv.reader(csvfile, dialect)
         # ... process CSV file contents here ...

The *note csv: 29. module defines the following constants:

 -- Data: csv.QUOTE_ALL

     Instructs *note writer: ec0. objects to quote all fields.

 -- Data: csv.QUOTE_MINIMAL

     Instructs *note writer: ec0. objects to only quote those fields
     which contain special characters such as `delimiter', `quotechar'
     or any of the characters in `lineterminator'.

 -- Data: csv.QUOTE_NONNUMERIC

     Instructs *note writer: ec0. objects to quote all non-numeric
     fields.

     Instructs the reader to convert all non-quoted fields to type
     `float'.

 -- Data: csv.QUOTE_NONE

     Instructs *note writer: ec0. objects to never quote fields.  When
     the current `delimiter' occurs in output data it is preceded by the
     current `escapechar' character.  If `escapechar' is not set, the
     writer will raise *note Error: 1f83. if any characters that require
     escaping are encountered.

     Instructs *note reader: 101a. to perform no special processing of
     quote characters.

The *note csv: 29. module defines the following exception:

 -- Exception: csv.Error

     Raised by any of the functions when an error is detected.

   ---------- Footnotes ----------

   (1) (1) If ‘newline=''’ is not specified, newlines embedded inside
quoted fields will not be interpreted correctly, and on platforms that
use ‘\r\n’ linendings on write an extra ‘\r’ will be added.  It should
always be safe to specify ‘newline=''’, since the csv module does its
own (*note universal: 6eb.) newline handling.

   (2) (1) If ‘newline=''’ is not specified, newlines embedded inside
quoted fields will not be interpreted correctly, and on platforms that
use ‘\r\n’ linendings on write an extra ‘\r’ will be added.  It should
always be safe to specify ‘newline=''’, since the csv module does its
own (*note universal: 6eb.) newline handling.


File: python.info,  Node: Dialects and Formatting Parameters,  Next: Reader Objects,  Prev: Module Contents<3>,  Up: csv — CSV File Reading and Writing

5.14.1.2 Dialects and Formatting Parameters
...........................................

To make it easier to specify the format of input and output records,
specific formatting parameters are grouped together into dialects.  A
dialect is a subclass of the *note Dialect: f6c. class having a set of
specific methods and a single ‘validate()’ method.  When creating *note
reader: 101a. or *note writer: ec0. objects, the programmer can specify
a string or a subclass of the *note Dialect: f6c. class as the dialect
parameter.  In addition to, or instead of, the `dialect' parameter, the
programmer can also specify individual formatting parameters, which have
the same names as the attributes defined below for the *note Dialect:
f6c. class.

Dialects support the following attributes:

 -- Attribute: Dialect.delimiter

     A one-character string used to separate fields.  It defaults to
     ‘','’.

 -- Attribute: Dialect.doublequote

     Controls how instances of `quotechar' appearing inside a field
     should themselves be quoted.  When *note True: 594, the character
     is doubled.  When *note False: 48f, the `escapechar' is used as a
     prefix to the `quotechar'.  It defaults to *note True: 594.

     On output, if `doublequote' is *note False: 48f. and no
     `escapechar' is set, *note Error: 1f83. is raised if a `quotechar'
     is found in a field.

 -- Attribute: Dialect.escapechar

     A one-character string used by the writer to escape the `delimiter'
     if `quoting' is set to *note QUOTE_NONE: 1f8e. and the `quotechar'
     if `doublequote' is *note False: 48f.  On reading, the `escapechar'
     removes any special meaning from the following character.  It
     defaults to *note None: 203, which disables escaping.

 -- Attribute: Dialect.lineterminator

     The string used to terminate lines produced by the *note writer:
     ec0.  It defaults to ‘'\r\n'’.

          Note: The *note reader: 101a. is hard-coded to recognise
          either ‘'\r'’ or ‘'\n'’ as end-of-line, and ignores
          `lineterminator'.  This behavior may change in the future.

 -- Attribute: Dialect.quotechar

     A one-character string used to quote fields containing special
     characters, such as the `delimiter' or `quotechar', or which
     contain new-line characters.  It defaults to ‘'"'’.

 -- Attribute: Dialect.quoting

     Controls when quotes should be generated by the writer and
     recognised by the reader.  It can take on any of the ‘QUOTE_*’
     constants (see section *note Module Contents: 1f7d.) and defaults
     to *note QUOTE_MINIMAL: 1f8c.

 -- Attribute: Dialect.skipinitialspace

     When *note True: 594, whitespace immediately following the
     `delimiter' is ignored.  The default is *note False: 48f.

 -- Attribute: Dialect.strict

     When ‘True’, raise exception *note Error: 1f83. on bad CSV input.
     The default is ‘False’.


File: python.info,  Node: Reader Objects,  Next: Writer Objects,  Prev: Dialects and Formatting Parameters,  Up: csv — CSV File Reading and Writing

5.14.1.3 Reader Objects
.......................

Reader objects (*note DictReader: 2ee. instances and objects returned by
the *note reader(): 101a. function) have the following public methods:

 -- Method: csvreader.__next__ ()

     Return the next row of the reader’s iterable object as a list (if
     the object was returned from *note reader(): 101a.) or a dict (if
     it is a *note DictReader: 2ee. instance), parsed according to the
     current *note Dialect: f6c.  Usually you should call this as
     ‘next(reader)’.

Reader objects have the following public attributes:

 -- Attribute: csvreader.dialect

     A read-only description of the dialect in use by the parser.

 -- Attribute: csvreader.line_num

     The number of lines read from the source iterator.  This is not the
     same as the number of records returned, as records can span
     multiple lines.

DictReader objects have the following public attribute:

 -- Attribute: csvreader.fieldnames

     If not passed as a parameter when creating the object, this
     attribute is initialized upon first access or when the first record
     is read from the file.


File: python.info,  Node: Writer Objects,  Next: Examples<8>,  Prev: Reader Objects,  Up: csv — CSV File Reading and Writing

5.14.1.4 Writer Objects
.......................

‘Writer’ objects (*note DictWriter: c4b. instances and objects returned
by the *note writer(): ec0. function) have the following public methods.
A `row' must be an iterable of strings or numbers for ‘Writer’ objects
and a dictionary mapping fieldnames to strings or numbers (by passing
them through *note str(): 205. first) for *note DictWriter: c4b.
objects.  Note that complex numbers are written out surrounded by
parens.  This may cause some problems for other programs which read CSV
files (assuming they support complex numbers at all).

 -- Method: csvwriter.writerow (row)

     Write the `row' parameter to the writer’s file object, formatted
     according to the current *note Dialect: f6c.  Return the return
     value of the call to the `write' method of the underlying file
     object.

     Changed in version 3.5: Added support of arbitrary iterables.

 -- Method: csvwriter.writerows (rows)

     Write all elements in `rows' (an iterable of `row' objects as
     described above) to the writer’s file object, formatted according
     to the current dialect.

Writer objects have the following public attribute:

 -- Attribute: csvwriter.dialect

     A read-only description of the dialect in use by the writer.

DictWriter objects have the following public method:

 -- Method: DictWriter.writeheader ()

     Write a row with the field names (as specified in the constructor)
     to the writer’s file object, formatted according to the current
     dialect.  Return the return value of the *note
     csvwriter.writerow(): 7b7. call used internally.

     New in version 3.2.

     Changed in version 3.8: *note writeheader(): c4c. now also returns
     the value returned by the *note csvwriter.writerow(): 7b7. method
     it uses internally.


File: python.info,  Node: Examples<8>,  Prev: Writer Objects,  Up: csv — CSV File Reading and Writing

5.14.1.5 Examples
.................

The simplest example of reading a CSV file:

     import csv
     with open('some.csv', newline='') as f:
         reader = csv.reader(f)
         for row in reader:
             print(row)

Reading a file with an alternate format:

     import csv
     with open('passwd', newline='') as f:
         reader = csv.reader(f, delimiter=':', quoting=csv.QUOTE_NONE)
         for row in reader:
             print(row)

The corresponding simplest possible writing example is:

     import csv
     with open('some.csv', 'w', newline='') as f:
         writer = csv.writer(f)
         writer.writerows(someiterable)

Since *note open(): 16f. is used to open a CSV file for reading, the
file will by default be decoded into unicode using the system default
encoding (see *note locale.getpreferredencoding(): 4ac.).  To decode a
file using a different encoding, use the ‘encoding’ argument of open:

     import csv
     with open('some.csv', newline='', encoding='utf-8') as f:
         reader = csv.reader(f)
         for row in reader:
             print(row)

The same applies to writing in something other than the system default
encoding: specify the encoding argument when opening the output file.

Registering a new dialect:

     import csv
     csv.register_dialect('unixpwd', delimiter=':', quoting=csv.QUOTE_NONE)
     with open('passwd', newline='') as f:
         reader = csv.reader(f, 'unixpwd')

A slightly more advanced use of the reader — catching and reporting
errors:

     import csv, sys
     filename = 'some.csv'
     with open(filename, newline='') as f:
         reader = csv.reader(f)
         try:
             for row in reader:
                 print(row)
         except csv.Error as e:
             sys.exit('file {}, line {}: {}'.format(filename, reader.line_num, e))

And while the module doesn’t directly support parsing strings, it can
easily be done:

     import csv
     for row in csv.reader(['one,two,three']):
         print(row)


File: python.info,  Node: configparser — Configuration file parser,  Next: netrc — netrc file processing,  Prev: csv — CSV File Reading and Writing,  Up: File Formats

5.14.2 ‘configparser’ — Configuration file parser
-------------------------------------------------

`Source code:' Lib/configparser.py(1)

__________________________________________________________________

This module provides the *note ConfigParser: 5a5. class which implements
a basic configuration language which provides a structure similar to
what’s found in Microsoft Windows INI files.  You can use this to write
Python programs which can be customized by end users easily.

     Note: This library does `not' interpret or write the value-type
     prefixes used in the Windows Registry extended version of INI
     syntax.

See also
........

Module *note shlex: e8.

     Support for creating Unix shell-like mini-languages which can be
     used as an alternate format for application configuration files.

Module *note json: a4.

     The json module implements a subset of JavaScript syntax which can
     also be used for this purpose.

* Menu:

* Quick Start::
* Supported Datatypes::
* Fallback Values::
* Supported INI File Structure::
* Interpolation of values::
* Mapping Protocol Access::
* Customizing Parser Behaviour::
* Legacy API Examples::
* ConfigParser Objects::
* RawConfigParser Objects::
* Exceptions: Exceptions<6>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/configparser.py


File: python.info,  Node: Quick Start,  Next: Supported Datatypes,  Up: configparser — Configuration file parser

5.14.2.1 Quick Start
....................

Let’s take a very basic configuration file that looks like this:

     [DEFAULT]
     ServerAliveInterval = 45
     Compression = yes
     CompressionLevel = 9
     ForwardX11 = yes

     [bitbucket.org]
     User = hg

     [topsecret.server.com]
     Port = 50022
     ForwardX11 = no

The structure of INI files is described *note in the following section:
1fa5.  Essentially, the file consists of sections, each of which
contains keys with values.  *note configparser: 22. classes can read and
write such files.  Let’s start by creating the above configuration file
programmatically.

     >>> import configparser
     >>> config = configparser.ConfigParser()
     >>> config['DEFAULT'] = {'ServerAliveInterval': '45',
     ...                      'Compression': 'yes',
     ...                      'CompressionLevel': '9'}
     >>> config['bitbucket.org'] = {}
     >>> config['bitbucket.org']['User'] = 'hg'
     >>> config['topsecret.server.com'] = {}
     >>> topsecret = config['topsecret.server.com']
     >>> topsecret['Port'] = '50022'     # mutates the parser
     >>> topsecret['ForwardX11'] = 'no'  # same here
     >>> config['DEFAULT']['ForwardX11'] = 'yes'
     >>> with open('example.ini', 'w') as configfile:
     ...   config.write(configfile)
     ...

As you can see, we can treat a config parser much like a dictionary.
There are differences, *note outlined later: 1fa6, but the behavior is
very close to what you would expect from a dictionary.

Now that we have created and saved a configuration file, let’s read it
back and explore the data it holds.

     >>> config = configparser.ConfigParser()
     >>> config.sections()
     []
     >>> config.read('example.ini')
     ['example.ini']
     >>> config.sections()
     ['bitbucket.org', 'topsecret.server.com']
     >>> 'bitbucket.org' in config
     True
     >>> 'bytebong.com' in config
     False
     >>> config['bitbucket.org']['User']
     'hg'
     >>> config['DEFAULT']['Compression']
     'yes'
     >>> topsecret = config['topsecret.server.com']
     >>> topsecret['ForwardX11']
     'no'
     >>> topsecret['Port']
     '50022'
     >>> for key in config['bitbucket.org']:
     ...     print(key)
     user
     compressionlevel
     serveraliveinterval
     compression
     forwardx11
     >>> config['bitbucket.org']['ForwardX11']
     'yes'

As we can see above, the API is pretty straightforward.  The only bit of
magic involves the ‘DEFAULT’ section which provides default values for
all other sections (1).  Note also that keys in sections are
case-insensitive and stored in lowercase (2).

   ---------- Footnotes ----------

   (1) (1) Config parsers allow for heavy customization.  If you are
interested in changing the behaviour outlined by the footnote reference,
consult the *note Customizing Parser Behaviour: 1fa7. section.

   (2) (1) Config parsers allow for heavy customization.  If you are
interested in changing the behaviour outlined by the footnote reference,
consult the *note Customizing Parser Behaviour: 1fa7. section.


File: python.info,  Node: Supported Datatypes,  Next: Fallback Values,  Prev: Quick Start,  Up: configparser — Configuration file parser

5.14.2.2 Supported Datatypes
............................

Config parsers do not guess datatypes of values in configuration files,
always storing them internally as strings.  This means that if you need
other datatypes, you should convert on your own:

     >>> int(topsecret['Port'])
     50022
     >>> float(topsecret['CompressionLevel'])
     9.0

Since this task is so common, config parsers provide a range of handy
getter methods to handle integers, floats and booleans.  The last one is
the most interesting because simply passing the value to ‘bool()’ would
do no good since ‘bool('False')’ is still ‘True’.  This is why config
parsers also provide *note getboolean(): 1fa9.  This method is
case-insensitive and recognizes Boolean values from ‘'yes'’/‘'no'’,
‘'on'’/‘'off'’, ‘'true'’/‘'false'’ and ‘'1'’/‘'0'’ (1).  For example:

     >>> topsecret.getboolean('ForwardX11')
     False
     >>> config['bitbucket.org'].getboolean('ForwardX11')
     True
     >>> config.getboolean('bitbucket.org', 'Compression')
     True

Apart from *note getboolean(): 1fa9, config parsers also provide
equivalent *note getint(): 1faa. and *note getfloat(): 1fab. methods.
You can register your own converters and customize the provided ones.
(2)

   ---------- Footnotes ----------

   (1) (1) Config parsers allow for heavy customization.  If you are
interested in changing the behaviour outlined by the footnote reference,
consult the *note Customizing Parser Behaviour: 1fa7. section.

   (2) (1) Config parsers allow for heavy customization.  If you are
interested in changing the behaviour outlined by the footnote reference,
consult the *note Customizing Parser Behaviour: 1fa7. section.


File: python.info,  Node: Fallback Values,  Next: Supported INI File Structure,  Prev: Supported Datatypes,  Up: configparser — Configuration file parser

5.14.2.3 Fallback Values
........................

As with a dictionary, you can use a section’s ‘get()’ method to provide
fallback values:

     >>> topsecret.get('Port')
     '50022'
     >>> topsecret.get('CompressionLevel')
     '9'
     >>> topsecret.get('Cipher')
     >>> topsecret.get('Cipher', '3des-cbc')
     '3des-cbc'

Please note that default values have precedence over fallback values.
For instance, in our example the ‘'CompressionLevel'’ key was specified
only in the ‘'DEFAULT'’ section.  If we try to get it from the section
‘'topsecret.server.com'’, we will always get the default, even if we
specify a fallback:

     >>> topsecret.get('CompressionLevel', '3')
     '9'

One more thing to be aware of is that the parser-level ‘get()’ method
provides a custom, more complex interface, maintained for backwards
compatibility.  When using this method, a fallback value can be provided
via the ‘fallback’ keyword-only argument:

     >>> config.get('bitbucket.org', 'monster',
     ...            fallback='No such things as monsters')
     'No such things as monsters'

The same ‘fallback’ argument can be used with the *note getint(): 1faa,
*note getfloat(): 1fab. and *note getboolean(): 1fa9. methods, for
example:

     >>> 'BatchMode' in topsecret
     False
     >>> topsecret.getboolean('BatchMode', fallback=True)
     True
     >>> config['DEFAULT']['BatchMode'] = 'no'
     >>> topsecret.getboolean('BatchMode', fallback=True)
     False


File: python.info,  Node: Supported INI File Structure,  Next: Interpolation of values,  Prev: Fallback Values,  Up: configparser — Configuration file parser

5.14.2.4 Supported INI File Structure
.....................................

A configuration file consists of sections, each led by a ‘[section]’
header, followed by key/value entries separated by a specific string
(‘=’ or ‘:’ by default (1)).  By default, section names are case
sensitive but keys are not (2).  Leading and trailing whitespace is
removed from keys and values.  Values can be omitted if the parser is
configured to allow it (3), in which case the key/value delimiter may
also be left out.  Values can also span multiple lines, as long as they
are indented deeper than the first line of the value.  Depending on the
parser’s mode, blank lines may be treated as parts of multiline values
or ignored.

Configuration files may include comments, prefixed by specific
characters (‘#’ and ‘;’ by default (4)).  Comments may appear on their
own on an otherwise empty line, possibly indented.  (5)

For example:

     [Simple Values]
     key=value
     spaces in keys=allowed
     spaces in values=allowed as well
     spaces around the delimiter = obviously
     you can also use : to delimit keys from values

     [All Values Are Strings]
     values like this: 1000000
     or this: 3.14159265359
     are they treated as numbers? : no
     integers, floats and booleans are held as: strings
     can use the API to get converted values directly: true

     [Multiline Values]
     chorus: I'm a lumberjack, and I'm okay
         I sleep all night and I work all day

     [No Values]
     key_without_value
     empty string value here =

     [You can use comments]
     # like this
     ; or this

     # By default only in an empty line.
     # Inline comments can be harmful because they prevent users
     # from using the delimiting characters as parts of values.
     # That being said, this can be customized.

         [Sections Can Be Indented]
             can_values_be_as_well = True
             does_that_mean_anything_special = False
             purpose = formatting for readability
             multiline_values = are
                 handled just fine as
                 long as they are indented
                 deeper than the first line
                 of a value
             # Did I mention we can indent comments, too?

   ---------- Footnotes ----------

   (1) (1) Config parsers allow for heavy customization.  If you are
interested in changing the behaviour outlined by the footnote reference,
consult the *note Customizing Parser Behaviour: 1fa7. section.

   (2) (1) Config parsers allow for heavy customization.  If you are
interested in changing the behaviour outlined by the footnote reference,
consult the *note Customizing Parser Behaviour: 1fa7. section.

   (3) (1) Config parsers allow for heavy customization.  If you are
interested in changing the behaviour outlined by the footnote reference,
consult the *note Customizing Parser Behaviour: 1fa7. section.

   (4) (1) Config parsers allow for heavy customization.  If you are
interested in changing the behaviour outlined by the footnote reference,
consult the *note Customizing Parser Behaviour: 1fa7. section.

   (5) (1) Config parsers allow for heavy customization.  If you are
interested in changing the behaviour outlined by the footnote reference,
consult the *note Customizing Parser Behaviour: 1fa7. section.


File: python.info,  Node: Interpolation of values,  Next: Mapping Protocol Access,  Prev: Supported INI File Structure,  Up: configparser — Configuration file parser

5.14.2.5 Interpolation of values
................................

On top of the core functionality, *note ConfigParser: 5a5. supports
interpolation.  This means values can be preprocessed before returning
them from ‘get()’ calls.

 -- Class: configparser.BasicInterpolation

     The default implementation used by *note ConfigParser: 5a5.  It
     enables values to contain format strings which refer to other
     values in the same section, or values in the special default
     section (1).  Additional default values can be provided on
     initialization.

     For example:

          [Paths]
          home_dir: /Users
          my_dir: %(home_dir)s/lumberjack
          my_pictures: %(my_dir)s/Pictures

          [Escape]
          gain: 80%%  # use a %% to escape the % sign (% is the only character that needs to be escaped)

     In the example above, *note ConfigParser: 5a5. with `interpolation'
     set to ‘BasicInterpolation()’ would resolve ‘%(home_dir)s’ to the
     value of ‘home_dir’ (‘/Users’ in this case).  ‘%(my_dir)s’ in
     effect would resolve to ‘/Users/lumberjack’.  All interpolations
     are done on demand so keys used in the chain of references do not
     have to be specified in any specific order in the configuration
     file.

     With ‘interpolation’ set to ‘None’, the parser would simply return
     ‘%(my_dir)s/Pictures’ as the value of ‘my_pictures’ and
     ‘%(home_dir)s/lumberjack’ as the value of ‘my_dir’.

 -- Class: configparser.ExtendedInterpolation

     An alternative handler for interpolation which implements a more
     advanced syntax, used for instance in ‘zc.buildout’.  Extended
     interpolation is using ‘${section:option}’ to denote a value from a
     foreign section.  Interpolation can span multiple levels.  For
     convenience, if the ‘section:’ part is omitted, interpolation
     defaults to the current section (and possibly the default values
     from the special section).

     For example, the configuration specified above with basic
     interpolation, would look like this with extended interpolation:

          [Paths]
          home_dir: /Users
          my_dir: ${home_dir}/lumberjack
          my_pictures: ${my_dir}/Pictures

          [Escape]
          cost: $$80  # use a $$ to escape the $ sign ($ is the only character that needs to be escaped)

     Values from other sections can be fetched as well:

          [Common]
          home_dir: /Users
          library_dir: /Library
          system_dir: /System
          macports_dir: /opt/local

          [Frameworks]
          Python: 3.2
          path: ${Common:system_dir}/Library/Frameworks/

          [Arthur]
          nickname: Two Sheds
          last_name: Jackson
          my_dir: ${Common:home_dir}/twosheds
          my_pictures: ${my_dir}/Pictures
          python_dir: ${Frameworks:path}/Python/Versions/${Frameworks:Python}

   ---------- Footnotes ----------

   (1) (1) Config parsers allow for heavy customization.  If you are
interested in changing the behaviour outlined by the footnote reference,
consult the *note Customizing Parser Behaviour: 1fa7. section.


File: python.info,  Node: Mapping Protocol Access,  Next: Customizing Parser Behaviour,  Prev: Interpolation of values,  Up: configparser — Configuration file parser

5.14.2.6 Mapping Protocol Access
................................

New in version 3.2.

Mapping protocol access is a generic name for functionality that enables
using custom objects as if they were dictionaries.  In case of *note
configparser: 22, the mapping interface implementation is using the
‘parser['section']['option']’ notation.

‘parser['section']’ in particular returns a proxy for the section’s data
in the parser.  This means that the values are not copied but they are
taken from the original parser on demand.  What’s even more important is
that when values are changed on a section proxy, they are actually
mutated in the original parser.

*note configparser: 22. objects behave as close to actual dictionaries
as possible.  The mapping interface is complete and adheres to the *note
MutableMapping: ace. ABC. However, there are a few differences that
should be taken into account:

   * By default, all keys in sections are accessible in a
     case-insensitive manner (1).  E.g.  ‘for option in
     parser["section"]’ yields only ‘optionxform’’ed option key names.
     This means lowercased keys by default.  At the same time, for a
     section that holds the key ‘'a'’, both expressions return ‘True’:

          "a" in parser["section"]
          "A" in parser["section"]

   * All sections include ‘DEFAULTSECT’ values as well which means that
     ‘.clear()’ on a section may not leave the section visibly empty.
     This is because default values cannot be deleted from the section
     (because technically they are not there).  If they are overridden
     in the section, deleting causes the default value to be visible
     again.  Trying to delete a default value causes a *note KeyError:
     3e9.

   * ‘DEFAULTSECT’ cannot be removed from the parser:

        * trying to delete it raises *note ValueError: 16d,

        * ‘parser.clear()’ leaves it intact,

        * ‘parser.popitem()’ never returns it.

   * ‘parser.get(section, option, **kwargs)’ - the second argument is
     `not' a fallback value.  Note however that the section-level
     ‘get()’ methods are compatible both with the mapping protocol and
     the classic configparser API.

   * ‘parser.items()’ is compatible with the mapping protocol (returns a
     list of `section_name', `section_proxy' pairs including the
     DEFAULTSECT). However, this method can also be invoked with
     arguments: ‘parser.items(section, raw, vars)’.  The latter call
     returns a list of `option', `value' pairs for a specified
     ‘section’, with all interpolations expanded (unless ‘raw=True’ is
     provided).

The mapping protocol is implemented on top of the existing legacy API so
that subclasses overriding the original interface still should have
mappings working as expected.

   ---------- Footnotes ----------

   (1) (1) Config parsers allow for heavy customization.  If you are
interested in changing the behaviour outlined by the footnote reference,
consult the *note Customizing Parser Behaviour: 1fa7. section.


File: python.info,  Node: Customizing Parser Behaviour,  Next: Legacy API Examples,  Prev: Mapping Protocol Access,  Up: configparser — Configuration file parser

5.14.2.7 Customizing Parser Behaviour
.....................................

There are nearly as many INI format variants as there are applications
using it.  *note configparser: 22. goes a long way to provide support
for the largest sensible set of INI styles available.  The default
functionality is mainly dictated by historical background and it’s very
likely that you will want to customize some of the features.

The most common way to change the way a specific config parser works is
to use the *note __init__(): e23. options:

   * `defaults', default value: ‘None’

     This option accepts a dictionary of key-value pairs which will be
     initially put in the ‘DEFAULT’ section.  This makes for an elegant
     way to support concise configuration files that don’t specify
     values which are the same as the documented default.

     Hint: if you want to specify default values for a specific section,
     use ‘read_dict()’ before you read the actual file.

   * `dict_type', default value: *note dict: 164.

     This option has a major impact on how the mapping protocol will
     behave and how the written configuration files look.  With the
     standard dictionary, every section is stored in the order they were
     added to the parser.  Same goes for options within sections.

     An alternative dictionary type can be used for example to sort
     sections and options on write-back.

     Please note: there are ways to add a set of key-value pairs in a
     single operation.  When you use a regular dictionary in those
     operations, the order of the keys will be ordered.  For example:

          >>> parser = configparser.ConfigParser()
          >>> parser.read_dict({'section1': {'key1': 'value1',
          ...                                'key2': 'value2',
          ...                                'key3': 'value3'},
          ...                   'section2': {'keyA': 'valueA',
          ...                                'keyB': 'valueB',
          ...                                'keyC': 'valueC'},
          ...                   'section3': {'foo': 'x',
          ...                                'bar': 'y',
          ...                                'baz': 'z'}
          ... })
          >>> parser.sections()
          ['section1', 'section2', 'section3']
          >>> [option for option in parser['section3']]
          ['foo', 'bar', 'baz']

   * `allow_no_value', default value: ‘False’

     Some configuration files are known to include settings without
     values, but which otherwise conform to the syntax supported by
     *note configparser: 22.  The `allow_no_value' parameter to the
     constructor can be used to indicate that such values should be
     accepted:

          >>> import configparser

          >>> sample_config = """
          ... [mysqld]
          ...   user = mysql
          ...   pid-file = /var/run/mysqld/mysqld.pid
          ...   skip-external-locking
          ...   old_passwords = 1
          ...   skip-bdb
          ...   # we don't need ACID today
          ...   skip-innodb
          ... """
          >>> config = configparser.ConfigParser(allow_no_value=True)
          >>> config.read_string(sample_config)

          >>> # Settings with values are treated as before:
          >>> config["mysqld"]["user"]
          'mysql'

          >>> # Settings without values provide None:
          >>> config["mysqld"]["skip-bdb"]

          >>> # Settings which aren't specified still raise an error:
          >>> config["mysqld"]["does-not-exist"]
          Traceback (most recent call last):
            ...
          KeyError: 'does-not-exist'

   * `delimiters', default value: ‘('=', ':')’

     Delimiters are substrings that delimit keys from values within a
     section.  The first occurrence of a delimiting substring on a line
     is considered a delimiter.  This means values (but not keys) can
     contain the delimiters.

     See also the `space_around_delimiters' argument to *note
     ConfigParser.write(): 1faf.

   * `comment_prefixes', default value: ‘('#', ';')’

   * `inline_comment_prefixes', default value: ‘None’

     Comment prefixes are strings that indicate the start of a valid
     comment within a config file.  `comment_prefixes' are used only on
     otherwise empty lines (optionally indented) whereas
     `inline_comment_prefixes' can be used after every valid value (e.g.
     section names, options and empty lines as well).  By default inline
     comments are disabled and ‘'#'’ and ‘';'’ are used as prefixes for
     whole line comments.

     Changed in version 3.2: In previous versions of *note configparser:
     22. behaviour matched ‘comment_prefixes=('#',';')’ and
     ‘inline_comment_prefixes=(';',)’.

     Please note that config parsers don’t support escaping of comment
     prefixes so using `inline_comment_prefixes' may prevent users from
     specifying option values with characters used as comment prefixes.
     When in doubt, avoid setting `inline_comment_prefixes'.  In any
     circumstances, the only way of storing comment prefix characters at
     the beginning of a line in multiline values is to interpolate the
     prefix, for example:

          >>> from configparser import ConfigParser, ExtendedInterpolation
          >>> parser = ConfigParser(interpolation=ExtendedInterpolation())
          >>> # the default BasicInterpolation could be used as well
          >>> parser.read_string("""
          ... [DEFAULT]
          ... hash = #
          ...
          ... [hashes]
          ... shebang =
          ...   ${hash}!/usr/bin/env python
          ...   ${hash} -*- coding: utf-8 -*-
          ...
          ... extensions =
          ...   enabled_extension
          ...   another_extension
          ...   #disabled_by_comment
          ...   yet_another_extension
          ...
          ... interpolation not necessary = if # is not at line start
          ... even in multiline values = line #1
          ...   line #2
          ...   line #3
          ... """)
          >>> print(parser['hashes']['shebang'])

          #!/usr/bin/env python
          # -*- coding: utf-8 -*-
          >>> print(parser['hashes']['extensions'])

          enabled_extension
          another_extension
          yet_another_extension
          >>> print(parser['hashes']['interpolation not necessary'])
          if # is not at line start
          >>> print(parser['hashes']['even in multiline values'])
          line #1
          line #2
          line #3

   * `strict', default value: ‘True’

     When set to ‘True’, the parser will not allow for any section or
     option duplicates while reading from a single source (using
     ‘read_file()’, ‘read_string()’ or ‘read_dict()’).  It is
     recommended to use strict parsers in new applications.

     Changed in version 3.2: In previous versions of *note configparser:
     22. behaviour matched ‘strict=False’.

   * `empty_lines_in_values', default value: ‘True’

     In config parsers, values can span multiple lines as long as they
     are indented more than the key that holds them.  By default parsers
     also let empty lines to be parts of values.  At the same time, keys
     can be arbitrarily indented themselves to improve readability.  In
     consequence, when configuration files get big and complex, it is
     easy for the user to lose track of the file structure.  Take for
     instance:

          [Section]
          key = multiline
            value with a gotcha

           this = is still a part of the multiline value of 'key'

     This can be especially problematic for the user to see if she’s
     using a proportional font to edit the file.  That is why when your
     application does not need values with empty lines, you should
     consider disallowing them.  This will make empty lines split keys
     every time.  In the example above, it would produce two keys, ‘key’
     and ‘this’.

   * `default_section', default value: ‘configparser.DEFAULTSECT’ (that
     is: ‘"DEFAULT"’)

     The convention of allowing a special section of default values for
     other sections or interpolation purposes is a powerful concept of
     this library, letting users create complex declarative
     configurations.  This section is normally called ‘"DEFAULT"’ but
     this can be customized to point to any other valid section name.
     Some typical values include: ‘"general"’ or ‘"common"’.  The name
     provided is used for recognizing default sections when reading from
     any source and is used when writing configuration back to a file.
     Its current value can be retrieved using the
     ‘parser_instance.default_section’ attribute and may be modified at
     runtime (i.e.  to convert files from one format to another).

   * `interpolation', default value: ‘configparser.BasicInterpolation’

     Interpolation behaviour may be customized by providing a custom
     handler through the `interpolation' argument.  ‘None’ can be used
     to turn off interpolation completely, ‘ExtendedInterpolation()’
     provides a more advanced variant inspired by ‘zc.buildout’.  More
     on the subject in the *note dedicated documentation section: 1fad.
     *note RawConfigParser: 95c. has a default value of ‘None’.

   * `converters', default value: not set

     Config parsers provide option value getters that perform type
     conversion.  By default *note getint(): 1faa, *note getfloat():
     1fab, and *note getboolean(): 1fa9. are implemented.  Should other
     getters be desirable, users may define them in a subclass or pass a
     dictionary where each key is a name of the converter and each value
     is a callable implementing said conversion.  For instance, passing
     ‘{'decimal': decimal.Decimal}’ would add ‘getdecimal()’ on both the
     parser object and all section proxies.  In other words, it will be
     possible to write both ‘parser_instance.getdecimal('section',
     'key', fallback=0)’ and
     ‘parser_instance['section'].getdecimal('key', 0)’.

     If the converter needs to access the state of the parser, it can be
     implemented as a method on a config parser subclass.  If the name
     of this method starts with ‘get’, it will be available on all
     section proxies, in the dict-compatible form (see the
     ‘getdecimal()’ example above).

More advanced customization may be achieved by overriding default values
of these parser attributes.  The defaults are defined on the classes, so
they may be overridden by subclasses or by attribute assignment.

 -- Attribute: ConfigParser.BOOLEAN_STATES

     By default when using *note getboolean(): 1fa9, config parsers
     consider the following values ‘True’: ‘'1'’, ‘'yes'’, ‘'true'’,
     ‘'on'’ and the following values ‘False’: ‘'0'’, ‘'no'’, ‘'false'’,
     ‘'off'’.  You can override this by specifying a custom dictionary
     of strings and their Boolean outcomes.  For example:

          >>> custom = configparser.ConfigParser()
          >>> custom['section1'] = {'funky': 'nope'}
          >>> custom['section1'].getboolean('funky')
          Traceback (most recent call last):
          ...
          ValueError: Not a boolean: nope
          >>> custom.BOOLEAN_STATES = {'sure': True, 'nope': False}
          >>> custom['section1'].getboolean('funky')
          False

     Other typical Boolean pairs include ‘accept’/‘reject’ or
     ‘enabled’/‘disabled’.

 -- Method: ConfigParser.optionxform (option)

     This method transforms option names on every read, get, or set
     operation.  The default converts the name to lowercase.  This also
     means that when a configuration file gets written, all keys will be
     lowercase.  Override this method if that’s unsuitable.  For
     example:

          >>> config = """
          ... [Section1]
          ... Key = Value
          ...
          ... [Section2]
          ... AnotherKey = Value
          ... """
          >>> typical = configparser.ConfigParser()
          >>> typical.read_string(config)
          >>> list(typical['Section1'].keys())
          ['key']
          >>> list(typical['Section2'].keys())
          ['anotherkey']
          >>> custom = configparser.RawConfigParser()
          >>> custom.optionxform = lambda option: option
          >>> custom.read_string(config)
          >>> list(custom['Section1'].keys())
          ['Key']
          >>> list(custom['Section2'].keys())
          ['AnotherKey']

          Note: The optionxform function transforms option names to a
          canonical form.  This should be an idempotent function: if the
          name is already in canonical form, it should be returned
          unchanged.

 -- Attribute: ConfigParser.SECTCRE

     A compiled regular expression used to parse section headers.  The
     default matches ‘[section]’ to the name ‘"section"’.  Whitespace is
     considered part of the section name, thus ‘[ larch ]’ will be read
     as a section of name ‘" larch "’.  Override this attribute if
     that’s unsuitable.  For example:

          >>> import re
          >>> config = """
          ... [Section 1]
          ... option = value
          ...
          ... [  Section 2  ]
          ... another = val
          ... """
          >>> typical = configparser.ConfigParser()
          >>> typical.read_string(config)
          >>> typical.sections()
          ['Section 1', '  Section 2  ']
          >>> custom = configparser.ConfigParser()
          >>> custom.SECTCRE = re.compile(r"\[ *(?P<header>[^]]+?) *\]")
          >>> custom.read_string(config)
          >>> custom.sections()
          ['Section 1', 'Section 2']

          Note: While ConfigParser objects also use an ‘OPTCRE’
          attribute for recognizing option lines, it’s not recommended
          to override it because that would interfere with constructor
          options `allow_no_value' and `delimiters'.


File: python.info,  Node: Legacy API Examples,  Next: ConfigParser Objects,  Prev: Customizing Parser Behaviour,  Up: configparser — Configuration file parser

5.14.2.8 Legacy API Examples
............................

Mainly because of backwards compatibility concerns, *note configparser:
22. provides also a legacy API with explicit ‘get’/‘set’ methods.  While
there are valid use cases for the methods outlined below, mapping
protocol access is preferred for new projects.  The legacy API is at
times more advanced, low-level and downright counterintuitive.

An example of writing to a configuration file:

     import configparser

     config = configparser.RawConfigParser()

     # Please note that using RawConfigParser's set functions, you can assign
     # non-string values to keys internally, but will receive an error when
     # attempting to write to a file or when you get it in non-raw mode. Setting
     # values using the mapping protocol or ConfigParser's set() does not allow
     # such assignments to take place.
     config.add_section('Section1')
     config.set('Section1', 'an_int', '15')
     config.set('Section1', 'a_bool', 'true')
     config.set('Section1', 'a_float', '3.1415')
     config.set('Section1', 'baz', 'fun')
     config.set('Section1', 'bar', 'Python')
     config.set('Section1', 'foo', '%(bar)s is %(baz)s!')

     # Writing our configuration file to 'example.cfg'
     with open('example.cfg', 'w') as configfile:
         config.write(configfile)

An example of reading the configuration file again:

     import configparser

     config = configparser.RawConfigParser()
     config.read('example.cfg')

     # getfloat() raises an exception if the value is not a float
     # getint() and getboolean() also do this for their respective types
     a_float = config.getfloat('Section1', 'a_float')
     an_int = config.getint('Section1', 'an_int')
     print(a_float + an_int)

     # Notice that the next output does not interpolate '%(bar)s' or '%(baz)s'.
     # This is because we are using a RawConfigParser().
     if config.getboolean('Section1', 'a_bool'):
         print(config.get('Section1', 'foo'))

To get interpolation, use *note ConfigParser: 5a5.:

     import configparser

     cfg = configparser.ConfigParser()
     cfg.read('example.cfg')

     # Set the optional *raw* argument of get() to True if you wish to disable
     # interpolation in a single get operation.
     print(cfg.get('Section1', 'foo', raw=False))  # -> "Python is fun!"
     print(cfg.get('Section1', 'foo', raw=True))   # -> "%(bar)s is %(baz)s!"

     # The optional *vars* argument is a dict with members that will take
     # precedence in interpolation.
     print(cfg.get('Section1', 'foo', vars={'bar': 'Documentation',
                                            'baz': 'evil'}))

     # The optional *fallback* argument can be used to provide a fallback value
     print(cfg.get('Section1', 'foo'))
           # -> "Python is fun!"

     print(cfg.get('Section1', 'foo', fallback='Monty is not.'))
           # -> "Python is fun!"

     print(cfg.get('Section1', 'monster', fallback='No such things as monsters.'))
           # -> "No such things as monsters."

     # A bare print(cfg.get('Section1', 'monster')) would raise NoOptionError
     # but we can also use:

     print(cfg.get('Section1', 'monster', fallback=None))
           # -> None

Default values are available in both types of ConfigParsers.  They are
used in interpolation if an option used is not defined elsewhere.

     import configparser

     # New instance with 'bar' and 'baz' defaulting to 'Life' and 'hard' each
     config = configparser.ConfigParser({'bar': 'Life', 'baz': 'hard'})
     config.read('example.cfg')

     print(config.get('Section1', 'foo'))     # -> "Python is fun!"
     config.remove_option('Section1', 'bar')
     config.remove_option('Section1', 'baz')
     print(config.get('Section1', 'foo'))     # -> "Life is hard!"


File: python.info,  Node: ConfigParser Objects,  Next: RawConfigParser Objects,  Prev: Legacy API Examples,  Up: configparser — Configuration file parser

5.14.2.9 ConfigParser Objects
.............................

 -- Class: configparser.ConfigParser (defaults=None, dict_type=dict,
          allow_no_value=False, delimiters=('=', ':'),
          comment_prefixes=('#', ';'), inline_comment_prefixes=None,
          strict=True, empty_lines_in_values=True,
          default_section=configparser.DEFAULTSECT,
          interpolation=BasicInterpolation(), converters={})

     The main configuration parser.  When `defaults' is given, it is
     initialized into the dictionary of intrinsic defaults.  When
     `dict_type' is given, it will be used to create the dictionary
     objects for the list of sections, for the options within a section,
     and for the default values.

     When `delimiters' is given, it is used as the set of substrings
     that divide keys from values.  When `comment_prefixes' is given, it
     will be used as the set of substrings that prefix comments in
     otherwise empty lines.  Comments can be indented.  When
     `inline_comment_prefixes' is given, it will be used as the set of
     substrings that prefix comments in non-empty lines.

     When `strict' is ‘True’ (the default), the parser won’t allow for
     any section or option duplicates while reading from a single source
     (file, string or dictionary), raising *note DuplicateSectionError:
     cd0. or *note DuplicateOptionError: cd1.  When
     `empty_lines_in_values' is ‘False’ (default: ‘True’), each empty
     line marks the end of an option.  Otherwise, internal empty lines
     of a multiline option are kept as part of the value.  When
     `allow_no_value' is ‘True’ (default: ‘False’), options without
     values are accepted; the value held for these is ‘None’ and they
     are serialized without the trailing delimiter.

     When `default_section' is given, it specifies the name for the
     special section holding default values for other sections and
     interpolation purposes (normally named ‘"DEFAULT"’).  This value
     can be retrieved and changed on runtime using the ‘default_section’
     instance attribute.

     Interpolation behaviour may be customized by providing a custom
     handler through the `interpolation' argument.  ‘None’ can be used
     to turn off interpolation completely, ‘ExtendedInterpolation()’
     provides a more advanced variant inspired by ‘zc.buildout’.  More
     on the subject in the *note dedicated documentation section: 1fad.

     All option names used in interpolation will be passed through the
     *note optionxform(): 1fb5. method just like any other option name
     reference.  For example, using the default implementation of *note
     optionxform(): 1fb5. (which converts option names to lower case),
     the values ‘foo %(bar)s’ and ‘foo %(BAR)s’ are equivalent.

     When `converters' is given, it should be a dictionary where each
     key represents the name of a type converter and each value is a
     callable implementing the conversion from string to the desired
     datatype.  Every converter gets its own corresponding ‘get*()’
     method on the parser object and section proxies.

     Changed in version 3.1: The default `dict_type' is *note
     collections.OrderedDict: 2ea.

     Changed in version 3.2: `allow_no_value', `delimiters',
     `comment_prefixes', `strict', `empty_lines_in_values',
     `default_section' and `interpolation' were added.

     Changed in version 3.5: The `converters' argument was added.

     Changed in version 3.7: The `defaults' argument is read with *note
     read_dict(): 1fb6, providing consistent behavior across the parser:
     non-string keys and values are implicitly converted to strings.

     Changed in version 3.8: The default `dict_type' is *note dict: 164,
     since it now preserves insertion order.

      -- Method: defaults ()

          Return a dictionary containing the instance-wide defaults.

      -- Method: sections ()

          Return a list of the sections available; the `default section'
          is not included in the list.

      -- Method: add_section (section)

          Add a section named `section' to the instance.  If a section
          by the given name already exists, *note DuplicateSectionError:
          cd0. is raised.  If the `default section' name is passed,
          *note ValueError: 16d. is raised.  The name of the section
          must be a string; if not, *note TypeError: 1fe. is raised.

          Changed in version 3.2: Non-string section names raise *note
          TypeError: 1fe.

      -- Method: has_section (section)

          Indicates whether the named `section' is present in the
          configuration.  The `default section' is not acknowledged.

      -- Method: options (section)

          Return a list of options available in the specified `section'.

      -- Method: has_option (section, option)

          If the given `section' exists, and contains the given
          `option', return *note True: 594.; otherwise return *note
          False: 48f.  If the specified `section' is *note None: 203. or
          an empty string, DEFAULT is assumed.

      -- Method: read (filenames, encoding=None)

          Attempt to read and parse an iterable of filenames, returning
          a list of filenames which were successfully parsed.

          If `filenames' is a string, a *note bytes: 172. object or a
          *note path-like object: 472, it is treated as a single
          filename.  If a file named in `filenames' cannot be opened,
          that file will be ignored.  This is designed so that you can
          specify an iterable of potential configuration file locations
          (for example, the current directory, the user’s home
          directory, and some system-wide directory), and all existing
          configuration files in the iterable will be read.

          If none of the named files exist, the *note ConfigParser: 5a5.
          instance will contain an empty dataset.  An application which
          requires initial values to be loaded from a file should load
          the required file or files using *note read_file(): 1fbc.
          before calling *note read(): 11d9. for any optional files:

               import configparser, os

               config = configparser.ConfigParser()
               config.read_file(open('defaults.cfg'))
               config.read(['site.cfg', os.path.expanduser('~/.myapp.cfg')],
                           encoding='cp1250')

          New in version 3.2: The `encoding' parameter.  Previously, all
          files were read using the default encoding for *note open():
          16f.

          New in version 3.6.1: The `filenames' parameter accepts a
          *note path-like object: 472.

          New in version 3.7: The `filenames' parameter accepts a *note
          bytes: 172. object.

      -- Method: read_file (f, source=None)

          Read and parse configuration data from `f' which must be an
          iterable yielding Unicode strings (for example files opened in
          text mode).

          Optional argument `source' specifies the name of the file
          being read.  If not given and `f' has a ‘name’ attribute, that
          is used for `source'; the default is ‘'<???>'’.

          New in version 3.2: Replaces *note readfp(): 1fbd.

      -- Method: read_string (string, source='<string>')

          Parse configuration data from a string.

          Optional argument `source' specifies a context-specific name
          of the string passed.  If not given, ‘'<string>'’ is used.
          This should commonly be a filesystem path or a URL.

          New in version 3.2.

      -- Method: read_dict (dictionary, source='<dict>')

          Load configuration from any object that provides a dict-like
          ‘items()’ method.  Keys are section names, values are
          dictionaries with keys and values that should be present in
          the section.  If the used dictionary type preserves order,
          sections and their keys will be added in order.  Values are
          automatically converted to strings.

          Optional argument `source' specifies a context-specific name
          of the dictionary passed.  If not given, ‘<dict>’ is used.

          This method can be used to copy state between parsers.

          New in version 3.2.

      -- Method: get (section, option, *, raw=False, vars=None[,
               fallback])

          Get an `option' value for the named `section'.  If `vars' is
          provided, it must be a dictionary.  The `option' is looked up
          in `vars' (if provided), `section', and in `DEFAULTSECT' in
          that order.  If the key is not found and `fallback' is
          provided, it is used as a fallback value.  ‘None’ can be
          provided as a `fallback' value.

          All the ‘'%'’ interpolations are expanded in the return
          values, unless the `raw' argument is true.  Values for
          interpolation keys are looked up in the same manner as the
          option.

          Changed in version 3.2: Arguments `raw', `vars' and `fallback'
          are keyword only to protect users from trying to use the third
          argument as the `fallback' fallback (especially when using the
          mapping protocol).

      -- Method: getint (section, option, *, raw=False, vars=None[,
               fallback])

          A convenience method which coerces the `option' in the
          specified `section' to an integer.  See *note get(): ccd. for
          explanation of `raw', `vars' and `fallback'.

      -- Method: getfloat (section, option, *, raw=False, vars=None[,
               fallback])

          A convenience method which coerces the `option' in the
          specified `section' to a floating point number.  See *note
          get(): ccd. for explanation of `raw', `vars' and `fallback'.

      -- Method: getboolean (section, option, *, raw=False, vars=None[,
               fallback])

          A convenience method which coerces the `option' in the
          specified `section' to a Boolean value.  Note that the
          accepted values for the option are ‘'1'’, ‘'yes'’, ‘'true'’,
          and ‘'on'’, which cause this method to return ‘True’, and
          ‘'0'’, ‘'no'’, ‘'false'’, and ‘'off'’, which cause it to
          return ‘False’.  These string values are checked in a
          case-insensitive manner.  Any other value will cause it to
          raise *note ValueError: 16d.  See *note get(): ccd. for
          explanation of `raw', `vars' and `fallback'.

      -- Method: items (raw=False, vars=None)

      -- Method: items (section, raw=False, vars=None)

          When `section' is not given, return a list of `section_name',
          `section_proxy' pairs, including DEFAULTSECT.

          Otherwise, return a list of `name', `value' pairs for the
          options in the given `section'.  Optional arguments have the
          same meaning as for the *note get(): ccd. method.

          Changed in version 3.8: Items present in `vars' no longer
          appear in the result.  The previous behaviour mixed actual
          parser options with variables provided for interpolation.

      -- Method: set (section, option, value)

          If the given section exists, set the given option to the
          specified value; otherwise raise *note NoSectionError: 1fc0.
          `option' and `value' must be strings; if not, *note TypeError:
          1fe. is raised.

      -- Method: write (fileobject, space_around_delimiters=True)

          Write a representation of the configuration to the specified
          *note file object: c14, which must be opened in text mode
          (accepting strings).  This representation can be parsed by a
          future *note read(): 11d9. call.  If `space_around_delimiters'
          is true, delimiters between keys and values are surrounded by
          spaces.

          Note: Comments in the original configuration file are not
          preserved when writing the configuration back.  What is
          considered a comment, depends on the given values for
          `comment_prefix' and `inline_comment_prefix'.

      -- Method: remove_option (section, option)

          Remove the specified `option' from the specified `section'.
          If the section does not exist, raise *note NoSectionError:
          1fc0.  If the option existed to be removed, return *note True:
          594.; otherwise return *note False: 48f.

      -- Method: remove_section (section)

          Remove the specified `section' from the configuration.  If the
          section in fact existed, return ‘True’.  Otherwise return
          ‘False’.

      -- Method: optionxform (option)

          Transforms the option name `option' as found in an input file
          or as passed in by client code to the form that should be used
          in the internal structures.  The default implementation
          returns a lower-case version of `option'; subclasses may
          override this or client code can set an attribute of this name
          on instances to affect this behavior.

          You don’t need to subclass the parser to use this method, you
          can also set it on an instance, to a function that takes a
          string argument and returns a string.  Setting it to ‘str’,
          for example, would make option names case sensitive:

               cfgparser = ConfigParser()
               cfgparser.optionxform = str

          Note that when reading configuration files, whitespace around
          the option names is stripped before *note optionxform(): 1fb5.
          is called.

      -- Method: readfp (fp, filename=None)

          Deprecated since version 3.2: Use *note read_file(): 1fbc.
          instead.

          Changed in version 3.2: *note readfp(): 1fbd. now iterates on
          `fp' instead of calling ‘fp.readline()’.

          For existing code calling *note readfp(): 1fbd. with arguments
          which don’t support iteration, the following generator may be
          used as a wrapper around the file-like object:

               def readline_generator(fp):
                   line = fp.readline()
                   while line:
                       yield line
                       line = fp.readline()

          Instead of ‘parser.readfp(fp)’ use
          ‘parser.read_file(readline_generator(fp))’.

 -- Data: configparser.MAX_INTERPOLATION_DEPTH

     The maximum depth for recursive interpolation for ‘get()’ when the
     `raw' parameter is false.  This is relevant only when the default
     `interpolation' is used.


File: python.info,  Node: RawConfigParser Objects,  Next: Exceptions<6>,  Prev: ConfigParser Objects,  Up: configparser — Configuration file parser

5.14.2.10 RawConfigParser Objects
.................................

 -- Class: configparser.RawConfigParser (defaults=None, dict_type=dict,
          allow_no_value=False, *, delimiters=('=', ':'),
          comment_prefixes=('#', ';'), inline_comment_prefixes=None,
          strict=True, empty_lines_in_values=True,
          default_section=configparser.DEFAULTSECT[, interpolation])

     Legacy variant of the *note ConfigParser: 5a5.  It has
     interpolation disabled by default and allows for non-string section
     names, option names, and values via its unsafe ‘add_section’ and
     ‘set’ methods, as well as the legacy ‘defaults=’ keyword argument
     handling.

     Changed in version 3.8: The default `dict_type' is *note dict: 164,
     since it now preserves insertion order.

          Note: Consider using *note ConfigParser: 5a5. instead which
          checks types of the values to be stored internally.  If you
          don’t want interpolation, you can use
          ‘ConfigParser(interpolation=None)’.

      -- Method: add_section (section)

          Add a section named `section' to the instance.  If a section
          by the given name already exists, *note DuplicateSectionError:
          cd0. is raised.  If the `default section' name is passed,
          *note ValueError: 16d. is raised.

          Type of `section' is not checked which lets users create
          non-string named sections.  This behaviour is unsupported and
          may cause internal errors.

      -- Method: set (section, option, value)

          If the given section exists, set the given option to the
          specified value; otherwise raise *note NoSectionError: 1fc0.
          While it is possible to use *note RawConfigParser: 95c. (or
          *note ConfigParser: 5a5. with `raw' parameters set to true)
          for `internal' storage of non-string values, full
          functionality (including interpolation and output to files)
          can only be achieved using string values.

          This method lets users assign non-string values to keys
          internally.  This behaviour is unsupported and will cause
          errors when attempting to write to a file or get it in non-raw
          mode.  `Use the mapping protocol API' which does not allow
          such assignments to take place.


File: python.info,  Node: Exceptions<6>,  Prev: RawConfigParser Objects,  Up: configparser — Configuration file parser

5.14.2.11 Exceptions
....................

 -- Exception: configparser.Error

     Base class for all other *note configparser: 22. exceptions.

 -- Exception: configparser.NoSectionError

     Exception raised when a specified section is not found.

 -- Exception: configparser.DuplicateSectionError

     Exception raised if ‘add_section()’ is called with the name of a
     section that is already present or in strict parsers when a section
     if found more than once in a single input file, string or
     dictionary.

     New in version 3.2: Optional ‘source’ and ‘lineno’ attributes and
     arguments to *note __init__(): e23. were added.

 -- Exception: configparser.DuplicateOptionError

     Exception raised by strict parsers if a single option appears twice
     during reading from a single file, string or dictionary.  This
     catches misspellings and case sensitivity-related errors, e.g.  a
     dictionary may have two keys representing the same case-insensitive
     configuration key.

 -- Exception: configparser.NoOptionError

     Exception raised when a specified option is not found in the
     specified section.

 -- Exception: configparser.InterpolationError

     Base class for exceptions raised when problems occur performing
     string interpolation.

 -- Exception: configparser.InterpolationDepthError

     Exception raised when string interpolation cannot be completed
     because the number of iterations exceeds *note
     MAX_INTERPOLATION_DEPTH: 1fc3.  Subclass of *note
     InterpolationError: 1fcb.

 -- Exception: configparser.InterpolationMissingOptionError

     Exception raised when an option referenced from a value does not
     exist.  Subclass of *note InterpolationError: 1fcb.

 -- Exception: configparser.InterpolationSyntaxError

     Exception raised when the source text into which substitutions are
     made does not conform to the required syntax.  Subclass of *note
     InterpolationError: 1fcb.

 -- Exception: configparser.MissingSectionHeaderError

     Exception raised when attempting to parse a file which has no
     section headers.

 -- Exception: configparser.ParsingError

     Exception raised when errors occur attempting to parse a file.

     Changed in version 3.2: The ‘filename’ attribute and *note
     __init__(): e23. argument were renamed to ‘source’ for consistency.


File: python.info,  Node: netrc — netrc file processing,  Next: xdrlib — Encode and decode XDR data,  Prev: configparser — Configuration file parser,  Up: File Formats

5.14.3 ‘netrc’ — netrc file processing
--------------------------------------

`Source code:' Lib/netrc.py(1)

__________________________________________________________________

The *note netrc: 11d5. class parses and encapsulates the netrc file
format used by the Unix ‘ftp’ program and other FTP clients.

 -- Class: netrc.netrc ([file])

     A *note netrc: 11d5. instance or subclass instance encapsulates
     data from a netrc file.  The initialization argument, if present,
     specifies the file to parse.  If no argument is given, the file
     ‘.netrc’ in the user’s home directory – as determined by *note
     os.path.expanduser(): 32c. – will be read.  Otherwise, a *note
     FileNotFoundError: 8ad. exception will be raised.  Parse errors
     will raise *note NetrcParseError: 1fd3. with diagnostic information
     including the file name, line number, and terminating token.  If no
     argument is specified on a POSIX system, the presence of passwords
     in the ‘.netrc’ file will raise a *note NetrcParseError: 1fd3. if
     the file ownership or permissions are insecure (owned by a user
     other than the user running the process, or accessible for read or
     write by any other user).  This implements security behavior
     equivalent to that of ftp and other programs that use ‘.netrc’.

     Changed in version 3.4: Added the POSIX permission check.

     Changed in version 3.7: *note os.path.expanduser(): 32c. is used to
     find the location of the ‘.netrc’ file when `file' is not passed as
     argument.

 -- Exception: netrc.NetrcParseError

     Exception raised by the *note netrc: 11d5. class when syntactical
     errors are encountered in source text.  Instances of this exception
     provide three interesting attributes: ‘msg’ is a textual
     explanation of the error, ‘filename’ is the name of the source
     file, and ‘lineno’ gives the line number on which the error was
     found.

* Menu:

* netrc Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/netrc.py


File: python.info,  Node: netrc Objects,  Up: netrc — netrc file processing

5.14.3.1 netrc Objects
......................

A *note netrc: 11d5. instance has the following methods:

 -- Method: netrc.authenticators (host)

     Return a 3-tuple ‘(login, account, password)’ of authenticators for
     `host'.  If the netrc file did not contain an entry for the given
     host, return the tuple associated with the ‘default’ entry.  If
     neither matching host nor default entry is available, return
     ‘None’.

 -- Method: netrc.__repr__ ()

     Dump the class data as a string in the format of a netrc file.
     (This discards comments and may reorder the entries.)

Instances of *note netrc: 11d5. have public instance variables:

 -- Attribute: netrc.hosts

     Dictionary mapping host names to ‘(login, account, password)’
     tuples.  The ‘default’ entry, if any, is represented as a
     pseudo-host by that name.

 -- Attribute: netrc.macros

     Dictionary mapping macro names to string lists.

     Note: Passwords are limited to a subset of the ASCII character set.
     All ASCII punctuation is allowed in passwords, however, note that
     whitespace and non-printable characters are not allowed in
     passwords.  This is a limitation of the way the .netrc file is
     parsed and may be removed in the future.


File: python.info,  Node: xdrlib — Encode and decode XDR data,  Next: plistlib — Generate and parse Apple plist files,  Prev: netrc — netrc file processing,  Up: File Formats

5.14.4 ‘xdrlib’ — Encode and decode XDR data
--------------------------------------------

`Source code:' Lib/xdrlib.py(1)

__________________________________________________________________

The *note xdrlib: 13b. module supports the External Data Representation
Standard as described in RFC 1014(2), written by Sun Microsystems, Inc.
June 1987.  It supports most of the data types described in the RFC.

The *note xdrlib: 13b. module defines two classes, one for packing
variables into XDR representation, and another for unpacking from XDR
representation.  There are also two exception classes.

 -- Class: xdrlib.Packer

     *note Packer: 1fdc. is the class for packing data into XDR
     representation.  The *note Packer: 1fdc. class is instantiated with
     no arguments.

 -- Class: xdrlib.Unpacker (data)

     ‘Unpacker’ is the complementary class which unpacks XDR data values
     from a string buffer.  The input buffer is given as `data'.

See also
........

RFC 1014(3) - XDR: External Data Representation Standard

     This RFC defined the encoding of data which was XDR at the time
     this module was originally written.  It has apparently been
     obsoleted by RFC 1832(4).

RFC 1832(5) - XDR: External Data Representation Standard

     Newer RFC that provides a revised definition of XDR.

* Menu:

* Packer Objects::
* Unpacker Objects::
* Exceptions: Exceptions<7>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/xdrlib.py

   (2) https://tools.ietf.org/html/rfc1014.html

   (3) https://tools.ietf.org/html/rfc1014.html

   (4) https://tools.ietf.org/html/rfc1832.html

   (5) https://tools.ietf.org/html/rfc1832.html


File: python.info,  Node: Packer Objects,  Next: Unpacker Objects,  Up: xdrlib — Encode and decode XDR data

5.14.4.1 Packer Objects
.......................

*note Packer: 1fdc. instances have the following methods:

 -- Method: Packer.get_buffer ()

     Returns the current pack buffer as a string.

 -- Method: Packer.reset ()

     Resets the pack buffer to the empty string.

In general, you can pack any of the most common XDR data types by
calling the appropriate ‘pack_type()’ method.  Each method takes a
single argument, the value to pack.  The following simple data type
packing methods are supported: ‘pack_uint()’, ‘pack_int()’,
‘pack_enum()’, ‘pack_bool()’, ‘pack_uhyper()’, and ‘pack_hyper()’.

 -- Method: Packer.pack_float (value)

     Packs the single-precision floating point number `value'.

 -- Method: Packer.pack_double (value)

     Packs the double-precision floating point number `value'.

The following methods support packing strings, bytes, and opaque data:

 -- Method: Packer.pack_fstring (n, s)

     Packs a fixed length string, `s'.  `n' is the length of the string
     but it is `not' packed into the data buffer.  The string is padded
     with null bytes if necessary to guaranteed 4 byte alignment.

 -- Method: Packer.pack_fopaque (n, data)

     Packs a fixed length opaque data stream, similarly to *note
     pack_fstring(): 1fe4.

 -- Method: Packer.pack_string (s)

     Packs a variable length string, `s'.  The length of the string is
     first packed as an unsigned integer, then the string data is packed
     with *note pack_fstring(): 1fe4.

 -- Method: Packer.pack_opaque (data)

     Packs a variable length opaque data string, similarly to *note
     pack_string(): 1fe6.

 -- Method: Packer.pack_bytes (bytes)

     Packs a variable length byte stream, similarly to *note
     pack_string(): 1fe6.

The following methods support packing arrays and lists:

 -- Method: Packer.pack_list (list, pack_item)

     Packs a `list' of homogeneous items.  This method is useful for
     lists with an indeterminate size; i.e.  the size is not available
     until the entire list has been walked.  For each item in the list,
     an unsigned integer ‘1’ is packed first, followed by the data value
     from the list.  `pack_item' is the function that is called to pack
     the individual item.  At the end of the list, an unsigned integer
     ‘0’ is packed.

     For example, to pack a list of integers, the code might appear like
     this:

          import xdrlib
          p = xdrlib.Packer()
          p.pack_list([1, 2, 3], p.pack_int)

 -- Method: Packer.pack_farray (n, array, pack_item)

     Packs a fixed length list (`array') of homogeneous items.  `n' is
     the length of the list; it is `not' packed into the buffer, but a
     *note ValueError: 16d. exception is raised if ‘len(array)’ is not
     equal to `n'.  As above, `pack_item' is the function used to pack
     each element.

 -- Method: Packer.pack_array (list, pack_item)

     Packs a variable length `list' of homogeneous items.  First, the
     length of the list is packed as an unsigned integer, then each
     element is packed as in *note pack_farray(): 1fea. above.


File: python.info,  Node: Unpacker Objects,  Next: Exceptions<7>,  Prev: Packer Objects,  Up: xdrlib — Encode and decode XDR data

5.14.4.2 Unpacker Objects
.........................

The *note Unpacker: 1fdd. class offers the following methods:

 -- Method: Unpacker.reset (data)

     Resets the string buffer with the given `data'.

 -- Method: Unpacker.get_position ()

     Returns the current unpack position in the data buffer.

 -- Method: Unpacker.set_position (position)

     Sets the data buffer unpack position to `position'.  You should be
     careful about using *note get_position(): 1fef. and *note
     set_position(): 1ff0.

 -- Method: Unpacker.get_buffer ()

     Returns the current unpack data buffer as a string.

 -- Method: Unpacker.done ()

     Indicates unpack completion.  Raises an *note Error: 1ff3.
     exception if all of the data has not been unpacked.

In addition, every data type that can be packed with a *note Packer:
1fdc, can be unpacked with an *note Unpacker: 1fdd.  Unpacking methods
are of the form ‘unpack_type()’, and take no arguments.  They return the
unpacked object.

 -- Method: Unpacker.unpack_float ()

     Unpacks a single-precision floating point number.

 -- Method: Unpacker.unpack_double ()

     Unpacks a double-precision floating point number, similarly to
     *note unpack_float(): 1ff4.

In addition, the following methods unpack strings, bytes, and opaque
data:

 -- Method: Unpacker.unpack_fstring (n)

     Unpacks and returns a fixed length string.  `n' is the number of
     characters expected.  Padding with null bytes to guaranteed 4 byte
     alignment is assumed.

 -- Method: Unpacker.unpack_fopaque (n)

     Unpacks and returns a fixed length opaque data stream, similarly to
     *note unpack_fstring(): 1ff6.

 -- Method: Unpacker.unpack_string ()

     Unpacks and returns a variable length string.  The length of the
     string is first unpacked as an unsigned integer, then the string
     data is unpacked with *note unpack_fstring(): 1ff6.

 -- Method: Unpacker.unpack_opaque ()

     Unpacks and returns a variable length opaque data string, similarly
     to *note unpack_string(): 1ff8.

 -- Method: Unpacker.unpack_bytes ()

     Unpacks and returns a variable length byte stream, similarly to
     *note unpack_string(): 1ff8.

The following methods support unpacking arrays and lists:

 -- Method: Unpacker.unpack_list (unpack_item)

     Unpacks and returns a list of homogeneous items.  The list is
     unpacked one element at a time by first unpacking an unsigned
     integer flag.  If the flag is ‘1’, then the item is unpacked and
     appended to the list.  A flag of ‘0’ indicates the end of the list.
     `unpack_item' is the function that is called to unpack the items.

 -- Method: Unpacker.unpack_farray (n, unpack_item)

     Unpacks and returns (as a list) a fixed length array of homogeneous
     items.  `n' is number of list elements to expect in the buffer.  As
     above, `unpack_item' is the function used to unpack each element.

 -- Method: Unpacker.unpack_array (unpack_item)

     Unpacks and returns a variable length `list' of homogeneous items.
     First, the length of the list is unpacked as an unsigned integer,
     then each element is unpacked as in *note unpack_farray(): 1ffc.
     above.


File: python.info,  Node: Exceptions<7>,  Prev: Unpacker Objects,  Up: xdrlib — Encode and decode XDR data

5.14.4.3 Exceptions
...................

Exceptions in this module are coded as class instances:

 -- Exception: xdrlib.Error

     The base exception class.  *note Error: 1ff3. has a single public
     attribute ‘msg’ containing the description of the error.

 -- Exception: xdrlib.ConversionError

     Class derived from *note Error: 1ff3.  Contains no additional
     instance variables.

Here is an example of how you would catch one of these exceptions:

     import xdrlib
     p = xdrlib.Packer()
     try:
         p.pack_double(8.01)
     except xdrlib.ConversionError as instance:
         print('packing the double failed:', instance.msg)


File: python.info,  Node: plistlib — Generate and parse Apple plist files,  Prev: xdrlib — Encode and decode XDR data,  Up: File Formats

5.14.5 ‘plistlib’ — Generate and parse Apple ‘.plist’ files
-----------------------------------------------------------

`Source code:' Lib/plistlib.py(1)

__________________________________________________________________

This module provides an interface for reading and writing the “property
list” files used by Apple, primarily on macOS and iOS. This module
supports both binary and XML plist files.

The property list (‘.plist’) file format is a simple serialization
supporting basic object types, like dictionaries, lists, numbers and
strings.  Usually the top level object is a dictionary.

To write out and to parse a plist file, use the *note dump(): 220. and
*note load(): 21e. functions.

To work with plist data in bytes objects, use *note dumps(): 221. and
*note loads(): 21f.

Values can be strings, integers, floats, booleans, tuples, lists,
dictionaries (but only with string keys), *note bytes: 172, *note
bytearray: 173. or *note datetime.datetime: 1a0. objects.

Changed in version 3.4: New API, old API deprecated.  Support for binary
format plists added.

Changed in version 3.8: Support added for reading and writing *note UID:
33e. tokens in binary plists as used by NSKeyedArchiver and
NSKeyedUnarchiver.

Changed in version 3.9: Old API removed.

See also
........

PList manual page(2)

     Apple’s documentation of the file format.

This module defines the following functions:

 -- Function: plistlib.load (fp, *, fmt=None, dict_type=dict)

     Read a plist file.  `fp' should be a readable and binary file
     object.  Return the unpacked root object (which usually is a
     dictionary).

     The `fmt' is the format of the file and the following values are
     valid:

        * *note None: 203.: Autodetect the file format

        * *note FMT_XML: 976.: XML file format

        * *note FMT_BINARY: 977.: Binary plist format

     The `dict_type' is the type used for dictionaries that are read
     from the plist file.

     XML data for the *note FMT_XML: 976. format is parsed using the
     Expat parser from *note xml.parsers.expat: 141. – see its
     documentation for possible exceptions on ill-formed XML. Unknown
     elements will simply be ignored by the plist parser.

     The parser for the binary format raises ‘InvalidFileException’ when
     the file cannot be parsed.

     New in version 3.4.

 -- Function: plistlib.loads (data, *, fmt=None, dict_type=dict)

     Load a plist from a bytes object.  See *note load(): 21e. for an
     explanation of the keyword arguments.

     New in version 3.4.

 -- Function: plistlib.dump (value, fp, *, fmt=FMT_XML, sort_keys=True,
          skipkeys=False)

     Write `value' to a plist file.  `Fp' should be a writable, binary
     file object.

     The `fmt' argument specifies the format of the plist file and can
     be one of the following values:

        * *note FMT_XML: 976.: XML formatted plist file

        * *note FMT_BINARY: 977.: Binary formatted plist file

     When `sort_keys' is true (the default) the keys for dictionaries
     will be written to the plist in sorted order, otherwise they will
     be written in the iteration order of the dictionary.

     When `skipkeys' is false (the default) the function raises *note
     TypeError: 1fe. when a key of a dictionary is not a string,
     otherwise such keys are skipped.

     A *note TypeError: 1fe. will be raised if the object is of an
     unsupported type or a container that contains objects of
     unsupported types.

     An *note OverflowError: a41. will be raised for integer values that
     cannot be represented in (binary) plist files.

     New in version 3.4.

 -- Function: plistlib.dumps (value, *, fmt=FMT_XML, sort_keys=True,
          skipkeys=False)

     Return `value' as a plist-formatted bytes object.  See the
     documentation for *note dump(): 220. for an explanation of the
     keyword arguments of this function.

     New in version 3.4.

The following classes are available:

 -- Class: plistlib.UID (data)

     Wraps an *note int: 204.  This is used when reading or writing
     NSKeyedArchiver encoded data, which contains UID (see PList
     manual).

     It has one attribute, ‘data’, which can be used to retrieve the int
     value of the UID. ‘data’ must be in the range ‘0 <= data < 2**64’.

     New in version 3.8.

The following constants are available:

 -- Data: plistlib.FMT_XML

     The XML format for plist files.

     New in version 3.4.

 -- Data: plistlib.FMT_BINARY

     The binary format for plist files

     New in version 3.4.

* Menu:

* Examples: Examples<9>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/plistlib.py

   (2) 
https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/PropertyLists/


File: python.info,  Node: Examples<9>,  Up: plistlib — Generate and parse Apple plist files

5.14.5.1 Examples
.................

Generating a plist:

     pl = dict(
         aString = "Doodah",
         aList = ["A", "B", 12, 32.1, [1, 2, 3]],
         aFloat = 0.1,
         anInt = 728,
         aDict = dict(
             anotherString = "<hello & hi there!>",
             aThirdString = "M\xe4ssig, Ma\xdf",
             aTrueValue = True,
             aFalseValue = False,
         ),
         someData = b"<binary gunk>",
         someMoreData = b"<lots of binary gunk>" * 10,
         aDate = datetime.datetime.fromtimestamp(time.mktime(time.gmtime())),
     )
     with open(fileName, 'wb') as fp:
         dump(pl, fp)

Parsing a plist:

     with open(fileName, 'rb') as fp:
         pl = load(fp)
     print(pl["aKey"])


File: python.info,  Node: Cryptographic Services,  Next: Generic Operating System Services,  Prev: File Formats,  Up: The Python Standard Library

5.15 Cryptographic Services
===========================

The modules described in this chapter implement various algorithms of a
cryptographic nature.  They are available at the discretion of the
installation.  On Unix systems, the *note crypt: 28. module may also be
available.  Here’s an overview:

* Menu:

* hashlib — Secure hashes and message digests::
* hmac — Keyed-Hashing for Message Authentication::
* secrets — Generate secure random numbers for managing secrets::


File: python.info,  Node: hashlib — Secure hashes and message digests,  Next: hmac — Keyed-Hashing for Message Authentication,  Up: Cryptographic Services

5.15.1 ‘hashlib’ — Secure hashes and message digests
----------------------------------------------------

`Source code:' Lib/hashlib.py(1)

__________________________________________________________________

This module implements a common interface to many different secure hash
and message digest algorithms.  Included are the FIPS secure hash
algorithms SHA1, SHA224, SHA256, SHA384, and SHA512 (defined in FIPS
180-2) as well as RSA’s MD5 algorithm (defined in Internet RFC 1321(2)).
The terms “secure hash” and “message digest” are interchangeable.  Older
algorithms were called message digests.  The modern term is secure hash.

     Note: If you want the adler32 or crc32 hash functions, they are
     available in the *note zlib: 14d. module.

     Warning: Some algorithms have known hash collision weaknesses,
     refer to the “See also” section at the end.

* Menu:

* Hash algorithms::
* SHAKE variable length digests::
* Key derivation::
* BLAKE2::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/hashlib.py

   (2) https://tools.ietf.org/html/rfc1321.html


File: python.info,  Node: Hash algorithms,  Next: SHAKE variable length digests,  Up: hashlib — Secure hashes and message digests

5.15.1.1 Hash algorithms
........................

There is one constructor method named for each type of `hash'.  All
return a hash object with the same simple interface.  For example: use
‘sha256()’ to create a SHA-256 hash object.  You can now feed this
object with *note bytes-like objects: 6df. (normally *note bytes: 172.)
using the ‘update()’ method.  At any point you can ask it for the
`digest' of the concatenation of the data fed to it so far using the
‘digest()’ or ‘hexdigest()’ methods.

     Note: For better multithreading performance, the Python *note GIL:
     20e. is released for data larger than 2047 bytes at object creation
     or on update.

     Note: Feeding string objects into ‘update()’ is not supported, as
     hashes work on bytes, not on characters.

Constructors for hash algorithms that are always present in this module
are ‘sha1()’, ‘sha224()’, ‘sha256()’, ‘sha384()’, ‘sha512()’, *note
blake2b(): 646, and *note blake2s(): 647.  ‘md5()’ is normally available
as well, though it may be missing or blocked if you are using a rare
“FIPS compliant” build of Python.  Additional algorithms may also be
available depending upon the OpenSSL library that Python uses on your
platform.  On most platforms the ‘sha3_224()’, ‘sha3_256()’,
‘sha3_384()’, ‘sha3_512()’, ‘shake_128()’, ‘shake_256()’ are also
available.

New in version 3.6: SHA3 (Keccak) and SHAKE constructors ‘sha3_224()’,
‘sha3_256()’, ‘sha3_384()’, ‘sha3_512()’, ‘shake_128()’, ‘shake_256()’.

New in version 3.6: *note blake2b(): 646. and *note blake2s(): 647. were
added.

Changed in version 3.9: All hashlib constructors take a keyword-only
argument `usedforsecurity' with default value ‘True’.  A false value
allows the use of insecure and blocked hashing algorithms in restricted
environments.  ‘False’ indicates that the hashing algorithm is not used
in a security context, e.g.  as a non-cryptographic one-way compression
function.

Hashlib now uses SHA3 and SHAKE from OpenSSL 1.1.1 and newer.

For example, to obtain the digest of the byte string ‘b'Nobody inspects
the spammish repetition'’:

     >>> import hashlib
     >>> m = hashlib.sha256()
     >>> m.update(b"Nobody inspects")
     >>> m.update(b" the spammish repetition")
     >>> m.digest()
     b'\x03\x1e\xdd}Ae\x15\x93\xc5\xfe\\\x00o\xa5u+7\xfd\xdf\xf7\xbcN\x84:\xa6\xaf\x0c\x95\x0fK\x94\x06'
     >>> m.digest_size
     32
     >>> m.block_size
     64

More condensed:

     >>> hashlib.sha224(b"Nobody inspects the spammish repetition").hexdigest()
     'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2'

 -- Function: hashlib.new (name[, data], *, usedforsecurity=True)

     Is a generic constructor that takes the string `name' of the
     desired algorithm as its first parameter.  It also exists to allow
     access to the above listed hashes as well as any other algorithms
     that your OpenSSL library may offer.  The named constructors are
     much faster than *note new(): 1030. and should be preferred.

Using *note new(): 1030. with an algorithm provided by OpenSSL:

     >>> h = hashlib.new('sha256')
     >>> h.update(b"Nobody inspects the spammish repetition")
     >>> h.hexdigest()
     '031edd7d41651593c5fe5c006fa5752b37fddff7bc4e843aa6af0c950f4b9406'

Hashlib provides the following constant attributes:

 -- Data: hashlib.algorithms_guaranteed

     A set containing the names of the hash algorithms guaranteed to be
     supported by this module on all platforms.  Note that ‘md5’ is in
     this list despite some upstream vendors offering an odd “FIPS
     compliant” Python build that excludes it.

     New in version 3.2.

 -- Data: hashlib.algorithms_available

     A set containing the names of the hash algorithms that are
     available in the running Python interpreter.  These names will be
     recognized when passed to *note new(): 1030.  *note
     algorithms_guaranteed: dc2. will always be a subset.  The same
     algorithm may appear multiple times in this set under different
     names (thanks to OpenSSL).

     New in version 3.2.

The following values are provided as constant attributes of the hash
objects returned by the constructors:

 -- Data: hash.digest_size

     The size of the resulting hash in bytes.

 -- Data: hash.block_size

     The internal block size of the hash algorithm in bytes.

A hash object has the following attributes:

 -- Attribute: hash.name

     The canonical name of this hash, always lowercase and always
     suitable as a parameter to *note new(): 1030. to create another
     hash of this type.

     Changed in version 3.4: The name attribute has been present in
     CPython since its inception, but until Python 3.4 was not formally
     specified, so may not exist on some platforms.

A hash object has the following methods:

 -- Method: hash.update (data)

     Update the hash object with the *note bytes-like object: 6df.
     Repeated calls are equivalent to a single call with the
     concatenation of all the arguments: ‘m.update(a); m.update(b)’ is
     equivalent to ‘m.update(a+b)’.

     Changed in version 3.1: The Python GIL is released to allow other
     threads to run while hash updates on data larger than 2047 bytes is
     taking place when using hash algorithms supplied by OpenSSL.

 -- Method: hash.digest ()

     Return the digest of the data passed to the *note update(): 200e.
     method so far.  This is a bytes object of size *note digest_size:
     200c. which may contain bytes in the whole range from 0 to 255.

 -- Method: hash.hexdigest ()

     Like *note digest(): 200f. except the digest is returned as a
     string object of double length, containing only hexadecimal digits.
     This may be used to exchange the value safely in email or other
     non-binary environments.

 -- Method: hash.copy ()

     Return a copy (“clone”) of the hash object.  This can be used to
     efficiently compute the digests of data sharing a common initial
     substring.


File: python.info,  Node: SHAKE variable length digests,  Next: Key derivation,  Prev: Hash algorithms,  Up: hashlib — Secure hashes and message digests

5.15.1.2 SHAKE variable length digests
......................................

The ‘shake_128()’ and ‘shake_256()’ algorithms provide variable length
digests with length_in_bits//2 up to 128 or 256 bits of security.  As
such, their digest methods require a length.  Maximum length is not
limited by the SHAKE algorithm.

 -- Method: shake.digest (length)

     Return the digest of the data passed to the ‘update()’ method so
     far.  This is a bytes object of size `length' which may contain
     bytes in the whole range from 0 to 255.

 -- Method: shake.hexdigest (length)

     Like *note digest(): 115d. except the digest is returned as a
     string object of double length, containing only hexadecimal digits.
     This may be used to exchange the value safely in email or other
     non-binary environments.


File: python.info,  Node: Key derivation,  Next: BLAKE2,  Prev: SHAKE variable length digests,  Up: hashlib — Secure hashes and message digests

5.15.1.3 Key derivation
.......................

Key derivation and key stretching algorithms are designed for secure
password hashing.  Naive algorithms such as ‘sha1(password)’ are not
resistant against brute-force attacks.  A good password hashing function
must be tunable, slow, and include a salt(1).

 -- Function: hashlib.pbkdf2_hmac (hash_name, password, salt,
          iterations, dklen=None)

     The function provides PKCS#5 password-based key derivation function
     2.  It uses HMAC as pseudorandom function.

     The string `hash_name' is the desired name of the hash digest
     algorithm for HMAC, e.g.  ‘sha1’ or ‘sha256’.  `password' and
     `salt' are interpreted as buffers of bytes.  Applications and
     libraries should limit `password' to a sensible length (e.g.
     1024).  `salt' should be about 16 or more bytes from a proper
     source, e.g.  *note os.urandom(): 5cc.

     The number of `iterations' should be chosen based on the hash
     algorithm and computing power.  As of 2013, at least 100,000
     iterations of SHA-256 are suggested.

     `dklen' is the length of the derived key.  If `dklen' is ‘None’
     then the digest size of the hash algorithm `hash_name' is used,
     e.g.  64 for SHA-512.

          >>> import hashlib
          >>> dk = hashlib.pbkdf2_hmac('sha256', b'password', b'salt', 100000)
          >>> dk.hex()
          '0394a2ede332c9a13eb82e9b24631604c31df978b4e2f0fbd2c549944f9d79a5'

     New in version 3.4.

          Note: A fast implementation of `pbkdf2_hmac' is available with
          OpenSSL. The Python implementation uses an inline version of
          *note hmac: 8e.  It is about three times slower and doesn’t
          release the GIL.

 -- Function: hashlib.scrypt (password, *, salt, n, r, p, maxmem=0,
          dklen=64)

     The function provides scrypt password-based key derivation function
     as defined in RFC 7914(2).

     `password' and `salt' must be *note bytes-like objects: 6df.
     Applications and libraries should limit `password' to a sensible
     length (e.g.  1024).  `salt' should be about 16 or more bytes from
     a proper source, e.g.  *note os.urandom(): 5cc.

     `n' is the CPU/Memory cost factor, `r' the block size, `p'
     parallelization factor and `maxmem' limits memory (OpenSSL 1.1.0
     defaults to 32 MiB). `dklen' is the length of the derived key.

     *note Availability: 1491.: OpenSSL 1.1+.

     New in version 3.6.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Salt_%28cryptography%29

   (2) https://tools.ietf.org/html/rfc7914.html


File: python.info,  Node: BLAKE2,  Prev: Key derivation,  Up: hashlib — Secure hashes and message digests

5.15.1.4 BLAKE2
...............

BLAKE2(1) is a cryptographic hash function defined in RFC 7693(2) that
comes in two flavors:

   * `BLAKE2b', optimized for 64-bit platforms and produces digests of
     any size between 1 and 64 bytes,

   * `BLAKE2s', optimized for 8- to 32-bit platforms and produces
     digests of any size between 1 and 32 bytes.

BLAKE2 supports `keyed mode' (a faster and simpler replacement for
HMAC(3)), `salted hashing', `personalization', and `tree hashing'.

Hash objects from this module follow the API of standard library’s *note
hashlib: 8c. objects.

* Menu:

* Creating hash objects::
* Constants: Constants<5>.
* Examples: Examples<10>.
* Credits::

   ---------- Footnotes ----------

   (1) https://blake2.net

   (2) https://tools.ietf.org/html/rfc7693.html

   (3) 
https://en.wikipedia.org/wiki/Hash-based_message_authentication_code


File: python.info,  Node: Creating hash objects,  Next: Constants<5>,  Up: BLAKE2

5.15.1.5 Creating hash objects
..............................

New hash objects are created by calling constructor functions:

 -- Function: hashlib.blake2b (data=b'', *, digest_size=64, key=b'',
          salt=b'', person=b'', fanout=1, depth=1, leaf_size=0,
          node_offset=0, node_depth=0, inner_size=0, last_node=False,
          usedforsecurity=True)

 -- Function: hashlib.blake2s (data=b'', *, digest_size=32, key=b'',
          salt=b'', person=b'', fanout=1, depth=1, leaf_size=0,
          node_offset=0, node_depth=0, inner_size=0, last_node=False,
          usedforsecurity=True)

These functions return the corresponding hash objects for calculating
BLAKE2b or BLAKE2s.  They optionally take these general parameters:

   * `data': initial chunk of data to hash, which must be *note
     bytes-like object: 6df.  It can be passed only as positional
     argument.

   * `digest_size': size of output digest in bytes.

   * `key': key for keyed hashing (up to 64 bytes for BLAKE2b, up to 32
     bytes for BLAKE2s).

   * `salt': salt for randomized hashing (up to 16 bytes for BLAKE2b, up
     to 8 bytes for BLAKE2s).

   * `person': personalization string (up to 16 bytes for BLAKE2b, up to
     8 bytes for BLAKE2s).

The following table shows limits for general parameters (in bytes):

Hash        digest_size     len(key)     len(salt)     len(person)
                                                       
-----------------------------------------------------------------------
                                                       
BLAKE2b     64              64           16            16
                                                       
                                                       
BLAKE2s     32              32           8             8
                                                       

     Note: BLAKE2 specification defines constant lengths for salt and
     personalization parameters, however, for convenience, this
     implementation accepts byte strings of any size up to the specified
     length.  If the length of the parameter is less than specified, it
     is padded with zeros, thus, for example, ‘b'salt'’ and
     ‘b'salt\x00'’ is the same value.  (This is not the case for `key'.)

These sizes are available as module *note constants: 2016. described
below.

Constructor functions also accept the following tree hashing parameters:

   * `fanout': fanout (0 to 255, 0 if unlimited, 1 in sequential mode).

   * `depth': maximal depth of tree (1 to 255, 255 if unlimited, 1 in
     sequential mode).

   * `leaf_size': maximal byte length of leaf (0 to ‘2**32-1’, 0 if
     unlimited or in sequential mode).

   * `node_offset': node offset (0 to ‘2**64-1’ for BLAKE2b, 0 to
     ‘2**48-1’ for BLAKE2s, 0 for the first, leftmost, leaf, or in
     sequential mode).

   * `node_depth': node depth (0 to 255, 0 for leaves, or in sequential
     mode).

   * `inner_size': inner digest size (0 to 64 for BLAKE2b, 0 to 32 for
     BLAKE2s, 0 in sequential mode).

   * `last_node': boolean indicating whether the processed node is the
     last one (‘False’ for sequential mode).

[Explanation of tree mode parameters.]
Figure

See section 2.10 in BLAKE2 specification(1) for comprehensive review of
tree hashing.

   ---------- Footnotes ----------

   (1) https://blake2.net/blake2_20130129.pdf


File: python.info,  Node: Constants<5>,  Next: Examples<10>,  Prev: Creating hash objects,  Up: BLAKE2

5.15.1.6 Constants
..................

 -- Data: blake2b.SALT_SIZE

 -- Data: blake2s.SALT_SIZE

Salt length (maximum length accepted by constructors).

 -- Data: blake2b.PERSON_SIZE

 -- Data: blake2s.PERSON_SIZE

Personalization string length (maximum length accepted by constructors).

 -- Data: blake2b.MAX_KEY_SIZE

 -- Data: blake2s.MAX_KEY_SIZE

Maximum key size.

 -- Data: blake2b.MAX_DIGEST_SIZE

 -- Data: blake2s.MAX_DIGEST_SIZE

Maximum digest size that the hash function can output.


File: python.info,  Node: Examples<10>,  Next: Credits,  Prev: Constants<5>,  Up: BLAKE2

5.15.1.7 Examples
.................

* Menu:

* Simple hashing::
* Using different digest sizes::
* Keyed hashing::
* Randomized hashing::
* Personalization::
* Tree mode::


File: python.info,  Node: Simple hashing,  Next: Using different digest sizes,  Up: Examples<10>

5.15.1.8 Simple hashing
.......................

To calculate hash of some data, you should first construct a hash object
by calling the appropriate constructor function (*note blake2b(): 646.
or *note blake2s(): 647.), then update it with the data by calling
‘update()’ on the object, and, finally, get the digest out of the object
by calling ‘digest()’ (or ‘hexdigest()’ for hex-encoded string).

     >>> from hashlib import blake2b
     >>> h = blake2b()
     >>> h.update(b'Hello world')
     >>> h.hexdigest()
     '6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183'

As a shortcut, you can pass the first chunk of data to update directly
to the constructor as the positional argument:

     >>> from hashlib import blake2b
     >>> blake2b(b'Hello world').hexdigest()
     '6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183'

You can call *note hash.update(): 200e. as many times as you need to
iteratively update the hash:

     >>> from hashlib import blake2b
     >>> items = [b'Hello', b' ', b'world']
     >>> h = blake2b()
     >>> for item in items:
     ...     h.update(item)
     >>> h.hexdigest()
     '6ff843ba685842aa82031d3f53c48b66326df7639a63d128974c5c14f31a0f33343a8c65551134ed1ae0f2b0dd2bb495dc81039e3eeb0aa1bb0388bbeac29183'


File: python.info,  Node: Using different digest sizes,  Next: Keyed hashing,  Prev: Simple hashing,  Up: Examples<10>

5.15.1.9 Using different digest sizes
.....................................

BLAKE2 has configurable size of digests up to 64 bytes for BLAKE2b and
up to 32 bytes for BLAKE2s.  For example, to replace SHA-1 with BLAKE2b
without changing the size of output, we can tell BLAKE2b to produce
20-byte digests:

     >>> from hashlib import blake2b
     >>> h = blake2b(digest_size=20)
     >>> h.update(b'Replacing SHA1 with the more secure function')
     >>> h.hexdigest()
     'd24f26cf8de66472d58d4e1b1774b4c9158b1f4c'
     >>> h.digest_size
     20
     >>> len(h.digest())
     20

Hash objects with different digest sizes have completely different
outputs (shorter hashes are `not' prefixes of longer hashes); BLAKE2b
and BLAKE2s produce different outputs even if the output length is the
same:

     >>> from hashlib import blake2b, blake2s
     >>> blake2b(digest_size=10).hexdigest()
     '6fa1d8fcfd719046d762'
     >>> blake2b(digest_size=11).hexdigest()
     'eb6ec15daf9546254f0809'
     >>> blake2s(digest_size=10).hexdigest()
     '1bf21a98c78a1c376ae9'
     >>> blake2s(digest_size=11).hexdigest()
     '567004bf96e4a25773ebf4'


File: python.info,  Node: Keyed hashing,  Next: Randomized hashing,  Prev: Using different digest sizes,  Up: Examples<10>

5.15.1.10 Keyed hashing
.......................

Keyed hashing can be used for authentication as a faster and simpler
replacement for Hash-based message authentication code(1) (HMAC). BLAKE2
can be securely used in prefix-MAC mode thanks to the
indifferentiability property inherited from BLAKE.

This example shows how to get a (hex-encoded) 128-bit authentication
code for message ‘b'message data'’ with key ‘b'pseudorandom key'’:

     >>> from hashlib import blake2b
     >>> h = blake2b(key=b'pseudorandom key', digest_size=16)
     >>> h.update(b'message data')
     >>> h.hexdigest()
     '3d363ff7401e02026f4a4687d4863ced'

As a practical example, a web application can symmetrically sign cookies
sent to users and later verify them to make sure they weren’t tampered
with:

     >>> from hashlib import blake2b
     >>> from hmac import compare_digest
     >>>
     >>> SECRET_KEY = b'pseudorandomly generated server secret key'
     >>> AUTH_SIZE = 16
     >>>
     >>> def sign(cookie):
     ...     h = blake2b(digest_size=AUTH_SIZE, key=SECRET_KEY)
     ...     h.update(cookie)
     ...     return h.hexdigest().encode('utf-8')
     >>>
     >>> def verify(cookie, sig):
     ...     good_sig = sign(cookie)
     ...     return compare_digest(good_sig, sig)
     >>>
     >>> cookie = b'user-alice'
     >>> sig = sign(cookie)
     >>> print("{0},{1}".format(cookie.decode('utf-8'), sig))
     user-alice,b'43b3c982cf697e0c5ab22172d1ca7421'
     >>> verify(cookie, sig)
     True
     >>> verify(b'user-bob', sig)
     False
     >>> verify(cookie, b'0102030405060708090a0b0c0d0e0f00')
     False

Even though there’s a native keyed hashing mode, BLAKE2 can, of course,
be used in HMAC construction with *note hmac: 8e. module:

     >>> import hmac, hashlib
     >>> m = hmac.new(b'secret key', digestmod=hashlib.blake2s)
     >>> m.update(b'message')
     >>> m.hexdigest()
     'e3c8102868d28b5ff85fc35dda07329970d1a01e273c37481326fe0c861c8142'

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/HMAC


File: python.info,  Node: Randomized hashing,  Next: Personalization,  Prev: Keyed hashing,  Up: Examples<10>

5.15.1.11 Randomized hashing
............................

By setting `salt' parameter users can introduce randomization to the
hash function.  Randomized hashing is useful for protecting against
collision attacks on the hash function used in digital signatures.

     Randomized hashing is designed for situations where one party, the
     message preparer, generates all or part of a message to be signed
     by a second party, the message signer.  If the message preparer is
     able to find cryptographic hash function collisions (i.e., two
     messages producing the same hash value), then they might prepare
     meaningful versions of the message that would produce the same hash
     value and digital signature, but with different results (e.g.,
     transferring $1,000,000 to an account, rather than $10).
     Cryptographic hash functions have been designed with collision
     resistance as a major goal, but the current concentration on
     attacking cryptographic hash functions may result in a given
     cryptographic hash function providing less collision resistance
     than expected.  Randomized hashing offers the signer additional
     protection by reducing the likelihood that a preparer can generate
     two or more messages that ultimately yield the same hash value
     during the digital signature generation process — even if it is
     practical to find collisions for the hash function.  However, the
     use of randomized hashing may reduce the amount of security
     provided by a digital signature when all portions of the message
     are prepared by the signer.

     (NIST SP-800-106 "Randomized Hashing for Digital Signatures"(1))

In BLAKE2 the salt is processed as a one-time input to the hash function
during initialization, rather than as an input to each compression
function.

     Warning: `Salted hashing' (or just hashing) with BLAKE2 or any
     other general-purpose cryptographic hash function, such as SHA-256,
     is not suitable for hashing passwords.  See BLAKE2 FAQ(2) for more
     information.

     >>> import os
     >>> from hashlib import blake2b
     >>> msg = b'some message'
     >>> # Calculate the first hash with a random salt.
     >>> salt1 = os.urandom(blake2b.SALT_SIZE)
     >>> h1 = blake2b(salt=salt1)
     >>> h1.update(msg)
     >>> # Calculate the second hash with a different random salt.
     >>> salt2 = os.urandom(blake2b.SALT_SIZE)
     >>> h2 = blake2b(salt=salt2)
     >>> h2.update(msg)
     >>> # The digests are different.
     >>> h1.digest() != h2.digest()
     True

   ---------- Footnotes ----------

   (1) https://csrc.nist.gov/publications/detail/sp/800-106/final

   (2) https://blake2.net/#qa


File: python.info,  Node: Personalization,  Next: Tree mode,  Prev: Randomized hashing,  Up: Examples<10>

5.15.1.12 Personalization
.........................

Sometimes it is useful to force hash function to produce different
digests for the same input for different purposes.  Quoting the authors
of the Skein hash function:

     We recommend that all application designers seriously consider
     doing this; we have seen many protocols where a hash that is
     computed in one part of the protocol can be used in an entirely
     different part because two hash computations were done on similar
     or related data, and the attacker can force the application to make
     the hash inputs the same.  Personalizing each hash function used in
     the protocol summarily stops this type of attack.

     (The Skein Hash Function Family(1), p.  21)

BLAKE2 can be personalized by passing bytes to the `person' argument:

     >>> from hashlib import blake2b
     >>> FILES_HASH_PERSON = b'MyApp Files Hash'
     >>> BLOCK_HASH_PERSON = b'MyApp Block Hash'
     >>> h = blake2b(digest_size=32, person=FILES_HASH_PERSON)
     >>> h.update(b'the same content')
     >>> h.hexdigest()
     '20d9cd024d4fb086aae819a1432dd2466de12947831b75c5a30cf2676095d3b4'
     >>> h = blake2b(digest_size=32, person=BLOCK_HASH_PERSON)
     >>> h.update(b'the same content')
     >>> h.hexdigest()
     'cf68fb5761b9c44e7878bfb2c4c9aea52264a80b75005e65619778de59f383a3'

Personalization together with the keyed mode can also be used to derive
different keys from a single one.

     >>> from hashlib import blake2s
     >>> from base64 import b64decode, b64encode
     >>> orig_key = b64decode(b'Rm5EPJai72qcK3RGBpW3vPNfZy5OZothY+kHY6h21KM=')
     >>> enc_key = blake2s(key=orig_key, person=b'kEncrypt').digest()
     >>> mac_key = blake2s(key=orig_key, person=b'kMAC').digest()
     >>> print(b64encode(enc_key).decode('utf-8'))
     rbPb15S/Z9t+agffno5wuhB77VbRi6F9Iv2qIxU7WHw=
     >>> print(b64encode(mac_key).decode('utf-8'))
     G9GtHFE1YluXY1zWPlYk1e/nWfu0WSEb0KRcjhDeP/o=

   ---------- Footnotes ----------

   (1) http://www.skein-hash.info/sites/default/files/skein1.3.pdf


File: python.info,  Node: Tree mode,  Prev: Personalization,  Up: Examples<10>

5.15.1.13 Tree mode
...................

Here’s an example of hashing a minimal tree with two leaf nodes:

       10
      /  \
     00  01

This example uses 64-byte internal digests, and returns the 32-byte
final digest:

     >>> from hashlib import blake2b
     >>>
     >>> FANOUT = 2
     >>> DEPTH = 2
     >>> LEAF_SIZE = 4096
     >>> INNER_SIZE = 64
     >>>
     >>> buf = bytearray(6000)
     >>>
     >>> # Left leaf
     ... h00 = blake2b(buf[0:LEAF_SIZE], fanout=FANOUT, depth=DEPTH,
     ...               leaf_size=LEAF_SIZE, inner_size=INNER_SIZE,
     ...               node_offset=0, node_depth=0, last_node=False)
     >>> # Right leaf
     ... h01 = blake2b(buf[LEAF_SIZE:], fanout=FANOUT, depth=DEPTH,
     ...               leaf_size=LEAF_SIZE, inner_size=INNER_SIZE,
     ...               node_offset=1, node_depth=0, last_node=True)
     >>> # Root node
     ... h10 = blake2b(digest_size=32, fanout=FANOUT, depth=DEPTH,
     ...               leaf_size=LEAF_SIZE, inner_size=INNER_SIZE,
     ...               node_offset=0, node_depth=1, last_node=True)
     >>> h10.update(h00.digest())
     >>> h10.update(h01.digest())
     >>> h10.hexdigest()
     '3ad2a9b37c6070e374c7a8c508fe20ca86b6ed54e286e93a0318e95e881db5aa'


File: python.info,  Node: Credits,  Prev: Examples<10>,  Up: BLAKE2

5.15.1.14 Credits
.................

BLAKE2(1) was designed by `Jean-Philippe Aumasson', `Samuel Neves',
`Zooko Wilcox-O’Hearn', and `Christian Winnerlein' based on SHA-3(2)
finalist BLAKE(3) created by `Jean-Philippe Aumasson', `Luca Henzen',
`Willi Meier', and `Raphael C.-W. Phan'.

It uses core algorithm from ChaCha(4) cipher designed by `Daniel J.
Bernstein'.

The stdlib implementation is based on pyblake2(5) module.  It was
written by `Dmitry Chestnykh' based on C implementation written by
`Samuel Neves'.  The documentation was copied from pyblake2(6) and
written by `Dmitry Chestnykh'.

The C code was partly rewritten for Python by `Christian Heimes'.

The following public domain dedication applies for both C hash function
implementation, extension code, and this documentation:

     To the extent possible under law, the author(s) have dedicated all
     copyright and related and neighboring rights to this software to
     the public domain worldwide.  This software is distributed without
     any warranty.

     You should have received a copy of the CC0 Public Domain Dedication
     along with this software.  If not, see
     ‘https://creativecommons.org/publicdomain/zero/1.0/’.

The following people have helped with development or contributed their
changes to the project and the public domain according to the Creative
Commons Public Domain Dedication 1.0 Universal:

   * `Alexandr Sokolovskiy'

See also
........

Module *note hmac: 8e.

     A module to generate message authentication codes using hashes.

Module *note base64: d.

     Another way to encode binary hashes for non-binary environments.

‘https://blake2.net’

     Official BLAKE2 website.

‘https://csrc.nist.gov/csrc/media/publications/fips/180/2/archive/2002-08-01/documents/fips180-2.pdf’

     The FIPS 180-2 publication on Secure Hash Algorithms.

‘https://en.wikipedia.org/wiki/Cryptographic_hash_function#Cryptographic_hash_algorithms’

     Wikipedia article with information on which algorithms have known
     issues and what that means regarding their use.

‘https://www.ietf.org/rfc/rfc2898.txt’

     PKCS #5: Password-Based Cryptography Specification Version 2.0

   ---------- Footnotes ----------

   (1) https://blake2.net

   (2) https://en.wikipedia.org/wiki/NIST_hash_function_competition

   (3) https://131002.net/blake/

   (4) https://cr.yp.to/chacha.html

   (5) https://pythonhosted.org/pyblake2/

   (6) https://pythonhosted.org/pyblake2/


File: python.info,  Node: hmac — Keyed-Hashing for Message Authentication,  Next: secrets — Generate secure random numbers for managing secrets,  Prev: hashlib — Secure hashes and message digests,  Up: Cryptographic Services

5.15.2 ‘hmac’ — Keyed-Hashing for Message Authentication
--------------------------------------------------------

`Source code:' Lib/hmac.py(1)

__________________________________________________________________

This module implements the HMAC algorithm as described by RFC 2104(2).

 -- Function: hmac.new (key, msg=None, digestmod='')

     Return a new hmac object.  `key' is a bytes or bytearray object
     giving the secret key.  If `msg' is present, the method call
     ‘update(msg)’ is made.  `digestmod' is the digest name, digest
     constructor or module for the HMAC object to use.  It may be any
     name suitable to *note hashlib.new(): 1030.  Despite its argument
     position, it is required.

     Changed in version 3.4: Parameter `key' can be a bytes or bytearray
     object.  Parameter `msg' can be of any type supported by *note
     hashlib: 8c.  Parameter `digestmod' can be the name of a hash
     algorithm.

     Deprecated since version 3.4, removed in version 3.8: MD5 as
     implicit default digest for `digestmod' is deprecated.  The
     digestmod parameter is now required.  Pass it as a keyword argument
     to avoid awkwardness when you do not have an initial msg.

 -- Function: hmac.digest (key, msg, digest)

     Return digest of `msg' for given secret `key' and `digest'.  The
     function is equivalent to ‘HMAC(key, msg, digest).digest()’, but
     uses an optimized C or inline implementation, which is faster for
     messages that fit into memory.  The parameters `key', `msg', and
     `digest' have the same meaning as in *note new(): 940.

     CPython implementation detail, the optimized C implementation is
     only used when `digest' is a string and name of a digest algorithm,
     which is supported by OpenSSL.

     New in version 3.7.

An HMAC object has the following methods:

 -- Method: HMAC.update (msg)

     Update the hmac object with `msg'.  Repeated calls are equivalent
     to a single call with the concatenation of all the arguments:
     ‘m.update(a); m.update(b)’ is equivalent to ‘m.update(a + b)’.

     Changed in version 3.4: Parameter `msg' can be of any type
     supported by *note hashlib: 8c.

 -- Method: HMAC.digest ()

     Return the digest of the bytes passed to the *note update(): 941.
     method so far.  This bytes object will be the same length as the
     `digest_size' of the digest given to the constructor.  It may
     contain non-ASCII bytes, including NUL bytes.

          Warning: When comparing the output of *note digest(): 497. to
          an externally-supplied digest during a verification routine,
          it is recommended to use the *note compare_digest(): aea.
          function instead of the ‘==’ operator to reduce the
          vulnerability to timing attacks.

 -- Method: HMAC.hexdigest ()

     Like *note digest(): 497. except the digest is returned as a string
     twice the length containing only hexadecimal digits.  This may be
     used to exchange the value safely in email or other non-binary
     environments.

          Warning: When comparing the output of *note hexdigest(): 202a.
          to an externally-supplied digest during a verification
          routine, it is recommended to use the *note compare_digest():
          aea. function instead of the ‘==’ operator to reduce the
          vulnerability to timing attacks.

 -- Method: HMAC.copy ()

     Return a copy (“clone”) of the hmac object.  This can be used to
     efficiently compute the digests of strings that share a common
     initial substring.

A hash object has the following attributes:

 -- Attribute: HMAC.digest_size

     The size of the resulting HMAC digest in bytes.

 -- Attribute: HMAC.block_size

     The internal block size of the hash algorithm in bytes.

     New in version 3.4.

 -- Attribute: HMAC.name

     The canonical name of this HMAC, always lowercase, e.g.
     ‘hmac-md5’.

     New in version 3.4.

Deprecated since version 3.9: The undocumented attributes
‘HMAC.digest_cons’, ‘HMAC.inner’, and ‘HMAC.outer’ are internal
implementation details and will be removed in Python 3.10.

This module also provides the following helper function:

 -- Function: hmac.compare_digest (a, b)

     Return ‘a == b’.  This function uses an approach designed to
     prevent timing analysis by avoiding content-based short circuiting
     behaviour, making it appropriate for cryptography.  `a' and `b'
     must both be of the same type: either *note str: 205. (ASCII only,
     as e.g.  returned by *note HMAC.hexdigest(): 202a.), or a *note
     bytes-like object: 6df.

          Note: If `a' and `b' are of different lengths, or if an error
          occurs, a timing attack could theoretically reveal information
          about the types and lengths of `a' and `b'—but not their
          values.

     New in version 3.3.

     Changed in version 3.9: The function uses OpenSSL’s
     ‘CRYPTO_memcmp()’ internally when available.

See also
........

Module *note hashlib: 8c.

     The Python module providing secure hash functions.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/hmac.py

   (2) https://tools.ietf.org/html/rfc2104.html


File: python.info,  Node: secrets — Generate secure random numbers for managing secrets,  Prev: hmac — Keyed-Hashing for Message Authentication,  Up: Cryptographic Services

5.15.3 ‘secrets’ — Generate secure random numbers for managing secrets
----------------------------------------------------------------------

New in version 3.6.

`Source code:' Lib/secrets.py(1)

__________________________________________________________________

The *note secrets: e4. module is used for generating cryptographically
strong random numbers suitable for managing data such as passwords,
account authentication, security tokens, and related secrets.

In particular, *note secrets: e4. should be used in preference to the
default pseudo-random number generator in the *note random: dc. module,
which is designed for modelling and simulation, not security or
cryptography.

See also
........

PEP 506(2)

* Menu:

* Random numbers::
* Generating tokens::
* Other functions::
* Recipes and best practices::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/secrets.py

   (2) https://www.python.org/dev/peps/pep-0506


File: python.info,  Node: Random numbers,  Next: Generating tokens,  Up: secrets — Generate secure random numbers for managing secrets

5.15.3.1 Random numbers
.......................

The *note secrets: e4. module provides access to the most secure source
of randomness that your operating system provides.

 -- Class: secrets.SystemRandom

     A class for generating random numbers using the highest-quality
     sources provided by the operating system.  See *note
     random.SystemRandom: 1c5f. for additional details.

 -- Function: secrets.choice (sequence)

     Return a randomly-chosen element from a non-empty sequence.

 -- Function: secrets.randbelow (n)

     Return a random int in the range [0, `n').

 -- Function: secrets.randbits (k)

     Return an int with `k' random bits.


File: python.info,  Node: Generating tokens,  Next: Other functions,  Prev: Random numbers,  Up: secrets — Generate secure random numbers for managing secrets

5.15.3.2 Generating tokens
..........................

The *note secrets: e4. module provides functions for generating secure
tokens, suitable for applications such as password resets, hard-to-guess
URLs, and similar.

 -- Function: secrets.token_bytes ([nbytes=None])

     Return a random byte string containing `nbytes' number of bytes.
     If `nbytes' is ‘None’ or not supplied, a reasonable default is
     used.

          >>> token_bytes(16)
          b'\xebr\x17D*t\xae\xd4\xe3S\xb6\xe2\xebP1\x8b'

 -- Function: secrets.token_hex ([nbytes=None])

     Return a random text string, in hexadecimal.  The string has
     `nbytes' random bytes, each byte converted to two hex digits.  If
     `nbytes' is ‘None’ or not supplied, a reasonable default is used.

          >>> token_hex(16)
          'f9bf78b9a18ce6d46a0cd2b0b86df9da'

 -- Function: secrets.token_urlsafe ([nbytes=None])

     Return a random URL-safe text string, containing `nbytes' random
     bytes.  The text is Base64 encoded, so on average each byte results
     in approximately 1.3 characters.  If `nbytes' is ‘None’ or not
     supplied, a reasonable default is used.

          >>> token_urlsafe(16)
          'Drmhze6EPcv0fN_81Bj-nA'

* Menu:

* How many bytes should tokens use?::


File: python.info,  Node: How many bytes should tokens use?,  Up: Generating tokens

5.15.3.3 How many bytes should tokens use?
..........................................

To be secure against brute-force attacks(1), tokens need to have
sufficient randomness.  Unfortunately, what is considered sufficient
will necessarily increase as computers get more powerful and able to
make more guesses in a shorter period.  As of 2015, it is believed that
32 bytes (256 bits) of randomness is sufficient for the typical use-case
expected for the *note secrets: e4. module.

For those who want to manage their own token length, you can explicitly
specify how much randomness is used for tokens by giving an *note int:
204. argument to the various ‘token_*’ functions.  That argument is
taken as the number of bytes of randomness to use.

Otherwise, if no argument is provided, or if the argument is ‘None’, the
‘token_*’ functions will use a reasonable default instead.

     Note: That default is subject to change at any time, including
     during maintenance releases.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Brute-force_attack


File: python.info,  Node: Other functions,  Next: Recipes and best practices,  Prev: Generating tokens,  Up: secrets — Generate secure random numbers for managing secrets

5.15.3.4 Other functions
........................

 -- Function: secrets.compare_digest (a, b)

     Return ‘True’ if strings `a' and `b' are equal, otherwise ‘False’,
     in such a way as to reduce the risk of timing attacks(1).  See
     *note hmac.compare_digest(): aea. for additional details.

   ---------- Footnotes ----------

   (1) https://codahale.com/a-lesson-in-timing-attacks/


File: python.info,  Node: Recipes and best practices,  Prev: Other functions,  Up: secrets — Generate secure random numbers for managing secrets

5.15.3.5 Recipes and best practices
...................................

This section shows recipes and best practices for using *note secrets:
e4. to manage a basic level of security.

Generate an eight-character alphanumeric password:

     import string
     import secrets
     alphabet = string.ascii_letters + string.digits
     password = ''.join(secrets.choice(alphabet) for i in range(8))

     Note: Applications should not store passwords in a recoverable
     format(1), whether plain text or encrypted.  They should be salted
     and hashed using a cryptographically-strong one-way (irreversible)
     hash function.

Generate a ten-character alphanumeric password with at least one
lowercase character, at least one uppercase character, and at least
three digits:

     import string
     import secrets
     alphabet = string.ascii_letters + string.digits
     while True:
         password = ''.join(secrets.choice(alphabet) for i in range(10))
         if (any(c.islower() for c in password)
                 and any(c.isupper() for c in password)
                 and sum(c.isdigit() for c in password) >= 3):
             break

Generate an XKCD-style passphrase(2):

     import secrets
     # On standard Linux systems, use a convenient dictionary file.
     # Other platforms may need to provide their own word-list.
     with open('/usr/share/dict/words') as f:
         words = [word.strip() for word in f]
         password = ' '.join(secrets.choice(words) for i in range(4))

Generate a hard-to-guess temporary URL containing a security token
suitable for password recovery applications:

     import secrets
     url = 'https://mydomain.com/reset=' + secrets.token_urlsafe()

   ---------- Footnotes ----------

   (1) http://cwe.mitre.org/data/definitions/257.html

   (2) https://xkcd.com/936/


File: python.info,  Node: Generic Operating System Services,  Next: Concurrent Execution,  Prev: Cryptographic Services,  Up: The Python Standard Library

5.16 Generic Operating System Services
======================================

The modules described in this chapter provide interfaces to operating
system features that are available on (almost) all operating systems,
such as files and a clock.  The interfaces are generally modeled after
the Unix or C interfaces, but they are available on most other systems
as well.  Here’s an overview:

* Menu:

* os — Miscellaneous operating system interfaces::
* io — Core tools for working with streams::
* time — Time access and conversions::
* argparse — Parser for command-line options, arguments and sub-commands: argparse — Parser for command-line options arguments and sub-commands.
* getopt — C-style parser for command line options::
* logging — Logging facility for Python::
* logging.config — Logging configuration: logging config — Logging configuration.
* logging.handlers — Logging handlers: logging handlers — Logging handlers.
* getpass — Portable password input::
* curses — Terminal handling for character-cell displays::
* curses.textpad — Text input widget for curses programs: curses textpad — Text input widget for curses programs.
* curses.ascii — Utilities for ASCII characters: curses ascii — Utilities for ASCII characters.
* curses.panel — A panel stack extension for curses: curses panel — A panel stack extension for curses.
* platform — Access to underlying platform’s identifying data::
* errno — Standard errno system symbols::
* ctypes — A foreign function library for Python::


File: python.info,  Node: os — Miscellaneous operating system interfaces,  Next: io — Core tools for working with streams,  Up: Generic Operating System Services

5.16.1 ‘os’ — Miscellaneous operating system interfaces
-------------------------------------------------------

`Source code:' Lib/os.py(1)

__________________________________________________________________

This module provides a portable way of using operating system dependent
functionality.  If you just want to read or write a file see *note
open(): 16f, if you want to manipulate paths, see the *note os.path: c5.
module, and if you want to read all the lines in all the files on the
command line see the *note fileinput: 7e. module.  For creating
temporary files and directories see the *note tempfile: 103. module, and
for high-level file and directory handling see the *note shutil: e9.
module.

Notes on the availability of these functions:

   * The design of all built-in operating system dependent modules of
     Python is such that as long as the same functionality is available,
     it uses the same interface; for example, the function
     ‘os.stat(path)’ returns stat information about `path' in the same
     format (which happens to have originated with the POSIX interface).

   * Extensions peculiar to a particular operating system are also
     available through the *note os: c4. module, but using them is of
     course a threat to portability.

   * All functions accepting path or file names accept both bytes and
     string objects, and result in an object of the same type, if a path
     or file name is returned.

   * On VxWorks, os.fork, os.execv and os.spawn*p* are not supported.

     Note: All functions in this module raise *note OSError: 304. (or
     subclasses thereof) in the case of invalid or inaccessible file
     names and paths, or other arguments that have the correct type, but
     are not accepted by the operating system.

 -- Exception: os.error

     An alias for the built-in *note OSError: 304. exception.

 -- Data: os.name

     The name of the operating system dependent module imported.  The
     following names have currently been registered: ‘'posix'’, ‘'nt'’,
     ‘'java'’.

     See also
     ........

     *note sys.platform: 3d3. has a finer granularity.  *note
     os.uname(): b38. gives system-dependent version information.

     The *note platform: ce. module provides detailed checks for the
     system’s identity.

* Menu:

* File Names, Command Line Arguments, and Environment Variables: File Names Command Line Arguments and Environment Variables.
* Process Parameters::
* File Object Creation::
* File Descriptor Operations::
* Files and Directories::
* Process Management::
* Interface to the scheduler::
* Miscellaneous System Information::
* Random numbers: Random numbers<2>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/os.py


File: python.info,  Node: File Names Command Line Arguments and Environment Variables,  Next: Process Parameters,  Up: os — Miscellaneous operating system interfaces

5.16.1.1 File Names, Command Line Arguments, and Environment Variables
......................................................................

In Python, file names, command line arguments, and environment variables
are represented using the string type.  On some systems, decoding these
strings to and from bytes is necessary before passing them to the
operating system.  Python uses the file system encoding to perform this
conversion (see *note sys.getfilesystemencoding(): 5f0.).

Changed in version 3.1: On some systems, conversion using the file
system encoding may fail.  In this case, Python uses the *note
surrogateescape encoding error handler: 198a, which means that
undecodable bytes are replaced by a Unicode character U+DCxx on
decoding, and these are again translated to the original byte on
encoding.

The file system encoding must guarantee to successfully decode all bytes
below 128.  If the file system encoding fails to provide this guarantee,
API functions may raise UnicodeErrors.


File: python.info,  Node: Process Parameters,  Next: File Object Creation,  Prev: File Names Command Line Arguments and Environment Variables,  Up: os — Miscellaneous operating system interfaces

5.16.1.2 Process Parameters
...........................

These functions and data items provide information and operate on the
current process and user.

 -- Function: os.ctermid ()

     Return the filename corresponding to the controlling terminal of
     the process.

     *note Availability: 1491.: Unix.

 -- Data: os.environ

     A *note mapping: c0b. object where keys and values are strings that
     represent the process environment.  For example, ‘environ['HOME']’
     is the pathname of your home directory (on some platforms), and is
     equivalent to ‘getenv("HOME")’ in C.

     This mapping is captured the first time the *note os: c4. module is
     imported, typically during Python startup as part of processing
     ‘site.py’.  Changes to the environment made after this time are not
     reflected in ‘os.environ’, except for changes made by modifying
     ‘os.environ’ directly.

     This mapping may be used to modify the environment as well as query
     the environment.  *note putenv(): 1cd. will be called automatically
     when the mapping is modified.

     On Unix, keys and values use *note sys.getfilesystemencoding():
     5f0. and ‘'surrogateescape'’ error handler.  Use *note environb:
     c65. if you would like to use a different encoding.

          Note: Calling *note putenv(): 1cd. directly does not change
          ‘os.environ’, so it’s better to modify ‘os.environ’.

          Note: On some platforms, including FreeBSD and macOS, setting
          ‘environ’ may cause memory leaks.  Refer to the system
          documentation for ‘putenv()’.

     You can delete items in this mapping to unset environment
     variables.  *note unsetenv(): 1cc. will be called automatically
     when an item is deleted from ‘os.environ’, and when one of the
     ‘pop()’ or ‘clear()’ methods is called.

     Changed in version 3.9: Updated to support PEP 584(1)’s merge (‘|’)
     and update (‘|=’) operators.

 -- Data: os.environb

     Bytes version of *note environ: c09.: a *note mapping: c0b. object
     where both keys and values are *note bytes: 172. objects
     representing the process environment.  *note environ: c09. and
     *note environb: c65. are synchronized (modifying *note environb:
     c65. updates *note environ: c09, and vice versa).

     *note environb: c65. is only available if *note
     supports_bytes_environ: c63. is ‘True’.

     New in version 3.2.

     Changed in version 3.9: Updated to support PEP 584(2)’s merge (‘|’)
     and update (‘|=’) operators.

 -- Function: os.chdir (path)

 -- Function: os.fchdir (fd)

 -- Function: os.getcwd ()

     These functions are described in *note Files and Directories: 2046.

 -- Function: os.fsencode (filename)

     Encode *note path-like: 472. `filename' to the filesystem encoding
     with ‘'surrogateescape'’ error handler, or ‘'strict'’ on Windows;
     return *note bytes: 172. unchanged.

     *note fsdecode(): 5e9. is the reverse function.

     New in version 3.2.

     Changed in version 3.6: Support added to accept objects
     implementing the *note os.PathLike: 5e6. interface.

 -- Function: os.fsdecode (filename)

     Decode the *note path-like: 472. `filename' from the filesystem
     encoding with ‘'surrogateescape'’ error handler, or ‘'strict'’ on
     Windows; return *note str: 205. unchanged.

     *note fsencode(): 5ea. is the reverse function.

     New in version 3.2.

     Changed in version 3.6: Support added to accept objects
     implementing the *note os.PathLike: 5e6. interface.

 -- Function: os.fspath (path)

     Return the file system representation of the path.

     If *note str: 205. or *note bytes: 172. is passed in, it is
     returned unchanged.  Otherwise *note __fspath__(): 5e7. is called
     and its value is returned as long as it is a *note str: 205. or
     *note bytes: 172. object.  In all other cases, *note TypeError:
     1fe. is raised.

     New in version 3.6.

 -- Class: os.PathLike

     An *note abstract base class: c05. for objects representing a file
     system path, e.g.  *note pathlib.PurePath: 235.

     New in version 3.6.

      -- Method: abstractmethod __fspath__ ()

          Return the file system path representation of the object.

          The method should only return a *note str: 205. or *note
          bytes: 172. object, with the preference being for *note str:
          205.

 -- Function: os.getenv (key, default=None)

     Return the value of the environment variable `key' if it exists, or
     `default' if it doesn’t.  `key', `default' and the result are str.

     On Unix, keys and values are decoded with *note
     sys.getfilesystemencoding(): 5f0. and ‘'surrogateescape'’ error
     handler.  Use *note os.getenvb(): c64. if you would like to use a
     different encoding.

     *note Availability: 1491.: most flavors of Unix, Windows.

 -- Function: os.getenvb (key, default=None)

     Return the value of the environment variable `key' if it exists, or
     `default' if it doesn’t.  `key', `default' and the result are
     bytes.

     *note getenvb(): c64. is only available if *note
     supports_bytes_environ: c63. is ‘True’.

     *note Availability: 1491.: most flavors of Unix.

     New in version 3.2.

 -- Function: os.get_exec_path (env=None)

     Returns the list of directories that will be searched for a named
     executable, similar to a shell, when launching a process.  `env',
     when specified, should be an environment variable dictionary to
     lookup the PATH in.  By default, when `env' is ‘None’, *note
     environ: c09. is used.

     New in version 3.2.

 -- Function: os.getegid ()

     Return the effective group id of the current process.  This
     corresponds to the “set id” bit on the file being executed in the
     current process.

     *note Availability: 1491.: Unix.

 -- Function: os.geteuid ()

     Return the current process’s effective user id.

     *note Availability: 1491.: Unix.

 -- Function: os.getgid ()

     Return the real group id of the current process.

     *note Availability: 1491.: Unix.

 -- Function: os.getgrouplist (user, group)

     Return list of group ids that `user' belongs to.  If `group' is not
     in the list, it is included; typically, `group' is specified as the
     group ID field from the password record for `user'.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: os.getgroups ()

     Return list of supplemental group ids associated with the current
     process.

     *note Availability: 1491.: Unix.

          Note: On macOS, *note getgroups(): 204c. behavior differs
          somewhat from other Unix platforms.  If the Python interpreter
          was built with a deployment target of ‘10.5’ or earlier, *note
          getgroups(): 204c. returns the list of effective group ids
          associated with the current user process; this list is limited
          to a system-defined number of entries, typically 16, and may
          be modified by calls to *note setgroups(): 204d. if suitably
          privileged.  If built with a deployment target greater than
          ‘10.5’, *note getgroups(): 204c. returns the current group
          access list for the user associated with the effective user id
          of the process; the group access list may change over the
          lifetime of the process, it is not affected by calls to *note
          setgroups(): 204d, and its length is not limited to 16.  The
          deployment target value, ‘MACOSX_DEPLOYMENT_TARGET’, can be
          obtained with *note sysconfig.get_config_var(): a45.

 -- Function: os.getlogin ()

     Return the name of the user logged in on the controlling terminal
     of the process.  For most purposes, it is more useful to use *note
     getpass.getuser(): 204f. since the latter checks the environment
     variables ‘LOGNAME’ or ‘USERNAME’ to find out who the user is, and
     falls back to ‘pwd.getpwuid(os.getuid())[0]’ to get the login name
     of the current real user id.

     *note Availability: 1491.: Unix, Windows.

 -- Function: os.getpgid (pid)

     Return the process group id of the process with process id `pid'.
     If `pid' is 0, the process group id of the current process is
     returned.

     *note Availability: 1491.: Unix.

 -- Function: os.getpgrp ()

     Return the id of the current process group.

     *note Availability: 1491.: Unix.

 -- Function: os.getpid ()

     Return the current process id.

 -- Function: os.getppid ()

     Return the parent’s process id.  When the parent process has
     exited, on Unix the id returned is the one of the init process (1),
     on Windows it is still the same id, which may be already reused by
     another process.

     *note Availability: 1491.: Unix, Windows.

     Changed in version 3.2: Added support for Windows.

 -- Function: os.getpriority (which, who)

     Get program scheduling priority.  The value `which' is one of *note
     PRIO_PROCESS: 2054, *note PRIO_PGRP: 2055, or *note PRIO_USER:
     2056, and `who' is interpreted relative to `which' (a process
     identifier for *note PRIO_PROCESS: 2054, process group identifier
     for *note PRIO_PGRP: 2055, and a user ID for *note PRIO_USER:
     2056.).  A zero value for `who' denotes (respectively) the calling
     process, the process group of the calling process, or the real user
     ID of the calling process.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Data: os.PRIO_PROCESS
 -- Data: os.PRIO_PGRP
 -- Data: os.PRIO_USER

     Parameters for the *note getpriority(): b21. and *note
     setpriority(): b22. functions.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: os.getresuid ()

     Return a tuple (ruid, euid, suid) denoting the current process’s
     real, effective, and saved user ids.

     *note Availability: 1491.: Unix.

     New in version 3.2.

 -- Function: os.getresgid ()

     Return a tuple (rgid, egid, sgid) denoting the current process’s
     real, effective, and saved group ids.

     *note Availability: 1491.: Unix.

     New in version 3.2.

 -- Function: os.getuid ()

     Return the current process’s real user id.

     *note Availability: 1491.: Unix.

 -- Function: os.initgroups (username, gid)

     Call the system initgroups() to initialize the group access list
     with all of the groups of which the specified username is a member,
     plus the specified group id.

     *note Availability: 1491.: Unix.

     New in version 3.2.

 -- Function: os.putenv (key, value)

     Set the environment variable named `key' to the string `value'.
     Such changes to the environment affect subprocesses started with
     *note os.system(): e86, *note popen(): 3cb. or *note fork(): a42.
     and *note execv(): 2058.

     Assignments to items in ‘os.environ’ are automatically translated
     into corresponding calls to *note putenv(): 1cd.; however, calls to
     *note putenv(): 1cd. don’t update ‘os.environ’, so it is actually
     preferable to assign to items of ‘os.environ’.

          Note: On some platforms, including FreeBSD and macOS, setting
          ‘environ’ may cause memory leaks.  Refer to the system
          documentation for ‘putenv()’.

     Raises an *note auditing event: fa1. ‘os.putenv’ with arguments
     ‘key’, ‘value’.

     Changed in version 3.9: The function is now always available.

 -- Function: os.setegid (egid)

     Set the current process’s effective group id.

     *note Availability: 1491.: Unix.

 -- Function: os.seteuid (euid)

     Set the current process’s effective user id.

     *note Availability: 1491.: Unix.

 -- Function: os.setgid (gid)

     Set the current process’ group id.

     *note Availability: 1491.: Unix.

 -- Function: os.setgroups (groups)

     Set the list of supplemental group ids associated with the current
     process to `groups'.  `groups' must be a sequence, and each element
     must be an integer identifying a group.  This operation is
     typically available only to the superuser.

     *note Availability: 1491.: Unix.

          Note: On macOS, the length of `groups' may not exceed the
          system-defined maximum number of effective group ids,
          typically 16.  See the documentation for *note getgroups():
          204c. for cases where it may not return the same group list
          set by calling setgroups().

 -- Function: os.setpgrp ()

     Call the system call ‘setpgrp()’ or ‘setpgrp(0, 0)’ depending on
     which version is implemented (if any).  See the Unix manual for the
     semantics.

     *note Availability: 1491.: Unix.

 -- Function: os.setpgid (pid, pgrp)

     Call the system call ‘setpgid()’ to set the process group id of the
     process with id `pid' to the process group with id `pgrp'.  See the
     Unix manual for the semantics.

     *note Availability: 1491.: Unix.

 -- Function: os.setpriority (which, who, priority)

     Set program scheduling priority.  The value `which' is one of *note
     PRIO_PROCESS: 2054, *note PRIO_PGRP: 2055, or *note PRIO_USER:
     2056, and `who' is interpreted relative to `which' (a process
     identifier for *note PRIO_PROCESS: 2054, process group identifier
     for *note PRIO_PGRP: 2055, and a user ID for *note PRIO_USER:
     2056.).  A zero value for `who' denotes (respectively) the calling
     process, the process group of the calling process, or the real user
     ID of the calling process.  `priority' is a value in the range -20
     to 19.  The default priority is 0; lower priorities cause more
     favorable scheduling.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: os.setregid (rgid, egid)

     Set the current process’s real and effective group ids.

     *note Availability: 1491.: Unix.

 -- Function: os.setresgid (rgid, egid, sgid)

     Set the current process’s real, effective, and saved group ids.

     *note Availability: 1491.: Unix.

     New in version 3.2.

 -- Function: os.setresuid (ruid, euid, suid)

     Set the current process’s real, effective, and saved user ids.

     *note Availability: 1491.: Unix.

     New in version 3.2.

 -- Function: os.setreuid (ruid, euid)

     Set the current process’s real and effective user ids.

     *note Availability: 1491.: Unix.

 -- Function: os.getsid (pid)

     Call the system call ‘getsid()’.  See the Unix manual for the
     semantics.

     *note Availability: 1491.: Unix.

 -- Function: os.setsid ()

     Call the system call ‘setsid()’.  See the Unix manual for the
     semantics.

     *note Availability: 1491.: Unix.

 -- Function: os.setuid (uid)

     Set the current process’s user id.

     *note Availability: 1491.: Unix.

 -- Function: os.strerror (code)

     Return the error message corresponding to the error code in `code'.
     On platforms where ‘strerror()’ returns ‘NULL’ when given an
     unknown error number, *note ValueError: 16d. is raised.

 -- Data: os.supports_bytes_environ

     ‘True’ if the native OS type of the environment is bytes (eg.
     ‘False’ on Windows).

     New in version 3.2.

 -- Function: os.umask (mask)

     Set the current numeric umask and return the previous umask.

 -- Function: os.uname ()

     Returns information identifying the current operating system.  The
     return value is an object with five attributes:

        * ‘sysname’ - operating system name

        * ‘nodename’ - name of machine on network
          (implementation-defined)

        * ‘release’ - operating system release

        * ‘version’ - operating system version

        * ‘machine’ - hardware identifier

     For backwards compatibility, this object is also iterable, behaving
     like a five-tuple containing ‘sysname’, ‘nodename’, ‘release’,
     ‘version’, and ‘machine’ in that order.

     Some systems truncate ‘nodename’ to 8 characters or to the leading
     component; a better way to get the hostname is *note
     socket.gethostname(): 2064. or even
     ‘socket.gethostbyaddr(socket.gethostname())’.

     *note Availability: 1491.: recent flavors of Unix.

     Changed in version 3.3: Return type changed from a tuple to a
     tuple-like object with named attributes.

 -- Function: os.unsetenv (key)

     Unset (delete) the environment variable named `key'.  Such changes
     to the environment affect subprocesses started with *note
     os.system(): e86, *note popen(): 3cb. or *note fork(): a42. and
     *note execv(): 2058.

     Deletion of items in ‘os.environ’ is automatically translated into
     a corresponding call to *note unsetenv(): 1cc.; however, calls to
     *note unsetenv(): 1cc. don’t update ‘os.environ’, so it is actually
     preferable to delete items of ‘os.environ’.

     Raises an *note auditing event: fa1. ‘os.unsetenv’ with argument
     ‘key’.

     Changed in version 3.9: The function is now always available and is
     also available on Windows.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0584

   (2) https://www.python.org/dev/peps/pep-0584


File: python.info,  Node: File Object Creation,  Next: File Descriptor Operations,  Prev: Process Parameters,  Up: os — Miscellaneous operating system interfaces

5.16.1.3 File Object Creation
.............................

These functions create new *note file objects: c14.  (See also *note
open(): 758. for opening file descriptors.)

 -- Function: os.fdopen (fd, *args, **kwargs)

     Return an open file object connected to the file descriptor `fd'.
     This is an alias of the *note open(): 16f. built-in function and
     accepts the same arguments.  The only difference is that the first
     argument of *note fdopen(): 1564. must always be an integer.


File: python.info,  Node: File Descriptor Operations,  Next: Files and Directories,  Prev: File Object Creation,  Up: os — Miscellaneous operating system interfaces

5.16.1.4 File Descriptor Operations
...................................

These functions operate on I/O streams referenced using file
descriptors.

File descriptors are small integers corresponding to a file that has
been opened by the current process.  For example, standard input is
usually file descriptor 0, standard output is 1, and standard error is
2.  Further files opened by a process will then be assigned 3, 4, 5, and
so forth.  The name “file descriptor” is slightly deceptive; on Unix
platforms, sockets and pipes are also referenced by file descriptors.

The *note fileno(): 2069. method can be used to obtain the file
descriptor associated with a *note file object: c14. when required.
Note that using the file descriptor directly will bypass the file object
methods, ignoring aspects such as internal buffering of data.

 -- Function: os.close (fd)

     Close file descriptor `fd'.

          Note: This function is intended for low-level I/O and must be
          applied to a file descriptor as returned by *note os.open():
          758. or *note pipe(): 206a.  To close a “file object” returned
          by the built-in function *note open(): 16f. or by *note
          popen(): 3cb. or *note fdopen(): 1564, use its *note close():
          1147. method.

 -- Function: os.closerange (fd_low, fd_high)

     Close all file descriptors from `fd_low' (inclusive) to `fd_high'
     (exclusive), ignoring errors.  Equivalent to (but much faster
     than):

          for fd in range(fd_low, fd_high):
              try:
                  os.close(fd)
              except OSError:
                  pass

 -- Function: os.copy_file_range (src, dst, count, offset_src=None,
          offset_dst=None)

     Copy `count' bytes from file descriptor `src', starting from offset
     `offset_src', to file descriptor `dst', starting from offset
     `offset_dst'.  If `offset_src' is None, then `src' is read from the
     current position; respectively for `offset_dst'.  The files pointed
     by `src' and `dst' must reside in the same filesystem, otherwise an
     *note OSError: 304. is raised with *note errno: 184b. set to *note
     errno.EXDEV: 206d.

     This copy is done without the additional cost of transferring data
     from the kernel to user space and then back into the kernel.
     Additionally, some filesystems could implement extra optimizations.
     The copy is done as if both files are opened as binary.

     The return value is the amount of bytes copied.  This could be less
     than the amount requested.

     *note Availability: 1491.: Linux kernel >= 4.5 or glibc >= 2.27.

     New in version 3.8.

 -- Function: os.device_encoding (fd)

     Return a string describing the encoding of the device associated
     with `fd' if it is connected to a terminal; else return *note None:
     203.

 -- Function: os.dup (fd)

     Return a duplicate of file descriptor `fd'.  The new file
     descriptor is *note non-inheritable: 8e7.

     On Windows, when duplicating a standard stream (0: stdin, 1:
     stdout, 2: stderr), the new file descriptor is *note inheritable:
     8e7.

     Changed in version 3.4: The new file descriptor is now
     non-inheritable.

 -- Function: os.dup2 (fd, fd2, inheritable=True)

     Duplicate file descriptor `fd' to `fd2', closing the latter first
     if necessary.  Return `fd2'.  The new file descriptor is *note
     inheritable: 8e7. by default or non-inheritable if `inheritable' is
     ‘False’.

     Changed in version 3.4: Add the optional `inheritable' parameter.

     Changed in version 3.7: Return `fd2' on success.  Previously,
     ‘None’ was always returned.

 -- Function: os.fchmod (fd, mode)

     Change the mode of the file given by `fd' to the numeric `mode'.
     See the docs for *note chmod(): b0f. for possible values of `mode'.
     As of Python 3.3, this is equivalent to ‘os.chmod(fd, mode)’.

     Raises an *note auditing event: fa1. ‘os.chmod’ with arguments
     ‘path’, ‘mode’, ‘dir_fd’.

     *note Availability: 1491.: Unix.

 -- Function: os.fchown (fd, uid, gid)

     Change the owner and group id of the file given by `fd' to the
     numeric `uid' and `gid'.  To leave one of the ids unchanged, set it
     to -1.  See *note chown(): b10.  As of Python 3.3, this is
     equivalent to ‘os.chown(fd, uid, gid)’.

     Raises an *note auditing event: fa1. ‘os.chown’ with arguments
     ‘path’, ‘uid’, ‘gid’, ‘dir_fd’.

     *note Availability: 1491.: Unix.

 -- Function: os.fdatasync (fd)

     Force write of file with filedescriptor `fd' to disk.  Does not
     force update of metadata.

     *note Availability: 1491.: Unix.

          Note: This function is not available on MacOS.

 -- Function: os.fpathconf (fd, name)

     Return system configuration information relevant to an open file.
     `name' specifies the configuration value to retrieve; it may be a
     string which is the name of a defined system value; these names are
     specified in a number of standards (POSIX.1, Unix 95, Unix 98, and
     others).  Some platforms define additional names as well.  The
     names known to the host operating system are given in the
     ‘pathconf_names’ dictionary.  For configuration variables not
     included in that mapping, passing an integer for `name' is also
     accepted.

     If `name' is a string and is not known, *note ValueError: 16d. is
     raised.  If a specific value for `name' is not supported by the
     host system, even if it is included in ‘pathconf_names’, an *note
     OSError: 304. is raised with *note errno.EINVAL: 1104. for the
     error number.

     As of Python 3.3, this is equivalent to ‘os.pathconf(fd, name)’.

     *note Availability: 1491.: Unix.

 -- Function: os.fstat (fd)

     Get the status of the file descriptor `fd'.  Return a *note
     stat_result: 11bf. object.

     As of Python 3.3, this is equivalent to ‘os.stat(fd)’.

     See also
     ........

     The *note stat(): 321. function.

 -- Function: os.fstatvfs (fd)

     Return information about the filesystem containing the file
     associated with file descriptor `fd', like *note statvfs(): b1e.
     As of Python 3.3, this is equivalent to ‘os.statvfs(fd)’.

     *note Availability: 1491.: Unix.

 -- Function: os.fsync (fd)

     Force write of file with filedescriptor `fd' to disk.  On Unix,
     this calls the native ‘fsync()’ function; on Windows, the MS
     ‘_commit()’ function.

     If you’re starting with a buffered Python *note file object: c14.
     `f', first do ‘f.flush()’, and then do ‘os.fsync(f.fileno())’, to
     ensure that all internal buffers associated with `f' are written to
     disk.

     *note Availability: 1491.: Unix, Windows.

 -- Function: os.ftruncate (fd, length)

     Truncate the file corresponding to file descriptor `fd', so that it
     is at most `length' bytes in size.  As of Python 3.3, this is
     equivalent to ‘os.truncate(fd, length)’.

     Raises an *note auditing event: fa1. ‘os.truncate’ with arguments
     ‘fd’, ‘length’.

     *note Availability: 1491.: Unix, Windows.

     Changed in version 3.5: Added support for Windows

 -- Function: os.get_blocking (fd)

     Get the blocking mode of the file descriptor: ‘False’ if the *note
     O_NONBLOCK: 812. flag is set, ‘True’ if the flag is cleared.

     See also *note set_blocking(): 811. and *note
     socket.socket.setblocking(): 206f.

     *note Availability: 1491.: Unix.

     New in version 3.5.

 -- Function: os.isatty (fd)

     Return ‘True’ if the file descriptor `fd' is open and connected to
     a tty(-like) device, else ‘False’.

 -- Function: os.lockf (fd, cmd, len)

     Apply, test or remove a POSIX lock on an open file descriptor.
     `fd' is an open file descriptor.  `cmd' specifies the command to
     use - one of *note F_LOCK: 2070, *note F_TLOCK: 2071, *note
     F_ULOCK: 2072. or *note F_TEST: 2073.  `len' specifies the section
     of the file to lock.

     Raises an *note auditing event: fa1. ‘os.lockf’ with arguments
     ‘fd’, ‘cmd’, ‘len’.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Data: os.F_LOCK
 -- Data: os.F_TLOCK
 -- Data: os.F_ULOCK
 -- Data: os.F_TEST

     Flags that specify what action *note lockf(): b35. will take.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: os.lseek (fd, pos, how)

     Set the current position of file descriptor `fd' to position `pos',
     modified by `how': *note SEEK_SET: e59. or ‘0’ to set the position
     relative to the beginning of the file; *note SEEK_CUR: e5a. or ‘1’
     to set it relative to the current position; *note SEEK_END: e5b. or
     ‘2’ to set it relative to the end of the file.  Return the new
     cursor position in bytes, starting from the beginning.

 -- Data: os.SEEK_SET
 -- Data: os.SEEK_CUR
 -- Data: os.SEEK_END

     Parameters to the *note lseek(): b39. function.  Their values are
     0, 1, and 2, respectively.

     New in version 3.3: Some operating systems could support additional
     values, like ‘os.SEEK_HOLE’ or ‘os.SEEK_DATA’.

 -- Function: os.open (path, flags, mode=0o777, *, dir_fd=None)

     Open the file `path' and set various flags according to `flags' and
     possibly its mode according to `mode'.  When computing `mode', the
     current umask value is first masked out.  Return the file
     descriptor for the newly opened file.  The new file descriptor is
     *note non-inheritable: 8e7.

     For a description of the flag and mode values, see the C run-time
     documentation; flag constants (like *note O_RDONLY: 2074. and *note
     O_WRONLY: 2075.) are defined in the *note os: c4. module.  In
     particular, on Windows adding *note O_BINARY: 2076. is needed to
     open files in binary mode.

     This function can support *note paths relative to directory
     descriptors: b0b. with the `dir_fd' parameter.

     Raises an *note auditing event: fa1. ‘open’ with arguments ‘path’,
     ‘mode’, ‘flags’.

     Changed in version 3.4: The new file descriptor is now
     non-inheritable.

          Note: This function is intended for low-level I/O. For normal
          usage, use the built-in function *note open(): 16f, which
          returns a *note file object: c14. with ‘read()’ and ‘write()’
          methods (and many more).  To wrap a file descriptor in a file
          object, use *note fdopen(): 1564.

     New in version 3.3: The `dir_fd' argument.

     Changed in version 3.5: If the system call is interrupted and the
     signal handler does not raise an exception, the function now
     retries the system call instead of raising an *note
     InterruptedError: 74c. exception (see PEP 475(1) for the
     rationale).

     Changed in version 3.6: Accepts a *note path-like object: 472.

The following constants are options for the `flags' parameter to the
*note open(): 758. function.  They can be combined using the bitwise OR
operator ‘|’.  Some of them are not available on all platforms.  For
descriptions of their availability and use, consult the ‘open(2)’ manual
page on Unix or the MSDN(2) on Windows.

 -- Data: os.O_RDONLY
 -- Data: os.O_WRONLY
 -- Data: os.O_RDWR
 -- Data: os.O_APPEND
 -- Data: os.O_CREAT
 -- Data: os.O_EXCL
 -- Data: os.O_TRUNC

     The above constants are available on Unix and Windows.

 -- Data: os.O_DSYNC
 -- Data: os.O_RSYNC
 -- Data: os.O_SYNC
 -- Data: os.O_NDELAY
 -- Data: os.O_NONBLOCK
 -- Data: os.O_NOCTTY
 -- Data: os.O_CLOEXEC

     The above constants are only available on Unix.

     Changed in version 3.3: Add *note O_CLOEXEC: aa2. constant.

 -- Data: os.O_BINARY
 -- Data: os.O_NOINHERIT
 -- Data: os.O_SHORT_LIVED
 -- Data: os.O_TEMPORARY
 -- Data: os.O_RANDOM
 -- Data: os.O_SEQUENTIAL
 -- Data: os.O_TEXT

     The above constants are only available on Windows.

 -- Data: os.O_ASYNC
 -- Data: os.O_DIRECT
 -- Data: os.O_DIRECTORY
 -- Data: os.O_NOFOLLOW
 -- Data: os.O_NOATIME
 -- Data: os.O_PATH
 -- Data: os.O_TMPFILE
 -- Data: os.O_SHLOCK
 -- Data: os.O_EXLOCK

     The above constants are extensions and not present if they are not
     defined by the C library.

     Changed in version 3.4: Add *note O_PATH: 96e. on systems that
     support it.  Add *note O_TMPFILE: 96f, only available on Linux
     Kernel 3.11 or newer.

 -- Function: os.openpty ()

     Open a new pseudo-terminal pair.  Return a pair of file descriptors
     ‘(master, slave)’ for the pty and the tty, respectively.  The new
     file descriptors are *note non-inheritable: 8e7.  For a (slightly)
     more portable approach, use the *note pty: d5. module.

     *note Availability: 1491.: some flavors of Unix.

     Changed in version 3.4: The new file descriptors are now
     non-inheritable.

 -- Function: os.pipe ()

     Create a pipe.  Return a pair of file descriptors ‘(r, w)’ usable
     for reading and writing, respectively.  The new file descriptor is
     *note non-inheritable: 8e7.

     *note Availability: 1491.: Unix, Windows.

     Changed in version 3.4: The new file descriptors are now
     non-inheritable.

 -- Function: os.pipe2 (flags)

     Create a pipe with `flags' set atomically.  `flags' can be
     constructed by ORing together one or more of these values: *note
     O_NONBLOCK: 812, *note O_CLOEXEC: aa2.  Return a pair of file
     descriptors ‘(r, w)’ usable for reading and writing, respectively.

     *note Availability: 1491.: some flavors of Unix.

     New in version 3.3.

 -- Function: os.posix_fallocate (fd, offset, len)

     Ensures that enough disk space is allocated for the file specified
     by `fd' starting from `offset' and continuing for `len' bytes.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: os.posix_fadvise (fd, offset, len, advice)

     Announces an intention to access data in a specific pattern thus
     allowing the kernel to make optimizations.  The advice applies to
     the region of the file specified by `fd' starting at `offset' and
     continuing for `len' bytes.  `advice' is one of *note
     POSIX_FADV_NORMAL: 208c, *note POSIX_FADV_SEQUENTIAL: 208d, *note
     POSIX_FADV_RANDOM: 208e, *note POSIX_FADV_NOREUSE: 208f, *note
     POSIX_FADV_WILLNEED: 2090. or *note POSIX_FADV_DONTNEED: 2091.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Data: os.POSIX_FADV_NORMAL
 -- Data: os.POSIX_FADV_SEQUENTIAL
 -- Data: os.POSIX_FADV_RANDOM
 -- Data: os.POSIX_FADV_NOREUSE
 -- Data: os.POSIX_FADV_WILLNEED
 -- Data: os.POSIX_FADV_DONTNEED

     Flags that can be used in `advice' in *note posix_fadvise(): 759.
     that specify the access pattern that is likely to be used.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: os.pread (fd, n, offset)

     Read at most `n' bytes from file descriptor `fd' at a position of
     `offset', leaving the file offset unchanged.

     Return a bytestring containing the bytes read.  If the end of the
     file referred to by `fd' has been reached, an empty bytes object is
     returned.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: os.preadv (fd, buffers, offset, flags=0)

     Read from a file descriptor `fd' at a position of `offset' into
     mutable *note bytes-like objects: 6df. `buffers', leaving the file
     offset unchanged.  Transfer data into each buffer until it is full
     and then move on to the next buffer in the sequence to hold the
     rest of the data.

     The flags argument contains a bitwise OR of zero or more of the
     following flags:

        - *note RWF_HIPRI: 2092.

        - *note RWF_NOWAIT: 2093.

     Return the total number of bytes actually read which can be less
     than the total capacity of all the objects.

     The operating system may set a limit (*note sysconf(): 2094. value
     ‘'SC_IOV_MAX'’) on the number of buffers that can be used.

     Combine the functionality of *note os.readv(): 4bf. and *note
     os.pread(): 4c0.

     *note Availability: 1491.: Linux 2.6.30 and newer, FreeBSD 6.0 and
     newer, OpenBSD 2.7 and newer, AIX 7.1 and newer.  Using flags
     requires Linux 4.6 or newer.

     New in version 3.7.

 -- Data: os.RWF_NOWAIT

     Do not wait for data which is not immediately available.  If this
     flag is specified, the system call will return instantly if it
     would have to read data from the backing storage or wait for a
     lock.

     If some data was successfully read, it will return the number of
     bytes read.  If no bytes were read, it will return ‘-1’ and set
     errno to *note errno.EAGAIN: 2095.

     *note Availability: 1491.: Linux 4.14 and newer.

     New in version 3.7.

 -- Data: os.RWF_HIPRI

     High priority read/write.  Allows block-based filesystems to use
     polling of the device, which provides lower latency, but may use
     additional resources.

     Currently, on Linux, this feature is usable only on a file
     descriptor opened using the *note O_DIRECT: 2087. flag.

     *note Availability: 1491.: Linux 4.6 and newer.

     New in version 3.7.

 -- Function: os.pwrite (fd, str, offset)

     Write the bytestring in `str' to file descriptor `fd' at position
     of `offset', leaving the file offset unchanged.

     Return the number of bytes actually written.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: os.pwritev (fd, buffers, offset, flags=0)

     Write the `buffers' contents to file descriptor `fd' at a offset
     `offset', leaving the file offset unchanged.  `buffers' must be a
     sequence of *note bytes-like objects: 6df.  Buffers are processed
     in array order.  Entire contents of the first buffer is written
     before proceeding to the second, and so on.

     The flags argument contains a bitwise OR of zero or more of the
     following flags:

        - *note RWF_DSYNC: 2096.

        - *note RWF_SYNC: 2097.

     Return the total number of bytes actually written.

     The operating system may set a limit (*note sysconf(): 2094. value
     ‘'SC_IOV_MAX'’) on the number of buffers that can be used.

     Combine the functionality of *note os.writev(): 4c2. and *note
     os.pwrite(): 4c3.

     *note Availability: 1491.: Linux 2.6.30 and newer, FreeBSD 6.0 and
     newer, OpenBSD 2.7 and newer, AIX 7.1 and newer.  Using flags
     requires Linux 4.7 or newer.

     New in version 3.7.

 -- Data: os.RWF_DSYNC

     Provide a per-write equivalent of the *note O_DSYNC: 207b.
     ‘open(2)’ flag.  This flag effect applies only to the data range
     written by the system call.

     *note Availability: 1491.: Linux 4.7 and newer.

     New in version 3.7.

 -- Data: os.RWF_SYNC

     Provide a per-write equivalent of the *note O_SYNC: 207d. ‘open(2)’
     flag.  This flag effect applies only to the data range written by
     the system call.

     *note Availability: 1491.: Linux 4.7 and newer.

     New in version 3.7.

 -- Function: os.read (fd, n)

     Read at most `n' bytes from file descriptor `fd'.

     Return a bytestring containing the bytes read.  If the end of the
     file referred to by `fd' has been reached, an empty bytes object is
     returned.

          Note: This function is intended for low-level I/O and must be
          applied to a file descriptor as returned by *note os.open():
          758. or *note pipe(): 206a.  To read a “file object” returned
          by the built-in function *note open(): 16f. or by *note
          popen(): 3cb. or *note fdopen(): 1564, or *note sys.stdin:
          41e, use its ‘read()’ or ‘readline()’ methods.

     Changed in version 3.5: If the system call is interrupted and the
     signal handler does not raise an exception, the function now
     retries the system call instead of raising an *note
     InterruptedError: 74c. exception (see PEP 475(3) for the
     rationale).

 -- Function: os.sendfile (out_fd, in_fd, offset, count)

 -- Function: os.sendfile (out_fd, in_fd, offset, count, headers=(),
          trailers=(), flags=0)

     Copy `count' bytes from file descriptor `in_fd' to file descriptor
     `out_fd' starting at `offset'.  Return the number of bytes sent.
     When EOF is reached return ‘0’.

     The first function notation is supported by all platforms that
     define *note sendfile(): 461.

     On Linux, if `offset' is given as ‘None’, the bytes are read from
     the current position of `in_fd' and the position of `in_fd' is
     updated.

     The second case may be used on macOS and FreeBSD where `headers'
     and `trailers' are arbitrary sequences of buffers that are written
     before and after the data from `in_fd' is written.  It returns the
     same as the first case.

     On macOS and FreeBSD, a value of ‘0’ for `count' specifies to send
     until the end of `in_fd' is reached.

     All platforms support sockets as `out_fd' file descriptor, and some
     platforms allow other types (e.g.  regular file, pipe) as well.

     Cross-platform applications should not use `headers', `trailers'
     and `flags' arguments.

     *note Availability: 1491.: Unix.

          Note: For a higher-level wrapper of *note sendfile(): 461, see
          *note socket.socket.sendfile(): 839.

     New in version 3.3.

     Changed in version 3.9: Parameters `out' and `in' was renamed to
     `out_fd' and `in_fd'.

 -- Function: os.set_blocking (fd, blocking)

     Set the blocking mode of the specified file descriptor.  Set the
     *note O_NONBLOCK: 812. flag if blocking is ‘False’, clear the flag
     otherwise.

     See also *note get_blocking(): 810. and *note
     socket.socket.setblocking(): 206f.

     *note Availability: 1491.: Unix.

     New in version 3.5.

 -- Data: os.SF_NODISKIO
 -- Data: os.SF_MNOWAIT
 -- Data: os.SF_SYNC

     Parameters to the *note sendfile(): 461. function, if the
     implementation supports them.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: os.readv (fd, buffers)

     Read from a file descriptor `fd' into a number of mutable *note
     bytes-like objects: 6df. `buffers'.  Transfer data into each buffer
     until it is full and then move on to the next buffer in the
     sequence to hold the rest of the data.

     Return the total number of bytes actually read which can be less
     than the total capacity of all the objects.

     The operating system may set a limit (*note sysconf(): 2094. value
     ‘'SC_IOV_MAX'’) on the number of buffers that can be used.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: os.tcgetpgrp (fd)

     Return the process group associated with the terminal given by `fd'
     (an open file descriptor as returned by *note os.open(): 758.).

     *note Availability: 1491.: Unix.

 -- Function: os.tcsetpgrp (fd, pg)

     Set the process group associated with the terminal given by `fd'
     (an open file descriptor as returned by *note os.open(): 758.) to
     `pg'.

     *note Availability: 1491.: Unix.

 -- Function: os.ttyname (fd)

     Return a string which specifies the terminal device associated with
     file descriptor `fd'.  If `fd' is not associated with a terminal
     device, an exception is raised.

     *note Availability: 1491.: Unix.

 -- Function: os.write (fd, str)

     Write the bytestring in `str' to file descriptor `fd'.

     Return the number of bytes actually written.

          Note: This function is intended for low-level I/O and must be
          applied to a file descriptor as returned by *note os.open():
          758. or *note pipe(): 206a.  To write a “file object” returned
          by the built-in function *note open(): 16f. or by *note
          popen(): 3cb. or *note fdopen(): 1564, or *note sys.stdout:
          41f. or *note sys.stderr: 1ea, use its ‘write()’ method.

     Changed in version 3.5: If the system call is interrupted and the
     signal handler does not raise an exception, the function now
     retries the system call instead of raising an *note
     InterruptedError: 74c. exception (see PEP 475(4) for the
     rationale).

 -- Function: os.writev (fd, buffers)

     Write the contents of `buffers' to file descriptor `fd'.  `buffers'
     must be a sequence of *note bytes-like objects: 6df.  Buffers are
     processed in array order.  Entire contents of the first buffer is
     written before proceeding to the second, and so on.

     Returns the total number of bytes actually written.

     The operating system may set a limit (*note sysconf(): 2094. value
     ‘'SC_IOV_MAX'’) on the number of buffers that can be used.

     *note Availability: 1491.: Unix.

     New in version 3.3.

* Menu:

* Querying the size of a terminal::
* Inheritance of File Descriptors::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0475

   (2) https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx

   (3) https://www.python.org/dev/peps/pep-0475

   (4) https://www.python.org/dev/peps/pep-0475


File: python.info,  Node: Querying the size of a terminal,  Next: Inheritance of File Descriptors,  Up: File Descriptor Operations

5.16.1.5 Querying the size of a terminal
........................................

New in version 3.3.

 -- Function: os.get_terminal_size (fd=STDOUT_FILENO)

     Return the size of the terminal window as ‘(columns, lines)’, tuple
     of type *note terminal_size: 1dfa.

     The optional argument ‘fd’ (default ‘STDOUT_FILENO’, or standard
     output) specifies which file descriptor should be queried.

     If the file descriptor is not connected to a terminal, an *note
     OSError: 304. is raised.

     *note shutil.get_terminal_size(): b25. is the high-level function
     which should normally be used, ‘os.get_terminal_size’ is the
     low-level implementation.

     *note Availability: 1491.: Unix, Windows.

 -- Class: os.terminal_size

     A subclass of tuple, holding ‘(columns, lines)’ of the terminal
     window size.

      -- Attribute: columns

          Width of the terminal window in characters.

      -- Attribute: lines

          Height of the terminal window in characters.


File: python.info,  Node: Inheritance of File Descriptors,  Prev: Querying the size of a terminal,  Up: File Descriptor Operations

5.16.1.6 Inheritance of File Descriptors
........................................

New in version 3.4.

A file descriptor has an “inheritable” flag which indicates if the file
descriptor can be inherited by child processes.  Since Python 3.4, file
descriptors created by Python are non-inheritable by default.

On UNIX, non-inheritable file descriptors are closed in child processes
at the execution of a new program, other file descriptors are inherited.

On Windows, non-inheritable handles and file descriptors are closed in
child processes, except for standard streams (file descriptors 0, 1 and
2: stdin, stdout and stderr), which are always inherited.  Using *note
spawn*: 20a3. functions, all inheritable handles and all inheritable
file descriptors are inherited.  Using the *note subprocess: f9. module,
all file descriptors except standard streams are closed, and inheritable
handles are only inherited if the `close_fds' parameter is ‘False’.

 -- Function: os.get_inheritable (fd)

     Get the “inheritable” flag of the specified file descriptor (a
     boolean).

 -- Function: os.set_inheritable (fd, inheritable)

     Set the “inheritable” flag of the specified file descriptor.

 -- Function: os.get_handle_inheritable (handle)

     Get the “inheritable” flag of the specified handle (a boolean).

     *note Availability: 1491.: Windows.

 -- Function: os.set_handle_inheritable (handle, inheritable)

     Set the “inheritable” flag of the specified handle.

     *note Availability: 1491.: Windows.


File: python.info,  Node: Files and Directories,  Next: Process Management,  Prev: File Descriptor Operations,  Up: os — Miscellaneous operating system interfaces

5.16.1.7 Files and Directories
..............................

On some Unix platforms, many of these functions support one or more of
these features:

   * `specifying a file descriptor:' Normally the `path' argument
     provided to functions in the *note os: c4. module must be a string
     specifying a file path.  However, some functions now alternatively
     accept an open file descriptor for their `path' argument.  The
     function will then operate on the file referred to by the
     descriptor.  (For POSIX systems, Python will call the variant of
     the function prefixed with ‘f’ (e.g.  call ‘fchdir’ instead of
     ‘chdir’).)

     You can check whether or not `path' can be specified as a file
     descriptor for a particular function on your platform using *note
     os.supports_fd: b1f.  If this functionality is unavailable, using
     it will raise a *note NotImplementedError: 704.

     If the function also supports `dir_fd' or `follow_symlinks'
     arguments, it’s an error to specify one of those when supplying
     `path' as a file descriptor.

   * `paths relative to directory descriptors:' If `dir_fd' is not
     ‘None’, it should be a file descriptor referring to a directory,
     and the path to operate on should be relative; path will then be
     relative to that directory.  If the path is absolute, `dir_fd' is
     ignored.  (For POSIX systems, Python will call the variant of the
     function with an ‘at’ suffix and possibly prefixed with ‘f’ (e.g.
     call ‘faccessat’ instead of ‘access’).

     You can check whether or not `dir_fd' is supported for a particular
     function on your platform using *note os.supports_dir_fd: b1a.  If
     it’s unavailable, using it will raise a *note NotImplementedError:
     704.

   * `not following symlinks:' If `follow_symlinks' is ‘False’, and the
     last element of the path to operate on is a symbolic link, the
     function will operate on the symbolic link itself rather than the
     file pointed to by the link.  (For POSIX systems, Python will call
     the ‘l...’ variant of the function.)

     You can check whether or not `follow_symlinks' is supported for a
     particular function on your platform using *note
     os.supports_follow_symlinks: 1de5.  If it’s unavailable, using it
     will raise a *note NotImplementedError: 704.

 -- Function: os.access (path, mode, *, dir_fd=None,
          effective_ids=False, follow_symlinks=True)

     Use the real uid/gid to test for access to `path'.  Note that most
     operations will use the effective uid/gid, therefore this routine
     can be used in a suid/sgid environment to test if the invoking user
     has the specified access to `path'.  `mode' should be *note F_OK:
     20a5. to test the existence of `path', or it can be the inclusive
     OR of one or more of *note R_OK: 20a6, *note W_OK: 20a7, and *note
     X_OK: 20a8. to test permissions.  Return *note True: 594. if access
     is allowed, *note False: 48f. if not.  See the Unix man page
     ‘access(2)’ for more information.

     This function can support specifying *note paths relative to
     directory descriptors: b0b. and *note not following symlinks: b0c.

     If `effective_ids' is ‘True’, *note access(): b0d. will perform its
     access checks using the effective uid/gid instead of the real
     uid/gid.  `effective_ids' may not be supported on your platform;
     you can check whether or not it is available using *note
     os.supports_effective_ids: b20.  If it is unavailable, using it
     will raise a *note NotImplementedError: 704.

          Note: Using *note access(): b0d. to check if a user is
          authorized to e.g.  open a file before actually doing so using
          *note open(): 16f. creates a security hole, because the user
          might exploit the short time interval between checking and
          opening the file to manipulate it.  It’s preferable to use
          *note EAFP: 20a9. techniques.  For example:

               if os.access("myfile", os.R_OK):
                   with open("myfile") as fp:
                       return fp.read()
               return "some default data"

          is better written as:

               try:
                   fp = open("myfile")
               except PermissionError:
                   return "some default data"
               else:
                   with fp:
                       return fp.read()

          Note: I/O operations may fail even when *note access(): b0d.
          indicates that they would succeed, particularly for operations
          on network filesystems which may have permissions semantics
          beyond the usual POSIX permission-bit model.

     Changed in version 3.3: Added the `dir_fd', `effective_ids', and
     `follow_symlinks' parameters.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Data: os.F_OK
 -- Data: os.R_OK
 -- Data: os.W_OK
 -- Data: os.X_OK

     Values to pass as the `mode' parameter of *note access(): b0d. to
     test the existence, readability, writability and executability of
     `path', respectively.

 -- Function: os.chdir (path)

     Change the current working directory to `path'.

     This function can support *note specifying a file descriptor: 4bc.
     The descriptor must refer to an opened directory, not an open file.

     This function can raise *note OSError: 304. and subclasses such as
     *note FileNotFoundError: 8ad, *note PermissionError: 6f6, and *note
     NotADirectoryError: a7b.

     Raises an *note auditing event: fa1. ‘os.chdir’ with argument
     ‘path’.

     New in version 3.3: Added support for specifying `path' as a file
     descriptor on some platforms.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.chflags (path, flags, *, follow_symlinks=True)

     Set the flags of `path' to the numeric `flags'.  `flags' may take a
     combination (bitwise OR) of the following values (as defined in the
     *note stat: f4. module):

        * *note stat.UF_NODUMP: 1d8b.

        * *note stat.UF_IMMUTABLE: 1d8c.

        * *note stat.UF_APPEND: 1d8d.

        * *note stat.UF_OPAQUE: 1d8e.

        * *note stat.UF_NOUNLINK: 1d8f.

        * *note stat.UF_COMPRESSED: 1d90.

        * *note stat.UF_HIDDEN: 1d91.

        * *note stat.SF_ARCHIVED: 1d92.

        * *note stat.SF_IMMUTABLE: 1d93.

        * *note stat.SF_APPEND: 1d94.

        * *note stat.SF_NOUNLINK: 1d95.

        * *note stat.SF_SNAPSHOT: 1d96.

     This function can support *note not following symlinks: b0c.

     Raises an *note auditing event: fa1. ‘os.chflags’ with arguments
     ‘path’, ‘flags’.

     *note Availability: 1491.: Unix.

     New in version 3.3: The `follow_symlinks' argument.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.chmod (path, mode, *, dir_fd=None,
          follow_symlinks=True)

     Change the mode of `path' to the numeric `mode'.  `mode' may take
     one of the following values (as defined in the *note stat: f4.
     module) or bitwise ORed combinations of them:

        * *note stat.S_ISUID: 1d78.

        * *note stat.S_ISGID: 1d79.

        * *note stat.S_ENFMT: 1d7b.

        * *note stat.S_ISVTX: 1d7c.

        * *note stat.S_IREAD: 1d88.

        * *note stat.S_IWRITE: 1d89.

        * *note stat.S_IEXEC: 1d8a.

        * *note stat.S_IRWXU: 1d7d.

        * *note stat.S_IRUSR: 1d7e.

        * *note stat.S_IWUSR: 1d7f.

        * *note stat.S_IXUSR: 1d80.

        * *note stat.S_IRWXG: 1d81.

        * *note stat.S_IRGRP: 1d82.

        * *note stat.S_IWGRP: 1d83.

        * *note stat.S_IXGRP: 1d7a.

        * *note stat.S_IRWXO: 1d84.

        * *note stat.S_IROTH: 1d85.

        * *note stat.S_IWOTH: 1d86.

        * *note stat.S_IXOTH: 1d87.

     This function can support *note specifying a file descriptor: 4bc,
     *note paths relative to directory descriptors: b0b. and *note not
     following symlinks: b0c.

          Note: Although Windows supports *note chmod(): b0f, you can
          only set the file’s read-only flag with it (via the
          ‘stat.S_IWRITE’ and ‘stat.S_IREAD’ constants or a
          corresponding integer value).  All other bits are ignored.

     Raises an *note auditing event: fa1. ‘os.chmod’ with arguments
     ‘path’, ‘mode’, ‘dir_fd’.

     New in version 3.3: Added support for specifying `path' as an open
     file descriptor, and the `dir_fd' and `follow_symlinks' arguments.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.chown (path, uid, gid, *, dir_fd=None,
          follow_symlinks=True)

     Change the owner and group id of `path' to the numeric `uid' and
     `gid'.  To leave one of the ids unchanged, set it to -1.

     This function can support *note specifying a file descriptor: 4bc,
     *note paths relative to directory descriptors: b0b. and *note not
     following symlinks: b0c.

     See *note shutil.chown(): b51. for a higher-level function that
     accepts names in addition to numeric ids.

     Raises an *note auditing event: fa1. ‘os.chown’ with arguments
     ‘path’, ‘uid’, ‘gid’, ‘dir_fd’.

     *note Availability: 1491.: Unix.

     New in version 3.3: Added support for specifying `path' as an open
     file descriptor, and the `dir_fd' and `follow_symlinks' arguments.

     Changed in version 3.6: Supports a *note path-like object: 472.

 -- Function: os.chroot (path)

     Change the root directory of the current process to `path'.

     *note Availability: 1491.: Unix.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.fchdir (fd)

     Change the current working directory to the directory represented
     by the file descriptor `fd'.  The descriptor must refer to an
     opened directory, not an open file.  As of Python 3.3, this is
     equivalent to ‘os.chdir(fd)’.

     Raises an *note auditing event: fa1. ‘os.chdir’ with argument
     ‘path’.

     *note Availability: 1491.: Unix.

 -- Function: os.getcwd ()

     Return a string representing the current working directory.

 -- Function: os.getcwdb ()

     Return a bytestring representing the current working directory.

     Changed in version 3.8: The function now uses the UTF-8 encoding on
     Windows, rather than the ANSI code page: see PEP 529(1) for the
     rationale.  The function is no longer deprecated on Windows.

 -- Function: os.lchflags (path, flags)

     Set the flags of `path' to the numeric `flags', like *note
     chflags(): b0e, but do not follow symbolic links.  As of Python
     3.3, this is equivalent to ‘os.chflags(path, flags,
     follow_symlinks=False)’.

     Raises an *note auditing event: fa1. ‘os.chflags’ with arguments
     ‘path’, ‘flags’.

     *note Availability: 1491.: Unix.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.lchmod (path, mode)

     Change the mode of `path' to the numeric `mode'.  If path is a
     symlink, this affects the symlink rather than the target.  See the
     docs for *note chmod(): b0f. for possible values of `mode'.  As of
     Python 3.3, this is equivalent to ‘os.chmod(path, mode,
     follow_symlinks=False)’.

     Raises an *note auditing event: fa1. ‘os.chmod’ with arguments
     ‘path’, ‘mode’, ‘dir_fd’.

     *note Availability: 1491.: Unix.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.lchown (path, uid, gid)

     Change the owner and group id of `path' to the numeric `uid' and
     `gid'.  This function will not follow symbolic links.  As of Python
     3.3, this is equivalent to ‘os.chown(path, uid, gid,
     follow_symlinks=False)’.

     Raises an *note auditing event: fa1. ‘os.chown’ with arguments
     ‘path’, ‘uid’, ‘gid’, ‘dir_fd’.

     *note Availability: 1491.: Unix.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.link (src, dst, *, src_dir_fd=None, dst_dir_fd=None,
          follow_symlinks=True)

     Create a hard link pointing to `src' named `dst'.

     This function can support specifying `src_dir_fd' and/or
     `dst_dir_fd' to supply *note paths relative to directory
     descriptors: b0b, and *note not following symlinks: b0c.

     Raises an *note auditing event: fa1. ‘os.link’ with arguments
     ‘src’, ‘dst’, ‘src_dir_fd’, ‘dst_dir_fd’.

     *note Availability: 1491.: Unix, Windows.

     Changed in version 3.2: Added Windows support.

     New in version 3.3: Added the `src_dir_fd', `dst_dir_fd', and
     `follow_symlinks' arguments.

     Changed in version 3.6: Accepts a *note path-like object: 472. for
     `src' and `dst'.

 -- Function: os.listdir (path='.')

     Return a list containing the names of the entries in the directory
     given by `path'.  The list is in arbitrary order, and does not
     include the special entries ‘'.'’ and ‘'..'’ even if they are
     present in the directory.  If a file is removed from or added to
     the directory during the call of this function, whether a name for
     that file be included is unspecified.

     `path' may be a *note path-like object: 472.  If `path' is of type
     ‘bytes’ (directly or indirectly through the *note PathLike: 5e6.
     interface), the filenames returned will also be of type ‘bytes’; in
     all other circumstances, they will be of type ‘str’.

     This function can also support *note specifying a file descriptor:
     4bc.; the file descriptor must refer to a directory.

     Raises an *note auditing event: fa1. ‘os.listdir’ with argument
     ‘path’.

          Note: To encode ‘str’ filenames to ‘bytes’, use *note
          fsencode(): 5ea.

     See also
     ........

     The *note scandir(): 389. function returns directory entries along
     with file attribute information, giving better performance for many
     common use cases.

     Changed in version 3.2: The `path' parameter became optional.

     New in version 3.3: Added support for specifying `path' as an open
     file descriptor.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.lstat (path, *, dir_fd=None)

     Perform the equivalent of an ‘lstat()’ system call on the given
     path.  Similar to *note stat(): 321, but does not follow symbolic
     links.  Return a *note stat_result: 11bf. object.

     On platforms that do not support symbolic links, this is an alias
     for *note stat(): 321.

     As of Python 3.3, this is equivalent to ‘os.stat(path,
     dir_fd=dir_fd, follow_symlinks=False)’.

     This function can also support *note paths relative to directory
     descriptors: b0b.

     See also
     ........

     The *note stat(): 321. function.

     Changed in version 3.2: Added support for Windows 6.0 (Vista)
     symbolic links.

     Changed in version 3.3: Added the `dir_fd' parameter.

     Changed in version 3.6: Accepts a *note path-like object: 472.

     Changed in version 3.8: On Windows, now opens reparse points that
     represent another path (name surrogates), including symbolic links
     and directory junctions.  Other kinds of reparse points are
     resolved by the operating system as for *note stat(): 321.

 -- Function: os.mkdir (path, mode=0o777, *, dir_fd=None)

     Create a directory named `path' with numeric mode `mode'.

     If the directory already exists, *note FileExistsError: a39. is
     raised.  On some systems, `mode' is ignored.  Where it is used, the
     current umask value is first masked out.  If bits other than the
     last 9 (i.e.  the last 3 digits of the octal representation of the
     `mode') are set, their meaning is platform-dependent.  On some
     platforms, they are ignored and you should call *note chmod(): b0f.
     explicitly to set them.

     This function can also support *note paths relative to directory
     descriptors: b0b.

     It is also possible to create temporary directories; see the *note
     tempfile: 103. module’s *note tempfile.mkdtemp(): 1dc5. function.

     Raises an *note auditing event: fa1. ‘os.mkdir’ with arguments
     ‘path’, ‘mode’, ‘dir_fd’.

     New in version 3.3: The `dir_fd' argument.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.makedirs (name, mode=0o777, exist_ok=False)

     Recursive directory creation function.  Like *note mkdir(): b12,
     but makes all intermediate-level directories needed to contain the
     leaf directory.

     The `mode' parameter is passed to *note mkdir(): b12. for creating
     the leaf directory; see *note the mkdir() description: 20ac. for
     how it is interpreted.  To set the file permission bits of any
     newly-created parent directories you can set the umask before
     invoking *note makedirs(): 4c4.  The file permission bits of
     existing parent directories are not changed.

     If `exist_ok' is ‘False’ (the default), an *note FileExistsError:
     a39. is raised if the target directory already exists.

          Note: *note makedirs(): 4c4. will become confused if the path
          elements to create include *note pardir: 20ad. (eg.  “..” on
          UNIX systems).

     This function handles UNC paths correctly.

     Raises an *note auditing event: fa1. ‘os.mkdir’ with arguments
     ‘path’, ‘mode’, ‘dir_fd’.

     New in version 3.2: The `exist_ok' parameter.

     Changed in version 3.4.1: Before Python 3.4.1, if `exist_ok' was
     ‘True’ and the directory existed, *note makedirs(): 4c4. would
     still raise an error if `mode' did not match the mode of the
     existing directory.  Since this behavior was impossible to
     implement safely, it was removed in Python 3.4.1.  See
     bpo-21082(2).

     Changed in version 3.6: Accepts a *note path-like object: 472.

     Changed in version 3.7: The `mode' argument no longer affects the
     file permission bits of newly-created intermediate-level
     directories.

 -- Function: os.mkfifo (path, mode=0o666, *, dir_fd=None)

     Create a FIFO (a named pipe) named `path' with numeric mode `mode'.
     The current umask value is first masked out from the mode.

     This function can also support *note paths relative to directory
     descriptors: b0b.

     FIFOs are pipes that can be accessed like regular files.  FIFOs
     exist until they are deleted (for example with *note os.unlink():
     b18.).  Generally, FIFOs are used as rendezvous between “client”
     and “server” type processes: the server opens the FIFO for reading,
     and the client opens it for writing.  Note that *note mkfifo():
     756. doesn’t open the FIFO — it just creates the rendezvous point.

     *note Availability: 1491.: Unix.

     New in version 3.3: The `dir_fd' argument.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.mknod (path, mode=0o600, device=0, *, dir_fd=None)

     Create a filesystem node (file, device special file or named pipe)
     named `path'.  `mode' specifies both the permissions to use and the
     type of node to be created, being combined (bitwise OR) with one of
     ‘stat.S_IFREG’, ‘stat.S_IFCHR’, ‘stat.S_IFBLK’, and ‘stat.S_IFIFO’
     (those constants are available in *note stat: f4.).  For
     ‘stat.S_IFCHR’ and ‘stat.S_IFBLK’, `device' defines the newly
     created device special file (probably using *note os.makedev():
     20ae.), otherwise it is ignored.

     This function can also support *note paths relative to directory
     descriptors: b0b.

     *note Availability: 1491.: Unix.

     New in version 3.3: The `dir_fd' argument.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.major (device)

     Extract the device major number from a raw device number (usually
     the ‘st_dev’ or ‘st_rdev’ field from ‘stat’).

 -- Function: os.minor (device)

     Extract the device minor number from a raw device number (usually
     the ‘st_dev’ or ‘st_rdev’ field from ‘stat’).

 -- Function: os.makedev (major, minor)

     Compose a raw device number from the major and minor device
     numbers.

 -- Function: os.pathconf (path, name)

     Return system configuration information relevant to a named file.
     `name' specifies the configuration value to retrieve; it may be a
     string which is the name of a defined system value; these names are
     specified in a number of standards (POSIX.1, Unix 95, Unix 98, and
     others).  Some platforms define additional names as well.  The
     names known to the host operating system are given in the
     ‘pathconf_names’ dictionary.  For configuration variables not
     included in that mapping, passing an integer for `name' is also
     accepted.

     If `name' is a string and is not known, *note ValueError: 16d. is
     raised.  If a specific value for `name' is not supported by the
     host system, even if it is included in ‘pathconf_names’, an *note
     OSError: 304. is raised with *note errno.EINVAL: 1104. for the
     error number.

     This function can support *note specifying a file descriptor: 4bc.

     *note Availability: 1491.: Unix.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Data: os.pathconf_names

     Dictionary mapping names accepted by *note pathconf(): b1d. and
     *note fpathconf(): 206e. to the integer values defined for those
     names by the host operating system.  This can be used to determine
     the set of names known to the system.

     *note Availability: 1491.: Unix.

 -- Function: os.readlink (path, *, dir_fd=None)

     Return a string representing the path to which the symbolic link
     points.  The result may be either an absolute or relative pathname;
     if it is relative, it may be converted to an absolute pathname
     using ‘os.path.join(os.path.dirname(path), result)’.

     If the `path' is a string object (directly or indirectly through a
     *note PathLike: 5e6. interface), the result will also be a string
     object, and the call may raise a UnicodeDecodeError.  If the `path'
     is a bytes object (direct or indirectly), the result will be a
     bytes object.

     This function can also support *note paths relative to directory
     descriptors: b0b.

     When trying to resolve a path that may contain links, use *note
     realpath(): 32d. to properly handle recursion and platform
     differences.

     *note Availability: 1491.: Unix, Windows.

     Changed in version 3.2: Added support for Windows 6.0 (Vista)
     symbolic links.

     New in version 3.3: The `dir_fd' argument.

     Changed in version 3.6: Accepts a *note path-like object: 472. on
     Unix.

     Changed in version 3.8: Accepts a *note path-like object: 472. and
     a bytes object on Windows.

     Changed in version 3.8: Added support for directory junctions, and
     changed to return the substitution path (which typically includes
     ‘\\?\’ prefix) rather than the optional “print name” field that was
     previously returned.

 -- Function: os.remove (path, *, dir_fd=None)

     Remove (delete) the file `path'.  If `path' is a directory, an
     *note IsADirectoryError: a7a. is raised.  Use *note rmdir(): b16.
     to remove directories.  If the file does not exist, a *note
     FileNotFoundError: 8ad. is raised.

     This function can support *note paths relative to directory
     descriptors: b0b.

     On Windows, attempting to remove a file that is in use causes an
     exception to be raised; on Unix, the directory entry is removed but
     the storage allocated to the file is not made available until the
     original file is no longer in use.

     This function is semantically identical to *note unlink(): b18.

     Raises an *note auditing event: fa1. ‘os.remove’ with arguments
     ‘path’, ‘dir_fd’.

     New in version 3.3: The `dir_fd' argument.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.removedirs (name)

     Remove directories recursively.  Works like *note rmdir(): b16.
     except that, if the leaf directory is successfully removed, *note
     removedirs(): 20b2. tries to successively remove every parent
     directory mentioned in `path' until an error is raised (which is
     ignored, because it generally means that a parent directory is not
     empty).  For example, ‘os.removedirs('foo/bar/baz')’ will first
     remove the directory ‘'foo/bar/baz'’, and then remove ‘'foo/bar'’
     and ‘'foo'’ if they are empty.  Raises *note OSError: 304. if the
     leaf directory could not be successfully removed.

     Raises an *note auditing event: fa1. ‘os.remove’ with arguments
     ‘path’, ‘dir_fd’.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.rename (src, dst, *, src_dir_fd=None, dst_dir_fd=None)

     Rename the file or directory `src' to `dst'.  If `dst' exists, the
     operation will fail with an *note OSError: 304. subclass in a
     number of cases:

     On Windows, if `dst' exists a *note FileExistsError: a39. is always
     raised.

     On Unix, if `src' is a file and `dst' is a directory or vice-versa,
     an *note IsADirectoryError: a7a. or a *note NotADirectoryError:
     a7b. will be raised respectively.  If both are directories and
     `dst' is empty, `dst' will be silently replaced.  If `dst' is a
     non-empty directory, an *note OSError: 304. is raised.  If both are
     files, `dst' it will be replaced silently if the user has
     permission.  The operation may fail on some Unix flavors if `src'
     and `dst' are on different filesystems.  If successful, the
     renaming will be an atomic operation (this is a POSIX requirement).

     This function can support specifying `src_dir_fd' and/or
     `dst_dir_fd' to supply *note paths relative to directory
     descriptors: b0b.

     If you want cross-platform overwriting of the destination, use
     *note replace(): b15.

     Raises an *note auditing event: fa1. ‘os.rename’ with arguments
     ‘src’, ‘dst’, ‘src_dir_fd’, ‘dst_dir_fd’.

     New in version 3.3: The `src_dir_fd' and `dst_dir_fd' arguments.

     Changed in version 3.6: Accepts a *note path-like object: 472. for
     `src' and `dst'.

 -- Function: os.renames (old, new)

     Recursive directory or file renaming function.  Works like *note
     rename(): b14, except creation of any intermediate directories
     needed to make the new pathname good is attempted first.  After the
     rename, directories corresponding to rightmost path segments of the
     old name will be pruned away using *note removedirs(): 20b2.

          Note: This function can fail with the new directory structure
          made if you lack permissions needed to remove the leaf
          directory or file.

     Raises an *note auditing event: fa1. ‘os.rename’ with arguments
     ‘src’, ‘dst’, ‘src_dir_fd’, ‘dst_dir_fd’.

     Changed in version 3.6: Accepts a *note path-like object: 472. for
     `old' and `new'.

 -- Function: os.replace (src, dst, *, src_dir_fd=None, dst_dir_fd=None)

     Rename the file or directory `src' to `dst'.  If `dst' is a
     directory, *note OSError: 304. will be raised.  If `dst' exists and
     is a file, it will be replaced silently if the user has permission.
     The operation may fail if `src' and `dst' are on different
     filesystems.  If successful, the renaming will be an atomic
     operation (this is a POSIX requirement).

     This function can support specifying `src_dir_fd' and/or
     `dst_dir_fd' to supply *note paths relative to directory
     descriptors: b0b.

     Raises an *note auditing event: fa1. ‘os.rename’ with arguments
     ‘src’, ‘dst’, ‘src_dir_fd’, ‘dst_dir_fd’.

     New in version 3.3.

     Changed in version 3.6: Accepts a *note path-like object: 472. for
     `src' and `dst'.

 -- Function: os.rmdir (path, *, dir_fd=None)

     Remove (delete) the directory `path'.  If the directory does not
     exist or is not empty, an *note FileNotFoundError: 8ad. or an *note
     OSError: 304. is raised respectively.  In order to remove whole
     directory trees, *note shutil.rmtree(): 349. can be used.

     This function can support *note paths relative to directory
     descriptors: b0b.

     Raises an *note auditing event: fa1. ‘os.rmdir’ with arguments
     ‘path’, ‘dir_fd’.

     New in version 3.3: The `dir_fd' parameter.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.scandir (path='.')

     Return an iterator of *note os.DirEntry: 5eb. objects corresponding
     to the entries in the directory given by `path'.  The entries are
     yielded in arbitrary order, and the special entries ‘'.'’ and
     ‘'..'’ are not included.  If a file is removed from or added to the
     directory after creating the iterator, whether an entry for that
     file be included is unspecified.

     Using *note scandir(): 389. instead of *note listdir(): b1c. can
     significantly increase the performance of code that also needs file
     type or file attribute information, because *note os.DirEntry: 5eb.
     objects expose this information if the operating system provides it
     when scanning a directory.  All *note os.DirEntry: 5eb. methods may
     perform a system call, but *note is_dir(): 20b4. and *note
     is_file(): 748. usually only require a system call for symbolic
     links; *note os.DirEntry.stat(): 20b5. always requires a system
     call on Unix but only requires one for symbolic links on Windows.

     `path' may be a *note path-like object: 472.  If `path' is of type
     ‘bytes’ (directly or indirectly through the *note PathLike: 5e6.
     interface), the type of the *note name: 20b6. and *note path: 20b7.
     attributes of each *note os.DirEntry: 5eb. will be ‘bytes’; in all
     other circumstances, they will be of type ‘str’.

     This function can also support *note specifying a file descriptor:
     4bc.; the file descriptor must refer to a directory.

     Raises an *note auditing event: fa1. ‘os.scandir’ with argument
     ‘path’.

     The *note scandir(): 389. iterator supports the *note context
     manager: 661. protocol and has the following method:

      -- Method: scandir.close ()

          Close the iterator and free acquired resources.

          This is called automatically when the iterator is exhausted or
          garbage collected, or when an error happens during iterating.
          However it is advisable to call it explicitly or use the *note
          with: 7da. statement.

          New in version 3.6.

     The following example shows a simple use of *note scandir(): 389.
     to display all the files (excluding directories) in the given
     `path' that don’t start with ‘'.'’.  The ‘entry.is_file()’ call
     will generally not make an additional system call:

          with os.scandir(path) as it:
              for entry in it:
                  if not entry.name.startswith('.') and entry.is_file():
                      print(entry.name)

          Note: On Unix-based systems, *note scandir(): 389. uses the
          system’s opendir()(3) and readdir()(4) functions.  On Windows,
          it uses the Win32 FindFirstFileW(5) and FindNextFileW(6)
          functions.

     New in version 3.5.

     New in version 3.6: Added support for the *note context manager:
     661. protocol and the *note close(): 660. method.  If a *note
     scandir(): 389. iterator is neither exhausted nor explicitly closed
     a *note ResourceWarning: 5cb. will be emitted in its destructor.

     The function accepts a *note path-like object: 472.

     Changed in version 3.7: Added support for *note file descriptors:
     4bc. on Unix.

 -- Class: os.DirEntry

     Object yielded by *note scandir(): 389. to expose the file path and
     other file attributes of a directory entry.

     *note scandir(): 389. will provide as much of this information as
     possible without making additional system calls.  When a ‘stat()’
     or ‘lstat()’ system call is made, the ‘os.DirEntry’ object will
     cache the result.

     ‘os.DirEntry’ instances are not intended to be stored in long-lived
     data structures; if you know the file metadata has changed or if a
     long time has elapsed since calling *note scandir(): 389, call
     ‘os.stat(entry.path)’ to fetch up-to-date information.

     Because the ‘os.DirEntry’ methods can make operating system calls,
     they may also raise *note OSError: 304.  If you need very
     fine-grained control over errors, you can catch *note OSError: 304.
     when calling one of the ‘os.DirEntry’ methods and handle as
     appropriate.

     To be directly usable as a *note path-like object: 472,
     ‘os.DirEntry’ implements the *note PathLike: 5e6. interface.

     Attributes and methods on a ‘os.DirEntry’ instance are as follows:

      -- Attribute: name

          The entry’s base filename, relative to the *note scandir():
          389. `path' argument.

          The *note name: 2040. attribute will be ‘bytes’ if the *note
          scandir(): 389. `path' argument is of type ‘bytes’ and ‘str’
          otherwise.  Use *note fsdecode(): 5e9. to decode byte
          filenames.

      -- Attribute: path

          The entry’s full path name: equivalent to
          ‘os.path.join(scandir_path, entry.name)’ where `scandir_path'
          is the *note scandir(): 389. `path' argument.  The path is
          only absolute if the *note scandir(): 389. `path' argument was
          absolute.  If the *note scandir(): 389. `path' argument was a
          *note file descriptor: 4bc, the *note path: c5. attribute is
          the same as the *note name: 2040. attribute.

          The *note path: c5. attribute will be ‘bytes’ if the *note
          scandir(): 389. `path' argument is of type ‘bytes’ and ‘str’
          otherwise.  Use *note fsdecode(): 5e9. to decode byte
          filenames.

      -- Method: inode ()

          Return the inode number of the entry.

          The result is cached on the ‘os.DirEntry’ object.  Use
          ‘os.stat(entry.path, follow_symlinks=False).st_ino’ to fetch
          up-to-date information.

          On the first, uncached call, a system call is required on
          Windows but not on Unix.

      -- Method: is_dir (*, follow_symlinks=True)

          Return ‘True’ if this entry is a directory or a symbolic link
          pointing to a directory; return ‘False’ if the entry is or
          points to any other kind of file, or if it doesn’t exist
          anymore.

          If `follow_symlinks' is ‘False’, return ‘True’ only if this
          entry is a directory (without following symlinks); return
          ‘False’ if the entry is any other kind of file or if it
          doesn’t exist anymore.

          The result is cached on the ‘os.DirEntry’ object, with a
          separate cache for `follow_symlinks' ‘True’ and ‘False’.  Call
          *note os.stat(): 321. along with *note stat.S_ISDIR(): 1d5f.
          to fetch up-to-date information.

          On the first, uncached call, no system call is required in
          most cases.  Specifically, for non-symlinks, neither Windows
          or Unix require a system call, except on certain Unix file
          systems, such as network file systems, that return
          ‘dirent.d_type == DT_UNKNOWN’.  If the entry is a symlink, a
          system call will be required to follow the symlink unless
          `follow_symlinks' is ‘False’.

          This method can raise *note OSError: 304, such as *note
          PermissionError: 6f6, but *note FileNotFoundError: 8ad. is
          caught and not raised.

      -- Method: is_file (*, follow_symlinks=True)

          Return ‘True’ if this entry is a file or a symbolic link
          pointing to a file; return ‘False’ if the entry is or points
          to a directory or other non-file entry, or if it doesn’t exist
          anymore.

          If `follow_symlinks' is ‘False’, return ‘True’ only if this
          entry is a file (without following symlinks); return ‘False’
          if the entry is a directory or other non-file entry, or if it
          doesn’t exist anymore.

          The result is cached on the ‘os.DirEntry’ object.  Caching,
          system calls made, and exceptions raised are as per *note
          is_dir(): 20b4.

      -- Method: is_symlink ()

          Return ‘True’ if this entry is a symbolic link (even if
          broken); return ‘False’ if the entry points to a directory or
          any kind of file, or if it doesn’t exist anymore.

          The result is cached on the ‘os.DirEntry’ object.  Call *note
          os.path.islink(): 323. to fetch up-to-date information.

          On the first, uncached call, no system call is required in
          most cases.  Specifically, neither Windows or Unix require a
          system call, except on certain Unix file systems, such as
          network file systems, that return ‘dirent.d_type ==
          DT_UNKNOWN’.

          This method can raise *note OSError: 304, such as *note
          PermissionError: 6f6, but *note FileNotFoundError: 8ad. is
          caught and not raised.

      -- Method: stat (*, follow_symlinks=True)

          Return a *note stat_result: 11bf. object for this entry.  This
          method follows symbolic links by default; to stat a symbolic
          link add the ‘follow_symlinks=False’ argument.

          On Unix, this method always requires a system call.  On
          Windows, it only requires a system call if `follow_symlinks'
          is ‘True’ and the entry is a reparse point (for example, a
          symbolic link or directory junction).

          On Windows, the ‘st_ino’, ‘st_dev’ and ‘st_nlink’ attributes
          of the *note stat_result: 11bf. are always set to zero.  Call
          *note os.stat(): 321. to get these attributes.

          The result is cached on the ‘os.DirEntry’ object, with a
          separate cache for `follow_symlinks' ‘True’ and ‘False’.  Call
          *note os.stat(): 321. to fetch up-to-date information.

     Note that there is a nice correspondence between several attributes
     and methods of ‘os.DirEntry’ and of *note pathlib.Path: 32f.  In
     particular, the ‘name’ attribute has the same meaning, as do the
     ‘is_dir()’, ‘is_file()’, ‘is_symlink()’ and ‘stat()’ methods.

     New in version 3.5.

     Changed in version 3.6: Added support for the *note PathLike: 5e6.
     interface.  Added support for *note bytes: 172. paths on Windows.

 -- Function: os.stat (path, *, dir_fd=None, follow_symlinks=True)

     Get the status of a file or a file descriptor.  Perform the
     equivalent of a ‘stat()’ system call on the given path.  `path' may
     be specified as either a string or bytes – directly or indirectly
     through the *note PathLike: 5e6. interface – or as an open file
     descriptor.  Return a *note stat_result: 11bf. object.

     This function normally follows symlinks; to stat a symlink add the
     argument ‘follow_symlinks=False’, or use *note lstat(): 322.

     This function can support *note specifying a file descriptor: 4bc.
     and *note not following symlinks: b0c.

     On Windows, passing ‘follow_symlinks=False’ will disable following
     all name-surrogate reparse points, which includes symlinks and
     directory junctions.  Other types of reparse points that do not
     resemble links or that the operating system is unable to follow
     will be opened directly.  When following a chain of multiple links,
     this may result in the original link being returned instead of the
     non-link that prevented full traversal.  To obtain stat results for
     the final path in this case, use the *note os.path.realpath(): 32d.
     function to resolve the path name as far as possible and call *note
     lstat(): 322. on the result.  This does not apply to dangling
     symlinks or junction points, which will raise the usual exceptions.

     Example:

          >>> import os
          >>> statinfo = os.stat('somefile.txt')
          >>> statinfo
          os.stat_result(st_mode=33188, st_ino=7876932, st_dev=234881026,
          st_nlink=1, st_uid=501, st_gid=501, st_size=264, st_atime=1297230295,
          st_mtime=1297230027, st_ctime=1297230027)
          >>> statinfo.st_size
          264

     See also
     ........

     *note fstat(): 752. and *note lstat(): 322. functions.

     New in version 3.3: Added the `dir_fd' and `follow_symlinks'
     arguments, specifying a file descriptor instead of a path.

     Changed in version 3.6: Accepts a *note path-like object: 472.

     Changed in version 3.8: On Windows, all reparse points that can be
     resolved by the operating system are now followed, and passing
     ‘follow_symlinks=False’ disables following all name surrogate
     reparse points.  If the operating system reaches a reparse point
     that it is not able to follow, `stat' now returns the information
     for the original path as if ‘follow_symlinks=False’ had been
     specified instead of raising an error.

 -- Class: os.stat_result

     Object whose attributes correspond roughly to the members of the
     ‘stat’ structure.  It is used for the result of *note os.stat():
     321, *note os.fstat(): 752. and *note os.lstat(): 322.

     Attributes:

      -- Attribute: st_mode

          File mode: file type and file mode bits (permissions).

      -- Attribute: st_ino

          Platform dependent, but if non-zero, uniquely identifies the
          file for a given value of ‘st_dev’.  Typically:

             * the inode number on Unix,

             * the file index(7) on Windows

      -- Attribute: st_dev

          Identifier of the device on which this file resides.

      -- Attribute: st_nlink

          Number of hard links.

      -- Attribute: st_uid

          User identifier of the file owner.

      -- Attribute: st_gid

          Group identifier of the file owner.

      -- Attribute: st_size

          Size of the file in bytes, if it is a regular file or a
          symbolic link.  The size of a symbolic link is the length of
          the pathname it contains, without a terminating null byte.

     Timestamps:

      -- Attribute: st_atime

          Time of most recent access expressed in seconds.

      -- Attribute: st_mtime

          Time of most recent content modification expressed in seconds.

      -- Attribute: st_ctime

          Platform dependent:

             * the time of most recent metadata change on Unix,

             * the time of creation on Windows, expressed in seconds.

      -- Attribute: st_atime_ns

          Time of most recent access expressed in nanoseconds as an
          integer.

      -- Attribute: st_mtime_ns

          Time of most recent content modification expressed in
          nanoseconds as an integer.

      -- Attribute: st_ctime_ns

          Platform dependent:

             * the time of most recent metadata change on Unix,

             * the time of creation on Windows, expressed in nanoseconds
               as an integer.

          Note: The exact meaning and resolution of the *note st_atime:
          20c1, *note st_mtime: 1eb9, and *note st_ctime: 20c2.
          attributes depend on the operating system and the file system.
          For example, on Windows systems using the FAT or FAT32 file
          systems, *note st_mtime: 1eb9. has 2-second resolution, and
          *note st_atime: 20c1. has only 1-day resolution.  See your
          operating system documentation for details.

          Similarly, although *note st_atime_ns: 20c3, *note
          st_mtime_ns: 20c4, and *note st_ctime_ns: 20c5. are always
          expressed in nanoseconds, many systems do not provide
          nanosecond precision.  On systems that do provide nanosecond
          precision, the floating-point object used to store *note
          st_atime: 20c1, *note st_mtime: 1eb9, and *note st_ctime:
          20c2. cannot preserve all of it, and as such will be slightly
          inexact.  If you need the exact timestamps you should always
          use *note st_atime_ns: 20c3, *note st_mtime_ns: 20c4, and
          *note st_ctime_ns: 20c5.

     On some Unix systems (such as Linux), the following attributes may
     also be available:

      -- Attribute: st_blocks

          Number of 512-byte blocks allocated for file.  This may be
          smaller than *note st_size: 20c0./512 when the file has holes.

      -- Attribute: st_blksize

          “Preferred” blocksize for efficient file system I/O. Writing
          to a file in smaller chunks may cause an inefficient
          read-modify-rewrite.

      -- Attribute: st_rdev

          Type of device if an inode device.

      -- Attribute: st_flags

          User defined flags for file.

     On other Unix systems (such as FreeBSD), the following attributes
     may be available (but may be only filled out if root tries to use
     them):

      -- Attribute: st_gen

          File generation number.

      -- Attribute: st_birthtime

          Time of file creation.

     On Solaris and derivatives, the following attributes may also be
     available:

      -- Attribute: st_fstype

          String that uniquely identifies the type of the filesystem
          that contains the file.

     On macOS systems, the following attributes may also be available:

      -- Attribute: st_rsize

          Real size of the file.

      -- Attribute: st_creator

          Creator of the file.

      -- Attribute: st_type

          File type.

     On Windows systems, the following attributes are also available:

      -- Attribute: st_file_attributes

          Windows file attributes: ‘dwFileAttributes’ member of the
          ‘BY_HANDLE_FILE_INFORMATION’ structure returned by
          ‘GetFileInformationByHandle()’.  See the ‘FILE_ATTRIBUTE_*’
          constants in the *note stat: f4. module.

      -- Attribute: st_reparse_tag

          When *note st_file_attributes: 80f. has the
          ‘FILE_ATTRIBUTE_REPARSE_POINT’ set, this field contains the
          tag identifying the type of reparse point.  See the
          ‘IO_REPARSE_TAG_*’ constants in the *note stat: f4. module.

     The standard module *note stat: f4. defines functions and constants
     that are useful for extracting information from a ‘stat’ structure.
     (On Windows, some items are filled with dummy values.)

     For backward compatibility, a *note stat_result: 11bf. instance is
     also accessible as a tuple of at least 10 integers giving the most
     important (and portable) members of the ‘stat’ structure, in the
     order *note st_mode: 20ba, *note st_ino: 20bb, *note st_dev: 20bc,
     *note st_nlink: 20bd, *note st_uid: 20be, *note st_gid: 20bf, *note
     st_size: 20c0, *note st_atime: 20c1, *note st_mtime: 1eb9, *note
     st_ctime: 20c2.  More items may be added at the end by some
     implementations.  For compatibility with older Python versions,
     accessing *note stat_result: 11bf. as a tuple always returns
     integers.

     New in version 3.3: Added the *note st_atime_ns: 20c3, *note
     st_mtime_ns: 20c4, and *note st_ctime_ns: 20c5. members.

     New in version 3.5: Added the *note st_file_attributes: 80f. member
     on Windows.

     Changed in version 3.5: Windows now returns the file index as *note
     st_ino: 20bb. when available.

     New in version 3.7: Added the *note st_fstype: 4c6. member to
     Solaris/derivatives.

     New in version 3.8: Added the *note st_reparse_tag: 20cf. member on
     Windows.

     Changed in version 3.8: On Windows, the *note st_mode: 20ba. member
     now identifies special files as ‘S_IFCHR’, ‘S_IFIFO’ or ‘S_IFBLK’
     as appropriate.

 -- Function: os.statvfs (path)

     Perform a ‘statvfs()’ system call on the given path.  The return
     value is an object whose attributes describe the filesystem on the
     given path, and correspond to the members of the ‘statvfs’
     structure, namely: ‘f_bsize’, ‘f_frsize’, ‘f_blocks’, ‘f_bfree’,
     ‘f_bavail’, ‘f_files’, ‘f_ffree’, ‘f_favail’, ‘f_flag’,
     ‘f_namemax’, ‘f_fsid’.

     Two module-level constants are defined for the ‘f_flag’ attribute’s
     bit-flags: if ‘ST_RDONLY’ is set, the filesystem is mounted
     read-only, and if ‘ST_NOSUID’ is set, the semantics of
     setuid/setgid bits are disabled or not supported.

     Additional module-level constants are defined for GNU/glibc based
     systems.  These are ‘ST_NODEV’ (disallow access to device special
     files), ‘ST_NOEXEC’ (disallow program execution), ‘ST_SYNCHRONOUS’
     (writes are synced at once), ‘ST_MANDLOCK’ (allow mandatory locks
     on an FS), ‘ST_WRITE’ (write on file/directory/symlink),
     ‘ST_APPEND’ (append-only file), ‘ST_IMMUTABLE’ (immutable file),
     ‘ST_NOATIME’ (do not update access times), ‘ST_NODIRATIME’ (do not
     update directory access times), ‘ST_RELATIME’ (update atime
     relative to mtime/ctime).

     This function can support *note specifying a file descriptor: 4bc.

     *note Availability: 1491.: Unix.

     Changed in version 3.2: The ‘ST_RDONLY’ and ‘ST_NOSUID’ constants
     were added.

     New in version 3.3: Added support for specifying `path' as an open
     file descriptor.

     Changed in version 3.4: The ‘ST_NODEV’, ‘ST_NOEXEC’,
     ‘ST_SYNCHRONOUS’, ‘ST_MANDLOCK’, ‘ST_WRITE’, ‘ST_APPEND’,
     ‘ST_IMMUTABLE’, ‘ST_NOATIME’, ‘ST_NODIRATIME’, and ‘ST_RELATIME’
     constants were added.

     Changed in version 3.6: Accepts a *note path-like object: 472.

     New in version 3.7: Added ‘f_fsid’.

 -- Data: os.supports_dir_fd

     A *note set: 1f6. object indicating which functions in the *note
     os: c4. module accept an open file descriptor for their `dir_fd'
     parameter.  Different platforms provide different features, and the
     underlying functionality Python uses to implement the `dir_fd'
     parameter is not available on all platforms Python supports.  For
     consistency’s sake, functions that may support `dir_fd' always
     allow specifying the parameter, but will throw an exception if the
     functionality is used when it’s not locally available.  (Specifying
     ‘None’ for `dir_fd' is always supported on all platforms.)

     To check whether a particular function accepts an open file
     descriptor for its `dir_fd' parameter, use the ‘in’ operator on
     ‘supports_dir_fd’.  As an example, this expression evaluates to
     ‘True’ if *note os.stat(): 321. accepts open file descriptors for
     `dir_fd' on the local platform:

          os.stat in os.supports_dir_fd

     Currently `dir_fd' parameters only work on Unix platforms; none of
     them work on Windows.

     New in version 3.3.

 -- Data: os.supports_effective_ids

     A *note set: 1f6. object indicating whether *note os.access(): b0d.
     permits specifying ‘True’ for its `effective_ids' parameter on the
     local platform.  (Specifying ‘False’ for `effective_ids' is always
     supported on all platforms.)  If the local platform supports it,
     the collection will contain *note os.access(): b0d.; otherwise it
     will be empty.

     This expression evaluates to ‘True’ if *note os.access(): b0d.
     supports ‘effective_ids=True’ on the local platform:

          os.access in os.supports_effective_ids

     Currently `effective_ids' is only supported on Unix platforms; it
     does not work on Windows.

     New in version 3.3.

 -- Data: os.supports_fd

     A *note set: 1f6. object indicating which functions in the *note
     os: c4. module permit specifying their `path' parameter as an open
     file descriptor on the local platform.  Different platforms provide
     different features, and the underlying functionality Python uses to
     accept open file descriptors as `path' arguments is not available
     on all platforms Python supports.

     To determine whether a particular function permits specifying an
     open file descriptor for its `path' parameter, use the ‘in’
     operator on ‘supports_fd’.  As an example, this expression
     evaluates to ‘True’ if *note os.chdir(): 16e. accepts open file
     descriptors for `path' on your local platform:

          os.chdir in os.supports_fd

     New in version 3.3.

 -- Data: os.supports_follow_symlinks

     A *note set: 1f6. object indicating which functions in the *note
     os: c4. module accept ‘False’ for their `follow_symlinks' parameter
     on the local platform.  Different platforms provide different
     features, and the underlying functionality Python uses to implement
     `follow_symlinks' is not available on all platforms Python
     supports.  For consistency’s sake, functions that may support
     `follow_symlinks' always allow specifying the parameter, but will
     throw an exception if the functionality is used when it’s not
     locally available.  (Specifying ‘True’ for `follow_symlinks' is
     always supported on all platforms.)

     To check whether a particular function accepts ‘False’ for its
     `follow_symlinks' parameter, use the ‘in’ operator on
     ‘supports_follow_symlinks’.  As an example, this expression
     evaluates to ‘True’ if you may specify ‘follow_symlinks=False’ when
     calling *note os.stat(): 321. on the local platform:

          os.stat in os.supports_follow_symlinks

     New in version 3.3.

 -- Function: os.symlink (src, dst, target_is_directory=False, *,
          dir_fd=None)

     Create a symbolic link pointing to `src' named `dst'.

     On Windows, a symlink represents either a file or a directory, and
     does not morph to the target dynamically.  If the target is
     present, the type of the symlink will be created to match.
     Otherwise, the symlink will be created as a directory if
     `target_is_directory' is ‘True’ or a file symlink (the default)
     otherwise.  On non-Windows platforms, `target_is_directory' is
     ignored.

     This function can support *note paths relative to directory
     descriptors: b0b.

          Note: On newer versions of Windows 10, unprivileged accounts
          can create symlinks if Developer Mode is enabled.  When
          Developer Mode is not available/enabled, the
          `SeCreateSymbolicLinkPrivilege' privilege is required, or the
          process must be run as an administrator.

          *note OSError: 304. is raised when the function is called by
          an unprivileged user.

     Raises an *note auditing event: fa1. ‘os.symlink’ with arguments
     ‘src’, ‘dst’, ‘dir_fd’.

     *note Availability: 1491.: Unix, Windows.

     Changed in version 3.2: Added support for Windows 6.0 (Vista)
     symbolic links.

     New in version 3.3: Added the `dir_fd' argument, and now allow
     `target_is_directory' on non-Windows platforms.

     Changed in version 3.6: Accepts a *note path-like object: 472. for
     `src' and `dst'.

     Changed in version 3.8: Added support for unelevated symlinks on
     Windows with Developer Mode.

 -- Function: os.sync ()

     Force write of everything to disk.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: os.truncate (path, length)

     Truncate the file corresponding to `path', so that it is at most
     `length' bytes in size.

     This function can support *note specifying a file descriptor: 4bc.

     Raises an *note auditing event: fa1. ‘os.truncate’ with arguments
     ‘path’, ‘length’.

     *note Availability: 1491.: Unix, Windows.

     New in version 3.3.

     Changed in version 3.5: Added support for Windows

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.unlink (path, *, dir_fd=None)

     Remove (delete) the file `path'.  This function is semantically
     identical to *note remove(): b13.; the ‘unlink’ name is its
     traditional Unix name.  Please see the documentation for *note
     remove(): b13. for further information.

     Raises an *note auditing event: fa1. ‘os.remove’ with arguments
     ‘path’, ‘dir_fd’.

     New in version 3.3: The `dir_fd' parameter.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.utime (path, times=None, *[, ns], dir_fd=None,
          follow_symlinks=True)

     Set the access and modified times of the file specified by `path'.

     *note utime(): b19. takes two optional parameters, `times' and
     `ns'.  These specify the times set on `path' and are used as
     follows:

        - If `ns' is specified, it must be a 2-tuple of the form
          ‘(atime_ns, mtime_ns)’ where each member is an int expressing
          nanoseconds.

        - If `times' is not ‘None’, it must be a 2-tuple of the form
          ‘(atime, mtime)’ where each member is an int or float
          expressing seconds.

        - If `times' is ‘None’ and `ns' is unspecified, this is
          equivalent to specifying ‘ns=(atime_ns, mtime_ns)’ where both
          times are the current time.

     It is an error to specify tuples for both `times' and `ns'.

     Note that the exact times you set here may not be returned by a
     subsequent *note stat(): 321. call, depending on the resolution
     with which your operating system records access and modification
     times; see *note stat(): 321.  The best way to preserve exact times
     is to use the `st_atime_ns' and `st_mtime_ns' fields from the *note
     os.stat(): 321. result object with the `ns' parameter to ‘utime’.

     This function can support *note specifying a file descriptor: 4bc,
     *note paths relative to directory descriptors: b0b. and *note not
     following symlinks: b0c.

     Raises an *note auditing event: fa1. ‘os.utime’ with arguments
     ‘path’, ‘times’, ‘ns’, ‘dir_fd’.

     New in version 3.3: Added support for specifying `path' as an open
     file descriptor, and the `dir_fd', `follow_symlinks', and `ns'
     parameters.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.walk (top, topdown=True, onerror=None,
          followlinks=False)

     Generate the file names in a directory tree by walking the tree
     either top-down or bottom-up.  For each directory in the tree
     rooted at directory `top' (including `top' itself), it yields a
     3-tuple ‘(dirpath, dirnames, filenames)’.

     `dirpath' is a string, the path to the directory.  `dirnames' is a
     list of the names of the subdirectories in `dirpath' (excluding
     ‘'.'’ and ‘'..'’).  `filenames' is a list of the names of the
     non-directory files in `dirpath'.  Note that the names in the lists
     contain no path components.  To get a full path (which begins with
     `top') to a file or directory in `dirpath', do
     ‘os.path.join(dirpath, name)’.  Whether or not the lists are sorted
     depends on the file system.  If a file is removed from or added to
     the `dirpath' directory during generating the lists, whether a name
     for that file be included is unspecified.

     If optional argument `topdown' is ‘True’ or not specified, the
     triple for a directory is generated before the triples for any of
     its subdirectories (directories are generated top-down).  If
     `topdown' is ‘False’, the triple for a directory is generated after
     the triples for all of its subdirectories (directories are
     generated bottom-up).  No matter the value of `topdown', the list
     of subdirectories is retrieved before the tuples for the directory
     and its subdirectories are generated.

     When `topdown' is ‘True’, the caller can modify the `dirnames' list
     in-place (perhaps using *note del: 13a2. or slice assignment), and
     *note walk(): 747. will only recurse into the subdirectories whose
     names remain in `dirnames'; this can be used to prune the search,
     impose a specific order of visiting, or even to inform *note
     walk(): 747. about directories the caller creates or renames before
     it resumes *note walk(): 747. again.  Modifying `dirnames' when
     `topdown' is ‘False’ has no effect on the behavior of the walk,
     because in bottom-up mode the directories in `dirnames' are
     generated before `dirpath' itself is generated.

     By default, errors from the *note scandir(): 389. call are ignored.
     If optional argument `onerror' is specified, it should be a
     function; it will be called with one argument, an *note OSError:
     304. instance.  It can report the error to continue with the walk,
     or raise the exception to abort the walk.  Note that the filename
     is available as the ‘filename’ attribute of the exception object.

     By default, *note walk(): 747. will not walk down into symbolic
     links that resolve to directories.  Set `followlinks' to ‘True’ to
     visit directories pointed to by symlinks, on systems that support
     them.

          Note: Be aware that setting `followlinks' to ‘True’ can lead
          to infinite recursion if a link points to a parent directory
          of itself.  *note walk(): 747. does not keep track of the
          directories it visited already.

          Note: If you pass a relative pathname, don’t change the
          current working directory between resumptions of *note walk():
          747.  *note walk(): 747. never changes the current directory,
          and assumes that its caller doesn’t either.

     This example displays the number of bytes taken by non-directory
     files in each directory under the starting directory, except that
     it doesn’t look under any CVS subdirectory:

          import os
          from os.path import join, getsize
          for root, dirs, files in os.walk('python/Lib/email'):
              print(root, "consumes", end=" ")
              print(sum(getsize(join(root, name)) for name in files), end=" ")
              print("bytes in", len(files), "non-directory files")
              if 'CVS' in dirs:
                  dirs.remove('CVS')  # don't visit CVS directories

     In the next example (simple implementation of *note
     shutil.rmtree(): 349.), walking the tree bottom-up is essential,
     *note rmdir(): b16. doesn’t allow deleting a directory before the
     directory is empty:

          # Delete everything reachable from the directory named in "top",
          # assuming there are no symbolic links.
          # CAUTION:  This is dangerous!  For example, if top == '/', it
          # could delete all your disk files.
          import os
          for root, dirs, files in os.walk(top, topdown=False):
              for name in files:
                  os.remove(os.path.join(root, name))
              for name in dirs:
                  os.rmdir(os.path.join(root, name))

     Raises an *note auditing event: fa1. ‘os.walk’ with arguments
     ‘top’, ‘topdown’, ‘onerror’, ‘followlinks’.

     Changed in version 3.5: This function now calls *note os.scandir():
     389. instead of *note os.listdir(): b1c, making it faster by
     reducing the number of calls to *note os.stat(): 321.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.fwalk (top='.', topdown=True, onerror=None, *,
          follow_symlinks=False, dir_fd=None)

     This behaves exactly like *note walk(): 747, except that it yields
     a 4-tuple ‘(dirpath, dirnames, filenames, dirfd)’, and it supports
     ‘dir_fd’.

     `dirpath', `dirnames' and `filenames' are identical to *note
     walk(): 747. output, and `dirfd' is a file descriptor referring to
     the directory `dirpath'.

     This function always supports *note paths relative to directory
     descriptors: b0b. and *note not following symlinks: b0c.  Note
     however that, unlike other functions, the *note fwalk(): 4bb.
     default value for `follow_symlinks' is ‘False’.

          Note: Since *note fwalk(): 4bb. yields file descriptors, those
          are only valid until the next iteration step, so you should
          duplicate them (e.g.  with *note dup(): 10e9.) if you want to
          keep them longer.

     This example displays the number of bytes taken by non-directory
     files in each directory under the starting directory, except that
     it doesn’t look under any CVS subdirectory:

          import os
          for root, dirs, files, rootfd in os.fwalk('python/Lib/email'):
              print(root, "consumes", end="")
              print(sum([os.stat(name, dir_fd=rootfd).st_size for name in files]),
                    end="")
              print("bytes in", len(files), "non-directory files")
              if 'CVS' in dirs:
                  dirs.remove('CVS')  # don't visit CVS directories

     In the next example, walking the tree bottom-up is essential: *note
     rmdir(): b16. doesn’t allow deleting a directory before the
     directory is empty:

          # Delete everything reachable from the directory named in "top",
          # assuming there are no symbolic links.
          # CAUTION:  This is dangerous!  For example, if top == '/', it
          # could delete all your disk files.
          import os
          for root, dirs, files, rootfd in os.fwalk(top, topdown=False):
              for name in files:
                  os.unlink(name, dir_fd=rootfd)
              for name in dirs:
                  os.rmdir(name, dir_fd=rootfd)

     Raises an *note auditing event: fa1. ‘os.fwalk’ with arguments
     ‘top’, ‘topdown’, ‘onerror’, ‘follow_symlinks’, ‘dir_fd’.

     *note Availability: 1491.: Unix.

     New in version 3.3.

     Changed in version 3.6: Accepts a *note path-like object: 472.

     Changed in version 3.7: Added support for *note bytes: 172. paths.

 -- Function: os.memfd_create (name[, flags=os.MFD_CLOEXEC])

     Create an anonymous file and return a file descriptor that refers
     to it.  `flags' must be one of the ‘os.MFD_*’ constants available
     on the system (or a bitwise ORed combination of them).  By default,
     the new file descriptor is *note non-inheritable: 8e7.

     The name supplied in `name' is used as a filename and will be
     displayed as the target of the corresponding symbolic link in the
     directory ‘/proc/self/fd/’.  The displayed name is always prefixed
     with ‘memfd:’ and serves only for debugging purposes.  Names do not
     affect the behavior of the file descriptor, and as such multiple
     files can have the same name without any side effects.

     *note Availability: 1491.: Linux 3.17 or newer with glibc 2.27 or
     newer.

     New in version 3.8.

 -- Data: os.MFD_CLOEXEC
 -- Data: os.MFD_ALLOW_SEALING
 -- Data: os.MFD_HUGETLB
 -- Data: os.MFD_HUGE_SHIFT
 -- Data: os.MFD_HUGE_MASK
 -- Data: os.MFD_HUGE_64KB
 -- Data: os.MFD_HUGE_512KB
 -- Data: os.MFD_HUGE_1MB
 -- Data: os.MFD_HUGE_2MB
 -- Data: os.MFD_HUGE_8MB
 -- Data: os.MFD_HUGE_16MB
 -- Data: os.MFD_HUGE_32MB
 -- Data: os.MFD_HUGE_256MB
 -- Data: os.MFD_HUGE_512MB
 -- Data: os.MFD_HUGE_1GB
 -- Data: os.MFD_HUGE_2GB
 -- Data: os.MFD_HUGE_16GB

     These flags can be passed to *note memfd_create(): 320.

     *note Availability: 1491.: Linux 3.17 or newer with glibc 2.27 or
     newer.  The ‘MFD_HUGE*’ flags are only available since Linux 4.14.

     New in version 3.8.

* Menu:

* Linux extended attributes::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0529

   (2) https://bugs.python.org/issue21082

   (3) 
http://pubs.opengroup.org/onlinepubs/009695399/functions/opendir.html

   (4) 
http://pubs.opengroup.org/onlinepubs/009695399/functions/readdir_r.html

   (5) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa364418(v=vs.85).aspx

   (6) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa364428(v=vs.85).aspx

   (7) https://msdn.microsoft.com/en-us/library/aa363788


File: python.info,  Node: Linux extended attributes,  Up: Files and Directories

5.16.1.8 Linux extended attributes
..................................

New in version 3.3.

These functions are all available on Linux only.

 -- Function: os.getxattr (path, attribute, *, follow_symlinks=True)

     Return the value of the extended filesystem attribute `attribute'
     for `path'.  `attribute' can be bytes or str (directly or
     indirectly through the *note PathLike: 5e6. interface).  If it is
     str, it is encoded with the filesystem encoding.

     This function can support *note specifying a file descriptor: 4bc.
     and *note not following symlinks: b0c.

     Raises an *note auditing event: fa1. ‘os.getxattr’ with arguments
     ‘path’, ‘attribute’.

     Changed in version 3.6: Accepts a *note path-like object: 472. for
     `path' and `attribute'.

 -- Function: os.listxattr (path=None, *, follow_symlinks=True)

     Return a list of the extended filesystem attributes on `path'.  The
     attributes in the list are represented as strings decoded with the
     filesystem encoding.  If `path' is ‘None’, *note listxattr(): b27.
     will examine the current directory.

     This function can support *note specifying a file descriptor: 4bc.
     and *note not following symlinks: b0c.

     Raises an *note auditing event: fa1. ‘os.listxattr’ with argument
     ‘path’.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os.removexattr (path, attribute, *, follow_symlinks=True)

     Removes the extended filesystem attribute `attribute' from `path'.
     `attribute' should be bytes or str (directly or indirectly through
     the *note PathLike: 5e6. interface).  If it is a string, it is
     encoded with the filesystem encoding.

     This function can support *note specifying a file descriptor: 4bc.
     and *note not following symlinks: b0c.

     Raises an *note auditing event: fa1. ‘os.removexattr’ with
     arguments ‘path’, ‘attribute’.

     Changed in version 3.6: Accepts a *note path-like object: 472. for
     `path' and `attribute'.

 -- Function: os.setxattr (path, attribute, value, flags=0, *,
          follow_symlinks=True)

     Set the extended filesystem attribute `attribute' on `path' to
     `value'.  `attribute' must be a bytes or str with no embedded NULs
     (directly or indirectly through the *note PathLike: 5e6.
     interface).  If it is a str, it is encoded with the filesystem
     encoding.  `flags' may be *note XATTR_REPLACE: 20e2. or *note
     XATTR_CREATE: 20e3.  If *note XATTR_REPLACE: 20e2. is given and the
     attribute does not exist, ‘ENODATA’ will be raised.  If *note
     XATTR_CREATE: 20e3. is given and the attribute already exists, the
     attribute will not be created and ‘EEXISTS’ will be raised.

     This function can support *note specifying a file descriptor: 4bc.
     and *note not following symlinks: b0c.

          Note: A bug in Linux kernel versions less than 2.6.39 caused
          the flags argument to be ignored on some filesystems.

     Raises an *note auditing event: fa1. ‘os.setxattr’ with arguments
     ‘path’, ‘attribute’, ‘value’, ‘flags’.

     Changed in version 3.6: Accepts a *note path-like object: 472. for
     `path' and `attribute'.

 -- Data: os.XATTR_SIZE_MAX

     The maximum size the value of an extended attribute can be.
     Currently, this is 64 KiB on Linux.

 -- Data: os.XATTR_CREATE

     This is a possible value for the flags argument in *note
     setxattr(): b29.  It indicates the operation must create an
     attribute.

 -- Data: os.XATTR_REPLACE

     This is a possible value for the flags argument in *note
     setxattr(): b29.  It indicates the operation must replace an
     existing attribute.


File: python.info,  Node: Process Management,  Next: Interface to the scheduler,  Prev: Files and Directories,  Up: os — Miscellaneous operating system interfaces

5.16.1.9 Process Management
...........................

These functions may be used to create and manage processes.

The various *note exec*: 20e7. functions take a list of arguments for
the new program loaded into the process.  In each case, the first of
these arguments is passed to the new program as its own name rather than
as an argument a user may have typed on a command line.  For the C
programmer, this is the ‘argv[0]’ passed to a program’s ‘main()’.  For
example, ‘os.execv('/bin/echo', ['foo', 'bar'])’ will only print ‘bar’
on standard output; ‘foo’ will seem to be ignored.

 -- Function: os.abort ()

     Generate a ‘SIGABRT’ signal to the current process.  On Unix, the
     default behavior is to produce a core dump; on Windows, the process
     immediately returns an exit code of ‘3’.  Be aware that calling
     this function will not call the Python signal handler registered
     for ‘SIGABRT’ with *note signal.signal(): b58.

 -- Function: os.add_dll_directory (path)

     Add a path to the DLL search path.

     This search path is used when resolving dependencies for imported
     extension modules (the module itself is resolved through sys.path),
     and also by *note ctypes: 2a.

     Remove the directory by calling `close()' on the returned object or
     using it in a *note with: 7da. statement.

     See the Microsoft documentation(1) for more information about how
     DLLs are loaded.

     Raises an *note auditing event: fa1. ‘os.add_dll_directory’ with
     argument ‘path’.

     *note Availability: 1491.: Windows.

     New in version 3.8: Previous versions of CPython would resolve DLLs
     using the default behavior for the current process.  This led to
     inconsistencies, such as only sometimes searching ‘PATH’ or the
     current working directory, and OS functions such as
     ‘AddDllDirectory’ having no effect.

     In 3.8, the two primary ways DLLs are loaded now explicitly
     override the process-wide behavior to ensure consistency.  See the
     *note porting notes: 3ec. for information on updating libraries.

 -- Function: os.execl (path, arg0, arg1, ...)
 -- Function: os.execle (path, arg0, arg1, ..., env)
 -- Function: os.execlp (file, arg0, arg1, ...)
 -- Function: os.execlpe (file, arg0, arg1, ..., env)
 -- Function: os.execv (path, args)
 -- Function: os.execve (path, args, env)
 -- Function: os.execvp (file, args)
 -- Function: os.execvpe (file, args, env)

     These functions all execute a new program, replacing the current
     process; they do not return.  On Unix, the new executable is loaded
     into the current process, and will have the same process id as the
     caller.  Errors will be reported as *note OSError: 304. exceptions.

     The current process is replaced immediately.  Open file objects and
     descriptors are not flushed, so if there may be data buffered on
     these open files, you should flush them using ‘sys.stdout.flush()’
     or *note os.fsync(): 754. before calling an *note exec*: 20e7.
     function.

     The “l” and “v” variants of the *note exec*: 20e7. functions differ
     in how command-line arguments are passed.  The “l” variants are
     perhaps the easiest to work with if the number of parameters is
     fixed when the code is written; the individual parameters simply
     become additional parameters to the ‘execl*()’ functions.  The “v”
     variants are good when the number of parameters is variable, with
     the arguments being passed in a list or tuple as the `args'
     parameter.  In either case, the arguments to the child process
     should start with the name of the command being run, but this is
     not enforced.

     The variants which include a “p” near the end (*note execlp():
     20ea, *note execlpe(): 20eb, *note execvp(): 20ec, and *note
     execvpe(): 20ed.) will use the ‘PATH’ environment variable to
     locate the program `file'.  When the environment is being replaced
     (using one of the *note exec*e: 20e7. variants, discussed in the
     next paragraph), the new environment is used as the source of the
     ‘PATH’ variable.  The other variants, *note execl(): 20e7, *note
     execle(): 20e9, *note execv(): 2058, and *note execve(): b1b, will
     not use the ‘PATH’ variable to locate the executable; `path' must
     contain an appropriate absolute or relative path.

     For *note execle(): 20e9, *note execlpe(): 20eb, *note execve():
     b1b, and *note execvpe(): 20ed. (note that these all end in “e”),
     the `env' parameter must be a mapping which is used to define the
     environment variables for the new process (these are used instead
     of the current process’ environment); the functions *note execl():
     20e7, *note execlp(): 20ea, *note execv(): 2058, and *note
     execvp(): 20ec. all cause the new process to inherit the
     environment of the current process.

     For *note execve(): b1b. on some platforms, `path' may also be
     specified as an open file descriptor.  This functionality may not
     be supported on your platform; you can check whether or not it is
     available using *note os.supports_fd: b1f.  If it is unavailable,
     using it will raise a *note NotImplementedError: 704.

     Raises an *note auditing event: fa1. ‘os.exec’ with arguments
     ‘path’, ‘args’, ‘env’.

     *note Availability: 1491.: Unix, Windows.

     New in version 3.3: Added support for specifying `path' as an open
     file descriptor for *note execve(): b1b.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: os._exit (n)

     Exit the process with status `n', without calling cleanup handlers,
     flushing stdio buffers, etc.

          Note: The standard way to exit is ‘sys.exit(n)’.  *note
          _exit(): 1854. should normally only be used in the child
          process after a *note fork(): a42.

The following exit codes are defined and can be used with *note _exit():
1854, although they are not required.  These are typically used for
system programs written in Python, such as a mail server’s external
command delivery program.

     Note: Some of these may not be available on all Unix platforms,
     since there is some variation.  These constants are defined where
     they are defined by the underlying platform.

 -- Data: os.EX_OK

     Exit code that means no error occurred.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_USAGE

     Exit code that means the command was used incorrectly, such as when
     the wrong number of arguments are given.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_DATAERR

     Exit code that means the input data was incorrect.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_NOINPUT

     Exit code that means an input file did not exist or was not
     readable.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_NOUSER

     Exit code that means a specified user did not exist.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_NOHOST

     Exit code that means a specified host did not exist.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_UNAVAILABLE

     Exit code that means that a required service is unavailable.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_SOFTWARE

     Exit code that means an internal software error was detected.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_OSERR

     Exit code that means an operating system error was detected, such
     as the inability to fork or create a pipe.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_OSFILE

     Exit code that means some system file did not exist, could not be
     opened, or had some other kind of error.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_CANTCREAT

     Exit code that means a user specified output file could not be
     created.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_IOERR

     Exit code that means that an error occurred while doing I/O on some
     file.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_TEMPFAIL

     Exit code that means a temporary failure occurred.  This indicates
     something that may not really be an error, such as a network
     connection that couldn’t be made during a retryable operation.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_PROTOCOL

     Exit code that means that a protocol exchange was illegal, invalid,
     or not understood.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_NOPERM

     Exit code that means that there were insufficient permissions to
     perform the operation (but not intended for file system problems).

     *note Availability: 1491.: Unix.

 -- Data: os.EX_CONFIG

     Exit code that means that some kind of configuration error
     occurred.

     *note Availability: 1491.: Unix.

 -- Data: os.EX_NOTFOUND

     Exit code that means something like “an entry was not found”.

     *note Availability: 1491.: Unix.

 -- Function: os.fork ()

     Fork a child process.  Return ‘0’ in the child and the child’s
     process id in the parent.  If an error occurs *note OSError: 304.
     is raised.

     Note that some platforms including FreeBSD <= 6.3 and Cygwin have
     known issues when using ‘fork()’ from a thread.

     Raises an *note auditing event: fa1. ‘os.fork’ with no arguments.

     Changed in version 3.8: Calling ‘fork()’ in a subinterpreter is no
     longer supported (*note RuntimeError: 3dc. is raised).

          Warning: See *note ssl: f3. for applications that use the SSL
          module with fork().

     *note Availability: 1491.: Unix.

 -- Function: os.forkpty ()

     Fork a child process, using a new pseudo-terminal as the child’s
     controlling terminal.  Return a pair of ‘(pid, fd)’, where `pid' is
     ‘0’ in the child, the new child’s process id in the parent, and
     `fd' is the file descriptor of the master end of the
     pseudo-terminal.  For a more portable approach, use the *note pty:
     d5. module.  If an error occurs *note OSError: 304. is raised.

     Raises an *note auditing event: fa1. ‘os.forkpty’ with no
     arguments.

     Changed in version 3.8: Calling ‘forkpty()’ in a subinterpreter is
     no longer supported (*note RuntimeError: 3dc. is raised).

     *note Availability: 1491.: some flavors of Unix.

 -- Function: os.kill (pid, sig)

     Send signal `sig' to the process `pid'.  Constants for the specific
     signals available on the host platform are defined in the *note
     signal: ea. module.

     Windows: The *note signal.CTRL_C_EVENT: 2100. and *note
     signal.CTRL_BREAK_EVENT: 2101. signals are special signals which
     can only be sent to console processes which share a common console
     window, e.g., some subprocesses.  Any other value for `sig' will
     cause the process to be unconditionally killed by the
     TerminateProcess API, and the exit code will be set to `sig'.  The
     Windows version of *note kill(): db9. additionally takes process
     handles to be killed.

     See also *note signal.pthread_kill(): b55.

     Raises an *note auditing event: fa1. ‘os.kill’ with arguments
     ‘pid’, ‘sig’.

     New in version 3.2: Windows support.

 -- Function: os.killpg (pgid, sig)

     Send the signal `sig' to the process group `pgid'.

     Raises an *note auditing event: fa1. ‘os.killpg’ with arguments
     ‘pgid’, ‘sig’.

     *note Availability: 1491.: Unix.

 -- Function: os.nice (increment)

     Add `increment' to the process’s “niceness”.  Return the new
     niceness.

     *note Availability: 1491.: Unix.

 -- Function: os.pidfd_open (pid, flags=0)

     Return a file descriptor referring to the process `pid'.  This
     descriptor can be used to perform process management without races
     and signals.  The `flags' argument is provided for future
     extensions; no flag values are currently defined.

     See the ‘pidfd_open(2)’ man page for more details.

     *note Availability: 1491.: Linux 5.3+

     New in version 3.9.

 -- Function: os.plock (op)

     Lock program segments into memory.  The value of `op' (defined in
     ‘<sys/lock.h>’) determines which segments are locked.

     *note Availability: 1491.: Unix.

 -- Function: os.popen (cmd, mode='r', buffering=-1)

     Open a pipe to or from command `cmd'.  The return value is an open
     file object connected to the pipe, which can be read or written
     depending on whether `mode' is ‘'r'’ (default) or ‘'w'’.  The
     `buffering' argument has the same meaning as the corresponding
     argument to the built-in *note open(): 16f. function.  The returned
     file object reads or writes text strings rather than bytes.

     The ‘close’ method returns *note None: 203. if the subprocess
     exited successfully, or the subprocess’s return code if there was
     an error.  On POSIX systems, if the return code is positive it
     represents the return value of the process left-shifted by one
     byte.  If the return code is negative, the process was terminated
     by the signal given by the negated value of the return code.  (For
     example, the return value might be ‘- signal.SIGKILL’ if the
     subprocess was killed.)  On Windows systems, the return value
     contains the signed integer return code from the child process.

     On Unix, *note waitstatus_to_exitcode(): 1ce. can be used to
     convert the ‘close’ method result (exit status) into an exit code
     if it is not ‘None’.  On Windows, the ‘close’ method result is
     directly the exit code (or ‘None’).

     This is implemented using *note subprocess.Popen: 3db.; see that
     class’s documentation for more powerful ways to manage and
     communicate with subprocesses.

 -- Function: os.posix_spawn (path, argv, env, *, file_actions=None,
          setpgroup=None, resetids=False, setsid=False, setsigmask=(),
          setsigdef=(), scheduler=None)

     Wraps the ‘posix_spawn()’ C library API for use from Python.

     Most users should use *note subprocess.run(): 4f3. instead of *note
     posix_spawn(): 381.

     The positional-only arguments `path', `args', and `env' are similar
     to *note execve(): b1b.

     The `path' parameter is the path to the executable file.  The
     `path' should contain a directory.  Use *note posix_spawnp(): 114d.
     to pass an executable file without directory.

     The `file_actions' argument may be a sequence of tuples describing
     actions to take on specific file descriptors in the child process
     between the C library implementation’s ‘fork()’ and ‘exec()’ steps.
     The first item in each tuple must be one of the three type
     indicator listed below describing the remaining tuple elements:

      -- Data: os.POSIX_SPAWN_OPEN

          (‘os.POSIX_SPAWN_OPEN’, `fd', `path', `flags', `mode')

          Performs ‘os.dup2(os.open(path, flags, mode), fd)’.

      -- Data: os.POSIX_SPAWN_CLOSE

          (‘os.POSIX_SPAWN_CLOSE’, `fd')

          Performs ‘os.close(fd)’.

      -- Data: os.POSIX_SPAWN_DUP2

          (‘os.POSIX_SPAWN_DUP2’, `fd', `new_fd')

          Performs ‘os.dup2(fd, new_fd)’.

     These tuples correspond to the C library
     ‘posix_spawn_file_actions_addopen()’,
     ‘posix_spawn_file_actions_addclose()’, and
     ‘posix_spawn_file_actions_adddup2()’ API calls used to prepare for
     the ‘posix_spawn()’ call itself.

     The `setpgroup' argument will set the process group of the child to
     the value specified.  If the value specified is 0, the child’s
     process group ID will be made the same as its process ID. If the
     value of `setpgroup' is not set, the child will inherit the
     parent’s process group ID. This argument corresponds to the C
     library ‘POSIX_SPAWN_SETPGROUP’ flag.

     If the `resetids' argument is ‘True’ it will reset the effective
     UID and GID of the child to the real UID and GID of the parent
     process.  If the argument is ‘False’, then the child retains the
     effective UID and GID of the parent.  In either case, if the
     set-user-ID and set-group-ID permission bits are enabled on the
     executable file, their effect will override the setting of the
     effective UID and GID. This argument corresponds to the C library
     ‘POSIX_SPAWN_RESETIDS’ flag.

     If the `setsid' argument is ‘True’, it will create a new session ID
     for ‘posix_spawn’.  `setsid' requires ‘POSIX_SPAWN_SETSID’ or
     ‘POSIX_SPAWN_SETSID_NP’ flag.  Otherwise, *note
     NotImplementedError: 704. is raised.

     The `setsigmask' argument will set the signal mask to the signal
     set specified.  If the parameter is not used, then the child
     inherits the parent’s signal mask.  This argument corresponds to
     the C library ‘POSIX_SPAWN_SETSIGMASK’ flag.

     The `sigdef' argument will reset the disposition of all signals in
     the set specified.  This argument corresponds to the C library
     ‘POSIX_SPAWN_SETSIGDEF’ flag.

     The `scheduler' argument must be a tuple containing the (optional)
     scheduler policy and an instance of *note sched_param: 2106. with
     the scheduler parameters.  A value of ‘None’ in the place of the
     scheduler policy indicates that is not being provided.  This
     argument is a combination of the C library
     ‘POSIX_SPAWN_SETSCHEDPARAM’ and ‘POSIX_SPAWN_SETSCHEDULER’ flags.

     Raises an *note auditing event: fa1. ‘os.posix_spawn’ with
     arguments ‘path’, ‘argv’, ‘env’.

     New in version 3.8.

     *note Availability: 1491.: Unix.

 -- Function: os.posix_spawnp (path, argv, env, *, file_actions=None,
          setpgroup=None, resetids=False, setsid=False, setsigmask=(),
          setsigdef=(), scheduler=None)

     Wraps the ‘posix_spawnp()’ C library API for use from Python.

     Similar to *note posix_spawn(): 381. except that the system
     searches for the `executable' file in the list of directories
     specified by the ‘PATH’ environment variable (in the same way as
     for ‘execvp(3)’).

     Raises an *note auditing event: fa1. ‘os.posix_spawn’ with
     arguments ‘path’, ‘argv’, ‘env’.

     New in version 3.8.

     *note Availability: 1491.: See *note posix_spawn(): 381.
     documentation.

 -- Function: os.register_at_fork (*, before=None, after_in_parent=None,
          after_in_child=None)

     Register callables to be executed when a new child process is
     forked using *note os.fork(): a42. or similar process cloning APIs.
     The parameters are optional and keyword-only.  Each specifies a
     different call point.

        * `before' is a function called before forking a child process.

        * `after_in_parent' is a function called from the parent process
          after forking a child process.

        * `after_in_child' is a function called from the child process.

     These calls are only made if control is expected to return to the
     Python interpreter.  A typical *note subprocess: f9. launch will
     not trigger them as the child is not going to re-enter the
     interpreter.

     Functions registered for execution before forking are called in
     reverse registration order.  Functions registered for execution
     after forking (either in the parent or in the child) are called in
     registration order.

     Note that ‘fork()’ calls made by third-party C code may not call
     those functions, unless it explicitly calls *note
     PyOS_BeforeFork(): 536, *note PyOS_AfterFork_Parent(): 537. and
     *note PyOS_AfterFork_Child(): 3ef.

     There is no way to unregister a function.

     *note Availability: 1491.: Unix.

     New in version 3.7.

 -- Function: os.spawnl (mode, path, ...)
 -- Function: os.spawnle (mode, path, ..., env)
 -- Function: os.spawnlp (mode, file, ...)
 -- Function: os.spawnlpe (mode, file, ..., env)
 -- Function: os.spawnv (mode, path, args)
 -- Function: os.spawnve (mode, path, args, env)
 -- Function: os.spawnvp (mode, file, args)
 -- Function: os.spawnvpe (mode, file, args, env)

     Execute the program `path' in a new process.

     (Note that the *note subprocess: f9. module provides more powerful
     facilities for spawning new processes and retrieving their results;
     using that module is preferable to using these functions.  Check
     especially the *note Replacing Older Functions with the subprocess
     Module: bc1. section.)

     If `mode' is *note P_NOWAIT: 210e, this function returns the
     process id of the new process; if `mode' is *note P_WAIT: 210f,
     returns the process’s exit code if it exits normally, or ‘-signal’,
     where `signal' is the signal that killed the process.  On Windows,
     the process id will actually be the process handle, so can be used
     with the *note waitpid(): 760. function.

     Note on VxWorks, this function doesn’t return ‘-signal’ when the
     new process is killed.  Instead it raises OSError exception.

     The “l” and “v” variants of the *note spawn*: 20a3. functions
     differ in how command-line arguments are passed.  The “l” variants
     are perhaps the easiest to work with if the number of parameters is
     fixed when the code is written; the individual parameters simply
     become additional parameters to the ‘spawnl*()’ functions.  The “v”
     variants are good when the number of parameters is variable, with
     the arguments being passed in a list or tuple as the `args'
     parameter.  In either case, the arguments to the child process must
     start with the name of the command being run.

     The variants which include a second “p” near the end (*note
     spawnlp(): 2108, *note spawnlpe(): 2109, *note spawnvp(): 210c, and
     *note spawnvpe(): 210d.) will use the ‘PATH’ environment variable
     to locate the program `file'.  When the environment is being
     replaced (using one of the *note spawn*e: 20a3. variants, discussed
     in the next paragraph), the new environment is used as the source
     of the ‘PATH’ variable.  The other variants, *note spawnl(): 20a3,
     *note spawnle(): 2107, *note spawnv(): 210a, and *note spawnve():
     210b, will not use the ‘PATH’ variable to locate the executable;
     `path' must contain an appropriate absolute or relative path.

     For *note spawnle(): 2107, *note spawnlpe(): 2109, *note spawnve():
     210b, and *note spawnvpe(): 210d. (note that these all end in “e”),
     the `env' parameter must be a mapping which is used to define the
     environment variables for the new process (they are used instead of
     the current process’ environment); the functions *note spawnl():
     20a3, *note spawnlp(): 2108, *note spawnv(): 210a, and *note
     spawnvp(): 210c. all cause the new process to inherit the
     environment of the current process.  Note that keys and values in
     the `env' dictionary must be strings; invalid keys or values will
     cause the function to fail, with a return value of ‘127’.

     As an example, the following calls to *note spawnlp(): 2108. and
     *note spawnvpe(): 210d. are equivalent:

          import os
          os.spawnlp(os.P_WAIT, 'cp', 'cp', 'index.html', '/dev/null')

          L = ['cp', 'index.html', '/dev/null']
          os.spawnvpe(os.P_WAIT, 'cp', L, os.environ)

     Raises an *note auditing event: fa1. ‘os.spawn’ with arguments
     ‘mode’, ‘path’, ‘args’, ‘env’.

     *note Availability: 1491.: Unix, Windows.  *note spawnlp(): 2108,
     *note spawnlpe(): 2109, *note spawnvp(): 210c. and *note
     spawnvpe(): 210d. are not available on Windows.  *note spawnle():
     2107. and *note spawnve(): 210b. are not thread-safe on Windows; we
     advise you to use the *note subprocess: f9. module instead.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Data: os.P_NOWAIT
 -- Data: os.P_NOWAITO

     Possible values for the `mode' parameter to the *note spawn*: 20a3.
     family of functions.  If either of these values is given, the
     ‘spawn*()’ functions will return as soon as the new process has
     been created, with the process id as the return value.

     *note Availability: 1491.: Unix, Windows.

 -- Data: os.P_WAIT

     Possible value for the `mode' parameter to the *note spawn*: 20a3.
     family of functions.  If this is given as `mode', the ‘spawn*()’
     functions will not return until the new process has run to
     completion and will return the exit code of the process the run is
     successful, or ‘-signal’ if a signal kills the process.

     *note Availability: 1491.: Unix, Windows.

 -- Data: os.P_DETACH
 -- Data: os.P_OVERLAY

     Possible values for the `mode' parameter to the *note spawn*: 20a3.
     family of functions.  These are less portable than those listed
     above.  *note P_DETACH: 2111. is similar to *note P_NOWAIT: 210e,
     but the new process is detached from the console of the calling
     process.  If *note P_OVERLAY: 2112. is used, the current process
     will be replaced; the *note spawn*: 20a3. function will not return.

     *note Availability: 1491.: Windows.

 -- Function: os.startfile (path[, operation])

     Start a file with its associated application.

     When `operation' is not specified or ‘'open'’, this acts like
     double-clicking the file in Windows Explorer, or giving the file
     name as an argument to the ‘start’ command from the interactive
     command shell: the file is opened with whatever application (if
     any) its extension is associated.

     When another `operation' is given, it must be a “command verb” that
     specifies what should be done with the file.  Common verbs
     documented by Microsoft are ‘'print'’ and ‘'edit'’ (to be used on
     files) as well as ‘'explore'’ and ‘'find'’ (to be used on
     directories).

     *note startfile(): 2113. returns as soon as the associated
     application is launched.  There is no option to wait for the
     application to close, and no way to retrieve the application’s exit
     status.  The `path' parameter is relative to the current directory.
     If you want to use an absolute path, make sure the first character
     is not a slash (‘'/'’); the underlying Win32 ‘ShellExecute()’
     function doesn’t work if it is.  Use the *note os.path.normpath():
     d77. function to ensure that the path is properly encoded for
     Win32.

     To reduce interpreter startup overhead, the Win32 ‘ShellExecute()’
     function is not resolved until this function is first called.  If
     the function cannot be resolved, *note NotImplementedError: 704.
     will be raised.

     Raises an *note auditing event: fa1. ‘os.startfile’ with arguments
     ‘path’, ‘operation’.

     *note Availability: 1491.: Windows.

 -- Function: os.system (command)

     Execute the command (a string) in a subshell.  This is implemented
     by calling the Standard C function ‘system()’, and has the same
     limitations.  Changes to *note sys.stdin: 41e, etc.  are not
     reflected in the environment of the executed command.  If `command'
     generates any output, it will be sent to the interpreter standard
     output stream.  The C standard does not specify the meaning of the
     return value of the C function, so the return value of the Python
     function is system-dependent.

     On Unix, the return value is the exit status of the process encoded
     in the format specified for *note wait(): 75e.

     On Windows, the return value is that returned by the system shell
     after running `command'.  The shell is given by the Windows
     environment variable ‘COMSPEC’: it is usually ‘cmd.exe’, which
     returns the exit status of the command run; on systems using a
     non-native shell, consult your shell documentation.

     The *note subprocess: f9. module provides more powerful facilities
     for spawning new processes and retrieving their results; using that
     module is preferable to using this function.  See the *note
     Replacing Older Functions with the subprocess Module: bc1. section
     in the *note subprocess: f9. documentation for some helpful
     recipes.

     On Unix, *note waitstatus_to_exitcode(): 1ce. can be used to
     convert the result (exit status) into an exit code.  On Windows,
     the result is directly the exit code.

     Raises an *note auditing event: fa1. ‘os.system’ with argument
     ‘command’.

     *note Availability: 1491.: Unix, Windows.

 -- Function: os.times ()

     Returns the current global process times.  The return value is an
     object with five attributes:

        * ‘user’ - user time

        * ‘system’ - system time

        * ‘children_user’ - user time of all child processes

        * ‘children_system’ - system time of all child processes

        * ‘elapsed’ - elapsed real time since a fixed point in the past

     For backwards compatibility, this object also behaves like a
     five-tuple containing ‘user’, ‘system’, ‘children_user’,
     ‘children_system’, and ‘elapsed’ in that order.

     See the Unix manual page ‘times(2)’ and ‘times(3)’ manual page on
     Unix or the GetProcessTimes MSDN(2) on Windows.  On Windows, only
     ‘user’ and ‘system’ are known; the other attributes are zero.

     *note Availability: 1491.: Unix, Windows.

     Changed in version 3.3: Return type changed from a tuple to a
     tuple-like object with named attributes.

 -- Function: os.wait ()

     Wait for completion of a child process, and return a tuple
     containing its pid and exit status indication: a 16-bit number,
     whose low byte is the signal number that killed the process, and
     whose high byte is the exit status (if the signal number is zero);
     the high bit of the low byte is set if a core file was produced.

     *note waitstatus_to_exitcode(): 1ce. can be used to convert the
     exit status into an exit code.

     *note Availability: 1491.: Unix.

     See also
     ........

     *note waitpid(): 760. can be used to wait for the completion of a
     specific child process and has more options.

 -- Function: os.waitid (idtype, id, options)

     Wait for the completion of one or more child processes.  `idtype'
     can be *note P_PID: 2114, *note P_PGID: 2115, *note P_ALL: 2116, or
     *note P_PIDFD: 1cb. on Linux.  `id' specifies the pid to wait on.
     `options' is constructed from the ORing of one or more of *note
     WEXITED: 2117, *note WSTOPPED: 2118. or *note WCONTINUED: 2119. and
     additionally may be ORed with *note WNOHANG: 211a. or *note
     WNOWAIT: 211b.  The return value is an object representing the data
     contained in the ‘siginfo_t’ structure, namely: ‘si_pid’, ‘si_uid’,
     ‘si_signo’, ‘si_status’, ‘si_code’ or ‘None’ if *note WNOHANG:
     211a. is specified and there are no children in a waitable state.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Data: os.P_PID
 -- Data: os.P_PGID
 -- Data: os.P_ALL

     These are the possible values for `idtype' in *note waitid(): 75f.
     They affect how `id' is interpreted.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Data: os.P_PIDFD

     This is a Linux-specific `idtype' that indicates that `id' is a
     file descriptor that refers to a process.

     *note Availability: 1491.: Linux 5.4+

     New in version 3.9.

 -- Data: os.WEXITED
 -- Data: os.WSTOPPED
 -- Data: os.WNOWAIT

     Flags that can be used in `options' in *note waitid(): 75f. that
     specify what child signal to wait for.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Data: os.CLD_EXITED
 -- Data: os.CLD_KILLED
 -- Data: os.CLD_DUMPED
 -- Data: os.CLD_TRAPPED
 -- Data: os.CLD_STOPPED
 -- Data: os.CLD_CONTINUED

     These are the possible values for ‘si_code’ in the result returned
     by *note waitid(): 75f.

     *note Availability: 1491.: Unix.

     New in version 3.3.

     Changed in version 3.9: Added *note CLD_KILLED: 1c9. and *note
     CLD_STOPPED: 1ca. values.

 -- Function: os.waitpid (pid, options)

     The details of this function differ on Unix and Windows.

     On Unix: Wait for completion of a child process given by process id
     `pid', and return a tuple containing its process id and exit status
     indication (encoded as for *note wait(): 75e.).  The semantics of
     the call are affected by the value of the integer `options', which
     should be ‘0’ for normal operation.

     If `pid' is greater than ‘0’, *note waitpid(): 760. requests status
     information for that specific process.  If `pid' is ‘0’, the
     request is for the status of any child in the process group of the
     current process.  If `pid' is ‘-1’, the request pertains to any
     child of the current process.  If `pid' is less than ‘-1’, status
     is requested for any process in the process group ‘-pid’ (the
     absolute value of `pid').

     An *note OSError: 304. is raised with the value of errno when the
     syscall returns -1.

     On Windows: Wait for completion of a process given by process
     handle `pid', and return a tuple containing `pid', and its exit
     status shifted left by 8 bits (shifting makes cross-platform use of
     the function easier).  A `pid' less than or equal to ‘0’ has no
     special meaning on Windows, and raises an exception.  The value of
     integer `options' has no effect.  `pid' can refer to any process
     whose id is known, not necessarily a child process.  The *note
     spawn*: 20a3. functions called with *note P_NOWAIT: 210e. return
     suitable process handles.

     *note waitstatus_to_exitcode(): 1ce. can be used to convert the
     exit status into an exit code.

     Changed in version 3.5: If the system call is interrupted and the
     signal handler does not raise an exception, the function now
     retries the system call instead of raising an *note
     InterruptedError: 74c. exception (see PEP 475(3) for the
     rationale).

 -- Function: os.wait3 (options)

     Similar to *note waitpid(): 760, except no process id argument is
     given and a 3-element tuple containing the child’s process id, exit
     status indication, and resource usage information is returned.
     Refer to *note resource: e0.*note getrusage(): e5e. for details on
     resource usage information.  The option argument is the same as
     that provided to *note waitpid(): 760. and *note wait4(): 75d.

     *note waitstatus_to_exitcode(): 1ce. can be used to convert the
     exit status into an exitcode.

     *note Availability: 1491.: Unix.

 -- Function: os.wait4 (pid, options)

     Similar to *note waitpid(): 760, except a 3-element tuple,
     containing the child’s process id, exit status indication, and
     resource usage information is returned.  Refer to *note resource:
     e0.*note getrusage(): e5e. for details on resource usage
     information.  The arguments to *note wait4(): 75d. are the same as
     those provided to *note waitpid(): 760.

     *note waitstatus_to_exitcode(): 1ce. can be used to convert the
     exit status into an exitcode.

     *note Availability: 1491.: Unix.

 -- Function: os.waitstatus_to_exitcode (status)

     Convert a wait status to an exit code.

     On Unix:

        * If the process exited normally (if ‘WIFEXITED(status)’ is
          true), return the process exit status (return
          ‘WEXITSTATUS(status)’): result greater than or equal to 0.

        * If the process was terminated by a signal (if
          ‘WIFSIGNALED(status)’ is true), return ‘-signum’ where
          `signum' is the number of the signal that caused the process
          to terminate (return ‘-WTERMSIG(status)’): result less than 0.

        * Otherwise, raise a *note ValueError: 16d.

     On Windows, return `status' shifted right by 8 bits.

     On Unix, if the process is being traced or if *note waitpid(): 760.
     was called with *note WUNTRACED: 2120. option, the caller must
     first check if ‘WIFSTOPPED(status)’ is true.  This function must
     not be called if ‘WIFSTOPPED(status)’ is true.

     See also
     ........

     *note WIFEXITED(): 2121, *note WEXITSTATUS(): 2122, *note
     WIFSIGNALED(): 2123, *note WTERMSIG(): 2124, *note WIFSTOPPED():
     2125, *note WSTOPSIG(): 2126. functions.

     New in version 3.9.

 -- Data: os.WNOHANG

     The option for *note waitpid(): 760. to return immediately if no
     child process status is available immediately.  The function
     returns ‘(0, 0)’ in this case.

     *note Availability: 1491.: Unix.

 -- Data: os.WCONTINUED

     This option causes child processes to be reported if they have been
     continued from a job control stop since their status was last
     reported.

     *note Availability: 1491.: some Unix systems.

 -- Data: os.WUNTRACED

     This option causes child processes to be reported if they have been
     stopped but their current state has not been reported since they
     were stopped.

     *note Availability: 1491.: Unix.

The following functions take a process status code as returned by *note
system(): e86, *note wait(): 75e, or *note waitpid(): 760. as a
parameter.  They may be used to determine the disposition of a process.

 -- Function: os.WCOREDUMP (status)

     Return ‘True’ if a core dump was generated for the process,
     otherwise return ‘False’.

     This function should be employed only if *note WIFSIGNALED(): 2123.
     is true.

     *note Availability: 1491.: Unix.

 -- Function: os.WIFCONTINUED (status)

     Return ‘True’ if a stopped child has been resumed by delivery of
     *note SIGCONT: 2129. (if the process has been continued from a job
     control stop), otherwise return ‘False’.

     See *note WCONTINUED: 2119. option.

     *note Availability: 1491.: Unix.

 -- Function: os.WIFSTOPPED (status)

     Return ‘True’ if the process was stopped by delivery of a signal,
     otherwise return ‘False’.

     *note WIFSTOPPED(): 2125. only returns ‘True’ if the *note
     waitpid(): 760. call was done using *note WUNTRACED: 2120. option
     or when the process is being traced (see ‘ptrace(2)’).

     *note Availability: 1491.: Unix.

 -- Function: os.WIFSIGNALED (status)

     Return ‘True’ if the process was terminated by a signal, otherwise
     return ‘False’.

     *note Availability: 1491.: Unix.

 -- Function: os.WIFEXITED (status)

     Return ‘True’ if the process exited terminated normally, that is,
     by calling ‘exit()’ or ‘_exit()’, or by returning from ‘main()’;
     otherwise return ‘False’.

     *note Availability: 1491.: Unix.

 -- Function: os.WEXITSTATUS (status)

     Return the process exit status.

     This function should be employed only if *note WIFEXITED(): 2121.
     is true.

     *note Availability: 1491.: Unix.

 -- Function: os.WSTOPSIG (status)

     Return the signal which caused the process to stop.

     This function should be employed only if *note WIFSTOPPED(): 2125.
     is true.

     *note Availability: 1491.: Unix.

 -- Function: os.WTERMSIG (status)

     Return the number of the signal that caused the process to
     terminate.

     This function should be employed only if *note WIFSIGNALED(): 2123.
     is true.

     *note Availability: 1491.: Unix.

   ---------- Footnotes ----------

   (1) https://msdn.microsoft.com/44228cf2-6306-466c-8f16-f513cd3ba8b5

   (2) 
https://docs.microsoft.com/windows/win32/api/processthreadsapi/nf-processthreadsapi-getprocesstimes

   (3) https://www.python.org/dev/peps/pep-0475


File: python.info,  Node: Interface to the scheduler,  Next: Miscellaneous System Information,  Prev: Process Management,  Up: os — Miscellaneous operating system interfaces

5.16.1.10 Interface to the scheduler
....................................

These functions control how a process is allocated CPU time by the
operating system.  They are only available on some Unix platforms.  For
more detailed information, consult your Unix manpages.

New in version 3.3.

The following scheduling policies are exposed if they are supported by
the operating system.

 -- Data: os.SCHED_OTHER

     The default scheduling policy.

 -- Data: os.SCHED_BATCH

     Scheduling policy for CPU-intensive processes that tries to
     preserve interactivity on the rest of the computer.

 -- Data: os.SCHED_IDLE

     Scheduling policy for extremely low priority background tasks.

 -- Data: os.SCHED_SPORADIC

     Scheduling policy for sporadic server programs.

 -- Data: os.SCHED_FIFO

     A First In First Out scheduling policy.

 -- Data: os.SCHED_RR

     A round-robin scheduling policy.

 -- Data: os.SCHED_RESET_ON_FORK

     This flag can be OR’ed with any other scheduling policy.  When a
     process with this flag set forks, its child’s scheduling policy and
     priority are reset to the default.

 -- Class: os.sched_param (sched_priority)

     This class represents tunable scheduling parameters used in *note
     sched_setparam(): b31, *note sched_setscheduler(): b32, and *note
     sched_getparam(): b2d.  It is immutable.

     At the moment, there is only one possible parameter:

      -- Attribute: sched_priority

          The scheduling priority for a scheduling policy.

 -- Function: os.sched_get_priority_min (policy)

     Get the minimum priority value for `policy'.  `policy' is one of
     the scheduling policy constants above.

 -- Function: os.sched_get_priority_max (policy)

     Get the maximum priority value for `policy'.  `policy' is one of
     the scheduling policy constants above.

 -- Function: os.sched_setscheduler (pid, policy, param)

     Set the scheduling policy for the process with PID `pid'.  A `pid'
     of 0 means the calling process.  `policy' is one of the scheduling
     policy constants above.  `param' is a *note sched_param: 2106.
     instance.

 -- Function: os.sched_getscheduler (pid)

     Return the scheduling policy for the process with PID `pid'.  A
     `pid' of 0 means the calling process.  The result is one of the
     scheduling policy constants above.

 -- Function: os.sched_setparam (pid, param)

     Set the scheduling parameters for the process with PID `pid'.  A
     `pid' of 0 means the calling process.  `param' is a *note
     sched_param: 2106. instance.

 -- Function: os.sched_getparam (pid)

     Return the scheduling parameters as a *note sched_param: 2106.
     instance for the process with PID `pid'.  A `pid' of 0 means the
     calling process.

 -- Function: os.sched_rr_get_interval (pid)

     Return the round-robin quantum in seconds for the process with PID
     `pid'.  A `pid' of 0 means the calling process.

 -- Function: os.sched_yield ()

     Voluntarily relinquish the CPU.

 -- Function: os.sched_setaffinity (pid, mask)

     Restrict the process with PID `pid' (or the current process if
     zero) to a set of CPUs.  `mask' is an iterable of integers
     representing the set of CPUs to which the process should be
     restricted.

 -- Function: os.sched_getaffinity (pid)

     Return the set of CPUs the process with PID `pid' (or the current
     process if zero) is restricted to.


File: python.info,  Node: Miscellaneous System Information,  Next: Random numbers<2>,  Prev: Interface to the scheduler,  Up: os — Miscellaneous operating system interfaces

5.16.1.11 Miscellaneous System Information
..........................................

 -- Function: os.confstr (name)

     Return string-valued system configuration values.  `name' specifies
     the configuration value to retrieve; it may be a string which is
     the name of a defined system value; these names are specified in a
     number of standards (POSIX, Unix 95, Unix 98, and others).  Some
     platforms define additional names as well.  The names known to the
     host operating system are given as the keys of the ‘confstr_names’
     dictionary.  For configuration variables not included in that
     mapping, passing an integer for `name' is also accepted.

     If the configuration value specified by `name' isn’t defined,
     ‘None’ is returned.

     If `name' is a string and is not known, *note ValueError: 16d. is
     raised.  If a specific value for `name' is not supported by the
     host system, even if it is included in ‘confstr_names’, an *note
     OSError: 304. is raised with *note errno.EINVAL: 1104. for the
     error number.

     *note Availability: 1491.: Unix.

 -- Data: os.confstr_names

     Dictionary mapping names accepted by *note confstr(): 2135. to the
     integer values defined for those names by the host operating
     system.  This can be used to determine the set of names known to
     the system.

     *note Availability: 1491.: Unix.

 -- Function: os.cpu_count ()

     Return the number of CPUs in the system.  Returns ‘None’ if
     undetermined.

     This number is not equivalent to the number of CPUs the current
     process can use.  The number of usable CPUs can be obtained with
     ‘len(os.sched_getaffinity(0))’

     New in version 3.4.

 -- Function: os.getloadavg ()

     Return the number of processes in the system run queue averaged
     over the last 1, 5, and 15 minutes or raises *note OSError: 304. if
     the load average was unobtainable.

     *note Availability: 1491.: Unix.

 -- Function: os.sysconf (name)

     Return integer-valued system configuration values.  If the
     configuration value specified by `name' isn’t defined, ‘-1’ is
     returned.  The comments regarding the `name' parameter for *note
     confstr(): 2135. apply here as well; the dictionary that provides
     information on the known names is given by ‘sysconf_names’.

     *note Availability: 1491.: Unix.

 -- Data: os.sysconf_names

     Dictionary mapping names accepted by *note sysconf(): 2094. to the
     integer values defined for those names by the host operating
     system.  This can be used to determine the set of names known to
     the system.

     *note Availability: 1491.: Unix.

The following data values are used to support path manipulation
operations.  These are defined for all platforms.

Higher-level operations on pathnames are defined in the *note os.path:
c5. module.

 -- Data: os.curdir

     The constant string used by the operating system to refer to the
     current directory.  This is ‘'.'’ for Windows and POSIX. Also
     available via *note os.path: c5.

 -- Data: os.pardir

     The constant string used by the operating system to refer to the
     parent directory.  This is ‘'..'’ for Windows and POSIX. Also
     available via *note os.path: c5.

 -- Data: os.sep

     The character used by the operating system to separate pathname
     components.  This is ‘'/'’ for POSIX and ‘'\\'’ for Windows.  Note
     that knowing this is not sufficient to be able to parse or
     concatenate pathnames — use *note os.path.split(): 1d49. and *note
     os.path.join(): 10c7. — but it is occasionally useful.  Also
     available via *note os.path: c5.

 -- Data: os.altsep

     An alternative character used by the operating system to separate
     pathname components, or ‘None’ if only one separator character
     exists.  This is set to ‘'/'’ on Windows systems where ‘sep’ is a
     backslash.  Also available via *note os.path: c5.

 -- Data: os.extsep

     The character which separates the base filename from the extension;
     for example, the ‘'.'’ in ‘os.py’.  Also available via *note
     os.path: c5.

 -- Data: os.pathsep

     The character conventionally used by the operating system to
     separate search path components (as in ‘PATH’), such as ‘':'’ for
     POSIX or ‘';'’ for Windows.  Also available via *note os.path: c5.

 -- Data: os.defpath

     The default search path used by *note exec*p*: 20e7. and *note
     spawn*p*: 20a3. if the environment doesn’t have a ‘'PATH'’ key.
     Also available via *note os.path: c5.

 -- Data: os.linesep

     The string used to separate (or, rather, terminate) lines on the
     current platform.  This may be a single character, such as ‘'\n'’
     for POSIX, or multiple characters, for example, ‘'\r\n'’ for
     Windows.  Do not use `os.linesep' as a line terminator when writing
     files opened in text mode (the default); use a single ‘'\n'’
     instead, on all platforms.

 -- Data: os.devnull

     The file path of the null device.  For example: ‘'/dev/null'’ for
     POSIX, ‘'nul'’ for Windows.  Also available via *note os.path: c5.

 -- Data: os.RTLD_LAZY
 -- Data: os.RTLD_NOW
 -- Data: os.RTLD_GLOBAL
 -- Data: os.RTLD_LOCAL
 -- Data: os.RTLD_NODELETE
 -- Data: os.RTLD_NOLOAD
 -- Data: os.RTLD_DEEPBIND

     Flags for use with the *note setdlopenflags(): b41. and *note
     getdlopenflags(): f10. functions.  See the Unix manual page
     ‘dlopen(3)’ for what the different flags mean.

     New in version 3.3.


File: python.info,  Node: Random numbers<2>,  Prev: Miscellaneous System Information,  Up: os — Miscellaneous operating system interfaces

5.16.1.12 Random numbers
........................

 -- Function: os.getrandom (size, flags=0)

     Get up to `size' random bytes.  The function can return less bytes
     than requested.

     These bytes can be used to seed user-space random number generators
     or for cryptographic purposes.

     ‘getrandom()’ relies on entropy gathered from device drivers and
     other sources of environmental noise.  Unnecessarily reading large
     quantities of data will have a negative impact on other users of
     the ‘/dev/random’ and ‘/dev/urandom’ devices.

     The flags argument is a bit mask that can contain zero or more of
     the following values ORed together: *note os.GRND_RANDOM: 213b. and
     *note GRND_NONBLOCK: 213c.

     See also the Linux getrandom() manual page(1).

     *note Availability: 1491.: Linux 3.17 and newer.

     New in version 3.6.

 -- Function: os.urandom (size)

     Return a string of `size' random bytes suitable for cryptographic
     use.

     This function returns random bytes from an OS-specific randomness
     source.  The returned data should be unpredictable enough for
     cryptographic applications, though its exact quality depends on the
     OS implementation.

     On Linux, if the ‘getrandom()’ syscall is available, it is used in
     blocking mode: block until the system urandom entropy pool is
     initialized (128 bits of entropy are collected by the kernel).  See
     the PEP 524(2) for the rationale.  On Linux, the *note getrandom():
     662. function can be used to get random bytes in non-blocking mode
     (using the *note GRND_NONBLOCK: 213c. flag) or to poll until the
     system urandom entropy pool is initialized.

     On a Unix-like system, random bytes are read from the
     ‘/dev/urandom’ device.  If the ‘/dev/urandom’ device is not
     available or not readable, the *note NotImplementedError: 704.
     exception is raised.

     On Windows, it will use ‘CryptGenRandom()’.

     See also
     ........

     The *note secrets: e4. module provides higher level functions.  For
     an easy-to-use interface to the random number generator provided by
     your platform, please see *note random.SystemRandom: 1c5f.

     Changed in version 3.6.0: On Linux, ‘getrandom()’ is now used in
     blocking mode to increase the security.

     Changed in version 3.5.2: On Linux, if the ‘getrandom()’ syscall
     blocks (the urandom entropy pool is not initialized yet), fall back
     on reading ‘/dev/urandom’.

     Changed in version 3.5: On Linux 3.17 and newer, the ‘getrandom()’
     syscall is now used when available.  On OpenBSD 5.6 and newer, the
     C ‘getentropy()’ function is now used.  These functions avoid the
     usage of an internal file descriptor.

 -- Data: os.GRND_NONBLOCK

     By default, when reading from ‘/dev/random’, *note getrandom():
     662. blocks if no random bytes are available, and when reading from
     ‘/dev/urandom’, it blocks if the entropy pool has not yet been
     initialized.

     If the *note GRND_NONBLOCK: 213c. flag is set, then *note
     getrandom(): 662. does not block in these cases, but instead
     immediately raises *note BlockingIOError: a78.

     New in version 3.6.

 -- Data: os.GRND_RANDOM

     If this bit is set, then random bytes are drawn from the
     ‘/dev/random’ pool instead of the ‘/dev/urandom’ pool.

     New in version 3.6.

   ---------- Footnotes ----------

   (1) http://man7.org/linux/man-pages/man2/getrandom.2.html

   (2) https://www.python.org/dev/peps/pep-0524


File: python.info,  Node: io — Core tools for working with streams,  Next: time — Time access and conversions,  Prev: os — Miscellaneous operating system interfaces,  Up: Generic Operating System Services

5.16.2 ‘io’ — Core tools for working with streams
-------------------------------------------------

`Source code:' Lib/io.py(1)

__________________________________________________________________

* Menu:

* Overview::
* High-level Module Interface::
* Class hierarchy::
* Performance: Performance<3>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/io.py


File: python.info,  Node: Overview,  Next: High-level Module Interface,  Up: io — Core tools for working with streams

5.16.2.1 Overview
.................

The *note io: a1. module provides Python’s main facilities for dealing
with various types of I/O. There are three main types of I/O: `text
I/O', `binary I/O' and `raw I/O'. These are generic categories, and
various backing stores can be used for each of them.  A concrete object
belonging to any of these categories is called a *note file object: c14.
Other common terms are `stream' and `file-like object'.

Independent of its category, each concrete stream object will also have
various capabilities: it can be read-only, write-only, or read-write.
It can also allow arbitrary random access (seeking forwards or backwards
to any location), or only sequential access (for example in the case of
a socket or pipe).

All streams are careful about the type of data you give to them.  For
example giving a *note str: 205. object to the ‘write()’ method of a
binary stream will raise a *note TypeError: 1fe.  So will giving a *note
bytes: 172. object to the ‘write()’ method of a text stream.

Changed in version 3.3: Operations that used to raise *note IOError:
a73. now raise *note OSError: 304, since *note IOError: a73. is now an
alias of *note OSError: 304.

* Menu:

* Text I/O::
* Binary I/O::
* Raw I/O::


File: python.info,  Node: Text I/O,  Next: Binary I/O,  Up: Overview

5.16.2.2 Text I/O
.................

Text I/O expects and produces *note str: 205. objects.  This means that
whenever the backing store is natively made of bytes (such as in the
case of a file), encoding and decoding of data is made transparently as
well as optional translation of platform-specific newline characters.

The easiest way to create a text stream is with *note open(): 16f,
optionally specifying an encoding:

     f = open("myfile.txt", "r", encoding="utf-8")

In-memory text streams are also available as *note StringIO: 91a.
objects:

     f = io.StringIO("some initial text data")

The text stream API is described in detail in the documentation of *note
TextIOBase: d01.


File: python.info,  Node: Binary I/O,  Next: Raw I/O,  Prev: Text I/O,  Up: Overview

5.16.2.3 Binary I/O
...................

Binary I/O (also called `buffered I/O') expects *note bytes-like
objects: 6df. and produces *note bytes: 172. objects.  No encoding,
decoding, or newline translation is performed.  This category of streams
can be used for all kinds of non-text data, and also when manual control
over the handling of text data is desired.

The easiest way to create a binary stream is with *note open(): 16f.
with ‘'b'’ in the mode string:

     f = open("myfile.jpg", "rb")

In-memory binary streams are also available as *note BytesIO: 88a.
objects:

     f = io.BytesIO(b"some initial binary data: \x00\x01")

The binary stream API is described in detail in the docs of *note
BufferedIOBase: 67f.

Other library modules may provide additional ways to create text or
binary streams.  See *note socket.socket.makefile(): bec. for example.


File: python.info,  Node: Raw I/O,  Prev: Binary I/O,  Up: Overview

5.16.2.4 Raw I/O
................

Raw I/O (also called `unbuffered I/O') is generally used as a low-level
building-block for binary and text streams; it is rarely useful to
directly manipulate a raw stream from user code.  Nevertheless, you can
create a raw stream by opening a file in binary mode with buffering
disabled:

     f = open("myfile.jpg", "rb", buffering=0)

The raw stream API is described in detail in the docs of *note
RawIOBase: af1.


File: python.info,  Node: High-level Module Interface,  Next: Class hierarchy,  Prev: Overview,  Up: io — Core tools for working with streams

5.16.2.5 High-level Module Interface
....................................

 -- Data: io.DEFAULT_BUFFER_SIZE

     An int containing the default buffer size used by the module’s
     buffered I/O classes.  *note open(): 16f. uses the file’s blksize
     (as obtained by *note os.stat(): 321.) if possible.

 -- Function: io.open (file, mode='r', buffering=-1, encoding=None,
          errors=None, newline=None, closefd=True, opener=None)

     This is an alias for the builtin *note open(): 16f. function.

     This function raises an *note auditing event: fa1. ‘open’ with
     arguments ‘path’, ‘mode’ and ‘flags’.  The ‘mode’ and ‘flags’
     arguments may have been modified or inferred from the original
     call.

 -- Function: io.open_code (path)

     Opens the provided file with mode ‘'rb'’.  This function should be
     used when the intent is to treat the contents as executable code.

     ‘path’ should be a *note str: 205. and an absolute path.

     The behavior of this function may be overridden by an earlier call
     to the *note PyFile_SetOpenCodeHook(): 2144.  However, assuming
     that ‘path’ is a *note str: 205. and an absolute path,
     ‘open_code(path)’ should always behave the same as ‘open(path,
     'rb')’.  Overriding the behavior is intended for additional
     validation or preprocessing of the file.

     New in version 3.8.

 -- Exception: io.BlockingIOError

     This is a compatibility alias for the builtin *note
     BlockingIOError: a78. exception.

 -- Exception: io.UnsupportedOperation

     An exception inheriting *note OSError: 304. and *note ValueError:
     16d. that is raised when an unsupported operation is called on a
     stream.

See also
........

*note sys: fd.

     contains the standard IO streams: *note sys.stdin: 41e, *note
     sys.stdout: 41f, and *note sys.stderr: 1ea.


File: python.info,  Node: Class hierarchy,  Next: Performance<3>,  Prev: High-level Module Interface,  Up: io — Core tools for working with streams

5.16.2.6 Class hierarchy
........................

The implementation of I/O streams is organized as a hierarchy of
classes.  First *note abstract base classes: c05. (ABCs), which are used
to specify the various categories of streams, then concrete classes
providing the standard stream implementations.

          Note: The abstract base classes also provide default
          implementations of some methods in order to help
          implementation of concrete stream classes.  For example, *note
          BufferedIOBase: 67f. provides unoptimized implementations of
          ‘readinto()’ and *note readline(): 1849.

At the top of the I/O hierarchy is the abstract base class *note IOBase:
30c.  It defines the basic interface to a stream.  Note, however, that
there is no separation between reading and writing to streams;
implementations are allowed to raise *note UnsupportedOperation: 1083.
if they do not support a given operation.

The *note RawIOBase: af1. ABC extends *note IOBase: 30c.  It deals with
the reading and writing of bytes to a stream.  *note FileIO: d6c.
subclasses *note RawIOBase: af1. to provide an interface to files in the
machine’s file system.

The *note BufferedIOBase: 67f. ABC extends *note IOBase: 30c.  It deals
with buffering on a raw binary stream (*note RawIOBase: af1.).  Its
subclasses, *note BufferedWriter: 1733, *note BufferedReader: c5b, and
*note BufferedRWPair: 2147. buffer raw binary streams that are readable,
writable, and both readable and writable, respectively.  *note
BufferedRandom: 1734. provides a buffered interface to seekable streams.
Another *note BufferedIOBase: 67f. subclass, *note BytesIO: 88a, is a
stream of in-memory bytes.

The *note TextIOBase: d01. ABC extends *note IOBase: 30c.  It deals with
streams whose bytes represent text, and handles encoding and decoding to
and from strings.  *note TextIOWrapper: 6ea, which extends *note
TextIOBase: d01, is a buffered text interface to a buffered raw stream
(*note BufferedIOBase: 67f.).  Finally, *note StringIO: 91a. is an
in-memory stream for text.

Argument names are not part of the specification, and only the arguments
of *note open(): 16f. are intended to be used as keyword arguments.

The following table summarizes the ABCs provided by the *note io: a1.
module:

ABC                           Inherits               Stub Methods                 Mixin Methods and Properties
                                                                                  
-----------------------------------------------------------------------------------------------------------------------------------------
                                                                                  
*note IOBase: 30c.                                   ‘fileno’, ‘seek’, and        ‘close’, ‘closed’, ‘__enter__’, ‘__exit__’, ‘flush’,
                                                     ‘truncate’                   ‘isatty’, ‘__iter__’, ‘__next__’, ‘readable’,
                                                                                  ‘readline’, ‘readlines’, ‘seekable’, ‘tell’,
                                                                                  ‘writable’, and ‘writelines’
                                                                                  
                                                                                  
*note RawIOBase: af1.         *note IOBase: 30c.     ‘readinto’ and ‘write’       Inherited *note IOBase: 30c. methods, ‘read’, and
                                                                                  ‘readall’
                                                                                  
                                                                                  
*note BufferedIOBase: 67f.    *note IOBase: 30c.     ‘detach’, ‘read’, ‘read1’,   Inherited *note IOBase: 30c. methods, ‘readinto’,
                                                     and ‘write’                  and ‘readinto1’
                                                                                  
                                                                                  
*note TextIOBase: d01.        *note IOBase: 30c.     ‘detach’, ‘read’,            Inherited *note IOBase: 30c. methods, ‘encoding’,
                                                     ‘readline’, and ‘write’      ‘errors’, and ‘newlines’
                                                                                  

* Menu:

* I/O Base Classes::
* Raw File I/O::
* Buffered Streams::
* Text I/O: Text I/O<2>.


File: python.info,  Node: I/O Base Classes,  Next: Raw File I/O,  Up: Class hierarchy

5.16.2.7 I/O Base Classes
.........................

 -- Class: io.IOBase

     The abstract base class for all I/O classes, acting on streams of
     bytes.  There is no public constructor.

     This class provides empty abstract implementations for many methods
     that derived classes can override selectively; the default
     implementations represent a file that cannot be read, written or
     seeked.

     Even though *note IOBase: 30c. does not declare ‘read()’ or
     ‘write()’ because their signatures will vary, implementations and
     clients should consider those methods part of the interface.  Also,
     implementations may raise a *note ValueError: 16d. (or *note
     UnsupportedOperation: 1083.) when operations they do not support
     are called.

     The basic type used for binary data read from or written to a file
     is *note bytes: 172.  Other *note bytes-like objects: 6df. are
     accepted as method arguments too.  Text I/O classes work with *note
     str: 205. data.

     Note that calling any method (even inquiries) on a closed stream is
     undefined.  Implementations may raise *note ValueError: 16d. in
     this case.

     *note IOBase: 30c. (and its subclasses) supports the iterator
     protocol, meaning that an *note IOBase: 30c. object can be iterated
     over yielding the lines in a stream.  Lines are defined slightly
     differently depending on whether the stream is a binary stream
     (yielding bytes), or a text stream (yielding character strings).
     See *note readline(): 1849. below.

     *note IOBase: 30c. is also a context manager and therefore supports
     the *note with: 7da. statement.  In this example, `file' is closed
     after the ‘with’ statement’s suite is finished—even if an exception
     occurs:

          with open('spam.txt', 'w') as file:
              file.write('Spam and eggs!')

     *note IOBase: 30c. provides these data attributes and methods:

      -- Method: close ()

          Flush and close this stream.  This method has no effect if the
          file is already closed.  Once the file is closed, any
          operation on the file (e.g.  reading or writing) will raise a
          *note ValueError: 16d.

          As a convenience, it is allowed to call this method more than
          once; only the first call, however, will have an effect.

      -- Attribute: closed

          ‘True’ if the stream is closed.

      -- Method: fileno ()

          Return the underlying file descriptor (an integer) of the
          stream if it exists.  An *note OSError: 304. is raised if the
          IO object does not use a file descriptor.

      -- Method: flush ()

          Flush the write buffers of the stream if applicable.  This
          does nothing for read-only and non-blocking streams.

      -- Method: isatty ()

          Return ‘True’ if the stream is interactive (i.e., connected to
          a terminal/tty device).

      -- Method: readable ()

          Return ‘True’ if the stream can be read from.  If ‘False’,
          ‘read()’ will raise *note OSError: 304.

      -- Method: readline (size=-1)

          Read and return one line from the stream.  If `size' is
          specified, at most `size' bytes will be read.

          The line terminator is always ‘b'\n'’ for binary files; for
          text files, the `newline' argument to *note open(): 16f. can
          be used to select the line terminator(s) recognized.

      -- Method: readlines (hint=-1)

          Read and return a list of lines from the stream.  `hint' can
          be specified to control the number of lines read: no more
          lines will be read if the total size (in bytes/characters) of
          all lines so far exceeds `hint'.

          `hint' values of ‘0’ or less, as well as ‘None’, are treated
          as no hint.

          Note that it’s already possible to iterate on file objects
          using ‘for line in file: ...’ without calling
          ‘file.readlines()’.

      -- Method: seek (offset, whence=SEEK_SET)

          Change the stream position to the given byte `offset'.
          `offset' is interpreted relative to the position indicated by
          `whence'.  The default value for `whence' is ‘SEEK_SET’.
          Values for `whence' are:

             * ‘SEEK_SET’ or ‘0’ – start of the stream (the default);
               `offset' should be zero or positive

             * ‘SEEK_CUR’ or ‘1’ – current stream position; `offset' may
               be negative

             * ‘SEEK_END’ or ‘2’ – end of the stream; `offset' is
               usually negative

          Return the new absolute position.

          New in version 3.1: The ‘SEEK_*’ constants.

          New in version 3.3: Some operating systems could support
          additional values, like ‘os.SEEK_HOLE’ or ‘os.SEEK_DATA’.  The
          valid values for a file could depend on it being open in text
          or binary mode.

      -- Method: seekable ()

          Return ‘True’ if the stream supports random access.  If
          ‘False’, *note seek(): 1efb, *note tell(): 1efc. and *note
          truncate(): d6d. will raise *note OSError: 304.

      -- Method: tell ()

          Return the current stream position.

      -- Method: truncate (size=None)

          Resize the stream to the given `size' in bytes (or the current
          position if `size' is not specified).  The current stream
          position isn’t changed.  This resizing can extend or reduce
          the current file size.  In case of extension, the contents of
          the new file area depend on the platform (on most systems,
          additional bytes are zero-filled).  The new file size is
          returned.

          Changed in version 3.5: Windows will now zero-fill files when
          extending.

      -- Method: writable ()

          Return ‘True’ if the stream supports writing.  If ‘False’,
          ‘write()’ and *note truncate(): d6d. will raise *note OSError:
          304.

      -- Method: writelines (lines)

          Write a list of lines to the stream.  Line separators are not
          added, so it is usual for each of the lines provided to have a
          line separator at the end.

      -- Method: __del__ ()

          Prepare for object destruction.  *note IOBase: 30c. provides a
          default implementation of this method that calls the
          instance’s *note close(): 1147. method.

 -- Class: io.RawIOBase

     Base class for raw binary streams.  It inherits *note IOBase: 30c.
     There is no public constructor.

     Raw binary streams typically provide low-level access to an
     underlying OS device or API, and do not try to encapsulate it in
     high-level primitives (this functionality is done at a higher-level
     in buffered binary streams and text streams, described later in
     this page).

     *note RawIOBase: af1. provides these methods in addition to those
     from *note IOBase: 30c.:

      -- Method: read (size=-1)

          Read up to `size' bytes from the object and return them.  As a
          convenience, if `size' is unspecified or -1, all bytes until
          EOF are returned.  Otherwise, only one system call is ever
          made.  Fewer than `size' bytes may be returned if the
          operating system call returns fewer than `size' bytes.

          If 0 bytes are returned, and `size' was not 0, this indicates
          end of file.  If the object is in non-blocking mode and no
          bytes are available, ‘None’ is returned.

          The default implementation defers to *note readall(): 214e.
          and *note readinto(): 7f4.

      -- Method: readall ()

          Read and return all the bytes from the stream until EOF, using
          multiple calls to the stream if necessary.

      -- Method: readinto (b)

          Read bytes into a pre-allocated, writable *note bytes-like
          object: 6df. `b', and return the number of bytes read.  For
          example, `b' might be a *note bytearray: 173.  If the object
          is in non-blocking mode and no bytes are available, ‘None’ is
          returned.

      -- Method: write (b)

          Write the given *note bytes-like object: 6df, `b', to the
          underlying raw stream, and return the number of bytes written.
          This can be less than the length of `b' in bytes, depending on
          specifics of the underlying raw stream, and especially if it
          is in non-blocking mode.  ‘None’ is returned if the raw stream
          is set not to block and no single byte could be readily
          written to it.  The caller may release or mutate `b' after
          this method returns, so the implementation should only access
          `b' during the method call.

 -- Class: io.BufferedIOBase

     Base class for binary streams that support some kind of buffering.
     It inherits *note IOBase: 30c.  There is no public constructor.

     The main difference with *note RawIOBase: af1. is that methods
     *note read(): 1ebb, *note readinto(): 2150. and *note write(): 680.
     will try (respectively) to read as much input as requested or to
     consume all given output, at the expense of making perhaps more
     than one system call.

     In addition, those methods can raise *note BlockingIOError: a78. if
     the underlying raw stream is in non-blocking mode and cannot take
     or give enough data; unlike their *note RawIOBase: af1.
     counterparts, they will never return ‘None’.

     Besides, the *note read(): 1ebb. method does not have a default
     implementation that defers to *note readinto(): 2150.

     A typical *note BufferedIOBase: 67f. implementation should not
     inherit from a *note RawIOBase: af1. implementation, but wrap one,
     like *note BufferedWriter: 1733. and *note BufferedReader: c5b. do.

     *note BufferedIOBase: 67f. provides or overrides these data
     attributes and methods in addition to those from *note IOBase:
     30c.:

      -- Attribute: raw

          The underlying raw stream (a *note RawIOBase: af1. instance)
          that *note BufferedIOBase: 67f. deals with.  This is not part
          of the *note BufferedIOBase: 67f. API and may not exist on
          some implementations.

      -- Method: detach ()

          Separate the underlying raw stream from the buffer and return
          it.

          After the raw stream has been detached, the buffer is in an
          unusable state.

          Some buffers, like *note BytesIO: 88a, do not have the concept
          of a single raw stream to return from this method.  They raise
          *note UnsupportedOperation: 1083.

          New in version 3.1.

      -- Method: read (size=-1)

          Read and return up to `size' bytes.  If the argument is
          omitted, ‘None’, or negative, data is read and returned until
          EOF is reached.  An empty *note bytes: 172. object is returned
          if the stream is already at EOF.

          If the argument is positive, and the underlying raw stream is
          not interactive, multiple raw reads may be issued to satisfy
          the byte count (unless EOF is reached first).  But for
          interactive raw streams, at most one raw read will be issued,
          and a short result does not imply that EOF is imminent.

          A *note BlockingIOError: a78. is raised if the underlying raw
          stream is in non blocking-mode, and has no data available at
          the moment.

      -- Method: read1 ([size])

          Read and return up to `size' bytes, with at most one call to
          the underlying raw stream’s *note read(): 7f3. (or *note
          readinto(): 7f4.) method.  This can be useful if you are
          implementing your own buffering on top of a *note
          BufferedIOBase: 67f. object.

          If `size' is ‘-1’ (the default), an arbitrary number of bytes
          are returned (more than zero unless EOF is reached).

      -- Method: readinto (b)

          Read bytes into a pre-allocated, writable *note bytes-like
          object: 6df. `b' and return the number of bytes read.  For
          example, `b' might be a *note bytearray: 173.

          Like *note read(): 1ebb, multiple reads may be issued to the
          underlying raw stream, unless the latter is interactive.

          A *note BlockingIOError: a78. is raised if the underlying raw
          stream is in non blocking-mode, and has no data available at
          the moment.

      -- Method: readinto1 (b)

          Read bytes into a pre-allocated, writable *note bytes-like
          object: 6df. `b', using at most one call to the underlying raw
          stream’s *note read(): 7f3. (or *note readinto(): 7f4.)
          method.  Return the number of bytes read.

          A *note BlockingIOError: a78. is raised if the underlying raw
          stream is in non blocking-mode, and has no data available at
          the moment.

          New in version 3.5.

      -- Method: write (b)

          Write the given *note bytes-like object: 6df, `b', and return
          the number of bytes written (always equal to the length of `b'
          in bytes, since if the write fails an *note OSError: 304. will
          be raised).  Depending on the actual implementation, these
          bytes may be readily written to the underlying stream, or held
          in a buffer for performance and latency reasons.

          When in non-blocking mode, a *note BlockingIOError: a78. is
          raised if the data needed to be written to the raw stream but
          it couldn’t accept all the data without blocking.

          The caller may release or mutate `b' after this method
          returns, so the implementation should only access `b' during
          the method call.


File: python.info,  Node: Raw File I/O,  Next: Buffered Streams,  Prev: I/O Base Classes,  Up: Class hierarchy

5.16.2.8 Raw File I/O
.....................

 -- Class: io.FileIO (name, mode='r', closefd=True, opener=None)

     A raw binary stream representing an OS-level file containing bytes
     data.  It inherits *note RawIOBase: af1.

     The `name' can be one of two things:

        * a character string or *note bytes: 172. object representing
          the path to the file which will be opened.  In this case
          closefd must be ‘True’ (the default) otherwise an error will
          be raised.

        * an integer representing the number of an existing OS-level
          file descriptor to which the resulting *note FileIO: d6c.
          object will give access.  When the FileIO object is closed
          this fd will be closed as well, unless `closefd' is set to
          ‘False’.

     The `mode' can be ‘'r'’, ‘'w'’, ‘'x'’ or ‘'a'’ for reading
     (default), writing, exclusive creation or appending.  The file will
     be created if it doesn’t exist when opened for writing or
     appending; it will be truncated when opened for writing.  *note
     FileExistsError: a39. will be raised if it already exists when
     opened for creating.  Opening a file for creating implies writing,
     so this mode behaves in a similar way to ‘'w'’.  Add a ‘'+'’ to the
     mode to allow simultaneous reading and writing.

     The ‘read()’ (when called with a positive argument), ‘readinto()’
     and ‘write()’ methods on this class will only make one system call.

     A custom opener can be used by passing a callable as `opener'.  The
     underlying file descriptor for the file object is then obtained by
     calling `opener' with (`name', `flags').  `opener' must return an
     open file descriptor (passing *note os.open: 758. as `opener'
     results in functionality similar to passing ‘None’).

     The newly created file is *note non-inheritable: 8e7.

     See the *note open(): 16f. built-in function for examples on using
     the `opener' parameter.

     Changed in version 3.3: The `opener' parameter was added.  The
     ‘'x'’ mode was added.

     Changed in version 3.4: The file is now non-inheritable.

     *note FileIO: d6c. provides these data attributes in addition to
     those from *note RawIOBase: af1. and *note IOBase: 30c.:

      -- Attribute: mode

          The mode as given in the constructor.

      -- Attribute: name

          The file name.  This is the file descriptor of the file when
          no name is given in the constructor.


File: python.info,  Node: Buffered Streams,  Next: Text I/O<2>,  Prev: Raw File I/O,  Up: Class hierarchy

5.16.2.9 Buffered Streams
.........................

Buffered I/O streams provide a higher-level interface to an I/O device
than raw I/O does.

 -- Class: io.BytesIO ([initial_bytes])

     A binary stream using an in-memory bytes buffer.  It inherits *note
     BufferedIOBase: 67f.  The buffer is discarded when the *note
     close(): 1147. method is called.

     The optional argument `initial_bytes' is a *note bytes-like object:
     6df. that contains initial data.

     *note BytesIO: 88a. provides or overrides these methods in addition
     to those from *note BufferedIOBase: 67f. and *note IOBase: 30c.:

      -- Method: getbuffer ()

          Return a readable and writable view over the contents of the
          buffer without copying them.  Also, mutating the view will
          transparently update the contents of the buffer:

               >>> b = io.BytesIO(b"abcdef")
               >>> view = b.getbuffer()
               >>> view[2:4] = b"56"
               >>> b.getvalue()
               b'ab56ef'

               Note: As long as the view exists, the *note BytesIO: 88a.
               object cannot be resized or closed.

          New in version 3.2.

      -- Method: getvalue ()

          Return *note bytes: 172. containing the entire contents of the
          buffer.

      -- Method: read1 ([size])

          In *note BytesIO: 88a, this is the same as *note read(): 1ebb.

          Changed in version 3.7: The `size' argument is now optional.

      -- Method: readinto1 (b)

          In *note BytesIO: 88a, this is the same as *note readinto():
          2150.

          New in version 3.5.

 -- Class: io.BufferedReader (raw, buffer_size=DEFAULT_BUFFER_SIZE)

     A buffered binary stream providing higher-level access to a
     readable, non seekable *note RawIOBase: af1. raw binary stream.  It
     inherits *note BufferedIOBase: 67f.

     When reading data from this object, a larger amount of data may be
     requested from the underlying raw stream, and kept in an internal
     buffer.  The buffered data can then be returned directly on
     subsequent reads.

     The constructor creates a *note BufferedReader: c5b. for the given
     readable `raw' stream and `buffer_size'.  If `buffer_size' is
     omitted, *note DEFAULT_BUFFER_SIZE: 172f. is used.

     *note BufferedReader: c5b. provides or overrides these methods in
     addition to those from *note BufferedIOBase: 67f. and *note IOBase:
     30c.:

      -- Method: peek ([size])

          Return bytes from the stream without advancing the position.
          At most one single read on the raw stream is done to satisfy
          the call.  The number of bytes returned may be less or more
          than requested.

      -- Method: read ([size])

          Read and return `size' bytes, or if `size' is not given or
          negative, until EOF or if the read call would block in
          non-blocking mode.

      -- Method: read1 ([size])

          Read and return up to `size' bytes with only one call on the
          raw stream.  If at least one byte is buffered, only buffered
          bytes are returned.  Otherwise, one raw stream read call is
          made.

          Changed in version 3.7: The `size' argument is now optional.

 -- Class: io.BufferedWriter (raw, buffer_size=DEFAULT_BUFFER_SIZE)

     A buffered binary stream providing higher-level access to a
     writeable, non seekable *note RawIOBase: af1. raw binary stream.
     It inherits *note BufferedIOBase: 67f.

     When writing to this object, data is normally placed into an
     internal buffer.  The buffer will be written out to the underlying
     *note RawIOBase: af1. object under various conditions, including:

        * when the buffer gets too small for all pending data;

        * when *note flush(): 215b. is called;

        * when a ‘seek()’ is requested (for *note BufferedRandom: 1734.
          objects);

        * when the *note BufferedWriter: 1733. object is closed or
          destroyed.

     The constructor creates a *note BufferedWriter: 1733. for the given
     writeable `raw' stream.  If the `buffer_size' is not given, it
     defaults to *note DEFAULT_BUFFER_SIZE: 172f.

     *note BufferedWriter: 1733. provides or overrides these methods in
     addition to those from *note BufferedIOBase: 67f. and *note IOBase:
     30c.:

      -- Method: flush ()

          Force bytes held in the buffer into the raw stream.  A *note
          BlockingIOError: a78. should be raised if the raw stream
          blocks.

      -- Method: write (b)

          Write the *note bytes-like object: 6df, `b', and return the
          number of bytes written.  When in non-blocking mode, a *note
          BlockingIOError: a78. is raised if the buffer needs to be
          written out but the raw stream blocks.

 -- Class: io.BufferedRandom (raw, buffer_size=DEFAULT_BUFFER_SIZE)

     A buffered binary stream providing higher-level access to a
     seekable *note RawIOBase: af1. raw binary stream.  It inherits
     *note BufferedReader: c5b. and *note BufferedWriter: 1733.

     The constructor creates a reader and writer for a seekable raw
     stream, given in the first argument.  If the `buffer_size' is
     omitted it defaults to *note DEFAULT_BUFFER_SIZE: 172f.

     *note BufferedRandom: 1734. is capable of anything *note
     BufferedReader: c5b. or *note BufferedWriter: 1733. can do.  In
     addition, ‘seek()’ and ‘tell()’ are guaranteed to be implemented.

 -- Class: io.BufferedRWPair (reader, writer,
          buffer_size=DEFAULT_BUFFER_SIZE)

     A buffered binary stream providing higher-level access to two non
     seekable *note RawIOBase: af1. raw binary streams—one readable, the
     other writeable.  It inherits *note BufferedIOBase: 67f.

     `reader' and `writer' are *note RawIOBase: af1. objects that are
     readable and writeable respectively.  If the `buffer_size' is
     omitted it defaults to *note DEFAULT_BUFFER_SIZE: 172f.

     *note BufferedRWPair: 2147. implements all of *note BufferedIOBase:
     67f.’s methods except for *note detach(): 2152, which raises *note
     UnsupportedOperation: 1083.

          Warning: *note BufferedRWPair: 2147. does not attempt to
          synchronize accesses to its underlying raw streams.  You
          should not pass it the same object as reader and writer; use
          *note BufferedRandom: 1734. instead.


File: python.info,  Node: Text I/O<2>,  Prev: Buffered Streams,  Up: Class hierarchy

5.16.2.10 Text I/O
..................

 -- Class: io.TextIOBase

     Base class for text streams.  This class provides a character and
     line based interface to stream I/O. It inherits *note IOBase: 30c.
     There is no public constructor.

     *note TextIOBase: d01. provides or overrides these data attributes
     and methods in addition to those from *note IOBase: 30c.:

      -- Attribute: encoding

          The name of the encoding used to decode the stream’s bytes
          into strings, and to encode strings into bytes.

      -- Attribute: errors

          The error setting of the decoder or encoder.

      -- Attribute: newlines

          A string, a tuple of strings, or ‘None’, indicating the
          newlines translated so far.  Depending on the implementation
          and the initial constructor flags, this may not be available.

      -- Attribute: buffer

          The underlying binary buffer (a *note BufferedIOBase: 67f.
          instance) that *note TextIOBase: d01. deals with.  This is not
          part of the *note TextIOBase: d01. API and may not exist in
          some implementations.

      -- Method: detach ()

          Separate the underlying binary buffer from the *note
          TextIOBase: d01. and return it.

          After the underlying buffer has been detached, the *note
          TextIOBase: d01. is in an unusable state.

          Some *note TextIOBase: d01. implementations, like *note
          StringIO: 91a, may not have the concept of an underlying
          buffer and calling this method will raise *note
          UnsupportedOperation: 1083.

          New in version 3.1.

      -- Method: read (size=-1)

          Read and return at most `size' characters from the stream as a
          single *note str: 205.  If `size' is negative or ‘None’, reads
          until EOF.

      -- Method: readline (size=-1)

          Read until newline or EOF and return a single ‘str’.  If the
          stream is already at EOF, an empty string is returned.

          If `size' is specified, at most `size' characters will be
          read.

      -- Method: seek (offset, whence=SEEK_SET)

          Change the stream position to the given `offset'.  Behaviour
          depends on the `whence' parameter.  The default value for
          `whence' is ‘SEEK_SET’.

             * ‘SEEK_SET’ or ‘0’: seek from the start of the stream (the
               default); `offset' must either be a number returned by
               *note TextIOBase.tell(): 2164, or zero.  Any other
               `offset' value produces undefined behaviour.

             * ‘SEEK_CUR’ or ‘1’: “seek” to the current position;
               `offset' must be zero, which is a no-operation (all other
               values are unsupported).

             * ‘SEEK_END’ or ‘2’: seek to the end of the stream;
               `offset' must be zero (all other values are unsupported).

          Return the new absolute position as an opaque number.

          New in version 3.1: The ‘SEEK_*’ constants.

      -- Method: tell ()

          Return the current stream position as an opaque number.  The
          number does not usually represent a number of bytes in the
          underlying binary storage.

      -- Method: write (s)

          Write the string `s' to the stream and return the number of
          characters written.

 -- Class: io.TextIOWrapper (buffer, encoding=None, errors=None,
          newline=None, line_buffering=False, write_through=False)

     A buffered text stream providing higher-level access to a *note
     BufferedIOBase: 67f. buffered binary stream.  It inherits *note
     TextIOBase: d01.

     `encoding' gives the name of the encoding that the stream will be
     decoded or encoded with.  It defaults to *note
     locale.getpreferredencoding(False): 4ac.

     `errors' is an optional string that specifies how encoding and
     decoding errors are to be handled.  Pass ‘'strict'’ to raise a
     *note ValueError: 16d. exception if there is an encoding error (the
     default of ‘None’ has the same effect), or pass ‘'ignore'’ to
     ignore errors.  (Note that ignoring encoding errors can lead to
     data loss.)  ‘'replace'’ causes a replacement marker (such as
     ‘'?'’) to be inserted where there is malformed data.
     ‘'backslashreplace'’ causes malformed data to be replaced by a
     backslashed escape sequence.  When writing, ‘'xmlcharrefreplace'’
     (replace with the appropriate XML character reference) or
     ‘'namereplace'’ (replace with ‘\N{...}’ escape sequences) can be
     used.  Any other error handling name that has been registered with
     *note codecs.register_error(): eb9. is also valid.

     `newline' controls how line endings are handled.  It can be ‘None’,
     ‘''’, ‘'\n'’, ‘'\r'’, and ‘'\r\n'’.  It works as follows:

        * When reading input from the stream, if `newline' is ‘None’,
          *note universal newlines: 6eb. mode is enabled.  Lines in the
          input can end in ‘'\n'’, ‘'\r'’, or ‘'\r\n'’, and these are
          translated into ‘'\n'’ before being returned to the caller.
          If `newline' is ‘''’, universal newlines mode is enabled, but
          line endings are returned to the caller untranslated.  If
          `newline' has any of the other legal values, input lines are
          only terminated by the given string, and the line ending is
          returned to the caller untranslated.

        * When writing output to the stream, if `newline' is ‘None’, any
          ‘'\n'’ characters written are translated to the system default
          line separator, *note os.linesep: 1732.  If `newline' is ‘''’
          or ‘'\n'’, no translation takes place.  If `newline' is any of
          the other legal values, any ‘'\n'’ characters written are
          translated to the given string.

     If `line_buffering' is ‘True’, ‘flush()’ is implied when a call to
     write contains a newline character or a carriage return.

     If `write_through' is ‘True’, calls to ‘write()’ are guaranteed not
     to be buffered: any data written on the *note TextIOWrapper: 6ea.
     object is immediately handled to its underlying binary `buffer'.

     Changed in version 3.3: The `write_through' argument has been
     added.

     Changed in version 3.3: The default `encoding' is now
     ‘locale.getpreferredencoding(False)’ instead of
     ‘locale.getpreferredencoding()’.  Don’t change temporary the locale
     encoding using *note locale.setlocale(): 2166, use the current
     locale encoding instead of the user preferred encoding.

     *note TextIOWrapper: 6ea. provides these data attributes and
     methods in addition to those from *note TextIOBase: d01. and *note
     IOBase: 30c.:

      -- Attribute: line_buffering

          Whether line buffering is enabled.

      -- Attribute: write_through

          Whether writes are passed immediately to the underlying binary
          buffer.

          New in version 3.7.

      -- Method: reconfigure (*[, encoding][, errors][, newline][,
               line_buffering][, write_through])

          Reconfigure this text stream using new settings for
          `encoding', `errors', `newline', `line_buffering' and
          `write_through'.

          Parameters not specified keep current settings, except
          ‘errors='strict'’ is used when `encoding' is specified but
          `errors' is not specified.

          It is not possible to change the encoding or newline if some
          data has already been read from the stream.  On the other
          hand, changing encoding after write is possible.

          This method does an implicit stream flush before setting the
          new parameters.

          New in version 3.7.

 -- Class: io.StringIO (initial_value='', newline='\n')

     A text stream using an in-memory text buffer.  It inherits *note
     TextIOBase: d01.

     The text buffer is discarded when the *note close(): 1147. method
     is called.

     The initial value of the buffer can be set by providing
     `initial_value'.  If newline translation is enabled, newlines will
     be encoded as if by *note write(): 2165.  The stream is positioned
     at the start of the buffer.

     The `newline' argument works like that of *note TextIOWrapper: 6ea,
     except that when writing output to the stream, if `newline' is
     ‘None’, newlines are written as ‘\n’ on all platforms.

     *note StringIO: 91a. provides this method in addition to those from
     *note TextIOBase: d01. and *note IOBase: 30c.:

      -- Method: getvalue ()

          Return a ‘str’ containing the entire contents of the buffer.
          Newlines are decoded as if by *note read(): 2162, although the
          stream position is not changed.

     Example usage:

          import io

          output = io.StringIO()
          output.write('First line.\n')
          print('Second line.', file=output)

          # Retrieve file contents -- this will be
          # 'First line.\nSecond line.\n'
          contents = output.getvalue()

          # Close object and discard memory buffer --
          # .getvalue() will now raise an exception.
          output.close()

 -- Class: io.IncrementalNewlineDecoder

     A helper codec that decodes newlines for *note universal newlines:
     6eb. mode.  It inherits *note codecs.IncrementalDecoder: 196f.


File: python.info,  Node: Performance<3>,  Prev: Class hierarchy,  Up: io — Core tools for working with streams

5.16.2.11 Performance
.....................

This section discusses the performance of the provided concrete I/O
implementations.

* Menu:

* Binary I/O: Binary I/O<2>.
* Text I/O: Text I/O<3>.
* Multi-threading: Multi-threading<3>.
* Reentrancy::


File: python.info,  Node: Binary I/O<2>,  Next: Text I/O<3>,  Up: Performance<3>

5.16.2.12 Binary I/O
....................

By reading and writing only large chunks of data even when the user asks
for a single byte, buffered I/O hides any inefficiency in calling and
executing the operating system’s unbuffered I/O routines.  The gain
depends on the OS and the kind of I/O which is performed.  For example,
on some modern OSes such as Linux, unbuffered disk I/O can be as fast as
buffered I/O. The bottom line, however, is that buffered I/O offers
predictable performance regardless of the platform and the backing
device.  Therefore, it is almost always preferable to use buffered I/O
rather than unbuffered I/O for binary data.


File: python.info,  Node: Text I/O<3>,  Next: Multi-threading<3>,  Prev: Binary I/O<2>,  Up: Performance<3>

5.16.2.13 Text I/O
..................

Text I/O over a binary storage (such as a file) is significantly slower
than binary I/O over the same storage, because it requires conversions
between unicode and binary data using a character codec.  This can
become noticeable handling huge amounts of text data like large log
files.  Also, ‘TextIOWrapper.tell()’ and ‘TextIOWrapper.seek()’ are both
quite slow due to the reconstruction algorithm used.

*note StringIO: 91a, however, is a native in-memory unicode container
and will exhibit similar speed to *note BytesIO: 88a.


File: python.info,  Node: Multi-threading<3>,  Next: Reentrancy,  Prev: Text I/O<3>,  Up: Performance<3>

5.16.2.14 Multi-threading
.........................

*note FileIO: d6c. objects are thread-safe to the extent that the
operating system calls (such as ‘read(2)’ under Unix) they wrap are
thread-safe too.

Binary buffered objects (instances of *note BufferedReader: c5b, *note
BufferedWriter: 1733, *note BufferedRandom: 1734. and *note
BufferedRWPair: 2147.) protect their internal structures using a lock;
it is therefore safe to call them from multiple threads at once.

*note TextIOWrapper: 6ea. objects are not thread-safe.


File: python.info,  Node: Reentrancy,  Prev: Multi-threading<3>,  Up: Performance<3>

5.16.2.15 Reentrancy
....................

Binary buffered objects (instances of *note BufferedReader: c5b, *note
BufferedWriter: 1733, *note BufferedRandom: 1734. and *note
BufferedRWPair: 2147.) are not reentrant.  While reentrant calls will
not happen in normal situations, they can arise from doing I/O in a
*note signal: ea. handler.  If a thread tries to re-enter a buffered
object which it is already accessing, a *note RuntimeError: 3dc. is
raised.  Note this doesn’t prohibit a different thread from entering the
buffered object.

The above implicitly extends to text files, since the *note open(): 16f.
function will wrap a buffered object inside a *note TextIOWrapper: 6ea.
This includes standard streams and therefore affects the built-in *note
print(): 971. function as well.


File: python.info,  Node: time — Time access and conversions,  Next: argparse — Parser for command-line options arguments and sub-commands,  Prev: io — Core tools for working with streams,  Up: Generic Operating System Services

5.16.3 ‘time’ — Time access and conversions
-------------------------------------------

__________________________________________________________________

This module provides various time-related functions.  For related
functionality, see also the *note datetime: 30. and *note calendar: 14.
modules.

Although this module is always available, not all functions are
available on all platforms.  Most of the functions defined in this
module call platform C library functions with the same name.  It may
sometimes be helpful to consult the platform documentation, because the
semantics of these functions varies among platforms.

An explanation of some terminology and conventions is in order.

   * The `epoch' is the point where the time starts, and is platform
     dependent.  For Unix, the epoch is January 1, 1970, 00:00:00 (UTC).
     To find out what the epoch is on a given platform, look at
     ‘time.gmtime(0)’.

   * The term `seconds since the epoch' refers to the total number of
     elapsed seconds since the epoch, typically excluding leap
     seconds(1).  Leap seconds are excluded from this total on all
     POSIX-compliant platforms.

   * The functions in this module may not handle dates and times before
     the epoch or far in the future.  The cut-off point in the future is
     determined by the C library; for 32-bit systems, it is typically in
     2038.

   * Function *note strptime(): e56. can parse 2-digit years when given
     ‘%y’ format code.  When 2-digit years are parsed, they are
     converted according to the POSIX and ISO C standards: values 69–99
     are mapped to 1969–1999, and values 0–68 are mapped to 2000–2068.

   * UTC is Coordinated Universal Time (formerly known as Greenwich Mean
     Time, or GMT). The acronym UTC is not a mistake but a compromise
     between English and French.

   * DST is Daylight Saving Time, an adjustment of the timezone by
     (usually) one hour during part of the year.  DST rules are magic
     (determined by local law) and can change from year to year.  The C
     library has a table containing the local rules (often it is read
     from a system file for flexibility) and is the only source of True
     Wisdom in this respect.

   * The precision of the various real-time functions may be less than
     suggested by the units in which their value or argument is
     expressed.  E.g.  on most Unix systems, the clock “ticks” only 50
     or 100 times a second.

   * On the other hand, the precision of *note time(): 42d. and *note
     sleep(): 773. is better than their Unix equivalents: times are
     expressed as floating point numbers, *note time(): 42d. returns the
     most accurate time available (using Unix ‘gettimeofday()’ where
     available), and *note sleep(): 773. will accept a time with a
     nonzero fraction (Unix ‘select()’ is used to implement this, where
     available).

   * The time value as returned by *note gmtime(): c11, *note
     localtime(): 1080, and *note strptime(): e56, and accepted by *note
     asctime(): c35, *note mktime(): c36. and *note strftime(): c37, is
     a sequence of 9 integers.  The return values of *note gmtime():
     c11, *note localtime(): 1080, and *note strptime(): e56. also offer
     attribute names for individual fields.

     See *note struct_time: 690. for a description of these objects.

     Changed in version 3.3: The *note struct_time: 690. type was
     extended to provide the ‘tm_gmtoff’ and ‘tm_zone’ attributes when
     platform supports corresponding ‘struct tm’ members.

     Changed in version 3.6: The *note struct_time: 690. attributes
     ‘tm_gmtoff’ and ‘tm_zone’ are now available on all platforms.

   * Use the following functions to convert between time
     representations:

     From                          To                            Use
                                                                 
     ------------------------------------------------------------------------------------------
                                                                 
     seconds since the epoch       *note struct_time: 690. in    *note gmtime(): c11.
                                   UTC                           
                                   
                                                                 
     seconds since the epoch       *note struct_time: 690. in    *note localtime(): 1080.
                                   local time                    
                                   
                                                                 
     *note struct_time: 690. in    seconds since the epoch       *note calendar.timegm(): 1a7a.
     UTC                                                         

     *note struct_time: 690. in    seconds since the epoch       *note mktime(): c36.
     local time                                                  

* Menu:

* Functions: Functions<3>.
* Clock ID Constants::
* Timezone Constants::

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Leap_second


File: python.info,  Node: Functions<3>,  Next: Clock ID Constants,  Up: time — Time access and conversions

5.16.3.1 Functions
..................

 -- Function: time.asctime ([t])

     Convert a tuple or *note struct_time: 690. representing a time as
     returned by *note gmtime(): c11. or *note localtime(): 1080. to a
     string of the following form: ‘'Sun Jun 20 23:21:05 1993'’.  The
     day field is two characters long and is space padded if the day is
     a single digit, e.g.: ‘'Wed Jun 9 04:26:40 1993'’.

     If `t' is not provided, the current time as returned by *note
     localtime(): 1080. is used.  Locale information is not used by
     *note asctime(): c35.

          Note: Unlike the C function of the same name, *note asctime():
          c35. does not add a trailing newline.

 -- Function: time.pthread_getcpuclockid (thread_id)

     Return the `clk_id' of the thread-specific CPU-time clock for the
     specified `thread_id'.

     Use *note threading.get_ident(): b87. or the *note ident: 2175.
     attribute of *note threading.Thread: 21a. objects to get a suitable
     value for `thread_id'.

          Warning: Passing an invalid or expired `thread_id' may result
          in undefined behavior, such as segmentation fault.

     *note Availability: 1491.: Unix (see the man page for
     ‘pthread_getcpuclockid(3)’ for further information).

     New in version 3.7.

 -- Function: time.clock_getres (clk_id)

     Return the resolution (precision) of the specified clock `clk_id'.
     Refer to *note Clock ID Constants: 2176. for a list of accepted
     values for `clk_id'.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: time.clock_gettime (clk_id) -> float

     Return the time of the specified clock `clk_id'.  Refer to *note
     Clock ID Constants: 2176. for a list of accepted values for
     `clk_id'.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: time.clock_gettime_ns (clk_id) -> int

     Similar to *note clock_gettime(): b8b. but return time as
     nanoseconds.

     *note Availability: 1491.: Unix.

     New in version 3.7.

 -- Function: time.clock_settime (clk_id, time: float)

     Set the time of the specified clock `clk_id'.  Currently, *note
     CLOCK_REALTIME: f6d. is the only accepted value for `clk_id'.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: time.clock_settime_ns (clk_id, time: int)

     Similar to *note clock_settime(): b8c. but set time with
     nanoseconds.

     *note Availability: 1491.: Unix.

     New in version 3.7.

 -- Function: time.ctime ([secs])

     Convert a time expressed in seconds since the epoch to a string of
     a form: ‘'Sun Jun 20 23:21:05 1993'’ representing local time.  The
     day field is two characters long and is space padded if the day is
     a single digit, e.g.: ‘'Wed Jun 9 04:26:40 1993'’.

     If `secs' is not provided or *note None: 203, the current time as
     returned by *note time(): 42d. is used.  ‘ctime(secs)’ is
     equivalent to ‘asctime(localtime(secs))’.  Locale information is
     not used by *note ctime(): 19f6.

 -- Function: time.get_clock_info (name)

     Get information on the specified clock as a namespace object.
     Supported clock names and the corresponding functions to read their
     value are:

        * ‘'monotonic'’: *note time.monotonic(): 85e.

        * ‘'perf_counter'’: *note time.perf_counter(): 3cc.

        * ‘'process_time'’: *note time.process_time(): 3cd.

        * ‘'thread_time'’: *note time.thread_time(): 1e7.

        * ‘'time'’: *note time.time(): 42d.

     The result has the following attributes:

        - `adjustable': ‘True’ if the clock can be changed automatically
          (e.g.  by a NTP daemon) or manually by the system
          administrator, ‘False’ otherwise

        - `implementation': The name of the underlying C function used
          to get the clock value.  Refer to *note Clock ID Constants:
          2176. for possible values.

        - `monotonic': ‘True’ if the clock cannot go backward, ‘False’
          otherwise

        - `resolution': The resolution of the clock in seconds (*note
          float: 1fd.)

     New in version 3.3.

 -- Function: time.gmtime ([secs])

     Convert a time expressed in seconds since the epoch to a *note
     struct_time: 690. in UTC in which the dst flag is always zero.  If
     `secs' is not provided or *note None: 203, the current time as
     returned by *note time(): 42d. is used.  Fractions of a second are
     ignored.  See above for a description of the *note struct_time:
     690. object.  See *note calendar.timegm(): 1a7a. for the inverse of
     this function.

 -- Function: time.localtime ([secs])

     Like *note gmtime(): c11. but converts to local time.  If `secs' is
     not provided or *note None: 203, the current time as returned by
     *note time(): 42d. is used.  The dst flag is set to ‘1’ when DST
     applies to the given time.

 -- Function: time.mktime (t)

     This is the inverse function of *note localtime(): 1080.  Its
     argument is the *note struct_time: 690. or full 9-tuple (since the
     dst flag is needed; use ‘-1’ as the dst flag if it is unknown)
     which expresses the time in `local' time, not UTC. It returns a
     floating point number, for compatibility with *note time(): 42d.
     If the input value cannot be represented as a valid time, either
     *note OverflowError: a41. or *note ValueError: 16d. will be raised
     (which depends on whether the invalid value is caught by Python or
     the underlying C libraries).  The earliest date for which it can
     generate a time is platform-dependent.

 -- Function: time.monotonic () -> float

     Return the value (in fractional seconds) of a monotonic clock, i.e.
     a clock that cannot go backwards.  The clock is not affected by
     system clock updates.  The reference point of the returned value is
     undefined, so that only the difference between the results of two
     calls is valid.

     New in version 3.3.

     Changed in version 3.5: The function is now always available and
     always system-wide.

 -- Function: time.monotonic_ns () -> int

     Similar to *note monotonic(): 85e, but return time as nanoseconds.

     New in version 3.7.

 -- Function: time.perf_counter () -> float

     Return the value (in fractional seconds) of a performance counter,
     i.e.  a clock with the highest available resolution to measure a
     short duration.  It does include time elapsed during sleep and is
     system-wide.  The reference point of the returned value is
     undefined, so that only the difference between the results of two
     calls is valid.

     New in version 3.3.

 -- Function: time.perf_counter_ns () -> int

     Similar to *note perf_counter(): 3cc, but return time as
     nanoseconds.

     New in version 3.7.

 -- Function: time.process_time () -> float

     Return the value (in fractional seconds) of the sum of the system
     and user CPU time of the current process.  It does not include time
     elapsed during sleep.  It is process-wide by definition.  The
     reference point of the returned value is undefined, so that only
     the difference between the results of two calls is valid.

     New in version 3.3.

 -- Function: time.process_time_ns () -> int

     Similar to *note process_time(): 3cd. but return time as
     nanoseconds.

     New in version 3.7.

 -- Function: time.sleep (secs)

     Suspend execution of the calling thread for the given number of
     seconds.  The argument may be a floating point number to indicate a
     more precise sleep time.  The actual suspension time may be less
     than that requested because any caught signal will terminate the
     *note sleep(): 773. following execution of that signal’s catching
     routine.  Also, the suspension time may be longer than requested by
     an arbitrary amount because of the scheduling of other activity in
     the system.

     Changed in version 3.5: The function now sleeps at least `secs'
     even if the sleep is interrupted by a signal, except if the signal
     handler raises an exception (see PEP 475(1) for the rationale).

 -- Function: time.strftime (format[, t])

     Convert a tuple or *note struct_time: 690. representing a time as
     returned by *note gmtime(): c11. or *note localtime(): 1080. to a
     string as specified by the `format' argument.  If `t' is not
     provided, the current time as returned by *note localtime(): 1080.
     is used.  `format' must be a string.  *note ValueError: 16d. is
     raised if any field in `t' is outside of the allowed range.

     0 is a legal argument for any position in the time tuple; if it is
     normally illegal the value is forced to a correct one.

     The following directives can be embedded in the `format' string.
     They are shown without the optional field width and precision
     specification, and are replaced by the indicated characters in the
     *note strftime(): c37. result:

     Directive       Meaning                                              Notes
                                                                          
     ---------------------------------------------------------------------------------
                                                                          
     ‘%a’            Locale’s abbreviated weekday name.
                     
                                                                          
     ‘%A’            Locale’s full weekday name.
                     
                                                                          
     ‘%b’            Locale’s abbreviated month name.
                     
                                                                          
     ‘%B’            Locale’s full month name.
                     
                                                                          
     ‘%c’            Locale’s appropriate date and time representation.
                     
                                                                          
     ‘%d’            Day of the month as a decimal number [01,31].
                     
                                                                          
     ‘%H’            Hour (24-hour clock) as a decimal number [00,23].
                     
                                                                          
     ‘%I’            Hour (12-hour clock) as a decimal number [01,12].
                     
                                                                          
     ‘%j’            Day of the year as a decimal number [001,366].
                     
                                                                          
     ‘%m’            Month as a decimal number [01,12].
                     
                                                                          
     ‘%M’            Minute as a decimal number [00,59].
                     
                                                                          
     ‘%p’            Locale’s equivalent of either AM or PM.              (1)
                                                                          
                                                                          
     ‘%S’            Second as a decimal number [00,61].                  (2)
                                                                          
                                                                          
     ‘%U’            Week number of the year (Sunday as the first day     (3)
                     of the week) as a decimal number [00,53].  All       
                     days in a new year preceding the first Sunday are
                     considered to be in week 0.
                     
                                                                          
     ‘%w’            Weekday as a decimal number [0(Sunday),6].
                     
                                                                          
     ‘%W’            Week number of the year (Monday as the first day     (3)
                     of the week) as a decimal number [00,53].  All       
                     days in a new year preceding the first Monday are
                     considered to be in week 0.
                     
                                                                          
     ‘%x’            Locale’s appropriate date representation.
                     
                                                                          
     ‘%X’            Locale’s appropriate time representation.
                     
                                                                          
     ‘%y’            Year without century as a decimal number [00,99].
                     
                                                                          
     ‘%Y’            Year with century as a decimal number.
                     
                                                                          
     ‘%z’            Time zone offset indicating a positive or negative
                     time difference from UTC/GMT of the form +HHMM or
                     -HHMM, where H represents decimal hour digits and
                     M represents decimal minute digits [-23:59,
                     +23:59].
                     
                                                                          
     ‘%Z’            Time zone name (no characters if no time zone
                     exists).
                     
                                                                          
     ‘%%’            A literal ‘'%'’ character.
                     

     Notes:

       1. When used with the *note strptime(): e56. function, the ‘%p’
          directive only affects the output hour field if the ‘%I’
          directive is used to parse the hour.

       2. The range really is ‘0’ to ‘61’; value ‘60’ is valid in
          timestamps representing leap seconds(2) and value ‘61’ is
          supported for historical reasons.

       3. When used with the *note strptime(): e56. function, ‘%U’ and
          ‘%W’ are only used in calculations when the day of the week
          and the year are specified.

     Here is an example, a format for dates compatible with that
     specified in the RFC 2822(3) Internet email standard.  (4)

          >>> from time import gmtime, strftime
          >>> strftime("%a, %d %b %Y %H:%M:%S +0000", gmtime())
          'Thu, 28 Jun 2001 14:17:15 +0000'

     Additional directives may be supported on certain platforms, but
     only the ones listed here have a meaning standardized by ANSI C. To
     see the full set of format codes supported on your platform,
     consult the ‘strftime(3)’ documentation.

     On some platforms, an optional field width and precision
     specification can immediately follow the initial ‘'%'’ of a
     directive in the following order; this is also not portable.  The
     field width is normally 2 except for ‘%j’ where it is 3.

 -- Function: time.strptime (string[, format])

     Parse a string representing a time according to a format.  The
     return value is a *note struct_time: 690. as returned by *note
     gmtime(): c11. or *note localtime(): 1080.

     The `format' parameter uses the same directives as those used by
     *note strftime(): c37.; it defaults to ‘"%a %b %d %H:%M:%S %Y"’
     which matches the formatting returned by *note ctime(): 19f6.  If
     `string' cannot be parsed according to `format', or if it has
     excess data after parsing, *note ValueError: 16d. is raised.  The
     default values used to fill in any missing data when more accurate
     values cannot be inferred are ‘(1900, 1, 1, 0, 0, 0, 0, 1, -1)’.
     Both `string' and `format' must be strings.

     For example:

          >>> import time
          >>> time.strptime("30 Nov 00", "%d %b %y")
          time.struct_time(tm_year=2000, tm_mon=11, tm_mday=30, tm_hour=0, tm_min=0,
                           tm_sec=0, tm_wday=3, tm_yday=335, tm_isdst=-1)

     Support for the ‘%Z’ directive is based on the values contained in
     ‘tzname’ and whether ‘daylight’ is true.  Because of this, it is
     platform-specific except for recognizing UTC and GMT which are
     always known (and are considered to be non-daylight savings
     timezones).

     Only the directives specified in the documentation are supported.
     Because ‘strftime()’ is implemented per platform it can sometimes
     offer more directives than those listed.  But ‘strptime()’ is
     independent of any platform and thus does not necessarily support
     all directives available that are not documented as supported.

 -- Class: time.struct_time

     The type of the time value sequence returned by *note gmtime():
     c11, *note localtime(): 1080, and *note strptime(): e56.  It is an
     object with a *note named tuple: b7b. interface: values can be
     accessed by index and by attribute name.  The following values are
     present:

     Index       Attribute               Values
                                         
     --------------------------------------------------------------------------
                                         
     0           ‘tm_year’               (for example, 1993)
                                         
                                         
     1           ‘tm_mon’                range [1, 12]
                                         
                                         
     2           ‘tm_mday’               range [1, 31]
                                         
                                         
     3           ‘tm_hour’               range [0, 23]
                                         
                                         
     4           ‘tm_min’                range [0, 59]
                                         
                                         
     5           ‘tm_sec’                range [0, 61]; see `(2)' in
                                         *note strftime(): c37. description
                                         
                                         
     6           ‘tm_wday’               range [0, 6], Monday is 0
                                         
                                         
     7           ‘tm_yday’               range [1, 366]
                                         
                                         
     8           ‘tm_isdst’              0, 1 or -1; see below
                                         
                                         
     N/A         ‘tm_zone’               abbreviation of timezone name
                                         
                                         
     N/A         ‘tm_gmtoff’             offset east of UTC in seconds
                                         

     Note that unlike the C structure, the month value is a range of [1,
     12], not [0, 11].

     In calls to *note mktime(): c36, ‘tm_isdst’ may be set to 1 when
     daylight savings time is in effect, and 0 when it is not.  A value
     of -1 indicates that this is not known, and will usually result in
     the correct state being filled in.

     When a tuple with an incorrect length is passed to a function
     expecting a *note struct_time: 690, or having elements of the wrong
     type, a *note TypeError: 1fe. is raised.

 -- Function: time.time () -> float

     Return the time in seconds since the *note epoch: 2172. as a
     floating point number.  The specific date of the epoch and the
     handling of leap seconds(5) is platform dependent.  On Windows and
     most Unix systems, the epoch is January 1, 1970, 00:00:00 (UTC) and
     leap seconds are not counted towards the time in seconds since the
     epoch.  This is commonly referred to as Unix time(6).  To find out
     what the epoch is on a given platform, look at ‘gmtime(0)’.

     Note that even though the time is always returned as a floating
     point number, not all systems provide time with a better precision
     than 1 second.  While this function normally returns non-decreasing
     values, it can return a lower value than a previous call if the
     system clock has been set back between the two calls.

     The number returned by *note time(): 42d. may be converted into a
     more common time format (i.e.  year, month, day, hour, etc…) in UTC
     by passing it to *note gmtime(): c11. function or in local time by
     passing it to the *note localtime(): 1080. function.  In both cases
     a *note struct_time: 690. object is returned, from which the
     components of the calendar date may be accessed as attributes.

 -- Function: time.thread_time () -> float

     Return the value (in fractional seconds) of the sum of the system
     and user CPU time of the current thread.  It does not include time
     elapsed during sleep.  It is thread-specific by definition.  The
     reference point of the returned value is undefined, so that only
     the difference between the results of two calls in the same thread
     is valid.

     *note Availability: 1491.: Windows, Linux, Unix systems supporting
     ‘CLOCK_THREAD_CPUTIME_ID’.

     New in version 3.7.

 -- Function: time.thread_time_ns () -> int

     Similar to *note thread_time(): 1e7. but return time as
     nanoseconds.

     New in version 3.7.

 -- Function: time.time_ns () -> int

     Similar to *note time(): 42d. but returns time as an integer number
     of nanoseconds since the *note epoch: 2172.

     New in version 3.7.

 -- Function: time.tzset ()

     Reset the time conversion rules used by the library routines.  The
     environment variable ‘TZ’ specifies how this is done.  It will also
     set the variables ‘tzname’ (from the ‘TZ’ environment variable),
     ‘timezone’ (non-DST seconds West of UTC), ‘altzone’ (DST seconds
     west of UTC) and ‘daylight’ (to 0 if this timezone does not have
     any daylight saving time rules, or to nonzero if there is a time,
     past, present or future when daylight saving time applies).

     *note Availability: 1491.: Unix.

          Note: Although in many cases, changing the ‘TZ’ environment
          variable may affect the output of functions like *note
          localtime(): 1080. without calling *note tzset(): 2177, this
          behavior should not be relied on.

          The ‘TZ’ environment variable should contain no whitespace.

     The standard format of the ‘TZ’ environment variable is (whitespace
     added for clarity):

          std offset [dst [offset [,start[/time], end[/time]]]]

     Where the components are:

     ‘std’ and ‘dst’

          Three or more alphanumerics giving the timezone abbreviations.
          These will be propagated into time.tzname

     ‘offset’

          The offset has the form: ‘± hh[:mm[:ss]]’.  This indicates the
          value added the local time to arrive at UTC. If preceded by a
          ‘-’, the timezone is east of the Prime Meridian; otherwise, it
          is west.  If no offset follows dst, summer time is assumed to
          be one hour ahead of standard time.

     ‘start[/time], end[/time]’

          Indicates when to change to and back from DST. The format of
          the start and end dates are one of the following:

          ‘J`n'’

               The Julian day `n' (1 <= `n' <= 365).  Leap days are not
               counted, so in all years February 28 is day 59 and March
               1 is day 60.

          ‘`n'’

               The zero-based Julian day (0 <= `n' <= 365).  Leap days
               are counted, and it is possible to refer to February 29.

          ‘M`m'.`n'.`d'’

               The `d'’th day (0 <= `d' <= 6) of week `n' of month `m'
               of the year (1 <= `n' <= 5, 1 <= `m' <= 12, where week 5
               means “the last `d' day in month `m'” which may occur in
               either the fourth or the fifth week).  Week 1 is the
               first week in which the `d'’th day occurs.  Day zero is a
               Sunday.

          ‘time’ has the same format as ‘offset’ except that no leading
          sign (‘-’ or ‘+’) is allowed.  The default, if time is not
          given, is 02:00:00.

          >>> os.environ['TZ'] = 'EST+05EDT,M4.1.0,M10.5.0'
          >>> time.tzset()
          >>> time.strftime('%X %x %Z')
          '02:07:36 05/08/03 EDT'
          >>> os.environ['TZ'] = 'AEST-10AEDT-11,M10.5.0,M3.5.0'
          >>> time.tzset()
          >>> time.strftime('%X %x %Z')
          '16:08:12 05/08/03 AEST'

     On many Unix systems (including *BSD, Linux, Solaris, and Darwin),
     it is more convenient to use the system’s zoneinfo (‘tzfile(5)’)
     database to specify the timezone rules.  To do this, set the ‘TZ’
     environment variable to the path of the required timezone datafile,
     relative to the root of the systems ‘zoneinfo’ timezone database,
     usually located at ‘/usr/share/zoneinfo’.  For example,
     ‘'US/Eastern'’, ‘'Australia/Melbourne'’, ‘'Egypt'’ or
     ‘'Europe/Amsterdam'’.

          >>> os.environ['TZ'] = 'US/Eastern'
          >>> time.tzset()
          >>> time.tzname
          ('EST', 'EDT')
          >>> os.environ['TZ'] = 'Egypt'
          >>> time.tzset()
          >>> time.tzname
          ('EET', 'EEST')

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0475

   (2) https://en.wikipedia.org/wiki/Leap_second

   (3) https://tools.ietf.org/html/rfc2822.html

   (4) (1) The use of ‘%Z’ is now deprecated, but the ‘%z’ escape that
expands to the preferred hour/minute offset is not supported by all ANSI
C libraries.  Also, a strict reading of the original 1982 RFC 822
(https://tools.ietf.org/html/rfc822.html) standard calls for a two-digit
year (%y rather than %Y), but practice moved to 4-digit years long
before the year 2000.  After that, RFC 822
(https://tools.ietf.org/html/rfc822.html) became obsolete and the
4-digit year has been first recommended by RFC 1123
(https://tools.ietf.org/html/rfc1123.html) and then mandated by RFC 2822
(https://tools.ietf.org/html/rfc2822.html).

   (5) https://en.wikipedia.org/wiki/Leap_second

   (6) https://en.wikipedia.org/wiki/Unix_time


File: python.info,  Node: Clock ID Constants,  Next: Timezone Constants,  Prev: Functions<3>,  Up: time — Time access and conversions

5.16.3.2 Clock ID Constants
...........................

These constants are used as parameters for *note clock_getres(): b8a.
and *note clock_gettime(): b8b.

 -- Data: time.CLOCK_BOOTTIME

     Identical to *note CLOCK_MONOTONIC: 4fc, except it also includes
     any time that the system is suspended.

     This allows applications to get a suspend-aware monotonic clock
     without having to deal with the complications of *note
     CLOCK_REALTIME: f6d, which may have discontinuities if the time is
     changed using ‘settimeofday()’ or similar.

     *note Availability: 1491.: Linux 2.6.39 or later.

     New in version 3.7.

 -- Data: time.CLOCK_HIGHRES

     The Solaris OS has a ‘CLOCK_HIGHRES’ timer that attempts to use an
     optimal hardware source, and may give close to nanosecond
     resolution.  ‘CLOCK_HIGHRES’ is the nonadjustable, high-resolution
     clock.

     *note Availability: 1491.: Solaris.

     New in version 3.3.

 -- Data: time.CLOCK_MONOTONIC

     Clock that cannot be set and represents monotonic time since some
     unspecified starting point.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Data: time.CLOCK_MONOTONIC_RAW

     Similar to *note CLOCK_MONOTONIC: 4fc, but provides access to a raw
     hardware-based time that is not subject to NTP adjustments.

     *note Availability: 1491.: Linux 2.6.28 and newer, macOS 10.12 and
     newer.

     New in version 3.3.

 -- Data: time.CLOCK_PROCESS_CPUTIME_ID

     High-resolution per-process timer from the CPU.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Data: time.CLOCK_PROF

     High-resolution per-process timer from the CPU.

     *note Availability: 1491.: FreeBSD, NetBSD 7 or later, OpenBSD.

     New in version 3.7.

 -- Data: time.CLOCK_TAI

     International Atomic Time(1)

     The system must have a current leap second table in order for this
     to give the correct answer.  PTP or NTP software can maintain a
     leap second table.

     *note Availability: 1491.: Linux.

     New in version 3.9.

 -- Data: time.CLOCK_THREAD_CPUTIME_ID

     Thread-specific CPU-time clock.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Data: time.CLOCK_UPTIME

     Time whose absolute value is the time the system has been running
     and not suspended, providing accurate uptime measurement, both
     absolute and interval.

     *note Availability: 1491.: FreeBSD, OpenBSD 5.5 or later.

     New in version 3.7.

 -- Data: time.CLOCK_UPTIME_RAW

     Clock that increments monotonically, tracking the time since an
     arbitrary point, unaffected by frequency or time adjustments and
     not incremented while the system is asleep.

     *note Availability: 1491.: macOS 10.12 and newer.

     New in version 3.8.

The following constant is the only parameter that can be sent to *note
clock_settime(): b8c.

 -- Data: time.CLOCK_REALTIME

     System-wide real-time clock.  Setting this clock requires
     appropriate privileges.

     *note Availability: 1491.: Unix.

     New in version 3.3.

   ---------- Footnotes ----------

   (1) 
https://www.nist.gov/pml/time-and-frequency-division/nist-time-frequently-asked-questions-faq#tai


File: python.info,  Node: Timezone Constants,  Prev: Clock ID Constants,  Up: time — Time access and conversions

5.16.3.3 Timezone Constants
...........................

 -- Data: time.altzone

     The offset of the local DST timezone, in seconds west of UTC, if
     one is defined.  This is negative if the local DST timezone is east
     of UTC (as in Western Europe, including the UK). Only use this if
     ‘daylight’ is nonzero.  See note below.

 -- Data: time.daylight

     Nonzero if a DST timezone is defined.  See note below.

 -- Data: time.timezone

     The offset of the local (non-DST) timezone, in seconds west of UTC
     (negative in most of Western Europe, positive in the US, zero in
     the UK). See note below.

 -- Data: time.tzname

     A tuple of two strings: the first is the name of the local non-DST
     timezone, the second is the name of the local DST timezone.  If no
     DST timezone is defined, the second string should not be used.  See
     note below.

     Note: For the above Timezone constants (*note altzone: 217f, *note
     daylight: 2180, *note timezone: 2181, and *note tzname: 2182.), the
     value is determined by the timezone rules in effect at module load
     time or the last time *note tzset(): 2177. is called and may be
     incorrect for times in the past.  It is recommended to use the
     ‘tm_gmtoff’ and ‘tm_zone’ results from *note localtime(): 1080. to
     obtain timezone information.

See also
........

Module *note datetime: 30.

     More object-oriented interface to dates and times.

Module *note locale: a9.

     Internationalization services.  The locale setting affects the
     interpretation of many format specifiers in *note strftime(): c37.
     and *note strptime(): e56.

Module *note calendar: 14.

     General calendar-related functions.  *note timegm(): 1a7a. is the
     inverse of *note gmtime(): c11. from this module.


File: python.info,  Node: argparse — Parser for command-line options arguments and sub-commands,  Next: getopt — C-style parser for command line options,  Prev: time — Time access and conversions,  Up: Generic Operating System Services

5.16.4 ‘argparse’ — Parser for command-line options, arguments and sub-commands
-------------------------------------------------------------------------------

New in version 3.2.

`Source code:' Lib/argparse.py(1)

__________________________________________________________________

Tutorial
........

This page contains the API reference information.  For a more gentle
introduction to Python command-line parsing, have a look at the *note
argparse tutorial: 2185.

The *note argparse: 5. module makes it easy to write user-friendly
command-line interfaces.  The program defines what arguments it
requires, and *note argparse: 5. will figure out how to parse those out
of *note sys.argv: cc6.  The *note argparse: 5. module also
automatically generates help and usage messages and issues errors when
users give the program invalid arguments.

* Menu:

* Example: Example<7>.
* ArgumentParser objects::
* The add_argument() method: The add_argument method.
* The parse_args() method: The parse_args method.
* Other utilities::
* Upgrading optparse code::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/argparse.py


File: python.info,  Node: Example<7>,  Next: ArgumentParser objects,  Up: argparse — Parser for command-line options arguments and sub-commands

5.16.4.1 Example
................

The following code is a Python program that takes a list of integers and
produces either the sum or the max:

     import argparse

     parser = argparse.ArgumentParser(description='Process some integers.')
     parser.add_argument('integers', metavar='N', type=int, nargs='+',
                         help='an integer for the accumulator')
     parser.add_argument('--sum', dest='accumulate', action='store_const',
                         const=sum, default=max,
                         help='sum the integers (default: find the max)')

     args = parser.parse_args()
     print(args.accumulate(args.integers))

Assuming the Python code above is saved into a file called ‘prog.py’, it
can be run at the command line and provides useful help messages:

     $ python prog.py -h
     usage: prog.py [-h] [--sum] N [N ...]

     Process some integers.

     positional arguments:
      N           an integer for the accumulator

     optional arguments:
      -h, --help  show this help message and exit
      --sum       sum the integers (default: find the max)

When run with the appropriate arguments, it prints either the sum or the
max of the command-line integers:

     $ python prog.py 1 2 3 4
     4

     $ python prog.py 1 2 3 4 --sum
     10

If invalid arguments are passed in, it will issue an error:

     $ python prog.py a b c
     usage: prog.py [-h] [--sum] N [N ...]
     prog.py: error: argument N: invalid int value: 'a'

The following sections walk you through this example.

* Menu:

* Creating a parser::
* Adding arguments::
* Parsing arguments::


File: python.info,  Node: Creating a parser,  Next: Adding arguments,  Up: Example<7>

5.16.4.2 Creating a parser
..........................

The first step in using the *note argparse: 5. is creating an *note
ArgumentParser: 788. object:

     >>> parser = argparse.ArgumentParser(description='Process some integers.')

The *note ArgumentParser: 788. object will hold all the information
necessary to parse the command line into Python data types.


File: python.info,  Node: Adding arguments,  Next: Parsing arguments,  Prev: Creating a parser,  Up: Example<7>

5.16.4.3 Adding arguments
.........................

Filling an *note ArgumentParser: 788. with information about program
arguments is done by making calls to the *note add_argument(): 2189.
method.  Generally, these calls tell the *note ArgumentParser: 788. how
to take the strings on the command line and turn them into objects.
This information is stored and used when *note parse_args(): 218a. is
called.  For example:

     >>> parser.add_argument('integers', metavar='N', type=int, nargs='+',
     ...                     help='an integer for the accumulator')
     >>> parser.add_argument('--sum', dest='accumulate', action='store_const',
     ...                     const=sum, default=max,
     ...                     help='sum the integers (default: find the max)')

Later, calling *note parse_args(): 218a. will return an object with two
attributes, ‘integers’ and ‘accumulate’.  The ‘integers’ attribute will
be a list of one or more ints, and the ‘accumulate’ attribute will be
either the *note sum(): 316. function, if ‘--sum’ was specified at the
command line, or the *note max(): 8f7. function if it was not.


File: python.info,  Node: Parsing arguments,  Prev: Adding arguments,  Up: Example<7>

5.16.4.4 Parsing arguments
..........................

*note ArgumentParser: 788. parses arguments through the *note
parse_args(): 218a. method.  This will inspect the command line, convert
each argument to the appropriate type and then invoke the appropriate
action.  In most cases, this means a simple *note Namespace: 218c.
object will be built up from attributes parsed out of the command line:

     >>> parser.parse_args(['--sum', '7', '-1', '42'])
     Namespace(accumulate=<built-in function sum>, integers=[7, -1, 42])

In a script, *note parse_args(): 218a. will typically be called with no
arguments, and the *note ArgumentParser: 788. will automatically
determine the command-line arguments from *note sys.argv: cc6.


File: python.info,  Node: ArgumentParser objects,  Next: The add_argument method,  Prev: Example<7>,  Up: argparse — Parser for command-line options arguments and sub-commands

5.16.4.5 ArgumentParser objects
...............................

 -- Class: argparse.ArgumentParser (prog=None, usage=None,
          description=None, epilog=None, parents=[],
          formatter_class=argparse.HelpFormatter, prefix_chars='-',
          fromfile_prefix_chars=None, argument_default=None,
          conflict_handler='error', add_help=True, allow_abbrev=True,
          exit_on_error=True)

     Create a new *note ArgumentParser: 788. object.  All parameters
     should be passed as keyword arguments.  Each parameter has its own
     more detailed description below, but in short they are:

        * *note prog: 218e. - The name of the program (default:
          ‘sys.argv[0]’)

        * *note usage: 218f. - The string describing the program usage
          (default: generated from arguments added to parser)

        * *note description: 2190. - Text to display before the argument
          help (default: none)

        * *note epilog: 2191. - Text to display after the argument help
          (default: none)

        * *note parents: 2192. - A list of *note ArgumentParser: 788.
          objects whose arguments should also be included

        * *note formatter_class: 2193. - A class for customizing the
          help output

        * *note prefix_chars: 2194. - The set of characters that prefix
          optional arguments (default: ‘-‘)

        * *note fromfile_prefix_chars: 2195. - The set of characters
          that prefix files from which additional arguments should be
          read (default: ‘None’)

        * *note argument_default: 2196. - The global default value for
          arguments (default: ‘None’)

        * *note conflict_handler: 2197. - The strategy for resolving
          conflicting optionals (usually unnecessary)

        * *note add_help: 2198. - Add a ‘-h/--help’ option to the parser
          (default: ‘True’)

        * *note allow_abbrev: 78a. - Allows long options to be
          abbreviated if the abbreviation is unambiguous.  (default:
          ‘True’)

        * *note exit_on_error: 2199. - Determines whether or not
          ArgumentParser exits with error info when an error occurs.
          (default: ‘True’)

     Changed in version 3.5: `allow_abbrev' parameter was added.

     Changed in version 3.8: In previous versions, `allow_abbrev' also
     disabled grouping of short flags such as ‘-vv’ to mean ‘-v -v’.

     Changed in version 3.9: `exit_on_error' parameter was added.

The following sections describe how each of these are used.

* Menu:

* prog::
* usage::
* description::
* epilog::
* parents::
* formatter_class::
* prefix_chars::
* fromfile_prefix_chars::
* argument_default::
* allow_abbrev::
* conflict_handler::
* add_help::
* exit_on_error::


File: python.info,  Node: prog,  Next: usage,  Up: ArgumentParser objects

5.16.4.6 prog
.............

By default, *note ArgumentParser: 788. objects use ‘sys.argv[0]’ to
determine how to display the name of the program in help messages.  This
default is almost always desirable because it will make the help
messages match how the program was invoked on the command line.  For
example, consider a file named ‘myprogram.py’ with the following code:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument('--foo', help='foo help')
     args = parser.parse_args()

The help for this program will display ‘myprogram.py’ as the program
name (regardless of where the program was invoked from):

     $ python myprogram.py --help
     usage: myprogram.py [-h] [--foo FOO]

     optional arguments:
      -h, --help  show this help message and exit
      --foo FOO   foo help
     $ cd ..
     $ python subdir/myprogram.py --help
     usage: myprogram.py [-h] [--foo FOO]

     optional arguments:
      -h, --help  show this help message and exit
      --foo FOO   foo help

To change this default behavior, another value can be supplied using the
‘prog=’ argument to *note ArgumentParser: 788.:

     >>> parser = argparse.ArgumentParser(prog='myprogram')
     >>> parser.print_help()
     usage: myprogram [-h]

     optional arguments:
      -h, --help  show this help message and exit

Note that the program name, whether determined from ‘sys.argv[0]’ or
from the ‘prog=’ argument, is available to help messages using the
‘%(prog)s’ format specifier.

     >>> parser = argparse.ArgumentParser(prog='myprogram')
     >>> parser.add_argument('--foo', help='foo of the %(prog)s program')
     >>> parser.print_help()
     usage: myprogram [-h] [--foo FOO]

     optional arguments:
      -h, --help  show this help message and exit
      --foo FOO   foo of the myprogram program


File: python.info,  Node: usage,  Next: description,  Prev: prog,  Up: ArgumentParser objects

5.16.4.7 usage
..............

By default, *note ArgumentParser: 788. calculates the usage message from
the arguments it contains:

     >>> parser = argparse.ArgumentParser(prog='PROG')
     >>> parser.add_argument('--foo', nargs='?', help='foo help')
     >>> parser.add_argument('bar', nargs='+', help='bar help')
     >>> parser.print_help()
     usage: PROG [-h] [--foo [FOO]] bar [bar ...]

     positional arguments:
      bar          bar help

     optional arguments:
      -h, --help   show this help message and exit
      --foo [FOO]  foo help

The default message can be overridden with the ‘usage=’ keyword
argument:

     >>> parser = argparse.ArgumentParser(prog='PROG', usage='%(prog)s [options]')
     >>> parser.add_argument('--foo', nargs='?', help='foo help')
     >>> parser.add_argument('bar', nargs='+', help='bar help')
     >>> parser.print_help()
     usage: PROG [options]

     positional arguments:
      bar          bar help

     optional arguments:
      -h, --help   show this help message and exit
      --foo [FOO]  foo help

The ‘%(prog)s’ format specifier is available to fill in the program name
in your usage messages.


File: python.info,  Node: description,  Next: epilog,  Prev: usage,  Up: ArgumentParser objects

5.16.4.8 description
....................

Most calls to the *note ArgumentParser: 788. constructor will use the
‘description=’ keyword argument.  This argument gives a brief
description of what the program does and how it works.  In help
messages, the description is displayed between the command-line usage
string and the help messages for the various arguments:

     >>> parser = argparse.ArgumentParser(description='A foo that bars')
     >>> parser.print_help()
     usage: argparse.py [-h]

     A foo that bars

     optional arguments:
      -h, --help  show this help message and exit

By default, the description will be line-wrapped so that it fits within
the given space.  To change this behavior, see the *note
formatter_class: 2193. argument.


File: python.info,  Node: epilog,  Next: parents,  Prev: description,  Up: ArgumentParser objects

5.16.4.9 epilog
...............

Some programs like to display additional description of the program
after the description of the arguments.  Such text can be specified
using the ‘epilog=’ argument to *note ArgumentParser: 788.:

     >>> parser = argparse.ArgumentParser(
     ...     description='A foo that bars',
     ...     epilog="And that's how you'd foo a bar")
     >>> parser.print_help()
     usage: argparse.py [-h]

     A foo that bars

     optional arguments:
      -h, --help  show this help message and exit

     And that's how you'd foo a bar

As with the *note description: 2190. argument, the ‘epilog=’ text is by
default line-wrapped, but this behavior can be adjusted with the *note
formatter_class: 2193. argument to *note ArgumentParser: 788.


File: python.info,  Node: parents,  Next: formatter_class,  Prev: epilog,  Up: ArgumentParser objects

5.16.4.10 parents
.................

Sometimes, several parsers share a common set of arguments.  Rather than
repeating the definitions of these arguments, a single parser with all
the shared arguments and passed to ‘parents=’ argument to *note
ArgumentParser: 788. can be used.  The ‘parents=’ argument takes a list
of *note ArgumentParser: 788. objects, collects all the positional and
optional actions from them, and adds these actions to the *note
ArgumentParser: 788. object being constructed:

     >>> parent_parser = argparse.ArgumentParser(add_help=False)
     >>> parent_parser.add_argument('--parent', type=int)

     >>> foo_parser = argparse.ArgumentParser(parents=[parent_parser])
     >>> foo_parser.add_argument('foo')
     >>> foo_parser.parse_args(['--parent', '2', 'XXX'])
     Namespace(foo='XXX', parent=2)

     >>> bar_parser = argparse.ArgumentParser(parents=[parent_parser])
     >>> bar_parser.add_argument('--bar')
     >>> bar_parser.parse_args(['--bar', 'YYY'])
     Namespace(bar='YYY', parent=None)

Note that most parent parsers will specify ‘add_help=False’.  Otherwise,
the *note ArgumentParser: 788. will see two ‘-h/--help’ options (one in
the parent and one in the child) and raise an error.

     Note: You must fully initialize the parsers before passing them via
     ‘parents=’.  If you change the parent parsers after the child
     parser, those changes will not be reflected in the child.


File: python.info,  Node: formatter_class,  Next: prefix_chars,  Prev: parents,  Up: ArgumentParser objects

5.16.4.11 formatter_class
.........................

*note ArgumentParser: 788. objects allow the help formatting to be
customized by specifying an alternate formatting class.  Currently,
there are four such classes:

 -- Class: argparse.RawDescriptionHelpFormatter
 -- Class: argparse.RawTextHelpFormatter
 -- Class: argparse.ArgumentDefaultsHelpFormatter
 -- Class: argparse.MetavarTypeHelpFormatter

*note RawDescriptionHelpFormatter: 219a. and *note RawTextHelpFormatter:
219b. give more control over how textual descriptions are displayed.  By
default, *note ArgumentParser: 788. objects line-wrap the *note
description: 2190. and *note epilog: 2191. texts in command-line help
messages:

     >>> parser = argparse.ArgumentParser(
     ...     prog='PROG',
     ...     description='''this description
     ...         was indented weird
     ...             but that is okay''',
     ...     epilog='''
     ...             likewise for this epilog whose whitespace will
     ...         be cleaned up and whose words will be wrapped
     ...         across a couple lines''')
     >>> parser.print_help()
     usage: PROG [-h]

     this description was indented weird but that is okay

     optional arguments:
      -h, --help  show this help message and exit

     likewise for this epilog whose whitespace will be cleaned up and whose words
     will be wrapped across a couple lines

Passing *note RawDescriptionHelpFormatter: 219a. as ‘formatter_class=’
indicates that *note description: 2190. and *note epilog: 2191. are
already correctly formatted and should not be line-wrapped:

     >>> parser = argparse.ArgumentParser(
     ...     prog='PROG',
     ...     formatter_class=argparse.RawDescriptionHelpFormatter,
     ...     description=textwrap.dedent('''\
     ...         Please do not mess up this text!
     ...         --------------------------------
     ...             I have indented it
     ...             exactly the way
     ...             I want it
     ...         '''))
     >>> parser.print_help()
     usage: PROG [-h]

     Please do not mess up this text!
     --------------------------------
        I have indented it
        exactly the way
        I want it

     optional arguments:
      -h, --help  show this help message and exit

*note RawTextHelpFormatter: 219b. maintains whitespace for all sorts of
help text, including argument descriptions.  However, multiple new lines
are replaced with one.  If you wish to preserve multiple blank lines,
add spaces between the newlines.

*note ArgumentDefaultsHelpFormatter: f80. automatically adds information
about default values to each of the argument help messages:

     >>> parser = argparse.ArgumentParser(
     ...     prog='PROG',
     ...     formatter_class=argparse.ArgumentDefaultsHelpFormatter)
     >>> parser.add_argument('--foo', type=int, default=42, help='FOO!')
     >>> parser.add_argument('bar', nargs='*', default=[1, 2, 3], help='BAR!')
     >>> parser.print_help()
     usage: PROG [-h] [--foo FOO] [bar ...]

     positional arguments:
      bar         BAR! (default: [1, 2, 3])

     optional arguments:
      -h, --help  show this help message and exit
      --foo FOO   FOO! (default: 42)

*note MetavarTypeHelpFormatter: 219c. uses the name of the *note type:
219d. argument for each argument as the display name for its values
(rather than using the *note dest: 219e. as the regular formatter does):

     >>> parser = argparse.ArgumentParser(
     ...     prog='PROG',
     ...     formatter_class=argparse.MetavarTypeHelpFormatter)
     >>> parser.add_argument('--foo', type=int)
     >>> parser.add_argument('bar', type=float)
     >>> parser.print_help()
     usage: PROG [-h] [--foo int] float

     positional arguments:
       float

     optional arguments:
       -h, --help  show this help message and exit
       --foo int


File: python.info,  Node: prefix_chars,  Next: fromfile_prefix_chars,  Prev: formatter_class,  Up: ArgumentParser objects

5.16.4.12 prefix_chars
......................

Most command-line options will use ‘-’ as the prefix, e.g.  ‘-f/--foo’.
Parsers that need to support different or additional prefix characters,
e.g.  for options like ‘+f’ or ‘/foo’, may specify them using the
‘prefix_chars=’ argument to the ArgumentParser constructor:

     >>> parser = argparse.ArgumentParser(prog='PROG', prefix_chars='-+')
     >>> parser.add_argument('+f')
     >>> parser.add_argument('++bar')
     >>> parser.parse_args('+f X ++bar Y'.split())
     Namespace(bar='Y', f='X')

The ‘prefix_chars=’ argument defaults to ‘'-'’.  Supplying a set of
characters that does not include ‘-’ will cause ‘-f/--foo’ options to be
disallowed.


File: python.info,  Node: fromfile_prefix_chars,  Next: argument_default,  Prev: prefix_chars,  Up: ArgumentParser objects

5.16.4.13 fromfile_prefix_chars
...............................

Sometimes, for example when dealing with a particularly long argument
lists, it may make sense to keep the list of arguments in a file rather
than typing it out at the command line.  If the ‘fromfile_prefix_chars=’
argument is given to the *note ArgumentParser: 788. constructor, then
arguments that start with any of the specified characters will be
treated as files, and will be replaced by the arguments they contain.
For example:

     >>> with open('args.txt', 'w') as fp:
     ...     fp.write('-f\nbar')
     >>> parser = argparse.ArgumentParser(fromfile_prefix_chars='@')
     >>> parser.add_argument('-f')
     >>> parser.parse_args(['-f', 'foo', '@args.txt'])
     Namespace(f='bar')

Arguments read from a file must by default be one per line (but see also
*note convert_arg_line_to_args(): 219f.) and are treated as if they were
in the same place as the original file referencing argument on the
command line.  So in the example above, the expression ‘['-f', 'foo',
'@args.txt']’ is considered equivalent to the expression ‘['-f', 'foo',
'-f', 'bar']’.

The ‘fromfile_prefix_chars=’ argument defaults to ‘None’, meaning that
arguments will never be treated as file references.


File: python.info,  Node: argument_default,  Next: allow_abbrev,  Prev: fromfile_prefix_chars,  Up: ArgumentParser objects

5.16.4.14 argument_default
..........................

Generally, argument defaults are specified either by passing a default
to *note add_argument(): 2189. or by calling the *note set_defaults():
21a0. methods with a specific set of name-value pairs.  Sometimes
however, it may be useful to specify a single parser-wide default for
arguments.  This can be accomplished by passing the ‘argument_default=’
keyword argument to *note ArgumentParser: 788.  For example, to globally
suppress attribute creation on *note parse_args(): 218a. calls, we
supply ‘argument_default=SUPPRESS’:

     >>> parser = argparse.ArgumentParser(argument_default=argparse.SUPPRESS)
     >>> parser.add_argument('--foo')
     >>> parser.add_argument('bar', nargs='?')
     >>> parser.parse_args(['--foo', '1', 'BAR'])
     Namespace(bar='BAR', foo='1')
     >>> parser.parse_args([])
     Namespace()


File: python.info,  Node: allow_abbrev,  Next: conflict_handler,  Prev: argument_default,  Up: ArgumentParser objects

5.16.4.15 allow_abbrev
......................

Normally, when you pass an argument list to the *note parse_args():
218a. method of an *note ArgumentParser: 788, it *note recognizes
abbreviations: 789. of long options.

This feature can be disabled by setting ‘allow_abbrev’ to ‘False’:

     >>> parser = argparse.ArgumentParser(prog='PROG', allow_abbrev=False)
     >>> parser.add_argument('--foobar', action='store_true')
     >>> parser.add_argument('--foonley', action='store_false')
     >>> parser.parse_args(['--foon'])
     usage: PROG [-h] [--foobar] [--foonley]
     PROG: error: unrecognized arguments: --foon

New in version 3.5.


File: python.info,  Node: conflict_handler,  Next: add_help,  Prev: allow_abbrev,  Up: ArgumentParser objects

5.16.4.16 conflict_handler
..........................

*note ArgumentParser: 788. objects do not allow two actions with the
same option string.  By default, *note ArgumentParser: 788. objects
raise an exception if an attempt is made to create an argument with an
option string that is already in use:

     >>> parser = argparse.ArgumentParser(prog='PROG')
     >>> parser.add_argument('-f', '--foo', help='old foo help')
     >>> parser.add_argument('--foo', help='new foo help')
     Traceback (most recent call last):
      ..
     ArgumentError: argument --foo: conflicting option string(s): --foo

Sometimes (e.g.  when using *note parents: 2192.) it may be useful to
simply override any older arguments with the same option string.  To get
this behavior, the value ‘'resolve'’ can be supplied to the
‘conflict_handler=’ argument of *note ArgumentParser: 788.:

     >>> parser = argparse.ArgumentParser(prog='PROG', conflict_handler='resolve')
     >>> parser.add_argument('-f', '--foo', help='old foo help')
     >>> parser.add_argument('--foo', help='new foo help')
     >>> parser.print_help()
     usage: PROG [-h] [-f FOO] [--foo FOO]

     optional arguments:
      -h, --help  show this help message and exit
      -f FOO      old foo help
      --foo FOO   new foo help

Note that *note ArgumentParser: 788. objects only remove an action if
all of its option strings are overridden.  So, in the example above, the
old ‘-f/--foo’ action is retained as the ‘-f’ action, because only the
‘--foo’ option string was overridden.


File: python.info,  Node: add_help,  Next: exit_on_error,  Prev: conflict_handler,  Up: ArgumentParser objects

5.16.4.17 add_help
..................

By default, ArgumentParser objects add an option which simply displays
the parser’s help message.  For example, consider a file named
‘myprogram.py’ containing the following code:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument('--foo', help='foo help')
     args = parser.parse_args()

If ‘-h’ or ‘--help’ is supplied at the command line, the ArgumentParser
help will be printed:

     $ python myprogram.py --help
     usage: myprogram.py [-h] [--foo FOO]

     optional arguments:
      -h, --help  show this help message and exit
      --foo FOO   foo help

Occasionally, it may be useful to disable the addition of this help
option.  This can be achieved by passing ‘False’ as the ‘add_help=’
argument to *note ArgumentParser: 788.:

     >>> parser = argparse.ArgumentParser(prog='PROG', add_help=False)
     >>> parser.add_argument('--foo', help='foo help')
     >>> parser.print_help()
     usage: PROG [--foo FOO]

     optional arguments:
      --foo FOO  foo help

The help option is typically ‘-h/--help’.  The exception to this is if
the ‘prefix_chars=’ is specified and does not include ‘-’, in which case
‘-h’ and ‘--help’ are not valid options.  In this case, the first
character in ‘prefix_chars’ is used to prefix the help options:

     >>> parser = argparse.ArgumentParser(prog='PROG', prefix_chars='+/')
     >>> parser.print_help()
     usage: PROG [+h]

     optional arguments:
       +h, ++help  show this help message and exit


File: python.info,  Node: exit_on_error,  Prev: add_help,  Up: ArgumentParser objects

5.16.4.18 exit_on_error
.......................

Normally, when you pass an invalid argument list to the *note
parse_args(): 218a. method of an *note ArgumentParser: 788, it will exit
with error info.

If the user would like to catch errors manually, the feature can be
enabled by setting ‘exit_on_error’ to ‘False’:

     >>> parser = argparse.ArgumentParser(exit_on_error=False)
     >>> parser.add_argument('--integers', type=int)
     _StoreAction(option_strings=['--integers'], dest='integers', nargs=None, const=None, default=None, type=<class 'int'>, choices=None, help=None, metavar=None)
     >>> try:
     ...     parser.parse_args('--integers a'.split())
     ... except argparse.ArgumentError:
     ...     print('Catching an argumentError')
     ...
     Catching an argumentError

New in version 3.9.


File: python.info,  Node: The add_argument method,  Next: The parse_args method,  Prev: ArgumentParser objects,  Up: argparse — Parser for command-line options arguments and sub-commands

5.16.4.19 The add_argument() method
...................................

 -- Method: ArgumentParser.add_argument (name or flags...[, action][,
          nargs][, const][, default][, type][, choices][, required][,
          help][, metavar][, dest])

     Define how a single command-line argument should be parsed.  Each
     parameter has its own more detailed description below, but in short
     they are:

        * *note name or flags: 21a3. - Either a name or a list of option
          strings, e.g.  ‘foo’ or ‘-f, --foo’.

        * *note action: 21a4. - The basic type of action to be taken
          when this argument is encountered at the command line.

        * *note nargs: 21a5. - The number of command-line arguments that
          should be consumed.

        * *note const: 21a6. - A constant value required by some *note
          action: 21a4. and *note nargs: 21a5. selections.

        * *note default: 21a7. - The value produced if the argument is
          absent from the command line and if it is absent from the
          namespace object.

        * *note type: 219d. - The type to which the command-line
          argument should be converted.

        * *note choices: 21a8. - A container of the allowable values for
          the argument.

        * *note required: 21a9. - Whether or not the command-line option
          may be omitted (optionals only).

        * *note help: 21aa. - A brief description of what the argument
          does.

        * *note metavar: 21ab. - A name for the argument in usage
          messages.

        * *note dest: 219e. - The name of the attribute to be added to
          the object returned by *note parse_args(): 218a.

The following sections describe how each of these are used.

* Menu:

* name or flags::
* action::
* nargs::
* const::
* default::
* type::
* choices::
* required::
* help::
* metavar::
* dest::
* Action classes::


File: python.info,  Node: name or flags,  Next: action,  Up: The add_argument method

5.16.4.20 name or flags
.......................

The *note add_argument(): 2189. method must know whether an optional
argument, like ‘-f’ or ‘--foo’, or a positional argument, like a list of
filenames, is expected.  The first arguments passed to *note
add_argument(): 2189. must therefore be either a series of flags, or a
simple argument name.  For example, an optional argument could be
created like:

     >>> parser.add_argument('-f', '--foo')

while a positional argument could be created like:

     >>> parser.add_argument('bar')

When *note parse_args(): 218a. is called, optional arguments will be
identified by the ‘-’ prefix, and the remaining arguments will be
assumed to be positional:

     >>> parser = argparse.ArgumentParser(prog='PROG')
     >>> parser.add_argument('-f', '--foo')
     >>> parser.add_argument('bar')
     >>> parser.parse_args(['BAR'])
     Namespace(bar='BAR', foo=None)
     >>> parser.parse_args(['BAR', '--foo', 'FOO'])
     Namespace(bar='BAR', foo='FOO')
     >>> parser.parse_args(['--foo', 'FOO'])
     usage: PROG [-h] [-f FOO] bar
     PROG: error: the following arguments are required: bar


File: python.info,  Node: action,  Next: nargs,  Prev: name or flags,  Up: The add_argument method

5.16.4.21 action
................

*note ArgumentParser: 788. objects associate command-line arguments with
actions.  These actions can do just about anything with the command-line
arguments associated with them, though most actions simply add an
attribute to the object returned by *note parse_args(): 218a.  The
‘action’ keyword argument specifies how the command-line arguments
should be handled.  The supplied actions are:

   * ‘'store'’ - This just stores the argument’s value.  This is the
     default action.  For example:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('--foo')
          >>> parser.parse_args('--foo 1'.split())
          Namespace(foo='1')

   * ‘'store_const'’ - This stores the value specified by the *note
     const: 21a6. keyword argument.  The ‘'store_const'’ action is most
     commonly used with optional arguments that specify some sort of
     flag.  For example:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('--foo', action='store_const', const=42)
          >>> parser.parse_args(['--foo'])
          Namespace(foo=42)

   * ‘'store_true'’ and ‘'store_false'’ - These are special cases of
     ‘'store_const'’ used for storing the values ‘True’ and ‘False’
     respectively.  In addition, they create default values of ‘False’
     and ‘True’ respectively.  For example:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('--foo', action='store_true')
          >>> parser.add_argument('--bar', action='store_false')
          >>> parser.add_argument('--baz', action='store_false')
          >>> parser.parse_args('--foo --bar'.split())
          Namespace(foo=True, bar=False, baz=True)

   * ‘'append'’ - This stores a list, and appends each argument value to
     the list.  This is useful to allow an option to be specified
     multiple times.  Example usage:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('--foo', action='append')
          >>> parser.parse_args('--foo 1 --foo 2'.split())
          Namespace(foo=['1', '2'])

   * ‘'append_const'’ - This stores a list, and appends the value
     specified by the *note const: 21a6. keyword argument to the list.
     (Note that the *note const: 21a6. keyword argument defaults to
     ‘None’.)  The ‘'append_const'’ action is typically useful when
     multiple arguments need to store constants to the same list.  For
     example:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('--str', dest='types', action='append_const', const=str)
          >>> parser.add_argument('--int', dest='types', action='append_const', const=int)
          >>> parser.parse_args('--str --int'.split())
          Namespace(types=[<class 'str'>, <class 'int'>])

   * ‘'count'’ - This counts the number of times a keyword argument
     occurs.  For example, this is useful for increasing verbosity
     levels:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('--verbose', '-v', action='count', default=0)
          >>> parser.parse_args(['-vvv'])
          Namespace(verbose=3)

     Note, the `default' will be ‘None’ unless explicitly set to `0'.

   * ‘'help'’ - This prints a complete help message for all the options
     in the current parser and then exits.  By default a help action is
     automatically added to the parser.  See *note ArgumentParser: 788.
     for details of how the output is created.

   * ‘'version'’ - This expects a ‘version=’ keyword argument in the
     *note add_argument(): 2189. call, and prints version information
     and exits when invoked:

          >>> import argparse
          >>> parser = argparse.ArgumentParser(prog='PROG')
          >>> parser.add_argument('--version', action='version', version='%(prog)s 2.0')
          >>> parser.parse_args(['--version'])
          PROG 2.0

   * ‘'extend'’ - This stores a list, and extends each argument value to
     the list.  Example usage:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument("--foo", action="extend", nargs="+", type=str)
          >>> parser.parse_args(["--foo", "f1", "--foo", "f2", "f3", "f4"])
          Namespace(foo=['f1', 'f2', 'f3', 'f4'])

     New in version 3.8.

You may also specify an arbitrary action by passing an Action subclass
or other object that implements the same interface.  The
‘BooleanOptionalAction’ is available in ‘argparse’ and adds support for
boolean actions such as ‘--foo’ and ‘--no-foo’:

     >>> import argparse
     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo', action=argparse.BooleanOptionalAction)
     >>> parser.parse_args(['--no-foo'])
     Namespace(foo=False)

New in version 3.9.

The recommended way to create a custom action is to extend *note Action:
21ac, overriding the ‘__call__’ method and optionally the ‘__init__’ and
‘format_usage’ methods.

An example of a custom action:

     >>> class FooAction(argparse.Action):
     ...     def __init__(self, option_strings, dest, nargs=None, **kwargs):
     ...         if nargs is not None:
     ...             raise ValueError("nargs not allowed")
     ...         super().__init__(option_strings, dest, **kwargs)
     ...     def __call__(self, parser, namespace, values, option_string=None):
     ...         print('%r %r %r' % (namespace, values, option_string))
     ...         setattr(namespace, self.dest, values)
     ...
     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo', action=FooAction)
     >>> parser.add_argument('bar', action=FooAction)
     >>> args = parser.parse_args('1 --foo 2'.split())
     Namespace(bar=None, foo=None) '1' None
     Namespace(bar='1', foo=None) '2' '--foo'
     >>> args
     Namespace(bar='1', foo='2')

For more details, see *note Action: 21ac.


File: python.info,  Node: nargs,  Next: const,  Prev: action,  Up: The add_argument method

5.16.4.22 nargs
...............

ArgumentParser objects usually associate a single command-line argument
with a single action to be taken.  The ‘nargs’ keyword argument
associates a different number of command-line arguments with a single
action.  The supported values are:

   * ‘N’ (an integer).  ‘N’ arguments from the command line will be
     gathered together into a list.  For example:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('--foo', nargs=2)
          >>> parser.add_argument('bar', nargs=1)
          >>> parser.parse_args('c --foo a b'.split())
          Namespace(bar=['c'], foo=['a', 'b'])

     Note that ‘nargs=1’ produces a list of one item.  This is different
     from the default, in which the item is produced by itself.

   * ‘'?'’.  One argument will be consumed from the command line if
     possible, and produced as a single item.  If no command-line
     argument is present, the value from *note default: 21a7. will be
     produced.  Note that for optional arguments, there is an additional
     case - the option string is present but not followed by a
     command-line argument.  In this case the value from *note const:
     21a6. will be produced.  Some examples to illustrate this:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('--foo', nargs='?', const='c', default='d')
          >>> parser.add_argument('bar', nargs='?', default='d')
          >>> parser.parse_args(['XX', '--foo', 'YY'])
          Namespace(bar='XX', foo='YY')
          >>> parser.parse_args(['XX', '--foo'])
          Namespace(bar='XX', foo='c')
          >>> parser.parse_args([])
          Namespace(bar='d', foo='d')

     One of the more common uses of ‘nargs='?'’ is to allow optional
     input and output files:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('infile', nargs='?', type=argparse.FileType('r'),
          ...                     default=sys.stdin)
          >>> parser.add_argument('outfile', nargs='?', type=argparse.FileType('w'),
          ...                     default=sys.stdout)
          >>> parser.parse_args(['input.txt', 'output.txt'])
          Namespace(infile=<_io.TextIOWrapper name='input.txt' encoding='UTF-8'>,
                    outfile=<_io.TextIOWrapper name='output.txt' encoding='UTF-8'>)
          >>> parser.parse_args([])
          Namespace(infile=<_io.TextIOWrapper name='<stdin>' encoding='UTF-8'>,
                    outfile=<_io.TextIOWrapper name='<stdout>' encoding='UTF-8'>)

   * ‘'*'’.  All command-line arguments present are gathered into a
     list.  Note that it generally doesn’t make much sense to have more
     than one positional argument with ‘nargs='*'’, but multiple
     optional arguments with ‘nargs='*'’ is possible.  For example:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('--foo', nargs='*')
          >>> parser.add_argument('--bar', nargs='*')
          >>> parser.add_argument('baz', nargs='*')
          >>> parser.parse_args('a b --foo x y --bar 1 2'.split())
          Namespace(bar=['1', '2'], baz=['a', 'b'], foo=['x', 'y'])

   * ‘'+'’.  Just like ‘'*'’, all command-line args present are gathered
     into a list.  Additionally, an error message will be generated if
     there wasn’t at least one command-line argument present.  For
     example:

          >>> parser = argparse.ArgumentParser(prog='PROG')
          >>> parser.add_argument('foo', nargs='+')
          >>> parser.parse_args(['a', 'b'])
          Namespace(foo=['a', 'b'])
          >>> parser.parse_args([])
          usage: PROG [-h] foo [foo ...]
          PROG: error: the following arguments are required: foo

If the ‘nargs’ keyword argument is not provided, the number of arguments
consumed is determined by the *note action: 21a4.  Generally this means
a single command-line argument will be consumed and a single item (not a
list) will be produced.


File: python.info,  Node: const,  Next: default,  Prev: nargs,  Up: The add_argument method

5.16.4.23 const
...............

The ‘const’ argument of *note add_argument(): 2189. is used to hold
constant values that are not read from the command line but are required
for the various *note ArgumentParser: 788. actions.  The two most common
uses of it are:

   * When *note add_argument(): 2189. is called with
     ‘action='store_const'’ or ‘action='append_const'’.  These actions
     add the ‘const’ value to one of the attributes of the object
     returned by *note parse_args(): 218a.  See the *note action: 21a4.
     description for examples.

   * When *note add_argument(): 2189. is called with option strings
     (like ‘-f’ or ‘--foo’) and ‘nargs='?'’.  This creates an optional
     argument that can be followed by zero or one command-line
     arguments.  When parsing the command line, if the option string is
     encountered with no command-line argument following it, the value
     of ‘const’ will be assumed instead.  See the *note nargs: 21a5.
     description for examples.

With the ‘'store_const'’ and ‘'append_const'’ actions, the ‘const’
keyword argument must be given.  For other actions, it defaults to
‘None’.


File: python.info,  Node: default,  Next: type,  Prev: const,  Up: The add_argument method

5.16.4.24 default
.................

All optional arguments and some positional arguments may be omitted at
the command line.  The ‘default’ keyword argument of *note
add_argument(): 2189, whose value defaults to ‘None’, specifies what
value should be used if the command-line argument is not present.  For
optional arguments, the ‘default’ value is used when the option string
was not present at the command line:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo', default=42)
     >>> parser.parse_args(['--foo', '2'])
     Namespace(foo='2')
     >>> parser.parse_args([])
     Namespace(foo=42)

If the target namespace already has an attribute set, the action
`default' will not over write it:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo', default=42)
     >>> parser.parse_args([], namespace=argparse.Namespace(foo=101))
     Namespace(foo=101)

If the ‘default’ value is a string, the parser parses the value as if it
were a command-line argument.  In particular, the parser applies any
*note type: 219d. conversion argument, if provided, before setting the
attribute on the *note Namespace: 218c. return value.  Otherwise, the
parser uses the value as is:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--length', default='10', type=int)
     >>> parser.add_argument('--width', default=10.5, type=int)
     >>> parser.parse_args()
     Namespace(length=10, width=10.5)

For positional arguments with *note nargs: 21a5. equal to ‘?’ or ‘*’,
the ‘default’ value is used when no command-line argument was present:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('foo', nargs='?', default=42)
     >>> parser.parse_args(['a'])
     Namespace(foo='a')
     >>> parser.parse_args([])
     Namespace(foo=42)

Providing ‘default=argparse.SUPPRESS’ causes no attribute to be added if
the command-line argument was not present:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo', default=argparse.SUPPRESS)
     >>> parser.parse_args([])
     Namespace()
     >>> parser.parse_args(['--foo', '1'])
     Namespace(foo='1')


File: python.info,  Node: type,  Next: choices,  Prev: default,  Up: The add_argument method

5.16.4.25 type
..............

By default, the parser reads command-line arguments in as simple
strings.  However, quite often the command-line string should instead be
interpreted as another type, such as a *note float: 1fd. or *note int:
204.  The ‘type’ keyword for *note add_argument(): 2189. allows any
necessary type-checking and type conversions to be performed.

If the *note type: 219d. keyword is used with the *note default: 21a7.
keyword, the type converter is only applied if the default is a string.

The argument to ‘type’ can be any callable that accepts a single string.
If the function raises ‘ArgumentTypeError’, *note TypeError: 1fe, or
*note ValueError: 16d, the exception is caught and a nicely formatted
error message is displayed.  No other exception types are handled.

Common built-in types and functions can be used as type converters:

     import argparse
     import pathlib

     parser = argparse.ArgumentParser()
     parser.add_argument('count', type=int)
     parser.add_argument('distance', type=float)
     parser.add_argument('street', type=ascii)
     parser.add_argument('code_point', type=ord)
     parser.add_argument('source_file', type=open)
     parser.add_argument('dest_file', type=argparse.FileType('w', encoding='latin-1'))
     parser.add_argument('datapath', type=pathlib.Path)

User defined functions can be used as well:

     >>> def hyphenated(string):
     ...     return '-'.join([word[:4] for word in string.casefold().split()])
     ...
     >>> parser = argparse.ArgumentParser()
     >>> _ = parser.add_argument('short_title', type=hyphenated)
     >>> parser.parse_args(['"The Tale of Two Cities"'])
     Namespace(short_title='"the-tale-of-two-citi')

The *note bool(): 2bd. function is not recommended as a type converter.
All it does is convert empty strings to ‘False’ and non-empty strings to
‘True’.  This is usually not what is desired.

In general, the ‘type’ keyword is a convenience that should only be used
for simple conversions that can only raise one of the three supported
exceptions.  Anything with more interesting error-handling or resource
management should be done downstream after the arguments are parsed.

For example, JSON or YAML conversions have complex error cases that
require better reporting than can be given by the ‘type’ keyword.  A
*note JSONDecodeError: 7f7. would not be well formatted and a
‘FileNotFound’ exception would not be handled at all.

Even *note FileType: 90d. has its limitations for use with the ‘type’
keyword.  If one argument uses `FileType' and then a subsequent argument
fails, an error is reported but the file is not automatically closed.
In this case, it would be better to wait until after the parser has run
and then use the *note with: 7da.-statement to manage the files.

For type checkers that simply check against a fixed set of values,
consider using the *note choices: 21a8. keyword instead.


File: python.info,  Node: choices,  Next: required,  Prev: type,  Up: The add_argument method

5.16.4.26 choices
.................

Some command-line arguments should be selected from a restricted set of
values.  These can be handled by passing a container object as the
`choices' keyword argument to *note add_argument(): 2189.  When the
command line is parsed, argument values will be checked, and an error
message will be displayed if the argument was not one of the acceptable
values:

     >>> parser = argparse.ArgumentParser(prog='game.py')
     >>> parser.add_argument('move', choices=['rock', 'paper', 'scissors'])
     >>> parser.parse_args(['rock'])
     Namespace(move='rock')
     >>> parser.parse_args(['fire'])
     usage: game.py [-h] {rock,paper,scissors}
     game.py: error: argument move: invalid choice: 'fire' (choose from 'rock',
     'paper', 'scissors')

Note that inclusion in the `choices' container is checked after any
*note type: 219d. conversions have been performed, so the type of the
objects in the `choices' container should match the *note type: 219d.
specified:

     >>> parser = argparse.ArgumentParser(prog='doors.py')
     >>> parser.add_argument('door', type=int, choices=range(1, 4))
     >>> print(parser.parse_args(['3']))
     Namespace(door=3)
     >>> parser.parse_args(['4'])
     usage: doors.py [-h] {1,2,3}
     doors.py: error: argument door: invalid choice: 4 (choose from 1, 2, 3)

Any container can be passed as the `choices' value, so *note list: 1f8.
objects, *note set: 1f6. objects, and custom containers are all
supported.

Use of *note enum.Enum: 48e. is not recommended because it is difficult
to control its appearance in usage, help, and error messages.

Formatted choices overrides the default `metavar' which is normally
derived from `dest'.  This is usually what you want because the user
never sees the `dest' parameter.  If this display isn’t desirable
(perhaps because there are many choices), just specify an explicit *note
metavar: 21ab.


File: python.info,  Node: required,  Next: help,  Prev: choices,  Up: The add_argument method

5.16.4.27 required
..................

In general, the *note argparse: 5. module assumes that flags like ‘-f’
and ‘--bar’ indicate `optional' arguments, which can always be omitted
at the command line.  To make an option `required', ‘True’ can be
specified for the ‘required=’ keyword argument to *note add_argument():
2189.:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo', required=True)
     >>> parser.parse_args(['--foo', 'BAR'])
     Namespace(foo='BAR')
     >>> parser.parse_args([])
     usage: [-h] --foo FOO
     : error: the following arguments are required: --foo

As the example shows, if an option is marked as ‘required’, *note
parse_args(): 218a. will report an error if that option is not present
at the command line.

     Note: Required options are generally considered bad form because
     users expect `options' to be `optional', and thus they should be
     avoided when possible.


File: python.info,  Node: help,  Next: metavar,  Prev: required,  Up: The add_argument method

5.16.4.28 help
..............

The ‘help’ value is a string containing a brief description of the
argument.  When a user requests help (usually by using ‘-h’ or ‘--help’
at the command line), these ‘help’ descriptions will be displayed with
each argument:

     >>> parser = argparse.ArgumentParser(prog='frobble')
     >>> parser.add_argument('--foo', action='store_true',
     ...                     help='foo the bars before frobbling')
     >>> parser.add_argument('bar', nargs='+',
     ...                     help='one of the bars to be frobbled')
     >>> parser.parse_args(['-h'])
     usage: frobble [-h] [--foo] bar [bar ...]

     positional arguments:
      bar     one of the bars to be frobbled

     optional arguments:
      -h, --help  show this help message and exit
      --foo   foo the bars before frobbling

The ‘help’ strings can include various format specifiers to avoid
repetition of things like the program name or the argument *note
default: 21a7.  The available specifiers include the program name,
‘%(prog)s’ and most keyword arguments to *note add_argument(): 2189,
e.g.  ‘%(default)s’, ‘%(type)s’, etc.:

     >>> parser = argparse.ArgumentParser(prog='frobble')
     >>> parser.add_argument('bar', nargs='?', type=int, default=42,
     ...                     help='the bar to %(prog)s (default: %(default)s)')
     >>> parser.print_help()
     usage: frobble [-h] [bar]

     positional arguments:
      bar     the bar to frobble (default: 42)

     optional arguments:
      -h, --help  show this help message and exit

As the help string supports %-formatting, if you want a literal ‘%’ to
appear in the help string, you must escape it as ‘%%’.

*note argparse: 5. supports silencing the help entry for certain
options, by setting the ‘help’ value to ‘argparse.SUPPRESS’:

     >>> parser = argparse.ArgumentParser(prog='frobble')
     >>> parser.add_argument('--foo', help=argparse.SUPPRESS)
     >>> parser.print_help()
     usage: frobble [-h]

     optional arguments:
       -h, --help  show this help message and exit


File: python.info,  Node: metavar,  Next: dest,  Prev: help,  Up: The add_argument method

5.16.4.29 metavar
.................

When *note ArgumentParser: 788. generates help messages, it needs some
way to refer to each expected argument.  By default, ArgumentParser
objects use the *note dest: 219e. value as the “name” of each object.
By default, for positional argument actions, the *note dest: 219e. value
is used directly, and for optional argument actions, the *note dest:
219e. value is uppercased.  So, a single positional argument with
‘dest='bar'’ will be referred to as ‘bar’.  A single optional argument
‘--foo’ that should be followed by a single command-line argument will
be referred to as ‘FOO’.  An example:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo')
     >>> parser.add_argument('bar')
     >>> parser.parse_args('X --foo Y'.split())
     Namespace(bar='X', foo='Y')
     >>> parser.print_help()
     usage:  [-h] [--foo FOO] bar

     positional arguments:
      bar

     optional arguments:
      -h, --help  show this help message and exit
      --foo FOO

An alternative name can be specified with ‘metavar’:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo', metavar='YYY')
     >>> parser.add_argument('bar', metavar='XXX')
     >>> parser.parse_args('X --foo Y'.split())
     Namespace(bar='X', foo='Y')
     >>> parser.print_help()
     usage:  [-h] [--foo YYY] XXX

     positional arguments:
      XXX

     optional arguments:
      -h, --help  show this help message and exit
      --foo YYY

Note that ‘metavar’ only changes the `displayed' name - the name of the
attribute on the *note parse_args(): 218a. object is still determined by
the *note dest: 219e. value.

Different values of ‘nargs’ may cause the metavar to be used multiple
times.  Providing a tuple to ‘metavar’ specifies a different display for
each of the arguments:

     >>> parser = argparse.ArgumentParser(prog='PROG')
     >>> parser.add_argument('-x', nargs=2)
     >>> parser.add_argument('--foo', nargs=2, metavar=('bar', 'baz'))
     >>> parser.print_help()
     usage: PROG [-h] [-x X X] [--foo bar baz]

     optional arguments:
      -h, --help     show this help message and exit
      -x X X
      --foo bar baz


File: python.info,  Node: dest,  Next: Action classes,  Prev: metavar,  Up: The add_argument method

5.16.4.30 dest
..............

Most *note ArgumentParser: 788. actions add some value as an attribute
of the object returned by *note parse_args(): 218a.  The name of this
attribute is determined by the ‘dest’ keyword argument of *note
add_argument(): 2189.  For positional argument actions, ‘dest’ is
normally supplied as the first argument to *note add_argument(): 2189.:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('bar')
     >>> parser.parse_args(['XXX'])
     Namespace(bar='XXX')

For optional argument actions, the value of ‘dest’ is normally inferred
from the option strings.  *note ArgumentParser: 788. generates the value
of ‘dest’ by taking the first long option string and stripping away the
initial ‘--’ string.  If no long option strings were supplied, ‘dest’
will be derived from the first short option string by stripping the
initial ‘-’ character.  Any internal ‘-’ characters will be converted to
‘_’ characters to make sure the string is a valid attribute name.  The
examples below illustrate this behavior:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('-f', '--foo-bar', '--foo')
     >>> parser.add_argument('-x', '-y')
     >>> parser.parse_args('-f 1 -x 2'.split())
     Namespace(foo_bar='1', x='2')
     >>> parser.parse_args('--foo 1 -y 2'.split())
     Namespace(foo_bar='1', x='2')

‘dest’ allows a custom attribute name to be provided:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo', dest='bar')
     >>> parser.parse_args('--foo XXX'.split())
     Namespace(bar='XXX')


File: python.info,  Node: Action classes,  Prev: dest,  Up: The add_argument method

5.16.4.31 Action classes
........................

Action classes implement the Action API, a callable which returns a
callable which processes arguments from the command-line.  Any object
which follows this API may be passed as the ‘action’ parameter to
‘add_argument()’.

 -- Class: argparse.Action (option_strings, dest, nargs=None,
          const=None, default=None, type=None, choices=None,
          required=False, help=None, metavar=None)

Action objects are used by an ArgumentParser to represent the
information needed to parse a single argument from one or more strings
from the command line.  The Action class must accept the two positional
arguments plus any keyword arguments passed to *note
ArgumentParser.add_argument(): 2189. except for the ‘action’ itself.

Instances of Action (or return value of any callable to the ‘action’
parameter) should have attributes “dest”, “option_strings”, “default”,
“type”, “required”, “help”, etc.  defined.  The easiest way to ensure
these attributes are defined is to call ‘Action.__init__’.

Action instances should be callable, so subclasses must override the
‘__call__’ method, which should accept four parameters:

   * ‘parser’ - The ArgumentParser object which contains this action.

   * ‘namespace’ - The *note Namespace: 218c. object that will be
     returned by *note parse_args(): 218a.  Most actions add an
     attribute to this object using *note setattr(): 1712.

   * ‘values’ - The associated command-line arguments, with any type
     conversions applied.  Type conversions are specified with the *note
     type: 219d. keyword argument to *note add_argument(): 2189.

   * ‘option_string’ - The option string that was used to invoke this
     action.  The ‘option_string’ argument is optional, and will be
     absent if the action is associated with a positional argument.

The ‘__call__’ method may perform arbitrary actions, but will typically
set attributes on the ‘namespace’ based on ‘dest’ and ‘values’.

Action subclasses can define a ‘format_usage’ method that takes no
argument and return a string which will be used when printing the usage
of the program.  If such method is not provided, a sensible default will
be used.


File: python.info,  Node: The parse_args method,  Next: Other utilities,  Prev: The add_argument method,  Up: argparse — Parser for command-line options arguments and sub-commands

5.16.4.32 The parse_args() method
.................................

 -- Method: ArgumentParser.parse_args (args=None, namespace=None)

     Convert argument strings to objects and assign them as attributes
     of the namespace.  Return the populated namespace.

     Previous calls to *note add_argument(): 2189. determine exactly
     what objects are created and how they are assigned.  See the
     documentation for *note add_argument(): 2189. for details.

        * *note args: 21af. - List of strings to parse.  The default is
          taken from *note sys.argv: cc6.

        * *note namespace: 21b0. - An object to take the attributes.
          The default is a new empty *note Namespace: 218c. object.

* Menu:

* Option value syntax::
* Invalid arguments::
* Arguments containing -::
* Argument abbreviations (prefix matching): Argument abbreviations prefix matching.
* Beyond sys.argv: Beyond sys argv.
* The Namespace object::


File: python.info,  Node: Option value syntax,  Next: Invalid arguments,  Up: The parse_args method

5.16.4.33 Option value syntax
.............................

The *note parse_args(): 218a. method supports several ways of specifying
the value of an option (if it takes one).  In the simplest case, the
option and its value are passed as two separate arguments:

     >>> parser = argparse.ArgumentParser(prog='PROG')
     >>> parser.add_argument('-x')
     >>> parser.add_argument('--foo')
     >>> parser.parse_args(['-x', 'X'])
     Namespace(foo=None, x='X')
     >>> parser.parse_args(['--foo', 'FOO'])
     Namespace(foo='FOO', x=None)

For long options (options with names longer than a single character),
the option and value can also be passed as a single command-line
argument, using ‘=’ to separate them:

     >>> parser.parse_args(['--foo=FOO'])
     Namespace(foo='FOO', x=None)

For short options (options only one character long), the option and its
value can be concatenated:

     >>> parser.parse_args(['-xX'])
     Namespace(foo=None, x='X')

Several short options can be joined together, using only a single ‘-’
prefix, as long as only the last option (or none of them) requires a
value:

     >>> parser = argparse.ArgumentParser(prog='PROG')
     >>> parser.add_argument('-x', action='store_true')
     >>> parser.add_argument('-y', action='store_true')
     >>> parser.add_argument('-z')
     >>> parser.parse_args(['-xyzZ'])
     Namespace(x=True, y=True, z='Z')


File: python.info,  Node: Invalid arguments,  Next: Arguments containing -,  Prev: Option value syntax,  Up: The parse_args method

5.16.4.34 Invalid arguments
...........................

While parsing the command line, *note parse_args(): 218a. checks for a
variety of errors, including ambiguous options, invalid types, invalid
options, wrong number of positional arguments, etc.  When it encounters
such an error, it exits and prints the error along with a usage message:

     >>> parser = argparse.ArgumentParser(prog='PROG')
     >>> parser.add_argument('--foo', type=int)
     >>> parser.add_argument('bar', nargs='?')

     >>> # invalid type
     >>> parser.parse_args(['--foo', 'spam'])
     usage: PROG [-h] [--foo FOO] [bar]
     PROG: error: argument --foo: invalid int value: 'spam'

     >>> # invalid option
     >>> parser.parse_args(['--bar'])
     usage: PROG [-h] [--foo FOO] [bar]
     PROG: error: no such option: --bar

     >>> # wrong number of arguments
     >>> parser.parse_args(['spam', 'badger'])
     usage: PROG [-h] [--foo FOO] [bar]
     PROG: error: extra arguments found: badger


File: python.info,  Node: Arguments containing -,  Next: Argument abbreviations prefix matching,  Prev: Invalid arguments,  Up: The parse_args method

5.16.4.35 Arguments containing ‘-’
..................................

The *note parse_args(): 218a. method attempts to give errors whenever
the user has clearly made a mistake, but some situations are inherently
ambiguous.  For example, the command-line argument ‘-1’ could either be
an attempt to specify an option or an attempt to provide a positional
argument.  The *note parse_args(): 218a. method is cautious here:
positional arguments may only begin with ‘-’ if they look like negative
numbers and there are no options in the parser that look like negative
numbers:

     >>> parser = argparse.ArgumentParser(prog='PROG')
     >>> parser.add_argument('-x')
     >>> parser.add_argument('foo', nargs='?')

     >>> # no negative number options, so -1 is a positional argument
     >>> parser.parse_args(['-x', '-1'])
     Namespace(foo=None, x='-1')

     >>> # no negative number options, so -1 and -5 are positional arguments
     >>> parser.parse_args(['-x', '-1', '-5'])
     Namespace(foo='-5', x='-1')

     >>> parser = argparse.ArgumentParser(prog='PROG')
     >>> parser.add_argument('-1', dest='one')
     >>> parser.add_argument('foo', nargs='?')

     >>> # negative number options present, so -1 is an option
     >>> parser.parse_args(['-1', 'X'])
     Namespace(foo=None, one='X')

     >>> # negative number options present, so -2 is an option
     >>> parser.parse_args(['-2'])
     usage: PROG [-h] [-1 ONE] [foo]
     PROG: error: no such option: -2

     >>> # negative number options present, so both -1s are options
     >>> parser.parse_args(['-1', '-1'])
     usage: PROG [-h] [-1 ONE] [foo]
     PROG: error: argument -1: expected one argument

If you have positional arguments that must begin with ‘-’ and don’t look
like negative numbers, you can insert the pseudo-argument ‘'--'’ which
tells *note parse_args(): 218a. that everything after that is a
positional argument:

     >>> parser.parse_args(['--', '-f'])
     Namespace(foo='-f', one=None)


File: python.info,  Node: Argument abbreviations prefix matching,  Next: Beyond sys argv,  Prev: Arguments containing -,  Up: The parse_args method

5.16.4.36 Argument abbreviations (prefix matching)
..................................................

The *note parse_args(): 218a. method *note by default: 78a. allows long
options to be abbreviated to a prefix, if the abbreviation is
unambiguous (the prefix matches a unique option):

     >>> parser = argparse.ArgumentParser(prog='PROG')
     >>> parser.add_argument('-bacon')
     >>> parser.add_argument('-badger')
     >>> parser.parse_args('-bac MMM'.split())
     Namespace(bacon='MMM', badger=None)
     >>> parser.parse_args('-bad WOOD'.split())
     Namespace(bacon=None, badger='WOOD')
     >>> parser.parse_args('-ba BA'.split())
     usage: PROG [-h] [-bacon BACON] [-badger BADGER]
     PROG: error: ambiguous option: -ba could match -badger, -bacon

An error is produced for arguments that could produce more than one
options.  This feature can be disabled by setting *note allow_abbrev:
78a. to ‘False’.


File: python.info,  Node: Beyond sys argv,  Next: The Namespace object,  Prev: Argument abbreviations prefix matching,  Up: The parse_args method

5.16.4.37 Beyond ‘sys.argv’
...........................

Sometimes it may be useful to have an ArgumentParser parse arguments
other than those of *note sys.argv: cc6.  This can be accomplished by
passing a list of strings to *note parse_args(): 218a.  This is useful
for testing at the interactive prompt:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument(
     ...     'integers', metavar='int', type=int, choices=range(10),
     ...     nargs='+', help='an integer in the range 0..9')
     >>> parser.add_argument(
     ...     '--sum', dest='accumulate', action='store_const', const=sum,
     ...     default=max, help='sum the integers (default: find the max)')
     >>> parser.parse_args(['1', '2', '3', '4'])
     Namespace(accumulate=<built-in function max>, integers=[1, 2, 3, 4])
     >>> parser.parse_args(['1', '2', '3', '4', '--sum'])
     Namespace(accumulate=<built-in function sum>, integers=[1, 2, 3, 4])


File: python.info,  Node: The Namespace object,  Prev: Beyond sys argv,  Up: The parse_args method

5.16.4.38 The Namespace object
..............................

 -- Class: argparse.Namespace

     Simple class used by default by *note parse_args(): 218a. to create
     an object holding attributes and return it.

This class is deliberately simple, just an *note object: 3d2. subclass
with a readable string representation.  If you prefer to have dict-like
view of the attributes, you can use the standard Python idiom, *note
vars(): 116d.:

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo')
     >>> args = parser.parse_args(['--foo', 'BAR'])
     >>> vars(args)
     {'foo': 'BAR'}

It may also be useful to have an *note ArgumentParser: 788. assign
attributes to an already existing object, rather than a new *note
Namespace: 218c. object.  This can be achieved by specifying the
‘namespace=’ keyword argument:

     >>> class C:
     ...     pass
     ...
     >>> c = C()
     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo')
     >>> parser.parse_args(args=['--foo', 'BAR'], namespace=c)
     >>> c.foo
     'BAR'


File: python.info,  Node: Other utilities,  Next: Upgrading optparse code,  Prev: The parse_args method,  Up: argparse — Parser for command-line options arguments and sub-commands

5.16.4.39 Other utilities
.........................

* Menu:

* Sub-commands::
* FileType objects::
* Argument groups::
* Mutual exclusion::
* Parser defaults::
* Printing help::
* Partial parsing::
* Customizing file parsing::
* Exiting methods::
* Intermixed parsing::


File: python.info,  Node: Sub-commands,  Next: FileType objects,  Up: Other utilities

5.16.4.40 Sub-commands
......................

 -- Method: ArgumentParser.add_subparsers ([title][, description][,
          prog][, parser_class][, action][, option_string][, dest][,
          required][, help][, metavar])

     Many programs split up their functionality into a number of
     sub-commands, for example, the ‘svn’ program can invoke
     sub-commands like ‘svn checkout’, ‘svn update’, and ‘svn commit’.
     Splitting up functionality this way can be a particularly good idea
     when a program performs several different functions which require
     different kinds of command-line arguments.  *note ArgumentParser:
     788. supports the creation of such sub-commands with the *note
     add_subparsers(): 59f. method.  The *note add_subparsers(): 59f.
     method is normally called with no arguments and returns a special
     action object.  This object has a single method, ‘add_parser()’,
     which takes a command name and any *note ArgumentParser: 788.
     constructor arguments, and returns an *note ArgumentParser: 788.
     object that can be modified as usual.

     Description of parameters:

        * title - title for the sub-parser group in help output; by
          default “subcommands” if description is provided, otherwise
          uses title for positional arguments

        * description - description for the sub-parser group in help
          output, by default ‘None’

        * prog - usage information that will be displayed with
          sub-command help, by default the name of the program and any
          positional arguments before the subparser argument

        * parser_class - class which will be used to create sub-parser
          instances, by default the class of the current parser (e.g.
          ArgumentParser)

        * *note action: 21a4. - the basic type of action to be taken
          when this argument is encountered at the command line

        * *note dest: 219e. - name of the attribute under which
          sub-command name will be stored; by default ‘None’ and no
          value is stored

        * *note required: 21a9. - Whether or not a subcommand must be
          provided, by default ‘False’ (added in 3.7)

        * *note help: 21aa. - help for sub-parser group in help output,
          by default ‘None’

        * *note metavar: 21ab. - string presenting available
          sub-commands in help; by default it is ‘None’ and presents
          sub-commands in form {cmd1, cmd2, ..}

     Some example usage:

          >>> # create the top-level parser
          >>> parser = argparse.ArgumentParser(prog='PROG')
          >>> parser.add_argument('--foo', action='store_true', help='foo help')
          >>> subparsers = parser.add_subparsers(help='sub-command help')
          >>>
          >>> # create the parser for the "a" command
          >>> parser_a = subparsers.add_parser('a', help='a help')
          >>> parser_a.add_argument('bar', type=int, help='bar help')
          >>>
          >>> # create the parser for the "b" command
          >>> parser_b = subparsers.add_parser('b', help='b help')
          >>> parser_b.add_argument('--baz', choices='XYZ', help='baz help')
          >>>
          >>> # parse some argument lists
          >>> parser.parse_args(['a', '12'])
          Namespace(bar=12, foo=False)
          >>> parser.parse_args(['--foo', 'b', '--baz', 'Z'])
          Namespace(baz='Z', foo=True)

     Note that the object returned by *note parse_args(): 218a. will
     only contain attributes for the main parser and the subparser that
     was selected by the command line (and not any other subparsers).
     So in the example above, when the ‘a’ command is specified, only
     the ‘foo’ and ‘bar’ attributes are present, and when the ‘b’
     command is specified, only the ‘foo’ and ‘baz’ attributes are
     present.

     Similarly, when a help message is requested from a subparser, only
     the help for that particular parser will be printed.  The help
     message will not include parent parser or sibling parser messages.
     (A help message for each subparser command, however, can be given
     by supplying the ‘help=’ argument to ‘add_parser()’ as above.)

          >>> parser.parse_args(['--help'])
          usage: PROG [-h] [--foo] {a,b} ...

          positional arguments:
            {a,b}   sub-command help
              a     a help
              b     b help

          optional arguments:
            -h, --help  show this help message and exit
            --foo   foo help

          >>> parser.parse_args(['a', '--help'])
          usage: PROG a [-h] bar

          positional arguments:
            bar     bar help

          optional arguments:
            -h, --help  show this help message and exit

          >>> parser.parse_args(['b', '--help'])
          usage: PROG b [-h] [--baz {X,Y,Z}]

          optional arguments:
            -h, --help     show this help message and exit
            --baz {X,Y,Z}  baz help

     The *note add_subparsers(): 59f. method also supports ‘title’ and
     ‘description’ keyword arguments.  When either is present, the
     subparser’s commands will appear in their own group in the help
     output.  For example:

          >>> parser = argparse.ArgumentParser()
          >>> subparsers = parser.add_subparsers(title='subcommands',
          ...                                    description='valid subcommands',
          ...                                    help='additional help')
          >>> subparsers.add_parser('foo')
          >>> subparsers.add_parser('bar')
          >>> parser.parse_args(['-h'])
          usage:  [-h] {foo,bar} ...

          optional arguments:
            -h, --help  show this help message and exit

          subcommands:
            valid subcommands

            {foo,bar}   additional help

     Furthermore, ‘add_parser’ supports an additional ‘aliases’
     argument, which allows multiple strings to refer to the same
     subparser.  This example, like ‘svn’, aliases ‘co’ as a shorthand
     for ‘checkout’:

          >>> parser = argparse.ArgumentParser()
          >>> subparsers = parser.add_subparsers()
          >>> checkout = subparsers.add_parser('checkout', aliases=['co'])
          >>> checkout.add_argument('foo')
          >>> parser.parse_args(['co', 'bar'])
          Namespace(foo='bar')

     One particularly effective way of handling sub-commands is to
     combine the use of the *note add_subparsers(): 59f. method with
     calls to *note set_defaults(): 21a0. so that each subparser knows
     which Python function it should execute.  For example:

          >>> # sub-command functions
          >>> def foo(args):
          ...     print(args.x * args.y)
          ...
          >>> def bar(args):
          ...     print('((%s))' % args.z)
          ...
          >>> # create the top-level parser
          >>> parser = argparse.ArgumentParser()
          >>> subparsers = parser.add_subparsers()
          >>>
          >>> # create the parser for the "foo" command
          >>> parser_foo = subparsers.add_parser('foo')
          >>> parser_foo.add_argument('-x', type=int, default=1)
          >>> parser_foo.add_argument('y', type=float)
          >>> parser_foo.set_defaults(func=foo)
          >>>
          >>> # create the parser for the "bar" command
          >>> parser_bar = subparsers.add_parser('bar')
          >>> parser_bar.add_argument('z')
          >>> parser_bar.set_defaults(func=bar)
          >>>
          >>> # parse the args and call whatever function was selected
          >>> args = parser.parse_args('foo 1 -x 2'.split())
          >>> args.func(args)
          2.0
          >>>
          >>> # parse the args and call whatever function was selected
          >>> args = parser.parse_args('bar XYZYX'.split())
          >>> args.func(args)
          ((XYZYX))

     This way, you can let *note parse_args(): 218a. do the job of
     calling the appropriate function after argument parsing is
     complete.  Associating functions with actions like this is
     typically the easiest way to handle the different actions for each
     of your subparsers.  However, if it is necessary to check the name
     of the subparser that was invoked, the ‘dest’ keyword argument to
     the *note add_subparsers(): 59f. call will work:

          >>> parser = argparse.ArgumentParser()
          >>> subparsers = parser.add_subparsers(dest='subparser_name')
          >>> subparser1 = subparsers.add_parser('1')
          >>> subparser1.add_argument('-x')
          >>> subparser2 = subparsers.add_parser('2')
          >>> subparser2.add_argument('y')
          >>> parser.parse_args(['2', 'frobble'])
          Namespace(subparser_name='2', y='frobble')

     Changed in version 3.7: New `required' keyword argument.


File: python.info,  Node: FileType objects,  Next: Argument groups,  Prev: Sub-commands,  Up: Other utilities

5.16.4.41 FileType objects
..........................

 -- Class: argparse.FileType (mode='r', bufsize=-1, encoding=None,
          errors=None)

     The *note FileType: 90d. factory creates objects that can be passed
     to the type argument of *note ArgumentParser.add_argument(): 2189.
     Arguments that have *note FileType: 90d. objects as their type will
     open command-line arguments as files with the requested modes,
     buffer sizes, encodings and error handling (see the *note open():
     16f. function for more details):

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('--raw', type=argparse.FileType('wb', 0))
          >>> parser.add_argument('out', type=argparse.FileType('w', encoding='UTF-8'))
          >>> parser.parse_args(['--raw', 'raw.dat', 'file.txt'])
          Namespace(out=<_io.TextIOWrapper name='file.txt' mode='w' encoding='UTF-8'>, raw=<_io.FileIO name='raw.dat' mode='wb'>)

     FileType objects understand the pseudo-argument ‘'-'’ and
     automatically convert this into ‘sys.stdin’ for readable *note
     FileType: 90d. objects and ‘sys.stdout’ for writable *note
     FileType: 90d. objects:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('infile', type=argparse.FileType('r'))
          >>> parser.parse_args(['-'])
          Namespace(infile=<_io.TextIOWrapper name='<stdin>' encoding='UTF-8'>)

     New in version 3.4: The `encodings' and `errors' keyword arguments.


File: python.info,  Node: Argument groups,  Next: Mutual exclusion,  Prev: FileType objects,  Up: Other utilities

5.16.4.42 Argument groups
.........................

 -- Method: ArgumentParser.add_argument_group (title=None,
          description=None)

     By default, *note ArgumentParser: 788. groups command-line
     arguments into “positional arguments” and “optional arguments” when
     displaying help messages.  When there is a better conceptual
     grouping of arguments than this default one, appropriate groups can
     be created using the *note add_argument_group(): 21bb. method:

          >>> parser = argparse.ArgumentParser(prog='PROG', add_help=False)
          >>> group = parser.add_argument_group('group')
          >>> group.add_argument('--foo', help='foo help')
          >>> group.add_argument('bar', help='bar help')
          >>> parser.print_help()
          usage: PROG [--foo FOO] bar

          group:
            bar    bar help
            --foo FOO  foo help

     The *note add_argument_group(): 21bb. method returns an argument
     group object which has an *note add_argument(): 2189. method just
     like a regular *note ArgumentParser: 788.  When an argument is
     added to the group, the parser treats it just like a normal
     argument, but displays the argument in a separate group for help
     messages.  The *note add_argument_group(): 21bb. method accepts
     `title' and `description' arguments which can be used to customize
     this display:

          >>> parser = argparse.ArgumentParser(prog='PROG', add_help=False)
          >>> group1 = parser.add_argument_group('group1', 'group1 description')
          >>> group1.add_argument('foo', help='foo help')
          >>> group2 = parser.add_argument_group('group2', 'group2 description')
          >>> group2.add_argument('--bar', help='bar help')
          >>> parser.print_help()
          usage: PROG [--bar BAR] foo

          group1:
            group1 description

            foo    foo help

          group2:
            group2 description

            --bar BAR  bar help

     Note that any arguments not in your user-defined groups will end up
     back in the usual “positional arguments” and “optional arguments”
     sections.


File: python.info,  Node: Mutual exclusion,  Next: Parser defaults,  Prev: Argument groups,  Up: Other utilities

5.16.4.43 Mutual exclusion
..........................

 -- Method: ArgumentParser.add_mutually_exclusive_group (required=False)

     Create a mutually exclusive group.  *note argparse: 5. will make
     sure that only one of the arguments in the mutually exclusive group
     was present on the command line:

          >>> parser = argparse.ArgumentParser(prog='PROG')
          >>> group = parser.add_mutually_exclusive_group()
          >>> group.add_argument('--foo', action='store_true')
          >>> group.add_argument('--bar', action='store_false')
          >>> parser.parse_args(['--foo'])
          Namespace(bar=True, foo=True)
          >>> parser.parse_args(['--bar'])
          Namespace(bar=False, foo=False)
          >>> parser.parse_args(['--foo', '--bar'])
          usage: PROG [-h] [--foo | --bar]
          PROG: error: argument --bar: not allowed with argument --foo

     The *note add_mutually_exclusive_group(): 21bd. method also accepts
     a `required' argument, to indicate that at least one of the
     mutually exclusive arguments is required:

          >>> parser = argparse.ArgumentParser(prog='PROG')
          >>> group = parser.add_mutually_exclusive_group(required=True)
          >>> group.add_argument('--foo', action='store_true')
          >>> group.add_argument('--bar', action='store_false')
          >>> parser.parse_args([])
          usage: PROG [-h] (--foo | --bar)
          PROG: error: one of the arguments --foo --bar is required

     Note that currently mutually exclusive argument groups do not
     support the `title' and `description' arguments of *note
     add_argument_group(): 21bb.


File: python.info,  Node: Parser defaults,  Next: Printing help,  Prev: Mutual exclusion,  Up: Other utilities

5.16.4.44 Parser defaults
.........................

 -- Method: ArgumentParser.set_defaults (**kwargs)

     Most of the time, the attributes of the object returned by *note
     parse_args(): 218a. will be fully determined by inspecting the
     command-line arguments and the argument actions.  *note
     set_defaults(): 21a0. allows some additional attributes that are
     determined without any inspection of the command line to be added:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('foo', type=int)
          >>> parser.set_defaults(bar=42, baz='badger')
          >>> parser.parse_args(['736'])
          Namespace(bar=42, baz='badger', foo=736)

     Note that parser-level defaults always override argument-level
     defaults:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('--foo', default='bar')
          >>> parser.set_defaults(foo='spam')
          >>> parser.parse_args([])
          Namespace(foo='spam')

     Parser-level defaults can be particularly useful when working with
     multiple parsers.  See the *note add_subparsers(): 59f. method for
     an example of this type.

 -- Method: ArgumentParser.get_default (dest)

     Get the default value for a namespace attribute, as set by either
     *note add_argument(): 2189. or by *note set_defaults(): 21a0.:

          >>> parser = argparse.ArgumentParser()
          >>> parser.add_argument('--foo', default='badger')
          >>> parser.get_default('foo')
          'badger'


File: python.info,  Node: Printing help,  Next: Partial parsing,  Prev: Parser defaults,  Up: Other utilities

5.16.4.45 Printing help
.......................

In most typical applications, *note parse_args(): 218a. will take care
of formatting and printing any usage or error messages.  However,
several formatting methods are available:

 -- Method: ArgumentParser.print_usage (file=None)

     Print a brief description of how the *note ArgumentParser: 788.
     should be invoked on the command line.  If `file' is ‘None’, *note
     sys.stdout: 41f. is assumed.

 -- Method: ArgumentParser.print_help (file=None)

     Print a help message, including the program usage and information
     about the arguments registered with the *note ArgumentParser: 788.
     If `file' is ‘None’, *note sys.stdout: 41f. is assumed.

There are also variants of these methods that simply return a string
instead of printing it:

 -- Method: ArgumentParser.format_usage ()

     Return a string containing a brief description of how the *note
     ArgumentParser: 788. should be invoked on the command line.

 -- Method: ArgumentParser.format_help ()

     Return a string containing a help message, including the program
     usage and information about the arguments registered with the *note
     ArgumentParser: 788.


File: python.info,  Node: Partial parsing,  Next: Customizing file parsing,  Prev: Printing help,  Up: Other utilities

5.16.4.46 Partial parsing
.........................

 -- Method: ArgumentParser.parse_known_args (args=None, namespace=None)

Sometimes a script may only parse a few of the command-line arguments,
passing the remaining arguments on to another script or program.  In
these cases, the *note parse_known_args(): 21c5. method can be useful.
It works much like *note parse_args(): 218a. except that it does not
produce an error when extra arguments are present.  Instead, it returns
a two item tuple containing the populated namespace and the list of
remaining argument strings.

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo', action='store_true')
     >>> parser.add_argument('bar')
     >>> parser.parse_known_args(['--foo', '--badger', 'BAR', 'spam'])
     (Namespace(bar='BAR', foo=True), ['--badger', 'spam'])

     Warning: *note Prefix matching: 789. rules apply to
     ‘parse_known_args()’.  The parser may consume an option even if
     it’s just a prefix of one of its known options, instead of leaving
     it in the remaining arguments list.


File: python.info,  Node: Customizing file parsing,  Next: Exiting methods,  Prev: Partial parsing,  Up: Other utilities

5.16.4.47 Customizing file parsing
..................................

 -- Method: ArgumentParser.convert_arg_line_to_args (arg_line)

     Arguments that are read from a file (see the
     `fromfile_prefix_chars' keyword argument to the *note
     ArgumentParser: 788. constructor) are read one argument per line.
     *note convert_arg_line_to_args(): 219f. can be overridden for
     fancier reading.

     This method takes a single argument `arg_line' which is a string
     read from the argument file.  It returns a list of arguments parsed
     from this string.  The method is called once per line read from the
     argument file, in order.

     A useful override of this method is one that treats each
     space-separated word as an argument.  The following example
     demonstrates how to do this:

          class MyArgumentParser(argparse.ArgumentParser):
              def convert_arg_line_to_args(self, arg_line):
                  return arg_line.split()


File: python.info,  Node: Exiting methods,  Next: Intermixed parsing,  Prev: Customizing file parsing,  Up: Other utilities

5.16.4.48 Exiting methods
.........................

 -- Method: ArgumentParser.exit (status=0, message=None)

     This method terminates the program, exiting with the specified
     `status' and, if given, it prints a `message' before that.  The
     user can override this method to handle these steps differently:

          class ErrorCatchingArgumentParser(argparse.ArgumentParser):
              def exit(self, status=0, message=None):
                  if status:
                      raise Exception(f'Exiting because of an error: {message}')
                  exit(status)

 -- Method: ArgumentParser.error (message)

     This method prints a usage message including the `message' to the
     standard error and terminates the program with a status code of 2.


File: python.info,  Node: Intermixed parsing,  Prev: Exiting methods,  Up: Other utilities

5.16.4.49 Intermixed parsing
............................

 -- Method: ArgumentParser.parse_intermixed_args (args=None,
          namespace=None)

 -- Method: ArgumentParser.parse_known_intermixed_args (args=None,
          namespace=None)

A number of Unix commands allow the user to intermix optional arguments
with positional arguments.  The *note parse_intermixed_args(): 451. and
*note parse_known_intermixed_args(): 21cb. methods support this parsing
style.

These parsers do not support all the argparse features, and will raise
exceptions if unsupported features are used.  In particular, subparsers,
‘argparse.REMAINDER’, and mutually exclusive groups that include both
optionals and positionals are not supported.

The following example shows the difference between *note
parse_known_args(): 21c5. and *note parse_intermixed_args(): 451.: the
former returns ‘['2', '3']’ as unparsed arguments, while the latter
collects all the positionals into ‘rest’.

     >>> parser = argparse.ArgumentParser()
     >>> parser.add_argument('--foo')
     >>> parser.add_argument('cmd')
     >>> parser.add_argument('rest', nargs='*', type=int)
     >>> parser.parse_known_args('doit 1 --foo bar 2 3'.split())
     (Namespace(cmd='doit', foo='bar', rest=[1]), ['2', '3'])
     >>> parser.parse_intermixed_args('doit 1 --foo bar 2 3'.split())
     Namespace(cmd='doit', foo='bar', rest=[1, 2, 3])

*note parse_known_intermixed_args(): 21cb. returns a two item tuple
containing the populated namespace and the list of remaining argument
strings.  *note parse_intermixed_args(): 451. raises an error if there
are any remaining unparsed argument strings.

New in version 3.7.


File: python.info,  Node: Upgrading optparse code,  Prev: Other utilities,  Up: argparse — Parser for command-line options arguments and sub-commands

5.16.4.50 Upgrading optparse code
.................................

Originally, the *note argparse: 5. module had attempted to maintain
compatibility with *note optparse: c3.  However, *note optparse: c3. was
difficult to extend transparently, particularly with the changes
required to support the new ‘nargs=’ specifiers and better usage
messages.  When most everything in *note optparse: c3. had either been
copy-pasted over or monkey-patched, it no longer seemed practical to try
to maintain the backwards compatibility.

The *note argparse: 5. module improves on the standard library *note
optparse: c3. module in a number of ways including:

   * Handling positional arguments.

   * Supporting sub-commands.

   * Allowing alternative option prefixes like ‘+’ and ‘/’.

   * Handling zero-or-more and one-or-more style arguments.

   * Producing more informative usage messages.

   * Providing a much simpler interface for custom ‘type’ and ‘action’.

A partial upgrade path from *note optparse: c3. to *note argparse: 5.:

   * Replace all *note optparse.OptionParser.add_option(): 21cd. calls
     with *note ArgumentParser.add_argument(): 2189. calls.

   * Replace ‘(options, args) = parser.parse_args()’ with ‘args =
     parser.parse_args()’ and add additional *note
     ArgumentParser.add_argument(): 2189. calls for the positional
     arguments.  Keep in mind that what was previously called ‘options’,
     now in the *note argparse: 5. context is called ‘args’.

   * Replace *note optparse.OptionParser.disable_interspersed_args():
     21ce. by using *note parse_intermixed_args(): 451. instead of *note
     parse_args(): 218a.

   * Replace callback actions and the ‘callback_*’ keyword arguments
     with ‘type’ or ‘action’ arguments.

   * Replace string names for ‘type’ keyword arguments with the
     corresponding type objects (e.g.  int, float, complex, etc).

   * Replace ‘optparse.Values’ with *note Namespace: 218c. and
     ‘optparse.OptionError’ and ‘optparse.OptionValueError’ with
     ‘ArgumentError’.

   * Replace strings with implicit arguments such as ‘%default’ or
     ‘%prog’ with the standard Python syntax to use dictionaries to
     format strings, that is, ‘%(default)s’ and ‘%(prog)s’.

   * Replace the OptionParser constructor ‘version’ argument with a call
     to ‘parser.add_argument('--version', action='version',
     version='<the version>')’.


File: python.info,  Node: getopt — C-style parser for command line options,  Next: logging — Logging facility for Python,  Prev: argparse — Parser for command-line options arguments and sub-commands,  Up: Generic Operating System Services

5.16.5 ‘getopt’ — C-style parser for command line options
---------------------------------------------------------

`Source code:' Lib/getopt.py(1)

     Note: The *note getopt: 85. module is a parser for command line
     options whose API is designed to be familiar to users of the C
     ‘getopt()’ function.  Users who are unfamiliar with the C
     ‘getopt()’ function or who would like to write less code and get
     better help and error messages should consider using the *note
     argparse: 5. module instead.

__________________________________________________________________

This module helps scripts to parse the command line arguments in
‘sys.argv’.  It supports the same conventions as the Unix ‘getopt()’
function (including the special meanings of arguments of the form ‘‘-’’
and ‘‘--’‘).  Long options similar to those supported by GNU software
may be used as well via an optional third argument.

This module provides two functions and an exception:

 -- Function: getopt.getopt (args, shortopts, longopts=[])

     Parses command line options and parameter list.  `args' is the
     argument list to be parsed, without the leading reference to the
     running program.  Typically, this means ‘sys.argv[1:]’.
     `shortopts' is the string of option letters that the script wants
     to recognize, with options that require an argument followed by a
     colon (‘':'’; i.e., the same format that Unix ‘getopt()’ uses).

          Note: Unlike GNU ‘getopt()’, after a non-option argument, all
          further arguments are considered also non-options.  This is
          similar to the way non-GNU Unix systems work.

     `longopts', if specified, must be a list of strings with the names
     of the long options which should be supported.  The leading ‘'--'’
     characters should not be included in the option name.  Long options
     which require an argument should be followed by an equal sign
     (‘'='’).  Optional arguments are not supported.  To accept only
     long options, `shortopts' should be an empty string.  Long options
     on the command line can be recognized so long as they provide a
     prefix of the option name that matches exactly one of the accepted
     options.  For example, if `longopts' is ‘['foo', 'frob']’, the
     option ‘--fo’ will match as ‘--foo’, but ‘--f’ will not match
     uniquely, so *note GetoptError: 21d2. will be raised.

     The return value consists of two elements: the first is a list of
     ‘(option, value)’ pairs; the second is the list of program
     arguments left after the option list was stripped (this is a
     trailing slice of `args').  Each option-and-value pair returned has
     the option as its first element, prefixed with a hyphen for short
     options (e.g., ‘'-x'’) or two hyphens for long options (e.g.,
     ‘'--long-option'’), and the option argument as its second element,
     or an empty string if the option has no argument.  The options
     occur in the list in the same order in which they were found, thus
     allowing multiple occurrences.  Long and short options may be
     mixed.

 -- Function: getopt.gnu_getopt (args, shortopts, longopts=[])

     This function works like *note getopt(): 85, except that GNU style
     scanning mode is used by default.  This means that option and
     non-option arguments may be intermixed.  The *note getopt(): 85.
     function stops processing options as soon as a non-option argument
     is encountered.

     If the first character of the option string is ‘'+'’, or if the
     environment variable ‘POSIXLY_CORRECT’ is set, then option
     processing stops as soon as a non-option argument is encountered.

 -- Exception: getopt.GetoptError

     This is raised when an unrecognized option is found in the argument
     list or when an option requiring an argument is given none.  The
     argument to the exception is a string indicating the cause of the
     error.  For long options, an argument given to an option which does
     not require one will also cause this exception to be raised.  The
     attributes ‘msg’ and ‘opt’ give the error message and related
     option; if there is no specific option to which the exception
     relates, ‘opt’ is an empty string.

 -- Exception: getopt.error

     Alias for *note GetoptError: 21d2.; for backward compatibility.

An example using only Unix style options:

     >>> import getopt
     >>> args = '-a -b -cfoo -d bar a1 a2'.split()
     >>> args
     ['-a', '-b', '-cfoo', '-d', 'bar', 'a1', 'a2']
     >>> optlist, args = getopt.getopt(args, 'abc:d:')
     >>> optlist
     [('-a', ''), ('-b', ''), ('-c', 'foo'), ('-d', 'bar')]
     >>> args
     ['a1', 'a2']

Using long option names is equally easy:

     >>> s = '--condition=foo --testing --output-file abc.def -x a1 a2'
     >>> args = s.split()
     >>> args
     ['--condition=foo', '--testing', '--output-file', 'abc.def', '-x', 'a1', 'a2']
     >>> optlist, args = getopt.getopt(args, 'x', [
     ...     'condition=', 'output-file=', 'testing'])
     >>> optlist
     [('--condition', 'foo'), ('--testing', ''), ('--output-file', 'abc.def'), ('-x', '')]
     >>> args
     ['a1', 'a2']

In a script, typical usage is something like this:

     import getopt, sys

     def main():
         try:
             opts, args = getopt.getopt(sys.argv[1:], "ho:v", ["help", "output="])
         except getopt.GetoptError as err:
             # print help information and exit:
             print(err)  # will print something like "option -a not recognized"
             usage()
             sys.exit(2)
         output = None
         verbose = False
         for o, a in opts:
             if o == "-v":
                 verbose = True
             elif o in ("-h", "--help"):
                 usage()
                 sys.exit()
             elif o in ("-o", "--output"):
                 output = a
             else:
                 assert False, "unhandled option"
         # ...

     if __name__ == "__main__":
         main()

Note that an equivalent command line interface could be produced with
less code and more informative help and error messages by using the
*note argparse: 5. module:

     import argparse

     if __name__ == '__main__':
         parser = argparse.ArgumentParser()
         parser.add_argument('-o', '--output')
         parser.add_argument('-v', dest='verbose', action='store_true')
         args = parser.parse_args()
         # ... do something with args.output ...
         # ... do something with args.verbose ..

See also
........

Module *note argparse: 5.

     Alternative command line option and argument parsing library.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/getopt.py


File: python.info,  Node: logging — Logging facility for Python,  Next: logging config — Logging configuration,  Prev: getopt — C-style parser for command line options,  Up: Generic Operating System Services

5.16.6 ‘logging’ — Logging facility for Python
----------------------------------------------

`Source code:' Lib/logging/__init__.py(1)

Important
.........

This page contains the API reference information.  For tutorial
information and discussion of more advanced topics, see

   * *note Basic Tutorial: c43.

   * *note Advanced Tutorial: c44.

   * *note Logging Cookbook: c45.

__________________________________________________________________

This module defines functions and classes which implement a flexible
event logging system for applications and libraries.

The key benefit of having the logging API provided by a standard library
module is that all Python modules can participate in logging, so your
application log can include your own messages integrated with messages
from third-party modules.

The module provides a lot of functionality and flexibility.  If you are
unfamiliar with logging, the best way to get to grips with it is to see
the tutorials (see the links on the right).

The basic classes defined by the module, together with their functions,
are listed below.

   * Loggers expose the interface that application code directly uses.

   * Handlers send the log records (created by loggers) to the
     appropriate destination.

   * Filters provide a finer grained facility for determining which log
     records to output.

   * Formatters specify the layout of log records in the final output.

* Menu:

* Logger Objects::
* Logging Levels::
* Handler Objects::
* Formatter Objects::
* Filter Objects::
* LogRecord Objects::
* LogRecord attributes::
* LoggerAdapter Objects::
* Thread Safety::
* Module-Level Functions::
* Module-Level Attributes::
* Integration with the warnings module::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/logging/__init__.py


File: python.info,  Node: Logger Objects,  Next: Logging Levels,  Up: logging — Logging facility for Python

5.16.6.1 Logger Objects
.......................

Loggers have the following attributes and methods.  Note that Loggers
should `NEVER' be instantiated directly, but always through the
module-level function ‘logging.getLogger(name)’.  Multiple calls to
*note getLogger(): 234. with the same name will always return a
reference to the same Logger object.

The ‘name’ is potentially a period-separated hierarchical value, like
‘foo.bar.baz’ (though it could also be just plain ‘foo’, for example).
Loggers that are further down in the hierarchical list are children of
loggers higher up in the list.  For example, given a logger with a name
of ‘foo’, loggers with names of ‘foo.bar’, ‘foo.bar.baz’, and ‘foo.bam’
are all descendants of ‘foo’.  The logger name hierarchy is analogous to
the Python package hierarchy, and identical to it if you organise your
loggers on a per-module basis using the recommended construction
‘logging.getLogger(__name__)’.  That’s because in a module, ‘__name__’
is the module’s name in the Python package namespace.

 -- Class: logging.Logger

      -- Attribute: propagate

          If this attribute evaluates to true, events logged to this
          logger will be passed to the handlers of higher level
          (ancestor) loggers, in addition to any handlers attached to
          this logger.  Messages are passed directly to the ancestor
          loggers’ handlers - neither the level nor filters of the
          ancestor loggers in question are considered.

          If this evaluates to false, logging messages are not passed to
          the handlers of ancestor loggers.

          Spelling it out with an example: If the propagate attribute of
          the logger named ‘A.B.C’ evaluates to true, any event logged
          to ‘A.B.C’ via a method call such as
          ‘logging.getLogger('A.B.C').error(...)’ will [subject to
          passing that logger’s level and filter settings] be passed in
          turn to any handlers attached to loggers named ‘A.B’, ‘A’ and
          the root logger, after first being passed to any handlers
          attached to ‘A.B.C’.  If any logger in the chain ‘A.B.C’,
          ‘A.B’, ‘A’ has its ‘propagate’ attribute set to false, then
          that is the last logger whose handlers are offered the event
          to handle, and propagation stops at that point.

          The constructor sets this attribute to ‘True’.

               Note: If you attach a handler to a logger `and' one or
               more of its ancestors, it may emit the same record
               multiple times.  In general, you should not need to
               attach a handler to more than one logger - if you just
               attach it to the appropriate logger which is highest in
               the logger hierarchy, then it will see all events logged
               by all descendant loggers, provided that their propagate
               setting is left set to ‘True’.  A common scenario is to
               attach handlers only to the root logger, and to let
               propagation take care of the rest.

      -- Method: setLevel (level)

          Sets the threshold for this logger to `level'.  Logging
          messages which are less severe than `level' will be ignored;
          logging messages which have severity `level' or higher will be
          emitted by whichever handler or handlers service this logger,
          unless a handler’s level has been set to a higher severity
          level than `level'.

          When a logger is created, the level is set to ‘NOTSET’ (which
          causes all messages to be processed when the logger is the
          root logger, or delegation to the parent when the logger is a
          non-root logger).  Note that the root logger is created with
          level ‘WARNING’.

          The term ‘delegation to the parent’ means that if a logger has
          a level of NOTSET, its chain of ancestor loggers is traversed
          until either an ancestor with a level other than NOTSET is
          found, or the root is reached.

          If an ancestor is found with a level other than NOTSET, then
          that ancestor’s level is treated as the effective level of the
          logger where the ancestor search began, and is used to
          determine how a logging event is handled.

          If the root is reached, and it has a level of NOTSET, then all
          messages will be processed.  Otherwise, the root’s level will
          be used as the effective level.

          See *note Logging Levels: 21db. for a list of levels.

          Changed in version 3.2: The `level' parameter now accepts a
          string representation of the level such as ‘INFO’ as an
          alternative to the integer constants such as ‘INFO’.  Note,
          however, that levels are internally stored as integers, and
          methods such as e.g.  *note getEffectiveLevel(): 21dc. and
          *note isEnabledFor(): 21dd. will return/expect to be passed
          integers.

      -- Method: isEnabledFor (level)

          Indicates if a message of severity `level' would be processed
          by this logger.  This method checks first the module-level
          level set by ‘logging.disable(level)’ and then the logger’s
          effective level as determined by *note getEffectiveLevel():
          21dc.

      -- Method: getEffectiveLevel ()

          Indicates the effective level for this logger.  If a value
          other than ‘NOTSET’ has been set using *note setLevel(): 21da,
          it is returned.  Otherwise, the hierarchy is traversed towards
          the root until a value other than ‘NOTSET’ is found, and that
          value is returned.  The value returned is an integer,
          typically one of ‘logging.DEBUG’, ‘logging.INFO’ etc.

      -- Method: getChild (suffix)

          Returns a logger which is a descendant to this logger, as
          determined by the suffix.  Thus,
          ‘logging.getLogger('abc').getChild('def.ghi')’ would return
          the same logger as would be returned by
          ‘logging.getLogger('abc.def.ghi')’.  This is a convenience
          method, useful when the parent logger is named using e.g.
          ‘__name__’ rather than a literal string.

          New in version 3.2.

      -- Method: debug (msg, *args, **kwargs)

          Logs a message with level ‘DEBUG’ on this logger.  The `msg'
          is the message format string, and the `args' are the arguments
          which are merged into `msg' using the string formatting
          operator.  (Note that this means that you can use keywords in
          the format string, together with a single dictionary
          argument.)  No % formatting operation is performed on `msg'
          when no `args' are supplied.

          There are four keyword arguments in `kwargs' which are
          inspected: `exc_info', `stack_info', `stacklevel' and `extra'.

          If `exc_info' does not evaluate as false, it causes exception
          information to be added to the logging message.  If an
          exception tuple (in the format returned by *note
          sys.exc_info(): d27.) or an exception instance is provided, it
          is used; otherwise, *note sys.exc_info(): d27. is called to
          get the exception information.

          The second optional keyword argument is `stack_info', which
          defaults to ‘False’.  If true, stack information is added to
          the logging message, including the actual logging call.  Note
          that this is not the same stack information as that displayed
          through specifying `exc_info': The former is stack frames from
          the bottom of the stack up to the logging call in the current
          thread, whereas the latter is information about stack frames
          which have been unwound, following an exception, while
          searching for exception handlers.

          You can specify `stack_info' independently of `exc_info', e.g.
          to just show how you got to a certain point in your code, even
          when no exceptions were raised.  The stack frames are printed
          following a header line which says:

               Stack (most recent call last):

          This mimics the ‘Traceback (most recent call last):’ which is
          used when displaying exception frames.

          The third optional keyword argument is `stacklevel', which
          defaults to ‘1’.  If greater than 1, the corresponding number
          of stack frames are skipped when computing the line number and
          function name set in the *note LogRecord: 9ec. created for the
          logging event.  This can be used in logging helpers so that
          the function name, filename and line number recorded are not
          the information for the helper function/method, but rather its
          caller.  The name of this parameter mirrors the equivalent one
          in the *note warnings: 12f. module.

          The fourth keyword argument is `extra' which can be used to
          pass a dictionary which is used to populate the __dict__ of
          the *note LogRecord: 9ec. created for the logging event with
          user-defined attributes.  These custom attributes can then be
          used as you like.  For example, they could be incorporated
          into logged messages.  For example:

               FORMAT = '%(asctime)s %(clientip)-15s %(user)-8s %(message)s'
               logging.basicConfig(format=FORMAT)
               d = {'clientip': '192.168.0.1', 'user': 'fbloggs'}
               logger = logging.getLogger('tcpserver')
               logger.warning('Protocol problem: %s', 'connection reset', extra=d)

          would print something like

               2006-02-08 22:20:02,165 192.168.0.1 fbloggs  Protocol problem: connection reset

          The keys in the dictionary passed in `extra' should not clash
          with the keys used by the logging system.  (See the *note
          Formatter: 21de. documentation for more information on which
          keys are used by the logging system.)

          If you choose to use these attributes in logged messages, you
          need to exercise some care.  In the above example, for
          instance, the *note Formatter: 21de. has been set up with a
          format string which expects ‘clientip’ and ‘user’ in the
          attribute dictionary of the *note LogRecord: 9ec.  If these
          are missing, the message will not be logged because a string
          formatting exception will occur.  So in this case, you always
          need to pass the `extra' dictionary with these keys.

          While this might be annoying, this feature is intended for use
          in specialized circumstances, such as multi-threaded servers
          where the same code executes in many contexts, and interesting
          conditions which arise are dependent on this context (such as
          remote client IP address and authenticated user name, in the
          above example).  In such circumstances, it is likely that
          specialized *note Formatter: 21de.s would be used with
          particular *note Handler: 21df.s.

          Changed in version 3.2: The `stack_info' parameter was added.

          Changed in version 3.5: The `exc_info' parameter can now
          accept exception instances.

          Changed in version 3.8: The `stacklevel' parameter was added.

      -- Method: info (msg, *args, **kwargs)

          Logs a message with level ‘INFO’ on this logger.  The
          arguments are interpreted as for *note debug(): 21e1.

      -- Method: warning (msg, *args, **kwargs)

          Logs a message with level ‘WARNING’ on this logger.  The
          arguments are interpreted as for *note debug(): 21e1.

               Note: There is an obsolete method ‘warn’ which is
               functionally identical to ‘warning’.  As ‘warn’ is
               deprecated, please do not use it - use ‘warning’ instead.

      -- Method: error (msg, *args, **kwargs)

          Logs a message with level ‘ERROR’ on this logger.  The
          arguments are interpreted as for *note debug(): 21e1.

      -- Method: critical (msg, *args, **kwargs)

          Logs a message with level ‘CRITICAL’ on this logger.  The
          arguments are interpreted as for *note debug(): 21e1.

      -- Method: log (level, msg, *args, **kwargs)

          Logs a message with integer level `level' on this logger.  The
          other arguments are interpreted as for *note debug(): 21e1.

      -- Method: exception (msg, *args, **kwargs)

          Logs a message with level ‘ERROR’ on this logger.  The
          arguments are interpreted as for *note debug(): 21e1.
          Exception info is added to the logging message.  This method
          should only be called from an exception handler.

      -- Method: addFilter (filter)

          Adds the specified filter `filter' to this logger.

      -- Method: removeFilter (filter)

          Removes the specified filter `filter' from this logger.

      -- Method: filter (record)

          Apply this logger’s filters to the record and return ‘True’ if
          the record is to be processed.  The filters are consulted in
          turn, until one of them returns a false value.  If none of
          them return a false value, the record will be processed
          (passed to handlers).  If one returns a false value, no
          further processing of the record occurs.

      -- Method: addHandler (hdlr)

          Adds the specified handler `hdlr' to this logger.

      -- Method: removeHandler (hdlr)

          Removes the specified handler `hdlr' from this logger.

      -- Method: findCaller (stack_info=False, stacklevel=1)

          Finds the caller’s source filename and line number.  Returns
          the filename, line number, function name and stack information
          as a 4-element tuple.  The stack information is returned as
          ‘None’ unless `stack_info' is ‘True’.

          The `stacklevel' parameter is passed from code calling the
          *note debug(): 21e1. and other APIs.  If greater than 1, the
          excess is used to skip stack frames before determining the
          values to be returned.  This will generally be useful when
          calling logging APIs from helper/wrapper code, so that the
          information in the event log refers not to the helper/wrapper
          code, but to the code that calls it.

      -- Method: handle (record)

          Handles a record by passing it to all handlers associated with
          this logger and its ancestors (until a false value of
          `propagate' is found).  This method is used for unpickled
          records received from a socket, as well as those created
          locally.  Logger-level filtering is applied using *note
          filter(): 21e6.

      -- Method: makeRecord (name, level, fn, lno, msg, args, exc_info,
               func=None, extra=None, sinfo=None)

          This is a factory method which can be overridden in subclasses
          to create specialized *note LogRecord: 9ec. instances.

      -- Method: hasHandlers ()

          Checks to see if this logger has any handlers configured.
          This is done by looking for handlers in this logger and its
          parents in the logger hierarchy.  Returns ‘True’ if a handler
          was found, else ‘False’.  The method stops searching up the
          hierarchy whenever a logger with the ‘propagate’ attribute set
          to false is found - that will be the last logger which is
          checked for the existence of handlers.

          New in version 3.2.

     Changed in version 3.7: Loggers can now be pickled and unpickled.


File: python.info,  Node: Logging Levels,  Next: Handler Objects,  Prev: Logger Objects,  Up: logging — Logging facility for Python

5.16.6.2 Logging Levels
.......................

The numeric values of logging levels are given in the following table.
These are primarily of interest if you want to define your own levels,
and need them to have specific values relative to the predefined levels.
If you define a level with the same numeric value, it overwrites the
predefined value; the predefined name is lost.

Level              Numeric value
                   
---------------------------------------
                   
‘CRITICAL’         50
                   
                   
‘ERROR’            40
                   
                   
‘WARNING’          30
                   
                   
‘INFO’             20
                   
                   
‘DEBUG’            10
                   
                   
‘NOTSET’           0
                   


File: python.info,  Node: Handler Objects,  Next: Formatter Objects,  Prev: Logging Levels,  Up: logging — Logging facility for Python

5.16.6.3 Handler Objects
........................

Handlers have the following attributes and methods.  Note that *note
Handler: 21df. is never instantiated directly; this class acts as a base
for more useful subclasses.  However, the *note __init__(): e23. method
in subclasses needs to call *note Handler.__init__(): 21f0.

 -- Class: logging.Handler

      -- Method: __init__ (level=NOTSET)

          Initializes the *note Handler: 21df. instance by setting its
          level, setting the list of filters to the empty list and
          creating a lock (using *note createLock(): 21f1.) for
          serializing access to an I/O mechanism.

      -- Method: createLock ()

          Initializes a thread lock which can be used to serialize
          access to underlying I/O functionality which may not be
          threadsafe.

      -- Method: acquire ()

          Acquires the thread lock created with *note createLock():
          21f1.

      -- Method: release ()

          Releases the thread lock acquired with *note acquire(): 21f2.

      -- Method: setLevel (level)

          Sets the threshold for this handler to `level'.  Logging
          messages which are less severe than `level' will be ignored.
          When a handler is created, the level is set to ‘NOTSET’ (which
          causes all messages to be processed).

          See *note Logging Levels: 21db. for a list of levels.

          Changed in version 3.2: The `level' parameter now accepts a
          string representation of the level such as ‘INFO’ as an
          alternative to the integer constants such as ‘INFO’.

      -- Method: setFormatter (fmt)

          Sets the *note Formatter: 21de. for this handler to `fmt'.

      -- Method: addFilter (filter)

          Adds the specified filter `filter' to this handler.

      -- Method: removeFilter (filter)

          Removes the specified filter `filter' from this handler.

      -- Method: filter (record)

          Apply this handler’s filters to the record and return ‘True’
          if the record is to be processed.  The filters are consulted
          in turn, until one of them returns a false value.  If none of
          them return a false value, the record will be emitted.  If one
          returns a false value, the handler will not emit the record.

      -- Method: flush ()

          Ensure all logging output has been flushed.  This version does
          nothing and is intended to be implemented by subclasses.

      -- Method: close ()

          Tidy up any resources used by the handler.  This version does
          no output but removes the handler from an internal list of
          handlers which is closed when *note shutdown(): 21fb. is
          called.  Subclasses should ensure that this gets called from
          overridden *note close(): 21fa. methods.

      -- Method: handle (record)

          Conditionally emits the specified logging record, depending on
          filters which may have been added to the handler.  Wraps the
          actual emission of the record with acquisition/release of the
          I/O thread lock.

      -- Method: handleError (record)

          This method should be called from handlers when an exception
          is encountered during an *note emit(): 21fe. call.  If the
          module-level attribute ‘raiseExceptions’ is ‘False’,
          exceptions get silently ignored.  This is what is mostly
          wanted for a logging system - most users will not care about
          errors in the logging system, they are more interested in
          application errors.  You could, however, replace this with a
          custom handler if you wish.  The specified record is the one
          which was being processed when the exception occurred.  (The
          default value of ‘raiseExceptions’ is ‘True’, as that is more
          useful during development).

      -- Method: format (record)

          Do formatting for a record - if a formatter is set, use it.
          Otherwise, use the default formatter for the module.

      -- Method: emit (record)

          Do whatever it takes to actually log the specified logging
          record.  This version is intended to be implemented by
          subclasses and so raises a *note NotImplementedError: 704.

For a list of handlers included as standard, see *note logging.handlers:
ac.


File: python.info,  Node: Formatter Objects,  Next: Filter Objects,  Prev: Handler Objects,  Up: logging — Logging facility for Python

5.16.6.4 Formatter Objects
..........................

*note Formatter: 21de. objects have the following attributes and
methods.  They are responsible for converting a *note LogRecord: 9ec. to
(usually) a string which can be interpreted by either a human or an
external system.  The base *note Formatter: 21de. allows a formatting
string to be specified.  If none is supplied, the default value of
‘'%(message)s'’ is used, which just includes the message in the logging
call.  To have additional items of information in the formatted output
(such as a timestamp), keep reading.

A Formatter can be initialized with a format string which makes use of
knowledge of the *note LogRecord: 9ec. attributes - such as the default
value mentioned above making use of the fact that the user’s message and
arguments are pre-formatted into a *note LogRecord: 9ec.’s `message'
attribute.  This format string contains standard Python %-style mapping
keys.  See section *note printf-style String Formatting: 1359. for more
information on string formatting.

The useful mapping keys in a *note LogRecord: 9ec. are given in the
section on *note LogRecord attributes: 2202.

 -- Class: logging.Formatter (fmt=None, datefmt=None, style='%',
          validate=True)

     Returns a new instance of the *note Formatter: 21de. class.  The
     instance is initialized with a format string for the message as a
     whole, as well as a format string for the date/time portion of a
     message.  If no `fmt' is specified, ‘'%(message)s'’ is used.  If no
     `datefmt' is specified, a format is used which is described in the
     *note formatTime(): 2203. documentation.

     The `style' parameter can be one of ‘%’, ‘{’ or ‘$’ and determines
     how the format string will be merged with its data: using one of
     %-formatting, *note str.format(): 5d5. or *note string.Template:
     4f1.  This only applies to the format string `fmt' (e.g.
     ‘'%(message)s'’ or ‘{message}’), not to the actual log messages
     passed to ‘Logger.debug’ etc; see *note Using particular formatting
     styles throughout your application: 2204. for more information on
     using {- and $-formatting for log messages.

     Changed in version 3.2: The `style' parameter was added.

     Changed in version 3.8: The `validate' parameter was added.
     Incorrect or mismatched style and fmt will raise a ‘ValueError’.
     For example: ‘logging.Formatter('%(asctime)s - %(message)s',
     style='{')’.

      -- Method: format (record)

          The record’s attribute dictionary is used as the operand to a
          string formatting operation.  Returns the resulting string.
          Before formatting the dictionary, a couple of preparatory
          steps are carried out.  The `message' attribute of the record
          is computed using `msg' % `args'.  If the formatting string
          contains ‘'(asctime)'’, *note formatTime(): 2203. is called to
          format the event time.  If there is exception information, it
          is formatted using *note formatException(): 2206. and appended
          to the message.  Note that the formatted exception information
          is cached in attribute `exc_text'.  This is useful because the
          exception information can be pickled and sent across the wire,
          but you should be careful if you have more than one *note
          Formatter: 21de. subclass which customizes the formatting of
          exception information.  In this case, you will have to clear
          the cached value after a formatter has done its formatting, so
          that the next formatter to handle the event doesn’t use the
          cached value but recalculates it afresh.

          If stack information is available, it’s appended after the
          exception information, using *note formatStack(): 2207. to
          transform it if necessary.

      -- Method: formatTime (record, datefmt=None)

          This method should be called from *note format(): 5d6. by a
          formatter which wants to make use of a formatted time.  This
          method can be overridden in formatters to provide for any
          specific requirement, but the basic behavior is as follows: if
          `datefmt' (a string) is specified, it is used with *note
          time.strftime(): c37. to format the creation time of the
          record.  Otherwise, the format ‘%Y-%m-%d %H:%M:%S,uuu’ is
          used, where the uuu part is a millisecond value and the other
          letters are as per the *note time.strftime(): c37.
          documentation.  An example time in this format is ‘2003-01-23
          00:29:50,411’.  The resulting string is returned.

          This function uses a user-configurable function to convert the
          creation time to a tuple.  By default, *note time.localtime():
          1080. is used; to change this for a particular formatter
          instance, set the ‘converter’ attribute to a function with the
          same signature as *note time.localtime(): 1080. or *note
          time.gmtime(): c11.  To change it for all formatters, for
          example if you want all logging times to be shown in GMT, set
          the ‘converter’ attribute in the ‘Formatter’ class.

          Changed in version 3.3: Previously, the default format was
          hard-coded as in this example: ‘2010-09-06 22:38:15,292’ where
          the part before the comma is handled by a strptime format
          string (‘'%Y-%m-%d %H:%M:%S'’), and the part after the comma
          is a millisecond value.  Because strptime does not have a
          format placeholder for milliseconds, the millisecond value is
          appended using another format string, ‘'%s,%03d'’ — and both
          of these format strings have been hardcoded into this method.
          With the change, these strings are defined as class-level
          attributes which can be overridden at the instance level when
          desired.  The names of the attributes are
          ‘default_time_format’ (for the strptime format string) and
          ‘default_msec_format’ (for appending the millisecond value).

          Changed in version 3.9: The ‘default_msec_format’ can be
          ‘None’.

      -- Method: formatException (exc_info)

          Formats the specified exception information (a standard
          exception tuple as returned by *note sys.exc_info(): d27.) as
          a string.  This default implementation just uses *note
          traceback.print_exception(): 2208.  The resulting string is
          returned.

      -- Method: formatStack (stack_info)

          Formats the specified stack information (a string as returned
          by *note traceback.print_stack(): 869, but with the last
          newline removed) as a string.  This default implementation
          just returns the input value.


File: python.info,  Node: Filter Objects,  Next: LogRecord Objects,  Prev: Formatter Objects,  Up: logging — Logging facility for Python

5.16.6.5 Filter Objects
.......................

‘Filters’ can be used by ‘Handlers’ and ‘Loggers’ for more sophisticated
filtering than is provided by levels.  The base filter class only allows
events which are below a certain point in the logger hierarchy.  For
example, a filter initialized with ‘A.B’ will allow events logged by
loggers ‘A.B’, ‘A.B.C’, ‘A.B.C.D’, ‘A.B.D’ etc.  but not ‘A.BB’, ‘B.A.B’
etc.  If initialized with the empty string, all events are passed.

 -- Class: logging.Filter (name='')

     Returns an instance of the *note Filter: c48. class.  If `name' is
     specified, it names a logger which, together with its children,
     will have its events allowed through the filter.  If `name' is the
     empty string, allows every event.

      -- Method: filter (record)

          Is the specified record to be logged?  Returns zero for no,
          nonzero for yes.  If deemed appropriate, the record may be
          modified in-place by this method.

Note that filters attached to handlers are consulted before an event is
emitted by the handler, whereas filters attached to loggers are
consulted whenever an event is logged (using *note debug(): 21e1, *note
info(): 220c, etc.), before sending an event to handlers.  This means
that events which have been generated by descendant loggers will not be
filtered by a logger’s filter setting, unless the filter has also been
applied to those descendant loggers.

You don’t actually need to subclass ‘Filter’: you can pass any instance
which has a ‘filter’ method with the same semantics.

Changed in version 3.2: You don’t need to create specialized ‘Filter’
classes, or use other classes with a ‘filter’ method: you can use a
function (or other callable) as a filter.  The filtering logic will
check to see if the filter object has a ‘filter’ attribute: if it does,
it’s assumed to be a ‘Filter’ and its *note filter(): 220b. method is
called.  Otherwise, it’s assumed to be a callable and called with the
record as the single parameter.  The returned value should conform to
that returned by *note filter(): 220b.

Although filters are used primarily to filter records based on more
sophisticated criteria than levels, they get to see every record which
is processed by the handler or logger they’re attached to: this can be
useful if you want to do things like counting how many records were
processed by a particular logger or handler, or adding, changing or
removing attributes in the *note LogRecord: 9ec. being processed.
Obviously changing the LogRecord needs to be done with some care, but it
does allow the injection of contextual information into logs (see *note
Using Filters to impart contextual information: 220d.).


File: python.info,  Node: LogRecord Objects,  Next: LogRecord attributes,  Prev: Filter Objects,  Up: logging — Logging facility for Python

5.16.6.6 LogRecord Objects
..........................

*note LogRecord: 9ec. instances are created automatically by the *note
Logger: 4ae. every time something is logged, and can be created manually
via *note makeLogRecord(): 2210. (for example, from a pickled event
received over the wire).

 -- Class: logging.LogRecord (name, level, pathname, lineno, msg, args,
          exc_info, func=None, sinfo=None)

     Contains all the information pertinent to the event being logged.

     The primary information is passed in ‘msg’ and ‘args’, which are
     combined using ‘msg % args’ to create the ‘message’ field of the
     record.


     Parameters:

        * ‘name’ – The name of the logger used to log the event
          represented by this LogRecord.  Note that this name will
          always have this value, even though it may be emitted by a
          handler attached to a different (ancestor) logger.

        * ‘level’ – The numeric level of the logging event (one of
          DEBUG, INFO etc.)  Note that this is converted to `two'
          attributes of the LogRecord: ‘levelno’ for the numeric value
          and ‘levelname’ for the corresponding level name.

        * ‘pathname’ – The full pathname of the source file where the
          logging call was made.

        * ‘lineno’ – The line number in the source file where the
          logging call was made.

        * ‘msg’ – The event description message, possibly a format
          string with placeholders for variable data.

        * ‘args’ – Variable data to merge into the `msg' argument to
          obtain the event description.

        * ‘exc_info’ – An exception tuple with the current exception
          information, or ‘None’ if no exception information is
          available.

        * ‘func’ – The name of the function or method from which the
          logging call was invoked.

        * ‘sinfo’ – A text string representing stack information from
          the base of the stack in the current thread, up to the logging
          call.

      -- Method: getMessage ()

          Returns the message for this *note LogRecord: 9ec. instance
          after merging any user-supplied arguments with the message.
          If the user-supplied message argument to the logging call is
          not a string, *note str(): 205. is called on it to convert it
          to a string.  This allows use of user-defined classes as
          messages, whose ‘__str__’ method can return the actual format
          string to be used.

     Changed in version 3.2: The creation of a *note LogRecord: 9ec. has
     been made more configurable by providing a factory which is used to
     create the record.  The factory can be set using *note
     getLogRecordFactory(): 2212. and *note setLogRecordFactory(): 2213.
     (see this for the factory’s signature).

     This functionality can be used to inject your own values into a
     *note LogRecord: 9ec. at creation time.  You can use the following
     pattern:

          old_factory = logging.getLogRecordFactory()

          def record_factory(*args, **kwargs):
              record = old_factory(*args, **kwargs)
              record.custom_attribute = 0xdecafbad
              return record

          logging.setLogRecordFactory(record_factory)

     With this pattern, multiple factories could be chained, and as long
     as they don’t overwrite each other’s attributes or unintentionally
     overwrite the standard attributes listed above, there should be no
     surprises.


File: python.info,  Node: LogRecord attributes,  Next: LoggerAdapter Objects,  Prev: LogRecord Objects,  Up: logging — Logging facility for Python

5.16.6.7 LogRecord attributes
.............................

The LogRecord has a number of attributes, most of which are derived from
the parameters to the constructor.  (Note that the names do not always
correspond exactly between the LogRecord constructor parameters and the
LogRecord attributes.)  These attributes can be used to merge data from
the record into the format string.  The following table lists (in
alphabetical order) the attribute names, their meanings and the
corresponding placeholder in a %-style format string.

If you are using {}-formatting (*note str.format(): 5d5.), you can use
‘{attrname}’ as the placeholder in the format string.  If you are using
$-formatting (*note string.Template: 4f1.), use the form ‘${attrname}’.
In both cases, of course, replace ‘attrname’ with the actual attribute
name you want to use.

In the case of {}-formatting, you can specify formatting flags by
placing them after the attribute name, separated from it with a colon.
For example: a placeholder of ‘{msecs:03d}’ would format a millisecond
value of ‘4’ as ‘004’.  Refer to the *note str.format(): 5d5.
documentation for full details on the options available to you.

Attribute name       Format                        Description
                                                   
-------------------------------------------------------------------------------------------------------
                                                   
args                 You shouldn’t need to         The tuple of arguments merged into ‘msg’ to
                     format this yourself.         produce ‘message’, or a dict whose values are
                                                   used for the merge (when there is only one
                                                   argument, and it is a dictionary).
                                                   
                                                   
asctime              ‘%(asctime)s’                 Human-readable time when the
                                                   *note LogRecord: 9ec. was created.  By default
                                                   this is of the form ‘2003-07-08 16:49:45,896’
                                                   (the numbers after the comma are millisecond
                                                   portion of the time).
                                                   
                                                   
created              ‘%(created)f’                 Time when the *note LogRecord: 9ec. was created
                                                   (as returned by *note time.time(): 42d.).
                                                   
                                                   
exc_info             You shouldn’t need to         Exception tuple (à la ‘sys.exc_info’) or, if no
                     format this yourself.         exception has occurred, ‘None’.
                                                   
                                                   
filename             ‘%(filename)s’                Filename portion of ‘pathname’.
                                                   
                                                   
funcName             ‘%(funcName)s’                Name of function containing the logging call.
                                                   
                                                   
levelname            ‘%(levelname)s’               Text logging level for the message (‘'DEBUG'’,
                                                   ‘'INFO'’, ‘'WARNING'’, ‘'ERROR'’, ‘'CRITICAL'’).
                                                   
                                                   
levelno              ‘%(levelno)s’                 Numeric logging level for the message (‘DEBUG’,
                                                   ‘INFO’, ‘WARNING’, ‘ERROR’, ‘CRITICAL’).
                                                   
                                                   
lineno               ‘%(lineno)d’                  Source line number where the logging call was
                                                   issued (if available).
                                                   
                                                   
message              ‘%(message)s’                 The logged message, computed as ‘msg % args’.
                                                   This is set when *note Formatter.format(): 2205.
                                                   is invoked.
                                                   
                                                   
module               ‘%(module)s’                  Module (name portion of ‘filename’).
                                                   
                                                   
msecs                ‘%(msecs)d’                   Millisecond portion of the time when the
                                                   *note LogRecord: 9ec. was created.
                                                   
                                                   
msg                  You shouldn’t need to         The format string passed in the original logging
                     format this yourself.         call.  Merged with ‘args’ to produce ‘message’,
                                                   or an arbitrary object (see
                                                   *note Using arbitrary objects as messages: 2215.).
                                                   
                                                   
name                 ‘%(name)s’                    Name of the logger used to log the call.
                                                   
                                                   
pathname             ‘%(pathname)s’                Full pathname of the source file where the
                                                   logging call was issued (if available).
                                                   
                                                   
process              ‘%(process)d’                 Process ID (if available).
                                                   
                                                   
processName          ‘%(processName)s’             Process name (if available).
                                                   
                                                   
relativeCreated      ‘%(relativeCreated)d’         Time in milliseconds when the LogRecord was
                                                   created, relative to the time the logging module
                                                   was loaded.
                                                   
                                                   
stack_info           You shouldn’t need to         Stack frame information (where available) from
                     format this yourself.         the bottom of the stack in the current thread, up
                                                   to and including the stack frame of the logging
                                                   call which resulted in the creation of this
                                                   record.
                                                   
                                                   
thread               ‘%(thread)d’                  Thread ID (if available).
                                                   
                                                   
threadName           ‘%(threadName)s’              Thread name (if available).
                                                   

Changed in version 3.1: `processName' was added.


File: python.info,  Node: LoggerAdapter Objects,  Next: Thread Safety,  Prev: LogRecord attributes,  Up: logging — Logging facility for Python

5.16.6.8 LoggerAdapter Objects
..............................

*note LoggerAdapter: d54. instances are used to conveniently pass
contextual information into logging calls.  For a usage example, see the
section on *note adding contextual information to your logging output:
2218.

 -- Class: logging.LoggerAdapter (logger, extra)

     Returns an instance of *note LoggerAdapter: d54. initialized with
     an underlying *note Logger: 4ae. instance and a dict-like object.

      -- Method: process (msg, kwargs)

          Modifies the message and/or keyword arguments passed to a
          logging call in order to insert contextual information.  This
          implementation takes the object passed as `extra' to the
          constructor and adds it to `kwargs' using key ‘extra’.  The
          return value is a (`msg', `kwargs') tuple which has the
          (possibly modified) versions of the arguments passed in.

In addition to the above, *note LoggerAdapter: d54. supports the
following methods of *note Logger: 4ae.: *note debug(): 801, *note
info(): 21e0, *note warning(): 21e2, *note error(): 21e3, *note
exception(): 7ff, *note critical(): 800, *note log(): 7fe, *note
isEnabledFor(): 21dd, *note getEffectiveLevel(): 21dc, *note setLevel():
21da. and *note hasHandlers(): 21ec.  These methods have the same
signatures as their counterparts in *note Logger: 4ae, so you can use
the two types of instances interchangeably.

Changed in version 3.2: The *note isEnabledFor(): 21dd, *note
getEffectiveLevel(): 21dc, *note setLevel(): 21da. and *note
hasHandlers(): 21ec. methods were added to *note LoggerAdapter: d54.
These methods delegate to the underlying logger.

Changed in version 3.6: Attribute ‘manager’ and method ‘_log()’ were
added, which delegate to the underlying logger and allow adapters to be
nested.


File: python.info,  Node: Thread Safety,  Next: Module-Level Functions,  Prev: LoggerAdapter Objects,  Up: logging — Logging facility for Python

5.16.6.9 Thread Safety
......................

The logging module is intended to be thread-safe without any special
work needing to be done by its clients.  It achieves this though using
threading locks; there is one lock to serialize access to the module’s
shared data, and each handler also creates a lock to serialize access to
its underlying I/O.

If you are implementing asynchronous signal handlers using the *note
signal: ea. module, you may not be able to use logging from within such
handlers.  This is because lock implementations in the *note threading:
10b. module are not always re-entrant, and so cannot be invoked from
such signal handlers.


File: python.info,  Node: Module-Level Functions,  Next: Module-Level Attributes,  Prev: Thread Safety,  Up: logging — Logging facility for Python

5.16.6.10 Module-Level Functions
................................

In addition to the classes described above, there are a number of
module-level functions.

 -- Function: logging.getLogger (name=None)

     Return a logger with the specified name or, if name is ‘None’,
     return a logger which is the root logger of the hierarchy.  If
     specified, the name is typically a dot-separated hierarchical name
     like `‘a’', `‘a.b’' or `‘a.b.c.d’'.  Choice of these names is
     entirely up to the developer who is using logging.

     All calls to this function with a given name return the same logger
     instance.  This means that logger instances never need to be passed
     between different parts of an application.

 -- Function: logging.getLoggerClass ()

     Return either the standard *note Logger: 4ae. class, or the last
     class passed to *note setLoggerClass(): 221d.  This function may be
     called from within a new class definition, to ensure that
     installing a customized *note Logger: 4ae. class will not undo
     customizations already applied by other code.  For example:

          class MyLogger(logging.getLoggerClass()):
              # ... override behaviour here

 -- Function: logging.getLogRecordFactory ()

     Return a callable which is used to create a *note LogRecord: 9ec.

     New in version 3.2: This function has been provided, along with
     *note setLogRecordFactory(): 2213, to allow developers more control
     over how the *note LogRecord: 9ec. representing a logging event is
     constructed.

     See *note setLogRecordFactory(): 2213. for more information about
     the how the factory is called.

 -- Function: logging.debug (msg, *args, **kwargs)

     Logs a message with level ‘DEBUG’ on the root logger.  The `msg' is
     the message format string, and the `args' are the arguments which
     are merged into `msg' using the string formatting operator.  (Note
     that this means that you can use keywords in the format string,
     together with a single dictionary argument.)

     There are three keyword arguments in `kwargs' which are inspected:
     `exc_info' which, if it does not evaluate as false, causes
     exception information to be added to the logging message.  If an
     exception tuple (in the format returned by *note sys.exc_info():
     d27.) or an exception instance is provided, it is used; otherwise,
     *note sys.exc_info(): d27. is called to get the exception
     information.

     The second optional keyword argument is `stack_info', which
     defaults to ‘False’.  If true, stack information is added to the
     logging message, including the actual logging call.  Note that this
     is not the same stack information as that displayed through
     specifying `exc_info': The former is stack frames from the bottom
     of the stack up to the logging call in the current thread, whereas
     the latter is information about stack frames which have been
     unwound, following an exception, while searching for exception
     handlers.

     You can specify `stack_info' independently of `exc_info', e.g.  to
     just show how you got to a certain point in your code, even when no
     exceptions were raised.  The stack frames are printed following a
     header line which says:

          Stack (most recent call last):

     This mimics the ‘Traceback (most recent call last):’ which is used
     when displaying exception frames.

     The third optional keyword argument is `extra' which can be used to
     pass a dictionary which is used to populate the __dict__ of the
     LogRecord created for the logging event with user-defined
     attributes.  These custom attributes can then be used as you like.
     For example, they could be incorporated into logged messages.  For
     example:

          FORMAT = '%(asctime)s %(clientip)-15s %(user)-8s %(message)s'
          logging.basicConfig(format=FORMAT)
          d = {'clientip': '192.168.0.1', 'user': 'fbloggs'}
          logging.warning('Protocol problem: %s', 'connection reset', extra=d)

     would print something like:

          2006-02-08 22:20:02,165 192.168.0.1 fbloggs  Protocol problem: connection reset

     The keys in the dictionary passed in `extra' should not clash with
     the keys used by the logging system.  (See the *note Formatter:
     21de. documentation for more information on which keys are used by
     the logging system.)

     If you choose to use these attributes in logged messages, you need
     to exercise some care.  In the above example, for instance, the
     *note Formatter: 21de. has been set up with a format string which
     expects ‘clientip’ and ‘user’ in the attribute dictionary of the
     LogRecord.  If these are missing, the message will not be logged
     because a string formatting exception will occur.  So in this case,
     you always need to pass the `extra' dictionary with these keys.

     While this might be annoying, this feature is intended for use in
     specialized circumstances, such as multi-threaded servers where the
     same code executes in many contexts, and interesting conditions
     which arise are dependent on this context (such as remote client IP
     address and authenticated user name, in the above example).  In
     such circumstances, it is likely that specialized *note Formatter:
     21de.s would be used with particular *note Handler: 21df.s.

     Changed in version 3.2: The `stack_info' parameter was added.

 -- Function: logging.info (msg, *args, **kwargs)

     Logs a message with level ‘INFO’ on the root logger.  The arguments
     are interpreted as for *note debug(): 21e1.

 -- Function: logging.warning (msg, *args, **kwargs)

     Logs a message with level ‘WARNING’ on the root logger.  The
     arguments are interpreted as for *note debug(): 21e1.

          Note: There is an obsolete function ‘warn’ which is
          functionally identical to ‘warning’.  As ‘warn’ is deprecated,
          please do not use it - use ‘warning’ instead.

 -- Function: logging.error (msg, *args, **kwargs)

     Logs a message with level ‘ERROR’ on the root logger.  The
     arguments are interpreted as for *note debug(): 21e1.

 -- Function: logging.critical (msg, *args, **kwargs)

     Logs a message with level ‘CRITICAL’ on the root logger.  The
     arguments are interpreted as for *note debug(): 21e1.

 -- Function: logging.exception (msg, *args, **kwargs)

     Logs a message with level ‘ERROR’ on the root logger.  The
     arguments are interpreted as for *note debug(): 21e1.  Exception
     info is added to the logging message.  This function should only be
     called from an exception handler.

 -- Function: logging.log (level, msg, *args, **kwargs)

     Logs a message with level `level' on the root logger.  The other
     arguments are interpreted as for *note debug(): 21e1.

          Note: The above module-level convenience functions, which
          delegate to the root logger, call *note basicConfig(): 311. to
          ensure that at least one handler is available.  Because of
          this, they should `not' be used in threads, in versions of
          Python earlier than 2.7.1 and 3.2, unless at least one handler
          has been added to the root logger `before' the threads are
          started.  In earlier versions of Python, due to a thread
          safety shortcoming in *note basicConfig(): 311, this can
          (under rare circumstances) lead to handlers being added
          multiple times to the root logger, which can in turn lead to
          multiple messages for the same event.

 -- Function: logging.disable (level=CRITICAL)

     Provides an overriding level `level' for all loggers which takes
     precedence over the logger’s own level.  When the need arises to
     temporarily throttle logging output down across the whole
     application, this function can be useful.  Its effect is to disable
     all logging calls of severity `level' and below, so that if you
     call it with a value of INFO, then all INFO and DEBUG events would
     be discarded, whereas those of severity WARNING and above would be
     processed according to the logger’s effective level.  If
     ‘logging.disable(logging.NOTSET)’ is called, it effectively removes
     this overriding level, so that logging output again depends on the
     effective levels of individual loggers.

     Note that if you have defined any custom logging level higher than
     ‘CRITICAL’ (this is not recommended), you won’t be able to rely on
     the default value for the `level' parameter, but will have to
     explicitly supply a suitable value.

     Changed in version 3.7: The `level' parameter was defaulted to
     level ‘CRITICAL’.  See bpo-28524(1) for more information about this
     change.

 -- Function: logging.addLevelName (level, levelName)

     Associates level `level' with text `levelName' in an internal
     dictionary, which is used to map numeric levels to a textual
     representation, for example when a *note Formatter: 21de. formats a
     message.  This function can also be used to define your own levels.
     The only constraints are that all levels used must be registered
     using this function, levels should be positive integers and they
     should increase in increasing order of severity.

          Note: If you are thinking of defining your own levels, please
          see the section on *note Custom Levels: 2224.

 -- Function: logging.getLevelName (level)

     Returns the textual or numeric representation of logging level
     `level'.

     If `level' is one of the predefined levels ‘CRITICAL’, ‘ERROR’,
     ‘WARNING’, ‘INFO’ or ‘DEBUG’ then you get the corresponding string.
     If you have associated levels with names using *note
     addLevelName(): 2223. then the name you have associated with
     `level' is returned.  If a numeric value corresponding to one of
     the defined levels is passed in, the corresponding string
     representation is returned.

     The `level' parameter also accepts a string representation of the
     level such as ‘INFO’.  In such cases, this functions returns the
     corresponding numeric value of the level.

     If no matching numeric or string value is passed in, the string
     ‘Level %s’ % level is returned.

          Note: Levels are internally integers (as they need to be
          compared in the logging logic).  This function is used to
          convert between an integer level and the level name displayed
          in the formatted log output by means of the ‘%(levelname)s’
          format specifier (see *note LogRecord attributes: 2202.), and
          vice versa.

     Changed in version 3.4: In Python versions earlier than 3.4, this
     function could also be passed a text level, and would return the
     corresponding numeric value of the level.  This undocumented
     behaviour was considered a mistake, and was removed in Python 3.4,
     but reinstated in 3.4.2 due to retain backward compatibility.

 -- Function: logging.makeLogRecord (attrdict)

     Creates and returns a new *note LogRecord: 9ec. instance whose
     attributes are defined by `attrdict'.  This function is useful for
     taking a pickled *note LogRecord: 9ec. attribute dictionary, sent
     over a socket, and reconstituting it as a *note LogRecord: 9ec.
     instance at the receiving end.

 -- Function: logging.basicConfig (**kwargs)

     Does basic configuration for the logging system by creating a *note
     StreamHandler: c46. with a default *note Formatter: 21de. and
     adding it to the root logger.  The functions *note debug(): 21e1,
     *note info(): 220c, *note warning(): 221e, *note error(): 221f. and
     *note critical(): 2220. will call *note basicConfig(): 311.
     automatically if no handlers are defined for the root logger.

     This function does nothing if the root logger already has handlers
     configured, unless the keyword argument `force' is set to ‘True’.

          Note: This function should be called from the main thread
          before other threads are started.  In versions of Python prior
          to 2.7.1 and 3.2, if this function is called from multiple
          threads, it is possible (in rare circumstances) that a handler
          will be added to the root logger more than once, leading to
          unexpected results such as messages being duplicated in the
          log.

     The following keyword arguments are supported.

     Format             Description
                        
     ---------------------------------------------------------------------
                        
     `filename'         Specifies that a FileHandler be created, using
                        the specified filename, rather than a
                        StreamHandler.
                        
                        
     `filemode'         If `filename' is specified, open the file in
                        this *note mode: 172c.  Defaults to ‘'a'’.
                        
                        
     `format'           Use the specified format string for the
                        handler.  Defaults to attributes ‘levelname’,
                        ‘name’ and ‘message’ separated by colons.
                        
                        
     `datefmt'          Use the specified date/time format, as accepted
                        by *note time.strftime(): c37.
                        
                        
     `style'            If `format' is specified, use this style for
                        the format string.  One of ‘'%'’, ‘'{'’ or
                        ‘'$'’ for *note printf-style: 1359,
                        *note str.format(): 5d5. or
                        *note string.Template: 4f1. respectively.
                        Defaults to ‘'%'’.
                        
                        
     `level'            Set the root logger level to the specified
                        *note level: 21db.
                        
                        
     `stream'           Use the specified stream to initialize the
                        StreamHandler.  Note that this argument is
                        incompatible with `filename' - if both are
                        present, a ‘ValueError’ is raised.
                        
                        
     `handlers'         If specified, this should be an iterable of
                        already created handlers to add to the root
                        logger.  Any handlers which don’t already have
                        a formatter set will be assigned the default
                        formatter created in this function.  Note that
                        this argument is incompatible with `filename'
                        or `stream' - if both are present, a
                        ‘ValueError’ is raised.
                        
                        
     `force'            If this keyword argument is specified as true,
                        any existing handlers attached to the root
                        logger are removed and closed, before carrying
                        out the configuration as specified by the other
                        arguments.
                        
                        
     `encoding'         If this keyword argument is specified along
                        with `filename', its value is used when the
                        FileHandler is created, and thus used when
                        opening the output file.
                        
                        
     `errors'           If this keyword argument is specified along
                        with `filename', its value is used when the
                        FileHandler is created, and thus used when
                        opening the output file.  If not specified, the
                        value ‘backslashreplace’ is used.  Note that if
                        ‘None’ is specified, it will be passed as such
                        to func:‘open’, which means that it will be
                        treated the same as passing ‘errors’.
                        

     Changed in version 3.2: The `style' argument was added.

     Changed in version 3.3: The `handlers' argument was added.
     Additional checks were added to catch situations where incompatible
     arguments are specified (e.g.  `handlers' together with `stream' or
     `filename', or `stream' together with `filename').

     Changed in version 3.8: The `force' argument was added.

     Changed in version 3.9: The `encoding' and `errors' arguments were
     added.

 -- Function: logging.shutdown ()

     Informs the logging system to perform an orderly shutdown by
     flushing and closing all handlers.  This should be called at
     application exit and no further use of the logging system should be
     made after this call.

     When the logging module is imported, it registers this function as
     an exit handler (see *note atexit: b.), so normally there’s no need
     to do that manually.

 -- Function: logging.setLoggerClass (klass)

     Tells the logging system to use the class `klass' when
     instantiating a logger.  The class should define *note __init__():
     e23. such that only a name argument is required, and the *note
     __init__(): e23. should call ‘Logger.__init__()’.  This function is
     typically called before any loggers are instantiated by
     applications which need to use custom logger behavior.  After this
     call, as at any other time, do not instantiate loggers directly
     using the subclass: continue to use the *note logging.getLogger():
     234. API to get your loggers.

 -- Function: logging.setLogRecordFactory (factory)

     Set a callable which is used to create a *note LogRecord: 9ec.


     Parameters: ‘factory’ – The factory callable to be used to
     instantiate a log record.

     New in version 3.2: This function has been provided, along with
     *note getLogRecordFactory(): 2212, to allow developers more control
     over how the *note LogRecord: 9ec. representing a logging event is
     constructed.

     The factory has the following signature:

     ‘factory(name, level, fn, lno, msg, args, exc_info, func=None,
     sinfo=None, **kwargs)’


          name: The logger name.


          level: The logging level (numeric).


          fn: The full pathname of the file where the logging call was
          made.


          lno: The line number in the file where the logging call was
          made.


          msg: The logging message.


          args: The arguments for the logging message.


          exc_info: An exception tuple, or ‘None’.


          func: The name of the function or method which invoked the
          logging call.


          sinfo: A stack traceback such as is provided by *note
          traceback.print_stack(): 869, showing the call hierarchy.


          kwargs: Additional keyword arguments.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue28524


File: python.info,  Node: Module-Level Attributes,  Next: Integration with the warnings module,  Prev: Module-Level Functions,  Up: logging — Logging facility for Python

5.16.6.11 Module-Level Attributes
.................................

 -- Attribute: logging.lastResort

     A “handler of last resort” is available through this attribute.
     This is a *note StreamHandler: c46. writing to ‘sys.stderr’ with a
     level of ‘WARNING’, and is used to handle logging events in the
     absence of any logging configuration.  The end result is to just
     print the message to ‘sys.stderr’.  This replaces the earlier error
     message saying that “no handlers could be found for logger XYZ”.
     If you need the earlier behaviour for some reason, ‘lastResort’ can
     be set to ‘None’.

     New in version 3.2.


File: python.info,  Node: Integration with the warnings module,  Prev: Module-Level Attributes,  Up: logging — Logging facility for Python

5.16.6.12 Integration with the warnings module
..............................................

The *note captureWarnings(): 2228. function can be used to integrate
*note logging: aa. with the *note warnings: 12f. module.

 -- Function: logging.captureWarnings (capture)

     This function is used to turn the capture of warnings by logging on
     and off.

     If `capture' is ‘True’, warnings issued by the *note warnings: 12f.
     module will be redirected to the logging system.  Specifically, a
     warning will be formatted using *note warnings.formatwarning():
     112d. and the resulting string logged to a logger named
     ‘'py.warnings'’ with a severity of ‘WARNING’.

     If `capture' is ‘False’, the redirection of warnings to the logging
     system will stop, and warnings will be redirected to their original
     destinations (i.e.  those in effect before ‘captureWarnings(True)’
     was called).

See also
........

Module *note logging.config: ab.

     Configuration API for the logging module.

Module *note logging.handlers: ac.

     Useful handlers included with the logging module.

PEP 282(1) - A Logging System

     The proposal which described this feature for inclusion in the
     Python standard library.

Original Python logging package(2)

     This is the original source for the *note logging: aa. package.
     The version of the package available from this site is suitable for
     use with Python 1.5.2, 2.1.x and 2.2.x, which do not include the
     *note logging: aa. package in the standard library.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0282

   (2) https://old.red-dove.com/python_logging.html


File: python.info,  Node: logging config — Logging configuration,  Next: logging handlers — Logging handlers,  Prev: logging — Logging facility for Python,  Up: Generic Operating System Services

5.16.7 ‘logging.config’ — Logging configuration
-----------------------------------------------

`Source code:' Lib/logging/config.py(1)

Important
.........

This page contains only reference information.  For tutorials, please
see

   * *note Basic Tutorial: c43.

   * *note Advanced Tutorial: c44.

   * *note Logging Cookbook: c45.

__________________________________________________________________

This section describes the API for configuring the logging module.

* Menu:

* Configuration functions::
* Security considerations::
* Configuration dictionary schema::
* Configuration file format::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/logging/config.py


File: python.info,  Node: Configuration functions,  Next: Security considerations,  Up: logging config — Logging configuration

5.16.7.1 Configuration functions
................................

The following functions configure the logging module.  They are located
in the *note logging.config: ab. module.  Their use is optional — you
can configure the logging module using these functions or by making
calls to the main API (defined in *note logging: aa. itself) and
defining handlers which are declared either in *note logging: aa. or
*note logging.handlers: ac.

 -- Function: logging.config.dictConfig (config)

     Takes the logging configuration from a dictionary.  The contents of
     this dictionary are described in *note Configuration dictionary
     schema: 222c. below.

     If an error is encountered during configuration, this function will
     raise a *note ValueError: 16d, *note TypeError: 1fe, *note
     AttributeError: 4a2. or *note ImportError: 16c. with a suitably
     descriptive message.  The following is a (possibly incomplete) list
     of conditions which will raise an error:

        * A ‘level’ which is not a string or which is a string not
          corresponding to an actual logging level.

        * A ‘propagate’ value which is not a boolean.

        * An id which does not have a corresponding destination.

        * A non-existent handler id found during an incremental call.

        * An invalid logger name.

        * Inability to resolve to an internal or external object.

     Parsing is performed by the ‘DictConfigurator’ class, whose
     constructor is passed the dictionary used for configuration, and
     has a ‘configure()’ method.  The *note logging.config: ab. module
     has a callable attribute ‘dictConfigClass’ which is initially set
     to ‘DictConfigurator’.  You can replace the value of
     ‘dictConfigClass’ with a suitable implementation of your own.

     *note dictConfig(): bfe. calls ‘dictConfigClass’ passing the
     specified dictionary, and then calls the ‘configure()’ method on
     the returned object to put the configuration into effect:

          def dictConfig(config):
              dictConfigClass(config).configure()

     For example, a subclass of ‘DictConfigurator’ could call
     ‘DictConfigurator.__init__()’ in its own *note __init__(): e23,
     then set up custom prefixes which would be usable in the subsequent
     ‘configure()’ call.  ‘dictConfigClass’ would be bound to this new
     subclass, and then *note dictConfig(): bfe. could be called exactly
     as in the default, uncustomized state.

     New in version 3.2.

 -- Function: logging.config.fileConfig (fname, defaults=None,
          disable_existing_loggers=True)

     Reads the logging configuration from a *note configparser:
     22.-format file.  The format of the file should be as described in
     *note Configuration file format: 222d.  This function can be called
     several times from an application, allowing an end user to select
     from various pre-canned configurations (if the developer provides a
     mechanism to present the choices and load the chosen
     configuration).


     Parameters:

        * ‘fname’ – A filename, or a file-like object, or an instance
          derived from *note RawConfigParser: 95c.  If a
          ‘RawConfigParser’-derived instance is passed, it is used as
          is.  Otherwise, a ‘Configparser’ is instantiated, and the
          configuration read by it from the object passed in ‘fname’.
          If that has a *note readline(): de. method, it is assumed to
          be a file-like object and read using *note read_file(): 1fbc.;
          otherwise, it is assumed to be a filename and passed to *note
          read(): 11d9.

        * ‘defaults’ – Defaults to be passed to the ConfigParser can be
          specified in this argument.

        * ‘disable_existing_loggers’ – If specified as ‘False’, loggers
          which exist when this call is made are left enabled.  The
          default is ‘True’ because this enables old behaviour in a
          backward-compatible way.  This behaviour is to disable any
          existing non-root loggers unless they or their ancestors are
          explicitly named in the logging configuration.

     Changed in version 3.4: An instance of a subclass of *note
     RawConfigParser: 95c. is now accepted as a value for ‘fname’.  This
     facilitates:

        * Use of a configuration file where logging configuration is
          just part of the overall application configuration.

        * Use of a configuration read from a file, and then modified by
          the using application (e.g.  based on command-line parameters
          or other aspects of the runtime environment) before being
          passed to ‘fileConfig’.

 -- Function: logging.config.listen (port=DEFAULT_LOGGING_CONFIG_PORT,
          verify=None)

     Starts up a socket server on the specified port, and listens for
     new configurations.  If no port is specified, the module’s default
     ‘DEFAULT_LOGGING_CONFIG_PORT’ is used.  Logging configurations will
     be sent as a file suitable for processing by *note dictConfig():
     bfe. or *note fileConfig(): 4b0.  Returns a *note Thread: 21a.
     instance on which you can call *note start(): 222e. to start the
     server, and which you can *note join(): c32. when appropriate.  To
     stop the server, call *note stopListening(): 222f.

     The ‘verify’ argument, if specified, should be a callable which
     should verify whether bytes received across the socket are valid
     and should be processed.  This could be done by encrypting and/or
     signing what is sent across the socket, such that the ‘verify’
     callable can perform signature verification and/or decryption.  The
     ‘verify’ callable is called with a single argument - the bytes
     received across the socket - and should return the bytes to be
     processed, or ‘None’ to indicate that the bytes should be
     discarded.  The returned bytes could be the same as the passed in
     bytes (e.g.  when only verification is done), or they could be
     completely different (perhaps if decryption were performed).

     To send a configuration to the socket, read in the configuration
     file and send it to the socket as a sequence of bytes preceded by a
     four-byte length string packed in binary using ‘struct.pack('>L',
     n)’.
          Note: Because portions of the configuration are passed through
          *note eval(): c61, use of this function may open its users to
          a security risk.  While the function only binds to a socket on
          ‘localhost’, and so does not accept connections from remote
          machines, there are scenarios where untrusted code could be
          run under the account of the process which calls *note
          listen(): 95d.  Specifically, if the process calling *note
          listen(): 95d. runs on a multi-user machine where users cannot
          trust each other, then a malicious user could arrange to run
          essentially arbitrary code in a victim user’s process, simply
          by connecting to the victim’s *note listen(): 95d. socket and
          sending a configuration which runs whatever code the attacker
          wants to have executed in the victim’s process.  This is
          especially easy to do if the default port is used, but not
          hard even if a different port is used.  To avoid the risk of
          this happening, use the ‘verify’ argument to *note listen():
          95d. to prevent unrecognised configurations from being
          applied.

     Changed in version 3.4: The ‘verify’ argument was added.

          Note: If you want to send configurations to the listener which
          don’t disable existing loggers, you will need to use a JSON
          format for the configuration, which will use *note
          dictConfig(): bfe. for configuration.  This method allows you
          to specify ‘disable_existing_loggers’ as ‘False’ in the
          configuration you send.

 -- Function: logging.config.stopListening ()

     Stops the listening server which was created with a call to *note
     listen(): 95d.  This is typically called before calling ‘join()’ on
     the return value from *note listen(): 95d.


File: python.info,  Node: Security considerations,  Next: Configuration dictionary schema,  Prev: Configuration functions,  Up: logging config — Logging configuration

5.16.7.2 Security considerations
................................

The logging configuration functionality tries to offer convenience, and
in part this is done by offering the ability to convert text in
configuration files into Python objects used in logging configuration -
for example, as described in *note User-defined objects: 2232.  However,
these same mechanisms (importing callables from user-defined modules and
calling them with parameters from the configuration) could be used to
invoke any code you like, and for this reason you should treat
configuration files from untrusted sources with `extreme caution' and
satisfy yourself that nothing bad can happen if you load them, before
actually loading them.


File: python.info,  Node: Configuration dictionary schema,  Next: Configuration file format,  Prev: Security considerations,  Up: logging config — Logging configuration

5.16.7.3 Configuration dictionary schema
........................................

Describing a logging configuration requires listing the various objects
to create and the connections between them; for example, you may create
a handler named ‘console’ and then say that the logger named ‘startup’
will send its messages to the ‘console’ handler.  These objects aren’t
limited to those provided by the *note logging: aa. module because you
might write your own formatter or handler class.  The parameters to
these classes may also need to include external objects such as
‘sys.stderr’.  The syntax for describing these objects and connections
is defined in *note Object connections: 2234. below.

* Menu:

* Dictionary Schema Details::
* Incremental Configuration::
* Object connections::
* User-defined objects::
* Access to external objects::
* Access to internal objects::
* Import resolution and custom importers::


File: python.info,  Node: Dictionary Schema Details,  Next: Incremental Configuration,  Up: Configuration dictionary schema

5.16.7.4 Dictionary Schema Details
..................................

The dictionary passed to *note dictConfig(): bfe. must contain the
following keys:

   * `version' - to be set to an integer value representing the schema
     version.  The only valid value at present is 1, but having this key
     allows the schema to evolve while still preserving backwards
     compatibility.

All other keys are optional, but if present they will be interpreted as
described below.  In all cases below where a ‘configuring dict’ is
mentioned, it will be checked for the special ‘'()'’ key to see if a
custom instantiation is required.  If so, the mechanism described in
*note User-defined objects: 2232. below is used to create an instance;
otherwise, the context is used to determine what to instantiate.

   * `formatters' - the corresponding value will be a dict in which each
     key is a formatter id and each value is a dict describing how to
     configure the corresponding *note Formatter: 21de. instance.

     The configuring dict is searched for keys ‘format’ and ‘datefmt’
     (with defaults of ‘None’) and these are used to construct a *note
     Formatter: 21de. instance.

     Changed in version 3.8: a ‘validate’ key (with default of ‘True’)
     can be added into the ‘formatters’ section of the configuring dict,
     this is to validate the format.

   * `filters' - the corresponding value will be a dict in which each
     key is a filter id and each value is a dict describing how to
     configure the corresponding Filter instance.

     The configuring dict is searched for the key ‘name’ (defaulting to
     the empty string) and this is used to construct a *note
     logging.Filter: c48. instance.

   * `handlers' - the corresponding value will be a dict in which each
     key is a handler id and each value is a dict describing how to
     configure the corresponding Handler instance.

     The configuring dict is searched for the following keys:

        * ‘class’ (mandatory).  This is the fully qualified name of the
          handler class.

        * ‘level’ (optional).  The level of the handler.

        * ‘formatter’ (optional).  The id of the formatter for this
          handler.

        * ‘filters’ (optional).  A list of ids of the filters for this
          handler.

     All `other' keys are passed through as keyword arguments to the
     handler’s constructor.  For example, given the snippet:

          handlers:
            console:
              class : logging.StreamHandler
              formatter: brief
              level   : INFO
              filters: [allow_foo]
              stream  : ext://sys.stdout
            file:
              class : logging.handlers.RotatingFileHandler
              formatter: precise
              filename: logconfig.log
              maxBytes: 1024
              backupCount: 3

     the handler with id ‘console’ is instantiated as a *note
     logging.StreamHandler: c46, using ‘sys.stdout’ as the underlying
     stream.  The handler with id ‘file’ is instantiated as a *note
     logging.handlers.RotatingFileHandler: 2236. with the keyword
     arguments ‘filename='logconfig.log', maxBytes=1024, backupCount=3’.

   * `loggers' - the corresponding value will be a dict in which each
     key is a logger name and each value is a dict describing how to
     configure the corresponding Logger instance.

     The configuring dict is searched for the following keys:

        * ‘level’ (optional).  The level of the logger.

        * ‘propagate’ (optional).  The propagation setting of the
          logger.

        * ‘filters’ (optional).  A list of ids of the filters for this
          logger.

        * ‘handlers’ (optional).  A list of ids of the handlers for this
          logger.

     The specified loggers will be configured according to the level,
     propagation, filters and handlers specified.

   * `root' - this will be the configuration for the root logger.
     Processing of the configuration will be as for any logger, except
     that the ‘propagate’ setting will not be applicable.

   * `incremental' - whether the configuration is to be interpreted as
     incremental to the existing configuration.  This value defaults to
     ‘False’, which means that the specified configuration replaces the
     existing configuration with the same semantics as used by the
     existing *note fileConfig(): 4b0. API.

     If the specified value is ‘True’, the configuration is processed as
     described in the section on *note Incremental Configuration: 2237.

   * `disable_existing_loggers' - whether any existing non-root loggers
     are to be disabled.  This setting mirrors the parameter of the same
     name in *note fileConfig(): 4b0.  If absent, this parameter
     defaults to ‘True’.  This value is ignored if `incremental' is
     ‘True’.


File: python.info,  Node: Incremental Configuration,  Next: Object connections,  Prev: Dictionary Schema Details,  Up: Configuration dictionary schema

5.16.7.5 Incremental Configuration
..................................

It is difficult to provide complete flexibility for incremental
configuration.  For example, because objects such as filters and
formatters are anonymous, once a configuration is set up, it is not
possible to refer to such anonymous objects when augmenting a
configuration.

Furthermore, there is not a compelling case for arbitrarily altering the
object graph of loggers, handlers, filters, formatters at run-time, once
a configuration is set up; the verbosity of loggers and handlers can be
controlled just by setting levels (and, in the case of loggers,
propagation flags).  Changing the object graph arbitrarily in a safe way
is problematic in a multi-threaded environment; while not impossible,
the benefits are not worth the complexity it adds to the implementation.

Thus, when the ‘incremental’ key of a configuration dict is present and
is ‘True’, the system will completely ignore any ‘formatters’ and
‘filters’ entries, and process only the ‘level’ settings in the
‘handlers’ entries, and the ‘level’ and ‘propagate’ settings in the
‘loggers’ and ‘root’ entries.

Using a value in the configuration dict lets configurations to be sent
over the wire as pickled dicts to a socket listener.  Thus, the logging
verbosity of a long-running application can be altered over time with no
need to stop and restart the application.


File: python.info,  Node: Object connections,  Next: User-defined objects,  Prev: Incremental Configuration,  Up: Configuration dictionary schema

5.16.7.6 Object connections
...........................

The schema describes a set of logging objects - loggers, handlers,
formatters, filters - which are connected to each other in an object
graph.  Thus, the schema needs to represent connections between the
objects.  For example, say that, once configured, a particular logger
has attached to it a particular handler.  For the purposes of this
discussion, we can say that the logger represents the source, and the
handler the destination, of a connection between the two.  Of course in
the configured objects this is represented by the logger holding a
reference to the handler.  In the configuration dict, this is done by
giving each destination object an id which identifies it unambiguously,
and then using the id in the source object’s configuration to indicate
that a connection exists between the source and the destination object
with that id.

So, for example, consider the following YAML snippet:

     formatters:
       brief:
         # configuration for formatter with id 'brief' goes here
       precise:
         # configuration for formatter with id 'precise' goes here
     handlers:
       h1: #This is an id
        # configuration of handler with id 'h1' goes here
        formatter: brief
       h2: #This is another id
        # configuration of handler with id 'h2' goes here
        formatter: precise
     loggers:
       foo.bar.baz:
         # other configuration for logger 'foo.bar.baz'
         handlers: [h1, h2]

(Note: YAML used here because it’s a little more readable than the
equivalent Python source form for the dictionary.)

The ids for loggers are the logger names which would be used
programmatically to obtain a reference to those loggers, e.g.
‘foo.bar.baz’.  The ids for Formatters and Filters can be any string
value (such as ‘brief’, ‘precise’ above) and they are transient, in that
they are only meaningful for processing the configuration dictionary and
used to determine connections between objects, and are not persisted
anywhere when the configuration call is complete.

The above snippet indicates that logger named ‘foo.bar.baz’ should have
two handlers attached to it, which are described by the handler ids ‘h1’
and ‘h2’.  The formatter for ‘h1’ is that described by id ‘brief’, and
the formatter for ‘h2’ is that described by id ‘precise’.


File: python.info,  Node: User-defined objects,  Next: Access to external objects,  Prev: Object connections,  Up: Configuration dictionary schema

5.16.7.7 User-defined objects
.............................

The schema supports user-defined objects for handlers, filters and
formatters.  (Loggers do not need to have different types for different
instances, so there is no support in this configuration schema for
user-defined logger classes.)

Objects to be configured are described by dictionaries which detail
their configuration.  In some places, the logging system will be able to
infer from the context how an object is to be instantiated, but when a
user-defined object is to be instantiated, the system will not know how
to do this.  In order to provide complete flexibility for user-defined
object instantiation, the user needs to provide a ‘factory’ - a callable
which is called with a configuration dictionary and which returns the
instantiated object.  This is signalled by an absolute import path to
the factory being made available under the special key ‘'()'’.  Here’s a
concrete example:

     formatters:
       brief:
         format: '%(message)s'
       default:
         format: '%(asctime)s %(levelname)-8s %(name)-15s %(message)s'
         datefmt: '%Y-%m-%d %H:%M:%S'
       custom:
           (): my.package.customFormatterFactory
           bar: baz
           spam: 99.9
           answer: 42

The above YAML snippet defines three formatters.  The first, with id
‘brief’, is a standard *note logging.Formatter: 21de. instance with the
specified format string.  The second, with id ‘default’, has a longer
format and also defines the time format explicitly, and will result in a
*note logging.Formatter: 21de. initialized with those two format
strings.  Shown in Python source form, the ‘brief’ and ‘default’
formatters have configuration sub-dictionaries:

     {
       'format' : '%(message)s'
     }

and:

     {
       'format' : '%(asctime)s %(levelname)-8s %(name)-15s %(message)s',
       'datefmt' : '%Y-%m-%d %H:%M:%S'
     }

respectively, and as these dictionaries do not contain the special key
‘'()'’, the instantiation is inferred from the context: as a result,
standard *note logging.Formatter: 21de. instances are created.  The
configuration sub-dictionary for the third formatter, with id ‘custom’,
is:

     {
       '()' : 'my.package.customFormatterFactory',
       'bar' : 'baz',
       'spam' : 99.9,
       'answer' : 42
     }

and this contains the special key ‘'()'’, which means that user-defined
instantiation is wanted.  In this case, the specified factory callable
will be used.  If it is an actual callable it will be used directly -
otherwise, if you specify a string (as in the example) the actual
callable will be located using normal import mechanisms.  The callable
will be called with the `remaining' items in the configuration
sub-dictionary as keyword arguments.  In the above example, the
formatter with id ‘custom’ will be assumed to be returned by the call:

     my.package.customFormatterFactory(bar='baz', spam=99.9, answer=42)

The key ‘'()'’ has been used as the special key because it is not a
valid keyword parameter name, and so will not clash with the names of
the keyword arguments used in the call.  The ‘'()'’ also serves as a
mnemonic that the corresponding value is a callable.


File: python.info,  Node: Access to external objects,  Next: Access to internal objects,  Prev: User-defined objects,  Up: Configuration dictionary schema

5.16.7.8 Access to external objects
...................................

There are times where a configuration needs to refer to objects external
to the configuration, for example ‘sys.stderr’.  If the configuration
dict is constructed using Python code, this is straightforward, but a
problem arises when the configuration is provided via a text file (e.g.
JSON, YAML). In a text file, there is no standard way to distinguish
‘sys.stderr’ from the literal string ‘'sys.stderr'’.  To facilitate this
distinction, the configuration system looks for certain special prefixes
in string values and treat them specially.  For example, if the literal
string ‘'ext://sys.stderr'’ is provided as a value in the configuration,
then the ‘ext://’ will be stripped off and the remainder of the value
processed using normal import mechanisms.

The handling of such prefixes is done in a way analogous to protocol
handling: there is a generic mechanism to look for prefixes which match
the regular expression ‘^(?P<prefix>[a-z]+)://(?P<suffix>.*)$’ whereby,
if the ‘prefix’ is recognised, the ‘suffix’ is processed in a
prefix-dependent manner and the result of the processing replaces the
string value.  If the prefix is not recognised, then the string value
will be left as-is.


File: python.info,  Node: Access to internal objects,  Next: Import resolution and custom importers,  Prev: Access to external objects,  Up: Configuration dictionary schema

5.16.7.9 Access to internal objects
...................................

As well as external objects, there is sometimes also a need to refer to
objects in the configuration.  This will be done implicitly by the
configuration system for things that it knows about.  For example, the
string value ‘'DEBUG'’ for a ‘level’ in a logger or handler will
automatically be converted to the value ‘logging.DEBUG’, and the
‘handlers’, ‘filters’ and ‘formatter’ entries will take an object id and
resolve to the appropriate destination object.

However, a more generic mechanism is needed for user-defined objects
which are not known to the *note logging: aa. module.  For example,
consider *note logging.handlers.MemoryHandler: 223f, which takes a
‘target’ argument which is another handler to delegate to.  Since the
system already knows about this class, then in the configuration, the
given ‘target’ just needs to be the object id of the relevant target
handler, and the system will resolve to the handler from the id.  If,
however, a user defines a ‘my.package.MyHandler’ which has an
‘alternate’ handler, the configuration system would not know that the
‘alternate’ referred to a handler.  To cater for this, a generic
resolution system allows the user to specify:

     handlers:
       file:
         # configuration of file handler goes here

       custom:
         (): my.package.MyHandler
         alternate: cfg://handlers.file

The literal string ‘'cfg://handlers.file'’ will be resolved in an
analogous way to strings with the ‘ext://’ prefix, but looking in the
configuration itself rather than the import namespace.  The mechanism
allows access by dot or by index, in a similar way to that provided by
‘str.format’.  Thus, given the following snippet:

     handlers:
       email:
         class: logging.handlers.SMTPHandler
         mailhost: localhost
         fromaddr: my_app@domain.tld
         toaddrs:
           - support_team@domain.tld
           - dev_team@domain.tld
         subject: Houston, we have a problem.

in the configuration, the string ‘'cfg://handlers'’ would resolve to the
dict with key ‘handlers’, the string ‘'cfg://handlers.email’ would
resolve to the dict with key ‘email’ in the ‘handlers’ dict, and so on.
The string ‘'cfg://handlers.email.toaddrs[1]’ would resolve to
‘'dev_team.domain.tld'’ and the string
‘'cfg://handlers.email.toaddrs[0]'’ would resolve to the value
‘'support_team@domain.tld'’.  The ‘subject’ value could be accessed
using either ‘'cfg://handlers.email.subject'’ or, equivalently,
‘'cfg://handlers.email[subject]'’.  The latter form only needs to be
used if the key contains spaces or non-alphanumeric characters.  If an
index value consists only of decimal digits, access will be attempted
using the corresponding integer value, falling back to the string value
if needed.

Given a string ‘cfg://handlers.myhandler.mykey.123’, this will resolve
to ‘config_dict['handlers']['myhandler']['mykey']['123']’.  If the
string is specified as ‘cfg://handlers.myhandler.mykey[123]’, the system
will attempt to retrieve the value from
‘config_dict['handlers']['myhandler']['mykey'][123]’, and fall back to
‘config_dict['handlers']['myhandler']['mykey']['123']’ if that fails.


File: python.info,  Node: Import resolution and custom importers,  Prev: Access to internal objects,  Up: Configuration dictionary schema

5.16.7.10 Import resolution and custom importers
................................................

Import resolution, by default, uses the builtin *note __import__(): 16b.
function to do its importing.  You may want to replace this with your
own importing mechanism: if so, you can replace the ‘importer’ attribute
of the ‘DictConfigurator’ or its superclass, the ‘BaseConfigurator’
class.  However, you need to be careful because of the way functions are
accessed from classes via descriptors.  If you are using a Python
callable to do your imports, and you want to define it at class level
rather than instance level, you need to wrap it with *note
staticmethod(): 30a.  For example:

     from importlib import import_module
     from logging.config import BaseConfigurator

     BaseConfigurator.importer = staticmethod(import_module)

You don’t need to wrap with *note staticmethod(): 30a. if you’re setting
the import callable on a configurator `instance'.


File: python.info,  Node: Configuration file format,  Prev: Configuration dictionary schema,  Up: logging config — Logging configuration

5.16.7.11 Configuration file format
...................................

The configuration file format understood by *note fileConfig(): 4b0. is
based on *note configparser: 22. functionality.  The file must contain
sections called ‘[loggers]’, ‘[handlers]’ and ‘[formatters]’ which
identify by name the entities of each type which are defined in the
file.  For each such entity, there is a separate section which
identifies how that entity is configured.  Thus, for a logger named
‘log01’ in the ‘[loggers]’ section, the relevant configuration details
are held in a section ‘[logger_log01]’.  Similarly, a handler called
‘hand01’ in the ‘[handlers]’ section will have its configuration held in
a section called ‘[handler_hand01]’, while a formatter called ‘form01’
in the ‘[formatters]’ section will have its configuration specified in a
section called ‘[formatter_form01]’.  The root logger configuration must
be specified in a section called ‘[logger_root]’.

     Note: The *note fileConfig(): 4b0. API is older than the *note
     dictConfig(): bfe. API and does not provide functionality to cover
     certain aspects of logging.  For example, you cannot configure
     *note Filter: c48. objects, which provide for filtering of messages
     beyond simple integer levels, using *note fileConfig(): 4b0.  If
     you need to have instances of *note Filter: c48. in your logging
     configuration, you will need to use *note dictConfig(): bfe.  Note
     that future enhancements to configuration functionality will be
     added to *note dictConfig(): bfe, so it’s worth considering
     transitioning to this newer API when it’s convenient to do so.

Examples of these sections in the file are given below.

     [loggers]
     keys=root,log02,log03,log04,log05,log06,log07

     [handlers]
     keys=hand01,hand02,hand03,hand04,hand05,hand06,hand07,hand08,hand09

     [formatters]
     keys=form01,form02,form03,form04,form05,form06,form07,form08,form09

The root logger must specify a level and a list of handlers.  An example
of a root logger section is given below.

     [logger_root]
     level=NOTSET
     handlers=hand01

The ‘level’ entry can be one of ‘DEBUG, INFO, WARNING, ERROR, CRITICAL’
or ‘NOTSET’.  For the root logger only, ‘NOTSET’ means that all messages
will be logged.  Level values are *note eval(): c61.uated in the context
of the ‘logging’ package’s namespace.

The ‘handlers’ entry is a comma-separated list of handler names, which
must appear in the ‘[handlers]’ section.  These names must appear in the
‘[handlers]’ section and have corresponding sections in the
configuration file.

For loggers other than the root logger, some additional information is
required.  This is illustrated by the following example.

     [logger_parser]
     level=DEBUG
     handlers=hand01
     propagate=1
     qualname=compiler.parser

The ‘level’ and ‘handlers’ entries are interpreted as for the root
logger, except that if a non-root logger’s level is specified as
‘NOTSET’, the system consults loggers higher up the hierarchy to
determine the effective level of the logger.  The ‘propagate’ entry is
set to 1 to indicate that messages must propagate to handlers higher up
the logger hierarchy from this logger, or 0 to indicate that messages
are `not' propagated to handlers up the hierarchy.  The ‘qualname’ entry
is the hierarchical channel name of the logger, that is to say the name
used by the application to get the logger.

Sections which specify handler configuration are exemplified by the
following.

     [handler_hand01]
     class=StreamHandler
     level=NOTSET
     formatter=form01
     args=(sys.stdout,)

The ‘class’ entry indicates the handler’s class (as determined by *note
eval(): c61. in the ‘logging’ package’s namespace).  The ‘level’ is
interpreted as for loggers, and ‘NOTSET’ is taken to mean ‘log
everything’.

The ‘formatter’ entry indicates the key name of the formatter for this
handler.  If blank, a default formatter (‘logging._defaultFormatter’) is
used.  If a name is specified, it must appear in the ‘[formatters]’
section and have a corresponding section in the configuration file.

The ‘args’ entry, when *note eval(): c61.uated in the context of the
‘logging’ package’s namespace, is the list of arguments to the
constructor for the handler class.  Refer to the constructors for the
relevant handlers, or to the examples below, to see how typical entries
are constructed.  If not provided, it defaults to ‘()’.

The optional ‘kwargs’ entry, when *note eval(): c61.uated in the context
of the ‘logging’ package’s namespace, is the keyword argument dict to
the constructor for the handler class.  If not provided, it defaults to
‘{}’.

     [handler_hand02]
     class=FileHandler
     level=DEBUG
     formatter=form02
     args=('python.log', 'w')

     [handler_hand03]
     class=handlers.SocketHandler
     level=INFO
     formatter=form03
     args=('localhost', handlers.DEFAULT_TCP_LOGGING_PORT)

     [handler_hand04]
     class=handlers.DatagramHandler
     level=WARN
     formatter=form04
     args=('localhost', handlers.DEFAULT_UDP_LOGGING_PORT)

     [handler_hand05]
     class=handlers.SysLogHandler
     level=ERROR
     formatter=form05
     args=(('localhost', handlers.SYSLOG_UDP_PORT), handlers.SysLogHandler.LOG_USER)

     [handler_hand06]
     class=handlers.NTEventLogHandler
     level=CRITICAL
     formatter=form06
     args=('Python Application', '', 'Application')

     [handler_hand07]
     class=handlers.SMTPHandler
     level=WARN
     formatter=form07
     args=('localhost', 'from@abc', ['user1@abc', 'user2@xyz'], 'Logger Subject')
     kwargs={'timeout': 10.0}

     [handler_hand08]
     class=handlers.MemoryHandler
     level=NOTSET
     formatter=form08
     target=
     args=(10, ERROR)

     [handler_hand09]
     class=handlers.HTTPHandler
     level=NOTSET
     formatter=form09
     args=('localhost:9022', '/log', 'GET')
     kwargs={'secure': True}

Sections which specify formatter configuration are typified by the
following.

     [formatter_form01]
     format=F1 %(asctime)s %(levelname)s %(message)s
     datefmt=
     class=logging.Formatter

The ‘format’ entry is the overall format string, and the ‘datefmt’ entry
is the ‘strftime()’-compatible date/time format string.  If empty, the
package substitutes something which is almost equivalent to specifying
the date format string ‘'%Y-%m-%d %H:%M:%S'’.  This format also
specifies milliseconds, which are appended to the result of using the
above format string, with a comma separator.  An example time in this
format is ‘2003-01-23 00:29:50,411’.

The ‘class’ entry is optional.  It indicates the name of the formatter’s
class (as a dotted module and class name.)  This option is useful for
instantiating a *note Formatter: 21de. subclass.  Subclasses of *note
Formatter: 21de. can present exception tracebacks in an expanded or
condensed format.

     Note: Due to the use of *note eval(): c61. as described above,
     there are potential security risks which result from using the
     *note listen(): 95d. to send and receive configurations via
     sockets.  The risks are limited to where multiple users with no
     mutual trust run code on the same machine; see the *note listen():
     95d. documentation for more information.

See also
........

Module *note logging: aa.

     API reference for the logging module.

Module *note logging.handlers: ac.

     Useful handlers included with the logging module.


File: python.info,  Node: logging handlers — Logging handlers,  Next: getpass — Portable password input,  Prev: logging config — Logging configuration,  Up: Generic Operating System Services

5.16.8 ‘logging.handlers’ — Logging handlers
--------------------------------------------

`Source code:' Lib/logging/handlers.py(1)

Important
.........

This page contains only reference information.  For tutorials, please
see

   * *note Basic Tutorial: c43.

   * *note Advanced Tutorial: c44.

   * *note Logging Cookbook: c45.

__________________________________________________________________

The following useful handlers are provided in the package.  Note that
three of the handlers (*note StreamHandler: c46, *note FileHandler:
2245. and *note NullHandler: ce6.) are actually defined in the *note
logging: aa. module itself, but have been documented here along with the
other handlers.

* Menu:

* StreamHandler::
* FileHandler::
* NullHandler::
* WatchedFileHandler::
* BaseRotatingHandler::
* RotatingFileHandler::
* TimedRotatingFileHandler::
* SocketHandler::
* DatagramHandler::
* SysLogHandler::
* NTEventLogHandler::
* SMTPHandler::
* MemoryHandler::
* HTTPHandler::
* QueueHandler::
* QueueListener::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/logging/handlers.py


File: python.info,  Node: StreamHandler,  Next: FileHandler,  Up: logging handlers — Logging handlers

5.16.8.1 StreamHandler
......................

The *note StreamHandler: c46. class, located in the core *note logging:
aa. package, sends logging output to streams such as `sys.stdout',
`sys.stderr' or any file-like object (or, more precisely, any object
which supports ‘write()’ and ‘flush()’ methods).

 -- Class: logging.StreamHandler (stream=None)

     Returns a new instance of the *note StreamHandler: c46. class.  If
     `stream' is specified, the instance will use it for logging output;
     otherwise, `sys.stderr' will be used.

      -- Method: emit (record)

          If a formatter is specified, it is used to format the record.
          The record is then written to the stream followed by *note
          terminator: 2249.  If exception information is present, it is
          formatted using *note traceback.print_exception(): 2208. and
          appended to the stream.

      -- Method: flush ()

          Flushes the stream by calling its *note flush(): 224a. method.
          Note that the ‘close()’ method is inherited from *note
          Handler: 21df. and so does no output, so an explicit *note
          flush(): 224a. call may be needed at times.

      -- Method: setStream (stream)

          Sets the instance’s stream to the specified value, if it is
          different.  The old stream is flushed before the new stream is
          set.


          Parameters: ‘stream’ – The stream that the handler should use.


          Returns: the old stream, if the stream was changed, or `None'
          if it wasn’t.

          New in version 3.7.

      -- Attribute: terminator

          String used as the terminator when writing a formatted record
          to a stream.  Default value is ‘'\n'’.

          If you don’t want a newline termination, you can set the
          handler instance’s ‘terminator’ attribute to the empty string.

          In earlier versions, the terminator was hardcoded as ‘'\n'’.

          New in version 3.2.


File: python.info,  Node: FileHandler,  Next: NullHandler,  Prev: StreamHandler,  Up: logging handlers — Logging handlers

5.16.8.2 FileHandler
....................

The *note FileHandler: 2245. class, located in the core *note logging:
aa. package, sends logging output to a disk file.  It inherits the
output functionality from *note StreamHandler: c46.

 -- Class: logging.FileHandler (filename, mode='a', encoding=None,
          delay=False, errors=None)

     Returns a new instance of the *note FileHandler: 2245. class.  The
     specified file is opened and used as the stream for logging.  If
     `mode' is not specified, ‘'a'’ is used.  If `encoding' is not
     ‘None’, it is used to open the file with that encoding.  If `delay'
     is true, then file opening is deferred until the first call to
     *note emit(): 224d.  By default, the file grows indefinitely.  If
     `errors' is specified, it’s used to determine how encoding errors
     are handled.

     Changed in version 3.6: As well as string values, *note Path: 32f.
     objects are also accepted for the `filename' argument.

     Changed in version 3.9: The `errors' parameter was added.

      -- Method: close ()

          Closes the file.

      -- Method: emit (record)

          Outputs the record to the file.


File: python.info,  Node: NullHandler,  Next: WatchedFileHandler,  Prev: FileHandler,  Up: logging handlers — Logging handlers

5.16.8.3 NullHandler
....................

New in version 3.1.

The *note NullHandler: ce6. class, located in the core *note logging:
aa. package, does not do any formatting or output.  It is essentially a
‘no-op’ handler for use by library developers.

 -- Class: logging.NullHandler

     Returns a new instance of the *note NullHandler: ce6. class.

      -- Method: emit (record)

          This method does nothing.

      -- Method: handle (record)

          This method does nothing.

      -- Method: createLock ()

          This method returns ‘None’ for the lock, since there is no
          underlying I/O to which access needs to be serialized.

See *note Configuring Logging for a Library: 2254. for more information
on how to use *note NullHandler: ce6.


File: python.info,  Node: WatchedFileHandler,  Next: BaseRotatingHandler,  Prev: NullHandler,  Up: logging handlers — Logging handlers

5.16.8.4 WatchedFileHandler
...........................

The *note WatchedFileHandler: 2257. class, located in the *note
logging.handlers: ac. module, is a ‘FileHandler’ which watches the file
it is logging to.  If the file changes, it is closed and reopened using
the file name.

A file change can happen because of usage of programs such as
`newsyslog' and `logrotate' which perform log file rotation.  This
handler, intended for use under Unix/Linux, watches the file to see if
it has changed since the last emit.  (A file is deemed to have changed
if its device or inode have changed.)  If the file has changed, the old
file stream is closed, and the file opened to get a new stream.

This handler is not appropriate for use under Windows, because under
Windows open log files cannot be moved or renamed - logging opens the
files with exclusive locks - and so there is no need for such a handler.
Furthermore, `ST_INO' is not supported under Windows; *note stat(): 321.
always returns zero for this value.

 -- Class: logging.handlers.WatchedFileHandler (filename, mode='a',
          encoding=None, delay=False, errors=None)

     Returns a new instance of the *note WatchedFileHandler: 2257.
     class.  The specified file is opened and used as the stream for
     logging.  If `mode' is not specified, ‘'a'’ is used.  If `encoding'
     is not ‘None’, it is used to open the file with that encoding.  If
     `delay' is true, then file opening is deferred until the first call
     to *note emit(): 2258.  By default, the file grows indefinitely.
     If `errors' is provided, it determines how encoding errors are
     handled.

     Changed in version 3.6: As well as string values, *note Path: 32f.
     objects are also accepted for the `filename' argument.

     Changed in version 3.9: The `errors' parameter was added.

      -- Method: reopenIfNeeded ()

          Checks to see if the file has changed.  If it has, the
          existing stream is flushed and closed and the file opened
          again, typically as a precursor to outputting the record to
          the file.

          New in version 3.6.

      -- Method: emit (record)

          Outputs the record to the file, but first calls *note
          reopenIfNeeded(): 65b. to reopen the file if it has changed.


File: python.info,  Node: BaseRotatingHandler,  Next: RotatingFileHandler,  Prev: WatchedFileHandler,  Up: logging handlers — Logging handlers

5.16.8.5 BaseRotatingHandler
............................

The *note BaseRotatingHandler: 225b. class, located in the *note
logging.handlers: ac. module, is the base class for the rotating file
handlers, *note RotatingFileHandler: 2236. and *note
TimedRotatingFileHandler: 959.  You should not need to instantiate this
class, but it has attributes and methods you may need to override.

 -- Class: logging.handlers.BaseRotatingHandler (filename, mode,
          encoding=None, delay=False, errors=None)

     The parameters are as for ‘FileHandler’.  The attributes are:

      -- Attribute: namer

          If this attribute is set to a callable, the *note
          rotation_filename(): 225d. method delegates to this callable.
          The parameters passed to the callable are those passed to
          *note rotation_filename(): 225d.

               Note: The namer function is called quite a few times
               during rollover, so it should be as simple and as fast as
               possible.  It should also return the same output every
               time for a given input, otherwise the rollover behaviour
               may not work as expected.

               It’s also worth noting that care should be taken when
               using a namer to preserve certain attributes in the
               filename which are used during rotation.  For example,
               *note RotatingFileHandler: 2236. expects to have a set of
               log files whose names contain successive integers, so
               that rotation works as expected, and *note
               TimedRotatingFileHandler: 959. deletes old log files
               (based on the ‘backupCount’ parameter passed to the
               handler’s initializer) by determining the oldest files to
               delete.  For this to happen, the filenames should be
               sortable using the date/time portion of the filename, and
               a namer needs to respect this.  (If a namer is wanted
               that doesn’t respect this scheme, it will need to be used
               in a subclass of *note TimedRotatingFileHandler: 959.
               which overrides the *note getFilesToDelete(): 225e.
               method to fit in with the custom naming scheme.)

          New in version 3.3.

      -- Attribute: rotator

          If this attribute is set to a callable, the *note rotate():
          2260. method delegates to this callable.  The parameters
          passed to the callable are those passed to *note rotate():
          2260.

          New in version 3.3.

      -- Method: rotation_filename (default_name)

          Modify the filename of a log file when rotating.

          This is provided so that a custom filename can be provided.

          The default implementation calls the ‘namer’ attribute of the
          handler, if it’s callable, passing the default name to it.  If
          the attribute isn’t callable (the default is ‘None’), the name
          is returned unchanged.


          Parameters: ‘default_name’ – The default name for the log
          file.

          New in version 3.3.

      -- Method: rotate (source, dest)

          When rotating, rotate the current log.

          The default implementation calls the ‘rotator’ attribute of
          the handler, if it’s callable, passing the source and dest
          arguments to it.  If the attribute isn’t callable (the default
          is ‘None’), the source is simply renamed to the destination.


          Parameters:

             * ‘source’ – The source filename.  This is normally the
               base filename, e.g.  ‘test.log’.

             * ‘dest’ – The destination filename.  This is normally what
               the source is rotated to, e.g.  ‘test.log.1’.

          New in version 3.3.

The reason the attributes exist is to save you having to subclass - you
can use the same callables for instances of *note RotatingFileHandler:
2236. and *note TimedRotatingFileHandler: 959.  If either the namer or
rotator callable raises an exception, this will be handled in the same
way as any other exception during an ‘emit()’ call, i.e.  via the
‘handleError()’ method of the handler.

If you need to make more significant changes to rotation processing, you
can override the methods.

For an example, see *note Using a rotator and namer to customize log
rotation processing: 2261.


File: python.info,  Node: RotatingFileHandler,  Next: TimedRotatingFileHandler,  Prev: BaseRotatingHandler,  Up: logging handlers — Logging handlers

5.16.8.6 RotatingFileHandler
............................

The *note RotatingFileHandler: 2236. class, located in the *note
logging.handlers: ac. module, supports rotation of disk log files.

 -- Class: logging.handlers.RotatingFileHandler (filename, mode='a',
          maxBytes=0, backupCount=0, encoding=None, delay=False,
          errors=None)

     Returns a new instance of the *note RotatingFileHandler: 2236.
     class.  The specified file is opened and used as the stream for
     logging.  If `mode' is not specified, ‘'a'’ is used.  If `encoding'
     is not ‘None’, it is used to open the file with that encoding.  If
     `delay' is true, then file opening is deferred until the first call
     to *note emit(): 2264.  By default, the file grows indefinitely.
     If `errors' is provided, it determines how encoding errors are
     handled.

     You can use the `maxBytes' and `backupCount' values to allow the
     file to `rollover' at a predetermined size.  When the size is about
     to be exceeded, the file is closed and a new file is silently
     opened for output.  Rollover occurs whenever the current log file
     is nearly `maxBytes' in length; but if either of `maxBytes' or
     `backupCount' is zero, rollover never occurs, so you generally want
     to set `backupCount' to at least 1, and have a non-zero `maxBytes'.
     When `backupCount' is non-zero, the system will save old log files
     by appending the extensions ‘.1’, ‘.2’ etc., to the filename.  For
     example, with a `backupCount' of 5 and a base file name of
     ‘app.log’, you would get ‘app.log’, ‘app.log.1’, ‘app.log.2’, up to
     ‘app.log.5’.  The file being written to is always ‘app.log’.  When
     this file is filled, it is closed and renamed to ‘app.log.1’, and
     if files ‘app.log.1’, ‘app.log.2’, etc.  exist, then they are
     renamed to ‘app.log.2’, ‘app.log.3’ etc.  respectively.

     Changed in version 3.6: As well as string values, *note Path: 32f.
     objects are also accepted for the `filename' argument.

     Changed in version 3.9: The `errors' parameter was added.

      -- Method: doRollover ()

          Does a rollover, as described above.

      -- Method: emit (record)

          Outputs the record to the file, catering for rollover as
          described previously.


File: python.info,  Node: TimedRotatingFileHandler,  Next: SocketHandler,  Prev: RotatingFileHandler,  Up: logging handlers — Logging handlers

5.16.8.7 TimedRotatingFileHandler
.................................

The *note TimedRotatingFileHandler: 959. class, located in the *note
logging.handlers: ac. module, supports rotation of disk log files at
certain timed intervals.

 -- Class: logging.handlers.TimedRotatingFileHandler (filename,
          when='h', interval=1, backupCount=0, encoding=None,
          delay=False, utc=False, atTime=None, errors=None)

     Returns a new instance of the *note TimedRotatingFileHandler: 959.
     class.  The specified file is opened and used as the stream for
     logging.  On rotating it also sets the filename suffix.  Rotating
     happens based on the product of `when' and `interval'.

     You can use the `when' to specify the type of `interval'.  The list
     of possible values is below.  Note that they are not case
     sensitive.

     Value                Type of interval                 If/how `atTime' is used
                                                           
     ------------------------------------------------------------------------------------
                                                           
     ‘'S'’                Seconds                          Ignored
                                                           
                                                           
     ‘'M'’                Minutes                          Ignored
                                                           
                                                           
     ‘'H'’                Hours                            Ignored
                                                           
                                                           
     ‘'D'’                Days                             Ignored
                                                           
                                                           
     ‘'W0'-'W6'’          Weekday (0=Monday)               Used to compute initial
                                                           rollover time
                                                           
                                                           
     ‘'midnight'’         Roll over at midnight, if        Used to compute initial
                          `atTime' not specified, else     rollover time
                          at time `atTime'                 
                          

     When using weekday-based rotation, specify ‘W0’ for Monday, ‘W1’
     for Tuesday, and so on up to ‘W6’ for Sunday.  In this case, the
     value passed for `interval' isn’t used.

     The system will save old log files by appending extensions to the
     filename.  The extensions are date-and-time based, using the
     strftime format ‘%Y-%m-%d_%H-%M-%S’ or a leading portion thereof,
     depending on the rollover interval.

     When computing the next rollover time for the first time (when the
     handler is created), the last modification time of an existing log
     file, or else the current time, is used to compute when the next
     rotation will occur.

     If the `utc' argument is true, times in UTC will be used; otherwise
     local time is used.

     If `backupCount' is nonzero, at most `backupCount' files will be
     kept, and if more would be created when rollover occurs, the oldest
     one is deleted.  The deletion logic uses the interval to determine
     which files to delete, so changing the interval may leave old files
     lying around.

     If `delay' is true, then file opening is deferred until the first
     call to *note emit(): 2268.

     If `atTime' is not ‘None’, it must be a ‘datetime.time’ instance
     which specifies the time of day when rollover occurs, for the cases
     where rollover is set to happen “at midnight” or “on a particular
     weekday”.  Note that in these cases, the `atTime' value is
     effectively used to compute the `initial' rollover, and subsequent
     rollovers would be calculated via the normal interval calculation.

     If `errors' is specified, it’s used to determine how encoding
     errors are handled.

          Note: Calculation of the initial rollover time is done when
          the handler is initialised.  Calculation of subsequent
          rollover times is done only when rollover occurs, and rollover
          occurs only when emitting output.  If this is not kept in
          mind, it might lead to some confusion.  For example, if an
          interval of “every minute” is set, that does not mean you will
          always see log files with times (in the filename) separated by
          a minute; if, during application execution, logging output is
          generated more frequently than once a minute, `then' you can
          expect to see log files with times separated by a minute.  If,
          on the other hand, logging messages are only output once every
          five minutes (say), then there will be gaps in the file times
          corresponding to the minutes where no output (and hence no
          rollover) occurred.

     Changed in version 3.4: `atTime' parameter was added.

     Changed in version 3.6: As well as string values, *note Path: 32f.
     objects are also accepted for the `filename' argument.

     Changed in version 3.9: The `errors' parameter was added.

      -- Method: doRollover ()

          Does a rollover, as described above.

      -- Method: emit (record)

          Outputs the record to the file, catering for rollover as
          described above.

      -- Method: getFilesToDelete ()

          Returns a list of filenames which should be deleted as part of
          rollover.  These are the absolute paths of the oldest backup
          log files written by the handler.


File: python.info,  Node: SocketHandler,  Next: DatagramHandler,  Prev: TimedRotatingFileHandler,  Up: logging handlers — Logging handlers

5.16.8.8 SocketHandler
......................

The *note SocketHandler: 95a. class, located in the *note
logging.handlers: ac. module, sends logging output to a network socket.
The base class uses a TCP socket.

 -- Class: logging.handlers.SocketHandler (host, port)

     Returns a new instance of the *note SocketHandler: 95a. class
     intended to communicate with a remote machine whose address is
     given by `host' and `port'.

     Changed in version 3.4: If ‘port’ is specified as ‘None’, a Unix
     domain socket is created using the value in ‘host’ - otherwise, a
     TCP socket is created.

      -- Method: close ()

          Closes the socket.

      -- Method: emit ()

          Pickles the record’s attribute dictionary and writes it to the
          socket in binary format.  If there is an error with the
          socket, silently drops the packet.  If the connection was
          previously lost, re-establishes the connection.  To unpickle
          the record at the receiving end into a *note LogRecord: 9ec,
          use the *note makeLogRecord(): 2210. function.

      -- Method: handleError ()

          Handles an error which has occurred during *note emit(): 226d.
          The most likely cause is a lost connection.  Closes the socket
          so that we can retry on the next event.

      -- Method: makeSocket ()

          This is a factory method which allows subclasses to define the
          precise type of socket they want.  The default implementation
          creates a TCP socket (*note socket.SOCK_STREAM: d52.).

      -- Method: makePickle (record)

          Pickles the record’s attribute dictionary in binary format
          with a length prefix, and returns it ready for transmission
          across the socket.  The details of this operation are
          equivalent to:

               data = pickle.dumps(record_attr_dict, 1)
               datalen = struct.pack('>L', len(data))
               return datalen + data

          Note that pickles aren’t completely secure.  If you are
          concerned about security, you may want to override this method
          to implement a more secure mechanism.  For example, you can
          sign pickles using HMAC and then verify them on the receiving
          end, or alternatively you can disable unpickling of global
          objects on the receiving end.

      -- Method: send (packet)

          Send a pickled byte-string `packet' to the socket.  The format
          of the sent byte-string is as described in the documentation
          for *note makePickle(): 2270.

          This function allows for partial sends, which can happen when
          the network is busy.

      -- Method: createSocket ()

          Tries to create a socket; on failure, uses an exponential
          back-off algorithm.  On initial failure, the handler will drop
          the message it was trying to send.  When subsequent messages
          are handled by the same instance, it will not try connecting
          until some time has passed.  The default parameters are such
          that the initial delay is one second, and if after that delay
          the connection still can’t be made, the handler will double
          the delay each time up to a maximum of 30 seconds.

          This behaviour is controlled by the following handler
          attributes:

             * ‘retryStart’ (initial delay, defaulting to 1.0 seconds).

             * ‘retryFactor’ (multiplier, defaulting to 2.0).

             * ‘retryMax’ (maximum delay, defaulting to 30.0 seconds).

          This means that if the remote listener starts up `after' the
          handler has been used, you could lose messages (since the
          handler won’t even attempt a connection until the delay has
          elapsed, but just silently drop messages during the delay
          period).


File: python.info,  Node: DatagramHandler,  Next: SysLogHandler,  Prev: SocketHandler,  Up: logging handlers — Logging handlers

5.16.8.9 DatagramHandler
........................

The *note DatagramHandler: 95b. class, located in the *note
logging.handlers: ac. module, inherits from *note SocketHandler: 95a. to
support sending logging messages over UDP sockets.

 -- Class: logging.handlers.DatagramHandler (host, port)

     Returns a new instance of the *note DatagramHandler: 95b. class
     intended to communicate with a remote machine whose address is
     given by `host' and `port'.

     Changed in version 3.4: If ‘port’ is specified as ‘None’, a Unix
     domain socket is created using the value in ‘host’ - otherwise, a
     UDP socket is created.

      -- Method: emit ()

          Pickles the record’s attribute dictionary and writes it to the
          socket in binary format.  If there is an error with the
          socket, silently drops the packet.  To unpickle the record at
          the receiving end into a *note LogRecord: 9ec, use the *note
          makeLogRecord(): 2210. function.

      -- Method: makeSocket ()

          The factory method of *note SocketHandler: 95a. is here
          overridden to create a UDP socket (*note socket.SOCK_DGRAM:
          d51.).

      -- Method: send (s)

          Send a pickled byte-string to a socket.  The format of the
          sent byte-string is as described in the documentation for
          *note SocketHandler.makePickle(): 2270.


File: python.info,  Node: SysLogHandler,  Next: NTEventLogHandler,  Prev: DatagramHandler,  Up: logging handlers — Logging handlers

5.16.8.10 SysLogHandler
.......................

The *note SysLogHandler: afb. class, located in the *note
logging.handlers: ac. module, supports sending logging messages to a
remote or local Unix syslog.

 -- Class: logging.handlers.SysLogHandler (address=('localhost',
          SYSLOG_UDP_PORT), facility=LOG_USER,
          socktype=socket.SOCK_DGRAM)

     Returns a new instance of the *note SysLogHandler: afb. class
     intended to communicate with a remote Unix machine whose address is
     given by `address' in the form of a ‘(host, port)’ tuple.  If
     `address' is not specified, ‘('localhost', 514)’ is used.  The
     address is used to open a socket.  An alternative to providing a
     ‘(host, port)’ tuple is providing an address as a string, for
     example ‘/dev/log’.  In this case, a Unix domain socket is used to
     send the message to the syslog.  If `facility' is not specified,
     ‘LOG_USER’ is used.  The type of socket opened depends on the
     `socktype' argument, which defaults to *note socket.SOCK_DGRAM:
     d51. and thus opens a UDP socket.  To open a TCP socket (for use
     with the newer syslog daemons such as rsyslog), specify a value of
     *note socket.SOCK_STREAM: d52.

     Note that if your server is not listening on UDP port 514, *note
     SysLogHandler: afb. may appear not to work.  In that case, check
     what address you should be using for a domain socket - it’s system
     dependent.  For example, on Linux it’s usually ‘/dev/log’ but on
     OS/X it’s ‘/var/run/syslog’.  You’ll need to check your platform
     and use the appropriate address (you may need to do this check at
     runtime if your application needs to run on several platforms).  On
     Windows, you pretty much have to use the UDP option.

     Changed in version 3.2: `socktype' was added.

      -- Method: close ()

          Closes the socket to the remote host.

      -- Method: emit (record)

          The record is formatted, and then sent to the syslog server.
          If exception information is present, it is `not' sent to the
          server.

          Changed in version 3.2.1: (See: bpo-12168(1).)  In earlier
          versions, the message sent to the syslog daemons was always
          terminated with a NUL byte, because early versions of these
          daemons expected a NUL terminated message - even though it’s
          not in the relevant specification ( RFC 5424(2)).  More recent
          versions of these daemons don’t expect the NUL byte but strip
          it off if it’s there, and even more recent daemons (which
          adhere more closely to RFC 5424) pass the NUL byte on as part
          of the message.

          To enable easier handling of syslog messages in the face of
          all these differing daemon behaviours, the appending of the
          NUL byte has been made configurable, through the use of a
          class-level attribute, ‘append_nul’.  This defaults to ‘True’
          (preserving the existing behaviour) but can be set to ‘False’
          on a ‘SysLogHandler’ instance in order for that instance to
          `not' append the NUL terminator.

          Changed in version 3.3: (See: bpo-12419(3).)  In earlier
          versions, there was no facility for an “ident” or “tag” prefix
          to identify the source of the message.  This can now be
          specified using a class-level attribute, defaulting to ‘""’ to
          preserve existing behaviour, but which can be overridden on a
          ‘SysLogHandler’ instance in order for that instance to prepend
          the ident to every message handled.  Note that the provided
          ident must be text, not bytes, and is prepended to the message
          exactly as is.

      -- Method: encodePriority (facility, priority)

          Encodes the facility and priority into an integer.  You can
          pass in strings or integers - if strings are passed, internal
          mapping dictionaries are used to convert them to integers.

          The symbolic ‘LOG_’ values are defined in *note SysLogHandler:
          afb. and mirror the values defined in the ‘sys/syslog.h’
          header file.

          `Priorities'

          Name (string)                  Symbolic value
                                         
          ---------------------------------------------------
                                         
          ‘alert’                        LOG_ALERT
                                         
                                         
          ‘crit’ or ‘critical’           LOG_CRIT
                                         
                                         
          ‘debug’                        LOG_DEBUG
                                         
                                         
          ‘emerg’ or ‘panic’             LOG_EMERG
                                         
                                         
          ‘err’ or ‘error’               LOG_ERR
                                         
                                         
          ‘info’                         LOG_INFO
                                         
                                         
          ‘notice’                       LOG_NOTICE
                                         
                                         
          ‘warn’ or ‘warning’            LOG_WARNING
                                         

          `Facilities'

          Name (string)       Symbolic value
                              
          ----------------------------------------
                              
          ‘auth’              LOG_AUTH
                              
                              
          ‘authpriv’          LOG_AUTHPRIV
                              
                              
          ‘cron’              LOG_CRON
                              
                              
          ‘daemon’            LOG_DAEMON
                              
                              
          ‘ftp’               LOG_FTP
                              
                              
          ‘kern’              LOG_KERN
                              
                              
          ‘lpr’               LOG_LPR
                              
                              
          ‘mail’              LOG_MAIL
                              
                              
          ‘news’              LOG_NEWS
                              
                              
          ‘syslog’            LOG_SYSLOG
                              
                              
          ‘user’              LOG_USER
                              
                              
          ‘uucp’              LOG_UUCP
                              
                              
          ‘local0’            LOG_LOCAL0
                              
                              
          ‘local1’            LOG_LOCAL1
                              
                              
          ‘local2’            LOG_LOCAL2
                              
                              
          ‘local3’            LOG_LOCAL3
                              
                              
          ‘local4’            LOG_LOCAL4
                              
                              
          ‘local5’            LOG_LOCAL5
                              
                              
          ‘local6’            LOG_LOCAL6
                              
                              
          ‘local7’            LOG_LOCAL7
                              

      -- Method: mapPriority (levelname)

          Maps a logging level name to a syslog priority name.  You may
          need to override this if you are using custom levels, or if
          the default algorithm is not suitable for your needs.  The
          default algorithm maps ‘DEBUG’, ‘INFO’, ‘WARNING’, ‘ERROR’ and
          ‘CRITICAL’ to the equivalent syslog names, and all other level
          names to ‘warning’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue12168

   (2) https://tools.ietf.org/html/rfc5424.html

   (3) https://bugs.python.org/issue12419


File: python.info,  Node: NTEventLogHandler,  Next: SMTPHandler,  Prev: SysLogHandler,  Up: logging handlers — Logging handlers

5.16.8.11 NTEventLogHandler
...........................

The *note NTEventLogHandler: 2280. class, located in the *note
logging.handlers: ac. module, supports sending logging messages to a
local Windows NT, Windows 2000 or Windows XP event log.  Before you can
use it, you need Mark Hammond’s Win32 extensions for Python installed.

 -- Class: logging.handlers.NTEventLogHandler (appname, dllname=None,
          logtype='Application')

     Returns a new instance of the *note NTEventLogHandler: 2280. class.
     The `appname' is used to define the application name as it appears
     in the event log.  An appropriate registry entry is created using
     this name.  The `dllname' should give the fully qualified pathname
     of a .dll or .exe which contains message definitions to hold in the
     log (if not specified, ‘'win32service.pyd'’ is used - this is
     installed with the Win32 extensions and contains some basic
     placeholder message definitions.  Note that use of these
     placeholders will make your event logs big, as the entire message
     source is held in the log.  If you want slimmer logs, you have to
     pass in the name of your own .dll or .exe which contains the
     message definitions you want to use in the event log).  The
     `logtype' is one of ‘'Application'’, ‘'System'’ or ‘'Security'’,
     and defaults to ‘'Application'’.

      -- Method: close ()

          At this point, you can remove the application name from the
          registry as a source of event log entries.  However, if you do
          this, you will not be able to see the events as you intended
          in the Event Log Viewer - it needs to be able to access the
          registry to get the .dll name.  The current version does not
          do this.

      -- Method: emit (record)

          Determines the message ID, event category and event type, and
          then logs the message in the NT event log.

      -- Method: getEventCategory (record)

          Returns the event category for the record.  Override this if
          you want to specify your own categories.  This version returns
          0.

      -- Method: getEventType (record)

          Returns the event type for the record.  Override this if you
          want to specify your own types.  This version does a mapping
          using the handler’s typemap attribute, which is set up in
          *note __init__(): e23. to a dictionary which contains mappings
          for ‘DEBUG’, ‘INFO’, ‘WARNING’, ‘ERROR’ and ‘CRITICAL’.  If
          you are using your own levels, you will either need to
          override this method or place a suitable dictionary in the
          handler’s `typemap' attribute.

      -- Method: getMessageID (record)

          Returns the message ID for the record.  If you are using your
          own messages, you could do this by having the `msg' passed to
          the logger being an ID rather than a format string.  Then, in
          here, you could use a dictionary lookup to get the message ID.
          This version returns 1, which is the base message ID in
          ‘win32service.pyd’.


File: python.info,  Node: SMTPHandler,  Next: MemoryHandler,  Prev: NTEventLogHandler,  Up: logging handlers — Logging handlers

5.16.8.12 SMTPHandler
.....................

The *note SMTPHandler: 2288. class, located in the *note
logging.handlers: ac. module, supports sending logging messages to an
email address via SMTP.

 -- Class: logging.handlers.SMTPHandler (mailhost, fromaddr, toaddrs,
          subject, credentials=None, secure=None, timeout=1.0)

     Returns a new instance of the *note SMTPHandler: 2288. class.  The
     instance is initialized with the from and to addresses and subject
     line of the email.  The `toaddrs' should be a list of strings.  To
     specify a non-standard SMTP port, use the (host, port) tuple format
     for the `mailhost' argument.  If you use a string, the standard
     SMTP port is used.  If your SMTP server requires authentication,
     you can specify a (username, password) tuple for the `credentials'
     argument.

     To specify the use of a secure protocol (TLS), pass in a tuple to
     the `secure' argument.  This will only be used when authentication
     credentials are supplied.  The tuple should be either an empty
     tuple, or a single-value tuple with the name of a keyfile, or a
     2-value tuple with the names of the keyfile and certificate file.
     (This tuple is passed to the *note smtplib.SMTP.starttls(): b5c.
     method.)

     A timeout can be specified for communication with the SMTP server
     using the `timeout' argument.

     New in version 3.3: The `timeout' argument was added.

      -- Method: emit (record)

          Formats the record and sends it to the specified addressees.

      -- Method: getSubject (record)

          If you want to specify a subject line which is
          record-dependent, override this method.


File: python.info,  Node: MemoryHandler,  Next: HTTPHandler,  Prev: SMTPHandler,  Up: logging handlers — Logging handlers

5.16.8.13 MemoryHandler
.......................

The *note MemoryHandler: 223f. class, located in the *note
logging.handlers: ac. module, supports buffering of logging records in
memory, periodically flushing them to a `target' handler.  Flushing
occurs whenever the buffer is full, or when an event of a certain
severity or greater is seen.

*note MemoryHandler: 223f. is a subclass of the more general *note
BufferingHandler: 228d, which is an abstract class.  This buffers
logging records in memory.  Whenever each record is added to the buffer,
a check is made by calling ‘shouldFlush()’ to see if the buffer should
be flushed.  If it should, then ‘flush()’ is expected to do the
flushing.

 -- Class: logging.handlers.BufferingHandler (capacity)

     Initializes the handler with a buffer of the specified capacity.
     Here, `capacity' means the number of logging records buffered.

      -- Method: emit (record)

          Append the record to the buffer.  If *note shouldFlush():
          228f. returns true, call *note flush(): 2290. to process the
          buffer.

      -- Method: flush ()

          You can override this to implement custom flushing behavior.
          This version just zaps the buffer to empty.

      -- Method: shouldFlush (record)

          Return ‘True’ if the buffer is up to capacity.  This method
          can be overridden to implement custom flushing strategies.

 -- Class: logging.handlers.MemoryHandler (capacity, flushLevel=ERROR,
          target=None, flushOnClose=True)

     Returns a new instance of the *note MemoryHandler: 223f. class.
     The instance is initialized with a buffer size of `capacity'
     (number of records buffered).  If `flushLevel' is not specified,
     ‘ERROR’ is used.  If no `target' is specified, the target will need
     to be set using *note setTarget(): 2291. before this handler does
     anything useful.  If `flushOnClose' is specified as ‘False’, then
     the buffer is `not' flushed when the handler is closed.  If not
     specified or specified as ‘True’, the previous behaviour of
     flushing the buffer will occur when the handler is closed.

     Changed in version 3.6: The `flushOnClose' parameter was added.

      -- Method: close ()

          Calls *note flush(): 2293, sets the target to ‘None’ and
          clears the buffer.

      -- Method: flush ()

          For a *note MemoryHandler: 223f, flushing means just sending
          the buffered records to the target, if there is one.  The
          buffer is also cleared when this happens.  Override if you
          want different behavior.

      -- Method: setTarget (target)

          Sets the target handler for this handler.

      -- Method: shouldFlush (record)

          Checks for buffer full or a record at the `flushLevel' or
          higher.


File: python.info,  Node: HTTPHandler,  Next: QueueHandler,  Prev: MemoryHandler,  Up: logging handlers — Logging handlers

5.16.8.14 HTTPHandler
.....................

The *note HTTPHandler: 802. class, located in the *note
logging.handlers: ac. module, supports sending logging messages to a Web
server, using either ‘GET’ or ‘POST’ semantics.

 -- Class: logging.handlers.HTTPHandler (host, url, method='GET',
          secure=False, credentials=None, context=None)

     Returns a new instance of the *note HTTPHandler: 802. class.  The
     `host' can be of the form ‘host:port’, should you need to use a
     specific port number.  If no `method' is specified, ‘GET’ is used.
     If `secure' is true, a HTTPS connection will be used.  The
     `context' parameter may be set to a *note ssl.SSLContext: 4ea.
     instance to configure the SSL settings used for the HTTPS
     connection.  If `credentials' is specified, it should be a 2-tuple
     consisting of userid and password, which will be placed in a HTTP
     ‘Authorization’ header using Basic authentication.  If you specify
     credentials, you should also specify secure=True so that your
     userid and password are not passed in cleartext across the wire.

     Changed in version 3.5: The `context' parameter was added.

      -- Method: mapLogRecord (record)

          Provides a dictionary, based on ‘record’, which is to be
          URL-encoded and sent to the web server.  The default
          implementation just returns ‘record.__dict__’.  This method
          can be overridden if e.g.  only a subset of *note LogRecord:
          9ec. is to be sent to the web server, or if more specific
          customization of what’s sent to the server is required.

      -- Method: emit (record)

          Sends the record to the Web server as a URL-encoded
          dictionary.  The *note mapLogRecord(): 2297. method is used to
          convert the record to the dictionary to be sent.

          Note: Since preparing a record for sending it to a Web server
          is not the same as a generic formatting operation, using *note
          setFormatter(): 21f5. to specify a *note Formatter: 21de. for
          a *note HTTPHandler: 802. has no effect.  Instead of calling
          *note format(): 21ff, this handler calls *note mapLogRecord():
          2297. and then *note urllib.parse.urlencode(): 87a. to encode
          the dictionary in a form suitable for sending to a Web server.


File: python.info,  Node: QueueHandler,  Next: QueueListener,  Prev: HTTPHandler,  Up: logging handlers — Logging handlers

5.16.8.15 QueueHandler
......................

New in version 3.2.

The *note QueueHandler: 229b. class, located in the *note
logging.handlers: ac. module, supports sending logging messages to a
queue, such as those implemented in the *note queue: da. or *note
multiprocessing: b7. modules.

Along with the *note QueueListener: 803. class, *note QueueHandler:
229b. can be used to let handlers do their work on a separate thread
from the one which does the logging.  This is important in Web
applications and also other service applications where threads servicing
clients need to respond as quickly as possible, while any potentially
slow operations (such as sending an email via *note SMTPHandler: 2288.)
are done on a separate thread.

 -- Class: logging.handlers.QueueHandler (queue)

     Returns a new instance of the *note QueueHandler: 229b. class.  The
     instance is initialized with the queue to send messages to.  The
     `queue' can be any queue-like object; it’s used as-is by the *note
     enqueue(): 229c. method, which needs to know how to send messages
     to it.  The queue is not `required' to have the task tracking API,
     which means that you can use *note SimpleQueue: 4cd. instances for
     `queue'.

      -- Method: emit (record)

          Enqueues the result of preparing the LogRecord.  Should an
          exception occur (e.g.  because a bounded queue has filled up),
          the *note handleError(): 21fd. method is called to handle the
          error.  This can result in the record silently being dropped
          (if ‘logging.raiseExceptions’ is ‘False’) or a message printed
          to ‘sys.stderr’ (if ‘logging.raiseExceptions’ is ‘True’).

      -- Method: prepare (record)

          Prepares a record for queuing.  The object returned by this
          method is enqueued.

          The base implementation formats the record to merge the
          message, arguments, and exception information, if present.  It
          also removes unpickleable items from the record in-place.

          You might want to override this method if you want to convert
          the record to a dict or JSON string, or send a modified copy
          of the record while leaving the original intact.

      -- Method: enqueue (record)

          Enqueues the record on the queue using ‘put_nowait()’; you may
          want to override this if you want to use blocking behaviour,
          or a timeout, or a customized queue implementation.


File: python.info,  Node: QueueListener,  Prev: QueueHandler,  Up: logging handlers — Logging handlers

5.16.8.16 QueueListener
.......................

New in version 3.2.

The *note QueueListener: 803. class, located in the *note
logging.handlers: ac. module, supports receiving logging messages from a
queue, such as those implemented in the *note queue: da. or *note
multiprocessing: b7. modules.  The messages are received from a queue in
an internal thread and passed, on the same thread, to one or more
handlers for processing.  While *note QueueListener: 803. is not itself
a handler, it is documented here because it works hand-in-hand with
*note QueueHandler: 229b.

Along with the *note QueueHandler: 229b. class, *note QueueListener:
803. can be used to let handlers do their work on a separate thread from
the one which does the logging.  This is important in Web applications
and also other service applications where threads servicing clients need
to respond as quickly as possible, while any potentially slow operations
(such as sending an email via *note SMTPHandler: 2288.) are done on a
separate thread.

 -- Class: logging.handlers.QueueListener (queue, *handlers,
          respect_handler_level=False)

     Returns a new instance of the *note QueueListener: 803. class.  The
     instance is initialized with the queue to send messages to and a
     list of handlers which will handle entries placed on the queue.
     The queue can be any queue-like object; it’s passed as-is to the
     *note dequeue(): 22a1. method, which needs to know how to get
     messages from it.  The queue is not `required' to have the task
     tracking API (though it’s used if available), which means that you
     can use *note SimpleQueue: 4cd. instances for `queue'.

     If ‘respect_handler_level’ is ‘True’, a handler’s level is
     respected (compared with the level for the message) when deciding
     whether to pass messages to that handler; otherwise, the behaviour
     is as in previous Python versions - to always pass each message to
     each handler.

     Changed in version 3.5: The ‘respect_handler_level’ argument was
     added.

      -- Method: dequeue (block)

          Dequeues a record and return it, optionally blocking.

          The base implementation uses ‘get()’.  You may want to
          override this method if you want to use timeouts or work with
          custom queue implementations.

      -- Method: prepare (record)

          Prepare a record for handling.

          This implementation just returns the passed-in record.  You
          may want to override this method if you need to do any custom
          marshalling or manipulation of the record before passing it to
          the handlers.

      -- Method: handle (record)

          Handle a record.

          This just loops through the handlers offering them the record
          to handle.  The actual object passed to the handlers is that
          which is returned from *note prepare(): 22a2.

      -- Method: start ()

          Starts the listener.

          This starts up a background thread to monitor the queue for
          LogRecords to process.

      -- Method: stop ()

          Stops the listener.

          This asks the thread to terminate, and then waits for it to do
          so.  Note that if you don’t call this before your application
          exits, there may be some records still left on the queue,
          which won’t be processed.

      -- Method: enqueue_sentinel ()

          Writes a sentinel to the queue to tell the listener to quit.
          This implementation uses ‘put_nowait()’.  You may want to
          override this method if you want to use timeouts or work with
          custom queue implementations.

          New in version 3.3.

See also
........

Module *note logging: aa.

     API reference for the logging module.

Module *note logging.config: ab.

     Configuration API for the logging module.


File: python.info,  Node: getpass — Portable password input,  Next: curses — Terminal handling for character-cell displays,  Prev: logging handlers — Logging handlers,  Up: Generic Operating System Services

5.16.9 ‘getpass’ — Portable password input
------------------------------------------

`Source code:' Lib/getpass.py(1)

__________________________________________________________________

The *note getpass: 86. module provides two functions:

 -- Function: getpass.getpass (prompt='Password: ', stream=None)

     Prompt the user for a password without echoing.  The user is
     prompted using the string `prompt', which defaults to ‘'Password:
     '’.  On Unix, the prompt is written to the file-like object
     `stream' using the replace error handler if needed.  `stream'
     defaults to the controlling terminal (‘/dev/tty’) or if that is
     unavailable to ‘sys.stderr’ (this argument is ignored on Windows).

     If echo free input is unavailable getpass() falls back to printing
     a warning message to `stream' and reading from ‘sys.stdin’ and
     issuing a *note GetPassWarning: 22aa.

          Note: If you call getpass from within IDLE, the input may be
          done in the terminal you launched IDLE from rather than the
          idle window itself.

 -- Exception: getpass.GetPassWarning

     A *note UserWarning: 1861. subclass issued when password input may
     be echoed.

 -- Function: getpass.getuser ()

     Return the “login name” of the user.

     This function checks the environment variables ‘LOGNAME’, ‘USER’,
     ‘LNAME’ and ‘USERNAME’, in order, and returns the value of the
     first one which is set to a non-empty string.  If none are set, the
     login name from the password database is returned on systems which
     support the *note pwd: d6. module, otherwise, an exception is
     raised.

     In general, this function should be preferred over *note
     os.getlogin(): 204e.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/getpass.py


File: python.info,  Node: curses — Terminal handling for character-cell displays,  Next: curses textpad — Text input widget for curses programs,  Prev: getpass — Portable password input,  Up: Generic Operating System Services

5.16.10 ‘curses’ — Terminal handling for character-cell displays
----------------------------------------------------------------

__________________________________________________________________

The *note curses: 2b. module provides an interface to the curses
library, the de-facto standard for portable advanced terminal handling.

While curses is most widely used in the Unix environment, versions are
available for Windows, DOS, and possibly other systems as well.  This
extension module is designed to match the API of ncurses, an open-source
curses library hosted on Linux and the BSD variants of Unix.

     Note: Whenever the documentation mentions a `character' it can be
     specified as an integer, a one-character Unicode string or a
     one-byte byte string.

     Whenever the documentation mentions a `character string' it can be
     specified as a Unicode string or a byte string.

     Note: Since version 5.4, the ncurses library decides how to
     interpret non-ASCII data using the ‘nl_langinfo’ function.  That
     means that you have to call *note locale.setlocale(): 2166. in the
     application and encode Unicode strings using one of the system’s
     available encodings.  This example uses the system’s default
     encoding:

          import locale
          locale.setlocale(locale.LC_ALL, '')
          code = locale.getpreferredencoding()

     Then use `code' as the encoding for *note str.encode(): 170. calls.

See also
........

Module *note curses.ascii: 2c.

     Utilities for working with ASCII characters, regardless of your
     locale settings.

Module *note curses.panel: 2d.

     A panel stack extension that adds depth to curses windows.

Module *note curses.textpad: 2e.

     Editable text widget for curses supporting ‘Emacs’-like bindings.

*note Curses Programming with Python: 22ad.

     Tutorial material on using curses with Python, by Andrew Kuchling
     and Eric Raymond.

The Tools/demo/(1) directory in the Python source distribution contains
some example programs using the curses bindings provided by this module.

* Menu:

* Functions: Functions<4>.
* Window Objects::
* Constants: Constants<6>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Tools/demo/


File: python.info,  Node: Functions<4>,  Next: Window Objects,  Up: curses — Terminal handling for character-cell displays

5.16.10.1 Functions
...................

The module *note curses: 2b. defines the following exception:

 -- Exception: curses.error

     Exception raised when a curses library function returns an error.

     Note: Whenever `x' or `y' arguments to a function or a method are
     optional, they default to the current cursor location.  Whenever
     `attr' is optional, it defaults to ‘A_NORMAL’.

The module *note curses: 2b. defines the following functions:

 -- Function: curses.baudrate ()

     Return the output speed of the terminal in bits per second.  On
     software terminal emulators it will have a fixed high value.
     Included for historical reasons; in former times, it was used to
     write output loops for time delays and occasionally to change
     interfaces depending on the line speed.

 -- Function: curses.beep ()

     Emit a short attention sound.

 -- Function: curses.can_change_color ()

     Return ‘True’ or ‘False’, depending on whether the programmer can
     change the colors displayed by the terminal.

 -- Function: curses.cbreak ()

     Enter cbreak mode.  In cbreak mode (sometimes called “rare” mode)
     normal tty line buffering is turned off and characters are
     available to be read one by one.  However, unlike raw mode, special
     characters (interrupt, quit, suspend, and flow control) retain
     their effects on the tty driver and calling program.  Calling first
     *note raw(): 22b5. then *note cbreak(): 22b4. leaves the terminal
     in cbreak mode.

 -- Function: curses.color_content (color_number)

     Return the intensity of the red, green, and blue (RGB) components
     in the color `color_number', which must be between ‘0’ and ‘COLORS
     - 1’.  Return a 3-tuple, containing the R,G,B values for the given
     color, which will be between ‘0’ (no component) and ‘1000’ (maximum
     amount of component).

 -- Function: curses.color_pair (pair_number)

     Return the attribute value for displaying text in the specified
     color pair.  Only the first 256 color pairs are supported.  This
     attribute value can be combined with ‘A_STANDOUT’, ‘A_REVERSE’, and
     the other ‘A_*’ attributes.  *note pair_number(): 22b8. is the
     counterpart to this function.

 -- Function: curses.curs_set (visibility)

     Set the cursor state.  `visibility' can be set to ‘0’, ‘1’, or ‘2’,
     for invisible, normal, or very visible.  If the terminal supports
     the visibility requested, return the previous cursor state;
     otherwise raise an exception.  On many terminals, the “visible”
     mode is an underline cursor and the “very visible” mode is a block
     cursor.

 -- Function: curses.def_prog_mode ()

     Save the current terminal mode as the “program” mode, the mode when
     the running program is using curses.  (Its counterpart is the
     “shell” mode, for when the program is not in curses.)  Subsequent
     calls to *note reset_prog_mode(): 22bb. will restore this mode.

 -- Function: curses.def_shell_mode ()

     Save the current terminal mode as the “shell” mode, the mode when
     the running program is not using curses.  (Its counterpart is the
     “program” mode, when the program is using curses capabilities.)
     Subsequent calls to *note reset_shell_mode(): 22bd. will restore
     this mode.

 -- Function: curses.delay_output (ms)

     Insert an `ms' millisecond pause in output.

 -- Function: curses.doupdate ()

     Update the physical screen.  The curses library keeps two data
     structures, one representing the current physical screen contents
     and a virtual screen representing the desired next state.  The
     *note doupdate(): 22bf. ground updates the physical screen to match
     the virtual screen.

     The virtual screen may be updated by a *note noutrefresh(): 22c0.
     call after write operations such as *note addstr(): 22c1. have been
     performed on a window.  The normal *note refresh(): 22c2. call is
     simply ‘noutrefresh()’ followed by ‘doupdate()’; if you have to
     update multiple windows, you can speed performance and perhaps
     reduce screen flicker by issuing ‘noutrefresh()’ calls on all
     windows, followed by a single ‘doupdate()’.

 -- Function: curses.echo ()

     Enter echo mode.  In echo mode, each character input is echoed to
     the screen as it is entered.

 -- Function: curses.endwin ()

     De-initialize the library, and return terminal to normal status.

 -- Function: curses.erasechar ()

     Return the user’s current erase character as a one-byte bytes
     object.  Under Unix operating systems this is a property of the
     controlling tty of the curses program, and is not set by the curses
     library itself.

 -- Function: curses.filter ()

     The *note filter(): 22c6. routine, if used, must be called before
     *note initscr(): 22c7. is called.  The effect is that, during those
     calls, ‘LINES’ is set to ‘1’; the capabilities ‘clear’, ‘cup’,
     ‘cud’, ‘cud1’, ‘cuu1’, ‘cuu’, ‘vpa’ are disabled; and the ‘home’
     string is set to the value of ‘cr’.  The effect is that the cursor
     is confined to the current line, and so are screen updates.  This
     may be used for enabling character-at-a-time line editing without
     touching the rest of the screen.

 -- Function: curses.flash ()

     Flash the screen.  That is, change it to reverse-video and then
     change it back in a short interval.  Some people prefer such as
     ‘visible bell’ to the audible attention signal produced by *note
     beep(): 22b2.

 -- Function: curses.flushinp ()

     Flush all input buffers.  This throws away any typeahead that has
     been typed by the user and has not yet been processed by the
     program.

 -- Function: curses.getmouse ()

     After *note getch(): 22cb. returns ‘KEY_MOUSE’ to signal a mouse
     event, this method should be called to retrieve the queued mouse
     event, represented as a 5-tuple ‘(id, x, y, z, bstate)’.  `id' is
     an ID value used to distinguish multiple devices, and `x', `y', `z'
     are the event’s coordinates.  (`z' is currently unused.)  `bstate'
     is an integer value whose bits will be set to indicate the type of
     event, and will be the bitwise OR of one or more of the following
     constants, where `n' is the button number from 1 to 4:
     ‘BUTTONn_PRESSED’, ‘BUTTONn_RELEASED’, ‘BUTTONn_CLICKED’,
     ‘BUTTONn_DOUBLE_CLICKED’, ‘BUTTONn_TRIPLE_CLICKED’, ‘BUTTON_SHIFT’,
     ‘BUTTON_CTRL’, ‘BUTTON_ALT’.

 -- Function: curses.getsyx ()

     Return the current coordinates of the virtual screen cursor as a
     tuple ‘(y, x)’.  If *note leaveok: 22cd. is currently ‘True’, then
     return ‘(-1, -1)’.

 -- Function: curses.getwin (file)

     Read window related data stored in the file by an earlier
     ‘putwin()’ call.  The routine then creates and initializes a new
     window using that data, returning the new window object.

 -- Function: curses.has_colors ()

     Return ‘True’ if the terminal can display colors; otherwise, return
     ‘False’.

 -- Function: curses.has_ic ()

     Return ‘True’ if the terminal has insert- and delete-character
     capabilities.  This function is included for historical reasons
     only, as all modern software terminal emulators have such
     capabilities.

 -- Function: curses.has_il ()

     Return ‘True’ if the terminal has insert- and delete-line
     capabilities, or can simulate them using scrolling regions.  This
     function is included for historical reasons only, as all modern
     software terminal emulators have such capabilities.

 -- Function: curses.has_key (ch)

     Take a key value `ch', and return ‘True’ if the current terminal
     type recognizes a key with that value.

 -- Function: curses.halfdelay (tenths)

     Used for half-delay mode, which is similar to cbreak mode in that
     characters typed by the user are immediately available to the
     program.  However, after blocking for `tenths' tenths of seconds,
     raise an exception if nothing has been typed.  The value of
     `tenths' must be a number between ‘1’ and ‘255’.  Use *note
     nocbreak(): 22d4. to leave half-delay mode.

 -- Function: curses.init_color (color_number, r, g, b)

     Change the definition of a color, taking the number of the color to
     be changed followed by three RGB values (for the amounts of red,
     green, and blue components).  The value of `color_number' must be
     between ‘0’ and ‘COLORS - 1’.  Each of `r', `g', `b', must be a
     value between ‘0’ and ‘1000’.  When *note init_color(): 22d5. is
     used, all occurrences of that color on the screen immediately
     change to the new definition.  This function is a no-op on most
     terminals; it is active only if *note can_change_color(): 22b3.
     returns ‘True’.

 -- Function: curses.init_pair (pair_number, fg, bg)

     Change the definition of a color-pair.  It takes three arguments:
     the number of the color-pair to be changed, the foreground color
     number, and the background color number.  The value of
     `pair_number' must be between ‘1’ and ‘COLOR_PAIRS - 1’ (the ‘0’
     color pair is wired to white on black and cannot be changed).  The
     value of `fg' and `bg' arguments must be between ‘0’ and ‘COLORS -
     1’, or, after calling *note use_default_colors(): 22d7, ‘-1’.  If
     the color-pair was previously initialized, the screen is refreshed
     and all occurrences of that color-pair are changed to the new
     definition.

 -- Function: curses.initscr ()

     Initialize the library.  Return a *note window: 22d8. object which
     represents the whole screen.

          Note: If there is an error opening the terminal, the
          underlying curses library may cause the interpreter to exit.

 -- Function: curses.is_term_resized (nlines, ncols)

     Return ‘True’ if *note resize_term(): 22da. would modify the window
     structure, ‘False’ otherwise.

 -- Function: curses.isendwin ()

     Return ‘True’ if *note endwin(): 22c4. has been called (that is,
     the curses library has been deinitialized).

 -- Function: curses.keyname (k)

     Return the name of the key numbered `k' as a bytes object.  The
     name of a key generating printable ASCII character is the key’s
     character.  The name of a control-key combination is a two-byte
     bytes object consisting of a caret (‘b'^'’) followed by the
     corresponding printable ASCII character.  The name of an alt-key
     combination (128–255) is a bytes object consisting of the prefix
     ‘b'M-'’ followed by the name of the corresponding ASCII character.

 -- Function: curses.killchar ()

     Return the user’s current line kill character as a one-byte bytes
     object.  Under Unix operating systems this is a property of the
     controlling tty of the curses program, and is not set by the curses
     library itself.

 -- Function: curses.longname ()

     Return a bytes object containing the terminfo long name field
     describing the current terminal.  The maximum length of a verbose
     description is 128 characters.  It is defined only after the call
     to *note initscr(): 22c7.

 -- Function: curses.meta (flag)

     If `flag' is ‘True’, allow 8-bit characters to be input.  If `flag'
     is ‘False’, allow only 7-bit chars.

 -- Function: curses.mouseinterval (interval)

     Set the maximum time in milliseconds that can elapse between press
     and release events in order for them to be recognized as a click,
     and return the previous interval value.  The default value is 200
     msec, or one fifth of a second.

 -- Function: curses.mousemask (mousemask)

     Set the mouse events to be reported, and return a tuple
     ‘(availmask, oldmask)’.  `availmask' indicates which of the
     specified mouse events can be reported; on complete failure it
     returns ‘0’.  `oldmask' is the previous value of the given window’s
     mouse event mask.  If this function is never called, no mouse
     events are ever reported.

 -- Function: curses.napms (ms)

     Sleep for `ms' milliseconds.

 -- Function: curses.newpad (nlines, ncols)

     Create and return a pointer to a new pad data structure with the
     given number of lines and columns.  Return a pad as a window
     object.

     A pad is like a window, except that it is not restricted by the
     screen size, and is not necessarily associated with a particular
     part of the screen.  Pads can be used when a large window is
     needed, and only a part of the window will be on the screen at one
     time.  Automatic refreshes of pads (such as from scrolling or
     echoing of input) do not occur.  The *note refresh(): 22c2. and
     *note noutrefresh(): 22c0. methods of a pad require 6 arguments to
     specify the part of the pad to be displayed and the location on the
     screen to be used for the display.  The arguments are `pminrow',
     `pmincol', `sminrow', `smincol', `smaxrow', `smaxcol'; the `p'
     arguments refer to the upper left corner of the pad region to be
     displayed and the `s' arguments define a clipping box on the screen
     within which the pad region is to be displayed.

 -- Function: curses.newwin (nlines, ncols)

 -- Function: curses.newwin (nlines, ncols, begin_y, begin_x)

     Return a new *note window: 22d8, whose left-upper corner is at
     ‘(begin_y, begin_x)’, and whose height/width is `nlines'/`ncols'.

     By default, the window will extend from the specified position to
     the lower right corner of the screen.

 -- Function: curses.nl ()

     Enter newline mode.  This mode translates the return key into
     newline on input, and translates newline into return and line-feed
     on output.  Newline mode is initially on.

 -- Function: curses.nocbreak ()

     Leave cbreak mode.  Return to normal “cooked” mode with line
     buffering.

 -- Function: curses.noecho ()

     Leave echo mode.  Echoing of input characters is turned off.

 -- Function: curses.nonl ()

     Leave newline mode.  Disable translation of return into newline on
     input, and disable low-level translation of newline into
     newline/return on output (but this does not change the behavior of
     ‘addch('\n')’, which always does the equivalent of return and line
     feed on the virtual screen).  With translation off, curses can
     sometimes speed up vertical motion a little; also, it will be able
     to detect the return key on input.

 -- Function: curses.noqiflush ()

     When the ‘noqiflush()’ routine is used, normal flush of input and
     output queues associated with the ‘INTR’, ‘QUIT’ and ‘SUSP’
     characters will not be done.  You may want to call ‘noqiflush()’ in
     a signal handler if you want output to continue as though the
     interrupt had not occurred, after the handler exits.

 -- Function: curses.noraw ()

     Leave raw mode.  Return to normal “cooked” mode with line
     buffering.

 -- Function: curses.pair_content (pair_number)

     Return a tuple ‘(fg, bg)’ containing the colors for the requested
     color pair.  The value of `pair_number' must be between ‘0’ and
     ‘COLOR_PAIRS - 1’.

 -- Function: curses.pair_number (attr)

     Return the number of the color-pair set by the attribute value
     `attr'.  *note color_pair(): 22b7. is the counterpart to this
     function.

 -- Function: curses.putp (str)

     Equivalent to ‘tputs(str, 1, putchar)’; emit the value of a
     specified terminfo capability for the current terminal.  Note that
     the output of *note putp(): 22eb. always goes to standard output.

 -- Function: curses.qiflush ([flag])

     If `flag' is ‘False’, the effect is the same as calling *note
     noqiflush(): 22e8.  If `flag' is ‘True’, or no argument is
     provided, the queues will be flushed when these control characters
     are read.

 -- Function: curses.raw ()

     Enter raw mode.  In raw mode, normal line buffering and processing
     of interrupt, quit, suspend, and flow control keys are turned off;
     characters are presented to curses input functions one by one.

 -- Function: curses.reset_prog_mode ()

     Restore the terminal to “program” mode, as previously saved by
     *note def_prog_mode(): 22ba.

 -- Function: curses.reset_shell_mode ()

     Restore the terminal to “shell” mode, as previously saved by *note
     def_shell_mode(): 22bc.

 -- Function: curses.resetty ()

     Restore the state of the terminal modes to what it was at the last
     call to *note savetty(): 22ee.

 -- Function: curses.resize_term (nlines, ncols)

     Backend function used by *note resizeterm(): 22ef, performing most
     of the work; when resizing the windows, *note resize_term(): 22da.
     blank-fills the areas that are extended.  The calling application
     should fill in these areas with appropriate data.  The
     ‘resize_term()’ function attempts to resize all windows.  However,
     due to the calling convention of pads, it is not possible to resize
     these without additional interaction with the application.

 -- Function: curses.resizeterm (nlines, ncols)

     Resize the standard and current windows to the specified
     dimensions, and adjusts other bookkeeping data used by the curses
     library that record the window dimensions (in particular the
     SIGWINCH handler).

 -- Function: curses.savetty ()

     Save the current state of the terminal modes in a buffer, usable by
     *note resetty(): 22ed.

 -- Function: curses.get_escdelay ()

     Retrieves the value set by *note set_escdelay(): 199.

     New in version 3.9.

 -- Function: curses.set_escdelay (ms)

     Sets the number of milliseconds to wait after reading an escape
     character, to distinguish between an individual escape character
     entered on the keyboard from escape sequences sent by cursor and
     function keys.

     New in version 3.9.

 -- Function: curses.get_tabsize ()

     Retrieves the value set by *note set_tabsize(): 19b.

     New in version 3.9.

 -- Function: curses.set_tabsize (size)

     Sets the number of columns used by the curses library when
     converting a tab character to spaces as it adds the tab to a
     window.

     New in version 3.9.

 -- Function: curses.setsyx (y, x)

     Set the virtual screen cursor to `y', `x'.  If `y' and `x' are both
     ‘-1’, then *note leaveok: 22cd. is set ‘True’.

 -- Function: curses.setupterm (term=None, fd=-1)

     Initialize the terminal.  `term' is a string giving the terminal
     name, or ‘None’; if omitted or ‘None’, the value of the ‘TERM’
     environment variable will be used.  `fd' is the file descriptor to
     which any initialization sequences will be sent; if not supplied or
     ‘-1’, the file descriptor for ‘sys.stdout’ will be used.

 -- Function: curses.start_color ()

     Must be called if the programmer wants to use colors, and before
     any other color manipulation routine is called.  It is good
     practice to call this routine right after *note initscr(): 22c7.

     *note start_color(): 22f2. initializes eight basic colors (black,
     red, green, yellow, blue, magenta, cyan, and white), and two global
     variables in the *note curses: 2b. module, ‘COLORS’ and
     ‘COLOR_PAIRS’, containing the maximum number of colors and
     color-pairs the terminal can support.  It also restores the colors
     on the terminal to the values they had when the terminal was just
     turned on.

 -- Function: curses.termattrs ()

     Return a logical OR of all video attributes supported by the
     terminal.  This information is useful when a curses program needs
     complete control over the appearance of the screen.

 -- Function: curses.termname ()

     Return the value of the environment variable ‘TERM’, as a bytes
     object, truncated to 14 characters.

 -- Function: curses.tigetflag (capname)

     Return the value of the Boolean capability corresponding to the
     terminfo capability name `capname' as an integer.  Return the value
     ‘-1’ if `capname' is not a Boolean capability, or ‘0’ if it is
     canceled or absent from the terminal description.

 -- Function: curses.tigetnum (capname)

     Return the value of the numeric capability corresponding to the
     terminfo capability name `capname' as an integer.  Return the value
     ‘-2’ if `capname' is not a numeric capability, or ‘-1’ if it is
     canceled or absent from the terminal description.

 -- Function: curses.tigetstr (capname)

     Return the value of the string capability corresponding to the
     terminfo capability name `capname' as a bytes object.  Return
     ‘None’ if `capname' is not a terminfo “string capability”, or is
     canceled or absent from the terminal description.

 -- Function: curses.tparm (str[, ...])

     Instantiate the bytes object `str' with the supplied parameters,
     where `str' should be a parameterized string obtained from the
     terminfo database.  E.g.  ‘tparm(tigetstr("cup"), 5, 3)’ could
     result in ‘b'\033[6;4H'’, the exact result depending on terminal
     type.

 -- Function: curses.typeahead (fd)

     Specify that the file descriptor `fd' be used for typeahead
     checking.  If `fd' is ‘-1’, then no typeahead checking is done.

     The curses library does “line-breakout optimization” by looking for
     typeahead periodically while updating the screen.  If input is
     found, and it is coming from a tty, the current update is postponed
     until refresh or doupdate is called again, allowing faster response
     to commands typed in advance.  This function allows specifying a
     different file descriptor for typeahead checking.

 -- Function: curses.unctrl (ch)

     Return a bytes object which is a printable representation of the
     character `ch'.  Control characters are represented as a caret
     followed by the character, for example as ‘b'^C'’.  Printing
     characters are left as they are.

 -- Function: curses.ungetch (ch)

     Push `ch' so the next *note getch(): 22cb. will return it.

          Note: Only one `ch' can be pushed before ‘getch()’ is called.

 -- Function: curses.update_lines_cols ()

     Update ‘LINES’ and ‘COLS’.  Useful for detecting manual screen
     resize.

     New in version 3.5.

 -- Function: curses.unget_wch (ch)

     Push `ch' so the next *note get_wch(): abe. will return it.

          Note: Only one `ch' can be pushed before ‘get_wch()’ is
          called.

     New in version 3.3.

 -- Function: curses.ungetmouse (id, x, y, z, bstate)

     Push a ‘KEY_MOUSE’ event onto the input queue, associating the
     given state data with it.

 -- Function: curses.use_env (flag)

     If used, this function should be called before *note initscr():
     22c7. or newterm are called.  When `flag' is ‘False’, the values of
     lines and columns specified in the terminfo database will be used,
     even if environment variables ‘LINES’ and ‘COLUMNS’ (used by
     default) are set, or if curses is running in a window (in which
     case default behavior would be to use the window size if ‘LINES’
     and ‘COLUMNS’ are not set).

 -- Function: curses.use_default_colors ()

     Allow use of default values for colors on terminals supporting this
     feature.  Use this to support transparency in your application.
     The default color is assigned to the color number ‘-1’.  After
     calling this function, ‘init_pair(x, curses.COLOR_RED, -1)’
     initializes, for instance, color pair `x' to a red foreground color
     on the default background.

 -- Function: curses.wrapper (func, /, *args, **kwargs)

     Initialize curses and call another callable object, `func', which
     should be the rest of your curses-using application.  If the
     application raises an exception, this function will restore the
     terminal to a sane state before re-raising the exception and
     generating a traceback.  The callable object `func' is then passed
     the main window ‘stdscr’ as its first argument, followed by any
     other arguments passed to ‘wrapper()’.  Before calling `func',
     ‘wrapper()’ turns on cbreak mode, turns off echo, enables the
     terminal keypad, and initializes colors if the terminal has color
     support.  On exit (whether normally or by exception) it restores
     cooked mode, turns on echo, and disables the terminal keypad.


File: python.info,  Node: Window Objects,  Next: Constants<6>,  Prev: Functions<4>,  Up: curses — Terminal handling for character-cell displays

5.16.10.2 Window Objects
........................

Window objects, as returned by *note initscr(): 22c7. and *note
newwin(): 22e4. above, have the following methods and attributes:

 -- Method: window.addch (ch[, attr])

 -- Method: window.addch (y, x, ch[, attr])

     Paint character `ch' at ‘(y, x)’ with attributes `attr',
     overwriting any character previously painted at that location.  By
     default, the character position and attributes are the current
     settings for the window object.

          Note: Writing outside the window, subwindow, or pad raises a
          *note curses.error: 22b0.  Attempting to write to the lower
          right corner of a window, subwindow, or pad will cause an
          exception to be raised after the character is printed.

 -- Method: window.addnstr (str, n[, attr])

 -- Method: window.addnstr (y, x, str, n[, attr])

     Paint at most `n' characters of the character string `str' at ‘(y,
     x)’ with attributes `attr', overwriting anything previously on the
     display.

 -- Method: window.addstr (str[, attr])

 -- Method: window.addstr (y, x, str[, attr])

     Paint the character string `str' at ‘(y, x)’ with attributes
     `attr', overwriting anything previously on the display.

          Note: 
             * Writing outside the window, subwindow, or pad raises
               *note curses.error: 22b0.  Attempting to write to the
               lower right corner of a window, subwindow, or pad will
               cause an exception to be raised after the string is
               printed.

             * A bug in ncurses(1), the backend for this Python module,
               can cause SegFaults when resizing windows.  This is fixed
               in ncurses-6.1-20190511.  If you are stuck with an
               earlier ncurses, you can avoid triggering this if you do
               not call *note addstr(): 22c1. with a `str' that has
               embedded newlines.  Instead, call *note addstr(): 22c1.
               separately for each line.

 -- Method: window.attroff (attr)

     Remove attribute `attr' from the “background” set applied to all
     writes to the current window.

 -- Method: window.attron (attr)

     Add attribute `attr' from the “background” set applied to all
     writes to the current window.

 -- Method: window.attrset (attr)

     Set the “background” set of attributes to `attr'.  This set is
     initially ‘0’ (no attributes).

 -- Method: window.bkgd (ch[, attr])

     Set the background property of the window to the character `ch',
     with attributes `attr'.  The change is then applied to every
     character position in that window:

        * The attribute of every character in the window is changed to
          the new background attribute.

        * Wherever the former background character appears, it is
          changed to the new background character.

 -- Method: window.bkgdset (ch[, attr])

     Set the window’s background.  A window’s background consists of a
     character and any combination of attributes.  The attribute part of
     the background is combined (OR’ed) with all non-blank characters
     that are written into the window.  Both the character and attribute
     parts of the background are combined with the blank characters.
     The background becomes a property of the character and moves with
     the character through any scrolling and insert/delete
     line/character operations.

 -- Method: window.border ([ls[, rs[, ts[, bs[, tl[, tr[, bl[,
          br]]]]]]]])

     Draw a border around the edges of the window.  Each parameter
     specifies the character to use for a specific part of the border;
     see the table below for more details.

          Note: A ‘0’ value for any parameter will cause the default
          character to be used for that parameter.  Keyword parameters
          can `not' be used.  The defaults are listed in this table:

     Parameter       Description               Default value
                                               
     ----------------------------------------------------------------------
                                               
     `ls'            Left side                 ‘ACS_VLINE’
                                               
                                               
     `rs'            Right side                ‘ACS_VLINE’
                                               
                                               
     `ts'            Top                       ‘ACS_HLINE’
                                               
                                               
     `bs'            Bottom                    ‘ACS_HLINE’
                                               
                                               
     `tl'            Upper-left corner         ‘ACS_ULCORNER’
                                               
                                               
     `tr'            Upper-right corner        ‘ACS_URCORNER’
                                               
                                               
     `bl'            Bottom-left corner        ‘ACS_LLCORNER’
                                               
                                               
     `br'            Bottom-right corner       ‘ACS_LRCORNER’
                                               

 -- Method: window.box ([vertch, horch])

     Similar to *note border(): 2306, but both `ls' and `rs' are
     `vertch' and both `ts' and `bs' are `horch'.  The default corner
     characters are always used by this function.

 -- Method: window.chgat (attr)

 -- Method: window.chgat (num, attr)

 -- Method: window.chgat (y, x, attr)

 -- Method: window.chgat (y, x, num, attr)

     Set the attributes of `num' characters at the current cursor
     position, or at position ‘(y, x)’ if supplied.  If `num' is not
     given or is ‘-1’, the attribute will be set on all the characters
     to the end of the line.  This function moves cursor to position
     ‘(y, x)’ if supplied.  The changed line will be touched using the
     *note touchline(): 2309. method so that the contents will be
     redisplayed by the next window refresh.

 -- Method: window.clear ()

     Like *note erase(): 230b, but also cause the whole window to be
     repainted upon next call to *note refresh(): 22c2.

 -- Method: window.clearok (flag)

     If `flag' is ‘True’, the next call to *note refresh(): 22c2. will
     clear the window completely.

 -- Method: window.clrtobot ()

     Erase from cursor to the end of the window: all lines below the
     cursor are deleted, and then the equivalent of *note clrtoeol():
     230e. is performed.

 -- Method: window.clrtoeol ()

     Erase from cursor to the end of the line.

 -- Method: window.cursyncup ()

     Update the current cursor position of all the ancestors of the
     window to reflect the current cursor position of the window.

 -- Method: window.delch ([y, x])

     Delete any character at ‘(y, x)’.

 -- Method: window.deleteln ()

     Delete the line under the cursor.  All following lines are moved up
     by one line.

 -- Method: window.derwin (begin_y, begin_x)

 -- Method: window.derwin (nlines, ncols, begin_y, begin_x)

     An abbreviation for “derive window”, *note derwin(): 2312. is the
     same as calling *note subwin(): 2313, except that `begin_y' and
     `begin_x' are relative to the origin of the window, rather than
     relative to the entire screen.  Return a window object for the
     derived window.

 -- Method: window.echochar (ch[, attr])

     Add character `ch' with attribute `attr', and immediately call
     *note refresh(): 22c2. on the window.

 -- Method: window.enclose (y, x)

     Test whether the given pair of screen-relative character-cell
     coordinates are enclosed by the given window, returning ‘True’ or
     ‘False’.  It is useful for determining what subset of the screen
     windows enclose the location of a mouse event.

 -- Attribute: window.encoding

     Encoding used to encode method arguments (Unicode strings and
     characters).  The encoding attribute is inherited from the parent
     window when a subwindow is created, for example with *note
     window.subwin(): 2313.  By default, the locale encoding is used
     (see *note locale.getpreferredencoding(): 4ac.).

     New in version 3.3.

 -- Method: window.erase ()

     Clear the window.

 -- Method: window.getbegyx ()

     Return a tuple ‘(y, x)’ of co-ordinates of upper-left corner.

 -- Method: window.getbkgd ()

     Return the given window’s current background character/attribute
     pair.

 -- Method: window.getch ([y, x])

     Get a character.  Note that the integer returned does `not' have to
     be in ASCII range: function keys, keypad keys and so on are
     represented by numbers higher than 255.  In no-delay mode, return
     ‘-1’ if there is no input, otherwise wait until a key is pressed.

 -- Method: window.get_wch ([y, x])

     Get a wide character.  Return a character for most keys, or an
     integer for function keys, keypad keys, and other special keys.  In
     no-delay mode, raise an exception if there is no input.

     New in version 3.3.

 -- Method: window.getkey ([y, x])

     Get a character, returning a string instead of an integer, as *note
     getch(): 22cb. does.  Function keys, keypad keys and other special
     keys return a multibyte string containing the key name.  In
     no-delay mode, raise an exception if there is no input.

 -- Method: window.getmaxyx ()

     Return a tuple ‘(y, x)’ of the height and width of the window.

 -- Method: window.getparyx ()

     Return the beginning coordinates of this window relative to its
     parent window as a tuple ‘(y, x)’.  Return ‘(-1, -1)’ if this
     window has no parent.

 -- Method: window.getstr ()

 -- Method: window.getstr (n)

 -- Method: window.getstr (y, x)

 -- Method: window.getstr (y, x, n)

     Read a bytes object from the user, with primitive line editing
     capacity.

 -- Method: window.getyx ()

     Return a tuple ‘(y, x)’ of current cursor position relative to the
     window’s upper-left corner.

 -- Method: window.hline (ch, n)

 -- Method: window.hline (y, x, ch, n)

     Display a horizontal line starting at ‘(y, x)’ with length `n'
     consisting of the character `ch'.

 -- Method: window.idcok (flag)

     If `flag' is ‘False’, curses no longer considers using the hardware
     insert/delete character feature of the terminal; if `flag' is
     ‘True’, use of character insertion and deletion is enabled.  When
     curses is first initialized, use of character insert/delete is
     enabled by default.

 -- Method: window.idlok (flag)

     If `flag' is ‘True’, *note curses: 2b. will try and use hardware
     line editing facilities.  Otherwise, line insertion/deletion are
     disabled.

 -- Method: window.immedok (flag)

     If `flag' is ‘True’, any change in the window image automatically
     causes the window to be refreshed; you no longer have to call *note
     refresh(): 22c2. yourself.  However, it may degrade performance
     considerably, due to repeated calls to wrefresh.  This option is
     disabled by default.

 -- Method: window.inch ([y, x])

     Return the character at the given position in the window.  The
     bottom 8 bits are the character proper, and upper bits are the
     attributes.

 -- Method: window.insch (ch[, attr])

 -- Method: window.insch (y, x, ch[, attr])

     Paint character `ch' at ‘(y, x)’ with attributes `attr', moving the
     line from position `x' right by one character.

 -- Method: window.insdelln (nlines)

     Insert `nlines' lines into the specified window above the current
     line.  The `nlines' bottom lines are lost.  For negative `nlines',
     delete `nlines' lines starting with the one under the cursor, and
     move the remaining lines up.  The bottom `nlines' lines are
     cleared.  The current cursor position remains the same.

 -- Method: window.insertln ()

     Insert a blank line under the cursor.  All following lines are
     moved down by one line.

 -- Method: window.insnstr (str, n[, attr])

 -- Method: window.insnstr (y, x, str, n[, attr])

     Insert a character string (as many characters as will fit on the
     line) before the character under the cursor, up to `n' characters.
     If `n' is zero or negative, the entire string is inserted.  All
     characters to the right of the cursor are shifted right, with the
     rightmost characters on the line being lost.  The cursor position
     does not change (after moving to `y', `x', if specified).

 -- Method: window.insstr (str[, attr])

 -- Method: window.insstr (y, x, str[, attr])

     Insert a character string (as many characters as will fit on the
     line) before the character under the cursor.  All characters to the
     right of the cursor are shifted right, with the rightmost
     characters on the line being lost.  The cursor position does not
     change (after moving to `y', `x', if specified).

 -- Method: window.instr ([n])

 -- Method: window.instr (y, x[, n])

     Return a bytes object of characters, extracted from the window
     starting at the current cursor position, or at `y', `x' if
     specified.  Attributes are stripped from the characters.  If `n' is
     specified, *note instr(): 2327. returns a string at most `n'
     characters long (exclusive of the trailing NUL).

 -- Method: window.is_linetouched (line)

     Return ‘True’ if the specified line was modified since the last
     call to *note refresh(): 22c2.; otherwise return ‘False’.  Raise a
     *note curses.error: 22b0. exception if `line' is not valid for the
     given window.

 -- Method: window.is_wintouched ()

     Return ‘True’ if the specified window was modified since the last
     call to *note refresh(): 22c2.; otherwise return ‘False’.

 -- Method: window.keypad (flag)

     If `flag' is ‘True’, escape sequences generated by some keys
     (keypad, function keys) will be interpreted by *note curses: 2b.
     If `flag' is ‘False’, escape sequences will be left as is in the
     input stream.

 -- Method: window.leaveok (flag)

     If `flag' is ‘True’, cursor is left where it is on update, instead
     of being at “cursor position.” This reduces cursor movement where
     possible.  If possible the cursor will be made invisible.

     If `flag' is ‘False’, cursor will always be at “cursor position”
     after an update.

 -- Method: window.move (new_y, new_x)

     Move cursor to ‘(new_y, new_x)’.

 -- Method: window.mvderwin (y, x)

     Move the window inside its parent window.  The screen-relative
     parameters of the window are not changed.  This routine is used to
     display different parts of the parent window at the same physical
     position on the screen.

 -- Method: window.mvwin (new_y, new_x)

     Move the window so its upper-left corner is at ‘(new_y, new_x)’.

 -- Method: window.nodelay (flag)

     If `flag' is ‘True’, *note getch(): 22cb. will be non-blocking.

 -- Method: window.notimeout (flag)

     If `flag' is ‘True’, escape sequences will not be timed out.

     If `flag' is ‘False’, after a few milliseconds, an escape sequence
     will not be interpreted, and will be left in the input stream as
     is.

 -- Method: window.noutrefresh ()

     Mark for refresh but wait.  This function updates the data
     structure representing the desired state of the window, but does
     not force an update of the physical screen.  To accomplish that,
     call *note doupdate(): 22bf.

 -- Method: window.overlay (destwin[, sminrow, smincol, dminrow,
          dmincol, dmaxrow, dmaxcol])

     Overlay the window on top of `destwin'.  The windows need not be
     the same size, only the overlapping region is copied.  This copy is
     non-destructive, which means that the current background character
     does not overwrite the old contents of `destwin'.

     To get fine-grained control over the copied region, the second form
     of *note overlay(): 2330. can be used.  `sminrow' and `smincol' are
     the upper-left coordinates of the source window, and the other
     variables mark a rectangle in the destination window.

 -- Method: window.overwrite (destwin[, sminrow, smincol, dminrow,
          dmincol, dmaxrow, dmaxcol])

     Overwrite the window on top of `destwin'.  The windows need not be
     the same size, in which case only the overlapping region is copied.
     This copy is destructive, which means that the current background
     character overwrites the old contents of `destwin'.

     To get fine-grained control over the copied region, the second form
     of *note overwrite(): 2331. can be used.  `sminrow' and `smincol'
     are the upper-left coordinates of the source window, the other
     variables mark a rectangle in the destination window.

 -- Method: window.putwin (file)

     Write all data associated with the window into the provided file
     object.  This information can be later retrieved using the *note
     getwin(): 22ce. function.

 -- Method: window.redrawln (beg, num)

     Indicate that the `num' screen lines, starting at line `beg', are
     corrupted and should be completely redrawn on the next *note
     refresh(): 22c2. call.

 -- Method: window.redrawwin ()

     Touch the entire window, causing it to be completely redrawn on the
     next *note refresh(): 22c2. call.

 -- Method: window.refresh ([pminrow, pmincol, sminrow, smincol,
          smaxrow, smaxcol])

     Update the display immediately (sync actual screen with previous
     drawing/deleting methods).

     The 6 optional arguments can only be specified when the window is a
     pad created with *note newpad(): 22e3.  The additional parameters
     are needed to indicate what part of the pad and screen are
     involved.  `pminrow' and `pmincol' specify the upper left-hand
     corner of the rectangle to be displayed in the pad.  `sminrow',
     `smincol', `smaxrow', and `smaxcol' specify the edges of the
     rectangle to be displayed on the screen.  The lower right-hand
     corner of the rectangle to be displayed in the pad is calculated
     from the screen coordinates, since the rectangles must be the same
     size.  Both rectangles must be entirely contained within their
     respective structures.  Negative values of `pminrow', `pmincol',
     `sminrow', or `smincol' are treated as if they were zero.

 -- Method: window.resize (nlines, ncols)

     Reallocate storage for a curses window to adjust its dimensions to
     the specified values.  If either dimension is larger than the
     current values, the window’s data is filled with blanks that have
     the current background rendition (as set by *note bkgdset(): 2305.)
     merged into them.

 -- Method: window.scroll ([lines=1])

     Scroll the screen or scrolling region upward by `lines' lines.

 -- Method: window.scrollok (flag)

     Control what happens when the cursor of a window is moved off the
     edge of the window or scrolling region, either as a result of a
     newline action on the bottom line, or typing the last character of
     the last line.  If `flag' is ‘False’, the cursor is left on the
     bottom line.  If `flag' is ‘True’, the window is scrolled up one
     line.  Note that in order to get the physical scrolling effect on
     the terminal, it is also necessary to call *note idlok(): 231f.

 -- Method: window.setscrreg (top, bottom)

     Set the scrolling region from line `top' to line `bottom'.  All
     scrolling actions will take place in this region.

 -- Method: window.standend ()

     Turn off the standout attribute.  On some terminals this has the
     side effect of turning off all attributes.

 -- Method: window.standout ()

     Turn on attribute `A_STANDOUT'.

 -- Method: window.subpad (begin_y, begin_x)

 -- Method: window.subpad (nlines, ncols, begin_y, begin_x)

     Return a sub-window, whose upper-left corner is at ‘(begin_y,
     begin_x)’, and whose width/height is `ncols'/`nlines'.

 -- Method: window.subwin (begin_y, begin_x)

 -- Method: window.subwin (nlines, ncols, begin_y, begin_x)

     Return a sub-window, whose upper-left corner is at ‘(begin_y,
     begin_x)’, and whose width/height is `ncols'/`nlines'.

     By default, the sub-window will extend from the specified position
     to the lower right corner of the window.

 -- Method: window.syncdown ()

     Touch each location in the window that has been touched in any of
     its ancestor windows.  This routine is called by *note refresh():
     22c2, so it should almost never be necessary to call it manually.

 -- Method: window.syncok (flag)

     If `flag' is ‘True’, then *note syncup(): 233e. is called
     automatically whenever there is a change in the window.

 -- Method: window.syncup ()

     Touch all locations in ancestors of the window that have been
     changed in the window.

 -- Method: window.timeout (delay)

     Set blocking or non-blocking read behavior for the window.  If
     `delay' is negative, blocking read is used (which will wait
     indefinitely for input).  If `delay' is zero, then non-blocking
     read is used, and *note getch(): 22cb. will return ‘-1’ if no input
     is waiting.  If `delay' is positive, then *note getch(): 22cb. will
     block for `delay' milliseconds, and return ‘-1’ if there is still
     no input at the end of that time.

 -- Method: window.touchline (start, count[, changed])

     Pretend `count' lines have been changed, starting with line
     `start'.  If `changed' is supplied, it specifies whether the
     affected lines are marked as having been changed (`changed'‘=True’)
     or unchanged (`changed'‘=False’).

 -- Method: window.touchwin ()

     Pretend the whole window has been changed, for purposes of drawing
     optimizations.

 -- Method: window.untouchwin ()

     Mark all lines in the window as unchanged since the last call to
     *note refresh(): 22c2.

 -- Method: window.vline (ch, n)

 -- Method: window.vline (y, x, ch, n)

     Display a vertical line starting at ‘(y, x)’ with length `n'
     consisting of the character `ch'.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue35924


File: python.info,  Node: Constants<6>,  Prev: Window Objects,  Up: curses — Terminal handling for character-cell displays

5.16.10.3 Constants
...................

The *note curses: 2b. module defines the following data members:

 -- Data: curses.ERR

     Some curses routines that return an integer, such as *note getch():
     22cb, return *note ERR: 2344. upon failure.

 -- Data: curses.OK

     Some curses routines that return an integer, such as *note napms():
     22e2, return *note OK: 2345. upon success.

 -- Data: curses.version

     A bytes object representing the current version of the module.
     Also available as ‘__version__’.

 -- Data: curses.ncurses_version

     A named tuple containing the three components of the ncurses
     library version: `major', `minor', and `patch'.  All values are
     integers.  The components can also be accessed by name, so
     ‘curses.ncurses_version[0]’ is equivalent to
     ‘curses.ncurses_version.major’ and so on.

     Availability: if the ncurses library is used.

     New in version 3.8.

Some constants are available to specify character cell attributes.  The
exact constants available are system dependent.

Attribute              Meaning
                       
-----------------------------------------------------------
                       
‘A_ALTCHARSET’         Alternate character set mode
                       
                       
‘A_BLINK’              Blink mode
                       
                       
‘A_BOLD’               Bold mode
                       
                       
‘A_DIM’                Dim mode
                       
                       
‘A_INVIS’              Invisible or blank mode
                       
                       
‘A_ITALIC’             Italic mode
                       
                       
‘A_NORMAL’             Normal attribute
                       
                       
‘A_PROTECT’            Protected mode
                       
                       
‘A_REVERSE’            Reverse background and foreground
                       colors
                       
                       
‘A_STANDOUT’           Standout mode
                       
                       
‘A_UNDERLINE’          Underline mode
                       
                       
‘A_HORIZONTAL’         Horizontal highlight
                       
                       
‘A_LEFT’               Left highlight
                       
                       
‘A_LOW’                Low highlight
                       
                       
‘A_RIGHT’              Right highlight
                       
                       
‘A_TOP’                Top highlight
                       
                       
‘A_VERTICAL’           Vertical highlight
                       
                       
‘A_CHARTEXT’           Bit-mask to extract a character
                       

New in version 3.7: ‘A_ITALIC’ was added.

Several constants are available to extract corresponding attributes
returned by some methods.

Bit-mask               Meaning
                       
-----------------------------------------------------------
                       
‘A_ATTRIBUTES’         Bit-mask to extract attributes
                       
                       
‘A_CHARTEXT’           Bit-mask to extract a character
                       
                       
‘A_COLOR’              Bit-mask to extract color-pair
                       field information
                       

Keys are referred to by integer constants with names starting with
‘KEY_’.  The exact keycaps available are system dependent.

Key constant            Key
                        
-------------------------------------------------------------------------
                        
‘KEY_MIN’               Minimum key value
                        
                        
‘KEY_BREAK’             Break key (unreliable)
                        
                        
‘KEY_DOWN’              Down-arrow
                        
                        
‘KEY_UP’                Up-arrow
                        
                        
‘KEY_LEFT’              Left-arrow
                        
                        
‘KEY_RIGHT’             Right-arrow
                        
                        
‘KEY_HOME’              Home key (upward+left arrow)
                        
                        
‘KEY_BACKSPACE’         Backspace (unreliable)
                        
                        
‘KEY_F0’                Function keys.  Up to 64 function keys are
                        supported.
                        
                        
‘KEY_Fn’                Value of function key `n'
                        
                        
‘KEY_DL’                Delete line
                        
                        
‘KEY_IL’                Insert line
                        
                        
‘KEY_DC’                Delete character
                        
                        
‘KEY_IC’                Insert char or enter insert mode
                        
                        
‘KEY_EIC’               Exit insert char mode
                        
                        
‘KEY_CLEAR’             Clear screen
                        
                        
‘KEY_EOS’               Clear to end of screen
                        
                        
‘KEY_EOL’               Clear to end of line
                        
                        
‘KEY_SF’                Scroll 1 line forward
                        
                        
‘KEY_SR’                Scroll 1 line backward (reverse)
                        
                        
‘KEY_NPAGE’             Next page
                        
                        
‘KEY_PPAGE’             Previous page
                        
                        
‘KEY_STAB’              Set tab
                        
                        
‘KEY_CTAB’              Clear tab
                        
                        
‘KEY_CATAB’             Clear all tabs
                        
                        
‘KEY_ENTER’             Enter or send (unreliable)
                        
                        
‘KEY_SRESET’            Soft (partial) reset (unreliable)
                        
                        
‘KEY_RESET’             Reset or hard reset (unreliable)
                        
                        
‘KEY_PRINT’             Print
                        
                        
‘KEY_LL’                Home down or bottom (lower left)
                        
                        
‘KEY_A1’                Upper left of keypad
                        
                        
‘KEY_A3’                Upper right of keypad
                        
                        
‘KEY_B2’                Center of keypad
                        
                        
‘KEY_C1’                Lower left of keypad
                        
                        
‘KEY_C3’                Lower right of keypad
                        
                        
‘KEY_BTAB’              Back tab
                        
                        
‘KEY_BEG’               Beg (beginning)
                        
                        
‘KEY_CANCEL’            Cancel
                        
                        
‘KEY_CLOSE’             Close
                        
                        
‘KEY_COMMAND’           Cmd (command)
                        
                        
‘KEY_COPY’              Copy
                        
                        
‘KEY_CREATE’            Create
                        
                        
‘KEY_END’               End
                        
                        
‘KEY_EXIT’              Exit
                        
                        
‘KEY_FIND’              Find
                        
                        
‘KEY_HELP’              Help
                        
                        
‘KEY_MARK’              Mark
                        
                        
‘KEY_MESSAGE’           Message
                        
                        
‘KEY_MOVE’              Move
                        
                        
‘KEY_NEXT’              Next
                        
                        
‘KEY_OPEN’              Open
                        
                        
‘KEY_OPTIONS’           Options
                        
                        
‘KEY_PREVIOUS’          Prev (previous)
                        
                        
‘KEY_REDO’              Redo
                        
                        
‘KEY_REFERENCE’         Ref (reference)
                        
                        
‘KEY_REFRESH’           Refresh
                        
                        
‘KEY_REPLACE’           Replace
                        
                        
‘KEY_RESTART’           Restart
                        
                        
‘KEY_RESUME’            Resume
                        
                        
‘KEY_SAVE’              Save
                        
                        
‘KEY_SBEG’              Shifted Beg (beginning)
                        
                        
‘KEY_SCANCEL’           Shifted Cancel
                        
                        
‘KEY_SCOMMAND’          Shifted Command
                        
                        
‘KEY_SCOPY’             Shifted Copy
                        
                        
‘KEY_SCREATE’           Shifted Create
                        
                        
‘KEY_SDC’               Shifted Delete char
                        
                        
‘KEY_SDL’               Shifted Delete line
                        
                        
‘KEY_SELECT’            Select
                        
                        
‘KEY_SEND’              Shifted End
                        
                        
‘KEY_SEOL’              Shifted Clear line
                        
                        
‘KEY_SEXIT’             Shifted Exit
                        
                        
‘KEY_SFIND’             Shifted Find
                        
                        
‘KEY_SHELP’             Shifted Help
                        
                        
‘KEY_SHOME’             Shifted Home
                        
                        
‘KEY_SIC’               Shifted Input
                        
                        
‘KEY_SLEFT’             Shifted Left arrow
                        
                        
‘KEY_SMESSAGE’          Shifted Message
                        
                        
‘KEY_SMOVE’             Shifted Move
                        
                        
‘KEY_SNEXT’             Shifted Next
                        
                        
‘KEY_SOPTIONS’          Shifted Options
                        
                        
‘KEY_SPREVIOUS’         Shifted Prev
                        
                        
‘KEY_SPRINT’            Shifted Print
                        
                        
‘KEY_SREDO’             Shifted Redo
                        
                        
‘KEY_SREPLACE’          Shifted Replace
                        
                        
‘KEY_SRIGHT’            Shifted Right arrow
                        
                        
‘KEY_SRSUME’            Shifted Resume
                        
                        
‘KEY_SSAVE’             Shifted Save
                        
                        
‘KEY_SSUSPEND’          Shifted Suspend
                        
                        
‘KEY_SUNDO’             Shifted Undo
                        
                        
‘KEY_SUSPEND’           Suspend
                        
                        
‘KEY_UNDO’              Undo
                        
                        
‘KEY_MOUSE’             Mouse event has occurred
                        
                        
‘KEY_RESIZE’            Terminal resize event
                        
                        
‘KEY_MAX’               Maximum key value
                        

On VT100s and their software emulations, such as X terminal emulators,
there are normally at least four function keys (‘KEY_F1’, ‘KEY_F2’,
‘KEY_F3’, ‘KEY_F4’) available, and the arrow keys mapped to ‘KEY_UP’,
‘KEY_DOWN’, ‘KEY_LEFT’ and ‘KEY_RIGHT’ in the obvious way.  If your
machine has a PC keyboard, it is safe to expect arrow keys and twelve
function keys (older PC keyboards may have only ten function keys);
also, the following keypad mappings are standard:

Keycap                 Constant
                       
---------------------------------------
                       
‘Insert’               KEY_IC
                       
                       
‘Delete’               KEY_DC
                       
                       
‘Home’                 KEY_HOME
                       
                       
‘End’                  KEY_END
                       
                       
‘Page Up’              KEY_PPAGE
                       
                       
‘Page Down’            KEY_NPAGE
                       

The following table lists characters from the alternate character set.
These are inherited from the VT100 terminal, and will generally be
available on software emulations such as X terminals.  When there is no
graphic available, curses falls back on a crude printable ASCII
approximation.

     Note: These are available only after *note initscr(): 22c7. has
     been called.

ACS code               Meaning
                       
----------------------------------------------------------------------
                       
‘ACS_BBSS’             alternate name for upper right corner
                       
                       
‘ACS_BLOCK’            solid square block
                       
                       
‘ACS_BOARD’            board of squares
                       
                       
‘ACS_BSBS’             alternate name for horizontal line
                       
                       
‘ACS_BSSB’             alternate name for upper left corner
                       
                       
‘ACS_BSSS’             alternate name for top tee
                       
                       
‘ACS_BTEE’             bottom tee
                       
                       
‘ACS_BULLET’           bullet
                       
                       
‘ACS_CKBOARD’          checker board (stipple)
                       
                       
‘ACS_DARROW’           arrow pointing down
                       
                       
‘ACS_DEGREE’           degree symbol
                       
                       
‘ACS_DIAMOND’          diamond
                       
                       
‘ACS_GEQUAL’           greater-than-or-equal-to
                       
                       
‘ACS_HLINE’            horizontal line
                       
                       
‘ACS_LANTERN’          lantern symbol
                       
                       
‘ACS_LARROW’           left arrow
                       
                       
‘ACS_LEQUAL’           less-than-or-equal-to
                       
                       
‘ACS_LLCORNER’         lower left-hand corner
                       
                       
‘ACS_LRCORNER’         lower right-hand corner
                       
                       
‘ACS_LTEE’             left tee
                       
                       
‘ACS_NEQUAL’           not-equal sign
                       
                       
‘ACS_PI’               letter pi
                       
                       
‘ACS_PLMINUS’          plus-or-minus sign
                       
                       
‘ACS_PLUS’             big plus sign
                       
                       
‘ACS_RARROW’           right arrow
                       
                       
‘ACS_RTEE’             right tee
                       
                       
‘ACS_S1’               scan line 1
                       
                       
‘ACS_S3’               scan line 3
                       
                       
‘ACS_S7’               scan line 7
                       
                       
‘ACS_S9’               scan line 9
                       
                       
‘ACS_SBBS’             alternate name for lower right corner
                       
                       
‘ACS_SBSB’             alternate name for vertical line
                       
                       
‘ACS_SBSS’             alternate name for right tee
                       
                       
‘ACS_SSBB’             alternate name for lower left corner
                       
                       
‘ACS_SSBS’             alternate name for bottom tee
                       
                       
‘ACS_SSSB’             alternate name for left tee
                       
                       
‘ACS_SSSS’             alternate name for crossover or big plus
                       
                       
‘ACS_STERLING’         pound sterling
                       
                       
‘ACS_TTEE’             top tee
                       
                       
‘ACS_UARROW’           up arrow
                       
                       
‘ACS_ULCORNER’         upper left corner
                       
                       
‘ACS_URCORNER’         upper right corner
                       
                       
‘ACS_VLINE’            vertical line
                       

The following table lists the predefined colors:

Constant                Color
                        
---------------------------------------------------------
                        
‘COLOR_BLACK’           Black
                        
                        
‘COLOR_BLUE’            Blue
                        
                        
‘COLOR_CYAN’            Cyan (light greenish blue)
                        
                        
‘COLOR_GREEN’           Green
                        
                        
‘COLOR_MAGENTA’         Magenta (purplish red)
                        
                        
‘COLOR_RED’             Red
                        
                        
‘COLOR_WHITE’           White
                        
                        
‘COLOR_YELLOW’          Yellow
                        


File: python.info,  Node: curses textpad — Text input widget for curses programs,  Next: curses ascii — Utilities for ASCII characters,  Prev: curses — Terminal handling for character-cell displays,  Up: Generic Operating System Services

5.16.11 ‘curses.textpad’ — Text input widget for curses programs
----------------------------------------------------------------

The *note curses.textpad: 2e. module provides a *note Textbox: 2348.
class that handles elementary text editing in a curses window,
supporting a set of keybindings resembling those of Emacs (thus, also of
Netscape Navigator, BBedit 6.x, FrameMaker, and many other programs).
The module also provides a rectangle-drawing function useful for framing
text boxes or for other purposes.

The module *note curses.textpad: 2e. defines the following function:

 -- Function: curses.textpad.rectangle (win, uly, ulx, lry, lrx)

     Draw a rectangle.  The first argument must be a window object; the
     remaining arguments are coordinates relative to that window.  The
     second and third arguments are the y and x coordinates of the upper
     left hand corner of the rectangle to be drawn; the fourth and fifth
     arguments are the y and x coordinates of the lower right hand
     corner.  The rectangle will be drawn using VT100/IBM PC forms
     characters on terminals that make this possible (including xterm
     and most other software terminal emulators).  Otherwise it will be
     drawn with ASCII dashes, vertical bars, and plus signs.

* Menu:

* Textbox objects::


File: python.info,  Node: Textbox objects,  Up: curses textpad — Text input widget for curses programs

5.16.11.1 Textbox objects
.........................

You can instantiate a *note Textbox: 2348. object as follows:

 -- Class: curses.textpad.Textbox (win)

     Return a textbox widget object.  The `win' argument should be a
     curses *note window: 22d8. object in which the textbox is to be
     contained.  The edit cursor of the textbox is initially located at
     the upper left hand corner of the containing window, with
     coordinates ‘(0, 0)’.  The instance’s *note stripspaces: 234c. flag
     is initially on.

     *note Textbox: 2348. objects have the following methods:

      -- Method: edit ([validator])

          This is the entry point you will normally use.  It accepts
          editing keystrokes until one of the termination keystrokes is
          entered.  If `validator' is supplied, it must be a function.
          It will be called for each keystroke entered with the
          keystroke as a parameter; command dispatch is done on the
          result.  This method returns the window contents as a string;
          whether blanks in the window are included is affected by the
          *note stripspaces: 234c. attribute.

      -- Method: do_command (ch)

          Process a single command keystroke.  Here are the supported
          special keystrokes:

          Keystroke              Action
                                 
          -----------------------------------------------------------------------
                                 
          ‘Control-A’            Go to left edge of window.
                                 
                                 
          ‘Control-B’            Cursor left, wrapping to previous line if
                                 appropriate.
                                 
                                 
          ‘Control-D’            Delete character under cursor.
                                 
                                 
          ‘Control-E’            Go to right edge (stripspaces off) or end of
                                 line (stripspaces on).
                                 
                                 
          ‘Control-F’            Cursor right, wrapping to next line when
                                 appropriate.
                                 
                                 
          ‘Control-G’            Terminate, returning the window contents.
                                 
                                 
          ‘Control-H’            Delete character backward.
                                 
                                 
          ‘Control-J’            Terminate if the window is 1 line, otherwise
                                 insert newline.
                                 
                                 
          ‘Control-K’            If line is blank, delete it, otherwise clear
                                 to end of line.
                                 
                                 
          ‘Control-L’            Refresh screen.
                                 
                                 
          ‘Control-N’            Cursor down; move down one line.
                                 
                                 
          ‘Control-O’            Insert a blank line at cursor location.
                                 
                                 
          ‘Control-P’            Cursor up; move up one line.
                                 

          Move operations do nothing if the cursor is at an edge where
          the movement is not possible.  The following synonyms are
          supported where possible:

          Constant                     Keystroke
                                       
          ----------------------------------------------------
                                       
          ‘KEY_LEFT’                   ‘Control-B’
                                       
                                       
          ‘KEY_RIGHT’                  ‘Control-F’
                                       
                                       
          ‘KEY_UP’                     ‘Control-P’
                                       
                                       
          ‘KEY_DOWN’                   ‘Control-N’
                                       
                                       
          ‘KEY_BACKSPACE’              ‘Control-h’
                                       

          All other keystrokes are treated as a command to insert the
          given character and move right (with line wrapping).

      -- Method: gather ()

          Return the window contents as a string; whether blanks in the
          window are included is affected by the *note stripspaces:
          234c. member.

      -- Attribute: stripspaces

          This attribute is a flag which controls the interpretation of
          blanks in the window.  When it is on, trailing blanks on each
          line are ignored; any cursor motion that would land the cursor
          on a trailing blank goes to the end of that line instead, and
          trailing blanks are stripped when the window contents are
          gathered.


File: python.info,  Node: curses ascii — Utilities for ASCII characters,  Next: curses panel — A panel stack extension for curses,  Prev: curses textpad — Text input widget for curses programs,  Up: Generic Operating System Services

5.16.12 ‘curses.ascii’ — Utilities for ASCII characters
-------------------------------------------------------

__________________________________________________________________

The *note curses.ascii: 2c. module supplies name constants for ASCII
characters and functions to test membership in various ASCII character
classes.  The constants supplied are names for control characters as
follows:

Name               Meaning
                   
----------------------------------------------------------------------
                   
‘NUL’

‘SOH’              Start of heading, console interrupt
                   
                   
‘STX’              Start of text
                   
                   
‘ETX’              End of text
                   
                   
‘EOT’              End of transmission
                   
                   
‘ENQ’              Enquiry, goes with ‘ACK’ flow control
                   
                   
‘ACK’              Acknowledgement
                   
                   
‘BEL’              Bell
                   
                   
‘BS’               Backspace
                   
                   
‘TAB’              Tab
                   
                   
‘HT’               Alias for ‘TAB’: “Horizontal tab”
                   
                   
‘LF’               Line feed
                   
                   
‘NL’               Alias for ‘LF’: “New line”
                   
                   
‘VT’               Vertical tab
                   
                   
‘FF’               Form feed
                   
                   
‘CR’               Carriage return
                   
                   
‘SO’               Shift-out, begin alternate character set
                   
                   
‘SI’               Shift-in, resume default character set
                   
                   
‘DLE’              Data-link escape
                   
                   
‘DC1’              XON, for flow control
                   
                   
‘DC2’              Device control 2, block-mode flow control
                   
                   
‘DC3’              XOFF, for flow control
                   
                   
‘DC4’              Device control 4
                   
                   
‘NAK’              Negative acknowledgement
                   
                   
‘SYN’              Synchronous idle
                   
                   
‘ETB’              End transmission block
                   
                   
‘CAN’              Cancel
                   
                   
‘EM’               End of medium
                   
                   
‘SUB’              Substitute
                   
                   
‘ESC’              Escape
                   
                   
‘FS’               File separator
                   
                   
‘GS’               Group separator
                   
                   
‘RS’               Record separator, block-mode terminator
                   
                   
‘US’               Unit separator
                   
                   
‘SP’               Space
                   
                   
‘DEL’              Delete
                   

Note that many of these have little practical significance in modern
usage.  The mnemonics derive from teleprinter conventions that predate
digital computers.

The module supplies the following functions, patterned on those in the
standard C library:

 -- Function: curses.ascii.isalnum (c)

     Checks for an ASCII alphanumeric character; it is equivalent to
     ‘isalpha(c) or isdigit(c)’.

 -- Function: curses.ascii.isalpha (c)

     Checks for an ASCII alphabetic character; it is equivalent to
     ‘isupper(c) or islower(c)’.

 -- Function: curses.ascii.isascii (c)

     Checks for a character value that fits in the 7-bit ASCII set.

 -- Function: curses.ascii.isblank (c)

     Checks for an ASCII whitespace character; space or horizontal tab.

 -- Function: curses.ascii.iscntrl (c)

     Checks for an ASCII control character (in the range 0x00 to 0x1f or
     0x7f).

 -- Function: curses.ascii.isdigit (c)

     Checks for an ASCII decimal digit, ‘'0'’ through ‘'9'’.  This is
     equivalent to ‘c in string.digits’.

 -- Function: curses.ascii.isgraph (c)

     Checks for ASCII any printable character except space.

 -- Function: curses.ascii.islower (c)

     Checks for an ASCII lower-case character.

 -- Function: curses.ascii.isprint (c)

     Checks for any ASCII printable character including space.

 -- Function: curses.ascii.ispunct (c)

     Checks for any printable ASCII character which is not a space or an
     alphanumeric character.

 -- Function: curses.ascii.isspace (c)

     Checks for ASCII white-space characters; space, line feed, carriage
     return, form feed, horizontal tab, vertical tab.

 -- Function: curses.ascii.isupper (c)

     Checks for an ASCII uppercase letter.

 -- Function: curses.ascii.isxdigit (c)

     Checks for an ASCII hexadecimal digit.  This is equivalent to ‘c in
     string.hexdigits’.

 -- Function: curses.ascii.isctrl (c)

     Checks for an ASCII control character (ordinal values 0 to 31).

 -- Function: curses.ascii.ismeta (c)

     Checks for a non-ASCII character (ordinal values 0x80 and above).

These functions accept either integers or single-character strings; when
the argument is a string, it is first converted using the built-in
function *note ord(): 1559.

Note that all these functions check ordinal bit values derived from the
character of the string you pass in; they do not actually know anything
about the host machine’s character encoding.

The following two functions take either a single-character string or
integer byte value; they return a value of the same type.

 -- Function: curses.ascii.ascii (c)

     Return the ASCII value corresponding to the low 7 bits of `c'.

 -- Function: curses.ascii.ctrl (c)

     Return the control character corresponding to the given character
     (the character bit value is bitwise-anded with 0x1f).

 -- Function: curses.ascii.alt (c)

     Return the 8-bit character corresponding to the given ASCII
     character (the character bit value is bitwise-ored with 0x80).

The following function takes either a single-character string or integer
value; it returns a string.

 -- Function: curses.ascii.unctrl (c)

     Return a string representation of the ASCII character `c'.  If `c'
     is printable, this string is the character itself.  If the
     character is a control character (0x00–0x1f) the string consists of
     a caret (‘'^'’) followed by the corresponding uppercase letter.  If
     the character is an ASCII delete (0x7f) the string is ‘'^?'’.  If
     the character has its meta bit (0x80) set, the meta bit is
     stripped, the preceding rules applied, and ‘'!'’ prepended to the
     result.

 -- Data: curses.ascii.controlnames

     A 33-element string array that contains the ASCII mnemonics for the
     thirty-two ASCII control characters from 0 (NUL) to 0x1f (US), in
     order, plus the mnemonic ‘SP’ for the space character.


File: python.info,  Node: curses panel — A panel stack extension for curses,  Next: platform — Access to underlying platform’s identifying data,  Prev: curses ascii — Utilities for ASCII characters,  Up: Generic Operating System Services

5.16.13 ‘curses.panel’ — A panel stack extension for curses
-----------------------------------------------------------

__________________________________________________________________

Panels are windows with the added feature of depth, so they can be
stacked on top of each other, and only the visible portions of each
window will be displayed.  Panels can be added, moved up or down in the
stack, and removed.

* Menu:

* Functions: Functions<5>.
* Panel Objects::


File: python.info,  Node: Functions<5>,  Next: Panel Objects,  Up: curses panel — A panel stack extension for curses

5.16.13.1 Functions
...................

The module *note curses.panel: 2d. defines the following functions:

 -- Function: curses.panel.bottom_panel ()

     Returns the bottom panel in the panel stack.

 -- Function: curses.panel.new_panel (win)

     Returns a panel object, associating it with the given window `win'.
     Be aware that you need to keep the returned panel object referenced
     explicitly.  If you don’t, the panel object is garbage collected
     and removed from the panel stack.

 -- Function: curses.panel.top_panel ()

     Returns the top panel in the panel stack.

 -- Function: curses.panel.update_panels ()

     Updates the virtual screen after changes in the panel stack.  This
     does not call *note curses.doupdate(): 22bf, so you’ll have to do
     this yourself.


File: python.info,  Node: Panel Objects,  Prev: Functions<5>,  Up: curses panel — A panel stack extension for curses

5.16.13.2 Panel Objects
.......................

Panel objects, as returned by *note new_panel(): 236b. above, are
windows with a stacking order.  There’s always a window associated with
a panel which determines the content, while the panel methods are
responsible for the window’s depth in the panel stack.

Panel objects have the following methods:

 -- Method: Panel.above ()

     Returns the panel above the current panel.

 -- Method: Panel.below ()

     Returns the panel below the current panel.

 -- Method: Panel.bottom ()

     Push the panel to the bottom of the stack.

 -- Method: Panel.hidden ()

     Returns ‘True’ if the panel is hidden (not visible), ‘False’
     otherwise.

 -- Method: Panel.hide ()

     Hide the panel.  This does not delete the object, it just makes the
     window on screen invisible.

 -- Method: Panel.move (y, x)

     Move the panel to the screen coordinates ‘(y, x)’.

 -- Method: Panel.replace (win)

     Change the window associated with the panel to the window `win'.

 -- Method: Panel.set_userptr (obj)

     Set the panel’s user pointer to `obj'.  This is used to associate
     an arbitrary piece of data with the panel, and can be any Python
     object.

 -- Method: Panel.show ()

     Display the panel (which might have been hidden).

 -- Method: Panel.top ()

     Push panel to the top of the stack.

 -- Method: Panel.userptr ()

     Returns the user pointer for the panel.  This might be any Python
     object.

 -- Method: Panel.window ()

     Returns the window object associated with the panel.


File: python.info,  Node: platform — Access to underlying platform’s identifying data,  Next: errno — Standard errno system symbols,  Prev: curses panel — A panel stack extension for curses,  Up: Generic Operating System Services

5.16.14 ‘platform’ — Access to underlying platform’s identifying data
---------------------------------------------------------------------

`Source code:' Lib/platform.py(1)

__________________________________________________________________

     Note: Specific platforms listed alphabetically, with Linux included
     in the Unix section.

* Menu:

* Cross Platform::
* Java Platform::
* Windows Platform::
* macOS Platform::
* Unix Platforms::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/platform.py


File: python.info,  Node: Cross Platform,  Next: Java Platform,  Up: platform — Access to underlying platform’s identifying data

5.16.14.1 Cross Platform
........................

 -- Function: platform.architecture (executable=sys.executable, bits='',
          linkage='')

     Queries the given executable (defaults to the Python interpreter
     binary) for various architecture information.

     Returns a tuple ‘(bits, linkage)’ which contain information about
     the bit architecture and the linkage format used for the
     executable.  Both values are returned as strings.

     Values that cannot be determined are returned as given by the
     parameter presets.  If bits is given as ‘''’, the ‘sizeof(pointer)’
     (or ‘sizeof(long)’ on Python version < 1.5.2) is used as indicator
     for the supported pointer size.

     The function relies on the system’s ‘file’ command to do the actual
     work.  This is available on most if not all Unix platforms and some
     non-Unix platforms and then only if the executable points to the
     Python interpreter.  Reasonable defaults are used when the above
     needs are not met.

          Note: On macOS (and perhaps other platforms), executable files
          may be universal files containing multiple architectures.

          To get at the “64-bitness” of the current interpreter, it is
          more reliable to query the *note sys.maxsize: c15. attribute:

               is_64bits = sys.maxsize > 2**32

 -- Function: platform.machine ()

     Returns the machine type, e.g.  ‘'i386'’.  An empty string is
     returned if the value cannot be determined.

 -- Function: platform.node ()

     Returns the computer’s network name (may not be fully qualified!).
     An empty string is returned if the value cannot be determined.

 -- Function: platform.platform (aliased=0, terse=0)

     Returns a single string identifying the underlying platform with as
     much useful information as possible.

     The output is intended to be `human readable' rather than machine
     parseable.  It may look different on different platforms and this
     is intended.

     If `aliased' is true, the function will use aliases for various
     platforms that report system names which differ from their common
     names, for example SunOS will be reported as Solaris.  The *note
     system_alias(): 2381. function is used to implement this.

     Setting `terse' to true causes the function to return only the
     absolute minimum information needed to identify the platform.

     Changed in version 3.8: On macOS, the function now uses *note
     mac_ver(): 1154, if it returns a non-empty release string, to get
     the macOS version rather than the darwin version.

 -- Function: platform.processor ()

     Returns the (real) processor name, e.g.  ‘'amdk6'’.

     An empty string is returned if the value cannot be determined.
     Note that many platforms do not provide this information or simply
     return the same value as for *note machine(): 237f.  NetBSD does
     this.

 -- Function: platform.python_build ()

     Returns a tuple ‘(buildno, builddate)’ stating the Python build
     number and date as strings.

 -- Function: platform.python_compiler ()

     Returns a string identifying the compiler used for compiling
     Python.

 -- Function: platform.python_branch ()

     Returns a string identifying the Python implementation SCM branch.

 -- Function: platform.python_implementation ()

     Returns a string identifying the Python implementation.  Possible
     return values are: ‘CPython’, ‘IronPython’, ‘Jython’, ‘PyPy’.

 -- Function: platform.python_revision ()

     Returns a string identifying the Python implementation SCM
     revision.

 -- Function: platform.python_version ()

     Returns the Python version as string ‘'major.minor.patchlevel'’.

     Note that unlike the Python ‘sys.version’, the returned value will
     always include the patchlevel (it defaults to 0).

 -- Function: platform.python_version_tuple ()

     Returns the Python version as tuple ‘(major, minor, patchlevel)’ of
     strings.

     Note that unlike the Python ‘sys.version’, the returned value will
     always include the patchlevel (it defaults to ‘'0'’).

 -- Function: platform.release ()

     Returns the system’s release, e.g.  ‘'2.2.0'’ or ‘'NT'’ An empty
     string is returned if the value cannot be determined.

 -- Function: platform.system ()

     Returns the system/OS name, such as ‘'Linux'’, ‘'Darwin'’,
     ‘'Java'’, ‘'Windows'’.  An empty string is returned if the value
     cannot be determined.

 -- Function: platform.system_alias (system, release, version)

     Returns ‘(system, release, version)’ aliased to common marketing
     names used for some systems.  It also does some reordering of the
     information in some cases where it would otherwise cause confusion.

 -- Function: platform.version ()

     Returns the system’s release version, e.g.  ‘'#3 on degas'’.  An
     empty string is returned if the value cannot be determined.

 -- Function: platform.uname ()

     Fairly portable uname interface.  Returns a *note namedtuple():
     1a1. containing six attributes: *note system: 238b, *note node:
     2380, *note release: 238a, *note version: 238c, *note machine:
     237f, and *note processor: 2382.

     Note that this adds a sixth attribute (*note processor: 2382.) not
     present in the *note os.uname(): b38. result.  Also, the attribute
     names are different for the first two attributes; *note os.uname():
     b38. names them ‘sysname’ and ‘nodename’.

     Entries which cannot be determined are set to ‘''’.

     Changed in version 3.3: Result changed from a tuple to a
     namedtuple.


File: python.info,  Node: Java Platform,  Next: Windows Platform,  Prev: Cross Platform,  Up: platform — Access to underlying platform’s identifying data

5.16.14.2 Java Platform
.......................

 -- Function: platform.java_ver (release='', vendor='', vminfo=('', '',
          ''), osinfo=('', '', ''))

     Version interface for Jython.

     Returns a tuple ‘(release, vendor, vminfo, osinfo)’ with `vminfo'
     being a tuple ‘(vm_name, vm_release, vm_vendor)’ and `osinfo' being
     a tuple ‘(os_name, os_version, os_arch)’.  Values which cannot be
     determined are set to the defaults given as parameters (which all
     default to ‘''’).


File: python.info,  Node: Windows Platform,  Next: macOS Platform,  Prev: Java Platform,  Up: platform — Access to underlying platform’s identifying data

5.16.14.3 Windows Platform
..........................

 -- Function: platform.win32_ver (release='', version='', csd='',
          ptype='')

     Get additional version information from the Windows Registry and
     return a tuple ‘(release, version, csd, ptype)’ referring to OS
     release, version number, CSD level (service pack) and OS type
     (multi/single processor).

     As a hint: `ptype' is ‘'Uniprocessor Free'’ on single processor NT
     machines and ‘'Multiprocessor Free'’ on multi processor machines.
     The `‘Free’' refers to the OS version being free of debugging code.
     It could also state `‘Checked’' which means the OS version uses
     debugging code, i.e.  code that checks arguments, ranges, etc.

 -- Function: platform.win32_edition ()

     Returns a string representing the current Windows edition.
     Possible values include but are not limited to ‘'Enterprise'’,
     ‘'IoTUAP'’, ‘'ServerStandard'’, and ‘'nanoserver'’.

     New in version 3.8.

 -- Function: platform.win32_is_iot ()

     Return ‘True’ if the Windows edition returned by *note
     win32_edition(): 2390. is recognized as an IoT edition.

     New in version 3.8.


File: python.info,  Node: macOS Platform,  Next: Unix Platforms,  Prev: Windows Platform,  Up: platform — Access to underlying platform’s identifying data

5.16.14.4 macOS Platform
........................

 -- Function: platform.mac_ver (release='', versioninfo=('', '', ''),
          machine='')

     Get macOS version information and return it as tuple ‘(release,
     versioninfo, machine)’ with `versioninfo' being a tuple ‘(version,
     dev_stage, non_release_version)’.

     Entries which cannot be determined are set to ‘''’.  All tuple
     entries are strings.


File: python.info,  Node: Unix Platforms,  Prev: macOS Platform,  Up: platform — Access to underlying platform’s identifying data

5.16.14.5 Unix Platforms
........................

 -- Function: platform.libc_ver (executable=sys.executable, lib='',
          version='', chunksize=16384)

     Tries to determine the libc version against which the file
     executable (defaults to the Python interpreter) is linked.  Returns
     a tuple of strings ‘(lib, version)’ which default to the given
     parameters in case the lookup fails.

     Note that this function has intimate knowledge of how different
     libc versions add symbols to the executable is probably only usable
     for executables compiled using ‘gcc’.

     The file is read and scanned in chunks of `chunksize' bytes.


File: python.info,  Node: errno — Standard errno system symbols,  Next: ctypes — A foreign function library for Python,  Prev: platform — Access to underlying platform’s identifying data,  Up: Generic Operating System Services

5.16.15 ‘errno’ — Standard errno system symbols
-----------------------------------------------

__________________________________________________________________

This module makes available standard ‘errno’ system symbols.  The value
of each symbol is the corresponding integer value.  The names and
descriptions are borrowed from ‘linux/include/errno.h’, which should be
pretty all-inclusive.

 -- Data: errno.errorcode

     Dictionary providing a mapping from the errno value to the string
     name in the underlying system.  For instance,
     ‘errno.errorcode[errno.EPERM]’ maps to ‘'EPERM'’.

To translate a numeric error code to an error message, use *note
os.strerror(): 2062.

Of the following list, symbols that are not used on the current platform
are not defined by the module.  The specific list of defined symbols is
available as ‘errno.errorcode.keys()’.  Symbols available can include:

 -- Data: errno.EPERM

     Operation not permitted

 -- Data: errno.ENOENT

     No such file or directory

 -- Data: errno.ESRCH

     No such process

 -- Data: errno.EINTR

     Interrupted system call.

     See also
     ........

     This error is mapped to the exception *note InterruptedError: 74c.

 -- Data: errno.EIO

     I/O error

 -- Data: errno.ENXIO

     No such device or address

 -- Data: errno.E2BIG

     Arg list too long

 -- Data: errno.ENOEXEC

     Exec format error

 -- Data: errno.EBADF

     Bad file number

 -- Data: errno.ECHILD

     No child processes

 -- Data: errno.EAGAIN

     Try again

 -- Data: errno.ENOMEM

     Out of memory

 -- Data: errno.EACCES

     Permission denied

 -- Data: errno.EFAULT

     Bad address

 -- Data: errno.ENOTBLK

     Block device required

 -- Data: errno.EBUSY

     Device or resource busy

 -- Data: errno.EEXIST

     File exists

 -- Data: errno.EXDEV

     Cross-device link

 -- Data: errno.ENODEV

     No such device

 -- Data: errno.ENOTDIR

     Not a directory

 -- Data: errno.EISDIR

     Is a directory

 -- Data: errno.EINVAL

     Invalid argument

 -- Data: errno.ENFILE

     File table overflow

 -- Data: errno.EMFILE

     Too many open files

 -- Data: errno.ENOTTY

     Not a typewriter

 -- Data: errno.ETXTBSY

     Text file busy

 -- Data: errno.EFBIG

     File too large

 -- Data: errno.ENOSPC

     No space left on device

 -- Data: errno.ESPIPE

     Illegal seek

 -- Data: errno.EROFS

     Read-only file system

 -- Data: errno.EMLINK

     Too many links

 -- Data: errno.EPIPE

     Broken pipe

 -- Data: errno.EDOM

     Math argument out of domain of func

 -- Data: errno.ERANGE

     Math result not representable

 -- Data: errno.EDEADLK

     Resource deadlock would occur

 -- Data: errno.ENAMETOOLONG

     File name too long

 -- Data: errno.ENOLCK

     No record locks available

 -- Data: errno.ENOSYS

     Function not implemented

 -- Data: errno.ENOTEMPTY

     Directory not empty

 -- Data: errno.ELOOP

     Too many symbolic links encountered

 -- Data: errno.EWOULDBLOCK

     Operation would block

 -- Data: errno.ENOMSG

     No message of desired type

 -- Data: errno.EIDRM

     Identifier removed

 -- Data: errno.ECHRNG

     Channel number out of range

 -- Data: errno.EL2NSYNC

     Level 2 not synchronized

 -- Data: errno.EL3HLT

     Level 3 halted

 -- Data: errno.EL3RST

     Level 3 reset

 -- Data: errno.ELNRNG

     Link number out of range

 -- Data: errno.EUNATCH

     Protocol driver not attached

 -- Data: errno.ENOCSI

     No CSI structure available

 -- Data: errno.EL2HLT

     Level 2 halted

 -- Data: errno.EBADE

     Invalid exchange

 -- Data: errno.EBADR

     Invalid request descriptor

 -- Data: errno.EXFULL

     Exchange full

 -- Data: errno.ENOANO

     No anode

 -- Data: errno.EBADRQC

     Invalid request code

 -- Data: errno.EBADSLT

     Invalid slot

 -- Data: errno.EDEADLOCK

     File locking deadlock error

 -- Data: errno.EBFONT

     Bad font file format

 -- Data: errno.ENOSTR

     Device not a stream

 -- Data: errno.ENODATA

     No data available

 -- Data: errno.ETIME

     Timer expired

 -- Data: errno.ENOSR

     Out of streams resources

 -- Data: errno.ENONET

     Machine is not on the network

 -- Data: errno.ENOPKG

     Package not installed

 -- Data: errno.EREMOTE

     Object is remote

 -- Data: errno.ENOLINK

     Link has been severed

 -- Data: errno.EADV

     Advertise error

 -- Data: errno.ESRMNT

     Srmount error

 -- Data: errno.ECOMM

     Communication error on send

 -- Data: errno.EPROTO

     Protocol error

 -- Data: errno.EMULTIHOP

     Multihop attempted

 -- Data: errno.EDOTDOT

     RFS specific error

 -- Data: errno.EBADMSG

     Not a data message

 -- Data: errno.EOVERFLOW

     Value too large for defined data type

 -- Data: errno.ENOTUNIQ

     Name not unique on network

 -- Data: errno.EBADFD

     File descriptor in bad state

 -- Data: errno.EREMCHG

     Remote address changed

 -- Data: errno.ELIBACC

     Can not access a needed shared library

 -- Data: errno.ELIBBAD

     Accessing a corrupted shared library

 -- Data: errno.ELIBSCN

     .lib section in a.out corrupted

 -- Data: errno.ELIBMAX

     Attempting to link in too many shared libraries

 -- Data: errno.ELIBEXEC

     Cannot exec a shared library directly

 -- Data: errno.EILSEQ

     Illegal byte sequence

 -- Data: errno.ERESTART

     Interrupted system call should be restarted

 -- Data: errno.ESTRPIPE

     Streams pipe error

 -- Data: errno.EUSERS

     Too many users

 -- Data: errno.ENOTSOCK

     Socket operation on non-socket

 -- Data: errno.EDESTADDRREQ

     Destination address required

 -- Data: errno.EMSGSIZE

     Message too long

 -- Data: errno.EPROTOTYPE

     Protocol wrong type for socket

 -- Data: errno.ENOPROTOOPT

     Protocol not available

 -- Data: errno.EPROTONOSUPPORT

     Protocol not supported

 -- Data: errno.ESOCKTNOSUPPORT

     Socket type not supported

 -- Data: errno.EOPNOTSUPP

     Operation not supported on transport endpoint

 -- Data: errno.EPFNOSUPPORT

     Protocol family not supported

 -- Data: errno.EAFNOSUPPORT

     Address family not supported by protocol

 -- Data: errno.EADDRINUSE

     Address already in use

 -- Data: errno.EADDRNOTAVAIL

     Cannot assign requested address

 -- Data: errno.ENETDOWN

     Network is down

 -- Data: errno.ENETUNREACH

     Network is unreachable

 -- Data: errno.ENETRESET

     Network dropped connection because of reset

 -- Data: errno.ECONNABORTED

     Software caused connection abort

 -- Data: errno.ECONNRESET

     Connection reset by peer

 -- Data: errno.ENOBUFS

     No buffer space available

 -- Data: errno.EISCONN

     Transport endpoint is already connected

 -- Data: errno.ENOTCONN

     Transport endpoint is not connected

 -- Data: errno.ESHUTDOWN

     Cannot send after transport endpoint shutdown

 -- Data: errno.ETOOMANYREFS

     Too many references: cannot splice

 -- Data: errno.ETIMEDOUT

     Connection timed out

 -- Data: errno.ECONNREFUSED

     Connection refused

 -- Data: errno.EHOSTDOWN

     Host is down

 -- Data: errno.EHOSTUNREACH

     No route to host

 -- Data: errno.EALREADY

     Operation already in progress

 -- Data: errno.EINPROGRESS

     Operation now in progress

 -- Data: errno.ESTALE

     Stale NFS file handle

 -- Data: errno.EUCLEAN

     Structure needs cleaning

 -- Data: errno.ENOTNAM

     Not a XENIX named type file

 -- Data: errno.ENAVAIL

     No XENIX semaphores available

 -- Data: errno.EISNAM

     Is a named type file

 -- Data: errno.EREMOTEIO

     Remote I/O error

 -- Data: errno.EDQUOT

     Quota exceeded


File: python.info,  Node: ctypes — A foreign function library for Python,  Prev: errno — Standard errno system symbols,  Up: Generic Operating System Services

5.16.16 ‘ctypes’ — A foreign function library for Python
--------------------------------------------------------

__________________________________________________________________

*note ctypes: 2a. is a foreign function library for Python.  It provides
C compatible data types, and allows calling functions in DLLs or shared
libraries.  It can be used to wrap these libraries in pure Python.

* Menu:

* ctypes tutorial::
* ctypes reference::


File: python.info,  Node: ctypes tutorial,  Next: ctypes reference,  Up: ctypes — A foreign function library for Python

5.16.16.1 ctypes tutorial
.........................

Note: The code samples in this tutorial use *note doctest: 66. to make
sure that they actually work.  Since some code samples behave
differently under Linux, Windows, or macOS, they contain doctest
directives in comments.

Note: Some code samples reference the ctypes *note c_int: 240f. type.
On platforms where ‘sizeof(long) == sizeof(int)’ it is an alias to *note
c_long: 2410.  So, you should not be confused if *note c_long: 2410. is
printed if you would expect *note c_int: 240f. — they are actually the
same type.

* Menu:

* Loading dynamic link libraries::
* Accessing functions from loaded dlls::
* Calling functions::
* Fundamental data types::
* Calling functions, continued: Calling functions continued.
* Calling functions with your own custom data types::
* Specifying the required argument types (function prototypes): Specifying the required argument types function prototypes.
* Return types::
* Passing pointers (or; passing parameters by reference): Passing pointers or passing parameters by reference.
* Structures and unions::
* Structure/union alignment and byte order::
* Bit fields in structures and unions::
* Arrays::
* Pointers::
* Type conversions::
* Incomplete Types::
* Callback functions::
* Accessing values exported from dlls::
* Surprises::
* Variable-sized data types::


File: python.info,  Node: Loading dynamic link libraries,  Next: Accessing functions from loaded dlls,  Up: ctypes tutorial

5.16.16.2 Loading dynamic link libraries
........................................

*note ctypes: 2a. exports the `cdll', and on Windows `windll' and
`oledll' objects, for loading dynamic link libraries.

You load libraries by accessing them as attributes of these objects.
`cdll' loads libraries which export functions using the standard ‘cdecl’
calling convention, while `windll' libraries call functions using the
‘stdcall’ calling convention.  `oledll' also uses the ‘stdcall’ calling
convention, and assumes the functions return a Windows ‘HRESULT’ error
code.  The error code is used to automatically raise an *note OSError:
304. exception when the function call fails.

Changed in version 3.3: Windows errors used to raise *note WindowsError:
a75, which is now an alias of *note OSError: 304.

Here are some examples for Windows.  Note that ‘msvcrt’ is the MS
standard C library containing most standard C functions, and uses the
cdecl calling convention:

     >>> from ctypes import *
     >>> print(windll.kernel32)
     <WinDLL 'kernel32', handle ... at ...>
     >>> print(cdll.msvcrt)
     <CDLL 'msvcrt', handle ... at ...>
     >>> libc = cdll.msvcrt
     >>>

Windows appends the usual ‘.dll’ file suffix automatically.

     Note: Accessing the standard C library through ‘cdll.msvcrt’ will
     use an outdated version of the library that may be incompatible
     with the one being used by Python.  Where possible, use native
     Python functionality, or else import and use the ‘msvcrt’ module.

On Linux, it is required to specify the filename `including' the
extension to load a library, so attribute access can not be used to load
libraries.  Either the ‘LoadLibrary()’ method of the dll loaders should
be used, or you should load the library by creating an instance of CDLL
by calling the constructor:

     >>> cdll.LoadLibrary("libc.so.6")
     <CDLL 'libc.so.6', handle ... at ...>
     >>> libc = CDLL("libc.so.6")
     >>> libc
     <CDLL 'libc.so.6', handle ... at ...>
     >>>


File: python.info,  Node: Accessing functions from loaded dlls,  Next: Calling functions,  Prev: Loading dynamic link libraries,  Up: ctypes tutorial

5.16.16.3 Accessing functions from loaded dlls
..............................................

Functions are accessed as attributes of dll objects:

     >>> from ctypes import *
     >>> libc.printf
     <_FuncPtr object at 0x...>
     >>> print(windll.kernel32.GetModuleHandleA)
     <_FuncPtr object at 0x...>
     >>> print(windll.kernel32.MyOwnFunction)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
       File "ctypes.py", line 239, in __getattr__
         func = _StdcallFuncPtr(name, self)
     AttributeError: function 'MyOwnFunction' not found
     >>>

Note that win32 system dlls like ‘kernel32’ and ‘user32’ often export
ANSI as well as UNICODE versions of a function.  The UNICODE version is
exported with an ‘W’ appended to the name, while the ANSI version is
exported with an ‘A’ appended to the name.  The win32 ‘GetModuleHandle’
function, which returns a `module handle' for a given module name, has
the following C prototype, and a macro is used to expose one of them as
‘GetModuleHandle’ depending on whether UNICODE is defined or not:

     /* ANSI version */
     HMODULE GetModuleHandleA(LPCSTR lpModuleName);
     /* UNICODE version */
     HMODULE GetModuleHandleW(LPCWSTR lpModuleName);

`windll' does not try to select one of them by magic, you must access
the version you need by specifying ‘GetModuleHandleA’ or
‘GetModuleHandleW’ explicitly, and then call it with bytes or string
objects respectively.

Sometimes, dlls export functions with names which aren’t valid Python
identifiers, like ‘"??2@YAPAXI@Z"’.  In this case you have to use *note
getattr(): 54b. to retrieve the function:

     >>> getattr(cdll.msvcrt, "??2@YAPAXI@Z")
     <_FuncPtr object at 0x...>
     >>>

On Windows, some dlls export functions not by name but by ordinal.
These functions can be accessed by indexing the dll object with the
ordinal number:

     >>> cdll.kernel32[1]
     <_FuncPtr object at 0x...>
     >>> cdll.kernel32[0]
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
       File "ctypes.py", line 310, in __getitem__
         func = _StdcallFuncPtr(name, self)
     AttributeError: function ordinal 0 not found
     >>>


File: python.info,  Node: Calling functions,  Next: Fundamental data types,  Prev: Accessing functions from loaded dlls,  Up: ctypes tutorial

5.16.16.4 Calling functions
...........................

You can call these functions like any other Python callable.  This
example uses the ‘time()’ function, which returns system time in seconds
since the Unix epoch, and the ‘GetModuleHandleA()’ function, which
returns a win32 module handle.

This example calls both functions with a ‘NULL’ pointer (‘None’ should
be used as the ‘NULL’ pointer):

     >>> print(libc.time(None))
     1150640792
     >>> print(hex(windll.kernel32.GetModuleHandleA(None)))
     0x1d000000
     >>>

*note ValueError: 16d. is raised when you call an ‘stdcall’ function
with the ‘cdecl’ calling convention, or vice versa:

     >>> cdll.kernel32.GetModuleHandleA(None)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ValueError: Procedure probably called with not enough arguments (4 bytes missing)
     >>>

     >>> windll.msvcrt.printf(b"spam")
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ValueError: Procedure probably called with too many arguments (4 bytes in excess)
     >>>

To find out the correct calling convention you have to look into the C
header file or the documentation for the function you want to call.

On Windows, *note ctypes: 2a. uses win32 structured exception handling
to prevent crashes from general protection faults when functions are
called with invalid argument values:

     >>> windll.kernel32.GetModuleHandleA(32)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     OSError: exception: access violation reading 0x00000020
     >>>

There are, however, enough ways to crash Python with *note ctypes: 2a,
so you should be careful anyway.  The *note faulthandler: 7b. module can
be helpful in debugging crashes (e.g.  from segmentation faults produced
by erroneous C library calls).

‘None’, integers, bytes objects and (unicode) strings are the only
native Python objects that can directly be used as parameters in these
function calls.  ‘None’ is passed as a C ‘NULL’ pointer, bytes objects
and strings are passed as pointer to the memory block that contains
their data (‘char *’ or ‘wchar_t *’).  Python integers are passed as the
platforms default C ‘int’ type, their value is masked to fit into the C
type.

Before we move on calling functions with other parameter types, we have
to learn more about *note ctypes: 2a. data types.


File: python.info,  Node: Fundamental data types,  Next: Calling functions continued,  Prev: Calling functions,  Up: ctypes tutorial

5.16.16.5 Fundamental data types
................................

*note ctypes: 2a. defines a number of primitive C compatible data types:

ctypes type                C type                                         Python type
                                                                          
-----------------------------------------------------------------------------------------------------------
                                                                          
*note c_bool: 2419.        ‘_Bool’                                        bool (1)
                                                                          
                                                                          
*note c_char: 241a.        ‘char’                                         1-character bytes object
                                                                          
                                                                          
*note c_wchar: 241b.       ‘wchar_t’                                      1-character string
                                                                          
                                                                          
*note c_byte: 241c.        ‘char’                                         int
                                                                          
                                                                          
*note c_ubyte: 241d.       ‘unsigned char’                                int
                                                                          
                                                                          
*note c_short: 241e.       ‘short’                                        int
                                                                          
                                                                          
*note c_ushort: 241f.      ‘unsigned short’                               int
                                                                          
                                                                          
*note c_int: 240f.         ‘int’                                          int
                                                                          
                                                                          
*note c_uint: 2420.        ‘unsigned int’                                 int
                                                                          
                                                                          
*note c_long: 2410.        ‘long’                                         int
                                                                          
                                                                          
*note c_ulong: 2421.       ‘unsigned long’                                int
                                                                          
                                                                          
*note c_longlong: 2422.    ‘__int64’ or ‘long long’                       int
                                                                          
                                                                          
*note c_ulonglong: 2423.   ‘unsigned __int64’ or ‘unsigned long long’     int
                                                                          
                                                                          
*note c_size_t: 2424.      ‘size_t’                                       int
                                                                          
                                                                          
*note c_ssize_t: c9f.      ‘ssize_t’ or ‘Py_ssize_t’                      int
                                                                          
                                                                          
*note c_float: 2425.       ‘float’                                        float
                                                                          
                                                                          
*note c_double: fc4.       ‘double’                                       float
                                                                          
                                                                          
*note c_longdouble: fc5.   ‘long double’                                  float
                                                                          
                                                                          
*note c_char_p: 2426.      ‘char *’ (NUL terminated)                      bytes object or ‘None’
                                                                          
                                                                          
*note c_wchar_p: fa9.      ‘wchar_t *’ (NUL terminated)                   string or ‘None’
                                                                          
                                                                          
*note c_void_p: 2427.      ‘void *’                                       int or ‘None’
                                                                          

  1. The constructor accepts any object with a truth value.

All these types can be created by calling them with an optional
initializer of the correct type and value:

     >>> c_int()
     c_long(0)
     >>> c_wchar_p("Hello, World")
     c_wchar_p(140018365411392)
     >>> c_ushort(-3)
     c_ushort(65533)
     >>>

Since these types are mutable, their value can also be changed
afterwards:

     >>> i = c_int(42)
     >>> print(i)
     c_long(42)
     >>> print(i.value)
     42
     >>> i.value = -99
     >>> print(i.value)
     -99
     >>>

Assigning a new value to instances of the pointer types *note c_char_p:
2426, *note c_wchar_p: fa9, and *note c_void_p: 2427. changes the
`memory location' they point to, `not the contents' of the memory block
(of course not, because Python bytes objects are immutable):

     >>> s = "Hello, World"
     >>> c_s = c_wchar_p(s)
     >>> print(c_s)
     c_wchar_p(139966785747344)
     >>> print(c_s.value)
     Hello World
     >>> c_s.value = "Hi, there"
     >>> print(c_s)              # the memory location has changed
     c_wchar_p(139966783348904)
     >>> print(c_s.value)
     Hi, there
     >>> print(s)                # first object is unchanged
     Hello, World
     >>>

You should be careful, however, not to pass them to functions expecting
pointers to mutable memory.  If you need mutable memory blocks, ctypes
has a *note create_string_buffer(): 2428. function which creates these
in various ways.  The current memory block contents can be accessed (or
changed) with the ‘raw’ property; if you want to access it as NUL
terminated string, use the ‘value’ property:

     >>> from ctypes import *
     >>> p = create_string_buffer(3)            # create a 3 byte buffer, initialized to NUL bytes
     >>> print(sizeof(p), repr(p.raw))
     3 b'\x00\x00\x00'
     >>> p = create_string_buffer(b"Hello")     # create a buffer containing a NUL terminated string
     >>> print(sizeof(p), repr(p.raw))
     6 b'Hello\x00'
     >>> print(repr(p.value))
     b'Hello'
     >>> p = create_string_buffer(b"Hello", 10) # create a 10 byte buffer
     >>> print(sizeof(p), repr(p.raw))
     10 b'Hello\x00\x00\x00\x00\x00'
     >>> p.value = b"Hi"
     >>> print(sizeof(p), repr(p.raw))
     10 b'Hi\x00lo\x00\x00\x00\x00\x00'
     >>>

The *note create_string_buffer(): 2428. function replaces the
‘c_buffer()’ function (which is still available as an alias), as well as
the ‘c_string()’ function from earlier ctypes releases.  To create a
mutable memory block containing unicode characters of the C type
‘wchar_t’ use the *note create_unicode_buffer(): 10d7. function.


File: python.info,  Node: Calling functions continued,  Next: Calling functions with your own custom data types,  Prev: Fundamental data types,  Up: ctypes tutorial

5.16.16.6 Calling functions, continued
......................................

Note that printf prints to the real standard output channel, `not' to
*note sys.stdout: 41f, so these examples will only work at the console
prompt, not from within `IDLE' or `PythonWin':

     >>> printf = libc.printf
     >>> printf(b"Hello, %s\n", b"World!")
     Hello, World!
     14
     >>> printf(b"Hello, %S\n", "World!")
     Hello, World!
     14
     >>> printf(b"%d bottles of beer\n", 42)
     42 bottles of beer
     19
     >>> printf(b"%f bottles of beer\n", 42.5)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ArgumentError: argument 2: exceptions.TypeError: Don't know how to convert parameter 2
     >>>

As has been mentioned before, all Python types except integers, strings,
and bytes objects have to be wrapped in their corresponding *note
ctypes: 2a. type, so that they can be converted to the required C data
type:

     >>> printf(b"An int %d, a double %f\n", 1234, c_double(3.14))
     An int 1234, a double 3.140000
     31
     >>>


File: python.info,  Node: Calling functions with your own custom data types,  Next: Specifying the required argument types function prototypes,  Prev: Calling functions continued,  Up: ctypes tutorial

5.16.16.7 Calling functions with your own custom data types
...........................................................

You can also customize *note ctypes: 2a. argument conversion to allow
instances of your own classes be used as function arguments.  *note
ctypes: 2a. looks for an ‘_as_parameter_’ attribute and uses this as the
function argument.  Of course, it must be one of integer, string, or
bytes:

     >>> class Bottles:
     ...     def __init__(self, number):
     ...         self._as_parameter_ = number
     ...
     >>> bottles = Bottles(42)
     >>> printf(b"%d bottles of beer\n", bottles)
     42 bottles of beer
     19
     >>>

If you don’t want to store the instance’s data in the ‘_as_parameter_’
instance variable, you could define a *note property: 308. which makes
the attribute available on request.


File: python.info,  Node: Specifying the required argument types function prototypes,  Next: Return types,  Prev: Calling functions with your own custom data types,  Up: ctypes tutorial

5.16.16.8 Specifying the required argument types (function prototypes)
......................................................................

It is possible to specify the required argument types of functions
exported from DLLs by setting the ‘argtypes’ attribute.

‘argtypes’ must be a sequence of C data types (the ‘printf’ function is
probably not a good example here, because it takes a variable number and
different types of parameters depending on the format string, on the
other hand this is quite handy to experiment with this feature):

     >>> printf.argtypes = [c_char_p, c_char_p, c_int, c_double]
     >>> printf(b"String '%s', Int %d, Double %f\n", b"Hi", 10, 2.2)
     String 'Hi', Int 10, Double 2.200000
     37
     >>>

Specifying a format protects against incompatible argument types (just
as a prototype for a C function), and tries to convert the arguments to
valid types:

     >>> printf(b"%d %d %d", 1, 2, 3)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ArgumentError: argument 2: exceptions.TypeError: wrong type
     >>> printf(b"%s %d %f\n", b"X", 2, 3)
     X 2 3.000000
     13
     >>>

If you have defined your own classes which you pass to function calls,
you have to implement a ‘from_param()’ class method for them to be able
to use them in the ‘argtypes’ sequence.  The ‘from_param()’ class method
receives the Python object passed to the function call, it should do a
typecheck or whatever is needed to make sure this object is acceptable,
and then return the object itself, its ‘_as_parameter_’ attribute, or
whatever you want to pass as the C function argument in this case.
Again, the result should be an integer, string, bytes, a *note ctypes:
2a. instance, or an object with an ‘_as_parameter_’ attribute.


File: python.info,  Node: Return types,  Next: Passing pointers or passing parameters by reference,  Prev: Specifying the required argument types function prototypes,  Up: ctypes tutorial

5.16.16.9 Return types
......................

By default functions are assumed to return the C ‘int’ type.  Other
return types can be specified by setting the ‘restype’ attribute of the
function object.

Here is a more advanced example, it uses the ‘strchr’ function, which
expects a string pointer and a char, and returns a pointer to a string:

     >>> strchr = libc.strchr
     >>> strchr(b"abcdef", ord("d"))
     8059983
     >>> strchr.restype = c_char_p    # c_char_p is a pointer to a string
     >>> strchr(b"abcdef", ord("d"))
     b'def'
     >>> print(strchr(b"abcdef", ord("x")))
     None
     >>>

If you want to avoid the ‘ord("x")’ calls above, you can set the
‘argtypes’ attribute, and the second argument will be converted from a
single character Python bytes object into a C char:

     >>> strchr.restype = c_char_p
     >>> strchr.argtypes = [c_char_p, c_char]
     >>> strchr(b"abcdef", b"d")
     'def'
     >>> strchr(b"abcdef", b"def")
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ArgumentError: argument 2: exceptions.TypeError: one character string expected
     >>> print(strchr(b"abcdef", b"x"))
     None
     >>> strchr(b"abcdef", b"d")
     'def'
     >>>

You can also use a callable Python object (a function or a class for
example) as the ‘restype’ attribute, if the foreign function returns an
integer.  The callable will be called with the `integer' the C function
returns, and the result of this call will be used as the result of your
function call.  This is useful to check for error return values and
automatically raise an exception:

     >>> GetModuleHandle = windll.kernel32.GetModuleHandleA
     >>> def ValidHandle(value):
     ...     if value == 0:
     ...         raise WinError()
     ...     return value
     ...
     >>>
     >>> GetModuleHandle.restype = ValidHandle
     >>> GetModuleHandle(None)
     486539264
     >>> GetModuleHandle("something silly")
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
       File "<stdin>", line 3, in ValidHandle
     OSError: [Errno 126] The specified module could not be found.
     >>>

‘WinError’ is a function which will call Windows ‘FormatMessage()’ api
to get the string representation of an error code, and `returns' an
exception.  ‘WinError’ takes an optional error code parameter, if no one
is used, it calls *note GetLastError(): 2431. to retrieve it.

Please note that a much more powerful error checking mechanism is
available through the ‘errcheck’ attribute; see the reference manual for
details.


File: python.info,  Node: Passing pointers or passing parameters by reference,  Next: Structures and unions,  Prev: Return types,  Up: ctypes tutorial

5.16.16.10 Passing pointers (or: passing parameters by reference)
.................................................................

Sometimes a C api function expects a `pointer' to a data type as
parameter, probably to write into the corresponding location, or if the
data is too large to be passed by value.  This is also known as `passing
parameters by reference'.

*note ctypes: 2a. exports the *note byref(): 2434. function which is
used to pass parameters by reference.  The same effect can be achieved
with the *note pointer(): 2435. function, although *note pointer():
2435. does a lot more work since it constructs a real pointer object, so
it is faster to use *note byref(): 2434. if you don’t need the pointer
object in Python itself:

     >>> i = c_int()
     >>> f = c_float()
     >>> s = create_string_buffer(b'\000' * 32)
     >>> print(i.value, f.value, repr(s.value))
     0 0.0 b''
     >>> libc.sscanf(b"1 3.14 Hello", b"%d %f %s",
     ...             byref(i), byref(f), s)
     3
     >>> print(i.value, f.value, repr(s.value))
     1 3.1400001049 b'Hello'
     >>>


File: python.info,  Node: Structures and unions,  Next: Structure/union alignment and byte order,  Prev: Passing pointers or passing parameters by reference,  Up: ctypes tutorial

5.16.16.11 Structures and unions
................................

Structures and unions must derive from the *note Structure: 2438. and
*note Union: 2439. base classes which are defined in the *note ctypes:
2a. module.  Each subclass must define a ‘_fields_’ attribute.
‘_fields_’ must be a list of `2-tuples', containing a `field name' and a
`field type'.

The field type must be a *note ctypes: 2a. type like *note c_int: 240f,
or any other derived *note ctypes: 2a. type: structure, union, array,
pointer.

Here is a simple example of a POINT structure, which contains two
integers named `x' and `y', and also shows how to initialize a structure
in the constructor:

     >>> from ctypes import *
     >>> class POINT(Structure):
     ...     _fields_ = [("x", c_int),
     ...                 ("y", c_int)]
     ...
     >>> point = POINT(10, 20)
     >>> print(point.x, point.y)
     10 20
     >>> point = POINT(y=5)
     >>> print(point.x, point.y)
     0 5
     >>> POINT(1, 2, 3)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: too many initializers
     >>>

You can, however, build much more complicated structures.  A structure
can itself contain other structures by using a structure as a field
type.

Here is a RECT structure which contains two POINTs named `upperleft' and
`lowerright':

     >>> class RECT(Structure):
     ...     _fields_ = [("upperleft", POINT),
     ...                 ("lowerright", POINT)]
     ...
     >>> rc = RECT(point)
     >>> print(rc.upperleft.x, rc.upperleft.y)
     0 5
     >>> print(rc.lowerright.x, rc.lowerright.y)
     0 0
     >>>

Nested structures can also be initialized in the constructor in several
ways:

     >>> r = RECT(POINT(1, 2), POINT(3, 4))
     >>> r = RECT((1, 2), (3, 4))

Field *note descriptor: 1579.s can be retrieved from the `class', they
are useful for debugging because they can provide useful information:

     >>> print(POINT.x)
     <Field type=c_long, ofs=0, size=4>
     >>> print(POINT.y)
     <Field type=c_long, ofs=4, size=4>
     >>>
     Warning: *note ctypes: 2a. does not support passing unions or
     structures with bit-fields to functions by value.  While this may
     work on 32-bit x86, it’s not guaranteed by the library to work in
     the general case.  Unions and structures with bit-fields should
     always be passed to functions by pointer.


File: python.info,  Node: Structure/union alignment and byte order,  Next: Bit fields in structures and unions,  Prev: Structures and unions,  Up: ctypes tutorial

5.16.16.12 Structure/union alignment and byte order
...................................................

By default, Structure and Union fields are aligned in the same way the C
compiler does it.  It is possible to override this behavior by
specifying a ‘_pack_’ class attribute in the subclass definition.  This
must be set to a positive integer and specifies the maximum alignment
for the fields.  This is what ‘#pragma pack(n)’ also does in MSVC.

*note ctypes: 2a. uses the native byte order for Structures and Unions.
To build structures with non-native byte order, you can use one of the
*note BigEndianStructure: 243c, *note LittleEndianStructure: 243d,
‘BigEndianUnion’, and ‘LittleEndianUnion’ base classes.  These classes
cannot contain pointer fields.


File: python.info,  Node: Bit fields in structures and unions,  Next: Arrays,  Prev: Structure/union alignment and byte order,  Up: ctypes tutorial

5.16.16.13 Bit fields in structures and unions
..............................................

It is possible to create structures and unions containing bit fields.
Bit fields are only possible for integer fields, the bit width is
specified as the third item in the ‘_fields_’ tuples:

     >>> class Int(Structure):
     ...     _fields_ = [("first_16", c_int, 16),
     ...                 ("second_16", c_int, 16)]
     ...
     >>> print(Int.first_16)
     <Field type=c_long, ofs=0:0, bits=16>
     >>> print(Int.second_16)
     <Field type=c_long, ofs=0:16, bits=16>
     >>>


File: python.info,  Node: Arrays,  Next: Pointers,  Prev: Bit fields in structures and unions,  Up: ctypes tutorial

5.16.16.14 Arrays
.................

Arrays are sequences, containing a fixed number of instances of the same
type.

The recommended way to create array types is by multiplying a data type
with a positive integer:

     TenPointsArrayType = POINT * 10

Here is an example of a somewhat artificial data type, a structure
containing 4 POINTs among other stuff:

     >>> from ctypes import *
     >>> class POINT(Structure):
     ...     _fields_ = ("x", c_int), ("y", c_int)
     ...
     >>> class MyStruct(Structure):
     ...     _fields_ = [("a", c_int),
     ...                 ("b", c_float),
     ...                 ("point_array", POINT * 4)]
     >>>
     >>> print(len(MyStruct().point_array))
     4
     >>>

Instances are created in the usual way, by calling the class:

     arr = TenPointsArrayType()
     for pt in arr:
         print(pt.x, pt.y)

The above code print a series of ‘0 0’ lines, because the array contents
is initialized to zeros.

Initializers of the correct type can also be specified:

     >>> from ctypes import *
     >>> TenIntegers = c_int * 10
     >>> ii = TenIntegers(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
     >>> print(ii)
     <c_long_Array_10 object at 0x...>
     >>> for i in ii: print(i, end=" ")
     ...
     1 2 3 4 5 6 7 8 9 10
     >>>


File: python.info,  Node: Pointers,  Next: Type conversions,  Prev: Arrays,  Up: ctypes tutorial

5.16.16.15 Pointers
...................

Pointer instances are created by calling the *note pointer(): 2435.
function on a *note ctypes: 2a. type:

     >>> from ctypes import *
     >>> i = c_int(42)
     >>> pi = pointer(i)
     >>>

Pointer instances have a *note contents: 2444. attribute which returns
the object to which the pointer points, the ‘i’ object above:

     >>> pi.contents
     c_long(42)
     >>>

Note that *note ctypes: 2a. does not have OOR (original object return),
it constructs a new, equivalent object each time you retrieve an
attribute:

     >>> pi.contents is i
     False
     >>> pi.contents is pi.contents
     False
     >>>

Assigning another *note c_int: 240f. instance to the pointer’s contents
attribute would cause the pointer to point to the memory location where
this is stored:

     >>> i = c_int(99)
     >>> pi.contents = i
     >>> pi.contents
     c_long(99)
     >>>

Pointer instances can also be indexed with integers:

     >>> pi[0]
     99
     >>>

Assigning to an integer index changes the pointed to value:

     >>> print(i)
     c_long(99)
     >>> pi[0] = 22
     >>> print(i)
     c_long(22)
     >>>

It is also possible to use indexes different from 0, but you must know
what you’re doing, just as in C: You can access or change arbitrary
memory locations.  Generally you only use this feature if you receive a
pointer from a C function, and you `know' that the pointer actually
points to an array instead of a single item.

Behind the scenes, the *note pointer(): 2435. function does more than
simply create pointer instances, it has to create pointer `types' first.
This is done with the *note POINTER(): 2445. function, which accepts any
*note ctypes: 2a. type, and returns a new type:

     >>> PI = POINTER(c_int)
     >>> PI
     <class 'ctypes.LP_c_long'>
     >>> PI(42)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: expected c_long instead of int
     >>> PI(c_int(42))
     <ctypes.LP_c_long object at 0x...>
     >>>

Calling the pointer type without an argument creates a ‘NULL’ pointer.
‘NULL’ pointers have a ‘False’ boolean value:

     >>> null_ptr = POINTER(c_int)()
     >>> print(bool(null_ptr))
     False
     >>>

*note ctypes: 2a. checks for ‘NULL’ when dereferencing pointers (but
dereferencing invalid non-‘NULL’ pointers would crash Python):

     >>> null_ptr[0]
     Traceback (most recent call last):
         ....
     ValueError: NULL pointer access
     >>>

     >>> null_ptr[0] = 1234
     Traceback (most recent call last):
         ....
     ValueError: NULL pointer access
     >>>


File: python.info,  Node: Type conversions,  Next: Incomplete Types,  Prev: Pointers,  Up: ctypes tutorial

5.16.16.16 Type conversions
...........................

Usually, ctypes does strict type checking.  This means, if you have
‘POINTER(c_int)’ in the ‘argtypes’ list of a function or as the type of
a member field in a structure definition, only instances of exactly the
same type are accepted.  There are some exceptions to this rule, where
ctypes accepts other objects.  For example, you can pass compatible
array instances instead of pointer types.  So, for ‘POINTER(c_int)’,
ctypes accepts an array of c_int:

     >>> class Bar(Structure):
     ...     _fields_ = [("count", c_int), ("values", POINTER(c_int))]
     ...
     >>> bar = Bar()
     >>> bar.values = (c_int * 3)(1, 2, 3)
     >>> bar.count = 3
     >>> for i in range(bar.count):
     ...     print(bar.values[i])
     ...
     1
     2
     3
     >>>

In addition, if a function argument is explicitly declared to be a
pointer type (such as ‘POINTER(c_int)’) in ‘argtypes’, an object of the
pointed type (‘c_int’ in this case) can be passed to the function.
ctypes will apply the required *note byref(): 2434. conversion in this
case automatically.

To set a POINTER type field to ‘NULL’, you can assign ‘None’:

     >>> bar.values = None
     >>>

Sometimes you have instances of incompatible types.  In C, you can cast
one type into another type.  *note ctypes: 2a. provides a *note cast():
114b. function which can be used in the same way.  The ‘Bar’ structure
defined above accepts ‘POINTER(c_int)’ pointers or *note c_int: 240f.
arrays for its ‘values’ field, but not instances of other types:

     >>> bar.values = (c_byte * 4)()
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: incompatible types, c_byte_Array_4 instance instead of LP_c_long instance
     >>>

For these cases, the *note cast(): 114b. function is handy.

The *note cast(): 114b. function can be used to cast a ctypes instance
into a pointer to a different ctypes data type.  *note cast(): 114b.
takes two parameters, a ctypes object that is or can be converted to a
pointer of some kind, and a ctypes pointer type.  It returns an instance
of the second argument, which references the same memory block as the
first argument:

     >>> a = (c_byte * 4)()
     >>> cast(a, POINTER(c_int))
     <ctypes.LP_c_long object at ...>
     >>>

So, *note cast(): 114b. can be used to assign to the ‘values’ field of
‘Bar’ the structure:

     >>> bar = Bar()
     >>> bar.values = cast((c_byte * 4)(), POINTER(c_int))
     >>> print(bar.values[0])
     0
     >>>


File: python.info,  Node: Incomplete Types,  Next: Callback functions,  Prev: Type conversions,  Up: ctypes tutorial

5.16.16.17 Incomplete Types
...........................

`Incomplete Types' are structures, unions or arrays whose members are
not yet specified.  In C, they are specified by forward declarations,
which are defined later:

     struct cell; /* forward declaration */

     struct cell {
         char *name;
         struct cell *next;
     };

The straightforward translation into ctypes code would be this, but it
does not work:

     >>> class cell(Structure):
     ...     _fields_ = [("name", c_char_p),
     ...                 ("next", POINTER(cell))]
     ...
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
       File "<stdin>", line 2, in cell
     NameError: name 'cell' is not defined
     >>>

because the new ‘class cell’ is not available in the class statement
itself.  In *note ctypes: 2a, we can define the ‘cell’ class and set the
‘_fields_’ attribute later, after the class statement:

     >>> from ctypes import *
     >>> class cell(Structure):
     ...     pass
     ...
     >>> cell._fields_ = [("name", c_char_p),
     ...                  ("next", POINTER(cell))]
     >>>

Let’s try it.  We create two instances of ‘cell’, and let them point to
each other, and finally follow the pointer chain a few times:

     >>> c1 = cell()
     >>> c1.name = b"foo"
     >>> c2 = cell()
     >>> c2.name = b"bar"
     >>> c1.next = pointer(c2)
     >>> c2.next = pointer(c1)
     >>> p = c1
     >>> for i in range(8):
     ...     print(p.name, end=" ")
     ...     p = p.next[0]
     ...
     foo bar foo bar foo bar foo bar
     >>>


File: python.info,  Node: Callback functions,  Next: Accessing values exported from dlls,  Prev: Incomplete Types,  Up: ctypes tutorial

5.16.16.18 Callback functions
.............................

*note ctypes: 2a. allows creating C callable function pointers from
Python callables.  These are sometimes called `callback functions'.

First, you must create a class for the callback function.  The class
knows the calling convention, the return type, and the number and types
of arguments this function will receive.

The *note CFUNCTYPE(): 244c. factory function creates types for callback
functions using the ‘cdecl’ calling convention.  On Windows, the *note
WINFUNCTYPE(): 244d. factory function creates types for callback
functions using the ‘stdcall’ calling convention.

Both of these factory functions are called with the result type as first
argument, and the callback functions expected argument types as the
remaining arguments.

I will present an example here which uses the standard C library’s
‘qsort()’ function, that is used to sort items with the help of a
callback function.  ‘qsort()’ will be used to sort an array of integers:

     >>> IntArray5 = c_int * 5
     >>> ia = IntArray5(5, 1, 7, 33, 99)
     >>> qsort = libc.qsort
     >>> qsort.restype = None
     >>>

‘qsort()’ must be called with a pointer to the data to sort, the number
of items in the data array, the size of one item, and a pointer to the
comparison function, the callback.  The callback will then be called
with two pointers to items, and it must return a negative integer if the
first item is smaller than the second, a zero if they are equal, and a
positive integer otherwise.

So our callback function receives pointers to integers, and must return
an integer.  First we create the ‘type’ for the callback function:

     >>> CMPFUNC = CFUNCTYPE(c_int, POINTER(c_int), POINTER(c_int))
     >>>

To get started, here is a simple callback that shows the values it gets
passed:

     >>> def py_cmp_func(a, b):
     ...     print("py_cmp_func", a[0], b[0])
     ...     return 0
     ...
     >>> cmp_func = CMPFUNC(py_cmp_func)
     >>>

The result:

     >>> qsort(ia, len(ia), sizeof(c_int), cmp_func)
     py_cmp_func 5 1
     py_cmp_func 33 99
     py_cmp_func 7 33
     py_cmp_func 5 7
     py_cmp_func 1 7
     >>>

Now we can actually compare the two items and return a useful result:

     >>> def py_cmp_func(a, b):
     ...     print("py_cmp_func", a[0], b[0])
     ...     return a[0] - b[0]
     ...
     >>>
     >>> qsort(ia, len(ia), sizeof(c_int), CMPFUNC(py_cmp_func))
     py_cmp_func 5 1
     py_cmp_func 33 99
     py_cmp_func 7 33
     py_cmp_func 1 7
     py_cmp_func 5 7
     >>>

As we can easily check, our array is sorted now:

     >>> for i in ia: print(i, end=" ")
     ...
     1 5 7 33 99
     >>>

The function factories can be used as decorator factories, so we may as
well write:

     >>> @CFUNCTYPE(c_int, POINTER(c_int), POINTER(c_int))
     ... def py_cmp_func(a, b):
     ...     print("py_cmp_func", a[0], b[0])
     ...     return a[0] - b[0]
     ...
     >>> qsort(ia, len(ia), sizeof(c_int), py_cmp_func)
     py_cmp_func 5 1
     py_cmp_func 33 99
     py_cmp_func 7 33
     py_cmp_func 1 7
     py_cmp_func 5 7
     >>>

     Note: Make sure you keep references to *note CFUNCTYPE(): 244c.
     objects as long as they are used from C code.  *note ctypes: 2a.
     doesn’t, and if you don’t, they may be garbage collected, crashing
     your program when a callback is made.

     Also, note that if the callback function is called in a thread
     created outside of Python’s control (e.g.  by the foreign code that
     calls the callback), ctypes creates a new dummy Python thread on
     every invocation.  This behavior is correct for most purposes, but
     it means that values stored with *note threading.local: 244e. will
     `not' survive across different callbacks, even when those calls are
     made from the same C thread.


File: python.info,  Node: Accessing values exported from dlls,  Next: Surprises,  Prev: Callback functions,  Up: ctypes tutorial

5.16.16.19 Accessing values exported from dlls
..............................................

Some shared libraries not only export functions, they also export
variables.  An example in the Python library itself is the *note
Py_OptimizeFlag: 2451, an integer set to 0, 1, or 2, depending on the
*note -O: 77e. or *note -OO: 77f. flag given on startup.

*note ctypes: 2a. can access values like this with the ‘in_dll()’ class
methods of the type.  `pythonapi' is a predefined symbol giving access
to the Python C api:

     >>> opt_flag = c_int.in_dll(pythonapi, "Py_OptimizeFlag")
     >>> print(opt_flag)
     c_long(0)
     >>>

If the interpreter would have been started with *note -O: 77e, the
sample would have printed ‘c_long(1)’, or ‘c_long(2)’ if *note -OO: 77f.
would have been specified.

An extended example which also demonstrates the use of pointers accesses
the *note PyImport_FrozenModules: 2452. pointer exported by Python.

Quoting the docs for that value:

     This pointer is initialized to point to an array of ‘struct
     _frozen’ records, terminated by one whose members are all ‘NULL’ or
     zero.  When a frozen module is imported, it is searched in this
     table.  Third-party code could play tricks with this to provide a
     dynamically created collection of frozen modules.

So manipulating this pointer could even prove useful.  To restrict the
example size, we show only how this table can be read with *note ctypes:
2a.:

     >>> from ctypes import *
     >>>
     >>> class struct_frozen(Structure):
     ...     _fields_ = [("name", c_char_p),
     ...                 ("code", POINTER(c_ubyte)),
     ...                 ("size", c_int)]
     ...
     >>>

We have defined the ‘struct _frozen’ data type, so we can get the
pointer to the table:

     >>> FrozenTable = POINTER(struct_frozen)
     >>> table = FrozenTable.in_dll(pythonapi, "PyImport_FrozenModules")
     >>>

Since ‘table’ is a ‘pointer’ to the array of ‘struct_frozen’ records, we
can iterate over it, but we just have to make sure that our loop
terminates, because pointers have no size.  Sooner or later it would
probably crash with an access violation or whatever, so it’s better to
break out of the loop when we hit the ‘NULL’ entry:

     >>> for item in table:
     ...     if item.name is None:
     ...         break
     ...     print(item.name.decode("ascii"), item.size)
     ...
     _frozen_importlib 31764
     _frozen_importlib_external 41499
     __hello__ 161
     __phello__ -161
     __phello__.spam 161
     >>>

The fact that standard Python has a frozen module and a frozen package
(indicated by the negative ‘size’ member) is not well known, it is only
used for testing.  Try it out with ‘import __hello__’ for example.


File: python.info,  Node: Surprises,  Next: Variable-sized data types,  Prev: Accessing values exported from dlls,  Up: ctypes tutorial

5.16.16.20 Surprises
....................

There are some edges in *note ctypes: 2a. where you might expect
something other than what actually happens.

Consider the following example:

     >>> from ctypes import *
     >>> class POINT(Structure):
     ...     _fields_ = ("x", c_int), ("y", c_int)
     ...
     >>> class RECT(Structure):
     ...     _fields_ = ("a", POINT), ("b", POINT)
     ...
     >>> p1 = POINT(1, 2)
     >>> p2 = POINT(3, 4)
     >>> rc = RECT(p1, p2)
     >>> print(rc.a.x, rc.a.y, rc.b.x, rc.b.y)
     1 2 3 4
     >>> # now swap the two points
     >>> rc.a, rc.b = rc.b, rc.a
     >>> print(rc.a.x, rc.a.y, rc.b.x, rc.b.y)
     3 4 3 4
     >>>

Hm.  We certainly expected the last statement to print ‘3 4 1 2’.  What
happened?  Here are the steps of the ‘rc.a, rc.b = rc.b, rc.a’ line
above:

     >>> temp0, temp1 = rc.b, rc.a
     >>> rc.a = temp0
     >>> rc.b = temp1
     >>>

Note that ‘temp0’ and ‘temp1’ are objects still using the internal
buffer of the ‘rc’ object above.  So executing ‘rc.a = temp0’ copies the
buffer contents of ‘temp0’ into ‘rc’ ‘s buffer.  This, in turn, changes
the contents of ‘temp1’.  So, the last assignment ‘rc.b = temp1’,
doesn’t have the expected effect.

Keep in mind that retrieving sub-objects from Structure, Unions, and
Arrays doesn’t `copy' the sub-object, instead it retrieves a wrapper
object accessing the root-object’s underlying buffer.

Another example that may behave differently from what one would expect
is this:

     >>> s = c_char_p()
     >>> s.value = b"abc def ghi"
     >>> s.value
     b'abc def ghi'
     >>> s.value is s.value
     False
     >>>

     Note: Objects instantiated from *note c_char_p: 2426. can only have
     their value set to bytes or integers.

Why is it printing ‘False’?  ctypes instances are objects containing a
memory block plus some *note descriptor: 1579.s accessing the contents
of the memory.  Storing a Python object in the memory block does not
store the object itself, instead the ‘contents’ of the object is stored.
Accessing the contents again constructs a new Python object each time!


File: python.info,  Node: Variable-sized data types,  Prev: Surprises,  Up: ctypes tutorial

5.16.16.21 Variable-sized data types
....................................

*note ctypes: 2a. provides some support for variable-sized arrays and
structures.

The *note resize(): 2457. function can be used to resize the memory
buffer of an existing ctypes object.  The function takes the object as
first argument, and the requested size in bytes as the second argument.
The memory block cannot be made smaller than the natural memory block
specified by the objects type, a *note ValueError: 16d. is raised if
this is tried:

     >>> short_array = (c_short * 4)()
     >>> print(sizeof(short_array))
     8
     >>> resize(short_array, 4)
     Traceback (most recent call last):
         ...
     ValueError: minimum size is 8
     >>> resize(short_array, 32)
     >>> sizeof(short_array)
     32
     >>> sizeof(type(short_array))
     8
     >>>

This is nice and fine, but how would one access the additional elements
contained in this array?  Since the type still only knows about 4
elements, we get errors accessing other elements:

     >>> short_array[:]
     [0, 0, 0, 0]
     >>> short_array[7]
     Traceback (most recent call last):
         ...
     IndexError: invalid index
     >>>

Another way to use variable-sized data types with *note ctypes: 2a. is
to use the dynamic nature of Python, and (re-)define the data type after
the required size is already known, on a case by case basis.


File: python.info,  Node: ctypes reference,  Prev: ctypes tutorial,  Up: ctypes — A foreign function library for Python

5.16.16.22 ctypes reference
...........................

* Menu:

* Finding shared libraries::
* Loading shared libraries::
* Foreign functions::
* Function prototypes::
* Utility functions::
* Data types::
* Fundamental data types: Fundamental data types<2>.
* Structured data types::
* Arrays and pointers::


File: python.info,  Node: Finding shared libraries,  Next: Loading shared libraries,  Up: ctypes reference

5.16.16.23 Finding shared libraries
...................................

When programming in a compiled language, shared libraries are accessed
when compiling/linking a program, and when the program is run.

The purpose of the ‘find_library()’ function is to locate a library in a
way similar to what the compiler or runtime loader does (on platforms
with several versions of a shared library the most recent should be
loaded), while the ctypes library loaders act like when a program is
run, and call the runtime loader directly.

The ‘ctypes.util’ module provides a function which can help to determine
the library to load.

 -- Data: ctypes.util.find_library (name)

     Try to find a library and return a pathname.  `name' is the library
     name without any prefix like `lib', suffix like ‘.so’, ‘.dylib’ or
     version number (this is the form used for the posix linker option
     ‘-l’).  If no library can be found, returns ‘None’.

The exact functionality is system dependent.

On Linux, ‘find_library()’ tries to run external programs
(‘/sbin/ldconfig’, ‘gcc’, ‘objdump’ and ‘ld’) to find the library file.
It returns the filename of the library file.

Changed in version 3.6: On Linux, the value of the environment variable
‘LD_LIBRARY_PATH’ is used when searching for libraries, if a library
cannot be found by any other means.

Here are some examples:

     >>> from ctypes.util import find_library
     >>> find_library("m")
     'libm.so.6'
     >>> find_library("c")
     'libc.so.6'
     >>> find_library("bz2")
     'libbz2.so.1.0'
     >>>

On macOS, ‘find_library()’ tries several predefined naming schemes and
paths to locate the library, and returns a full pathname if successful:

     >>> from ctypes.util import find_library
     >>> find_library("c")
     '/usr/lib/libc.dylib'
     >>> find_library("m")
     '/usr/lib/libm.dylib'
     >>> find_library("bz2")
     '/usr/lib/libbz2.dylib'
     >>> find_library("AGL")
     '/System/Library/Frameworks/AGL.framework/AGL'
     >>>

On Windows, ‘find_library()’ searches along the system search path, and
returns the full pathname, but since there is no predefined naming
scheme a call like ‘find_library("c")’ will fail and return ‘None’.

If wrapping a shared library with *note ctypes: 2a, it `may' be better
to determine the shared library name at development time, and hardcode
that into the wrapper module instead of using ‘find_library()’ to locate
the library at runtime.


File: python.info,  Node: Loading shared libraries,  Next: Foreign functions,  Prev: Finding shared libraries,  Up: ctypes reference

5.16.16.24 Loading shared libraries
...................................

There are several ways to load shared libraries into the Python process.
One way is to instantiate one of the following classes:

 -- Class: ctypes.CDLL (name, mode=DEFAULT_MODE, handle=None,
          use_errno=False, use_last_error=False, winmode=None)

     Instances of this class represent loaded shared libraries.
     Functions in these libraries use the standard C calling convention,
     and are assumed to return ‘int’.

     On Windows creating a *note CDLL: 2f2. instance may fail even if
     the DLL name exists.  When a dependent DLL of the loaded DLL is not
     found, a *note OSError: 304. error is raised with the message
     `“[WinError 126] The specified module could not be found”.'  This
     error message does not contain the name of the missing DLL because
     the Windows API does not return this information making this error
     hard to diagnose.  To resolve this error and determine which DLL is
     not found, you need to find the list of dependent DLLs and
     determine which one is not found using Windows debugging and
     tracing tools.

See also
........

Microsoft DUMPBIN tool(1) – A tool to find DLL dependents.

 -- Class: ctypes.OleDLL (name, mode=DEFAULT_MODE, handle=None,
          use_errno=False, use_last_error=False, winmode=None)

     Windows only: Instances of this class represent loaded shared
     libraries, functions in these libraries use the ‘stdcall’ calling
     convention, and are assumed to return the windows specific *note
     HRESULT: 245f. code.  *note HRESULT: 245f. values contain
     information specifying whether the function call failed or
     succeeded, together with additional error code.  If the return
     value signals a failure, an *note OSError: 304. is automatically
     raised.

     Changed in version 3.3: *note WindowsError: a75. used to be raised.

 -- Class: ctypes.WinDLL (name, mode=DEFAULT_MODE, handle=None,
          use_errno=False, use_last_error=False, winmode=None)

     Windows only: Instances of this class represent loaded shared
     libraries, functions in these libraries use the ‘stdcall’ calling
     convention, and are assumed to return ‘int’ by default.

     On Windows CE only the standard calling convention is used, for
     convenience the *note WinDLL: 2460. and *note OleDLL: 245e. use the
     standard calling convention on this platform.

The Python *note global interpreter lock: 600. is released before
calling any function exported by these libraries, and reacquired
afterwards.

 -- Class: ctypes.PyDLL (name, mode=DEFAULT_MODE, handle=None)

     Instances of this class behave like *note CDLL: 2f2. instances,
     except that the Python GIL is `not' released during the function
     call, and after the function execution the Python error flag is
     checked.  If the error flag is set, a Python exception is raised.

     Thus, this is only useful to call Python C api functions directly.

All these classes can be instantiated by calling them with at least one
argument, the pathname of the shared library.  If you have an existing
handle to an already loaded shared library, it can be passed as the
‘handle’ named parameter, otherwise the underlying platforms ‘dlopen’ or
‘LoadLibrary’ function is used to load the library into the process, and
to get a handle to it.

The `mode' parameter can be used to specify how the library is loaded.
For details, consult the ‘dlopen(3)’ manpage.  On Windows, `mode' is
ignored.  On posix systems, RTLD_NOW is always added, and is not
configurable.

The `use_errno' parameter, when set to true, enables a ctypes mechanism
that allows accessing the system *note errno: 7a. error number in a safe
way.  *note ctypes: 2a. maintains a thread-local copy of the systems
*note errno: 7a. variable; if you call foreign functions created with
‘use_errno=True’ then the *note errno: 7a. value before the function
call is swapped with the ctypes private copy, the same happens
immediately after the function call.

The function *note ctypes.get_errno(): 2462. returns the value of the
ctypes private copy, and the function *note ctypes.set_errno(): 2463.
changes the ctypes private copy to a new value and returns the former
value.

The `use_last_error' parameter, when set to true, enables the same
mechanism for the Windows error code which is managed by the *note
GetLastError(): 2431. and ‘SetLastError()’ Windows API functions; *note
ctypes.get_last_error(): 2464. and *note ctypes.set_last_error(): 2465.
are used to request and change the ctypes private copy of the windows
error code.

The `winmode' parameter is used on Windows to specify how the library is
loaded (since `mode' is ignored).  It takes any value that is valid for
the Win32 API ‘LoadLibraryEx’ flags parameter.  When omitted, the
default is to use the flags that result in the most secure DLL load to
avoiding issues such as DLL hijacking.  Passing the full path to the DLL
is the safest way to ensure the correct library and dependencies are
loaded.

Changed in version 3.8: Added `winmode' parameter.

 -- Data: ctypes.RTLD_GLOBAL

     Flag to use as `mode' parameter.  On platforms where this flag is
     not available, it is defined as the integer zero.

 -- Data: ctypes.RTLD_LOCAL

     Flag to use as `mode' parameter.  On platforms where this is not
     available, it is the same as `RTLD_GLOBAL'.

 -- Data: ctypes.DEFAULT_MODE

     The default mode which is used to load shared libraries.  On OSX
     10.3, this is `RTLD_GLOBAL', otherwise it is the same as
     `RTLD_LOCAL'.

Instances of these classes have no public methods.  Functions exported
by the shared library can be accessed as attributes or by index.  Please
note that accessing the function through an attribute caches the result
and therefore accessing it repeatedly returns the same object each time.
On the other hand, accessing it through an index returns a new object
each time:

     >>> from ctypes import CDLL
     >>> libc = CDLL("libc.so.6")  # On Linux
     >>> libc.time == libc.time
     True
     >>> libc['time'] == libc['time']
     False

The following public attributes are available, their name starts with an
underscore to not clash with exported function names:

 -- Attribute: PyDLL._handle

     The system handle used to access the library.

 -- Attribute: PyDLL._name

     The name of the library passed in the constructor.

Shared libraries can also be loaded by using one of the prefabricated
objects, which are instances of the *note LibraryLoader: 2468. class,
either by calling the ‘LoadLibrary()’ method, or by retrieving the
library as attribute of the loader instance.

 -- Class: ctypes.LibraryLoader (dlltype)

     Class which loads shared libraries.  `dlltype' should be one of the
     *note CDLL: 2f2, *note PyDLL: 2461, *note WinDLL: 2460, or *note
     OleDLL: 245e. types.

     *note __getattr__(): 42a. has special behavior: It allows loading a
     shared library by accessing it as attribute of a library loader
     instance.  The result is cached, so repeated attribute accesses
     return the same library each time.

      -- Method: LoadLibrary (name)

          Load a shared library into the process and return it.  This
          method always returns a new instance of the library.

These prefabricated library loaders are available:

 -- Data: ctypes.cdll

     Creates *note CDLL: 2f2. instances.

 -- Data: ctypes.windll

     Windows only: Creates *note WinDLL: 2460. instances.

 -- Data: ctypes.oledll

     Windows only: Creates *note OleDLL: 245e. instances.

 -- Data: ctypes.pydll

     Creates *note PyDLL: 2461. instances.

For accessing the C Python api directly, a ready-to-use Python shared
library object is available:

 -- Data: ctypes.pythonapi

     An instance of *note PyDLL: 2461. that exposes Python C API
     functions as attributes.  Note that all these functions are assumed
     to return C ‘int’, which is of course not always the truth, so you
     have to assign the correct ‘restype’ attribute to use these
     functions.

Loading a library through any of these objects raises an *note auditing
event: fa1. ‘ctypes.dlopen’ with string argument ‘name’, the name used
to load the library.

Accessing a function on a loaded library raises an auditing event
‘ctypes.dlsym’ with arguments ‘library’ (the library object) and ‘name’
(the symbol’s name as a string or integer).

In cases when only the library handle is available rather than the
object, accessing a function raises an auditing event
‘ctypes.dlsym/handle’ with arguments ‘handle’ (the raw library handle)
and ‘name’.

   ---------- Footnotes ----------

   (1) https://docs.microsoft.com/cpp/build/reference/dependents


File: python.info,  Node: Foreign functions,  Next: Function prototypes,  Prev: Loading shared libraries,  Up: ctypes reference

5.16.16.25 Foreign functions
............................

As explained in the previous section, foreign functions can be accessed
as attributes of loaded shared libraries.  The function objects created
in this way by default accept any number of arguments, accept any ctypes
data instances as arguments, and return the default result type
specified by the library loader.  They are instances of a private class:

 -- Class: ctypes._FuncPtr

     Base class for C callable foreign functions.

     Instances of foreign functions are also C compatible data types;
     they represent C function pointers.

     This behavior can be customized by assigning to special attributes
     of the foreign function object.

      -- Attribute: restype

          Assign a ctypes type to specify the result type of the foreign
          function.  Use ‘None’ for ‘void’, a function not returning
          anything.

          It is possible to assign a callable Python object that is not
          a ctypes type, in this case the function is assumed to return
          a C ‘int’, and the callable will be called with this integer,
          allowing further processing or error checking.  Using this is
          deprecated, for more flexible post processing or error
          checking use a ctypes data type as *note restype: 246d. and
          assign a callable to the *note errcheck: 246e. attribute.

      -- Attribute: argtypes

          Assign a tuple of ctypes types to specify the argument types
          that the function accepts.  Functions using the ‘stdcall’
          calling convention can only be called with the same number of
          arguments as the length of this tuple; functions using the C
          calling convention accept additional, unspecified arguments as
          well.

          When a foreign function is called, each actual argument is
          passed to the ‘from_param()’ class method of the items in the
          *note argtypes: 246f. tuple, this method allows adapting the
          actual argument to an object that the foreign function
          accepts.  For example, a *note c_char_p: 2426. item in the
          *note argtypes: 246f. tuple will convert a string passed as
          argument into a bytes object using ctypes conversion rules.

          New: It is now possible to put items in argtypes which are not
          ctypes types, but each item must have a ‘from_param()’ method
          which returns a value usable as argument (integer, string,
          ctypes instance).  This allows defining adapters that can
          adapt custom objects as function parameters.

      -- Attribute: errcheck

          Assign a Python function or another callable to this
          attribute.  The callable will be called with three or more
          arguments:

           -- Function: callable (result, func, arguments)

               `result' is what the foreign function returns, as
               specified by the ‘restype’ attribute.

               `func' is the foreign function object itself, this allows
               reusing the same callable object to check or post process
               the results of several functions.

               `arguments' is a tuple containing the parameters
               originally passed to the function call, this allows
               specializing the behavior on the arguments used.

          The object that this function returns will be returned from
          the foreign function call, but it can also check the result
          value and raise an exception if the foreign function call
          failed.

 -- Exception: ctypes.ArgumentError

     This exception is raised when a foreign function call cannot
     convert one of the passed arguments.

On Windows, when a foreign function call raises a system exception (for
example, due to an access violation), it will be captured and replaced
with a suitable Python exception.  Further, an auditing event
‘ctypes.seh_exception’ with argument ‘code’ will be raised, allowing an
audit hook to replace the exception with its own.

Some ways to invoke foreign function calls may raise an auditing event
‘ctypes.call_function’ with arguments ‘function pointer’ and
‘arguments’.


File: python.info,  Node: Function prototypes,  Next: Utility functions,  Prev: Foreign functions,  Up: ctypes reference

5.16.16.26 Function prototypes
..............................

Foreign functions can also be created by instantiating function
prototypes.  Function prototypes are similar to function prototypes in
C; they describe a function (return type, argument types, calling
convention) without defining an implementation.  The factory functions
must be called with the desired result type and the argument types of
the function, and can be used as decorator factories, and as such, be
applied to functions through the ‘@wrapper’ syntax.  See *note Callback
functions: 244b. for examples.

 -- Function: ctypes.CFUNCTYPE (restype, *argtypes, use_errno=False,
          use_last_error=False)

     The returned function prototype creates functions that use the
     standard C calling convention.  The function will release the GIL
     during the call.  If `use_errno' is set to true, the ctypes private
     copy of the system *note errno: 7a. variable is exchanged with the
     real *note errno: 7a. value before and after the call;
     `use_last_error' does the same for the Windows error code.

 -- Function: ctypes.WINFUNCTYPE (restype, *argtypes, use_errno=False,
          use_last_error=False)

     Windows only: The returned function prototype creates functions
     that use the ‘stdcall’ calling convention, except on Windows CE
     where *note WINFUNCTYPE(): 244d. is the same as *note CFUNCTYPE():
     244c.  The function will release the GIL during the call.
     `use_errno' and `use_last_error' have the same meaning as above.

 -- Function: ctypes.PYFUNCTYPE (restype, *argtypes)

     The returned function prototype creates functions that use the
     Python calling convention.  The function will `not' release the GIL
     during the call.

Function prototypes created by these factory functions can be
instantiated in different ways, depending on the type and number of the
parameters in the call:

      -- Function: prototype (address)

          Returns a foreign function at the specified address which must
          be an integer.

      -- Function: prototype (callable)

          Create a C callable function (a callback function) from a
          Python `callable'.

      -- Function: prototype (func_spec[, paramflags])

          Returns a foreign function exported by a shared library.
          `func_spec' must be a 2-tuple ‘(name_or_ordinal, library)’.
          The first item is the name of the exported function as string,
          or the ordinal of the exported function as small integer.  The
          second item is the shared library instance.

      -- Function: prototype (vtbl_index, name[, paramflags[, iid]])

          Returns a foreign function that will call a COM method.
          `vtbl_index' is the index into the virtual function table, a
          small non-negative integer.  `name' is name of the COM method.
          `iid' is an optional pointer to the interface identifier which
          is used in extended error reporting.

          COM methods use a special calling convention: They require a
          pointer to the COM interface as first argument, in addition to
          those parameters that are specified in the ‘argtypes’ tuple.

     The optional `paramflags' parameter creates foreign function
     wrappers with much more functionality than the features described
     above.

     `paramflags' must be a tuple of the same length as ‘argtypes’.

     Each item in this tuple contains further information about a
     parameter, it must be a tuple containing one, two, or three items.

     The first item is an integer containing a combination of direction
     flags for the parameter:

          1

               Specifies an input parameter to the function.

          2

               Output parameter.  The foreign function fills in a value.

          4

               Input parameter which defaults to the integer zero.

     The optional second item is the parameter name as string.  If this
     is specified, the foreign function can be called with named
     parameters.

     The optional third item is the default value for this parameter.

This example demonstrates how to wrap the Windows ‘MessageBoxW’ function
so that it supports default parameters and named arguments.  The C
declaration from the windows header file is this:

     WINUSERAPI int WINAPI
     MessageBoxW(
         HWND hWnd,
         LPCWSTR lpText,
         LPCWSTR lpCaption,
         UINT uType);

Here is the wrapping with *note ctypes: 2a.:

     >>> from ctypes import c_int, WINFUNCTYPE, windll
     >>> from ctypes.wintypes import HWND, LPCWSTR, UINT
     >>> prototype = WINFUNCTYPE(c_int, HWND, LPCWSTR, LPCWSTR, UINT)
     >>> paramflags = (1, "hwnd", 0), (1, "text", "Hi"), (1, "caption", "Hello from ctypes"), (1, "flags", 0)
     >>> MessageBox = prototype(("MessageBoxW", windll.user32), paramflags)

The ‘MessageBox’ foreign function can now be called in these ways:

     >>> MessageBox()
     >>> MessageBox(text="Spam, spam, spam")
     >>> MessageBox(flags=2, text="foo bar")

A second example demonstrates output parameters.  The win32
‘GetWindowRect’ function retrieves the dimensions of a specified window
by copying them into ‘RECT’ structure that the caller has to supply.
Here is the C declaration:

     WINUSERAPI BOOL WINAPI
     GetWindowRect(
          HWND hWnd,
          LPRECT lpRect);

Here is the wrapping with *note ctypes: 2a.:

     >>> from ctypes import POINTER, WINFUNCTYPE, windll, WinError
     >>> from ctypes.wintypes import BOOL, HWND, RECT
     >>> prototype = WINFUNCTYPE(BOOL, HWND, POINTER(RECT))
     >>> paramflags = (1, "hwnd"), (2, "lprect")
     >>> GetWindowRect = prototype(("GetWindowRect", windll.user32), paramflags)
     >>>

Functions with output parameters will automatically return the output
parameter value if there is a single one, or a tuple containing the
output parameter values when there are more than one, so the
GetWindowRect function now returns a RECT instance, when called.

Output parameters can be combined with the ‘errcheck’ protocol to do
further output processing and error checking.  The win32 ‘GetWindowRect’
api function returns a ‘BOOL’ to signal success or failure, so this
function could do the error checking, and raises an exception when the
api call failed:

     >>> def errcheck(result, func, args):
     ...     if not result:
     ...         raise WinError()
     ...     return args
     ...
     >>> GetWindowRect.errcheck = errcheck
     >>>

If the ‘errcheck’ function returns the argument tuple it receives
unchanged, *note ctypes: 2a. continues the normal processing it does on
the output parameters.  If you want to return a tuple of window
coordinates instead of a ‘RECT’ instance, you can retrieve the fields in
the function and return them instead, the normal processing will no
longer take place:

     >>> def errcheck(result, func, args):
     ...     if not result:
     ...         raise WinError()
     ...     rc = args[1]
     ...     return rc.left, rc.top, rc.bottom, rc.right
     ...
     >>> GetWindowRect.errcheck = errcheck
     >>>


File: python.info,  Node: Utility functions,  Next: Data types,  Prev: Function prototypes,  Up: ctypes reference

5.16.16.27 Utility functions
............................

 -- Function: ctypes.addressof (obj)

     Returns the address of the memory buffer as integer.  `obj' must be
     an instance of a ctypes type.

     Raises an *note auditing event: fa1. ‘ctypes.addressof’ with
     argument ‘obj’.

 -- Function: ctypes.alignment (obj_or_type)

     Returns the alignment requirements of a ctypes type.  `obj_or_type'
     must be a ctypes type or instance.

 -- Function: ctypes.byref (obj[, offset])

     Returns a light-weight pointer to `obj', which must be an instance
     of a ctypes type.  `offset' defaults to zero, and must be an
     integer that will be added to the internal pointer value.

     ‘byref(obj, offset)’ corresponds to this C code:

          (((char *)&obj) + offset)

     The returned object can only be used as a foreign function call
     parameter.  It behaves similar to ‘pointer(obj)’, but the
     construction is a lot faster.

 -- Function: ctypes.cast (obj, type)

     This function is similar to the cast operator in C. It returns a
     new instance of `type' which points to the same memory block as
     `obj'.  `type' must be a pointer type, and `obj' must be an object
     that can be interpreted as a pointer.

 -- Function: ctypes.create_string_buffer (init_or_size, size=None)

     This function creates a mutable character buffer.  The returned
     object is a ctypes array of *note c_char: 241a.

     `init_or_size' must be an integer which specifies the size of the
     array, or a bytes object which will be used to initialize the array
     items.

     If a bytes object is specified as first argument, the buffer is
     made one item larger than its length so that the last element in
     the array is a NUL termination character.  An integer can be passed
     as second argument which allows specifying the size of the array if
     the length of the bytes should not be used.

     Raises an *note auditing event: fa1. ‘ctypes.create_string_buffer’
     with arguments ‘init’, ‘size’.

 -- Function: ctypes.create_unicode_buffer (init_or_size, size=None)

     This function creates a mutable unicode character buffer.  The
     returned object is a ctypes array of *note c_wchar: 241b.

     `init_or_size' must be an integer which specifies the size of the
     array, or a string which will be used to initialize the array
     items.

     If a string is specified as first argument, the buffer is made one
     item larger than the length of the string so that the last element
     in the array is a NUL termination character.  An integer can be
     passed as second argument which allows specifying the size of the
     array if the length of the string should not be used.

     Raises an *note auditing event: fa1. ‘ctypes.create_unicode_buffer’
     with arguments ‘init’, ‘size’.

 -- Function: ctypes.DllCanUnloadNow ()

     Windows only: This function is a hook which allows implementing
     in-process COM servers with ctypes.  It is called from the
     DllCanUnloadNow function that the _ctypes extension dll exports.

 -- Function: ctypes.DllGetClassObject ()

     Windows only: This function is a hook which allows implementing
     in-process COM servers with ctypes.  It is called from the
     DllGetClassObject function that the ‘_ctypes’ extension dll
     exports.

 -- Function: ctypes.util.find_library (name)

     Try to find a library and return a pathname.  `name' is the library
     name without any prefix like ‘lib’, suffix like ‘.so’, ‘.dylib’ or
     version number (this is the form used for the posix linker option
     ‘-l’).  If no library can be found, returns ‘None’.

     The exact functionality is system dependent.

 -- Function: ctypes.util.find_msvcrt ()

     Windows only: return the filename of the VC runtime library used by
     Python, and by the extension modules.  If the name of the library
     cannot be determined, ‘None’ is returned.

     If you need to free memory, for example, allocated by an extension
     module with a call to the ‘free(void *)’, it is important that you
     use the function in the same library that allocated the memory.

 -- Function: ctypes.FormatError ([code])

     Windows only: Returns a textual description of the error code
     `code'.  If no error code is specified, the last error code is used
     by calling the Windows api function GetLastError.

 -- Function: ctypes.GetLastError ()

     Windows only: Returns the last error code set by Windows in the
     calling thread.  This function calls the Windows ‘GetLastError()’
     function directly, it does not return the ctypes-private copy of
     the error code.

 -- Function: ctypes.get_errno ()

     Returns the current value of the ctypes-private copy of the system
     *note errno: 7a. variable in the calling thread.

     Raises an *note auditing event: fa1. ‘ctypes.get_errno’ with no
     arguments.

 -- Function: ctypes.get_last_error ()

     Windows only: returns the current value of the ctypes-private copy
     of the system ‘LastError’ variable in the calling thread.

     Raises an *note auditing event: fa1. ‘ctypes.get_last_error’ with
     no arguments.

 -- Function: ctypes.memmove (dst, src, count)

     Same as the standard C memmove library function: copies `count'
     bytes from `src' to `dst'.  `dst' and `src' must be integers or
     ctypes instances that can be converted to pointers.

 -- Function: ctypes.memset (dst, c, count)

     Same as the standard C memset library function: fills the memory
     block at address `dst' with `count' bytes of value `c'.  `dst' must
     be an integer specifying an address, or a ctypes instance.

 -- Function: ctypes.POINTER (type)

     This factory function creates and returns a new ctypes pointer
     type.  Pointer types are cached and reused internally, so calling
     this function repeatedly is cheap.  `type' must be a ctypes type.

 -- Function: ctypes.pointer (obj)

     This function creates a new pointer instance, pointing to `obj'.
     The returned object is of the type ‘POINTER(type(obj))’.

     Note: If you just want to pass a pointer to an object to a foreign
     function call, you should use ‘byref(obj)’ which is much faster.

 -- Function: ctypes.resize (obj, size)

     This function resizes the internal memory buffer of `obj', which
     must be an instance of a ctypes type.  It is not possible to make
     the buffer smaller than the native size of the objects type, as
     given by ‘sizeof(type(obj))’, but it is possible to enlarge the
     buffer.

 -- Function: ctypes.set_errno (value)

     Set the current value of the ctypes-private copy of the system
     *note errno: 7a. variable in the calling thread to `value' and
     return the previous value.

     Raises an *note auditing event: fa1. ‘ctypes.set_errno’ with
     argument ‘errno’.

 -- Function: ctypes.set_last_error (value)

     Windows only: set the current value of the ctypes-private copy of
     the system ‘LastError’ variable in the calling thread to `value'
     and return the previous value.

     Raises an *note auditing event: fa1. ‘ctypes.set_last_error’ with
     argument ‘error’.

 -- Function: ctypes.sizeof (obj_or_type)

     Returns the size in bytes of a ctypes type or instance memory
     buffer.  Does the same as the C ‘sizeof’ operator.

 -- Function: ctypes.string_at (address, size=-1)

     This function returns the C string starting at memory address
     `address' as a bytes object.  If size is specified, it is used as
     size, otherwise the string is assumed to be zero-terminated.

     Raises an *note auditing event: fa1. ‘ctypes.string_at’ with
     arguments ‘address’, ‘size’.

 -- Function: ctypes.WinError (code=None, descr=None)

     Windows only: this function is probably the worst-named thing in
     ctypes.  It creates an instance of OSError.  If `code' is not
     specified, ‘GetLastError’ is called to determine the error code.
     If `descr' is not specified, *note FormatError(): 247b. is called
     to get a textual description of the error.

     Changed in version 3.3: An instance of *note WindowsError: a75.
     used to be created.

 -- Function: ctypes.wstring_at (address, size=-1)

     This function returns the wide character string starting at memory
     address `address' as a string.  If `size' is specified, it is used
     as the number of characters of the string, otherwise the string is
     assumed to be zero-terminated.

     Raises an *note auditing event: fa1. ‘ctypes.wstring_at’ with
     arguments ‘address’, ‘size’.


File: python.info,  Node: Data types,  Next: Fundamental data types<2>,  Prev: Utility functions,  Up: ctypes reference

5.16.16.28 Data types
.....................

 -- Class: ctypes._CData

     This non-public class is the common base class of all ctypes data
     types.  Among other things, all ctypes type instances contain a
     memory block that hold C compatible data; the address of the memory
     block is returned by the *note addressof(): 2476. helper function.
     Another instance variable is exposed as *note _objects: 2484.; this
     contains other Python objects that need to be kept alive in case
     the memory block contains pointers.

     Common methods of ctypes data types, these are all class methods
     (to be exact, they are methods of the *note metaclass: 1590.):

      -- Method: from_buffer (source[, offset])

          This method returns a ctypes instance that shares the buffer
          of the `source' object.  The `source' object must support the
          writeable buffer interface.  The optional `offset' parameter
          specifies an offset into the source buffer in bytes; the
          default is zero.  If the source buffer is not large enough a
          *note ValueError: 16d. is raised.

          Raises an *note auditing event: fa1. ‘ctypes.cdata/buffer’
          with arguments ‘pointer’, ‘size’, ‘offset’.

      -- Method: from_buffer_copy (source[, offset])

          This method creates a ctypes instance, copying the buffer from
          the `source' object buffer which must be readable.  The
          optional `offset' parameter specifies an offset into the
          source buffer in bytes; the default is zero.  If the source
          buffer is not large enough a *note ValueError: 16d. is raised.

          Raises an *note auditing event: fa1. ‘ctypes.cdata/buffer’
          with arguments ‘pointer’, ‘size’, ‘offset’.

      -- Method: from_address (address)

          This method returns a ctypes type instance using the memory
          specified by `address' which must be an integer.

          This method, and others that indirectly call this method,
          raises an *note auditing event: fa1. ‘ctypes.cdata’ with
          argument ‘address’.

      -- Method: from_param (obj)

          This method adapts `obj' to a ctypes type.  It is called with
          the actual object used in a foreign function call when the
          type is present in the foreign function’s ‘argtypes’ tuple; it
          must return an object that can be used as a function call
          parameter.

          All ctypes data types have a default implementation of this
          classmethod that normally returns `obj' if that is an instance
          of the type.  Some types accept other objects as well.

      -- Method: in_dll (library, name)

          This method returns a ctypes type instance exported by a
          shared library.  `name' is the name of the symbol that exports
          the data, `library' is the loaded shared library.

     Common instance variables of ctypes data types:

      -- Attribute: _b_base_

          Sometimes ctypes data instances do not own the memory block
          they contain, instead they share part of the memory block of a
          base object.  The *note _b_base_: 248a. read-only member is
          the root ctypes object that owns the memory block.

      -- Attribute: _b_needsfree_

          This read-only variable is true when the ctypes data instance
          has allocated the memory block itself, false otherwise.

      -- Attribute: _objects

          This member is either ‘None’ or a dictionary containing Python
          objects that need to be kept alive so that the memory block
          contents is kept valid.  This object is only exposed for
          debugging; never modify the contents of this dictionary.


File: python.info,  Node: Fundamental data types<2>,  Next: Structured data types,  Prev: Data types,  Up: ctypes reference

5.16.16.29 Fundamental data types
.................................

 -- Class: ctypes._SimpleCData

     This non-public class is the base class of all fundamental ctypes
     data types.  It is mentioned here because it contains the common
     attributes of the fundamental ctypes data types.  *note
     _SimpleCData: 248e. is a subclass of *note _CData: 11e5, so it
     inherits their methods and attributes.  ctypes data types that are
     not and do not contain pointers can now be pickled.

     Instances have a single attribute:

      -- Attribute: value

          This attribute contains the actual value of the instance.  For
          integer and pointer types, it is an integer, for character
          types, it is a single character bytes object or string, for
          character pointer types it is a Python bytes object or string.

          When the ‘value’ attribute is retrieved from a ctypes
          instance, usually a new object is returned each time.  *note
          ctypes: 2a. does `not' implement original object return,
          always a new object is constructed.  The same is true for all
          other ctypes object instances.

Fundamental data types, when returned as foreign function call results,
or, for example, by retrieving structure field members or array items,
are transparently converted to native Python types.  In other words, if
a foreign function has a ‘restype’ of *note c_char_p: 2426, you will
always receive a Python bytes object, `not' a *note c_char_p: 2426.
instance.

Subclasses of fundamental data types do `not' inherit this behavior.
So, if a foreign functions ‘restype’ is a subclass of *note c_void_p:
2427, you will receive an instance of this subclass from the function
call.  Of course, you can get the value of the pointer by accessing the
‘value’ attribute.

These are the fundamental ctypes data types:

 -- Class: ctypes.c_byte

     Represents the C ‘signed char’ datatype, and interprets the value
     as small integer.  The constructor accepts an optional integer
     initializer; no overflow checking is done.

 -- Class: ctypes.c_char

     Represents the C ‘char’ datatype, and interprets the value as a
     single character.  The constructor accepts an optional string
     initializer, the length of the string must be exactly one
     character.

 -- Class: ctypes.c_char_p

     Represents the C ‘char *’ datatype when it points to a
     zero-terminated string.  For a general character pointer that may
     also point to binary data, ‘POINTER(c_char)’ must be used.  The
     constructor accepts an integer address, or a bytes object.

 -- Class: ctypes.c_double

     Represents the C ‘double’ datatype.  The constructor accepts an
     optional float initializer.

 -- Class: ctypes.c_longdouble

     Represents the C ‘long double’ datatype.  The constructor accepts
     an optional float initializer.  On platforms where ‘sizeof(long
     double) == sizeof(double)’ it is an alias to *note c_double: fc4.

 -- Class: ctypes.c_float

     Represents the C ‘float’ datatype.  The constructor accepts an
     optional float initializer.

 -- Class: ctypes.c_int

     Represents the C ‘signed int’ datatype.  The constructor accepts an
     optional integer initializer; no overflow checking is done.  On
     platforms where ‘sizeof(int) == sizeof(long)’ it is an alias to
     *note c_long: 2410.

 -- Class: ctypes.c_int8

     Represents the C 8-bit ‘signed int’ datatype.  Usually an alias for
     *note c_byte: 241c.

 -- Class: ctypes.c_int16

     Represents the C 16-bit ‘signed int’ datatype.  Usually an alias
     for *note c_short: 241e.

 -- Class: ctypes.c_int32

     Represents the C 32-bit ‘signed int’ datatype.  Usually an alias
     for *note c_int: 240f.

 -- Class: ctypes.c_int64

     Represents the C 64-bit ‘signed int’ datatype.  Usually an alias
     for *note c_longlong: 2422.

 -- Class: ctypes.c_long

     Represents the C ‘signed long’ datatype.  The constructor accepts
     an optional integer initializer; no overflow checking is done.

 -- Class: ctypes.c_longlong

     Represents the C ‘signed long long’ datatype.  The constructor
     accepts an optional integer initializer; no overflow checking is
     done.

 -- Class: ctypes.c_short

     Represents the C ‘signed short’ datatype.  The constructor accepts
     an optional integer initializer; no overflow checking is done.

 -- Class: ctypes.c_size_t

     Represents the C ‘size_t’ datatype.

 -- Class: ctypes.c_ssize_t

     Represents the C ‘ssize_t’ datatype.

     New in version 3.2.

 -- Class: ctypes.c_ubyte

     Represents the C ‘unsigned char’ datatype, it interprets the value
     as small integer.  The constructor accepts an optional integer
     initializer; no overflow checking is done.

 -- Class: ctypes.c_uint

     Represents the C ‘unsigned int’ datatype.  The constructor accepts
     an optional integer initializer; no overflow checking is done.  On
     platforms where ‘sizeof(int) == sizeof(long)’ it is an alias for
     *note c_ulong: 2421.

 -- Class: ctypes.c_uint8

     Represents the C 8-bit ‘unsigned int’ datatype.  Usually an alias
     for *note c_ubyte: 241d.

 -- Class: ctypes.c_uint16

     Represents the C 16-bit ‘unsigned int’ datatype.  Usually an alias
     for *note c_ushort: 241f.

 -- Class: ctypes.c_uint32

     Represents the C 32-bit ‘unsigned int’ datatype.  Usually an alias
     for *note c_uint: 2420.

 -- Class: ctypes.c_uint64

     Represents the C 64-bit ‘unsigned int’ datatype.  Usually an alias
     for *note c_ulonglong: 2423.

 -- Class: ctypes.c_ulong

     Represents the C ‘unsigned long’ datatype.  The constructor accepts
     an optional integer initializer; no overflow checking is done.

 -- Class: ctypes.c_ulonglong

     Represents the C ‘unsigned long long’ datatype.  The constructor
     accepts an optional integer initializer; no overflow checking is
     done.

 -- Class: ctypes.c_ushort

     Represents the C ‘unsigned short’ datatype.  The constructor
     accepts an optional integer initializer; no overflow checking is
     done.

 -- Class: ctypes.c_void_p

     Represents the C ‘void *’ type.  The value is represented as
     integer.  The constructor accepts an optional integer initializer.

 -- Class: ctypes.c_wchar

     Represents the C ‘wchar_t’ datatype, and interprets the value as a
     single character unicode string.  The constructor accepts an
     optional string initializer, the length of the string must be
     exactly one character.

 -- Class: ctypes.c_wchar_p

     Represents the C ‘wchar_t *’ datatype, which must be a pointer to a
     zero-terminated wide character string.  The constructor accepts an
     integer address, or a string.

 -- Class: ctypes.c_bool

     Represent the C ‘bool’ datatype (more accurately, ‘_Bool’ from
     C99).  Its value can be ‘True’ or ‘False’, and the constructor
     accepts any object that has a truth value.

 -- Class: ctypes.HRESULT

     Windows only: Represents a ‘HRESULT’ value, which contains success
     or error information for a function or method call.

 -- Class: ctypes.py_object

     Represents the C *note PyObject *: 5b5. datatype.  Calling this
     without an argument creates a ‘NULL’ *note PyObject *: 5b5.
     pointer.

The ‘ctypes.wintypes’ module provides quite some other Windows specific
data types, for example ‘HWND’, ‘WPARAM’, or ‘DWORD’.  Some useful
structures like ‘MSG’ or ‘RECT’ are also defined.


File: python.info,  Node: Structured data types,  Next: Arrays and pointers,  Prev: Fundamental data types<2>,  Up: ctypes reference

5.16.16.30 Structured data types
................................

 -- Class: ctypes.Union (*args, **kw)

     Abstract base class for unions in native byte order.

 -- Class: ctypes.BigEndianStructure (*args, **kw)

     Abstract base class for structures in `big endian' byte order.

 -- Class: ctypes.LittleEndianStructure (*args, **kw)

     Abstract base class for structures in `little endian' byte order.

Structures with non-native byte order cannot contain pointer type
fields, or any other data types containing pointer type fields.

 -- Class: ctypes.Structure (*args, **kw)

     Abstract base class for structures in `native' byte order.

     Concrete structure and union types must be created by subclassing
     one of these types, and at least define a *note _fields_: 249b.
     class variable.  *note ctypes: 2a. will create *note descriptor:
     1579.s which allow reading and writing the fields by direct
     attribute accesses.  These are the

      -- Attribute: _fields_

          A sequence defining the structure fields.  The items must be
          2-tuples or 3-tuples.  The first item is the name of the
          field, the second item specifies the type of the field; it can
          be any ctypes data type.

          For integer type fields like *note c_int: 240f, a third
          optional item can be given.  It must be a small positive
          integer defining the bit width of the field.

          Field names must be unique within one structure or union.
          This is not checked, only one field can be accessed when names
          are repeated.

          It is possible to define the *note _fields_: 249b. class
          variable `after' the class statement that defines the
          Structure subclass, this allows creating data types that
          directly or indirectly reference themselves:

               class List(Structure):
                   pass
               List._fields_ = [("pnext", POINTER(List)),
                                ...
                               ]

          The *note _fields_: 249b. class variable must, however, be
          defined before the type is first used (an instance is created,
          *note sizeof(): 247e. is called on it, and so on).  Later
          assignments to the *note _fields_: 249b. class variable will
          raise an AttributeError.

          It is possible to define sub-subclasses of structure types,
          they inherit the fields of the base class plus the *note
          _fields_: 249b. defined in the sub-subclass, if any.

      -- Attribute: _pack_

          An optional small integer that allows overriding the alignment
          of structure fields in the instance.  *note _pack_: 249c. must
          already be defined when *note _fields_: 249b. is assigned,
          otherwise it will have no effect.

      -- Attribute: _anonymous_

          An optional sequence that lists the names of unnamed
          (anonymous) fields.  *note _anonymous_: 249d. must be already
          defined when *note _fields_: 249b. is assigned, otherwise it
          will have no effect.

          The fields listed in this variable must be structure or union
          type fields.  *note ctypes: 2a. will create descriptors in the
          structure type that allows accessing the nested fields
          directly, without the need to create the structure or union
          field.

          Here is an example type (Windows):

               class _U(Union):
                   _fields_ = [("lptdesc", POINTER(TYPEDESC)),
                               ("lpadesc", POINTER(ARRAYDESC)),
                               ("hreftype", HREFTYPE)]

               class TYPEDESC(Structure):
                   _anonymous_ = ("u",)
                   _fields_ = [("u", _U),
                               ("vt", VARTYPE)]

          The ‘TYPEDESC’ structure describes a COM data type, the ‘vt’
          field specifies which one of the union fields is valid.  Since
          the ‘u’ field is defined as anonymous field, it is now
          possible to access the members directly off the TYPEDESC
          instance.  ‘td.lptdesc’ and ‘td.u.lptdesc’ are equivalent, but
          the former is faster since it does not need to create a
          temporary union instance:

               td = TYPEDESC()
               td.vt = VT_PTR
               td.lptdesc = POINTER(some_type)
               td.u.lptdesc = POINTER(some_type)

     It is possible to define sub-subclasses of structures, they inherit
     the fields of the base class.  If the subclass definition has a
     separate *note _fields_: 249b. variable, the fields specified in
     this are appended to the fields of the base class.

     Structure and union constructors accept both positional and keyword
     arguments.  Positional arguments are used to initialize member
     fields in the same order as they are appear in *note _fields_:
     249b.  Keyword arguments in the constructor are interpreted as
     attribute assignments, so they will initialize *note _fields_:
     249b. with the same name, or create new attributes for names not
     present in *note _fields_: 249b.


File: python.info,  Node: Arrays and pointers,  Prev: Structured data types,  Up: ctypes reference

5.16.16.31 Arrays and pointers
..............................

 -- Class: ctypes.Array (*args)

     Abstract base class for arrays.

     The recommended way to create concrete array types is by
     multiplying any *note ctypes: 2a. data type with a positive
     integer.  Alternatively, you can subclass this type and define
     *note _length_: 24a0. and *note _type_: 24a1. class variables.
     Array elements can be read and written using standard subscript and
     slice accesses; for slice reads, the resulting object is `not'
     itself an *note Array: 1145.

      -- Attribute: _length_

          A positive integer specifying the number of elements in the
          array.  Out-of-range subscripts result in an *note IndexError:
          f36.  Will be returned by *note len(): 28b.

      -- Attribute: _type_

          Specifies the type of each element in the array.

     Array subclass constructors accept positional arguments, used to
     initialize the elements in order.

 -- Class: ctypes._Pointer

     Private, abstract base class for pointers.

     Concrete pointer types are created by calling *note POINTER():
     2445. with the type that will be pointed to; this is done
     automatically by *note pointer(): 2435.

     If a pointer points to an array, its elements can be read and
     written using standard subscript and slice accesses.  Pointer
     objects have no size, so *note len(): 28b. will raise *note
     TypeError: 1fe.  Negative subscripts will read from the memory
     `before' the pointer (as in C), and out-of-range subscripts will
     probably crash with an access violation (if you’re lucky).

      -- Attribute: _type_

          Specifies the type pointed to.

      -- Attribute: contents

          Returns the object to which to pointer points.  Assigning to
          this attribute changes the pointer to point to the assigned
          object.


File: python.info,  Node: Concurrent Execution,  Next: Networking and Interprocess Communication,  Prev: Generic Operating System Services,  Up: The Python Standard Library

5.17 Concurrent Execution
=========================

The modules described in this chapter provide support for concurrent
execution of code.  The appropriate choice of tool will depend on the
task to be executed (CPU bound vs IO bound) and preferred style of
development (event driven cooperative multitasking vs preemptive
multitasking).  Here’s an overview:

* Menu:

* threading — Thread-based parallelism::
* multiprocessing — Process-based parallelism::
* multiprocessing.shared_memory — Provides shared memory for direct access across processes: multiprocessing shared_memory — Provides shared memory for direct access across processes.
* The concurrent package::
* concurrent.futures — Launching parallel tasks: concurrent futures — Launching parallel tasks.
* subprocess — Subprocess management::
* sched — Event scheduler::
* queue — A synchronized queue class::
* contextvars — Context Variables::
* _thread — Low-level threading API::


File: python.info,  Node: threading — Thread-based parallelism,  Next: multiprocessing — Process-based parallelism,  Up: Concurrent Execution

5.17.1 ‘threading’ — Thread-based parallelism
---------------------------------------------

`Source code:' Lib/threading.py(1)

__________________________________________________________________

This module constructs higher-level threading interfaces on top of the
lower level *note _thread: 2. module.  See also the *note queue: da.
module.

Changed in version 3.7: This module used to be optional, it is now
always available.

     Note: While they are not listed below, the ‘camelCase’ names used
     for some methods and functions in this module in the Python 2.x
     series are still supported by this module.

`CPython implementation detail:' In CPython, due to the *note Global
Interpreter Lock: 600, only one thread can execute Python code at once
(even though certain performance-oriented libraries might overcome this
limitation).  If you want your application to make better use of the
computational resources of multi-core machines, you are advised to use
*note multiprocessing: b7. or *note
concurrent.futures.ProcessPoolExecutor: 196.  However, threading is
still an appropriate model if you want to run multiple I/O-bound tasks
simultaneously.

This module defines the following functions:

 -- Function: threading.active_count ()

     Return the number of *note Thread: 21a. objects currently alive.
     The returned count is equal to the length of the list returned by
     *note enumerate(): f90.

 -- Function: threading.current_thread ()

     Return the current *note Thread: 21a. object, corresponding to the
     caller’s thread of control.  If the caller’s thread of control was
     not created through the *note threading: 10b. module, a dummy
     thread object with limited functionality is returned.

 -- Function: threading.excepthook (args, /)

     Handle uncaught exception raised by *note Thread.run(): 35f.

     The `args' argument has the following attributes:

        * `exc_type': Exception type.

        * `exc_value': Exception value, can be ‘None’.

        * `exc_traceback': Exception traceback, can be ‘None’.

        * `thread': Thread which raised the exception, can be ‘None’.

     If `exc_type' is *note SystemExit: 6f3, the exception is silently
     ignored.  Otherwise, the exception is printed out on *note
     sys.stderr: 1ea.

     If this function raises an exception, *note sys.excepthook(): f24.
     is called to handle it.

     *note threading.excepthook(): 35e. can be overridden to control how
     uncaught exceptions raised by *note Thread.run(): 35f. are handled.

     Storing `exc_value' using a custom hook can create a reference
     cycle.  It should be cleared explicitly to break the reference
     cycle when the exception is no longer needed.

     Storing `thread' using a custom hook can resurrect it if it is set
     to an object which is being finalized.  Avoid storing `thread'
     after the custom hook completes to avoid resurrecting objects.

     See also
     ........

     *note sys.excepthook(): f24. handles uncaught exceptions.

     New in version 3.8.

 -- Function: threading.get_ident ()

     Return the ‘thread identifier’ of the current thread.  This is a
     nonzero integer.  Its value has no direct meaning; it is intended
     as a magic cookie to be used e.g.  to index a dictionary of
     thread-specific data.  Thread identifiers may be recycled when a
     thread exits and another thread is created.

     New in version 3.3.

 -- Function: threading.get_native_id ()

     Return the native integral Thread ID of the current thread assigned
     by the kernel.  This is a non-negative integer.  Its value may be
     used to uniquely identify this particular thread system-wide (until
     the thread terminates, after which the value may be recycled by the
     OS).

     *note Availability: 1491.: Windows, FreeBSD, Linux, macOS, OpenBSD,
     NetBSD, AIX.

     New in version 3.8.

 -- Function: threading.enumerate ()

     Return a list of all *note Thread: 21a. objects currently active.
     The list includes daemonic threads and dummy thread objects created
     by *note current_thread(): 24aa.  It excludes terminated threads
     and threads that have not yet been started.  However, the main
     thread is always part of the result, even when terminated.

 -- Function: threading.main_thread ()

     Return the main *note Thread: 21a. object.  In normal conditions,
     the main thread is the thread from which the Python interpreter was
     started.

     New in version 3.4.

 -- Function: threading.settrace (func)

     Set a trace function for all threads started from the *note
     threading: 10b. module.  The `func' will be passed to *note
     sys.settrace(): f00. for each thread, before its *note run(): 35f.
     method is called.

 -- Function: threading.setprofile (func)

     Set a profile function for all threads started from the *note
     threading: 10b. module.  The `func' will be passed to *note
     sys.setprofile(): eff. for each thread, before its *note run():
     35f. method is called.

 -- Function: threading.stack_size ([size])

     Return the thread stack size used when creating new threads.  The
     optional `size' argument specifies the stack size to be used for
     subsequently created threads, and must be 0 (use platform or
     configured default) or a positive integer value of at least 32,768
     (32 KiB). If `size' is not specified, 0 is used.  If changing the
     thread stack size is unsupported, a *note RuntimeError: 3dc. is
     raised.  If the specified stack size is invalid, a *note
     ValueError: 16d. is raised and the stack size is unmodified.  32
     KiB is currently the minimum supported stack size value to
     guarantee sufficient stack space for the interpreter itself.  Note
     that some platforms may have particular restrictions on values for
     the stack size, such as requiring a minimum stack size > 32 KiB or
     requiring allocation in multiples of the system memory page size -
     platform documentation should be referred to for more information
     (4 KiB pages are common; using multiples of 4096 for the stack size
     is the suggested approach in the absence of more specific
     information).

     *note Availability: 1491.: Windows, systems with POSIX threads.

This module also defines the following constant:

 -- Data: threading.TIMEOUT_MAX

     The maximum value allowed for the `timeout' parameter of blocking
     functions (*note Lock.acquire(): 85b, *note RLock.acquire(): 85c,
     *note Condition.wait(): f97, etc.).  Specifying a timeout greater
     than this value will raise an *note OverflowError: a41.

     New in version 3.2.

This module defines a number of classes, which are detailed in the
sections below.

The design of this module is loosely based on Java’s threading model.
However, where Java makes locks and condition variables basic behavior
of every object, they are separate objects in Python.  Python’s *note
Thread: 21a. class supports a subset of the behavior of Java’s Thread
class; currently, there are no priorities, no thread groups, and threads
cannot be destroyed, stopped, suspended, resumed, or interrupted.  The
static methods of Java’s Thread class, when implemented, are mapped to
module-level functions.

All of the methods described below are executed atomically.

* Menu:

* Thread-Local Data::
* Thread Objects::
* Lock Objects::
* RLock Objects::
* Condition Objects::
* Semaphore Objects::
* Event Objects::
* Timer Objects::
* Barrier Objects::
* Using locks, conditions, and semaphores in the with statement: Using locks conditions and semaphores in the with statement.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/threading.py


File: python.info,  Node: Thread-Local Data,  Next: Thread Objects,  Up: threading — Thread-based parallelism

5.17.1.1 Thread-Local Data
..........................

Thread-local data is data whose values are thread specific.  To manage
thread-local data, just create an instance of *note local: 244e. (or a
subclass) and store attributes on it:

     mydata = threading.local()
     mydata.x = 1

The instance’s values will be different for separate threads.

 -- Class: threading.local

     A class that represents thread-local data.

     For more details and extensive examples, see the documentation
     string of the ‘_threading_local’ module.


File: python.info,  Node: Thread Objects,  Next: Lock Objects,  Prev: Thread-Local Data,  Up: threading — Thread-based parallelism

5.17.1.2 Thread Objects
.......................

The *note Thread: 21a. class represents an activity that is run in a
separate thread of control.  There are two ways to specify the activity:
by passing a callable object to the constructor, or by overriding the
*note run(): 35f. method in a subclass.  No other methods (except for
the constructor) should be overridden in a subclass.  In other words,
`only' override the ‘__init__()’ and *note run(): 35f. methods of this
class.

Once a thread object is created, its activity must be started by calling
the thread’s *note start(): 222e. method.  This invokes the *note run():
35f. method in a separate thread of control.

Once the thread’s activity is started, the thread is considered ‘alive’.
It stops being alive when its *note run(): 35f. method terminates –
either normally, or by raising an unhandled exception.  The *note
is_alive(): 21b. method tests whether the thread is alive.

Other threads can call a thread’s *note join(): c32. method.  This
blocks the calling thread until the thread whose *note join(): c32.
method is called is terminated.

A thread has a name.  The name can be passed to the constructor, and
read or changed through the *note name: 24b2. attribute.

If the *note run(): 35f. method raises an exception, *note
threading.excepthook(): 35e. is called to handle it.  By default, *note
threading.excepthook(): 35e. ignores silently *note SystemExit: 6f3.

A thread can be flagged as a “daemon thread”.  The significance of this
flag is that the entire Python program exits when only daemon threads
are left.  The initial value is inherited from the creating thread.  The
flag can be set through the *note daemon: 24b3. property or the `daemon'
constructor argument.

     Note: Daemon threads are abruptly stopped at shutdown.  Their
     resources (such as open files, database transactions, etc.)  may
     not be released properly.  If you want your threads to stop
     gracefully, make them non-daemonic and use a suitable signalling
     mechanism such as an *note Event: b85.

There is a “main thread” object; this corresponds to the initial thread
of control in the Python program.  It is not a daemon thread.

There is the possibility that “dummy thread objects” are created.  These
are thread objects corresponding to “alien threads”, which are threads
of control started outside the threading module, such as directly from C
code.  Dummy thread objects have limited functionality; they are always
considered alive and daemonic, and cannot be *note join(): c32.ed.  They
are never deleted, since it is impossible to detect the termination of
alien threads.

 -- Class: threading.Thread (group=None, target=None, name=None,
          args=(), kwargs={}, *, daemon=None)

     This constructor should always be called with keyword arguments.
     Arguments are:

     `group' should be ‘None’; reserved for future extension when a
     ‘ThreadGroup’ class is implemented.

     `target' is the callable object to be invoked by the *note run():
     35f. method.  Defaults to ‘None’, meaning nothing is called.

     `name' is the thread name.  By default, a unique name is
     constructed of the form “Thread-`N'” where `N' is a small decimal
     number.

     `args' is the argument tuple for the target invocation.  Defaults
     to ‘()’.

     `kwargs' is a dictionary of keyword arguments for the target
     invocation.  Defaults to ‘{}’.

     If not ‘None’, `daemon' explicitly sets whether the thread is
     daemonic.  If ‘None’ (the default), the daemonic property is
     inherited from the current thread.

     If the subclass overrides the constructor, it must make sure to
     invoke the base class constructor (‘Thread.__init__()’) before
     doing anything else to the thread.

     Changed in version 3.3: Added the `daemon' argument.

      -- Method: start ()

          Start the thread’s activity.

          It must be called at most once per thread object.  It arranges
          for the object’s *note run(): 35f. method to be invoked in a
          separate thread of control.

          This method will raise a *note RuntimeError: 3dc. if called
          more than once on the same thread object.

      -- Method: run ()

          Method representing the thread’s activity.

          You may override this method in a subclass.  The standard
          *note run(): 35f. method invokes the callable object passed to
          the object’s constructor as the `target' argument, if any,
          with positional and keyword arguments taken from the `args'
          and `kwargs' arguments, respectively.

      -- Method: join (timeout=None)

          Wait until the thread terminates.  This blocks the calling
          thread until the thread whose *note join(): c32. method is
          called terminates – either normally or through an unhandled
          exception – or until the optional timeout occurs.

          When the `timeout' argument is present and not ‘None’, it
          should be a floating point number specifying a timeout for the
          operation in seconds (or fractions thereof).  As *note join():
          c32. always returns ‘None’, you must call *note is_alive():
          21b. after *note join(): c32. to decide whether a timeout
          happened – if the thread is still alive, the *note join():
          c32. call timed out.

          When the `timeout' argument is not present or ‘None’, the
          operation will block until the thread terminates.

          A thread can be *note join(): c32.ed many times.

          *note join(): c32. raises a *note RuntimeError: 3dc. if an
          attempt is made to join the current thread as that would cause
          a deadlock.  It is also an error to *note join(): c32. a
          thread before it has been started and attempts to do so raise
          the same exception.

      -- Attribute: name

          A string used for identification purposes only.  It has no
          semantics.  Multiple threads may be given the same name.  The
          initial name is set by the constructor.

      -- Method: getName ()
      -- Method: setName ()

          Old getter/setter API for *note name: 24b2.; use it directly
          as a property instead.

      -- Attribute: ident

          The ‘thread identifier’ of this thread or ‘None’ if the thread
          has not been started.  This is a nonzero integer.  See the
          *note get_ident(): b87. function.  Thread identifiers may be
          recycled when a thread exits and another thread is created.
          The identifier is available even after the thread has exited.

      -- Attribute: native_id

          The native integral thread ID of this thread.  This is a
          non-negative integer, or ‘None’ if the thread has not been
          started.  See the *note get_native_id(): 360. function.  This
          represents the Thread ID (‘TID’) as assigned to the thread by
          the OS (kernel).  Its value may be used to uniquely identify
          this particular thread system-wide (until the thread
          terminates, after which the value may be recycled by the OS).

               Note: Similar to Process IDs, Thread IDs are only valid
               (guaranteed unique system-wide) from the time the thread
               is created until the thread has been terminated.

          *note Availability: 1491.: Requires *note get_native_id():
          360. function.

          New in version 3.8.

      -- Method: is_alive ()

          Return whether the thread is alive.

          This method returns ‘True’ just before the *note run(): 35f.
          method starts until just after the *note run(): 35f. method
          terminates.  The module function *note enumerate(): f90.
          returns a list of all alive threads.

      -- Attribute: daemon

          A boolean value indicating whether this thread is a daemon
          thread (True) or not (False).  This must be set before *note
          start(): 222e. is called, otherwise *note RuntimeError: 3dc.
          is raised.  Its initial value is inherited from the creating
          thread; the main thread is not a daemon thread and therefore
          all threads created in the main thread default to *note
          daemon: 24b3. = ‘False’.

          The entire Python program exits when no alive non-daemon
          threads are left.

      -- Method: isDaemon ()
      -- Method: setDaemon ()

          Old getter/setter API for *note daemon: 24b3.; use it directly
          as a property instead.


File: python.info,  Node: Lock Objects,  Next: RLock Objects,  Prev: Thread Objects,  Up: threading — Thread-based parallelism

5.17.1.3 Lock Objects
.....................

A primitive lock is a synchronization primitive that is not owned by a
particular thread when locked.  In Python, it is currently the lowest
level synchronization primitive available, implemented directly by the
*note _thread: 2. extension module.

A primitive lock is in one of two states, “locked” or “unlocked”.  It is
created in the unlocked state.  It has two basic methods, *note
acquire(): 85b. and *note release(): 24ba.  When the state is unlocked,
*note acquire(): 85b. changes the state to locked and returns
immediately.  When the state is locked, *note acquire(): 85b. blocks
until a call to *note release(): 24ba. in another thread changes it to
unlocked, then the *note acquire(): 85b. call resets it to locked and
returns.  The *note release(): 24ba. method should only be called in the
locked state; it changes the state to unlocked and returns immediately.
If an attempt is made to release an unlocked lock, a *note RuntimeError:
3dc. will be raised.

Locks also support the *note context management protocol: 24bb.

When more than one thread is blocked in *note acquire(): 85b. waiting
for the state to turn to unlocked, only one thread proceeds when a *note
release(): 24ba. call resets the state to unlocked; which one of the
waiting threads proceeds is not defined, and may vary across
implementations.

All methods are executed atomically.

 -- Class: threading.Lock

     The class implementing primitive lock objects.  Once a thread has
     acquired a lock, subsequent attempts to acquire it block, until it
     is released; any thread may release it.

     Note that ‘Lock’ is actually a factory function which returns an
     instance of the most efficient version of the concrete Lock class
     that is supported by the platform.

      -- Method: acquire (blocking=True, timeout=-1)

          Acquire a lock, blocking or non-blocking.

          When invoked with the `blocking' argument set to ‘True’ (the
          default), block until the lock is unlocked, then set it to
          locked and return ‘True’.

          When invoked with the `blocking' argument set to ‘False’, do
          not block.  If a call with `blocking' set to ‘True’ would
          block, return ‘False’ immediately; otherwise, set the lock to
          locked and return ‘True’.

          When invoked with the floating-point `timeout' argument set to
          a positive value, block for at most the number of seconds
          specified by `timeout' and as long as the lock cannot be
          acquired.  A `timeout' argument of ‘-1’ specifies an unbounded
          wait.  It is forbidden to specify a `timeout' when `blocking'
          is false.

          The return value is ‘True’ if the lock is acquired
          successfully, ‘False’ if not (for example if the `timeout'
          expired).

          Changed in version 3.2: The `timeout' parameter is new.

          Changed in version 3.2: Lock acquisition can now be
          interrupted by signals on POSIX if the underlying threading
          implementation supports it.

      -- Method: release ()

          Release a lock.  This can be called from any thread, not only
          the thread which has acquired the lock.

          When the lock is locked, reset it to unlocked, and return.  If
          any other threads are blocked waiting for the lock to become
          unlocked, allow exactly one of them to proceed.

          When invoked on an unlocked lock, a *note RuntimeError: 3dc.
          is raised.

          There is no return value.

      -- Method: locked ()

          Return true if the lock is acquired.


File: python.info,  Node: RLock Objects,  Next: Condition Objects,  Prev: Lock Objects,  Up: threading — Thread-based parallelism

5.17.1.4 RLock Objects
......................

A reentrant lock is a synchronization primitive that may be acquired
multiple times by the same thread.  Internally, it uses the concepts of
“owning thread” and “recursion level” in addition to the locked/unlocked
state used by primitive locks.  In the locked state, some thread owns
the lock; in the unlocked state, no thread owns it.

To lock the lock, a thread calls its *note acquire(): 85c. method; this
returns once the thread owns the lock.  To unlock the lock, a thread
calls its *note release(): 24ba. method.  *note acquire(): 85b./*note
release(): 24ba. call pairs may be nested; only the final *note
release(): 24ba. (the *note release(): 24ba. of the outermost pair)
resets the lock to unlocked and allows another thread blocked in *note
acquire(): 85b. to proceed.

Reentrant locks also support the *note context management protocol:
24bb.

 -- Class: threading.RLock

     This class implements reentrant lock objects.  A reentrant lock
     must be released by the thread that acquired it.  Once a thread has
     acquired a reentrant lock, the same thread may acquire it again
     without blocking; the thread must release it once for each time it
     has acquired it.

     Note that ‘RLock’ is actually a factory function which returns an
     instance of the most efficient version of the concrete RLock class
     that is supported by the platform.

      -- Method: acquire (blocking=True, timeout=-1)

          Acquire a lock, blocking or non-blocking.

          When invoked without arguments: if this thread already owns
          the lock, increment the recursion level by one, and return
          immediately.  Otherwise, if another thread owns the lock,
          block until the lock is unlocked.  Once the lock is unlocked
          (not owned by any thread), then grab ownership, set the
          recursion level to one, and return.  If more than one thread
          is blocked waiting until the lock is unlocked, only one at a
          time will be able to grab ownership of the lock.  There is no
          return value in this case.

          When invoked with the `blocking' argument set to true, do the
          same thing as when called without arguments, and return
          ‘True’.

          When invoked with the `blocking' argument set to false, do not
          block.  If a call without an argument would block, return
          ‘False’ immediately; otherwise, do the same thing as when
          called without arguments, and return ‘True’.

          When invoked with the floating-point `timeout' argument set to
          a positive value, block for at most the number of seconds
          specified by `timeout' and as long as the lock cannot be
          acquired.  Return ‘True’ if the lock has been acquired, false
          if the timeout has elapsed.

          Changed in version 3.2: The `timeout' parameter is new.

      -- Method: release ()

          Release a lock, decrementing the recursion level.  If after
          the decrement it is zero, reset the lock to unlocked (not
          owned by any thread), and if any other threads are blocked
          waiting for the lock to become unlocked, allow exactly one of
          them to proceed.  If after the decrement the recursion level
          is still nonzero, the lock remains locked and owned by the
          calling thread.

          Only call this method when the calling thread owns the lock.
          A *note RuntimeError: 3dc. is raised if this method is called
          when the lock is unlocked.

          There is no return value.


File: python.info,  Node: Condition Objects,  Next: Semaphore Objects,  Prev: RLock Objects,  Up: threading — Thread-based parallelism

5.17.1.5 Condition Objects
..........................

A condition variable is always associated with some kind of lock; this
can be passed in or one will be created by default.  Passing one in is
useful when several condition variables must share the same lock.  The
lock is part of the condition object: you don’t have to track it
separately.

A condition variable obeys the *note context management protocol: 24bb.:
using the ‘with’ statement acquires the associated lock for the duration
of the enclosed block.  The *note acquire(): 24c3. and *note release():
24c4. methods also call the corresponding methods of the associated
lock.

Other methods must be called with the associated lock held.  The *note
wait(): f97. method releases the lock, and then blocks until another
thread awakens it by calling *note notify(): 24c5. or *note
notify_all(): 24c6.  Once awakened, *note wait(): f97. re-acquires the
lock and returns.  It is also possible to specify a timeout.

The *note notify(): 24c5. method wakes up one of the threads waiting for
the condition variable, if any are waiting.  The *note notify_all():
24c6. method wakes up all threads waiting for the condition variable.

Note: the *note notify(): 24c5. and *note notify_all(): 24c6. methods
don’t release the lock; this means that the thread or threads awakened
will not return from their *note wait(): f97. call immediately, but only
when the thread that called *note notify(): 24c5. or *note notify_all():
24c6. finally relinquishes ownership of the lock.

The typical programming style using condition variables uses the lock to
synchronize access to some shared state; threads that are interested in
a particular change of state call *note wait(): f97. repeatedly until
they see the desired state, while threads that modify the state call
*note notify(): 24c5. or *note notify_all(): 24c6. when they change the
state in such a way that it could possibly be a desired state for one of
the waiters.  For example, the following code is a generic
producer-consumer situation with unlimited buffer capacity:

     # Consume one item
     with cv:
         while not an_item_is_available():
             cv.wait()
         get_an_available_item()

     # Produce one item
     with cv:
         make_an_item_available()
         cv.notify()

The ‘while’ loop checking for the application’s condition is necessary
because *note wait(): f97. can return after an arbitrary long time, and
the condition which prompted the *note notify(): 24c5. call may no
longer hold true.  This is inherent to multi-threaded programming.  The
*note wait_for(): 24c7. method can be used to automate the condition
checking, and eases the computation of timeouts:

     # Consume an item
     with cv:
         cv.wait_for(an_item_is_available)
         get_an_available_item()

To choose between *note notify(): 24c5. and *note notify_all(): 24c6,
consider whether one state change can be interesting for only one or
several waiting threads.  E.g.  in a typical producer-consumer
situation, adding one item to the buffer only needs to wake up one
consumer thread.

 -- Class: threading.Condition (lock=None)

     This class implements condition variable objects.  A condition
     variable allows one or more threads to wait until they are notified
     by another thread.

     If the `lock' argument is given and not ‘None’, it must be a *note
     Lock: 24bc. or *note RLock: cba. object, and it is used as the
     underlying lock.  Otherwise, a new *note RLock: cba. object is
     created and used as the underlying lock.

     Changed in version 3.3: changed from a factory function to a class.

      -- Method: acquire (*args)

          Acquire the underlying lock.  This method calls the
          corresponding method on the underlying lock; the return value
          is whatever that method returns.

      -- Method: release ()

          Release the underlying lock.  This method calls the
          corresponding method on the underlying lock; there is no
          return value.

      -- Method: wait (timeout=None)

          Wait until notified or until a timeout occurs.  If the calling
          thread has not acquired the lock when this method is called, a
          *note RuntimeError: 3dc. is raised.

          This method releases the underlying lock, and then blocks
          until it is awakened by a *note notify(): 24c5. or *note
          notify_all(): 24c6. call for the same condition variable in
          another thread, or until the optional timeout occurs.  Once
          awakened or timed out, it re-acquires the lock and returns.

          When the `timeout' argument is present and not ‘None’, it
          should be a floating point number specifying a timeout for the
          operation in seconds (or fractions thereof).

          When the underlying lock is an *note RLock: cba, it is not
          released using its *note release(): 24c4. method, since this
          may not actually unlock the lock when it was acquired multiple
          times recursively.  Instead, an internal interface of the
          *note RLock: cba. class is used, which really unlocks it even
          when it has been recursively acquired several times.  Another
          internal interface is then used to restore the recursion level
          when the lock is reacquired.

          The return value is ‘True’ unless a given `timeout' expired,
          in which case it is ‘False’.

          Changed in version 3.2: Previously, the method always returned
          ‘None’.

      -- Method: wait_for (predicate, timeout=None)

          Wait until a condition evaluates to true.  `predicate' should
          be a callable which result will be interpreted as a boolean
          value.  A `timeout' may be provided giving the maximum time to
          wait.

          This utility method may call *note wait(): f97. repeatedly
          until the predicate is satisfied, or until a timeout occurs.
          The return value is the last return value of the predicate and
          will evaluate to ‘False’ if the method timed out.

          Ignoring the timeout feature, calling this method is roughly
          equivalent to writing:

               while not predicate():
                   cv.wait()

          Therefore, the same rules apply as with *note wait(): f97.:
          The lock must be held when called and is re-acquired on
          return.  The predicate is evaluated with the lock held.

          New in version 3.2.

      -- Method: notify (n=1)

          By default, wake up one thread waiting on this condition, if
          any.  If the calling thread has not acquired the lock when
          this method is called, a *note RuntimeError: 3dc. is raised.

          This method wakes up at most `n' of the threads waiting for
          the condition variable; it is a no-op if no threads are
          waiting.

          The current implementation wakes up exactly `n' threads, if at
          least `n' threads are waiting.  However, it’s not safe to rely
          on this behavior.  A future, optimized implementation may
          occasionally wake up more than `n' threads.

          Note: an awakened thread does not actually return from its
          *note wait(): f97. call until it can reacquire the lock.
          Since *note notify(): 24c5. does not release the lock, its
          caller should.

      -- Method: notify_all ()

          Wake up all threads waiting on this condition.  This method
          acts like *note notify(): 24c5, but wakes up all waiting
          threads instead of one.  If the calling thread has not
          acquired the lock when this method is called, a *note
          RuntimeError: 3dc. is raised.


File: python.info,  Node: Semaphore Objects,  Next: Event Objects,  Prev: Condition Objects,  Up: threading — Thread-based parallelism

5.17.1.6 Semaphore Objects
..........................

This is one of the oldest synchronization primitives in the history of
computer science, invented by the early Dutch computer scientist Edsger
W. Dijkstra (he used the names ‘P()’ and ‘V()’ instead of *note
acquire(): cb8. and *note release(): 24ca.).

A semaphore manages an internal counter which is decremented by each
*note acquire(): cb8. call and incremented by each *note release():
24ca. call.  The counter can never go below zero; when *note acquire():
cb8. finds that it is zero, it blocks, waiting until some other thread
calls *note release(): 24ca.

Semaphores also support the *note context management protocol: 24bb.

 -- Class: threading.Semaphore (value=1)

     This class implements semaphore objects.  A semaphore manages an
     atomic counter representing the number of *note release(): 24ca.
     calls minus the number of *note acquire(): cb8. calls, plus an
     initial value.  The *note acquire(): cb8. method blocks if
     necessary until it can return without making the counter negative.
     If not given, `value' defaults to 1.

     The optional argument gives the initial `value' for the internal
     counter; it defaults to ‘1’.  If the `value' given is less than 0,
     *note ValueError: 16d. is raised.

     Changed in version 3.3: changed from a factory function to a class.

      -- Method: acquire (blocking=True, timeout=None)

          Acquire a semaphore.

          When invoked without arguments:

             * If the internal counter is larger than zero on entry,
               decrement it by one and return ‘True’ immediately.

             * If the internal counter is zero on entry, block until
               awoken by a call to *note release(): 24ca.  Once awoken
               (and the counter is greater than 0), decrement the
               counter by 1 and return ‘True’.  Exactly one thread will
               be awoken by each call to *note release(): 24ca.  The
               order in which threads are awoken should not be relied
               on.

          When invoked with `blocking' set to false, do not block.  If a
          call without an argument would block, return ‘False’
          immediately; otherwise, do the same thing as when called
          without arguments, and return ‘True’.

          When invoked with a `timeout' other than ‘None’, it will block
          for at most `timeout' seconds.  If acquire does not complete
          successfully in that interval, return ‘False’.  Return ‘True’
          otherwise.

          Changed in version 3.2: The `timeout' parameter is new.

      -- Method: release (n=1)

          Release a semaphore, incrementing the internal counter by `n'.
          When it was zero on entry and other threads are waiting for it
          to become larger than zero again, wake up `n' of those
          threads.

          Changed in version 3.9: Added the `n' parameter to release
          multiple waiting threads at once.

 -- Class: threading.BoundedSemaphore (value=1)

     Class implementing bounded semaphore objects.  A bounded semaphore
     checks to make sure its current value doesn’t exceed its initial
     value.  If it does, *note ValueError: 16d. is raised.  In most
     situations semaphores are used to guard resources with limited
     capacity.  If the semaphore is released too many times it’s a sign
     of a bug.  If not given, `value' defaults to 1.

     Changed in version 3.3: changed from a factory function to a class.

* Menu:

* Semaphore Example::


File: python.info,  Node: Semaphore Example,  Up: Semaphore Objects

5.17.1.7 ‘Semaphore’ Example
............................

Semaphores are often used to guard resources with limited capacity, for
example, a database server.  In any situation where the size of the
resource is fixed, you should use a bounded semaphore.  Before spawning
any worker threads, your main thread would initialize the semaphore:

     maxconnections = 5
     # ...
     pool_sema = BoundedSemaphore(value=maxconnections)

Once spawned, worker threads call the semaphore’s acquire and release
methods when they need to connect to the server:

     with pool_sema:
         conn = connectdb()
         try:
             # ... use connection ...
         finally:
             conn.close()

The use of a bounded semaphore reduces the chance that a programming
error which causes the semaphore to be released more than it’s acquired
will go undetected.


File: python.info,  Node: Event Objects,  Next: Timer Objects,  Prev: Semaphore Objects,  Up: threading — Thread-based parallelism

5.17.1.8 Event Objects
......................

This is one of the simplest mechanisms for communication between
threads: one thread signals an event and other threads wait for it.

An event object manages an internal flag that can be set to true with
the *note set(): 24cf. method and reset to false with the *note clear():
24d0. method.  The *note wait(): d7f. method blocks until the flag is
true.

 -- Class: threading.Event

     Class implementing event objects.  An event manages a flag that can
     be set to true with the *note set(): 24cf. method and reset to
     false with the *note clear(): 24d0. method.  The *note wait(): d7f.
     method blocks until the flag is true.  The flag is initially false.

     Changed in version 3.3: changed from a factory function to a class.

      -- Method: is_set ()

          Return ‘True’ if and only if the internal flag is true.

      -- Method: set ()

          Set the internal flag to true.  All threads waiting for it to
          become true are awakened.  Threads that call *note wait():
          d7f. once the flag is true will not block at all.

      -- Method: clear ()

          Reset the internal flag to false.  Subsequently, threads
          calling *note wait(): d7f. will block until *note set(): 24cf.
          is called to set the internal flag to true again.

      -- Method: wait (timeout=None)

          Block until the internal flag is true.  If the internal flag
          is true on entry, return immediately.  Otherwise, block until
          another thread calls *note set(): 24cf. to set the flag to
          true, or until the optional timeout occurs.

          When the timeout argument is present and not ‘None’, it should
          be a floating point number specifying a timeout for the
          operation in seconds (or fractions thereof).

          This method returns ‘True’ if and only if the internal flag
          has been set to true, either before the wait call or after the
          wait starts, so it will always return ‘True’ except if a
          timeout is given and the operation times out.

          Changed in version 3.1: Previously, the method always returned
          ‘None’.


File: python.info,  Node: Timer Objects,  Next: Barrier Objects,  Prev: Event Objects,  Up: threading — Thread-based parallelism

5.17.1.9 Timer Objects
......................

This class represents an action that should be run only after a certain
amount of time has passed — a timer.  *note Timer: b86. is a subclass of
*note Thread: 21a. and as such also functions as an example of creating
custom threads.

Timers are started, as with threads, by calling their ‘start()’ method.
The timer can be stopped (before its action has begun) by calling the
*note cancel(): 24d4. method.  The interval the timer will wait before
executing its action may not be exactly the same as the interval
specified by the user.

For example:

     def hello():
         print("hello, world")

     t = Timer(30.0, hello)
     t.start()  # after 30 seconds, "hello, world" will be printed

 -- Class: threading.Timer (interval, function, args=None, kwargs=None)

     Create a timer that will run `function' with arguments `args' and
     keyword arguments `kwargs', after `interval' seconds have passed.
     If `args' is ‘None’ (the default) then an empty list will be used.
     If `kwargs' is ‘None’ (the default) then an empty dict will be
     used.

     Changed in version 3.3: changed from a factory function to a class.

      -- Method: cancel ()

          Stop the timer, and cancel the execution of the timer’s
          action.  This will only work if the timer is still in its
          waiting stage.


File: python.info,  Node: Barrier Objects,  Next: Using locks conditions and semaphores in the with statement,  Prev: Timer Objects,  Up: threading — Thread-based parallelism

5.17.1.10 Barrier Objects
.........................

New in version 3.2.

This class provides a simple synchronization primitive for use by a
fixed number of threads that need to wait for each other.  Each of the
threads tries to pass the barrier by calling the *note wait(): 24d6.
method and will block until all of the threads have made their *note
wait(): 24d6. calls.  At this point, the threads are released
simultaneously.

The barrier can be reused any number of times for the same number of
threads.

As an example, here is a simple way to synchronize a client and server
thread:

     b = Barrier(2, timeout=5)

     def server():
         start_server()
         b.wait()
         while True:
             connection = accept_connection()
             process_server_connection(connection)

     def client():
         b.wait()
         while True:
             connection = make_connection()
             process_client_connection(connection)

 -- Class: threading.Barrier (parties, action=None, timeout=None)

     Create a barrier object for `parties' number of threads.  An
     `action', when provided, is a callable to be called by one of the
     threads when they are released.  `timeout' is the default timeout
     value if none is specified for the *note wait(): 24d6. method.

      -- Method: wait (timeout=None)

          Pass the barrier.  When all the threads party to the barrier
          have called this function, they are all released
          simultaneously.  If a `timeout' is provided, it is used in
          preference to any that was supplied to the class constructor.

          The return value is an integer in the range 0 to `parties' –
          1, different for each thread.  This can be used to select a
          thread to do some special housekeeping, e.g.:

               i = barrier.wait()
               if i == 0:
                   # Only one thread needs to print this
                   print("passed the barrier")

          If an `action' was provided to the constructor, one of the
          threads will have called it prior to being released.  Should
          this call raise an error, the barrier is put into the broken
          state.

          If the call times out, the barrier is put into the broken
          state.

          This method may raise a *note BrokenBarrierError: c33.
          exception if the barrier is broken or reset while a thread is
          waiting.

      -- Method: reset ()

          Return the barrier to the default, empty state.  Any threads
          waiting on it will receive the *note BrokenBarrierError: c33.
          exception.

          Note that using this function may require some external
          synchronization if there are other threads whose state is
          unknown.  If a barrier is broken it may be better to just
          leave it and create a new one.

      -- Method: abort ()

          Put the barrier into a broken state.  This causes any active
          or future calls to *note wait(): 24d6. to fail with the *note
          BrokenBarrierError: c33.  Use this for example if one of the
          threads needs to abort, to avoid deadlocking the application.

          It may be preferable to simply create the barrier with a
          sensible `timeout' value to automatically guard against one of
          the threads going awry.

      -- Attribute: parties

          The number of threads required to pass the barrier.

      -- Attribute: n_waiting

          The number of threads currently waiting in the barrier.

      -- Attribute: broken

          A boolean that is ‘True’ if the barrier is in the broken
          state.

 -- Exception: threading.BrokenBarrierError

     This exception, a subclass of *note RuntimeError: 3dc, is raised
     when the *note Barrier: c31. object is reset or broken.


File: python.info,  Node: Using locks conditions and semaphores in the with statement,  Prev: Barrier Objects,  Up: threading — Thread-based parallelism

5.17.1.11 Using locks, conditions, and semaphores in the ‘with’ statement
.........................................................................

All of the objects provided by this module that have ‘acquire()’ and
‘release()’ methods can be used as context managers for a *note with:
7da. statement.  The ‘acquire()’ method will be called when the block is
entered, and ‘release()’ will be called when the block is exited.
Hence, the following snippet:

     with some_lock:
         # do something...

is equivalent to:

     some_lock.acquire()
     try:
         # do something...
     finally:
         some_lock.release()

Currently, *note Lock: 24bc, *note RLock: cba, *note Condition: b82,
*note Semaphore: b83, and *note BoundedSemaphore: b84. objects may be
used as *note with: 7da. statement context managers.


File: python.info,  Node: multiprocessing — Process-based parallelism,  Next: multiprocessing shared_memory — Provides shared memory for direct access across processes,  Prev: threading — Thread-based parallelism,  Up: Concurrent Execution

5.17.2 ‘multiprocessing’ — Process-based parallelism
----------------------------------------------------

`Source code:' Lib/multiprocessing/(1)

__________________________________________________________________

* Menu:

* Introduction: Introduction<8>.
* Reference::
* Programming guidelines::
* Examples: Examples<11>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/multiprocessing/


File: python.info,  Node: Introduction<8>,  Next: Reference,  Up: multiprocessing — Process-based parallelism

5.17.2.1 Introduction
.....................

*note multiprocessing: b7. is a package that supports spawning processes
using an API similar to the *note threading: 10b. module.  The *note
multiprocessing: b7. package offers both local and remote concurrency,
effectively side-stepping the *note Global Interpreter Lock: 600. by
using subprocesses instead of threads.  Due to this, the *note
multiprocessing: b7. module allows the programmer to fully leverage
multiple processors on a given machine.  It runs on both Unix and
Windows.

The *note multiprocessing: b7. module also introduces APIs which do not
have analogs in the *note threading: 10b. module.  A prime example of
this is the *note Pool: 966. object which offers a convenient means of
parallelizing the execution of a function across multiple input values,
distributing the input data across processes (data parallelism).  The
following example demonstrates the common practice of defining such
functions in a module so that child processes can successfully import
that module.  This basic example of data parallelism using *note Pool:
966,

     from multiprocessing import Pool

     def f(x):
         return x*x

     if __name__ == '__main__':
         with Pool(5) as p:
             print(p.map(f, [1, 2, 3]))

will print to standard output

     [1, 4, 9]

* Menu:

* The Process class::
* Contexts and start methods::
* Exchanging objects between processes::
* Synchronization between processes::
* Sharing state between processes::
* Using a pool of workers::


File: python.info,  Node: The Process class,  Next: Contexts and start methods,  Up: Introduction<8>

5.17.2.2 The ‘Process’ class
............................

In *note multiprocessing: b7, processes are spawned by creating a *note
Process: 4b9. object and then calling its *note start(): 24e1. method.
*note Process: 4b9. follows the API of *note threading.Thread: 21a.  A
trivial example of a multiprocess program is

     from multiprocessing import Process

     def f(name):
         print('hello', name)

     if __name__ == '__main__':
         p = Process(target=f, args=('bob',))
         p.start()
         p.join()

To show the individual process IDs involved, here is an expanded
example:

     from multiprocessing import Process
     import os

     def info(title):
         print(title)
         print('module name:', __name__)
         print('parent process:', os.getppid())
         print('process id:', os.getpid())

     def f(name):
         info('function f')
         print('hello', name)

     if __name__ == '__main__':
         info('main line')
         p = Process(target=f, args=('bob',))
         p.start()
         p.join()

For an explanation of why the ‘if __name__ == '__main__'’ part is
necessary, see *note Programming guidelines: 24e2.


File: python.info,  Node: Contexts and start methods,  Next: Exchanging objects between processes,  Prev: The Process class,  Up: Introduction<8>

5.17.2.3 Contexts and start methods
...................................

Depending on the platform, *note multiprocessing: b7. supports three
ways to start a process.  These `start methods' are

     `spawn'

          The parent process starts a fresh python interpreter process.
          The child process will only inherit those resources necessary
          to run the process object’s *note run(): 24e4. method.  In
          particular, unnecessary file descriptors and handles from the
          parent process will not be inherited.  Starting a process
          using this method is rather slow compared to using `fork' or
          `forkserver'.

          Available on Unix and Windows.  The default on Windows and
          macOS.

     `fork'

          The parent process uses *note os.fork(): a42. to fork the
          Python interpreter.  The child process, when it begins, is
          effectively identical to the parent process.  All resources of
          the parent are inherited by the child process.  Note that
          safely forking a multithreaded process is problematic.

          Available on Unix only.  The default on Unix.

     `forkserver'

          When the program starts and selects the `forkserver' start
          method, a server process is started.  From then on, whenever a
          new process is needed, the parent process connects to the
          server and requests that it fork a new process.  The fork
          server process is single threaded so it is safe for it to use
          *note os.fork(): a42.  No unnecessary resources are inherited.

          Available on Unix platforms which support passing file
          descriptors over Unix pipes.

Changed in version 3.8: On macOS, the `spawn' start method is now the
default.  The `fork' start method should be considered unsafe as it can
lead to crashes of the subprocess.  See bpo-33725(1).

Changed in version 3.4: `spawn' added on all unix platforms, and
`forkserver' added for some unix platforms.  Child processes no longer
inherit all of the parents inheritable handles on Windows.

On Unix using the `spawn' or `forkserver' start methods will also start
a `resource tracker' process which tracks the unlinked named system
resources (such as named semaphores or *note SharedMemory: 24e5.
objects) created by processes of the program.  When all processes have
exited the resource tracker unlinks any remaining tracked object.
Usually there should be none, but if a process was killed by a signal
there may be some “leaked” resources.  (Neither leaked semaphores nor
shared memory segments will be automatically unlinked until the next
reboot.  This is problematic for both objects because the system allows
only a limited number of named semaphores, and shared memory segments
occupy some space in the main memory.)

To select a start method you use the *note set_start_method(): 964. in
the ‘if __name__ == '__main__'’ clause of the main module.  For example:

     import multiprocessing as mp

     def foo(q):
         q.put('hello')

     if __name__ == '__main__':
         mp.set_start_method('spawn')
         q = mp.Queue()
         p = mp.Process(target=foo, args=(q,))
         p.start()
         print(q.get())
         p.join()

*note set_start_method(): 964. should not be used more than once in the
program.

Alternatively, you can use *note get_context(): 965. to obtain a context
object.  Context objects have the same API as the multiprocessing
module, and allow one to use multiple start methods in the same program.

     import multiprocessing as mp

     def foo(q):
         q.put('hello')

     if __name__ == '__main__':
         ctx = mp.get_context('spawn')
         q = ctx.Queue()
         p = ctx.Process(target=foo, args=(q,))
         p.start()
         print(q.get())
         p.join()

Note that objects related to one context may not be compatible with
processes for a different context.  In particular, locks created using
the `fork' context cannot be passed to processes started using the
`spawn' or `forkserver' start methods.

A library which wants to use a particular start method should probably
use *note get_context(): 965. to avoid interfering with the choice of
the library user.

     Warning: The ‘'spawn'’ and ‘'forkserver'’ start methods cannot
     currently be used with “frozen” executables (i.e., binaries
     produced by packages like `PyInstaller' and `cx_Freeze') on Unix.
     The ‘'fork'’ start method does work.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33725


File: python.info,  Node: Exchanging objects between processes,  Next: Synchronization between processes,  Prev: Contexts and start methods,  Up: Introduction<8>

5.17.2.4 Exchanging objects between processes
.............................................

*note multiprocessing: b7. supports two types of communication channel
between processes:

`Queues'

     The *note Queue: 24e7. class is a near clone of *note queue.Queue:
     dde.  For example:

          from multiprocessing import Process, Queue

          def f(q):
              q.put([42, None, 'hello'])

          if __name__ == '__main__':
              q = Queue()
              p = Process(target=f, args=(q,))
              p.start()
              print(q.get())    # prints "[42, None, 'hello']"
              p.join()

     Queues are thread and process safe.

`Pipes'

     The *note Pipe(): 24e8. function returns a pair of connection
     objects connected by a pipe which by default is duplex (two-way).
     For example:

          from multiprocessing import Process, Pipe

          def f(conn):
              conn.send([42, None, 'hello'])
              conn.close()

          if __name__ == '__main__':
              parent_conn, child_conn = Pipe()
              p = Process(target=f, args=(child_conn,))
              p.start()
              print(parent_conn.recv())   # prints "[42, None, 'hello']"
              p.join()

     The two connection objects returned by *note Pipe(): 24e8.
     represent the two ends of the pipe.  Each connection object has
     ‘send()’ and ‘recv()’ methods (among others).  Note that data in a
     pipe may become corrupted if two processes (or threads) try to read
     from or write to the `same' end of the pipe at the same time.  Of
     course there is no risk of corruption from processes using
     different ends of the pipe at the same time.


File: python.info,  Node: Synchronization between processes,  Next: Sharing state between processes,  Prev: Exchanging objects between processes,  Up: Introduction<8>

5.17.2.5 Synchronization between processes
..........................................

*note multiprocessing: b7. contains equivalents of all the
synchronization primitives from *note threading: 10b.  For instance one
can use a lock to ensure that only one process prints to standard output
at a time:

     from multiprocessing import Process, Lock

     def f(l, i):
         l.acquire()
         try:
             print('hello world', i)
         finally:
             l.release()

     if __name__ == '__main__':
         lock = Lock()

         for num in range(10):
             Process(target=f, args=(lock, num)).start()

Without using the lock output from the different processes is liable to
get all mixed up.


File: python.info,  Node: Sharing state between processes,  Next: Using a pool of workers,  Prev: Synchronization between processes,  Up: Introduction<8>

5.17.2.6 Sharing state between processes
........................................

As mentioned above, when doing concurrent programming it is usually best
to avoid using shared state as far as possible.  This is particularly
true when using multiple processes.

However, if you really do need to use some shared data then *note
multiprocessing: b7. provides a couple of ways of doing so.

`Shared memory'

     Data can be stored in a shared memory map using *note Value: 24eb.
     or *note Array: 24ec.  For example, the following code

          from multiprocessing import Process, Value, Array

          def f(n, a):
              n.value = 3.1415927
              for i in range(len(a)):
                  a[i] = -a[i]

          if __name__ == '__main__':
              num = Value('d', 0.0)
              arr = Array('i', range(10))

              p = Process(target=f, args=(num, arr))
              p.start()
              p.join()

              print(num.value)
              print(arr[:])

     will print

          3.1415927
          [0, -1, -2, -3, -4, -5, -6, -7, -8, -9]

     The ‘'d'’ and ‘'i'’ arguments used when creating ‘num’ and ‘arr’
     are typecodes of the kind used by the *note array: 6. module: ‘'d'’
     indicates a double precision float and ‘'i'’ indicates a signed
     integer.  These shared objects will be process and thread-safe.

     For more flexibility in using shared memory one can use the *note
     multiprocessing.sharedctypes: bd. module which supports the
     creation of arbitrary ctypes objects allocated from shared memory.

`Server process'

     A manager object returned by ‘Manager()’ controls a server process
     which holds Python objects and allows other processes to manipulate
     them using proxies.

     A manager returned by ‘Manager()’ will support types *note list:
     1f8, *note dict: 164, *note Namespace: 24ed, *note Lock: 24ee,
     *note RLock: 24ef, *note Semaphore: 24f0, *note BoundedSemaphore:
     24f1, *note Condition: 24f2, *note Event: 24f3, *note Barrier:
     24f4, *note Queue: 24e7, *note Value: 24eb. and *note Array: 24ec.
     For example,

          from multiprocessing import Process, Manager

          def f(d, l):
              d[1] = '1'
              d['2'] = 2
              d[0.25] = None
              l.reverse()

          if __name__ == '__main__':
              with Manager() as manager:
                  d = manager.dict()
                  l = manager.list(range(10))

                  p = Process(target=f, args=(d, l))
                  p.start()
                  p.join()

                  print(d)
                  print(l)

     will print

          {0.25: None, 1: '1', '2': 2}
          [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

     Server process managers are more flexible than using shared memory
     objects because they can be made to support arbitrary object types.
     Also, a single manager can be shared by processes on different
     computers over a network.  They are, however, slower than using
     shared memory.


File: python.info,  Node: Using a pool of workers,  Prev: Sharing state between processes,  Up: Introduction<8>

5.17.2.7 Using a pool of workers
................................

The *note Pool: 966. class represents a pool of worker processes.  It
has methods which allows tasks to be offloaded to the worker processes
in a few different ways.

For example:

     from multiprocessing import Pool, TimeoutError
     import time
     import os

     def f(x):
         return x*x

     if __name__ == '__main__':
         # start 4 worker processes
         with Pool(processes=4) as pool:

             # print "[0, 1, 4,..., 81]"
             print(pool.map(f, range(10)))

             # print same numbers in arbitrary order
             for i in pool.imap_unordered(f, range(10)):
                 print(i)

             # evaluate "f(20)" asynchronously
             res = pool.apply_async(f, (20,))      # runs in *only* one process
             print(res.get(timeout=1))             # prints "400"

             # evaluate "os.getpid()" asynchronously
             res = pool.apply_async(os.getpid, ()) # runs in *only* one process
             print(res.get(timeout=1))             # prints the PID of that process

             # launching multiple evaluations asynchronously *may* use more processes
             multiple_results = [pool.apply_async(os.getpid, ()) for i in range(4)]
             print([res.get(timeout=1) for res in multiple_results])

             # make a single worker sleep for 10 secs
             res = pool.apply_async(time.sleep, (10,))
             try:
                 print(res.get(timeout=1))
             except TimeoutError:
                 print("We lacked patience and got a multiprocessing.TimeoutError")

             print("For the moment, the pool remains available for more work")

         # exiting the 'with'-block has stopped the pool
         print("Now the pool is closed and no longer available")

Note that the methods of a pool should only ever be used by the process
which created it.

     Note: Functionality within this package requires that the
     ‘__main__’ module be importable by the children.  This is covered
     in *note Programming guidelines: 24e2. however it is worth pointing
     out here.  This means that some examples, such as the *note
     multiprocessing.pool.Pool: 966. examples will not work in the
     interactive interpreter.  For example:

          >>> from multiprocessing import Pool
          >>> p = Pool(5)
          >>> def f(x):
          ...     return x*x
          ...
          >>> with p:
          ...   p.map(f, [1,2,3])
          Process PoolWorker-1:
          Process PoolWorker-2:
          Process PoolWorker-3:
          Traceback (most recent call last):
          Traceback (most recent call last):
          Traceback (most recent call last):
          AttributeError: 'module' object has no attribute 'f'
          AttributeError: 'module' object has no attribute 'f'
          AttributeError: 'module' object has no attribute 'f'

     (If you try this it will actually output three full tracebacks
     interleaved in a semi-random fashion, and then you may have to stop
     the parent process somehow.)


File: python.info,  Node: Reference,  Next: Programming guidelines,  Prev: Introduction<8>,  Up: multiprocessing — Process-based parallelism

5.17.2.8 Reference
..................

The *note multiprocessing: b7. package mostly replicates the API of the
*note threading: 10b. module.

* Menu:

* Process and exceptions::
* Pipes and Queues::
* Miscellaneous: Miscellaneous<3>.
* Connection Objects: Connection Objects<2>.
* Synchronization primitives::
* Shared ctypes Objects::
* Managers::
* Proxy Objects::
* Process Pools::
* Listeners and Clients::
* Authentication keys::
* Logging: Logging<2>.
* The multiprocessing.dummy module: The multiprocessing dummy module.


File: python.info,  Node: Process and exceptions,  Next: Pipes and Queues,  Up: Reference

5.17.2.9 ‘Process’ and exceptions
.................................

 -- Class: multiprocessing.Process (group=None, target=None, name=None,
          args=(), kwargs={}, *, daemon=None)

     Process objects represent activity that is run in a separate
     process.  The *note Process: 4b9. class has equivalents of all the
     methods of *note threading.Thread: 21a.

     The constructor should always be called with keyword arguments.
     `group' should always be ‘None’; it exists solely for compatibility
     with *note threading.Thread: 21a.  `target' is the callable object
     to be invoked by the *note run(): 24e4. method.  It defaults to
     ‘None’, meaning nothing is called.  `name' is the process name (see
     *note name: 24f8. for more details).  `args' is the argument tuple
     for the target invocation.  `kwargs' is a dictionary of keyword
     arguments for the target invocation.  If provided, the keyword-only
     `daemon' argument sets the process *note daemon: 24f9. flag to
     ‘True’ or ‘False’.  If ‘None’ (the default), this flag will be
     inherited from the creating process.

     By default, no arguments are passed to `target'.

     If a subclass overrides the constructor, it must make sure it
     invokes the base class constructor (‘Process.__init__()’) before
     doing anything else to the process.

     Changed in version 3.3: Added the `daemon' argument.

      -- Method: run ()

          Method representing the process’s activity.

          You may override this method in a subclass.  The standard
          *note run(): 24e4. method invokes the callable object passed
          to the object’s constructor as the target argument, if any,
          with sequential and keyword arguments taken from the `args'
          and `kwargs' arguments, respectively.

      -- Method: start ()

          Start the process’s activity.

          This must be called at most once per process object.  It
          arranges for the object’s *note run(): 24e4. method to be
          invoked in a separate process.

      -- Method: join ([timeout])

          If the optional argument `timeout' is ‘None’ (the default),
          the method blocks until the process whose *note join(): 24fa.
          method is called terminates.  If `timeout' is a positive
          number, it blocks at most `timeout' seconds.  Note that the
          method returns ‘None’ if its process terminates or if the
          method times out.  Check the process’s *note exitcode: 24fb.
          to determine if it terminated.

          A process can be joined many times.

          A process cannot join itself because this would cause a
          deadlock.  It is an error to attempt to join a process before
          it has been started.

      -- Attribute: name

          The process’s name.  The name is a string used for
          identification purposes only.  It has no semantics.  Multiple
          processes may be given the same name.

          The initial name is set by the constructor.  If no explicit
          name is provided to the constructor, a name of the form
          ‘Process-N[1]:N[2]:…:N[k]’ is constructed, where each N[k] is
          the N-th child of its parent.

      -- Method: is_alive ()

          Return whether the process is alive.

          Roughly, a process object is alive from the moment the *note
          start(): 24e1. method returns until the child process
          terminates.

      -- Attribute: daemon

          The process’s daemon flag, a Boolean value.  This must be set
          before *note start(): 24e1. is called.

          The initial value is inherited from the creating process.

          When a process exits, it attempts to terminate all of its
          daemonic child processes.

          Note that a daemonic process is not allowed to create child
          processes.  Otherwise a daemonic process would leave its
          children orphaned if it gets terminated when its parent
          process exits.  Additionally, these are `not' Unix daemons or
          services, they are normal processes that will be terminated
          (and not joined) if non-daemonic processes have exited.

     In addition to the *note threading.Thread: 21a. API, *note Process:
     4b9. objects also support the following attributes and methods:

      -- Attribute: pid

          Return the process ID. Before the process is spawned, this
          will be ‘None’.

      -- Attribute: exitcode

          The child’s exit code.  This will be ‘None’ if the process has
          not yet terminated.  A negative value `-N' indicates that the
          child was terminated by signal `N'.

      -- Attribute: authkey

          The process’s authentication key (a byte string).

          When *note multiprocessing: b7. is initialized the main
          process is assigned a random string using *note os.urandom():
          5cc.

          When a *note Process: 4b9. object is created, it will inherit
          the authentication key of its parent process, although this
          may be changed by setting *note authkey: 24fe. to another byte
          string.

          See *note Authentication keys: 24ff.

      -- Attribute: sentinel

          A numeric handle of a system object which will become “ready”
          when the process ends.

          You can use this value if you want to wait on several events
          at once using *note multiprocessing.connection.wait(): b01.
          Otherwise calling *note join(): 24fa. is simpler.

          On Windows, this is an OS handle usable with the
          ‘WaitForSingleObject’ and ‘WaitForMultipleObjects’ family of
          API calls.  On Unix, this is a file descriptor usable with
          primitives from the *note select: e5. module.

          New in version 3.3.

      -- Method: terminate ()

          Terminate the process.  On Unix this is done using the
          ‘SIGTERM’ signal; on Windows ‘TerminateProcess()’ is used.
          Note that exit handlers and finally clauses, etc., will not be
          executed.

          Note that descendant processes of the process will `not' be
          terminated – they will simply become orphaned.

               Warning: If this method is used when the associated
               process is using a pipe or queue then the pipe or queue
               is liable to become corrupted and may become unusable by
               other process.  Similarly, if the process has acquired a
               lock or semaphore etc.  then terminating it is liable to
               cause other processes to deadlock.

      -- Method: kill ()

          Same as *note terminate(): 2500. but using the ‘SIGKILL’
          signal on Unix.

          New in version 3.7.

      -- Method: close ()

          Close the *note Process: 4b9. object, releasing all resources
          associated with it.  *note ValueError: 16d. is raised if the
          underlying process is still running.  Once *note close(): 4b7.
          returns successfully, most other methods and attributes of the
          *note Process: 4b9. object will raise *note ValueError: 16d.

          New in version 3.7.

     Note that the *note start(): 24e1, *note join(): 24fa, *note
     is_alive(): 24fc, *note terminate(): 2500. and *note exitcode:
     24fb. methods should only be called by the process that created the
     process object.

     Example usage of some of the methods of *note Process: 4b9.:

           >>> import multiprocessing, time, signal
           >>> p = multiprocessing.Process(target=time.sleep, args=(1000,))
           >>> print(p, p.is_alive())
           <Process ... initial> False
           >>> p.start()
           >>> print(p, p.is_alive())
           <Process ... started> True
           >>> p.terminate()
           >>> time.sleep(0.1)
           >>> print(p, p.is_alive())
           <Process ... stopped exitcode=-SIGTERM> False
           >>> p.exitcode == -signal.SIGTERM
           True

 -- Exception: multiprocessing.ProcessError

     The base class of all *note multiprocessing: b7. exceptions.

 -- Exception: multiprocessing.BufferTooShort

     Exception raised by ‘Connection.recv_bytes_into()’ when the
     supplied buffer object is too small for the message read.

     If ‘e’ is an instance of *note BufferTooShort: 2502. then
     ‘e.args[0]’ will give the message as a byte string.

 -- Exception: multiprocessing.AuthenticationError

     Raised when there is an authentication error.

 -- Exception: multiprocessing.TimeoutError

     Raised by methods with a timeout when the timeout expires.


File: python.info,  Node: Pipes and Queues,  Next: Miscellaneous<3>,  Prev: Process and exceptions,  Up: Reference

5.17.2.10 Pipes and Queues
..........................

When using multiple processes, one generally uses message passing for
communication between processes and avoids having to use any
synchronization primitives like locks.

For passing messages one can use *note Pipe(): 24e8. (for a connection
between two processes) or a queue (which allows multiple producers and
consumers).

The *note Queue: 24e7, *note SimpleQueue: 1c3. and *note JoinableQueue:
2506. types are multi-producer, multi-consumer FIFO queues modelled on
the *note queue.Queue: dde. class in the standard library.  They differ
in that *note Queue: 24e7. lacks the *note task_done(): 2507. and *note
join(): 2508. methods introduced into Python 2.5’s *note queue.Queue:
dde. class.

If you use *note JoinableQueue: 2506. then you `must' call *note
JoinableQueue.task_done(): 2509. for each task removed from the queue or
else the semaphore used to count the number of unfinished tasks may
eventually overflow, raising an exception.

Note that one can also create a shared queue by using a manager object –
see *note Managers: 250a.

     Note: *note multiprocessing: b7. uses the usual *note queue.Empty:
     250b. and *note queue.Full: 250c. exceptions to signal a timeout.
     They are not available in the *note multiprocessing: b7. namespace
     so you need to import them from *note queue: da.

     Note: When an object is put on a queue, the object is pickled and a
     background thread later flushes the pickled data to an underlying
     pipe.  This has some consequences which are a little surprising,
     but should not cause any practical difficulties – if they really
     bother you then you can instead use a queue created with a *note
     manager: 250a.

       1. After putting an object on an empty queue there may be an
          infinitesimal delay before the queue’s *note empty(): 250d.
          method returns *note False: 48f. and *note get_nowait(): 250e.
          can return without raising *note queue.Empty: 250b.

       2. If multiple processes are enqueuing objects, it is possible
          for the objects to be received at the other end out-of-order.
          However, objects enqueued by the same process will always be
          in the expected order with respect to each other.

     Warning: If a process is killed using *note Process.terminate():
     2500. or *note os.kill(): db9. while it is trying to use a *note
     Queue: 24e7, then the data in the queue is likely to become
     corrupted.  This may cause any other process to get an exception
     when it tries to use the queue later on.

     Warning: As mentioned above, if a child process has put items on a
     queue (and it has not used *note JoinableQueue.cancel_join_thread:
     250f.), then that process will not terminate until all buffered
     items have been flushed to the pipe.

     This means that if you try joining that process you may get a
     deadlock unless you are sure that all items which have been put on
     the queue have been consumed.  Similarly, if the child process is
     non-daemonic then the parent process may hang on exit when it tries
     to join all its non-daemonic children.

     Note that a queue created using a manager does not have this issue.
     See *note Programming guidelines: 24e2.

For an example of the usage of queues for interprocess communication see
*note Examples: 2510.

 -- Function: multiprocessing.Pipe ([duplex])

     Returns a pair ‘(conn1, conn2)’ of *note Connection: 2511. objects
     representing the ends of a pipe.

     If `duplex' is ‘True’ (the default) then the pipe is bidirectional.
     If `duplex' is ‘False’ then the pipe is unidirectional: ‘conn1’ can
     only be used for receiving messages and ‘conn2’ can only be used
     for sending messages.

 -- Class: multiprocessing.Queue ([maxsize])

     Returns a process shared queue implemented using a pipe and a few
     locks/semaphores.  When a process first puts an item on the queue a
     feeder thread is started which transfers objects from a buffer into
     the pipe.

     The usual *note queue.Empty: 250b. and *note queue.Full: 250c.
     exceptions from the standard library’s *note queue: da. module are
     raised to signal timeouts.

     *note Queue: 24e7. implements all the methods of *note queue.Queue:
     dde. except for *note task_done(): 2507. and *note join(): 2508.

      -- Method: qsize ()

          Return the approximate size of the queue.  Because of
          multithreading/multiprocessing semantics, this number is not
          reliable.

          Note that this may raise *note NotImplementedError: 704. on
          Unix platforms like macOS where ‘sem_getvalue()’ is not
          implemented.

      -- Method: empty ()

          Return ‘True’ if the queue is empty, ‘False’ otherwise.
          Because of multithreading/multiprocessing semantics, this is
          not reliable.

      -- Method: full ()

          Return ‘True’ if the queue is full, ‘False’ otherwise.
          Because of multithreading/multiprocessing semantics, this is
          not reliable.

      -- Method: put (obj[, block[, timeout]])

          Put obj into the queue.  If the optional argument `block' is
          ‘True’ (the default) and `timeout' is ‘None’ (the default),
          block if necessary until a free slot is available.  If
          `timeout' is a positive number, it blocks at most `timeout'
          seconds and raises the *note queue.Full: 250c. exception if no
          free slot was available within that time.  Otherwise (`block'
          is ‘False’), put an item on the queue if a free slot is
          immediately available, else raise the *note queue.Full: 250c.
          exception (`timeout' is ignored in that case).

          Changed in version 3.8: If the queue is closed, *note
          ValueError: 16d. is raised instead of *note AssertionError:
          240.

      -- Method: put_nowait (obj)

          Equivalent to ‘put(obj, False)’.

      -- Method: get ([block[, timeout]])

          Remove and return an item from the queue.  If optional args
          `block' is ‘True’ (the default) and `timeout' is ‘None’ (the
          default), block if necessary until an item is available.  If
          `timeout' is a positive number, it blocks at most `timeout'
          seconds and raises the *note queue.Empty: 250b. exception if
          no item was available within that time.  Otherwise (block is
          ‘False’), return an item if one is immediately available, else
          raise the *note queue.Empty: 250b. exception (`timeout' is
          ignored in that case).

          Changed in version 3.8: If the queue is closed, *note
          ValueError: 16d. is raised instead of *note OSError: 304.

      -- Method: get_nowait ()

          Equivalent to ‘get(False)’.

     *note multiprocessing.Queue: 24e7. has a few additional methods not
     found in *note queue.Queue: dde.  These methods are usually
     unnecessary for most code:

      -- Method: close ()

          Indicate that no more data will be put on this queue by the
          current process.  The background thread will quit once it has
          flushed all buffered data to the pipe.  This is called
          automatically when the queue is garbage collected.

      -- Method: join_thread ()

          Join the background thread.  This can only be used after *note
          close(): 2515. has been called.  It blocks until the
          background thread exits, ensuring that all data in the buffer
          has been flushed to the pipe.

          By default if a process is not the creator of the queue then
          on exit it will attempt to join the queue’s background thread.
          The process can call *note cancel_join_thread(): 250f. to make
          *note join_thread(): 2516. do nothing.

      -- Method: cancel_join_thread ()

          Prevent *note join_thread(): 2516. from blocking.  In
          particular, this prevents the background thread from being
          joined automatically when the process exits – see *note
          join_thread(): 2516.

          A better name for this method might be
          ‘allow_exit_without_flush()’.  It is likely to cause enqueued
          data to lost, and you almost certainly will not need to use
          it.  It is really only there if you need the current process
          to exit immediately without waiting to flush enqueued data to
          the underlying pipe, and you don’t care about lost data.

          Note: This class’s functionality requires a functioning shared
          semaphore implementation on the host operating system.
          Without one, the functionality in this class will be disabled,
          and attempts to instantiate a *note Queue: 24e7. will result
          in an *note ImportError: 16c.  See bpo-3770(1) for additional
          information.  The same holds true for any of the specialized
          queue types listed below.

 -- Class: multiprocessing.SimpleQueue

     It is a simplified *note Queue: 24e7. type, very close to a locked
     *note Pipe: 24e8.

      -- Method: close ()

          Close the queue: release internal resources.

          A queue must not be used anymore after it is closed.  For
          example, *note get(): 2517, *note put(): 2518. and *note
          empty(): 2519. methods must no longer be called.

          New in version 3.9.

      -- Method: empty ()

          Return ‘True’ if the queue is empty, ‘False’ otherwise.

      -- Method: get ()

          Remove and return an item from the queue.

      -- Method: put (item)

          Put `item' into the queue.

 -- Class: multiprocessing.JoinableQueue ([maxsize])

     *note JoinableQueue: 2506, a *note Queue: 24e7. subclass, is a
     queue which additionally has *note task_done(): 2509. and *note
     join(): 251a. methods.

      -- Method: task_done ()

          Indicate that a formerly enqueued task is complete.  Used by
          queue consumers.  For each *note get(): 1164. used to fetch a
          task, a subsequent call to *note task_done(): 2509. tells the
          queue that the processing on the task is complete.

          If a *note join(): 2508. is currently blocking, it will resume
          when all items have been processed (meaning that a *note
          task_done(): 2509. call was received for every item that had
          been *note put(): 1163. into the queue).

          Raises a *note ValueError: 16d. if called more times than
          there were items placed in the queue.

      -- Method: join ()

          Block until all items in the queue have been gotten and
          processed.

          The count of unfinished tasks goes up whenever an item is
          added to the queue.  The count goes down whenever a consumer
          calls *note task_done(): 2509. to indicate that the item was
          retrieved and all work on it is complete.  When the count of
          unfinished tasks drops to zero, *note join(): 2508. unblocks.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue3770


File: python.info,  Node: Miscellaneous<3>,  Next: Connection Objects<2>,  Prev: Pipes and Queues,  Up: Reference

5.17.2.11 Miscellaneous
.......................

 -- Function: multiprocessing.active_children ()

     Return list of all live children of the current process.

     Calling this has the side effect of “joining” any processes which
     have already finished.

 -- Function: multiprocessing.cpu_count ()

     Return the number of CPUs in the system.

     This number is not equivalent to the number of CPUs the current
     process can use.  The number of usable CPUs can be obtained with
     ‘len(os.sched_getaffinity(0))’

     When the number of CPUs cannot be determined a *note
     NotImplementedError: 704. is raised.

     See also
     ........

     *note os.cpu_count(): 96a.

 -- Function: multiprocessing.current_process ()

     Return the *note Process: 4b9. object corresponding to the current
     process.

     An analogue of *note threading.current_thread(): 24aa.

 -- Function: multiprocessing.parent_process ()

     Return the *note Process: 4b9. object corresponding to the parent
     process of the *note current_process(): 251d.  For the main
     process, ‘parent_process’ will be ‘None’.

     New in version 3.8.

 -- Function: multiprocessing.freeze_support ()

     Add support for when a program which uses *note multiprocessing:
     b7. has been frozen to produce a Windows executable.  (Has been
     tested with `py2exe', `PyInstaller' and `cx_Freeze'.)

     One needs to call this function straight after the ‘if __name__ ==
     '__main__'’ line of the main module.  For example:

          from multiprocessing import Process, freeze_support

          def f():
              print('hello world!')

          if __name__ == '__main__':
              freeze_support()
              Process(target=f).start()

     If the ‘freeze_support()’ line is omitted then trying to run the
     frozen executable will raise *note RuntimeError: 3dc.

     Calling ‘freeze_support()’ has no effect when invoked on any
     operating system other than Windows.  In addition, if the module is
     being run normally by the Python interpreter on Windows (the
     program has not been frozen), then ‘freeze_support()’ has no
     effect.

 -- Function: multiprocessing.get_all_start_methods ()

     Returns a list of the supported start methods, the first of which
     is the default.  The possible start methods are ‘'fork'’, ‘'spawn'’
     and ‘'forkserver'’.  On Windows only ‘'spawn'’ is available.  On
     Unix ‘'fork'’ and ‘'spawn'’ are always supported, with ‘'fork'’
     being the default.

     New in version 3.4.

 -- Function: multiprocessing.get_context (method=None)

     Return a context object which has the same attributes as the *note
     multiprocessing: b7. module.

     If `method' is ‘None’ then the default context is returned.
     Otherwise `method' should be ‘'fork'’, ‘'spawn'’, ‘'forkserver'’.
     *note ValueError: 16d. is raised if the specified start method is
     not available.

     New in version 3.4.

 -- Function: multiprocessing.get_start_method (allow_none=False)

     Return the name of start method used for starting processes.

     If the start method has not been fixed and `allow_none' is false,
     then the start method is fixed to the default and the name is
     returned.  If the start method has not been fixed and `allow_none'
     is true then ‘None’ is returned.

     The return value can be ‘'fork'’, ‘'spawn'’, ‘'forkserver'’ or
     ‘None’.  ‘'fork'’ is the default on Unix, while ‘'spawn'’ is the
     default on Windows and macOS.

Changed in version 3.8: On macOS, the `spawn' start method is now the
default.  The `fork' start method should be considered unsafe as it can
lead to crashes of the subprocess.  See bpo-33725(1).

New in version 3.4.

 -- Function: multiprocessing.set_executable ()

     Sets the path of the Python interpreter to use when starting a
     child process.  (By default *note sys.executable: 39d. is used).
     Embedders will probably need to do some thing like

          set_executable(os.path.join(sys.exec_prefix, 'pythonw.exe'))

     before they can create child processes.

     Changed in version 3.4: Now supported on Unix when the ‘'spawn'’
     start method is used.

 -- Function: multiprocessing.set_start_method (method)

     Set the method which should be used to start child processes.
     `method' can be ‘'fork'’, ‘'spawn'’ or ‘'forkserver'’.

     Note that this should be called at most once, and it should be
     protected inside the ‘if __name__ == '__main__'’ clause of the main
     module.

     New in version 3.4.

     Note: *note multiprocessing: b7. contains no analogues of *note
     threading.active_count(): 24a9, *note threading.enumerate(): f90,
     *note threading.settrace(): 24ab, *note threading.setprofile():
     24ac, *note threading.Timer: b86, or *note threading.local: 244e.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue33725


File: python.info,  Node: Connection Objects<2>,  Next: Synchronization primitives,  Prev: Miscellaneous<3>,  Up: Reference

5.17.2.12 Connection Objects
............................

Connection objects allow the sending and receiving of picklable objects
or strings.  They can be thought of as message oriented connected
sockets.

Connection objects are usually created using *note Pipe: 24e8. – see
also *note Listeners and Clients: 2522.

 -- Class: multiprocessing.connection.Connection

      -- Method: send (obj)

          Send an object to the other end of the connection which should
          be read using *note recv(): 2524.

          The object must be picklable.  Very large pickles
          (approximately 32 MiB+, though it depends on the OS) may raise
          a *note ValueError: 16d. exception.

      -- Method: recv ()

          Return an object sent from the other end of the connection
          using *note send(): 2523.  Blocks until there is something to
          receive.  Raises *note EOFError: d34. if there is nothing left
          to receive and the other end was closed.

      -- Method: fileno ()

          Return the file descriptor or handle used by the connection.

      -- Method: close ()

          Close the connection.

          This is called automatically when the connection is garbage
          collected.

      -- Method: poll ([timeout])

          Return whether there is any data available to be read.

          If `timeout' is not specified then it will return immediately.
          If `timeout' is a number then this specifies the maximum time
          in seconds to block.  If `timeout' is ‘None’ then an infinite
          timeout is used.

          Note that multiple connection objects may be polled at once by
          using *note multiprocessing.connection.wait(): b01.

      -- Method: send_bytes (buffer[, offset[, size]])

          Send byte data from a *note bytes-like object: 6df. as a
          complete message.

          If `offset' is given then data is read from that position in
          `buffer'.  If `size' is given then that many bytes will be
          read from buffer.  Very large buffers (approximately 32 MiB+,
          though it depends on the OS) may raise a *note ValueError:
          16d. exception

      -- Method: recv_bytes ([maxlength])

          Return a complete message of byte data sent from the other end
          of the connection as a string.  Blocks until there is
          something to receive.  Raises *note EOFError: d34. if there is
          nothing left to receive and the other end has closed.

          If `maxlength' is specified and the message is longer than
          `maxlength' then *note OSError: 304. is raised and the
          connection will no longer be readable.

          Changed in version 3.3: This function used to raise *note
          IOError: a73, which is now an alias of *note OSError: 304.

      -- Method: recv_bytes_into (buffer[, offset])

          Read into `buffer' a complete message of byte data sent from
          the other end of the connection and return the number of bytes
          in the message.  Blocks until there is something to receive.
          Raises *note EOFError: d34. if there is nothing left to
          receive and the other end was closed.

          `buffer' must be a writable *note bytes-like object: 6df.  If
          `offset' is given then the message will be written into the
          buffer from that position.  Offset must be a non-negative
          integer less than the length of `buffer' (in bytes).

          If the buffer is too short then a ‘BufferTooShort’ exception
          is raised and the complete message is available as ‘e.args[0]’
          where ‘e’ is the exception instance.

     Changed in version 3.3: Connection objects themselves can now be
     transferred between processes using *note Connection.send(): 2523.
     and *note Connection.recv(): 2524.

     New in version 3.3: Connection objects now support the context
     management protocol – see *note Context Manager Types: 15c6.  *note
     __enter__(): 1812. returns the connection object, and *note
     __exit__(): 1814. calls *note close(): 2526.

For example:

     >>> from multiprocessing import Pipe
     >>> a, b = Pipe()
     >>> a.send([1, 'hello', None])
     >>> b.recv()
     [1, 'hello', None]
     >>> b.send_bytes(b'thank you')
     >>> a.recv_bytes()
     b'thank you'
     >>> import array
     >>> arr1 = array.array('i', range(5))
     >>> arr2 = array.array('i', [0] * 10)
     >>> a.send_bytes(arr1)
     >>> count = b.recv_bytes_into(arr2)
     >>> assert count == len(arr1) * arr1.itemsize
     >>> arr2
     array('i', [0, 1, 2, 3, 4, 0, 0, 0, 0, 0])
     Warning: The *note Connection.recv(): 2524. method automatically
     unpickles the data it receives, which can be a security risk unless
     you can trust the process which sent the message.

     Therefore, unless the connection object was produced using ‘Pipe()’
     you should only use the *note recv(): 2524. and *note send(): 2523.
     methods after performing some sort of authentication.  See *note
     Authentication keys: 24ff.

     Warning: If a process is killed while it is trying to read or write
     to a pipe then the data in the pipe is likely to become corrupted,
     because it may become impossible to be sure where the message
     boundaries lie.


File: python.info,  Node: Synchronization primitives,  Next: Shared ctypes Objects,  Prev: Connection Objects<2>,  Up: Reference

5.17.2.13 Synchronization primitives
....................................

Generally synchronization primitives are not as necessary in a
multiprocess program as they are in a multithreaded program.  See the
documentation for *note threading: 10b. module.

Note that one can also create synchronization primitives by using a
manager object – see *note Managers: 250a.

 -- Class: multiprocessing.Barrier (parties[, action[, timeout]])

     A barrier object: a clone of *note threading.Barrier: c31.

     New in version 3.3.

 -- Class: multiprocessing.BoundedSemaphore ([value])

     A bounded semaphore object: a close analog of *note
     threading.BoundedSemaphore: b84.

     A solitary difference from its close analog exists: its ‘acquire’
     method’s first argument is named `block', as is consistent with
     *note Lock.acquire(): 252d.

          Note: On macOS, this is indistinguishable from *note
          Semaphore: 24f0. because ‘sem_getvalue()’ is not implemented
          on that platform.

 -- Class: multiprocessing.Condition ([lock])

     A condition variable: an alias for *note threading.Condition: b82.

     If `lock' is specified then it should be a *note Lock: 24ee. or
     *note RLock: 24ef. object from *note multiprocessing: b7.

     Changed in version 3.3: The *note wait_for(): 24c7. method was
     added.

 -- Class: multiprocessing.Event

     A clone of *note threading.Event: b85.

 -- Class: multiprocessing.Lock

     A non-recursive lock object: a close analog of *note
     threading.Lock: 24bc.  Once a process or thread has acquired a
     lock, subsequent attempts to acquire it from any process or thread
     will block until it is released; any process or thread may release
     it.  The concepts and behaviors of *note threading.Lock: 24bc. as
     it applies to threads are replicated here in *note
     multiprocessing.Lock: 24ee. as it applies to either processes or
     threads, except as noted.

     Note that *note Lock: 24ee. is actually a factory function which
     returns an instance of ‘multiprocessing.synchronize.Lock’
     initialized with a default context.

     *note Lock: 24ee. supports the *note context manager: 661. protocol
     and thus may be used in *note with: 7da. statements.

      -- Method: acquire (block=True, timeout=None)

          Acquire a lock, blocking or non-blocking.

          With the `block' argument set to ‘True’ (the default), the
          method call will block until the lock is in an unlocked state,
          then set it to locked and return ‘True’.  Note that the name
          of this first argument differs from that in *note
          threading.Lock.acquire(): 85b.

          With the `block' argument set to ‘False’, the method call does
          not block.  If the lock is currently in a locked state, return
          ‘False’; otherwise set the lock to a locked state and return
          ‘True’.

          When invoked with a positive, floating-point value for
          `timeout', block for at most the number of seconds specified
          by `timeout' as long as the lock can not be acquired.
          Invocations with a negative value for `timeout' are equivalent
          to a `timeout' of zero.  Invocations with a `timeout' value of
          ‘None’ (the default) set the timeout period to infinite.  Note
          that the treatment of negative or ‘None’ values for `timeout'
          differs from the implemented behavior in *note
          threading.Lock.acquire(): 85b.  The `timeout' argument has no
          practical implications if the `block' argument is set to
          ‘False’ and is thus ignored.  Returns ‘True’ if the lock has
          been acquired or ‘False’ if the timeout period has elapsed.

      -- Method: release ()

          Release a lock.  This can be called from any process or
          thread, not only the process or thread which originally
          acquired the lock.

          Behavior is the same as in *note threading.Lock.release():
          24ba. except that when invoked on an unlocked lock, a *note
          ValueError: 16d. is raised.

 -- Class: multiprocessing.RLock

     A recursive lock object: a close analog of *note threading.RLock:
     cba.  A recursive lock must be released by the process or thread
     that acquired it.  Once a process or thread has acquired a
     recursive lock, the same process or thread may acquire it again
     without blocking; that process or thread must release it once for
     each time it has been acquired.

     Note that *note RLock: 24ef. is actually a factory function which
     returns an instance of ‘multiprocessing.synchronize.RLock’
     initialized with a default context.

     *note RLock: 24ef. supports the *note context manager: 661.
     protocol and thus may be used in *note with: 7da. statements.

      -- Method: acquire (block=True, timeout=None)

          Acquire a lock, blocking or non-blocking.

          When invoked with the `block' argument set to ‘True’, block
          until the lock is in an unlocked state (not owned by any
          process or thread) unless the lock is already owned by the
          current process or thread.  The current process or thread then
          takes ownership of the lock (if it does not already have
          ownership) and the recursion level inside the lock increments
          by one, resulting in a return value of ‘True’.  Note that
          there are several differences in this first argument’s
          behavior compared to the implementation of *note
          threading.RLock.acquire(): 85c, starting with the name of the
          argument itself.

          When invoked with the `block' argument set to ‘False’, do not
          block.  If the lock has already been acquired (and thus is
          owned) by another process or thread, the current process or
          thread does not take ownership and the recursion level within
          the lock is not changed, resulting in a return value of
          ‘False’.  If the lock is in an unlocked state, the current
          process or thread takes ownership and the recursion level is
          incremented, resulting in a return value of ‘True’.

          Use and behaviors of the `timeout' argument are the same as in
          *note Lock.acquire(): 252d.  Note that some of these behaviors
          of `timeout' differ from the implemented behaviors in *note
          threading.RLock.acquire(): 85c.

      -- Method: release ()

          Release a lock, decrementing the recursion level.  If after
          the decrement the recursion level is zero, reset the lock to
          unlocked (not owned by any process or thread) and if any other
          processes or threads are blocked waiting for the lock to
          become unlocked, allow exactly one of them to proceed.  If
          after the decrement the recursion level is still nonzero, the
          lock remains locked and owned by the calling process or
          thread.

          Only call this method when the calling process or thread owns
          the lock.  An *note AssertionError: 240. is raised if this
          method is called by a process or thread other than the owner
          or if the lock is in an unlocked (unowned) state.  Note that
          the type of exception raised in this situation differs from
          the implemented behavior in *note threading.RLock.release():
          24c0.

 -- Class: multiprocessing.Semaphore ([value])

     A semaphore object: a close analog of *note threading.Semaphore:
     b83.

     A solitary difference from its close analog exists: its ‘acquire’
     method’s first argument is named `block', as is consistent with
     *note Lock.acquire(): 252d.

     Note: On macOS, ‘sem_timedwait’ is unsupported, so calling
     ‘acquire()’ with a timeout will emulate that function’s behavior
     using a sleeping loop.

     Note: If the SIGINT signal generated by ‘Ctrl-C’ arrives while the
     main thread is blocked by a call to ‘BoundedSemaphore.acquire()’,
     *note Lock.acquire(): 252d, *note RLock.acquire(): 252f,
     ‘Semaphore.acquire()’, ‘Condition.acquire()’ or ‘Condition.wait()’
     then the call will be immediately interrupted and *note
     KeyboardInterrupt: 2cc. will be raised.

     This differs from the behaviour of *note threading: 10b. where
     SIGINT will be ignored while the equivalent blocking calls are in
     progress.

     Note: Some of this package’s functionality requires a functioning
     shared semaphore implementation on the host operating system.
     Without one, the ‘multiprocessing.synchronize’ module will be
     disabled, and attempts to import it will result in an *note
     ImportError: 16c.  See bpo-3770(1) for additional information.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue3770


File: python.info,  Node: Shared ctypes Objects,  Next: Managers,  Prev: Synchronization primitives,  Up: Reference

5.17.2.14 Shared ‘ctypes’ Objects
.................................

It is possible to create shared objects using shared memory which can be
inherited by child processes.

 -- Function: multiprocessing.Value (typecode_or_type, *args, lock=True)

     Return a *note ctypes: 2a. object allocated from shared memory.  By
     default the return value is actually a synchronized wrapper for the
     object.  The object itself can be accessed via the `value'
     attribute of a *note Value: 24eb.

     `typecode_or_type' determines the type of the returned object: it
     is either a ctypes type or a one character typecode of the kind
     used by the *note array: 6. module.  `*args' is passed on to the
     constructor for the type.

     If `lock' is ‘True’ (the default) then a new recursive lock object
     is created to synchronize access to the value.  If `lock' is a
     *note Lock: 24ee. or *note RLock: 24ef. object then that will be
     used to synchronize access to the value.  If `lock' is ‘False’ then
     access to the returned object will not be automatically protected
     by a lock, so it will not necessarily be “process-safe”.

     Operations like ‘+=’ which involve a read and write are not atomic.
     So if, for instance, you want to atomically increment a shared
     value it is insufficient to just do

          counter.value += 1

     Assuming the associated lock is recursive (which it is by default)
     you can instead do

          with counter.get_lock():
              counter.value += 1

     Note that `lock' is a keyword-only argument.

 -- Function: multiprocessing.Array (typecode_or_type,
          size_or_initializer, *, lock=True)

     Return a ctypes array allocated from shared memory.  By default the
     return value is actually a synchronized wrapper for the array.

     `typecode_or_type' determines the type of the elements of the
     returned array: it is either a ctypes type or a one character
     typecode of the kind used by the *note array: 6. module.  If
     `size_or_initializer' is an integer, then it determines the length
     of the array, and the array will be initially zeroed.  Otherwise,
     `size_or_initializer' is a sequence which is used to initialize the
     array and whose length determines the length of the array.

     If `lock' is ‘True’ (the default) then a new lock object is created
     to synchronize access to the value.  If `lock' is a *note Lock:
     24ee. or *note RLock: 24ef. object then that will be used to
     synchronize access to the value.  If `lock' is ‘False’ then access
     to the returned object will not be automatically protected by a
     lock, so it will not necessarily be “process-safe”.

     Note that `lock' is a keyword only argument.

     Note that an array of *note ctypes.c_char: 241a. has `value' and
     `raw' attributes which allow one to use it to store and retrieve
     strings.

* Menu:

* The multiprocessing.sharedctypes module: The multiprocessing sharedctypes module.


File: python.info,  Node: The multiprocessing sharedctypes module,  Up: Shared ctypes Objects

5.17.2.15 The ‘multiprocessing.sharedctypes’ module
...................................................

The *note multiprocessing.sharedctypes: bd. module provides functions
for allocating *note ctypes: 2a. objects from shared memory which can be
inherited by child processes.

     Note: Although it is possible to store a pointer in shared memory
     remember that this will refer to a location in the address space of
     a specific process.  However, the pointer is quite likely to be
     invalid in the context of a second process and trying to
     dereference the pointer from the second process may cause a crash.

 -- Function: multiprocessing.sharedctypes.RawArray (typecode_or_type,
          size_or_initializer)

     Return a ctypes array allocated from shared memory.

     `typecode_or_type' determines the type of the elements of the
     returned array: it is either a ctypes type or a one character
     typecode of the kind used by the *note array: 6. module.  If
     `size_or_initializer' is an integer then it determines the length
     of the array, and the array will be initially zeroed.  Otherwise
     `size_or_initializer' is a sequence which is used to initialize the
     array and whose length determines the length of the array.

     Note that setting and getting an element is potentially non-atomic
     – use *note Array(): 2534. instead to make sure that access is
     automatically synchronized using a lock.

 -- Function: multiprocessing.sharedctypes.RawValue (typecode_or_type,
          *args)

     Return a ctypes object allocated from shared memory.

     `typecode_or_type' determines the type of the returned object: it
     is either a ctypes type or a one character typecode of the kind
     used by the *note array: 6. module.  `*args' is passed on to the
     constructor for the type.

     Note that setting and getting the value is potentially non-atomic –
     use *note Value(): 2536. instead to make sure that access is
     automatically synchronized using a lock.

     Note that an array of *note ctypes.c_char: 241a. has ‘value’ and
     ‘raw’ attributes which allow one to use it to store and retrieve
     strings – see documentation for *note ctypes: 2a.

 -- Function: multiprocessing.sharedctypes.Array (typecode_or_type,
          size_or_initializer, *, lock=True)

     The same as *note RawArray(): 2533. except that depending on the
     value of `lock' a process-safe synchronization wrapper may be
     returned instead of a raw ctypes array.

     If `lock' is ‘True’ (the default) then a new lock object is created
     to synchronize access to the value.  If `lock' is a *note Lock:
     24ee. or *note RLock: 24ef. object then that will be used to
     synchronize access to the value.  If `lock' is ‘False’ then access
     to the returned object will not be automatically protected by a
     lock, so it will not necessarily be “process-safe”.

     Note that `lock' is a keyword-only argument.

 -- Function: multiprocessing.sharedctypes.Value (typecode_or_type,
          *args, lock=True)

     The same as *note RawValue(): 2535. except that depending on the
     value of `lock' a process-safe synchronization wrapper may be
     returned instead of a raw ctypes object.

     If `lock' is ‘True’ (the default) then a new lock object is created
     to synchronize access to the value.  If `lock' is a *note Lock:
     24ee. or *note RLock: 24ef. object then that will be used to
     synchronize access to the value.  If `lock' is ‘False’ then access
     to the returned object will not be automatically protected by a
     lock, so it will not necessarily be “process-safe”.

     Note that `lock' is a keyword-only argument.

 -- Function: multiprocessing.sharedctypes.copy (obj)

     Return a ctypes object allocated from shared memory which is a copy
     of the ctypes object `obj'.

 -- Function: multiprocessing.sharedctypes.synchronized (obj[, lock])

     Return a process-safe wrapper object for a ctypes object which uses
     `lock' to synchronize access.  If `lock' is ‘None’ (the default)
     then a *note multiprocessing.RLock: 24ef. object is created
     automatically.

     A synchronized wrapper will have two methods in addition to those
     of the object it wraps: ‘get_obj()’ returns the wrapped object and
     ‘get_lock()’ returns the lock object used for synchronization.

     Note that accessing the ctypes object through the wrapper can be a
     lot slower than accessing the raw ctypes object.

     Changed in version 3.5: Synchronized objects support the *note
     context manager: 661. protocol.

The table below compares the syntax for creating shared ctypes objects
from shared memory with the normal ctypes syntax.  (In the table
‘MyStruct’ is some subclass of *note ctypes.Structure: 2438.)

ctypes                   sharedctypes using type        sharedctypes using typecode
                                                        
----------------------------------------------------------------------------------------
                                                        
c_double(2.4)            RawValue(c_double, 2.4)        RawValue(‘d’, 2.4)
                                                        
                                                        
MyStruct(4, 6)           RawValue(MyStruct, 4, 6)
                         
                                                        
(c_short * 7)()          RawArray(c_short, 7)           RawArray(‘h’, 7)
                                                        
                                                        
(c_int * 3)(9, 2, 8)     RawArray(c_int, (9, 2, 8))     RawArray(‘i’, (9, 2, 8))
                                                        

Below is an example where a number of ctypes objects are modified by a
child process:

     from multiprocessing import Process, Lock
     from multiprocessing.sharedctypes import Value, Array
     from ctypes import Structure, c_double

     class Point(Structure):
         _fields_ = [('x', c_double), ('y', c_double)]

     def modify(n, x, s, A):
         n.value **= 2
         x.value **= 2
         s.value = s.value.upper()
         for a in A:
             a.x **= 2
             a.y **= 2

     if __name__ == '__main__':
         lock = Lock()

         n = Value('i', 7)
         x = Value(c_double, 1.0/3.0, lock=False)
         s = Array('c', b'hello world', lock=lock)
         A = Array(Point, [(1.875,-6.25), (-5.75,2.0), (2.375,9.5)], lock=lock)

         p = Process(target=modify, args=(n, x, s, A))
         p.start()
         p.join()

         print(n.value)
         print(x.value)
         print(s.value)
         print([(a.x, a.y) for a in A])

The results printed are

     49
     0.1111111111111111
     HELLO WORLD
     [(3.515625, 39.0625), (33.0625, 4.0), (5.640625, 90.25)]


File: python.info,  Node: Managers,  Next: Proxy Objects,  Prev: Shared ctypes Objects,  Up: Reference

5.17.2.16 Managers
..................

Managers provide a way to create data which can be shared between
different processes, including sharing over a network between processes
running on different machines.  A manager object controls a server
process which manages `shared objects'.  Other processes can access the
shared objects by using proxies.

 -- Function: multiprocessing.Manager ()

     Returns a started *note SyncManager: 253a. object which can be used
     for sharing objects between processes.  The returned manager object
     corresponds to a spawned child process and has methods which will
     create shared objects and return corresponding proxies.

Manager processes will be shutdown as soon as they are garbage collected
or their parent process exits.  The manager classes are defined in the
*note multiprocessing.managers: ba. module:

 -- Class: multiprocessing.managers.BaseManager ([address[, authkey]])

     Create a BaseManager object.

     Once created one should call *note start(): 253c. or
     ‘get_server().serve_forever()’ to ensure that the manager object
     refers to a started manager process.

     `address' is the address on which the manager process listens for
     new connections.  If `address' is ‘None’ then an arbitrary one is
     chosen.

     `authkey' is the authentication key which will be used to check the
     validity of incoming connections to the server process.  If
     `authkey' is ‘None’ then ‘current_process().authkey’ is used.
     Otherwise `authkey' is used and it must be a byte string.

      -- Method: start ([initializer[, initargs]])

          Start a subprocess to start the manager.  If `initializer' is
          not ‘None’ then the subprocess will call
          ‘initializer(*initargs)’ when it starts.

      -- Method: get_server ()

          Returns a ‘Server’ object which represents the actual server
          under the control of the Manager.  The ‘Server’ object
          supports the ‘serve_forever()’ method:

               >>> from multiprocessing.managers import BaseManager
               >>> manager = BaseManager(address=('', 50000), authkey=b'abc')
               >>> server = manager.get_server()
               >>> server.serve_forever()

          ‘Server’ additionally has an *note address: 253e. attribute.

      -- Method: connect ()

          Connect a local manager object to a remote manager process:

               >>> from multiprocessing.managers import BaseManager
               >>> m = BaseManager(address=('127.0.0.1', 50000), authkey=b'abc')
               >>> m.connect()

      -- Method: shutdown ()

          Stop the process used by the manager.  This is only available
          if *note start(): 253c. has been used to start the server
          process.

          This can be called multiple times.

      -- Method: register (typeid[, callable[, proxytype[, exposed[,
               method_to_typeid[, create_method]]]]])

          A classmethod which can be used for registering a type or
          callable with the manager class.

          `typeid' is a “type identifier” which is used to identify a
          particular type of shared object.  This must be a string.

          `callable' is a callable used for creating objects for this
          type identifier.  If a manager instance will be connected to
          the server using the *note connect(): 253f. method, or if the
          `create_method' argument is ‘False’ then this can be left as
          ‘None’.

          `proxytype' is a subclass of *note BaseProxy: 2542. which is
          used to create proxies for shared objects with this `typeid'.
          If ‘None’ then a proxy class is created automatically.

          `exposed' is used to specify a sequence of method names which
          proxies for this typeid should be allowed to access using
          *note BaseProxy._callmethod(): 2543.  (If `exposed' is ‘None’
          then ‘proxytype._exposed_’ is used instead if it exists.)  In
          the case where no exposed list is specified, all “public
          methods” of the shared object will be accessible.  (Here a
          “public method” means any attribute which has a *note
          __call__(): 1560. method and whose name does not begin with
          ‘'_'’.)

          `method_to_typeid' is a mapping used to specify the return
          type of those exposed methods which should return a proxy.  It
          maps method names to typeid strings.  (If `method_to_typeid'
          is ‘None’ then ‘proxytype._method_to_typeid_’ is used instead
          if it exists.)  If a method’s name is not a key of this
          mapping or if the mapping is ‘None’ then the object returned
          by the method will be copied by value.

          `create_method' determines whether a method should be created
          with name `typeid' which can be used to tell the server
          process to create a new shared object and return a proxy for
          it.  By default it is ‘True’.

     *note BaseManager: 253b. instances also have one read-only
     property:

      -- Attribute: address

          The address used by the manager.

     Changed in version 3.3: Manager objects support the context
     management protocol – see *note Context Manager Types: 15c6.  *note
     __enter__(): 1812. starts the server process (if it has not already
     started) and then returns the manager object.  *note __exit__():
     1814. calls *note shutdown(): 2540.

     In previous versions *note __enter__(): 1812. did not start the
     manager’s server process if it was not already started.

 -- Class: multiprocessing.managers.SyncManager

     A subclass of *note BaseManager: 253b. which can be used for the
     synchronization of processes.  Objects of this type are returned by
     ‘multiprocessing.Manager()’.

     Its methods create and return *note Proxy Objects: 65e. for a
     number of commonly used data types to be synchronized across
     processes.  This notably includes shared lists and dictionaries.

      -- Method: Barrier (parties[, action[, timeout]])

          Create a shared *note threading.Barrier: c31. object and
          return a proxy for it.

          New in version 3.3.

      -- Method: BoundedSemaphore ([value])

          Create a shared *note threading.BoundedSemaphore: b84. object
          and return a proxy for it.

      -- Method: Condition ([lock])

          Create a shared *note threading.Condition: b82. object and
          return a proxy for it.

          If `lock' is supplied then it should be a proxy for a *note
          threading.Lock: 24bc. or *note threading.RLock: cba. object.

          Changed in version 3.3: The *note wait_for(): 24c7. method was
          added.

      -- Method: Event ()

          Create a shared *note threading.Event: b85. object and return
          a proxy for it.

      -- Method: Lock ()

          Create a shared *note threading.Lock: 24bc. object and return
          a proxy for it.

      -- Method: Namespace ()

          Create a shared *note Namespace: 24ed. object and return a
          proxy for it.

      -- Method: Queue ([maxsize])

          Create a shared *note queue.Queue: dde. object and return a
          proxy for it.

      -- Method: RLock ()

          Create a shared *note threading.RLock: cba. object and return
          a proxy for it.

      -- Method: Semaphore ([value])

          Create a shared *note threading.Semaphore: b83. object and
          return a proxy for it.

      -- Method: Array (typecode, sequence)

          Create an array and return a proxy for it.

      -- Method: Value (typecode, value)

          Create an object with a writable ‘value’ attribute and return
          a proxy for it.

      -- Method: dict ()

      -- Method: dict (mapping)

      -- Method: dict (sequence)

          Create a shared *note dict: 164. object and return a proxy for
          it.

      -- Method: list ()

      -- Method: list (sequence)

          Create a shared *note list: 1f8. object and return a proxy for
          it.

     Changed in version 3.6: Shared objects are capable of being nested.
     For example, a shared container object such as a shared list can
     contain other shared objects which will all be managed and
     synchronized by the *note SyncManager: 253a.

 -- Class: multiprocessing.managers.Namespace

     A type that can register with *note SyncManager: 253a.

     A namespace object has no public methods, but does have writable
     attributes.  Its representation shows the values of its attributes.

     However, when using a proxy for a namespace object, an attribute
     beginning with ‘'_'’ will be an attribute of the proxy and not an
     attribute of the referent:

          >>> manager = multiprocessing.Manager()
          >>> Global = manager.Namespace()
          >>> Global.x = 10
          >>> Global.y = 'hello'
          >>> Global._z = 12.3    # this is an attribute of the proxy
          >>> print(Global)
          Namespace(x=10, y='hello')

* Menu:

* Customized managers::
* Using a remote manager::


File: python.info,  Node: Customized managers,  Next: Using a remote manager,  Up: Managers

5.17.2.17 Customized managers
.............................

To create one’s own manager, one creates a subclass of *note
BaseManager: 253b. and uses the *note register(): 2541. classmethod to
register new types or callables with the manager class.  For example:

     from multiprocessing.managers import BaseManager

     class MathsClass:
         def add(self, x, y):
             return x + y
         def mul(self, x, y):
             return x * y

     class MyManager(BaseManager):
         pass

     MyManager.register('Maths', MathsClass)

     if __name__ == '__main__':
         with MyManager() as manager:
             maths = manager.Maths()
             print(maths.add(4, 3))         # prints 7
             print(maths.mul(7, 8))         # prints 56


File: python.info,  Node: Using a remote manager,  Prev: Customized managers,  Up: Managers

5.17.2.18 Using a remote manager
................................

It is possible to run a manager server on one machine and have clients
use it from other machines (assuming that the firewalls involved allow
it).

Running the following commands creates a server for a single shared
queue which remote clients can access:

     >>> from multiprocessing.managers import BaseManager
     >>> from queue import Queue
     >>> queue = Queue()
     >>> class QueueManager(BaseManager): pass
     >>> QueueManager.register('get_queue', callable=lambda:queue)
     >>> m = QueueManager(address=('', 50000), authkey=b'abracadabra')
     >>> s = m.get_server()
     >>> s.serve_forever()

One client can access the server as follows:

     >>> from multiprocessing.managers import BaseManager
     >>> class QueueManager(BaseManager): pass
     >>> QueueManager.register('get_queue')
     >>> m = QueueManager(address=('foo.bar.org', 50000), authkey=b'abracadabra')
     >>> m.connect()
     >>> queue = m.get_queue()
     >>> queue.put('hello')

Another client can also use it:

     >>> from multiprocessing.managers import BaseManager
     >>> class QueueManager(BaseManager): pass
     >>> QueueManager.register('get_queue')
     >>> m = QueueManager(address=('foo.bar.org', 50000), authkey=b'abracadabra')
     >>> m.connect()
     >>> queue = m.get_queue()
     >>> queue.get()
     'hello'

Local processes can also access that queue, using the code from above on
the client to access it remotely:

     >>> from multiprocessing import Process, Queue
     >>> from multiprocessing.managers import BaseManager
     >>> class Worker(Process):
     ...     def __init__(self, q):
     ...         self.q = q
     ...         super().__init__()
     ...     def run(self):
     ...         self.q.put('local hello')
     ...
     >>> queue = Queue()
     >>> w = Worker(queue)
     >>> w.start()
     >>> class QueueManager(BaseManager): pass
     ...
     >>> QueueManager.register('get_queue', callable=lambda: queue)
     >>> m = QueueManager(address=('', 50000), authkey=b'abracadabra')
     >>> s = m.get_server()
     >>> s.serve_forever()


File: python.info,  Node: Proxy Objects,  Next: Process Pools,  Prev: Managers,  Up: Reference

5.17.2.19 Proxy Objects
.......................

A proxy is an object which `refers' to a shared object which lives
(presumably) in a different process.  The shared object is said to be
the `referent' of the proxy.  Multiple proxy objects may have the same
referent.

A proxy object has methods which invoke corresponding methods of its
referent (although not every method of the referent will necessarily be
available through the proxy).  In this way, a proxy can be used just
like its referent can:

     >>> from multiprocessing import Manager
     >>> manager = Manager()
     >>> l = manager.list([i*i for i in range(10)])
     >>> print(l)
     [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
     >>> print(repr(l))
     <ListProxy object, typeid 'list' at 0x...>
     >>> l[4]
     16
     >>> l[2:5]
     [4, 9, 16]

Notice that applying *note str(): 205. to a proxy will return the
representation of the referent, whereas applying *note repr(): 8b9. will
return the representation of the proxy.

An important feature of proxy objects is that they are picklable so they
can be passed between processes.  As such, a referent can contain *note
Proxy Objects: 65e.  This permits nesting of these managed lists, dicts,
and other *note Proxy Objects: 65e.:

     >>> a = manager.list()
     >>> b = manager.list()
     >>> a.append(b)         # referent of a now contains referent of b
     >>> print(a, b)
     [<ListProxy object, typeid 'list' at ...>] []
     >>> b.append('hello')
     >>> print(a[0], b)
     ['hello'] ['hello']

Similarly, dict and list proxies may be nested inside one another:

     >>> l_outer = manager.list([ manager.dict() for i in range(2) ])
     >>> d_first_inner = l_outer[0]
     >>> d_first_inner['a'] = 1
     >>> d_first_inner['b'] = 2
     >>> l_outer[1]['c'] = 3
     >>> l_outer[1]['z'] = 26
     >>> print(l_outer[0])
     {'a': 1, 'b': 2}
     >>> print(l_outer[1])
     {'c': 3, 'z': 26}

If standard (non-proxy) *note list: 1f8. or *note dict: 164. objects are
contained in a referent, modifications to those mutable values will not
be propagated through the manager because the proxy has no way of
knowing when the values contained within are modified.  However, storing
a value in a container proxy (which triggers a ‘__setitem__’ on the
proxy object) does propagate through the manager and so to effectively
modify such an item, one could re-assign the modified value to the
container proxy:

     # create a list proxy and append a mutable object (a dictionary)
     lproxy = manager.list()
     lproxy.append({})
     # now mutate the dictionary
     d = lproxy[0]
     d['a'] = 1
     d['b'] = 2
     # at this point, the changes to d are not yet synced, but by
     # updating the dictionary, the proxy is notified of the change
     lproxy[0] = d

This approach is perhaps less convenient than employing nested *note
Proxy Objects: 65e. for most use cases but also demonstrates a level of
control over the synchronization.

     Note: The proxy types in *note multiprocessing: b7. do nothing to
     support comparisons by value.  So, for instance, we have:

          >>> manager.list([1,2,3]) == [1,2,3]
          False

     One should just use a copy of the referent instead when making
     comparisons.

 -- Class: multiprocessing.managers.BaseProxy

     Proxy objects are instances of subclasses of *note BaseProxy: 2542.

      -- Method: _callmethod (methodname[, args[, kwds]])

          Call and return the result of a method of the proxy’s
          referent.

          If ‘proxy’ is a proxy whose referent is ‘obj’ then the
          expression

               proxy._callmethod(methodname, args, kwds)

          will evaluate the expression

               getattr(obj, methodname)(*args, **kwds)

          in the manager’s process.

          The returned value will be a copy of the result of the call or
          a proxy to a new shared object – see documentation for the
          `method_to_typeid' argument of *note BaseManager.register():
          2541.

          If an exception is raised by the call, then is re-raised by
          *note _callmethod(): 2543.  If some other exception is raised
          in the manager’s process then this is converted into a
          ‘RemoteError’ exception and is raised by *note _callmethod():
          2543.

          Note in particular that an exception will be raised if
          `methodname' has not been `exposed'.

          An example of the usage of *note _callmethod(): 2543.:

               >>> l = manager.list(range(10))
               >>> l._callmethod('__len__')
               10
               >>> l._callmethod('__getitem__', (slice(2, 7),)) # equivalent to l[2:7]
               [2, 3, 4, 5, 6]
               >>> l._callmethod('__getitem__', (20,))          # equivalent to l[20]
               Traceback (most recent call last):
               ...
               IndexError: list index out of range

      -- Method: _getvalue ()

          Return a copy of the referent.

          If the referent is unpicklable then this will raise an
          exception.

      -- Method: __repr__ ()

          Return a representation of the proxy object.

      -- Method: __str__ ()

          Return the representation of the referent.

* Menu:

* Cleanup::


File: python.info,  Node: Cleanup,  Up: Proxy Objects

5.17.2.20 Cleanup
.................

A proxy object uses a weakref callback so that when it gets garbage
collected it deregisters itself from the manager which owns its
referent.

A shared object gets deleted from the manager process when there are no
longer any proxies referring to it.


File: python.info,  Node: Process Pools,  Next: Listeners and Clients,  Prev: Proxy Objects,  Up: Reference

5.17.2.21 Process Pools
.......................

One can create a pool of processes which will carry out tasks submitted
to it with the *note Pool: 966. class.

 -- Class: multiprocessing.pool.Pool ([processes[, initializer[,
          initargs[, maxtasksperchild[, context]]]]])

     A process pool object which controls a pool of worker processes to
     which jobs can be submitted.  It supports asynchronous results with
     timeouts and callbacks and has a parallel map implementation.

     `processes' is the number of worker processes to use.  If
     `processes' is ‘None’ then the number returned by *note
     os.cpu_count(): 96a. is used.

     If `initializer' is not ‘None’ then each worker process will call
     ‘initializer(*initargs)’ when it starts.

     `maxtasksperchild' is the number of tasks a worker process can
     complete before it will exit and be replaced with a fresh worker
     process, to enable unused resources to be freed.  The default
     `maxtasksperchild' is ‘None’, which means worker processes will
     live as long as the pool.

     `context' can be used to specify the context used for starting the
     worker processes.  Usually a pool is created using the function
     ‘multiprocessing.Pool()’ or the *note Pool(): 966. method of a
     context object.  In both cases `context' is set appropriately.

     Note that the methods of the pool object should only be called by
     the process which created the pool.

          Warning: *note multiprocessing.pool: bb. objects have internal
          resources that need to be properly managed (like any other
          resource) by using the pool as a context manager or by calling
          *note close(): 2559. and *note terminate(): 255a. manually.
          Failure to do this can lead to the process hanging on
          finalization.

          Note that is `not correct' to rely on the garbage colletor to
          destroy the pool as CPython does not assure that the finalizer
          of the pool will be called (see *note object.__del__(): a04.
          for more information).

     New in version 3.2: `maxtasksperchild'

     New in version 3.4: `context'

          Note: Worker processes within a *note Pool: 966. typically
          live for the complete duration of the Pool’s work queue.  A
          frequent pattern found in other systems (such as Apache,
          mod_wsgi, etc) to free resources held by workers is to allow a
          worker within a pool to complete only a set amount of work
          before being exiting, being cleaned up and a new process
          spawned to replace the old one.  The `maxtasksperchild'
          argument to the *note Pool: 966. exposes this ability to the
          end user.

      -- Method: apply (func[, args[, kwds]])

          Call `func' with arguments `args' and keyword arguments
          `kwds'.  It blocks until the result is ready.  Given this
          blocks, *note apply_async(): 255c. is better suited for
          performing work in parallel.  Additionally, `func' is only
          executed in one of the workers of the pool.

      -- Method: apply_async (func[, args[, kwds[, callback[,
               error_callback]]]])

          A variant of the *note apply(): 255b. method which returns a
          *note AsyncResult: 255d. object.

          If `callback' is specified then it should be a callable which
          accepts a single argument.  When the result becomes ready
          `callback' is applied to it, that is unless the call failed,
          in which case the `error_callback' is applied instead.

          If `error_callback' is specified then it should be a callable
          which accepts a single argument.  If the target function
          fails, then the `error_callback' is called with the exception
          instance.

          Callbacks should complete immediately since otherwise the
          thread which handles the results will get blocked.

      -- Method: map (func, iterable[, chunksize])

          A parallel equivalent of the *note map(): cf7. built-in
          function (it supports only one `iterable' argument though, for
          multiple iterables see *note starmap(): b03.).  It blocks
          until the result is ready.

          This method chops the iterable into a number of chunks which
          it submits to the process pool as separate tasks.  The
          (approximate) size of these chunks can be specified by setting
          `chunksize' to a positive integer.

          Note that it may cause high memory usage for very long
          iterables.  Consider using *note imap(): 255e. or *note
          imap_unordered(): 255f. with explicit `chunksize' option for
          better efficiency.

      -- Method: map_async (func, iterable[, chunksize[, callback[,
               error_callback]]])

          A variant of the *note map(): b06. method which returns a
          *note AsyncResult: 255d. object.

          If `callback' is specified then it should be a callable which
          accepts a single argument.  When the result becomes ready
          `callback' is applied to it, that is unless the call failed,
          in which case the `error_callback' is applied instead.

          If `error_callback' is specified then it should be a callable
          which accepts a single argument.  If the target function
          fails, then the `error_callback' is called with the exception
          instance.

          Callbacks should complete immediately since otherwise the
          thread which handles the results will get blocked.

      -- Method: imap (func, iterable[, chunksize])

          A lazier version of *note map(): b06.

          The `chunksize' argument is the same as the one used by the
          *note map(): b06. method.  For very long iterables using a
          large value for `chunksize' can make the job complete `much'
          faster than using the default value of ‘1’.

          Also if `chunksize' is ‘1’ then the ‘next()’ method of the
          iterator returned by the *note imap(): 255e. method has an
          optional `timeout' parameter: ‘next(timeout)’ will raise *note
          multiprocessing.TimeoutError: 2504. if the result cannot be
          returned within `timeout' seconds.

      -- Method: imap_unordered (func, iterable[, chunksize])

          The same as *note imap(): 255e. except that the ordering of
          the results from the returned iterator should be considered
          arbitrary.  (Only when there is only one worker process is the
          order guaranteed to be “correct”.)

      -- Method: starmap (func, iterable[, chunksize])

          Like *note map(): b06. except that the elements of the
          `iterable' are expected to be iterables that are unpacked as
          arguments.

          Hence an `iterable' of ‘[(1,2), (3, 4)]’ results in
          ‘[func(1,2), func(3,4)]’.

          New in version 3.3.

      -- Method: starmap_async (func, iterable[, chunksize[, callback[,
               error_callback]]])

          A combination of *note starmap(): b03. and *note map_async():
          b07. that iterates over `iterable' of iterables and calls
          `func' with the iterables unpacked.  Returns a result object.

          New in version 3.3.

      -- Method: close ()

          Prevents any more tasks from being submitted to the pool.
          Once all the tasks have been completed the worker processes
          will exit.

      -- Method: terminate ()

          Stops the worker processes immediately without completing
          outstanding work.  When the pool object is garbage collected
          *note terminate(): 255a. will be called immediately.

      -- Method: join ()

          Wait for the worker processes to exit.  One must call *note
          close(): 2559. or *note terminate(): 255a. before using *note
          join(): 2560.

     New in version 3.3: Pool objects now support the context management
     protocol – see *note Context Manager Types: 15c6.  *note
     __enter__(): 1812. returns the pool object, and *note __exit__():
     1814. calls *note terminate(): 255a.

 -- Class: multiprocessing.pool.AsyncResult

     The class of the result returned by *note Pool.apply_async(): 255c.
     and *note Pool.map_async(): b07.

      -- Method: get ([timeout])

          Return the result when it arrives.  If `timeout' is not ‘None’
          and the result does not arrive within `timeout' seconds then
          *note multiprocessing.TimeoutError: 2504. is raised.  If the
          remote call raised an exception then that exception will be
          reraised by *note get(): 2561.

      -- Method: wait ([timeout])

          Wait until the result is available or until `timeout' seconds
          pass.

      -- Method: ready ()

          Return whether the call has completed.

      -- Method: successful ()

          Return whether the call completed without raising an
          exception.  Will raise *note ValueError: 16d. if the result is
          not ready.

          Changed in version 3.7: If the result is not ready, *note
          ValueError: 16d. is raised instead of *note AssertionError:
          240.

The following example demonstrates the use of a pool:

     from multiprocessing import Pool
     import time

     def f(x):
         return x*x

     if __name__ == '__main__':
         with Pool(processes=4) as pool:         # start 4 worker processes
             result = pool.apply_async(f, (10,)) # evaluate "f(10)" asynchronously in a single process
             print(result.get(timeout=1))        # prints "100" unless your computer is *very* slow

             print(pool.map(f, range(10)))       # prints "[0, 1, 4,..., 81]"

             it = pool.imap(f, range(10))
             print(next(it))                     # prints "0"
             print(next(it))                     # prints "1"
             print(it.next(timeout=1))           # prints "4" unless your computer is *very* slow

             result = pool.apply_async(time.sleep, (10,))
             print(result.get(timeout=1))        # raises multiprocessing.TimeoutError


File: python.info,  Node: Listeners and Clients,  Next: Authentication keys,  Prev: Process Pools,  Up: Reference

5.17.2.22 Listeners and Clients
...............................

Usually message passing between processes is done using queues or by
using *note Connection: 2511. objects returned by *note Pipe(): 24e8.

However, the *note multiprocessing.connection: b8. module allows some
extra flexibility.  It basically gives a high level message oriented API
for dealing with sockets or Windows named pipes.  It also has support
for `digest authentication' using the *note hmac: 8e. module, and for
polling multiple connections at the same time.

 -- Function: multiprocessing.connection.deliver_challenge (connection,
          authkey)

     Send a randomly generated message to the other end of the
     connection and wait for a reply.

     If the reply matches the digest of the message using `authkey' as
     the key then a welcome message is sent to the other end of the
     connection.  Otherwise *note AuthenticationError: 2503. is raised.

 -- Function: multiprocessing.connection.answer_challenge (connection,
          authkey)

     Receive a message, calculate the digest of the message using
     `authkey' as the key, and then send the digest back.

     If a welcome message is not received, then *note
     AuthenticationError: 2503. is raised.

 -- Function: multiprocessing.connection.Client (address[, family[,
          authkey]])

     Attempt to set up a connection to the listener which is using
     address `address', returning a *note Connection: 2511.

     The type of the connection is determined by `family' argument, but
     this can generally be omitted since it can usually be inferred from
     the format of `address'.  (See *note Address Formats: 2569.)

     If `authkey' is given and not None, it should be a byte string and
     will be used as the secret key for an HMAC-based authentication
     challenge.  No authentication is done if `authkey' is None.  *note
     AuthenticationError: 2503. is raised if authentication fails.  See
     *note Authentication keys: 24ff.

 -- Class: multiprocessing.connection.Listener ([address[, family[,
          backlog[, authkey]]]])

     A wrapper for a bound socket or Windows named pipe which is
     ‘listening’ for connections.

     `address' is the address to be used by the bound socket or named
     pipe of the listener object.

          Note: If an address of ‘0.0.0.0’ is used, the address will not
          be a connectable end point on Windows.  If you require a
          connectable end-point, you should use ‘127.0.0.1’.

     `family' is the type of socket (or named pipe) to use.  This can be
     one of the strings ‘'AF_INET'’ (for a TCP socket), ‘'AF_UNIX'’ (for
     a Unix domain socket) or ‘'AF_PIPE'’ (for a Windows named pipe).
     Of these only the first is guaranteed to be available.  If `family'
     is ‘None’ then the family is inferred from the format of `address'.
     If `address' is also ‘None’ then a default is chosen.  This default
     is the family which is assumed to be the fastest available.  See
     *note Address Formats: 2569.  Note that if `family' is ‘'AF_UNIX'’
     and address is ‘None’ then the socket will be created in a private
     temporary directory created using *note tempfile.mkstemp(): 1dc4.

     If the listener object uses a socket then `backlog' (1 by default)
     is passed to the *note listen(): 83a. method of the socket once it
     has been bound.

     If `authkey' is given and not None, it should be a byte string and
     will be used as the secret key for an HMAC-based authentication
     challenge.  No authentication is done if `authkey' is None.  *note
     AuthenticationError: 2503. is raised if authentication fails.  See
     *note Authentication keys: 24ff.

      -- Method: accept ()

          Accept a connection on the bound socket or named pipe of the
          listener object and return a *note Connection: 2511. object.
          If authentication is attempted and fails, then *note
          AuthenticationError: 2503. is raised.

      -- Method: close ()

          Close the bound socket or named pipe of the listener object.
          This is called automatically when the listener is garbage
          collected.  However it is advisable to call it explicitly.

     Listener objects have the following read-only properties:

      -- Attribute: address

          The address which is being used by the Listener object.

      -- Attribute: last_accepted

          The address from which the last accepted connection came.  If
          this is unavailable then it is ‘None’.

     New in version 3.3: Listener objects now support the context
     management protocol – see *note Context Manager Types: 15c6.  *note
     __enter__(): 1812. returns the listener object, and *note
     __exit__(): 1814. calls *note close(): 256b.

 -- Function: multiprocessing.connection.wait (object_list,
          timeout=None)

     Wait till an object in `object_list' is ready.  Returns the list of
     those objects in `object_list' which are ready.  If `timeout' is a
     float then the call blocks for at most that many seconds.  If
     `timeout' is ‘None’ then it will block for an unlimited period.  A
     negative timeout is equivalent to a zero timeout.

     For both Unix and Windows, an object can appear in `object_list' if
     it is

        * a readable *note Connection: 2511. object;

        * a connected and readable *note socket.socket: 767. object; or

        * the *note sentinel: b02. attribute of a *note Process: 4b9.
          object.

     A connection or socket object is ready when there is data available
     to be read from it, or the other end has been closed.

     `Unix': ‘wait(object_list, timeout)’ almost equivalent
     ‘select.select(object_list, [], [], timeout)’.  The difference is
     that, if *note select.select(): 766. is interrupted by a signal, it
     can raise *note OSError: 304. with an error number of ‘EINTR’,
     whereas *note wait(): b01. will not.

     `Windows': An item in `object_list' must either be an integer
     handle which is waitable (according to the definition used by the
     documentation of the Win32 function ‘WaitForMultipleObjects()’) or
     it can be an object with a ‘fileno()’ method which returns a socket
     handle or pipe handle.  (Note that pipe handles and socket handles
     are `not' waitable handles.)

     New in version 3.3.

`Examples'

The following server code creates a listener which uses ‘'secret
password'’ as an authentication key.  It then waits for a connection and
sends some data to the client:

     from multiprocessing.connection import Listener
     from array import array

     address = ('localhost', 6000)     # family is deduced to be 'AF_INET'

     with Listener(address, authkey=b'secret password') as listener:
         with listener.accept() as conn:
             print('connection accepted from', listener.last_accepted)

             conn.send([2.25, None, 'junk', float])

             conn.send_bytes(b'hello')

             conn.send_bytes(array('i', [42, 1729]))

The following code connects to the server and receives some data from
the server:

     from multiprocessing.connection import Client
     from array import array

     address = ('localhost', 6000)

     with Client(address, authkey=b'secret password') as conn:
         print(conn.recv())                  # => [2.25, None, 'junk', float]

         print(conn.recv_bytes())            # => 'hello'

         arr = array('i', [0, 0, 0, 0, 0])
         print(conn.recv_bytes_into(arr))    # => 8
         print(arr)                          # => array('i', [42, 1729, 0, 0, 0])

The following code uses *note wait(): b01. to wait for messages from
multiple processes at once:

     import time, random
     from multiprocessing import Process, Pipe, current_process
     from multiprocessing.connection import wait

     def foo(w):
         for i in range(10):
             w.send((i, current_process().name))
         w.close()

     if __name__ == '__main__':
         readers = []

         for i in range(4):
             r, w = Pipe(duplex=False)
             readers.append(r)
             p = Process(target=foo, args=(w,))
             p.start()
             # We close the writable end of the pipe now to be sure that
             # p is the only process which owns a handle for it.  This
             # ensures that when p closes its handle for the writable end,
             # wait() will promptly report the readable end as being ready.
             w.close()

         while readers:
             for r in wait(readers):
                 try:
                     msg = r.recv()
                 except EOFError:
                     readers.remove(r)
                 else:
                     print(msg)

* Menu:

* Address Formats::


File: python.info,  Node: Address Formats,  Up: Listeners and Clients

5.17.2.23 Address Formats
.........................

   * An ‘'AF_INET'’ address is a tuple of the form ‘(hostname, port)’
     where `hostname' is a string and `port' is an integer.

   * An ‘'AF_UNIX'’ address is a string representing a filename on the
     filesystem.

   * An ‘'AF_PIPE'’ address is a string of the form
     ‘r'\.\pipe{PipeName}'’.  To use *note Client(): 2568. to connect to
     a named pipe on a remote computer called `ServerName' one should
     use an address of the form ‘r'\`ServerName'\pipe{PipeName}'’
     instead.

Note that any string beginning with two backslashes is assumed by
default to be an ‘'AF_PIPE'’ address rather than an ‘'AF_UNIX'’ address.


File: python.info,  Node: Authentication keys,  Next: Logging<2>,  Prev: Listeners and Clients,  Up: Reference

5.17.2.24 Authentication keys
.............................

When one uses *note Connection.recv: 2524, the data received is
automatically unpickled.  Unfortunately unpickling data from an
untrusted source is a security risk.  Therefore *note Listener: 106b.
and *note Client(): 2568. use the *note hmac: 8e. module to provide
digest authentication.

An authentication key is a byte string which can be thought of as a
password: once a connection is established both ends will demand proof
that the other knows the authentication key.  (Demonstrating that both
ends are using the same key does `not' involve sending the key over the
connection.)

If authentication is requested but no authentication key is specified
then the return value of ‘current_process().authkey’ is used (see *note
Process: 4b9.).  This value will be automatically inherited by any *note
Process: 4b9. object that the current process creates.  This means that
(by default) all processes of a multi-process program will share a
single authentication key which can be used when setting up connections
between themselves.

Suitable authentication keys can also be generated by using *note
os.urandom(): 5cc.


File: python.info,  Node: Logging<2>,  Next: The multiprocessing dummy module,  Prev: Authentication keys,  Up: Reference

5.17.2.25 Logging
.................

Some support for logging is available.  Note, however, that the *note
logging: aa. package does not use process shared locks so it is possible
(depending on the handler type) for messages from different processes to
get mixed up.

 -- Function: multiprocessing.get_logger ()

     Returns the logger used by *note multiprocessing: b7.  If
     necessary, a new one will be created.

     When first created the logger has level ‘logging.NOTSET’ and no
     default handler.  Messages sent to this logger will not by default
     propagate to the root logger.

     Note that on Windows child processes will only inherit the level of
     the parent process’s logger – any other customization of the logger
     will not be inherited.

 -- Function: multiprocessing.log_to_stderr (level=None)

     This function performs a call to *note get_logger(): 2571. but in
     addition to returning the logger created by get_logger, it adds a
     handler which sends output to *note sys.stderr: 1ea. using format
     ‘'[%(levelname)s/%(processName)s] %(message)s'’.  You can modify
     ‘levelname’ of the logger by passing a ‘level’ argument.

Below is an example session with logging turned on:

     >>> import multiprocessing, logging
     >>> logger = multiprocessing.log_to_stderr()
     >>> logger.setLevel(logging.INFO)
     >>> logger.warning('doomed')
     [WARNING/MainProcess] doomed
     >>> m = multiprocessing.Manager()
     [INFO/SyncManager-...] child process calling self.run()
     [INFO/SyncManager-...] created temp directory /.../pymp-...
     [INFO/SyncManager-...] manager serving at '/.../listener-...'
     >>> del m
     [INFO/MainProcess] sending shutdown message to manager
     [INFO/SyncManager-...] manager exiting with exitcode 0

For a full table of logging levels, see the *note logging: aa. module.


File: python.info,  Node: The multiprocessing dummy module,  Prev: Logging<2>,  Up: Reference

5.17.2.26 The ‘multiprocessing.dummy’ module
............................................

*note multiprocessing.dummy: b9. replicates the API of *note
multiprocessing: b7. but is no more than a wrapper around the *note
threading: 10b. module.

In particular, the ‘Pool’ function provided by *note
multiprocessing.dummy: b9. returns an instance of *note ThreadPool: fce,
which is a subclass of *note Pool: 966. that supports all the same
method calls but uses a pool of worker threads rather than worker
processes.

 -- Class: multiprocessing.pool.ThreadPool ([processes[, initializer[,
          initargs]]])

     A thread pool object which controls a pool of worker threads to
     which jobs can be submitted.  *note ThreadPool: fce. instances are
     fully interface compatible with *note Pool: 966. instances, and
     their resources must also be properly managed, either by using the
     pool as a context manager or by calling *note close(): 2559. and
     *note terminate(): 255a. manually.

     `processes' is the number of worker threads to use.  If `processes'
     is ‘None’ then the number returned by *note os.cpu_count(): 96a. is
     used.

     If `initializer' is not ‘None’ then each worker process will call
     ‘initializer(*initargs)’ when it starts.

     Unlike *note Pool: 966, `maxtasksperchild' and `context' cannot be
     provided.

               Note: A *note ThreadPool: fce. shares the same interface
               as *note Pool: 966, which is designed around a pool of
               processes and predates the introduction of the *note
               concurrent.futures: 21. module.  As such, it inherits
               some operations that don’t make sense for a pool backed
               by threads, and it has its own type for representing the
               status of asynchronous jobs, *note AsyncResult: 255d,
               that is not understood by any other libraries.

               Users should generally prefer to use *note
               concurrent.futures.ThreadPoolExecutor: 18c, which has a
               simpler interface that was designed around threads from
               the start, and which returns *note
               concurrent.futures.Future: c00. instances that are
               compatible with many other libraries, including *note
               asyncio: 9.


File: python.info,  Node: Programming guidelines,  Next: Examples<11>,  Prev: Reference,  Up: multiprocessing — Process-based parallelism

5.17.2.27 Programming guidelines
................................

There are certain guidelines and idioms which should be adhered to when
using *note multiprocessing: b7.

* Menu:

* All start methods::
* The spawn and forkserver start methods::


File: python.info,  Node: All start methods,  Next: The spawn and forkserver start methods,  Up: Programming guidelines

5.17.2.28 All start methods
...........................

The following applies to all start methods.

Avoid shared state

     As far as possible one should try to avoid shifting large amounts
     of data between processes.

     It is probably best to stick to using queues or pipes for
     communication between processes rather than using the lower level
     synchronization primitives.

Picklability

     Ensure that the arguments to the methods of proxies are picklable.

Thread safety of proxies

     Do not use a proxy object from more than one thread unless you
     protect it with a lock.

     (There is never a problem with different processes using the `same'
     proxy.)

Joining zombie processes

     On Unix when a process finishes but has not been joined it becomes
     a zombie.  There should never be very many because each time a new
     process starts (or *note active_children(): 251c. is called) all
     completed processes which have not yet been joined will be joined.
     Also calling a finished process’s *note Process.is_alive: 24fc.
     will join the process.  Even so it is probably good practice to
     explicitly join all the processes that you start.

Better to inherit than pickle/unpickle

     When using the `spawn' or `forkserver' start methods many types
     from *note multiprocessing: b7. need to be picklable so that child
     processes can use them.  However, one should generally avoid
     sending shared objects to other processes using pipes or queues.
     Instead you should arrange the program so that a process which
     needs access to a shared resource created elsewhere can inherit it
     from an ancestor process.

Avoid terminating processes

     Using the *note Process.terminate: 2500. method to stop a process
     is liable to cause any shared resources (such as locks, semaphores,
     pipes and queues) currently being used by the process to become
     broken or unavailable to other processes.

     Therefore it is probably best to only consider using *note
     Process.terminate: 2500. on processes which never use any shared
     resources.

Joining processes that use queues

     Bear in mind that a process that has put items in a queue will wait
     before terminating until all the buffered items are fed by the
     “feeder” thread to the underlying pipe.  (The child process can
     call the *note Queue.cancel_join_thread: 250f. method of the queue
     to avoid this behaviour.)

     This means that whenever you use a queue you need to make sure that
     all items which have been put on the queue will eventually be
     removed before the process is joined.  Otherwise you cannot be sure
     that processes which have put items on the queue will terminate.
     Remember also that non-daemonic processes will be joined
     automatically.

     An example which will deadlock is the following:

          from multiprocessing import Process, Queue

          def f(q):
              q.put('X' * 1000000)

          if __name__ == '__main__':
              queue = Queue()
              p = Process(target=f, args=(queue,))
              p.start()
              p.join()                    # this deadlocks
              obj = queue.get()

     A fix here would be to swap the last two lines (or simply remove
     the ‘p.join()’ line).

Explicitly pass resources to child processes

     On Unix using the `fork' start method, a child process can make use
     of a shared resource created in a parent process using a global
     resource.  However, it is better to pass the object as an argument
     to the constructor for the child process.

     Apart from making the code (potentially) compatible with Windows
     and the other start methods this also ensures that as long as the
     child process is still alive the object will not be garbage
     collected in the parent process.  This might be important if some
     resource is freed when the object is garbage collected in the
     parent process.

     So for instance

          from multiprocessing import Process, Lock

          def f():
              ... do something using "lock" ...

          if __name__ == '__main__':
              lock = Lock()
              for i in range(10):
                  Process(target=f).start()

     should be rewritten as

          from multiprocessing import Process, Lock

          def f(l):
              ... do something using "l" ...

          if __name__ == '__main__':
              lock = Lock()
              for i in range(10):
                  Process(target=f, args=(lock,)).start()

Beware of replacing *note sys.stdin: 41e. with a “file like object”

     *note multiprocessing: b7. originally unconditionally called:

          os.close(sys.stdin.fileno())

     in the ‘multiprocessing.Process._bootstrap()’ method — this
     resulted in issues with processes-in-processes.  This has been
     changed to:

          sys.stdin.close()
          sys.stdin = open(os.open(os.devnull, os.O_RDONLY), closefd=False)

     Which solves the fundamental issue of processes colliding with each
     other resulting in a bad file descriptor error, but introduces a
     potential danger to applications which replace *note sys.stdin():
     41e. with a “file-like object” with output buffering.  This danger
     is that if multiple processes call *note close(): 1147. on this
     file-like object, it could result in the same data being flushed to
     the object multiple times, resulting in corruption.

     If you write a file-like object and implement your own caching, you
     can make it fork-safe by storing the pid whenever you append to the
     cache, and discarding the cache when the pid changes.  For example:

          @property
          def cache(self):
              pid = os.getpid()
              if pid != self._pid:
                  self._pid = pid
                  self._cache = []
              return self._cache

     For more information, see bpo-5155(1), bpo-5313(2) and bpo-5331(3)

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue5155

   (2) https://bugs.python.org/issue5313

   (3) https://bugs.python.org/issue5331


File: python.info,  Node: The spawn and forkserver start methods,  Prev: All start methods,  Up: Programming guidelines

5.17.2.29 The `spawn' and `forkserver' start methods
....................................................

There are a few extra restriction which don’t apply to the `fork' start
method.

More picklability

     Ensure that all arguments to ‘Process.__init__()’ are picklable.
     Also, if you subclass *note Process: 4b9. then make sure that
     instances will be picklable when the *note Process.start: 24e1.
     method is called.

Global variables

     Bear in mind that if code run in a child process tries to access a
     global variable, then the value it sees (if any) may not be the
     same as the value in the parent process at the time that *note
     Process.start: 24e1. was called.

     However, global variables which are just module level constants
     cause no problems.

Safe importing of main module

     Make sure that the main module can be safely imported by a new
     Python interpreter without causing unintended side effects (such a
     starting a new process).

     For example, using the `spawn' or `forkserver' start method running
     the following module would fail with a *note RuntimeError: 3dc.:

          from multiprocessing import Process

          def foo():
              print('hello')

          p = Process(target=foo)
          p.start()

     Instead one should protect the “entry point” of the program by
     using ‘if __name__ == '__main__':’ as follows:

          from multiprocessing import Process, freeze_support, set_start_method

          def foo():
              print('hello')

          if __name__ == '__main__':
              freeze_support()
              set_start_method('spawn')
              p = Process(target=foo)
              p.start()

     (The ‘freeze_support()’ line can be omitted if the program will be
     run normally instead of frozen.)

     This allows the newly spawned Python interpreter to safely import
     the module and then run the module’s ‘foo()’ function.

     Similar restrictions apply if a pool or manager is created in the
     main module.


File: python.info,  Node: Examples<11>,  Prev: Programming guidelines,  Up: multiprocessing — Process-based parallelism

5.17.2.30 Examples
..................

Demonstration of how to create and use customized managers and proxies:

     from multiprocessing import freeze_support
     from multiprocessing.managers import BaseManager, BaseProxy
     import operator

     ##

     class Foo:
         def f(self):
             print('you called Foo.f()')
         def g(self):
             print('you called Foo.g()')
         def _h(self):
             print('you called Foo._h()')

     # A simple generator function
     def baz():
         for i in range(10):
             yield i*i

     # Proxy type for generator objects
     class GeneratorProxy(BaseProxy):
         _exposed_ = ['__next__']
         def __iter__(self):
             return self
         def __next__(self):
             return self._callmethod('__next__')

     # Function to return the operator module
     def get_operator_module():
         return operator

     ##

     class MyManager(BaseManager):
         pass

     # register the Foo class; make `f()` and `g()` accessible via proxy
     MyManager.register('Foo1', Foo)

     # register the Foo class; make `g()` and `_h()` accessible via proxy
     MyManager.register('Foo2', Foo, exposed=('g', '_h'))

     # register the generator function baz; use `GeneratorProxy` to make proxies
     MyManager.register('baz', baz, proxytype=GeneratorProxy)

     # register get_operator_module(); make public functions accessible via proxy
     MyManager.register('operator', get_operator_module)

     ##

     def test():
         manager = MyManager()
         manager.start()

         print('-' * 20)

         f1 = manager.Foo1()
         f1.f()
         f1.g()
         assert not hasattr(f1, '_h')
         assert sorted(f1._exposed_) == sorted(['f', 'g'])

         print('-' * 20)

         f2 = manager.Foo2()
         f2.g()
         f2._h()
         assert not hasattr(f2, 'f')
         assert sorted(f2._exposed_) == sorted(['g', '_h'])

         print('-' * 20)

         it = manager.baz()
         for i in it:
             print('<%d>' % i, end=' ')
         print()

         print('-' * 20)

         op = manager.operator()
         print('op.add(23, 45) =', op.add(23, 45))
         print('op.pow(2, 94) =', op.pow(2, 94))
         print('op._exposed_ =', op._exposed_)

     ##

     if __name__ == '__main__':
         freeze_support()
         test()

Using *note Pool: 966.:

     import multiprocessing
     import time
     import random
     import sys

     #
     # Functions used by test code
     #

     def calculate(func, args):
         result = func(*args)
         return '%s says that %s%s = %s' % (
             multiprocessing.current_process().name,
             func.__name__, args, result
             )

     def calculatestar(args):
         return calculate(*args)

     def mul(a, b):
         time.sleep(0.5 * random.random())
         return a * b

     def plus(a, b):
         time.sleep(0.5 * random.random())
         return a + b

     def f(x):
         return 1.0 / (x - 5.0)

     def pow3(x):
         return x ** 3

     def noop(x):
         pass

     #
     # Test code
     #

     def test():
         PROCESSES = 4
         print('Creating pool with %d processes\n' % PROCESSES)

         with multiprocessing.Pool(PROCESSES) as pool:
             #
             # Tests
             #

             TASKS = [(mul, (i, 7)) for i in range(10)] + \
                     [(plus, (i, 8)) for i in range(10)]

             results = [pool.apply_async(calculate, t) for t in TASKS]
             imap_it = pool.imap(calculatestar, TASKS)
             imap_unordered_it = pool.imap_unordered(calculatestar, TASKS)

             print('Ordered results using pool.apply_async():')
             for r in results:
                 print('\t', r.get())
             print()

             print('Ordered results using pool.imap():')
             for x in imap_it:
                 print('\t', x)
             print()

             print('Unordered results using pool.imap_unordered():')
             for x in imap_unordered_it:
                 print('\t', x)
             print()

             print('Ordered results using pool.map() --- will block till complete:')
             for x in pool.map(calculatestar, TASKS):
                 print('\t', x)
             print()

             #
             # Test error handling
             #

             print('Testing error handling:')

             try:
                 print(pool.apply(f, (5,)))
             except ZeroDivisionError:
                 print('\tGot ZeroDivisionError as expected from pool.apply()')
             else:
                 raise AssertionError('expected ZeroDivisionError')

             try:
                 print(pool.map(f, list(range(10))))
             except ZeroDivisionError:
                 print('\tGot ZeroDivisionError as expected from pool.map()')
             else:
                 raise AssertionError('expected ZeroDivisionError')

             try:
                 print(list(pool.imap(f, list(range(10)))))
             except ZeroDivisionError:
                 print('\tGot ZeroDivisionError as expected from list(pool.imap())')
             else:
                 raise AssertionError('expected ZeroDivisionError')

             it = pool.imap(f, list(range(10)))
             for i in range(10):
                 try:
                     x = next(it)
                 except ZeroDivisionError:
                     if i == 5:
                         pass
                 except StopIteration:
                     break
                 else:
                     if i == 5:
                         raise AssertionError('expected ZeroDivisionError')

             assert i == 9
             print('\tGot ZeroDivisionError as expected from IMapIterator.next()')
             print()

             #
             # Testing timeouts
             #

             print('Testing ApplyResult.get() with timeout:', end=' ')
             res = pool.apply_async(calculate, TASKS[0])
             while 1:
                 sys.stdout.flush()
                 try:
                     sys.stdout.write('\n\t%s' % res.get(0.02))
                     break
                 except multiprocessing.TimeoutError:
                     sys.stdout.write('.')
             print()
             print()

             print('Testing IMapIterator.next() with timeout:', end=' ')
             it = pool.imap(calculatestar, TASKS)
             while 1:
                 sys.stdout.flush()
                 try:
                     sys.stdout.write('\n\t%s' % it.next(0.02))
                 except StopIteration:
                     break
                 except multiprocessing.TimeoutError:
                     sys.stdout.write('.')
             print()
             print()


     if __name__ == '__main__':
         multiprocessing.freeze_support()
         test()

An example showing how to use queues to feed tasks to a collection of
worker processes and collect the results:

     import time
     import random

     from multiprocessing import Process, Queue, current_process, freeze_support

     #
     # Function run by worker processes
     #

     def worker(input, output):
         for func, args in iter(input.get, 'STOP'):
             result = calculate(func, args)
             output.put(result)

     #
     # Function used to calculate result
     #

     def calculate(func, args):
         result = func(*args)
         return '%s says that %s%s = %s' % \
             (current_process().name, func.__name__, args, result)

     #
     # Functions referenced by tasks
     #

     def mul(a, b):
         time.sleep(0.5*random.random())
         return a * b

     def plus(a, b):
         time.sleep(0.5*random.random())
         return a + b

     #
     #
     #

     def test():
         NUMBER_OF_PROCESSES = 4
         TASKS1 = [(mul, (i, 7)) for i in range(20)]
         TASKS2 = [(plus, (i, 8)) for i in range(10)]

         # Create queues
         task_queue = Queue()
         done_queue = Queue()

         # Submit tasks
         for task in TASKS1:
             task_queue.put(task)

         # Start worker processes
         for i in range(NUMBER_OF_PROCESSES):
             Process(target=worker, args=(task_queue, done_queue)).start()

         # Get and print results
         print('Unordered results:')
         for i in range(len(TASKS1)):
             print('\t', done_queue.get())

         # Add more tasks using `put()`
         for task in TASKS2:
             task_queue.put(task)

         # Get and print some more results
         for i in range(len(TASKS2)):
             print('\t', done_queue.get())

         # Tell child processes to stop
         for i in range(NUMBER_OF_PROCESSES):
             task_queue.put('STOP')


     if __name__ == '__main__':
         freeze_support()
         test()


File: python.info,  Node: multiprocessing shared_memory — Provides shared memory for direct access across processes,  Next: The concurrent package,  Prev: multiprocessing — Process-based parallelism,  Up: Concurrent Execution

5.17.3 ‘multiprocessing.shared_memory’ — Provides shared memory for direct access across processes
--------------------------------------------------------------------------------------------------

`Source code:' Lib/multiprocessing/shared_memory.py(1)

New in version 3.8.

__________________________________________________________________

This module provides a class, *note SharedMemory: 24e5, for the
allocation and management of shared memory to be accessed by one or more
processes on a multicore or symmetric multiprocessor (SMP) machine.  To
assist with the life-cycle management of shared memory especially across
distinct processes, a *note BaseManager: 253b. subclass,
‘SharedMemoryManager’, is also provided in the
‘multiprocessing.managers’ module.

In this module, shared memory refers to “System V style” shared memory
blocks (though is not necessarily implemented explicitly as such) and
does not refer to “distributed shared memory”.  This style of shared
memory permits distinct processes to potentially read and write to a
common (or shared) region of volatile memory.  Processes are
conventionally limited to only have access to their own process memory
space but shared memory permits the sharing of data between processes,
avoiding the need to instead send messages between processes containing
that data.  Sharing data directly via memory can provide significant
performance benefits compared to sharing data via disk or socket or
other communications requiring the serialization/deserialization and
copying of data.

 -- Class: multiprocessing.shared_memory.SharedMemory (name=None,
          create=False, size=0)

     Creates a new shared memory block or attaches to an existing shared
     memory block.  Each shared memory block is assigned a unique name.
     In this way, one process can create a shared memory block with a
     particular name and a different process can attach to that same
     shared memory block using that same name.

     As a resource for sharing data across processes, shared memory
     blocks may outlive the original process that created them.  When
     one process no longer needs access to a shared memory block that
     might still be needed by other processes, the *note close(): 257a.
     method should be called.  When a shared memory block is no longer
     needed by any process, the *note unlink(): 257b. method should be
     called to ensure proper cleanup.

     `name' is the unique name for the requested shared memory,
     specified as a string.  When creating a new shared memory block, if
     ‘None’ (the default) is supplied for the name, a novel name will be
     generated.

     `create' controls whether a new shared memory block is created
     (‘True’) or an existing shared memory block is attached (‘False’).

     `size' specifies the requested number of bytes when creating a new
     shared memory block.  Because some platforms choose to allocate
     chunks of memory based upon that platform’s memory page size, the
     exact size of the shared memory block may be larger or equal to the
     size requested.  When attaching to an existing shared memory block,
     the ‘size’ parameter is ignored.

      -- Method: close ()

          Closes access to the shared memory from this instance.  In
          order to ensure proper cleanup of resources, all instances
          should call ‘close()’ once the instance is no longer needed.
          Note that calling ‘close()’ does not cause the shared memory
          block itself to be destroyed.

      -- Method: unlink ()

          Requests that the underlying shared memory block be destroyed.
          In order to ensure proper cleanup of resources, ‘unlink()’
          should be called once (and only once) across all processes
          which have need for the shared memory block.  After requesting
          its destruction, a shared memory block may or may not be
          immediately destroyed and this behavior may differ across
          platforms.  Attempts to access data inside the shared memory
          block after ‘unlink()’ has been called may result in memory
          access errors.  Note: the last process relinquishing its hold
          on a shared memory block may call ‘unlink()’ and *note
          close(): 257a. in either order.

      -- Attribute: buf

          A memoryview of contents of the shared memory block.

      -- Attribute: name

          Read-only access to the unique name of the shared memory
          block.

      -- Attribute: size

          Read-only access to size in bytes of the shared memory block.

The following example demonstrates low-level use of *note SharedMemory:
24e5. instances:

     >>> from multiprocessing import shared_memory
     >>> shm_a = shared_memory.SharedMemory(create=True, size=10)
     >>> type(shm_a.buf)
     <class 'memoryview'>
     >>> buffer = shm_a.buf
     >>> len(buffer)
     10
     >>> buffer[:4] = bytearray([22, 33, 44, 55])  # Modify multiple at once
     >>> buffer[4] = 100                           # Modify single byte at a time
     >>> # Attach to an existing shared memory block
     >>> shm_b = shared_memory.SharedMemory(shm_a.name)
     >>> import array
     >>> array.array('b', shm_b.buf[:5])  # Copy the data into a new array.array
     array('b', [22, 33, 44, 55, 100])
     >>> shm_b.buf[:5] = b'howdy'  # Modify via shm_b using bytes
     >>> bytes(shm_a.buf[:5])      # Access via shm_a
     b'howdy'
     >>> shm_b.close()   # Close each SharedMemory instance
     >>> shm_a.close()
     >>> shm_a.unlink()  # Call unlink only once to release the shared memory

The following example demonstrates a practical use of the *note
SharedMemory: 24e5. class with NumPy arrays(2), accessing the same
‘numpy.ndarray’ from two distinct Python shells:

     >>> # In the first Python interactive shell
     >>> import numpy as np
     >>> a = np.array([1, 1, 2, 3, 5, 8])  # Start with an existing NumPy array
     >>> from multiprocessing import shared_memory
     >>> shm = shared_memory.SharedMemory(create=True, size=a.nbytes)
     >>> # Now create a NumPy array backed by shared memory
     >>> b = np.ndarray(a.shape, dtype=a.dtype, buffer=shm.buf)
     >>> b[:] = a[:]  # Copy the original data into shared memory
     >>> b
     array([1, 1, 2, 3, 5, 8])
     >>> type(b)
     <class 'numpy.ndarray'>
     >>> type(a)
     <class 'numpy.ndarray'>
     >>> shm.name  # We did not specify a name so one was chosen for us
     'psm_21467_46075'

     >>> # In either the same shell or a new Python shell on the same machine
     >>> import numpy as np
     >>> from multiprocessing import shared_memory
     >>> # Attach to the existing shared memory block
     >>> existing_shm = shared_memory.SharedMemory(name='psm_21467_46075')
     >>> # Note that a.shape is (6,) and a.dtype is np.int64 in this example
     >>> c = np.ndarray((6,), dtype=np.int64, buffer=existing_shm.buf)
     >>> c
     array([1, 1, 2, 3, 5, 8])
     >>> c[-1] = 888
     >>> c
     array([  1,   1,   2,   3,   5, 888])

     >>> # Back in the first Python interactive shell, b reflects this change
     >>> b
     array([  1,   1,   2,   3,   5, 888])

     >>> # Clean up from within the second Python shell
     >>> del c  # Unnecessary; merely emphasizing the array is no longer used
     >>> existing_shm.close()

     >>> # Clean up from within the first Python shell
     >>> del b  # Unnecessary; merely emphasizing the array is no longer used
     >>> shm.close()
     >>> shm.unlink()  # Free and release the shared memory block at the very end

 -- Class: multiprocessing.managers.SharedMemoryManager ([address[,
          authkey]])

     A subclass of *note BaseManager: 253b. which can be used for the
     management of shared memory blocks across processes.

     A call to *note start(): 253c. on a *note SharedMemoryManager:
     257f. instance causes a new process to be started.  This new
     process’s sole purpose is to manage the life cycle of all shared
     memory blocks created through it.  To trigger the release of all
     shared memory blocks managed by that process, call *note
     shutdown(): 2540. on the instance.  This triggers a
     ‘SharedMemory.unlink()’ call on all of the *note SharedMemory:
     2580. objects managed by that process and then stops the process
     itself.  By creating ‘SharedMemory’ instances through a
     ‘SharedMemoryManager’, we avoid the need to manually track and
     trigger the freeing of shared memory resources.

     This class provides methods for creating and returning *note
     SharedMemory: 2580. instances and for creating a list-like object
     (*note ShareableList: 2581.) backed by shared memory.

     Refer to *note multiprocessing.managers.BaseManager: 253b. for a
     description of the inherited `address' and `authkey' optional input
     arguments and how they may be used to connect to an existing
     ‘SharedMemoryManager’ service from other processes.

      -- Method: SharedMemory (size)

          Create and return a new *note SharedMemory: 2580. object with
          the specified ‘size’ in bytes.

      -- Method: ShareableList (sequence)

          Create and return a new *note ShareableList: 2581. object,
          initialized by the values from the input ‘sequence’.

The following example demonstrates the basic mechanisms of a
‘SharedMemoryManager’:

     >>> from multiprocessing.managers import SharedMemoryManager
     >>> smm = SharedMemoryManager()
     >>> smm.start()  # Start the process that manages the shared memory blocks
     >>> sl = smm.ShareableList(range(4))
     >>> sl
     ShareableList([0, 1, 2, 3], name='psm_6572_7512')
     >>> raw_shm = smm.SharedMemory(size=128)
     >>> another_sl = smm.ShareableList('alpha')
     >>> another_sl
     ShareableList(['a', 'l', 'p', 'h', 'a'], name='psm_6572_12221')
     >>> smm.shutdown()  # Calls unlink() on sl, raw_shm, and another_sl

The following example depicts a potentially more convenient pattern for
using ‘SharedMemoryManager’ objects via the *note with: 7da. statement
to ensure that all shared memory blocks are released after they are no
longer needed:

     >>> with SharedMemoryManager() as smm:
     ...     sl = smm.ShareableList(range(2000))
     ...     # Divide the work among two processes, storing partial results in sl
     ...     p1 = Process(target=do_work, args=(sl, 0, 1000))
     ...     p2 = Process(target=do_work, args=(sl, 1000, 2000))
     ...     p1.start()
     ...     p2.start()  # A multiprocessing.Pool might be more efficient
     ...     p1.join()
     ...     p2.join()   # Wait for all work to complete in both processes
     ...     total_result = sum(sl)  # Consolidate the partial results now in sl

When using a ‘SharedMemoryManager’ in a *note with: 7da. statement, the
shared memory blocks created using that manager are all released when
the *note with: 7da. statement’s code block finishes execution.

 -- Class: multiprocessing.shared_memory.ShareableList (sequence=None,
          *, name=None)

     Provides a mutable list-like object where all values stored within
     are stored in a shared memory block.  This constrains storable
     values to only the ‘int’, ‘float’, ‘bool’, ‘str’ (less than 10M
     bytes each), ‘bytes’ (less than 10M bytes each), and ‘None’
     built-in data types.  It also notably differs from the built-in
     ‘list’ type in that these lists can not change their overall length
     (i.e.  no append, insert, etc.)  and do not support the dynamic
     creation of new *note ShareableList: 1055. instances via slicing.

     `sequence' is used in populating a new ‘ShareableList’ full of
     values.  Set to ‘None’ to instead attach to an already existing
     ‘ShareableList’ by its unique shared memory name.

     `name' is the unique name for the requested shared memory, as
     described in the definition for *note SharedMemory: 24e5.  When
     attaching to an existing ‘ShareableList’, specify its shared memory
     block’s unique name while leaving ‘sequence’ set to ‘None’.

      -- Method: count (value)

          Returns the number of occurrences of ‘value’.

      -- Method: index (value)

          Returns first index position of ‘value’.  Raises *note
          ValueError: 16d. if ‘value’ is not present.

      -- Attribute: format

          Read-only attribute containing the *note struct: f8. packing
          format used by all currently stored values.

      -- Attribute: shm

          The *note SharedMemory: 24e5. instance where the values are
          stored.

The following example demonstrates basic use of a *note ShareableList:
1055. instance:

     >>> from multiprocessing import shared_memory
     >>> a = shared_memory.ShareableList(['howdy', b'HoWdY', -273.154, 100, None, True, 42])
     >>> [ type(entry) for entry in a ]
     [<class 'str'>, <class 'bytes'>, <class 'float'>, <class 'int'>, <class 'NoneType'>, <class 'bool'>, <class 'int'>]
     >>> a[2]
     -273.154
     >>> a[2] = -78.5
     >>> a[2]
     -78.5
     >>> a[2] = 'dry ice'  # Changing data types is supported as well
     >>> a[2]
     'dry ice'
     >>> a[2] = 'larger than previously allocated storage space'
     Traceback (most recent call last):
       ...
     ValueError: exceeds available storage for existing str
     >>> a[2]
     'dry ice'
     >>> len(a)
     7
     >>> a.index(42)
     6
     >>> a.count(b'howdy')
     0
     >>> a.count(b'HoWdY')
     1
     >>> a.shm.close()
     >>> a.shm.unlink()
     >>> del a  # Use of a ShareableList after call to unlink() is unsupported

The following example depicts how one, two, or many processes may access
the same *note ShareableList: 1055. by supplying the name of the shared
memory block behind it:

     >>> b = shared_memory.ShareableList(range(5))         # In a first process
     >>> c = shared_memory.ShareableList(name=b.shm.name)  # In a second process
     >>> c
     ShareableList([0, 1, 2, 3, 4], name='...')
     >>> c[-1] = -999
     >>> b[-1]
     -999
     >>> b.shm.close()
     >>> c.shm.close()
     >>> c.shm.unlink()

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/multiprocessing/shared_memory.py

   (2) https://www.numpy.org/


File: python.info,  Node: The concurrent package,  Next: concurrent futures — Launching parallel tasks,  Prev: multiprocessing shared_memory — Provides shared memory for direct access across processes,  Up: Concurrent Execution

5.17.4 The ‘concurrent’ package
-------------------------------

Currently, there is only one module in this package:

   * *note concurrent.futures: 21. – Launching parallel tasks


File: python.info,  Node: concurrent futures — Launching parallel tasks,  Next: subprocess — Subprocess management,  Prev: The concurrent package,  Up: Concurrent Execution

5.17.5 ‘concurrent.futures’ — Launching parallel tasks
------------------------------------------------------

New in version 3.2.

`Source code:' Lib/concurrent/futures/thread.py(1) and
Lib/concurrent/futures/process.py(2)

__________________________________________________________________

The *note concurrent.futures: 21. module provides a high-level interface
for asynchronously executing callables.

The asynchronous execution can be performed with threads, using *note
ThreadPoolExecutor: 18c, or separate processes, using *note
ProcessPoolExecutor: 196.  Both implement the same interface, which is
defined by the abstract *note Executor: 258a. class.

* Menu:

* Executor Objects::
* ThreadPoolExecutor::
* ProcessPoolExecutor::
* Future Objects::
* Module Functions::
* Exception classes::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/concurrent/futures/thread.py

   (2) 
https://github.com/python/cpython/tree/3.9/Lib/concurrent/futures/process.py


File: python.info,  Node: Executor Objects,  Next: ThreadPoolExecutor,  Up: concurrent futures — Launching parallel tasks

5.17.5.1 Executor Objects
.........................

 -- Class: concurrent.futures.Executor

     An abstract class that provides methods to execute calls
     asynchronously.  It should not be used directly, but through its
     concrete subclasses.

           -- Method: submit (fn, /, *args, **kwargs)

               Schedules the callable, `fn', to be executed as
               ‘fn(*args, **kwargs)’ and returns a *note Future: c00.
               object representing the execution of the callable.

                    with ThreadPoolExecutor(max_workers=1) as executor:
                        future = executor.submit(pow, 323, 1235)
                        print(future.result())

           -- Method: map (func, *iterables, timeout=None, chunksize=1)

               Similar to *note map(func, *iterables): cf7. except:

                  * the `iterables' are collected immediately rather
                    than lazily;

                  * `func' is executed asynchronously and several calls
                    to `func' may be made concurrently.

               The returned iterator raises a *note
               concurrent.futures.TimeoutError: 258c. if *note
               __next__(): d2c. is called and the result isn’t available
               after `timeout' seconds from the original call to *note
               Executor.map(): 7b1.  `timeout' can be an int or a float.
               If `timeout' is not specified or ‘None’, there is no
               limit to the wait time.

               If a `func' call raises an exception, then that exception
               will be raised when its value is retrieved from the
               iterator.

               When using *note ProcessPoolExecutor: 196, this method
               chops `iterables' into a number of chunks which it
               submits to the pool as separate tasks.  The (approximate)
               size of these chunks can be specified by setting
               `chunksize' to a positive integer.  For very long
               iterables, using a large value for `chunksize' can
               significantly improve performance compared to the default
               size of 1.  With *note ThreadPoolExecutor: 18c,
               `chunksize' has no effect.

               Changed in version 3.5: Added the `chunksize' argument.

           -- Method: shutdown (wait=True, *, cancel_futures=False)

               Signal the executor that it should free any resources
               that it is using when the currently pending futures are
               done executing.  Calls to *note Executor.submit(): 3c6.
               and *note Executor.map(): 7b1. made after shutdown will
               raise *note RuntimeError: 3dc.

               If `wait' is ‘True’ then this method will not return
               until all the pending futures are done executing and the
               resources associated with the executor have been freed.
               If `wait' is ‘False’ then this method will return
               immediately and the resources associated with the
               executor will be freed when all pending futures are done
               executing.  Regardless of the value of `wait', the entire
               Python program will not exit until all pending futures
               are done executing.

               If `cancel_futures' is ‘True’, this method will cancel
               all pending futures that the executor has not started
               running.  Any futures that are completed or running won’t
               be cancelled, regardless of the value of
               `cancel_futures'.

               If both `cancel_futures' and `wait' are ‘True’, all
               futures that the executor has started running will be
               completed prior to this method returning.  The remaining
               futures are cancelled.

               You can avoid having to call this method explicitly if
               you use the *note with: 7da. statement, which will
               shutdown the *note Executor: 258a. (waiting as if *note
               Executor.shutdown(): 195. were called with `wait' set to
               ‘True’):

                    import shutil
                    with ThreadPoolExecutor(max_workers=4) as e:
                        e.submit(shutil.copy, 'src1.txt', 'dest1.txt')
                        e.submit(shutil.copy, 'src2.txt', 'dest2.txt')
                        e.submit(shutil.copy, 'src3.txt', 'dest3.txt')
                        e.submit(shutil.copy, 'src4.txt', 'dest4.txt')

               Changed in version 3.9: Added `cancel_futures'.


File: python.info,  Node: ThreadPoolExecutor,  Next: ProcessPoolExecutor,  Prev: Executor Objects,  Up: concurrent futures — Launching parallel tasks

5.17.5.2 ThreadPoolExecutor
...........................

*note ThreadPoolExecutor: 18c. is an *note Executor: 258a. subclass that
uses a pool of threads to execute calls asynchronously.

Deadlocks can occur when the callable associated with a *note Future:
c00. waits on the results of another *note Future: c00.  For example:

     import time
     def wait_on_b():
         time.sleep(5)
         print(b.result())  # b will never complete because it is waiting on a.
         return 5

     def wait_on_a():
         time.sleep(5)
         print(a.result())  # a will never complete because it is waiting on b.
         return 6


     executor = ThreadPoolExecutor(max_workers=2)
     a = executor.submit(wait_on_b)
     b = executor.submit(wait_on_a)

And:

     def wait_on_future():
         f = executor.submit(pow, 5, 2)
         # This will never complete because there is only one worker thread and
         # it is executing this function.
         print(f.result())

     executor = ThreadPoolExecutor(max_workers=1)
     executor.submit(wait_on_future)

 -- Class: concurrent.futures.ThreadPoolExecutor (max_workers=None,
          thread_name_prefix='', initializer=None, initargs=())

     An *note Executor: 258a. subclass that uses a pool of at most
     `max_workers' threads to execute calls asynchronously.

     `initializer' is an optional callable that is called at the start
     of each worker thread; `initargs' is a tuple of arguments passed to
     the initializer.  Should `initializer' raise an exception, all
     currently pending jobs will raise a *note BrokenThreadPool: 258e,
     as well as any attempt to submit more jobs to the pool.

     Changed in version 3.5: If `max_workers' is ‘None’ or not given, it
     will default to the number of processors on the machine, multiplied
     by ‘5’, assuming that *note ThreadPoolExecutor: 18c. is often used
     to overlap I/O instead of CPU work and the number of workers should
     be higher than the number of workers for *note ProcessPoolExecutor:
     196.

     New in version 3.6: The `thread_name_prefix' argument was added to
     allow users to control the *note threading.Thread: 21a. names for
     worker threads created by the pool for easier debugging.

     Changed in version 3.7: Added the `initializer' and `initargs'
     arguments.

     Changed in version 3.8: Default value of `max_workers' is changed
     to ‘min(32, os.cpu_count() + 4)’.  This default value preserves at
     least 5 workers for I/O bound tasks.  It utilizes at most 32 CPU
     cores for CPU bound tasks which release the GIL. And it avoids
     using very large resources implicitly on many-core machines.

     ThreadPoolExecutor now reuses idle worker threads before starting
     `max_workers' worker threads too.

* Menu:

* ThreadPoolExecutor Example::


File: python.info,  Node: ThreadPoolExecutor Example,  Up: ThreadPoolExecutor

5.17.5.3 ThreadPoolExecutor Example
...................................

     import concurrent.futures
     import urllib.request

     URLS = ['http://www.foxnews.com/',
             'http://www.cnn.com/',
             'http://europe.wsj.com/',
             'http://www.bbc.co.uk/',
             'http://some-made-up-domain.com/']

     # Retrieve a single page and report the URL and contents
     def load_url(url, timeout):
         with urllib.request.urlopen(url, timeout=timeout) as conn:
             return conn.read()

     # We can use a with statement to ensure threads are cleaned up promptly
     with concurrent.futures.ThreadPoolExecutor(max_workers=5) as executor:
         # Start the load operations and mark each future with its URL
         future_to_url = {executor.submit(load_url, url, 60): url for url in URLS}
         for future in concurrent.futures.as_completed(future_to_url):
             url = future_to_url[future]
             try:
                 data = future.result()
             except Exception as exc:
                 print('%r generated an exception: %s' % (url, exc))
             else:
                 print('%r page is %d bytes' % (url, len(data)))


File: python.info,  Node: ProcessPoolExecutor,  Next: Future Objects,  Prev: ThreadPoolExecutor,  Up: concurrent futures — Launching parallel tasks

5.17.5.4 ProcessPoolExecutor
............................

The *note ProcessPoolExecutor: 196. class is an *note Executor: 258a.
subclass that uses a pool of processes to execute calls asynchronously.
*note ProcessPoolExecutor: 196. uses the *note multiprocessing: b7.
module, which allows it to side-step the *note Global Interpreter Lock:
600. but also means that only picklable objects can be executed and
returned.

The ‘__main__’ module must be importable by worker subprocesses.  This
means that *note ProcessPoolExecutor: 196. will not work in the
interactive interpreter.

Calling *note Executor: 258a. or *note Future: c00. methods from a
callable submitted to a *note ProcessPoolExecutor: 196. will result in
deadlock.

 -- Class: concurrent.futures.ProcessPoolExecutor (max_workers=None,
          mp_context=None, initializer=None, initargs=())

     An *note Executor: 258a. subclass that executes calls
     asynchronously using a pool of at most `max_workers' processes.  If
     `max_workers' is ‘None’ or not given, it will default to the number
     of processors on the machine.  If `max_workers' is less than or
     equal to ‘0’, then a *note ValueError: 16d. will be raised.  On
     Windows, `max_workers' must be less than or equal to ‘61’.  If it
     is not then *note ValueError: 16d. will be raised.  If
     `max_workers' is ‘None’, then the default chosen will be at most
     ‘61’, even if more processors are available.  `mp_context' can be a
     multiprocessing context or None.  It will be used to launch the
     workers.  If `mp_context' is ‘None’ or not given, the default
     multiprocessing context is used.

     `initializer' is an optional callable that is called at the start
     of each worker process; `initargs' is a tuple of arguments passed
     to the initializer.  Should `initializer' raise an exception, all
     currently pending jobs will raise a *note BrokenProcessPool: 2591,
     as well as any attempt to submit more jobs to the pool.

     Changed in version 3.3: When one of the worker processes terminates
     abruptly, a ‘BrokenProcessPool’ error is now raised.  Previously,
     behaviour was undefined but operations on the executor or its
     futures would often freeze or deadlock.

     Changed in version 3.7: The `mp_context' argument was added to
     allow users to control the start_method for worker processes
     created by the pool.

     Added the `initializer' and `initargs' arguments.

* Menu:

* ProcessPoolExecutor Example::


File: python.info,  Node: ProcessPoolExecutor Example,  Up: ProcessPoolExecutor

5.17.5.5 ProcessPoolExecutor Example
....................................

     import concurrent.futures
     import math

     PRIMES = [
         112272535095293,
         112582705942171,
         112272535095293,
         115280095190773,
         115797848077099,
         1099726899285419]

     def is_prime(n):
         if n < 2:
             return False
         if n == 2:
             return True
         if n % 2 == 0:
             return False

         sqrt_n = int(math.floor(math.sqrt(n)))
         for i in range(3, sqrt_n + 1, 2):
             if n % i == 0:
                 return False
         return True

     def main():
         with concurrent.futures.ProcessPoolExecutor() as executor:
             for number, prime in zip(PRIMES, executor.map(is_prime, PRIMES)):
                 print('%d is prime: %s' % (number, prime))

     if __name__ == '__main__':
         main()


File: python.info,  Node: Future Objects,  Next: Module Functions,  Prev: ProcessPoolExecutor,  Up: concurrent futures — Launching parallel tasks

5.17.5.6 Future Objects
.......................

The *note Future: c00. class encapsulates the asynchronous execution of
a callable.  *note Future: c00. instances are created by *note
Executor.submit(): 3c6.

 -- Class: concurrent.futures.Future

     Encapsulates the asynchronous execution of a callable.  *note
     Future: c00. instances are created by *note Executor.submit(): 3c6.
     and should not be created directly except for testing.

           -- Method: cancel ()

               Attempt to cancel the call.  If the call is currently
               being executed or finished running and cannot be
               cancelled then the method will return ‘False’, otherwise
               the call will be cancelled and the method will return
               ‘True’.

           -- Method: cancelled ()

               Return ‘True’ if the call was successfully cancelled.

           -- Method: running ()

               Return ‘True’ if the call is currently being executed and
               cannot be cancelled.

           -- Method: done ()

               Return ‘True’ if the call was successfully cancelled or
               finished running.

           -- Method: result (timeout=None)

               Return the value returned by the call.  If the call
               hasn’t yet completed then this method will wait up to
               `timeout' seconds.  If the call hasn’t completed in
               `timeout' seconds, then a *note
               concurrent.futures.TimeoutError: 258c. will be raised.
               `timeout' can be an int or float.  If `timeout' is not
               specified or ‘None’, there is no limit to the wait time.

               If the future is cancelled before completing then *note
               CancelledError: 2dd. will be raised.

               If the call raised an exception, this method will raise
               the same exception.

           -- Method: exception (timeout=None)

               Return the exception raised by the call.  If the call
               hasn’t yet completed then this method will wait up to
               `timeout' seconds.  If the call hasn’t completed in
               `timeout' seconds, then a *note
               concurrent.futures.TimeoutError: 258c. will be raised.
               `timeout' can be an int or float.  If `timeout' is not
               specified or ‘None’, there is no limit to the wait time.

               If the future is cancelled before completing then *note
               CancelledError: 2dd. will be raised.

               If the call completed without raising, ‘None’ is
               returned.

           -- Method: add_done_callback (fn)

               Attaches the callable `fn' to the future.  `fn' will be
               called, with the future as its only argument, when the
               future is cancelled or finishes running.

               Added callables are called in the order that they were
               added and are always called in a thread belonging to the
               process that added them.  If the callable raises an *note
               Exception: 2dc. subclass, it will be logged and ignored.
               If the callable raises a *note BaseException: 2db.
               subclass, the behavior is undefined.

               If the future has already completed or been cancelled,
               `fn' will be called immediately.

     The following *note Future: c00. methods are meant for use in unit
     tests and *note Executor: 258a. implementations.

           -- Method: set_running_or_notify_cancel ()

               This method should only be called by *note Executor:
               258a. implementations before executing the work
               associated with the *note Future: c00. and by unit tests.

               If the method returns ‘False’ then the *note Future: c00.
               was cancelled, i.e.  *note Future.cancel(): 2594. was
               called and returned ‘True’.  Any threads waiting on the
               *note Future: c00. completing (i.e.  through *note
               as_completed(): 1223. or *note wait(): f50.) will be
               woken up.

               If the method returns ‘True’ then the *note Future: c00.
               was not cancelled and has been put in the running state,
               i.e.  calls to *note Future.running(): 2596. will return
               ‘True’.

               This method can only be called once and cannot be called
               after *note Future.set_result(): 259c. or *note
               Future.set_exception(): 259d. have been called.

           -- Method: set_result (result)

               Sets the result of the work associated with the *note
               Future: c00. to `result'.

               This method should only be used by *note Executor: 258a.
               implementations and unit tests.

               Changed in version 3.8: This method raises *note
               concurrent.futures.InvalidStateError: 259e. if the *note
               Future: c00. is already done.

           -- Method: set_exception (exception)

               Sets the result of the work associated with the *note
               Future: c00. to the *note Exception: 2dc. `exception'.

               This method should only be used by *note Executor: 258a.
               implementations and unit tests.

               Changed in version 3.8: This method raises *note
               concurrent.futures.InvalidStateError: 259e. if the *note
               Future: c00. is already done.


File: python.info,  Node: Module Functions,  Next: Exception classes,  Prev: Future Objects,  Up: concurrent futures — Launching parallel tasks

5.17.5.7 Module Functions
.........................

 -- Function: concurrent.futures.wait (fs, timeout=None,
          return_when=ALL_COMPLETED)

     Wait for the *note Future: c00. instances (possibly created by
     different *note Executor: 258a. instances) given by `fs' to
     complete.  Duplicate futures given to `fs' are removed and will be
     returned only once.  Returns a named 2-tuple of sets.  The first
     set, named ‘done’, contains the futures that completed (finished or
     cancelled futures) before the wait completed.  The second set,
     named ‘not_done’, contains the futures that did not complete
     (pending or running futures).

     `timeout' can be used to control the maximum number of seconds to
     wait before returning.  `timeout' can be an int or float.  If
     `timeout' is not specified or ‘None’, there is no limit to the wait
     time.

     `return_when' indicates when this function should return.  It must
     be one of the following constants:

     Constant                          Description
                                       
     -------------------------------------------------------------------------------
                                       
     ‘FIRST_COMPLETED’                 The function will return when any future
                                       finishes or is cancelled.
                                       
                                       
     ‘FIRST_EXCEPTION’                 The function will return when any future
                                       finishes by raising an exception.  If no
                                       future raises an exception then it is
                                       equivalent to ‘ALL_COMPLETED’.
                                       
                                       
     ‘ALL_COMPLETED’                   The function will return when all futures
                                       finish or are cancelled.
                                       

 -- Function: concurrent.futures.as_completed (fs, timeout=None)

     Returns an iterator over the *note Future: c00. instances (possibly
     created by different *note Executor: 258a. instances) given by `fs'
     that yields futures as they complete (finished or cancelled
     futures).  Any futures given by `fs' that are duplicated will be
     returned once.  Any futures that completed before *note
     as_completed(): 1223. is called will be yielded first.  The
     returned iterator raises a *note concurrent.futures.TimeoutError:
     258c. if *note __next__(): d2c. is called and the result isn’t
     available after `timeout' seconds from the original call to *note
     as_completed(): 1223.  `timeout' can be an int or float.  If
     `timeout' is not specified or ‘None’, there is no limit to the wait
     time.

See also
........

PEP 3148(1) – futures - execute computations asynchronously

     The proposal which described this feature for inclusion in the
     Python standard library.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3148


File: python.info,  Node: Exception classes,  Prev: Module Functions,  Up: concurrent futures — Launching parallel tasks

5.17.5.8 Exception classes
..........................

 -- Exception: concurrent.futures.CancelledError

     Raised when a future is cancelled.

 -- Exception: concurrent.futures.TimeoutError

     Raised when a future operation exceeds the given timeout.

 -- Exception: concurrent.futures.BrokenExecutor

     Derived from *note RuntimeError: 3dc, this exception class is
     raised when an executor is broken for some reason, and cannot be
     used to submit or execute new tasks.

     New in version 3.7.

 -- Exception: concurrent.futures.InvalidStateError

     Raised when an operation is performed on a future that is not
     allowed in the current state.

     New in version 3.8.

 -- Exception: concurrent.futures.thread.BrokenThreadPool

     Derived from *note BrokenExecutor: 25a1, this exception class is
     raised when one of the workers of a ‘ThreadPoolExecutor’ has failed
     initializing.

     New in version 3.7.

 -- Exception: concurrent.futures.process.BrokenProcessPool

     Derived from *note BrokenExecutor: 25a1. (formerly *note
     RuntimeError: 3dc.), this exception class is raised when one of the
     workers of a ‘ProcessPoolExecutor’ has terminated in a non-clean
     fashion (for example, if it was killed from the outside).

     New in version 3.3.


File: python.info,  Node: subprocess — Subprocess management,  Next: sched — Event scheduler,  Prev: concurrent futures — Launching parallel tasks,  Up: Concurrent Execution

5.17.6 ‘subprocess’ — Subprocess management
-------------------------------------------

`Source code:' Lib/subprocess.py(1)

__________________________________________________________________

The *note subprocess: f9. module allows you to spawn new processes,
connect to their input/output/error pipes, and obtain their return
codes.  This module intends to replace several older modules and
functions:

     os.system
     os.spawn*

Information about how the *note subprocess: f9. module can be used to
replace these modules and functions can be found in the following
sections.

See also
........

PEP 324(2) – PEP proposing the subprocess module

* Menu:

* Using the subprocess Module::
* Security Considerations::
* Popen Objects::
* Windows Popen Helpers::
* Older high-level API::
* Replacing Older Functions with the subprocess Module::
* Legacy Shell Invocation Functions::
* Notes::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/subprocess.py

   (2) https://www.python.org/dev/peps/pep-0324


File: python.info,  Node: Using the subprocess Module,  Next: Security Considerations,  Up: subprocess — Subprocess management

5.17.6.1 Using the ‘subprocess’ Module
......................................

The recommended approach to invoking subprocesses is to use the *note
run(): 4f3. function for all use cases it can handle.  For more advanced
use cases, the underlying *note Popen: 3db. interface can be used
directly.

The *note run(): 4f3. function was added in Python 3.5; if you need to
retain compatibility with older versions, see the *note Older high-level
API: 25a5. section.

 -- Function: subprocess.run (args, *, stdin=None, input=None,
          stdout=None, stderr=None, capture_output=False, shell=False,
          cwd=None, timeout=None, check=False, encoding=None,
          errors=None, text=None, env=None, universal_newlines=None,
          **other_popen_kwargs)

     Run the command described by `args'.  Wait for command to complete,
     then return a *note CompletedProcess: 84f. instance.

     The arguments shown above are merely the most common ones,
     described below in *note Frequently Used Arguments: 25a6. (hence
     the use of keyword-only notation in the abbreviated signature).
     The full function signature is largely the same as that of the
     *note Popen: 3db. constructor - most of the arguments to this
     function are passed through to that interface.  (`timeout',
     `input', `check', and `capture_output' are not.)

     If `capture_output' is true, stdout and stderr will be captured.
     When used, the internal *note Popen: 3db. object is automatically
     created with ‘stdout=PIPE’ and ‘stderr=PIPE’.  The `stdout' and
     `stderr' arguments may not be supplied at the same time as
     `capture_output'.  If you wish to capture and combine both streams
     into one, use ‘stdout=PIPE’ and ‘stderr=STDOUT’ instead of
     `capture_output'.

     The `timeout' argument is passed to *note Popen.communicate():
     25a7.  If the timeout expires, the child process will be killed and
     waited for.  The *note TimeoutExpired: 25a8. exception will be
     re-raised after the child process has terminated.

     The `input' argument is passed to *note Popen.communicate(): 25a7.
     and thus to the subprocess’s stdin.  If used it must be a byte
     sequence, or a string if `encoding' or `errors' is specified or
     `text' is true.  When used, the internal *note Popen: 3db. object
     is automatically created with ‘stdin=PIPE’, and the `stdin'
     argument may not be used as well.

     If `check' is true, and the process exits with a non-zero exit
     code, a *note CalledProcessError: d7d. exception will be raised.
     Attributes of that exception hold the arguments, the exit code, and
     stdout and stderr if they were captured.

     If `encoding' or `errors' are specified, or `text' is true, file
     objects for stdin, stdout and stderr are opened in text mode using
     the specified `encoding' and `errors' or the *note
     io.TextIOWrapper: 6ea. default.  The `universal_newlines' argument
     is equivalent to `text' and is provided for backwards
     compatibility.  By default, file objects are opened in binary mode.

     If `env' is not ‘None’, it must be a mapping that defines the
     environment variables for the new process; these are used instead
     of the default behavior of inheriting the current process’
     environment.  It is passed directly to *note Popen: 3db.

     Examples:

          >>> subprocess.run(["ls", "-l"])  # doesn't capture output
          CompletedProcess(args=['ls', '-l'], returncode=0)

          >>> subprocess.run("exit 1", shell=True, check=True)
          Traceback (most recent call last):
            ...
          subprocess.CalledProcessError: Command 'exit 1' returned non-zero exit status 1

          >>> subprocess.run(["ls", "-l", "/dev/null"], capture_output=True)
          CompletedProcess(args=['ls', '-l', '/dev/null'], returncode=0,
          stdout=b'crw-rw-rw- 1 root root 1, 3 Jan 23 16:23 /dev/null\n', stderr=b'')

     New in version 3.5.

     Changed in version 3.6: Added `encoding' and `errors' parameters

     Changed in version 3.7: Added the `text' parameter, as a more
     understandable alias of `universal_newlines'.  Added the
     `capture_output' parameter.

 -- Class: subprocess.CompletedProcess

     The return value from *note run(): 4f3, representing a process that
     has finished.

      -- Attribute: args

          The arguments used to launch the process.  This may be a list
          or a string.

      -- Attribute: returncode

          Exit status of the child process.  Typically, an exit status
          of 0 indicates that it ran successfully.

          A negative value ‘-N’ indicates that the child was terminated
          by signal ‘N’ (POSIX only).

      -- Attribute: stdout

          Captured stdout from the child process.  A bytes sequence, or
          a string if *note run(): 4f3. was called with an encoding,
          errors, or text=True.  ‘None’ if stdout was not captured.

          If you ran the process with ‘stderr=subprocess.STDOUT’, stdout
          and stderr will be combined in this attribute, and *note
          stderr: 25ac. will be ‘None’.

      -- Attribute: stderr

          Captured stderr from the child process.  A bytes sequence, or
          a string if *note run(): 4f3. was called with an encoding,
          errors, or text=True.  ‘None’ if stderr was not captured.

      -- Method: check_returncode ()

          If *note returncode: 25aa. is non-zero, raise a *note
          CalledProcessError: d7d.

     New in version 3.5.

 -- Data: subprocess.DEVNULL

     Special value that can be used as the `stdin', `stdout' or `stderr'
     argument to *note Popen: 3db. and indicates that the special file
     *note os.devnull: 1152. will be used.

     New in version 3.3.

 -- Data: subprocess.PIPE

     Special value that can be used as the `stdin', `stdout' or `stderr'
     argument to *note Popen: 3db. and indicates that a pipe to the
     standard stream should be opened.  Most useful with *note
     Popen.communicate(): 25a7.

 -- Data: subprocess.STDOUT

     Special value that can be used as the `stderr' argument to *note
     Popen: 3db. and indicates that standard error should go into the
     same handle as standard output.

 -- Exception: subprocess.SubprocessError

     Base class for all other exceptions from this module.

     New in version 3.3.

 -- Exception: subprocess.TimeoutExpired

     Subclass of *note SubprocessError: 25af, raised when a timeout
     expires while waiting for a child process.

      -- Attribute: cmd

          Command that was used to spawn the child process.

      -- Attribute: timeout

          Timeout in seconds.

      -- Attribute: output

          Output of the child process if it was captured by *note run():
          4f3. or *note check_output(): 9c1.  Otherwise, ‘None’.

      -- Attribute: stdout

          Alias for output, for symmetry with *note stderr: 25b4.

      -- Attribute: stderr

          Stderr output of the child process if it was captured by *note
          run(): 4f3.  Otherwise, ‘None’.

     New in version 3.3.

     Changed in version 3.5: `stdout' and `stderr' attributes added

 -- Exception: subprocess.CalledProcessError

     Subclass of *note SubprocessError: 25af, raised when a process run
     by *note check_call(): 25b5. or *note check_output(): 9c1. returns
     a non-zero exit status.

      -- Attribute: returncode

          Exit status of the child process.  If the process exited due
          to a signal, this will be the negative signal number.

      -- Attribute: cmd

          Command that was used to spawn the child process.

      -- Attribute: output

          Output of the child process if it was captured by *note run():
          4f3. or *note check_output(): 9c1.  Otherwise, ‘None’.

      -- Attribute: stdout

          Alias for output, for symmetry with *note stderr: 25ba.

      -- Attribute: stderr

          Stderr output of the child process if it was captured by *note
          run(): 4f3.  Otherwise, ‘None’.

     Changed in version 3.5: `stdout' and `stderr' attributes added

* Menu:

* Frequently Used Arguments::
* Popen Constructor::
* Exceptions: Exceptions<8>.


File: python.info,  Node: Frequently Used Arguments,  Next: Popen Constructor,  Up: Using the subprocess Module

5.17.6.2 Frequently Used Arguments
..................................

To support a wide variety of use cases, the *note Popen: 3db.
constructor (and the convenience functions) accept a large number of
optional arguments.  For most typical use cases, many of these arguments
can be safely left at their default values.  The arguments that are most
commonly needed are:

     `args' is required for all calls and should be a string, or a
     sequence of program arguments.  Providing a sequence of arguments
     is generally preferred, as it allows the module to take care of any
     required escaping and quoting of arguments (e.g.  to permit spaces
     in file names).  If passing a single string, either `shell' must be
     *note True: 594. (see below) or else the string must simply name
     the program to be executed without specifying any arguments.

     `stdin', `stdout' and `stderr' specify the executed program’s
     standard input, standard output and standard error file handles,
     respectively.  Valid values are *note PIPE: 4f4, *note DEVNULL:
     b78, an existing file descriptor (a positive integer), an existing
     file object, and ‘None’.  *note PIPE: 4f4. indicates that a new
     pipe to the child should be created.  *note DEVNULL: b78. indicates
     that the special file *note os.devnull: 1152. will be used.  With
     the default settings of ‘None’, no redirection will occur; the
     child’s file handles will be inherited from the parent.
     Additionally, `stderr' can be *note STDOUT: 25ae, which indicates
     that the stderr data from the child process should be captured into
     the same file handle as for `stdout'.

     If `encoding' or `errors' are specified, or `text' (also known as
     `universal_newlines') is true, the file objects `stdin', `stdout'
     and `stderr' will be opened in text mode using the `encoding' and
     `errors' specified in the call or the defaults for *note
     io.TextIOWrapper: 6ea.

     For `stdin', line ending characters ‘'\n'’ in the input will be
     converted to the default line separator *note os.linesep: 1732.
     For `stdout' and `stderr', all line endings in the output will be
     converted to ‘'\n'’.  For more information see the documentation of
     the *note io.TextIOWrapper: 6ea. class when the `newline' argument
     to its constructor is ‘None’.

     If text mode is not used, `stdin', `stdout' and `stderr' will be
     opened as binary streams.  No encoding or line ending conversion is
     performed.

     New in version 3.6: Added `encoding' and `errors' parameters.

     New in version 3.7: Added the `text' parameter as an alias for
     `universal_newlines'.

          Note: The newlines attribute of the file objects *note
          Popen.stdin: 25bc, *note Popen.stdout: 25bd. and *note
          Popen.stderr: 25be. are not updated by the *note
          Popen.communicate(): 25a7. method.

     If `shell' is ‘True’, the specified command will be executed
     through the shell.  This can be useful if you are using Python
     primarily for the enhanced control flow it offers over most system
     shells and still want convenient access to other shell features
     such as shell pipes, filename wildcards, environment variable
     expansion, and expansion of ‘~’ to a user’s home directory.
     However, note that Python itself offers implementations of many
     shell-like features (in particular, *note glob: 88, *note fnmatch:
     7f, *note os.walk(): 747, *note os.path.expandvars(): e09, *note
     os.path.expanduser(): 32c, and *note shutil: e9.).

     Changed in version 3.3: When `universal_newlines' is ‘True’, the
     class uses the encoding *note locale.getpreferredencoding(False):
     4ac. instead of ‘locale.getpreferredencoding()’.  See the *note
     io.TextIOWrapper: 6ea. class for more information on this change.

          Note: Read the *note Security Considerations: 25bf. section
          before using ‘shell=True’.

These options, along with all of the other options, are described in
more detail in the *note Popen: 3db. constructor documentation.


File: python.info,  Node: Popen Constructor,  Next: Exceptions<8>,  Prev: Frequently Used Arguments,  Up: Using the subprocess Module

5.17.6.3 Popen Constructor
..........................

The underlying process creation and management in this module is handled
by the *note Popen: 3db. class.  It offers a lot of flexibility so that
developers are able to handle the less common cases not covered by the
convenience functions.

 -- Class: subprocess.Popen (args, bufsize=-1, executable=None,
          stdin=None, stdout=None, stderr=None, preexec_fn=None,
          close_fds=True, shell=False, cwd=None, env=None,
          universal_newlines=None, startupinfo=None, creationflags=0,
          restore_signals=True, start_new_session=False, pass_fds=(), *,
          group=None, extra_groups=None, user=None, umask=-1,
          encoding=None, errors=None, text=None)

     Execute a child program in a new process.  On POSIX, the class uses
     *note os.execvp(): 20ec.-like behavior to execute the child
     program.  On Windows, the class uses the Windows ‘CreateProcess()’
     function.  The arguments to *note Popen: 3db. are as follows.

     `args' should be a sequence of program arguments or else a single
     string or *note path-like object: 472.  By default, the program to
     execute is the first item in `args' if `args' is a sequence.  If
     `args' is a string, the interpretation is platform-dependent and
     described below.  See the `shell' and `executable' arguments for
     additional differences from the default behavior.  Unless otherwise
     stated, it is recommended to pass `args' as a sequence.

     An example of passing some arguments to an external program as a
     sequence is:

          Popen(["/usr/bin/git", "commit", "-m", "Fixes a bug."])

     On POSIX, if `args' is a string, the string is interpreted as the
     name or path of the program to execute.  However, this can only be
     done if not passing arguments to the program.

          Note: It may not be obvious how to break a shell command into
          a sequence of arguments, especially in complex cases.  *note
          shlex.split(): 210. can illustrate how to determine the
          correct tokenization for `args':

               >>> import shlex, subprocess
               >>> command_line = input()
               /bin/vikings -input eggs.txt -output "spam spam.txt" -cmd "echo '$MONEY'"
               >>> args = shlex.split(command_line)
               >>> print(args)
               ['/bin/vikings', '-input', 'eggs.txt', '-output', 'spam spam.txt', '-cmd', "echo '$MONEY'"]
               >>> p = subprocess.Popen(args) # Success!

          Note in particular that options (such as `-input') and
          arguments (such as `eggs.txt') that are separated by
          whitespace in the shell go in separate list elements, while
          arguments that need quoting or backslash escaping when used in
          the shell (such as filenames containing spaces or the `echo'
          command shown above) are single list elements.

     On Windows, if `args' is a sequence, it will be converted to a
     string in a manner described in *note Converting an argument
     sequence to a string on Windows: 25c1.  This is because the
     underlying ‘CreateProcess()’ operates on strings.

     Changed in version 3.6: `args' parameter accepts a *note path-like
     object: 472. if `shell' is ‘False’ and a sequence containing
     path-like objects on POSIX.

     Changed in version 3.8: `args' parameter accepts a *note path-like
     object: 472. if `shell' is ‘False’ and a sequence containing bytes
     and path-like objects on Windows.

     The `shell' argument (which defaults to ‘False’) specifies whether
     to use the shell as the program to execute.  If `shell' is ‘True’,
     it is recommended to pass `args' as a string rather than as a
     sequence.

     On POSIX with ‘shell=True’, the shell defaults to ‘/bin/sh’.  If
     `args' is a string, the string specifies the command to execute
     through the shell.  This means that the string must be formatted
     exactly as it would be when typed at the shell prompt.  This
     includes, for example, quoting or backslash escaping filenames with
     spaces in them.  If `args' is a sequence, the first item specifies
     the command string, and any additional items will be treated as
     additional arguments to the shell itself.  That is to say, *note
     Popen: 3db. does the equivalent of:

          Popen(['/bin/sh', '-c', args[0], args[1], ...])

     On Windows with ‘shell=True’, the ‘COMSPEC’ environment variable
     specifies the default shell.  The only time you need to specify
     ‘shell=True’ on Windows is when the command you wish to execute is
     built into the shell (e.g.  ‘dir’ or ‘copy’).  You do not need
     ‘shell=True’ to run a batch file or console-based executable.

          Note: Read the *note Security Considerations: 25bf. section
          before using ‘shell=True’.

     `bufsize' will be supplied as the corresponding argument to the
     *note open(): 16f. function when creating the stdin/stdout/stderr
     pipe file objects:

        - ‘0’ means unbuffered (read and write are one system call and
          can return short)

        - ‘1’ means line buffered (only usable if
          ‘universal_newlines=True’ i.e., in a text mode)

        - any other positive value means use a buffer of approximately
          that size

        - negative bufsize (the default) means the system default of
          io.DEFAULT_BUFFER_SIZE will be used.

     Changed in version 3.3.1: `bufsize' now defaults to -1 to enable
     buffering by default to match the behavior that most code expects.
     In versions prior to Python 3.2.4 and 3.3.1 it incorrectly
     defaulted to ‘0’ which was unbuffered and allowed short reads.
     This was unintentional and did not match the behavior of Python 2
     as most code expected.

     The `executable' argument specifies a replacement program to
     execute.  It is very seldom needed.  When ‘shell=False’,
     `executable' replaces the program to execute specified by `args'.
     However, the original `args' is still passed to the program.  Most
     programs treat the program specified by `args' as the command name,
     which can then be different from the program actually executed.  On
     POSIX, the `args' name becomes the display name for the executable
     in utilities such as ‘ps’.  If ‘shell=True’, on POSIX the
     `executable' argument specifies a replacement shell for the default
     ‘/bin/sh’.

     Changed in version 3.6: `executable' parameter accepts a *note
     path-like object: 472. on POSIX.

     Changed in version 3.8: `executable' parameter accepts a bytes and
     *note path-like object: 472. on Windows.

     `stdin', `stdout' and `stderr' specify the executed program’s
     standard input, standard output and standard error file handles,
     respectively.  Valid values are *note PIPE: 4f4, *note DEVNULL:
     b78, an existing file descriptor (a positive integer), an existing
     *note file object: c14, and ‘None’.  *note PIPE: 4f4. indicates
     that a new pipe to the child should be created.  *note DEVNULL:
     b78. indicates that the special file *note os.devnull: 1152. will
     be used.  With the default settings of ‘None’, no redirection will
     occur; the child’s file handles will be inherited from the parent.
     Additionally, `stderr' can be *note STDOUT: 25ae, which indicates
     that the stderr data from the applications should be captured into
     the same file handle as for stdout.

     If `preexec_fn' is set to a callable object, this object will be
     called in the child process just before the child is executed.
     (POSIX only)

          Warning: The `preexec_fn' parameter is not safe to use in the
          presence of threads in your application.  The child process
          could deadlock before exec is called.  If you must use it,
          keep it trivial!  Minimize the number of libraries you call
          into.

          Note: If you need to modify the environment for the child use
          the `env' parameter rather than doing it in a `preexec_fn'.
          The `start_new_session' parameter can take the place of a
          previously common use of `preexec_fn' to call os.setsid() in
          the child.

     Changed in version 3.8: The `preexec_fn' parameter is no longer
     supported in subinterpreters.  The use of the parameter in a
     subinterpreter raises *note RuntimeError: 3dc.  The new restriction
     may affect applications that are deployed in mod_wsgi, uWSGI, and
     other embedded environments.

     If `close_fds' is true, all file descriptors except ‘0’, ‘1’ and
     ‘2’ will be closed before the child process is executed.  Otherwise
     when `close_fds' is false, file descriptors obey their inheritable
     flag as described in *note Inheritance of File Descriptors: 8e7.

     On Windows, if `close_fds' is true then no handles will be
     inherited by the child process unless explicitly passed in the
     ‘handle_list’ element of *note STARTUPINFO.lpAttributeList: 595, or
     by standard handle redirection.

     Changed in version 3.2: The default for `close_fds' was changed
     from *note False: 48f. to what is described above.

     Changed in version 3.7: On Windows the default for `close_fds' was
     changed from *note False: 48f. to *note True: 594. when redirecting
     the standard handles.  It’s now possible to set `close_fds' to
     *note True: 594. when redirecting the standard handles.

     `pass_fds' is an optional sequence of file descriptors to keep open
     between the parent and child.  Providing any `pass_fds' forces
     `close_fds' to be *note True: 594.  (POSIX only)

     Changed in version 3.2: The `pass_fds' parameter was added.

     If `cwd' is not ‘None’, the function changes the working directory
     to `cwd' before executing the child.  `cwd' can be a string, bytes
     or *note path-like: 472. object.  In particular, the function looks
     for `executable' (or for the first item in `args') relative to
     `cwd' if the executable path is a relative path.

     Changed in version 3.6: `cwd' parameter accepts a *note path-like
     object: 472. on POSIX.

     Changed in version 3.7: `cwd' parameter accepts a *note path-like
     object: 472. on Windows.

     Changed in version 3.8: `cwd' parameter accepts a bytes object on
     Windows.

     If `restore_signals' is true (the default) all signals that Python
     has set to SIG_IGN are restored to SIG_DFL in the child process
     before the exec.  Currently this includes the SIGPIPE, SIGXFZ and
     SIGXFSZ signals.  (POSIX only)

     Changed in version 3.2: `restore_signals' was added.

     If `start_new_session' is true the setsid() system call will be
     made in the child process prior to the execution of the subprocess.
     (POSIX only)

     Changed in version 3.2: `start_new_session' was added.

     If `group' is not ‘None’, the setregid() system call will be made
     in the child process prior to the execution of the subprocess.  If
     the provided value is a string, it will be looked up via *note
     grp.getgrnam(): 1162. and the value in ‘gr_gid’ will be used.  If
     the value is an integer, it will be passed verbatim.  (POSIX only)

     *note Availability: 1491.: POSIX

     New in version 3.9.

     If `extra_groups' is not ‘None’, the setgroups() system call will
     be made in the child process prior to the execution of the
     subprocess.  Strings provided in `extra_groups' will be looked up
     via *note grp.getgrnam(): 1162. and the values in ‘gr_gid’ will be
     used.  Integer values will be passed verbatim.  (POSIX only)

     *note Availability: 1491.: POSIX

     New in version 3.9.

     If `user' is not ‘None’, the setreuid() system call will be made in
     the child process prior to the execution of the subprocess.  If the
     provided value is a string, it will be looked up via *note
     pwd.getpwnam(): 1161. and the value in ‘pw_uid’ will be used.  If
     the value is an integer, it will be passed verbatim.  (POSIX only)

     *note Availability: 1491.: POSIX

     New in version 3.9.

     If `umask' is not negative, the umask() system call will be made in
     the child process prior to the execution of the subprocess.

     *note Availability: 1491.: POSIX

     New in version 3.9.

     If `env' is not ‘None’, it must be a mapping that defines the
     environment variables for the new process; these are used instead
     of the default behavior of inheriting the current process’
     environment.

          Note: If specified, `env' must provide any variables required
          for the program to execute.  On Windows, in order to run a
          side-by-side assembly(1) the specified `env' `must' include a
          valid ‘SystemRoot’.

     If `encoding' or `errors' are specified, or `text' is true, the
     file objects `stdin', `stdout' and `stderr' are opened in text mode
     with the specified encoding and `errors', as described above in
     *note Frequently Used Arguments: 25a6.  The `universal_newlines'
     argument is equivalent to `text' and is provided for backwards
     compatibility.  By default, file objects are opened in binary mode.

     New in version 3.6: `encoding' and `errors' were added.

     New in version 3.7: `text' was added as a more readable alias for
     `universal_newlines'.

     If given, `startupinfo' will be a *note STARTUPINFO: 25c2. object,
     which is passed to the underlying ‘CreateProcess’ function.
     `creationflags', if given, can be one or more of the following
     flags:

             * *note CREATE_NEW_CONSOLE: 25c3.

             * *note CREATE_NEW_PROCESS_GROUP: 25c4.

             * *note ABOVE_NORMAL_PRIORITY_CLASS: 25c5.

             * *note BELOW_NORMAL_PRIORITY_CLASS: 25c6.

             * *note HIGH_PRIORITY_CLASS: 25c7.

             * *note IDLE_PRIORITY_CLASS: 25c8.

             * *note NORMAL_PRIORITY_CLASS: 25c9.

             * *note REALTIME_PRIORITY_CLASS: 25ca.

             * *note CREATE_NO_WINDOW: 25cb.

             * *note DETACHED_PROCESS: 25cc.

             * *note CREATE_DEFAULT_ERROR_MODE: 25cd.

             * *note CREATE_BREAKAWAY_FROM_JOB: 25ce.

     Popen objects are supported as context managers via the *note with:
     7da. statement: on exit, standard file descriptors are closed, and
     the process is waited for.

          with Popen(["ifconfig"], stdout=PIPE) as proc:
              log.write(proc.stdout.read())

     Popen and the other functions in this module that use it raise an
     *note auditing event: fa1. ‘subprocess.Popen’ with arguments
     ‘executable’, ‘args’, ‘cwd’, and ‘env’.  The value for ‘args’ may
     be a single string or a list of strings, depending on platform.

     Changed in version 3.2: Added context manager support.

     Changed in version 3.6: Popen destructor now emits a *note
     ResourceWarning: 5cb. warning if the child process is still
     running.

     Changed in version 3.8: Popen can use *note os.posix_spawn(): 381.
     in some cases for better performance.  On Windows Subsystem for
     Linux and QEMU User Emulation, Popen constructor using *note
     os.posix_spawn(): 381. no longer raise an exception on errors like
     missing program, but the child process fails with a non-zero *note
     returncode: 10a5.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Side-by-Side_Assembly


File: python.info,  Node: Exceptions<8>,  Prev: Popen Constructor,  Up: Using the subprocess Module

5.17.6.4 Exceptions
...................

Exceptions raised in the child process, before the new program has
started to execute, will be re-raised in the parent.

The most common exception raised is *note OSError: 304.  This occurs,
for example, when trying to execute a non-existent file.  Applications
should prepare for *note OSError: 304. exceptions.  Note that, when
‘shell=True’, *note OSError: 304. will be raised by the child only if
the selected shell itself was not found.  To determine if the shell
failed to find the requested application, it is necessary to check the
return code or output from the subprocess.

A *note ValueError: 16d. will be raised if *note Popen: 3db. is called
with invalid arguments.

*note check_call(): 25b5. and *note check_output(): 9c1. will raise
*note CalledProcessError: d7d. if the called process returns a non-zero
return code.

All of the functions and methods that accept a `timeout' parameter, such
as *note call(): 4f5. and *note Popen.communicate(): 25a7. will raise
*note TimeoutExpired: 25a8. if the timeout expires before the process
exits.

Exceptions defined in this module all inherit from *note
SubprocessError: 25af.

     New in version 3.3: The *note SubprocessError: 25af. base class was
     added.


File: python.info,  Node: Security Considerations,  Next: Popen Objects,  Prev: Using the subprocess Module,  Up: subprocess — Subprocess management

5.17.6.5 Security Considerations
................................

Unlike some other popen functions, this implementation will never
implicitly call a system shell.  This means that all characters,
including shell metacharacters, can safely be passed to child processes.
If the shell is invoked explicitly, via ‘shell=True’, it is the
application’s responsibility to ensure that all whitespace and
metacharacters are quoted appropriately to avoid shell injection(1)
vulnerabilities.

When using ‘shell=True’, the *note shlex.quote(): b4e. function can be
used to properly escape whitespace and shell metacharacters in strings
that are going to be used to construct shell commands.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Shell_injection#Shell_injection


File: python.info,  Node: Popen Objects,  Next: Windows Popen Helpers,  Prev: Security Considerations,  Up: subprocess — Subprocess management

5.17.6.6 Popen Objects
......................

Instances of the *note Popen: 3db. class have the following methods:

 -- Method: Popen.poll ()

     Check if child process has terminated.  Set and return *note
     returncode: 10a5. attribute.  Otherwise, returns ‘None’.

 -- Method: Popen.wait (timeout=None)

     Wait for child process to terminate.  Set and return *note
     returncode: 10a5. attribute.

     If the process does not terminate after `timeout' seconds, raise a
     *note TimeoutExpired: 25a8. exception.  It is safe to catch this
     exception and retry the wait.

          Note: This will deadlock when using ‘stdout=PIPE’ or
          ‘stderr=PIPE’ and the child process generates enough output to
          a pipe such that it blocks waiting for the OS pipe buffer to
          accept more data.  Use *note Popen.communicate(): 25a7. when
          using pipes to avoid that.

          Note: The function is implemented using a busy loop
          (non-blocking call and short sleeps).  Use the *note asyncio:
          9. module for an asynchronous wait: see *note
          asyncio.create_subprocess_exec: 3b4.

     Changed in version 3.3: `timeout' was added.

 -- Method: Popen.communicate (input=None, timeout=None)

     Interact with process: Send data to stdin.  Read data from stdout
     and stderr, until end-of-file is reached.  Wait for process to
     terminate and set the *note returncode: 10a5. attribute.  The
     optional `input' argument should be data to be sent to the child
     process, or ‘None’, if no data should be sent to the child.  If
     streams were opened in text mode, `input' must be a string.
     Otherwise, it must be bytes.

     *note communicate(): 25a7. returns a tuple ‘(stdout_data,
     stderr_data)’.  The data will be strings if streams were opened in
     text mode; otherwise, bytes.

     Note that if you want to send data to the process’s stdin, you need
     to create the Popen object with ‘stdin=PIPE’.  Similarly, to get
     anything other than ‘None’ in the result tuple, you need to give
     ‘stdout=PIPE’ and/or ‘stderr=PIPE’ too.

     If the process does not terminate after `timeout' seconds, a *note
     TimeoutExpired: 25a8. exception will be raised.  Catching this
     exception and retrying communication will not lose any output.

     The child process is not killed if the timeout expires, so in order
     to cleanup properly a well-behaved application should kill the
     child process and finish communication:

          proc = subprocess.Popen(...)
          try:
              outs, errs = proc.communicate(timeout=15)
          except TimeoutExpired:
              proc.kill()
              outs, errs = proc.communicate()

          Note: The data read is buffered in memory, so do not use this
          method if the data size is large or unlimited.

     Changed in version 3.3: `timeout' was added.

 -- Method: Popen.send_signal (signal)

     Sends the signal `signal' to the child.

     Do nothing if the process completed.

          Note: On Windows, SIGTERM is an alias for *note terminate():
          25d3.  CTRL_C_EVENT and CTRL_BREAK_EVENT can be sent to
          processes started with a `creationflags' parameter which
          includes ‘CREATE_NEW_PROCESS_GROUP’.

 -- Method: Popen.terminate ()

     Stop the child.  On POSIX OSs the method sends SIGTERM to the
     child.  On Windows the Win32 API function ‘TerminateProcess()’ is
     called to stop the child.

 -- Method: Popen.kill ()

     Kills the child.  On POSIX OSs the function sends SIGKILL to the
     child.  On Windows *note kill(): 25d4. is an alias for *note
     terminate(): 25d3.

The following attributes are also available:

 -- Attribute: Popen.args

     The `args' argument as it was passed to *note Popen: 3db. – a
     sequence of program arguments or else a single string.

     New in version 3.3.

 -- Attribute: Popen.stdin

     If the `stdin' argument was *note PIPE: 4f4, this attribute is a
     writeable stream object as returned by *note open(): 16f.  If the
     `encoding' or `errors' arguments were specified or the
     `universal_newlines' argument was ‘True’, the stream is a text
     stream, otherwise it is a byte stream.  If the `stdin' argument was
     not *note PIPE: 4f4, this attribute is ‘None’.

 -- Attribute: Popen.stdout

     If the `stdout' argument was *note PIPE: 4f4, this attribute is a
     readable stream object as returned by *note open(): 16f.  Reading
     from the stream provides output from the child process.  If the
     `encoding' or `errors' arguments were specified or the
     `universal_newlines' argument was ‘True’, the stream is a text
     stream, otherwise it is a byte stream.  If the `stdout' argument
     was not *note PIPE: 4f4, this attribute is ‘None’.

 -- Attribute: Popen.stderr

     If the `stderr' argument was *note PIPE: 4f4, this attribute is a
     readable stream object as returned by *note open(): 16f.  Reading
     from the stream provides error output from the child process.  If
     the `encoding' or `errors' arguments were specified or the
     `universal_newlines' argument was ‘True’, the stream is a text
     stream, otherwise it is a byte stream.  If the `stderr' argument
     was not *note PIPE: 4f4, this attribute is ‘None’.

     Warning: Use *note communicate(): 25a7. rather than *note
     .stdin.write: 25bc, *note .stdout.read: 25bd. or *note
     .stderr.read: 25be. to avoid deadlocks due to any of the other OS
     pipe buffers filling up and blocking the child process.

 -- Attribute: Popen.pid

     The process ID of the child process.

     Note that if you set the `shell' argument to ‘True’, this is the
     process ID of the spawned shell.

 -- Attribute: Popen.returncode

     The child return code, set by *note poll(): 25d2. and *note wait():
     689. (and indirectly by *note communicate(): 25a7.).  A ‘None’
     value indicates that the process hasn’t terminated yet.

     A negative value ‘-N’ indicates that the child was terminated by
     signal ‘N’ (POSIX only).


File: python.info,  Node: Windows Popen Helpers,  Next: Older high-level API,  Prev: Popen Objects,  Up: subprocess — Subprocess management

5.17.6.7 Windows Popen Helpers
..............................

The *note STARTUPINFO: 25c2. class and following constants are only
available on Windows.

 -- Class: subprocess.STARTUPINFO (*, dwFlags=0, hStdInput=None,
          hStdOutput=None, hStdError=None, wShowWindow=0,
          lpAttributeList=None)

     Partial support of the Windows STARTUPINFO(1) structure is used for
     *note Popen: 3db. creation.  The following attributes can be set by
     passing them as keyword-only arguments.

     Changed in version 3.7: Keyword-only argument support was added.

      -- Attribute: dwFlags

          A bit field that determines whether certain *note STARTUPINFO:
          25c2. attributes are used when the process creates a window.

               si = subprocess.STARTUPINFO()
               si.dwFlags = subprocess.STARTF_USESTDHANDLES | subprocess.STARTF_USESHOWWINDOW

      -- Attribute: hStdInput

          If *note dwFlags: 25d8. specifies *note STARTF_USESTDHANDLES:
          25da, this attribute is the standard input handle for the
          process.  If *note STARTF_USESTDHANDLES: 25da. is not
          specified, the default for standard input is the keyboard
          buffer.

      -- Attribute: hStdOutput

          If *note dwFlags: 25d8. specifies *note STARTF_USESTDHANDLES:
          25da, this attribute is the standard output handle for the
          process.  Otherwise, this attribute is ignored and the default
          for standard output is the console window’s buffer.

      -- Attribute: hStdError

          If *note dwFlags: 25d8. specifies *note STARTF_USESTDHANDLES:
          25da, this attribute is the standard error handle for the
          process.  Otherwise, this attribute is ignored and the default
          for standard error is the console window’s buffer.

      -- Attribute: wShowWindow

          If *note dwFlags: 25d8. specifies *note STARTF_USESHOWWINDOW:
          25de, this attribute can be any of the values that can be
          specified in the ‘nCmdShow’ parameter for the ShowWindow(2)
          function, except for ‘SW_SHOWDEFAULT’.  Otherwise, this
          attribute is ignored.

          *note SW_HIDE: 25df. is provided for this attribute.  It is
          used when *note Popen: 3db. is called with ‘shell=True’.

      -- Attribute: lpAttributeList

          A dictionary of additional attributes for process creation as
          given in ‘STARTUPINFOEX’, see UpdateProcThreadAttribute(3).

          Supported attributes:

          `handle_list'

               Sequence of handles that will be inherited.  `close_fds'
               must be true if non-empty.

               The handles must be temporarily made inheritable by *note
               os.set_handle_inheritable(): 8eb. when passed to the
               *note Popen: 3db. constructor, else *note OSError: 304.
               will be raised with Windows error
               ‘ERROR_INVALID_PARAMETER’ (87).

                    Warning: In a multithreaded process, use caution to
                    avoid leaking handles that are marked inheritable
                    when combining this feature with concurrent calls to
                    other process creation functions that inherit all
                    handles such as *note os.system(): e86.  This also
                    applies to standard handle redirection, which
                    temporarily creates inheritable handles.

          New in version 3.7.

* Menu:

* Windows Constants::

   ---------- Footnotes ----------

   (1) https://msdn.microsoft.com/en-us/library/ms686331(v=vs.85).aspx

   (2) https://msdn.microsoft.com/en-us/library/ms633548(v=vs.85).aspx

   (3) 
https://msdn.microsoft.com/en-us/library/windows/desktop/ms686880(v=vs.85).aspx


File: python.info,  Node: Windows Constants,  Up: Windows Popen Helpers

5.17.6.8 Windows Constants
..........................

The *note subprocess: f9. module exposes the following constants.

 -- Data: subprocess.STD_INPUT_HANDLE

     The standard input device.  Initially, this is the console input
     buffer, ‘CONIN$’.

 -- Data: subprocess.STD_OUTPUT_HANDLE

     The standard output device.  Initially, this is the active console
     screen buffer, ‘CONOUT$’.

 -- Data: subprocess.STD_ERROR_HANDLE

     The standard error device.  Initially, this is the active console
     screen buffer, ‘CONOUT$’.

 -- Data: subprocess.SW_HIDE

     Hides the window.  Another window will be activated.

 -- Data: subprocess.STARTF_USESTDHANDLES

     Specifies that the *note STARTUPINFO.hStdInput: 25d9, *note
     STARTUPINFO.hStdOutput: 25db, and *note STARTUPINFO.hStdError:
     25dc. attributes contain additional information.

 -- Data: subprocess.STARTF_USESHOWWINDOW

     Specifies that the *note STARTUPINFO.wShowWindow: 25dd. attribute
     contains additional information.

 -- Data: subprocess.CREATE_NEW_CONSOLE

     The new process has a new console, instead of inheriting its
     parent’s console (the default).

 -- Data: subprocess.CREATE_NEW_PROCESS_GROUP

     A *note Popen: 3db. ‘creationflags’ parameter to specify that a new
     process group will be created.  This flag is necessary for using
     *note os.kill(): db9. on the subprocess.

     This flag is ignored if *note CREATE_NEW_CONSOLE: 25c3. is
     specified.

 -- Data: subprocess.ABOVE_NORMAL_PRIORITY_CLASS

     A *note Popen: 3db. ‘creationflags’ parameter to specify that a new
     process will have an above average priority.

     New in version 3.7.

 -- Data: subprocess.BELOW_NORMAL_PRIORITY_CLASS

     A *note Popen: 3db. ‘creationflags’ parameter to specify that a new
     process will have a below average priority.

     New in version 3.7.

 -- Data: subprocess.HIGH_PRIORITY_CLASS

     A *note Popen: 3db. ‘creationflags’ parameter to specify that a new
     process will have a high priority.

     New in version 3.7.

 -- Data: subprocess.IDLE_PRIORITY_CLASS

     A *note Popen: 3db. ‘creationflags’ parameter to specify that a new
     process will have an idle (lowest) priority.

     New in version 3.7.

 -- Data: subprocess.NORMAL_PRIORITY_CLASS

     A *note Popen: 3db. ‘creationflags’ parameter to specify that a new
     process will have an normal priority.  (default)

     New in version 3.7.

 -- Data: subprocess.REALTIME_PRIORITY_CLASS

     A *note Popen: 3db. ‘creationflags’ parameter to specify that a new
     process will have realtime priority.  You should almost never use
     REALTIME_PRIORITY_CLASS, because this interrupts system threads
     that manage mouse input, keyboard input, and background disk
     flushing.  This class can be appropriate for applications that
     “talk” directly to hardware or that perform brief tasks that should
     have limited interruptions.

     New in version 3.7.

 -- Data: subprocess.CREATE_NO_WINDOW

     A *note Popen: 3db. ‘creationflags’ parameter to specify that a new
     process will not create a window.

     New in version 3.7.

 -- Data: subprocess.DETACHED_PROCESS

     A *note Popen: 3db. ‘creationflags’ parameter to specify that a new
     process will not inherit its parent’s console.  This value cannot
     be used with CREATE_NEW_CONSOLE.

     New in version 3.7.

 -- Data: subprocess.CREATE_DEFAULT_ERROR_MODE

     A *note Popen: 3db. ‘creationflags’ parameter to specify that a new
     process does not inherit the error mode of the calling process.
     Instead, the new process gets the default error mode.  This feature
     is particularly useful for multithreaded shell applications that
     run with hard errors disabled.

     New in version 3.7.

 -- Data: subprocess.CREATE_BREAKAWAY_FROM_JOB

     A *note Popen: 3db. ‘creationflags’ parameter to specify that a new
     process is not associated with the job.

     New in version 3.7.


File: python.info,  Node: Older high-level API,  Next: Replacing Older Functions with the subprocess Module,  Prev: Windows Popen Helpers,  Up: subprocess — Subprocess management

5.17.6.9 Older high-level API
.............................

Prior to Python 3.5, these three functions comprised the high level API
to subprocess.  You can now use *note run(): 4f3. in many cases, but
lots of existing code calls these functions.

 -- Function: subprocess.call (args, *, stdin=None, stdout=None,
          stderr=None, shell=False, cwd=None, timeout=None,
          **other_popen_kwargs)

     Run the command described by `args'.  Wait for command to complete,
     then return the *note returncode: 10a5. attribute.

     Code needing to capture stdout or stderr should use *note run():
     4f3. instead:

          run(...).returncode

     To suppress stdout or stderr, supply a value of *note DEVNULL: b78.

     The arguments shown above are merely some common ones.  The full
     function signature is the same as that of the *note Popen: 3db.
     constructor - this function passes all supplied arguments other
     than `timeout' directly through to that interface.

          Note: Do not use ‘stdout=PIPE’ or ‘stderr=PIPE’ with this
          function.  The child process will block if it generates enough
          output to a pipe to fill up the OS pipe buffer as the pipes
          are not being read from.

     Changed in version 3.3: `timeout' was added.

 -- Function: subprocess.check_call (args, *, stdin=None, stdout=None,
          stderr=None, shell=False, cwd=None, timeout=None,
          **other_popen_kwargs)

     Run command with arguments.  Wait for command to complete.  If the
     return code was zero then return, otherwise raise *note
     CalledProcessError: d7d.  The *note CalledProcessError: d7d. object
     will have the return code in the *note returncode: 25b6. attribute.
     If *note check_call(): 25b5. was unable to start the process it
     will propagate the exception that was raised.

     Code needing to capture stdout or stderr should use *note run():
     4f3. instead:

          run(..., check=True)

     To suppress stdout or stderr, supply a value of *note DEVNULL: b78.

     The arguments shown above are merely some common ones.  The full
     function signature is the same as that of the *note Popen: 3db.
     constructor - this function passes all supplied arguments other
     than `timeout' directly through to that interface.

          Note: Do not use ‘stdout=PIPE’ or ‘stderr=PIPE’ with this
          function.  The child process will block if it generates enough
          output to a pipe to fill up the OS pipe buffer as the pipes
          are not being read from.

     Changed in version 3.3: `timeout' was added.

 -- Function: subprocess.check_output (args, *, stdin=None, stderr=None,
          shell=False, cwd=None, encoding=None, errors=None,
          universal_newlines=None, timeout=None, text=None,
          **other_popen_kwargs)

     Run command with arguments and return its output.

     If the return code was non-zero it raises a *note
     CalledProcessError: d7d.  The *note CalledProcessError: d7d. object
     will have the return code in the *note returncode: 25b6. attribute
     and any output in the *note output: 25b8. attribute.

     This is equivalent to:

          run(..., check=True, stdout=PIPE).stdout

     The arguments shown above are merely some common ones.  The full
     function signature is largely the same as that of *note run(): 4f3.
     - most arguments are passed directly through to that interface.
     One API deviation from *note run(): 4f3. behavior exists: passing
     ‘input=None’ will behave the same as ‘input=b''’ (or ‘input=''’,
     depending on other arguments) rather than using the parent’s
     standard input file handle.

     By default, this function will return the data as encoded bytes.
     The actual encoding of the output data may depend on the command
     being invoked, so the decoding to text will often need to be
     handled at the application level.

     This behaviour may be overridden by setting `text', `encoding',
     `errors', or `universal_newlines' to ‘True’ as described in *note
     Frequently Used Arguments: 25a6. and *note run(): 4f3.

     To also capture standard error in the result, use
     ‘stderr=subprocess.STDOUT’:

          >>> subprocess.check_output(
          ...     "ls non_existent_file; exit 0",
          ...     stderr=subprocess.STDOUT,
          ...     shell=True)
          'ls: non_existent_file: No such file or directory\n'

     New in version 3.1.

     Changed in version 3.3: `timeout' was added.

     Changed in version 3.4: Support for the `input' keyword argument
     was added.

     Changed in version 3.6: `encoding' and `errors' were added.  See
     *note run(): 4f3. for details.

     New in version 3.7: `text' was added as a more readable alias for
     `universal_newlines'.


File: python.info,  Node: Replacing Older Functions with the subprocess Module,  Next: Legacy Shell Invocation Functions,  Prev: Older high-level API,  Up: subprocess — Subprocess management

5.17.6.10 Replacing Older Functions with the ‘subprocess’ Module
................................................................

In this section, “a becomes b” means that b can be used as a replacement
for a.

     Note: All “a” functions in this section fail (more or less)
     silently if the executed program cannot be found; the “b”
     replacements raise *note OSError: 304. instead.

     In addition, the replacements using *note check_output(): 9c1. will
     fail with a *note CalledProcessError: d7d. if the requested
     operation produces a non-zero return code.  The output is still
     available as the *note output: 25b8. attribute of the raised
     exception.

In the following examples, we assume that the relevant functions have
already been imported from the *note subprocess: f9. module.

* Menu:

* Replacing /bin/sh shell command substitution::
* Replacing shell pipeline::
* Replacing os.system(): Replacing os system.
* Replacing the os.spawn family: Replacing the os spawn family.
* Replacing os.popen(), os.popen2(), os.popen3(): Replacing os popen os popen2 os popen3.
* Replacing functions from the popen2 module::


File: python.info,  Node: Replacing /bin/sh shell command substitution,  Next: Replacing shell pipeline,  Up: Replacing Older Functions with the subprocess Module

5.17.6.11 Replacing ‘/bin/sh’ shell command substitution
........................................................

     output=$(mycmd myarg)

becomes:

     output = check_output(["mycmd", "myarg"])


File: python.info,  Node: Replacing shell pipeline,  Next: Replacing os system,  Prev: Replacing /bin/sh shell command substitution,  Up: Replacing Older Functions with the subprocess Module

5.17.6.12 Replacing shell pipeline
..................................

     output=$(dmesg | grep hda)

becomes:

     p1 = Popen(["dmesg"], stdout=PIPE)
     p2 = Popen(["grep", "hda"], stdin=p1.stdout, stdout=PIPE)
     p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
     output = p2.communicate()[0]

The ‘p1.stdout.close()’ call after starting the p2 is important in order
for p1 to receive a SIGPIPE if p2 exits before p1.

Alternatively, for trusted input, the shell’s own pipeline support may
still be used directly:

     output=$(dmesg | grep hda)

becomes:

     output=check_output("dmesg | grep hda", shell=True)


File: python.info,  Node: Replacing os system,  Next: Replacing the os spawn family,  Prev: Replacing shell pipeline,  Up: Replacing Older Functions with the subprocess Module

5.17.6.13 Replacing ‘os.system()’
.................................

     sts = os.system("mycmd" + " myarg")
     # becomes
     retcode = call("mycmd" + " myarg", shell=True)

Notes:

   * Calling the program through the shell is usually not required.

   * The *note call(): 4f5. return value is encoded differently to that
     of *note os.system(): e86.

   * The *note os.system(): e86. function ignores SIGINT and SIGQUIT
     signals while the command is running, but the caller must do this
     separately when using the *note subprocess: f9. module.

A more realistic example would look like this:

     try:
         retcode = call("mycmd" + " myarg", shell=True)
         if retcode < 0:
             print("Child was terminated by signal", -retcode, file=sys.stderr)
         else:
             print("Child returned", retcode, file=sys.stderr)
     except OSError as e:
         print("Execution failed:", e, file=sys.stderr)


File: python.info,  Node: Replacing the os spawn family,  Next: Replacing os popen os popen2 os popen3,  Prev: Replacing os system,  Up: Replacing Older Functions with the subprocess Module

5.17.6.14 Replacing the ‘os.spawn’ family
.........................................

P_NOWAIT example:

     pid = os.spawnlp(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg")
     ==>
     pid = Popen(["/bin/mycmd", "myarg"]).pid

P_WAIT example:

     retcode = os.spawnlp(os.P_WAIT, "/bin/mycmd", "mycmd", "myarg")
     ==>
     retcode = call(["/bin/mycmd", "myarg"])

Vector example:

     os.spawnvp(os.P_NOWAIT, path, args)
     ==>
     Popen([path] + args[1:])

Environment example:

     os.spawnlpe(os.P_NOWAIT, "/bin/mycmd", "mycmd", "myarg", env)
     ==>
     Popen(["/bin/mycmd", "myarg"], env={"PATH": "/usr/bin"})


File: python.info,  Node: Replacing os popen os popen2 os popen3,  Next: Replacing functions from the popen2 module,  Prev: Replacing the os spawn family,  Up: Replacing Older Functions with the subprocess Module

5.17.6.15 Replacing ‘os.popen()’, ‘os.popen2()’, ‘os.popen3()’
..............................................................

     (child_stdin, child_stdout) = os.popen2(cmd, mode, bufsize)
     ==>
     p = Popen(cmd, shell=True, bufsize=bufsize,
               stdin=PIPE, stdout=PIPE, close_fds=True)
     (child_stdin, child_stdout) = (p.stdin, p.stdout)

     (child_stdin,
      child_stdout,
      child_stderr) = os.popen3(cmd, mode, bufsize)
     ==>
     p = Popen(cmd, shell=True, bufsize=bufsize,
               stdin=PIPE, stdout=PIPE, stderr=PIPE, close_fds=True)
     (child_stdin,
      child_stdout,
      child_stderr) = (p.stdin, p.stdout, p.stderr)

     (child_stdin, child_stdout_and_stderr) = os.popen4(cmd, mode, bufsize)
     ==>
     p = Popen(cmd, shell=True, bufsize=bufsize,
               stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True)
     (child_stdin, child_stdout_and_stderr) = (p.stdin, p.stdout)

Return code handling translates as follows:

     pipe = os.popen(cmd, 'w')
     ...
     rc = pipe.close()
     if rc is not None and rc >> 8:
         print("There were some errors")
     ==>
     process = Popen(cmd, stdin=PIPE)
     ...
     process.stdin.close()
     if process.wait() != 0:
         print("There were some errors")


File: python.info,  Node: Replacing functions from the popen2 module,  Prev: Replacing os popen os popen2 os popen3,  Up: Replacing Older Functions with the subprocess Module

5.17.6.16 Replacing functions from the ‘popen2’ module
......................................................

     Note: If the cmd argument to popen2 functions is a string, the
     command is executed through /bin/sh.  If it is a list, the command
     is directly executed.

     (child_stdout, child_stdin) = popen2.popen2("somestring", bufsize, mode)
     ==>
     p = Popen("somestring", shell=True, bufsize=bufsize,
               stdin=PIPE, stdout=PIPE, close_fds=True)
     (child_stdout, child_stdin) = (p.stdout, p.stdin)

     (child_stdout, child_stdin) = popen2.popen2(["mycmd", "myarg"], bufsize, mode)
     ==>
     p = Popen(["mycmd", "myarg"], bufsize=bufsize,
               stdin=PIPE, stdout=PIPE, close_fds=True)
     (child_stdout, child_stdin) = (p.stdout, p.stdin)

‘popen2.Popen3’ and ‘popen2.Popen4’ basically work as *note
subprocess.Popen: 3db, except that:

   * *note Popen: 3db. raises an exception if the execution fails.

   * The `capturestderr' argument is replaced with the `stderr'
     argument.

   * ‘stdin=PIPE’ and ‘stdout=PIPE’ must be specified.

   * popen2 closes all file descriptors by default, but you have to
     specify ‘close_fds=True’ with *note Popen: 3db. to guarantee this
     behavior on all platforms or past Python versions.


File: python.info,  Node: Legacy Shell Invocation Functions,  Next: Notes,  Prev: Replacing Older Functions with the subprocess Module,  Up: subprocess — Subprocess management

5.17.6.17 Legacy Shell Invocation Functions
...........................................

This module also provides the following legacy functions from the 2.x
‘commands’ module.  These operations implicitly invoke the system shell
and none of the guarantees described above regarding security and
exception handling consistency are valid for these functions.

 -- Function: subprocess.getstatusoutput (cmd)

     Return ‘(exitcode, output)’ of executing `cmd' in a shell.

     Execute the string `cmd' in a shell with ‘Popen.check_output()’ and
     return a 2-tuple ‘(exitcode, output)’.  The locale encoding is
     used; see the notes on *note Frequently Used Arguments: 25a6. for
     more details.

     A trailing newline is stripped from the output.  The exit code for
     the command can be interpreted as the return code of subprocess.
     Example:

          >>> subprocess.getstatusoutput('ls /bin/ls')
          (0, '/bin/ls')
          >>> subprocess.getstatusoutput('cat /bin/junk')
          (1, 'cat: /bin/junk: No such file or directory')
          >>> subprocess.getstatusoutput('/bin/junk')
          (127, 'sh: /bin/junk: not found')
          >>> subprocess.getstatusoutput('/bin/kill $$')
          (-15, '')

     *note Availability: 1491.: POSIX & Windows.

     Changed in version 3.3.4: Windows support was added.

     The function now returns (exitcode, output) instead of (status,
     output) as it did in Python 3.3.3 and earlier.  exitcode has the
     same value as *note returncode: 10a5.

 -- Function: subprocess.getoutput (cmd)

     Return output (stdout and stderr) of executing `cmd' in a shell.

     Like *note getstatusoutput(): 9c2, except the exit code is ignored
     and the return value is a string containing the command’s output.
     Example:

          >>> subprocess.getoutput('ls /bin/ls')
          '/bin/ls'

     *note Availability: 1491.: POSIX & Windows.

     Changed in version 3.3.4: Windows support added


File: python.info,  Node: Notes,  Prev: Legacy Shell Invocation Functions,  Up: subprocess — Subprocess management

5.17.6.18 Notes
...............

* Menu:

* Converting an argument sequence to a string on Windows::


File: python.info,  Node: Converting an argument sequence to a string on Windows,  Up: Notes

5.17.6.19 Converting an argument sequence to a string on Windows
................................................................

On Windows, an `args' sequence is converted to a string that can be
parsed using the following rules (which correspond to the rules used by
the MS C runtime):

  1. Arguments are delimited by white space, which is either a space or
     a tab.

  2. A string surrounded by double quotation marks is interpreted as a
     single argument, regardless of white space contained within.  A
     quoted string can be embedded in an argument.

  3. A double quotation mark preceded by a backslash is interpreted as a
     literal double quotation mark.

  4. Backslashes are interpreted literally, unless they immediately
     precede a double quotation mark.

  5. If backslashes immediately precede a double quotation mark, every
     pair of backslashes is interpreted as a literal backslash.  If the
     number of backslashes is odd, the last backslash escapes the next
     double quotation mark as described in rule 3.

See also
........

*note shlex: e8.

     Module which provides function to parse and escape command lines.


File: python.info,  Node: sched — Event scheduler,  Next: queue — A synchronized queue class,  Prev: subprocess — Subprocess management,  Up: Concurrent Execution

5.17.7 ‘sched’ — Event scheduler
--------------------------------

`Source code:' Lib/sched.py(1)

__________________________________________________________________

The *note sched: e3. module defines a class which implements a general
purpose event scheduler:

 -- Class: sched.scheduler (timefunc=time.monotonic,
          delayfunc=time.sleep)

     The *note scheduler: b49. class defines a generic interface to
     scheduling events.  It needs two functions to actually deal with
     the “outside world” — `timefunc' should be callable without
     arguments, and return a number (the “time”, in any units
     whatsoever).  The `delayfunc' function should be callable with one
     argument, compatible with the output of `timefunc', and should
     delay that many time units.  `delayfunc' will also be called with
     the argument ‘0’ after each event is run to allow other threads an
     opportunity to run in multi-threaded applications.

     Changed in version 3.3: `timefunc' and `delayfunc' parameters are
     optional.

     Changed in version 3.3: *note scheduler: b49. class can be safely
     used in multi-threaded environments.

Example:

     >>> import sched, time
     >>> s = sched.scheduler(time.time, time.sleep)
     >>> def print_time(a='default'):
     ...     print("From print_time", time.time(), a)
     ...
     >>> def print_some_times():
     ...     print(time.time())
     ...     s.enter(10, 1, print_time)
     ...     s.enter(5, 2, print_time, argument=('positional',))
     ...     s.enter(5, 1, print_time, kwargs={'a': 'keyword'})
     ...     s.run()
     ...     print(time.time())
     ...
     >>> print_some_times()
     930343690.257
     From print_time 930343695.274 positional
     From print_time 930343695.275 keyword
     From print_time 930343700.273 default
     930343700.276

* Menu:

* Scheduler Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/sched.py


File: python.info,  Node: Scheduler Objects,  Up: sched — Event scheduler

5.17.7.1 Scheduler Objects
..........................

*note scheduler: b49. instances have the following methods and
attributes:

 -- Method: scheduler.enterabs (time, priority, action, argument=(),
          kwargs={})

     Schedule a new event.  The `time' argument should be a numeric type
     compatible with the return value of the `timefunc' function passed
     to the constructor.  Events scheduled for the same `time' will be
     executed in the order of their `priority'.  A lower number
     represents a higher priority.

     Executing the event means executing ‘action(*argument, **kwargs)’.
     `argument' is a sequence holding the positional arguments for
     `action'.  `kwargs' is a dictionary holding the keyword arguments
     for `action'.

     Return value is an event which may be used for later cancellation
     of the event (see *note cancel(): 25f4.).

     Changed in version 3.3: `argument' parameter is optional.

     Changed in version 3.3: `kwargs' parameter was added.

 -- Method: scheduler.enter (delay, priority, action, argument=(),
          kwargs={})

     Schedule an event for `delay' more time units.  Other than the
     relative time, the other arguments, the effect and the return value
     are the same as those for *note enterabs(): b4b.

     Changed in version 3.3: `argument' parameter is optional.

     Changed in version 3.3: `kwargs' parameter was added.

 -- Method: scheduler.cancel (event)

     Remove the event from the queue.  If `event' is not an event
     currently in the queue, this method will raise a *note ValueError:
     16d.

 -- Method: scheduler.empty ()

     Return ‘True’ if the event queue is empty.

 -- Method: scheduler.run (blocking=True)

     Run all scheduled events.  This method will wait (using the
     ‘delayfunc()’ function passed to the constructor) for the next
     event, then execute it and so on until there are no more scheduled
     events.

     If `blocking' is false executes the scheduled events due to expire
     soonest (if any) and then return the deadline of the next scheduled
     call in the scheduler (if any).

     Either `action' or `delayfunc' can raise an exception.  In either
     case, the scheduler will maintain a consistent state and propagate
     the exception.  If an exception is raised by `action', the event
     will not be attempted in future calls to *note run(): b48.

     If a sequence of events takes longer to run than the time available
     before the next event, the scheduler will simply fall behind.  No
     events will be dropped; the calling code is responsible for
     canceling events which are no longer pertinent.

     Changed in version 3.3: `blocking' parameter was added.

 -- Attribute: scheduler.queue

     Read-only attribute returning a list of upcoming events in the
     order they will be run.  Each event is shown as a *note named
     tuple: b7b. with the following fields: time, priority, action,
     argument, kwargs.


File: python.info,  Node: queue — A synchronized queue class,  Next: contextvars — Context Variables,  Prev: sched — Event scheduler,  Up: Concurrent Execution

5.17.8 ‘queue’ — A synchronized queue class
-------------------------------------------

`Source code:' Lib/queue.py(1)

__________________________________________________________________

The *note queue: da. module implements multi-producer, multi-consumer
queues.  It is especially useful in threaded programming when
information must be exchanged safely between multiple threads.  The
*note Queue: dde. class in this module implements all the required
locking semantics.

The module implements three types of queue, which differ only in the
order in which the entries are retrieved.  In a FIFO queue, the first
tasks added are the first retrieved.  In a LIFO queue, the most recently
added entry is the first retrieved (operating like a stack).  With a
priority queue, the entries are kept sorted (using the *note heapq: 8d.
module) and the lowest valued entry is retrieved first.

Internally, those three types of queues use locks to temporarily block
competing threads; however, they are not designed to handle reentrancy
within a thread.

In addition, the module implements a “simple” FIFO queue type, *note
SimpleQueue: 4cd, whose specific implementation provides additional
guarantees in exchange for the smaller functionality.

The *note queue: da. module defines the following classes and
exceptions:

 -- Class: queue.Queue (maxsize=0)

     Constructor for a FIFO queue.  `maxsize' is an integer that sets
     the upperbound limit on the number of items that can be placed in
     the queue.  Insertion will block once this size has been reached,
     until queue items are consumed.  If `maxsize' is less than or equal
     to zero, the queue size is infinite.

 -- Class: queue.LifoQueue (maxsize=0)

     Constructor for a LIFO queue.  `maxsize' is an integer that sets
     the upperbound limit on the number of items that can be placed in
     the queue.  Insertion will block once this size has been reached,
     until queue items are consumed.  If `maxsize' is less than or equal
     to zero, the queue size is infinite.

 -- Class: queue.PriorityQueue (maxsize=0)

     Constructor for a priority queue.  `maxsize' is an integer that
     sets the upperbound limit on the number of items that can be placed
     in the queue.  Insertion will block once this size has been
     reached, until queue items are consumed.  If `maxsize' is less than
     or equal to zero, the queue size is infinite.

     The lowest valued entries are retrieved first (the lowest valued
     entry is the one returned by ‘sorted(list(entries))[0]’).  A
     typical pattern for entries is a tuple in the form:
     ‘(priority_number, data)’.

     If the `data' elements are not comparable, the data can be wrapped
     in a class that ignores the data item and only compares the
     priority number:

          from dataclasses import dataclass, field
          from typing import Any

          @dataclass(order=True)
          class PrioritizedItem:
              priority: int
              item: Any=field(compare=False)

 -- Class: queue.SimpleQueue

     Constructor for an unbounded FIFO queue.  Simple queues lack
     advanced functionality such as task tracking.

     New in version 3.7.

 -- Exception: queue.Empty

     Exception raised when non-blocking *note get(): 25fb. (or *note
     get_nowait(): 25fc.) is called on a *note Queue: dde. object which
     is empty.

 -- Exception: queue.Full

     Exception raised when non-blocking *note put(): 25fd. (or *note
     put_nowait(): 25fe.) is called on a *note Queue: dde. object which
     is full.

* Menu:

* Queue Objects::
* SimpleQueue Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/queue.py


File: python.info,  Node: Queue Objects,  Next: SimpleQueue Objects,  Up: queue — A synchronized queue class

5.17.8.1 Queue Objects
......................

Queue objects (*note Queue: dde, *note LifoQueue: 25f9, or *note
PriorityQueue: 25fa.) provide the public methods described below.

 -- Method: Queue.qsize ()

     Return the approximate size of the queue.  Note, qsize() > 0
     doesn’t guarantee that a subsequent get() will not block, nor will
     qsize() < maxsize guarantee that put() will not block.

 -- Method: Queue.empty ()

     Return ‘True’ if the queue is empty, ‘False’ otherwise.  If empty()
     returns ‘True’ it doesn’t guarantee that a subsequent call to put()
     will not block.  Similarly, if empty() returns ‘False’ it doesn’t
     guarantee that a subsequent call to get() will not block.

 -- Method: Queue.full ()

     Return ‘True’ if the queue is full, ‘False’ otherwise.  If full()
     returns ‘True’ it doesn’t guarantee that a subsequent call to get()
     will not block.  Similarly, if full() returns ‘False’ it doesn’t
     guarantee that a subsequent call to put() will not block.

 -- Method: Queue.put (item, block=True, timeout=None)

     Put `item' into the queue.  If optional args `block' is true and
     `timeout' is ‘None’ (the default), block if necessary until a free
     slot is available.  If `timeout' is a positive number, it blocks at
     most `timeout' seconds and raises the *note Full: 250c. exception
     if no free slot was available within that time.  Otherwise (`block'
     is false), put an item on the queue if a free slot is immediately
     available, else raise the *note Full: 250c. exception (`timeout' is
     ignored in that case).

 -- Method: Queue.put_nowait (item)

     Equivalent to ‘put(item, False)’.

 -- Method: Queue.get (block=True, timeout=None)

     Remove and return an item from the queue.  If optional args `block'
     is true and `timeout' is ‘None’ (the default), block if necessary
     until an item is available.  If `timeout' is a positive number, it
     blocks at most `timeout' seconds and raises the *note Empty: 250b.
     exception if no item was available within that time.  Otherwise
     (`block' is false), return an item if one is immediately available,
     else raise the *note Empty: 250b. exception (`timeout' is ignored
     in that case).

     Prior to 3.0 on POSIX systems, and for all versions on Windows, if
     `block' is true and `timeout' is ‘None’, this operation goes into
     an uninterruptible wait on an underlying lock.  This means that no
     exceptions can occur, and in particular a SIGINT will not trigger a
     *note KeyboardInterrupt: 2cc.

 -- Method: Queue.get_nowait ()

     Equivalent to ‘get(False)’.

Two methods are offered to support tracking whether enqueued tasks have
been fully processed by daemon consumer threads.

 -- Method: Queue.task_done ()

     Indicate that a formerly enqueued task is complete.  Used by queue
     consumer threads.  For each *note get(): 25fb. used to fetch a
     task, a subsequent call to *note task_done(): 2507. tells the queue
     that the processing on the task is complete.

     If a *note join(): 2508. is currently blocking, it will resume when
     all items have been processed (meaning that a *note task_done():
     2507. call was received for every item that had been *note put():
     25fd. into the queue).

     Raises a *note ValueError: 16d. if called more times than there
     were items placed in the queue.

 -- Method: Queue.join ()

     Blocks until all items in the queue have been gotten and processed.

     The count of unfinished tasks goes up whenever an item is added to
     the queue.  The count goes down whenever a consumer thread calls
     *note task_done(): 2507. to indicate that the item was retrieved
     and all work on it is complete.  When the count of unfinished tasks
     drops to zero, *note join(): 2508. unblocks.

Example of how to wait for enqueued tasks to be completed:

     import threading, queue

     q = queue.Queue()

     def worker():
         while True:
             item = q.get()
             print(f'Working on {item}')
             print(f'Finished {item}')
             q.task_done()

     # turn-on the worker thread
     threading.Thread(target=worker, daemon=True).start()

     # send thirty task requests to the worker
     for item in range(30):
         q.put(item)
     print('All task requests sent\n', end='')

     # block until all tasks are done
     q.join()
     print('All work completed')


File: python.info,  Node: SimpleQueue Objects,  Prev: Queue Objects,  Up: queue — A synchronized queue class

5.17.8.2 SimpleQueue Objects
............................

*note SimpleQueue: 4cd. objects provide the public methods described
below.

 -- Method: SimpleQueue.qsize ()

     Return the approximate size of the queue.  Note, qsize() > 0
     doesn’t guarantee that a subsequent get() will not block.

 -- Method: SimpleQueue.empty ()

     Return ‘True’ if the queue is empty, ‘False’ otherwise.  If empty()
     returns ‘False’ it doesn’t guarantee that a subsequent call to
     get() will not block.

 -- Method: SimpleQueue.put (item, block=True, timeout=None)

     Put `item' into the queue.  The method never blocks and always
     succeeds (except for potential low-level errors such as failure to
     allocate memory).  The optional args `block' and `timeout' are
     ignored and only provided for compatibility with *note Queue.put():
     25fd.

     `CPython implementation detail:' This method has a C implementation
     which is reentrant.  That is, a ‘put()’ or ‘get()’ call can be
     interrupted by another ‘put()’ call in the same thread without
     deadlocking or corrupting internal state inside the queue.  This
     makes it appropriate for use in destructors such as ‘__del__’
     methods or *note weakref: 131. callbacks.

 -- Method: SimpleQueue.put_nowait (item)

     Equivalent to ‘put(item)’, provided for compatibility with *note
     Queue.put_nowait(): 25fe.

 -- Method: SimpleQueue.get (block=True, timeout=None)

     Remove and return an item from the queue.  If optional args `block'
     is true and `timeout' is ‘None’ (the default), block if necessary
     until an item is available.  If `timeout' is a positive number, it
     blocks at most `timeout' seconds and raises the *note Empty: 250b.
     exception if no item was available within that time.  Otherwise
     (`block' is false), return an item if one is immediately available,
     else raise the *note Empty: 250b. exception (`timeout' is ignored
     in that case).

 -- Method: SimpleQueue.get_nowait ()

     Equivalent to ‘get(False)’.

See also
........

Class *note multiprocessing.Queue: 24e7.

     A queue class for use in a multi-processing (rather than
     multi-threading) context.

*note collections.deque: 62b. is an alternative implementation of
unbounded queues with fast atomic *note append(): 1a8a. and *note
popleft(): 1a90. operations that do not require locking and also support
indexing.


File: python.info,  Node: contextvars — Context Variables,  Next: _thread — Low-level threading API,  Prev: queue — A synchronized queue class,  Up: Concurrent Execution

5.17.9 ‘contextvars’ — Context Variables
----------------------------------------

__________________________________________________________________

This module provides APIs to manage, store, and access context-local
state.  The *note ContextVar: 260d. class is used to declare and work
with `Context Variables'.  The *note copy_context(): 260e. function and
the *note Context: 260f. class should be used to manage the current
context in asynchronous frameworks.

Context managers that have state should use Context Variables instead of
*note threading.local(): 244e. to prevent their state from bleeding to
other code unexpectedly, when used in concurrent code.

See also PEP 567(1) for additional details.

New in version 3.7.

* Menu:

* Context Variables::
* Manual Context Management::
* asyncio support::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0567


File: python.info,  Node: Context Variables,  Next: Manual Context Management,  Up: contextvars — Context Variables

5.17.9.1 Context Variables
..........................

 -- Class: contextvars.ContextVar (name[, *, default])

     This class is used to declare a new Context Variable, e.g.:

          var: ContextVar[int] = ContextVar('var', default=42)

     The required `name' parameter is used for introspection and debug
     purposes.

     The optional keyword-only `default' parameter is returned by *note
     ContextVar.get(): 2611. when no value for the variable is found in
     the current context.

     `Important:' Context Variables should be created at the top module
     level and never in closures.  *note Context: 260f. objects hold
     strong references to context variables which prevents context
     variables from being properly garbage collected.

      -- Attribute: name

          The name of the variable.  This is a read-only property.

          New in version 3.7.1.

      -- Method: get ([default])

          Return a value for the context variable for the current
          context.

          If there is no value for the variable in the current context,
          the method will:

             * return the value of the `default' argument of the method,
               if provided; or

             * return the default value for the context variable, if it
               was created with one; or

             * raise a *note LookupError: 1790.

      -- Method: set (value)

          Call to set a new value for the context variable in the
          current context.

          The required `value' argument is the new value for the context
          variable.

          Returns a *note Token: 2614. object that can be used to
          restore the variable to its previous value via the *note
          ContextVar.reset(): 2615. method.

      -- Method: reset (token)

          Reset the context variable to the value it had before the
          *note ContextVar.set(): 2613. that created the `token' was
          used.

          For example:

               var = ContextVar('var')

               token = var.set('new value')
               # code that uses 'var'; var.get() returns 'new value'.
               var.reset(token)

               # After the reset call the var has no value again, so
               # var.get() would raise a LookupError.

 -- Class: contextvars.Token

     `Token' objects are returned by the *note ContextVar.set(): 2613.
     method.  They can be passed to the *note ContextVar.reset(): 2615.
     method to revert the value of the variable to what it was before
     the corresponding `set'.

      -- Attribute: var

          A read-only property.  Points to the *note ContextVar: 260d.
          object that created the token.

      -- Attribute: old_value

          A read-only property.  Set to the value the variable had
          before the *note ContextVar.set(): 2613. method call that
          created the token.  It points to *note Token.MISSING: 2618. is
          the variable was not set before the call.

      -- Attribute: MISSING

          A marker object used by *note Token.old_value: 2617.


File: python.info,  Node: Manual Context Management,  Next: asyncio support,  Prev: Context Variables,  Up: contextvars — Context Variables

5.17.9.2 Manual Context Management
..................................

 -- Function: contextvars.copy_context ()

     Returns a copy of the current *note Context: 260f. object.

     The following snippet gets a copy of the current context and prints
     all variables and their values that are set in it:

          ctx: Context = copy_context()
          print(list(ctx.items()))

     The function has an O(1) complexity, i.e.  works equally fast for
     contexts with a few context variables and for contexts that have a
     lot of them.

 -- Class: contextvars.Context

     A mapping of *note ContextVars: 260d. to their values.

     ‘Context()’ creates an empty context with no values in it.  To get
     a copy of the current context use the *note copy_context(): 260e.
     function.

     Context implements the *note collections.abc.Mapping: 15f.
     interface.

      -- Method: run (callable, *args, **kwargs)

          Execute ‘callable(*args, **kwargs)’ code in the context object
          the `run' method is called on.  Return the result of the
          execution or propagate an exception if one occurred.

          Any changes to any context variables that `callable' makes
          will be contained in the context object:

               var = ContextVar('var')
               var.set('spam')

               def main():
                   # 'var' was set to 'spam' before
                   # calling 'copy_context()' and 'ctx.run(main)', so:
                   # var.get() == ctx[var] == 'spam'

                   var.set('ham')

                   # Now, after setting 'var' to 'ham':
                   # var.get() == ctx[var] == 'ham'

               ctx = copy_context()

               # Any changes that the 'main' function makes to 'var'
               # will be contained in 'ctx'.
               ctx.run(main)

               # The 'main()' function was run in the 'ctx' context,
               # so changes to 'var' are contained in it:
               # ctx[var] == 'ham'

               # However, outside of 'ctx', 'var' is still set to 'spam':
               # var.get() == 'spam'

          The method raises a *note RuntimeError: 3dc. when called on
          the same context object from more than one OS thread, or when
          called recursively.

      -- Method: copy ()

          Return a shallow copy of the context object.

      -- Describe: var in context

          Return ‘True’ if the `context' has a value for `var' set;
          return ‘False’ otherwise.

      -- Describe: context[var]

          Return the value of the `var' *note ContextVar: 260d.
          variable.  If the variable is not set in the context object, a
          *note KeyError: 3e9. is raised.

      -- Method: get (var[, default])

          Return the value for `var' if `var' has the value in the
          context object.  Return `default' otherwise.  If `default' is
          not given, return ‘None’.

      -- Describe: iter(context)

          Return an iterator over the variables stored in the context
          object.

      -- Describe: len(proxy)

          Return the number of variables set in the context object.

      -- Method: keys ()

          Return a list of all variables in the context object.

      -- Method: values ()

          Return a list of all variables’ values in the context object.

      -- Method: items ()

          Return a list of 2-tuples containing all variables and their
          values in the context object.


File: python.info,  Node: asyncio support,  Prev: Manual Context Management,  Up: contextvars — Context Variables

5.17.9.3 asyncio support
........................

Context variables are natively supported in *note asyncio: 9. and are
ready to be used without any extra configuration.  For example, here is
a simple echo server, that uses a context variable to make the address
of a remote client available in the Task that handles that client:

     import asyncio
     import contextvars

     client_addr_var = contextvars.ContextVar('client_addr')

     def render_goodbye():
         # The address of the currently handled client can be accessed
         # without passing it explicitly to this function.

         client_addr = client_addr_var.get()
         return f'Good bye, client @ {client_addr}\n'.encode()

     async def handle_request(reader, writer):
         addr = writer.transport.get_extra_info('socket').getpeername()
         client_addr_var.set(addr)

         # In any code that we call is now possible to get
         # client's address by calling 'client_addr_var.get()'.

         while True:
             line = await reader.readline()
             print(line)
             if not line.strip():
                 break
             writer.write(line)

         writer.write(render_goodbye())
         writer.close()

     async def main():
         srv = await asyncio.start_server(
             handle_request, '127.0.0.1', 8081)

         async with srv:
             await srv.serve_forever()

     asyncio.run(main())

     # To test it you can use telnet:
     #     telnet 127.0.0.1 8081

The following are support modules for some of the above services:


File: python.info,  Node: _thread — Low-level threading API,  Prev: contextvars — Context Variables,  Up: Concurrent Execution

5.17.10 ‘_thread’ — Low-level threading API
-------------------------------------------

__________________________________________________________________

This module provides low-level primitives for working with multiple
threads (also called `light-weight processes' or `tasks') — multiple
threads of control sharing their global data space.  For
synchronization, simple locks (also called `mutexes' or `binary
semaphores') are provided.  The *note threading: 10b. module provides an
easier to use and higher-level threading API built on top of this
module.

Changed in version 3.7: This module used to be optional, it is now
always available.

This module defines the following constants and functions:

 -- Exception: _thread.error

     Raised on thread-specific errors.

     Changed in version 3.3: This is now a synonym of the built-in *note
     RuntimeError: 3dc.

 -- Data: _thread.LockType

     This is the type of lock objects.

 -- Function: _thread.start_new_thread (function, args[, kwargs])

     Start a new thread and return its identifier.  The thread executes
     the function `function' with the argument list `args' (which must
     be a tuple).  The optional `kwargs' argument specifies a dictionary
     of keyword arguments.

     When the function returns, the thread silently exits.

     When the function terminates with an unhandled exception, *note
     sys.unraisablehook(): 35a. is called to handle the exception.  The
     `object' attribute of the hook argument is `function'.  By default,
     a stack trace is printed and then the thread exits (but other
     threads continue to run).

     When the function raises a *note SystemExit: 6f3. exception, it is
     silently ignored.

     Changed in version 3.8: *note sys.unraisablehook(): 35a. is now
     used to handle unhandled exceptions.

 -- Function: _thread.interrupt_main ()

     Simulate the effect of a *note signal.SIGINT: 2626. signal arriving
     in the main thread.  A thread can use this function to interrupt
     the main thread.

     If *note signal.SIGINT: 2626. isn’t handled by Python (it was set
     to *note signal.SIG_DFL: 2627. or *note signal.SIG_IGN: 2628.),
     this function does nothing.

 -- Function: _thread.exit ()

     Raise the *note SystemExit: 6f3. exception.  When not caught, this
     will cause the thread to exit silently.

 -- Function: _thread.allocate_lock ()

     Return a new lock object.  Methods of locks are described below.
     The lock is initially unlocked.

 -- Function: _thread.get_ident ()

     Return the ‘thread identifier’ of the current thread.  This is a
     nonzero integer.  Its value has no direct meaning; it is intended
     as a magic cookie to be used e.g.  to index a dictionary of
     thread-specific data.  Thread identifiers may be recycled when a
     thread exits and another thread is created.

 -- Function: _thread.get_native_id ()

     Return the native integral Thread ID of the current thread assigned
     by the kernel.  This is a non-negative integer.  Its value may be
     used to uniquely identify this particular thread system-wide (until
     the thread terminates, after which the value may be recycled by the
     OS).

     *note Availability: 1491.: Windows, FreeBSD, Linux, macOS, OpenBSD,
     NetBSD, AIX.

     New in version 3.8.

 -- Function: _thread.stack_size ([size])

     Return the thread stack size used when creating new threads.  The
     optional `size' argument specifies the stack size to be used for
     subsequently created threads, and must be 0 (use platform or
     configured default) or a positive integer value of at least 32,768
     (32 KiB). If `size' is not specified, 0 is used.  If changing the
     thread stack size is unsupported, a *note RuntimeError: 3dc. is
     raised.  If the specified stack size is invalid, a *note
     ValueError: 16d. is raised and the stack size is unmodified.  32
     KiB is currently the minimum supported stack size value to
     guarantee sufficient stack space for the interpreter itself.  Note
     that some platforms may have particular restrictions on values for
     the stack size, such as requiring a minimum stack size > 32 KiB or
     requiring allocation in multiples of the system memory page size -
     platform documentation should be referred to for more information
     (4 KiB pages are common; using multiples of 4096 for the stack size
     is the suggested approach in the absence of more specific
     information).

     *note Availability: 1491.: Windows, systems with POSIX threads.

 -- Data: _thread.TIMEOUT_MAX

     The maximum value allowed for the `timeout' parameter of
     ‘Lock.acquire()’.  Specifying a timeout greater than this value
     will raise an *note OverflowError: a41.

     New in version 3.2.

Lock objects have the following methods:

 -- Method: lock.acquire (waitflag=1, timeout=-1)

     Without any optional argument, this method acquires the lock
     unconditionally, if necessary waiting until it is released by
     another thread (only one thread at a time can acquire a lock —
     that’s their reason for existence).

     If the integer `waitflag' argument is present, the action depends
     on its value: if it is zero, the lock is only acquired if it can be
     acquired immediately without waiting, while if it is nonzero, the
     lock is acquired unconditionally as above.

     If the floating-point `timeout' argument is present and positive,
     it specifies the maximum wait time in seconds before returning.  A
     negative `timeout' argument specifies an unbounded wait.  You
     cannot specify a `timeout' if `waitflag' is zero.

     The return value is ‘True’ if the lock is acquired successfully,
     ‘False’ if not.

     Changed in version 3.2: The `timeout' parameter is new.

     Changed in version 3.2: Lock acquires can now be interrupted by
     signals on POSIX.

 -- Method: lock.release ()

     Releases the lock.  The lock must have been acquired earlier, but
     not necessarily by the same thread.

 -- Method: lock.locked ()

     Return the status of the lock: ‘True’ if it has been acquired by
     some thread, ‘False’ if not.

In addition to these methods, lock objects can also be used via the
*note with: 7da. statement, e.g.:

     import _thread

     a_lock = _thread.allocate_lock()

     with a_lock:
         print("a_lock is locked while this executes")

`Caveats:'

   * Threads interact strangely with interrupts: the *note
     KeyboardInterrupt: 2cc. exception will be received by an arbitrary
     thread.  (When the *note signal: ea. module is available,
     interrupts always go to the main thread.)

   * Calling *note sys.exit(): daa. or raising the *note SystemExit:
     6f3. exception is equivalent to calling *note _thread.exit(): 2629.

   * It is not possible to interrupt the ‘acquire()’ method on a lock —
     the *note KeyboardInterrupt: 2cc. exception will happen after the
     lock has been acquired.

   * When the main thread exits, it is system defined whether the other
     threads survive.  On most systems, they are killed without
     executing *note try: e37. … *note finally: 2bc. clauses or
     executing object destructors.

   * When the main thread exits, it does not do any of its usual cleanup
     (except that *note try: e37. … *note finally: 2bc. clauses are
     honored), and the standard I/O files are not flushed.


File: python.info,  Node: Networking and Interprocess Communication,  Next: Internet Data Handling,  Prev: Concurrent Execution,  Up: The Python Standard Library

5.18 Networking and Interprocess Communication
==============================================

The modules described in this chapter provide mechanisms for networking
and inter-processes communication.

Some modules only work for two processes that are on the same machine,
e.g.  *note signal: ea. and *note mmap: b3.  Other modules support
networking protocols that two or more processes can use to communicate
across machines.

The list of modules described in this chapter is:

* Menu:

* asyncio — Asynchronous I/O::
* socket — Low-level networking interface::
* ssl — TLS/SSL wrapper for socket objects::
* select — Waiting for I/O completion::
* selectors — High-level I/O multiplexing::
* asyncore — Asynchronous socket handler::
* asynchat — Asynchronous socket command/response handler::
* signal — Set handlers for asynchronous events::
* mmap — Memory-mapped file support::


File: python.info,  Node: asyncio — Asynchronous I/O,  Next: socket — Low-level networking interface,  Up: Networking and Interprocess Communication

5.18.1 ‘asyncio’ — Asynchronous I/O
-----------------------------------

__________________________________________________________________

Hello World!
............

     import asyncio

     async def main():
         print('Hello ...')
         await asyncio.sleep(1)
         print('... World!')

     # Python 3.7+
     asyncio.run(main())

asyncio is a library to write `concurrent' code using the `async/await'
syntax.

asyncio is used as a foundation for multiple Python asynchronous
frameworks that provide high-performance network and web-servers,
database connection libraries, distributed task queues, etc.

asyncio is often a perfect fit for IO-bound and high-level `structured'
network code.

asyncio provides a set of `high-level' APIs to:

   * *note run Python coroutines: 2637. concurrently and have full
     control over their execution;

   * perform *note network IO and IPC: 2638.;

   * control *note subprocesses: 2639.;

   * distribute tasks via *note queues: 263a.;

   * *note synchronize: 263b. concurrent code;

Additionally, there are `low-level' APIs for `library and framework
developers' to:

   * create and manage *note event loops: 737, which provide
     asynchronous APIs for *note networking: 465, running *note
     subprocesses: 263c, handling *note OS signals: 263d, etc;

   * implement efficient protocols using *note transports: 263e.;

   * *note bridge: 263f. callback-based libraries and code with
     async/await syntax.

Reference
.........

* Menu:

* Coroutines and Tasks::
* Streams::
* Synchronization Primitives::
* Subprocesses::
* Queues::
* Exceptions: Exceptions<10>.
* Event Loop::
* Futures::
* Transports and Protocols::
* Policies::
* Platform Support::
* High-level API Index::
* Low-level API Index::
* Developing with asyncio::


File: python.info,  Node: Coroutines and Tasks,  Next: Streams,  Up: asyncio — Asynchronous I/O

5.18.1.1 Coroutines and Tasks
.............................

This section outlines high-level asyncio APIs to work with coroutines
and Tasks.

* Menu:

* Coroutines: Coroutines<3>.
* Awaitables::
* Running an asyncio Program::
* Creating Tasks::
* Sleeping::
* Running Tasks Concurrently::
* Shielding From Cancellation::
* Timeouts::
* Waiting Primitives::
* Running in Threads::
* Scheduling From Other Threads::
* Introspection::
* Task Object::
* Generator-based Coroutines::


File: python.info,  Node: Coroutines<3>,  Next: Awaitables,  Up: Coroutines and Tasks

5.18.1.2 Coroutines
...................

*note Coroutines: 18a. declared with the async/await syntax is the
preferred way of writing asyncio applications.  For example, the
following snippet of code (requires Python 3.7+) prints “hello”, waits 1
second, and then prints “world”:

     >>> import asyncio

     >>> async def main():
     ...     print('hello')
     ...     await asyncio.sleep(1)
     ...     print('world')

     >>> asyncio.run(main())
     hello
     world

Note that simply calling a coroutine will not schedule it to be
executed:

     >>> main()
     <coroutine object main at 0x1053bb7c8>

To actually run a coroutine, asyncio provides three main mechanisms:

   * The *note asyncio.run(): 18d. function to run the top-level entry
     point “main()” function (see the above example.)

   * Awaiting on a coroutine.  The following snippet of code will print
     “hello” after waiting for 1 second, and then print “world” after
     waiting for `another' 2 seconds:

          import asyncio
          import time

          async def say_after(delay, what):
              await asyncio.sleep(delay)
              print(what)

          async def main():
              print(f"started at {time.strftime('%X')}")

              await say_after(1, 'hello')
              await say_after(2, 'world')

              print(f"finished at {time.strftime('%X')}")

          asyncio.run(main())

     Expected output:

          started at 17:13:52
          hello
          world
          finished at 17:13:55

   * The *note asyncio.create_task(): 2e1. function to run coroutines
     concurrently as asyncio *note Tasks: 2e0.

     Let’s modify the above example and run two ‘say_after’ coroutines
     `concurrently':

          async def main():
              task1 = asyncio.create_task(
                  say_after(1, 'hello'))

              task2 = asyncio.create_task(
                  say_after(2, 'world'))

              print(f"started at {time.strftime('%X')}")

              # Wait until both tasks are completed (should take
              # around 2 seconds.)
              await task1
              await task2

              print(f"finished at {time.strftime('%X')}")

     Note that expected output now shows that the snippet runs 1 second
     faster than before:

          started at 17:14:32
          hello
          world
          finished at 17:14:34


File: python.info,  Node: Awaitables,  Next: Running an asyncio Program,  Prev: Coroutines<3>,  Up: Coroutines and Tasks

5.18.1.3 Awaitables
...................

We say that an object is an `awaitable' object if it can be used in an
*note await: 2d8. expression.  Many asyncio APIs are designed to accept
awaitables.

There are three main types of `awaitable' objects: `coroutines',
`Tasks', and `Futures'.

Coroutines
..........

Python coroutines are `awaitables' and therefore can be awaited from
other coroutines:

     import asyncio

     async def nested():
         return 42

     async def main():
         # Nothing happens if we just call "nested()".
         # A coroutine object is created but not awaited,
         # so it *won't run at all*.
         nested()

         # Let's do it differently now and await it:
         print(await nested())  # will print "42".

     asyncio.run(main())

     Important: In this documentation the term “coroutine” can be used
     for two closely related concepts:

        * a `coroutine function': an *note async def: 3a9. function;

        * a `coroutine object': an object returned by calling a
          `coroutine function'.

asyncio also supports legacy *note generator-based: 2645. coroutines.

Tasks
.....

`Tasks' are used to schedule coroutines `concurrently'.

When a coroutine is wrapped into a `Task' with functions like *note
asyncio.create_task(): 2e1. the coroutine is automatically scheduled to
run soon:

     import asyncio

     async def nested():
         return 42

     async def main():
         # Schedule nested() to run soon concurrently
         # with "main()".
         task = asyncio.create_task(nested())

         # "task" can now be used to cancel "nested()", or
         # can simply be awaited to wait until it is complete:
         await task

     asyncio.run(main())

Futures
.......

A *note Future: 546. is a special `low-level' awaitable object that
represents an `eventual result' of an asynchronous operation.

When a Future object is `awaited' it means that the coroutine will wait
until the Future is resolved in some other place.

Future objects in asyncio are needed to allow callback-based code to be
used with async/await.

Normally `there is no need' to create Future objects at the application
level code.

Future objects, sometimes exposed by libraries and some asyncio APIs,
can be awaited:

     async def main():
         await function_that_returns_a_future_object()

         # this is also valid:
         await asyncio.gather(
             function_that_returns_a_future_object(),
             some_python_coroutine()
         )

A good example of a low-level function that returns a Future object is
*note loop.run_in_executor(): 190.


File: python.info,  Node: Running an asyncio Program,  Next: Creating Tasks,  Prev: Awaitables,  Up: Coroutines and Tasks

5.18.1.4 Running an asyncio Program
...................................

 -- Function: asyncio.run (coro, *, debug=False)

     Execute the *note coroutine: 18a. `coro' and return the result.

     This function runs the passed coroutine, taking care of managing
     the asyncio event loop, `finalizing asynchronous generators', and
     closing the threadpool.

     This function cannot be called when another asyncio event loop is
     running in the same thread.

     If `debug' is ‘True’, the event loop will be run in debug mode.

     This function always creates a new event loop and closes it at the
     end.  It should be used as a main entry point for asyncio programs,
     and should ideally only be called once.

     Example:

          async def main():
              await asyncio.sleep(1)
              print('hello')

          asyncio.run(main())

     New in version 3.7.

     Changed in version 3.9: Updated to use *note
     loop.shutdown_default_executor(): 18b.

          Note: The source code for ‘asyncio.run()’ can be found in
          Lib/asyncio/runners.py(1).

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/asyncio/runners.py


File: python.info,  Node: Creating Tasks,  Next: Sleeping,  Prev: Running an asyncio Program,  Up: Coroutines and Tasks

5.18.1.5 Creating Tasks
.......................

 -- Function: asyncio.create_task (coro, *, name=None)

     Wrap the `coro' *note coroutine: 2637. into a *note Task: 2e0. and
     schedule its execution.  Return the Task object.

     If `name' is not ‘None’, it is set as the name of the task using
     *note Task.set_name(): 2e3.

     The task is executed in the loop returned by *note
     get_running_loop(): 45c, *note RuntimeError: 3dc. is raised if
     there is no running loop in current thread.

     This function has been `added in Python 3.7'.  Prior to Python 3.7,
     the low-level *note asyncio.ensure_future(): 611. function can be
     used instead:

          async def coro():
              ...

          # In Python 3.7+
          task = asyncio.create_task(coro())
          ...

          # This works in all Python versions but is less readable
          task = asyncio.ensure_future(coro())
          ...

          Important: Save a reference to the result of this function, to
          avoid a task disappearing mid execution.

     New in version 3.7.

     Changed in version 3.8: Added the ‘name’ parameter.


File: python.info,  Node: Sleeping,  Next: Running Tasks Concurrently,  Prev: Creating Tasks,  Up: Coroutines and Tasks

5.18.1.6 Sleeping
.................

 -- Function: coroutine asyncio.sleep (delay, result=None, *, loop=None)

     Block for `delay' seconds.

     If `result' is provided, it is returned to the caller when the
     coroutine completes.

     ‘sleep()’ always suspends the current task, allowing other tasks to
     run.

     Setting the delay to 0 provides an optimized path to allow other
     tasks to run.  This can be used by long-running functions to avoid
     blocking the event loop for the full duration of the function call.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

     Example of coroutine displaying the current date every second for 5
     seconds:

          import asyncio
          import datetime

          async def display_date():
              loop = asyncio.get_running_loop()
              end_time = loop.time() + 5.0
              while True:
                  print(datetime.datetime.now())
                  if (loop.time() + 1.0) >= end_time:
                      break
                  await asyncio.sleep(1)

          asyncio.run(display_date())


File: python.info,  Node: Running Tasks Concurrently,  Next: Shielding From Cancellation,  Prev: Sleeping,  Up: Coroutines and Tasks

5.18.1.7 Running Tasks Concurrently
...................................

 -- Function: awaitable asyncio.gather (*aws, loop=None,
          return_exceptions=False)

     Run *note awaitable objects: 2643. in the `aws' sequence
     `concurrently'.

     If any awaitable in `aws' is a coroutine, it is automatically
     scheduled as a Task.

     If all awaitables are completed successfully, the result is an
     aggregate list of returned values.  The order of result values
     corresponds to the order of awaitables in `aws'.

     If `return_exceptions' is ‘False’ (default), the first raised
     exception is immediately propagated to the task that awaits on
     ‘gather()’.  Other awaitables in the `aws' sequence `won’t be
     cancelled' and will continue to run.

     If `return_exceptions' is ‘True’, exceptions are treated the same
     as successful results, and aggregated in the result list.

     If ‘gather()’ is `cancelled', all submitted awaitables (that have
     not completed yet) are also `cancelled'.

     If any Task or Future from the `aws' sequence is `cancelled', it is
     treated as if it raised *note CancelledError: 2da. – the ‘gather()’
     call is `not' cancelled in this case.  This is to prevent the
     cancellation of one submitted Task/Future to cause other
     Tasks/Futures to be cancelled.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

     Example:

          import asyncio

          async def factorial(name, number):
              f = 1
              for i in range(2, number + 1):
                  print(f"Task {name}: Compute factorial({number}), currently i={i}...")
                  await asyncio.sleep(1)
                  f *= i
              print(f"Task {name}: factorial({number}) = {f}")
              return f

          async def main():
              # Schedule three calls *concurrently*:
              L = await asyncio.gather(
                  factorial("A", 2),
                  factorial("B", 3),
                  factorial("C", 4),
              )
              print(L)

          asyncio.run(main())

          # Expected output:
          #
          #     Task A: Compute factorial(2), currently i=2...
          #     Task B: Compute factorial(3), currently i=2...
          #     Task C: Compute factorial(4), currently i=2...
          #     Task A: factorial(2) = 2
          #     Task B: Compute factorial(3), currently i=3...
          #     Task C: Compute factorial(4), currently i=3...
          #     Task B: factorial(3) = 6
          #     Task C: Compute factorial(4), currently i=4...
          #     Task C: factorial(4) = 24
          #     [2, 6, 24]

          Note: If `return_exceptions' is False, cancelling gather()
          after it has been marked done won’t cancel any submitted
          awaitables.  For instance, gather can be marked done after
          propagating an exception to the caller, therefore, calling
          ‘gather.cancel()’ after catching an exception (raised by one
          of the awaitables) from gather won’t cancel any other
          awaitables.

     Changed in version 3.7: If the `gather' itself is cancelled, the
     cancellation is propagated regardless of `return_exceptions'.


File: python.info,  Node: Shielding From Cancellation,  Next: Timeouts,  Prev: Running Tasks Concurrently,  Up: Coroutines and Tasks

5.18.1.8 Shielding From Cancellation
....................................

 -- Function: awaitable asyncio.shield (aw, *, loop=None)

     Protect an *note awaitable object: 2643. from being *note
     cancelled: 264d.

     If `aw' is a coroutine it is automatically scheduled as a Task.

     The statement:

          res = await shield(something())

     is equivalent to:

          res = await something()

     `except' that if the coroutine containing it is cancelled, the Task
     running in ‘something()’ is not cancelled.  From the point of view
     of ‘something()’, the cancellation did not happen.  Although its
     caller is still cancelled, so the “await” expression still raises a
     *note CancelledError: 2da.

     If ‘something()’ is cancelled by other means (i.e.  from within
     itself) that would also cancel ‘shield()’.

     If it is desired to completely ignore cancellation (not
     recommended) the ‘shield()’ function should be combined with a
     try/except clause, as follows:

          try:
              res = await shield(something())
          except CancelledError:
              res = None

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.


File: python.info,  Node: Timeouts,  Next: Waiting Primitives,  Prev: Shielding From Cancellation,  Up: Coroutines and Tasks

5.18.1.9 Timeouts
.................

 -- Function: coroutine asyncio.wait_for (aw, timeout, *, loop=None)

     Wait for the `aw' *note awaitable: 2643. to complete with a
     timeout.

     If `aw' is a coroutine it is automatically scheduled as a Task.

     `timeout' can either be ‘None’ or a float or int number of seconds
     to wait for.  If `timeout' is ‘None’, block until the future
     completes.

     If a timeout occurs, it cancels the task and raises *note
     asyncio.TimeoutError: 264f.

     To avoid the task *note cancellation: 264d, wrap it in *note
     shield(): 3ac.

     The function will wait until the future is actually cancelled, so
     the total wait time may exceed the `timeout'.  If an exception
     happens during cancellation, it is propagated.

     If the wait is cancelled, the future `aw' is also cancelled.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

     Example:

          async def eternity():
              # Sleep for one hour
              await asyncio.sleep(3600)
              print('yay!')

          async def main():
              # Wait for at most 1 second
              try:
                  await asyncio.wait_for(eternity(), timeout=1.0)
              except asyncio.TimeoutError:
                  print('timeout!')

          asyncio.run(main())

          # Expected output:
          #
          #     timeout!

     Changed in version 3.7: When `aw' is cancelled due to a timeout,
     ‘wait_for’ waits for `aw' to be cancelled.  Previously, it raised
     *note asyncio.TimeoutError: 264f. immediately.


File: python.info,  Node: Waiting Primitives,  Next: Running in Threads,  Prev: Timeouts,  Up: Coroutines and Tasks

5.18.1.10 Waiting Primitives
............................

 -- Function: coroutine asyncio.wait (aws, *, loop=None, timeout=None,
          return_when=ALL_COMPLETED)

     Run *note awaitable objects: 2643. in the `aws' iterable
     concurrently and block until the condition specified by
     `return_when'.

     The `aws' iterable must not be empty.

     Returns two sets of Tasks/Futures: ‘(done, pending)’.

     Usage:

          done, pending = await asyncio.wait(aws)

     `timeout' (a float or int), if specified, can be used to control
     the maximum number of seconds to wait before returning.

     Note that this function does not raise *note asyncio.TimeoutError:
     264f.  Futures or Tasks that aren’t done when the timeout occurs
     are simply returned in the second set.

     `return_when' indicates when this function should return.  It must
     be one of the following constants:

     Constant                          Description
                                       
     -------------------------------------------------------------------------------
                                       
     ‘FIRST_COMPLETED’                 The function will return when any future
                                       finishes or is cancelled.
                                       
                                       
     ‘FIRST_EXCEPTION’                 The function will return when any future
                                       finishes by raising an exception.  If no
                                       future raises an exception then it is
                                       equivalent to ‘ALL_COMPLETED’.
                                       
                                       
     ‘ALL_COMPLETED’                   The function will return when all futures
                                       finish or are cancelled.
                                       

     Unlike *note wait_for(): 191, ‘wait()’ does not cancel the futures
     when a timeout occurs.

     Deprecated since version 3.8: If any awaitable in `aws' is a
     coroutine, it is automatically scheduled as a Task.  Passing
     coroutines objects to ‘wait()’ directly is deprecated as it leads
     to *note confusing behavior: 2652.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

          Note: ‘wait()’ schedules coroutines as Tasks automatically and
          later returns those implicitly created Task objects in ‘(done,
          pending)’ sets.  Therefore the following code won’t work as
          expected:

               async def foo():
                   return 42

               coro = foo()
               done, pending = await asyncio.wait({coro})

               if coro in done:
                   # This branch will never be run!

          Here is how the above snippet can be fixed:

               async def foo():
                   return 42

               task = asyncio.create_task(foo())
               done, pending = await asyncio.wait({task})

               if task in done:
                   # Everything will work as expected now.

     Deprecated since version 3.8, will be removed in version 3.11:
     Passing coroutine objects to ‘wait()’ directly is deprecated.

 -- Function: asyncio.as_completed (aws, *, loop=None, timeout=None)

     Run *note awaitable objects: 2643. in the `aws' iterable
     concurrently.  Return an iterator of coroutines.  Each coroutine
     returned can be awaited to get the earliest next result from the
     iterable of the remaining awaitables.

     Raises *note asyncio.TimeoutError: 264f. if the timeout occurs
     before all Futures are done.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

     Example:

          for coro in as_completed(aws):
              earliest_result = await coro
              # ...


File: python.info,  Node: Running in Threads,  Next: Scheduling From Other Threads,  Prev: Waiting Primitives,  Up: Coroutines and Tasks

5.18.1.11 Running in Threads
............................

 -- Function: coroutine asyncio.to_thread (func, /, *args, **kwargs)

     Asynchronously run function `func' in a separate thread.

     Any *args and **kwargs supplied for this function are directly
     passed to `func'.  Also, the current *note contextvars.Context:
     260f. is propagated, allowing context variables from the event loop
     thread to be accessed in the separate thread.

     Return a coroutine that can be awaited to get the eventual result
     of `func'.

     This coroutine function is primarily intended to be used for
     executing IO-bound functions/methods that would otherwise block the
     event loop if they were ran in the main thread.  For example:

          def blocking_io():
              print(f"start blocking_io at {time.strftime('%X')}")
              # Note that time.sleep() can be replaced with any blocking
              # IO-bound operation, such as file operations.
              time.sleep(1)
              print(f"blocking_io complete at {time.strftime('%X')}")

          async def main():
              print(f"started main at {time.strftime('%X')}")

              await asyncio.gather(
                  asyncio.to_thread(blocking_io),
                  asyncio.sleep(1))

              print(f"finished main at {time.strftime('%X')}")


          asyncio.run(main())

          # Expected output:
          #
          # started main at 19:50:53
          # start blocking_io at 19:50:53
          # blocking_io complete at 19:50:54
          # finished main at 19:50:54

     Directly calling ‘blocking_io()’ in any coroutine would block the
     event loop for its duration, resulting in an additional 1 second of
     run time.  Instead, by using ‘asyncio.to_thread()’, we can run it
     in a separate thread without blocking the event loop.

          Note: Due to the *note GIL: 20e, ‘asyncio.to_thread()’ can
          typically only be used to make IO-bound functions
          non-blocking.  However, for extension modules that release the
          GIL or alternative Python implementations that don’t have one,
          ‘asyncio.to_thread()’ can also be used for CPU-bound
          functions.

     New in version 3.9.


File: python.info,  Node: Scheduling From Other Threads,  Next: Introspection,  Prev: Running in Threads,  Up: Coroutines and Tasks

5.18.1.12 Scheduling From Other Threads
.......................................

 -- Function: asyncio.run_coroutine_threadsafe (coro, loop)

     Submit a coroutine to the given event loop.  Thread-safe.

     Return a *note concurrent.futures.Future: c00. to wait for the
     result from another OS thread.

     This function is meant to be called from a different OS thread than
     the one where the event loop is running.  Example:

          # Create a coroutine
          coro = asyncio.sleep(1, result=3)

          # Submit the coroutine to a given loop
          future = asyncio.run_coroutine_threadsafe(coro, loop)

          # Wait for the result with an optional timeout argument
          assert future.result(timeout) == 3

     If an exception is raised in the coroutine, the returned Future
     will be notified.  It can also be used to cancel the task in the
     event loop:

          try:
              result = future.result(timeout)
          except asyncio.TimeoutError:
              print('The coroutine took too long, cancelling the task...')
              future.cancel()
          except Exception as exc:
              print(f'The coroutine raised an exception: {exc!r}')
          else:
              print(f'The coroutine returned: {result!r}')

     See the *note concurrency and multithreading: 2655. section of the
     documentation.

     Unlike other asyncio functions this function requires the `loop'
     argument to be passed explicitly.

     New in version 3.5.1.


File: python.info,  Node: Introspection,  Next: Task Object,  Prev: Scheduling From Other Threads,  Up: Coroutines and Tasks

5.18.1.13 Introspection
.......................

 -- Function: asyncio.current_task (loop=None)

     Return the currently running *note Task: 2e0. instance, or ‘None’
     if no task is running.

     If `loop' is ‘None’ *note get_running_loop(): 45c. is used to get
     the current loop.

     New in version 3.7.

 -- Function: asyncio.all_tasks (loop=None)

     Return a set of not yet finished *note Task: 2e0. objects run by
     the loop.

     If `loop' is ‘None’, *note get_running_loop(): 45c. is used for
     getting current loop.

     New in version 3.7.


File: python.info,  Node: Task Object,  Next: Generator-based Coroutines,  Prev: Introspection,  Up: Coroutines and Tasks

5.18.1.14 Task Object
.....................

 -- Class: asyncio.Task (coro, *, loop=None, name=None)

     A *note Future-like: 546. object that runs a Python *note
     coroutine: 2637.  Not thread-safe.

     Tasks are used to run coroutines in event loops.  If a coroutine
     awaits on a Future, the Task suspends the execution of the
     coroutine and waits for the completion of the Future.  When the
     Future is `done', the execution of the wrapped coroutine resumes.

     Event loops use cooperative scheduling: an event loop runs one Task
     at a time.  While a Task awaits for the completion of a Future, the
     event loop runs other Tasks, callbacks, or performs IO operations.

     Use the high-level *note asyncio.create_task(): 2e1. function to
     create Tasks, or the low-level *note loop.create_task(): 2e2. or
     *note ensure_future(): 611. functions.  Manual instantiation of
     Tasks is discouraged.

     To cancel a running Task use the *note cancel(): 264d. method.
     Calling it will cause the Task to throw a *note CancelledError:
     2da. exception into the wrapped coroutine.  If a coroutine is
     awaiting on a Future object during cancellation, the Future object
     will be cancelled.

     *note cancelled(): 2658. can be used to check if the Task was
     cancelled.  The method returns ‘True’ if the wrapped coroutine did
     not suppress the *note CancelledError: 2da. exception and was
     actually cancelled.

     *note asyncio.Task: 2e0. inherits from *note Future: 546. all of
     its APIs except *note Future.set_result(): 2659. and *note
     Future.set_exception(): 265a.

     Tasks support the *note contextvars: 24. module.  When a Task is
     created it copies the current context and later runs its coroutine
     in the copied context.

     Changed in version 3.7: Added support for the *note contextvars:
     24. module.

     Changed in version 3.8: Added the ‘name’ parameter.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

      -- Method: cancel (msg=None)

          Request the Task to be cancelled.

          This arranges for a *note CancelledError: 2da. exception to be
          thrown into the wrapped coroutine on the next cycle of the
          event loop.

          The coroutine then has a chance to clean up or even deny the
          request by suppressing the exception with a *note try: e37. …
          … ‘except CancelledError’ … *note finally: 2bc. block.
          Therefore, unlike *note Future.cancel(): 265b, *note
          Task.cancel(): 264d. does not guarantee that the Task will be
          cancelled, although suppressing cancellation completely is not
          common and is actively discouraged.

          Changed in version 3.9: Added the ‘msg’ parameter.

          The following example illustrates how coroutines can intercept
          the cancellation request:

               async def cancel_me():
                   print('cancel_me(): before sleep')

                   try:
                       # Wait for 1 hour
                       await asyncio.sleep(3600)
                   except asyncio.CancelledError:
                       print('cancel_me(): cancel sleep')
                       raise
                   finally:
                       print('cancel_me(): after sleep')

               async def main():
                   # Create a "cancel_me" Task
                   task = asyncio.create_task(cancel_me())

                   # Wait for 1 second
                   await asyncio.sleep(1)

                   task.cancel()
                   try:
                       await task
                   except asyncio.CancelledError:
                       print("main(): cancel_me is cancelled now")

               asyncio.run(main())

               # Expected output:
               #
               #     cancel_me(): before sleep
               #     cancel_me(): cancel sleep
               #     cancel_me(): after sleep
               #     main(): cancel_me is cancelled now

      -- Method: cancelled ()

          Return ‘True’ if the Task is `cancelled'.

          The Task is `cancelled' when the cancellation was requested
          with *note cancel(): 264d. and the wrapped coroutine
          propagated the *note CancelledError: 2da. exception thrown
          into it.

      -- Method: done ()

          Return ‘True’ if the Task is `done'.

          A Task is `done' when the wrapped coroutine either returned a
          value, raised an exception, or the Task was cancelled.

      -- Method: result ()

          Return the result of the Task.

          If the Task is `done', the result of the wrapped coroutine is
          returned (or if the coroutine raised an exception, that
          exception is re-raised.)

          If the Task has been `cancelled', this method raises a *note
          CancelledError: 2da. exception.

          If the Task’s result isn’t yet available, this method raises a
          *note InvalidStateError: 265f. exception.

      -- Method: exception ()

          Return the exception of the Task.

          If the wrapped coroutine raised an exception that exception is
          returned.  If the wrapped coroutine returned normally this
          method returns ‘None’.

          If the Task has been `cancelled', this method raises a *note
          CancelledError: 2da. exception.

          If the Task isn’t `done' yet, this method raises an *note
          InvalidStateError: 265f. exception.

      -- Method: add_done_callback (callback, *, context=None)

          Add a callback to be run when the Task is `done'.

          This method should only be used in low-level callback-based
          code.

          See the documentation of *note Future.add_done_callback():
          459. for more details.

      -- Method: remove_done_callback (callback)

          Remove `callback' from the callbacks list.

          This method should only be used in low-level callback-based
          code.

          See the documentation of *note Future.remove_done_callback():
          2663. for more details.

      -- Method: get_stack (*, limit=None)

          Return the list of stack frames for this Task.

          If the wrapped coroutine is not done, this returns the stack
          where it is suspended.  If the coroutine has completed
          successfully or was cancelled, this returns an empty list.  If
          the coroutine was terminated by an exception, this returns the
          list of traceback frames.

          The frames are always ordered from oldest to newest.

          Only one stack frame is returned for a suspended coroutine.

          The optional `limit' argument sets the maximum number of
          frames to return; by default all available frames are
          returned.  The ordering of the returned list differs depending
          on whether a stack or a traceback is returned: the newest
          frames of a stack are returned, but the oldest frames of a
          traceback are returned.  (This matches the behavior of the
          traceback module.)

      -- Method: print_stack (*, limit=None, file=None)

          Print the stack or traceback for this Task.

          This produces output similar to that of the traceback module
          for the frames retrieved by *note get_stack(): 2664.

          The `limit' argument is passed to *note get_stack(): 2664.
          directly.

          The `file' argument is an I/O stream to which the output is
          written; by default output is written to *note sys.stderr:
          1ea.

      -- Method: get_coro ()

          Return the coroutine object wrapped by the *note Task: 2e0.

          New in version 3.8.

      -- Method: get_name ()

          Return the name of the Task.

          If no name has been explicitly assigned to the Task, the
          default asyncio Task implementation generates a default name
          during instantiation.

          New in version 3.8.

      -- Method: set_name (value)

          Set the name of the Task.

          The `value' argument can be any object, which is then
          converted to a string.

          In the default Task implementation, the name will be visible
          in the *note repr(): 8b9. output of a task object.

          New in version 3.8.


File: python.info,  Node: Generator-based Coroutines,  Prev: Task Object,  Up: Coroutines and Tasks

5.18.1.15 Generator-based Coroutines
....................................

     Note: Support for generator-based coroutines is `deprecated' and is
     scheduled for removal in Python 3.10.

Generator-based coroutines predate async/await syntax.  They are Python
generators that use ‘yield from’ expressions to await on Futures and
other coroutines.

Generator-based coroutines should be decorated with *note
@asyncio.coroutine: 3a8, although this is not enforced.

 -- Function: @asyncio.coroutine

     Decorator to mark generator-based coroutines.

     This decorator enables legacy generator-based coroutines to be
     compatible with async/await code:

          @asyncio.coroutine
          def old_style_coroutine():
              yield from asyncio.sleep(1)

          async def main():
              await old_style_coroutine()

     This decorator should not be used for *note async def: 3a9.
     coroutines.

     Deprecated since version 3.8, will be removed in version 3.10: Use
     *note async def: 3a9. instead.

 -- Function: asyncio.iscoroutine (obj)

     Return ‘True’ if `obj' is a *note coroutine object: 2637.

     This method is different from *note inspect.iscoroutine(): 7e8.
     because it returns ‘True’ for generator-based coroutines.

 -- Function: asyncio.iscoroutinefunction (func)

     Return ‘True’ if `func' is a *note coroutine function: 2637.

     This method is different from *note inspect.iscoroutinefunction():
     7e9. because it returns ‘True’ for generator-based coroutine
     functions decorated with *note @coroutine: 3a8.


File: python.info,  Node: Streams,  Next: Synchronization Primitives,  Prev: Coroutines and Tasks,  Up: asyncio — Asynchronous I/O

5.18.1.16 Streams
.................

`Source code:' Lib/asyncio/streams.py(1)

__________________________________________________________________

Streams are high-level async/await-ready primitives to work with network
connections.  Streams allow sending and receiving data without using
callbacks or low-level protocols and transports.  Here is an example of
a TCP echo client written using asyncio streams:

     import asyncio

     async def tcp_echo_client(message):
         reader, writer = await asyncio.open_connection(
             '127.0.0.1', 8888)

         print(f'Send: {message!r}')
         writer.write(message.encode())
         await writer.drain()

         data = await reader.read(100)
         print(f'Received: {data.decode()!r}')

         print('Close the connection')
         writer.close()
         await writer.wait_closed()

     asyncio.run(tcp_echo_client('Hello World!'))

See also the *note Examples: 266c. section below.

Stream Functions
................

The following top-level asyncio functions can be used to create and work
with streams:

 -- Function: coroutine asyncio.open_connection (host=None, port=None,
          *, loop=None, limit=None, ssl=None, family=0, proto=0,
          flags=0, sock=None, local_addr=None, server_hostname=None,
          ssl_handshake_timeout=None)

     Establish a network connection and return a pair of ‘(reader,
     writer)’ objects.

     The returned `reader' and `writer' objects are instances of *note
     StreamReader: 1105. and *note StreamWriter: 1106. classes.

     The `loop' argument is optional and can always be determined
     automatically when this function is awaited from a coroutine.

     `limit' determines the buffer size limit used by the returned *note
     StreamReader: 1105. instance.  By default the `limit' is set to 64
     KiB.

     The rest of the arguments are passed directly to *note
     loop.create_connection(): 2e5.

     New in version 3.7: The `ssl_handshake_timeout' parameter.

 -- Function: coroutine asyncio.start_server (client_connected_cb,
          host=None, port=None, *, loop=None, limit=None,
          family=socket.AF_UNSPEC, flags=socket.AI_PASSIVE, sock=None,
          backlog=100, ssl=None, reuse_address=None, reuse_port=None,
          ssl_handshake_timeout=None, start_serving=True)

     Start a socket server.

     The `client_connected_cb' callback is called whenever a new client
     connection is established.  It receives a ‘(reader, writer)’ pair
     as two arguments, instances of the *note StreamReader: 1105. and
     *note StreamWriter: 1106. classes.

     `client_connected_cb' can be a plain callable or a *note coroutine
     function: 2637.; if it is a coroutine function, it will be
     automatically scheduled as a *note Task: 2e0.

     The `loop' argument is optional and can always be determined
     automatically when this method is awaited from a coroutine.

     `limit' determines the buffer size limit used by the returned *note
     StreamReader: 1105. instance.  By default the `limit' is set to 64
     KiB.

     The rest of the arguments are passed directly to *note
     loop.create_server(): 465.

     New in version 3.7: The `ssl_handshake_timeout' and `start_serving'
     parameters.

Unix Sockets
............

 -- Function: coroutine asyncio.open_unix_connection (path=None, *,
          loop=None, limit=None, ssl=None, sock=None,
          server_hostname=None, ssl_handshake_timeout=None)

     Establish a Unix socket connection and return a pair of ‘(reader,
     writer)’.

     Similar to *note open_connection(): 46b. but operates on Unix
     sockets.

     See also the documentation of *note loop.create_unix_connection():
     266e.

     *note Availability: 1491.: Unix.

     New in version 3.7: The `ssl_handshake_timeout' parameter.

     Changed in version 3.7: The `path' parameter can now be a *note
     path-like object: 472.

 -- Function: coroutine asyncio.start_unix_server (client_connected_cb,
          path=None, *, loop=None, limit=None, sock=None, backlog=100,
          ssl=None, ssl_handshake_timeout=None, start_serving=True)

     Start a Unix socket server.

     Similar to *note start_server(): 46c. but works with Unix sockets.

     See also the documentation of *note loop.create_unix_server(): 466.

     *note Availability: 1491.: Unix.

     New in version 3.7: The `ssl_handshake_timeout' and `start_serving'
     parameters.

     Changed in version 3.7: The `path' parameter can now be a *note
     path-like object: 472.

* Menu:

* StreamReader::
* StreamWriter::
* Examples: Examples<12>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/asyncio/streams.py


File: python.info,  Node: StreamReader,  Next: StreamWriter,  Up: Streams

5.18.1.17 StreamReader
......................

 -- Class: asyncio.StreamReader

     Represents a reader object that provides APIs to read data from the
     IO stream.

     It is not recommended to instantiate `StreamReader' objects
     directly; use *note open_connection(): 46b. and *note
     start_server(): 46c. instead.

      -- Method: coroutine read (n=-1)

          Read up to `n' bytes.  If `n' is not provided, or set to ‘-1’,
          read until EOF and return all read bytes.

          If EOF was received and the internal buffer is empty, return
          an empty ‘bytes’ object.

      -- Method: coroutine readline ()

          Read one line, where “line” is a sequence of bytes ending with
          ‘\n’.

          If EOF is received and ‘\n’ was not found, the method returns
          partially read data.

          If EOF is received and the internal buffer is empty, return an
          empty ‘bytes’ object.

      -- Method: coroutine readexactly (n)

          Read exactly `n' bytes.

          Raise an *note IncompleteReadError: fdb. if EOF is reached
          before `n' can be read.  Use the *note
          IncompleteReadError.partial: 2673. attribute to get the
          partially read data.

      -- Method: coroutine readuntil (separator=b'\n')

          Read data from the stream until `separator' is found.

          On success, the data and separator will be removed from the
          internal buffer (consumed).  Returned data will include the
          separator at the end.

          If the amount of data read exceeds the configured stream
          limit, a *note LimitOverrunError: 2674. exception is raised,
          and the data is left in the internal buffer and can be read
          again.

          If EOF is reached before the complete separator is found, an
          *note IncompleteReadError: fdb. exception is raised, and the
          internal buffer is reset.  The *note
          IncompleteReadError.partial: 2673. attribute may contain a
          portion of the separator.

          New in version 3.5.2.

      -- Method: at_eof ()

          Return ‘True’ if the buffer is empty and ‘feed_eof()’ was
          called.


File: python.info,  Node: StreamWriter,  Next: Examples<12>,  Prev: StreamReader,  Up: Streams

5.18.1.18 StreamWriter
......................

 -- Class: asyncio.StreamWriter

     Represents a writer object that provides APIs to write data to the
     IO stream.

     It is not recommended to instantiate `StreamWriter' objects
     directly; use *note open_connection(): 46b. and *note
     start_server(): 46c. instead.

      -- Method: write (data)

          The method attempts to write the `data' to the underlying
          socket immediately.  If that fails, the data is queued in an
          internal write buffer until it can be sent.

          The method should be used along with the ‘drain()’ method:

               stream.write(data)
               await stream.drain()

      -- Method: writelines (data)

          The method writes a list (or any iterable) of bytes to the
          underlying socket immediately.  If that fails, the data is
          queued in an internal write buffer until it can be sent.

          The method should be used along with the ‘drain()’ method:

               stream.writelines(lines)
               await stream.drain()

      -- Method: close ()

          The method closes the stream and the underlying socket.

          The method should be used along with the ‘wait_closed()’
          method:

               stream.close()
               await stream.wait_closed()

      -- Method: can_write_eof ()

          Return ‘True’ if the underlying transport supports the *note
          write_eof(): 267b. method, ‘False’ otherwise.

      -- Method: write_eof ()

          Close the write end of the stream after the buffered write
          data is flushed.

      -- Attribute: transport

          Return the underlying asyncio transport.

      -- Method: get_extra_info (name, default=None)

          Access optional transport information; see *note
          BaseTransport.get_extra_info(): 3ea. for details.

      -- Method: coroutine drain ()

          Wait until it is appropriate to resume writing to the stream.
          Example:

               writer.write(data)
               await writer.drain()

          This is a flow control method that interacts with the
          underlying IO write buffer.  When the size of the buffer
          reaches the high watermark, `drain()' blocks until the size of
          the buffer is drained down to the low watermark and writing
          can be resumed.  When there is nothing to wait for, the *note
          drain(): 267e. returns immediately.

      -- Method: is_closing ()

          Return ‘True’ if the stream is closed or in the process of
          being closed.

          New in version 3.7.

      -- Method: coroutine wait_closed ()

          Wait until the stream is closed.

          Should be called after *note close(): 2679. to wait until the
          underlying connection is closed.

          New in version 3.7.


File: python.info,  Node: Examples<12>,  Prev: StreamWriter,  Up: Streams

5.18.1.19 Examples
..................

* Menu:

* TCP echo client using streams::
* TCP echo server using streams::
* Get HTTP headers::
* Register an open socket to wait for data using streams::


File: python.info,  Node: TCP echo client using streams,  Next: TCP echo server using streams,  Up: Examples<12>

5.18.1.20 TCP echo client using streams
.......................................

TCP echo client using the *note asyncio.open_connection(): 46b.
function:

     import asyncio

     async def tcp_echo_client(message):
         reader, writer = await asyncio.open_connection(
             '127.0.0.1', 8888)

         print(f'Send: {message!r}')
         writer.write(message.encode())

         data = await reader.read(100)
         print(f'Received: {data.decode()!r}')

         print('Close the connection')
         writer.close()

     asyncio.run(tcp_echo_client('Hello World!'))

See also
........

The *note TCP echo client protocol: 2681. example uses the low-level
*note loop.create_connection(): 2e5. method.


File: python.info,  Node: TCP echo server using streams,  Next: Get HTTP headers,  Prev: TCP echo client using streams,  Up: Examples<12>

5.18.1.21 TCP echo server using streams
.......................................

TCP echo server using the *note asyncio.start_server(): 46c. function:

     import asyncio

     async def handle_echo(reader, writer):
         data = await reader.read(100)
         message = data.decode()
         addr = writer.get_extra_info('peername')

         print(f"Received {message!r} from {addr!r}")

         print(f"Send: {message!r}")
         writer.write(data)
         await writer.drain()

         print("Close the connection")
         writer.close()

     async def main():
         server = await asyncio.start_server(
             handle_echo, '127.0.0.1', 8888)

         addrs = ', '.join(str(sock.getsockname()) for sock in server.sockets)
         print(f'Serving on {addrs}')

         async with server:
             await server.serve_forever()

     asyncio.run(main())

See also
........

The *note TCP echo server protocol: 2684. example uses the *note
loop.create_server(): 465. method.


File: python.info,  Node: Get HTTP headers,  Next: Register an open socket to wait for data using streams,  Prev: TCP echo server using streams,  Up: Examples<12>

5.18.1.22 Get HTTP headers
..........................

Simple example querying HTTP headers of the URL passed on the command
line:

     import asyncio
     import urllib.parse
     import sys

     async def print_http_headers(url):
         url = urllib.parse.urlsplit(url)
         if url.scheme == 'https':
             reader, writer = await asyncio.open_connection(
                 url.hostname, 443, ssl=True)
         else:
             reader, writer = await asyncio.open_connection(
                 url.hostname, 80)

         query = (
             f"HEAD {url.path or '/'} HTTP/1.0\r\n"
             f"Host: {url.hostname}\r\n"
             f"\r\n"
         )

         writer.write(query.encode('latin-1'))
         while True:
             line = await reader.readline()
             if not line:
                 break

             line = line.decode('latin1').rstrip()
             if line:
                 print(f'HTTP header> {line}')

         # Ignore the body, close the socket
         writer.close()

     url = sys.argv[1]
     asyncio.run(print_http_headers(url))

Usage:

     python example.py http://example.com/path/page.html

or with HTTPS:

     python example.py https://example.com/path/page.html


File: python.info,  Node: Register an open socket to wait for data using streams,  Prev: Get HTTP headers,  Up: Examples<12>

5.18.1.23 Register an open socket to wait for data using streams
................................................................

Coroutine waiting until a socket receives data using the *note
open_connection(): 46b. function:

     import asyncio
     import socket

     async def wait_for_data():
         # Get a reference to the current event loop because
         # we want to access low-level APIs.
         loop = asyncio.get_running_loop()

         # Create a pair of connected sockets.
         rsock, wsock = socket.socketpair()

         # Register the open socket to wait for data.
         reader, writer = await asyncio.open_connection(sock=rsock)

         # Simulate the reception of data from the network
         loop.call_soon(wsock.send, 'abc'.encode())

         # Wait for data
         data = await reader.read(100)

         # Got data, we are done: close the socket
         print("Received:", data.decode())
         writer.close()

         # Close the second socket
         wsock.close()

     asyncio.run(wait_for_data())

See also
........

The *note register an open socket to wait for data using a protocol:
2688. example uses a low-level protocol and the *note
loop.create_connection(): 2e5. method.

The *note watch a file descriptor for read events: 2689. example uses
the low-level *note loop.add_reader(): 268a. method to watch a file
descriptor.


File: python.info,  Node: Synchronization Primitives,  Next: Subprocesses,  Prev: Streams,  Up: asyncio — Asynchronous I/O

5.18.1.24 Synchronization Primitives
....................................

`Source code:' Lib/asyncio/locks.py(1)

__________________________________________________________________

asyncio synchronization primitives are designed to be similar to those
of the *note threading: 10b. module with two important caveats:

   * asyncio primitives are not thread-safe, therefore they should not
     be used for OS thread synchronization (use *note threading: 10b.
     for that);

   * methods of these synchronization primitives do not accept the
     `timeout' argument; use the *note asyncio.wait_for(): 191. function
     to perform operations with timeouts.

asyncio has the following basic synchronization primitives:

   * *note Lock: 3ae.

   * *note Event: 3af.

   * *note Condition: 3b0.

   * *note Semaphore: 3b1.

   * *note BoundedSemaphore: 3b2.

__________________________________________________________________

* Menu:

* Lock::
* Event::
* Condition::
* Semaphore::
* BoundedSemaphore::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/asyncio/locks.py


File: python.info,  Node: Lock,  Next: Event,  Up: Synchronization Primitives

5.18.1.25 Lock
..............

 -- Class: asyncio.Lock (*, loop=None)

     Implements a mutex lock for asyncio tasks.  Not thread-safe.

     An asyncio lock can be used to guarantee exclusive access to a
     shared resource.

     The preferred way to use a Lock is an *note async with: 736.
     statement:

          lock = asyncio.Lock()

          # ... later
          async with lock:
              # access shared state

     which is equivalent to:

          lock = asyncio.Lock()

          # ... later
          await lock.acquire()
          try:
              # access shared state
          finally:
              lock.release()

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

      -- Method: coroutine acquire ()

          Acquire the lock.

          This method waits until the lock is `unlocked', sets it to
          `locked' and returns ‘True’.

          When more than one coroutine is blocked in *note acquire():
          268e. waiting for the lock to be unlocked, only one coroutine
          eventually proceeds.

          Acquiring a lock is `fair': the coroutine that proceeds will
          be the first coroutine that started waiting on the lock.

      -- Method: release ()

          Release the lock.

          When the lock is `locked', reset it to `unlocked' and return.

          If the lock is `unlocked', a *note RuntimeError: 3dc. is
          raised.

      -- Method: locked ()

          Return ‘True’ if the lock is `locked'.


File: python.info,  Node: Event,  Next: Condition,  Prev: Lock,  Up: Synchronization Primitives

5.18.1.26 Event
...............

 -- Class: asyncio.Event (*, loop=None)

     An event object.  Not thread-safe.

     An asyncio event can be used to notify multiple asyncio tasks that
     some event has happened.

     An Event object manages an internal flag that can be set to `true'
     with the *note set(): 2692. method and reset to `false' with the
     *note clear(): 2693. method.  The *note wait(): 2694. method blocks
     until the flag is set to `true'.  The flag is set to `false'
     initially.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

     Example:

          async def waiter(event):
              print('waiting for it ...')
              await event.wait()
              print('... got it!')

          async def main():
              # Create an Event object.
              event = asyncio.Event()

              # Spawn a Task to wait until 'event' is set.
              waiter_task = asyncio.create_task(waiter(event))

              # Sleep for 1 second and set the event.
              await asyncio.sleep(1)
              event.set()

              # Wait until the waiter task is finished.
              await waiter_task

          asyncio.run(main())

      -- Method: coroutine wait ()

          Wait until the event is set.

          If the event is set, return ‘True’ immediately.  Otherwise
          block until another task calls *note set(): 2692.

      -- Method: set ()

          Set the event.

          All tasks waiting for event to be set will be immediately
          awakened.

      -- Method: clear ()

          Clear (unset) the event.

          Tasks awaiting on *note wait(): 2694. will now block until the
          *note set(): 2692. method is called again.

      -- Method: is_set ()

          Return ‘True’ if the event is set.


File: python.info,  Node: Condition,  Next: Semaphore,  Prev: Event,  Up: Synchronization Primitives

5.18.1.27 Condition
...................

 -- Class: asyncio.Condition (lock=None, *, loop=None)

     A Condition object.  Not thread-safe.

     An asyncio condition primitive can be used by a task to wait for
     some event to happen and then get exclusive access to a shared
     resource.

     In essence, a Condition object combines the functionality of an
     *note Event: 3af. and a *note Lock: 3ae.  It is possible to have
     multiple Condition objects share one Lock, which allows
     coordinating exclusive access to a shared resource between
     different tasks interested in particular states of that shared
     resource.

     The optional `lock' argument must be a *note Lock: 3ae. object or
     ‘None’.  In the latter case a new Lock object is created
     automatically.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

     The preferred way to use a Condition is an *note async with: 736.
     statement:

          cond = asyncio.Condition()

          # ... later
          async with cond:
              await cond.wait()

     which is equivalent to:

          cond = asyncio.Condition()

          # ... later
          await cond.acquire()
          try:
              await cond.wait()
          finally:
              cond.release()

      -- Method: coroutine acquire ()

          Acquire the underlying lock.

          This method waits until the underlying lock is `unlocked',
          sets it to `locked' and returns ‘True’.

      -- Method: notify (n=1)

          Wake up at most `n' tasks (1 by default) waiting on this
          condition.  The method is no-op if no tasks are waiting.

          The lock must be acquired before this method is called and
          released shortly after.  If called with an `unlocked' lock a
          *note RuntimeError: 3dc. error is raised.

      -- Method: locked ()

          Return ‘True’ if the underlying lock is acquired.

      -- Method: notify_all ()

          Wake up all tasks waiting on this condition.

          This method acts like *note notify(): 2699, but wakes up all
          waiting tasks.

          The lock must be acquired before this method is called and
          released shortly after.  If called with an `unlocked' lock a
          *note RuntimeError: 3dc. error is raised.

      -- Method: release ()

          Release the underlying lock.

          When invoked on an unlocked lock, a *note RuntimeError: 3dc.
          is raised.

      -- Method: coroutine wait ()

          Wait until notified.

          If the calling task has not acquired the lock when this method
          is called, a *note RuntimeError: 3dc. is raised.

          This method releases the underlying lock, and then blocks
          until it is awakened by a *note notify(): 2699. or *note
          notify_all(): 269b. call.  Once awakened, the Condition
          re-acquires its lock and this method returns ‘True’.

      -- Method: coroutine wait_for (predicate)

          Wait until a predicate becomes `true'.

          The predicate must be a callable which result will be
          interpreted as a boolean value.  The final value is the return
          value.


File: python.info,  Node: Semaphore,  Next: BoundedSemaphore,  Prev: Condition,  Up: Synchronization Primitives

5.18.1.28 Semaphore
...................

 -- Class: asyncio.Semaphore (value=1, *, loop=None)

     A Semaphore object.  Not thread-safe.

     A semaphore manages an internal counter which is decremented by
     each *note acquire(): 26a0. call and incremented by each *note
     release(): 26a1. call.  The counter can never go below zero; when
     *note acquire(): 26a0. finds that it is zero, it blocks, waiting
     until some task calls *note release(): 26a1.

     The optional `value' argument gives the initial value for the
     internal counter (‘1’ by default).  If the given value is less than
     ‘0’ a *note ValueError: 16d. is raised.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

     The preferred way to use a Semaphore is an *note async with: 736.
     statement:

          sem = asyncio.Semaphore(10)

          # ... later
          async with sem:
              # work with shared resource

     which is equivalent to:

          sem = asyncio.Semaphore(10)

          # ... later
          await sem.acquire()
          try:
              # work with shared resource
          finally:
              sem.release()

      -- Method: coroutine acquire ()

          Acquire a semaphore.

          If the internal counter is greater than zero, decrement it by
          one and return ‘True’ immediately.  If it is zero, wait until
          a *note release(): 26a1. is called and return ‘True’.

      -- Method: locked ()

          Returns ‘True’ if semaphore can not be acquired immediately.

      -- Method: release ()

          Release a semaphore, incrementing the internal counter by one.
          Can wake up a task waiting to acquire the semaphore.

          Unlike *note BoundedSemaphore: 3b2, *note Semaphore: 3b1.
          allows making more ‘release()’ calls than ‘acquire()’ calls.


File: python.info,  Node: BoundedSemaphore,  Prev: Semaphore,  Up: Synchronization Primitives

5.18.1.29 BoundedSemaphore
..........................

 -- Class: asyncio.BoundedSemaphore (value=1, *, loop=None)

     A bounded semaphore object.  Not thread-safe.

     Bounded Semaphore is a version of *note Semaphore: 3b1. that raises
     a *note ValueError: 16d. in *note release(): 26a1. if it increases
     the internal counter above the initial `value'.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

__________________________________________________________________

Changed in version 3.9: Acquiring a lock using ‘await lock’ or ‘yield
from lock’ and/or *note with: 7da. statement (‘with await lock’, ‘with
(yield from lock)’) was removed.  Use ‘async with lock’ instead.


File: python.info,  Node: Subprocesses,  Next: Queues,  Prev: Synchronization Primitives,  Up: asyncio — Asynchronous I/O

5.18.1.30 Subprocesses
......................

`Source code:' Lib/asyncio/subprocess.py(1),
Lib/asyncio/base_subprocess.py(2)

__________________________________________________________________

This section describes high-level async/await asyncio APIs to create and
manage subprocesses.  Here’s an example of how asyncio can run a shell
command and obtain its result:

     import asyncio

     async def run(cmd):
         proc = await asyncio.create_subprocess_shell(
             cmd,
             stdout=asyncio.subprocess.PIPE,
             stderr=asyncio.subprocess.PIPE)

         stdout, stderr = await proc.communicate()

         print(f'[{cmd!r} exited with {proc.returncode}]')
         if stdout:
             print(f'[stdout]\n{stdout.decode()}')
         if stderr:
             print(f'[stderr]\n{stderr.decode()}')

     asyncio.run(run('ls /zzz'))

will print:

     ['ls /zzz' exited with 1]
     [stderr]
     ls: /zzz: No such file or directory

Because all asyncio subprocess functions are asynchronous and asyncio
provides many tools to work with such functions, it is easy to execute
and monitor multiple subprocesses in parallel.  It is indeed trivial to
modify the above example to run several commands simultaneously:

     async def main():
         await asyncio.gather(
             run('ls /zzz'),
             run('sleep 1; echo "hello"'))

     asyncio.run(main())

See also the *note Examples: 26a7. subsection.

* Menu:

* Creating Subprocesses::
* Constants: Constants<7>.
* Interacting with Subprocesses::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/asyncio/subprocess.py

   (2) 
https://github.com/python/cpython/tree/3.9/Lib/asyncio/base_subprocess.py


File: python.info,  Node: Creating Subprocesses,  Next: Constants<7>,  Up: Subprocesses

5.18.1.31 Creating Subprocesses
...............................

 -- Function: coroutine asyncio.create_subprocess_exec (program, *args,
          stdin=None, stdout=None, stderr=None, loop=None, limit=None,
          **kwds)

     Create a subprocess.

     The `limit' argument sets the buffer limit for *note StreamReader:
     1105. wrappers for ‘Process.stdout’ and ‘Process.stderr’ (if *note
     subprocess.PIPE: 4f4. is passed to `stdout' and `stderr'
     arguments).

     Return a *note Process: 26a9. instance.

     See the documentation of *note loop.subprocess_exec(): 263c. for
     other parameters.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

 -- Function: coroutine asyncio.create_subprocess_shell (cmd,
          stdin=None, stdout=None, stderr=None, loop=None, limit=None,
          **kwds)

     Run the `cmd' shell command.

     The `limit' argument sets the buffer limit for *note StreamReader:
     1105. wrappers for ‘Process.stdout’ and ‘Process.stderr’ (if *note
     subprocess.PIPE: 4f4. is passed to `stdout' and `stderr'
     arguments).

     Return a *note Process: 26a9. instance.

     See the documentation of *note loop.subprocess_shell(): 26aa. for
     other parameters.

          Important: It is the application’s responsibility to ensure
          that all whitespace and special characters are quoted
          appropriately to avoid shell injection(1) vulnerabilities.
          The *note shlex.quote(): b4e. function can be used to properly
          escape whitespace and special shell characters in strings that
          are going to be used to construct shell commands.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

     Note: Subprocesses are available for Windows if a *note
     ProactorEventLoop: 2de. is used.  See *note Subprocess Support on
     Windows: 26ab. for details.

See also
........

asyncio also has the following `low-level' APIs to work with
subprocesses: *note loop.subprocess_exec(): 263c, *note
loop.subprocess_shell(): 26aa, *note loop.connect_read_pipe(): 26ac,
*note loop.connect_write_pipe(): 26ad, as well as the *note Subprocess
Transports: 26ae. and *note Subprocess Protocols: 26af.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Shell_injection#Shell_injection


File: python.info,  Node: Constants<7>,  Next: Interacting with Subprocesses,  Prev: Creating Subprocesses,  Up: Subprocesses

5.18.1.32 Constants
...................

 -- Data: asyncio.subprocess.PIPE

     Can be passed to the `stdin', `stdout' or `stderr' parameters.

     If `PIPE' is passed to `stdin' argument, the *note Process.stdin:
     26b2. attribute will point to a *note StreamWriter: 1106. instance.

     If `PIPE' is passed to `stdout' or `stderr' arguments, the *note
     Process.stdout: 26b3. and *note Process.stderr: 26b4. attributes
     will point to *note StreamReader: 1105. instances.

 -- Data: asyncio.subprocess.STDOUT

     Special value that can be used as the `stderr' argument and
     indicates that standard error should be redirected into standard
     output.

 -- Data: asyncio.subprocess.DEVNULL

     Special value that can be used as the `stdin', `stdout' or `stderr'
     argument to process creation functions.  It indicates that the
     special file *note os.devnull: 1152. will be used for the
     corresponding subprocess stream.


File: python.info,  Node: Interacting with Subprocesses,  Prev: Constants<7>,  Up: Subprocesses

5.18.1.33 Interacting with Subprocesses
.......................................

Both *note create_subprocess_exec(): 3b4. and *note
create_subprocess_shell(): 3b5. functions return instances of the
`Process' class.  `Process' is a high-level wrapper that allows
communicating with subprocesses and watching for their completion.

 -- Class: asyncio.subprocess.Process

     An object that wraps OS processes created by the *note
     create_subprocess_exec(): 3b4. and *note create_subprocess_shell():
     3b5. functions.

     This class is designed to have a similar API to the *note
     subprocess.Popen: 3db. class, but there are some notable
     differences:

        * unlike Popen, Process instances do not have an equivalent to
          the *note poll(): 25d2. method;

        * the *note communicate(): 26b8. and *note wait(): 26b9. methods
          don’t have a `timeout' parameter: use the *note wait_for():
          191. function;

        * the *note Process.wait(): 26b9. method is asynchronous,
          whereas *note subprocess.Popen.wait(): 689. method is
          implemented as a blocking busy loop;

        * the `universal_newlines' parameter is not supported.

     This class is *note not thread safe: 2655.

     See also the *note Subprocess and Threads: 26ba. section.

      -- Method: coroutine wait ()

          Wait for the child process to terminate.

          Set and return the *note returncode: 26bb. attribute.

               Note: This method can deadlock when using ‘stdout=PIPE’
               or ‘stderr=PIPE’ and the child process generates so much
               output that it blocks waiting for the OS pipe buffer to
               accept more data.  Use the *note communicate(): 26b8.
               method when using pipes to avoid this condition.

      -- Method: coroutine communicate (input=None)

          Interact with process:

            1. send data to `stdin' (if `input' is not ‘None’);

            2. read data from `stdout' and `stderr', until EOF is
               reached;

            3. wait for process to terminate.

          The optional `input' argument is the data (*note bytes: 172.
          object) that will be sent to the child process.

          Return a tuple ‘(stdout_data, stderr_data)’.

          If either *note BrokenPipeError: a7e. or *note
          ConnectionResetError: a81. exception is raised when writing
          `input' into `stdin', the exception is ignored.  This
          condition occurs when the process exits before all data are
          written into `stdin'.

          If it is desired to send data to the process’ `stdin', the
          process needs to be created with ‘stdin=PIPE’.  Similarly, to
          get anything other than ‘None’ in the result tuple, the
          process has to be created with ‘stdout=PIPE’ and/or
          ‘stderr=PIPE’ arguments.

          Note, that the data read is buffered in memory, so do not use
          this method if the data size is large or unlimited.

      -- Method: send_signal (signal)

          Sends the signal `signal' to the child process.

               Note: On Windows, ‘SIGTERM’ is an alias for *note
               terminate(): 26bd.  ‘CTRL_C_EVENT’ and ‘CTRL_BREAK_EVENT’
               can be sent to processes started with a `creationflags'
               parameter which includes ‘CREATE_NEW_PROCESS_GROUP’.

      -- Method: terminate ()

          Stop the child process.

          On POSIX systems this method sends *note signal.SIGTERM: 26be.
          to the child process.

          On Windows the Win32 API function ‘TerminateProcess()’ is
          called to stop the child process.

      -- Method: kill ()

          Kill the child process.

          On POSIX systems this method sends ‘SIGKILL’ to the child
          process.

          On Windows this method is an alias for *note terminate():
          26bd.

      -- Attribute: stdin

          Standard input stream (*note StreamWriter: 1106.) or ‘None’ if
          the process was created with ‘stdin=None’.

      -- Attribute: stdout

          Standard output stream (*note StreamReader: 1105.) or ‘None’
          if the process was created with ‘stdout=None’.

      -- Attribute: stderr

          Standard error stream (*note StreamReader: 1105.) or ‘None’ if
          the process was created with ‘stderr=None’.

          Warning: Use the *note communicate(): 26b8. method rather than
          *note process.stdin.write(): 26b2, *note await
          process.stdout.read(): 26b3. or *note await
          process.stderr.read: 26b4.  This avoids deadlocks due to
          streams pausing reading or writing and blocking the child
          process.

      -- Attribute: pid

          Process identification number (PID).

          Note that for processes created by the *note
          create_subprocess_shell(): 3b5. function, this attribute is
          the PID of the spawned shell.

      -- Attribute: returncode

          Return code of the process when it exits.

          A ‘None’ value indicates that the process has not terminated
          yet.

          A negative value ‘-N’ indicates that the child was terminated
          by signal ‘N’ (POSIX only).

* Menu:

* Subprocess and Threads::
* Examples: Examples<13>.


File: python.info,  Node: Subprocess and Threads,  Next: Examples<13>,  Up: Interacting with Subprocesses

5.18.1.34 Subprocess and Threads
................................

Standard asyncio event loop supports running subprocesses from different
threads by default.

On Windows subprocesses are provided by *note ProactorEventLoop: 2de.
only (default), *note SelectorEventLoop: 26c2. has no subprocess
support.

On UNIX `child watchers' are used for subprocess finish waiting, see
*note Process Watchers: 26c3. for more info.

Changed in version 3.8: UNIX switched to use *note ThreadedChildWatcher:
26c4. for spawning subprocesses from different threads without any
limitation.

Spawning a subprocess with `inactive' current child watcher raises *note
RuntimeError: 3dc.

Note that alternative event loop implementations might have own
limitations; please refer to their documentation.

See also
........

The *note Concurrency and multithreading in asyncio: 2655. section.


File: python.info,  Node: Examples<13>,  Prev: Subprocess and Threads,  Up: Interacting with Subprocesses

5.18.1.35 Examples
..................

An example using the *note Process: 26a9. class to control a subprocess
and the *note StreamReader: 1105. class to read from its standard
output.  The subprocess is created by the *note
create_subprocess_exec(): 3b4. function:

     import asyncio
     import sys

     async def get_date():
         code = 'import datetime; print(datetime.datetime.now())'

         # Create the subprocess; redirect the standard output
         # into a pipe.
         proc = await asyncio.create_subprocess_exec(
             sys.executable, '-c', code,
             stdout=asyncio.subprocess.PIPE)

         # Read one line of output.
         data = await proc.stdout.readline()
         line = data.decode('ascii').rstrip()

         # Wait for the subprocess exit.
         await proc.wait()
         return line

     date = asyncio.run(get_date())
     print(f"Current date: {date}")

See also the *note same example: 26c6. written using low-level APIs.


File: python.info,  Node: Queues,  Next: Exceptions<10>,  Prev: Subprocesses,  Up: asyncio — Asynchronous I/O

5.18.1.36 Queues
................

`Source code:' Lib/asyncio/queues.py(1)

__________________________________________________________________

asyncio queues are designed to be similar to classes of the *note queue:
da. module.  Although asyncio queues are not thread-safe, they are
designed to be used specifically in async/await code.

Note that methods of asyncio queues don’t have a `timeout' parameter;
use *note asyncio.wait_for(): 191. function to do queue operations with
a timeout.

See also the *note Examples: 26c9. section below.

* Menu:

* Queue::
* Priority Queue::
* LIFO Queue::
* Exceptions: Exceptions<9>.
* Examples: Examples<14>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/asyncio/queues.py


File: python.info,  Node: Queue,  Next: Priority Queue,  Up: Queues

5.18.1.37 Queue
...............

 -- Class: asyncio.Queue (maxsize=0, *, loop=None)

     A first in, first out (FIFO) queue.

     If `maxsize' is less than or equal to zero, the queue size is
     infinite.  If it is an integer greater than ‘0’, then ‘await put()’
     blocks when the queue reaches `maxsize' until an item is removed by
     *note get(): 26cb.

     Unlike the standard library threading *note queue: da, the size of
     the queue is always known and can be returned by calling the *note
     qsize(): 26cc. method.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `loop' parameter.

     This class is *note not thread safe: 2655.

      -- Attribute: maxsize

          Number of items allowed in the queue.

      -- Method: empty ()

          Return ‘True’ if the queue is empty, ‘False’ otherwise.

      -- Method: full ()

          Return ‘True’ if there are *note maxsize: 26cd. items in the
          queue.

          If the queue was initialized with ‘maxsize=0’ (the default),
          then *note full(): 26cf. never returns ‘True’.

      -- Method: coroutine get ()

          Remove and return an item from the queue.  If queue is empty,
          wait until an item is available.

      -- Method: get_nowait ()

          Return an item if one is immediately available, else raise
          *note QueueEmpty: 26d1.

      -- Method: coroutine join ()

          Block until all items in the queue have been received and
          processed.

          The count of unfinished tasks goes up whenever an item is
          added to the queue.  The count goes down whenever a consumer
          coroutine calls *note task_done(): 793. to indicate that the
          item was retrieved and all work on it is complete.  When the
          count of unfinished tasks drops to zero, *note join(): 792.
          unblocks.

      -- Method: coroutine put (item)

          Put an item into the queue.  If the queue is full, wait until
          a free slot is available before adding the item.

      -- Method: put_nowait (item)

          Put an item into the queue without blocking.

          If no free slot is immediately available, raise *note
          QueueFull: 26d4.

      -- Method: qsize ()

          Return the number of items in the queue.

      -- Method: task_done ()

          Indicate that a formerly enqueued task is complete.

          Used by queue consumers.  For each *note get(): 26cb. used to
          fetch a task, a subsequent call to *note task_done(): 793.
          tells the queue that the processing on the task is complete.

          If a *note join(): 792. is currently blocking, it will resume
          when all items have been processed (meaning that a *note
          task_done(): 793. call was received for every item that had
          been *note put(): 26d2. into the queue).

          Raises *note ValueError: 16d. if called more times than there
          were items placed in the queue.


File: python.info,  Node: Priority Queue,  Next: LIFO Queue,  Prev: Queue,  Up: Queues

5.18.1.38 Priority Queue
........................

 -- Class: asyncio.PriorityQueue

     A variant of *note Queue: 3b3.; retrieves entries in priority order
     (lowest first).

     Entries are typically tuples of the form ‘(priority_number, data)’.


File: python.info,  Node: LIFO Queue,  Next: Exceptions<9>,  Prev: Priority Queue,  Up: Queues

5.18.1.39 LIFO Queue
....................

 -- Class: asyncio.LifoQueue

     A variant of *note Queue: 3b3. that retrieves most recently added
     entries first (last in, first out).


File: python.info,  Node: Exceptions<9>,  Next: Examples<14>,  Prev: LIFO Queue,  Up: Queues

5.18.1.40 Exceptions
....................

 -- Exception: asyncio.QueueEmpty

     This exception is raised when the *note get_nowait(): 26d0. method
     is called on an empty queue.

 -- Exception: asyncio.QueueFull

     Exception raised when the *note put_nowait(): 26d3. method is
     called on a queue that has reached its `maxsize'.


File: python.info,  Node: Examples<14>,  Prev: Exceptions<9>,  Up: Queues

5.18.1.41 Examples
..................

Queues can be used to distribute workload between several concurrent
tasks:

     import asyncio
     import random
     import time


     async def worker(name, queue):
         while True:
             # Get a "work item" out of the queue.
             sleep_for = await queue.get()

             # Sleep for the "sleep_for" seconds.
             await asyncio.sleep(sleep_for)

             # Notify the queue that the "work item" has been processed.
             queue.task_done()

             print(f'{name} has slept for {sleep_for:.2f} seconds')


     async def main():
         # Create a queue that we will use to store our "workload".
         queue = asyncio.Queue()

         # Generate random timings and put them into the queue.
         total_sleep_time = 0
         for _ in range(20):
             sleep_for = random.uniform(0.05, 1.0)
             total_sleep_time += sleep_for
             queue.put_nowait(sleep_for)

         # Create three worker tasks to process the queue concurrently.
         tasks = []
         for i in range(3):
             task = asyncio.create_task(worker(f'worker-{i}', queue))
             tasks.append(task)

         # Wait until the queue is fully processed.
         started_at = time.monotonic()
         await queue.join()
         total_slept_for = time.monotonic() - started_at

         # Cancel our worker tasks.
         for task in tasks:
             task.cancel()
         # Wait until all worker tasks are cancelled.
         await asyncio.gather(*tasks, return_exceptions=True)

         print('====')
         print(f'3 workers slept in parallel for {total_slept_for:.2f} seconds')
         print(f'total expected sleep time: {total_sleep_time:.2f} seconds')


     asyncio.run(main())


File: python.info,  Node: Exceptions<10>,  Next: Event Loop,  Prev: Queues,  Up: asyncio — Asynchronous I/O

5.18.1.42 Exceptions
....................

`Source code:' Lib/asyncio/exceptions.py(1)

__________________________________________________________________

 -- Exception: asyncio.TimeoutError

     The operation has exceeded the given deadline.

          Important: This exception is different from the builtin *note
          TimeoutError: a7d. exception.

 -- Exception: asyncio.CancelledError

     The operation has been cancelled.

     This exception can be caught to perform custom operations when
     asyncio Tasks are cancelled.  In almost all situations the
     exception must be re-raised.

     Changed in version 3.8: *note CancelledError: 2da. is now a
     subclass of *note BaseException: 2db.

 -- Exception: asyncio.InvalidStateError

     Invalid internal state of *note Task: 2e0. or *note Future: 546.

     Can be raised in situations like setting a result value for a
     `Future' object that already has a result value set.

 -- Exception: asyncio.SendfileNotAvailableError

     The “sendfile” syscall is not available for the given socket or
     file type.

     A subclass of *note RuntimeError: 3dc.

 -- Exception: asyncio.IncompleteReadError

     The requested read operation did not complete fully.

     Raised by the *note asyncio stream APIs: 2638.

     This exception is a subclass of *note EOFError: d34.

      -- Attribute: expected

          The total number (*note int: 204.) of expected bytes.

      -- Attribute: partial

          A string of *note bytes: 172. read before the end of stream
          was reached.

 -- Exception: asyncio.LimitOverrunError

     Reached the buffer size limit while looking for a separator.

     Raised by the *note asyncio stream APIs: 2638.

      -- Attribute: consumed

          The total number of to be consumed bytes.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/asyncio/exceptions.py


File: python.info,  Node: Event Loop,  Next: Futures,  Prev: Exceptions<10>,  Up: asyncio — Asynchronous I/O

5.18.1.43 Event Loop
....................

`Source code:' Lib/asyncio/events.py(1), Lib/asyncio/base_events.py(2)

__________________________________________________________________

Preface
.......

The event loop is the core of every asyncio application.  Event loops
run asynchronous tasks and callbacks, perform network IO operations, and
run subprocesses.

Application developers should typically use the high-level asyncio
functions, such as *note asyncio.run(): 18d, and should rarely need to
reference the loop object or call its methods.  This section is intended
mostly for authors of lower-level code, libraries, and frameworks, who
need finer control over the event loop behavior.

Obtaining the Event Loop
........................

The following low-level functions can be used to get, set, or create an
event loop:

 -- Function: asyncio.get_running_loop ()

     Return the running event loop in the current OS thread.

     If there is no running event loop a *note RuntimeError: 3dc. is
     raised.  This function can only be called from a coroutine or a
     callback.

     New in version 3.7.

 -- Function: asyncio.get_event_loop ()

     Get the current event loop.

     If there is no current event loop set in the current OS thread, the
     OS thread is main, and *note set_event_loop(): 26e3. has not yet
     been called, asyncio will create a new event loop and set it as the
     current one.

     Because this function has rather complex behavior (especially when
     custom event loop policies are in use), using the *note
     get_running_loop(): 45c. function is preferred to *note
     get_event_loop(): 45d. in coroutines and callbacks.

     Consider also using the *note asyncio.run(): 18d. function instead
     of using lower level functions to manually create and close an
     event loop.

 -- Function: asyncio.set_event_loop (loop)

     Set `loop' as a current event loop for the current OS thread.

 -- Function: asyncio.new_event_loop ()

     Create and return a new event loop object.

Note that the behaviour of *note get_event_loop(): 45d, *note
set_event_loop(): 26e3, and *note new_event_loop(): 26e4. functions can
be altered by *note setting a custom event loop policy: 26e5.

Contents
........

This documentation page contains the following sections:

   * The *note Event Loop Methods: 26e6. section is the reference
     documentation of the event loop APIs;

   * The *note Callback Handles: 26e7. section documents the *note
     Handle: 11d7. and *note TimerHandle: 26e8. instances which are
     returned from scheduling methods such as *note loop.call_soon():
     455. and *note loop.call_later(): 457.;

   * The *note Server Objects: 26e9. section documents types returned
     from event loop methods like *note loop.create_server(): 465.;

   * The *note Event Loop Implementations: 26ea. section documents the
     *note SelectorEventLoop: 26c2. and *note ProactorEventLoop: 2de.
     classes;

   * The *note Examples: 26eb. section showcases how to work with some
     event loop APIs.

* Menu:

* Event Loop Methods::
* Callback Handles::
* Server Objects::
* Event Loop Implementations::
* Examples: Examples<15>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/asyncio/events.py

   (2) 
https://github.com/python/cpython/tree/3.9/Lib/asyncio/base_events.py


File: python.info,  Node: Event Loop Methods,  Next: Callback Handles,  Up: Event Loop

5.18.1.44 Event Loop Methods
............................

Event loops have `low-level' APIs for the following:

* Menu:

* Running and stopping the loop::
* Scheduling callbacks::
* Scheduling delayed callbacks::
* Creating Futures and Tasks::
* Opening network connections::
* Creating network servers::
* Transferring files::
* TLS Upgrade::
* Watching file descriptors::
* Working with socket objects directly::
* DNS::
* Working with pipes::
* Unix signals::
* Executing code in thread or process pools::
* Error Handling API::
* Enabling debug mode::
* Running Subprocesses::


File: python.info,  Node: Running and stopping the loop,  Next: Scheduling callbacks,  Up: Event Loop Methods

5.18.1.45 Running and stopping the loop
.......................................

 -- Method: loop.run_until_complete (future)

     Run until the `future' (an instance of *note Future: 546.) has
     completed.

     If the argument is a *note coroutine object: 2637. it is implicitly
     scheduled to run as a *note asyncio.Task: 2e0.

     Return the Future’s result or raise its exception.

 -- Method: loop.run_forever ()

     Run the event loop until *note stop(): 61a. is called.

     If *note stop(): 61a. is called before *note run_forever(): 26ed.
     is called, the loop will poll the I/O selector once with a timeout
     of zero, run all callbacks scheduled in response to I/O events (and
     those that were already scheduled), and then exit.

     If *note stop(): 61a. is called while *note run_forever(): 26ed. is
     running, the loop will run the current batch of callbacks and then
     exit.  Note that new callbacks scheduled by callbacks will not run
     in this case; instead, they will run the next time *note
     run_forever(): 26ed. or *note run_until_complete(): 612. is called.

 -- Method: loop.stop ()

     Stop the event loop.

 -- Method: loop.is_running ()

     Return ‘True’ if the event loop is currently running.

 -- Method: loop.is_closed ()

     Return ‘True’ if the event loop was closed.

 -- Method: loop.close ()

     Close the event loop.

     The loop must not be running when this function is called.  Any
     pending callbacks will be discarded.

     This method clears all queues and shuts down the executor, but does
     not wait for the executor to finish.

     This method is idempotent and irreversible.  No other methods
     should be called after the event loop is closed.

 -- Method: coroutine loop.shutdown_asyncgens ()

     Schedule all currently open *note asynchronous generator: 1640.
     objects to close with an *note aclose(): 176. call.  After calling
     this method, the event loop will issue a warning if a new
     asynchronous generator is iterated.  This should be used to
     reliably finalize all scheduled asynchronous generators.

     Note that there is no need to call this function when *note
     asyncio.run(): 18d. is used.

     Example:

          try:
              loop.run_forever()
          finally:
              loop.run_until_complete(loop.shutdown_asyncgens())
              loop.close()

     New in version 3.6.

 -- Method: coroutine loop.shutdown_default_executor ()

     Schedule the closure of the default executor and wait for it to
     join all of the threads in the ‘ThreadPoolExecutor’.  After calling
     this method, a *note RuntimeError: 3dc. will be raised if *note
     loop.run_in_executor(): 190. is called while using the default
     executor.

     Note that there is no need to call this function when *note
     asyncio.run(): 18d. is used.

     New in version 3.9.


File: python.info,  Node: Scheduling callbacks,  Next: Scheduling delayed callbacks,  Prev: Running and stopping the loop,  Up: Event Loop Methods

5.18.1.46 Scheduling callbacks
..............................

 -- Method: loop.call_soon (callback, *args, context=None)

     Schedule the `callback' *note callback: 26f1. to be called with
     `args' arguments at the next iteration of the event loop.

     Callbacks are called in the order in which they are registered.
     Each callback will be called exactly once.

     An optional keyword-only `context' argument allows specifying a
     custom *note contextvars.Context: 260f. for the `callback' to run
     in.  The current context is used when no `context' is provided.

     An instance of *note asyncio.Handle: 11d7. is returned, which can
     be used later to cancel the callback.

     This method is not thread-safe.

 -- Method: loop.call_soon_threadsafe (callback, *args, context=None)

     A thread-safe variant of *note call_soon(): 455.  Must be used to
     schedule callbacks `from another thread'.

     Raises *note RuntimeError: 3dc. if called on a loop that’s been
     closed.  This can happen on a secondary thread when the main
     application is shutting down.

     See the *note concurrency and multithreading: 2655. section of the
     documentation.

Changed in version 3.7: The `context' keyword-only parameter was added.
See PEP 567(1) for more details.

     Note: Most *note asyncio: 9. scheduling functions don’t allow
     passing keyword arguments.  To do that, use *note
     functools.partial(): 8b5.:

          # will schedule "print("Hello", flush=True)"
          loop.call_soon(
              functools.partial(print, "Hello", flush=True))

     Using partial objects is usually more convenient than using
     lambdas, as asyncio can render partial objects better in debug and
     error messages.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0567


File: python.info,  Node: Scheduling delayed callbacks,  Next: Creating Futures and Tasks,  Prev: Scheduling callbacks,  Up: Event Loop Methods

5.18.1.47 Scheduling delayed callbacks
......................................

Event loop provides mechanisms to schedule callback functions to be
called at some point in the future.  Event loop uses monotonic clocks to
track time.

 -- Method: loop.call_later (delay, callback, *args, context=None)

     Schedule `callback' to be called after the given `delay' number of
     seconds (can be either an int or a float).

     An instance of *note asyncio.TimerHandle: 26e8. is returned which
     can be used to cancel the callback.

     `callback' will be called exactly once.  If two callbacks are
     scheduled for exactly the same time, the order in which they are
     called is undefined.

     The optional positional `args' will be passed to the callback when
     it is called.  If you want the callback to be called with keyword
     arguments use *note functools.partial(): 8b5.

     An optional keyword-only `context' argument allows specifying a
     custom *note contextvars.Context: 260f. for the `callback' to run
     in.  The current context is used when no `context' is provided.

     Changed in version 3.7: The `context' keyword-only parameter was
     added.  See PEP 567(1) for more details.

     Changed in version 3.8: In Python 3.7 and earlier with the default
     event loop implementation, the `delay' could not exceed one day.
     This has been fixed in Python 3.8.

 -- Method: loop.call_at (when, callback, *args, context=None)

     Schedule `callback' to be called at the given absolute timestamp
     `when' (an int or a float), using the same time reference as *note
     loop.time(): 26f5.

     This method’s behavior is the same as *note call_later(): 457.

     An instance of *note asyncio.TimerHandle: 26e8. is returned which
     can be used to cancel the callback.

     Changed in version 3.7: The `context' keyword-only parameter was
     added.  See PEP 567(2) for more details.

     Changed in version 3.8: In Python 3.7 and earlier with the default
     event loop implementation, the difference between `when' and the
     current time could not exceed one day.  This has been fixed in
     Python 3.8.

 -- Method: loop.time ()

     Return the current time, as a *note float: 1fd. value, according to
     the event loop’s internal monotonic clock.

     Note: 
     Changed in version 3.8: In Python 3.7 and earlier timeouts
     (relative `delay' or absolute `when') should not exceed one day.
     This has been fixed in Python 3.8.

See also
........

The *note asyncio.sleep(): 3aa. function.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0567

   (2) https://www.python.org/dev/peps/pep-0567


File: python.info,  Node: Creating Futures and Tasks,  Next: Opening network connections,  Prev: Scheduling delayed callbacks,  Up: Event Loop Methods

5.18.1.48 Creating Futures and Tasks
....................................

 -- Method: loop.create_future ()

     Create an *note asyncio.Future: 546. object attached to the event
     loop.

     This is the preferred way to create Futures in asyncio.  This lets
     third-party event loops provide alternative implementations of the
     Future object (with better performance or instrumentation).

     New in version 3.5.2.

 -- Method: loop.create_task (coro, *, name=None)

     Schedule the execution of a *note Coroutines: 2637.  Return a *note
     Task: 2e0. object.

     Third-party event loops can use their own subclass of *note Task:
     2e0. for interoperability.  In this case, the result type is a
     subclass of *note Task: 2e0.

     If the `name' argument is provided and not ‘None’, it is set as the
     name of the task using *note Task.set_name(): 2e3.

     Changed in version 3.8: Added the ‘name’ parameter.

 -- Method: loop.set_task_factory (factory)

     Set a task factory that will be used by *note loop.create_task():
     2e2.

     If `factory' is ‘None’ the default task factory will be set.
     Otherwise, `factory' must be a `callable' with the signature
     matching ‘(loop, coro)’, where `loop' is a reference to the active
     event loop, and `coro' is a coroutine object.  The callable must
     return a *note asyncio.Future: 546.-compatible object.

 -- Method: loop.get_task_factory ()

     Return a task factory or ‘None’ if the default one is in use.


File: python.info,  Node: Opening network connections,  Next: Creating network servers,  Prev: Creating Futures and Tasks,  Up: Event Loop Methods

5.18.1.49 Opening network connections
.....................................

 -- Method: coroutine loop.create_connection (protocol_factory,
          host=None, port=None, *, ssl=None, family=0, proto=0, flags=0,
          sock=None, local_addr=None, server_hostname=None,
          ssl_handshake_timeout=None, happy_eyeballs_delay=None,
          interleave=None)

     Open a streaming transport connection to a given address specified
     by `host' and `port'.

     The socket family can be either *note AF_INET: 26f8. or *note
     AF_INET6: 26f9. depending on `host' (or the `family' argument, if
     provided).

     The socket type will be *note SOCK_STREAM: d52.

     `protocol_factory' must be a callable returning an *note asyncio
     protocol: 26fa. implementation.

     This method will try to establish the connection in the background.
     When successful, it returns a ‘(transport, protocol)’ pair.

     The chronological synopsis of the underlying operation is as
     follows:

       1. The connection is established and a *note transport: 26fb. is
          created for it.

       2. `protocol_factory' is called without arguments and is expected
          to return a *note protocol: 26fa. instance.

       3. The protocol instance is coupled with the transport by calling
          its *note connection_made(): 26fc. method.

       4. A ‘(transport, protocol)’ tuple is returned on success.

     The created transport is an implementation-dependent bidirectional
     stream.

     Other arguments:

        * `ssl': if given and not false, a SSL/TLS transport is created
          (by default a plain TCP transport is created).  If `ssl' is a
          *note ssl.SSLContext: 4ea. object, this context is used to
          create the transport; if `ssl' is *note True: 594, a default
          context returned from *note ssl.create_default_context(): 9a7.
          is used.

          See also
          ........

          *note SSL/TLS security considerations: 26fd.

        * `server_hostname' sets or overrides the hostname that the
          target server’s certificate will be matched against.  Should
          only be passed if `ssl' is not ‘None’.  By default the value
          of the `host' argument is used.  If `host' is empty, there is
          no default and you must pass a value for `server_hostname'.
          If `server_hostname' is an empty string, hostname matching is
          disabled (which is a serious security risk, allowing for
          potential man-in-the-middle attacks).

        * `family', `proto', `flags' are the optional address family,
          protocol and flags to be passed through to getaddrinfo() for
          `host' resolution.  If given, these should all be integers
          from the corresponding *note socket: ef. module constants.

        * `happy_eyeballs_delay', if given, enables Happy Eyeballs for
          this connection.  It should be a floating-point number
          representing the amount of time in seconds to wait for a
          connection attempt to complete, before starting the next
          attempt in parallel.  This is the “Connection Attempt Delay”
          as defined in RFC 8305(1).  A sensible default value
          recommended by the RFC is ‘0.25’ (250 milliseconds).

        * `interleave' controls address reordering when a host name
          resolves to multiple IP addresses.  If ‘0’ or unspecified, no
          reordering is done, and addresses are tried in the order
          returned by *note getaddrinfo(): 59c.  If a positive integer
          is specified, the addresses are interleaved by address family,
          and the given integer is interpreted as “First Address Family
          Count” as defined in RFC 8305(2).  The default is ‘0’ if
          `happy_eyeballs_delay' is not specified, and ‘1’ if it is.

        * `sock', if given, should be an existing, already connected
          *note socket.socket: 767. object to be used by the transport.
          If `sock' is given, none of `host', `port', `family', `proto',
          `flags', `happy_eyeballs_delay', `interleave' and `local_addr'
          should be specified.

        * `local_addr', if given, is a ‘(local_host, local_port)’ tuple
          used to bind the socket locally.  The `local_host' and
          `local_port' are looked up using ‘getaddrinfo()’, similarly to
          `host' and `port'.

        * `ssl_handshake_timeout' is (for a TLS connection) the time in
          seconds to wait for the TLS handshake to complete before
          aborting the connection.  ‘60.0’ seconds if ‘None’ (default).

     New in version 3.8: Added the `happy_eyeballs_delay' and
     `interleave' parameters.

     Happy Eyeballs Algorithm: Success with Dual-Stack Hosts.  When a
     server’s IPv4 path and protocol are working, but the server’s IPv6
     path and protocol are not working, a dual-stack client application
     experiences significant connection delay compared to an IPv4-only
     client.  This is undesirable because it causes the dual- stack
     client to have a worse user experience.  This document specifies
     requirements for algorithms that reduce this user-visible delay and
     provides an algorithm.

     For more information: ‘https://tools.ietf.org/html/rfc6555’

     New in version 3.7: The `ssl_handshake_timeout' parameter.

     Changed in version 3.6: The socket option ‘TCP_NODELAY’ is set by
     default for all TCP connections.

     Changed in version 3.5: Added support for SSL/TLS in *note
     ProactorEventLoop: 2de.

     See also
     ........

     The *note open_connection(): 46b. function is a high-level
     alternative API. It returns a pair of (*note StreamReader: 1105,
     *note StreamWriter: 1106.) that can be used directly in async/await
     code.

 -- Method: coroutine loop.create_datagram_endpoint (protocol_factory,
          local_addr=None, remote_addr=None, *, family=0, proto=0,
          flags=0, reuse_address=None, reuse_port=None,
          allow_broadcast=None, sock=None)

          Note: The parameter `reuse_address' is no longer supported, as
          using ‘SO_REUSEADDR’ poses a significant security concern for
          UDP. Explicitly passing ‘reuse_address=True’ will raise an
          exception.

          When multiple processes with differing UIDs assign sockets to
          an identical UDP socket address with ‘SO_REUSEADDR’, incoming
          packets can become randomly distributed among the sockets.

          For supported platforms, `reuse_port' can be used as a
          replacement for similar functionality.  With `reuse_port',
          ‘SO_REUSEPORT’ is used instead, which specifically prevents
          processes with differing UIDs from assigning sockets to the
          same socket address.

     Create a datagram connection.

     The socket family can be either *note AF_INET: 26f8, *note
     AF_INET6: 26f9, or *note AF_UNIX: 26fe, depending on `host' (or the
     `family' argument, if provided).

     The socket type will be *note SOCK_DGRAM: d51.

     `protocol_factory' must be a callable returning a *note protocol:
     26fa. implementation.

     A tuple of ‘(transport, protocol)’ is returned on success.

     Other arguments:

        * `local_addr', if given, is a ‘(local_host, local_port)’ tuple
          used to bind the socket locally.  The `local_host' and
          `local_port' are looked up using *note getaddrinfo(): 59c.

        * `remote_addr', if given, is a ‘(remote_host, remote_port)’
          tuple used to connect the socket to a remote address.  The
          `remote_host' and `remote_port' are looked up using *note
          getaddrinfo(): 59c.

        * `family', `proto', `flags' are the optional address family,
          protocol and flags to be passed through to *note
          getaddrinfo(): 59c. for `host' resolution.  If given, these
          should all be integers from the corresponding *note socket:
          ef. module constants.

        * `reuse_port' tells the kernel to allow this endpoint to be
          bound to the same port as other existing endpoints are bound
          to, so long as they all set this flag when being created.
          This option is not supported on Windows and some Unixes.  If
          the ‘SO_REUSEPORT’ constant is not defined then this
          capability is unsupported.

        * `allow_broadcast' tells the kernel to allow this endpoint to
          send messages to the broadcast address.

        * `sock' can optionally be specified in order to use a
          preexisting, already connected, *note socket.socket: 767.
          object to be used by the transport.  If specified,
          `local_addr' and `remote_addr' should be omitted (must be
          *note None: 203.).

     See *note UDP echo client protocol: 26ff. and *note UDP echo server
     protocol: 2700. examples.

     Changed in version 3.4.4: The `family', `proto', `flags',
     `reuse_address', `reuse_port, *allow_broadcast', and `sock'
     parameters were added.

     Changed in version 3.8.1: The `reuse_address' parameter is no
     longer supported due to security concerns.

     Changed in version 3.8: Added support for Windows.

 -- Method: coroutine loop.create_unix_connection (protocol_factory,
          path=None, *, ssl=None, sock=None, server_hostname=None,
          ssl_handshake_timeout=None)

     Create a Unix connection.

     The socket family will be *note AF_UNIX: 26fe.; socket type will be
     *note SOCK_STREAM: d52.

     A tuple of ‘(transport, protocol)’ is returned on success.

     `path' is the name of a Unix domain socket and is required, unless
     a `sock' parameter is specified.  Abstract Unix sockets, *note str:
     205, *note bytes: 172, and *note Path: 32f. paths are supported.

     See the documentation of the *note loop.create_connection(): 2e5.
     method for information about arguments to this method.

     *note Availability: 1491.: Unix.

     New in version 3.7: The `ssl_handshake_timeout' parameter.

     Changed in version 3.7: The `path' parameter can now be a *note
     path-like object: 472.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc8305.html

   (2) https://tools.ietf.org/html/rfc8305.html


File: python.info,  Node: Creating network servers,  Next: Transferring files,  Prev: Opening network connections,  Up: Event Loop Methods

5.18.1.50 Creating network servers
..................................

 -- Method: coroutine loop.create_server (protocol_factory, host=None,
          port=None, *, family=socket.AF_UNSPEC,
          flags=socket.AI_PASSIVE, sock=None, backlog=100, ssl=None,
          reuse_address=None, reuse_port=None,
          ssl_handshake_timeout=None, start_serving=True)

     Create a TCP server (socket type *note SOCK_STREAM: d52.) listening
     on `port' of the `host' address.

     Returns a *note Server: 464. object.

     Arguments:

        * `protocol_factory' must be a callable returning a *note
          protocol: 26fa. implementation.

        * The `host' parameter can be set to several types which
          determine where the server would be listening:

             - If `host' is a string, the TCP server is bound to a
               single network interface specified by `host'.

             - If `host' is a sequence of strings, the TCP server is
               bound to all network interfaces specified by the
               sequence.

             - If `host' is an empty string or ‘None’, all interfaces
               are assumed and a list of multiple sockets will be
               returned (most likely one for IPv4 and another one for
               IPv6).

        * The `port' parameter can be set to specify which port the
          server should listen on.  If ‘0’ or ‘None’ (the default), a
          random unused port will be selected (note that if `host'
          resolves to multiple network interfaces, a different random
          port will be selected for each interface).

        * `family' can be set to either *note socket.AF_INET: 26f8. or
          *note AF_INET6: 26f9. to force the socket to use IPv4 or IPv6.
          If not set, the `family' will be determined from host name
          (defaults to ‘AF_UNSPEC’).

        * `flags' is a bitmask for *note getaddrinfo(): 59c.

        * `sock' can optionally be specified in order to use a
          preexisting socket object.  If specified, `host' and `port'
          must not be specified.

        * `backlog' is the maximum number of queued connections passed
          to *note listen(): 83a. (defaults to 100).

        * `ssl' can be set to an *note SSLContext: 4ea. instance to
          enable TLS over the accepted connections.

        * `reuse_address' tells the kernel to reuse a local socket in
          ‘TIME_WAIT’ state, without waiting for its natural timeout to
          expire.  If not specified will automatically be set to ‘True’
          on Unix.

        * `reuse_port' tells the kernel to allow this endpoint to be
          bound to the same port as other existing endpoints are bound
          to, so long as they all set this flag when being created.
          This option is not supported on Windows.

        * `ssl_handshake_timeout' is (for a TLS server) the time in
          seconds to wait for the TLS handshake to complete before
          aborting the connection.  ‘60.0’ seconds if ‘None’ (default).

        * `start_serving' set to ‘True’ (the default) causes the created
          server to start accepting connections immediately.  When set
          to ‘False’, the user should await on *note
          Server.start_serving(): 467. or *note Server.serve_forever():
          468. to make the server to start accepting connections.

     New in version 3.7: Added `ssl_handshake_timeout' and
     `start_serving' parameters.

     Changed in version 3.6: The socket option ‘TCP_NODELAY’ is set by
     default for all TCP connections.

     Changed in version 3.5: Added support for SSL/TLS in *note
     ProactorEventLoop: 2de.

     Changed in version 3.5.1: The `host' parameter can be a sequence of
     strings.

     See also
     ........

     The *note start_server(): 46c. function is a higher-level
     alternative API that returns a pair of *note StreamReader: 1105.
     and *note StreamWriter: 1106. that can be used in an async/await
     code.

 -- Method: coroutine loop.create_unix_server (protocol_factory,
          path=None, *, sock=None, backlog=100, ssl=None,
          ssl_handshake_timeout=None, start_serving=True)

     Similar to *note loop.create_server(): 465. but works with the
     *note AF_UNIX: 26fe. socket family.

     `path' is the name of a Unix domain socket, and is required, unless
     a `sock' argument is provided.  Abstract Unix sockets, *note str:
     205, *note bytes: 172, and *note Path: 32f. paths are supported.

     See the documentation of the *note loop.create_server(): 465.
     method for information about arguments to this method.

     *note Availability: 1491.: Unix.

     New in version 3.7: The `ssl_handshake_timeout' and `start_serving'
     parameters.

     Changed in version 3.7: The `path' parameter can now be a *note
     Path: 32f. object.

 -- Method: coroutine loop.connect_accepted_socket (protocol_factory,
          sock, *, ssl=None, ssl_handshake_timeout=None)

     Wrap an already accepted connection into a transport/protocol pair.

     This method can be used by servers that accept connections outside
     of asyncio but that use asyncio to handle them.

     Parameters:

        * `protocol_factory' must be a callable returning a *note
          protocol: 26fa. implementation.

        * `sock' is a preexisting socket object returned from *note
          socket.accept: 768.

        * `ssl' can be set to an *note SSLContext: 4ea. to enable SSL
          over the accepted connections.

        * `ssl_handshake_timeout' is (for an SSL connection) the time in
          seconds to wait for the SSL handshake to complete before
          aborting the connection.  ‘60.0’ seconds if ‘None’ (default).

     Returns a ‘(transport, protocol)’ pair.

     New in version 3.7: The `ssl_handshake_timeout' parameter.

     New in version 3.5.3.


File: python.info,  Node: Transferring files,  Next: TLS Upgrade,  Prev: Creating network servers,  Up: Event Loop Methods

5.18.1.51 Transferring files
............................

 -- Method: coroutine loop.sendfile (transport, file, offset=0,
          count=None, *, fallback=True)

     Send a `file' over a `transport'.  Return the total number of bytes
     sent.

     The method uses high-performance *note os.sendfile(): 461. if
     available.

     `file' must be a regular file object opened in binary mode.

     `offset' tells from where to start reading the file.  If specified,
     `count' is the total number of bytes to transmit as opposed to
     sending the file until EOF is reached.  File position is always
     updated, even when this method raises an error, and *note
     file.tell(): 1efc. can be used to obtain the actual number of bytes
     sent.

     `fallback' set to ‘True’ makes asyncio to manually read and send
     the file when the platform does not support the sendfile system
     call (e.g.  Windows or SSL socket on Unix).

     Raise *note SendfileNotAvailableError: 26de. if the system does not
     support the `sendfile' syscall and `fallback' is ‘False’.

     New in version 3.7.


File: python.info,  Node: TLS Upgrade,  Next: Watching file descriptors,  Prev: Transferring files,  Up: Event Loop Methods

5.18.1.52 TLS Upgrade
.....................

 -- Method: coroutine loop.start_tls (transport, protocol, sslcontext,
          *, server_side=False, server_hostname=None,
          ssl_handshake_timeout=None)

     Upgrade an existing transport-based connection to TLS.

     Return a new transport instance, that the `protocol' must start
     using immediately after the `await'.  The `transport' instance
     passed to the `start_tls' method should never be used again.

     Parameters:

        * `transport' and `protocol' instances that methods like *note
          create_server(): 465. and *note create_connection(): 2e5.
          return.

        * `sslcontext': a configured instance of *note SSLContext: 4ea.

        * `server_side' pass ‘True’ when a server-side connection is
          being upgraded (like the one created by *note create_server():
          465.).

        * `server_hostname': sets or overrides the host name that the
          target server’s certificate will be matched against.

        * `ssl_handshake_timeout' is (for a TLS connection) the time in
          seconds to wait for the TLS handshake to complete before
          aborting the connection.  ‘60.0’ seconds if ‘None’ (default).

     New in version 3.7.


File: python.info,  Node: Watching file descriptors,  Next: Working with socket objects directly,  Prev: TLS Upgrade,  Up: Event Loop Methods

5.18.1.53 Watching file descriptors
...................................

 -- Method: loop.add_reader (fd, callback, *args)

     Start monitoring the `fd' file descriptor for read availability and
     invoke `callback' with the specified arguments once `fd' is
     available for reading.

 -- Method: loop.remove_reader (fd)

     Stop monitoring the `fd' file descriptor for read availability.

 -- Method: loop.add_writer (fd, callback, *args)

     Start monitoring the `fd' file descriptor for write availability
     and invoke `callback' with the specified arguments once `fd' is
     available for writing.

     Use *note functools.partial(): 8b5. *note to pass keyword
     arguments: 26f2. to `callback'.

 -- Method: loop.remove_writer (fd)

     Stop monitoring the `fd' file descriptor for write availability.

See also *note Platform Support: 2709. section for some limitations of
these methods.


File: python.info,  Node: Working with socket objects directly,  Next: DNS,  Prev: Watching file descriptors,  Up: Event Loop Methods

5.18.1.54 Working with socket objects directly
..............................................

In general, protocol implementations that use transport-based APIs such
as *note loop.create_connection(): 2e5. and *note loop.create_server():
465. are faster than implementations that work with sockets directly.
However, there are some use cases when performance is not critical, and
working with *note socket: 767. objects directly is more convenient.

 -- Method: coroutine loop.sock_recv (sock, nbytes)

     Receive up to `nbytes' from `sock'.  Asynchronous version of *note
     socket.recv(): 76a.

     Return the received data as a bytes object.

     `sock' must be a non-blocking socket.

     Changed in version 3.7: Even though this method was always
     documented as a coroutine method, releases before Python 3.7
     returned a *note Future: 546.  Since Python 3.7 this is an ‘async
     def’ method.

 -- Method: coroutine loop.sock_recv_into (sock, buf)

     Receive data from `sock' into the `buf' buffer.  Modeled after the
     blocking *note socket.recv_into(): d7a. method.

     Return the number of bytes written to the buffer.

     `sock' must be a non-blocking socket.

     New in version 3.7.

 -- Method: coroutine loop.sock_sendall (sock, data)

     Send `data' to the `sock' socket.  Asynchronous version of *note
     socket.sendall(): 76e.

     This method continues to send to the socket until either all data
     in `data' has been sent or an error occurs.  ‘None’ is returned on
     success.  On error, an exception is raised.  Additionally, there is
     no way to determine how much data, if any, was successfully
     processed by the receiving end of the connection.

     `sock' must be a non-blocking socket.

     Changed in version 3.7: Even though the method was always
     documented as a coroutine method, before Python 3.7 it returned an
     *note Future: 546.  Since Python 3.7, this is an ‘async def’
     method.

 -- Method: coroutine loop.sock_connect (sock, address)

     Connect `sock' to a remote socket at `address'.

     Asynchronous version of *note socket.connect(): 769.

     `sock' must be a non-blocking socket.

     Changed in version 3.5.2: ‘address’ no longer needs to be resolved.
     ‘sock_connect’ will try to check if the `address' is already
     resolved by calling *note socket.inet_pton(): 237.  If not, *note
     loop.getaddrinfo(): 59c. will be used to resolve the `address'.

     See also
     ........

     *note loop.create_connection(): 2e5. and *note
     asyncio.open_connection(): 46b.

 -- Method: coroutine loop.sock_accept (sock)

     Accept a connection.  Modeled after the blocking *note
     socket.accept(): 768. method.

     The socket must be bound to an address and listening for
     connections.  The return value is a pair ‘(conn, address)’ where
     `conn' is a `new' socket object usable to send and receive data on
     the connection, and `address' is the address bound to the socket on
     the other end of the connection.

     `sock' must be a non-blocking socket.

     Changed in version 3.7: Even though the method was always
     documented as a coroutine method, before Python 3.7 it returned a
     *note Future: 546.  Since Python 3.7, this is an ‘async def’
     method.

     See also
     ........

     *note loop.create_server(): 465. and *note start_server(): 46c.

 -- Method: coroutine loop.sock_sendfile (sock, file, offset=0,
          count=None, *, fallback=True)

     Send a file using high-performance *note os.sendfile: 461. if
     possible.  Return the total number of bytes sent.

     Asynchronous version of *note socket.sendfile(): 839.

     `sock' must be a non-blocking *note socket.SOCK_STREAM: d52. *note
     socket: 767.

     `file' must be a regular file object open in binary mode.

     `offset' tells from where to start reading the file.  If specified,
     `count' is the total number of bytes to transmit as opposed to
     sending the file until EOF is reached.  File position is always
     updated, even when this method raises an error, and *note
     file.tell(): 1efc. can be used to obtain the actual number of bytes
     sent.

     `fallback', when set to ‘True’, makes asyncio manually read and
     send the file when the platform does not support the sendfile
     syscall (e.g.  Windows or SSL socket on Unix).

     Raise *note SendfileNotAvailableError: 26de. if the system does not
     support `sendfile' syscall and `fallback' is ‘False’.

     `sock' must be a non-blocking socket.

     New in version 3.7.


File: python.info,  Node: DNS,  Next: Working with pipes,  Prev: Working with socket objects directly,  Up: Event Loop Methods

5.18.1.55 DNS
.............

 -- Method: coroutine loop.getaddrinfo (host, port, *, family=0, type=0,
          proto=0, flags=0)

     Asynchronous version of *note socket.getaddrinfo(): 270c.

 -- Method: coroutine loop.getnameinfo (sockaddr, flags=0)

     Asynchronous version of *note socket.getnameinfo(): 270d.

Changed in version 3.7: Both `getaddrinfo' and `getnameinfo' methods
were always documented to return a coroutine, but prior to Python 3.7
they were, in fact, returning *note asyncio.Future: 546. objects.
Starting with Python 3.7 both methods are coroutines.


File: python.info,  Node: Working with pipes,  Next: Unix signals,  Prev: DNS,  Up: Event Loop Methods

5.18.1.56 Working with pipes
............................

 -- Method: coroutine loop.connect_read_pipe (protocol_factory, pipe)

     Register the read end of `pipe' in the event loop.

     `protocol_factory' must be a callable returning an *note asyncio
     protocol: 26fa. implementation.

     `pipe' is a *note file-like object: c14.

     Return pair ‘(transport, protocol)’, where `transport' supports the
     *note ReadTransport: 270f. interface and `protocol' is an object
     instantiated by the `protocol_factory'.

     With *note SelectorEventLoop: 26c2. event loop, the `pipe' is set
     to non-blocking mode.

 -- Method: coroutine loop.connect_write_pipe (protocol_factory, pipe)

     Register the write end of `pipe' in the event loop.

     `protocol_factory' must be a callable returning an *note asyncio
     protocol: 26fa. implementation.

     `pipe' is *note file-like object: c14.

     Return pair ‘(transport, protocol)’, where `transport' supports
     *note WriteTransport: 2710. interface and `protocol' is an object
     instantiated by the `protocol_factory'.

     With *note SelectorEventLoop: 26c2. event loop, the `pipe' is set
     to non-blocking mode.

     Note: *note SelectorEventLoop: 26c2. does not support the above
     methods on Windows.  Use *note ProactorEventLoop: 2de. instead for
     Windows.

See also
........

The *note loop.subprocess_exec(): 263c. and *note
loop.subprocess_shell(): 26aa. methods.


File: python.info,  Node: Unix signals,  Next: Executing code in thread or process pools,  Prev: Working with pipes,  Up: Event Loop Methods

5.18.1.57 Unix signals
......................

 -- Method: loop.add_signal_handler (signum, callback, *args)

     Set `callback' as the handler for the `signum' signal.

     The callback will be invoked by `loop', along with other queued
     callbacks and runnable coroutines of that event loop.  Unlike
     signal handlers registered using *note signal.signal(): b58, a
     callback registered with this function is allowed to interact with
     the event loop.

     Raise *note ValueError: 16d. if the signal number is invalid or
     uncatchable.  Raise *note RuntimeError: 3dc. if there is a problem
     setting up the handler.

     Use *note functools.partial(): 8b5. *note to pass keyword
     arguments: 26f2. to `callback'.

     Like *note signal.signal(): b58, this function must be invoked in
     the main thread.

 -- Method: loop.remove_signal_handler (sig)

     Remove the handler for the `sig' signal.

     Return ‘True’ if the signal handler was removed, or ‘False’ if no
     handler was set for the given signal.

     *note Availability: 1491.: Unix.

See also
........

The *note signal: ea. module.


File: python.info,  Node: Executing code in thread or process pools,  Next: Error Handling API,  Prev: Unix signals,  Up: Event Loop Methods

5.18.1.58 Executing code in thread or process pools
...................................................

 -- Method: awaitable loop.run_in_executor (executor, func, *args)

     Arrange for `func' to be called in the specified executor.

     The `executor' argument should be an *note
     concurrent.futures.Executor: 258a. instance.  The default executor
     is used if `executor' is ‘None’.

     Example:

          import asyncio
          import concurrent.futures

          def blocking_io():
              # File operations (such as logging) can block the
              # event loop: run them in a thread pool.
              with open('/dev/urandom', 'rb') as f:
                  return f.read(100)

          def cpu_bound():
              # CPU-bound operations will block the event loop:
              # in general it is preferable to run them in a
              # process pool.
              return sum(i * i for i in range(10 ** 7))

          async def main():
              loop = asyncio.get_running_loop()

              ## Options:

              # 1. Run in the default loop's executor:
              result = await loop.run_in_executor(
                  None, blocking_io)
              print('default thread pool', result)

              # 2. Run in a custom thread pool:
              with concurrent.futures.ThreadPoolExecutor() as pool:
                  result = await loop.run_in_executor(
                      pool, blocking_io)
                  print('custom thread pool', result)

              # 3. Run in a custom process pool:
              with concurrent.futures.ProcessPoolExecutor() as pool:
                  result = await loop.run_in_executor(
                      pool, cpu_bound)
                  print('custom process pool', result)

          asyncio.run(main())

     This method returns a *note asyncio.Future: 546. object.

     Use *note functools.partial(): 8b5. *note to pass keyword
     arguments: 26f2. to `func'.

     Changed in version 3.5.3: *note loop.run_in_executor(): 190. no
     longer configures the ‘max_workers’ of the thread pool executor it
     creates, instead leaving it up to the thread pool executor (*note
     ThreadPoolExecutor: 18c.) to set the default.

 -- Method: loop.set_default_executor (executor)

     Set `executor' as the default executor used by *note
     run_in_executor(): 190.  `executor' should be an instance of *note
     ThreadPoolExecutor: 18c.

     Deprecated since version 3.8: Using an executor that is not an
     instance of *note ThreadPoolExecutor: 18c. is deprecated and will
     trigger an error in Python 3.9.

     `executor' must be an instance of *note
     concurrent.futures.ThreadPoolExecutor: 18c.


File: python.info,  Node: Error Handling API,  Next: Enabling debug mode,  Prev: Executing code in thread or process pools,  Up: Event Loop Methods

5.18.1.59 Error Handling API
............................

Allows customizing how exceptions are handled in the event loop.

 -- Method: loop.set_exception_handler (handler)

     Set `handler' as the new event loop exception handler.

     If `handler' is ‘None’, the default exception handler will be set.
     Otherwise, `handler' must be a callable with the signature matching
     ‘(loop, context)’, where ‘loop’ is a reference to the active event
     loop, and ‘context’ is a ‘dict’ object containing the details of
     the exception (see *note call_exception_handler(): 2716.
     documentation for details about context).

 -- Method: loop.get_exception_handler ()

     Return the current exception handler, or ‘None’ if no custom
     exception handler was set.

     New in version 3.5.2.

 -- Method: loop.default_exception_handler (context)

     Default exception handler.

     This is called when an exception occurs and no exception handler is
     set.  This can be called by a custom exception handler that wants
     to defer to the default handler behavior.

     `context' parameter has the same meaning as in *note
     call_exception_handler(): 2716.

 -- Method: loop.call_exception_handler (context)

     Call the current event loop exception handler.

     `context' is a ‘dict’ object containing the following keys (new
     keys may be introduced in future Python versions):

        * ‘message’: Error message;

        * ‘exception’ (optional): Exception object;

        * ‘future’ (optional): *note asyncio.Future: 546. instance;

        * ‘handle’ (optional): *note asyncio.Handle: 11d7. instance;

        * ‘protocol’ (optional): *note Protocol: 26fa. instance;

        * ‘transport’ (optional): *note Transport: 26fb. instance;

        * ‘socket’ (optional): *note socket.socket: 767. instance.

          Note: This method should not be overloaded in subclassed event
          loops.  For custom exception handling, use the *note
          set_exception_handler(): 2715. method.


File: python.info,  Node: Enabling debug mode,  Next: Running Subprocesses,  Prev: Error Handling API,  Up: Event Loop Methods

5.18.1.60 Enabling debug mode
.............................

 -- Method: loop.get_debug ()

     Get the debug mode (*note bool: 2bd.) of the event loop.

     The default value is ‘True’ if the environment variable *note
     PYTHONASYNCIODEBUG: 148d. is set to a non-empty string, ‘False’
     otherwise.

 -- Method: loop.set_debug (enabled: bool)

     Set the debug mode of the event loop.

     Changed in version 3.7: The new *note Python Development Mode: 160.
     can now also be used to enable the debug mode.

See also
........

The *note debug mode of asyncio: 148e.


File: python.info,  Node: Running Subprocesses,  Prev: Enabling debug mode,  Up: Event Loop Methods

5.18.1.61 Running Subprocesses
..............................

Methods described in this subsections are low-level.  In regular
async/await code consider using the high-level *note
asyncio.create_subprocess_shell(): 3b5. and *note
asyncio.create_subprocess_exec(): 3b4. convenience functions instead.

     Note: On Windows, the default event loop *note ProactorEventLoop:
     2de. supports subprocesses, whereas *note SelectorEventLoop: 26c2.
     does not.  See *note Subprocess Support on Windows: 26ab. for
     details.

 -- Method: coroutine loop.subprocess_exec (protocol_factory, *args,
          stdin=subprocess.PIPE, stdout=subprocess.PIPE,
          stderr=subprocess.PIPE, **kwargs)

     Create a subprocess from one or more string arguments specified by
     `args'.

     `args' must be a list of strings represented by:

        * *note str: 205.;

        * or *note bytes: 172, encoded to the *note filesystem encoding:
          2042.

     The first string specifies the program executable, and the
     remaining strings specify the arguments.  Together, string
     arguments form the ‘argv’ of the program.

     This is similar to the standard library *note subprocess.Popen:
     3db. class called with ‘shell=False’ and the list of strings passed
     as the first argument; however, where *note Popen: 3db. takes a
     single argument which is list of strings, `subprocess_exec' takes
     multiple string arguments.

     The `protocol_factory' must be a callable returning a subclass of
     the *note asyncio.SubprocessProtocol: 271a. class.

     Other parameters:

        * `stdin' can be any of these:

             * a file-like object representing a pipe to be connected to
               the subprocess’s standard input stream using *note
               connect_write_pipe(): 26ad.

             * the *note subprocess.PIPE: 4f4. constant (default) which
               will create a new pipe and connect it,

             * the value ‘None’ which will make the subprocess inherit
               the file descriptor from this process

             * the *note subprocess.DEVNULL: b78. constant which
               indicates that the special *note os.devnull: 1152. file
               will be used

        * `stdout' can be any of these:

             * a file-like object representing a pipe to be connected to
               the subprocess’s standard output stream using *note
               connect_write_pipe(): 26ad.

             * the *note subprocess.PIPE: 4f4. constant (default) which
               will create a new pipe and connect it,

             * the value ‘None’ which will make the subprocess inherit
               the file descriptor from this process

             * the *note subprocess.DEVNULL: b78. constant which
               indicates that the special *note os.devnull: 1152. file
               will be used

        * `stderr' can be any of these:

             * a file-like object representing a pipe to be connected to
               the subprocess’s standard error stream using *note
               connect_write_pipe(): 26ad.

             * the *note subprocess.PIPE: 4f4. constant (default) which
               will create a new pipe and connect it,

             * the value ‘None’ which will make the subprocess inherit
               the file descriptor from this process

             * the *note subprocess.DEVNULL: b78. constant which
               indicates that the special *note os.devnull: 1152. file
               will be used

             * the *note subprocess.STDOUT: 25ae. constant which will
               connect the standard error stream to the process’
               standard output stream

        * All other keyword arguments are passed to *note
          subprocess.Popen: 3db. without interpretation, except for
          `bufsize', `universal_newlines', `shell', `text', `encoding'
          and `errors', which should not be specified at all.

          The ‘asyncio’ subprocess API does not support decoding the
          streams as text.  *note bytes.decode(): 171. can be used to
          convert the bytes returned from the stream to text.

     See the constructor of the *note subprocess.Popen: 3db. class for
     documentation on other arguments.

     Returns a pair of ‘(transport, protocol)’, where `transport'
     conforms to the *note asyncio.SubprocessTransport: 271b. base class
     and `protocol' is an object instantiated by the `protocol_factory'.

 -- Method: coroutine loop.subprocess_shell (protocol_factory, cmd, *,
          stdin=subprocess.PIPE, stdout=subprocess.PIPE,
          stderr=subprocess.PIPE, **kwargs)

     Create a subprocess from `cmd', which can be a *note str: 205. or a
     *note bytes: 172. string encoded to the *note filesystem encoding:
     2042, using the platform’s “shell” syntax.

     This is similar to the standard library *note subprocess.Popen:
     3db. class called with ‘shell=True’.

     The `protocol_factory' must be a callable returning a subclass of
     the *note SubprocessProtocol: 271a. class.

     See *note subprocess_exec(): 263c. for more details about the
     remaining arguments.

     Returns a pair of ‘(transport, protocol)’, where `transport'
     conforms to the *note SubprocessTransport: 271b. base class and
     `protocol' is an object instantiated by the `protocol_factory'.

     Note: It is the application’s responsibility to ensure that all
     whitespace and special characters are quoted appropriately to avoid
     shell injection(1) vulnerabilities.  The *note shlex.quote(): b4e.
     function can be used to properly escape whitespace and special
     characters in strings that are going to be used to construct shell
     commands.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Shell_injection#Shell_injection


File: python.info,  Node: Callback Handles,  Next: Server Objects,  Prev: Event Loop Methods,  Up: Event Loop

5.18.1.62 Callback Handles
..........................

 -- Class: asyncio.Handle

     A callback wrapper object returned by *note loop.call_soon(): 455,
     *note loop.call_soon_threadsafe(): 456.

      -- Method: cancel ()

          Cancel the callback.  If the callback has already been
          canceled or executed, this method has no effect.

      -- Method: cancelled ()

          Return ‘True’ if the callback was cancelled.

          New in version 3.7.

 -- Class: asyncio.TimerHandle

     A callback wrapper object returned by *note loop.call_later(): 457,
     and *note loop.call_at(): 458.

     This class is a subclass of *note Handle: 11d7.

      -- Method: when ()

          Return a scheduled callback time as *note float: 1fd. seconds.

          The time is an absolute timestamp, using the same time
          reference as *note loop.time(): 26f5.

          New in version 3.7.


File: python.info,  Node: Server Objects,  Next: Event Loop Implementations,  Prev: Callback Handles,  Up: Event Loop

5.18.1.63 Server Objects
........................

Server objects are created by *note loop.create_server(): 465, *note
loop.create_unix_server(): 466, *note start_server(): 46c, and *note
start_unix_server(): 266f. functions.

Do not instantiate the class directly.

 -- Class: asyncio.Server

     `Server' objects are asynchronous context managers.  When used in
     an ‘async with’ statement, it’s guaranteed that the Server object
     is closed and not accepting new connections when the ‘async with’
     statement is completed:

          srv = await loop.create_server(...)

          async with srv:
              # some code

          # At this point, srv is closed and no longer accepts new connections.

     Changed in version 3.7: Server object is an asynchronous context
     manager since Python 3.7.

      -- Method: close ()

          Stop serving: close listening sockets and set the *note
          sockets: 59e. attribute to ‘None’.

          The sockets that represent existing incoming client
          connections are left open.

          The server is closed asynchronously, use the *note
          wait_closed(): 271e. coroutine to wait until the server is
          closed.

      -- Method: get_loop ()

          Return the event loop associated with the server object.

          New in version 3.7.

      -- Method: coroutine start_serving ()

          Start accepting connections.

          This method is idempotent, so it can be called when the server
          is already being serving.

          The `start_serving' keyword-only parameter to *note
          loop.create_server(): 465. and *note asyncio.start_server():
          46c. allows creating a Server object that is not accepting
          connections initially.  In this case ‘Server.start_serving()’,
          or *note Server.serve_forever(): 468. can be used to make the
          Server start accepting connections.

          New in version 3.7.

      -- Method: coroutine serve_forever ()

          Start accepting connections until the coroutine is cancelled.
          Cancellation of ‘serve_forever’ task causes the server to be
          closed.

          This method can be called if the server is already accepting
          connections.  Only one ‘serve_forever’ task can exist per one
          `Server' object.

          Example:

               async def client_connected(reader, writer):
                   # Communicate with the client with
                   # reader/writer streams.  For example:
                   await reader.readline()

               async def main(host, port):
                   srv = await asyncio.start_server(
                       client_connected, host, port)
                   await srv.serve_forever()

               asyncio.run(main('127.0.0.1', 0))

          New in version 3.7.

      -- Method: is_serving ()

          Return ‘True’ if the server is accepting new connections.

          New in version 3.7.

      -- Method: coroutine wait_closed ()

          Wait until the *note close(): 271d. method completes.

      -- Attribute: sockets

          List of *note socket.socket: 767. objects the server is
          listening on.

          Changed in version 3.7: Prior to Python 3.7 ‘Server.sockets’
          used to return an internal list of server sockets directly.
          In 3.7 a copy of that list is returned.


File: python.info,  Node: Event Loop Implementations,  Next: Examples<15>,  Prev: Server Objects,  Up: Event Loop

5.18.1.64 Event Loop Implementations
....................................

asyncio ships with two different event loop implementations: *note
SelectorEventLoop: 26c2. and *note ProactorEventLoop: 2de.

By default asyncio is configured to use *note SelectorEventLoop: 26c2.
on Unix and *note ProactorEventLoop: 2de. on Windows.

 -- Class: asyncio.SelectorEventLoop

     An event loop based on the *note selectors: e6. module.

     Uses the most efficient `selector' available for the given
     platform.  It is also possible to manually configure the exact
     selector implementation to be used:

          import asyncio
          import selectors

          selector = selectors.SelectSelector()
          loop = asyncio.SelectorEventLoop(selector)
          asyncio.set_event_loop(loop)

     *note Availability: 1491.: Unix, Windows.

 -- Class: asyncio.ProactorEventLoop

     An event loop for Windows that uses “I/O Completion Ports” (IOCP).

     *note Availability: 1491.: Windows.

     See also
     ........

     MSDN documentation on I/O Completion Ports(1).

 -- Class: asyncio.AbstractEventLoop

     Abstract base class for asyncio-compliant event loops.

     The *note Event Loop Methods: 737. section lists all methods that
     an alternative implementation of ‘AbstractEventLoop’ should have
     defined.

   ---------- Footnotes ----------

   (1) 
https://docs.microsoft.com/en-ca/windows/desktop/FileIO/i-o-completion-ports


File: python.info,  Node: Examples<15>,  Prev: Event Loop Implementations,  Up: Event Loop

5.18.1.65 Examples
..................

Note that all examples in this section `purposefully' show how to use
the low-level event loop APIs, such as *note loop.run_forever(): 26ed.
and *note loop.call_soon(): 455.  Modern asyncio applications rarely
need to be written this way; consider using the high-level functions
like *note asyncio.run(): 18d.

* Menu:

* Hello World with call_soon(): Hello World with call_soon.
* Display the current date with call_later(): Display the current date with call_later.
* Watch a file descriptor for read events::
* Set signal handlers for SIGINT and SIGTERM::


File: python.info,  Node: Hello World with call_soon,  Next: Display the current date with call_later,  Up: Examples<15>

5.18.1.66 Hello World with call_soon()
......................................

An example using the *note loop.call_soon(): 455. method to schedule a
callback.  The callback displays ‘"Hello World"’ and then stops the
event loop:

     import asyncio

     def hello_world(loop):
         """A callback to print 'Hello World' and stop the event loop"""
         print('Hello World')
         loop.stop()

     loop = asyncio.get_event_loop()

     # Schedule a call to hello_world()
     loop.call_soon(hello_world, loop)

     # Blocking call interrupted by loop.stop()
     try:
         loop.run_forever()
     finally:
         loop.close()

See also
........

A similar *note Hello World: 2637. example created with a coroutine and
the *note run(): 18d. function.


File: python.info,  Node: Display the current date with call_later,  Next: Watch a file descriptor for read events,  Prev: Hello World with call_soon,  Up: Examples<15>

5.18.1.67 Display the current date with call_later()
....................................................

An example of a callback displaying the current date every second.  The
callback uses the *note loop.call_later(): 457. method to reschedule
itself after 5 seconds, and then stops the event loop:

     import asyncio
     import datetime

     def display_date(end_time, loop):
         print(datetime.datetime.now())
         if (loop.time() + 1.0) < end_time:
             loop.call_later(1, display_date, end_time, loop)
         else:
             loop.stop()

     loop = asyncio.get_event_loop()

     # Schedule the first call to display_date()
     end_time = loop.time() + 5.0
     loop.call_soon(display_date, end_time, loop)

     # Blocking call interrupted by loop.stop()
     try:
         loop.run_forever()
     finally:
         loop.close()

See also
........

A similar *note current date: 2649. example created with a coroutine and
the *note run(): 18d. function.


File: python.info,  Node: Watch a file descriptor for read events,  Next: Set signal handlers for SIGINT and SIGTERM,  Prev: Display the current date with call_later,  Up: Examples<15>

5.18.1.68 Watch a file descriptor for read events
.................................................

Wait until a file descriptor received some data using the *note
loop.add_reader(): 268a. method and then close the event loop:

     import asyncio
     from socket import socketpair

     # Create a pair of connected file descriptors
     rsock, wsock = socketpair()

     loop = asyncio.get_event_loop()

     def reader():
         data = rsock.recv(100)
         print("Received:", data.decode())

         # We are done: unregister the file descriptor
         loop.remove_reader(rsock)

         # Stop the event loop
         loop.stop()

     # Register the file descriptor for read event
     loop.add_reader(rsock, reader)

     # Simulate the reception of data from the network
     loop.call_soon(wsock.send, 'abc'.encode())

     try:
         # Run the event loop
         loop.run_forever()
     finally:
         # We are done. Close sockets and the event loop.
         rsock.close()
         wsock.close()
         loop.close()

See also
........

   * A similar *note example: 2688. using transports, protocols, and the
     *note loop.create_connection(): 2e5. method.

   * Another similar *note example: 2686. using the high-level *note
     asyncio.open_connection(): 46b. function and streams.


File: python.info,  Node: Set signal handlers for SIGINT and SIGTERM,  Prev: Watch a file descriptor for read events,  Up: Examples<15>

5.18.1.69 Set signal handlers for SIGINT and SIGTERM
....................................................

(This ‘signals’ example only works on Unix.)

Register handlers for signals ‘SIGINT’ and ‘SIGTERM’ using the *note
loop.add_signal_handler(): 263d. method:

     import asyncio
     import functools
     import os
     import signal

     def ask_exit(signame, loop):
         print("got signal %s: exit" % signame)
         loop.stop()

     async def main():
         loop = asyncio.get_running_loop()

         for signame in {'SIGINT', 'SIGTERM'}:
             loop.add_signal_handler(
                 getattr(signal, signame),
                 functools.partial(ask_exit, signame, loop))

         await asyncio.sleep(3600)

     print("Event loop running for 1 hour, press Ctrl+C to interrupt.")
     print(f"pid {os.getpid()}: send SIGINT or SIGTERM to exit.")

     asyncio.run(main())


File: python.info,  Node: Futures,  Next: Transports and Protocols,  Prev: Event Loop,  Up: asyncio — Asynchronous I/O

5.18.1.70 Futures
.................

`Source code:' Lib/asyncio/futures.py(1), Lib/asyncio/base_futures.py(2)

__________________________________________________________________

`Future' objects are used to bridge `low-level callback-based code' with
high-level async/await code.

* Menu:

* Future Functions::
* Future Object::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/asyncio/futures.py

   (2) 
https://github.com/python/cpython/tree/3.9/Lib/asyncio/base_futures.py


File: python.info,  Node: Future Functions,  Next: Future Object,  Up: Futures

5.18.1.71 Future Functions
..........................

 -- Function: asyncio.isfuture (obj)

     Return ‘True’ if `obj' is either of:

        * an instance of *note asyncio.Future: 546,

        * an instance of *note asyncio.Task: 2e0,

        * a Future-like object with a ‘_asyncio_future_blocking’
          attribute.

     New in version 3.5.

 -- Function: asyncio.ensure_future (obj, *, loop=None)

     Return:

        * `obj' argument as is, if `obj' is a *note Future: 546, a *note
          Task: 2e0, or a Future-like object (*note isfuture(): 272a. is
          used for the test.)

        * a *note Task: 2e0. object wrapping `obj', if `obj' is a
          coroutine (*note iscoroutine(): 2667. is used for the test);
          in this case the coroutine will be scheduled by
          ‘ensure_future()’.

        * a *note Task: 2e0. object that would await on `obj', if `obj'
          is an awaitable (*note inspect.isawaitable(): 7ea. is used for
          the test.)

     If `obj' is neither of the above a *note TypeError: 1fe. is raised.

          Important: See also the *note create_task(): 2e1. function
          which is the preferred way for creating new Tasks.

          Save a reference to the result of this function, to avoid a
          task disappearing mid execution.

     Changed in version 3.5.1: The function accepts any *note awaitable:
     613. object.

 -- Function: asyncio.wrap_future (future, *, loop=None)

     Wrap a *note concurrent.futures.Future: c00. object in a *note
     asyncio.Future: 546. object.


File: python.info,  Node: Future Object,  Prev: Future Functions,  Up: Futures

5.18.1.72 Future Object
.......................

 -- Class: asyncio.Future (*, loop=None)

     A Future represents an eventual result of an asynchronous
     operation.  Not thread-safe.

     Future is an *note awaitable: 613. object.  Coroutines can await on
     Future objects until they either have a result or an exception set,
     or until they are cancelled.

     Typically Futures are used to enable low-level callback-based code
     (e.g.  in protocols implemented using asyncio *note transports:
     263e.) to interoperate with high-level async/await code.

     The rule of thumb is to never expose Future objects in user-facing
     APIs, and the recommended way to create a Future object is to call
     *note loop.create_future(): 616.  This way alternative event loop
     implementations can inject their own optimized implementations of a
     Future object.

     Changed in version 3.7: Added support for the *note contextvars:
     24. module.

      -- Method: result ()

          Return the result of the Future.

          If the Future is `done' and has a result set by the *note
          set_result(): 2659. method, the result value is returned.

          If the Future is `done' and has an exception set by the *note
          set_exception(): 265a. method, this method raises the
          exception.

          If the Future has been `cancelled', this method raises a *note
          CancelledError: 2da. exception.

          If the Future’s result isn’t yet available, this method raises
          a *note InvalidStateError: 265f. exception.

      -- Method: set_result (result)

          Mark the Future as `done' and set its result.

          Raises a *note InvalidStateError: 265f. error if the Future is
          already `done'.

      -- Method: set_exception (exception)

          Mark the Future as `done' and set an exception.

          Raises a *note InvalidStateError: 265f. error if the Future is
          already `done'.

      -- Method: done ()

          Return ‘True’ if the Future is `done'.

          A Future is `done' if it was `cancelled' or if it has a result
          or an exception set with *note set_result(): 2659. or *note
          set_exception(): 265a. calls.

      -- Method: cancelled ()

          Return ‘True’ if the Future was `cancelled'.

          The method is usually used to check if a Future is not
          `cancelled' before setting a result or an exception for it:

               if not fut.cancelled():
                   fut.set_result(42)

      -- Method: add_done_callback (callback, *, context=None)

          Add a callback to be run when the Future is `done'.

          The `callback' is called with the Future object as its only
          argument.

          If the Future is already `done' when this method is called,
          the callback is scheduled with *note loop.call_soon(): 455.

          An optional keyword-only `context' argument allows specifying
          a custom *note contextvars.Context: 260f. for the `callback'
          to run in.  The current context is used when no `context' is
          provided.

          *note functools.partial(): 8b5. can be used to pass parameters
          to the callback, e.g.:

               # Call 'print("Future:", fut)' when "fut" is done.
               fut.add_done_callback(
                   functools.partial(print, "Future:"))

          Changed in version 3.7: The `context' keyword-only parameter
          was added.  See PEP 567(1) for more details.

      -- Method: remove_done_callback (callback)

          Remove `callback' from the callbacks list.

          Returns the number of callbacks removed, which is typically 1,
          unless a callback was added more than once.

      -- Method: cancel (msg=None)

          Cancel the Future and schedule callbacks.

          If the Future is already `done' or `cancelled', return
          ‘False’.  Otherwise, change the Future’s state to `cancelled',
          schedule the callbacks, and return ‘True’.

          Changed in version 3.9: Added the ‘msg’ parameter.

      -- Method: exception ()

          Return the exception that was set on this Future.

          The exception (or ‘None’ if no exception was set) is returned
          only if the Future is `done'.

          If the Future has been `cancelled', this method raises a *note
          CancelledError: 2da. exception.

          If the Future isn’t `done' yet, this method raises an *note
          InvalidStateError: 265f. exception.

      -- Method: get_loop ()

          Return the event loop the Future object is bound to.

          New in version 3.7.

This example creates a Future object, creates and schedules an
asynchronous Task to set result for the Future, and waits until the
Future has a result:

     async def set_after(fut, delay, value):
         # Sleep for *delay* seconds.
         await asyncio.sleep(delay)

         # Set *value* as a result of *fut* Future.
         fut.set_result(value)

     async def main():
         # Get the current event loop.
         loop = asyncio.get_running_loop()

         # Create a new Future object.
         fut = loop.create_future()

         # Run "set_after()" coroutine in a parallel Task.
         # We are using the low-level "loop.create_task()" API here because
         # we already have a reference to the event loop at hand.
         # Otherwise we could have just used "asyncio.create_task()".
         loop.create_task(
             set_after(fut, 1, '... world'))

         print('hello ...')

         # Wait until *fut* has a result (1 second) and print it.
         print(await fut)

     asyncio.run(main())

     Important: The Future object was designed to mimic *note
     concurrent.futures.Future: c00.  Key differences include:

        - unlike asyncio Futures, *note concurrent.futures.Future: c00.
          instances cannot be awaited.

        - *note asyncio.Future.result(): 272d. and *note
          asyncio.Future.exception(): 2730. do not accept the `timeout'
          argument.

        - *note asyncio.Future.result(): 272d. and *note
          asyncio.Future.exception(): 2730. raise an *note
          InvalidStateError: 265f. exception when the Future is not
          `done'.

        - Callbacks registered with *note
          asyncio.Future.add_done_callback(): 459. are not called
          immediately.  They are scheduled with *note loop.call_soon():
          455. instead.

        - asyncio Future is not compatible with the *note
          concurrent.futures.wait(): f50. and *note
          concurrent.futures.as_completed(): 1223. functions.

        - *note asyncio.Future.cancel(): 265b. accepts an optional ‘msg’
          argument, but ‘concurrent.futures.cancel()’ does not.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0567


File: python.info,  Node: Transports and Protocols,  Next: Policies,  Prev: Futures,  Up: asyncio — Asynchronous I/O

5.18.1.73 Transports and Protocols
..................................

Preface
.......

Transports and Protocols are used by the `low-level' event loop APIs
such as *note loop.create_connection(): 2e5.  They use callback-based
programming style and enable high-performance implementations of network
or IPC protocols (e.g.  HTTP).

Essentially, transports and protocols should only be used in libraries
and frameworks and never in high-level asyncio applications.

This documentation page covers both *note Transports: 2734. and *note
Protocols: 2735.

Introduction
............

At the highest level, the transport is concerned with `how' bytes are
transmitted, while the protocol determines `which' bytes to transmit
(and to some extent when).

A different way of saying the same thing: a transport is an abstraction
for a socket (or similar I/O endpoint) while a protocol is an
abstraction for an application, from the transport’s point of view.

Yet another view is the transport and protocol interfaces together
define an abstract interface for using network I/O and interprocess I/O.

There is always a 1:1 relationship between transport and protocol
objects: the protocol calls transport methods to send data, while the
transport calls protocol methods to pass it data that has been received.

Most of connection oriented event loop methods (such as *note
loop.create_connection(): 2e5.) usually accept a `protocol_factory'
argument used to create a `Protocol' object for an accepted connection,
represented by a `Transport' object.  Such methods usually return a
tuple of ‘(transport, protocol)’.

Contents
........

This documentation page contains the following sections:

   * The *note Transports: 2734. section documents asyncio *note
     BaseTransport: 2736, *note ReadTransport: 270f, *note
     WriteTransport: 2710, *note Transport: 2737, *note
     DatagramTransport: 2738, and *note SubprocessTransport: 271b.
     classes.

   * The *note Protocols: 2735. section documents asyncio *note
     BaseProtocol: 2739, *note Protocol: 273a, *note BufferedProtocol:
     3eb, *note DatagramProtocol: 273b, and *note SubprocessProtocol:
     271a. classes.

   * The *note Examples: 273c. section showcases how to work with
     transports, protocols, and low-level event loop APIs.

* Menu:

* Transports::
* Protocols::
* Examples: Examples<16>.


File: python.info,  Node: Transports,  Next: Protocols,  Up: Transports and Protocols

5.18.1.74 Transports
....................

`Source code:' Lib/asyncio/transports.py(1)

__________________________________________________________________

Transports are classes provided by *note asyncio: 9. in order to
abstract various kinds of communication channels.

Transport objects are always instantiated by an *note asyncio event
loop: 737.

asyncio implements transports for TCP, UDP, SSL, and subprocess pipes.
The methods available on a transport depend on the transport’s kind.

The transport classes are *note not thread safe: 2655.

* Menu:

* Transports Hierarchy::
* Base Transport::
* Read-only Transports::
* Write-only Transports::
* Datagram Transports::
* Subprocess Transports::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/asyncio/transports.py


File: python.info,  Node: Transports Hierarchy,  Next: Base Transport,  Up: Transports

5.18.1.75 Transports Hierarchy
..............................

 -- Class: asyncio.BaseTransport

     Base class for all transports.  Contains methods that all asyncio
     transports share.

 -- Class: asyncio.WriteTransport (BaseTransport)

     A base transport for write-only connections.

     Instances of the `WriteTransport' class are returned from the *note
     loop.connect_write_pipe(): 26ad. event loop method and are also
     used by subprocess-related methods like *note
     loop.subprocess_exec(): 263c.

 -- Class: asyncio.ReadTransport (BaseTransport)

     A base transport for read-only connections.

     Instances of the `ReadTransport' class are returned from the *note
     loop.connect_read_pipe(): 26ac. event loop method and are also used
     by subprocess-related methods like *note loop.subprocess_exec():
     263c.

 -- Class: asyncio.Transport (WriteTransport, ReadTransport)

     Interface representing a bidirectional transport, such as a TCP
     connection.

     The user does not instantiate a transport directly; they call a
     utility function, passing it a protocol factory and other
     information necessary to create the transport and protocol.

     Instances of the `Transport' class are returned from or used by
     event loop methods like *note loop.create_connection(): 2e5, *note
     loop.create_unix_connection(): 266e, *note loop.create_server():
     465, *note loop.sendfile(): 2703, etc.

 -- Class: asyncio.DatagramTransport (BaseTransport)

     A transport for datagram (UDP) connections.

     Instances of the `DatagramTransport' class are returned from the
     *note loop.create_datagram_endpoint(): 189. event loop method.

 -- Class: asyncio.SubprocessTransport (BaseTransport)

     An abstraction to represent a connection between a parent and its
     child OS process.

     Instances of the `SubprocessTransport' class are returned from
     event loop methods *note loop.subprocess_shell(): 26aa. and *note
     loop.subprocess_exec(): 263c.


File: python.info,  Node: Base Transport,  Next: Read-only Transports,  Prev: Transports Hierarchy,  Up: Transports

5.18.1.76 Base Transport
........................

 -- Method: BaseTransport.close ()

     Close the transport.

     If the transport has a buffer for outgoing data, buffered data will
     be flushed asynchronously.  No more data will be received.  After
     all buffered data is flushed, the protocol’s *note
     protocol.connection_lost(): 2740. method will be called with *note
     None: 203. as its argument.

 -- Method: BaseTransport.is_closing ()

     Return ‘True’ if the transport is closing or is closed.

 -- Method: BaseTransport.get_extra_info (name, default=None)

     Return information about the transport or underlying resources it
     uses.

     `name' is a string representing the piece of transport-specific
     information to get.

     `default' is the value to return if the information is not
     available, or if the transport does not support querying it with
     the given third-party event loop implementation or on the current
     platform.

     For example, the following code attempts to get the underlying
     socket object of the transport:

          sock = transport.get_extra_info('socket')
          if sock is not None:
              print(sock.getsockopt(...))

     Categories of information that can be queried on some transports:

        * socket:

             - ‘'peername'’: the remote address to which the socket is
               connected, result of *note socket.socket.getpeername():
               2741. (‘None’ on error)

             - ‘'socket'’: *note socket.socket: 767. instance

             - ‘'sockname'’: the socket’s own address, result of *note
               socket.socket.getsockname(): 2742.

        * SSL socket:

             - ‘'compression'’: the compression algorithm being used as
               a string, or ‘None’ if the connection isn’t compressed;
               result of *note ssl.SSLSocket.compression(): b6d.

             - ‘'cipher'’: a three-value tuple containing the name of
               the cipher being used, the version of the SSL protocol
               that defines its use, and the number of secret bits being
               used; result of *note ssl.SSLSocket.cipher(): 2743.

             - ‘'peercert'’: peer certificate; result of *note
               ssl.SSLSocket.getpeercert(): 9b7.

             - ‘'sslcontext'’: *note ssl.SSLContext: 4ea. instance

             - ‘'ssl_object'’: *note ssl.SSLObject: 4e9. or *note
               ssl.SSLSocket: 192. instance

        * pipe:

             - ‘'pipe'’: pipe object

        * subprocess:

             - ‘'subprocess'’: *note subprocess.Popen: 3db. instance

 -- Method: BaseTransport.set_protocol (protocol)

     Set a new protocol.

     Switching protocol should only be done when both protocols are
     documented to support the switch.

 -- Method: BaseTransport.get_protocol ()

     Return the current protocol.


File: python.info,  Node: Read-only Transports,  Next: Write-only Transports,  Prev: Base Transport,  Up: Transports

5.18.1.77 Read-only Transports
..............................

 -- Method: ReadTransport.is_reading ()

     Return ‘True’ if the transport is receiving new data.

     New in version 3.7.

 -- Method: ReadTransport.pause_reading ()

     Pause the receiving end of the transport.  No data will be passed
     to the protocol’s *note protocol.data_received(): 2747. method
     until *note resume_reading(): 470. is called.

     Changed in version 3.7: The method is idempotent, i.e.  it can be
     called when the transport is already paused or closed.

 -- Method: ReadTransport.resume_reading ()

     Resume the receiving end.  The protocol’s *note
     protocol.data_received(): 2747. method will be called once again if
     some data is available for reading.

     Changed in version 3.7: The method is idempotent, i.e.  it can be
     called when the transport is already reading.


File: python.info,  Node: Write-only Transports,  Next: Datagram Transports,  Prev: Read-only Transports,  Up: Transports

5.18.1.78 Write-only Transports
...............................

 -- Method: WriteTransport.abort ()

     Close the transport immediately, without waiting for pending
     operations to complete.  Buffered data will be lost.  No more data
     will be received.  The protocol’s *note protocol.connection_lost():
     2740. method will eventually be called with *note None: 203. as its
     argument.

 -- Method: WriteTransport.can_write_eof ()

     Return *note True: 594. if the transport supports *note
     write_eof(): 274b, *note False: 48f. if not.

 -- Method: WriteTransport.get_write_buffer_size ()

     Return the current size of the output buffer used by the transport.

 -- Method: WriteTransport.get_write_buffer_limits ()

     Get the `high' and `low' watermarks for write flow control.  Return
     a tuple ‘(low, high)’ where `low' and `high' are positive number of
     bytes.

     Use *note set_write_buffer_limits(): 274d. to set the limits.

     New in version 3.4.2.

 -- Method: WriteTransport.set_write_buffer_limits (high=None, low=None)

     Set the `high' and `low' watermarks for write flow control.

     These two values (measured in number of bytes) control when the
     protocol’s *note protocol.pause_writing(): 274e. and *note
     protocol.resume_writing(): 274f. methods are called.  If specified,
     the low watermark must be less than or equal to the high watermark.
     Neither `high' nor `low' can be negative.

     *note pause_writing(): 274e. is called when the buffer size becomes
     greater than or equal to the `high' value.  If writing has been
     paused, *note resume_writing(): 274f. is called when the buffer
     size becomes less than or equal to the `low' value.

     The defaults are implementation-specific.  If only the high
     watermark is given, the low watermark defaults to an
     implementation-specific value less than or equal to the high
     watermark.  Setting `high' to zero forces `low' to zero as well,
     and causes *note pause_writing(): 274e. to be called whenever the
     buffer becomes non-empty.  Setting `low' to zero causes *note
     resume_writing(): 274f. to be called only once the buffer is empty.
     Use of zero for either limit is generally sub-optimal as it reduces
     opportunities for doing I/O and computation concurrently.

     Use *note get_write_buffer_limits(): 78f. to get the limits.

 -- Method: WriteTransport.write (data)

     Write some `data' bytes to the transport.

     This method does not block; it buffers the data and arranges for it
     to be sent out asynchronously.

 -- Method: WriteTransport.writelines (list_of_data)

     Write a list (or any iterable) of data bytes to the transport.
     This is functionally equivalent to calling *note write(): 2750. on
     each element yielded by the iterable, but may be implemented more
     efficiently.

 -- Method: WriteTransport.write_eof ()

     Close the write end of the transport after flushing all buffered
     data.  Data may still be received.

     This method can raise *note NotImplementedError: 704. if the
     transport (e.g.  SSL) doesn’t support half-closed connections.


File: python.info,  Node: Datagram Transports,  Next: Subprocess Transports,  Prev: Write-only Transports,  Up: Transports

5.18.1.79 Datagram Transports
.............................

 -- Method: DatagramTransport.sendto (data, addr=None)

     Send the `data' bytes to the remote peer given by `addr' (a
     transport-dependent target address).  If `addr' is *note None: 203,
     the data is sent to the target address given on transport creation.

     This method does not block; it buffers the data and arranges for it
     to be sent out asynchronously.

 -- Method: DatagramTransport.abort ()

     Close the transport immediately, without waiting for pending
     operations to complete.  Buffered data will be lost.  No more data
     will be received.  The protocol’s *note protocol.connection_lost():
     2740. method will eventually be called with *note None: 203. as its
     argument.


File: python.info,  Node: Subprocess Transports,  Prev: Datagram Transports,  Up: Transports

5.18.1.80 Subprocess Transports
...............................

 -- Method: SubprocessTransport.get_pid ()

     Return the subprocess process id as an integer.

 -- Method: SubprocessTransport.get_pipe_transport (fd)

     Return the transport for the communication pipe corresponding to
     the integer file descriptor `fd':

        * ‘0’: readable streaming transport of the standard input
          (`stdin'), or *note None: 203. if the subprocess was not
          created with ‘stdin=PIPE’

        * ‘1’: writable streaming transport of the standard output
          (`stdout'), or *note None: 203. if the subprocess was not
          created with ‘stdout=PIPE’

        * ‘2’: writable streaming transport of the standard error
          (`stderr'), or *note None: 203. if the subprocess was not
          created with ‘stderr=PIPE’

        * other `fd': *note None: 203.

 -- Method: SubprocessTransport.get_returncode ()

     Return the subprocess return code as an integer or *note None: 203.
     if it hasn’t returned, which is similar to the *note
     subprocess.Popen.returncode: 10a5. attribute.

 -- Method: SubprocessTransport.kill ()

     Kill the subprocess.

     On POSIX systems, the function sends SIGKILL to the subprocess.  On
     Windows, this method is an alias for *note terminate(): 275a.

     See also *note subprocess.Popen.kill(): 25d4.

 -- Method: SubprocessTransport.send_signal (signal)

     Send the `signal' number to the subprocess, as in *note
     subprocess.Popen.send_signal(): 10a4.

 -- Method: SubprocessTransport.terminate ()

     Stop the subprocess.

     On POSIX systems, this method sends SIGTERM to the subprocess.  On
     Windows, the Windows API function TerminateProcess() is called to
     stop the subprocess.

     See also *note subprocess.Popen.terminate(): 25d3.

 -- Method: SubprocessTransport.close ()

     Kill the subprocess by calling the *note kill(): 2759. method.

     If the subprocess hasn’t returned yet, and close transports of
     `stdin', `stdout', and `stderr' pipes.


File: python.info,  Node: Protocols,  Next: Examples<16>,  Prev: Transports,  Up: Transports and Protocols

5.18.1.81 Protocols
...................

`Source code:' Lib/asyncio/protocols.py(1)

__________________________________________________________________

asyncio provides a set of abstract base classes that should be used to
implement network protocols.  Those classes are meant to be used
together with *note transports: 26fb.

Subclasses of abstract base protocol classes may implement some or all
methods.  All these methods are callbacks: they are called by transports
on certain events, for example when some data is received.  A base
protocol method should be called by the corresponding transport.

* Menu:

* Base Protocols::
* Base Protocol::
* Streaming Protocols::
* Buffered Streaming Protocols::
* Datagram Protocols::
* Subprocess Protocols::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/asyncio/protocols.py


File: python.info,  Node: Base Protocols,  Next: Base Protocol,  Up: Protocols

5.18.1.82 Base Protocols
........................

 -- Class: asyncio.BaseProtocol

     Base protocol with methods that all protocols share.

 -- Class: asyncio.Protocol (BaseProtocol)

     The base class for implementing streaming protocols (TCP, Unix
     sockets, etc).

 -- Class: asyncio.BufferedProtocol (BaseProtocol)

     A base class for implementing streaming protocols with manual
     control of the receive buffer.

 -- Class: asyncio.DatagramProtocol (BaseProtocol)

     The base class for implementing datagram (UDP) protocols.

 -- Class: asyncio.SubprocessProtocol (BaseProtocol)

     The base class for implementing protocols communicating with child
     processes (unidirectional pipes).


File: python.info,  Node: Base Protocol,  Next: Streaming Protocols,  Prev: Base Protocols,  Up: Protocols

5.18.1.83 Base Protocol
.......................

All asyncio protocols can implement Base Protocol callbacks.

Connection Callbacks
....................

Connection callbacks are called on all protocols, exactly once per a
successful connection.  All other protocol callbacks can only be called
between those two methods.

 -- Method: BaseProtocol.connection_made (transport)

     Called when a connection is made.

     The `transport' argument is the transport representing the
     connection.  The protocol is responsible for storing the reference
     to its transport.

 -- Method: BaseProtocol.connection_lost (exc)

     Called when the connection is lost or closed.

     The argument is either an exception object or *note None: 203.  The
     latter means a regular EOF is received, or the connection was
     aborted or closed by this side of the connection.

Flow Control Callbacks
......................

Flow control callbacks can be called by transports to pause or resume
writing performed by the protocol.

See the documentation of the *note set_write_buffer_limits(): 274d.
method for more details.

 -- Method: BaseProtocol.pause_writing ()

     Called when the transport’s buffer goes over the high watermark.

 -- Method: BaseProtocol.resume_writing ()

     Called when the transport’s buffer drains below the low watermark.

If the buffer size equals the high watermark, *note pause_writing():
274e. is not called: the buffer size must go strictly over.

Conversely, *note resume_writing(): 274f. is called when the buffer size
is equal or lower than the low watermark.  These end conditions are
important to ensure that things go as expected when either mark is zero.


File: python.info,  Node: Streaming Protocols,  Next: Buffered Streaming Protocols,  Prev: Base Protocol,  Up: Protocols

5.18.1.84 Streaming Protocols
.............................

Event methods, such as *note loop.create_server(): 465, *note
loop.create_unix_server(): 466, *note loop.create_connection(): 2e5,
*note loop.create_unix_connection(): 266e, *note
loop.connect_accepted_socket(): 46d, *note loop.connect_read_pipe():
26ac, and *note loop.connect_write_pipe(): 26ad. accept factories that
return streaming protocols.

 -- Method: Protocol.data_received (data)

     Called when some data is received.  `data' is a non-empty bytes
     object containing the incoming data.

     Whether the data is buffered, chunked or reassembled depends on the
     transport.  In general, you shouldn’t rely on specific semantics
     and instead make your parsing generic and flexible.  However, data
     is always received in the correct order.

     The method can be called an arbitrary number of times while a
     connection is open.

     However, *note protocol.eof_received(): 2760. is called at most
     once.  Once ‘eof_received()’ is called, ‘data_received()’ is not
     called anymore.

 -- Method: Protocol.eof_received ()

     Called when the other end signals it won’t send any more data (for
     example by calling *note transport.write_eof(): 274b, if the other
     end also uses asyncio).

     This method may return a false value (including ‘None’), in which
     case the transport will close itself.  Conversely, if this method
     returns a true value, the protocol used determines whether to close
     the transport.  Since the default implementation returns ‘None’, it
     implicitly closes the connection.

     Some transports, including SSL, don’t support half-closed
     connections, in which case returning true from this method will
     result in the connection being closed.

State machine:

     start -> connection_made
         [-> data_received]*
         [-> eof_received]?
     -> connection_lost -> end


File: python.info,  Node: Buffered Streaming Protocols,  Next: Datagram Protocols,  Prev: Streaming Protocols,  Up: Protocols

5.18.1.85 Buffered Streaming Protocols
......................................

New in version 3.7.

Buffered Protocols can be used with any event loop method that supports
*note Streaming Protocols: 275f.

‘BufferedProtocol’ implementations allow explicit manual allocation and
control of the receive buffer.  Event loops can then use the buffer
provided by the protocol to avoid unnecessary data copies.  This can
result in noticeable performance improvement for protocols that receive
big amounts of data.  Sophisticated protocol implementations can
significantly reduce the number of buffer allocations.

The following callbacks are called on *note BufferedProtocol: 3eb.
instances:

 -- Method: BufferedProtocol.get_buffer (sizehint)

     Called to allocate a new receive buffer.

     `sizehint' is the recommended minimum size for the returned buffer.
     It is acceptable to return smaller or larger buffers than what
     `sizehint' suggests.  When set to -1, the buffer size can be
     arbitrary.  It is an error to return a buffer with a zero size.

     ‘get_buffer()’ must return an object implementing the *note buffer
     protocol: 171c.

 -- Method: BufferedProtocol.buffer_updated (nbytes)

     Called when the buffer was updated with the received data.

     `nbytes' is the total number of bytes that were written to the
     buffer.

 -- Method: BufferedProtocol.eof_received ()

     See the documentation of the *note protocol.eof_received(): 2760.
     method.

*note get_buffer(): 2762. can be called an arbitrary number of times
during a connection.  However, *note protocol.eof_received(): 2760. is
called at most once and, if called, *note get_buffer(): 2762. and *note
buffer_updated(): 2763. won’t be called after it.

State machine:

     start -> connection_made
         [-> get_buffer
             [-> buffer_updated]?
         ]*
         [-> eof_received]?
     -> connection_lost -> end


File: python.info,  Node: Datagram Protocols,  Next: Subprocess Protocols,  Prev: Buffered Streaming Protocols,  Up: Protocols

5.18.1.86 Datagram Protocols
............................

Datagram Protocol instances should be constructed by protocol factories
passed to the *note loop.create_datagram_endpoint(): 189. method.

 -- Method: DatagramProtocol.datagram_received (data, addr)

     Called when a datagram is received.  `data' is a bytes object
     containing the incoming data.  `addr' is the address of the peer
     sending the data; the exact format depends on the transport.

 -- Method: DatagramProtocol.error_received (exc)

     Called when a previous send or receive operation raises an *note
     OSError: 304.  `exc' is the *note OSError: 304. instance.

     This method is called in rare conditions, when the transport (e.g.
     UDP) detects that a datagram could not be delivered to its
     recipient.  In many conditions though, undeliverable datagrams will
     be silently dropped.

     Note: On BSD systems (macOS, FreeBSD, etc.)  flow control is not
     supported for datagram protocols, because there is no reliable way
     to detect send failures caused by writing too many packets.

     The socket always appears ‘ready’ and excess packets are dropped.
     An *note OSError: 304. with ‘errno’ set to *note errno.ENOBUFS:
     23f9. may or may not be raised; if it is raised, it will be
     reported to *note DatagramProtocol.error_received(): 2767. but
     otherwise ignored.


File: python.info,  Node: Subprocess Protocols,  Prev: Datagram Protocols,  Up: Protocols

5.18.1.87 Subprocess Protocols
..............................

Subprocess Protocol instances should be constructed by protocol
factories passed to the *note loop.subprocess_exec(): 263c. and *note
loop.subprocess_shell(): 26aa. methods.

 -- Method: SubprocessProtocol.pipe_data_received (fd, data)

     Called when the child process writes data into its stdout or stderr
     pipe.

     `fd' is the integer file descriptor of the pipe.

     `data' is a non-empty bytes object containing the received data.

 -- Method: SubprocessProtocol.pipe_connection_lost (fd, exc)

     Called when one of the pipes communicating with the child process
     is closed.

     `fd' is the integer file descriptor that was closed.

 -- Method: SubprocessProtocol.process_exited ()

     Called when the child process has exited.


File: python.info,  Node: Examples<16>,  Prev: Protocols,  Up: Transports and Protocols

5.18.1.88 Examples
..................

* Menu:

* TCP Echo Server::
* TCP Echo Client::
* UDP Echo Server::
* UDP Echo Client::
* Connecting Existing Sockets::
* loop.subprocess_exec() and SubprocessProtocol: loop subprocess_exec and SubprocessProtocol.


File: python.info,  Node: TCP Echo Server,  Next: TCP Echo Client,  Up: Examples<16>

5.18.1.89 TCP Echo Server
.........................

Create a TCP echo server using the *note loop.create_server(): 465.
method, send back received data, and close the connection:

     import asyncio


     class EchoServerProtocol(asyncio.Protocol):
         def connection_made(self, transport):
             peername = transport.get_extra_info('peername')
             print('Connection from {}'.format(peername))
             self.transport = transport

         def data_received(self, data):
             message = data.decode()
             print('Data received: {!r}'.format(message))

             print('Send: {!r}'.format(message))
             self.transport.write(data)

             print('Close the client socket')
             self.transport.close()


     async def main():
         # Get a reference to the event loop as we plan to use
         # low-level APIs.
         loop = asyncio.get_running_loop()

         server = await loop.create_server(
             lambda: EchoServerProtocol(),
             '127.0.0.1', 8888)

         async with server:
             await server.serve_forever()


     asyncio.run(main())

See also
........

The *note TCP echo server using streams: 2682. example uses the
high-level *note asyncio.start_server(): 46c. function.


File: python.info,  Node: TCP Echo Client,  Next: UDP Echo Server,  Prev: TCP Echo Server,  Up: Examples<16>

5.18.1.90 TCP Echo Client
.........................

A TCP echo client using the *note loop.create_connection(): 2e5. method,
sends data, and waits until the connection is closed:

     import asyncio


     class EchoClientProtocol(asyncio.Protocol):
         def __init__(self, message, on_con_lost):
             self.message = message
             self.on_con_lost = on_con_lost

         def connection_made(self, transport):
             transport.write(self.message.encode())
             print('Data sent: {!r}'.format(self.message))

         def data_received(self, data):
             print('Data received: {!r}'.format(data.decode()))

         def connection_lost(self, exc):
             print('The server closed the connection')
             self.on_con_lost.set_result(True)


     async def main():
         # Get a reference to the event loop as we plan to use
         # low-level APIs.
         loop = asyncio.get_running_loop()

         on_con_lost = loop.create_future()
         message = 'Hello World!'

         transport, protocol = await loop.create_connection(
             lambda: EchoClientProtocol(message, on_con_lost),
             '127.0.0.1', 8888)

         # Wait until the protocol signals that the connection
         # is lost and close the transport.
         try:
             await on_con_lost
         finally:
             transport.close()


     asyncio.run(main())

See also
........

The *note TCP echo client using streams: 267f. example uses the
high-level *note asyncio.open_connection(): 46b. function.


File: python.info,  Node: UDP Echo Server,  Next: UDP Echo Client,  Prev: TCP Echo Client,  Up: Examples<16>

5.18.1.91 UDP Echo Server
.........................

A UDP echo server, using the *note loop.create_datagram_endpoint(): 189.
method, sends back received data:

     import asyncio


     class EchoServerProtocol:
         def connection_made(self, transport):
             self.transport = transport

         def datagram_received(self, data, addr):
             message = data.decode()
             print('Received %r from %s' % (message, addr))
             print('Send %r to %s' % (message, addr))
             self.transport.sendto(data, addr)


     async def main():
         print("Starting UDP server")

         # Get a reference to the event loop as we plan to use
         # low-level APIs.
         loop = asyncio.get_running_loop()

         # One protocol instance will be created to serve all
         # client requests.
         transport, protocol = await loop.create_datagram_endpoint(
             lambda: EchoServerProtocol(),
             local_addr=('127.0.0.1', 9999))

         try:
             await asyncio.sleep(3600)  # Serve for 1 hour.
         finally:
             transport.close()


     asyncio.run(main())


File: python.info,  Node: UDP Echo Client,  Next: Connecting Existing Sockets,  Prev: UDP Echo Server,  Up: Examples<16>

5.18.1.92 UDP Echo Client
.........................

A UDP echo client, using the *note loop.create_datagram_endpoint(): 189.
method, sends data and closes the transport when it receives the answer:

     import asyncio


     class EchoClientProtocol:
         def __init__(self, message, on_con_lost):
             self.message = message
             self.on_con_lost = on_con_lost
             self.transport = None

         def connection_made(self, transport):
             self.transport = transport
             print('Send:', self.message)
             self.transport.sendto(self.message.encode())

         def datagram_received(self, data, addr):
             print("Received:", data.decode())

             print("Close the socket")
             self.transport.close()

         def error_received(self, exc):
             print('Error received:', exc)

         def connection_lost(self, exc):
             print("Connection closed")
             self.on_con_lost.set_result(True)


     async def main():
         # Get a reference to the event loop as we plan to use
         # low-level APIs.
         loop = asyncio.get_running_loop()

         on_con_lost = loop.create_future()
         message = "Hello World!"

         transport, protocol = await loop.create_datagram_endpoint(
             lambda: EchoClientProtocol(message, on_con_lost),
             remote_addr=('127.0.0.1', 9999))

         try:
             await on_con_lost
         finally:
             transport.close()


     asyncio.run(main())


File: python.info,  Node: Connecting Existing Sockets,  Next: loop subprocess_exec and SubprocessProtocol,  Prev: UDP Echo Client,  Up: Examples<16>

5.18.1.93 Connecting Existing Sockets
.....................................

Wait until a socket receives data using the *note
loop.create_connection(): 2e5. method with a protocol:

     import asyncio
     import socket


     class MyProtocol(asyncio.Protocol):

         def __init__(self, on_con_lost):
             self.transport = None
             self.on_con_lost = on_con_lost

         def connection_made(self, transport):
             self.transport = transport

         def data_received(self, data):
             print("Received:", data.decode())

             # We are done: close the transport;
             # connection_lost() will be called automatically.
             self.transport.close()

         def connection_lost(self, exc):
             # The socket has been closed
             self.on_con_lost.set_result(True)


     async def main():
         # Get a reference to the event loop as we plan to use
         # low-level APIs.
         loop = asyncio.get_running_loop()
         on_con_lost = loop.create_future()

         # Create a pair of connected sockets
         rsock, wsock = socket.socketpair()

         # Register the socket to wait for data.
         transport, protocol = await loop.create_connection(
             lambda: MyProtocol(on_con_lost), sock=rsock)

         # Simulate the reception of data from the network.
         loop.call_soon(wsock.send, 'abc'.encode())

         try:
             await protocol.on_con_lost
         finally:
             transport.close()
             wsock.close()

     asyncio.run(main())

See also
........

The *note watch a file descriptor for read events: 2689. example uses
the low-level *note loop.add_reader(): 268a. method to register an FD.

The *note register an open socket to wait for data using streams: 2686.
example uses high-level streams created by the *note open_connection():
46b. function in a coroutine.


File: python.info,  Node: loop subprocess_exec and SubprocessProtocol,  Prev: Connecting Existing Sockets,  Up: Examples<16>

5.18.1.94 loop.subprocess_exec() and SubprocessProtocol
.......................................................

An example of a subprocess protocol used to get the output of a
subprocess and to wait for the subprocess exit.

The subprocess is created by the *note loop.subprocess_exec(): 263c.
method:

     import asyncio
     import sys

     class DateProtocol(asyncio.SubprocessProtocol):
         def __init__(self, exit_future):
             self.exit_future = exit_future
             self.output = bytearray()

         def pipe_data_received(self, fd, data):
             self.output.extend(data)

         def process_exited(self):
             self.exit_future.set_result(True)

     async def get_date():
         # Get a reference to the event loop as we plan to use
         # low-level APIs.
         loop = asyncio.get_running_loop()

         code = 'import datetime; print(datetime.datetime.now())'
         exit_future = asyncio.Future(loop=loop)

         # Create the subprocess controlled by DateProtocol;
         # redirect the standard output into a pipe.
         transport, protocol = await loop.subprocess_exec(
             lambda: DateProtocol(exit_future),
             sys.executable, '-c', code,
             stdin=None, stderr=None)

         # Wait for the subprocess exit using the process_exited()
         # method of the protocol.
         await exit_future

         # Close the stdout pipe.
         transport.close()

         # Read the output which was collected by the
         # pipe_data_received() method of the protocol.
         data = bytes(protocol.output)
         return data.decode('ascii').rstrip()

     date = asyncio.run(get_date())
     print(f"Current date: {date}")

See also the *note same example: 26c5. written using high-level APIs.


File: python.info,  Node: Policies,  Next: Platform Support,  Prev: Transports and Protocols,  Up: asyncio — Asynchronous I/O

5.18.1.95 Policies
..................

An event loop policy is a global per-process object that controls the
management of the event loop.  Each event loop has a default policy,
which can be changed and customized using the policy API.

A policy defines the notion of `context' and manages a separate event
loop per context.  The default policy defines `context' to be the
current thread.

By using a custom event loop policy, the behavior of *note
get_event_loop(): 45d, *note set_event_loop(): 26e3, and *note
new_event_loop(): 26e4. functions can be customized.

Policy objects should implement the APIs defined in the *note
AbstractEventLoopPolicy: 2774. abstract base class.

* Menu:

* Getting and Setting the Policy::
* Policy Objects::
* Process Watchers::
* Custom Policies::


File: python.info,  Node: Getting and Setting the Policy,  Next: Policy Objects,  Up: Policies

5.18.1.96 Getting and Setting the Policy
........................................

The following functions can be used to get and set the policy for the
current process:

 -- Function: asyncio.get_event_loop_policy ()

     Return the current process-wide policy.

 -- Function: asyncio.set_event_loop_policy (policy)

     Set the current process-wide policy to `policy'.

     If `policy' is set to ‘None’, the default policy is restored.


File: python.info,  Node: Policy Objects,  Next: Process Watchers,  Prev: Getting and Setting the Policy,  Up: Policies

5.18.1.97 Policy Objects
........................

The abstract event loop policy base class is defined as follows:

 -- Class: asyncio.AbstractEventLoopPolicy

     An abstract base class for asyncio policies.

      -- Method: get_event_loop ()

          Get the event loop for the current context.

          Return an event loop object implementing the *note
          AbstractEventLoop: 233. interface.

          This method should never return ‘None’.

          Changed in version 3.6.

      -- Method: set_event_loop (loop)

          Set the event loop for the current context to `loop'.

      -- Method: new_event_loop ()

          Create and return a new event loop object.

          This method should never return ‘None’.

      -- Method: get_child_watcher ()

          Get a child process watcher object.

          Return a watcher object implementing the *note
          AbstractChildWatcher: 277d. interface.

          This function is Unix specific.

      -- Method: set_child_watcher (watcher)

          Set the current child process watcher to `watcher'.

          This function is Unix specific.

asyncio ships with the following built-in policies:

 -- Class: asyncio.DefaultEventLoopPolicy

     The default asyncio policy.  Uses *note SelectorEventLoop: 26c2. on
     Unix and *note ProactorEventLoop: 2de. on Windows.

     There is no need to install the default policy manually.  asyncio
     is configured to use the default policy automatically.

     Changed in version 3.8: On Windows, *note ProactorEventLoop: 2de.
     is now used by default.

 -- Class: asyncio.WindowsSelectorEventLoopPolicy

     An alternative event loop policy that uses the *note
     SelectorEventLoop: 26c2. event loop implementation.

     *note Availability: 1491.: Windows.

 -- Class: asyncio.WindowsProactorEventLoopPolicy

     An alternative event loop policy that uses the *note
     ProactorEventLoop: 2de. event loop implementation.

     *note Availability: 1491.: Windows.


File: python.info,  Node: Process Watchers,  Next: Custom Policies,  Prev: Policy Objects,  Up: Policies

5.18.1.98 Process Watchers
..........................

A process watcher allows customization of how an event loop monitors
child processes on Unix.  Specifically, the event loop needs to know
when a child process has exited.

In asyncio, child processes are created with *note
create_subprocess_exec(): 3b4. and *note loop.subprocess_exec(): 263c.
functions.

asyncio defines the *note AbstractChildWatcher: 277d. abstract base
class, which child watchers should implement, and has four different
implementations: *note ThreadedChildWatcher: 26c4. (configured to be
used by default), *note MultiLoopChildWatcher: 2783, *note
SafeChildWatcher: 2784, and *note FastChildWatcher: 2785.

See also the *note Subprocess and Threads: 26ba. section.

The following two functions can be used to customize the child process
watcher implementation used by the asyncio event loop:

 -- Function: asyncio.get_child_watcher ()

     Return the current child watcher for the current policy.

 -- Function: asyncio.set_child_watcher (watcher)

     Set the current child watcher to `watcher' for the current policy.
     `watcher' must implement methods defined in the *note
     AbstractChildWatcher: 277d. base class.

     Note: Third-party event loops implementations might not support
     custom child watchers.  For such event loops, using *note
     set_child_watcher(): 2787. might be prohibited or have no effect.

 -- Class: asyncio.AbstractChildWatcher

      -- Method: add_child_handler (pid, callback, *args)

          Register a new child handler.

          Arrange for ‘callback(pid, returncode, *args)’ to be called
          when a process with PID equal to `pid' terminates.  Specifying
          another callback for the same process replaces the previous
          handler.

          The `callback' callable must be thread-safe.

      -- Method: remove_child_handler (pid)

          Removes the handler for process with PID equal to `pid'.

          The function returns ‘True’ if the handler was successfully
          removed, ‘False’ if there was nothing to remove.

      -- Method: attach_loop (loop)

          Attach the watcher to an event loop.

          If the watcher was previously attached to an event loop, then
          it is first detached before attaching to the new loop.

          Note: loop may be ‘None’.

      -- Method: is_active ()

          Return ‘True’ if the watcher is ready to use.

          Spawning a subprocess with `inactive' current child watcher
          raises *note RuntimeError: 3dc.

          New in version 3.8.

      -- Method: close ()

          Close the watcher.

          This method has to be called to ensure that underlying
          resources are cleaned-up.

 -- Class: asyncio.ThreadedChildWatcher

     This implementation starts a new waiting thread for every
     subprocess spawn.

     It works reliably even when the asyncio event loop is run in a
     non-main OS thread.

     There is no noticeable overhead when handling a big number of
     children (`O(1)' each time a child terminates), but starting a
     thread per process requires extra memory.

     This watcher is used by default.

     New in version 3.8.

 -- Class: asyncio.MultiLoopChildWatcher

     This implementation registers a ‘SIGCHLD’ signal handler on
     instantiation.  That can break third-party code that installs a
     custom handler for ‘SIGCHLD’ signal.

     The watcher avoids disrupting other code spawning processes by
     polling every process explicitly on a ‘SIGCHLD’ signal.

     There is no limitation for running subprocesses from different
     threads once the watcher is installed.

     The solution is safe but it has a significant overhead when
     handling a big number of processes (`O(n)' each time a ‘SIGCHLD’ is
     received).

     New in version 3.8.

 -- Class: asyncio.SafeChildWatcher

     This implementation uses active event loop from the main thread to
     handle ‘SIGCHLD’ signal.  If the main thread has no running event
     loop another thread cannot spawn a subprocess (*note RuntimeError:
     3dc. is raised).

     The watcher avoids disrupting other code spawning processes by
     polling every process explicitly on a ‘SIGCHLD’ signal.

     This solution is as safe as *note MultiLoopChildWatcher: 2783. and
     has the same `O(N)' complexity but requires a running event loop in
     the main thread to work.

 -- Class: asyncio.FastChildWatcher

     This implementation reaps every terminated processes by calling
     ‘os.waitpid(-1)’ directly, possibly breaking other code spawning
     processes and waiting for their termination.

     There is no noticeable overhead when handling a big number of
     children (`O(1)' each time a child terminates).

     This solution requires a running event loop in the main thread to
     work, as *note SafeChildWatcher: 2784.

 -- Class: asyncio.PidfdChildWatcher

     This implementation polls process file descriptors (pidfds) to
     await child process termination.  In some respects, *note
     PidfdChildWatcher: 18e. is a “Goldilocks” child watcher
     implementation.  It doesn’t require signals or threads, doesn’t
     interfere with any processes launched outside the event loop, and
     scales linearly with the number of subprocesses launched by the
     event loop.  The main disadvantage is that pidfds are specific to
     Linux, and only work on recent (5.3+) kernels.

     New in version 3.9.


File: python.info,  Node: Custom Policies,  Prev: Process Watchers,  Up: Policies

5.18.1.99 Custom Policies
.........................

To implement a new event loop policy, it is recommended to subclass
*note DefaultEventLoopPolicy: 277f. and override the methods for which
custom behavior is wanted, e.g.:

     class MyEventLoopPolicy(asyncio.DefaultEventLoopPolicy):

         def get_event_loop(self):
             """Get the event loop.

             This may be None or an instance of EventLoop.
             """
             loop = super().get_event_loop()
             # Do something with loop ...
             return loop

     asyncio.set_event_loop_policy(MyEventLoopPolicy())


File: python.info,  Node: Platform Support,  Next: High-level API Index,  Prev: Policies,  Up: asyncio — Asynchronous I/O

5.18.1.100 Platform Support
...........................

The *note asyncio: 9. module is designed to be portable, but some
platforms have subtle differences and limitations due to the platforms’
underlying architecture and capabilities.

* Menu:

* All Platforms::
* Windows: Windows<55>.
* macOS: macOS<30>.


File: python.info,  Node: All Platforms,  Next: Windows<55>,  Up: Platform Support

5.18.1.101 All Platforms
........................

   * *note loop.add_reader(): 268a. and *note loop.add_writer(): 2707.
     cannot be used to monitor file I/O.


File: python.info,  Node: Windows<55>,  Next: macOS<30>,  Prev: All Platforms,  Up: Platform Support

5.18.1.102 Windows
..................

`Source code:' Lib/asyncio/proactor_events.py(1),
Lib/asyncio/windows_events.py(2), Lib/asyncio/windows_utils.py(3)

__________________________________________________________________

Changed in version 3.8: On Windows, *note ProactorEventLoop: 2de. is now
the default event loop.

All event loops on Windows do not support the following methods:

   * *note loop.create_unix_connection(): 266e. and *note
     loop.create_unix_server(): 466. are not supported.  The *note
     socket.AF_UNIX: 26fe. socket family is specific to Unix.

   * *note loop.add_signal_handler(): 263d. and *note
     loop.remove_signal_handler(): 2712. are not supported.

*note SelectorEventLoop: 26c2. has the following limitations:

   * *note SelectSelector: 2792. is used to wait on socket events: it
     supports sockets and is limited to 512 sockets.

   * *note loop.add_reader(): 268a. and *note loop.add_writer(): 2707.
     only accept socket handles (e.g.  pipe file descriptors are not
     supported).

   * Pipes are not supported, so the *note loop.connect_read_pipe():
     26ac. and *note loop.connect_write_pipe(): 26ad. methods are not
     implemented.

   * *note Subprocesses: 2639. are not supported, i.e.  *note
     loop.subprocess_exec(): 263c. and *note loop.subprocess_shell():
     26aa. methods are not implemented.

*note ProactorEventLoop: 2de. has the following limitations:

   * The *note loop.add_reader(): 268a. and *note loop.add_writer():
     2707. methods are not supported.

The resolution of the monotonic clock on Windows is usually around 15.6
msec.  The best resolution is 0.5 msec.  The resolution depends on the
hardware (availability of HPET(4)) and on the Windows configuration.

* Menu:

* Subprocess Support on Windows::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/asyncio/proactor_events.py

   (2) 
https://github.com/python/cpython/tree/3.9/Lib/asyncio/windows_events.py

   (3) 
https://github.com/python/cpython/tree/3.9/Lib/asyncio/windows_utils.py

   (4) https://en.wikipedia.org/wiki/High_Precision_Event_Timer


File: python.info,  Node: Subprocess Support on Windows,  Up: Windows<55>

5.18.1.103 Subprocess Support on Windows
........................................

On Windows, the default event loop *note ProactorEventLoop: 2de.
supports subprocesses, whereas *note SelectorEventLoop: 26c2. does not.

The *note policy.set_child_watcher(): 277e. function is also not
supported, as *note ProactorEventLoop: 2de. has a different mechanism to
watch child processes.


File: python.info,  Node: macOS<30>,  Prev: Windows<55>,  Up: Platform Support

5.18.1.104 macOS
................

Modern macOS versions are fully supported.

macOS <= 10.8
.............

On macOS 10.6, 10.7 and 10.8, the default event loop uses *note
selectors.KqueueSelector: 2795, which does not support character devices
on these versions.  The *note SelectorEventLoop: 26c2. can be manually
configured to use *note SelectSelector: 2792. or *note PollSelector:
550. to support character devices on these older versions of macOS.
Example:

     import asyncio
     import selectors

     selector = selectors.SelectSelector()
     loop = asyncio.SelectorEventLoop(selector)
     asyncio.set_event_loop(loop)


File: python.info,  Node: High-level API Index,  Next: Low-level API Index,  Prev: Platform Support,  Up: asyncio — Asynchronous I/O

5.18.1.105 High-level API Index
...............................

This page lists all high-level async/await enabled asyncio APIs.

* Menu:

* Tasks::
* Queues: Queues<2>.
* Subprocesses: Subprocesses<2>.
* Streams: Streams<2>.
* Synchronization::
* Exceptions: Exceptions<11>.


File: python.info,  Node: Tasks,  Next: Queues<2>,  Up: High-level API Index

5.18.1.106 Tasks
................

Utilities to run asyncio programs, create Tasks, and await on multiple
things with timeouts.

*note run(): 18d.                                      Create event loop, run a coroutine, close the loop.
                                                       
                                                       
*note create_task(): 2e1.                              Start an asyncio Task.
                                                       
                                                       
‘await’ *note sleep(): 3aa.                            Sleep for a number of seconds.
                                                       
                                                       
‘await’ *note gather(): 3ab.                           Schedule and wait for things concurrently.
                                                       
                                                       
‘await’ *note wait_for(): 191.                         Run with a timeout.
                                                       
                                                       
‘await’ *note shield(): 3ac.                           Shield from cancellation.
                                                       
                                                       
‘await’ *note wait(): 207.                             Monitor for completion.
                                                       
                                                       
*note current_task(): 228.                             Return the current Task.
                                                       
                                                       
*note all_tasks(): 229.                                Return all tasks for an event loop.
                                                       
                                                       
*note Task: 2e0.                                       Task object.
                                                       
                                                       
*note to_thread(): 18f.                                Asychronously run a function in a separate OS
                                                       thread.
                                                       
                                                       
*note run_coroutine_threadsafe(): 614.                 Schedule a coroutine from another OS thread.
                                                       
                                                       
‘for in’ *note as_completed(): 3ad.                    Monitor for completion with a ‘for’ loop.
                                                       

Examples
........

   * *note Using asyncio.gather() to run things in parallel: 264b.

   * *note Using asyncio.wait_for() to enforce a timeout: 2650.

   * *note Cancellation: 265c.

   * *note Using asyncio.sleep(): 2649.

   * See also the main *note Tasks documentation page: 2637.


File: python.info,  Node: Queues<2>,  Next: Subprocesses<2>,  Prev: Tasks,  Up: High-level API Index

5.18.1.107 Queues
.................

Queues should be used to distribute work amongst multiple asyncio Tasks,
implement connection pools, and pub/sub patterns.

*note Queue: 3b3.                                      A FIFO queue.
                                                       
                                                       
*note PriorityQueue: 26d6.                             A priority queue.
                                                       
                                                       
*note LifoQueue: 26d8.                                 A LIFO queue.
                                                       

Examples
........

   * *note Using asyncio.Queue to distribute workload between several
     Tasks: 26da.

   * See also the *note Queues documentation page: 263a.


File: python.info,  Node: Subprocesses<2>,  Next: Streams<2>,  Prev: Queues<2>,  Up: High-level API Index

5.18.1.108 Subprocesses
.......................

Utilities to spawn subprocesses and run shell commands.

‘await’ *note create_subprocess_exec(): 3b4.           Create a subprocess.
                                                       
                                                       
‘await’ *note create_subprocess_shell(): 3b5.          Run a shell command.
                                                       

Examples
........

   * *note Executing a shell command: 26a6.

   * See also the *note subprocess APIs: 2639. documentation.


File: python.info,  Node: Streams<2>,  Next: Synchronization,  Prev: Subprocesses<2>,  Up: High-level API Index

5.18.1.109 Streams
..................

High-level APIs to work with network IO.

‘await’ *note open_connection(): 46b.                  Establish a TCP connection.
                                                       
                                                       
‘await’ *note open_unix_connection(): 266d.            Establish a Unix socket connection.
                                                       
                                                       
‘await’ *note start_server(): 46c.                     Start a TCP server.
                                                       
                                                       
‘await’ *note start_unix_server(): 266f.               Start a Unix socket server.
                                                       
                                                       
*note StreamReader: 1105.                              High-level async/await object to receive network
                                                       data.
                                                       
                                                       
*note StreamWriter: 1106.                              High-level async/await object to send network data.
                                                       

Examples
........

   * *note Example TCP client: 266b.

   * See also the *note streams APIs: 2638. documentation.


File: python.info,  Node: Synchronization,  Next: Exceptions<11>,  Prev: Streams<2>,  Up: High-level API Index

5.18.1.110 Synchronization
..........................

Threading-like synchronization primitives that can be used in Tasks.

*note Lock: 3ae.                                       A mutex lock.
                                                       
                                                       
*note Event: 3af.                                      An event object.
                                                       
                                                       
*note Condition: 3b0.                                  A condition object.
                                                       
                                                       
*note Semaphore: 3b1.                                  A semaphore.
                                                       
                                                       
*note BoundedSemaphore: 3b2.                           A bounded semaphore.
                                                       

Examples
........

   * *note Using asyncio.Event: 2695.

   * See also the documentation of asyncio *note synchronization
     primitives: 263b.


File: python.info,  Node: Exceptions<11>,  Prev: Synchronization,  Up: High-level API Index

5.18.1.111 Exceptions
.....................

*note asyncio.TimeoutError: 264f.                      Raised on timeout by functions like
                                                       *note wait_for(): 191.  Keep in mind that
                                                       ‘asyncio.TimeoutError’ is `unrelated' to the
                                                       built-in *note TimeoutError: a7d. exception.
                                                       
                                                       
*note asyncio.CancelledError: 2da.                     Raised when a Task is cancelled.  See also
                                                       *note Task.cancel(): 264d.
                                                       

Examples
........

   * *note Handling CancelledError to run code on cancellation request:
     265c.

   * See also the full list of *note asyncio-specific exceptions: 26dc.


File: python.info,  Node: Low-level API Index,  Next: Developing with asyncio,  Prev: High-level API Index,  Up: asyncio — Asynchronous I/O

5.18.1.112 Low-level API Index
..............................

This page lists all low-level asyncio APIs.

* Menu:

* Obtaining the Event Loop::
* Event Loop Methods: Event Loop Methods<2>.
* Transports: Transports<2>.
* Protocols: Protocols<2>.
* Event Loop Policies::


File: python.info,  Node: Obtaining the Event Loop,  Next: Event Loop Methods<2>,  Up: Low-level API Index

5.18.1.113 Obtaining the Event Loop
...................................

*note asyncio.get_running_loop(): 45c.                 The `preferred' function to get the running event
                                                       loop.
                                                       
                                                       
*note asyncio.get_event_loop(): 45d.                   Get an event loop instance (current or via the
                                                       policy).
                                                       
                                                       
*note asyncio.set_event_loop(): 26e3.                  Set the event loop as current via the current
                                                       policy.
                                                       
                                                       
*note asyncio.new_event_loop(): 26e4.                  Create a new event loop.
                                                       

Examples
........

   * *note Using asyncio.get_running_loop(): 2731.


File: python.info,  Node: Event Loop Methods<2>,  Next: Transports<2>,  Prev: Obtaining the Event Loop,  Up: Low-level API Index

5.18.1.114 Event Loop Methods
.............................

See also the main documentation section about the *note event loop
methods: 737.

Lifecycle
.........

*note loop.run_until_complete(): 612.                  Run a Future/Task/awaitable until complete.
                                                       
                                                       
*note loop.run_forever(): 26ed.                        Run the event loop forever.
                                                       
                                                       
*note loop.stop(): 61a.                                Stop the event loop.
                                                       
                                                       
*note loop.close(): 26ef.                              Close the event loop.
                                                       
                                                       
*note loop.is_running(): 26ee.                         Return ‘True’ if the event loop is running.
                                                       
                                                       
*note loop.is_closed(): 78e.                           Return ‘True’ if the event loop is closed.
                                                       
                                                       
‘await’ *note loop.shutdown_asyncgens(): 61b.          Close asynchronous generators.
                                                       

Debugging
.........

*note loop.set_debug(): 78c.                           Enable or disable the debug mode.
                                                       
                                                       
*note loop.get_debug(): 78d.                           Get the current debug mode.
                                                       

Scheduling Callbacks
....................

*note loop.call_soon(): 455.                           Invoke a callback soon.
                                                       
                                                       
*note loop.call_soon_threadsafe(): 456.                A thread-safe variant of
                                                       *note loop.call_soon(): 455.
                                                       
                                                       
*note loop.call_later(): 457.                          Invoke a callback `after' the given time.
                                                       
                                                       
*note loop.call_at(): 458.                             Invoke a callback `at' the given time.
                                                       

Thread/Process Pool
...................

‘await’ *note loop.run_in_executor(): 190.             Run a CPU-bound or other blocking function in a
                                                       *note concurrent.futures: 21. executor.
                                                       
                                                       
*note loop.set_default_executor(): 3a1.                Set the default executor for
                                                       *note loop.run_in_executor(): 190.
                                                       

Tasks and Futures
.................

*note loop.create_future(): 616.                       Create a *note Future: 546. object.
                                                       
                                                       
*note loop.create_task(): 2e2.                         Schedule coroutine as a *note Task: 2e0.
                                                       
                                                       
*note loop.set_task_factory(): 790.                    Set a factory used by *note loop.create_task(): 2e2.
                                                       to create *note Tasks: 2e0.
                                                       
                                                       
*note loop.get_task_factory(): 791.                    Get the factory *note loop.create_task(): 2e2. uses
                                                       to create *note Tasks: 2e0.
                                                       

DNS
...

‘await’ *note loop.getaddrinfo(): 59c.                 Asynchronous version of
                                                       *note socket.getaddrinfo(): 270c.
                                                       
                                                       
‘await’ *note loop.getnameinfo(): 59d.                 Asynchronous version of
                                                       *note socket.getnameinfo(): 270d.
                                                       

Networking and IPC
..................

‘await’ *note loop.create_connection(): 2e5.           Open a TCP connection.
                                                       
                                                       
‘await’ *note loop.create_server(): 465.               Create a TCP server.
                                                       
                                                       
‘await’ *note loop.create_unix_connection(): 266e.     Open a Unix socket connection.
                                                       
                                                       
‘await’ *note loop.create_unix_server(): 466.          Create a Unix socket server.
                                                       
                                                       
‘await’ *note loop.connect_accepted_socket(): 46d.     Wrap a *note socket: 767. into a ‘(transport,
                                                       protocol)’ pair.
                                                       
                                                       
‘await’ *note loop.create_datagram_endpoint(): 189.    Open a datagram (UDP) connection.
                                                       
                                                       
‘await’ *note loop.sendfile(): 2703.                   Send a file over a transport.
                                                       
                                                       
‘await’ *note loop.start_tls(): 45a.                   Upgrade an existing connection to TLS.
                                                       
                                                       
‘await’ *note loop.connect_read_pipe(): 26ac.          Wrap a read end of a pipe into a ‘(transport,
                                                       protocol)’ pair.
                                                       
                                                       
‘await’ *note loop.connect_write_pipe(): 26ad.         Wrap a write end of a pipe into a ‘(transport,
                                                       protocol)’ pair.
                                                       

Sockets
.......

‘await’ *note loop.sock_recv(): 599.                   Receive data from the *note socket: 767.
                                                       
                                                       
‘await’ *note loop.sock_recv_into(): 45b.              Receive data from the *note socket: 767. into a
                                                       buffer.
                                                       
                                                       
‘await’ *note loop.sock_sendall(): 59a.                Send data to the *note socket: 767.
                                                       
                                                       
‘await’ *note loop.sock_connect(): 794.                Connect the *note socket: 767.
                                                       
                                                       
‘await’ *note loop.sock_accept(): 59b.                 Accept a *note socket: 767. connection.
                                                       
                                                       
‘await’ *note loop.sock_sendfile(): 460.               Send a file over the *note socket: 767.
                                                       
                                                       
*note loop.add_reader(): 268a.                         Start watching a file descriptor for read
                                                       availability.
                                                       
                                                       
*note loop.remove_reader(): 2706.                      Stop watching a file descriptor for read
                                                       availability.
                                                       
                                                       
*note loop.add_writer(): 2707.                         Start watching a file descriptor for write
                                                       availability.
                                                       
                                                       
*note loop.remove_writer(): 2708.                      Stop watching a file descriptor for write
                                                       availability.
                                                       

Unix Signals
............

*note loop.add_signal_handler(): 263d.                 Add a handler for a *note signal: ea.
                                                       
                                                       
*note loop.remove_signal_handler(): 2712.              Remove a handler for a *note signal: ea.
                                                       

Subprocesses
............

*note loop.subprocess_exec(): 263c.                    Spawn a subprocess.
                                                       
                                                       
*note loop.subprocess_shell(): 26aa.                   Spawn a subprocess from a shell command.
                                                       

Error Handling
..............

*note loop.call_exception_handler(): 2716.             Call the exception handler.
                                                       
                                                       
*note loop.set_exception_handler(): 2715.              Set a new exception handler.
                                                       
                                                       
*note loop.get_exception_handler(): 617.               Get the current exception handler.
                                                       
                                                       
*note loop.default_exception_handler(): 2717.          The default exception handler implementation.
                                                       

Examples
........

   * *note Using asyncio.get_event_loop() and loop.run_forever(): 2720.

   * *note Using loop.call_later(): 2722.

   * Using ‘loop.create_connection()’ to implement *note an echo-client:
     2681.

   * Using ‘loop.create_connection()’ to *note connect a socket: 2688.

   * *note Using add_reader() to watch an FD for read events: 2689.

   * *note Using loop.add_signal_handler(): 2725.

   * *note Using loop.subprocess_exec(): 26c6.


File: python.info,  Node: Transports<2>,  Next: Protocols<2>,  Prev: Event Loop Methods<2>,  Up: Low-level API Index

5.18.1.115 Transports
.....................

All transports implement the following methods:

*note transport.close(): 273f.                         Close the transport.
                                                       
                                                       
*note transport.is_closing(): 615.                     Return ‘True’ if the transport is closing or is
                                                       closed.
                                                       
                                                       
*note transport.get_extra_info(): 3ea.                 Request for information about the transport.
                                                       
                                                       
*note transport.set_protocol(): 2744.                  Set a new protocol.
                                                       
                                                       
*note transport.get_protocol(): 2745.                  Return the current protocol.
                                                       

Transports that can receive data (TCP and Unix connections, pipes, etc).
Returned from methods like *note loop.create_connection(): 2e5, *note
loop.create_unix_connection(): 266e, *note loop.connect_read_pipe():
26ac, etc:

Read Transports
...............

*note transport.is_reading(): 46f.                     Return ‘True’ if the transport is receiving.
                                                       
                                                       
*note transport.pause_reading(): 471.                  Pause receiving.
                                                       
                                                       
*note transport.resume_reading(): 470.                 Resume receiving.
                                                       

Transports that can Send data (TCP and Unix connections, pipes, etc).
Returned from methods like *note loop.create_connection(): 2e5, *note
loop.create_unix_connection(): 266e, *note loop.connect_write_pipe():
26ad, etc:

Write Transports
................

*note transport.write(): 2750.                         Write data to the transport.
                                                       
                                                       
*note transport.writelines(): 2751.                    Write buffers to the transport.
                                                       
                                                       
*note transport.can_write_eof(): 274a.                 Return *note True: 594. if the transport supports
                                                       sending EOF.
                                                       
                                                       
*note transport.write_eof(): 274b.                     Close and send EOF after flushing buffered data.
                                                       
                                                       
*note transport.abort(): 2749.                         Close the transport immediately.
                                                       
                                                       
*note transport.get_write_buffer_size(): 274c.         Return high and low water marks for write flow
                                                       control.
                                                       
                                                       
*note transport.set_write_buffer_limits(): 274d.       Set new high and low water marks for write flow
                                                       control.
                                                       

Transports returned by *note loop.create_datagram_endpoint(): 189.:

Datagram Transports
...................

*note transport.sendto(): 2753.                        Send data to the remote peer.
                                                       
                                                       
*note transport.abort(): 2754.                         Close the transport immediately.
                                                       

Low-level transport abstraction over subprocesses.  Returned by *note
loop.subprocess_exec(): 263c. and *note loop.subprocess_shell(): 26aa.:

Subprocess Transports
.....................

*note transport.get_pid(): 2756.                       Return the subprocess process id.
                                                       
                                                       
*note transport.get_pipe_transport(): 2757.            Return the transport for the requested communication
                                                       pipe (`stdin', `stdout', or `stderr').
                                                       
                                                       
*note transport.get_returncode(): 2758.                Return the subprocess return code.
                                                       
                                                       
*note transport.kill(): 2759.                          Kill the subprocess.
                                                       
                                                       
*note transport.send_signal(): 275b.                   Send a signal to the subprocess.
                                                       
                                                       
*note transport.terminate(): 275a.                     Stop the subprocess.
                                                       
                                                       
*note transport.close(): 275c.                         Kill the subprocess and close all pipes.
                                                       


File: python.info,  Node: Protocols<2>,  Next: Event Loop Policies,  Prev: Transports<2>,  Up: Low-level API Index

5.18.1.116 Protocols
....................

Protocol classes can implement the following `callback methods':

‘callback’ *note connection_made(): 26fc.              Called when a connection is made.
                                                       
                                                       
‘callback’ *note connection_lost(): 2740.              Called when the connection is lost or closed.
                                                       
                                                       
‘callback’ *note pause_writing(): 274e.                Called when the transport’s buffer goes over the
                                                       high water mark.
                                                       
                                                       
‘callback’ *note resume_writing(): 274f.               Called when the transport’s buffer drains below the
                                                       low water mark.
                                                       

Streaming Protocols (TCP, Unix Sockets, Pipes)
..............................................

‘callback’ *note data_received(): 2747.                Called when some data is received.
                                                       
                                                       
‘callback’ *note eof_received(): 2760.                 Called when an EOF is received.
                                                       

Buffered Streaming Protocols
............................

‘callback’ *note get_buffer(): 2762.                   Called to allocate a new receive buffer.
                                                       
                                                       
‘callback’ *note buffer_updated(): 2763.               Called when the buffer was updated with the received
                                                       data.
                                                       
                                                       
‘callback’ *note eof_received(): 2764.                 Called when an EOF is received.
                                                       

Datagram Protocols
..................

‘callback’ *note datagram_received(): 2766.            Called when a datagram is received.
                                                       
                                                       
‘callback’ *note error_received(): 2767.               Called when a previous send or receive operation
                                                       raises an *note OSError: 304.
                                                       

Subprocess Protocols
....................

‘callback’ *note pipe_data_received(): 2769.           Called when the child process writes data into its
                                                       `stdout' or `stderr' pipe.
                                                       
                                                       
‘callback’ *note pipe_connection_lost(): 276a.         Called when one of the pipes communicating with the
                                                       child process is closed.
                                                       
                                                       
‘callback’ *note process_exited(): 276b.               Called when the child process has exited.
                                                       


File: python.info,  Node: Event Loop Policies,  Prev: Protocols<2>,  Up: Low-level API Index

5.18.1.117 Event Loop Policies
..............................

Policies is a low-level mechanism to alter the behavior of functions
like *note asyncio.get_event_loop(): 45d.  See also the main *note
policies section: 26e5. for more details.

Accessing Policies
..................

*note asyncio.get_event_loop_policy(): 2776.           Return the current process-wide policy.
                                                       
                                                       
*note asyncio.set_event_loop_policy(): 2777.           Set a new process-wide policy.
                                                       
                                                       
*note AbstractEventLoopPolicy: 2774.                   Base class for policy objects.
                                                       


File: python.info,  Node: Developing with asyncio,  Prev: Low-level API Index,  Up: asyncio — Asynchronous I/O

5.18.1.118 Developing with asyncio
..................................

Asynchronous programming is different from classic “sequential”
programming.

This page lists common mistakes and traps and explains how to avoid
them.

* Menu:

* Debug Mode::
* Concurrency and Multithreading::
* Running Blocking Code::
* Logging: Logging<3>.
* Detect never-awaited coroutines::
* Detect never-retrieved exceptions::


File: python.info,  Node: Debug Mode,  Next: Concurrency and Multithreading,  Up: Developing with asyncio

5.18.1.119 Debug Mode
.....................

By default asyncio runs in production mode.  In order to ease the
development asyncio has a `debug mode'.

There are several ways to enable asyncio debug mode:

   * Setting the *note PYTHONASYNCIODEBUG: 148d. environment variable to
     ‘1’.

   * Using the *note Python Development Mode: 160.

   * Passing ‘debug=True’ to *note asyncio.run(): 18d.

   * Calling *note loop.set_debug(): 78c.

In addition to enabling the debug mode, consider also:

   * setting the log level of the *note asyncio logger: 27a9. to
     ‘logging.DEBUG’, for example the following snippet of code can be
     run at startup of the application:

          logging.basicConfig(level=logging.DEBUG)

   * configuring the *note warnings: 12f. module to display *note
     ResourceWarning: 5cb. warnings.  One way of doing that is by using
     the *note -W: 15b. ‘default’ command line option.

When the debug mode is enabled:

   * asyncio checks for *note coroutines that were not awaited: 27aa.
     and logs them; this mitigates the “forgotten await” pitfall.

   * Many non-threadsafe asyncio APIs (such as *note loop.call_soon():
     455. and *note loop.call_at(): 458. methods) raise an exception if
     they are called from a wrong thread.

   * The execution time of the I/O selector is logged if it takes too
     long to perform an I/O operation.

   * Callbacks taking longer than 100ms are logged.  The
     ‘loop.slow_callback_duration’ attribute can be used to set the
     minimum execution duration in seconds that is considered “slow”.


File: python.info,  Node: Concurrency and Multithreading,  Next: Running Blocking Code,  Prev: Debug Mode,  Up: Developing with asyncio

5.18.1.120 Concurrency and Multithreading
.........................................

An event loop runs in a thread (typically the main thread) and executes
all callbacks and Tasks in its thread.  While a Task is running in the
event loop, no other Tasks can run in the same thread.  When a Task
executes an ‘await’ expression, the running Task gets suspended, and the
event loop executes the next Task.

To schedule a *note callback: 26f1. from another OS thread, the *note
loop.call_soon_threadsafe(): 456. method should be used.  Example:

     loop.call_soon_threadsafe(callback, *args)

Almost all asyncio objects are not thread safe, which is typically not a
problem unless there is code that works with them from outside of a Task
or a callback.  If there’s a need for such code to call a low-level
asyncio API, the *note loop.call_soon_threadsafe(): 456. method should
be used, e.g.:

     loop.call_soon_threadsafe(fut.cancel)

To schedule a coroutine object from a different OS thread, the *note
run_coroutine_threadsafe(): 614. function should be used.  It returns a
*note concurrent.futures.Future: c00. to access the result:

     async def coro_func():
          return await asyncio.sleep(1, 42)

     # Later in another OS thread:

     future = asyncio.run_coroutine_threadsafe(coro_func(), loop)
     # Wait for the result:
     result = future.result()

To handle signals and to execute subprocesses, the event loop must be
run in the main thread.

The *note loop.run_in_executor(): 190. method can be used with a *note
concurrent.futures.ThreadPoolExecutor: 18c. to execute blocking code in
a different OS thread without blocking the OS thread that the event loop
runs in.

There is currently no way to schedule coroutines or callbacks directly
from a different process (such as one started with *note
multiprocessing: b7.).  The *note Event Loop Methods: 737. section lists
APIs that can read from pipes and watch file descriptors without
blocking the event loop.  In addition, asyncio’s *note Subprocess: 2639.
APIs provide a way to start a process and communicate with it from the
event loop.  Lastly, the aforementioned *note loop.run_in_executor():
190. method can also be used with a *note
concurrent.futures.ProcessPoolExecutor: 196. to execute code in a
different process.


File: python.info,  Node: Running Blocking Code,  Next: Logging<3>,  Prev: Concurrency and Multithreading,  Up: Developing with asyncio

5.18.1.121 Running Blocking Code
................................

Blocking (CPU-bound) code should not be called directly.  For example,
if a function performs a CPU-intensive calculation for 1 second, all
concurrent asyncio Tasks and IO operations would be delayed by 1 second.

An executor can be used to run a task in a different thread or even in a
different process to avoid blocking the OS thread with the event loop.
See the *note loop.run_in_executor(): 190. method for more details.


File: python.info,  Node: Logging<3>,  Next: Detect never-awaited coroutines,  Prev: Running Blocking Code,  Up: Developing with asyncio

5.18.1.122 Logging
..................

asyncio uses the *note logging: aa. module and all logging is performed
via the ‘"asyncio"’ logger.

The default log level is ‘logging.INFO’, which can be easily adjusted:

     logging.getLogger("asyncio").setLevel(logging.WARNING)


File: python.info,  Node: Detect never-awaited coroutines,  Next: Detect never-retrieved exceptions,  Prev: Logging<3>,  Up: Developing with asyncio

5.18.1.123 Detect never-awaited coroutines
..........................................

When a coroutine function is called, but not awaited (e.g.  ‘coro()’
instead of ‘await coro()’) or the coroutine is not scheduled with *note
asyncio.create_task(): 2e1, asyncio will emit a *note RuntimeWarning:
3e2.:

     import asyncio

     async def test():
         print("never scheduled")

     async def main():
         test()

     asyncio.run(main())

Output:

     test.py:7: RuntimeWarning: coroutine 'test' was never awaited
       test()

Output in debug mode:

     test.py:7: RuntimeWarning: coroutine 'test' was never awaited
     Coroutine created at (most recent call last)
       File "../t.py", line 9, in <module>
         asyncio.run(main(), debug=True)

       < .. >

       File "../t.py", line 7, in main
         test()
       test()

The usual fix is to either await the coroutine or call the *note
asyncio.create_task(): 2e1. function:

     async def main():
         await test()


File: python.info,  Node: Detect never-retrieved exceptions,  Prev: Detect never-awaited coroutines,  Up: Developing with asyncio

5.18.1.124 Detect never-retrieved exceptions
............................................

If a *note Future.set_exception(): 265a. is called but the Future object
is never awaited on, the exception would never be propagated to the user
code.  In this case, asyncio would emit a log message when the Future
object is garbage collected.

Example of an unhandled exception:

     import asyncio

     async def bug():
         raise Exception("not consumed")

     async def main():
         asyncio.create_task(bug())

     asyncio.run(main())

Output:

     Task exception was never retrieved
     future: <Task finished coro=<bug() done, defined at test.py:3>
       exception=Exception('not consumed')>

     Traceback (most recent call last):
       File "test.py", line 4, in bug
         raise Exception("not consumed")
     Exception: not consumed

*note Enable the debug mode: 148e. to get the traceback where the task
was created:

     asyncio.run(main(), debug=True)

Output in debug mode:

     Task exception was never retrieved
     future: <Task finished coro=<bug() done, defined at test.py:3>
         exception=Exception('not consumed') created at asyncio/tasks.py:321>

     source_traceback: Object created at (most recent call last):
       File "../t.py", line 9, in <module>
         asyncio.run(main(), debug=True)

     < .. >

     Traceback (most recent call last):
       File "../t.py", line 4, in bug
         raise Exception("not consumed")
     Exception: not consumed

     Note: The source code for asyncio can be found in Lib/asyncio/(1).

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/asyncio/


File: python.info,  Node: socket — Low-level networking interface,  Next: ssl — TLS/SSL wrapper for socket objects,  Prev: asyncio — Asynchronous I/O,  Up: Networking and Interprocess Communication

5.18.2 ‘socket’ — Low-level networking interface
------------------------------------------------

`Source code:' Lib/socket.py(1)

__________________________________________________________________

This module provides access to the BSD `socket' interface.  It is
available on all modern Unix systems, Windows, MacOS, and probably
additional platforms.

     Note: Some behavior may be platform dependent, since calls are made
     to the operating system socket APIs.

The Python interface is a straightforward transliteration of the Unix
system call and library interface for sockets to Python’s
object-oriented style: the ‘socket()’ function returns a `socket object'
whose methods implement the various socket system calls.  Parameter
types are somewhat higher-level than in the C interface: as with
‘read()’ and ‘write()’ operations on Python files, buffer allocation on
receive operations is automatic, and buffer length is implicit on send
operations.

See also
........

Module *note socketserver: f0.

     Classes that simplify writing network servers.

Module *note ssl: f3.

     A TLS/SSL wrapper for socket objects.

* Menu:

* Socket families::
* Module contents::
* Socket Objects::
* Notes on socket timeouts::
* Example: Example<8>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/socket.py


File: python.info,  Node: Socket families,  Next: Module contents,  Up: socket — Low-level networking interface

5.18.2.1 Socket families
........................

Depending on the system and the build options, various socket families
are supported by this module.

The address format required by a particular socket object is
automatically selected based on the address family specified when the
socket object was created.  Socket addresses are represented as follows:

   - The address of an *note AF_UNIX: 26fe. socket bound to a file
     system node is represented as a string, using the file system
     encoding and the ‘'surrogateescape'’ error handler (see PEP
     383(1)).  An address in Linux’s abstract namespace is returned as a
     *note bytes-like object: 6df. with an initial null byte; note that
     sockets in this namespace can communicate with normal file system
     sockets, so programs intended to run on Linux may need to deal with
     both types of address.  A string or bytes-like object can be used
     for either type of address when passing it as an argument.

     Changed in version 3.3: Previously, *note AF_UNIX: 26fe. socket
     paths were assumed to use UTF-8 encoding.

     Changed in version 3.5: Writable *note bytes-like object: 6df. is
     now accepted.

   - A pair ‘(host, port)’ is used for the *note AF_INET: 26f8. address
     family, where `host' is a string representing either a hostname in
     Internet domain notation like ‘'daring.cwi.nl'’ or an IPv4 address
     like ‘'100.50.200.5'’, and `port' is an integer.

        - For IPv4 addresses, two special forms are accepted instead of
          a host address: ‘''’ represents ‘INADDR_ANY’, which is used to
          bind to all interfaces, and the string ‘'<broadcast>'’
          represents ‘INADDR_BROADCAST’.  This behavior is not
          compatible with IPv6, therefore, you may want to avoid these
          if you intend to support IPv6 with your Python programs.

   - For *note AF_INET6: 26f9. address family, a four-tuple ‘(host,
     port, flowinfo, scope_id)’ is used, where `flowinfo' and `scope_id'
     represent the ‘sin6_flowinfo’ and ‘sin6_scope_id’ members in
     ‘struct sockaddr_in6’ in C. For *note socket: ef. module methods,
     `flowinfo' and `scope_id' can be omitted just for backward
     compatibility.  Note, however, omission of `scope_id' can cause
     problems in manipulating scoped IPv6 addresses.

     Changed in version 3.7: For multicast addresses (with `scope_id'
     meaningful) `address' may not contain ‘%scope_id’ (or ‘zone id’)
     part.  This information is superfluous and may be safely omitted
     (recommended).

   - ‘AF_NETLINK’ sockets are represented as pairs ‘(pid, groups)’.

   - Linux-only support for TIPC is available using the ‘AF_TIPC’
     address family.  TIPC is an open, non-IP based networked protocol
     designed for use in clustered computer environments.  Addresses are
     represented by a tuple, and the fields depend on the address type.
     The general tuple form is ‘(addr_type, v1, v2, v3 [, scope])’,
     where:

        - `addr_type' is one of ‘TIPC_ADDR_NAMESEQ’, ‘TIPC_ADDR_NAME’,
          or ‘TIPC_ADDR_ID’.

        - `scope' is one of ‘TIPC_ZONE_SCOPE’, ‘TIPC_CLUSTER_SCOPE’, and
          ‘TIPC_NODE_SCOPE’.

        - If `addr_type' is ‘TIPC_ADDR_NAME’, then `v1' is the server
          type, `v2' is the port identifier, and `v3' should be 0.

          If `addr_type' is ‘TIPC_ADDR_NAMESEQ’, then `v1' is the server
          type, `v2' is the lower port number, and `v3' is the upper
          port number.

          If `addr_type' is ‘TIPC_ADDR_ID’, then `v1' is the node, `v2'
          is the reference, and `v3' should be set to 0.

   - A tuple ‘(interface, )’ is used for the *note AF_CAN: 27b5. address
     family, where `interface' is a string representing a network
     interface name like ‘'can0'’.  The network interface name ‘''’ can
     be used to receive packets from all network interfaces of this
     family.

        - *note CAN_ISOTP: 27b6. protocol require a tuple ‘(interface,
          rx_addr, tx_addr)’ where both additional parameters are
          unsigned long integer that represent a CAN identifier
          (standard or extended).

        - *note CAN_J1939: 1e3. protocol require a tuple ‘(interface,
          name, pgn, addr)’ where additional parameters are 64-bit
          unsigned integer representing the ECU name, a 32-bit unsigned
          integer representing the Parameter Group Number (PGN), and an
          8-bit integer representing the address.

   - A string or a tuple ‘(id, unit)’ is used for the ‘SYSPROTO_CONTROL’
     protocol of the ‘PF_SYSTEM’ family.  The string is the name of a
     kernel control using a dynamically-assigned ID. The tuple can be
     used if ID and unit number of the kernel control are known or if a
     registered ID is used.

     New in version 3.3.

   - ‘AF_BLUETOOTH’ supports the following protocols and address
     formats:

        - ‘BTPROTO_L2CAP’ accepts ‘(bdaddr, psm)’ where ‘bdaddr’ is the
          Bluetooth address as a string and ‘psm’ is an integer.

        - ‘BTPROTO_RFCOMM’ accepts ‘(bdaddr, channel)’ where ‘bdaddr’ is
          the Bluetooth address as a string and ‘channel’ is an integer.

        - ‘BTPROTO_HCI’ accepts ‘(device_id,)’ where ‘device_id’ is
          either an integer or a string with the Bluetooth address of
          the interface.  (This depends on your OS; NetBSD and
          DragonFlyBSD expect a Bluetooth address while everything else
          expects an integer.)

          Changed in version 3.2: NetBSD and DragonFlyBSD support added.

        - ‘BTPROTO_SCO’ accepts ‘bdaddr’ where ‘bdaddr’ is a *note
          bytes: 172. object containing the Bluetooth address in a
          string format.  (ex.  ‘b'12:23:34:45:56:67'’) This protocol is
          not supported under FreeBSD.

   - *note AF_ALG: 67b. is a Linux-only socket based interface to Kernel
     cryptography.  An algorithm socket is configured with a tuple of
     two to four elements ‘(type, name [, feat [, mask]])’, where:

        - `type' is the algorithm type as string, e.g.  ‘aead’, ‘hash’,
          ‘skcipher’ or ‘rng’.

        - `name' is the algorithm name and operation mode as string,
          e.g.  ‘sha256’, ‘hmac(sha256)’, ‘cbc(aes)’ or
          ‘drbg_nopr_ctr_aes256’.

        - `feat' and `mask' are unsigned 32bit integers.

     *note Availability: 1491.: Linux 2.6.38, some algorithm types
     require more recent Kernels.

     New in version 3.6.

   - *note AF_VSOCK: 4da. allows communication between virtual machines
     and their hosts.  The sockets are represented as a ‘(CID, port)’
     tuple where the context ID or CID and port are integers.

     *note Availability: 1491.: Linux >= 4.8 QEMU >= 2.8 ESX >= 4.0 ESX
     Workstation >= 6.5.

     New in version 3.7.

   - *note AF_PACKET: 27b7. is a low-level interface directly to network
     devices.  The packets are represented by the tuple ‘(ifname,
     proto[, pkttype[, hatype[, addr]]])’ where:

        - `ifname' - String specifying the device name.

        - `proto' - An in network-byte-order integer specifying the
          Ethernet protocol number.

        - `pkttype' - Optional integer specifying the packet type:

             - ‘PACKET_HOST’ (the default) - Packet addressed to the
               local host.

             - ‘PACKET_BROADCAST’ - Physical-layer broadcast packet.

             - ‘PACKET_MULTIHOST’ - Packet sent to a physical-layer
               multicast address.

             - ‘PACKET_OTHERHOST’ - Packet to some other host that has
               been caught by a device driver in promiscuous mode.

             - ‘PACKET_OUTGOING’ - Packet originating from the local
               host that is looped back to a packet socket.

        - `hatype' - Optional integer specifying the ARP hardware
          address type.

        - `addr' - Optional bytes-like object specifying the hardware
          physical address, whose interpretation depends on the device.

          *note Availability: 1491.: Linux >= 2.2.

   - *note AF_QIPCRTR: 27b8. is a Linux-only socket based interface for
     communicating with services running on co-processors in Qualcomm
     platforms.  The address family is represented as a ‘(node, port)’
     tuple where the `node' and `port' are non-negative integers.

          *note Availability: 1491.: Linux >= 4.7.

     New in version 3.8.

   - ‘IPPROTO_UDPLITE’ is a variant of UDP which allows you to specify
     what portion of a packet is covered with the checksum.  It adds two
     socket options that you can change.
     ‘self.setsockopt(IPPROTO_UDPLITE, UDPLITE_SEND_CSCOV, length)’ will
     change what portion of outgoing packets are covered by the checksum
     and ‘self.setsockopt(IPPROTO_UDPLITE, UDPLITE_RECV_CSCOV, length)’
     will filter out packets which cover too little of their data.  In
     both cases ‘length’ should be in ‘range(8, 2**16, 8)’.

     Such a socket should be constructed with ‘socket(AF_INET,
     SOCK_DGRAM, IPPROTO_UDPLITE)’ for IPv4 or ‘socket(AF_INET6,
     SOCK_DGRAM, IPPROTO_UDPLITE)’ for IPv6.

     *note Availability: 1491.: Linux >= 2.6.20, FreeBSD >= 10.1-RELEASE

     New in version 3.9.

If you use a hostname in the `host' portion of IPv4/v6 socket address,
the program may show a nondeterministic behavior, as Python uses the
first address returned from the DNS resolution.  The socket address will
be resolved differently into an actual IPv4/v6 address, depending on the
results from DNS resolution and/or the host configuration.  For
deterministic behavior use a numeric address in `host' portion.

All errors raise exceptions.  The normal exceptions for invalid argument
types and out-of-memory conditions can be raised; starting from Python
3.3, errors related to socket or address semantics raise *note OSError:
304. or one of its subclasses (they used to raise *note socket.error:
a76.).

Non-blocking mode is supported through *note setblocking(): 206f.  A
generalization of this based on timeouts is supported through *note
settimeout(): 27b9.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0383


File: python.info,  Node: Module contents,  Next: Socket Objects,  Prev: Socket families,  Up: socket — Low-level networking interface

5.18.2.2 Module contents
........................

The module *note socket: ef. exports the following elements.

* Menu:

* Exceptions: Exceptions<12>.
* Constants: Constants<8>.
* Functions: Functions<6>.


File: python.info,  Node: Exceptions<12>,  Next: Constants<8>,  Up: Module contents

5.18.2.3 Exceptions
...................

 -- Exception: socket.error

     A deprecated alias of *note OSError: 304.

     Changed in version 3.3: Following PEP 3151(1), this class was made
     an alias of *note OSError: 304.

 -- Exception: socket.herror

     A subclass of *note OSError: 304, this exception is raised for
     address-related errors, i.e.  for functions that use `h_errno' in
     the POSIX C API, including *note gethostbyname_ex(): fae. and *note
     gethostbyaddr(): fad.  The accompanying value is a pair ‘(h_errno,
     string)’ representing an error returned by a library call.
     `h_errno' is a numeric value, while `string' represents the
     description of `h_errno', as returned by the ‘hstrerror()’ C
     function.

     Changed in version 3.3: This class was made a subclass of *note
     OSError: 304.

 -- Exception: socket.gaierror

     A subclass of *note OSError: 304, this exception is raised for
     address-related errors by *note getaddrinfo(): 270c. and *note
     getnameinfo(): 270d.  The accompanying value is a pair ‘(error,
     string)’ representing an error returned by a library call.
     `string' represents the description of `error', as returned by the
     ‘gai_strerror()’ C function.  The numeric `error' value will match
     one of the ‘EAI_*’ constants defined in this module.

     Changed in version 3.3: This class was made a subclass of *note
     OSError: 304.

 -- Exception: socket.timeout

     A subclass of *note OSError: 304, this exception is raised when a
     timeout occurs on a socket which has had timeouts enabled via a
     prior call to *note settimeout(): 27b9. (or implicitly through
     *note setdefaulttimeout(): 27be.).  The accompanying value is a
     string whose value is currently always “timed out”.

     Changed in version 3.3: This class was made a subclass of *note
     OSError: 304.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3151


File: python.info,  Node: Constants<8>,  Next: Functions<6>,  Prev: Exceptions<12>,  Up: Module contents

5.18.2.4 Constants
..................

     The AF_* and SOCK_* constants are now ‘AddressFamily’ and
     ‘SocketKind’ *note IntEnum: 684. collections.

     New in version 3.4.

 -- Data: socket.AF_UNIX
 -- Data: socket.AF_INET
 -- Data: socket.AF_INET6

     These constants represent the address (and protocol) families, used
     for the first argument to ‘socket()’.  If the *note AF_UNIX: 26fe.
     constant is not defined then this protocol is unsupported.  More
     constants may be available depending on the system.

 -- Data: socket.SOCK_STREAM
 -- Data: socket.SOCK_DGRAM
 -- Data: socket.SOCK_RAW
 -- Data: socket.SOCK_RDM
 -- Data: socket.SOCK_SEQPACKET

     These constants represent the socket types, used for the second
     argument to ‘socket()’.  More constants may be available depending
     on the system.  (Only *note SOCK_STREAM: d52. and *note SOCK_DGRAM:
     d51. appear to be generally useful.)

 -- Data: socket.SOCK_CLOEXEC
 -- Data: socket.SOCK_NONBLOCK

     These two constants, if defined, can be combined with the socket
     types and allow you to set some flags atomically (thus avoiding
     possible race conditions and the need for separate calls).

     See also
     ........

     Secure File Descriptor Handling(1) for a more thorough explanation.

     *note Availability: 1491.: Linux >= 2.6.27.

     New in version 3.2.

 -- Data: SO_*
 -- Data: socket.SOMAXCONN

 -- Data: MSG_*

 -- Data: SOL_*

 -- Data: SCM_*

 -- Data: IPPROTO_*

 -- Data: IPPORT_*

 -- Data: INADDR_*

 -- Data: IP_*

 -- Data: IPV6_*

 -- Data: EAI_*

 -- Data: AI_*

 -- Data: NI_*

 -- Data: TCP_*

     Many constants of these forms, documented in the Unix documentation
     on sockets and/or the IP protocol, are also defined in the socket
     module.  They are generally used in arguments to the ‘setsockopt()’
     and ‘getsockopt()’ methods of socket objects.  In most cases, only
     those symbols that are defined in the Unix header files are
     defined; for a few symbols, default values are provided.

     Changed in version 3.6: ‘SO_DOMAIN’, ‘SO_PROTOCOL’, ‘SO_PEERSEC’,
     ‘SO_PASSSEC’, ‘TCP_USER_TIMEOUT’, ‘TCP_CONGESTION’ were added.

     Changed in version 3.6.5: On Windows, ‘TCP_FASTOPEN’, ‘TCP_KEEPCNT’
     appear if run-time Windows supports.

     Changed in version 3.7: ‘TCP_NOTSENT_LOWAT’ was added.

     On Windows, ‘TCP_KEEPIDLE’, ‘TCP_KEEPINTVL’ appear if run-time
     Windows supports.

 -- Data: socket.AF_CAN
 -- Data: socket.PF_CAN

 -- Data: SOL_CAN_*

 -- Data: CAN_*

     Many constants of these forms, documented in the Linux
     documentation, are also defined in the socket module.

     *note Availability: 1491.: Linux >= 2.6.25.

     New in version 3.3.

 -- Data: socket.CAN_BCM

 -- Data: CAN_BCM_*

     CAN_BCM, in the CAN protocol family, is the broadcast manager (BCM)
     protocol.  Broadcast manager constants, documented in the Linux
     documentation, are also defined in the socket module.

     *note Availability: 1491.: Linux >= 2.6.25.

          Note: The ‘CAN_BCM_CAN_FD_FRAME’ flag is only available on
          Linux >= 4.8.

     New in version 3.4.

 -- Data: socket.CAN_RAW_FD_FRAMES

     Enables CAN FD support in a CAN_RAW socket.  This is disabled by
     default.  This allows your application to send both CAN and CAN FD
     frames; however, you must accept both CAN and CAN FD frames when
     reading from the socket.

     This constant is documented in the Linux documentation.

     *note Availability: 1491.: Linux >= 3.6.

     New in version 3.5.

 -- Data: socket.CAN_RAW_JOIN_FILTERS

     Joins the applied CAN filters such that only CAN frames that match
     all given CAN filters are passed to user space.

     This constant is documented in the Linux documentation.

     *note Availability: 1491.: Linux >= 4.1.

     New in version 3.9.

 -- Data: socket.CAN_ISOTP

     CAN_ISOTP, in the CAN protocol family, is the ISO-TP (ISO 15765-2)
     protocol.  ISO-TP constants, documented in the Linux documentation.

     *note Availability: 1491.: Linux >= 2.6.25.

     New in version 3.7.

 -- Data: socket.CAN_J1939

     CAN_J1939, in the CAN protocol family, is the SAE J1939 protocol.
     J1939 constants, documented in the Linux documentation.

     *note Availability: 1491.: Linux >= 5.4.

     New in version 3.9.

 -- Data: socket.AF_PACKET
 -- Data: socket.PF_PACKET

 -- Data: PACKET_*

     Many constants of these forms, documented in the Linux
     documentation, are also defined in the socket module.

     *note Availability: 1491.: Linux >= 2.2.

 -- Data: socket.AF_RDS
 -- Data: socket.PF_RDS
 -- Data: socket.SOL_RDS

 -- Data: RDS_*

     Many constants of these forms, documented in the Linux
     documentation, are also defined in the socket module.

     *note Availability: 1491.: Linux >= 2.6.30.

     New in version 3.3.

 -- Data: socket.SIO_RCVALL
 -- Data: socket.SIO_KEEPALIVE_VALS
 -- Data: socket.SIO_LOOPBACK_FAST_PATH

 -- Data: RCVALL_*

     Constants for Windows’ WSAIoctl().  The constants are used as
     arguments to the *note ioctl(): 677. method of socket objects.

     Changed in version 3.6: ‘SIO_LOOPBACK_FAST_PATH’ was added.

 -- Data: TIPC_*

     TIPC related constants, matching the ones exported by the C socket
     API. See the TIPC documentation for more information.

 -- Data: socket.AF_ALG
 -- Data: socket.SOL_ALG

 -- Data: ALG_*

     Constants for Linux Kernel cryptography.

     *note Availability: 1491.: Linux >= 2.6.38.

     New in version 3.6.

 -- Data: socket.AF_VSOCK
 -- Data: socket.IOCTL_VM_SOCKETS_GET_LOCAL_CID

 -- Data: VMADDR*

 -- Data: SO_VM*

     Constants for Linux host/guest communication.

     *note Availability: 1491.: Linux >= 4.8.

     New in version 3.7.

 -- Data: socket.AF_LINK

     *note Availability: 1491.: BSD, macOS.

     New in version 3.4.

 -- Data: socket.has_ipv6

     This constant contains a boolean value which indicates if IPv6 is
     supported on this platform.

 -- Data: socket.BDADDR_ANY
 -- Data: socket.BDADDR_LOCAL

     These are string constants containing Bluetooth addresses with
     special meanings.  For example, *note BDADDR_ANY: 27cd. can be used
     to indicate any address when specifying the binding socket with
     ‘BTPROTO_RFCOMM’.

 -- Data: socket.HCI_FILTER
 -- Data: socket.HCI_TIME_STAMP
 -- Data: socket.HCI_DATA_DIR

     For use with ‘BTPROTO_HCI’.  *note HCI_FILTER: 27cf. is not
     available for NetBSD or DragonFlyBSD. *note HCI_TIME_STAMP: 27d0.
     and *note HCI_DATA_DIR: 27d1. are not available for FreeBSD,
     NetBSD, or DragonFlyBSD.

 -- Data: socket.AF_QIPCRTR

     Constant for Qualcomm’s IPC router protocol, used to communicate
     with service providing remote processors.

     *note Availability: 1491.: Linux >= 4.7.

   ---------- Footnotes ----------

   (1) http://udrepper.livejournal.com/20407.html


File: python.info,  Node: Functions<6>,  Prev: Constants<8>,  Up: Module contents

5.18.2.5 Functions
..................

* Menu:

* Creating sockets::
* Other functions: Other functions<2>.


File: python.info,  Node: Creating sockets,  Next: Other functions<2>,  Up: Functions<6>

5.18.2.6 Creating sockets
.........................

The following functions all create *note socket objects: 27d4.

 -- Class: socket.socket (family=AF_INET, type=SOCK_STREAM, proto=0,
          fileno=None)

     Create a new socket using the given address family, socket type and
     protocol number.  The address family should be *note AF_INET: 26f8.
     (the default), *note AF_INET6: 26f9, *note AF_UNIX: 26fe, *note
     AF_CAN: 27b5, *note AF_PACKET: 27b7, or *note AF_RDS: 27c5.  The
     socket type should be *note SOCK_STREAM: d52. (the default), *note
     SOCK_DGRAM: d51, *note SOCK_RAW: 27c0. or perhaps one of the other
     ‘SOCK_’ constants.  The protocol number is usually zero and may be
     omitted or in the case where the address family is *note AF_CAN:
     27b5. the protocol should be one of ‘CAN_RAW’, *note CAN_BCM: 9a0,
     *note CAN_ISOTP: 27b6. or *note CAN_J1939: 1e3.

     If `fileno' is specified, the values for `family', `type', and
     `proto' are auto-detected from the specified file descriptor.
     Auto-detection can be overruled by calling the function with
     explicit `family', `type', or `proto' arguments.  This only affects
     how Python represents e.g.  the return value of *note
     socket.getpeername(): 2741. but not the actual OS resource.  Unlike
     *note socket.fromfd(): 27d5, `fileno' will return the same socket
     and not a duplicate.  This may help close a detached socket using
     *note socket.close(): 4d8.

     The newly created socket is *note non-inheritable: 8e7.

     Raises an *note auditing event: fa1. ‘socket.__new__’ with
     arguments ‘self’, ‘family’, ‘type’, ‘protocol’.

     Changed in version 3.3: The AF_CAN family was added.  The AF_RDS
     family was added.

     Changed in version 3.4: The CAN_BCM protocol was added.

     Changed in version 3.4: The returned socket is now non-inheritable.

     Changed in version 3.7: The CAN_ISOTP protocol was added.

     Changed in version 3.7: When *note SOCK_NONBLOCK: 591. or *note
     SOCK_CLOEXEC: 592. bit flags are applied to `type' they are
     cleared, and *note socket.type: 593. will not reflect them.  They
     are still passed to the underlying system ‘socket()’ call.
     Therefore,

          sock = socket.socket(
              socket.AF_INET,
              socket.SOCK_STREAM | socket.SOCK_NONBLOCK)

     will still create a non-blocking socket on OSes that support
     ‘SOCK_NONBLOCK’, but ‘sock.type’ will be set to
     ‘socket.SOCK_STREAM’.

     Changed in version 3.9: The CAN_J1939 protocol was added.

 -- Function: socket.socketpair ([family[, type[, proto]]])

     Build a pair of connected socket objects using the given address
     family, socket type, and protocol number.  Address family, socket
     type, and protocol number are as for the ‘socket()’ function above.
     The default family is *note AF_UNIX: 26fe. if defined on the
     platform; otherwise, the default is *note AF_INET: 26f8.

     The newly created sockets are *note non-inheritable: 8e7.

     Changed in version 3.2: The returned socket objects now support the
     whole socket API, rather than a subset.

     Changed in version 3.4: The returned sockets are now
     non-inheritable.

     Changed in version 3.5: Windows support added.

 -- Function: socket.create_connection (address[, timeout[,
          source_address]])

     Connect to a TCP service listening on the Internet `address' (a
     2-tuple ‘(host, port)’), and return the socket object.  This is a
     higher-level function than *note socket.connect(): 769.: if `host'
     is a non-numeric hostname, it will try to resolve it for both *note
     AF_INET: 26f8. and *note AF_INET6: 26f9, and then try to connect to
     all possible addresses in turn until a connection succeeds.  This
     makes it easy to write clients that are compatible to both IPv4 and
     IPv6.

     Passing the optional `timeout' parameter will set the timeout on
     the socket instance before attempting to connect.  If no `timeout'
     is supplied, the global default timeout setting returned by *note
     getdefaulttimeout(): 27d6. is used.

     If supplied, `source_address' must be a 2-tuple ‘(host, port)’ for
     the socket to bind to as its source address before connecting.  If
     host or port are ‘’ or 0 respectively the OS default behavior will
     be used.

     Changed in version 3.2: `source_address' was added.

 -- Function: socket.create_server (address, *, family=AF_INET,
          backlog=None, reuse_port=False, dualstack_ipv6=False)

     Convenience function which creates a TCP socket bound to `address'
     (a 2-tuple ‘(host, port)’) and return the socket object.

     `family' should be either *note AF_INET: 26f8. or *note AF_INET6:
     26f9.  `backlog' is the queue size passed to *note socket.listen():
     83a.; when ‘0’ a default reasonable value is chosen.  `reuse_port'
     dictates whether to set the ‘SO_REUSEPORT’ socket option.

     If `dualstack_ipv6' is true and the platform supports it the socket
     will be able to accept both IPv4 and IPv6 connections, else it will
     raise *note ValueError: 16d.  Most POSIX platforms and Windows are
     supposed to support this functionality.  When this functionality is
     enabled the address returned by *note socket.getpeername(): 2741.
     when an IPv4 connection occurs will be an IPv6 address represented
     as an IPv4-mapped IPv6 address.  If `dualstack_ipv6' is false it
     will explicitly disable this functionality on platforms that enable
     it by default (e.g.  Linux).  This parameter can be used in
     conjunction with *note has_dualstack_ipv6(): 34c.:

          import socket

          addr = ("", 8080)  # all interfaces, port 8080
          if socket.has_dualstack_ipv6():
              s = socket.create_server(addr, family=socket.AF_INET6, dualstack_ipv6=True)
          else:
              s = socket.create_server(addr)

          Note: On POSIX platforms the ‘SO_REUSEADDR’ socket option is
          set in order to immediately reuse previous sockets which were
          bound on the same `address' and remained in TIME_WAIT state.

     New in version 3.8.

 -- Function: socket.has_dualstack_ipv6 ()

     Return ‘True’ if the platform supports creating a TCP socket which
     can handle both IPv4 and IPv6 connections.

     New in version 3.8.

 -- Function: socket.fromfd (fd, family, type, proto=0)

     Duplicate the file descriptor `fd' (an integer as returned by a
     file object’s ‘fileno()’ method) and build a socket object from the
     result.  Address family, socket type and protocol number are as for
     the ‘socket()’ function above.  The file descriptor should refer to
     a socket, but this is not checked — subsequent operations on the
     object may fail if the file descriptor is invalid.  This function
     is rarely needed, but can be used to get or set socket options on a
     socket passed to a program as standard input or output (such as a
     server started by the Unix inet daemon).  The socket is assumed to
     be in blocking mode.

     The newly created socket is *note non-inheritable: 8e7.

     Changed in version 3.4: The returned socket is now non-inheritable.

 -- Function: socket.fromshare (data)

     Instantiate a socket from data obtained from the *note
     socket.share(): 58f. method.  The socket is assumed to be in
     blocking mode.

     *note Availability: 1491.: Windows.

     New in version 3.3.

 -- Data: socket.SocketType

     This is a Python type object that represents the socket object
     type.  It is the same as ‘type(socket(...))’.


File: python.info,  Node: Other functions<2>,  Prev: Creating sockets,  Up: Functions<6>

5.18.2.7 Other functions
........................

The *note socket: ef. module also offers various network-related
services:

 -- Function: socket.close (fd)

     Close a socket file descriptor.  This is like *note os.close():
     4d9, but for sockets.  On some platforms (most noticeable Windows)
     *note os.close(): 4d9. does not work for socket file descriptors.

     New in version 3.7.

 -- Function: socket.getaddrinfo (host, port, family=0, type=0, proto=0,
          flags=0)

     Translate the `host'/`port' argument into a sequence of 5-tuples
     that contain all the necessary arguments for creating a socket
     connected to that service.  `host' is a domain name, a string
     representation of an IPv4/v6 address or ‘None’.  `port' is a string
     service name such as ‘'http'’, a numeric port number or ‘None’.  By
     passing ‘None’ as the value of `host' and `port', you can pass
     ‘NULL’ to the underlying C API.

     The `family', `type' and `proto' arguments can be optionally
     specified in order to narrow the list of addresses returned.
     Passing zero as a value for each of these arguments selects the
     full range of results.  The `flags' argument can be one or several
     of the ‘AI_*’ constants, and will influence how results are
     computed and returned.  For example, ‘AI_NUMERICHOST’ will disable
     domain name resolution and will raise an error if `host' is a
     domain name.

     The function returns a list of 5-tuples with the following
     structure:

     ‘(family, type, proto, canonname, sockaddr)’

     In these tuples, `family', `type', `proto' are all integers and are
     meant to be passed to the ‘socket()’ function.  `canonname' will be
     a string representing the canonical name of the `host' if
     ‘AI_CANONNAME’ is part of the `flags' argument; else `canonname'
     will be empty.  `sockaddr' is a tuple describing a socket address,
     whose format depends on the returned `family' (a ‘(address, port)’
     2-tuple for *note AF_INET: 26f8, a ‘(address, port, flowinfo,
     scope_id)’ 4-tuple for *note AF_INET6: 26f9.), and is meant to be
     passed to the *note socket.connect(): 769. method.

     Raises an *note auditing event: fa1. ‘socket.getaddrinfo’ with
     arguments ‘host’, ‘port’, ‘family’, ‘type’, ‘protocol’.

     The following example fetches address information for a
     hypothetical TCP connection to ‘example.org’ on port 80 (results
     may differ on your system if IPv6 isn’t enabled):

          >>> socket.getaddrinfo("example.org", 80, proto=socket.IPPROTO_TCP)
          [(<AddressFamily.AF_INET6: 10>, <SocketType.SOCK_STREAM: 1>,
           6, '', ('2606:2800:220:1:248:1893:25c8:1946', 80, 0, 0)),
           (<AddressFamily.AF_INET: 2>, <SocketType.SOCK_STREAM: 1>,
           6, '', ('93.184.216.34', 80))]

     Changed in version 3.2: parameters can now be passed using keyword
     arguments.

     Changed in version 3.7: for IPv6 multicast addresses, string
     representing an address will not contain ‘%scope_id’ part.

 -- Function: socket.getfqdn ([name])

     Return a fully qualified domain name for `name'.  If `name' is
     omitted or empty, it is interpreted as the local host.  To find the
     fully qualified name, the hostname returned by *note
     gethostbyaddr(): fad. is checked, followed by aliases for the host,
     if available.  The first name which includes a period is selected.
     In case no fully qualified domain name is available and `name' was
     provided, it is returned unchanged.  If `name' was empty or equal
     to ‘'0.0.0.0'’, the hostname from *note gethostname(): 2064. is
     returned.

 -- Function: socket.gethostbyname (hostname)

     Translate a host name to IPv4 address format.  The IPv4 address is
     returned as a string, such as ‘'100.50.200.5'’.  If the host name
     is an IPv4 address itself it is returned unchanged.  See *note
     gethostbyname_ex(): fae. for a more complete interface.  *note
     gethostbyname(): 27da. does not support IPv6 name resolution, and
     *note getaddrinfo(): 270c. should be used instead for IPv4/v6 dual
     stack support.

     Raises an *note auditing event: fa1. ‘socket.gethostbyname’ with
     argument ‘hostname’.

 -- Function: socket.gethostbyname_ex (hostname)

     Translate a host name to IPv4 address format, extended interface.
     Return a triple ‘(hostname, aliaslist, ipaddrlist)’ where
     `hostname' is the host’s primary host name, `aliaslist' is a
     (possibly empty) list of alternative host names for the same
     address, and `ipaddrlist' is a list of IPv4 addresses for the same
     interface on the same host (often but not always a single address).
     *note gethostbyname_ex(): fae. does not support IPv6 name
     resolution, and *note getaddrinfo(): 270c. should be used instead
     for IPv4/v6 dual stack support.

     Raises an *note auditing event: fa1. ‘socket.gethostbyname’ with
     argument ‘hostname’.

 -- Function: socket.gethostname ()

     Return a string containing the hostname of the machine where the
     Python interpreter is currently executing.

     Raises an *note auditing event: fa1. ‘socket.gethostname’ with no
     arguments.

     Note: *note gethostname(): 2064. doesn’t always return the fully
     qualified domain name; use *note getfqdn(): 27d9. for that.

 -- Function: socket.gethostbyaddr (ip_address)

     Return a triple ‘(hostname, aliaslist, ipaddrlist)’ where
     `hostname' is the primary host name responding to the given
     `ip_address', `aliaslist' is a (possibly empty) list of alternative
     host names for the same address, and `ipaddrlist' is a list of
     IPv4/v6 addresses for the same interface on the same host (most
     likely containing only a single address).  To find the fully
     qualified domain name, use the function *note getfqdn(): 27d9.
     *note gethostbyaddr(): fad. supports both IPv4 and IPv6.

     Raises an *note auditing event: fa1. ‘socket.gethostbyaddr’ with
     argument ‘ip_address’.

 -- Function: socket.getnameinfo (sockaddr, flags)

     Translate a socket address `sockaddr' into a 2-tuple ‘(host,
     port)’.  Depending on the settings of `flags', the result can
     contain a fully-qualified domain name or numeric address
     representation in `host'.  Similarly, `port' can contain a string
     port name or a numeric port number.

     For IPv6 addresses, ‘%scope_id’ is appended to the host part if
     `sockaddr' contains meaningful `scope_id'.  Usually this happens
     for multicast addresses.

     For more information about `flags' you can consult
     ‘getnameinfo(3)’.

     Raises an *note auditing event: fa1. ‘socket.getnameinfo’ with
     argument ‘sockaddr’.

 -- Function: socket.getprotobyname (protocolname)

     Translate an Internet protocol name (for example, ‘'icmp'’) to a
     constant suitable for passing as the (optional) third argument to
     the ‘socket()’ function.  This is usually only needed for sockets
     opened in “raw” mode (*note SOCK_RAW: 27c0.); for the normal socket
     modes, the correct protocol is chosen automatically if the protocol
     is omitted or zero.

 -- Function: socket.getservbyname (servicename[, protocolname])

     Translate an Internet service name and protocol name to a port
     number for that service.  The optional protocol name, if given,
     should be ‘'tcp'’ or ‘'udp'’, otherwise any protocol will match.

     Raises an *note auditing event: fa1. ‘socket.getservbyname’ with
     arguments ‘servicename’, ‘protocolname’.

 -- Function: socket.getservbyport (port[, protocolname])

     Translate an Internet port number and protocol name to a service
     name for that service.  The optional protocol name, if given,
     should be ‘'tcp'’ or ‘'udp'’, otherwise any protocol will match.

     Raises an *note auditing event: fa1. ‘socket.getservbyport’ with
     arguments ‘port’, ‘protocolname’.

 -- Function: socket.ntohl (x)

     Convert 32-bit positive integers from network to host byte order.
     On machines where the host byte order is the same as network byte
     order, this is a no-op; otherwise, it performs a 4-byte swap
     operation.

 -- Function: socket.ntohs (x)

     Convert 16-bit positive integers from network to host byte order.
     On machines where the host byte order is the same as network byte
     order, this is a no-op; otherwise, it performs a 2-byte swap
     operation.

     Deprecated since version 3.7: In case `x' does not fit in 16-bit
     unsigned integer, but does fit in a positive C int, it is silently
     truncated to 16-bit unsigned integer.  This silent truncation
     feature is deprecated, and will raise an exception in future
     versions of Python.

 -- Function: socket.htonl (x)

     Convert 32-bit positive integers from host to network byte order.
     On machines where the host byte order is the same as network byte
     order, this is a no-op; otherwise, it performs a 4-byte swap
     operation.

 -- Function: socket.htons (x)

     Convert 16-bit positive integers from host to network byte order.
     On machines where the host byte order is the same as network byte
     order, this is a no-op; otherwise, it performs a 2-byte swap
     operation.

     Deprecated since version 3.7: In case `x' does not fit in 16-bit
     unsigned integer, but does fit in a positive C int, it is silently
     truncated to 16-bit unsigned integer.  This silent truncation
     feature is deprecated, and will raise an exception in future
     versions of Python.

 -- Function: socket.inet_aton (ip_string)

     Convert an IPv4 address from dotted-quad string format (for
     example, ‘123.45.67.89’) to 32-bit packed binary format, as a bytes
     object four characters in length.  This is useful when conversing
     with a program that uses the standard C library and needs objects
     of type ‘struct in_addr’, which is the C type for the 32-bit packed
     binary this function returns.

     *note inet_aton(): 236. also accepts strings with less than three
     dots; see the Unix manual page ‘inet(3)’ for details.

     If the IPv4 address string passed to this function is invalid,
     *note OSError: 304. will be raised.  Note that exactly what is
     valid depends on the underlying C implementation of ‘inet_aton()’.

     *note inet_aton(): 236. does not support IPv6, and *note
     inet_pton(): 237. should be used instead for IPv4/v6 dual stack
     support.

 -- Function: socket.inet_ntoa (packed_ip)

     Convert a 32-bit packed IPv4 address (a *note bytes-like object:
     6df. four bytes in length) to its standard dotted-quad string
     representation (for example, ‘123.45.67.89’).  This is useful when
     conversing with a program that uses the standard C library and
     needs objects of type ‘struct in_addr’, which is the C type for the
     32-bit packed binary data this function takes as an argument.

     If the byte sequence passed to this function is not exactly 4 bytes
     in length, *note OSError: 304. will be raised.  *note inet_ntoa():
     27e0. does not support IPv6, and *note inet_ntop(): 9a2. should be
     used instead for IPv4/v6 dual stack support.

     Changed in version 3.5: Writable *note bytes-like object: 6df. is
     now accepted.

 -- Function: socket.inet_pton (address_family, ip_string)

     Convert an IP address from its family-specific string format to a
     packed, binary format.  *note inet_pton(): 237. is useful when a
     library or network protocol calls for an object of type ‘struct
     in_addr’ (similar to *note inet_aton(): 236.) or ‘struct in6_addr’.

     Supported values for `address_family' are currently *note AF_INET:
     26f8. and *note AF_INET6: 26f9.  If the IP address string
     `ip_string' is invalid, *note OSError: 304. will be raised.  Note
     that exactly what is valid depends on both the value of
     `address_family' and the underlying implementation of
     ‘inet_pton()’.

     *note Availability: 1491.: Unix (maybe not all platforms), Windows.

     Changed in version 3.4: Windows support added

 -- Function: socket.inet_ntop (address_family, packed_ip)

     Convert a packed IP address (a *note bytes-like object: 6df. of
     some number of bytes) to its standard, family-specific string
     representation (for example, ‘'7.10.0.5'’ or ‘'5aef:2b::8'’).
     *note inet_ntop(): 9a2. is useful when a library or network
     protocol returns an object of type ‘struct in_addr’ (similar to
     *note inet_ntoa(): 27e0.) or ‘struct in6_addr’.

     Supported values for `address_family' are currently *note AF_INET:
     26f8. and *note AF_INET6: 26f9.  If the bytes object `packed_ip' is
     not the correct length for the specified address family, *note
     ValueError: 16d. will be raised.  *note OSError: 304. is raised for
     errors from the call to *note inet_ntop(): 9a2.

     *note Availability: 1491.: Unix (maybe not all platforms), Windows.

     Changed in version 3.4: Windows support added

     Changed in version 3.5: Writable *note bytes-like object: 6df. is
     now accepted.

 -- Function: socket.CMSG_LEN (length)

     Return the total length, without trailing padding, of an ancillary
     data item with associated data of the given `length'.  This value
     can often be used as the buffer size for *note recvmsg(): 76c. to
     receive a single item of ancillary data, but RFC 3542(1) requires
     portable applications to use *note CMSG_SPACE(): 1158. and thus
     include space for padding, even when the item will be the last in
     the buffer.  Raises *note OverflowError: a41. if `length' is
     outside the permissible range of values.

     *note Availability: 1491.: most Unix platforms, possibly others.

     New in version 3.3.

 -- Function: socket.CMSG_SPACE (length)

     Return the buffer size needed for *note recvmsg(): 76c. to receive
     an ancillary data item with associated data of the given `length',
     along with any trailing padding.  The buffer space needed to
     receive multiple items is the sum of the *note CMSG_SPACE(): 1158.
     values for their associated data lengths.  Raises *note
     OverflowError: a41. if `length' is outside the permissible range of
     values.

     Note that some systems might support ancillary data without
     providing this function.  Also note that setting the buffer size
     using the results of this function may not precisely limit the
     amount of ancillary data that can be received, since additional
     data may be able to fit into the padding area.

     *note Availability: 1491.: most Unix platforms, possibly others.

     New in version 3.3.

 -- Function: socket.getdefaulttimeout ()

     Return the default timeout in seconds (float) for new socket
     objects.  A value of ‘None’ indicates that new socket objects have
     no timeout.  When the socket module is first imported, the default
     is ‘None’.

 -- Function: socket.setdefaulttimeout (timeout)

     Set the default timeout in seconds (float) for new socket objects.
     When the socket module is first imported, the default is ‘None’.
     See *note settimeout(): 27b9. for possible values and their
     respective meanings.

 -- Function: socket.sethostname (name)

     Set the machine’s hostname to `name'.  This will raise an *note
     OSError: 304. if you don’t have enough rights.

     Raises an *note auditing event: fa1. ‘socket.sethostname’ with
     argument ‘name’.

     *note Availability: 1491.: Unix.

     New in version 3.3.

 -- Function: socket.if_nameindex ()

     Return a list of network interface information (index int, name
     string) tuples.  *note OSError: 304. if the system call fails.

     *note Availability: 1491.: Unix, Windows.

     New in version 3.3.

     Changed in version 3.8: Windows support was added.

          Note: On Windows network interfaces have different names in
          different contexts (all names are examples):

             * UUID: ‘{FB605B73-AAC2-49A6-9A2F-25416AEA0573}’

             * name: ‘ethernet_32770’

             * friendly name: ‘vEthernet (nat)’

             * description: ‘Hyper-V Virtual Ethernet Adapter’

          This function returns names of the second form from the list,
          ‘ethernet_32770’ in this example case.

 -- Function: socket.if_nametoindex (if_name)

     Return a network interface index number corresponding to an
     interface name.  *note OSError: 304. if no interface with the given
     name exists.

     *note Availability: 1491.: Unix, Windows.

     New in version 3.3.

     Changed in version 3.8: Windows support was added.

     See also
     ........

     “Interface name” is a name as documented in *note if_nameindex():
     34d.

 -- Function: socket.if_indextoname (if_index)

     Return a network interface name corresponding to an interface index
     number.  *note OSError: 304. if no interface with the given index
     exists.

     *note Availability: 1491.: Unix, Windows.

     New in version 3.3.

     Changed in version 3.8: Windows support was added.

     See also
     ........

     “Interface name” is a name as documented in *note if_nameindex():
     34d.

 -- Function: socket.send_fds (sock, buffers, fds[, flags[, address]])

     Send the list of file descriptors `fds' over an *note AF_UNIX:
     26fe. socket `sock'.  The `fds' parameter is a sequence of file
     descriptors.  Consult ‘sendmsg()’ for the documentation of these
     parameters.

     *note Availability: 1491.: Unix supporting *note sendmsg(): 76f.
     and ‘SCM_RIGHTS’ mechanism.

     New in version 3.9.

 -- Function: socket.recv_fds (sock, bufsize, maxfds[, flags])

     Receive up to `maxfds' file descriptors from an *note AF_UNIX:
     26fe. socket `sock'.  Return ‘(msg, list(fds), flags, addr)’.
     Consult ‘recvmsg()’ for the documentation of these parameters.

     *note Availability: 1491.: Unix supporting *note recvmsg(): 76c.
     and ‘SCM_RIGHTS’ mechanism.

     New in version 3.9.

          Note: Any truncated integers at the end of the list of file
          descriptors.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3542.html


File: python.info,  Node: Socket Objects,  Next: Notes on socket timeouts,  Prev: Module contents,  Up: socket — Low-level networking interface

5.18.2.8 Socket Objects
.......................

Socket objects have the following methods.  Except for *note makefile():
bec, these correspond to Unix system calls applicable to sockets.

Changed in version 3.2: Support for the *note context manager: 661.
protocol was added.  Exiting the context manager is equivalent to
calling *note close(): 4d8.

 -- Method: socket.accept ()

     Accept a connection.  The socket must be bound to an address and
     listening for connections.  The return value is a pair ‘(conn,
     address)’ where `conn' is a `new' socket object usable to send and
     receive data on the connection, and `address' is the address bound
     to the socket on the other end of the connection.

     The newly created socket is *note non-inheritable: 8e7.

     Changed in version 3.4: The socket is now non-inheritable.

     Changed in version 3.5: If the system call is interrupted and the
     signal handler does not raise an exception, the method now retries
     the system call instead of raising an *note InterruptedError: 74c.
     exception (see PEP 475(1) for the rationale).

 -- Method: socket.bind (address)

     Bind the socket to `address'.  The socket must not already be
     bound.  (The format of `address' depends on the address family —
     see above.)

     Raises an *note auditing event: fa1. ‘socket.bind’ with arguments
     ‘self’, ‘address’.

 -- Method: socket.close ()

     Mark the socket closed.  The underlying system resource (e.g.  a
     file descriptor) is also closed when all file objects from *note
     makefile(): bec. are closed.  Once that happens, all future
     operations on the socket object will fail.  The remote end will
     receive no more data (after queued data is flushed).

     Sockets are automatically closed when they are garbage-collected,
     but it is recommended to *note close(): 4d8. them explicitly, or to
     use a *note with: 7da. statement around them.

     Changed in version 3.6: *note OSError: 304. is now raised if an
     error occurs when the underlying ‘close()’ call is made.

          Note: *note close(): 4d8. releases the resource associated
          with a connection but does not necessarily close the
          connection immediately.  If you want to close the connection
          in a timely fashion, call *note shutdown(): 27e3. before *note
          close(): 4d8.

 -- Method: socket.connect (address)

     Connect to a remote socket at `address'.  (The format of `address'
     depends on the address family — see above.)

     If the connection is interrupted by a signal, the method waits
     until the connection completes, or raise a *note socket.timeout:
     cd9. on timeout, if the signal handler doesn’t raise an exception
     and the socket is blocking or has a timeout.  For non-blocking
     sockets, the method raises an *note InterruptedError: 74c.
     exception if the connection is interrupted by a signal (or the
     exception raised by the signal handler).

     Raises an *note auditing event: fa1. ‘socket.connect’ with
     arguments ‘self’, ‘address’.

     Changed in version 3.5: The method now waits until the connection
     completes instead of raising an *note InterruptedError: 74c.
     exception if the connection is interrupted by a signal, the signal
     handler doesn’t raise an exception and the socket is blocking or
     has a timeout (see the PEP 475(2) for the rationale).

 -- Method: socket.connect_ex (address)

     Like ‘connect(address)’, but return an error indicator instead of
     raising an exception for errors returned by the C-level ‘connect()’
     call (other problems, such as “host not found,” can still raise
     exceptions).  The error indicator is ‘0’ if the operation
     succeeded, otherwise the value of the ‘errno’ variable.  This is
     useful to support, for example, asynchronous connects.

     Raises an *note auditing event: fa1. ‘socket.connect’ with
     arguments ‘self’, ‘address’.

 -- Method: socket.detach ()

     Put the socket object into closed state without actually closing
     the underlying file descriptor.  The file descriptor is returned,
     and can be reused for other purposes.

     New in version 3.2.

 -- Method: socket.dup ()

     Duplicate the socket.

     The newly created socket is *note non-inheritable: 8e7.

     Changed in version 3.4: The socket is now non-inheritable.

 -- Method: socket.fileno ()

     Return the socket’s file descriptor (a small integer), or -1 on
     failure.  This is useful with *note select.select(): 766.

     Under Windows the small integer returned by this method cannot be
     used where a file descriptor can be used (such as *note
     os.fdopen(): 1564.).  Unix does not have this limitation.

 -- Method: socket.get_inheritable ()

     Get the *note inheritable flag: 8e7. of the socket’s file
     descriptor or socket’s handle: ‘True’ if the socket can be
     inherited in child processes, ‘False’ if it cannot.

     New in version 3.4.

 -- Method: socket.getpeername ()

     Return the remote address to which the socket is connected.  This
     is useful to find out the port number of a remote IPv4/v6 socket,
     for instance.  (The format of the address returned depends on the
     address family — see above.)  On some systems this function is not
     supported.

 -- Method: socket.getsockname ()

     Return the socket’s own address.  This is useful to find out the
     port number of an IPv4/v6 socket, for instance.  (The format of the
     address returned depends on the address family — see above.)

 -- Method: socket.getsockopt (level, optname[, buflen])

     Return the value of the given socket option (see the Unix man page
     ‘getsockopt(2)’).  The needed symbolic constants (‘SO_*’ etc.)  are
     defined in this module.  If `buflen' is absent, an integer option
     is assumed and its integer value is returned by the function.  If
     `buflen' is present, it specifies the maximum length of the buffer
     used to receive the option in, and this buffer is returned as a
     bytes object.  It is up to the caller to decode the contents of the
     buffer (see the optional built-in module *note struct: f8. for a
     way to decode C structures encoded as byte strings).

 -- Method: socket.getblocking ()

     Return ‘True’ if socket is in blocking mode, ‘False’ if in
     non-blocking.

     This is equivalent to checking ‘socket.gettimeout() == 0’.

     New in version 3.7.

 -- Method: socket.gettimeout ()

     Return the timeout in seconds (float) associated with socket
     operations, or ‘None’ if no timeout is set.  This reflects the last
     call to *note setblocking(): 206f. or *note settimeout(): 27b9.

 -- Method: socket.ioctl (control, option)


     Platform: Windows

     The *note ioctl(): 677. method is a limited interface to the
     WSAIoctl system interface.  Please refer to the Win32
     documentation(3) for more information.

     On other platforms, the generic *note fcntl.fcntl(): 27e8. and
     *note fcntl.ioctl(): ea2. functions may be used; they accept a
     socket object as their first argument.

     Currently only the following control codes are supported:
     ‘SIO_RCVALL’, ‘SIO_KEEPALIVE_VALS’, and ‘SIO_LOOPBACK_FAST_PATH’.

     Changed in version 3.6: ‘SIO_LOOPBACK_FAST_PATH’ was added.

 -- Method: socket.listen ([backlog])

     Enable a server to accept connections.  If `backlog' is specified,
     it must be at least 0 (if it is lower, it is set to 0); it
     specifies the number of unaccepted connections that the system will
     allow before refusing new connections.  If not specified, a default
     reasonable value is chosen.

     Changed in version 3.5: The `backlog' parameter is now optional.

 -- Method: socket.makefile (mode='r', buffering=None, *, encoding=None,
          errors=None, newline=None)

     Return a *note file object: c14. associated with the socket.  The
     exact returned type depends on the arguments given to *note
     makefile(): bec.  These arguments are interpreted the same way as
     by the built-in *note open(): 16f. function, except the only
     supported `mode' values are ‘'r'’ (default), ‘'w'’ and ‘'b'’.

     The socket must be in blocking mode; it can have a timeout, but the
     file object’s internal buffer may end up in an inconsistent state
     if a timeout occurs.

     Closing the file object returned by *note makefile(): bec. won’t
     close the original socket unless all other file objects have been
     closed and *note socket.close(): 4d8. has been called on the socket
     object.

          Note: On Windows, the file-like object created by *note
          makefile(): bec. cannot be used where a file object with a
          file descriptor is expected, such as the stream arguments of
          *note subprocess.Popen(): 3db.

 -- Method: socket.recv (bufsize[, flags])

     Receive data from the socket.  The return value is a bytes object
     representing the data received.  The maximum amount of data to be
     received at once is specified by `bufsize'.  See the Unix manual
     page ‘recv(2)’ for the meaning of the optional argument `flags'; it
     defaults to zero.

          Note: For best match with hardware and network realities, the
          value of `bufsize' should be a relatively small power of 2,
          for example, 4096.

     Changed in version 3.5: If the system call is interrupted and the
     signal handler does not raise an exception, the method now retries
     the system call instead of raising an *note InterruptedError: 74c.
     exception (see PEP 475(4) for the rationale).

 -- Method: socket.recvfrom (bufsize[, flags])

     Receive data from the socket.  The return value is a pair ‘(bytes,
     address)’ where `bytes' is a bytes object representing the data
     received and `address' is the address of the socket sending the
     data.  See the Unix manual page ‘recv(2)’ for the meaning of the
     optional argument `flags'; it defaults to zero.  (The format of
     `address' depends on the address family — see above.)

     Changed in version 3.5: If the system call is interrupted and the
     signal handler does not raise an exception, the method now retries
     the system call instead of raising an *note InterruptedError: 74c.
     exception (see PEP 475(5) for the rationale).

     Changed in version 3.7: For multicast IPv6 address, first item of
     `address' does not contain ‘%scope_id’ part anymore.  In order to
     get full IPv6 address use *note getnameinfo(): 270d.

 -- Method: socket.recvmsg (bufsize[, ancbufsize[, flags]])

     Receive normal data (up to `bufsize' bytes) and ancillary data from
     the socket.  The `ancbufsize' argument sets the size in bytes of
     the internal buffer used to receive the ancillary data; it defaults
     to 0, meaning that no ancillary data will be received.  Appropriate
     buffer sizes for ancillary data can be calculated using *note
     CMSG_SPACE(): 1158. or *note CMSG_LEN(): 1159, and items which do
     not fit into the buffer might be truncated or discarded.  The
     `flags' argument defaults to 0 and has the same meaning as for
     *note recv(): 76a.

     The return value is a 4-tuple: ‘(data, ancdata, msg_flags,
     address)’.  The `data' item is a *note bytes: 172. object holding
     the non-ancillary data received.  The `ancdata' item is a list of
     zero or more tuples ‘(cmsg_level, cmsg_type, cmsg_data)’
     representing the ancillary data (control messages) received:
     `cmsg_level' and `cmsg_type' are integers specifying the protocol
     level and protocol-specific type respectively, and `cmsg_data' is a
     *note bytes: 172. object holding the associated data.  The
     `msg_flags' item is the bitwise OR of various flags indicating
     conditions on the received message; see your system documentation
     for details.  If the receiving socket is unconnected, `address' is
     the address of the sending socket, if available; otherwise, its
     value is unspecified.

     On some systems, *note sendmsg(): 76f. and *note recvmsg(): 76c.
     can be used to pass file descriptors between processes over an
     *note AF_UNIX: 26fe. socket.  When this facility is used (it is
     often restricted to *note SOCK_STREAM: d52. sockets), *note
     recvmsg(): 76c. will return, in its ancillary data, items of the
     form ‘(socket.SOL_SOCKET, socket.SCM_RIGHTS, fds)’, where `fds' is
     a *note bytes: 172. object representing the new file descriptors as
     a binary array of the native C ‘int’ type.  If *note recvmsg():
     76c. raises an exception after the system call returns, it will
     first attempt to close any file descriptors received via this
     mechanism.

     Some systems do not indicate the truncated length of ancillary data
     items which have been only partially received.  If an item appears
     to extend beyond the end of the buffer, *note recvmsg(): 76c. will
     issue a *note RuntimeWarning: 3e2, and will return the part of it
     which is inside the buffer provided it has not been truncated
     before the start of its associated data.

     On systems which support the ‘SCM_RIGHTS’ mechanism, the following
     function will receive up to `maxfds' file descriptors, returning
     the message data and a list containing the descriptors (while
     ignoring unexpected conditions such as unrelated control messages
     being received).  See also *note sendmsg(): 76f.

          import socket, array

          def recv_fds(sock, msglen, maxfds):
              fds = array.array("i")   # Array of ints
              msg, ancdata, flags, addr = sock.recvmsg(msglen, socket.CMSG_LEN(maxfds * fds.itemsize))
              for cmsg_level, cmsg_type, cmsg_data in ancdata:
                  if cmsg_level == socket.SOL_SOCKET and cmsg_type == socket.SCM_RIGHTS:
                      # Append data, ignoring any truncated integers at the end.
                      fds.frombytes(cmsg_data[:len(cmsg_data) - (len(cmsg_data) % fds.itemsize)])
              return msg, list(fds)

     *note Availability: 1491.: most Unix platforms, possibly others.

     New in version 3.3.

     Changed in version 3.5: If the system call is interrupted and the
     signal handler does not raise an exception, the method now retries
     the system call instead of raising an *note InterruptedError: 74c.
     exception (see PEP 475(6) for the rationale).

 -- Method: socket.recvmsg_into (buffers[, ancbufsize[, flags]])

     Receive normal data and ancillary data from the socket, behaving as
     *note recvmsg(): 76c. would, but scatter the non-ancillary data
     into a series of buffers instead of returning a new bytes object.
     The `buffers' argument must be an iterable of objects that export
     writable buffers (e.g.  *note bytearray: 173. objects); these will
     be filled with successive chunks of the non-ancillary data until it
     has all been written or there are no more buffers.  The operating
     system may set a limit (*note sysconf(): 2094. value ‘SC_IOV_MAX’)
     on the number of buffers that can be used.  The `ancbufsize' and
     `flags' arguments have the same meaning as for *note recvmsg():
     76c.

     The return value is a 4-tuple: ‘(nbytes, ancdata, msg_flags,
     address)’, where `nbytes' is the total number of bytes of
     non-ancillary data written into the buffers, and `ancdata',
     `msg_flags' and `address' are the same as for *note recvmsg(): 76c.

     Example:

          >>> import socket
          >>> s1, s2 = socket.socketpair()
          >>> b1 = bytearray(b'----')
          >>> b2 = bytearray(b'0123456789')
          >>> b3 = bytearray(b'--------------')
          >>> s1.send(b'Mary had a little lamb')
          22
          >>> s2.recvmsg_into([b1, memoryview(b2)[2:9], b3])
          (22, [], 0, None)
          >>> [b1, b2, b3]
          [bytearray(b'Mary'), bytearray(b'01 had a 9'), bytearray(b'little lamb---')]

     *note Availability: 1491.: most Unix platforms, possibly others.

     New in version 3.3.

 -- Method: socket.recvfrom_into (buffer[, nbytes[, flags]])

     Receive data from the socket, writing it into `buffer' instead of
     creating a new bytestring.  The return value is a pair ‘(nbytes,
     address)’ where `nbytes' is the number of bytes received and
     `address' is the address of the socket sending the data.  See the
     Unix manual page ‘recv(2)’ for the meaning of the optional argument
     `flags'; it defaults to zero.  (The format of `address' depends on
     the address family — see above.)

 -- Method: socket.recv_into (buffer[, nbytes[, flags]])

     Receive up to `nbytes' bytes from the socket, storing the data into
     a buffer rather than creating a new bytestring.  If `nbytes' is not
     specified (or 0), receive up to the size available in the given
     buffer.  Returns the number of bytes received.  See the Unix manual
     page ‘recv(2)’ for the meaning of the optional argument `flags'; it
     defaults to zero.

 -- Method: socket.send (bytes[, flags])

     Send data to the socket.  The socket must be connected to a remote
     socket.  The optional `flags' argument has the same meaning as for
     *note recv(): 76a. above.  Returns the number of bytes sent.
     Applications are responsible for checking that all data has been
     sent; if only some of the data was transmitted, the application
     needs to attempt delivery of the remaining data.  For further
     information on this topic, consult the *note Socket Programming
     HOWTO: 27e9.

     Changed in version 3.5: If the system call is interrupted and the
     signal handler does not raise an exception, the method now retries
     the system call instead of raising an *note InterruptedError: 74c.
     exception (see PEP 475(7) for the rationale).

 -- Method: socket.sendall (bytes[, flags])

     Send data to the socket.  The socket must be connected to a remote
     socket.  The optional `flags' argument has the same meaning as for
     *note recv(): 76a. above.  Unlike *note send(): 76d, this method
     continues to send data from `bytes' until either all data has been
     sent or an error occurs.  ‘None’ is returned on success.  On error,
     an exception is raised, and there is no way to determine how much
     data, if any, was successfully sent.

     Changed in version 3.5: The socket timeout is no more reset each
     time data is sent successfully.  The socket timeout is now the
     maximum total duration to send all data.

     Changed in version 3.5: If the system call is interrupted and the
     signal handler does not raise an exception, the method now retries
     the system call instead of raising an *note InterruptedError: 74c.
     exception (see PEP 475(8) for the rationale).

 -- Method: socket.sendto (bytes, address)

 -- Method: socket.sendto (bytes, flags, address)

     Send data to the socket.  The socket should not be connected to a
     remote socket, since the destination socket is specified by
     `address'.  The optional `flags' argument has the same meaning as
     for *note recv(): 76a. above.  Return the number of bytes sent.
     (The format of `address' depends on the address family — see
     above.)

     Raises an *note auditing event: fa1. ‘socket.sendto’ with arguments
     ‘self’, ‘address’.

     Changed in version 3.5: If the system call is interrupted and the
     signal handler does not raise an exception, the method now retries
     the system call instead of raising an *note InterruptedError: 74c.
     exception (see PEP 475(9) for the rationale).

 -- Method: socket.sendmsg (buffers[, ancdata[, flags[, address]]])

     Send normal and ancillary data to the socket, gathering the
     non-ancillary data from a series of buffers and concatenating it
     into a single message.  The `buffers' argument specifies the
     non-ancillary data as an iterable of *note bytes-like objects: 6df.
     (e.g.  *note bytes: 172. objects); the operating system may set a
     limit (*note sysconf(): 2094. value ‘SC_IOV_MAX’) on the number of
     buffers that can be used.  The `ancdata' argument specifies the
     ancillary data (control messages) as an iterable of zero or more
     tuples ‘(cmsg_level, cmsg_type, cmsg_data)’, where `cmsg_level' and
     `cmsg_type' are integers specifying the protocol level and
     protocol-specific type respectively, and `cmsg_data' is a
     bytes-like object holding the associated data.  Note that some
     systems (in particular, systems without *note CMSG_SPACE(): 1158.)
     might support sending only one control message per call.  The
     `flags' argument defaults to 0 and has the same meaning as for
     *note send(): 76d.  If `address' is supplied and not ‘None’, it
     sets a destination address for the message.  The return value is
     the number of bytes of non-ancillary data sent.

     The following function sends the list of file descriptors `fds'
     over an *note AF_UNIX: 26fe. socket, on systems which support the
     ‘SCM_RIGHTS’ mechanism.  See also *note recvmsg(): 76c.

          import socket, array

          def send_fds(sock, msg, fds):
              return sock.sendmsg([msg], [(socket.SOL_SOCKET, socket.SCM_RIGHTS, array.array("i", fds))])

     *note Availability: 1491.: most Unix platforms, possibly others.

     Raises an *note auditing event: fa1. ‘socket.sendmsg’ with
     arguments ‘self’, ‘address’.

     New in version 3.3.

     Changed in version 3.5: If the system call is interrupted and the
     signal handler does not raise an exception, the method now retries
     the system call instead of raising an *note InterruptedError: 74c.
     exception (see PEP 475(10) for the rationale).

 -- Method: socket.sendmsg_afalg ([msg], *, op[, iv[, assoclen[,
          flags]]])

     Specialized version of *note sendmsg(): 76f. for *note AF_ALG: 67b.
     socket.  Set mode, IV, AEAD associated data length and flags for
     *note AF_ALG: 67b. socket.

     *note Availability: 1491.: Linux >= 2.6.38.

     New in version 3.6.

 -- Method: socket.sendfile (file, offset=0, count=None)

     Send a file until EOF is reached by using high-performance *note
     os.sendfile: 461. and return the total number of bytes which were
     sent.  `file' must be a regular file object opened in binary mode.
     If *note os.sendfile: 461. is not available (e.g.  Windows) or
     `file' is not a regular file *note send(): 76d. will be used
     instead.  `offset' tells from where to start reading the file.  If
     specified, `count' is the total number of bytes to transmit as
     opposed to sending the file until EOF is reached.  File position is
     updated on return or also in case of error in which case *note
     file.tell(): 1efc. can be used to figure out the number of bytes
     which were sent.  The socket must be of *note SOCK_STREAM: d52.
     type.  Non-blocking sockets are not supported.

     New in version 3.5.

 -- Method: socket.set_inheritable (inheritable)

     Set the *note inheritable flag: 8e7. of the socket’s file
     descriptor or socket’s handle.

     New in version 3.4.

 -- Method: socket.setblocking (flag)

     Set blocking or non-blocking mode of the socket: if `flag' is
     false, the socket is set to non-blocking, else to blocking mode.

     This method is a shorthand for certain *note settimeout(): 27b9.
     calls:

        * ‘sock.setblocking(True)’ is equivalent to
          ‘sock.settimeout(None)’

        * ‘sock.setblocking(False)’ is equivalent to
          ‘sock.settimeout(0.0)’

     Changed in version 3.7: The method no longer applies *note
     SOCK_NONBLOCK: 591. flag on *note socket.type: 593.

 -- Method: socket.settimeout (value)

     Set a timeout on blocking socket operations.  The `value' argument
     can be a nonnegative floating point number expressing seconds, or
     ‘None’.  If a non-zero value is given, subsequent socket operations
     will raise a *note timeout: cd9. exception if the timeout period
     `value' has elapsed before the operation has completed.  If zero is
     given, the socket is put in non-blocking mode.  If ‘None’ is given,
     the socket is put in blocking mode.

     For further information, please consult the *note notes on socket
     timeouts: 27ea.

     Changed in version 3.7: The method no longer toggles *note
     SOCK_NONBLOCK: 591. flag on *note socket.type: 593.

 -- Method: socket.setsockopt (level, optname, value: int)

 -- Method: socket.setsockopt (level, optname, value: buffer)

 -- Method: socket.setsockopt (level, optname, None, optlen: int)

     Set the value of the given socket option (see the Unix manual page
     ‘setsockopt(2)’).  The needed symbolic constants are defined in the
     *note socket: ef. module (‘SO_*’ etc.).  The value can be an
     integer, ‘None’ or a *note bytes-like object: 6df. representing a
     buffer.  In the later case it is up to the caller to ensure that
     the bytestring contains the proper bits (see the optional built-in
     module *note struct: f8. for a way to encode C structures as
     bytestrings).  When `value' is set to ‘None’, `optlen' argument is
     required.  It’s equivalent to call ‘setsockopt()’ C function with
     ‘optval=NULL’ and ‘optlen=optlen’.

     Changed in version 3.5: Writable *note bytes-like object: 6df. is
     now accepted.

     Changed in version 3.6: setsockopt(level, optname, None, optlen:
     int) form added.

 -- Method: socket.shutdown (how)

     Shut down one or both halves of the connection.  If `how' is
     ‘SHUT_RD’, further receives are disallowed.  If `how' is ‘SHUT_WR’,
     further sends are disallowed.  If `how' is ‘SHUT_RDWR’, further
     sends and receives are disallowed.

 -- Method: socket.share (process_id)

     Duplicate a socket and prepare it for sharing with a target
     process.  The target process must be provided with `process_id'.
     The resulting bytes object can then be passed to the target process
     using some form of interprocess communication and the socket can be
     recreated there using *note fromshare(): 58e.  Once this method has
     been called, it is safe to close the socket since the operating
     system has already duplicated it for the target process.

     *note Availability: 1491.: Windows.

     New in version 3.3.

Note that there are no methods ‘read()’ or ‘write()’; use *note recv():
76a. and *note send(): 76d. without `flags' argument instead.

Socket objects also have these (read-only) attributes that correspond to
the values given to the *note socket: 767. constructor.

 -- Attribute: socket.family

     The socket family.

 -- Attribute: socket.type

     The socket type.

 -- Attribute: socket.proto

     The socket protocol.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0475

   (2) https://www.python.org/dev/peps/pep-0475

   (3) https://msdn.microsoft.com/en-us/library/ms741621%28VS.85%29.aspx

   (4) https://www.python.org/dev/peps/pep-0475

   (5) https://www.python.org/dev/peps/pep-0475

   (6) https://www.python.org/dev/peps/pep-0475

   (7) https://www.python.org/dev/peps/pep-0475

   (8) https://www.python.org/dev/peps/pep-0475

   (9) https://www.python.org/dev/peps/pep-0475

   (10) https://www.python.org/dev/peps/pep-0475


File: python.info,  Node: Notes on socket timeouts,  Next: Example<8>,  Prev: Socket Objects,  Up: socket — Low-level networking interface

5.18.2.9 Notes on socket timeouts
.................................

A socket object can be in one of three modes: blocking, non-blocking, or
timeout.  Sockets are by default always created in blocking mode, but
this can be changed by calling *note setdefaulttimeout(): 27be.

   * In `blocking mode', operations block until complete or the system
     returns an error (such as connection timed out).

   * In `non-blocking mode', operations fail (with an error that is
     unfortunately system-dependent) if they cannot be completed
     immediately: functions from the *note select: e5. can be used to
     know when and whether a socket is available for reading or writing.

   * In `timeout mode', operations fail if they cannot be completed
     within the timeout specified for the socket (they raise a *note
     timeout: cd9. exception) or if the system returns an error.

     Note: At the operating system level, sockets in `timeout mode' are
     internally set in non-blocking mode.  Also, the blocking and
     timeout modes are shared between file descriptors and socket
     objects that refer to the same network endpoint.  This
     implementation detail can have visible consequences if e.g.  you
     decide to use the *note fileno(): 27e6. of a socket.

* Menu:

* Timeouts and the connect method::
* Timeouts and the accept method::


File: python.info,  Node: Timeouts and the connect method,  Next: Timeouts and the accept method,  Up: Notes on socket timeouts

5.18.2.10 Timeouts and the ‘connect’ method
...........................................

The *note connect(): 769. operation is also subject to the timeout
setting, and in general it is recommended to call *note settimeout():
27b9. before calling *note connect(): 769. or pass a timeout parameter
to *note create_connection(): c6f.  However, the system network stack
may also return a connection timeout error of its own regardless of any
Python socket timeout setting.


File: python.info,  Node: Timeouts and the accept method,  Prev: Timeouts and the connect method,  Up: Notes on socket timeouts

5.18.2.11 Timeouts and the ‘accept’ method
..........................................

If *note getdefaulttimeout(): 27d6. is not *note None: 203, sockets
returned by the *note accept(): 768. method inherit that timeout.
Otherwise, the behaviour depends on settings of the listening socket:

   * if the listening socket is in `blocking mode' or in `timeout mode',
     the socket returned by *note accept(): 768. is in `blocking mode';

   * if the listening socket is in `non-blocking mode', whether the
     socket returned by *note accept(): 768. is in blocking or
     non-blocking mode is operating system-dependent.  If you want to
     ensure cross-platform behaviour, it is recommended you manually
     override this setting.


File: python.info,  Node: Example<8>,  Prev: Notes on socket timeouts,  Up: socket — Low-level networking interface

5.18.2.12 Example
.................

Here are four minimal example programs using the TCP/IP protocol: a
server that echoes all data that it receives back (servicing only one
client), and a client using it.  Note that a server must perform the
sequence ‘socket()’, *note bind(): 27e2, *note listen(): 83a, *note
accept(): 768. (possibly repeating the *note accept(): 768. to service
more than one client), while a client only needs the sequence
‘socket()’, *note connect(): 769.  Also note that the server does not
*note sendall(): 76e./*note recv(): 76a. on the socket it is listening
on but on the new socket returned by *note accept(): 768.

The first two examples support IPv4 only.

     # Echo server program
     import socket

     HOST = ''                 # Symbolic name meaning all available interfaces
     PORT = 50007              # Arbitrary non-privileged port
     with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
         s.bind((HOST, PORT))
         s.listen(1)
         conn, addr = s.accept()
         with conn:
             print('Connected by', addr)
             while True:
                 data = conn.recv(1024)
                 if not data: break
                 conn.sendall(data)

     # Echo client program
     import socket

     HOST = 'daring.cwi.nl'    # The remote host
     PORT = 50007              # The same port as used by the server
     with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
         s.connect((HOST, PORT))
         s.sendall(b'Hello, world')
         data = s.recv(1024)
     print('Received', repr(data))

The next two examples are identical to the above two, but support both
IPv4 and IPv6.  The server side will listen to the first address family
available (it should listen to both instead).  On most of IPv6-ready
systems, IPv6 will take precedence and the server may not accept IPv4
traffic.  The client side will try to connect to the all addresses
returned as a result of the name resolution, and sends traffic to the
first one connected successfully.

     # Echo server program
     import socket
     import sys

     HOST = None               # Symbolic name meaning all available interfaces
     PORT = 50007              # Arbitrary non-privileged port
     s = None
     for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC,
                                   socket.SOCK_STREAM, 0, socket.AI_PASSIVE):
         af, socktype, proto, canonname, sa = res
         try:
             s = socket.socket(af, socktype, proto)
         except OSError as msg:
             s = None
             continue
         try:
             s.bind(sa)
             s.listen(1)
         except OSError as msg:
             s.close()
             s = None
             continue
         break
     if s is None:
         print('could not open socket')
         sys.exit(1)
     conn, addr = s.accept()
     with conn:
         print('Connected by', addr)
         while True:
             data = conn.recv(1024)
             if not data: break
             conn.send(data)

     # Echo client program
     import socket
     import sys

     HOST = 'daring.cwi.nl'    # The remote host
     PORT = 50007              # The same port as used by the server
     s = None
     for res in socket.getaddrinfo(HOST, PORT, socket.AF_UNSPEC, socket.SOCK_STREAM):
         af, socktype, proto, canonname, sa = res
         try:
             s = socket.socket(af, socktype, proto)
         except OSError as msg:
             s = None
             continue
         try:
             s.connect(sa)
         except OSError as msg:
             s.close()
             s = None
             continue
         break
     if s is None:
         print('could not open socket')
         sys.exit(1)
     with s:
         s.sendall(b'Hello, world')
         data = s.recv(1024)
     print('Received', repr(data))

The next example shows how to write a very simple network sniffer with
raw sockets on Windows.  The example requires administrator privileges
to modify the interface:

     import socket

     # the public network interface
     HOST = socket.gethostbyname(socket.gethostname())

     # create a raw socket and bind it to the public interface
     s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_IP)
     s.bind((HOST, 0))

     # Include IP headers
     s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)

     # receive all packages
     s.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON)

     # receive a package
     print(s.recvfrom(65565))

     # disabled promiscuous mode
     s.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF)

The next example shows how to use the socket interface to communicate to
a CAN network using the raw socket protocol.  To use CAN with the
broadcast manager protocol instead, open a socket with:

     socket.socket(socket.AF_CAN, socket.SOCK_DGRAM, socket.CAN_BCM)

After binding (‘CAN_RAW’) or connecting (*note CAN_BCM: 9a0.) the
socket, you can use the *note socket.send(): 76d, and the *note
socket.recv(): 76a. operations (and their counterparts) on the socket
object as usual.

This last example might require special privileges:

     import socket
     import struct


     # CAN frame packing/unpacking (see 'struct can_frame' in <linux/can.h>)

     can_frame_fmt = "=IB3x8s"
     can_frame_size = struct.calcsize(can_frame_fmt)

     def build_can_frame(can_id, data):
         can_dlc = len(data)
         data = data.ljust(8, b'\x00')
         return struct.pack(can_frame_fmt, can_id, can_dlc, data)

     def dissect_can_frame(frame):
         can_id, can_dlc, data = struct.unpack(can_frame_fmt, frame)
         return (can_id, can_dlc, data[:can_dlc])


     # create a raw socket and bind it to the 'vcan0' interface
     s = socket.socket(socket.AF_CAN, socket.SOCK_RAW, socket.CAN_RAW)
     s.bind(('vcan0',))

     while True:
         cf, addr = s.recvfrom(can_frame_size)

         print('Received: can_id=%x, can_dlc=%x, data=%s' % dissect_can_frame(cf))

         try:
             s.send(cf)
         except OSError:
             print('Error sending CAN frame')

         try:
             s.send(build_can_frame(0x01, b'\x01\x02\x03'))
         except OSError:
             print('Error sending CAN frame')

Running an example several times with too small delay between
executions, could lead to this error:

     OSError: [Errno 98] Address already in use

This is because the previous execution has left the socket in a
‘TIME_WAIT’ state, and can’t be immediately reused.

There is a *note socket: ef. flag to set, in order to prevent this,
‘socket.SO_REUSEADDR’:

     s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
     s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
     s.bind((HOST, PORT))

the ‘SO_REUSEADDR’ flag tells the kernel to reuse a local socket in
‘TIME_WAIT’ state, without waiting for its natural timeout to expire.

See also
........

For an introduction to socket programming (in C), see the following
papers:

   - `An Introductory 4.3BSD Interprocess Communication Tutorial', by
     Stuart Sechrest

   - `An Advanced 4.3BSD Interprocess Communication Tutorial', by Samuel
     J. Leffler et al,

both in the UNIX Programmer’s Manual, Supplementary Documents 1
(sections PS1:7 and PS1:8).  The platform-specific reference material
for the various socket-related system calls are also a valuable source
of information on the details of socket semantics.  For Unix, refer to
the manual pages; for Windows, see the WinSock (or Winsock 2)
specification.  For IPv6-ready APIs, readers may want to refer to RFC
3493(1) titled Basic Socket Interface Extensions for IPv6.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3493.html


File: python.info,  Node: ssl — TLS/SSL wrapper for socket objects,  Next: select — Waiting for I/O completion,  Prev: socket — Low-level networking interface,  Up: Networking and Interprocess Communication

5.18.3 ‘ssl’ — TLS/SSL wrapper for socket objects
-------------------------------------------------

`Source code:' Lib/ssl.py(1)

__________________________________________________________________

This module provides access to Transport Layer Security (often known as
“Secure Sockets Layer”) encryption and peer authentication facilities
for network sockets, both client-side and server-side.  This module uses
the OpenSSL library.  It is available on all modern Unix systems,
Windows, macOS, and probably additional platforms, as long as OpenSSL is
installed on that platform.

     Note: Some behavior may be platform dependent, since calls are made
     to the operating system socket APIs.  The installed version of
     OpenSSL may also cause variations in behavior.  For example,
     TLSv1.1 and TLSv1.2 come with openssl version 1.0.1.

     Warning: Don’t use this module without reading the *note Security
     considerations: 26fd.  Doing so may lead to a false sense of
     security, as the default settings of the ssl module are not
     necessarily appropriate for your application.

This section documents the objects and functions in the ‘ssl’ module;
for more general information about TLS, SSL, and certificates, the
reader is referred to the documents in the “See Also” section at the
bottom.

This module provides a class, *note ssl.SSLSocket: 192, which is derived
from the *note socket.socket: 767. type, and provides a socket-like
wrapper that also encrypts and decrypts the data going over the socket
with SSL. It supports additional methods such as ‘getpeercert()’, which
retrieves the certificate of the other side of the connection, and
‘cipher()’, which retrieves the cipher being used for the secure
connection.

For more sophisticated applications, the *note ssl.SSLContext: 4ea.
class helps manage settings and certificates, which can then be
inherited by SSL sockets created through the *note
SSLContext.wrap_socket(): 4eb. method.

Changed in version 3.5.3: Updated to support linking with OpenSSL 1.1.0

Changed in version 3.6: OpenSSL 0.9.8, 1.0.0 and 1.0.1 are deprecated
and no longer supported.  In the future the ssl module will require at
least OpenSSL 1.0.2 or 1.1.0.

* Menu:

* Functions, Constants, and Exceptions: Functions Constants and Exceptions.
* SSL Sockets::
* SSL Contexts::
* Certificates::
* Examples: Examples<17>.
* Notes on non-blocking sockets::
* Memory BIO Support: Memory BIO Support<2>.
* SSL session::
* Security considerations: Security considerations<2>.
* TLS 1.3: TLS 1 3.
* LibreSSL support::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/ssl.py


File: python.info,  Node: Functions Constants and Exceptions,  Next: SSL Sockets,  Up: ssl — TLS/SSL wrapper for socket objects

5.18.3.1 Functions, Constants, and Exceptions
.............................................

* Menu:

* Socket creation::
* Context creation::
* Exceptions: Exceptions<13>.
* Random generation::
* Certificate handling::
* Constants: Constants<9>.


File: python.info,  Node: Socket creation,  Next: Context creation,  Up: Functions Constants and Exceptions

5.18.3.2 Socket creation
........................

Since Python 3.2 and 2.7.9, it is recommended to use the *note
SSLContext.wrap_socket(): 4eb. of an *note SSLContext: 4ea. instance to
wrap sockets as *note SSLSocket: 192. objects.  The helper functions
*note create_default_context(): 9a7. returns a new context with secure
default settings.  The old *note wrap_socket(): 571. function is
deprecated since it is both inefficient and has no support for server
name indication (SNI) and hostname matching.

Client socket example with default context and IPv4/IPv6 dual stack:

     import socket
     import ssl

     hostname = 'www.python.org'
     context = ssl.create_default_context()

     with socket.create_connection((hostname, 443)) as sock:
         with context.wrap_socket(sock, server_hostname=hostname) as ssock:
             print(ssock.version())

Client socket example with custom context and IPv4:

     hostname = 'www.python.org'
     # PROTOCOL_TLS_CLIENT requires valid cert chain and hostname
     context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
     context.load_verify_locations('path/to/cabundle.pem')

     with socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) as sock:
         with context.wrap_socket(sock, server_hostname=hostname) as ssock:
             print(ssock.version())

Server socket example listening on localhost IPv4:

     context = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
     context.load_cert_chain('/path/to/certchain.pem', '/path/to/private.key')

     with socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) as sock:
         sock.bind(('127.0.0.1', 8443))
         sock.listen(5)
         with context.wrap_socket(sock, server_side=True) as ssock:
             conn, addr = ssock.accept()
             ...


File: python.info,  Node: Context creation,  Next: Exceptions<13>,  Prev: Socket creation,  Up: Functions Constants and Exceptions

5.18.3.3 Context creation
.........................

A convenience function helps create *note SSLContext: 4ea. objects for
common purposes.

 -- Function: ssl.create_default_context (purpose=Purpose.SERVER_AUTH,
          cafile=None, capath=None, cadata=None)

     Return a new *note SSLContext: 4ea. object with default settings
     for the given `purpose'.  The settings are chosen by the *note ssl:
     f3. module, and usually represent a higher security level than when
     calling the *note SSLContext: 4ea. constructor directly.

     `cafile', `capath', `cadata' represent optional CA certificates to
     trust for certificate verification, as in *note
     SSLContext.load_verify_locations(): 8d8.  If all three are *note
     None: 203, this function can choose to trust the system’s default
     CA certificates instead.

     The settings are: *note PROTOCOL_TLS: 27f7, *note OP_NO_SSLv2: c71,
     and *note OP_NO_SSLv3: 27f8. with high encryption cipher suites
     without RC4 and without unauthenticated cipher suites.  Passing
     *note SERVER_AUTH: 9b2. as `purpose' sets *note verify_mode: 27f9.
     to *note CERT_REQUIRED: 27fa. and either loads CA certificates
     (when at least one of `cafile', `capath' or `cadata' is given) or
     uses *note SSLContext.load_default_certs(): 9b1. to load default CA
     certificates.

     When *note keylog_filename: 27fb. is supported and the environment
     variable ‘SSLKEYLOGFILE’ is set, *note create_default_context():
     9a7. enables key logging.

          Note: The protocol, options, cipher and other settings may
          change to more restrictive values anytime without prior
          deprecation.  The values represent a fair balance between
          compatibility and security.

          If your application needs specific settings, you should create
          a *note SSLContext: 4ea. and apply the settings yourself.

          Note: If you find that when certain older clients or servers
          attempt to connect with a *note SSLContext: 4ea. created by
          this function that they get an error stating “Protocol or
          cipher suite mismatch”, it may be that they only support
          SSL3.0 which this function excludes using the *note
          OP_NO_SSLv3: 27f8.  SSL3.0 is widely considered to be
          completely broken(1).  If you still wish to continue to use
          this function but still allow SSL 3.0 connections you can
          re-enable them using:

               ctx = ssl.create_default_context(Purpose.CLIENT_AUTH)
               ctx.options &= ~ssl.OP_NO_SSLv3

     New in version 3.4.

     Changed in version 3.4.4: RC4 was dropped from the default cipher
     string.

     Changed in version 3.6: ChaCha20/Poly1305 was added to the default
     cipher string.

     3DES was dropped from the default cipher string.

     Changed in version 3.8: Support for key logging to ‘SSLKEYLOGFILE’
     was added.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/POODLE


File: python.info,  Node: Exceptions<13>,  Next: Random generation,  Prev: Context creation,  Up: Functions Constants and Exceptions

5.18.3.4 Exceptions
...................

 -- Exception: ssl.SSLError

     Raised to signal an error from the underlying SSL implementation
     (currently provided by the OpenSSL library).  This signifies some
     problem in the higher-level encryption and authentication layer
     that’s superimposed on the underlying network connection.  This
     error is a subtype of *note OSError: 304.  The error code and
     message of *note SSLError: cda. instances are provided by the
     OpenSSL library.

     Changed in version 3.3: *note SSLError: cda. used to be a subtype
     of *note socket.error: a76.

      -- Attribute: library

          A string mnemonic designating the OpenSSL submodule in which
          the error occurred, such as ‘SSL’, ‘PEM’ or ‘X509’.  The range
          of possible values depends on the OpenSSL version.

          New in version 3.3.

      -- Attribute: reason

          A string mnemonic designating the reason this error occurred,
          for example ‘CERTIFICATE_VERIFY_FAILED’.  The range of
          possible values depends on the OpenSSL version.

          New in version 3.3.

 -- Exception: ssl.SSLZeroReturnError

     A subclass of *note SSLError: cda. raised when trying to read or
     write and the SSL connection has been closed cleanly.  Note that
     this doesn’t mean that the underlying transport (read TCP) has been
     closed.

     New in version 3.3.

 -- Exception: ssl.SSLWantReadError

     A subclass of *note SSLError: cda. raised by a *note non-blocking
     SSL socket: 27fe. when trying to read or write data, but more data
     needs to be received on the underlying TCP transport before the
     request can be fulfilled.

     New in version 3.3.

 -- Exception: ssl.SSLWantWriteError

     A subclass of *note SSLError: cda. raised by a *note non-blocking
     SSL socket: 27fe. when trying to read or write data, but more data
     needs to be sent on the underlying TCP transport before the request
     can be fulfilled.

     New in version 3.3.

 -- Exception: ssl.SSLSyscallError

     A subclass of *note SSLError: cda. raised when a system error was
     encountered while trying to fulfill an operation on a SSL socket.
     Unfortunately, there is no easy way to inspect the original errno
     number.

     New in version 3.3.

 -- Exception: ssl.SSLEOFError

     A subclass of *note SSLError: cda. raised when the SSL connection
     has been terminated abruptly.  Generally, you shouldn’t try to
     reuse the underlying transport when this error is encountered.

     New in version 3.3.

 -- Exception: ssl.SSLCertVerificationError

     A subclass of *note SSLError: cda. raised when certificate
     validation has failed.

     New in version 3.7.

      -- Attribute: verify_code

          A numeric error number that denotes the verification error.

      -- Attribute: verify_message

          A human readable string of the verification error.

 -- Exception: ssl.CertificateError

     An alias for *note SSLCertVerificationError: 4e4.

     Changed in version 3.7: The exception is now an alias for *note
     SSLCertVerificationError: 4e4.


File: python.info,  Node: Random generation,  Next: Certificate handling,  Prev: Exceptions<13>,  Up: Functions Constants and Exceptions

5.18.3.5 Random generation
..........................

 -- Function: ssl.RAND_bytes (num)

     Return `num' cryptographically strong pseudo-random bytes.  Raises
     an *note SSLError: cda. if the PRNG has not been seeded with enough
     data or if the operation is not supported by the current RAND
     method.  *note RAND_status(): 2805. can be used to check the status
     of the PRNG and *note RAND_add(): 2806. can be used to seed the
     PRNG.

     For almost all applications *note os.urandom(): 5cc. is preferable.

     Read the Wikipedia article, Cryptographically secure pseudorandom
     number generator (CSPRNG)(1), to get the requirements of a
     cryptographically strong generator.

     New in version 3.3.

 -- Function: ssl.RAND_pseudo_bytes (num)

     Return (bytes, is_cryptographic): bytes are `num' pseudo-random
     bytes, is_cryptographic is ‘True’ if the bytes generated are
     cryptographically strong.  Raises an *note SSLError: cda. if the
     operation is not supported by the current RAND method.

     Generated pseudo-random byte sequences will be unique if they are
     of sufficient length, but are not necessarily unpredictable.  They
     can be used for non-cryptographic purposes and for certain purposes
     in cryptographic protocols, but usually not for key generation etc.

     For almost all applications *note os.urandom(): 5cc. is preferable.

     New in version 3.3.

     Deprecated since version 3.6: OpenSSL has deprecated *note
     ssl.RAND_pseudo_bytes(): b68, use *note ssl.RAND_bytes(): b67.
     instead.

 -- Function: ssl.RAND_status ()

     Return ‘True’ if the SSL pseudo-random number generator has been
     seeded with ‘enough’ randomness, and ‘False’ otherwise.  You can
     use *note ssl.RAND_egd(): 2807. and *note ssl.RAND_add(): 2806. to
     increase the randomness of the pseudo-random number generator.

 -- Function: ssl.RAND_egd (path)

     If you are running an entropy-gathering daemon (EGD) somewhere, and
     `path' is the pathname of a socket connection open to it, this will
     read 256 bytes of randomness from the socket, and add it to the SSL
     pseudo-random number generator to increase the security of
     generated secret keys.  This is typically only necessary on systems
     without better sources of randomness.

     See ‘http://egd.sourceforge.net/’ or
     ‘http://prngd.sourceforge.net/’ for sources of entropy-gathering
     daemons.

     *note Availability: 1491.: not available with LibreSSL and OpenSSL
     > 1.1.0.

 -- Function: ssl.RAND_add (bytes, entropy)

     Mix the given `bytes' into the SSL pseudo-random number generator.
     The parameter `entropy' (a float) is a lower bound on the entropy
     contained in string (so you can always use ‘0.0’).  See RFC 1750(2)
     for more information on sources of entropy.

     Changed in version 3.5: Writable *note bytes-like object: 6df. is
     now accepted.

   ---------- Footnotes ----------

   (1) 
https://en.wikipedia.org/wiki/Cryptographically_secure_pseudorandom_number_generator

   (2) https://tools.ietf.org/html/rfc1750.html


File: python.info,  Node: Certificate handling,  Next: Constants<9>,  Prev: Random generation,  Up: Functions Constants and Exceptions

5.18.3.6 Certificate handling
.............................

 -- Function: ssl.match_hostname (cert, hostname)

     Verify that `cert' (in decoded format as returned by *note
     SSLSocket.getpeercert(): 9b7.) matches the given `hostname'.  The
     rules applied are those for checking the identity of HTTPS servers
     as outlined in RFC 2818(1), RFC 5280(2) and RFC 6125(3).  In
     addition to HTTPS, this function should be suitable for checking
     the identity of servers in various SSL-based protocols such as
     FTPS, IMAPS, POPS and others.

     *note CertificateError: 2803. is raised on failure.  On success,
     the function returns nothing:

          >>> cert = {'subject': ((('commonName', 'example.com'),),)}
          >>> ssl.match_hostname(cert, "example.com")
          >>> ssl.match_hostname(cert, "example.org")
          Traceback (most recent call last):
            File "<stdin>", line 1, in <module>
            File "/home/py3k/Lib/ssl.py", line 130, in match_hostname
          ssl.CertificateError: hostname 'example.org' doesn't match 'example.com'

     New in version 3.2.

     Changed in version 3.3.3: The function now follows RFC 6125(4),
     section 6.4.3 and does neither match multiple wildcards (e.g.
     ‘*.*.com’ or ‘*a*.example.org’) nor a wildcard inside an
     internationalized domain names (IDN) fragment.  IDN A-labels such
     as ‘www*.xn--pthon-kva.org’ are still supported, but
     ‘x*.python.org’ no longer matches ‘xn--tda.python.org’.

     Changed in version 3.5: Matching of IP addresses, when present in
     the subjectAltName field of the certificate, is now supported.

     Changed in version 3.7: The function is no longer used to TLS
     connections.  Hostname matching is now performed by OpenSSL.

     Allow wildcard when it is the leftmost and the only character in
     that segment.  Partial wildcards like ‘www*.example.com’ are no
     longer supported.

     Deprecated since version 3.7.

 -- Function: ssl.cert_time_to_seconds (cert_time)

     Return the time in seconds since the Epoch, given the ‘cert_time’
     string representing the “notBefore” or “notAfter” date from a
     certificate in ‘"%b %d %H:%M:%S %Y %Z"’ strptime format (C locale).

     Here’s an example:

          >>> import ssl
          >>> timestamp = ssl.cert_time_to_seconds("Jan  5 09:34:43 2018 GMT")
          >>> timestamp
          1515144883
          >>> from datetime import datetime
          >>> print(datetime.utcfromtimestamp(timestamp))
          2018-01-05 09:34:43

     “notBefore” or “notAfter” dates must use GMT ( RFC 5280(5)).

     Changed in version 3.5: Interpret the input time as a time in UTC
     as specified by ‘GMT’ timezone in the input string.  Local timezone
     was used previously.  Return an integer (no fractions of a second
     in the input format)

 -- Function: ssl.get_server_certificate (addr,
          ssl_version=PROTOCOL_TLS, ca_certs=None)

     Given the address ‘addr’ of an SSL-protected server, as a
     (`hostname', `port-number') pair, fetches the server’s certificate,
     and returns it as a PEM-encoded string.  If ‘ssl_version’ is
     specified, uses that version of the SSL protocol to attempt to
     connect to the server.  If ‘ca_certs’ is specified, it should be a
     file containing a list of root certificates, the same format as
     used for the same parameter in *note SSLContext.wrap_socket(): 4eb.
     The call will attempt to validate the server certificate against
     that set of root certificates, and will fail if the validation
     attempt fails.

     Changed in version 3.3: This function is now IPv6-compatible.

     Changed in version 3.5: The default `ssl_version' is changed from
     *note PROTOCOL_SSLv3: 2809. to *note PROTOCOL_TLS: 27f7. for
     maximum compatibility with modern servers.

 -- Function: ssl.DER_cert_to_PEM_cert (DER_cert_bytes)

     Given a certificate as a DER-encoded blob of bytes, returns a
     PEM-encoded string version of the same certificate.

 -- Function: ssl.PEM_cert_to_DER_cert (PEM_cert_string)

     Given a certificate as an ASCII PEM string, returns a DER-encoded
     sequence of bytes for that same certificate.

 -- Function: ssl.get_default_verify_paths ()

     Returns a named tuple with paths to OpenSSL’s default cafile and
     capath.  The paths are the same as used by *note
     SSLContext.set_default_verify_paths(): 9a9.  The return value is a
     *note named tuple: b7b. ‘DefaultVerifyPaths’:

        * ‘cafile’ - resolved path to cafile or ‘None’ if the file
          doesn’t exist,

        * ‘capath’ - resolved path to capath or ‘None’ if the directory
          doesn’t exist,

        * ‘openssl_cafile_env’ - OpenSSL’s environment key that points
          to a cafile,

        * ‘openssl_cafile’ - hard coded path to a cafile,

        * ‘openssl_capath_env’ - OpenSSL’s environment key that points
          to a capath,

        * ‘openssl_capath’ - hard coded path to a capath directory

     *note Availability: 1491.: LibreSSL ignores the environment vars
     ‘openssl_cafile_env’ and ‘openssl_capath_env’.

     New in version 3.4.

 -- Function: ssl.enum_certificates (store_name)

     Retrieve certificates from Windows’ system cert store.
     `store_name' may be one of ‘CA’, ‘ROOT’ or ‘MY’.  Windows may
     provide additional cert stores, too.

     The function returns a list of (cert_bytes, encoding_type, trust)
     tuples.  The encoding_type specifies the encoding of cert_bytes.
     It is either ‘x509_asn’ for X.509 ASN.1 data or ‘pkcs_7_asn’ for
     PKCS#7 ASN.1 data.  Trust specifies the purpose of the certificate
     as a set of OIDS or exactly ‘True’ if the certificate is
     trustworthy for all purposes.

     Example:

          >>> ssl.enum_certificates("CA")
          [(b'data...', 'x509_asn', {'1.3.6.1.5.5.7.3.1', '1.3.6.1.5.5.7.3.2'}),
           (b'data...', 'x509_asn', True)]

     *note Availability: 1491.: Windows.

     New in version 3.4.

 -- Function: ssl.enum_crls (store_name)

     Retrieve CRLs from Windows’ system cert store.  `store_name' may be
     one of ‘CA’, ‘ROOT’ or ‘MY’.  Windows may provide additional cert
     stores, too.

     The function returns a list of (cert_bytes, encoding_type, trust)
     tuples.  The encoding_type specifies the encoding of cert_bytes.
     It is either ‘x509_asn’ for X.509 ASN.1 data or ‘pkcs_7_asn’ for
     PKCS#7 ASN.1 data.

     *note Availability: 1491.: Windows.

     New in version 3.4.

 -- Function: ssl.wrap_socket (sock, keyfile=None, certfile=None,
          server_side=False, cert_reqs=CERT_NONE,
          ssl_version=PROTOCOL_TLS, ca_certs=None,
          do_handshake_on_connect=True, suppress_ragged_eofs=True,
          ciphers=None)

     Takes an instance ‘sock’ of *note socket.socket: 767, and returns
     an instance of *note ssl.SSLSocket: 192, a subtype of *note
     socket.socket: 767, which wraps the underlying socket in an SSL
     context.  ‘sock’ must be a *note SOCK_STREAM: d52. socket; other
     socket types are unsupported.

     Internally, function creates a *note SSLContext: 4ea. with protocol
     `ssl_version' and *note SSLContext.options: 280c. set to
     `cert_reqs'.  If parameters `keyfile', `certfile', `ca_certs' or
     `ciphers' are set, then the values are passed to *note
     SSLContext.load_cert_chain(): b69, *note
     SSLContext.load_verify_locations(): 8d8, and *note
     SSLContext.set_ciphers(): 280d.

     The arguments `server_side', `do_handshake_on_connect', and
     `suppress_ragged_eofs' have the same meaning as *note
     SSLContext.wrap_socket(): 4eb.

     Deprecated since version 3.7: Since Python 3.2 and 2.7.9, it is
     recommended to use the *note SSLContext.wrap_socket(): 4eb. instead
     of *note wrap_socket(): 571.  The top-level function is limited and
     creates an insecure client socket without server name indication or
     hostname matching.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2818.html

   (2) https://tools.ietf.org/html/rfc5280.html

   (3) https://tools.ietf.org/html/rfc6125.html

   (4) https://tools.ietf.org/html/rfc6125.html

   (5) https://tools.ietf.org/html/rfc5280.html


File: python.info,  Node: Constants<9>,  Prev: Certificate handling,  Up: Functions Constants and Exceptions

5.18.3.7 Constants
..................

     All constants are now *note enum.IntEnum: 684. or *note
     enum.IntFlag: 18a1. collections.

     New in version 3.6.

 -- Data: ssl.CERT_NONE

     Possible value for *note SSLContext.verify_mode: 27f9, or the
     ‘cert_reqs’ parameter to *note wrap_socket(): 571.  Except for
     *note PROTOCOL_TLS_CLIENT: 2810, it is the default mode.  With
     client-side sockets, just about any cert is accepted.  Validation
     errors, such as untrusted or expired cert, are ignored and do not
     abort the TLS/SSL handshake.

     In server mode, no certificate is requested from the client, so the
     client does not send any for client cert authentication.

     See the discussion of *note Security considerations: 26fd. below.

 -- Data: ssl.CERT_OPTIONAL

     Possible value for *note SSLContext.verify_mode: 27f9, or the
     ‘cert_reqs’ parameter to *note wrap_socket(): 571.  In client mode,
     *note CERT_OPTIONAL: 2811. has the same meaning as *note
     CERT_REQUIRED: 27fa.  It is recommended to use *note CERT_REQUIRED:
     27fa. for client-side sockets instead.

     In server mode, a client certificate request is sent to the client.
     The client may either ignore the request or send a certificate in
     order perform TLS client cert authentication.  If the client
     chooses to send a certificate, it is verified.  Any verification
     error immediately aborts the TLS handshake.

     Use of this setting requires a valid set of CA certificates to be
     passed, either to *note SSLContext.load_verify_locations(): 8d8. or
     as a value of the ‘ca_certs’ parameter to *note wrap_socket(): 571.

 -- Data: ssl.CERT_REQUIRED

     Possible value for *note SSLContext.verify_mode: 27f9, or the
     ‘cert_reqs’ parameter to *note wrap_socket(): 571.  In this mode,
     certificates are required from the other side of the socket
     connection; an *note SSLError: cda. will be raised if no
     certificate is provided, or if its validation fails.  This mode is
     `not' sufficient to verify a certificate in client mode as it does
     not match hostnames.  *note check_hostname: 2812. must be enabled
     as well to verify the authenticity of a cert.  *note
     PROTOCOL_TLS_CLIENT: 2810. uses *note CERT_REQUIRED: 27fa. and
     enables *note check_hostname: 2812. by default.

     With server socket, this mode provides mandatory TLS client cert
     authentication.  A client certificate request is sent to the client
     and the client must provide a valid and trusted certificate.

     Use of this setting requires a valid set of CA certificates to be
     passed, either to *note SSLContext.load_verify_locations(): 8d8. or
     as a value of the ‘ca_certs’ parameter to *note wrap_socket(): 571.

 -- Class: ssl.VerifyMode

     *note enum.IntEnum: 684. collection of CERT_* constants.

     New in version 3.6.

 -- Data: ssl.VERIFY_DEFAULT

     Possible value for *note SSLContext.verify_flags: 9ac.  In this
     mode, certificate revocation lists (CRLs) are not checked.  By
     default OpenSSL does neither require nor verify CRLs.

     New in version 3.4.

 -- Data: ssl.VERIFY_CRL_CHECK_LEAF

     Possible value for *note SSLContext.verify_flags: 9ac.  In this
     mode, only the peer cert is checked but none of the intermediate CA
     certificates.  The mode requires a valid CRL that is signed by the
     peer cert’s issuer (its direct ancestor CA). If no proper CRL has
     been loaded with *note SSLContext.load_verify_locations: 8d8,
     validation will fail.

     New in version 3.4.

 -- Data: ssl.VERIFY_CRL_CHECK_CHAIN

     Possible value for *note SSLContext.verify_flags: 9ac.  In this
     mode, CRLs of all certificates in the peer cert chain are checked.

     New in version 3.4.

 -- Data: ssl.VERIFY_X509_STRICT

     Possible value for *note SSLContext.verify_flags: 9ac. to disable
     workarounds for broken X.509 certificates.

     New in version 3.4.

 -- Data: ssl.VERIFY_X509_TRUSTED_FIRST

     Possible value for *note SSLContext.verify_flags: 9ac.  It
     instructs OpenSSL to prefer trusted certificates when building the
     trust chain to validate a certificate.  This flag is enabled by
     default.

     New in version 3.4.4.

 -- Class: ssl.VerifyFlags

     *note enum.IntFlag: 18a1. collection of VERIFY_* constants.

     New in version 3.6.

 -- Data: ssl.PROTOCOL_TLS

     Selects the highest protocol version that both the client and
     server support.  Despite the name, this option can select both
     “SSL” and “TLS” protocols.

     New in version 3.6.

 -- Data: ssl.PROTOCOL_TLS_CLIENT

     Auto-negotiate the highest protocol version like *note
     PROTOCOL_TLS: 27f7, but only support client-side *note SSLSocket:
     192. connections.  The protocol enables *note CERT_REQUIRED: 27fa.
     and *note check_hostname: 2812. by default.

     New in version 3.6.

 -- Data: ssl.PROTOCOL_TLS_SERVER

     Auto-negotiate the highest protocol version like *note
     PROTOCOL_TLS: 27f7, but only support server-side *note SSLSocket:
     192. connections.

     New in version 3.6.

 -- Data: ssl.PROTOCOL_SSLv23

     Alias for *note PROTOCOL_TLS: 27f7.

     Deprecated since version 3.6: Use *note PROTOCOL_TLS: 27f7.
     instead.

 -- Data: ssl.PROTOCOL_SSLv2

     Selects SSL version 2 as the channel encryption protocol.

     This protocol is not available if OpenSSL is compiled with the
     ‘OPENSSL_NO_SSL2’ flag.

          Warning: SSL version 2 is insecure.  Its use is highly
          discouraged.

     Deprecated since version 3.6: OpenSSL has removed support for
     SSLv2.

 -- Data: ssl.PROTOCOL_SSLv3

     Selects SSL version 3 as the channel encryption protocol.

     This protocol is not be available if OpenSSL is compiled with the
     ‘OPENSSL_NO_SSLv3’ flag.

          Warning: SSL version 3 is insecure.  Its use is highly
          discouraged.

     Deprecated since version 3.6: OpenSSL has deprecated all version
     specific protocols.  Use the default protocol *note PROTOCOL_TLS:
     27f7. with flags like *note OP_NO_SSLv3: 27f8. instead.

 -- Data: ssl.PROTOCOL_TLSv1

     Selects TLS version 1.0 as the channel encryption protocol.

     Deprecated since version 3.6: OpenSSL has deprecated all version
     specific protocols.  Use the default protocol *note PROTOCOL_TLS:
     27f7. with flags like *note OP_NO_SSLv3: 27f8. instead.

 -- Data: ssl.PROTOCOL_TLSv1_1

     Selects TLS version 1.1 as the channel encryption protocol.
     Available only with openssl version 1.0.1+.

     New in version 3.4.

     Deprecated since version 3.6: OpenSSL has deprecated all version
     specific protocols.  Use the default protocol *note PROTOCOL_TLS:
     27f7. with flags like *note OP_NO_SSLv3: 27f8. instead.

 -- Data: ssl.PROTOCOL_TLSv1_2

     Selects TLS version 1.2 as the channel encryption protocol.  This
     is the most modern version, and probably the best choice for
     maximum protection, if both sides can speak it.  Available only
     with openssl version 1.0.1+.

     New in version 3.4.

     Deprecated since version 3.6: OpenSSL has deprecated all version
     specific protocols.  Use the default protocol *note PROTOCOL_TLS:
     27f7. with flags like *note OP_NO_SSLv3: 27f8. instead.

 -- Data: ssl.OP_ALL

     Enables workarounds for various bugs present in other SSL
     implementations.  This option is set by default.  It does not
     necessarily set the same flags as OpenSSL’s ‘SSL_OP_ALL’ constant.

     New in version 3.2.

 -- Data: ssl.OP_NO_SSLv2

     Prevents an SSLv2 connection.  This option is only applicable in
     conjunction with *note PROTOCOL_TLS: 27f7.  It prevents the peers
     from choosing SSLv2 as the protocol version.

     New in version 3.2.

     Deprecated since version 3.6: SSLv2 is deprecated

 -- Data: ssl.OP_NO_SSLv3

     Prevents an SSLv3 connection.  This option is only applicable in
     conjunction with *note PROTOCOL_TLS: 27f7.  It prevents the peers
     from choosing SSLv3 as the protocol version.

     New in version 3.2.

     Deprecated since version 3.6: SSLv3 is deprecated

 -- Data: ssl.OP_NO_TLSv1

     Prevents a TLSv1 connection.  This option is only applicable in
     conjunction with *note PROTOCOL_TLS: 27f7.  It prevents the peers
     from choosing TLSv1 as the protocol version.

     New in version 3.2.

     Deprecated since version 3.7: The option is deprecated since
     OpenSSL 1.1.0, use the new *note SSLContext.minimum_version: 4ed.
     and *note SSLContext.maximum_version: 4ee. instead.

 -- Data: ssl.OP_NO_TLSv1_1

     Prevents a TLSv1.1 connection.  This option is only applicable in
     conjunction with *note PROTOCOL_TLS: 27f7.  It prevents the peers
     from choosing TLSv1.1 as the protocol version.  Available only with
     openssl version 1.0.1+.

     New in version 3.4.

     Deprecated since version 3.7: The option is deprecated since
     OpenSSL 1.1.0.

 -- Data: ssl.OP_NO_TLSv1_2

     Prevents a TLSv1.2 connection.  This option is only applicable in
     conjunction with *note PROTOCOL_TLS: 27f7.  It prevents the peers
     from choosing TLSv1.2 as the protocol version.  Available only with
     openssl version 1.0.1+.

     New in version 3.4.

     Deprecated since version 3.7: The option is deprecated since
     OpenSSL 1.1.0.

 -- Data: ssl.OP_NO_TLSv1_3

     Prevents a TLSv1.3 connection.  This option is only applicable in
     conjunction with *note PROTOCOL_TLS: 27f7.  It prevents the peers
     from choosing TLSv1.3 as the protocol version.  TLS 1.3 is
     available with OpenSSL 1.1.1 or later.  When Python has been
     compiled against an older version of OpenSSL, the flag defaults to
     `0'.

     New in version 3.7.

     Deprecated since version 3.7: The option is deprecated since
     OpenSSL 1.1.0.  It was added to 2.7.15, 3.6.3 and 3.7.0 for
     backwards compatibility with OpenSSL 1.0.2.

 -- Data: ssl.OP_NO_RENEGOTIATION

     Disable all renegotiation in TLSv1.2 and earlier.  Do not send
     HelloRequest messages, and ignore renegotiation requests via
     ClientHello.

     This option is only available with OpenSSL 1.1.0h and later.

     New in version 3.7.

 -- Data: ssl.OP_CIPHER_SERVER_PREFERENCE

     Use the server’s cipher ordering preference, rather than the
     client’s.  This option has no effect on client sockets and SSLv2
     server sockets.

     New in version 3.3.

 -- Data: ssl.OP_SINGLE_DH_USE

     Prevents re-use of the same DH key for distinct SSL sessions.  This
     improves forward secrecy but requires more computational resources.
     This option only applies to server sockets.

     New in version 3.3.

 -- Data: ssl.OP_SINGLE_ECDH_USE

     Prevents re-use of the same ECDH key for distinct SSL sessions.
     This improves forward secrecy but requires more computational
     resources.  This option only applies to server sockets.

     New in version 3.3.

 -- Data: ssl.OP_ENABLE_MIDDLEBOX_COMPAT

     Send dummy Change Cipher Spec (CCS) messages in TLS 1.3 handshake
     to make a TLS 1.3 connection look more like a TLS 1.2 connection.

     This option is only available with OpenSSL 1.1.1 and later.

     New in version 3.8.

 -- Data: ssl.OP_NO_COMPRESSION

     Disable compression on the SSL channel.  This is useful if the
     application protocol supports its own compression scheme.

     This option is only available with OpenSSL 1.0.0 and later.

     New in version 3.3.

 -- Class: ssl.Options

     *note enum.IntFlag: 18a1. collection of OP_* constants.

 -- Data: ssl.OP_NO_TICKET

     Prevent client side from requesting a session ticket.

     New in version 3.6.

 -- Data: ssl.OP_IGNORE_UNEXPECTED_EOF

     Ignore unexpected shutdown of TLS connections.

     This option is only available with OpenSSL 3.0.0 and later.

     New in version 3.10.

 -- Data: ssl.HAS_ALPN

     Whether the OpenSSL library has built-in support for the
     `Application-Layer Protocol Negotiation' TLS extension as described
     in RFC 7301(1).

     New in version 3.5.

 -- Data: ssl.HAS_NEVER_CHECK_COMMON_NAME

     Whether the OpenSSL library has built-in support not checking
     subject common name and *note
     SSLContext.hostname_checks_common_name: 4e5. is writeable.

     New in version 3.7.

 -- Data: ssl.HAS_ECDH

     Whether the OpenSSL library has built-in support for the Elliptic
     Curve-based Diffie-Hellman key exchange.  This should be true
     unless the feature was explicitly disabled by the distributor.

     New in version 3.3.

 -- Data: ssl.HAS_SNI

     Whether the OpenSSL library has built-in support for the `Server
     Name Indication' extension (as defined in RFC 6066(2)).

     New in version 3.2.

 -- Data: ssl.HAS_NPN

     Whether the OpenSSL library has built-in support for the `Next
     Protocol Negotiation' as described in the Application Layer
     Protocol Negotiation(3).  When true, you can use the *note
     SSLContext.set_npn_protocols(): b6f. method to advertise which
     protocols you want to support.

     New in version 3.3.

 -- Data: ssl.HAS_SSLv2

     Whether the OpenSSL library has built-in support for the SSL 2.0
     protocol.

     New in version 3.7.

 -- Data: ssl.HAS_SSLv3

     Whether the OpenSSL library has built-in support for the SSL 3.0
     protocol.

     New in version 3.7.

 -- Data: ssl.HAS_TLSv1

     Whether the OpenSSL library has built-in support for the TLS 1.0
     protocol.

     New in version 3.7.

 -- Data: ssl.HAS_TLSv1_1

     Whether the OpenSSL library has built-in support for the TLS 1.1
     protocol.

     New in version 3.7.

 -- Data: ssl.HAS_TLSv1_2

     Whether the OpenSSL library has built-in support for the TLS 1.2
     protocol.

     New in version 3.7.

 -- Data: ssl.HAS_TLSv1_3

     Whether the OpenSSL library has built-in support for the TLS 1.3
     protocol.

     New in version 3.7.

 -- Data: ssl.CHANNEL_BINDING_TYPES

     List of supported TLS channel binding types.  Strings in this list
     can be used as arguments to *note SSLSocket.get_channel_binding():
     b6c.

     New in version 3.3.

 -- Data: ssl.OPENSSL_VERSION

     The version string of the OpenSSL library loaded by the
     interpreter:

          >>> ssl.OPENSSL_VERSION
          'OpenSSL 1.0.2k  26 Jan 2017'

     New in version 3.2.

 -- Data: ssl.OPENSSL_VERSION_INFO

     A tuple of five integers representing version information about the
     OpenSSL library:

          >>> ssl.OPENSSL_VERSION_INFO
          (1, 0, 2, 11, 15)

     New in version 3.2.

 -- Data: ssl.OPENSSL_VERSION_NUMBER

     The raw version number of the OpenSSL library, as a single integer:

          >>> ssl.OPENSSL_VERSION_NUMBER
          268443839
          >>> hex(ssl.OPENSSL_VERSION_NUMBER)
          '0x100020bf'

     New in version 3.2.

 -- Data: ssl.ALERT_DESCRIPTION_HANDSHAKE_FAILURE
 -- Data: ssl.ALERT_DESCRIPTION_INTERNAL_ERROR

 -- Data: ALERT_DESCRIPTION_*

     Alert Descriptions from RFC 5246(4) and others.  The IANA TLS Alert
     Registry(5) contains this list and references to the RFCs where
     their meaning is defined.

     Used as the return value of the callback function in *note
     SSLContext.set_servername_callback(): 9b6.

     New in version 3.4.

 -- Class: ssl.AlertDescription

     *note enum.IntEnum: 684. collection of ALERT_DESCRIPTION_*
     constants.

     New in version 3.6.

 -- Data: Purpose.SERVER_AUTH

     Option for *note create_default_context(): 9a7. and *note
     SSLContext.load_default_certs(): 9b1.  This value indicates that
     the context may be used to authenticate Web servers (therefore, it
     will be used to create client-side sockets).

     New in version 3.4.

 -- Data: Purpose.CLIENT_AUTH

     Option for *note create_default_context(): 9a7. and *note
     SSLContext.load_default_certs(): 9b1.  This value indicates that
     the context may be used to authenticate Web clients (therefore, it
     will be used to create server-side sockets).

     New in version 3.4.

 -- Class: ssl.SSLErrorNumber

     *note enum.IntEnum: 684. collection of SSL_ERROR_* constants.

     New in version 3.6.

 -- Class: ssl.TLSVersion

     *note enum.IntEnum: 684. collection of SSL and TLS versions for
     *note SSLContext.maximum_version: 4ee. and *note
     SSLContext.minimum_version: 4ed.

     New in version 3.7.

 -- Attribute: TLSVersion.MINIMUM_SUPPORTED

 -- Attribute: TLSVersion.MAXIMUM_SUPPORTED

     The minimum or maximum supported SSL or TLS version.  These are
     magic constants.  Their values don’t reflect the lowest and highest
     available TLS/SSL versions.

 -- Attribute: TLSVersion.SSLv3

 -- Attribute: TLSVersion.TLSv1

 -- Attribute: TLSVersion.TLSv1_1

 -- Attribute: TLSVersion.TLSv1_2

 -- Attribute: TLSVersion.TLSv1_3

     SSL 3.0 to TLS 1.3.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc7301.html

   (2) https://tools.ietf.org/html/rfc6066.html

   (3) 
https://en.wikipedia.org/wiki/Application-Layer_Protocol_Negotiation

   (4) https://tools.ietf.org/html/rfc5246.html

   (5) 
https://www.iana.org/assignments/tls-parameters/tls-parameters.xml#tls-parameters-6


File: python.info,  Node: SSL Sockets,  Next: SSL Contexts,  Prev: Functions Constants and Exceptions,  Up: ssl — TLS/SSL wrapper for socket objects

5.18.3.8 SSL Sockets
....................

 -- Class: ssl.SSLSocket (socket.socket)

     SSL sockets provide the following methods of *note Socket Objects:
     27d4.:

        - *note accept(): 768.

        - *note bind(): 27e2.

        - *note close(): 6f7.

        - *note connect(): 769.

        - *note detach(): c6e.

        - *note fileno(): 27e6.

        - *note getpeername(): 2741, *note getsockname(): 2742.

        - *note getsockopt(): 679, *note setsockopt(): 67a.

        - *note gettimeout(): 27e7, *note settimeout(): 27b9, *note
          setblocking(): 206f.

        - *note listen(): 83a.

        - *note makefile(): bec.

        - *note recv(): 76a, *note recv_into(): d7a. (but passing a
          non-zero ‘flags’ argument is not allowed)

        - *note send(): 76d, *note sendall(): 76e. (with the same
          limitation)

        - *note sendfile(): 839. (but *note os.sendfile: 461. will be
          used for plain-text sockets only, else *note send(): 76d. will
          be used)

        - *note shutdown(): 27e3.

     However, since the SSL (and TLS) protocol has its own framing atop
     of TCP, the SSL sockets abstraction can, in certain respects,
     diverge from the specification of normal, OS-level sockets.  See
     especially the *note notes on non-blocking sockets: 27fe.

     Instances of *note SSLSocket: 192. must be created using the *note
     SSLContext.wrap_socket(): 4eb. method.

     Changed in version 3.5: The ‘sendfile()’ method was added.

     Changed in version 3.5: The ‘shutdown()’ does not reset the socket
     timeout each time bytes are received or sent.  The socket timeout
     is now to maximum total duration of the shutdown.

     Deprecated since version 3.6: It is deprecated to create a *note
     SSLSocket: 192. instance directly, use *note
     SSLContext.wrap_socket(): 4eb. to wrap a socket.

     Changed in version 3.7: *note SSLSocket: 192. instances must to
     created with *note wrap_socket(): 4eb.  In earlier versions, it was
     possible to create instances directly.  This was never documented
     or officially supported.

SSL sockets also have the following additional methods and attributes:

 -- Method: SSLSocket.read (len=1024, buffer=None)

     Read up to `len' bytes of data from the SSL socket and return the
     result as a ‘bytes’ instance.  If `buffer' is specified, then read
     into the buffer instead, and return the number of bytes read.

     Raise *note SSLWantReadError: 845. or *note SSLWantWriteError: 846.
     if the socket is *note non-blocking: 27fe. and the read would
     block.

     As at any time a re-negotiation is possible, a call to *note
     read(): 84a. can also cause write operations.

     Changed in version 3.5: The socket timeout is no more reset each
     time bytes are received or sent.  The socket timeout is now to
     maximum total duration to read up to `len' bytes.

     Deprecated since version 3.6: Use ‘recv()’ instead of *note read():
     84a.

 -- Method: SSLSocket.write (buf)

     Write `buf' to the SSL socket and return the number of bytes
     written.  The `buf' argument must be an object supporting the
     buffer interface.

     Raise *note SSLWantReadError: 845. or *note SSLWantWriteError: 846.
     if the socket is *note non-blocking: 27fe. and the write would
     block.

     As at any time a re-negotiation is possible, a call to *note
     write(): 84b. can also cause read operations.

     Changed in version 3.5: The socket timeout is no more reset each
     time bytes are received or sent.  The socket timeout is now to
     maximum total duration to write `buf'.

     Deprecated since version 3.6: Use ‘send()’ instead of *note
     write(): 84b.

     Note: The *note read(): 84a. and *note write(): 84b. methods are
     the low-level methods that read and write unencrypted,
     application-level data and decrypt/encrypt it to encrypted,
     wire-level data.  These methods require an active SSL connection,
     i.e.  the handshake was completed and *note SSLSocket.unwrap():
     283c. was not called.

     Normally you should use the socket API methods like *note recv():
     76a. and *note send(): 76d. instead of these methods.

 -- Method: SSLSocket.do_handshake ()

     Perform the SSL setup handshake.

     Changed in version 3.4: The handshake method also performs *note
     match_hostname(): 4e3. when the *note check_hostname: 2812.
     attribute of the socket’s *note context: 283d. is true.

     Changed in version 3.5: The socket timeout is no more reset each
     time bytes are received or sent.  The socket timeout is now to
     maximum total duration of the handshake.

     Changed in version 3.7: Hostname or IP address is matched by
     OpenSSL during handshake.  The function *note match_hostname():
     4e3. is no longer used.  In case OpenSSL refuses a hostname or IP
     address, the handshake is aborted early and a TLS alert message is
     send to the peer.

 -- Method: SSLSocket.getpeercert (binary_form=False)

     If there is no certificate for the peer on the other end of the
     connection, return ‘None’.  If the SSL handshake hasn’t been done
     yet, raise *note ValueError: 16d.

     If the ‘binary_form’ parameter is *note False: 48f, and a
     certificate was received from the peer, this method returns a *note
     dict: 164. instance.  If the certificate was not validated, the
     dict is empty.  If the certificate was validated, it returns a dict
     with several keys, amongst them ‘subject’ (the principal for which
     the certificate was issued) and ‘issuer’ (the principal issuing the
     certificate).  If a certificate contains an instance of the
     `Subject Alternative Name' extension (see RFC 3280(1)), there will
     also be a ‘subjectAltName’ key in the dictionary.

     The ‘subject’ and ‘issuer’ fields are tuples containing the
     sequence of relative distinguished names (RDNs) given in the
     certificate’s data structure for the respective fields, and each
     RDN is a sequence of name-value pairs.  Here is a real-world
     example:

          {'issuer': ((('countryName', 'IL'),),
                      (('organizationName', 'StartCom Ltd.'),),
                      (('organizationalUnitName',
                        'Secure Digital Certificate Signing'),),
                      (('commonName',
                        'StartCom Class 2 Primary Intermediate Server CA'),)),
           'notAfter': 'Nov 22 08:15:19 2013 GMT',
           'notBefore': 'Nov 21 03:09:52 2011 GMT',
           'serialNumber': '95F0',
           'subject': ((('description', '571208-SLe257oHY9fVQ07Z'),),
                       (('countryName', 'US'),),
                       (('stateOrProvinceName', 'California'),),
                       (('localityName', 'San Francisco'),),
                       (('organizationName', 'Electronic Frontier Foundation, Inc.'),),
                       (('commonName', '*.eff.org'),),
                       (('emailAddress', 'hostmaster@eff.org'),)),
           'subjectAltName': (('DNS', '*.eff.org'), ('DNS', 'eff.org')),
           'version': 3}

          Note: To validate a certificate for a particular service, you
          can use the *note match_hostname(): 4e3. function.

     If the ‘binary_form’ parameter is *note True: 594, and a
     certificate was provided, this method returns the DER-encoded form
     of the entire certificate as a sequence of bytes, or *note None:
     203. if the peer did not provide a certificate.  Whether the peer
     provides a certificate depends on the SSL socket’s role:

        * for a client SSL socket, the server will always provide a
          certificate, regardless of whether validation was required;

        * for a server SSL socket, the client will only provide a
          certificate when requested by the server; therefore *note
          getpeercert(): 9b7. will return *note None: 203. if you used
          *note CERT_NONE: 280f. (rather than *note CERT_OPTIONAL: 2811.
          or *note CERT_REQUIRED: 27fa.).

     Changed in version 3.2: The returned dictionary includes additional
     items such as ‘issuer’ and ‘notBefore’.

     Changed in version 3.4: *note ValueError: 16d. is raised when the
     handshake isn’t done.  The returned dictionary includes additional
     X509v3 extension items such as ‘crlDistributionPoints’, ‘caIssuers’
     and ‘OCSP’ URIs.

     Changed in version 3.9: IPv6 address strings no longer have a
     trailing new line.

 -- Method: SSLSocket.cipher ()

     Returns a three-value tuple containing the name of the cipher being
     used, the version of the SSL protocol that defines its use, and the
     number of secret bits being used.  If no connection has been
     established, returns ‘None’.

 -- Method: SSLSocket.shared_ciphers ()

     Return the list of ciphers shared by the client during the
     handshake.  Each entry of the returned list is a three-value tuple
     containing the name of the cipher, the version of the SSL protocol
     that defines its use, and the number of secret bits the cipher
     uses.  *note shared_ciphers(): 848. returns ‘None’ if no connection
     has been established or the socket is a client socket.

     New in version 3.5.

 -- Method: SSLSocket.compression ()

     Return the compression algorithm being used as a string, or ‘None’
     if the connection isn’t compressed.

     If the higher-level protocol supports its own compression
     mechanism, you can use *note OP_NO_COMPRESSION: b6e. to disable
     SSL-level compression.

     New in version 3.3.

 -- Method: SSLSocket.get_channel_binding (cb_type="tls-unique")

     Get channel binding data for current connection, as a bytes object.
     Returns ‘None’ if not connected or the handshake has not been
     completed.

     The `cb_type' parameter allow selection of the desired channel
     binding type.  Valid channel binding types are listed in the *note
     CHANNEL_BINDING_TYPES: 282e. list.  Currently only the ‘tls-unique’
     channel binding, defined by RFC 5929(2), is supported.  *note
     ValueError: 16d. will be raised if an unsupported channel binding
     type is requested.

     New in version 3.3.

 -- Method: SSLSocket.selected_alpn_protocol ()

     Return the protocol that was selected during the TLS handshake.  If
     *note SSLContext.set_alpn_protocols(): 840. was not called, if the
     other party does not support ALPN, if this socket does not support
     any of the client’s proposed protocols, or if the handshake has not
     happened yet, ‘None’ is returned.

     New in version 3.5.

 -- Method: SSLSocket.selected_npn_protocol ()

     Return the higher-level protocol that was selected during the
     TLS/SSL handshake.  If *note SSLContext.set_npn_protocols(): b6f.
     was not called, or if the other party does not support NPN, or if
     the handshake has not yet happened, this will return ‘None’.

     New in version 3.3.

 -- Method: SSLSocket.unwrap ()

     Performs the SSL shutdown handshake, which removes the TLS layer
     from the underlying socket, and returns the underlying socket
     object.  This can be used to go from encrypted operation over a
     connection to unencrypted.  The returned socket should always be
     used for further communication with the other side of the
     connection, rather than the original socket.

 -- Method: SSLSocket.verify_client_post_handshake ()

     Requests post-handshake authentication (PHA) from a TLS 1.3 client.
     PHA can only be initiated for a TLS 1.3 connection from a
     server-side socket, after the initial TLS handshake and with PHA
     enabled on both sides, see *note SSLContext.post_handshake_auth:
     351.

     The method does not perform a cert exchange immediately.  The
     server-side sends a CertificateRequest during the next write event
     and expects the client to respond with a certificate on the next
     read event.

     If any precondition isn’t met (e.g.  not TLS 1.3, PHA not enabled),
     an *note SSLError: cda. is raised.

          Note: Only available with OpenSSL 1.1.1 and TLS 1.3 enabled.
          Without TLS 1.3 support, the method raises *note
          NotImplementedError: 704.

     New in version 3.8.

 -- Method: SSLSocket.version ()

     Return the actual SSL protocol version negotiated by the connection
     as a string, or ‘None’ is no secure connection is established.  As
     of this writing, possible return values include ‘"SSLv2"’,
     ‘"SSLv3"’, ‘"TLSv1"’, ‘"TLSv1.1"’ and ‘"TLSv1.2"’.  Recent OpenSSL
     versions may define more return values.

     New in version 3.5.

 -- Method: SSLSocket.pending ()

     Returns the number of already decrypted bytes available for read,
     pending on the connection.

 -- Attribute: SSLSocket.context

     The *note SSLContext: 4ea. object this SSL socket is tied to.  If
     the SSL socket was created using the deprecated *note
     wrap_socket(): 571. function (rather than *note
     SSLContext.wrap_socket(): 4eb.), this is a custom context object
     created for this SSL socket.

     New in version 3.2.

 -- Attribute: SSLSocket.server_side

     A boolean which is ‘True’ for server-side sockets and ‘False’ for
     client-side sockets.

     New in version 3.2.

 -- Attribute: SSLSocket.server_hostname

     Hostname of the server: *note str: 205. type, or ‘None’ for
     server-side socket or if the hostname was not specified in the
     constructor.

     New in version 3.2.

     Changed in version 3.7: The attribute is now always ASCII text.
     When ‘server_hostname’ is an internationalized domain name (IDN),
     this attribute now stores the A-label form (‘"xn--pythn-mua.org"’),
     rather than the U-label form (‘"pythön.org"’).

 -- Attribute: SSLSocket.session

     The *note SSLSession: 682. for this SSL connection.  The session is
     available for client and server side sockets after the TLS
     handshake has been performed.  For client sockets the session can
     be set before *note do_handshake(): 849. has been called to reuse a
     session.

     New in version 3.6.

 -- Attribute: SSLSocket.session_reused

     New in version 3.6.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3280.html

   (2) https://tools.ietf.org/html/rfc5929.html


File: python.info,  Node: SSL Contexts,  Next: Certificates,  Prev: SSL Sockets,  Up: ssl — TLS/SSL wrapper for socket objects

5.18.3.9 SSL Contexts
.....................

New in version 3.2.

An SSL context holds various data longer-lived than single SSL
connections, such as SSL configuration options, certificate(s) and
private key(s).  It also manages a cache of SSL sessions for server-side
sockets, in order to speed up repeated connections from the same
clients.

 -- Class: ssl.SSLContext (protocol=PROTOCOL_TLS)

     Create a new SSL context.  You may pass `protocol' which must be
     one of the ‘PROTOCOL_*’ constants defined in this module.  The
     parameter specifies which version of the SSL protocol to use.
     Typically, the server chooses a particular protocol version, and
     the client must adapt to the server’s choice.  Most of the versions
     are not interoperable with the other versions.  If not specified,
     the default is *note PROTOCOL_TLS: 27f7.; it provides the most
     compatibility with other versions.

     Here’s a table showing which versions in a client (down the side)
     can connect to which versions in a server (along the top):

          `client' / `server'          `SSLv2'          `SSLv3'          `TLS' (1)         `TLSv1'       `TLSv1.1'       `TLSv1.2'
                                                                                                                         
                                                                                                                         
          `SSLv2'                      yes              no               no (2)            no            no              no
                                                                                                                         
                                                                                                                         
          `SSLv3'                      no               yes              no (3)            no            no              no
                                                                                                                         
                                                                                                                         
          `TLS' (`SSLv23') (4)         no (5)           no (6)           yes               yes           yes             yes
                                                                                                                         
                                                                                                                         
          `TLSv1'                      no               no               yes               yes           no              no
                                                                                                                         
                                                                                                                         
          `TLSv1.1'                    no               no               yes               no            yes             no
                                                                                                                         
                                                                                                                         
          `TLSv1.2'                    no               no               yes               no            no              yes
                                                                                                                         

     See also
     ........

     *note create_default_context(): 9a7. lets the *note ssl: f3. module
     choose security settings for a given purpose.

     Changed in version 3.6: The context is created with secure default
     values.  The options *note OP_NO_COMPRESSION: b6e, *note
     OP_CIPHER_SERVER_PREFERENCE: b73, *note OP_SINGLE_DH_USE: 2820,
     *note OP_SINGLE_ECDH_USE: 2821, *note OP_NO_SSLv2: c71. (except for
     *note PROTOCOL_SSLv2: 2818.), and *note OP_NO_SSLv3: 27f8. (except
     for *note PROTOCOL_SSLv3: 2809.) are set by default.  The initial
     cipher suite list contains only ‘HIGH’ ciphers, no ‘NULL’ ciphers
     and no ‘MD5’ ciphers (except for *note PROTOCOL_SSLv2: 2818.).

*note SSLContext: 4ea. objects have the following methods and
attributes:

 -- Method: SSLContext.cert_store_stats ()

     Get statistics about quantities of loaded X.509 certificates, count
     of X.509 certificates flagged as CA certificates and certificate
     revocation lists as dictionary.

     Example for a context with one CA cert and one other cert:

          >>> context.cert_store_stats()
          {'crl': 0, 'x509_ca': 1, 'x509': 2}

     New in version 3.4.

 -- Method: SSLContext.load_cert_chain (certfile, keyfile=None,
          password=None)

     Load a private key and the corresponding certificate.  The
     `certfile' string must be the path to a single file in PEM format
     containing the certificate as well as any number of CA certificates
     needed to establish the certificate’s authenticity.  The `keyfile'
     string, if present, must point to a file containing the private key
     in.  Otherwise the private key will be taken from `certfile' as
     well.  See the discussion of *note Certificates: 2844. for more
     information on how the certificate is stored in the `certfile'.

     The `password' argument may be a function to call to get the
     password for decrypting the private key.  It will only be called if
     the private key is encrypted and a password is necessary.  It will
     be called with no arguments, and it should return a string, bytes,
     or bytearray.  If the return value is a string it will be encoded
     as UTF-8 before using it to decrypt the key.  Alternatively a
     string, bytes, or bytearray value may be supplied directly as the
     `password' argument.  It will be ignored if the private key is not
     encrypted and no password is needed.

     If the `password' argument is not specified and a password is
     required, OpenSSL’s built-in password prompting mechanism will be
     used to interactively prompt the user for a password.

     An *note SSLError: cda. is raised if the private key doesn’t match
     with the certificate.

     Changed in version 3.3: New optional argument `password'.

 -- Method: SSLContext.load_default_certs (purpose=Purpose.SERVER_AUTH)

     Load a set of default “certification authority” (CA) certificates
     from default locations.  On Windows it loads CA certs from the ‘CA’
     and ‘ROOT’ system stores.  On all systems it calls *note
     SSLContext.set_default_verify_paths(): 9a9.  In the future the
     method may load CA certificates from other locations, too.

     The `purpose' flag specifies what kind of CA certificates are
     loaded.  The default settings *note Purpose.SERVER_AUTH: 9b2. loads
     certificates, that are flagged and trusted for TLS web server
     authentication (client side sockets).  *note Purpose.CLIENT_AUTH:
     9b3. loads CA certificates for client certificate verification on
     the server side.

     New in version 3.4.

 -- Method: SSLContext.load_verify_locations (cafile=None, capath=None,
          cadata=None)

     Load a set of “certification authority” (CA) certificates used to
     validate other peers’ certificates when *note verify_mode: 27f9. is
     other than *note CERT_NONE: 280f.  At least one of `cafile' or
     `capath' must be specified.

     This method can also load certification revocation lists (CRLs) in
     PEM or DER format.  In order to make use of CRLs, *note
     SSLContext.verify_flags: 9ac. must be configured properly.

     The `cafile' string, if present, is the path to a file of
     concatenated CA certificates in PEM format.  See the discussion of
     *note Certificates: 2844. for more information about how to arrange
     the certificates in this file.

     The `capath' string, if present, is the path to a directory
     containing several CA certificates in PEM format, following an
     OpenSSL specific layout(7).

     The `cadata' object, if present, is either an ASCII string of one
     or more PEM-encoded certificates or a *note bytes-like object: 6df.
     of DER-encoded certificates.  Like with `capath' extra lines around
     PEM-encoded certificates are ignored but at least one certificate
     must be present.

     Changed in version 3.4: New optional argument `cadata'

 -- Method: SSLContext.get_ca_certs (binary_form=False)

     Get a list of loaded “certification authority” (CA) certificates.
     If the ‘binary_form’ parameter is *note False: 48f. each list entry
     is a dict like the output of *note SSLSocket.getpeercert(): 9b7.
     Otherwise the method returns a list of DER-encoded certificates.
     The returned list does not contain certificates from `capath'
     unless a certificate was requested and loaded by a SSL connection.

          Note: Certificates in a capath directory aren’t loaded unless
          they have been used at least once.

     New in version 3.4.

 -- Method: SSLContext.get_ciphers ()

     Get a list of enabled ciphers.  The list is in order of cipher
     priority.  See *note SSLContext.set_ciphers(): 280d.

     Example:

          >>> ctx = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
          >>> ctx.set_ciphers('ECDHE+AESGCM:!ECDSA')
          >>> ctx.get_ciphers()  # OpenSSL 1.0.x
          [{'alg_bits': 256,
            'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH     Au=RSA  '
                           'Enc=AESGCM(256) Mac=AEAD',
            'id': 50380848,
            'name': 'ECDHE-RSA-AES256-GCM-SHA384',
            'protocol': 'TLSv1/SSLv3',
            'strength_bits': 256},
           {'alg_bits': 128,
            'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH     Au=RSA  '
                           'Enc=AESGCM(128) Mac=AEAD',
            'id': 50380847,
            'name': 'ECDHE-RSA-AES128-GCM-SHA256',
            'protocol': 'TLSv1/SSLv3',
            'strength_bits': 128}]

     On OpenSSL 1.1 and newer the cipher dict contains additional
     fields:

          >>> ctx.get_ciphers()  # OpenSSL 1.1+
          [{'aead': True,
            'alg_bits': 256,
            'auth': 'auth-rsa',
            'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH     Au=RSA  '
                           'Enc=AESGCM(256) Mac=AEAD',
            'digest': None,
            'id': 50380848,
            'kea': 'kx-ecdhe',
            'name': 'ECDHE-RSA-AES256-GCM-SHA384',
            'protocol': 'TLSv1.2',
            'strength_bits': 256,
            'symmetric': 'aes-256-gcm'},
           {'aead': True,
            'alg_bits': 128,
            'auth': 'auth-rsa',
            'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH     Au=RSA  '
                           'Enc=AESGCM(128) Mac=AEAD',
            'digest': None,
            'id': 50380847,
            'kea': 'kx-ecdhe',
            'name': 'ECDHE-RSA-AES128-GCM-SHA256',
            'protocol': 'TLSv1.2',
            'strength_bits': 128,
            'symmetric': 'aes-128-gcm'}]

     *note Availability: 1491.: OpenSSL 1.0.2+.

     New in version 3.6.

 -- Method: SSLContext.set_default_verify_paths ()

     Load a set of default “certification authority” (CA) certificates
     from a filesystem path defined when building the OpenSSL library.
     Unfortunately, there’s no easy way to know whether this method
     succeeds: no error is returned if no certificates are to be found.
     When the OpenSSL library is provided as part of the operating
     system, though, it is likely to be configured properly.

 -- Method: SSLContext.set_ciphers (ciphers)

     Set the available ciphers for sockets created with this context.
     It should be a string in the OpenSSL cipher list format(8).  If no
     cipher can be selected (because compile-time options or other
     configuration forbids use of all the specified ciphers), an *note
     SSLError: cda. will be raised.

          Note: when connected, the *note SSLSocket.cipher(): 2743.
          method of SSL sockets will give the currently selected cipher.

          OpenSSL 1.1.1 has TLS 1.3 cipher suites enabled by default.
          The suites cannot be disabled with *note set_ciphers(): 280d.

 -- Method: SSLContext.set_alpn_protocols (protocols)

     Specify which protocols the socket should advertise during the
     SSL/TLS handshake.  It should be a list of ASCII strings, like
     ‘['http/1.1', 'spdy/2']’, ordered by preference.  The selection of
     a protocol will happen during the handshake, and will play out
     according to RFC 7301(9).  After a successful handshake, the *note
     SSLSocket.selected_alpn_protocol(): 841. method will return the
     agreed-upon protocol.

     This method will raise *note NotImplementedError: 704. if *note
     HAS_ALPN: 842. is ‘False’.

     OpenSSL 1.1.0 to 1.1.0e will abort the handshake and raise *note
     SSLError: cda. when both sides support ALPN but cannot agree on a
     protocol.  1.1.0f+ behaves like 1.0.2, *note
     SSLSocket.selected_alpn_protocol(): 841. returns None.

     New in version 3.5.

 -- Method: SSLContext.set_npn_protocols (protocols)

     Specify which protocols the socket should advertise during the
     SSL/TLS handshake.  It should be a list of strings, like
     ‘['http/1.1', 'spdy/2']’, ordered by preference.  The selection of
     a protocol will happen during the handshake, and will play out
     according to the Application Layer Protocol Negotiation(10).  After
     a successful handshake, the *note
     SSLSocket.selected_npn_protocol(): 283e. method will return the
     agreed-upon protocol.

     This method will raise *note NotImplementedError: 704. if *note
     HAS_NPN: 2828. is ‘False’.

     New in version 3.3.

 -- Attribute: SSLContext.sni_callback

     Register a callback function that will be called after the TLS
     Client Hello handshake message has been received by the SSL/TLS
     server when the TLS client specifies a server name indication.  The
     server name indication mechanism is specified in RFC 6066(11)
     section 3 - Server Name Indication.

     Only one callback can be set per ‘SSLContext’.  If `sni_callback'
     is set to ‘None’ then the callback is disabled.  Calling this
     function a subsequent time will disable the previously registered
     callback.

     The callback function will be called with three arguments; the
     first being the *note ssl.SSLSocket: 192, the second is a string
     that represents the server name that the client is intending to
     communicate (or *note None: 203. if the TLS Client Hello does not
     contain a server name) and the third argument is the original *note
     SSLContext: 4ea.  The server name argument is text.  For
     internationalized domain name, the server name is an IDN A-label
     (‘"xn--pythn-mua.org"’).

     A typical use of this callback is to change the *note
     ssl.SSLSocket: 192.’s *note SSLSocket.context: 283d. attribute to a
     new object of type *note SSLContext: 4ea. representing a
     certificate chain that matches the server name.

     Due to the early negotiation phase of the TLS connection, only
     limited methods and attributes are usable like *note
     SSLSocket.selected_alpn_protocol(): 841. and *note
     SSLSocket.context: 283d.  *note SSLSocket.getpeercert(): 9b7, *note
     SSLSocket.getpeercert(): 9b7, *note SSLSocket.cipher(): 2743. and
     ‘SSLSocket.compress()’ methods require that the TLS connection has
     progressed beyond the TLS Client Hello and therefore will not
     contain return meaningful values nor can they be called safely.

     The `sni_callback' function must return ‘None’ to allow the TLS
     negotiation to continue.  If a TLS failure is required, a constant
     *note ALERT_DESCRIPTION_*: 2830. can be returned.  Other return
     values will result in a TLS fatal error with *note
     ALERT_DESCRIPTION_INTERNAL_ERROR: 2830.

     If an exception is raised from the `sni_callback' function the TLS
     connection will terminate with a fatal TLS alert message *note
     ALERT_DESCRIPTION_HANDSHAKE_FAILURE: 282f.

     This method will raise *note NotImplementedError: 704. if the
     OpenSSL library had OPENSSL_NO_TLSEXT defined when it was built.

     New in version 3.7.

 -- Attribute: SSLContext.set_servername_callback (server_name_callback)

     This is a legacy API retained for backwards compatibility.  When
     possible, you should use *note sni_callback: fba. instead.  The
     given `server_name_callback' is similar to `sni_callback', except
     that when the server hostname is an IDN-encoded internationalized
     domain name, the `server_name_callback' receives a decoded U-label
     (‘"pythön.org"’).

     If there is an decoding error on the server name, the TLS
     connection will terminate with an *note
     ALERT_DESCRIPTION_INTERNAL_ERROR: 2830. fatal TLS alert message to
     the client.

     New in version 3.4.

 -- Method: SSLContext.load_dh_params (dhfile)

     Load the key generation parameters for Diffie-Hellman (DH) key
     exchange.  Using DH key exchange improves forward secrecy at the
     expense of computational resources (both on the server and on the
     client).  The `dhfile' parameter should be the path to a file
     containing DH parameters in PEM format.

     This setting doesn’t apply to client sockets.  You can also use the
     *note OP_SINGLE_DH_USE: 2820. option to further improve security.

     New in version 3.3.

 -- Method: SSLContext.set_ecdh_curve (curve_name)

     Set the curve name for Elliptic Curve-based Diffie-Hellman (ECDH)
     key exchange.  ECDH is significantly faster than regular DH while
     arguably as secure.  The `curve_name' parameter should be a string
     describing a well-known elliptic curve, for example ‘prime256v1’
     for a widely supported curve.

     This setting doesn’t apply to client sockets.  You can also use the
     *note OP_SINGLE_ECDH_USE: 2821. option to further improve security.

     This method is not available if *note HAS_ECDH: 2826. is ‘False’.

     New in version 3.3.

     See also
     ........

     SSL/TLS & Perfect Forward Secrecy(12)

          Vincent Bernat.

 -- Method: SSLContext.wrap_socket (sock, server_side=False,
          do_handshake_on_connect=True, suppress_ragged_eofs=True,
          server_hostname=None, session=None)

     Wrap an existing Python socket `sock' and return an instance of
     *note SSLContext.sslsocket_class: 2845. (default *note SSLSocket:
     192.).  The returned SSL socket is tied to the context, its
     settings and certificates.  `sock' must be a *note SOCK_STREAM:
     d52. socket; other socket types are unsupported.

     The parameter ‘server_side’ is a boolean which identifies whether
     server-side or client-side behavior is desired from this socket.

     For client-side sockets, the context construction is lazy; if the
     underlying socket isn’t connected yet, the context construction
     will be performed after ‘connect()’ is called on the socket.  For
     server-side sockets, if the socket has no remote peer, it is
     assumed to be a listening socket, and the server-side SSL wrapping
     is automatically performed on client connections accepted via the
     ‘accept()’ method.  The method may raise *note SSLError: cda.

     On client connections, the optional parameter `server_hostname'
     specifies the hostname of the service which we are connecting to.
     This allows a single server to host multiple SSL-based services
     with distinct certificates, quite similarly to HTTP virtual hosts.
     Specifying `server_hostname' will raise a *note ValueError: 16d. if
     `server_side' is true.

     The parameter ‘do_handshake_on_connect’ specifies whether to do the
     SSL handshake automatically after doing a ‘socket.connect()’, or
     whether the application program will call it explicitly, by
     invoking the *note SSLSocket.do_handshake(): 849. method.  Calling
     *note SSLSocket.do_handshake(): 849. explicitly gives the program
     control over the blocking behavior of the socket I/O involved in
     the handshake.

     The parameter ‘suppress_ragged_eofs’ specifies how the
     ‘SSLSocket.recv()’ method should signal unexpected EOF from the
     other end of the connection.  If specified as *note True: 594. (the
     default), it returns a normal EOF (an empty bytes object) in
     response to unexpected EOF errors raised from the underlying
     socket; if *note False: 48f, it will raise the exceptions back to
     the caller.

     `session', see *note session: 2841.

     Changed in version 3.5: Always allow a server_hostname to be
     passed, even if OpenSSL does not have SNI.

     Changed in version 3.6: `session' argument was added.

     Changed in version 3.7: The method returns on instance of *note
     SSLContext.sslsocket_class: 2845. instead of hard-coded *note
     SSLSocket: 192.

 -- Attribute: SSLContext.sslsocket_class

     The return type of *note SSLContext.wrap_socket(): 4eb, defaults to
     *note SSLSocket: 192.  The attribute can be overridden on instance
     of class in order to return a custom subclass of *note SSLSocket:
     192.

     New in version 3.7.

 -- Method: SSLContext.wrap_bio (incoming, outgoing, server_side=False,
          server_hostname=None, session=None)

     Wrap the BIO objects `incoming' and `outgoing' and return an
     instance of *note SSLContext.sslobject_class: 2846. (default *note
     SSLObject: 4e9.).  The SSL routines will read input data from the
     incoming BIO and write data to the outgoing BIO.

     The `server_side', `server_hostname' and `session' parameters have
     the same meaning as in *note SSLContext.wrap_socket(): 4eb.

     Changed in version 3.6: `session' argument was added.

     Changed in version 3.7: The method returns on instance of *note
     SSLContext.sslobject_class: 2846. instead of hard-coded *note
     SSLObject: 4e9.

 -- Attribute: SSLContext.sslobject_class

     The return type of *note SSLContext.wrap_bio(): 4ec, defaults to
     *note SSLObject: 4e9.  The attribute can be overridden on instance
     of class in order to return a custom subclass of *note SSLObject:
     4e9.

     New in version 3.7.

 -- Method: SSLContext.session_stats ()

     Get statistics about the SSL sessions created or managed by this
     context.  A dictionary is returned which maps the names of each
     piece of information(13) to their numeric values.  For example,
     here is the total number of hits and misses in the session cache
     since the context was created:

          >>> stats = context.session_stats()
          >>> stats['hits'], stats['misses']
          (0, 0)

 -- Attribute: SSLContext.check_hostname

     Whether to match the peer cert’s hostname in *note
     SSLSocket.do_handshake(): 849.  The context’s *note verify_mode:
     27f9. must be set to *note CERT_OPTIONAL: 2811. or *note
     CERT_REQUIRED: 27fa, and you must pass `server_hostname' to *note
     wrap_socket(): 4eb. in order to match the hostname.  Enabling
     hostname checking automatically sets *note verify_mode: 27f9. from
     *note CERT_NONE: 280f. to *note CERT_REQUIRED: 27fa.  It cannot be
     set back to *note CERT_NONE: 280f. as long as hostname checking is
     enabled.  The *note PROTOCOL_TLS_CLIENT: 2810. protocol enables
     hostname checking by default.  With other protocols, hostname
     checking must be enabled explicitly.

     Example:

          import socket, ssl

          context = ssl.SSLContext(ssl.PROTOCOL_TLSv1_2)
          context.verify_mode = ssl.CERT_REQUIRED
          context.check_hostname = True
          context.load_default_certs()

          s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
          ssl_sock = context.wrap_socket(s, server_hostname='www.verisign.com')
          ssl_sock.connect(('www.verisign.com', 443))

     New in version 3.4.

     Changed in version 3.7: *note verify_mode: 27f9. is now
     automatically changed to *note CERT_REQUIRED: 27fa. when hostname
     checking is enabled and *note verify_mode: 27f9. is *note
     CERT_NONE: 280f.  Previously the same operation would have failed
     with a *note ValueError: 16d.

          Note: This features requires OpenSSL 0.9.8f or newer.

 -- Attribute: SSLContext.keylog_filename

     Write TLS keys to a keylog file, whenever key material is generated
     or received.  The keylog file is designed for debugging purposes
     only.  The file format is specified by NSS and used by many traffic
     analyzers such as Wireshark.  The log file is opened in append-only
     mode.  Writes are synchronized between threads, but not between
     processes.

     New in version 3.8.

          Note: This features requires OpenSSL 1.1.1 or newer.

 -- Attribute: SSLContext.maximum_version

     A *note TLSVersion: 2833. enum member representing the highest
     supported TLS version.  The value defaults to *note
     TLSVersion.MAXIMUM_SUPPORTED: 2835.  The attribute is read-only for
     protocols other than *note PROTOCOL_TLS: 27f7, *note
     PROTOCOL_TLS_CLIENT: 2810, and *note PROTOCOL_TLS_SERVER: 2816.

     The attributes *note maximum_version: 4ee, *note minimum_version:
     4ed. and *note SSLContext.options: 280c. all affect the supported
     SSL and TLS versions of the context.  The implementation does not
     prevent invalid combination.  For example a context with *note
     OP_NO_TLSv1_2: 281d. in *note options: 280c. and *note
     maximum_version: 4ee. set to *note TLSVersion.TLSv1_2: 2839. will
     not be able to establish a TLS 1.2 connection.

          Note: This attribute is not available unless the ssl module is
          compiled with OpenSSL 1.1.0g or newer.

     New in version 3.7.

 -- Attribute: SSLContext.minimum_version

     Like *note SSLContext.maximum_version: 4ee. except it is the lowest
     supported version or *note TLSVersion.MINIMUM_SUPPORTED: 2834.

          Note: This attribute is not available unless the ssl module is
          compiled with OpenSSL 1.1.0g or newer.

     New in version 3.7.

 -- Attribute: SSLContext.num_tickets

     Control the number of TLS 1.3 session tickets of a
     ‘TLS_PROTOCOL_SERVER’ context.  The setting has no impact on TLS
     1.0 to 1.2 connections.

          Note: This attribute is not available unless the ssl module is
          compiled with OpenSSL 1.1.1 or newer.

     New in version 3.8.

 -- Attribute: SSLContext.options

     An integer representing the set of SSL options enabled on this
     context.  The default value is *note OP_ALL: 281a, but you can
     specify other options such as *note OP_NO_SSLv2: c71. by ORing them
     together.

          Note: With versions of OpenSSL older than 0.9.8m, it is only
          possible to set options, not to clear them.  Attempting to
          clear an option (by resetting the corresponding bits) will
          raise a *note ValueError: 16d.

     Changed in version 3.6: *note SSLContext.options: 280c. returns
     *note Options: 2823. flags:

          >>> ssl.create_default_context().options
          <Options.OP_ALL|OP_NO_SSLv3|OP_NO_SSLv2|OP_NO_COMPRESSION: 2197947391>

 -- Attribute: SSLContext.post_handshake_auth

     Enable TLS 1.3 post-handshake client authentication.
     Post-handshake auth is disabled by default and a server can only
     request a TLS client certificate during the initial handshake.
     When enabled, a server may request a TLS client certificate at any
     time after the handshake.

     When enabled on client-side sockets, the client signals the server
     that it supports post-handshake authentication.

     When enabled on server-side sockets, *note SSLContext.verify_mode:
     27f9. must be set to *note CERT_OPTIONAL: 2811. or *note
     CERT_REQUIRED: 27fa, too.  The actual client cert exchange is
     delayed until *note SSLSocket.verify_client_post_handshake(): 352.
     is called and some I/O is performed.

          Note: Only available with OpenSSL 1.1.1 and TLS 1.3 enabled.
          Without TLS 1.3 support, the property value is None and can’t
          be modified

     New in version 3.8.

 -- Attribute: SSLContext.protocol

     The protocol version chosen when constructing the context.  This
     attribute is read-only.

 -- Attribute: SSLContext.hostname_checks_common_name

     Whether *note check_hostname: 2812. falls back to verify the cert’s
     subject common name in the absence of a subject alternative name
     extension (default: true).

          Note: Only writeable with OpenSSL 1.1.0 or higher.

     New in version 3.7.

     Changed in version 3.9.3: The flag had no effect with OpenSSL
     before version 1.1.1k.  Python 3.8.9, 3.9.3, and 3.10 include
     workarounds for previous versions.

 -- Attribute: SSLContext.verify_flags

     The flags for certificate verification operations.  You can set
     flags like *note VERIFY_CRL_CHECK_LEAF: 9ae. by ORing them
     together.  By default OpenSSL does neither require nor verify
     certificate revocation lists (CRLs).  Available only with openssl
     version 0.9.8+.

     New in version 3.4.

     Changed in version 3.6: *note SSLContext.verify_flags: 9ac. returns
     *note VerifyFlags: 2815. flags:

          >>> ssl.create_default_context().verify_flags
          <VerifyFlags.VERIFY_X509_TRUSTED_FIRST: 32768>

 -- Attribute: SSLContext.verify_mode

     Whether to try to verify other peers’ certificates and how to
     behave if verification fails.  This attribute must be one of *note
     CERT_NONE: 280f, *note CERT_OPTIONAL: 2811. or *note CERT_REQUIRED:
     27fa.

     Changed in version 3.6: *note SSLContext.verify_mode: 27f9. returns
     *note VerifyMode: 2813. enum:

          >>> ssl.create_default_context().verify_mode
          <VerifyMode.CERT_REQUIRED: 2>

   ---------- Footnotes ----------

   (1) (3) TLS 1.3 protocol will be available with *note PROTOCOL_TLS:
27f7. in OpenSSL >= 1.1.1.  There is no dedicated PROTOCOL constant for
just TLS 1.3.

   (2) (1) *note SSLContext: 4ea. disables SSLv2 with *note OP_NO_SSLv2:
c71. by default.

   (3) (2) *note SSLContext: 4ea. disables SSLv3 with *note OP_NO_SSLv3:
27f8. by default.

   (4) (3) TLS 1.3 protocol will be available with *note PROTOCOL_TLS:
27f7. in OpenSSL >= 1.1.1.  There is no dedicated PROTOCOL constant for
just TLS 1.3.

   (5) (1) *note SSLContext: 4ea. disables SSLv2 with *note OP_NO_SSLv2:
c71. by default.

   (6) (2) *note SSLContext: 4ea. disables SSLv3 with *note OP_NO_SSLv3:
27f8. by default.

   (7) 
https://www.openssl.org/docs/manmaster/man3/SSL_CTX_load_verify_locations.html

   (8) https://www.openssl.org/docs/manmaster/man1/ciphers.html

   (9) https://tools.ietf.org/html/rfc7301.html

   (10) 
https://en.wikipedia.org/wiki/Application-Layer_Protocol_Negotiation

   (11) https://tools.ietf.org/html/rfc6066.html

   (12) 
https://vincent.bernat.im/en/blog/2011-ssl-perfect-forward-secrecy

   (13) 
https://www.openssl.org/docs/man1.1.0/ssl/SSL_CTX_sess_number.html


File: python.info,  Node: Certificates,  Next: Examples<17>,  Prev: SSL Contexts,  Up: ssl — TLS/SSL wrapper for socket objects

5.18.3.10 Certificates
......................

Certificates in general are part of a public-key / private-key system.
In this system, each `principal', (which may be a machine, or a person,
or an organization) is assigned a unique two-part encryption key.  One
part of the key is public, and is called the `public key'; the other
part is kept secret, and is called the `private key'.  The two parts are
related, in that if you encrypt a message with one of the parts, you can
decrypt it with the other part, and `only' with the other part.

A certificate contains information about two principals.  It contains
the name of a `subject', and the subject’s public key.  It also contains
a statement by a second principal, the `issuer', that the subject is who
they claim to be, and that this is indeed the subject’s public key.  The
issuer’s statement is signed with the issuer’s private key, which only
the issuer knows.  However, anyone can verify the issuer’s statement by
finding the issuer’s public key, decrypting the statement with it, and
comparing it to the other information in the certificate.  The
certificate also contains information about the time period over which
it is valid.  This is expressed as two fields, called “notBefore” and
“notAfter”.

In the Python use of certificates, a client or server can use a
certificate to prove who they are.  The other side of a network
connection can also be required to produce a certificate, and that
certificate can be validated to the satisfaction of the client or server
that requires such validation.  The connection attempt can be set to
raise an exception if the validation fails.  Validation is done
automatically, by the underlying OpenSSL framework; the application need
not concern itself with its mechanics.  But the application does usually
need to provide sets of certificates to allow this process to take
place.

Python uses files to contain certificates.  They should be formatted as
“PEM” (see RFC 1422(1)), which is a base-64 encoded form wrapped with a
header line and a footer line:

     -----BEGIN CERTIFICATE-----
     ... (certificate in base64 PEM encoding) ...
     -----END CERTIFICATE-----

* Menu:

* Certificate chains::
* CA certificates::
* Combined key and certificate::
* Self-signed certificates::

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc1422.html


File: python.info,  Node: Certificate chains,  Next: CA certificates,  Up: Certificates

5.18.3.11 Certificate chains
............................

The Python files which contain certificates can contain a sequence of
certificates, sometimes called a `certificate chain'.  This chain should
start with the specific certificate for the principal who “is” the
client or server, and then the certificate for the issuer of that
certificate, and then the certificate for the issuer of `that'
certificate, and so on up the chain till you get to a certificate which
is `self-signed', that is, a certificate which has the same subject and
issuer, sometimes called a `root certificate'.  The certificates should
just be concatenated together in the certificate file.  For example,
suppose we had a three certificate chain, from our server certificate to
the certificate of the certification authority that signed our server
certificate, to the root certificate of the agency which issued the
certification authority’s certificate:

     -----BEGIN CERTIFICATE-----
     ... (certificate for your server)...
     -----END CERTIFICATE-----
     -----BEGIN CERTIFICATE-----
     ... (the certificate for the CA)...
     -----END CERTIFICATE-----
     -----BEGIN CERTIFICATE-----
     ... (the root certificate for the CA's issuer)...
     -----END CERTIFICATE-----


File: python.info,  Node: CA certificates,  Next: Combined key and certificate,  Prev: Certificate chains,  Up: Certificates

5.18.3.12 CA certificates
.........................

If you are going to require validation of the other side of the
connection’s certificate, you need to provide a “CA certs” file, filled
with the certificate chains for each issuer you are willing to trust.
Again, this file just contains these chains concatenated together.  For
validation, Python will use the first chain it finds in the file which
matches.  The platform’s certificates file can be used by calling *note
SSLContext.load_default_certs(): 9b1, this is done automatically with
*note create_default_context(): 9a7.


File: python.info,  Node: Combined key and certificate,  Next: Self-signed certificates,  Prev: CA certificates,  Up: Certificates

5.18.3.13 Combined key and certificate
......................................

Often the private key is stored in the same file as the certificate; in
this case, only the ‘certfile’ parameter to *note
SSLContext.load_cert_chain(): b69. and *note wrap_socket(): 571. needs
to be passed.  If the private key is stored with the certificate, it
should come before the first certificate in the certificate chain:

     -----BEGIN RSA PRIVATE KEY-----
     ... (private key in base64 encoding) ...
     -----END RSA PRIVATE KEY-----
     -----BEGIN CERTIFICATE-----
     ... (certificate in base64 PEM encoding) ...
     -----END CERTIFICATE-----


File: python.info,  Node: Self-signed certificates,  Prev: Combined key and certificate,  Up: Certificates

5.18.3.14 Self-signed certificates
..................................

If you are going to create a server that provides SSL-encrypted
connection services, you will need to acquire a certificate for that
service.  There are many ways of acquiring appropriate certificates,
such as buying one from a certification authority.  Another common
practice is to generate a self-signed certificate.  The simplest way to
do this is with the OpenSSL package, using something like the following:

     % openssl req -new -x509 -days 365 -nodes -out cert.pem -keyout cert.pem
     Generating a 1024 bit RSA private key
     .......++++++
     .............................++++++
     writing new private key to 'cert.pem'
     -----
     You are about to be asked to enter information that will be incorporated
     into your certificate request.
     What you are about to enter is what is called a Distinguished Name or a DN.
     There are quite a few fields but you can leave some blank
     For some fields there will be a default value,
     If you enter '.', the field will be left blank.
     -----
     Country Name (2 letter code) [AU]:US
     State or Province Name (full name) [Some-State]:MyState
     Locality Name (eg, city) []:Some City
     Organization Name (eg, company) [Internet Widgits Pty Ltd]:My Organization, Inc.
     Organizational Unit Name (eg, section) []:My Group
     Common Name (eg, YOUR name) []:myserver.mygroup.myorganization.com
     Email Address []:ops@myserver.mygroup.myorganization.com
     %

The disadvantage of a self-signed certificate is that it is its own root
certificate, and no one else will have it in their cache of known (and
trusted) root certificates.


File: python.info,  Node: Examples<17>,  Next: Notes on non-blocking sockets,  Prev: Certificates,  Up: ssl — TLS/SSL wrapper for socket objects

5.18.3.15 Examples
..................

* Menu:

* Testing for SSL support::
* Client-side operation::
* Server-side operation::


File: python.info,  Node: Testing for SSL support,  Next: Client-side operation,  Up: Examples<17>

5.18.3.16 Testing for SSL support
.................................

To test for the presence of SSL support in a Python installation, user
code should use the following idiom:

     try:
         import ssl
     except ImportError:
         pass
     else:
         ...  # do something that requires SSL support


File: python.info,  Node: Client-side operation,  Next: Server-side operation,  Prev: Testing for SSL support,  Up: Examples<17>

5.18.3.17 Client-side operation
...............................

This example creates a SSL context with the recommended security
settings for client sockets, including automatic certificate
verification:

     >>> context = ssl.create_default_context()

If you prefer to tune security settings yourself, you might create a
context from scratch (but beware that you might not get the settings
right):

     >>> context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
     >>> context.load_verify_locations("/etc/ssl/certs/ca-bundle.crt")

(this snippet assumes your operating system places a bundle of all CA
certificates in ‘/etc/ssl/certs/ca-bundle.crt’; if not, you’ll get an
error and have to adjust the location)

The *note PROTOCOL_TLS_CLIENT: 2810. protocol configures the context for
cert validation and hostname verification.  *note verify_mode: 27f9. is
set to *note CERT_REQUIRED: 27fa. and *note check_hostname: 2812. is set
to ‘True’.  All other protocols create SSL contexts with insecure
defaults.

When you use the context to connect to a server, *note CERT_REQUIRED:
27fa. and *note check_hostname: 2812. validate the server certificate:
it ensures that the server certificate was signed with one of the CA
certificates, checks the signature for correctness, and verifies other
properties like validity and identity of the hostname:

     >>> conn = context.wrap_socket(socket.socket(socket.AF_INET),
     ...                            server_hostname="www.python.org")
     >>> conn.connect(("www.python.org", 443))

You may then fetch the certificate:

     >>> cert = conn.getpeercert()

Visual inspection shows that the certificate does identify the desired
service (that is, the HTTPS host ‘www.python.org’):

     >>> pprint.pprint(cert)
     {'OCSP': ('http://ocsp.digicert.com',),
      'caIssuers': ('http://cacerts.digicert.com/DigiCertSHA2ExtendedValidationServerCA.crt',),
      'crlDistributionPoints': ('http://crl3.digicert.com/sha2-ev-server-g1.crl',
                                'http://crl4.digicert.com/sha2-ev-server-g1.crl'),
      'issuer': ((('countryName', 'US'),),
                 (('organizationName', 'DigiCert Inc'),),
                 (('organizationalUnitName', 'www.digicert.com'),),
                 (('commonName', 'DigiCert SHA2 Extended Validation Server CA'),)),
      'notAfter': 'Sep  9 12:00:00 2016 GMT',
      'notBefore': 'Sep  5 00:00:00 2014 GMT',
      'serialNumber': '01BB6F00122B177F36CAB49CEA8B6B26',
      'subject': ((('businessCategory', 'Private Organization'),),
                  (('1.3.6.1.4.1.311.60.2.1.3', 'US'),),
                  (('1.3.6.1.4.1.311.60.2.1.2', 'Delaware'),),
                  (('serialNumber', '3359300'),),
                  (('streetAddress', '16 Allen Rd'),),
                  (('postalCode', '03894-4801'),),
                  (('countryName', 'US'),),
                  (('stateOrProvinceName', 'NH'),),
                  (('localityName', 'Wolfeboro'),),
                  (('organizationName', 'Python Software Foundation'),),
                  (('commonName', 'www.python.org'),)),
      'subjectAltName': (('DNS', 'www.python.org'),
                         ('DNS', 'python.org'),
                         ('DNS', 'pypi.org'),
                         ('DNS', 'docs.python.org'),
                         ('DNS', 'testpypi.org'),
                         ('DNS', 'bugs.python.org'),
                         ('DNS', 'wiki.python.org'),
                         ('DNS', 'hg.python.org'),
                         ('DNS', 'mail.python.org'),
                         ('DNS', 'packaging.python.org'),
                         ('DNS', 'pythonhosted.org'),
                         ('DNS', 'www.pythonhosted.org'),
                         ('DNS', 'test.pythonhosted.org'),
                         ('DNS', 'us.pycon.org'),
                         ('DNS', 'id.python.org')),
      'version': 3}

Now the SSL channel is established and the certificate verified, you can
proceed to talk with the server:

     >>> conn.sendall(b"HEAD / HTTP/1.0\r\nHost: linuxfr.org\r\n\r\n")
     >>> pprint.pprint(conn.recv(1024).split(b"\r\n"))
     [b'HTTP/1.1 200 OK',
      b'Date: Sat, 18 Oct 2014 18:27:20 GMT',
      b'Server: nginx',
      b'Content-Type: text/html; charset=utf-8',
      b'X-Frame-Options: SAMEORIGIN',
      b'Content-Length: 45679',
      b'Accept-Ranges: bytes',
      b'Via: 1.1 varnish',
      b'Age: 2188',
      b'X-Served-By: cache-lcy1134-LCY',
      b'X-Cache: HIT',
      b'X-Cache-Hits: 11',
      b'Vary: Cookie',
      b'Strict-Transport-Security: max-age=63072000; includeSubDomains',
      b'Connection: close',
      b'',
      b'']

See the discussion of *note Security considerations: 26fd. below.


File: python.info,  Node: Server-side operation,  Prev: Client-side operation,  Up: Examples<17>

5.18.3.18 Server-side operation
...............................

For server operation, typically you’ll need to have a server
certificate, and private key, each in a file.  You’ll first create a
context holding the key and the certificate, so that clients can check
your authenticity.  Then you’ll open a socket, bind it to a port, call
‘listen()’ on it, and start waiting for clients to connect:

     import socket, ssl

     context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
     context.load_cert_chain(certfile="mycertfile", keyfile="mykeyfile")

     bindsocket = socket.socket()
     bindsocket.bind(('myaddr.mydomain.com', 10023))
     bindsocket.listen(5)

When a client connects, you’ll call ‘accept()’ on the socket to get the
new socket from the other end, and use the context’s *note
SSLContext.wrap_socket(): 4eb. method to create a server-side SSL socket
for the connection:

     while True:
         newsocket, fromaddr = bindsocket.accept()
         connstream = context.wrap_socket(newsocket, server_side=True)
         try:
             deal_with_client(connstream)
         finally:
             connstream.shutdown(socket.SHUT_RDWR)
             connstream.close()

Then you’ll read data from the ‘connstream’ and do something with it
till you are finished with the client (or the client is finished with
you):

     def deal_with_client(connstream):
         data = connstream.recv(1024)
         # empty data means the client is finished with us
         while data:
             if not do_something(connstream, data):
                 # we'll assume do_something returns False
                 # when we're finished with client
                 break
             data = connstream.recv(1024)
         # finished with client

And go back to listening for new client connections (of course, a real
server would probably handle each client connection in a separate
thread, or put the sockets in *note non-blocking mode: 27fe. and use an
event loop).


File: python.info,  Node: Notes on non-blocking sockets,  Next: Memory BIO Support<2>,  Prev: Examples<17>,  Up: ssl — TLS/SSL wrapper for socket objects

5.18.3.19 Notes on non-blocking sockets
.......................................

SSL sockets behave slightly different than regular sockets in
non-blocking mode.  When working with non-blocking sockets, there are
thus several things you need to be aware of:

   - Most *note SSLSocket: 192. methods will raise either *note
     SSLWantWriteError: 846. or *note SSLWantReadError: 845. instead of
     *note BlockingIOError: a78. if an I/O operation would block.  *note
     SSLWantReadError: 845. will be raised if a read operation on the
     underlying socket is necessary, and *note SSLWantWriteError: 846.
     for a write operation on the underlying socket.  Note that attempts
     to `write' to an SSL socket may require `reading' from the
     underlying socket first, and attempts to `read' from the SSL socket
     may require a prior `write' to the underlying socket.

     Changed in version 3.5: In earlier Python versions, the
     ‘SSLSocket.send()’ method returned zero instead of raising *note
     SSLWantWriteError: 846. or *note SSLWantReadError: 845.

   - Calling *note select(): 766. tells you that the OS-level socket can
     be read from (or written to), but it does not imply that there is
     sufficient data at the upper SSL layer.  For example, only part of
     an SSL frame might have arrived.  Therefore, you must be ready to
     handle ‘SSLSocket.recv()’ and ‘SSLSocket.send()’ failures, and
     retry after another call to *note select(): 766.

   - Conversely, since the SSL layer has its own framing, a SSL socket
     may still have data available for reading without *note select():
     766. being aware of it.  Therefore, you should first call
     ‘SSLSocket.recv()’ to drain any potentially available data, and
     then only block on a *note select(): 766. call if still necessary.

     (of course, similar provisions apply when using other primitives
     such as *note poll(): 2854, or those in the *note selectors: e6.
     module)

   - The SSL handshake itself will be non-blocking: the *note
     SSLSocket.do_handshake(): 849. method has to be retried until it
     returns successfully.  Here is a synopsis using *note select():
     766. to wait for the socket’s readiness:

          while True:
              try:
                  sock.do_handshake()
                  break
              except ssl.SSLWantReadError:
                  select.select([sock], [], [])
              except ssl.SSLWantWriteError:
                  select.select([], [sock], [])

See also
........

The *note asyncio: 9. module supports *note non-blocking SSL sockets:
27fe. and provides a higher level API. It polls for events using the
*note selectors: e6. module and handles *note SSLWantWriteError: 846,
*note SSLWantReadError: 845. and *note BlockingIOError: a78. exceptions.
It runs the SSL handshake asynchronously as well.


File: python.info,  Node: Memory BIO Support<2>,  Next: SSL session,  Prev: Notes on non-blocking sockets,  Up: ssl — TLS/SSL wrapper for socket objects

5.18.3.20 Memory BIO Support
............................

New in version 3.5.

Ever since the SSL module was introduced in Python 2.6, the *note
SSLSocket: 192. class has provided two related but distinct areas of
functionality:

   - SSL protocol handling

   - Network IO

The network IO API is identical to that provided by *note socket.socket:
767, from which *note SSLSocket: 192. also inherits.  This allows an SSL
socket to be used as a drop-in replacement for a regular socket, making
it very easy to add SSL support to an existing application.

Combining SSL protocol handling and network IO usually works well, but
there are some cases where it doesn’t.  An example is async IO
frameworks that want to use a different IO multiplexing model than the
“select/poll on a file descriptor” (readiness based) model that is
assumed by *note socket.socket: 767. and by the internal OpenSSL socket
IO routines.  This is mostly relevant for platforms like Windows where
this model is not efficient.  For this purpose, a reduced scope variant
of *note SSLSocket: 192. called *note SSLObject: 4e9. is provided.

 -- Class: ssl.SSLObject

     A reduced-scope variant of *note SSLSocket: 192. representing an
     SSL protocol instance that does not contain any network IO methods.
     This class is typically used by framework authors that want to
     implement asynchronous IO for SSL through memory buffers.

     This class implements an interface on top of a low-level SSL object
     as implemented by OpenSSL. This object captures the state of an SSL
     connection but does not provide any network IO itself.  IO needs to
     be performed through separate “BIO” objects which are OpenSSL’s IO
     abstraction layer.

     This class has no public constructor.  An *note SSLObject: 4e9.
     instance must be created using the *note wrap_bio(): 4ec. method.
     This method will create the *note SSLObject: 4e9. instance and bind
     it to a pair of BIOs.  The `incoming' BIO is used to pass data from
     Python to the SSL protocol instance, while the `outgoing' BIO is
     used to pass data the other way around.

     The following methods are available:

        - *note context: 283d.

        - *note server_side: 2840.

        - *note server_hostname: 4e7.

        - *note session: 2841.

        - *note session_reused: 2842.

        - *note read(): 84a.

        - *note write(): 84b.

        - *note getpeercert(): 9b7.

        - *note selected_alpn_protocol(): 841.

        - *note selected_npn_protocol(): 283e.

        - *note cipher(): 2743.

        - *note shared_ciphers(): 848.

        - *note compression(): b6d.

        - *note pending(): 283f.

        - *note do_handshake(): 849.

        - *note verify_client_post_handshake(): 352.

        - *note unwrap(): 283c.

        - *note get_channel_binding(): b6c.

        - *note version(): 844.

     When compared to *note SSLSocket: 192, this object lacks the
     following features:

        - Any form of network IO; ‘recv()’ and ‘send()’ read and write
          only to the underlying *note MemoryBIO: 83e. buffers.

        - There is no `do_handshake_on_connect' machinery.  You must
          always manually call *note do_handshake(): 849. to start the
          handshake.

        - There is no handling of `suppress_ragged_eofs'.  All
          end-of-file conditions that are in violation of the protocol
          are reported via the *note SSLEOFError: 2800. exception.

        - The method *note unwrap(): 283c. call does not return
          anything, unlike for an SSL socket where it returns the
          underlying socket.

        - The `server_name_callback' callback passed to *note
          SSLContext.set_servername_callback(): 9b6. will get an *note
          SSLObject: 4e9. instance instead of a *note SSLSocket: 192.
          instance as its first parameter.

     Some notes related to the use of *note SSLObject: 4e9.:

        - All IO on an *note SSLObject: 4e9. is *note non-blocking:
          27fe.  This means that for example *note read(): 84a. will
          raise an *note SSLWantReadError: 845. if it needs more data
          than the incoming BIO has available.

        - There is no module-level ‘wrap_bio()’ call like there is for
          *note wrap_socket(): 4eb.  An *note SSLObject: 4e9. is always
          created via an *note SSLContext: 4ea.

     Changed in version 3.7: *note SSLObject: 4e9. instances must to
     created with *note wrap_bio(): 4ec.  In earlier versions, it was
     possible to create instances directly.  This was never documented
     or officially supported.

An SSLObject communicates with the outside world using memory buffers.
The class *note MemoryBIO: 83e. provides a memory buffer that can be
used for this purpose.  It wraps an OpenSSL memory BIO (Basic IO)
object:

 -- Class: ssl.MemoryBIO

     A memory buffer that can be used to pass data between Python and an
     SSL protocol instance.

      -- Attribute: pending

          Return the number of bytes currently in the memory buffer.

      -- Attribute: eof

          A boolean indicating whether the memory BIO is current at the
          end-of-file position.

      -- Method: read (n=-1)

          Read up to `n' bytes from the memory buffer.  If `n' is not
          specified or negative, all bytes are returned.

      -- Method: write (buf)

          Write the bytes from `buf' to the memory BIO. The `buf'
          argument must be an object supporting the buffer protocol.

          The return value is the number of bytes written, which is
          always equal to the length of `buf'.

      -- Method: write_eof ()

          Write an EOF marker to the memory BIO. After this method has
          been called, it is illegal to call *note write(): 2859.  The
          attribute *note eof: 2857. will become true after all data
          currently in the buffer has been read.


File: python.info,  Node: SSL session,  Next: Security considerations<2>,  Prev: Memory BIO Support<2>,  Up: ssl — TLS/SSL wrapper for socket objects

5.18.3.21 SSL session
.....................

New in version 3.6.

 -- Class: ssl.SSLSession

     Session object used by *note session: 2841.

      -- Attribute: id

      -- Attribute: time

      -- Attribute: timeout

      -- Attribute: ticket_lifetime_hint

      -- Attribute: has_ticket


File: python.info,  Node: Security considerations<2>,  Next: TLS 1 3,  Prev: SSL session,  Up: ssl — TLS/SSL wrapper for socket objects

5.18.3.22 Security considerations
.................................

* Menu:

* Best defaults::
* Manual settings::
* Multi-processing::


File: python.info,  Node: Best defaults,  Next: Manual settings,  Up: Security considerations<2>

5.18.3.23 Best defaults
.......................

For `client use', if you don’t have any special requirements for your
security policy, it is highly recommended that you use the *note
create_default_context(): 9a7. function to create your SSL context.  It
will load the system’s trusted CA certificates, enable certificate
validation and hostname checking, and try to choose reasonably secure
protocol and cipher settings.

For example, here is how you would use the *note smtplib.SMTP: 1de.
class to create a trusted, secure connection to a SMTP server:

     >>> import ssl, smtplib
     >>> smtp = smtplib.SMTP("mail.python.org", port=587)
     >>> context = ssl.create_default_context()
     >>> smtp.starttls(context=context)
     (220, b'2.0.0 Ready to start TLS')

If a client certificate is needed for the connection, it can be added
with *note SSLContext.load_cert_chain(): b69.

By contrast, if you create the SSL context by calling the *note
SSLContext: 4ea. constructor yourself, it will not have certificate
validation nor hostname checking enabled by default.  If you do so,
please read the paragraphs below to achieve a good security level.


File: python.info,  Node: Manual settings,  Next: Multi-processing,  Prev: Best defaults,  Up: Security considerations<2>

5.18.3.24 Manual settings
.........................

* Menu:

* Verifying certificates::
* Protocol versions::
* Cipher selection::


File: python.info,  Node: Verifying certificates,  Next: Protocol versions,  Up: Manual settings

5.18.3.25 Verifying certificates
................................

When calling the *note SSLContext: 4ea. constructor directly, *note
CERT_NONE: 280f. is the default.  Since it does not authenticate the
other peer, it can be insecure, especially in client mode where most of
time you would like to ensure the authenticity of the server you’re
talking to.  Therefore, when in client mode, it is highly recommended to
use *note CERT_REQUIRED: 27fa.  However, it is in itself not sufficient;
you also have to check that the server certificate, which can be
obtained by calling *note SSLSocket.getpeercert(): 9b7, matches the
desired service.  For many protocols and applications, the service can
be identified by the hostname; in this case, the *note match_hostname():
4e3. function can be used.  This common check is automatically performed
when *note SSLContext.check_hostname: 2812. is enabled.

Changed in version 3.7: Hostname matchings is now performed by OpenSSL.
Python no longer uses *note match_hostname(): 4e3.

In server mode, if you want to authenticate your clients using the SSL
layer (rather than using a higher-level authentication mechanism),
you’ll also have to specify *note CERT_REQUIRED: 27fa. and similarly
check the client certificate.


File: python.info,  Node: Protocol versions,  Next: Cipher selection,  Prev: Verifying certificates,  Up: Manual settings

5.18.3.26 Protocol versions
...........................

SSL versions 2 and 3 are considered insecure and are therefore dangerous
to use.  If you want maximum compatibility between clients and servers,
it is recommended to use *note PROTOCOL_TLS_CLIENT: 2810. or *note
PROTOCOL_TLS_SERVER: 2816. as the protocol version.  SSLv2 and SSLv3 are
disabled by default.

     >>> client_context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
     >>> client_context.options |= ssl.OP_NO_TLSv1
     >>> client_context.options |= ssl.OP_NO_TLSv1_1

The SSL context created above will only allow TLSv1.2 and later (if
supported by your system) connections to a server.  *note
PROTOCOL_TLS_CLIENT: 2810. implies certificate validation and hostname
checks by default.  You have to load certificates into the context.


File: python.info,  Node: Cipher selection,  Prev: Protocol versions,  Up: Manual settings

5.18.3.27 Cipher selection
..........................

If you have advanced security requirements, fine-tuning of the ciphers
enabled when negotiating a SSL session is possible through the *note
SSLContext.set_ciphers(): 280d. method.  Starting from Python 3.2.3, the
ssl module disables certain weak ciphers by default, but you may want to
further restrict the cipher choice.  Be sure to read OpenSSL’s
documentation about the cipher list format(1).  If you want to check
which ciphers are enabled by a given cipher list, use *note
SSLContext.get_ciphers(): 683. or the ‘openssl ciphers’ command on your
system.

   ---------- Footnotes ----------

   (1) 
https://www.openssl.org/docs/manmaster/man1/ciphers.html#CIPHER-LIST-FORMAT


File: python.info,  Node: Multi-processing,  Prev: Manual settings,  Up: Security considerations<2>

5.18.3.28 Multi-processing
..........................

If using this module as part of a multi-processed application (using,
for example the *note multiprocessing: b7. or *note concurrent.futures:
21. modules), be aware that OpenSSL’s internal random number generator
does not properly handle forked processes.  Applications must change the
PRNG state of the parent process if they use any SSL feature with *note
os.fork(): a42.  Any successful call of *note RAND_add(): 2806, *note
RAND_bytes(): b67. or *note RAND_pseudo_bytes(): b68. is sufficient.


File: python.info,  Node: TLS 1 3,  Next: LibreSSL support,  Prev: Security considerations<2>,  Up: ssl — TLS/SSL wrapper for socket objects

5.18.3.29 TLS 1.3
.................

New in version 3.7.

Python has provisional and experimental support for TLS 1.3 with OpenSSL
1.1.1.  The new protocol behaves slightly differently than previous
version of TLS/SSL. Some new TLS 1.3 features are not yet available.

   - TLS 1.3 uses a disjunct set of cipher suites.  All AES-GCM and
     ChaCha20 cipher suites are enabled by default.  The method *note
     SSLContext.set_ciphers(): 280d. cannot enable or disable any TLS
     1.3 ciphers yet, but *note SSLContext.get_ciphers(): 683. returns
     them.

   - Session tickets are no longer sent as part of the initial handshake
     and are handled differently.  *note SSLSocket.session: 2841. and
     *note SSLSession: 682. are not compatible with TLS 1.3.

   - Client-side certificates are also no longer verified during the
     initial handshake.  A server can request a certificate at any time.
     Clients process certificate requests while they send or receive
     application data from the server.

   - TLS 1.3 features like early data, deferred TLS client cert request,
     signature algorithm configuration, and rekeying are not supported
     yet.


File: python.info,  Node: LibreSSL support,  Prev: TLS 1 3,  Up: ssl — TLS/SSL wrapper for socket objects

5.18.3.30 LibreSSL support
..........................

LibreSSL is a fork of OpenSSL 1.0.1.  The ssl module has limited support
for LibreSSL. Some features are not available when the ssl module is
compiled with LibreSSL.

   * LibreSSL >= 2.6.1 no longer supports NPN. The methods *note
     SSLContext.set_npn_protocols(): b6f. and *note
     SSLSocket.selected_npn_protocol(): 283e. are not available.

   * *note SSLContext.set_default_verify_paths(): 9a9. ignores the env
     vars ‘SSL_CERT_FILE’ and ‘SSL_CERT_PATH’ although *note
     get_default_verify_paths(): 9a8. still reports them.

See also
........

Class *note socket.socket: 767.

     Documentation of underlying *note socket: ef. class

SSL/TLS Strong Encryption: An Introduction(1)

     Intro from the Apache HTTP Server documentation

RFC 1422: Privacy Enhancement for Internet Electronic Mail: Part II: Certificate-Based Key Management(2)

     Steve Kent

RFC 4086: Randomness Requirements for Security(3)

     Donald E., Jeffrey I. Schiller

RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile(4)

     D. Cooper

RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2(5)

     T. Dierks et.  al.

RFC 6066: Transport Layer Security (TLS) Extensions(6)

     D. Eastlake

IANA TLS: Transport Layer Security (TLS) Parameters(7)

     IANA

RFC 7525: Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)(8)

     IETF

Mozilla’s Server Side TLS recommendations(9)

     Mozilla

   ---------- Footnotes ----------

   (1) https://httpd.apache.org/docs/trunk/en/ssl/ssl_intro.html

   (2) https://tools.ietf.org/html/rfc1422.html

   (3) https://tools.ietf.org/html/rfc4086.html

   (4) https://tools.ietf.org/html/rfc5280.html

   (5) https://tools.ietf.org/html/rfc5246.html

   (6) https://tools.ietf.org/html/rfc6066.html

   (7) 
https://www.iana.org/assignments/tls-parameters/tls-parameters.xml

   (8) https://tools.ietf.org/html/rfc7525.html

   (9) https://wiki.mozilla.org/Security/Server_Side_TLS


File: python.info,  Node: select — Waiting for I/O completion,  Next: selectors — High-level I/O multiplexing,  Prev: ssl — TLS/SSL wrapper for socket objects,  Up: Networking and Interprocess Communication

5.18.4 ‘select’ — Waiting for I/O completion
--------------------------------------------

__________________________________________________________________

This module provides access to the ‘select()’ and ‘poll()’ functions
available in most operating systems, ‘devpoll()’ available on Solaris
and derivatives, ‘epoll()’ available on Linux 2.5+ and ‘kqueue()’
available on most BSD. Note that on Windows, it only works for sockets;
on other operating systems, it also works for other file types (in
particular, on Unix, it works on pipes).  It cannot be used on regular
files to determine whether a file has grown since it was last read.

     Note: The *note selectors: e6. module allows high-level and
     efficient I/O multiplexing, built upon the *note select: e5. module
     primitives.  Users are encouraged to use the *note selectors: e6.
     module instead, unless they want precise control over the OS-level
     primitives used.

The module defines the following:

 -- Exception: select.error

     A deprecated alias of *note OSError: 304.

     Changed in version 3.3: Following PEP 3151(1), this class was made
     an alias of *note OSError: 304.

 -- Function: select.devpoll ()

     (Only supported on Solaris and derivatives.)  Returns a ‘/dev/poll’
     polling object; see section *note /dev/poll Polling Objects: 286d.
     below for the methods supported by devpoll objects.

     ‘devpoll()’ objects are linked to the number of file descriptors
     allowed at the time of instantiation.  If your program reduces this
     value, ‘devpoll()’ will fail.  If your program increases this
     value, ‘devpoll()’ may return an incomplete list of active file
     descriptors.

     The new file descriptor is *note non-inheritable: 8e7.

     New in version 3.3.

     Changed in version 3.4: The new file descriptor is now
     non-inheritable.

 -- Function: select.epoll (sizehint=-1, flags=0)

     (Only supported on Linux 2.5.44 and newer.)  Return an edge polling
     object, which can be used as Edge or Level Triggered interface for
     I/O events.

     `sizehint' informs epoll about the expected number of events to be
     registered.  It must be positive, or ‘-1’ to use the default.  It
     is only used on older systems where ‘epoll_create1()’ is not
     available; otherwise it has no effect (though its value is still
     checked).

     `flags' is deprecated and completely ignored.  However, when
     supplied, its value must be ‘0’ or ‘select.EPOLL_CLOEXEC’,
     otherwise ‘OSError’ is raised.

     See the *note Edge and Level Trigger Polling (epoll) Objects: 286e.
     section below for the methods supported by epolling objects.

     ‘epoll’ objects support the context management protocol: when used
     in a *note with: 7da. statement, the new file descriptor is
     automatically closed at the end of the block.

     The new file descriptor is *note non-inheritable: 8e7.

     Changed in version 3.3: Added the `flags' parameter.

     Changed in version 3.4: Support for the *note with: 7da. statement
     was added.  The new file descriptor is now non-inheritable.

     Deprecated since version 3.4: The `flags' parameter.
     ‘select.EPOLL_CLOEXEC’ is used by default now.  Use *note
     os.set_inheritable(): 8e9. to make the file descriptor inheritable.

 -- Function: select.poll ()

     (Not supported by all operating systems.)  Returns a polling
     object, which supports registering and unregistering file
     descriptors, and then polling them for I/O events; see section
     *note Polling Objects: 286f. below for the methods supported by
     polling objects.

 -- Function: select.kqueue ()

     (Only supported on BSD.) Returns a kernel queue object; see section
     *note Kqueue Objects: 2871. below for the methods supported by
     kqueue objects.

     The new file descriptor is *note non-inheritable: 8e7.

     Changed in version 3.4: The new file descriptor is now
     non-inheritable.

 -- Function: select.kevent (ident, filter=KQ_FILTER_READ,
          flags=KQ_EV_ADD, fflags=0, data=0, udata=0)

     (Only supported on BSD.) Returns a kernel event object; see section
     *note Kevent Objects: 2873. below for the methods supported by
     kevent objects.

 -- Function: select.select (rlist, wlist, xlist[, timeout])

     This is a straightforward interface to the Unix ‘select()’ system
     call.  The first three arguments are iterables of ‘waitable
     objects’: either integers representing file descriptors or objects
     with a parameterless method named *note fileno(): 2069. returning
     such an integer:

        * `rlist': wait until ready for reading

        * `wlist': wait until ready for writing

        * `xlist': wait for an “exceptional condition” (see the manual
          page for what your system considers such a condition)

     Empty iterables are allowed, but acceptance of three empty
     iterables is platform-dependent.  (It is known to work on Unix but
     not on Windows.)  The optional `timeout' argument specifies a
     time-out as a floating point number in seconds.  When the `timeout'
     argument is omitted the function blocks until at least one file
     descriptor is ready.  A time-out value of zero specifies a poll and
     never blocks.

     The return value is a triple of lists of objects that are ready:
     subsets of the first three arguments.  When the time-out is reached
     without a file descriptor becoming ready, three empty lists are
     returned.

     Among the acceptable object types in the iterables are Python *note
     file objects: c14. (e.g.  ‘sys.stdin’, or objects returned by *note
     open(): 16f. or *note os.popen(): 3cb.), socket objects returned by
     *note socket.socket(): 767.  You may also define a `wrapper' class
     yourself, as long as it has an appropriate *note fileno(): 2069.
     method (that really returns a file descriptor, not just a random
     integer).

          Note: 
          File objects on Windows are not acceptable, but sockets are.
          On Windows, the underlying ‘select()’ function is provided by
          the WinSock library, and does not handle file descriptors that
          don’t originate from WinSock.

     Changed in version 3.5: The function is now retried with a
     recomputed timeout when interrupted by a signal, except if the
     signal handler raises an exception (see PEP 475(2) for the
     rationale), instead of raising *note InterruptedError: 74c.

 -- Attribute: select.PIPE_BUF

     The minimum number of bytes which can be written without blocking
     to a pipe when the pipe has been reported as ready for writing by
     *note select(): 766, *note poll(): 2854. or another interface in
     this module.  This doesn’t apply to other kind of file-like objects
     such as sockets.

     This value is guaranteed by POSIX to be at least 512.

     *note Availability: 1491.: Unix

     New in version 3.2.

* Menu:

* /dev/poll Polling Objects::
* Edge and Level Trigger Polling (epoll) Objects: Edge and Level Trigger Polling epoll Objects.
* Polling Objects::
* Kqueue Objects::
* Kevent Objects::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3151

   (2) https://www.python.org/dev/peps/pep-0475


File: python.info,  Node: /dev/poll Polling Objects,  Next: Edge and Level Trigger Polling epoll Objects,  Up: select — Waiting for I/O completion

5.18.4.1 ‘/dev/poll’ Polling Objects
....................................

Solaris and derivatives have ‘/dev/poll’.  While ‘select()’ is O(highest
file descriptor) and ‘poll()’ is O(number of file descriptors),
‘/dev/poll’ is O(active file descriptors).

‘/dev/poll’ behaviour is very close to the standard ‘poll()’ object.

 -- Method: devpoll.close ()

     Close the file descriptor of the polling object.

     New in version 3.4.

 -- Attribute: devpoll.closed

     ‘True’ if the polling object is closed.

     New in version 3.4.

 -- Method: devpoll.fileno ()

     Return the file descriptor number of the polling object.

     New in version 3.4.

 -- Method: devpoll.register (fd[, eventmask])

     Register a file descriptor with the polling object.  Future calls
     to the *note poll(): 2854. method will then check whether the file
     descriptor has any pending I/O events.  `fd' can be either an
     integer, or an object with a *note fileno(): 2069. method that
     returns an integer.  File objects implement ‘fileno()’, so they can
     also be used as the argument.

     `eventmask' is an optional bitmask describing the type of events
     you want to check for.  The constants are the same that with
     ‘poll()’ object.  The default value is a combination of the
     constants ‘POLLIN’, ‘POLLPRI’, and ‘POLLOUT’.

          Warning: Registering a file descriptor that’s already
          registered is not an error, but the result is undefined.  The
          appropriate action is to unregister or modify it first.  This
          is an important difference compared with ‘poll()’.

 -- Method: devpoll.modify (fd[, eventmask])

     This method does an *note unregister(): 2877. followed by a *note
     register(): 2875.  It is (a bit) more efficient that doing the same
     explicitly.

 -- Method: devpoll.unregister (fd)

     Remove a file descriptor being tracked by a polling object.  Just
     like the *note register(): 2875. method, `fd' can be an integer or
     an object with a *note fileno(): 2069. method that returns an
     integer.

     Attempting to remove a file descriptor that was never registered is
     safely ignored.

 -- Method: devpoll.poll ([timeout])

     Polls the set of registered file descriptors, and returns a
     possibly-empty list containing ‘(fd, event)’ 2-tuples for the
     descriptors that have events or errors to report.  `fd' is the file
     descriptor, and `event' is a bitmask with bits set for the reported
     events for that descriptor — ‘POLLIN’ for waiting input, ‘POLLOUT’
     to indicate that the descriptor can be written to, and so forth.
     An empty list indicates that the call timed out and no file
     descriptors had any events to report.  If `timeout' is given, it
     specifies the length of time in milliseconds which the system will
     wait for events before returning.  If `timeout' is omitted, -1, or
     *note None: 203, the call will block until there is an event for
     this poll object.

     Changed in version 3.5: The function is now retried with a
     recomputed timeout when interrupted by a signal, except if the
     signal handler raises an exception (see PEP 475(1) for the
     rationale), instead of raising *note InterruptedError: 74c.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0475


File: python.info,  Node: Edge and Level Trigger Polling epoll Objects,  Next: Polling Objects,  Prev: /dev/poll Polling Objects,  Up: select — Waiting for I/O completion

5.18.4.2 Edge and Level Trigger Polling (epoll) Objects
.......................................................

     ‘https://linux.die.net/man/4/epoll’

     `eventmask'

     Constant                      Meaning
                                   
     ----------------------------------------------------------------------------------
                                   
     ‘EPOLLIN’                     Available for read
                                   
                                   
     ‘EPOLLOUT’                    Available for write
                                   
                                   
     ‘EPOLLPRI’                    Urgent data for read
                                   
                                   
     ‘EPOLLERR’                    Error condition happened on the assoc.  fd
                                   
                                   
     ‘EPOLLHUP’                    Hang up happened on the assoc.  fd
                                   
                                   
     ‘EPOLLET’                     Set Edge Trigger behavior, the default is Level
                                   Trigger behavior
                                   
                                   
     ‘EPOLLONESHOT’                Set one-shot behavior.  After one event is pulled
                                   out, the fd is internally disabled
                                   
                                   
     ‘EPOLLEXCLUSIVE’              Wake only one epoll object when the associated fd
                                   has an event.  The default (if this flag is not
                                   set) is to wake all epoll objects polling on a
                                   fd.
                                   
                                   
     ‘EPOLLRDHUP’                  Stream socket peer closed connection or shut down
                                   writing half of connection.
                                   
                                   
     ‘EPOLLRDNORM’                 Equivalent to ‘EPOLLIN’
                                   
                                   
     ‘EPOLLRDBAND’                 Priority data band can be read.
                                   
                                   
     ‘EPOLLWRNORM’                 Equivalent to ‘EPOLLOUT’
                                   
                                   
     ‘EPOLLWRBAND’                 Priority data may be written.
                                   
                                   
     ‘EPOLLMSG’                    Ignored.
                                   

     New in version 3.6: ‘EPOLLEXCLUSIVE’ was added.  It’s only
     supported by Linux Kernel 4.5 or later.

 -- Method: epoll.close ()

     Close the control file descriptor of the epoll object.

 -- Attribute: epoll.closed

     ‘True’ if the epoll object is closed.

 -- Method: epoll.fileno ()

     Return the file descriptor number of the control fd.

 -- Method: epoll.fromfd (fd)

     Create an epoll object from a given file descriptor.

 -- Method: epoll.register (fd[, eventmask])

     Register a fd descriptor with the epoll object.

 -- Method: epoll.modify (fd, eventmask)

     Modify a registered file descriptor.

 -- Method: epoll.unregister (fd)

     Remove a registered file descriptor from the epoll object.

     Changed in version 3.9: The method no longer ignores the *note
     EBADF: 22f. error.

 -- Method: epoll.poll (timeout=None, maxevents=-1)

     Wait for events.  timeout in seconds (float)

     Changed in version 3.5: The function is now retried with a
     recomputed timeout when interrupted by a signal, except if the
     signal handler raises an exception (see PEP 475(1) for the
     rationale), instead of raising *note InterruptedError: 74c.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0475


File: python.info,  Node: Polling Objects,  Next: Kqueue Objects,  Prev: Edge and Level Trigger Polling epoll Objects,  Up: select — Waiting for I/O completion

5.18.4.3 Polling Objects
........................

The ‘poll()’ system call, supported on most Unix systems, provides
better scalability for network servers that service many, many clients
at the same time.  ‘poll()’ scales better because the system call only
requires listing the file descriptors of interest, while ‘select()’
builds a bitmap, turns on bits for the fds of interest, and then
afterward the whole bitmap has to be linearly scanned again.  ‘select()’
is O(highest file descriptor), while ‘poll()’ is O(number of file
descriptors).

 -- Method: poll.register (fd[, eventmask])

     Register a file descriptor with the polling object.  Future calls
     to the *note poll(): 2854. method will then check whether the file
     descriptor has any pending I/O events.  `fd' can be either an
     integer, or an object with a *note fileno(): 2069. method that
     returns an integer.  File objects implement ‘fileno()’, so they can
     also be used as the argument.

     `eventmask' is an optional bitmask describing the type of events
     you want to check for, and can be a combination of the constants
     ‘POLLIN’, ‘POLLPRI’, and ‘POLLOUT’, described in the table below.
     If not specified, the default value used will check for all 3 types
     of events.

     Constant                Meaning
                             
     -----------------------------------------------------------------------
                             
     ‘POLLIN’                There is data to read
                             
                             
     ‘POLLPRI’               There is urgent data to read
                             
                             
     ‘POLLOUT’               Ready for output: writing will not block
                             
                             
     ‘POLLERR’               Error condition of some sort
                             
                             
     ‘POLLHUP’               Hung up
                             
                             
     ‘POLLRDHUP’             Stream socket peer closed connection, or
                             shut down writing half of connection
                             
                             
     ‘POLLNVAL’              Invalid request: descriptor not open
                             

     Registering a file descriptor that’s already registered is not an
     error, and has the same effect as registering the descriptor
     exactly once.

 -- Method: poll.modify (fd, eventmask)

     Modifies an already registered fd.  This has the same effect as
     ‘register(fd, eventmask)’.  Attempting to modify a file descriptor
     that was never registered causes an *note OSError: 304. exception
     with errno ‘ENOENT’ to be raised.

 -- Method: poll.unregister (fd)

     Remove a file descriptor being tracked by a polling object.  Just
     like the *note register(): 287f. method, `fd' can be an integer or
     an object with a *note fileno(): 2069. method that returns an
     integer.

     Attempting to remove a file descriptor that was never registered
     causes a *note KeyError: 3e9. exception to be raised.

 -- Method: poll.poll ([timeout])

     Polls the set of registered file descriptors, and returns a
     possibly-empty list containing ‘(fd, event)’ 2-tuples for the
     descriptors that have events or errors to report.  `fd' is the file
     descriptor, and `event' is a bitmask with bits set for the reported
     events for that descriptor — ‘POLLIN’ for waiting input, ‘POLLOUT’
     to indicate that the descriptor can be written to, and so forth.
     An empty list indicates that the call timed out and no file
     descriptors had any events to report.  If `timeout' is given, it
     specifies the length of time in milliseconds which the system will
     wait for events before returning.  If `timeout' is omitted,
     negative, or *note None: 203, the call will block until there is an
     event for this poll object.

     Changed in version 3.5: The function is now retried with a
     recomputed timeout when interrupted by a signal, except if the
     signal handler raises an exception (see PEP 475(1) for the
     rationale), instead of raising *note InterruptedError: 74c.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0475


File: python.info,  Node: Kqueue Objects,  Next: Kevent Objects,  Prev: Polling Objects,  Up: select — Waiting for I/O completion

5.18.4.4 Kqueue Objects
.......................

 -- Method: kqueue.close ()

     Close the control file descriptor of the kqueue object.

 -- Attribute: kqueue.closed

     ‘True’ if the kqueue object is closed.

 -- Method: kqueue.fileno ()

     Return the file descriptor number of the control fd.

 -- Method: kqueue.fromfd (fd)

     Create a kqueue object from a given file descriptor.

 -- Method: kqueue.control (changelist, max_events[, timeout]) ->
          eventlist

     Low level interface to kevent

        - changelist must be an iterable of kevent objects or ‘None’

        - max_events must be 0 or a positive integer

        - timeout in seconds (floats possible); the default is ‘None’,
          to wait forever

     Changed in version 3.5: The function is now retried with a
     recomputed timeout when interrupted by a signal, except if the
     signal handler raises an exception (see PEP 475(1) for the
     rationale), instead of raising *note InterruptedError: 74c.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0475


File: python.info,  Node: Kevent Objects,  Prev: Kqueue Objects,  Up: select — Waiting for I/O completion

5.18.4.5 Kevent Objects
.......................

‘https://www.freebsd.org/cgi/man.cgi?query=kqueue&sektion=2’

 -- Attribute: kevent.ident

     Value used to identify the event.  The interpretation depends on
     the filter but it’s usually the file descriptor.  In the
     constructor ident can either be an int or an object with a *note
     fileno(): 2069. method.  kevent stores the integer internally.

 -- Attribute: kevent.filter

     Name of the kernel filter.

     Constant                        Meaning
                                     
     ----------------------------------------------------------------------------------
                                     
     ‘KQ_FILTER_READ’                Takes a descriptor and returns whenever there
                                     is data available to read
                                     
                                     
     ‘KQ_FILTER_WRITE’               Takes a descriptor and returns whenever there
                                     is data available to write
                                     
                                     
     ‘KQ_FILTER_AIO’                 AIO requests
                                     
                                     
     ‘KQ_FILTER_VNODE’               Returns when one or more of the requested
                                     events watched in `fflag' occurs
                                     
                                     
     ‘KQ_FILTER_PROC’                Watch for events on a process id
                                     
                                     
     ‘KQ_FILTER_NETDEV’              Watch for events on a network device [not
                                     available on macOS]
                                     
                                     
     ‘KQ_FILTER_SIGNAL’              Returns whenever the watched signal is
                                     delivered to the process
                                     
                                     
     ‘KQ_FILTER_TIMER’               Establishes an arbitrary timer
                                     

 -- Attribute: kevent.flags

     Filter action.

     Constant                        Meaning
                                     
     ----------------------------------------------------------------------------------
                                     
     ‘KQ_EV_ADD’                     Adds or modifies an event
                                     
                                     
     ‘KQ_EV_DELETE’                  Removes an event from the queue
                                     
                                     
     ‘KQ_EV_ENABLE’                  Permitscontrol() to returns the event
                                     
                                     
     ‘KQ_EV_DISABLE’                 Disablesevent
                                     
                                     
     ‘KQ_EV_ONESHOT’                 Removes event after first occurrence
                                     
                                     
     ‘KQ_EV_CLEAR’                   Reset the state after an event is retrieved
                                     
                                     
     ‘KQ_EV_SYSFLAGS’                internal event
                                     
                                     
     ‘KQ_EV_FLAG1’                   internal event
                                     
                                     
     ‘KQ_EV_EOF’                     Filter specific EOF condition
                                     
                                     
     ‘KQ_EV_ERROR’                   See return values
                                     

 -- Attribute: kevent.fflags

     Filter specific flags.

     ‘KQ_FILTER_READ’ and ‘KQ_FILTER_WRITE’ filter flags:

     Constant                         Meaning
                                      
     ----------------------------------------------------------------------------------
                                      
     ‘KQ_NOTE_LOWAT’                  low water mark of a socket buffer
                                      

     ‘KQ_FILTER_VNODE’ filter flags:

     Constant                         Meaning
                                      
     ----------------------------------------------------------------------------------
                                      
     ‘KQ_NOTE_DELETE’                 `unlink()' was called
                                      
                                      
     ‘KQ_NOTE_WRITE’                  a write occurred
                                      
                                      
     ‘KQ_NOTE_EXTEND’                 the file was extended
                                      
                                      
     ‘KQ_NOTE_ATTRIB’                 an attribute was changed
                                      
                                      
     ‘KQ_NOTE_LINK’                   the link count has changed
                                      
                                      
     ‘KQ_NOTE_RENAME’                 the file was renamed
                                      
                                      
     ‘KQ_NOTE_REVOKE’                 access to the file was revoked
                                      

     ‘KQ_FILTER_PROC’ filter flags:

     Constant                         Meaning
                                      
     ----------------------------------------------------------------------------------
                                      
     ‘KQ_NOTE_EXIT’                   the process has exited
                                      
                                      
     ‘KQ_NOTE_FORK’                   the process has called `fork()'
                                      
                                      
     ‘KQ_NOTE_EXEC’                   the process has executed a new process
                                      
                                      
     ‘KQ_NOTE_PCTRLMASK’              internal filter flag
                                      
                                      
     ‘KQ_NOTE_PDATAMASK’              internal filter flag
                                      
                                      
     ‘KQ_NOTE_TRACK’                  follow a process across `fork()'
                                      
                                      
     ‘KQ_NOTE_CHILD’                  returned on the child process for `NOTE_TRACK'
                                      
                                      
     ‘KQ_NOTE_TRACKERR’               unable to attach to a child
                                      

     ‘KQ_FILTER_NETDEV’ filter flags (not available on macOS):

     Constant                         Meaning
                                      
     ----------------------------------------------------------------------------------
                                      
     ‘KQ_NOTE_LINKUP’                 link is up
                                      
                                      
     ‘KQ_NOTE_LINKDOWN’               link is down
                                      
                                      
     ‘KQ_NOTE_LINKINV’                link state is invalid
                                      

 -- Attribute: kevent.data

     Filter specific data.

 -- Attribute: kevent.udata

     User defined value.


File: python.info,  Node: selectors — High-level I/O multiplexing,  Next: asyncore — Asynchronous socket handler,  Prev: select — Waiting for I/O completion,  Up: Networking and Interprocess Communication

5.18.5 ‘selectors’ — High-level I/O multiplexing
------------------------------------------------

New in version 3.4.

`Source code:' Lib/selectors.py(1)

__________________________________________________________________

* Menu:

* Introduction: Introduction<9>.
* Classes: Classes<3>.
* Examples: Examples<18>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/selectors.py


File: python.info,  Node: Introduction<9>,  Next: Classes<3>,  Up: selectors — High-level I/O multiplexing

5.18.5.1 Introduction
.....................

This module allows high-level and efficient I/O multiplexing, built upon
the *note select: e5. module primitives.  Users are encouraged to use
this module instead, unless they want precise control over the OS-level
primitives used.

It defines a *note BaseSelector: 2891. abstract base class, along with
several concrete implementations (*note KqueueSelector: 2795, *note
EpollSelector: 54f.…), that can be used to wait for I/O readiness
notification on multiple file objects.  In the following, “file object”
refers to any object with a ‘fileno()’ method, or a raw file descriptor.
See *note file object: c14.

*note DefaultSelector: 2892. is an alias to the most efficient
implementation available on the current platform: this should be the
default choice for most users.

     Note: The type of file objects supported depends on the platform:
     on Windows, sockets are supported, but not pipes, whereas on Unix,
     both are supported (some other types may be supported as well, such
     as fifos or special file devices).

See also
........

*note select: e5.

     Low-level I/O multiplexing module.


File: python.info,  Node: Classes<3>,  Next: Examples<18>,  Prev: Introduction<9>,  Up: selectors — High-level I/O multiplexing

5.18.5.2 Classes
................

Classes hierarchy:

     BaseSelector
     +-- SelectSelector
     +-- PollSelector
     +-- EpollSelector
     +-- DevpollSelector
     +-- KqueueSelector

In the following, `events' is a bitwise mask indicating which I/O events
should be waited for on a given file object.  It can be a combination of
the modules constants below:

     Constant                    Meaning
                                 
     --------------------------------------------------------------------------------
                                 
     ‘EVENT_READ’                Available for read
                                 
                                 
     ‘EVENT_WRITE’               Available for write
                                 

 -- Class: selectors.SelectorKey

     A *note SelectorKey: 2894. is a *note namedtuple: 1a1. used to
     associate a file object to its underlying file descriptor, selected
     event mask and attached data.  It is returned by several *note
     BaseSelector: 2891. methods.

      -- Attribute: fileobj

          File object registered.

      -- Attribute: fd

          Underlying file descriptor.

      -- Attribute: events

          Events that must be waited for on this file object.

      -- Attribute: data

          Optional opaque data associated to this file object: for
          example, this could be used to store a per-client session ID.

 -- Class: selectors.BaseSelector

     A *note BaseSelector: 2891. is used to wait for I/O event readiness
     on multiple file objects.  It supports file stream registration,
     unregistration, and a method to wait for I/O events on those
     streams, with an optional timeout.  It’s an abstract base class, so
     cannot be instantiated.  Use *note DefaultSelector: 2892. instead,
     or one of *note SelectSelector: 2792, *note KqueueSelector: 2795.
     etc.  if you want to specifically use an implementation, and your
     platform supports it.  *note BaseSelector: 2891. and its concrete
     implementations support the *note context manager: 661. protocol.

      -- Method: abstractmethod register (fileobj, events, data=None)

          Register a file object for selection, monitoring it for I/O
          events.

          `fileobj' is the file object to monitor.  It may either be an
          integer file descriptor or an object with a ‘fileno()’ method.
          `events' is a bitwise mask of events to monitor.  `data' is an
          opaque object.

          This returns a new *note SelectorKey: 2894. instance, or
          raises a *note ValueError: 16d. in case of invalid event mask
          or file descriptor, or *note KeyError: 3e9. if the file object
          is already registered.

      -- Method: abstractmethod unregister (fileobj)

          Unregister a file object from selection, removing it from
          monitoring.  A file object shall be unregistered prior to
          being closed.

          `fileobj' must be a file object previously registered.

          This returns the associated *note SelectorKey: 2894. instance,
          or raises a *note KeyError: 3e9. if `fileobj' is not
          registered.  It will raise *note ValueError: 16d. if `fileobj'
          is invalid (e.g.  it has no ‘fileno()’ method or its
          ‘fileno()’ method has an invalid return value).

      -- Method: modify (fileobj, events, data=None)

          Change a registered file object’s monitored events or attached
          data.

          This is equivalent to ‘BaseSelector.unregister(fileobj)()’
          followed by ‘BaseSelector.register(fileobj, events, data)()’,
          except that it can be implemented more efficiently.

          This returns a new *note SelectorKey: 2894. instance, or
          raises a *note ValueError: 16d. in case of invalid event mask
          or file descriptor, or *note KeyError: 3e9. if the file object
          is not registered.

      -- Method: abstractmethod select (timeout=None)

          Wait until some registered file objects become ready, or the
          timeout expires.

          If ‘timeout > 0’, this specifies the maximum wait time, in
          seconds.  If ‘timeout <= 0’, the call won’t block, and will
          report the currently ready file objects.  If `timeout' is
          ‘None’, the call will block until a monitored file object
          becomes ready.

          This returns a list of ‘(key, events)’ tuples, one for each
          ready file object.

          `key' is the *note SelectorKey: 2894. instance corresponding
          to a ready file object.  `events' is a bitmask of events ready
          on this file object.

               Note: This method can return before any file object
               becomes ready or the timeout has elapsed if the current
               process receives a signal: in this case, an empty list
               will be returned.

          Changed in version 3.5: The selector is now retried with a
          recomputed timeout when interrupted by a signal if the signal
          handler did not raise an exception (see PEP 475(1) for the
          rationale), instead of returning an empty list of events
          before the timeout.

      -- Method: close ()

          Close the selector.

          This must be called to make sure that any underlying resource
          is freed.  The selector shall not be used once it has been
          closed.

      -- Method: get_key (fileobj)

          Return the key associated with a registered file object.

          This returns the *note SelectorKey: 2894. instance associated
          to this file object, or raises *note KeyError: 3e9. if the
          file object is not registered.

      -- Method: abstractmethod get_map ()

          Return a mapping of file objects to selector keys.

          This returns a *note Mapping: 15f. instance mapping registered
          file objects to their associated *note SelectorKey: 2894.
          instance.

 -- Class: selectors.DefaultSelector

     The default selector class, using the most efficient implementation
     available on the current platform.  This should be the default
     choice for most users.

 -- Class: selectors.SelectSelector

     *note select.select(): 766.-based selector.

 -- Class: selectors.PollSelector

     *note select.poll(): 2854.-based selector.

 -- Class: selectors.EpollSelector

     *note select.epoll(): 990.-based selector.

      -- Method: fileno ()

          This returns the file descriptor used by the underlying *note
          select.epoll(): 990. object.

 -- Class: selectors.DevpollSelector

     *note select.devpoll(): 992.-based selector.

      -- Method: fileno ()

          This returns the file descriptor used by the underlying *note
          select.devpoll(): 992. object.

     New in version 3.5.

 -- Class: selectors.KqueueSelector

     *note select.kqueue(): 2870.-based selector.

      -- Method: fileno ()

          This returns the file descriptor used by the underlying *note
          select.kqueue(): 2870. object.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0475


File: python.info,  Node: Examples<18>,  Prev: Classes<3>,  Up: selectors — High-level I/O multiplexing

5.18.5.3 Examples
.................

Here is a simple echo server implementation:

     import selectors
     import socket

     sel = selectors.DefaultSelector()

     def accept(sock, mask):
         conn, addr = sock.accept()  # Should be ready
         print('accepted', conn, 'from', addr)
         conn.setblocking(False)
         sel.register(conn, selectors.EVENT_READ, read)

     def read(conn, mask):
         data = conn.recv(1000)  # Should be ready
         if data:
             print('echoing', repr(data), 'to', conn)
             conn.send(data)  # Hope it won't block
         else:
             print('closing', conn)
             sel.unregister(conn)
             conn.close()

     sock = socket.socket()
     sock.bind(('localhost', 1234))
     sock.listen(100)
     sock.setblocking(False)
     sel.register(sock, selectors.EVENT_READ, accept)

     while True:
         events = sel.select()
         for key, mask in events:
             callback = key.data
             callback(key.fileobj, mask)


File: python.info,  Node: asyncore — Asynchronous socket handler,  Next: asynchat — Asynchronous socket command/response handler,  Prev: selectors — High-level I/O multiplexing,  Up: Networking and Interprocess Communication

5.18.6 ‘asyncore’ — Asynchronous socket handler
-----------------------------------------------

`Source code:' Lib/asyncore.py(1)

Deprecated since version 3.6: Please use *note asyncio: 9. instead.

__________________________________________________________________

     Note: This module exists for backwards compatibility only.  For new
     code we recommend using *note asyncio: 9.

This module provides the basic infrastructure for writing asynchronous
socket service clients and servers.

There are only two ways to have a program on a single processor do “more
than one thing at a time.” Multi-threaded programming is the simplest
and most popular way to do it, but there is another very different
technique, that lets you have nearly all the advantages of
multi-threading, without actually using multiple threads.  It’s really
only practical if your program is largely I/O bound.  If your program is
processor bound, then pre-emptive scheduled threads are probably what
you really need.  Network servers are rarely processor bound, however.

If your operating system supports the ‘select()’ system call in its I/O
library (and nearly all do), then you can use it to juggle multiple
communication channels at once; doing other work while your I/O is
taking place in the “background.” Although this strategy can seem
strange and complex, especially at first, it is in many ways easier to
understand and control than multi-threaded programming.  The *note
asyncore: a. module solves many of the difficult problems for you,
making the task of building sophisticated high-performance network
servers and clients a snap.  For “conversational” applications and
protocols the companion *note asynchat: 8. module is invaluable.

The basic idea behind both modules is to create one or more network
`channels', instances of class *note asyncore.dispatcher: c91. and *note
asynchat.async_chat: 99c.  Creating the channels adds them to a global
map, used by the *note loop(): 28a5. function if you do not provide it
with your own `map'.

Once the initial channel(s) is(are) created, calling the *note loop():
28a5. function activates channel service, which continues until the last
channel (including any that have been added to the map during
asynchronous service) is closed.

 -- Function: asyncore.loop ([timeout[, use_poll[, map[, count]]]])

     Enter a polling loop that terminates after count passes or all open
     channels have been closed.  All arguments are optional.  The
     `count' parameter defaults to ‘None’, resulting in the loop
     terminating only when all channels have been closed.  The `timeout'
     argument sets the timeout parameter for the appropriate *note
     select(): 766. or *note poll(): 2854. call, measured in seconds;
     the default is 30 seconds.  The `use_poll' parameter, if true,
     indicates that *note poll(): 2854. should be used in preference to
     *note select(): 766. (the default is ‘False’).

     The `map' parameter is a dictionary whose items are the channels to
     watch.  As channels are closed they are deleted from their map.  If
     `map' is omitted, a global map is used.  Channels (instances of
     *note asyncore.dispatcher: c91, *note asynchat.async_chat: 99c. and
     subclasses thereof) can freely be mixed in the map.

 -- Class: asyncore.dispatcher

     The *note dispatcher: c91. class is a thin wrapper around a
     low-level socket object.  To make it more useful, it has a few
     methods for event-handling which are called from the asynchronous
     loop.  Otherwise, it can be treated as a normal non-blocking socket
     object.

     The firing of low-level events at certain times or in certain
     connection states tells the asynchronous loop that certain
     higher-level events have taken place.  For example, if we have
     asked for a socket to connect to another host, we know that the
     connection has been made when the socket becomes writable for the
     first time (at this point you know that you may write to it with
     the expectation of success).  The implied higher-level events are:

     Event                      Description
                                
     ------------------------------------------------------------------------
                                
     ‘handle_connect()’         Implied by the first read or write event
                                
                                
     ‘handle_close()’           Implied by a read event with no data
                                available
                                
                                
     ‘handle_accepted()’        Implied by a read event on a listening
                                socket
                                

     During asynchronous processing, each mapped channel’s *note
     readable(): 28a6. and *note writable(): 28a7. methods are used to
     determine whether the channel’s socket should be added to the list
     of channels ‘select()’ed or ‘poll()’ed for read and write events.

     Thus, the set of channel events is larger than the basic socket
     events.  The full set of methods that can be overridden in your
     subclass follows:

      -- Method: handle_read ()

          Called when the asynchronous loop detects that a ‘read()’ call
          on the channel’s socket will succeed.

      -- Method: handle_write ()

          Called when the asynchronous loop detects that a writable
          socket can be written.  Often this method will implement the
          necessary buffering for performance.  For example:

               def handle_write(self):
                   sent = self.send(self.buffer)
                   self.buffer = self.buffer[sent:]

      -- Method: handle_expt ()

          Called when there is out of band (OOB) data for a socket
          connection.  This will almost never happen, as OOB is
          tenuously supported and rarely used.

      -- Method: handle_connect ()

          Called when the active opener’s socket actually makes a
          connection.  Might send a “welcome” banner, or initiate a
          protocol negotiation with the remote endpoint, for example.

      -- Method: handle_close ()

          Called when the socket is closed.

      -- Method: handle_error ()

          Called when an exception is raised and not otherwise handled.
          The default version prints a condensed traceback.

      -- Method: handle_accept ()

          Called on listening channels (passive openers) when a
          connection can be established with a new remote endpoint that
          has issued a *note connect(): 28ae. call for the local
          endpoint.  Deprecated in version 3.2; use *note
          handle_accepted(): c92. instead.

          Deprecated since version 3.2.

      -- Method: handle_accepted (sock, addr)

          Called on listening channels (passive openers) when a
          connection has been established with a new remote endpoint
          that has issued a *note connect(): 28ae. call for the local
          endpoint.  `sock' is a `new' socket object usable to send and
          receive data on the connection, and `addr' is the address
          bound to the socket on the other end of the connection.

          New in version 3.2.

      -- Method: readable ()

          Called each time around the asynchronous loop to determine
          whether a channel’s socket should be added to the list on
          which read events can occur.  The default method simply
          returns ‘True’, indicating that by default, all channels will
          be interested in read events.

      -- Method: writable ()

          Called each time around the asynchronous loop to determine
          whether a channel’s socket should be added to the list on
          which write events can occur.  The default method simply
          returns ‘True’, indicating that by default, all channels will
          be interested in write events.

     In addition, each channel delegates or extends many of the socket
     methods.  Most of these are nearly identical to their socket
     partners.

      -- Method: create_socket (family=socket.AF_INET,
               type=socket.SOCK_STREAM)

          This is identical to the creation of a normal socket, and will
          use the same options for creation.  Refer to the *note socket:
          ef. documentation for information on creating sockets.

          Changed in version 3.3: `family' and `type' arguments can be
          omitted.

      -- Method: connect (address)

          As with the normal socket object, `address' is a tuple with
          the first element the host to connect to, and the second the
          port number.

      -- Method: send (data)

          Send `data' to the remote end-point of the socket.

      -- Method: recv (buffer_size)

          Read at most `buffer_size' bytes from the socket’s remote
          end-point.  An empty bytes object implies that the channel has
          been closed from the other end.

          Note that *note recv(): 28b1. may raise *note BlockingIOError:
          a78. , even though *note select.select(): 766. or *note
          select.poll(): 2854. has reported the socket ready for
          reading.

      -- Method: listen (backlog)

          Listen for connections made to the socket.  The `backlog'
          argument specifies the maximum number of queued connections
          and should be at least 1; the maximum value is
          system-dependent (usually 5).

      -- Method: bind (address)

          Bind the socket to `address'.  The socket must not already be
          bound.  (The format of `address' depends on the address family
          — refer to the *note socket: ef. documentation for more
          information.)  To mark the socket as re-usable (setting the
          ‘SO_REUSEADDR’ option), call the *note dispatcher: c91.
          object’s ‘set_reuse_addr()’ method.

      -- Method: accept ()

          Accept a connection.  The socket must be bound to an address
          and listening for connections.  The return value can be either
          ‘None’ or a pair ‘(conn, address)’ where `conn' is a `new'
          socket object usable to send and receive data on the
          connection, and `address' is the address bound to the socket
          on the other end of the connection.  When ‘None’ is returned
          it means the connection didn’t take place, in which case the
          server should just ignore this event and keep listening for
          further incoming connections.

      -- Method: close ()

          Close the socket.  All future operations on the socket object
          will fail.  The remote end-point will receive no more data
          (after queued data is flushed).  Sockets are automatically
          closed when they are garbage-collected.

 -- Class: asyncore.dispatcher_with_send

     A *note dispatcher: c91. subclass which adds simple buffered output
     capability, useful for simple clients.  For more sophisticated
     usage use *note asynchat.async_chat: 99c.

 -- Class: asyncore.file_dispatcher

     A file_dispatcher takes a file descriptor or *note file object:
     c14. along with an optional map argument and wraps it for use with
     the ‘poll()’ or ‘loop()’ functions.  If provided a file object or
     anything with a ‘fileno()’ method, that method will be called and
     passed to the *note file_wrapper: 28b7. constructor.

     *note Availability: 1491.: Unix.

 -- Class: asyncore.file_wrapper

     A file_wrapper takes an integer file descriptor and calls *note
     os.dup(): 10e9. to duplicate the handle so that the original handle
     may be closed independently of the file_wrapper.  This class
     implements sufficient methods to emulate a socket for use by the
     *note file_dispatcher: 28b6. class.

     *note Availability: 1491.: Unix.

* Menu:

* asyncore Example basic HTTP client::
* asyncore Example basic echo server::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/asyncore.py


File: python.info,  Node: asyncore Example basic HTTP client,  Next: asyncore Example basic echo server,  Up: asyncore — Asynchronous socket handler

5.18.6.1 asyncore Example basic HTTP client
...........................................

Here is a very basic HTTP client that uses the *note dispatcher: c91.
class to implement its socket handling:

     import asyncore

     class HTTPClient(asyncore.dispatcher):

         def __init__(self, host, path):
             asyncore.dispatcher.__init__(self)
             self.create_socket()
             self.connect( (host, 80) )
             self.buffer = bytes('GET %s HTTP/1.0\r\nHost: %s\r\n\r\n' %
                                 (path, host), 'ascii')

         def handle_connect(self):
             pass

         def handle_close(self):
             self.close()

         def handle_read(self):
             print(self.recv(8192))

         def writable(self):
             return (len(self.buffer) > 0)

         def handle_write(self):
             sent = self.send(self.buffer)
             self.buffer = self.buffer[sent:]


     client = HTTPClient('www.python.org', '/')
     asyncore.loop()


File: python.info,  Node: asyncore Example basic echo server,  Prev: asyncore Example basic HTTP client,  Up: asyncore — Asynchronous socket handler

5.18.6.2 asyncore Example basic echo server
...........................................

Here is a basic echo server that uses the *note dispatcher: c91. class
to accept connections and dispatches the incoming connections to a
handler:

     import asyncore

     class EchoHandler(asyncore.dispatcher_with_send):

         def handle_read(self):
             data = self.recv(8192)
             if data:
                 self.send(data)

     class EchoServer(asyncore.dispatcher):

         def __init__(self, host, port):
             asyncore.dispatcher.__init__(self)
             self.create_socket()
             self.set_reuse_addr()
             self.bind((host, port))
             self.listen(5)

         def handle_accepted(self, sock, addr):
             print('Incoming connection from %s' % repr(addr))
             handler = EchoHandler(sock)

     server = EchoServer('localhost', 8080)
     asyncore.loop()


File: python.info,  Node: asynchat — Asynchronous socket command/response handler,  Next: signal — Set handlers for asynchronous events,  Prev: asyncore — Asynchronous socket handler,  Up: Networking and Interprocess Communication

5.18.7 ‘asynchat’ — Asynchronous socket command/response handler
----------------------------------------------------------------

`Source code:' Lib/asynchat.py(1)

Deprecated since version 3.6: Please use *note asyncio: 9. instead.

__________________________________________________________________

     Note: This module exists for backwards compatibility only.  For new
     code we recommend using *note asyncio: 9.

This module builds on the *note asyncore: a. infrastructure, simplifying
asynchronous clients and servers and making it easier to handle
protocols whose elements are terminated by arbitrary strings, or are of
variable length.  *note asynchat: 8. defines the abstract class *note
async_chat: 99c. that you subclass, providing implementations of the
‘collect_incoming_data()’ and ‘found_terminator()’ methods.  It uses the
same asynchronous loop as *note asyncore: a, and the two types of
channel, *note asyncore.dispatcher: c91. and *note asynchat.async_chat:
99c, can freely be mixed in the channel map.  Typically an *note
asyncore.dispatcher: c91. server channel generates new *note
asynchat.async_chat: 99c. channel objects as it receives incoming
connection requests.

 -- Class: asynchat.async_chat

     This class is an abstract subclass of *note asyncore.dispatcher:
     c91.  To make practical use of the code you must subclass *note
     async_chat: 99c, providing meaningful *note
     collect_incoming_data(): 28be. and *note found_terminator(): 28bf.
     methods.  The *note asyncore.dispatcher: c91. methods can be used,
     although not all make sense in a message/response context.

     Like *note asyncore.dispatcher: c91, *note async_chat: 99c. defines
     a set of events that are generated by an analysis of socket
     conditions after a ‘select()’ call.  Once the polling loop has been
     started the *note async_chat: 99c. object’s methods are called by
     the event-processing framework with no action on the part of the
     programmer.

     Two class attributes can be modified, to improve performance, or
     possibly even to conserve memory.

      -- Data: ac_in_buffer_size

          The asynchronous input buffer size (default ‘4096’).

      -- Data: ac_out_buffer_size

          The asynchronous output buffer size (default ‘4096’).

     Unlike *note asyncore.dispatcher: c91, *note async_chat: 99c.
     allows you to define a FIFO queue of `producers'.  A producer need
     have only one method, ‘more()’, which should return data to be
     transmitted on the channel.  The producer indicates exhaustion
     (`i.e.'  that it contains no more data) by having its ‘more()’
     method return the empty bytes object.  At this point the *note
     async_chat: 99c. object removes the producer from the queue and
     starts using the next producer, if any.  When the producer queue is
     empty the ‘handle_write()’ method does nothing.  You use the
     channel object’s *note set_terminator(): 28c2. method to describe
     how to recognize the end of, or an important breakpoint in, an
     incoming transmission from the remote endpoint.

     To build a functioning *note async_chat: 99c. subclass your input
     methods *note collect_incoming_data(): 28be. and *note
     found_terminator(): 28bf. must handle the data that the channel
     receives asynchronously.  The methods are described below.

 -- Method: async_chat.close_when_done ()

     Pushes a ‘None’ on to the producer queue.  When this producer is
     popped off the queue it causes the channel to be closed.

 -- Method: async_chat.collect_incoming_data (data)

     Called with `data' holding an arbitrary amount of received data.
     The default method, which must be overridden, raises a *note
     NotImplementedError: 704. exception.

 -- Method: async_chat.discard_buffers ()

     In emergencies this method will discard any data held in the input
     and/or output buffers and the producer queue.

 -- Method: async_chat.found_terminator ()

     Called when the incoming data stream matches the termination
     condition set by *note set_terminator(): 28c2.  The default method,
     which must be overridden, raises a *note NotImplementedError: 704.
     exception.  The buffered input data should be available via an
     instance attribute.

 -- Method: async_chat.get_terminator ()

     Returns the current terminator for the channel.

 -- Method: async_chat.push (data)

     Pushes data on to the channel’s queue to ensure its transmission.
     This is all you need to do to have the channel write the data out
     to the network, although it is possible to use your own producers
     in more complex schemes to implement encryption and chunking, for
     example.

 -- Method: async_chat.push_with_producer (producer)

     Takes a producer object and adds it to the producer queue
     associated with the channel.  When all currently-pushed producers
     have been exhausted the channel will consume this producer’s data
     by calling its ‘more()’ method and send the data to the remote
     endpoint.

 -- Method: async_chat.set_terminator (term)

     Sets the terminating condition to be recognized on the channel.
     ‘term’ may be any of three types of value, corresponding to three
     different ways to handle incoming protocol data.

     term            Description
                     
     ------------------------------------------------------------------
                     
     `string'        Will call *note found_terminator(): 28bf. when
                     the string is found in the input stream
                     
                     
     `integer'       Will call *note found_terminator(): 28bf. when
                     the indicated number of characters have been
                     received
                     
                     
     ‘None’          The channel continues to collect data forever
                     

     Note that any data following the terminator will be available for
     reading by the channel after *note found_terminator(): 28bf. is
     called.

* Menu:

* asynchat Example::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/asynchat.py


File: python.info,  Node: asynchat Example,  Up: asynchat — Asynchronous socket command/response handler

5.18.7.1 asynchat Example
.........................

The following partial example shows how HTTP requests can be read with
*note async_chat: 99c.  A web server might create an
‘http_request_handler’ object for each incoming client connection.
Notice that initially the channel terminator is set to match the blank
line at the end of the HTTP headers, and a flag indicates that the
headers are being read.

Once the headers have been read, if the request is of type POST
(indicating that further data are present in the input stream) then the
‘Content-Length:’ header is used to set a numeric terminator to read the
right amount of data from the channel.

The ‘handle_request()’ method is called once all relevant input has been
marshalled, after setting the channel terminator to ‘None’ to ensure
that any extraneous data sent by the web client are ignored.

     import asynchat

     class http_request_handler(asynchat.async_chat):

         def __init__(self, sock, addr, sessions, log):
             asynchat.async_chat.__init__(self, sock=sock)
             self.addr = addr
             self.sessions = sessions
             self.ibuffer = []
             self.obuffer = b""
             self.set_terminator(b"\r\n\r\n")
             self.reading_headers = True
             self.handling = False
             self.cgi_data = None
             self.log = log

         def collect_incoming_data(self, data):
             """Buffer the data"""
             self.ibuffer.append(data)

         def found_terminator(self):
             if self.reading_headers:
                 self.reading_headers = False
                 self.parse_headers(b"".join(self.ibuffer))
                 self.ibuffer = []
                 if self.op.upper() == b"POST":
                     clen = self.headers.getheader("content-length")
                     self.set_terminator(int(clen))
                 else:
                     self.handling = True
                     self.set_terminator(None)
                     self.handle_request()
             elif not self.handling:
                 self.set_terminator(None)  # browsers sometimes over-send
                 self.cgi_data = parse(self.headers, b"".join(self.ibuffer))
                 self.handling = True
                 self.ibuffer = []
                 self.handle_request()


File: python.info,  Node: signal — Set handlers for asynchronous events,  Next: mmap — Memory-mapped file support,  Prev: asynchat — Asynchronous socket command/response handler,  Up: Networking and Interprocess Communication

5.18.8 ‘signal’ — Set handlers for asynchronous events
------------------------------------------------------

__________________________________________________________________

This module provides mechanisms to use signal handlers in Python.

* Menu:

* General rules::
* Module contents: Module contents<2>.
* Example: Example<9>.
* Note on SIGPIPE::


File: python.info,  Node: General rules,  Next: Module contents<2>,  Up: signal — Set handlers for asynchronous events

5.18.8.1 General rules
......................

The *note signal.signal(): b58. function allows defining custom handlers
to be executed when a signal is received.  A small number of default
handlers are installed: *note SIGPIPE: 28cd. is ignored (so write errors
on pipes and sockets can be reported as ordinary Python exceptions) and
*note SIGINT: 2626. is translated into a *note KeyboardInterrupt: 2cc.
exception if the parent process has not changed it.

A handler for a particular signal, once set, remains installed until it
is explicitly reset (Python emulates the BSD style interface regardless
of the underlying implementation), with the exception of the handler for
*note SIGCHLD: 28ce, which follows the underlying implementation.

* Menu:

* Execution of Python signal handlers::
* Signals and threads::


File: python.info,  Node: Execution of Python signal handlers,  Next: Signals and threads,  Up: General rules

5.18.8.2 Execution of Python signal handlers
............................................

A Python signal handler does not get executed inside the low-level (C)
signal handler.  Instead, the low-level signal handler sets a flag which
tells the *note virtual machine: 28d0. to execute the corresponding
Python signal handler at a later point(for example at the next *note
bytecode: 709. instruction).  This has consequences:

   * It makes little sense to catch synchronous errors like *note
     SIGFPE: 28d1. or *note SIGSEGV: 28d2. that are caused by an invalid
     operation in C code.  Python will return from the signal handler to
     the C code, which is likely to raise the same signal again, causing
     Python to apparently hang.  From Python 3.3 onwards, you can use
     the *note faulthandler: 7b. module to report on synchronous errors.

   * A long-running calculation implemented purely in C (such as regular
     expression matching on a large body of text) may run uninterrupted
     for an arbitrary amount of time, regardless of any signals
     received.  The Python signal handlers will be called when the
     calculation finishes.


File: python.info,  Node: Signals and threads,  Prev: Execution of Python signal handlers,  Up: General rules

5.18.8.3 Signals and threads
............................

Python signal handlers are always executed in the main Python thread of
the main interpreter, even if the signal was received in another thread.
This means that signals can’t be used as a means of inter-thread
communication.  You can use the synchronization primitives from the
*note threading: 10b. module instead.

Besides, only the main thread of the main interpreter is allowed to set
a new signal handler.


File: python.info,  Node: Module contents<2>,  Next: Example<9>,  Prev: General rules,  Up: signal — Set handlers for asynchronous events

5.18.8.4 Module contents
........................

Changed in version 3.5: signal (SIG*), handler (*note SIG_DFL: 2627,
*note SIG_IGN: 2628.) and sigmask (*note SIG_BLOCK: 28d6, *note
SIG_UNBLOCK: 28d7, *note SIG_SETMASK: 28d8.) related constants listed
below were turned into *note enums: 684.  *note getsignal(): 28d9, *note
pthread_sigmask(): b54, *note sigpending(): b56. and *note sigwait():
b57. functions return human-readable *note enums: 684.

The variables defined in the *note signal: ea. module are:

 -- Data: signal.SIG_DFL

     This is one of two standard signal handling options; it will simply
     perform the default function for the signal.  For example, on most
     systems the default action for ‘SIGQUIT’ is to dump core and exit,
     while the default action for *note SIGCHLD: 28ce. is to simply
     ignore it.

 -- Data: signal.SIG_IGN

     This is another standard signal handler, which will simply ignore
     the given signal.

 -- Data: signal.SIGABRT

     Abort signal from ‘abort(3)’.

 -- Data: signal.SIGALRM

     Timer signal from ‘alarm(2)’.

     *note Availability: 1491.: Unix.

 -- Data: signal.SIGBREAK

     Interrupt from keyboard (CTRL + BREAK).

     *note Availability: 1491.: Windows.

 -- Data: signal.SIGBUS

     Bus error (bad memory access).

     *note Availability: 1491.: Unix.

 -- Data: signal.SIGCHLD

     Child process stopped or terminated.

     *note Availability: 1491.: Unix.

 -- Data: signal.SIGCLD

     Alias to *note SIGCHLD: 28ce.

 -- Data: signal.SIGCONT

     Continue the process if it is currently stopped

     *note Availability: 1491.: Unix.

 -- Data: signal.SIGFPE

     Floating-point exception.  For example, division by zero.

     See also
     ........

     *note ZeroDivisionError: 1fa. is raised when the second argument of
     a division or modulo operation is zero.

 -- Data: signal.SIGHUP

     Hangup detected on controlling terminal or death of controlling
     process.

     *note Availability: 1491.: Unix.

 -- Data: signal.SIGILL

     Illegal instruction.

 -- Data: signal.SIGINT

     Interrupt from keyboard (CTRL + C).

     Default action is to raise *note KeyboardInterrupt: 2cc.

 -- Data: signal.SIGKILL

     Kill signal.

     It cannot be caught, blocked, or ignored.

     *note Availability: 1491.: Unix.

 -- Data: signal.SIGPIPE

     Broken pipe: write to pipe with no readers.

     Default action is to ignore the signal.

     *note Availability: 1491.: Unix.

 -- Data: signal.SIGSEGV

     Segmentation fault: invalid memory reference.

 -- Data: signal.SIGTERM

     Termination signal.

 -- Data: signal.SIGUSR1

     User-defined signal 1.

     *note Availability: 1491.: Unix.

 -- Data: signal.SIGUSR2

     User-defined signal 2.

     *note Availability: 1491.: Unix.

 -- Data: signal.SIGWINCH

     Window resize signal.

     *note Availability: 1491.: Unix.

 -- Data: SIG*

     All the signal numbers are defined symbolically.  For example, the
     hangup signal is defined as *note signal.SIGHUP: 28df.; the
     variable names are identical to the names used in C programs, as
     found in ‘<signal.h>’.  The Unix man page for ‘‘signal()’’ lists
     the existing signals (on some systems this is ‘signal(2)’, on
     others the list is in ‘signal(7)’).  Note that not all systems
     define the same set of signal names; only those names defined by
     the system are defined by this module.

 -- Data: signal.CTRL_C_EVENT

     The signal corresponding to the ‘Ctrl+C’ keystroke event.  This
     signal can only be used with *note os.kill(): db9.

     *note Availability: 1491.: Windows.

     New in version 3.2.

 -- Data: signal.CTRL_BREAK_EVENT

     The signal corresponding to the ‘Ctrl+Break’ keystroke event.  This
     signal can only be used with *note os.kill(): db9.

     *note Availability: 1491.: Windows.

     New in version 3.2.

 -- Data: signal.NSIG

     One more than the number of the highest signal number.

 -- Data: signal.ITIMER_REAL

     Decrements interval timer in real time, and delivers *note SIGALRM:
     28db. upon expiration.

 -- Data: signal.ITIMER_VIRTUAL

     Decrements interval timer only when the process is executing, and
     delivers SIGVTALRM upon expiration.

 -- Data: signal.ITIMER_PROF

     Decrements interval timer both when the process executes and when
     the system is executing on behalf of the process.  Coupled with
     ITIMER_VIRTUAL, this timer is usually used to profile the time
     spent by the application in user and kernel space.  SIGPROF is
     delivered upon expiration.

 -- Data: signal.SIG_BLOCK

     A possible value for the `how' parameter to *note
     pthread_sigmask(): b54. indicating that signals are to be blocked.

     New in version 3.3.

 -- Data: signal.SIG_UNBLOCK

     A possible value for the `how' parameter to *note
     pthread_sigmask(): b54. indicating that signals are to be
     unblocked.

     New in version 3.3.

 -- Data: signal.SIG_SETMASK

     A possible value for the `how' parameter to *note
     pthread_sigmask(): b54. indicating that the signal mask is to be
     replaced.

     New in version 3.3.

The *note signal: ea. module defines one exception:

 -- Exception: signal.ItimerError

     Raised to signal an error from the underlying *note setitimer():
     28ea. or *note getitimer(): 28eb. implementation.  Expect this
     error if an invalid interval timer or a negative time is passed to
     *note setitimer(): 28ea.  This error is a subtype of *note OSError:
     304.

     New in version 3.3: This error used to be a subtype of *note
     IOError: a73, which is now an alias of *note OSError: 304.

The *note signal: ea. module defines the following functions:

 -- Function: signal.alarm (time)

     If `time' is non-zero, this function requests that a *note SIGALRM:
     28db. signal be sent to the process in `time' seconds.  Any
     previously scheduled alarm is canceled (only one alarm can be
     scheduled at any time).  The returned value is then the number of
     seconds before any previously set alarm was to have been delivered.
     If `time' is zero, no alarm is scheduled, and any scheduled alarm
     is canceled.  If the return value is zero, no alarm is currently
     scheduled.

     *note Availability: 1491.: Unix.  See the man page ‘alarm(2)’ for
     further information.

 -- Function: signal.getsignal (signalnum)

     Return the current signal handler for the signal `signalnum'.  The
     returned value may be a callable Python object, or one of the
     special values *note signal.SIG_IGN: 2628, *note signal.SIG_DFL:
     2627. or *note None: 203.  Here, *note signal.SIG_IGN: 2628. means
     that the signal was previously ignored, *note signal.SIG_DFL: 2627.
     means that the default way of handling the signal was previously in
     use, and ‘None’ means that the previous signal handler was not
     installed from Python.

 -- Function: signal.strsignal (signalnum)

     Return the system description of the signal `signalnum', such as
     “Interrupt”, “Segmentation fault”, etc.  Returns *note None: 203.
     if the signal is not recognized.

     New in version 3.8.

 -- Function: signal.valid_signals ()

     Return the set of valid signal numbers on this platform.  This can
     be less than ‘range(1, NSIG)’ if some signals are reserved by the
     system for internal use.

     New in version 3.8.

 -- Function: signal.pause ()

     Cause the process to sleep until a signal is received; the
     appropriate handler will then be called.  Returns nothing.

     *note Availability: 1491.: Unix.  See the man page ‘signal(2)’ for
     further information.

     See also *note sigwait(): b57, *note sigwaitinfo(): 772, *note
     sigtimedwait(): 771. and *note sigpending(): b56.

 -- Function: signal.raise_signal (signum)

     Sends a signal to the calling process.  Returns nothing.

     New in version 3.8.

 -- Function: signal.pidfd_send_signal (pidfd, sig, siginfo=None,
          flags=0)

     Send signal `sig' to the process referred to by file descriptor
     `pidfd'.  Python does not currently support the `siginfo'
     parameter; it must be ‘None’.  The `flags' argument is provided for
     future extensions; no flag values are currently defined.

     See the ‘pidfd_send_signal(2)’ man page for more information.

     *note Availability: 1491.: Linux 5.1+

     New in version 3.9.

 -- Function: signal.pthread_kill (thread_id, signalnum)

     Send the signal `signalnum' to the thread `thread_id', another
     thread in the same process as the caller.  The target thread can be
     executing any code (Python or not).  However, if the target thread
     is executing the Python interpreter, the Python signal handlers
     will be *note executed by the main thread of the main interpreter:
     28d4.  Therefore, the only point of sending a signal to a
     particular Python thread would be to force a running system call to
     fail with *note InterruptedError: 74c.

     Use *note threading.get_ident(): b87. or the *note ident: 2175.
     attribute of *note threading.Thread: 21a. objects to get a suitable
     value for `thread_id'.

     If `signalnum' is 0, then no signal is sent, but error checking is
     still performed; this can be used to check if the target thread is
     still running.

     Raises an *note auditing event: fa1. ‘signal.pthread_kill’ with
     arguments ‘thread_id’, ‘signalnum’.

     *note Availability: 1491.: Unix.  See the man page
     ‘pthread_kill(3)’ for further information.

     See also *note os.kill(): db9.

     New in version 3.3.

 -- Function: signal.pthread_sigmask (how, mask)

     Fetch and/or change the signal mask of the calling thread.  The
     signal mask is the set of signals whose delivery is currently
     blocked for the caller.  Return the old signal mask as a set of
     signals.

     The behavior of the call is dependent on the value of `how', as
     follows.

        * *note SIG_BLOCK: 28d6.: The set of blocked signals is the
          union of the current set and the `mask' argument.

        * *note SIG_UNBLOCK: 28d7.: The signals in `mask' are removed
          from the current set of blocked signals.  It is permissible to
          attempt to unblock a signal which is not blocked.

        * *note SIG_SETMASK: 28d8.: The set of blocked signals is set to
          the `mask' argument.

     `mask' is a set of signal numbers (e.g.  {*note signal.SIGINT:
     2626, *note signal.SIGTERM: 26be.}).  Use *note valid_signals():
     28ed. for a full mask including all signals.

     For example, ‘signal.pthread_sigmask(signal.SIG_BLOCK, [])’ reads
     the signal mask of the calling thread.

     *note SIGKILL: 28e1. and ‘SIGSTOP’ cannot be blocked.

     *note Availability: 1491.: Unix.  See the man page ‘sigprocmask(3)’
     and ‘pthread_sigmask(3)’ for further information.

     See also *note pause(): 28ee, *note sigpending(): b56. and *note
     sigwait(): b57.

     New in version 3.3.

 -- Function: signal.setitimer (which, seconds, interval=0.0)

     Sets given interval timer (one of *note signal.ITIMER_REAL: 28e6,
     *note signal.ITIMER_VIRTUAL: 28e7. or *note signal.ITIMER_PROF:
     28e8.) specified by `which' to fire after `seconds' (float is
     accepted, different from *note alarm(): 28ec.) and after that every
     `interval' seconds (if `interval' is non-zero).  The interval timer
     specified by `which' can be cleared by setting `seconds' to zero.

     When an interval timer fires, a signal is sent to the process.  The
     signal sent is dependent on the timer being used; *note
     signal.ITIMER_REAL: 28e6. will deliver *note SIGALRM: 28db, *note
     signal.ITIMER_VIRTUAL: 28e7. sends ‘SIGVTALRM’, and *note
     signal.ITIMER_PROF: 28e8. will deliver ‘SIGPROF’.

     The old values are returned as a tuple: (delay, interval).

     Attempting to pass an invalid interval timer will cause an *note
     ItimerError: 28e9.

     *note Availability: 1491.: Unix.

 -- Function: signal.getitimer (which)

     Returns current value of a given interval timer specified by
     `which'.

     *note Availability: 1491.: Unix.

 -- Function: signal.set_wakeup_fd (fd, *, warn_on_full_buffer=True)

     Set the wakeup file descriptor to `fd'.  When a signal is received,
     the signal number is written as a single byte into the fd.  This
     can be used by a library to wakeup a poll or select call, allowing
     the signal to be fully processed.

     The old wakeup fd is returned (or -1 if file descriptor wakeup was
     not enabled).  If `fd' is -1, file descriptor wakeup is disabled.
     If not -1, `fd' must be non-blocking.  It is up to the library to
     remove any bytes from `fd' before calling poll or select again.

     When threads are enabled, this function can only be called from
     *note the main thread of the main interpreter: 28d4.; attempting to
     call it from other threads will cause a *note ValueError: 16d.
     exception to be raised.

     There are two common ways to use this function.  In both
     approaches, you use the fd to wake up when a signal arrives, but
     then they differ in how they determine `which' signal or signals
     have arrived.

     In the first approach, we read the data out of the fd’s buffer, and
     the byte values give you the signal numbers.  This is simple, but
     in rare cases it can run into a problem: generally the fd will have
     a limited amount of buffer space, and if too many signals arrive
     too quickly, then the buffer may become full, and some signals may
     be lost.  If you use this approach, then you should set
     ‘warn_on_full_buffer=True’, which will at least cause a warning to
     be printed to stderr when signals are lost.

     In the second approach, we use the wakeup fd `only' for wakeups,
     and ignore the actual byte values.  In this case, all we care about
     is whether the fd’s buffer is empty or non-empty; a full buffer
     doesn’t indicate a problem at all.  If you use this approach, then
     you should set ‘warn_on_full_buffer=False’, so that your users are
     not confused by spurious warning messages.

     Changed in version 3.5: On Windows, the function now also supports
     socket handles.

     Changed in version 3.7: Added ‘warn_on_full_buffer’ parameter.

 -- Function: signal.siginterrupt (signalnum, flag)

     Change system call restart behaviour: if `flag' is *note False:
     48f, system calls will be restarted when interrupted by signal
     `signalnum', otherwise system calls will be interrupted.  Returns
     nothing.

     *note Availability: 1491.: Unix.  See the man page
     ‘siginterrupt(3)’ for further information.

     Note that installing a signal handler with *note signal(): ea. will
     reset the restart behaviour to interruptible by implicitly calling
     ‘siginterrupt()’ with a true `flag' value for the given signal.

 -- Function: signal.signal (signalnum, handler)

     Set the handler for signal `signalnum' to the function `handler'.
     `handler' can be a callable Python object taking two arguments (see
     below), or one of the special values *note signal.SIG_IGN: 2628. or
     *note signal.SIG_DFL: 2627.  The previous signal handler will be
     returned (see the description of *note getsignal(): 28d9. above).
     (See the Unix man page ‘signal(2)’ for further information.)

     When threads are enabled, this function can only be called from
     *note the main thread of the main interpreter: 28d4.; attempting to
     call it from other threads will cause a *note ValueError: 16d.
     exception to be raised.

     The `handler' is called with two arguments: the signal number and
     the current stack frame (‘None’ or a frame object; for a
     description of frame objects, see the *note description in the type
     hierarchy: 1565. or see the attribute descriptions in the *note
     inspect: a0. module).

     On Windows, *note signal(): ea. can only be called with *note
     SIGABRT: 28da, *note SIGFPE: 28d1, *note SIGILL: 28e0, *note
     SIGINT: 2626, *note SIGSEGV: 28d2, *note SIGTERM: 26be, or *note
     SIGBREAK: 28dc.  A *note ValueError: 16d. will be raised in any
     other case.  Note that not all systems define the same set of
     signal names; an *note AttributeError: 4a2. will be raised if a
     signal name is not defined as ‘SIG*’ module level constant.

 -- Function: signal.sigpending ()

     Examine the set of signals that are pending for delivery to the
     calling thread (i.e., the signals which have been raised while
     blocked).  Return the set of the pending signals.

     *note Availability: 1491.: Unix.  See the man page ‘sigpending(2)’
     for further information.

     See also *note pause(): 28ee, *note pthread_sigmask(): b54. and
     *note sigwait(): b57.

     New in version 3.3.

 -- Function: signal.sigwait (sigset)

     Suspend execution of the calling thread until the delivery of one
     of the signals specified in the signal set `sigset'.  The function
     accepts the signal (removes it from the pending list of signals),
     and returns the signal number.

     *note Availability: 1491.: Unix.  See the man page ‘sigwait(3)’ for
     further information.

     See also *note pause(): 28ee, *note pthread_sigmask(): b54, *note
     sigpending(): b56, *note sigwaitinfo(): 772. and *note
     sigtimedwait(): 771.

     New in version 3.3.

 -- Function: signal.sigwaitinfo (sigset)

     Suspend execution of the calling thread until the delivery of one
     of the signals specified in the signal set `sigset'.  The function
     accepts the signal and removes it from the pending list of signals.
     If one of the signals in `sigset' is already pending for the
     calling thread, the function will return immediately with
     information about that signal.  The signal handler is not called
     for the delivered signal.  The function raises an *note
     InterruptedError: 74c. if it is interrupted by a signal that is not
     in `sigset'.

     The return value is an object representing the data contained in
     the ‘siginfo_t’ structure, namely: ‘si_signo’, ‘si_code’,
     ‘si_errno’, ‘si_pid’, ‘si_uid’, ‘si_status’, ‘si_band’.

     *note Availability: 1491.: Unix.  See the man page ‘sigwaitinfo(2)’
     for further information.

     See also *note pause(): 28ee, *note sigwait(): b57. and *note
     sigtimedwait(): 771.

     New in version 3.3.

     Changed in version 3.5: The function is now retried if interrupted
     by a signal not in `sigset' and the signal handler does not raise
     an exception (see PEP 475(1) for the rationale).

 -- Function: signal.sigtimedwait (sigset, timeout)

     Like *note sigwaitinfo(): 772, but takes an additional `timeout'
     argument specifying a timeout.  If `timeout' is specified as ‘0’, a
     poll is performed.  Returns *note None: 203. if a timeout occurs.

     *note Availability: 1491.: Unix.  See the man page
     ‘sigtimedwait(2)’ for further information.

     See also *note pause(): 28ee, *note sigwait(): b57. and *note
     sigwaitinfo(): 772.

     New in version 3.3.

     Changed in version 3.5: The function is now retried with the
     recomputed `timeout' if interrupted by a signal not in `sigset' and
     the signal handler does not raise an exception (see PEP 475(2) for
     the rationale).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0475

   (2) https://www.python.org/dev/peps/pep-0475


File: python.info,  Node: Example<9>,  Next: Note on SIGPIPE,  Prev: Module contents<2>,  Up: signal — Set handlers for asynchronous events

5.18.8.5 Example
................

Here is a minimal example program.  It uses the *note alarm(): 28ec.
function to limit the time spent waiting to open a file; this is useful
if the file is for a serial device that may not be turned on, which
would normally cause the *note os.open(): 758. to hang indefinitely.
The solution is to set a 5-second alarm before opening the file; if the
operation takes too long, the alarm signal will be sent, and the handler
raises an exception.

     import signal, os

     def handler(signum, frame):
         print('Signal handler called with signal', signum)
         raise OSError("Couldn't open device!")

     # Set the signal handler and a 5-second alarm
     signal.signal(signal.SIGALRM, handler)
     signal.alarm(5)

     # This open() may hang indefinitely
     fd = os.open('/dev/ttyS0', os.O_RDWR)

     signal.alarm(0)          # Disable the alarm


File: python.info,  Node: Note on SIGPIPE,  Prev: Example<9>,  Up: signal — Set handlers for asynchronous events

5.18.8.6 Note on SIGPIPE
........................

Piping output of your program to tools like ‘head(1)’ will cause a *note
SIGPIPE: 28cd. signal to be sent to your process when the receiver of
its standard output closes early.  This results in an exception like
‘BrokenPipeError: [Errno 32] Broken pipe’.  To handle this case, wrap
your entry point to catch this exception as follows:

     import os
     import sys

     def main():
         try:
             # simulate large output (your code replaces this loop)
             for x in range(10000):
                 print("y")
             # flush output here to force SIGPIPE to be triggered
             # while inside this try block.
             sys.stdout.flush()
         except BrokenPipeError:
             # Python flushes standard streams on exit; redirect remaining output
             # to devnull to avoid another BrokenPipeError at shutdown
             devnull = os.open(os.devnull, os.O_WRONLY)
             os.dup2(devnull, sys.stdout.fileno())
             sys.exit(1)  # Python exits with error code 1 on EPIPE

     if __name__ == '__main__':
         main()

Do not set *note SIGPIPE: 28cd.’s disposition to *note SIG_DFL: 2627. in
order to avoid *note BrokenPipeError: a7e.  Doing that would cause your
program to exit unexpectedly also whenever any socket connection is
interrupted while your program is still writing to it.


File: python.info,  Node: mmap — Memory-mapped file support,  Prev: signal — Set handlers for asynchronous events,  Up: Networking and Interprocess Communication

5.18.9 ‘mmap’ — Memory-mapped file support
------------------------------------------

__________________________________________________________________

Memory-mapped file objects behave like both *note bytearray: 173. and
like *note file objects: c14.  You can use mmap objects in most places
where *note bytearray: 173. are expected; for example, you can use the
*note re: dd. module to search through a memory-mapped file.  You can
also change a single byte by doing ‘obj[index] = 97’, or change a
subsequence by assigning to a slice: ‘obj[i1:i2] = b'...'’.  You can
also read and write data starting at the current file position, and
‘seek()’ through the file to different positions.

A memory-mapped file is created by the *note mmap: 31c. constructor,
which is different on Unix and on Windows.  In either case you must
provide a file descriptor for a file opened for update.  If you wish to
map an existing Python file object, use its ‘fileno()’ method to obtain
the correct value for the `fileno' parameter.  Otherwise, you can open
the file using the *note os.open(): 758. function, which returns a file
descriptor directly (the file still needs to be closed when done).

     Note: If you want to create a memory-mapping for a writable,
     buffered file, you should *note flush(): 2149. the file first.
     This is necessary to ensure that local modifications to the buffers
     are actually available to the mapping.

For both the Unix and Windows versions of the constructor, `access' may
be specified as an optional keyword parameter.  `access' accepts one of
four values: ‘ACCESS_READ’, ‘ACCESS_WRITE’, or ‘ACCESS_COPY’ to specify
read-only, write-through or copy-on-write memory respectively, or
‘ACCESS_DEFAULT’ to defer to `prot'.  `access' can be used on both Unix
and Windows.  If `access' is not specified, Windows mmap returns a
write-through mapping.  The initial memory values for all three access
types are taken from the specified file.  Assignment to an ‘ACCESS_READ’
memory map raises a *note TypeError: 1fe. exception.  Assignment to an
‘ACCESS_WRITE’ memory map affects both memory and the underlying file.
Assignment to an ‘ACCESS_COPY’ memory map affects memory but does not
update the underlying file.

Changed in version 3.7: Added ‘ACCESS_DEFAULT’ constant.

To map anonymous memory, -1 should be passed as the fileno along with
the length.

 -- Class: mmap.mmap (fileno, length, tagname=None,
          access=ACCESS_DEFAULT[, offset])

     `(Windows version)' Maps `length' bytes from the file specified by
     the file handle `fileno', and creates a mmap object.  If `length'
     is larger than the current size of the file, the file is extended
     to contain `length' bytes.  If `length' is ‘0’, the maximum length
     of the map is the current size of the file, except that if the file
     is empty Windows raises an exception (you cannot create an empty
     mapping on Windows).

     `tagname', if specified and not ‘None’, is a string giving a tag
     name for the mapping.  Windows allows you to have many different
     mappings against the same file.  If you specify the name of an
     existing tag, that tag is opened, otherwise a new tag of this name
     is created.  If this parameter is omitted or ‘None’, the mapping is
     created without a name.  Avoiding the use of the tag parameter will
     assist in keeping your code portable between Unix and Windows.

     `offset' may be specified as a non-negative integer offset.  mmap
     references will be relative to the offset from the beginning of the
     file.  `offset' defaults to 0.  `offset' must be a multiple of the
     ‘ALLOCATIONGRANULARITY’.

     Raises an *note auditing event: fa1. ‘mmap.__new__’ with arguments
     ‘fileno’, ‘length’, ‘access’, ‘offset’.

 -- Class: mmap.mmap (fileno, length, flags=MAP_SHARED,
          prot=PROT_WRITE|PROT_READ, access=ACCESS_DEFAULT[, offset])

     `(Unix version)' Maps `length' bytes from the file specified by the
     file descriptor `fileno', and returns a mmap object.  If `length'
     is ‘0’, the maximum length of the map will be the current size of
     the file when *note mmap: 31c. is called.

     `flags' specifies the nature of the mapping.  ‘MAP_PRIVATE’ creates
     a private copy-on-write mapping, so changes to the contents of the
     mmap object will be private to this process, and ‘MAP_SHARED’
     creates a mapping that’s shared with all other processes mapping
     the same areas of the file.  The default value is ‘MAP_SHARED’.

     `prot', if specified, gives the desired memory protection; the two
     most useful values are ‘PROT_READ’ and ‘PROT_WRITE’, to specify
     that the pages may be read or written.  `prot' defaults to
     ‘PROT_READ | PROT_WRITE’.

     `access' may be specified in lieu of `flags' and `prot' as an
     optional keyword parameter.  It is an error to specify both
     `flags', `prot' and `access'.  See the description of `access'
     above for information on how to use this parameter.

     `offset' may be specified as a non-negative integer offset.  mmap
     references will be relative to the offset from the beginning of the
     file.  `offset' defaults to 0.  `offset' must be a multiple of
     ‘ALLOCATIONGRANULARITY’ which is equal to ‘PAGESIZE’ on Unix
     systems.

     To ensure validity of the created memory mapping the file specified
     by the descriptor `fileno' is internally automatically synchronized
     with physical backing store on macOS and OpenVMS.

     This example shows a simple way of using *note mmap: 31c.:

          import mmap

          # write a simple example file
          with open("hello.txt", "wb") as f:
              f.write(b"Hello Python!\n")

          with open("hello.txt", "r+b") as f:
              # memory-map the file, size 0 means whole file
              mm = mmap.mmap(f.fileno(), 0)
              # read content via standard file methods
              print(mm.readline())  # prints b"Hello Python!\n"
              # read content via slice notation
              print(mm[:5])  # prints b"Hello"
              # update content using slice notation;
              # note that new content must have same size
              mm[6:] = b" world!\n"
              # ... and read again using standard file methods
              mm.seek(0)
              print(mm.readline())  # prints b"Hello  world!\n"
              # close the map
              mm.close()

     *note mmap: 31c. can also be used as a context manager in a *note
     with: 7da. statement:

          import mmap

          with mmap.mmap(-1, 13) as mm:
              mm.write(b"Hello world!")

     New in version 3.2: Context manager support.

     The next example demonstrates how to create an anonymous map and
     exchange data between the parent and child processes:

          import mmap
          import os

          mm = mmap.mmap(-1, 13)
          mm.write(b"Hello world!")

          pid = os.fork()

          if pid == 0:  # In a child process
              mm.seek(0)
              print(mm.readline())

              mm.close()

     Raises an *note auditing event: fa1. ‘mmap.__new__’ with arguments
     ‘fileno’, ‘length’, ‘access’, ‘offset’.

     Memory-mapped file objects support the following methods:

      -- Method: close ()

          Closes the mmap.  Subsequent calls to other methods of the
          object will result in a ValueError exception being raised.
          This will not close the open file.

      -- Attribute: closed

          ‘True’ if the file is closed.

          New in version 3.2.

      -- Method: find (sub[, start[, end]])

          Returns the lowest index in the object where the subsequence
          `sub' is found, such that `sub' is contained in the range
          [`start', `end'].  Optional arguments `start' and `end' are
          interpreted as in slice notation.  Returns ‘-1’ on failure.

          Changed in version 3.5: Writable *note bytes-like object: 6df.
          is now accepted.

      -- Method: flush ([offset[, size]])

          Flushes changes made to the in-memory copy of a file back to
          disk.  Without use of this call there is no guarantee that
          changes are written back before the object is destroyed.  If
          `offset' and `size' are specified, only changes to the given
          range of bytes will be flushed to disk; otherwise, the whole
          extent of the mapping is flushed.  `offset' must be a multiple
          of the ‘PAGESIZE’ or ‘ALLOCATIONGRANULARITY’.

          ‘None’ is returned to indicate success.  An exception is
          raised when the call failed.

          Changed in version 3.8: Previously, a nonzero value was
          returned on success; zero was returned on error under Windows.
          A zero value was returned on success; an exception was raised
          on error under Unix.

      -- Method: madvise (option[, start[, length]])

          Send advice `option' to the kernel about the memory region
          beginning at `start' and extending `length' bytes.  `option'
          must be one of the *note MADV_* constants: 28f8. available on
          the system.  If `start' and `length' are omitted, the entire
          mapping is spanned.  On some systems (including Linux),
          `start' must be a multiple of the ‘PAGESIZE’.

          Availability: Systems with the ‘madvise()’ system call.

          New in version 3.8.

      -- Method: move (dest, src, count)

          Copy the `count' bytes starting at offset `src' to the
          destination index `dest'.  If the mmap was created with
          ‘ACCESS_READ’, then calls to move will raise a *note
          TypeError: 1fe. exception.

      -- Method: read ([n])

          Return a *note bytes: 172. containing up to `n' bytes starting
          from the current file position.  If the argument is omitted,
          ‘None’ or negative, return all bytes from the current file
          position to the end of the mapping.  The file position is
          updated to point after the bytes that were returned.

          Changed in version 3.3: Argument can be omitted or ‘None’.

      -- Method: read_byte ()

          Returns a byte at the current file position as an integer, and
          advances the file position by 1.

      -- Method: readline ()

          Returns a single line, starting at the current file position
          and up to the next newline.  The file position is updated to
          point after the bytes that were returned.

      -- Method: resize (newsize)

          Resizes the map and the underlying file, if any.  If the mmap
          was created with ‘ACCESS_READ’ or ‘ACCESS_COPY’, resizing the
          map will raise a *note TypeError: 1fe. exception.

      -- Method: rfind (sub[, start[, end]])

          Returns the highest index in the object where the subsequence
          `sub' is found, such that `sub' is contained in the range
          [`start', `end'].  Optional arguments `start' and `end' are
          interpreted as in slice notation.  Returns ‘-1’ on failure.

          Changed in version 3.5: Writable *note bytes-like object: 6df.
          is now accepted.

      -- Method: seek (pos[, whence])

          Set the file’s current position.  `whence' argument is
          optional and defaults to ‘os.SEEK_SET’ or ‘0’ (absolute file
          positioning); other values are ‘os.SEEK_CUR’ or ‘1’ (seek
          relative to the current position) and ‘os.SEEK_END’ or ‘2’
          (seek relative to the file’s end).

      -- Method: size ()

          Return the length of the file, which can be larger than the
          size of the memory-mapped area.

      -- Method: tell ()

          Returns the current position of the file pointer.

      -- Method: write (bytes)

          Write the bytes in `bytes' into memory at the current position
          of the file pointer and return the number of bytes written
          (never less than ‘len(bytes)’, since if the write fails, a
          *note ValueError: 16d. will be raised).  The file position is
          updated to point after the bytes that were written.  If the
          mmap was created with ‘ACCESS_READ’, then writing to it will
          raise a *note TypeError: 1fe. exception.

          Changed in version 3.5: Writable *note bytes-like object: 6df.
          is now accepted.

          Changed in version 3.6: The number of bytes written is now
          returned.

      -- Method: write_byte (byte)

          Write the integer `byte' into memory at the current position
          of the file pointer; the file position is advanced by ‘1’.  If
          the mmap was created with ‘ACCESS_READ’, then writing to it
          will raise a *note TypeError: 1fe. exception.

* Menu:

* MADV_* Constants::


File: python.info,  Node: MADV_* Constants,  Up: mmap — Memory-mapped file support

5.18.9.1 MADV_* Constants
.........................

 -- Data: mmap.MADV_NORMAL
 -- Data: mmap.MADV_RANDOM
 -- Data: mmap.MADV_SEQUENTIAL
 -- Data: mmap.MADV_WILLNEED
 -- Data: mmap.MADV_DONTNEED
 -- Data: mmap.MADV_REMOVE
 -- Data: mmap.MADV_DONTFORK
 -- Data: mmap.MADV_DOFORK
 -- Data: mmap.MADV_HWPOISON
 -- Data: mmap.MADV_MERGEABLE
 -- Data: mmap.MADV_UNMERGEABLE
 -- Data: mmap.MADV_SOFT_OFFLINE
 -- Data: mmap.MADV_HUGEPAGE
 -- Data: mmap.MADV_NOHUGEPAGE
 -- Data: mmap.MADV_DONTDUMP
 -- Data: mmap.MADV_DODUMP
 -- Data: mmap.MADV_FREE
 -- Data: mmap.MADV_NOSYNC
 -- Data: mmap.MADV_AUTOSYNC
 -- Data: mmap.MADV_NOCORE
 -- Data: mmap.MADV_CORE
 -- Data: mmap.MADV_PROTECT

     These options can be passed to *note mmap.madvise(): 31d.  Not
     every option will be present on every system.

     Availability: Systems with the madvise() system call.

     New in version 3.8.


File: python.info,  Node: Internet Data Handling,  Next: Structured Markup Processing Tools,  Prev: Networking and Interprocess Communication,  Up: The Python Standard Library

5.19 Internet Data Handling
===========================

This chapter describes modules which support handling data formats
commonly used on the Internet.

* Menu:

* email — An email and MIME handling package::
* json — JSON encoder and decoder::
* mailcap — Mailcap file handling::
* mailbox — Manipulate mailboxes in various formats::
* mimetypes — Map filenames to MIME types::
* base64 — Base16, Base32, Base64, Base85 Data Encodings: base64 — Base16 Base32 Base64 Base85 Data Encodings.
* binhex — Encode and decode binhex4 files::
* binascii — Convert between binary and ASCII::
* quopri — Encode and decode MIME quoted-printable data::
* uu — Encode and decode uuencode files::


File: python.info,  Node: email — An email and MIME handling package,  Next: json — JSON encoder and decoder,  Up: Internet Data Handling

5.19.1 ‘email’ — An email and MIME handling package
---------------------------------------------------

`Source code:' Lib/email/__init__.py(1)

__________________________________________________________________

The *note email: 67. package is a library for managing email messages.
It is specifically `not' designed to do any sending of email messages to
SMTP ( RFC 2821(2)), NNTP, or other servers; those are functions of
modules such as *note smtplib: ed. and *note nntplib: c0.  The *note
email: 67. package attempts to be as RFC-compliant as possible,
supporting RFC 5322(3) and RFC 6532(4), as well as such MIME-related
RFCs as RFC 2045(5), RFC 2046(6), RFC 2047(7), RFC 2183(8), and RFC
2231(9).

The overall structure of the email package can be divided into three
major components, plus a fourth component that controls the behavior of
the other components.

The central component of the package is an “object model” that
represents email messages.  An application interacts with the package
primarily through the object model interface defined in the *note
message: 70. sub-module.  The application can use this API to ask
questions about an existing email, to construct a new email, or to add
or remove email subcomponents that themselves use the same object model
interface.  That is, following the nature of email messages and their
MIME subcomponents, the email object model is a tree structure of
objects that all provide the *note EmailMessage: 63c. API.

The other two major components of the package are the *note parser: 72.
and the *note generator: 6c.  The parser takes the serialized version of
an email message (a stream of bytes) and converts it into a tree of
*note EmailMessage: 63c. objects.  The generator takes an *note
EmailMessage: 63c. and turns it back into a serialized byte stream.
(The parser and generator also handle streams of text characters, but
this usage is discouraged as it is too easy to end up with messages that
are not valid in one way or another.)

The control component is the *note policy: 73. module.  Every *note
EmailMessage: 63c, every *note generator: 6c, and every *note parser:
72. has an associated *note policy: 73. object that controls its
behavior.  Usually an application only needs to specify the policy when
an *note EmailMessage: 63c. is created, either by directly instantiating
an *note EmailMessage: 63c. to create a new email, or by parsing an
input stream using a *note parser: 72.  But the policy can be changed
when the message is serialized using a *note generator: 6c.  This
allows, for example, a generic email message to be parsed from disk, but
to serialize it using standard SMTP settings when sending it to an email
server.

The email package does its best to hide the details of the various
governing RFCs from the application.  Conceptually the application
should be able to treat the email message as a structured tree of
unicode text and binary attachments, without having to worry about how
these are represented when serialized.  In practice, however, it is
often necessary to be aware of at least some of the rules governing MIME
messages and their structure, specifically the names and nature of the
MIME “content types” and how they identify multipart documents.  For the
most part this knowledge should only be required for more complex
applications, and even then it should only be the high level structure
in question, and not the details of how those structures are
represented.  Since MIME content types are used widely in modern
internet software (not just email), this will be a familiar concept to
many programmers.

The following sections describe the functionality of the *note email:
67. package.  We start with the *note message: 70. object model, which
is the primary interface an application will use, and follow that with
the *note parser: 72. and *note generator: 6c. components.  Then we
cover the *note policy: 73. controls, which completes the treatment of
the main components of the library.

The next three sections cover the exceptions the package may raise and
the defects (non-compliance with the RFCs) that the *note parser: 72.
may detect.  Then we cover the *note headerregistry: 6e. and the *note
contentmanager: 69. sub-components, which provide tools for doing more
detailed manipulation of headers and payloads, respectively.  Both of
these components contain features relevant to consuming and producing
non-trivial messages, but also document their extensibility APIs, which
will be of interest to advanced applications.

Following those is a set of examples of using the fundamental parts of
the APIs covered in the preceding sections.

The foregoing represent the modern (unicode friendly) API of the email
package.  The remaining sections, starting with the *note Message: 63b.
class, cover the legacy *note compat32: 63a. API that deals much more
directly with the details of how email messages are represented.  The
*note compat32: 63a. API does `not' hide the details of the RFCs from
the application, but for applications that need to operate at that
level, they can be useful tools.  This documentation is also relevant
for applications that are still using the *note compat32: 63a. API for
backward compatibility reasons.

Changed in version 3.6: Docs reorganized and rewritten to promote the
new *note EmailMessage: 63c./*note EmailPolicy: ad7. API.

Contents of the *note email: 67. package documentation:

* Menu:

* email.message; Representing an email message: email message Representing an email message.
* email.parser; Parsing email messages: email parser Parsing email messages.
* email.generator; Generating MIME documents: email generator Generating MIME documents.
* email.policy; Policy Objects: email policy Policy Objects.
* email.errors; Exception and Defect classes: email errors Exception and Defect classes.
* email.headerregistry; Custom Header Objects: email headerregistry Custom Header Objects.
* email.contentmanager; Managing MIME Content: email contentmanager Managing MIME Content.
* email; Examples: email Examples.
* email.message.Message; Representing an email message using the compat32 API: email message Message Representing an email message using the compat32 API.
* email.mime; Creating email and MIME objects from scratch: email mime Creating email and MIME objects from scratch.
* email.header; Internationalized headers: email header Internationalized headers.
* email.charset; Representing character sets: email charset Representing character sets.
* email.encoders; Encoders: email encoders Encoders.
* email.utils; Miscellaneous utilities: email utils Miscellaneous utilities.
* email.iterators; Iterators: email iterators Iterators.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/email/__init__.py

   (2) https://tools.ietf.org/html/rfc2821.html

   (3) https://tools.ietf.org/html/rfc5322.html

   (4) https://tools.ietf.org/html/rfc6532.html

   (5) https://tools.ietf.org/html/rfc2045.html

   (6) https://tools.ietf.org/html/rfc2046.html

   (7) https://tools.ietf.org/html/rfc2047.html

   (8) https://tools.ietf.org/html/rfc2183.html

   (9) https://tools.ietf.org/html/rfc2231.html


File: python.info,  Node: email message Representing an email message,  Next: email parser Parsing email messages,  Up: email — An email and MIME handling package

5.19.1.1 ‘email.message’: Representing an email message
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`Source code:' Lib/email/message.py(1)

__________________________________________________________________

New in version 3.6: (2)

The central class in the *note email: 67. package is the *note
EmailMessage: 63c. class, imported from the *note email.message: 70.
module.  It is the base class for the *note email: 67. object model.
*note EmailMessage: 63c. provides the core functionality for setting and
querying header fields, for accessing message bodies, and for creating
or modifying structured messages.

An email message consists of `headers' and a `payload' (which is also
referred to as the `content').  Headers are RFC 5322(3) or RFC 6532(4)
style field names and values, where the field name and value are
separated by a colon.  The colon is not part of either the field name or
the field value.  The payload may be a simple text message, or a binary
object, or a structured sequence of sub-messages each with their own set
of headers and their own payload.  The latter type of payload is
indicated by the message having a MIME type such as ‘multipart/*’ or
‘message/rfc822’.

The conceptual model provided by an *note EmailMessage: 63c. object is
that of an ordered dictionary of headers coupled with a `payload' that
represents the RFC 5322(5) body of the message, which might be a list of
sub-‘EmailMessage’ objects.  In addition to the normal dictionary
methods for accessing the header names and values, there are methods for
accessing specialized information from the headers (for example the MIME
content type), for operating on the payload, for generating a serialized
version of the message, and for recursively walking over the object
tree.

The *note EmailMessage: 63c. dictionary-like interface is indexed by the
header names, which must be ASCII values.  The values of the dictionary
are strings with some extra methods.  Headers are stored and returned in
case-preserving form, but field names are matched case-insensitively.
Unlike a real dict, there is an ordering to the keys, and there can be
duplicate keys.  Additional methods are provided for working with
headers that have duplicate keys.

The `payload' is either a string or bytes object, in the case of simple
message objects, or a list of *note EmailMessage: 63c. objects, for MIME
container documents such as ‘multipart/*’ and ‘message/rfc822’ message
objects.

 -- Class: email.message.EmailMessage (policy=default)

     If `policy' is specified use the rules it specifies to update and
     serialize the representation of the message.  If `policy' is not
     set, use the *note default: 2922. policy, which follows the rules
     of the email RFCs except for line endings (instead of the RFC
     mandated ‘\r\n’, it uses the Python standard ‘\n’ line endings).
     For more information see the *note policy: 73. documentation.

      -- Method: as_string (unixfrom=False, maxheaderlen=None,
               policy=None)

          Return the entire message flattened as a string.  When
          optional `unixfrom' is true, the envelope header is included
          in the returned string.  `unixfrom' defaults to ‘False’.  For
          backward compatibility with the base *note Message: 63b. class
          `maxheaderlen' is accepted, but defaults to ‘None’, which
          means that by default the line length is controlled by the
          ‘max_line_length’ of the policy.  The `policy' argument may be
          used to override the default policy obtained from the message
          instance.  This can be used to control some of the formatting
          produced by the method, since the specified `policy' will be
          passed to the *note Generator: c1e.

          Flattening the message may trigger changes to the *note
          EmailMessage: 63c. if defaults need to be filled in to
          complete the transformation to a string (for example, MIME
          boundaries may be generated or modified).

          Note that this method is provided as a convenience and may not
          be the most useful way to serialize messages in your
          application, especially if you are dealing with multiple
          messages.  See *note email.generator.Generator: c1e. for a
          more flexible API for serializing messages.  Note also that
          this method is restricted to producing messages serialized as
          “7 bit clean” when *note utf8: 7c5. is ‘False’, which is the
          default.

          Changed in version 3.6: the default behavior when
          `maxheaderlen' is not specified was changed from defaulting to
          0 to defaulting to the value of `max_line_length' from the
          policy.

      -- Method: __str__ ()

          Equivalent to
          ‘as_string(policy=self.policy.clone(utf8=True))’.  Allows
          ‘str(msg)’ to produce a string containing the serialized
          message in a readable format.

          Changed in version 3.4: the method was changed to use
          ‘utf8=True’, thus producing an RFC 6531(6)-like message
          representation, instead of being a direct alias for *note
          as_string(): 2923.

      -- Method: as_bytes (unixfrom=False, policy=None)

          Return the entire message flattened as a bytes object.  When
          optional `unixfrom' is true, the envelope header is included
          in the returned string.  `unixfrom' defaults to ‘False’.  The
          `policy' argument may be used to override the default policy
          obtained from the message instance.  This can be used to
          control some of the formatting produced by the method, since
          the specified `policy' will be passed to the *note
          BytesGenerator: c1f.

          Flattening the message may trigger changes to the *note
          EmailMessage: 63c. if defaults need to be filled in to
          complete the transformation to a string (for example, MIME
          boundaries may be generated or modified).

          Note that this method is provided as a convenience and may not
          be the most useful way to serialize messages in your
          application, especially if you are dealing with multiple
          messages.  See *note email.generator.BytesGenerator: c1f. for
          a more flexible API for serializing messages.

      -- Method: __bytes__ ()

          Equivalent to *note as_bytes(): 2925.  Allows ‘bytes(msg)’ to
          produce a bytes object containing the serialized message.

      -- Method: is_multipart ()

          Return ‘True’ if the message’s payload is a list of sub-*note
          EmailMessage: 63c. objects, otherwise return ‘False’.  When
          *note is_multipart(): 2927. returns ‘False’, the payload
          should be a string object (which might be a CTE encoded binary
          payload).  Note that *note is_multipart(): 2927. returning
          ‘True’ does not necessarily mean that
          “msg.get_content_maintype() == ‘multipart’” will return the
          ‘True’.  For example, ‘is_multipart’ will return ‘True’ when
          the *note EmailMessage: 63c. is of type ‘message/rfc822’.

      -- Method: set_unixfrom (unixfrom)

          Set the message’s envelope header to `unixfrom', which should
          be a string.  (See *note mboxMessage: 2929. for a brief
          description of this header.)

      -- Method: get_unixfrom ()

          Return the message’s envelope header.  Defaults to ‘None’ if
          the envelope header was never set.

     The following methods implement the mapping-like interface for
     accessing the message’s headers.  Note that there are some semantic
     differences between these methods and a normal mapping (i.e.
     dictionary) interface.  For example, in a dictionary there are no
     duplicate keys, but here there may be duplicate message headers.
     Also, in dictionaries there is no guaranteed order to the keys
     returned by *note keys(): 292b, but in an *note EmailMessage: 63c.
     object, headers are always returned in the order they appeared in
     the original message, or in which they were added to the message
     later.  Any header deleted and then re-added is always appended to
     the end of the header list.

     These semantic differences are intentional and are biased toward
     convenience in the most common use cases.

     Note that in all cases, any envelope header present in the message
     is not included in the mapping interface.

      -- Method: __len__ ()

          Return the total number of headers, including duplicates.

      -- Method: __contains__ (name)

          Return ‘True’ if the message object has a field named `name'.
          Matching is done without regard to case and `name' does not
          include the trailing colon.  Used for the ‘in’ operator.  For
          example:

               if 'message-id' in myMessage:
                  print('Message-ID:', myMessage['message-id'])

      -- Method: __getitem__ (name)

          Return the value of the named header field.  `name' does not
          include the colon field separator.  If the header is missing,
          ‘None’ is returned; a *note KeyError: 3e9. is never raised.

          Note that if the named field appears more than once in the
          message’s headers, exactly which of those field values will be
          returned is undefined.  Use the *note get_all(): 292f. method
          to get the values of all the extant headers named `name'.

          Using the standard (non-‘compat32’) policies, the returned
          value is an instance of a subclass of *note
          email.headerregistry.BaseHeader: 2930.

      -- Method: __setitem__ (name, val)

          Add a header to the message with field name `name' and value
          `val'.  The field is appended to the end of the message’s
          existing headers.

          Note that this does `not' overwrite or delete any existing
          header with the same name.  If you want to ensure that the new
          header is the only one present in the message with field name
          `name', delete the field first, e.g.:

               del msg['subject']
               msg['subject'] = 'Python roolz!'

          If the ‘policy’ defines certain headers to be unique (as the
          standard policies do), this method may raise a *note
          ValueError: 16d. when an attempt is made to assign a value to
          such a header when one already exists.  This behavior is
          intentional for consistency’s sake, but do not depend on it as
          we may choose to make such assignments do an automatic
          deletion of the existing header in the future.

      -- Method: __delitem__ (name)

          Delete all occurrences of the field with name `name' from the
          message’s headers.  No exception is raised if the named field
          isn’t present in the headers.

      -- Method: keys ()

          Return a list of all the message’s header field names.

      -- Method: values ()

          Return a list of all the message’s field values.

      -- Method: items ()

          Return a list of 2-tuples containing all the message’s field
          headers and values.

      -- Method: get (name, failobj=None)

          Return the value of the named header field.  This is identical
          to *note __getitem__(): 292e. except that optional `failobj'
          is returned if the named header is missing (`failobj' defaults
          to ‘None’).

     Here are some additional useful header related methods:

      -- Method: get_all (name, failobj=None)

          Return a list of all the values for the field named `name'.
          If there are no such named headers in the message, `failobj'
          is returned (defaults to ‘None’).

      -- Method: add_header (_name, _value, **_params)

          Extended header setting.  This method is similar to *note
          __setitem__(): 2931. except that additional header parameters
          can be provided as keyword arguments.  `_name' is the header
          field to add and `_value' is the `primary' value for the
          header.

          For each item in the keyword argument dictionary `_params',
          the key is taken as the parameter name, with underscores
          converted to dashes (since dashes are illegal in Python
          identifiers).  Normally, the parameter will be added as
          ‘key="value"’ unless the value is ‘None’, in which case only
          the key will be added.

          If the value contains non-ASCII characters, the charset and
          language may be explicitly controlled by specifying the value
          as a three tuple in the format ‘(CHARSET, LANGUAGE, VALUE)’,
          where ‘CHARSET’ is a string naming the charset to be used to
          encode the value, ‘LANGUAGE’ can usually be set to ‘None’ or
          the empty string (see RFC 2231(7) for other possibilities),
          and ‘VALUE’ is the string value containing non-ASCII code
          points.  If a three tuple is not passed and the value contains
          non-ASCII characters, it is automatically encoded in RFC
          2231(8) format using a ‘CHARSET’ of ‘utf-8’ and a ‘LANGUAGE’
          of ‘None’.

          Here is an example:

               msg.add_header('Content-Disposition', 'attachment', filename='bud.gif')

          This will add a header that looks like

               Content-Disposition: attachment; filename="bud.gif"

          An example of the extended interface with non-ASCII
          characters:

               msg.add_header('Content-Disposition', 'attachment',
                              filename=('iso-8859-1', '', 'Fußballer.ppt'))

      -- Method: replace_header (_name, _value)

          Replace a header.  Replace the first header found in the
          message that matches `_name', retaining header order and field
          name case of the original header.  If no matching header is
          found, raise a *note KeyError: 3e9.

      -- Method: get_content_type ()

          Return the message’s content type, coerced to lower case of
          the form ‘maintype/subtype’.  If there is no ‘Content-Type’
          header in the message return the value returned by *note
          get_default_type(): 2939.  If the ‘Content-Type’ header is
          invalid, return ‘text/plain’.

          (According to RFC 2045(9), messages always have a default
          type, *note get_content_type(): 2938. will always return a
          value.  RFC 2045(10) defines a message’s default type to be
          ‘text/plain’ unless it appears inside a ‘multipart/digest’
          container, in which case it would be ‘message/rfc822’.  If the
          ‘Content-Type’ header has an invalid type specification, RFC
          2045(11) mandates that the default type be ‘text/plain’.)

      -- Method: get_content_maintype ()

          Return the message’s main content type.  This is the
          ‘maintype’ part of the string returned by *note
          get_content_type(): 2938.

      -- Method: get_content_subtype ()

          Return the message’s sub-content type.  This is the ‘subtype’
          part of the string returned by *note get_content_type(): 2938.

      -- Method: get_default_type ()

          Return the default content type.  Most messages have a default
          content type of ‘text/plain’, except for messages that are
          subparts of ‘multipart/digest’ containers.  Such subparts have
          a default content type of ‘message/rfc822’.

      -- Method: set_default_type (ctype)

          Set the default content type.  `ctype' should either be
          ‘text/plain’ or ‘message/rfc822’, although this is not
          enforced.  The default content type is not stored in the
          ‘Content-Type’ header, so it only affects the return value of
          the ‘get_content_type’ methods when no ‘Content-Type’ header
          is present in the message.

      -- Method: set_param (param, value, header='Content-Type',
               requote=True, charset=None, language='', replace=False)

          Set a parameter in the ‘Content-Type’ header.  If the
          parameter already exists in the header, replace its value with
          `value'.  When `header' is ‘Content-Type’ (the default) and
          the header does not yet exist in the message, add it, set its
          value to ‘text/plain’, and append the new parameter value.
          Optional `header' specifies an alternative header to
          ‘Content-Type’.

          If the value contains non-ASCII characters, the charset and
          language may be explicitly specified using the optional
          `charset' and `language' parameters.  Optional `language'
          specifies the RFC 2231(12) language, defaulting to the empty
          string.  Both `charset' and `language' should be strings.  The
          default is to use the ‘utf8’ `charset' and ‘None’ for the
          `language'.

          If `replace' is ‘False’ (the default) the header is moved to
          the end of the list of headers.  If `replace' is ‘True’, the
          header will be updated in place.

          Use of the `requote' parameter with *note EmailMessage: 63c.
          objects is deprecated.

          Note that existing parameter values of headers may be accessed
          through the ‘params’ attribute of the header value (for
          example, ‘msg['Content-Type'].params['charset']’).

          Changed in version 3.4: ‘replace’ keyword was added.

      -- Method: del_param (param, header='content-type', requote=True)

          Remove the given parameter completely from the ‘Content-Type’
          header.  The header will be re-written in place without the
          parameter or its value.  Optional `header' specifies an
          alternative to ‘Content-Type’.

          Use of the `requote' parameter with *note EmailMessage: 63c.
          objects is deprecated.

      -- Method: get_filename (failobj=None)

          Return the value of the ‘filename’ parameter of the
          ‘Content-Disposition’ header of the message.  If the header
          does not have a ‘filename’ parameter, this method falls back
          to looking for the ‘name’ parameter on the ‘Content-Type’
          header.  If neither is found, or the header is missing, then
          `failobj' is returned.  The returned string will always be
          unquoted as per *note email.utils.unquote(): 2940.

      -- Method: get_boundary (failobj=None)

          Return the value of the ‘boundary’ parameter of the
          ‘Content-Type’ header of the message, or `failobj' if either
          the header is missing, or has no ‘boundary’ parameter.  The
          returned string will always be unquoted as per *note
          email.utils.unquote(): 2940.

      -- Method: set_boundary (boundary)

          Set the ‘boundary’ parameter of the ‘Content-Type’ header to
          `boundary'.  *note set_boundary(): 2942. will always quote
          `boundary' if necessary.  A *note HeaderParseError: 2943. is
          raised if the message object has no ‘Content-Type’ header.

          Note that using this method is subtly different from deleting
          the old ‘Content-Type’ header and adding a new one with the
          new boundary via *note add_header(): 2936, because *note
          set_boundary(): 2942. preserves the order of the
          ‘Content-Type’ header in the list of headers.

      -- Method: get_content_charset (failobj=None)

          Return the ‘charset’ parameter of the ‘Content-Type’ header,
          coerced to lower case.  If there is no ‘Content-Type’ header,
          or if that header has no ‘charset’ parameter, `failobj' is
          returned.

      -- Method: get_charsets (failobj=None)

          Return a list containing the character set names in the
          message.  If the message is a ‘multipart’, then the list will
          contain one element for each subpart in the payload,
          otherwise, it will be a list of length 1.

          Each item in the list will be a string which is the value of
          the ‘charset’ parameter in the ‘Content-Type’ header for the
          represented subpart.  If the subpart has no ‘Content-Type’
          header, no ‘charset’ parameter, or is not of the ‘text’ main
          MIME type, then that item in the returned list will be
          `failobj'.

      -- Method: is_attachment ()

          Return ‘True’ if there is a ‘Content-Disposition’ header and
          its (case insensitive) value is ‘attachment’, ‘False’
          otherwise.

          Changed in version 3.4.2: is_attachment is now a method
          instead of a property, for consistency with *note
          is_multipart(): 2947.

      -- Method: get_content_disposition ()

          Return the lowercased value (without parameters) of the
          message’s ‘Content-Disposition’ header if it has one, or
          ‘None’.  The possible values for this method are `inline',
          `attachment' or ‘None’ if the message follows RFC 2183(13).

          New in version 3.5.

     The following methods relate to interrogating and manipulating the
     content (payload) of the message.

      -- Method: walk ()

          The *note walk(): 2949. method is an all-purpose generator
          which can be used to iterate over all the parts and subparts
          of a message object tree, in depth-first traversal order.  You
          will typically use *note walk(): 2949. as the iterator in a
          ‘for’ loop; each iteration returns the next subpart.

          Here’s an example that prints the MIME type of every part of a
          multipart message structure:

               >>> for part in msg.walk():
               ...     print(part.get_content_type())
               multipart/report
               text/plain
               message/delivery-status
               text/plain
               text/plain
               message/rfc822
               text/plain

          ‘walk’ iterates over the subparts of any part where *note
          is_multipart(): 2927. returns ‘True’, even though
          ‘msg.get_content_maintype() == 'multipart'’ may return
          ‘False’.  We can see this in our example by making use of the
          ‘_structure’ debug helper function:

               >>> from email.iterators import _structure
               >>> for part in msg.walk():
               ...     print(part.get_content_maintype() == 'multipart',
               ...           part.is_multipart())
               True True
               False False
               False True
               False False
               False False
               False True
               False False
               >>> _structure(msg)
               multipart/report
                   text/plain
                   message/delivery-status
                       text/plain
                       text/plain
                   message/rfc822
                       text/plain

          Here the ‘message’ parts are not ‘multiparts’, but they do
          contain subparts.  ‘is_multipart()’ returns ‘True’ and ‘walk’
          descends into the subparts.

      -- Method: get_body (preferencelist=('related', 'html', 'plain'))

          Return the MIME part that is the best candidate to be the
          “body” of the message.

          `preferencelist' must be a sequence of strings from the set
          ‘related’, ‘html’, and ‘plain’, and indicates the order of
          preference for the content type of the part returned.

          Start looking for candidate matches with the object on which
          the ‘get_body’ method is called.

          If ‘related’ is not included in `preferencelist', consider the
          root part (or subpart of the root part) of any related
          encountered as a candidate if the (sub-)part matches a
          preference.

          When encountering a ‘multipart/related’, check the ‘start’
          parameter and if a part with a matching ‘Content-ID’ is found,
          consider only it when looking for candidate matches.
          Otherwise consider only the first (default root) part of the
          ‘multipart/related’.

          If a part has a ‘Content-Disposition’ header, only consider
          the part a candidate match if the value of the header is
          ‘inline’.

          If none of the candidates matches any of the preferences in
          `preferencelist', return ‘None’.

          Notes: (1) For most applications the only `preferencelist'
          combinations that really make sense are ‘('plain',)’,
          ‘('html', 'plain')’, and the default ‘('related', 'html',
          'plain')’.  (2) Because matching starts with the object on
          which ‘get_body’ is called, calling ‘get_body’ on a
          ‘multipart/related’ will return the object itself unless
          `preferencelist' has a non-default value.  (3) Messages (or
          message parts) that do not specify a ‘Content-Type’ or whose
          ‘Content-Type’ header is invalid will be treated as if they
          are of type ‘text/plain’, which may occasionally cause
          ‘get_body’ to return unexpected results.

      -- Method: iter_attachments ()

          Return an iterator over all of the immediate sub-parts of the
          message that are not candidate “body” parts.  That is, skip
          the first occurrence of each of ‘text/plain’, ‘text/html’,
          ‘multipart/related’, or ‘multipart/alternative’ (unless they
          are explicitly marked as attachments via ‘Content-Disposition:
          attachment’), and return all remaining parts.  When applied
          directly to a ‘multipart/related’, return an iterator over the
          all the related parts except the root part (ie: the part
          pointed to by the ‘start’ parameter, or the first part if
          there is no ‘start’ parameter or the ‘start’ parameter doesn’t
          match the ‘Content-ID’ of any of the parts).  When applied
          directly to a ‘multipart/alternative’ or a non-‘multipart’,
          return an empty iterator.

      -- Method: iter_parts ()

          Return an iterator over all of the immediate sub-parts of the
          message, which will be empty for a non-‘multipart’.  (See also
          *note walk(): 2949.)

      -- Method: get_content (*args, content_manager=None, **kw)

          Call the *note get_content(): 294e. method of the
          `content_manager', passing self as the message object, and
          passing along any other arguments or keywords as additional
          arguments.  If `content_manager' is not specified, use the
          ‘content_manager’ specified by the current *note policy: 73.

      -- Method: set_content (*args, content_manager=None, **kw)

          Call the *note set_content(): 294f. method of the
          `content_manager', passing self as the message object, and
          passing along any other arguments or keywords as additional
          arguments.  If `content_manager' is not specified, use the
          ‘content_manager’ specified by the current *note policy: 73.

      -- Method: make_related (boundary=None)

          Convert a non-‘multipart’ message into a ‘multipart/related’
          message, moving any existing ‘Content-’ headers and payload
          into a (new) first part of the ‘multipart’.  If `boundary' is
          specified, use it as the boundary string in the multipart,
          otherwise leave the boundary to be automatically created when
          it is needed (for example, when the message is serialized).

      -- Method: make_alternative (boundary=None)

          Convert a non-‘multipart’ or a ‘multipart/related’ into a
          ‘multipart/alternative’, moving any existing ‘Content-’
          headers and payload into a (new) first part of the
          ‘multipart’.  If `boundary' is specified, use it as the
          boundary string in the multipart, otherwise leave the boundary
          to be automatically created when it is needed (for example,
          when the message is serialized).

      -- Method: make_mixed (boundary=None)

          Convert a non-‘multipart’, a ‘multipart/related’, or a
          ‘multipart-alternative’ into a ‘multipart/mixed’, moving any
          existing ‘Content-’ headers and payload into a (new) first
          part of the ‘multipart’.  If `boundary' is specified, use it
          as the boundary string in the multipart, otherwise leave the
          boundary to be automatically created when it is needed (for
          example, when the message is serialized).

      -- Method: add_related (*args, content_manager=None, **kw)

          If the message is a ‘multipart/related’, create a new message
          object, pass all of the arguments to its *note set_content():
          f81. method, and *note attach(): 2954. it to the ‘multipart’.
          If the message is a non-‘multipart’, call *note
          make_related(): 2950. and then proceed as above.  If the
          message is any other type of ‘multipart’, raise a *note
          TypeError: 1fe.  If `content_manager' is not specified, use
          the ‘content_manager’ specified by the current *note policy:
          73.  If the added part has no ‘Content-Disposition’ header,
          add one with the value ‘inline’.

      -- Method: add_alternative (*args, content_manager=None, **kw)

          If the message is a ‘multipart/alternative’, create a new
          message object, pass all of the arguments to its *note
          set_content(): f81. method, and *note attach(): 2954. it to
          the ‘multipart’.  If the message is a non-‘multipart’ or
          ‘multipart/related’, call *note make_alternative(): 2951. and
          then proceed as above.  If the message is any other type of
          ‘multipart’, raise a *note TypeError: 1fe.  If
          `content_manager' is not specified, use the ‘content_manager’
          specified by the current *note policy: 73.

      -- Method: add_attachment (*args, content_manager=None, **kw)

          If the message is a ‘multipart/mixed’, create a new message
          object, pass all of the arguments to its *note set_content():
          f81. method, and *note attach(): 2954. it to the ‘multipart’.
          If the message is a non-‘multipart’, ‘multipart/related’, or
          ‘multipart/alternative’, call *note make_mixed(): 2952. and
          then proceed as above.  If `content_manager' is not specified,
          use the ‘content_manager’ specified by the current *note
          policy: 73.  If the added part has no ‘Content-Disposition’
          header, add one with the value ‘attachment’.  This method can
          be used both for explicit attachments (‘Content-Disposition:
          attachment’) and ‘inline’ attachments (‘Content-Disposition:
          inline’), by passing appropriate options to the
          ‘content_manager’.

      -- Method: clear ()

          Remove the payload and all of the headers.

      -- Method: clear_content ()

          Remove the payload and all of the ‘Content-’ headers, leaving
          all other headers intact and in their original order.

     *note EmailMessage: 63c. objects have the following instance
     attributes:

      -- Attribute: preamble

          The format of a MIME document allows for some text between the
          blank line following the headers, and the first multipart
          boundary string.  Normally, this text is never visible in a
          MIME-aware mail reader because it falls outside the standard
          MIME armor.  However, when viewing the raw text of the
          message, or when viewing the message in a non-MIME aware
          reader, this text can become visible.

          The `preamble' attribute contains this leading extra-armor
          text for MIME documents.  When the *note Parser: beb.
          discovers some text after the headers but before the first
          boundary string, it assigns this text to the message’s
          `preamble' attribute.  When the *note Generator: c1e. is
          writing out the plain text representation of a MIME message,
          and it finds the message has a `preamble' attribute, it will
          write this text in the area between the headers and the first
          boundary.  See *note email.parser: 72. and *note
          email.generator: 6c. for details.

          Note that if the message object has no preamble, the
          `preamble' attribute will be ‘None’.

      -- Attribute: epilogue

          The `epilogue' attribute acts the same way as the `preamble'
          attribute, except that it contains text that appears between
          the last boundary and the end of the message.  As with the
          *note preamble: 2959, if there is no epilog text this
          attribute will be ‘None’.

      -- Attribute: defects

          The `defects' attribute contains a list of all the problems
          found when parsing this message.  See *note email.errors: 6b.
          for a detailed description of the possible parsing defects.

 -- Class: email.message.MIMEPart (policy=default)

     This class represents a subpart of a MIME message.  It is identical
     to *note EmailMessage: 63c, except that no ‘MIME-Version’ headers
     are added when *note set_content(): f81. is called, since sub-parts
     do not need their own ‘MIME-Version’ headers.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/email/message.py

   (2) (1) Originally added in 3.4 as a *note provisional module: a61.
Docs for legacy message class moved to *note email.message.Message;
Representing an email message using the compat32 API: 2921.

   (3) https://tools.ietf.org/html/rfc5322.html

   (4) https://tools.ietf.org/html/rfc6532.html

   (5) https://tools.ietf.org/html/rfc5322.html

   (6) https://tools.ietf.org/html/rfc6531.html

   (7) https://tools.ietf.org/html/rfc2231.html

   (8) https://tools.ietf.org/html/rfc2231.html

   (9) https://tools.ietf.org/html/rfc2045.html

   (10) https://tools.ietf.org/html/rfc2045.html

   (11) https://tools.ietf.org/html/rfc2045.html

   (12) https://tools.ietf.org/html/rfc2231.html

   (13) https://tools.ietf.org/html/rfc2183.html


File: python.info,  Node: email parser Parsing email messages,  Next: email generator Generating MIME documents,  Prev: email message Representing an email message,  Up: email — An email and MIME handling package

5.19.1.2 ‘email.parser’: Parsing email messages
...............................................

`Source code:' Lib/email/parser.py(1)

__________________________________________________________________

Message object structures can be created in one of two ways: they can be
created from whole cloth by creating an *note EmailMessage: 63c. object,
adding headers using the dictionary interface, and adding payload(s)
using *note set_content(): f81. and related methods, or they can be
created by parsing a serialized representation of the email message.

The *note email: 67. package provides a standard parser that understands
most email document structures, including MIME documents.  You can pass
the parser a bytes, string or file object, and the parser will return to
you the root *note EmailMessage: 63c. instance of the object structure.
For simple, non-MIME messages the payload of this root object will
likely be a string containing the text of the message.  For MIME
messages, the root object will return ‘True’ from its *note
is_multipart(): 2927. method, and the subparts can be accessed via the
payload manipulation methods, such as *note get_body(): 294a, *note
iter_parts(): 294c, and *note walk(): 2949.

There are actually two parser interfaces available for use, the *note
Parser: beb. API and the incremental *note FeedParser: 295e. API. The
*note Parser: beb. API is most useful if you have the entire text of the
message in memory, or if the entire message lives in a file on the file
system.  *note FeedParser: 295e. is more appropriate when you are
reading the message from a stream which might block waiting for more
input (such as reading an email message from a socket).  The *note
FeedParser: 295e. can consume and parse the message incrementally, and
only returns the root object when you close the parser.

Note that the parser can be extended in limited ways, and of course you
can implement your own parser completely from scratch.  All of the logic
that connects the *note email: 67. package’s bundled parser and the
*note EmailMessage: 63c. class is embodied in the ‘policy’ class, so a
custom parser can create message object trees any way it finds necessary
by implementing custom versions of the appropriate ‘policy’ methods.

* Menu:

* FeedParser API::
* Parser API::
* Additional notes::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/email/parser.py


File: python.info,  Node: FeedParser API,  Next: Parser API,  Up: email parser Parsing email messages

5.19.1.3 FeedParser API
.......................

The *note BytesFeedParser: c1b, imported from the ‘email.feedparser’
module, provides an API that is conducive to incremental parsing of
email messages, such as would be necessary when reading the text of an
email message from a source that can block (such as a socket).  The
*note BytesFeedParser: c1b. can of course be used to parse an email
message fully contained in a *note bytes-like object: 6df, string, or
file, but the *note BytesParser: c1c. API may be more convenient for
such use cases.  The semantics and results of the two parser APIs are
identical.

The *note BytesFeedParser: c1b.’s API is simple; you create an instance,
feed it a bunch of bytes until there’s no more to feed it, then close
the parser to retrieve the root message object.  The *note
BytesFeedParser: c1b. is extremely accurate when parsing
standards-compliant messages, and it does a very good job of parsing
non-compliant messages, providing information about how a message was
deemed broken.  It will populate a message object’s *note defects: 295b.
attribute with a list of any problems it found in a message.  See the
*note email.errors: 6b. module for the list of defects that it can find.

Here is the API for the *note BytesFeedParser: c1b.:

 -- Class: email.parser.BytesFeedParser (_factory=None, *,
          policy=policy.compat32)

     Create a *note BytesFeedParser: c1b. instance.  Optional `_factory'
     is a no-argument callable; if not specified use the *note
     message_factory: 639. from the `policy'.  Call `_factory' whenever
     a new message object is needed.

     If `policy' is specified use the rules it specifies to update the
     representation of the message.  If `policy' is not set, use the
     *note compat32: ad4. policy, which maintains backward compatibility
     with the Python 3.2 version of the email package and provides *note
     Message: 63b. as the default factory.  All other policies provide
     *note EmailMessage: 63c. as the default `_factory'.  For more
     information on what else `policy' controls, see the *note policy:
     73. documentation.

     Note: `The policy keyword should always be specified'; The default
     will change to *note email.policy.default: 2922. in a future
     version of Python.

     New in version 3.2.

     Changed in version 3.3: Added the `policy' keyword.

     Changed in version 3.6: `_factory' defaults to the policy
     ‘message_factory’.

      -- Method: feed (data)

          Feed the parser some more data.  `data' should be a *note
          bytes-like object: 6df. containing one or more lines.  The
          lines can be partial and the parser will stitch such partial
          lines together properly.  The lines can have any of the three
          common line endings: carriage return, newline, or carriage
          return and newline (they can even be mixed).

      -- Method: close ()

          Complete the parsing of all previously fed data and return the
          root message object.  It is undefined what happens if *note
          feed(): 2960. is called after this method has been called.

 -- Class: email.parser.FeedParser (_factory=None, *,
          policy=policy.compat32)

     Works like *note BytesFeedParser: c1b. except that the input to the
     *note feed(): 2960. method must be a string.  This is of limited
     utility, since the only way for such a message to be valid is for
     it to contain only ASCII text or, if ‘utf8’ is ‘True’, no binary
     attachments.

     Changed in version 3.3: Added the `policy' keyword.


File: python.info,  Node: Parser API,  Next: Additional notes,  Prev: FeedParser API,  Up: email parser Parsing email messages

5.19.1.4 Parser API
...................

The *note BytesParser: c1c. class, imported from the *note email.parser:
72. module, provides an API that can be used to parse a message when the
complete contents of the message are available in a *note bytes-like
object: 6df. or file.  The *note email.parser: 72. module also provides
*note Parser: beb. for parsing strings, and header-only parsers, *note
BytesHeaderParser: adb. and *note HeaderParser: adc, which can be used
if you’re only interested in the headers of the message.  *note
BytesHeaderParser: adb. and *note HeaderParser: adc. can be much faster
in these situations, since they do not attempt to parse the message
body, instead setting the payload to the raw body.

 -- Class: email.parser.BytesParser (_class=None, *,
          policy=policy.compat32)

     Create a *note BytesParser: c1c. instance.  The `_class' and
     `policy' arguments have the same meaning and semantics as the
     `_factory' and `policy' arguments of *note BytesFeedParser: c1b.

     Note: `The policy keyword should always be specified'; The default
     will change to *note email.policy.default: 2922. in a future
     version of Python.

     Changed in version 3.3: Removed the `strict' argument that was
     deprecated in 2.4.  Added the `policy' keyword.

     Changed in version 3.6: `_class' defaults to the policy
     ‘message_factory’.

      -- Method: parse (fp, headersonly=False)

          Read all the data from the binary file-like object `fp', parse
          the resulting bytes, and return the message object.  `fp' must
          support both the *note readline(): 1849. and the ‘read()’
          methods.

          The bytes contained in `fp' must be formatted as a block of
          RFC 5322(1) (or, if ‘utf8’ is ‘True’, RFC 6532(2)) style
          headers and header continuation lines, optionally preceded by
          an envelope header.  The header block is terminated either by
          the end of the data or by a blank line.  Following the header
          block is the body of the message (which may contain
          MIME-encoded subparts, including subparts with a
          ‘Content-Transfer-Encoding’ of ‘8bit’).

          Optional `headersonly' is a flag specifying whether to stop
          parsing after reading the headers or not.  The default is
          ‘False’, meaning it parses the entire contents of the file.

      -- Method: parsebytes (bytes, headersonly=False)

          Similar to the *note parse(): 2963. method, except it takes a
          *note bytes-like object: 6df. instead of a file-like object.
          Calling this method on a *note bytes-like object: 6df. is
          equivalent to wrapping `bytes' in a *note BytesIO: 88a.
          instance first and calling *note parse(): 2963.

          Optional `headersonly' is as with the *note parse(): 2963.
          method.

     New in version 3.2.

 -- Class: email.parser.BytesHeaderParser (_class=None, *,
          policy=policy.compat32)

     Exactly like *note BytesParser: c1c, except that `headersonly'
     defaults to ‘True’.

     New in version 3.3.

 -- Class: email.parser.Parser (_class=None, *, policy=policy.compat32)

     This class is parallel to *note BytesParser: c1c, but handles
     string input.

     Changed in version 3.3: Removed the `strict' argument.  Added the
     `policy' keyword.

     Changed in version 3.6: `_class' defaults to the policy
     ‘message_factory’.

      -- Method: parse (fp, headersonly=False)

          Read all the data from the text-mode file-like object `fp',
          parse the resulting text, and return the root message object.
          `fp' must support both the *note readline(): 1d5b. and the
          *note read(): 2162. methods on file-like objects.

          Other than the text mode requirement, this method operates
          like *note BytesParser.parse(): 2963.

      -- Method: parsestr (text, headersonly=False)

          Similar to the *note parse(): 2965. method, except it takes a
          string object instead of a file-like object.  Calling this
          method on a string is equivalent to wrapping `text' in a *note
          StringIO: 91a. instance first and calling *note parse(): 2965.

          Optional `headersonly' is as with the *note parse(): 2965.
          method.

 -- Class: email.parser.HeaderParser (_class=None, *,
          policy=policy.compat32)

     Exactly like *note Parser: beb, except that `headersonly' defaults
     to ‘True’.

Since creating a message object structure from a string or a file object
is such a common task, four functions are provided as a convenience.
They are available in the top-level *note email: 67. package namespace.

 -- Function: email.message_from_bytes (s, _class=None, *,
          policy=policy.compat32)

     Return a message object structure from a *note bytes-like object:
     6df.  This is equivalent to ‘BytesParser().parsebytes(s)’.
     Optional `_class' and `policy' are interpreted as with the *note
     BytesParser: c1c. class constructor.

     New in version 3.2.

     Changed in version 3.3: Removed the `strict' argument.  Added the
     `policy' keyword.

 -- Function: email.message_from_binary_file (fp, _class=None, *,
          policy=policy.compat32)

     Return a message object structure tree from an open binary *note
     file object: c14.  This is equivalent to ‘BytesParser().parse(fp)’.
     `_class' and `policy' are interpreted as with the *note
     BytesParser: c1c. class constructor.

     New in version 3.2.

     Changed in version 3.3: Removed the `strict' argument.  Added the
     `policy' keyword.

 -- Function: email.message_from_string (s, _class=None, *,
          policy=policy.compat32)

     Return a message object structure from a string.  This is
     equivalent to ‘Parser().parsestr(s)’.  `_class' and `policy' are
     interpreted as with the *note Parser: beb. class constructor.

     Changed in version 3.3: Removed the `strict' argument.  Added the
     `policy' keyword.

 -- Function: email.message_from_file (fp, _class=None, *,
          policy=policy.compat32)

     Return a message object structure tree from an open *note file
     object: c14.  This is equivalent to ‘Parser().parse(fp)’.  `_class'
     and `policy' are interpreted as with the *note Parser: beb. class
     constructor.

     Changed in version 3.3: Removed the `strict' argument.  Added the
     `policy' keyword.

     Changed in version 3.6: `_class' defaults to the policy
     ‘message_factory’.

Here’s an example of how you might use *note message_from_bytes(): c19.
at an interactive Python prompt:

     >>> import email
     >>> msg = email.message_from_bytes(myBytes)

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc5322.html

   (2) https://tools.ietf.org/html/rfc6532.html


File: python.info,  Node: Additional notes,  Prev: Parser API,  Up: email parser Parsing email messages

5.19.1.5 Additional notes
.........................

Here are some notes on the parsing semantics:

   * Most non-‘multipart’ type messages are parsed as a single message
     object with a string payload.  These objects will return ‘False’
     for *note is_multipart(): 2927, and *note iter_parts(): 294c. will
     yield an empty list.

   * All ‘multipart’ type messages will be parsed as a container message
     object with a list of sub-message objects for their payload.  The
     outer container message will return ‘True’ for *note
     is_multipart(): 2927, and *note iter_parts(): 294c. will yield a
     list of subparts.

   * Most messages with a content type of ‘message/*’ (such as
     ‘message/delivery-status’ and ‘message/rfc822’) will also be parsed
     as container object containing a list payload of length 1.  Their
     *note is_multipart(): 2927. method will return ‘True’.  The single
     element yielded by *note iter_parts(): 294c. will be a sub-message
     object.

   * Some non-standards-compliant messages may not be internally
     consistent about their ‘multipart’-edness.  Such messages may have
     a ‘Content-Type’ header of type ‘multipart’, but their *note
     is_multipart(): 2927. method may return ‘False’.  If such messages
     were parsed with the *note FeedParser: 295e, they will have an
     instance of the ‘MultipartInvariantViolationDefect’ class in their
     `defects' attribute list.  See *note email.errors: 6b. for details.


File: python.info,  Node: email generator Generating MIME documents,  Next: email policy Policy Objects,  Prev: email parser Parsing email messages,  Up: email — An email and MIME handling package

5.19.1.6 ‘email.generator’: Generating MIME documents
.....................................................

`Source code:' Lib/email/generator.py(1)

__________________________________________________________________

One of the most common tasks is to generate the flat (serialized)
version of the email message represented by a message object structure.
You will need to do this if you want to send your message via *note
smtplib.SMTP.sendmail(): 833. or the *note nntplib: c0. module, or print
the message on the console.  Taking a message object structure and
producing a serialized representation is the job of the generator
classes.

As with the *note email.parser: 72. module, you aren’t limited to the
functionality of the bundled generator; you could write one from scratch
yourself.  However the bundled generator knows how to generate most
email in a standards-compliant way, should handle MIME and non-MIME
email messages just fine, and is designed so that the bytes-oriented
parsing and generation operations are inverses, assuming the same
non-transforming *note policy: 73. is used for both.  That is, parsing
the serialized byte stream via the *note BytesParser: c1c. class and
then regenerating the serialized byte stream using *note BytesGenerator:
c1f. should produce output identical to the input (2).  (On the other
hand, using the generator on an *note EmailMessage: 63c. constructed by
program may result in changes to the *note EmailMessage: 63c. object as
defaults are filled in.)

The *note Generator: c1e. class can be used to flatten a message into a
text (as opposed to binary) serialized representation, but since Unicode
cannot represent binary data directly, the message is of necessity
transformed into something that contains only ASCII characters, using
the standard email RFC Content Transfer Encoding techniques for encoding
email messages for transport over channels that are not “8 bit clean”.

To accommodate reproducible processing of SMIME-signed messages *note
Generator: c1e. disables header folding for message parts of type
‘multipart/signed’ and all subparts.

 -- Class: email.generator.BytesGenerator (outfp, mangle_from_=None,
          maxheaderlen=None, *, policy=None)

     Return a *note BytesGenerator: c1f. object that will write any
     message provided to the *note flatten(): 296c. method, or any
     surrogateescape encoded text provided to the *note write(): 296d.
     method, to the *note file-like object: 1dc6. `outfp'.  `outfp' must
     support a ‘write’ method that accepts binary data.

     If optional `mangle_from_' is ‘True’, put a ‘>’ character in front
     of any line in the body that starts with the exact string ‘"From
     "’, that is ‘From’ followed by a space at the beginning of a line.
     `mangle_from_' defaults to the value of the *note mangle_from_:
     7c3. setting of the `policy' (which is ‘True’ for the *note
     compat32: 63a. policy and ‘False’ for all others).  `mangle_from_'
     is intended for use when messages are stored in unix mbox format
     (see *note mailbox: ae. and WHY THE CONTENT-LENGTH FORMAT IS
     BAD(3)).

     If `maxheaderlen' is not ‘None’, refold any header lines that are
     longer than `maxheaderlen', or if ‘0’, do not rewrap any headers.
     If `manheaderlen' is ‘None’ (the default), wrap headers and other
     message lines according to the `policy' settings.

     If `policy' is specified, use that policy to control message
     generation.  If `policy' is ‘None’ (the default), use the policy
     associated with the *note Message: 63b. or *note EmailMessage: 63c.
     object passed to ‘flatten’ to control the message generation.  See
     *note email.policy: 73. for details on what `policy' controls.

     New in version 3.2.

     Changed in version 3.3: Added the `policy' keyword.

     Changed in version 3.6: The default behavior of the `mangle_from_'
     and `maxheaderlen' parameters is to follow the policy.

      -- Method: flatten (msg, unixfrom=False, linesep=None)

          Print the textual representation of the message object
          structure rooted at `msg' to the output file specified when
          the *note BytesGenerator: c1f. instance was created.

          If the *note policy: 73. option *note cte_type: 296e. is
          ‘8bit’ (the default), copy any headers in the original parsed
          message that have not been modified to the output with any
          bytes with the high bit set reproduced as in the original, and
          preserve the non-ASCII ‘Content-Transfer-Encoding’ of any body
          parts that have them.  If ‘cte_type’ is ‘7bit’, convert the
          bytes with the high bit set as needed using an
          ASCII-compatible ‘Content-Transfer-Encoding’.  That is,
          transform parts with non-ASCII ‘Content-Transfer-Encoding’
          (‘Content-Transfer-Encoding: 8bit’) to an ASCII compatible
          ‘Content-Transfer-Encoding’, and encode RFC-invalid non-ASCII
          bytes in headers using the MIME ‘unknown-8bit’ character set,
          thus rendering them RFC-compliant.

          If `unixfrom' is ‘True’, print the envelope header delimiter
          used by the Unix mailbox format (see *note mailbox: ae.)
          before the first of the RFC 5322(4) headers of the root
          message object.  If the root object has no envelope header,
          craft a standard one.  The default is ‘False’.  Note that for
          subparts, no envelope header is ever printed.

          If `linesep' is not ‘None’, use it as the separator character
          between all the lines of the flattened message.  If `linesep'
          is ‘None’ (the default), use the value specified in the
          `policy'.

      -- Method: clone (fp)

          Return an independent clone of this *note BytesGenerator: c1f.
          instance with the exact same option settings, and `fp' as the
          new `outfp'.

      -- Method: write (s)

          Encode `s' using the ‘ASCII’ codec and the ‘surrogateescape’
          error handler, and pass it to the `write' method of the
          `outfp' passed to the *note BytesGenerator: c1f.’s
          constructor.

As a convenience, *note EmailMessage: 63c. provides the methods *note
as_bytes(): 2925. and ‘bytes(aMessage)’ (a.k.a.  *note __bytes__():
2926.), which simplify the generation of a serialized binary
representation of a message object.  For more detail, see *note
email.message: 70.

Because strings cannot represent binary data, the *note Generator: c1e.
class must convert any binary data in any message it flattens to an
ASCII compatible format, by converting them to an ASCII compatible
‘Content-Transfer_Encoding’.  Using the terminology of the email RFCs,
you can think of this as *note Generator: c1e. serializing to an I/O
stream that is not “8 bit clean”.  In other words, most applications
will want to be using *note BytesGenerator: c1f, and not *note
Generator: c1e.

 -- Class: email.generator.Generator (outfp, mangle_from_=None,
          maxheaderlen=None, *, policy=None)

     Return a *note Generator: c1e. object that will write any message
     provided to the *note flatten(): 2970. method, or any text provided
     to the *note write(): 2971. method, to the *note file-like object:
     1dc6. `outfp'.  `outfp' must support a ‘write’ method that accepts
     string data.

     If optional `mangle_from_' is ‘True’, put a ‘>’ character in front
     of any line in the body that starts with the exact string ‘"From
     "’, that is ‘From’ followed by a space at the beginning of a line.
     `mangle_from_' defaults to the value of the *note mangle_from_:
     7c3. setting of the `policy' (which is ‘True’ for the *note
     compat32: 63a. policy and ‘False’ for all others).  `mangle_from_'
     is intended for use when messages are stored in unix mbox format
     (see *note mailbox: ae. and WHY THE CONTENT-LENGTH FORMAT IS
     BAD(5)).

     If `maxheaderlen' is not ‘None’, refold any header lines that are
     longer than `maxheaderlen', or if ‘0’, do not rewrap any headers.
     If `manheaderlen' is ‘None’ (the default), wrap headers and other
     message lines according to the `policy' settings.

     If `policy' is specified, use that policy to control message
     generation.  If `policy' is ‘None’ (the default), use the policy
     associated with the *note Message: 63b. or *note EmailMessage: 63c.
     object passed to ‘flatten’ to control the message generation.  See
     *note email.policy: 73. for details on what `policy' controls.

     Changed in version 3.3: Added the `policy' keyword.

     Changed in version 3.6: The default behavior of the `mangle_from_'
     and `maxheaderlen' parameters is to follow the policy.

      -- Method: flatten (msg, unixfrom=False, linesep=None)

          Print the textual representation of the message object
          structure rooted at `msg' to the output file specified when
          the *note Generator: c1e. instance was created.

          If the *note policy: 73. option *note cte_type: 296e. is
          ‘8bit’, generate the message as if the option were set to
          ‘7bit’.  (This is required because strings cannot represent
          non-ASCII bytes.)  Convert any bytes with the high bit set as
          needed using an ASCII-compatible ‘Content-Transfer-Encoding’.
          That is, transform parts with non-ASCII
          ‘Content-Transfer-Encoding’ (‘Content-Transfer-Encoding:
          8bit’) to an ASCII compatible ‘Content-Transfer-Encoding’, and
          encode RFC-invalid non-ASCII bytes in headers using the MIME
          ‘unknown-8bit’ character set, thus rendering them
          RFC-compliant.

          If `unixfrom' is ‘True’, print the envelope header delimiter
          used by the Unix mailbox format (see *note mailbox: ae.)
          before the first of the RFC 5322(6) headers of the root
          message object.  If the root object has no envelope header,
          craft a standard one.  The default is ‘False’.  Note that for
          subparts, no envelope header is ever printed.

          If `linesep' is not ‘None’, use it as the separator character
          between all the lines of the flattened message.  If `linesep'
          is ‘None’ (the default), use the value specified in the
          `policy'.

          Changed in version 3.2: Added support for re-encoding ‘8bit’
          message bodies, and the `linesep' argument.

      -- Method: clone (fp)

          Return an independent clone of this *note Generator: c1e.
          instance with the exact same options, and `fp' as the new
          `outfp'.

      -- Method: write (s)

          Write `s' to the `write' method of the `outfp' passed to the
          *note Generator: c1e.’s constructor.  This provides just
          enough file-like API for *note Generator: c1e. instances to be
          used in the *note print(): 971. function.

As a convenience, *note EmailMessage: 63c. provides the methods *note
as_string(): 2923. and ‘str(aMessage)’ (a.k.a.  *note __str__(): 2924.),
which simplify the generation of a formatted string representation of a
message object.  For more detail, see *note email.message: 70.

The *note email.generator: 6c. module also provides a derived class,
*note DecodedGenerator: 638, which is like the *note Generator: c1e.
base class, except that non-‘text’ parts are not serialized, but are
instead represented in the output stream by a string derived from a
template filled in with information about the part.

 -- Class: email.generator.DecodedGenerator (outfp, mangle_from_=None,
          maxheaderlen=None, fmt=None, *, policy=None)

     Act like *note Generator: c1e, except that for any subpart of the
     message passed to *note Generator.flatten(): 2970, if the subpart
     is of main type ‘text’, print the decoded payload of the subpart,
     and if the main type is not ‘text’, instead of printing it fill in
     the string `fmt' using information from the part and print the
     resulting filled-in string.

     To fill in `fmt', execute ‘fmt % part_info’, where ‘part_info’ is a
     dictionary composed of the following keys and values:

        * ‘type’ – Full MIME type of the non-‘text’ part

        * ‘maintype’ – Main MIME type of the non-‘text’ part

        * ‘subtype’ – Sub-MIME type of the non-‘text’ part

        * ‘filename’ – Filename of the non-‘text’ part

        * ‘description’ – Description associated with the non-‘text’
          part

        * ‘encoding’ – Content transfer encoding of the non-‘text’ part

     If `fmt' is ‘None’, use the following default `fmt':

          “[Non-text (%(type)s) part of message omitted, filename
          %(filename)s]”

     Optional `_mangle_from_' and `maxheaderlen' are as with the *note
     Generator: c1e. base class.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/email/generator.py

   (2) (1) This statement assumes that you use the appropriate setting
for ‘unixfrom’, and that there are no ‘policy’ settings calling for
automatic adjustments (for example, ‘refold_source’ must be ‘none’,
which is `not' the default).  It is also not 100% true, since if the
message does not conform to the RFC standards occasionally information
about the exact original text is lost during parsing error recovery.  It
is a goal to fix these latter edge cases when possible.

   (3) https://www.jwz.org/doc/content-length.html

   (4) https://tools.ietf.org/html/rfc5322.html

   (5) https://www.jwz.org/doc/content-length.html

   (6) https://tools.ietf.org/html/rfc5322.html


File: python.info,  Node: email policy Policy Objects,  Next: email errors Exception and Defect classes,  Prev: email generator Generating MIME documents,  Up: email — An email and MIME handling package

5.19.1.7 ‘email.policy’: Policy Objects
.......................................

New in version 3.3.

`Source code:' Lib/email/policy.py(1)

__________________________________________________________________

The *note email: 67. package’s prime focus is the handling of email
messages as described by the various email and MIME RFCs.  However, the
general format of email messages (a block of header fields each
consisting of a name followed by a colon followed by a value, the whole
block followed by a blank line and an arbitrary ‘body’), is a format
that has found utility outside of the realm of email.  Some of these
uses conform fairly closely to the main email RFCs, some do not.  Even
when working with email, there are times when it is desirable to break
strict compliance with the RFCs, such as generating emails that
interoperate with email servers that do not themselves follow the
standards, or that implement extensions you want to use in ways that
violate the standards.

Policy objects give the email package the flexibility to handle all
these disparate use cases.

A *note Policy: ad3. object encapsulates a set of attributes and methods
that control the behavior of various components of the email package
during use.  *note Policy: ad3. instances can be passed to various
classes and methods in the email package to alter the default behavior.
The settable values and their defaults are described below.

There is a default policy used by all classes in the email package.  For
all of the *note parser: 72. classes and the related convenience
functions, and for the *note Message: 63b. class, this is the *note
Compat32: ad4. policy, via its corresponding pre-defined instance *note
compat32: 63a.  This policy provides for complete backward compatibility
(in some cases, including bug compatibility) with the pre-Python3.3
version of the email package.

This default value for the `policy' keyword to *note EmailMessage: 63c.
is the *note EmailPolicy: ad7. policy, via its pre-defined instance
*note default: 2922.

When a *note Message: 63b. or *note EmailMessage: 63c. object is
created, it acquires a policy.  If the message is created by a *note
parser: 72, a policy passed to the parser will be the policy used by the
message it creates.  If the message is created by the program, then the
policy can be specified when it is created.  When a message is passed to
a *note generator: 6c, the generator uses the policy from the message by
default, but you can also pass a specific policy to the generator that
will override the one stored on the message object.

The default value for the `policy' keyword for the *note email.parser:
72. classes and the parser convenience functions `will be changing' in a
future version of Python.  Therefore you should `always specify
explicitly which policy you want to use' when calling any of the classes
and functions described in the *note parser: 72. module.

The first part of this documentation covers the features of *note
Policy: ad3, an *note abstract base class: c05. that defines the
features that are common to all policy objects, including *note
compat32: 63a.  This includes certain hook methods that are called
internally by the email package, which a custom policy could override to
obtain different behavior.  The second part describes the concrete
classes *note EmailPolicy: ad7. and *note Compat32: ad4, which implement
the hooks that provide the standard behavior and the backward compatible
behavior and features, respectively.

*note Policy: ad3. instances are immutable, but they can be cloned,
accepting the same keyword arguments as the class constructor and
returning a new *note Policy: ad3. instance that is a copy of the
original but with the specified attributes values changed.

As an example, the following code could be used to read an email message
from a file on disk and pass it to the system ‘sendmail’ program on a
Unix system:

     >>> from email import message_from_binary_file
     >>> from email.generator import BytesGenerator
     >>> from email import policy
     >>> from subprocess import Popen, PIPE
     >>> with open('mymsg.txt', 'rb') as f:
     ...     msg = message_from_binary_file(f, policy=policy.default)
     >>> p = Popen(['sendmail', msg['To'].addresses[0]], stdin=PIPE)
     >>> g = BytesGenerator(p.stdin, policy=msg.policy.clone(linesep='\r\n'))
     >>> g.flatten(msg)
     >>> p.stdin.close()
     >>> rc = p.wait()

Here we are telling *note BytesGenerator: c1f. to use the RFC correct
line separator characters when creating the binary string to feed into
‘sendmail's’ ‘stdin’, where the default policy would use ‘\n’ line
separators.

Some email package methods accept a `policy' keyword argument, allowing
the policy to be overridden for that method.  For example, the following
code uses the *note as_bytes(): 92d. method of the `msg' object from the
previous example and writes the message to a file using the native line
separators for the platform on which it is running:

     >>> import os
     >>> with open('converted.txt', 'wb') as f:
     ...     f.write(msg.as_bytes(policy=msg.policy.clone(linesep=os.linesep)))
     17

Policy objects can also be combined using the addition operator,
producing a policy object whose settings are a combination of the
non-default values of the summed objects:

     >>> compat_SMTP = policy.compat32.clone(linesep='\r\n')
     >>> compat_strict = policy.compat32.clone(raise_on_defect=True)
     >>> compat_strict_SMTP = compat_SMTP + compat_strict

This operation is not commutative; that is, the order in which the
objects are added matters.  To illustrate:

     >>> policy100 = policy.compat32.clone(max_line_length=100)
     >>> policy80 = policy.compat32.clone(max_line_length=80)
     >>> apolicy = policy100 + policy80
     >>> apolicy.max_line_length
     80
     >>> apolicy = policy80 + policy100
     >>> apolicy.max_line_length
     100

 -- Class: email.policy.Policy (**kw)

     This is the *note abstract base class: c05. for all policy classes.
     It provides default implementations for a couple of trivial
     methods, as well as the implementation of the immutability
     property, the *note clone(): ad5. method, and the constructor
     semantics.

     The constructor of a policy class can be passed various keyword
     arguments.  The arguments that may be specified are any non-method
     properties on this class, plus any additional non-method properties
     on the concrete class.  A value specified in the constructor will
     override the default value for the corresponding attribute.

     This class defines the following properties, and thus values for
     the following may be passed in the constructor of any policy class:

      -- Attribute: max_line_length

          The maximum length of any line in the serialized output, not
          counting the end of line character(s).  Default is 78, per RFC
          5322(2).  A value of ‘0’ or *note None: 203. indicates that no
          line wrapping should be done at all.

      -- Attribute: linesep

          The string to be used to terminate lines in serialized output.
          The default is ‘\n’ because that’s the internal end-of-line
          discipline used by Python, though ‘\r\n’ is required by the
          RFCs.

      -- Attribute: cte_type

          Controls the type of Content Transfer Encodings that may be or
          are required to be used.  The possible values are:

          ‘7bit’       all data must be “7 bit clean” (ASCII-only).  This means that
                       where necessary data will be encoded using either
                       quoted-printable or base64 encoding.
                       
                       
          ‘8bit’       data is not constrained to be 7 bit clean.  Data in headers is
                       still required to be ASCII-only and so will be encoded (see
                       *note fold_binary(): 2977. and *note utf8: 7c5. below for
                       exceptions), but body parts may use the ‘8bit’ CTE.
                       

          A ‘cte_type’ value of ‘8bit’ only works with ‘BytesGenerator’,
          not ‘Generator’, because strings cannot contain binary data.
          If a ‘Generator’ is operating under a policy that specifies
          ‘cte_type=8bit’, it will act as if ‘cte_type’ is ‘7bit’.

      -- Attribute: raise_on_defect

          If *note True: 594, any defects encountered will be raised as
          errors.  If *note False: 48f. (the default), defects will be
          passed to the *note register_defect(): 2979. method.

      -- Attribute: mangle_from_

          If *note True: 594, lines starting with `“From “' in the body
          are escaped by putting a ‘>’ in front of them.  This parameter
          is used when the message is being serialized by a generator.
          Default: *note False: 48f.

          New in version 3.5: The `mangle_from_' parameter.

      -- Attribute: message_factory

          A factory function for constructing a new empty message
          object.  Used by the parser when building messages.  Defaults
          to ‘None’, in which case *note Message: 63b. is used.

          New in version 3.6.

     The following *note Policy: ad3. method is intended to be called by
     code using the email library to create policy instances with custom
     settings:

      -- Method: clone (**kw)

          Return a new *note Policy: ad3. instance whose attributes have
          the same values as the current instance, except where those
          attributes are given new values by the keyword arguments.

     The remaining *note Policy: ad3. methods are called by the email
     package code, and are not intended to be called by an application
     using the email package.  A custom policy must implement all of
     these methods.

      -- Method: handle_defect (obj, defect)

          Handle a `defect' found on `obj'.  When the email package
          calls this method, `defect' will always be a subclass of
          ‘Defect’.

          The default implementation checks the *note raise_on_defect:
          2978. flag.  If it is ‘True’, `defect' is raised as an
          exception.  If it is ‘False’ (the default), `obj' and `defect'
          are passed to *note register_defect(): 2979.

      -- Method: register_defect (obj, defect)

          Register a `defect' on `obj'.  In the email package, `defect'
          will always be a subclass of ‘Defect’.

          The default implementation calls the ‘append’ method of the
          ‘defects’ attribute of `obj'.  When the email package calls
          *note handle_defect: 297a, `obj' will normally have a
          ‘defects’ attribute that has an ‘append’ method.  Custom
          object types used with the email package (for example, custom
          ‘Message’ objects) should also provide such an attribute,
          otherwise defects in parsed messages will raise unexpected
          errors.

      -- Method: header_max_count (name)

          Return the maximum allowed number of headers named `name'.

          Called when a header is added to an *note EmailMessage: 63c.
          or *note Message: 63b. object.  If the returned value is not
          ‘0’ or ‘None’, and there are already a number of headers with
          the name `name' greater than or equal to the value returned, a
          *note ValueError: 16d. is raised.

          Because the default behavior of ‘Message.__setitem__’ is to
          append the value to the list of headers, it is easy to create
          duplicate headers without realizing it.  This method allows
          certain headers to be limited in the number of instances of
          that header that may be added to a ‘Message’ programmatically.
          (The limit is not observed by the parser, which will
          faithfully produce as many headers as exist in the message
          being parsed.)

          The default implementation returns ‘None’ for all header
          names.

      -- Method: header_source_parse (sourcelines)

          The email package calls this method with a list of strings,
          each string ending with the line separation characters found
          in the source being parsed.  The first line includes the field
          header name and separator.  All whitespace in the source is
          preserved.  The method should return the ‘(name, value)’ tuple
          that is to be stored in the ‘Message’ to represent the parsed
          header.

          If an implementation wishes to retain compatibility with the
          existing email package policies, `name' should be the case
          preserved name (all characters up to the ‘‘:’’ separator),
          while `value' should be the unfolded value (all line separator
          characters removed, but whitespace kept intact), stripped of
          leading whitespace.

          `sourcelines' may contain surrogateescaped binary data.

          There is no default implementation

      -- Method: header_store_parse (name, value)

          The email package calls this method with the name and value
          provided by the application program when the application
          program is modifying a ‘Message’ programmatically (as opposed
          to a ‘Message’ created by a parser).  The method should return
          the ‘(name, value)’ tuple that is to be stored in the
          ‘Message’ to represent the header.

          If an implementation wishes to retain compatibility with the
          existing email package policies, the `name' and `value' should
          be strings or string subclasses that do not change the content
          of the passed in arguments.

          There is no default implementation

      -- Method: header_fetch_parse (name, value)

          The email package calls this method with the `name' and
          `value' currently stored in the ‘Message’ when that header is
          requested by the application program, and whatever the method
          returns is what is passed back to the application as the value
          of the header being retrieved.  Note that there may be more
          than one header with the same name stored in the ‘Message’;
          the method is passed the specific name and value of the header
          destined to be returned to the application.

          `value' may contain surrogateescaped binary data.  There
          should be no surrogateescaped binary data in the value
          returned by the method.

          There is no default implementation

      -- Method: fold (name, value)

          The email package calls this method with the `name' and
          `value' currently stored in the ‘Message’ for a given header.
          The method should return a string that represents that header
          “folded” correctly (according to the policy settings) by
          composing the `name' with the `value' and inserting *note
          linesep: 2976. characters at the appropriate places.  See RFC
          5322(3) for a discussion of the rules for folding email
          headers.

          `value' may contain surrogateescaped binary data.  There
          should be no surrogateescaped binary data in the string
          returned by the method.

      -- Method: fold_binary (name, value)

          The same as *note fold(): 297f, except that the returned value
          should be a bytes object rather than a string.

          `value' may contain surrogateescaped binary data.  These could
          be converted back into binary data in the returned bytes
          object.

 -- Class: email.policy.EmailPolicy (**kw)

     This concrete *note Policy: ad3. provides behavior that is intended
     to be fully compliant with the current email RFCs.  These include
     (but are not limited to) RFC 5322(4), RFC 2047(5), and the current
     MIME RFCs.

     This policy adds new header parsing and folding algorithms.
     Instead of simple strings, headers are ‘str’ subclasses with
     attributes that depend on the type of the field.  The parsing and
     folding algorithm fully implement RFC 2047(6) and RFC 5322(7).

     The default value for the *note message_factory: 639. attribute is
     *note EmailMessage: 63c.

     In addition to the settable attributes listed above that apply to
     all policies, this policy adds the following additional attributes:

     New in version 3.6: (8)

      -- Attribute: utf8

          If ‘False’, follow RFC 5322(9), supporting non-ASCII
          characters in headers by encoding them as “encoded words”.  If
          ‘True’, follow RFC 6532(10) and use ‘utf-8’ encoding for
          headers.  Messages formatted in this way may be passed to SMTP
          servers that support the ‘SMTPUTF8’ extension ( RFC 6531(11)).

      -- Attribute: refold_source

          If the value for a header in the ‘Message’ object originated
          from a *note parser: 72. (as opposed to being set by a
          program), this attribute indicates whether or not a generator
          should refold that value when transforming the message back
          into serialized form.  The possible values are:

          ‘none’       all source values use original folding
                       
                       
          ‘long’       source values that have any line that is longer than
                       ‘max_line_length’ will be refolded
                       
                       
          ‘all’        all values are refolded.
                       

          The default is ‘long’.

      -- Attribute: header_factory

          A callable that takes two arguments, ‘name’ and ‘value’, where
          ‘name’ is a header field name and ‘value’ is an unfolded
          header field value, and returns a string subclass that
          represents that header.  A default ‘header_factory’ (see *note
          headerregistry: 6e.) is provided that supports custom parsing
          for the various address and date RFC 5322(12) header field
          types, and the major MIME header field stypes.  Support for
          additional custom parsing will be added in the future.

      -- Attribute: content_manager

          An object with at least two methods: get_content and
          set_content.  When the *note get_content(): 294d. or *note
          set_content(): f81. method of an *note EmailMessage: 63c.
          object is called, it calls the corresponding method of this
          object, passing it the message object as its first argument,
          and any arguments or keywords that were passed to it as
          additional arguments.  By default ‘content_manager’ is set to
          *note raw_data_manager: 2982.

          New in version 3.4.

     The class provides the following concrete implementations of the
     abstract methods of *note Policy: ad3.:

      -- Method: header_max_count (name)

          Returns the value of the *note max_count: 2984. attribute of
          the specialized class used to represent the header with the
          given name.

      -- Method: header_source_parse (sourcelines)

          The name is parsed as everything up to the ‘‘:’’ and returned
          unmodified.  The value is determined by stripping leading
          whitespace off the remainder of the first line, joining all
          subsequent lines together, and stripping any trailing carriage
          return or linefeed characters.

      -- Method: header_store_parse (name, value)

          The name is returned unchanged.  If the input value has a
          ‘name’ attribute and it matches `name' ignoring case, the
          value is returned unchanged.  Otherwise the `name' and `value'
          are passed to ‘header_factory’, and the resulting header
          object is returned as the value.  In this case a ‘ValueError’
          is raised if the input value contains CR or LF characters.

      -- Method: header_fetch_parse (name, value)

          If the value has a ‘name’ attribute, it is returned to
          unmodified.  Otherwise the `name', and the `value' with any CR
          or LF characters removed, are passed to the ‘header_factory’,
          and the resulting header object is returned.  Any
          surrogateescaped bytes get turned into the unicode
          unknown-character glyph.

      -- Method: fold (name, value)

          Header folding is controlled by the *note refold_source: 2980.
          policy setting.  A value is considered to be a ‘source value’
          if and only if it does not have a ‘name’ attribute (having a
          ‘name’ attribute means it is a header object of some sort).
          If a source value needs to be refolded according to the
          policy, it is converted into a header object by passing the
          `name' and the `value' with any CR and LF characters removed
          to the ‘header_factory’.  Folding of a header object is done
          by calling its ‘fold’ method with the current policy.

          Source values are split into lines using *note splitlines():
          178c.  If the value is not to be refolded, the lines are
          rejoined using the ‘linesep’ from the policy and returned.
          The exception is lines containing non-ascii binary data.  In
          that case the value is refolded regardless of the
          ‘refold_source’ setting, which causes the binary data to be
          CTE encoded using the ‘unknown-8bit’ charset.

      -- Method: fold_binary (name, value)

          The same as *note fold(): 2988. if *note cte_type: 296e. is
          ‘7bit’, except that the returned value is bytes.

          If *note cte_type: 296e. is ‘8bit’, non-ASCII binary data is
          converted back into bytes.  Headers with binary data are not
          refolded, regardless of the ‘refold_header’ setting, since
          there is no way to know whether the binary data consists of
          single byte characters or multibyte characters.

The following instances of *note EmailPolicy: ad7. provide defaults
suitable for specific application domains.  Note that in the future the
behavior of these instances (in particular the ‘HTTP’ instance) may be
adjusted to conform even more closely to the RFCs relevant to their
domains.

 -- Data: email.policy.default

     An instance of ‘EmailPolicy’ with all defaults unchanged.  This
     policy uses the standard Python ‘\n’ line endings rather than the
     RFC-correct ‘\r\n’.

 -- Data: email.policy.SMTP

     Suitable for serializing messages in conformance with the email
     RFCs.  Like ‘default’, but with ‘linesep’ set to ‘\r\n’, which is
     RFC compliant.

 -- Data: email.policy.SMTPUTF8

     The same as ‘SMTP’ except that *note utf8: 7c5. is ‘True’.  Useful
     for serializing messages to a message store without using encoded
     words in the headers.  Should only be used for SMTP transmission if
     the sender or recipient addresses have non-ASCII characters (the
     *note smtplib.SMTP.send_message(): 834. method handles this
     automatically).

 -- Data: email.policy.HTTP

     Suitable for serializing headers with for use in HTTP traffic.
     Like ‘SMTP’ except that ‘max_line_length’ is set to ‘None’
     (unlimited).

 -- Data: email.policy.strict

     Convenience instance.  The same as ‘default’ except that
     ‘raise_on_defect’ is set to ‘True’.  This allows any policy to be
     made strict by writing:

          somepolicy + policy.strict

With all of these *note EmailPolicies: ad7, the effective API of the
email package is changed from the Python 3.2 API in the following ways:

        * Setting a header on a *note Message: 63b. results in that
          header being parsed and a header object created.

        * Fetching a header value from a *note Message: 63b. results in
          that header being parsed and a header object created and
          returned.

        * Any header object, or any header that is refolded due to the
          policy settings, is folded using an algorithm that fully
          implements the RFC folding algorithms, including knowing where
          encoded words are required and allowed.

From the application view, this means that any header obtained through
the *note EmailMessage: 63c. is a header object with extra attributes,
whose string value is the fully decoded unicode value of the header.
Likewise, a header may be assigned a new value, or a new header created,
using a unicode string, and the policy will take care of converting the
unicode string into the correct RFC encoded form.

The header objects and their attributes are described in *note
headerregistry: 6e.

 -- Class: email.policy.Compat32 (**kw)

     This concrete *note Policy: ad3. is the backward compatibility
     policy.  It replicates the behavior of the email package in Python
     3.2.  The *note policy: 73. module also defines an instance of this
     class, *note compat32: 63a, that is used as the default policy.
     Thus the default behavior of the email package is to maintain
     compatibility with Python 3.2.

     The following attributes have values that are different from the
     *note Policy: ad3. default:

      -- Attribute: mangle_from_

          The default is ‘True’.

     The class provides the following concrete implementations of the
     abstract methods of *note Policy: ad3.:

      -- Method: header_source_parse (sourcelines)

          The name is parsed as everything up to the ‘‘:’’ and returned
          unmodified.  The value is determined by stripping leading
          whitespace off the remainder of the first line, joining all
          subsequent lines together, and stripping any trailing carriage
          return or linefeed characters.

      -- Method: header_store_parse (name, value)

          The name and value are returned unmodified.

      -- Method: header_fetch_parse (name, value)

          If the value contains binary data, it is converted into a
          *note Header: f83. object using the ‘unknown-8bit’ charset.
          Otherwise it is returned unmodified.

      -- Method: fold (name, value)

          Headers are folded using the *note Header: f83. folding
          algorithm, which preserves existing line breaks in the value,
          and wraps each resulting line to the ‘max_line_length’.
          Non-ASCII binary data are CTE encoded using the ‘unknown-8bit’
          charset.

      -- Method: fold_binary (name, value)

          Headers are folded using the *note Header: f83. folding
          algorithm, which preserves existing line breaks in the value,
          and wraps each resulting line to the ‘max_line_length’.  If
          ‘cte_type’ is ‘7bit’, non-ascii binary data is CTE encoded
          using the ‘unknown-8bit’ charset.  Otherwise the original
          source header is used, with its existing line breaks and any
          (RFC invalid) binary data it may contain.

 -- Data: email.policy.compat32

     An instance of *note Compat32: ad4, providing backward
     compatibility with the behavior of the email package in Python 3.2.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/email/policy.py

   (2) https://tools.ietf.org/html/rfc5322.html

   (3) https://tools.ietf.org/html/rfc5322.html

   (4) https://tools.ietf.org/html/rfc5322.html

   (5) https://tools.ietf.org/html/rfc2047.html

   (6) https://tools.ietf.org/html/rfc2047.html

   (7) https://tools.ietf.org/html/rfc5322.html

   (8) (1) Originally added in 3.3 as a *note provisional feature: a61.

   (9) https://tools.ietf.org/html/rfc5322.html

   (10) https://tools.ietf.org/html/rfc6532.html

   (11) https://tools.ietf.org/html/rfc6531.html

   (12) https://tools.ietf.org/html/rfc5322.html


File: python.info,  Node: email errors Exception and Defect classes,  Next: email headerregistry Custom Header Objects,  Prev: email policy Policy Objects,  Up: email — An email and MIME handling package

5.19.1.8 ‘email.errors’: Exception and Defect classes
.....................................................

`Source code:' Lib/email/errors.py(1)

__________________________________________________________________

The following exception classes are defined in the *note email.errors:
6b. module:

 -- Exception: email.errors.MessageError

     This is the base class for all exceptions that the *note email: 67.
     package can raise.  It is derived from the standard *note
     Exception: 2dc. class and defines no additional methods.

 -- Exception: email.errors.MessageParseError

     This is the base class for exceptions raised by the *note Parser:
     beb. class.  It is derived from *note MessageError: 2996.  This
     class is also used internally by the parser used by *note
     headerregistry: 6e.

 -- Exception: email.errors.HeaderParseError

     Raised under some error conditions when parsing the RFC 5322(2)
     headers of a message, this class is derived from *note
     MessageParseError: 2997.  The *note set_boundary(): 2942. method
     will raise this error if the content type is unknown when the
     method is called.  *note Header: f83. may raise this error for
     certain base64 decoding errors, and when an attempt is made to
     create a header that appears to contain an embedded header (that
     is, there is what is supposed to be a continuation line that has no
     leading whitespace and looks like a header).

 -- Exception: email.errors.BoundaryError

     Deprecated and no longer used.

 -- Exception: email.errors.MultipartConversionError

     Raised when a payload is added to a *note Message: 63b. object
     using ‘add_payload()’, but the payload is already a scalar and the
     message’s ‘Content-Type’ main type is not either ‘multipart’ or
     missing.  *note MultipartConversionError: 2999. multiply inherits
     from *note MessageError: 2996. and the built-in *note TypeError:
     1fe.

     Since ‘Message.add_payload()’ is deprecated, this exception is
     rarely raised in practice.  However the exception may also be
     raised if the *note attach(): 2954. method is called on an instance
     of a class derived from *note MIMENonMultipart: f59. (e.g.  *note
     MIMEImage: 299a.).

Here is the list of the defects that the *note FeedParser: 295e. can
find while parsing messages.  Note that the defects are added to the
message where the problem was found, so for example, if a message nested
inside a ‘multipart/alternative’ had a malformed header, that nested
message object would have a defect, but the containing messages would
not.

All defect classes are subclassed from ‘email.errors.MessageDefect’.

   * ‘NoBoundaryInMultipartDefect’ – A message claimed to be a
     multipart, but had no ‘boundary’ parameter.

   * ‘StartBoundaryNotFoundDefect’ – The start boundary claimed in the
     ‘Content-Type’ header was never found.

   * ‘CloseBoundaryNotFoundDefect’ – A start boundary was found, but no
     corresponding close boundary was ever found.

     New in version 3.3.

   * ‘FirstHeaderLineIsContinuationDefect’ – The message had a
     continuation line as its first header line.

   * ‘MisplacedEnvelopeHeaderDefect’ - A “Unix From” header was found in
     the middle of a header block.

   * ‘MissingHeaderBodySeparatorDefect’ - A line was found while parsing
     headers that had no leading white space but contained no ‘:’.
     Parsing continues assuming that the line represents the first line
     of the body.

     New in version 3.3.

   * ‘MalformedHeaderDefect’ – A header was found that was missing a
     colon, or was otherwise malformed.

     Deprecated since version 3.3: This defect has not been used for
     several Python versions.

   * ‘MultipartInvariantViolationDefect’ – A message claimed to be a
     ‘multipart’, but no subparts were found.  Note that when a message
     has this defect, its *note is_multipart(): 2947. method may return
     ‘False’ even though its content type claims to be ‘multipart’.

   * ‘InvalidBase64PaddingDefect’ – When decoding a block of base64
     encoded bytes, the padding was not correct.  Enough padding is
     added to perform the decode, but the resulting decoded bytes may be
     invalid.

   * ‘InvalidBase64CharactersDefect’ – When decoding a block of base64
     encoded bytes, characters outside the base64 alphabet were
     encountered.  The characters are ignored, but the resulting decoded
     bytes may be invalid.

   * ‘InvalidBase64LengthDefect’ – When decoding a block of base64
     encoded bytes, the number of non-padding base64 characters was
     invalid (1 more than a multiple of 4).  The encoded block was kept
     as-is.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/email/errors.py

   (2) https://tools.ietf.org/html/rfc5322.html


File: python.info,  Node: email headerregistry Custom Header Objects,  Next: email contentmanager Managing MIME Content,  Prev: email errors Exception and Defect classes,  Up: email — An email and MIME handling package

5.19.1.9 ‘email.headerregistry’: Custom Header Objects
......................................................

`Source code:' Lib/email/headerregistry.py(1)

__________________________________________________________________

New in version 3.6: (2)

Headers are represented by customized subclasses of *note str: 205.  The
particular class used to represent a given header is determined by the
*note header_factory: 2981. of the *note policy: 73. in effect when the
headers are created.  This section documents the particular
‘header_factory’ implemented by the email package for handling RFC
5322(3) compliant email messages, which not only provides customized
header objects for various header types, but also provides an extension
mechanism for applications to add their own custom header types.

When using any of the policy objects derived from *note EmailPolicy:
ad7, all headers are produced by *note HeaderRegistry: 299d. and have
*note BaseHeader: 2930. as their last base class.  Each header class has
an additional base class that is determined by the type of the header.
For example, many headers have the class *note UnstructuredHeader: 299e.
as their other base class.  The specialized second class for a header is
determined by the name of the header, using a lookup table stored in the
*note HeaderRegistry: 299d.  All of this is managed transparently for
the typical application program, but interfaces are provided for
modifying the default behavior for use by more complex applications.

The sections below first document the header base classes and their
attributes, followed by the API for modifying the behavior of *note
HeaderRegistry: 299d, and finally the support classes used to represent
the data parsed from structured headers.

 -- Class: email.headerregistry.BaseHeader (name, value)

     `name' and `value' are passed to ‘BaseHeader’ from the *note
     header_factory: 2981. call.  The string value of any header object
     is the `value' fully decoded to unicode.

     This base class defines the following read-only properties:

      -- Attribute: name

          The name of the header (the portion of the field before the
          ‘:’).  This is exactly the value passed in the *note
          header_factory: 2981. call for `name'; that is, case is
          preserved.

      -- Attribute: defects

          A tuple of ‘HeaderDefect’ instances reporting any RFC
          compliance problems found during parsing.  The email package
          tries to be complete about detecting compliance issues.  See
          the *note errors: 6b. module for a discussion of the types of
          defects that may be reported.

      -- Attribute: max_count

          The maximum number of headers of this type that can have the
          same ‘name’.  A value of ‘None’ means unlimited.  The
          ‘BaseHeader’ value for this attribute is ‘None’; it is
          expected that specialized header classes will override this
          value as needed.

     ‘BaseHeader’ also provides the following method, which is called by
     the email library code and should not in general be called by
     application programs:

      -- Method: fold (*, policy)

          Return a string containing *note linesep: 2976. characters as
          required to correctly fold the header according to `policy'.
          A *note cte_type: 296e. of ‘8bit’ will be treated as if it
          were ‘7bit’, since headers may not contain arbitrary binary
          data.  If *note utf8: 7c5. is ‘False’, non-ASCII data will be
          RFC 2047(4) encoded.

     ‘BaseHeader’ by itself cannot be used to create a header object.
     It defines a protocol that each specialized header cooperates with
     in order to produce the header object.  Specifically, ‘BaseHeader’
     requires that the specialized class provide a *note classmethod():
     309. named ‘parse’.  This method is called as follows:

          parse(string, kwds)

     ‘kwds’ is a dictionary containing one pre-initialized key,
     ‘defects’.  ‘defects’ is an empty list.  The parse method should
     append any detected defects to this list.  On return, the ‘kwds’
     dictionary `must' contain values for at least the keys ‘decoded’
     and ‘defects’.  ‘decoded’ should be the string value for the header
     (that is, the header value fully decoded to unicode).  The parse
     method should assume that `string' may contain
     content-transfer-encoded parts, but should correctly handle all
     valid unicode characters as well so that it can parse un-encoded
     header values.

     ‘BaseHeader’’s ‘__new__’ then creates the header instance, and
     calls its ‘init’ method.  The specialized class only needs to
     provide an ‘init’ method if it wishes to set additional attributes
     beyond those provided by ‘BaseHeader’ itself.  Such an ‘init’
     method should look like this:

          def init(self, /, *args, **kw):
              self._myattr = kw.pop('myattr')
              super().init(*args, **kw)

     That is, anything extra that the specialized class puts in to the
     ‘kwds’ dictionary should be removed and handled, and the remaining
     contents of ‘kw’ (and ‘args’) passed to the ‘BaseHeader’ ‘init’
     method.

 -- Class: email.headerregistry.UnstructuredHeader

     An “unstructured” header is the default type of header in RFC
     5322(5).  Any header that does not have a specified syntax is
     treated as unstructured.  The classic example of an unstructured
     header is the ‘Subject’ header.

     In RFC 5322(6), an unstructured header is a run of arbitrary text
     in the ASCII character set.  RFC 2047(7), however, has an RFC
     5322(8) compatible mechanism for encoding non-ASCII text as ASCII
     characters within a header value.  When a `value' containing
     encoded words is passed to the constructor, the
     ‘UnstructuredHeader’ parser converts such encoded words into
     unicode, following the RFC 2047(9) rules for unstructured text.
     The parser uses heuristics to attempt to decode certain
     non-compliant encoded words.  Defects are registered in such cases,
     as well as defects for issues such as invalid characters within the
     encoded words or the non-encoded text.

     This header type provides no additional attributes.

 -- Class: email.headerregistry.DateHeader

     RFC 5322(10) specifies a very specific format for dates within
     email headers.  The ‘DateHeader’ parser recognizes that date
     format, as well as recognizing a number of variant forms that are
     sometimes found “in the wild”.

     This header type provides the following additional attributes:

      -- Attribute: datetime

          If the header value can be recognized as a valid date of one
          form or another, this attribute will contain a *note datetime:
          1a0. instance representing that date.  If the timezone of the
          input date is specified as ‘-0000’ (indicating it is in UTC
          but contains no information about the source timezone), then
          *note datetime: 29a3. will be a naive *note datetime: 1a0.  If
          a specific timezone offset is found (including ‘+0000’), then
          *note datetime: 29a3. will contain an aware ‘datetime’ that
          uses *note datetime.timezone: ae0. to record the timezone
          offset.

     The ‘decoded’ value of the header is determined by formatting the
     ‘datetime’ according to the RFC 5322(11) rules; that is, it is set
     to:

          email.utils.format_datetime(self.datetime)

     When creating a ‘DateHeader’, `value' may be *note datetime: 1a0.
     instance.  This means, for example, that the following code is
     valid and does what one would expect:

          msg['Date'] = datetime(2011, 7, 15, 21)

     Because this is a naive ‘datetime’ it will be interpreted as a UTC
     timestamp, and the resulting value will have a timezone of ‘-0000’.
     Much more useful is to use the *note localtime(): adf. function
     from the *note utils: 74. module:

          msg['Date'] = utils.localtime()

     This example sets the date header to the current time and date
     using the current timezone offset.

 -- Class: email.headerregistry.AddressHeader

     Address headers are one of the most complex structured header
     types.  The ‘AddressHeader’ class provides a generic interface to
     any address header.

     This header type provides the following additional attributes:

      -- Attribute: groups

          A tuple of *note Group: 29a6. objects encoding the addresses
          and groups found in the header value.  Addresses that are not
          part of a group are represented in this list as single-address
          ‘Groups’ whose *note display_name: 29a7. is ‘None’.

      -- Attribute: addresses

          A tuple of *note Address: 29a9. objects encoding all of the
          individual addresses from the header value.  If the header
          value contains any groups, the individual addresses from the
          group are included in the list at the point where the group
          occurs in the value (that is, the list of addresses is
          “flattened” into a one dimensional list).

     The ‘decoded’ value of the header will have all encoded words
     decoded to unicode.  *note idna: 75. encoded domain names are also
     decoded to unicode.  The ‘decoded’ value is set by *note join:
     1766.ing the *note str: 205. value of the elements of the ‘groups’
     attribute with ‘', '’.

     A list of *note Address: 29a9. and *note Group: 29a6. objects in
     any combination may be used to set the value of an address header.
     ‘Group’ objects whose ‘display_name’ is ‘None’ will be interpreted
     as single addresses, which allows an address list to be copied with
     groups intact by using the list obtained from the ‘groups’
     attribute of the source header.

 -- Class: email.headerregistry.SingleAddressHeader

     A subclass of *note AddressHeader: 29a4. that adds one additional
     attribute:

      -- Attribute: address

          The single address encoded by the header value.  If the header
          value actually contains more than one address (which would be
          a violation of the RFC under the default *note policy: 73.),
          accessing this attribute will result in a *note ValueError:
          16d.

Many of the above classes also have a ‘Unique’ variant (for example,
‘UniqueUnstructuredHeader’).  The only difference is that in the
‘Unique’ variant, *note max_count: 2984. is set to 1.

 -- Class: email.headerregistry.MIMEVersionHeader

     There is really only one valid value for the ‘MIME-Version’ header,
     and that is ‘1.0’.  For future proofing, this header class supports
     other valid version numbers.  If a version number has a valid value
     per RFC 2045(12), then the header object will have non-‘None’
     values for the following attributes:

      -- Attribute: version

          The version number as a string, with any whitespace and/or
          comments removed.

      -- Attribute: major

          The major version number as an integer

      -- Attribute: minor

          The minor version number as an integer

 -- Class: email.headerregistry.ParameterizedMIMEHeader

     MIME headers all start with the prefix ‘Content-’.  Each specific
     header has a certain value, described under the class for that
     header.  Some can also take a list of supplemental parameters,
     which have a common format.  This class serves as a base for all
     the MIME headers that take parameters.

      -- Attribute: params

          A dictionary mapping parameter names to parameter values.

 -- Class: email.headerregistry.ContentTypeHeader

     A *note ParameterizedMIMEHeader: 29b0. class that handles the
     ‘Content-Type’ header.

      -- Attribute: content_type

          The content type string, in the form ‘maintype/subtype’.

      -- Attribute: maintype

      -- Attribute: subtype

 -- Class: email.headerregistry.ContentDispositionHeader

     A *note ParameterizedMIMEHeader: 29b0. class that handles the
     ‘Content-Disposition’ header.

      -- Attribute: content_disposition

          ‘inline’ and ‘attachment’ are the only valid values in common
          use.

 -- Class: email.headerregistry.ContentTransferEncoding

     Handles the ‘Content-Transfer-Encoding’ header.

      -- Attribute: cte

          Valid values are ‘7bit’, ‘8bit’, ‘base64’, and
          ‘quoted-printable’.  See RFC 2045(13) for more information.

 -- Class: email.headerregistry.HeaderRegistry (base_class=BaseHeader,
          default_class=UnstructuredHeader, use_default_map=True)

     This is the factory used by *note EmailPolicy: ad7. by default.
     ‘HeaderRegistry’ builds the class used to create a header instance
     dynamically, using `base_class' and a specialized class retrieved
     from a registry that it holds.  When a given header name does not
     appear in the registry, the class specified by `default_class' is
     used as the specialized class.  When `use_default_map' is ‘True’
     (the default), the standard mapping of header names to classes is
     copied in to the registry during initialization.  `base_class' is
     always the last class in the generated class’s ‘__bases__’ list.

     The default mappings are:


          subject: UniqueUnstructuredHeader


          date: UniqueDateHeader


          resent-date: DateHeader


          orig-date: UniqueDateHeader


          sender: UniqueSingleAddressHeader


          resent-sender: SingleAddressHeader


          to: UniqueAddressHeader


          resent-to: AddressHeader


          cc: UniqueAddressHeader


          resent-cc: AddressHeader


          bcc: UniqueAddressHeader


          resent-bcc: AddressHeader


          from: UniqueAddressHeader


          resent-from: AddressHeader


          reply-to: UniqueAddressHeader


          mime-version: MIMEVersionHeader


          content-type: ContentTypeHeader


          content-disposition: ContentDispositionHeader


          content-transfer-encoding: ContentTransferEncodingHeader


          message-id: MessageIDHeader

     ‘HeaderRegistry’ has the following methods:

      -- Method: map_to_type (self, name, cls)

          `name' is the name of the header to be mapped.  It will be
          converted to lower case in the registry.  `cls' is the
          specialized class to be used, along with `base_class', to
          create the class used to instantiate headers that match
          `name'.

      -- Method: __getitem__ (name)

          Construct and return a class to handle creating a `name'
          header.

      -- Method: __call__ (name, value)

          Retrieves the specialized header associated with `name' from
          the registry (using `default_class' if `name' does not appear
          in the registry) and composes it with `base_class' to produce
          a class, calls the constructed class’s constructor, passing it
          the same argument list, and finally returns the class instance
          created thereby.

The following classes are the classes used to represent data parsed from
structured headers and can, in general, be used by an application
program to construct structured values to assign to specific headers.

 -- Class: email.headerregistry.Address (display_name='', username='',
          domain='', addr_spec=None)

     The class used to represent an email address.  The general form of
     an address is:

          [display_name] <username@domain>

     or:

          username@domain

     where each part must conform to specific syntax rules spelled out
     in RFC 5322(14).

     As a convenience `addr_spec' can be specified instead of `username'
     and `domain', in which case `username' and `domain' will be parsed
     from the `addr_spec'.  An `addr_spec' must be a properly RFC quoted
     string; if it is not ‘Address’ will raise an error.  Unicode
     characters are allowed and will be property encoded when
     serialized.  However, per the RFCs, unicode is `not' allowed in the
     username portion of the address.

      -- Attribute: display_name

          The display name portion of the address, if any, with all
          quoting removed.  If the address does not have a display name,
          this attribute will be an empty string.

      -- Attribute: username

          The ‘username’ portion of the address, with all quoting
          removed.

      -- Attribute: domain

          The ‘domain’ portion of the address.

      -- Attribute: addr_spec

          The ‘username@domain’ portion of the address, correctly quoted
          for use as a bare address (the second form shown above).  This
          attribute is not mutable.

      -- Method: __str__ ()

          The ‘str’ value of the object is the address quoted according
          to RFC 5322(15) rules, but with no Content Transfer Encoding
          of any non-ASCII characters.

     To support SMTP ( RFC 5321(16)), ‘Address’ handles one special
     case: if ‘username’ and ‘domain’ are both the empty string (or
     ‘None’), then the string value of the ‘Address’ is ‘<>’.

 -- Class: email.headerregistry.Group (display_name=None,
          addresses=None)

     The class used to represent an address group.  The general form of
     an address group is:

          display_name: [address-list];

     As a convenience for processing lists of addresses that consist of
     a mixture of groups and single addresses, a ‘Group’ may also be
     used to represent single addresses that are not part of a group by
     setting `display_name' to ‘None’ and providing a list of the single
     address as `addresses'.

      -- Attribute: display_name

          The ‘display_name’ of the group.  If it is ‘None’ and there is
          exactly one ‘Address’ in ‘addresses’, then the ‘Group’
          represents a single address that is not in a group.

      -- Attribute: addresses

          A possibly empty tuple of *note Address: 29a9. objects
          representing the addresses in the group.

      -- Method: __str__ ()

          The ‘str’ value of a ‘Group’ is formatted according to RFC
          5322(17), but with no Content Transfer Encoding of any
          non-ASCII characters.  If ‘display_name’ is none and there is
          a single ‘Address’ in the ‘addresses’ list, the ‘str’ value
          will be the same as the ‘str’ of that single ‘Address’.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/email/headerregistry.py

   (2) (1) Originally added in 3.3 as a *note provisional module: a61.

   (3) https://tools.ietf.org/html/rfc5322.html

   (4) https://tools.ietf.org/html/rfc2047.html

   (5) https://tools.ietf.org/html/rfc5322.html

   (6) https://tools.ietf.org/html/rfc5322.html

   (7) https://tools.ietf.org/html/rfc2047.html

   (8) https://tools.ietf.org/html/rfc5322.html

   (9) https://tools.ietf.org/html/rfc2047.html

   (10) https://tools.ietf.org/html/rfc5322.html

   (11) https://tools.ietf.org/html/rfc5322.html

   (12) https://tools.ietf.org/html/rfc2045.html

   (13) https://tools.ietf.org/html/rfc2045.html

   (14) https://tools.ietf.org/html/rfc5322.html

   (15) https://tools.ietf.org/html/rfc5322.html

   (16) https://tools.ietf.org/html/rfc5321.html

   (17) https://tools.ietf.org/html/rfc5322.html


File: python.info,  Node: email contentmanager Managing MIME Content,  Next: email Examples,  Prev: email headerregistry Custom Header Objects,  Up: email — An email and MIME handling package

5.19.1.10 ‘email.contentmanager’: Managing MIME Content
.......................................................

`Source code:' Lib/email/contentmanager.py(1)

__________________________________________________________________

New in version 3.6: (2)

 -- Class: email.contentmanager.ContentManager

     Base class for content managers.  Provides the standard registry
     mechanisms to register converters between MIME content and other
     representations, as well as the ‘get_content’ and ‘set_content’
     dispatch methods.

      -- Method: get_content (msg, *args, **kw)

          Look up a handler function based on the ‘mimetype’ of `msg'
          (see next paragraph), call it, passing through all arguments,
          and return the result of the call.  The expectation is that
          the handler will extract the payload from `msg' and return an
          object that encodes information about the extracted data.

          To find the handler, look for the following keys in the
          registry, stopping with the first one found:

                  * the string representing the full MIME type
                    (‘maintype/subtype’)

                  * the string representing the ‘maintype’

                  * the empty string

          If none of these keys produce a handler, raise a *note
          KeyError: 3e9. for the full MIME type.

      -- Method: set_content (msg, obj, *args, **kw)

          If the ‘maintype’ is ‘multipart’, raise a *note TypeError:
          1fe.; otherwise look up a handler function based on the type
          of `obj' (see next paragraph), call *note clear_content():
          2958. on the `msg', and call the handler function, passing
          through all arguments.  The expectation is that the handler
          will transform and store `obj' into `msg', possibly making
          other changes to `msg' as well, such as adding various MIME
          headers to encode information needed to interpret the stored
          data.

          To find the handler, obtain the type of `obj' (‘typ =
          type(obj)’), and look for the following keys in the registry,
          stopping with the first one found:

                  * the type itself (‘typ’)

                  * the type’s fully qualified name (‘typ.__module__ +
                    '.' + typ.__qualname__’).

                  * the type’s qualname (‘typ.__qualname__’)

                  * the type’s name (‘typ.__name__’).

          If none of the above match, repeat all of the checks above for
          each of the types in the *note MRO: 29c7. (‘typ.__mro__’).
          Finally, if no other key yields a handler, check for a handler
          for the key ‘None’.  If there is no handler for ‘None’, raise
          a *note KeyError: 3e9. for the fully qualified name of the
          type.

          Also add a ‘MIME-Version’ header if one is not present (see
          also *note MIMEPart: 930.).

      -- Method: add_get_handler (key, handler)

          Record the function `handler' as the handler for `key'.  For
          the possible values of `key', see *note get_content(): 29c9.

      -- Method: add_set_handler (typekey, handler)

          Record `handler' as the function to call when an object of a
          type matching `typekey' is passed to *note set_content():
          29cb.  For the possible values of `typekey', see *note
          set_content(): 29cb.

* Menu:

* Content Manager Instances::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/email/contentmanager.py

   (2) (1) Originally added in 3.4 as a *note provisional module: a61.


File: python.info,  Node: Content Manager Instances,  Up: email contentmanager Managing MIME Content

5.19.1.11 Content Manager Instances
...................................

Currently the email package provides only one concrete content manager,
*note raw_data_manager: 2982, although more may be added in the future.
*note raw_data_manager: 2982. is the *note content_manager: 931.
provided by *note EmailPolicy: ad7. and its derivatives.

 -- Data: email.contentmanager.raw_data_manager

     This content manager provides only a minimum interface beyond that
     provided by *note Message: 63b. itself: it deals only with text,
     raw byte strings, and *note Message: 63b. objects.  Nevertheless,
     it provides significant advantages compared to the base API:
     ‘get_content’ on a text part will return a unicode string without
     the application needing to manually decode it, ‘set_content’
     provides a rich set of options for controlling the headers added to
     a part and controlling the content transfer encoding, and it
     enables the use of the various ‘add_’ methods, thereby simplifying
     the creation of multipart messages.

      -- Method: email.contentmanager.get_content (msg,
               errors='replace')

          Return the payload of the part as either a string (for ‘text’
          parts), an *note EmailMessage: 63c. object (for
          ‘message/rfc822’ parts), or a ‘bytes’ object (for all other
          non-multipart types).  Raise a *note KeyError: 3e9. if called
          on a ‘multipart’.  If the part is a ‘text’ part and `errors'
          is specified, use it as the error handler when decoding the
          payload to unicode.  The default error handler is ‘replace’.

      -- Method: email.contentmanager.set_content (msg, <'str'>,
               subtype="plain", charset='utf-8', cte=None,
               disposition=None, filename=None, cid=None, params=None,
               headers=None)

      -- Method: email.contentmanager.set_content (msg, <'bytes'>,
               maintype, subtype, cte="base64", disposition=None,
               filename=None, cid=None, params=None, headers=None)

      -- Method: email.contentmanager.set_content (msg,
               <'EmailMessage'>, cte=None, disposition=None,
               filename=None, cid=None, params=None, headers=None)

          Add headers and payload to `msg':

          Add a ‘Content-Type’ header with a ‘maintype/subtype’ value.

                  * For ‘str’, set the MIME ‘maintype’ to ‘text’, and
                    set the subtype to `subtype' if it is specified, or
                    ‘plain’ if it is not.

                  * For ‘bytes’, use the specified `maintype' and
                    `subtype', or raise a *note TypeError: 1fe. if they
                    are not specified.

                  * For *note EmailMessage: 63c. objects, set the
                    maintype to ‘message’, and set the subtype to
                    `subtype' if it is specified or ‘rfc822’ if it is
                    not.  If `subtype' is ‘partial’, raise an error
                    (‘bytes’ objects must be used to construct
                    ‘message/partial’ parts).

          If `charset' is provided (which is valid only for ‘str’),
          encode the string to bytes using the specified character set.
          The default is ‘utf-8’.  If the specified `charset' is a known
          alias for a standard MIME charset name, use the standard
          charset instead.

          If `cte' is set, encode the payload using the specified
          content transfer encoding, and set the
          ‘Content-Transfer-Encoding’ header to that value.  Possible
          values for `cte' are ‘quoted-printable’, ‘base64’, ‘7bit’,
          ‘8bit’, and ‘binary’.  If the input cannot be encoded in the
          specified encoding (for example, specifying a `cte' of ‘7bit’
          for an input that contains non-ASCII values), raise a *note
          ValueError: 16d.

                  * For ‘str’ objects, if `cte' is not set use
                    heuristics to determine the most compact encoding.

                  * For *note EmailMessage: 63c, per RFC 2046(1), raise
                    an error if a `cte' of ‘quoted-printable’ or
                    ‘base64’ is requested for `subtype' ‘rfc822’, and
                    for any `cte' other than ‘7bit’ for `subtype'
                    ‘external-body’.  For ‘message/rfc822’, use ‘8bit’
                    if `cte' is not specified.  For all other values of
                    `subtype', use ‘7bit’.

               Note: A `cte' of ‘binary’ does not actually work
               correctly yet.  The ‘EmailMessage’ object as modified by
               ‘set_content’ is correct, but *note BytesGenerator: c1f.
               does not serialize it correctly.

          If `disposition' is set, use it as the value of the
          ‘Content-Disposition’ header.  If not specified, and
          `filename' is specified, add the header with the value
          ‘attachment’.  If `disposition' is not specified and
          `filename' is also not specified, do not add the header.  The
          only valid values for `disposition' are ‘attachment’ and
          ‘inline’.

          If `filename' is specified, use it as the value of the
          ‘filename’ parameter of the ‘Content-Disposition’ header.

          If `cid' is specified, add a ‘Content-ID’ header with `cid' as
          its value.

          If `params' is specified, iterate its ‘items’ method and use
          the resulting ‘(key, value)’ pairs to set additional
          parameters on the ‘Content-Type’ header.

          If `headers' is specified and is a list of strings of the form
          ‘headername: headervalue’ or a list of ‘header’ objects
          (distinguished from strings by having a ‘name’ attribute), add
          the headers to `msg'.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2046.html


File: python.info,  Node: email Examples,  Next: email message Message Representing an email message using the compat32 API,  Prev: email contentmanager Managing MIME Content,  Up: email — An email and MIME handling package

5.19.1.12 ‘email’: Examples
...........................

Here are a few examples of how to use the *note email: 67. package to
read, write, and send simple email messages, as well as more complex
MIME messages.

First, let’s see how to create and send a simple text message (both the
text content and the addresses may contain unicode characters):

     # Import smtplib for the actual sending function
     import smtplib

     # Import the email modules we'll need
     from email.message import EmailMessage

     # Open the plain text file whose name is in textfile for reading.
     with open(textfile) as fp:
         # Create a text/plain message
         msg = EmailMessage()
         msg.set_content(fp.read())

     # me == the sender's email address
     # you == the recipient's email address
     msg['Subject'] = f'The contents of {textfile}'
     msg['From'] = me
     msg['To'] = you

     # Send the message via our own SMTP server.
     s = smtplib.SMTP('localhost')
     s.send_message(msg)
     s.quit()

Parsing RFC 822(1) headers can easily be done by the using the classes
from the *note parser: 72. module:

     # Import the email modules we'll need
     from email.parser import BytesParser, Parser
     from email.policy import default

     # If the e-mail headers are in a file, uncomment these two lines:
     # with open(messagefile, 'rb') as fp:
     #     headers = BytesParser(policy=default).parse(fp)

     #  Or for parsing headers in a string (this is an uncommon operation), use:
     headers = Parser(policy=default).parsestr(
             'From: Foo Bar <user@example.com>\n'
             'To: <someone_else@example.com>\n'
             'Subject: Test message\n'
             '\n'
             'Body would go here\n')

     #  Now the header items can be accessed as a dictionary:
     print('To: {}'.format(headers['to']))
     print('From: {}'.format(headers['from']))
     print('Subject: {}'.format(headers['subject']))

     # You can also access the parts of the addresses:
     print('Recipient username: {}'.format(headers['to'].addresses[0].username))
     print('Sender name: {}'.format(headers['from'].addresses[0].display_name))

Here’s an example of how to send a MIME message containing a bunch of
family pictures that may be residing in a directory:

     # Import smtplib for the actual sending function
     import smtplib

     # And imghdr to find the types of our images
     import imghdr

     # Here are the email package modules we'll need
     from email.message import EmailMessage

     # Create the container email message.
     msg = EmailMessage()
     msg['Subject'] = 'Our family reunion'
     # me == the sender's email address
     # family = the list of all recipients' email addresses
     msg['From'] = me
     msg['To'] = ', '.join(family)
     msg.preamble = 'You will not see this in a MIME-aware mail reader.\n'

     # Open the files in binary mode.  Use imghdr to figure out the
     # MIME subtype for each specific image.
     for file in pngfiles:
         with open(file, 'rb') as fp:
             img_data = fp.read()
         msg.add_attachment(img_data, maintype='image',
                                      subtype=imghdr.what(None, img_data))

     # Send the email via our own SMTP server.
     with smtplib.SMTP('localhost') as s:
         s.send_message(msg)

Here’s an example of how to send the entire contents of a directory as
an email message: (2)

     #!/usr/bin/env python3

     """Send the contents of a directory as a MIME message."""

     import os
     import smtplib
     # For guessing MIME type based on file name extension
     import mimetypes

     from argparse import ArgumentParser

     from email.message import EmailMessage
     from email.policy import SMTP


     def main():
         parser = ArgumentParser(description="""\
     Send the contents of a directory as a MIME message.
     Unless the -o option is given, the email is sent by forwarding to your local
     SMTP server, which then does the normal delivery process.  Your local machine
     must be running an SMTP server.
     """)
         parser.add_argument('-d', '--directory',
                             help="""Mail the contents of the specified directory,
                             otherwise use the current directory.  Only the regular
                             files in the directory are sent, and we don't recurse to
                             subdirectories.""")
         parser.add_argument('-o', '--output',
                             metavar='FILE',
                             help="""Print the composed message to FILE instead of
                             sending the message to the SMTP server.""")
         parser.add_argument('-s', '--sender', required=True,
                             help='The value of the From: header (required)')
         parser.add_argument('-r', '--recipient', required=True,
                             action='append', metavar='RECIPIENT',
                             default=[], dest='recipients',
                             help='A To: header value (at least one required)')
         args = parser.parse_args()
         directory = args.directory
         if not directory:
             directory = '.'
         # Create the message
         msg = EmailMessage()
         msg['Subject'] = f'Contents of directory {os.path.abspath(directory)}'
         msg['To'] = ', '.join(args.recipients)
         msg['From'] = args.sender
         msg.preamble = 'You will not see this in a MIME-aware mail reader.\n'

         for filename in os.listdir(directory):
             path = os.path.join(directory, filename)
             if not os.path.isfile(path):
                 continue
             # Guess the content type based on the file's extension.  Encoding
             # will be ignored, although we should check for simple things like
             # gzip'd or compressed files.
             ctype, encoding = mimetypes.guess_type(path)
             if ctype is None or encoding is not None:
                 # No guess could be made, or the file is encoded (compressed), so
                 # use a generic bag-of-bits type.
                 ctype = 'application/octet-stream'
             maintype, subtype = ctype.split('/', 1)
             with open(path, 'rb') as fp:
                 msg.add_attachment(fp.read(),
                                    maintype=maintype,
                                    subtype=subtype,
                                    filename=filename)
         # Now send or store the message
         if args.output:
             with open(args.output, 'wb') as fp:
                 fp.write(msg.as_bytes(policy=SMTP))
         else:
             with smtplib.SMTP('localhost') as s:
                 s.send_message(msg)


     if __name__ == '__main__':
         main()

Here’s an example of how to unpack a MIME message like the one above,
into a directory of files:

     #!/usr/bin/env python3

     """Unpack a MIME message into a directory of files."""

     import os
     import email
     import mimetypes

     from email.policy import default

     from argparse import ArgumentParser


     def main():
         parser = ArgumentParser(description="""\
     Unpack a MIME message into a directory of files.
     """)
         parser.add_argument('-d', '--directory', required=True,
                             help="""Unpack the MIME message into the named
                             directory, which will be created if it doesn't already
                             exist.""")
         parser.add_argument('msgfile')
         args = parser.parse_args()

         with open(args.msgfile, 'rb') as fp:
             msg = email.message_from_binary_file(fp, policy=default)

         try:
             os.mkdir(args.directory)
         except FileExistsError:
             pass

         counter = 1
         for part in msg.walk():
             # multipart/* are just containers
             if part.get_content_maintype() == 'multipart':
                 continue
             # Applications should really sanitize the given filename so that an
             # email message can't be used to overwrite important files
             filename = part.get_filename()
             if not filename:
                 ext = mimetypes.guess_extension(part.get_content_type())
                 if not ext:
                     # Use a generic bag-of-bits extension
                     ext = '.bin'
                 filename = f'part-{counter:03d}{ext}'
             counter += 1
             with open(os.path.join(args.directory, filename), 'wb') as fp:
                 fp.write(part.get_payload(decode=True))


     if __name__ == '__main__':
         main()

Here’s an example of how to create an HTML message with an alternative
plain text version.  To make things a bit more interesting, we include a
related image in the html part, and we save a copy of what we are going
to send to disk, as well as sending it.

     #!/usr/bin/env python3

     import smtplib

     from email.message import EmailMessage
     from email.headerregistry import Address
     from email.utils import make_msgid

     # Create the base text message.
     msg = EmailMessage()
     msg['Subject'] = "Ayons asperges pour le déjeuner"
     msg['From'] = Address("Pepé Le Pew", "pepe", "example.com")
     msg['To'] = (Address("Penelope Pussycat", "penelope", "example.com"),
                  Address("Fabrette Pussycat", "fabrette", "example.com"))
     msg.set_content("""\
     Salut!

     Cela ressemble à un excellent recipie[1] déjeuner.

     [1] http://www.yummly.com/recipe/Roasted-Asparagus-Epicurious-203718

     --Pepé
     """)

     # Add the html version.  This converts the message into a multipart/alternative
     # container, with the original text message as the first part and the new html
     # message as the second part.
     asparagus_cid = make_msgid()
     msg.add_alternative("""\
     <html>
       <head></head>
       <body>
         <p>Salut!</p>
         <p>Cela ressemble à un excellent
             <a href="http://www.yummly.com/recipe/Roasted-Asparagus-Epicurious-203718">
                 recipie
             </a> déjeuner.
         </p>
         <img src="cid:{asparagus_cid}" />
       </body>
     </html>
     """.format(asparagus_cid=asparagus_cid[1:-1]), subtype='html')
     # note that we needed to peel the <> off the msgid for use in the html.

     # Now add the related image to the html part.
     with open("roasted-asparagus.jpg", 'rb') as img:
         msg.get_payload()[1].add_related(img.read(), 'image', 'jpeg',
                                          cid=asparagus_cid)

     # Make a local copy of what we are going to send.
     with open('outgoing.msg', 'wb') as f:
         f.write(bytes(msg))

     # Send the message via local SMTP server.
     with smtplib.SMTP('localhost') as s:
         s.send_message(msg)

If we were sent the message from the last example, here is one way we
could process it:

     import os
     import sys
     import tempfile
     import mimetypes
     import webbrowser

     # Import the email modules we'll need
     from email import policy
     from email.parser import BytesParser

     # An imaginary module that would make this work and be safe.
     from imaginary import magic_html_parser

     # In a real program you'd get the filename from the arguments.
     with open('outgoing.msg', 'rb') as fp:
         msg = BytesParser(policy=policy.default).parse(fp)

     # Now the header items can be accessed as a dictionary, and any non-ASCII will
     # be converted to unicode:
     print('To:', msg['to'])
     print('From:', msg['from'])
     print('Subject:', msg['subject'])

     # If we want to print a preview of the message content, we can extract whatever
     # the least formatted payload is and print the first three lines.  Of course,
     # if the message has no plain text part printing the first three lines of html
     # is probably useless, but this is just a conceptual example.
     simplest = msg.get_body(preferencelist=('plain', 'html'))
     print()
     print(''.join(simplest.get_content().splitlines(keepends=True)[:3]))

     ans = input("View full message?")
     if ans.lower()[0] == 'n':
         sys.exit()

     # We can extract the richest alternative in order to display it:
     richest = msg.get_body()
     partfiles = {}
     if richest['content-type'].maintype == 'text':
         if richest['content-type'].subtype == 'plain':
             for line in richest.get_content().splitlines():
                 print(line)
             sys.exit()
         elif richest['content-type'].subtype == 'html':
             body = richest
         else:
             print("Don't know how to display {}".format(richest.get_content_type()))
             sys.exit()
     elif richest['content-type'].content_type == 'multipart/related':
         body = richest.get_body(preferencelist=('html'))
         for part in richest.iter_attachments():
             fn = part.get_filename()
             if fn:
                 extension = os.path.splitext(part.get_filename())[1]
             else:
                 extension = mimetypes.guess_extension(part.get_content_type())
             with tempfile.NamedTemporaryFile(suffix=extension, delete=False) as f:
                 f.write(part.get_content())
                 # again strip the <> to go from email form of cid to html form.
                 partfiles[part['content-id'][1:-1]] = f.name
     else:
         print("Don't know how to display {}".format(richest.get_content_type()))
         sys.exit()
     with tempfile.NamedTemporaryFile(mode='w', delete=False) as f:
         # The magic_html_parser has to rewrite the href="cid:...." attributes to
         # point to the filenames in partfiles.  It also has to do a safety-sanitize
         # of the html.  It could be written using html.parser.
         f.write(magic_html_parser(body.get_content(), partfiles))
     webbrowser.open(f.name)
     os.remove(f.name)
     for fn in partfiles.values():
         os.remove(fn)

     # Of course, there are lots of email messages that could break this simple
     # minded program, but it will handle the most common ones.

Up to the prompt, the output from the above is:

     To: Penelope Pussycat <penelope@example.com>, Fabrette Pussycat <fabrette@example.com>
     From: Pepé Le Pew <pepe@example.com>
     Subject: Ayons asperges pour le déjeuner

     Salut!

     Cela ressemble à un excellent recipie[1] déjeuner.

Legacy API:

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc822.html

   (2) (1) Thanks to Matthew Dixon Cowles for the original inspiration
and examples.


File: python.info,  Node: email message Message Representing an email message using the compat32 API,  Next: email mime Creating email and MIME objects from scratch,  Prev: email Examples,  Up: email — An email and MIME handling package

5.19.1.13 ‘email.message.Message’: Representing an email message using the ‘compat32’ API
.........................................................................................

The *note Message: 63b. class is very similar to the *note EmailMessage:
63c. class, without the methods added by that class, and with the
default behavior of certain other methods being slightly different.  We
also document here some methods that, while supported by the *note
EmailMessage: 63c. class, are not recommended unless you are dealing
with legacy code.

The philosophy and structure of the two classes is otherwise the same.

This document describes the behavior under the default (for *note
Message: 63b.) policy *note Compat32: ad4.  If you are going to use
another policy, you should be using the *note EmailMessage: 63c. class
instead.

An email message consists of `headers' and a `payload'.  Headers must be
RFC 5322(1) style names and values, where the field name and value are
separated by a colon.  The colon is not part of either the field name or
the field value.  The payload may be a simple text message, or a binary
object, or a structured sequence of sub-messages each with their own set
of headers and their own payload.  The latter type of payload is
indicated by the message having a MIME type such as ‘multipart/*’ or
‘message/rfc822’.

The conceptual model provided by a *note Message: 63b. object is that of
an ordered dictionary of headers with additional methods for accessing
both specialized information from the headers, for accessing the
payload, for generating a serialized version of the message, and for
recursively walking over the object tree.  Note that duplicate headers
are supported but special methods must be used to access them.

The *note Message: 63b. pseudo-dictionary is indexed by the header
names, which must be ASCII values.  The values of the dictionary are
strings that are supposed to contain only ASCII characters; there is
some special handling for non-ASCII input, but it doesn’t always produce
the correct results.  Headers are stored and returned in case-preserving
form, but field names are matched case-insensitively.  There may also be
a single envelope header, also known as the `Unix-From' header or the
‘From_’ header.  The `payload' is either a string or bytes, in the case
of simple message objects, or a list of *note Message: 63b. objects, for
MIME container documents (e.g.  ‘multipart/*’ and ‘message/rfc822’).

Here are the methods of the *note Message: 63b. class:

 -- Class: email.message.Message (policy=compat32)

     If `policy' is specified (it must be an instance of a *note policy:
     73. class) use the rules it specifies to update and serialize the
     representation of the message.  If `policy' is not set, use the
     *note compat32: ad4. policy, which maintains backward compatibility
     with the Python 3.2 version of the email package.  For more
     information see the *note policy: 73. documentation.

     Changed in version 3.3: The `policy' keyword argument was added.

      -- Method: as_string (unixfrom=False, maxheaderlen=0, policy=None)

          Return the entire message flattened as a string.  When
          optional `unixfrom' is true, the envelope header is included
          in the returned string.  `unixfrom' defaults to ‘False’.  For
          backward compatibility reasons, `maxheaderlen' defaults to
          ‘0’, so if you want a different value you must override it
          explicitly (the value specified for `max_line_length' in the
          policy will be ignored by this method).  The `policy' argument
          may be used to override the default policy obtained from the
          message instance.  This can be used to control some of the
          formatting produced by the method, since the specified
          `policy' will be passed to the ‘Generator’.

          Flattening the message may trigger changes to the *note
          Message: 63b. if defaults need to be filled in to complete the
          transformation to a string (for example, MIME boundaries may
          be generated or modified).

          Note that this method is provided as a convenience and may not
          always format the message the way you want.  For example, by
          default it does not do the mangling of lines that begin with
          ‘From’ that is required by the unix mbox format.  For more
          flexibility, instantiate a *note Generator: c1e. instance and
          use its *note flatten(): 2970. method directly.  For example:

               from io import StringIO
               from email.generator import Generator
               fp = StringIO()
               g = Generator(fp, mangle_from_=True, maxheaderlen=60)
               g.flatten(msg)
               text = fp.getvalue()

          If the message object contains binary data that is not encoded
          according to RFC standards, the non-compliant data will be
          replaced by unicode “unknown character” code points.  (See
          also *note as_bytes(): 92d. and *note BytesGenerator: c1f.)

          Changed in version 3.4: the `policy' keyword argument was
          added.

      -- Method: __str__ ()

          Equivalent to *note as_string(): 92c.  Allows ‘str(msg)’ to
          produce a string containing the formatted message.

      -- Method: as_bytes (unixfrom=False, policy=None)

          Return the entire message flattened as a bytes object.  When
          optional `unixfrom' is true, the envelope header is included
          in the returned string.  `unixfrom' defaults to ‘False’.  The
          `policy' argument may be used to override the default policy
          obtained from the message instance.  This can be used to
          control some of the formatting produced by the method, since
          the specified `policy' will be passed to the ‘BytesGenerator’.

          Flattening the message may trigger changes to the *note
          Message: 63b. if defaults need to be filled in to complete the
          transformation to a string (for example, MIME boundaries may
          be generated or modified).

          Note that this method is provided as a convenience and may not
          always format the message the way you want.  For example, by
          default it does not do the mangling of lines that begin with
          ‘From’ that is required by the unix mbox format.  For more
          flexibility, instantiate a *note BytesGenerator: c1f. instance
          and use its *note flatten(): 296c. method directly.  For
          example:

               from io import BytesIO
               from email.generator import BytesGenerator
               fp = BytesIO()
               g = BytesGenerator(fp, mangle_from_=True, maxheaderlen=60)
               g.flatten(msg)
               text = fp.getvalue()

          New in version 3.4.

      -- Method: __bytes__ ()

          Equivalent to *note as_bytes(): 92d.  Allows ‘bytes(msg)’ to
          produce a bytes object containing the formatted message.

          New in version 3.4.

      -- Method: is_multipart ()

          Return ‘True’ if the message’s payload is a list of sub-*note
          Message: 63b. objects, otherwise return ‘False’.  When *note
          is_multipart(): 2947. returns ‘False’, the payload should be a
          string object (which might be a CTE encoded binary payload).
          (Note that *note is_multipart(): 2947. returning ‘True’ does
          not necessarily mean that “msg.get_content_maintype() ==
          ‘multipart’” will return the ‘True’.  For example,
          ‘is_multipart’ will return ‘True’ when the *note Message: 63b.
          is of type ‘message/rfc822’.)

      -- Method: set_unixfrom (unixfrom)

          Set the message’s envelope header to `unixfrom', which should
          be a string.

      -- Method: get_unixfrom ()

          Return the message’s envelope header.  Defaults to ‘None’ if
          the envelope header was never set.

      -- Method: attach (payload)

          Add the given `payload' to the current payload, which must be
          ‘None’ or a list of *note Message: 63b. objects before the
          call.  After the call, the payload will always be a list of
          *note Message: 63b. objects.  If you want to set the payload
          to a scalar object (e.g.  a string), use *note set_payload():
          29d4. instead.

          This is a legacy method.  On the ‘EmailMessage’ class its
          functionality is replaced by *note set_content(): f81. and the
          related ‘make’ and ‘add’ methods.

      -- Method: get_payload (i=None, decode=False)

          Return the current payload, which will be a list of *note
          Message: 63b. objects when *note is_multipart(): 2947. is
          ‘True’, or a string when *note is_multipart(): 2947. is
          ‘False’.  If the payload is a list and you mutate the list
          object, you modify the message’s payload in place.

          With optional argument `i', *note get_payload(): c1d. will
          return the `i'-th element of the payload, counting from zero,
          if *note is_multipart(): 2947. is ‘True’.  An *note
          IndexError: f36. will be raised if `i' is less than 0 or
          greater than or equal to the number of items in the payload.
          If the payload is a string (i.e.  *note is_multipart(): 2947.
          is ‘False’) and `i' is given, a *note TypeError: 1fe. is
          raised.

          Optional `decode' is a flag indicating whether the payload
          should be decoded or not, according to the
          ‘Content-Transfer-Encoding’ header.  When ‘True’ and the
          message is not a multipart, the payload will be decoded if
          this header’s value is ‘quoted-printable’ or ‘base64’.  If
          some other encoding is used, or ‘Content-Transfer-Encoding’
          header is missing, the payload is returned as-is (undecoded).
          In all cases the returned value is binary data.  If the
          message is a multipart and the `decode' flag is ‘True’, then
          ‘None’ is returned.  If the payload is base64 and it was not
          perfectly formed (missing padding, characters outside the
          base64 alphabet), then an appropriate defect will be added to
          the message’s defect property (‘InvalidBase64PaddingDefect’ or
          ‘InvalidBase64CharactersDefect’, respectively).

          When `decode' is ‘False’ (the default) the body is returned as
          a string without decoding the ‘Content-Transfer-Encoding’.
          However, for a ‘Content-Transfer-Encoding’ of 8bit, an attempt
          is made to decode the original bytes using the ‘charset’
          specified by the ‘Content-Type’ header, using the ‘replace’
          error handler.  If no ‘charset’ is specified, or if the
          ‘charset’ given is not recognized by the email package, the
          body is decoded using the default ASCII charset.

          This is a legacy method.  On the ‘EmailMessage’ class its
          functionality is replaced by *note get_content(): 294d. and
          *note iter_parts(): 294c.

      -- Method: set_payload (payload, charset=None)

          Set the entire message object’s payload to `payload'.  It is
          the client’s responsibility to ensure the payload invariants.
          Optional `charset' sets the message’s default character set;
          see *note set_charset(): 29d5. for details.

          This is a legacy method.  On the ‘EmailMessage’ class its
          functionality is replaced by *note set_content(): f81.

      -- Method: set_charset (charset)

          Set the character set of the payload to `charset', which can
          either be a *note Charset: 7c7. instance (see *note
          email.charset: 68.), a string naming a character set, or
          ‘None’.  If it is a string, it will be converted to a *note
          Charset: 7c7. instance.  If `charset' is ‘None’, the ‘charset’
          parameter will be removed from the ‘Content-Type’ header (the
          message will not be otherwise modified).  Anything else will
          generate a *note TypeError: 1fe.

          If there is no existing ‘MIME-Version’ header one will be
          added.  If there is no existing ‘Content-Type’ header, one
          will be added with a value of ‘text/plain’.  Whether the
          ‘Content-Type’ header already exists or not, its ‘charset’
          parameter will be set to `charset.output_charset'.  If
          `charset.input_charset' and `charset.output_charset' differ,
          the payload will be re-encoded to the `output_charset'.  If
          there is no existing ‘Content-Transfer-Encoding’ header, then
          the payload will be transfer-encoded, if needed, using the
          specified *note Charset: 7c7, and a header with the
          appropriate value will be added.  If a
          ‘Content-Transfer-Encoding’ header already exists, the payload
          is assumed to already be correctly encoded using that
          ‘Content-Transfer-Encoding’ and is not modified.

          This is a legacy method.  On the ‘EmailMessage’ class its
          functionality is replaced by the `charset' parameter of the
          ‘email.emailmessage.EmailMessage.set_content()’ method.

      -- Method: get_charset ()

          Return the *note Charset: 7c7. instance associated with the
          message’s payload.

          This is a legacy method.  On the ‘EmailMessage’ class it
          always returns ‘None’.

     The following methods implement a mapping-like interface for
     accessing the message’s RFC 2822(2) headers.  Note that there are
     some semantic differences between these methods and a normal
     mapping (i.e.  dictionary) interface.  For example, in a dictionary
     there are no duplicate keys, but here there may be duplicate
     message headers.  Also, in dictionaries there is no guaranteed
     order to the keys returned by *note keys(): 29d7, but in a *note
     Message: 63b. object, headers are always returned in the order they
     appeared in the original message, or were added to the message
     later.  Any header deleted and then re-added are always appended to
     the end of the header list.

     These semantic differences are intentional and are biased toward
     maximal convenience.

     Note that in all cases, any envelope header present in the message
     is not included in the mapping interface.

     In a model generated from bytes, any header values that (in
     contravention of the RFCs) contain non-ASCII bytes will, when
     retrieved through this interface, be represented as *note Header:
     f83. objects with a charset of ‘unknown-8bit’.

      -- Method: __len__ ()

          Return the total number of headers, including duplicates.

      -- Method: __contains__ (name)

          Return ‘True’ if the message object has a field named `name'.
          Matching is done case-insensitively and `name' should not
          include the trailing colon.  Used for the ‘in’ operator, e.g.:

               if 'message-id' in myMessage:
                  print('Message-ID:', myMessage['message-id'])

      -- Method: __getitem__ (name)

          Return the value of the named header field.  `name' should not
          include the colon field separator.  If the header is missing,
          ‘None’ is returned; a *note KeyError: 3e9. is never raised.

          Note that if the named field appears more than once in the
          message’s headers, exactly which of those field values will be
          returned is undefined.  Use the *note get_all(): 29db. method
          to get the values of all the extant named headers.

      -- Method: __setitem__ (name, val)

          Add a header to the message with field name `name' and value
          `val'.  The field is appended to the end of the message’s
          existing fields.

          Note that this does `not' overwrite or delete any existing
          header with the same name.  If you want to ensure that the new
          header is the only one present in the message with field name
          `name', delete the field first, e.g.:

               del msg['subject']
               msg['subject'] = 'Python roolz!'

      -- Method: __delitem__ (name)

          Delete all occurrences of the field with name `name' from the
          message’s headers.  No exception is raised if the named field
          isn’t present in the headers.

      -- Method: keys ()

          Return a list of all the message’s header field names.

      -- Method: values ()

          Return a list of all the message’s field values.

      -- Method: items ()

          Return a list of 2-tuples containing all the message’s field
          headers and values.

      -- Method: get (name, failobj=None)

          Return the value of the named header field.  This is identical
          to *note __getitem__(): 29da. except that optional `failobj'
          is returned if the named header is missing (defaults to
          ‘None’).

     Here are some additional useful methods:

      -- Method: get_all (name, failobj=None)

          Return a list of all the values for the field named `name'.
          If there are no such named headers in the message, `failobj'
          is returned (defaults to ‘None’).

      -- Method: add_header (_name, _value, **_params)

          Extended header setting.  This method is similar to *note
          __setitem__(): 29dc. except that additional header parameters
          can be provided as keyword arguments.  `_name' is the header
          field to add and `_value' is the `primary' value for the
          header.

          For each item in the keyword argument dictionary `_params',
          the key is taken as the parameter name, with underscores
          converted to dashes (since dashes are illegal in Python
          identifiers).  Normally, the parameter will be added as
          ‘key="value"’ unless the value is ‘None’, in which case only
          the key will be added.  If the value contains non-ASCII
          characters, it can be specified as a three tuple in the format
          ‘(CHARSET, LANGUAGE, VALUE)’, where ‘CHARSET’ is a string
          naming the charset to be used to encode the value, ‘LANGUAGE’
          can usually be set to ‘None’ or the empty string (see RFC
          2231(3) for other possibilities), and ‘VALUE’ is the string
          value containing non-ASCII code points.  If a three tuple is
          not passed and the value contains non-ASCII characters, it is
          automatically encoded in RFC 2231(4) format using a ‘CHARSET’
          of ‘utf-8’ and a ‘LANGUAGE’ of ‘None’.

          Here’s an example:

               msg.add_header('Content-Disposition', 'attachment', filename='bud.gif')

          This will add a header that looks like

               Content-Disposition: attachment; filename="bud.gif"

          An example with non-ASCII characters:

               msg.add_header('Content-Disposition', 'attachment',
                              filename=('iso-8859-1', '', 'Fußballer.ppt'))

          Which produces

               Content-Disposition: attachment; filename*="iso-8859-1''Fu%DFballer.ppt"

      -- Method: replace_header (_name, _value)

          Replace a header.  Replace the first header found in the
          message that matches `_name', retaining header order and field
          name case.  If no matching header was found, a *note KeyError:
          3e9. is raised.

      -- Method: get_content_type ()

          Return the message’s content type.  The returned string is
          coerced to lower case of the form ‘maintype/subtype’.  If
          there was no ‘Content-Type’ header in the message the default
          type as given by *note get_default_type(): 29e4. will be
          returned.  Since according to RFC 2045(5), messages always
          have a default type, *note get_content_type(): 29e3. will
          always return a value.

          RFC 2045(6) defines a message’s default type to be
          ‘text/plain’ unless it appears inside a ‘multipart/digest’
          container, in which case it would be ‘message/rfc822’.  If the
          ‘Content-Type’ header has an invalid type specification, RFC
          2045(7) mandates that the default type be ‘text/plain’.

      -- Method: get_content_maintype ()

          Return the message’s main content type.  This is the
          ‘maintype’ part of the string returned by *note
          get_content_type(): 29e3.

      -- Method: get_content_subtype ()

          Return the message’s sub-content type.  This is the ‘subtype’
          part of the string returned by *note get_content_type(): 29e3.

      -- Method: get_default_type ()

          Return the default content type.  Most messages have a default
          content type of ‘text/plain’, except for messages that are
          subparts of ‘multipart/digest’ containers.  Such subparts have
          a default content type of ‘message/rfc822’.

      -- Method: set_default_type (ctype)

          Set the default content type.  `ctype' should either be
          ‘text/plain’ or ‘message/rfc822’, although this is not
          enforced.  The default content type is not stored in the
          ‘Content-Type’ header.

      -- Method: get_params (failobj=None, header='content-type',
               unquote=True)

          Return the message’s ‘Content-Type’ parameters, as a list.
          The elements of the returned list are 2-tuples of key/value
          pairs, as split on the ‘'='’ sign.  The left hand side of the
          ‘'='’ is the key, while the right hand side is the value.  If
          there is no ‘'='’ sign in the parameter the value is the empty
          string, otherwise the value is as described in *note
          get_param(): 29e9. and is unquoted if optional `unquote' is
          ‘True’ (the default).

          Optional `failobj' is the object to return if there is no
          ‘Content-Type’ header.  Optional `header' is the header to
          search instead of ‘Content-Type’.

          This is a legacy method.  On the ‘EmailMessage’ class its
          functionality is replaced by the `params' property of the
          individual header objects returned by the header access
          methods.

      -- Method: get_param (param, failobj=None, header='content-type',
               unquote=True)

          Return the value of the ‘Content-Type’ header’s parameter
          `param' as a string.  If the message has no ‘Content-Type’
          header or if there is no such parameter, then `failobj' is
          returned (defaults to ‘None’).

          Optional `header' if given, specifies the message header to
          use instead of ‘Content-Type’.

          Parameter keys are always compared case insensitively.  The
          return value can either be a string, or a 3-tuple if the
          parameter was RFC 2231(8) encoded.  When it’s a 3-tuple, the
          elements of the value are of the form ‘(CHARSET, LANGUAGE,
          VALUE)’.  Note that both ‘CHARSET’ and ‘LANGUAGE’ can be
          ‘None’, in which case you should consider ‘VALUE’ to be
          encoded in the ‘us-ascii’ charset.  You can usually ignore
          ‘LANGUAGE’.

          If your application doesn’t care whether the parameter was
          encoded as in RFC 2231(9), you can collapse the parameter
          value by calling *note email.utils.collapse_rfc2231_value():
          29ea, passing in the return value from *note get_param():
          29e9.  This will return a suitably decoded Unicode string when
          the value is a tuple, or the original string unquoted if it
          isn’t.  For example:

               rawparam = msg.get_param('foo')
               param = email.utils.collapse_rfc2231_value(rawparam)

          In any case, the parameter value (either the returned string,
          or the ‘VALUE’ item in the 3-tuple) is always unquoted, unless
          `unquote' is set to ‘False’.

          This is a legacy method.  On the ‘EmailMessage’ class its
          functionality is replaced by the `params' property of the
          individual header objects returned by the header access
          methods.

      -- Method: set_param (param, value, header='Content-Type',
               requote=True, charset=None, language='', replace=False)

          Set a parameter in the ‘Content-Type’ header.  If the
          parameter already exists in the header, its value will be
          replaced with `value'.  If the ‘Content-Type’ header as not
          yet been defined for this message, it will be set to
          ‘text/plain’ and the new parameter value will be appended as
          per RFC 2045(10).

          Optional `header' specifies an alternative header to
          ‘Content-Type’, and all parameters will be quoted as necessary
          unless optional `requote' is ‘False’ (the default is ‘True’).

          If optional `charset' is specified, the parameter will be
          encoded according to RFC 2231(11).  Optional `language'
          specifies the RFC 2231 language, defaulting to the empty
          string.  Both `charset' and `language' should be strings.

          If `replace' is ‘False’ (the default) the header is moved to
          the end of the list of headers.  If `replace' is ‘True’, the
          header will be updated in place.

          Changed in version 3.4: ‘replace’ keyword was added.

      -- Method: del_param (param, header='content-type', requote=True)

          Remove the given parameter completely from the ‘Content-Type’
          header.  The header will be re-written in place without the
          parameter or its value.  All values will be quoted as
          necessary unless `requote' is ‘False’ (the default is ‘True’).
          Optional `header' specifies an alternative to ‘Content-Type’.

      -- Method: set_type (type, header='Content-Type', requote=True)

          Set the main type and subtype for the ‘Content-Type’ header.
          `type' must be a string in the form ‘maintype/subtype’,
          otherwise a *note ValueError: 16d. is raised.

          This method replaces the ‘Content-Type’ header, keeping all
          the parameters in place.  If `requote' is ‘False’, this leaves
          the existing header’s quoting as is, otherwise the parameters
          will be quoted (the default).

          An alternative header can be specified in the `header'
          argument.  When the ‘Content-Type’ header is set a
          ‘MIME-Version’ header is also added.

          This is a legacy method.  On the ‘EmailMessage’ class its
          functionality is replaced by the ‘make_’ and ‘add_’ methods.

      -- Method: get_filename (failobj=None)

          Return the value of the ‘filename’ parameter of the
          ‘Content-Disposition’ header of the message.  If the header
          does not have a ‘filename’ parameter, this method falls back
          to looking for the ‘name’ parameter on the ‘Content-Type’
          header.  If neither is found, or the header is missing, then
          `failobj' is returned.  The returned string will always be
          unquoted as per *note email.utils.unquote(): 2940.

      -- Method: get_boundary (failobj=None)

          Return the value of the ‘boundary’ parameter of the
          ‘Content-Type’ header of the message, or `failobj' if either
          the header is missing, or has no ‘boundary’ parameter.  The
          returned string will always be unquoted as per *note
          email.utils.unquote(): 2940.

      -- Method: set_boundary (boundary)

          Set the ‘boundary’ parameter of the ‘Content-Type’ header to
          `boundary'.  *note set_boundary(): 29ef. will always quote
          `boundary' if necessary.  A *note HeaderParseError: 2943. is
          raised if the message object has no ‘Content-Type’ header.

          Note that using this method is subtly different than deleting
          the old ‘Content-Type’ header and adding a new one with the
          new boundary via *note add_header(): 29e1, because *note
          set_boundary(): 29ef. preserves the order of the
          ‘Content-Type’ header in the list of headers.  However, it
          does `not' preserve any continuation lines which may have been
          present in the original ‘Content-Type’ header.

      -- Method: get_content_charset (failobj=None)

          Return the ‘charset’ parameter of the ‘Content-Type’ header,
          coerced to lower case.  If there is no ‘Content-Type’ header,
          or if that header has no ‘charset’ parameter, `failobj' is
          returned.

          Note that this method differs from *note get_charset(): 29d6.
          which returns the *note Charset: 7c7. instance for the default
          encoding of the message body.

      -- Method: get_charsets (failobj=None)

          Return a list containing the character set names in the
          message.  If the message is a ‘multipart’, then the list will
          contain one element for each subpart in the payload,
          otherwise, it will be a list of length 1.

          Each item in the list will be a string which is the value of
          the ‘charset’ parameter in the ‘Content-Type’ header for the
          represented subpart.  However, if the subpart has no
          ‘Content-Type’ header, no ‘charset’ parameter, or is not of
          the ‘text’ main MIME type, then that item in the returned list
          will be `failobj'.

      -- Method: get_content_disposition ()

          Return the lowercased value (without parameters) of the
          message’s ‘Content-Disposition’ header if it has one, or
          ‘None’.  The possible values for this method are `inline',
          `attachment' or ‘None’ if the message follows RFC 2183(12).

          New in version 3.5.

      -- Method: walk ()

          The *note walk(): 29f2. method is an all-purpose generator
          which can be used to iterate over all the parts and subparts
          of a message object tree, in depth-first traversal order.  You
          will typically use *note walk(): 29f2. as the iterator in a
          ‘for’ loop; each iteration returns the next subpart.

          Here’s an example that prints the MIME type of every part of a
          multipart message structure:

               >>> for part in msg.walk():
               ...     print(part.get_content_type())
               multipart/report
               text/plain
               message/delivery-status
               text/plain
               text/plain
               message/rfc822
               text/plain

          ‘walk’ iterates over the subparts of any part where *note
          is_multipart(): 2947. returns ‘True’, even though
          ‘msg.get_content_maintype() == 'multipart'’ may return
          ‘False’.  We can see this in our example by making use of the
          ‘_structure’ debug helper function:

               >>> for part in msg.walk():
               ...     print(part.get_content_maintype() == 'multipart',
               ...           part.is_multipart())
               True True
               False False
               False True
               False False
               False False
               False True
               False False
               >>> _structure(msg)
               multipart/report
                   text/plain
                   message/delivery-status
                       text/plain
                       text/plain
                   message/rfc822
                       text/plain

          Here the ‘message’ parts are not ‘multiparts’, but they do
          contain subparts.  ‘is_multipart()’ returns ‘True’ and ‘walk’
          descends into the subparts.

     *note Message: 63b. objects can also optionally contain two
     instance attributes, which can be used when generating the plain
     text of a MIME message.

      -- Attribute: preamble

          The format of a MIME document allows for some text between the
          blank line following the headers, and the first multipart
          boundary string.  Normally, this text is never visible in a
          MIME-aware mail reader because it falls outside the standard
          MIME armor.  However, when viewing the raw text of the
          message, or when viewing the message in a non-MIME aware
          reader, this text can become visible.

          The `preamble' attribute contains this leading extra-armor
          text for MIME documents.  When the *note Parser: beb.
          discovers some text after the headers but before the first
          boundary string, it assigns this text to the message’s
          `preamble' attribute.  When the *note Generator: c1e. is
          writing out the plain text representation of a MIME message,
          and it finds the message has a `preamble' attribute, it will
          write this text in the area between the headers and the first
          boundary.  See *note email.parser: 72. and *note
          email.generator: 6c. for details.

          Note that if the message object has no preamble, the
          `preamble' attribute will be ‘None’.

      -- Attribute: epilogue

          The `epilogue' attribute acts the same way as the `preamble'
          attribute, except that it contains text that appears between
          the last boundary and the end of the message.

          You do not need to set the epilogue to the empty string in
          order for the *note Generator: c1e. to print a newline at the
          end of the file.

      -- Attribute: defects

          The `defects' attribute contains a list of all the problems
          found when parsing this message.  See *note email.errors: 6b.
          for a detailed description of the possible parsing defects.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc5322.html

   (2) https://tools.ietf.org/html/rfc2822.html

   (3) https://tools.ietf.org/html/rfc2231.html

   (4) https://tools.ietf.org/html/rfc2231.html

   (5) https://tools.ietf.org/html/rfc2045.html

   (6) https://tools.ietf.org/html/rfc2045.html

   (7) https://tools.ietf.org/html/rfc2045.html

   (8) https://tools.ietf.org/html/rfc2231.html

   (9) https://tools.ietf.org/html/rfc2231.html

   (10) https://tools.ietf.org/html/rfc2045.html

   (11) https://tools.ietf.org/html/rfc2231.html

   (12) https://tools.ietf.org/html/rfc2183.html


File: python.info,  Node: email mime Creating email and MIME objects from scratch,  Next: email header Internationalized headers,  Prev: email message Message Representing an email message using the compat32 API,  Up: email — An email and MIME handling package

5.19.1.14 ‘email.mime’: Creating email and MIME objects from scratch
....................................................................

`Source code:' Lib/email/mime/(1)

__________________________________________________________________

This module is part of the legacy (‘Compat32’) email API. Its
functionality is partially replaced by the *note contentmanager: 69. in
the new API, but in certain applications these classes may still be
useful, even in non-legacy code.

Ordinarily, you get a message object structure by passing a file or some
text to a parser, which parses the text and returns the root message
object.  However you can also build a complete message structure from
scratch, or even individual *note Message: 63b. objects by hand.  In
fact, you can also take an existing structure and add new *note Message:
63b. objects, move them around, etc.  This makes a very convenient
interface for slicing-and-dicing MIME messages.

You can create a new object structure by creating *note Message: 63b.
instances, adding attachments and all the appropriate headers manually.
For MIME messages though, the *note email: 67. package provides some
convenient subclasses to make things easier.

Here are the classes:

 -- Class: email.mime.base.MIMEBase (_maintype, _subtype, *,
          policy=compat32, **_params)

     Module: ‘email.mime.base’

     This is the base class for all the MIME-specific subclasses of
     *note Message: 63b.  Ordinarily you won’t create instances
     specifically of *note MIMEBase: 29f8, although you could.  *note
     MIMEBase: 29f8. is provided primarily as a convenient base class
     for more specific MIME-aware subclasses.

     `_maintype' is the ‘Content-Type’ major type (e.g.  ‘text’ or
     ‘image’), and `_subtype' is the ‘Content-Type’ minor type (e.g.
     ‘plain’ or ‘gif’).  `_params' is a parameter key/value dictionary
     and is passed directly to *note Message.add_header: 29e1.

     If `policy' is specified, (defaults to the *note compat32: ad4.
     policy) it will be passed to *note Message: 63b.

     The *note MIMEBase: 29f8. class always adds a ‘Content-Type’ header
     (based on `_maintype', `_subtype', and `_params'), and a
     ‘MIME-Version’ header (always set to ‘1.0’).

     Changed in version 3.6: Added `policy' keyword-only parameter.

 -- Class: email.mime.nonmultipart.MIMENonMultipart

     Module: ‘email.mime.nonmultipart’

     A subclass of *note MIMEBase: 29f8, this is an intermediate base
     class for MIME messages that are not ‘multipart’.  The primary
     purpose of this class is to prevent the use of the *note attach():
     2954. method, which only makes sense for ‘multipart’ messages.  If
     *note attach(): 2954. is called, a *note MultipartConversionError:
     2999. exception is raised.

 -- Class: email.mime.multipart.MIMEMultipart (_subtype='mixed',
          boundary=None, _subparts=None, *, policy=compat32, **_params)

     Module: ‘email.mime.multipart’

     A subclass of *note MIMEBase: 29f8, this is an intermediate base
     class for MIME messages that are ‘multipart’.  Optional `_subtype'
     defaults to ‘mixed’, but can be used to specify the subtype of the
     message.  A ‘Content-Type’ header of ‘multipart/_subtype’ will be
     added to the message object.  A ‘MIME-Version’ header will also be
     added.

     Optional `boundary' is the multipart boundary string.  When ‘None’
     (the default), the boundary is calculated when needed (for example,
     when the message is serialized).

     `_subparts' is a sequence of initial subparts for the payload.  It
     must be possible to convert this sequence to a list.  You can
     always attach new subparts to the message by using the *note
     Message.attach: 2954. method.

     Optional `policy' argument defaults to *note compat32: ad4.

     Additional parameters for the ‘Content-Type’ header are taken from
     the keyword arguments, or passed into the `_params' argument, which
     is a keyword dictionary.

     Changed in version 3.6: Added `policy' keyword-only parameter.

 -- Class: email.mime.application.MIMEApplication (_data,
          _subtype='octet-stream',
          _encoder=email.encoders.encode_base64, *, policy=compat32,
          **_params)

     Module: ‘email.mime.application’

     A subclass of *note MIMENonMultipart: f59, the *note
     MIMEApplication: 29fa. class is used to represent MIME message
     objects of major type ‘application’.  `_data' is a string
     containing the raw byte data.  Optional `_subtype' specifies the
     MIME subtype and defaults to ‘octet-stream’.

     Optional `_encoder' is a callable (i.e.  function) which will
     perform the actual encoding of the data for transport.  This
     callable takes one argument, which is the *note MIMEApplication:
     29fa. instance.  It should use *note get_payload(): c1d. and *note
     set_payload(): 29d4. to change the payload to encoded form.  It
     should also add any ‘Content-Transfer-Encoding’ or other headers to
     the message object as necessary.  The default encoding is base64.
     See the *note email.encoders: 6a. module for a list of the built-in
     encoders.

     Optional `policy' argument defaults to *note compat32: ad4.

     `_params' are passed straight through to the base class
     constructor.

     Changed in version 3.6: Added `policy' keyword-only parameter.

 -- Class: email.mime.audio.MIMEAudio (_audiodata, _subtype=None,
          _encoder=email.encoders.encode_base64, *, policy=compat32,
          **_params)

     Module: ‘email.mime.audio’

     A subclass of *note MIMENonMultipart: f59, the *note MIMEAudio:
     29fb. class is used to create MIME message objects of major type
     ‘audio’.  `_audiodata' is a string containing the raw audio data.
     If this data can be decoded by the standard Python module *note
     sndhdr: ee, then the subtype will be automatically included in the
     ‘Content-Type’ header.  Otherwise you can explicitly specify the
     audio subtype via the `_subtype' argument.  If the minor type could
     not be guessed and `_subtype' was not given, then *note TypeError:
     1fe. is raised.

     Optional `_encoder' is a callable (i.e.  function) which will
     perform the actual encoding of the audio data for transport.  This
     callable takes one argument, which is the *note MIMEAudio: 29fb.
     instance.  It should use *note get_payload(): c1d. and *note
     set_payload(): 29d4. to change the payload to encoded form.  It
     should also add any ‘Content-Transfer-Encoding’ or other headers to
     the message object as necessary.  The default encoding is base64.
     See the *note email.encoders: 6a. module for a list of the built-in
     encoders.

     Optional `policy' argument defaults to *note compat32: ad4.

     `_params' are passed straight through to the base class
     constructor.

     Changed in version 3.6: Added `policy' keyword-only parameter.

 -- Class: email.mime.image.MIMEImage (_imagedata, _subtype=None,
          _encoder=email.encoders.encode_base64, *, policy=compat32,
          **_params)

     Module: ‘email.mime.image’

     A subclass of *note MIMENonMultipart: f59, the *note MIMEImage:
     299a. class is used to create MIME message objects of major type
     ‘image’.  `_imagedata' is a string containing the raw image data.
     If this data can be decoded by the standard Python module *note
     imghdr: 98, then the subtype will be automatically included in the
     ‘Content-Type’ header.  Otherwise you can explicitly specify the
     image subtype via the `_subtype' argument.  If the minor type could
     not be guessed and `_subtype' was not given, then *note TypeError:
     1fe. is raised.

     Optional `_encoder' is a callable (i.e.  function) which will
     perform the actual encoding of the image data for transport.  This
     callable takes one argument, which is the *note MIMEImage: 299a.
     instance.  It should use *note get_payload(): c1d. and *note
     set_payload(): 29d4. to change the payload to encoded form.  It
     should also add any ‘Content-Transfer-Encoding’ or other headers to
     the message object as necessary.  The default encoding is base64.
     See the *note email.encoders: 6a. module for a list of the built-in
     encoders.

     Optional `policy' argument defaults to *note compat32: ad4.

     `_params' are passed straight through to the *note MIMEBase: 29f8.
     constructor.

     Changed in version 3.6: Added `policy' keyword-only parameter.

 -- Class: email.mime.message.MIMEMessage (_msg, _subtype='rfc822', *,
          policy=compat32)

     Module: ‘email.mime.message’

     A subclass of *note MIMENonMultipart: f59, the *note MIMEMessage:
     29fc. class is used to create MIME objects of main type ‘message’.
     `_msg' is used as the payload, and must be an instance of class
     *note Message: 63b. (or a subclass thereof), otherwise a *note
     TypeError: 1fe. is raised.

     Optional `_subtype' sets the subtype of the message; it defaults to
     ‘rfc822’.

     Optional `policy' argument defaults to *note compat32: ad4.

     Changed in version 3.6: Added `policy' keyword-only parameter.

 -- Class: email.mime.text.MIMEText (_text, _subtype='plain',
          _charset=None, *, policy=compat32)

     Module: ‘email.mime.text’

     A subclass of *note MIMENonMultipart: f59, the *note MIMEText: 7c6.
     class is used to create MIME objects of major type ‘text’.  `_text'
     is the string for the payload.  `_subtype' is the minor type and
     defaults to ‘plain’.  `_charset' is the character set of the text
     and is passed as an argument to the *note MIMENonMultipart: f59.
     constructor; it defaults to ‘us-ascii’ if the string contains only
     ‘ascii’ code points, and ‘utf-8’ otherwise.  The `_charset'
     parameter accepts either a string or a *note Charset: 7c7.
     instance.

     Unless the `_charset' argument is explicitly set to ‘None’, the
     MIMEText object created will have both a ‘Content-Type’ header with
     a ‘charset’ parameter, and a ‘Content-Transfer-Encoding’ header.
     This means that a subsequent ‘set_payload’ call will not result in
     an encoded payload, even if a charset is passed in the
     ‘set_payload’ command.  You can “reset” this behavior by deleting
     the ‘Content-Transfer-Encoding’ header, after which a ‘set_payload’
     call will automatically encode the new payload (and add a new
     ‘Content-Transfer-Encoding’ header).

     Optional `policy' argument defaults to *note compat32: ad4.

     Changed in version 3.5: `_charset' also accepts *note Charset: 7c7.
     instances.

     Changed in version 3.6: Added `policy' keyword-only parameter.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/email/mime/


File: python.info,  Node: email header Internationalized headers,  Next: email charset Representing character sets,  Prev: email mime Creating email and MIME objects from scratch,  Up: email — An email and MIME handling package

5.19.1.15 ‘email.header’: Internationalized headers
...................................................

`Source code:' Lib/email/header.py(1)

__________________________________________________________________

This module is part of the legacy (‘Compat32’) email API. In the current
API encoding and decoding of headers is handled transparently by the
dictionary-like API of the *note EmailMessage: 63c. class.  In addition
to uses in legacy code, this module can be useful in applications that
need to completely control the character sets used when encoding
headers.

The remaining text in this section is the original documentation of the
module.

RFC 2822(2) is the base standard that describes the format of email
messages.  It derives from the older RFC 822(3) standard which came into
widespread use at a time when most email was composed of ASCII
characters only.  RFC 2822(4) is a specification written assuming email
contains only 7-bit ASCII characters.

Of course, as email has been deployed worldwide, it has become
internationalized, such that language specific character sets can now be
used in email messages.  The base standard still requires email messages
to be transferred using only 7-bit ASCII characters, so a slew of RFCs
have been written describing how to encode email containing non-ASCII
characters into RFC 2822(5)-compliant format.  These RFCs include RFC
2045(6), RFC 2046(7), RFC 2047(8), and RFC 2231(9).  The *note email:
67. package supports these standards in its *note email.header: 6d. and
*note email.charset: 68. modules.

If you want to include non-ASCII characters in your email headers, say
in the ‘Subject’ or ‘To’ fields, you should use the *note Header: f83.
class and assign the field in the *note Message: 63b. object to an
instance of *note Header: f83. instead of using a string for the header
value.  Import the *note Header: f83. class from the *note email.header:
6d. module.  For example:

     >>> from email.message import Message
     >>> from email.header import Header
     >>> msg = Message()
     >>> h = Header('p\xf6stal', 'iso-8859-1')
     >>> msg['Subject'] = h
     >>> msg.as_string()
     'Subject: =?iso-8859-1?q?p=F6stal?=\n\n'

Notice here how we wanted the ‘Subject’ field to contain a non-ASCII
character?  We did this by creating a *note Header: f83. instance and
passing in the character set that the byte string was encoded in.  When
the subsequent *note Message: 63b. instance was flattened, the ‘Subject’
field was properly RFC 2047(10) encoded.  MIME-aware mail readers would
show this header using the embedded ISO-8859-1 character.

Here is the *note Header: f83. class description:

 -- Class: email.header.Header (s=None, charset=None, maxlinelen=None,
          header_name=None, continuation_ws=' ', errors='strict')

     Create a MIME-compliant header that can contain strings in
     different character sets.

     Optional `s' is the initial header value.  If ‘None’ (the default),
     the initial header value is not set.  You can later append to the
     header with *note append(): 29ff. method calls.  `s' may be an
     instance of *note bytes: 172. or *note str: 205, but see the *note
     append(): 29ff. documentation for semantics.

     Optional `charset' serves two purposes: it has the same meaning as
     the `charset' argument to the *note append(): 29ff. method.  It
     also sets the default character set for all subsequent *note
     append(): 29ff. calls that omit the `charset' argument.  If
     `charset' is not provided in the constructor (the default), the
     ‘us-ascii’ character set is used both as `s'’s initial charset and
     as the default for subsequent *note append(): 29ff. calls.

     The maximum line length can be specified explicitly via
     `maxlinelen'.  For splitting the first line to a shorter value (to
     account for the field header which isn’t included in `s', e.g.
     ‘Subject’) pass in the name of the field in `header_name'.  The
     default `maxlinelen' is 76, and the default value for `header_name'
     is ‘None’, meaning it is not taken into account for the first line
     of a long, split header.

     Optional `continuation_ws' must be RFC 2822(11)-compliant folding
     whitespace, and is usually either a space or a hard tab character.
     This character will be prepended to continuation lines.
     `continuation_ws' defaults to a single space character.

     Optional `errors' is passed straight through to the *note append():
     29ff. method.

      -- Method: append (s, charset=None, errors='strict')

          Append the string `s' to the MIME header.

          Optional `charset', if given, should be a *note Charset: 7c7.
          instance (see *note email.charset: 68.) or the name of a
          character set, which will be converted to a *note Charset:
          7c7. instance.  A value of ‘None’ (the default) means that the
          `charset' given in the constructor is used.

          `s' may be an instance of *note bytes: 172. or *note str: 205.
          If it is an instance of *note bytes: 172, then `charset' is
          the encoding of that byte string, and a *note UnicodeError:
          d03. will be raised if the string cannot be decoded with that
          character set.

          If `s' is an instance of *note str: 205, then `charset' is a
          hint specifying the character set of the characters in the
          string.

          In either case, when producing an RFC 2822(12)-compliant
          header using RFC 2047(13) rules, the string will be encoded
          using the output codec of the charset.  If the string cannot
          be encoded using the output codec, a UnicodeError will be
          raised.

          Optional `errors' is passed as the errors argument to the
          decode call if `s' is a byte string.

      -- Method: encode (splitchars=';, \t', maxlinelen=None,
               linesep='\n')

          Encode a message header into an RFC-compliant format, possibly
          wrapping long lines and encapsulating non-ASCII parts in
          base64 or quoted-printable encodings.

          Optional `splitchars' is a string containing characters which
          should be given extra weight by the splitting algorithm during
          normal header wrapping.  This is in very rough support of RFC
          2822(14)’s ‘higher level syntactic breaks’: split points
          preceded by a splitchar are preferred during line splitting,
          with the characters preferred in the order in which they
          appear in the string.  Space and tab may be included in the
          string to indicate whether preference should be given to one
          over the other as a split point when other split chars do not
          appear in the line being split.  Splitchars does not affect
          RFC 2047(15) encoded lines.

          `maxlinelen', if given, overrides the instance’s value for the
          maximum line length.

          `linesep' specifies the characters used to separate the lines
          of the folded header.  It defaults to the most useful value
          for Python application code (‘\n’), but ‘\r\n’ can be
          specified in order to produce headers with RFC-compliant line
          separators.

          Changed in version 3.2: Added the `linesep' argument.

     The *note Header: f83. class also provides a number of methods to
     support standard operators and built-in functions.

      -- Method: __str__ ()

          Returns an approximation of the *note Header: f83. as a
          string, using an unlimited line length.  All pieces are
          converted to unicode using the specified encoding and joined
          together appropriately.  Any pieces with a charset of
          ‘'unknown-8bit'’ are decoded as ASCII using the ‘'replace'’
          error handler.

          Changed in version 3.2: Added handling for the
          ‘'unknown-8bit'’ charset.

      -- Method: __eq__ (other)

          This method allows you to compare two *note Header: f83.
          instances for equality.

      -- Method: __ne__ (other)

          This method allows you to compare two *note Header: f83.
          instances for inequality.

The *note email.header: 6d. module also provides the following
convenient functions.

 -- Function: email.header.decode_header (header)

     Decode a message header value without converting the character set.
     The header value is in `header'.

     This function returns a list of ‘(decoded_string, charset)’ pairs
     containing each of the decoded parts of the header.  `charset' is
     ‘None’ for non-encoded parts of the header, otherwise a lower case
     string containing the name of the character set specified in the
     encoded string.

     Here’s an example:

          >>> from email.header import decode_header
          >>> decode_header('=?iso-8859-1?q?p=F6stal?=')
          [(b'p\xf6stal', 'iso-8859-1')]

 -- Function: email.header.make_header (decoded_seq, maxlinelen=None,
          header_name=None, continuation_ws=' ')

     Create a *note Header: f83. instance from a sequence of pairs as
     returned by *note decode_header(): ad8.

     *note decode_header(): ad8. takes a header value string and returns
     a sequence of pairs of the format ‘(decoded_string, charset)’ where
     `charset' is the name of the character set.

     This function takes one of those sequence of pairs and returns a
     *note Header: f83. instance.  Optional `maxlinelen', `header_name',
     and `continuation_ws' are as in the *note Header: f83. constructor.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/email/header.py

   (2) https://tools.ietf.org/html/rfc2822.html

   (3) https://tools.ietf.org/html/rfc822.html

   (4) https://tools.ietf.org/html/rfc2822.html

   (5) https://tools.ietf.org/html/rfc2822.html

   (6) https://tools.ietf.org/html/rfc2045.html

   (7) https://tools.ietf.org/html/rfc2046.html

   (8) https://tools.ietf.org/html/rfc2047.html

   (9) https://tools.ietf.org/html/rfc2231.html

   (10) https://tools.ietf.org/html/rfc2047.html

   (11) https://tools.ietf.org/html/rfc2822.html

   (12) https://tools.ietf.org/html/rfc2822.html

   (13) https://tools.ietf.org/html/rfc2047.html

   (14) https://tools.ietf.org/html/rfc2822.html

   (15) https://tools.ietf.org/html/rfc2047.html


File: python.info,  Node: email charset Representing character sets,  Next: email encoders Encoders,  Prev: email header Internationalized headers,  Up: email — An email and MIME handling package

5.19.1.16 ‘email.charset’: Representing character sets
......................................................

`Source code:' Lib/email/charset.py(1)

__________________________________________________________________

This module is part of the legacy (‘Compat32’) email API. In the new API
only the aliases table is used.

The remaining text in this section is the original documentation of the
module.

This module provides a class *note Charset: 7c7. for representing
character sets and character set conversions in email messages, as well
as a character set registry and several convenience methods for
manipulating this registry.  Instances of *note Charset: 7c7. are used
in several other modules within the *note email: 67. package.

Import this class from the *note email.charset: 68. module.

 -- Class: email.charset.Charset (input_charset=DEFAULT_CHARSET)

     Map character sets to their email properties.

     This class provides information about the requirements imposed on
     email for a specific character set.  It also provides convenience
     routines for converting between character sets, given the
     availability of the applicable codecs.  Given a character set, it
     will do its best to provide information on how to use that
     character set in an email message in an RFC-compliant way.

     Certain character sets must be encoded with quoted-printable or
     base64 when used in email headers or bodies.  Certain character
     sets must be converted outright, and are not allowed in email.

     Optional `input_charset' is as described below; it is always
     coerced to lower case.  After being alias normalized it is also
     used as a lookup into the registry of character sets to find out
     the header encoding, body encoding, and output conversion codec to
     be used for the character set.  For example, if `input_charset' is
     ‘iso-8859-1’, then headers and bodies will be encoded using
     quoted-printable and no output conversion codec is necessary.  If
     `input_charset' is ‘euc-jp’, then headers will be encoded with
     base64, bodies will not be encoded, but output text will be
     converted from the ‘euc-jp’ character set to the ‘iso-2022-jp’
     character set.

     *note Charset: 7c7. instances have the following data attributes:

      -- Attribute: input_charset

          The initial character set specified.  Common aliases are
          converted to their `official' email names (e.g.  ‘latin_1’ is
          converted to ‘iso-8859-1’).  Defaults to 7-bit ‘us-ascii’.

      -- Attribute: header_encoding

          If the character set must be encoded before it can be used in
          an email header, this attribute will be set to ‘Charset.QP’
          (for quoted-printable), ‘Charset.BASE64’ (for base64
          encoding), or ‘Charset.SHORTEST’ for the shortest of QP or
          BASE64 encoding.  Otherwise, it will be ‘None’.

      -- Attribute: body_encoding

          Same as `header_encoding', but describes the encoding for the
          mail message’s body, which indeed may be different than the
          header encoding.  ‘Charset.SHORTEST’ is not allowed for
          `body_encoding'.

      -- Attribute: output_charset

          Some character sets must be converted before they can be used
          in email headers or bodies.  If the `input_charset' is one of
          them, this attribute will contain the name of the character
          set output will be converted to.  Otherwise, it will be
          ‘None’.

      -- Attribute: input_codec

          The name of the Python codec used to convert the
          `input_charset' to Unicode.  If no conversion codec is
          necessary, this attribute will be ‘None’.

      -- Attribute: output_codec

          The name of the Python codec used to convert Unicode to the
          `output_charset'.  If no conversion codec is necessary, this
          attribute will have the same value as the `input_codec'.

     *note Charset: 7c7. instances also have the following methods:

      -- Method: get_body_encoding ()

          Return the content transfer encoding used for body encoding.

          This is either the string ‘quoted-printable’ or ‘base64’
          depending on the encoding used, or it is a function, in which
          case you should call the function with a single argument, the
          Message object being encoded.  The function should then set
          the ‘Content-Transfer-Encoding’ header itself to whatever is
          appropriate.

          Returns the string ‘quoted-printable’ if `body_encoding' is
          ‘QP’, returns the string ‘base64’ if `body_encoding' is
          ‘BASE64’, and returns the string ‘7bit’ otherwise.

      -- Method: get_output_charset ()

          Return the output character set.

          This is the `output_charset' attribute if that is not ‘None’,
          otherwise it is `input_charset'.

      -- Method: header_encode (string)

          Header-encode the string `string'.

          The type of encoding (base64 or quoted-printable) will be
          based on the `header_encoding' attribute.

      -- Method: header_encode_lines (string, maxlengths)

          Header-encode a `string' by converting it first to bytes.

          This is similar to *note header_encode(): 2a0e. except that
          the string is fit into maximum line lengths as given by the
          argument `maxlengths', which must be an iterator: each element
          returned from this iterator will provide the next maximum line
          length.

      -- Method: body_encode (string)

          Body-encode the string `string'.

          The type of encoding (base64 or quoted-printable) will be
          based on the `body_encoding' attribute.

     The *note Charset: 7c7. class also provides a number of methods to
     support standard operations and built-in functions.

      -- Method: __str__ ()

          Returns `input_charset' as a string coerced to lower case.
          *note __repr__(): 44a. is an alias for *note __str__(): 2a11.

      -- Method: __eq__ (other)

          This method allows you to compare two *note Charset: 7c7.
          instances for equality.

      -- Method: __ne__ (other)

          This method allows you to compare two *note Charset: 7c7.
          instances for inequality.

The *note email.charset: 68. module also provides the following
functions for adding new entries to the global character set, alias, and
codec registries:

 -- Function: email.charset.add_charset (charset, header_enc=None,
          body_enc=None, output_charset=None)

     Add character properties to the global registry.

     `charset' is the input character set, and must be the canonical
     name of a character set.

     Optional `header_enc' and `body_enc' is either ‘Charset.QP’ for
     quoted-printable, ‘Charset.BASE64’ for base64 encoding,
     ‘Charset.SHORTEST’ for the shortest of quoted-printable or base64
     encoding, or ‘None’ for no encoding.  ‘SHORTEST’ is only valid for
     `header_enc'.  The default is ‘None’ for no encoding.

     Optional `output_charset' is the character set that the output
     should be in.  Conversions will proceed from input charset, to
     Unicode, to the output charset when the method ‘Charset.convert()’
     is called.  The default is to output in the same character set as
     the input.

     Both `input_charset' and `output_charset' must have Unicode codec
     entries in the module’s character set-to-codec mapping; use *note
     add_codec(): 2a15. to add codecs the module does not know about.
     See the *note codecs: 1b. module’s documentation for more
     information.

     The global character set registry is kept in the module global
     dictionary ‘CHARSETS’.

 -- Function: email.charset.add_alias (alias, canonical)

     Add a character set alias.  `alias' is the alias name, e.g.
     ‘latin-1’.  `canonical' is the character set’s canonical name, e.g.
     ‘iso-8859-1’.

     The global charset alias registry is kept in the module global
     dictionary ‘ALIASES’.

 -- Function: email.charset.add_codec (charset, codecname)

     Add a codec that map characters in the given character set to and
     from Unicode.

     `charset' is the canonical name of a character set.  `codecname' is
     the name of a Python codec, as appropriate for the second argument
     to the *note str: 205.’s *note encode(): 170. method.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/email/charset.py


File: python.info,  Node: email encoders Encoders,  Next: email utils Miscellaneous utilities,  Prev: email charset Representing character sets,  Up: email — An email and MIME handling package

5.19.1.17 ‘email.encoders’: Encoders
....................................

`Source code:' Lib/email/encoders.py(1)

__________________________________________________________________

This module is part of the legacy (‘Compat32’) email API. In the new API
the functionality is provided by the `cte' parameter of the *note
set_content(): f81. method.

This module is deprecated in Python 3.  The functions provided here
should not be called explicitly since the *note MIMEText: 7c6. class
sets the content type and CTE header using the `_subtype' and `_charset'
values passed during the instantiation of that class.

The remaining text in this section is the original documentation of the
module.

When creating *note Message: 63b. objects from scratch, you often need
to encode the payloads for transport through compliant mail servers.
This is especially true for ‘image/*’ and ‘text/*’ type messages
containing binary data.

The *note email: 67. package provides some convenient encoders in its
‘encoders’ module.  These encoders are actually used by the *note
MIMEAudio: 29fb. and *note MIMEImage: 299a. class constructors to
provide default encodings.  All encoder functions take exactly one
argument, the message object to encode.  They usually extract the
payload, encode it, and reset the payload to this newly encoded value.
They should also set the ‘Content-Transfer-Encoding’ header as
appropriate.

Note that these functions are not meaningful for a multipart message.
They must be applied to individual subparts instead, and will raise a
*note TypeError: 1fe. if passed a message whose type is multipart.

Here are the encoding functions provided:

 -- Function: email.encoders.encode_quopri (msg)

     Encodes the payload into quoted-printable form and sets the
     ‘Content-Transfer-Encoding’ header to ‘quoted-printable’ (2).  This
     is a good encoding to use when most of your payload is normal
     printable data, but contains a few unprintable characters.

 -- Function: email.encoders.encode_base64 (msg)

     Encodes the payload into base64 form and sets the
     ‘Content-Transfer-Encoding’ header to ‘base64’.  This is a good
     encoding to use when most of your payload is unprintable data since
     it is a more compact form than quoted-printable.  The drawback of
     base64 encoding is that it renders the text non-human readable.

 -- Function: email.encoders.encode_7or8bit (msg)

     This doesn’t actually modify the message’s payload, but it does set
     the ‘Content-Transfer-Encoding’ header to either ‘7bit’ or ‘8bit’
     as appropriate, based on the payload data.

 -- Function: email.encoders.encode_noop (msg)

     This does nothing; it doesn’t even set the
     ‘Content-Transfer-Encoding’ header.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/email/encoders.py

   (2) (1) Note that encoding with *note encode_quopri(): 2a19. also
encodes all tabs and space characters in the data.


File: python.info,  Node: email utils Miscellaneous utilities,  Next: email iterators Iterators,  Prev: email encoders Encoders,  Up: email — An email and MIME handling package

5.19.1.18 ‘email.utils’: Miscellaneous utilities
................................................

`Source code:' Lib/email/utils.py(1)

__________________________________________________________________

There are a couple of useful utilities provided in the *note
email.utils: 74. module:

 -- Function: email.utils.localtime (dt=None)

     Return local time as an aware datetime object.  If called without
     arguments, return current time.  Otherwise `dt' argument should be
     a *note datetime: 1a0. instance, and it is converted to the local
     time zone according to the system time zone database.  If `dt' is
     naive (that is, ‘dt.tzinfo’ is ‘None’), it is assumed to be in
     local time.  In this case, a positive or zero value for `isdst'
     causes ‘localtime’ to presume initially that summer time (for
     example, Daylight Saving Time) is or is not (respectively) in
     effect for the specified time.  A negative value for `isdst' causes
     the ‘localtime’ to attempt to divine whether summer time is in
     effect for the specified time.

     New in version 3.3.

 -- Function: email.utils.make_msgid (idstring=None, domain=None)

     Returns a string suitable for an RFC 2822(2)-compliant ‘Message-ID’
     header.  Optional `idstring' if given, is a string used to
     strengthen the uniqueness of the message id.  Optional `domain' if
     given provides the portion of the msgid after the ‘@’.  The default
     is the local hostname.  It is not normally necessary to override
     this default, but may be useful certain cases, such as a
     constructing distributed system that uses a consistent domain name
     across multiple hosts.

     Changed in version 3.2: Added the `domain' keyword.

The remaining functions are part of the legacy (‘Compat32’) email API.
There is no need to directly use these with the new API, since the
parsing and formatting they provide is done automatically by the header
parsing machinery of the new API.

 -- Function: email.utils.quote (str)

     Return a new string with backslashes in `str' replaced by two
     backslashes, and double quotes replaced by backslash-double quote.

 -- Function: email.utils.unquote (str)

     Return a new string which is an `unquoted' version of `str'.  If
     `str' ends and begins with double quotes, they are stripped off.
     Likewise if `str' ends and begins with angle brackets, they are
     stripped off.

 -- Function: email.utils.parseaddr (address)

     Parse address – which should be the value of some
     address-containing field such as ‘To’ or ‘Cc’ – into its
     constituent `realname' and `email address' parts.  Returns a tuple
     of that information, unless the parse fails, in which case a
     2-tuple of ‘('', '')’ is returned.

 -- Function: email.utils.formataddr (pair, charset='utf-8')

     The inverse of *note parseaddr(): 2a21, this takes a 2-tuple of the
     form ‘(realname, email_address)’ and returns the string value
     suitable for a ‘To’ or ‘Cc’ header.  If the first element of `pair'
     is false, then the second element is returned unmodified.

     Optional `charset' is the character set that will be used in the
     RFC 2047(3) encoding of the ‘realname’ if the ‘realname’ contains
     non-ASCII characters.  Can be an instance of *note str: 205. or a
     *note Charset: 7c7.  Defaults to ‘utf-8’.

     Changed in version 3.3: Added the `charset' option.

 -- Function: email.utils.getaddresses (fieldvalues)

     This method returns a list of 2-tuples of the form returned by
     ‘parseaddr()’.  `fieldvalues' is a sequence of header field values
     as might be returned by *note Message.get_all: 29db.  Here’s a
     simple example that gets all the recipients of a message:

          from email.utils import getaddresses

          tos = msg.get_all('to', [])
          ccs = msg.get_all('cc', [])
          resent_tos = msg.get_all('resent-to', [])
          resent_ccs = msg.get_all('resent-cc', [])
          all_recipients = getaddresses(tos + ccs + resent_tos + resent_ccs)

 -- Function: email.utils.parsedate (date)

     Attempts to parse a date according to the rules in RFC 2822(4).
     however, some mailers don’t follow that format as specified, so
     *note parsedate(): 2a22. tries to guess correctly in such cases.
     `date' is a string containing an RFC 2822(5) date, such as ‘"Mon,
     20 Nov 1995 19:12:08 -0500"’.  If it succeeds in parsing the date,
     *note parsedate(): 2a22. returns a 9-tuple that can be passed
     directly to *note time.mktime(): c36.; otherwise ‘None’ will be
     returned.  Note that indexes 6, 7, and 8 of the result tuple are
     not usable.

 -- Function: email.utils.parsedate_tz (date)

     Performs the same function as *note parsedate(): 2a22, but returns
     either ‘None’ or a 10-tuple; the first 9 elements make up a tuple
     that can be passed directly to *note time.mktime(): c36, and the
     tenth is the offset of the date’s timezone from UTC (which is the
     official term for Greenwich Mean Time) (6).  If the input string
     has no timezone, the last element of the tuple returned is ‘0’,
     which represents UTC. Note that indexes 6, 7, and 8 of the result
     tuple are not usable.

 -- Function: email.utils.parsedate_to_datetime (date)

     The inverse of *note format_datetime(): add.  Performs the same
     function as *note parsedate(): 2a22, but on success returns a *note
     datetime: 1a0.  If the input date has a timezone of ‘-0000’, the
     ‘datetime’ will be a naive ‘datetime’, and if the date is
     conforming to the RFCs it will represent a time in UTC but with no
     indication of the actual source timezone of the message the date
     comes from.  If the input date has any other valid timezone offset,
     the ‘datetime’ will be an aware ‘datetime’ with the corresponding a
     *note timezone: ae0. *note tzinfo: 180.

     New in version 3.3.

 -- Function: email.utils.mktime_tz (tuple)

     Turn a 10-tuple as returned by *note parsedate_tz(): f6a. into a
     UTC timestamp (seconds since the Epoch).  If the timezone item in
     the tuple is ‘None’, assume local time.

 -- Function: email.utils.formatdate (timeval=None, localtime=False,
          usegmt=False)

     Returns a date string as per RFC 2822(7), e.g.:

          Fri, 09 Nov 2001 01:08:47 -0000

     Optional `timeval' if given is a floating point time value as
     accepted by *note time.gmtime(): c11. and *note time.localtime():
     1080, otherwise the current time is used.

     Optional `localtime' is a flag that when ‘True’, interprets
     `timeval', and returns a date relative to the local timezone
     instead of UTC, properly taking daylight savings time into account.
     The default is ‘False’ meaning UTC is used.

     Optional `usegmt' is a flag that when ‘True’, outputs a date string
     with the timezone as an ascii string ‘GMT’, rather than a numeric
     ‘-0000’.  This is needed for some protocols (such as HTTP). This
     only applies when `localtime' is ‘False’.  The default is ‘False’.

 -- Function: email.utils.format_datetime (dt, usegmt=False)

     Like ‘formatdate’, but the input is a *note datetime: 30. instance.
     If it is a naive datetime, it is assumed to be “UTC with no
     information about the source timezone”, and the conventional
     ‘-0000’ is used for the timezone.  If it is an aware ‘datetime’,
     then the numeric timezone offset is used.  If it is an aware
     timezone with offset zero, then `usegmt' may be set to ‘True’, in
     which case the string ‘GMT’ is used instead of the numeric timezone
     offset.  This provides a way to generate standards conformant HTTP
     date headers.

     New in version 3.3.

 -- Function: email.utils.decode_rfc2231 (s)

     Decode the string `s' according to RFC 2231(8).

 -- Function: email.utils.encode_rfc2231 (s, charset=None,
          language=None)

     Encode the string `s' according to RFC 2231(9).  Optional `charset'
     and `language', if given is the character set name and language
     name to use.  If neither is given, `s' is returned as-is.  If
     `charset' is given but `language' is not, the string is encoded
     using the empty string for `language'.

 -- Function: email.utils.collapse_rfc2231_value (value,
          errors='replace', fallback_charset='us-ascii')

     When a header parameter is encoded in RFC 2231(10) format, *note
     Message.get_param: 29e9. may return a 3-tuple containing the
     character set, language, and value.  *note
     collapse_rfc2231_value(): 29ea. turns this into a unicode string.
     Optional `errors' is passed to the `errors' argument of *note str:
     205.’s *note encode(): 170. method; it defaults to ‘'replace'’.
     Optional `fallback_charset' specifies the character set to use if
     the one in the RFC 2231(11) header is not known by Python; it
     defaults to ‘'us-ascii'’.

     For convenience, if the `value' passed to *note
     collapse_rfc2231_value(): 29ea. is not a tuple, it should be a
     string and it is returned unquoted.

 -- Function: email.utils.decode_params (params)

     Decode parameters list according to RFC 2231(12).  `params' is a
     sequence of 2-tuples containing elements of the form
     ‘(content-type, string-value)’.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/email/utils.py

   (2) https://tools.ietf.org/html/rfc2822.html

   (3) https://tools.ietf.org/html/rfc2047.html

   (4) https://tools.ietf.org/html/rfc2822.html

   (5) https://tools.ietf.org/html/rfc2822.html

   (6) (1) Note that the sign of the timezone offset is the opposite of
the sign of the ‘time.timezone’ variable for the same timezone; the
latter variable follows the POSIX standard while this module follows RFC
2822 (https://tools.ietf.org/html/rfc2822.html).

   (7) https://tools.ietf.org/html/rfc2822.html

   (8) https://tools.ietf.org/html/rfc2231.html

   (9) https://tools.ietf.org/html/rfc2231.html

   (10) https://tools.ietf.org/html/rfc2231.html

   (11) https://tools.ietf.org/html/rfc2231.html

   (12) https://tools.ietf.org/html/rfc2231.html


File: python.info,  Node: email iterators Iterators,  Prev: email utils Miscellaneous utilities,  Up: email — An email and MIME handling package

5.19.1.19 ‘email.iterators’: Iterators
......................................

`Source code:' Lib/email/iterators.py(1)

__________________________________________________________________

Iterating over a message object tree is fairly easy with the *note
Message.walk: 29f2. method.  The *note email.iterators: 6f. module
provides some useful higher level iterations over message object trees.

 -- Function: email.iterators.body_line_iterator (msg, decode=False)

     This iterates over all the payloads in all the subparts of `msg',
     returning the string payloads line-by-line.  It skips over all the
     subpart headers, and it skips over any subpart with a payload that
     isn’t a Python string.  This is somewhat equivalent to reading the
     flat text representation of the message from a file using *note
     readline(): 1d5b, skipping over all the intervening headers.

     Optional `decode' is passed through to *note Message.get_payload:
     c1d.

 -- Function: email.iterators.typed_subpart_iterator (msg,
          maintype='text', subtype=None)

     This iterates over all the subparts of `msg', returning only those
     subparts that match the MIME type specified by `maintype' and
     `subtype'.

     Note that `subtype' is optional; if omitted, then subpart MIME type
     matching is done only with the main type.  `maintype' is optional
     too; it defaults to ‘text’.

     Thus, by default *note typed_subpart_iterator(): 2a2b. returns each
     subpart that has a MIME type of ‘text/*’.

The following function has been added as a useful debugging tool.  It
should `not' be considered part of the supported public interface for
the package.

 -- Function: email.iterators._structure (msg, fp=None, level=0,
          include_default=False)

     Prints an indented representation of the content types of the
     message object structure.  For example:

          >>> msg = email.message_from_file(somefile)
          >>> _structure(msg)
          multipart/mixed
              text/plain
              text/plain
              multipart/digest
                  message/rfc822
                      text/plain
                  message/rfc822
                      text/plain
                  message/rfc822
                      text/plain
                  message/rfc822
                      text/plain
                  message/rfc822
                      text/plain
              text/plain

     Optional `fp' is a file-like object to print the output to.  It
     must be suitable for Python’s *note print(): 971. function.
     `level' is used internally.  `include_default', if true, prints the
     default type as well.

See also
........

Module *note smtplib: ed.

     SMTP (Simple Mail Transport Protocol) client

Module *note poplib: d0.

     POP (Post Office Protocol) client

Module *note imaplib: 97.

     IMAP (Internet Message Access Protocol) client

Module *note nntplib: c0.

     NNTP (Net News Transport Protocol) client

Module *note mailbox: ae.

     Tools for creating, reading, and managing collections of messages
     on disk using a variety standard formats.

Module *note smtpd: ec.

     SMTP server framework (primarily useful for testing)

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/email/iterators.py


File: python.info,  Node: json — JSON encoder and decoder,  Next: mailcap — Mailcap file handling,  Prev: email — An email and MIME handling package,  Up: Internet Data Handling

5.19.2 ‘json’ — JSON encoder and decoder
----------------------------------------

`Source code:' Lib/json/__init__.py(1)

__________________________________________________________________

JSON (JavaScript Object Notation)(2), specified by RFC 7159(3) (which
obsoletes RFC 4627(4)) and by ECMA-404(5), is a lightweight data
interchange format inspired by JavaScript(6) object literal syntax
(although it is not a strict subset of JavaScript (7) ).

*note json: a4. exposes an API familiar to users of the standard library
*note marshal: b0. and *note pickle: ca. modules.

Encoding basic Python object hierarchies:

     >>> import json
     >>> json.dumps(['foo', {'bar': ('baz', None, 1.0, 2)}])
     '["foo", {"bar": ["baz", null, 1.0, 2]}]'
     >>> print(json.dumps("\"foo\bar"))
     "\"foo\bar"
     >>> print(json.dumps('\u1234'))
     "\u1234"
     >>> print(json.dumps('\\'))
     "\\"
     >>> print(json.dumps({"c": 0, "b": 0, "a": 0}, sort_keys=True))
     {"a": 0, "b": 0, "c": 0}
     >>> from io import StringIO
     >>> io = StringIO()
     >>> json.dump(['streaming API'], io)
     >>> io.getvalue()
     '["streaming API"]'

Compact encoding:

     >>> import json
     >>> json.dumps([1, 2, 3, {'4': 5, '6': 7}], separators=(',', ':'))
     '[1,2,3,{"4":5,"6":7}]'

Pretty printing:

     >>> import json
     >>> print(json.dumps({'4': 5, '6': 7}, sort_keys=True, indent=4))
     {
         "4": 5,
         "6": 7
     }

Decoding JSON:

     >>> import json
     >>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]')
     ['foo', {'bar': ['baz', None, 1.0, 2]}]
     >>> json.loads('"\\"foo\\bar"')
     '"foo\x08ar'
     >>> from io import StringIO
     >>> io = StringIO('["streaming API"]')
     >>> json.load(io)
     ['streaming API']

Specializing JSON object decoding:

     >>> import json
     >>> def as_complex(dct):
     ...     if '__complex__' in dct:
     ...         return complex(dct['real'], dct['imag'])
     ...     return dct
     ...
     >>> json.loads('{"__complex__": true, "real": 1, "imag": 2}',
     ...     object_hook=as_complex)
     (1+2j)
     >>> import decimal
     >>> json.loads('1.1', parse_float=decimal.Decimal)
     Decimal('1.1')

Extending *note JSONEncoder: 6fd.:

     >>> import json
     >>> class ComplexEncoder(json.JSONEncoder):
     ...     def default(self, obj):
     ...         if isinstance(obj, complex):
     ...             return [obj.real, obj.imag]
     ...         # Let the base class default method raise the TypeError
     ...         return json.JSONEncoder.default(self, obj)
     ...
     >>> json.dumps(2 + 1j, cls=ComplexEncoder)
     '[2.0, 1.0]'
     >>> ComplexEncoder().encode(2 + 1j)
     '[2.0, 1.0]'
     >>> list(ComplexEncoder().iterencode(2 + 1j))
     ['[2.0', ', 1.0', ']']

Using *note json.tool: a5. from the shell to validate and pretty-print:

     $ echo '{"json":"obj"}' | python -m json.tool
     {
         "json": "obj"
     }
     $ echo '{1.2:3.4}' | python -m json.tool
     Expecting property name enclosed in double quotes: line 1 column 2 (char 1)

See *note Command Line Interface: 2a2f. for detailed documentation.

     Note: JSON is a subset of YAML(8) 1.2.  The JSON produced by this
     module’s default settings (in particular, the default `separators'
     value) is also a subset of YAML 1.0 and 1.1.  This module can thus
     also be used as a YAML serializer.

     Note: This module’s encoders and decoders preserve input and output
     order by default.  Order is only lost if the underlying containers
     are unordered.

     Prior to Python 3.7, *note dict: 164. was not guaranteed to be
     ordered, so inputs and outputs were typically scrambled unless
     *note collections.OrderedDict: 2ea. was specifically requested.
     Starting with Python 3.7, the regular *note dict: 164. became order
     preserving, so it is no longer necessary to specify *note
     collections.OrderedDict: 2ea. for JSON generation and parsing.

* Menu:

* Basic Usage::
* Encoders and Decoders::
* Exceptions: Exceptions<14>.
* Standard Compliance and Interoperability::
* Command Line Interface: Command Line Interface<2>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/json/__init__.py

   (2) https://json.org

   (3) https://tools.ietf.org/html/rfc7159.html

   (4) https://tools.ietf.org/html/rfc4627.html

   (5) 
https://www.ecma-international.org/publications-and-standards/standards/ecma-404/

   (6) https://en.wikipedia.org/wiki/JavaScript

   (7) (1) As noted in the errata for RFC 7159
(https://www.rfc-editor.org/errata_search.php?rfc=7159), JSON permits
literal U+2028 (LINE SEPARATOR) and U+2029 (PARAGRAPH SEPARATOR)
characters in strings, whereas JavaScript (as of ECMAScript Edition 5.1)
does not.

   (8) http://yaml.org/


File: python.info,  Node: Basic Usage,  Next: Encoders and Decoders,  Up: json — JSON encoder and decoder

5.19.2.1 Basic Usage
....................

 -- Function: json.dump (obj, fp, *, skipkeys=False, ensure_ascii=True,
          check_circular=True, allow_nan=True, cls=None, indent=None,
          separators=None, default=None, sort_keys=False, **kw)

     Serialize `obj' as a JSON formatted stream to `fp' (a
     ‘.write()’-supporting *note file-like object: 1dc6.) using this
     *note conversion table: 2a31.

     If `skipkeys' is true (default: ‘False’), then dict keys that are
     not of a basic type (*note str: 205, *note int: 204, *note float:
     1fd, *note bool: 2bd, ‘None’) will be skipped instead of raising a
     *note TypeError: 1fe.

     The *note json: a4. module always produces *note str: 205. objects,
     not *note bytes: 172. objects.  Therefore, ‘fp.write()’ must
     support *note str: 205. input.

     If `ensure_ascii' is true (the default), the output is guaranteed
     to have all incoming non-ASCII characters escaped.  If
     `ensure_ascii' is false, these characters will be output as-is.

     If `check_circular' is false (default: ‘True’), then the circular
     reference check for container types will be skipped and a circular
     reference will result in an *note RecursionError: 727. (or worse).

     If `allow_nan' is false (default: ‘True’), then it will be a *note
     ValueError: 16d. to serialize out of range *note float: 1fd. values
     (‘nan’, ‘inf’, ‘-inf’) in strict compliance of the JSON
     specification.  If `allow_nan' is true, their JavaScript
     equivalents (‘NaN’, ‘Infinity’, ‘-Infinity’) will be used.

     If `indent' is a non-negative integer or string, then JSON array
     elements and object members will be pretty-printed with that indent
     level.  An indent level of 0, negative, or ‘""’ will only insert
     newlines.  ‘None’ (the default) selects the most compact
     representation.  Using a positive integer indent indents that many
     spaces per level.  If `indent' is a string (such as ‘"\t"’), that
     string is used to indent each level.

     Changed in version 3.2: Allow strings for `indent' in addition to
     integers.

     If specified, `separators' should be an ‘(item_separator,
     key_separator)’ tuple.  The default is ‘(', ', ': ')’ if `indent'
     is ‘None’ and ‘(',', ': ')’ otherwise.  To get the most compact
     JSON representation, you should specify ‘(',', ':')’ to eliminate
     whitespace.

     Changed in version 3.4: Use ‘(',', ': ')’ as default if `indent' is
     not ‘None’.

     If specified, `default' should be a function that gets called for
     objects that can’t otherwise be serialized.  It should return a
     JSON encodable version of the object or raise a *note TypeError:
     1fe.  If not specified, *note TypeError: 1fe. is raised.

     If `sort_keys' is true (default: ‘False’), then the output of
     dictionaries will be sorted by key.

     To use a custom *note JSONEncoder: 6fd. subclass (e.g.  one that
     overrides the ‘default()’ method to serialize additional types),
     specify it with the `cls' kwarg; otherwise *note JSONEncoder: 6fd.
     is used.

     Changed in version 3.6: All optional parameters are now *note
     keyword-only: 3ce.

          Note: Unlike *note pickle: ca. and *note marshal: b0, JSON is
          not a framed protocol, so trying to serialize multiple objects
          with repeated calls to *note dump(): 6fb. using the same `fp'
          will result in an invalid JSON file.

 -- Function: json.dumps (obj, *, skipkeys=False, ensure_ascii=True,
          check_circular=True, allow_nan=True, cls=None, indent=None,
          separators=None, default=None, sort_keys=False, **kw)

     Serialize `obj' to a JSON formatted *note str: 205. using this
     *note conversion table: 2a31.  The arguments have the same meaning
     as in *note dump(): 6fb.

          Note: Keys in key/value pairs of JSON are always of the type
          *note str: 205.  When a dictionary is converted into JSON, all
          the keys of the dictionary are coerced to strings.  As a
          result of this, if a dictionary is converted into JSON and
          then back into a dictionary, the dictionary may not equal the
          original one.  That is, ‘loads(dumps(x)) != x’ if x has
          non-string keys.

 -- Function: json.load (fp, *, cls=None, object_hook=None,
          parse_float=None, parse_int=None, parse_constant=None,
          object_pairs_hook=None, **kw)

     Deserialize `fp' (a ‘.read()’-supporting *note text file: 13d9. or
     *note binary file: 1e01. containing a JSON document) to a Python
     object using this *note conversion table: 2a32.

     `object_hook' is an optional function that will be called with the
     result of any object literal decoded (a *note dict: 164.).  The
     return value of `object_hook' will be used instead of the *note
     dict: 164.  This feature can be used to implement custom decoders
     (e.g.  JSON-RPC(1) class hinting).

     `object_pairs_hook' is an optional function that will be called
     with the result of any object literal decoded with an ordered list
     of pairs.  The return value of `object_pairs_hook' will be used
     instead of the *note dict: 164.  This feature can be used to
     implement custom decoders.  If `object_hook' is also defined, the
     `object_pairs_hook' takes priority.

     Changed in version 3.1: Added support for `object_pairs_hook'.

     `parse_float', if specified, will be called with the string of
     every JSON float to be decoded.  By default, this is equivalent to
     ‘float(num_str)’.  This can be used to use another datatype or
     parser for JSON floats (e.g.  *note decimal.Decimal: 2c0.).

     `parse_int', if specified, will be called with the string of every
     JSON int to be decoded.  By default, this is equivalent to
     ‘int(num_str)’.  This can be used to use another datatype or parser
     for JSON integers (e.g.  *note float: 1fd.).

     `parse_constant', if specified, will be called with one of the
     following strings: ‘'-Infinity'’, ‘'Infinity'’, ‘'NaN'’.  This can
     be used to raise an exception if invalid JSON numbers are
     encountered.

     Changed in version 3.1: `parse_constant' doesn’t get called on
     ‘null’, ‘true’, ‘false’ anymore.

     To use a custom *note JSONDecoder: 6fe. subclass, specify it with
     the ‘cls’ kwarg; otherwise *note JSONDecoder: 6fe. is used.
     Additional keyword arguments will be passed to the constructor of
     the class.

     If the data being deserialized is not a valid JSON document, a
     *note JSONDecodeError: 7f7. will be raised.

     Changed in version 3.6: All optional parameters are now *note
     keyword-only: 3ce.

     Changed in version 3.6: `fp' can now be a *note binary file: 1e01.
     The input encoding should be UTF-8, UTF-16 or UTF-32.

 -- Function: json.loads (s, *, cls=None, object_hook=None,
          parse_float=None, parse_int=None, parse_constant=None,
          object_pairs_hook=None, **kw)

     Deserialize `s' (a *note str: 205, *note bytes: 172. or *note
     bytearray: 173. instance containing a JSON document) to a Python
     object using this *note conversion table: 2a32.

     The other arguments have the same meaning as in *note load(): 659.

     If the data being deserialized is not a valid JSON document, a
     *note JSONDecodeError: 7f7. will be raised.

     Changed in version 3.6: `s' can now be of type *note bytes: 172. or
     *note bytearray: 173.  The input encoding should be UTF-8, UTF-16
     or UTF-32.

     Changed in version 3.9: The keyword argument `encoding' has been
     removed.

   ---------- Footnotes ----------

   (1) http://www.jsonrpc.org


File: python.info,  Node: Encoders and Decoders,  Next: Exceptions<14>,  Prev: Basic Usage,  Up: json — JSON encoder and decoder

5.19.2.2 Encoders and Decoders
..............................

 -- Class: json.JSONDecoder (*, object_hook=None, parse_float=None,
          parse_int=None, parse_constant=None, strict=True,
          object_pairs_hook=None)

     Simple JSON decoder.

     Performs the following translations in decoding by default:

     JSON                Python
                         
     --------------------------------------------
                         
     object              dict
                         
                         
     array               list
                         
                         
     string              str
                         
                         
     number (int)        int
                         
                         
     number (real)       float
                         
                         
     true                True
                         
                         
     false               False
                         
                         
     null                None
                         

     It also understands ‘NaN’, ‘Infinity’, and ‘-Infinity’ as their
     corresponding ‘float’ values, which is outside the JSON spec.

     `object_hook', if specified, will be called with the result of
     every JSON object decoded and its return value will be used in
     place of the given *note dict: 164.  This can be used to provide
     custom deserializations (e.g.  to support JSON-RPC(1) class
     hinting).

     `object_pairs_hook', if specified will be called with the result of
     every JSON object decoded with an ordered list of pairs.  The
     return value of `object_pairs_hook' will be used instead of the
     *note dict: 164.  This feature can be used to implement custom
     decoders.  If `object_hook' is also defined, the
     `object_pairs_hook' takes priority.

     Changed in version 3.1: Added support for `object_pairs_hook'.

     `parse_float', if specified, will be called with the string of
     every JSON float to be decoded.  By default, this is equivalent to
     ‘float(num_str)’.  This can be used to use another datatype or
     parser for JSON floats (e.g.  *note decimal.Decimal: 2c0.).

     `parse_int', if specified, will be called with the string of every
     JSON int to be decoded.  By default, this is equivalent to
     ‘int(num_str)’.  This can be used to use another datatype or parser
     for JSON integers (e.g.  *note float: 1fd.).

     `parse_constant', if specified, will be called with one of the
     following strings: ‘'-Infinity'’, ‘'Infinity'’, ‘'NaN'’.  This can
     be used to raise an exception if invalid JSON numbers are
     encountered.

     If `strict' is false (‘True’ is the default), then control
     characters will be allowed inside strings.  Control characters in
     this context are those with character codes in the 0–31 range,
     including ‘'\t'’ (tab), ‘'\n'’, ‘'\r'’ and ‘'\0'’.

     If the data being deserialized is not a valid JSON document, a
     *note JSONDecodeError: 7f7. will be raised.

     Changed in version 3.6: All parameters are now *note keyword-only:
     3ce.

      -- Method: decode (s)

          Return the Python representation of `s' (a *note str: 205.
          instance containing a JSON document).

          *note JSONDecodeError: 7f7. will be raised if the given JSON
          document is not valid.

      -- Method: raw_decode (s)

          Decode a JSON document from `s' (a *note str: 205. beginning
          with a JSON document) and return a 2-tuple of the Python
          representation and the index in `s' where the document ended.

          This can be used to decode a JSON document from a string that
          may have extraneous data at the end.

 -- Class: json.JSONEncoder (*, skipkeys=False, ensure_ascii=True,
          check_circular=True, allow_nan=True, sort_keys=False,
          indent=None, separators=None, default=None)

     Extensible JSON encoder for Python data structures.

     Supports the following objects and types by default:

     Python                                       JSON
                                                  
     -----------------------------------------------------------------
                                                  
     dict                                         object
                                                  
                                                  
     list, tuple                                  array
                                                  
                                                  
     str                                          string
                                                  
                                                  
     int, float, int- & float-derived Enums       number
                                                  
                                                  
     True                                         true
                                                  
                                                  
     False                                        false
                                                  
                                                  
     None                                         null
                                                  

     Changed in version 3.4: Added support for int- and float-derived
     Enum classes.

     To extend this to recognize other objects, subclass and implement a
     *note default(): 2a36. method with another method that returns a
     serializable object for ‘o’ if possible, otherwise it should call
     the superclass implementation (to raise *note TypeError: 1fe.).

     If `skipkeys' is false (the default), a *note TypeError: 1fe. will
     be raised when trying to encode keys that are not *note str: 205,
     *note int: 204, *note float: 1fd. or ‘None’.  If `skipkeys' is
     true, such items are simply skipped.

     If `ensure_ascii' is true (the default), the output is guaranteed
     to have all incoming non-ASCII characters escaped.  If
     `ensure_ascii' is false, these characters will be output as-is.

     If `check_circular' is true (the default), then lists, dicts, and
     custom encoded objects will be checked for circular references
     during encoding to prevent an infinite recursion (which would cause
     an *note RecursionError: 727.).  Otherwise, no such check takes
     place.

     If `allow_nan' is true (the default), then ‘NaN’, ‘Infinity’, and
     ‘-Infinity’ will be encoded as such.  This behavior is not JSON
     specification compliant, but is consistent with most JavaScript
     based encoders and decoders.  Otherwise, it will be a *note
     ValueError: 16d. to encode such floats.

     If `sort_keys' is true (default: ‘False’), then the output of
     dictionaries will be sorted by key; this is useful for regression
     tests to ensure that JSON serializations can be compared on a
     day-to-day basis.

     If `indent' is a non-negative integer or string, then JSON array
     elements and object members will be pretty-printed with that indent
     level.  An indent level of 0, negative, or ‘""’ will only insert
     newlines.  ‘None’ (the default) selects the most compact
     representation.  Using a positive integer indent indents that many
     spaces per level.  If `indent' is a string (such as ‘"\t"’), that
     string is used to indent each level.

     Changed in version 3.2: Allow strings for `indent' in addition to
     integers.

     If specified, `separators' should be an ‘(item_separator,
     key_separator)’ tuple.  The default is ‘(', ', ': ')’ if `indent'
     is ‘None’ and ‘(',', ': ')’ otherwise.  To get the most compact
     JSON representation, you should specify ‘(',', ':')’ to eliminate
     whitespace.

     Changed in version 3.4: Use ‘(',', ': ')’ as default if `indent' is
     not ‘None’.

     If specified, `default' should be a function that gets called for
     objects that can’t otherwise be serialized.  It should return a
     JSON encodable version of the object or raise a *note TypeError:
     1fe.  If not specified, *note TypeError: 1fe. is raised.

     Changed in version 3.6: All parameters are now *note keyword-only:
     3ce.

      -- Method: default (o)

          Implement this method in a subclass such that it returns a
          serializable object for `o', or calls the base implementation
          (to raise a *note TypeError: 1fe.).

          For example, to support arbitrary iterators, you could
          implement *note default(): 2a36. like this:

               def default(self, o):
                  try:
                      iterable = iter(o)
                  except TypeError:
                      pass
                  else:
                      return list(iterable)
                  # Let the base class default method raise the TypeError
                  return json.JSONEncoder.default(self, o)

      -- Method: encode (o)

          Return a JSON string representation of a Python data
          structure, `o'.  For example:

               >>> json.JSONEncoder().encode({"foo": ["bar", "baz"]})
               '{"foo": ["bar", "baz"]}'

      -- Method: iterencode (o)

          Encode the given object, `o', and yield each string
          representation as available.  For example:

               for chunk in json.JSONEncoder().iterencode(bigobject):
                   mysocket.write(chunk)

   ---------- Footnotes ----------

   (1) http://www.jsonrpc.org


File: python.info,  Node: Exceptions<14>,  Next: Standard Compliance and Interoperability,  Prev: Encoders and Decoders,  Up: json — JSON encoder and decoder

5.19.2.3 Exceptions
...................

 -- Exception: json.JSONDecodeError (msg, doc, pos)

     Subclass of *note ValueError: 16d. with the following additional
     attributes:

      -- Attribute: msg

          The unformatted error message.

      -- Attribute: doc

          The JSON document being parsed.

      -- Attribute: pos

          The start index of `doc' where parsing failed.

      -- Attribute: lineno

          The line corresponding to `pos'.

      -- Attribute: colno

          The column corresponding to `pos'.

     New in version 3.5.


File: python.info,  Node: Standard Compliance and Interoperability,  Next: Command Line Interface<2>,  Prev: Exceptions<14>,  Up: json — JSON encoder and decoder

5.19.2.4 Standard Compliance and Interoperability
.................................................

The JSON format is specified by RFC 7159(1) and by ECMA-404(2).  This
section details this module’s level of compliance with the RFC. For
simplicity, *note JSONEncoder: 6fd. and *note JSONDecoder: 6fe.
subclasses, and parameters other than those explicitly mentioned, are
not considered.

This module does not comply with the RFC in a strict fashion,
implementing some extensions that are valid JavaScript but not valid
JSON. In particular:

   - Infinite and NaN number values are accepted and output;

   - Repeated names within an object are accepted, and only the value of
     the last name-value pair is used.

Since the RFC permits RFC-compliant parsers to accept input texts that
are not RFC-compliant, this module’s deserializer is technically
RFC-compliant under default settings.

* Menu:

* Character Encodings::
* Infinite and NaN Number Values::
* Repeated Names Within an Object::
* Top-level Non-Object, Non-Array Values: Top-level Non-Object Non-Array Values.
* Implementation Limitations::

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc7159.html

   (2) 
https://www.ecma-international.org/publications-and-standards/standards/ecma-404/


File: python.info,  Node: Character Encodings,  Next: Infinite and NaN Number Values,  Up: Standard Compliance and Interoperability

5.19.2.5 Character Encodings
............................

The RFC requires that JSON be represented using either UTF-8, UTF-16, or
UTF-32, with UTF-8 being the recommended default for maximum
interoperability.

As permitted, though not required, by the RFC, this module’s serializer
sets `ensure_ascii=True' by default, thus escaping the output so that
the resulting strings only contain ASCII characters.

Other than the `ensure_ascii' parameter, this module is defined strictly
in terms of conversion between Python objects and *note Unicode strings:
205, and thus does not otherwise directly address the issue of character
encodings.

The RFC prohibits adding a byte order mark (BOM) to the start of a JSON
text, and this module’s serializer does not add a BOM to its output.
The RFC permits, but does not require, JSON deserializers to ignore an
initial BOM in their input.  This module’s deserializer raises a *note
ValueError: 16d. when an initial BOM is present.

The RFC does not explicitly forbid JSON strings which contain byte
sequences that don’t correspond to valid Unicode characters (e.g.
unpaired UTF-16 surrogates), but it does note that they may cause
interoperability problems.  By default, this module accepts and outputs
(when present in the original *note str: 205.) code points for such
sequences.


File: python.info,  Node: Infinite and NaN Number Values,  Next: Repeated Names Within an Object,  Prev: Character Encodings,  Up: Standard Compliance and Interoperability

5.19.2.6 Infinite and NaN Number Values
.......................................

The RFC does not permit the representation of infinite or NaN number
values.  Despite that, by default, this module accepts and outputs
‘Infinity’, ‘-Infinity’, and ‘NaN’ as if they were valid JSON number
literal values:

     >>> # Neither of these calls raises an exception, but the results are not valid JSON
     >>> json.dumps(float('-inf'))
     '-Infinity'
     >>> json.dumps(float('nan'))
     'NaN'
     >>> # Same when deserializing
     >>> json.loads('-Infinity')
     -inf
     >>> json.loads('NaN')
     nan

In the serializer, the `allow_nan' parameter can be used to alter this
behavior.  In the deserializer, the `parse_constant' parameter can be
used to alter this behavior.


File: python.info,  Node: Repeated Names Within an Object,  Next: Top-level Non-Object Non-Array Values,  Prev: Infinite and NaN Number Values,  Up: Standard Compliance and Interoperability

5.19.2.7 Repeated Names Within an Object
........................................

The RFC specifies that the names within a JSON object should be unique,
but does not mandate how repeated names in JSON objects should be
handled.  By default, this module does not raise an exception; instead,
it ignores all but the last name-value pair for a given name:

     >>> weird_json = '{"x": 1, "x": 2, "x": 3}'
     >>> json.loads(weird_json)
     {'x': 3}

The `object_pairs_hook' parameter can be used to alter this behavior.


File: python.info,  Node: Top-level Non-Object Non-Array Values,  Next: Implementation Limitations,  Prev: Repeated Names Within an Object,  Up: Standard Compliance and Interoperability

5.19.2.8 Top-level Non-Object, Non-Array Values
...............................................

The old version of JSON specified by the obsolete RFC 4627(1) required
that the top-level value of a JSON text must be either a JSON object or
array (Python *note dict: 164. or *note list: 1f8.), and could not be a
JSON null, boolean, number, or string value.  RFC 7159(2) removed that
restriction, and this module does not and has never implemented that
restriction in either its serializer or its deserializer.

Regardless, for maximum interoperability, you may wish to voluntarily
adhere to the restriction yourself.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc4627.html

   (2) https://tools.ietf.org/html/rfc7159.html


File: python.info,  Node: Implementation Limitations,  Prev: Top-level Non-Object Non-Array Values,  Up: Standard Compliance and Interoperability

5.19.2.9 Implementation Limitations
...................................

Some JSON deserializer implementations may set limits on:

   * the size of accepted JSON texts

   * the maximum level of nesting of JSON objects and arrays

   * the range and precision of JSON numbers

   * the content and maximum length of JSON strings

This module does not impose any such limits beyond those of the relevant
Python datatypes themselves or the Python interpreter itself.

When serializing to JSON, beware any such limitations in applications
that may consume your JSON. In particular, it is common for JSON numbers
to be deserialized into IEEE 754 double precision numbers and thus
subject to that representation’s range and precision limitations.  This
is especially relevant when serializing Python *note int: 204. values of
extremely large magnitude, or when serializing instances of “exotic”
numerical types such as *note decimal.Decimal: 2c0.


File: python.info,  Node: Command Line Interface<2>,  Prev: Standard Compliance and Interoperability,  Up: json — JSON encoder and decoder

5.19.2.10 Command Line Interface
................................

`Source code:' Lib/json/tool.py(1)

__________________________________________________________________

The *note json.tool: a5. module provides a simple command line interface
to validate and pretty-print JSON objects.

If the optional ‘infile’ and ‘outfile’ arguments are not specified,
*note sys.stdin: 41e. and *note sys.stdout: 41f. will be used
respectively:

     $ echo '{"json": "obj"}' | python -m json.tool
     {
         "json": "obj"
     }
     $ echo '{1.2:3.4}' | python -m json.tool
     Expecting property name enclosed in double quotes: line 1 column 2 (char 1)

Changed in version 3.5: The output is now in the same order as the
input.  Use the *note –sort-keys: 2a46. option to sort the output of
dictionaries alphabetically by key.

* Menu:

* Command line options: Command line options<2>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/json/tool.py


File: python.info,  Node: Command line options<2>,  Up: Command Line Interface<2>

5.19.2.11 Command line options
..............................

 -- Program Option: infile

     The JSON file to be validated or pretty-printed:

          $ python -m json.tool mp_films.json
          [
              {
                  "title": "And Now for Something Completely Different",
                  "year": 1971
              },
              {
                  "title": "Monty Python and the Holy Grail",
                  "year": 1975
              }
          ]

     If `infile' is not specified, read from *note sys.stdin: 41e.

 -- Program Option: outfile

     Write the output of the `infile' to the given `outfile'.
     Otherwise, write it to *note sys.stdout: 41f.

 -- Program Option: --sort-keys

     Sort the output of dictionaries alphabetically by key.

     New in version 3.5.

 -- Program Option: --no-ensure-ascii

     Disable escaping of non-ascii characters, see *note json.dumps():
     6fc. for more information.

     New in version 3.9.

 -- Program Option: --json-lines

     Parse every input line as separate JSON object.

     New in version 3.8.

 -- Program Option: --indent, --tab, --no-indent, --compact

     Mutually exclusive options for whitespace control.

     New in version 3.9.

 -- Program Option: -h, --help

     Show the help message.


File: python.info,  Node: mailcap — Mailcap file handling,  Next: mailbox — Manipulate mailboxes in various formats,  Prev: json — JSON encoder and decoder,  Up: Internet Data Handling

5.19.3 ‘mailcap’ — Mailcap file handling
----------------------------------------

`Source code:' Lib/mailcap.py(1)

__________________________________________________________________

Mailcap files are used to configure how MIME-aware applications such as
mail readers and Web browsers react to files with different MIME types.
(The name “mailcap” is derived from the phrase “mail capability”.)  For
example, a mailcap file might contain a line like ‘video/mpeg; xmpeg
%s’.  Then, if the user encounters an email message or Web document with
the MIME type ‘video/mpeg’, ‘%s’ will be replaced by a filename (usually
one belonging to a temporary file) and the ‘xmpeg’ program can be
automatically started to view the file.

The mailcap format is documented in RFC 1524(2), “A User Agent
Configuration Mechanism For Multimedia Mail Format Information”, but is
not an Internet standard.  However, mailcap files are supported on most
Unix systems.

 -- Function: mailcap.findmatch (caps, MIMEtype, key='view',
          filename='/dev/null', plist=[])

     Return a 2-tuple; the first element is a string containing the
     command line to be executed (which can be passed to *note
     os.system(): e86.), and the second element is the mailcap entry for
     a given MIME type.  If no matching MIME type can be found, ‘(None,
     None)’ is returned.

     `key' is the name of the field desired, which represents the type
     of activity to be performed; the default value is ‘view’, since in
     the most common case you simply want to view the body of the
     MIME-typed data.  Other possible values might be ‘compose’ and
     ‘edit’, if you wanted to create a new body of the given MIME type
     or alter the existing body data.  See RFC 1524(3) for a complete
     list of these fields.

     `filename' is the filename to be substituted for ‘%s’ in the
     command line; the default value is ‘'/dev/null'’ which is almost
     certainly not what you want, so usually you’ll override it by
     specifying a filename.

     `plist' can be a list containing named parameters; the default
     value is simply an empty list.  Each entry in the list must be a
     string containing the parameter name, an equals sign (‘'='’), and
     the parameter’s value.  Mailcap entries can contain named
     parameters like ‘%{foo}’, which will be replaced by the value of
     the parameter named ‘foo’.  For example, if the command line
     ‘showpartial %{id} %{number} %{total}’ was in a mailcap file, and
     `plist' was set to ‘['id=1', 'number=2', 'total=3']’, the resulting
     command line would be ‘'showpartial 1 2 3'’.

     In a mailcap file, the “test” field can optionally be specified to
     test some external condition (such as the machine architecture, or
     the window system in use) to determine whether or not the mailcap
     line applies.  *note findmatch(): 2a50. will automatically check
     such conditions and skip the entry if the check fails.

 -- Function: mailcap.getcaps ()

     Returns a dictionary mapping MIME types to a list of mailcap file
     entries.  This dictionary must be passed to the *note findmatch():
     2a50. function.  An entry is stored as a list of dictionaries, but
     it shouldn’t be necessary to know the details of this
     representation.

     The information is derived from all of the mailcap files found on
     the system.  Settings in the user’s mailcap file ‘$HOME/.mailcap’
     will override settings in the system mailcap files ‘/etc/mailcap’,
     ‘/usr/etc/mailcap’, and ‘/usr/local/etc/mailcap’.

An example usage:

     >>> import mailcap
     >>> d = mailcap.getcaps()
     >>> mailcap.findmatch(d, 'video/mpeg', filename='tmp1223')
     ('xmpeg tmp1223', {'view': 'xmpeg %s'})

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/mailcap.py

   (2) https://tools.ietf.org/html/rfc1524.html

   (3) https://tools.ietf.org/html/rfc1524.html


File: python.info,  Node: mailbox — Manipulate mailboxes in various formats,  Next: mimetypes — Map filenames to MIME types,  Prev: mailcap — Mailcap file handling,  Up: Internet Data Handling

5.19.4 ‘mailbox’ — Manipulate mailboxes in various formats
----------------------------------------------------------

`Source code:' Lib/mailbox.py(1)

__________________________________________________________________

This module defines two classes, *note Mailbox: cb1. and *note Message:
cb5, for accessing and manipulating on-disk mailboxes and the messages
they contain.  *note Mailbox: cb1. offers a dictionary-like mapping from
keys to messages.  *note Message: cb5. extends the *note email.message:
70. module’s *note Message: 63b. class with format-specific state and
behavior.  Supported mailbox formats are Maildir, mbox, MH, Babyl, and
MMDF.

See also
........

Module *note email: 67.

     Represent and manipulate messages.

* Menu:

* Mailbox objects::
* Message objects::
* Exceptions: Exceptions<15>.
* Examples: Examples<19>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/mailbox.py


File: python.info,  Node: Mailbox objects,  Next: Message objects,  Up: mailbox — Manipulate mailboxes in various formats

5.19.4.1 ‘Mailbox’ objects
..........................

 -- Class: mailbox.Mailbox

     A mailbox, which may be inspected and modified.

     The *note Mailbox: cb1. class defines an interface and is not
     intended to be instantiated.  Instead, format-specific subclasses
     should inherit from *note Mailbox: cb1. and your code should
     instantiate a particular subclass.

     The *note Mailbox: cb1. interface is dictionary-like, with small
     keys corresponding to messages.  Keys are issued by the *note
     Mailbox: cb1. instance with which they will be used and are only
     meaningful to that *note Mailbox: cb1. instance.  A key continues
     to identify a message even if the corresponding message is
     modified, such as by replacing it with another message.

     Messages may be added to a *note Mailbox: cb1. instance using the
     set-like method *note add(): cb0. and removed using a ‘del’
     statement or the set-like methods *note remove(): 2a56. and *note
     discard(): 2a57.

     *note Mailbox: cb1. interface semantics differ from dictionary
     semantics in some noteworthy ways.  Each time a message is
     requested, a new representation (typically a *note Message: cb5.
     instance) is generated based upon the current state of the mailbox.
     Similarly, when a message is added to a *note Mailbox: cb1.
     instance, the provided message representation’s contents are
     copied.  In neither case is a reference to the message
     representation kept by the *note Mailbox: cb1. instance.

     The default *note Mailbox: cb1. iterator iterates over message
     representations, not keys as the default dictionary iterator does.
     Moreover, modification of a mailbox during iteration is safe and
     well-defined.  Messages added to the mailbox after an iterator is
     created will not be seen by the iterator.  Messages removed from
     the mailbox before the iterator yields them will be silently
     skipped, though using a key from an iterator may result in a *note
     KeyError: 3e9. exception if the corresponding message is
     subsequently removed.

          Warning: Be very cautious when modifying mailboxes that might
          be simultaneously changed by some other process.  The safest
          mailbox format to use for such tasks is Maildir; try to avoid
          using single-file formats such as mbox for concurrent writing.
          If you’re modifying a mailbox, you `must' lock it by calling
          the *note lock(): 2a58. and *note unlock(): 2a59. methods
          `before' reading any messages in the file or making any
          changes by adding or deleting a message.  Failing to lock the
          mailbox runs the risk of losing messages or corrupting the
          entire mailbox.

     *note Mailbox: cb1. instances have the following methods:

      -- Method: add (message)

          Add `message' to the mailbox and return the key that has been
          assigned to it.

          Parameter `message' may be a *note Message: cb5. instance, an
          *note email.message.Message: 63b. instance, a string, a byte
          string, or a file-like object (which should be open in binary
          mode).  If `message' is an instance of the appropriate
          format-specific *note Message: cb5. subclass (e.g., if it’s an
          *note mboxMessage: 2929. instance and this is an *note mbox:
          2a5a. instance), its format-specific information is used.
          Otherwise, reasonable defaults for format-specific information
          are used.

          Changed in version 3.2: Support for binary input was added.

      -- Method: remove (key)
      -- Method: __delitem__ (key)
      -- Method: discard (key)

          Delete the message corresponding to `key' from the mailbox.

          If no such message exists, a *note KeyError: 3e9. exception is
          raised if the method was called as *note remove(): 2a56. or
          *note __delitem__(): 2a5b. but no exception is raised if the
          method was called as *note discard(): 2a57.  The behavior of
          *note discard(): 2a57. may be preferred if the underlying
          mailbox format supports concurrent modification by other
          processes.

      -- Method: __setitem__ (key, message)

          Replace the message corresponding to `key' with `message'.
          Raise a *note KeyError: 3e9. exception if no message already
          corresponds to `key'.

          As with *note add(): cb0, parameter `message' may be a *note
          Message: cb5. instance, an *note email.message.Message: 63b.
          instance, a string, a byte string, or a file-like object
          (which should be open in binary mode).  If `message' is an
          instance of the appropriate format-specific *note Message:
          cb5. subclass (e.g., if it’s an *note mboxMessage: 2929.
          instance and this is an *note mbox: 2a5a. instance), its
          format-specific information is used.  Otherwise, the
          format-specific information of the message that currently
          corresponds to `key' is left unchanged.

      -- Method: iterkeys ()
      -- Method: keys ()

          Return an iterator over all keys if called as *note
          iterkeys(): 2a5d. or return a list of keys if called as *note
          keys(): 2a5e.

      -- Method: itervalues ()
      -- Method: __iter__ ()
      -- Method: values ()

          Return an iterator over representations of all messages if
          called as *note itervalues(): 2a5f. or *note __iter__(): 2a60.
          or return a list of such representations if called as *note
          values(): 2a61.  The messages are represented as instances of
          the appropriate format-specific *note Message: cb5. subclass
          unless a custom message factory was specified when the *note
          Mailbox: cb1. instance was initialized.

               Note: The behavior of *note __iter__(): 2a60. is unlike
               that of dictionaries, which iterate over keys.

      -- Method: iteritems ()
      -- Method: items ()

          Return an iterator over (`key', `message') pairs, where `key'
          is a key and `message' is a message representation, if called
          as *note iteritems(): 2a62. or return a list of such pairs if
          called as *note items(): 2a63.  The messages are represented
          as instances of the appropriate format-specific *note Message:
          cb5. subclass unless a custom message factory was specified
          when the *note Mailbox: cb1. instance was initialized.

      -- Method: get (key, default=None)
      -- Method: __getitem__ (key)

          Return a representation of the message corresponding to `key'.
          If no such message exists, `default' is returned if the method
          was called as *note get(): 2a64. and a *note KeyError: 3e9.
          exception is raised if the method was called as *note
          __getitem__(): 2a65.  The message is represented as an
          instance of the appropriate format-specific *note Message:
          cb5. subclass unless a custom message factory was specified
          when the *note Mailbox: cb1. instance was initialized.

      -- Method: get_message (key)

          Return a representation of the message corresponding to `key'
          as an instance of the appropriate format-specific *note
          Message: cb5. subclass, or raise a *note KeyError: 3e9.
          exception if no such message exists.

      -- Method: get_bytes (key)

          Return a byte representation of the message corresponding to
          `key', or raise a *note KeyError: 3e9. exception if no such
          message exists.

          New in version 3.2.

      -- Method: get_string (key)

          Return a string representation of the message corresponding to
          `key', or raise a *note KeyError: 3e9. exception if no such
          message exists.  The message is processed through *note
          email.message.Message: 63b. to convert it to a 7bit clean
          representation.

      -- Method: get_file (key)

          Return a file-like representation of the message corresponding
          to `key', or raise a *note KeyError: 3e9. exception if no such
          message exists.  The file-like object behaves as if open in
          binary mode.  This file should be closed once it is no longer
          needed.

          Changed in version 3.2: The file object really is a binary
          file; previously it was incorrectly returned in text mode.
          Also, the file-like object now supports the context management
          protocol: you can use a *note with: 7da. statement to
          automatically close it.

               Note: Unlike other representations of messages, file-like
               representations are not necessarily independent of the
               *note Mailbox: cb1. instance that created them or of the
               underlying mailbox.  More specific documentation is
               provided by each subclass.

      -- Method: __contains__ (key)

          Return ‘True’ if `key' corresponds to a message, ‘False’
          otherwise.

      -- Method: __len__ ()

          Return a count of messages in the mailbox.

      -- Method: clear ()

          Delete all messages from the mailbox.

      -- Method: pop (key, default=None)

          Return a representation of the message corresponding to `key'
          and delete the message.  If no such message exists, return
          `default'.  The message is represented as an instance of the
          appropriate format-specific *note Message: cb5. subclass
          unless a custom message factory was specified when the *note
          Mailbox: cb1. instance was initialized.

      -- Method: popitem ()

          Return an arbitrary (`key', `message') pair, where `key' is a
          key and `message' is a message representation, and delete the
          corresponding message.  If the mailbox is empty, raise a *note
          KeyError: 3e9. exception.  The message is represented as an
          instance of the appropriate format-specific *note Message:
          cb5. subclass unless a custom message factory was specified
          when the *note Mailbox: cb1. instance was initialized.

      -- Method: update (arg)

          Parameter `arg' should be a `key'-to-`message' mapping or an
          iterable of (`key', `message') pairs.  Updates the mailbox so
          that, for each given `key' and `message', the message
          corresponding to `key' is set to `message' as if by using
          *note __setitem__(): 2a5c.  As with *note __setitem__(): 2a5c,
          each `key' must already correspond to a message in the mailbox
          or else a *note KeyError: 3e9. exception will be raised, so in
          general it is incorrect for `arg' to be a *note Mailbox: cb1.
          instance.

               Note: Unlike with dictionaries, keyword arguments are not
               supported.

      -- Method: flush ()

          Write any pending changes to the filesystem.  For some *note
          Mailbox: cb1. subclasses, changes are always written
          immediately and *note flush(): 2a6d. does nothing, but you
          should still make a habit of calling this method.

      -- Method: lock ()

          Acquire an exclusive advisory lock on the mailbox so that
          other processes know not to modify it.  An *note
          ExternalClashError: 2a6e. is raised if the lock is not
          available.  The particular locking mechanisms used depend upon
          the mailbox format.  You should `always' lock the mailbox
          before making any modifications to its contents.

      -- Method: unlock ()

          Release the lock on the mailbox, if any.

      -- Method: close ()

          Flush the mailbox, unlock it if necessary, and close any open
          files.  For some *note Mailbox: cb1. subclasses, this method
          does nothing.

* Menu:

* Maildir::
* mbox::
* MH::
* Babyl::
* MMDF::


File: python.info,  Node: Maildir,  Next: mbox,  Up: Mailbox objects

5.19.4.2 ‘Maildir’
..................

 -- Class: mailbox.Maildir (dirname, factory=None, create=True)

     A subclass of *note Mailbox: cb1. for mailboxes in Maildir format.
     Parameter `factory' is a callable object that accepts a file-like
     message representation (which behaves as if opened in binary mode)
     and returns a custom representation.  If `factory' is ‘None’, *note
     MaildirMessage: 2a72. is used as the default message
     representation.  If `create' is ‘True’, the mailbox is created if
     it does not exist.

     If `create' is ‘True’ and the `dirname' path exists, it will be
     treated as an existing maildir without attempting to verify its
     directory layout.

     It is for historical reasons that `dirname' is named as such rather
     than `path'.

     Maildir is a directory-based mailbox format invented for the qmail
     mail transfer agent and now widely supported by other programs.
     Messages in a Maildir mailbox are stored in separate files within a
     common directory structure.  This design allows Maildir mailboxes
     to be accessed and modified by multiple unrelated programs without
     data corruption, so file locking is unnecessary.

     Maildir mailboxes contain three subdirectories, namely: ‘tmp’,
     ‘new’, and ‘cur’.  Messages are created momentarily in the ‘tmp’
     subdirectory and then moved to the ‘new’ subdirectory to finalize
     delivery.  A mail user agent may subsequently move the message to
     the ‘cur’ subdirectory and store information about the state of the
     message in a special “info” section appended to its file name.

     Folders of the style introduced by the Courier mail transfer agent
     are also supported.  Any subdirectory of the main mailbox is
     considered a folder if ‘'.'’ is the first character in its name.
     Folder names are represented by *note Maildir: d70. without the
     leading ‘'.'’.  Each folder is itself a Maildir mailbox but should
     not contain other folders.  Instead, a logical nesting is indicated
     using ‘'.'’ to delimit levels, e.g., “Archived.2005.07”.

          Note: The Maildir specification requires the use of a colon
          (‘':'’) in certain message file names.  However, some
          operating systems do not permit this character in file names,
          If you wish to use a Maildir-like format on such an operating
          system, you should specify another character to use instead.
          The exclamation point (‘'!'’) is a popular choice.  For
          example:

               import mailbox
               mailbox.Maildir.colon = '!'

          The ‘colon’ attribute may also be set on a per-instance basis.

     *note Maildir: d70. instances have all of the methods of *note
     Mailbox: cb1. in addition to the following:

      -- Method: list_folders ()

          Return a list of the names of all folders.

      -- Method: get_folder (folder)

          Return a *note Maildir: d70. instance representing the folder
          whose name is `folder'.  A *note NoSuchMailboxError: 2a75.
          exception is raised if the folder does not exist.

      -- Method: add_folder (folder)

          Create a folder whose name is `folder' and return a *note
          Maildir: d70. instance representing it.

      -- Method: remove_folder (folder)

          Delete the folder whose name is `folder'.  If the folder
          contains any messages, a *note NotEmptyError: 2a78. exception
          will be raised and the folder will not be deleted.

      -- Method: clean ()

          Delete temporary files from the mailbox that have not been
          accessed in the last 36 hours.  The Maildir specification says
          that mail-reading programs should do this occasionally.

     Some *note Mailbox: cb1. methods implemented by *note Maildir: d70.
     deserve special remarks:

      -- Method: add (message)
      -- Method: __setitem__ (key, message)
      -- Method: update (arg)

               Warning: These methods generate unique file names based
               upon the current process ID. When using multiple threads,
               undetected name clashes may occur and cause corruption of
               the mailbox unless threads are coordinated to avoid using
               these methods to manipulate the same mailbox
               simultaneously.

      -- Method: flush ()

          All changes to Maildir mailboxes are immediately applied, so
          this method does nothing.

      -- Method: lock ()
      -- Method: unlock ()

          Maildir mailboxes do not support (or require) locking, so
          these methods do nothing.

      -- Method: close ()

          *note Maildir: d70. instances do not keep any open files and
          the underlying mailboxes do not support locking, so this
          method does nothing.

      -- Method: get_file (key)

          Depending upon the host platform, it may not be possible to
          modify or remove the underlying message while the returned
          file remains open.

See also
........

maildir man page from Courier(1)

     A specification of the format.  Describes a common extension for
     supporting folders.

Using maildir format(2)

     Notes on Maildir by its inventor.  Includes an updated
     name-creation scheme and details on “info” semantics.

   ---------- Footnotes ----------

   (1) http://www.courier-mta.org/maildir.html

   (2) https://cr.yp.to/proto/maildir.html


File: python.info,  Node: mbox,  Next: MH,  Prev: Maildir,  Up: Mailbox objects

5.19.4.3 ‘mbox’
...............

 -- Class: mailbox.mbox (path, factory=None, create=True)

     A subclass of *note Mailbox: cb1. for mailboxes in mbox format.
     Parameter `factory' is a callable object that accepts a file-like
     message representation (which behaves as if opened in binary mode)
     and returns a custom representation.  If `factory' is ‘None’, *note
     mboxMessage: 2929. is used as the default message representation.
     If `create' is ‘True’, the mailbox is created if it does not exist.

     The mbox format is the classic format for storing mail on Unix
     systems.  All messages in an mbox mailbox are stored in a single
     file with the beginning of each message indicated by a line whose
     first five characters are “From “.

     Several variations of the mbox format exist to address perceived
     shortcomings in the original.  In the interest of compatibility,
     *note mbox: 2a5a. implements the original format, which is
     sometimes referred to as `mboxo'.  This means that the
     ‘Content-Length’ header, if present, is ignored and that any
     occurrences of “From ” at the beginning of a line in a message body
     are transformed to “>From ” when storing the message, although
     occurrences of “>From ” are not transformed to “From ” when reading
     the message.

     Some *note Mailbox: cb1. methods implemented by *note mbox: 2a5a.
     deserve special remarks:

      -- Method: get_file (key)

          Using the file after calling ‘flush()’ or ‘close()’ on the
          *note mbox: 2a5a. instance may yield unpredictable results or
          raise an exception.

      -- Method: lock ()
      -- Method: unlock ()

          Three locking mechanisms are used—dot locking and, if
          available, the ‘flock()’ and ‘lockf()’ system calls.

See also
........

mbox man page from tin(1)

     A specification of the format, with details on locking.

Configuring Netscape Mail on Unix: Why The Content-Length Format is Bad(2)

     An argument for using the original mbox format rather than a
     variation.

"mbox" is a family of several mutually incompatible mailbox formats(3)

     A history of mbox variations.

   ---------- Footnotes ----------

   (1) http://www.tin.org/bin/man.cgi?section=5&topic=mbox

   (2) https://www.jwz.org/doc/content-length.html

   (3) 
https://www.loc.gov/preservation/digital/formats/fdd/fdd000383.shtml


File: python.info,  Node: MH,  Next: Babyl,  Prev: mbox,  Up: Mailbox objects

5.19.4.4 ‘MH’
.............

 -- Class: mailbox.MH (path, factory=None, create=True)

     A subclass of *note Mailbox: cb1. for mailboxes in MH format.
     Parameter `factory' is a callable object that accepts a file-like
     message representation (which behaves as if opened in binary mode)
     and returns a custom representation.  If `factory' is ‘None’, *note
     MHMessage: 2a8a. is used as the default message representation.  If
     `create' is ‘True’, the mailbox is created if it does not exist.

     MH is a directory-based mailbox format invented for the MH Message
     Handling System, a mail user agent.  Each message in an MH mailbox
     resides in its own file.  An MH mailbox may contain other MH
     mailboxes (called `folders') in addition to messages.  Folders may
     be nested indefinitely.  MH mailboxes also support `sequences',
     which are named lists used to logically group messages without
     moving them to sub-folders.  Sequences are defined in a file called
     ‘.mh_sequences’ in each folder.

     The *note MH: 2a89. class manipulates MH mailboxes, but it does not
     attempt to emulate all of ‘mh’’s behaviors.  In particular, it does
     not modify and is not affected by the ‘context’ or ‘.mh_profile’
     files that are used by ‘mh’ to store its state and configuration.

     *note MH: 2a89. instances have all of the methods of *note Mailbox:
     cb1. in addition to the following:

      -- Method: list_folders ()

          Return a list of the names of all folders.

      -- Method: get_folder (folder)

          Return an *note MH: 2a89. instance representing the folder
          whose name is `folder'.  A *note NoSuchMailboxError: 2a75.
          exception is raised if the folder does not exist.

      -- Method: add_folder (folder)

          Create a folder whose name is `folder' and return an *note MH:
          2a89. instance representing it.

      -- Method: remove_folder (folder)

          Delete the folder whose name is `folder'.  If the folder
          contains any messages, a *note NotEmptyError: 2a78. exception
          will be raised and the folder will not be deleted.

      -- Method: get_sequences ()

          Return a dictionary of sequence names mapped to key lists.  If
          there are no sequences, the empty dictionary is returned.

      -- Method: set_sequences (sequences)

          Re-define the sequences that exist in the mailbox based upon
          `sequences', a dictionary of names mapped to key lists, like
          returned by *note get_sequences(): 2a8f.

      -- Method: pack ()

          Rename messages in the mailbox as necessary to eliminate gaps
          in numbering.  Entries in the sequences list are updated
          correspondingly.

               Note: Already-issued keys are invalidated by this
               operation and should not be subsequently used.

     Some *note Mailbox: cb1. methods implemented by *note MH: 2a89.
     deserve special remarks:

      -- Method: remove (key)
      -- Method: __delitem__ (key)
      -- Method: discard (key)

          These methods immediately delete the message.  The MH
          convention of marking a message for deletion by prepending a
          comma to its name is not used.

      -- Method: lock ()
      -- Method: unlock ()

          Three locking mechanisms are used—dot locking and, if
          available, the ‘flock()’ and ‘lockf()’ system calls.  For MH
          mailboxes, locking the mailbox means locking the
          ‘.mh_sequences’ file and, only for the duration of any
          operations that affect them, locking individual message files.

      -- Method: get_file (key)

          Depending upon the host platform, it may not be possible to
          remove the underlying message while the returned file remains
          open.

      -- Method: flush ()

          All changes to MH mailboxes are immediately applied, so this
          method does nothing.

      -- Method: close ()

          *note MH: 2a89. instances do not keep any open files, so this
          method is equivalent to *note unlock(): 2a96.

See also
........

nmh - Message Handling System(1)

     Home page of ‘nmh’, an updated version of the original ‘mh’.

MH & nmh: Email for Users & Programmers(2)

     A GPL-licensed book on ‘mh’ and ‘nmh’, with some information on the
     mailbox format.

   ---------- Footnotes ----------

   (1) http://www.nongnu.org/nmh/

   (2) https://rand-mh.sourceforge.io/book/


File: python.info,  Node: Babyl,  Next: MMDF,  Prev: MH,  Up: Mailbox objects

5.19.4.5 ‘Babyl’
................

 -- Class: mailbox.Babyl (path, factory=None, create=True)

     A subclass of *note Mailbox: cb1. for mailboxes in Babyl format.
     Parameter `factory' is a callable object that accepts a file-like
     message representation (which behaves as if opened in binary mode)
     and returns a custom representation.  If `factory' is ‘None’, *note
     BabylMessage: 2a9d. is used as the default message representation.
     If `create' is ‘True’, the mailbox is created if it does not exist.

     Babyl is a single-file mailbox format used by the Rmail mail user
     agent included with Emacs.  The beginning of a message is indicated
     by a line containing the two characters Control-Underscore
     (‘'\037'’) and Control-L (‘'\014'’).  The end of a message is
     indicated by the start of the next message or, in the case of the
     last message, a line containing a Control-Underscore (‘'\037'’)
     character.

     Messages in a Babyl mailbox have two sets of headers, original
     headers and so-called visible headers.  Visible headers are
     typically a subset of the original headers that have been
     reformatted or abridged to be more attractive.  Each message in a
     Babyl mailbox also has an accompanying list of `labels', or short
     strings that record extra information about the message, and a list
     of all user-defined labels found in the mailbox is kept in the
     Babyl options section.

     *note Babyl: 2a9c. instances have all of the methods of *note
     Mailbox: cb1. in addition to the following:

      -- Method: get_labels ()

          Return a list of the names of all user-defined labels used in
          the mailbox.

               Note: The actual messages are inspected to determine
               which labels exist in the mailbox rather than consulting
               the list of labels in the Babyl options section, but the
               Babyl section is updated whenever the mailbox is
               modified.

     Some *note Mailbox: cb1. methods implemented by *note Babyl: 2a9c.
     deserve special remarks:

      -- Method: get_file (key)

          In Babyl mailboxes, the headers of a message are not stored
          contiguously with the body of the message.  To generate a
          file-like representation, the headers and body are copied
          together into an *note io.BytesIO: 88a. instance, which has an
          API identical to that of a file.  As a result, the file-like
          object is truly independent of the underlying mailbox but does
          not save memory compared to a string representation.

      -- Method: lock ()
      -- Method: unlock ()

          Three locking mechanisms are used—dot locking and, if
          available, the ‘flock()’ and ‘lockf()’ system calls.

See also
........

Format of Version 5 Babyl Files(1)

     A specification of the Babyl format.

Reading Mail with Rmail(2)

     The Rmail manual, with some information on Babyl semantics.

   ---------- Footnotes ----------

   (1) https://quimby.gnus.org/notes/BABYL

   (2) 
https://www.gnu.org/software/emacs/manual/html_node/emacs/Rmail.html


File: python.info,  Node: MMDF,  Prev: Babyl,  Up: Mailbox objects

5.19.4.6 ‘MMDF’
...............

 -- Class: mailbox.MMDF (path, factory=None, create=True)

     A subclass of *note Mailbox: cb1. for mailboxes in MMDF format.
     Parameter `factory' is a callable object that accepts a file-like
     message representation (which behaves as if opened in binary mode)
     and returns a custom representation.  If `factory' is ‘None’, *note
     MMDFMessage: 2aa5. is used as the default message representation.
     If `create' is ‘True’, the mailbox is created if it does not exist.

     MMDF is a single-file mailbox format invented for the Multichannel
     Memorandum Distribution Facility, a mail transfer agent.  Each
     message is in the same form as an mbox message but is bracketed
     before and after by lines containing four Control-A (‘'\001'’)
     characters.  As with the mbox format, the beginning of each message
     is indicated by a line whose first five characters are “From “, but
     additional occurrences of “From ” are not transformed to “>From ”
     when storing messages because the extra message separator lines
     prevent mistaking such occurrences for the starts of subsequent
     messages.

     Some *note Mailbox: cb1. methods implemented by *note MMDF: 2aa4.
     deserve special remarks:

      -- Method: get_file (key)

          Using the file after calling ‘flush()’ or ‘close()’ on the
          *note MMDF: 2aa4. instance may yield unpredictable results or
          raise an exception.

      -- Method: lock ()
      -- Method: unlock ()

          Three locking mechanisms are used—dot locking and, if
          available, the ‘flock()’ and ‘lockf()’ system calls.

See also
........

mmdf man page from tin(1)

     A specification of MMDF format from the documentation of tin, a
     newsreader.

MMDF(2)

     A Wikipedia article describing the Multichannel Memorandum
     Distribution Facility.

   ---------- Footnotes ----------

   (1) http://www.tin.org/bin/man.cgi?section=5&topic=mmdf

   (2) https://en.wikipedia.org/wiki/MMDF


File: python.info,  Node: Message objects,  Next: Exceptions<15>,  Prev: Mailbox objects,  Up: mailbox — Manipulate mailboxes in various formats

5.19.4.7 ‘Message’ objects
..........................

 -- Class: mailbox.Message (message=None)

     A subclass of the *note email.message: 70. module’s *note Message:
     63b.  Subclasses of *note mailbox.Message: cb5. add
     mailbox-format-specific state and behavior.

     If `message' is omitted, the new instance is created in a default,
     empty state.  If `message' is an *note email.message.Message: 63b.
     instance, its contents are copied; furthermore, any format-specific
     information is converted insofar as possible if `message' is a
     *note Message: cb5. instance.  If `message' is a string, a byte
     string, or a file, it should contain an RFC 2822(1)-compliant
     message, which is read and parsed.  Files should be open in binary
     mode, but text mode files are accepted for backward compatibility.

     The format-specific state and behaviors offered by subclasses vary,
     but in general it is only the properties that are not specific to a
     particular mailbox that are supported (although presumably the
     properties are specific to a particular mailbox format).  For
     example, file offsets for single-file mailbox formats and file
     names for directory-based mailbox formats are not retained, because
     they are only applicable to the original mailbox.  But state such
     as whether a message has been read by the user or marked as
     important is retained, because it applies to the message itself.

     There is no requirement that *note Message: cb5. instances be used
     to represent messages retrieved using *note Mailbox: cb1.
     instances.  In some situations, the time and memory required to
     generate *note Message: cb5. representations might not be
     acceptable.  For such situations, *note Mailbox: cb1. instances
     also offer string and file-like representations, and a custom
     message factory may be specified when a *note Mailbox: cb1.
     instance is initialized.

* Menu:

* MaildirMessage::
* mboxMessage::
* MHMessage::
* BabylMessage::
* MMDFMessage::

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2822.html


File: python.info,  Node: MaildirMessage,  Next: mboxMessage,  Up: Message objects

5.19.4.8 ‘MaildirMessage’
.........................

 -- Class: mailbox.MaildirMessage (message=None)

     A message with Maildir-specific behaviors.  Parameter `message' has
     the same meaning as with the *note Message: cb5. constructor.

     Typically, a mail user agent application moves all of the messages
     in the ‘new’ subdirectory to the ‘cur’ subdirectory after the first
     time the user opens and closes the mailbox, recording that the
     messages are old whether or not they’ve actually been read.  Each
     message in ‘cur’ has an “info” section added to its file name to
     store information about its state.  (Some mail readers may also add
     an “info” section to messages in ‘new’.)  The “info” section may
     take one of two forms: it may contain “2,” followed by a list of
     standardized flags (e.g., “2,FR”) or it may contain “1,” followed
     by so-called experimental information.  Standard flags for Maildir
     messages are as follows:

     Flag       Meaning       Explanation
                              
     --------------------------------------------------------------
                              
     D          Draft         Under composition
                              
                              
     F          Flagged       Marked as important
                              
                              
     P          Passed        Forwarded, resent, or bounced
                              
                              
     R          Replied       Replied to
                              
                              
     S          Seen          Read
                              
                              
     T          Trashed       Marked for subsequent deletion
                              

     *note MaildirMessage: 2a72. instances offer the following methods:

      -- Method: get_subdir ()

          Return either “new” (if the message should be stored in the
          ‘new’ subdirectory) or “cur” (if the message should be stored
          in the ‘cur’ subdirectory).

               Note: A message is typically moved from ‘new’ to ‘cur’
               after its mailbox has been accessed, whether or not the
               message is has been read.  A message ‘msg’ has been read
               if ‘"S" in msg.get_flags()’ is ‘True’.

      -- Method: set_subdir (subdir)

          Set the subdirectory the message should be stored in.
          Parameter `subdir' must be either “new” or “cur”.

      -- Method: get_flags ()

          Return a string specifying the flags that are currently set.
          If the message complies with the standard Maildir format, the
          result is the concatenation in alphabetical order of zero or
          one occurrence of each of ‘'D'’, ‘'F'’, ‘'P'’, ‘'R'’, ‘'S'’,
          and ‘'T'’.  The empty string is returned if no flags are set
          or if “info” contains experimental semantics.

      -- Method: set_flags (flags)

          Set the flags specified by `flags' and unset all others.

      -- Method: add_flag (flag)

          Set the flag(s) specified by `flag' without changing other
          flags.  To add more than one flag at a time, `flag' may be a
          string of more than one character.  The current “info” is
          overwritten whether or not it contains experimental
          information rather than flags.

      -- Method: remove_flag (flag)

          Unset the flag(s) specified by `flag' without changing other
          flags.  To remove more than one flag at a time, `flag' maybe a
          string of more than one character.  If “info” contains
          experimental information rather than flags, the current “info”
          is not modified.

      -- Method: get_date ()

          Return the delivery date of the message as a floating-point
          number representing seconds since the epoch.

      -- Method: set_date (date)

          Set the delivery date of the message to `date', a
          floating-point number representing seconds since the epoch.

      -- Method: get_info ()

          Return a string containing the “info” for a message.  This is
          useful for accessing and modifying “info” that is experimental
          (i.e., not a list of flags).

      -- Method: set_info (info)

          Set “info” to `info', which should be a string.

When a *note MaildirMessage: 2a72. instance is created based upon an
*note mboxMessage: 2929. or *note MMDFMessage: 2aa5. instance, the
‘Status’ and ‘X-Status’ headers are omitted and the following
conversions take place:

Resulting state          *note mboxMessage: 2929. or
                         *note MMDFMessage: 2aa5. state
                         
----------------------------------------------------------------------------
                         
“cur” subdirectory       O flag
                         
                         
F flag                   F flag
                         
                         
R flag                   A flag
                         
                         
S flag                   R flag
                         
                         
T flag                   D flag
                         

When a *note MaildirMessage: 2a72. instance is created based upon an
*note MHMessage: 2a8a. instance, the following conversions take place:

Resulting state                     *note MHMessage: 2a8a. state
                                    
-------------------------------------------------------------------
                                    
“cur” subdirectory                  “unseen” sequence
                                    
                                    
“cur” subdirectory and S flag       no “unseen” sequence
                                    
                                    
F flag                              “flagged” sequence
                                    
                                    
R flag                              “replied” sequence
                                    

When a *note MaildirMessage: 2a72. instance is created based upon a
*note BabylMessage: 2a9d. instance, the following conversions take
place:

Resulting state                     *note BabylMessage: 2a9d. state
                                    
------------------------------------------------------------------------
                                    
“cur” subdirectory                  “unseen” label
                                    
                                    
“cur” subdirectory and S flag       no “unseen” label
                                    
                                    
P flag                              “forwarded” or “resent” label
                                    
                                    
R flag                              “answered” label
                                    
                                    
T flag                              “deleted” label
                                    


File: python.info,  Node: mboxMessage,  Next: MHMessage,  Prev: MaildirMessage,  Up: Message objects

5.19.4.9 ‘mboxMessage’
......................

 -- Class: mailbox.mboxMessage (message=None)

     A message with mbox-specific behaviors.  Parameter `message' has
     the same meaning as with the *note Message: cb5. constructor.

     Messages in an mbox mailbox are stored together in a single file.
     The sender’s envelope address and the time of delivery are
     typically stored in a line beginning with “From ” that is used to
     indicate the start of a message, though there is considerable
     variation in the exact format of this data among mbox
     implementations.  Flags that indicate the state of the message,
     such as whether it has been read or marked as important, are
     typically stored in ‘Status’ and ‘X-Status’ headers.

     Conventional flags for mbox messages are as follows:

     Flag       Meaning        Explanation
                               
     ---------------------------------------------------------------
                               
     R          Read           Read
                               
                               
     O          Old            Previously detected by MUA
                               
                               
     D          Deleted        Marked for subsequent deletion
                               
                               
     F          Flagged        Marked as important
                               
                               
     A          Answered       Replied to
                               

     The “R” and “O” flags are stored in the ‘Status’ header, and the
     “D”, “F”, and “A” flags are stored in the ‘X-Status’ header.  The
     flags and headers typically appear in the order mentioned.

     *note mboxMessage: 2929. instances offer the following methods:

      -- Method: get_from ()

          Return a string representing the “From ” line that marks the
          start of the message in an mbox mailbox.  The leading “From ”
          and the trailing newline are excluded.

      -- Method: set_from (from_, time_=None)

          Set the “From ” line to `from_', which should be specified
          without a leading “From ” or trailing newline.  For
          convenience, `time_' may be specified and will be formatted
          appropriately and appended to `from_'.  If `time_' is
          specified, it should be a *note time.struct_time: 690.
          instance, a tuple suitable for passing to *note
          time.strftime(): c37, or ‘True’ (to use *note time.gmtime():
          c11.).

      -- Method: get_flags ()

          Return a string specifying the flags that are currently set.
          If the message complies with the conventional format, the
          result is the concatenation in the following order of zero or
          one occurrence of each of ‘'R'’, ‘'O'’, ‘'D'’, ‘'F'’, and
          ‘'A'’.

      -- Method: set_flags (flags)

          Set the flags specified by `flags' and unset all others.
          Parameter `flags' should be the concatenation in any order of
          zero or more occurrences of each of ‘'R'’, ‘'O'’, ‘'D'’,
          ‘'F'’, and ‘'A'’.

      -- Method: add_flag (flag)

          Set the flag(s) specified by `flag' without changing other
          flags.  To add more than one flag at a time, `flag' may be a
          string of more than one character.

      -- Method: remove_flag (flag)

          Unset the flag(s) specified by `flag' without changing other
          flags.  To remove more than one flag at a time, `flag' maybe a
          string of more than one character.

When an *note mboxMessage: 2929. instance is created based upon a *note
MaildirMessage: 2a72. instance, a “From ” line is generated based upon
the *note MaildirMessage: 2a72. instance’s delivery date, and the
following conversions take place:

Resulting state       *note MaildirMessage: 2a72. state
                      
----------------------------------------------------------
                      
R flag                S flag
                      
                      
O flag                “cur” subdirectory
                      
                      
D flag                T flag
                      
                      
F flag                F flag
                      
                      
A flag                R flag
                      

When an *note mboxMessage: 2929. instance is created based upon an *note
MHMessage: 2a8a. instance, the following conversions take place:

Resulting state         *note MHMessage: 2a8a. state
                        
-------------------------------------------------------
                        
R flag and O flag       no “unseen” sequence
                        
                        
O flag                  “unseen” sequence
                        
                        
F flag                  “flagged” sequence
                        
                        
A flag                  “replied” sequence
                        

When an *note mboxMessage: 2929. instance is created based upon a *note
BabylMessage: 2a9d. instance, the following conversions take place:

Resulting state         *note BabylMessage: 2a9d. state
                        
----------------------------------------------------------
                        
R flag and O flag       no “unseen” label
                        
                        
O flag                  “unseen” label
                        
                        
D flag                  “deleted” label
                        
                        
A flag                  “answered” label
                        

When a *note Message: cb5. instance is created based upon an *note
MMDFMessage: 2aa5. instance, the “From ” line is copied and all flags
directly correspond:

Resulting state       *note MMDFMessage: 2aa5. state
                      
-------------------------------------------------------
                      
R flag                R flag
                      
                      
O flag                O flag
                      
                      
D flag                D flag
                      
                      
F flag                F flag
                      
                      
A flag                A flag
                      


File: python.info,  Node: MHMessage,  Next: BabylMessage,  Prev: mboxMessage,  Up: Message objects

5.19.4.10 ‘MHMessage’
.....................

 -- Class: mailbox.MHMessage (message=None)

     A message with MH-specific behaviors.  Parameter `message' has the
     same meaning as with the *note Message: cb5. constructor.

     MH messages do not support marks or flags in the traditional sense,
     but they do support sequences, which are logical groupings of
     arbitrary messages.  Some mail reading programs (although not the
     standard ‘mh’ and ‘nmh’) use sequences in much the same way flags
     are used with other formats, as follows:

     Sequence       Explanation
                    
     --------------------------------------------------------------
                    
     unseen         Not read, but previously detected by MUA
                    
                    
     replied        Replied to
                    
                    
     flagged        Marked as important
                    

     *note MHMessage: 2a8a. instances offer the following methods:

      -- Method: get_sequences ()

          Return a list of the names of sequences that include this
          message.

      -- Method: set_sequences (sequences)

          Set the list of sequences that include this message.

      -- Method: add_sequence (sequence)

          Add `sequence' to the list of sequences that include this
          message.

      -- Method: remove_sequence (sequence)

          Remove `sequence' from the list of sequences that include this
          message.

When an *note MHMessage: 2a8a. instance is created based upon a *note
MaildirMessage: 2a72. instance, the following conversions take place:

Resulting state          *note MaildirMessage: 2a72. state
                         
-------------------------------------------------------------
                         
“unseen” sequence        no S flag
                         
                         
“replied” sequence       R flag
                         
                         
“flagged” sequence       F flag
                         

When an *note MHMessage: 2a8a. instance is created based upon an *note
mboxMessage: 2929. or *note MMDFMessage: 2aa5. instance, the ‘Status’
and ‘X-Status’ headers are omitted and the following conversions take
place:

Resulting state          *note mboxMessage: 2929. or
                         *note MMDFMessage: 2aa5. state
                         
----------------------------------------------------------------------------
                         
“unseen” sequence        no R flag
                         
                         
“replied” sequence       A flag
                         
                         
“flagged” sequence       F flag
                         

When an *note MHMessage: 2a8a. instance is created based upon a *note
BabylMessage: 2a9d. instance, the following conversions take place:

Resulting state          *note BabylMessage: 2a9d. state
                         
-----------------------------------------------------------
                         
“unseen” sequence        “unseen” label
                         
                         
“replied” sequence       “answered” label
                         


File: python.info,  Node: BabylMessage,  Next: MMDFMessage,  Prev: MHMessage,  Up: Message objects

5.19.4.11 ‘BabylMessage’
........................

 -- Class: mailbox.BabylMessage (message=None)

     A message with Babyl-specific behaviors.  Parameter `message' has
     the same meaning as with the *note Message: cb5. constructor.

     Certain message labels, called `attributes', are defined by
     convention to have special meanings.  The attributes are as
     follows:

     Label           Explanation
                     
     ---------------------------------------------------------------
                     
     unseen          Not read, but previously detected by MUA
                     
                     
     deleted         Marked for subsequent deletion
                     
                     
     filed           Copied to another file or mailbox
                     
                     
     answered        Replied to
                     
                     
     forwarded       Forwarded
                     
                     
     edited          Modified by the user
                     
                     
     resent          Resent
                     

     By default, Rmail displays only visible headers.  The *note
     BabylMessage: 2a9d. class, though, uses the original headers
     because they are more complete.  Visible headers may be accessed
     explicitly if desired.

     *note BabylMessage: 2a9d. instances offer the following methods:

      -- Method: get_labels ()

          Return a list of labels on the message.

      -- Method: set_labels (labels)

          Set the list of labels on the message to `labels'.

      -- Method: add_label (label)

          Add `label' to the list of labels on the message.

      -- Method: remove_label (label)

          Remove `label' from the list of labels on the message.

      -- Method: get_visible ()

          Return an *note Message: cb5. instance whose headers are the
          message’s visible headers and whose body is empty.

      -- Method: set_visible (visible)

          Set the message’s visible headers to be the same as the
          headers in `message'.  Parameter `visible' should be a *note
          Message: cb5. instance, an *note email.message.Message: 63b.
          instance, a string, or a file-like object (which should be
          open in text mode).

      -- Method: update_visible ()

          When a *note BabylMessage: 2a9d. instance’s original headers
          are modified, the visible headers are not automatically
          modified to correspond.  This method updates the visible
          headers as follows: each visible header with a corresponding
          original header is set to the value of the original header,
          each visible header without a corresponding original header is
          removed, and any of ‘Date’, ‘From’, ‘Reply-To’, ‘To’, ‘CC’,
          and ‘Subject’ that are present in the original headers but not
          the visible headers are added to the visible headers.

When a *note BabylMessage: 2a9d. instance is created based upon a *note
MaildirMessage: 2a72. instance, the following conversions take place:

Resulting state         *note MaildirMessage: 2a72. state
                        
------------------------------------------------------------
                        
“unseen” label          no S flag
                        
                        
“deleted” label         T flag
                        
                        
“answered” label        R flag
                        
                        
“forwarded” label       P flag
                        

When a *note BabylMessage: 2a9d. instance is created based upon an *note
mboxMessage: 2929. or *note MMDFMessage: 2aa5. instance, the ‘Status’
and ‘X-Status’ headers are omitted and the following conversions take
place:

Resulting state        *note mboxMessage: 2929. or
                       *note MMDFMessage: 2aa5. state
                       
--------------------------------------------------------------------------
                       
“unseen” label         no R flag
                       
                       
“deleted” label        D flag
                       
                       
“answered” label       A flag
                       

When a *note BabylMessage: 2a9d. instance is created based upon an *note
MHMessage: 2a8a. instance, the following conversions take place:

Resulting state        *note MHMessage: 2a8a. state
                       
------------------------------------------------------
                       
“unseen” label         “unseen” sequence
                       
                       
“answered” label       “replied” sequence
                       


File: python.info,  Node: MMDFMessage,  Prev: BabylMessage,  Up: Message objects

5.19.4.12 ‘MMDFMessage’
.......................

 -- Class: mailbox.MMDFMessage (message=None)

     A message with MMDF-specific behaviors.  Parameter `message' has
     the same meaning as with the *note Message: cb5. constructor.

     As with message in an mbox mailbox, MMDF messages are stored with
     the sender’s address and the delivery date in an initial line
     beginning with “From “.  Likewise, flags that indicate the state of
     the message are typically stored in ‘Status’ and ‘X-Status’
     headers.

     Conventional flags for MMDF messages are identical to those of mbox
     message and are as follows:

     Flag       Meaning        Explanation
                               
     ---------------------------------------------------------------
                               
     R          Read           Read
                               
                               
     O          Old            Previously detected by MUA
                               
                               
     D          Deleted        Marked for subsequent deletion
                               
                               
     F          Flagged        Marked as important
                               
                               
     A          Answered       Replied to
                               

     The “R” and “O” flags are stored in the ‘Status’ header, and the
     “D”, “F”, and “A” flags are stored in the ‘X-Status’ header.  The
     flags and headers typically appear in the order mentioned.

     *note MMDFMessage: 2aa5. instances offer the following methods,
     which are identical to those offered by *note mboxMessage: 2929.:

      -- Method: get_from ()

          Return a string representing the “From ” line that marks the
          start of the message in an mbox mailbox.  The leading “From ”
          and the trailing newline are excluded.

      -- Method: set_from (from_, time_=None)

          Set the “From ” line to `from_', which should be specified
          without a leading “From ” or trailing newline.  For
          convenience, `time_' may be specified and will be formatted
          appropriately and appended to `from_'.  If `time_' is
          specified, it should be a *note time.struct_time: 690.
          instance, a tuple suitable for passing to *note
          time.strftime(): c37, or ‘True’ (to use *note time.gmtime():
          c11.).

      -- Method: get_flags ()

          Return a string specifying the flags that are currently set.
          If the message complies with the conventional format, the
          result is the concatenation in the following order of zero or
          one occurrence of each of ‘'R'’, ‘'O'’, ‘'D'’, ‘'F'’, and
          ‘'A'’.

      -- Method: set_flags (flags)

          Set the flags specified by `flags' and unset all others.
          Parameter `flags' should be the concatenation in any order of
          zero or more occurrences of each of ‘'R'’, ‘'O'’, ‘'D'’,
          ‘'F'’, and ‘'A'’.

      -- Method: add_flag (flag)

          Set the flag(s) specified by `flag' without changing other
          flags.  To add more than one flag at a time, `flag' may be a
          string of more than one character.

      -- Method: remove_flag (flag)

          Unset the flag(s) specified by `flag' without changing other
          flags.  To remove more than one flag at a time, `flag' maybe a
          string of more than one character.

When an *note MMDFMessage: 2aa5. instance is created based upon a *note
MaildirMessage: 2a72. instance, a “From ” line is generated based upon
the *note MaildirMessage: 2a72. instance’s delivery date, and the
following conversions take place:

Resulting state       *note MaildirMessage: 2a72. state
                      
----------------------------------------------------------
                      
R flag                S flag
                      
                      
O flag                “cur” subdirectory
                      
                      
D flag                T flag
                      
                      
F flag                F flag
                      
                      
A flag                R flag
                      

When an *note MMDFMessage: 2aa5. instance is created based upon an *note
MHMessage: 2a8a. instance, the following conversions take place:

Resulting state         *note MHMessage: 2a8a. state
                        
-------------------------------------------------------
                        
R flag and O flag       no “unseen” sequence
                        
                        
O flag                  “unseen” sequence
                        
                        
F flag                  “flagged” sequence
                        
                        
A flag                  “replied” sequence
                        

When an *note MMDFMessage: 2aa5. instance is created based upon a *note
BabylMessage: 2a9d. instance, the following conversions take place:

Resulting state         *note BabylMessage: 2a9d. state
                        
----------------------------------------------------------
                        
R flag and O flag       no “unseen” label
                        
                        
O flag                  “unseen” label
                        
                        
D flag                  “deleted” label
                        
                        
A flag                  “answered” label
                        

When an *note MMDFMessage: 2aa5. instance is created based upon an *note
mboxMessage: 2929. instance, the “From ” line is copied and all flags
directly correspond:

Resulting state       *note mboxMessage: 2929. state
                      
-------------------------------------------------------
                      
R flag                R flag
                      
                      
O flag                O flag
                      
                      
D flag                D flag
                      
                      
F flag                F flag
                      
                      
A flag                A flag
                      


File: python.info,  Node: Exceptions<15>,  Next: Examples<19>,  Prev: Message objects,  Up: mailbox — Manipulate mailboxes in various formats

5.19.4.13 Exceptions
....................

The following exception classes are defined in the *note mailbox: ae.
module:

 -- Exception: mailbox.Error

     The based class for all other module-specific exceptions.

 -- Exception: mailbox.NoSuchMailboxError

     Raised when a mailbox is expected but is not found, such as when
     instantiating a *note Mailbox: cb1. subclass with a path that does
     not exist (and with the `create' parameter set to ‘False’), or when
     opening a folder that does not exist.

 -- Exception: mailbox.NotEmptyError

     Raised when a mailbox is not empty but is expected to be, such as
     when deleting a folder that contains messages.

 -- Exception: mailbox.ExternalClashError

     Raised when some mailbox-related condition beyond the control of
     the program causes it to be unable to proceed, such as when failing
     to acquire a lock that another program already holds a lock, or
     when a uniquely-generated file name already exists.

 -- Exception: mailbox.FormatError

     Raised when the data in a file cannot be parsed, such as when an
     *note MH: 2a89. instance attempts to read a corrupted
     ‘.mh_sequences’ file.


File: python.info,  Node: Examples<19>,  Prev: Exceptions<15>,  Up: mailbox — Manipulate mailboxes in various formats

5.19.4.14 Examples
..................

A simple example of printing the subjects of all messages in a mailbox
that seem interesting:

     import mailbox
     for message in mailbox.mbox('~/mbox'):
         subject = message['subject']       # Could possibly be None.
         if subject and 'python' in subject.lower():
             print(subject)

To copy all mail from a Babyl mailbox to an MH mailbox, converting all
of the format-specific information that can be converted:

     import mailbox
     destination = mailbox.MH('~/Mail')
     destination.lock()
     for message in mailbox.Babyl('~/RMAIL'):
         destination.add(mailbox.MHMessage(message))
     destination.flush()
     destination.unlock()

This example sorts mail from several mailing lists into different
mailboxes, being careful to avoid mail corruption due to concurrent
modification by other programs, mail loss due to interruption of the
program, or premature termination due to malformed messages in the
mailbox:

     import mailbox
     import email.errors

     list_names = ('python-list', 'python-dev', 'python-bugs')

     boxes = {name: mailbox.mbox('~/email/%s' % name) for name in list_names}
     inbox = mailbox.Maildir('~/Maildir', factory=None)

     for key in inbox.iterkeys():
         try:
             message = inbox[key]
         except email.errors.MessageParseError:
             continue                # The message is malformed. Just leave it.

         for name in list_names:
             list_id = message['list-id']
             if list_id and name in list_id:
                 # Get mailbox to use
                 box = boxes[name]

                 # Write copy to disk before removing original.
                 # If there's a crash, you might duplicate a message, but
                 # that's better than losing a message completely.
                 box.lock()
                 box.add(message)
                 box.flush()
                 box.unlock()

                 # Remove original message
                 inbox.lock()
                 inbox.discard(key)
                 inbox.flush()
                 inbox.unlock()
                 break               # Found destination, so stop looking.

     for box in boxes.itervalues():
         box.close()


File: python.info,  Node: mimetypes — Map filenames to MIME types,  Next: base64 — Base16 Base32 Base64 Base85 Data Encodings,  Prev: mailbox — Manipulate mailboxes in various formats,  Up: Internet Data Handling

5.19.5 ‘mimetypes’ — Map filenames to MIME types
------------------------------------------------

`Source code:' Lib/mimetypes.py(1)

__________________________________________________________________

The *note mimetypes: b2. module converts between a filename or URL and
the MIME type associated with the filename extension.  Conversions are
provided from filename to MIME type and from MIME type to filename
extension; encodings are not supported for the latter conversion.

The module provides one class and a number of convenience functions.
The functions are the normal interface to this module, but some
applications may be interested in the class as well.

The functions described below provide the primary interface for this
module.  If the module has not been initialized, they will call *note
init(): 10a2. if they rely on the information *note init(): 10a2. sets
up.

 -- Function: mimetypes.guess_type (url, strict=True)

     Guess the type of a file based on its filename, path or URL, given
     by `url'.  URL can be a string or a *note path-like object: 472.

     The return value is a tuple ‘(type, encoding)’ where `type' is
     ‘None’ if the type can’t be guessed (missing or unknown suffix) or
     a string of the form ‘'type/subtype'’, usable for a MIME
     ‘content-type’ header.

     `encoding' is ‘None’ for no encoding or the name of the program
     used to encode (e.g.  ‘compress’ or ‘gzip’).  The encoding is
     suitable for use as a ‘Content-Encoding’ header, `not' as a
     ‘Content-Transfer-Encoding’ header.  The mappings are table driven.
     Encoding suffixes are case sensitive; type suffixes are first tried
     case sensitively, then case insensitively.

     The optional `strict' argument is a flag specifying whether the
     list of known MIME types is limited to only the official types
     registered with IANA(2). When `strict' is ‘True’ (the default),
     only the IANA types are supported; when `strict' is ‘False’, some
     additional non-standard but commonly used MIME types are also
     recognized.

     Changed in version 3.8: Added support for url being a *note
     path-like object: 472.

 -- Function: mimetypes.guess_all_extensions (type, strict=True)

     Guess the extensions for a file based on its MIME type, given by
     `type'.  The return value is a list of strings giving all possible
     filename extensions, including the leading dot (‘'.'’).  The
     extensions are not guaranteed to have been associated with any
     particular data stream, but would be mapped to the MIME type `type'
     by *note guess_type(): 10a1.

     The optional `strict' argument has the same meaning as with the
     *note guess_type(): 10a1. function.

 -- Function: mimetypes.guess_extension (type, strict=True)

     Guess the extension for a file based on its MIME type, given by
     `type'.  The return value is a string giving a filename extension,
     including the leading dot (‘'.'’).  The extension is not guaranteed
     to have been associated with any particular data stream, but would
     be mapped to the MIME type `type' by *note guess_type(): 10a1.  If
     no extension can be guessed for `type', ‘None’ is returned.

     The optional `strict' argument has the same meaning as with the
     *note guess_type(): 10a1. function.

Some additional functions and data items are available for controlling
the behavior of the module.

 -- Function: mimetypes.init (files=None)

     Initialize the internal data structures.  If given, `files' must be
     a sequence of file names which should be used to augment the
     default type map.  If omitted, the file names to use are taken from
     *note knownfiles: 2ade.; on Windows, the current registry settings
     are loaded.  Each file named in `files' or *note knownfiles: 2ade.
     takes precedence over those named before it.  Calling *note init():
     10a2. repeatedly is allowed.

     Specifying an empty list for `files' will prevent the system
     defaults from being applied: only the well-known values will be
     present from a built-in list.

     If `files' is ‘None’ the internal data structure is completely
     rebuilt to its initial default value.  This is a stable operation
     and will produce the same results when called multiple times.

     Changed in version 3.2: Previously, Windows registry settings were
     ignored.

 -- Function: mimetypes.read_mime_types (filename)

     Load the type map given in the file `filename', if it exists.  The
     type map is returned as a dictionary mapping filename extensions,
     including the leading dot (‘'.'’), to strings of the form
     ‘'type/subtype'’.  If the file `filename' does not exist or cannot
     be read, ‘None’ is returned.

 -- Function: mimetypes.add_type (type, ext, strict=True)

     Add a mapping from the MIME type `type' to the extension `ext'.
     When the extension is already known, the new type will replace the
     old one.  When the type is already known the extension will be
     added to the list of known extensions.

     When `strict' is ‘True’ (the default), the mapping will be added to
     the official MIME types, otherwise to the non-standard ones.

 -- Data: mimetypes.inited

     Flag indicating whether or not the global data structures have been
     initialized.  This is set to ‘True’ by *note init(): 10a2.

 -- Data: mimetypes.knownfiles

     List of type map file names commonly installed.  These files are
     typically named ‘mime.types’ and are installed in different
     locations by different packages.

 -- Data: mimetypes.suffix_map

     Dictionary mapping suffixes to suffixes.  This is used to allow
     recognition of encoded files for which the encoding and the type
     are indicated by the same extension.  For example, the ‘.tgz’
     extension is mapped to ‘.tar.gz’ to allow the encoding and type to
     be recognized separately.

 -- Data: mimetypes.encodings_map

     Dictionary mapping filename extensions to encoding types.

 -- Data: mimetypes.types_map

     Dictionary mapping filename extensions to MIME types.

 -- Data: mimetypes.common_types

     Dictionary mapping filename extensions to non-standard, but
     commonly found MIME types.

An example usage of the module:

     >>> import mimetypes
     >>> mimetypes.init()
     >>> mimetypes.knownfiles
     ['/etc/mime.types', '/etc/httpd/mime.types', ... ]
     >>> mimetypes.suffix_map['.tgz']
     '.tar.gz'
     >>> mimetypes.encodings_map['.gz']
     'gzip'
     >>> mimetypes.types_map['.tgz']
     'application/x-tar-gz'

* Menu:

* MimeTypes Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/mimetypes.py

   (2) https://www.iana.org/assignments/media-types/media-types.xhtml


File: python.info,  Node: MimeTypes Objects,  Up: mimetypes — Map filenames to MIME types

5.19.5.1 MimeTypes Objects
..........................

The *note MimeTypes: 2ae7. class may be useful for applications which
may want more than one MIME-type database; it provides an interface
similar to the one of the *note mimetypes: b2. module.

 -- Class: mimetypes.MimeTypes (filenames=(), strict=True)

     This class represents a MIME-types database.  By default, it
     provides access to the same database as the rest of this module.
     The initial database is a copy of that provided by the module, and
     may be extended by loading additional ‘mime.types’-style files into
     the database using the *note read(): 2ae8. or *note readfp(): 2ae9.
     methods.  The mapping dictionaries may also be cleared before
     loading additional data if the default data is not desired.

     The optional `filenames' parameter can be used to cause additional
     files to be loaded “on top” of the default database.

      -- Attribute: suffix_map

          Dictionary mapping suffixes to suffixes.  This is used to
          allow recognition of encoded files for which the encoding and
          the type are indicated by the same extension.  For example,
          the ‘.tgz’ extension is mapped to ‘.tar.gz’ to allow the
          encoding and type to be recognized separately.  This is
          initially a copy of the global *note suffix_map: 2ae1. defined
          in the module.

      -- Attribute: encodings_map

          Dictionary mapping filename extensions to encoding types.
          This is initially a copy of the global *note encodings_map:
          2ae2. defined in the module.

      -- Attribute: types_map

          Tuple containing two dictionaries, mapping filename extensions
          to MIME types: the first dictionary is for the non-standards
          types and the second one is for the standard types.  They are
          initialized by *note common_types: 2ae4. and *note types_map:
          2ae3.

      -- Attribute: types_map_inv

          Tuple containing two dictionaries, mapping MIME types to a
          list of filename extensions: the first dictionary is for the
          non-standards types and the second one is for the standard
          types.  They are initialized by *note common_types: 2ae4. and
          *note types_map: 2ae3.

      -- Method: guess_extension (type, strict=True)

          Similar to the *note guess_extension(): 2add. function, using
          the tables stored as part of the object.

      -- Method: guess_type (url, strict=True)

          Similar to the *note guess_type(): 10a1. function, using the
          tables stored as part of the object.

      -- Method: guess_all_extensions (type, strict=True)

          Similar to the *note guess_all_extensions(): f6f. function,
          using the tables stored as part of the object.

      -- Method: read (filename, strict=True)

          Load MIME information from a file named `filename'.  This uses
          *note readfp(): 2ae9. to parse the file.

          If `strict' is ‘True’, information will be added to list of
          standard types, else to the list of non-standard types.

      -- Method: readfp (fp, strict=True)

          Load MIME type information from an open file `fp'.  The file
          must have the format of the standard ‘mime.types’ files.

          If `strict' is ‘True’, information will be added to the list
          of standard types, else to the list of non-standard types.

      -- Method: read_windows_registry (strict=True)

          Load MIME type information from the Windows registry.

          *note Availability: 1491.: Windows.

          If `strict' is ‘True’, information will be added to the list
          of standard types, else to the list of non-standard types.

          New in version 3.2.


File: python.info,  Node: base64 — Base16 Base32 Base64 Base85 Data Encodings,  Next: binhex — Encode and decode binhex4 files,  Prev: mimetypes — Map filenames to MIME types,  Up: Internet Data Handling

5.19.6 ‘base64’ — Base16, Base32, Base64, Base85 Data Encodings
---------------------------------------------------------------

`Source code:' Lib/base64.py(1)

__________________________________________________________________

This module provides functions for encoding binary data to printable
ASCII characters and decoding such encodings back to binary data.  It
provides encoding and decoding functions for the encodings specified in
RFC 3548(2), which defines the Base16, Base32, and Base64 algorithms,
and for the de-facto standard Ascii85 and Base85 encodings.

The RFC 3548(3) encodings are suitable for encoding binary data so that
it can safely sent by email, used as parts of URLs, or included as part
of an HTTP POST request.  The encoding algorithm is not the same as the
‘uuencode’ program.

There are two interfaces provided by this module.  The modern interface
supports encoding *note bytes-like objects: 6df. to ASCII *note bytes:
172, and decoding *note bytes-like objects: 6df. or strings containing
ASCII to *note bytes: 172.  Both base-64 alphabets defined in RFC
3548(4) (normal, and URL- and filesystem-safe) are supported.

The legacy interface does not support decoding from strings, but it does
provide functions for encoding and decoding to and from *note file
objects: c14.  It only supports the Base64 standard alphabet, and it
adds newlines every 76 characters as per RFC 2045(5).  Note that if you
are looking for RFC 2045(6) support you probably want to be looking at
the *note email: 67. package instead.

Changed in version 3.3: ASCII-only Unicode strings are now accepted by
the decoding functions of the modern interface.

Changed in version 3.4: Any *note bytes-like objects: 6df. are now
accepted by all encoding and decoding functions in this module.
Ascii85/Base85 support added.

The modern interface provides:

 -- Function: base64.b64encode (s, altchars=None)

     Encode the *note bytes-like object: 6df. `s' using Base64 and
     return the encoded *note bytes: 172.

     Optional `altchars' must be a *note bytes-like object: 6df. of at
     least length 2 (additional characters are ignored) which specifies
     an alternative alphabet for the ‘+’ and ‘/’ characters.  This
     allows an application to e.g.  generate URL or filesystem safe
     Base64 strings.  The default is ‘None’, for which the standard
     Base64 alphabet is used.

 -- Function: base64.b64decode (s, altchars=None, validate=False)

     Decode the Base64 encoded *note bytes-like object: 6df. or ASCII
     string `s' and return the decoded *note bytes: 172.

     Optional `altchars' must be a *note bytes-like object: 6df. or
     ASCII string of at least length 2 (additional characters are
     ignored) which specifies the alternative alphabet used instead of
     the ‘+’ and ‘/’ characters.

     A *note binascii.Error: a3f. exception is raised if `s' is
     incorrectly padded.

     If `validate' is ‘False’ (the default), characters that are neither
     in the normal base-64 alphabet nor the alternative alphabet are
     discarded prior to the padding check.  If `validate' is ‘True’,
     these non-alphabet characters in the input result in a *note
     binascii.Error: a3f.

 -- Function: base64.standard_b64encode (s)

     Encode *note bytes-like object: 6df. `s' using the standard Base64
     alphabet and return the encoded *note bytes: 172.

 -- Function: base64.standard_b64decode (s)

     Decode *note bytes-like object: 6df. or ASCII string `s' using the
     standard Base64 alphabet and return the decoded *note bytes: 172.

 -- Function: base64.urlsafe_b64encode (s)

     Encode *note bytes-like object: 6df. `s' using the URL- and
     filesystem-safe alphabet, which substitutes ‘-’ instead of ‘+’ and
     ‘_’ instead of ‘/’ in the standard Base64 alphabet, and return the
     encoded *note bytes: 172.  The result can still contain ‘=’.

 -- Function: base64.urlsafe_b64decode (s)

     Decode *note bytes-like object: 6df. or ASCII string `s' using the
     URL- and filesystem-safe alphabet, which substitutes ‘-’ instead of
     ‘+’ and ‘_’ instead of ‘/’ in the standard Base64 alphabet, and
     return the decoded *note bytes: 172.

 -- Function: base64.b32encode (s)

     Encode the *note bytes-like object: 6df. `s' using Base32 and
     return the encoded *note bytes: 172.

 -- Function: base64.b32decode (s, casefold=False, map01=None)

     Decode the Base32 encoded *note bytes-like object: 6df. or ASCII
     string `s' and return the decoded *note bytes: 172.

     Optional `casefold' is a flag specifying whether a lowercase
     alphabet is acceptable as input.  For security purposes, the
     default is ‘False’.

     RFC 3548(7) allows for optional mapping of the digit 0 (zero) to
     the letter O (oh), and for optional mapping of the digit 1 (one) to
     either the letter I (eye) or letter L (el).  The optional argument
     `map01' when not ‘None’, specifies which letter the digit 1 should
     be mapped to (when `map01' is not ‘None’, the digit 0 is always
     mapped to the letter O). For security purposes the default is
     ‘None’, so that 0 and 1 are not allowed in the input.

     A *note binascii.Error: a3f. is raised if `s' is incorrectly padded
     or if there are non-alphabet characters present in the input.

 -- Function: base64.b16encode (s)

     Encode the *note bytes-like object: 6df. `s' using Base16 and
     return the encoded *note bytes: 172.

 -- Function: base64.b16decode (s, casefold=False)

     Decode the Base16 encoded *note bytes-like object: 6df. or ASCII
     string `s' and return the decoded *note bytes: 172.

     Optional `casefold' is a flag specifying whether a lowercase
     alphabet is acceptable as input.  For security purposes, the
     default is ‘False’.

     A *note binascii.Error: a3f. is raised if `s' is incorrectly padded
     or if there are non-alphabet characters present in the input.

 -- Function: base64.a85encode (b, *, foldspaces=False, wrapcol=0,
          pad=False, adobe=False)

     Encode the *note bytes-like object: 6df. `b' using Ascii85 and
     return the encoded *note bytes: 172.

     `foldspaces' is an optional flag that uses the special short
     sequence ‘y’ instead of 4 consecutive spaces (ASCII 0x20) as
     supported by ‘btoa’.  This feature is not supported by the
     “standard” Ascii85 encoding.

     `wrapcol' controls whether the output should have newline (‘b'\n'’)
     characters added to it.  If this is non-zero, each output line will
     be at most this many characters long.

     `pad' controls whether the input is padded to a multiple of 4
     before encoding.  Note that the ‘btoa’ implementation always pads.

     `adobe' controls whether the encoded byte sequence is framed with
     ‘<~’ and ‘~>’, which is used by the Adobe implementation.

     New in version 3.4.

 -- Function: base64.a85decode (b, *, foldspaces=False, adobe=False,
          ignorechars=b' \t\n\r\v')

     Decode the Ascii85 encoded *note bytes-like object: 6df. or ASCII
     string `b' and return the decoded *note bytes: 172.

     `foldspaces' is a flag that specifies whether the ‘y’ short
     sequence should be accepted as shorthand for 4 consecutive spaces
     (ASCII 0x20).  This feature is not supported by the “standard”
     Ascii85 encoding.

     `adobe' controls whether the input sequence is in Adobe Ascii85
     format (i.e.  is framed with <~ and ~>).

     `ignorechars' should be a *note bytes-like object: 6df. or ASCII
     string containing characters to ignore from the input.  This should
     only contain whitespace characters, and by default contains all
     whitespace characters in ASCII.

     New in version 3.4.

 -- Function: base64.b85encode (b, pad=False)

     Encode the *note bytes-like object: 6df. `b' using base85 (as used
     in e.g.  git-style binary diffs) and return the encoded *note
     bytes: 172.

     If `pad' is true, the input is padded with ‘b'\0'’ so its length is
     a multiple of 4 bytes before encoding.

     New in version 3.4.

 -- Function: base64.b85decode (b)

     Decode the base85-encoded *note bytes-like object: 6df. or ASCII
     string `b' and return the decoded *note bytes: 172.  Padding is
     implicitly removed, if necessary.

     New in version 3.4.

The legacy interface:

 -- Function: base64.decode (input, output)

     Decode the contents of the binary `input' file and write the
     resulting binary data to the `output' file.  `input' and `output'
     must be *note file objects: c14.  `input' will be read until
     ‘input.readline()’ returns an empty bytes object.

 -- Function: base64.decodebytes (s)

     Decode the *note bytes-like object: 6df. `s', which must contain
     one or more lines of base64 encoded data, and return the decoded
     *note bytes: 172.

     New in version 3.1.

 -- Function: base64.encode (input, output)

     Encode the contents of the binary `input' file and write the
     resulting base64 encoded data to the `output' file.  `input' and
     `output' must be *note file objects: c14.  `input' will be read
     until ‘input.read()’ returns an empty bytes object.  *note
     encode(): 2afc. inserts a newline character (‘b'\n'’) after every
     76 bytes of the output, as well as ensuring that the output always
     ends with a newline, as per RFC 2045(8) (MIME).

 -- Function: base64.encodebytes (s)

     Encode the *note bytes-like object: 6df. `s', which can contain
     arbitrary binary data, and return *note bytes: 172. containing the
     base64-encoded data, with newlines (‘b'\n'’) inserted after every
     76 bytes of output, and ensuring that there is a trailing newline,
     as per RFC 2045(9) (MIME).

     New in version 3.1.

An example usage of the module:

     >>> import base64
     >>> encoded = base64.b64encode(b'data to be encoded')
     >>> encoded
     b'ZGF0YSB0byBiZSBlbmNvZGVk'
     >>> data = base64.b64decode(encoded)
     >>> data
     b'data to be encoded'

See also
........

Module *note binascii: f.

     Support module containing ASCII-to-binary and binary-to-ASCII
     conversions.

RFC 1521(10) - MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies

     Section 5.2, “Base64 Content-Transfer-Encoding,” provides the
     definition of the base64 encoding.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/base64.py

   (2) https://tools.ietf.org/html/rfc3548.html

   (3) https://tools.ietf.org/html/rfc3548.html

   (4) https://tools.ietf.org/html/rfc3548.html

   (5) https://tools.ietf.org/html/rfc2045.html

   (6) https://tools.ietf.org/html/rfc2045.html

   (7) https://tools.ietf.org/html/rfc3548.html

   (8) https://tools.ietf.org/html/rfc2045.html

   (9) https://tools.ietf.org/html/rfc2045.html

   (10) https://tools.ietf.org/html/rfc1521.html


File: python.info,  Node: binhex — Encode and decode binhex4 files,  Next: binascii — Convert between binary and ASCII,  Prev: base64 — Base16 Base32 Base64 Base85 Data Encodings,  Up: Internet Data Handling

5.19.7 ‘binhex’ — Encode and decode binhex4 files
-------------------------------------------------

`Source code:' Lib/binhex.py(1)

Deprecated since version 3.9.

__________________________________________________________________

This module encodes and decodes files in binhex4 format, a format
allowing representation of Macintosh files in ASCII. Only the data fork
is handled.

The *note binhex: 10. module defines the following functions:

 -- Function: binhex.binhex (input, output)

     Convert a binary file with filename `input' to binhex file
     `output'.  The `output' parameter can either be a filename or a
     file-like object (any object supporting a ‘write()’ and ‘close()’
     method).

 -- Function: binhex.hexbin (input, output)

     Decode a binhex file `input'.  `input' may be a filename or a
     file-like object supporting ‘read()’ and ‘close()’ methods.  The
     resulting file is written to a file named `output', unless the
     argument is ‘None’ in which case the output filename is read from
     the binhex file.

The following exception is also defined:

 -- Exception: binhex.Error

     Exception raised when something can’t be encoded using the binhex
     format (for example, a filename is too long to fit in the filename
     field), or when input is not properly encoded binhex data.

See also
........

Module *note binascii: f.

     Support module containing ASCII-to-binary and binary-to-ASCII
     conversions.

* Menu:

* Notes: Notes<2>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/binhex.py


File: python.info,  Node: Notes<2>,  Up: binhex — Encode and decode binhex4 files

5.19.7.1 Notes
..............

There is an alternative, more powerful interface to the coder and
decoder, see the source for details.

If you code or decode textfiles on non-Macintosh platforms they will
still use the old Macintosh newline convention (carriage-return as end
of line).


File: python.info,  Node: binascii — Convert between binary and ASCII,  Next: quopri — Encode and decode MIME quoted-printable data,  Prev: binhex — Encode and decode binhex4 files,  Up: Internet Data Handling

5.19.8 ‘binascii’ — Convert between binary and ASCII
----------------------------------------------------

__________________________________________________________________

The *note binascii: f. module contains a number of methods to convert
between binary and various ASCII-encoded binary representations.
Normally, you will not use these functions directly but use wrapper
modules like *note uu: 12c, *note base64: d, or *note binhex: 10.
instead.  The *note binascii: f. module contains low-level functions
written in C for greater speed that are used by the higher-level
modules.

     Note: ‘a2b_*’ functions accept Unicode strings containing only
     ASCII characters.  Other functions only accept *note bytes-like
     objects: 6df. (such as *note bytes: 172, *note bytearray: 173. and
     other objects that support the buffer protocol).

     Changed in version 3.3: ASCII-only unicode strings are now accepted
     by the ‘a2b_*’ functions.

The *note binascii: f. module defines the following functions:

 -- Function: binascii.a2b_uu (string)

     Convert a single line of uuencoded data back to binary and return
     the binary data.  Lines normally contain 45 (binary) bytes, except
     for the last line.  Line data may be followed by whitespace.

 -- Function: binascii.b2a_uu (data, *, backtick=False)

     Convert binary data to a line of ASCII characters, the return value
     is the converted line, including a newline char.  The length of
     `data' should be at most 45.  If `backtick' is true, zeros are
     represented by ‘'`'’ instead of spaces.

     Changed in version 3.7: Added the `backtick' parameter.

 -- Function: binascii.a2b_base64 (string)

     Convert a block of base64 data back to binary and return the binary
     data.  More than one line may be passed at a time.

 -- Function: binascii.b2a_base64 (data, *, newline=True)

     Convert binary data to a line of ASCII characters in base64 coding.
     The return value is the converted line, including a newline char if
     `newline' is true.  The output of this function conforms to RFC
     3548(1).

     Changed in version 3.6: Added the `newline' parameter.

 -- Function: binascii.a2b_qp (data, header=False)

     Convert a block of quoted-printable data back to binary and return
     the binary data.  More than one line may be passed at a time.  If
     the optional argument `header' is present and true, underscores
     will be decoded as spaces.

 -- Function: binascii.b2a_qp (data, quotetabs=False, istext=True,
          header=False)

     Convert binary data to a line(s) of ASCII characters in
     quoted-printable encoding.  The return value is the converted
     line(s).  If the optional argument `quotetabs' is present and true,
     all tabs and spaces will be encoded.  If the optional argument
     `istext' is present and true, newlines are not encoded but trailing
     whitespace will be encoded.  If the optional argument `header' is
     present and true, spaces will be encoded as underscores per RFC
     1522(2).  If the optional argument `header' is present and false,
     newline characters will be encoded as well; otherwise linefeed
     conversion might corrupt the binary data stream.

 -- Function: binascii.a2b_hqx (string)

     Convert binhex4 formatted ASCII data to binary, without doing
     RLE-decompression.  The string should contain a complete number of
     binary bytes, or (in case of the last portion of the binhex4 data)
     have the remaining bits zero.

     Deprecated since version 3.9.

 -- Function: binascii.rledecode_hqx (data)

     Perform RLE-decompression on the data, as per the binhex4 standard.
     The algorithm uses ‘0x90’ after a byte as a repeat indicator,
     followed by a count.  A count of ‘0’ specifies a byte value of
     ‘0x90’.  The routine returns the decompressed data, unless data
     input data ends in an orphaned repeat indicator, in which case the
     *note Incomplete: 2b09. exception is raised.

     Changed in version 3.2: Accept only bytestring or bytearray objects
     as input.

     Deprecated since version 3.9.

 -- Function: binascii.rlecode_hqx (data)

     Perform binhex4 style RLE-compression on `data' and return the
     result.

     Deprecated since version 3.9.

 -- Function: binascii.b2a_hqx (data)

     Perform hexbin4 binary-to-ASCII translation and return the
     resulting string.  The argument should already be RLE-coded, and
     have a length divisible by 3 (except possibly the last fragment).

     Deprecated since version 3.9.

 -- Function: binascii.crc_hqx (data, value)

     Compute a 16-bit CRC value of `data', starting with `value' as the
     initial CRC, and return the result.  This uses the CRC-CCITT
     polynomial `x'^16 + `x'^12 + `x'^5 + 1, often represented as
     0x1021.  This CRC is used in the binhex4 format.

 -- Function: binascii.crc32 (data[, value])

     Compute CRC-32, the 32-bit checksum of `data', starting with an
     initial CRC of `value'.  The default initial CRC is zero.  The
     algorithm is consistent with the ZIP file checksum.  Since the
     algorithm is designed for use as a checksum algorithm, it is not
     suitable for use as a general hash algorithm.  Use as follows:

          print(binascii.crc32(b"hello world"))
          # Or, in two pieces:
          crc = binascii.crc32(b"hello")
          crc = binascii.crc32(b" world", crc)
          print('crc32 = {:#010x}'.format(crc))

     Changed in version 3.0: The result is always unsigned.  To generate
     the same numeric value across all Python versions and platforms,
     use ‘crc32(data) & 0xffffffff’.

 -- Function: binascii.b2a_hex (data[, sep[, bytes_per_sep=1]])
 -- Function: binascii.hexlify (data[, sep[, bytes_per_sep=1]])

     Return the hexadecimal representation of the binary `data'.  Every
     byte of `data' is converted into the corresponding 2-digit hex
     representation.  The returned bytes object is therefore twice as
     long as the length of `data'.

     Similar functionality (but returning a text string) is also
     conveniently accessible using the *note bytes.hex(): 724. method.

     If `sep' is specified, it must be a single character str or bytes
     object.  It will be inserted in the output after every
     `bytes_per_sep' input bytes.  Separator placement is counted from
     the right end of the output by default, if you wish to count from
     the left, supply a negative `bytes_per_sep' value.

          >>> import binascii
          >>> binascii.b2a_hex(b'\xb9\x01\xef')
          b'b901ef'
          >>> binascii.hexlify(b'\xb9\x01\xef', '-')
          b'b9-01-ef'
          >>> binascii.b2a_hex(b'\xb9\x01\xef', b'_', 2)
          b'b9_01ef'
          >>> binascii.b2a_hex(b'\xb9\x01\xef', b' ', -2)
          b'b901 ef'

     Changed in version 3.8: The `sep' and `bytes_per_sep' parameters
     were added.

 -- Function: binascii.a2b_hex (hexstr)
 -- Function: binascii.unhexlify (hexstr)

     Return the binary data represented by the hexadecimal string
     `hexstr'.  This function is the inverse of *note b2a_hex(): 19b7.
     `hexstr' must contain an even number of hexadecimal digits (which
     can be upper or lower case), otherwise an *note Error: a3f.
     exception is raised.

     Similar functionality (accepting only text string arguments, but
     more liberal towards whitespace) is also accessible using the *note
     bytes.fromhex(): 43e. class method.

 -- Exception: binascii.Error

     Exception raised on errors.  These are usually programming errors.

 -- Exception: binascii.Incomplete

     Exception raised on incomplete data.  These are usually not
     programming errors, but may be handled by reading a little more
     data and trying again.

See also
........

Module *note base64: d.

     Support for RFC compliant base64-style encoding in base 16, 32, 64,
     and 85.

Module *note binhex: 10.

     Support for the binhex format used on the Macintosh.

Module *note uu: 12c.

     Support for UU encoding used on Unix.

Module *note quopri: db.

     Support for quoted-printable encoding used in MIME email messages.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3548.html

   (2) https://tools.ietf.org/html/rfc1522.html


File: python.info,  Node: quopri — Encode and decode MIME quoted-printable data,  Next: uu — Encode and decode uuencode files,  Prev: binascii — Convert between binary and ASCII,  Up: Internet Data Handling

5.19.9 ‘quopri’ — Encode and decode MIME quoted-printable data
--------------------------------------------------------------

`Source code:' Lib/quopri.py(1)

__________________________________________________________________

This module performs quoted-printable transport encoding and decoding,
as defined in RFC 1521(2): “MIME (Multipurpose Internet Mail Extensions)
Part One: Mechanisms for Specifying and Describing the Format of
Internet Message Bodies”.  The quoted-printable encoding is designed for
data where there are relatively few nonprintable characters; the base64
encoding scheme available via the *note base64: d. module is more
compact if there are many such characters, as when sending a graphics
file.

 -- Function: quopri.decode (input, output, header=False)

     Decode the contents of the `input' file and write the resulting
     decoded binary data to the `output' file.  `input' and `output'
     must be *note binary file objects: c14.  If the optional argument
     `header' is present and true, underscore will be decoded as space.
     This is used to decode “Q”-encoded headers as described in RFC
     1522(3): “MIME (Multipurpose Internet Mail Extensions) Part Two:
     Message Header Extensions for Non-ASCII Text”.

 -- Function: quopri.encode (input, output, quotetabs, header=False)

     Encode the contents of the `input' file and write the resulting
     quoted-printable data to the `output' file.  `input' and `output'
     must be *note binary file objects: c14.  `quotetabs', a
     non-optional flag which controls whether to encode embedded spaces
     and tabs; when true it encodes such embedded whitespace, and when
     false it leaves them unencoded.  Note that spaces and tabs
     appearing at the end of lines are always encoded, as per RFC
     1521(4).  `header' is a flag which controls if spaces are encoded
     as underscores as per RFC 1522(5).

 -- Function: quopri.decodestring (s, header=False)

     Like *note decode(): 19ba, except that it accepts a source *note
     bytes: 172. and returns the corresponding decoded *note bytes: 172.

 -- Function: quopri.encodestring (s, quotetabs=False, header=False)

     Like *note encode(): 19b9, except that it accepts a source *note
     bytes: 172. and returns the corresponding encoded *note bytes: 172.
     By default, it sends a ‘False’ value to `quotetabs' parameter of
     the *note encode(): 19b9. function.

See also
........

Module *note base64: d.

     Encode and decode MIME base64 data

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/quopri.py

   (2) https://tools.ietf.org/html/rfc1521.html

   (3) https://tools.ietf.org/html/rfc1522.html

   (4) https://tools.ietf.org/html/rfc1521.html

   (5) https://tools.ietf.org/html/rfc1522.html


File: python.info,  Node: uu — Encode and decode uuencode files,  Prev: quopri — Encode and decode MIME quoted-printable data,  Up: Internet Data Handling

5.19.10 ‘uu’ — Encode and decode uuencode files
-----------------------------------------------

`Source code:' Lib/uu.py(1)

__________________________________________________________________

This module encodes and decodes files in uuencode format, allowing
arbitrary binary data to be transferred over ASCII-only connections.
Wherever a file argument is expected, the methods accept a file-like
object.  For backwards compatibility, a string containing a pathname is
also accepted, and the corresponding file will be opened for reading and
writing; the pathname ‘'-'’ is understood to mean the standard input or
output.  However, this interface is deprecated; it’s better for the
caller to open the file itself, and be sure that, when required, the
mode is ‘'rb'’ or ‘'wb'’ on Windows.

This code was contributed by Lance Ellinghouse, and modified by Jack
Jansen.

The *note uu: 12c. module defines the following functions:

 -- Function: uu.encode (in_file, out_file, name=None, mode=None, *,
          backtick=False)

     Uuencode file `in_file' into file `out_file'.  The uuencoded file
     will have the header specifying `name' and `mode' as the defaults
     for the results of decoding the file.  The default defaults are
     taken from `in_file', or ‘'-'’ and ‘0o666’ respectively.  If
     `backtick' is true, zeros are represented by ‘'`'’ instead of
     spaces.

     Changed in version 3.7: Added the `backtick' parameter.

 -- Function: uu.decode (in_file, out_file=None, mode=None, quiet=False)

     This call decodes uuencoded file `in_file' placing the result on
     file `out_file'.  If `out_file' is a pathname, `mode' is used to
     set the permission bits if the file must be created.  Defaults for
     `out_file' and `mode' are taken from the uuencode header.  However,
     if the file specified in the header already exists, a *note
     uu.Error: 2b11. is raised.

     *note decode(): 19bb. may print a warning to standard error if the
     input was produced by an incorrect uuencoder and Python could
     recover from that error.  Setting `quiet' to a true value silences
     this warning.

 -- Exception: uu.Error

     Subclass of *note Exception: 2dc, this can be raised by *note
     uu.decode(): 19bb. under various situations, such as described
     above, but also including a badly formatted header, or truncated
     input file.

See also
........

Module *note binascii: f.

     Support module containing ASCII-to-binary and binary-to-ASCII
     conversions.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/uu.py


File: python.info,  Node: Structured Markup Processing Tools,  Next: Internet Protocols and Support,  Prev: Internet Data Handling,  Up: The Python Standard Library

5.20 Structured Markup Processing Tools
=======================================

Python supports a variety of modules to work with various forms of
structured data markup.  This includes modules to work with the Standard
Generalized Markup Language (SGML) and the Hypertext Markup Language
(HTML), and several interfaces for working with the Extensible Markup
Language (XML).

* Menu:

* html — HyperText Markup Language support::
* html.parser — Simple HTML and XHTML parser: html parser — Simple HTML and XHTML parser.
* html.entities — Definitions of HTML general entities: html entities — Definitions of HTML general entities.
* XML Processing Modules::
* xml.etree.ElementTree — The ElementTree XML API: xml etree ElementTree — The ElementTree XML API.
* xml.dom — The Document Object Model API: xml dom — The Document Object Model API.
* xml.dom.minidom — Minimal DOM implementation: xml dom minidom — Minimal DOM implementation.
* xml.dom.pulldom — Support for building partial DOM trees: xml dom pulldom — Support for building partial DOM trees.
* xml.sax — Support for SAX2 parsers: xml sax — Support for SAX2 parsers.
* xml.sax.handler — Base classes for SAX handlers: xml sax handler — Base classes for SAX handlers.
* xml.sax.saxutils — SAX Utilities: xml sax saxutils — SAX Utilities.
* xml.sax.xmlreader — Interface for XML parsers: xml sax xmlreader — Interface for XML parsers.
* xml.parsers.expat — Fast XML parsing using Expat: xml parsers expat — Fast XML parsing using Expat.


File: python.info,  Node: html — HyperText Markup Language support,  Next: html parser — Simple HTML and XHTML parser,  Up: Structured Markup Processing Tools

5.20.1 ‘html’ — HyperText Markup Language support
-------------------------------------------------

`Source code:' Lib/html/__init__.py(1)

__________________________________________________________________

This module defines utilities to manipulate HTML.

 -- Function: html.escape (s, quote=True)

     Convert the characters ‘&’, ‘<’ and ‘>’ in string `s' to HTML-safe
     sequences.  Use this if you need to display text that might contain
     such characters in HTML. If the optional flag `quote' is true, the
     characters (‘"’) and (‘'’) are also translated; this helps for
     inclusion in an HTML attribute value delimited by quotes, as in ‘<a
     href="...">’.

     New in version 3.2.

 -- Function: html.unescape (s)

     Convert all named and numeric character references (e.g.  ‘&gt;’,
     ‘&#62;’, ‘&#x3e;’) in the string `s' to the corresponding Unicode
     characters.  This function uses the rules defined by the HTML 5
     standard for both valid and invalid character references, and the
     *note list of HTML 5 named character references: af3.

     New in version 3.4.

__________________________________________________________________

Submodules in the ‘html’ package are:

   * *note html.parser: 91. – HTML/XHTML parser with lenient parsing
     mode

   * *note html.entities: 90. – HTML entity definitions

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/html/__init__.py


File: python.info,  Node: html parser — Simple HTML and XHTML parser,  Next: html entities — Definitions of HTML general entities,  Prev: html — HyperText Markup Language support,  Up: Structured Markup Processing Tools

5.20.2 ‘html.parser’ — Simple HTML and XHTML parser
---------------------------------------------------

`Source code:' Lib/html/parser.py(1)

__________________________________________________________________

This module defines a class *note HTMLParser: 22a. which serves as the
basis for parsing text files formatted in HTML (HyperText Mark-up
Language) and XHTML.

 -- Class: html.parser.HTMLParser (*, convert_charrefs=True)

     Create a parser instance able to parse invalid markup.

     If `convert_charrefs' is ‘True’ (the default), all character
     references (except the ones in ‘script’/‘style’ elements) are
     automatically converted to the corresponding Unicode characters.

     An *note HTMLParser: 22a. instance is fed HTML data and calls
     handler methods when start tags, end tags, text, comments, and
     other markup elements are encountered.  The user should subclass
     *note HTMLParser: 22a. and override its methods to implement the
     desired behavior.

     This parser does not check that end tags match start tags or call
     the end-tag handler for elements which are closed implicitly by
     closing an outer element.

     Changed in version 3.4: `convert_charrefs' keyword argument added.

     Changed in version 3.5: The default value for argument
     `convert_charrefs' is now ‘True’.

* Menu:

* Example HTML Parser Application::
* HTMLParser Methods::
* Examples: Examples<20>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/html/parser.py


File: python.info,  Node: Example HTML Parser Application,  Next: HTMLParser Methods,  Up: html parser — Simple HTML and XHTML parser

5.20.2.1 Example HTML Parser Application
........................................

As a basic example, below is a simple HTML parser that uses the *note
HTMLParser: 22a. class to print out start tags, end tags, and data as
they are encountered:

     from html.parser import HTMLParser

     class MyHTMLParser(HTMLParser):
         def handle_starttag(self, tag, attrs):
             print("Encountered a start tag:", tag)

         def handle_endtag(self, tag):
             print("Encountered an end tag :", tag)

         def handle_data(self, data):
             print("Encountered some data  :", data)

     parser = MyHTMLParser()
     parser.feed('<html><head><title>Test</title></head>'
                 '<body><h1>Parse me!</h1></body></html>')

The output will then be:

     Encountered a start tag: html
     Encountered a start tag: head
     Encountered a start tag: title
     Encountered some data  : Test
     Encountered an end tag : title
     Encountered an end tag : head
     Encountered a start tag: body
     Encountered a start tag: h1
     Encountered some data  : Parse me!
     Encountered an end tag : h1
     Encountered an end tag : body
     Encountered an end tag : html


File: python.info,  Node: HTMLParser Methods,  Next: Examples<20>,  Prev: Example HTML Parser Application,  Up: html parser — Simple HTML and XHTML parser

5.20.2.2 ‘HTMLParser’ Methods
.............................

*note HTMLParser: 22a. instances have the following methods:

 -- Method: HTMLParser.feed (data)

     Feed some text to the parser.  It is processed insofar as it
     consists of complete elements; incomplete data is buffered until
     more data is fed or *note close(): 2b1c. is called.  `data' must be
     *note str: 205.

 -- Method: HTMLParser.close ()

     Force processing of all buffered data as if it were followed by an
     end-of-file mark.  This method may be redefined by a derived class
     to define additional processing at the end of the input, but the
     redefined version should always call the *note HTMLParser: 22a.
     base class method *note close(): 2b1c.

 -- Method: HTMLParser.reset ()

     Reset the instance.  Loses all unprocessed data.  This is called
     implicitly at instantiation time.

 -- Method: HTMLParser.getpos ()

     Return current line number and offset.

 -- Method: HTMLParser.get_starttag_text ()

     Return the text of the most recently opened start tag.  This should
     not normally be needed for structured processing, but may be useful
     in dealing with HTML “as deployed” or for re-generating input with
     minimal changes (whitespace between attributes can be preserved,
     etc.).

The following methods are called when data or markup elements are
encountered and they are meant to be overridden in a subclass.  The base
class implementations do nothing (except for *note handle_startendtag():
2b20.):

 -- Method: HTMLParser.handle_starttag (tag, attrs)

     This method is called to handle the start of a tag (e.g.  ‘<div
     id="main">’).

     The `tag' argument is the name of the tag converted to lower case.
     The `attrs' argument is a list of ‘(name, value)’ pairs containing
     the attributes found inside the tag’s ‘<>’ brackets.  The `name'
     will be translated to lower case, and quotes in the `value' have
     been removed, and character and entity references have been
     replaced.

     For instance, for the tag ‘<A HREF="https://www.cwi.nl/">’, this
     method would be called as ‘handle_starttag('a', [('href',
     'https://www.cwi.nl/')])’.

     All entity references from *note html.entities: 90. are replaced in
     the attribute values.

 -- Method: HTMLParser.handle_endtag (tag)

     This method is called to handle the end tag of an element (e.g.
     ‘</div>’).

     The `tag' argument is the name of the tag converted to lower case.

 -- Method: HTMLParser.handle_startendtag (tag, attrs)

     Similar to *note handle_starttag(): 2b21, but called when the
     parser encounters an XHTML-style empty tag (‘<img ... />’).  This
     method may be overridden by subclasses which require this
     particular lexical information; the default implementation simply
     calls *note handle_starttag(): 2b21. and *note handle_endtag():
     2b22.

 -- Method: HTMLParser.handle_data (data)

     This method is called to process arbitrary data (e.g.  text nodes
     and the content of ‘<script>...</script>’ and
     ‘<style>...</style>’).

 -- Method: HTMLParser.handle_entityref (name)

     This method is called to process a named character reference of the
     form ‘&name;’ (e.g.  ‘&gt;’), where `name' is a general entity
     reference (e.g.  ‘'gt'’).  This method is never called if
     `convert_charrefs' is ‘True’.

 -- Method: HTMLParser.handle_charref (name)

     This method is called to process decimal and hexadecimal numeric
     character references of the form ‘&#NNN;’ and ‘&#xNNN;’.  For
     example, the decimal equivalent for ‘&gt;’ is ‘&#62;’, whereas the
     hexadecimal is ‘&#x3E;’; in this case the method will receive
     ‘'62'’ or ‘'x3E'’.  This method is never called if
     `convert_charrefs' is ‘True’.

 -- Method: HTMLParser.handle_comment (data)

     This method is called when a comment is encountered (e.g.
     ‘<!--comment-->’).

     For example, the comment ‘<!-- comment -->’ will cause this method
     to be called with the argument ‘' comment '’.

     The content of Internet Explorer conditional comments (condcoms)
     will also be sent to this method, so, for ‘<!--[if IE
     9]>IE9-specific content<![endif]-->’, this method will receive
     ‘'[if IE 9]>IE9-specific content<![endif]'’.

 -- Method: HTMLParser.handle_decl (decl)

     This method is called to handle an HTML doctype declaration (e.g.
     ‘<!DOCTYPE html>’).

     The `decl' parameter will be the entire contents of the declaration
     inside the ‘<!...>’ markup (e.g.  ‘'DOCTYPE html'’).

 -- Method: HTMLParser.handle_pi (data)

     Method called when a processing instruction is encountered.  The
     `data' parameter will contain the entire processing instruction.
     For example, for the processing instruction ‘<?proc color='red'>’,
     this method would be called as ‘handle_pi("proc color='red'")’.  It
     is intended to be overridden by a derived class; the base class
     implementation does nothing.

          Note: The *note HTMLParser: 22a. class uses the SGML syntactic
          rules for processing instructions.  An XHTML processing
          instruction using the trailing ‘'?'’ will cause the ‘'?'’ to
          be included in `data'.

 -- Method: HTMLParser.unknown_decl (data)

     This method is called when an unrecognized declaration is read by
     the parser.

     The `data' parameter will be the entire contents of the declaration
     inside the ‘<![...]>’ markup.  It is sometimes useful to be
     overridden by a derived class.  The base class implementation does
     nothing.


File: python.info,  Node: Examples<20>,  Prev: HTMLParser Methods,  Up: html parser — Simple HTML and XHTML parser

5.20.2.3 Examples
.................

The following class implements a parser that will be used to illustrate
more examples:

     from html.parser import HTMLParser
     from html.entities import name2codepoint

     class MyHTMLParser(HTMLParser):
         def handle_starttag(self, tag, attrs):
             print("Start tag:", tag)
             for attr in attrs:
                 print("     attr:", attr)

         def handle_endtag(self, tag):
             print("End tag  :", tag)

         def handle_data(self, data):
             print("Data     :", data)

         def handle_comment(self, data):
             print("Comment  :", data)

         def handle_entityref(self, name):
             c = chr(name2codepoint[name])
             print("Named ent:", c)

         def handle_charref(self, name):
             if name.startswith('x'):
                 c = chr(int(name[1:], 16))
             else:
                 c = chr(int(name))
             print("Num ent  :", c)

         def handle_decl(self, data):
             print("Decl     :", data)

     parser = MyHTMLParser()

Parsing a doctype:

     >>> parser.feed('<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" '
     ...             '"http://www.w3.org/TR/html4/strict.dtd">')
     Decl     : DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"

Parsing an element with a few attributes and a title:

     >>> parser.feed('<img src="python-logo.png" alt="The Python logo">')
     Start tag: img
          attr: ('src', 'python-logo.png')
          attr: ('alt', 'The Python logo')
     >>>
     >>> parser.feed('<h1>Python</h1>')
     Start tag: h1
     Data     : Python
     End tag  : h1

The content of ‘script’ and ‘style’ elements is returned as is, without
further parsing:

     >>> parser.feed('<style type="text/css">#python { color: green }</style>')
     Start tag: style
          attr: ('type', 'text/css')
     Data     : #python { color: green }
     End tag  : style

     >>> parser.feed('<script type="text/javascript">'
     ...             'alert("<strong>hello!</strong>");</script>')
     Start tag: script
          attr: ('type', 'text/javascript')
     Data     : alert("<strong>hello!</strong>");
     End tag  : script

Parsing comments:

     >>> parser.feed('<!-- a comment -->'
     ...             '<!--[if IE 9]>IE-specific content<![endif]-->')
     Comment  :  a comment
     Comment  : [if IE 9]>IE-specific content<![endif]

Parsing named and numeric character references and converting them to
the correct char (note: these 3 references are all equivalent to ‘'>'’):

     >>> parser.feed('&gt;&#62;&#x3E;')
     Named ent: >
     Num ent  : >
     Num ent  : >

Feeding incomplete chunks to *note feed(): 2b1b. works, but *note
handle_data(): 2b23. might be called more than once (unless
`convert_charrefs' is set to ‘True’):

     >>> for chunk in ['<sp', 'an>buff', 'ered ', 'text</s', 'pan>']:
     ...     parser.feed(chunk)
     ...
     Start tag: span
     Data     : buff
     Data     : ered
     Data     : text
     End tag  : span

Parsing invalid HTML (e.g.  unquoted attributes) also works:

     >>> parser.feed('<p><a class=link href=#main>tag soup</p ></a>')
     Start tag: p
     Start tag: a
          attr: ('class', 'link')
          attr: ('href', '#main')
     Data     : tag soup
     End tag  : p
     End tag  : a


File: python.info,  Node: html entities — Definitions of HTML general entities,  Next: XML Processing Modules,  Prev: html parser — Simple HTML and XHTML parser,  Up: Structured Markup Processing Tools

5.20.3 ‘html.entities’ — Definitions of HTML general entities
-------------------------------------------------------------

`Source code:' Lib/html/entities.py(1)

__________________________________________________________________

This module defines four dictionaries, *note html5: af3, *note
name2codepoint: 2b2e, *note codepoint2name: 2b2f, and *note entitydefs:
2b30.

 -- Data: html.entities.html5

     A dictionary that maps HTML5 named character references (2) to the
     equivalent Unicode character(s), e.g.  ‘html5['gt;'] == '>'’.  Note
     that the trailing semicolon is included in the name (e.g.
     ‘'gt;'’), however some of the names are accepted by the standard
     even without the semicolon: in this case the name is present with
     and without the ‘';'’.  See also *note html.unescape(): 22b.

     New in version 3.3.

 -- Data: html.entities.entitydefs

     A dictionary mapping XHTML 1.0 entity definitions to their
     replacement text in ISO Latin-1.

 -- Data: html.entities.name2codepoint

     A dictionary that maps HTML entity names to the Unicode code
     points.

 -- Data: html.entities.codepoint2name

     A dictionary that maps Unicode code points to HTML entity names.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/html/entities.py

   (2) (1) See
‘https://html.spec.whatwg.org/multipage/syntax.html#named-character-references’


File: python.info,  Node: XML Processing Modules,  Next: xml etree ElementTree — The ElementTree XML API,  Prev: html entities — Definitions of HTML general entities,  Up: Structured Markup Processing Tools

5.20.4 XML Processing Modules
-----------------------------

`Source code:' Lib/xml/(1)

__________________________________________________________________

Python’s interfaces for processing XML are grouped in the ‘xml’ package.

     Warning: The XML modules are not secure against erroneous or
     maliciously constructed data.  If you need to parse untrusted or
     unauthenticated data see the *note XML vulnerabilities: 2b34. and
     *note The defusedxml Package: 2b35. sections.

It is important to note that modules in the *note xml: 13c. package
require that there be at least one SAX-compliant XML parser available.
The Expat parser is included with Python, so the *note
xml.parsers.expat: 141. module will always be available.

The documentation for the *note xml.dom: 13d. and *note xml.sax: 144.
packages are the definition of the Python bindings for the DOM and SAX
interfaces.

The XML handling submodules are:

   * *note xml.etree.ElementTree: 140.: the ElementTree API, a simple
     and lightweight XML processor

   * *note xml.dom: 13d.: the DOM API definition

   * *note xml.dom.minidom: 13e.: a minimal DOM implementation

   * *note xml.dom.pulldom: 13f.: support for building partial DOM trees

   * *note xml.sax: 144.: SAX2 base classes and convenience functions

   * *note xml.parsers.expat: 141.: the Expat parser binding

* Menu:

* XML vulnerabilities::
* The defusedxml Package::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/xml/


File: python.info,  Node: XML vulnerabilities,  Next: The defusedxml Package,  Up: XML Processing Modules

5.20.4.1 XML vulnerabilities
............................

The XML processing modules are not secure against maliciously
constructed data.  An attacker can abuse XML features to carry out
denial of service attacks, access local files, generate network
connections to other machines, or circumvent firewalls.

The following table gives an overview of the known attacks and whether
the various modules are vulnerable to them.

kind                          sax                    etree                  minidom                pulldom                xmlrpc
                                                                                                                          
-------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                          
billion laughs                `Vulnerable' (1)       `Vulnerable' (1)       `Vulnerable' (1)       `Vulnerable' (1)       `Vulnerable' (1)
                                                                                                                          
                                                                                                                          
quadratic blowup              `Vulnerable' (1)       `Vulnerable' (1)       `Vulnerable' (1)       `Vulnerable' (1)       `Vulnerable' (1)
                                                                                                                          
                                                                                                                          
external entity expansion     Safe (5)               Safe (2)               Safe (3)               Safe (5)               Safe (4)
                                                                                                                          
                                                                                                                          
DTD(1) retrieval              Safe (5)               Safe                   Safe                   Safe (5)               Safe
                                                                                                                          
                                                                                                                          
decompression bomb            Safe                   Safe                   Safe                   Safe                   `Vulnerable'
                                                                                                                          

  1. Expat 2.4.1 and newer is not vulnerable to the “billion laughs” and
     “quadratic blowup” vulnerabilities.  Items still listed as
     vulnerable due to potential reliance on system-provided libraries.
     Check ‘pyexpat.EXPAT_VERSION’.

  2. *note xml.etree.ElementTree: 140. doesn’t expand external entities
     and raises a ‘ParserError’ when an entity occurs.

  3. *note xml.dom.minidom: 13e. doesn’t expand external entities and
     simply returns the unexpanded entity verbatim.

  4. ‘xmlrpclib’ doesn’t expand external entities and omits them.

  5. Since Python 3.7.1, external general entities are no longer
     processed by default.

billion laughs / exponential entity expansion

     The Billion Laughs(2) attack – also known as exponential entity
     expansion – uses multiple levels of nested entities.  Each entity
     refers to another entity several times, and the final entity
     definition contains a small string.  The exponential expansion
     results in several gigabytes of text and consumes lots of memory
     and CPU time.

quadratic blowup entity expansion

     A quadratic blowup attack is similar to a Billion Laughs(3) attack;
     it abuses entity expansion, too.  Instead of nested entities it
     repeats one large entity with a couple of thousand chars over and
     over again.  The attack isn’t as efficient as the exponential case
     but it avoids triggering parser countermeasures that forbid
     deeply-nested entities.

external entity expansion

     Entity declarations can contain more than just text for
     replacement.  They can also point to external resources or local
     files.  The XML parser accesses the resource and embeds the content
     into the XML document.

DTD(4) retrieval

     Some XML libraries like Python’s *note xml.dom.pulldom: 13f.
     retrieve document type definitions from remote or local locations.
     The feature has similar implications as the external entity
     expansion issue.

decompression bomb

     Decompression bombs (aka ZIP bomb(5)) apply to all XML libraries
     that can parse compressed XML streams such as gzipped HTTP streams
     or LZMA-compressed files.  For an attacker it can reduce the amount
     of transmitted data by three magnitudes or more.

The documentation for defusedxml(6) on PyPI has further information
about all known attack vectors with examples and references.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Document_type_definition

   (2) https://en.wikipedia.org/wiki/Billion_laughs

   (3) https://en.wikipedia.org/wiki/Billion_laughs

   (4) https://en.wikipedia.org/wiki/Document_type_definition

   (5) https://en.wikipedia.org/wiki/Zip_bomb

   (6) https://pypi.org/project/defusedxml/


File: python.info,  Node: The defusedxml Package,  Prev: XML vulnerabilities,  Up: XML Processing Modules

5.20.4.2 The ‘defusedxml’ Package
.................................

defusedxml(1) is a pure Python package with modified subclasses of all
stdlib XML parsers that prevent any potentially malicious operation.
Use of this package is recommended for any server code that parses
untrusted XML data.  The package also ships with example exploits and
extended documentation on more XML exploits such as XPath injection.

   ---------- Footnotes ----------

   (1) https://pypi.org/project/defusedxml/


File: python.info,  Node: xml etree ElementTree — The ElementTree XML API,  Next: xml dom — The Document Object Model API,  Prev: XML Processing Modules,  Up: Structured Markup Processing Tools

5.20.5 ‘xml.etree.ElementTree’ — The ElementTree XML API
--------------------------------------------------------

`Source code:' Lib/xml/etree/ElementTree.py(1)

__________________________________________________________________

The *note xml.etree.ElementTree: 140. module implements a simple and
efficient API for parsing and creating XML data.

Changed in version 3.3: This module will use a fast implementation
whenever available.

Deprecated since version 3.3: The ‘xml.etree.cElementTree’ module is
deprecated.

     Warning: The *note xml.etree.ElementTree: 140. module is not secure
     against maliciously constructed data.  If you need to parse
     untrusted or unauthenticated data see *note XML vulnerabilities:
     2b34.

* Menu:

* Tutorial::
* XPath support::
* Reference: Reference<2>.
* XInclude support::
* Reference: Reference<3>.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/xml/etree/ElementTree.py


File: python.info,  Node: Tutorial,  Next: XPath support,  Up: xml etree ElementTree — The ElementTree XML API

5.20.5.1 Tutorial
.................

This is a short tutorial for using *note xml.etree.ElementTree: 140.
(‘ET’ in short).  The goal is to demonstrate some of the building blocks
and basic concepts of the module.

* Menu:

* XML tree and elements::
* Parsing XML::
* Pull API for non-blocking parsing::
* Finding interesting elements::
* Modifying an XML File::
* Building XML documents::
* Parsing XML with Namespaces::
* Additional resources::


File: python.info,  Node: XML tree and elements,  Next: Parsing XML,  Up: Tutorial

5.20.5.2 XML tree and elements
..............................

XML is an inherently hierarchical data format, and the most natural way
to represent it is with a tree.  ‘ET’ has two classes for this purpose -
*note ElementTree: 21c. represents the whole XML document as a tree, and
*note Element: 21d. represents a single node in this tree.  Interactions
with the whole document (reading and writing to/from files) are usually
done on the *note ElementTree: 21c. level.  Interactions with a single
XML element and its sub-elements are done on the *note Element: 21d.
level.


File: python.info,  Node: Parsing XML,  Next: Pull API for non-blocking parsing,  Prev: XML tree and elements,  Up: Tutorial

5.20.5.3 Parsing XML
....................

We’ll be using the following XML document as the sample data for this
section:

     <?xml version="1.0"?>
     <data>
         <country name="Liechtenstein">
             <rank>1</rank>
             <year>2008</year>
             <gdppc>141100</gdppc>
             <neighbor name="Austria" direction="E"/>
             <neighbor name="Switzerland" direction="W"/>
         </country>
         <country name="Singapore">
             <rank>4</rank>
             <year>2011</year>
             <gdppc>59900</gdppc>
             <neighbor name="Malaysia" direction="N"/>
         </country>
         <country name="Panama">
             <rank>68</rank>
             <year>2011</year>
             <gdppc>13600</gdppc>
             <neighbor name="Costa Rica" direction="W"/>
             <neighbor name="Colombia" direction="E"/>
         </country>
     </data>

We can import this data by reading from a file:

     import xml.etree.ElementTree as ET
     tree = ET.parse('country_data.xml')
     root = tree.getroot()

Or directly from a string:

     root = ET.fromstring(country_data_as_string)

*note fromstring(): 2b3f. parses XML from a string directly into an
*note Element: 21d, which is the root element of the parsed tree.  Other
parsing functions may create an *note ElementTree: 21c.  Check the
documentation to be sure.

As an *note Element: 21d, ‘root’ has a tag and a dictionary of
attributes:

     >>> root.tag
     'data'
     >>> root.attrib
     {}

It also has children nodes over which we can iterate:

     >>> for child in root:
     ...     print(child.tag, child.attrib)
     ...
     country {'name': 'Liechtenstein'}
     country {'name': 'Singapore'}
     country {'name': 'Panama'}

Children are nested, and we can access specific child nodes by index:

     >>> root[0][1].text
     '2008'

     Note: Not all elements of the XML input will end up as elements of
     the parsed tree.  Currently, this module skips over any XML
     comments, processing instructions, and document type declarations
     in the input.  Nevertheless, trees built using this module’s API
     rather than parsing from XML text can have comments and processing
     instructions in them; they will be included when generating XML
     output.  A document type declaration may be accessed by passing a
     custom *note TreeBuilder: 37d. instance to the *note XMLParser:
     37c. constructor.


File: python.info,  Node: Pull API for non-blocking parsing,  Next: Finding interesting elements,  Prev: Parsing XML,  Up: Tutorial

5.20.5.4 Pull API for non-blocking parsing
..........................................

Most parsing functions provided by this module require the whole
document to be read at once before returning any result.  It is possible
to use an *note XMLParser: 37c. and feed data into it incrementally, but
it is a push API that calls methods on a callback target, which is too
low-level and inconvenient for most needs.  Sometimes what the user
really wants is to be able to parse XML incrementally, without blocking
operations, while enjoying the convenience of fully constructed *note
Element: 21d. objects.

The most powerful tool for doing this is *note XMLPullParser: 9f9.  It
does not require a blocking read to obtain the XML data, and is instead
fed with data incrementally with *note XMLPullParser.feed(): 2b41.
calls.  To get the parsed XML elements, call *note
XMLPullParser.read_events(): 2b42.  Here is an example:

     >>> parser = ET.XMLPullParser(['start', 'end'])
     >>> parser.feed('<mytag>sometext')
     >>> list(parser.read_events())
     [('start', <Element 'mytag' at 0x7fa66db2be58>)]
     >>> parser.feed(' more text</mytag>')
     >>> for event, elem in parser.read_events():
     ...     print(event)
     ...     print(elem.tag, 'text=', elem.text)
     ...
     end

The obvious use case is applications that operate in a non-blocking
fashion where the XML data is being received from a socket or read
incrementally from some storage device.  In such cases, blocking reads
are unacceptable.

Because it’s so flexible, *note XMLPullParser: 9f9. can be inconvenient
to use for simpler use-cases.  If you don’t mind your application
blocking on reading XML data but would still like to have incremental
parsing capabilities, take a look at *note iterparse(): a29.  It can be
useful when you’re reading a large XML document and don’t want to hold
it wholly in memory.


File: python.info,  Node: Finding interesting elements,  Next: Modifying an XML File,  Prev: Pull API for non-blocking parsing,  Up: Tutorial

5.20.5.5 Finding interesting elements
.....................................

*note Element: 21d. has some useful methods that help iterate
recursively over all the sub-tree below it (its children, their
children, and so on).  For example, *note Element.iter(): daf.:

     >>> for neighbor in root.iter('neighbor'):
     ...     print(neighbor.attrib)
     ...
     {'name': 'Austria', 'direction': 'E'}
     {'name': 'Switzerland', 'direction': 'W'}
     {'name': 'Malaysia', 'direction': 'N'}
     {'name': 'Costa Rica', 'direction': 'W'}
     {'name': 'Colombia', 'direction': 'E'}

*note Element.findall(): 2b44. finds only elements with a tag which are
direct children of the current element.  *note Element.find(): 2b45.
finds the `first' child with a particular tag, and *note Element.text:
2b46. accesses the element’s text content.  *note Element.get(): 2b47.
accesses the element’s attributes:

     >>> for country in root.findall('country'):
     ...     rank = country.find('rank').text
     ...     name = country.get('name')
     ...     print(name, rank)
     ...
     Liechtenstein 1
     Singapore 4
     Panama 68

More sophisticated specification of which elements to look for is
possible by using *note XPath: 51e.


File: python.info,  Node: Modifying an XML File,  Next: Building XML documents,  Prev: Finding interesting elements,  Up: Tutorial

5.20.5.6 Modifying an XML File
..............................

*note ElementTree: 21c. provides a simple way to build XML documents and
write them to files.  The *note ElementTree.write(): 9fd. method serves
this purpose.

Once created, an *note Element: 21d. object may be manipulated by
directly changing its fields (such as *note Element.text: 2b46.), adding
and modifying attributes (*note Element.set(): 2b49. method), as well as
adding new children (for example with *note Element.append(): 2b4a.).

Let’s say we want to add one to each country’s rank, and add an
‘updated’ attribute to the rank element:

     >>> for rank in root.iter('rank'):
     ...     new_rank = int(rank.text) + 1
     ...     rank.text = str(new_rank)
     ...     rank.set('updated', 'yes')
     ...
     >>> tree.write('output.xml')

Our XML now looks like this:

     <?xml version="1.0"?>
     <data>
         <country name="Liechtenstein">
             <rank updated="yes">2</rank>
             <year>2008</year>
             <gdppc>141100</gdppc>
             <neighbor name="Austria" direction="E"/>
             <neighbor name="Switzerland" direction="W"/>
         </country>
         <country name="Singapore">
             <rank updated="yes">5</rank>
             <year>2011</year>
             <gdppc>59900</gdppc>
             <neighbor name="Malaysia" direction="N"/>
         </country>
         <country name="Panama">
             <rank updated="yes">69</rank>
             <year>2011</year>
             <gdppc>13600</gdppc>
             <neighbor name="Costa Rica" direction="W"/>
             <neighbor name="Colombia" direction="E"/>
         </country>
     </data>

We can remove elements using *note Element.remove(): 2b4b.  Let’s say we
want to remove all countries with a rank higher than 50:

     >>> for country in root.findall('country'):
     ...     # using root.findall() to avoid removal during traversal
     ...     rank = int(country.find('rank').text)
     ...     if rank > 50:
     ...         root.remove(country)
     ...
     >>> tree.write('output.xml')

Note that concurrent modification while iterating can lead to problems,
just like when iterating and modifying Python lists or dicts.
Therefore, the example first collects all matching elements with
‘root.findall()’, and only then iterates over the list of matches.

Our XML now looks like this:

     <?xml version="1.0"?>
     <data>
         <country name="Liechtenstein">
             <rank updated="yes">2</rank>
             <year>2008</year>
             <gdppc>141100</gdppc>
             <neighbor name="Austria" direction="E"/>
             <neighbor name="Switzerland" direction="W"/>
         </country>
         <country name="Singapore">
             <rank updated="yes">5</rank>
             <year>2011</year>
             <gdppc>59900</gdppc>
             <neighbor name="Malaysia" direction="N"/>
         </country>
     </data>


File: python.info,  Node: Building XML documents,  Next: Parsing XML with Namespaces,  Prev: Modifying an XML File,  Up: Tutorial

5.20.5.7 Building XML documents
...............................

The *note SubElement(): 2b4d. function also provides a convenient way to
create new sub-elements for a given element:

     >>> a = ET.Element('a')
     >>> b = ET.SubElement(a, 'b')
     >>> c = ET.SubElement(a, 'c')
     >>> d = ET.SubElement(c, 'd')
     >>> ET.dump(a)
     <a><b /><c><d /></c></a>


File: python.info,  Node: Parsing XML with Namespaces,  Next: Additional resources,  Prev: Building XML documents,  Up: Tutorial

5.20.5.8 Parsing XML with Namespaces
....................................

If the XML input has namespaces(1), tags and attributes with prefixes in
the form ‘prefix:sometag’ get expanded to ‘{uri}sometag’ where the
`prefix' is replaced by the full `URI'. Also, if there is a default
namespace(2), that full URI gets prepended to all of the non-prefixed
tags.

Here is an XML example that incorporates two namespaces, one with the
prefix “fictional” and the other serving as the default namespace:

     <?xml version="1.0"?>
     <actors xmlns:fictional="http://characters.example.com"
             xmlns="http://people.example.com">
         <actor>
             <name>John Cleese</name>
             <fictional:character>Lancelot</fictional:character>
             <fictional:character>Archie Leach</fictional:character>
         </actor>
         <actor>
             <name>Eric Idle</name>
             <fictional:character>Sir Robin</fictional:character>
             <fictional:character>Gunther</fictional:character>
             <fictional:character>Commander Clement</fictional:character>
         </actor>
     </actors>

One way to search and explore this XML example is to manually add the
URI to every tag or attribute in the xpath of a *note find(): 2b45. or
*note findall(): 2b44.:

     root = fromstring(xml_text)
     for actor in root.findall('{http://people.example.com}actor'):
         name = actor.find('{http://people.example.com}name')
         print(name.text)
         for char in actor.findall('{http://characters.example.com}character'):
             print(' |-->', char.text)

A better way to search the namespaced XML example is to create a
dictionary with your own prefixes and use those in the search functions:

     ns = {'real_person': 'http://people.example.com',
           'role': 'http://characters.example.com'}

     for actor in root.findall('real_person:actor', ns):
         name = actor.find('real_person:name', ns)
         print(name.text)
         for char in actor.findall('role:character', ns):
             print(' |-->', char.text)

These two approaches both output:

     John Cleese
      |--> Lancelot
      |--> Archie Leach
     Eric Idle
      |--> Sir Robin
      |--> Gunther
      |--> Commander Clement

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/XML_namespace

   (2) https://www.w3.org/TR/xml-names/#defaulting


File: python.info,  Node: Additional resources,  Prev: Parsing XML with Namespaces,  Up: Tutorial

5.20.5.9 Additional resources
.............................

See ‘http://effbot.org/zone/element-index.htm’ for tutorials and links
to other docs.


File: python.info,  Node: XPath support,  Next: Reference<2>,  Prev: Tutorial,  Up: xml etree ElementTree — The ElementTree XML API

5.20.5.10 XPath support
.......................

This module provides limited support for XPath expressions(1) for
locating elements in a tree.  The goal is to support a small subset of
the abbreviated syntax; a full XPath engine is outside the scope of the
module.

* Menu:

* Example: Example<10>.
* Supported XPath syntax::

   ---------- Footnotes ----------

   (1) https://www.w3.org/TR/xpath


File: python.info,  Node: Example<10>,  Next: Supported XPath syntax,  Up: XPath support

5.20.5.11 Example
.................

Here’s an example that demonstrates some of the XPath capabilities of
the module.  We’ll be using the ‘countrydata’ XML document from the
*note Parsing XML: 2b3d. section:

     import xml.etree.ElementTree as ET

     root = ET.fromstring(countrydata)

     # Top-level elements
     root.findall(".")

     # All 'neighbor' grand-children of 'country' children of the top-level
     # elements
     root.findall("./country/neighbor")

     # Nodes with name='Singapore' that have a 'year' child
     root.findall(".//year/..[@name='Singapore']")

     # 'year' nodes that are children of nodes with name='Singapore'
     root.findall(".//*[@name='Singapore']/year")

     # All 'neighbor' nodes that are the second child of their parent
     root.findall(".//neighbor[2]")

For XML with namespaces, use the usual qualified ‘{namespace}tag’
notation:

     # All dublin-core "title" tags in the document
     root.findall(".//{http://purl.org/dc/elements/1.1/}title")


File: python.info,  Node: Supported XPath syntax,  Prev: Example<10>,  Up: XPath support

5.20.5.12 Supported XPath syntax
................................

Syntax                      Meaning
                            
---------------------------------------------------------------------------------------
                            
‘tag’                       Selects all child elements with the given tag.  For
                            example, ‘spam’ selects all child elements named ‘spam’,
                            and ‘spam/egg’ selects all grandchildren named ‘egg’ in
                            all children named ‘spam’.  ‘{namespace}*’ selects all
                            tags in the given namespace, ‘{*}spam’ selects tags
                            named ‘spam’ in any (or no) namespace, and ‘{}*’ only
                            selects tags that are not in a namespace.
                            
                            Changed in version 3.8: Support for star-wildcards was
                            added.
                            
                            
‘*’                         Selects all child elements, including comments and
                            processing instructions.  For example, ‘*/egg’ selects
                            all grandchildren named ‘egg’.
                            
                            
‘.’                         Selects the current node.  This is mostly useful at the
                            beginning of the path, to indicate that it’s a relative
                            path.
                            
                            
‘//’                        Selects all subelements, on all levels beneath the
                            current element.  For example, ‘.//egg’ selects all
                            ‘egg’ elements in the entire tree.
                            
                            
‘..’                        Selects the parent element.  Returns ‘None’ if the path
                            attempts to reach the ancestors of the start element
                            (the element ‘find’ was called on).
                            
                            
‘[@attrib]’                 Selects all elements that have the given attribute.
                            
                            
‘[@attrib='value']’         Selects all elements for which the given attribute has
                            the given value.  The value cannot contain quotes.
                            
                            
‘[tag]’                     Selects all elements that have a child named ‘tag’.
                            Only immediate children are supported.
                            
                            
‘[.='text']’                Selects all elements whose complete text content,
                            including descendants, equals the given ‘text’.
                            
                            New in version 3.7.
                            
                            
‘[tag='text']’              Selects all elements that have a child named ‘tag’ whose
                            complete text content, including descendants, equals the
                            given ‘text’.
                            
                            
‘[position]’                Selects all elements that are located at the given
                            position.  The position can be either an integer (1 is
                            the first position), the expression ‘last()’ (for the
                            last position), or a position relative to the last
                            position (e.g.  ‘last()-1’).
                            

Predicates (expressions within square brackets) must be preceded by a
tag name, an asterisk, or another predicate.  ‘position’ predicates must
be preceded by a tag name.


File: python.info,  Node: Reference<2>,  Next: XInclude support,  Prev: XPath support,  Up: xml etree ElementTree — The ElementTree XML API

5.20.5.13 Reference
...................

* Menu:

* Functions: Functions<7>.


File: python.info,  Node: Functions<7>,  Up: Reference<2>

5.20.5.14 Functions
...................

 -- Function: xml.etree.ElementTree.canonicalize (xml_data=None, *,
          out=None, from_file=None, **options)

     C14N 2.0(1) transformation function.

     Canonicalization is a way to normalise XML output in a way that
     allows byte-by-byte comparisons and digital signatures.  It reduced
     the freedom that XML serializers have and instead generates a more
     constrained XML representation.  The main restrictions regard the
     placement of namespace declarations, the ordering of attributes,
     and ignorable whitespace.

     This function takes an XML data string (`xml_data') or a file path
     or file-like object (`from_file') as input, converts it to the
     canonical form, and writes it out using the `out' file(-like)
     object, if provided, or returns it as a text string if not.  The
     output file receives text, not bytes.  It should therefore be
     opened in text mode with ‘utf-8’ encoding.

     Typical uses:

          xml_data = "<root>...</root>"
          print(canonicalize(xml_data))

          with open("c14n_output.xml", mode='w', encoding='utf-8') as out_file:
              canonicalize(xml_data, out=out_file)

          with open("c14n_output.xml", mode='w', encoding='utf-8') as out_file:
              canonicalize(from_file="inputfile.xml", out=out_file)

     The configuration `options' are as follows:

        - `with_comments': set to true to include comments (default:
          false)

        - 
          `strip_text': set to true to strip whitespace before and after text content

               (default: false)

        - 
          `rewrite_prefixes': set to true to replace namespace prefixes by “n{number}”

               (default: false)

        - 
          `qname_aware_tags': a set of qname aware tag names in which prefixes

               should be replaced in text content (default: empty)

        - 
          `qname_aware_attrs': a set of qname aware attribute names in which prefixes

               should be replaced in text content (default: empty)

        - `exclude_attrs': a set of attribute names that should not be
          serialised

        - `exclude_tags': a set of tag names that should not be
          serialised

     In the option list above, “a set” refers to any collection or
     iterable of strings, no ordering is expected.

     New in version 3.8.

 -- Function: xml.etree.ElementTree.Comment (text=None)

     Comment element factory.  This factory function creates a special
     element that will be serialized as an XML comment by the standard
     serializer.  The comment string can be either a bytestring or a
     Unicode string.  `text' is a string containing the comment string.
     Returns an element instance representing a comment.

     Note that *note XMLParser: 37c. skips over comments in the input
     instead of creating comment objects for them.  An *note
     ElementTree: 21c. will only contain comment nodes if they have been
     inserted into to the tree using one of the *note Element: 21d.
     methods.

 -- Function: xml.etree.ElementTree.dump (elem)

     Writes an element tree or element structure to sys.stdout.  This
     function should be used for debugging only.

     The exact output format is implementation dependent.  In this
     version, it’s written as an ordinary XML file.

     `elem' is an element tree or an individual element.

     Changed in version 3.8: The *note dump(): 2b58. function now
     preserves the attribute order specified by the user.

 -- Function: xml.etree.ElementTree.fromstring (text, parser=None)

     Parses an XML section from a string constant.  Same as *note XML():
     2b59.  `text' is a string containing XML data.  `parser' is an
     optional parser instance.  If not given, the standard *note
     XMLParser: 37c. parser is used.  Returns an *note Element: 21d.
     instance.

 -- Function: xml.etree.ElementTree.fromstringlist (sequence,
          parser=None)

     Parses an XML document from a sequence of string fragments.
     `sequence' is a list or other sequence containing XML data
     fragments.  `parser' is an optional parser instance.  If not given,
     the standard *note XMLParser: 37c. parser is used.  Returns an
     *note Element: 21d. instance.

     New in version 3.2.

 -- Function: xml.etree.ElementTree.indent (tree, space=" ", level=0)

     Appends whitespace to the subtree to indent the tree visually.
     This can be used to generate pretty-printed XML output.  `tree' can
     be an Element or ElementTree.  `space' is the whitespace string
     that will be inserted for each indentation level, two space
     characters by default.  For indenting partial subtrees inside of an
     already indented tree, pass the initial indentation level as
     `level'.

     New in version 3.9.

 -- Function: xml.etree.ElementTree.iselement (element)

     Check if an object appears to be a valid element object.  `element'
     is an element instance.  Return ‘True’ if this is an element
     object.

 -- Function: xml.etree.ElementTree.iterparse (source, events=None,
          parser=None)

     Parses an XML section into an element tree incrementally, and
     reports what’s going on to the user.  `source' is a filename or
     *note file object: c14. containing XML data.  `events' is a
     sequence of events to report back.  The supported events are the
     strings ‘"start"’, ‘"end"’, ‘"comment"’, ‘"pi"’, ‘"start-ns"’ and
     ‘"end-ns"’ (the “ns” events are used to get detailed namespace
     information).  If `events' is omitted, only ‘"end"’ events are
     reported.  `parser' is an optional parser instance.  If not given,
     the standard *note XMLParser: 37c. parser is used.  `parser' must
     be a subclass of *note XMLParser: 37c. and can only use the default
     *note TreeBuilder: 37d. as a target.  Returns an *note iterator:
     1171. providing ‘(event, elem)’ pairs.

     Note that while *note iterparse(): a29. builds the tree
     incrementally, it issues blocking reads on `source' (or the file it
     names).  As such, it’s unsuitable for applications where blocking
     reads can’t be made.  For fully non-blocking parsing, see *note
     XMLPullParser: 9f9.

          Note: *note iterparse(): a29. only guarantees that it has seen
          the “>” character of a starting tag when it emits a “start”
          event, so the attributes are defined, but the contents of the
          text and tail attributes are undefined at that point.  The
          same applies to the element children; they may or may not be
          present.

          If you need a fully populated element, look for “end” events
          instead.

     Deprecated since version 3.4: The `parser' argument.

     Changed in version 3.8: The ‘comment’ and ‘pi’ events were added.

 -- Function: xml.etree.ElementTree.parse (source, parser=None)

     Parses an XML section into an element tree.  `source' is a filename
     or file object containing XML data.  `parser' is an optional parser
     instance.  If not given, the standard *note XMLParser: 37c. parser
     is used.  Returns an *note ElementTree: 21c. instance.

 -- Function: xml.etree.ElementTree.ProcessingInstruction (target,
          text=None)

     PI element factory.  This factory function creates a special
     element that will be serialized as an XML processing instruction.
     `target' is a string containing the PI target.  `text' is a string
     containing the PI contents, if given.  Returns an element instance,
     representing a processing instruction.

     Note that *note XMLParser: 37c. skips over processing instructions
     in the input instead of creating comment objects for them.  An
     *note ElementTree: 21c. will only contain processing instruction
     nodes if they have been inserted into to the tree using one of the
     *note Element: 21d. methods.

 -- Function: xml.etree.ElementTree.register_namespace (prefix, uri)

     Registers a namespace prefix.  The registry is global, and any
     existing mapping for either the given prefix or the namespace URI
     will be removed.  `prefix' is a namespace prefix.  `uri' is a
     namespace uri.  Tags and attributes in this namespace will be
     serialized with the given prefix, if at all possible.

     New in version 3.2.

 -- Function: xml.etree.ElementTree.SubElement (parent, tag, attrib={},
          **extra)

     Subelement factory.  This function creates an element instance, and
     appends it to an existing element.

     The element name, attribute names, and attribute values can be
     either bytestrings or Unicode strings.  `parent' is the parent
     element.  `tag' is the subelement name.  `attrib' is an optional
     dictionary, containing element attributes.  `extra' contains
     additional attributes, given as keyword arguments.  Returns an
     element instance.

 -- Function: xml.etree.ElementTree.tostring (element,
          encoding="us-ascii", method="xml", *, xml_declaration=None,
          default_namespace=None, short_empty_elements=True)

     Generates a string representation of an XML element, including all
     subelements.  `element' is an *note Element: 21d. instance.
     `encoding' (2) is the output encoding (default is US-ASCII). Use
     ‘encoding="unicode"’ to generate a Unicode string (otherwise, a
     bytestring is generated).  `method' is either ‘"xml"’, ‘"html"’ or
     ‘"text"’ (default is ‘"xml"’).  `xml_declaration',
     `default_namespace' and `short_empty_elements' has the same meaning
     as in *note ElementTree.write(): 9fd.  Returns an (optionally)
     encoded string containing the XML data.

     New in version 3.4: The `short_empty_elements' parameter.

     New in version 3.8: The `xml_declaration' and `default_namespace'
     parameters.

     Changed in version 3.8: The *note tostring(): 9fb. function now
     preserves the attribute order specified by the user.

 -- Function: xml.etree.ElementTree.tostringlist (element,
          encoding="us-ascii", method="xml", *, xml_declaration=None,
          default_namespace=None, short_empty_elements=True)

     Generates a string representation of an XML element, including all
     subelements.  `element' is an *note Element: 21d. instance.
     `encoding' (3) is the output encoding (default is US-ASCII). Use
     ‘encoding="unicode"’ to generate a Unicode string (otherwise, a
     bytestring is generated).  `method' is either ‘"xml"’, ‘"html"’ or
     ‘"text"’ (default is ‘"xml"’).  `xml_declaration',
     `default_namespace' and `short_empty_elements' has the same meaning
     as in *note ElementTree.write(): 9fd.  Returns a list of
     (optionally) encoded strings containing the XML data.  It does not
     guarantee any specific sequence, except that
     ‘b"".join(tostringlist(element)) == tostring(element)’.

     New in version 3.2.

     New in version 3.4: The `short_empty_elements' parameter.

     New in version 3.8: The `xml_declaration' and `default_namespace'
     parameters.

     Changed in version 3.8: The *note tostringlist(): 9fc. function now
     preserves the attribute order specified by the user.

 -- Function: xml.etree.ElementTree.XML (text, parser=None)

     Parses an XML section from a string constant.  This function can be
     used to embed “XML literals” in Python code.  `text' is a string
     containing XML data.  `parser' is an optional parser instance.  If
     not given, the standard *note XMLParser: 37c. parser is used.
     Returns an *note Element: 21d. instance.

 -- Function: xml.etree.ElementTree.XMLID (text, parser=None)

     Parses an XML section from a string constant, and also returns a
     dictionary which maps from element id:s to elements.  `text' is a
     string containing XML data.  `parser' is an optional parser
     instance.  If not given, the standard *note XMLParser: 37c. parser
     is used.  Returns a tuple containing an *note Element: 21d.
     instance and a dictionary.

   ---------- Footnotes ----------

   (1) https://www.w3.org/TR/xml-c14n2/

   (2) (1) The encoding string included in XML output should conform to
the appropriate standards.  For example, “UTF-8” is valid, but “UTF8” is
not.  See
‘https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl’ and
‘https://www.iana.org/assignments/character-sets/character-sets.xhtml’.

   (3) (1) The encoding string included in XML output should conform to
the appropriate standards.  For example, “UTF-8” is valid, but “UTF8” is
not.  See
‘https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl’ and
‘https://www.iana.org/assignments/character-sets/character-sets.xhtml’.


File: python.info,  Node: XInclude support,  Next: Reference<3>,  Prev: Reference<2>,  Up: xml etree ElementTree — The ElementTree XML API

5.20.5.15 XInclude support
..........................

This module provides limited support for XInclude directives(1), via the
‘xml.etree.ElementInclude’ helper module.  This module can be used to
insert subtrees and text strings into element trees, based on
information in the tree.

* Menu:

* Example: Example<11>.

   ---------- Footnotes ----------

   (1) https://www.w3.org/TR/xinclude/


File: python.info,  Node: Example<11>,  Up: XInclude support

5.20.5.16 Example
.................

Here’s an example that demonstrates use of the XInclude module.  To
include an XML document in the current document, use the
‘{http://www.w3.org/2001/XInclude}include’ element and set the `parse'
attribute to ‘"xml"’, and use the `href' attribute to specify the
document to include.

     <?xml version="1.0"?>
     <document xmlns:xi="http://www.w3.org/2001/XInclude">
       <xi:include href="source.xml" parse="xml" />
     </document>

By default, the `href' attribute is treated as a file name.  You can use
custom loaders to override this behaviour.  Also note that the standard
helper does not support XPointer syntax.

To process this file, load it as usual, and pass the root element to the
*note xml.etree.ElementTree: 140. module:

     from xml.etree import ElementTree, ElementInclude

     tree = ElementTree.parse("document.xml")
     root = tree.getroot()

     ElementInclude.include(root)

The ElementInclude module replaces the
‘{http://www.w3.org/2001/XInclude}include’ element with the root element
from the `source.xml' document.  The result might look something like
this:

     <document xmlns:xi="http://www.w3.org/2001/XInclude">
       <para>This is a paragraph.</para>
     </document>

If the `parse' attribute is omitted, it defaults to “xml”.  The href
attribute is required.

To include a text document, use the
‘{http://www.w3.org/2001/XInclude}include’ element, and set the `parse'
attribute to “text”:

     <?xml version="1.0"?>
     <document xmlns:xi="http://www.w3.org/2001/XInclude">
       Copyright (c) <xi:include href="year.txt" parse="text" />.
     </document>

The result might look something like:

     <document xmlns:xi="http://www.w3.org/2001/XInclude">
       Copyright (c) 2003.
     </document>


File: python.info,  Node: Reference<3>,  Prev: XInclude support,  Up: xml etree ElementTree — The ElementTree XML API

5.20.5.17 Reference
...................

* Menu:

* Functions: Functions<8>.
* Element Objects::
* ElementTree Objects::
* QName Objects::
* TreeBuilder Objects::
* XMLParser Objects::
* XMLPullParser Objects::
* Exceptions: Exceptions<16>.


File: python.info,  Node: Functions<8>,  Next: Element Objects,  Up: Reference<3>

5.20.5.18 Functions
...................

 -- Function: xml.etree.ElementInclude.default_loader (href, parse,
          encoding=None)

     Default loader.  This default loader reads an included resource
     from disk.  `href' is a URL. `parse' is for parse mode either “xml”
     or “text”.  `encoding' is an optional text encoding.  If not given,
     encoding is ‘utf-8’.  Returns the expanded resource.  If the parse
     mode is ‘"xml"’, this is an ElementTree instance.  If the parse
     mode is “text”, this is a Unicode string.  If the loader fails, it
     can return None or raise an exception.

 -- Function: xml.etree.ElementInclude.include (elem, loader=None,
          base_url=None, max_depth=6)

     This function expands XInclude directives.  `elem' is the root
     element.  `loader' is an optional resource loader.  If omitted, it
     defaults to *note default_loader(): 2b65.  If given, it should be a
     callable that implements the same interface as *note
     default_loader(): 2b65.  `base_url' is base URL of the original
     file, to resolve relative include file references.  `max_depth' is
     the maximum number of recursive inclusions.  Limited to reduce the
     risk of malicious content explosion.  Pass a negative value to
     disable the limitation.

     Returns the expanded resource.  If the parse mode is ‘"xml"’, this
     is an ElementTree instance.  If the parse mode is “text”, this is a
     Unicode string.  If the loader fails, it can return None or raise
     an exception.

     New in version 3.9: The `base_url' and `max_depth' parameters.


File: python.info,  Node: Element Objects,  Next: ElementTree Objects,  Prev: Functions<8>,  Up: Reference<3>

5.20.5.19 Element Objects
.........................

 -- Class: xml.etree.ElementTree.Element (tag, attrib={}, **extra)

     Element class.  This class defines the Element interface, and
     provides a reference implementation of this interface.

     The element name, attribute names, and attribute values can be
     either bytestrings or Unicode strings.  `tag' is the element name.
     `attrib' is an optional dictionary, containing element attributes.
     `extra' contains additional attributes, given as keyword arguments.

      -- Attribute: tag

          A string identifying what kind of data this element represents
          (the element type, in other words).

      -- Attribute: text
      -- Attribute: tail

          These attributes can be used to hold additional data
          associated with the element.  Their values are usually strings
          but may be any application-specific object.  If the element is
          created from an XML file, the `text' attribute holds either
          the text between the element’s start tag and its first child
          or end tag, or ‘None’, and the `tail' attribute holds either
          the text between the element’s end tag and the next tag, or
          ‘None’.  For the XML data

               <a><b>1<c>2<d/>3</c></b>4</a>

          the `a' element has ‘None’ for both `text' and `tail'
          attributes, the `b' element has `text' ‘"1"’ and `tail' ‘"4"’,
          the `c' element has `text' ‘"2"’ and `tail' ‘None’, and the
          `d' element has `text' ‘None’ and `tail' ‘"3"’.

          To collect the inner text of an element, see *note itertext():
          c25, for example ‘"".join(element.itertext())’.

          Applications may store arbitrary objects in these attributes.

      -- Attribute: attrib

          A dictionary containing the element’s attributes.  Note that
          while the `attrib' value is always a real mutable Python
          dictionary, an ElementTree implementation may choose to use
          another internal representation, and create the dictionary
          only if someone asks for it.  To take advantage of such
          implementations, use the dictionary methods below whenever
          possible.

     The following dictionary-like methods work on the element
     attributes.

      -- Method: clear ()

          Resets an element.  This function removes all subelements,
          clears all attributes, and sets the text and tail attributes
          to ‘None’.

      -- Method: get (key, default=None)

          Gets the element attribute named `key'.

          Returns the attribute value, or `default' if the attribute was
          not found.

      -- Method: items ()

          Returns the element attributes as a sequence of (name, value)
          pairs.  The attributes are returned in an arbitrary order.

      -- Method: keys ()

          Returns the elements attribute names as a list.  The names are
          returned in an arbitrary order.

      -- Method: set (key, value)

          Set the attribute `key' on the element to `value'.

     The following methods work on the element’s children (subelements).

      -- Method: append (subelement)

          Adds the element `subelement' to the end of this element’s
          internal list of subelements.  Raises *note TypeError: 1fe. if
          `subelement' is not an *note Element: 21d.

      -- Method: extend (subelements)

          Appends `subelements' from a sequence object with zero or more
          elements.  Raises *note TypeError: 1fe. if a subelement is not
          an *note Element: 21d.

          New in version 3.2.

      -- Method: find (match, namespaces=None)

          Finds the first subelement matching `match'.  `match' may be a
          tag name or a *note path: 51e.  Returns an element instance or
          ‘None’.  `namespaces' is an optional mapping from namespace
          prefix to full name.  Pass ‘''’ as prefix to move all
          unprefixed tag names in the expression into the given
          namespace.

      -- Method: findall (match, namespaces=None)

          Finds all matching subelements, by tag name or *note path:
          51e.  Returns a list containing all matching elements in
          document order.  `namespaces' is an optional mapping from
          namespace prefix to full name.  Pass ‘''’ as prefix to move
          all unprefixed tag names in the expression into the given
          namespace.

      -- Method: findtext (match, default=None, namespaces=None)

          Finds text for the first subelement matching `match'.  `match'
          may be a tag name or a *note path: 51e.  Returns the text
          content of the first matching element, or `default' if no
          element was found.  Note that if the matching element has no
          text content an empty string is returned.  `namespaces' is an
          optional mapping from namespace prefix to full name.  Pass
          ‘''’ as prefix to move all unprefixed tag names in the
          expression into the given namespace.

      -- Method: insert (index, subelement)

          Inserts `subelement' at the given position in this element.
          Raises *note TypeError: 1fe. if `subelement' is not an *note
          Element: 21d.

      -- Method: iter (tag=None)

          Creates a tree *note iterator: 1171. with the current element
          as the root.  The iterator iterates over this element and all
          elements below it, in document (depth first) order.  If `tag'
          is not ‘None’ or ‘'*'’, only elements whose tag equals `tag'
          are returned from the iterator.  If the tree structure is
          modified during iteration, the result is undefined.

          New in version 3.2.

      -- Method: iterfind (match, namespaces=None)

          Finds all matching subelements, by tag name or *note path:
          51e.  Returns an iterable yielding all matching elements in
          document order.  `namespaces' is an optional mapping from
          namespace prefix to full name.

          New in version 3.2.

      -- Method: itertext ()

          Creates a text iterator.  The iterator loops over this element
          and all subelements, in document order, and returns all inner
          text.

          New in version 3.2.

      -- Method: makeelement (tag, attrib)

          Creates a new element object of the same type as this element.
          Do not call this method, use the *note SubElement(): 2b4d.
          factory function instead.

      -- Method: remove (subelement)

          Removes `subelement' from the element.  Unlike the find*
          methods this method compares elements based on the instance
          identity, not on tag value or contents.

     *note Element: 21d. objects also support the following sequence
     type methods for working with subelements: *note __delitem__():
     d2b, *note __getitem__(): 3a2, *note __setitem__(): d2a, *note
     __len__(): e90.

     Caution: Elements with no subelements will test as ‘False’.  This
     behavior will change in future versions.  Use specific ‘len(elem)’
     or ‘elem is None’ test instead.

          element = root.find('foo')

          if not element:  # careful!
              print("element not found, or element has no subelements")

          if element is None:
              print("element not found")

     Prior to Python 3.8, the serialisation order of the XML attributes
     of elements was artificially made predictable by sorting the
     attributes by their name.  Based on the now guaranteed ordering of
     dicts, this arbitrary reordering was removed in Python 3.8 to
     preserve the order in which attributes were originally parsed or
     created by user code.

     In general, user code should try not to depend on a specific
     ordering of attributes, given that the XML Information Set(1)
     explicitly excludes the attribute order from conveying information.
     Code should be prepared to deal with any ordering on input.  In
     cases where deterministic XML output is required, e.g.  for
     cryptographic signing or test data sets, canonical serialisation is
     available with the *note canonicalize(): 2b56. function.

     In cases where canonical output is not applicable but a specific
     attribute order is still desirable on output, code should aim for
     creating the attributes directly in the desired order, to avoid
     perceptual mismatches for readers of the code.  In cases where this
     is difficult to achieve, a recipe like the following can be applied
     prior to serialisation to enforce an order independently from the
     Element creation:

          def reorder_attributes(root):
              for el in root.iter():
                  attrib = el.attrib
                  if len(attrib) > 1:
                      # adjust attribute order, e.g. by sorting
                      attribs = sorted(attrib.items())
                      attrib.clear()
                      attrib.update(attribs)

   ---------- Footnotes ----------

   (1) https://www.w3.org/TR/xml-infoset/


File: python.info,  Node: ElementTree Objects,  Next: QName Objects,  Prev: Element Objects,  Up: Reference<3>

5.20.5.20 ElementTree Objects
.............................

 -- Class: xml.etree.ElementTree.ElementTree (element=None, file=None)

     ElementTree wrapper class.  This class represents an entire element
     hierarchy, and adds some extra support for serialization to and
     from standard XML.

     `element' is the root element.  The tree is initialized with the
     contents of the XML `file' if given.

      -- Method: _setroot (element)

          Replaces the root element for this tree.  This discards the
          current contents of the tree, and replaces it with the given
          element.  Use with care.  `element' is an element instance.

      -- Method: find (match, namespaces=None)

          Same as *note Element.find(): 2b45, starting at the root of
          the tree.

      -- Method: findall (match, namespaces=None)

          Same as *note Element.findall(): 2b44, starting at the root of
          the tree.

      -- Method: findtext (match, default=None, namespaces=None)

          Same as *note Element.findtext(): 2b6f, starting at the root
          of the tree.

      -- Method: getroot ()

          Returns the root element for this tree.

      -- Method: iter (tag=None)

          Creates and returns a tree iterator for the root element.  The
          iterator loops over all elements in this tree, in section
          order.  `tag' is the tag to look for (default is to return all
          elements).

      -- Method: iterfind (match, namespaces=None)

          Same as *note Element.iterfind(): c24, starting at the root of
          the tree.

          New in version 3.2.

      -- Method: parse (source, parser=None)

          Loads an external XML section into this element tree.
          `source' is a file name or *note file object: c14.  `parser'
          is an optional parser instance.  If not given, the standard
          *note XMLParser: 37c. parser is used.  Returns the section
          root element.

      -- Method: write (file, encoding="us-ascii", xml_declaration=None,
               default_namespace=None, method="xml", *,
               short_empty_elements=True)

          Writes the element tree to a file, as XML. `file' is a file
          name, or a *note file object: c14. opened for writing.
          `encoding' (1) is the output encoding (default is US-ASCII).
          `xml_declaration' controls if an XML declaration should be
          added to the file.  Use ‘False’ for never, ‘True’ for always,
          ‘None’ for only if not US-ASCII or UTF-8 or Unicode (default
          is ‘None’).  `default_namespace' sets the default XML
          namespace (for “xmlns”).  `method' is either ‘"xml"’, ‘"html"’
          or ‘"text"’ (default is ‘"xml"’).  The keyword-only
          `short_empty_elements' parameter controls the formatting of
          elements that contain no content.  If ‘True’ (the default),
          they are emitted as a single self-closed tag, otherwise they
          are emitted as a pair of start/end tags.

          The output is either a string (*note str: 205.) or binary
          (*note bytes: 172.).  This is controlled by the `encoding'
          argument.  If `encoding' is ‘"unicode"’, the output is a
          string; otherwise, it’s binary.  Note that this may conflict
          with the type of `file' if it’s an open *note file object:
          c14.; make sure you do not try to write a string to a binary
          stream and vice versa.

          New in version 3.4: The `short_empty_elements' parameter.

          Changed in version 3.8: The *note write(): 9fd. method now
          preserves the attribute order specified by the user.

This is the XML file that is going to be manipulated:

     <html>
         <head>
             <title>Example page</title>
         </head>
         <body>
             <p>Moved to <a href="http://example.org/">example.org</a>
             or <a href="http://example.com/">example.com</a>.</p>
         </body>
     </html>

Example of changing the attribute “target” of every link in first
paragraph:

     >>> from xml.etree.ElementTree import ElementTree
     >>> tree = ElementTree()
     >>> tree.parse("index.xhtml")
     <Element 'html' at 0xb77e6fac>
     >>> p = tree.find("body/p")     # Finds first occurrence of tag p in body
     >>> p
     <Element 'p' at 0xb77ec26c>
     >>> links = list(p.iter("a"))   # Returns list of all links
     >>> links
     [<Element 'a' at 0xb77ec2ac>, <Element 'a' at 0xb77ec1cc>]
     >>> for i in links:             # Iterates through all found links
     ...     i.attrib["target"] = "blank"
     >>> tree.write("output.xhtml")

   ---------- Footnotes ----------

   (1) (1) The encoding string included in XML output should conform to
the appropriate standards.  For example, “UTF-8” is valid, but “UTF8” is
not.  See
‘https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl’ and
‘https://www.iana.org/assignments/character-sets/character-sets.xhtml’.


File: python.info,  Node: QName Objects,  Next: TreeBuilder Objects,  Prev: ElementTree Objects,  Up: Reference<3>

5.20.5.21 QName Objects
.......................

 -- Class: xml.etree.ElementTree.QName (text_or_uri, tag=None)

     QName wrapper.  This can be used to wrap a QName attribute value,
     in order to get proper namespace handling on output.  `text_or_uri'
     is a string containing the QName value, in the form {uri}local, or,
     if the tag argument is given, the URI part of a QName.  If `tag' is
     given, the first argument is interpreted as a URI, and this
     argument is interpreted as a local name.  *note QName: 2b7e.
     instances are opaque.


File: python.info,  Node: TreeBuilder Objects,  Next: XMLParser Objects,  Prev: QName Objects,  Up: Reference<3>

5.20.5.22 TreeBuilder Objects
.............................

 -- Class: xml.etree.ElementTree.TreeBuilder (element_factory=None, *,
          comment_factory=None, pi_factory=None, insert_comments=False,
          insert_pis=False)

     Generic element structure builder.  This builder converts a
     sequence of start, data, end, comment and pi method calls to a
     well-formed element structure.  You can use this class to build an
     element structure using a custom XML parser, or a parser for some
     other XML-like format.

     `element_factory', when given, must be a callable accepting two
     positional arguments: a tag and a dict of attributes.  It is
     expected to return a new element instance.

     The `comment_factory' and `pi_factory' functions, when given,
     should behave like the *note Comment(): 2b57. and *note
     ProcessingInstruction(): 2b5d. functions to create comments and
     processing instructions.  When not given, the default factories
     will be used.  When `insert_comments' and/or `insert_pis' is true,
     comments/pis will be inserted into the tree if they appear within
     the root element (but not outside of it).

      -- Method: close ()

          Flushes the builder buffers, and returns the toplevel document
          element.  Returns an *note Element: 21d. instance.

      -- Method: data (data)

          Adds text to the current element.  `data' is a string.  This
          should be either a bytestring, or a Unicode string.

      -- Method: end (tag)

          Closes the current element.  `tag' is the element name.
          Returns the closed element.

      -- Method: start (tag, attrs)

          Opens a new element.  `tag' is the element name.  `attrs' is a
          dictionary containing element attributes.  Returns the opened
          element.

      -- Method: comment (text)

          Creates a comment with the given `text'.  If ‘insert_comments’
          is true, this will also add it to the tree.

          New in version 3.8.

      -- Method: pi (target, text)

          Creates a comment with the given `target' name and `text'.  If
          ‘insert_pis’ is true, this will also add it to the tree.

          New in version 3.8.

     In addition, a custom *note TreeBuilder: 37d. object can provide
     the following methods:

      -- Method: doctype (name, pubid, system)

          Handles a doctype declaration.  `name' is the doctype name.
          `pubid' is the public identifier.  `system' is the system
          identifier.  This method does not exist on the default *note
          TreeBuilder: 37d. class.

          New in version 3.2.

      -- Method: start_ns (prefix, uri)

          Is called whenever the parser encounters a new namespace
          declaration, before the ‘start()’ callback for the opening
          element that defines it.  `prefix' is ‘''’ for the default
          namespace and the declared namespace prefix name otherwise.
          `uri' is the namespace URI.

          New in version 3.8.

      -- Method: end_ns (prefix)

          Is called after the ‘end()’ callback of an element that
          declared a namespace prefix mapping, with the name of the
          `prefix' that went out of scope.

          New in version 3.8.

 -- Class: xml.etree.ElementTree.C14NWriterTarget (write, *,
          with_comments=False, strip_text=False, rewrite_prefixes=False,
          qname_aware_tags=None, qname_aware_attrs=None,
          exclude_attrs=None, exclude_tags=None)

     A C14N 2.0(1) writer.  Arguments are the same as for the *note
     canonicalize(): 2b56. function.  This class does not build a tree
     but translates the callback events directly into a serialised form
     using the `write' function.

     New in version 3.8.

   ---------- Footnotes ----------

   (1) https://www.w3.org/TR/xml-c14n2/


File: python.info,  Node: XMLParser Objects,  Next: XMLPullParser Objects,  Prev: TreeBuilder Objects,  Up: Reference<3>

5.20.5.23 XMLParser Objects
...........................

 -- Class: xml.etree.ElementTree.XMLParser (*, target=None,
          encoding=None)

     This class is the low-level building block of the module.  It uses
     *note xml.parsers.expat: 141. for efficient, event-based parsing of
     XML. It can be fed XML data incrementally with the *note feed():
     2b8a. method, and parsing events are translated to a push API - by
     invoking callbacks on the `target' object.  If `target' is omitted,
     the standard *note TreeBuilder: 37d. is used.  If `encoding' (1) is
     given, the value overrides the encoding specified in the XML file.

     Changed in version 3.8: Parameters are now *note keyword-only: 3ce.
     The `html' argument no longer supported.

      -- Method: close ()

          Finishes feeding data to the parser.  Returns the result of
          calling the ‘close()’ method of the `target' passed during
          construction; by default, this is the toplevel document
          element.

      -- Method: feed (data)

          Feeds data to the parser.  `data' is encoded data.

     *note XMLParser.feed(): 2b8a. calls `target'’s ‘start(tag,
     attrs_dict)’ method for each opening tag, its ‘end(tag)’ method for
     each closing tag, and data is processed by method ‘data(data)’.
     For further supported callback methods, see the *note TreeBuilder:
     37d. class.  *note XMLParser.close(): 2b8b. calls `target'’s method
     ‘close()’.  *note XMLParser: 37c. can be used not only for building
     a tree structure.  This is an example of counting the maximum depth
     of an XML file:

          >>> from xml.etree.ElementTree import XMLParser
          >>> class MaxDepth:                     # The target object of the parser
          ...     maxDepth = 0
          ...     depth = 0
          ...     def start(self, tag, attrib):   # Called for each opening tag.
          ...         self.depth += 1
          ...         if self.depth > self.maxDepth:
          ...             self.maxDepth = self.depth
          ...     def end(self, tag):             # Called for each closing tag.
          ...         self.depth -= 1
          ...     def data(self, data):
          ...         pass            # We do not need to do anything with data.
          ...     def close(self):    # Called when all data has been parsed.
          ...         return self.maxDepth
          ...
          >>> target = MaxDepth()
          >>> parser = XMLParser(target=target)
          >>> exampleXml = """
          ... <a>
          ...   <b>
          ...   </b>
          ...   <b>
          ...     <c>
          ...       <d>
          ...       </d>
          ...     </c>
          ...   </b>
          ... </a>"""
          >>> parser.feed(exampleXml)
          >>> parser.close()
          4

   ---------- Footnotes ----------

   (1) (1) The encoding string included in XML output should conform to
the appropriate standards.  For example, “UTF-8” is valid, but “UTF8” is
not.  See
‘https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl’ and
‘https://www.iana.org/assignments/character-sets/character-sets.xhtml’.


File: python.info,  Node: XMLPullParser Objects,  Next: Exceptions<16>,  Prev: XMLParser Objects,  Up: Reference<3>

5.20.5.24 XMLPullParser Objects
...............................

 -- Class: xml.etree.ElementTree.XMLPullParser (events=None)

     A pull parser suitable for non-blocking applications.  Its
     input-side API is similar to that of *note XMLParser: 37c, but
     instead of pushing calls to a callback target, *note XMLPullParser:
     9f9. collects an internal list of parsing events and lets the user
     read from it.  `events' is a sequence of events to report back.
     The supported events are the strings ‘"start"’, ‘"end"’,
     ‘"comment"’, ‘"pi"’, ‘"start-ns"’ and ‘"end-ns"’ (the “ns” events
     are used to get detailed namespace information).  If `events' is
     omitted, only ‘"end"’ events are reported.

      -- Method: feed (data)

          Feed the given bytes data to the parser.

      -- Method: close ()

          Signal the parser that the data stream is terminated.  Unlike
          *note XMLParser.close(): 2b8b, this method always returns
          *note None: 203.  Any events not yet retrieved when the parser
          is closed can still be read with *note read_events(): 2b42.

      -- Method: read_events ()

          Return an iterator over the events which have been encountered
          in the data fed to the parser.  The iterator yields ‘(event,
          elem)’ pairs, where `event' is a string representing the type
          of event (e.g.  ‘"end"’) and `elem' is the encountered *note
          Element: 21d. object, or other context value as follows.

             * ‘start’, ‘end’: the current Element.

             * ‘comment’, ‘pi’: the current comment / processing
               instruction

             * ‘start-ns’: a tuple ‘(prefix, uri)’ naming the declared
               namespace mapping.

             * ‘end-ns’: *note None: 203. (this may change in a future
               version)

          Events provided in a previous call to *note read_events():
          2b42. will not be yielded again.  Events are consumed from the
          internal queue only when they are retrieved from the iterator,
          so multiple readers iterating in parallel over iterators
          obtained from *note read_events(): 2b42. will have
          unpredictable results.

          Note: *note XMLPullParser: 9f9. only guarantees that it has
          seen the “>” character of a starting tag when it emits a
          “start” event, so the attributes are defined, but the contents
          of the text and tail attributes are undefined at that point.
          The same applies to the element children; they may or may not
          be present.

          If you need a fully populated element, look for “end” events
          instead.

     New in version 3.4.

     Changed in version 3.8: The ‘comment’ and ‘pi’ events were added.


File: python.info,  Node: Exceptions<16>,  Prev: XMLPullParser Objects,  Up: Reference<3>

5.20.5.25 Exceptions
....................

 -- Class: xml.etree.ElementTree.ParseError

     XML parse error, raised by the various parsing methods in this
     module when parsing fails.  The string representation of an
     instance of this exception will contain a user-friendly error
     message.  In addition, it will have the following attributes
     available:

      -- Attribute: code

          A numeric error code from the expat parser.  See the
          documentation of *note xml.parsers.expat: 141. for the list of
          error codes and their meanings.

      -- Attribute: position

          A tuple of `line', `column' numbers, specifying where the
          error occurred.


File: python.info,  Node: xml dom — The Document Object Model API,  Next: xml dom minidom — Minimal DOM implementation,  Prev: xml etree ElementTree — The ElementTree XML API,  Up: Structured Markup Processing Tools

5.20.6 ‘xml.dom’ — The Document Object Model API
------------------------------------------------

`Source code:' Lib/xml/dom/__init__.py(1)

__________________________________________________________________

The Document Object Model, or “DOM,” is a cross-language API from the
World Wide Web Consortium (W3C) for accessing and modifying XML
documents.  A DOM implementation presents an XML document as a tree
structure, or allows client code to build such a structure from scratch.
It then gives access to the structure through a set of objects which
provided well-known interfaces.

The DOM is extremely useful for random-access applications.  SAX only
allows you a view of one bit of the document at a time.  If you are
looking at one SAX element, you have no access to another.  If you are
looking at a text node, you have no access to a containing element.
When you write a SAX application, you need to keep track of your
program’s position in the document somewhere in your own code.  SAX does
not do it for you.  Also, if you need to look ahead in the XML document,
you are just out of luck.

Some applications are simply impossible in an event driven model with no
access to a tree.  Of course you could build some sort of tree yourself
in SAX events, but the DOM allows you to avoid writing that code.  The
DOM is a standard tree representation for XML data.

The Document Object Model is being defined by the W3C in stages, or
“levels” in their terminology.  The Python mapping of the API is
substantially based on the DOM Level 2 recommendation.

DOM applications typically start by parsing some XML into a DOM. How
this is accomplished is not covered at all by DOM Level 1, and Level 2
provides only limited improvements: There is a ‘DOMImplementation’
object class which provides access to ‘Document’ creation methods, but
no way to access an XML reader/parser/Document builder in an
implementation-independent way.  There is also no well-defined way to
access these methods without an existing ‘Document’ object.  In Python,
each DOM implementation will provide a function *note
getDOMImplementation(): 2b94.  DOM Level 3 adds a Load/Store
specification, which defines an interface to the reader, but this is not
yet available in the Python standard library.

Once you have a DOM document object, you can access the parts of your
XML document through its properties and methods.  These properties are
defined in the DOM specification; this portion of the reference manual
describes the interpretation of the specification in Python.

The specification provided by the W3C defines the DOM API for Java,
ECMAScript, and OMG IDL. The Python mapping defined here is based in
large part on the IDL version of the specification, but strict
compliance is not required (though implementations are free to support
the strict mapping from IDL). See section *note Conformance: 2b95. for a
detailed discussion of mapping requirements.

See also
........

Document Object Model (DOM) Level 2 Specification(2)

     The W3C recommendation upon which the Python DOM API is based.

Document Object Model (DOM) Level 1 Specification(3)

     The W3C recommendation for the DOM supported by *note
     xml.dom.minidom: 13e.

Python Language Mapping Specification(4)

     This specifies the mapping from OMG IDL to Python.

* Menu:

* Module Contents: Module Contents<4>.
* Objects in the DOM::
* Conformance::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/xml/dom/__init__.py

   (2) https://www.w3.org/TR/2000/REC-DOM-Level-2-Core-20001113/

   (3) https://www.w3.org/TR/REC-DOM-Level-1/

   (4) http://www.omg.org/cgi-bin/doc?formal/02-11-05.pdf


File: python.info,  Node: Module Contents<4>,  Next: Objects in the DOM,  Up: xml dom — The Document Object Model API

5.20.6.1 Module Contents
........................

The *note xml.dom: 13d. contains the following functions:

 -- Function: xml.dom.registerDOMImplementation (name, factory)

     Register the `factory' function with the name `name'.  The factory
     function should return an object which implements the
     ‘DOMImplementation’ interface.  The factory function can return the
     same object every time, or a new one for each call, as appropriate
     for the specific implementation (e.g.  if that implementation
     supports some customization).

 -- Function: xml.dom.getDOMImplementation (name=None, features=())

     Return a suitable DOM implementation.  The `name' is either
     well-known, the module name of a DOM implementation, or ‘None’.  If
     it is not ‘None’, imports the corresponding module and returns a
     ‘DOMImplementation’ object if the import succeeds.  If no name is
     given, and if the environment variable ‘PYTHON_DOM’ is set, this
     variable is used to find the implementation.

     If name is not given, this examines the available implementations
     to find one with the required feature set.  If no implementation
     can be found, raise an *note ImportError: 16c.  The features list
     must be a sequence of ‘(feature, version)’ pairs which are passed
     to the ‘hasFeature()’ method on available ‘DOMImplementation’
     objects.

Some convenience constants are also provided:

 -- Data: xml.dom.EMPTY_NAMESPACE

     The value used to indicate that no namespace is associated with a
     node in the DOM. This is typically found as the ‘namespaceURI’ of a
     node, or used as the `namespaceURI' parameter to a
     namespaces-specific method.

 -- Data: xml.dom.XML_NAMESPACE

     The namespace URI associated with the reserved prefix ‘xml’, as
     defined by Namespaces in XML(1) (section 4).

 -- Data: xml.dom.XMLNS_NAMESPACE

     The namespace URI for namespace declarations, as defined by
     Document Object Model (DOM) Level 2 Core Specification(2) (section
     1.1.8).

 -- Data: xml.dom.XHTML_NAMESPACE

     The URI of the XHTML namespace as defined by XHTML 1.0: The
     Extensible HyperText Markup Language(3) (section 3.1.1).

In addition, *note xml.dom: 13d. contains a base ‘Node’ class and the
DOM exception classes.  The ‘Node’ class provided by this module does
not implement any of the methods or attributes defined by the DOM
specification; concrete DOM implementations must provide those.  The
‘Node’ class provided as part of this module does provide the constants
used for the ‘nodeType’ attribute on concrete ‘Node’ objects; they are
located within the class rather than at the module level to conform with
the DOM specifications.

   ---------- Footnotes ----------

   (1) https://www.w3.org/TR/REC-xml-names/

   (2) https://www.w3.org/TR/DOM-Level-2-Core/core.html

   (3) https://www.w3.org/TR/xhtml1/


File: python.info,  Node: Objects in the DOM,  Next: Conformance,  Prev: Module Contents<4>,  Up: xml dom — The Document Object Model API

5.20.6.2 Objects in the DOM
...........................

The definitive documentation for the DOM is the DOM specification from
the W3C.

Note that DOM attributes may also be manipulated as nodes instead of as
simple strings.  It is fairly rare that you must do this, however, so
this usage is not yet documented.

Interface                            Section                                 Purpose
                                                                             
-------------------------------------------------------------------------------------------------------------------
                                                                             
‘DOMImplementation’                  *note DOMImplementation Objects: 2b9e.  Interface to the underlying
                                                                             implementation.
                                                                             
                                                                             
‘Node’                               *note Node Objects: 2b9f.               Base interface for most objects in
                                                                             a document.
                                                                             
                                                                             
‘NodeList’                           *note NodeList Objects: 2ba0.           Interface for a sequence of nodes.
                                                                             
                                                                             
‘DocumentType’                       *note DocumentType Objects: 2ba1.       Information about the declarations
                                                                             needed to process a document.
                                                                             
                                                                             
‘Document’                           *note Document Objects: 2ba2.           Object which represents an entire
                                                                             document.
                                                                             
                                                                             
‘Element’                            *note Element Objects: 2ba3.            Element nodes in the document
                                                                             hierarchy.
                                                                             
                                                                             
‘Attr’                               *note Attr Objects: 2ba4.               Attribute value nodes on element
                                                                             nodes.
                                                                             
                                                                             
‘Comment’                            *note Comment Objects: 2ba5.            Representation of comments in the
                                                                             source document.
                                                                             
                                                                             
‘Text’                               *note Text and CDATASection Objects: 2ba6.Nodes containing textual content
                                                                             from the document.
                                                                             
                                                                             
‘ProcessingInstruction’              *note ProcessingInstruction Objects: 2ba7.Processing instruction
                                                                             representation.
                                                                             

An additional section describes the exceptions defined for working with
the DOM in Python.

* Menu:

* DOMImplementation Objects::
* Node Objects::
* NodeList Objects::
* DocumentType Objects::
* Document Objects::
* Element Objects: Element Objects<2>.
* Attr Objects::
* NamedNodeMap Objects::
* Comment Objects::
* Text and CDATASection Objects::
* ProcessingInstruction Objects::
* Exceptions: Exceptions<17>.


File: python.info,  Node: DOMImplementation Objects,  Next: Node Objects,  Up: Objects in the DOM

5.20.6.3 DOMImplementation Objects
..................................

The ‘DOMImplementation’ interface provides a way for applications to
determine the availability of particular features in the DOM they are
using.  DOM Level 2 added the ability to create new ‘Document’ and
‘DocumentType’ objects using the ‘DOMImplementation’ as well.

 -- Method: DOMImplementation.hasFeature (feature, version)

     Return ‘True’ if the feature identified by the pair of strings
     `feature' and `version' is implemented.

 -- Method: DOMImplementation.createDocument (namespaceUri,
          qualifiedName, doctype)

     Return a new ‘Document’ object (the root of the DOM), with a child
     ‘Element’ object having the given `namespaceUri' and
     `qualifiedName'.  The `doctype' must be a ‘DocumentType’ object
     created by *note createDocumentType(): 2bab, or ‘None’.  In the
     Python DOM API, the first two arguments can also be ‘None’ in order
     to indicate that no ‘Element’ child is to be created.

 -- Method: DOMImplementation.createDocumentType (qualifiedName,
          publicId, systemId)

     Return a new ‘DocumentType’ object that encapsulates the given
     `qualifiedName', `publicId', and `systemId' strings, representing
     the information contained in an XML document type declaration.


File: python.info,  Node: Node Objects,  Next: NodeList Objects,  Prev: DOMImplementation Objects,  Up: Objects in the DOM

5.20.6.4 Node Objects
.....................

All of the components of an XML document are subclasses of ‘Node’.

 -- Attribute: Node.nodeType

     An integer representing the node type.  Symbolic constants for the
     types are on the ‘Node’ object: ‘ELEMENT_NODE’, ‘ATTRIBUTE_NODE’,
     ‘TEXT_NODE’, ‘CDATA_SECTION_NODE’, ‘ENTITY_NODE’,
     ‘PROCESSING_INSTRUCTION_NODE’, ‘COMMENT_NODE’, ‘DOCUMENT_NODE’,
     ‘DOCUMENT_TYPE_NODE’, ‘NOTATION_NODE’.  This is a read-only
     attribute.

 -- Attribute: Node.parentNode

     The parent of the current node, or ‘None’ for the document node.
     The value is always a ‘Node’ object or ‘None’.  For ‘Element’
     nodes, this will be the parent element, except for the root
     element, in which case it will be the ‘Document’ object.  For
     ‘Attr’ nodes, this is always ‘None’.  This is a read-only
     attribute.

 -- Attribute: Node.attributes

     A ‘NamedNodeMap’ of attribute objects.  Only elements have actual
     values for this; others provide ‘None’ for this attribute.  This is
     a read-only attribute.

 -- Attribute: Node.previousSibling

     The node that immediately precedes this one with the same parent.
     For instance the element with an end-tag that comes just before the
     `self' element’s start-tag.  Of course, XML documents are made up
     of more than just elements so the previous sibling could be text, a
     comment, or something else.  If this node is the first child of the
     parent, this attribute will be ‘None’.  This is a read-only
     attribute.

 -- Attribute: Node.nextSibling

     The node that immediately follows this one with the same parent.
     See also *note previousSibling: 2bb0.  If this is the last child of
     the parent, this attribute will be ‘None’.  This is a read-only
     attribute.

 -- Attribute: Node.childNodes

     A list of nodes contained within this node.  This is a read-only
     attribute.

 -- Attribute: Node.firstChild

     The first child of the node, if there are any, or ‘None’.  This is
     a read-only attribute.

 -- Attribute: Node.lastChild

     The last child of the node, if there are any, or ‘None’.  This is a
     read-only attribute.

 -- Attribute: Node.localName

     The part of the ‘tagName’ following the colon if there is one, else
     the entire ‘tagName’.  The value is a string.

 -- Attribute: Node.prefix

     The part of the ‘tagName’ preceding the colon if there is one, else
     the empty string.  The value is a string, or ‘None’.

 -- Attribute: Node.namespaceURI

     The namespace associated with the element name.  This will be a
     string or ‘None’.  This is a read-only attribute.

 -- Attribute: Node.nodeName

     This has a different meaning for each node type; see the DOM
     specification for details.  You can always get the information you
     would get here from another property such as the ‘tagName’ property
     for elements or the ‘name’ property for attributes.  For all node
     types, the value of this attribute will be either a string or
     ‘None’.  This is a read-only attribute.

 -- Attribute: Node.nodeValue

     This has a different meaning for each node type; see the DOM
     specification for details.  The situation is similar to that with
     *note nodeName: 2bb8.  The value is a string or ‘None’.

 -- Method: Node.hasAttributes ()

     Return ‘True’ if the node has any attributes.

 -- Method: Node.hasChildNodes ()

     Return ‘True’ if the node has any child nodes.

 -- Method: Node.isSameNode (other)

     Return ‘True’ if `other' refers to the same node as this node.
     This is especially useful for DOM implementations which use any
     sort of proxy architecture (because more than one object can refer
     to the same node).

          Note: This is based on a proposed DOM Level 3 API which is
          still in the “working draft” stage, but this particular
          interface appears uncontroversial.  Changes from the W3C will
          not necessarily affect this method in the Python DOM interface
          (though any new W3C API for this would also be supported).

 -- Method: Node.appendChild (newChild)

     Add a new child node to this node at the end of the list of
     children, returning `newChild'.  If the node was already in the
     tree, it is removed first.

 -- Method: Node.insertBefore (newChild, refChild)

     Insert a new child node before an existing child.  It must be the
     case that `refChild' is a child of this node; if not, *note
     ValueError: 16d. is raised.  `newChild' is returned.  If `refChild'
     is ‘None’, it inserts `newChild' at the end of the children’s list.

 -- Method: Node.removeChild (oldChild)

     Remove a child node.  `oldChild' must be a child of this node; if
     not, *note ValueError: 16d. is raised.  `oldChild' is returned on
     success.  If `oldChild' will not be used further, its ‘unlink()’
     method should be called.

 -- Method: Node.replaceChild (newChild, oldChild)

     Replace an existing node with a new node.  It must be the case that
     `oldChild' is a child of this node; if not, *note ValueError: 16d.
     is raised.

 -- Method: Node.normalize ()

     Join adjacent text nodes so that all stretches of text are stored
     as single ‘Text’ instances.  This simplifies processing text from a
     DOM tree for many applications.

 -- Method: Node.cloneNode (deep)

     Clone this node.  Setting `deep' means to clone all child nodes as
     well.  This returns the clone.


File: python.info,  Node: NodeList Objects,  Next: DocumentType Objects,  Prev: Node Objects,  Up: Objects in the DOM

5.20.6.5 NodeList Objects
.........................

A ‘NodeList’ represents a sequence of nodes.  These objects are used in
two ways in the DOM Core recommendation: an ‘Element’ object provides
one as its list of child nodes, and the ‘getElementsByTagName()’ and
‘getElementsByTagNameNS()’ methods of ‘Node’ return objects with this
interface to represent query results.

The DOM Level 2 recommendation defines one method and one attribute for
these objects:

 -- Method: NodeList.item (i)

     Return the `i'’th item from the sequence, if there is one, or
     ‘None’.  The index `i' is not allowed to be less than zero or
     greater than or equal to the length of the sequence.

 -- Attribute: NodeList.length

     The number of nodes in the sequence.

In addition, the Python DOM interface requires that some additional
support is provided to allow ‘NodeList’ objects to be used as Python
sequences.  All ‘NodeList’ implementations must include support for
*note __len__(): e90. and *note __getitem__(): 3a2.; this allows
iteration over the ‘NodeList’ in *note for: cfa. statements and proper
support for the *note len(): 28b. built-in function.

If a DOM implementation supports modification of the document, the
‘NodeList’ implementation must also support the *note __setitem__():
d2a. and *note __delitem__(): d2b. methods.


File: python.info,  Node: DocumentType Objects,  Next: Document Objects,  Prev: NodeList Objects,  Up: Objects in the DOM

5.20.6.6 DocumentType Objects
.............................

Information about the notations and entities declared by a document
(including the external subset if the parser uses it and can provide the
information) is available from a ‘DocumentType’ object.  The
‘DocumentType’ for a document is available from the ‘Document’ object’s
‘doctype’ attribute; if there is no ‘DOCTYPE’ declaration for the
document, the document’s ‘doctype’ attribute will be set to ‘None’
instead of an instance of this interface.

‘DocumentType’ is a specialization of ‘Node’, and adds the following
attributes:

 -- Attribute: DocumentType.publicId

     The public identifier for the external subset of the document type
     definition.  This will be a string or ‘None’.

 -- Attribute: DocumentType.systemId

     The system identifier for the external subset of the document type
     definition.  This will be a URI as a string, or ‘None’.

 -- Attribute: DocumentType.internalSubset

     A string giving the complete internal subset from the document.
     This does not include the brackets which enclose the subset.  If
     the document has no internal subset, this should be ‘None’.

 -- Attribute: DocumentType.name

     The name of the root element as given in the ‘DOCTYPE’ declaration,
     if present.

 -- Attribute: DocumentType.entities

     This is a ‘NamedNodeMap’ giving the definitions of external
     entities.  For entity names defined more than once, only the first
     definition is provided (others are ignored as required by the XML
     recommendation).  This may be ‘None’ if the information is not
     provided by the parser, or if no entities are defined.

 -- Attribute: DocumentType.notations

     This is a ‘NamedNodeMap’ giving the definitions of notations.  For
     notation names defined more than once, only the first definition is
     provided (others are ignored as required by the XML
     recommendation).  This may be ‘None’ if the information is not
     provided by the parser, or if no notations are defined.


File: python.info,  Node: Document Objects,  Next: Element Objects<2>,  Prev: DocumentType Objects,  Up: Objects in the DOM

5.20.6.7 Document Objects
.........................

A ‘Document’ represents an entire XML document, including its
constituent elements, attributes, processing instructions, comments etc.
Remember that it inherits properties from ‘Node’.

 -- Attribute: Document.documentElement

     The one and only root element of the document.

 -- Method: Document.createElement (tagName)

     Create and return a new element node.  The element is not inserted
     into the document when it is created.  You need to explicitly
     insert it with one of the other methods such as ‘insertBefore()’ or
     ‘appendChild()’.

 -- Method: Document.createElementNS (namespaceURI, tagName)

     Create and return a new element with a namespace.  The `tagName'
     may have a prefix.  The element is not inserted into the document
     when it is created.  You need to explicitly insert it with one of
     the other methods such as ‘insertBefore()’ or ‘appendChild()’.

 -- Method: Document.createTextNode (data)

     Create and return a text node containing the data passed as a
     parameter.  As with the other creation methods, this one does not
     insert the node into the tree.

 -- Method: Document.createComment (data)

     Create and return a comment node containing the data passed as a
     parameter.  As with the other creation methods, this one does not
     insert the node into the tree.

 -- Method: Document.createProcessingInstruction (target, data)

     Create and return a processing instruction node containing the
     `target' and `data' passed as parameters.  As with the other
     creation methods, this one does not insert the node into the tree.

 -- Method: Document.createAttribute (name)

     Create and return an attribute node.  This method does not
     associate the attribute node with any particular element.  You must
     use ‘setAttributeNode()’ on the appropriate ‘Element’ object to use
     the newly created attribute instance.

 -- Method: Document.createAttributeNS (namespaceURI, qualifiedName)

     Create and return an attribute node with a namespace.  The
     `tagName' may have a prefix.  This method does not associate the
     attribute node with any particular element.  You must use
     ‘setAttributeNode()’ on the appropriate ‘Element’ object to use the
     newly created attribute instance.

 -- Method: Document.getElementsByTagName (tagName)

     Search for all descendants (direct children, children’s children,
     etc.)  with a particular element type name.

 -- Method: Document.getElementsByTagNameNS (namespaceURI, localName)

     Search for all descendants (direct children, children’s children,
     etc.)  with a particular namespace URI and localname.  The
     localname is the part of the namespace after the prefix.


File: python.info,  Node: Element Objects<2>,  Next: Attr Objects,  Prev: Document Objects,  Up: Objects in the DOM

5.20.6.8 Element Objects
........................

‘Element’ is a subclass of ‘Node’, so inherits all the attributes of
that class.

 -- Attribute: Element.tagName

     The element type name.  In a namespace-using document it may have
     colons in it.  The value is a string.

 -- Method: Element.getElementsByTagName (tagName)

     Same as equivalent method in the ‘Document’ class.

 -- Method: Element.getElementsByTagNameNS (namespaceURI, localName)

     Same as equivalent method in the ‘Document’ class.

 -- Method: Element.hasAttribute (name)

     Return ‘True’ if the element has an attribute named by `name'.

 -- Method: Element.hasAttributeNS (namespaceURI, localName)

     Return ‘True’ if the element has an attribute named by
     `namespaceURI' and `localName'.

 -- Method: Element.getAttribute (name)

     Return the value of the attribute named by `name' as a string.  If
     no such attribute exists, an empty string is returned, as if the
     attribute had no value.

 -- Method: Element.getAttributeNode (attrname)

     Return the ‘Attr’ node for the attribute named by `attrname'.

 -- Method: Element.getAttributeNS (namespaceURI, localName)

     Return the value of the attribute named by `namespaceURI' and
     `localName' as a string.  If no such attribute exists, an empty
     string is returned, as if the attribute had no value.

 -- Method: Element.getAttributeNodeNS (namespaceURI, localName)

     Return an attribute value as a node, given a `namespaceURI' and
     `localName'.

 -- Method: Element.removeAttribute (name)

     Remove an attribute by name.  If there is no matching attribute, a
     *note NotFoundErr: 2be3. is raised.

 -- Method: Element.removeAttributeNode (oldAttr)

     Remove and return `oldAttr' from the attribute list, if present.
     If `oldAttr' is not present, *note NotFoundErr: 2be3. is raised.

 -- Method: Element.removeAttributeNS (namespaceURI, localName)

     Remove an attribute by name.  Note that it uses a localName, not a
     qname.  No exception is raised if there is no matching attribute.

 -- Method: Element.setAttribute (name, value)

     Set an attribute value from a string.

 -- Method: Element.setAttributeNode (newAttr)

     Add a new attribute node to the element, replacing an existing
     attribute if necessary if the ‘name’ attribute matches.  If a
     replacement occurs, the old attribute node will be returned.  If
     `newAttr' is already in use, *note InuseAttributeErr: 2be8. will be
     raised.

 -- Method: Element.setAttributeNodeNS (newAttr)

     Add a new attribute node to the element, replacing an existing
     attribute if necessary if the ‘namespaceURI’ and ‘localName’
     attributes match.  If a replacement occurs, the old attribute node
     will be returned.  If `newAttr' is already in use, *note
     InuseAttributeErr: 2be8. will be raised.

 -- Method: Element.setAttributeNS (namespaceURI, qname, value)

     Set an attribute value from a string, given a `namespaceURI' and a
     `qname'.  Note that a qname is the whole attribute name.  This is
     different than above.


File: python.info,  Node: Attr Objects,  Next: NamedNodeMap Objects,  Prev: Element Objects<2>,  Up: Objects in the DOM

5.20.6.9 Attr Objects
.....................

‘Attr’ inherits from ‘Node’, so inherits all its attributes.

 -- Attribute: Attr.name

     The attribute name.  In a namespace-using document it may include a
     colon.

 -- Attribute: Attr.localName

     The part of the name following the colon if there is one, else the
     entire name.  This is a read-only attribute.

 -- Attribute: Attr.prefix

     The part of the name preceding the colon if there is one, else the
     empty string.

 -- Attribute: Attr.value

     The text value of the attribute.  This is a synonym for the
     ‘nodeValue’ attribute.


File: python.info,  Node: NamedNodeMap Objects,  Next: Comment Objects,  Prev: Attr Objects,  Up: Objects in the DOM

5.20.6.10 NamedNodeMap Objects
..............................

‘NamedNodeMap’ does `not' inherit from ‘Node’.

 -- Attribute: NamedNodeMap.length

     The length of the attribute list.

 -- Method: NamedNodeMap.item (index)

     Return an attribute with a particular index.  The order you get the
     attributes in is arbitrary but will be consistent for the life of a
     DOM. Each item is an attribute node.  Get its value with the
     ‘value’ attribute.

There are also experimental methods that give this class more mapping
behavior.  You can use them or you can use the standardized
‘getAttribute*()’ family of methods on the ‘Element’ objects.


File: python.info,  Node: Comment Objects,  Next: Text and CDATASection Objects,  Prev: NamedNodeMap Objects,  Up: Objects in the DOM

5.20.6.11 Comment Objects
.........................

‘Comment’ represents a comment in the XML document.  It is a subclass of
‘Node’, but cannot have child nodes.

 -- Attribute: Comment.data

     The content of the comment as a string.  The attribute contains all
     characters between the leading ‘<!-’‘-’ and trailing ‘-’‘->’, but
     does not include them.


File: python.info,  Node: Text and CDATASection Objects,  Next: ProcessingInstruction Objects,  Prev: Comment Objects,  Up: Objects in the DOM

5.20.6.12 Text and CDATASection Objects
.......................................

The ‘Text’ interface represents text in the XML document.  If the parser
and DOM implementation support the DOM’s XML extension, portions of the
text enclosed in CDATA marked sections are stored in ‘CDATASection’
objects.  These two interfaces are identical, but provide different
values for the ‘nodeType’ attribute.

These interfaces extend the ‘Node’ interface.  They cannot have child
nodes.

 -- Attribute: Text.data

     The content of the text node as a string.

     Note: The use of a ‘CDATASection’ node does not indicate that the
     node represents a complete CDATA marked section, only that the
     content of the node was part of a CDATA section.  A single CDATA
     section may be represented by more than one node in the document
     tree.  There is no way to determine whether two adjacent
     ‘CDATASection’ nodes represent different CDATA marked sections.


File: python.info,  Node: ProcessingInstruction Objects,  Next: Exceptions<17>,  Prev: Text and CDATASection Objects,  Up: Objects in the DOM

5.20.6.13 ProcessingInstruction Objects
.......................................

Represents a processing instruction in the XML document; this inherits
from the ‘Node’ interface and cannot have child nodes.

 -- Attribute: ProcessingInstruction.target

     The content of the processing instruction up to the first
     whitespace character.  This is a read-only attribute.

 -- Attribute: ProcessingInstruction.data

     The content of the processing instruction following the first
     whitespace character.


File: python.info,  Node: Exceptions<17>,  Prev: ProcessingInstruction Objects,  Up: Objects in the DOM

5.20.6.14 Exceptions
....................

The DOM Level 2 recommendation defines a single exception, *note
DOMException: 2bfd, and a number of constants that allow applications to
determine what sort of error occurred.  *note DOMException: 2bfd.
instances carry a *note code: 1a. attribute that provides the
appropriate value for the specific exception.

The Python DOM interface provides the constants, but also expands the
set of exceptions so that a specific exception exists for each of the
exception codes defined by the DOM. The implementations must raise the
appropriate specific exception, each of which carries the appropriate
value for the *note code: 1a. attribute.

 -- Exception: xml.dom.DOMException

     Base exception class used for all specific DOM exceptions.  This
     exception class cannot be directly instantiated.

 -- Exception: xml.dom.DomstringSizeErr

     Raised when a specified range of text does not fit into a string.
     This is not known to be used in the Python DOM implementations, but
     may be received from DOM implementations not written in Python.

 -- Exception: xml.dom.HierarchyRequestErr

     Raised when an attempt is made to insert a node where the node type
     is not allowed.

 -- Exception: xml.dom.IndexSizeErr

     Raised when an index or size parameter to a method is negative or
     exceeds the allowed values.

 -- Exception: xml.dom.InuseAttributeErr

     Raised when an attempt is made to insert an ‘Attr’ node that is
     already present elsewhere in the document.

 -- Exception: xml.dom.InvalidAccessErr

     Raised if a parameter or an operation is not supported on the
     underlying object.

 -- Exception: xml.dom.InvalidCharacterErr

     This exception is raised when a string parameter contains a
     character that is not permitted in the context it’s being used in
     by the XML 1.0 recommendation.  For example, attempting to create
     an ‘Element’ node with a space in the element type name will cause
     this error to be raised.

 -- Exception: xml.dom.InvalidModificationErr

     Raised when an attempt is made to modify the type of a node.

 -- Exception: xml.dom.InvalidStateErr

     Raised when an attempt is made to use an object that is not defined
     or is no longer usable.

 -- Exception: xml.dom.NamespaceErr

     If an attempt is made to change any object in a way that is not
     permitted with regard to the Namespaces in XML(1) recommendation,
     this exception is raised.

 -- Exception: xml.dom.NotFoundErr

     Exception when a node does not exist in the referenced context.
     For example, ‘NamedNodeMap.removeNamedItem()’ will raise this if
     the node passed in does not exist in the map.

 -- Exception: xml.dom.NotSupportedErr

     Raised when the implementation does not support the requested type
     of object or operation.

 -- Exception: xml.dom.NoDataAllowedErr

     This is raised if data is specified for a node which does not
     support data.

 -- Exception: xml.dom.NoModificationAllowedErr

     Raised on attempts to modify an object where modifications are not
     allowed (such as for read-only nodes).

 -- Exception: xml.dom.SyntaxErr

     Raised when an invalid or illegal string is specified.

 -- Exception: xml.dom.WrongDocumentErr

     Raised when a node is inserted in a different document than it
     currently belongs to, and the implementation does not support
     migrating the node from one document to the other.

The exception codes defined in the DOM recommendation map to the
exceptions described above according to this table:

Constant                                   Exception
                                           
---------------------------------------------------------------------------------
                                           
‘DOMSTRING_SIZE_ERR’                       *note DomstringSizeErr: 2bfe.
                                           
                                           
‘HIERARCHY_REQUEST_ERR’                    *note HierarchyRequestErr: 2bff.
                                           
                                           
‘INDEX_SIZE_ERR’                           *note IndexSizeErr: 2c00.
                                           
                                           
‘INUSE_ATTRIBUTE_ERR’                      *note InuseAttributeErr: 2be8.
                                           
                                           
‘INVALID_ACCESS_ERR’                       *note InvalidAccessErr: 2c01.
                                           
                                           
‘INVALID_CHARACTER_ERR’                    *note InvalidCharacterErr: 2c02.
                                           
                                           
‘INVALID_MODIFICATION_ERR’                 *note InvalidModificationErr: 2c03.
                                           
                                           
‘INVALID_STATE_ERR’                        *note InvalidStateErr: 2c04.
                                           
                                           
‘NAMESPACE_ERR’                            *note NamespaceErr: 2c05.
                                           
                                           
‘NOT_FOUND_ERR’                            *note NotFoundErr: 2be3.
                                           
                                           
‘NOT_SUPPORTED_ERR’                        *note NotSupportedErr: 2c06.
                                           
                                           
‘NO_DATA_ALLOWED_ERR’                      *note NoDataAllowedErr: 2c07.
                                           
                                           
‘NO_MODIFICATION_ALLOWED_ERR’              *note NoModificationAllowedErr: 2c08.
                                           
                                           
‘SYNTAX_ERR’                               *note SyntaxErr: 2c09.
                                           
                                           
‘WRONG_DOCUMENT_ERR’                       *note WrongDocumentErr: 2c0a.
                                           

   ---------- Footnotes ----------

   (1) https://www.w3.org/TR/REC-xml-names/


File: python.info,  Node: Conformance,  Prev: Objects in the DOM,  Up: xml dom — The Document Object Model API

5.20.6.15 Conformance
.....................

This section describes the conformance requirements and relationships
between the Python DOM API, the W3C DOM recommendations, and the OMG IDL
mapping for Python.

* Menu:

* Type Mapping::
* Accessor Methods::


File: python.info,  Node: Type Mapping,  Next: Accessor Methods,  Up: Conformance

5.20.6.16 Type Mapping
......................

The IDL types used in the DOM specification are mapped to Python types
according to the following table.

IDL Type               Python Type
                       
-----------------------------------------------------------------------
                       
‘boolean’              ‘bool’ or ‘int’
                       
                       
‘int’                  ‘int’
                       
                       
‘long int’             ‘int’
                       
                       
‘unsigned int’         ‘int’
                       
                       
‘DOMString’            ‘str’ or ‘bytes’
                       
                       
‘null’                 ‘None’
                       


File: python.info,  Node: Accessor Methods,  Prev: Type Mapping,  Up: Conformance

5.20.6.17 Accessor Methods
..........................

The mapping from OMG IDL to Python defines accessor functions for IDL
‘attribute’ declarations in much the way the Java mapping does.  Mapping
the IDL declarations

     readonly attribute string someValue;
              attribute string anotherValue;

yields three accessor functions: a “get” method for ‘someValue’
(‘_get_someValue()’), and “get” and “set” methods for ‘anotherValue’
(‘_get_anotherValue()’ and ‘_set_anotherValue()’).  The mapping, in
particular, does not require that the IDL attributes are accessible as
normal Python attributes: ‘object.someValue’ is `not' required to work,
and may raise an *note AttributeError: 4a2.

The Python DOM API, however, `does' require that normal attribute access
work.  This means that the typical surrogates generated by Python IDL
compilers are not likely to work, and wrapper objects may be needed on
the client if the DOM objects are accessed via CORBA. While this does
require some additional consideration for CORBA DOM clients, the
implementers with experience using DOM over CORBA from Python do not
consider this a problem.  Attributes that are declared ‘readonly’ may
not restrict write access in all DOM implementations.

In the Python DOM API, accessor functions are not required.  If
provided, they should take the form defined by the Python IDL mapping,
but these methods are considered unnecessary since the attributes are
accessible directly from Python.  “Set” accessors should never be
provided for ‘readonly’ attributes.

The IDL definitions do not fully embody the requirements of the W3C DOM
API, such as the notion of certain objects, such as the return value of
‘getElementsByTagName()’, being “live”.  The Python DOM API does not
require implementations to enforce such requirements.


File: python.info,  Node: xml dom minidom — Minimal DOM implementation,  Next: xml dom pulldom — Support for building partial DOM trees,  Prev: xml dom — The Document Object Model API,  Up: Structured Markup Processing Tools

5.20.7 ‘xml.dom.minidom’ — Minimal DOM implementation
-----------------------------------------------------

`Source code:' Lib/xml/dom/minidom.py(1)

__________________________________________________________________

*note xml.dom.minidom: 13e. is a minimal implementation of the Document
Object Model interface, with an API similar to that in other languages.
It is intended to be simpler than the full DOM and also significantly
smaller.  Users who are not already proficient with the DOM should
consider using the *note xml.etree.ElementTree: 140. module for their
XML processing instead.

     Warning: The *note xml.dom.minidom: 13e. module is not secure
     against maliciously constructed data.  If you need to parse
     untrusted or unauthenticated data see *note XML vulnerabilities:
     2b34.

DOM applications typically start by parsing some XML into a DOM. With
*note xml.dom.minidom: 13e, this is done through the parse functions:

     from xml.dom.minidom import parse, parseString

     dom1 = parse('c:\\temp\\mydata.xml')  # parse an XML file by name

     datasource = open('c:\\temp\\mydata.xml')
     dom2 = parse(datasource)  # parse an open file

     dom3 = parseString('<myxml>Some data<empty/> some more data</myxml>')

The *note parse(): 2c12. function can take either a filename or an open
file object.

 -- Function: xml.dom.minidom.parse (filename_or_file, parser=None,
          bufsize=None)

     Return a ‘Document’ from the given input.  `filename_or_file' may
     be either a file name, or a file-like object.  `parser', if given,
     must be a SAX2 parser object.  This function will change the
     document handler of the parser and activate namespace support;
     other parser configuration (like setting an entity resolver) must
     have been done in advance.

If you have XML in a string, you can use the *note parseString(): 2c13.
function instead:

 -- Function: xml.dom.minidom.parseString (string, parser=None)

     Return a ‘Document’ that represents the `string'.  This method
     creates an *note io.StringIO: 91a. object for the string and passes
     that on to *note parse(): 2c12.

Both functions return a ‘Document’ object representing the content of
the document.

What the *note parse(): 2c12. and *note parseString(): 2c13. functions
do is connect an XML parser with a “DOM builder” that can accept parse
events from any SAX parser and convert them into a DOM tree.  The name
of the functions are perhaps misleading, but are easy to grasp when
learning the interfaces.  The parsing of the document will be completed
before these functions return; it’s simply that these functions do not
provide a parser implementation themselves.

You can also create a ‘Document’ by calling a method on a “DOM
Implementation” object.  You can get this object either by calling the
‘getDOMImplementation()’ function in the *note xml.dom: 13d. package or
the *note xml.dom.minidom: 13e. module.  Once you have a ‘Document’, you
can add child nodes to it to populate the DOM:

     from xml.dom.minidom import getDOMImplementation

     impl = getDOMImplementation()

     newdoc = impl.createDocument(None, "some_tag", None)
     top_element = newdoc.documentElement
     text = newdoc.createTextNode('Some textual content.')
     top_element.appendChild(text)

Once you have a DOM document object, you can access the parts of your
XML document through its properties and methods.  These properties are
defined in the DOM specification.  The main property of the document
object is the ‘documentElement’ property.  It gives you the main element
in the XML document: the one that holds all others.  Here is an example
program:

     dom3 = parseString("<myxml>Some data</myxml>")
     assert dom3.documentElement.tagName == "myxml"

When you are finished with a DOM tree, you may optionally call the
‘unlink()’ method to encourage early cleanup of the now-unneeded
objects.  ‘unlink()’ is an *note xml.dom.minidom: 13e.-specific
extension to the DOM API that renders the node and its descendants are
essentially useless.  Otherwise, Python’s garbage collector will
eventually take care of the objects in the tree.

See also
........

Document Object Model (DOM) Level 1 Specification(2)

     The W3C recommendation for the DOM supported by *note
     xml.dom.minidom: 13e.

* Menu:

* DOM Objects::
* DOM Example::
* minidom and the DOM standard::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/xml/dom/minidom.py

   (2) https://www.w3.org/TR/REC-DOM-Level-1/


File: python.info,  Node: DOM Objects,  Next: DOM Example,  Up: xml dom minidom — Minimal DOM implementation

5.20.7.1 DOM Objects
....................

The definition of the DOM API for Python is given as part of the *note
xml.dom: 13d. module documentation.  This section lists the differences
between the API and *note xml.dom.minidom: 13e.

 -- Method: Node.unlink ()

     Break internal references within the DOM so that it will be garbage
     collected on versions of Python without cyclic GC. Even when cyclic
     GC is available, using this can make large amounts of memory
     available sooner, so calling this on DOM objects as soon as they
     are no longer needed is good practice.  This only needs to be
     called on the ‘Document’ object, but may be called on child nodes
     to discard children of that node.

     You can avoid calling this method explicitly by using the *note
     with: 7da. statement.  The following code will automatically unlink
     `dom' when the ‘with’ block is exited:

          with xml.dom.minidom.parse(datasource) as dom:
              ... # Work with dom.

 -- Method: Node.writexml (writer, indent="", addindent="", newl="",
          encoding=None, standalone=None)

     Write XML to the writer object.  The writer receives texts but not
     bytes as input, it should have a ‘write()’ method which matches
     that of the file object interface.  The `indent' parameter is the
     indentation of the current node.  The `addindent' parameter is the
     incremental indentation to use for subnodes of the current one.
     The `newl' parameter specifies the string to use to terminate
     newlines.

     For the ‘Document’ node, an additional keyword argument `encoding'
     can be used to specify the encoding field of the XML header.

     Similarly, explicitly stating the `standalone' argument causes the
     standalone document declarations to be added to the prologue of the
     XML document.  If the value is set to ‘True’, ‘standalone=”yes”’ is
     added, otherwise it is set to ‘“no”’.  Not stating the argument
     will omit the declaration from the document.

     Changed in version 3.8: The *note writexml(): 2c17. method now
     preserves the attribute order specified by the user.

     Changed in version 3.9: The `standalone' parameter was added.

 -- Method: Node.toxml (encoding=None, standalone=None)

     Return a string or byte string containing the XML represented by
     the DOM node.

     With an explicit `encoding' (1) argument, the result is a byte
     string in the specified encoding.  With no `encoding' argument, the
     result is a Unicode string, and the XML declaration in the
     resulting string does not specify an encoding.  Encoding this
     string in an encoding other than UTF-8 is likely incorrect, since
     UTF-8 is the default encoding of XML.

     The `standalone' argument behaves exactly as in *note writexml():
     2c17.

     Changed in version 3.8: The *note toxml(): 2c18. method now
     preserves the attribute order specified by the user.

     Changed in version 3.9: The `standalone' parameter was added.

 -- Method: Node.toprettyxml (indent="\t", newl="\n", encoding=None,
          standalone=None)

     Return a pretty-printed version of the document.  `indent'
     specifies the indentation string and defaults to a tabulator;
     `newl' specifies the string emitted at the end of each line and
     defaults to ‘\n’.

     The `encoding' argument behaves like the corresponding argument of
     *note toxml(): 2c18.

     The `standalone' argument behaves exactly as in *note writexml():
     2c17.

     Changed in version 3.8: The *note toprettyxml(): 2c19. method now
     preserves the attribute order specified by the user.

     Changed in version 3.9: The `standalone' parameter was added.

   ---------- Footnotes ----------

   (1) (1) The encoding name included in the XML output should conform
to the appropriate standards.  For example, “UTF-8” is valid, but “UTF8”
is not valid in an XML document’s declaration, even though Python
accepts it as an encoding name.  See
‘https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl’ and
‘https://www.iana.org/assignments/character-sets/character-sets.xhtml’.


File: python.info,  Node: DOM Example,  Next: minidom and the DOM standard,  Prev: DOM Objects,  Up: xml dom minidom — Minimal DOM implementation

5.20.7.2 DOM Example
....................

This example program is a fairly realistic example of a simple program.
In this particular case, we do not take much advantage of the
flexibility of the DOM.

     import xml.dom.minidom

     document = """\
     <slideshow>
     <title>Demo slideshow</title>
     <slide><title>Slide title</title>
     <point>This is a demo</point>
     <point>Of a program for processing slides</point>
     </slide>

     <slide><title>Another demo slide</title>
     <point>It is important</point>
     <point>To have more than</point>
     <point>one slide</point>
     </slide>
     </slideshow>
     """

     dom = xml.dom.minidom.parseString(document)

     def getText(nodelist):
         rc = []
         for node in nodelist:
             if node.nodeType == node.TEXT_NODE:
                 rc.append(node.data)
         return ''.join(rc)

     def handleSlideshow(slideshow):
         print("<html>")
         handleSlideshowTitle(slideshow.getElementsByTagName("title")[0])
         slides = slideshow.getElementsByTagName("slide")
         handleToc(slides)
         handleSlides(slides)
         print("</html>")

     def handleSlides(slides):
         for slide in slides:
             handleSlide(slide)

     def handleSlide(slide):
         handleSlideTitle(slide.getElementsByTagName("title")[0])
         handlePoints(slide.getElementsByTagName("point"))

     def handleSlideshowTitle(title):
         print("<title>%s</title>" % getText(title.childNodes))

     def handleSlideTitle(title):
         print("<h2>%s</h2>" % getText(title.childNodes))

     def handlePoints(points):
         print("<ul>")
         for point in points:
             handlePoint(point)
         print("</ul>")

     def handlePoint(point):
         print("<li>%s</li>" % getText(point.childNodes))

     def handleToc(slides):
         for slide in slides:
             title = slide.getElementsByTagName("title")[0]
             print("<p>%s</p>" % getText(title.childNodes))

     handleSlideshow(dom)


File: python.info,  Node: minidom and the DOM standard,  Prev: DOM Example,  Up: xml dom minidom — Minimal DOM implementation

5.20.7.3 minidom and the DOM standard
.....................................

The *note xml.dom.minidom: 13e. module is essentially a DOM
1.0-compatible DOM with some DOM 2 features (primarily namespace
features).

Usage of the DOM interface in Python is straight-forward.  The following
mapping rules apply:

   * Interfaces are accessed through instance objects.  Applications
     should not instantiate the classes themselves; they should use the
     creator functions available on the ‘Document’ object.  Derived
     interfaces support all operations (and attributes) from the base
     interfaces, plus any new operations.

   * Operations are used as methods.  Since the DOM uses only *note in:
     179. parameters, the arguments are passed in normal order (from
     left to right).  There are no optional arguments.  ‘void’
     operations return ‘None’.

   * IDL attributes map to instance attributes.  For compatibility with
     the OMG IDL language mapping for Python, an attribute ‘foo’ can
     also be accessed through accessor methods ‘_get_foo()’ and
     ‘_set_foo()’.  ‘readonly’ attributes must not be changed; this is
     not enforced at runtime.

   * The types ‘short int’, ‘unsigned int’, ‘unsigned long long’, and
     ‘boolean’ all map to Python integer objects.

   * The type ‘DOMString’ maps to Python strings.  *note
     xml.dom.minidom: 13e. supports either bytes or strings, but will
     normally produce strings.  Values of type ‘DOMString’ may also be
     ‘None’ where allowed to have the IDL ‘null’ value by the DOM
     specification from the W3C.

   * ‘const’ declarations map to variables in their respective scope
     (e.g.  ‘xml.dom.minidom.Node.PROCESSING_INSTRUCTION_NODE’); they
     must not be changed.

   * ‘DOMException’ is currently not supported in *note xml.dom.minidom:
     13e.  Instead, *note xml.dom.minidom: 13e. uses standard Python
     exceptions such as *note TypeError: 1fe. and *note AttributeError:
     4a2.

   * ‘NodeList’ objects are implemented using Python’s built-in list
     type.  These objects provide the interface defined in the DOM
     specification, but with earlier versions of Python they do not
     support the official API. They are, however, much more “Pythonic”
     than the interface defined in the W3C recommendations.

The following interfaces have no implementation in *note
xml.dom.minidom: 13e.:

   * ‘DOMTimeStamp’

   * ‘EntityReference’

Most of these reflect information in the XML document that is not of
general utility to most DOM users.


File: python.info,  Node: xml dom pulldom — Support for building partial DOM trees,  Next: xml sax — Support for SAX2 parsers,  Prev: xml dom minidom — Minimal DOM implementation,  Up: Structured Markup Processing Tools

5.20.8 ‘xml.dom.pulldom’ — Support for building partial DOM trees
-----------------------------------------------------------------

`Source code:' Lib/xml/dom/pulldom.py(1)

__________________________________________________________________

The *note xml.dom.pulldom: 13f. module provides a “pull parser” which
can also be asked to produce DOM-accessible fragments of the document
where necessary.  The basic concept involves pulling “events” from a
stream of incoming XML and processing them.  In contrast to SAX which
also employs an event-driven processing model together with callbacks,
the user of a pull parser is responsible for explicitly pulling events
from the stream, looping over those events until either processing is
finished or an error condition occurs.

     Warning: The *note xml.dom.pulldom: 13f. module is not secure
     against maliciously constructed data.  If you need to parse
     untrusted or unauthenticated data see *note XML vulnerabilities:
     2b34.

Changed in version 3.7.1: The SAX parser no longer processes general
external entities by default to increase security by default.  To enable
processing of external entities, pass a custom parser instance in:

     from xml.dom.pulldom import parse
     from xml.sax import make_parser
     from xml.sax.handler import feature_external_ges

     parser = make_parser()
     parser.setFeature(feature_external_ges, True)
     parse(filename, parser=parser)

Example:

     from xml.dom import pulldom

     doc = pulldom.parse('sales_items.xml')
     for event, node in doc:
         if event == pulldom.START_ELEMENT and node.tagName == 'item':
             if int(node.getAttribute('price')) > 50:
                 doc.expandNode(node)
                 print(node.toxml())

‘event’ is a constant and can be one of:

   * ‘START_ELEMENT’

   * ‘END_ELEMENT’

   * ‘COMMENT’

   * ‘START_DOCUMENT’

   * ‘END_DOCUMENT’

   * ‘CHARACTERS’

   * ‘PROCESSING_INSTRUCTION’

   * ‘IGNORABLE_WHITESPACE’

‘node’ is an object of type ‘xml.dom.minidom.Document’,
‘xml.dom.minidom.Element’ or ‘xml.dom.minidom.Text’.

Since the document is treated as a “flat” stream of events, the document
“tree” is implicitly traversed and the desired elements are found
regardless of their depth in the tree.  In other words, one does not
need to consider hierarchical issues such as recursive searching of the
document nodes, although if the context of elements were important, one
would either need to maintain some context-related state (i.e.
remembering where one is in the document at any given point) or to make
use of the *note DOMEventStream.expandNode(): 2c20. method and switch to
DOM-related processing.

 -- Class: xml.dom.pulldom.PullDom (documentFactory=None)

     Subclass of *note xml.sax.handler.ContentHandler: 2c22.

 -- Class: xml.dom.pulldom.SAX2DOM (documentFactory=None)

     Subclass of *note xml.sax.handler.ContentHandler: 2c22.

 -- Function: xml.dom.pulldom.parse (stream_or_string, parser=None,
          bufsize=None)

     Return a *note DOMEventStream: 3a3. from the given input.
     `stream_or_string' may be either a file name, or a file-like
     object.  `parser', if given, must be an *note XMLReader: 2c25.
     object.  This function will change the document handler of the
     parser and activate namespace support; other parser configuration
     (like setting an entity resolver) must have been done in advance.

If you have XML in a string, you can use the *note parseString(): 2c26.
function instead:

 -- Function: xml.dom.pulldom.parseString (string, parser=None)

     Return a *note DOMEventStream: 3a3. that represents the (Unicode)
     `string'.

 -- Data: xml.dom.pulldom.default_bufsize

     Default value for the `bufsize' parameter to *note parse(): 2c24.

     The value of this variable can be changed before calling *note
     parse(): 2c24. and the new value will take effect.

* Menu:

* DOMEventStream Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/xml/dom/pulldom.py


File: python.info,  Node: DOMEventStream Objects,  Up: xml dom pulldom — Support for building partial DOM trees

5.20.8.1 DOMEventStream Objects
...............................

 -- Class: xml.dom.pulldom.DOMEventStream (stream, parser, bufsize)

     Deprecated since version 3.8: Support for *note sequence protocol:
     3a2. is deprecated.

      -- Method: getEvent ()

          Return a tuple containing `event' and the current `node' as
          ‘xml.dom.minidom.Document’ if event equals ‘START_DOCUMENT’,
          ‘xml.dom.minidom.Element’ if event equals ‘START_ELEMENT’ or
          ‘END_ELEMENT’ or ‘xml.dom.minidom.Text’ if event equals
          ‘CHARACTERS’.  The current node does not contain information
          about its children, unless *note expandNode(): 2c20. is
          called.

      -- Method: expandNode (node)

          Expands all children of `node' into `node'.  Example:

               from xml.dom import pulldom

               xml = '<html><title>Foo</title> <p>Some text <div>and more</div></p> </html>'
               doc = pulldom.parseString(xml)
               for event, node in doc:
                   if event == pulldom.START_ELEMENT and node.tagName == 'p':
                       # Following statement only prints '<p/>'
                       print(node.toxml())
                       doc.expandNode(node)
                       # Following statement prints node with all its children '<p>Some text <div>and more</div></p>'
                       print(node.toxml())

      -- Method: reset ()


File: python.info,  Node: xml sax — Support for SAX2 parsers,  Next: xml sax handler — Base classes for SAX handlers,  Prev: xml dom pulldom — Support for building partial DOM trees,  Up: Structured Markup Processing Tools

5.20.9 ‘xml.sax’ — Support for SAX2 parsers
-------------------------------------------

`Source code:' Lib/xml/sax/__init__.py(1)

__________________________________________________________________

The *note xml.sax: 144. package provides a number of modules which
implement the Simple API for XML (SAX) interface for Python.  The
package itself provides the SAX exceptions and the convenience functions
which will be most used by users of the SAX API.

     Warning: The *note xml.sax: 144. module is not secure against
     maliciously constructed data.  If you need to parse untrusted or
     unauthenticated data see *note XML vulnerabilities: 2b34.

Changed in version 3.7.1: The SAX parser no longer processes general
external entities by default to increase security.  Before, the parser
created network connections to fetch remote files or loaded local files
from the file system for DTD and entities.  The feature can be enabled
again with method *note setFeature(): 2c2e. on the parser object and
argument *note feature_external_ges: 2c2f.

The convenience functions are:

 -- Function: xml.sax.make_parser (parser_list=[])

     Create and return a SAX *note XMLReader: 2c25. object.  The first
     parser found will be used.  If `parser_list' is provided, it must
     be an iterable of strings which name modules that have a function
     named ‘create_parser()’.  Modules listed in `parser_list' will be
     used before modules in the default list of parsers.

     Changed in version 3.8: The `parser_list' argument can be any
     iterable, not just a list.

 -- Function: xml.sax.parse (filename_or_stream, handler,
          error_handler=handler.ErrorHandler())

     Create a SAX parser and use it to parse a document.  The document,
     passed in as `filename_or_stream', can be a filename or a file
     object.  The `handler' parameter needs to be a SAX *note
     ContentHandler: 2c22. instance.  If `error_handler' is given, it
     must be a SAX *note ErrorHandler: 2c30. instance; if omitted, *note
     SAXParseException: 2c31. will be raised on all errors.  There is no
     return value; all work must be done by the `handler' passed in.

 -- Function: xml.sax.parseString (string, handler,
          error_handler=handler.ErrorHandler())

     Similar to *note parse(): 111c, but parses from a buffer `string'
     received as a parameter.  `string' must be a *note str: 205.
     instance or a *note bytes-like object: 6df.

     Changed in version 3.5: Added support of *note str: 205. instances.

A typical SAX application uses three kinds of objects: readers, handlers
and input sources.  “Reader” in this context is another term for parser,
i.e.  some piece of code that reads the bytes or characters from the
input source, and produces a sequence of events.  The events then get
distributed to the handler objects, i.e.  the reader invokes a method on
the handler.  A SAX application must therefore obtain a reader object,
create or open the input sources, create the handlers, and connect these
objects all together.  As the final step of preparation, the reader is
called to parse the input.  During parsing, methods on the handler
objects are called based on structural and syntactic events from the
input data.

For these objects, only the interfaces are relevant; they are normally
not instantiated by the application itself.  Since Python does not have
an explicit notion of interface, they are formally introduced as
classes, but applications may use implementations which do not inherit
from the provided classes.  The *note InputSource: 881, *note Locator:
2c32, ‘Attributes’, ‘AttributesNS’, and *note XMLReader: 2c25.
interfaces are defined in the module *note xml.sax.xmlreader: 147.  The
handler interfaces are defined in *note xml.sax.handler: 145.  For
convenience, *note InputSource: 881. (which is often instantiated
directly) and the handler classes are also available from *note xml.sax:
144.  These interfaces are described below.

In addition to these classes, *note xml.sax: 144. provides the following
exception classes.

 -- Exception: xml.sax.SAXException (msg, exception=None)

     Encapsulate an XML error or warning.  This class can contain basic
     error or warning information from either the XML parser or the
     application: it can be subclassed to provide additional
     functionality or to add localization.  Note that although the
     handlers defined in the *note ErrorHandler: 2c30. interface receive
     instances of this exception, it is not required to actually raise
     the exception — it is also useful as a container for information.

     When instantiated, `msg' should be a human-readable description of
     the error.  The optional `exception' parameter, if given, should be
     ‘None’ or an exception that was caught by the parsing code and is
     being passed along as information.

     This is the base class for the other SAX exception classes.

 -- Exception: xml.sax.SAXParseException (msg, exception, locator)

     Subclass of *note SAXException: 2c33. raised on parse errors.
     Instances of this class are passed to the methods of the SAX *note
     ErrorHandler: 2c30. interface to provide information about the
     parse error.  This class supports the SAX *note Locator: 2c32.
     interface as well as the *note SAXException: 2c33. interface.

 -- Exception: xml.sax.SAXNotRecognizedException (msg, exception=None)

     Subclass of *note SAXException: 2c33. raised when a SAX *note
     XMLReader: 2c25. is confronted with an unrecognized feature or
     property.  SAX applications and extensions may use this class for
     similar purposes.

 -- Exception: xml.sax.SAXNotSupportedException (msg, exception=None)

     Subclass of *note SAXException: 2c33. raised when a SAX *note
     XMLReader: 2c25. is asked to enable a feature that is not
     supported, or to set a property to a value that the implementation
     does not support.  SAX applications and extensions may use this
     class for similar purposes.

See also
........

SAX: The Simple API for XML(2)

     This site is the focal point for the definition of the SAX API. It
     provides a Java implementation and online documentation.  Links to
     implementations and historical information are also available.

Module *note xml.sax.handler: 145.

     Definitions of the interfaces for application-provided objects.

Module *note xml.sax.saxutils: 146.

     Convenience functions for use in SAX applications.

Module *note xml.sax.xmlreader: 147.

     Definitions of the interfaces for parser-provided objects.

* Menu:

* SAXException Objects::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/xml/sax/__init__.py

   (2) http://www.saxproject.org/


File: python.info,  Node: SAXException Objects,  Up: xml sax — Support for SAX2 parsers

5.20.9.1 SAXException Objects
.............................

The *note SAXException: 2c33. exception class supports the following
methods:

 -- Method: SAXException.getMessage ()

     Return a human-readable message describing the error condition.

 -- Method: SAXException.getException ()

     Return an encapsulated exception object, or ‘None’.


File: python.info,  Node: xml sax handler — Base classes for SAX handlers,  Next: xml sax saxutils — SAX Utilities,  Prev: xml sax — Support for SAX2 parsers,  Up: Structured Markup Processing Tools

5.20.10 ‘xml.sax.handler’ — Base classes for SAX handlers
---------------------------------------------------------

`Source code:' Lib/xml/sax/handler.py(1)

__________________________________________________________________

The SAX API defines four kinds of handlers: content handlers, DTD
handlers, error handlers, and entity resolvers.  Applications normally
only need to implement those interfaces whose events they are interested
in; they can implement the interfaces in a single object or in multiple
objects.  Handler implementations should inherit from the base classes
provided in the module *note xml.sax.handler: 145, so that all methods
get default implementations.

 -- Class: xml.sax.handler.ContentHandler

     This is the main callback interface in SAX, and the one most
     important to applications.  The order of events in this interface
     mirrors the order of the information in the document.

 -- Class: xml.sax.handler.DTDHandler

     Handle DTD events.

     This interface specifies only those DTD events required for basic
     parsing (unparsed entities and attributes).

 -- Class: xml.sax.handler.EntityResolver

     Basic interface for resolving entities.  If you create an object
     implementing this interface, then register the object with your
     Parser, the parser will call the method in your object to resolve
     all external entities.

 -- Class: xml.sax.handler.ErrorHandler

     Interface used by the parser to present error and warning messages
     to the application.  The methods of this object control whether
     errors are immediately converted to exceptions or are handled in
     some other way.

In addition to these classes, *note xml.sax.handler: 145. provides
symbolic constants for the feature and property names.

 -- Data: xml.sax.handler.feature_namespaces

          value: ‘"http://xml.org/sax/features/namespaces"’ 
          true: Perform Namespace processing. 
          false: Optionally do not perform Namespace processing (implies namespace-prefixes; default). 
          access: (parsing) read-only; (not parsing) read/write 

 -- Data: xml.sax.handler.feature_namespace_prefixes

          value: ‘"http://xml.org/sax/features/namespace-prefixes"’ 
          true: Report the original prefixed names and attributes used for Namespace declarations. 
          false: Do not report attributes used for Namespace declarations, and optionally do not report original prefixed names (default). 
          access: (parsing) read-only; (not parsing) read/write 

 -- Data: xml.sax.handler.feature_string_interning

          value: ‘"http://xml.org/sax/features/string-interning"’ 
          true: All element names, prefixes, attribute names, Namespace URIs, and local names are interned using the built-in intern function. 
          false: Names are not necessarily interned, although they may be (default). 
          access: (parsing) read-only; (not parsing) read/write 

 -- Data: xml.sax.handler.feature_validation

          value: ‘"http://xml.org/sax/features/validation"’ 
          true: Report all validation errors (implies external-general-entities and external-parameter-entities). 
          false: Do not report validation errors. 
          access: (parsing) read-only; (not parsing) read/write 

 -- Data: xml.sax.handler.feature_external_ges

          value: ‘"http://xml.org/sax/features/external-general-entities"’ 
          true: Include all external general (text) entities. 
          false: Do not include external general entities. 
          access: (parsing) read-only; (not parsing) read/write 

 -- Data: xml.sax.handler.feature_external_pes

          value: ‘"http://xml.org/sax/features/external-parameter-entities"’ 
          true: Include all external parameter entities, including the external DTD subset. 
          false: Do not include any external parameter entities, even the external DTD subset. 
          access: (parsing) read-only; (not parsing) read/write 

 -- Data: xml.sax.handler.all_features

     List of all features.

 -- Data: xml.sax.handler.property_lexical_handler

          value: ‘"http://xml.org/sax/properties/lexical-handler"’ 
          data type: xml.sax.sax2lib.LexicalHandler (not supported in Python 2) 
          description: An optional extension handler for lexical events like comments. 
          access: read/write 

 -- Data: xml.sax.handler.property_declaration_handler

          value: ‘"http://xml.org/sax/properties/declaration-handler"’ 
          data type: xml.sax.sax2lib.DeclHandler (not supported in Python 2) 
          description: An optional extension handler for DTD-related events other than notations and unparsed entities. 
          access: read/write 

 -- Data: xml.sax.handler.property_dom_node

          value: ‘"http://xml.org/sax/properties/dom-node"’ 
          data type: org.w3c.dom.Node (not supported in Python 2) 
          description: When parsing, the current DOM node being visited if this is a DOM iterator; when not parsing, the root DOM node for iteration. 
          access: (parsing) read-only; (not parsing) read/write 

 -- Data: xml.sax.handler.property_xml_string

          value: ‘"http://xml.org/sax/properties/xml-string"’ 
          data type: String 
          description: The literal string of characters that was the source for the current event. 
          access: read-only 

 -- Data: xml.sax.handler.all_properties

     List of all known property names.

* Menu:

* ContentHandler Objects::
* DTDHandler Objects::
* EntityResolver Objects::
* ErrorHandler Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/xml/sax/handler.py


File: python.info,  Node: ContentHandler Objects,  Next: DTDHandler Objects,  Up: xml sax handler — Base classes for SAX handlers

5.20.10.1 ContentHandler Objects
................................

Users are expected to subclass *note ContentHandler: 2c22. to support
their application.  The following methods are called by the parser on
the appropriate events in the input document:

 -- Method: ContentHandler.setDocumentLocator (locator)

     Called by the parser to give the application a locator for locating
     the origin of document events.

     SAX parsers are strongly encouraged (though not absolutely
     required) to supply a locator: if it does so, it must supply the
     locator to the application by invoking this method before invoking
     any of the other methods in the DocumentHandler interface.

     The locator allows the application to determine the end position of
     any document-related event, even if the parser is not reporting an
     error.  Typically, the application will use this information for
     reporting its own errors (such as character content that does not
     match an application’s business rules).  The information returned
     by the locator is probably not sufficient for use with a search
     engine.

     Note that the locator will return correct information only during
     the invocation of the events in this interface.  The application
     should not attempt to use it at any other time.

 -- Method: ContentHandler.startDocument ()

     Receive notification of the beginning of a document.

     The SAX parser will invoke this method only once, before any other
     methods in this interface or in DTDHandler (except for *note
     setDocumentLocator(): 2c4b.).

 -- Method: ContentHandler.endDocument ()

     Receive notification of the end of a document.

     The SAX parser will invoke this method only once, and it will be
     the last method invoked during the parse.  The parser shall not
     invoke this method until it has either abandoned parsing (because
     of an unrecoverable error) or reached the end of input.

 -- Method: ContentHandler.startPrefixMapping (prefix, uri)

     Begin the scope of a prefix-URI Namespace mapping.

     The information from this event is not necessary for normal
     Namespace processing: the SAX XML reader will automatically replace
     prefixes for element and attribute names when the
     ‘feature_namespaces’ feature is enabled (the default).

     There are cases, however, when applications need to use prefixes in
     character data or in attribute values, where they cannot safely be
     expanded automatically; the *note startPrefixMapping(): 2c4e. and
     *note endPrefixMapping(): 2c4f. events supply the information to
     the application to expand prefixes in those contexts itself, if
     necessary.

     Note that *note startPrefixMapping(): 2c4e. and *note
     endPrefixMapping(): 2c4f. events are not guaranteed to be properly
     nested relative to each-other: all *note startPrefixMapping():
     2c4e. events will occur before the corresponding *note
     startElement(): 2c50. event, and all *note endPrefixMapping():
     2c4f. events will occur after the corresponding *note endElement():
     2c51. event, but their order is not guaranteed.

 -- Method: ContentHandler.endPrefixMapping (prefix)

     End the scope of a prefix-URI mapping.

     See *note startPrefixMapping(): 2c4e. for details.  This event will
     always occur after the corresponding *note endElement(): 2c51.
     event, but the order of *note endPrefixMapping(): 2c4f. events is
     not otherwise guaranteed.

 -- Method: ContentHandler.startElement (name, attrs)

     Signals the start of an element in non-namespace mode.

     The `name' parameter contains the raw XML 1.0 name of the element
     type as a string and the `attrs' parameter holds an object of the
     ‘Attributes’ interface (see *note The Attributes Interface: 2c52.)
     containing the attributes of the element.  The object passed as
     `attrs' may be re-used by the parser; holding on to a reference to
     it is not a reliable way to keep a copy of the attributes.  To keep
     a copy of the attributes, use the *note copy(): 25. method of the
     `attrs' object.

 -- Method: ContentHandler.endElement (name)

     Signals the end of an element in non-namespace mode.

     The `name' parameter contains the name of the element type, just as
     with the *note startElement(): 2c50. event.

 -- Method: ContentHandler.startElementNS (name, qname, attrs)

     Signals the start of an element in namespace mode.

     The `name' parameter contains the name of the element type as a
     ‘(uri, localname)’ tuple, the `qname' parameter contains the raw
     XML 1.0 name used in the source document, and the `attrs' parameter
     holds an instance of the ‘AttributesNS’ interface (see *note The
     AttributesNS Interface: 2c54.) containing the attributes of the
     element.  If no namespace is associated with the element, the `uri'
     component of `name' will be ‘None’.  The object passed as `attrs'
     may be re-used by the parser; holding on to a reference to it is
     not a reliable way to keep a copy of the attributes.  To keep a
     copy of the attributes, use the *note copy(): 25. method of the
     `attrs' object.

     Parsers may set the `qname' parameter to ‘None’, unless the
     ‘feature_namespace_prefixes’ feature is activated.

 -- Method: ContentHandler.endElementNS (name, qname)

     Signals the end of an element in namespace mode.

     The `name' parameter contains the name of the element type, just as
     with the *note startElementNS(): 2c53. method, likewise the `qname'
     parameter.

 -- Method: ContentHandler.characters (content)

     Receive notification of character data.

     The Parser will call this method to report each chunk of character
     data.  SAX parsers may return all contiguous character data in a
     single chunk, or they may split it into several chunks; however,
     all of the characters in any single event must come from the same
     external entity so that the Locator provides useful information.

     `content' may be a string or bytes instance; the ‘expat’ reader
     module always produces strings.

          Note: The earlier SAX 1 interface provided by the Python XML
          Special Interest Group used a more Java-like interface for
          this method.  Since most parsers used from Python did not take
          advantage of the older interface, the simpler signature was
          chosen to replace it.  To convert old code to the new
          interface, use `content' instead of slicing content with the
          old `offset' and `length' parameters.

 -- Method: ContentHandler.ignorableWhitespace (whitespace)

     Receive notification of ignorable whitespace in element content.

     Validating Parsers must use this method to report each chunk of
     ignorable whitespace (see the W3C XML 1.0 recommendation, section
     2.10): non-validating parsers may also use this method if they are
     capable of parsing and using content models.

     SAX parsers may return all contiguous whitespace in a single chunk,
     or they may split it into several chunks; however, all of the
     characters in any single event must come from the same external
     entity, so that the Locator provides useful information.

 -- Method: ContentHandler.processingInstruction (target, data)

     Receive notification of a processing instruction.

     The Parser will invoke this method once for each processing
     instruction found: note that processing instructions may occur
     before or after the main document element.

     A SAX parser should never report an XML declaration (XML 1.0,
     section 2.8) or a text declaration (XML 1.0, section 4.3.1) using
     this method.

 -- Method: ContentHandler.skippedEntity (name)

     Receive notification of a skipped entity.

     The Parser will invoke this method once for each entity skipped.
     Non-validating processors may skip entities if they have not seen
     the declarations (because, for example, the entity was declared in
     an external DTD subset).  All processors may skip external
     entities, depending on the values of the ‘feature_external_ges’ and
     the ‘feature_external_pes’ properties.


File: python.info,  Node: DTDHandler Objects,  Next: EntityResolver Objects,  Prev: ContentHandler Objects,  Up: xml sax handler — Base classes for SAX handlers

5.20.10.2 DTDHandler Objects
............................

*note DTDHandler: 2c3c. instances provide the following methods:

 -- Method: DTDHandler.notationDecl (name, publicId, systemId)

     Handle a notation declaration event.

 -- Method: DTDHandler.unparsedEntityDecl (name, publicId, systemId,
          ndata)

     Handle an unparsed entity declaration event.


File: python.info,  Node: EntityResolver Objects,  Next: ErrorHandler Objects,  Prev: DTDHandler Objects,  Up: xml sax handler — Base classes for SAX handlers

5.20.10.3 EntityResolver Objects
................................

 -- Method: EntityResolver.resolveEntity (publicId, systemId)

     Resolve the system identifier of an entity and return either the
     system identifier to read from as a string, or an InputSource to
     read from.  The default implementation returns `systemId'.


File: python.info,  Node: ErrorHandler Objects,  Prev: EntityResolver Objects,  Up: xml sax handler — Base classes for SAX handlers

5.20.10.4 ErrorHandler Objects
..............................

Objects with this interface are used to receive error and warning
information from the *note XMLReader: 2c25.  If you create an object
that implements this interface, then register the object with your *note
XMLReader: 2c25, the parser will call the methods in your object to
report all warnings and errors.  There are three levels of errors
available: warnings, (possibly) recoverable errors, and unrecoverable
errors.  All methods take a ‘SAXParseException’ as the only parameter.
Errors and warnings may be converted to an exception by raising the
passed-in exception object.

 -- Method: ErrorHandler.error (exception)

     Called when the parser encounters a recoverable error.  If this
     method does not raise an exception, parsing may continue, but
     further document information should not be expected by the
     application.  Allowing the parser to continue may allow additional
     errors to be discovered in the input document.

 -- Method: ErrorHandler.fatalError (exception)

     Called when the parser encounters an error it cannot recover from;
     parsing is expected to terminate when this method returns.

 -- Method: ErrorHandler.warning (exception)

     Called when the parser presents minor warning information to the
     application.  Parsing is expected to continue when this method
     returns, and document information will continue to be passed to the
     application.  Raising an exception in this method will cause
     parsing to end.


File: python.info,  Node: xml sax saxutils — SAX Utilities,  Next: xml sax xmlreader — Interface for XML parsers,  Prev: xml sax handler — Base classes for SAX handlers,  Up: Structured Markup Processing Tools

5.20.11 ‘xml.sax.saxutils’ — SAX Utilities
------------------------------------------

`Source code:' Lib/xml/sax/saxutils.py(1)

__________________________________________________________________

The module *note xml.sax.saxutils: 146. contains a number of classes and
functions that are commonly useful when creating SAX applications,
either in direct use, or as base classes.

 -- Function: xml.sax.saxutils.escape (data, entities={})

     Escape ‘'&'’, ‘'<'’, and ‘'>'’ in a string of data.

     You can escape other strings of data by passing a dictionary as the
     optional `entities' parameter.  The keys and values must all be
     strings; each key will be replaced with its corresponding value.
     The characters ‘'&'’, ‘'<'’ and ‘'>'’ are always escaped, even if
     `entities' is provided.

 -- Function: xml.sax.saxutils.unescape (data, entities={})

     Unescape ‘'&amp;'’, ‘'&lt;'’, and ‘'&gt;'’ in a string of data.

     You can unescape other strings of data by passing a dictionary as
     the optional `entities' parameter.  The keys and values must all be
     strings; each key will be replaced with its corresponding value.
     ‘'&amp'’, ‘'&lt;'’, and ‘'&gt;'’ are always unescaped, even if
     `entities' is provided.

 -- Function: xml.sax.saxutils.quoteattr (data, entities={})

     Similar to *note escape(): 2c68, but also prepares `data' to be
     used as an attribute value.  The return value is a quoted version
     of `data' with any additional required replacements.  *note
     quoteattr(): 2c6a. will select a quote character based on the
     content of `data', attempting to avoid encoding any quote
     characters in the string.  If both single- and double-quote
     characters are already in `data', the double-quote characters will
     be encoded and `data' will be wrapped in double-quotes.  The
     resulting string can be used directly as an attribute value:

          >>> print("<element attr=%s>" % quoteattr("ab ' cd \" ef"))
          <element attr="ab ' cd &quot; ef">

     This function is useful when generating attribute values for HTML
     or any SGML using the reference concrete syntax.

 -- Class: xml.sax.saxutils.XMLGenerator (out=None,
          encoding='iso-8859-1', short_empty_elements=False)

     This class implements the *note ContentHandler: 2c22. interface by
     writing SAX events back into an XML document.  In other words,
     using an *note XMLGenerator: 2c6b. as the content handler will
     reproduce the original document being parsed.  `out' should be a
     file-like object which will default to `sys.stdout'.  `encoding' is
     the encoding of the output stream which defaults to ‘'iso-8859-1'’.
     `short_empty_elements' controls the formatting of elements that
     contain no content: if ‘False’ (the default) they are emitted as a
     pair of start/end tags, if set to ‘True’ they are emitted as a
     single self-closed tag.

     New in version 3.2: The `short_empty_elements' parameter.

 -- Class: xml.sax.saxutils.XMLFilterBase (base)

     This class is designed to sit between an *note XMLReader: 2c25. and
     the client application’s event handlers.  By default, it does
     nothing but pass requests up to the reader and events on to the
     handlers unmodified, but subclasses can override specific methods
     to modify the event stream or the configuration requests as they
     pass through.

 -- Function: xml.sax.saxutils.prepare_input_source (source, base='')

     This function takes an input source and an optional base URL and
     returns a fully resolved *note InputSource: 881. object ready for
     reading.  The input source can be given as a string, a file-like
     object, or an *note InputSource: 881. object; parsers will use this
     function to implement the polymorphic `source' argument to their
     ‘parse()’ method.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/xml/sax/saxutils.py


File: python.info,  Node: xml sax xmlreader — Interface for XML parsers,  Next: xml parsers expat — Fast XML parsing using Expat,  Prev: xml sax saxutils — SAX Utilities,  Up: Structured Markup Processing Tools

5.20.12 ‘xml.sax.xmlreader’ — Interface for XML parsers
-------------------------------------------------------

`Source code:' Lib/xml/sax/xmlreader.py(1)

__________________________________________________________________

SAX parsers implement the *note XMLReader: 2c25. interface.  They are
implemented in a Python module, which must provide a function
‘create_parser()’.  This function is invoked by *note
xml.sax.make_parser(): 115f. with no arguments to create a new parser
object.

 -- Class: xml.sax.xmlreader.XMLReader

     Base class which can be inherited by SAX parsers.

 -- Class: xml.sax.xmlreader.IncrementalParser

     In some cases, it is desirable not to parse an input source at
     once, but to feed chunks of the document as they get available.
     Note that the reader will normally not read the entire file, but
     read it in chunks as well; still ‘parse()’ won’t return until the
     entire document is processed.  So these interfaces should be used
     if the blocking behaviour of ‘parse()’ is not desirable.

     When the parser is instantiated it is ready to begin accepting data
     from the feed method immediately.  After parsing has been finished
     with a call to close the reset method must be called to make the
     parser ready to accept new data, either from feed or using the
     parse method.

     Note that these methods must `not' be called during parsing, that
     is, after parse has been called and before it returns.

     By default, the class also implements the parse method of the
     XMLReader interface using the feed, close and reset methods of the
     IncrementalParser interface as a convenience to SAX 2.0 driver
     writers.

 -- Class: xml.sax.xmlreader.Locator

     Interface for associating a SAX event with a document location.  A
     locator object will return valid results only during calls to
     DocumentHandler methods; at any other time, the results are
     unpredictable.  If information is not available, methods may return
     ‘None’.

 -- Class: xml.sax.xmlreader.InputSource (system_id=None)

     Encapsulation of the information needed by the *note XMLReader:
     2c25. to read entities.

     This class may include information about the public identifier,
     system identifier, byte stream (possibly with character encoding
     information) and/or the character stream of an entity.

     Applications will create objects of this class for use in the *note
     XMLReader.parse(): 2c71. method and for returning from
     EntityResolver.resolveEntity.

     An *note InputSource: 881. belongs to the application, the *note
     XMLReader: 2c25. is not allowed to modify *note InputSource: 881.
     objects passed to it from the application, although it may make
     copies and modify those.

 -- Class: xml.sax.xmlreader.AttributesImpl (attrs)

     This is an implementation of the ‘Attributes’ interface (see
     section *note The Attributes Interface: 2c52.).  This is a
     dictionary-like object which represents the element attributes in a
     ‘startElement()’ call.  In addition to the most useful dictionary
     operations, it supports a number of other methods as described by
     the interface.  Objects of this class should be instantiated by
     readers; `attrs' must be a dictionary-like object containing a
     mapping from attribute names to attribute values.

 -- Class: xml.sax.xmlreader.AttributesNSImpl (attrs, qnames)

     Namespace-aware variant of *note AttributesImpl: 2c72, which will
     be passed to ‘startElementNS()’.  It is derived from *note
     AttributesImpl: 2c72, but understands attribute names as two-tuples
     of `namespaceURI' and `localname'.  In addition, it provides a
     number of methods expecting qualified names as they appear in the
     original document.  This class implements the ‘AttributesNS’
     interface (see section *note The AttributesNS Interface: 2c54.).

* Menu:

* XMLReader Objects::
* IncrementalParser Objects::
* Locator Objects::
* InputSource Objects::
* The Attributes Interface::
* The AttributesNS Interface::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/xml/sax/xmlreader.py


File: python.info,  Node: XMLReader Objects,  Next: IncrementalParser Objects,  Up: xml sax xmlreader — Interface for XML parsers

5.20.12.1 XMLReader Objects
...........................

The *note XMLReader: 2c25. interface supports the following methods:

 -- Method: XMLReader.parse (source)

     Process an input source, producing SAX events.  The `source' object
     can be a system identifier (a string identifying the input source –
     typically a file name or a URL), a *note pathlib.Path: 32f. or
     *note path-like: 472. object, or an *note InputSource: 881. object.
     When *note parse(): 2c71. returns, the input is completely
     processed, and the parser object can be discarded or reset.

     Changed in version 3.5: Added support of character streams.

     Changed in version 3.8: Added support of path-like objects.

 -- Method: XMLReader.getContentHandler ()

     Return the current *note ContentHandler: 2c22.

 -- Method: XMLReader.setContentHandler (handler)

     Set the current *note ContentHandler: 2c22.  If no *note
     ContentHandler: 2c22. is set, content events will be discarded.

 -- Method: XMLReader.getDTDHandler ()

     Return the current *note DTDHandler: 2c3c.

 -- Method: XMLReader.setDTDHandler (handler)

     Set the current *note DTDHandler: 2c3c.  If no *note DTDHandler:
     2c3c. is set, DTD events will be discarded.

 -- Method: XMLReader.getEntityResolver ()

     Return the current *note EntityResolver: 2c3d.

 -- Method: XMLReader.setEntityResolver (handler)

     Set the current *note EntityResolver: 2c3d.  If no *note
     EntityResolver: 2c3d. is set, attempts to resolve an external
     entity will result in opening the system identifier for the entity,
     and fail if it is not available.

 -- Method: XMLReader.getErrorHandler ()

     Return the current *note ErrorHandler: 2c30.

 -- Method: XMLReader.setErrorHandler (handler)

     Set the current error handler.  If no *note ErrorHandler: 2c30. is
     set, errors will be raised as exceptions, and warnings will be
     printed.

 -- Method: XMLReader.setLocale (locale)

     Allow an application to set the locale for errors and warnings.

     SAX parsers are not required to provide localization for errors and
     warnings; if they cannot support the requested locale, however,
     they must raise a SAX exception.  Applications may request a locale
     change in the middle of a parse.

 -- Method: XMLReader.getFeature (featurename)

     Return the current setting for feature `featurename'.  If the
     feature is not recognized, ‘SAXNotRecognizedException’ is raised.
     The well-known featurenames are listed in the module *note
     xml.sax.handler: 145.

 -- Method: XMLReader.setFeature (featurename, value)

     Set the `featurename' to `value'.  If the feature is not
     recognized, ‘SAXNotRecognizedException’ is raised.  If the feature
     or its setting is not supported by the parser,
     `SAXNotSupportedException' is raised.

 -- Method: XMLReader.getProperty (propertyname)

     Return the current setting for property `propertyname'.  If the
     property is not recognized, a ‘SAXNotRecognizedException’ is
     raised.  The well-known propertynames are listed in the module
     *note xml.sax.handler: 145.

 -- Method: XMLReader.setProperty (propertyname, value)

     Set the `propertyname' to `value'.  If the property is not
     recognized, ‘SAXNotRecognizedException’ is raised.  If the property
     or its setting is not supported by the parser,
     `SAXNotSupportedException' is raised.


File: python.info,  Node: IncrementalParser Objects,  Next: Locator Objects,  Prev: XMLReader Objects,  Up: xml sax xmlreader — Interface for XML parsers

5.20.12.2 IncrementalParser Objects
...................................

Instances of *note IncrementalParser: 2c70. offer the following
additional methods:

 -- Method: IncrementalParser.feed (data)

     Process a chunk of `data'.

 -- Method: IncrementalParser.close ()

     Assume the end of the document.  That will check well-formedness
     conditions that can be checked only at the end, invoke handlers,
     and may clean up resources allocated during parsing.

 -- Method: IncrementalParser.reset ()

     This method is called after close has been called to reset the
     parser so that it is ready to parse new documents.  The results of
     calling parse or feed after close without calling reset are
     undefined.


File: python.info,  Node: Locator Objects,  Next: InputSource Objects,  Prev: IncrementalParser Objects,  Up: xml sax xmlreader — Interface for XML parsers

5.20.12.3 Locator Objects
.........................

Instances of *note Locator: 2c32. provide these methods:

 -- Method: Locator.getColumnNumber ()

     Return the column number where the current event begins.

 -- Method: Locator.getLineNumber ()

     Return the line number where the current event begins.

 -- Method: Locator.getPublicId ()

     Return the public identifier for the current event.

 -- Method: Locator.getSystemId ()

     Return the system identifier for the current event.


File: python.info,  Node: InputSource Objects,  Next: The Attributes Interface,  Prev: Locator Objects,  Up: xml sax xmlreader — Interface for XML parsers

5.20.12.4 InputSource Objects
.............................

 -- Method: InputSource.setPublicId (id)

     Sets the public identifier of this *note InputSource: 881.

 -- Method: InputSource.getPublicId ()

     Returns the public identifier of this *note InputSource: 881.

 -- Method: InputSource.setSystemId (id)

     Sets the system identifier of this *note InputSource: 881.

 -- Method: InputSource.getSystemId ()

     Returns the system identifier of this *note InputSource: 881.

 -- Method: InputSource.setEncoding (encoding)

     Sets the character encoding of this *note InputSource: 881.

     The encoding must be a string acceptable for an XML encoding
     declaration (see section 4.3.3 of the XML recommendation).

     The encoding attribute of the *note InputSource: 881. is ignored if
     the *note InputSource: 881. also contains a character stream.

 -- Method: InputSource.getEncoding ()

     Get the character encoding of this InputSource.

 -- Method: InputSource.setByteStream (bytefile)

     Set the byte stream (a *note binary file: 1e01.) for this input
     source.

     The SAX parser will ignore this if there is also a character stream
     specified, but it will use a byte stream in preference to opening a
     URI connection itself.

     If the application knows the character encoding of the byte stream,
     it should set it with the setEncoding method.

 -- Method: InputSource.getByteStream ()

     Get the byte stream for this input source.

     The getEncoding method will return the character encoding for this
     byte stream, or ‘None’ if unknown.

 -- Method: InputSource.setCharacterStream (charfile)

     Set the character stream (a *note text file: 13d9.) for this input
     source.

     If there is a character stream specified, the SAX parser will
     ignore any byte stream and will not attempt to open a URI
     connection to the system identifier.

 -- Method: InputSource.getCharacterStream ()

     Get the character stream for this input source.


File: python.info,  Node: The Attributes Interface,  Next: The AttributesNS Interface,  Prev: InputSource Objects,  Up: xml sax xmlreader — Interface for XML parsers

5.20.12.5 The ‘Attributes’ Interface
....................................

‘Attributes’ objects implement a portion of the *note mapping protocol:
c0b, including the methods ‘copy()’, ‘get()’, *note __contains__(): dee,
‘items()’, ‘keys()’, and ‘values()’.  The following methods are also
provided:

 -- Method: Attributes.getLength ()

     Return the number of attributes.

 -- Method: Attributes.getNames ()

     Return the names of the attributes.

 -- Method: Attributes.getType (name)

     Returns the type of the attribute `name', which is normally
     ‘'CDATA'’.

 -- Method: Attributes.getValue (name)

     Return the value of attribute `name'.


File: python.info,  Node: The AttributesNS Interface,  Prev: The Attributes Interface,  Up: xml sax xmlreader — Interface for XML parsers

5.20.12.6 The ‘AttributesNS’ Interface
......................................

This interface is a subtype of the ‘Attributes’ interface (see section
*note The Attributes Interface: 2c52.).  All methods supported by that
interface are also available on ‘AttributesNS’ objects.

The following methods are also available:

 -- Method: AttributesNS.getValueByQName (name)

     Return the value for a qualified name.

 -- Method: AttributesNS.getNameByQName (name)

     Return the ‘(namespace, localname)’ pair for a qualified `name'.

 -- Method: AttributesNS.getQNameByName (name)

     Return the qualified name for a ‘(namespace, localname)’ pair.

 -- Method: AttributesNS.getQNames ()

     Return the qualified names of all attributes.


File: python.info,  Node: xml parsers expat — Fast XML parsing using Expat,  Prev: xml sax xmlreader — Interface for XML parsers,  Up: Structured Markup Processing Tools

5.20.13 ‘xml.parsers.expat’ — Fast XML parsing using Expat
----------------------------------------------------------

__________________________________________________________________

     Warning: The ‘pyexpat’ module is not secure against maliciously
     constructed data.  If you need to parse untrusted or
     unauthenticated data see *note XML vulnerabilities: 2b34.

The *note xml.parsers.expat: 141. module is a Python interface to the
Expat non-validating XML parser.  The module provides a single extension
type, ‘xmlparser’, that represents the current state of an XML parser.
After an ‘xmlparser’ object has been created, various attributes of the
object can be set to handler functions.  When an XML document is then
fed to the parser, the handler functions are called for the character
data and markup in the XML document.

This module uses the ‘pyexpat’ module to provide access to the Expat
parser.  Direct use of the ‘pyexpat’ module is deprecated.

This module provides one exception and one type object:

 -- Exception: xml.parsers.expat.ExpatError

     The exception raised when Expat reports an error.  See section
     *note ExpatError Exceptions: 2ca5. for more information on
     interpreting Expat errors.

 -- Exception: xml.parsers.expat.error

     Alias for *note ExpatError: cd8.

 -- Data: xml.parsers.expat.XMLParserType

     The type of the return values from the *note ParserCreate(): 2ca8.
     function.

The *note xml.parsers.expat: 141. module contains two functions:

 -- Function: xml.parsers.expat.ErrorString (errno)

     Returns an explanatory string for a given error number `errno'.

 -- Function: xml.parsers.expat.ParserCreate (encoding=None,
          namespace_separator=None)

     Creates and returns a new ‘xmlparser’ object.  `encoding', if
     specified, must be a string naming the encoding used by the XML
     data.  Expat doesn’t support as many encodings as Python does, and
     its repertoire of encodings can’t be extended; it supports UTF-8,
     UTF-16, ISO-8859-1 (Latin1), and ASCII. If `encoding' (1) is given
     it will override the implicit or explicit encoding of the document.

     Expat can optionally do XML namespace processing for you, enabled
     by providing a value for `namespace_separator'.  The value must be
     a one-character string; a *note ValueError: 16d. will be raised if
     the string has an illegal length (‘None’ is considered the same as
     omission).  When namespace processing is enabled, element type
     names and attribute names that belong to a namespace will be
     expanded.  The element name passed to the element handlers
     ‘StartElementHandler’ and ‘EndElementHandler’ will be the
     concatenation of the namespace URI, the namespace separator
     character, and the local part of the name.  If the namespace
     separator is a zero byte (‘chr(0)’) then the namespace URI and the
     local part will be concatenated without any separator.

     For example, if `namespace_separator' is set to a space character
     (‘' '’) and the following document is parsed:

          <?xml version="1.0"?>
          <root xmlns    = "http://default-namespace.org/"
                xmlns:py = "http://www.python.org/ns/">
            <py:elem1 />
            <elem2 xmlns="" />
          </root>

     ‘StartElementHandler’ will receive the following strings for each
     element:

          http://default-namespace.org/ root
          http://www.python.org/ns/ elem1
          elem2

     Due to limitations in the ‘Expat’ library used by ‘pyexpat’, the
     ‘xmlparser’ instance returned can only be used to parse a single
     XML document.  Call ‘ParserCreate’ for each document to provide
     unique parser instances.

See also
........

The Expat XML Parser(2)

     Home page of the Expat project.

* Menu:

* XMLParser Objects: XMLParser Objects<2>.
* ExpatError Exceptions::
* Example: Example<12>.
* Content Model Descriptions::
* Expat error constants::

   ---------- Footnotes ----------

   (1) (1) The encoding string included in XML output should conform to
the appropriate standards.  For example, “UTF-8” is valid, but “UTF8” is
not.  See
‘https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl’ and
‘https://www.iana.org/assignments/character-sets/character-sets.xhtml’.

   (2) http://www.libexpat.org/


File: python.info,  Node: XMLParser Objects<2>,  Next: ExpatError Exceptions,  Up: xml parsers expat — Fast XML parsing using Expat

5.20.13.1 XMLParser Objects
...........................

‘xmlparser’ objects have the following methods:

 -- Method: xmlparser.Parse (data[, isfinal])

     Parses the contents of the string `data', calling the appropriate
     handler functions to process the parsed data.  `isfinal' must be
     true on the final call to this method; it allows the parsing of a
     single file in fragments, not the submission of multiple files.
     `data' can be the empty string at any time.

 -- Method: xmlparser.ParseFile (file)

     Parse XML data reading from the object `file'.  `file' only needs
     to provide the ‘read(nbytes)’ method, returning the empty string
     when there’s no more data.

 -- Method: xmlparser.SetBase (base)

     Sets the base to be used for resolving relative URIs in system
     identifiers in declarations.  Resolving relative identifiers is
     left to the application: this value will be passed through as the
     `base' argument to the *note ExternalEntityRefHandler(): 2caf,
     *note NotationDeclHandler(): 2cb0, and *note
     UnparsedEntityDeclHandler(): 2cb1. functions.

 -- Method: xmlparser.GetBase ()

     Returns a string containing the base set by a previous call to
     *note SetBase(): 2cae, or ‘None’ if *note SetBase(): 2cae. hasn’t
     been called.

 -- Method: xmlparser.GetInputContext ()

     Returns the input data that generated the current event as a
     string.  The data is in the encoding of the entity which contains
     the text.  When called while an event handler is not active, the
     return value is ‘None’.

 -- Method: xmlparser.ExternalEntityParserCreate (context[, encoding])

     Create a “child” parser which can be used to parse an external
     parsed entity referred to by content parsed by the parent parser.
     The `context' parameter should be the string passed to the *note
     ExternalEntityRefHandler(): 2caf. handler function, described
     below.  The child parser is created with the *note
     ordered_attributes: 2cb5. and *note specified_attributes: 2cb6. set
     to the values of this parser.

 -- Method: xmlparser.SetParamEntityParsing (flag)

     Control parsing of parameter entities (including the external DTD
     subset).  Possible `flag' values are
     ‘XML_PARAM_ENTITY_PARSING_NEVER’,
     ‘XML_PARAM_ENTITY_PARSING_UNLESS_STANDALONE’ and
     ‘XML_PARAM_ENTITY_PARSING_ALWAYS’.  Return true if setting the flag
     was successful.

 -- Method: xmlparser.UseForeignDTD ([flag])

     Calling this with a true value for `flag' (the default) will cause
     Expat to call the *note ExternalEntityRefHandler: 2caf. with *note
     None: 203. for all arguments to allow an alternate DTD to be
     loaded.  If the document does not contain a document type
     declaration, the *note ExternalEntityRefHandler: 2caf. will still
     be called, but the *note StartDoctypeDeclHandler: 2cb9. and *note
     EndDoctypeDeclHandler: 2cba. will not be called.

     Passing a false value for `flag' will cancel a previous call that
     passed a true value, but otherwise has no effect.

     This method can only be called before the *note Parse(): 2cac. or
     *note ParseFile(): 2cad. methods are called; calling it after
     either of those have been called causes *note ExpatError: cd8. to
     be raised with the *note code: 1a. attribute set to
     ‘errors.codes[errors.XML_ERROR_CANT_CHANGE_FEATURE_ONCE_PARSING]’.

‘xmlparser’ objects have the following attributes:

 -- Attribute: xmlparser.buffer_size

     The size of the buffer used when *note buffer_text: 2cbc. is true.
     A new buffer size can be set by assigning a new integer value to
     this attribute.  When the size is changed, the buffer will be
     flushed.

 -- Attribute: xmlparser.buffer_text

     Setting this to true causes the ‘xmlparser’ object to buffer
     textual content returned by Expat to avoid multiple calls to the
     *note CharacterDataHandler(): 2cbd. callback whenever possible.
     This can improve performance substantially since Expat normally
     breaks character data into chunks at every line ending.  This
     attribute is false by default, and may be changed at any time.

 -- Attribute: xmlparser.buffer_used

     If *note buffer_text: 2cbc. is enabled, the number of bytes stored
     in the buffer.  These bytes represent UTF-8 encoded text.  This
     attribute has no meaningful interpretation when *note buffer_text:
     2cbc. is false.

 -- Attribute: xmlparser.ordered_attributes

     Setting this attribute to a non-zero integer causes the attributes
     to be reported as a list rather than a dictionary.  The attributes
     are presented in the order found in the document text.  For each
     attribute, two list entries are presented: the attribute name and
     the attribute value.  (Older versions of this module also used this
     format.)  By default, this attribute is false; it may be changed at
     any time.

 -- Attribute: xmlparser.specified_attributes

     If set to a non-zero integer, the parser will report only those
     attributes which were specified in the document instance and not
     those which were derived from attribute declarations.  Applications
     which set this need to be especially careful to use what additional
     information is available from the declarations as needed to comply
     with the standards for the behavior of XML processors.  By default,
     this attribute is false; it may be changed at any time.

The following attributes contain values relating to the most recent
error encountered by an ‘xmlparser’ object, and will only have correct
values once a call to ‘Parse()’ or ‘ParseFile()’ has raised an *note
xml.parsers.expat.ExpatError: cd8. exception.

 -- Attribute: xmlparser.ErrorByteIndex

     Byte index at which an error occurred.

 -- Attribute: xmlparser.ErrorCode

     Numeric code specifying the problem.  This value can be passed to
     the *note ErrorString(): 2ca9. function, or compared to one of the
     constants defined in the ‘errors’ object.

 -- Attribute: xmlparser.ErrorColumnNumber

     Column number at which an error occurred.

 -- Attribute: xmlparser.ErrorLineNumber

     Line number at which an error occurred.

The following attributes contain values relating to the current parse
location in an ‘xmlparser’ object.  During a callback reporting a parse
event they indicate the location of the first of the sequence of
characters that generated the event.  When called outside of a callback,
the position indicated will be just past the last parse event
(regardless of whether there was an associated callback).

 -- Attribute: xmlparser.CurrentByteIndex

     Current byte index in the parser input.

 -- Attribute: xmlparser.CurrentColumnNumber

     Current column number in the parser input.

 -- Attribute: xmlparser.CurrentLineNumber

     Current line number in the parser input.

Here is the list of handlers that can be set.  To set a handler on an
‘xmlparser’ object `o', use ‘o.handlername = func’.  `handlername' must
be taken from the following list, and `func' must be a callable object
accepting the correct number of arguments.  The arguments are all
strings, unless otherwise stated.

 -- Method: xmlparser.XmlDeclHandler (version, encoding, standalone)

     Called when the XML declaration is parsed.  The XML declaration is
     the (optional) declaration of the applicable version of the XML
     recommendation, the encoding of the document text, and an optional
     “standalone” declaration.  `version' and `encoding' will be
     strings, and `standalone' will be ‘1’ if the document is declared
     standalone, ‘0’ if it is declared not to be standalone, or ‘-1’ if
     the standalone clause was omitted.  This is only available with
     Expat version 1.95.0 or newer.

 -- Method: xmlparser.StartDoctypeDeclHandler (doctypeName, systemId,
          publicId, has_internal_subset)

     Called when Expat begins parsing the document type declaration
     (‘<!DOCTYPE ...’).  The `doctypeName' is provided exactly as
     presented.  The `systemId' and `publicId' parameters give the
     system and public identifiers if specified, or ‘None’ if omitted.
     `has_internal_subset' will be true if the document contains and
     internal document declaration subset.  This requires Expat version
     1.2 or newer.

 -- Method: xmlparser.EndDoctypeDeclHandler ()

     Called when Expat is done parsing the document type declaration.
     This requires Expat version 1.2 or newer.

 -- Method: xmlparser.ElementDeclHandler (name, model)

     Called once for each element type declaration.  `name' is the name
     of the element type, and `model' is a representation of the content
     model.

 -- Method: xmlparser.AttlistDeclHandler (elname, attname, type,
          default, required)

     Called for each declared attribute for an element type.  If an
     attribute list declaration declares three attributes, this handler
     is called three times, once for each attribute.  `elname' is the
     name of the element to which the declaration applies and `attname'
     is the name of the attribute declared.  The attribute type is a
     string passed as `type'; the possible values are ‘'CDATA'’, ‘'ID'’,
     ‘'IDREF'’, … `default' gives the default value for the attribute
     used when the attribute is not specified by the document instance,
     or ‘None’ if there is no default value (‘#IMPLIED’ values).  If the
     attribute is required to be given in the document instance,
     `required' will be true.  This requires Expat version 1.95.0 or
     newer.

 -- Method: xmlparser.StartElementHandler (name, attributes)

     Called for the start of every element.  `name' is a string
     containing the element name, and `attributes' is the element
     attributes.  If *note ordered_attributes: 2cb5. is true, this is a
     list (see *note ordered_attributes: 2cb5. for a full description).
     Otherwise it’s a dictionary mapping names to values.

 -- Method: xmlparser.EndElementHandler (name)

     Called for the end of every element.

 -- Method: xmlparser.ProcessingInstructionHandler (target, data)

     Called for every processing instruction.

 -- Method: xmlparser.CharacterDataHandler (data)

     Called for character data.  This will be called for normal
     character data, CDATA marked content, and ignorable whitespace.
     Applications which must distinguish these cases can use the *note
     StartCdataSectionHandler: 2ccc, *note EndCdataSectionHandler: 2ccd,
     and *note ElementDeclHandler: 2cc7. callbacks to collect the
     required information.

 -- Method: xmlparser.UnparsedEntityDeclHandler (entityName, base,
          systemId, publicId, notationName)

     Called for unparsed (NDATA) entity declarations.  This is only
     present for version 1.2 of the Expat library; for more recent
     versions, use *note EntityDeclHandler: 2cce. instead.  (The
     underlying function in the Expat library has been declared
     obsolete.)

 -- Method: xmlparser.EntityDeclHandler (entityName,
          is_parameter_entity, value, base, systemId, publicId,
          notationName)

     Called for all entity declarations.  For parameter and internal
     entities, `value' will be a string giving the declared contents of
     the entity; this will be ‘None’ for external entities.  The
     `notationName' parameter will be ‘None’ for parsed entities, and
     the name of the notation for unparsed entities.
     `is_parameter_entity' will be true if the entity is a parameter
     entity or false for general entities (most applications only need
     to be concerned with general entities).  This is only available
     starting with version 1.95.0 of the Expat library.

 -- Method: xmlparser.NotationDeclHandler (notationName, base, systemId,
          publicId)

     Called for notation declarations.  `notationName', `base', and
     `systemId', and `publicId' are strings if given.  If the public
     identifier is omitted, `publicId' will be ‘None’.

 -- Method: xmlparser.StartNamespaceDeclHandler (prefix, uri)

     Called when an element contains a namespace declaration.  Namespace
     declarations are processed before the *note StartElementHandler:
     2cc9. is called for the element on which declarations are placed.

 -- Method: xmlparser.EndNamespaceDeclHandler (prefix)

     Called when the closing tag is reached for an element that
     contained a namespace declaration.  This is called once for each
     namespace declaration on the element in the reverse of the order
     for which the *note StartNamespaceDeclHandler: 2ccf. was called to
     indicate the start of each namespace declaration’s scope.  Calls to
     this handler are made after the corresponding *note
     EndElementHandler: 2cca. for the end of the element.

 -- Method: xmlparser.CommentHandler (data)

     Called for comments.  `data' is the text of the comment, excluding
     the leading ‘'<!-’‘-'’ and trailing ‘'-’‘->'’.

 -- Method: xmlparser.StartCdataSectionHandler ()

     Called at the start of a CDATA section.  This and *note
     EndCdataSectionHandler: 2ccd. are needed to be able to identify the
     syntactical start and end for CDATA sections.

 -- Method: xmlparser.EndCdataSectionHandler ()

     Called at the end of a CDATA section.

 -- Method: xmlparser.DefaultHandler (data)

     Called for any characters in the XML document for which no
     applicable handler has been specified.  This means characters that
     are part of a construct which could be reported, but for which no
     handler has been supplied.

 -- Method: xmlparser.DefaultHandlerExpand (data)

     This is the same as the *note DefaultHandler(): 2cd2, but doesn’t
     inhibit expansion of internal entities.  The entity reference will
     not be passed to the default handler.

 -- Method: xmlparser.NotStandaloneHandler ()

     Called if the XML document hasn’t been declared as being a
     standalone document.  This happens when there is an external subset
     or a reference to a parameter entity, but the XML declaration does
     not set standalone to ‘yes’ in an XML declaration.  If this handler
     returns ‘0’, then the parser will raise an
     ‘XML_ERROR_NOT_STANDALONE’ error.  If this handler is not set, no
     exception is raised by the parser for this condition.

 -- Method: xmlparser.ExternalEntityRefHandler (context, base, systemId,
          publicId)

     Called for references to external entities.  `base' is the current
     base, as set by a previous call to *note SetBase(): 2cae.  The
     public and system identifiers, `systemId' and `publicId', are
     strings if given; if the public identifier is not given, `publicId'
     will be ‘None’.  The `context' value is opaque and should only be
     used as described below.

     For external entities to be parsed, this handler must be
     implemented.  It is responsible for creating the sub-parser using
     ‘ExternalEntityParserCreate(context)’, initializing it with the
     appropriate callbacks, and parsing the entity.  This handler should
     return an integer; if it returns ‘0’, the parser will raise an
     ‘XML_ERROR_EXTERNAL_ENTITY_HANDLING’ error, otherwise parsing will
     continue.

     If this handler is not provided, external entities are reported by
     the *note DefaultHandler: 2cd2. callback, if provided.


File: python.info,  Node: ExpatError Exceptions,  Next: Example<12>,  Prev: XMLParser Objects<2>,  Up: xml parsers expat — Fast XML parsing using Expat

5.20.13.2 ExpatError Exceptions
...............................

*note ExpatError: cd8. exceptions have a number of interesting
attributes:

 -- Attribute: ExpatError.code

     Expat’s internal error number for the specific error.  The *note
     errors.messages: 2cd7. dictionary maps these error numbers to
     Expat’s error messages.  For example:

          from xml.parsers.expat import ParserCreate, ExpatError, errors

          p = ParserCreate()
          try:
              p.Parse(some_xml_document)
          except ExpatError as err:
              print("Error:", errors.messages[err.code])

     The *note errors: 142. module also provides error message constants
     and a dictionary *note codes: 2cd8. mapping these messages back to
     the error codes, see below.

 -- Attribute: ExpatError.lineno

     Line number on which the error was detected.  The first line is
     numbered ‘1’.

 -- Attribute: ExpatError.offset

     Character offset into the line where the error occurred.  The first
     column is numbered ‘0’.


File: python.info,  Node: Example<12>,  Next: Content Model Descriptions,  Prev: ExpatError Exceptions,  Up: xml parsers expat — Fast XML parsing using Expat

5.20.13.3 Example
.................

The following program defines three handlers that just print out their
arguments.

     import xml.parsers.expat

     # 3 handler functions
     def start_element(name, attrs):
         print('Start element:', name, attrs)
     def end_element(name):
         print('End element:', name)
     def char_data(data):
         print('Character data:', repr(data))

     p = xml.parsers.expat.ParserCreate()

     p.StartElementHandler = start_element
     p.EndElementHandler = end_element
     p.CharacterDataHandler = char_data

     p.Parse("""<?xml version="1.0"?>
     <parent id="top"><child1 name="paul">Text goes here</child1>
     <child2 name="fred">More text</child2>
     </parent>""", 1)

The output from this program is:

     Start element: parent {'id': 'top'}
     Start element: child1 {'name': 'paul'}
     Character data: 'Text goes here'
     End element: child1
     Character data: '\n'
     Start element: child2 {'name': 'fred'}
     Character data: 'More text'
     End element: child2
     Character data: '\n'
     End element: parent


File: python.info,  Node: Content Model Descriptions,  Next: Expat error constants,  Prev: Example<12>,  Up: xml parsers expat — Fast XML parsing using Expat

5.20.13.4 Content Model Descriptions
....................................

Content models are described using nested tuples.  Each tuple contains
four values: the type, the quantifier, the name, and a tuple of
children.  Children are simply additional content model descriptions.

The values of the first two fields are constants defined in the *note
xml.parsers.expat.model: 143. module.  These constants can be collected
in two groups: the model type group and the quantifier group.

The constants in the model type group are:

 -- Data: xml.parsers.expat.model.XML_CTYPE_ANY

     The element named by the model name was declared to have a content
     model of ‘ANY’.

 -- Data: xml.parsers.expat.model.XML_CTYPE_CHOICE

     The named element allows a choice from a number of options; this is
     used for content models such as ‘(A | B | C)’.

 -- Data: xml.parsers.expat.model.XML_CTYPE_EMPTY

     Elements which are declared to be ‘EMPTY’ have this model type.

 -- Data: xml.parsers.expat.model.XML_CTYPE_MIXED

 -- Data: xml.parsers.expat.model.XML_CTYPE_NAME

 -- Data: xml.parsers.expat.model.XML_CTYPE_SEQ

     Models which represent a series of models which follow one after
     the other are indicated with this model type.  This is used for
     models such as ‘(A, B, C)’.

The constants in the quantifier group are:

 -- Data: xml.parsers.expat.model.XML_CQUANT_NONE

     No modifier is given, so it can appear exactly once, as for ‘A’.

 -- Data: xml.parsers.expat.model.XML_CQUANT_OPT

     The model is optional: it can appear once or not at all, as for
     ‘A?’.

 -- Data: xml.parsers.expat.model.XML_CQUANT_PLUS

     The model must occur one or more times (like ‘A+’).

 -- Data: xml.parsers.expat.model.XML_CQUANT_REP

     The model must occur zero or more times, as for ‘A*’.


File: python.info,  Node: Expat error constants,  Prev: Content Model Descriptions,  Up: xml parsers expat — Fast XML parsing using Expat

5.20.13.5 Expat error constants
...............................

The following constants are provided in the *note
xml.parsers.expat.errors: 142. module.  These constants are useful in
interpreting some of the attributes of the ‘ExpatError’ exception
objects raised when an error has occurred.  Since for backwards
compatibility reasons, the constants’ value is the error `message' and
not the numeric error `code', you do this by comparing its *note code:
1a. attribute with ‘errors.codes[errors.XML_ERROR_`CONSTANT_NAME']’.

The ‘errors’ module has the following attributes:

 -- Data: xml.parsers.expat.errors.codes

     A dictionary mapping string descriptions to their error codes.

     New in version 3.2.

 -- Data: xml.parsers.expat.errors.messages

     A dictionary mapping numeric error codes to their string
     descriptions.

     New in version 3.2.

 -- Data: xml.parsers.expat.errors.XML_ERROR_ASYNC_ENTITY

 -- Data:
          xml.parsers.expat.errors.XML_ERROR_ATTRIBUTE_EXTERNAL_ENTITY_REF

     An entity reference in an attribute value referred to an external
     entity instead of an internal entity.

 -- Data: xml.parsers.expat.errors.XML_ERROR_BAD_CHAR_REF

     A character reference referred to a character which is illegal in
     XML (for example, character ‘0’, or ‘‘&#0;’’).

 -- Data: xml.parsers.expat.errors.XML_ERROR_BINARY_ENTITY_REF

     An entity reference referred to an entity which was declared with a
     notation, so cannot be parsed.

 -- Data: xml.parsers.expat.errors.XML_ERROR_DUPLICATE_ATTRIBUTE

     An attribute was used more than once in a start tag.

 -- Data: xml.parsers.expat.errors.XML_ERROR_INCORRECT_ENCODING

 -- Data: xml.parsers.expat.errors.XML_ERROR_INVALID_TOKEN

     Raised when an input byte could not properly be assigned to a
     character; for example, a NUL byte (value ‘0’) in a UTF-8 input
     stream.

 -- Data: xml.parsers.expat.errors.XML_ERROR_JUNK_AFTER_DOC_ELEMENT

     Something other than whitespace occurred after the document
     element.

 -- Data: xml.parsers.expat.errors.XML_ERROR_MISPLACED_XML_PI

     An XML declaration was found somewhere other than the start of the
     input data.

 -- Data: xml.parsers.expat.errors.XML_ERROR_NO_ELEMENTS

     The document contains no elements (XML requires all documents to
     contain exactly one top-level element)..

 -- Data: xml.parsers.expat.errors.XML_ERROR_NO_MEMORY

     Expat was not able to allocate memory internally.

 -- Data: xml.parsers.expat.errors.XML_ERROR_PARAM_ENTITY_REF

     A parameter entity reference was found where it was not allowed.

 -- Data: xml.parsers.expat.errors.XML_ERROR_PARTIAL_CHAR

     An incomplete character was found in the input.

 -- Data: xml.parsers.expat.errors.XML_ERROR_RECURSIVE_ENTITY_REF

     An entity reference contained another reference to the same entity;
     possibly via a different name, and possibly indirectly.

 -- Data: xml.parsers.expat.errors.XML_ERROR_SYNTAX

     Some unspecified syntax error was encountered.

 -- Data: xml.parsers.expat.errors.XML_ERROR_TAG_MISMATCH

     An end tag did not match the innermost open start tag.

 -- Data: xml.parsers.expat.errors.XML_ERROR_UNCLOSED_TOKEN

     Some token (such as a start tag) was not closed before the end of
     the stream or the next token was encountered.

 -- Data: xml.parsers.expat.errors.XML_ERROR_UNDEFINED_ENTITY

     A reference was made to an entity which was not defined.

 -- Data: xml.parsers.expat.errors.XML_ERROR_UNKNOWN_ENCODING

     The document encoding is not supported by Expat.

 -- Data: xml.parsers.expat.errors.XML_ERROR_UNCLOSED_CDATA_SECTION

     A CDATA marked section was not closed.

 -- Data: xml.parsers.expat.errors.XML_ERROR_EXTERNAL_ENTITY_HANDLING

 -- Data: xml.parsers.expat.errors.XML_ERROR_NOT_STANDALONE

     The parser determined that the document was not “standalone” though
     it declared itself to be in the XML declaration, and the
     ‘NotStandaloneHandler’ was set and returned ‘0’.

 -- Data: xml.parsers.expat.errors.XML_ERROR_UNEXPECTED_STATE

 -- Data: xml.parsers.expat.errors.XML_ERROR_ENTITY_DECLARED_IN_PE

 -- Data: xml.parsers.expat.errors.XML_ERROR_FEATURE_REQUIRES_XML_DTD

     An operation was requested that requires DTD support to be compiled
     in, but Expat was configured without DTD support.  This should
     never be reported by a standard build of the *note
     xml.parsers.expat: 141. module.

 -- Data:
          xml.parsers.expat.errors.XML_ERROR_CANT_CHANGE_FEATURE_ONCE_PARSING

     A behavioral change was requested after parsing started that can
     only be changed before parsing has started.  This is (currently)
     only raised by ‘UseForeignDTD()’.

 -- Data: xml.parsers.expat.errors.XML_ERROR_UNBOUND_PREFIX

     An undeclared prefix was found when namespace processing was
     enabled.

 -- Data: xml.parsers.expat.errors.XML_ERROR_UNDECLARING_PREFIX

     The document attempted to remove the namespace declaration
     associated with a prefix.

 -- Data: xml.parsers.expat.errors.XML_ERROR_INCOMPLETE_PE

     A parameter entity contained incomplete markup.

 -- Data: xml.parsers.expat.errors.XML_ERROR_XML_DECL

     The document contained no document element at all.

 -- Data: xml.parsers.expat.errors.XML_ERROR_TEXT_DECL

     There was an error parsing a text declaration in an external
     entity.

 -- Data: xml.parsers.expat.errors.XML_ERROR_PUBLICID

     Characters were found in the public id that are not allowed.

 -- Data: xml.parsers.expat.errors.XML_ERROR_SUSPENDED

     The requested operation was made on a suspended parser, but isn’t
     allowed.  This includes attempts to provide additional input or to
     stop the parser.

 -- Data: xml.parsers.expat.errors.XML_ERROR_NOT_SUSPENDED

     An attempt to resume the parser was made when the parser had not
     been suspended.

 -- Data: xml.parsers.expat.errors.XML_ERROR_ABORTED

     This should not be reported to Python applications.

 -- Data: xml.parsers.expat.errors.XML_ERROR_FINISHED

     The requested operation was made on a parser which was finished
     parsing input, but isn’t allowed.  This includes attempts to
     provide additional input or to stop the parser.

 -- Data: xml.parsers.expat.errors.XML_ERROR_SUSPEND_PE


File: python.info,  Node: Internet Protocols and Support,  Next: Multimedia Services,  Prev: Structured Markup Processing Tools,  Up: The Python Standard Library

5.21 Internet Protocols and Support
===================================

The modules described in this chapter implement Internet protocols and
support for related technology.  They are all implemented in Python.
Most of these modules require the presence of the system-dependent
module *note socket: ef, which is currently supported on most popular
platforms.  Here is an overview:

* Menu:

* webbrowser — Convenient Web-browser controller::
* cgi — Common Gateway Interface support::
* cgitb — Traceback manager for CGI scripts::
* wsgiref — WSGI Utilities and Reference Implementation::
* urllib — URL handling modules::
* urllib.request — Extensible library for opening URLs: urllib request — Extensible library for opening URLs.
* urllib.response — Response classes used by urllib: urllib response — Response classes used by urllib.
* urllib.parse — Parse URLs into components: urllib parse — Parse URLs into components.
* urllib.error — Exception classes raised by urllib.request: urllib error — Exception classes raised by urllib request.
* urllib.robotparser — Parser for robots.txt: urllib robotparser — Parser for robots txt.
* http — HTTP modules::
* http.client — HTTP protocol client: http client — HTTP protocol client.
* ftplib — FTP protocol client::
* poplib — POP3 protocol client::
* imaplib — IMAP4 protocol client::
* nntplib — NNTP protocol client::
* smtplib — SMTP protocol client::
* smtpd — SMTP Server::
* telnetlib — Telnet client::
* uuid — UUID objects according to RFC 4122::
* socketserver — A framework for network servers::
* http.server — HTTP servers: http server — HTTP servers.
* http.cookies — HTTP state management: http cookies — HTTP state management.
* http.cookiejar — Cookie handling for HTTP clients: http cookiejar — Cookie handling for HTTP clients.
* xmlrpc — XMLRPC server and client modules::
* xmlrpc.client — XML-RPC client access: xmlrpc client — XML-RPC client access.
* xmlrpc.server — Basic XML-RPC servers: xmlrpc server — Basic XML-RPC servers.
* ipaddress — IPv4/IPv6 manipulation library::


File: python.info,  Node: webbrowser — Convenient Web-browser controller,  Next: cgi — Common Gateway Interface support,  Up: Internet Protocols and Support

5.21.1 ‘webbrowser’ — Convenient Web-browser controller
-------------------------------------------------------

`Source code:' Lib/webbrowser.py(1)

__________________________________________________________________

The *note webbrowser: 132. module provides a high-level interface to
allow displaying Web-based documents to users.  Under most
circumstances, simply calling the *note open(): 2d0b. function from this
module will do the right thing.

Under Unix, graphical browsers are preferred under X11, but text-mode
browsers will be used if graphical browsers are not available or an X11
display isn’t available.  If text-mode browsers are used, the calling
process will block until the user exits the browser.

If the environment variable ‘BROWSER’ exists, it is interpreted as the
*note os.pathsep: 1486.-separated list of browsers to try ahead of the
platform defaults.  When the value of a list part contains the string
‘%s’, then it is interpreted as a literal browser command line to be
used with the argument URL substituted for ‘%s’; if the part does not
contain ‘%s’, it is simply interpreted as the name of the browser to
launch.  (2)

For non-Unix platforms, or when a remote browser is available on Unix,
the controlling process will not wait for the user to finish with the
browser, but allow the remote browser to maintain its own windows on the
display.  If remote browsers are not available on Unix, the controlling
process will launch a new browser and wait.

The script ‘webbrowser’ can be used as a command-line interface for the
module.  It accepts a URL as the argument.  It accepts the following
optional parameters: ‘-n’ opens the URL in a new browser window, if
possible; ‘-t’ opens the URL in a new browser page (“tab”).  The options
are, naturally, mutually exclusive.  Usage example:

     python -m webbrowser -t "https://www.python.org"

The following exception is defined:

 -- Exception: webbrowser.Error

     Exception raised when a browser control error occurs.

The following functions are defined:

 -- Function: webbrowser.open (url, new=0, autoraise=True)

     Display `url' using the default browser.  If `new' is 0, the `url'
     is opened in the same browser window if possible.  If `new' is 1, a
     new browser window is opened if possible.  If `new' is 2, a new
     browser page (“tab”) is opened if possible.  If `autoraise' is
     ‘True’, the window is raised if possible (note that under many
     window managers this will occur regardless of the setting of this
     variable).

     Note that on some platforms, trying to open a filename using this
     function, may work and start the operating system’s associated
     program.  However, this is neither supported nor portable.

     Raises an *note auditing event: fa1. ‘webbrowser.open’ with
     argument ‘url’.

 -- Function: webbrowser.open_new (url)

     Open `url' in a new window of the default browser, if possible,
     otherwise, open `url' in the only browser window.

 -- Function: webbrowser.open_new_tab (url)

     Open `url' in a new page (“tab”) of the default browser, if
     possible, otherwise equivalent to *note open_new(): 2d0d.

 -- Function: webbrowser.get (using=None)

     Return a controller object for the browser type `using'.  If
     `using' is ‘None’, return a controller for a default browser
     appropriate to the caller’s environment.

 -- Function: webbrowser.register (name, constructor, instance=None, *,
          preferred=False)

     Register the browser type `name'.  Once a browser type is
     registered, the *note get(): 2d0f. function can return a controller
     for that browser type.  If `instance' is not provided, or is
     ‘None’, `constructor' will be called without parameters to create
     an instance when needed.  If `instance' is provided, `constructor'
     will never be called, and may be ‘None’.

     Setting `preferred' to ‘True’ makes this browser a preferred result
     for a *note get(): 2d0f. call with no argument.  Otherwise, this
     entry point is only useful if you plan to either set the ‘BROWSER’
     variable or call *note get(): 2d0f. with a nonempty argument
     matching the name of a handler you declare.

     Changed in version 3.7: `preferred' keyword-only parameter was
     added.

A number of browser types are predefined.  This table gives the type
names that may be passed to the *note get(): 2d0f. function and the
corresponding instantiations for the controller classes, all defined in
this module.

Type Name                    Class Name                                    Notes
                                                                           
---------------------------------------------------------------------------------------
                                                                           
‘'mozilla'’                  ‘Mozilla('mozilla')’
                             
                                                                           
‘'firefox'’                  ‘Mozilla('mozilla')’
                             
                                                                           
‘'netscape'’                 ‘Mozilla('netscape')’
                             
                                                                           
‘'galeon'’                   ‘Galeon('galeon')’
                             
                                                                           
‘'epiphany'’                 ‘Galeon('epiphany')’
                             
                                                                           
‘'skipstone'’                ‘BackgroundBrowser('skipstone')’
                             
                                                                           
‘'kfmclient'’                ‘Konqueror()’                                 (1)
                                                                           
                                                                           
‘'konqueror'’                ‘Konqueror()’                                 (1)
                                                                           
                                                                           
‘'kfm'’                      ‘Konqueror()’                                 (1)
                                                                           
                                                                           
‘'mosaic'’                   ‘BackgroundBrowser('mosaic')’
                             
                                                                           
‘'opera'’                    ‘Opera()’
                             
                                                                           
‘'grail'’                    ‘Grail()’
                             
                                                                           
‘'links'’                    ‘GenericBrowser('links')’
                             
                                                                           
‘'elinks'’                   ‘Elinks('elinks')’
                             
                                                                           
‘'lynx'’                     ‘GenericBrowser('lynx')’
                             
                                                                           
‘'w3m'’                      ‘GenericBrowser('w3m')’
                             
                                                                           
‘'windows-default'’          ‘WindowsDefault’                              (2)
                                                                           
                                                                           
‘'macosx'’                   ‘MacOSXOSAScript('default')’                  (3)
                                                                           
                                                                           
‘'safari'’                   ‘MacOSXOSAScript('safari')’                   (3)
                                                                           
                                                                           
‘'google-chrome'’            ‘Chrome('google-chrome')’
                             
                                                                           
‘'chrome'’                   ‘Chrome('chrome')’
                             
                                                                           
‘'chromium'’                 ‘Chromium('chromium')’
                             
                                                                           
‘'chromium-browser'’         ‘Chromium('chromium-browser')’
                             

Notes:

  1. “Konqueror” is the file manager for the KDE desktop environment for
     Unix, and only makes sense to use if KDE is running.  Some way of
     reliably detecting KDE would be nice; the ‘KDEDIR’ variable is not
     sufficient.  Note also that the name “kfm” is used even when using
     the ‘konqueror’ command with KDE 2 — the implementation selects the
     best strategy for running Konqueror.

  2. Only on Windows platforms.

  3. Only on macOS platform.

New in version 3.3: Support for Chrome/Chromium has been added.

Here are some simple examples:

     url = 'https://docs.python.org/'

     # Open URL in a new tab, if a browser window is already open.
     webbrowser.open_new_tab(url)

     # Open URL in new window, raising the window if possible.
     webbrowser.open_new(url)

* Menu:

* Browser Controller Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/webbrowser.py

   (2) (1) Executables named here without a full path will be searched
in the directories given in the ‘PATH’ environment variable.


File: python.info,  Node: Browser Controller Objects,  Up: webbrowser — Convenient Web-browser controller

5.21.1.1 Browser Controller Objects
...................................

Browser controllers provide these methods which parallel three of the
module-level convenience functions:

 -- Method: controller.open (url, new=0, autoraise=True)

     Display `url' using the browser handled by this controller.  If
     `new' is 1, a new browser window is opened if possible.  If `new'
     is 2, a new browser page (“tab”) is opened if possible.

 -- Method: controller.open_new (url)

     Open `url' in a new window of the browser handled by this
     controller, if possible, otherwise, open `url' in the only browser
     window.  Alias *note open_new(): 2d0d.

 -- Method: controller.open_new_tab (url)

     Open `url' in a new page (“tab”) of the browser handled by this
     controller, if possible, otherwise equivalent to *note open_new():
     2d0d.


File: python.info,  Node: cgi — Common Gateway Interface support,  Next: cgitb — Traceback manager for CGI scripts,  Prev: webbrowser — Convenient Web-browser controller,  Up: Internet Protocols and Support

5.21.2 ‘cgi’ — Common Gateway Interface support
-----------------------------------------------

`Source code:' Lib/cgi.py(1)

__________________________________________________________________

Support module for Common Gateway Interface (CGI) scripts.

This module defines a number of utilities for use by CGI scripts written
in Python.

* Menu:

* Introduction: Introduction<10>.
* Using the cgi module::
* Higher Level Interface::
* Functions: Functions<9>.
* Caring about security::
* Installing your CGI script on a Unix system::
* Testing your CGI script::
* Debugging CGI scripts::
* Common problems and solutions::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/cgi.py


File: python.info,  Node: Introduction<10>,  Next: Using the cgi module,  Up: cgi — Common Gateway Interface support

5.21.2.1 Introduction
.....................

A CGI script is invoked by an HTTP server, usually to process user input
submitted through an HTML ‘<FORM>’ or ‘<ISINDEX>’ element.

Most often, CGI scripts live in the server’s special ‘cgi-bin’
directory.  The HTTP server places all sorts of information about the
request (such as the client’s hostname, the requested URL, the query
string, and lots of other goodies) in the script’s shell environment,
executes the script, and sends the script’s output back to the client.

The script’s input is connected to the client too, and sometimes the
form data is read this way; at other times the form data is passed via
the “query string” part of the URL. This module is intended to take care
of the different cases and provide a simpler interface to the Python
script.  It also provides a number of utilities that help in debugging
scripts, and the latest addition is support for file uploads from a form
(if your browser supports it).

The output of a CGI script should consist of two sections, separated by
a blank line.  The first section contains a number of headers, telling
the client what kind of data is following.  Python code to generate a
minimal header section looks like this:

     print("Content-Type: text/html")    # HTML is following
     print()                             # blank line, end of headers

The second section is usually HTML, which allows the client software to
display nicely formatted text with header, in-line images, etc.  Here’s
Python code that prints a simple piece of HTML:

     print("<TITLE>CGI script output</TITLE>")
     print("<H1>This is my first CGI script</H1>")
     print("Hello, world!")


File: python.info,  Node: Using the cgi module,  Next: Higher Level Interface,  Prev: Introduction<10>,  Up: cgi — Common Gateway Interface support

5.21.2.2 Using the cgi module
.............................

Begin by writing ‘import cgi’.

When you write a new script, consider adding these lines:

     import cgitb
     cgitb.enable()

This activates a special exception handler that will display detailed
reports in the Web browser if any errors occur.  If you’d rather not
show the guts of your program to users of your script, you can have the
reports saved to files instead, with code like this:

     import cgitb
     cgitb.enable(display=0, logdir="/path/to/logdir")

It’s very helpful to use this feature during script development.  The
reports produced by *note cgitb: 16. provide information that can save
you a lot of time in tracking down bugs.  You can always remove the
‘cgitb’ line later when you have tested your script and are confident
that it works correctly.

To get at submitted form data, use the ‘FieldStorage’ class.  If the
form contains non-ASCII characters, use the `encoding' keyword parameter
set to the value of the encoding defined for the document.  It is
usually contained in the META tag in the HEAD section of the HTML
document or by the ‘Content-Type’ header.  This reads the form contents
from the standard input or the environment (depending on the value of
various environment variables set according to the CGI standard).  Since
it may consume standard input, it should be instantiated only once.

The ‘FieldStorage’ instance can be indexed like a Python dictionary.  It
allows membership testing with the *note in: 179. operator, and also
supports the standard dictionary method *note keys(): cf4. and the
built-in function *note len(): 28b.  Form fields containing empty
strings are ignored and do not appear in the dictionary; to keep such
values, provide a true value for the optional `keep_blank_values'
keyword parameter when creating the ‘FieldStorage’ instance.

For instance, the following code (which assumes that the ‘Content-Type’
header and blank line have already been printed) checks that the fields
‘name’ and ‘addr’ are both set to a non-empty string:

     form = cgi.FieldStorage()
     if "name" not in form or "addr" not in form:
         print("<H1>Error</H1>")
         print("Please fill in the name and addr fields.")
         return
     print("<p>name:", form["name"].value)
     print("<p>addr:", form["addr"].value)
     ...further form processing here...

Here the fields, accessed through ‘form[key]’, are themselves instances
of ‘FieldStorage’ (or ‘MiniFieldStorage’, depending on the form
encoding).  The ‘value’ attribute of the instance yields the string
value of the field.  The ‘getvalue()’ method returns this string value
directly; it also accepts an optional second argument as a default to
return if the requested key is not present.

If the submitted form data contains more than one field with the same
name, the object retrieved by ‘form[key]’ is not a ‘FieldStorage’ or
‘MiniFieldStorage’ instance but a list of such instances.  Similarly, in
this situation, ‘form.getvalue(key)’ would return a list of strings.  If
you expect this possibility (when your HTML form contains multiple
fields with the same name), use the *note getlist(): 2d1c. method, which
always returns a list of values (so that you do not need to special-case
the single item case).  For example, this code concatenates any number
of username fields, separated by commas:

     value = form.getlist("username")
     usernames = ",".join(value)

If a field represents an uploaded file, accessing the value via the
‘value’ attribute or the ‘getvalue()’ method reads the entire file in
memory as bytes.  This may not be what you want.  You can test for an
uploaded file by testing either the ‘filename’ attribute or the ‘file’
attribute.  You can then read the data from the ‘file’ attribute before
it is automatically closed as part of the garbage collection of the
‘FieldStorage’ instance (the *note read(): 7f3. and *note readline():
1849. methods will return bytes):

     fileitem = form["userfile"]
     if fileitem.file:
         # It's an uploaded file; count lines
         linecount = 0
         while True:
             line = fileitem.file.readline()
             if not line: break
             linecount = linecount + 1

‘FieldStorage’ objects also support being used in a *note with: 7da.
statement, which will automatically close them when done.

If an error is encountered when obtaining the contents of an uploaded
file (for example, when the user interrupts the form submission by
clicking on a Back or Cancel button) the ‘done’ attribute of the object
for the field will be set to the value -1.

The file upload draft standard entertains the possibility of uploading
multiple files from one field (using a recursive ‘multipart/*’
encoding).  When this occurs, the item will be a dictionary-like
‘FieldStorage’ item.  This can be determined by testing its ‘type’
attribute, which should be ‘multipart/form-data’ (or perhaps another
MIME type matching ‘multipart/*’).  In this case, it can be iterated
over recursively just like the top-level form object.

When a form is submitted in the “old” format (as the query string or as
a single data part of type ‘application/x-www-form-urlencoded’), the
items will actually be instances of the class ‘MiniFieldStorage’.  In
this case, the ‘list’, ‘file’, and ‘filename’ attributes are always
‘None’.

A form submitted via POST that also has a query string will contain both
‘FieldStorage’ and ‘MiniFieldStorage’ items.

Changed in version 3.4: The ‘file’ attribute is automatically closed
upon the garbage collection of the creating ‘FieldStorage’ instance.

Changed in version 3.5: Added support for the context management
protocol to the ‘FieldStorage’ class.


File: python.info,  Node: Higher Level Interface,  Next: Functions<9>,  Prev: Using the cgi module,  Up: cgi — Common Gateway Interface support

5.21.2.3 Higher Level Interface
...............................

The previous section explains how to read CGI form data using the
‘FieldStorage’ class.  This section describes a higher level interface
which was added to this class to allow one to do it in a more readable
and intuitive way.  The interface doesn’t make the techniques described
in previous sections obsolete — they are still useful to process file
uploads efficiently, for example.

The interface consists of two simple methods.  Using the methods you can
process form data in a generic way, without the need to worry whether
only one or more values were posted under one name.

In the previous section, you learned to write following code anytime you
expected a user to post more than one value under one name:

     item = form.getvalue("item")
     if isinstance(item, list):
         # The user is requesting more than one item.
     else:
         # The user is requesting only one item.

This situation is common for example when a form contains a group of
multiple checkboxes with the same name:

     <input type="checkbox" name="item" value="1" />
     <input type="checkbox" name="item" value="2" />

In most situations, however, there’s only one form control with a
particular name in a form and then you expect and need only one value
associated with this name.  So you write a script containing for example
this code:

     user = form.getvalue("user").upper()

The problem with the code is that you should never expect that a client
will provide valid input to your scripts.  For example, if a curious
user appends another ‘user=foo’ pair to the query string, then the
script would crash, because in this situation the ‘getvalue("user")’
method call returns a list instead of a string.  Calling the *note
upper(): 1791. method on a list is not valid (since lists do not have a
method of this name) and results in an *note AttributeError: 4a2.
exception.

Therefore, the appropriate way to read form data values was to always
use the code which checks whether the obtained value is a single value
or a list of values.  That’s annoying and leads to less readable
scripts.

A more convenient approach is to use the methods *note getfirst(): 2d1e.
and *note getlist(): 2d1c. provided by this higher level interface.

 -- Method: FieldStorage.getfirst (name, default=None)

     This method always returns only one value associated with form
     field `name'.  The method returns only the first value in case that
     more values were posted under such name.  Please note that the
     order in which the values are received may vary from browser to
     browser and should not be counted on.  (1) If no such form field or
     value exists then the method returns the value specified by the
     optional parameter `default'.  This parameter defaults to ‘None’ if
     not specified.

 -- Method: FieldStorage.getlist (name)

     This method always returns a list of values associated with form
     field `name'.  The method returns an empty list if no such form
     field or value exists for `name'.  It returns a list consisting of
     one item if only one such value exists.

Using these methods you can write nice compact code:

     import cgi
     form = cgi.FieldStorage()
     user = form.getfirst("user", "").upper()    # This way it's safe.
     for item in form.getlist("item"):
         do_something(item)

   ---------- Footnotes ----------

   (1) (1) Note that some recent versions of the HTML specification do
state what order the field values should be supplied in, but knowing
whether a request was received from a conforming browser, or even from a
browser at all, is tedious and error-prone.


File: python.info,  Node: Functions<9>,  Next: Caring about security,  Prev: Higher Level Interface,  Up: cgi — Common Gateway Interface support

5.21.2.4 Functions
..................

These are useful if you want more control, or if you want to employ some
of the algorithms implemented in this module in other circumstances.

 -- Function: cgi.parse (fp=None, environ=os.environ,
          keep_blank_values=False, strict_parsing=False, separator="&")

     Parse a query in the environment or from a file (the file defaults
     to ‘sys.stdin’).  The `keep_blank_values', `strict_parsing' and
     `separator' parameters are passed to *note urllib.parse.parse_qs():
     27f. unchanged.

 -- Function: cgi.parse_multipart (fp, pdict, encoding="utf-8",
          errors="replace", separator="&")

     Parse input of type ‘multipart/form-data’ (for file uploads).
     Arguments are `fp' for the input file, `pdict' for a dictionary
     containing other parameters in the ‘Content-Type’ header, and
     `encoding', the request encoding.

     Returns a dictionary just like *note urllib.parse.parse_qs(): 27f.:
     keys are the field names, each value is a list of values for that
     field.  For non-file fields, the value is a list of strings.

     This is easy to use but not much good if you are expecting
     megabytes to be uploaded — in that case, use the ‘FieldStorage’
     class instead which is much more flexible.

     Changed in version 3.7: Added the `encoding' and `errors'
     parameters.  For non-file fields, the value is now a list of
     strings, not bytes.

     Changed in version 3.9.2: Added the `separator' parameter.

 -- Function: cgi.parse_header (string)

     Parse a MIME header (such as ‘Content-Type’) into a main value and
     a dictionary of parameters.

 -- Function: cgi.test ()

     Robust test CGI script, usable as main program.  Writes minimal
     HTTP headers and formats all information provided to the script in
     HTML format.

 -- Function: cgi.print_environ ()

     Format the shell environment in HTML.

 -- Function: cgi.print_form (form)

     Format a form in HTML.

 -- Function: cgi.print_directory ()

     Format the current directory in HTML.

 -- Function: cgi.print_environ_usage ()

     Print a list of useful (used by CGI) environment variables in HTML.


File: python.info,  Node: Caring about security,  Next: Installing your CGI script on a Unix system,  Prev: Functions<9>,  Up: cgi — Common Gateway Interface support

5.21.2.5 Caring about security
..............................

There’s one important rule: if you invoke an external program (via *note
os.system(): e86, *note os.popen(): 3cb. or other functions with similar
functionality), make very sure you don’t pass arbitrary strings received
from the client to the shell.  This is a well-known security hole
whereby clever hackers anywhere on the Web can exploit a gullible CGI
script to invoke arbitrary shell commands.  Even parts of the URL or
field names cannot be trusted, since the request doesn’t have to come
from your form!

To be on the safe side, if you must pass a string gotten from a form to
a shell command, you should make sure the string contains only
alphanumeric characters, dashes, underscores, and periods.


File: python.info,  Node: Installing your CGI script on a Unix system,  Next: Testing your CGI script,  Prev: Caring about security,  Up: cgi — Common Gateway Interface support

5.21.2.6 Installing your CGI script on a Unix system
....................................................

Read the documentation for your HTTP server and check with your local
system administrator to find the directory where CGI scripts should be
installed; usually this is in a directory ‘cgi-bin’ in the server tree.

Make sure that your script is readable and executable by “others”; the
Unix file mode should be ‘0o755’ octal (use ‘chmod 0755 filename’).
Make sure that the first line of the script contains ‘#!’ starting in
column 1 followed by the pathname of the Python interpreter, for
instance:

     #!/usr/local/bin/python

Make sure the Python interpreter exists and is executable by “others”.

Make sure that any files your script needs to read or write are readable
or writable, respectively, by “others” — their mode should be ‘0o644’
for readable and ‘0o666’ for writable.  This is because, for security
reasons, the HTTP server executes your script as user “nobody”, without
any special privileges.  It can only read (write, execute) files that
everybody can read (write, execute).  The current directory at execution
time is also different (it is usually the server’s cgi-bin directory)
and the set of environment variables is also different from what you get
when you log in.  In particular, don’t count on the shell’s search path
for executables ( ‘PATH’) or the Python module search path ( *note
PYTHONPATH: a34.) to be set to anything interesting.

If you need to load modules from a directory which is not on Python’s
default module search path, you can change the path in your script,
before importing other modules.  For example:

     import sys
     sys.path.insert(0, "/usr/home/joe/lib/python")
     sys.path.insert(0, "/usr/local/lib/python")

(This way, the directory inserted last will be searched first!)

Instructions for non-Unix systems will vary; check your HTTP server’s
documentation (it will usually have a section on CGI scripts).


File: python.info,  Node: Testing your CGI script,  Next: Debugging CGI scripts,  Prev: Installing your CGI script on a Unix system,  Up: cgi — Common Gateway Interface support

5.21.2.7 Testing your CGI script
................................

Unfortunately, a CGI script will generally not run when you try it from
the command line, and a script that works perfectly from the command
line may fail mysteriously when run from the server.  There’s one reason
why you should still test your script from the command line: if it
contains a syntax error, the Python interpreter won’t execute it at all,
and the HTTP server will most likely send a cryptic error to the client.

Assuming your script has no syntax errors, yet it does not work, you
have no choice but to read the next section.


File: python.info,  Node: Debugging CGI scripts,  Next: Common problems and solutions,  Prev: Testing your CGI script,  Up: cgi — Common Gateway Interface support

5.21.2.8 Debugging CGI scripts
..............................

First of all, check for trivial installation errors — reading the
section above on installing your CGI script carefully can save you a lot
of time.  If you wonder whether you have understood the installation
procedure correctly, try installing a copy of this module file
(‘cgi.py’) as a CGI script.  When invoked as a script, the file will
dump its environment and the contents of the form in HTML format.  Give
it the right mode etc., and send it a request.  If it’s installed in the
standard ‘cgi-bin’ directory, it should be possible to send it a request
by entering a URL into your browser of the form:

     http://yourhostname/cgi-bin/cgi.py?name=Joe+Blow&addr=At+Home

If this gives an error of type 404, the server cannot find the script –
perhaps you need to install it in a different directory.  If it gives
another error, there’s an installation problem that you should fix
before trying to go any further.  If you get a nicely formatted listing
of the environment and form content (in this example, the fields should
be listed as “addr” with value “At Home” and “name” with value “Joe
Blow”), the ‘cgi.py’ script has been installed correctly.  If you follow
the same procedure for your own script, you should now be able to debug
it.

The next step could be to call the *note cgi: 15. module’s *note test():
105. function from your script: replace its main code with the single
statement

     cgi.test()

This should produce the same results as those gotten from installing the
‘cgi.py’ file itself.

When an ordinary Python script raises an unhandled exception (for
whatever reason: of a typo in a module name, a file that can’t be
opened, etc.), the Python interpreter prints a nice traceback and exits.
While the Python interpreter will still do this when your CGI script
raises an exception, most likely the traceback will end up in one of the
HTTP server’s log files, or be discarded altogether.

Fortunately, once you have managed to get your script to execute `some'
code, you can easily send tracebacks to the Web browser using the *note
cgitb: 16. module.  If you haven’t done so already, just add the lines:

     import cgitb
     cgitb.enable()

to the top of your script.  Then try running it again; when a problem
occurs, you should see a detailed report that will likely make apparent
the cause of the crash.

If you suspect that there may be a problem in importing the *note cgitb:
16. module, you can use an even more robust approach (which only uses
built-in modules):

     import sys
     sys.stderr = sys.stdout
     print("Content-Type: text/plain")
     print()
     ...your code here...

This relies on the Python interpreter to print the traceback.  The
content type of the output is set to plain text, which disables all HTML
processing.  If your script works, the raw HTML will be displayed by
your client.  If it raises an exception, most likely after the first two
lines have been printed, a traceback will be displayed.  Because no HTML
interpretation is going on, the traceback will be readable.


File: python.info,  Node: Common problems and solutions,  Prev: Debugging CGI scripts,  Up: cgi — Common Gateway Interface support

5.21.2.9 Common problems and solutions
......................................

   * Most HTTP servers buffer the output from CGI scripts until the
     script is completed.  This means that it is not possible to display
     a progress report on the client’s display while the script is
     running.

   * Check the installation instructions above.

   * Check the HTTP server’s log files.  (‘tail -f logfile’ in a
     separate window may be useful!)

   * Always check a script for syntax errors first, by doing something
     like ‘python script.py’.

   * If your script does not have any syntax errors, try adding ‘import
     cgitb; cgitb.enable()’ to the top of the script.

   * When invoking external programs, make sure they can be found.
     Usually, this means using absolute path names — ‘PATH’ is usually
     not set to a very useful value in a CGI script.

   * When reading or writing external files, make sure they can be read
     or written by the userid under which your CGI script will be
     running: this is typically the userid under which the web server is
     running, or some explicitly specified userid for a web server’s
     ‘suexec’ feature.

   * Don’t try to give a CGI script a set-uid mode.  This doesn’t work
     on most systems, and is a security liability as well.


File: python.info,  Node: cgitb — Traceback manager for CGI scripts,  Next: wsgiref — WSGI Utilities and Reference Implementation,  Prev: cgi — Common Gateway Interface support,  Up: Internet Protocols and Support

5.21.3 ‘cgitb’ — Traceback manager for CGI scripts
--------------------------------------------------

`Source code:' Lib/cgitb.py(1)

__________________________________________________________________

The *note cgitb: 16. module provides a special exception handler for
Python scripts.  (Its name is a bit misleading.  It was originally
designed to display extensive traceback information in HTML for CGI
scripts.  It was later generalized to also display this information in
plain text.)  After this module is activated, if an uncaught exception
occurs, a detailed, formatted report will be displayed.  The report
includes a traceback showing excerpts of the source code for each level,
as well as the values of the arguments and local variables to currently
running functions, to help you debug the problem.  Optionally, you can
save this information to a file instead of sending it to the browser.

To enable this feature, simply add this to the top of your CGI script:

     import cgitb
     cgitb.enable()

The options to the *note enable(): 2d2f. function control whether the
report is displayed in the browser and whether the report is logged to a
file for later analysis.

 -- Function: cgitb.enable (display=1, logdir=None, context=5,
          format="html")

     This function causes the *note cgitb: 16. module to take over the
     interpreter’s default handling for exceptions by setting the value
     of *note sys.excepthook: f24.

     The optional argument `display' defaults to ‘1’ and can be set to
     ‘0’ to suppress sending the traceback to the browser.  If the
     argument `logdir' is present, the traceback reports are written to
     files.  The value of `logdir' should be a directory where these
     files will be placed.  The optional argument `context' is the
     number of lines of context to display around the current line of
     source code in the traceback; this defaults to ‘5’.  If the
     optional argument `format' is ‘"html"’, the output is formatted as
     HTML. Any other value forces plain text output.  The default value
     is ‘"html"’.

 -- Function: cgitb.text (info, context=5)

     This function handles the exception described by `info' (a 3-tuple
     containing the result of *note sys.exc_info(): d27.), formatting
     its traceback as text and returning the result as a string.  The
     optional argument `context' is the number of lines of context to
     display around the current line of source code in the traceback;
     this defaults to ‘5’.

 -- Function: cgitb.html (info, context=5)

     This function handles the exception described by `info' (a 3-tuple
     containing the result of *note sys.exc_info(): d27.), formatting
     its traceback as HTML and returning the result as a string.  The
     optional argument `context' is the number of lines of context to
     display around the current line of source code in the traceback;
     this defaults to ‘5’.

 -- Function: cgitb.handler (info=None)

     This function handles an exception using the default settings (that
     is, show a report in the browser, but don’t log to a file).  This
     can be used when you’ve caught an exception and want to report it
     using *note cgitb: 16.  The optional `info' argument should be a
     3-tuple containing an exception type, exception value, and
     traceback object, exactly like the tuple returned by *note
     sys.exc_info(): d27.  If the `info' argument is not supplied, the
     current exception is obtained from *note sys.exc_info(): d27.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/cgitb.py


File: python.info,  Node: wsgiref — WSGI Utilities and Reference Implementation,  Next: urllib — URL handling modules,  Prev: cgitb — Traceback manager for CGI scripts,  Up: Internet Protocols and Support

5.21.4 ‘wsgiref’ — WSGI Utilities and Reference Implementation
--------------------------------------------------------------

__________________________________________________________________

The Web Server Gateway Interface (WSGI) is a standard interface between
web server software and web applications written in Python.  Having a
standard interface makes it easy to use an application that supports
WSGI with a number of different web servers.

Only authors of web servers and programming frameworks need to know
every detail and corner case of the WSGI design.  You don’t need to
understand every detail of WSGI just to install a WSGI application or to
write a web application using an existing framework.

*note wsgiref: 135. is a reference implementation of the WSGI
specification that can be used to add WSGI support to a web server or
framework.  It provides utilities for manipulating WSGI environment
variables and response headers, base classes for implementing WSGI
servers, a demo HTTP server that serves WSGI applications, and a
validation tool that checks WSGI servers and applications for
conformance to the WSGI specification ( PEP 3333(1)).

See wsgi.readthedocs.io(2) for more information about WSGI, and links to
tutorials and other resources.

* Menu:

* wsgiref.util – WSGI environment utilities: wsgiref util – WSGI environment utilities.
* wsgiref.headers – WSGI response header tools: wsgiref headers – WSGI response header tools.
* wsgiref.simple_server – a simple WSGI HTTP server: wsgiref simple_server – a simple WSGI HTTP server.
* wsgiref.validate — WSGI conformance checker: wsgiref validate — WSGI conformance checker.
* wsgiref.handlers – server/gateway base classes: wsgiref handlers – server/gateway base classes.
* Examples: Examples<21>.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3333

   (2) https://wsgi.readthedocs.io/


File: python.info,  Node: wsgiref util – WSGI environment utilities,  Next: wsgiref headers – WSGI response header tools,  Up: wsgiref — WSGI Utilities and Reference Implementation

5.21.4.1 ‘wsgiref.util’ – WSGI environment utilities
....................................................

This module provides a variety of utility functions for working with
WSGI environments.  A WSGI environment is a dictionary containing HTTP
request variables as described in PEP 3333(1).  All of the functions
taking an `environ' parameter expect a WSGI-compliant dictionary to be
supplied; please see PEP 3333(2) for a detailed specification.

 -- Function: wsgiref.util.guess_scheme (environ)

     Return a guess for whether ‘wsgi.url_scheme’ should be “http” or
     “https”, by checking for a ‘HTTPS’ environment variable in the
     `environ' dictionary.  The return value is a string.

     This function is useful when creating a gateway that wraps CGI or a
     CGI-like protocol such as FastCGI. Typically, servers providing
     such protocols will include a ‘HTTPS’ variable with a value of “1”,
     “yes”, or “on” when a request is received via SSL. So, this
     function returns “https” if such a value is found, and “http”
     otherwise.

 -- Function: wsgiref.util.request_uri (environ, include_query=True)

     Return the full request URI, optionally including the query string,
     using the algorithm found in the “URL Reconstruction” section of
     PEP 3333(3).  If `include_query' is false, the query string is not
     included in the resulting URI.

 -- Function: wsgiref.util.application_uri (environ)

     Similar to *note request_uri(): 2d37, except that the ‘PATH_INFO’
     and ‘QUERY_STRING’ variables are ignored.  The result is the base
     URI of the application object addressed by the request.

 -- Function: wsgiref.util.shift_path_info (environ)

     Shift a single name from ‘PATH_INFO’ to ‘SCRIPT_NAME’ and return
     the name.  The `environ' dictionary is `modified' in-place; use a
     copy if you need to keep the original ‘PATH_INFO’ or ‘SCRIPT_NAME’
     intact.

     If there are no remaining path segments in ‘PATH_INFO’, ‘None’ is
     returned.

     Typically, this routine is used to process each portion of a
     request URI path, for example to treat the path as a series of
     dictionary keys.  This routine modifies the passed-in environment
     to make it suitable for invoking another WSGI application that is
     located at the target URI. For example, if there is a WSGI
     application at ‘/foo’, and the request URI path is ‘/foo/bar/baz’,
     and the WSGI application at ‘/foo’ calls *note shift_path_info():
     2d39, it will receive the string “bar”, and the environment will be
     updated to be suitable for passing to a WSGI application at
     ‘/foo/bar’.  That is, ‘SCRIPT_NAME’ will change from ‘/foo’ to
     ‘/foo/bar’, and ‘PATH_INFO’ will change from ‘/bar/baz’ to ‘/baz’.

     When ‘PATH_INFO’ is just a “/”, this routine returns an empty
     string and appends a trailing slash to ‘SCRIPT_NAME’, even though
     empty path segments are normally ignored, and ‘SCRIPT_NAME’ doesn’t
     normally end in a slash.  This is intentional behavior, to ensure
     that an application can tell the difference between URIs ending in
     ‘/x’ from ones ending in ‘/x/’ when using this routine to do object
     traversal.

 -- Function: wsgiref.util.setup_testing_defaults (environ)

     Update `environ' with trivial defaults for testing purposes.

     This routine adds various parameters required for WSGI, including
     ‘HTTP_HOST’, ‘SERVER_NAME’, ‘SERVER_PORT’, ‘REQUEST_METHOD’,
     ‘SCRIPT_NAME’, ‘PATH_INFO’, and all of the PEP 3333(4)-defined
     ‘wsgi.*’ variables.  It only supplies default values, and does not
     replace any existing settings for these variables.

     This routine is intended to make it easier for unit tests of WSGI
     servers and applications to set up dummy environments.  It should
     NOT be used by actual WSGI servers or applications, since the data
     is fake!

     Example usage:

          from wsgiref.util import setup_testing_defaults
          from wsgiref.simple_server import make_server

          # A relatively simple WSGI application. It's going to print out the
          # environment dictionary after being updated by setup_testing_defaults
          def simple_app(environ, start_response):
              setup_testing_defaults(environ)

              status = '200 OK'
              headers = [('Content-type', 'text/plain; charset=utf-8')]

              start_response(status, headers)

              ret = [("%s: %s\n" % (key, value)).encode("utf-8")
                     for key, value in environ.items()]
              return ret

          with make_server('', 8000, simple_app) as httpd:
              print("Serving on port 8000...")
              httpd.serve_forever()

In addition to the environment functions above, the *note wsgiref.util:
139. module also provides these miscellaneous utilities:

 -- Function: wsgiref.util.is_hop_by_hop (header_name)

     Return ‘True’ if ‘header_name’ is an HTTP/1.1 “Hop-by-Hop” header,
     as defined by RFC 2616(5).

 -- Class: wsgiref.util.FileWrapper (filelike, blksize=8192)

     A wrapper to convert a file-like object to an *note iterator: 1171.
     The resulting objects support both *note __getitem__(): 3a2. and
     *note __iter__(): 609. iteration styles, for compatibility with
     Python 2.1 and Jython.  As the object is iterated over, the
     optional `blksize' parameter will be repeatedly passed to the
     `filelike' object’s ‘read()’ method to obtain bytestrings to yield.
     When ‘read()’ returns an empty bytestring, iteration is ended and
     is not resumable.

     If `filelike' has a ‘close()’ method, the returned object will also
     have a ‘close()’ method, and it will invoke the `filelike' object’s
     ‘close()’ method when called.

     Example usage:

          from io import StringIO
          from wsgiref.util import FileWrapper

          # We're using a StringIO-buffer for as the file-like object
          filelike = StringIO("This is an example file-like object"*10)
          wrapper = FileWrapper(filelike, blksize=5)

          for chunk in wrapper:
              print(chunk)

     Deprecated since version 3.8: Support for *note sequence protocol:
     3a2. is deprecated.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3333

   (2) https://www.python.org/dev/peps/pep-3333

   (3) https://www.python.org/dev/peps/pep-3333

   (4) https://www.python.org/dev/peps/pep-3333

   (5) https://tools.ietf.org/html/rfc2616.html


File: python.info,  Node: wsgiref headers – WSGI response header tools,  Next: wsgiref simple_server – a simple WSGI HTTP server,  Prev: wsgiref util – WSGI environment utilities,  Up: wsgiref — WSGI Utilities and Reference Implementation

5.21.4.2 ‘wsgiref.headers’ – WSGI response header tools
.......................................................

This module provides a single class, *note Headers: 87e, for convenient
manipulation of WSGI response headers using a mapping-like interface.

 -- Class: wsgiref.headers.Headers ([headers])

     Create a mapping-like object wrapping `headers', which must be a
     list of header name/value tuples as described in PEP 3333(1).  The
     default value of `headers' is an empty list.

     *note Headers: 87e. objects support typical mapping operations
     including *note __getitem__(): 3a2, ‘get()’, *note __setitem__():
     d2a, ‘setdefault()’, *note __delitem__(): d2b. and *note
     __contains__(): dee.  For each of these methods, the key is the
     header name (treated case-insensitively), and the value is the
     first value associated with that header name.  Setting a header
     deletes any existing values for that header, then adds a new value
     at the end of the wrapped header list.  Headers’ existing order is
     generally maintained, with new headers added to the end of the
     wrapped list.

     Unlike a dictionary, *note Headers: 87e. objects do not raise an
     error when you try to get or delete a key that isn’t in the wrapped
     header list.  Getting a nonexistent header just returns ‘None’, and
     deleting a nonexistent header does nothing.

     *note Headers: 87e. objects also support ‘keys()’, ‘values()’, and
     ‘items()’ methods.  The lists returned by ‘keys()’ and ‘items()’
     can include the same key more than once if there is a multi-valued
     header.  The ‘len()’ of a *note Headers: 87e. object is the same as
     the length of its ‘items()’, which is the same as the length of the
     wrapped header list.  In fact, the ‘items()’ method just returns a
     copy of the wrapped header list.

     Calling ‘bytes()’ on a *note Headers: 87e. object returns a
     formatted bytestring suitable for transmission as HTTP response
     headers.  Each header is placed on a line with its value, separated
     by a colon and a space.  Each line is terminated by a carriage
     return and line feed, and the bytestring is terminated with a blank
     line.

     In addition to their mapping interface and formatting features,
     *note Headers: 87e. objects also have the following methods for
     querying and adding multi-valued headers, and for adding headers
     with MIME parameters:

      -- Method: get_all (name)

          Return a list of all the values for the named header.

          The returned list will be sorted in the order they appeared in
          the original header list or were added to this instance, and
          may contain duplicates.  Any fields deleted and re-inserted
          are always appended to the header list.  If no fields exist
          with the given name, returns an empty list.

      -- Method: add_header (name, value, **_params)

          Add a (possibly multi-valued) header, with optional MIME
          parameters specified via keyword arguments.

          `name' is the header field to add.  Keyword arguments can be
          used to set MIME parameters for the header field.  Each
          parameter must be a string or ‘None’.  Underscores in
          parameter names are converted to dashes, since dashes are
          illegal in Python identifiers, but many MIME parameter names
          include dashes.  If the parameter value is a string, it is
          added to the header value parameters in the form
          ‘name="value"’.  If it is ‘None’, only the parameter name is
          added.  (This is used for MIME parameters without a value.)
          Example usage:

               h.add_header('content-disposition', 'attachment', filename='bud.gif')

          The above will add a header that looks like this:

               Content-Disposition: attachment; filename="bud.gif"

     Changed in version 3.5: `headers' parameter is optional.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3333


File: python.info,  Node: wsgiref simple_server – a simple WSGI HTTP server,  Next: wsgiref validate — WSGI conformance checker,  Prev: wsgiref headers – WSGI response header tools,  Up: wsgiref — WSGI Utilities and Reference Implementation

5.21.4.3 ‘wsgiref.simple_server’ – a simple WSGI HTTP server
............................................................

This module implements a simple HTTP server (based on *note http.server:
96.) that serves WSGI applications.  Each server instance serves a
single WSGI application on a given host and port.  If you want to serve
multiple applications on a single host and port, you should create a
WSGI application that parses ‘PATH_INFO’ to select which application to
invoke for each request.  (E.g., using the ‘shift_path_info()’ function
from *note wsgiref.util: 139.)

 -- Function: wsgiref.simple_server.make_server (host, port, app,
          server_class=WSGIServer, handler_class=WSGIRequestHandler)

     Create a new WSGI server listening on `host' and `port', accepting
     connections for `app'.  The return value is an instance of the
     supplied `server_class', and will process requests using the
     specified `handler_class'.  `app' must be a WSGI application
     object, as defined by PEP 3333(1).

     Example usage:

          from wsgiref.simple_server import make_server, demo_app

          with make_server('', 8000, demo_app) as httpd:
              print("Serving HTTP on port 8000...")

              # Respond to requests until process is killed
              httpd.serve_forever()

              # Alternative: serve one request, then exit
              httpd.handle_request()

 -- Function: wsgiref.simple_server.demo_app (environ, start_response)

     This function is a small but complete WSGI application that returns
     a text page containing the message “Hello world!” and a list of the
     key/value pairs provided in the `environ' parameter.  It’s useful
     for verifying that a WSGI server (such as *note
     wsgiref.simple_server: 138.) is able to run a simple WSGI
     application correctly.

 -- Class: wsgiref.simple_server.WSGIServer (server_address,
          RequestHandlerClass)

     Create a *note WSGIServer: 2d42. instance.  `server_address' should
     be a ‘(host,port)’ tuple, and `RequestHandlerClass' should be the
     subclass of *note http.server.BaseHTTPRequestHandler: aec. that
     will be used to process requests.

     You do not normally need to call this constructor, as the *note
     make_server(): 2d40. function can handle all the details for you.

     *note WSGIServer: 2d42. is a subclass of *note
     http.server.HTTPServer: 2d43, so all of its methods (such as
     ‘serve_forever()’ and ‘handle_request()’) are available.  *note
     WSGIServer: 2d42. also provides these WSGI-specific methods:

      -- Method: set_app (application)

          Sets the callable `application' as the WSGI application that
          will receive requests.

      -- Method: get_app ()

          Returns the currently-set application callable.

     Normally, however, you do not need to use these additional methods,
     as *note set_app(): 2d44. is normally called by *note
     make_server(): 2d40, and the *note get_app(): 2d45. exists mainly
     for the benefit of request handler instances.

 -- Class: wsgiref.simple_server.WSGIRequestHandler (request,
          client_address, server)

     Create an HTTP handler for the given `request' (i.e.  a socket),
     `client_address' (a ‘(host,port)’ tuple), and `server' (*note
     WSGIServer: 2d42. instance).

     You do not need to create instances of this class directly; they
     are automatically created as needed by *note WSGIServer: 2d42.
     objects.  You can, however, subclass this class and supply it as a
     `handler_class' to the *note make_server(): 2d40. function.  Some
     possibly relevant methods for overriding in subclasses:

      -- Method: get_environ ()

          Returns a dictionary containing the WSGI environment for a
          request.  The default implementation copies the contents of
          the *note WSGIServer: 2d42. object’s ‘base_environ’ dictionary
          attribute and then adds various headers derived from the HTTP
          request.  Each call to this method should return a new
          dictionary containing all of the relevant CGI environment
          variables as specified in PEP 3333(2).

      -- Method: get_stderr ()

          Return the object that should be used as the ‘wsgi.errors’
          stream.  The default implementation just returns ‘sys.stderr’.

      -- Method: handle ()

          Process the HTTP request.  The default implementation creates
          a handler instance using a *note wsgiref.handlers: 136. class
          to implement the actual WSGI application interface.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3333

   (2) https://www.python.org/dev/peps/pep-3333


File: python.info,  Node: wsgiref validate — WSGI conformance checker,  Next: wsgiref handlers – server/gateway base classes,  Prev: wsgiref simple_server – a simple WSGI HTTP server,  Up: wsgiref — WSGI Utilities and Reference Implementation

5.21.4.4 ‘wsgiref.validate’ — WSGI conformance checker
......................................................

When creating new WSGI application objects, frameworks, servers, or
middleware, it can be useful to validate the new code’s conformance
using *note wsgiref.validate: 13a.  This module provides a function that
creates WSGI application objects that validate communications between a
WSGI server or gateway and a WSGI application object, to check both
sides for protocol conformance.

Note that this utility does not guarantee complete PEP 3333(1)
compliance; an absence of errors from this module does not necessarily
mean that errors do not exist.  However, if this module does produce an
error, then it is virtually certain that either the server or
application is not 100% compliant.

This module is based on the ‘paste.lint’ module from Ian Bicking’s
“Python Paste” library.

 -- Function: wsgiref.validate.validator (application)

     Wrap `application' and return a new WSGI application object.  The
     returned application will forward all requests to the original
     `application', and will check that both the `application' and the
     server invoking it are conforming to the WSGI specification and to
     RFC 2616(2).

     Any detected nonconformance results in an *note AssertionError:
     240. being raised; note, however, that how these errors are handled
     is server-dependent.  For example, *note wsgiref.simple_server:
     138. and other servers based on *note wsgiref.handlers: 136. (that
     don’t override the error handling methods to do something else)
     will simply output a message that an error has occurred, and dump
     the traceback to ‘sys.stderr’ or some other error stream.

     This wrapper may also generate output using the *note warnings:
     12f. module to indicate behaviors that are questionable but which
     may not actually be prohibited by PEP 3333(3).  Unless they are
     suppressed using Python command-line options or the *note warnings:
     12f. API, any such warnings will be written to ‘sys.stderr’ (`not'
     ‘wsgi.errors’, unless they happen to be the same object).

     Example usage:

          from wsgiref.validate import validator
          from wsgiref.simple_server import make_server

          # Our callable object which is intentionally not compliant to the
          # standard, so the validator is going to break
          def simple_app(environ, start_response):
              status = '200 OK'  # HTTP Status
              headers = [('Content-type', 'text/plain')]  # HTTP Headers
              start_response(status, headers)

              # This is going to break because we need to return a list, and
              # the validator is going to inform us
              return b"Hello World"

          # This is the application wrapped in a validator
          validator_app = validator(simple_app)

          with make_server('', 8000, validator_app) as httpd:
              print("Listening on port 8000....")
              httpd.serve_forever()

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3333

   (2) https://tools.ietf.org/html/rfc2616.html

   (3) https://www.python.org/dev/peps/pep-3333


File: python.info,  Node: wsgiref handlers – server/gateway base classes,  Next: Examples<21>,  Prev: wsgiref validate — WSGI conformance checker,  Up: wsgiref — WSGI Utilities and Reference Implementation

5.21.4.5 ‘wsgiref.handlers’ – server/gateway base classes
.........................................................

This module provides base handler classes for implementing WSGI servers
and gateways.  These base classes handle most of the work of
communicating with a WSGI application, as long as they are given a
CGI-like environment, along with input, output, and error streams.

 -- Class: wsgiref.handlers.CGIHandler

     CGI-based invocation via ‘sys.stdin’, ‘sys.stdout’, ‘sys.stderr’
     and ‘os.environ’.  This is useful when you have a WSGI application
     and want to run it as a CGI script.  Simply invoke
     ‘CGIHandler().run(app)’, where ‘app’ is the WSGI application object
     you wish to invoke.

     This class is a subclass of *note BaseCGIHandler: 2d4e. that sets
     ‘wsgi.run_once’ to true, ‘wsgi.multithread’ to false, and
     ‘wsgi.multiprocess’ to true, and always uses *note sys: fd. and
     *note os: c4. to obtain the necessary CGI streams and environment.

 -- Class: wsgiref.handlers.IISCGIHandler

     A specialized alternative to *note CGIHandler: 2d4d, for use when
     deploying on Microsoft’s IIS web server, without having set the
     config allowPathInfo option (IIS>=7) or metabase
     allowPathInfoForScriptMappings (IIS<7).

     By default, IIS gives a ‘PATH_INFO’ that duplicates the
     ‘SCRIPT_NAME’ at the front, causing problems for WSGI applications
     that wish to implement routing.  This handler strips any such
     duplicated path.

     IIS can be configured to pass the correct ‘PATH_INFO’, but this
     causes another bug where ‘PATH_TRANSLATED’ is wrong.  Luckily this
     variable is rarely used and is not guaranteed by WSGI. On IIS<7,
     though, the setting can only be made on a vhost level, affecting
     all other script mappings, many of which break when exposed to the
     ‘PATH_TRANSLATED’ bug.  For this reason IIS<7 is almost never
     deployed with the fix (Even IIS7 rarely uses it because there is
     still no UI for it.).

     There is no way for CGI code to tell whether the option was set, so
     a separate handler class is provided.  It is used in the same way
     as *note CGIHandler: 2d4d, i.e., by calling
     ‘IISCGIHandler().run(app)’, where ‘app’ is the WSGI application
     object you wish to invoke.

     New in version 3.2.

 -- Class: wsgiref.handlers.BaseCGIHandler (stdin, stdout, stderr,
          environ, multithread=True, multiprocess=False)

     Similar to *note CGIHandler: 2d4d, but instead of using the *note
     sys: fd. and *note os: c4. modules, the CGI environment and I/O
     streams are specified explicitly.  The `multithread' and
     `multiprocess' values are used to set the ‘wsgi.multithread’ and
     ‘wsgi.multiprocess’ flags for any applications run by the handler
     instance.

     This class is a subclass of *note SimpleHandler: 2d50. intended for
     use with software other than HTTP “origin servers”.  If you are
     writing a gateway protocol implementation (such as CGI, FastCGI,
     SCGI, etc.)  that uses a ‘Status:’ header to send an HTTP status,
     you probably want to subclass this instead of *note SimpleHandler:
     2d50.

 -- Class: wsgiref.handlers.SimpleHandler (stdin, stdout, stderr,
          environ, multithread=True, multiprocess=False)

     Similar to *note BaseCGIHandler: 2d4e, but designed for use with
     HTTP origin servers.  If you are writing an HTTP server
     implementation, you will probably want to subclass this instead of
     *note BaseCGIHandler: 2d4e.

     This class is a subclass of *note BaseHandler: 1107.  It overrides
     the *note __init__(): e23, ‘get_stdin()’, ‘get_stderr()’,
     ‘add_cgi_vars()’, ‘_write()’, and ‘_flush()’ methods to support
     explicitly setting the environment and streams via the constructor.
     The supplied environment and streams are stored in the ‘stdin’,
     ‘stdout’, ‘stderr’, and ‘environ’ attributes.

     The *note write(): 680. method of `stdout' should write each chunk
     in full, like *note io.BufferedIOBase: 67f.

 -- Class: wsgiref.handlers.BaseHandler

     This is an abstract base class for running WSGI applications.  Each
     instance will handle a single HTTP request, although in principle
     you could create a subclass that was reusable for multiple
     requests.

     *note BaseHandler: 1107. instances have only one method intended
     for external use:

      -- Method: run (app)

          Run the specified WSGI application, `app'.

     All of the other *note BaseHandler: 1107. methods are invoked by
     this method in the process of running the application, and thus
     exist primarily to allow customizing the process.

     The following methods MUST be overridden in a subclass:

      -- Method: _write (data)

          Buffer the bytes `data' for transmission to the client.  It’s
          okay if this method actually transmits the data; *note
          BaseHandler: 1107. just separates write and flush operations
          for greater efficiency when the underlying system actually has
          such a distinction.

      -- Method: _flush ()

          Force buffered data to be transmitted to the client.  It’s
          okay if this method is a no-op (i.e., if *note _write(): 2d52.
          actually sends the data).

      -- Method: get_stdin ()

          Return an input stream object suitable for use as the
          ‘wsgi.input’ of the request currently being processed.

      -- Method: get_stderr ()

          Return an output stream object suitable for use as the
          ‘wsgi.errors’ of the request currently being processed.

      -- Method: add_cgi_vars ()

          Insert CGI variables for the current request into the
          ‘environ’ attribute.

     Here are some other methods and attributes you may wish to
     override.  This list is only a summary, however, and does not
     include every method that can be overridden.  You should consult
     the docstrings and source code for additional information before
     attempting to create a customized *note BaseHandler: 1107.
     subclass.

     Attributes and methods for customizing the WSGI environment:

      -- Attribute: wsgi_multithread

          The value to be used for the ‘wsgi.multithread’ environment
          variable.  It defaults to true in *note BaseHandler: 1107, but
          may have a different default (or be set by the constructor) in
          the other subclasses.

      -- Attribute: wsgi_multiprocess

          The value to be used for the ‘wsgi.multiprocess’ environment
          variable.  It defaults to true in *note BaseHandler: 1107, but
          may have a different default (or be set by the constructor) in
          the other subclasses.

      -- Attribute: wsgi_run_once

          The value to be used for the ‘wsgi.run_once’ environment
          variable.  It defaults to false in *note BaseHandler: 1107,
          but *note CGIHandler: 2d4d. sets it to true by default.

      -- Attribute: os_environ

          The default environment variables to be included in every
          request’s WSGI environment.  By default, this is a copy of
          ‘os.environ’ at the time that *note wsgiref.handlers: 136. was
          imported, but subclasses can either create their own at the
          class or instance level.  Note that the dictionary should be
          considered read-only, since the default value is shared
          between multiple classes and instances.

      -- Attribute: server_software

          If the *note origin_server: 2d5c. attribute is set, this
          attribute’s value is used to set the default ‘SERVER_SOFTWARE’
          WSGI environment variable, and also to set a default ‘Server:’
          header in HTTP responses.  It is ignored for handlers (such as
          *note BaseCGIHandler: 2d4e. and *note CGIHandler: 2d4d.) that
          are not HTTP origin servers.

          Changed in version 3.3: The term “Python” is replaced with
          implementation specific term like “CPython”, “Jython” etc.

      -- Method: get_scheme ()

          Return the URL scheme being used for the current request.  The
          default implementation uses the ‘guess_scheme()’ function from
          *note wsgiref.util: 139. to guess whether the scheme should be
          “http” or “https”, based on the current request’s ‘environ’
          variables.

      -- Method: setup_environ ()

          Set the ‘environ’ attribute to a fully-populated WSGI
          environment.  The default implementation uses all of the above
          methods and attributes, plus the *note get_stdin(): 2d54,
          *note get_stderr(): 2d55, and *note add_cgi_vars(): 2d56.
          methods and the *note wsgi_file_wrapper: 2d5f. attribute.  It
          also inserts a ‘SERVER_SOFTWARE’ key if not present, as long
          as the *note origin_server: 2d5c. attribute is a true value
          and the *note server_software: 2d5b. attribute is set.

     Methods and attributes for customizing exception handling:

      -- Method: log_exception (exc_info)

          Log the `exc_info' tuple in the server log.  `exc_info' is a
          ‘(type, value, traceback)’ tuple.  The default implementation
          simply writes the traceback to the request’s ‘wsgi.errors’
          stream and flushes it.  Subclasses can override this method to
          change the format or retarget the output, mail the traceback
          to an administrator, or whatever other action may be deemed
          suitable.

      -- Attribute: traceback_limit

          The maximum number of frames to include in tracebacks output
          by the default *note log_exception(): 2d60. method.  If
          ‘None’, all frames are included.

      -- Method: error_output (environ, start_response)

          This method is a WSGI application to generate an error page
          for the user.  It is only invoked if an error occurs before
          headers are sent to the client.

          This method can access the current error information using
          ‘sys.exc_info()’, and should pass that information to
          `start_response' when calling it (as described in the “Error
          Handling” section of PEP 3333(1)).

          The default implementation just uses the *note error_status:
          2d63, *note error_headers: 2d64, and *note error_body: 2d65.
          attributes to generate an output page.  Subclasses can
          override this to produce more dynamic error output.

          Note, however, that it’s not recommended from a security
          perspective to spit out diagnostics to any old user; ideally,
          you should have to do something special to enable diagnostic
          output, which is why the default implementation doesn’t
          include any.

      -- Attribute: error_status

          The HTTP status used for error responses.  This should be a
          status string as defined in PEP 3333(2); it defaults to a 500
          code and message.

      -- Attribute: error_headers

          The HTTP headers used for error responses.  This should be a
          list of WSGI response headers (‘(name, value)’ tuples), as
          described in PEP 3333(3).  The default list just sets the
          content type to ‘text/plain’.

      -- Attribute: error_body

          The error response body.  This should be an HTTP response body
          bytestring.  It defaults to the plain text, “A server error
          occurred.  Please contact the administrator.”

     Methods and attributes for PEP 3333(4)’s “Optional
     Platform-Specific File Handling” feature:

      -- Attribute: wsgi_file_wrapper

          A ‘wsgi.file_wrapper’ factory, or ‘None’.  The default value
          of this attribute is the *note wsgiref.util.FileWrapper: 3a4.
          class.

      -- Method: sendfile ()

          Override to implement platform-specific file transmission.
          This method is called only if the application’s return value
          is an instance of the class specified by the *note
          wsgi_file_wrapper: 2d5f. attribute.  It should return a true
          value if it was able to successfully transmit the file, so
          that the default transmission code will not be executed.  The
          default implementation of this method just returns a false
          value.

     Miscellaneous methods and attributes:

      -- Attribute: origin_server

          This attribute should be set to a true value if the handler’s
          *note _write(): 2d52. and *note _flush(): 2d53. are being used
          to communicate directly to the client, rather than via a
          CGI-like gateway protocol that wants the HTTP status in a
          special ‘Status:’ header.

          This attribute’s default value is true in *note BaseHandler:
          1107, but false in *note BaseCGIHandler: 2d4e. and *note
          CGIHandler: 2d4d.

      -- Attribute: http_version

          If *note origin_server: 2d5c. is true, this string attribute
          is used to set the HTTP version of the response set to the
          client.  It defaults to ‘"1.0"’.

 -- Function: wsgiref.handlers.read_environ ()

     Transcode CGI variables from ‘os.environ’ to PEP 3333(5) “bytes in
     unicode” strings, returning a new dictionary.  This function is
     used by *note CGIHandler: 2d4d. and *note IISCGIHandler: 2d4f. in
     place of directly using ‘os.environ’, which is not necessarily
     WSGI-compliant on all platforms and web servers using Python 3 –
     specifically, ones where the OS’s actual environment is Unicode
     (i.e.  Windows), or ones where the environment is bytes, but the
     system encoding used by Python to decode it is anything other than
     ISO-8859-1 (e.g.  Unix systems using UTF-8).

     If you are implementing a CGI-based handler of your own, you
     probably want to use this routine instead of just copying values
     out of ‘os.environ’ directly.

     New in version 3.2.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3333

   (2) https://www.python.org/dev/peps/pep-3333

   (3) https://www.python.org/dev/peps/pep-3333

   (4) https://www.python.org/dev/peps/pep-3333

   (5) https://www.python.org/dev/peps/pep-3333


File: python.info,  Node: Examples<21>,  Prev: wsgiref handlers – server/gateway base classes,  Up: wsgiref — WSGI Utilities and Reference Implementation

5.21.4.6 Examples
.................

This is a working “Hello World” WSGI application:

     from wsgiref.simple_server import make_server

     # Every WSGI application must have an application object - a callable
     # object that accepts two arguments. For that purpose, we're going to
     # use a function (note that you're not limited to a function, you can
     # use a class for example). The first argument passed to the function
     # is a dictionary containing CGI-style environment variables and the
     # second variable is the callable object.
     def hello_world_app(environ, start_response):
         status = '200 OK'  # HTTP Status
         headers = [('Content-type', 'text/plain; charset=utf-8')]  # HTTP Headers
         start_response(status, headers)

         # The returned object is going to be printed
         return [b"Hello World"]

     with make_server('', 8000, hello_world_app) as httpd:
         print("Serving on port 8000...")

         # Serve until process is killed
         httpd.serve_forever()

Example of a WSGI application serving the current directory, accept
optional directory and port number (default: 8000) on the command line:

     #!/usr/bin/env python3
     '''
     Small wsgiref based web server. Takes a path to serve from and an
     optional port number (defaults to 8000), then tries to serve files.
     Mime types are guessed from the file names, 404 errors are raised
     if the file is not found. Used for the make serve target in Doc.
     '''
     import sys
     import os
     import mimetypes
     from wsgiref import simple_server, util

     def app(environ, respond):

         fn = os.path.join(path, environ['PATH_INFO'][1:])
         if '.' not in fn.split(os.path.sep)[-1]:
             fn = os.path.join(fn, 'index.html')
         type = mimetypes.guess_type(fn)[0]

         if os.path.exists(fn):
             respond('200 OK', [('Content-Type', type)])
             return util.FileWrapper(open(fn, "rb"))
         else:
             respond('404 Not Found', [('Content-Type', 'text/plain')])
             return [b'not found']

     if __name__ == '__main__':
         path = sys.argv[1] if len(sys.argv) > 1 else os.getcwd()
         port = int(sys.argv[2]) if len(sys.argv) > 2 else 8000
         httpd = simple_server.make_server('', port, app)
         print("Serving {} on port {}, control-C to stop".format(path, port))
         try:
             httpd.serve_forever()
         except KeyboardInterrupt:
             print("Shutting down.")
             httpd.server_close()


File: python.info,  Node: urllib — URL handling modules,  Next: urllib request — Extensible library for opening URLs,  Prev: wsgiref — WSGI Utilities and Reference Implementation,  Up: Internet Protocols and Support

5.21.5 ‘urllib’ — URL handling modules
--------------------------------------

`Source code:' Lib/urllib/(1)

__________________________________________________________________

‘urllib’ is a package that collects several modules for working with
URLs:

   * *note urllib.request: 129. for opening and reading URLs

   * *note urllib.error: 127. containing the exceptions raised by *note
     urllib.request: 129.

   * *note urllib.parse: 128. for parsing URLs

   * *note urllib.robotparser: 12b. for parsing ‘robots.txt’ files

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/urllib/


File: python.info,  Node: urllib request — Extensible library for opening URLs,  Next: urllib response — Response classes used by urllib,  Prev: urllib — URL handling modules,  Up: Internet Protocols and Support

5.21.6 ‘urllib.request’ — Extensible library for opening URLs
-------------------------------------------------------------

`Source code:' Lib/urllib/request.py(1)

__________________________________________________________________

The *note urllib.request: 129. module defines functions and classes
which help in opening URLs (mostly HTTP) in a complex world — basic and
digest authentication, redirections, cookies and more.

See also
........

The Requests package(2) is recommended for a higher-level HTTP client
interface.

The *note urllib.request: 129. module defines the following functions:

 -- Function: urllib.request.urlopen (url, data=None[, timeout], *,
          cafile=None, capath=None, cadefault=False, context=None)

     Open the URL `url', which can be either a string or a *note
     Request: 9dc. object.

     `data' must be an object specifying additional data to be sent to
     the server, or ‘None’ if no such data is needed.  See *note
     Request: 9dc. for details.

     urllib.request module uses HTTP/1.1 and includes ‘Connection:close’
     header in its HTTP requests.

     The optional `timeout' parameter specifies a timeout in seconds for
     blocking operations like the connection attempt (if not specified,
     the global default timeout setting will be used).  This actually
     only works for HTTP, HTTPS and FTP connections.

     If `context' is specified, it must be a *note ssl.SSLContext: 4ea.
     instance describing the various SSL options.  See *note
     HTTPSConnection: 49a. for more details.

     The optional `cafile' and `capath' parameters specify a set of
     trusted CA certificates for HTTPS requests.  `cafile' should point
     to a single file containing a bundle of CA certificates, whereas
     `capath' should point to a directory of hashed certificate files.
     More information can be found in *note
     ssl.SSLContext.load_verify_locations(): 8d8.

     The `cadefault' parameter is ignored.

     This function always returns an object which can work as a *note
     context manager: 661. and has the properties `url', `headers', and
     `status'.  See *note urllib.response.addinfourl: 2d6d. for more
     detail on these properties.

     For HTTP and HTTPS URLs, this function returns a *note
     http.client.HTTPResponse: aef. object slightly modified.  In
     addition to the three new methods above, the msg attribute contains
     the same information as the *note reason: 2d6e. attribute — the
     reason phrase returned by server — instead of the response headers
     as it is specified in the documentation for *note HTTPResponse:
     aef.

     For FTP, file, and data URLs and requests explicitly handled by
     legacy *note URLopener: 2d6f. and *note FancyURLopener: 2d70.
     classes, this function returns a *note urllib.response.addinfourl:
     2d6d. object.

     Raises *note URLError: 2d71. on protocol errors.

     Note that ‘None’ may be returned if no handler handles the request
     (though the default installed global *note OpenerDirector: 2d72.
     uses *note UnknownHandler: 2d73. to ensure this never happens).

     In addition, if proxy settings are detected (for example, when a
     ‘*_proxy’ environment variable like ‘http_proxy’ is set), *note
     ProxyHandler: 10d8. is default installed and makes sure the
     requests are handled through the proxy.

     The legacy ‘urllib.urlopen’ function from Python 2.6 and earlier
     has been discontinued; *note urllib.request.urlopen(): 87b.
     corresponds to the old ‘urllib2.urlopen’.  Proxy handling, which
     was done by passing a dictionary parameter to ‘urllib.urlopen’, can
     be obtained by using *note ProxyHandler: 10d8. objects.

     The default opener raises an *note auditing event: fa1.
     ‘urllib.Request’ with arguments ‘fullurl’, ‘data’, ‘headers’,
     ‘method’ taken from the request object.

     Changed in version 3.2: `cafile' and `capath' were added.

     Changed in version 3.2: HTTPS virtual hosts are now supported if
     possible (that is, if *note ssl.HAS_SNI: 2827. is true).

     New in version 3.2: `data' can be an iterable object.

     Changed in version 3.3: `cadefault' was added.

     Changed in version 3.4.3: `context' was added.

     Deprecated since version 3.6: `cafile', `capath' and `cadefault'
     are deprecated in favor of `context'.  Please use *note
     ssl.SSLContext.load_cert_chain(): b69. instead, or let *note
     ssl.create_default_context(): 9a7. select the system’s trusted CA
     certificates for you.

 -- Function: urllib.request.install_opener (opener)

     Install an *note OpenerDirector: 2d72. instance as the default
     global opener.  Installing an opener is only necessary if you want
     urlopen to use that opener; otherwise, simply call *note
     OpenerDirector.open(): 9e0. instead of *note urlopen(): 87b.  The
     code does not check for a real *note OpenerDirector: 2d72, and any
     class with the appropriate interface will work.

 -- Function: urllib.request.build_opener ([handler, ...])

     Return an *note OpenerDirector: 2d72. instance, which chains the
     handlers in the order given.  `handler's can be either instances of
     *note BaseHandler: 2d76, or subclasses of *note BaseHandler: 2d76.
     (in which case it must be possible to call the constructor without
     any parameters).  Instances of the following classes will be in
     front of the `handler's, unless the `handler's contain them,
     instances of them or subclasses of them: *note ProxyHandler: 10d8.
     (if proxy settings are detected), *note UnknownHandler: 2d73, *note
     HTTPHandler: 2d77, *note HTTPDefaultErrorHandler: 2d78, *note
     HTTPRedirectHandler: 2d79, *note FTPHandler: 2d7a, *note
     FileHandler: 2d7b, *note HTTPErrorProcessor: 2d7c.

     If the Python installation has SSL support (i.e., if the *note ssl:
     f3. module can be imported), *note HTTPSHandler: c78. will also be
     added.

     A *note BaseHandler: 2d76. subclass may also change its
     ‘handler_order’ attribute to modify its position in the handlers
     list.

 -- Function: urllib.request.pathname2url (path)

     Convert the pathname `path' from the local syntax for a path to the
     form used in the path component of a URL. This does not produce a
     complete URL. The return value will already be quoted using the
     *note quote(): 512. function.

 -- Function: urllib.request.url2pathname (path)

     Convert the path component `path' from a percent-encoded URL to the
     local syntax for a path.  This does not accept a complete URL. This
     function uses *note unquote(): 10db. to decode `path'.

 -- Function: urllib.request.getproxies ()

     This helper function returns a dictionary of scheme to proxy server
     URL mappings.  It scans the environment for variables named
     ‘<scheme>_proxy’, in a case insensitive approach, for all operating
     systems first, and when it cannot find it, looks for proxy
     information from System Configuration for macOS and Windows Systems
     Registry for Windows.  If both lowercase and uppercase environment
     variables exist (and disagree), lowercase is preferred.

          Note: If the environment variable ‘REQUEST_METHOD’ is set,
          which usually indicates your script is running in a CGI
          environment, the environment variable ‘HTTP_PROXY’ (uppercase
          ‘_PROXY’) will be ignored.  This is because that variable can
          be injected by a client using the “Proxy:” HTTP header.  If
          you need to use an HTTP proxy in a CGI environment, either use
          ‘ProxyHandler’ explicitly, or make sure the variable name is
          in lowercase (or at least the ‘_proxy’ suffix).

The following classes are provided:

 -- Class: urllib.request.Request (url, data=None, headers={},
          origin_req_host=None, unverifiable=False, method=None)

     This class is an abstraction of a URL request.

     `url' should be a string containing a valid URL.

     `data' must be an object specifying additional data to send to the
     server, or ‘None’ if no such data is needed.  Currently HTTP
     requests are the only ones that use `data'.  The supported object
     types include bytes, file-like objects, and iterables of bytes-like
     objects.  If no ‘Content-Length’ nor ‘Transfer-Encoding’ header
     field has been provided, *note HTTPHandler: 2d77. will set these
     headers according to the type of `data'.  ‘Content-Length’ will be
     used to send bytes objects, while ‘Transfer-Encoding: chunked’ as
     specified in RFC 7230(3), Section 3.3.1 will be used to send files
     and other iterables.

     For an HTTP POST request method, `data' should be a buffer in the
     standard ‘application/x-www-form-urlencoded’ format.  The *note
     urllib.parse.urlencode(): 87a. function takes a mapping or sequence
     of 2-tuples and returns an ASCII string in this format.  It should
     be encoded to bytes before being used as the `data' parameter.

     `headers' should be a dictionary, and will be treated as if *note
     add_header(): 2d80. was called with each key and value as
     arguments.  This is often used to “spoof” the ‘User-Agent’ header
     value, which is used by a browser to identify itself – some HTTP
     servers only allow requests coming from common browsers as opposed
     to scripts.  For example, Mozilla Firefox may identify itself as
     ‘"Mozilla/5.0 (X11; U; Linux i686) Gecko/20071127
     Firefox/2.0.0.11"’, while *note urllib: 126.’s default user agent
     string is ‘"Python-urllib/2.6"’ (on Python 2.6).

     An appropriate ‘Content-Type’ header should be included if the
     `data' argument is present.  If this header has not been provided
     and `data' is not None, ‘Content-Type:
     application/x-www-form-urlencoded’ will be added as a default.

     The next two arguments are only of interest for correct handling of
     third-party HTTP cookies:

     `origin_req_host' should be the request-host of the origin
     transaction, as defined by RFC 2965(4).  It defaults to
     ‘http.cookiejar.request_host(self)’.  This is the host name or IP
     address of the original request that was initiated by the user.
     For example, if the request is for an image in an HTML document,
     this should be the request-host of the request for the page
     containing the image.

     `unverifiable' should indicate whether the request is unverifiable,
     as defined by RFC 2965(5).  It defaults to ‘False’.  An
     unverifiable request is one whose URL the user did not have the
     option to approve.  For example, if the request is for an image in
     an HTML document, and the user had no option to approve the
     automatic fetching of the image, this should be true.

     `method' should be a string that indicates the HTTP request method
     that will be used (e.g.  ‘'HEAD'’).  If provided, its value is
     stored in the *note method: 9dd. attribute and is used by *note
     get_method(): b99.  The default is ‘'GET'’ if `data' is ‘None’ or
     ‘'POST'’ otherwise.  Subclasses may indicate a different default
     method by setting the *note method: 9dd. attribute in the class
     itself.

          Note: The request will not work as expected if the data object
          is unable to deliver its content more than once (e.g.  a file
          or an iterable that can produce the content only once) and the
          request is retried for HTTP redirects or authentication.  The
          `data' is sent to the HTTP server right away after the
          headers.  There is no support for a 100-continue expectation
          in the library.

     Changed in version 3.3: *note Request.method: 9dd. argument is
     added to the Request class.

     Changed in version 3.4: Default *note Request.method: 9dd. may be
     indicated at the class level.

     Changed in version 3.6: Do not raise an error if the
     ‘Content-Length’ has not been provided and `data' is neither ‘None’
     nor a bytes object.  Fall back to use chunked transfer encoding
     instead.

 -- Class: urllib.request.OpenerDirector

     The *note OpenerDirector: 2d72. class opens URLs via *note
     BaseHandler: 2d76.s chained together.  It manages the chaining of
     handlers, and recovery from errors.

 -- Class: urllib.request.BaseHandler

     This is the base class for all registered handlers — and handles
     only the simple mechanics of registration.

 -- Class: urllib.request.HTTPDefaultErrorHandler

     A class which defines a default handler for HTTP error responses;
     all responses are turned into *note HTTPError: 9e2. exceptions.

 -- Class: urllib.request.HTTPRedirectHandler

     A class to handle redirections.

 -- Class: urllib.request.HTTPCookieProcessor (cookiejar=None)

     A class to handle HTTP Cookies.

 -- Class: urllib.request.ProxyHandler (proxies=None)

     Cause requests to go through a proxy.  If `proxies' is given, it
     must be a dictionary mapping protocol names to URLs of proxies.
     The default is to read the list of proxies from the environment
     variables ‘<protocol>_proxy’.  If no proxy environment variables
     are set, then in a Windows environment proxy settings are obtained
     from the registry’s Internet Settings section, and in a macOS
     environment proxy information is retrieved from the System
     Configuration Framework.

     To disable autodetected proxy pass an empty dictionary.

     The ‘no_proxy’ environment variable can be used to specify hosts
     which shouldn’t be reached via proxy; if set, it should be a
     comma-separated list of hostname suffixes, optionally with ‘:port’
     appended, for example ‘cern.ch,ncsa.uiuc.edu,some.host:8080’.

               Note: ‘HTTP_PROXY’ will be ignored if a variable
               ‘REQUEST_METHOD’ is set; see the documentation on *note
               getproxies(): 2d7f.

 -- Class: urllib.request.HTTPPasswordMgr

     Keep a database of ‘(realm, uri) -> (user, password)’ mappings.

 -- Class: urllib.request.HTTPPasswordMgrWithDefaultRealm

     Keep a database of ‘(realm, uri) -> (user, password)’ mappings.  A
     realm of ‘None’ is considered a catch-all realm, which is searched
     if no other realm fits.

 -- Class: urllib.request.HTTPPasswordMgrWithPriorAuth

     A variant of *note HTTPPasswordMgrWithDefaultRealm: 2d83. that also
     has a database of ‘uri -> is_authenticated’ mappings.  Can be used
     by a BasicAuth handler to determine when to send authentication
     credentials immediately instead of waiting for a ‘401’ response
     first.

     New in version 3.5.

 -- Class: urllib.request.AbstractBasicAuthHandler (password_mgr=None)

     This is a mixin class that helps with HTTP authentication, both to
     the remote host and to a proxy.  `password_mgr', if given, should
     be something that is compatible with *note HTTPPasswordMgr: 2d82.;
     refer to section *note HTTPPasswordMgr Objects: 2d84. for
     information on the interface that must be supported.  If
     `passwd_mgr' also provides ‘is_authenticated’ and
     ‘update_authenticated’ methods (see *note
     HTTPPasswordMgrWithPriorAuth Objects: 2d85.), then the handler will
     use the ‘is_authenticated’ result for a given URI to determine
     whether or not to send authentication credentials with the request.
     If ‘is_authenticated’ returns ‘True’ for the URI, credentials are
     sent.  If ‘is_authenticated’ is ‘False’, credentials are not sent,
     and then if a ‘401’ response is received the request is re-sent
     with the authentication credentials.  If authentication succeeds,
     ‘update_authenticated’ is called to set ‘is_authenticated’ ‘True’
     for the URI, so that subsequent requests to the URI or any of its
     super-URIs will automatically include the authentication
     credentials.

     New in version 3.5: Added ‘is_authenticated’ support.

 -- Class: urllib.request.HTTPBasicAuthHandler (password_mgr=None)

     Handle authentication with the remote host.  `password_mgr', if
     given, should be something that is compatible with *note
     HTTPPasswordMgr: 2d82.; refer to section *note HTTPPasswordMgr
     Objects: 2d84. for information on the interface that must be
     supported.  HTTPBasicAuthHandler will raise a *note ValueError:
     16d. when presented with a wrong Authentication scheme.

 -- Class: urllib.request.ProxyBasicAuthHandler (password_mgr=None)

     Handle authentication with the proxy.  `password_mgr', if given,
     should be something that is compatible with *note HTTPPasswordMgr:
     2d82.; refer to section *note HTTPPasswordMgr Objects: 2d84. for
     information on the interface that must be supported.

 -- Class: urllib.request.AbstractDigestAuthHandler (password_mgr=None)

     This is a mixin class that helps with HTTP authentication, both to
     the remote host and to a proxy.  `password_mgr', if given, should
     be something that is compatible with *note HTTPPasswordMgr: 2d82.;
     refer to section *note HTTPPasswordMgr Objects: 2d84. for
     information on the interface that must be supported.

 -- Class: urllib.request.HTTPDigestAuthHandler (password_mgr=None)

     Handle authentication with the remote host.  `password_mgr', if
     given, should be something that is compatible with *note
     HTTPPasswordMgr: 2d82.; refer to section *note HTTPPasswordMgr
     Objects: 2d84. for information on the interface that must be
     supported.  When both Digest Authentication Handler and Basic
     Authentication Handler are both added, Digest Authentication is
     always tried first.  If the Digest Authentication returns a 40x
     response again, it is sent to Basic Authentication handler to
     Handle.  This Handler method will raise a *note ValueError: 16d.
     when presented with an authentication scheme other than Digest or
     Basic.

     Changed in version 3.3: Raise *note ValueError: 16d. on unsupported
     Authentication Scheme.

 -- Class: urllib.request.ProxyDigestAuthHandler (password_mgr=None)

     Handle authentication with the proxy.  `password_mgr', if given,
     should be something that is compatible with *note HTTPPasswordMgr:
     2d82.; refer to section *note HTTPPasswordMgr Objects: 2d84. for
     information on the interface that must be supported.

 -- Class: urllib.request.HTTPHandler

     A class to handle opening of HTTP URLs.

 -- Class: urllib.request.HTTPSHandler (debuglevel=0, context=None,
          check_hostname=None)

     A class to handle opening of HTTPS URLs.  `context' and
     `check_hostname' have the same meaning as in *note
     http.client.HTTPSConnection: 49a.

     Changed in version 3.2: `context' and `check_hostname' were added.

 -- Class: urllib.request.FileHandler

     Open local files.

 -- Class: urllib.request.DataHandler

     Open data URLs.

     New in version 3.4.

 -- Class: urllib.request.FTPHandler

     Open FTP URLs.

 -- Class: urllib.request.CacheFTPHandler

     Open FTP URLs, keeping a cache of open FTP connections to minimize
     delays.

 -- Class: urllib.request.UnknownHandler

     A catch-all class to handle unknown URLs.

 -- Class: urllib.request.HTTPErrorProcessor

     Process HTTP error responses.

* Menu:

* Request Objects::
* OpenerDirector Objects::
* BaseHandler Objects::
* HTTPRedirectHandler Objects::
* HTTPCookieProcessor Objects::
* ProxyHandler Objects::
* HTTPPasswordMgr Objects::
* HTTPPasswordMgrWithPriorAuth Objects::
* AbstractBasicAuthHandler Objects::
* HTTPBasicAuthHandler Objects::
* ProxyBasicAuthHandler Objects::
* AbstractDigestAuthHandler Objects::
* HTTPDigestAuthHandler Objects::
* ProxyDigestAuthHandler Objects::
* HTTPHandler Objects::
* HTTPSHandler Objects::
* FileHandler Objects::
* DataHandler Objects::
* FTPHandler Objects::
* CacheFTPHandler Objects::
* UnknownHandler Objects::
* HTTPErrorProcessor Objects::
* Examples: Examples<22>.
* Legacy interface::
* urllib.request Restrictions: urllib request Restrictions.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/urllib/request.py

   (2) https://requests.readthedocs.io/en/master/

   (3) https://tools.ietf.org/html/rfc7230.html

   (4) https://tools.ietf.org/html/rfc2965.html

   (5) https://tools.ietf.org/html/rfc2965.html


File: python.info,  Node: Request Objects,  Next: OpenerDirector Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.1 Request Objects
........................

The following methods describe *note Request: 9dc.’s public interface,
and so all may be overridden in subclasses.  It also defines several
public attributes that can be used by clients to inspect the parsed
request.

 -- Attribute: Request.full_url

     The original URL passed to the constructor.

     Changed in version 3.4.

     Request.full_url is a property with setter, getter and a deleter.
     Getting *note full_url: 9de. returns the original request URL with
     the fragment, if it was present.

 -- Attribute: Request.type

     The URI scheme.

 -- Attribute: Request.host

     The URI authority, typically a host, but may also contain a port
     separated by a colon.

 -- Attribute: Request.origin_req_host

     The original host for the request, without port.

 -- Attribute: Request.selector

     The URI path.  If the *note Request: 9dc. uses a proxy, then
     selector will be the full URL that is passed to the proxy.

 -- Attribute: Request.data

     The entity body for the request, or ‘None’ if not specified.

     Changed in version 3.4: Changing value of *note Request.data: 9df.
     now deletes “Content-Length” header if it was previously set or
     calculated.

 -- Attribute: Request.unverifiable

     boolean, indicates whether the request is unverifiable as defined
     by RFC 2965(1).

 -- Attribute: Request.method

     The HTTP request method to use.  By default its value is *note
     None: 203, which means that *note get_method(): b99. will do its
     normal computation of the method to be used.  Its value can be set
     (thus overriding the default computation in *note get_method():
     b99.) either by providing a default value by setting it at the
     class level in a *note Request: 9dc. subclass, or by passing a
     value in to the *note Request: 9dc. constructor via the `method'
     argument.

     New in version 3.3.

     Changed in version 3.4: A default value can now be set in
     subclasses; previously it could only be set via the constructor
     argument.

 -- Method: Request.get_method ()

     Return a string indicating the HTTP request method.  If *note
     Request.method: 9dd. is not ‘None’, return its value, otherwise
     return ‘'GET'’ if *note Request.data: 9df. is ‘None’, or ‘'POST'’
     if it’s not.  This is only meaningful for HTTP requests.

     Changed in version 3.3: get_method now looks at the value of *note
     Request.method: 9dd.

 -- Method: Request.add_header (key, val)

     Add another header to the request.  Headers are currently ignored
     by all handlers except HTTP handlers, where they are added to the
     list of headers sent to the server.  Note that there cannot be more
     than one header with the same name, and later calls will overwrite
     previous calls in case the `key' collides.  Currently, this is no
     loss of HTTP functionality, since all headers which have meaning
     when used more than once have a (header-specific) way of gaining
     the same functionality using only one header.

 -- Method: Request.add_unredirected_header (key, header)

     Add a header that will not be added to a redirected request.

 -- Method: Request.has_header (header)

     Return whether the instance has the named header (checks both
     regular and unredirected).

 -- Method: Request.remove_header (header)

     Remove named header from the request instance (both from regular
     and unredirected headers).

     New in version 3.4.

 -- Method: Request.get_full_url ()

     Return the URL given in the constructor.

     Changed in version 3.4.

     Returns *note Request.full_url: 9de.

 -- Method: Request.set_proxy (host, type)

     Prepare the request by connecting to a proxy server.  The `host'
     and `type' will replace those of the instance, and the instance’s
     selector will be the original URL given in the constructor.

 -- Method: Request.get_header (header_name, default=None)

     Return the value of the given header.  If the header is not
     present, return the default value.

 -- Method: Request.header_items ()

     Return a list of tuples (header_name, header_value) of the Request
     headers.

Changed in version 3.4: The request methods add_data, has_data,
get_data, get_type, get_host, get_selector, get_origin_req_host and
is_unverifiable that were deprecated since 3.3 have been removed.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2965.html


File: python.info,  Node: OpenerDirector Objects,  Next: BaseHandler Objects,  Prev: Request Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.2 OpenerDirector Objects
...............................

*note OpenerDirector: 2d72. instances have the following methods:

 -- Method: OpenerDirector.add_handler (handler)

     `handler' should be an instance of *note BaseHandler: 2d76.  The
     following methods are searched, and added to the possible chains
     (note that HTTP errors are a special case).  Note that, in the
     following, `protocol' should be replaced with the actual protocol
     to handle, for example ‘http_response()’ would be the HTTP protocol
     response handler.  Also `type' should be replaced with the actual
     HTTP code, for example ‘http_error_404()’ would handle HTTP 404
     errors.

        * ‘<protocol>_open()’ — signal that the handler knows how to
          open `protocol' URLs.

          See *note BaseHandler.<protocol>_open(): 2d9b. for more
          information.

        * ‘http_error_<type>()’ — signal that the handler knows how to
          handle HTTP errors with HTTP error code `type'.

          See *note BaseHandler.http_error_<nnn>(): 2d9c. for more
          information.

        * ‘<protocol>_error()’ — signal that the handler knows how to
          handle errors from (non-‘http’) `protocol'.

        * ‘<protocol>_request()’ — signal that the handler knows how to
          pre-process `protocol' requests.

          See *note BaseHandler.<protocol>_request(): 2d9d. for more
          information.

        * ‘<protocol>_response()’ — signal that the handler knows how to
          post-process `protocol' responses.

          See *note BaseHandler.<protocol>_response(): 2d9e. for more
          information.

 -- Method: OpenerDirector.open (url, data=None[, timeout])

     Open the given `url' (which can be a request object or a string),
     optionally passing the given `data'.  Arguments, return values and
     exceptions raised are the same as those of *note urlopen(): 87b.
     (which simply calls the *note open(): 16f. method on the currently
     installed global *note OpenerDirector: 2d72.).  The optional
     `timeout' parameter specifies a timeout in seconds for blocking
     operations like the connection attempt (if not specified, the
     global default timeout setting will be used).  The timeout feature
     actually works only for HTTP, HTTPS and FTP connections.

 -- Method: OpenerDirector.error (proto, *args)

     Handle an error of the given protocol.  This will call the
     registered error handlers for the given protocol with the given
     arguments (which are protocol specific).  The HTTP protocol is a
     special case which uses the HTTP response code to determine the
     specific error handler; refer to the ‘http_error_<type>()’ methods
     of the handler classes.

     Return values and exceptions raised are the same as those of *note
     urlopen(): 87b.

OpenerDirector objects open URLs in three stages:

The order in which these methods are called within each stage is
determined by sorting the handler instances.

  1. Every handler with a method named like ‘<protocol>_request()’ has
     that method called to pre-process the request.

  2. Handlers with a method named like ‘<protocol>_open()’ are called to
     handle the request.  This stage ends when a handler either returns
     a non-*note None: 203. value (ie.  a response), or raises an
     exception (usually *note URLError: 2d71.).  Exceptions are allowed
     to propagate.

     In fact, the above algorithm is first tried for methods named
     ‘default_open()’.  If all such methods return *note None: 203, the
     algorithm is repeated for methods named like ‘<protocol>_open()’.
     If all such methods return *note None: 203, the algorithm is
     repeated for methods named ‘unknown_open()’.

     Note that the implementation of these methods may involve calls of
     the parent *note OpenerDirector: 2d72. instance’s *note open():
     9e0. and *note error(): 2d9f. methods.

  3. Every handler with a method named like ‘<protocol>_response()’ has
     that method called to post-process the response.


File: python.info,  Node: BaseHandler Objects,  Next: HTTPRedirectHandler Objects,  Prev: OpenerDirector Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.3 BaseHandler Objects
............................

*note BaseHandler: 2d76. objects provide a couple of methods that are
directly useful, and others that are meant to be used by derived
classes.  These are intended for direct use:

 -- Method: BaseHandler.add_parent (director)

     Add a director as parent.

 -- Method: BaseHandler.close ()

     Remove any parents.

The following attribute and methods should only be used by classes
derived from *note BaseHandler: 2d76.

     Note: The convention has been adopted that subclasses defining
     ‘<protocol>_request()’ or ‘<protocol>_response()’ methods are named
     ‘*Processor’; all others are named ‘*Handler’.

 -- Attribute: BaseHandler.parent

     A valid *note OpenerDirector: 2d72, which can be used to open using
     a different protocol, or handle errors.

 -- Method: BaseHandler.default_open (req)

     This method is `not' defined in *note BaseHandler: 2d76, but
     subclasses should define it if they want to catch all URLs.

     This method, if implemented, will be called by the parent *note
     OpenerDirector: 2d72.  It should return a file-like object as
     described in the return value of the *note open(): 16f. of *note
     OpenerDirector: 2d72, or ‘None’.  It should raise *note URLError:
     2d71, unless a truly exceptional thing happens (for example, *note
     MemoryError: f69. should not be mapped to ‘URLError’).

     This method will be called before any protocol-specific open
     method.

 -- Method: BaseHandler.<protocol>_open(req)

     This method is `not' defined in *note BaseHandler: 2d76, but
     subclasses should define it if they want to handle URLs with the
     given protocol.

     This method, if defined, will be called by the parent *note
     OpenerDirector: 2d72.  Return values should be the same as for
     ‘default_open()’.

 -- Method: BaseHandler.unknown_open (req)

     This method is `not' defined in *note BaseHandler: 2d76, but
     subclasses should define it if they want to catch all URLs with no
     specific registered handler to open it.

     This method, if implemented, will be called by the *note parent:
     2da4. *note OpenerDirector: 2d72.  Return values should be the same
     as for *note default_open(): 2da5.

 -- Method: BaseHandler.http_error_default (req, fp, code, msg, hdrs)

     This method is `not' defined in *note BaseHandler: 2d76, but
     subclasses should override it if they intend to provide a catch-all
     for otherwise unhandled HTTP errors.  It will be called
     automatically by the *note OpenerDirector: 2d72. getting the error,
     and should not normally be called in other circumstances.

     `req' will be a *note Request: 9dc. object, `fp' will be a
     file-like object with the HTTP error body, `code' will be the
     three-digit code of the error, `msg' will be the user-visible
     explanation of the code and `hdrs' will be a mapping object with
     the headers of the error.

     Return values and exceptions raised should be the same as those of
     *note urlopen(): 87b.

 -- Method: BaseHandler.http_error_<nnn>(req, fp, code, msg, hdrs)

     `nnn' should be a three-digit HTTP error code.  This method is also
     not defined in *note BaseHandler: 2d76, but will be called, if it
     exists, on an instance of a subclass, when an HTTP error with code
     `nnn' occurs.

     Subclasses should override this method to handle specific HTTP
     errors.

     Arguments, return values and exceptions raised should be the same
     as for ‘http_error_default()’.

 -- Method: BaseHandler.<protocol>_request(req)

     This method is `not' defined in *note BaseHandler: 2d76, but
     subclasses should define it if they want to pre-process requests of
     the given protocol.

     This method, if defined, will be called by the parent *note
     OpenerDirector: 2d72.  `req' will be a *note Request: 9dc. object.
     The return value should be a *note Request: 9dc. object.

 -- Method: BaseHandler.<protocol>_response(req, response)

     This method is `not' defined in *note BaseHandler: 2d76, but
     subclasses should define it if they want to post-process responses
     of the given protocol.

     This method, if defined, will be called by the parent *note
     OpenerDirector: 2d72.  `req' will be a *note Request: 9dc. object.
     `response' will be an object implementing the same interface as the
     return value of *note urlopen(): 87b.  The return value should
     implement the same interface as the return value of *note
     urlopen(): 87b.


File: python.info,  Node: HTTPRedirectHandler Objects,  Next: HTTPCookieProcessor Objects,  Prev: BaseHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.4 HTTPRedirectHandler Objects
....................................

     Note: Some HTTP redirections require action from this module’s
     client code.  If this is the case, *note HTTPError: 9e2. is raised.
     See RFC 2616(1) for details of the precise meanings of the various
     redirection codes.

     An ‘HTTPError’ exception raised as a security consideration if the
     HTTPRedirectHandler is presented with a redirected URL which is not
     an HTTP, HTTPS or FTP URL.

 -- Method: HTTPRedirectHandler.redirect_request (req, fp, code, msg,
          hdrs, newurl)

     Return a *note Request: 9dc. or ‘None’ in response to a redirect.
     This is called by the default implementations of the
     ‘http_error_30*()’ methods when a redirection is received from the
     server.  If a redirection should take place, return a new *note
     Request: 9dc. to allow ‘http_error_30*()’ to perform the redirect
     to `newurl'.  Otherwise, raise *note HTTPError: 9e2. if no other
     handler should try to handle this URL, or return ‘None’ if you
     can’t but another handler might.

          Note: The default implementation of this method does not
          strictly follow RFC 2616(2), which says that 301 and 302
          responses to ‘POST’ requests must not be automatically
          redirected without confirmation by the user.  In reality,
          browsers do allow automatic redirection of these responses,
          changing the POST to a ‘GET’, and the default implementation
          reproduces this behavior.

 -- Method: HTTPRedirectHandler.http_error_301 (req, fp, code, msg,
          hdrs)

     Redirect to the ‘Location:’ or ‘URI:’ URL. This method is called by
     the parent *note OpenerDirector: 2d72. when getting an HTTP ‘moved
     permanently’ response.

 -- Method: HTTPRedirectHandler.http_error_302 (req, fp, code, msg,
          hdrs)

     The same as *note http_error_301(): 2dab, but called for the
     ‘found’ response.

 -- Method: HTTPRedirectHandler.http_error_303 (req, fp, code, msg,
          hdrs)

     The same as *note http_error_301(): 2dab, but called for the ‘see
     other’ response.

 -- Method: HTTPRedirectHandler.http_error_307 (req, fp, code, msg,
          hdrs)

     The same as *note http_error_301(): 2dab, but called for the
     ‘temporary redirect’ response.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2616.html

   (2) https://tools.ietf.org/html/rfc2616.html


File: python.info,  Node: HTTPCookieProcessor Objects,  Next: ProxyHandler Objects,  Prev: HTTPRedirectHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.5 HTTPCookieProcessor Objects
....................................

*note HTTPCookieProcessor: 2d81. instances have one attribute:

 -- Attribute: HTTPCookieProcessor.cookiejar

     The *note http.cookiejar.CookieJar: 2db2. in which cookies are
     stored.


File: python.info,  Node: ProxyHandler Objects,  Next: HTTPPasswordMgr Objects,  Prev: HTTPCookieProcessor Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.6 ProxyHandler Objects
.............................

 -- Method: ProxyHandler.<protocol>_open(request)

     The *note ProxyHandler: 10d8. will have a method
     ‘<protocol>_open()’ for every `protocol' which has a proxy in the
     `proxies' dictionary given in the constructor.  The method will
     modify requests to go through the proxy, by calling
     ‘request.set_proxy()’, and call the next handler in the chain to
     actually execute the protocol.


File: python.info,  Node: HTTPPasswordMgr Objects,  Next: HTTPPasswordMgrWithPriorAuth Objects,  Prev: ProxyHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.7 HTTPPasswordMgr Objects
................................

These methods are available on *note HTTPPasswordMgr: 2d82. and *note
HTTPPasswordMgrWithDefaultRealm: 2d83. objects.

 -- Method: HTTPPasswordMgr.add_password (realm, uri, user, passwd)

     `uri' can be either a single URI, or a sequence of URIs.  `realm',
     `user' and `passwd' must be strings.  This causes ‘(user, passwd)’
     to be used as authentication tokens when authentication for `realm'
     and a super-URI of any of the given URIs is given.

 -- Method: HTTPPasswordMgr.find_user_password (realm, authuri)

     Get user/password for given realm and URI, if any.  This method
     will return ‘(None, None)’ if there is no matching user/password.

     For *note HTTPPasswordMgrWithDefaultRealm: 2d83. objects, the realm
     ‘None’ will be searched if the given `realm' has no matching
     user/password.


File: python.info,  Node: HTTPPasswordMgrWithPriorAuth Objects,  Next: AbstractBasicAuthHandler Objects,  Prev: HTTPPasswordMgr Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.8 HTTPPasswordMgrWithPriorAuth Objects
.............................................

This password manager extends *note HTTPPasswordMgrWithDefaultRealm:
2d83. to support tracking URIs for which authentication credentials
should always be sent.

 -- Method: HTTPPasswordMgrWithPriorAuth.add_password (realm, uri, user,
          passwd, is_authenticated=False)

     `realm', `uri', `user', `passwd' are as for *note
     HTTPPasswordMgr.add_password(): 2db6.  `is_authenticated' sets the
     initial value of the ‘is_authenticated’ flag for the given URI or
     list of URIs.  If `is_authenticated' is specified as ‘True’,
     `realm' is ignored.

 -- Method: HTTPPasswordMgrWithPriorAuth.find_user_password (realm,
          authuri)

     Same as for *note HTTPPasswordMgrWithDefaultRealm: 2d83. objects

 -- Method: HTTPPasswordMgrWithPriorAuth.update_authenticated (self,
          uri, is_authenticated=False)

     Update the ‘is_authenticated’ flag for the given `uri' or list of
     URIs.

 -- Method: HTTPPasswordMgrWithPriorAuth.is_authenticated (self,
          authuri)

     Returns the current state of the ‘is_authenticated’ flag for the
     given URI.


File: python.info,  Node: AbstractBasicAuthHandler Objects,  Next: HTTPBasicAuthHandler Objects,  Prev: HTTPPasswordMgrWithPriorAuth Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.9 AbstractBasicAuthHandler Objects
.........................................

 -- Method: AbstractBasicAuthHandler.http_error_auth_reqed (authreq,
          host, req, headers)

     Handle an authentication request by getting a user/password pair,
     and re-trying the request.  `authreq' should be the name of the
     header where the information about the realm is included in the
     request, `host' specifies the URL and path to authenticate for,
     `req' should be the (failed) *note Request: 9dc. object, and
     `headers' should be the error headers.

     `host' is either an authority (e.g.  ‘"python.org"’) or a URL
     containing an authority component (e.g.  ‘"http://python.org/"’).
     In either case, the authority must not contain a userinfo component
     (so, ‘"python.org"’ and ‘"python.org:80"’ are fine,
     ‘"joe:password@python.org"’ is not).


File: python.info,  Node: HTTPBasicAuthHandler Objects,  Next: ProxyBasicAuthHandler Objects,  Prev: AbstractBasicAuthHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.10 HTTPBasicAuthHandler Objects
......................................

 -- Method: HTTPBasicAuthHandler.http_error_401 (req, fp, code, msg,
          hdrs)

     Retry the request with authentication information, if available.


File: python.info,  Node: ProxyBasicAuthHandler Objects,  Next: AbstractDigestAuthHandler Objects,  Prev: HTTPBasicAuthHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.11 ProxyBasicAuthHandler Objects
.......................................

 -- Method: ProxyBasicAuthHandler.http_error_407 (req, fp, code, msg,
          hdrs)

     Retry the request with authentication information, if available.


File: python.info,  Node: AbstractDigestAuthHandler Objects,  Next: HTTPDigestAuthHandler Objects,  Prev: ProxyBasicAuthHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.12 AbstractDigestAuthHandler Objects
...........................................

 -- Method: AbstractDigestAuthHandler.http_error_auth_reqed (authreq,
          host, req, headers)

     `authreq' should be the name of the header where the information
     about the realm is included in the request, `host' should be the
     host to authenticate to, `req' should be the (failed) *note
     Request: 9dc. object, and `headers' should be the error headers.


File: python.info,  Node: HTTPDigestAuthHandler Objects,  Next: ProxyDigestAuthHandler Objects,  Prev: AbstractDigestAuthHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.13 HTTPDigestAuthHandler Objects
.......................................

 -- Method: HTTPDigestAuthHandler.http_error_401 (req, fp, code, msg,
          hdrs)

     Retry the request with authentication information, if available.


File: python.info,  Node: ProxyDigestAuthHandler Objects,  Next: HTTPHandler Objects,  Prev: HTTPDigestAuthHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.14 ProxyDigestAuthHandler Objects
........................................

 -- Method: ProxyDigestAuthHandler.http_error_407 (req, fp, code, msg,
          hdrs)

     Retry the request with authentication information, if available.


File: python.info,  Node: HTTPHandler Objects,  Next: HTTPSHandler Objects,  Prev: ProxyDigestAuthHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.15 HTTPHandler Objects
.............................

 -- Method: HTTPHandler.http_open (req)

     Send an HTTP request, which can be either GET or POST, depending on
     ‘req.has_data()’.


File: python.info,  Node: HTTPSHandler Objects,  Next: FileHandler Objects,  Prev: HTTPHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.16 HTTPSHandler Objects
..............................

 -- Method: HTTPSHandler.https_open (req)

     Send an HTTPS request, which can be either GET or POST, depending
     on ‘req.has_data()’.


File: python.info,  Node: FileHandler Objects,  Next: DataHandler Objects,  Prev: HTTPSHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.17 FileHandler Objects
.............................

 -- Method: FileHandler.file_open (req)

     Open the file locally, if there is no host name, or the host name
     is ‘'localhost'’.

     Changed in version 3.2: This method is applicable only for local
     hostnames.  When a remote hostname is given, an *note URLError:
     2d71. is raised.


File: python.info,  Node: DataHandler Objects,  Next: FTPHandler Objects,  Prev: FileHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.18 DataHandler Objects
.............................

 -- Method: DataHandler.data_open (req)

     Read a data URL. This kind of URL contains the content encoded in
     the URL itself.  The data URL syntax is specified in RFC 2397(1).
     This implementation ignores white spaces in base64 encoded data
     URLs so the URL may be wrapped in whatever source file it comes
     from.  But even though some browsers don’t mind about a missing
     padding at the end of a base64 encoded data URL, this
     implementation will raise an *note ValueError: 16d. in that case.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2397.html


File: python.info,  Node: FTPHandler Objects,  Next: CacheFTPHandler Objects,  Prev: DataHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.19 FTPHandler Objects
............................

 -- Method: FTPHandler.ftp_open (req)

     Open the FTP file indicated by `req'.  The login is always done
     with empty username and password.


File: python.info,  Node: CacheFTPHandler Objects,  Next: UnknownHandler Objects,  Prev: FTPHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.20 CacheFTPHandler Objects
.................................

*note CacheFTPHandler: 2d8a. objects are *note FTPHandler: 2d7a. objects
with the following additional methods:

 -- Method: CacheFTPHandler.setTimeout (t)

     Set timeout of connections to `t' seconds.

 -- Method: CacheFTPHandler.setMaxConns (m)

     Set maximum number of cached connections to `m'.


File: python.info,  Node: UnknownHandler Objects,  Next: HTTPErrorProcessor Objects,  Prev: CacheFTPHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.21 UnknownHandler Objects
................................

 -- Method: UnknownHandler.unknown_open ()

     Raise a *note URLError: 2d71. exception.


File: python.info,  Node: HTTPErrorProcessor Objects,  Next: Examples<22>,  Prev: UnknownHandler Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.22 HTTPErrorProcessor Objects
....................................

 -- Method: HTTPErrorProcessor.http_response (request, response)

     Process HTTP error responses.

     For 200 error codes, the response object is returned immediately.

     For non-200 error codes, this simply passes the job on to the
     ‘http_error_<type>()’ handler methods, via *note
     OpenerDirector.error(): 2d9f.  Eventually, *note
     HTTPDefaultErrorHandler: 2d78. will raise an *note HTTPError: 9e2.
     if no other handler handles the error.

 -- Method: HTTPErrorProcessor.https_response (request, response)

     Process HTTPS error responses.

     The behavior is same as *note http_response(): 2de7.


File: python.info,  Node: Examples<22>,  Next: Legacy interface,  Prev: HTTPErrorProcessor Objects,  Up: urllib request — Extensible library for opening URLs

5.21.6.23 Examples
..................

In addition to the examples below, more examples are given in *note
HOWTO Fetch Internet Resources Using The urllib Package: 2deb.

This example gets the python.org main page and displays the first 300
bytes of it.

     >>> import urllib.request
     >>> with urllib.request.urlopen('http://www.python.org/') as f:
     ...     print(f.read(300))
     ...
     b'<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
     "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">\n\n\n<html
     xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">\n\n<head>\n
     <meta http-equiv="content-type" content="text/html; charset=utf-8" />\n
     <title>Python Programming '

Note that urlopen returns a bytes object.  This is because there is no
way for urlopen to automatically determine the encoding of the byte
stream it receives from the HTTP server.  In general, a program will
decode the returned bytes object to string once it determines or guesses
the appropriate encoding.

The following W3C document,
‘https://www.w3.org/International/O-charset’, lists the various ways in
which an (X)HTML or an XML document could have specified its encoding
information.

As the python.org website uses `utf-8' encoding as specified in its meta
tag, we will use the same for decoding the bytes object.

     >>> with urllib.request.urlopen('http://www.python.org/') as f:
     ...     print(f.read(100).decode('utf-8'))
     ...
     <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
     "http://www.w3.org/TR/xhtml1/DTD/xhtm

It is also possible to achieve the same result without using the *note
context manager: 661. approach.

     >>> import urllib.request
     >>> f = urllib.request.urlopen('http://www.python.org/')
     >>> print(f.read(100).decode('utf-8'))
     <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
     "http://www.w3.org/TR/xhtml1/DTD/xhtm

In the following example, we are sending a data-stream to the stdin of a
CGI and reading the data it returns to us.  Note that this example will
only work when the Python installation supports SSL.

     >>> import urllib.request
     >>> req = urllib.request.Request(url='https://localhost/cgi-bin/test.cgi',
     ...                       data=b'This data is passed to stdin of the CGI')
     >>> with urllib.request.urlopen(req) as f:
     ...     print(f.read().decode('utf-8'))
     ...
     Got Data: "This data is passed to stdin of the CGI"

The code for the sample CGI used in the above example is:

     #!/usr/bin/env python
     import sys
     data = sys.stdin.read()
     print('Content-type: text/plain\n\nGot Data: "%s"' % data)

Here is an example of doing a ‘PUT’ request using *note Request: 9dc.:

     import urllib.request
     DATA = b'some data'
     req = urllib.request.Request(url='http://localhost:8080', data=DATA,method='PUT')
     with urllib.request.urlopen(req) as f:
         pass
     print(f.status)
     print(f.reason)

Use of Basic HTTP Authentication:

     import urllib.request
     # Create an OpenerDirector with support for Basic HTTP Authentication...
     auth_handler = urllib.request.HTTPBasicAuthHandler()
     auth_handler.add_password(realm='PDQ Application',
                               uri='https://mahler:8092/site-updates.py',
                               user='klem',
                               passwd='kadidd!ehopper')
     opener = urllib.request.build_opener(auth_handler)
     # ...and install it globally so it can be used with urlopen.
     urllib.request.install_opener(opener)
     urllib.request.urlopen('http://www.example.com/login.html')

*note build_opener(): 2d75. provides many handlers by default, including
a *note ProxyHandler: 10d8.  By default, *note ProxyHandler: 10d8. uses
the environment variables named ‘<scheme>_proxy’, where ‘<scheme>’ is
the URL scheme involved.  For example, the ‘http_proxy’ environment
variable is read to obtain the HTTP proxy’s URL.

This example replaces the default *note ProxyHandler: 10d8. with one
that uses programmatically-supplied proxy URLs, and adds proxy
authorization support with *note ProxyBasicAuthHandler: 2d87.

     proxy_handler = urllib.request.ProxyHandler({'http': 'http://www.example.com:3128/'})
     proxy_auth_handler = urllib.request.ProxyBasicAuthHandler()
     proxy_auth_handler.add_password('realm', 'host', 'username', 'password')

     opener = urllib.request.build_opener(proxy_handler, proxy_auth_handler)
     # This time, rather than install the OpenerDirector, we use it directly:
     opener.open('http://www.example.com/login.html')

Adding HTTP headers:

Use the `headers' argument to the *note Request: 9dc. constructor, or:

     import urllib.request
     req = urllib.request.Request('http://www.example.com/')
     req.add_header('Referer', 'http://www.python.org/')
     # Customize the default User-Agent header value:
     req.add_header('User-Agent', 'urllib-example/0.1 (Contact: . . .)')
     r = urllib.request.urlopen(req)

*note OpenerDirector: 2d72. automatically adds a ‘User-Agent’ header to
every *note Request: 9dc.  To change this:

     import urllib.request
     opener = urllib.request.build_opener()
     opener.addheaders = [('User-agent', 'Mozilla/5.0')]
     opener.open('http://www.example.com/')

Also, remember that a few standard headers (‘Content-Length’,
‘Content-Type’ and ‘Host’) are added when the *note Request: 9dc. is
passed to *note urlopen(): 87b. (or *note OpenerDirector.open(): 9e0.).
Here is an example session that uses the ‘GET’ method to retrieve a URL
containing parameters:

     >>> import urllib.request
     >>> import urllib.parse
     >>> params = urllib.parse.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
     >>> url = "http://www.musi-cal.com/cgi-bin/query?%s" % params
     >>> with urllib.request.urlopen(url) as f:
     ...     print(f.read().decode('utf-8'))
     ...

The following example uses the ‘POST’ method instead.  Note that params
output from urlencode is encoded to bytes before it is sent to urlopen
as data:

     >>> import urllib.request
     >>> import urllib.parse
     >>> data = urllib.parse.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
     >>> data = data.encode('ascii')
     >>> with urllib.request.urlopen("http://requestb.in/xrbl82xr", data) as f:
     ...     print(f.read().decode('utf-8'))
     ...

The following example uses an explicitly specified HTTP proxy,
overriding environment settings:

     >>> import urllib.request
     >>> proxies = {'http': 'http://proxy.example.com:8080/'}
     >>> opener = urllib.request.FancyURLopener(proxies)
     >>> with opener.open("http://www.python.org") as f:
     ...     f.read().decode('utf-8')
     ...

The following example uses no proxies at all, overriding environment
settings:

     >>> import urllib.request
     >>> opener = urllib.request.FancyURLopener({})
     >>> with opener.open("http://www.python.org/") as f:
     ...     f.read().decode('utf-8')
     ...


File: python.info,  Node: Legacy interface,  Next: urllib request Restrictions,  Prev: Examples<22>,  Up: urllib request — Extensible library for opening URLs

5.21.6.24 Legacy interface
..........................

The following functions and classes are ported from the Python 2 module
‘urllib’ (as opposed to ‘urllib2’).  They might become deprecated at
some point in the future.

 -- Function: urllib.request.urlretrieve (url, filename=None,
          reporthook=None, data=None)

     Copy a network object denoted by a URL to a local file.  If the URL
     points to a local file, the object will not be copied unless
     filename is supplied.  Return a tuple ‘(filename, headers)’ where
     `filename' is the local file name under which the object can be
     found, and `headers' is whatever the ‘info()’ method of the object
     returned by *note urlopen(): 87b. returned (for a remote object).
     Exceptions are the same as for *note urlopen(): 87b.

     The second argument, if present, specifies the file location to
     copy to (if absent, the location will be a tempfile with a
     generated name).  The third argument, if present, is a callable
     that will be called once on establishment of the network connection
     and once after each block read thereafter.  The callable will be
     passed three arguments; a count of blocks transferred so far, a
     block size in bytes, and the total size of the file.  The third
     argument may be ‘-1’ on older FTP servers which do not return a
     file size in response to a retrieval request.

     The following example illustrates the most common usage scenario:

          >>> import urllib.request
          >>> local_filename, headers = urllib.request.urlretrieve('http://python.org/')
          >>> html = open(local_filename)
          >>> html.close()

     If the `url' uses the ‘http:’ scheme identifier, the optional
     `data' argument may be given to specify a ‘POST’ request (normally
     the request type is ‘GET’).  The `data' argument must be a bytes
     object in standard ‘application/x-www-form-urlencoded’ format; see
     the *note urllib.parse.urlencode(): 87a. function.

     *note urlretrieve(): 2dee. will raise ‘ContentTooShortError’ when
     it detects that the amount of data available was less than the
     expected amount (which is the size reported by a `Content-Length'
     header).  This can occur, for example, when the download is
     interrupted.

     The `Content-Length' is treated as a lower bound: if there’s more
     data to read, urlretrieve reads more data, but if less data is
     available, it raises the exception.

     You can still retrieve the downloaded data in this case, it is
     stored in the ‘content’ attribute of the exception instance.

     If no `Content-Length' header was supplied, urlretrieve can not
     check the size of the data it has downloaded, and just returns it.
     In this case you just have to assume that the download was
     successful.

 -- Function: urllib.request.urlcleanup ()

     Cleans up temporary files that may have been left behind by
     previous calls to *note urlretrieve(): 2dee.

 -- Class: urllib.request.URLopener (proxies=None, **x509)

     Deprecated since version 3.3.

     Base class for opening and reading URLs.  Unless you need to
     support opening objects using schemes other than ‘http:’, ‘ftp:’,
     or ‘file:’, you probably want to use *note FancyURLopener: 2d70.

     By default, the *note URLopener: 2d6f. class sends a ‘User-Agent’
     header of ‘urllib/VVV’, where `VVV' is the *note urllib: 126.
     version number.  Applications can define their own ‘User-Agent’
     header by subclassing *note URLopener: 2d6f. or *note
     FancyURLopener: 2d70. and setting the class attribute *note
     version: 2def. to an appropriate string value in the subclass
     definition.

     The optional `proxies' parameter should be a dictionary mapping
     scheme names to proxy URLs, where an empty dictionary turns proxies
     off completely.  Its default value is ‘None’, in which case
     environmental proxy settings will be used if present, as discussed
     in the definition of *note urlopen(): 87b, above.

     Additional keyword parameters, collected in `x509', may be used for
     authentication of the client when using the ‘https:’ scheme.  The
     keywords `key_file' and `cert_file' are supported to provide an SSL
     key and certificate; both are needed to support client
     authentication.

     *note URLopener: 2d6f. objects will raise an *note OSError: 304.
     exception if the server returns an error code.

      -- Method: open (fullurl, data=None)

          Open `fullurl' using the appropriate protocol.  This method
          sets up cache and proxy information, then calls the
          appropriate open method with its input arguments.  If the
          scheme is not recognized, *note open_unknown(): 2df1. is
          called.  The `data' argument has the same meaning as the
          `data' argument of *note urlopen(): 87b.

          This method always quotes `fullurl' using *note quote(): 512.

      -- Method: open_unknown (fullurl, data=None)

          Overridable interface to open unknown URL types.

      -- Method: retrieve (url, filename=None, reporthook=None,
               data=None)

          Retrieves the contents of `url' and places it in `filename'.
          The return value is a tuple consisting of a local filename and
          either an *note email.message.Message: 63b. object containing
          the response headers (for remote URLs) or ‘None’ (for local
          URLs).  The caller must then open and read the contents of
          `filename'.  If `filename' is not given and the URL refers to
          a local file, the input filename is returned.  If the URL is
          non-local and `filename' is not given, the filename is the
          output of *note tempfile.mktemp(): f7d. with a suffix that
          matches the suffix of the last path component of the input
          URL. If `reporthook' is given, it must be a function accepting
          three numeric parameters: A chunk number, the maximum size
          chunks are read in and the total size of the download (-1 if
          unknown).  It will be called once at the start and after each
          chunk of data is read from the network.  `reporthook' is
          ignored for local URLs.

          If the `url' uses the ‘http:’ scheme identifier, the optional
          `data' argument may be given to specify a ‘POST’ request
          (normally the request type is ‘GET’).  The `data' argument
          must in standard ‘application/x-www-form-urlencoded’ format;
          see the *note urllib.parse.urlencode(): 87a. function.

      -- Attribute: version

          Variable that specifies the user agent of the opener object.
          To get *note urllib: 126. to tell servers that it is a
          particular user agent, set this in a subclass as a class
          variable or in the constructor before calling the base
          constructor.

 -- Class: urllib.request.FancyURLopener (...)

     Deprecated since version 3.3.

     *note FancyURLopener: 2d70. subclasses *note URLopener: 2d6f.
     providing default handling for the following HTTP response codes:
     301, 302, 303, 307 and 401.  For the 30x response codes listed
     above, the ‘Location’ header is used to fetch the actual URL. For
     401 response codes (authentication required), basic HTTP
     authentication is performed.  For the 30x response codes, recursion
     is bounded by the value of the `maxtries' attribute, which defaults
     to 10.

     For all other response codes, the method ‘http_error_default()’ is
     called which you can override in subclasses to handle the error
     appropriately.

          Note: According to the letter of RFC 2616(1), 301 and 302
          responses to POST requests must not be automatically
          redirected without confirmation by the user.  In reality,
          browsers do allow automatic redirection of these responses,
          changing the POST to a GET, and *note urllib: 126. reproduces
          this behaviour.

     The parameters to the constructor are the same as those for *note
     URLopener: 2d6f.

          Note: When performing basic authentication, a *note
          FancyURLopener: 2d70. instance calls its *note
          prompt_user_passwd(): 2df2. method.  The default
          implementation asks the users for the required information on
          the controlling terminal.  A subclass may override this method
          to support more appropriate behavior if needed.

     The *note FancyURLopener: 2d70. class offers one additional method
     that should be overloaded to provide the appropriate behavior:

      -- Method: prompt_user_passwd (host, realm)

          Return information needed to authenticate the user at the
          given host in the specified security realm.  The return value
          should be a tuple, ‘(user, password)’, which can be used for
          basic authentication.

          The implementation prompts for this information on the
          terminal; an application should override this method to use an
          appropriate interaction model in the local environment.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2616.html


File: python.info,  Node: urllib request Restrictions,  Prev: Legacy interface,  Up: urllib request — Extensible library for opening URLs

5.21.6.25 ‘urllib.request’ Restrictions
.......................................

   * Currently, only the following protocols are supported: HTTP
     (versions 0.9 and 1.0), FTP, local files, and data URLs.

     Changed in version 3.4: Added support for data URLs.

   * The caching feature of *note urlretrieve(): 2dee. has been disabled
     until someone finds the time to hack proper processing of
     Expiration time headers.

   * There should be a function to query whether a particular URL is in
     the cache.

   * For backward compatibility, if a URL appears to point to a local
     file but the file can’t be opened, the URL is re-interpreted using
     the FTP protocol.  This can sometimes cause confusing error
     messages.

   * The *note urlopen(): 87b. and *note urlretrieve(): 2dee. functions
     can cause arbitrarily long delays while waiting for a network
     connection to be set up.  This means that it is difficult to build
     an interactive Web client using these functions without using
     threads.

   * The data returned by *note urlopen(): 87b. or *note urlretrieve():
     2dee. is the raw data returned by the server.  This may be binary
     data (such as an image), plain text or (for example) HTML. The HTTP
     protocol provides type information in the reply header, which can
     be inspected by looking at the ‘Content-Type’ header.  If the
     returned data is HTML, you can use the module *note html.parser:
     91. to parse it.

   * The code handling the FTP protocol cannot differentiate between a
     file and a directory.  This can lead to unexpected behavior when
     attempting to read a URL that points to a file that is not
     accessible.  If the URL ends in a ‘/’, it is assumed to refer to a
     directory and will be handled accordingly.  But if an attempt to
     read a file leads to a 550 error (meaning the URL cannot be found
     or is not accessible, often for permission reasons), then the path
     is treated as a directory in order to handle the case when a
     directory is specified by a URL but the trailing ‘/’ has been left
     off.  This can cause misleading results when you try to fetch a
     file whose read permissions make it inaccessible; the FTP code will
     try to read it, fail with a 550 error, and then perform a directory
     listing for the unreadable file.  If fine-grained control is
     needed, consider using the *note ftplib: 82. module, subclassing
     *note FancyURLopener: 2d70, or changing `_urlopener' to meet your
     needs.


File: python.info,  Node: urllib response — Response classes used by urllib,  Next: urllib parse — Parse URLs into components,  Prev: urllib request — Extensible library for opening URLs,  Up: Internet Protocols and Support

5.21.7 ‘urllib.response’ — Response classes used by urllib
----------------------------------------------------------

The *note urllib.response: 12a. module defines functions and classes
which define a minimal file-like interface, including ‘read()’ and
‘readline()’.  Functions defined by this module are used internally by
the *note urllib.request: 129. module.  The typical response object is a
*note urllib.response.addinfourl: 2d6d. instance:

 -- Class: urllib.response.addinfourl

      -- Attribute: url

          URL of the resource retrieved, commonly used to determine if a
          redirect was followed.

      -- Attribute: headers

          Returns the headers of the response in the form of an *note
          EmailMessage: 63c. instance.

      -- Attribute: status

          New in version 3.9.

          Status code returned by server.

      -- Method: geturl ()

          Deprecated since version 3.9: Deprecated in favor of *note
          url: 2df5.

      -- Method: info ()

          Deprecated since version 3.9: Deprecated in favor of *note
          headers: 2df6.

      -- Attribute: code

          Deprecated since version 3.9: Deprecated in favor of *note
          status: 2df7.

      -- Method: getstatus ()

          Deprecated since version 3.9: Deprecated in favor of *note
          status: 2df7.


File: python.info,  Node: urllib parse — Parse URLs into components,  Next: urllib error — Exception classes raised by urllib request,  Prev: urllib response — Response classes used by urllib,  Up: Internet Protocols and Support

5.21.8 ‘urllib.parse’ — Parse URLs into components
--------------------------------------------------

`Source code:' Lib/urllib/parse.py(1)

__________________________________________________________________

This module defines a standard interface to break Uniform Resource
Locator (URL) strings up in components (addressing scheme, network
location, path etc.), to combine the components back into a URL string,
and to convert a “relative URL” to an absolute URL given a “base URL.”

The module has been designed to match the Internet RFC on Relative
Uniform Resource Locators.  It supports the following URL schemes:
‘file’, ‘ftp’, ‘gopher’, ‘hdl’, ‘http’, ‘https’, ‘imap’, ‘mailto’,
‘mms’, ‘news’, ‘nntp’, ‘prospero’, ‘rsync’, ‘rtsp’, ‘rtspu’, ‘sftp’,
‘shttp’, ‘sip’, ‘sips’, ‘snews’, ‘svn’, ‘svn+ssh’, ‘telnet’, ‘wais’,
‘ws’, ‘wss’.

The *note urllib.parse: 128. module defines functions that fall into two
broad categories: URL parsing and URL quoting.  These are covered in
detail in the following sections.

* Menu:

* URL Parsing::
* Parsing ASCII Encoded Bytes::
* Structured Parse Results::
* URL Quoting::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/urllib/parse.py


File: python.info,  Node: URL Parsing,  Next: Parsing ASCII Encoded Bytes,  Up: urllib parse — Parse URLs into components

5.21.8.1 URL Parsing
....................

The URL parsing functions focus on splitting a URL string into its
components, or on combining URL components into a URL string.

 -- Function: urllib.parse.urlparse (urlstring, scheme='',
          allow_fragments=True)

     Parse a URL into six components, returning a 6-item *note named
     tuple: b7b.  This corresponds to the general structure of a URL:
     ‘scheme://netloc/path;parameters?query#fragment’.  Each tuple item
     is a string, possibly empty.  The components are not broken up into
     smaller parts (for example, the network location is a single
     string), and % escapes are not expanded.  The delimiters as shown
     above are not part of the result, except for a leading slash in the
     `path' component, which is retained if present.  For example:

          >>> from urllib.parse import urlparse
          >>> urlparse("scheme://netloc/path;parameters?query#fragment")
          ParseResult(scheme='scheme', netloc='netloc', path='/path;parameters', params='',
                      query='query', fragment='fragment')
          >>> o = urlparse("http://docs.python.org:80/3/library/urllib.parse.html?"
          ...              "highlight=params#url-parsing")
          >>> o
          ParseResult(scheme='http', netloc='docs.python.org:80',
                      path='/3/library/urllib.parse.html', params='',
                      query='highlight=params', fragment='url-parsing')
          >>> o.scheme
          'http'
          >>> o.netloc
          'docs.python.org:80'
          >>> o.hostname
          'docs.python.org'
          >>> o.port
          80
          >>> o._replace(fragment="").geturl()
          'http://docs.python.org:80/3/library/urllib.parse.html?highlight=params'

     Following the syntax specifications in RFC 1808(1), urlparse
     recognizes a netloc only if it is properly introduced by ‘//’.
     Otherwise the input is presumed to be a relative URL and thus to
     start with a path component.

          >>> from urllib.parse import urlparse
          >>> urlparse('//www.cwi.nl:80/%7Eguido/Python.html')
          ParseResult(scheme='', netloc='www.cwi.nl:80', path='/%7Eguido/Python.html',
                      params='', query='', fragment='')
          >>> urlparse('www.cwi.nl/%7Eguido/Python.html')
          ParseResult(scheme='', netloc='', path='www.cwi.nl/%7Eguido/Python.html',
                      params='', query='', fragment='')
          >>> urlparse('help/Python.html')
          ParseResult(scheme='', netloc='', path='help/Python.html', params='',
                      query='', fragment='')

     The `scheme' argument gives the default addressing scheme, to be
     used only if the URL does not specify one.  It should be the same
     type (text or bytes) as `urlstring', except that the default value
     ‘''’ is always allowed, and is automatically converted to ‘b''’ if
     appropriate.

     If the `allow_fragments' argument is false, fragment identifiers
     are not recognized.  Instead, they are parsed as part of the path,
     parameters or query component, and ‘fragment’ is set to the empty
     string in the return value.

     The return value is a *note named tuple: b7b, which means that its
     items can be accessed by index or as named attributes, which are:

     Attribute              Index       Value                         Value if not present
                                                                      
     ----------------------------------------------------------------------------------------------
                                                                      
     ‘scheme’               0           URL scheme specifier          `scheme' parameter
                                                                      
                                                                      
     ‘netloc’               1           Network location part         empty string
                                                                      
                                                                      
     ‘path’                 2           Hierarchical path             empty string
                                                                      
                                                                      
     ‘params’               3           No longer used                always an empty string
                                                                      
                                                                      
     ‘query’                4           Query component               empty string
                                                                      
                                                                      
     ‘fragment’             5           Fragment identifier           empty string
                                                                      
                                                                      
     ‘username’                         User name                     *note None: 203.
                                                                      
                                                                      
     ‘password’                         Password                      *note None: 203.
                                                                      
                                                                      
     ‘hostname’                         Host name (lower case)        *note None: 203.
                                                                      
                                                                      
     ‘port’                             Port number as integer, if    *note None: 203.
                                        present                       
                                        

     Reading the ‘port’ attribute will raise a *note ValueError: 16d. if
     an invalid port is specified in the URL. See section *note
     Structured Parse Results: 2dff. for more information on the result
     object.

     Unmatched square brackets in the ‘netloc’ attribute will raise a
     *note ValueError: 16d.

     Characters in the ‘netloc’ attribute that decompose under NFKC
     normalization (as used by the IDNA encoding) into any of ‘/’, ‘?’,
     ‘#’, ‘@’, or ‘:’ will raise a *note ValueError: 16d.  If the URL is
     decomposed before parsing, no error will be raised.

     As is the case with all named tuples, the subclass has a few
     additional methods and attributes that are particularly useful.
     One such method is ‘_replace()’.  The ‘_replace()’ method will
     return a new ParseResult object replacing specified fields with new
     values.

          >>> from urllib.parse import urlparse
          >>> u = urlparse('//www.cwi.nl:80/%7Eguido/Python.html')
          >>> u
          ParseResult(scheme='', netloc='www.cwi.nl:80', path='/%7Eguido/Python.html',
                      params='', query='', fragment='')
          >>> u._replace(scheme='http')
          ParseResult(scheme='http', netloc='www.cwi.nl:80', path='/%7Eguido/Python.html',
                      params='', query='', fragment='')

     Changed in version 3.2: Added IPv6 URL parsing capabilities.

     Changed in version 3.3: The fragment is now parsed for all URL
     schemes (unless `allow_fragment' is false), in accordance with RFC
     3986(2).  Previously, a whitelist of schemes that support fragments
     existed.

     Changed in version 3.6: Out-of-range port numbers now raise *note
     ValueError: 16d, instead of returning *note None: 203.

     Changed in version 3.8: Characters that affect netloc parsing under
     NFKC normalization will now raise *note ValueError: 16d.

 -- Function: urllib.parse.parse_qs (qs, keep_blank_values=False,
          strict_parsing=False, encoding='utf-8', errors='replace',
          max_num_fields=None, separator='&')

     Parse a query string given as a string argument (data of type
     ‘application/x-www-form-urlencoded’).  Data are returned as a
     dictionary.  The dictionary keys are the unique query variable
     names and the values are lists of values for each name.

     The optional argument `keep_blank_values' is a flag indicating
     whether blank values in percent-encoded queries should be treated
     as blank strings.  A true value indicates that blanks should be
     retained as blank strings.  The default false value indicates that
     blank values are to be ignored and treated as if they were not
     included.

     The optional argument `strict_parsing' is a flag indicating what to
     do with parsing errors.  If false (the default), errors are
     silently ignored.  If true, errors raise a *note ValueError: 16d.
     exception.

     The optional `encoding' and `errors' parameters specify how to
     decode percent-encoded sequences into Unicode characters, as
     accepted by the *note bytes.decode(): 171. method.

     The optional argument `max_num_fields' is the maximum number of
     fields to read.  If set, then throws a *note ValueError: 16d. if
     there are more than `max_num_fields' fields read.

     The optional argument `separator' is the symbol to use for
     separating the query arguments.  It defaults to ‘&’.

     Use the *note urllib.parse.urlencode(): 87a. function (with the
     ‘doseq’ parameter set to ‘True’) to convert such dictionaries into
     query strings.

     Changed in version 3.2: Add `encoding' and `errors' parameters.

     Changed in version 3.8: Added `max_num_fields' parameter.

     Changed in version 3.9.2: Added `separator' parameter with the
     default value of ‘&’.  Python versions earlier than Python 3.9.2
     allowed using both ‘;’ and ‘&’ as query parameter separator.  This
     has been changed to allow only a single separator key, with ‘&’ as
     the default separator.

 -- Function: urllib.parse.parse_qsl (qs, keep_blank_values=False,
          strict_parsing=False, encoding='utf-8', errors='replace',
          max_num_fields=None, separator='&')

     Parse a query string given as a string argument (data of type
     ‘application/x-www-form-urlencoded’).  Data are returned as a list
     of name, value pairs.

     The optional argument `keep_blank_values' is a flag indicating
     whether blank values in percent-encoded queries should be treated
     as blank strings.  A true value indicates that blanks should be
     retained as blank strings.  The default false value indicates that
     blank values are to be ignored and treated as if they were not
     included.

     The optional argument `strict_parsing' is a flag indicating what to
     do with parsing errors.  If false (the default), errors are
     silently ignored.  If true, errors raise a *note ValueError: 16d.
     exception.

     The optional `encoding' and `errors' parameters specify how to
     decode percent-encoded sequences into Unicode characters, as
     accepted by the *note bytes.decode(): 171. method.

     The optional argument `max_num_fields' is the maximum number of
     fields to read.  If set, then throws a *note ValueError: 16d. if
     there are more than `max_num_fields' fields read.

     The optional argument `separator' is the symbol to use for
     separating the query arguments.  It defaults to ‘&’.

     Use the *note urllib.parse.urlencode(): 87a. function to convert
     such lists of pairs into query strings.

     Changed in version 3.2: Add `encoding' and `errors' parameters.

     Changed in version 3.8: Added `max_num_fields' parameter.

     Changed in version 3.9.2: Added `separator' parameter with the
     default value of ‘&’.  Python versions earlier than Python 3.9.2
     allowed using both ‘;’ and ‘&’ as query parameter separator.  This
     has been changed to allow only a single separator key, with ‘&’ as
     the default separator.

 -- Function: urllib.parse.urlunparse (parts)

     Construct a URL from a tuple as returned by ‘urlparse()’.  The
     `parts' argument can be any six-item iterable.  This may result in
     a slightly different, but equivalent URL, if the URL that was
     parsed originally had unnecessary delimiters (for example, a ‘?’
     with an empty query; the RFC states that these are equivalent).

 -- Function: urllib.parse.urlsplit (urlstring, scheme='',
          allow_fragments=True)

     This is similar to *note urlparse(): 6f1, but does not split the
     params from the URL. This should generally be used instead of *note
     urlparse(): 6f1. if the more recent URL syntax allowing parameters
     to be applied to each segment of the `path' portion of the URL (see
     RFC 2396(3)) is wanted.  A separate function is needed to separate
     the path segments and parameters.  This function returns a 5-item
     *note named tuple: b7b.:

          (addressing scheme, network location, path, query, fragment identifier).

     The return value is a *note named tuple: b7b, its items can be
     accessed by index or as named attributes:

     Attribute              Index       Value                         Value if not present
                                                                      
     --------------------------------------------------------------------------------------------
                                                                      
     ‘scheme’               0           URL scheme specifier          `scheme' parameter
                                                                      
                                                                      
     ‘netloc’               1           Network location part         empty string
                                                                      
                                                                      
     ‘path’                 2           Hierarchical path             empty string
                                                                      
                                                                      
     ‘query’                3           Query component               empty string
                                                                      
                                                                      
     ‘fragment’             4           Fragment identifier           empty string
                                                                      
                                                                      
     ‘username’                         User name                     *note None: 203.
                                                                      
                                                                      
     ‘password’                         Password                      *note None: 203.
                                                                      
                                                                      
     ‘hostname’                         Host name (lower case)        *note None: 203.
                                                                      
                                                                      
     ‘port’                             Port number as integer, if    *note None: 203.
                                        present                       
                                        

     Reading the ‘port’ attribute will raise a *note ValueError: 16d. if
     an invalid port is specified in the URL. See section *note
     Structured Parse Results: 2dff. for more information on the result
     object.

     Unmatched square brackets in the ‘netloc’ attribute will raise a
     *note ValueError: 16d.

     Characters in the ‘netloc’ attribute that decompose under NFKC
     normalization (as used by the IDNA encoding) into any of ‘/’, ‘?’,
     ‘#’, ‘@’, or ‘:’ will raise a *note ValueError: 16d.  If the URL is
     decomposed before parsing, no error will be raised.

     Following the WHATWG spec(4) that updates RFC 3986, ASCII newline
     ‘\n’, ‘\r’ and tab ‘\t’ characters are stripped from the URL.

     Changed in version 3.6: Out-of-range port numbers now raise *note
     ValueError: 16d, instead of returning *note None: 203.

     Changed in version 3.8: Characters that affect netloc parsing under
     NFKC normalization will now raise *note ValueError: 16d.

     Changed in version 3.9.5: ASCII newline and tab characters are
     stripped from the URL.

 -- Function: urllib.parse.urlunsplit (parts)

     Combine the elements of a tuple as returned by *note urlsplit():
     6f0. into a complete URL as a string.  The `parts' argument can be
     any five-item iterable.  This may result in a slightly different,
     but equivalent URL, if the URL that was parsed originally had
     unnecessary delimiters (for example, a ?  with an empty query; the
     RFC states that these are equivalent).

 -- Function: urllib.parse.urljoin (base, url, allow_fragments=True)

     Construct a full (“absolute”) URL by combining a “base URL”
     (`base') with another URL (`url').  Informally, this uses
     components of the base URL, in particular the addressing scheme,
     the network location and (part of) the path, to provide missing
     components in the relative URL. For example:

          >>> from urllib.parse import urljoin
          >>> urljoin('http://www.cwi.nl/%7Eguido/Python.html', 'FAQ.html')
          'http://www.cwi.nl/%7Eguido/FAQ.html'

     The `allow_fragments' argument has the same meaning and default as
     for *note urlparse(): 6f1.

          Note: If `url' is an absolute URL (that is, it starts with
          ‘//’ or ‘scheme://’), the `url'’s hostname and/or scheme will
          be present in the result.  For example:

               >>> urljoin('http://www.cwi.nl/%7Eguido/Python.html',
               ...         '//www.python.org/%7Eguido')
               'http://www.python.org/%7Eguido'

          If you do not want that behavior, preprocess the `url' with
          *note urlsplit(): 6f0. and *note urlunsplit(): 2e01, removing
          possible `scheme' and `netloc' parts.

     Changed in version 3.5: Behavior updated to match the semantics
     defined in RFC 3986(5).

 -- Function: urllib.parse.urldefrag (url)

     If `url' contains a fragment identifier, return a modified version
     of `url' with no fragment identifier, and the fragment identifier
     as a separate string.  If there is no fragment identifier in `url',
     return `url' unmodified and an empty string.

     The return value is a *note named tuple: b7b, its items can be
     accessed by index or as named attributes:

     Attribute              Index       Value                         Value if not present
                                                                      
     --------------------------------------------------------------------------------------------
                                                                      
     ‘url’                  0           URL with no fragment          empty string
                                                                      
                                                                      
     ‘fragment’             1           Fragment identifier           empty string
                                                                      

     See section *note Structured Parse Results: 2dff. for more
     information on the result object.

     Changed in version 3.2: Result is a structured object rather than a
     simple 2-tuple.

 -- Function: urllib.parse.unwrap (url)

     Extract the url from a wrapped URL (that is, a string formatted as
     ‘<URL:scheme://host/path>’, ‘<scheme://host/path>’,
     ‘URL:scheme://host/path’ or ‘scheme://host/path’).  If `url' is not
     a wrapped URL, it is returned without changes.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc1808.html

   (2) https://tools.ietf.org/html/rfc3986.html

   (3) https://tools.ietf.org/html/rfc2396.html

   (4) https://url.spec.whatwg.org/#concept-basic-url-parser

   (5) https://tools.ietf.org/html/rfc3986.html


File: python.info,  Node: Parsing ASCII Encoded Bytes,  Next: Structured Parse Results,  Prev: URL Parsing,  Up: urllib parse — Parse URLs into components

5.21.8.2 Parsing ASCII Encoded Bytes
....................................

The URL parsing functions were originally designed to operate on
character strings only.  In practice, it is useful to be able to
manipulate properly quoted and encoded URLs as sequences of ASCII bytes.
Accordingly, the URL parsing functions in this module all operate on
*note bytes: 172. and *note bytearray: 173. objects in addition to *note
str: 205. objects.

If *note str: 205. data is passed in, the result will also contain only
*note str: 205. data.  If *note bytes: 172. or *note bytearray: 173.
data is passed in, the result will contain only *note bytes: 172. data.

Attempting to mix *note str: 205. data with *note bytes: 172. or *note
bytearray: 173. in a single function call will result in a *note
TypeError: 1fe. being raised, while attempting to pass in non-ASCII byte
values will trigger *note UnicodeDecodeError: 32b.

To support easier conversion of result objects between *note str: 205.
and *note bytes: 172, all return values from URL parsing functions
provide either an ‘encode()’ method (when the result contains *note str:
205. data) or a ‘decode()’ method (when the result contains *note bytes:
172. data).  The signatures of these methods match those of the
corresponding *note str: 205. and *note bytes: 172. methods (except that
the default encoding is ‘'ascii'’ rather than ‘'utf-8'’).  Each produces
a value of a corresponding type that contains either *note bytes: 172.
data (for ‘encode()’ methods) or *note str: 205. data (for ‘decode()’
methods).

Applications that need to operate on potentially improperly quoted URLs
that may contain non-ASCII data will need to do their own decoding from
bytes to characters before invoking the URL parsing methods.

The behaviour described in this section applies only to the URL parsing
functions.  The URL quoting functions use their own rules when producing
or consuming byte sequences as detailed in the documentation of the
individual URL quoting functions.

Changed in version 3.2: URL parsing functions now accept ASCII encoded
byte sequences


File: python.info,  Node: Structured Parse Results,  Next: URL Quoting,  Prev: Parsing ASCII Encoded Bytes,  Up: urllib parse — Parse URLs into components

5.21.8.3 Structured Parse Results
.................................

The result objects from the *note urlparse(): 6f1, *note urlsplit():
6f0. and *note urldefrag(): cac. functions are subclasses of the *note
tuple: 1a2. type.  These subclasses add the attributes listed in the
documentation for those functions, the encoding and decoding support
described in the previous section, as well as an additional method:

 -- Method: urllib.parse.SplitResult.geturl ()

     Return the re-combined version of the original URL as a string.
     This may differ from the original URL in that the scheme may be
     normalized to lower case and empty components may be dropped.
     Specifically, empty parameters, queries, and fragment identifiers
     will be removed.

     For *note urldefrag(): cac. results, only empty fragment
     identifiers will be removed.  For *note urlsplit(): 6f0. and *note
     urlparse(): 6f1. results, all noted changes will be made to the URL
     returned by this method.

     The result of this method remains unchanged if passed back through
     the original parsing function:

          >>> from urllib.parse import urlsplit
          >>> url = 'HTTP://www.Python.org/doc/#'
          >>> r1 = urlsplit(url)
          >>> r1.geturl()
          'http://www.Python.org/doc/'
          >>> r2 = urlsplit(r1.geturl())
          >>> r2.geturl()
          'http://www.Python.org/doc/'

The following classes provide the implementations of the structured
parse results when operating on *note str: 205. objects:

 -- Class: urllib.parse.DefragResult (url, fragment)

     Concrete class for *note urldefrag(): cac. results containing *note
     str: 205. data.  The ‘encode()’ method returns a *note
     DefragResultBytes: 2e07. instance.

     New in version 3.2.

 -- Class: urllib.parse.ParseResult (scheme, netloc, path, params,
          query, fragment)

     Concrete class for *note urlparse(): 6f1. results containing *note
     str: 205. data.  The ‘encode()’ method returns a *note
     ParseResultBytes: 2e09. instance.

 -- Class: urllib.parse.SplitResult (scheme, netloc, path, query,
          fragment)

     Concrete class for *note urlsplit(): 6f0. results containing *note
     str: 205. data.  The ‘encode()’ method returns a *note
     SplitResultBytes: 2e0b. instance.

The following classes provide the implementations of the parse results
when operating on *note bytes: 172. or *note bytearray: 173. objects:

 -- Class: urllib.parse.DefragResultBytes (url, fragment)

     Concrete class for *note urldefrag(): cac. results containing *note
     bytes: 172. data.  The ‘decode()’ method returns a *note
     DefragResult: 2e06. instance.

     New in version 3.2.

 -- Class: urllib.parse.ParseResultBytes (scheme, netloc, path, params,
          query, fragment)

     Concrete class for *note urlparse(): 6f1. results containing *note
     bytes: 172. data.  The ‘decode()’ method returns a *note
     ParseResult: 2e08. instance.

     New in version 3.2.

 -- Class: urllib.parse.SplitResultBytes (scheme, netloc, path, query,
          fragment)

     Concrete class for *note urlsplit(): 6f0. results containing *note
     bytes: 172. data.  The ‘decode()’ method returns a *note
     SplitResult: 2e0a. instance.

     New in version 3.2.


File: python.info,  Node: URL Quoting,  Prev: Structured Parse Results,  Up: urllib parse — Parse URLs into components

5.21.8.4 URL Quoting
....................

The URL quoting functions focus on taking program data and making it
safe for use as URL components by quoting special characters and
appropriately encoding non-ASCII text.  They also support reversing
these operations to recreate the original data from the contents of a
URL component if that task isn’t already covered by the URL parsing
functions above.

 -- Function: urllib.parse.quote (string, safe='/', encoding=None,
          errors=None)

     Replace special characters in `string' using the ‘%xx’ escape.
     Letters, digits, and the characters ‘'_.-~'’ are never quoted.  By
     default, this function is intended for quoting the path section of
     a URL. The optional `safe' parameter specifies additional ASCII
     characters that should not be quoted — its default value is ‘'/'’.

     `string' may be either a *note str: 205. or a *note bytes: 172.
     object.

     Changed in version 3.7: Moved from RFC 2396(1) to RFC 3986(2) for
     quoting URL strings.  “~” is now included in the set of unreserved
     characters.

     The optional `encoding' and `errors' parameters specify how to deal
     with non-ASCII characters, as accepted by the *note str.encode():
     170. method.  `encoding' defaults to ‘'utf-8'’.  `errors' defaults
     to ‘'strict'’, meaning unsupported characters raise a *note
     UnicodeEncodeError: 32a.  `encoding' and `errors' must not be
     supplied if `string' is a *note bytes: 172, or a *note TypeError:
     1fe. is raised.

     Note that ‘quote(string, safe, encoding, errors)’ is equivalent to
     ‘quote_from_bytes(string.encode(encoding, errors), safe)’.

     Example: ‘quote('/El Niño/')’ yields ‘'/El%20Ni%C3%B1o/'’.

 -- Function: urllib.parse.quote_plus (string, safe='', encoding=None,
          errors=None)

     Like *note quote(): 512, but also replace spaces with plus signs,
     as required for quoting HTML form values when building up a query
     string to go into a URL. Plus signs in the original string are
     escaped unless they are included in `safe'.  It also does not have
     `safe' default to ‘'/'’.

     Example: ‘quote_plus('/El Niño/')’ yields ‘'%2FEl+Ni%C3%B1o%2F'’.

 -- Function: urllib.parse.quote_from_bytes (bytes, safe='/')

     Like *note quote(): 512, but accepts a *note bytes: 172. object
     rather than a *note str: 205, and does not perform string-to-bytes
     encoding.

     Example: ‘quote_from_bytes(b'a&\xef')’ yields ‘'a%26%EF'’.

 -- Function: urllib.parse.unquote (string, encoding='utf-8',
          errors='replace')

     Replace ‘%xx’ escapes with their single-character equivalent.  The
     optional `encoding' and `errors' parameters specify how to decode
     percent-encoded sequences into Unicode characters, as accepted by
     the *note bytes.decode(): 171. method.

     `string' may be either a *note str: 205. or a *note bytes: 172.
     object.

     `encoding' defaults to ‘'utf-8'’.  `errors' defaults to
     ‘'replace'’, meaning invalid sequences are replaced by a
     placeholder character.

     Example: ‘unquote('/El%20Ni%C3%B1o/')’ yields ‘'/El Niño/'’.

     Changed in version 3.9: `string' parameter supports bytes and str
     objects (previously only str).

 -- Function: urllib.parse.unquote_plus (string, encoding='utf-8',
          errors='replace')

     Like *note unquote(): 10db, but also replace plus signs with
     spaces, as required for unquoting HTML form values.

     `string' must be a *note str: 205.

     Example: ‘unquote_plus('/El+Ni%C3%B1o/')’ yields ‘'/El Niño/'’.

 -- Function: urllib.parse.unquote_to_bytes (string)

     Replace ‘%xx’ escapes with their single-octet equivalent, and
     return a *note bytes: 172. object.

     `string' may be either a *note str: 205. or a *note bytes: 172.
     object.

     If it is a *note str: 205, unescaped non-ASCII characters in
     `string' are encoded into UTF-8 bytes.

     Example: ‘unquote_to_bytes('a%26%EF')’ yields ‘b'a&\xef'’.

 -- Function: urllib.parse.urlencode (query, doseq=False, safe='',
          encoding=None, errors=None, quote_via=quote_plus)

     Convert a mapping object or a sequence of two-element tuples, which
     may contain *note str: 205. or *note bytes: 172. objects, to a
     percent-encoded ASCII text string.  If the resultant string is to
     be used as a `data' for POST operation with the *note urlopen():
     87b. function, then it should be encoded to bytes, otherwise it
     would result in a *note TypeError: 1fe.

     The resulting string is a series of ‘key=value’ pairs separated by
     ‘'&'’ characters, where both `key' and `value' are quoted using the
     `quote_via' function.  By default, *note quote_plus(): cad. is used
     to quote the values, which means spaces are quoted as a ‘'+'’
     character and ‘/’ characters are encoded as ‘%2F’, which follows
     the standard for GET requests
     (‘application/x-www-form-urlencoded’).  An alternate function that
     can be passed as `quote_via' is *note quote(): 512, which will
     encode spaces as ‘%20’ and not encode ‘/’ characters.  For maximum
     control of what is quoted, use ‘quote’ and specify a value for
     `safe'.

     When a sequence of two-element tuples is used as the `query'
     argument, the first element of each tuple is a key and the second
     is a value.  The value element in itself can be a sequence and in
     that case, if the optional parameter `doseq' evaluates to ‘True’,
     individual ‘key=value’ pairs separated by ‘'&'’ are generated for
     each element of the value sequence for the key.  The order of
     parameters in the encoded string will match the order of parameter
     tuples in the sequence.

     The `safe', `encoding', and `errors' parameters are passed down to
     `quote_via' (the `encoding' and `errors' parameters are only passed
     when a query element is a *note str: 205.).

     To reverse this encoding process, *note parse_qs(): 27f. and *note
     parse_qsl(): 280. are provided in this module to parse query
     strings into Python data structures.

     Refer to *note urllib examples: 2dec. to find out how the *note
     urllib.parse.urlencode(): 87a. method can be used for generating
     the query string of a URL or data for a POST request.

     Changed in version 3.2: `query' supports bytes and string objects.

     New in version 3.5: `quote_via' parameter.

See also
........

WHATWG(3) - URL Living standard

     Working Group for the URL Standard that defines URLs, domains, IP
     addresses, the application/x-www-form-urlencoded format, and their
     API.

RFC 3986(4) - Uniform Resource Identifiers

     This is the current standard (STD66).  Any changes to urllib.parse
     module should conform to this.  Certain deviations could be
     observed, which are mostly for backward compatibility purposes and
     for certain de-facto parsing requirements as commonly observed in
     major browsers.

RFC 2732(5) - Format for Literal IPv6 Addresses in URL’s.

     This specifies the parsing requirements of IPv6 URLs.

RFC 2396(6) - Uniform Resource Identifiers (URI): Generic Syntax

     Document describing the generic syntactic requirements for both
     Uniform Resource Names (URNs) and Uniform Resource Locators (URLs).

RFC 2368(7) - The mailto URL scheme.

     Parsing requirements for mailto URL schemes.

RFC 1808(8) - Relative Uniform Resource Locators

     This Request For Comments includes the rules for joining an
     absolute and a relative URL, including a fair number of “Abnormal
     Examples” which govern the treatment of border cases.

RFC 1738(9) - Uniform Resource Locators (URL)

     This specifies the formal syntax and semantics of absolute URLs.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2396.html

   (2) https://tools.ietf.org/html/rfc3986.html

   (3) https://url.spec.whatwg.org/

   (4) https://tools.ietf.org/html/rfc3986.html

   (5) https://tools.ietf.org/html/rfc2732.html

   (6) https://tools.ietf.org/html/rfc2396.html

   (7) https://tools.ietf.org/html/rfc2368.html

   (8) https://tools.ietf.org/html/rfc1808.html

   (9) https://tools.ietf.org/html/rfc1738.html


File: python.info,  Node: urllib error — Exception classes raised by urllib request,  Next: urllib robotparser — Parser for robots txt,  Prev: urllib parse — Parse URLs into components,  Up: Internet Protocols and Support

5.21.9 ‘urllib.error’ — Exception classes raised by urllib.request
------------------------------------------------------------------

`Source code:' Lib/urllib/error.py(1)

__________________________________________________________________

The *note urllib.error: 127. module defines the exception classes for
exceptions raised by *note urllib.request: 129.  The base exception
class is *note URLError: 2d71.

The following exceptions are raised by *note urllib.error: 127. as
appropriate:

 -- Exception: urllib.error.URLError

     The handlers raise this exception (or derived exceptions) when they
     run into a problem.  It is a subclass of *note OSError: 304.

      -- Attribute: reason

          The reason for this error.  It can be a message string or
          another exception instance.

     Changed in version 3.3: *note URLError: 2d71. has been made a
     subclass of *note OSError: 304. instead of *note IOError: a73.

 -- Exception: urllib.error.HTTPError

     Though being an exception (a subclass of *note URLError: 2d71.), an
     *note HTTPError: 9e2. can also function as a non-exceptional
     file-like return value (the same thing that *note urlopen(): 87b.
     returns).  This is useful when handling exotic HTTP errors, such as
     requests for authentication.

      -- Attribute: code

          An HTTP status code as defined in RFC 2616(2).  This numeric
          value corresponds to a value found in the dictionary of codes
          as found in *note
          http.server.BaseHTTPRequestHandler.responses: 2e15.

      -- Attribute: reason

          This is usually a string explaining the reason for this error.

      -- Attribute: headers

          The HTTP response headers for the HTTP request that caused the
          *note HTTPError: 9e2.

          New in version 3.4.

 -- Exception: urllib.error.ContentTooShortError (msg, content)

     This exception is raised when the *note urlretrieve(): 2dee.
     function detects that the amount of the downloaded data is less
     than the expected amount (given by the `Content-Length' header).
     The ‘content’ attribute stores the downloaded (and supposedly
     truncated) data.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/urllib/error.py

   (2) https://tools.ietf.org/html/rfc2616.html


File: python.info,  Node: urllib robotparser — Parser for robots txt,  Next: http — HTTP modules,  Prev: urllib error — Exception classes raised by urllib request,  Up: Internet Protocols and Support

5.21.10 ‘urllib.robotparser’ — Parser for robots.txt
----------------------------------------------------

`Source code:' Lib/urllib/robotparser.py(1)

__________________________________________________________________

This module provides a single class, *note RobotFileParser: 6a4, which
answers questions about whether or not a particular user agent can fetch
a URL on the Web site that published the ‘robots.txt’ file.  For more
details on the structure of ‘robots.txt’ files, see
‘http://www.robotstxt.org/orig.html’.

 -- Class: urllib.robotparser.RobotFileParser (url='')

     This class provides methods to read, parse and answer questions
     about the ‘robots.txt’ file at `url'.

      -- Method: set_url (url)

          Sets the URL referring to a ‘robots.txt’ file.

      -- Method: read ()

          Reads the ‘robots.txt’ URL and feeds it to the parser.

      -- Method: parse (lines)

          Parses the lines argument.

      -- Method: can_fetch (useragent, url)

          Returns ‘True’ if the `useragent' is allowed to fetch the
          `url' according to the rules contained in the parsed
          ‘robots.txt’ file.

      -- Method: mtime ()

          Returns the time the ‘robots.txt’ file was last fetched.  This
          is useful for long-running web spiders that need to check for
          new ‘robots.txt’ files periodically.

      -- Method: modified ()

          Sets the time the ‘robots.txt’ file was last fetched to the
          current time.

      -- Method: crawl_delay (useragent)

          Returns the value of the ‘Crawl-delay’ parameter from
          ‘robots.txt’ for the `useragent' in question.  If there is no
          such parameter or it doesn’t apply to the `useragent'
          specified or the ‘robots.txt’ entry for this parameter has
          invalid syntax, return ‘None’.

          New in version 3.6.

      -- Method: request_rate (useragent)

          Returns the contents of the ‘Request-rate’ parameter from
          ‘robots.txt’ as a *note named tuple: b7b.
          ‘RequestRate(requests, seconds)’.  If there is no such
          parameter or it doesn’t apply to the `useragent' specified or
          the ‘robots.txt’ entry for this parameter has invalid syntax,
          return ‘None’.

          New in version 3.6.

      -- Method: site_maps ()

          Returns the contents of the ‘Sitemap’ parameter from
          ‘robots.txt’ in the form of a *note list(): 1f8.  If there is
          no such parameter or the ‘robots.txt’ entry for this parameter
          has invalid syntax, return ‘None’.

          New in version 3.8.

The following example demonstrates basic use of the *note
RobotFileParser: 6a4. class:

     >>> import urllib.robotparser
     >>> rp = urllib.robotparser.RobotFileParser()
     >>> rp.set_url("http://www.musi-cal.com/robots.txt")
     >>> rp.read()
     >>> rrate = rp.request_rate("*")
     >>> rrate.requests
     3
     >>> rrate.seconds
     20
     >>> rp.crawl_delay("*")
     6
     >>> rp.can_fetch("*", "http://www.musi-cal.com/cgi-bin/search?city=San+Francisco")
     False
     >>> rp.can_fetch("*", "http://www.musi-cal.com/")
     True

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/urllib/robotparser.py


File: python.info,  Node: http — HTTP modules,  Next: http client — HTTP protocol client,  Prev: urllib robotparser — Parser for robots txt,  Up: Internet Protocols and Support

5.21.11 ‘http’ — HTTP modules
-----------------------------

`Source code:' Lib/http/__init__.py(1)

__________________________________________________________________

*note http: 92. is a package that collects several modules for working
with the HyperText Transfer Protocol:

   * *note http.client: 93. is a low-level HTTP protocol client; for
     high-level URL opening use *note urllib.request: 129.

   * *note http.server: 96. contains basic HTTP server classes based on
     *note socketserver: f0.

   * *note http.cookies: 95. has utilities for implementing state
     management with cookies

   * *note http.cookiejar: 94. provides persistence of cookies

*note http: 92. is also a module that defines a number of HTTP status
codes and associated messages through the *note http.HTTPStatus: 1ac.
enum:

 -- Class: http.HTTPStatus

     New in version 3.5.

     A subclass of *note enum.IntEnum: 684. that defines a set of HTTP
     status codes, reason phrases and long descriptions written in
     English.

     Usage:

          >>> from http import HTTPStatus
          >>> HTTPStatus.OK
          <HTTPStatus.OK: 200>
          >>> HTTPStatus.OK == 200
          True
          >>> HTTPStatus.OK.value
          200
          >>> HTTPStatus.OK.phrase
          'OK'
          >>> HTTPStatus.OK.description
          'Request fulfilled, document follows'
          >>> list(HTTPStatus)
          [<HTTPStatus.CONTINUE: 100>, <HTTPStatus.SWITCHING_PROTOCOLS: 101>, ...]

* Menu:

* HTTP status codes::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/http/__init__.py


File: python.info,  Node: HTTP status codes,  Up: http — HTTP modules

5.21.11.1 HTTP status codes
...........................

Supported, IANA-registered(1) status codes available in *note
http.HTTPStatus: 1ac. are:

Code        Enum Name                               Details
                                                    
----------------------------------------------------------------------------------------------------------------------------------------
                                                    
‘100’       ‘CONTINUE’                              HTTP/1.1 RFC 7231(2), Section 6.2.1
                                                    
                                                    
‘101’       ‘SWITCHING_PROTOCOLS’                   HTTP/1.1 RFC 7231(3), Section 6.2.2
                                                    
                                                    
‘102’       ‘PROCESSING’                            WebDAV RFC 2518(4), Section 10.1
                                                    
                                                    
‘103’       ‘EARLY_HINTS’                           An HTTP Status Code for Indicating Hints RFC 8297(5)
                                                    
                                                    
‘200’       ‘OK’                                    HTTP/1.1 RFC 7231(6), Section 6.3.1
                                                    
                                                    
‘201’       ‘CREATED’                               HTTP/1.1 RFC 7231(7), Section 6.3.2
                                                    
                                                    
‘202’       ‘ACCEPTED’                              HTTP/1.1 RFC 7231(8), Section 6.3.3
                                                    
                                                    
‘203’       ‘NON_AUTHORITATIVE_INFORMATION’         HTTP/1.1 RFC 7231(9), Section 6.3.4
                                                    
                                                    
‘204’       ‘NO_CONTENT’                            HTTP/1.1 RFC 7231(10), Section 6.3.5
                                                    
                                                    
‘205’       ‘RESET_CONTENT’                         HTTP/1.1 RFC 7231(11), Section 6.3.6
                                                    
                                                    
‘206’       ‘PARTIAL_CONTENT’                       HTTP/1.1 RFC 7233(12), Section 4.1
                                                    
                                                    
‘207’       ‘MULTI_STATUS’                          WebDAV RFC 4918(13), Section 11.1
                                                    
                                                    
‘208’       ‘ALREADY_REPORTED’                      WebDAV Binding Extensions RFC 5842(14), Section 7.1 (Experimental)
                                                    
                                                    
‘226’       ‘IM_USED’                               Delta Encoding in HTTP RFC 3229(15), Section 10.4.1
                                                    
                                                    
‘300’       ‘MULTIPLE_CHOICES’                      HTTP/1.1 RFC 7231(16), Section 6.4.1
                                                    
                                                    
‘301’       ‘MOVED_PERMANENTLY’                     HTTP/1.1 RFC 7231(17), Section 6.4.2
                                                    
                                                    
‘302’       ‘FOUND’                                 HTTP/1.1 RFC 7231(18), Section 6.4.3
                                                    
                                                    
‘303’       ‘SEE_OTHER’                             HTTP/1.1 RFC 7231(19), Section 6.4.4
                                                    
                                                    
‘304’       ‘NOT_MODIFIED’                          HTTP/1.1 RFC 7232(20), Section 4.1
                                                    
                                                    
‘305’       ‘USE_PROXY’                             HTTP/1.1 RFC 7231(21), Section 6.4.5
                                                    
                                                    
‘307’       ‘TEMPORARY_REDIRECT’                    HTTP/1.1 RFC 7231(22), Section 6.4.7
                                                    
                                                    
‘308’       ‘PERMANENT_REDIRECT’                    Permanent Redirect RFC 7238(23), Section 3 (Experimental)
                                                    
                                                    
‘400’       ‘BAD_REQUEST’                           HTTP/1.1 RFC 7231(24), Section 6.5.1
                                                    
                                                    
‘401’       ‘UNAUTHORIZED’                          HTTP/1.1 Authentication RFC 7235(25), Section 3.1
                                                    
                                                    
‘402’       ‘PAYMENT_REQUIRED’                      HTTP/1.1 RFC 7231(26), Section 6.5.2
                                                    
                                                    
‘403’       ‘FORBIDDEN’                             HTTP/1.1 RFC 7231(27), Section 6.5.3
                                                    
                                                    
‘404’       ‘NOT_FOUND’                             HTTP/1.1 RFC 7231(28), Section 6.5.4
                                                    
                                                    
‘405’       ‘METHOD_NOT_ALLOWED’                    HTTP/1.1 RFC 7231(29), Section 6.5.5
                                                    
                                                    
‘406’       ‘NOT_ACCEPTABLE’                        HTTP/1.1 RFC 7231(30), Section 6.5.6
                                                    
                                                    
‘407’       ‘PROXY_AUTHENTICATION_REQUIRED’         HTTP/1.1 Authentication RFC 7235(31), Section 3.2
                                                    
                                                    
‘408’       ‘REQUEST_TIMEOUT’                       HTTP/1.1 RFC 7231(32), Section 6.5.7
                                                    
                                                    
‘409’       ‘CONFLICT’                              HTTP/1.1 RFC 7231(33), Section 6.5.8
                                                    
                                                    
‘410’       ‘GONE’                                  HTTP/1.1 RFC 7231(34), Section 6.5.9
                                                    
                                                    
‘411’       ‘LENGTH_REQUIRED’                       HTTP/1.1 RFC 7231(35), Section 6.5.10
                                                    
                                                    
‘412’       ‘PRECONDITION_FAILED’                   HTTP/1.1 RFC 7232(36), Section 4.2
                                                    
                                                    
‘413’       ‘REQUEST_ENTITY_TOO_LARGE’              HTTP/1.1 RFC 7231(37), Section 6.5.11
                                                    
                                                    
‘414’       ‘REQUEST_URI_TOO_LONG’                  HTTP/1.1 RFC 7231(38), Section 6.5.12
                                                    
                                                    
‘415’       ‘UNSUPPORTED_MEDIA_TYPE’                HTTP/1.1 RFC 7231(39), Section 6.5.13
                                                    
                                                    
‘416’       ‘REQUESTED_RANGE_NOT_SATISFIABLE’       HTTP/1.1 Range Requests RFC 7233(40), Section 4.4
                                                    
                                                    
‘417’       ‘EXPECTATION_FAILED’                    HTTP/1.1 RFC 7231(41), Section 6.5.14
                                                    
                                                    
‘418’       ‘IM_A_TEAPOT’                           HTCPCP/1.0 RFC 2324(42), Section 2.3.2
                                                    
                                                    
‘421’       ‘MISDIRECTED_REQUEST’                   HTTP/2 RFC 7540(43), Section 9.1.2
                                                    
                                                    
‘422’       ‘UNPROCESSABLE_ENTITY’                  WebDAV RFC 4918(44), Section 11.2
                                                    
                                                    
‘423’       ‘LOCKED’                                WebDAV RFC 4918(45), Section 11.3
                                                    
                                                    
‘424’       ‘FAILED_DEPENDENCY’                     WebDAV RFC 4918(46), Section 11.4
                                                    
                                                    
‘425’       ‘TOO_EARLY’                             Using Early Data in HTTP RFC 8470(47)
                                                    
                                                    
‘426’       ‘UPGRADE_REQUIRED’                      HTTP/1.1 RFC 7231(48), Section 6.5.15
                                                    
                                                    
‘428’       ‘PRECONDITION_REQUIRED’                 Additional HTTP Status Codes RFC 6585(49)
                                                    
                                                    
‘429’       ‘TOO_MANY_REQUESTS’                     Additional HTTP Status Codes RFC 6585(50)
                                                    
                                                    
‘431’       ‘REQUEST_HEADER_FIELDS_TOO_LARGE’       Additional HTTP Status Codes RFC 6585(51)
                                                    
                                                    
‘451’       ‘UNAVAILABLE_FOR_LEGAL_REASONS’         An HTTP Status Code to Report Legal Obstacles RFC 7725(52)
                                                    
                                                    
‘500’       ‘INTERNAL_SERVER_ERROR’                 HTTP/1.1 RFC 7231(53), Section 6.6.1
                                                    
                                                    
‘501’       ‘NOT_IMPLEMENTED’                       HTTP/1.1 RFC 7231(54), Section 6.6.2
                                                    
                                                    
‘502’       ‘BAD_GATEWAY’                           HTTP/1.1 RFC 7231(55), Section 6.6.3
                                                    
                                                    
‘503’       ‘SERVICE_UNAVAILABLE’                   HTTP/1.1 RFC 7231(56), Section 6.6.4
                                                    
                                                    
‘504’       ‘GATEWAY_TIMEOUT’                       HTTP/1.1 RFC 7231(57), Section 6.6.5
                                                    
                                                    
‘505’       ‘HTTP_VERSION_NOT_SUPPORTED’            HTTP/1.1 RFC 7231(58), Section 6.6.6
                                                    
                                                    
‘506’       ‘VARIANT_ALSO_NEGOTIATES’               Transparent Content Negotiation in HTTP RFC 2295(59), Section 8.1 (Experimental)
                                                    
                                                    
‘507’       ‘INSUFFICIENT_STORAGE’                  WebDAV RFC 4918(60), Section 11.5
                                                    
                                                    
‘508’       ‘LOOP_DETECTED’                         WebDAV Binding Extensions RFC 5842(61), Section 7.2 (Experimental)
                                                    
                                                    
‘510’       ‘NOT_EXTENDED’                          An HTTP Extension Framework RFC 2774(62), Section 7 (Experimental)
                                                    
                                                    
‘511’       ‘NETWORK_AUTHENTICATION_REQUIRED’       Additional HTTP Status Codes RFC 6585(63), Section 6
                                                    

In order to preserve backwards compatibility, enum values are also
present in the *note http.client: 93. module in the form of constants.
The enum name is equal to the constant name (i.e.  ‘http.HTTPStatus.OK’
is also available as ‘http.client.OK’).

Changed in version 3.7: Added ‘421 MISDIRECTED_REQUEST’ status code.

New in version 3.8: Added ‘451 UNAVAILABLE_FOR_LEGAL_REASONS’ status
code.

New in version 3.9: Added ‘103 EARLY_HINTS’, ‘418 IM_A_TEAPOT’ and ‘425
TOO_EARLY’ status codes.

   ---------- Footnotes ----------

   (1) 
https://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml

   (2) https://tools.ietf.org/html/rfc7231.html

   (3) https://tools.ietf.org/html/rfc7231.html

   (4) https://tools.ietf.org/html/rfc2518.html

   (5) https://tools.ietf.org/html/rfc8297.html

   (6) https://tools.ietf.org/html/rfc7231.html

   (7) https://tools.ietf.org/html/rfc7231.html

   (8) https://tools.ietf.org/html/rfc7231.html

   (9) https://tools.ietf.org/html/rfc7231.html

   (10) https://tools.ietf.org/html/rfc7231.html

   (11) https://tools.ietf.org/html/rfc7231.html

   (12) https://tools.ietf.org/html/rfc7233.html

   (13) https://tools.ietf.org/html/rfc4918.html

   (14) https://tools.ietf.org/html/rfc5842.html

   (15) https://tools.ietf.org/html/rfc3229.html

   (16) https://tools.ietf.org/html/rfc7231.html

   (17) https://tools.ietf.org/html/rfc7231.html

   (18) https://tools.ietf.org/html/rfc7231.html

   (19) https://tools.ietf.org/html/rfc7231.html

   (20) https://tools.ietf.org/html/rfc7232.html

   (21) https://tools.ietf.org/html/rfc7231.html

   (22) https://tools.ietf.org/html/rfc7231.html

   (23) https://tools.ietf.org/html/rfc7238.html

   (24) https://tools.ietf.org/html/rfc7231.html

   (25) https://tools.ietf.org/html/rfc7235.html

   (26) https://tools.ietf.org/html/rfc7231.html

   (27) https://tools.ietf.org/html/rfc7231.html

   (28) https://tools.ietf.org/html/rfc7231.html

   (29) https://tools.ietf.org/html/rfc7231.html

   (30) https://tools.ietf.org/html/rfc7231.html

   (31) https://tools.ietf.org/html/rfc7235.html

   (32) https://tools.ietf.org/html/rfc7231.html

   (33) https://tools.ietf.org/html/rfc7231.html

   (34) https://tools.ietf.org/html/rfc7231.html

   (35) https://tools.ietf.org/html/rfc7231.html

   (36) https://tools.ietf.org/html/rfc7232.html

   (37) https://tools.ietf.org/html/rfc7231.html

   (38) https://tools.ietf.org/html/rfc7231.html

   (39) https://tools.ietf.org/html/rfc7231.html

   (40) https://tools.ietf.org/html/rfc7233.html

   (41) https://tools.ietf.org/html/rfc7231.html

   (42) https://tools.ietf.org/html/rfc2324.html

   (43) https://tools.ietf.org/html/rfc7540.html

   (44) https://tools.ietf.org/html/rfc4918.html

   (45) https://tools.ietf.org/html/rfc4918.html

   (46) https://tools.ietf.org/html/rfc4918.html

   (47) https://tools.ietf.org/html/rfc8470.html

   (48) https://tools.ietf.org/html/rfc7231.html

   (49) https://tools.ietf.org/html/rfc6585.html

   (50) https://tools.ietf.org/html/rfc6585.html

   (51) https://tools.ietf.org/html/rfc6585.html

   (52) https://tools.ietf.org/html/rfc7725.html

   (53) https://tools.ietf.org/html/rfc7231.html

   (54) https://tools.ietf.org/html/rfc7231.html

   (55) https://tools.ietf.org/html/rfc7231.html

   (56) https://tools.ietf.org/html/rfc7231.html

   (57) https://tools.ietf.org/html/rfc7231.html

   (58) https://tools.ietf.org/html/rfc7231.html

   (59) https://tools.ietf.org/html/rfc2295.html

   (60) https://tools.ietf.org/html/rfc4918.html

   (61) https://tools.ietf.org/html/rfc5842.html

   (62) https://tools.ietf.org/html/rfc2774.html

   (63) https://tools.ietf.org/html/rfc6585.html


File: python.info,  Node: http client — HTTP protocol client,  Next: ftplib — FTP protocol client,  Prev: http — HTTP modules,  Up: Internet Protocols and Support

5.21.12 ‘http.client’ — HTTP protocol client
--------------------------------------------

`Source code:' Lib/http/client.py(1)

__________________________________________________________________

This module defines classes which implement the client side of the HTTP
and HTTPS protocols.  It is normally not used directly — the module
*note urllib.request: 129. uses it to handle URLs that use HTTP and
HTTPS.

See also
........

The Requests package(2) is recommended for a higher-level HTTP client
interface.

     Note: HTTPS support is only available if Python was compiled with
     SSL support (through the *note ssl: f3. module).

The module provides the following classes:

 -- Class: http.client.HTTPConnection (host, port=None[, timeout],
          source_address=None, blocksize=8192)

     An *note HTTPConnection: 499. instance represents one transaction
     with an HTTP server.  It should be instantiated passing it a host
     and optional port number.  If no port number is passed, the port is
     extracted from the host string if it has the form ‘host:port’, else
     the default HTTP port (80) is used.  If the optional `timeout'
     parameter is given, blocking operations (like connection attempts)
     will timeout after that many seconds (if it is not given, the
     global default timeout setting is used).  The optional
     `source_address' parameter may be a tuple of a (host, port) to use
     as the source address the HTTP connection is made from.  The
     optional `blocksize' parameter sets the buffer size in bytes for
     sending a file-like message body.

     For example, the following calls all create instances that connect
     to the server at the same host and port:

          >>> h1 = http.client.HTTPConnection('www.python.org')
          >>> h2 = http.client.HTTPConnection('www.python.org:80')
          >>> h3 = http.client.HTTPConnection('www.python.org', 80)
          >>> h4 = http.client.HTTPConnection('www.python.org', 80, timeout=10)

     Changed in version 3.2: `source_address' was added.

     Changed in version 3.4: The `strict' parameter was removed.  HTTP
     0.9-style “Simple Responses” are not longer supported.

     Changed in version 3.7: `blocksize' parameter was added.

 -- Class: http.client.HTTPSConnection (host, port=None, key_file=None,
          cert_file=None[, timeout], source_address=None, *,
          context=None, check_hostname=None, blocksize=8192)

     A subclass of *note HTTPConnection: 499. that uses SSL for
     communication with secure servers.  Default port is ‘443’.  If
     `context' is specified, it must be a *note ssl.SSLContext: 4ea.
     instance describing the various SSL options.

     Please read *note Security considerations: 26fd. for more
     information on best practices.

     Changed in version 3.2: `source_address', `context' and
     `check_hostname' were added.

     Changed in version 3.2: This class now supports HTTPS virtual hosts
     if possible (that is, if *note ssl.HAS_SNI: 2827. is true).

     Changed in version 3.4: The `strict' parameter was removed.  HTTP
     0.9-style “Simple Responses” are no longer supported.

     Changed in version 3.4.3: This class now performs all the necessary
     certificate and hostname checks by default.  To revert to the
     previous, unverified, behavior ‘ssl._create_unverified_context()’
     can be passed to the `context' parameter.

     Changed in version 3.8: This class now enables TLS 1.3 *note
     ssl.SSLContext.post_handshake_auth: 351. for the default `context'
     or when `cert_file' is passed with a custom `context'.

     Deprecated since version 3.6: `key_file' and `cert_file' are
     deprecated in favor of `context'.  Please use *note
     ssl.SSLContext.load_cert_chain(): b69. instead, or let *note
     ssl.create_default_context(): 9a7. select the system’s trusted CA
     certificates for you.

     The `check_hostname' parameter is also deprecated; the *note
     ssl.SSLContext.check_hostname: 2812. attribute of `context' should
     be used instead.

 -- Class: http.client.HTTPResponse (sock, debuglevel=0, method=None,
          url=None)

     Class whose instances are returned upon successful connection.  Not
     instantiated directly by user.

     Changed in version 3.4: The `strict' parameter was removed.  HTTP
     0.9 style “Simple Responses” are no longer supported.

This module provides the following function:

 -- Function: http.client.parse_headers (fp)

     Parse the headers from a file pointer `fp' representing a HTTP
     request/response.  The file has to be a ‘BufferedIOBase’ reader
     (i.e.  not text) and must provide a valid RFC 2822(3) style header.

     This function returns an instance of ‘http.client.HTTPMessage’ that
     holds the header fields, but no payload (the same as *note
     HTTPResponse.msg: 2e27. and *note
     http.server.BaseHTTPRequestHandler.headers: 2e28.).  After
     returning, the file pointer `fp' is ready to read the HTTP body.

          Note: *note parse_headers(): 1176. does not parse the
          start-line of a HTTP message; it only parses the ‘Name: value’
          lines.  The file has to be ready to read these field lines, so
          the first line should already be consumed before calling the
          function.

The following exceptions are raised as appropriate:

 -- Exception: http.client.HTTPException

     The base class of the other exceptions in this module.  It is a
     subclass of *note Exception: 2dc.

 -- Exception: http.client.NotConnected

     A subclass of *note HTTPException: 2e29.

 -- Exception: http.client.InvalidURL

     A subclass of *note HTTPException: 2e29, raised if a port is given
     and is either non-numeric or empty.

 -- Exception: http.client.UnknownProtocol

     A subclass of *note HTTPException: 2e29.

 -- Exception: http.client.UnknownTransferEncoding

     A subclass of *note HTTPException: 2e29.

 -- Exception: http.client.UnimplementedFileMode

     A subclass of *note HTTPException: 2e29.

 -- Exception: http.client.IncompleteRead

     A subclass of *note HTTPException: 2e29.

 -- Exception: http.client.ImproperConnectionState

     A subclass of *note HTTPException: 2e29.

 -- Exception: http.client.CannotSendRequest

     A subclass of *note ImproperConnectionState: 2e30.

 -- Exception: http.client.CannotSendHeader

     A subclass of *note ImproperConnectionState: 2e30.

 -- Exception: http.client.ResponseNotReady

     A subclass of *note ImproperConnectionState: 2e30.

 -- Exception: http.client.BadStatusLine

     A subclass of *note HTTPException: 2e29.  Raised if a server
     responds with a HTTP status code that we don’t understand.

 -- Exception: http.client.LineTooLong

     A subclass of *note HTTPException: 2e29.  Raised if an excessively
     long line is received in the HTTP protocol from the server.

 -- Exception: http.client.RemoteDisconnected

     A subclass of *note ConnectionResetError: a81. and *note
     BadStatusLine: 2e34.  Raised by *note HTTPConnection.getresponse():
     7d5. when the attempt to read the response results in no data read
     from the connection, indicating that the remote end has closed the
     connection.

     New in version 3.5: Previously, *note BadStatusLine: 2e34.‘('')’
     was raised.

The constants defined in this module are:

 -- Data: http.client.HTTP_PORT

     The default port for the HTTP protocol (always ‘80’).

 -- Data: http.client.HTTPS_PORT

     The default port for the HTTPS protocol (always ‘443’).

 -- Data: http.client.responses

     This dictionary maps the HTTP 1.1 status codes to the W3C names.

     Example: ‘http.client.responses[http.client.NOT_FOUND]’ is ‘'Not
     Found'’.

See *note HTTP status codes: 2e23. for a list of HTTP status codes that
are available in this module as constants.

* Menu:

* HTTPConnection Objects::
* HTTPResponse Objects::
* Examples: Examples<23>.
* HTTPMessage Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/http/client.py

   (2) https://requests.readthedocs.io/en/master/

   (3) https://tools.ietf.org/html/rfc2822.html


File: python.info,  Node: HTTPConnection Objects,  Next: HTTPResponse Objects,  Up: http client — HTTP protocol client

5.21.12.1 HTTPConnection Objects
................................

*note HTTPConnection: 499. instances have the following methods:

 -- Method: HTTPConnection.request (method, url, body=None, headers={},
          *, encode_chunked=False)

     This will send a request to the server using the HTTP request
     method `method' and the selector `url'.

     If `body' is specified, the specified data is sent after the
     headers are finished.  It may be a *note str: 205, a *note
     bytes-like object: 6df, an open *note file object: c14, or an
     iterable of *note bytes: 172.  If `body' is a string, it is encoded
     as ISO-8859-1, the default for HTTP. If it is a bytes-like object,
     the bytes are sent as is.  If it is a *note file object: c14, the
     contents of the file is sent; this file object should support at
     least the ‘read()’ method.  If the file object is an instance of
     *note io.TextIOBase: d01, the data returned by the ‘read()’ method
     will be encoded as ISO-8859-1, otherwise the data returned by
     ‘read()’ is sent as is.  If `body' is an iterable, the elements of
     the iterable are sent as is until the iterable is exhausted.

     The `headers' argument should be a mapping of extra HTTP headers to
     send with the request.

     If `headers' contains neither Content-Length nor Transfer-Encoding,
     but there is a request body, one of those header fields will be
     added automatically.  If `body' is ‘None’, the Content-Length
     header is set to ‘0’ for methods that expect a body (‘PUT’, ‘POST’,
     and ‘PATCH’).  If `body' is a string or a bytes-like object that is
     not also a *note file: c14, the Content-Length header is set to its
     length.  Any other type of `body' (files and iterables in general)
     will be chunk-encoded, and the Transfer-Encoding header will
     automatically be set instead of Content-Length.

     The `encode_chunked' argument is only relevant if Transfer-Encoding
     is specified in `headers'.  If `encode_chunked' is ‘False’, the
     HTTPConnection object assumes that all encoding is handled by the
     calling code.  If it is ‘True’, the body will be chunk-encoded.

          Note: Chunked transfer encoding has been added to the HTTP
          protocol version 1.1.  Unless the HTTP server is known to
          handle HTTP 1.1, the caller must either specify the
          Content-Length, or must pass a *note str: 205. or bytes-like
          object that is not also a file as the body representation.

     New in version 3.2: `body' can now be an iterable.

     Changed in version 3.6: If neither Content-Length nor
     Transfer-Encoding are set in `headers', file and iterable `body'
     objects are now chunk-encoded.  The `encode_chunked' argument was
     added.  No attempt is made to determine the Content-Length for file
     objects.

 -- Method: HTTPConnection.getresponse ()

     Should be called after a request is sent to get the response from
     the server.  Returns an *note HTTPResponse: aef. instance.

          Note: Note that you must have read the whole response before
          you can send a new request to the server.

     Changed in version 3.5: If a *note ConnectionError: 7d7. or
     subclass is raised, the *note HTTPConnection: 499. object will be
     ready to reconnect when a new request is sent.

 -- Method: HTTPConnection.set_debuglevel (level)

     Set the debugging level.  The default debug level is ‘0’, meaning
     no debugging output is printed.  Any value greater than ‘0’ will
     cause all currently defined debug output to be printed to stdout.
     The ‘debuglevel’ is passed to any new *note HTTPResponse: aef.
     objects that are created.

     New in version 3.1.

 -- Method: HTTPConnection.set_tunnel (host, port=None, headers=None)

     Set the host and the port for HTTP Connect Tunnelling.  This allows
     running the connection through a proxy server.

     The host and port arguments specify the endpoint of the tunneled
     connection (i.e.  the address included in the CONNECT request,
     `not' the address of the proxy server).

     The headers argument should be a mapping of extra HTTP headers to
     send with the CONNECT request.

     For example, to tunnel through a HTTPS proxy server running locally
     on port 8080, we would pass the address of the proxy to the *note
     HTTPSConnection: 49a. constructor, and the address of the host that
     we eventually want to reach to the *note set_tunnel(): c7d. method:

          >>> import http.client
          >>> conn = http.client.HTTPSConnection("localhost", 8080)
          >>> conn.set_tunnel("www.python.org")
          >>> conn.request("HEAD","/index.html")

     New in version 3.2.

 -- Method: HTTPConnection.connect ()

     Connect to the server specified when the object was created.  By
     default, this is called automatically when making a request if the
     client does not already have a connection.

 -- Method: HTTPConnection.close ()

     Close the connection to the server.

 -- Attribute: HTTPConnection.blocksize

     Buffer size in bytes for sending a file-like message body.

     New in version 3.7.

As an alternative to using the ‘request()’ method described above, you
can also send your request step by step, by using the four functions
below.

 -- Method: HTTPConnection.putrequest (method, url, skip_host=False,
          skip_accept_encoding=False)

     This should be the first call after the connection to the server
     has been made.  It sends a line to the server consisting of the
     `method' string, the `url' string, and the HTTP version
     (‘HTTP/1.1’).  To disable automatic sending of ‘Host:’ or
     ‘Accept-Encoding:’ headers (for example to accept additional
     content encodings), specify `skip_host' or `skip_accept_encoding'
     with non-False values.

 -- Method: HTTPConnection.putheader (header, argument[, ...])

     Send an RFC 822(1)-style header to the server.  It sends a line to
     the server consisting of the header, a colon and a space, and the
     first argument.  If more arguments are given, continuation lines
     are sent, each consisting of a tab and an argument.

 -- Method: HTTPConnection.endheaders (message_body=None, *,
          encode_chunked=False)

     Send a blank line to the server, signalling the end of the headers.
     The optional `message_body' argument can be used to pass a message
     body associated with the request.

     If `encode_chunked' is ‘True’, the result of each iteration of
     `message_body' will be chunk-encoded as specified in RFC 7230(2),
     Section 3.3.1.  How the data is encoded is dependent on the type of
     `message_body'.  If `message_body' implements the *note buffer
     interface: 171c. the encoding will result in a single chunk.  If
     `message_body' is a *note collections.abc.Iterable: 1818, each
     iteration of `message_body' will result in a chunk.  If
     `message_body' is a *note file object: c14, each call to ‘.read()’
     will result in a chunk.  The method automatically signals the end
     of the chunk-encoded data immediately after `message_body'.

          Note: Due to the chunked encoding specification, empty chunks
          yielded by an iterator body will be ignored by the
          chunk-encoder.  This is to avoid premature termination of the
          read of the request by the target server due to malformed
          encoding.

     New in version 3.6: Chunked encoding support.  The `encode_chunked'
     parameter was added.

 -- Method: HTTPConnection.send (data)

     Send data to the server.  This should be used directly only after
     the *note endheaders(): 64a. method has been called and before
     *note getresponse(): 7d5. is called.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc822.html

   (2) https://tools.ietf.org/html/rfc7230.html


File: python.info,  Node: HTTPResponse Objects,  Next: Examples<23>,  Prev: HTTPConnection Objects,  Up: http client — HTTP protocol client

5.21.12.2 HTTPResponse Objects
..............................

An *note HTTPResponse: aef. instance wraps the HTTP response from the
server.  It provides access to the request headers and the entity body.
The response is an iterable object and can be used in a with statement.

Changed in version 3.5: The *note io.BufferedIOBase: 67f. interface is
now implemented and all of its reader operations are supported.

 -- Method: HTTPResponse.read ([amt])

     Reads and returns the response body, or up to the next `amt' bytes.

 -- Method: HTTPResponse.readinto (b)

     Reads up to the next len(b) bytes of the response body into the
     buffer `b'.  Returns the number of bytes read.

     New in version 3.3.

 -- Method: HTTPResponse.getheader (name, default=None)

     Return the value of the header `name', or `default' if there is no
     header matching `name'.  If there is more than one header with the
     name `name', return all of the values joined by ‘, ‘.  If ‘default’
     is any iterable other than a single string, its elements are
     similarly returned joined by commas.

 -- Method: HTTPResponse.getheaders ()

     Return a list of (header, value) tuples.

 -- Method: HTTPResponse.fileno ()

     Return the ‘fileno’ of the underlying socket.

 -- Attribute: HTTPResponse.msg

     A ‘http.client.HTTPMessage’ instance containing the response
     headers.  ‘http.client.HTTPMessage’ is a subclass of *note
     email.message.Message: 63b.

 -- Attribute: HTTPResponse.version

     HTTP protocol version used by server.  10 for HTTP/1.0, 11 for
     HTTP/1.1.

 -- Attribute: HTTPResponse.url

     URL of the resource retrieved, commonly used to determine if a
     redirect was followed.

 -- Attribute: HTTPResponse.headers

     Headers of the response in the form of an *note
     email.message.EmailMessage: 63c. instance.

 -- Attribute: HTTPResponse.status

     Status code returned by server.

 -- Attribute: HTTPResponse.reason

     Reason phrase returned by server.

 -- Attribute: HTTPResponse.debuglevel

     A debugging hook.  If *note debuglevel: 2e4c. is greater than zero,
     messages will be printed to stdout as the response is read and
     parsed.

 -- Attribute: HTTPResponse.closed

     Is ‘True’ if the stream is closed.

 -- Method: HTTPResponse.geturl ()

     Deprecated since version 3.9: Deprecated in favor of *note url:
     2e49.

 -- Method: HTTPResponse.info ()

     Deprecated since version 3.9: Deprecated in favor of *note headers:
     2e4a.

 -- Method: HTTPResponse.getstatus ()

     Deprecated since version 3.9: Deprecated in favor of *note status:
     2e4b.


File: python.info,  Node: Examples<23>,  Next: HTTPMessage Objects,  Prev: HTTPResponse Objects,  Up: http client — HTTP protocol client

5.21.12.3 Examples
..................

Here is an example session that uses the ‘GET’ method:

     >>> import http.client
     >>> conn = http.client.HTTPSConnection("www.python.org")
     >>> conn.request("GET", "/")
     >>> r1 = conn.getresponse()
     >>> print(r1.status, r1.reason)
     200 OK
     >>> data1 = r1.read()  # This will return entire content.
     >>> # The following example demonstrates reading data in chunks.
     >>> conn.request("GET", "/")
     >>> r1 = conn.getresponse()
     >>> while chunk := r1.read(200):
     ...     print(repr(chunk))
     b'<!doctype html>\n<!--[if"...
     ...
     >>> # Example of an invalid request
     >>> conn = http.client.HTTPSConnection("docs.python.org")
     >>> conn.request("GET", "/parrot.spam")
     >>> r2 = conn.getresponse()
     >>> print(r2.status, r2.reason)
     404 Not Found
     >>> data2 = r2.read()
     >>> conn.close()

Here is an example session that uses the ‘HEAD’ method.  Note that the
‘HEAD’ method never returns any data.

     >>> import http.client
     >>> conn = http.client.HTTPSConnection("www.python.org")
     >>> conn.request("HEAD", "/")
     >>> res = conn.getresponse()
     >>> print(res.status, res.reason)
     200 OK
     >>> data = res.read()
     >>> print(len(data))
     0
     >>> data == b''
     True

Here is an example session that shows how to ‘POST’ requests:

     >>> import http.client, urllib.parse
     >>> params = urllib.parse.urlencode({'@number': 12524, '@type': 'issue', '@action': 'show'})
     >>> headers = {"Content-type": "application/x-www-form-urlencoded",
     ...            "Accept": "text/plain"}
     >>> conn = http.client.HTTPConnection("bugs.python.org")
     >>> conn.request("POST", "", params, headers)
     >>> response = conn.getresponse()
     >>> print(response.status, response.reason)
     302 Found
     >>> data = response.read()
     >>> data
     b'Redirecting to <a href="http://bugs.python.org/issue12524">http://bugs.python.org/issue12524</a>'
     >>> conn.close()

Client side ‘HTTP PUT’ requests are very similar to ‘POST’ requests.
The difference lies only the server side where HTTP server will allow
resources to be created via ‘PUT’ request.  It should be noted that
custom HTTP methods are also handled in *note urllib.request.Request:
9dc. by setting the appropriate method attribute.  Here is an example
session that shows how to send a ‘PUT’ request using http.client:

     >>> # This creates an HTTP message
     >>> # with the content of BODY as the enclosed representation
     >>> # for the resource http://localhost:8080/file
     ...
     >>> import http.client
     >>> BODY = "***filecontents***"
     >>> conn = http.client.HTTPConnection("localhost", 8080)
     >>> conn.request("PUT", "/file", BODY)
     >>> response = conn.getresponse()
     >>> print(response.status, response.reason)
     200, OK


File: python.info,  Node: HTTPMessage Objects,  Prev: Examples<23>,  Up: http client — HTTP protocol client

5.21.12.4 HTTPMessage Objects
.............................

An ‘http.client.HTTPMessage’ instance holds the headers from an HTTP
response.  It is implemented using the *note email.message.Message: 63b.
class.


File: python.info,  Node: ftplib — FTP protocol client,  Next: poplib — POP3 protocol client,  Prev: http client — HTTP protocol client,  Up: Internet Protocols and Support

5.21.13 ‘ftplib’ — FTP protocol client
--------------------------------------

`Source code:' Lib/ftplib.py(1)

__________________________________________________________________

This module defines the class *note FTP: 1a6. and a few related items.
The *note FTP: 1a6. class implements the client side of the FTP
protocol.  You can use this to write Python programs that perform a
variety of automated FTP jobs, such as mirroring other FTP servers.  It
is also used by the module *note urllib.request: 129. to handle URLs
that use FTP. For more information on FTP (File Transfer Protocol), see
Internet RFC 959(2).

The default encoding is UTF-8, following RFC 2640(3).

Here’s a sample session using the *note ftplib: 82. module:

     >>> from ftplib import FTP
     >>> ftp = FTP('ftp.us.debian.org')  # connect to host, default port
     >>> ftp.login()                     # user anonymous, passwd anonymous@
     '230 Login successful.'
     >>> ftp.cwd('debian')               # change into "debian" directory
     '250 Directory successfully changed.'
     >>> ftp.retrlines('LIST')           # list directory contents
     -rw-rw-r--    1 1176     1176         1063 Jun 15 10:18 README
     ...
     drwxr-sr-x    5 1176     1176         4096 Dec 19  2000 pool
     drwxr-sr-x    4 1176     1176         4096 Nov 17  2008 project
     drwxr-xr-x    3 1176     1176         4096 Oct 10  2012 tools
     '226 Directory send OK.'
     >>> with open('README', 'wb') as fp:
     >>>     ftp.retrbinary('RETR README', fp.write)
     '226 Transfer complete.'
     >>> ftp.quit()
     '221 Goodbye.'

The module defines the following items:

 -- Class: ftplib.FTP (host='', user='', passwd='', acct='',
          timeout=None, source_address=None, *, encoding='utf-8')

     Return a new instance of the *note FTP: 1a6. class.  When `host' is
     given, the method call ‘connect(host)’ is made.  When `user' is
     given, additionally the method call ‘login(user, passwd, acct)’ is
     made (where `passwd' and `acct' default to the empty string when
     not given).  The optional `timeout' parameter specifies a timeout
     in seconds for blocking operations like the connection attempt (if
     is not specified, the global default timeout setting will be used).
     `source_address' is a 2-tuple ‘(host, port)’ for the socket to bind
     to as its source address before connecting.  The `encoding'
     parameter specifies the encoding for directories and filenames.

     The *note FTP: 1a6. class supports the *note with: 7da. statement,
     e.g.:

          >>> from ftplib import FTP
          >>> with FTP("ftp1.at.proftpd.org") as ftp:
          ...     ftp.login()
          ...     ftp.dir()
          ...
          '230 Anonymous login ok, restrictions apply.'
          dr-xr-xr-x   9 ftp      ftp           154 May  6 10:43 .
          dr-xr-xr-x   9 ftp      ftp           154 May  6 10:43 ..
          dr-xr-xr-x   5 ftp      ftp          4096 May  6 10:43 CentOS
          dr-xr-xr-x   3 ftp      ftp            18 Jul 10  2008 Fedora
          >>>

     Changed in version 3.2: Support for the *note with: 7da. statement
     was added.

     Changed in version 3.3: `source_address' parameter was added.

     Changed in version 3.9: If the `timeout' parameter is set to be
     zero, it will raise a *note ValueError: 16d. to prevent the
     creation of a non-blocking socket.  The `encoding' parameter was
     added, and the default was changed from Latin-1 to UTF-8 to follow
     RFC 2640(4).

 -- Class: ftplib.FTP_TLS (host='', user='', passwd='', acct='',
          keyfile=None, certfile=None, context=None, timeout=None,
          source_address=None, *, encoding='utf-8')

     A *note FTP: 1a6. subclass which adds TLS support to FTP as
     described in RFC 4217(5).  Connect as usual to port 21 implicitly
     securing the FTP control connection before authenticating.
     Securing the data connection requires the user to explicitly ask
     for it by calling the *note prot_p(): 2e56. method.  `context' is a
     *note ssl.SSLContext: 4ea. object which allows bundling SSL
     configuration options, certificates and private keys into a single
     (potentially long-lived) structure.  Please read *note Security
     considerations: 26fd. for best practices.

     `keyfile' and `certfile' are a legacy alternative to `context' –
     they can point to PEM-formatted private key and certificate chain
     files (respectively) for the SSL connection.

     New in version 3.2.

     Changed in version 3.3: `source_address' parameter was added.

     Changed in version 3.4: The class now supports hostname check with
     *note ssl.SSLContext.check_hostname: 2812. and `Server Name
     Indication' (see *note ssl.HAS_SNI: 2827.).

     Deprecated since version 3.6: `keyfile' and `certfile' are
     deprecated in favor of `context'.  Please use *note
     ssl.SSLContext.load_cert_chain(): b69. instead, or let *note
     ssl.create_default_context(): 9a7. select the system’s trusted CA
     certificates for you.

     Changed in version 3.9: If the `timeout' parameter is set to be
     zero, it will raise a *note ValueError: 16d. to prevent the
     creation of a non-blocking socket.  The `encoding' parameter was
     added, and the default was changed from Latin-1 to UTF-8 to follow
     RFC 2640(6).

     Here’s a sample session using the *note FTP_TLS: 1a7. class:

          >>> ftps = FTP_TLS('ftp.pureftpd.org')
          >>> ftps.login()
          '230 Anonymous user logged in'
          >>> ftps.prot_p()
          '200 Data protection level set to "private"'
          >>> ftps.nlst()
          ['6jack', 'OpenBSD', 'antilink', 'blogbench', 'bsdcam', 'clockspeed', 'djbdns-jedi', 'docs', 'eaccelerator-jedi', 'favicon.ico', 'francotone', 'fugu', 'ignore', 'libpuzzle', 'metalog', 'minidentd', 'misc', 'mysql-udf-global-user-variables', 'php-jenkins-hash', 'php-skein-hash', 'php-webdav', 'phpaudit', 'phpbench', 'pincaster', 'ping', 'posto', 'pub', 'public', 'public_keys', 'pure-ftpd', 'qscan', 'qtc', 'sharedance', 'skycache', 'sound', 'tmp', 'ucarp']

 -- Exception: ftplib.error_reply

     Exception raised when an unexpected reply is received from the
     server.

 -- Exception: ftplib.error_temp

     Exception raised when an error code signifying a temporary error
     (response codes in the range 400–499) is received.

 -- Exception: ftplib.error_perm

     Exception raised when an error code signifying a permanent error
     (response codes in the range 500–599) is received.

 -- Exception: ftplib.error_proto

     Exception raised when a reply is received from the server that does
     not fit the response specifications of the File Transfer Protocol,
     i.e.  begin with a digit in the range 1–5.

 -- Data: ftplib.all_errors

     The set of all exceptions (as a tuple) that methods of *note FTP:
     1a6. instances may raise as a result of problems with the FTP
     connection (as opposed to programming errors made by the caller).
     This set includes the four exceptions listed above as well as *note
     OSError: 304. and *note EOFError: d34.

See also
........

Module *note netrc: be.

     Parser for the ‘.netrc’ file format.  The file ‘.netrc’ is
     typically used by FTP clients to load user authentication
     information before prompting the user.

* Menu:

* FTP Objects::
* FTP_TLS Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/ftplib.py

   (2) https://tools.ietf.org/html/rfc959.html

   (3) https://tools.ietf.org/html/rfc2640.html

   (4) https://tools.ietf.org/html/rfc2640.html

   (5) https://tools.ietf.org/html/rfc4217.html

   (6) https://tools.ietf.org/html/rfc2640.html


File: python.info,  Node: FTP Objects,  Next: FTP_TLS Objects,  Up: ftplib — FTP protocol client

5.21.13.1 FTP Objects
.....................

Several methods are available in two flavors: one for handling text
files and another for binary files.  These are named for the command
which is used followed by ‘lines’ for the text version or ‘binary’ for
the binary version.

*note FTP: 1a6. instances have the following methods:

 -- Method: FTP.set_debuglevel (level)

     Set the instance’s debugging level.  This controls the amount of
     debugging output printed.  The default, ‘0’, produces no debugging
     output.  A value of ‘1’ produces a moderate amount of debugging
     output, generally a single line per request.  A value of ‘2’ or
     higher produces the maximum amount of debugging output, logging
     each line sent and received on the control connection.

 -- Method: FTP.connect (host='', port=0, timeout=None,
          source_address=None)

     Connect to the given host and port.  The default port number is
     ‘21’, as specified by the FTP protocol specification.  It is rarely
     needed to specify a different port number.  This function should be
     called only once for each instance; it should not be called at all
     if a host was given when the instance was created.  All other
     methods can only be used after a connection has been made.  The
     optional `timeout' parameter specifies a timeout in seconds for the
     connection attempt.  If no `timeout' is passed, the global default
     timeout setting will be used.  `source_address' is a 2-tuple
     ‘(host, port)’ for the socket to bind to as its source address
     before connecting.

     Raises an *note auditing event: fa1. ‘ftplib.connect’ with
     arguments ‘self’, ‘host’, ‘port’.

     Changed in version 3.3: `source_address' parameter was added.

 -- Method: FTP.getwelcome ()

     Return the welcome message sent by the server in reply to the
     initial connection.  (This message sometimes contains disclaimers
     or help information that may be relevant to the user.)

 -- Method: FTP.login (user='anonymous', passwd='', acct='')

     Log in as the given `user'.  The `passwd' and `acct' parameters are
     optional and default to the empty string.  If no `user' is
     specified, it defaults to ‘'anonymous'’.  If `user' is
     ‘'anonymous'’, the default `passwd' is ‘'anonymous@'’.  This
     function should be called only once for each instance, after a
     connection has been established; it should not be called at all if
     a host and user were given when the instance was created.  Most FTP
     commands are only allowed after the client has logged in.  The
     `acct' parameter supplies “accounting information”; few systems
     implement this.

 -- Method: FTP.abort ()

     Abort a file transfer that is in progress.  Using this does not
     always work, but it’s worth a try.

 -- Method: FTP.sendcmd (cmd)

     Send a simple command string to the server and return the response
     string.

     Raises an *note auditing event: fa1. ‘ftplib.sendcmd’ with
     arguments ‘self’, ‘cmd’.

 -- Method: FTP.voidcmd (cmd)

     Send a simple command string to the server and handle the response.
     Return nothing if a response code corresponding to success (codes
     in the range 200–299) is received.  Raise *note error_reply: 2e57.
     otherwise.

     Raises an *note auditing event: fa1. ‘ftplib.sendcmd’ with
     arguments ‘self’, ‘cmd’.

 -- Method: FTP.retrbinary (cmd, callback, blocksize=8192, rest=None)

     Retrieve a file in binary transfer mode.  `cmd' should be an
     appropriate ‘RETR’ command: ‘'RETR filename'’.  The `callback'
     function is called for each block of data received, with a single
     bytes argument giving the data block.  The optional `blocksize'
     argument specifies the maximum chunk size to read on the low-level
     socket object created to do the actual transfer (which will also be
     the largest size of the data blocks passed to `callback').  A
     reasonable default is chosen.  `rest' means the same thing as in
     the *note transfercmd(): 2e66. method.

 -- Method: FTP.retrlines (cmd, callback=None)

     Retrieve a file or directory listing in the encoding specified by
     the `encoding' parameter at initialization.  `cmd' should be an
     appropriate ‘RETR’ command (see *note retrbinary(): 2e65.) or a
     command such as ‘LIST’ or ‘NLST’ (usually just the string
     ‘'LIST'’).  ‘LIST’ retrieves a list of files and information about
     those files.  ‘NLST’ retrieves a list of file names.  The
     `callback' function is called for each line with a string argument
     containing the line with the trailing CRLF stripped.  The default
     `callback' prints the line to ‘sys.stdout’.

 -- Method: FTP.set_pasv (val)

     Enable “passive” mode if `val' is true, otherwise disable passive
     mode.  Passive mode is on by default.

 -- Method: FTP.storbinary (cmd, fp, blocksize=8192, callback=None,
          rest=None)

     Store a file in binary transfer mode.  `cmd' should be an
     appropriate ‘STOR’ command: ‘"STOR filename"’.  `fp' is a *note
     file object: c14. (opened in binary mode) which is read until EOF
     using its ‘read()’ method in blocks of size `blocksize' to provide
     the data to be stored.  The `blocksize' argument defaults to 8192.
     `callback' is an optional single parameter callable that is called
     on each block of data after it is sent.  `rest' means the same
     thing as in the *note transfercmd(): 2e66. method.

     Changed in version 3.2: `rest' parameter added.

 -- Method: FTP.storlines (cmd, fp, callback=None)

     Store a file in line mode.  `cmd' should be an appropriate ‘STOR’
     command (see *note storbinary(): d67.).  Lines are read until EOF
     from the *note file object: c14. `fp' (opened in binary mode) using
     its *note readline(): 1849. method to provide the data to be
     stored.  `callback' is an optional single parameter callable that
     is called on each line after it is sent.

 -- Method: FTP.transfercmd (cmd, rest=None)

     Initiate a transfer over the data connection.  If the transfer is
     active, send an ‘EPRT’ or ‘PORT’ command and the transfer command
     specified by `cmd', and accept the connection.  If the server is
     passive, send an ‘EPSV’ or ‘PASV’ command, connect to it, and start
     the transfer command.  Either way, return the socket for the
     connection.

     If optional `rest' is given, a ‘REST’ command is sent to the
     server, passing `rest' as an argument.  `rest' is usually a byte
     offset into the requested file, telling the server to restart
     sending the file’s bytes at the requested offset, skipping over the
     initial bytes.  Note however that the *note transfercmd(): 2e66.
     method converts `rest' to a string with the `encoding' parameter
     specified at initialization, but no check is performed on the
     string’s contents.  If the server does not recognize the ‘REST’
     command, an *note error_reply: 2e57. exception will be raised.  If
     this happens, simply call *note transfercmd(): 2e66. without a
     `rest' argument.

 -- Method: FTP.ntransfercmd (cmd, rest=None)

     Like *note transfercmd(): 2e66, but returns a tuple of the data
     connection and the expected size of the data.  If the expected size
     could not be computed, ‘None’ will be returned as the expected
     size.  `cmd' and `rest' means the same thing as in *note
     transfercmd(): 2e66.

 -- Method: FTP.mlsd (path="", facts=[])

     List a directory in a standardized format by using ‘MLSD’ command (
     RFC 3659(1)).  If `path' is omitted the current directory is
     assumed.  `facts' is a list of strings representing the type of
     information desired (e.g.  ‘["type", "size", "perm"]’).  Return a
     generator object yielding a tuple of two elements for every file
     found in path.  First element is the file name, the second one is a
     dictionary containing facts about the file name.  Content of this
     dictionary might be limited by the `facts' argument but server is
     not guaranteed to return all requested facts.

     New in version 3.3.

 -- Method: FTP.nlst (argument[, ...])

     Return a list of file names as returned by the ‘NLST’ command.  The
     optional `argument' is a directory to list (default is the current
     server directory).  Multiple arguments can be used to pass
     non-standard options to the ‘NLST’ command.

          Note: If your server supports the command, *note mlsd(): ae3.
          offers a better API.

 -- Method: FTP.dir (argument[, ...])

     Produce a directory listing as returned by the ‘LIST’ command,
     printing it to standard output.  The optional `argument' is a
     directory to list (default is the current server directory).
     Multiple arguments can be used to pass non-standard options to the
     ‘LIST’ command.  If the last argument is a function, it is used as
     a `callback' function as for *note retrlines(): 2e67.; the default
     prints to ‘sys.stdout’.  This method returns ‘None’.

          Note: If your server supports the command, *note mlsd(): ae3.
          offers a better API.

 -- Method: FTP.rename (fromname, toname)

     Rename file `fromname' on the server to `toname'.

 -- Method: FTP.delete (filename)

     Remove the file named `filename' from the server.  If successful,
     returns the text of the response, otherwise raises *note
     error_perm: 2e59. on permission errors or *note error_reply: 2e57.
     on other errors.

 -- Method: FTP.cwd (pathname)

     Set the current directory on the server.

 -- Method: FTP.mkd (pathname)

     Create a new directory on the server.

 -- Method: FTP.pwd ()

     Return the pathname of the current directory on the server.

 -- Method: FTP.rmd (dirname)

     Remove the directory named `dirname' on the server.

 -- Method: FTP.size (filename)

     Request the size of the file named `filename' on the server.  On
     success, the size of the file is returned as an integer, otherwise
     ‘None’ is returned.  Note that the ‘SIZE’ command is not
     standardized, but is supported by many common server
     implementations.

 -- Method: FTP.quit ()

     Send a ‘QUIT’ command to the server and close the connection.  This
     is the “polite” way to close a connection, but it may raise an
     exception if the server responds with an error to the ‘QUIT’
     command.  This implies a call to the *note close(): 2e73. method
     which renders the *note FTP: 1a6. instance useless for subsequent
     calls (see below).

 -- Method: FTP.close ()

     Close the connection unilaterally.  This should not be applied to
     an already closed connection such as after a successful call to
     *note quit(): 2e72.  After this call the *note FTP: 1a6. instance
     should not be used any more (after a call to *note close(): 2e73.
     or *note quit(): 2e72. you cannot reopen the connection by issuing
     another *note login(): 2e61. method).

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3659.html


File: python.info,  Node: FTP_TLS Objects,  Prev: FTP Objects,  Up: ftplib — FTP protocol client

5.21.13.2 FTP_TLS Objects
.........................

*note FTP_TLS: 1a7. class inherits from *note FTP: 1a6, defining these
additional objects:

 -- Attribute: FTP_TLS.ssl_version

     The SSL version to use (defaults to *note ssl.PROTOCOL_SSLv23:
     2817.).

 -- Method: FTP_TLS.auth ()

     Set up a secure control connection by using TLS or SSL, depending
     on what is specified in the *note ssl_version: 2e75. attribute.

     Changed in version 3.4: The method now supports hostname check with
     *note ssl.SSLContext.check_hostname: 2812. and `Server Name
     Indication' (see *note ssl.HAS_SNI: 2827.).

 -- Method: FTP_TLS.ccc ()

     Revert control channel back to plaintext.  This can be useful to
     take advantage of firewalls that know how to handle NAT with
     non-secure FTP without opening fixed ports.

     New in version 3.3.

 -- Method: FTP_TLS.prot_p ()

     Set up secure data connection.

 -- Method: FTP_TLS.prot_c ()

     Set up clear text data connection.


File: python.info,  Node: poplib — POP3 protocol client,  Next: imaplib — IMAP4 protocol client,  Prev: ftplib — FTP protocol client,  Up: Internet Protocols and Support

5.21.14 ‘poplib’ — POP3 protocol client
---------------------------------------

`Source code:' Lib/poplib.py(1)

__________________________________________________________________

This module defines a class, *note POP3: 1d5, which encapsulates a
connection to a POP3 server and implements the protocol as defined in
RFC 1939(2).  The *note POP3: 1d5. class supports both the minimal and
optional command sets from RFC 1939(3).  The *note POP3: 1d5. class also
supports the ‘STLS’ command introduced in RFC 2595(4) to enable
encrypted communication on an already established connection.

Additionally, this module provides a class *note POP3_SSL: 1d6, which
provides support for connecting to POP3 servers that use SSL as an
underlying protocol layer.

Note that POP3, though widely supported, is obsolescent.  The
implementation quality of POP3 servers varies widely, and too many are
quite poor.  If your mailserver supports IMAP, you would be better off
using the *note imaplib.IMAP4: 1af. class, as IMAP servers tend to be
better implemented.

The *note poplib: d0. module provides two classes:

 -- Class: poplib.POP3 (host, port=POP3_PORT[, timeout])

     This class implements the actual POP3 protocol.  The connection is
     created when the instance is initialized.  If `port' is omitted,
     the standard POP3 port (110) is used.  The optional `timeout'
     parameter specifies a timeout in seconds for the connection attempt
     (if not specified, the global default timeout setting will be
     used).

     Raises an *note auditing event: fa1. ‘poplib.connect’ with
     arguments ‘self’, ‘host’, ‘port’.

     All commands will raise an *note auditing event: fa1.
     ‘poplib.putline’ with arguments ‘self’ and ‘line’, where ‘line’ is
     the bytes about to be sent to the remote host.

     Changed in version 3.9: If the `timeout' parameter is set to be
     zero, it will raise a *note ValueError: 16d. to prevent the
     creation of a non-blocking socket.

 -- Class: poplib.POP3_SSL (host, port=POP3_SSL_PORT, keyfile=None,
          certfile=None, timeout=None, context=None)

     This is a subclass of *note POP3: 1d5. that connects to the server
     over an SSL encrypted socket.  If `port' is not specified, 995, the
     standard POP3-over-SSL port is used.  `timeout' works as in the
     *note POP3: 1d5. constructor.  `context' is an optional *note
     ssl.SSLContext: 4ea. object which allows bundling SSL configuration
     options, certificates and private keys into a single (potentially
     long-lived) structure.  Please read *note Security considerations:
     26fd. for best practices.

     `keyfile' and `certfile' are a legacy alternative to `context' -
     they can point to PEM-formatted private key and certificate chain
     files, respectively, for the SSL connection.

     Raises an *note auditing event: fa1. ‘poplib.connect’ with
     arguments ‘self’, ‘host’, ‘port’.

     All commands will raise an *note auditing event: fa1.
     ‘poplib.putline’ with arguments ‘self’ and ‘line’, where ‘line’ is
     the bytes about to be sent to the remote host.

     Changed in version 3.2: `context' parameter added.

     Changed in version 3.4: The class now supports hostname check with
     *note ssl.SSLContext.check_hostname: 2812. and `Server Name
     Indication' (see *note ssl.HAS_SNI: 2827.).

     Deprecated since version 3.6: `keyfile' and `certfile' are
     deprecated in favor of `context'.  Please use *note
     ssl.SSLContext.load_cert_chain(): b69. instead, or let *note
     ssl.create_default_context(): 9a7. select the system’s trusted CA
     certificates for you.

     Changed in version 3.9: If the `timeout' parameter is set to be
     zero, it will raise a *note ValueError: 16d. to prevent the
     creation of a non-blocking socket.

One exception is defined as an attribute of the *note poplib: d0.
module:

 -- Exception: poplib.error_proto

     Exception raised on any errors from this module (errors from *note
     socket: ef. module are not caught).  The reason for the exception
     is passed to the constructor as a string.

See also
........

Module *note imaplib: 97.

     The standard Python IMAP module.

Frequently Asked Questions About Fetchmail(5)

     The FAQ for the ‘fetchmail’ POP/IMAP client collects information on
     POP3 server variations and RFC noncompliance that may be useful if
     you need to write an application based on the POP protocol.

* Menu:

* POP3 Objects::
* POP3 Example::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/poplib.py

   (2) https://tools.ietf.org/html/rfc1939.html

   (3) https://tools.ietf.org/html/rfc1939.html

   (4) https://tools.ietf.org/html/rfc2595.html

   (5) http://www.catb.org/~esr/fetchmail/fetchmail-FAQ.html


File: python.info,  Node: POP3 Objects,  Next: POP3 Example,  Up: poplib — POP3 protocol client

5.21.14.1 POP3 Objects
......................

All POP3 commands are represented by methods of the same name, in
lower-case; most return the response text sent by the server.

An *note POP3: 1d5. instance has the following methods:

 -- Method: POP3.set_debuglevel (level)

     Set the instance’s debugging level.  This controls the amount of
     debugging output printed.  The default, ‘0’, produces no debugging
     output.  A value of ‘1’ produces a moderate amount of debugging
     output, generally a single line per request.  A value of ‘2’ or
     higher produces the maximum amount of debugging output, logging
     each line sent and received on the control connection.

 -- Method: POP3.getwelcome ()

     Returns the greeting string sent by the POP3 server.

 -- Method: POP3.capa ()

     Query the server’s capabilities as specified in RFC 2449(1).
     Returns a dictionary in the form ‘{'name': ['param'...]}’.

     New in version 3.4.

 -- Method: POP3.user (username)

     Send user command, response should indicate that a password is
     required.

 -- Method: POP3.pass_ (password)

     Send password, response includes message count and mailbox size.
     Note: the mailbox on the server is locked until ‘quit()’ is called.

 -- Method: POP3.apop (user, secret)

     Use the more secure APOP authentication to log into the POP3
     server.

 -- Method: POP3.rpop (user)

     Use RPOP authentication (similar to UNIX r-commands) to log into
     POP3 server.

 -- Method: POP3.stat ()

     Get mailbox status.  The result is a tuple of 2 integers: ‘(message
     count, mailbox size)’.

 -- Method: POP3.list ([which])

     Request message list, result is in the form ‘(response, ['mesg_num
     octets', ...], octets)’.  If `which' is set, it is the message to
     list.

 -- Method: POP3.retr (which)

     Retrieve whole message number `which', and set its seen flag.
     Result is in form ‘(response, ['line', ...], octets)’.

 -- Method: POP3.dele (which)

     Flag message number `which' for deletion.  On most servers
     deletions are not actually performed until QUIT (the major
     exception is Eudora QPOP, which deliberately violates the RFCs by
     doing pending deletes on any disconnect).

 -- Method: POP3.rset ()

     Remove any deletion marks for the mailbox.

 -- Method: POP3.noop ()

     Do nothing.  Might be used as a keep-alive.

 -- Method: POP3.quit ()

     Signoff: commit changes, unlock mailbox, drop connection.

 -- Method: POP3.top (which, howmuch)

     Retrieves the message header plus `howmuch' lines of the message
     after the header of message number `which'.  Result is in form
     ‘(response, ['line', ...], octets)’.

     The POP3 TOP command this method uses, unlike the RETR command,
     doesn’t set the message’s seen flag; unfortunately, TOP is poorly
     specified in the RFCs and is frequently broken in off-brand
     servers.  Test this method by hand against the POP3 servers you
     will use before trusting it.

 -- Method: POP3.uidl (which=None)

     Return message digest (unique id) list.  If `which' is specified,
     result contains the unique id for that message in the form
     ‘'response mesgnum uid’, otherwise result is list ‘(response,
     ['mesgnum uid', ...], octets)’.

 -- Method: POP3.utf8 ()

     Try to switch to UTF-8 mode.  Returns the server response if
     successful, raises *note error_proto: bea. if not.  Specified in
     RFC 6856(2).

     New in version 3.5.

 -- Method: POP3.stls (context=None)

     Start a TLS session on the active connection as specified in RFC
     2595(3).  This is only allowed before user authentication

     `context' parameter is a *note ssl.SSLContext: 4ea. object which
     allows bundling SSL configuration options, certificates and private
     keys into a single (potentially long-lived) structure.  Please read
     *note Security considerations: 26fd. for best practices.

     This method supports hostname checking via *note
     ssl.SSLContext.check_hostname: 2812. and `Server Name Indication'
     (see *note ssl.HAS_SNI: 2827.).

     New in version 3.4.

Instances of *note POP3_SSL: 1d6. have no additional methods.  The
interface of this subclass is identical to its parent.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2449.html

   (2) https://tools.ietf.org/html/rfc6856.html

   (3) https://tools.ietf.org/html/rfc2595.html


File: python.info,  Node: POP3 Example,  Prev: POP3 Objects,  Up: poplib — POP3 protocol client

5.21.14.2 POP3 Example
......................

Here is a minimal example (without error checking) that opens a mailbox
and retrieves and prints all messages:

     import getpass, poplib

     M = poplib.POP3('localhost')
     M.user(getpass.getuser())
     M.pass_(getpass.getpass())
     numMessages = len(M.list()[1])
     for i in range(numMessages):
         for j in M.retr(i+1)[1]:
             print(j)

At the end of the module, there is a test section that contains a more
extensive example of usage.


File: python.info,  Node: imaplib — IMAP4 protocol client,  Next: nntplib — NNTP protocol client,  Prev: poplib — POP3 protocol client,  Up: Internet Protocols and Support

5.21.15 ‘imaplib’ — IMAP4 protocol client
-----------------------------------------

`Source code:' Lib/imaplib.py(1)

__________________________________________________________________

This module defines three classes, *note IMAP4: 1af, *note IMAP4_SSL:
1b0. and *note IMAP4_stream: 1b2, which encapsulate a connection to an
IMAP4 server and implement a large subset of the IMAP4rev1 client
protocol as defined in RFC 2060(2).  It is backward compatible with
IMAP4 ( RFC 1730(3)) servers, but note that the ‘STATUS’ command is not
supported in IMAP4.

Three classes are provided by the *note imaplib: 97. module, *note
IMAP4: 1af. is the base class:

 -- Class: imaplib.IMAP4 (host='', port=IMAP4_PORT, timeout=None)

     This class implements the actual IMAP4 protocol.  The connection is
     created and protocol version (IMAP4 or IMAP4rev1) is determined
     when the instance is initialized.  If `host' is not specified, ‘''’
     (the local host) is used.  If `port' is omitted, the standard IMAP4
     port (143) is used.  The optional `timeout' parameter specifies a
     timeout in seconds for the connection attempt.  If timeout is not
     given or is None, the global default socket timeout is used.

     The *note IMAP4: 1af. class supports the *note with: 7da.
     statement.  When used like this, the IMAP4 ‘LOGOUT’ command is
     issued automatically when the ‘with’ statement exits.  E.g.:

          >>> from imaplib import IMAP4
          >>> with IMAP4("domain.org") as M:
          ...     M.noop()
          ...
          ('OK', [b'Nothing Accomplished. d25if65hy903weo.87'])

     Changed in version 3.5: Support for the *note with: 7da. statement
     was added.

     Changed in version 3.9: The optional `timeout' parameter was added.

Three exceptions are defined as attributes of the *note IMAP4: 1af.
class:

 -- Exception: IMAP4.error

     Exception raised on any errors.  The reason for the exception is
     passed to the constructor as a string.

 -- Exception: IMAP4.abort

     IMAP4 server errors cause this exception to be raised.  This is a
     sub-class of *note IMAP4.error: 2e8e.  Note that closing the
     instance and instantiating a new one will usually allow recovery
     from this exception.

 -- Exception: IMAP4.readonly

     This exception is raised when a writable mailbox has its status
     changed by the server.  This is a sub-class of *note IMAP4.error:
     2e8e.  Some other client now has write permission, and the mailbox
     will need to be re-opened to re-obtain write permission.

There’s also a subclass for secure connections:

 -- Class: imaplib.IMAP4_SSL (host='', port=IMAP4_SSL_PORT,
          keyfile=None, certfile=None, ssl_context=None, timeout=None)

     This is a subclass derived from *note IMAP4: 1af. that connects
     over an SSL encrypted socket (to use this class you need a socket
     module that was compiled with SSL support).  If `host' is not
     specified, ‘''’ (the local host) is used.  If `port' is omitted,
     the standard IMAP4-over-SSL port (993) is used.  `ssl_context' is a
     *note ssl.SSLContext: 4ea. object which allows bundling SSL
     configuration options, certificates and private keys into a single
     (potentially long-lived) structure.  Please read *note Security
     considerations: 26fd. for best practices.

     `keyfile' and `certfile' are a legacy alternative to `ssl_context'
     - they can point to PEM-formatted private key and certificate chain
     files for the SSL connection.  Note that the `keyfile'/`certfile'
     parameters are mutually exclusive with `ssl_context', a *note
     ValueError: 16d. is raised if `keyfile'/`certfile' is provided
     along with `ssl_context'.

     The optional `timeout' parameter specifies a timeout in seconds for
     the connection attempt.  If timeout is not given or is None, the
     global default socket timeout is used.

     Changed in version 3.3: `ssl_context' parameter was added.

     Changed in version 3.4: The class now supports hostname check with
     *note ssl.SSLContext.check_hostname: 2812. and `Server Name
     Indication' (see *note ssl.HAS_SNI: 2827.).

     Deprecated since version 3.6: `keyfile' and `certfile' are
     deprecated in favor of `ssl_context'.  Please use *note
     ssl.SSLContext.load_cert_chain(): b69. instead, or let *note
     ssl.create_default_context(): 9a7. select the system’s trusted CA
     certificates for you.

     Changed in version 3.9: The optional `timeout' parameter was added.

The second subclass allows for connections created by a child process:

 -- Class: imaplib.IMAP4_stream (command)

     This is a subclass derived from *note IMAP4: 1af. that connects to
     the ‘stdin/stdout’ file descriptors created by passing `command' to
     ‘subprocess.Popen()’.

The following utility functions are defined:

 -- Function: imaplib.Internaldate2tuple (datestr)

     Parse an IMAP4 ‘INTERNALDATE’ string and return corresponding local
     time.  The return value is a *note time.struct_time: 690. tuple or
     ‘None’ if the string has wrong format.

 -- Function: imaplib.Int2AP (num)

     Converts an integer into a bytes representation using characters
     from the set [‘A’ ..  ‘P’].

 -- Function: imaplib.ParseFlags (flagstr)

     Converts an IMAP4 ‘FLAGS’ response to a tuple of individual flags.

 -- Function: imaplib.Time2Internaldate (date_time)

     Convert `date_time' to an IMAP4 ‘INTERNALDATE’ representation.  The
     return value is a string in the form: ‘"DD-Mmm-YYYY HH:MM:SS
     +HHMM"’ (including double-quotes).  The `date_time' argument can be
     a number (int or float) representing seconds since epoch (as
     returned by *note time.time(): 42d.), a 9-tuple representing local
     time an instance of *note time.struct_time: 690. (as returned by
     *note time.localtime(): 1080.), an aware instance of *note
     datetime.datetime: 1a0, or a double-quoted string.  In the last
     case, it is assumed to already be in the correct format.

Note that IMAP4 message numbers change as the mailbox changes; in
particular, after an ‘EXPUNGE’ command performs deletions the remaining
messages are renumbered.  So it is highly advisable to use UIDs instead,
with the UID command.

At the end of the module, there is a test section that contains a more
extensive example of usage.

See also
........

Documents describing the protocol, sources for servers implementing it,
by the University of Washington’s IMAP Information Center can all be
found at (`Source Code') ‘https://github.com/uw-imap/imap’ (`Not
Maintained').

* Menu:

* IMAP4 Objects::
* IMAP4 Example::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/imaplib.py

   (2) https://tools.ietf.org/html/rfc2060.html

   (3) https://tools.ietf.org/html/rfc1730.html


File: python.info,  Node: IMAP4 Objects,  Next: IMAP4 Example,  Up: imaplib — IMAP4 protocol client

5.21.15.1 IMAP4 Objects
.......................

All IMAP4rev1 commands are represented by methods of the same name,
either upper-case or lower-case.

All arguments to commands are converted to strings, except for
‘AUTHENTICATE’, and the last argument to ‘APPEND’ which is passed as an
IMAP4 literal.  If necessary (the string contains IMAP4
protocol-sensitive characters and isn’t enclosed with either parentheses
or double quotes) each string is quoted.  However, the `password'
argument to the ‘LOGIN’ command is always quoted.  If you want to avoid
having an argument string quoted (eg: the `flags' argument to ‘STORE’)
then enclose the string in parentheses (eg: ‘r'(\Deleted)'’).

Each command returns a tuple: ‘(type, [data, ...])’ where `type' is
usually ‘'OK'’ or ‘'NO'’, and `data' is either the text from the command
response, or mandated results from the command.  Each `data' is either a
‘bytes’, or a tuple.  If a tuple, then the first part is the header of
the response, and the second part contains the data (ie: ‘literal’
value).

The `message_set' options to commands below is a string specifying one
or more messages to be acted upon.  It may be a simple message number
(‘'1'’), a range of message numbers (‘'2:4'’), or a group of
non-contiguous ranges separated by commas (‘'1:3,6:9'’).  A range can
contain an asterisk to indicate an infinite upper bound (‘'3:*'’).

An *note IMAP4: 1af. instance has the following methods:

 -- Method: IMAP4.append (mailbox, flags, date_time, message)

     Append `message' to named mailbox.

 -- Method: IMAP4.authenticate (mechanism, authobject)

     Authenticate command — requires response processing.

     `mechanism' specifies which authentication mechanism is to be used
     - it should appear in the instance variable ‘capabilities’ in the
     form ‘AUTH=mechanism’.

     `authobject' must be a callable object:

          data = authobject(response)

     It will be called to process server continuation responses; the
     `response' argument it is passed will be ‘bytes’.  It should return
     ‘bytes’ `data' that will be base64 encoded and sent to the server.
     It should return ‘None’ if the client abort response ‘*’ should be
     sent instead.

     Changed in version 3.5: string usernames and passwords are now
     encoded to ‘utf-8’ instead of being limited to ASCII.

 -- Method: IMAP4.check ()

     Checkpoint mailbox on server.

 -- Method: IMAP4.close ()

     Close currently selected mailbox.  Deleted messages are removed
     from writable mailbox.  This is the recommended command before
     ‘LOGOUT’.

 -- Method: IMAP4.copy (message_set, new_mailbox)

     Copy `message_set' messages onto end of `new_mailbox'.

 -- Method: IMAP4.create (mailbox)

     Create new mailbox named `mailbox'.

 -- Method: IMAP4.delete (mailbox)

     Delete old mailbox named `mailbox'.

 -- Method: IMAP4.deleteacl (mailbox, who)

     Delete the ACLs (remove any rights) set for who on mailbox.

 -- Method: IMAP4.enable (capability)

     Enable `capability' (see RFC 5161(1)).  Most capabilities do not
     need to be enabled.  Currently only the ‘UTF8=ACCEPT’ capability is
     supported (see RFC 6855(2)).

     New in version 3.5: The *note enable(): 7db. method itself, and RFC
     6855(3) support.

 -- Method: IMAP4.expunge ()

     Permanently remove deleted items from selected mailbox.  Generates
     an ‘EXPUNGE’ response for each deleted message.  Returned data
     contains a list of ‘EXPUNGE’ message numbers in order received.

 -- Method: IMAP4.fetch (message_set, message_parts)

     Fetch (parts of) messages.  `message_parts' should be a string of
     message part names enclosed within parentheses, eg: ‘"(UID
     BODY[TEXT])"’.  Returned data are tuples of message part envelope
     and data.

 -- Method: IMAP4.getacl (mailbox)

     Get the ‘ACL’s for `mailbox'.  The method is non-standard, but is
     supported by the ‘Cyrus’ server.

 -- Method: IMAP4.getannotation (mailbox, entry, attribute)

     Retrieve the specified ‘ANNOTATION’s for `mailbox'.  The method is
     non-standard, but is supported by the ‘Cyrus’ server.

 -- Method: IMAP4.getquota (root)

     Get the ‘quota’ `root'’s resource usage and limits.  This method is
     part of the IMAP4 QUOTA extension defined in rfc2087.

 -- Method: IMAP4.getquotaroot (mailbox)

     Get the list of ‘quota’ ‘roots’ for the named `mailbox'.  This
     method is part of the IMAP4 QUOTA extension defined in rfc2087.

 -- Method: IMAP4.list ([directory[, pattern]])

     List mailbox names in `directory' matching `pattern'.  `directory'
     defaults to the top-level mail folder, and `pattern' defaults to
     match anything.  Returned data contains a list of ‘LIST’ responses.

 -- Method: IMAP4.login (user, password)

     Identify the client using a plaintext password.  The `password'
     will be quoted.

 -- Method: IMAP4.login_cram_md5 (user, password)

     Force use of ‘CRAM-MD5’ authentication when identifying the client
     to protect the password.  Will only work if the server ‘CAPABILITY’
     response includes the phrase ‘AUTH=CRAM-MD5’.

 -- Method: IMAP4.logout ()

     Shutdown connection to server.  Returns server ‘BYE’ response.

     Changed in version 3.8: The method no longer ignores silently
     arbitrary exceptions.

 -- Method: IMAP4.lsub (directory='""', pattern='*')

     List subscribed mailbox names in directory matching pattern.
     `directory' defaults to the top level directory and `pattern'
     defaults to match any mailbox.  Returned data are tuples of message
     part envelope and data.

 -- Method: IMAP4.myrights (mailbox)

     Show my ACLs for a mailbox (i.e.  the rights that I have on
     mailbox).

 -- Method: IMAP4.namespace ()

     Returns IMAP namespaces as defined in RFC 2342(4).

 -- Method: IMAP4.noop ()

     Send ‘NOOP’ to server.

 -- Method: IMAP4.open (host, port, timeout=None)

     Opens socket to `port' at `host'.  The optional `timeout' parameter
     specifies a timeout in seconds for the connection attempt.  If
     timeout is not given or is None, the global default socket timeout
     is used.  Also note that if the `timeout' parameter is set to be
     zero, it will raise a *note ValueError: 16d. to reject creating a
     non-blocking socket.  This method is implicitly called by the *note
     IMAP4: 1af. constructor.  The connection objects established by
     this method will be used in the *note IMAP4.read(): 2eac, *note
     IMAP4.readline(): 2ead, *note IMAP4.send(): 2eae, and *note
     IMAP4.shutdown(): 2eaf. methods.  You may override this method.

     Raises an *note auditing event: fa1. ‘imaplib.open’ with arguments
     ‘self’, ‘host’, ‘port’.

     Changed in version 3.9: The `timeout' parameter was added.

 -- Method: IMAP4.partial (message_num, message_part, start, length)

     Fetch truncated part of a message.  Returned data is a tuple of
     message part envelope and data.

 -- Method: IMAP4.proxyauth (user)

     Assume authentication as `user'.  Allows an authorised
     administrator to proxy into any user’s mailbox.

 -- Method: IMAP4.read (size)

     Reads `size' bytes from the remote server.  You may override this
     method.

 -- Method: IMAP4.readline ()

     Reads one line from the remote server.  You may override this
     method.

 -- Method: IMAP4.recent ()

     Prompt server for an update.  Returned data is ‘None’ if no new
     messages, else value of ‘RECENT’ response.

 -- Method: IMAP4.rename (oldmailbox, newmailbox)

     Rename mailbox named `oldmailbox' to `newmailbox'.

 -- Method: IMAP4.response (code)

     Return data for response `code' if received, or ‘None’.  Returns
     the given code, instead of the usual type.

 -- Method: IMAP4.search (charset, criterion[, ...])

     Search mailbox for matching messages.  `charset' may be ‘None’, in
     which case no ‘CHARSET’ will be specified in the request to the
     server.  The IMAP protocol requires that at least one criterion be
     specified; an exception will be raised when the server returns an
     error.  `charset' must be ‘None’ if the ‘UTF8=ACCEPT’ capability
     was enabled using the *note enable(): 7db. command.

     Example:

          # M is a connected IMAP4 instance...
          typ, msgnums = M.search(None, 'FROM', '"LDJ"')

          # or:
          typ, msgnums = M.search(None, '(FROM "LDJ")')

 -- Method: IMAP4.select (mailbox='INBOX', readonly=False)

     Select a mailbox.  Returned data is the count of messages in
     `mailbox' (‘EXISTS’ response).  The default `mailbox' is ‘'INBOX'’.
     If the `readonly' flag is set, modifications to the mailbox are not
     allowed.

 -- Method: IMAP4.send (data)

     Sends ‘data’ to the remote server.  You may override this method.

     Raises an *note auditing event: fa1. ‘imaplib.send’ with arguments
     ‘self’, ‘data’.

 -- Method: IMAP4.setacl (mailbox, who, what)

     Set an ‘ACL’ for `mailbox'.  The method is non-standard, but is
     supported by the ‘Cyrus’ server.

 -- Method: IMAP4.setannotation (mailbox, entry, attribute[, ...])

     Set ‘ANNOTATION’s for `mailbox'.  The method is non-standard, but
     is supported by the ‘Cyrus’ server.

 -- Method: IMAP4.setquota (root, limits)

     Set the ‘quota’ `root'’s resource `limits'.  This method is part of
     the IMAP4 QUOTA extension defined in rfc2087.

 -- Method: IMAP4.shutdown ()

     Close connection established in ‘open’.  This method is implicitly
     called by *note IMAP4.logout(): 2ea7.  You may override this
     method.

 -- Method: IMAP4.socket ()

     Returns socket instance used to connect to server.

 -- Method: IMAP4.sort (sort_criteria, charset, search_criterion[, ...])

     The ‘sort’ command is a variant of ‘search’ with sorting semantics
     for the results.  Returned data contains a space separated list of
     matching message numbers.

     Sort has two arguments before the `search_criterion' argument(s); a
     parenthesized list of `sort_criteria', and the searching `charset'.
     Note that unlike ‘search’, the searching `charset' argument is
     mandatory.  There is also a ‘uid sort’ command which corresponds to
     ‘sort’ the way that ‘uid search’ corresponds to ‘search’.  The
     ‘sort’ command first searches the mailbox for messages that match
     the given searching criteria using the charset argument for the
     interpretation of strings in the searching criteria.  It then
     returns the numbers of matching messages.

     This is an ‘IMAP4rev1’ extension command.

 -- Method: IMAP4.starttls (ssl_context=None)

     Send a ‘STARTTLS’ command.  The `ssl_context' argument is optional
     and should be a *note ssl.SSLContext: 4ea. object.  This will
     enable encryption on the IMAP connection.  Please read *note
     Security considerations: 26fd. for best practices.

     New in version 3.2.

     Changed in version 3.4: The method now supports hostname check with
     *note ssl.SSLContext.check_hostname: 2812. and `Server Name
     Indication' (see *note ssl.HAS_SNI: 2827.).

 -- Method: IMAP4.status (mailbox, names)

     Request named status conditions for `mailbox'.

 -- Method: IMAP4.store (message_set, command, flag_list)

     Alters flag dispositions for messages in mailbox.  `command' is
     specified by section 6.4.6 of RFC 2060(5) as being one of “FLAGS”,
     “+FLAGS”, or “-FLAGS”, optionally with a suffix of “.SILENT”.

     For example, to set the delete flag on all messages:

          typ, data = M.search(None, 'ALL')
          for num in data[0].split():
             M.store(num, '+FLAGS', '\\Deleted')
          M.expunge()

          Note: Creating flags containing ‘]’ (for example: “[test]”)
          violates RFC 3501(6) (the IMAP protocol).  However, imaplib
          has historically allowed creation of such tags, and popular
          IMAP servers, such as Gmail, accept and produce such flags.
          There are non-Python programs which also create such tags.
          Although it is an RFC violation and IMAP clients and servers
          are supposed to be strict, imaplib nonetheless continues to
          allow such tags to be created for backward compatibility
          reasons, and as of Python 3.6, handles them if they are sent
          from the server, since this improves real-world compatibility.

 -- Method: IMAP4.subscribe (mailbox)

     Subscribe to new mailbox.

 -- Method: IMAP4.thread (threading_algorithm, charset,
          search_criterion[, ...])

     The ‘thread’ command is a variant of ‘search’ with threading
     semantics for the results.  Returned data contains a space
     separated list of thread members.

     Thread members consist of zero or more messages numbers, delimited
     by spaces, indicating successive parent and child.

     Thread has two arguments before the `search_criterion' argument(s);
     a `threading_algorithm', and the searching `charset'.  Note that
     unlike ‘search’, the searching `charset' argument is mandatory.
     There is also a ‘uid thread’ command which corresponds to ‘thread’
     the way that ‘uid search’ corresponds to ‘search’.  The ‘thread’
     command first searches the mailbox for messages that match the
     given searching criteria using the charset argument for the
     interpretation of strings in the searching criteria.  It then
     returns the matching messages threaded according to the specified
     threading algorithm.

     This is an ‘IMAP4rev1’ extension command.

 -- Method: IMAP4.uid (command, arg[, ...])

     Execute command args with messages identified by UID, rather than
     message number.  Returns response appropriate to command.  At least
     one argument must be supplied; if none are provided, the server
     will return an error and an exception will be raised.

 -- Method: IMAP4.unsubscribe (mailbox)

     Unsubscribe from old mailbox.

 -- Method: IMAP4.unselect ()

     *note imaplib.IMAP4.unselect(): 1b3. frees server’s resources
     associated with the selected mailbox and returns the server to the
     authenticated state.  This command performs the same actions as
     *note imaplib.IMAP4.close(): 1b4, except that no messages are
     permanently removed from the currently selected mailbox.

     New in version 3.9.

 -- Method: IMAP4.xatom (name[, ...])

     Allow simple extension commands notified by server in ‘CAPABILITY’
     response.

The following attributes are defined on instances of *note IMAP4: 1af.:

 -- Attribute: IMAP4.PROTOCOL_VERSION

     The most recent supported protocol in the ‘CAPABILITY’ response
     from the server.

 -- Attribute: IMAP4.debug

     Integer value to control debugging output.  The initialize value is
     taken from the module variable ‘Debug’.  Values greater than three
     trace each command.

 -- Attribute: IMAP4.utf8_enabled

     Boolean value that is normally ‘False’, but is set to ‘True’ if an
     *note enable(): 7db. command is successfully issued for the
     ‘UTF8=ACCEPT’ capability.

     New in version 3.5.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc5161.html

   (2) https://tools.ietf.org/html/rfc6855.html

   (3) https://tools.ietf.org/html/rfc6855.html

   (4) https://tools.ietf.org/html/rfc2342.html

   (5) https://tools.ietf.org/html/rfc2060.html

   (6) https://tools.ietf.org/html/rfc3501.html


File: python.info,  Node: IMAP4 Example,  Prev: IMAP4 Objects,  Up: imaplib — IMAP4 protocol client

5.21.15.2 IMAP4 Example
.......................

Here is a minimal example (without error checking) that opens a mailbox
and retrieves and prints all messages:

     import getpass, imaplib

     M = imaplib.IMAP4()
     M.login(getpass.getuser(), getpass.getpass())
     M.select()
     typ, data = M.search(None, 'ALL')
     for num in data[0].split():
         typ, data = M.fetch(num, '(RFC822)')
         print('Message %s\n%s\n' % (num, data[0][1]))
     M.close()
     M.logout()


File: python.info,  Node: nntplib — NNTP protocol client,  Next: smtplib — SMTP protocol client,  Prev: imaplib — IMAP4 protocol client,  Up: Internet Protocols and Support

5.21.16 ‘nntplib’ — NNTP protocol client
----------------------------------------

`Source code:' Lib/nntplib.py(1)

__________________________________________________________________

This module defines the class *note NNTP: 1c6. which implements the
client side of the Network News Transfer Protocol.  It can be used to
implement a news reader or poster, or automated news processors.  It is
compatible with RFC 3977(2) as well as the older RFC 977(3) and RFC
2980(4).

Here are two small examples of how it can be used.  To list some
statistics about a newsgroup and print the subjects of the last 10
articles:

     >>> s = nntplib.NNTP('news.gmane.io')
     >>> resp, count, first, last, name = s.group('gmane.comp.python.committers')
     >>> print('Group', name, 'has', count, 'articles, range', first, 'to', last)
     Group gmane.comp.python.committers has 1096 articles, range 1 to 1096
     >>> resp, overviews = s.over((last - 9, last))
     >>> for id, over in overviews:
     ...     print(id, nntplib.decode_header(over['subject']))
     ...
     1087 Re: Commit privileges for Łukasz Langa
     1088 Re: 3.2 alpha 2 freeze
     1089 Re: 3.2 alpha 2 freeze
     1090 Re: Commit privileges for Łukasz Langa
     1091 Re: Commit privileges for Łukasz Langa
     1092 Updated ssh key
     1093 Re: Updated ssh key
     1094 Re: Updated ssh key
     1095 Hello fellow committers!
     1096 Re: Hello fellow committers!
     >>> s.quit()
     '205 Bye!'

To post an article from a binary file (this assumes that the article has
valid headers, and that you have right to post on the particular
newsgroup):

     >>> s = nntplib.NNTP('news.gmane.io')
     >>> f = open('article.txt', 'rb')
     >>> s.post(f)
     '240 Article posted successfully.'
     >>> s.quit()
     '205 Bye!'

The module itself defines the following classes:

 -- Class: nntplib.NNTP (host, port=119, user=None, password=None,
          readermode=None, usenetrc=False[, timeout])

     Return a new *note NNTP: 1c6. object, representing a connection to
     the NNTP server running on host `host', listening at port `port'.
     An optional `timeout' can be specified for the socket connection.
     If the optional `user' and `password' are provided, or if suitable
     credentials are present in ‘/.netrc’ and the optional flag
     `usenetrc' is true, the ‘AUTHINFO USER’ and ‘AUTHINFO PASS’
     commands are used to identify and authenticate the user to the
     server.  If the optional flag `readermode' is true, then a ‘mode
     reader’ command is sent before authentication is performed.  Reader
     mode is sometimes necessary if you are connecting to an NNTP server
     on the local machine and intend to call reader-specific commands,
     such as ‘group’.  If you get unexpected *note NNTPPermanentError:
     2ec9.s, you might need to set `readermode'.  The *note NNTP: 1c6.
     class supports the *note with: 7da. statement to unconditionally
     consume *note OSError: 304. exceptions and to close the NNTP
     connection when done, e.g.:

          >>> from nntplib import NNTP
          >>> with NNTP('news.gmane.io') as n:
          ...     n.group('gmane.comp.python.committers')
          ...
          ('211 1755 1 1755 gmane.comp.python.committers', 1755, 1, 1755, 'gmane.comp.python.committers')
          >>>

     Raises an *note auditing event: fa1. ‘nntplib.connect’ with
     arguments ‘self’, ‘host’, ‘port’.

     All commands will raise an *note auditing event: fa1.
     ‘nntplib.putline’ with arguments ‘self’ and ‘line’, where ‘line’ is
     the bytes about to be sent to the remote host.

     Changed in version 3.2: `usenetrc' is now ‘False’ by default.

     Changed in version 3.3: Support for the *note with: 7da. statement
     was added.

     Changed in version 3.9: If the `timeout' parameter is set to be
     zero, it will raise a *note ValueError: 16d. to prevent the
     creation of a non-blocking socket.

 -- Class: nntplib.NNTP_SSL (host, port=563, user=None, password=None,
          ssl_context=None, readermode=None, usenetrc=False[, timeout])

     Return a new *note NNTP_SSL: 1c7. object, representing an encrypted
     connection to the NNTP server running on host `host', listening at
     port `port'.  *note NNTP_SSL: 1c7. objects have the same methods as
     *note NNTP: 1c6. objects.  If `port' is omitted, port 563 (NNTPS)
     is used.  `ssl_context' is also optional, and is a *note
     SSLContext: 4ea. object.  Please read *note Security
     considerations: 26fd. for best practices.  All other parameters
     behave the same as for *note NNTP: 1c6.

     Note that SSL-on-563 is discouraged per RFC 4642(5), in favor of
     STARTTLS as described below.  However, some servers only support
     the former.

     Raises an *note auditing event: fa1. ‘nntplib.connect’ with
     arguments ‘self’, ‘host’, ‘port’.

     All commands will raise an *note auditing event: fa1.
     ‘nntplib.putline’ with arguments ‘self’ and ‘line’, where ‘line’ is
     the bytes about to be sent to the remote host.

     New in version 3.2.

     Changed in version 3.4: The class now supports hostname check with
     *note ssl.SSLContext.check_hostname: 2812. and `Server Name
     Indication' (see *note ssl.HAS_SNI: 2827.).

     Changed in version 3.9: If the `timeout' parameter is set to be
     zero, it will raise a *note ValueError: 16d. to prevent the
     creation of a non-blocking socket.

 -- Exception: nntplib.NNTPError

     Derived from the standard exception *note Exception: 2dc, this is
     the base class for all exceptions raised by the *note nntplib: c0.
     module.  Instances of this class have the following attribute:

      -- Attribute: response

          The response of the server if available, as a *note str: 205.
          object.

 -- Exception: nntplib.NNTPReplyError

     Exception raised when an unexpected reply is received from the
     server.

 -- Exception: nntplib.NNTPTemporaryError

     Exception raised when a response code in the range 400–499 is
     received.

 -- Exception: nntplib.NNTPPermanentError

     Exception raised when a response code in the range 500–599 is
     received.

 -- Exception: nntplib.NNTPProtocolError

     Exception raised when a reply is received from the server that does
     not begin with a digit in the range 1–5.

 -- Exception: nntplib.NNTPDataError

     Exception raised when there is some error in the response data.

* Menu:

* NNTP Objects::
* Utility functions: Utility functions<2>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/nntplib.py

   (2) https://tools.ietf.org/html/rfc3977.html

   (3) https://tools.ietf.org/html/rfc977.html

   (4) https://tools.ietf.org/html/rfc2980.html

   (5) https://tools.ietf.org/html/rfc4642.html


File: python.info,  Node: NNTP Objects,  Next: Utility functions<2>,  Up: nntplib — NNTP protocol client

5.21.16.1 NNTP Objects
......................

When connected, *note NNTP: 1c6. and *note NNTP_SSL: 1c7. objects
support the following methods and attributes.

* Menu:

* Attributes::
* Methods: Methods<3>.


File: python.info,  Node: Attributes,  Next: Methods<3>,  Up: NNTP Objects

5.21.16.2 Attributes
....................

 -- Attribute: NNTP.nntp_version

     An integer representing the version of the NNTP protocol supported
     by the server.  In practice, this should be ‘2’ for servers
     advertising RFC 3977(1) compliance and ‘1’ for others.

     New in version 3.2.

 -- Attribute: NNTP.nntp_implementation

     A string describing the software name and version of the NNTP
     server, or *note None: 203. if not advertised by the server.

     New in version 3.2.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3977.html


File: python.info,  Node: Methods<3>,  Prev: Attributes,  Up: NNTP Objects

5.21.16.3 Methods
.................

The `response' that is returned as the first item in the return tuple of
almost all methods is the server’s response: a string beginning with a
three-digit code.  If the server’s response indicates an error, the
method raises one of the above exceptions.

Many of the following methods take an optional keyword-only argument
`file'.  When the `file' argument is supplied, it must be either a *note
file object: c14. opened for binary writing, or the name of an on-disk
file to be written to.  The method will then write any data returned by
the server (except for the response line and the terminating dot) to the
file; any list of lines, tuples or objects that the method normally
returns will be empty.

Changed in version 3.2: Many of the following methods have been reworked
and fixed, which makes them incompatible with their 3.1 counterparts.

 -- Method: NNTP.quit ()

     Send a ‘QUIT’ command and close the connection.  Once this method
     has been called, no other methods of the NNTP object should be
     called.

 -- Method: NNTP.getwelcome ()

     Return the welcome message sent by the server in reply to the
     initial connection.  (This message sometimes contains disclaimers
     or help information that may be relevant to the user.)

 -- Method: NNTP.getcapabilities ()

     Return the RFC 3977(1) capabilities advertised by the server, as a
     *note dict: 164. instance mapping capability names to (possibly
     empty) lists of values.  On legacy servers which don’t understand
     the ‘CAPABILITIES’ command, an empty dictionary is returned
     instead.

          >>> s = NNTP('news.gmane.io')
          >>> 'POST' in s.getcapabilities()
          True

     New in version 3.2.

 -- Method: NNTP.login (user=None, password=None, usenetrc=True)

     Send ‘AUTHINFO’ commands with the user name and password.  If
     `user' and `password' are ‘None’ and `usenetrc' is true,
     credentials from ‘~/.netrc’ will be used if possible.

     Unless intentionally delayed, login is normally performed during
     the *note NNTP: 1c6. object initialization and separately calling
     this function is unnecessary.  To force authentication to be
     delayed, you must not set `user' or `password' when creating the
     object, and must set `usenetrc' to False.

     New in version 3.2.

 -- Method: NNTP.starttls (context=None)

     Send a ‘STARTTLS’ command.  This will enable encryption on the NNTP
     connection.  The `context' argument is optional and should be a
     *note ssl.SSLContext: 4ea. object.  Please read *note Security
     considerations: 26fd. for best practices.

     Note that this may not be done after authentication information has
     been transmitted, and authentication occurs by default if possible
     during a *note NNTP: 1c6. object initialization.  See *note
     NNTP.login(): 2ed9. for information on suppressing this behavior.

     New in version 3.2.

     Changed in version 3.4: The method now supports hostname check with
     *note ssl.SSLContext.check_hostname: 2812. and `Server Name
     Indication' (see *note ssl.HAS_SNI: 2827.).

 -- Method: NNTP.newgroups (date, *, file=None)

     Send a ‘NEWGROUPS’ command.  The `date' argument should be a *note
     datetime.date: 19e. or *note datetime.datetime: 1a0. object.
     Return a pair ‘(response, groups)’ where `groups' is a list
     representing the groups that are new since the given `date'.  If
     `file' is supplied, though, then `groups' will be empty.

          >>> from datetime import date, timedelta
          >>> resp, groups = s.newgroups(date.today() - timedelta(days=3))
          >>> len(groups)
          85
          >>> groups[0]
          GroupInfo(group='gmane.network.tor.devel', last='4', first='1', flag='m')

 -- Method: NNTP.newnews (group, date, *, file=None)

     Send a ‘NEWNEWS’ command.  Here, `group' is a group name or ‘'*'’,
     and `date' has the same meaning as for *note newgroups(): 2eda.
     Return a pair ‘(response, articles)’ where `articles' is a list of
     message ids.

     This command is frequently disabled by NNTP server administrators.

 -- Method: NNTP.list (group_pattern=None, *, file=None)

     Send a ‘LIST’ or ‘LIST ACTIVE’ command.  Return a pair ‘(response,
     list)’ where `list' is a list of tuples representing all the groups
     available from this NNTP server, optionally matching the pattern
     string `group_pattern'.  Each tuple has the form ‘(group, last,
     first, flag)’, where `group' is a group name, `last' and `first'
     are the last and first article numbers, and `flag' usually takes
     one of these values:

        * ‘y’: Local postings and articles from peers are allowed.

        * ‘m’: The group is moderated and all postings must be approved.

        * ‘n’: No local postings are allowed, only articles from peers.

        * ‘j’: Articles from peers are filed in the junk group instead.

        * ‘x’: No local postings, and articles from peers are ignored.

        * ‘=foo.bar’: Articles are filed in the ‘foo.bar’ group instead.

     If `flag' has another value, then the status of the newsgroup
     should be considered unknown.

     This command can return very large results, especially if
     `group_pattern' is not specified.  It is best to cache the results
     offline unless you really need to refresh them.

     Changed in version 3.2: `group_pattern' was added.

 -- Method: NNTP.descriptions (grouppattern)

     Send a ‘LIST NEWSGROUPS’ command, where `grouppattern' is a wildmat
     string as specified in RFC 3977(2) (it’s essentially the same as
     DOS or UNIX shell wildcard strings).  Return a pair ‘(response,
     descriptions)’, where `descriptions' is a dictionary mapping group
     names to textual descriptions.

          >>> resp, descs = s.descriptions('gmane.comp.python.*')
          >>> len(descs)
          295
          >>> descs.popitem()
          ('gmane.comp.python.bio.general', 'BioPython discussion list (Moderated)')

 -- Method: NNTP.description (group)

     Get a description for a single group `group'.  If more than one
     group matches (if ‘group’ is a real wildmat string), return the
     first match.  If no group matches, return an empty string.

     This elides the response code from the server.  If the response
     code is needed, use *note descriptions(): 214.

 -- Method: NNTP.group (name)

     Send a ‘GROUP’ command, where `name' is the group name.  The group
     is selected as the current group, if it exists.  Return a tuple
     ‘(response, count, first, last, name)’ where `count' is the
     (estimated) number of articles in the group, `first' is the first
     article number in the group, `last' is the last article number in
     the group, and `name' is the group name.

 -- Method: NNTP.over (message_spec, *, file=None)

     Send an ‘OVER’ command, or an ‘XOVER’ command on legacy servers.
     `message_spec' can be either a string representing a message id, or
     a ‘(first, last)’ tuple of numbers indicating a range of articles
     in the current group, or a ‘(first, None)’ tuple indicating a range
     of articles starting from `first' to the last article in the
     current group, or *note None: 203. to select the current article in
     the current group.

     Return a pair ‘(response, overviews)’.  `overviews' is a list of
     ‘(article_number, overview)’ tuples, one for each article selected
     by `message_spec'.  Each `overview' is a dictionary with the same
     number of items, but this number depends on the server.  These
     items are either message headers (the key is then the lower-cased
     header name) or metadata items (the key is then the metadata name
     prepended with ‘":"’).  The following items are guaranteed to be
     present by the NNTP specification:

        * the ‘subject’, ‘from’, ‘date’, ‘message-id’ and ‘references’
          headers

        * the ‘:bytes’ metadata: the number of bytes in the entire raw
          article (including headers and body)

        * the ‘:lines’ metadata: the number of lines in the article body

     The value of each item is either a string, or *note None: 203. if
     not present.

     It is advisable to use the *note decode_header(): 2edf. function on
     header values when they may contain non-ASCII characters:

          >>> _, _, first, last, _ = s.group('gmane.comp.python.devel')
          >>> resp, overviews = s.over((last, last))
          >>> art_num, over = overviews[0]
          >>> art_num
          117216
          >>> list(over.keys())
          ['xref', 'from', ':lines', ':bytes', 'references', 'date', 'message-id', 'subject']
          >>> over['from']
          '=?UTF-8?B?Ik1hcnRpbiB2LiBMw7Z3aXMi?= <martin@v.loewis.de>'
          >>> nntplib.decode_header(over['from'])
          '"Martin v. Löwis" <martin@v.loewis.de>'

     New in version 3.2.

 -- Method: NNTP.help (*, file=None)

     Send a ‘HELP’ command.  Return a pair ‘(response, list)’ where
     `list' is a list of help strings.

 -- Method: NNTP.stat (message_spec=None)

     Send a ‘STAT’ command, where `message_spec' is either a message id
     (enclosed in ‘'<'’ and ‘'>'’) or an article number in the current
     group.  If `message_spec' is omitted or *note None: 203, the
     current article in the current group is considered.  Return a
     triple ‘(response, number, id)’ where `number' is the article
     number and `id' is the message id.

          >>> _, _, first, last, _ = s.group('gmane.comp.python.devel')
          >>> resp, number, message_id = s.stat(first)
          >>> number, message_id
          (9099, '<20030112190404.GE29873@epoch.metaslash.com>')

 -- Method: NNTP.next ()

     Send a ‘NEXT’ command.  Return as for *note stat(): 2ee1.

 -- Method: NNTP.last ()

     Send a ‘LAST’ command.  Return as for *note stat(): 2ee1.

 -- Method: NNTP.article (message_spec=None, *, file=None)

     Send an ‘ARTICLE’ command, where `message_spec' has the same
     meaning as for *note stat(): 2ee1.  Return a tuple ‘(response,
     info)’ where `info' is a *note namedtuple: 1a1. with three
     attributes `number', `message_id' and `lines' (in that order).
     `number' is the article number in the group (or 0 if the
     information is not available), `message_id' the message id as a
     string, and `lines' a list of lines (without terminating newlines)
     comprising the raw message including headers and body.

          >>> resp, info = s.article('<20030112190404.GE29873@epoch.metaslash.com>')
          >>> info.number
          0
          >>> info.message_id
          '<20030112190404.GE29873@epoch.metaslash.com>'
          >>> len(info.lines)
          65
          >>> info.lines[0]
          b'Path: main.gmane.org!not-for-mail'
          >>> info.lines[1]
          b'From: Neal Norwitz <neal@metaslash.com>'
          >>> info.lines[-3:]
          [b'There is a patch for 2.3 as well as 2.2.', b'', b'Neal']

 -- Method: NNTP.head (message_spec=None, *, file=None)

     Same as *note article(): 2ee4, but sends a ‘HEAD’ command.  The
     `lines' returned (or written to `file') will only contain the
     message headers, not the body.

 -- Method: NNTP.body (message_spec=None, *, file=None)

     Same as *note article(): 2ee4, but sends a ‘BODY’ command.  The
     `lines' returned (or written to `file') will only contain the
     message body, not the headers.

 -- Method: NNTP.post (data)

     Post an article using the ‘POST’ command.  The `data' argument is
     either a *note file object: c14. opened for binary reading, or any
     iterable of bytes objects (representing raw lines of the article to
     be posted).  It should represent a well-formed news article,
     including the required headers.  The *note post(): 2ee7. method
     automatically escapes lines beginning with ‘.’ and appends the
     termination line.

     If the method succeeds, the server’s response is returned.  If the
     server refuses posting, a *note NNTPReplyError: 2ecc. is raised.

 -- Method: NNTP.ihave (message_id, data)

     Send an ‘IHAVE’ command.  `message_id' is the id of the message to
     send to the server (enclosed in ‘'<'’ and ‘'>'’).  The `data'
     parameter and the return value are the same as for *note post():
     2ee7.

 -- Method: NNTP.date ()

     Return a pair ‘(response, date)’.  `date' is a *note datetime: 1a0.
     object containing the current date and time of the server.

 -- Method: NNTP.slave ()

     Send a ‘SLAVE’ command.  Return the server’s `response'.

 -- Method: NNTP.set_debuglevel (level)

     Set the instance’s debugging level.  This controls the amount of
     debugging output printed.  The default, ‘0’, produces no debugging
     output.  A value of ‘1’ produces a moderate amount of debugging
     output, generally a single line per request or response.  A value
     of ‘2’ or higher produces the maximum amount of debugging output,
     logging each line sent and received on the connection (including
     message text).

The following are optional NNTP extensions defined in RFC 2980(3).  Some
of them have been superseded by newer commands in RFC 3977(4).

 -- Method: NNTP.xhdr (hdr, str, *, file=None)

     Send an ‘XHDR’ command.  The `hdr' argument is a header keyword,
     e.g.  ‘'subject'’.  The `str' argument should have the form
     ‘'first-last'’ where `first' and `last' are the first and last
     article numbers to search.  Return a pair ‘(response, list)’, where
     `list' is a list of pairs ‘(id, text)’, where `id' is an article
     number (as a string) and `text' is the text of the requested header
     for that article.  If the `file' parameter is supplied, then the
     output of the ‘XHDR’ command is stored in a file.  If `file' is a
     string, then the method will open a file with that name, write to
     it then close it.  If `file' is a *note file object: c14, then it
     will start calling ‘write()’ on it to store the lines of the
     command output.  If `file' is supplied, then the returned `list' is
     an empty list.

 -- Method: NNTP.xover (start, end, *, file=None)

     Send an ‘XOVER’ command.  `start' and `end' are article numbers
     delimiting the range of articles to select.  The return value is
     the same of for *note over(): 2ede.  It is recommended to use *note
     over(): 2ede. instead, since it will automatically use the newer
     ‘OVER’ command if available.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3977.html

   (2) https://tools.ietf.org/html/rfc3977.html

   (3) https://tools.ietf.org/html/rfc2980.html

   (4) https://tools.ietf.org/html/rfc3977.html


File: python.info,  Node: Utility functions<2>,  Prev: NNTP Objects,  Up: nntplib — NNTP protocol client

5.21.16.4 Utility functions
...........................

The module also defines the following utility function:

 -- Function: nntplib.decode_header (header_str)

     Decode a header value, un-escaping any escaped non-ASCII
     characters.  `header_str' must be a *note str: 205. object.  The
     unescaped value is returned.  Using this function is recommended to
     display some headers in a human readable form:

          >>> decode_header("Some subject")
          'Some subject'
          >>> decode_header("=?ISO-8859-15?Q?D=E9buter_en_Python?=")
          'Débuter en Python'
          >>> decode_header("Re: =?UTF-8?B?cHJvYmzDqG1lIGRlIG1hdHJpY2U=?=")
          'Re: problème de matrice'


File: python.info,  Node: smtplib — SMTP protocol client,  Next: smtpd — SMTP Server,  Prev: nntplib — NNTP protocol client,  Up: Internet Protocols and Support

5.21.17 ‘smtplib’ — SMTP protocol client
----------------------------------------

`Source code:' Lib/smtplib.py(1)

__________________________________________________________________

The *note smtplib: ed. module defines an SMTP client session object that
can be used to send mail to any Internet machine with an SMTP or ESMTP
listener daemon.  For details of SMTP and ESMTP operation, consult RFC
821(2) (Simple Mail Transfer Protocol) and RFC 1869(3) (SMTP Service
Extensions).

 -- Class: smtplib.SMTP (host='', port=0, local_hostname=None[,
          timeout], source_address=None)

     An *note SMTP: 1de. instance encapsulates an SMTP connection.  It
     has methods that support a full repertoire of SMTP and ESMTP
     operations.  If the optional host and port parameters are given,
     the SMTP *note connect(): 10cd. method is called with those
     parameters during initialization.  If specified, `local_hostname'
     is used as the FQDN of the local host in the HELO/EHLO command.
     Otherwise, the local hostname is found using *note
     socket.getfqdn(): 27d9.  If the *note connect(): 10cd. call returns
     anything other than a success code, an *note SMTPConnectError:
     2ef1. is raised.  The optional `timeout' parameter specifies a
     timeout in seconds for blocking operations like the connection
     attempt (if not specified, the global default timeout setting will
     be used).  If the timeout expires, *note socket.timeout: cd9. is
     raised.  The optional source_address parameter allows binding to
     some specific source address in a machine with multiple network
     interfaces, and/or to some specific source TCP port.  It takes a
     2-tuple (host, port), for the socket to bind to as its source
     address before connecting.  If omitted (or if host or port are ‘''’
     and/or 0 respectively) the OS default behavior will be used.

     For normal use, you should only require the initialization/connect,
     *note sendmail(): 833, and *note SMTP.quit(): 2ef2. methods.  An
     example is included below.

     The *note SMTP: 1de. class supports the *note with: 7da. statement.
     When used like this, the SMTP ‘QUIT’ command is issued
     automatically when the ‘with’ statement exits.  E.g.:

          >>> from smtplib import SMTP
          >>> with SMTP("domain.org") as smtp:
          ...     smtp.noop()
          ...
          (250, b'Ok')
          >>>

     All commands will raise an *note auditing event: fa1.
     ‘smtplib.SMTP.send’ with arguments ‘self’ and ‘data’, where ‘data’
     is the bytes about to be sent to the remote host.

     Changed in version 3.3: Support for the *note with: 7da. statement
     was added.

     Changed in version 3.3: source_address argument was added.

     New in version 3.5: The SMTPUTF8 extension ( RFC 6531(4)) is now
     supported.

     Changed in version 3.9: If the `timeout' parameter is set to be
     zero, it will raise a *note ValueError: 16d. to prevent the
     creation of a non-blocking socket

 -- Class: smtplib.SMTP_SSL (host='', port=0, local_hostname=None,
          keyfile=None, certfile=None[, timeout], context=None,
          source_address=None)

     An *note SMTP_SSL: 1df. instance behaves exactly the same as
     instances of *note SMTP: 1de.  *note SMTP_SSL: 1df. should be used
     for situations where SSL is required from the beginning of the
     connection and using ‘starttls()’ is not appropriate.  If `host' is
     not specified, the local host is used.  If `port' is zero, the
     standard SMTP-over-SSL port (465) is used.  The optional arguments
     `local_hostname', `timeout' and `source_address' have the same
     meaning as they do in the *note SMTP: 1de. class.  `context', also
     optional, can contain a *note SSLContext: 4ea. and allows
     configuring various aspects of the secure connection.  Please read
     *note Security considerations: 26fd. for best practices.

     `keyfile' and `certfile' are a legacy alternative to `context', and
     can point to a PEM formatted private key and certificate chain file
     for the SSL connection.

     Changed in version 3.3: `context' was added.

     Changed in version 3.3: source_address argument was added.

     Changed in version 3.4: The class now supports hostname check with
     *note ssl.SSLContext.check_hostname: 2812. and `Server Name
     Indication' (see *note ssl.HAS_SNI: 2827.).

     Deprecated since version 3.6: `keyfile' and `certfile' are
     deprecated in favor of `context'.  Please use *note
     ssl.SSLContext.load_cert_chain(): b69. instead, or let *note
     ssl.create_default_context(): 9a7. select the system’s trusted CA
     certificates for you.

     Changed in version 3.9: If the `timeout' parameter is set to be
     zero, it will raise a *note ValueError: 16d. to prevent the
     creation of a non-blocking socket

 -- Class: smtplib.LMTP (host='', port=LMTP_PORT, local_hostname=None,
          source_address=None[, timeout])

     The LMTP protocol, which is very similar to ESMTP, is heavily based
     on the standard SMTP client.  It’s common to use Unix sockets for
     LMTP, so our ‘connect()’ method must support that as well as a
     regular host:port server.  The optional arguments local_hostname
     and source_address have the same meaning as they do in the *note
     SMTP: 1de. class.  To specify a Unix socket, you must use an
     absolute path for `host', starting with a ‘/’.

     Authentication is supported, using the regular SMTP mechanism.
     When using a Unix socket, LMTP generally don’t support or require
     any authentication, but your mileage might vary.

     Changed in version 3.9: The optional `timeout' parameter was added.

A nice selection of exceptions is defined as well:

 -- Exception: smtplib.SMTPException

     Subclass of *note OSError: 304. that is the base exception class
     for all the other exceptions provided by this module.

     Changed in version 3.4: SMTPException became subclass of *note
     OSError: 304.

 -- Exception: smtplib.SMTPServerDisconnected

     This exception is raised when the server unexpectedly disconnects,
     or when an attempt is made to use the *note SMTP: 1de. instance
     before connecting it to a server.

 -- Exception: smtplib.SMTPResponseException

     Base class for all exceptions that include an SMTP error code.
     These exceptions are generated in some instances when the SMTP
     server returns an error code.  The error code is stored in the
     ‘smtp_code’ attribute of the error, and the ‘smtp_error’ attribute
     is set to the error message.

 -- Exception: smtplib.SMTPSenderRefused

     Sender address refused.  In addition to the attributes set by on
     all *note SMTPResponseException: 2ef4. exceptions, this sets
     ‘sender’ to the string that the SMTP server refused.

 -- Exception: smtplib.SMTPRecipientsRefused

     All recipient addresses refused.  The errors for each recipient are
     accessible through the attribute ‘recipients’, which is a
     dictionary of exactly the same sort as *note SMTP.sendmail(): 833.
     returns.

 -- Exception: smtplib.SMTPDataError

     The SMTP server refused to accept the message data.

 -- Exception: smtplib.SMTPConnectError

     Error occurred during establishment of a connection with the
     server.

 -- Exception: smtplib.SMTPHeloError

     The server refused our ‘HELO’ message.

 -- Exception: smtplib.SMTPNotSupportedError

     The command or option attempted is not supported by the server.

     New in version 3.5.

 -- Exception: smtplib.SMTPAuthenticationError

     SMTP authentication went wrong.  Most probably the server didn’t
     accept the username/password combination provided.

See also
........

RFC 821(5) - Simple Mail Transfer Protocol

     Protocol definition for SMTP. This document covers the model,
     operating procedure, and protocol details for SMTP.

RFC 1869(6) - SMTP Service Extensions

     Definition of the ESMTP extensions for SMTP. This describes a
     framework for extending SMTP with new commands, supporting dynamic
     discovery of the commands provided by the server, and defines a few
     additional commands.

* Menu:

* SMTP Objects::
* SMTP Example::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/smtplib.py

   (2) https://tools.ietf.org/html/rfc821.html

   (3) https://tools.ietf.org/html/rfc1869.html

   (4) https://tools.ietf.org/html/rfc6531.html

   (5) https://tools.ietf.org/html/rfc821.html

   (6) https://tools.ietf.org/html/rfc1869.html


File: python.info,  Node: SMTP Objects,  Next: SMTP Example,  Up: smtplib — SMTP protocol client

5.21.17.1 SMTP Objects
......................

An *note SMTP: 1de. instance has the following methods:

 -- Method: SMTP.set_debuglevel (level)

     Set the debug output level.  A value of 1 or ‘True’ for `level'
     results in debug messages for connection and for all messages sent
     to and received from the server.  A value of 2 for `level' results
     in these messages being timestamped.

     Changed in version 3.5: Added debuglevel 2.

 -- Method: SMTP.docmd (cmd, args='')

     Send a command `cmd' to the server.  The optional argument `args'
     is simply concatenated to the command, separated by a space.

     This returns a 2-tuple composed of a numeric response code and the
     actual response line (multiline responses are joined into one long
     line.)

     In normal operation it should not be necessary to call this method
     explicitly.  It is used to implement other methods and may be
     useful for testing private extensions.

     If the connection to the server is lost while waiting for the
     reply, *note SMTPServerDisconnected: 2ef3. will be raised.

 -- Method: SMTP.connect (host='localhost', port=0)

     Connect to a host on a given port.  The defaults are to connect to
     the local host at the standard SMTP port (25).  If the hostname
     ends with a colon (‘':'’) followed by a number, that suffix will be
     stripped off and the number interpreted as the port number to use.
     This method is automatically invoked by the constructor if a host
     is specified during instantiation.  Returns a 2-tuple of the
     response code and message sent by the server in its connection
     response.

     Raises an *note auditing event: fa1. ‘smtplib.connect’ with
     arguments ‘self’, ‘host’, ‘port’.

 -- Method: SMTP.helo (name='')

     Identify yourself to the SMTP server using ‘HELO’.  The hostname
     argument defaults to the fully qualified domain name of the local
     host.  The message returned by the server is stored as the
     ‘helo_resp’ attribute of the object.

     In normal operation it should not be necessary to call this method
     explicitly.  It will be implicitly called by the *note sendmail():
     833. when necessary.

 -- Method: SMTP.ehlo (name='')

     Identify yourself to an ESMTP server using ‘EHLO’.  The hostname
     argument defaults to the fully qualified domain name of the local
     host.  Examine the response for ESMTP option and store them for use
     by *note has_extn(): 2eff.  Also sets several informational
     attributes: the message returned by the server is stored as the
     ‘ehlo_resp’ attribute, ‘does_esmtp’ is set to true or false
     depending on whether the server supports ESMTP, and
     ‘esmtp_features’ will be a dictionary containing the names of the
     SMTP service extensions this server supports, and their parameters
     (if any).

     Unless you wish to use *note has_extn(): 2eff. before sending mail,
     it should not be necessary to call this method explicitly.  It will
     be implicitly called by *note sendmail(): 833. when necessary.

 -- Method: SMTP.ehlo_or_helo_if_needed ()

     This method calls *note ehlo(): 2efe. and/or *note helo(): 2efd. if
     there has been no previous ‘EHLO’ or ‘HELO’ command this session.
     It tries ESMTP ‘EHLO’ first.

     *note SMTPHeloError: 2ef8.

          The server didn’t reply properly to the ‘HELO’ greeting.

 -- Method: SMTP.has_extn (name)

     Return *note True: 594. if `name' is in the set of SMTP service
     extensions returned by the server, *note False: 48f. otherwise.
     Case is ignored.

 -- Method: SMTP.verify (address)

     Check the validity of an address on this server using SMTP ‘VRFY’.
     Returns a tuple consisting of code 250 and a full RFC 822(1)
     address (including human name) if the user address is valid.
     Otherwise returns an SMTP error code of 400 or greater and an error
     string.

          Note: Many sites disable SMTP ‘VRFY’ in order to foil
          spammers.

 -- Method: SMTP.login (user, password, *, initial_response_ok=True)

     Log in on an SMTP server that requires authentication.  The
     arguments are the username and the password to authenticate with.
     If there has been no previous ‘EHLO’ or ‘HELO’ command this
     session, this method tries ESMTP ‘EHLO’ first.  This method will
     return normally if the authentication was successful, or may raise
     the following exceptions:

     *note SMTPHeloError: 2ef8.

          The server didn’t reply properly to the ‘HELO’ greeting.

     *note SMTPAuthenticationError: 2ef9.

          The server didn’t accept the username/password combination.

     *note SMTPNotSupportedError: 10cb.

          The ‘AUTH’ command is not supported by the server.

     *note SMTPException: 99e.

          No suitable authentication method was found.

     Each of the authentication methods supported by *note smtplib: ed.
     are tried in turn if they are advertised as supported by the
     server.  See *note auth(): 831. for a list of supported
     authentication methods.  `initial_response_ok' is passed through to
     *note auth(): 831.

     Optional keyword argument `initial_response_ok' specifies whether,
     for authentication methods that support it, an “initial response”
     as specified in RFC 4954(2) can be sent along with the ‘AUTH’
     command, rather than requiring a challenge/response.

     Changed in version 3.5: *note SMTPNotSupportedError: 10cb. may be
     raised, and the `initial_response_ok' parameter was added.

 -- Method: SMTP.auth (mechanism, authobject, *,
          initial_response_ok=True)

     Issue an ‘SMTP’ ‘AUTH’ command for the specified authentication
     `mechanism', and handle the challenge response via `authobject'.

     `mechanism' specifies which authentication mechanism is to be used
     as argument to the ‘AUTH’ command; the valid values are those
     listed in the ‘auth’ element of ‘esmtp_features’.

     `authobject' must be a callable object taking an optional single
     argument:

          data = authobject(challenge=None)

     If optional keyword argument `initial_response_ok' is true,
     ‘authobject()’ will be called first with no argument.  It can
     return the RFC 4954(3) “initial response” ASCII ‘str’ which will be
     encoded and sent with the ‘AUTH’ command as below.  If the
     ‘authobject()’ does not support an initial response (e.g.  because
     it requires a challenge), it should return ‘None’ when called with
     ‘challenge=None’.  If `initial_response_ok' is false, then
     ‘authobject()’ will not be called first with ‘None’.

     If the initial response check returns ‘None’, or if
     `initial_response_ok' is false, ‘authobject()’ will be called to
     process the server’s challenge response; the `challenge' argument
     it is passed will be a ‘bytes’.  It should return ASCII ‘str’
     `data' that will be base64 encoded and sent to the server.

     The ‘SMTP’ class provides ‘authobjects’ for the ‘CRAM-MD5’,
     ‘PLAIN’, and ‘LOGIN’ mechanisms; they are named
     ‘SMTP.auth_cram_md5’, ‘SMTP.auth_plain’, and ‘SMTP.auth_login’
     respectively.  They all require that the ‘user’ and ‘password’
     properties of the ‘SMTP’ instance are set to appropriate values.

     User code does not normally need to call ‘auth’ directly, but can
     instead call the *note login(): 2f02. method, which will try each
     of the above mechanisms in turn, in the order listed.  ‘auth’ is
     exposed to facilitate the implementation of authentication methods
     not (or not yet) supported directly by *note smtplib: ed.

     New in version 3.5.

 -- Method: SMTP.starttls (keyfile=None, certfile=None, context=None)

     Put the SMTP connection in TLS (Transport Layer Security) mode.
     All SMTP commands that follow will be encrypted.  You should then
     call *note ehlo(): 2efe. again.

     If `keyfile' and `certfile' are provided, they are used to create
     an *note ssl.SSLContext: 4ea.

     Optional `context' parameter is an *note ssl.SSLContext: 4ea.
     object; This is an alternative to using a keyfile and a certfile
     and if specified both `keyfile' and `certfile' should be ‘None’.

     If there has been no previous ‘EHLO’ or ‘HELO’ command this
     session, this method tries ESMTP ‘EHLO’ first.

     Deprecated since version 3.6: `keyfile' and `certfile' are
     deprecated in favor of `context'.  Please use *note
     ssl.SSLContext.load_cert_chain(): b69. instead, or let *note
     ssl.create_default_context(): 9a7. select the system’s trusted CA
     certificates for you.

     *note SMTPHeloError: 2ef8.

          The server didn’t reply properly to the ‘HELO’ greeting.

     *note SMTPNotSupportedError: 10cb.

          The server does not support the STARTTLS extension.

     *note RuntimeError: 3dc.

          SSL/TLS support is not available to your Python interpreter.

     Changed in version 3.3: `context' was added.

     Changed in version 3.4: The method now supports hostname check with
     ‘SSLContext.check_hostname’ and `Server Name Indicator' (see *note
     HAS_SNI: 2827.).

     Changed in version 3.5: The error raised for lack of STARTTLS
     support is now the *note SMTPNotSupportedError: 10cb. subclass
     instead of the base *note SMTPException: 99e.

 -- Method: SMTP.sendmail (from_addr, to_addrs, msg, mail_options=(),
          rcpt_options=())

     Send mail.  The required arguments are an RFC 822(4) from-address
     string, a list of RFC 822(5) to-address strings (a bare string will
     be treated as a list with 1 address), and a message string.  The
     caller may pass a list of ESMTP options (such as ‘8bitmime’) to be
     used in ‘MAIL FROM’ commands as `mail_options'.  ESMTP options
     (such as ‘DSN’ commands) that should be used with all ‘RCPT’
     commands can be passed as `rcpt_options'.  (If you need to use
     different ESMTP options to different recipients you have to use the
     low-level methods such as ‘mail()’, ‘rcpt()’ and ‘data()’ to send
     the message.)

          Note: The `from_addr' and `to_addrs' parameters are used to
          construct the message envelope used by the transport agents.
          ‘sendmail’ does not modify the message headers in any way.

     `msg' may be a string containing characters in the ASCII range, or
     a byte string.  A string is encoded to bytes using the ascii codec,
     and lone ‘\r’ and ‘\n’ characters are converted to ‘\r\n’
     characters.  A byte string is not modified.

     If there has been no previous ‘EHLO’ or ‘HELO’ command this
     session, this method tries ESMTP ‘EHLO’ first.  If the server does
     ESMTP, message size and each of the specified options will be
     passed to it (if the option is in the feature set the server
     advertises).  If ‘EHLO’ fails, ‘HELO’ will be tried and ESMTP
     options suppressed.

     This method will return normally if the mail is accepted for at
     least one recipient.  Otherwise it will raise an exception.  That
     is, if this method does not raise an exception, then someone should
     get your mail.  If this method does not raise an exception, it
     returns a dictionary, with one entry for each recipient that was
     refused.  Each entry contains a tuple of the SMTP error code and
     the accompanying error message sent by the server.

     If ‘SMTPUTF8’ is included in `mail_options', and the server
     supports it, `from_addr' and `to_addrs' may contain non-ASCII
     characters.

     This method may raise the following exceptions:

     *note SMTPRecipientsRefused: 2ef6.

          All recipients were refused.  Nobody got the mail.  The
          ‘recipients’ attribute of the exception object is a dictionary
          with information about the refused recipients (like the one
          returned when at least one recipient was accepted).

     *note SMTPHeloError: 2ef8.

          The server didn’t reply properly to the ‘HELO’ greeting.

     *note SMTPSenderRefused: 2ef5.

          The server didn’t accept the `from_addr'.

     *note SMTPDataError: 2ef7.

          The server replied with an unexpected error code (other than a
          refusal of a recipient).

     *note SMTPNotSupportedError: 10cb.

          ‘SMTPUTF8’ was given in the `mail_options' but is not
          supported by the server.

     Unless otherwise noted, the connection will be open even after an
     exception is raised.

     Changed in version 3.2: `msg' may be a byte string.

     Changed in version 3.5: ‘SMTPUTF8’ support added, and *note
     SMTPNotSupportedError: 10cb. may be raised if ‘SMTPUTF8’ is
     specified but the server does not support it.

 -- Method: SMTP.send_message (msg, from_addr=None, to_addrs=None,
          mail_options=(), rcpt_options=())

     This is a convenience method for calling *note sendmail(): 833.
     with the message represented by an *note email.message.Message:
     63b. object.  The arguments have the same meaning as for *note
     sendmail(): 833, except that `msg' is a ‘Message’ object.

     If `from_addr' is ‘None’ or `to_addrs' is ‘None’, ‘send_message’
     fills those arguments with addresses extracted from the headers of
     `msg' as specified in RFC 5322(6): `from_addr' is set to the
     ‘Sender’ field if it is present, and otherwise to the ‘From’ field.
     `to_addrs' combines the values (if any) of the ‘To’, ‘Cc’, and
     ‘Bcc’ fields from `msg'.  If exactly one set of ‘Resent-*’ headers
     appear in the message, the regular headers are ignored and the
     ‘Resent-*’ headers are used instead.  If the message contains more
     than one set of ‘Resent-*’ headers, a *note ValueError: 16d. is
     raised, since there is no way to unambiguously detect the most
     recent set of ‘Resent-’ headers.

     ‘send_message’ serializes `msg' using *note BytesGenerator: c1f.
     with ‘\r\n’ as the `linesep', and calls *note sendmail(): 833. to
     transmit the resulting message.  Regardless of the values of
     `from_addr' and `to_addrs', ‘send_message’ does not transmit any
     ‘Bcc’ or ‘Resent-Bcc’ headers that may appear in `msg'.  If any of
     the addresses in `from_addr' and `to_addrs' contain non-ASCII
     characters and the server does not advertise ‘SMTPUTF8’ support, an
     ‘SMTPNotSupported’ error is raised.  Otherwise the ‘Message’ is
     serialized with a clone of its *note policy: 73. with the *note
     utf8: 7c5. attribute set to ‘True’, and ‘SMTPUTF8’ and
     ‘BODY=8BITMIME’ are added to `mail_options'.

     New in version 3.2.

     New in version 3.5: Support for internationalized addresses
     (‘SMTPUTF8’).

 -- Method: SMTP.quit ()

     Terminate the SMTP session and close the connection.  Return the
     result of the SMTP ‘QUIT’ command.

Low-level methods corresponding to the standard SMTP/ESMTP commands
‘HELP’, ‘RSET’, ‘NOOP’, ‘MAIL’, ‘RCPT’, and ‘DATA’ are also supported.
Normally these do not need to be called directly, so they are not
documented here.  For details, consult the module code.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc822.html

   (2) https://tools.ietf.org/html/rfc4954.html

   (3) https://tools.ietf.org/html/rfc4954.html

   (4) https://tools.ietf.org/html/rfc822.html

   (5) https://tools.ietf.org/html/rfc822.html

   (6) https://tools.ietf.org/html/rfc5322.html


File: python.info,  Node: SMTP Example,  Prev: SMTP Objects,  Up: smtplib — SMTP protocol client

5.21.17.2 SMTP Example
......................

This example prompts the user for addresses needed in the message
envelope (‘To’ and ‘From’ addresses), and the message to be delivered.
Note that the headers to be included with the message must be included
in the message as entered; this example doesn’t do any processing of the
RFC 822(1) headers.  In particular, the ‘To’ and ‘From’ addresses must
be included in the message headers explicitly.

     import smtplib

     def prompt(prompt):
         return input(prompt).strip()

     fromaddr = prompt("From: ")
     toaddrs  = prompt("To: ").split()
     print("Enter message, end with ^D (Unix) or ^Z (Windows):")

     # Add the From: and To: headers at the start!
     msg = ("From: %s\r\nTo: %s\r\n\r\n"
            % (fromaddr, ", ".join(toaddrs)))
     while True:
         try:
             line = input()
         except EOFError:
             break
         if not line:
             break
         msg = msg + line

     print("Message length is", len(msg))

     server = smtplib.SMTP('localhost')
     server.set_debuglevel(1)
     server.sendmail(fromaddr, toaddrs, msg)
     server.quit()

     Note: In general, you will want to use the *note email: 67.
     package’s features to construct an email message, which you can
     then send via *note send_message(): 834.; see *note email;
     Examples: 932.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc822.html


File: python.info,  Node: smtpd — SMTP Server,  Next: telnetlib — Telnet client,  Prev: smtplib — SMTP protocol client,  Up: Internet Protocols and Support

5.21.18 ‘smtpd’ — SMTP Server
-----------------------------

`Source code:' Lib/smtpd.py(1)

__________________________________________________________________

This module offers several classes to implement SMTP (email) servers.

See also
........

The aiosmtpd(2) package is a recommended replacement for this module.
It is based on *note asyncio: 9. and provides a more straightforward
API. *note smtpd: ec. should be considered deprecated.

Several server implementations are present; one is a generic do-nothing
implementation, which can be overridden, while the other two offer
specific mail-sending strategies.

Additionally the SMTPChannel may be extended to implement very specific
interaction behaviour with SMTP clients.

The code supports RFC 5321(3), plus the RFC 1870(4) SIZE and RFC 6531(5)
SMTPUTF8 extensions.

* Menu:

* SMTPServer Objects::
* DebuggingServer Objects::
* PureProxy Objects::
* MailmanProxy Objects::
* SMTPChannel Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/smtpd.py

   (2) http://aiosmtpd.readthedocs.io/

   (3) https://tools.ietf.org/html/rfc5321.html

   (4) https://tools.ietf.org/html/rfc1870.html

   (5) https://tools.ietf.org/html/rfc6531.html


File: python.info,  Node: SMTPServer Objects,  Next: DebuggingServer Objects,  Up: smtpd — SMTP Server

5.21.18.1 SMTPServer Objects
............................

 -- Class: smtpd.SMTPServer (localaddr, remoteaddr,
          data_size_limit=33554432, map=None, enable_SMTPUTF8=False,
          decode_data=False)

     Create a new *note SMTPServer: 6f9. object, which binds to local
     address `localaddr'.  It will treat `remoteaddr' as an upstream
     SMTP relayer.  Both `localaddr' and `remoteaddr' should be a *note
     (host, port): 27b4. tuple.  The object inherits from *note
     asyncore.dispatcher: c91, and so will insert itself into *note
     asyncore: a.’s event loop on instantiation.

     `data_size_limit' specifies the maximum number of bytes that will
     be accepted in a ‘DATA’ command.  A value of ‘None’ or ‘0’ means no
     limit.

     `map' is the socket map to use for connections (an initially empty
     dictionary is a suitable value).  If not specified the *note
     asyncore: a. global socket map is used.

     `enable_SMTPUTF8' determines whether the ‘SMTPUTF8’ extension (as
     defined in RFC 6531(1)) should be enabled.  The default is ‘False’.
     When ‘True’, ‘SMTPUTF8’ is accepted as a parameter to the ‘MAIL’
     command and when present is passed to *note process_message(): 6fa.
     in the ‘kwargs['mail_options']’ list.  `decode_data' and
     `enable_SMTPUTF8' cannot be set to ‘True’ at the same time.

     `decode_data' specifies whether the data portion of the SMTP
     transaction should be decoded using UTF-8.  When `decode_data' is
     ‘False’ (the default), the server advertises the ‘8BITMIME’
     extension ( RFC 6152(2)), accepts the ‘BODY=8BITMIME’ parameter to
     the ‘MAIL’ command, and when present passes it to *note
     process_message(): 6fa. in the ‘kwargs['mail_options']’ list.
     `decode_data' and `enable_SMTPUTF8' cannot be set to ‘True’ at the
     same time.

      -- Method: process_message (peer, mailfrom, rcpttos, data,
               **kwargs)

          Raise a *note NotImplementedError: 704. exception.  Override
          this in subclasses to do something useful with this message.
          Whatever was passed in the constructor as `remoteaddr' will be
          available as the ‘_remoteaddr’ attribute.  `peer' is the
          remote host’s address, `mailfrom' is the envelope originator,
          `rcpttos' are the envelope recipients and `data' is a string
          containing the contents of the e-mail (which should be in RFC
          5321(3) format).

          If the `decode_data' constructor keyword is set to ‘True’, the
          `data' argument will be a unicode string.  If it is set to
          ‘False’, it will be a bytes object.

          `kwargs' is a dictionary containing additional information.
          It is empty if ‘decode_data=True’ was given as an init
          argument, otherwise it contains the following keys:

               `mail_options':

                    a list of all received parameters to the ‘MAIL’
                    command (the elements are uppercase strings;
                    example: ‘['BODY=8BITMIME', 'SMTPUTF8']’).

               `rcpt_options':

                    same as `mail_options' but for the ‘RCPT’ command.
                    Currently no ‘RCPT TO’ options are supported, so for
                    now this will always be an empty list.

          Implementations of ‘process_message’ should use the ‘**kwargs’
          signature to accept arbitrary keyword arguments, since future
          feature enhancements may add keys to the kwargs dictionary.

          Return ‘None’ to request a normal ‘250 Ok’ response; otherwise
          return the desired response string in RFC 5321(4) format.

      -- Attribute: channel_class

          Override this in subclasses to use a custom *note SMTPChannel:
          6f8. for managing SMTP clients.

     New in version 3.4: The `map' constructor argument.

     Changed in version 3.5: `localaddr' and `remoteaddr' may now
     contain IPv6 addresses.

     New in version 3.5: The `decode_data' and `enable_SMTPUTF8'
     constructor parameters, and the `kwargs' parameter to *note
     process_message(): 6fa. when `decode_data' is ‘False’.

     Changed in version 3.6: `decode_data' is now ‘False’ by default.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc6531.html

   (2) https://tools.ietf.org/html/rfc6152.html

   (3) https://tools.ietf.org/html/rfc5321.html

   (4) https://tools.ietf.org/html/rfc5321.html


File: python.info,  Node: DebuggingServer Objects,  Next: PureProxy Objects,  Prev: SMTPServer Objects,  Up: smtpd — SMTP Server

5.21.18.2 DebuggingServer Objects
.................................

 -- Class: smtpd.DebuggingServer (localaddr, remoteaddr)

     Create a new debugging server.  Arguments are as per *note
     SMTPServer: 6f9.  Messages will be discarded, and printed on
     stdout.


File: python.info,  Node: PureProxy Objects,  Next: MailmanProxy Objects,  Prev: DebuggingServer Objects,  Up: smtpd — SMTP Server

5.21.18.3 PureProxy Objects
...........................

 -- Class: smtpd.PureProxy (localaddr, remoteaddr)

     Create a new pure proxy server.  Arguments are as per *note
     SMTPServer: 6f9.  Everything will be relayed to `remoteaddr'.  Note
     that running this has a good chance to make you into an open relay,
     so please be careful.


File: python.info,  Node: MailmanProxy Objects,  Next: SMTPChannel Objects,  Prev: PureProxy Objects,  Up: smtpd — SMTP Server

5.21.18.4 MailmanProxy Objects
..............................

 -- Class: smtpd.MailmanProxy (localaddr, remoteaddr)

     Deprecated since version 3.9, will be removed in version 3.11:
     *note MailmanProxy: 211. is deprecated, it depends on a ‘Mailman’
     module which no longer exists and therefore is already broken.

     Create a new pure proxy server.  Arguments are as per *note
     SMTPServer: 6f9.  Everything will be relayed to `remoteaddr',
     unless local mailman configurations knows about an address, in
     which case it will be handled via mailman.  Note that running this
     has a good chance to make you into an open relay, so please be
     careful.


File: python.info,  Node: SMTPChannel Objects,  Prev: MailmanProxy Objects,  Up: smtpd — SMTP Server

5.21.18.5 SMTPChannel Objects
.............................

 -- Class: smtpd.SMTPChannel (server, conn, addr,
          data_size_limit=33554432, map=None, enable_SMTPUTF8=False,
          decode_data=False)

     Create a new *note SMTPChannel: 6f8. object which manages the
     communication between the server and a single SMTP client.

     `conn' and `addr' are as per the instance variables described
     below.

     `data_size_limit' specifies the maximum number of bytes that will
     be accepted in a ‘DATA’ command.  A value of ‘None’ or ‘0’ means no
     limit.

     `enable_SMTPUTF8' determines whether the ‘SMTPUTF8’ extension (as
     defined in RFC 6531(1)) should be enabled.  The default is ‘False’.
     `decode_data' and `enable_SMTPUTF8' cannot be set to ‘True’ at the
     same time.

     A dictionary can be specified in `map' to avoid using a global
     socket map.

     `decode_data' specifies whether the data portion of the SMTP
     transaction should be decoded using UTF-8.  The default is ‘False’.
     `decode_data' and `enable_SMTPUTF8' cannot be set to ‘True’ at the
     same time.

     To use a custom SMTPChannel implementation you need to override the
     *note SMTPServer.channel_class: 2f08. of your *note SMTPServer:
     6f9.

     Changed in version 3.5: The `decode_data' and `enable_SMTPUTF8'
     parameters were added.

     Changed in version 3.6: `decode_data' is now ‘False’ by default.

     The *note SMTPChannel: 6f8. has the following instance variables:

      -- Attribute: smtp_server

          Holds the *note SMTPServer: 6f9. that spawned this channel.

      -- Attribute: conn

          Holds the socket object connecting to the client.

      -- Attribute: addr

          Holds the address of the client, the second value returned by
          *note socket.accept: 768.

      -- Attribute: received_lines

          Holds a list of the line strings (decoded using UTF-8)
          received from the client.  The lines have their ‘"\r\n"’ line
          ending translated to ‘"\n"’.

      -- Attribute: smtp_state

          Holds the current state of the channel.  This will be either
          ‘COMMAND’ initially and then ‘DATA’ after the client sends a
          “DATA” line.

      -- Attribute: seen_greeting

          Holds a string containing the greeting sent by the client in
          its “HELO”.

      -- Attribute: mailfrom

          Holds a string containing the address identified in the “MAIL
          FROM:” line from the client.

      -- Attribute: rcpttos

          Holds a list of strings containing the addresses identified in
          the “RCPT TO:” lines from the client.

      -- Attribute: received_data

          Holds a string containing all of the data sent by the client
          during the DATA state, up to but not including the terminating
          ‘"\r\n.\r\n"’.

      -- Attribute: fqdn

          Holds the fully-qualified domain name of the server as
          returned by *note socket.getfqdn(): 27d9.

      -- Attribute: peer

          Holds the name of the client peer as returned by
          ‘conn.getpeername()’ where ‘conn’ is *note conn: 2f10.

     The *note SMTPChannel: 6f8. operates by invoking methods named
     ‘smtp_<command>’ upon reception of a command line from the client.
     Built into the base *note SMTPChannel: 6f8. class are methods for
     handling the following commands (and responding to them
     appropriately):

     Command      Action taken
                  
     -------------------------------------------------------------------------------------
                  
     HELO         Accepts the greeting from the client and stores it in
                  *note seen_greeting: 2f14.  Sets server to base command mode.
                  
                  
     EHLO         Accepts the greeting from the client and stores it in
                  *note seen_greeting: 2f14.  Sets server to extended command mode.
                  
                  
     NOOP         Takes no action.
                  
                  
     QUIT         Closes the connection cleanly.
                  
                  
     MAIL         Accepts the “MAIL FROM:” syntax and stores the supplied address as
                  *note mailfrom: 2f15.  In extended command mode, accepts the RFC
                  1870(2) SIZE attribute and responds appropriately based on the value
                  of `data_size_limit'.
                  
                  
     RCPT         Accepts the “RCPT TO:” syntax and stores the supplied addresses in
                  the *note rcpttos: 2f16. list.
                  
                  
     RSET         Resets the *note mailfrom: 2f15, *note rcpttos: 2f16, and
                  *note received_data: 2f17, but not the greeting.
                  
                  
     DATA         Sets the internal state to ‘DATA’ and stores remaining lines from the
                  client in *note received_data: 2f17. until the terminator
                  ‘"\r\n.\r\n"’ is received.
                  
                  
     HELP         Returns minimal information on command syntax
                  
                  
     VRFY         Returns code 252 (the server doesn’t know if the address is valid)
                  
                  
     EXPN         Reports that the command is not implemented.
                  

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc6531.html

   (2) https://tools.ietf.org/html/rfc1870.html


File: python.info,  Node: telnetlib — Telnet client,  Next: uuid — UUID objects according to RFC 4122,  Prev: smtpd — SMTP Server,  Up: Internet Protocols and Support

5.21.19 ‘telnetlib’ — Telnet client
-----------------------------------

`Source code:' Lib/telnetlib.py(1)

__________________________________________________________________

The *note telnetlib: 102. module provides a *note Telnet: 68e. class
that implements the Telnet protocol.  See RFC 854(2) for details about
the protocol.  In addition, it provides symbolic constants for the
protocol characters (see below), and for the telnet options.  The
symbolic names of the telnet options follow the definitions in
‘arpa/telnet.h’, with the leading ‘TELOPT_’ removed.  For symbolic names
of options which are traditionally not included in ‘arpa/telnet.h’, see
the module source itself.

The symbolic constants for the telnet commands are: IAC, DONT, DO, WONT,
WILL, SE (Subnegotiation End), NOP (No Operation), DM (Data Mark), BRK
(Break), IP (Interrupt process), AO (Abort output), AYT (Are You There),
EC (Erase Character), EL (Erase Line), GA (Go Ahead), SB (Subnegotiation
Begin).

 -- Class: telnetlib.Telnet (host=None, port=0[, timeout])

     *note Telnet: 68e. represents a connection to a Telnet server.  The
     instance is initially not connected by default; the *note open():
     2f1c. method must be used to establish a connection.
     Alternatively, the host name and optional port number can be passed
     to the constructor too, in which case the connection to the server
     will be established before the constructor returns.  The optional
     `timeout' parameter specifies a timeout in seconds for blocking
     operations like the connection attempt (if not specified, the
     global default timeout setting will be used).

     Do not reopen an already connected instance.

     This class has many ‘read_*()’ methods.  Note that some of them
     raise *note EOFError: d34. when the end of the connection is read,
     because they can return an empty string for other reasons.  See the
     individual descriptions below.

     A *note Telnet: 68e. object is a context manager and can be used in
     a *note with: 7da. statement.  When the ‘with’ block ends, the
     *note close(): 2f1d. method is called:

          >>> from telnetlib import Telnet
          >>> with Telnet('localhost', 23) as tn:
          ...     tn.interact()
          ...

     Changed in version 3.6: Context manager support added

See also
........

RFC 854(3) - Telnet Protocol Specification

     Definition of the Telnet protocol.

* Menu:

* Telnet Objects::
* Telnet Example::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/telnetlib.py

   (2) https://tools.ietf.org/html/rfc854.html

   (3) https://tools.ietf.org/html/rfc854.html


File: python.info,  Node: Telnet Objects,  Next: Telnet Example,  Up: telnetlib — Telnet client

5.21.19.1 Telnet Objects
........................

*note Telnet: 68e. instances have the following methods:

 -- Method: Telnet.read_until (expected, timeout=None)

     Read until a given byte string, `expected', is encountered or until
     `timeout' seconds have passed.

     When no match is found, return whatever is available instead,
     possibly empty bytes.  Raise *note EOFError: d34. if the connection
     is closed and no cooked data is available.

 -- Method: Telnet.read_all ()

     Read all data until EOF as bytes; block until connection closed.

 -- Method: Telnet.read_some ()

     Read at least one byte of cooked data unless EOF is hit.  Return
     ‘b''’ if EOF is hit.  Block if no data is immediately available.

 -- Method: Telnet.read_very_eager ()

     Read everything that can be without blocking in I/O (eager).

     Raise *note EOFError: d34. if connection closed and no cooked data
     available.  Return ‘b''’ if no cooked data available otherwise.  Do
     not block unless in the midst of an IAC sequence.

 -- Method: Telnet.read_eager ()

     Read readily available data.

     Raise *note EOFError: d34. if connection closed and no cooked data
     available.  Return ‘b''’ if no cooked data available otherwise.  Do
     not block unless in the midst of an IAC sequence.

 -- Method: Telnet.read_lazy ()

     Process and return data already in the queues (lazy).

     Raise *note EOFError: d34. if connection closed and no data
     available.  Return ‘b''’ if no cooked data available otherwise.  Do
     not block unless in the midst of an IAC sequence.

 -- Method: Telnet.read_very_lazy ()

     Return any data available in the cooked queue (very lazy).

     Raise *note EOFError: d34. if connection closed and no data
     available.  Return ‘b''’ if no cooked data available otherwise.
     This method never blocks.

 -- Method: Telnet.read_sb_data ()

     Return the data collected between a SB/SE pair (suboption
     begin/end).  The callback should access these data when it was
     invoked with a ‘SE’ command.  This method never blocks.

 -- Method: Telnet.open (host, port=0[, timeout])

     Connect to a host.  The optional second argument is the port
     number, which defaults to the standard Telnet port (23).  The
     optional `timeout' parameter specifies a timeout in seconds for
     blocking operations like the connection attempt (if not specified,
     the global default timeout setting will be used).

     Do not try to reopen an already connected instance.

     Raises an *note auditing event: fa1. ‘telnetlib.Telnet.open’ with
     arguments ‘self’, ‘host’, ‘port’.

 -- Method: Telnet.msg (msg, *args)

     Print a debug message when the debug level is ‘>’ 0.  If extra
     arguments are present, they are substituted in the message using
     the standard string formatting operator.

 -- Method: Telnet.set_debuglevel (debuglevel)

     Set the debug level.  The higher the value of `debuglevel', the
     more debug output you get (on ‘sys.stdout’).

 -- Method: Telnet.close ()

     Close the connection.

 -- Method: Telnet.get_socket ()

     Return the socket object used internally.

 -- Method: Telnet.fileno ()

     Return the file descriptor of the socket object used internally.

 -- Method: Telnet.write (buffer)

     Write a byte string to the socket, doubling any IAC characters.
     This can block if the connection is blocked.  May raise *note
     OSError: 304. if the connection is closed.

     Raises an *note auditing event: fa1. ‘telnetlib.Telnet.write’ with
     arguments ‘self’, ‘buffer’.

     Changed in version 3.3: This method used to raise *note
     socket.error: a76, which is now an alias of *note OSError: 304.

 -- Method: Telnet.interact ()

     Interaction function, emulates a very dumb Telnet client.

 -- Method: Telnet.mt_interact ()

     Multithreaded version of *note interact(): 2f2d.

 -- Method: Telnet.expect (list, timeout=None)

     Read until one from a list of a regular expressions matches.

     The first argument is a list of regular expressions, either
     compiled (*note regex objects: 983.) or uncompiled (byte strings).
     The optional second argument is a timeout, in seconds; the default
     is to block indefinitely.

     Return a tuple of three items: the index in the list of the first
     regular expression that matches; the match object returned; and the
     bytes read up till and including the match.

     If end of file is found and no bytes were read, raise *note
     EOFError: d34.  Otherwise, when nothing matches, return ‘(-1, None,
     data)’ where `data' is the bytes received so far (may be empty
     bytes if a timeout happened).

     If a regular expression ends with a greedy match (such as ‘.*’) or
     if more than one expression can match the same input, the results
     are non-deterministic, and may depend on the I/O timing.

 -- Method: Telnet.set_option_negotiation_callback (callback)

     Each time a telnet option is read on the input flow, this
     `callback' (if set) is called with the following parameters:
     callback(telnet socket, command (DO/DONT/WILL/WONT), option).  No
     other action is done afterwards by telnetlib.


File: python.info,  Node: Telnet Example,  Prev: Telnet Objects,  Up: telnetlib — Telnet client

5.21.19.2 Telnet Example
........................

A simple example illustrating typical use:

     import getpass
     import telnetlib

     HOST = "localhost"
     user = input("Enter your remote account: ")
     password = getpass.getpass()

     tn = telnetlib.Telnet(HOST)

     tn.read_until(b"login: ")
     tn.write(user.encode('ascii') + b"\n")
     if password:
         tn.read_until(b"Password: ")
         tn.write(password.encode('ascii') + b"\n")

     tn.write(b"ls\n")
     tn.write(b"exit\n")

     print(tn.read_all().decode('ascii'))


File: python.info,  Node: uuid — UUID objects according to RFC 4122,  Next: socketserver — A framework for network servers,  Prev: telnetlib — Telnet client,  Up: Internet Protocols and Support

5.21.20 ‘uuid’ — UUID objects according to `RFC 4122'
-----------------------------------------------------

`Source code:' Lib/uuid.py(1)

__________________________________________________________________

This module provides immutable *note UUID: 38a. objects (the *note UUID:
38a. class) and the functions *note uuid1(): 518, *note uuid3(): 2f35,
*note uuid4(): 2f36, *note uuid5(): 2f37. for generating version 1, 3,
4, and 5 UUIDs as specified in RFC 4122(2).

If all you want is a unique ID, you should probably call *note uuid1():
518. or *note uuid4(): 2f36.  Note that *note uuid1(): 518. may
compromise privacy since it creates a UUID containing the computer’s
network address.  *note uuid4(): 2f36. creates a random UUID.

Depending on support from the underlying platform, *note uuid1(): 518.
may or may not return a “safe” UUID. A safe UUID is one which is
generated using synchronization methods that ensure no two processes can
obtain the same UUID. All instances of *note UUID: 38a. have an
‘is_safe’ attribute which relays any information about the UUID’s
safety, using this enumeration:

 -- Class: uuid.SafeUUID

     New in version 3.7.

      -- Attribute: safe

          The UUID was generated by the platform in a
          multiprocessing-safe way.

      -- Attribute: unsafe

          The UUID was not generated in a multiprocessing-safe way.

      -- Attribute: unknown

          The platform does not provide information on whether the UUID
          was generated safely or not.

 -- Class: uuid.UUID (hex=None, bytes=None, bytes_le=None, fields=None,
          int=None, version=None, *, is_safe=SafeUUID.unknown)

     Create a UUID from either a string of 32 hexadecimal digits, a
     string of 16 bytes in big-endian order as the `bytes' argument, a
     string of 16 bytes in little-endian order as the `bytes_le'
     argument, a tuple of six integers (32-bit `time_low', 16-bit
     `time_mid', 16-bit `time_hi_version', 8-bit `clock_seq_hi_variant',
     8-bit `clock_seq_low', 48-bit `node') as the `fields' argument, or
     a single 128-bit integer as the `int' argument.  When a string of
     hex digits is given, curly braces, hyphens, and a URN prefix are
     all optional.  For example, these expressions all yield the same
     UUID:

          UUID('{12345678-1234-5678-1234-567812345678}')
          UUID('12345678123456781234567812345678')
          UUID('urn:uuid:12345678-1234-5678-1234-567812345678')
          UUID(bytes=b'\x12\x34\x56\x78'*4)
          UUID(bytes_le=b'\x78\x56\x34\x12\x34\x12\x78\x56' +
                        b'\x12\x34\x56\x78\x12\x34\x56\x78')
          UUID(fields=(0x12345678, 0x1234, 0x5678, 0x12, 0x34, 0x567812345678))
          UUID(int=0x12345678123456781234567812345678)

     Exactly one of `hex', `bytes', `bytes_le', `fields', or `int' must
     be given.  The `version' argument is optional; if given, the
     resulting UUID will have its variant and version number set
     according to RFC 4122(3), overriding bits in the given `hex',
     `bytes', `bytes_le', `fields', or `int'.

     Comparison of UUID objects are made by way of comparing their *note
     UUID.int: 2f3c. attributes.  Comparison with a non-UUID object
     raises a *note TypeError: 1fe.

     ‘str(uuid)’ returns a string in the form
     ‘12345678-1234-5678-1234-567812345678’ where the 32 hexadecimal
     digits represent the UUID.

*note UUID: 38a. instances have these read-only attributes:

 -- Attribute: UUID.bytes

     The UUID as a 16-byte string (containing the six integer fields in
     big-endian byte order).

 -- Attribute: UUID.bytes_le

     The UUID as a 16-byte string (with `time_low', `time_mid', and
     `time_hi_version' in little-endian byte order).

 -- Attribute: UUID.fields

     A tuple of the six integer fields of the UUID, which are also
     available as six individual attributes and two derived attributes:

     Field                              Meaning
                                        
     -----------------------------------------------------------------------
                                        
     ‘time_low’                         the first 32 bits of the UUID
                                        
                                        
     ‘time_mid’                         the next 16 bits of the UUID
                                        
                                        
     ‘time_hi_version’                  the next 16 bits of the UUID
                                        
                                        
     ‘clock_seq_hi_variant’             the next 8 bits of the UUID
                                        
                                        
     ‘clock_seq_low’                    the next 8 bits of the UUID
                                        
                                        
     ‘node’                             the last 48 bits of the UUID
                                        
                                        
     *note time: 10c.                   the 60-bit timestamp
                                        
                                        
     ‘clock_seq’                        the 14-bit sequence number
                                        

 -- Attribute: UUID.hex

     The UUID as a 32-character hexadecimal string.

 -- Attribute: UUID.int

     The UUID as a 128-bit integer.

 -- Attribute: UUID.urn

     The UUID as a URN as specified in RFC 4122(4).

 -- Attribute: UUID.variant

     The UUID variant, which determines the internal layout of the UUID.
     This will be one of the constants *note RESERVED_NCS: 2f43, *note
     RFC_4122: 2f44, *note RESERVED_MICROSOFT: 2f45, or *note
     RESERVED_FUTURE: 2f46.

 -- Attribute: UUID.version

     The UUID version number (1 through 5, meaningful only when the
     variant is *note RFC_4122: 2f44.).

 -- Attribute: UUID.is_safe

     An enumeration of *note SafeUUID: 2f38. which indicates whether the
     platform generated the UUID in a multiprocessing-safe way.

     New in version 3.7.

The *note uuid: 12d. module defines the following functions:

 -- Function: uuid.getnode ()

     Get the hardware address as a 48-bit positive integer.  The first
     time this runs, it may launch a separate program, which could be
     quite slow.  If all attempts to obtain the hardware address fail,
     we choose a random 48-bit number with the multicast bit (least
     significant bit of the first octet) set to 1 as recommended in RFC
     4122(5).  “Hardware address” means the MAC address of a network
     interface.  On a machine with multiple network interfaces,
     universally administered MAC addresses (i.e.  where the second
     least significant bit of the first octet is `unset') will be
     preferred over locally administered MAC addresses, but with no
     other ordering guarantees.

     Changed in version 3.7: Universally administered MAC addresses are
     preferred over locally administered MAC addresses, since the former
     are guaranteed to be globally unique, while the latter are not.

 -- Function: uuid.uuid1 (node=None, clock_seq=None)

     Generate a UUID from a host ID, sequence number, and the current
     time.  If `node' is not given, *note getnode(): 517. is used to
     obtain the hardware address.  If `clock_seq' is given, it is used
     as the sequence number; otherwise a random 14-bit sequence number
     is chosen.

 -- Function: uuid.uuid3 (namespace, name)

     Generate a UUID based on the MD5 hash of a namespace identifier
     (which is a UUID) and a name (which is a string).

 -- Function: uuid.uuid4 ()

     Generate a random UUID.

 -- Function: uuid.uuid5 (namespace, name)

     Generate a UUID based on the SHA-1 hash of a namespace identifier
     (which is a UUID) and a name (which is a string).

The *note uuid: 12d. module defines the following namespace identifiers
for use with *note uuid3(): 2f35. or *note uuid5(): 2f37.

 -- Data: uuid.NAMESPACE_DNS

     When this namespace is specified, the `name' string is a
     fully-qualified domain name.

 -- Data: uuid.NAMESPACE_URL

     When this namespace is specified, the `name' string is a URL.

 -- Data: uuid.NAMESPACE_OID

     When this namespace is specified, the `name' string is an ISO OID.

 -- Data: uuid.NAMESPACE_X500

     When this namespace is specified, the `name' string is an X.500 DN
     in DER or a text output format.

The *note uuid: 12d. module defines the following constants for the
possible values of the ‘variant’ attribute:

 -- Data: uuid.RESERVED_NCS

     Reserved for NCS compatibility.

 -- Data: uuid.RFC_4122

     Specifies the UUID layout given in RFC 4122(6).

 -- Data: uuid.RESERVED_MICROSOFT

     Reserved for Microsoft compatibility.

 -- Data: uuid.RESERVED_FUTURE

     Reserved for future definition.

See also
........

RFC 4122(7) - A Universally Unique IDentifier (UUID) URN Namespace

     This specification defines a Uniform Resource Name namespace for
     UUIDs, the internal format of UUIDs, and methods of generating
     UUIDs.

* Menu:

* Example: Example<13>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/uuid.py

   (2) https://tools.ietf.org/html/rfc4122.html

   (3) https://tools.ietf.org/html/rfc4122.html

   (4) https://tools.ietf.org/html/rfc4122.html

   (5) https://tools.ietf.org/html/rfc4122.html

   (6) https://tools.ietf.org/html/rfc4122.html

   (7) https://tools.ietf.org/html/rfc4122.html


File: python.info,  Node: Example<13>,  Up: uuid — UUID objects according to RFC 4122

5.21.20.1 Example
.................

Here are some examples of typical usage of the *note uuid: 12d. module:

     >>> import uuid

     >>> # make a UUID based on the host ID and current time
     >>> uuid.uuid1()
     UUID('a8098c1a-f86e-11da-bd1a-00112444be1e')

     >>> # make a UUID using an MD5 hash of a namespace UUID and a name
     >>> uuid.uuid3(uuid.NAMESPACE_DNS, 'python.org')
     UUID('6fa459ea-ee8a-3ca4-894e-db77e160355e')

     >>> # make a random UUID
     >>> uuid.uuid4()
     UUID('16fd2706-8baf-433b-82eb-8c7fada847da')

     >>> # make a UUID using a SHA-1 hash of a namespace UUID and a name
     >>> uuid.uuid5(uuid.NAMESPACE_DNS, 'python.org')
     UUID('886313e1-3b8a-5372-9b90-0c9aee199e5d')

     >>> # make a UUID from a string of hex digits (braces and hyphens ignored)
     >>> x = uuid.UUID('{00010203-0405-0607-0809-0a0b0c0d0e0f}')

     >>> # convert a UUID to a string of hex digits in standard form
     >>> str(x)
     '00010203-0405-0607-0809-0a0b0c0d0e0f'

     >>> # get the raw 16 bytes of the UUID
     >>> x.bytes
     b'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f'

     >>> # make a UUID from a 16-byte string
     >>> uuid.UUID(bytes=x.bytes)
     UUID('00010203-0405-0607-0809-0a0b0c0d0e0f')


File: python.info,  Node: socketserver — A framework for network servers,  Next: http server — HTTP servers,  Prev: uuid — UUID objects according to RFC 4122,  Up: Internet Protocols and Support

5.21.21 ‘socketserver’ — A framework for network servers
--------------------------------------------------------

`Source code:' Lib/socketserver.py(1)

__________________________________________________________________

The *note socketserver: f0. module simplifies the task of writing
network servers.

There are four basic concrete server classes:

 -- Class: socketserver.TCPServer (server_address, RequestHandlerClass,
          bind_and_activate=True)

     This uses the Internet TCP protocol, which provides for continuous
     streams of data between the client and server.  If
     `bind_and_activate' is true, the constructor automatically attempts
     to invoke *note server_bind(): 2f51. and *note server_activate():
     2f52.  The other parameters are passed to the *note BaseServer:
     b61. base class.

 -- Class: socketserver.UDPServer (server_address, RequestHandlerClass,
          bind_and_activate=True)

     This uses datagrams, which are discrete packets of information that
     may arrive out of order or be lost while in transit.  The
     parameters are the same as for *note TCPServer: 2f50.

 -- Class: socketserver.UnixStreamServer (server_address,
          RequestHandlerClass, bind_and_activate=True)
 -- Class: socketserver.UnixDatagramServer (server_address,
          RequestHandlerClass, bind_and_activate=True)

     These more infrequently used classes are similar to the TCP and UDP
     classes, but use Unix domain sockets; they’re not available on
     non-Unix platforms.  The parameters are the same as for *note
     TCPServer: 2f50.

These four classes process requests `synchronously'; each request must
be completed before the next request can be started.  This isn’t
suitable if each request takes a long time to complete, because it
requires a lot of computation, or because it returns a lot of data which
the client is slow to process.  The solution is to create a separate
process or thread to handle each request; the *note ForkingMixIn: 4dc.
and *note ThreadingMixIn: 4dd. mix-in classes can be used to support
asynchronous behaviour.

Creating a server requires several steps.  First, you must create a
request handler class by subclassing the *note BaseRequestHandler: 2f56.
class and overriding its *note handle(): 2f57. method; this method will
process incoming requests.  Second, you must instantiate one of the
server classes, passing it the server’s address and the request handler
class.  It is recommended to use the server in a *note with: 7da.
statement.  Then call the *note handle_request(): 2f58. or *note
serve_forever(): b63. method of the server object to process one or many
requests.  Finally, call *note server_close(): 2f59. to close the socket
(unless you used a ‘with’ statement).

When inheriting from *note ThreadingMixIn: 4dd. for threaded connection
behavior, you should explicitly declare how you want your threads to
behave on an abrupt shutdown.  The *note ThreadingMixIn: 4dd. class
defines an attribute `daemon_threads', which indicates whether or not
the server should wait for thread termination.  You should set the flag
explicitly if you would like threads to behave autonomously; the default
is *note False: 48f, meaning that Python will not exit until all threads
created by *note ThreadingMixIn: 4dd. have exited.

Server classes have the same external methods and attributes, no matter
what network protocol they use.

* Menu:

* Server Creation Notes::
* Server Objects: Server Objects<2>.
* Request Handler Objects::
* Examples: Examples<24>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/socketserver.py


File: python.info,  Node: Server Creation Notes,  Next: Server Objects<2>,  Up: socketserver — A framework for network servers

5.21.21.1 Server Creation Notes
...............................

There are five classes in an inheritance diagram, four of which
represent synchronous servers of four types:

     +------------+
     | BaseServer |
     +------------+
           |
           v
     +-----------+        +------------------+
     | TCPServer |------->| UnixStreamServer |
     +-----------+        +------------------+
           |
           v
     +-----------+        +--------------------+
     | UDPServer |------->| UnixDatagramServer |
     +-----------+        +--------------------+

Note that *note UnixDatagramServer: 2f55. derives from *note UDPServer:
2f53, not from *note UnixStreamServer: 2f54. — the only difference
between an IP and a Unix stream server is the address family, which is
simply repeated in both Unix server classes.

 -- Class: socketserver.ForkingMixIn
 -- Class: socketserver.ThreadingMixIn

     Forking and threading versions of each type of server can be
     created using these mix-in classes.  For instance, *note
     ThreadingUDPServer: 2f5b. is created as follows:

          class ThreadingUDPServer(ThreadingMixIn, UDPServer):
              pass

     The mix-in class comes first, since it overrides a method defined
     in *note UDPServer: 2f53.  Setting the various attributes also
     changes the behavior of the underlying server mechanism.

     *note ForkingMixIn: 4dc. and the Forking classes mentioned below
     are only available on POSIX platforms that support *note fork():
     a42.

     ‘socketserver.ForkingMixIn.server_close()’ waits until all child
     processes complete, except if
     ‘socketserver.ForkingMixIn.block_on_close’ attribute is false.

     ‘socketserver.ThreadingMixIn.server_close()’ waits until all
     non-daemon threads complete, except if
     ‘socketserver.ThreadingMixIn.block_on_close’ attribute is false.
     Use daemonic threads by setting ‘ThreadingMixIn.daemon_threads’ to
     ‘True’ to not wait until threads complete.

     Changed in version 3.7: ‘socketserver.ForkingMixIn.server_close()’
     and ‘socketserver.ThreadingMixIn.server_close()’ now waits until
     all child processes and non-daemonic threads complete.  Add a new
     ‘socketserver.ForkingMixIn.block_on_close’ class attribute to
     opt-in for the pre-3.7 behaviour.

 -- Class: socketserver.ForkingTCPServer
 -- Class: socketserver.ForkingUDPServer
 -- Class: socketserver.ThreadingTCPServer
 -- Class: socketserver.ThreadingUDPServer

     These classes are pre-defined using the mix-in classes.

To implement a service, you must derive a class from *note
BaseRequestHandler: 2f56. and redefine its *note handle(): 2f57. method.
You can then run various versions of the service by combining one of the
server classes with your request handler class.  The request handler
class must be different for datagram or stream services.  This can be
hidden by using the handler subclasses *note StreamRequestHandler: 67e.
or *note DatagramRequestHandler: 2f5f.

Of course, you still have to use your head!  For instance, it makes no
sense to use a forking server if the service contains state in memory
that can be modified by different requests, since the modifications in
the child process would never reach the initial state kept in the parent
process and passed to each child.  In this case, you can use a threading
server, but you will probably have to use locks to protect the integrity
of the shared data.

On the other hand, if you are building an HTTP server where all data is
stored externally (for instance, in the file system), a synchronous
class will essentially render the service “deaf” while one request is
being handled – which may be for a very long time if a client is slow to
receive all the data it has requested.  Here a threading or forking
server is appropriate.

In some cases, it may be appropriate to process part of a request
synchronously, but to finish processing in a forked child depending on
the request data.  This can be implemented by using a synchronous server
and doing an explicit fork in the request handler class *note handle():
2f57. method.

Another approach to handling multiple simultaneous requests in an
environment that supports neither threads nor *note fork(): a42. (or
where these are too expensive or inappropriate for the service) is to
maintain an explicit table of partially finished requests and to use
*note selectors: e6. to decide which request to work on next (or whether
to handle a new incoming request).  This is particularly important for
stream services where each client can potentially be connected for a
long time (if threads or subprocesses cannot be used).  See *note
asyncore: a. for another way to manage this.


File: python.info,  Node: Server Objects<2>,  Next: Request Handler Objects,  Prev: Server Creation Notes,  Up: socketserver — A framework for network servers

5.21.21.2 Server Objects
........................

 -- Class: socketserver.BaseServer (server_address, RequestHandlerClass)

     This is the superclass of all Server objects in the module.  It
     defines the interface, given below, but does not implement most of
     the methods, which is done in subclasses.  The two parameters are
     stored in the respective *note server_address: 2f61. and *note
     RequestHandlerClass: 2f62. attributes.

      -- Method: fileno ()

          Return an integer file descriptor for the socket on which the
          server is listening.  This function is most commonly passed to
          *note selectors: e6, to allow monitoring multiple servers in
          the same process.

      -- Method: handle_request ()

          Process a single request.  This function calls the following
          methods in order: *note get_request(): 2f64, *note
          verify_request(): 2f65, and *note process_request(): 2f66.  If
          the user-provided *note handle(): 2f57. method of the handler
          class raises an exception, the server’s *note handle_error():
          6f4. method will be called.  If no request is received within
          *note timeout: 2f67. seconds, *note handle_timeout(): 2f68.
          will be called and *note handle_request(): 2f58. will return.

      -- Method: serve_forever (poll_interval=0.5)

          Handle requests until an explicit *note shutdown(): 1155.
          request.  Poll for shutdown every `poll_interval' seconds.
          Ignores the *note timeout: 2f67. attribute.  It also calls
          *note service_actions(): b62, which may be used by a subclass
          or mixin to provide actions specific to a given service.  For
          example, the *note ForkingMixIn: 4dc. class uses *note
          service_actions(): b62. to clean up zombie child processes.

          Changed in version 3.3: Added ‘service_actions’ call to the
          ‘serve_forever’ method.

      -- Method: service_actions ()

          This is called in the *note serve_forever(): b63. loop.  This
          method can be overridden by subclasses or mixin classes to
          perform actions specific to a given service, such as cleanup
          actions.

          New in version 3.3.

      -- Method: shutdown ()

          Tell the *note serve_forever(): b63. loop to stop and wait
          until it does.  *note shutdown(): 1155. must be called while
          *note serve_forever(): b63. is running in a different thread
          otherwise it will deadlock.

      -- Method: server_close ()

          Clean up the server.  May be overridden.

      -- Attribute: address_family

          The family of protocols to which the server’s socket belongs.
          Common examples are *note socket.AF_INET: 26f8. and *note
          socket.AF_UNIX: 26fe.

      -- Attribute: RequestHandlerClass

          The user-provided request handler class; an instance of this
          class is created for each request.

      -- Attribute: server_address

          The address on which the server is listening.  The format of
          addresses varies depending on the protocol family; see the
          documentation for the *note socket: ef. module for details.
          For Internet protocols, this is a tuple containing a string
          giving the address, and an integer port number: ‘('127.0.0.1',
          80)’, for example.

      -- Attribute: socket

          The socket object on which the server will listen for incoming
          requests.

     The server classes support the following class variables:

      -- Attribute: allow_reuse_address

          Whether the server will allow the reuse of an address.  This
          defaults to *note False: 48f, and can be set in subclasses to
          change the policy.

      -- Attribute: request_queue_size

          The size of the request queue.  If it takes a long time to
          process a single request, any requests that arrive while the
          server is busy are placed into a queue, up to *note
          request_queue_size: 2f6c. requests.  Once the queue is full,
          further requests from clients will get a “Connection denied”
          error.  The default value is usually 5, but this can be
          overridden by subclasses.

      -- Attribute: socket_type

          The type of socket used by the server; *note
          socket.SOCK_STREAM: d52. and *note socket.SOCK_DGRAM: d51. are
          two common values.

      -- Attribute: timeout

          Timeout duration, measured in seconds, or *note None: 203. if
          no timeout is desired.  If *note handle_request(): 2f58.
          receives no incoming requests within the timeout period, the
          *note handle_timeout(): 2f68. method is called.

     There are various server methods that can be overridden by
     subclasses of base server classes like *note TCPServer: 2f50.;
     these methods aren’t useful to external users of the server object.

      -- Method: finish_request (request, client_address)

          Actually processes the request by instantiating *note
          RequestHandlerClass: 2f62. and calling its *note handle():
          2f57. method.

      -- Method: get_request ()

          Must accept a request from the socket, and return a 2-tuple
          containing the `new' socket object to be used to communicate
          with the client, and the client’s address.

      -- Method: handle_error (request, client_address)

          This function is called if the *note handle(): 2f57. method of
          a *note RequestHandlerClass: 2f62. instance raises an
          exception.  The default action is to print the traceback to
          standard error and continue handling further requests.

          Changed in version 3.6: Now only called for exceptions derived
          from the *note Exception: 2dc. class.

      -- Method: handle_timeout ()

          This function is called when the *note timeout: 2f67.
          attribute has been set to a value other than *note None: 203.
          and the timeout period has passed with no requests being
          received.  The default action for forking servers is to
          collect the status of any child processes that have exited,
          while in threading servers this method does nothing.

      -- Method: process_request (request, client_address)

          Calls *note finish_request(): 2f6e. to create an instance of
          the *note RequestHandlerClass: 2f62.  If desired, this
          function can create a new process or thread to handle the
          request; the *note ForkingMixIn: 4dc. and *note
          ThreadingMixIn: 4dd. classes do this.

      -- Method: server_activate ()

          Called by the server’s constructor to activate the server.
          The default behavior for a TCP server just invokes *note
          listen(): 83a. on the server’s socket.  May be overridden.

      -- Method: server_bind ()

          Called by the server’s constructor to bind the socket to the
          desired address.  May be overridden.

      -- Method: verify_request (request, client_address)

          Must return a Boolean value; if the value is *note True: 594,
          the request will be processed, and if it’s *note False: 48f,
          the request will be denied.  This function can be overridden
          to implement access controls for a server.  The default
          implementation always returns *note True: 594.

     Changed in version 3.6: Support for the *note context manager: 661.
     protocol was added.  Exiting the context manager is equivalent to
     calling *note server_close(): 2f59.


File: python.info,  Node: Request Handler Objects,  Next: Examples<24>,  Prev: Server Objects<2>,  Up: socketserver — A framework for network servers

5.21.21.3 Request Handler Objects
.................................

 -- Class: socketserver.BaseRequestHandler

     This is the superclass of all request handler objects.  It defines
     the interface, given below.  A concrete request handler subclass
     must define a new *note handle(): 2f57. method, and can override
     any of the other methods.  A new instance of the subclass is
     created for each request.

      -- Method: setup ()

          Called before the *note handle(): 2f57. method to perform any
          initialization actions required.  The default implementation
          does nothing.

      -- Method: handle ()

          This function must do all the work required to service a
          request.  The default implementation does nothing.  Several
          instance attributes are available to it; the request is
          available as ‘self.request’; the client address as
          ‘self.client_address’; and the server instance as
          ‘self.server’, in case it needs access to per-server
          information.

          The type of ‘self.request’ is different for datagram or stream
          services.  For stream services, ‘self.request’ is a socket
          object; for datagram services, ‘self.request’ is a pair of
          string and socket.

      -- Method: finish ()

          Called after the *note handle(): 2f57. method to perform any
          clean-up actions required.  The default implementation does
          nothing.  If *note setup(): 2f70. raises an exception, this
          function will not be called.

 -- Class: socketserver.StreamRequestHandler
 -- Class: socketserver.DatagramRequestHandler

     These *note BaseRequestHandler: 2f56. subclasses override the *note
     setup(): 2f70. and *note finish(): 2f71. methods, and provide
     ‘self.rfile’ and ‘self.wfile’ attributes.  The ‘self.rfile’ and
     ‘self.wfile’ attributes can be read or written, respectively, to
     get the request data or return data to the client.

     The ‘rfile’ attributes of both classes support the *note
     io.BufferedIOBase: 67f. readable interface, and
     ‘DatagramRequestHandler.wfile’ supports the *note
     io.BufferedIOBase: 67f. writable interface.

     Changed in version 3.6: ‘StreamRequestHandler.wfile’ also supports
     the *note io.BufferedIOBase: 67f. writable interface.


File: python.info,  Node: Examples<24>,  Prev: Request Handler Objects,  Up: socketserver — A framework for network servers

5.21.21.4 Examples
..................

* Menu:

* socketserver.TCPServer Example: socketserver TCPServer Example.
* socketserver.UDPServer Example: socketserver UDPServer Example.
* Asynchronous Mixins::


File: python.info,  Node: socketserver TCPServer Example,  Next: socketserver UDPServer Example,  Up: Examples<24>

5.21.21.5 ‘socketserver.TCPServer’ Example
..........................................

This is the server side:

     import socketserver

     class MyTCPHandler(socketserver.BaseRequestHandler):
         """
         The request handler class for our server.

         It is instantiated once per connection to the server, and must
         override the handle() method to implement communication to the
         client.
         """

         def handle(self):
             # self.request is the TCP socket connected to the client
             self.data = self.request.recv(1024).strip()
             print("{} wrote:".format(self.client_address[0]))
             print(self.data)
             # just send back the same data, but upper-cased
             self.request.sendall(self.data.upper())

     if __name__ == "__main__":
         HOST, PORT = "localhost", 9999

         # Create the server, binding to localhost on port 9999
         with socketserver.TCPServer((HOST, PORT), MyTCPHandler) as server:
             # Activate the server; this will keep running until you
             # interrupt the program with Ctrl-C
             server.serve_forever()

An alternative request handler class that makes use of streams
(file-like objects that simplify communication by providing the standard
file interface):

     class MyTCPHandler(socketserver.StreamRequestHandler):

         def handle(self):
             # self.rfile is a file-like object created by the handler;
             # we can now use e.g. readline() instead of raw recv() calls
             self.data = self.rfile.readline().strip()
             print("{} wrote:".format(self.client_address[0]))
             print(self.data)
             # Likewise, self.wfile is a file-like object used to write back
             # to the client
             self.wfile.write(self.data.upper())

The difference is that the ‘readline()’ call in the second handler will
call ‘recv()’ multiple times until it encounters a newline character,
while the single ‘recv()’ call in the first handler will just return
what has been sent from the client in one ‘sendall()’ call.

This is the client side:

     import socket
     import sys

     HOST, PORT = "localhost", 9999
     data = " ".join(sys.argv[1:])

     # Create a socket (SOCK_STREAM means a TCP socket)
     with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
         # Connect to server and send data
         sock.connect((HOST, PORT))
         sock.sendall(bytes(data + "\n", "utf-8"))

         # Receive data from the server and shut down
         received = str(sock.recv(1024), "utf-8")

     print("Sent:     {}".format(data))
     print("Received: {}".format(received))

The output of the example should look something like this:

Server:

     $ python TCPServer.py
     127.0.0.1 wrote:
     b'hello world with TCP'
     127.0.0.1 wrote:
     b'python is nice'

Client:

     $ python TCPClient.py hello world with TCP
     Sent:     hello world with TCP
     Received: HELLO WORLD WITH TCP
     $ python TCPClient.py python is nice
     Sent:     python is nice
     Received: PYTHON IS NICE


File: python.info,  Node: socketserver UDPServer Example,  Next: Asynchronous Mixins,  Prev: socketserver TCPServer Example,  Up: Examples<24>

5.21.21.6 ‘socketserver.UDPServer’ Example
..........................................

This is the server side:

     import socketserver

     class MyUDPHandler(socketserver.BaseRequestHandler):
         """
         This class works similar to the TCP handler class, except that
         self.request consists of a pair of data and client socket, and since
         there is no connection the client address must be given explicitly
         when sending data back via sendto().
         """

         def handle(self):
             data = self.request[0].strip()
             socket = self.request[1]
             print("{} wrote:".format(self.client_address[0]))
             print(data)
             socket.sendto(data.upper(), self.client_address)

     if __name__ == "__main__":
         HOST, PORT = "localhost", 9999
         with socketserver.UDPServer((HOST, PORT), MyUDPHandler) as server:
             server.serve_forever()

This is the client side:

     import socket
     import sys

     HOST, PORT = "localhost", 9999
     data = " ".join(sys.argv[1:])

     # SOCK_DGRAM is the socket type to use for UDP sockets
     sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

     # As you can see, there is no connect() call; UDP has no connections.
     # Instead, data is directly sent to the recipient via sendto().
     sock.sendto(bytes(data + "\n", "utf-8"), (HOST, PORT))
     received = str(sock.recv(1024), "utf-8")

     print("Sent:     {}".format(data))
     print("Received: {}".format(received))

The output of the example should look exactly like for the TCP server
example.


File: python.info,  Node: Asynchronous Mixins,  Prev: socketserver UDPServer Example,  Up: Examples<24>

5.21.21.7 Asynchronous Mixins
.............................

To build asynchronous handlers, use the *note ThreadingMixIn: 4dd. and
*note ForkingMixIn: 4dc. classes.

An example for the *note ThreadingMixIn: 4dd. class:

     import socket
     import threading
     import socketserver

     class ThreadedTCPRequestHandler(socketserver.BaseRequestHandler):

         def handle(self):
             data = str(self.request.recv(1024), 'ascii')
             cur_thread = threading.current_thread()
             response = bytes("{}: {}".format(cur_thread.name, data), 'ascii')
             self.request.sendall(response)

     class ThreadedTCPServer(socketserver.ThreadingMixIn, socketserver.TCPServer):
         pass

     def client(ip, port, message):
         with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
             sock.connect((ip, port))
             sock.sendall(bytes(message, 'ascii'))
             response = str(sock.recv(1024), 'ascii')
             print("Received: {}".format(response))

     if __name__ == "__main__":
         # Port 0 means to select an arbitrary unused port
         HOST, PORT = "localhost", 0

         server = ThreadedTCPServer((HOST, PORT), ThreadedTCPRequestHandler)
         with server:
             ip, port = server.server_address

             # Start a thread with the server -- that thread will then start one
             # more thread for each request
             server_thread = threading.Thread(target=server.serve_forever)
             # Exit the server thread when the main thread terminates
             server_thread.daemon = True
             server_thread.start()
             print("Server loop running in thread:", server_thread.name)

             client(ip, port, "Hello World 1")
             client(ip, port, "Hello World 2")
             client(ip, port, "Hello World 3")

             server.shutdown()

The output of the example should look something like this:

     $ python ThreadedTCPServer.py
     Server loop running in thread: Thread-1
     Received: Thread-2: Hello World 1
     Received: Thread-3: Hello World 2
     Received: Thread-4: Hello World 3

The *note ForkingMixIn: 4dc. class is used in the same way, except that
the server will spawn a new process for each request.  Available only on
POSIX platforms that support *note fork(): a42.


File: python.info,  Node: http server — HTTP servers,  Next: http cookies — HTTP state management,  Prev: socketserver — A framework for network servers,  Up: Internet Protocols and Support

5.21.22 ‘http.server’ — HTTP servers
------------------------------------

`Source code:' Lib/http/server.py(1)

__________________________________________________________________

This module defines classes for implementing HTTP servers (Web servers).

     Warning: *note http.server: 96. is not recommended for production.
     It only implements basic security checks.

One class, *note HTTPServer: 2d43, is a *note socketserver.TCPServer:
2f50. subclass.  It creates and listens at the HTTP socket, dispatching
the requests to a handler.  Code to create and run the server looks like
this:

     def run(server_class=HTTPServer, handler_class=BaseHTTPRequestHandler):
         server_address = ('', 8000)
         httpd = server_class(server_address, handler_class)
         httpd.serve_forever()

 -- Class: http.server.HTTPServer (server_address, RequestHandlerClass)

     This class builds on the *note TCPServer: 2f50. class by storing
     the server address as instance variables named ‘server_name’ and
     ‘server_port’.  The server is accessible by the handler, typically
     through the handler’s ‘server’ instance variable.

 -- Class: http.server.ThreadingHTTPServer (server_address,
          RequestHandlerClass)

     This class is identical to HTTPServer but uses threads to handle
     requests by using the *note ThreadingMixIn: 4dd.  This is useful to
     handle web browsers pre-opening sockets, on which *note HTTPServer:
     2d43. would wait indefinitely.

     New in version 3.7.

The *note HTTPServer: 2d43. and *note ThreadingHTTPServer: 49d. must be
given a `RequestHandlerClass' on instantiation, of which this module
provides three different variants:

 -- Class: http.server.BaseHTTPRequestHandler (request, client_address,
          server)

     This class is used to handle the HTTP requests that arrive at the
     server.  By itself, it cannot respond to any actual HTTP requests;
     it must be subclassed to handle each request method (e.g.  GET or
     POST). *note BaseHTTPRequestHandler: aec. provides a number of
     class and instance variables, and methods for use by subclasses.

     The handler will parse the request and the headers, then call a
     method specific to the request type.  The method name is
     constructed from the request.  For example, for the request method
     ‘SPAM’, the ‘do_SPAM()’ method will be called with no arguments.
     All of the relevant information is stored in instance variables of
     the handler.  Subclasses should not need to override or extend the
     *note __init__(): e23. method.

     *note BaseHTTPRequestHandler: aec. has the following instance
     variables:

      -- Attribute: client_address

          Contains a tuple of the form ‘(host, port)’ referring to the
          client’s address.

      -- Attribute: server

          Contains the server instance.

      -- Attribute: close_connection

          Boolean that should be set before *note handle_one_request():
          2f7b. returns, indicating if another request may be expected,
          or if the connection should be shut down.

      -- Attribute: requestline

          Contains the string representation of the HTTP request line.
          The terminating CRLF is stripped.  This attribute should be
          set by *note handle_one_request(): 2f7b.  If no valid request
          line was processed, it should be set to the empty string.

      -- Attribute: command

          Contains the command (request type).  For example, ‘'GET'’.

      -- Attribute: path

          Contains the request path.  If query component of the URL is
          present, then ‘path’ includes the query.  Using the
          terminology of RFC 3986(2), ‘path’ here includes ‘hier-part’
          and the ‘query’.

      -- Attribute: request_version

          Contains the version string from the request.  For example,
          ‘'HTTP/1.0'’.

      -- Attribute: headers

          Holds an instance of the class specified by the *note
          MessageClass: 2f80. class variable.  This instance parses and
          manages the headers in the HTTP request.  The *note
          parse_headers(): 1176. function from *note http.client: 93. is
          used to parse the headers and it requires that the HTTP
          request provide a valid RFC 2822(3) style header.

      -- Attribute: rfile

          An *note io.BufferedIOBase: 67f. input stream, ready to read
          from the start of the optional input data.

      -- Attribute: wfile

          Contains the output stream for writing a response back to the
          client.  Proper adherence to the HTTP protocol must be used
          when writing to this stream in order to achieve successful
          interoperation with HTTP clients.

          Changed in version 3.6: This is an *note io.BufferedIOBase:
          67f. stream.

     *note BaseHTTPRequestHandler: aec. has the following attributes:

      -- Attribute: server_version

          Specifies the server software version.  You may want to
          override this.  The format is multiple whitespace-separated
          strings, where each string is of the form name[/version].  For
          example, ‘'BaseHTTP/0.2'’.

      -- Attribute: sys_version

          Contains the Python system version, in a form usable by the
          *note version_string: 2f85. method and the *note
          server_version: 2f83. class variable.  For example,
          ‘'Python/1.4'’.

      -- Attribute: error_message_format

          Specifies a format string that should be used by *note
          send_error(): 947. method for building an error response to
          the client.  The string is filled by default with variables
          from *note responses: 2e15. based on the status code that
          passed to *note send_error(): 947.

      -- Attribute: error_content_type

          Specifies the Content-Type HTTP header of error responses sent
          to the client.  The default value is ‘'text/html'’.

      -- Attribute: protocol_version

          This specifies the HTTP protocol version used in responses.
          If set to ‘'HTTP/1.1'’, the server will permit HTTP persistent
          connections; however, your server `must' then include an
          accurate ‘Content-Length’ header (using *note send_header():
          2f89.) in all of its responses to clients.  For backwards
          compatibility, the setting defaults to ‘'HTTP/1.0'’.

      -- Attribute: MessageClass

          Specifies an *note email.message.Message: 63b.-like class to
          parse HTTP headers.  Typically, this is not overridden, and it
          defaults to ‘http.client.HTTPMessage’.

      -- Attribute: responses

          This attribute contains a mapping of error code integers to
          two-element tuples containing a short and long message.  For
          example, ‘{code: (shortmessage, longmessage)}’.  The
          `shortmessage' is usually used as the `message' key in an
          error response, and `longmessage' as the `explain' key.  It is
          used by *note send_response_only(): 2f8a. and *note
          send_error(): 947. methods.

     A *note BaseHTTPRequestHandler: aec. instance has the following
     methods:

      -- Method: handle ()

          Calls *note handle_one_request(): 2f7b. once (or, if
          persistent connections are enabled, multiple times) to handle
          incoming HTTP requests.  You should never need to override it;
          instead, implement appropriate ‘do_*()’ methods.

      -- Method: handle_one_request ()

          This method will parse and dispatch the request to the
          appropriate ‘do_*()’ method.  You should never need to
          override it.

      -- Method: handle_expect_100 ()

          When a HTTP/1.1 compliant server receives an ‘Expect:
          100-continue’ request header it responds back with a ‘100
          Continue’ followed by ‘200 OK’ headers.  This method can be
          overridden to raise an error if the server does not want the
          client to continue.  For e.g.  server can choose to send ‘417
          Expectation Failed’ as a response header and ‘return False’.

          New in version 3.2.

      -- Method: send_error (code, message=None, explain=None)

          Sends and logs a complete error reply to the client.  The
          numeric `code' specifies the HTTP error code, with `message'
          as an optional, short, human readable description of the
          error.  The `explain' argument can be used to provide more
          detailed information about the error; it will be formatted
          using the *note error_message_format: 2f86. attribute and
          emitted, after a complete set of headers, as the response
          body.  The *note responses: 2e15. attribute holds the default
          values for `message' and `explain' that will be used if no
          value is provided; for unknown codes the default value for
          both is the string ‘???’.  The body will be empty if the
          method is HEAD or the response code is one of the following:
          ‘1xx’, ‘204 No Content’, ‘205 Reset Content’, ‘304 Not
          Modified’.

          Changed in version 3.4: The error response includes a
          Content-Length header.  Added the `explain' argument.

      -- Method: send_response (code, message=None)

          Adds a response header to the headers buffer and logs the
          accepted request.  The HTTP response line is written to the
          internal buffer, followed by `Server' and `Date' headers.  The
          values for these two headers are picked up from the *note
          version_string(): 2f85. and *note date_time_string(): 2f8e.
          methods, respectively.  If the server does not intend to send
          any other headers using the *note send_header(): 2f89. method,
          then *note send_response(): 2f8d. should be followed by an
          *note end_headers(): aed. call.

          Changed in version 3.3: Headers are stored to an internal
          buffer and *note end_headers(): aed. needs to be called
          explicitly.

      -- Method: send_header (keyword, value)

          Adds the HTTP header to an internal buffer which will be
          written to the output stream when either *note end_headers():
          aed. or *note flush_headers(): aee. is invoked.  `keyword'
          should specify the header keyword, with `value' specifying its
          value.  Note that, after the send_header calls are done, *note
          end_headers(): aed. MUST BE called in order to complete the
          operation.

          Changed in version 3.2: Headers are stored in an internal
          buffer.

      -- Method: send_response_only (code, message=None)

          Sends the response header only, used for the purposes when
          ‘100 Continue’ response is sent by the server to the client.
          The headers not buffered and sent directly the output
          stream.If the `message' is not specified, the HTTP message
          corresponding the response `code' is sent.

          New in version 3.2.

      -- Method: end_headers ()

          Adds a blank line (indicating the end of the HTTP headers in
          the response) to the headers buffer and calls *note
          flush_headers(): aee.

          Changed in version 3.2: The buffered headers are written to
          the output stream.

      -- Method: flush_headers ()

          Finally send the headers to the output stream and flush the
          internal headers buffer.

          New in version 3.3.

      -- Method: log_request (code='-', size='-')

          Logs an accepted (successful) request.  `code' should specify
          the numeric HTTP code associated with the response.  If a size
          of the response is available, then it should be passed as the
          `size' parameter.

      -- Method: log_error (...)

          Logs an error when a request cannot be fulfilled.  By default,
          it passes the message to *note log_message(): 2f91, so it
          takes the same arguments (`format' and additional values).

      -- Method: log_message (format, ...)

          Logs an arbitrary message to ‘sys.stderr’.  This is typically
          overridden to create custom error logging mechanisms.  The
          `format' argument is a standard printf-style format string,
          where the additional arguments to *note log_message(): 2f91.
          are applied as inputs to the formatting.  The client ip
          address and current date and time are prefixed to every
          message logged.

      -- Method: version_string ()

          Returns the server software’s version string.  This is a
          combination of the *note server_version: 2f83. and *note
          sys_version: 2f84. attributes.

      -- Method: date_time_string (timestamp=None)

          Returns the date and time given by `timestamp' (which must be
          ‘None’ or in the format returned by *note time.time(): 42d.),
          formatted for a message header.  If `timestamp' is omitted, it
          uses the current date and time.

          The result looks like ‘'Sun, 06 Nov 1994 08:49:37 GMT'’.

      -- Method: log_date_time_string ()

          Returns the current date and time, formatted for logging.

      -- Method: address_string ()

          Returns the client address.

          Changed in version 3.3: Previously, a name lookup was
          performed.  To avoid name resolution delays, it now always
          returns the IP address.

 -- Class: http.server.SimpleHTTPRequestHandler (request,
          client_address, server, directory=None)

     This class serves files from the directory `directory' and below,
     or the current directory if `directory' is not provided, directly
     mapping the directory structure to HTTP requests.

     New in version 3.7: The `directory' parameter.

     Changed in version 3.9: The `directory' parameter accepts a *note
     path-like object: 472.

     A lot of the work, such as parsing the request, is done by the base
     class *note BaseHTTPRequestHandler: aec.  This class implements the
     *note do_GET(): 2f94. and *note do_HEAD(): 2f95. functions.

     The following are defined as class-level attributes of *note
     SimpleHTTPRequestHandler: 49c.:

      -- Attribute: server_version

          This will be ‘"SimpleHTTP/" + __version__’, where
          ‘__version__’ is defined at the module level.

      -- Attribute: extensions_map

          A dictionary mapping suffixes into MIME types, contains custom
          overrides for the default system mappings.  The mapping is
          used case-insensitively, and so should contain only
          lower-cased keys.

          Changed in version 3.9: This dictionary is no longer filled
          with the default system mappings, but only contains overrides.

     The *note SimpleHTTPRequestHandler: 49c. class defines the
     following methods:

      -- Method: do_HEAD ()

          This method serves the ‘'HEAD'’ request type: it sends the
          headers it would send for the equivalent ‘GET’ request.  See
          the *note do_GET(): 2f94. method for a more complete
          explanation of the possible headers.

      -- Method: do_GET ()

          The request is mapped to a local file by interpreting the
          request as a path relative to the current working directory.

          If the request was mapped to a directory, the directory is
          checked for a file named ‘index.html’ or ‘index.htm’ (in that
          order).  If found, the file’s contents are returned; otherwise
          a directory listing is generated by calling the
          ‘list_directory()’ method.  This method uses *note
          os.listdir(): b1c. to scan the directory, and returns a ‘404’
          error response if the *note listdir(): b1c. fails.

          If the request was mapped to a file, it is opened.  Any *note
          OSError: 304. exception in opening the requested file is
          mapped to a ‘404’, ‘'File not found'’ error.  If there was a
          ‘'If-Modified-Since'’ header in the request, and the file was
          not modified after this time, a ‘304’, ‘'Not Modified'’
          response is sent.  Otherwise, the content type is guessed by
          calling the ‘guess_type()’ method, which in turn uses the
          `extensions_map' variable, and the file contents are returned.

          A ‘'Content-type:'’ header with the guessed content type is
          output, followed by a ‘'Content-Length:'’ header with the
          file’s size and a ‘'Last-Modified:'’ header with the file’s
          modification time.

          Then follows a blank line signifying the end of the headers,
          and then the contents of the file are output.  If the file’s
          MIME type starts with ‘text/’ the file is opened in text mode;
          otherwise binary mode is used.

          For example usage, see the implementation of the *note test():
          105. function invocation in the *note http.server: 96. module.

          Changed in version 3.7: Support of the ‘'If-Modified-Since'’
          header.

The *note SimpleHTTPRequestHandler: 49c. class can be used in the
following manner in order to create a very basic webserver serving files
relative to the current directory:

     import http.server
     import socketserver

     PORT = 8000

     Handler = http.server.SimpleHTTPRequestHandler

     with socketserver.TCPServer(("", PORT), Handler) as httpd:
         print("serving at port", PORT)
         httpd.serve_forever()
*note http.server: 96. can also be invoked directly using the *note -m:
443. switch of the interpreter with a ‘port number’ argument.  Similar
to the previous example, this serves files relative to the current
directory:

     python -m http.server 8000

By default, server binds itself to all interfaces.  The option
‘-b/--bind’ specifies a specific address to which it should bind.  Both
IPv4 and IPv6 addresses are supported.  For example, the following
command causes the server to bind to localhost only:

     python -m http.server 8000 --bind 127.0.0.1

New in version 3.4: ‘--bind’ argument was introduced.

New in version 3.8: ‘--bind’ argument enhanced to support IPv6

By default, server uses the current directory.  The option
‘-d/--directory’ specifies a directory to which it should serve the
files.  For example, the following command uses a specific directory:

     python -m http.server --directory /tmp/

New in version 3.7: ‘--directory’ specify alternate directory

 -- Class: http.server.CGIHTTPRequestHandler (request, client_address,
          server)

     This class is used to serve either files or output of CGI scripts
     from the current directory and below.  Note that mapping HTTP
     hierarchic structure to local directory structure is exactly as in
     *note SimpleHTTPRequestHandler: 49c.

          Note: CGI scripts run by the *note CGIHTTPRequestHandler:
          2f98. class cannot execute redirects (HTTP code 302), because
          code 200 (script output follows) is sent prior to execution of
          the CGI script.  This pre-empts the status code.

     The class will however, run the CGI script, instead of serving it
     as a file, if it guesses it to be a CGI script.  Only
     directory-based CGI are used — the other common server
     configuration is to treat special extensions as denoting CGI
     scripts.

     The ‘do_GET()’ and ‘do_HEAD()’ functions are modified to run CGI
     scripts and serve the output, instead of serving files, if the
     request leads to somewhere below the ‘cgi_directories’ path.

     The *note CGIHTTPRequestHandler: 2f98. defines the following data
     member:

      -- Attribute: cgi_directories

          This defaults to ‘['/cgi-bin', '/htbin']’ and describes
          directories to treat as containing CGI scripts.

     The *note CGIHTTPRequestHandler: 2f98. defines the following
     method:

      -- Method: do_POST ()

          This method serves the ‘'POST'’ request type, only allowed for
          CGI scripts.  Error 501, “Can only POST to CGI scripts”, is
          output when trying to POST to a non-CGI url.

     Note that CGI scripts will be run with UID of user nobody, for
     security reasons.  Problems with the CGI script will be translated
     to error 403.

*note CGIHTTPRequestHandler: 2f98. can be enabled in the command line by
passing the ‘--cgi’ option:

     python -m http.server --cgi 8000

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/http/server.py

   (2) https://tools.ietf.org/html/rfc3986.html

   (3) https://tools.ietf.org/html/rfc2822.html


File: python.info,  Node: http cookies — HTTP state management,  Next: http cookiejar — Cookie handling for HTTP clients,  Prev: http server — HTTP servers,  Up: Internet Protocols and Support

5.21.23 ‘http.cookies’ — HTTP state management
----------------------------------------------

`Source code:' Lib/http/cookies.py(1)

__________________________________________________________________

The *note http.cookies: 95. module defines classes for abstracting the
concept of cookies, an HTTP state management mechanism.  It supports
both simple string-only cookies, and provides an abstraction for having
any serializable data-type as cookie value.

The module formerly strictly applied the parsing rules described in the
RFC 2109(2) and RFC 2068(3) specifications.  It has since been
discovered that MSIE 3.0x doesn’t follow the character rules outlined in
those specs and also many current day browsers and servers have relaxed
parsing rules when comes to Cookie handling.  As a result, the parsing
rules used are a bit less strict.

The character set, *note string.ascii_letters: d24, *note string.digits:
186b. and ‘!#$%&'*+-.^_`|~:’ denote the set of valid characters allowed
by this module in Cookie name (as *note key: 588.).

Changed in version 3.3: Allowed ‘:’ as a valid Cookie name character.

     Note: On encountering an invalid cookie, *note CookieError: 2f9d.
     is raised, so if your cookie data comes from a browser you should
     always prepare for invalid data and catch *note CookieError: 2f9d.
     on parsing.

 -- Exception: http.cookies.CookieError

     Exception failing because of RFC 2109(4) invalidity: incorrect
     attributes, incorrect ‘Set-Cookie’ header, etc.

 -- Class: http.cookies.BaseCookie ([input])

     This class is a dictionary-like object whose keys are strings and
     whose values are *note Morsel: 58b. instances.  Note that upon
     setting a key to a value, the value is first converted to a *note
     Morsel: 58b. containing the key and the value.

     If `input' is given, it is passed to the *note load(): 2f9f.
     method.

 -- Class: http.cookies.SimpleCookie ([input])

     This class derives from *note BaseCookie: 2f9e. and overrides
     ‘value_decode()’ and ‘value_encode()’.  SimpleCookie supports
     strings as cookie values.  When setting the value, SimpleCookie
     calls the builtin *note str(): 205. to convert the value to a
     string.  Values received from HTTP are kept as strings.

See also
........

Module *note http.cookiejar: 94.

     HTTP cookie handling for web `clients'.  The *note http.cookiejar:
     94. and *note http.cookies: 95. modules do not depend on each
     other.

RFC 2109(5) - HTTP State Management Mechanism

     This is the state management specification implemented by this
     module.

* Menu:

* Cookie Objects::
* Morsel Objects::
* Example: Example<14>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/http/cookies.py

   (2) https://tools.ietf.org/html/rfc2109.html

   (3) https://tools.ietf.org/html/rfc2068.html

   (4) https://tools.ietf.org/html/rfc2109.html

   (5) https://tools.ietf.org/html/rfc2109.html


File: python.info,  Node: Cookie Objects,  Next: Morsel Objects,  Up: http cookies — HTTP state management

5.21.23.1 Cookie Objects
........................

 -- Method: BaseCookie.value_decode (val)

     Return a tuple ‘(real_value, coded_value)’ from a string
     representation.  ‘real_value’ can be any type.  This method does no
     decoding in *note BaseCookie: 2f9e. — it exists so it can be
     overridden.

 -- Method: BaseCookie.value_encode (val)

     Return a tuple ‘(real_value, coded_value)’.  `val' can be any type,
     but ‘coded_value’ will always be converted to a string.  This
     method does no encoding in *note BaseCookie: 2f9e. — it exists so
     it can be overridden.

     In general, it should be the case that *note value_encode(): 2fa3.
     and *note value_decode(): 2fa2. are inverses on the range of
     `value_decode'.

 -- Method: BaseCookie.output (attrs=None, header='Set-Cookie:',
          sep='\r\n')

     Return a string representation suitable to be sent as HTTP headers.
     `attrs' and `header' are sent to each *note Morsel: 58b.’s *note
     output(): 2fa4. method.  `sep' is used to join the headers
     together, and is by default the combination ‘'\r\n'’ (CRLF).

 -- Method: BaseCookie.js_output (attrs=None)

     Return an embeddable JavaScript snippet, which, if run on a browser
     which supports JavaScript, will act the same as if the HTTP headers
     was sent.

     The meaning for `attrs' is the same as in *note output(): 2fa4.

 -- Method: BaseCookie.load (rawdata)

     If `rawdata' is a string, parse it as an ‘HTTP_COOKIE’ and add the
     values found there as *note Morsel: 58b.s.  If it is a dictionary,
     it is equivalent to:

          for k, v in rawdata.items():
              cookie[k] = v


File: python.info,  Node: Morsel Objects,  Next: Example<14>,  Prev: Cookie Objects,  Up: http cookies — HTTP state management

5.21.23.2 Morsel Objects
........................

 -- Class: http.cookies.Morsel

     Abstract a key/value pair, which has some RFC 2109(1) attributes.

     Morsels are dictionary-like objects, whose set of keys is constant
     — the valid RFC 2109(2) attributes, which are

        * ‘expires’

        * ‘path’

        * ‘comment’

        * ‘domain’

        * ‘max-age’

        * ‘secure’

        * ‘version’

        * ‘httponly’

        * ‘samesite’

     The attribute ‘httponly’ specifies that the cookie is only
     transferred in HTTP requests, and is not accessible through
     JavaScript.  This is intended to mitigate some forms of cross-site
     scripting.

     The attribute ‘samesite’ specifies that the browser is not allowed
     to send the cookie along with cross-site requests.  This helps to
     mitigate CSRF attacks.  Valid values for this attribute are
     “Strict” and “Lax”.

     The keys are case-insensitive and their default value is ‘''’.

     Changed in version 3.5: ‘__eq__()’ now takes *note key: 588. and
     *note value: 589. into account.

     Changed in version 3.7: Attributes *note key: 588, *note value:
     589. and *note coded_value: 58a. are read-only.  Use *note set():
     58c. for setting them.

     Changed in version 3.8: Added support for the ‘samesite’ attribute.

 -- Attribute: Morsel.value

     The value of the cookie.

 -- Attribute: Morsel.coded_value

     The encoded value of the cookie — this is what should be sent.

 -- Attribute: Morsel.key

     The name of the cookie.

 -- Method: Morsel.set (key, value, coded_value)

     Set the `key', `value' and `coded_value' attributes.

 -- Method: Morsel.isReservedKey (K)

     Whether `K' is a member of the set of keys of a *note Morsel: 58b.

 -- Method: Morsel.output (attrs=None, header='Set-Cookie:')

     Return a string representation of the Morsel, suitable to be sent
     as an HTTP header.  By default, all the attributes are included,
     unless `attrs' is given, in which case it should be a list of
     attributes to use.  `header' is by default ‘"Set-Cookie:"’.

 -- Method: Morsel.js_output (attrs=None)

     Return an embeddable JavaScript snippet, which, if run on a browser
     which supports JavaScript, will act the same as if the HTTP header
     was sent.

     The meaning for `attrs' is the same as in *note output(): 2fa9.

 -- Method: Morsel.OutputString (attrs=None)

     Return a string representing the Morsel, without any surrounding
     HTTP or JavaScript.

     The meaning for `attrs' is the same as in *note output(): 2fa9.

 -- Method: Morsel.update (values)

     Update the values in the Morsel dictionary with the values in the
     dictionary `values'.  Raise an error if any of the keys in the
     `values' dict is not a valid RFC 2109(3) attribute.

     Changed in version 3.5: an error is raised for invalid keys.

 -- Method: Morsel.copy (value)

     Return a shallow copy of the Morsel object.

     Changed in version 3.5: return a Morsel object instead of a dict.

 -- Method: Morsel.setdefault (key, value=None)

     Raise an error if key is not a valid RFC 2109(4) attribute,
     otherwise behave the same as *note dict.setdefault(): a9e.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2109.html

   (2) https://tools.ietf.org/html/rfc2109.html

   (3) https://tools.ietf.org/html/rfc2109.html

   (4) https://tools.ietf.org/html/rfc2109.html


File: python.info,  Node: Example<14>,  Prev: Morsel Objects,  Up: http cookies — HTTP state management

5.21.23.3 Example
.................

The following example demonstrates how to use the *note http.cookies:
95. module.

     >>> from http import cookies
     >>> C = cookies.SimpleCookie()
     >>> C["fig"] = "newton"
     >>> C["sugar"] = "wafer"
     >>> print(C) # generate HTTP headers
     Set-Cookie: fig=newton
     Set-Cookie: sugar=wafer
     >>> print(C.output()) # same thing
     Set-Cookie: fig=newton
     Set-Cookie: sugar=wafer
     >>> C = cookies.SimpleCookie()
     >>> C["rocky"] = "road"
     >>> C["rocky"]["path"] = "/cookie"
     >>> print(C.output(header="Cookie:"))
     Cookie: rocky=road; Path=/cookie
     >>> print(C.output(attrs=[], header="Cookie:"))
     Cookie: rocky=road
     >>> C = cookies.SimpleCookie()
     >>> C.load("chips=ahoy; vienna=finger") # load from a string (HTTP header)
     >>> print(C)
     Set-Cookie: chips=ahoy
     Set-Cookie: vienna=finger
     >>> C = cookies.SimpleCookie()
     >>> C.load('keebler="E=everybody; L=\\"Loves\\"; fudge=\\012;";')
     >>> print(C)
     Set-Cookie: keebler="E=everybody; L=\"Loves\"; fudge=\012;"
     >>> C = cookies.SimpleCookie()
     >>> C["oreo"] = "doublestuff"
     >>> C["oreo"]["path"] = "/"
     >>> print(C)
     Set-Cookie: oreo=doublestuff; Path=/
     >>> C = cookies.SimpleCookie()
     >>> C["twix"] = "none for you"
     >>> C["twix"].value
     'none for you'
     >>> C = cookies.SimpleCookie()
     >>> C["number"] = 7 # equivalent to C["number"] = str(7)
     >>> C["string"] = "seven"
     >>> C["number"].value
     '7'
     >>> C["string"].value
     'seven'
     >>> print(C)
     Set-Cookie: number=7
     Set-Cookie: string=seven


File: python.info,  Node: http cookiejar — Cookie handling for HTTP clients,  Next: xmlrpc — XMLRPC server and client modules,  Prev: http cookies — HTTP state management,  Up: Internet Protocols and Support

5.21.24 ‘http.cookiejar’ — Cookie handling for HTTP clients
-----------------------------------------------------------

`Source code:' Lib/http/cookiejar.py(1)

__________________________________________________________________

The *note http.cookiejar: 94. module defines classes for automatic
handling of HTTP cookies.  It is useful for accessing web sites that
require small pieces of data – `cookies' – to be set on the client
machine by an HTTP response from a web server, and then returned to the
server in later HTTP requests.

Both the regular Netscape cookie protocol and the protocol defined by
RFC 2965(2) are handled.  RFC 2965 handling is switched off by default.
RFC 2109(3) cookies are parsed as Netscape cookies and subsequently
treated either as Netscape or RFC 2965 cookies according to the ‘policy’
in effect.  Note that the great majority of cookies on the Internet are
Netscape cookies.  *note http.cookiejar: 94. attempts to follow the
de-facto Netscape cookie protocol (which differs substantially from that
set out in the original Netscape specification), including taking note
of the ‘max-age’ and ‘port’ cookie-attributes introduced with RFC 2965.

     Note: The various named parameters found in ‘Set-Cookie’ and
     ‘Set-Cookie2’ headers (eg.  ‘domain’ and ‘expires’) are
     conventionally referred to as `attributes'.  To distinguish them
     from Python attributes, the documentation for this module uses the
     term `cookie-attribute' instead.

The module defines the following exception:

 -- Exception: http.cookiejar.LoadError

     Instances of *note FileCookieJar: 2fb2. raise this exception on
     failure to load cookies from a file.  *note LoadError: 2fb1. is a
     subclass of *note OSError: 304.

     Changed in version 3.3: LoadError was made a subclass of *note
     OSError: 304. instead of *note IOError: a73.

The following classes are provided:

 -- Class: http.cookiejar.CookieJar (policy=None)

     `policy' is an object implementing the *note CookiePolicy: 2fb3.
     interface.

     The *note CookieJar: 2db2. class stores HTTP cookies.  It extracts
     cookies from HTTP requests, and returns them in HTTP responses.
     *note CookieJar: 2db2. instances automatically expire contained
     cookies when necessary.  Subclasses are also responsible for
     storing and retrieving cookies from a file or database.

 -- Class: http.cookiejar.FileCookieJar (filename, delayload=None,
          policy=None)

     `policy' is an object implementing the *note CookiePolicy: 2fb3.
     interface.  For the other arguments, see the documentation for the
     corresponding attributes.

     A *note CookieJar: 2db2. which can load cookies from, and perhaps
     save cookies to, a file on disk.  Cookies are `NOT' loaded from the
     named file until either the *note load(): 2fb4. or *note revert():
     2fb5. method is called.  Subclasses of this class are documented in
     section *note FileCookieJar subclasses and co-operation with web
     browsers: 2fb6.

     Changed in version 3.8: The filename parameter supports a *note
     path-like object: 472.

 -- Class: http.cookiejar.CookiePolicy

     This class is responsible for deciding whether each cookie should
     be accepted from / returned to the server.

 -- Class: http.cookiejar.DefaultCookiePolicy (blocked_domains=None,
          allowed_domains=None, netscape=True, rfc2965=False,
          rfc2109_as_netscape=None, hide_cookie2=False,
          strict_domain=False, strict_rfc2965_unverifiable=True,
          strict_ns_unverifiable=False,
          strict_ns_domain=DefaultCookiePolicy.DomainLiberal,
          strict_ns_set_initial_dollar=False, strict_ns_set_path=False,
          secure_protocols=("https", "wss"))

     Constructor arguments should be passed as keyword arguments only.
     `blocked_domains' is a sequence of domain names that we never
     accept cookies from, nor return cookies to.  `allowed_domains' if
     not *note None: 203, this is a sequence of the only domains for
     which we accept and return cookies.  `secure_protocols' is a
     sequence of protocols for which secure cookies can be added to.  By
     default `https' and `wss' (secure websocket) are considered secure
     protocols.  For all other arguments, see the documentation for
     *note CookiePolicy: 2fb3. and *note DefaultCookiePolicy: 1129.
     objects.

     *note DefaultCookiePolicy: 1129. implements the standard accept /
     reject rules for Netscape and RFC 2965(4) cookies.  By default, RFC
     2109(5) cookies (ie.  cookies received in a ‘Set-Cookie’ header
     with a version cookie-attribute of 1) are treated according to the
     RFC 2965 rules.  However, if RFC 2965 handling is turned off or
     *note rfc2109_as_netscape: 2fb7. is ‘True’, RFC 2109 cookies are
     ‘downgraded’ by the *note CookieJar: 2db2. instance to Netscape
     cookies, by setting the ‘version’ attribute of the *note Cookie:
     2fb8. instance to 0.  *note DefaultCookiePolicy: 1129. also
     provides some parameters to allow some fine-tuning of policy.

 -- Class: http.cookiejar.Cookie

     This class represents Netscape, RFC 2109(6) and RFC 2965(7)
     cookies.  It is not expected that users of *note http.cookiejar:
     94. construct their own *note Cookie: 2fb8. instances.  Instead, if
     necessary, call ‘make_cookies()’ on a *note CookieJar: 2db2.
     instance.

See also
........

Module *note urllib.request: 129.

     URL opening with automatic cookie handling.

Module *note http.cookies: 95.

     HTTP cookie classes, principally useful for server-side code.  The
     *note http.cookiejar: 94. and *note http.cookies: 95. modules do
     not depend on each other.

‘https://curl.se/rfc/cookie_spec.html’

     The specification of the original Netscape cookie protocol.  Though
     this is still the dominant protocol, the ‘Netscape cookie protocol’
     implemented by all the major browsers (and *note http.cookiejar:
     94.) only bears a passing resemblance to the one sketched out in
     ‘cookie_spec.html’.

RFC 2109(8) - HTTP State Management Mechanism

     Obsoleted by RFC 2965(9).  Uses ‘Set-Cookie’ with version=1.

RFC 2965(10) - HTTP State Management Mechanism

     The Netscape protocol with the bugs fixed.  Uses ‘Set-Cookie2’ in
     place of ‘Set-Cookie’.  Not widely used.

‘http://kristol.org/cookie/errata.html’

     Unfinished errata to RFC 2965(11).

RFC 2964(12) - Use of HTTP State Management

* Menu:

* CookieJar and FileCookieJar Objects::
* FileCookieJar subclasses and co-operation with web browsers::
* CookiePolicy Objects::
* DefaultCookiePolicy Objects::
* Cookie Objects: Cookie Objects<2>.
* Examples: Examples<25>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/http/cookiejar.py

   (2) https://tools.ietf.org/html/rfc2965.html

   (3) https://tools.ietf.org/html/rfc2109.html

   (4) https://tools.ietf.org/html/rfc2965.html

   (5) https://tools.ietf.org/html/rfc2109.html

   (6) https://tools.ietf.org/html/rfc2109.html

   (7) https://tools.ietf.org/html/rfc2965.html

   (8) https://tools.ietf.org/html/rfc2109.html

   (9) https://tools.ietf.org/html/rfc2965.html

   (10) https://tools.ietf.org/html/rfc2965.html

   (11) https://tools.ietf.org/html/rfc2965.html

   (12) https://tools.ietf.org/html/rfc2964.html


File: python.info,  Node: CookieJar and FileCookieJar Objects,  Next: FileCookieJar subclasses and co-operation with web browsers,  Up: http cookiejar — Cookie handling for HTTP clients

5.21.24.1 CookieJar and FileCookieJar Objects
.............................................

*note CookieJar: 2db2. objects support the *note iterator: 1171.
protocol for iterating over contained *note Cookie: 2fb8. objects.

*note CookieJar: 2db2. has the following methods:

 -- Method: CookieJar.add_cookie_header (request)

     Add correct ‘Cookie’ header to `request'.

     If policy allows (ie.  the ‘rfc2965’ and ‘hide_cookie2’ attributes
     of the *note CookieJar: 2db2.’s *note CookiePolicy: 2fb3. instance
     are true and false respectively), the ‘Cookie2’ header is also
     added when appropriate.

     The `request' object (usually a *note urllib.request.Request: 9dc.
     instance) must support the methods ‘get_full_url()’, ‘get_host()’,
     ‘get_type()’, ‘unverifiable()’, ‘has_header()’, ‘get_header()’,
     ‘header_items()’, ‘add_unredirected_header()’ and ‘origin_req_host’
     attribute as documented by *note urllib.request: 129.

     Changed in version 3.3: `request' object needs ‘origin_req_host’
     attribute.  Dependency on a deprecated method
     ‘get_origin_req_host()’ has been removed.

 -- Method: CookieJar.extract_cookies (response, request)

     Extract cookies from HTTP `response' and store them in the *note
     CookieJar: 2db2, where allowed by policy.

     The *note CookieJar: 2db2. will look for allowable ‘Set-Cookie’ and
     ‘Set-Cookie2’ headers in the `response' argument, and store cookies
     as appropriate (subject to the *note CookiePolicy.set_ok(): 2fbd.
     method’s approval).

     The `response' object (usually the result of a call to *note
     urllib.request.urlopen(): 87b, or similar) should support an
     ‘info()’ method, which returns an *note email.message.Message: 63b.
     instance.

     The `request' object (usually a *note urllib.request.Request: 9dc.
     instance) must support the methods ‘get_full_url()’, ‘get_host()’,
     ‘unverifiable()’, and ‘origin_req_host’ attribute, as documented by
     *note urllib.request: 129.  The request is used to set default
     values for cookie-attributes as well as for checking that the
     cookie is allowed to be set.

     Changed in version 3.3: `request' object needs ‘origin_req_host’
     attribute.  Dependency on a deprecated method
     ‘get_origin_req_host()’ has been removed.

 -- Method: CookieJar.set_policy (policy)

     Set the *note CookiePolicy: 2fb3. instance to be used.

 -- Method: CookieJar.make_cookies (response, request)

     Return sequence of *note Cookie: 2fb8. objects extracted from
     `response' object.

     See the documentation for *note extract_cookies(): 2fbc. for the
     interfaces required of the `response' and `request' arguments.

 -- Method: CookieJar.set_cookie_if_ok (cookie, request)

     Set a *note Cookie: 2fb8. if policy says it’s OK to do so.

 -- Method: CookieJar.set_cookie (cookie)

     Set a *note Cookie: 2fb8, without checking with policy to see
     whether or not it should be set.

 -- Method: CookieJar.clear ([domain[, path[, name]]])

     Clear some cookies.

     If invoked without arguments, clear all cookies.  If given a single
     argument, only cookies belonging to that `domain' will be removed.
     If given two arguments, cookies belonging to the specified `domain'
     and URL `path' are removed.  If given three arguments, then the
     cookie with the specified `domain', `path' and `name' is removed.

     Raises *note KeyError: 3e9. if no matching cookie exists.

 -- Method: CookieJar.clear_session_cookies ()

     Discard all session cookies.

     Discards all contained cookies that have a true ‘discard’ attribute
     (usually because they had either no ‘max-age’ or ‘expires’
     cookie-attribute, or an explicit ‘discard’ cookie-attribute).  For
     interactive browsers, the end of a session usually corresponds to
     closing the browser window.

     Note that the ‘save()’ method won’t save session cookies anyway,
     unless you ask otherwise by passing a true `ignore_discard'
     argument.

*note FileCookieJar: 2fb2. implements the following additional methods:

 -- Method: FileCookieJar.save (filename=None, ignore_discard=False,
          ignore_expires=False)

     Save cookies to a file.

     This base class raises *note NotImplementedError: 704.  Subclasses
     may leave this method unimplemented.

     `filename' is the name of file in which to save cookies.  If
     `filename' is not specified, ‘self.filename’ is used (whose default
     is the value passed to the constructor, if any); if ‘self.filename’
     is *note None: 203, *note ValueError: 16d. is raised.

     `ignore_discard': save even cookies set to be discarded.
     `ignore_expires': save even cookies that have expired

     The file is overwritten if it already exists, thus wiping all the
     cookies it contains.  Saved cookies can be restored later using the
     *note load(): 2fb4. or *note revert(): 2fb5. methods.

 -- Method: FileCookieJar.load (filename=None, ignore_discard=False,
          ignore_expires=False)

     Load cookies from a file.

     Old cookies are kept unless overwritten by newly loaded ones.

     Arguments are as for *note save(): 2fc4.

     The named file must be in the format understood by the class, or
     *note LoadError: 2fb1. will be raised.  Also, *note OSError: 304.
     may be raised, for example if the file does not exist.

     Changed in version 3.3: *note IOError: a73. used to be raised, it
     is now an alias of *note OSError: 304.

 -- Method: FileCookieJar.revert (filename=None, ignore_discard=False,
          ignore_expires=False)

     Clear all cookies and reload cookies from a saved file.

     *note revert(): 2fb5. can raise the same exceptions as *note
     load(): 2fb4.  If there is a failure, the object’s state will not
     be altered.

*note FileCookieJar: 2fb2. instances have the following public
attributes:

 -- Attribute: FileCookieJar.filename

     Filename of default file in which to keep cookies.  This attribute
     may be assigned to.

 -- Attribute: FileCookieJar.delayload

     If true, load cookies lazily from disk.  This attribute should not
     be assigned to.  This is only a hint, since this only affects
     performance, not behaviour (unless the cookies on disk are
     changing).  A *note CookieJar: 2db2. object may ignore it.  None of
     the *note FileCookieJar: 2fb2. classes included in the standard
     library lazily loads cookies.


File: python.info,  Node: FileCookieJar subclasses and co-operation with web browsers,  Next: CookiePolicy Objects,  Prev: CookieJar and FileCookieJar Objects,  Up: http cookiejar — Cookie handling for HTTP clients

5.21.24.2 FileCookieJar subclasses and co-operation with web browsers
.....................................................................

The following *note CookieJar: 2db2. subclasses are provided for reading
and writing.

 -- Class: http.cookiejar.MozillaCookieJar (filename, delayload=None,
          policy=None)

     A *note FileCookieJar: 2fb2. that can load from and save cookies to
     disk in the Mozilla ‘cookies.txt’ file format (which is also used
     by the Lynx and Netscape browsers).

          Note: This loses information about RFC 2965(1) cookies, and
          also about newer or non-standard cookie-attributes such as
          ‘port’.

          Warning: Back up your cookies before saving if you have
          cookies whose loss / corruption would be inconvenient (there
          are some subtleties which may lead to slight changes in the
          file over a load / save round-trip).

     Also note that cookies saved while Mozilla is running will get
     clobbered by Mozilla.

 -- Class: http.cookiejar.LWPCookieJar (filename, delayload=None,
          policy=None)

     A *note FileCookieJar: 2fb2. that can load from and save cookies to
     disk in format compatible with the libwww-perl library’s
     ‘Set-Cookie3’ file format.  This is convenient if you want to store
     cookies in a human-readable file.

     Changed in version 3.8: The filename parameter supports a *note
     path-like object: 472.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2965.html


File: python.info,  Node: CookiePolicy Objects,  Next: DefaultCookiePolicy Objects,  Prev: FileCookieJar subclasses and co-operation with web browsers,  Up: http cookiejar — Cookie handling for HTTP clients

5.21.24.3 CookiePolicy Objects
..............................

Objects implementing the *note CookiePolicy: 2fb3. interface have the
following methods:

 -- Method: CookiePolicy.set_ok (cookie, request)

     Return boolean value indicating whether cookie should be accepted
     from server.

     `cookie' is a *note Cookie: 2fb8. instance.  `request' is an object
     implementing the interface defined by the documentation for *note
     CookieJar.extract_cookies(): 2fbc.

 -- Method: CookiePolicy.return_ok (cookie, request)

     Return boolean value indicating whether cookie should be returned
     to server.

     `cookie' is a *note Cookie: 2fb8. instance.  `request' is an object
     implementing the interface defined by the documentation for *note
     CookieJar.add_cookie_header(): 2fbb.

 -- Method: CookiePolicy.domain_return_ok (domain, request)

     Return ‘False’ if cookies should not be returned, given cookie
     domain.

     This method is an optimization.  It removes the need for checking
     every cookie with a particular domain (which might involve reading
     many files).  Returning true from *note domain_return_ok(): 2fcd.
     and *note path_return_ok(): 2fce. leaves all the work to *note
     return_ok(): 2fcc.

     If *note domain_return_ok(): 2fcd. returns true for the cookie
     domain, *note path_return_ok(): 2fce. is called for the cookie
     path.  Otherwise, *note path_return_ok(): 2fce. and *note
     return_ok(): 2fcc. are never called for that cookie domain.  If
     *note path_return_ok(): 2fce. returns true, *note return_ok():
     2fcc. is called with the *note Cookie: 2fb8. object itself for a
     full check.  Otherwise, *note return_ok(): 2fcc. is never called
     for that cookie path.

     Note that *note domain_return_ok(): 2fcd. is called for every
     `cookie' domain, not just for the `request' domain.  For example,
     the function might be called with both ‘".example.com"’ and
     ‘"www.example.com"’ if the request domain is ‘"www.example.com"’.
     The same goes for *note path_return_ok(): 2fce.

     The `request' argument is as documented for *note return_ok():
     2fcc.

 -- Method: CookiePolicy.path_return_ok (path, request)

     Return ‘False’ if cookies should not be returned, given cookie
     path.

     See the documentation for *note domain_return_ok(): 2fcd.

In addition to implementing the methods above, implementations of the
*note CookiePolicy: 2fb3. interface must also supply the following
attributes, indicating which protocols should be used, and how.  All of
these attributes may be assigned to.

 -- Attribute: CookiePolicy.netscape

     Implement Netscape protocol.

 -- Attribute: CookiePolicy.rfc2965

     Implement RFC 2965(1) protocol.

 -- Attribute: CookiePolicy.hide_cookie2

     Don’t add ‘Cookie2’ header to requests (the presence of this header
     indicates to the server that we understand RFC 2965(2) cookies).

The most useful way to define a *note CookiePolicy: 2fb3. class is by
subclassing from *note DefaultCookiePolicy: 1129. and overriding some or
all of the methods above.  *note CookiePolicy: 2fb3. itself may be used
as a ‘null policy’ to allow setting and receiving any and all cookies
(this is unlikely to be useful).

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2965.html

   (2) https://tools.ietf.org/html/rfc2965.html


File: python.info,  Node: DefaultCookiePolicy Objects,  Next: Cookie Objects<2>,  Prev: CookiePolicy Objects,  Up: http cookiejar — Cookie handling for HTTP clients

5.21.24.4 DefaultCookiePolicy Objects
.....................................

Implements the standard rules for accepting and returning cookies.

Both RFC 2965(1) and Netscape cookies are covered.  RFC 2965 handling is
switched off by default.

The easiest way to provide your own policy is to override this class and
call its methods in your overridden implementations before adding your
own additional checks:

     import http.cookiejar
     class MyCookiePolicy(http.cookiejar.DefaultCookiePolicy):
         def set_ok(self, cookie, request):
             if not http.cookiejar.DefaultCookiePolicy.set_ok(self, cookie, request):
                 return False
             if i_dont_want_to_store_this_cookie(cookie):
                 return False
             return True

In addition to the features required to implement the *note
CookiePolicy: 2fb3. interface, this class allows you to block and allow
domains from setting and receiving cookies.  There are also some
strictness switches that allow you to tighten up the rather loose
Netscape protocol rules a little bit (at the cost of blocking some
benign cookies).

A domain blacklist and whitelist is provided (both off by default).
Only domains not in the blacklist and present in the whitelist (if the
whitelist is active) participate in cookie setting and returning.  Use
the `blocked_domains' constructor argument, and ‘blocked_domains()’ and
‘set_blocked_domains()’ methods (and the corresponding argument and
methods for `allowed_domains').  If you set a whitelist, you can turn it
off again by setting it to *note None: 203.

Domains in block or allow lists that do not start with a dot must equal
the cookie domain to be matched.  For example, ‘"example.com"’ matches a
blacklist entry of ‘"example.com"’, but ‘"www.example.com"’ does not.
Domains that do start with a dot are matched by more specific domains
too.  For example, both ‘"www.example.com"’ and
‘"www.coyote.example.com"’ match ‘".example.com"’ (but ‘"example.com"’
itself does not).  IP addresses are an exception, and must match
exactly.  For example, if blocked_domains contains ‘"192.168.1.2"’ and
‘".168.1.2"’, 192.168.1.2 is blocked, but 193.168.1.2 is not.

*note DefaultCookiePolicy: 1129. implements the following additional
methods:

 -- Method: DefaultCookiePolicy.blocked_domains ()

     Return the sequence of blocked domains (as a tuple).

 -- Method: DefaultCookiePolicy.set_blocked_domains (blocked_domains)

     Set the sequence of blocked domains.

 -- Method: DefaultCookiePolicy.is_blocked (domain)

     Return whether `domain' is on the blacklist for setting or
     receiving cookies.

 -- Method: DefaultCookiePolicy.allowed_domains ()

     Return *note None: 203, or the sequence of allowed domains (as a
     tuple).

 -- Method: DefaultCookiePolicy.set_allowed_domains (allowed_domains)

     Set the sequence of allowed domains, or *note None: 203.

 -- Method: DefaultCookiePolicy.is_not_allowed (domain)

     Return whether `domain' is not on the whitelist for setting or
     receiving cookies.

*note DefaultCookiePolicy: 1129. instances have the following
attributes, which are all initialised from the constructor arguments of
the same name, and which may all be assigned to.

 -- Attribute: DefaultCookiePolicy.rfc2109_as_netscape

     If true, request that the *note CookieJar: 2db2. instance downgrade
     RFC 2109(2) cookies (ie.  cookies received in a ‘Set-Cookie’ header
     with a version cookie-attribute of 1) to Netscape cookies by
     setting the version attribute of the *note Cookie: 2fb8. instance
     to 0.  The default value is *note None: 203, in which case RFC 2109
     cookies are downgraded if and only if RFC 2965(3) handling is
     turned off.  Therefore, RFC 2109 cookies are downgraded by default.

General strictness switches:

 -- Attribute: DefaultCookiePolicy.strict_domain

     Don’t allow sites to set two-component domains with country-code
     top-level domains like ‘.co.uk’, ‘.gov.uk’, ‘.co.nz’.etc.  This is
     far from perfect and isn’t guaranteed to work!

RFC 2965(4) protocol strictness switches:

 -- Attribute: DefaultCookiePolicy.strict_rfc2965_unverifiable

     Follow RFC 2965(5) rules on unverifiable transactions (usually, an
     unverifiable transaction is one resulting from a redirect or a
     request for an image hosted on another site).  If this is false,
     cookies are `never' blocked on the basis of verifiability

Netscape protocol strictness switches:

 -- Attribute: DefaultCookiePolicy.strict_ns_unverifiable

     Apply RFC 2965(6) rules on unverifiable transactions even to
     Netscape cookies.

 -- Attribute: DefaultCookiePolicy.strict_ns_domain

     Flags indicating how strict to be with domain-matching rules for
     Netscape cookies.  See below for acceptable values.

 -- Attribute: DefaultCookiePolicy.strict_ns_set_initial_dollar

     Ignore cookies in Set-Cookie: headers that have names starting with
     ‘'$'’.

 -- Attribute: DefaultCookiePolicy.strict_ns_set_path

     Don’t allow setting cookies whose path doesn’t path-match request
     URI.

‘strict_ns_domain’ is a collection of flags.  Its value is constructed
by or-ing together (for example,
‘DomainStrictNoDots|DomainStrictNonDomain’ means both flags are set).

 -- Attribute: DefaultCookiePolicy.DomainStrictNoDots

     When setting cookies, the ‘host prefix’ must not contain a dot (eg.
     ‘www.foo.bar.com’ can’t set a cookie for ‘.bar.com’, because
     ‘www.foo’ contains a dot).

 -- Attribute: DefaultCookiePolicy.DomainStrictNonDomain

     Cookies that did not explicitly specify a ‘domain’ cookie-attribute
     can only be returned to a domain equal to the domain that set the
     cookie (eg.  ‘spam.example.com’ won’t be returned cookies from
     ‘example.com’ that had no ‘domain’ cookie-attribute).

 -- Attribute: DefaultCookiePolicy.DomainRFC2965Match

     When setting cookies, require a full RFC 2965(7) domain-match.

The following attributes are provided for convenience, and are the most
useful combinations of the above flags:

 -- Attribute: DefaultCookiePolicy.DomainLiberal

     Equivalent to 0 (ie.  all of the above Netscape domain strictness
     flags switched off).

 -- Attribute: DefaultCookiePolicy.DomainStrict

     Equivalent to ‘DomainStrictNoDots|DomainStrictNonDomain’.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2965.html

   (2) https://tools.ietf.org/html/rfc2109.html

   (3) https://tools.ietf.org/html/rfc2965.html

   (4) https://tools.ietf.org/html/rfc2965.html

   (5) https://tools.ietf.org/html/rfc2965.html

   (6) https://tools.ietf.org/html/rfc2965.html

   (7) https://tools.ietf.org/html/rfc2965.html


File: python.info,  Node: Cookie Objects<2>,  Next: Examples<25>,  Prev: DefaultCookiePolicy Objects,  Up: http cookiejar — Cookie handling for HTTP clients

5.21.24.5 Cookie Objects
........................

*note Cookie: 2fb8. instances have Python attributes roughly
corresponding to the standard cookie-attributes specified in the various
cookie standards.  The correspondence is not one-to-one, because there
are complicated rules for assigning default values, because the
‘max-age’ and ‘expires’ cookie-attributes contain equivalent
information, and because RFC 2109(1) cookies may be ‘downgraded’ by
*note http.cookiejar: 94. from version 1 to version 0 (Netscape)
cookies.

Assignment to these attributes should not be necessary other than in
rare circumstances in a *note CookiePolicy: 2fb3. method.  The class
does not enforce internal consistency, so you should know what you’re
doing if you do that.

 -- Attribute: Cookie.version

     Integer or *note None: 203.  Netscape cookies have *note version:
     2fe6. 0.  RFC 2965(2) and RFC 2109(3) cookies have a ‘version’
     cookie-attribute of 1.  However, note that *note http.cookiejar:
     94. may ‘downgrade’ RFC 2109 cookies to Netscape cookies, in which
     case *note version: 2fe6. is 0.

 -- Attribute: Cookie.name

     Cookie name (a string).

 -- Attribute: Cookie.value

     Cookie value (a string), or *note None: 203.

 -- Attribute: Cookie.port

     String representing a port or a set of ports (eg.  ‘80’, or
     ‘80,8080’), or *note None: 203.

 -- Attribute: Cookie.path

     Cookie path (a string, eg.  ‘'/acme/rocket_launchers'’).

 -- Attribute: Cookie.secure

     ‘True’ if cookie should only be returned over a secure connection.

 -- Attribute: Cookie.expires

     Integer expiry date in seconds since epoch, or *note None: 203.
     See also the *note is_expired(): 2fed. method.

 -- Attribute: Cookie.discard

     ‘True’ if this is a session cookie.

 -- Attribute: Cookie.comment

     String comment from the server explaining the function of this
     cookie, or *note None: 203.

 -- Attribute: Cookie.comment_url

     URL linking to a comment from the server explaining the function of
     this cookie, or *note None: 203.

 -- Attribute: Cookie.rfc2109

     ‘True’ if this cookie was received as an RFC 2109(4) cookie (ie.
     the cookie arrived in a ‘Set-Cookie’ header, and the value of the
     Version cookie-attribute in that header was 1).  This attribute is
     provided because *note http.cookiejar: 94. may ‘downgrade’ RFC 2109
     cookies to Netscape cookies, in which case *note version: 2fe6. is
     0.

 -- Attribute: Cookie.port_specified

     ‘True’ if a port or set of ports was explicitly specified by the
     server (in the ‘Set-Cookie’ / ‘Set-Cookie2’ header).

 -- Attribute: Cookie.domain_specified

     ‘True’ if a domain was explicitly specified by the server.

 -- Attribute: Cookie.domain_initial_dot

     ‘True’ if the domain explicitly specified by the server began with
     a dot (‘'.'’).

Cookies may have additional non-standard cookie-attributes.  These may
be accessed using the following methods:

 -- Method: Cookie.has_nonstandard_attr (name)

     Return ‘True’ if cookie has the named cookie-attribute.

 -- Method: Cookie.get_nonstandard_attr (name, default=None)

     If cookie has the named cookie-attribute, return its value.
     Otherwise, return `default'.

 -- Method: Cookie.set_nonstandard_attr (name, value)

     Set the value of the named cookie-attribute.

The *note Cookie: 2fb8. class also defines the following method:

 -- Method: Cookie.is_expired (now=None)

     ‘True’ if cookie has passed the time at which the server requested
     it should expire.  If `now' is given (in seconds since the epoch),
     return whether the cookie has expired at the specified time.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2109.html

   (2) https://tools.ietf.org/html/rfc2965.html

   (3) https://tools.ietf.org/html/rfc2109.html

   (4) https://tools.ietf.org/html/rfc2109.html


File: python.info,  Node: Examples<25>,  Prev: Cookie Objects<2>,  Up: http cookiejar — Cookie handling for HTTP clients

5.21.24.6 Examples
..................

The first example shows the most common usage of *note http.cookiejar:
94.:

     import http.cookiejar, urllib.request
     cj = http.cookiejar.CookieJar()
     opener = urllib.request.build_opener(urllib.request.HTTPCookieProcessor(cj))
     r = opener.open("http://example.com/")

This example illustrates how to open a URL using your Netscape, Mozilla,
or Lynx cookies (assumes Unix/Netscape convention for location of the
cookies file):

     import os, http.cookiejar, urllib.request
     cj = http.cookiejar.MozillaCookieJar()
     cj.load(os.path.join(os.path.expanduser("~"), ".netscape", "cookies.txt"))
     opener = urllib.request.build_opener(urllib.request.HTTPCookieProcessor(cj))
     r = opener.open("http://example.com/")

The next example illustrates the use of *note DefaultCookiePolicy: 1129.
Turn on RFC 2965(1) cookies, be more strict about domains when setting
and returning Netscape cookies, and block some domains from setting
cookies or having them returned:

     import urllib.request
     from http.cookiejar import CookieJar, DefaultCookiePolicy
     policy = DefaultCookiePolicy(
         rfc2965=True, strict_ns_domain=Policy.DomainStrict,
         blocked_domains=["ads.net", ".ads.net"])
     cj = CookieJar(policy)
     opener = urllib.request.build_opener(urllib.request.HTTPCookieProcessor(cj))
     r = opener.open("http://example.com/")

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2965.html


File: python.info,  Node: xmlrpc — XMLRPC server and client modules,  Next: xmlrpc client — XML-RPC client access,  Prev: http cookiejar — Cookie handling for HTTP clients,  Up: Internet Protocols and Support

5.21.25 ‘xmlrpc’ — XMLRPC server and client modules
---------------------------------------------------

XML-RPC is a Remote Procedure Call method that uses XML passed via HTTP
as a transport.  With it, a client can call methods with parameters on a
remote server (the server is named by a URI) and get back structured
data.

‘xmlrpc’ is a package that collects server and client modules
implementing XML-RPC. The modules are:

   * *note xmlrpc.client: 148.

   * *note xmlrpc.server: 149.


File: python.info,  Node: xmlrpc client — XML-RPC client access,  Next: xmlrpc server — Basic XML-RPC servers,  Prev: xmlrpc — XMLRPC server and client modules,  Up: Internet Protocols and Support

5.21.26 ‘xmlrpc.client’ — XML-RPC client access
-----------------------------------------------

`Source code:' Lib/xmlrpc/client.py(1)

__________________________________________________________________

XML-RPC is a Remote Procedure Call method that uses XML passed via
HTTP(S) as a transport.  With it, a client can call methods with
parameters on a remote server (the server is named by a URI) and get
back structured data.  This module supports writing XML-RPC client code;
it handles all the details of translating between conformable Python
objects and XML on the wire.

     Warning: The *note xmlrpc.client: 148. module is not secure against
     maliciously constructed data.  If you need to parse untrusted or
     unauthenticated data see *note XML vulnerabilities: 2b34.

Changed in version 3.5: For HTTPS URIs, *note xmlrpc.client: 148. now
performs all the necessary certificate and hostname checks by default.

 -- Class: xmlrpc.client.ServerProxy (uri, transport=None,
          encoding=None, verbose=False, allow_none=False,
          use_datetime=False, use_builtin_types=False, *, headers=(),
          context=None)

     A *note ServerProxy: 37f. instance is an object that manages
     communication with a remote XML-RPC server.  The required first
     argument is a URI (Uniform Resource Indicator), and will normally
     be the URL of the server.  The optional second argument is a
     transport factory instance; by default it is an internal
     ‘SafeTransport’ instance for https: URLs and an internal HTTP
     ‘Transport’ instance otherwise.  The optional third argument is an
     encoding, by default UTF-8.  The optional fourth argument is a
     debugging flag.

     The following parameters govern the use of the returned proxy
     instance.  If `allow_none' is true, the Python constant ‘None’ will
     be translated into XML; the default behaviour is for ‘None’ to
     raise a *note TypeError: 1fe.  This is a commonly-used extension to
     the XML-RPC specification, but isn’t supported by all clients and
     servers; see http://ontosys.com/xml-rpc/extensions.php(2) for a
     description.  The `use_builtin_types' flag can be used to cause
     date/time values to be presented as *note datetime.datetime: 1a0.
     objects and binary data to be presented as *note bytes: 172.
     objects; this flag is false by default.  *note datetime.datetime:
     1a0, *note bytes: 172. and *note bytearray: 173. objects may be
     passed to calls.  The `headers' parameter is an optional sequence
     of HTTP headers to send with each request, expressed as a sequence
     of 2-tuples representing the header name and value.  (e.g.
     ‘[(‘Header-Name’, ‘value’)]’).  The obsolete `use_datetime' flag is
     similar to `use_builtin_types' but it applies only to date/time
     values.

Changed in version 3.3: The `use_builtin_types' flag was added.

Changed in version 3.8: The `headers' parameter was added.

Both the HTTP and HTTPS transports support the URL syntax extension for
HTTP Basic Authentication: ‘http://user:pass@host:port/path’.  The
‘user:pass’ portion will be base64-encoded as an HTTP ‘Authorization’
header, and sent to the remote server as part of the connection process
when invoking an XML-RPC method.  You only need to use this if the
remote server requires a Basic Authentication user and password.  If an
HTTPS URL is provided, `context' may be *note ssl.SSLContext: 4ea. and
configures the SSL settings of the underlying HTTPS connection.

The returned instance is a proxy object with methods that can be used to
invoke corresponding RPC calls on the remote server.  If the remote
server supports the introspection API, the proxy can also be used to
query the remote server for the methods it supports (service discovery)
and fetch other server-associated metadata.

Types that are conformable (e.g.  that can be marshalled through XML),
include the following (and except where noted, they are unmarshalled as
the same Python type):

XML-RPC type               Python type
                           
---------------------------------------------------------------------------------------
                           
‘boolean’                  *note bool: 2bd.
                           
                           
‘int’, ‘i1’, ‘i2’, ‘i4’,   *note int: 204. in range from -2147483648 to 2147483647.
‘i8’ or ‘biginteger’       Values get the ‘<int>’ tag.
                           
                           
‘double’ or ‘float’        *note float: 1fd.  Values get the ‘<double>’ tag.
                           
                           
‘string’                   *note str: 205.
                           
                           
‘array’                    *note list: 1f8. or *note tuple: 1a2. containing
                           conformable elements.  Arrays are returned as
                           *note lists: 1f8.
                           
                           
‘struct’                   *note dict: 164.  Keys must be strings, values may be any
                           conformable type.  Objects of user-defined classes can be
                           passed in; only their *note __dict__: 5f6. attribute is
                           transmitted.
                           
                           
‘dateTime.iso8601’         *note DateTime: 2ffd. or *note datetime.datetime: 1a0.
                           Returned type depends on values of `use_builtin_types'
                           and `use_datetime' flags.
                           
                           
‘base64’                   *note Binary: 2ffe, *note bytes: 172. or
                           *note bytearray: 173.  Returned type depends on the value
                           of the `use_builtin_types' flag.
                           
                           
‘nil’                      The ‘None’ constant.  Passing is allowed only if
                           `allow_none' is true.
                           
                           
‘bigdecimal’               *note decimal.Decimal: 2c0.  Returned type only.
                           

This is the full set of data types supported by XML-RPC. Method calls
may also raise a special *note Fault: 2fff. instance, used to signal
XML-RPC server errors, or *note ProtocolError: 3000. used to signal an
error in the HTTP/HTTPS transport layer.  Both *note Fault: 2fff. and
*note ProtocolError: 3000. derive from a base class called ‘Error’.
Note that the xmlrpc client module currently does not marshal instances
of subclasses of built-in types.

When passing strings, characters special to XML such as ‘<’, ‘>’, and
‘&’ will be automatically escaped.  However, it’s the caller’s
responsibility to ensure that the string is free of characters that
aren’t allowed in XML, such as the control characters with ASCII values
between 0 and 31 (except, of course, tab, newline and carriage return);
failing to do this will result in an XML-RPC request that isn’t
well-formed XML. If you have to pass arbitrary bytes via XML-RPC, use
*note bytes: 172. or *note bytearray: 173. classes or the *note Binary:
2ffe. wrapper class described below.

‘Server’ is retained as an alias for *note ServerProxy: 37f. for
backwards compatibility.  New code should use *note ServerProxy: 37f.

Changed in version 3.5: Added the `context' argument.

Changed in version 3.6: Added support of type tags with prefixes (e.g.
‘ex:nil’).  Added support of unmarshalling additional types used by
Apache XML-RPC implementation for numerics: ‘i1’, ‘i2’, ‘i8’,
‘biginteger’, ‘float’ and ‘bigdecimal’.  See
‘http://ws.apache.org/xmlrpc/types.html’ for a description.

See also
........

XML-RPC HOWTO(3)

     A good description of XML-RPC operation and client software in
     several languages.  Contains pretty much everything an XML-RPC
     client developer needs to know.

XML-RPC Introspection(4)

     Describes the XML-RPC protocol extension for introspection.

XML-RPC Specification(5)

     The official specification.

Unofficial XML-RPC Errata(6)

     Fredrik Lundh’s “unofficial errata, intended to clarify certain
     details in the XML-RPC specification, as well as hint at ‘best
     practices’ to use when designing your own XML-RPC implementations.”

* Menu:

* ServerProxy Objects::
* DateTime Objects::
* Binary Objects::
* Fault Objects::
* ProtocolError Objects::
* MultiCall Objects::
* Convenience Functions::
* Example of Client Usage::
* Example of Client and Server Usage::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/xmlrpc/client.py

   (2) 
https://web.archive.org/web/20130120074804/http://ontosys.com/xml-rpc/extensions.php

   (3) http://www.tldp.org/HOWTO/XML-RPC-HOWTO/index.html

   (4) http://xmlrpc-c.sourceforge.net/introspection.html

   (5) http://xmlrpc.scripting.com/spec.html

   (6) http://effbot.org/zone/xmlrpc-errata.htm


File: python.info,  Node: ServerProxy Objects,  Next: DateTime Objects,  Up: xmlrpc client — XML-RPC client access

5.21.26.1 ServerProxy Objects
.............................

A *note ServerProxy: 37f. instance has a method corresponding to each
remote procedure call accepted by the XML-RPC server.  Calling the
method performs an RPC, dispatched by both name and argument signature
(e.g.  the same method name can be overloaded with multiple argument
signatures).  The RPC finishes by returning a value, which may be either
returned data in a conformant type or a *note Fault: 2fff. or *note
ProtocolError: 3000. object indicating an error.

Servers that support the XML introspection API support some common
methods grouped under the reserved ‘system’ attribute:

 -- Method: ServerProxy.system.listMethods ()

     This method returns a list of strings, one for each (non-system)
     method supported by the XML-RPC server.

 -- Method: ServerProxy.system.methodSignature (name)

     This method takes one parameter, the name of a method implemented
     by the XML-RPC server.  It returns an array of possible signatures
     for this method.  A signature is an array of types.  The first of
     these types is the return type of the method, the rest are
     parameters.

     Because multiple signatures (ie.  overloading) is permitted, this
     method returns a list of signatures rather than a singleton.

     Signatures themselves are restricted to the top level parameters
     expected by a method.  For instance if a method expects one array
     of structs as a parameter, and it returns a string, its signature
     is simply “string, array”.  If it expects three integers and
     returns a string, its signature is “string, int, int, int”.

     If no signature is defined for the method, a non-array value is
     returned.  In Python this means that the type of the returned value
     will be something other than list.

 -- Method: ServerProxy.system.methodHelp (name)

     This method takes one parameter, the name of a method implemented
     by the XML-RPC server.  It returns a documentation string
     describing the use of that method.  If no such string is available,
     an empty string is returned.  The documentation string may contain
     HTML markup.

Changed in version 3.5: Instances of *note ServerProxy: 37f. support the
*note context manager: 661. protocol for closing the underlying
transport.

A working example follows.  The server code:

     from xmlrpc.server import SimpleXMLRPCServer

     def is_even(n):
         return n % 2 == 0

     server = SimpleXMLRPCServer(("localhost", 8000))
     print("Listening on port 8000...")
     server.register_function(is_even, "is_even")
     server.serve_forever()

The client code for the preceding server:

     import xmlrpc.client

     with xmlrpc.client.ServerProxy("http://localhost:8000/") as proxy:
         print("3 is even: %s" % str(proxy.is_even(3)))
         print("100 is even: %s" % str(proxy.is_even(100)))


File: python.info,  Node: DateTime Objects,  Next: Binary Objects,  Prev: ServerProxy Objects,  Up: xmlrpc client — XML-RPC client access

5.21.26.2 DateTime Objects
..........................

 -- Class: xmlrpc.client.DateTime

     This class may be initialized with seconds since the epoch, a time
     tuple, an ISO 8601 time/date string, or a *note datetime.datetime:
     1a0. instance.  It has the following methods, supported mainly for
     internal use by the marshalling/unmarshalling code:

      -- Method: decode (string)

          Accept a string as the instance’s new time value.

      -- Method: encode (out)

          Write the XML-RPC encoding of this *note DateTime: 2ffd. item
          to the `out' stream object.

     It also supports certain of Python’s built-in operators through
     rich comparison and *note __repr__(): 44a. methods.

A working example follows.  The server code:

     import datetime
     from xmlrpc.server import SimpleXMLRPCServer
     import xmlrpc.client

     def today():
         today = datetime.datetime.today()
         return xmlrpc.client.DateTime(today)

     server = SimpleXMLRPCServer(("localhost", 8000))
     print("Listening on port 8000...")
     server.register_function(today, "today")
     server.serve_forever()

The client code for the preceding server:

     import xmlrpc.client
     import datetime

     proxy = xmlrpc.client.ServerProxy("http://localhost:8000/")

     today = proxy.today()
     # convert the ISO8601 string to a datetime object
     converted = datetime.datetime.strptime(today.value, "%Y%m%dT%H:%M:%S")
     print("Today: %s" % converted.strftime("%d.%m.%Y, %H:%M"))


File: python.info,  Node: Binary Objects,  Next: Fault Objects,  Prev: DateTime Objects,  Up: xmlrpc client — XML-RPC client access

5.21.26.3 Binary Objects
........................

 -- Class: xmlrpc.client.Binary

     This class may be initialized from bytes data (which may include
     NULs).  The primary access to the content of a *note Binary: 2ffe.
     object is provided by an attribute:

      -- Attribute: data

          The binary data encapsulated by the *note Binary: 2ffe.
          instance.  The data is provided as a *note bytes: 172. object.

     *note Binary: 2ffe. objects have the following methods, supported
     mainly for internal use by the marshalling/unmarshalling code:

      -- Method: decode (bytes)

          Accept a base64 *note bytes: 172. object and decode it as the
          instance’s new data.

      -- Method: encode (out)

          Write the XML-RPC base 64 encoding of this binary item to the
          `out' stream object.

          The encoded data will have newlines every 76 characters as per
          RFC 2045 section 6.8(1), which was the de facto standard
          base64 specification when the XML-RPC spec was written.

     It also supports certain of Python’s built-in operators through
     *note __eq__(): 44b. and *note __ne__(): f18. methods.

Example usage of the binary objects.  We’re going to transfer an image
over XMLRPC:

     from xmlrpc.server import SimpleXMLRPCServer
     import xmlrpc.client

     def python_logo():
         with open("python_logo.jpg", "rb") as handle:
             return xmlrpc.client.Binary(handle.read())

     server = SimpleXMLRPCServer(("localhost", 8000))
     print("Listening on port 8000...")
     server.register_function(python_logo, 'python_logo')

     server.serve_forever()

The client gets the image and saves it to a file:

     import xmlrpc.client

     proxy = xmlrpc.client.ServerProxy("http://localhost:8000/")
     with open("fetched_python_logo.jpg", "wb") as handle:
         handle.write(proxy.python_logo().data)

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2045.html#section-6.8


File: python.info,  Node: Fault Objects,  Next: ProtocolError Objects,  Prev: Binary Objects,  Up: xmlrpc client — XML-RPC client access

5.21.26.4 Fault Objects
.......................

 -- Class: xmlrpc.client.Fault

     A *note Fault: 2fff. object encapsulates the content of an XML-RPC
     fault tag.  Fault objects have the following attributes:

      -- Attribute: faultCode

          A string indicating the fault type.

      -- Attribute: faultString

          A string containing a diagnostic message associated with the
          fault.

In the following example we’re going to intentionally cause a *note
Fault: 2fff. by returning a complex type object.  The server code:

     from xmlrpc.server import SimpleXMLRPCServer

     # A marshalling error is going to occur because we're returning a
     # complex number
     def add(x, y):
         return x+y+0j

     server = SimpleXMLRPCServer(("localhost", 8000))
     print("Listening on port 8000...")
     server.register_function(add, 'add')

     server.serve_forever()

The client code for the preceding server:

     import xmlrpc.client

     proxy = xmlrpc.client.ServerProxy("http://localhost:8000/")
     try:
         proxy.add(2, 5)
     except xmlrpc.client.Fault as err:
         print("A fault occurred")
         print("Fault code: %d" % err.faultCode)
         print("Fault string: %s" % err.faultString)


File: python.info,  Node: ProtocolError Objects,  Next: MultiCall Objects,  Prev: Fault Objects,  Up: xmlrpc client — XML-RPC client access

5.21.26.5 ProtocolError Objects
...............................

 -- Class: xmlrpc.client.ProtocolError

     A *note ProtocolError: 3000. object describes a protocol error in
     the underlying transport layer (such as a 404 ‘not found’ error if
     the server named by the URI does not exist).  It has the following
     attributes:

      -- Attribute: url

          The URI or URL that triggered the error.

      -- Attribute: errcode

          The error code.

      -- Attribute: errmsg

          The error message or diagnostic string.

      -- Attribute: headers

          A dict containing the headers of the HTTP/HTTPS request that
          triggered the error.

In the following example we’re going to intentionally cause a *note
ProtocolError: 3000. by providing an invalid URI:

     import xmlrpc.client

     # create a ServerProxy with a URI that doesn't respond to XMLRPC requests
     proxy = xmlrpc.client.ServerProxy("http://google.com/")

     try:
         proxy.some_method()
     except xmlrpc.client.ProtocolError as err:
         print("A protocol error occurred")
         print("URL: %s" % err.url)
         print("HTTP/HTTPS headers: %s" % err.headers)
         print("Error code: %d" % err.errcode)
         print("Error message: %s" % err.errmsg)


File: python.info,  Node: MultiCall Objects,  Next: Convenience Functions,  Prev: ProtocolError Objects,  Up: xmlrpc client — XML-RPC client access

5.21.26.6 MultiCall Objects
...........................

The *note MultiCall: 301a. object provides a way to encapsulate multiple
calls to a remote server into a single request (1).

 -- Class: xmlrpc.client.MultiCall (server)

     Create an object used to boxcar method calls.  `server' is the
     eventual target of the call.  Calls can be made to the result
     object, but they will immediately return ‘None’, and only store the
     call name and parameters in the *note MultiCall: 301a. object.
     Calling the object itself causes all stored calls to be transmitted
     as a single ‘system.multicall’ request.  The result of this call is
     a *note generator: a83.; iterating over this generator yields the
     individual results.

A usage example of this class follows.  The server code:

     from xmlrpc.server import SimpleXMLRPCServer

     def add(x, y):
         return x + y

     def subtract(x, y):
         return x - y

     def multiply(x, y):
         return x * y

     def divide(x, y):
         return x // y

     # A simple server with simple arithmetic functions
     server = SimpleXMLRPCServer(("localhost", 8000))
     print("Listening on port 8000...")
     server.register_multicall_functions()
     server.register_function(add, 'add')
     server.register_function(subtract, 'subtract')
     server.register_function(multiply, 'multiply')
     server.register_function(divide, 'divide')
     server.serve_forever()

The client code for the preceding server:

     import xmlrpc.client

     proxy = xmlrpc.client.ServerProxy("http://localhost:8000/")
     multicall = xmlrpc.client.MultiCall(proxy)
     multicall.add(7, 3)
     multicall.subtract(7, 3)
     multicall.multiply(7, 3)
     multicall.divide(7, 3)
     result = multicall()

     print("7+3=%d, 7-3=%d, 7*3=%d, 7//3=%d" % tuple(result))

   ---------- Footnotes ----------

   (1) (1) This approach has been first presented in a discussion on
xmlrpc.com
(https://web.archive.org/web/20060624230303/http://www.xmlrpc.com/discuss/msgReader$1208?mode=topic).


File: python.info,  Node: Convenience Functions,  Next: Example of Client Usage,  Prev: MultiCall Objects,  Up: xmlrpc client — XML-RPC client access

5.21.26.7 Convenience Functions
...............................

 -- Function: xmlrpc.client.dumps (params, methodname=None,
          methodresponse=None, encoding=None, allow_none=False)

     Convert `params' into an XML-RPC request.  or into a response if
     `methodresponse' is true.  `params' can be either a tuple of
     arguments or an instance of the *note Fault: 2fff. exception class.
     If `methodresponse' is true, only a single value can be returned,
     meaning that `params' must be of length 1.  `encoding', if
     supplied, is the encoding to use in the generated XML; the default
     is UTF-8.  Python’s *note None: 203. value cannot be used in
     standard XML-RPC; to allow using it via an extension, provide a
     true value for `allow_none'.

 -- Function: xmlrpc.client.loads (data, use_datetime=False,
          use_builtin_types=False)

     Convert an XML-RPC request or response into Python objects, a
     ‘(params, methodname)’.  `params' is a tuple of argument;
     `methodname' is a string, or ‘None’ if no method name is present in
     the packet.  If the XML-RPC packet represents a fault condition,
     this function will raise a *note Fault: 2fff. exception.  The
     `use_builtin_types' flag can be used to cause date/time values to
     be presented as *note datetime.datetime: 1a0. objects and binary
     data to be presented as *note bytes: 172. objects; this flag is
     false by default.

     The obsolete `use_datetime' flag is similar to `use_builtin_types'
     but it applies only to date/time values.

     Changed in version 3.3: The `use_builtin_types' flag was added.


File: python.info,  Node: Example of Client Usage,  Next: Example of Client and Server Usage,  Prev: Convenience Functions,  Up: xmlrpc client — XML-RPC client access

5.21.26.8 Example of Client Usage
.................................

     # simple test program (from the XML-RPC specification)
     from xmlrpc.client import ServerProxy, Error

     # server = ServerProxy("http://localhost:8000") # local server
     with ServerProxy("http://betty.userland.com") as proxy:

         print(proxy)

         try:
             print(proxy.examples.getStateName(41))
         except Error as v:
             print("ERROR", v)

To access an XML-RPC server through a HTTP proxy, you need to define a
custom transport.  The following example shows how:

     import http.client
     import xmlrpc.client

     class ProxiedTransport(xmlrpc.client.Transport):

         def set_proxy(self, host, port=None, headers=None):
             self.proxy = host, port
             self.proxy_headers = headers

         def make_connection(self, host):
             connection = http.client.HTTPConnection(*self.proxy)
             connection.set_tunnel(host, headers=self.proxy_headers)
             self._connection = host, connection
             return connection

     transport = ProxiedTransport()
     transport.set_proxy('proxy-server', 8080)
     server = xmlrpc.client.ServerProxy('http://betty.userland.com', transport=transport)
     print(server.examples.getStateName(41))


File: python.info,  Node: Example of Client and Server Usage,  Prev: Example of Client Usage,  Up: xmlrpc client — XML-RPC client access

5.21.26.9 Example of Client and Server Usage
............................................

See *note SimpleXMLRPCServer Example: 3021.


File: python.info,  Node: xmlrpc server — Basic XML-RPC servers,  Next: ipaddress — IPv4/IPv6 manipulation library,  Prev: xmlrpc client — XML-RPC client access,  Up: Internet Protocols and Support

5.21.27 ‘xmlrpc.server’ — Basic XML-RPC servers
-----------------------------------------------

`Source code:' Lib/xmlrpc/server.py(1)

__________________________________________________________________

The *note xmlrpc.server: 149. module provides a basic server framework
for XML-RPC servers written in Python.  Servers can either be free
standing, using *note SimpleXMLRPCServer: 3024, or embedded in a CGI
environment, using *note CGIXMLRPCRequestHandler: 3025.

     Warning: The *note xmlrpc.server: 149. module is not secure against
     maliciously constructed data.  If you need to parse untrusted or
     unauthenticated data see *note XML vulnerabilities: 2b34.

 -- Class: xmlrpc.server.SimpleXMLRPCServer (addr,
          requestHandler=SimpleXMLRPCRequestHandler, logRequests=True,
          allow_none=False, encoding=None, bind_and_activate=True,
          use_builtin_types=False)

     Create a new server instance.  This class provides methods for
     registration of functions that can be called by the XML-RPC
     protocol.  The `requestHandler' parameter should be a factory for
     request handler instances; it defaults to *note
     SimpleXMLRPCRequestHandler: 3026.  The `addr' and `requestHandler'
     parameters are passed to the *note socketserver.TCPServer: 2f50.
     constructor.  If `logRequests' is true (the default), requests will
     be logged; setting this parameter to false will turn off logging.
     The `allow_none' and `encoding' parameters are passed on to *note
     xmlrpc.client: 148. and control the XML-RPC responses that will be
     returned from the server.  The `bind_and_activate' parameter
     controls whether ‘server_bind()’ and ‘server_activate()’ are called
     immediately by the constructor; it defaults to true.  Setting it to
     false allows code to manipulate the `allow_reuse_address' class
     variable before the address is bound.  The `use_builtin_types'
     parameter is passed to the *note loads(): 301d. function and
     controls which types are processed when date/times values or binary
     data are received; it defaults to false.

     Changed in version 3.3: The `use_builtin_types' flag was added.

 -- Class: xmlrpc.server.CGIXMLRPCRequestHandler (allow_none=False,
          encoding=None, use_builtin_types=False)

     Create a new instance to handle XML-RPC requests in a CGI
     environment.  The `allow_none' and `encoding' parameters are passed
     on to *note xmlrpc.client: 148. and control the XML-RPC responses
     that will be returned from the server.  The `use_builtin_types'
     parameter is passed to the *note loads(): 301d. function and
     controls which types are processed when date/times values or binary
     data are received; it defaults to false.

     Changed in version 3.3: The `use_builtin_types' flag was added.

 -- Class: xmlrpc.server.SimpleXMLRPCRequestHandler

     Create a new request handler instance.  This request handler
     supports ‘POST’ requests and modifies logging so that the
     `logRequests' parameter to the *note SimpleXMLRPCServer: 3024.
     constructor parameter is honored.

* Menu:

* SimpleXMLRPCServer Objects::
* CGIXMLRPCRequestHandler::
* Documenting XMLRPC server::
* DocXMLRPCServer Objects::
* DocCGIXMLRPCRequestHandler::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/xmlrpc/server.py


File: python.info,  Node: SimpleXMLRPCServer Objects,  Next: CGIXMLRPCRequestHandler,  Up: xmlrpc server — Basic XML-RPC servers

5.21.27.1 SimpleXMLRPCServer Objects
....................................

The *note SimpleXMLRPCServer: 3024. class is based on *note
socketserver.TCPServer: 2f50. and provides a means of creating simple,
stand alone XML-RPC servers.

 -- Method: SimpleXMLRPCServer.register_function (function=None,
          name=None)

     Register a function that can respond to XML-RPC requests.  If
     `name' is given, it will be the method name associated with
     `function', otherwise ‘function.__name__’ will be used.  `name' is
     a string, and may contain characters not legal in Python
     identifiers, including the period character.

     This method can also be used as a decorator.  When used as a
     decorator, `name' can only be given as a keyword argument to
     register `function' under `name'.  If no `name' is given,
     ‘function.__name__’ will be used.

     Changed in version 3.7: *note register_function(): 3029. can be
     used as a decorator.

 -- Method: SimpleXMLRPCServer.register_instance (instance,
          allow_dotted_names=False)

     Register an object which is used to expose method names which have
     not been registered using *note register_function(): 3029.  If
     `instance' contains a ‘_dispatch()’ method, it is called with the
     requested method name and the parameters from the request.  Its API
     is ‘def _dispatch(self, method, params)’ (note that `params' does
     not represent a variable argument list).  If it calls an underlying
     function to perform its task, that function is called as
     ‘func(*params)’, expanding the parameter list.  The return value
     from ‘_dispatch()’ is returned to the client as the result.  If
     `instance' does not have a ‘_dispatch()’ method, it is searched for
     an attribute matching the name of the requested method.

     If the optional `allow_dotted_names' argument is true and the
     instance does not have a ‘_dispatch()’ method, then if the
     requested method name contains periods, each component of the
     method name is searched for individually, with the effect that a
     simple hierarchical search is performed.  The value found from this
     search is then called with the parameters from the request, and the
     return value is passed back to the client.

          Warning: Enabling the `allow_dotted_names' option allows
          intruders to access your module’s global variables and may
          allow intruders to execute arbitrary code on your machine.
          Only use this option on a secure, closed network.

 -- Method: SimpleXMLRPCServer.register_introspection_functions ()

     Registers the XML-RPC introspection functions ‘system.listMethods’,
     ‘system.methodHelp’ and ‘system.methodSignature’.

 -- Method: SimpleXMLRPCServer.register_multicall_functions ()

     Registers the XML-RPC multicall function system.multicall.

 -- Attribute: SimpleXMLRPCRequestHandler.rpc_paths

     An attribute value that must be a tuple listing valid path portions
     of the URL for receiving XML-RPC requests.  Requests posted to
     other paths will result in a 404 “no such page” HTTP error.  If
     this tuple is empty, all paths will be considered valid.  The
     default value is ‘('/', '/RPC2')’.

* Menu:

* SimpleXMLRPCServer Example::


File: python.info,  Node: SimpleXMLRPCServer Example,  Up: SimpleXMLRPCServer Objects

5.21.27.2 SimpleXMLRPCServer Example
....................................

Server code:

     from xmlrpc.server import SimpleXMLRPCServer
     from xmlrpc.server import SimpleXMLRPCRequestHandler

     # Restrict to a particular path.
     class RequestHandler(SimpleXMLRPCRequestHandler):
         rpc_paths = ('/RPC2',)

     # Create server
     with SimpleXMLRPCServer(('localhost', 8000),
                             requestHandler=RequestHandler) as server:
         server.register_introspection_functions()

         # Register pow() function; this will use the value of
         # pow.__name__ as the name, which is just 'pow'.
         server.register_function(pow)

         # Register a function under a different name
         def adder_function(x, y):
             return x + y
         server.register_function(adder_function, 'add')

         # Register an instance; all the methods of the instance are
         # published as XML-RPC methods (in this case, just 'mul').
         class MyFuncs:
             def mul(self, x, y):
                 return x * y

         server.register_instance(MyFuncs())

         # Run the server's main loop
         server.serve_forever()

The following client code will call the methods made available by the
preceding server:

     import xmlrpc.client

     s = xmlrpc.client.ServerProxy('http://localhost:8000')
     print(s.pow(2,3))  # Returns 2**3 = 8
     print(s.add(2,3))  # Returns 5
     print(s.mul(5,2))  # Returns 5*2 = 10

     # Print list of available methods
     print(s.system.listMethods())

‘register_function()’ can also be used as a decorator.  The previous
server example can register functions in a decorator way:

     from xmlrpc.server import SimpleXMLRPCServer
     from xmlrpc.server import SimpleXMLRPCRequestHandler

     class RequestHandler(SimpleXMLRPCRequestHandler):
         rpc_paths = ('/RPC2',)

     with SimpleXMLRPCServer(('localhost', 8000),
                             requestHandler=RequestHandler) as server:
         server.register_introspection_functions()

         # Register pow() function; this will use the value of
         # pow.__name__ as the name, which is just 'pow'.
         server.register_function(pow)

         # Register a function under a different name, using
         # register_function as a decorator. *name* can only be given
         # as a keyword argument.
         @server.register_function(name='add')
         def adder_function(x, y):
             return x + y

         # Register a function under function.__name__.
         @server.register_function
         def mul(x, y):
             return x * y

         server.serve_forever()

The following example included in the ‘Lib/xmlrpc/server.py’ module
shows a server allowing dotted names and registering a multicall
function.

     Warning: Enabling the `allow_dotted_names' option allows intruders
     to access your module’s global variables and may allow intruders to
     execute arbitrary code on your machine.  Only use this example only
     within a secure, closed network.

     import datetime

     class ExampleService:
         def getData(self):
             return '42'

         class currentTime:
             @staticmethod
             def getCurrentTime():
                 return datetime.datetime.now()

     with SimpleXMLRPCServer(("localhost", 8000)) as server:
         server.register_function(pow)
         server.register_function(lambda x,y: x+y, 'add')
         server.register_instance(ExampleService(), allow_dotted_names=True)
         server.register_multicall_functions()
         print('Serving XML-RPC on localhost port 8000')
         try:
             server.serve_forever()
         except KeyboardInterrupt:
             print("\nKeyboard interrupt received, exiting.")
             sys.exit(0)

This ExampleService demo can be invoked from the command line:

     python -m xmlrpc.server

The client that interacts with the above server is included in
‘Lib/xmlrpc/client.py’:

     server = ServerProxy("http://localhost:8000")

     try:
         print(server.currentTime.getCurrentTime())
     except Error as v:
         print("ERROR", v)

     multi = MultiCall(server)
     multi.getData()
     multi.pow(2,9)
     multi.add(1,2)
     try:
         for response in multi():
             print(response)
     except Error as v:
         print("ERROR", v)

This client which interacts with the demo XMLRPC server can be invoked
as:

     python -m xmlrpc.client


File: python.info,  Node: CGIXMLRPCRequestHandler,  Next: Documenting XMLRPC server,  Prev: SimpleXMLRPCServer Objects,  Up: xmlrpc server — Basic XML-RPC servers

5.21.27.3 CGIXMLRPCRequestHandler
.................................

The *note CGIXMLRPCRequestHandler: 3025. class can be used to handle
XML-RPC requests sent to Python CGI scripts.

 -- Method: CGIXMLRPCRequestHandler.register_function (function=None,
          name=None)

     Register a function that can respond to XML-RPC requests.  If
     `name' is given, it will be the method name associated with
     `function', otherwise ‘function.__name__’ will be used.  `name' is
     a string, and may contain characters not legal in Python
     identifiers, including the period character.

     This method can also be used as a decorator.  When used as a
     decorator, `name' can only be given as a keyword argument to
     register `function' under `name'.  If no `name' is given,
     ‘function.__name__’ will be used.

     Changed in version 3.7: *note register_function(): 3030. can be
     used as a decorator.

 -- Method: CGIXMLRPCRequestHandler.register_instance (instance)

     Register an object which is used to expose method names which have
     not been registered using *note register_function(): 3030.  If
     instance contains a ‘_dispatch()’ method, it is called with the
     requested method name and the parameters from the request; the
     return value is returned to the client as the result.  If instance
     does not have a ‘_dispatch()’ method, it is searched for an
     attribute matching the name of the requested method; if the
     requested method name contains periods, each component of the
     method name is searched for individually, with the effect that a
     simple hierarchical search is performed.  The value found from this
     search is then called with the parameters from the request, and the
     return value is passed back to the client.

 -- Method: CGIXMLRPCRequestHandler.register_introspection_functions ()

     Register the XML-RPC introspection functions ‘system.listMethods’,
     ‘system.methodHelp’ and ‘system.methodSignature’.

 -- Method: CGIXMLRPCRequestHandler.register_multicall_functions ()

     Register the XML-RPC multicall function ‘system.multicall’.

 -- Method: CGIXMLRPCRequestHandler.handle_request (request_text=None)

     Handle an XML-RPC request.  If `request_text' is given, it should
     be the POST data provided by the HTTP server, otherwise the
     contents of stdin will be used.

Example:

     class MyFuncs:
         def mul(self, x, y):
             return x * y


     handler = CGIXMLRPCRequestHandler()
     handler.register_function(pow)
     handler.register_function(lambda x,y: x+y, 'add')
     handler.register_introspection_functions()
     handler.register_instance(MyFuncs())
     handler.handle_request()


File: python.info,  Node: Documenting XMLRPC server,  Next: DocXMLRPCServer Objects,  Prev: CGIXMLRPCRequestHandler,  Up: xmlrpc server — Basic XML-RPC servers

5.21.27.4 Documenting XMLRPC server
...................................

These classes extend the above classes to serve HTML documentation in
response to HTTP GET requests.  Servers can either be free standing,
using *note DocXMLRPCServer: 10bc, or embedded in a CGI environment,
using *note DocCGIXMLRPCRequestHandler: 3036.

 -- Class: xmlrpc.server.DocXMLRPCServer (addr,
          requestHandler=DocXMLRPCRequestHandler, logRequests=True,
          allow_none=False, encoding=None, bind_and_activate=True,
          use_builtin_types=True)

     Create a new server instance.  All parameters have the same meaning
     as for *note SimpleXMLRPCServer: 3024.; `requestHandler' defaults
     to *note DocXMLRPCRequestHandler: 3037.

     Changed in version 3.3: The `use_builtin_types' flag was added.

 -- Class: xmlrpc.server.DocCGIXMLRPCRequestHandler

     Create a new instance to handle XML-RPC requests in a CGI
     environment.

 -- Class: xmlrpc.server.DocXMLRPCRequestHandler

     Create a new request handler instance.  This request handler
     supports XML-RPC POST requests, documentation GET requests, and
     modifies logging so that the `logRequests' parameter to the *note
     DocXMLRPCServer: 10bc. constructor parameter is honored.


File: python.info,  Node: DocXMLRPCServer Objects,  Next: DocCGIXMLRPCRequestHandler,  Prev: Documenting XMLRPC server,  Up: xmlrpc server — Basic XML-RPC servers

5.21.27.5 DocXMLRPCServer Objects
.................................

The *note DocXMLRPCServer: 10bc. class is derived from *note
SimpleXMLRPCServer: 3024. and provides a means of creating
self-documenting, stand alone XML-RPC servers.  HTTP POST requests are
handled as XML-RPC method calls.  HTTP GET requests are handled by
generating pydoc-style HTML documentation.  This allows a server to
provide its own web-based documentation.

 -- Method: DocXMLRPCServer.set_server_title (server_title)

     Set the title used in the generated HTML documentation.  This title
     will be used inside the HTML “title” element.

 -- Method: DocXMLRPCServer.set_server_name (server_name)

     Set the name used in the generated HTML documentation.  This name
     will appear at the top of the generated documentation inside a “h1”
     element.

 -- Method: DocXMLRPCServer.set_server_documentation
          (server_documentation)

     Set the description used in the generated HTML documentation.  This
     description will appear as a paragraph, below the server name, in
     the documentation.


File: python.info,  Node: DocCGIXMLRPCRequestHandler,  Prev: DocXMLRPCServer Objects,  Up: xmlrpc server — Basic XML-RPC servers

5.21.27.6 DocCGIXMLRPCRequestHandler
....................................

The *note DocCGIXMLRPCRequestHandler: 3036. class is derived from *note
CGIXMLRPCRequestHandler: 3025. and provides a means of creating
self-documenting, XML-RPC CGI scripts.  HTTP POST requests are handled
as XML-RPC method calls.  HTTP GET requests are handled by generating
pydoc-style HTML documentation.  This allows a server to provide its own
web-based documentation.

 -- Method: DocCGIXMLRPCRequestHandler.set_server_title (server_title)

     Set the title used in the generated HTML documentation.  This title
     will be used inside the HTML “title” element.

 -- Method: DocCGIXMLRPCRequestHandler.set_server_name (server_name)

     Set the name used in the generated HTML documentation.  This name
     will appear at the top of the generated documentation inside a “h1”
     element.

 -- Method: DocCGIXMLRPCRequestHandler.set_server_documentation
          (server_documentation)

     Set the description used in the generated HTML documentation.  This
     description will appear as a paragraph, below the server name, in
     the documentation.


File: python.info,  Node: ipaddress — IPv4/IPv6 manipulation library,  Prev: xmlrpc server — Basic XML-RPC servers,  Up: Internet Protocols and Support

5.21.28 ‘ipaddress’ — IPv4/IPv6 manipulation library
----------------------------------------------------

`Source code:' Lib/ipaddress.py(1)

__________________________________________________________________

*note ipaddress: a2. provides the capabilities to create, manipulate and
operate on IPv4 and IPv6 addresses and networks.

The functions and classes in this module make it straightforward to
handle various tasks related to IP addresses, including checking whether
or not two hosts are on the same subnet, iterating over all hosts in a
particular subnet, checking whether or not a string represents a valid
IP address or network definition, and so on.

This is the full module API reference—for an overview and introduction,
see *note An introduction to the ipaddress module: 3043.

New in version 3.3.

* Menu:

* Convenience factory functions::
* IP Addresses::
* IP Network definitions::
* Interface objects::
* Other Module Level Functions::
* Custom Exceptions::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/ipaddress.py


File: python.info,  Node: Convenience factory functions,  Next: IP Addresses,  Up: ipaddress — IPv4/IPv6 manipulation library

5.21.28.1 Convenience factory functions
.......................................

The *note ipaddress: a2. module provides factory functions to
conveniently create IP addresses, networks and interfaces:

 -- Function: ipaddress.ip_address (address)

     Return an *note IPv4Address: 3046. or *note IPv6Address: 1bb.
     object depending on the IP address passed as argument.  Either IPv4
     or IPv6 addresses may be supplied; integers less than ‘2**32’ will
     be considered to be IPv4 by default.  A *note ValueError: 16d. is
     raised if `address' does not represent a valid IPv4 or IPv6
     address.

          >>> ipaddress.ip_address('192.168.0.1')
          IPv4Address('192.168.0.1')
          >>> ipaddress.ip_address('2001:db8::')
          IPv6Address('2001:db8::')

 -- Function: ipaddress.ip_network (address, strict=True)

     Return an *note IPv4Network: 4a7. or *note IPv6Network: 4a6. object
     depending on the IP address passed as argument.  `address' is a
     string or integer representing the IP network.  Either IPv4 or IPv6
     networks may be supplied; integers less than ‘2**32’ will be
     considered to be IPv4 by default.  `strict' is passed to *note
     IPv4Network: 4a7. or *note IPv6Network: 4a6. constructor.  A *note
     ValueError: 16d. is raised if `address' does not represent a valid
     IPv4 or IPv6 address, or if the network has host bits set.

          >>> ipaddress.ip_network('192.168.0.0/28')
          IPv4Network('192.168.0.0/28')

 -- Function: ipaddress.ip_interface (address)

     Return an *note IPv4Interface: 3049. or *note IPv6Interface: 304a.
     object depending on the IP address passed as argument.  `address'
     is a string or integer representing the IP address.  Either IPv4 or
     IPv6 addresses may be supplied; integers less than ‘2**32’ will be
     considered to be IPv4 by default.  A *note ValueError: 16d. is
     raised if `address' does not represent a valid IPv4 or IPv6
     address.

One downside of these convenience functions is that the need to handle
both IPv4 and IPv6 formats means that error messages provide minimal
information on the precise error, as the functions don’t know whether
the IPv4 or IPv6 format was intended.  More detailed error reporting can
be obtained by calling the appropriate version specific class
constructors directly.


File: python.info,  Node: IP Addresses,  Next: IP Network definitions,  Prev: Convenience factory functions,  Up: ipaddress — IPv4/IPv6 manipulation library

5.21.28.2 IP Addresses
......................

* Menu:

* Address objects::
* Conversion to Strings and Integers::
* Operators: Operators<3>.


File: python.info,  Node: Address objects,  Next: Conversion to Strings and Integers,  Up: IP Addresses

5.21.28.3 Address objects
.........................

The *note IPv4Address: 3046. and *note IPv6Address: 1bb. objects share a
lot of common attributes.  Some attributes that are only meaningful for
IPv6 addresses are also implemented by *note IPv4Address: 3046. objects,
in order to make it easier to write code that handles both IP versions
correctly.  Address objects are *note hashable: 276, so they can be used
as keys in dictionaries.

 -- Class: ipaddress.IPv4Address (address)

     Construct an IPv4 address.  An *note AddressValueError: 304d. is
     raised if `address' is not a valid IPv4 address.

     The following constitutes a valid IPv4 address:

       1. A string in decimal-dot notation, consisting of four decimal
          integers in the inclusive range 0–255, separated by dots (e.g.
          ‘192.168.0.1’).  Each integer represents an octet (byte) in
          the address.  Leading zeroes are not tolerated to prevent
          confusion with octal notation.

       2. An integer that fits into 32 bits.

       3. An integer packed into a *note bytes: 172. object of length 4
          (most significant octet first).

          >>> ipaddress.IPv4Address('192.168.0.1')
          IPv4Address('192.168.0.1')
          >>> ipaddress.IPv4Address(3232235521)
          IPv4Address('192.168.0.1')
          >>> ipaddress.IPv4Address(b'\xC0\xA8\x00\x01')
          IPv4Address('192.168.0.1')

     Changed in version 3.8: Leading zeros are tolerated, even in
     ambiguous cases that look like octal notation.

     Changed in version 3.10: Leading zeros are no longer tolerated and
     are treated as an error.  IPv4 address strings are now parsed as
     strict as glibc *note inet_pton(): 237.

     Changed in version 3.9.5: The above change was also included in
     Python 3.9 starting with version 3.9.5.

     Changed in version 3.8.12: The above change was also included in
     Python 3.8 starting with version 3.8.12.

      -- Attribute: version

          The appropriate version number: ‘4’ for IPv4, ‘6’ for IPv6.

      -- Attribute: max_prefixlen

          The total number of bits in the address representation for
          this version: ‘32’ for IPv4, ‘128’ for IPv6.

          The prefix defines the number of leading bits in an address
          that are compared to determine whether or not an address is
          part of a network.

      -- Attribute: compressed

      -- Attribute: exploded

          The string representation in dotted decimal notation.  Leading
          zeroes are never included in the representation.

          As IPv4 does not define a shorthand notation for addresses
          with octets set to zero, these two attributes are always the
          same as ‘str(addr)’ for IPv4 addresses.  Exposing these
          attributes makes it easier to write display code that can
          handle both IPv4 and IPv6 addresses.

      -- Attribute: packed

          The binary representation of this address - a *note bytes:
          172. object of the appropriate length (most significant octet
          first).  This is 4 bytes for IPv4 and 16 bytes for IPv6.

      -- Attribute: reverse_pointer

          The name of the reverse DNS PTR record for the IP address,
          e.g.:

               >>> ipaddress.ip_address("127.0.0.1").reverse_pointer
               '1.0.0.127.in-addr.arpa'
               >>> ipaddress.ip_address("2001:db8::1").reverse_pointer
               '1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa'

          This is the name that could be used for performing a PTR
          lookup, not the resolved hostname itself.

          New in version 3.5.

      -- Attribute: is_multicast

          ‘True’ if the address is reserved for multicast use.  See RFC
          3171(1) (for IPv4) or RFC 2373(2) (for IPv6).

      -- Attribute: is_private

          ‘True’ if the address is allocated for private networks.  See
          iana-ipv4-special-registry(3) (for IPv4) or
          iana-ipv6-special-registry(4) (for IPv6).

      -- Attribute: is_global

          ‘True’ if the address is allocated for public networks.  See
          iana-ipv4-special-registry(5) (for IPv4) or
          iana-ipv6-special-registry(6) (for IPv6).

          New in version 3.4.

      -- Attribute: is_unspecified

          ‘True’ if the address is unspecified.  See RFC 5735(7) (for
          IPv4) or RFC 2373(8) (for IPv6).

      -- Attribute: is_reserved

          ‘True’ if the address is otherwise IETF reserved.

      -- Attribute: is_loopback

          ‘True’ if this is a loopback address.  See RFC 3330(9) (for
          IPv4) or RFC 2373(10) (for IPv6).

      -- Attribute: is_link_local

          ‘True’ if the address is reserved for link-local usage.  See
          RFC 3927(11).

 -- Method: IPv4Address.__format__ (fmt)

     Returns a string representation of the IP address, controlled by an
     explicit format string.  `fmt' can be one of the following: ‘'s'’,
     the default option, equivalent to *note str(): 205, ‘'b'’ for a
     zero-padded binary string, ‘'X'’ or ‘'x'’ for an uppercase or
     lowercase hexadecimal representation, or ‘'n'’, which is equivalent
     to ‘'b'’ for IPv4 addresses and ‘'x'’ for IPv6.  For binary and
     hexadecimal representations, the form specifier ‘'#'’ and the
     grouping option ‘'_'’ are available.  ‘__format__’ is used by
     ‘format’, ‘str.format’ and f-strings.

          >>> format(ipaddress.IPv4Address('192.168.0.1'))
          '192.168.0.1'
          >>> '{:#b}'.format(ipaddress.IPv4Address('192.168.0.1'))
          '0b11000000101010000000000000000001'
          >>> f'{ipaddress.IPv6Address("2001:db8::1000"):s}'
          '2001:db8::1000'
          >>> format(ipaddress.IPv6Address('2001:db8::1000'), '_X')
          '2001_0DB8_0000_0000_0000_0000_0000_1000'
          >>> '{:#_n}'.format(ipaddress.IPv6Address('2001:db8::1000'))
          '0x2001_0db8_0000_0000_0000_0000_0000_1000'

     New in version 3.9.

 -- Class: ipaddress.IPv6Address (address)

     Construct an IPv6 address.  An *note AddressValueError: 304d. is
     raised if `address' is not a valid IPv6 address.

     The following constitutes a valid IPv6 address:

       1. A string consisting of eight groups of four hexadecimal
          digits, each group representing 16 bits.  The groups are
          separated by colons.  This describes an `exploded' (longhand)
          notation.  The string can also be `compressed' (shorthand
          notation) by various means.  See RFC 4291(12) for details.
          For example, ‘"0000:0000:0000:0000:0000:0abc:0007:0def"’ can
          be compressed to ‘"::abc:7:def"’.

          Optionally, the string may also have a scope zone ID,
          expressed with a suffix ‘%scope_id’.  If present, the scope ID
          must be non-empty, and may not contain ‘%’.  See RFC 4007(13)
          for details.  For example, ‘fe80::1234%1’ might identify
          address ‘fe80::1234’ on the first link of the node.

       2. An integer that fits into 128 bits.

       3. An integer packed into a *note bytes: 172. object of length
          16, big-endian.

          >>> ipaddress.IPv6Address('2001:db8::1000')
          IPv6Address('2001:db8::1000')
          >>> ipaddress.IPv6Address('ff02::5678%1')
          IPv6Address('ff02::5678%1')

      -- Attribute: compressed

     The short form of the address representation, with leading zeroes
     in groups omitted and the longest sequence of groups consisting
     entirely of zeroes collapsed to a single empty group.

     This is also the value returned by ‘str(addr)’ for IPv6 addresses.

      -- Attribute: exploded

     The long form of the address representation, with all leading
     zeroes and groups consisting entirely of zeroes included.

     For the following attributes and methods, see the corresponding
     documentation of the *note IPv4Address: 3046. class:

      -- Attribute: packed

      -- Attribute: reverse_pointer

      -- Attribute: version

      -- Attribute: max_prefixlen

      -- Attribute: is_multicast

      -- Attribute: is_private

      -- Attribute: is_global

      -- Attribute: is_unspecified

      -- Attribute: is_reserved

      -- Attribute: is_loopback

      -- Attribute: is_link_local

          New in version 3.4: is_global

      -- Attribute: is_site_local

          ‘True’ if the address is reserved for site-local usage.  Note
          that the site-local address space has been deprecated by RFC
          3879(14).  Use *note is_private: 3055. to test if this address
          is in the space of unique local addresses as defined by RFC
          4193(15).

      -- Attribute: ipv4_mapped

          For addresses that appear to be IPv4 mapped addresses
          (starting with ‘::FFFF/96’), this property will report the
          embedded IPv4 address.  For any other address, this property
          will be ‘None’.

      -- Attribute: scope_id

          For scoped addresses as defined by RFC 4007(16), this property
          identifies the particular zone of the address’s scope that the
          address belongs to, as a string.  When no scope zone is
          specified, this property will be ‘None’.

      -- Attribute: sixtofour

          For addresses that appear to be 6to4 addresses (starting with
          ‘2002::/16’) as defined by RFC 3056(17), this property will
          report the embedded IPv4 address.  For any other address, this
          property will be ‘None’.

      -- Attribute: teredo

          For addresses that appear to be Teredo addresses (starting
          with ‘2001::/32’) as defined by RFC 4380(18), this property
          will report the embedded ‘(server, client)’ IP address pair.
          For any other address, this property will be ‘None’.

 -- Method: IPv6Address.__format__ (fmt)

     Refer to the corresponding method documentation in *note
     IPv4Address: 3046.

     New in version 3.9.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3171.html

   (2) https://tools.ietf.org/html/rfc2373.html

   (3) 
https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml

   (4) 
https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml

   (5) 
https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml

   (6) 
https://www.iana.org/assignments/iana-ipv6-special-registry/iana-ipv6-special-registry.xhtml

   (7) https://tools.ietf.org/html/rfc5735.html

   (8) https://tools.ietf.org/html/rfc2373.html

   (9) https://tools.ietf.org/html/rfc3330.html

   (10) https://tools.ietf.org/html/rfc2373.html

   (11) https://tools.ietf.org/html/rfc3927.html

   (12) https://tools.ietf.org/html/rfc4291.html

   (13) https://tools.ietf.org/html/rfc4007.html

   (14) https://tools.ietf.org/html/rfc3879.html

   (15) https://tools.ietf.org/html/rfc4193.html

   (16) https://tools.ietf.org/html/rfc4007.html

   (17) https://tools.ietf.org/html/rfc3056.html

   (18) https://tools.ietf.org/html/rfc4380.html


File: python.info,  Node: Conversion to Strings and Integers,  Next: Operators<3>,  Prev: Address objects,  Up: IP Addresses

5.21.28.4 Conversion to Strings and Integers
............................................

To interoperate with networking interfaces such as the socket module,
addresses must be converted to strings or integers.  This is handled
using the *note str(): 205. and *note int(): 204. builtin functions:

     >>> str(ipaddress.IPv4Address('192.168.0.1'))
     '192.168.0.1'
     >>> int(ipaddress.IPv4Address('192.168.0.1'))
     3232235521
     >>> str(ipaddress.IPv6Address('::1'))
     '::1'
     >>> int(ipaddress.IPv6Address('::1'))
     1

Note that IPv6 scoped addresses are converted to integers without scope
zone ID.


File: python.info,  Node: Operators<3>,  Prev: Conversion to Strings and Integers,  Up: IP Addresses

5.21.28.5 Operators
...................

Address objects support some operators.  Unless stated otherwise,
operators can only be applied between compatible objects (i.e.  IPv4
with IPv4, IPv6 with IPv6).

* Menu:

* Comparison operators::
* Arithmetic operators::


File: python.info,  Node: Comparison operators,  Next: Arithmetic operators,  Up: Operators<3>

5.21.28.6 Comparison operators
..............................

Address objects can be compared with the usual set of comparison
operators.  Same IPv6 addresses with different scope zone IDs are not
equal.  Some examples:

     >>> IPv4Address('127.0.0.2') > IPv4Address('127.0.0.1')
     True
     >>> IPv4Address('127.0.0.2') == IPv4Address('127.0.0.1')
     False
     >>> IPv4Address('127.0.0.2') != IPv4Address('127.0.0.1')
     True
     >>> IPv6Address('fe80::1234') == IPv6Address('fe80::1234%1')
     False
     >>> IPv6Address('fe80::1234%1') != IPv6Address('fe80::1234%2')
     True


File: python.info,  Node: Arithmetic operators,  Prev: Comparison operators,  Up: Operators<3>

5.21.28.7 Arithmetic operators
..............................

Integers can be added to or subtracted from address objects.  Some
examples:

     >>> IPv4Address('127.0.0.2') + 3
     IPv4Address('127.0.0.5')
     >>> IPv4Address('127.0.0.2') - 3
     IPv4Address('126.255.255.255')
     >>> IPv4Address('255.255.255.255') + 1
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ipaddress.AddressValueError: 4294967296 (>= 2**32) is not permitted as an IPv4 address


File: python.info,  Node: IP Network definitions,  Next: Interface objects,  Prev: IP Addresses,  Up: ipaddress — IPv4/IPv6 manipulation library

5.21.28.8 IP Network definitions
................................

The *note IPv4Network: 4a7. and *note IPv6Network: 4a6. objects provide
a mechanism for defining and inspecting IP network definitions.  A
network definition consists of a `mask' and a `network address', and as
such defines a range of IP addresses that equal the network address when
masked (binary AND) with the mask.  For example, a network definition
with the mask ‘255.255.255.0’ and the network address ‘192.168.1.0’
consists of IP addresses in the inclusive range ‘192.168.1.0’ to
‘192.168.1.255’.

* Menu:

* Prefix, net mask and host mask: Prefix net mask and host mask.
* Network objects::
* Operators: Operators<4>.


File: python.info,  Node: Prefix net mask and host mask,  Next: Network objects,  Up: IP Network definitions

5.21.28.9 Prefix, net mask and host mask
........................................

There are several equivalent ways to specify IP network masks.  A
`prefix' ‘/<nbits>’ is a notation that denotes how many high-order bits
are set in the network mask.  A `net mask' is an IP address with some
number of high-order bits set.  Thus the prefix ‘/24’ is equivalent to
the net mask ‘255.255.255.0’ in IPv4, or ‘ffff:ff00::’ in IPv6.  In
addition, a `host mask' is the logical inverse of a `net mask', and is
sometimes used (for example in Cisco access control lists) to denote a
network mask.  The host mask equivalent to ‘/24’ in IPv4 is ‘0.0.0.255’.


File: python.info,  Node: Network objects,  Next: Operators<4>,  Prev: Prefix net mask and host mask,  Up: IP Network definitions

5.21.28.10 Network objects
..........................

All attributes implemented by address objects are implemented by network
objects as well.  In addition, network objects implement additional
attributes.  All of these are common between *note IPv4Network: 4a7. and
*note IPv6Network: 4a6, so to avoid duplication they are only documented
for *note IPv4Network: 4a7.  Network objects are *note hashable: 276, so
they can be used as keys in dictionaries.

 -- Class: ipaddress.IPv4Network (address, strict=True)

     Construct an IPv4 network definition.  `address' can be one of the
     following:

       1. A string consisting of an IP address and an optional mask,
          separated by a slash (‘/’).  The IP address is the network
          address, and the mask can be either a single number, which
          means it’s a `prefix', or a string representation of an IPv4
          address.  If it’s the latter, the mask is interpreted as a
          `net mask' if it starts with a non-zero field, or as a `host
          mask' if it starts with a zero field, with the single
          exception of an all-zero mask which is treated as a `net
          mask'.  If no mask is provided, it’s considered to be ‘/32’.

          For example, the following `address' specifications are
          equivalent: ‘192.168.1.0/24’, ‘192.168.1.0/255.255.255.0’ and
          ‘192.168.1.0/0.0.0.255’.

       2. An integer that fits into 32 bits.  This is equivalent to a
          single-address network, with the network address being
          `address' and the mask being ‘/32’.

       3. An integer packed into a *note bytes: 172. object of length 4,
          big-endian.  The interpretation is similar to an integer
          `address'.

       4. A two-tuple of an address description and a netmask, where the
          address description is either a string, a 32-bits integer, a
          4-bytes packed integer, or an existing IPv4Address object; and
          the netmask is either an integer representing the prefix
          length (e.g.  ‘24’) or a string representing the prefix mask
          (e.g.  ‘255.255.255.0’).

     An *note AddressValueError: 304d. is raised if `address' is not a
     valid IPv4 address.  A *note NetmaskValueError: 3074. is raised if
     the mask is not valid for an IPv4 address.

     If `strict' is ‘True’ and host bits are set in the supplied
     address, then *note ValueError: 16d. is raised.  Otherwise, the
     host bits are masked out to determine the appropriate network
     address.

     Unless stated otherwise, all network methods accepting other
     network/address objects will raise *note TypeError: 1fe. if the
     argument’s IP version is incompatible to ‘self’.

     Changed in version 3.5: Added the two-tuple form for the `address'
     constructor parameter.

      -- Attribute: version

      -- Attribute: max_prefixlen

          Refer to the corresponding attribute documentation in *note
          IPv4Address: 3046.

      -- Attribute: is_multicast

      -- Attribute: is_private

      -- Attribute: is_unspecified

      -- Attribute: is_reserved

      -- Attribute: is_loopback

      -- Attribute: is_link_local

          These attributes are true for the network as a whole if they
          are true for both the network address and the broadcast
          address.

      -- Attribute: network_address

          The network address for the network.  The network address and
          the prefix length together uniquely define a network.

      -- Attribute: broadcast_address

          The broadcast address for the network.  Packets sent to the
          broadcast address should be received by every host on the
          network.

      -- Attribute: hostmask

          The host mask, as an *note IPv4Address: 3046. object.

      -- Attribute: netmask

          The net mask, as an *note IPv4Address: 3046. object.

      -- Attribute: with_prefixlen

      -- Attribute: compressed

      -- Attribute: exploded

          A string representation of the network, with the mask in
          prefix notation.

          ‘with_prefixlen’ and ‘compressed’ are always the same as
          ‘str(network)’.  ‘exploded’ uses the exploded form the network
          address.

      -- Attribute: with_netmask

          A string representation of the network, with the mask in net
          mask notation.

      -- Attribute: with_hostmask

          A string representation of the network, with the mask in host
          mask notation.

      -- Attribute: num_addresses

          The total number of addresses in the network.

      -- Attribute: prefixlen

          Length of the network prefix, in bits.

      -- Method: hosts ()

          Returns an iterator over the usable hosts in the network.  The
          usable hosts are all the IP addresses that belong to the
          network, except the network address itself and the network
          broadcast address.  For networks with a mask length of 31, the
          network address and network broadcast address are also
          included in the result.  Networks with a mask of 32 will
          return a list containing the single host address.

               >>> list(ip_network('192.0.2.0/29').hosts())
               [IPv4Address('192.0.2.1'), IPv4Address('192.0.2.2'),
                IPv4Address('192.0.2.3'), IPv4Address('192.0.2.4'),
                IPv4Address('192.0.2.5'), IPv4Address('192.0.2.6')]
               >>> list(ip_network('192.0.2.0/31').hosts())
               [IPv4Address('192.0.2.0'), IPv4Address('192.0.2.1')]
               >>> list(ip_network('192.0.2.1/32').hosts())
               [IPv4Address('192.0.2.1')]

      -- Method: overlaps (other)

          ‘True’ if this network is partly or wholly contained in
          `other' or `other' is wholly contained in this network.

      -- Method: address_exclude (network)

          Computes the network definitions resulting from removing the
          given `network' from this one.  Returns an iterator of network
          objects.  Raises *note ValueError: 16d. if `network' is not
          completely contained in this network.

               >>> n1 = ip_network('192.0.2.0/28')
               >>> n2 = ip_network('192.0.2.1/32')
               >>> list(n1.address_exclude(n2))
               [IPv4Network('192.0.2.8/29'), IPv4Network('192.0.2.4/30'),
                IPv4Network('192.0.2.2/31'), IPv4Network('192.0.2.0/32')]

      -- Method: subnets (prefixlen_diff=1, new_prefix=None)

          The subnets that join to make the current network definition,
          depending on the argument values.  `prefixlen_diff' is the
          amount our prefix length should be increased by.  `new_prefix'
          is the desired new prefix of the subnets; it must be larger
          than our prefix.  One and only one of `prefixlen_diff' and
          `new_prefix' must be set.  Returns an iterator of network
          objects.

               >>> list(ip_network('192.0.2.0/24').subnets())
               [IPv4Network('192.0.2.0/25'), IPv4Network('192.0.2.128/25')]
               >>> list(ip_network('192.0.2.0/24').subnets(prefixlen_diff=2))
               [IPv4Network('192.0.2.0/26'), IPv4Network('192.0.2.64/26'),
                IPv4Network('192.0.2.128/26'), IPv4Network('192.0.2.192/26')]
               >>> list(ip_network('192.0.2.0/24').subnets(new_prefix=26))
               [IPv4Network('192.0.2.0/26'), IPv4Network('192.0.2.64/26'),
                IPv4Network('192.0.2.128/26'), IPv4Network('192.0.2.192/26')]
               >>> list(ip_network('192.0.2.0/24').subnets(new_prefix=23))
               Traceback (most recent call last):
                 File "<stdin>", line 1, in <module>
                   raise ValueError('new prefix must be longer')
               ValueError: new prefix must be longer
               >>> list(ip_network('192.0.2.0/24').subnets(new_prefix=25))
               [IPv4Network('192.0.2.0/25'), IPv4Network('192.0.2.128/25')]

      -- Method: supernet (prefixlen_diff=1, new_prefix=None)

          The supernet containing this network definition, depending on
          the argument values.  `prefixlen_diff' is the amount our
          prefix length should be decreased by.  `new_prefix' is the
          desired new prefix of the supernet; it must be smaller than
          our prefix.  One and only one of `prefixlen_diff' and
          `new_prefix' must be set.  Returns a single network object.

               >>> ip_network('192.0.2.0/24').supernet()
               IPv4Network('192.0.2.0/23')
               >>> ip_network('192.0.2.0/24').supernet(prefixlen_diff=2)
               IPv4Network('192.0.0.0/22')
               >>> ip_network('192.0.2.0/24').supernet(new_prefix=20)
               IPv4Network('192.0.0.0/20')

      -- Method: subnet_of (other)

          Return ‘True’ if this network is a subnet of `other'.

               >>> a = ip_network('192.168.1.0/24')
               >>> b = ip_network('192.168.1.128/30')
               >>> b.subnet_of(a)
               True

          New in version 3.7.

      -- Method: supernet_of (other)

          Return ‘True’ if this network is a supernet of `other'.

               >>> a = ip_network('192.168.1.0/24')
               >>> b = ip_network('192.168.1.128/30')
               >>> a.supernet_of(b)
               True

          New in version 3.7.

      -- Method: compare_networks (other)

          Compare this network to `other'.  In this comparison only the
          network addresses are considered; host bits aren’t.  Returns
          either ‘-1’, ‘0’ or ‘1’.

               >>> ip_network('192.0.2.1/32').compare_networks(ip_network('192.0.2.2/32'))
               -1
               >>> ip_network('192.0.2.1/32').compare_networks(ip_network('192.0.2.0/32'))
               1
               >>> ip_network('192.0.2.1/32').compare_networks(ip_network('192.0.2.1/32'))
               0

          Deprecated since version 3.7: It uses the same ordering and
          comparison algorithm as “<”, “==”, and “>”

 -- Class: ipaddress.IPv6Network (address, strict=True)

     Construct an IPv6 network definition.  `address' can be one of the
     following:

       1. A string consisting of an IP address and an optional prefix
          length, separated by a slash (‘/’).  The IP address is the
          network address, and the prefix length must be a single
          number, the `prefix'.  If no prefix length is provided, it’s
          considered to be ‘/128’.

          Note that currently expanded netmasks are not supported.  That
          means ‘2001:db00::0/24’ is a valid argument while
          ‘2001:db00::0/ffff:ff00::’ is not.

       2. An integer that fits into 128 bits.  This is equivalent to a
          single-address network, with the network address being
          `address' and the mask being ‘/128’.

       3. An integer packed into a *note bytes: 172. object of length
          16, big-endian.  The interpretation is similar to an integer
          `address'.

       4. A two-tuple of an address description and a netmask, where the
          address description is either a string, a 128-bits integer, a
          16-bytes packed integer, or an existing IPv6Address object;
          and the netmask is an integer representing the prefix length.

     An *note AddressValueError: 304d. is raised if `address' is not a
     valid IPv6 address.  A *note NetmaskValueError: 3074. is raised if
     the mask is not valid for an IPv6 address.

     If `strict' is ‘True’ and host bits are set in the supplied
     address, then *note ValueError: 16d. is raised.  Otherwise, the
     host bits are masked out to determine the appropriate network
     address.

     Changed in version 3.5: Added the two-tuple form for the `address'
     constructor parameter.

      -- Attribute: version

      -- Attribute: max_prefixlen

      -- Attribute: is_multicast

      -- Attribute: is_private

      -- Attribute: is_unspecified

      -- Attribute: is_reserved

      -- Attribute: is_loopback

      -- Attribute: is_link_local

      -- Attribute: network_address

      -- Attribute: broadcast_address

      -- Attribute: hostmask

      -- Attribute: netmask

      -- Attribute: with_prefixlen

      -- Attribute: compressed

      -- Attribute: exploded

      -- Attribute: with_netmask

      -- Attribute: with_hostmask

      -- Attribute: num_addresses

      -- Attribute: prefixlen

      -- Method: hosts ()

          Returns an iterator over the usable hosts in the network.  The
          usable hosts are all the IP addresses that belong to the
          network, except the Subnet-Router anycast address.  For
          networks with a mask length of 127, the Subnet-Router anycast
          address is also included in the result.  Networks with a mask
          of 128 will return a list containing the single host address.

      -- Method: overlaps (other)

      -- Method: address_exclude (network)

      -- Method: subnets (prefixlen_diff=1, new_prefix=None)

      -- Method: supernet (prefixlen_diff=1, new_prefix=None)

      -- Method: subnet_of (other)

      -- Method: supernet_of (other)

      -- Method: compare_networks (other)

          Refer to the corresponding attribute documentation in *note
          IPv4Network: 4a7.

      -- Attribute: is_site_local

          These attribute is true for the network as a whole if it is
          true for both the network address and the broadcast address.


File: python.info,  Node: Operators<4>,  Prev: Network objects,  Up: IP Network definitions

5.21.28.11 Operators
....................

Network objects support some operators.  Unless stated otherwise,
operators can only be applied between compatible objects (i.e.  IPv4
with IPv4, IPv6 with IPv6).

* Menu:

* Logical operators::
* Iteration: Iteration<2>.
* Networks as containers of addresses::


File: python.info,  Node: Logical operators,  Next: Iteration<2>,  Up: Operators<4>

5.21.28.12 Logical operators
............................

Network objects can be compared with the usual set of logical operators.
Network objects are ordered first by network address, then by net mask.


File: python.info,  Node: Iteration<2>,  Next: Networks as containers of addresses,  Prev: Logical operators,  Up: Operators<4>

5.21.28.13 Iteration
....................

Network objects can be iterated to list all the addresses belonging to
the network.  For iteration, `all' hosts are returned, including
unusable hosts (for usable hosts, use the *note hosts(): 3088. method).
An example:

     >>> for addr in IPv4Network('192.0.2.0/28'):
     ...     addr
     ...
     IPv4Address('192.0.2.0')
     IPv4Address('192.0.2.1')
     IPv4Address('192.0.2.2')
     IPv4Address('192.0.2.3')
     IPv4Address('192.0.2.4')
     IPv4Address('192.0.2.5')
     IPv4Address('192.0.2.6')
     IPv4Address('192.0.2.7')
     IPv4Address('192.0.2.8')
     IPv4Address('192.0.2.9')
     IPv4Address('192.0.2.10')
     IPv4Address('192.0.2.11')
     IPv4Address('192.0.2.12')
     IPv4Address('192.0.2.13')
     IPv4Address('192.0.2.14')
     IPv4Address('192.0.2.15')


File: python.info,  Node: Networks as containers of addresses,  Prev: Iteration<2>,  Up: Operators<4>

5.21.28.14 Networks as containers of addresses
..............................................

Network objects can act as containers of addresses.  Some examples:

     >>> IPv4Network('192.0.2.0/28')[0]
     IPv4Address('192.0.2.0')
     >>> IPv4Network('192.0.2.0/28')[15]
     IPv4Address('192.0.2.15')
     >>> IPv4Address('192.0.2.6') in IPv4Network('192.0.2.0/28')
     True
     >>> IPv4Address('192.0.3.6') in IPv4Network('192.0.2.0/28')
     False


File: python.info,  Node: Interface objects,  Next: Other Module Level Functions,  Prev: IP Network definitions,  Up: ipaddress — IPv4/IPv6 manipulation library

5.21.28.15 Interface objects
............................

Interface objects are *note hashable: 276, so they can be used as keys
in dictionaries.

 -- Class: ipaddress.IPv4Interface (address)

     Construct an IPv4 interface.  The meaning of `address' is as in the
     constructor of *note IPv4Network: 4a7, except that arbitrary host
     addresses are always accepted.

     *note IPv4Interface: 3049. is a subclass of *note IPv4Address:
     3046, so it inherits all the attributes from that class.  In
     addition, the following attributes are available:

      -- Attribute: ip

          The address (*note IPv4Address: 3046.) without network
          information.

               >>> interface = IPv4Interface('192.0.2.5/24')
               >>> interface.ip
               IPv4Address('192.0.2.5')

      -- Attribute: network

          The network (*note IPv4Network: 4a7.) this interface belongs
          to.

               >>> interface = IPv4Interface('192.0.2.5/24')
               >>> interface.network
               IPv4Network('192.0.2.0/24')

      -- Attribute: with_prefixlen

          A string representation of the interface with the mask in
          prefix notation.

               >>> interface = IPv4Interface('192.0.2.5/24')
               >>> interface.with_prefixlen
               '192.0.2.5/24'

      -- Attribute: with_netmask

          A string representation of the interface with the network as a
          net mask.

               >>> interface = IPv4Interface('192.0.2.5/24')
               >>> interface.with_netmask
               '192.0.2.5/255.255.255.0'

      -- Attribute: with_hostmask

          A string representation of the interface with the network as a
          host mask.

               >>> interface = IPv4Interface('192.0.2.5/24')
               >>> interface.with_hostmask
               '192.0.2.5/0.0.0.255'

 -- Class: ipaddress.IPv6Interface (address)

     Construct an IPv6 interface.  The meaning of `address' is as in the
     constructor of *note IPv6Network: 4a6, except that arbitrary host
     addresses are always accepted.

     *note IPv6Interface: 304a. is a subclass of *note IPv6Address: 1bb,
     so it inherits all the attributes from that class.  In addition,
     the following attributes are available:

      -- Attribute: ip

      -- Attribute: network

      -- Attribute: with_prefixlen

      -- Attribute: with_netmask

      -- Attribute: with_hostmask

          Refer to the corresponding attribute documentation in *note
          IPv4Interface: 3049.

* Menu:

* Operators: Operators<5>.


File: python.info,  Node: Operators<5>,  Up: Interface objects

5.21.28.16 Operators
....................

Interface objects support some operators.  Unless stated otherwise,
operators can only be applied between compatible objects (i.e.  IPv4
with IPv4, IPv6 with IPv6).

* Menu:

* Logical operators: Logical operators<2>.


File: python.info,  Node: Logical operators<2>,  Up: Operators<5>

5.21.28.17 Logical operators
............................

Interface objects can be compared with the usual set of logical
operators.

For equality comparison (‘==’ and ‘!=’), both the IP address and network
must be the same for the objects to be equal.  An interface will not
compare equal to any address or network object.

For ordering (‘<’, ‘>’, etc) the rules are different.  Interface and
address objects with the same IP version can be compared, and the
address objects will always sort before the interface objects.  Two
interface objects are first compared by their networks and, if those are
the same, then by their IP addresses.


File: python.info,  Node: Other Module Level Functions,  Next: Custom Exceptions,  Prev: Interface objects,  Up: ipaddress — IPv4/IPv6 manipulation library

5.21.28.18 Other Module Level Functions
.......................................

The module also provides the following module level functions:

 -- Function: ipaddress.v4_int_to_packed (address)

     Represent an address as 4 packed bytes in network (big-endian)
     order.  `address' is an integer representation of an IPv4 IP
     address.  A *note ValueError: 16d. is raised if the integer is
     negative or too large to be an IPv4 IP address.

          >>> ipaddress.ip_address(3221225985)
          IPv4Address('192.0.2.1')
          >>> ipaddress.v4_int_to_packed(3221225985)
          b'\xc0\x00\x02\x01'

 -- Function: ipaddress.v6_int_to_packed (address)

     Represent an address as 16 packed bytes in network (big-endian)
     order.  `address' is an integer representation of an IPv6 IP
     address.  A *note ValueError: 16d. is raised if the integer is
     negative or too large to be an IPv6 IP address.

 -- Function: ipaddress.summarize_address_range (first, last)

     Return an iterator of the summarized network range given the first
     and last IP addresses.  `first' is the first *note IPv4Address:
     3046. or *note IPv6Address: 1bb. in the range and `last' is the
     last *note IPv4Address: 3046. or *note IPv6Address: 1bb. in the
     range.  A *note TypeError: 1fe. is raised if `first' or `last' are
     not IP addresses or are not of the same version.  A *note
     ValueError: 16d. is raised if `last' is not greater than `first' or
     if `first' address version is not 4 or 6.

          >>> [ipaddr for ipaddr in ipaddress.summarize_address_range(
          ...    ipaddress.IPv4Address('192.0.2.0'),
          ...    ipaddress.IPv4Address('192.0.2.130'))]
          [IPv4Network('192.0.2.0/25'), IPv4Network('192.0.2.128/31'), IPv4Network('192.0.2.130/32')]

 -- Function: ipaddress.collapse_addresses (addresses)

     Return an iterator of the collapsed *note IPv4Network: 4a7. or
     *note IPv6Network: 4a6. objects.  `addresses' is an iterator of
     *note IPv4Network: 4a7. or *note IPv6Network: 4a6. objects.  A
     *note TypeError: 1fe. is raised if `addresses' contains mixed
     version objects.

          >>> [ipaddr for ipaddr in
          ... ipaddress.collapse_addresses([ipaddress.IPv4Network('192.0.2.0/25'),
          ... ipaddress.IPv4Network('192.0.2.128/25')])]
          [IPv4Network('192.0.2.0/24')]

 -- Function: ipaddress.get_mixed_type_key (obj)

     Return a key suitable for sorting between networks and addresses.
     Address and Network objects are not sortable by default; they’re
     fundamentally different, so the expression:

          IPv4Address('192.0.2.0') <= IPv4Network('192.0.2.0/24')

     doesn’t make sense.  There are some times however, where you may
     wish to have *note ipaddress: a2. sort these anyway.  If you need
     to do this, you can use this function as the `key' argument to
     *note sorted(): 547.

     `obj' is either a network or address object.


File: python.info,  Node: Custom Exceptions,  Prev: Other Module Level Functions,  Up: ipaddress — IPv4/IPv6 manipulation library

5.21.28.19 Custom Exceptions
............................

To support more specific error reporting from class constructors, the
module defines the following exceptions:

 -- Exception: ipaddress.AddressValueError (ValueError)

     Any value error related to the address.

 -- Exception: ipaddress.NetmaskValueError (ValueError)

     Any value error related to the net mask.


File: python.info,  Node: Multimedia Services,  Next: Internationalization,  Prev: Internet Protocols and Support,  Up: The Python Standard Library

5.22 Multimedia Services
========================

The modules described in this chapter implement various algorithms or
interfaces that are mainly useful for multimedia applications.  They are
available at the discretion of the installation.  Here’s an overview:

* Menu:

* audioop — Manipulate raw audio data::
* aifc — Read and write AIFF and AIFC files::
* sunau — Read and write Sun AU files::
* wave — Read and write WAV files::
* chunk — Read IFF chunked data::
* colorsys — Conversions between color systems::
* imghdr — Determine the type of an image::
* sndhdr — Determine type of sound file::
* ossaudiodev — Access to OSS-compatible audio devices::


File: python.info,  Node: audioop — Manipulate raw audio data,  Next: aifc — Read and write AIFF and AIFC files,  Up: Multimedia Services

5.22.1 ‘audioop’ — Manipulate raw audio data
--------------------------------------------

__________________________________________________________________

The *note audioop: c. module contains some useful operations on sound
fragments.  It operates on sound fragments consisting of signed integer
samples 8, 16, 24 or 32 bits wide, stored in *note bytes-like objects:
6df.  All scalar items are integers, unless specified otherwise.

Changed in version 3.4: Support for 24-bit samples was added.  All
functions now accept any *note bytes-like object: 6df.  String input now
results in an immediate error.

This module provides support for a-LAW, u-LAW and Intel/DVI ADPCM
encodings.

A few of the more complicated operations only take 16-bit samples,
otherwise the sample size (in bytes) is always a parameter of the
operation.

The module defines the following variables and functions:

 -- Exception: audioop.error

     This exception is raised on all errors, such as unknown number of
     bytes per sample, etc.

 -- Function: audioop.add (fragment1, fragment2, width)

     Return a fragment which is the addition of the two samples passed
     as parameters.  `width' is the sample width in bytes, either ‘1’,
     ‘2’, ‘3’ or ‘4’.  Both fragments should have the same length.
     Samples are truncated in case of overflow.

 -- Function: audioop.adpcm2lin (adpcmfragment, width, state)

     Decode an Intel/DVI ADPCM coded fragment to a linear fragment.  See
     the description of *note lin2adpcm(): 30c8. for details on ADPCM
     coding.  Return a tuple ‘(sample, newstate)’ where the sample has
     the width specified in `width'.

 -- Function: audioop.alaw2lin (fragment, width)

     Convert sound fragments in a-LAW encoding to linearly encoded sound
     fragments.  a-LAW encoding always uses 8 bits samples, so `width'
     refers only to the sample width of the output fragment here.

 -- Function: audioop.avg (fragment, width)

     Return the average over all samples in the fragment.

 -- Function: audioop.avgpp (fragment, width)

     Return the average peak-peak value over all samples in the
     fragment.  No filtering is done, so the usefulness of this routine
     is questionable.

 -- Function: audioop.bias (fragment, width, bias)

     Return a fragment that is the original fragment with a bias added
     to each sample.  Samples wrap around in case of overflow.

 -- Function: audioop.byteswap (fragment, width)

     “Byteswap” all samples in a fragment and returns the modified
     fragment.  Converts big-endian samples to little-endian and vice
     versa.

     New in version 3.4.

 -- Function: audioop.cross (fragment, width)

     Return the number of zero crossings in the fragment passed as an
     argument.

 -- Function: audioop.findfactor (fragment, reference)

     Return a factor `F' such that ‘rms(add(fragment, mul(reference,
     -F)))’ is minimal, i.e., return the factor with which you should
     multiply `reference' to make it match as well as possible to
     `fragment'.  The fragments should both contain 2-byte samples.

     The time taken by this routine is proportional to ‘len(fragment)’.

 -- Function: audioop.findfit (fragment, reference)

     Try to match `reference' as well as possible to a portion of
     `fragment' (which should be the longer fragment).  This is
     (conceptually) done by taking slices out of `fragment', using *note
     findfactor(): 30ce. to compute the best match, and minimizing the
     result.  The fragments should both contain 2-byte samples.  Return
     a tuple ‘(offset, factor)’ where `offset' is the (integer) offset
     into `fragment' where the optimal match started and `factor' is the
     (floating-point) factor as per *note findfactor(): 30ce.

 -- Function: audioop.findmax (fragment, length)

     Search `fragment' for a slice of length `length' samples (not
     bytes!)  with maximum energy, i.e., return `i' for which
     ‘rms(fragment[i*2:(i+length)*2])’ is maximal.  The fragments should
     both contain 2-byte samples.

     The routine takes time proportional to ‘len(fragment)’.

 -- Function: audioop.getsample (fragment, width, index)

     Return the value of sample `index' from the fragment.

 -- Function: audioop.lin2adpcm (fragment, width, state)

     Convert samples to 4 bit Intel/DVI ADPCM encoding.  ADPCM coding is
     an adaptive coding scheme, whereby each 4 bit number is the
     difference between one sample and the next, divided by a (varying)
     step.  The Intel/DVI ADPCM algorithm has been selected for use by
     the IMA, so it may well become a standard.

     `state' is a tuple containing the state of the coder.  The coder
     returns a tuple ‘(adpcmfrag, newstate)’, and the `newstate' should
     be passed to the next call of *note lin2adpcm(): 30c8.  In the
     initial call, ‘None’ can be passed as the state.  `adpcmfrag' is
     the ADPCM coded fragment packed 2 4-bit values per byte.

 -- Function: audioop.lin2alaw (fragment, width)

     Convert samples in the audio fragment to a-LAW encoding and return
     this as a bytes object.  a-LAW is an audio encoding format whereby
     you get a dynamic range of about 13 bits using only 8 bit samples.
     It is used by the Sun audio hardware, among others.

 -- Function: audioop.lin2lin (fragment, width, newwidth)

     Convert samples between 1-, 2-, 3- and 4-byte formats.

          Note: In some audio formats, such as .WAV files, 16, 24 and 32
          bit samples are signed, but 8 bit samples are unsigned.  So
          when converting to 8 bit wide samples for these formats, you
          need to also add 128 to the result:

               new_frames = audioop.lin2lin(frames, old_width, 1)
               new_frames = audioop.bias(new_frames, 1, 128)

          The same, in reverse, has to be applied when converting from 8
          to 16, 24 or 32 bit width samples.

 -- Function: audioop.lin2ulaw (fragment, width)

     Convert samples in the audio fragment to u-LAW encoding and return
     this as a bytes object.  u-LAW is an audio encoding format whereby
     you get a dynamic range of about 14 bits using only 8 bit samples.
     It is used by the Sun audio hardware, among others.

 -- Function: audioop.max (fragment, width)

     Return the maximum of the `absolute value' of all samples in a
     fragment.

 -- Function: audioop.maxpp (fragment, width)

     Return the maximum peak-peak value in the sound fragment.

 -- Function: audioop.minmax (fragment, width)

     Return a tuple consisting of the minimum and maximum values of all
     samples in the sound fragment.

 -- Function: audioop.mul (fragment, width, factor)

     Return a fragment that has all samples in the original fragment
     multiplied by the floating-point value `factor'.  Samples are
     truncated in case of overflow.

 -- Function: audioop.ratecv (fragment, width, nchannels, inrate,
          outrate, state[, weightA[, weightB]])

     Convert the frame rate of the input fragment.

     `state' is a tuple containing the state of the converter.  The
     converter returns a tuple ‘(newfragment, newstate)’, and `newstate'
     should be passed to the next call of *note ratecv(): 30d9.  The
     initial call should pass ‘None’ as the state.

     The `weightA' and `weightB' arguments are parameters for a simple
     digital filter and default to ‘1’ and ‘0’ respectively.

 -- Function: audioop.reverse (fragment, width)

     Reverse the samples in a fragment and returns the modified
     fragment.

 -- Function: audioop.rms (fragment, width)

     Return the root-mean-square of the fragment, i.e.
     ‘sqrt(sum(S_i^2)/n)’.

     This is a measure of the power in an audio signal.

 -- Function: audioop.tomono (fragment, width, lfactor, rfactor)

     Convert a stereo fragment to a mono fragment.  The left channel is
     multiplied by `lfactor' and the right channel by `rfactor' before
     adding the two channels to give a mono signal.

 -- Function: audioop.tostereo (fragment, width, lfactor, rfactor)

     Generate a stereo fragment from a mono fragment.  Each pair of
     samples in the stereo fragment are computed from the mono sample,
     whereby left channel samples are multiplied by `lfactor' and right
     channel samples by `rfactor'.

 -- Function: audioop.ulaw2lin (fragment, width)

     Convert sound fragments in u-LAW encoding to linearly encoded sound
     fragments.  u-LAW encoding always uses 8 bits samples, so `width'
     refers only to the sample width of the output fragment here.

Note that operations such as *note mul(): 30d8. or *note max(): 30d5.
make no distinction between mono and stereo fragments, i.e.  all samples
are treated equal.  If this is a problem the stereo fragment should be
split into two mono fragments first and recombined later.  Here is an
example of how to do that:

     def mul_stereo(sample, width, lfactor, rfactor):
         lsample = audioop.tomono(sample, width, 1, 0)
         rsample = audioop.tomono(sample, width, 0, 1)
         lsample = audioop.mul(lsample, width, lfactor)
         rsample = audioop.mul(rsample, width, rfactor)
         lsample = audioop.tostereo(lsample, width, 1, 0)
         rsample = audioop.tostereo(rsample, width, 0, 1)
         return audioop.add(lsample, rsample, width)

If you use the ADPCM coder to build network packets and you want your
protocol to be stateless (i.e.  to be able to tolerate packet loss) you
should not only transmit the data but also the state.  Note that you
should send the `initial' state (the one you passed to *note
lin2adpcm(): 30c8.) along to the decoder, not the final state (as
returned by the coder).  If you want to use *note struct.Struct: 1950.
to store the state in binary you can code the first element (the
predicted value) in 16 bits and the second (the delta index) in 8.

The ADPCM coders have never been tried against other ADPCM coders, only
against themselves.  It could well be that I misinterpreted the
standards in which case they will not be interoperable with the
respective standards.

The ‘find*()’ routines might look a bit funny at first sight.  They are
primarily meant to do echo cancellation.  A reasonably fast way to do
this is to pick the most energetic piece of the output sample, locate
that in the input sample and subtract the whole output sample from the
input sample:

     def echocancel(outputdata, inputdata):
         pos = audioop.findmax(outputdata, 800)    # one tenth second
         out_test = outputdata[pos*2:]
         in_test = inputdata[pos*2:]
         ipos, factor = audioop.findfit(in_test, out_test)
         # Optional (for better cancellation):
         # factor = audioop.findfactor(in_test[ipos*2:ipos*2+len(out_test)],
         #              out_test)
         prefill = '\0'*(pos+ipos)*2
         postfill = '\0'*(len(inputdata)-len(prefill)-len(outputdata))
         outputdata = prefill + audioop.mul(outputdata, 2, -factor) + postfill
         return audioop.add(inputdata, outputdata, 2)


File: python.info,  Node: aifc — Read and write AIFF and AIFC files,  Next: sunau — Read and write Sun AU files,  Prev: audioop — Manipulate raw audio data,  Up: Multimedia Services

5.22.2 ‘aifc’ — Read and write AIFF and AIFC files
--------------------------------------------------

`Source code:' Lib/aifc.py(1)

__________________________________________________________________

This module provides support for reading and writing AIFF and AIFF-C
files.  AIFF is Audio Interchange File Format, a format for storing
digital audio samples in a file.  AIFF-C is a newer version of the
format that includes the ability to compress the audio data.

Audio files have a number of parameters that describe the audio data.
The sampling rate or frame rate is the number of times per second the
sound is sampled.  The number of channels indicate if the audio is mono,
stereo, or quadro.  Each frame consists of one sample per channel.  The
sample size is the size in bytes of each sample.  Thus a frame consists
of ‘nchannels * samplesize’ bytes, and a second’s worth of audio
consists of ‘nchannels * samplesize * framerate’ bytes.

For example, CD quality audio has a sample size of two bytes (16 bits),
uses two channels (stereo) and has a frame rate of 44,100 frames/second.
This gives a frame size of 4 bytes (2*2), and a second’s worth occupies
2*2*44100 bytes (176,400 bytes).

Module *note aifc: 4. defines the following function:

 -- Function: aifc.open (file, mode=None)

     Open an AIFF or AIFF-C file and return an object instance with
     methods that are described below.  The argument `file' is either a
     string naming a file or a *note file object: c14.  `mode' must be
     ‘'r'’ or ‘'rb'’ when the file must be opened for reading, or ‘'w'’
     or ‘'wb'’ when the file must be opened for writing.  If omitted,
     ‘file.mode’ is used if it exists, otherwise ‘'rb'’ is used.  When
     used for writing, the file object should be seekable, unless you
     know ahead of time how many samples you are going to write in total
     and use ‘writeframesraw()’ and ‘setnframes()’.  The *note open():
     55d. function may be used in a *note with: 7da. statement.  When
     the ‘with’ block completes, the *note close(): 909. method is
     called.

     Changed in version 3.4: Support for the *note with: 7da. statement
     was added.

Objects returned by *note open(): 55d. when a file is opened for reading
have the following methods:

 -- Method: aifc.getnchannels ()

     Return the number of audio channels (1 for mono, 2 for stereo).

 -- Method: aifc.getsampwidth ()

     Return the size in bytes of individual samples.

 -- Method: aifc.getframerate ()

     Return the sampling rate (number of audio frames per second).

 -- Method: aifc.getnframes ()

     Return the number of audio frames in the file.

 -- Method: aifc.getcomptype ()

     Return a bytes array of length 4 describing the type of compression
     used in the audio file.  For AIFF files, the returned value is
     ‘b'NONE'’.

 -- Method: aifc.getcompname ()

     Return a bytes array convertible to a human-readable description of
     the type of compression used in the audio file.  For AIFF files,
     the returned value is ‘b'not compressed'’.

 -- Method: aifc.getparams ()

     Returns a *note namedtuple(): 1a1. ‘(nchannels, sampwidth,
     framerate, nframes, comptype, compname)’, equivalent to output of
     the ‘get*()’ methods.

 -- Method: aifc.getmarkers ()

     Return a list of markers in the audio file.  A marker consists of a
     tuple of three elements.  The first is the mark ID (an integer),
     the second is the mark position in frames from the beginning of the
     data (an integer), the third is the name of the mark (a string).

 -- Method: aifc.getmark (id)

     Return the tuple as described in *note getmarkers(): 30e7. for the
     mark with the given `id'.

 -- Method: aifc.readframes (nframes)

     Read and return the next `nframes' frames from the audio file.  The
     returned data is a string containing for each frame the
     uncompressed samples of all channels.

 -- Method: aifc.rewind ()

     Rewind the read pointer.  The next *note readframes(): 30e9. will
     start from the beginning.

 -- Method: aifc.setpos (pos)

     Seek to the specified frame number.

 -- Method: aifc.tell ()

     Return the current frame number.

 -- Method: aifc.close ()

     Close the AIFF file.  After calling this method, the object can no
     longer be used.

Objects returned by *note open(): 55d. when a file is opened for writing
have all the above methods, except for ‘readframes()’ and ‘setpos()’.
In addition the following methods exist.  The ‘get*()’ methods can only
be called after the corresponding ‘set*()’ methods have been called.
Before the first ‘writeframes()’ or ‘writeframesraw()’, all parameters
except for the number of frames must be filled in.

 -- Method: aifc.aiff ()

     Create an AIFF file.  The default is that an AIFF-C file is
     created, unless the name of the file ends in ‘'.aiff'’ in which
     case the default is an AIFF file.

 -- Method: aifc.aifc ()

     Create an AIFF-C file.  The default is that an AIFF-C file is
     created, unless the name of the file ends in ‘'.aiff'’ in which
     case the default is an AIFF file.

 -- Method: aifc.setnchannels (nchannels)

     Specify the number of channels in the audio file.

 -- Method: aifc.setsampwidth (width)

     Specify the size in bytes of audio samples.

 -- Method: aifc.setframerate (rate)

     Specify the sampling frequency in frames per second.

 -- Method: aifc.setnframes (nframes)

     Specify the number of frames that are to be written to the audio
     file.  If this parameter is not set, or not set correctly, the file
     needs to support seeking.

 -- Method: aifc.setcomptype (type, name)

     Specify the compression type.  If not specified, the audio data
     will not be compressed.  In AIFF files, compression is not
     possible.  The name parameter should be a human-readable
     description of the compression type as a bytes array, the type
     parameter should be a bytes array of length 4.  Currently the
     following compression types are supported: ‘b'NONE'’, ‘b'ULAW'’,
     ‘b'ALAW'’, ‘b'G722'’.

 -- Method: aifc.setparams (nchannels, sampwidth, framerate, comptype,
          compname)

     Set all the above parameters at once.  The argument is a tuple
     consisting of the various parameters.  This means that it is
     possible to use the result of a *note getparams(): 908. call as
     argument to *note setparams(): 30f4.

 -- Method: aifc.setmark (id, pos, name)

     Add a mark with the given id (larger than 0), and the given name at
     the given position.  This method can be called at any time before
     *note close(): 909.

 -- Method: aifc.tell ()

     Return the current write position in the output file.  Useful in
     combination with *note setmark(): 30f5.

 -- Method: aifc.writeframes (data)

     Write data to the output file.  This method can only be called
     after the audio file parameters have been set.

     Changed in version 3.4: Any *note bytes-like object: 6df. is now
     accepted.

 -- Method: aifc.writeframesraw (data)

     Like *note writeframes(): 90b, except that the header of the audio
     file is not updated.

     Changed in version 3.4: Any *note bytes-like object: 6df. is now
     accepted.

 -- Method: aifc.close ()

     Close the AIFF file.  The header of the file is updated to reflect
     the actual size of the audio data.  After calling this method, the
     object can no longer be used.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/aifc.py


File: python.info,  Node: sunau — Read and write Sun AU files,  Next: wave — Read and write WAV files,  Prev: aifc — Read and write AIFF and AIFC files,  Up: Multimedia Services

5.22.3 ‘sunau’ — Read and write Sun AU files
--------------------------------------------

`Source code:' Lib/sunau.py(1)

__________________________________________________________________

The *note sunau: fa. module provides a convenient interface to the Sun
AU sound format.  Note that this module is interface-compatible with the
modules *note aifc: 4. and *note wave: 130.

An audio file consists of a header followed by the data.  The fields of
the header are:

Field               Contents
                    
------------------------------------------------------------------------
                    
magic word          The four bytes ‘.snd’.
                    
                    
header size         Size of the header, including info, in bytes.
                    
                    
data size           Physical size of the data, in bytes.
                    
                    
encoding            Indicates how the audio samples are encoded.
                    
                    
sample rate         The sampling rate.
                    
                    
# of channels       The number of channels in the samples.
                    
                    
info                ASCII string giving a description of the audio
                    file (padded with null bytes).
                    

Apart from the info field, all header fields are 4 bytes in size.  They
are all 32-bit unsigned integers encoded in big-endian byte order.

The *note sunau: fa. module defines the following functions:

 -- Function: sunau.open (file, mode)

     If `file' is a string, open the file by that name, otherwise treat
     it as a seekable file-like object.  `mode' can be any of

     ‘'r'’

          Read only mode.

     ‘'w'’

          Write only mode.

     Note that it does not allow read/write files.

     A `mode' of ‘'r'’ returns an ‘AU_read’ object, while a `mode' of
     ‘'w'’ or ‘'wb'’ returns an ‘AU_write’ object.

The *note sunau: fa. module defines the following exception:

 -- Exception: sunau.Error

     An error raised when something is impossible because of Sun AU
     specs or implementation deficiency.

The *note sunau: fa. module defines the following data items:

 -- Data: sunau.AUDIO_FILE_MAGIC

     An integer every valid Sun AU file begins with, stored in
     big-endian form.  This is the string ‘.snd’ interpreted as an
     integer.

 -- Data: sunau.AUDIO_FILE_ENCODING_MULAW_8
 -- Data: sunau.AUDIO_FILE_ENCODING_LINEAR_8
 -- Data: sunau.AUDIO_FILE_ENCODING_LINEAR_16
 -- Data: sunau.AUDIO_FILE_ENCODING_LINEAR_24
 -- Data: sunau.AUDIO_FILE_ENCODING_LINEAR_32
 -- Data: sunau.AUDIO_FILE_ENCODING_ALAW_8

     Values of the encoding field from the AU header which are supported
     by this module.

 -- Data: sunau.AUDIO_FILE_ENCODING_FLOAT
 -- Data: sunau.AUDIO_FILE_ENCODING_DOUBLE
 -- Data: sunau.AUDIO_FILE_ENCODING_ADPCM_G721
 -- Data: sunau.AUDIO_FILE_ENCODING_ADPCM_G722
 -- Data: sunau.AUDIO_FILE_ENCODING_ADPCM_G723_3
 -- Data: sunau.AUDIO_FILE_ENCODING_ADPCM_G723_5

     Additional known values of the encoding field from the AU header,
     but which are not supported by this module.

* Menu:

* AU_read Objects::
* AU_write Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/sunau.py


File: python.info,  Node: AU_read Objects,  Next: AU_write Objects,  Up: sunau — Read and write Sun AU files

5.22.3.1 AU_read Objects
........................

AU_read objects, as returned by *note open(): 573. above, have the
following methods:

 -- Method: AU_read.close ()

     Close the stream, and make the instance unusable.  (This is called
     automatically on deletion.)

 -- Method: AU_read.getnchannels ()

     Returns number of audio channels (1 for mono, 2 for stereo).

 -- Method: AU_read.getsampwidth ()

     Returns sample width in bytes.

 -- Method: AU_read.getframerate ()

     Returns sampling frequency.

 -- Method: AU_read.getnframes ()

     Returns number of audio frames.

 -- Method: AU_read.getcomptype ()

     Returns compression type.  Supported compression types are
     ‘'ULAW'’, ‘'ALAW'’ and ‘'NONE'’.

 -- Method: AU_read.getcompname ()

     Human-readable version of *note getcomptype(): 310d.  The supported
     types have the respective names ‘'CCITT G.711 u-law'’, ‘'CCITT
     G.711 A-law'’ and ‘'not compressed'’.

 -- Method: AU_read.getparams ()

     Returns a *note namedtuple(): 1a1. ‘(nchannels, sampwidth,
     framerate, nframes, comptype, compname)’, equivalent to output of
     the ‘get*()’ methods.

 -- Method: AU_read.readframes (n)

     Reads and returns at most `n' frames of audio, as a *note bytes:
     172. object.  The data will be returned in linear format.  If the
     original data is in u-LAW format, it will be converted.

 -- Method: AU_read.rewind ()

     Rewind the file pointer to the beginning of the audio stream.

The following two methods define a term “position” which is compatible
between them, and is otherwise implementation dependent.

 -- Method: AU_read.setpos (pos)

     Set the file pointer to the specified position.  Only values
     returned from *note tell(): 3113. should be used for `pos'.

 -- Method: AU_read.tell ()

     Return current file pointer position.  Note that the returned value
     has nothing to do with the actual position in the file.

The following two functions are defined for compatibility with the *note
aifc: 4, and don’t do anything interesting.

 -- Method: AU_read.getmarkers ()

     Returns ‘None’.

 -- Method: AU_read.getmark (id)

     Raise an error.


File: python.info,  Node: AU_write Objects,  Prev: AU_read Objects,  Up: sunau — Read and write Sun AU files

5.22.3.2 AU_write Objects
.........................

AU_write objects, as returned by *note open(): 573. above, have the
following methods:

 -- Method: AU_write.setnchannels (n)

     Set the number of channels.

 -- Method: AU_write.setsampwidth (n)

     Set the sample width (in bytes.)

     Changed in version 3.4: Added support for 24-bit samples.

 -- Method: AU_write.setframerate (n)

     Set the frame rate.

 -- Method: AU_write.setnframes (n)

     Set the number of frames.  This can be later changed, when and if
     more frames are written.

 -- Method: AU_write.setcomptype (type, name)

     Set the compression type and description.  Only ‘'NONE'’ and
     ‘'ULAW'’ are supported on output.

 -- Method: AU_write.setparams (tuple)

     The `tuple' should be ‘(nchannels, sampwidth, framerate, nframes,
     comptype, compname)’, with values valid for the ‘set*()’ methods.
     Set all parameters.

 -- Method: AU_write.tell ()

     Return current position in the file, with the same disclaimer for
     the *note AU_read.tell(): 3113. and *note AU_read.setpos(): 3112.
     methods.

 -- Method: AU_write.writeframesraw (data)

     Write audio frames, without correcting `nframes'.

     Changed in version 3.4: Any *note bytes-like object: 6df. is now
     accepted.

 -- Method: AU_write.writeframes (data)

     Write audio frames and make sure `nframes' is correct.

     Changed in version 3.4: Any *note bytes-like object: 6df. is now
     accepted.

 -- Method: AU_write.close ()

     Make sure `nframes' is correct, and close the file.

     This method is called upon deletion.

Note that it is invalid to set any parameters after calling
‘writeframes()’ or ‘writeframesraw()’.


File: python.info,  Node: wave — Read and write WAV files,  Next: chunk — Read IFF chunked data,  Prev: sunau — Read and write Sun AU files,  Up: Multimedia Services

5.22.4 ‘wave’ — Read and write WAV files
----------------------------------------

`Source code:' Lib/wave.py(1)

__________________________________________________________________

The *note wave: 130. module provides a convenient interface to the WAV
sound format.  It does not support compression/decompression, but it
does support mono/stereo.

The *note wave: 130. module defines the following function and
exception:

 -- Function: wave.open (file, mode=None)

     If `file' is a string, open the file by that name, otherwise treat
     it as a file-like object.  `mode' can be:

     ‘'rb'’

          Read only mode.

     ‘'wb'’

          Write only mode.

     Note that it does not allow read/write WAV files.

     A `mode' of ‘'rb'’ returns a ‘Wave_read’ object, while a `mode' of
     ‘'wb'’ returns a ‘Wave_write’ object.  If `mode' is omitted and a
     file-like object is passed as `file', ‘file.mode’ is used as the
     default value for `mode'.

     If you pass in a file-like object, the wave object will not close
     it when its ‘close()’ method is called; it is the caller’s
     responsibility to close the file object.

     The *note open(): 219. function may be used in a *note with: 7da.
     statement.  When the ‘with’ block completes, the *note
     Wave_read.close(): 3121. or *note Wave_write.close(): 3122. method
     is called.

     Changed in version 3.4: Added support for unseekable files.

 -- Exception: wave.Error

     An error raised when something is impossible because it violates
     the WAV specification or hits an implementation deficiency.

* Menu:

* Wave_read Objects::
* Wave_write Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/wave.py


File: python.info,  Node: Wave_read Objects,  Next: Wave_write Objects,  Up: wave — Read and write WAV files

5.22.4.1 Wave_read Objects
..........................

Wave_read objects, as returned by *note open(): 219, have the following
methods:

 -- Method: Wave_read.close ()

     Close the stream if it was opened by *note wave: 130, and make the
     instance unusable.  This is called automatically on object
     collection.

 -- Method: Wave_read.getnchannels ()

     Returns number of audio channels (‘1’ for mono, ‘2’ for stereo).

 -- Method: Wave_read.getsampwidth ()

     Returns sample width in bytes.

 -- Method: Wave_read.getframerate ()

     Returns sampling frequency.

 -- Method: Wave_read.getnframes ()

     Returns number of audio frames.

 -- Method: Wave_read.getcomptype ()

     Returns compression type (‘'NONE'’ is the only supported type).

 -- Method: Wave_read.getcompname ()

     Human-readable version of *note getcomptype(): 312a.  Usually ‘'not
     compressed'’ parallels ‘'NONE'’.

 -- Method: Wave_read.getparams ()

     Returns a *note namedtuple(): 1a1. ‘(nchannels, sampwidth,
     framerate, nframes, comptype, compname)’, equivalent to output of
     the ‘get*()’ methods.

 -- Method: Wave_read.readframes (n)

     Reads and returns at most `n' frames of audio, as a *note bytes:
     172. object.

 -- Method: Wave_read.rewind ()

     Rewind the file pointer to the beginning of the audio stream.

The following two methods are defined for compatibility with the *note
aifc: 4. module, and don’t do anything interesting.

 -- Method: Wave_read.getmarkers ()

     Returns ‘None’.

 -- Method: Wave_read.getmark (id)

     Raise an error.

The following two methods define a term “position” which is compatible
between them, and is otherwise implementation dependent.

 -- Method: Wave_read.setpos (pos)

     Set the file pointer to the specified position.

 -- Method: Wave_read.tell ()

     Return current file pointer position.


File: python.info,  Node: Wave_write Objects,  Prev: Wave_read Objects,  Up: wave — Read and write WAV files

5.22.4.2 Wave_write Objects
...........................

For seekable output streams, the ‘wave’ header will automatically be
updated to reflect the number of frames actually written.  For
unseekable streams, the `nframes' value must be accurate when the first
frame data is written.  An accurate `nframes' value can be achieved
either by calling *note setnframes(): 3134. or *note setparams(): 3135.
with the number of frames that will be written before *note close():
3122. is called and then using *note writeframesraw(): 9f2. to write the
frame data, or by calling *note writeframes(): 9f3. with all of the
frame data to be written.  In the latter case *note writeframes(): 9f3.
will calculate the number of frames in the data and set `nframes'
accordingly before writing the frame data.

Wave_write objects, as returned by *note open(): 219, have the following
methods:

Changed in version 3.4: Added support for unseekable files.

 -- Method: Wave_write.close ()

     Make sure `nframes' is correct, and close the file if it was opened
     by *note wave: 130.  This method is called upon object collection.
     It will raise an exception if the output stream is not seekable and
     `nframes' does not match the number of frames actually written.

 -- Method: Wave_write.setnchannels (n)

     Set the number of channels.

 -- Method: Wave_write.setsampwidth (n)

     Set the sample width to `n' bytes.

 -- Method: Wave_write.setframerate (n)

     Set the frame rate to `n'.

     Changed in version 3.2: A non-integral input to this method is
     rounded to the nearest integer.

 -- Method: Wave_write.setnframes (n)

     Set the number of frames to `n'.  This will be changed later if the
     number of frames actually written is different (this update attempt
     will raise an error if the output stream is not seekable).

 -- Method: Wave_write.setcomptype (type, name)

     Set the compression type and description.  At the moment, only
     compression type ‘NONE’ is supported, meaning no compression.

 -- Method: Wave_write.setparams (tuple)

     The `tuple' should be ‘(nchannels, sampwidth, framerate, nframes,
     comptype, compname)’, with values valid for the ‘set*()’ methods.
     Sets all parameters.

 -- Method: Wave_write.tell ()

     Return current position in the file, with the same disclaimer for
     the *note Wave_read.tell(): 3132. and *note Wave_read.setpos():
     3131. methods.

 -- Method: Wave_write.writeframesraw (data)

     Write audio frames, without correcting `nframes'.

     Changed in version 3.4: Any *note bytes-like object: 6df. is now
     accepted.

 -- Method: Wave_write.writeframes (data)

     Write audio frames and make sure `nframes' is correct.  It will
     raise an error if the output stream is not seekable and the total
     number of frames that have been written after `data' has been
     written does not match the previously set value for `nframes'.

     Changed in version 3.4: Any *note bytes-like object: 6df. is now
     accepted.

Note that it is invalid to set any parameters after calling
‘writeframes()’ or ‘writeframesraw()’, and any attempt to do so will
raise *note wave.Error: 3123.


File: python.info,  Node: chunk — Read IFF chunked data,  Next: colorsys — Conversions between color systems,  Prev: wave — Read and write WAV files,  Up: Multimedia Services

5.22.5 ‘chunk’ — Read IFF chunked data
--------------------------------------

`Source code:' Lib/chunk.py(1)

__________________________________________________________________

This module provides an interface for reading files that use EA IFF 85
chunks.  (2) This format is used in at least the Audio Interchange File
Format (AIFF/AIFF-C) and the Real Media File Format (RMFF). The WAVE
audio file format is closely related and can also be read using this
module.

A chunk has the following structure:

Offset        Length       Contents
                           
---------------------------------------------------------------
                           
0             4            Chunk ID
                           
                           
4             4            Size of chunk in big-endian byte
                           order, not including the header
                           
                           
8             `n'          Data bytes, where `n' is the size
                           given in the preceding field
                           
                           
8 + `n'       0 or 1       Pad byte needed if `n' is odd and
                           chunk alignment is used
                           

The ID is a 4-byte string which identifies the type of chunk.

The size field (a 32-bit value, encoded using big-endian byte order)
gives the size of the chunk data, not including the 8-byte header.

Usually an IFF-type file consists of one or more chunks.  The proposed
usage of the *note Chunk: 313d. class defined here is to instantiate an
instance at the start of each chunk and read from the instance until it
reaches the end, after which a new instance can be instantiated.  At the
end of the file, creating a new instance will fail with an *note
EOFError: d34. exception.

 -- Class: chunk.Chunk (file, align=True, bigendian=True,
          inclheader=False)

     Class which represents a chunk.  The `file' argument is expected to
     be a file-like object.  An instance of this class is specifically
     allowed.  The only method that is needed is ‘read()’.  If the
     methods *note seek(): 1efb. and *note tell(): 1efc. are present and
     don’t raise an exception, they are also used.  If these methods are
     present and raise an exception, they are expected to not have
     altered the object.  If the optional argument `align' is true,
     chunks are assumed to be aligned on 2-byte boundaries.  If `align'
     is false, no alignment is assumed.  The default value is true.  If
     the optional argument `bigendian' is false, the chunk size is
     assumed to be in little-endian order.  This is needed for WAVE
     audio files.  The default value is true.  If the optional argument
     `inclheader' is true, the size given in the chunk header includes
     the size of the header.  The default value is false.

     A *note Chunk: 313d. object supports the following methods:

      -- Method: getname ()

          Returns the name (ID) of the chunk.  This is the first 4 bytes
          of the chunk.

      -- Method: getsize ()

          Returns the size of the chunk.

      -- Method: close ()

          Close and skip to the end of the chunk.  This does not close
          the underlying file.

     The remaining methods will raise *note OSError: 304. if called
     after the *note close(): 3140. method has been called.  Before
     Python 3.3, they used to raise *note IOError: a73, now an alias of
     *note OSError: 304.

      -- Method: isatty ()

          Returns ‘False’.

      -- Method: seek (pos, whence=0)

          Set the chunk’s current position.  The `whence' argument is
          optional and defaults to ‘0’ (absolute file positioning);
          other values are ‘1’ (seek relative to the current position)
          and ‘2’ (seek relative to the file’s end).  There is no return
          value.  If the underlying file does not allow seek, only
          forward seeks are allowed.

      -- Method: tell ()

          Return the current position into the chunk.

      -- Method: read (size=-1)

          Read at most `size' bytes from the chunk (less if the read
          hits the end of the chunk before obtaining `size' bytes).  If
          the `size' argument is negative or omitted, read all data
          until the end of the chunk.  An empty bytes object is returned
          when the end of the chunk is encountered immediately.

      -- Method: skip ()

          Skip to the end of the chunk.  All further calls to *note
          read(): 3144. for the chunk will return ‘b''’.  If you are not
          interested in the contents of the chunk, this method should be
          called so that the file points to the start of the next chunk.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/chunk.py

   (2) (1) “EA IFF 85” Standard for Interchange Format Files, Jerry
Morrison, Electronic Arts, January 1985.


File: python.info,  Node: colorsys — Conversions between color systems,  Next: imghdr — Determine the type of an image,  Prev: chunk — Read IFF chunked data,  Up: Multimedia Services

5.22.6 ‘colorsys’ — Conversions between color systems
-----------------------------------------------------

`Source code:' Lib/colorsys.py(1)

__________________________________________________________________

The *note colorsys: 1f. module defines bidirectional conversions of
color values between colors expressed in the RGB (Red Green Blue) color
space used in computer monitors and three other coordinate systems: YIQ,
HLS (Hue Lightness Saturation) and HSV (Hue Saturation Value).
Coordinates in all of these color spaces are floating point values.  In
the YIQ space, the Y coordinate is between 0 and 1, but the I and Q
coordinates can be positive or negative.  In all other spaces, the
coordinates are all between 0 and 1.

See also
........

More information about color spaces can be found at
‘https://poynton.ca/ColorFAQ.html’ and
‘https://www.cambridgeincolour.com/tutorials/color-spaces.htm’.

The *note colorsys: 1f. module defines the following functions:

 -- Function: colorsys.rgb_to_yiq (r, g, b)

     Convert the color from RGB coordinates to YIQ coordinates.

 -- Function: colorsys.yiq_to_rgb (y, i, q)

     Convert the color from YIQ coordinates to RGB coordinates.

 -- Function: colorsys.rgb_to_hls (r, g, b)

     Convert the color from RGB coordinates to HLS coordinates.

 -- Function: colorsys.hls_to_rgb (h, l, s)

     Convert the color from HLS coordinates to RGB coordinates.

 -- Function: colorsys.rgb_to_hsv (r, g, b)

     Convert the color from RGB coordinates to HSV coordinates.

 -- Function: colorsys.hsv_to_rgb (h, s, v)

     Convert the color from HSV coordinates to RGB coordinates.

Example:

     >>> import colorsys
     >>> colorsys.rgb_to_hsv(0.2, 0.4, 0.4)
     (0.5, 0.5, 0.4)
     >>> colorsys.hsv_to_rgb(0.5, 0.5, 0.4)
     (0.2, 0.4, 0.4)

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/colorsys.py


File: python.info,  Node: imghdr — Determine the type of an image,  Next: sndhdr — Determine type of sound file,  Prev: colorsys — Conversions between color systems,  Up: Multimedia Services

5.22.7 ‘imghdr’ — Determine the type of an image
------------------------------------------------

`Source code:' Lib/imghdr.py(1)

__________________________________________________________________

The *note imghdr: 98. module determines the type of image contained in a
file or byte stream.

The *note imghdr: 98. module defines the following function:

 -- Function: imghdr.what (filename, h=None)

     Tests the image data contained in the file named by `filename', and
     returns a string describing the image type.  If optional `h' is
     provided, the `filename' is ignored and `h' is assumed to contain
     the byte stream to test.

     Changed in version 3.6: Accepts a *note path-like object: 472.

The following image types are recognized, as listed below with the
return value from *note what(): 7de.:

Value            Image format
                 
---------------------------------------------------------
                 
‘'rgb'’          SGI ImgLib Files
                 
                 
‘'gif'’          GIF 87a and 89a Files
                 
                 
‘'pbm'’          Portable Bitmap Files
                 
                 
‘'pgm'’          Portable Graymap Files
                 
                 
‘'ppm'’          Portable Pixmap Files
                 
                 
‘'tiff'’         TIFF Files
                 
                 
‘'rast'’         Sun Raster Files
                 
                 
‘'xbm'’          X Bitmap Files
                 
                 
‘'jpeg'’         JPEG data in JFIF or Exif formats
                 
                 
‘'bmp'’          BMP files
                 
                 
‘'png'’          Portable Network Graphics
                 
                 
‘'webp'’         WebP files
                 
                 
‘'exr'’          OpenEXR Files
                 

New in version 3.5: The `exr' and `webp' formats were added.

You can extend the list of file types *note imghdr: 98. can recognize by
appending to this variable:

 -- Data: imghdr.tests

     A list of functions performing the individual tests.  Each function
     takes two arguments: the byte-stream and an open file-like object.
     When *note what(): 7de. is called with a byte-stream, the file-like
     object will be ‘None’.

     The test function should return a string describing the image type
     if the test succeeded, or ‘None’ if it failed.

Example:

     >>> import imghdr
     >>> imghdr.what('bass.gif')
     'gif'

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/imghdr.py


File: python.info,  Node: sndhdr — Determine type of sound file,  Next: ossaudiodev — Access to OSS-compatible audio devices,  Prev: imghdr — Determine the type of an image,  Up: Multimedia Services

5.22.8 ‘sndhdr’ — Determine type of sound file
----------------------------------------------

`Source code:' Lib/sndhdr.py(1)

__________________________________________________________________

The *note sndhdr: ee. provides utility functions which attempt to
determine the type of sound data which is in a file.  When these
functions are able to determine what type of sound data is stored in a
file, they return a *note namedtuple(): 1a1, containing five attributes:
(‘filetype’, ‘framerate’, ‘nchannels’, ‘nframes’, ‘sampwidth’).  The
value for `type' indicates the data type and will be one of the strings
‘'aifc'’, ‘'aiff'’, ‘'au'’, ‘'hcom'’, ‘'sndr'’, ‘'sndt'’, ‘'voc'’,
‘'wav'’, ‘'8svx'’, ‘'sb'’, ‘'ub'’, or ‘'ul'’.  The `sampling_rate' will
be either the actual value or ‘0’ if unknown or difficult to decode.
Similarly, `channels' will be either the number of channels or ‘0’ if it
cannot be determined or if the value is difficult to decode.  The value
for `frames' will be either the number of frames or ‘-1’.  The last item
in the tuple, `bits_per_sample', will either be the sample size in bits
or ‘'A'’ for A-LAW or ‘'U'’ for u-LAW.

 -- Function: sndhdr.what (filename)

     Determines the type of sound data stored in the file `filename'
     using *note whathdr(): 837.  If it succeeds, returns a namedtuple
     as described above, otherwise ‘None’ is returned.

     Changed in version 3.5: Result changed from a tuple to a
     namedtuple.

 -- Function: sndhdr.whathdr (filename)

     Determines the type of sound data stored in a file based on the
     file header.  The name of the file is given by `filename'.  This
     function returns a namedtuple as described above on success, or
     ‘None’.

     Changed in version 3.5: Result changed from a tuple to a
     namedtuple.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/sndhdr.py


File: python.info,  Node: ossaudiodev — Access to OSS-compatible audio devices,  Prev: sndhdr — Determine type of sound file,  Up: Multimedia Services

5.22.9 ‘ossaudiodev’ — Access to OSS-compatible audio devices
-------------------------------------------------------------

__________________________________________________________________

This module allows you to access the OSS (Open Sound System) audio
interface.  OSS is available for a wide range of open-source and
commercial Unices, and is the standard audio interface for Linux and
recent versions of FreeBSD.

Changed in version 3.3: Operations in this module now raise *note
OSError: 304. where *note IOError: a73. was raised.

See also
........

Open Sound System Programmer’s Guide(1)

     the official documentation for the OSS C API

The module defines a large number of constants supplied by the OSS
device driver; see ‘<sys/soundcard.h>’ on either Linux or FreeBSD for a
listing.

*note ossaudiodev: c6. defines the following variables and functions:

 -- Exception: ossaudiodev.OSSAudioError

     This exception is raised on certain errors.  The argument is a
     string describing what went wrong.

     (If *note ossaudiodev: c6. receives an error from a system call
     such as ‘open()’, ‘write()’, or ‘ioctl()’, it raises *note OSError:
     304.  Errors detected directly by *note ossaudiodev: c6. result in
     *note OSSAudioError: 3155.)

     (For backwards compatibility, the exception class is also available
     as ‘ossaudiodev.error’.)

 -- Function: ossaudiodev.open (mode)

 -- Function: ossaudiodev.open (device, mode)

     Open an audio device and return an OSS audio device object.  This
     object supports many file-like methods, such as ‘read()’,
     ‘write()’, and ‘fileno()’ (although there are subtle differences
     between conventional Unix read/write semantics and those of OSS
     audio devices).  It also supports a number of audio-specific
     methods; see below for the complete list of methods.

     `device' is the audio device filename to use.  If it is not
     specified, this module first looks in the environment variable
     ‘AUDIODEV’ for a device to use.  If not found, it falls back to
     ‘/dev/dsp’.

     `mode' is one of ‘'r'’ for read-only (record) access, ‘'w'’ for
     write-only (playback) access and ‘'rw'’ for both.  Since many sound
     cards only allow one process to have the recorder or player open at
     a time, it is a good idea to open the device only for the activity
     needed.  Further, some sound cards are half-duplex: they can be
     opened for reading or writing, but not both at once.

     Note the unusual calling syntax: the `first' argument is optional,
     and the second is required.  This is a historical artifact for
     compatibility with the older ‘linuxaudiodev’ module which *note
     ossaudiodev: c6. supersedes.

 -- Function: ossaudiodev.openmixer ([device])

     Open a mixer device and return an OSS mixer device object.
     `device' is the mixer device filename to use.  If it is not
     specified, this module first looks in the environment variable
     ‘MIXERDEV’ for a device to use.  If not found, it falls back to
     ‘/dev/mixer’.

* Menu:

* Audio Device Objects::
* Mixer Device Objects::

   ---------- Footnotes ----------

   (1) http://www.opensound.com/pguide/oss.pdf


File: python.info,  Node: Audio Device Objects,  Next: Mixer Device Objects,  Up: ossaudiodev — Access to OSS-compatible audio devices

5.22.9.1 Audio Device Objects
.............................

Before you can write to or read from an audio device, you must call
three methods in the correct order:

  1. ‘setfmt()’ to set the output format

  2. ‘channels()’ to set the number of channels

  3. ‘speed()’ to set the sample rate

Alternately, you can use the ‘setparameters()’ method to set all three
audio parameters at once.  This is more convenient, but may not be as
flexible in all cases.

The audio device objects returned by *note open(): 3156. define the
following methods and (read-only) attributes:

 -- Method: oss_audio_device.close ()

     Explicitly close the audio device.  When you are done writing to or
     reading from an audio device, you should explicitly close it.  A
     closed device cannot be used again.

 -- Method: oss_audio_device.fileno ()

     Return the file descriptor associated with the device.

 -- Method: oss_audio_device.read (size)

     Read `size' bytes from the audio input and return them as a Python
     string.  Unlike most Unix device drivers, OSS audio devices in
     blocking mode (the default) will block *note read(): 315c. until
     the entire requested amount of data is available.

 -- Method: oss_audio_device.write (data)

     Write a *note bytes-like object: 6df. `data' to the audio device
     and return the number of bytes written.  If the audio device is in
     blocking mode (the default), the entire data is always written
     (again, this is different from usual Unix device semantics).  If
     the device is in non-blocking mode, some data may not be
     written—see *note writeall(): 315e.

     Changed in version 3.5: Writable *note bytes-like object: 6df. is
     now accepted.

 -- Method: oss_audio_device.writeall (data)

     Write a *note bytes-like object: 6df. `data' to the audio device:
     waits until the audio device is able to accept data, writes as much
     data as it will accept, and repeats until `data' has been
     completely written.  If the device is in blocking mode (the
     default), this has the same effect as *note write(): 315d.; *note
     writeall(): 315e. is only useful in non-blocking mode.  Has no
     return value, since the amount of data written is always equal to
     the amount of data supplied.

     Changed in version 3.5: Writable *note bytes-like object: 6df. is
     now accepted.

Changed in version 3.2: Audio device objects also support the context
management protocol, i.e.  they can be used in a *note with: 7da.
statement.

The following methods each map to exactly one ‘ioctl()’ system call.
The correspondence is obvious: for example, ‘setfmt()’ corresponds to
the ‘SNDCTL_DSP_SETFMT’ ioctl, and ‘sync()’ to ‘SNDCTL_DSP_SYNC’ (this
can be useful when consulting the OSS documentation).  If the underlying
‘ioctl()’ fails, they all raise *note OSError: 304.

 -- Method: oss_audio_device.nonblock ()

     Put the device into non-blocking mode.  Once in non-blocking mode,
     there is no way to return it to blocking mode.

 -- Method: oss_audio_device.getfmts ()

     Return a bitmask of the audio output formats supported by the
     soundcard.  Some of the formats supported by OSS are:

     Format                        Description
                                   
     --------------------------------------------------------------------------------
                                   
     ‘AFMT_MU_LAW’                 a logarithmic encoding (used by Sun ‘.au’ files
                                   and ‘/dev/audio’)
                                   
                                   
     ‘AFMT_A_LAW’                  a logarithmic encoding
                                   
                                   
     ‘AFMT_IMA_ADPCM’              a 4:1 compressed format defined by the
                                   Interactive Multimedia Association
                                   
                                   
     ‘AFMT_U8’                     Unsigned, 8-bit audio
                                   
                                   
     ‘AFMT_S16_LE’                 Signed, 16-bit audio, little-endian byte order
                                   (as used by Intel processors)
                                   
                                   
     ‘AFMT_S16_BE’                 Signed, 16-bit audio, big-endian byte order (as
                                   used by 68k, PowerPC, Sparc)
                                   
                                   
     ‘AFMT_S8’                     Signed, 8 bit audio
                                   
                                   
     ‘AFMT_U16_LE’                 Unsigned, 16-bit little-endian audio
                                   
                                   
     ‘AFMT_U16_BE’                 Unsigned, 16-bit big-endian audio
                                   

     Consult the OSS documentation for a full list of audio formats, and
     note that most devices support only a subset of these formats.
     Some older devices only support ‘AFMT_U8’; the most common format
     used today is ‘AFMT_S16_LE’.

 -- Method: oss_audio_device.setfmt (format)

     Try to set the current audio format to `format'—see *note
     getfmts(): 3160. for a list.  Returns the audio format that the
     device was set to, which may not be the requested format.  May also
     be used to return the current audio format—do this by passing an
     “audio format” of ‘AFMT_QUERY’.

 -- Method: oss_audio_device.channels (nchannels)

     Set the number of output channels to `nchannels'.  A value of 1
     indicates monophonic sound, 2 stereophonic.  Some devices may have
     more than 2 channels, and some high-end devices may not support
     mono.  Returns the number of channels the device was set to.

 -- Method: oss_audio_device.speed (samplerate)

     Try to set the audio sampling rate to `samplerate' samples per
     second.  Returns the rate actually set.  Most sound devices don’t
     support arbitrary sampling rates.  Common rates are:

     Rate        Description
                 
     ------------------------------------------------------------
                 
     8000        default rate for ‘/dev/audio’
                 
                 
     11025       speech recording
                 
                 
     22050

     44100       CD quality audio (at 16 bits/sample and 2
                 channels)
                 
                 
     96000       DVD quality audio (at 24 bits/sample)
                 

 -- Method: oss_audio_device.sync ()

     Wait until the sound device has played every byte in its buffer.
     (This happens implicitly when the device is closed.)  The OSS
     documentation recommends closing and re-opening the device rather
     than using *note sync(): 3164.

 -- Method: oss_audio_device.reset ()

     Immediately stop playing or recording and return the device to a
     state where it can accept commands.  The OSS documentation
     recommends closing and re-opening the device after calling *note
     reset(): 3165.

 -- Method: oss_audio_device.post ()

     Tell the driver that there is likely to be a pause in the output,
     making it possible for the device to handle the pause more
     intelligently.  You might use this after playing a spot sound
     effect, before waiting for user input, or before doing disk I/O.

The following convenience methods combine several ioctls, or one ioctl
and some simple calculations.

 -- Method: oss_audio_device.setparameters (format, nchannels,
          samplerate[, strict=False])

     Set the key audio sampling parameters—sample format, number of
     channels, and sampling rate—in one method call.  `format',
     `nchannels', and `samplerate' should be as specified in the *note
     setfmt(): 3161, *note channels(): 3162, and *note speed(): 3163.
     methods.  If `strict' is true, *note setparameters(): 3167. checks
     to see if each parameter was actually set to the requested value,
     and raises *note OSSAudioError: 3155. if not.  Returns a tuple
     (`format', `nchannels', `samplerate') indicating the parameter
     values that were actually set by the device driver (i.e., the same
     as the return values of *note setfmt(): 3161, *note channels():
     3162, and *note speed(): 3163.).

     For example,

          (fmt, channels, rate) = dsp.setparameters(fmt, channels, rate)

     is equivalent to

          fmt = dsp.setfmt(fmt)
          channels = dsp.channels(channels)
          rate = dsp.rate(rate)

 -- Method: oss_audio_device.bufsize ()

     Returns the size of the hardware buffer, in samples.

 -- Method: oss_audio_device.obufcount ()

     Returns the number of samples that are in the hardware buffer yet
     to be played.

 -- Method: oss_audio_device.obuffree ()

     Returns the number of samples that could be queued into the
     hardware buffer to be played without blocking.

Audio device objects also support several read-only attributes:

 -- Attribute: oss_audio_device.closed

     Boolean indicating whether the device has been closed.

 -- Attribute: oss_audio_device.name

     String containing the name of the device file.

 -- Attribute: oss_audio_device.mode

     The I/O mode for the file, either ‘"r"’, ‘"rw"’, or ‘"w"’.


File: python.info,  Node: Mixer Device Objects,  Prev: Audio Device Objects,  Up: ossaudiodev — Access to OSS-compatible audio devices

5.22.9.2 Mixer Device Objects
.............................

The mixer object provides two file-like methods:

 -- Method: oss_mixer_device.close ()

     This method closes the open mixer device file.  Any further
     attempts to use the mixer after this file is closed will raise an
     *note OSError: 304.

 -- Method: oss_mixer_device.fileno ()

     Returns the file handle number of the open mixer device file.

Changed in version 3.2: Mixer objects also support the context
management protocol.

The remaining methods are specific to audio mixing:

 -- Method: oss_mixer_device.controls ()

     This method returns a bitmask specifying the available mixer
     controls (“Control” being a specific mixable “channel”, such as
     ‘SOUND_MIXER_PCM’ or ‘SOUND_MIXER_SYNTH’).  This bitmask indicates
     a subset of all available mixer controls—the ‘SOUND_MIXER_*’
     constants defined at module level.  To determine if, for example,
     the current mixer object supports a PCM mixer, use the following
     Python code:

          mixer=ossaudiodev.openmixer()
          if mixer.controls() & (1 << ossaudiodev.SOUND_MIXER_PCM):
              # PCM is supported
              ... code ...

     For most purposes, the ‘SOUND_MIXER_VOLUME’ (master volume) and
     ‘SOUND_MIXER_PCM’ controls should suffice—but code that uses the
     mixer should be flexible when it comes to choosing mixer controls.
     On the Gravis Ultrasound, for example, ‘SOUND_MIXER_VOLUME’ does
     not exist.

 -- Method: oss_mixer_device.stereocontrols ()

     Returns a bitmask indicating stereo mixer controls.  If a bit is
     set, the corresponding control is stereo; if it is unset, the
     control is either monophonic or not supported by the mixer (use in
     combination with *note controls(): 3172. to determine which).

     See the code example for the *note controls(): 3172. function for
     an example of getting data from a bitmask.

 -- Method: oss_mixer_device.reccontrols ()

     Returns a bitmask specifying the mixer controls that may be used to
     record.  See the code example for *note controls(): 3172. for an
     example of reading from a bitmask.

 -- Method: oss_mixer_device.get (control)

     Returns the volume of a given mixer control.  The returned volume
     is a 2-tuple ‘(left_volume,right_volume)’.  Volumes are specified
     as numbers from 0 (silent) to 100 (full volume).  If the control is
     monophonic, a 2-tuple is still returned, but both volumes are the
     same.

     Raises *note OSSAudioError: 3155. if an invalid control is
     specified, or *note OSError: 304. if an unsupported control is
     specified.

 -- Method: oss_mixer_device.set (control, (left, right))

     Sets the volume for a given mixer control to ‘(left,right)’.
     ‘left’ and ‘right’ must be ints and between 0 (silent) and 100
     (full volume).  On success, the new volume is returned as a
     2-tuple.  Note that this may not be exactly the same as the volume
     specified, because of the limited resolution of some soundcard’s
     mixers.

     Raises *note OSSAudioError: 3155. if an invalid mixer control was
     specified, or if the specified volumes were out-of-range.

 -- Method: oss_mixer_device.get_recsrc ()

     This method returns a bitmask indicating which control(s) are
     currently being used as a recording source.

 -- Method: oss_mixer_device.set_recsrc (bitmask)

     Call this function to specify a recording source.  Returns a
     bitmask indicating the new recording source (or sources) if
     successful; raises *note OSError: 304. if an invalid source was
     specified.  To set the current recording source to the microphone
     input:

          mixer.setrecsrc (1 << ossaudiodev.SOUND_MIXER_MIC)


File: python.info,  Node: Internationalization,  Next: Program Frameworks,  Prev: Multimedia Services,  Up: The Python Standard Library

5.23 Internationalization
=========================

The modules described in this chapter help you write software that is
independent of language and locale by providing mechanisms for selecting
a language to be used in program messages or by tailoring output to
match local conventions.

The list of modules described in this chapter is:

* Menu:

* gettext — Multilingual internationalization services::
* locale — Internationalization services::


File: python.info,  Node: gettext — Multilingual internationalization services,  Next: locale — Internationalization services,  Up: Internationalization

5.23.1 ‘gettext’ — Multilingual internationalization services
-------------------------------------------------------------

`Source code:' Lib/gettext.py(1)

__________________________________________________________________

The *note gettext: 87. module provides internationalization (I18N) and
localization (L10N) services for your Python modules and applications.
It supports both the GNU ‘gettext’ message catalog API and a higher
level, class-based API that may be more appropriate for Python files.
The interface described below allows you to write your module and
application messages in one natural language, and provide a catalog of
translated messages for running under different natural languages.

Some hints on localizing your Python modules and applications are also
given.

* Menu:

* GNU gettext API::
* Class-based API::
* Internationalizing your programs and modules::
* Acknowledgements: Acknowledgements<9>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/gettext.py


File: python.info,  Node: GNU gettext API,  Next: Class-based API,  Up: gettext — Multilingual internationalization services

5.23.1.1 GNU ‘gettext’ API
..........................

The *note gettext: 87. module defines the following API, which is very
similar to the GNU ‘gettext’ API. If you use this API you will affect
the translation of your entire application globally.  Often this is what
you want if your application is monolingual, with the choice of language
dependent on the locale of your user.  If you are localizing a Python
module, or if your application needs to switch languages on the fly, you
probably want to use the class-based API instead.

 -- Function: gettext.bindtextdomain (domain, localedir=None)

     Bind the `domain' to the locale directory `localedir'.  More
     concretely, *note gettext: 87. will look for binary ‘.mo’ files for
     the given domain using the path (on Unix):
     ‘`localedir'/`language'/LC_MESSAGES/`domain'.mo’, where `language'
     is searched for in the environment variables ‘LANGUAGE’, ‘LC_ALL’,
     ‘LC_MESSAGES’, and ‘LANG’ respectively.

     If `localedir' is omitted or ‘None’, then the current binding for
     `domain' is returned.  (1)

 -- Function: gettext.bind_textdomain_codeset (domain, codeset=None)

     Bind the `domain' to `codeset', changing the encoding of byte
     strings returned by the *note lgettext(): 3b6, *note ldgettext():
     3b7, *note lngettext(): 3b8. and *note ldngettext(): 3b9.
     functions.  If `codeset' is omitted, then the current binding is
     returned.

     Deprecated since version 3.8, will be removed in version 3.10.

 -- Function: gettext.textdomain (domain=None)

     Change or query the current global domain.  If `domain' is ‘None’,
     then the current global domain is returned, otherwise the global
     domain is set to `domain', which is returned.

 -- Function: gettext.gettext (message)

     Return the localized translation of `message', based on the current
     global domain, language, and locale directory.  This function is
     usually aliased as ‘_()’ in the local namespace (see examples
     below).

 -- Function: gettext.dgettext (domain, message)

     Like *note gettext(): e92, but look the message up in the specified
     `domain'.

 -- Function: gettext.ngettext (singular, plural, n)

     Like *note gettext(): e92, but consider plural forms.  If a
     translation is found, apply the plural formula to `n', and return
     the resulting message (some languages have more than two plural
     forms).  If no translation is found, return `singular' if `n' is 1;
     return `plural' otherwise.

     The Plural formula is taken from the catalog header.  It is a C or
     Python expression that has a free variable `n'; the expression
     evaluates to the index of the plural in the catalog.  See the GNU
     gettext documentation(2) for the precise syntax to be used in ‘.po’
     files and the formulas for a variety of languages.

 -- Function: gettext.dngettext (domain, singular, plural, n)

     Like *note ngettext(): 3183, but look the message up in the
     specified `domain'.

 -- Function: gettext.pgettext (context, message)

 -- Function: gettext.dpgettext (domain, context, message)

 -- Function: gettext.npgettext (context, singular, plural, n)

 -- Function: gettext.dnpgettext (domain, context, singular, plural, n)

     Similar to the corresponding functions without the ‘p’ in the
     prefix (that is, *note gettext(): 87, *note dgettext(): 3182, *note
     ngettext(): 3183, *note dngettext(): 3184.), but the translation is
     restricted to the given message `context'.

     New in version 3.8.

 -- Function: gettext.lgettext (message)

 -- Function: gettext.ldgettext (domain, message)

 -- Function: gettext.lngettext (singular, plural, n)

 -- Function: gettext.ldngettext (domain, singular, plural, n)

     Equivalent to the corresponding functions without the ‘l’ prefix
     (*note gettext(): e92, *note dgettext(): 3182, *note ngettext():
     3183. and *note dngettext(): 3184.), but the translation is
     returned as a byte string encoded in the preferred system encoding
     if no other encoding was explicitly set with *note
     bind_textdomain_codeset(): 3ba.

          Warning: These functions should be avoided in Python 3,
          because they return encoded bytes.  It’s much better to use
          alternatives which return Unicode strings instead, since most
          Python applications will want to manipulate human readable
          text as strings instead of bytes.  Further, it’s possible that
          you may get unexpected Unicode-related exceptions if there are
          encoding problems with the translated strings.

     Deprecated since version 3.8, will be removed in version 3.10.

Note that GNU ‘gettext’ also defines a ‘dcgettext()’ method, but this
was deemed not useful and so it is currently unimplemented.

Here’s an example of typical usage for this API:

     import gettext
     gettext.bindtextdomain('myapplication', '/path/to/my/language/directory')
     gettext.textdomain('myapplication')
     _ = gettext.gettext
     # ...
     print(_('This is a translatable string.'))

   ---------- Footnotes ----------

   (1) (1) The default locale directory is system dependent; for
example, on RedHat Linux it is ‘/usr/share/locale’, but on Solaris it is
‘/usr/lib/locale’.  The *note gettext: 87. module does not try to
support these system dependent defaults; instead its default is
‘`sys.base_prefix'/share/locale’ (see *note sys.base_prefix: 3180.).
For this reason, it is always best to call *note bindtextdomain(): 317f.
with an explicit absolute path at the start of your application.

   (2) https://www.gnu.org/software/gettext/manual/gettext.html


File: python.info,  Node: Class-based API,  Next: Internationalizing your programs and modules,  Prev: GNU gettext API,  Up: gettext — Multilingual internationalization services

5.23.1.2 Class-based API
........................

The class-based API of the *note gettext: 87. module gives you more
flexibility and greater convenience than the GNU ‘gettext’ API. It is
the recommended way of localizing your Python applications and modules.
‘gettext’ defines a *note GNUTranslations: 3189. class which implements
the parsing of GNU ‘.mo’ format files, and has methods for returning
strings.  Instances of this class can also install themselves in the
built-in namespace as the function ‘_()’.

 -- Function: gettext.find (domain, localedir=None, languages=None,
          all=False)

     This function implements the standard ‘.mo’ file search algorithm.
     It takes a `domain', identical to what *note textdomain(): 3181.
     takes.  Optional `localedir' is as in *note bindtextdomain(): 317f.
     Optional `languages' is a list of strings, where each string is a
     language code.

     If `localedir' is not given, then the default system locale
     directory is used.  (1) If `languages' is not given, then the
     following environment variables are searched: ‘LANGUAGE’, ‘LC_ALL’,
     ‘LC_MESSAGES’, and ‘LANG’.  The first one returning a non-empty
     value is used for the `languages' variable.  The environment
     variables should contain a colon separated list of languages, which
     will be split on the colon to produce the expected list of language
     code strings.

     *note find(): 318a. then expands and normalizes the languages, and
     then iterates through them, searching for an existing file built of
     these components:

     ‘`localedir'/`language'/LC_MESSAGES/`domain'.mo’

     The first such file name that exists is returned by *note find():
     318a.  If no such file is found, then ‘None’ is returned.  If `all'
     is given, it returns a list of all file names, in the order in
     which they appear in the languages list or the environment
     variables.

 -- Function: gettext.translation (domain, localedir=None,
          languages=None, class_=None, fallback=False, codeset=None)

     Return a ‘*Translations’ instance based on the `domain',
     `localedir', and `languages', which are first passed to *note
     find(): 318a. to get a list of the associated ‘.mo’ file paths.
     Instances with identical ‘.mo’ file names are cached.  The actual
     class instantiated is `class_' if provided, otherwise *note
     GNUTranslations: 3189.  The class’s constructor must take a single
     *note file object: c14. argument.  If provided, `codeset' will
     change the charset used to encode translated strings in the *note
     lgettext(): 318b. and *note lngettext(): 318c. methods.

     If multiple files are found, later files are used as fallbacks for
     earlier ones.  To allow setting the fallback, *note copy.copy():
     4d2. is used to clone each translation object from the cache; the
     actual instance data is still shared with the cache.

     If no ‘.mo’ file is found, this function raises *note OSError: 304.
     if `fallback' is false (which is the default), and returns a *note
     NullTranslations: 318d. instance if `fallback' is true.

     Changed in version 3.3: *note IOError: a73. used to be raised
     instead of *note OSError: 304.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `codeset' parameter.

 -- Function: gettext.install (domain, localedir=None, codeset=None,
          names=None)

     This installs the function ‘_()’ in Python’s builtins namespace,
     based on `domain', `localedir', and `codeset' which are passed to
     the function *note translation(): 3bd.

     For the `names' parameter, please see the description of the
     translation object’s *note install(): 318e. method.

     As seen below, you usually mark the strings in your application
     that are candidates for translation, by wrapping them in a call to
     the ‘_()’ function, like this:

          print(_('This string will be translated.'))

     For convenience, you want the ‘_()’ function to be installed in
     Python’s builtins namespace, so it is easily accessible in all
     modules of your application.

     Deprecated since version 3.8, will be removed in version 3.10: The
     `codeset' parameter.

* Menu:

* The NullTranslations class::
* The GNUTranslations class::
* Solaris message catalog support::
* The Catalog constructor::

   ---------- Footnotes ----------

   (1) (2) See the footnote for *note bindtextdomain(): 317f. above.


File: python.info,  Node: The NullTranslations class,  Next: The GNUTranslations class,  Up: Class-based API

5.23.1.3 The ‘NullTranslations’ class
.....................................

Translation classes are what actually implement the translation of
original source file message strings to translated message strings.  The
base class used by all translation classes is *note NullTranslations:
318d.; this provides the basic interface you can use to write your own
specialized translation classes.  Here are the methods of
‘NullTranslations’:

 -- Class: gettext.NullTranslations (fp=None)

     Takes an optional *note file object: c14. `fp', which is ignored by
     the base class.  Initializes “protected” instance variables `_info'
     and `_charset' which are set by derived classes, as well as
     `_fallback', which is set through *note add_fallback(): 3190.  It
     then calls ‘self._parse(fp)’ if `fp' is not ‘None’.

      -- Method: _parse (fp)

          No-op in the base class, this method takes file object `fp',
          and reads the data from the file, initializing its message
          catalog.  If you have an unsupported message catalog file
          format, you should override this method to parse your format.

      -- Method: add_fallback (fallback)

          Add `fallback' as the fallback object for the current
          translation object.  A translation object should consult the
          fallback if it cannot provide a translation for a given
          message.

      -- Method: gettext (message)

          If a fallback has been set, forward ‘gettext()’ to the
          fallback.  Otherwise, return `message'.  Overridden in derived
          classes.

      -- Method: ngettext (singular, plural, n)

          If a fallback has been set, forward ‘ngettext()’ to the
          fallback.  Otherwise, return `singular' if `n' is 1; return
          `plural' otherwise.  Overridden in derived classes.

      -- Method: pgettext (context, message)

          If a fallback has been set, forward *note pgettext(): 300. to
          the fallback.  Otherwise, return the translated message.
          Overridden in derived classes.

          New in version 3.8.

      -- Method: npgettext (context, singular, plural, n)

          If a fallback has been set, forward *note npgettext(): 3186.
          to the fallback.  Otherwise, return the translated message.
          Overridden in derived classes.

          New in version 3.8.

      -- Method: lgettext (message)

      -- Method: lngettext (singular, plural, n)

          Equivalent to *note gettext(): 3192. and *note ngettext():
          3193, but the translation is returned as a byte string encoded
          in the preferred system encoding if no encoding was explicitly
          set with *note set_output_charset(): 3bc.  Overridden in
          derived classes.

               Warning: These methods should be avoided in Python 3.
               See the warning for the *note lgettext(): 3b6. function.

          Deprecated since version 3.8, will be removed in version 3.10.

      -- Method: info ()

          Return the “protected” ‘_info’ variable, a dictionary
          containing the metadata found in the message catalog file.

      -- Method: charset ()

          Return the encoding of the message catalog file.

      -- Method: output_charset ()

          Return the encoding used to return translated messages in
          *note lgettext(): 318b. and *note lngettext(): 318c.

          Deprecated since version 3.8, will be removed in version 3.10.

      -- Method: set_output_charset (charset)

          Change the encoding used to return translated messages.

          Deprecated since version 3.8, will be removed in version 3.10.

      -- Method: install (names=None)

          This method installs *note gettext(): 3192. into the built-in
          namespace, binding it to ‘_’.

          If the `names' parameter is given, it must be a sequence
          containing the names of functions you want to install in the
          builtins namespace in addition to ‘_()’.  Supported names are
          ‘'gettext'’, ‘'ngettext'’, ‘'pgettext'’, ‘'npgettext'’,
          ‘'lgettext'’, and ‘'lngettext'’.

          Note that this is only one way, albeit the most convenient
          way, to make the ‘_()’ function available to your application.
          Because it affects the entire application globally, and
          specifically the built-in namespace, localized modules should
          never install ‘_()’.  Instead, they should use this code to
          make ‘_()’ available to their module:

               import gettext
               t = gettext.translation('mymodule', ...)
               _ = t.gettext

          This puts ‘_()’ only in the module’s global namespace and so
          only affects calls within this module.

          Changed in version 3.8: Added ‘'pgettext'’ and ‘'npgettext'’.


File: python.info,  Node: The GNUTranslations class,  Next: Solaris message catalog support,  Prev: The NullTranslations class,  Up: Class-based API

5.23.1.4 The ‘GNUTranslations’ class
....................................

The *note gettext: 87. module provides one additional class derived from
*note NullTranslations: 318d.: *note GNUTranslations: 3189.  This class
overrides ‘_parse()’ to enable reading GNU ‘gettext’ format ‘.mo’ files
in both big-endian and little-endian format.

*note GNUTranslations: 3189. parses optional metadata out of the
translation catalog.  It is convention with GNU ‘gettext’ to include
metadata as the translation for the empty string.  This metadata is in
RFC 822(1)-style ‘key: value’ pairs, and should contain the
‘Project-Id-Version’ key.  If the key ‘Content-Type’ is found, then the
‘charset’ property is used to initialize the “protected” ‘_charset’
instance variable, defaulting to ‘None’ if not found.  If the charset
encoding is specified, then all message ids and message strings read
from the catalog are converted to Unicode using this encoding, else
ASCII is assumed.

Since message ids are read as Unicode strings too, all ‘*gettext()’
methods will assume message ids as Unicode strings, not byte strings.

The entire set of key/value pairs are placed into a dictionary and set
as the “protected” ‘_info’ instance variable.

If the ‘.mo’ file’s magic number is invalid, the major version number is
unexpected, or if other problems occur while reading the file,
instantiating a *note GNUTranslations: 3189. class can raise *note
OSError: 304.

 -- Class: gettext.GNUTranslations

     The following methods are overridden from the base class
     implementation:

      -- Method: gettext (message)

          Look up the `message' id in the catalog and return the
          corresponding message string, as a Unicode string.  If there
          is no entry in the catalog for the `message' id, and a
          fallback has been set, the look up is forwarded to the
          fallback’s *note gettext(): 3192. method.  Otherwise, the
          `message' id is returned.

      -- Method: ngettext (singular, plural, n)

          Do a plural-forms lookup of a message id.  `singular' is used
          as the message id for purposes of lookup in the catalog, while
          `n' is used to determine which plural form to use.  The
          returned message string is a Unicode string.

          If the message id is not found in the catalog, and a fallback
          is specified, the request is forwarded to the fallback’s *note
          ngettext(): 3193. method.  Otherwise, when `n' is 1 `singular'
          is returned, and `plural' is returned in all other cases.

          Here is an example:

               n = len(os.listdir('.'))
               cat = GNUTranslations(somefile)
               message = cat.ngettext(
                   'There is %(num)d file in this directory',
                   'There are %(num)d files in this directory',
                   n) % {'num': n}

      -- Method: pgettext (context, message)

          Look up the `context' and `message' id in the catalog and
          return the corresponding message string, as a Unicode string.
          If there is no entry in the catalog for the `message' id and
          `context', and a fallback has been set, the look up is
          forwarded to the fallback’s *note pgettext(): 300. method.
          Otherwise, the `message' id is returned.

          New in version 3.8.

      -- Method: npgettext (context, singular, plural, n)

          Do a plural-forms lookup of a message id.  `singular' is used
          as the message id for purposes of lookup in the catalog, while
          `n' is used to determine which plural form to use.

          If the message id for `context' is not found in the catalog,
          and a fallback is specified, the request is forwarded to the
          fallback’s *note npgettext(): 3186. method.  Otherwise, when
          `n' is 1 `singular' is returned, and `plural' is returned in
          all other cases.

          New in version 3.8.

      -- Method: lgettext (message)

      -- Method: lngettext (singular, plural, n)

          Equivalent to *note gettext(): 3199. and *note ngettext():
          319a, but the translation is returned as a byte string encoded
          in the preferred system encoding if no encoding was explicitly
          set with *note set_output_charset(): 3bc.

               Warning: These methods should be avoided in Python 3.
               See the warning for the *note lgettext(): 3b6. function.

          Deprecated since version 3.8, will be removed in version 3.10.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc822.html


File: python.info,  Node: Solaris message catalog support,  Next: The Catalog constructor,  Prev: The GNUTranslations class,  Up: Class-based API

5.23.1.5 Solaris message catalog support
........................................

The Solaris operating system defines its own binary ‘.mo’ file format,
but since no documentation can be found on this format, it is not
supported at this time.


File: python.info,  Node: The Catalog constructor,  Prev: Solaris message catalog support,  Up: Class-based API

5.23.1.6 The Catalog constructor
................................

GNOME uses a version of the *note gettext: 87. module by James
Henstridge, but this version has a slightly different API. Its
documented usage was:

     import gettext
     cat = gettext.Catalog(domain, localedir)
     _ = cat.gettext
     print(_('hello world'))

For compatibility with this older module, the function ‘Catalog()’ is an
alias for the *note translation(): 3bd. function described above.

One difference between this module and Henstridge’s: his catalog objects
supported access through a mapping API, but this appears to be unused
and so is not currently supported.


File: python.info,  Node: Internationalizing your programs and modules,  Next: Acknowledgements<9>,  Prev: Class-based API,  Up: gettext — Multilingual internationalization services

5.23.1.7 Internationalizing your programs and modules
.....................................................

Internationalization (I18N) refers to the operation by which a program
is made aware of multiple languages.  Localization (L10N) refers to the
adaptation of your program, once internationalized, to the local
language and cultural habits.  In order to provide multilingual messages
for your Python programs, you need to take the following steps:

  1. prepare your program or module by specially marking translatable
     strings

  2. run a suite of tools over your marked files to generate raw
     messages catalogs

  3. create language-specific translations of the message catalogs

  4. use the *note gettext: 87. module so that message strings are
     properly translated

In order to prepare your code for I18N, you need to look at all the
strings in your files.  Any string that needs to be translated should be
marked by wrapping it in ‘_('...')’ — that is, a call to the function
‘_()’.  For example:

     filename = 'mylog.txt'
     message = _('writing a log message')
     with open(filename, 'w') as fp:
         fp.write(message)

In this example, the string ‘'writing a log message'’ is marked as a
candidate for translation, while the strings ‘'mylog.txt'’ and ‘'w'’ are
not.

There are a few tools to extract the strings meant for translation.  The
original GNU ‘gettext’ only supported C or C++ source code but its
extended version ‘xgettext’ scans code written in a number of languages,
including Python, to find strings marked as translatable.  Babel(1) is a
Python internationalization library that includes a ‘pybabel’ script to
extract and compile message catalogs.  François Pinard’s program called
‘xpot’ does a similar job and is available as part of his po-utils
package(2).

(Python also includes pure-Python versions of these programs, called
‘pygettext.py’ and ‘msgfmt.py’; some Python distributions will install
them for you.  ‘pygettext.py’ is similar to ‘xgettext’, but only
understands Python source code and cannot handle other programming
languages such as C or C++.  ‘pygettext.py’ supports a command-line
interface similar to ‘xgettext’; for details on its use, run
‘pygettext.py --help’.  ‘msgfmt.py’ is binary compatible with GNU
‘msgfmt’.  With these two programs, you may not need the GNU ‘gettext’
package to internationalize your Python applications.)

‘xgettext’, ‘pygettext’, and similar tools generate ‘.po’ files that are
message catalogs.  They are structured human-readable files that contain
every marked string in the source code, along with a placeholder for the
translated versions of these strings.

Copies of these ‘.po’ files are then handed over to the individual human
translators who write translations for every supported natural language.
They send back the completed language-specific versions as a
‘<language-name>.po’ file that’s compiled into a machine-readable ‘.mo’
binary catalog file using the ‘msgfmt’ program.  The ‘.mo’ files are
used by the *note gettext: 87. module for the actual translation
processing at run-time.

How you use the *note gettext: 87. module in your code depends on
whether you are internationalizing a single module or your entire
application.  The next two sections will discuss each case.

* Menu:

* Localizing your module::
* Localizing your application::
* Changing languages on the fly::
* Deferred translations::

   ---------- Footnotes ----------

   (1) http://babel.pocoo.org/

   (2) https://github.com/pinard/po-utils


File: python.info,  Node: Localizing your module,  Next: Localizing your application,  Up: Internationalizing your programs and modules

5.23.1.8 Localizing your module
...............................

If you are localizing your module, you must take care not to make global
changes, e.g.  to the built-in namespace.  You should not use the GNU
‘gettext’ API but instead the class-based API.

Let’s say your module is called “spam” and the module’s various natural
language translation ‘.mo’ files reside in ‘/usr/share/locale’ in GNU
‘gettext’ format.  Here’s what you would put at the top of your module:

     import gettext
     t = gettext.translation('spam', '/usr/share/locale')
     _ = t.gettext


File: python.info,  Node: Localizing your application,  Next: Changing languages on the fly,  Prev: Localizing your module,  Up: Internationalizing your programs and modules

5.23.1.9 Localizing your application
....................................

If you are localizing your application, you can install the ‘_()’
function globally into the built-in namespace, usually in the main
driver file of your application.  This will let all your
application-specific files just use ‘_('...')’ without having to
explicitly install it in each file.

In the simple case then, you need only add the following bit of code to
the main driver file of your application:

     import gettext
     gettext.install('myapplication')

If you need to set the locale directory, you can pass it into the *note
install(): 3be. function:

     import gettext
     gettext.install('myapplication', '/usr/share/locale')


File: python.info,  Node: Changing languages on the fly,  Next: Deferred translations,  Prev: Localizing your application,  Up: Internationalizing your programs and modules

5.23.1.10 Changing languages on the fly
.......................................

If your program needs to support many languages at the same time, you
may want to create multiple translation instances and then switch
between them explicitly, like so:

     import gettext

     lang1 = gettext.translation('myapplication', languages=['en'])
     lang2 = gettext.translation('myapplication', languages=['fr'])
     lang3 = gettext.translation('myapplication', languages=['de'])

     # start by using language1
     lang1.install()

     # ... time goes by, user selects language 2
     lang2.install()

     # ... more time goes by, user selects language 3
     lang3.install()


File: python.info,  Node: Deferred translations,  Prev: Changing languages on the fly,  Up: Internationalizing your programs and modules

5.23.1.11 Deferred translations
...............................

In most coding situations, strings are translated where they are coded.
Occasionally however, you need to mark strings for translation, but
defer actual translation until later.  A classic example is:

     animals = ['mollusk',
                'albatross',
                'rat',
                'penguin',
                'python', ]
     # ...
     for a in animals:
         print(a)

Here, you want to mark the strings in the ‘animals’ list as being
translatable, but you don’t actually want to translate them until they
are printed.

Here is one way you can handle this situation:

     def _(message): return message

     animals = [_('mollusk'),
                _('albatross'),
                _('rat'),
                _('penguin'),
                _('python'), ]

     del _

     # ...
     for a in animals:
         print(_(a))

This works because the dummy definition of ‘_()’ simply returns the
string unchanged.  And this dummy definition will temporarily override
any definition of ‘_()’ in the built-in namespace (until the *note del:
13a2. command).  Take care, though if you have a previous definition of
‘_()’ in the local namespace.

Note that the second use of ‘_()’ will not identify “a” as being
translatable to the ‘gettext’ program, because the parameter is not a
string literal.

Another way to handle this is with the following example:

     def N_(message): return message

     animals = [N_('mollusk'),
                N_('albatross'),
                N_('rat'),
                N_('penguin'),
                N_('python'), ]

     # ...
     for a in animals:
         print(_(a))

In this case, you are marking translatable strings with the function
‘N_()’, which won’t conflict with any definition of ‘_()’.  However, you
will need to teach your message extraction program to look for
translatable strings marked with ‘N_()’.  ‘xgettext’, ‘pygettext’,
‘pybabel extract’, and ‘xpot’ all support this through the use of the
‘-k’ command-line switch.  The choice of ‘N_()’ here is totally
arbitrary; it could have just as easily been
‘MarkThisStringForTranslation()’.


File: python.info,  Node: Acknowledgements<9>,  Prev: Internationalizing your programs and modules,  Up: gettext — Multilingual internationalization services

5.23.1.12 Acknowledgements
..........................

The following people contributed code, feedback, design suggestions,
previous implementations, and valuable experience to the creation of
this module:

   * Peter Funk

   * James Henstridge

   * Juan David Ibáñez Palomar

   * Marc-André Lemburg

   * Martin von Löwis

   * François Pinard

   * Barry Warsaw

   * Gustavo Niemeyer


File: python.info,  Node: locale — Internationalization services,  Prev: gettext — Multilingual internationalization services,  Up: Internationalization

5.23.2 ‘locale’ — Internationalization services
-----------------------------------------------

`Source code:' Lib/locale.py(1)

__________________________________________________________________

The *note locale: a9. module opens access to the POSIX locale database
and functionality.  The POSIX locale mechanism allows programmers to
deal with certain cultural issues in an application, without requiring
the programmer to know all the specifics of each country where the
software is executed.

The *note locale: a9. module is implemented on top of the ‘_locale’
module, which in turn uses an ANSI C locale implementation if available.

The *note locale: a9. module defines the following exception and
functions:

 -- Exception: locale.Error

     Exception raised when the locale passed to *note setlocale(): 2166.
     is not recognized.

 -- Function: locale.setlocale (category, locale=None)

     If `locale' is given and not ‘None’, *note setlocale(): 2166.
     modifies the locale setting for the `category'.  The available
     categories are listed in the data description below.  `locale' may
     be a string, or an iterable of two strings (language code and
     encoding).  If it’s an iterable, it’s converted to a locale name
     using the locale aliasing engine.  An empty string specifies the
     user’s default settings.  If the modification of the locale fails,
     the exception *note Error: 31a9. is raised.  If successful, the new
     locale setting is returned.

     If `locale' is omitted or ‘None’, the current setting for
     `category' is returned.

     *note setlocale(): 2166. is not thread-safe on most systems.
     Applications typically start with a call of

          import locale
          locale.setlocale(locale.LC_ALL, '')

     This sets the locale for all categories to the user’s default
     setting (typically specified in the ‘LANG’ environment variable).
     If the locale is not changed thereafter, using multithreading
     should not cause problems.

 -- Function: locale.localeconv ()

     Returns the database of the local conventions as a dictionary.
     This dictionary has the following strings as keys:

     Category                   Key                                       Meaning
                                                                          
     ----------------------------------------------------------------------------------------------------------
                                                                          
     *note LC_NUMERIC: 31aa.    ‘'decimal_point'’                         Decimal point character.
                                                                          
                                                                          
                                ‘'grouping'’                              Sequence of numbers specifying
                                                                          which relative positions the
                                                                          ‘'thousands_sep'’ is expected.  If
                                                                          the sequence is terminated with
                                                                          *note CHAR_MAX: 31ab, no further
                                                                          grouping is performed.  If the
                                                                          sequence terminates with a ‘0’,
                                                                          the last group size is repeatedly
                                                                          used.
                                                                          
                                                                          
                                ‘'thousands_sep'’                         Character used between groups.
                                                                          
                                                                          
     *note LC_MONETARY: 31ac.   ‘'int_curr_symbol'’                       International currency symbol.
                                                                          
                                                                          
                                ‘'currency_symbol'’                       Local currency symbol.
                                                                          
                                                                          
                                ‘'p_cs_precedes/n_cs_precedes'’           Whether the currency symbol
                                                                          precedes the value (for positive
                                                                          resp.  negative values).
                                                                          
                                                                          
                                ‘'p_sep_by_space/n_sep_by_space'’         Whether the currency symbol is
                                                                          separated from the value by a
                                                                          space (for positive resp.
                                                                          negative values).
                                                                          
                                                                          
                                ‘'mon_decimal_point'’                     Decimal point used for monetary
                                                                          values.
                                                                          
                                                                          
                                ‘'frac_digits'’                           Number of fractional digits used
                                                                          in local formatting of monetary
                                                                          values.
                                                                          
                                                                          
                                ‘'int_frac_digits'’                       Number of fractional digits used
                                                                          in international formatting of
                                                                          monetary values.
                                                                          
                                                                          
                                ‘'mon_thousands_sep'’                     Group separator used for monetary
                                                                          values.
                                                                          
                                                                          
                                ‘'mon_grouping'’                          Equivalent to ‘'grouping'’, used
                                                                          for monetary values.
                                                                          
                                                                          
                                ‘'positive_sign'’                         Symbol used to annotate a positive
                                                                          monetary value.
                                                                          
                                                                          
                                ‘'negative_sign'’                         Symbol used to annotate a negative
                                                                          monetary value.
                                                                          
                                                                          
                                ‘'p_sign_posn/n_sign_posn'’               The position of the sign (for
                                                                          positive resp.  negative values),
                                                                          see below.
                                                                          

     All numeric values can be set to *note CHAR_MAX: 31ab. to indicate
     that there is no value specified in this locale.

     The possible values for ‘'p_sign_posn'’ and ‘'n_sign_posn'’ are
     given below.

     Value              Explanation
                        
     -----------------------------------------------------------------
                        
     ‘0’                Currency and value are surrounded by
                        parentheses.
                        
                        
     ‘1’                The sign should precede the value and
                        currency symbol.
                        
                        
     ‘2’                The sign should follow the value and
                        currency symbol.
                        
                        
     ‘3’                The sign should immediately precede the
                        value.
                        
                        
     ‘4’                The sign should immediately follow the
                        value.
                        
                        
     ‘CHAR_MAX’         Nothing is specified in this locale.
                        

     The function sets temporarily the ‘LC_CTYPE’ locale to the
     ‘LC_NUMERIC’ locale or the ‘LC_MONETARY’ locale if locales are
     different and numeric or monetary strings are non-ASCII. This
     temporary change affects other threads.

     Changed in version 3.7: The function now sets temporarily the
     ‘LC_CTYPE’ locale to the ‘LC_NUMERIC’ locale in some cases.

 -- Function: locale.nl_langinfo (option)

     Return some locale-specific information as a string.  This function
     is not available on all systems, and the set of possible options
     might also vary across platforms.  The possible argument values are
     numbers, for which symbolic constants are available in the locale
     module.

     The *note nl_langinfo(): 31ad. function accepts one of the
     following keys.  Most descriptions are taken from the corresponding
     description in the GNU C library.

      -- Data: locale.CODESET

          Get a string with the name of the character encoding used in
          the selected locale.

      -- Data: locale.D_T_FMT

          Get a string that can be used as a format string for *note
          time.strftime(): c37. to represent date and time in a
          locale-specific way.

      -- Data: locale.D_FMT

          Get a string that can be used as a format string for *note
          time.strftime(): c37. to represent a date in a locale-specific
          way.

      -- Data: locale.T_FMT

          Get a string that can be used as a format string for *note
          time.strftime(): c37. to represent a time in a locale-specific
          way.

      -- Data: locale.T_FMT_AMPM

          Get a format string for *note time.strftime(): c37. to
          represent time in the am/pm format.

      -- Data: DAY_1 ... DAY_7

          Get the name of the n-th day of the week.

               Note: This follows the US convention of ‘DAY_1’ being
               Sunday, not the international convention (ISO 8601) that
               Monday is the first day of the week.

      -- Data: ABDAY_1 ... ABDAY_7

          Get the abbreviated name of the n-th day of the week.

      -- Data: MON_1 ... MON_12

          Get the name of the n-th month.

      -- Data: ABMON_1 ... ABMON_12

          Get the abbreviated name of the n-th month.

      -- Data: locale.RADIXCHAR

          Get the radix character (decimal dot, decimal comma, etc.).

      -- Data: locale.THOUSEP

          Get the separator character for thousands (groups of three
          digits).

      -- Data: locale.YESEXPR

          Get a regular expression that can be used with the regex
          function to recognize a positive response to a yes/no
          question.

               Note: The expression is in the syntax suitable for the
               ‘regex()’ function from the C library, which might differ
               from the syntax used in *note re: dd.

      -- Data: locale.NOEXPR

          Get a regular expression that can be used with the regex(3)
          function to recognize a negative response to a yes/no
          question.

      -- Data: locale.CRNCYSTR

          Get the currency symbol, preceded by “-” if the symbol should
          appear before the value, “+” if the symbol should appear after
          the value, or “.” if the symbol should replace the radix
          character.

      -- Data: locale.ERA

          Get a string that represents the era used in the current
          locale.

          Most locales do not define this value.  An example of a locale
          which does define this value is the Japanese one.  In Japan,
          the traditional representation of dates includes the name of
          the era corresponding to the then-emperor’s reign.

          Normally it should not be necessary to use this value
          directly.  Specifying the ‘E’ modifier in their format strings
          causes the *note time.strftime(): c37. function to use this
          information.  The format of the returned string is not
          specified, and therefore you should not assume knowledge of it
          on different systems.

      -- Data: locale.ERA_D_T_FMT

          Get a format string for *note time.strftime(): c37. to
          represent date and time in a locale-specific era-based way.

      -- Data: locale.ERA_D_FMT

          Get a format string for *note time.strftime(): c37. to
          represent a date in a locale-specific era-based way.

      -- Data: locale.ERA_T_FMT

          Get a format string for *note time.strftime(): c37. to
          represent a time in a locale-specific era-based way.

      -- Data: locale.ALT_DIGITS

          Get a representation of up to 100 values used to represent the
          values 0 to 99.

 -- Function: locale.getdefaultlocale ([envvars])

     Tries to determine the default locale settings and returns them as
     a tuple of the form ‘(language code, encoding)’.

     According to POSIX, a program which has not called
     ‘setlocale(LC_ALL, '')’ runs using the portable ‘'C'’ locale.
     Calling ‘setlocale(LC_ALL, '')’ lets it use the default locale as
     defined by the ‘LANG’ variable.  Since we do not want to interfere
     with the current locale setting we thus emulate the behavior in the
     way described above.

     To maintain compatibility with other platforms, not only the ‘LANG’
     variable is tested, but a list of variables given as envvars
     parameter.  The first found to be defined will be used.  `envvars'
     defaults to the search path used in GNU gettext; it must always
     contain the variable name ‘'LANG'’.  The GNU gettext search path
     contains ‘'LC_ALL'’, ‘'LC_CTYPE'’, ‘'LANG'’ and ‘'LANGUAGE'’, in
     that order.

     Except for the code ‘'C'’, the language code corresponds to RFC
     1766(2).  `language code' and `encoding' may be ‘None’ if their
     values cannot be determined.

 -- Function: locale.getlocale (category=LC_CTYPE)

     Returns the current setting for the given locale category as
     sequence containing `language code', `encoding'.  `category' may be
     one of the ‘LC_*’ values except *note LC_ALL: 31bd.  It defaults to
     *note LC_CTYPE: 31be.

     Except for the code ‘'C'’, the language code corresponds to RFC
     1766(3).  `language code' and `encoding' may be ‘None’ if their
     values cannot be determined.

 -- Function: locale.getpreferredencoding (do_setlocale=True)

     Return the encoding used for text data, according to user
     preferences.  User preferences are expressed differently on
     different systems, and might not be available programmatically on
     some systems, so this function only returns a guess.

     On some systems, it is necessary to invoke *note setlocale(): 2166.
     to obtain the user preferences, so this function is not
     thread-safe.  If invoking setlocale is not necessary or desired,
     `do_setlocale' should be set to ‘False’.

     On Android or in the UTF-8 mode (*note -X: 290. ‘utf8’ option),
     always return ‘'UTF-8'’, the locale and the `do_setlocale' argument
     are ignored.

     Changed in version 3.7: The function now always returns ‘UTF-8’ on
     Android or if the UTF-8 mode is enabled.

 -- Function: locale.normalize (localename)

     Returns a normalized locale code for the given locale name.  The
     returned locale code is formatted for use with *note setlocale():
     2166.  If normalization fails, the original name is returned
     unchanged.

     If the given encoding is not known, the function defaults to the
     default encoding for the locale code just like *note setlocale():
     2166.

 -- Function: locale.resetlocale (category=LC_ALL)

     Sets the locale for `category' to the default setting.

     The default setting is determined by calling *note
     getdefaultlocale(): 1492.  `category' defaults to *note LC_ALL:
     31bd.

 -- Function: locale.strcoll (string1, string2)

     Compares two strings according to the current *note LC_COLLATE:
     31c2. setting.  As any other compare function, returns a negative,
     or a positive value, or ‘0’, depending on whether `string1'
     collates before or after `string2' or is equal to it.

 -- Function: locale.strxfrm (string)

     Transforms a string to one that can be used in locale-aware
     comparisons.  For example, ‘strxfrm(s1) < strxfrm(s2)’ is
     equivalent to ‘strcoll(s1, s2) < 0’.  This function can be used
     when the same string is compared repeatedly, e.g.  when collating a
     sequence of strings.

 -- Function: locale.format_string (format, val, grouping=False,
          monetary=False)

     Formats a number `val' according to the current *note LC_NUMERIC:
     31aa. setting.  The format follows the conventions of the ‘%’
     operator.  For floating point values, the decimal point is modified
     if appropriate.  If `grouping' is true, also takes the grouping
     into account.

     If `monetary' is true, the conversion uses monetary thousands
     separator and grouping strings.

     Processes formatting specifiers as in ‘format % val’, but takes the
     current locale settings into account.

     Changed in version 3.7: The `monetary' keyword parameter was added.

 -- Function: locale.format (format, val, grouping=False,
          monetary=False)

     Please note that this function works like *note format_string():
     4ab. but will only work for exactly one ‘%char’ specifier.  For
     example, ‘'%f'’ and ‘'%.0f'’ are both valid specifiers, but ‘'%f
     KiB'’ is not.

     For whole format strings, use *note format_string(): 4ab.

     Deprecated since version 3.7: Use *note format_string(): 4ab.
     instead.

 -- Function: locale.currency (val, symbol=True, grouping=False,
          international=False)

     Formats a number `val' according to the current *note LC_MONETARY:
     31ac. settings.

     The returned string includes the currency symbol if `symbol' is
     true, which is the default.  If `grouping' is true (which is not
     the default), grouping is done with the value.  If `international'
     is true (which is not the default), the international currency
     symbol is used.

     Note that this function will not work with the ‘C’ locale, so you
     have to set a locale via *note setlocale(): 2166. first.

 -- Function: locale.str (float)

     Formats a floating point number using the same format as the
     built-in function ‘str(float)’, but takes the decimal point into
     account.

 -- Function: locale.delocalize (string)

     Converts a string into a normalized number string, following the
     *note LC_NUMERIC: 31aa. settings.

     New in version 3.5.

 -- Function: locale.atof (string)

     Converts a string to a floating point number, following the *note
     LC_NUMERIC: 31aa. settings.

 -- Function: locale.atoi (string)

     Converts a string to an integer, following the *note LC_NUMERIC:
     31aa. conventions.

 -- Data: locale.LC_CTYPE

     Locale category for the character type functions.  Depending on the
     settings of this category, the functions of module *note string:
     f6. dealing with case change their behaviour.

 -- Data: locale.LC_COLLATE

     Locale category for sorting strings.  The functions *note
     strcoll(): 31c1. and *note strxfrm(): 31c3. of the *note locale:
     a9. module are affected.

 -- Data: locale.LC_TIME

     Locale category for the formatting of time.  The function *note
     time.strftime(): c37. follows these conventions.

 -- Data: locale.LC_MONETARY

     Locale category for formatting of monetary values.  The available
     options are available from the *note localeconv(): 585. function.

 -- Data: locale.LC_MESSAGES

     Locale category for message display.  Python currently does not
     support application specific locale-aware messages.  Messages
     displayed by the operating system, like those returned by *note
     os.strerror(): 2062. might be affected by this category.

 -- Data: locale.LC_NUMERIC

     Locale category for formatting numbers.  The functions *note
     format(): 56a, *note atoi(): 31c7, *note atof(): 31c6. and *note
     str(): 31c5. of the *note locale: a9. module are affected by that
     category.  All other numeric formatting operations are not
     affected.

 -- Data: locale.LC_ALL

     Combination of all locale settings.  If this flag is used when the
     locale is changed, setting the locale for all categories is
     attempted.  If that fails for any category, no category is changed
     at all.  When the locale is retrieved using this flag, a string
     indicating the setting for all categories is returned.  This string
     can be later used to restore the settings.

 -- Data: locale.CHAR_MAX

     This is a symbolic constant used for different values returned by
     *note localeconv(): 585.

Example:

     >>> import locale
     >>> loc = locale.getlocale()  # get current locale
     # use German locale; name might vary with platform
     >>> locale.setlocale(locale.LC_ALL, 'de_DE')
     >>> locale.strcoll('f\xe4n', 'foo')  # compare a string containing an umlaut
     >>> locale.setlocale(locale.LC_ALL, '')   # use user's preferred locale
     >>> locale.setlocale(locale.LC_ALL, 'C')  # use default (C) locale
     >>> locale.setlocale(locale.LC_ALL, loc)  # restore saved locale

* Menu:

* Background, details, hints, tips and caveats: Background details hints tips and caveats.
* For extension writers and programs that embed Python::
* Access to message catalogs::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/locale.py

   (2) https://tools.ietf.org/html/rfc1766.html

   (3) https://tools.ietf.org/html/rfc1766.html


File: python.info,  Node: Background details hints tips and caveats,  Next: For extension writers and programs that embed Python,  Up: locale — Internationalization services

5.23.2.1 Background, details, hints, tips and caveats
.....................................................

The C standard defines the locale as a program-wide property that may be
relatively expensive to change.  On top of that, some implementation are
broken in such a way that frequent locale changes may cause core dumps.
This makes the locale somewhat painful to use correctly.

Initially, when a program is started, the locale is the ‘C’ locale, no
matter what the user’s preferred locale is.  There is one exception: the
*note LC_CTYPE: 31be. category is changed at startup to set the current
locale encoding to the user’s preferred locale encoding.  The program
must explicitly say that it wants the user’s preferred locale settings
for other categories by calling ‘setlocale(LC_ALL, '')’.

It is generally a bad idea to call *note setlocale(): 2166. in some
library routine, since as a side effect it affects the entire program.
Saving and restoring it is almost as bad: it is expensive and affects
other threads that happen to run before the settings have been restored.

If, when coding a module for general use, you need a locale independent
version of an operation that is affected by the locale (such as certain
formats used with *note time.strftime(): c37.), you will have to find a
way to do it without using the standard library routine.  Even better is
convincing yourself that using locale settings is okay.  Only as a last
resort should you document that your module is not compatible with
non-‘C’ locale settings.

The only way to perform numeric operations according to the locale is to
use the special functions defined by this module: *note atof(): 31c6,
*note atoi(): 31c7, *note format(): 56a, *note str(): 31c5.

There is no way to perform case conversions and character
classifications according to the locale.  For (Unicode) text strings
these are done according to the character value only, while for byte
strings, the conversions and classifications are done according to the
ASCII value of the byte, and bytes whose high bit is set (i.e.,
non-ASCII bytes) are never converted or considered part of a character
class such as letter or whitespace.


File: python.info,  Node: For extension writers and programs that embed Python,  Next: Access to message catalogs,  Prev: Background details hints tips and caveats,  Up: locale — Internationalization services

5.23.2.2 For extension writers and programs that embed Python
.............................................................

Extension modules should never call *note setlocale(): 2166, except to
find out what the current locale is.  But since the return value can
only be used portably to restore it, that is not very useful (except
perhaps to find out whether or not the locale is ‘C’).

When Python code uses the *note locale: a9. module to change the locale,
this also affects the embedding application.  If the embedding
application doesn’t want this to happen, it should remove the ‘_locale’
extension module (which does all the work) from the table of built-in
modules in the ‘config.c’ file, and make sure that the ‘_locale’ module
is not accessible as a shared library.


File: python.info,  Node: Access to message catalogs,  Prev: For extension writers and programs that embed Python,  Up: locale — Internationalization services

5.23.2.3 Access to message catalogs
...................................

 -- Function: locale.gettext (msg)

 -- Function: locale.dgettext (domain, msg)

 -- Function: locale.dcgettext (domain, msg, category)

 -- Function: locale.textdomain (domain)

 -- Function: locale.bindtextdomain (domain, dir)

The locale module exposes the C library’s gettext interface on systems
that provide this interface.  It consists of the functions ‘gettext()’,
‘dgettext()’, ‘dcgettext()’, ‘textdomain()’, ‘bindtextdomain()’, and
‘bind_textdomain_codeset()’.  These are similar to the same functions in
the *note gettext: 87. module, but use the C library’s binary format for
message catalogs, and the C library’s search algorithms for locating
message catalogs.

Python applications should normally find no need to invoke these
functions, and should use *note gettext: 87. instead.  A known exception
to this rule are applications that link with additional C libraries
which internally invoke ‘gettext()’ or ‘dcgettext()’.  For these
applications, it may be necessary to bind the text domain, so that the
libraries can properly locate their message catalogs.


File: python.info,  Node: Program Frameworks,  Next: Graphical User Interfaces with Tk,  Prev: Internationalization,  Up: The Python Standard Library

5.24 Program Frameworks
=======================

The modules described in this chapter are frameworks that will largely
dictate the structure of your program.  Currently the modules described
here are all oriented toward writing command-line interfaces.

The full list of modules described in this chapter is:

* Menu:

* turtle — Turtle graphics::
* cmd — Support for line-oriented command interpreters::
* shlex — Simple lexical analysis::


File: python.info,  Node: turtle — Turtle graphics,  Next: cmd — Support for line-oriented command interpreters,  Up: Program Frameworks

5.24.1 ‘turtle’ — Turtle graphics
---------------------------------

`Source code:' Lib/turtle.py(1)

__________________________________________________________________

* Menu:

* Introduction: Introduction<11>.
* Overview of available Turtle and Screen methods::
* Methods of RawTurtle/Turtle and corresponding functions::
* Methods of TurtleScreen/Screen and corresponding functions::
* Public classes::
* Help and configuration::
* turtledemo — Demo scripts::
* Changes since Python 2.6: Changes since Python 2 6.
* Changes since Python 3.0: Changes since Python 3 0.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/turtle.py


File: python.info,  Node: Introduction<11>,  Next: Overview of available Turtle and Screen methods,  Up: turtle — Turtle graphics

5.24.1.1 Introduction
.....................

Turtle graphics is a popular way for introducing programming to kids.
It was part of the original Logo programming language developed by Wally
Feurzeig, Seymour Papert and Cynthia Solomon in 1967.

Imagine a robotic turtle starting at (0, 0) in the x-y plane.  After an
‘import turtle’, give it the command ‘turtle.forward(15)’, and it moves
(on-screen!)  15 pixels in the direction it is facing, drawing a line as
it moves.  Give it the command ‘turtle.right(25)’, and it rotates
in-place 25 degrees clockwise.

Turtle star
...........

Turtle can draw intricate shapes using programs that repeat simple
moves.

[python-figures/turtle-star]
     from turtle import *
     color('red', 'yellow')
     begin_fill()
     while True:
         forward(200)
         left(170)
         if abs(pos()) < 1:
             break
     end_fill()
     done()

By combining together these and similar commands, intricate shapes and
pictures can easily be drawn.

The *note turtle: 11f. module is an extended reimplementation of the
same-named module from the Python standard distribution up to version
Python 2.5.

It tries to keep the merits of the old turtle module and to be (nearly)
100% compatible with it.  This means in the first place to enable the
learning programmer to use all the commands, classes and methods
interactively when using the module from within IDLE run with the ‘-n’
switch.

The turtle module provides turtle graphics primitives, in both
object-oriented and procedure-oriented ways.  Because it uses *note
tkinter: 10e. for the underlying graphics, it needs a version of Python
installed with Tk support.

The object-oriented interface uses essentially two+two classes:

  1. The *note TurtleScreen: 31da. class defines graphics windows as a
     playground for the drawing turtles.  Its constructor needs a
     ‘tkinter.Canvas’ or a *note ScrolledCanvas: 31db. as argument.  It
     should be used when *note turtle: 11f. is used as part of some
     application.

     The function *note Screen(): 31dc. returns a singleton object of a
     *note TurtleScreen: 31da. subclass.  This function should be used
     when *note turtle: 11f. is used as a standalone tool for doing
     graphics.  As a singleton object, inheriting from its class is not
     possible.

     All methods of TurtleScreen/Screen also exist as functions, i.e.
     as part of the procedure-oriented interface.

  2. *note RawTurtle: 31dd. (alias: *note RawPen: 31de.) defines Turtle
     objects which draw on a *note TurtleScreen: 31da.  Its constructor
     needs a Canvas, ScrolledCanvas or TurtleScreen as argument, so the
     RawTurtle objects know where to draw.

     Derived from RawTurtle is the subclass *note Turtle: 31df. (alias:
     ‘Pen’), which draws on “the” *note Screen: 31dc. instance which is
     automatically created, if not already present.

     All methods of RawTurtle/Turtle also exist as functions, i.e.  part
     of the procedure-oriented interface.

The procedural interface provides functions which are derived from the
methods of the classes *note Screen: 31dc. and *note Turtle: 31df.  They
have the same names as the corresponding methods.  A screen object is
automatically created whenever a function derived from a Screen method
is called.  An (unnamed) turtle object is automatically created whenever
any of the functions derived from a Turtle method is called.

To use multiple turtles on a screen one has to use the object-oriented
interface.

     Note: In the following documentation the argument list for
     functions is given.  Methods, of course, have the additional first
     argument `self' which is omitted here.


File: python.info,  Node: Overview of available Turtle and Screen methods,  Next: Methods of RawTurtle/Turtle and corresponding functions,  Prev: Introduction<11>,  Up: turtle — Turtle graphics

5.24.1.2 Overview of available Turtle and Screen methods
........................................................

* Menu:

* Turtle methods::
* Methods of TurtleScreen/Screen::


File: python.info,  Node: Turtle methods,  Next: Methods of TurtleScreen/Screen,  Up: Overview of available Turtle and Screen methods

5.24.1.3 Turtle methods
.......................

Turtle motion

     Move and draw

               *note forward(): 31e2. | *note fd(): 31e3. 
               *note backward(): 31e4. | *note bk(): 31e5. | *note back(): 31e6. 
               *note right(): 31e7. | *note rt(): 31e8. 
               *note left(): 31e9. | *note lt(): 31ea. 
               *note goto(): 31eb. | *note setpos(): 31ec. | *note setposition(): 31ed. 
               *note setx(): 31ee. 
               *note sety(): 31ef. 
               *note setheading(): 31f0. | *note seth(): 31f1. 
               *note home(): 31f2. 
               *note circle(): 31f3. 
               *note dot(): 31f4. 
               *note stamp(): 31f5. 
               *note clearstamp(): 31f6. 
               *note clearstamps(): 31f7. 
               *note undo(): 31f8. 
               *note speed(): 31f9. 

     Tell Turtle’s state

               *note position(): 31fa. | *note pos(): 31fb. 
               *note towards(): 31fc. 
               *note xcor(): 31fd. 
               *note ycor(): 31fe. 
               *note heading(): 31ff. 
               *note distance(): 3200. 

     Setting and measurement

               *note degrees(): 3201. 
               *note radians(): 3202. 

Pen control

     Drawing state

               *note pendown(): 3203. | *note pd(): 3204. | *note down(): 3205. 
               *note penup(): 3206. | *note pu(): 3207. | *note up(): 3208. 
               *note pensize(): 3209. | *note width(): 320a. 
               *note pen(): 320b. 
               *note isdown(): 320c. 

     Color control

               *note color(): 320d. 
               *note pencolor(): 320e. 
               *note fillcolor(): 320f. 

     Filling

               *note filling(): 3210. 
               *note begin_fill(): 3211. 
               *note end_fill(): 3212. 

     More drawing control

               *note reset(): 3213. 
               *note clear(): 3214. 
               *note write(): 3215. 

Turtle state

     Visibility

               *note showturtle(): 3216. | *note st(): 3217. 
               *note hideturtle(): 3218. | *note ht(): 3219. 
               *note isvisible(): 321a. 

     Appearance

               *note shape(): 321b. 
               *note resizemode(): 321c. 
               *note shapesize(): 321d. | *note turtlesize(): 321e. 
               *note shearfactor(): 321f. 
               *note settiltangle(): 3220. 
               *note tiltangle(): 3221. 
               *note tilt(): 3222. 
               *note shapetransform(): 3223. 
               *note get_shapepoly(): 3224. 

Using events

          *note onclick(): 3225. 
          *note onrelease(): 3226. 
          *note ondrag(): 3227. 

Special Turtle methods

          *note begin_poly(): 3228. 
          *note end_poly(): 3229. 
          *note get_poly(): 322a. 
          *note clone(): 322b. 
          *note getturtle(): 322c. | *note getpen(): 322d. 
          *note getscreen(): 322e. 
          *note setundobuffer(): 322f. 
          *note undobufferentries(): 3230. 


File: python.info,  Node: Methods of TurtleScreen/Screen,  Prev: Turtle methods,  Up: Overview of available Turtle and Screen methods

5.24.1.4 Methods of TurtleScreen/Screen
.......................................

Window control

          *note bgcolor(): 3232. 
          *note bgpic(): 3233. 
          *note clearscreen(): 3234. 
          *note resetscreen(): 3235. 
          *note screensize(): 3236. 
          *note setworldcoordinates(): 3237. 

Animation control

          *note delay(): 3238. 
          *note tracer(): 3239. 
          *note update(): 323a. 

Using screen events

          *note listen(): 323b. 
          *note onkey(): 323c. | *note onkeyrelease(): 323d. 
          *note onkeypress(): 323e. 
          *note onclick(): 3225. | *note onscreenclick(): 323f. 
          *note ontimer(): 3240. 
          *note mainloop(): 3241. | *note done(): 3242. 

Settings and special methods

          *note mode(): 3243. 
          *note colormode(): 3244. 
          *note getcanvas(): 3245. 
          *note getshapes(): 3246. 
          *note register_shape(): 3247. | *note addshape(): 3248. 
          *note turtles(): 3249. 
          *note window_height(): 324a. 
          *note window_width(): 324b. 

Input methods

          *note textinput(): fa6. 
          *note numinput(): fa7. 

Methods specific to Screen

          *note bye(): 324c. 
          *note exitonclick(): 324d. 
          *note setup(): 324e. 
          *note title(): 324f. 


File: python.info,  Node: Methods of RawTurtle/Turtle and corresponding functions,  Next: Methods of TurtleScreen/Screen and corresponding functions,  Prev: Overview of available Turtle and Screen methods,  Up: turtle — Turtle graphics

5.24.1.5 Methods of RawTurtle/Turtle and corresponding functions
................................................................

Most of the examples in this section refer to a Turtle instance called
‘turtle’.

* Menu:

* Turtle motion::
* Tell Turtle’s state::
* Settings for measurement::
* Pen control::
* Turtle state::
* Using events::
* Special Turtle methods::
* Compound shapes::


File: python.info,  Node: Turtle motion,  Next: Tell Turtle’s state,  Up: Methods of RawTurtle/Turtle and corresponding functions

5.24.1.6 Turtle motion
......................

 -- Function: turtle.forward (distance)
 -- Function: turtle.fd (distance)


     Parameters: ‘distance’ – a number (integer or float)

     Move the turtle forward by the specified `distance', in the
     direction the turtle is headed.

          >>> turtle.position()
          (0.00,0.00)
          >>> turtle.forward(25)
          >>> turtle.position()
          (25.00,0.00)
          >>> turtle.forward(-75)
          >>> turtle.position()
          (-50.00,0.00)

 -- Function: turtle.back (distance)
 -- Function: turtle.bk (distance)
 -- Function: turtle.backward (distance)


     Parameters: ‘distance’ – a number

     Move the turtle backward by `distance', opposite to the direction
     the turtle is headed.  Do not change the turtle’s heading.

          >>> turtle.position()
          (0.00,0.00)
          >>> turtle.backward(30)
          >>> turtle.position()
          (-30.00,0.00)

 -- Function: turtle.right (angle)
 -- Function: turtle.rt (angle)


     Parameters: ‘angle’ – a number (integer or float)

     Turn turtle right by `angle' units.  (Units are by default degrees,
     but can be set via the *note degrees(): 3201. and *note radians():
     3202. functions.)  Angle orientation depends on the turtle mode,
     see *note mode(): 3243.

          >>> turtle.heading()
          22.0
          >>> turtle.right(45)
          >>> turtle.heading()
          337.0

 -- Function: turtle.left (angle)
 -- Function: turtle.lt (angle)


     Parameters: ‘angle’ – a number (integer or float)

     Turn turtle left by `angle' units.  (Units are by default degrees,
     but can be set via the *note degrees(): 3201. and *note radians():
     3202. functions.)  Angle orientation depends on the turtle mode,
     see *note mode(): 3243.

          >>> turtle.heading()
          22.0
          >>> turtle.left(45)
          >>> turtle.heading()
          67.0

 -- Function: turtle.goto (x, y=None)
 -- Function: turtle.setpos (x, y=None)
 -- Function: turtle.setposition (x, y=None)


     Parameters:

        * ‘x’ – a number or a pair/vector of numbers

        * ‘y’ – a number or ‘None’

     If `y' is ‘None’, `x' must be a pair of coordinates or a *note
     Vec2D: 3252. (e.g.  as returned by *note pos(): 31fb.).

     Move turtle to an absolute position.  If the pen is down, draw
     line.  Do not change the turtle’s orientation.

           >>> tp = turtle.pos()
           >>> tp
           (0.00,0.00)
           >>> turtle.setpos(60,30)
           >>> turtle.pos()
           (60.00,30.00)
           >>> turtle.setpos((20,80))
           >>> turtle.pos()
           (20.00,80.00)
           >>> turtle.setpos(tp)
           >>> turtle.pos()
           (0.00,0.00)

 -- Function: turtle.setx (x)


     Parameters: ‘x’ – a number (integer or float)

     Set the turtle’s first coordinate to `x', leave second coordinate
     unchanged.

          >>> turtle.position()
          (0.00,240.00)
          >>> turtle.setx(10)
          >>> turtle.position()
          (10.00,240.00)

 -- Function: turtle.sety (y)


     Parameters: ‘y’ – a number (integer or float)

     Set the turtle’s second coordinate to `y', leave first coordinate
     unchanged.

          >>> turtle.position()
          (0.00,40.00)
          >>> turtle.sety(-10)
          >>> turtle.position()
          (0.00,-10.00)

 -- Function: turtle.setheading (to_angle)
 -- Function: turtle.seth (to_angle)


     Parameters: ‘to_angle’ – a number (integer or float)

     Set the orientation of the turtle to `to_angle'.  Here are some
     common directions in degrees:

     standard mode           logo mode
                             
     -------------------------------------------------
                             
     0 - east                0 - north
                             
                             
     90 - north              90 - east
                             
                             
     180 - west              180 - south
                             
                             
     270 - south             270 - west
                             

          >>> turtle.setheading(90)
          >>> turtle.heading()
          90.0

 -- Function: turtle.home ()

     Move turtle to the origin – coordinates (0,0) – and set its heading
     to its start-orientation (which depends on the mode, see *note
     mode(): 3243.).

          >>> turtle.heading()
          90.0
          >>> turtle.position()
          (0.00,-10.00)
          >>> turtle.home()
          >>> turtle.position()
          (0.00,0.00)
          >>> turtle.heading()
          0.0

 -- Function: turtle.circle (radius, extent=None, steps=None)


     Parameters:

        * ‘radius’ – a number

        * ‘extent’ – a number (or ‘None’)

        * ‘steps’ – an integer (or ‘None’)

     Draw a circle with given `radius'.  The center is `radius' units
     left of the turtle; `extent' – an angle – determines which part of
     the circle is drawn.  If `extent' is not given, draw the entire
     circle.  If `extent' is not a full circle, one endpoint of the arc
     is the current pen position.  Draw the arc in counterclockwise
     direction if `radius' is positive, otherwise in clockwise
     direction.  Finally the direction of the turtle is changed by the
     amount of `extent'.

     As the circle is approximated by an inscribed regular polygon,
     `steps' determines the number of steps to use.  If not given, it
     will be calculated automatically.  May be used to draw regular
     polygons.

          >>> turtle.home()
          >>> turtle.position()
          (0.00,0.00)
          >>> turtle.heading()
          0.0
          >>> turtle.circle(50)
          >>> turtle.position()
          (-0.00,0.00)
          >>> turtle.heading()
          0.0
          >>> turtle.circle(120, 180)  # draw a semicircle
          >>> turtle.position()
          (0.00,240.00)
          >>> turtle.heading()
          180.0

 -- Function: turtle.dot (size=None, *color)


     Parameters:

        * ‘size’ – an integer >= 1 (if given)

        * ‘color’ – a colorstring or a numeric color tuple

     Draw a circular dot with diameter `size', using `color'.  If `size'
     is not given, the maximum of pensize+4 and 2*pensize is used.

          >>> turtle.home()
          >>> turtle.dot()
          >>> turtle.fd(50); turtle.dot(20, "blue"); turtle.fd(50)
          >>> turtle.position()
          (100.00,-0.00)
          >>> turtle.heading()
          0.0

 -- Function: turtle.stamp ()

     Stamp a copy of the turtle shape onto the canvas at the current
     turtle position.  Return a stamp_id for that stamp, which can be
     used to delete it by calling ‘clearstamp(stamp_id)’.

          >>> turtle.color("blue")
          >>> turtle.stamp()
          11
          >>> turtle.fd(50)

 -- Function: turtle.clearstamp (stampid)


     Parameters: ‘stampid’ – an integer, must be return value of
     previous *note stamp(): 31f5. call

     Delete stamp with given `stampid'.

          >>> turtle.position()
          (150.00,-0.00)
          >>> turtle.color("blue")
          >>> astamp = turtle.stamp()
          >>> turtle.fd(50)
          >>> turtle.position()
          (200.00,-0.00)
          >>> turtle.clearstamp(astamp)
          >>> turtle.position()
          (200.00,-0.00)

 -- Function: turtle.clearstamps (n=None)


     Parameters: ‘n’ – an integer (or ‘None’)

     Delete all or first/last `n' of turtle’s stamps.  If `n' is ‘None’,
     delete all stamps, if `n' > 0 delete first `n' stamps, else if `n'
     < 0 delete last `n' stamps.

          >>> for i in range(8):
          ...     turtle.stamp(); turtle.fd(30)
          13
          14
          15
          16
          17
          18
          19
          20
          >>> turtle.clearstamps(2)
          >>> turtle.clearstamps(-2)
          >>> turtle.clearstamps()

 -- Function: turtle.undo ()

     Undo (repeatedly) the last turtle action(s).  Number of available
     undo actions is determined by the size of the undobuffer.

          >>> for i in range(4):
          ...     turtle.fd(50); turtle.lt(80)
          ...
          >>> for i in range(8):
          ...     turtle.undo()

 -- Function: turtle.speed (speed=None)


     Parameters: ‘speed’ – an integer in the range 0..10 or a
     speedstring (see below)

     Set the turtle’s speed to an integer value in the range 0..10.  If
     no argument is given, return current speed.

     If input is a number greater than 10 or smaller than 0.5, speed is
     set to 0.  Speedstrings are mapped to speedvalues as follows:

        * “fastest”: 0

        * “fast”: 10

        * “normal”: 6

        * “slow”: 3

        * “slowest”: 1

     Speeds from 1 to 10 enforce increasingly faster animation of line
     drawing and turtle turning.

     Attention: `speed' = 0 means that `no' animation takes place.
     forward/back makes turtle jump and likewise left/right make the
     turtle turn instantly.

          >>> turtle.speed()
          3
          >>> turtle.speed('normal')
          >>> turtle.speed()
          6
          >>> turtle.speed(9)
          >>> turtle.speed()
          9


File: python.info,  Node: Tell Turtle’s state,  Next: Settings for measurement,  Prev: Turtle motion,  Up: Methods of RawTurtle/Turtle and corresponding functions

5.24.1.7 Tell Turtle’s state
............................

 -- Function: turtle.position ()
 -- Function: turtle.pos ()

     Return the turtle’s current location (x,y) (as a *note Vec2D: 3252.
     vector).

          >>> turtle.pos()
          (440.00,-0.00)

 -- Function: turtle.towards (x, y=None)


     Parameters:

        * ‘x’ – a number or a pair/vector of numbers or a turtle
          instance

        * ‘y’ – a number if `x' is a number, else ‘None’

     Return the angle between the line from turtle position to position
     specified by (x,y), the vector or the other turtle.  This depends
     on the turtle’s start orientation which depends on the mode -
     “standard”/”world” or “logo”.

          >>> turtle.goto(10, 10)
          >>> turtle.towards(0,0)
          225.0

 -- Function: turtle.xcor ()

     Return the turtle’s x coordinate.

          >>> turtle.home()
          >>> turtle.left(50)
          >>> turtle.forward(100)
          >>> turtle.pos()
          (64.28,76.60)
          >>> print(round(turtle.xcor(), 5))
          64.27876

 -- Function: turtle.ycor ()

     Return the turtle’s y coordinate.

          >>> turtle.home()
          >>> turtle.left(60)
          >>> turtle.forward(100)
          >>> print(turtle.pos())
          (50.00,86.60)
          >>> print(round(turtle.ycor(), 5))
          86.60254

 -- Function: turtle.heading ()

     Return the turtle’s current heading (value depends on the turtle
     mode, see *note mode(): 3243.).

          >>> turtle.home()
          >>> turtle.left(67)
          >>> turtle.heading()
          67.0

 -- Function: turtle.distance (x, y=None)


     Parameters:

        * ‘x’ – a number or a pair/vector of numbers or a turtle
          instance

        * ‘y’ – a number if `x' is a number, else ‘None’

     Return the distance from the turtle to (x,y), the given vector, or
     the given other turtle, in turtle step units.

          >>> turtle.home()
          >>> turtle.distance(30,40)
          50.0
          >>> turtle.distance((30,40))
          50.0
          >>> joe = Turtle()
          >>> joe.forward(77)
          >>> turtle.distance(joe)
          77.0


File: python.info,  Node: Settings for measurement,  Next: Pen control,  Prev: Tell Turtle’s state,  Up: Methods of RawTurtle/Turtle and corresponding functions

5.24.1.8 Settings for measurement
.................................

 -- Function: turtle.degrees (fullcircle=360.0)


     Parameters: ‘fullcircle’ – a number

     Set angle measurement units, i.e.  set number of “degrees” for a
     full circle.  Default value is 360 degrees.

          >>> turtle.home()
          >>> turtle.left(90)
          >>> turtle.heading()
          90.0

          Change angle measurement unit to grad (also known as gon,
          grade, or gradian and equals 1/100-th of the right angle.)
          >>> turtle.degrees(400.0)
          >>> turtle.heading()
          100.0
          >>> turtle.degrees(360)
          >>> turtle.heading()
          90.0

 -- Function: turtle.radians ()

     Set the angle measurement units to radians.  Equivalent to
     ‘degrees(2*math.pi)’.

          >>> turtle.home()
          >>> turtle.left(90)
          >>> turtle.heading()
          90.0
          >>> turtle.radians()
          >>> turtle.heading()
          1.5707963267948966


File: python.info,  Node: Pen control,  Next: Turtle state,  Prev: Settings for measurement,  Up: Methods of RawTurtle/Turtle and corresponding functions

5.24.1.9 Pen control
....................

* Menu:

* Drawing state::
* Color control::
* Filling::
* More drawing control::


File: python.info,  Node: Drawing state,  Next: Color control,  Up: Pen control

5.24.1.10 Drawing state
.......................

 -- Function: turtle.pendown ()
 -- Function: turtle.pd ()
 -- Function: turtle.down ()

     Pull the pen down – drawing when moving.

 -- Function: turtle.penup ()
 -- Function: turtle.pu ()
 -- Function: turtle.up ()

     Pull the pen up – no drawing when moving.

 -- Function: turtle.pensize (width=None)
 -- Function: turtle.width (width=None)


     Parameters: ‘width’ – a positive number

     Set the line thickness to `width' or return it.  If resizemode is
     set to “auto” and turtleshape is a polygon, that polygon is drawn
     with the same line thickness.  If no argument is given, the current
     pensize is returned.

          >>> turtle.pensize()
          1
          >>> turtle.pensize(10)   # from here on lines of width 10 are drawn

 -- Function: turtle.pen (pen=None, **pendict)


     Parameters:

        * ‘pen’ – a dictionary with some or all of the below listed keys

        * ‘pendict’ – one or more keyword-arguments with the below
          listed keys as keywords

     Return or set the pen’s attributes in a “pen-dictionary” with the
     following key/value pairs:

        * “shown”: True/False

        * “pendown”: True/False

        * “pencolor”: color-string or color-tuple

        * “fillcolor”: color-string or color-tuple

        * “pensize”: positive number

        * “speed”: number in range 0..10

        * “resizemode”: “auto” or “user” or “noresize”

        * “stretchfactor”: (positive number, positive number)

        * “outline”: positive number

        * “tilt”: number

     This dictionary can be used as argument for a subsequent call to
     *note pen(): 320b. to restore the former pen-state.  Moreover one
     or more of these attributes can be provided as keyword-arguments.
     This can be used to set several pen attributes in one statement.

          >>> turtle.pen(fillcolor="black", pencolor="red", pensize=10)
          >>> sorted(turtle.pen().items())
          [('fillcolor', 'black'), ('outline', 1), ('pencolor', 'red'),
           ('pendown', True), ('pensize', 10), ('resizemode', 'noresize'),
           ('shearfactor', 0.0), ('shown', True), ('speed', 9),
           ('stretchfactor', (1.0, 1.0)), ('tilt', 0.0)]
          >>> penstate=turtle.pen()
          >>> turtle.color("yellow", "")
          >>> turtle.penup()
          >>> sorted(turtle.pen().items())[:3]
          [('fillcolor', ''), ('outline', 1), ('pencolor', 'yellow')]
          >>> turtle.pen(penstate, fillcolor="green")
          >>> sorted(turtle.pen().items())[:3]
          [('fillcolor', 'green'), ('outline', 1), ('pencolor', 'red')]

 -- Function: turtle.isdown ()

     Return ‘True’ if pen is down, ‘False’ if it’s up.

          >>> turtle.penup()
          >>> turtle.isdown()
          False
          >>> turtle.pendown()
          >>> turtle.isdown()
          True


File: python.info,  Node: Color control,  Next: Filling,  Prev: Drawing state,  Up: Pen control

5.24.1.11 Color control
.......................

 -- Function: turtle.pencolor (*args)

     Return or set the pencolor.

     Four input formats are allowed:

     ‘pencolor()’

          Return the current pencolor as color specification string or
          as a tuple (see example).  May be used as input to another
          color/pencolor/fillcolor call.

     ‘pencolor(colorstring)’

          Set pencolor to `colorstring', which is a Tk color
          specification string, such as ‘"red"’, ‘"yellow"’, or
          ‘"#33cc8c"’.

     ‘pencolor((r, g, b))’

          Set pencolor to the RGB color represented by the tuple of `r',
          `g', and `b'.  Each of `r', `g', and `b' must be in the range
          0..colormode, where colormode is either 1.0 or 255 (see *note
          colormode(): 3244.).

     ‘pencolor(r, g, b)’

          Set pencolor to the RGB color represented by `r', `g', and
          `b'.  Each of `r', `g', and `b' must be in the range
          0..colormode.

     If turtleshape is a polygon, the outline of that polygon is drawn
     with the newly set pencolor.

           >>> colormode()
           1.0
           >>> turtle.pencolor()
           'red'
           >>> turtle.pencolor("brown")
           >>> turtle.pencolor()
           'brown'
           >>> tup = (0.2, 0.8, 0.55)
           >>> turtle.pencolor(tup)
           >>> turtle.pencolor()
           (0.2, 0.8, 0.5490196078431373)
           >>> colormode(255)
           >>> turtle.pencolor()
           (51.0, 204.0, 140.0)
           >>> turtle.pencolor('#32c18f')
           >>> turtle.pencolor()
           (50.0, 193.0, 143.0)

 -- Function: turtle.fillcolor (*args)

     Return or set the fillcolor.

     Four input formats are allowed:

     ‘fillcolor()’

          Return the current fillcolor as color specification string,
          possibly in tuple format (see example).  May be used as input
          to another color/pencolor/fillcolor call.

     ‘fillcolor(colorstring)’

          Set fillcolor to `colorstring', which is a Tk color
          specification string, such as ‘"red"’, ‘"yellow"’, or
          ‘"#33cc8c"’.

     ‘fillcolor((r, g, b))’

          Set fillcolor to the RGB color represented by the tuple of
          `r', `g', and `b'.  Each of `r', `g', and `b' must be in the
          range 0..colormode, where colormode is either 1.0 or 255 (see
          *note colormode(): 3244.).

     ‘fillcolor(r, g, b)’

          Set fillcolor to the RGB color represented by `r', `g', and
          `b'.  Each of `r', `g', and `b' must be in the range
          0..colormode.

     If turtleshape is a polygon, the interior of that polygon is drawn
     with the newly set fillcolor.

           >>> turtle.fillcolor("violet")
           >>> turtle.fillcolor()
           'violet'
           >>> turtle.pencolor()
           (50.0, 193.0, 143.0)
           >>> turtle.fillcolor((50, 193, 143))  # Integers, not floats
           >>> turtle.fillcolor()
           (50.0, 193.0, 143.0)
           >>> turtle.fillcolor('#ffffff')
           >>> turtle.fillcolor()
           (255.0, 255.0, 255.0)

 -- Function: turtle.color (*args)

     Return or set pencolor and fillcolor.

     Several input formats are allowed.  They use 0 to 3 arguments as
     follows:

     ‘color()’

          Return the current pencolor and the current fillcolor as a
          pair of color specification strings or tuples as returned by
          *note pencolor(): 320e. and *note fillcolor(): 320f.

     ‘color(colorstring)’, ‘color((r,g,b))’, ‘color(r,g,b)’

          Inputs as in *note pencolor(): 320e, set both, fillcolor and
          pencolor, to the given value.

     ‘color(colorstring1, colorstring2)’, ‘color((r1,g1,b1), (r2,g2,b2))’

          Equivalent to ‘pencolor(colorstring1)’ and
          ‘fillcolor(colorstring2)’ and analogously if the other input
          format is used.

     If turtleshape is a polygon, outline and interior of that polygon
     is drawn with the newly set colors.

           >>> turtle.color("red", "green")
           >>> turtle.color()
           ('red', 'green')
           >>> color("#285078", "#a0c8f0")
           >>> color()
           ((40.0, 80.0, 120.0), (160.0, 200.0, 240.0))

See also: Screen method *note colormode(): 3244.


File: python.info,  Node: Filling,  Next: More drawing control,  Prev: Color control,  Up: Pen control

5.24.1.12 Filling
.................

 -- Function: turtle.filling ()

     Return fillstate (‘True’ if filling, ‘False’ else).

           >>> turtle.begin_fill()
           >>> if turtle.filling():
           ...    turtle.pensize(5)
           ... else:
           ...    turtle.pensize(3)

 -- Function: turtle.begin_fill ()

     To be called just before drawing a shape to be filled.

 -- Function: turtle.end_fill ()

     Fill the shape drawn after the last call to *note begin_fill():
     3211.

     Whether or not overlap regions for self-intersecting polygons or
     multiple shapes are filled depends on the operating system
     graphics, type of overlap, and number of overlaps.  For example,
     the Turtle star above may be either all yellow or have some white
     regions.

          >>> turtle.color("black", "red")
          >>> turtle.begin_fill()
          >>> turtle.circle(80)
          >>> turtle.end_fill()


File: python.info,  Node: More drawing control,  Prev: Filling,  Up: Pen control

5.24.1.13 More drawing control
..............................

 -- Function: turtle.reset ()

     Delete the turtle’s drawings from the screen, re-center the turtle
     and set variables to the default values.

          >>> turtle.goto(0,-22)
          >>> turtle.left(100)
          >>> turtle.position()
          (0.00,-22.00)
          >>> turtle.heading()
          100.0
          >>> turtle.reset()
          >>> turtle.position()
          (0.00,0.00)
          >>> turtle.heading()
          0.0

 -- Function: turtle.clear ()

     Delete the turtle’s drawings from the screen.  Do not move turtle.
     State and position of the turtle as well as drawings of other
     turtles are not affected.

 -- Function: turtle.write (arg, move=False, align="left",
          font=("Arial", 8, "normal"))


     Parameters:

        * ‘arg’ – object to be written to the TurtleScreen

        * ‘move’ – True/False

        * ‘align’ – one of the strings “left”, “center” or right”

        * ‘font’ – a triple (fontname, fontsize, fonttype)

     Write text - the string representation of `arg' - at the current
     turtle position according to `align' (“left”, “center” or “right”)
     and with the given font.  If `move' is true, the pen is moved to
     the bottom-right corner of the text.  By default, `move' is
     ‘False’.

          >>> turtle.write("Home = ", True, align="center")
          >>> turtle.write((0,0), True)


File: python.info,  Node: Turtle state,  Next: Using events,  Prev: Pen control,  Up: Methods of RawTurtle/Turtle and corresponding functions

5.24.1.14 Turtle state
......................

* Menu:

* Visibility::
* Appearance::


File: python.info,  Node: Visibility,  Next: Appearance,  Up: Turtle state

5.24.1.15 Visibility
....................

 -- Function: turtle.hideturtle ()
 -- Function: turtle.ht ()

     Make the turtle invisible.  It’s a good idea to do this while
     you’re in the middle of doing some complex drawing, because hiding
     the turtle speeds up the drawing observably.

          >>> turtle.hideturtle()

 -- Function: turtle.showturtle ()
 -- Function: turtle.st ()

     Make the turtle visible.

          >>> turtle.showturtle()

 -- Function: turtle.isvisible ()

     Return ‘True’ if the Turtle is shown, ‘False’ if it’s hidden.

          >>> turtle.hideturtle()
          >>> turtle.isvisible()
          False
          >>> turtle.showturtle()
          >>> turtle.isvisible()
          True


File: python.info,  Node: Appearance,  Prev: Visibility,  Up: Turtle state

5.24.1.16 Appearance
....................

 -- Function: turtle.shape (name=None)


     Parameters: ‘name’ – a string which is a valid shapename

     Set turtle shape to shape with given `name' or, if name is not
     given, return name of current shape.  Shape with `name' must exist
     in the TurtleScreen’s shape dictionary.  Initially there are the
     following polygon shapes: “arrow”, “turtle”, “circle”, “square”,
     “triangle”, “classic”.  To learn about how to deal with shapes see
     Screen method *note register_shape(): 3247.

          >>> turtle.shape()
          'classic'
          >>> turtle.shape("turtle")
          >>> turtle.shape()
          'turtle'

 -- Function: turtle.resizemode (rmode=None)


     Parameters: ‘rmode’ – one of the strings “auto”, “user”, “noresize”

     Set resizemode to one of the values: “auto”, “user”, “noresize”.
     If `rmode' is not given, return current resizemode.  Different
     resizemodes have the following effects:

        - “auto”: adapts the appearance of the turtle corresponding to
          the value of pensize.

        - “user”: adapts the appearance of the turtle according to the
          values of stretchfactor and outlinewidth (outline), which are
          set by *note shapesize(): 321d.

        - “noresize”: no adaption of the turtle’s appearance takes
          place.

     ‘resizemode("user")’ is called by *note shapesize(): 321d. when
     used with arguments.

          >>> turtle.resizemode()
          'noresize'
          >>> turtle.resizemode("auto")
          >>> turtle.resizemode()
          'auto'

 -- Function: turtle.shapesize (stretch_wid=None, stretch_len=None,
          outline=None)
 -- Function: turtle.turtlesize (stretch_wid=None, stretch_len=None,
          outline=None)


     Parameters:

        * ‘stretch_wid’ – positive number

        * ‘stretch_len’ – positive number

        * ‘outline’ – positive number

     Return or set the pen’s attributes x/y-stretchfactors and/or
     outline.  Set resizemode to “user”.  If and only if resizemode is
     set to “user”, the turtle will be displayed stretched according to
     its stretchfactors: `stretch_wid' is stretchfactor perpendicular to
     its orientation, `stretch_len' is stretchfactor in direction of its
     orientation, `outline' determines the width of the shapes’s
     outline.

          >>> turtle.shapesize()
          (1.0, 1.0, 1)
          >>> turtle.resizemode("user")
          >>> turtle.shapesize(5, 5, 12)
          >>> turtle.shapesize()
          (5, 5, 12)
          >>> turtle.shapesize(outline=8)
          >>> turtle.shapesize()
          (5, 5, 8)

 -- Function: turtle.shearfactor (shear=None)


     Parameters: ‘shear’ – number (optional)

     Set or return the current shearfactor.  Shear the turtleshape
     according to the given shearfactor shear, which is the tangent of
     the shear angle.  Do `not' change the turtle’s heading (direction
     of movement).  If shear is not given: return the current
     shearfactor, i.  e.  the tangent of the shear angle, by which lines
     parallel to the heading of the turtle are sheared.

           >>> turtle.shape("circle")
           >>> turtle.shapesize(5,2)
           >>> turtle.shearfactor(0.5)
           >>> turtle.shearfactor()
           0.5

 -- Function: turtle.tilt (angle)


     Parameters: ‘angle’ – a number

     Rotate the turtleshape by `angle' from its current tilt-angle, but
     do `not' change the turtle’s heading (direction of movement).

          >>> turtle.reset()
          >>> turtle.shape("circle")
          >>> turtle.shapesize(5,2)
          >>> turtle.tilt(30)
          >>> turtle.fd(50)
          >>> turtle.tilt(30)
          >>> turtle.fd(50)

 -- Function: turtle.settiltangle (angle)


     Parameters: ‘angle’ – a number

     Rotate the turtleshape to point in the direction specified by
     `angle', regardless of its current tilt-angle.  `Do not' change the
     turtle’s heading (direction of movement).

          >>> turtle.reset()
          >>> turtle.shape("circle")
          >>> turtle.shapesize(5,2)
          >>> turtle.settiltangle(45)
          >>> turtle.fd(50)
          >>> turtle.settiltangle(-45)
          >>> turtle.fd(50)

     Deprecated since version 3.1.

 -- Function: turtle.tiltangle (angle=None)


     Parameters: ‘angle’ – a number (optional)

     Set or return the current tilt-angle.  If angle is given, rotate
     the turtleshape to point in the direction specified by angle,
     regardless of its current tilt-angle.  Do `not' change the turtle’s
     heading (direction of movement).  If angle is not given: return the
     current tilt-angle, i.  e.  the angle between the orientation of
     the turtleshape and the heading of the turtle (its direction of
     movement).

          >>> turtle.reset()
          >>> turtle.shape("circle")
          >>> turtle.shapesize(5,2)
          >>> turtle.tilt(45)
          >>> turtle.tiltangle()
          45.0

 -- Function: turtle.shapetransform (t11=None, t12=None, t21=None,
          t22=None)


     Parameters:

        * ‘t11’ – a number (optional)

        * ‘t12’ – a number (optional)

        * ‘t21’ – a number (optional)

        * ‘t12’ – a number (optional)

     Set or return the current transformation matrix of the turtle
     shape.

     If none of the matrix elements are given, return the transformation
     matrix as a tuple of 4 elements.  Otherwise set the given elements
     and transform the turtleshape according to the matrix consisting of
     first row t11, t12 and second row t21, t22.  The determinant t11 *
     t22 - t12 * t21 must not be zero, otherwise an error is raised.
     Modify stretchfactor, shearfactor and tiltangle according to the
     given matrix.

          >>> turtle = Turtle()
          >>> turtle.shape("square")
          >>> turtle.shapesize(4,2)
          >>> turtle.shearfactor(-0.5)
          >>> turtle.shapetransform()
          (4.0, -1.0, -0.0, 2.0)

 -- Function: turtle.get_shapepoly ()

     Return the current shape polygon as tuple of coordinate pairs.
     This can be used to define a new shape or components of a compound
     shape.

          >>> turtle.shape("square")
          >>> turtle.shapetransform(4, -1, 0, 2)
          >>> turtle.get_shapepoly()
          ((50, -20), (30, 20), (-50, 20), (-30, -20))


File: python.info,  Node: Using events,  Next: Special Turtle methods,  Prev: Turtle state,  Up: Methods of RawTurtle/Turtle and corresponding functions

5.24.1.17 Using events
......................

 -- Function: turtle.onclick (fun, btn=1, add=None)


     Parameters:

        * ‘fun’ – a function with two arguments which will be called
          with the coordinates of the clicked point on the canvas

        * ‘btn’ – number of the mouse-button, defaults to 1 (left mouse
          button)

        * ‘add’ – ‘True’ or ‘False’ – if ‘True’, a new binding will be
          added, otherwise it will replace a former binding

     Bind `fun' to mouse-click events on this turtle.  If `fun' is
     ‘None’, existing bindings are removed.  Example for the anonymous
     turtle, i.e.  the procedural way:

          >>> def turn(x, y):
          ...     left(180)
          ...
          >>> onclick(turn)  # Now clicking into the turtle will turn it.
          >>> onclick(None)  # event-binding will be removed

 -- Function: turtle.onrelease (fun, btn=1, add=None)


     Parameters:

        * ‘fun’ – a function with two arguments which will be called
          with the coordinates of the clicked point on the canvas

        * ‘btn’ – number of the mouse-button, defaults to 1 (left mouse
          button)

        * ‘add’ – ‘True’ or ‘False’ – if ‘True’, a new binding will be
          added, otherwise it will replace a former binding

     Bind `fun' to mouse-button-release events on this turtle.  If `fun'
     is ‘None’, existing bindings are removed.

          >>> class MyTurtle(Turtle):
          ...     def glow(self,x,y):
          ...         self.fillcolor("red")
          ...     def unglow(self,x,y):
          ...         self.fillcolor("")
          ...
          >>> turtle = MyTurtle()
          >>> turtle.onclick(turtle.glow)     # clicking on turtle turns fillcolor red,
          >>> turtle.onrelease(turtle.unglow) # releasing turns it to transparent.

 -- Function: turtle.ondrag (fun, btn=1, add=None)


     Parameters:

        * ‘fun’ – a function with two arguments which will be called
          with the coordinates of the clicked point on the canvas

        * ‘btn’ – number of the mouse-button, defaults to 1 (left mouse
          button)

        * ‘add’ – ‘True’ or ‘False’ – if ‘True’, a new binding will be
          added, otherwise it will replace a former binding

     Bind `fun' to mouse-move events on this turtle.  If `fun' is
     ‘None’, existing bindings are removed.

     Remark: Every sequence of mouse-move-events on a turtle is preceded
     by a mouse-click event on that turtle.

          >>> turtle.ondrag(turtle.goto)

     Subsequently, clicking and dragging the Turtle will move it across
     the screen thereby producing handdrawings (if pen is down).


File: python.info,  Node: Special Turtle methods,  Next: Compound shapes,  Prev: Using events,  Up: Methods of RawTurtle/Turtle and corresponding functions

5.24.1.18 Special Turtle methods
................................

 -- Function: turtle.begin_poly ()

     Start recording the vertices of a polygon.  Current turtle position
     is first vertex of polygon.

 -- Function: turtle.end_poly ()

     Stop recording the vertices of a polygon.  Current turtle position
     is last vertex of polygon.  This will be connected with the first
     vertex.

 -- Function: turtle.get_poly ()

     Return the last recorded polygon.

          >>> turtle.home()
          >>> turtle.begin_poly()
          >>> turtle.fd(100)
          >>> turtle.left(20)
          >>> turtle.fd(30)
          >>> turtle.left(60)
          >>> turtle.fd(50)
          >>> turtle.end_poly()
          >>> p = turtle.get_poly()
          >>> register_shape("myFavouriteShape", p)

 -- Function: turtle.clone ()

     Create and return a clone of the turtle with same position, heading
     and turtle properties.

          >>> mick = Turtle()
          >>> joe = mick.clone()

 -- Function: turtle.getturtle ()
 -- Function: turtle.getpen ()

     Return the Turtle object itself.  Only reasonable use: as a
     function to return the “anonymous turtle”:

          >>> pet = getturtle()
          >>> pet.fd(50)
          >>> pet
          <turtle.Turtle object at 0x...>

 -- Function: turtle.getscreen ()

     Return the *note TurtleScreen: 31da. object the turtle is drawing
     on.  TurtleScreen methods can then be called for that object.

          >>> ts = turtle.getscreen()
          >>> ts
          <turtle._Screen object at 0x...>
          >>> ts.bgcolor("pink")

 -- Function: turtle.setundobuffer (size)


     Parameters: ‘size’ – an integer or ‘None’

     Set or disable undobuffer.  If `size' is an integer, an empty
     undobuffer of given size is installed.  `size' gives the maximum
     number of turtle actions that can be undone by the *note undo():
     31f8. method/function.  If `size' is ‘None’, the undobuffer is
     disabled.

          >>> turtle.setundobuffer(42)

 -- Function: turtle.undobufferentries ()

     Return number of entries in the undobuffer.

          >>> while undobufferentries():
          ...     undo()


File: python.info,  Node: Compound shapes,  Prev: Special Turtle methods,  Up: Methods of RawTurtle/Turtle and corresponding functions

5.24.1.19 Compound shapes
.........................

To use compound turtle shapes, which consist of several polygons of
different color, you must use the helper class *note Shape: 3261.
explicitly as described below:

  1. Create an empty Shape object of type “compound”.

  2. Add as many components to this object as desired, using the
     ‘addcomponent()’ method.

     For example:

          >>> s = Shape("compound")
          >>> poly1 = ((0,0),(10,-5),(0,10),(-10,-5))
          >>> s.addcomponent(poly1, "red", "blue")
          >>> poly2 = ((0,0),(10,-5),(-10,-5))
          >>> s.addcomponent(poly2, "blue", "red")

  3. Now add the Shape to the Screen’s shapelist and use it:

          >>> register_shape("myshape", s)
          >>> shape("myshape")

     Note: The *note Shape: 3261. class is used internally by the *note
     register_shape(): 3247. method in different ways.  The application
     programmer has to deal with the Shape class `only' when using
     compound shapes like shown above!


File: python.info,  Node: Methods of TurtleScreen/Screen and corresponding functions,  Next: Public classes,  Prev: Methods of RawTurtle/Turtle and corresponding functions,  Up: turtle — Turtle graphics

5.24.1.20 Methods of TurtleScreen/Screen and corresponding functions
....................................................................

Most of the examples in this section refer to a TurtleScreen instance
called ‘screen’.

* Menu:

* Window control::
* Animation control::
* Using screen events::
* Input methods::
* Settings and special methods::
* Methods specific to Screen, not inherited from TurtleScreen: Methods specific to Screen not inherited from TurtleScreen.


File: python.info,  Node: Window control,  Next: Animation control,  Up: Methods of TurtleScreen/Screen and corresponding functions

5.24.1.21 Window control
........................

 -- Function: turtle.bgcolor (*args)


     Parameters: ‘args’ – a color string or three numbers in the range
     0..colormode or a 3-tuple of such numbers

     Set or return background color of the TurtleScreen.

          >>> screen.bgcolor("orange")
          >>> screen.bgcolor()
          'orange'
          >>> screen.bgcolor("#800080")
          >>> screen.bgcolor()
          (128.0, 0.0, 128.0)

 -- Function: turtle.bgpic (picname=None)


     Parameters: ‘picname’ – a string, name of a gif-file or ‘"nopic"’,
     or ‘None’

     Set background image or return name of current backgroundimage.  If
     `picname' is a filename, set the corresponding image as background.
     If `picname' is ‘"nopic"’, delete background image, if present.  If
     `picname' is ‘None’, return the filename of the current
     backgroundimage.

          >>> screen.bgpic()
          'nopic'
          >>> screen.bgpic("landscape.gif")
          >>> screen.bgpic()
          "landscape.gif"

 -- Function: turtle.clear ()

          Note: This TurtleScreen method is available as a global
          function only under the name ‘clearscreen’.  The global
          function ‘clear’ is a different one derived from the Turtle
          method ‘clear’.

 -- Function: turtle.clearscreen ()

     Delete all drawings and all turtles from the TurtleScreen.  Reset
     the now empty TurtleScreen to its initial state: white background,
     no background image, no event bindings and tracing on.

 -- Function: turtle.reset ()

          Note: This TurtleScreen method is available as a global
          function only under the name ‘resetscreen’.  The global
          function ‘reset’ is another one derived from the Turtle method
          ‘reset’.

 -- Function: turtle.resetscreen ()

     Reset all Turtles on the Screen to their initial state.

 -- Function: turtle.screensize (canvwidth=None, canvheight=None,
          bg=None)


     Parameters:

        * ‘canvwidth’ – positive integer, new width of canvas in pixels

        * ‘canvheight’ – positive integer, new height of canvas in
          pixels

        * ‘bg’ – colorstring or color-tuple, new background color

     If no arguments are given, return current (canvaswidth,
     canvasheight).  Else resize the canvas the turtles are drawing on.
     Do not alter the drawing window.  To observe hidden parts of the
     canvas, use the scrollbars.  With this method, one can make visible
     those parts of a drawing which were outside the canvas before.

          >>> screen.screensize()
          (400, 300)
          >>> screen.screensize(2000,1500)
          >>> screen.screensize()
          (2000, 1500)

     e.g.  to search for an erroneously escaped turtle ;-)

 -- Function: turtle.setworldcoordinates (llx, lly, urx, ury)


     Parameters:

        * ‘llx’ – a number, x-coordinate of lower left corner of canvas

        * ‘lly’ – a number, y-coordinate of lower left corner of canvas

        * ‘urx’ – a number, x-coordinate of upper right corner of canvas

        * ‘ury’ – a number, y-coordinate of upper right corner of canvas

     Set up user-defined coordinate system and switch to mode “world” if
     necessary.  This performs a ‘screen.reset()’.  If mode “world” is
     already active, all drawings are redrawn according to the new
     coordinates.

     `ATTENTION': in user-defined coordinate systems angles may appear
     distorted.

          >>> screen.reset()
          >>> screen.setworldcoordinates(-50,-7.5,50,7.5)
          >>> for _ in range(72):
          ...     left(10)
          ...
          >>> for _ in range(8):
          ...     left(45); fd(2)   # a regular octagon


File: python.info,  Node: Animation control,  Next: Using screen events,  Prev: Window control,  Up: Methods of TurtleScreen/Screen and corresponding functions

5.24.1.22 Animation control
...........................

 -- Function: turtle.delay (delay=None)


     Parameters: ‘delay’ – positive integer

     Set or return the drawing `delay' in milliseconds.  (This is
     approximately the time interval between two consecutive canvas
     updates.)  The longer the drawing delay, the slower the animation.

     Optional argument:

          >>> screen.delay()
          10
          >>> screen.delay(5)
          >>> screen.delay()
          5

 -- Function: turtle.tracer (n=None, delay=None)


     Parameters:

        * ‘n’ – nonnegative integer

        * ‘delay’ – nonnegative integer

     Turn turtle animation on/off and set delay for update drawings.  If
     `n' is given, only each n-th regular screen update is really
     performed.  (Can be used to accelerate the drawing of complex
     graphics.)  When called without arguments, returns the currently
     stored value of n.  Second argument sets delay value (see *note
     delay(): 3238.).

          >>> screen.tracer(8, 25)
          >>> dist = 2
          >>> for i in range(200):
          ...     fd(dist)
          ...     rt(90)
          ...     dist += 2

 -- Function: turtle.update ()

     Perform a TurtleScreen update.  To be used when tracer is turned
     off.

See also the RawTurtle/Turtle method *note speed(): 31f9.


File: python.info,  Node: Using screen events,  Next: Input methods,  Prev: Animation control,  Up: Methods of TurtleScreen/Screen and corresponding functions

5.24.1.23 Using screen events
.............................

 -- Function: turtle.listen (xdummy=None, ydummy=None)

     Set focus on TurtleScreen (in order to collect key-events).  Dummy
     arguments are provided in order to be able to pass *note listen():
     323b. to the onclick method.

 -- Function: turtle.onkey (fun, key)
 -- Function: turtle.onkeyrelease (fun, key)


     Parameters:

        * ‘fun’ – a function with no arguments or ‘None’

        * ‘key’ – a string: key (e.g.  “a”) or key-symbol (e.g.
          “space”)

     Bind `fun' to key-release event of key.  If `fun' is ‘None’, event
     bindings are removed.  Remark: in order to be able to register
     key-events, TurtleScreen must have the focus.  (See method *note
     listen(): 323b.)

          >>> def f():
          ...     fd(50)
          ...     lt(60)
          ...
          >>> screen.onkey(f, "Up")
          >>> screen.listen()

 -- Function: turtle.onkeypress (fun, key=None)


     Parameters:

        * ‘fun’ – a function with no arguments or ‘None’

        * ‘key’ – a string: key (e.g.  “a”) or key-symbol (e.g.
          “space”)

     Bind `fun' to key-press event of key if key is given, or to any
     key-press-event if no key is given.  Remark: in order to be able to
     register key-events, TurtleScreen must have focus.  (See method
     *note listen(): 323b.)

          >>> def f():
          ...     fd(50)
          ...
          >>> screen.onkey(f, "Up")
          >>> screen.listen()

 -- Function: turtle.onclick (fun, btn=1, add=None)
 -- Function: turtle.onscreenclick (fun, btn=1, add=None)


     Parameters:

        * ‘fun’ – a function with two arguments which will be called
          with the coordinates of the clicked point on the canvas

        * ‘btn’ – number of the mouse-button, defaults to 1 (left mouse
          button)

        * ‘add’ – ‘True’ or ‘False’ – if ‘True’, a new binding will be
          added, otherwise it will replace a former binding

     Bind `fun' to mouse-click events on this screen.  If `fun' is
     ‘None’, existing bindings are removed.

     Example for a TurtleScreen instance named ‘screen’ and a Turtle
     instance named ‘turtle’:

          >>> screen.onclick(turtle.goto) # Subsequently clicking into the TurtleScreen will
          >>>                             # make the turtle move to the clicked point.
          >>> screen.onclick(None)        # remove event binding again

          Note: This TurtleScreen method is available as a global
          function only under the name ‘onscreenclick’.  The global
          function ‘onclick’ is another one derived from the Turtle
          method ‘onclick’.

 -- Function: turtle.ontimer (fun, t=0)


     Parameters:

        * ‘fun’ – a function with no arguments

        * ‘t’ – a number >= 0

     Install a timer that calls `fun' after `t' milliseconds.

          >>> running = True
          >>> def f():
          ...     if running:
          ...         fd(50)
          ...         lt(60)
          ...         screen.ontimer(f, 250)
          >>> f()   ### makes the turtle march around
          >>> running = False

 -- Function: turtle.mainloop ()
 -- Function: turtle.done ()

     Starts event loop - calling Tkinter’s mainloop function.  Must be
     the last statement in a turtle graphics program.  Must `not' be
     used if a script is run from within IDLE in -n mode (No subprocess)
     - for interactive use of turtle graphics.

          >>> screen.mainloop()


File: python.info,  Node: Input methods,  Next: Settings and special methods,  Prev: Using screen events,  Up: Methods of TurtleScreen/Screen and corresponding functions

5.24.1.24 Input methods
.......................

 -- Function: turtle.textinput (title, prompt)


     Parameters:

        * ‘title’ – string

        * ‘prompt’ – string

     Pop up a dialog window for input of a string.  Parameter title is
     the title of the dialog window, prompt is a text mostly describing
     what information to input.  Return the string input.  If the dialog
     is canceled, return ‘None’.

          >>> screen.textinput("NIM", "Name of first player:")

 -- Function: turtle.numinput (title, prompt, default=None, minval=None,
          maxval=None)


     Parameters:

        * ‘title’ – string

        * ‘prompt’ – string

        * ‘default’ – number (optional)

        * ‘minval’ – number (optional)

        * ‘maxval’ – number (optional)

     Pop up a dialog window for input of a number.  title is the title
     of the dialog window, prompt is a text mostly describing what
     numerical information to input.  default: default value, minval:
     minimum value for input, maxval: maximum value for input The number
     input must be in the range minval ..  maxval if these are given.
     If not, a hint is issued and the dialog remains open for
     correction.  Return the number input.  If the dialog is canceled,
     return ‘None’.

          >>> screen.numinput("Poker", "Your stakes:", 1000, minval=10, maxval=10000)


File: python.info,  Node: Settings and special methods,  Next: Methods specific to Screen not inherited from TurtleScreen,  Prev: Input methods,  Up: Methods of TurtleScreen/Screen and corresponding functions

5.24.1.25 Settings and special methods
......................................

 -- Function: turtle.mode (mode=None)


     Parameters: ‘mode’ – one of the strings “standard”, “logo” or
     “world”

     Set turtle mode (“standard”, “logo” or “world”) and perform reset.
     If mode is not given, current mode is returned.

     Mode “standard” is compatible with old *note turtle: 11f.  Mode
     “logo” is compatible with most Logo turtle graphics.  Mode “world”
     uses user-defined “world coordinates”.  `Attention': in this mode
     angles appear distorted if ‘x/y’ unit-ratio doesn’t equal 1.

     Mode             Initial turtle heading        positive angles
                                                    
     -----------------------------------------------------------------------
                                                    
     “standard”       to the right (east)           counterclockwise
                                                    
                                                    
     “logo”           upward (north)                clockwise
                                                    

          >>> mode("logo")   # resets turtle heading to north
          >>> mode()
          'logo'

 -- Function: turtle.colormode (cmode=None)


     Parameters: ‘cmode’ – one of the values 1.0 or 255

     Return the colormode or set it to 1.0 or 255.  Subsequently `r',
     `g', `b' values of color triples have to be in the range
     0..`cmode'.

          >>> screen.colormode(1)
          >>> turtle.pencolor(240, 160, 80)
          Traceback (most recent call last):
               ...
          TurtleGraphicsError: bad color sequence: (240, 160, 80)
          >>> screen.colormode()
          1.0
          >>> screen.colormode(255)
          >>> screen.colormode()
          255
          >>> turtle.pencolor(240,160,80)

 -- Function: turtle.getcanvas ()

     Return the Canvas of this TurtleScreen.  Useful for insiders who
     know what to do with a Tkinter Canvas.

          >>> cv = screen.getcanvas()
          >>> cv
          <turtle.ScrolledCanvas object ...>

 -- Function: turtle.getshapes ()

     Return a list of names of all currently available turtle shapes.

          >>> screen.getshapes()
          ['arrow', 'blank', 'circle', ..., 'turtle']

 -- Function: turtle.register_shape (name, shape=None)
 -- Function: turtle.addshape (name, shape=None)

     There are three different ways to call this function:

       1. `name' is the name of a gif-file and `shape' is ‘None’:
          Install the corresponding image shape.

               >>> screen.register_shape("turtle.gif")

               Note: Image shapes `do not' rotate when turning the
               turtle, so they do not display the heading of the turtle!

       2. `name' is an arbitrary string and `shape' is a tuple of pairs
          of coordinates: Install the corresponding polygon shape.

               >>> screen.register_shape("triangle", ((5,-3), (0,5), (-5,-3)))

       3. `name' is an arbitrary string and shape is a (compound) *note
          Shape: 3261. object: Install the corresponding compound shape.

     Add a turtle shape to TurtleScreen’s shapelist.  Only thusly
     registered shapes can be used by issuing the command
     ‘shape(shapename)’.

 -- Function: turtle.turtles ()

     Return the list of turtles on the screen.

          >>> for turtle in screen.turtles():
          ...     turtle.color("red")

 -- Function: turtle.window_height ()

     Return the height of the turtle window.

          >>> screen.window_height()
          480

 -- Function: turtle.window_width ()

     Return the width of the turtle window.

          >>> screen.window_width()
          640


File: python.info,  Node: Methods specific to Screen not inherited from TurtleScreen,  Prev: Settings and special methods,  Up: Methods of TurtleScreen/Screen and corresponding functions

5.24.1.26 Methods specific to Screen, not inherited from TurtleScreen
.....................................................................

 -- Function: turtle.bye ()

     Shut the turtlegraphics window.

 -- Function: turtle.exitonclick ()

     Bind ‘bye()’ method to mouse clicks on the Screen.

     If the value “using_IDLE” in the configuration dictionary is
     ‘False’ (default value), also enter mainloop.  Remark: If IDLE with
     the ‘-n’ switch (no subprocess) is used, this value should be set
     to ‘True’ in ‘turtle.cfg’.  In this case IDLE’s own mainloop is
     active also for the client script.

 -- Function: turtle.setup (width=_CFG["width"], height=_CFG["height"],
          startx=_CFG["leftright"], starty=_CFG["topbottom"])

     Set the size and position of the main window.  Default values of
     arguments are stored in the configuration dictionary and can be
     changed via a ‘turtle.cfg’ file.


     Parameters:

        * ‘width’ – if an integer, a size in pixels, if a float, a
          fraction of the screen; default is 50% of screen

        * ‘height’ – if an integer, the height in pixels, if a float, a
          fraction of the screen; default is 75% of screen

        * ‘startx’ – if positive, starting position in pixels from the
          left edge of the screen, if negative from the right edge, if
          ‘None’, center window horizontally

        * ‘starty’ – if positive, starting position in pixels from the
          top edge of the screen, if negative from the bottom edge, if
          ‘None’, center window vertically

          >>> screen.setup (width=200, height=200, startx=0, starty=0)
          >>>              # sets window to 200x200 pixels, in upper left of screen
          >>> screen.setup(width=.75, height=0.5, startx=None, starty=None)
          >>>              # sets window to 75% of screen by 50% of screen and centers

 -- Function: turtle.title (titlestring)


     Parameters: ‘titlestring’ – a string that is shown in the titlebar
     of the turtle graphics window

     Set title of turtle window to `titlestring'.

          >>> screen.title("Welcome to the turtle zoo!")


File: python.info,  Node: Public classes,  Next: Help and configuration,  Prev: Methods of TurtleScreen/Screen and corresponding functions,  Up: turtle — Turtle graphics

5.24.1.27 Public classes
........................

 -- Class: turtle.RawTurtle (canvas)
 -- Class: turtle.RawPen (canvas)


     Parameters: ‘canvas’ – a ‘tkinter.Canvas’, a *note ScrolledCanvas:
     31db. or a *note TurtleScreen: 31da.

     Create a turtle.  The turtle has all methods described above as
     “methods of Turtle/RawTurtle”.

 -- Class: turtle.Turtle

     Subclass of RawTurtle, has the same interface but draws on a
     default *note Screen: 31dc. object created automatically when
     needed for the first time.

 -- Class: turtle.TurtleScreen (cv)


     Parameters: ‘cv’ – a ‘tkinter.Canvas’

     Provides screen oriented methods like ‘setbg()’ etc.  that are
     described above.

 -- Class: turtle.Screen

     Subclass of TurtleScreen, with *note four methods added: 3269.

 -- Class: turtle.ScrolledCanvas (master)


     Parameters: ‘master’ – some Tkinter widget to contain the
     ScrolledCanvas, i.e.  a Tkinter-canvas with scrollbars added

     Used by class Screen, which thus automatically provides a
     ScrolledCanvas as playground for the turtles.

 -- Class: turtle.Shape (type_, data)


     Parameters: ‘type_’ – one of the strings “polygon”, “image”,
     “compound”

     Data structure modeling shapes.  The pair ‘(type_, data)’ must
     follow this specification:

     `type_'         `data'
                     
     -------------------------------------------------------------------------------
                     
     “polygon”       a polygon-tuple, i.e.  a tuple of pairs of coordinates
                     
                     
     “image”         an image (in this form only used internally!)
                     
                     
     “compound”      ‘None’ (a compound shape has to be constructed using the
                     *note addcomponent(): 326b. method)
                     

      -- Method: addcomponent (poly, fill, outline=None)


          Parameters:

             * ‘poly’ – a polygon, i.e.  a tuple of pairs of numbers

             * ‘fill’ – a color the `poly' will be filled with

             * ‘outline’ – a color for the poly’s outline (if given)

          Example:

               >>> poly = ((0,0),(10,-5),(0,10),(-10,-5))
               >>> s = Shape("compound")
               >>> s.addcomponent(poly, "red", "blue")
               >>> # ... add more components and then use register_shape()

          See *note Compound shapes: 3260.

 -- Class: turtle.Vec2D (x, y)

     A two-dimensional vector class, used as a helper class for
     implementing turtle graphics.  May be useful for turtle graphics
     programs too.  Derived from tuple, so a vector is a tuple!

     Provides (for `a', `b' vectors, `k' number):

        * ‘a + b’ vector addition

        * ‘a - b’ vector subtraction

        * ‘a * b’ inner product

        * ‘k * a’ and ‘a * k’ multiplication with scalar

        * ‘abs(a)’ absolute value of a

        * ‘a.rotate(angle)’ rotation


File: python.info,  Node: Help and configuration,  Next: turtledemo — Demo scripts,  Prev: Public classes,  Up: turtle — Turtle graphics

5.24.1.28 Help and configuration
................................

* Menu:

* How to use help::
* Translation of docstrings into different languages::
* How to configure Screen and Turtles::


File: python.info,  Node: How to use help,  Next: Translation of docstrings into different languages,  Up: Help and configuration

5.24.1.29 How to use help
.........................

The public methods of the Screen and Turtle classes are documented
extensively via docstrings.  So these can be used as online-help via the
Python help facilities:

   - When using IDLE, tooltips show the signatures and first lines of
     the docstrings of typed in function-/method calls.

   - Calling *note help(): 175. on methods or functions displays the
     docstrings:

          >>> help(Screen.bgcolor)
          Help on method bgcolor in module turtle:

          bgcolor(self, *args) unbound turtle.Screen method
              Set or return backgroundcolor of the TurtleScreen.

              Arguments (if given): a color string or three numbers
              in the range 0..colormode or a 3-tuple of such numbers.


                >>> screen.bgcolor("orange")
                >>> screen.bgcolor()
                "orange"
                >>> screen.bgcolor(0.5,0,0.5)
                >>> screen.bgcolor()
                "#800080"

          >>> help(Turtle.penup)
          Help on method penup in module turtle:

          penup(self) unbound turtle.Turtle method
              Pull the pen up -- no drawing when moving.

              Aliases: penup | pu | up

              No argument

              >>> turtle.penup()

   - The docstrings of the functions which are derived from methods have
     a modified form:

          >>> help(bgcolor)
          Help on function bgcolor in module turtle:

          bgcolor(*args)
              Set or return backgroundcolor of the TurtleScreen.

              Arguments (if given): a color string or three numbers
              in the range 0..colormode or a 3-tuple of such numbers.

              Example::

                >>> bgcolor("orange")
                >>> bgcolor()
                "orange"
                >>> bgcolor(0.5,0,0.5)
                >>> bgcolor()
                "#800080"

          >>> help(penup)
          Help on function penup in module turtle:

          penup()
              Pull the pen up -- no drawing when moving.

              Aliases: penup | pu | up

              No argument

              Example:
              >>> penup()

These modified docstrings are created automatically together with the
function definitions that are derived from the methods at import time.


File: python.info,  Node: Translation of docstrings into different languages,  Next: How to configure Screen and Turtles,  Prev: How to use help,  Up: Help and configuration

5.24.1.30 Translation of docstrings into different languages
............................................................

There is a utility to create a dictionary the keys of which are the
method names and the values of which are the docstrings of the public
methods of the classes Screen and Turtle.

 -- Function: turtle.write_docstringdict
          (filename="turtle_docstringdict")


     Parameters: ‘filename’ – a string, used as filename

     Create and write docstring-dictionary to a Python script with the
     given filename.  This function has to be called explicitly (it is
     not used by the turtle graphics classes).  The docstring dictionary
     will be written to the Python script ‘`filename'.py’.  It is
     intended to serve as a template for translation of the docstrings
     into different languages.

If you (or your students) want to use *note turtle: 11f. with online
help in your native language, you have to translate the docstrings and
save the resulting file as e.g.  ‘turtle_docstringdict_german.py’.

If you have an appropriate entry in your ‘turtle.cfg’ file this
dictionary will be read in at import time and will replace the original
English docstrings.

At the time of this writing there are docstring dictionaries in German
and in Italian.  (Requests please to <glingl@aon.at>.)


File: python.info,  Node: How to configure Screen and Turtles,  Prev: Translation of docstrings into different languages,  Up: Help and configuration

5.24.1.31 How to configure Screen and Turtles
.............................................

The built-in default configuration mimics the appearance and behaviour
of the old turtle module in order to retain best possible compatibility
with it.

If you want to use a different configuration which better reflects the
features of this module or which better fits to your needs, e.g.  for
use in a classroom, you can prepare a configuration file ‘turtle.cfg’
which will be read at import time and modify the configuration according
to its settings.

The built in configuration would correspond to the following turtle.cfg:

     width = 0.5
     height = 0.75
     leftright = None
     topbottom = None
     canvwidth = 400
     canvheight = 300
     mode = standard
     colormode = 1.0
     delay = 10
     undobuffersize = 1000
     shape = classic
     pencolor = black
     fillcolor = black
     resizemode = noresize
     visible = True
     language = english
     exampleturtle = turtle
     examplescreen = screen
     title = Python Turtle Graphics
     using_IDLE = False

Short explanation of selected entries:

   - The first four lines correspond to the arguments of the
     ‘Screen.setup()’ method.

   - Line 5 and 6 correspond to the arguments of the method
     ‘Screen.screensize()’.

   - `shape' can be any of the built-in shapes, e.g: arrow, turtle, etc.
     For more info try ‘help(shape)’.

   - If you want to use no fillcolor (i.e.  make the turtle
     transparent), you have to write ‘fillcolor = ""’ (but all nonempty
     strings must not have quotes in the cfg-file).

   - If you want to reflect the turtle its state, you have to use
     ‘resizemode = auto’.

   - If you set e.g.  ‘language = italian’ the docstringdict
     ‘turtle_docstringdict_italian.py’ will be loaded at import time (if
     present on the import path, e.g.  in the same directory as *note
     turtle: 11f.

   - The entries `exampleturtle' and `examplescreen' define the names of
     these objects as they occur in the docstrings.  The transformation
     of method-docstrings to function-docstrings will delete these names
     from the docstrings.

   - `using_IDLE': Set this to ‘True’ if you regularly work with IDLE
     and its -n switch (“no subprocess”).  This will prevent *note
     exitonclick(): 324d. to enter the mainloop.

There can be a ‘turtle.cfg’ file in the directory where *note turtle:
11f. is stored and an additional one in the current working directory.
The latter will override the settings of the first one.

The ‘Lib/turtledemo’ directory contains a ‘turtle.cfg’ file.  You can
study it as an example and see its effects when running the demos
(preferably not from within the demo-viewer).


File: python.info,  Node: turtledemo — Demo scripts,  Next: Changes since Python 2 6,  Prev: Help and configuration,  Up: turtle — Turtle graphics

5.24.1.32 ‘turtledemo’ — Demo scripts
.....................................

The *note turtledemo: 120. package includes a set of demo scripts.
These scripts can be run and viewed using the supplied demo viewer as
follows:

     python -m turtledemo

Alternatively, you can run the demo scripts individually.  For example,

     python -m turtledemo.bytedesign

The *note turtledemo: 120. package directory contains:

   - A demo viewer ‘__main__.py’ which can be used to view the
     sourcecode of the scripts and run them at the same time.

   - Multiple scripts demonstrating different features of the *note
     turtle: 11f. module.  Examples can be accessed via the Examples
     menu.  They can also be run standalone.

   - A ‘turtle.cfg’ file which serves as an example of how to write and
     use such files.

The demo scripts are:

Name                 Description                        Features
                                                        
------------------------------------------------------------------------------------
                                                        
bytedesign           complex classical turtle           ‘tracer()’, delay,
                     graphics pattern                   ‘update()’
                                                        
                                                        
chaos                graphs Verhulst dynamics, shows    world coordinates
                     that computer’s computations can   
                     generate results sometimes
                     against the common sense
                     expectations
                     
                                                        
clock                analog clock showing time of       turtles as clock’s hands,
                     your computer                      ontimer
                                                        
                                                        
colormixer           experiment with r, g, b            ‘ondrag()’
                                                        
                                                        
forest               3 breadth-first trees              randomization
                                                        
                                                        
fractalcurves        Hilbert & Koch curves              recursion
                                                        
                                                        
lindenmayer          ethnomathematics (indian kolams)   L-System
                                                        
                                                        
minimal_hanoi        Towers of Hanoi                    Rectangular Turtles as
                                                        Hanoi discs (shape,
                                                        shapesize)
                                                        
                                                        
nim                  play the classical nim game with   turtles as nimsticks,
                     three heaps of sticks against      event driven (mouse,
                     the computer.                      keyboard)
                                                        
                                                        
paint                super minimalistic drawing         ‘onclick()’
                     program                            
                     
                                                        
peace                elementary                         turtle: appearance and
                                                        animation
                                                        
                                                        
penrose              aperiodic tiling with kites and    ‘stamp()’
                     darts                              
                     
                                                        
planet_and_moon      simulation of gravitational        compound shapes, ‘Vec2D’
                     system                             
                     
                                                        
round_dance          dancing turtles rotating           compound shapes, clone
                     pairwise in opposite direction     shapesize, tilt,
                                                        get_shapepoly, update
                                                        
                                                        
sorting_animate      visual demonstration of            simple alignment,
                     different sorting methods          randomization
                                                        
                                                        
tree                 a (graphical) breadth first tree   ‘clone()’
                     (using generators)                 
                     
                                                        
two_canvases         simple design                      turtles on two canvases
                                                        
                                                        
wikipedia            a pattern from the wikipedia       ‘clone()’, ‘undo()’
                     article on turtle graphics         
                     
                                                        
yinyang              another elementary example         ‘circle()’
                                                        

Have fun!


File: python.info,  Node: Changes since Python 2 6,  Next: Changes since Python 3 0,  Prev: turtledemo — Demo scripts,  Up: turtle — Turtle graphics

5.24.1.33 Changes since Python 2.6
..................................

   - The methods ‘Turtle.tracer()’, ‘Turtle.window_width()’ and
     ‘Turtle.window_height()’ have been eliminated.  Methods with these
     names and functionality are now available only as methods of
     ‘Screen’.  The functions derived from these remain available.  (In
     fact already in Python 2.6 these methods were merely duplications
     of the corresponding ‘TurtleScreen’/‘Screen’-methods.)

   - The method ‘Turtle.fill()’ has been eliminated.  The behaviour of
     ‘begin_fill()’ and ‘end_fill()’ have changed slightly: now every
     filling-process must be completed with an ‘end_fill()’ call.

   - A method ‘Turtle.filling()’ has been added.  It returns a boolean
     value: ‘True’ if a filling process is under way, ‘False’ otherwise.
     This behaviour corresponds to a ‘fill()’ call without arguments in
     Python 2.6.


File: python.info,  Node: Changes since Python 3 0,  Prev: Changes since Python 2 6,  Up: turtle — Turtle graphics

5.24.1.34 Changes since Python 3.0
..................................

   - The methods ‘Turtle.shearfactor()’, ‘Turtle.shapetransform()’ and
     ‘Turtle.get_shapepoly()’ have been added.  Thus the full range of
     regular linear transforms is now available for transforming turtle
     shapes.  ‘Turtle.tiltangle()’ has been enhanced in functionality:
     it now can be used to get or set the tiltangle.
     ‘Turtle.settiltangle()’ has been deprecated.

   - The method ‘Screen.onkeypress()’ has been added as a complement to
     ‘Screen.onkey()’ which in fact binds actions to the keyrelease
     event.  Accordingly the latter has got an alias:
     ‘Screen.onkeyrelease()’.

   - The method ‘Screen.mainloop()’ has been added.  So when working
     only with Screen and Turtle objects one must not additionally
     import ‘mainloop()’ anymore.

   - Two input methods has been added ‘Screen.textinput()’ and
     ‘Screen.numinput()’.  These popup input dialogs and return strings
     and numbers respectively.

   - Two example scripts ‘tdemo_nim.py’ and ‘tdemo_round_dance.py’ have
     been added to the ‘Lib/turtledemo’ directory.


File: python.info,  Node: cmd — Support for line-oriented command interpreters,  Next: shlex — Simple lexical analysis,  Prev: turtle — Turtle graphics,  Up: Program Frameworks

5.24.2 ‘cmd’ — Support for line-oriented command interpreters
-------------------------------------------------------------

`Source code:' Lib/cmd.py(1)

__________________________________________________________________

The *note Cmd: 3276. class provides a simple framework for writing
line-oriented command interpreters.  These are often useful for test
harnesses, administrative tools, and prototypes that will later be
wrapped in a more sophisticated interface.

 -- Class: cmd.Cmd (completekey='tab', stdin=None, stdout=None)

     A *note Cmd: 3276. instance or subclass instance is a line-oriented
     interpreter framework.  There is no good reason to instantiate
     *note Cmd: 3276. itself; rather, it’s useful as a superclass of an
     interpreter class you define yourself in order to inherit *note
     Cmd: 3276.’s methods and encapsulate action methods.

     The optional argument `completekey' is the *note readline: de. name
     of a completion key; it defaults to ‘Tab’.  If `completekey' is not
     *note None: 203. and *note readline: de. is available, command
     completion is done automatically.

     The optional arguments `stdin' and `stdout' specify the input and
     output file objects that the Cmd instance or subclass instance will
     use for input and output.  If not specified, they will default to
     *note sys.stdin: 41e. and *note sys.stdout: 41f.

     If you want a given `stdin' to be used, make sure to set the
     instance’s *note use_rawinput: 3277. attribute to ‘False’,
     otherwise `stdin' will be ignored.

* Menu:

* Cmd Objects::
* Cmd Example::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/cmd.py


File: python.info,  Node: Cmd Objects,  Next: Cmd Example,  Up: cmd — Support for line-oriented command interpreters

5.24.2.1 Cmd Objects
....................

A *note Cmd: 3276. instance has the following methods:

 -- Method: Cmd.cmdloop (intro=None)

     Repeatedly issue a prompt, accept input, parse an initial prefix
     off the received input, and dispatch to action methods, passing
     them the remainder of the line as argument.

     The optional argument is a banner or intro string to be issued
     before the first prompt (this overrides the *note intro: 327b.
     class attribute).

     If the *note readline: de. module is loaded, input will
     automatically inherit ‘bash’-like history-list editing (e.g.
     ‘Control-P’ scrolls back to the last command, ‘Control-N’ forward
     to the next one, ‘Control-F’ moves the cursor to the right
     non-destructively, ‘Control-B’ moves the cursor to the left
     non-destructively, etc.).

     An end-of-file on input is passed back as the string ‘'EOF'’.

     An interpreter instance will recognize a command name ‘foo’ if and
     only if it has a method ‘do_foo()’.  As a special case, a line
     beginning with the character ‘'?'’ is dispatched to the method
     ‘do_help()’.  As another special case, a line beginning with the
     character ‘'!'’ is dispatched to the method ‘do_shell()’ (if such a
     method is defined).

     This method will return when the *note postcmd(): 327c. method
     returns a true value.  The `stop' argument to *note postcmd():
     327c. is the return value from the command’s corresponding ‘do_*()’
     method.

     If completion is enabled, completing commands will be done
     automatically, and completing of commands args is done by calling
     ‘complete_foo()’ with arguments `text', `line', `begidx', and
     `endidx'.  `text' is the string prefix we are attempting to match:
     all returned matches must begin with it.  `line' is the current
     input line with leading whitespace removed, `begidx' and `endidx'
     are the beginning and ending indexes of the prefix text, which
     could be used to provide different completion depending upon which
     position the argument is in.

     All subclasses of *note Cmd: 3276. inherit a predefined
     ‘do_help()’.  This method, called with an argument ‘'bar'’, invokes
     the corresponding method ‘help_bar()’, and if that is not present,
     prints the docstring of ‘do_bar()’, if available.  With no
     argument, ‘do_help()’ lists all available help topics (that is, all
     commands with corresponding ‘help_*()’ methods or commands that
     have docstrings), and also lists any undocumented commands.

 -- Method: Cmd.onecmd (str)

     Interpret the argument as though it had been typed in response to
     the prompt.  This may be overridden, but should not normally need
     to be; see the *note precmd(): 327e. and *note postcmd(): 327c.
     methods for useful execution hooks.  The return value is a flag
     indicating whether interpretation of commands by the interpreter
     should stop.  If there is a ‘do_*()’ method for the command `str',
     the return value of that method is returned, otherwise the return
     value from the *note default(): 327f. method is returned.

 -- Method: Cmd.emptyline ()

     Method called when an empty line is entered in response to the
     prompt.  If this method is not overridden, it repeats the last
     nonempty command entered.

 -- Method: Cmd.default (line)

     Method called on an input line when the command prefix is not
     recognized.  If this method is not overridden, it prints an error
     message and returns.

 -- Method: Cmd.completedefault (text, line, begidx, endidx)

     Method called to complete an input line when no command-specific
     ‘complete_*()’ method is available.  By default, it returns an
     empty list.

 -- Method: Cmd.precmd (line)

     Hook method executed just before the command line `line' is
     interpreted, but after the input prompt is generated and issued.
     This method is a stub in *note Cmd: 3276.; it exists to be
     overridden by subclasses.  The return value is used as the command
     which will be executed by the *note onecmd(): 327d. method; the
     *note precmd(): 327e. implementation may re-write the command or
     simply return `line' unchanged.

 -- Method: Cmd.postcmd (stop, line)

     Hook method executed just after a command dispatch is finished.
     This method is a stub in *note Cmd: 3276.; it exists to be
     overridden by subclasses.  `line' is the command line which was
     executed, and `stop' is a flag which indicates whether execution
     will be terminated after the call to *note postcmd(): 327c.; this
     will be the return value of the *note onecmd(): 327d. method.  The
     return value of this method will be used as the new value for the
     internal flag which corresponds to `stop'; returning false will
     cause interpretation to continue.

 -- Method: Cmd.preloop ()

     Hook method executed once when *note cmdloop(): 327a. is called.
     This method is a stub in *note Cmd: 3276.; it exists to be
     overridden by subclasses.

 -- Method: Cmd.postloop ()

     Hook method executed once when *note cmdloop(): 327a. is about to
     return.  This method is a stub in *note Cmd: 3276.; it exists to be
     overridden by subclasses.

Instances of *note Cmd: 3276. subclasses have some public instance
variables:

 -- Attribute: Cmd.prompt

     The prompt issued to solicit input.

 -- Attribute: Cmd.identchars

     The string of characters accepted for the command prefix.

 -- Attribute: Cmd.lastcmd

     The last nonempty command prefix seen.

 -- Attribute: Cmd.cmdqueue

     A list of queued input lines.  The cmdqueue list is checked in
     *note cmdloop(): 327a. when new input is needed; if it is nonempty,
     its elements will be processed in order, as if entered at the
     prompt.

 -- Attribute: Cmd.intro

     A string to issue as an intro or banner.  May be overridden by
     giving the *note cmdloop(): 327a. method an argument.

 -- Attribute: Cmd.doc_header

     The header to issue if the help output has a section for documented
     commands.

 -- Attribute: Cmd.misc_header

     The header to issue if the help output has a section for
     miscellaneous help topics (that is, there are ‘help_*()’ methods
     without corresponding ‘do_*()’ methods).

 -- Attribute: Cmd.undoc_header

     The header to issue if the help output has a section for
     undocumented commands (that is, there are ‘do_*()’ methods without
     corresponding ‘help_*()’ methods).

 -- Attribute: Cmd.ruler

     The character used to draw separator lines under the help-message
     headers.  If empty, no ruler line is drawn.  It defaults to ‘'='’.

 -- Attribute: Cmd.use_rawinput

     A flag, defaulting to true.  If true, *note cmdloop(): 327a. uses
     *note input(): d33. to display a prompt and read the next command;
     if false, ‘sys.stdout.write()’ and ‘sys.stdin.readline()’ are used.
     (This means that by importing *note readline: de, on systems that
     support it, the interpreter will automatically support ‘Emacs’-like
     line editing and command-history keystrokes.)


File: python.info,  Node: Cmd Example,  Prev: Cmd Objects,  Up: cmd — Support for line-oriented command interpreters

5.24.2.2 Cmd Example
....................

The *note cmd: 19. module is mainly useful for building custom shells
that let a user work with a program interactively.

This section presents a simple example of how to build a shell around a
few of the commands in the *note turtle: 11f. module.

Basic turtle commands such as *note forward(): 31e2. are added to a
*note Cmd: 3276. subclass with method named ‘do_forward()’.  The
argument is converted to a number and dispatched to the turtle module.
The docstring is used in the help utility provided by the shell.

The example also includes a basic record and playback facility
implemented with the *note precmd(): 327e. method which is responsible
for converting the input to lowercase and writing the commands to a
file.  The ‘do_playback()’ method reads the file and adds the recorded
commands to the ‘cmdqueue’ for immediate playback:

     import cmd, sys
     from turtle import *

     class TurtleShell(cmd.Cmd):
         intro = 'Welcome to the turtle shell.   Type help or ? to list commands.\n'
         prompt = '(turtle) '
         file = None

         # ----- basic turtle commands -----
         def do_forward(self, arg):
             'Move the turtle forward by the specified distance:  FORWARD 10'
             forward(*parse(arg))
         def do_right(self, arg):
             'Turn turtle right by given number of degrees:  RIGHT 20'
             right(*parse(arg))
         def do_left(self, arg):
             'Turn turtle left by given number of degrees:  LEFT 90'
             left(*parse(arg))
         def do_goto(self, arg):
             'Move turtle to an absolute position with changing orientation.  GOTO 100 200'
             goto(*parse(arg))
         def do_home(self, arg):
             'Return turtle to the home position:  HOME'
             home()
         def do_circle(self, arg):
             'Draw circle with given radius an options extent and steps:  CIRCLE 50'
             circle(*parse(arg))
         def do_position(self, arg):
             'Print the current turtle position:  POSITION'
             print('Current position is %d %d\n' % position())
         def do_heading(self, arg):
             'Print the current turtle heading in degrees:  HEADING'
             print('Current heading is %d\n' % (heading(),))
         def do_color(self, arg):
             'Set the color:  COLOR BLUE'
             color(arg.lower())
         def do_undo(self, arg):
             'Undo (repeatedly) the last turtle action(s):  UNDO'
         def do_reset(self, arg):
             'Clear the screen and return turtle to center:  RESET'
             reset()
         def do_bye(self, arg):
             'Stop recording, close the turtle window, and exit:  BYE'
             print('Thank you for using Turtle')
             self.close()
             bye()
             return True

         # ----- record and playback -----
         def do_record(self, arg):
             'Save future commands to filename:  RECORD rose.cmd'
             self.file = open(arg, 'w')
         def do_playback(self, arg):
             'Playback commands from a file:  PLAYBACK rose.cmd'
             self.close()
             with open(arg) as f:
                 self.cmdqueue.extend(f.read().splitlines())
         def precmd(self, line):
             line = line.lower()
             if self.file and 'playback' not in line:
                 print(line, file=self.file)
             return line
         def close(self):
             if self.file:
                 self.file.close()
                 self.file = None

     def parse(arg):
         'Convert a series of zero or more numbers to an argument tuple'
         return tuple(map(int, arg.split()))

     if __name__ == '__main__':
         TurtleShell().cmdloop()

Here is a sample session with the turtle shell showing the help
functions, using blank lines to repeat commands, and the simple record
and playback facility:

     Welcome to the turtle shell.   Type help or ? to list commands.

     (turtle) ?

     Documented commands (type help <topic>):
     ========================================
     bye     color    goto     home  playback  record  right
     circle  forward  heading  left  position  reset   undo

     (turtle) help forward
     Move the turtle forward by the specified distance:  FORWARD 10
     (turtle) record spiral.cmd
     (turtle) position
     Current position is 0 0

     (turtle) heading
     Current heading is 0

     (turtle) reset
     (turtle) circle 20
     (turtle) right 30
     (turtle) circle 40
     (turtle) right 30
     (turtle) circle 60
     (turtle) right 30
     (turtle) circle 80
     (turtle) right 30
     (turtle) circle 100
     (turtle) right 30
     (turtle) circle 120
     (turtle) right 30
     (turtle) circle 120
     (turtle) heading
     Current heading is 180

     (turtle) forward 100
     (turtle)
     (turtle) right 90
     (turtle) forward 100
     (turtle)
     (turtle) right 90
     (turtle) forward 400
     (turtle) right 90
     (turtle) forward 500
     (turtle) right 90
     (turtle) forward 400
     (turtle) right 90
     (turtle) forward 300
     (turtle) playback spiral.cmd
     Current position is 0 0

     Current heading is 0

     Current heading is 180

     (turtle) bye
     Thank you for using Turtle


File: python.info,  Node: shlex — Simple lexical analysis,  Prev: cmd — Support for line-oriented command interpreters,  Up: Program Frameworks

5.24.3 ‘shlex’ — Simple lexical analysis
----------------------------------------

`Source code:' Lib/shlex.py(1)

__________________________________________________________________

The *note shlex: 671. class makes it easy to write lexical analyzers for
simple syntaxes resembling that of the Unix shell.  This will often be
useful for writing minilanguages, (for example, in run control files for
Python applications) or for parsing quoted strings.

The *note shlex: e8. module defines the following functions:

 -- Function: shlex.split (s, comments=False, posix=True)

     Split the string `s' using shell-like syntax.  If `comments' is
     *note False: 48f. (the default), the parsing of comments in the
     given string will be disabled (setting the *note commenters: 3290.
     attribute of the *note shlex: 671. instance to the empty string).
     This function operates in POSIX mode by default, but uses non-POSIX
     mode if the `posix' argument is false.

          Note: Since the *note split(): 210. function instantiates a
          *note shlex: 671. instance, passing ‘None’ for `s' will read
          the string to split from standard input.

     Deprecated since version 3.9: Passing ‘None’ for `s' will raise an
     exception in future Python versions.

 -- Function: shlex.join (split_command)

     Concatenate the tokens of the list `split_command' and return a
     string.  This function is the inverse of *note split(): 210.

          >>> from shlex import join
          >>> print(join(['echo', '-n', 'Multiple words']))
          echo -n 'Multiple words'

     The returned value is shell-escaped to protect against injection
     vulnerabilities (see *note quote(): b4e.).

     New in version 3.8.

 -- Function: shlex.quote (s)

     Return a shell-escaped version of the string `s'.  The returned
     value is a string that can safely be used as one token in a shell
     command line, for cases where you cannot use a list.

     This idiom would be unsafe:

          >>> filename = 'somefile; rm -rf ~'
          >>> command = 'ls -l {}'.format(filename)
          >>> print(command)  # executed by a shell: boom!
          ls -l somefile; rm -rf ~

     *note quote(): b4e. lets you plug the security hole:

          >>> from shlex import quote
          >>> command = 'ls -l {}'.format(quote(filename))
          >>> print(command)
          ls -l 'somefile; rm -rf ~'
          >>> remote_command = 'ssh home {}'.format(quote(command))
          >>> print(remote_command)
          ssh home 'ls -l '"'"'somefile; rm -rf ~'"'"''

     The quoting is compatible with UNIX shells and with *note split():
     210.:

          >>> from shlex import split
          >>> remote_command = split(remote_command)
          >>> remote_command
          ['ssh', 'home', "ls -l 'somefile; rm -rf ~'"]
          >>> command = split(remote_command[-1])
          >>> command
          ['ls', '-l', 'somefile; rm -rf ~']

     New in version 3.3.

The *note shlex: e8. module defines the following class:

 -- Class: shlex.shlex (instream=None, infile=None, posix=False,
          punctuation_chars=False)

     A *note shlex: 671. instance or subclass instance is a lexical
     analyzer object.  The initialization argument, if present,
     specifies where to read characters from.  It must be a
     file-/stream-like object with *note read(): 2162. and *note
     readline(): 1d5b. methods, or a string.  If no argument is given,
     input will be taken from ‘sys.stdin’.  The second optional argument
     is a filename string, which sets the initial value of the *note
     infile: 3291. attribute.  If the `instream' argument is omitted or
     equal to ‘sys.stdin’, this second argument defaults to “stdin”.
     The `posix' argument defines the operational mode: when `posix' is
     not true (default), the *note shlex: 671. instance will operate in
     compatibility mode.  When operating in POSIX mode, *note shlex:
     671. will try to be as close as possible to the POSIX shell parsing
     rules.  The `punctuation_chars' argument provides a way to make the
     behaviour even closer to how real shells parse.  This can take a
     number of values: the default value, ‘False’, preserves the
     behaviour seen under Python 3.5 and earlier.  If set to ‘True’,
     then parsing of the characters ‘();<>|&’ is changed: any run of
     these characters (considered punctuation characters) is returned as
     a single token.  If set to a non-empty string of characters, those
     characters will be used as the punctuation characters.  Any
     characters in the *note wordchars: 3292. attribute that appear in
     `punctuation_chars' will be removed from *note wordchars: 3292.
     See *note Improved Compatibility with Shells: 672. for more
     information.  `punctuation_chars' can be set only upon *note shlex:
     671. instance creation and can’t be modified later.

     Changed in version 3.6: The `punctuation_chars' parameter was
     added.

See also
........

Module *note configparser: 22.

     Parser for configuration files similar to the Windows ‘.ini’ files.

* Menu:

* shlex Objects::
* Parsing Rules::
* Improved Compatibility with Shells::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/shlex.py


File: python.info,  Node: shlex Objects,  Next: Parsing Rules,  Up: shlex — Simple lexical analysis

5.24.3.1 shlex Objects
......................

A *note shlex: 671. instance has the following methods:

 -- Method: shlex.get_token ()

     Return a token.  If tokens have been stacked using *note
     push_token(): 3296, pop a token off the stack.  Otherwise, read one
     from the input stream.  If reading encounters an immediate
     end-of-file, *note eof: 3297. is returned (the empty string (‘''’)
     in non-POSIX mode, and ‘None’ in POSIX mode).

 -- Method: shlex.push_token (str)

     Push the argument onto the token stack.

 -- Method: shlex.read_token ()

     Read a raw token.  Ignore the pushback stack, and do not interpret
     source requests.  (This is not ordinarily a useful entry point, and
     is documented here only for the sake of completeness.)

 -- Method: shlex.sourcehook (filename)

     When *note shlex: 671. detects a source request (see *note source:
     329a. below) this method is given the following token as argument,
     and expected to return a tuple consisting of a filename and an open
     file-like object.

     Normally, this method first strips any quotes off the argument.  If
     the result is an absolute pathname, or there was no previous source
     request in effect, or the previous source was a stream (such as
     ‘sys.stdin’), the result is left alone.  Otherwise, if the result
     is a relative pathname, the directory part of the name of the file
     immediately before it on the source inclusion stack is prepended
     (this behavior is like the way the C preprocessor handles ‘#include
     "file.h"’).

     The result of the manipulations is treated as a filename, and
     returned as the first component of the tuple, with *note open():
     16f. called on it to yield the second component.  (Note: this is
     the reverse of the order of arguments in instance initialization!)

     This hook is exposed so that you can use it to implement directory
     search paths, addition of file extensions, and other namespace
     hacks.  There is no corresponding ‘close’ hook, but a shlex
     instance will call the *note close(): 1147. method of the sourced
     input stream when it returns EOF.

     For more explicit control of source stacking, use the *note
     push_source(): 329b. and *note pop_source(): 329c. methods.

 -- Method: shlex.push_source (newstream, newfile=None)

     Push an input source stream onto the input stack.  If the filename
     argument is specified it will later be available for use in error
     messages.  This is the same method used internally by the *note
     sourcehook(): 3299. method.

 -- Method: shlex.pop_source ()

     Pop the last-pushed input source from the input stack.  This is the
     same method used internally when the lexer reaches EOF on a stacked
     input stream.

 -- Method: shlex.error_leader (infile=None, lineno=None)

     This method generates an error message leader in the format of a
     Unix C compiler error label; the format is ‘'"%s", line %d: '’,
     where the ‘%s’ is replaced with the name of the current source file
     and the ‘%d’ with the current input line number (the optional
     arguments can be used to override these).

     This convenience is provided to encourage *note shlex: e8. users to
     generate error messages in the standard, parseable format
     understood by Emacs and other Unix tools.

Instances of *note shlex: 671. subclasses have some public instance
variables which either control lexical analysis or can be used for
debugging:

 -- Attribute: shlex.commenters

     The string of characters that are recognized as comment beginners.
     All characters from the comment beginner to end of line are
     ignored.  Includes just ‘'#'’ by default.

 -- Attribute: shlex.wordchars

     The string of characters that will accumulate into multi-character
     tokens.  By default, includes all ASCII alphanumerics and
     underscore.  In POSIX mode, the accented characters in the Latin-1
     set are also included.  If *note punctuation_chars: 10d9. is not
     empty, the characters ‘~-./*?=’, which can appear in filename
     specifications and command line parameters, will also be included
     in this attribute, and any characters which appear in
     ‘punctuation_chars’ will be removed from ‘wordchars’ if they are
     present there.  If *note whitespace_split: 329e. is set to ‘True’,
     this will have no effect.

 -- Attribute: shlex.whitespace

     Characters that will be considered whitespace and skipped.
     Whitespace bounds tokens.  By default, includes space, tab,
     linefeed and carriage-return.

 -- Attribute: shlex.escape

     Characters that will be considered as escape.  This will be only
     used in POSIX mode, and includes just ‘'\'’ by default.

 -- Attribute: shlex.quotes

     Characters that will be considered string quotes.  The token
     accumulates until the same quote is encountered again (thus,
     different quote types protect each other as in the shell.)  By
     default, includes ASCII single and double quotes.

 -- Attribute: shlex.escapedquotes

     Characters in *note quotes: 32a1. that will interpret escape
     characters defined in *note escape: 32a0.  This is only used in
     POSIX mode, and includes just ‘'"'’ by default.

 -- Attribute: shlex.whitespace_split

     If ‘True’, tokens will only be split in whitespaces.  This is
     useful, for example, for parsing command lines with *note shlex:
     671, getting tokens in a similar way to shell arguments.  When used
     in combination with *note punctuation_chars: 10d9, tokens will be
     split on whitespace in addition to those characters.

     Changed in version 3.8: The *note punctuation_chars: 10d9.
     attribute was made compatible with the *note whitespace_split:
     329e. attribute.

 -- Attribute: shlex.infile

     The name of the current input file, as initially set at class
     instantiation time or stacked by later source requests.  It may be
     useful to examine this when constructing error messages.

 -- Attribute: shlex.instream

     The input stream from which this *note shlex: 671. instance is
     reading characters.

 -- Attribute: shlex.source

     This attribute is ‘None’ by default.  If you assign a string to it,
     that string will be recognized as a lexical-level inclusion request
     similar to the ‘source’ keyword in various shells.  That is, the
     immediately following token will be opened as a filename and input
     will be taken from that stream until EOF, at which point the *note
     close(): 1147. method of that stream will be called and the input
     source will again become the original input stream.  Source
     requests may be stacked any number of levels deep.

 -- Attribute: shlex.debug

     If this attribute is numeric and ‘1’ or more, a *note shlex: 671.
     instance will print verbose progress output on its behavior.  If
     you need to use this, you can read the module source code to learn
     the details.

 -- Attribute: shlex.lineno

     Source line number (count of newlines seen so far plus one).

 -- Attribute: shlex.token

     The token buffer.  It may be useful to examine this when catching
     exceptions.

 -- Attribute: shlex.eof

     Token used to determine end of file.  This will be set to the empty
     string (‘''’), in non-POSIX mode, and to ‘None’ in POSIX mode.

 -- Attribute: shlex.punctuation_chars

     A read-only property.  Characters that will be considered
     punctuation.  Runs of punctuation characters will be returned as a
     single token.  However, note that no semantic validity checking
     will be performed: for example, ‘>>>’ could be returned as a token,
     even though it may not be recognised as such by shells.

     New in version 3.6.


File: python.info,  Node: Parsing Rules,  Next: Improved Compatibility with Shells,  Prev: shlex Objects,  Up: shlex — Simple lexical analysis

5.24.3.2 Parsing Rules
......................

When operating in non-POSIX mode, *note shlex: 671. will try to obey to
the following rules.

   * Quote characters are not recognized within words (‘Do"Not"Separate’
     is parsed as the single word ‘Do"Not"Separate’);

   * Escape characters are not recognized;

   * Enclosing characters in quotes preserve the literal value of all
     characters within the quotes;

   * Closing quotes separate words (‘"Do"Separate’ is parsed as ‘"Do"’
     and ‘Separate’);

   * If *note whitespace_split: 329e. is ‘False’, any character not
     declared to be a word character, whitespace, or a quote will be
     returned as a single-character token.  If it is ‘True’, *note
     shlex: 671. will only split words in whitespaces;

   * EOF is signaled with an empty string (‘''’);

   * It’s not possible to parse empty strings, even if quoted.

When operating in POSIX mode, *note shlex: 671. will try to obey to the
following parsing rules.

   * Quotes are stripped out, and do not separate words
     (‘"Do"Not"Separate"’ is parsed as the single word ‘DoNotSeparate’);

   * Non-quoted escape characters (e.g.  ‘'\'’) preserve the literal
     value of the next character that follows;

   * Enclosing characters in quotes which are not part of *note
     escapedquotes: 32a2. (e.g.  ‘"'"’) preserve the literal value of
     all characters within the quotes;

   * Enclosing characters in quotes which are part of *note
     escapedquotes: 32a2. (e.g.  ‘'"'’) preserves the literal value of
     all characters within the quotes, with the exception of the
     characters mentioned in *note escape: 32a0.  The escape characters
     retain its special meaning only when followed by the quote in use,
     or the escape character itself.  Otherwise the escape character
     will be considered a normal character.

   * EOF is signaled with a *note None: 203. value;

   * Quoted empty strings (‘''’) are allowed.


File: python.info,  Node: Improved Compatibility with Shells,  Prev: Parsing Rules,  Up: shlex — Simple lexical analysis

5.24.3.3 Improved Compatibility with Shells
...........................................

New in version 3.6.

The *note shlex: e8. class provides compatibility with the parsing
performed by common Unix shells like ‘bash’, ‘dash’, and ‘sh’.  To take
advantage of this compatibility, specify the ‘punctuation_chars’
argument in the constructor.  This defaults to ‘False’, which preserves
pre-3.6 behaviour.  However, if it is set to ‘True’, then parsing of the
characters ‘();<>|&’ is changed: any run of these characters is returned
as a single token.  While this is short of a full parser for shells
(which would be out of scope for the standard library, given the
multiplicity of shells out there), it does allow you to perform
processing of command lines more easily than you could otherwise.  To
illustrate, you can see the difference in the following snippet:

      >>> import shlex
      >>> text = "a && b; c && d || e; f >'abc'; (def \"ghi\")"
      >>> s = shlex.shlex(text, posix=True)
      >>> s.whitespace_split = True
      >>> list(s)
      ['a', '&&', 'b;', 'c', '&&', 'd', '||', 'e;', 'f', '>abc;', '(def', 'ghi)']
      >>> s = shlex.shlex(text, posix=True, punctuation_chars=True)
      >>> s.whitespace_split = True
      >>> list(s)
      ['a', '&&', 'b', ';', 'c', '&&', 'd', '||', 'e', ';', 'f', '>', 'abc', ';',
      '(', 'def', 'ghi', ')']

Of course, tokens will be returned which are not valid for shells, and
you’ll need to implement your own error checks on the returned tokens.

Instead of passing ‘True’ as the value for the punctuation_chars
parameter, you can pass a string with specific characters, which will be
used to determine which characters constitute punctuation.  For example:

     >>> import shlex
     >>> s = shlex.shlex("a && b || c", punctuation_chars="|")
     >>> list(s)
     ['a', '&', '&', 'b', '||', 'c']

     Note: When ‘punctuation_chars’ is specified, the *note wordchars:
     3292. attribute is augmented with the characters ‘~-./*?=’.  That
     is because these characters can appear in file names (including
     wildcards) and command-line arguments (e.g.  ‘--color=auto’).
     Hence:

          >>> import shlex
          >>> s = shlex.shlex('~/a && b-c --color=auto || d *.py?',
          ...                 punctuation_chars=True)
          >>> list(s)
          ['~/a', '&&', 'b-c', '--color=auto', '||', 'd', '*.py?']

     However, to match the shell as closely as possible, it is
     recommended to always use ‘posix’ and *note whitespace_split: 329e.
     when using *note punctuation_chars: 10d9, which will negate *note
     wordchars: 3292. entirely.

For best effect, ‘punctuation_chars’ should be set in conjunction with
‘posix=True’.  (Note that ‘posix=False’ is the default for *note shlex:
671.)


File: python.info,  Node: Graphical User Interfaces with Tk,  Next: Development Tools,  Prev: Program Frameworks,  Up: The Python Standard Library

5.25 Graphical User Interfaces with Tk
======================================

Tk/Tcl has long been an integral part of Python.  It provides a robust
and platform independent windowing toolkit, that is available to Python
programmers using the *note tkinter: 10e. package, and its extension,
the *note tkinter.tix: 117. and the *note tkinter.ttk: 118. modules.

The *note tkinter: 10e. package is a thin object-oriented layer on top
of Tcl/Tk.  To use *note tkinter: 10e, you don’t need to write Tcl code,
but you will need to consult the Tk documentation, and occasionally the
Tcl documentation.  *note tkinter: 10e. is a set of wrappers that
implement the Tk widgets as Python classes.

*note tkinter: 10e.’s chief virtues are that it is fast, and that it
usually comes bundled with Python.  Although its standard documentation
is weak, good material is available, which includes: references,
tutorials, a book and others.  *note tkinter: 10e. is also famous for
having an outdated look and feel, which has been vastly improved in Tk
8.5.  Nevertheless, there are many other GUI libraries that you could be
interested in.  The Python wiki lists several alternative GUI frameworks
and tools(1).

* Menu:

* tkinter — Python interface to Tcl/Tk::
* tkinter.colorchooser — Color choosing dialog: tkinter colorchooser — Color choosing dialog.
* tkinter.font — Tkinter font wrapper: tkinter font — Tkinter font wrapper.
* Tkinter Dialogs::
* tkinter.messagebox — Tkinter message prompts: tkinter messagebox — Tkinter message prompts.
* tkinter.scrolledtext — Scrolled Text Widget: tkinter scrolledtext — Scrolled Text Widget.
* tkinter.dnd — Drag and drop support: tkinter dnd — Drag and drop support.
* tkinter.ttk — Tk themed widgets: tkinter ttk — Tk themed widgets.
* tkinter.tix — Extension widgets for Tk: tkinter tix — Extension widgets for Tk.
* IDLE: IDLE<51>.

   ---------- Footnotes ----------

   (1) https://wiki.python.org/moin/GuiProgramming


File: python.info,  Node: tkinter — Python interface to Tcl/Tk,  Next: tkinter colorchooser — Color choosing dialog,  Up: Graphical User Interfaces with Tk

5.25.1 ‘tkinter’ — Python interface to Tcl/Tk
---------------------------------------------

`Source code:' Lib/tkinter/__init__.py(1)

__________________________________________________________________

The *note tkinter: 10e. package (“Tk interface”) is the standard Python
interface to the Tcl/Tk GUI toolkit.  Both Tk and *note tkinter: 10e.
are available on most Unix platforms, including macOS, as well as on
Windows systems.

Running ‘python -m tkinter’ from the command line should open a window
demonstrating a simple Tk interface, letting you know that *note
tkinter: 10e. is properly installed on your system, and also showing
what version of Tcl/Tk is installed, so you can read the Tcl/Tk
documentation specific to that version.

See also
........

   * 
     TkDocs(2)

          Extensive tutorial on creating user interfaces with Tkinter.
          Explains key concepts, and illustrates recommended approaches
          using the modern API.

   * 
     Tkinter 8.5 reference: a GUI for Python(3)

          Reference documentation for Tkinter 8.5 detailing available
          classes, methods, and options.

Tcl/Tk Resources:

   * 
     Tk commands(4)

          Comprehensive reference to each of the underlying Tcl/Tk
          commands used by Tkinter.

   * 
     Tcl/Tk Home Page(5)

          Additional documentation, and links to Tcl/Tk core
          development.

Books:

   * 
     Modern Tkinter for Busy Python Developers(6)

          By Mark Roseman.  (ISBN 978-1999149567)

   * 
     Python and Tkinter Programming(7)

          By Alan Moore.  (ISBN 978-1788835886)

   * 
     Programming Python(8)

          By Mark Lutz; has excellent coverage of Tkinter.  (ISBN
          978-0596158101)

   * 
     Tcl and the Tk Toolkit (2nd edition)(9)

          By John Ousterhout, inventor of Tcl/Tk, and Ken Jones; does
          not cover Tkinter.  (ISBN 978-0321336330)

* Menu:

* Tkinter Modules::
* Tkinter Life Preserver::
* A (Very) Quick Look at Tcl/Tk: A Very Quick Look at Tcl/Tk.
* Mapping Basic Tk into Tkinter::
* How Tk and Tkinter are Related::
* Handy Reference::
* File Handlers::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/tkinter/__init__.py

   (2) http://tkdocs.com/

   (3) https://www.tkdocs.com/shipman/

   (4) https://www.tcl.tk/man/tcl8.6/TkCmd/contents.htm

   (5) https://www.tcl.tk

   (6) https://tkdocs.com/book.html

   (7) 
https://www.packtpub.com/product/python-gui-programming-with-tkinter/9781788835886

   (8) http://learning-python.com/about-pp4e.html

   (9) https://www.amazon.com/exec/obidos/ASIN/032133633X


File: python.info,  Node: Tkinter Modules,  Next: Tkinter Life Preserver,  Up: tkinter — Python interface to Tcl/Tk

5.25.1.1 Tkinter Modules
........................

Support for Tkinter is spread across several modules.  Most applications
will need the main *note tkinter: 10e. module, as well as the *note
tkinter.ttk: 118. module, which provides the modern themed widget set
and API:

     from tkinter import *
     from tkinter import ttk

 -- Class: tkinter.Tk (screenName=None, baseName=None, className='Tk',
          useTk=1)

     The *note Tk: 32b0. class is instantiated without arguments.  This
     creates a toplevel widget of Tk which usually is the main window of
     an application.  Each instance has its own associated Tcl
     interpreter.

 -- Function: tkinter.Tcl (screenName=None, baseName=None,
          className='Tk', useTk=0)

     The *note Tcl(): 32b1. function is a factory function which creates
     an object much like that created by the *note Tk: 32b0. class,
     except that it does not initialize the Tk subsystem.  This is most
     often useful when driving the Tcl interpreter in an environment
     where one doesn’t want to create extraneous toplevel windows, or
     where one cannot (such as Unix/Linux systems without an X server).
     An object created by the *note Tcl(): 32b1. object can have a
     Toplevel window created (and the Tk subsystem initialized) by
     calling its ‘loadtk()’ method.

The modules that provide Tk support include:

*note tkinter: 10e.

     Main Tkinter module.

*note tkinter.colorchooser: 10f.

     Dialog to let the user choose a color.

*note tkinter.commondialog: 110.

     Base class for the dialogs defined in the other modules listed
     here.

*note tkinter.filedialog: 112.

     Common dialogs to allow the user to specify a file to open or save.

*note tkinter.font: 113.

     Utilities to help work with fonts.

*note tkinter.messagebox: 114.

     Access to standard Tk dialog boxes.

*note tkinter.scrolledtext: 115.

     Text widget with a vertical scroll bar built in.

*note tkinter.simpledialog: 116.

     Basic dialogs and convenience functions.

*note tkinter.ttk: 118.

     Themed widget set introduced in Tk 8.5, providing modern
     alternatives for many of the classic widgets in the main *note
     tkinter: 10e. module.

Additional modules:

‘_tkinter’

     A binary module that contains the low-level interface to Tcl/Tk.
     It is automatically imported by the main *note tkinter: 10e.
     module, and should never be used directly by application
     programmers.  It is usually a shared library (or DLL), but might in
     some cases be statically linked with the Python interpreter.

‘idlelib’

     Python’s Integrated Development and Learning Environment (IDLE).
     Based on *note tkinter: 10e.

‘tkinter.constants’

     Symbolic constants that can be used in place of strings when
     passing various parameters to Tkinter calls.  Automatically
     imported by the main *note tkinter: 10e. module.

*note tkinter.dnd: 111.

     (experimental) Drag-and-drop support for *note tkinter: 10e.  This
     will become deprecated when it is replaced with the Tk DND.

*note tkinter.tix: 117.

     (deprecated) An older third-party Tcl/Tk package that adds several
     new widgets.  Better alternatives for most can be found in *note
     tkinter.ttk: 118.

*note turtle: 11f.

     Turtle graphics in a Tk window.


File: python.info,  Node: Tkinter Life Preserver,  Next: A Very Quick Look at Tcl/Tk,  Prev: Tkinter Modules,  Up: tkinter — Python interface to Tcl/Tk

5.25.1.2 Tkinter Life Preserver
...............................

This section is not designed to be an exhaustive tutorial on either Tk
or Tkinter.  Rather, it is intended as a stop gap, providing some
introductory orientation on the system.

Credits:

   * Tk was written by John Ousterhout while at Berkeley.

   * Tkinter was written by Steen Lumholt and Guido van Rossum.

   * This Life Preserver was written by Matt Conway at the University of
     Virginia.

   * The HTML rendering, and some liberal editing, was produced from a
     FrameMaker version by Ken Manheimer.

   * Fredrik Lundh elaborated and revised the class interface
     descriptions, to get them current with Tk 4.2.

   * Mike Clarkson converted the documentation to LaTeX, and compiled
     the User Interface chapter of the reference manual.

* Menu:

* How To Use This Section::
* A Simple Hello World Program::


File: python.info,  Node: How To Use This Section,  Next: A Simple Hello World Program,  Up: Tkinter Life Preserver

5.25.1.3 How To Use This Section
................................

This section is designed in two parts: the first half (roughly) covers
background material, while the second half can be taken to the keyboard
as a handy reference.

When trying to answer questions of the form “how do I do blah”, it is
often best to find out how to do “blah” in straight Tk, and then convert
this back into the corresponding *note tkinter: 10e. call.  Python
programmers can often guess at the correct Python command by looking at
the Tk documentation.  This means that in order to use Tkinter, you will
have to know a little bit about Tk.  This document can’t fulfill that
role, so the best we can do is point you to the best documentation that
exists.  Here are some hints:

   * The authors strongly suggest getting a copy of the Tk man pages.
     Specifically, the man pages in the ‘manN’ directory are most
     useful.  The ‘man3’ man pages describe the C interface to the Tk
     library and thus are not especially helpful for script writers.

   * Addison-Wesley publishes a book called Tcl and the Tk Toolkit by
     John Ousterhout (ISBN 0-201-63337-X) which is a good introduction
     to Tcl and Tk for the novice.  The book is not exhaustive, and for
     many details it defers to the man pages.

   * ‘tkinter/__init__.py’ is a last resort for most, but can be a good
     place to go when nothing else makes sense.


File: python.info,  Node: A Simple Hello World Program,  Prev: How To Use This Section,  Up: Tkinter Life Preserver

5.25.1.4 A Simple Hello World Program
.....................................

     import tkinter as tk

     class Application(tk.Frame):
         def __init__(self, master=None):
             super().__init__(master)
             self.master = master
             self.pack()
             self.create_widgets()

         def create_widgets(self):
             self.hi_there = tk.Button(self)
             self.hi_there["text"] = "Hello World\n(click me)"
             self.hi_there["command"] = self.say_hi
             self.hi_there.pack(side="top")

             self.quit = tk.Button(self, text="QUIT", fg="red",
                                   command=self.master.destroy)
             self.quit.pack(side="bottom")

         def say_hi(self):
             print("hi there, everyone!")

     root = tk.Tk()
     app = Application(master=root)
     app.mainloop()


File: python.info,  Node: A Very Quick Look at Tcl/Tk,  Next: Mapping Basic Tk into Tkinter,  Prev: Tkinter Life Preserver,  Up: tkinter — Python interface to Tcl/Tk

5.25.1.5 A (Very) Quick Look at Tcl/Tk
......................................

The class hierarchy looks complicated, but in actual practice,
application programmers almost always refer to the classes at the very
bottom of the hierarchy.

Notes:

   * These classes are provided for the purposes of organizing certain
     functions under one namespace.  They aren’t meant to be
     instantiated independently.

   * The *note Tk: 32b0. class is meant to be instantiated only once in
     an application.  Application programmers need not instantiate one
     explicitly, the system creates one whenever any of the other
     classes are instantiated.

   * The ‘Widget’ class is not meant to be instantiated, it is meant
     only for subclassing to make “real” widgets (in C++, this is called
     an ‘abstract class’).

To make use of this reference material, there will be times when you
will need to know how to read short passages of Tk and how to identify
the various parts of a Tk command.  (See section *note Mapping Basic Tk
into Tkinter: 32b6. for the *note tkinter: 10e. equivalents of what’s
below.)

Tk scripts are Tcl programs.  Like all Tcl programs, Tk scripts are just
lists of tokens separated by spaces.  A Tk widget is just its `class',
the `options' that help configure it, and the `actions' that make it do
useful things.

To make a widget in Tk, the command is always of the form:

     classCommand newPathname options

`classCommand'

     denotes which kind of widget to make (a button, a label, a menu…)

`newPathname'

     is the new name for this widget.  All names in Tk must be unique.
     To help enforce this, widgets in Tk are named with `pathnames',
     just like files in a file system.  The top level widget, the
     `root', is called ‘.’ (period) and children are delimited by more
     periods.  For example, ‘.myApp.controlPanel.okButton’ might be the
     name of a widget.

`options'

     configure the widget’s appearance and in some cases, its behavior.
     The options come in the form of a list of flags and values.  Flags
     are preceded by a ‘-‘, like Unix shell command flags, and values
     are put in quotes if they are more than one word.

For example:

     button   .fred   -fg red -text "hi there"
        ^       ^     \______________________/
        |       |                |
      class    new            options
     command  widget  (-opt val -opt val ...)

Once created, the pathname to the widget becomes a new command.  This
new `widget command' is the programmer’s handle for getting the new
widget to perform some `action'.  In C, you’d express this as
someAction(fred, someOptions), in C++, you would express this as
fred.someAction(someOptions), and in Tk, you say:

     .fred someAction someOptions

Note that the object name, ‘.fred’, starts with a dot.

As you’d expect, the legal values for `someAction' will depend on the
widget’s class: ‘.fred disable’ works if fred is a button (fred gets
greyed out), but does not work if fred is a label (disabling of labels
is not supported in Tk).

The legal values of `someOptions' is action dependent.  Some actions,
like ‘disable’, require no arguments, others, like a text-entry box’s
‘delete’ command, would need arguments to specify what range of text to
delete.


File: python.info,  Node: Mapping Basic Tk into Tkinter,  Next: How Tk and Tkinter are Related,  Prev: A Very Quick Look at Tcl/Tk,  Up: tkinter — Python interface to Tcl/Tk

5.25.1.6 Mapping Basic Tk into Tkinter
......................................

Class commands in Tk correspond to class constructors in Tkinter.

     button .fred                =====>  fred = Button()

The master of an object is implicit in the new name given to it at
creation time.  In Tkinter, masters are specified explicitly.

     button .panel.fred          =====>  fred = Button(panel)

The configuration options in Tk are given in lists of hyphened tags
followed by values.  In Tkinter, options are specified as
keyword-arguments in the instance constructor, and keyword-args for
configure calls or as instance indices, in dictionary style, for
established instances.  See section *note Setting Options: 32b8. on
setting options.

     button .fred -fg red        =====>  fred = Button(panel, fg="red")
     .fred configure -fg red     =====>  fred["fg"] = red
                                 OR ==>  fred.config(fg="red")

In Tk, to perform an action on a widget, use the widget name as a
command, and follow it with an action name, possibly with arguments
(options).  In Tkinter, you call methods on the class instance to invoke
actions on the widget.  The actions (methods) that a given widget can
perform are listed in ‘tkinter/__init__.py’.

     .fred invoke                =====>  fred.invoke()

To give a widget to the packer (geometry manager), you call pack with
optional arguments.  In Tkinter, the Pack class holds all this
functionality, and the various forms of the pack command are implemented
as methods.  All widgets in *note tkinter: 10e. are subclassed from the
Packer, and so inherit all the packing methods.  See the *note
tkinter.tix: 117. module documentation for additional information on the
Form geometry manager.

     pack .fred -side left       =====>  fred.pack(side="left")


File: python.info,  Node: How Tk and Tkinter are Related,  Next: Handy Reference,  Prev: Mapping Basic Tk into Tkinter,  Up: tkinter — Python interface to Tcl/Tk

5.25.1.7 How Tk and Tkinter are Related
.......................................

From the top down:

Your App Here (Python)

     A Python application makes a *note tkinter: 10e. call.

tkinter (Python Package)

     This call (say, for example, creating a button widget), is
     implemented in the *note tkinter: 10e. package, which is written in
     Python.  This Python function will parse the commands and the
     arguments and convert them into a form that makes them look as if
     they had come from a Tk script instead of a Python script.

_tkinter (C)

     These commands and their arguments will be passed to a C function
     in the ‘_tkinter’ - note the underscore - extension module.

Tk Widgets (C and Tcl)

     This C function is able to make calls into other C modules,
     including the C functions that make up the Tk library.  Tk is
     implemented in C and some Tcl.  The Tcl part of the Tk widgets is
     used to bind certain default behaviors to widgets, and is executed
     once at the point where the Python *note tkinter: 10e. package is
     imported.  (The user never sees this stage).

Tk (C)

     The Tk part of the Tk Widgets implement the final mapping to …

Xlib (C)

     the Xlib library to draw graphics on the screen.


File: python.info,  Node: Handy Reference,  Next: File Handlers,  Prev: How Tk and Tkinter are Related,  Up: tkinter — Python interface to Tcl/Tk

5.25.1.8 Handy Reference
........................

* Menu:

* Setting Options::
* The Packer::
* Packer Options::
* Coupling Widget Variables::
* The Window Manager::
* Tk Option Data Types::
* Bindings and Events::
* The index Parameter::
* Images::


File: python.info,  Node: Setting Options,  Next: The Packer,  Up: Handy Reference

5.25.1.9 Setting Options
........................

Options control things like the color and border width of a widget.
Options can be set in three ways:

At object creation time, using keyword arguments

          fred = Button(self, fg="red", bg="blue")

After object creation, treating the option name like a dictionary index

          fred["fg"] = "red"
          fred["bg"] = "blue"

Use the config() method to update multiple attrs subsequent to object creation

          fred.config(fg="red", bg="blue")

For a complete explanation of a given option and its behavior, see the
Tk man pages for the widget in question.

Note that the man pages list “STANDARD OPTIONS” and “WIDGET SPECIFIC
OPTIONS” for each widget.  The former is a list of options that are
common to many widgets, the latter are the options that are
idiosyncratic to that particular widget.  The Standard Options are
documented on the ‘options(3)’ man page.

No distinction between standard and widget-specific options is made in
this document.  Some options don’t apply to some kinds of widgets.
Whether a given widget responds to a particular option depends on the
class of the widget; buttons have a ‘command’ option, labels do not.

The options supported by a given widget are listed in that widget’s man
page, or can be queried at runtime by calling the ‘config()’ method
without arguments, or by calling the ‘keys()’ method on that widget.
The return value of these calls is a dictionary whose key is the name of
the option as a string (for example, ‘'relief'’) and whose values are
5-tuples.

Some options, like ‘bg’ are synonyms for common options with long names
(‘bg’ is shorthand for “background”).  Passing the ‘config()’ method the
name of a shorthand option will return a 2-tuple, not 5-tuple.  The
2-tuple passed back will contain the name of the synonym and the “real”
option (such as ‘('bg', 'background')’).

Index       Meaning                               Example
                                                  
---------------------------------------------------------------------
                                                  
0           option name                           ‘'relief'’
                                                  
                                                  
1           option name for database lookup       ‘'relief'’
                                                  
                                                  
2           option class for database lookup      ‘'Relief'’
                                                  
                                                  
3           default value                         ‘'raised'’
                                                  
                                                  
4           current value                         ‘'groove'’
                                                  

Example:

     >>> print(fred.config())
     {'relief': ('relief', 'relief', 'Relief', 'raised', 'groove')}

Of course, the dictionary printed will include all the options available
and their values.  This is meant only as an example.


File: python.info,  Node: The Packer,  Next: Packer Options,  Prev: Setting Options,  Up: Handy Reference

5.25.1.10 The Packer
....................

The packer is one of Tk’s geometry-management mechanisms.  Geometry
managers are used to specify the relative positioning of widgets within
their container - their mutual `master'.  In contrast to the more
cumbersome `placer' (which is used less commonly, and we do not cover
here), the packer takes qualitative relationship specification -
`above', `to the left of', `filling', etc - and works everything out to
determine the exact placement coordinates for you.

The size of any `master' widget is determined by the size of the “slave
widgets” inside.  The packer is used to control where slave widgets
appear inside the master into which they are packed.  You can pack
widgets into frames, and frames into other frames, in order to achieve
the kind of layout you desire.  Additionally, the arrangement is
dynamically adjusted to accommodate incremental changes to the
configuration, once it is packed.

Note that widgets do not appear until they have had their geometry
specified with a geometry manager.  It’s a common early mistake to leave
out the geometry specification, and then be surprised when the widget is
created but nothing appears.  A widget will appear only after it has
had, for example, the packer’s ‘pack()’ method applied to it.

The pack() method can be called with keyword-option/value pairs that
control where the widget is to appear within its container, and how it
is to behave when the main application window is resized.  Here are some
examples:

     fred.pack()                     # defaults to side = "top"
     fred.pack(side="left")
     fred.pack(expand=1)


File: python.info,  Node: Packer Options,  Next: Coupling Widget Variables,  Prev: The Packer,  Up: Handy Reference

5.25.1.11 Packer Options
........................

For more extensive information on the packer and the options that it can
take, see the man pages and page 183 of John Ousterhout’s book.

anchor

     Anchor type.  Denotes where the packer is to place each slave in
     its parcel.

expand

     Boolean, ‘0’ or ‘1’.

fill

     Legal values: ‘'x'’, ‘'y'’, ‘'both'’, ‘'none'’.

ipadx and ipady

     A distance - designating internal padding on each side of the slave
     widget.

padx and pady

     A distance - designating external padding on each side of the slave
     widget.

side

     Legal values are: ‘'left'’, ‘'right'’, ‘'top'’, ‘'bottom'’.


File: python.info,  Node: Coupling Widget Variables,  Next: The Window Manager,  Prev: Packer Options,  Up: Handy Reference

5.25.1.12 Coupling Widget Variables
...................................

The current-value setting of some widgets (like text entry widgets) can
be connected directly to application variables by using special options.
These options are ‘variable’, ‘textvariable’, ‘onvalue’, ‘offvalue’, and
‘value’.  This connection works both ways: if the variable changes for
any reason, the widget it’s connected to will be updated to reflect the
new value.

Unfortunately, in the current implementation of *note tkinter: 10e. it
is not possible to hand over an arbitrary Python variable to a widget
through a ‘variable’ or ‘textvariable’ option.  The only kinds of
variables for which this works are variables that are subclassed from a
class called Variable, defined in *note tkinter: 10e.

There are many useful subclasses of Variable already defined:
‘StringVar’, ‘IntVar’, ‘DoubleVar’, and ‘BooleanVar’.  To read the
current value of such a variable, call the ‘get()’ method on it, and to
change its value you call the ‘set()’ method.  If you follow this
protocol, the widget will always track the value of the variable, with
no further intervention on your part.

For example:

     import tkinter as tk

     class App(tk.Frame):
         def __init__(self, master):
             super().__init__(master)
             self.pack()

             self.entrythingy = tk.Entry()
             self.entrythingy.pack()

             # Create the application variable.
             self.contents = tk.StringVar()
             # Set it to some value.
             self.contents.set("this is a variable")
             # Tell the entry widget to watch this variable.
             self.entrythingy["textvariable"] = self.contents

             # Define a callback for when the user hits return.
             # It prints the current value of the variable.
             self.entrythingy.bind('<Key-Return>',
                                  self.print_contents)

         def print_contents(self, event):
             print("Hi. The current entry content is:",
                   self.contents.get())

     root = tk.Tk()
     myapp = App(root)
     myapp.mainloop()


File: python.info,  Node: The Window Manager,  Next: Tk Option Data Types,  Prev: Coupling Widget Variables,  Up: Handy Reference

5.25.1.13 The Window Manager
............................

In Tk, there is a utility command, ‘wm’, for interacting with the window
manager.  Options to the ‘wm’ command allow you to control things like
titles, placement, icon bitmaps, and the like.  In *note tkinter: 10e,
these commands have been implemented as methods on the ‘Wm’ class.
Toplevel widgets are subclassed from the ‘Wm’ class, and so can call the
‘Wm’ methods directly.

To get at the toplevel window that contains a given widget, you can
often just refer to the widget’s master.  Of course if the widget has
been packed inside of a frame, the master won’t represent a toplevel
window.  To get at the toplevel window that contains an arbitrary
widget, you can call the ‘_root()’ method.  This method begins with an
underscore to denote the fact that this function is part of the
implementation, and not an interface to Tk functionality.

Here are some examples of typical usage:

     import tkinter as tk

     class App(tk.Frame):
         def __init__(self, master=None):
             super().__init__(master)
             self.pack()

     # create the application
     myapp = App()

     #
     # here are method calls to the window manager class
     #
     myapp.master.title("My Do-Nothing Application")
     myapp.master.maxsize(1000, 400)

     # start the program
     myapp.mainloop()


File: python.info,  Node: Tk Option Data Types,  Next: Bindings and Events,  Prev: The Window Manager,  Up: Handy Reference

5.25.1.14 Tk Option Data Types
..............................

anchor

     Legal values are points of the compass: ‘"n"’, ‘"ne"’, ‘"e"’,
     ‘"se"’, ‘"s"’, ‘"sw"’, ‘"w"’, ‘"nw"’, and also ‘"center"’.

bitmap

     There are eight built-in, named bitmaps: ‘'error'’, ‘'gray25'’,
     ‘'gray50'’, ‘'hourglass'’, ‘'info'’, ‘'questhead'’, ‘'question'’,
     ‘'warning'’.  To specify an X bitmap filename, give the full path
     to the file, preceded with an ‘@’, as in
     ‘"@/usr/contrib/bitmap/gumby.bit"’.

boolean

     You can pass integers 0 or 1 or the strings ‘"yes"’ or ‘"no"’.

callback

     This is any Python function that takes no arguments.  For example:

          def print_it():
              print("hi there")
          fred["command"] = print_it

color

     Colors can be given as the names of X colors in the rgb.txt file,
     or as strings representing RGB values in 4 bit: ‘"#RGB"’, 8 bit:
     ‘"#RRGGBB"’, 12 bit” ‘"#RRRGGGBBB"’, or 16 bit ‘"#RRRRGGGGBBBB"’
     ranges, where R,G,B here represent any legal hex digit.  See page
     160 of Ousterhout’s book for details.

cursor

     The standard X cursor names from ‘cursorfont.h’ can be used,
     without the ‘XC_’ prefix.  For example to get a hand cursor
     (‘XC_hand2’), use the string ‘"hand2"’.  You can also specify a
     bitmap and mask file of your own.  See page 179 of Ousterhout’s
     book.

distance

     Screen distances can be specified in either pixels or absolute
     distances.  Pixels are given as numbers and absolute distances as
     strings, with the trailing character denoting units: ‘c’ for
     centimetres, ‘i’ for inches, ‘m’ for millimetres, ‘p’ for printer’s
     points.  For example, 3.5 inches is expressed as ‘"3.5i"’.

font

     Tk uses a list font name format, such as ‘{courier 10 bold}’.  Font
     sizes with positive numbers are measured in points; sizes with
     negative numbers are measured in pixels.

geometry

     This is a string of the form ‘widthxheight’, where width and height
     are measured in pixels for most widgets (in characters for widgets
     displaying text).  For example: ‘fred["geometry"] = "200x100"’.

justify

     Legal values are the strings: ‘"left"’, ‘"center"’, ‘"right"’, and
     ‘"fill"’.

region

     This is a string with four space-delimited elements, each of which
     is a legal distance (see above).  For example: ‘"2 3 4 5"’ and ‘"3i
     2i 4.5i 2i"’ and ‘"3c 2c 4c 10.43c"’ are all legal regions.

relief

     Determines what the border style of a widget will be.  Legal values
     are: ‘"raised"’, ‘"sunken"’, ‘"flat"’, ‘"groove"’, and ‘"ridge"’.

scrollcommand

     This is almost always the ‘set()’ method of some scrollbar widget,
     but can be any widget method that takes a single argument.

wrap

     Must be one of: ‘"none"’, ‘"char"’, or ‘"word"’.


File: python.info,  Node: Bindings and Events,  Next: The index Parameter,  Prev: Tk Option Data Types,  Up: Handy Reference

5.25.1.15 Bindings and Events
.............................

The bind method from the widget command allows you to watch for certain
events and to have a callback function trigger when that event type
occurs.  The form of the bind method is:

     def bind(self, sequence, func, add=''):

where:

sequence

     is a string that denotes the target kind of event.  (See the bind
     man page and page 201 of John Ousterhout’s book for details).

func

     is a Python function, taking one argument, to be invoked when the
     event occurs.  An Event instance will be passed as the argument.
     (Functions deployed this way are commonly known as `callbacks'.)

add

     is optional, either ‘''’ or ‘'+'’.  Passing an empty string denotes
     that this binding is to replace any other bindings that this event
     is associated with.  Passing a ‘'+'’ means that this function is to
     be added to the list of functions bound to this event type.

For example:

     def turn_red(self, event):
         event.widget["activeforeground"] = "red"

     self.button.bind("<Enter>", self.turn_red)

Notice how the widget field of the event is being accessed in the
‘turn_red()’ callback.  This field contains the widget that caught the X
event.  The following table lists the other event fields you can access,
and how they are denoted in Tk, which can be useful when referring to
the Tk man pages.

Tk       Tkinter Event Field       Tk       Tkinter Event Field
                                            
----------------------------------------------------------------------
                                            
%f       focus                     %A       char
                                            
                                            
%h       height                    %E       send_event
                                            
                                            
%k       keycode                   %K       keysym
                                            
                                            
%s       state                     %N       keysym_num
                                            
                                            
%t       time                      %T       type
                                            
                                            
%w       width                     %W       widget
                                            
                                            
%x       x                         %X       x_root
                                            
                                            
%y       y                         %Y       y_root
                                            


File: python.info,  Node: The index Parameter,  Next: Images,  Prev: Bindings and Events,  Up: Handy Reference

5.25.1.16 The index Parameter
.............................

A number of widgets require “index” parameters to be passed.  These are
used to point at a specific place in a Text widget, or to particular
characters in an Entry widget, or to particular menu items in a Menu
widget.

Entry widget indexes (index, view index, etc.)

     Entry widgets have options that refer to character positions in the
     text being displayed.  You can use these *note tkinter: 10e.
     functions to access these special points in text widgets:

Text widget indexes

     The index notation for Text widgets is very rich and is best
     described in the Tk man pages.

Menu indexes (menu.invoke(), menu.entryconfig(), etc.)

     Some options and methods for menus manipulate specific menu
     entries.  Anytime a menu index is needed for an option or a
     parameter, you may pass in:

        * an integer which refers to the numeric position of the entry
          in the widget, counted from the top, starting with 0;

        * the string ‘"active"’, which refers to the menu position that
          is currently under the cursor;

        * the string ‘"last"’ which refers to the last menu item;

        * An integer preceded by ‘@’, as in ‘@6’, where the integer is
          interpreted as a y pixel coordinate in the menu’s coordinate
          system;

        * the string ‘"none"’, which indicates no menu entry at all,
          most often used with menu.activate() to deactivate all
          entries, and finally,

        * a text string that is pattern matched against the label of the
          menu entry, as scanned from the top of the menu to the bottom.
          Note that this index type is considered after all the others,
          which means that matches for menu items labelled ‘last’,
          ‘active’, or ‘none’ may be interpreted as the above literals,
          instead.


File: python.info,  Node: Images,  Prev: The index Parameter,  Up: Handy Reference

5.25.1.17 Images
................

Images of different formats can be created through the corresponding
subclass of ‘tkinter.Image’:

   * ‘BitmapImage’ for images in XBM format.

   * ‘PhotoImage’ for images in PGM, PPM, GIF and PNG formats.  The
     latter is supported starting with Tk 8.6.

Either type of image is created through either the ‘file’ or the ‘data’
option (other options are available as well).

The image object can then be used wherever an ‘image’ option is
supported by some widget (e.g.  labels, buttons, menus).  In these
cases, Tk will not keep a reference to the image.  When the last Python
reference to the image object is deleted, the image data is deleted as
well, and Tk will display an empty box wherever the image was used.

See also
........

The Pillow(1) package adds support for formats such as BMP, JPEG, TIFF,
and WebP, among others.

   ---------- Footnotes ----------

   (1) http://python-pillow.org/


File: python.info,  Node: File Handlers,  Prev: Handy Reference,  Up: tkinter — Python interface to Tcl/Tk

5.25.1.18 File Handlers
.......................

Tk allows you to register and unregister a callback function which will
be called from the Tk mainloop when I/O is possible on a file
descriptor.  Only one handler may be registered per file descriptor.
Example code:

     import tkinter
     widget = tkinter.Tk()
     mask = tkinter.READABLE | tkinter.WRITABLE
     widget.tk.createfilehandler(file, mask, callback)
     ...
     widget.tk.deletefilehandler(file)

This feature is not available on Windows.

Since you don’t know how many bytes are available for reading, you may
not want to use the *note BufferedIOBase: 67f. or *note TextIOBase: d01.
*note read(): 1ebb. or *note readline(): 1849. methods, since these will
insist on reading a predefined number of bytes.  For sockets, the *note
recv(): 76a. or *note recvfrom(): 76b. methods will work fine; for other
files, use raw reads or ‘os.read(file.fileno(), maxbytecount)’.

 -- Method: Widget.tk.createfilehandler (file, mask, func)

     Registers the file handler callback function `func'.  The `file'
     argument may either be an object with a *note fileno(): 2069.
     method (such as a file or socket object), or an integer file
     descriptor.  The `mask' argument is an ORed combination of any of
     the three constants below.  The callback is called as follows:

          callback(file, mask)

 -- Method: Widget.tk.deletefilehandler (file)

     Unregisters a file handler.

 -- Data: tkinter.READABLE
 -- Data: tkinter.WRITABLE
 -- Data: tkinter.EXCEPTION

     Constants used in the `mask' arguments.


File: python.info,  Node: tkinter colorchooser — Color choosing dialog,  Next: tkinter font — Tkinter font wrapper,  Prev: tkinter — Python interface to Tcl/Tk,  Up: Graphical User Interfaces with Tk

5.25.2 ‘tkinter.colorchooser’ — Color choosing dialog
-----------------------------------------------------

`Source code:' Lib/tkinter/colorchooser.py(1)

__________________________________________________________________

The *note tkinter.colorchooser: 10f. module provides the *note Chooser:
32ce. class as an interface to the native color picker dialog.
‘Chooser’ implements a modal color choosing dialog window.  The
‘Chooser’ class inherits from the *note Dialog: 32cf. class.

 -- Class: tkinter.colorchooser.Chooser (master=None, **options)

 -- Function: tkinter.colorchooser.askcolor (color=None, **options)

     Create a color choosing dialog.  A call to this method will show
     the window, wait for the user to make a selection, and return the
     selected color (or ‘None’) to the caller.

See also
........

Module *note tkinter.commondialog: 110.

     Tkinter standard dialog module

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/tkinter/colorchooser.py


File: python.info,  Node: tkinter font — Tkinter font wrapper,  Next: Tkinter Dialogs,  Prev: tkinter colorchooser — Color choosing dialog,  Up: Graphical User Interfaces with Tk

5.25.3 ‘tkinter.font’ — Tkinter font wrapper
--------------------------------------------

`Source code:' Lib/tkinter/font.py(1)

__________________________________________________________________

The *note tkinter.font: 113. module provides the *note Font: fcb. class
for creating and using named fonts.

The different font weights and slants are:

 -- Data: tkinter.font.NORMAL
 -- Data: tkinter.font.BOLD
 -- Data: tkinter.font.ITALIC
 -- Data: tkinter.font.ROMAN

 -- Class: tkinter.font.Font (root=None, font=None, name=None,
          exists=False, **options)

     The *note Font: fcb. class represents a named font.  `Font'
     instances are given unique names and can be specified by their
     family, size, and style configuration.  Named fonts are Tk’s method
     of creating and identifying fonts as a single object, rather than
     specifying a font by its attributes with each occurrence.

          arguments:

                    `font' - font specifier tuple (family, size, options) 
                    `name' - unique font name 
                    `exists' - self points to existing named font if true 

          additional keyword options (ignored if `font' is specified):

                    `family' - font family i.e. Courier, Times 
                    `size' - font size 
                         If `size' is positive it is interpreted as size in points. 
                         If `size' is a negative number its absolute value is treated 
                         as size in pixels. 
                    `weight' - font emphasis (NORMAL, BOLD) 
                    `slant' - ROMAN, ITALIC 
                    `underline' - font underlining (0 - none, 1 - underline) 
                    `overstrike' - font strikeout (0 - none, 1 - strikeout) 

      -- Method: actual (option=None, displayof=None)

          Return the attributes of the font.

      -- Method: cget (option)

          Retrieve an attribute of the font.

      -- Method: config (**options)

          Modify attributes of the font.

      -- Method: copy ()

          Return new instance of the current font.

      -- Method: measure (text, displayof=None)

          Return amount of space the text would occupy on the specified
          display when formatted in the current font.  If no display is
          specified then the main application window is assumed.

      -- Method: metrics (*options, **kw)

          Return font-specific data.  Options include:

          `ascent' - distance between baseline and highest point that a

               character of the font can occupy

          `descent' - distance between baseline and lowest point that a

               character of the font can occupy

          `linespace' - minimum vertical separation necessary between any two

               characters of the font that ensures no vertical overlap
               between lines.

          `fixed' - 1 if font is fixed-width else 0

 -- Function: tkinter.font.families (root=None, displayof=None)

     Return the different font families.

 -- Function: tkinter.font.names (root=None)

     Return the names of defined fonts.

 -- Function: tkinter.font.nametofont (name)

     Return a *note Font: fcb. representation of a tk named font.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/tkinter/font.py


File: python.info,  Node: Tkinter Dialogs,  Next: tkinter messagebox — Tkinter message prompts,  Prev: tkinter font — Tkinter font wrapper,  Up: Graphical User Interfaces with Tk

5.25.4 Tkinter Dialogs
----------------------

* Menu:

* tkinter.simpledialog — Standard Tkinter input dialogs: tkinter simpledialog — Standard Tkinter input dialogs.
* tkinter.filedialog — File selection dialogs: tkinter filedialog — File selection dialogs.
* tkinter.commondialog — Dialog window templates: tkinter commondialog — Dialog window templates.


File: python.info,  Node: tkinter simpledialog — Standard Tkinter input dialogs,  Next: tkinter filedialog — File selection dialogs,  Up: Tkinter Dialogs

5.25.4.1 ‘tkinter.simpledialog’ — Standard Tkinter input dialogs
................................................................

`Source code:' Lib/tkinter/simpledialog.py(1)

__________________________________________________________________

The *note tkinter.simpledialog: 116. module contains convenience classes
and functions for creating simple modal dialogs to get a value from the
user.

 -- Function: tkinter.simpledialog.askfloat (title, prompt, **kw)
 -- Function: tkinter.simpledialog.askinteger (title, prompt, **kw)
 -- Function: tkinter.simpledialog.askstring (title, prompt, **kw)

     The above three functions provide dialogs that prompt the user to
     enter a value of the desired type.

 -- Class: tkinter.simpledialog.Dialog (parent, title=None)

     The base class for custom dialogs.

           -- Method: body (master)

               Override to construct the dialog’s interface and return
               the widget that should have initial focus.

           -- Method: buttonbox ()

               Default behaviour adds OK and Cancel buttons.  Override
               for custom button layouts.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/tkinter/simpledialog.py


File: python.info,  Node: tkinter filedialog — File selection dialogs,  Next: tkinter commondialog — Dialog window templates,  Prev: tkinter simpledialog — Standard Tkinter input dialogs,  Up: Tkinter Dialogs

5.25.4.2 ‘tkinter.filedialog’ — File selection dialogs
......................................................

`Source code:' Lib/tkinter/filedialog.py(1)

__________________________________________________________________

The *note tkinter.filedialog: 112. module provides classes and factory
functions for creating file/directory selection windows.

* Menu:

* Native Load/Save Dialogs::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/tkinter/filedialog.py


File: python.info,  Node: Native Load/Save Dialogs,  Up: tkinter filedialog — File selection dialogs

5.25.4.3 Native Load/Save Dialogs
.................................

The following classes and functions provide file dialog windows that
combine a native look-and-feel with configuration options to customize
behaviour.  The following keyword arguments are applicable to the
classes and functions listed below:

          `parent' - the window to place the dialog on top of 

          `title' - the title of the window 

          `initialdir' - the directory that the dialog starts in 

          `initialfile' - the file selected upon opening of the dialog 

          `filetypes' - a sequence of (label, pattern) tuples, ‘*’ wildcard is allowed 

          `defaultextension' - default extension to append to file (save dialogs) 

          `multiple' - when true, selection of multiple items is allowed 

`Static factory functions'

The below functions when called create a modal, native look-and-feel
dialog, wait for the user’s selection, then return the selected value(s)
or ‘None’ to the caller.

 -- Function: tkinter.filedialog.askopenfile (mode="r", **options)
 -- Function: tkinter.filedialog.askopenfiles (mode="r", **options)

     The above two functions create an *note Open: 32ed. dialog and
     return the opened file object(s) in read-only mode.

 -- Function: tkinter.filedialog.asksaveasfile (mode="w", **options)

     Create a *note SaveAs: 32ef. dialog and return a file object opened
     in write-only mode.

 -- Function: tkinter.filedialog.askopenfilename (**options)
 -- Function: tkinter.filedialog.askopenfilenames (**options)

     The above two functions create an *note Open: 32ed. dialog and
     return the selected filename(s) that correspond to existing
     file(s).

 -- Function: tkinter.filedialog.asksaveasfilename (**options)

     Create a *note SaveAs: 32ef. dialog and return the selected
     filename.

 -- Function: tkinter.filedialog.askdirectory (**options)

          Prompt user to select a directory. 
          Additional keyword option: 
               `mustexist' - determines if selection must be an existing directory. 

 -- Class: tkinter.filedialog.Open (master=None, **options)
 -- Class: tkinter.filedialog.SaveAs (master=None, **options)

     The above two classes provide native dialog windows for saving and
     loading files.

`Convenience classes'

The below classes are used for creating file/directory windows from
scratch.  These do not emulate the native look-and-feel of the platform.

 -- Class: tkinter.filedialog.Directory (master=None, **options)

     Create a dialog prompting the user to select a directory.

     Note: The `FileDialog' class should be subclassed for custom event
     handling and behaviour.

 -- Class: tkinter.filedialog.FileDialog (master, title=None)

     Create a basic file selection dialog.

      -- Method: cancel_command (event=None)

          Trigger the termination of the dialog window.

      -- Method: dirs_double_event (event)

          Event handler for double-click event on directory.

      -- Method: dirs_select_event (event)

          Event handler for click event on directory.

      -- Method: files_double_event (event)

          Event handler for double-click event on file.

      -- Method: files_select_event (event)

          Event handler for single-click event on file.

      -- Method: filter_command (event=None)

          Filter the files by directory.

      -- Method: get_filter ()

          Retrieve the file filter currently in use.

      -- Method: get_selection ()

          Retrieve the currently selected item.

      -- Method: go (dir_or_file=os.curdir, pattern="*", default="",
               key=None)

          Render dialog and start event loop.

      -- Method: ok_event (event)

          Exit dialog returning current selection.

      -- Method: quit (how=None)

          Exit dialog returning filename, if any.

      -- Method: set_filter (dir, pat)

          Set the file filter.

      -- Method: set_selection (file)

          Update the current file selection to `file'.

 -- Class: tkinter.filedialog.LoadFileDialog (master, title=None)

     A subclass of FileDialog that creates a dialog window for selecting
     an existing file.

      -- Method: ok_command ()

          Test that a file is provided and that the selection indicates
          an already existing file.

 -- Class: tkinter.filedialog.SaveFileDialog (master, title=None)

     A subclass of FileDialog that creates a dialog window for selecting
     a destination file.

      -- Method: ok_command ()

          Test whether or not the selection points to a valid file that
          is not a directory.  Confirmation is required if an already
          existing file is selected.


File: python.info,  Node: tkinter commondialog — Dialog window templates,  Prev: tkinter filedialog — File selection dialogs,  Up: Tkinter Dialogs

5.25.4.4 ‘tkinter.commondialog’ — Dialog window templates
.........................................................

`Source code:' Lib/tkinter/commondialog.py(1)

__________________________________________________________________

The *note tkinter.commondialog: 110. module provides the *note Dialog:
32cf. class that is the base class for dialogs defined in other
supporting modules.

 -- Class: tkinter.commondialog.Dialog (master=None, **options)

      -- Method: show (color=None, **options)

          Render the Dialog window.

See also
........

Modules *note tkinter.messagebox: 114, *note Reading and Writing Files:
13d4.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/tkinter/commondialog.py


File: python.info,  Node: tkinter messagebox — Tkinter message prompts,  Next: tkinter scrolledtext — Scrolled Text Widget,  Prev: Tkinter Dialogs,  Up: Graphical User Interfaces with Tk

5.25.5 ‘tkinter.messagebox’ — Tkinter message prompts
-----------------------------------------------------

`Source code:' Lib/tkinter/messagebox.py(1)

__________________________________________________________________

The *note tkinter.messagebox: 114. module provides a template base class
as well as a variety of convenience methods for commonly used
configurations.  The message boxes are modal and will return a subset of
(True, False, OK, None, Yes, No) based on the user’s selection.  Common
message box styles and layouts include but are not limited to:

[python-figures/tk_msg]
Figure

 -- Class: tkinter.messagebox.Message (master=None, **options)

     Create a default information message box.

`Information message box'

 -- Method: tkinter.messagebox.showinfo (title=None, message=None,
          **options)

`Warning message boxes'

 -- Method: tkinter.messagebox.showwarning (title=None, message=None,
          **options)
 -- Method: tkinter.messagebox.showerror (title=None, message=None,
          **options)

`Question message boxes'

 -- Method: tkinter.messagebox.askquestion (title=None, message=None,
          **options)
 -- Method: tkinter.messagebox.askokcancel (title=None, message=None,
          **options)
 -- Method: tkinter.messagebox.askretrycancel (title=None, message=None,
          **options)
 -- Method: tkinter.messagebox.askyesno (title=None, message=None,
          **options)
 -- Method: tkinter.messagebox.askyesnocancel (title=None, message=None,
          **options)

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/tkinter/messagebox.py


File: python.info,  Node: tkinter scrolledtext — Scrolled Text Widget,  Next: tkinter dnd — Drag and drop support,  Prev: tkinter messagebox — Tkinter message prompts,  Up: Graphical User Interfaces with Tk

5.25.6 ‘tkinter.scrolledtext’ — Scrolled Text Widget
----------------------------------------------------

`Source code:' Lib/tkinter/scrolledtext.py(1)

__________________________________________________________________

The *note tkinter.scrolledtext: 115. module provides a class of the same
name which implements a basic text widget which has a vertical scroll
bar configured to do the “right thing.” Using the *note ScrolledText:
3316. class is a lot easier than setting up a text widget and scroll bar
directly.

The text widget and scrollbar are packed together in a ‘Frame’, and the
methods of the ‘Grid’ and ‘Pack’ geometry managers are acquired from the
‘Frame’ object.  This allows the *note ScrolledText: 3316. widget to be
used directly to achieve most normal geometry management behavior.

Should more specific control be necessary, the following attributes are
available:

 -- Class: tkinter.scrolledtext.ScrolledText (master=None, **kw)

      -- Attribute: frame

          The frame which surrounds the text and scroll bar widgets.

      -- Attribute: vbar

          The scroll bar widget.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/tkinter/scrolledtext.py


File: python.info,  Node: tkinter dnd — Drag and drop support,  Next: tkinter ttk — Tk themed widgets,  Prev: tkinter scrolledtext — Scrolled Text Widget,  Up: Graphical User Interfaces with Tk

5.25.7 ‘tkinter.dnd’ — Drag and drop support
--------------------------------------------

`Source code:' Lib/tkinter/dnd.py(1)

__________________________________________________________________

     Note: This is experimental and due to be deprecated when it is
     replaced with the Tk DND.

The *note tkinter.dnd: 111. module provides drag-and-drop support for
objects within a single application, within the same window or between
windows.  To enable an object to be dragged, you must create an event
binding for it that starts the drag-and-drop process.  Typically, you
bind a ButtonPress event to a callback function that you write (see
*note Bindings and Events: 32c1.).  The function should call *note
dnd_start(): 331b, where ‘source’ is the object to be dragged, and
‘event’ is the event that invoked the call (the argument to your
callback function).

Selection of a target object occurs as follows:

  1. Top-down search of area under mouse for target widget

        * Target widget should have a callable `dnd_accept' attribute

        * If `dnd_accept' is not present or returns None, search moves
          to parent widget

        * If no target widget is found, then the target object is None

  2. Call to `<old_target>.dnd_leave(source, event)'

  3. Call to `<new_target>.dnd_enter(source, event)'

  4. Call to `<target>.dnd_commit(source, event)' to notify of drop

  5. Call to `<source>.dnd_end(target, event)' to signal end of
     drag-and-drop

 -- Class: tkinter.dnd.DndHandler (source, event)

     The `DndHandler' class handles drag-and-drop events tracking Motion
     and ButtonRelease events on the root of the event widget.

      -- Method: cancel (event=None)

          Cancel the drag-and-drop process.

      -- Method: finish (event, commit=0)

          Execute end of drag-and-drop functions.

      -- Method: on_motion (event)

          Inspect area below mouse for target objects while drag is
          performed.

      -- Method: on_release (event)

          Signal end of drag when the release pattern is triggered.

 -- Function: tkinter.dnd.dnd_start (source, event)

     Factory function for drag-and-drop process.

See also
........

*note Bindings and Events: 32c1.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/tkinter/dnd.py


File: python.info,  Node: tkinter ttk — Tk themed widgets,  Next: tkinter tix — Extension widgets for Tk,  Prev: tkinter dnd — Drag and drop support,  Up: Graphical User Interfaces with Tk

5.25.8 ‘tkinter.ttk’ — Tk themed widgets
----------------------------------------

`Source code:' Lib/tkinter/ttk.py(1)

__________________________________________________________________

The *note tkinter.ttk: 118. module provides access to the Tk themed
widget set, introduced in Tk 8.5.  If Python has not been compiled
against Tk 8.5, this module can still be accessed if `Tile' has been
installed.  The former method using Tk 8.5 provides additional benefits
including anti-aliased font rendering under X11 and window transparency
(requiring a composition window manager on X11).

The basic idea for *note tkinter.ttk: 118. is to separate, to the extent
possible, the code implementing a widget’s behavior from the code
implementing its appearance.

See also
........

Tk Widget Styling Support(2)

     A document introducing theming support for Tk

* Menu:

* Using Ttk::
* Ttk Widgets::
* Widget::
* Combobox::
* Spinbox::
* Notebook::
* Progressbar::
* Separator::
* Sizegrip::
* Treeview::
* Ttk Styling::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/tkinter/ttk.py

   (2) https://core.tcl.tk/tips/doc/trunk/tip/48.md


File: python.info,  Node: Using Ttk,  Next: Ttk Widgets,  Up: tkinter ttk — Tk themed widgets

5.25.8.1 Using Ttk
..................

To start using Ttk, import its module:

     from tkinter import ttk

To override the basic Tk widgets, the import should follow the Tk
import:

     from tkinter import *
     from tkinter.ttk import *

That code causes several *note tkinter.ttk: 118. widgets (‘Button’,
‘Checkbutton’, ‘Entry’, ‘Frame’, ‘Label’, ‘LabelFrame’, ‘Menubutton’,
‘PanedWindow’, ‘Radiobutton’, ‘Scale’ and ‘Scrollbar’) to automatically
replace the Tk widgets.

This has the direct benefit of using the new widgets which gives a
better look and feel across platforms; however, the replacement widgets
are not completely compatible.  The main difference is that widget
options such as “fg”, “bg” and others related to widget styling are no
longer present in Ttk widgets.  Instead, use the ‘ttk.Style’ class for
improved styling effects.

See also
........

Converting existing applications to use Tile widgets(1)

     A monograph (using Tcl terminology) about differences typically
     encountered when moving applications to use the new widgets.

   ---------- Footnotes ----------

   (1) http://tktable.sourceforge.net/tile/doc/converting.txt


File: python.info,  Node: Ttk Widgets,  Next: Widget,  Prev: Using Ttk,  Up: tkinter ttk — Tk themed widgets

5.25.8.2 Ttk Widgets
....................

Ttk comes with 18 widgets, twelve of which already existed in tkinter:
‘Button’, ‘Checkbutton’, ‘Entry’, ‘Frame’, ‘Label’, ‘LabelFrame’,
‘Menubutton’, ‘PanedWindow’, ‘Radiobutton’, ‘Scale’, ‘Scrollbar’, and
*note Spinbox: 502.  The other six are new: *note Combobox: 3325, *note
Notebook: 3326, *note Progressbar: 3327, ‘Separator’, ‘Sizegrip’ and
*note Treeview: 3df.  And all them are subclasses of *note Widget: 3328.

Using the Ttk widgets gives the application an improved look and feel.
As discussed above, there are differences in how the styling is coded.

Tk code:

     l1 = tkinter.Label(text="Test", fg="black", bg="white")
     l2 = tkinter.Label(text="Test", fg="black", bg="white")

Ttk code:

     style = ttk.Style()
     style.configure("BW.TLabel", foreground="black", background="white")

     l1 = ttk.Label(text="Test", style="BW.TLabel")
     l2 = ttk.Label(text="Test", style="BW.TLabel")

For more information about *note TtkStyling: 3329, see the *note Style:
332a. class documentation.


File: python.info,  Node: Widget,  Next: Combobox,  Prev: Ttk Widgets,  Up: tkinter ttk — Tk themed widgets

5.25.8.3 Widget
...............

‘ttk.Widget’ defines standard options and methods supported by Tk themed
widgets and is not supposed to be directly instantiated.

* Menu:

* Standard Options::
* Scrollable Widget Options::
* Label Options::
* Compatibility Options::
* Widget States::
* ttk.Widget: ttk Widget.


File: python.info,  Node: Standard Options,  Next: Scrollable Widget Options,  Up: Widget

5.25.8.4 Standard Options
.........................

All the ‘ttk’ Widgets accepts the following options:

     Option          Description
                     
     -----------------------------------------------------------------------------------
                     
     class           Specifies the window class.  The class is used when querying the
                     option database for the window’s other options, to determine the
                     default bindtags for the window, and to select the widget’s
                     default layout and style.  This option is read-only, and may
                     only be specified when the window is created.
                     
                     
     cursor          Specifies the mouse cursor to be used for the widget.  If set to
                     the empty string (the default), the cursor is inherited for the
                     parent widget.
                     
                     
     takefocus       Determines whether the window accepts the focus during keyboard
                     traversal.  0, 1 or an empty string is returned.  If 0 is
                     returned, it means that the window should be skipped entirely
                     during keyboard traversal.  If 1, it means that the window
                     should receive the input focus as long as it is viewable.  And
                     an empty string means that the traversal scripts make the
                     decision about whether or not to focus on the window.
                     
                     
     style           May be used to specify a custom widget style.
                     


File: python.info,  Node: Scrollable Widget Options,  Next: Label Options,  Prev: Standard Options,  Up: Widget

5.25.8.5 Scrollable Widget Options
..................................

The following options are supported by widgets that are controlled by a
scrollbar.

     Option               Description
                          
     -----------------------------------------------------------------------------------
                          
     xscrollcommand       Used to communicate with horizontal scrollbars.
                          
                          When the view in the widget’s window change, the widget
                          will generate a Tcl command based on the scrollcommand.
                          
                          Usually this option consists of the method
                          ‘Scrollbar.set()’ of some scrollbar.  This will cause the
                          scrollbar to be updated whenever the view in the window
                          changes.
                          
                          
     yscrollcommand       Used to communicate with vertical scrollbars.  For some
                          more information, see above.
                          


File: python.info,  Node: Label Options,  Next: Compatibility Options,  Prev: Scrollable Widget Options,  Up: Widget

5.25.8.6 Label Options
......................

The following options are supported by labels, buttons and other
button-like widgets.

     Option             Description
                        
     -----------------------------------------------------------------------------------
                        
     text               Specifies a text string to be displayed inside the widget.
                        
                        
     textvariable       Specifies a name whose value will be used in place of the
                        text option resource.
                        
                        
     underline          If set, specifies the index (0-based) of a character to
                        underline in the text string.  The underline character is
                        used for mnemonic activation.
                        
                        
     image              Specifies an image to display.  This is a list of 1 or more
                        elements.  The first element is the default image name.  The
                        rest of the list if a sequence of statespec/value pairs as
                        defined by *note Style.map(): fe4, specifying different
                        images to use when the widget is in a particular state or a
                        combination of states.  All images in the list should have
                        the same size.
                        
                        
     compound           Specifies how to display the image relative to the text, in
                        the case both text and images options are present.  Valid
                        values are:
                        
                           * text: display text only
                        
                           * image: display image only
                        
                           * top, bottom, left, right: display image above, below,
                             left of, or right of the text, respectively.
                        
                           * none: the default.  display the image if present,
                             otherwise the text.
                        
                        
     width              If greater than zero, specifies how much space, in character
                        widths, to allocate for the text label, if less than zero,
                        specifies a minimum width.  If zero or unspecified, the
                        natural width of the text label is used.
                        


File: python.info,  Node: Compatibility Options,  Next: Widget States,  Prev: Label Options,  Up: Widget

5.25.8.7 Compatibility Options
..............................

     Option       Description
                  
     ----------------------------------------------------------------------------------
                  
     state        May be set to “normal” or “disabled” to control the “disabled”
                  state bit.  This is a write-only option: setting it changes the
                  widget state, but the *note Widget.state(): 3330. method does not
                  affect this option.
                  


File: python.info,  Node: Widget States,  Next: ttk Widget,  Prev: Compatibility Options,  Up: Widget

5.25.8.8 Widget States
......................

The widget state is a bitmap of independent state flags.

     Flag             Description
                      
     -----------------------------------------------------------------------------------
                      
     active           The mouse cursor is over the widget and pressing a mouse button
                      will cause some action to occur
                      
                      
     disabled         Widget is disabled under program control
                      
                      
     focus            Widget has keyboard focus
                      
                      
     pressed          Widget is being pressed
                      
                      
     selected         “On”, “true”, or “current” for things like Checkbuttons and
                      radiobuttons
                      
                      
     background       Windows and Mac have a notion of an “active” or foreground
                      window.  The `background' state is set for widgets in a
                      background window, and cleared for those in the foreground
                      window
                      
                      
     readonly         Widget should not allow user modification
                      
                      
     alternate        A widget-specific alternate display format
                      
                      
     invalid          The widget’s value is invalid
                      

A state specification is a sequence of state names, optionally prefixed
with an exclamation point indicating that the bit is off.


File: python.info,  Node: ttk Widget,  Prev: Widget States,  Up: Widget

5.25.8.9 ttk.Widget
...................

Besides the methods described below, the ‘ttk.Widget’ supports the
methods ‘tkinter.Widget.cget()’ and ‘tkinter.Widget.configure()’.

 -- Class: tkinter.ttk.Widget

      -- Method: identify (x, y)

          Returns the name of the element at position `x' `y', or the
          empty string if the point does not lie within any element.

          `x' and `y' are pixel coordinates relative to the widget.

      -- Method: instate (statespec, callback=None, *args, **kw)

          Test the widget’s state.  If a callback is not specified,
          returns ‘True’ if the widget state matches `statespec' and
          ‘False’ otherwise.  If callback is specified then it is called
          with args if widget state matches `statespec'.

      -- Method: state (statespec=None)

          Modify or inquire widget state.  If `statespec' is specified,
          sets the widget state according to it and return a new
          `statespec' indicating which flags were changed.  If
          `statespec' is not specified, returns the currently-enabled
          state flags.

     `statespec' will usually be a list or a tuple.


File: python.info,  Node: Combobox,  Next: Spinbox,  Prev: Widget,  Up: tkinter ttk — Tk themed widgets

5.25.8.10 Combobox
..................

The ‘ttk.Combobox’ widget combines a text field with a pop-down list of
values.  This widget is a subclass of ‘Entry’.

Besides the methods inherited from *note Widget: 3328.: ‘Widget.cget()’,
‘Widget.configure()’, *note Widget.identify(): 3333, *note
Widget.instate(): 3334. and *note Widget.state(): 3330, and the
following inherited from ‘Entry’: ‘Entry.bbox()’, ‘Entry.delete()’,
‘Entry.icursor()’, ‘Entry.index()’, ‘Entry.insert()’,
‘Entry.selection()’, ‘Entry.xview()’, it has some other methods,
described at ‘ttk.Combobox’.

* Menu:

* Options::
* Virtual events::
* ttk.Combobox: ttk Combobox.


File: python.info,  Node: Options,  Next: Virtual events,  Up: Combobox

5.25.8.11 Options
.................

This widget accepts the following specific options:

     Option                Description
                           
     -----------------------------------------------------------------------------------
                           
     exportselection       Boolean value.  If set, the widget selection is linked to
                           the Window Manager selection (which can be returned by
                           invoking Misc.selection_get, for example).
                           
                           
     justify               Specifies how the text is aligned within the widget.  One
                           of “left”, “center”, or “right”.
                           
                           
     height                Specifies the height of the pop-down listbox, in rows.
                           
                           
     postcommand           A script (possibly registered with Misc.register) that is
                           called immediately before displaying the values.  It may
                           specify which values to display.
                           
                           
     state                 One of “normal”, “readonly”, or “disabled”.  In the
                           “readonly” state, the value may not be edited directly,
                           and the user can only selection of the values from the
                           dropdown list.  In the “normal” state, the text field is
                           directly editable.  In the “disabled” state, no
                           interaction is possible.
                           
                           
     textvariable          Specifies a name whose value is linked to the widget
                           value.  Whenever the value associated with that name
                           changes, the widget value is updated, and vice versa.  See
                           ‘tkinter.StringVar’.
                           
                           
     values                Specifies the list of values to display in the drop-down
                           listbox.
                           
                           
     width                 Specifies an integer value indicating the desired width of
                           the entry window, in average-size characters of the
                           widget’s font.
                           


File: python.info,  Node: Virtual events,  Next: ttk Combobox,  Prev: Options,  Up: Combobox

5.25.8.12 Virtual events
........................

The combobox widgets generates a `<<ComboboxSelected>>' virtual event
when the user selects an element from the list of values.


File: python.info,  Node: ttk Combobox,  Prev: Virtual events,  Up: Combobox

5.25.8.13 ttk.Combobox
......................

 -- Class: tkinter.ttk.Combobox

      -- Method: current (newindex=None)

          If `newindex' is specified, sets the combobox value to the
          element position `newindex'.  Otherwise, returns the index of
          the current value or -1 if the current value is not in the
          values list.

      -- Method: get ()

          Returns the current value of the combobox.

      -- Method: set (value)

          Sets the value of the combobox to `value'.


File: python.info,  Node: Spinbox,  Next: Notebook,  Prev: Combobox,  Up: tkinter ttk — Tk themed widgets

5.25.8.14 Spinbox
.................

The ‘ttk.Spinbox’ widget is a ‘ttk.Entry’ enhanced with increment and
decrement arrows.  It can be used for numbers or lists of string values.
This widget is a subclass of ‘Entry’.

Besides the methods inherited from *note Widget: 3328.: ‘Widget.cget()’,
‘Widget.configure()’, *note Widget.identify(): 3333, *note
Widget.instate(): 3334. and *note Widget.state(): 3330, and the
following inherited from ‘Entry’: ‘Entry.bbox()’, ‘Entry.delete()’,
‘Entry.icursor()’, ‘Entry.index()’, ‘Entry.insert()’, ‘Entry.xview()’,
it has some other methods, described at ‘ttk.Spinbox’.

* Menu:

* Options: Options<2>.
* Virtual events: Virtual events<2>.
* ttk.Spinbox: ttk Spinbox.


File: python.info,  Node: Options<2>,  Next: Virtual events<2>,  Up: Spinbox

5.25.8.15 Options
.................

This widget accepts the following specific options:

Option                     Description
                           
--------------------------------------------------------------------------------------
                           
from                       Float value.  If set, this is the minimum value to which
                           the decrement button will decrement.  Must be spelled as
                           ‘from_’ when used as an argument, since ‘from’ is a
                           Python keyword.
                           
                           
to                         Float value.  If set, this is the maximum value to which
                           the increment button will increment.
                           
                           
increment                  Float value.  Specifies the amount which the
                           increment/decrement buttons change the value.  Defaults
                           to 1.0.
                           
                           
values                     Sequence of string or float values.  If specified, the
                           increment/decrement buttons will cycle through the items
                           in this sequence rather than incrementing or
                           decrementing numbers.
                           
                           
wrap                       Boolean value.  If ‘True’, increment and decrement
                           buttons will cycle from the ‘to’ value to the ‘from’
                           value or the ‘from’ value to the ‘to’ value,
                           respectively.
                           
                           
format                     String value.  This specifies the format of numbers set
                           by the increment/decrement buttons.  It must be in the
                           form “%W.Pf”, where W is the padded width of the value,
                           P is the precision, and ‘%’ and ‘f’ are literal.
                           
                           
command                    Python callable.  Will be called with no arguments
                           whenever either of the increment or decrement buttons
                           are pressed.
                           


File: python.info,  Node: Virtual events<2>,  Next: ttk Spinbox,  Prev: Options<2>,  Up: Spinbox

5.25.8.16 Virtual events
........................

The spinbox widget generates an `<<Increment>>' virtual event when the
user presses <Up>, and a `<<Decrement>>' virtual event when the user
presses <Down>.


File: python.info,  Node: ttk Spinbox,  Prev: Virtual events<2>,  Up: Spinbox

5.25.8.17 ttk.Spinbox
.....................

 -- Class: tkinter.ttk.Spinbox

      -- Method: get ()

          Returns the current value of the spinbox.

      -- Method: set (value)

          Sets the value of the spinbox to `value'.


File: python.info,  Node: Notebook,  Next: Progressbar,  Prev: Spinbox,  Up: tkinter ttk — Tk themed widgets

5.25.8.18 Notebook
..................

Ttk Notebook widget manages a collection of windows and displays a
single one at a time.  Each child window is associated with a tab, which
the user may select to change the currently-displayed window.

* Menu:

* Options: Options<3>.
* Tab Options::
* Tab Identifiers::
* Virtual Events::
* ttk.Notebook: ttk Notebook.


File: python.info,  Node: Options<3>,  Next: Tab Options,  Up: Notebook

5.25.8.19 Options
.................

This widget accepts the following specific options:

     Option        Description
                   
     -----------------------------------------------------------------------------------
                   
     height        If present and greater than zero, specifies the desired height of
                   the pane area (not including internal padding or tabs).
                   Otherwise, the maximum height of all panes is used.
                   
                   
     padding       Specifies the amount of extra space to add around the outside of
                   the notebook.  The padding is a list up to four length
                   specifications left top right bottom.  If fewer than four elements
                   are specified, bottom defaults to top, right defaults to left, and
                   top defaults to left.
                   
                   
     width         If present and greater than zero, specified the desired width of
                   the pane area (not including internal padding).  Otherwise, the
                   maximum width of all panes is used.
                   


File: python.info,  Node: Tab Options,  Next: Tab Identifiers,  Prev: Options<3>,  Up: Notebook

5.25.8.20 Tab Options
.....................

There are also specific options for tabs:

     Option          Description
                     
     -----------------------------------------------------------------------------------
                     
     state           Either “normal”, “disabled” or “hidden”.  If “disabled”, then
                     the tab is not selectable.  If “hidden”, then the tab is not
                     shown.
                     
                     
     sticky          Specifies how the child window is positioned within the pane
                     area.  Value is a string containing zero or more of the
                     characters “n”, “s”, “e” or “w”.  Each letter refers to a side
                     (north, south, east or west) that the child window will stick
                     to, as per the ‘grid()’ geometry manager.
                     
                     
     padding         Specifies the amount of extra space to add between the notebook
                     and this pane.  Syntax is the same as for the option padding
                     used by this widget.
                     
                     
     text            Specifies a text to be displayed in the tab.
                     
                     
     image           Specifies an image to display in the tab.  See the option image
                     described in *note Widget: 3328.
                     
                     
     compound        Specifies how to display the image relative to the text, in the
                     case both options text and image are present.  See
                     *note Label Options: 332e. for legal values.
                     
                     
     underline       Specifies the index (0-based) of a character to underline in the
                     text string.  The underlined character is used for mnemonic
                     activation if *note Notebook.enable_traversal(): 3345. is
                     called.
                     


File: python.info,  Node: Tab Identifiers,  Next: Virtual Events,  Prev: Tab Options,  Up: Notebook

5.25.8.21 Tab Identifiers
.........................

The tab_id present in several methods of ‘ttk.Notebook’ may take any of
the following forms:

   * An integer between zero and the number of tabs

   * The name of a child window

   * A positional specification of the form “@x,y”, which identifies the
     tab

   * The literal string “current”, which identifies the
     currently-selected tab

   * The literal string “end”, which returns the number of tabs (only
     valid for *note Notebook.index(): 3347.)


File: python.info,  Node: Virtual Events,  Next: ttk Notebook,  Prev: Tab Identifiers,  Up: Notebook

5.25.8.22 Virtual Events
........................

This widget generates a `<<NotebookTabChanged>>' virtual event after a
new tab is selected.


File: python.info,  Node: ttk Notebook,  Prev: Virtual Events,  Up: Notebook

5.25.8.23 ttk.Notebook
......................

 -- Class: tkinter.ttk.Notebook

      -- Method: add (child, **kw)

          Adds a new tab to the notebook.

          If window is currently managed by the notebook but hidden, it
          is restored to its previous position.

          See *note Tab Options: 3344. for the list of available
          options.

      -- Method: forget (tab_id)

          Removes the tab specified by `tab_id', unmaps and unmanages
          the associated window.

      -- Method: hide (tab_id)

          Hides the tab specified by `tab_id'.

          The tab will not be displayed, but the associated window
          remains managed by the notebook and its configuration
          remembered.  Hidden tabs may be restored with the *note add():
          334a. command.

      -- Method: identify (x, y)

          Returns the name of the tab element at position `x', `y', or
          the empty string if none.

      -- Method: index (tab_id)

          Returns the numeric index of the tab specified by `tab_id', or
          the total number of tabs if `tab_id' is the string “end”.

      -- Method: insert (pos, child, **kw)

          Inserts a pane at the specified position.

          `pos' is either the string “end”, an integer index, or the
          name of a managed child.  If `child' is already managed by the
          notebook, moves it to the specified position.

          See *note Tab Options: 3344. for the list of available
          options.

      -- Method: select (tab_id=None)

          Selects the specified `tab_id'.

          The associated child window will be displayed, and the
          previously-selected window (if different) is unmapped.  If
          `tab_id' is omitted, returns the widget name of the currently
          selected pane.

      -- Method: tab (tab_id, option=None, **kw)

          Query or modify the options of the specific `tab_id'.

          If `kw' is not given, returns a dictionary of the tab option
          values.  If `option' is specified, returns the value of that
          `option'.  Otherwise, sets the options to the corresponding
          values.

      -- Method: tabs ()

          Returns a list of windows managed by the notebook.

      -- Method: enable_traversal ()

          Enable keyboard traversal for a toplevel window containing
          this notebook.

          This will extend the bindings for the toplevel window
          containing the notebook as follows:

             * ‘Control-Tab’: selects the tab following the currently
               selected one.

             * ‘Shift-Control-Tab’: selects the tab preceding the
               currently selected one.

             * ‘Alt-K’: where `K' is the mnemonic (underlined) character
               of any tab, will select that tab.

          Multiple notebooks in a single toplevel may be enabled for
          traversal, including nested notebooks.  However, notebook
          traversal only works properly if all panes have the notebook
          they are in as master.


File: python.info,  Node: Progressbar,  Next: Separator,  Prev: Notebook,  Up: tkinter ttk — Tk themed widgets

5.25.8.24 Progressbar
.....................

The ‘ttk.Progressbar’ widget shows the status of a long-running
operation.  It can operate in two modes: 1) the determinate mode which
shows the amount completed relative to the total amount of work to be
done and 2) the indeterminate mode which provides an animated display to
let the user know that work is progressing.

* Menu:

* Options: Options<4>.
* ttk.Progressbar: ttk Progressbar.


File: python.info,  Node: Options<4>,  Next: ttk Progressbar,  Up: Progressbar

5.25.8.25 Options
.................

This widget accepts the following specific options:

     Option         Description
                    
     -----------------------------------------------------------------------------------
                    
     orient         One of “horizontal” or “vertical”.  Specifies the orientation of
                    the progress bar.
                    
                    
     length         Specifies the length of the long axis of the progress bar (width
                    if horizontal, height if vertical).
                    
                    
     mode           One of “determinate” or “indeterminate”.
                    
                    
     maximum        A number specifying the maximum value.  Defaults to 100.
                    
                    
     value          The current value of the progress bar.  In “determinate” mode,
                    this represents the amount of work completed.  In “indeterminate”
                    mode, it is interpreted as modulo `maximum'; that is, the
                    progress bar completes one “cycle” when its value increases by
                    `maximum'.
                    
                    
     variable       A name which is linked to the option value.  If specified, the
                    value of the progress bar is automatically set to the value of
                    this name whenever the latter is modified.
                    
                    
     phase          Read-only option.  The widget periodically increments the value
                    of this option whenever its value is greater than 0 and, in
                    determinate mode, less than maximum.  This option may be used by
                    the current theme to provide additional animation effects.
                    


File: python.info,  Node: ttk Progressbar,  Prev: Options<4>,  Up: Progressbar

5.25.8.26 ttk.Progressbar
.........................

 -- Class: tkinter.ttk.Progressbar

      -- Method: start (interval=None)

          Begin autoincrement mode: schedules a recurring timer event
          that calls *note Progressbar.step(): 3356. every `interval'
          milliseconds.  If omitted, `interval' defaults to 50
          milliseconds.

      -- Method: step (amount=None)

          Increments the progress bar’s value by `amount'.

          `amount' defaults to 1.0 if omitted.

      -- Method: stop ()

          Stop autoincrement mode: cancels any recurring timer event
          initiated by *note Progressbar.start(): 3355. for this
          progress bar.


File: python.info,  Node: Separator,  Next: Sizegrip,  Prev: Progressbar,  Up: tkinter ttk — Tk themed widgets

5.25.8.27 Separator
...................

The ‘ttk.Separator’ widget displays a horizontal or vertical separator
bar.

It has no other methods besides the ones inherited from ‘ttk.Widget’.

* Menu:

* Options: Options<5>.


File: python.info,  Node: Options<5>,  Up: Separator

5.25.8.28 Options
.................

This widget accepts the following specific option:

     Option       Description
                  
     ----------------------------------------------------------------------------------
                  
     orient       One of “horizontal” or “vertical”.  Specifies the orientation of
                  the separator.
                  


File: python.info,  Node: Sizegrip,  Next: Treeview,  Prev: Separator,  Up: tkinter ttk — Tk themed widgets

5.25.8.29 Sizegrip
..................

The ‘ttk.Sizegrip’ widget (also known as a grow box) allows the user to
resize the containing toplevel window by pressing and dragging the grip.

This widget has neither specific options nor specific methods, besides
the ones inherited from ‘ttk.Widget’.

* Menu:

* Platform-specific notes::
* Bugs::


File: python.info,  Node: Platform-specific notes,  Next: Bugs,  Up: Sizegrip

5.25.8.30 Platform-specific notes
.................................

   * On macOS, toplevel windows automatically include a built-in size
     grip by default.  Adding a ‘Sizegrip’ is harmless, since the
     built-in grip will just mask the widget.


File: python.info,  Node: Bugs,  Prev: Platform-specific notes,  Up: Sizegrip

5.25.8.31 Bugs
..............

   * If the containing toplevel’s position was specified relative to the
     right or bottom of the screen (e.g.  ….), the ‘Sizegrip’ widget
     will not resize the window.

   * This widget supports only “southeast” resizing.


File: python.info,  Node: Treeview,  Next: Ttk Styling,  Prev: Sizegrip,  Up: tkinter ttk — Tk themed widgets

5.25.8.32 Treeview
..................

The ‘ttk.Treeview’ widget displays a hierarchical collection of items.
Each item has a textual label, an optional image, and an optional list
of data values.  The data values are displayed in successive columns
after the tree label.

The order in which data values are displayed may be controlled by
setting the widget option ‘displaycolumns’.  The tree widget can also
display column headings.  Columns may be accessed by number or symbolic
names listed in the widget option columns.  See *note Column
Identifiers: 335e.

Each item is identified by a unique name.  The widget will generate item
IDs if they are not supplied by the caller.  There is a distinguished
root item, named ‘{}’.  The root item itself is not displayed; its
children appear at the top level of the hierarchy.

Each item also has a list of tags, which can be used to associate event
bindings with individual items and control the appearance of the item.

The Treeview widget supports horizontal and vertical scrolling,
according to the options described in *note Scrollable Widget Options:
332d. and the methods *note Treeview.xview(): 335f. and *note
Treeview.yview(): 3360.

* Menu:

* Options: Options<6>.
* Item Options::
* Tag Options::
* Column Identifiers::
* Virtual Events: Virtual Events<2>.
* ttk.Treeview: ttk Treeview.


File: python.info,  Node: Options<6>,  Next: Item Options,  Up: Treeview

5.25.8.33 Options
.................

This widget accepts the following specific options:

     Option               Description
                          
     ----------------------------------------------------------------------------------
                          
     columns              A list of column identifiers, specifying the number of
                          columns and their names.
                          
                          
     displaycolumns       A list of column identifiers (either symbolic or integer
                          indices) specifying which data columns are displayed and
                          the order in which they appear, or the string “#all”.
                          
                          
     height               Specifies the number of rows which should be visible.
                          Note: the requested width is determined from the sum of
                          the column widths.
                          
                          
     padding              Specifies the internal padding for the widget.  The
                          padding is a list of up to four length specifications.
                          
                          
     selectmode           Controls how the built-in class bindings manage the
                          selection.  One of “extended”, “browse” or “none”.  If set
                          to “extended” (the default), multiple items may be
                          selected.  If “browse”, only a single item will be
                          selected at a time.  If “none”, the selection will not be
                          changed.
                          
                          Note that the application code and tag bindings can set
                          the selection however they wish, regardless of the value
                          of this option.
                          
                          
     show                 A list containing zero or more of the following values,
                          specifying which elements of the tree to display.
                          
                             * tree: display tree labels in column #0.
                          
                             * headings: display the heading row.
                          
                          The default is “tree headings”, i.e., show all elements.
                          
                          `Note': Column #0 always refers to the tree column, even
                          if show=”tree” is not specified.
                          


File: python.info,  Node: Item Options,  Next: Tag Options,  Prev: Options<6>,  Up: Treeview

5.25.8.34 Item Options
......................

The following item options may be specified for items in the insert and
item widget commands.

     Option       Description
                  
     ---------------------------------------------------------------------------------
                  
     text         The textual label to display for the item.
                  
                  
     image        A Tk Image, displayed to the left of the label.
                  
                  
     values       The list of values associated with the item.
                  
                  Each item should have the same number of values as the widget
                  option columns.  If there are fewer values than columns, the
                  remaining values are assumed empty.  If there are more values
                  than columns, the extra values are ignored.
                  
                  
     open         ‘True’/‘False’ value indicating whether the item’s children
                  should be displayed or hidden.
                  
                  
     tags         A list of tags associated with this item.
                  


File: python.info,  Node: Tag Options,  Next: Column Identifiers,  Prev: Item Options,  Up: Treeview

5.25.8.35 Tag Options
.....................

The following options may be specified on tags:

     Option           Description
                      
     ---------------------------------------------------------------------------------
                      
     foreground       Specifies the text foreground color.
                      
                      
     background       Specifies the cell or item background color.
                      
                      
     font             Specifies the font to use when drawing text.
                      
                      
     image            Specifies the item image, in case the item’s image option is
                      empty.
                      


File: python.info,  Node: Column Identifiers,  Next: Virtual Events<2>,  Prev: Tag Options,  Up: Treeview

5.25.8.36 Column Identifiers
............................

Column identifiers take any of the following forms:

   * A symbolic name from the list of columns option.

   * An integer n, specifying the nth data column.

   * A string of the form #n, where n is an integer, specifying the nth
     display column.

Notes:

   * Item’s option values may be displayed in a different order than the
     order in which they are stored.

   * Column #0 always refers to the tree column, even if show=”tree” is
     not specified.

A data column number is an index into an item’s option values list; a
display column number is the column number in the tree where the values
are displayed.  Tree labels are displayed in column #0.  If option
displaycolumns is not set, then data column n is displayed in column
#n+1.  Again, `column #0 always refers to the tree column'.


File: python.info,  Node: Virtual Events<2>,  Next: ttk Treeview,  Prev: Column Identifiers,  Up: Treeview

5.25.8.37 Virtual Events
........................

The Treeview widget generates the following virtual events.

     Event                    Description
                              
     --------------------------------------------------------------------------------
                              
     <<TreeviewSelect>>       Generated whenever the selection changes.
                              
                              
     <<TreeviewOpen>>         Generated just before settings the focus item to
                              open=True.
                              
                              
     <<TreeviewClose>>        Generated just after setting the focus item to
                              open=False.
                              

The *note Treeview.focus(): 3365. and *note Treeview.selection(): 3de.
methods can be used to determine the affected item or items.


File: python.info,  Node: ttk Treeview,  Prev: Virtual Events<2>,  Up: Treeview

5.25.8.38 ttk.Treeview
......................

 -- Class: tkinter.ttk.Treeview

      -- Method: bbox (item, column=None)

          Returns the bounding box (relative to the treeview widget’s
          window) of the specified `item' in the form (x, y, width,
          height).

          If `column' is specified, returns the bounding box of that
          cell.  If the `item' is not visible (i.e., if it is a
          descendant of a closed item or is scrolled offscreen), returns
          an empty string.

      -- Method: get_children (item=None)

          Returns the list of children belonging to `item'.

          If `item' is not specified, returns root children.

      -- Method: set_children (item, *newchildren)

          Replaces `item'’s child with `newchildren'.

          Children present in `item' that are not present in
          `newchildren' are detached from the tree.  No items in
          `newchildren' may be an ancestor of `item'.  Note that not
          specifying `newchildren' results in detaching `item'’s
          children.

      -- Method: column (column, option=None, **kw)

          Query or modify the options for the specified `column'.

          If `kw' is not given, returns a dict of the column option
          values.  If `option' is specified then the value for that
          `option' is returned.  Otherwise, sets the options to the
          corresponding values.

          The valid options/values are:

             * 
               id

                    Returns the column name.  This is a read-only
                    option.

             * 
               anchor: One of the standard Tk anchor values.

                    Specifies how the text in this column should be
                    aligned with respect to the cell.

             * 
               minwidth: width

                    The minimum width of the column in pixels.  The
                    treeview widget will not make the column any smaller
                    than specified by this option when the widget is
                    resized or the user drags a column.

             * 
               stretch: ‘True’/‘False’

                    Specifies whether the column’s width should be
                    adjusted when the widget is resized.

             * 
               width: width

                    The width of the column in pixels.

          To configure the tree column, call this with column = “#0”

      -- Method: delete (*items)

          Delete all specified `items' and all their descendants.

          The root item may not be deleted.

      -- Method: detach (*items)

          Unlinks all of the specified `items' from the tree.

          The items and all of their descendants are still present, and
          may be reinserted at another point in the tree, but will not
          be displayed.

          The root item may not be detached.

      -- Method: exists (item)

          Returns ‘True’ if the specified `item' is present in the tree.

      -- Method: focus (item=None)

          If `item' is specified, sets the focus item to `item'.
          Otherwise, returns the current focus item, or ‘’ if there is
          none.

      -- Method: heading (column, option=None, **kw)

          Query or modify the heading options for the specified
          `column'.

          If `kw' is not given, returns a dict of the heading option
          values.  If `option' is specified then the value for that
          `option' is returned.  Otherwise, sets the options to the
          corresponding values.

          The valid options/values are:

             * 
               text: text

                    The text to display in the column heading.

             * 
               image: imageName

                    Specifies an image to display to the right of the
                    column heading.

             * 
               anchor: anchor

                    Specifies how the heading text should be aligned.
                    One of the standard Tk anchor values.

             * 
               command: callback

                    A callback to be invoked when the heading label is
                    pressed.

          To configure the tree column heading, call this with column =
          “#0”.

      -- Method: identify (component, x, y)

          Returns a description of the specified `component' under the
          point given by `x' and `y', or the empty string if no such
          `component' is present at that position.

      -- Method: identify_row (y)

          Returns the item ID of the item at position `y'.

      -- Method: identify_column (x)

          Returns the data column identifier of the cell at position
          `x'.

          The tree column has ID #0.

      -- Method: identify_region (x, y)

          Returns one of:

          region          meaning
                          
          -----------------------------------------------------------
                          
          heading         Tree heading area.
                          
                          
          separator       Space between two columns headings.
                          
                          
          tree            The tree area.
                          
                          
          cell            A data cell.
                          

          Availability: Tk 8.6.

      -- Method: identify_element (x, y)

          Returns the element at position `x', `y'.

          Availability: Tk 8.6.

      -- Method: index (item)

          Returns the integer index of `item' within its parent’s list
          of children.

      -- Method: insert (parent, index, iid=None, **kw)

          Creates a new item and returns the item identifier of the
          newly created item.

          `parent' is the item ID of the parent item, or the empty
          string to create a new top-level item.  `index' is an integer,
          or the value “end”, specifying where in the list of parent’s
          children to insert the new item.  If `index' is less than or
          equal to zero, the new node is inserted at the beginning; if
          `index' is greater than or equal to the current number of
          children, it is inserted at the end.  If `iid' is specified,
          it is used as the item identifier; `iid' must not already
          exist in the tree.  Otherwise, a new unique identifier is
          generated.

          See *note Item Options: 3362. for the list of available
          points.

      -- Method: item (item, option=None, **kw)

          Query or modify the options for the specified `item'.

          If no options are given, a dict with options/values for the
          item is returned.  If `option' is specified then the value for
          that option is returned.  Otherwise, sets the options to the
          corresponding values as given by `kw'.

      -- Method: move (item, parent, index)

          Moves `item' to position `index' in `parent'’s list of
          children.

          It is illegal to move an item under one of its descendants.
          If `index' is less than or equal to zero, `item' is moved to
          the beginning; if greater than or equal to the number of
          children, it is moved to the end.  If `item' was detached it
          is reattached.

      -- Method: next (item)

          Returns the identifier of `item'’s next sibling, or ‘’ if
          `item' is the last child of its parent.

      -- Method: parent (item)

          Returns the ID of the parent of `item', or ‘’ if `item' is at
          the top level of the hierarchy.

      -- Method: prev (item)

          Returns the identifier of `item'’s previous sibling, or ‘’ if
          `item' is the first child of its parent.

      -- Method: reattach (item, parent, index)

          An alias for *note Treeview.move(): 3377.

      -- Method: see (item)

          Ensure that `item' is visible.

          Sets all of `item'’s ancestors open option to ‘True’, and
          scrolls the widget if necessary so that `item' is within the
          visible portion of the tree.

      -- Method: selection ()

          Returns a tuple of selected items.

          Changed in version 3.8: ‘selection()’ no longer takes
          arguments.  For changing the selection state use the following
          selection methods.

      -- Method: selection_set (*items)

          `items' becomes the new selection.

          Changed in version 3.6: `items' can be passed as separate
          arguments, not just as a single tuple.

      -- Method: selection_add (*items)

          Add `items' to the selection.

          Changed in version 3.6: `items' can be passed as separate
          arguments, not just as a single tuple.

      -- Method: selection_remove (*items)

          Remove `items' from the selection.

          Changed in version 3.6: `items' can be passed as separate
          arguments, not just as a single tuple.

      -- Method: selection_toggle (*items)

          Toggle the selection state of each item in `items'.

          Changed in version 3.6: `items' can be passed as separate
          arguments, not just as a single tuple.

      -- Method: set (item, column=None, value=None)

          With one argument, returns a dictionary of column/value pairs
          for the specified `item'.  With two arguments, returns the
          current value of the specified `column'.  With three
          arguments, sets the value of given `column' in given `item' to
          the specified `value'.

      -- Method: tag_bind (tagname, sequence=None, callback=None)

          Bind a callback for the given event `sequence' to the tag
          `tagname'.  When an event is delivered to an item, the
          callbacks for each of the item’s tags option are called.

      -- Method: tag_configure (tagname, option=None, **kw)

          Query or modify the options for the specified `tagname'.

          If `kw' is not given, returns a dict of the option settings
          for `tagname'.  If `option' is specified, returns the value
          for that `option' for the specified `tagname'.  Otherwise,
          sets the options to the corresponding values for the given
          `tagname'.

      -- Method: tag_has (tagname, item=None)

          If `item' is specified, returns 1 or 0 depending on whether
          the specified `item' has the given `tagname'.  Otherwise,
          returns a list of all items that have the specified tag.

          Availability: Tk 8.6

      -- Method: xview (*args)

          Query or modify horizontal position of the treeview.

      -- Method: yview (*args)

          Query or modify vertical position of the treeview.


File: python.info,  Node: Ttk Styling,  Prev: Treeview,  Up: tkinter ttk — Tk themed widgets

5.25.8.39 Ttk Styling
.....................

Each widget in ‘ttk’ is assigned a style, which specifies the set of
elements making up the widget and how they are arranged, along with
dynamic and default settings for element options.  By default the style
name is the same as the widget’s class name, but it may be overridden by
the widget’s style option.  If you don’t know the class name of a
widget, use the method ‘Misc.winfo_class()’ (somewidget.winfo_class()).

See also
........

Tcl’2004 conference presentation(1)

     This document explains how the theme engine works

 -- Class: tkinter.ttk.Style

     This class is used to manipulate the style database.

      -- Method: configure (style, query_opt=None, **kw)

          Query or set the default value of the specified option(s) in
          `style'.

          Each key in `kw' is an option and each value is a string
          identifying the value for that option.

          For example, to change every default button to be a flat
          button with some padding and a different background color:

               from tkinter import ttk
               import tkinter

               root = tkinter.Tk()

               ttk.Style().configure("TButton", padding=6, relief="flat",
                  background="#ccc")

               btn = ttk.Button(text="Sample")
               btn.pack()

               root.mainloop()

      -- Method: map (style, query_opt=None, **kw)

          Query or sets dynamic values of the specified option(s) in
          `style'.

          Each key in `kw' is an option and each value should be a list
          or a tuple (usually) containing statespecs grouped in tuples,
          lists, or some other preference.  A statespec is a compound of
          one or more states and then a value.

          An example may make it more understandable:

               import tkinter
               from tkinter import ttk

               root = tkinter.Tk()

               style = ttk.Style()
               style.map("C.TButton",
                   foreground=[('pressed', 'red'), ('active', 'blue')],
                   background=[('pressed', '!disabled', 'black'), ('active', 'white')]
                   )

               colored_btn = ttk.Button(text="Test", style="C.TButton").pack()

               root.mainloop()

          Note that the order of the (states, value) sequences for an
          option does matter, if the order is changed to ‘[('active',
          'blue'), ('pressed', 'red')]’ in the foreground option, for
          example, the result would be a blue foreground when the widget
          were in active or pressed states.

      -- Method: lookup (style, option, state=None, default=None)

          Returns the value specified for `option' in `style'.

          If `state' is specified, it is expected to be a sequence of
          one or more states.  If the `default' argument is set, it is
          used as a fallback value in case no specification for option
          is found.

          To check what font a Button uses by default:

               from tkinter import ttk

               print(ttk.Style().lookup("TButton", "font"))

      -- Method: layout (style, layoutspec=None)

          Define the widget layout for given `style'.  If `layoutspec'
          is omitted, return the layout specification for given style.

          `layoutspec', if specified, is expected to be a list or some
          other sequence type (excluding strings), where each item
          should be a tuple and the first item is the layout name and
          the second item should have the format described in *note
          Layouts: 3388.

          To understand the format, see the following example (it is not
          intended to do anything useful):

               from tkinter import ttk
               import tkinter

               root = tkinter.Tk()

               style = ttk.Style()
               style.layout("TMenubutton", [
                  ("Menubutton.background", None),
                  ("Menubutton.button", {"children":
                      [("Menubutton.focus", {"children":
                          [("Menubutton.padding", {"children":
                              [("Menubutton.label", {"side": "left", "expand": 1})]
                          })]
                      })]
                  }),
               ])

               mbtn = ttk.Menubutton(text='Text')
               mbtn.pack()
               root.mainloop()

      -- Method: element_create (elementname, etype, *args, **kw)

          Create a new element in the current theme, of the given
          `etype' which is expected to be either “image”, “from” or
          “vsapi”.  The latter is only available in Tk 8.6a for Windows
          XP and Vista and is not described here.

          If “image” is used, `args' should contain the default image
          name followed by statespec/value pairs (this is the
          imagespec), and `kw' may have the following options:

                  * 
                    border=padding

                         padding is a list of up to four integers,
                         specifying the left, top, right, and bottom
                         borders, respectively.

                  * 
                    height=height

                         Specifies a minimum height for the element.  If
                         less than zero, the base image’s height is used
                         as a default.

                  * 
                    padding=padding

                         Specifies the element’s interior padding.
                         Defaults to border’s value if not specified.

                  * 
                    sticky=spec

                         Specifies how the image is placed within the
                         final parcel.  spec contains zero or more
                         characters “n”, “s”, “w”, or “e”.

                  * 
                    width=width

                         Specifies a minimum width for the element.  If
                         less than zero, the base image’s width is used
                         as a default.

          If “from” is used as the value of `etype', *note
          element_create(): 3389. will clone an existing element.
          `args' is expected to contain a themename, from which the
          element will be cloned, and optionally an element to clone
          from.  If this element to clone from is not specified, an
          empty element will be used.  `kw' is discarded.

      -- Method: element_names ()

          Returns the list of elements defined in the current theme.

      -- Method: element_options (elementname)

          Returns the list of `elementname'’s options.

      -- Method: theme_create (themename, parent=None, settings=None)

          Create a new theme.

          It is an error if `themename' already exists.  If `parent' is
          specified, the new theme will inherit styles, elements and
          layouts from the parent theme.  If `settings' are present they
          are expected to have the same syntax used for *note
          theme_settings(): 338d.

      -- Method: theme_settings (themename, settings)

          Temporarily sets the current theme to `themename', apply
          specified `settings' and then restore the previous theme.

          Each key in `settings' is a style and each value may contain
          the keys ‘configure’, ‘map’, ‘layout’ and ‘element create’ and
          they are expected to have the same format as specified by the
          methods *note Style.configure(): 3385, *note Style.map(): fe4,
          *note Style.layout(): 3387. and *note Style.element_create():
          3389. respectively.

          As an example, let’s change the Combobox for the default theme
          a bit:

               from tkinter import ttk
               import tkinter

               root = tkinter.Tk()

               style = ttk.Style()
               style.theme_settings("default", {
                  "TCombobox": {
                      "configure": {"padding": 5},
                      "map": {
                          "background": [("active", "green2"),
                                         ("!disabled", "green4")],
                          "fieldbackground": [("!disabled", "green3")],
                          "foreground": [("focus", "OliveDrab1"),
                                         ("!disabled", "OliveDrab2")]
                      }
                  }
               })

               combo = ttk.Combobox().pack()

               root.mainloop()

      -- Method: theme_names ()

          Returns a list of all known themes.

      -- Method: theme_use (themename=None)

          If `themename' is not given, returns the theme in use.
          Otherwise, sets the current theme to `themename', refreshes
          all widgets and emits a <<ThemeChanged>> event.

* Menu:

* Layouts::

   ---------- Footnotes ----------

   (1) http://tktable.sourceforge.net/tile/tile-tcl2004.pdf


File: python.info,  Node: Layouts,  Up: Ttk Styling

5.25.8.40 Layouts
.................

A layout can be just ‘None’, if it takes no options, or a dict of
options specifying how to arrange the element.  The layout mechanism
uses a simplified version of the pack geometry manager: given an initial
cavity, each element is allocated a parcel.  Valid options/values are:

        * 
          side: whichside

               Specifies which side of the cavity to place the element;
               one of top, right, bottom or left.  If omitted, the
               element occupies the entire cavity.

        * 
          sticky: nswe

               Specifies where the element is placed inside its
               allocated parcel.

        * 
          unit: 0 or 1

               If set to 1, causes the element and all of its
               descendants to be treated as a single element for the
               purposes of *note Widget.identify(): 3333. et al.  It’s
               used for things like scrollbar thumbs with grips.

        * 
          children: [sublayout… ]

               Specifies a list of elements to place inside the element.
               Each element is a tuple (or other sequence type) where
               the first item is the layout name, and the other is a
               *note Layout: 3388.


File: python.info,  Node: tkinter tix — Extension widgets for Tk,  Next: IDLE<51>,  Prev: tkinter ttk — Tk themed widgets,  Up: Graphical User Interfaces with Tk

5.25.9 ‘tkinter.tix’ — Extension widgets for Tk
-----------------------------------------------

`Source code:' Lib/tkinter/tix.py(1)

Deprecated since version 3.6: This Tk extension is unmaintained and
should not be used in new code.  Use *note tkinter.ttk: 118. instead.

__________________________________________________________________

The *note tkinter.tix: 117. (Tk Interface Extension) module provides an
additional rich set of widgets.  Although the standard Tk library has
many useful widgets, they are far from complete.  The *note tkinter.tix:
117. library provides most of the commonly needed widgets that are
missing from standard Tk: *note HList: 3394, *note ComboBox: 3395, *note
Control: 3396. (a.k.a.  SpinBox) and an assortment of scrollable
widgets.  *note tkinter.tix: 117. also includes many more widgets that
are generally useful in a wide range of applications: *note NoteBook:
3397, *note FileEntry: 3398, *note PanedWindow: 3399, etc; there are
more than 40 of them.

With all these new widgets, you can introduce new interaction techniques
into applications, creating more useful and more intuitive user
interfaces.  You can design your application by choosing the most
appropriate widgets to match the special needs of your application and
users.

See also
........

Tix Homepage(2)

     The home page for ‘Tix’.  This includes links to additional
     documentation and downloads.

Tix Man Pages(3)

     On-line version of the man pages and reference material.

Tix Programming Guide(4)

     On-line version of the programmer’s reference material.

Tix Development Applications(5)

     Tix applications for development of Tix and Tkinter programs.  Tide
     applications work under Tk or Tkinter, and include ‘TixInspect’, an
     inspector to remotely modify and debug Tix/Tk/Tkinter applications.

* Menu:

* Using Tix::
* Tix Widgets::
* Tix Commands::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/tkinter/tix.py

   (2) http://tix.sourceforge.net/

   (3) http://tix.sourceforge.net/dist/current/man/

   (4) 
http://tix.sourceforge.net/dist/current/docs/tix-book/tix.book.html

   (5) http://tix.sourceforge.net/Tixapps/src/Tide.html


File: python.info,  Node: Using Tix,  Next: Tix Widgets,  Up: tkinter tix — Extension widgets for Tk

5.25.9.1 Using Tix
..................

 -- Class: tkinter.tix.Tk (screenName=None, baseName=None,
          className='Tix')

     Toplevel widget of Tix which represents mostly the main window of
     an application.  It has an associated Tcl interpreter.

     Classes in the *note tkinter.tix: 117. module subclasses the
     classes in the *note tkinter: 10e.  The former imports the latter,
     so to use *note tkinter.tix: 117. with Tkinter, all you need to do
     is to import one module.  In general, you can just import *note
     tkinter.tix: 117, and replace the toplevel call to *note
     tkinter.Tk: 32b0. with ‘tix.Tk’:

          from tkinter import tix
          from tkinter.constants import *
          root = tix.Tk()

To use *note tkinter.tix: 117, you must have the Tix widgets installed,
usually alongside your installation of the Tk widgets.  To test your
installation, try the following:

     from tkinter import tix
     root = tix.Tk()
     root.tk.eval('package require Tix')


File: python.info,  Node: Tix Widgets,  Next: Tix Commands,  Prev: Using Tix,  Up: tkinter tix — Extension widgets for Tk

5.25.9.2 Tix Widgets
....................

Tix(1) introduces over 40 widget classes to the *note tkinter: 10e.
repertoire.

* Menu:

* Basic Widgets::
* File Selectors::
* Hierarchical ListBox::
* Tabular ListBox::
* Manager Widgets::
* Image Types::
* Miscellaneous Widgets::
* Form Geometry Manager::

   ---------- Footnotes ----------

   (1) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/TixIntro.htm


File: python.info,  Node: Basic Widgets,  Next: File Selectors,  Up: Tix Widgets

5.25.9.3 Basic Widgets
......................

 -- Class: tkinter.tix.Balloon

     A Balloon(1) that pops up over a widget to provide help.  When the
     user moves the cursor inside a widget to which a Balloon widget has
     been bound, a small pop-up window with a descriptive message will
     be shown on the screen.

 -- Class: tkinter.tix.ButtonBox

     The ButtonBox(2) widget creates a box of buttons, such as is
     commonly used for ‘Ok Cancel’.

 -- Class: tkinter.tix.ComboBox

     The ComboBox(3) widget is similar to the combo box control in MS
     Windows.  The user can select a choice by either typing in the
     entry subwidget or selecting from the listbox subwidget.

 -- Class: tkinter.tix.Control

     The Control(4) widget is also known as the ‘SpinBox’ widget.  The
     user can adjust the value by pressing the two arrow buttons or by
     entering the value directly into the entry.  The new value will be
     checked against the user-defined upper and lower limits.

 -- Class: tkinter.tix.LabelEntry

     The LabelEntry(5) widget packages an entry widget and a label into
     one mega widget.  It can be used to simplify the creation of
     “entry-form” type of interface.

 -- Class: tkinter.tix.LabelFrame

     The LabelFrame(6) widget packages a frame widget and a label into
     one mega widget.  To create widgets inside a LabelFrame widget, one
     creates the new widgets relative to the ‘frame’ subwidget and
     manage them inside the ‘frame’ subwidget.

 -- Class: tkinter.tix.Meter

     The Meter(7) widget can be used to show the progress of a
     background job which may take a long time to execute.

 -- Class: tkinter.tix.OptionMenu

     The OptionMenu(8) creates a menu button of options.

 -- Class: tkinter.tix.PopupMenu

     The PopupMenu(9) widget can be used as a replacement of the
     ‘tk_popup’ command.  The advantage of the ‘Tix’ *note PopupMenu:
     33a4. widget is it requires less application code to manipulate.

 -- Class: tkinter.tix.Select

     The Select(10) widget is a container of button subwidgets.  It can
     be used to provide radio-box or check-box style of selection
     options for the user.

 -- Class: tkinter.tix.StdButtonBox

     The StdButtonBox(11) widget is a group of standard buttons for
     Motif-like dialog boxes.

   ---------- Footnotes ----------

   (1) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixBalloon.htm

   (2) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixButtonBox.htm

   (3) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixComboBox.htm

   (4) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixControl.htm

   (5) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixLabelEntry.htm

   (6) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixLabelFrame.htm

   (7) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixMeter.htm

   (8) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixOptionMenu.htm

   (9) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixPopupMenu.htm

   (10) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixSelect.htm

   (11) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixStdButtonBox.htm


File: python.info,  Node: File Selectors,  Next: Hierarchical ListBox,  Prev: Basic Widgets,  Up: Tix Widgets

5.25.9.4 File Selectors
.......................

 -- Class: tkinter.tix.DirList

     The DirList(1) widget displays a list view of a directory, its
     previous directories and its sub-directories.  The user can choose
     one of the directories displayed in the list or change to another
     directory.

 -- Class: tkinter.tix.DirTree

     The DirTree(2) widget displays a tree view of a directory, its
     previous directories and its sub-directories.  The user can choose
     one of the directories displayed in the list or change to another
     directory.

 -- Class: tkinter.tix.DirSelectDialog

     The DirSelectDialog(3) widget presents the directories in the file
     system in a dialog window.  The user can use this dialog window to
     navigate through the file system to select the desired directory.

 -- Class: tkinter.tix.DirSelectBox

     The *note DirSelectBox: 33ab. is similar to the standard Motif(TM)
     directory-selection box.  It is generally used for the user to
     choose a directory.  DirSelectBox stores the directories mostly
     recently selected into a ComboBox widget so that they can be
     quickly selected again.

 -- Class: tkinter.tix.ExFileSelectBox

     The ExFileSelectBox(4) widget is usually embedded in a
     tixExFileSelectDialog widget.  It provides a convenient method for
     the user to select files.  The style of the *note ExFileSelectBox:
     33ac. widget is very similar to the standard file dialog on MS
     Windows 3.1.

 -- Class: tkinter.tix.FileSelectBox

     The FileSelectBox(5) is similar to the standard Motif(TM)
     file-selection box.  It is generally used for the user to choose a
     file.  FileSelectBox stores the files mostly recently selected into
     a *note ComboBox: 3395. widget so that they can be quickly selected
     again.

 -- Class: tkinter.tix.FileEntry

     The FileEntry(6) widget can be used to input a filename.  The user
     can type in the filename manually.  Alternatively, the user can
     press the button widget that sits next to the entry, which will
     bring up a file selection dialog.

   ---------- Footnotes ----------

   (1) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixDirList.htm

   (2) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixDirTree.htm

   (3) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixDirSelectDialog.htm

   (4) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixExFileSelectBox.htm

   (5) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixFileSelectBox.htm

   (6) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixFileEntry.htm


File: python.info,  Node: Hierarchical ListBox,  Next: Tabular ListBox,  Prev: File Selectors,  Up: Tix Widgets

5.25.9.5 Hierarchical ListBox
.............................

 -- Class: tkinter.tix.HList

     The HList(1) widget can be used to display any data that have a
     hierarchical structure, for example, file system directory trees.
     The list entries are indented and connected by branch lines
     according to their places in the hierarchy.

 -- Class: tkinter.tix.CheckList

     The CheckList(2) widget displays a list of items to be selected by
     the user.  CheckList acts similarly to the Tk checkbutton or
     radiobutton widgets, except it is capable of handling many more
     items than checkbuttons or radiobuttons.

 -- Class: tkinter.tix.Tree

     The Tree(3) widget can be used to display hierarchical data in a
     tree form.  The user can adjust the view of the tree by opening or
     closing parts of the tree.

   ---------- Footnotes ----------

   (1) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixHList.htm

   (2) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixCheckList.htm

   (3) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixTree.htm


File: python.info,  Node: Tabular ListBox,  Next: Manager Widgets,  Prev: Hierarchical ListBox,  Up: Tix Widgets

5.25.9.6 Tabular ListBox
........................

 -- Class: tkinter.tix.TList

     The TList(1) widget can be used to display data in a tabular
     format.  The list entries of a *note TList: 33b2. widget are
     similar to the entries in the Tk listbox widget.  The main
     differences are (1) the *note TList: 33b2. widget can display the
     list entries in a two dimensional format and (2) you can use
     graphical images as well as multiple colors and fonts for the list
     entries.

   ---------- Footnotes ----------

   (1) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixTList.htm


File: python.info,  Node: Manager Widgets,  Next: Image Types,  Prev: Tabular ListBox,  Up: Tix Widgets

5.25.9.7 Manager Widgets
........................

 -- Class: tkinter.tix.PanedWindow

     The PanedWindow(1) widget allows the user to interactively
     manipulate the sizes of several panes.  The panes can be arranged
     either vertically or horizontally.  The user changes the sizes of
     the panes by dragging the resize handle between two panes.

 -- Class: tkinter.tix.ListNoteBook

     The ListNoteBook(2) widget is very similar to the ‘TixNoteBook’
     widget: it can be used to display many windows in a limited space
     using a notebook metaphor.  The notebook is divided into a stack of
     pages (windows).  At one time only one of these pages can be shown.
     The user can navigate through these pages by choosing the name of
     the desired page in the ‘hlist’ subwidget.

 -- Class: tkinter.tix.NoteBook

     The NoteBook(3) widget can be used to display many windows in a
     limited space using a notebook metaphor.  The notebook is divided
     into a stack of pages.  At one time only one of these pages can be
     shown.  The user can navigate through these pages by choosing the
     visual “tabs” at the top of the NoteBook widget.

   ---------- Footnotes ----------

   (1) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixPanedWindow.htm

   (2) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixListNoteBook.htm

   (3) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixNoteBook.htm


File: python.info,  Node: Image Types,  Next: Miscellaneous Widgets,  Prev: Manager Widgets,  Up: Tix Widgets

5.25.9.8 Image Types
....................

The *note tkinter.tix: 117. module adds:

   * pixmap(1) capabilities to all *note tkinter.tix: 117. and *note
     tkinter: 10e. widgets to create color images from XPM files.

   * Compound(2) image types can be used to create images that consists
     of multiple horizontal lines; each line is composed of a series of
     items (texts, bitmaps, images or spaces) arranged from left to
     right.  For example, a compound image can be used to display a
     bitmap and a text string simultaneously in a Tk ‘Button’ widget.

   ---------- Footnotes ----------

   (1) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/pixmap.htm

   (2) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/compound.htm


File: python.info,  Node: Miscellaneous Widgets,  Next: Form Geometry Manager,  Prev: Image Types,  Up: Tix Widgets

5.25.9.9 Miscellaneous Widgets
..............................

 -- Class: tkinter.tix.InputOnly

     The InputOnly(1) widgets are to accept inputs from the user, which
     can be done with the ‘bind’ command (Unix only).

   ---------- Footnotes ----------

   (1) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixInputOnly.htm


File: python.info,  Node: Form Geometry Manager,  Prev: Miscellaneous Widgets,  Up: Tix Widgets

5.25.9.10 Form Geometry Manager
...............................

In addition, *note tkinter.tix: 117. augments *note tkinter: 10e. by
providing:

 -- Class: tkinter.tix.Form

     The Form(1) geometry manager based on attachment rules for all Tk
     widgets.

   ---------- Footnotes ----------

   (1) 
http://tix.sourceforge.net/dist/current/man/html/TixCmd/tixForm.htm


File: python.info,  Node: Tix Commands,  Prev: Tix Widgets,  Up: tkinter tix — Extension widgets for Tk

5.25.9.11 Tix Commands
......................

 -- Class: tkinter.tix.tixCommand

     The tix commands(1) provide access to miscellaneous elements of
     ‘Tix’’s internal state and the ‘Tix’ application context.  Most of
     the information manipulated by these methods pertains to the
     application as a whole, or to a screen or display, rather than to a
     particular window.

     To view the current settings, the common usage is:

          from tkinter import tix
          root = tix.Tk()
          print(root.tix_configure())

 -- Method: tixCommand.tix_configure (cnf=None, **kw)

     Query or modify the configuration options of the Tix application
     context.  If no option is specified, returns a dictionary all of
     the available options.  If option is specified with no value, then
     the method returns a list describing the one named option (this
     list will be identical to the corresponding sublist of the value
     returned if no option is specified).  If one or more option-value
     pairs are specified, then the method modifies the given option(s)
     to have the given value(s); in this case the method returns an
     empty string.  Option may be any of the configuration options.

 -- Method: tixCommand.tix_cget (option)

     Returns the current value of the configuration option given by
     `option'.  Option may be any of the configuration options.

 -- Method: tixCommand.tix_getbitmap (name)

     Locates a bitmap file of the name ‘name.xpm’ or ‘name’ in one of
     the bitmap directories (see the *note tix_addbitmapdir(): 33bf.
     method).  By using *note tix_getbitmap(): 33be, you can avoid hard
     coding the pathnames of the bitmap files in your application.  When
     successful, it returns the complete pathname of the bitmap file,
     prefixed with the character ‘@’.  The returned value can be used to
     configure the ‘bitmap’ option of the Tk and Tix widgets.

 -- Method: tixCommand.tix_addbitmapdir (directory)

     Tix maintains a list of directories under which the *note
     tix_getimage(): 33c0. and *note tix_getbitmap(): 33be. methods will
     search for image files.  The standard bitmap directory is
     ‘$TIX_LIBRARY/bitmaps’.  The *note tix_addbitmapdir(): 33bf. method
     adds `directory' into this list.  By using this method, the image
     files of an applications can also be located using the *note
     tix_getimage(): 33c0. or *note tix_getbitmap(): 33be. method.

 -- Method: tixCommand.tix_filedialog ([dlgclass])

     Returns the file selection dialog that may be shared among
     different calls from this application.  This method will create a
     file selection dialog widget when it is called the first time.
     This dialog will be returned by all subsequent calls to *note
     tix_filedialog(): 33c1.  An optional dlgclass parameter can be
     passed as a string to specified what type of file selection dialog
     widget is desired.  Possible options are ‘tix’, ‘FileSelectDialog’
     or ‘tixExFileSelectDialog’.

 -- Method: tixCommand.tix_getimage (self, name)

     Locates an image file of the name ‘name.xpm’, ‘name.xbm’ or
     ‘name.ppm’ in one of the bitmap directories (see the *note
     tix_addbitmapdir(): 33bf. method above).  If more than one file
     with the same name (but different extensions) exist, then the image
     type is chosen according to the depth of the X display: xbm images
     are chosen on monochrome displays and color images are chosen on
     color displays.  By using *note tix_getimage(): 33c0, you can avoid
     hard coding the pathnames of the image files in your application.
     When successful, this method returns the name of the newly created
     image, which can be used to configure the ‘image’ option of the Tk
     and Tix widgets.

 -- Method: tixCommand.tix_option_get (name)

     Gets the options maintained by the Tix scheme mechanism.

 -- Method: tixCommand.tix_resetoptions (newScheme, newFontSet[,
          newScmPrio])

     Resets the scheme and fontset of the Tix application to `newScheme'
     and `newFontSet', respectively.  This affects only those widgets
     created after this call.  Therefore, it is best to call the
     resetoptions method before the creation of any widgets in a Tix
     application.

     The optional parameter `newScmPrio' can be given to reset the
     priority level of the Tk options set by the Tix schemes.

     Because of the way Tk handles the X option database, after Tix has
     been has imported and inited, it is not possible to reset the color
     schemes and font sets using the ‘tix_config()’ method.  Instead,
     the *note tix_resetoptions(): 33c3. method must be used.

   ---------- Footnotes ----------

   (1) http://tix.sourceforge.net/dist/current/man/html/TixCmd/tix.htm


File: python.info,  Node: IDLE<51>,  Prev: tkinter tix — Extension widgets for Tk,  Up: Graphical User Interfaces with Tk

5.25.10 IDLE
------------

`Source code:' Lib/idlelib/(1)

__________________________________________________________________

IDLE is Python’s Integrated Development and Learning Environment.

IDLE has the following features:

   * coded in 100% pure Python, using the *note tkinter: 10e. GUI
     toolkit

   * cross-platform: works mostly the same on Windows, Unix, and macOS

   * Python shell window (interactive interpreter) with colorizing of
     code input, output, and error messages

   * multi-window text editor with multiple undo, Python colorizing,
     smart indent, call tips, auto completion, and other features

   * search within any window, replace within editor windows, and search
     through multiple files (grep)

   * debugger with persistent breakpoints, stepping, and viewing of
     global and local namespaces

   * configuration, browsers, and other dialogs

* Menu:

* Menus::
* Editing and navigation::
* Startup and code execution::
* Help and preferences::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/idlelib/


File: python.info,  Node: Menus,  Next: Editing and navigation,  Up: IDLE<51>

5.25.10.1 Menus
...............

IDLE has two main window types, the Shell window and the Editor window.
It is possible to have multiple editor windows simultaneously.  On
Windows and Linux, each has its own top menu.  Each menu documented
below indicates which window type it is associated with.

Output windows, such as used for Edit => Find in Files, are a subtype of
editor window.  They currently have the same top menu but a different
default title and context menu.

On macOS, there is one application menu.  It dynamically changes
according to the window currently selected.  It has an IDLE menu, and
some entries described below are moved around to conform to Apple
guidelines.

* Menu:

* File menu (Shell and Editor): File menu Shell and Editor.
* Edit menu (Shell and Editor): Edit menu Shell and Editor.
* Format menu (Editor window only): Format menu Editor window only.
* Run menu (Editor window only): Run menu Editor window only.
* Shell menu (Shell window only): Shell menu Shell window only.
* Debug menu (Shell window only): Debug menu Shell window only.
* Options menu (Shell and Editor): Options menu Shell and Editor.
* Window menu (Shell and Editor): Window menu Shell and Editor.
* Help menu (Shell and Editor): Help menu Shell and Editor.
* Context Menus::


File: python.info,  Node: File menu Shell and Editor,  Next: Edit menu Shell and Editor,  Up: Menus

5.25.10.2 File menu (Shell and Editor)
......................................

New File

     Create a new file editing window.

Open…

     Open an existing file with an Open dialog.

Recent Files

     Open a list of recent files.  Click one to open it.

Open Module…

     Open an existing module (searches sys.path).

Class Browser

     Show functions, classes, and methods in the current Editor file in
     a tree structure.  In the shell, open a module first.

Path Browser

     Show sys.path directories, modules, functions, classes and methods
     in a tree structure.

Save

     Save the current window to the associated file, if there is one.
     Windows that have been changed since being opened or last saved
     have a * before and after the window title.  If there is no
     associated file, do Save As instead.

Save As…

     Save the current window with a Save As dialog.  The file saved
     becomes the new associated file for the window.

Save Copy As…

     Save the current window to different file without changing the
     associated file.

Print Window

     Print the current window to the default printer.

Close

     Close the current window (ask to save if unsaved).

Exit

     Close all windows and quit IDLE (ask to save unsaved windows).


File: python.info,  Node: Edit menu Shell and Editor,  Next: Format menu Editor window only,  Prev: File menu Shell and Editor,  Up: Menus

5.25.10.3 Edit menu (Shell and Editor)
......................................

Undo

     Undo the last change to the current window.  A maximum of 1000
     changes may be undone.

Redo

     Redo the last undone change to the current window.

Cut

     Copy selection into the system-wide clipboard; then delete the
     selection.

Copy

     Copy selection into the system-wide clipboard.

Paste

     Insert contents of the system-wide clipboard into the current
     window.

The clipboard functions are also available in context menus.

Select All

     Select the entire contents of the current window.

Find…

     Open a search dialog with many options

Find Again

     Repeat the last search, if there is one.

Find Selection

     Search for the currently selected string, if there is one.

Find in Files…

     Open a file search dialog.  Put results in a new output window.

Replace…

     Open a search-and-replace dialog.

Go to Line

     Move the cursor to the beginning of the line requested and make
     that line visible.  A request past the end of the file goes to the
     end.  Clear any selection and update the line and column status.

Show Completions

     Open a scrollable list allowing selection of existing names.  See
     *note Completions: 33c9. in the Editing and navigation section
     below.

Expand Word

     Expand a prefix you have typed to match a full word in the same
     window; repeat to get a different expansion.

Show call tip

     After an unclosed parenthesis for a function, open a small window
     with function parameter hints.  See *note Calltips: 33ca. in the
     Editing and navigation section below.

Show surrounding parens

     Highlight the surrounding parenthesis.


File: python.info,  Node: Format menu Editor window only,  Next: Run menu Editor window only,  Prev: Edit menu Shell and Editor,  Up: Menus

5.25.10.4 Format menu (Editor window only)
..........................................

Indent Region

     Shift selected lines right by the indent width (default 4 spaces).

Dedent Region

     Shift selected lines left by the indent width (default 4 spaces).

Comment Out Region

     Insert ## in front of selected lines.

Uncomment Region

     Remove leading # or ## from selected lines.

Tabify Region

     Turn `leading' stretches of spaces into tabs.  (Note: We recommend
     using 4 space blocks to indent Python code.)

Untabify Region

     Turn `all' tabs into the correct number of spaces.

Toggle Tabs

     Open a dialog to switch between indenting with spaces and tabs.

New Indent Width

     Open a dialog to change indent width.  The accepted default by the
     Python community is 4 spaces.

Format Paragraph

     Reformat the current blank-line-delimited paragraph in comment
     block or multiline string or selected line in a string.  All lines
     in the paragraph will be formatted to less than N columns, where N
     defaults to 72.

Strip trailing whitespace

     Remove trailing space and other whitespace characters after the
     last non-whitespace character of a line by applying str.rstrip to
     each line, including lines within multiline strings.  Except for
     Shell windows, remove extra newlines at the end of the file.


File: python.info,  Node: Run menu Editor window only,  Next: Shell menu Shell window only,  Prev: Format menu Editor window only,  Up: Menus

5.25.10.5 Run menu (Editor window only)
.......................................

Run Module

     Do *note Check Module: 33cf.  If no error, restart the shell to
     clean the environment, then execute the module.  Output is
     displayed in the Shell window.  Note that output requires use of
     ‘print’ or ‘write’.  When execution is complete, the Shell retains
     focus and displays a prompt.  At this point, one may interactively
     explore the result of execution.  This is similar to executing a
     file with ‘python -i file’ at a command line.

Run… Customized

     Same as *note Run Module: 33ce, but run the module with customized
     settings.  `Command Line Arguments' extend *note sys.argv: cc6. as
     if passed on a command line.  The module can be run in the Shell
     without restarting.

Check Module

     Check the syntax of the module currently open in the Editor window.
     If the module has not been saved IDLE will either prompt the user
     to save or autosave, as selected in the General tab of the Idle
     Settings dialog.  If there is a syntax error, the approximate
     location is indicated in the Editor window.

Python Shell

     Open or wake up the Python Shell window.


File: python.info,  Node: Shell menu Shell window only,  Next: Debug menu Shell window only,  Prev: Run menu Editor window only,  Up: Menus

5.25.10.6 Shell menu (Shell window only)
........................................

View Last Restart

     Scroll the shell window to the last Shell restart.

Restart Shell

     Restart the shell to clean the environment and reset display and
     exception handling.

Previous History

     Cycle through earlier commands in history which match the current
     entry.

Next History

     Cycle through later commands in history which match the current
     entry.

Interrupt Execution

     Stop a running program.


File: python.info,  Node: Debug menu Shell window only,  Next: Options menu Shell and Editor,  Prev: Shell menu Shell window only,  Up: Menus

5.25.10.7 Debug menu (Shell window only)
........................................

Go to File/Line

     Look on the current line.  with the cursor, and the line above for
     a filename and line number.  If found, open the file if not already
     open, and show the line.  Use this to view source lines referenced
     in an exception traceback and lines found by Find in Files.  Also
     available in the context menu of the Shell window and Output
     windows.

Debugger (toggle)

     When activated, code entered in the Shell or run from an Editor
     will run under the debugger.  In the Editor, breakpoints can be set
     with the context menu.  This feature is still incomplete and
     somewhat experimental.

Stack Viewer

     Show the stack traceback of the last exception in a tree widget,
     with access to locals and globals.

Auto-open Stack Viewer

     Toggle automatically opening the stack viewer on an unhandled
     exception.


File: python.info,  Node: Options menu Shell and Editor,  Next: Window menu Shell and Editor,  Prev: Debug menu Shell window only,  Up: Menus

5.25.10.8 Options menu (Shell and Editor)
.........................................

Configure IDLE

     Open a configuration dialog and change preferences for the
     following: fonts, indentation, keybindings, text color themes,
     startup windows and size, additional help sources, and extensions.
     On macOS, open the configuration dialog by selecting Preferences in
     the application menu.  For more details, see *note Setting
     preferences: 33d5. under Help and preferences.

Most configuration options apply to all windows or all future windows.
The option items below only apply to the active window.

Show/Hide Code Context (Editor Window only)

     Open a pane at the top of the edit window which shows the block
     context of the code which has scrolled above the top of the window.
     See *note Code Context: 33d6. in the Editing and Navigation section
     below.

Show/Hide Line Numbers (Editor Window only)

     Open a column to the left of the edit window which shows the number
     of each line of text.  The default is off, which may be changed in
     the preferences (see *note Setting preferences: 33d5.).

Zoom/Restore Height

     Toggles the window between normal size and maximum height.  The
     initial size defaults to 40 lines by 80 chars unless changed on the
     General tab of the Configure IDLE dialog.  The maximum height for a
     screen is determined by momentarily maximizing a window the first
     time one is zoomed on the screen.  Changing screen settings may
     invalidate the saved height.  This toggle has no effect when a
     window is maximized.


File: python.info,  Node: Window menu Shell and Editor,  Next: Help menu Shell and Editor,  Prev: Options menu Shell and Editor,  Up: Menus

5.25.10.9 Window menu (Shell and Editor)
........................................

Lists the names of all open windows; select one to bring it to the
foreground (deiconifying it if necessary).


File: python.info,  Node: Help menu Shell and Editor,  Next: Context Menus,  Prev: Window menu Shell and Editor,  Up: Menus

5.25.10.10 Help menu (Shell and Editor)
.......................................

About IDLE

     Display version, copyright, license, credits, and more.

IDLE Help

     Display this IDLE document, detailing the menu options, basic
     editing and navigation, and other tips.

Python Docs

     Access local Python documentation, if installed, or start a web
     browser and open docs.python.org showing the latest Python
     documentation.

Turtle Demo

     Run the turtledemo module with example Python code and turtle
     drawings.

Additional help sources may be added here with the Configure IDLE dialog
under the General tab.  See the *note Help sources: 33d9. subsection
below for more on Help menu choices.


File: python.info,  Node: Context Menus,  Prev: Help menu Shell and Editor,  Up: Menus

5.25.10.11 Context Menus
........................

Open a context menu by right-clicking in a window (Control-click on
macOS). Context menus have the standard clipboard functions also on the
Edit menu.

Cut

     Copy selection into the system-wide clipboard; then delete the
     selection.

Copy

     Copy selection into the system-wide clipboard.

Paste

     Insert contents of the system-wide clipboard into the current
     window.

Editor windows also have breakpoint functions.  Lines with a breakpoint
set are specially marked.  Breakpoints only have an effect when running
under the debugger.  Breakpoints for a file are saved in the user’s
‘.idlerc’ directory.

Set Breakpoint

     Set a breakpoint on the current line.

Clear Breakpoint

     Clear the breakpoint on that line.

Shell and Output windows also have the following.

Go to file/line

     Same as in Debug menu.

The Shell window also has an output squeezing facility explained in the
`Python Shell window' subsection below.

Squeeze

     If the cursor is over an output line, squeeze all the output
     between the code above and the prompt below down to a ‘Squeezed
     text’ label.


File: python.info,  Node: Editing and navigation,  Next: Startup and code execution,  Prev: Menus,  Up: IDLE<51>

5.25.10.12 Editing and navigation
.................................

* Menu:

* Editor windows::
* Key bindings::
* Automatic indentation::
* Completions::
* Calltips::
* Code Context::
* Python Shell window::
* Text colors::


File: python.info,  Node: Editor windows,  Next: Key bindings,  Up: Editing and navigation

5.25.10.13 Editor windows
.........................

IDLE may open editor windows when it starts, depending on settings and
how you start IDLE. Thereafter, use the File menu.  There can be only
one open editor window for a given file.

The title bar contains the name of the file, the full path, and the
version of Python and IDLE running the window.  The status bar contains
the line number (‘Ln’) and column number (‘Col’).  Line numbers start
with 1; column numbers with 0.

IDLE assumes that files with a known .py* extension contain Python code
and that other files do not.  Run Python code with the Run menu.


File: python.info,  Node: Key bindings,  Next: Automatic indentation,  Prev: Editor windows,  Up: Editing and navigation

5.25.10.14 Key bindings
.......................

In this section, ‘C’ refers to the ‘Control’ key on Windows and Unix and
the ‘Command’ key on macOS.

   * ‘Backspace’ deletes to the left; ‘Del’ deletes to the right

   * ‘C-Backspace’ delete word left; ‘C-Del’ delete word to the right

   * Arrow keys and ‘Page Up’/‘Page Down’ to move around

   * ‘C-LeftArrow’ and ‘C-RightArrow’ moves by words

   * ‘Home’/‘End’ go to begin/end of line

   * ‘C-Home’/‘C-End’ go to begin/end of file

   * Some useful Emacs bindings are inherited from Tcl/Tk:

             * ‘C-a’ beginning of line

             * ‘C-e’ end of line

             * ‘C-k’ kill line (but doesn’t put it in clipboard)

             * ‘C-l’ center window around the insertion point

             * ‘C-b’ go backward one character without deleting (usually
               you can also use the cursor key for this)

             * ‘C-f’ go forward one character without deleting (usually
               you can also use the cursor key for this)

             * ‘C-p’ go up one line (usually you can also use the cursor
               key for this)

             * ‘C-d’ delete next character

Standard keybindings (like ‘C-c’ to copy and ‘C-v’ to paste) may work.
Keybindings are selected in the Configure IDLE dialog.


File: python.info,  Node: Automatic indentation,  Next: Completions,  Prev: Key bindings,  Up: Editing and navigation

5.25.10.15 Automatic indentation
................................

After a block-opening statement, the next line is indented by 4 spaces
(in the Python Shell window by one tab).  After certain keywords (break,
return etc.)  the next line is dedented.  In leading indentation,
‘Backspace’ deletes up to 4 spaces if they are there.  ‘Tab’ inserts
spaces (in the Python Shell window one tab), number depends on Indent
width.  Currently, tabs are restricted to four spaces due to Tcl/Tk
limitations.

See also the indent/dedent region commands on the *note Format menu:
33cb.


File: python.info,  Node: Completions,  Next: Calltips,  Prev: Automatic indentation,  Up: Editing and navigation

5.25.10.16 Completions
......................

Completions are supplied, when requested and available, for module
names, attributes of classes or functions, or filenames.  Each request
method displays a completion box with existing names.  (See tab
completions below for an exception.)  For any box, change the name being
completed and the item highlighted in the box by typing and deleting
characters; by hitting ‘Up’, ‘Down’, ‘PageUp’, ‘PageDown’, ‘Home’, and
‘End’ keys; and by a single click within the box.  Close the box with
‘Escape’, ‘Enter’, and double ‘Tab’ keys or clicks outside the box.  A
double click within the box selects and closes.

One way to open a box is to type a key character and wait for a
predefined interval.  This defaults to 2 seconds; customize it in the
settings dialog.  (To prevent auto popups, set the delay to a large
number of milliseconds, such as 100000000.)  For imported module names
or class or function attributes, type ‘.’.  For filenames in the root
directory, type *note os.sep: 1dd4. or *note os.altsep: 1dd5.
immediately after an opening quote.  (On Windows, one can specify a
drive first.)  Move into subdirectories by typing a directory name and a
separator.

Instead of waiting, or after a box is closed, open a completion box
immediately with Show Completions on the Edit menu.  The default hot key
is ‘C-space’.  If one types a prefix for the desired name before opening
the box, the first match or near miss is made visible.  The result is
the same as if one enters a prefix after the box is displayed.  Show
Completions after a quote completes filenames in the current directory
instead of a root directory.

Hitting ‘Tab’ after a prefix usually has the same effect as Show
Completions.  (With no prefix, it indents.)  However, if there is only
one match to the prefix, that match is immediately added to the editor
text without opening a box.

Invoking ‘Show Completions’, or hitting ‘Tab’ after a prefix, outside of
a string and without a preceding ‘.’ opens a box with keywords, builtin
names, and available module-level names.

When editing code in an editor (as oppose to Shell), increase the
available module-level names by running your code and not restarting the
Shell thereafter.  This is especially useful after adding imports at the
top of a file.  This also increases possible attribute completions.

Completion boxes initially exclude names beginning with ‘_’ or, for
modules, not included in ‘__all__’.  The hidden names can be accessed by
typing ‘_’ after ‘.’, either before or after the box is opened.


File: python.info,  Node: Calltips,  Next: Code Context,  Prev: Completions,  Up: Editing and navigation

5.25.10.17 Calltips
...................

A calltip is shown automatically when one types ‘(’ after the name of an
`accessible' function.  A function name expression may include dots and
subscripts.  A calltip remains until it is clicked, the cursor is moved
out of the argument area, or ‘)’ is typed.  Whenever the cursor is in
the argument part of a definition, select Edit and “Show Call Tip” on
the menu or enter its shortcut to display a calltip.

The calltip consists of the function’s signature and docstring up to the
latter’s first blank line or the fifth non-blank line.  (Some builtin
functions lack an accessible signature.)  A ‘/’ or ‘*’ in the signature
indicates that the preceding or following arguments are passed by
position or name (keyword) only.  Details are subject to change.

In Shell, the accessible functions depends on what modules have been
imported into the user process, including those imported by Idle itself,
and which definitions have been run, all since the last restart.

For example, restart the Shell and enter ‘itertools.count(’.  A calltip
appears because Idle imports itertools into the user process for its own
use.  (This could change.)  Enter ‘turtle.write(’ and nothing appears.
Idle does not itself import turtle.  The menu entry and shortcut also do
nothing.  Enter ‘import turtle’.  Thereafter, ‘turtle.write(’ will
display a calltip.

In an editor, import statements have no effect until one runs the file.
One might want to run a file after writing import statements, after
adding function definitions, or after opening an existing file.


File: python.info,  Node: Code Context,  Next: Python Shell window,  Prev: Calltips,  Up: Editing and navigation

5.25.10.18 Code Context
.......................

Within an editor window containing Python code, code context can be
toggled in order to show or hide a pane at the top of the window.  When
shown, this pane freezes the opening lines for block code, such as those
beginning with ‘class’, ‘def’, or ‘if’ keywords, that would have
otherwise scrolled out of view.  The size of the pane will be expanded
and contracted as needed to show the all current levels of context, up
to the maximum number of lines defined in the Configure IDLE dialog
(which defaults to 15).  If there are no current context lines and the
feature is toggled on, a single blank line will display.  Clicking on a
line in the context pane will move that line to the top of the editor.

The text and background colors for the context pane can be configured
under the Highlights tab in the Configure IDLE dialog.


File: python.info,  Node: Python Shell window,  Next: Text colors,  Prev: Code Context,  Up: Editing and navigation

5.25.10.19 Python Shell window
..............................

With IDLE’s Shell, one enters, edits, and recalls complete statements.
Most consoles and terminals only work with a single physical line at a
time.

When one pastes code into Shell, it is not compiled and possibly
executed until one hits ‘Return’.  One may edit pasted code first.  If
one pastes more that one statement into Shell, the result will be a
*note SyntaxError: 55a. when multiple statements are compiled as if they
were one.

The editing features described in previous subsections work when
entering code interactively.  IDLE’s Shell window also responds to the
following keys.

   * ‘C-c’ interrupts executing command

   * ‘C-d’ sends end-of-file; closes window if typed at a ‘>>>’ prompt

   * ‘Alt-/’ (Expand word) is also useful to reduce typing

     Command history

        * ‘Alt-p’ retrieves previous command matching what you have
          typed.  On macOS use ‘C-p’.

        * ‘Alt-n’ retrieves next.  On macOS use ‘C-n’.

        * ‘Return’ while on any previous command retrieves that command


File: python.info,  Node: Text colors,  Prev: Python Shell window,  Up: Editing and navigation

5.25.10.20 Text colors
......................

Idle defaults to black on white text, but colors text with special
meanings.  For the shell, these are shell output, shell error, user
output, and user error.  For Python code, at the shell prompt or in an
editor, these are keywords, builtin class and function names, names
following ‘class’ and ‘def’, strings, and comments.  For any text
window, these are the cursor (when present), found text (when possible),
and selected text.

Text coloring is done in the background, so uncolorized text is
occasionally visible.  To change the color scheme, use the Configure
IDLE dialog Highlighting tab.  The marking of debugger breakpoint lines
in the editor and text in popups and dialogs is not user-configurable.


File: python.info,  Node: Startup and code execution,  Next: Help and preferences,  Prev: Editing and navigation,  Up: IDLE<51>

5.25.10.21 Startup and code execution
.....................................

Upon startup with the ‘-s’ option, IDLE will execute the file referenced
by the environment variables ‘IDLESTARTUP’ or *note PYTHONSTARTUP: 9cb.
IDLE first checks for ‘IDLESTARTUP’; if ‘IDLESTARTUP’ is present the
file referenced is run.  If ‘IDLESTARTUP’ is not present, IDLE checks
for ‘PYTHONSTARTUP’.  Files referenced by these environment variables
are convenient places to store functions that are used frequently from
the IDLE shell, or for executing import statements to import common
modules.

In addition, ‘Tk’ also loads a startup file if it is present.  Note that
the Tk file is loaded unconditionally.  This additional file is
‘.Idle.py’ and is looked for in the user’s home directory.  Statements
in this file will be executed in the Tk namespace, so this file is not
useful for importing functions to be used from IDLE’s Python shell.

* Menu:

* Command line usage::
* Startup failure::
* Running user code::
* User output in Shell::
* Developing tkinter applications::
* Running without a subprocess::


File: python.info,  Node: Command line usage,  Next: Startup failure,  Up: Startup and code execution

5.25.10.22 Command line usage
.............................

     idle.py [-c command] [-d] [-e] [-h] [-i] [-r file] [-s] [-t title] [-] [arg] ...

     -c command  run command in the shell window
     -d          enable debugger and open shell window
     -e          open editor window
     -h          print help message with legal combinations and exit
     -i          open shell window
     -r file     run file in shell window
     -s          run $IDLESTARTUP or $PYTHONSTARTUP first, in shell window
     -t title    set title of shell window
     -           run stdin in shell (- must be last option before args)

If there are arguments:

   * If ‘-’, ‘-c’, or ‘r’ is used, all arguments are placed in
     ‘sys.argv[1:...]’ and ‘sys.argv[0]’ is set to ‘''’, ‘'-c'’, or
     ‘'-r'’.  No editor window is opened, even if that is the default
     set in the Options dialog.

   * Otherwise, arguments are files opened for editing and ‘sys.argv’
     reflects the arguments passed to IDLE itself.


File: python.info,  Node: Startup failure,  Next: Running user code,  Prev: Command line usage,  Up: Startup and code execution

5.25.10.23 Startup failure
..........................

IDLE uses a socket to communicate between the IDLE GUI process and the
user code execution process.  A connection must be established whenever
the Shell starts or restarts.  (The latter is indicated by a divider
line that says ‘RESTART’).  If the user process fails to connect to the
GUI process, it usually displays a ‘Tk’ error box with a ‘cannot
connect’ message that directs the user here.  It then exits.

One specific connection failure on Unix systems results from
misconfigured masquerading rules somewhere in a system’s network setup.
When IDLE is started from a terminal, one will see a message starting
with ‘** Invalid host:’.  The valid value is ‘127.0.0.1
(idlelib.rpc.LOCALHOST)’.  One can diagnose with ‘tcpconnect -irv
127.0.0.1 6543’ in one terminal window and ‘tcplisten <same args>’ in
another.

A common cause of failure is a user-written file with the same name as a
standard library module, such as `random.py' and `tkinter.py'.  When
such a file is located in the same directory as a file that is about to
be run, IDLE cannot import the stdlib file.  The current fix is to
rename the user file.

Though less common than in the past, an antivirus or firewall program
may stop the connection.  If the program cannot be taught to allow the
connection, then it must be turned off for IDLE to work.  It is safe to
allow this internal connection because no data is visible on external
ports.  A similar problem is a network mis-configuration that blocks
connections.

Python installation issues occasionally stop IDLE: multiple versions can
clash, or a single installation might need admin access.  If one undo
the clash, or cannot or does not want to run as admin, it might be
easiest to completely remove Python and start over.

A zombie pythonw.exe process could be a problem.  On Windows, use Task
Manager to check for one and stop it if there is.  Sometimes a restart
initiated by a program crash or Keyboard Interrupt (control-C) may fail
to connect.  Dismissing the error box or using Restart Shell on the
Shell menu may fix a temporary problem.

When IDLE first starts, it attempts to read user configuration files in
‘~/.idlerc/’ (~ is one’s home directory).  If there is a problem, an
error message should be displayed.  Leaving aside random disk glitches,
this can be prevented by never editing the files by hand.  Instead, use
the configuration dialog, under Options.  Once there is an error in a
user configuration file, the best solution may be to delete it and start
over with the settings dialog.

If IDLE quits with no message, and it was not started from a console,
try starting it from a console or terminal (‘python -m idlelib’) and see
if this results in an error message.

On Unix-based systems with tcl/tk older than ‘8.6.11’ (see ‘About IDLE’)
certain characters of certain fonts can cause a tk failure with a
message to the terminal.  This can happen either if one starts IDLE to
edit a file with such a character or later when entering such a
character.  If one cannot upgrade tcl/tk, then re-configure IDLE to use
a font that works better.


File: python.info,  Node: Running user code,  Next: User output in Shell,  Prev: Startup failure,  Up: Startup and code execution

5.25.10.24 Running user code
............................

With rare exceptions, the result of executing Python code with IDLE is
intended to be the same as executing the same code by the default
method, directly with Python in a text-mode system console or terminal
window.  However, the different interface and operation occasionally
affect visible results.  For instance, ‘sys.modules’ starts with more
entries, and ‘threading.active_count()’ returns 2 instead of 1.

By default, IDLE runs user code in a separate OS process rather than in
the user interface process that runs the shell and editor.  In the
execution process, it replaces ‘sys.stdin’, ‘sys.stdout’, and
‘sys.stderr’ with objects that get input from and send output to the
Shell window.  The original values stored in ‘sys.__stdin__’,
‘sys.__stdout__’, and ‘sys.__stderr__’ are not touched, but may be
‘None’.

Sending print output from one process to a text widget in another is
slower than printing to a system terminal in the same process.  This has
the most effect when printing multiple arguments, as the string for each
argument, each separator, the newline are sent separately.  For
development, this is usually not a problem, but if one wants to print
faster in IDLE, format and join together everything one wants displayed
together and then print a single string.  Both format strings and *note
str.join(): 1766. can help combine fields and lines.

IDLE’s standard stream replacements are not inherited by subprocesses
created in the execution process, whether directly by user code or by
modules such as multiprocessing.  If such subprocess use ‘input’ from
sys.stdin or ‘print’ or ‘write’ to sys.stdout or sys.stderr, IDLE should
be started in a command line window.  The secondary subprocess will then
be attached to that window for input and output.

If ‘sys’ is reset by user code, such as with ‘importlib.reload(sys)’,
IDLE’s changes are lost and input from the keyboard and output to the
screen will not work correctly.

When Shell has the focus, it controls the keyboard and screen.  This is
normally transparent, but functions that directly access the keyboard
and screen will not work.  These include system-specific functions that
determine whether a key has been pressed and if so, which.

The IDLE code running in the execution process adds frames to the call
stack that would not be there otherwise.  IDLE wraps
‘sys.getrecursionlimit’ and ‘sys.setrecursionlimit’ to reduce the effect
of the additional stack frames.

When user code raises SystemExit either directly or by calling sys.exit,
IDLE returns to a Shell prompt instead of exiting.


File: python.info,  Node: User output in Shell,  Next: Developing tkinter applications,  Prev: Running user code,  Up: Startup and code execution

5.25.10.25 User output in Shell
...............................

When a program outputs text, the result is determined by the
corresponding output device.  When IDLE executes user code, ‘sys.stdout’
and ‘sys.stderr’ are connected to the display area of IDLE’s Shell.
Some of its features are inherited from the underlying Tk Text widget.
Others are programmed additions.  Where it matters, Shell is designed
for development rather than production runs.

For instance, Shell never throws away output.  A program that sends
unlimited output to Shell will eventually fill memory, resulting in a
memory error.  In contrast, some system text windows only keep the last
n lines of output.  A Windows console, for instance, keeps a
user-settable 1 to 9999 lines, with 300 the default.

A Tk Text widget, and hence IDLE’s Shell, displays characters
(codepoints) in the BMP (Basic Multilingual Plane) subset of Unicode.
Which characters are displayed with a proper glyph and which with a
replacement box depends on the operating system and installed fonts.
Tab characters cause the following text to begin after the next tab
stop.  (They occur every 8 ‘characters’).  Newline characters cause
following text to appear on a new line.  Other control characters are
ignored or displayed as a space, box, or something else, depending on
the operating system and font.  (Moving the text cursor through such
output with arrow keys may exhibit some surprising spacing behavior.)

     >>> s = 'a\tb\a<\x02><\r>\bc\nd'  # Enter 22 chars.
     >>> len(s)
     14
     >>> s  # Display repr(s)
     'a\tb\x07<\x02><\r>\x08c\nd'
     >>> print(s, end='')  # Display s as is.
     # Result varies by OS and font.  Try it.

The ‘repr’ function is used for interactive echo of expression values.
It returns an altered version of the input string in which control
codes, some BMP codepoints, and all non-BMP codepoints are replaced with
escape codes.  As demonstrated above, it allows one to identify the
characters in a string, regardless of how they are displayed.

Normal and error output are generally kept separate (on separate lines)
from code input and each other.  They each get different highlight
colors.

For SyntaxError tracebacks, the normal ‘^’ marking where the error was
detected is replaced by coloring the text with an error highlight.  When
code run from a file causes other exceptions, one may right click on a
traceback line to jump to the corresponding line in an IDLE editor.  The
file will be opened if necessary.

Shell has a special facility for squeezing output lines down to a
‘Squeezed text’ label.  This is done automatically for output over N
lines (N = 50 by default).  N can be changed in the PyShell section of
the General page of the Settings dialog.  Output with fewer lines can be
squeezed by right clicking on the output.  This can be useful lines long
enough to slow down scrolling.

Squeezed output is expanded in place by double-clicking the label.  It
can also be sent to the clipboard or a separate view window by
right-clicking the label.


File: python.info,  Node: Developing tkinter applications,  Next: Running without a subprocess,  Prev: User output in Shell,  Up: Startup and code execution

5.25.10.26 Developing tkinter applications
..........................................

IDLE is intentionally different from standard Python in order to
facilitate development of tkinter programs.  Enter ‘import tkinter as
tk; root = tk.Tk()’ in standard Python and nothing appears.  Enter the
same in IDLE and a tk window appears.  In standard Python, one must also
enter ‘root.update()’ to see the window.  IDLE does the equivalent in
the background, about 20 times a second, which is about every 50
milliseconds.  Next enter ‘b = tk.Button(root, text='button');
b.pack()’.  Again, nothing visibly changes in standard Python until one
enters ‘root.update()’.

Most tkinter programs run ‘root.mainloop()’, which usually does not
return until the tk app is destroyed.  If the program is run with
‘python -i’ or from an IDLE editor, a ‘>>>’ shell prompt does not appear
until ‘mainloop()’ returns, at which time there is nothing left to
interact with.

When running a tkinter program from an IDLE editor, one can comment out
the mainloop call.  One then gets a shell prompt immediately and can
interact with the live application.  One just has to remember to
re-enable the mainloop call when running in standard Python.


File: python.info,  Node: Running without a subprocess,  Prev: Developing tkinter applications,  Up: Startup and code execution

5.25.10.27 Running without a subprocess
.......................................

By default, IDLE executes user code in a separate subprocess via a
socket, which uses the internal loopback interface.  This connection is
not externally visible and no data is sent to or received from the
Internet.  If firewall software complains anyway, you can ignore it.

If the attempt to make the socket connection fails, Idle will notify
you.  Such failures are sometimes transient, but if persistent, the
problem may be either a firewall blocking the connection or
misconfiguration of a particular system.  Until the problem is fixed,
one can run Idle with the -n command line switch.

If IDLE is started with the -n command line switch it will run in a
single process and will not create the subprocess which runs the RPC
Python execution server.  This can be useful if Python cannot create the
subprocess or the RPC socket interface on your platform.  However, in
this mode user code is not isolated from IDLE itself.  Also, the
environment is not restarted when Run/Run Module (F5) is selected.  If
your code has been modified, you must reload() the affected modules and
re-import any specific items (e.g.  from foo import baz) if the changes
are to take effect.  For these reasons, it is preferable to run IDLE
with the default subprocess if at all possible.

Deprecated since version 3.4.


File: python.info,  Node: Help and preferences,  Prev: Startup and code execution,  Up: IDLE<51>

5.25.10.28 Help and preferences
...............................

* Menu:

* Help sources::
* Setting preferences::
* IDLE on macOS::
* Extensions::


File: python.info,  Node: Help sources,  Next: Setting preferences,  Up: Help and preferences

5.25.10.29 Help sources
.......................

Help menu entry “IDLE Help” displays a formatted html version of the
IDLE chapter of the Library Reference.  The result, in a read-only
tkinter text window, is close to what one sees in a web browser.
Navigate through the text with a mousewheel, the scrollbar, or up and
down arrow keys held down.  Or click the TOC (Table of Contents) button
and select a section header in the opened box.

Help menu entry “Python Docs” opens the extensive sources of help,
including tutorials, available at ‘docs.python.org/x.y’, where ‘x.y’ is
the currently running Python version.  If your system has an off-line
copy of the docs (this may be an installation option), that will be
opened instead.

Selected URLs can be added or removed from the help menu at any time
using the General tab of the Configure IDLE dialog.


File: python.info,  Node: Setting preferences,  Next: IDLE on macOS,  Prev: Help sources,  Up: Help and preferences

5.25.10.30 Setting preferences
..............................

The font preferences, highlighting, keys, and general preferences can be
changed via Configure IDLE on the Option menu.  Non-default user
settings are saved in a ‘.idlerc’ directory in the user’s home
directory.  Problems caused by bad user configuration files are solved
by editing or deleting one or more of the files in ‘.idlerc’.

On the Font tab, see the text sample for the effect of font face and
size on multiple characters in multiple languages.  Edit the sample to
add other characters of personal interest.  Use the sample to select
monospaced fonts.  If particular characters have problems in Shell or an
editor, add them to the top of the sample and try changing first size
and then font.

On the Highlights and Keys tab, select a built-in or custom color theme
and key set.  To use a newer built-in color theme or key set with older
IDLEs, save it as a new custom theme or key set and it well be
accessible to older IDLEs.


File: python.info,  Node: IDLE on macOS,  Next: Extensions,  Prev: Setting preferences,  Up: Help and preferences

5.25.10.31 IDLE on macOS
........................

Under System Preferences: Dock, one can set “Prefer tabs when opening
documents” to “Always”.  This setting is not compatible with the
tk/tkinter GUI framework used by IDLE, and it breaks a few IDLE
features.


File: python.info,  Node: Extensions,  Prev: IDLE on macOS,  Up: Help and preferences

5.25.10.32 Extensions
.....................

IDLE contains an extension facility.  Preferences for extensions can be
changed with the Extensions tab of the preferences dialog.  See the
beginning of config-extensions.def in the idlelib directory for further
information.  The only current default extension is zzdummy, an example
also used for testing.


File: python.info,  Node: Development Tools,  Next: Debugging and Profiling,  Prev: Graphical User Interfaces with Tk,  Up: The Python Standard Library

5.26 Development Tools
======================

The modules described in this chapter help you write software.  For
example, the *note pydoc: d9. module takes a module and generates
documentation based on the module’s contents.  The *note doctest: 66.
and *note unittest: 124. modules contains frameworks for writing unit
tests that automatically exercise code and verify that the expected
output is produced.  ‘2to3’ can translate Python 2.x source code into
valid Python 3.x code.

The list of modules described in this chapter is:

* Menu:

* typing — Support for type hints::
* pydoc — Documentation generator and online help system::
* Python Development Mode::
* Effects of the Python Development Mode::
* ResourceWarning Example::
* Bad file descriptor error example::
* doctest — Test interactive Python examples::
* unittest — Unit testing framework::
* unittest.mock — mock object library: unittest mock — mock object library.
* unittest.mock — getting started: unittest mock — getting started.
* 2to3 - Automated Python 2 to 3 code translation::
* test — Regression tests package for Python::
* test.support — Utilities for the Python test suite: test support — Utilities for the Python test suite.
* test.support.socket_helper — Utilities for socket tests: test support socket_helper — Utilities for socket tests.
* test.support.script_helper — Utilities for the Python execution tests: test support script_helper — Utilities for the Python execution tests.
* test.support.bytecode_helper — Support tools for testing correct bytecode generation: test support bytecode_helper — Support tools for testing correct bytecode generation.


File: python.info,  Node: typing — Support for type hints,  Next: pydoc — Documentation generator and online help system,  Up: Development Tools

5.26.1 ‘typing’ — Support for type hints
----------------------------------------

New in version 3.5.

`Source code:' Lib/typing.py(1)

     Note: The Python runtime does not enforce function and variable
     type annotations.  They can be used by third party tools such as
     type checkers, IDEs, linters, etc.

__________________________________________________________________

This module provides runtime support for type hints.  The most
fundamental support consists of the types *note Any: 745, *note Union:
116a, *note Callable: 27b, *note TypeVar: 104e, and *note Generic: 100b.
For a full specification, please see PEP 484(2).  For a simplified
introduction to type hints, see PEP 483(3).

The function below takes and returns a string and is annotated as
follows:

     def greeting(name: str) -> str:
         return 'Hello ' + name

In the function ‘greeting’, the argument ‘name’ is expected to be of
type *note str: 205. and the return type *note str: 205.  Subtypes are
accepted as arguments.

* Menu:

* Relevant PEPs::
* Type aliases::
* NewType::
* Callable::
* Generics::
* User-defined generic types::
* The Any type::
* Nominal vs structural subtyping::
* Module contents: Module contents<3>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/typing.py

   (2) https://www.python.org/dev/peps/pep-0484

   (3) https://www.python.org/dev/peps/pep-0483


File: python.info,  Node: Relevant PEPs,  Next: Type aliases,  Up: typing — Support for type hints

5.26.1.1 Relevant PEPs
......................

Since the initial introduction of type hints in PEP 484(1) and PEP
483(2), a number of PEPs have modified and enhanced Python’s framework
for type annotations.  These include:

   * 
     PEP 526(3): Syntax for Variable Annotations

          `Introducing' syntax for annotating variables outside of
          function definitions, and *note ClassVar: 69a.

   * 
     PEP 544(4): Protocols: Structural subtyping (static duck typing)

          `Introducing' *note Protocol: 36a. and the *note
          @runtime_checkable: 36b. decorator

   * 
     PEP 585(5): Type Hinting Generics In Standard Collections

          `Introducing' *note types.GenericAlias: 27c. and the ability
          to use standard library classes as *note generic types: fe5.

   * 
     PEP 586(6): Literal Types

          `Introducing' *note Literal: 275.

   * 
     PEP 589(7): TypedDict: Type Hints for Dictionaries with a Fixed Set of Keys

          `Introducing' *note TypedDict: 367.

   * 
     PEP 591(8): Adding a final qualifier to typing

          `Introducing' *note Final: 368. and the *note @final: 369.
          decorator

   * 
     PEP 593(9): Flexible function and variable annotations

          `Introducing' *note Annotated: 1ee.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0484

   (2) https://www.python.org/dev/peps/pep-0483

   (3) https://www.python.org/dev/peps/pep-0526

   (4) https://www.python.org/dev/peps/pep-0544

   (5) https://www.python.org/dev/peps/pep-0585

   (6) https://www.python.org/dev/peps/pep-0586

   (7) https://www.python.org/dev/peps/pep-0589

   (8) https://www.python.org/dev/peps/pep-0591

   (9) https://www.python.org/dev/peps/pep-0593


File: python.info,  Node: Type aliases,  Next: NewType,  Prev: Relevant PEPs,  Up: typing — Support for type hints

5.26.1.2 Type aliases
.....................

A type alias is defined by assigning the type to the alias.  In this
example, ‘Vector’ and ‘list[float]’ will be treated as interchangeable
synonyms:

     Vector = list[float]

     def scale(scalar: float, vector: Vector) -> Vector:
         return [scalar * num for num in vector]

     # typechecks; a list of floats qualifies as a Vector.
     new_vector = scale(2.0, [1.0, -4.2, 5.4])

Type aliases are useful for simplifying complex type signatures.  For
example:

     from collections.abc import Sequence

     ConnectionOptions = dict[str, str]
     Address = tuple[str, int]
     Server = tuple[Address, ConnectionOptions]

     def broadcast_message(message: str, servers: Sequence[Server]) -> None:
         ...

     # The static type checker will treat the previous type signature as
     # being exactly equivalent to this one.
     def broadcast_message(
             message: str,
             servers: Sequence[tuple[tuple[str, int], dict[str, str]]]) -> None:
         ...

Note that ‘None’ as a type hint is a special case and is replaced by
‘type(None)’.


File: python.info,  Node: NewType,  Next: Callable,  Prev: Type aliases,  Up: typing — Support for type hints

5.26.1.3 NewType
................

Use the *note NewType(): 69c. helper function to create distinct types:

     from typing import NewType

     UserId = NewType('UserId', int)
     some_id = UserId(524313)

The static type checker will treat the new type as if it were a subclass
of the original type.  This is useful in helping catch logical errors:

     def get_user_name(user_id: UserId) -> str:
         ...

     # typechecks
     user_a = get_user_name(UserId(42351))

     # does not typecheck; an int is not a UserId
     user_b = get_user_name(-1)

You may still perform all ‘int’ operations on a variable of type
‘UserId’, but the result will always be of type ‘int’.  This lets you
pass in a ‘UserId’ wherever an ‘int’ might be expected, but will prevent
you from accidentally creating a ‘UserId’ in an invalid way:

     # 'output' is of type 'int', not 'UserId'
     output = UserId(23413) + UserId(54341)

Note that these checks are enforced only by the static type checker.  At
runtime, the statement ‘Derived = NewType('Derived', Base)’ will make
‘Derived’ a function that immediately returns whatever parameter you
pass it.  That means the expression ‘Derived(some_value)’ does not
create a new class or introduce any overhead beyond that of a regular
function call.

More precisely, the expression ‘some_value is Derived(some_value)’ is
always true at runtime.

This also means that it is not possible to create a subtype of ‘Derived’
since it is an identity function at runtime, not an actual type:

     from typing import NewType

     UserId = NewType('UserId', int)

     # Fails at runtime and does not typecheck
     class AdminUserId(UserId): pass

However, it is possible to create a *note NewType(): 69c. based on a
‘derived’ ‘NewType’:

     from typing import NewType

     UserId = NewType('UserId', int)

     ProUserId = NewType('ProUserId', UserId)

and typechecking for ‘ProUserId’ will work as expected.

See PEP 484(1) for more details.

     Note: Recall that the use of a type alias declares two types to be
     `equivalent' to one another.  Doing ‘Alias = Original’ will make
     the static type checker treat ‘Alias’ as being `exactly equivalent'
     to ‘Original’ in all cases.  This is useful when you want to
     simplify complex type signatures.

     In contrast, ‘NewType’ declares one type to be a `subtype' of
     another.  Doing ‘Derived = NewType('Derived', Original)’ will make
     the static type checker treat ‘Derived’ as a `subclass' of
     ‘Original’, which means a value of type ‘Original’ cannot be used
     in places where a value of type ‘Derived’ is expected.  This is
     useful when you want to prevent logic errors with minimal runtime
     cost.

New in version 3.5.2.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0484


File: python.info,  Node: Callable,  Next: Generics,  Prev: NewType,  Up: typing — Support for type hints

5.26.1.4 Callable
.................

Frameworks expecting callback functions of specific signatures might be
type hinted using ‘Callable[[Arg1Type, Arg2Type], ReturnType]’.

For example:

     from collections.abc import Callable

     def feeder(get_next_item: Callable[[], str]) -> None:
         # Body

     def async_query(on_success: Callable[[int], None],
                     on_error: Callable[[int, Exception], None]) -> None:
         # Body

It is possible to declare the return type of a callable without
specifying the call signature by substituting a literal ellipsis for the
list of arguments in the type hint: ‘Callable[..., ReturnType]’.


File: python.info,  Node: Generics,  Next: User-defined generic types,  Prev: Callable,  Up: typing — Support for type hints

5.26.1.5 Generics
.................

Since type information about objects kept in containers cannot be
statically inferred in a generic way, abstract base classes have been
extended to support subscription to denote expected types for container
elements.

     from collections.abc import Mapping, Sequence

     def notify_by_email(employees: Sequence[Employee],
                         overrides: Mapping[str, str]) -> None: ...

Generics can be parameterized by using a new factory available in typing
called *note TypeVar: 104e.

     from collections.abc import Sequence
     from typing import TypeVar

     T = TypeVar('T')      # Declare type variable

     def first(l: Sequence[T]) -> T:   # Generic function
         return l[0]


File: python.info,  Node: User-defined generic types,  Next: The Any type,  Prev: Generics,  Up: typing — Support for type hints

5.26.1.6 User-defined generic types
...................................

A user-defined class can be defined as a generic class.

     from typing import TypeVar, Generic
     from logging import Logger

     T = TypeVar('T')

     class LoggedVar(Generic[T]):
         def __init__(self, value: T, name: str, logger: Logger) -> None:
             self.name = name
             self.logger = logger
             self.value = value

         def set(self, new: T) -> None:
             self.log('Set ' + repr(self.value))
             self.value = new

         def get(self) -> T:
             self.log('Get ' + repr(self.value))
             return self.value

         def log(self, message: str) -> None:
             self.logger.info('%s: %s', self.name, message)

‘Generic[T]’ as a base class defines that the class ‘LoggedVar’ takes a
single type parameter ‘T’ .  This also makes ‘T’ valid as a type within
the class body.

The *note Generic: 100b. base class defines *note __class_getitem__():
437. so that ‘LoggedVar[t]’ is valid as a type:

     from collections.abc import Iterable

     def zero_all_vars(vars: Iterable[LoggedVar[int]]) -> None:
         for var in vars:
             var.set(0)

A generic type can have any number of type variables, and type variables
may be constrained:

     from typing import TypeVar, Generic
     ...

     T = TypeVar('T')
     S = TypeVar('S', int, str)

     class StrangePair(Generic[T, S]):
         ...

Each type variable argument to *note Generic: 100b. must be distinct.
This is thus invalid:

     from typing import TypeVar, Generic
     ...

     T = TypeVar('T')

     class Pair(Generic[T, T]):   # INVALID
         ...

You can use multiple inheritance with *note Generic: 100b.:

     from collections.abc import Sized
     from typing import TypeVar, Generic

     T = TypeVar('T')

     class LinkedList(Sized, Generic[T]):
         ...

When inheriting from generic classes, some type variables could be
fixed:

     from collections.abc import Mapping
     from typing import TypeVar

     T = TypeVar('T')

     class MyDict(Mapping[str, T]):
         ...

In this case ‘MyDict’ has a single parameter, ‘T’.

Using a generic class without specifying type parameters assumes *note
Any: 745. for each position.  In the following example, ‘MyIterable’ is
not generic but implicitly inherits from ‘Iterable[Any]’:

     from collections.abc import Iterable

     class MyIterable(Iterable): # Same as Iterable[Any]

User defined generic type aliases are also supported.  Examples:

     from collections.abc import Iterable
     from typing import TypeVar, Union
     S = TypeVar('S')
     Response = Union[Iterable[S], int]

     # Return type here is same as Union[Iterable[str], int]
     def response(query: str) -> Response[str]:
         ...

     T = TypeVar('T', int, float, complex)
     Vec = Iterable[tuple[T, T]]

     def inproduct(v: Vec[T]) -> T: # Same as Iterable[tuple[T, T]]
         return sum(x*y for x, y in v)

Changed in version 3.7: *note Generic: 100b. no longer has a custom
metaclass.

A user-defined generic class can have ABCs as base classes without a
metaclass conflict.  Generic metaclasses are not supported.  The outcome
of parameterizing generics is cached, and most types in the typing
module are hashable and comparable for equality.


File: python.info,  Node: The Any type,  Next: Nominal vs structural subtyping,  Prev: User-defined generic types,  Up: typing — Support for type hints

5.26.1.7 The ‘Any’ type
.......................

A special kind of type is *note Any: 745.  A static type checker will
treat every type as being compatible with *note Any: 745. and *note Any:
745. as being compatible with every type.

This means that it is possible to perform any operation or method call
on a value of type *note Any: 745. and assign it to any variable:

     from typing import Any

     a: Any = None
     a = []          # OK
     a = 2           # OK

     s: str = ''
     s = a           # OK

     def foo(item: Any) -> int:
         # Typechecks; 'item' could be any type,
         # and that type might have a 'bar' method
         item.bar()
         ...

Notice that no typechecking is performed when assigning a value of type
*note Any: 745. to a more precise type.  For example, the static type
checker did not report an error when assigning ‘a’ to ‘s’ even though
‘s’ was declared to be of type *note str: 205. and receives an *note
int: 204. value at runtime!

Furthermore, all functions without a return type or parameter types will
implicitly default to using *note Any: 745.:

     def legacy_parser(text):
         ...
         return data

     # A static type checker will treat the above
     # as having the same signature as:
     def legacy_parser(text: Any) -> Any:
         ...
         return data

This behavior allows *note Any: 745. to be used as an `escape hatch'
when you need to mix dynamically and statically typed code.

Contrast the behavior of *note Any: 745. with the behavior of *note
object: 3d2.  Similar to *note Any: 745, every type is a subtype of
*note object: 3d2.  However, unlike *note Any: 745, the reverse is not
true: *note object: 3d2. is `not' a subtype of every other type.

That means when the type of a value is *note object: 3d2, a type checker
will reject almost all operations on it, and assigning it to a variable
(or using it as a return value) of a more specialized type is a type
error.  For example:

     def hash_a(item: object) -> int:
         # Fails; an object does not have a 'magic' method.
         item.magic()
         ...

     def hash_b(item: Any) -> int:
         # Typechecks
         item.magic()
         ...

     # Typechecks, since ints and strs are subclasses of object
     hash_a(42)
     hash_a("foo")

     # Typechecks, since Any is compatible with all types
     hash_b(42)
     hash_b("foo")

Use *note object: 3d2. to indicate that a value could be any type in a
typesafe manner.  Use *note Any: 745. to indicate that a value is
dynamically typed.


File: python.info,  Node: Nominal vs structural subtyping,  Next: Module contents<3>,  Prev: The Any type,  Up: typing — Support for type hints

5.26.1.8 Nominal vs structural subtyping
........................................

Initially PEP 484(1) defined Python static type system as using `nominal
subtyping'.  This means that a class ‘A’ is allowed where a class ‘B’ is
expected if and only if ‘A’ is a subclass of ‘B’.

This requirement previously also applied to abstract base classes, such
as *note Iterable: 1818.  The problem with this approach is that a class
had to be explicitly marked to support them, which is unpythonic and
unlike what one would normally do in idiomatic dynamically typed Python
code.  For example, this conforms to PEP 484(2):

     from collections.abc import Sized, Iterable, Iterator

     class Bucket(Sized, Iterable[int]):
         ...
         def __len__(self) -> int: ...
         def __iter__(self) -> Iterator[int]: ...

PEP 544(3) allows to solve this problem by allowing users to write the
above code without explicit base classes in the class definition,
allowing ‘Bucket’ to be implicitly considered a subtype of both ‘Sized’
and ‘Iterable[int]’ by static type checkers.  This is known as
`structural subtyping' (or static duck-typing):

     from collections.abc import Iterator, Iterable

     class Bucket:  # Note: no base classes
         ...
         def __len__(self) -> int: ...
         def __iter__(self) -> Iterator[int]: ...

     def collect(items: Iterable[int]) -> int: ...
     result = collect(Bucket())  # Passes type check

Moreover, by subclassing a special class *note Protocol: 36a, a user can
define new custom protocols to fully enjoy structural subtyping (see
examples below).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0484

   (2) https://www.python.org/dev/peps/pep-0484

   (3) https://www.python.org/dev/peps/pep-0544


File: python.info,  Node: Module contents<3>,  Prev: Nominal vs structural subtyping,  Up: typing — Support for type hints

5.26.1.9 Module contents
........................

The module defines the following classes, functions and decorators.

     Note: This module defines several types that are subclasses of
     pre-existing standard library classes which also extend *note
     Generic: 100b. to support type variables inside ‘[]’.  These types
     became redundant in Python 3.9 when the corresponding pre-existing
     classes were enhanced to support ‘[]’.

     The redundant types are deprecated as of Python 3.9 but no
     deprecation warnings will be issued by the interpreter.  It is
     expected that type checkers will flag the deprecated types when the
     checked program targets Python 3.9 or newer.

     The deprecated types will be removed from the *note typing: 122.
     module in the first Python version released 5 years after the
     release of Python 3.9.0.  See details in PEP 585(1)—`Type Hinting
     Generics In Standard Collections'.

* Menu:

* Special typing primitives::
* Generic concrete collections::
* Abstract Base Classes::
* Protocols: Protocols<3>.
* Functions and decorators::
* Introspection helpers::
* Constant::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0585


File: python.info,  Node: Special typing primitives,  Next: Generic concrete collections,  Up: Module contents<3>

5.26.1.10 Special typing primitives
...................................

* Menu:

* Special types::
* Special forms::
* Building generic types::
* Other special directives::


File: python.info,  Node: Special types,  Next: Special forms,  Up: Special typing primitives

5.26.1.11 Special types
.......................

These can be used as types in annotations and do not support ‘[]’.

 -- Data: typing.Any

     Special type indicating an unconstrained type.

        * Every type is compatible with *note Any: 745.

        * *note Any: 745. is compatible with every type.

 -- Data: typing.NoReturn

     Special type indicating that a function never returns.  For
     example:

          from typing import NoReturn

          def stop() -> NoReturn:
              raise RuntimeError('no way')

     New in version 3.5.4.

     New in version 3.6.2.


File: python.info,  Node: Special forms,  Next: Building generic types,  Prev: Special types,  Up: Special typing primitives

5.26.1.12 Special forms
.......................

These can be used as types in annotations using ‘[]’, each having a
unique syntax.

 -- Data: typing.Tuple

     Tuple type; ‘Tuple[X, Y]’ is the type of a tuple of two items with
     the first item of type X and the second of type Y. The type of the
     empty tuple can be written as ‘Tuple[()]’.

     Example: ‘Tuple[T1, T2]’ is a tuple of two elements corresponding
     to type variables T1 and T2.  ‘Tuple[int, float, str]’ is a tuple
     of an int, a float and a string.

     To specify a variable-length tuple of homogeneous type, use literal
     ellipsis, e.g.  ‘Tuple[int, ...]’.  A plain *note Tuple: 3405. is
     equivalent to ‘Tuple[Any, ...]’, and in turn to *note tuple: 1a2.

     Deprecated since version 3.9: *note builtins.tuple: 1a2. now
     supports ‘[]’.  See PEP 585(1) and *note Generic Alias Type: fe5.

 -- Data: typing.Union

     Union type; ‘Union[X, Y]’ means either X or Y.

     To define a union, use e.g.  ‘Union[int, str]’.  Details:

        * The arguments must be types and there must be at least one.

        * Unions of unions are flattened, e.g.:

               Union[Union[int, str], float] == Union[int, str, float]

        * Unions of a single argument vanish, e.g.:

               Union[int] == int  # The constructor actually returns int

        * Redundant arguments are skipped, e.g.:

               Union[int, str, int] == Union[int, str]

        * When comparing unions, the argument order is ignored, e.g.:

               Union[int, str] == Union[str, int]

        * You cannot subclass or instantiate a union.

        * You cannot write ‘Union[X][Y]’.

        * You can use ‘Optional[X]’ as a shorthand for ‘Union[X, None]’.

     Changed in version 3.7: Don’t remove explicit subclasses from
     unions at runtime.

 -- Data: typing.Optional

     Optional type.

     ‘Optional[X]’ is equivalent to ‘Union[X, None]’.

     Note that this is not the same concept as an optional argument,
     which is one that has a default.  An optional argument with a
     default does not require the ‘Optional’ qualifier on its type
     annotation just because it is optional.  For example:

          def foo(arg: int = 0) -> None:
              ...

     On the other hand, if an explicit value of ‘None’ is allowed, the
     use of ‘Optional’ is appropriate, whether the argument is optional
     or not.  For example:

          def foo(arg: Optional[int] = None) -> None:
              ...

 -- Data: typing.Callable

     Callable type; ‘Callable[[int], str]’ is a function of (int) ->
     str.

     The subscription syntax must always be used with exactly two
     values: the argument list and the return type.  The argument list
     must be a list of types or an ellipsis; the return type must be a
     single type.

     There is no syntax to indicate optional or keyword arguments; such
     function types are rarely used as callback types.  ‘Callable[...,
     ReturnType]’ (literal ellipsis) can be used to type hint a callable
     taking any number of arguments and returning ‘ReturnType’.  A plain
     *note Callable: 27b. is equivalent to ‘Callable[..., Any]’, and in
     turn to *note collections.abc.Callable: 27a.

     Deprecated since version 3.9: *note collections.abc.Callable: 27a.
     now supports ‘[]’.  See PEP 585(2) and *note Generic Alias Type:
     fe5.

 -- Class: typing.Type (Generic[CT_co])

     A variable annotated with ‘C’ may accept a value of type ‘C’.  In
     contrast, a variable annotated with ‘Type[C]’ may accept values
     that are classes themselves – specifically, it will accept the
     `class object' of ‘C’.  For example:

          a = 3         # Has type 'int'
          b = int       # Has type 'Type[int]'
          c = type(a)   # Also has type 'Type[int]'

     Note that ‘Type[C]’ is covariant:

          class User: ...
          class BasicUser(User): ...
          class ProUser(User): ...
          class TeamUser(User): ...

          # Accepts User, BasicUser, ProUser, TeamUser, ...
          def make_new_user(user_class: Type[User]) -> User:
              # ...
              return user_class()

     The fact that ‘Type[C]’ is covariant implies that all subclasses of
     ‘C’ should implement the same constructor signature and class
     method signatures as ‘C’.  The type checker should flag violations
     of this, but should also allow constructor calls in subclasses that
     match the constructor calls in the indicated base class.  How the
     type checker is required to handle this particular case may change
     in future revisions of PEP 484(3).

     The only legal parameters for *note Type: 3407. are classes, *note
     Any: 745, *note type variables: 1588, and unions of any of these
     types.  For example:

          def new_non_team_user(user_class: Type[Union[BasicUser, ProUser]]): ...

     ‘Type[Any]’ is equivalent to ‘Type’ which in turn is equivalent to
     ‘type’, which is the root of Python’s metaclass hierarchy.

     New in version 3.5.2.

     Deprecated since version 3.9: *note builtins.type: 6ff. now
     supports ‘[]’.  See PEP 585(4) and *note Generic Alias Type: fe5.

 -- Data: typing.Literal

     A type that can be used to indicate to type checkers that the
     corresponding variable or function parameter has a value equivalent
     to the provided literal (or one of several literals).  For example:

          def validate_simple(data: Any) -> Literal[True]:  # always returns True
              ...

          MODE = Literal['r', 'rb', 'w', 'wb']
          def open_helper(file: str, mode: MODE) -> str:
              ...

          open_helper('/some/path', 'r')  # Passes type check
          open_helper('/other/path', 'typo')  # Error in type checker

     ‘Literal[...]’ cannot be subclassed.  At runtime, an arbitrary
     value is allowed as type argument to ‘Literal[...]’, but type
     checkers may impose restrictions.  See PEP 586(5) for more details
     about literal types.

     New in version 3.8.

     Changed in version 3.9.1: ‘Literal’ now de-duplicates parameters.
     Equality comparisons of ‘Literal’ objects are no longer order
     dependent.  ‘Literal’ objects will now raise a *note TypeError:
     1fe. exception during equality comparisons if one of their
     parameters are not *note hashable: 276.

 -- Data: typing.ClassVar

     Special type construct to mark class variables.

     As introduced in PEP 526(6), a variable annotation wrapped in
     ClassVar indicates that a given attribute is intended to be used as
     a class variable and should not be set on instances of that class.
     Usage:

          class Starship:
              stats: ClassVar[dict[str, int]] = {} # class variable
              damage: int = 10                     # instance variable

     *note ClassVar: 69a. accepts only types and cannot be further
     subscribed.

     *note ClassVar: 69a. is not a class itself, and should not be used
     with *note isinstance(): 552. or *note issubclass(): 553.  *note
     ClassVar: 69a. does not change Python runtime behavior, but it can
     be used by third-party type checkers.  For example, a type checker
     might flag the following code as an error:

          enterprise_d = Starship(3000)
          enterprise_d.stats = {} # Error, setting class variable on instance
          Starship.stats = {}     # This is OK

     New in version 3.5.3.

 -- Data: typing.Final

     A special typing construct to indicate to type checkers that a name
     cannot be re-assigned or overridden in a subclass.  For example:

          MAX_SIZE: Final = 9000
          MAX_SIZE += 1  # Error reported by type checker

          class Connection:
              TIMEOUT: Final[int] = 10

          class FastConnector(Connection):
              TIMEOUT = 1  # Error reported by type checker

     There is no runtime checking of these properties.  See PEP 591(7)
     for more details.

     New in version 3.8.

 -- Data: typing.Annotated

     A type, introduced in PEP 593(8) (‘Flexible function and variable
     annotations’), to decorate existing types with context-specific
     metadata (possibly multiple pieces of it, as ‘Annotated’ is
     variadic).  Specifically, a type ‘T’ can be annotated with metadata
     ‘x’ via the typehint ‘Annotated[T, x]’.  This metadata can be used
     for either static analysis or at runtime.  If a library (or tool)
     encounters a typehint ‘Annotated[T, x]’ and has no special logic
     for metadata ‘x’, it should ignore it and simply treat the type as
     ‘T’.  Unlike the ‘no_type_check’ functionality that currently
     exists in the ‘typing’ module which completely disables
     typechecking annotations on a function or a class, the ‘Annotated’
     type allows for both static typechecking of ‘T’ (e.g., via mypy or
     Pyre, which can safely ignore ‘x’) together with runtime access to
     ‘x’ within a specific application.

     Ultimately, the responsibility of how to interpret the annotations
     (if at all) is the responsibility of the tool or library
     encountering the ‘Annotated’ type.  A tool or library encountering
     an ‘Annotated’ type can scan through the annotations to determine
     if they are of interest (e.g., using ‘isinstance()’).

     When a tool or a library does not support annotations or encounters
     an unknown annotation it should just ignore it and treat annotated
     type as the underlying type.

     It’s up to the tool consuming the annotations to decide whether the
     client is allowed to have several annotations on one type and how
     to merge those annotations.

     Since the ‘Annotated’ type allows you to put several annotations of
     the same (or different) type(s) on any node, the tools or libraries
     consuming those annotations are in charge of dealing with potential
     duplicates.  For example, if you are doing value range analysis you
     might allow this:

          T1 = Annotated[int, ValueRange(-10, 5)]
          T2 = Annotated[T1, ValueRange(-20, 3)]

     Passing ‘include_extras=True’ to *note get_type_hints(): 1ef. lets
     one access the extra annotations at runtime.

     The details of the syntax:

        * The first argument to ‘Annotated’ must be a valid type

        * Multiple type annotations are supported (‘Annotated’ supports
          variadic arguments):

               Annotated[int, ValueRange(3, 10), ctype("char")]

        * ‘Annotated’ must be called with at least two arguments (
          ‘Annotated[int]’ is not valid)

        * The order of the annotations is preserved and matters for
          equality checks:

               Annotated[int, ValueRange(3, 10), ctype("char")] != Annotated[
                   int, ctype("char"), ValueRange(3, 10)
               ]

        * Nested ‘Annotated’ types are flattened, with metadata ordered
          starting with the innermost annotation:

               Annotated[Annotated[int, ValueRange(3, 10)], ctype("char")] == Annotated[
                   int, ValueRange(3, 10), ctype("char")
               ]

        * Duplicated annotations are not removed:

               Annotated[int, ValueRange(3, 10)] != Annotated[
                   int, ValueRange(3, 10), ValueRange(3, 10)
               ]

        * ‘Annotated’ can be used with nested and generic aliases:

               T = TypeVar('T')
               Vec = Annotated[list[tuple[T, T]], MaxLen(10)]
               V = Vec[int]

               V == Annotated[list[tuple[int, int]], MaxLen(10)]

     New in version 3.9.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0585

   (2) https://www.python.org/dev/peps/pep-0585

   (3) https://www.python.org/dev/peps/pep-0484

   (4) https://www.python.org/dev/peps/pep-0585

   (5) https://www.python.org/dev/peps/pep-0586

   (6) https://www.python.org/dev/peps/pep-0526

   (7) https://www.python.org/dev/peps/pep-0591

   (8) https://www.python.org/dev/peps/pep-0593


File: python.info,  Node: Building generic types,  Next: Other special directives,  Prev: Special forms,  Up: Special typing primitives

5.26.1.13 Building generic types
................................

These are not used in annotations.  They are building blocks for
creating generic types.

 -- Class: typing.Generic

     Abstract base class for generic types.

     A generic type is typically declared by inheriting from an
     instantiation of this class with one or more type variables.  For
     example, a generic mapping type might be defined as:

          class Mapping(Generic[KT, VT]):
              def __getitem__(self, key: KT) -> VT:
                  ...
                  # Etc.

     This class can then be used as follows:

          X = TypeVar('X')
          Y = TypeVar('Y')

          def lookup_name(mapping: Mapping[X, Y], key: X, default: Y) -> Y:
              try:
                  return mapping[key]
              except KeyError:
                  return default

 -- Class: typing.TypeVar

     Type variable.

     Usage:

          T = TypeVar('T')  # Can be anything
          A = TypeVar('A', str, bytes)  # Must be str or bytes

     Type variables exist primarily for the benefit of static type
     checkers.  They serve as the parameters for generic types as well
     as for generic function definitions.  See *note Generic: 100b. for
     more information on generic types.  Generic functions work as
     follows:

          def repeat(x: T, n: int) -> Sequence[T]:
              """Return a list containing n references to x."""
              return [x]*n

          def longest(x: A, y: A) -> A:
              """Return the longest of two strings."""
              return x if len(x) >= len(y) else y

     The latter example’s signature is essentially the overloading of
     ‘(str, str) -> str’ and ‘(bytes, bytes) -> bytes’.  Also note that
     if the arguments are instances of some subclass of *note str: 205,
     the return type is still plain *note str: 205.

     At runtime, ‘isinstance(x, T)’ will raise *note TypeError: 1fe.  In
     general, *note isinstance(): 552. and *note issubclass(): 553.
     should not be used with types.

     Type variables may be marked covariant or contravariant by passing
     ‘covariant=True’ or ‘contravariant=True’.  See PEP 484(1) for more
     details.  By default type variables are invariant.  Alternatively,
     a type variable may specify an upper bound using ‘bound=<type>’.
     This means that an actual type substituted (explicitly or
     implicitly) for the type variable must be a subclass of the
     boundary type, see PEP 484(2).

 -- Data: typing.AnyStr

     ‘AnyStr’ is a type variable defined as ‘AnyStr = TypeVar('AnyStr',
     str, bytes)’.

     It is meant to be used for functions that may accept any kind of
     string without allowing different kinds of strings to mix.  For
     example:

          def concat(a: AnyStr, b: AnyStr) -> AnyStr:
              return a + b

          concat(u"foo", u"bar")  # Ok, output has type 'unicode'
          concat(b"foo", b"bar")  # Ok, output has type 'bytes'
          concat(u"foo", b"bar")  # Error, cannot mix unicode and bytes

 -- Class: typing.Protocol (Generic)

     Base class for protocol classes.  Protocol classes are defined like
     this:

          class Proto(Protocol):
              def meth(self) -> int:
                  ...

     Such classes are primarily used with static type checkers that
     recognize structural subtyping (static duck-typing), for example:

          class C:
              def meth(self) -> int:
                  return 0

          def func(x: Proto) -> int:
              return x.meth()

          func(C())  # Passes static type check

     See PEP 544(3) for details.  Protocol classes decorated with *note
     runtime_checkable(): 36b. (described later) act as simple-minded
     runtime protocols that check only the presence of given attributes,
     ignoring their type signatures.

     Protocol classes can be generic, for example:

          class GenProto(Protocol[T]):
              def meth(self) -> T:
                  ...

     New in version 3.8.

 -- Function: @typing.runtime_checkable

     Mark a protocol class as a runtime protocol.

     Such a protocol can be used with *note isinstance(): 552. and *note
     issubclass(): 553.  This raises *note TypeError: 1fe. when applied
     to a non-protocol class.  This allows a simple-minded structural
     check, very similar to “one trick ponies” in *note collections.abc:
     1e. such as *note Iterable: 1818.  For example:

          @runtime_checkable
          class Closable(Protocol):
              def close(self): ...

          assert isinstance(open('/some/file'), Closable)

          Note: *note runtime_checkable(): 36b. will check only the
          presence of the required methods, not their type signatures!
          For example, *note builtins.complex: 2c1. implements *note
          __float__(): 2c4, therefore it passes an *note issubclass():
          553. check against *note SupportsFloat: 340a.  However, the
          ‘complex.__float__’ method exists only to raise a *note
          TypeError: 1fe. with a more informative message.

     New in version 3.8.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0484

   (2) https://www.python.org/dev/peps/pep-0484

   (3) https://www.python.org/dev/peps/pep-0544


File: python.info,  Node: Other special directives,  Prev: Building generic types,  Up: Special typing primitives

5.26.1.14 Other special directives
..................................

These are not used in annotations.  They are building blocks for
declaring types.

 -- Class: typing.NamedTuple

     Typed version of *note collections.namedtuple(): 1a1.

     Usage:

          class Employee(NamedTuple):
              name: str
              id: int

     This is equivalent to:

          Employee = collections.namedtuple('Employee', ['name', 'id'])

     To give a field a default value, you can assign to it in the class
     body:

          class Employee(NamedTuple):
              name: str
              id: int = 3

          employee = Employee('Guido')
          assert employee.id == 3

     Fields with a default value must come after any fields without a
     default.

     The resulting class has an extra attribute ‘__annotations__’ giving
     a dict that maps the field names to the field types.  (The field
     names are in the ‘_fields’ attribute and the default values are in
     the ‘_field_defaults’ attribute both of which are part of the
     namedtuple API.)

     ‘NamedTuple’ subclasses can also have docstrings and methods:

          class Employee(NamedTuple):
              """Represents an employee."""
              name: str
              id: int = 3

              def __repr__(self) -> str:
                  return f'<Employee {self.name}, id={self.id}>'

     Backward-compatible usage:

          Employee = NamedTuple('Employee', [('name', str), ('id', int)])

     Changed in version 3.6: Added support for PEP 526(1) variable
     annotation syntax.

     Changed in version 3.6.1: Added support for default values,
     methods, and docstrings.

     Changed in version 3.8: The ‘_field_types’ and ‘__annotations__’
     attributes are now regular dictionaries instead of instances of
     ‘OrderedDict’.

     Changed in version 3.9: Removed the ‘_field_types’ attribute in
     favor of the more standard ‘__annotations__’ attribute which has
     the same information.

 -- Function: typing.NewType (name, tp)

     A helper function to indicate a distinct type to a typechecker, see
     *note NewType: 33f9.  At runtime it returns a function that returns
     its argument.  Usage:

          UserId = NewType('UserId', int)
          first_user = UserId(1)

     New in version 3.5.2.

 -- Class: typing.TypedDict (dict)

     Special construct to add type hints to a dictionary.  At runtime it
     is a plain *note dict: 164.

     ‘TypedDict’ declares a dictionary type that expects all of its
     instances to have a certain set of keys, where each key is
     associated with a value of a consistent type.  This expectation is
     not checked at runtime but is only enforced by type checkers.
     Usage:

          class Point2D(TypedDict):
              x: int
              y: int
              label: str

          a: Point2D = {'x': 1, 'y': 2, 'label': 'good'}  # OK
          b: Point2D = {'z': 3, 'label': 'bad'}           # Fails type check

          assert Point2D(x=1, y=2, label='first') == dict(x=1, y=2, label='first')

     The type info for introspection can be accessed via
     ‘Point2D.__annotations__’ and ‘Point2D.__total__’.  To allow using
     this feature with older versions of Python that do not support PEP
     526(2), ‘TypedDict’ supports two additional equivalent syntactic
     forms:

          Point2D = TypedDict('Point2D', x=int, y=int, label=str)
          Point2D = TypedDict('Point2D', {'x': int, 'y': int, 'label': str})

     By default, all keys must be present in a TypedDict.  It is
     possible to override this by specifying totality.  Usage:

          class point2D(TypedDict, total=False):
              x: int
              y: int

     This means that a point2D TypedDict can have any of the keys
     omitted.  A type checker is only expected to support a literal
     False or True as the value of the total argument.  True is the
     default, and makes all items defined in the class body be required.

     See PEP 589(3) for more examples and detailed rules of using
     ‘TypedDict’.

     New in version 3.8.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0526

   (2) https://www.python.org/dev/peps/pep-0526

   (3) https://www.python.org/dev/peps/pep-0589


File: python.info,  Node: Generic concrete collections,  Next: Abstract Base Classes,  Prev: Special typing primitives,  Up: Module contents<3>

5.26.1.15 Generic concrete collections
......................................

* Menu:

* Corresponding to built-in types::
* Corresponding to types in collections::
* Other concrete types::


File: python.info,  Node: Corresponding to built-in types,  Next: Corresponding to types in collections,  Up: Generic concrete collections

5.26.1.16 Corresponding to built-in types
.........................................

 -- Class: typing.Dict (dict, MutableMapping[KT, VT])

     A generic version of *note dict: 164.  Useful for annotating return
     types.  To annotate arguments it is preferred to use an abstract
     collection type such as *note Mapping: 340f.

     This type can be used as follows:

          def count_words(text: str) -> Dict[str, int]:
              ...

     Deprecated since version 3.9: *note builtins.dict: 164. now
     supports ‘[]’.  See PEP 585(1) and *note Generic Alias Type: fe5.

 -- Class: typing.List (list, MutableSequence[T])

     Generic version of *note list: 1f8.  Useful for annotating return
     types.  To annotate arguments it is preferred to use an abstract
     collection type such as *note Sequence: 3411. or *note Iterable:
     3412.

     This type may be used as follows:

          T = TypeVar('T', int, float)

          def vec2(x: T, y: T) -> List[T]:
              return [x, y]

          def keep_positives(vector: Sequence[T]) -> List[T]:
              return [item for item in vector if item > 0]

     Deprecated since version 3.9: *note builtins.list: 1f8. now
     supports ‘[]’.  See PEP 585(2) and *note Generic Alias Type: fe5.

 -- Class: typing.Set (set, MutableSet[T])

     A generic version of *note builtins.set: 1f6.  Useful for
     annotating return types.  To annotate arguments it is preferred to
     use an abstract collection type such as *note AbstractSet: 3414.

     Deprecated since version 3.9: *note builtins.set: 1f6. now supports
     ‘[]’.  See PEP 585(3) and *note Generic Alias Type: fe5.

 -- Class: typing.FrozenSet (frozenset, AbstractSet[T_co])

     A generic version of *note builtins.frozenset: 1f7.

     Deprecated since version 3.9: *note builtins.frozenset: 1f7. now
     supports ‘[]’.  See PEP 585(4) and *note Generic Alias Type: fe5.

     Note: *note Tuple: 3405. is a special form.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0585

   (2) https://www.python.org/dev/peps/pep-0585

   (3) https://www.python.org/dev/peps/pep-0585

   (4) https://www.python.org/dev/peps/pep-0585


File: python.info,  Node: Corresponding to types in collections,  Next: Other concrete types,  Prev: Corresponding to built-in types,  Up: Generic concrete collections

5.26.1.17 Corresponding to types in ‘collections’
.................................................

 -- Class: typing.DefaultDict (collections.defaultdict,
          MutableMapping[KT, VT])

     A generic version of *note collections.defaultdict: c0c.

     New in version 3.5.2.

     Deprecated since version 3.9: *note collections.defaultdict: c0c.
     now supports ‘[]’.  See PEP 585(1) and *note Generic Alias Type:
     fe5.

 -- Class: typing.OrderedDict (collections.OrderedDict,
          MutableMapping[KT, VT])

     A generic version of *note collections.OrderedDict: 2ea.

     New in version 3.7.2.

     Deprecated since version 3.9: *note collections.OrderedDict: 2ea.
     now supports ‘[]’.  See PEP 585(2) and *note Generic Alias Type:
     fe5.

 -- Class: typing.ChainMap (collections.ChainMap, MutableMapping[KT,
          VT])

     A generic version of *note collections.ChainMap: 5a4.

     New in version 3.5.4.

     New in version 3.6.1.

     Deprecated since version 3.9: *note collections.ChainMap: 5a4. now
     supports ‘[]’.  See PEP 585(3) and *note Generic Alias Type: fe5.

 -- Class: typing.Counter (collections.Counter, Dict[T, int])

     A generic version of *note collections.Counter: ab9.

     New in version 3.5.4.

     New in version 3.6.1.

     Deprecated since version 3.9: *note collections.Counter: ab9. now
     supports ‘[]’.  See PEP 585(4) and *note Generic Alias Type: fe5.

 -- Class: typing.Deque (deque, MutableSequence[T])

     A generic version of *note collections.deque: 62b.

     New in version 3.5.4.

     New in version 3.6.1.

     Deprecated since version 3.9: *note collections.deque: 62b. now
     supports ‘[]’.  See PEP 585(5) and *note Generic Alias Type: fe5.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0585

   (2) https://www.python.org/dev/peps/pep-0585

   (3) https://www.python.org/dev/peps/pep-0585

   (4) https://www.python.org/dev/peps/pep-0585

   (5) https://www.python.org/dev/peps/pep-0585


File: python.info,  Node: Other concrete types,  Prev: Corresponding to types in collections,  Up: Generic concrete collections

5.26.1.18 Other concrete types
..............................

 -- Class: typing.IO
 -- Class: typing.TextIO
 -- Class: typing.BinaryIO

     Generic type ‘IO[AnyStr]’ and its subclasses ‘TextIO(IO[str])’ and
     ‘BinaryIO(IO[bytes])’ represent the types of I/O streams such as
     returned by *note open(): 16f.

     Deprecated since version 3.8, will be removed in version 3.12:
     These types are also in the ‘typing.io’ namespace, which was never
     supported by type checkers and will be removed.

 -- Class: typing.Pattern
 -- Class: typing.Match

     These type aliases correspond to the return types from *note
     re.compile(): 54d. and *note re.match(): c83.  These types (and the
     corresponding functions) are generic in ‘AnyStr’ and can be made
     specific by writing ‘Pattern[str]’, ‘Pattern[bytes]’, ‘Match[str]’,
     or ‘Match[bytes]’.

     Deprecated since version 3.8, will be removed in version 3.12:
     These types are also in the ‘typing.re’ namespace, which was never
     supported by type checkers and will be removed.

     Deprecated since version 3.9: Classes ‘Pattern’ and ‘Match’ from
     *note re: dd. now support ‘[]’.  See PEP 585(1) and *note Generic
     Alias Type: fe5.

 -- Class: typing.Text

     ‘Text’ is an alias for ‘str’.  It is provided to supply a forward
     compatible path for Python 2 code: in Python 2, ‘Text’ is an alias
     for ‘unicode’.

     Use ‘Text’ to indicate that a value must contain a unicode string
     in a manner that is compatible with both Python 2 and Python 3:

          def add_unicode_checkmark(text: Text) -> Text:
              return text + u' \u2713'

     New in version 3.5.2.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0585


File: python.info,  Node: Abstract Base Classes,  Next: Protocols<3>,  Prev: Generic concrete collections,  Up: Module contents<3>

5.26.1.19 Abstract Base Classes
...............................

* Menu:

* Corresponding to collections in collections.abc: Corresponding to collections in collections abc.
* Corresponding to other types in collections.abc: Corresponding to other types in collections abc.
* Asynchronous programming::
* Context manager types::


File: python.info,  Node: Corresponding to collections in collections abc,  Next: Corresponding to other types in collections abc,  Up: Abstract Base Classes

5.26.1.20 Corresponding to collections in ‘collections.abc’
...........................................................

 -- Class: typing.AbstractSet (Sized, Collection[T_co])

     A generic version of *note collections.abc.Set: 1810.

     Deprecated since version 3.9: *note collections.abc.Set: 1810. now
     supports ‘[]’.  See PEP 585(1) and *note Generic Alias Type: fe5.

 -- Class: typing.ByteString (Sequence[int])

     A generic version of *note collections.abc.ByteString: 181c.

     This type represents the types *note bytes: 172, *note bytearray:
     173, and *note memoryview: 386. of byte sequences.

     As a shorthand for this type, *note bytes: 172. can be used to
     annotate arguments of any of the types mentioned above.

     Deprecated since version 3.9: *note collections.abc.ByteString:
     181c. now supports ‘[]’.  See PEP 585(2) and *note Generic Alias
     Type: fe5.

 -- Class: typing.Collection (Sized, Iterable[T_co], Container[T_co])

     A generic version of *note collections.abc.Collection: 627.

     New in version 3.6.0.

     Deprecated since version 3.9: *note collections.abc.Collection:
     627. now supports ‘[]’.  See PEP 585(3) and *note Generic Alias
     Type: fe5.

 -- Class: typing.Container (Generic[T_co])

     A generic version of *note collections.abc.Container: 181a.

     Deprecated since version 3.9: *note collections.abc.Container:
     181a. now supports ‘[]’.  See PEP 585(4) and *note Generic Alias
     Type: fe5.

 -- Class: typing.ItemsView (MappingView, Generic[KT_co, VT_co])

     A generic version of *note collections.abc.ItemsView: 181f.

     Deprecated since version 3.9: *note collections.abc.ItemsView:
     181f. now supports ‘[]’.  See PEP 585(5) and *note Generic Alias
     Type: fe5.

 -- Class: typing.KeysView (MappingView[KT_co], AbstractSet[KT_co])

     A generic version of *note collections.abc.KeysView: 181e.

     Deprecated since version 3.9: *note collections.abc.KeysView: 181e.
     now supports ‘[]’.  See PEP 585(6) and *note Generic Alias Type:
     fe5.

 -- Class: typing.Mapping (Sized, Collection[KT], Generic[VT_co])

     A generic version of *note collections.abc.Mapping: 15f.  This type
     can be used as follows:

          def get_position_in_index(word_list: Mapping[str, int], word: str) -> int:
              return word_list[word]

     Deprecated since version 3.9: *note collections.abc.Mapping: 15f.
     now supports ‘[]’.  See PEP 585(7) and *note Generic Alias Type:
     fe5.

 -- Class: typing.MappingView (Sized, Iterable[T_co])

     A generic version of *note collections.abc.MappingView: 181d.

     Deprecated since version 3.9: *note collections.abc.MappingView:
     181d. now supports ‘[]’.  See PEP 585(8) and *note Generic Alias
     Type: fe5.

 -- Class: typing.MutableMapping (Mapping[KT, VT])

     A generic version of *note collections.abc.MutableMapping: ace.

     Deprecated since version 3.9: *note collections.abc.MutableMapping:
     ace. now supports ‘[]’.  See PEP 585(9) and *note Generic Alias
     Type: fe5.

 -- Class: typing.MutableSequence (Sequence[T])

     A generic version of *note collections.abc.MutableSequence: 79f.

     Deprecated since version 3.9: *note
     collections.abc.MutableSequence: 79f. now supports ‘[]’.  See PEP
     585(10) and *note Generic Alias Type: fe5.

 -- Class: typing.MutableSet (AbstractSet[T])

     A generic version of *note collections.abc.MutableSet: 181b.

     Deprecated since version 3.9: *note collections.abc.MutableSet:
     181b. now supports ‘[]’.  See PEP 585(11) and *note Generic Alias
     Type: fe5.

 -- Class: typing.Sequence (Reversible[T_co], Collection[T_co])

     A generic version of *note collections.abc.Sequence: 1764.

     Deprecated since version 3.9: *note collections.abc.Sequence: 1764.
     now supports ‘[]’.  See PEP 585(12) and *note Generic Alias Type:
     fe5.

 -- Class: typing.ValuesView (MappingView[VT_co])

     A generic version of *note collections.abc.ValuesView: 1820.

     Deprecated since version 3.9: *note collections.abc.ValuesView:
     1820. now supports ‘[]’.  See PEP 585(13) and *note Generic Alias
     Type: fe5.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0585

   (2) https://www.python.org/dev/peps/pep-0585

   (3) https://www.python.org/dev/peps/pep-0585

   (4) https://www.python.org/dev/peps/pep-0585

   (5) https://www.python.org/dev/peps/pep-0585

   (6) https://www.python.org/dev/peps/pep-0585

   (7) https://www.python.org/dev/peps/pep-0585

   (8) https://www.python.org/dev/peps/pep-0585

   (9) https://www.python.org/dev/peps/pep-0585

   (10) https://www.python.org/dev/peps/pep-0585

   (11) https://www.python.org/dev/peps/pep-0585

   (12) https://www.python.org/dev/peps/pep-0585

   (13) https://www.python.org/dev/peps/pep-0585


File: python.info,  Node: Corresponding to other types in collections abc,  Next: Asynchronous programming,  Prev: Corresponding to collections in collections abc,  Up: Abstract Base Classes

5.26.1.21 Corresponding to other types in ‘collections.abc’
...........................................................

 -- Class: typing.Iterable (Generic[T_co])

     A generic version of *note collections.abc.Iterable: 1818.

     Deprecated since version 3.9: *note collections.abc.Iterable: 1818.
     now supports ‘[]’.  See PEP 585(1) and *note Generic Alias Type:
     fe5.

 -- Class: typing.Iterator (Iterable[T_co])

     A generic version of *note collections.abc.Iterator: 1819.

     Deprecated since version 3.9: *note collections.abc.Iterator: 1819.
     now supports ‘[]’.  See PEP 585(2) and *note Generic Alias Type:
     fe5.

 -- Class: typing.Generator (Iterator[T_co], Generic[T_co, T_contra,
          V_co])

     A generator can be annotated by the generic type
     ‘Generator[YieldType, SendType, ReturnType]’.  For example:

          def echo_round() -> Generator[int, float, str]:
              sent = yield 0
              while sent >= 0:
                  sent = yield round(sent)
              return 'Done'

     Note that unlike many other generics in the typing module, the
     ‘SendType’ of *note Generator: 3430. behaves contravariantly, not
     covariantly or invariantly.

     If your generator will only yield values, set the ‘SendType’ and
     ‘ReturnType’ to ‘None’:

          def infinite_stream(start: int) -> Generator[int, None, None]:
              while True:
                  yield start
                  start += 1

     Alternatively, annotate your generator as having a return type of
     either ‘Iterable[YieldType]’ or ‘Iterator[YieldType]’:

          def infinite_stream(start: int) -> Iterator[int]:
              while True:
                  yield start
                  start += 1

     Deprecated since version 3.9: *note collections.abc.Generator: 7a8.
     now supports ‘[]’.  See PEP 585(3) and *note Generic Alias Type:
     fe5.

 -- Class: typing.Hashable

     An alias to *note collections.abc.Hashable: 1aa9.

 -- Class: typing.Reversible (Iterable[T_co])

     A generic version of *note collections.abc.Reversible: 628.

     Deprecated since version 3.9: *note collections.abc.Reversible:
     628. now supports ‘[]’.  See PEP 585(4) and *note Generic Alias
     Type: fe5.

 -- Class: typing.Sized

     An alias to *note collections.abc.Sized: 1aaa.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0585

   (2) https://www.python.org/dev/peps/pep-0585

   (3) https://www.python.org/dev/peps/pep-0585

   (4) https://www.python.org/dev/peps/pep-0585


File: python.info,  Node: Asynchronous programming,  Next: Context manager types,  Prev: Corresponding to other types in collections abc,  Up: Abstract Base Classes

5.26.1.22 Asynchronous programming
..................................

 -- Class: typing.Coroutine (Awaitable[V_co], Generic[T_co, T_contra,
          V_co])

     A generic version of *note collections.abc.Coroutine: 7aa.  The
     variance and order of type variables correspond to those of *note
     Generator: 3430, for example:

          from collections.abc import Coroutine
          c: Coroutine[list[str], str, int]  # Some coroutine defined elsewhere
          x = c.send('hi')                   # Inferred type of 'x' is list[str]
          async def bar() -> None:
              y = await c                    # Inferred type of 'y' is int

     New in version 3.5.3.

     Deprecated since version 3.9: *note collections.abc.Coroutine: 7aa.
     now supports ‘[]’.  See PEP 585(1) and *note Generic Alias Type:
     fe5.

 -- Class: typing.AsyncGenerator (AsyncIterator[T_co], Generic[T_co,
          T_contra])

     An async generator can be annotated by the generic type
     ‘AsyncGenerator[YieldType, SendType]’.  For example:

          async def echo_round() -> AsyncGenerator[int, float]:
              sent = yield 0
              while sent >= 0.0:
                  rounded = await round(sent)
                  sent = yield rounded

     Unlike normal generators, async generators cannot return a value,
     so there is no ‘ReturnType’ type parameter.  As with *note
     Generator: 3430, the ‘SendType’ behaves contravariantly.

     If your generator will only yield values, set the ‘SendType’ to
     ‘None’:

          async def infinite_stream(start: int) -> AsyncGenerator[int, None]:
              while True:
                  yield start
                  start = await increment(start)

     Alternatively, annotate your generator as having a return type of
     either ‘AsyncIterable[YieldType]’ or ‘AsyncIterator[YieldType]’:

          async def infinite_stream(start: int) -> AsyncIterator[int]:
              while True:
                  yield start
                  start = await increment(start)

     New in version 3.6.1.

     Deprecated since version 3.9: *note collections.abc.AsyncGenerator:
     62a. now supports ‘[]’.  See PEP 585(2) and *note Generic Alias
     Type: fe5.

 -- Class: typing.AsyncIterable (Generic[T_co])

     A generic version of *note collections.abc.AsyncIterable: 7ac.

     New in version 3.5.2.

     Deprecated since version 3.9: *note collections.abc.AsyncIterable:
     7ac. now supports ‘[]’.  See PEP 585(3) and *note Generic Alias
     Type: fe5.

 -- Class: typing.AsyncIterator (AsyncIterable[T_co])

     A generic version of *note collections.abc.AsyncIterator: 7ab.

     New in version 3.5.2.

     Deprecated since version 3.9: *note collections.abc.AsyncIterator:
     7ab. now supports ‘[]’.  See PEP 585(4) and *note Generic Alias
     Type: fe5.

 -- Class: typing.Awaitable (Generic[T_co])

     A generic version of *note collections.abc.Awaitable: 7a9.

     New in version 3.5.2.

     Deprecated since version 3.9: *note collections.abc.Awaitable: 7a9.
     now supports ‘[]’.  See PEP 585(5) and *note Generic Alias Type:
     fe5.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0585

   (2) https://www.python.org/dev/peps/pep-0585

   (3) https://www.python.org/dev/peps/pep-0585

   (4) https://www.python.org/dev/peps/pep-0585

   (5) https://www.python.org/dev/peps/pep-0585


File: python.info,  Node: Context manager types,  Prev: Asynchronous programming,  Up: Abstract Base Classes

5.26.1.23 Context manager types
...............................

 -- Class: typing.ContextManager (Generic[T_co])

     A generic version of *note contextlib.AbstractContextManager: 62e.

     New in version 3.5.4.

     New in version 3.6.0.

     Deprecated since version 3.9: *note
     contextlib.AbstractContextManager: 62e. now supports ‘[]’.  See PEP
     585(1) and *note Generic Alias Type: fe5.

 -- Class: typing.AsyncContextManager (Generic[T_co])

     A generic version of *note contextlib.AbstractAsyncContextManager:
     480.

     New in version 3.5.4.

     New in version 3.6.2.

     Deprecated since version 3.9: *note
     contextlib.AbstractAsyncContextManager: 480. now supports ‘[]’.
     See PEP 585(2) and *note Generic Alias Type: fe5.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0585

   (2) https://www.python.org/dev/peps/pep-0585


File: python.info,  Node: Protocols<3>,  Next: Functions and decorators,  Prev: Abstract Base Classes,  Up: Module contents<3>

5.26.1.24 Protocols
...................

These protocols are decorated with *note runtime_checkable(): 36b.

 -- Class: typing.SupportsAbs

     An ABC with one abstract method ‘__abs__’ that is covariant in its
     return type.

 -- Class: typing.SupportsBytes

     An ABC with one abstract method ‘__bytes__’.

 -- Class: typing.SupportsComplex

     An ABC with one abstract method ‘__complex__’.

 -- Class: typing.SupportsFloat

     An ABC with one abstract method ‘__float__’.

 -- Class: typing.SupportsIndex

     An ABC with one abstract method ‘__index__’.

     New in version 3.8.

 -- Class: typing.SupportsInt

     An ABC with one abstract method ‘__int__’.

 -- Class: typing.SupportsRound

     An ABC with one abstract method ‘__round__’ that is covariant in
     its return type.


File: python.info,  Node: Functions and decorators,  Next: Introspection helpers,  Prev: Protocols<3>,  Up: Module contents<3>

5.26.1.25 Functions and decorators
..................................

 -- Function: typing.cast (typ, val)

     Cast a value to a type.

     This returns the value unchanged.  To the type checker this signals
     that the return value has the designated type, but at runtime we
     intentionally don’t check anything (we want this to be as fast as
     possible).

 -- Function: @typing.overload

     The ‘@overload’ decorator allows describing functions and methods
     that support multiple different combinations of argument types.  A
     series of ‘@overload’-decorated definitions must be followed by
     exactly one non-‘@overload’-decorated definition (for the same
     function/method).  The ‘@overload’-decorated definitions are for
     the benefit of the type checker only, since they will be
     overwritten by the non-‘@overload’-decorated definition, while the
     latter is used at runtime but should be ignored by a type checker.
     At runtime, calling a ‘@overload’-decorated function directly will
     raise *note NotImplementedError: 704.  An example of overload that
     gives a more precise type than can be expressed using a union or a
     type variable:

          @overload
          def process(response: None) -> None:
              ...
          @overload
          def process(response: int) -> tuple[int, str]:
              ...
          @overload
          def process(response: bytes) -> str:
              ...
          def process(response):
              <actual implementation>

     See PEP 484(1) for details and comparison with other typing
     semantics.

 -- Function: @typing.final

     A decorator to indicate to type checkers that the decorated method
     cannot be overridden, and the decorated class cannot be subclassed.
     For example:

          class Base:
              @final
              def done(self) -> None:
                  ...
          class Sub(Base):
              def done(self) -> None:  # Error reported by type checker
                    ...

          @final
          class Leaf:
              ...
          class Other(Leaf):  # Error reported by type checker
              ...

     There is no runtime checking of these properties.  See PEP 591(2)
     for more details.

     New in version 3.8.

 -- Function: @typing.no_type_check

     Decorator to indicate that annotations are not type hints.

     This works as class or function *note decorator: 174.  With a
     class, it applies recursively to all methods defined in that class
     (but not to methods defined in its superclasses or subclasses).

     This mutates the function(s) in place.

 -- Function: @typing.no_type_check_decorator

     Decorator to give another decorator the *note no_type_check():
     3443. effect.

     This wraps the decorator with something that wraps the decorated
     function in *note no_type_check(): 3443.

 -- Function: @typing.type_check_only

     Decorator to mark a class or function to be unavailable at runtime.

     This decorator is itself not available at runtime.  It is mainly
     intended to mark classes that are defined in type stub files if an
     implementation returns an instance of a private class:

          @type_check_only
          class Response:  # private or not available at runtime
              code: int
              def get_header(self, name: str) -> str: ...

          def fetch_response() -> Response: ...

     Note that returning instances of private classes is not
     recommended.  It is usually preferable to make such classes public.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0484

   (2) https://www.python.org/dev/peps/pep-0591


File: python.info,  Node: Introspection helpers,  Next: Constant,  Prev: Functions and decorators,  Up: Module contents<3>

5.26.1.26 Introspection helpers
...............................

 -- Function: typing.get_type_hints (obj, globalns=None, localns=None,
          include_extras=False)

     Return a dictionary containing type hints for a function, method,
     module or class object.

     This is often the same as ‘obj.__annotations__’.  In addition,
     forward references encoded as string literals are handled by
     evaluating them in ‘globals’ and ‘locals’ namespaces.  If
     necessary, ‘Optional[t]’ is added for function and method
     annotations if a default value equal to ‘None’ is set.  For a class
     ‘C’, return a dictionary constructed by merging all the
     ‘__annotations__’ along ‘C.__mro__’ in reverse order.

     The function recursively replaces all ‘Annotated[T, ...]’ with ‘T’,
     unless ‘include_extras’ is set to ‘True’ (see *note Annotated: 1ee.
     for more information).  For example:

          class Student(NamedTuple):
              name: Annotated[str, 'some marker']

          get_type_hints(Student) == {'name': str}
          get_type_hints(Student, include_extras=False) == {'name': str}
          get_type_hints(Student, include_extras=True) == {
              'name': Annotated[str, 'some marker']
          }

     Changed in version 3.9: Added ‘include_extras’ parameter as part of
     PEP 593(1).

 -- Function: typing.get_args (tp)

 -- Function: typing.get_origin (tp)

     Provide basic introspection for generic types and special typing
     forms.

     For a typing object of the form ‘X[Y, Z, ...]’ these functions
     return ‘X’ and ‘(Y, Z, ...)’.  If ‘X’ is a generic alias for a
     builtin or *note collections: 1d. class, it gets normalized to the
     original class.  If ‘X’ is a *note Union: 116a. or *note Literal:
     275. contained in another generic type, the order of ‘(Y, Z, ...)’
     may be different from the order of the original arguments ‘[Y, Z,
     ...]’ due to type caching.  For unsupported objects return ‘None’
     and ‘()’ correspondingly.  Examples:

          assert get_origin(Dict[str, int]) is dict
          assert get_args(Dict[int, str]) == (int, str)

          assert get_origin(Union[int, str]) is Union
          assert get_args(Union[int, str]) == (int, str)

     New in version 3.8.

 -- Class: typing.ForwardRef

     A class used for internal typing representation of string forward
     references.  For example, ‘List["SomeClass"]’ is implicitly
     transformed into ‘List[ForwardRef("SomeClass")]’.  This class
     should not be instantiated by a user, but may be used by
     introspection tools.

          Note: PEP 585(2) generic types such as ‘list["SomeClass"]’
          will not be implicitly transformed into
          ‘list[ForwardRef("SomeClass")]’ and thus will not
          automatically resolve to ‘list[SomeClass]’.

     New in version 3.7.4.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0593

   (2) https://www.python.org/dev/peps/pep-0585


File: python.info,  Node: Constant,  Prev: Introspection helpers,  Up: Module contents<3>

5.26.1.27 Constant
..................

 -- Data: typing.TYPE_CHECKING

     A special constant that is assumed to be ‘True’ by 3rd party static
     type checkers.  It is ‘False’ at runtime.  Usage:

          if TYPE_CHECKING:
              import expensive_mod

          def fun(arg: 'expensive_mod.SomeType') -> None:
              local_var: expensive_mod.AnotherType = other_fun()

     The first type annotation must be enclosed in quotes, making it a
     “forward reference”, to hide the ‘expensive_mod’ reference from the
     interpreter runtime.  Type annotations for local variables are not
     evaluated, so the second annotation does not need to be enclosed in
     quotes.

          Note: If ‘from __future__ import annotations’ is used in
          Python 3.7 or later, annotations are not evaluated at function
          definition time.  Instead, they are stored as strings in
          ‘__annotations__’, This makes it unnecessary to use quotes
          around the annotation.  (see PEP 563(1)).

     New in version 3.5.2.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0563


File: python.info,  Node: pydoc — Documentation generator and online help system,  Next: Python Development Mode,  Prev: typing — Support for type hints,  Up: Development Tools

5.26.2 ‘pydoc’ — Documentation generator and online help system
---------------------------------------------------------------

`Source code:' Lib/pydoc.py(1)

__________________________________________________________________

The *note pydoc: d9. module automatically generates documentation from
Python modules.  The documentation can be presented as pages of text on
the console, served to a Web browser, or saved to HTML files.

For modules, classes, functions and methods, the displayed documentation
is derived from the docstring (i.e.  the ‘__doc__’ attribute) of the
object, and recursively of its documentable members.  If there is no
docstring, *note pydoc: d9. tries to obtain a description from the block
of comment lines just above the definition of the class, function or
method in the source file, or at the top of the module (see *note
inspect.getcomments(): 344a.).

The built-in function *note help(): 175. invokes the online help system
in the interactive interpreter, which uses *note pydoc: d9. to generate
its documentation as text on the console.  The same text documentation
can also be viewed from outside the Python interpreter by running
‘pydoc’ as a script at the operating system’s command prompt.  For
example, running

     pydoc sys

at a shell prompt will display documentation on the *note sys: fd.
module, in a style similar to the manual pages shown by the Unix ‘man’
command.  The argument to ‘pydoc’ can be the name of a function, module,
or package, or a dotted reference to a class, method, or function within
a module or module in a package.  If the argument to ‘pydoc’ looks like
a path (that is, it contains the path separator for your operating
system, such as a slash in Unix), and refers to an existing Python
source file, then documentation is produced for that file.

     Note: In order to find objects and their documentation, *note
     pydoc: d9. imports the module(s) to be documented.  Therefore, any
     code on module level will be executed on that occasion.  Use an ‘if
     __name__ == '__main__':’ guard to only execute code when a file is
     invoked as a script and not just imported.

When printing output to the console, ‘pydoc’ attempts to paginate the
output for easier reading.  If the ‘PAGER’ environment variable is set,
‘pydoc’ will use its value as a pagination program.

Specifying a ‘-w’ flag before the argument will cause HTML documentation
to be written out to a file in the current directory, instead of
displaying text on the console.

Specifying a ‘-k’ flag before the argument will search the synopsis
lines of all available modules for the keyword given as the argument,
again in a manner similar to the Unix ‘man’ command.  The synopsis line
of a module is the first line of its documentation string.

You can also use ‘pydoc’ to start an HTTP server on the local machine
that will serve documentation to visiting Web browsers.  ‘pydoc -p 1234’
will start a HTTP server on port 1234, allowing you to browse the
documentation at ‘http://localhost:1234/’ in your preferred Web browser.
Specifying ‘0’ as the port number will select an arbitrary unused port.

‘pydoc -n <hostname>’ will start the server listening at the given
hostname.  By default the hostname is ‘localhost’ but if you want the
server to be reached from other machines, you may want to change the
host name that the server responds to.  During development this is
especially useful if you want to run pydoc from within a container.

‘pydoc -b’ will start the server and additionally open a web browser to
a module index page.  Each served page has a navigation bar at the top
where you can `Get' help on an individual item, `Search' all modules
with a keyword in their synopsis line, and go to the `Module index',
`Topics' and `Keywords' pages.

When ‘pydoc’ generates documentation, it uses the current environment
and path to locate modules.  Thus, invoking ‘pydoc spam’ documents
precisely the version of the module you would get if you started the
Python interpreter and typed ‘import spam’.

Module docs for core modules are assumed to reside in
‘https://docs.python.org/X.Y/library/’ where ‘X’ and ‘Y’ are the major
and minor version numbers of the Python interpreter.  This can be
overridden by setting the ‘PYTHONDOCS’ environment variable to a
different URL or to a local directory containing the Library Reference
Manual pages.

Changed in version 3.2: Added the ‘-b’ option.

Changed in version 3.3: The ‘-g’ command line option was removed.

Changed in version 3.4: *note pydoc: d9. now uses *note
inspect.signature(): 655. rather than *note inspect.getfullargspec():
657. to extract signature information from callables.

Changed in version 3.7: Added the ‘-n’ option.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/pydoc.py


File: python.info,  Node: Python Development Mode,  Next: Effects of the Python Development Mode,  Prev: pydoc — Documentation generator and online help system,  Up: Development Tools

5.26.3 Python Development Mode
------------------------------

New in version 3.7.

The Python Development Mode introduces additional runtime checks that
are too expensive to be enabled by default.  It should not be more
verbose than the default if the code is correct; new warnings are only
emitted when an issue is detected.

It can be enabled using the *note -X dev: 290. command line option or by
setting the *note PYTHONDEVMODE: 43c. environment variable to ‘1’.


File: python.info,  Node: Effects of the Python Development Mode,  Next: ResourceWarning Example,  Prev: Python Development Mode,  Up: Development Tools

5.26.4 Effects of the Python Development Mode
---------------------------------------------

Enabling the Python Development Mode is similar to the following
command, but with additional effects described below:

     PYTHONMALLOC=debug PYTHONASYNCIODEBUG=1 python3 -W default -X faulthandler

Effects of the Python Development Mode:

   * Add ‘default’ *note warning filter: 147e.  The following warnings
     are shown:

        * *note DeprecationWarning: 15a.

        * *note ImportWarning: 6cf.

        * *note PendingDeprecationWarning: 15c.

        * *note ResourceWarning: 5cb.

     Normally, the above warnings are filtered by the default *note
     warning filters: 147e.

     It behaves as if the *note -W default: 15b. command line option is
     used.

     Use the *note -W error: 15b. command line option or set the *note
     PYTHONWARNINGS: 51c. environment variable to ‘error’ to treat
     warnings as errors.

   * Install debug hooks on memory allocators to check for:

        * Buffer underflow

        * Buffer overflow

        * Memory allocator API violation

        * Unsafe usage of the GIL

     See the *note PyMem_SetupDebugHooks(): 604. C function.

     It behaves as if the *note PYTHONMALLOC: 5fd. environment variable
     is set to ‘debug’.

     To enable the Python Development Mode without installing debug
     hooks on memory allocators, set the *note PYTHONMALLOC: 5fd.
     environment variable to ‘default’.

   * Call *note faulthandler.enable(): 642. at Python startup to install
     handlers for the ‘SIGSEGV’, ‘SIGFPE’, ‘SIGABRT’, ‘SIGBUS’ and
     ‘SIGILL’ signals to dump the Python traceback on a crash.

     It behaves as if the *note -X faulthandler: 290. command line
     option is used or if the *note PYTHONFAULTHANDLER: aa7. environment
     variable is set to ‘1’.

   * Enable *note asyncio debug mode: 148e.  For example, *note asyncio:
     9. checks for coroutines that were not awaited and logs them.

     It behaves as if the *note PYTHONASYNCIODEBUG: 148d. environment
     variable is set to ‘1’.

   * Check the `encoding' and `errors' arguments for string encoding and
     decoding operations.  Examples: *note open(): 16f, *note
     str.encode(): 170. and *note bytes.decode(): 171.

     By default, for best performance, the `errors' argument is only
     checked at the first encoding/decoding error and the `encoding'
     argument is sometimes ignored for empty strings.

   * The *note io.IOBase: 30c. destructor logs ‘close()’ exceptions.

   * Set the ‘dev_mode’ attribute of *note sys.flags: c0e. to ‘True’.

The Python Development Mode does not enable the *note tracemalloc: 11d.
module by default, because the overhead cost (to performance and memory)
would be too large.  Enabling the *note tracemalloc: 11d. module
provides additional information on the origin of some errors.  For
example, *note ResourceWarning: 5cb. logs the traceback where the
resource was allocated, and a buffer overflow error logs the traceback
where the memory block was allocated.

The Python Development Mode does not prevent the *note -O: 77e. command
line option from removing *note assert: 23f. statements nor from setting
*note __debug__: 1137. to ‘False’.

Changed in version 3.8: The *note io.IOBase: 30c. destructor now logs
‘close()’ exceptions.

Changed in version 3.9: The `encoding' and `errors' arguments are now
checked for string encoding and decoding operations.


File: python.info,  Node: ResourceWarning Example,  Next: Bad file descriptor error example,  Prev: Effects of the Python Development Mode,  Up: Development Tools

5.26.5 ResourceWarning Example
------------------------------

Example of a script counting the number of lines of the text file
specified in the command line:

     import sys

     def main():
         fp = open(sys.argv[1])
         nlines = len(fp.readlines())
         print(nlines)
         # The file is closed implicitly

     if __name__ == "__main__":
         main()

The script does not close the file explicitly.  By default, Python does
not emit any warning.  Example using README.txt, which has 269 lines:

     $ python3 script.py README.txt
     269

Enabling the Python Development Mode displays a *note ResourceWarning:
5cb. warning:

     $ python3 -X dev script.py README.txt
     269
     script.py:10: ResourceWarning: unclosed file <_io.TextIOWrapper name='README.rst' mode='r' encoding='UTF-8'>
       main()
     ResourceWarning: Enable tracemalloc to get the object allocation traceback

In addition, enabling *note tracemalloc: 11d. shows the line where the
file was opened:

     $ python3 -X dev -X tracemalloc=5 script.py README.rst
     269
     script.py:10: ResourceWarning: unclosed file <_io.TextIOWrapper name='README.rst' mode='r' encoding='UTF-8'>
       main()
     Object allocated at (most recent call last):
       File "script.py", lineno 10
         main()
       File "script.py", lineno 4
         fp = open(sys.argv[1])

The fix is to close explicitly the file.  Example using a context
manager:

     def main():
         # Close the file explicitly when exiting the with block
         with open(sys.argv[1]) as fp:
             nlines = len(fp.readlines())
         print(nlines)

Not closing a resource explicitly can leave a resource open for way
longer than expected; it can cause severe issues upon exiting Python.
It is bad in CPython, but it is even worse in PyPy.  Closing resources
explicitly makes an application more deterministic and more reliable.


File: python.info,  Node: Bad file descriptor error example,  Next: doctest — Test interactive Python examples,  Prev: ResourceWarning Example,  Up: Development Tools

5.26.6 Bad file descriptor error example
----------------------------------------

Script displaying the first line of itself:

     import os

     def main():
         fp = open(__file__)
         firstline = fp.readline()
         print(firstline.rstrip())
         os.close(fp.fileno())
         # The file is closed implicitly

     main()

By default, Python does not emit any warning:

     $ python3 script.py
     import os

The Python Development Mode shows a *note ResourceWarning: 5cb. and logs
a “Bad file descriptor” error when finalizing the file object:

     $ python3 script.py
     import os
     script.py:10: ResourceWarning: unclosed file <_io.TextIOWrapper name='script.py' mode='r' encoding='UTF-8'>
       main()
     ResourceWarning: Enable tracemalloc to get the object allocation traceback
     Exception ignored in: <_io.TextIOWrapper name='script.py' mode='r' encoding='UTF-8'>
     Traceback (most recent call last):
       File "script.py", line 10, in <module>
         main()
     OSError: [Errno 9] Bad file descriptor

‘os.close(fp.fileno())’ closes the file descriptor.  When the file
object finalizer tries to close the file descriptor again, it fails with
the ‘Bad file descriptor’ error.  A file descriptor must be closed only
once.  In the worst case scenario, closing it twice can lead to a crash
(see bpo-18748(1) for an example).

The fix is to remove the ‘os.close(fp.fileno())’ line, or open the file
with ‘closefd=False’.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue18748


File: python.info,  Node: doctest — Test interactive Python examples,  Next: unittest — Unit testing framework,  Prev: Bad file descriptor error example,  Up: Development Tools

5.26.7 ‘doctest’ — Test interactive Python examples
---------------------------------------------------

`Source code:' Lib/doctest.py(1)

__________________________________________________________________

The *note doctest: 66. module searches for pieces of text that look like
interactive Python sessions, and then executes those sessions to verify
that they work exactly as shown.  There are several common ways to use
doctest:

   * To check that a module’s docstrings are up-to-date by verifying
     that all interactive examples still work as documented.

   * To perform regression testing by verifying that interactive
     examples from a test file or a test object work as expected.

   * To write tutorial documentation for a package, liberally
     illustrated with input-output examples.  Depending on whether the
     examples or the expository text are emphasized, this has the flavor
     of “literate testing” or “executable documentation”.

Here’s a complete but small example module:

     """
     This is the "example" module.

     The example module supplies one function, factorial().  For example,

     >>> factorial(5)
     120
     """

     def factorial(n):
         """Return the factorial of n, an exact integer >= 0.

         >>> [factorial(n) for n in range(6)]
         [1, 1, 2, 6, 24, 120]
         >>> factorial(30)
         265252859812191058636308480000000
         >>> factorial(-1)
         Traceback (most recent call last):
             ...
         ValueError: n must be >= 0

         Factorials of floats are OK, but the float must be an exact integer:
         >>> factorial(30.1)
         Traceback (most recent call last):
             ...
         ValueError: n must be exact integer
         >>> factorial(30.0)
         265252859812191058636308480000000

         It must also not be ridiculously large:
         >>> factorial(1e100)
         Traceback (most recent call last):
             ...
         OverflowError: n too large
         """

         import math
         if not n >= 0:
             raise ValueError("n must be >= 0")
         if math.floor(n) != n:
             raise ValueError("n must be exact integer")
         if n+1 == n:  # catch a value like 1e300
             raise OverflowError("n too large")
         result = 1
         factor = 2
         while factor <= n:
             result *= factor
             factor += 1
         return result


     if __name__ == "__main__":
         import doctest
         doctest.testmod()

If you run ‘example.py’ directly from the command line, *note doctest:
66. works its magic:

     $ python example.py
     $

There’s no output!  That’s normal, and it means all the examples worked.
Pass ‘-v’ to the script, and *note doctest: 66. prints a detailed log of
what it’s trying, and prints a summary at the end:

     $ python example.py -v
     Trying:
         factorial(5)
     Expecting:
         120
     ok
     Trying:
         [factorial(n) for n in range(6)]
     Expecting:
         [1, 1, 2, 6, 24, 120]
     ok

And so on, eventually ending with:

     Trying:
         factorial(1e100)
     Expecting:
         Traceback (most recent call last):
             ...
         OverflowError: n too large
     ok
     2 items passed all tests:
        1 tests in __main__
        8 tests in __main__.factorial
     9 tests in 2 items.
     9 passed and 0 failed.
     Test passed.
     $

That’s all you need to know to start making productive use of *note
doctest: 66.!  Jump in.  The following sections provide full details.
Note that there are many examples of doctests in the standard Python
test suite and libraries.  Especially useful examples can be found in
the standard test file ‘Lib/test/test_doctest.py’.

* Menu:

* Simple Usage; Checking Examples in Docstrings: Simple Usage Checking Examples in Docstrings.
* Simple Usage; Checking Examples in a Text File: Simple Usage Checking Examples in a Text File.
* How It Works::
* Basic API::
* Unittest API::
* Advanced API::
* Debugging::
* Soapbox::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/doctest.py


File: python.info,  Node: Simple Usage Checking Examples in Docstrings,  Next: Simple Usage Checking Examples in a Text File,  Up: doctest — Test interactive Python examples

5.26.7.1 Simple Usage: Checking Examples in Docstrings
......................................................

The simplest way to start using doctest (but not necessarily the way
you’ll continue to do it) is to end each module ‘M’ with:

     if __name__ == "__main__":
         import doctest
         doctest.testmod()

*note doctest: 66. then examines docstrings in module ‘M’.

Running the module as a script causes the examples in the docstrings to
get executed and verified:

     python M.py

This won’t display anything unless an example fails, in which case the
failing example(s) and the cause(s) of the failure(s) are printed to
stdout, and the final line of output is ‘***Test Failed*** N failures.’,
where `N' is the number of examples that failed.

Run it with the ‘-v’ switch instead:

     python M.py -v

and a detailed report of all examples tried is printed to standard
output, along with assorted summaries at the end.

You can force verbose mode by passing ‘verbose=True’ to *note testmod():
e95, or prohibit it by passing ‘verbose=False’.  In either of those
cases, ‘sys.argv’ is not examined by *note testmod(): e95. (so passing
‘-v’ or not has no effect).

There is also a command line shortcut for running *note testmod(): e95.
You can instruct the Python interpreter to run the doctest module
directly from the standard library and pass the module name(s) on the
command line:

     python -m doctest -v example.py

This will import ‘example.py’ as a standalone module and run *note
testmod(): e95. on it.  Note that this may not work correctly if the
file is part of a package and imports other submodules from that
package.

For more information on *note testmod(): e95, see section *note Basic
API: 3454.


File: python.info,  Node: Simple Usage Checking Examples in a Text File,  Next: How It Works,  Prev: Simple Usage Checking Examples in Docstrings,  Up: doctest — Test interactive Python examples

5.26.7.2 Simple Usage: Checking Examples in a Text File
.......................................................

Another simple application of doctest is testing interactive examples in
a text file.  This can be done with the *note testfile(): 3457.
function:

     import doctest
     doctest.testfile("example.txt")

That short script executes and verifies any interactive Python examples
contained in the file ‘example.txt’.  The file content is treated as if
it were a single giant docstring; the file doesn’t need to contain a
Python program!  For example, perhaps ‘example.txt’ contains this:

     The ``example`` module
     ======================

     Using ``factorial``
     -------------------

     This is an example text file in reStructuredText format.  First import
     ``factorial`` from the ``example`` module:

         >>> from example import factorial

     Now use it:

         >>> factorial(6)
         120

Running ‘doctest.testfile("example.txt")’ then finds the error in this
documentation:

     File "./example.txt", line 14, in example.txt
     Failed example:
         factorial(6)
     Expected:
         120
     Got:
         720

As with *note testmod(): e95, *note testfile(): 3457. won’t display
anything unless an example fails.  If an example does fail, then the
failing example(s) and the cause(s) of the failure(s) are printed to
stdout, using the same format as *note testmod(): e95.

By default, *note testfile(): 3457. looks for files in the calling
module’s directory.  See section *note Basic API: 3454. for a
description of the optional arguments that can be used to tell it to
look for files in other locations.

Like *note testmod(): e95, *note testfile(): 3457.’s verbosity can be
set with the ‘-v’ command-line switch or with the optional keyword
argument `verbose'.

There is also a command line shortcut for running *note testfile():
3457.  You can instruct the Python interpreter to run the doctest module
directly from the standard library and pass the file name(s) on the
command line:

     python -m doctest -v example.txt

Because the file name does not end with ‘.py’, *note doctest: 66. infers
that it must be run with *note testfile(): 3457, not *note testmod():
e95.

For more information on *note testfile(): 3457, see section *note Basic
API: 3454.


File: python.info,  Node: How It Works,  Next: Basic API,  Prev: Simple Usage Checking Examples in a Text File,  Up: doctest — Test interactive Python examples

5.26.7.3 How It Works
.....................

This section examines in detail how doctest works: which docstrings it
looks at, how it finds interactive examples, what execution context it
uses, how it handles exceptions, and how option flags can be used to
control its behavior.  This is the information that you need to know to
write doctest examples; for information about actually running doctest
on these examples, see the following sections.

* Menu:

* Which Docstrings Are Examined?::
* How are Docstring Examples Recognized?::
* What’s the Execution Context?::
* What About Exceptions?::
* Option Flags::
* Directives::
* Warnings: Warnings<2>.


File: python.info,  Node: Which Docstrings Are Examined?,  Next: How are Docstring Examples Recognized?,  Up: How It Works

5.26.7.4 Which Docstrings Are Examined?
.......................................

The module docstring, and all function, class and method docstrings are
searched.  Objects imported into the module are not searched.

In addition, if ‘M.__test__’ exists and “is true”, it must be a dict,
and each entry maps a (string) name to a function object, class object,
or string.  Function and class object docstrings found from ‘M.__test__’
are searched, and strings are treated as if they were docstrings.  In
output, a key ‘K’ in ‘M.__test__’ appears with name

     <name of M>.__test__.K

Any classes found are recursively searched similarly, to test docstrings
in their contained methods and nested classes.

`CPython implementation detail:' Prior to version 3.4, extension modules
written in C were not fully searched by doctest.


File: python.info,  Node: How are Docstring Examples Recognized?,  Next: What’s the Execution Context?,  Prev: Which Docstrings Are Examined?,  Up: How It Works

5.26.7.5 How are Docstring Examples Recognized?
...............................................

In most cases a copy-and-paste of an interactive console session works
fine, but doctest isn’t trying to do an exact emulation of any specific
Python shell.

     >>> # comments are ignored
     >>> x = 12
     >>> x
     12
     >>> if x == 13:
     ...     print("yes")
     ... else:
     ...     print("no")
     ...     print("NO")
     ...     print("NO!!!")
     ...
     no
     NO
     NO!!!
     >>>

Any expected output must immediately follow the final ‘'>>> '’ or ‘'...
'’ line containing the code, and the expected output (if any) extends to
the next ‘'>>> '’ or all-whitespace line.

The fine print:

   * Expected output cannot contain an all-whitespace line, since such a
     line is taken to signal the end of expected output.  If expected
     output does contain a blank line, put ‘<BLANKLINE>’ in your doctest
     example each place a blank line is expected.

   * All hard tab characters are expanded to spaces, using 8-column tab
     stops.  Tabs in output generated by the tested code are not
     modified.  Because any hard tabs in the sample output `are'
     expanded, this means that if the code output includes hard tabs,
     the only way the doctest can pass is if the *note
     NORMALIZE_WHITESPACE: 345e. option or *note directive: 345f. is in
     effect.  Alternatively, the test can be rewritten to capture the
     output and compare it to an expected value as part of the test.
     This handling of tabs in the source was arrived at through trial
     and error, and has proven to be the least error prone way of
     handling them.  It is possible to use a different algorithm for
     handling tabs by writing a custom *note DocTestParser: 3460. class.

   * Output to stdout is captured, but not output to stderr (exception
     tracebacks are captured via a different means).

   * If you continue a line via backslashing in an interactive session,
     or for any other reason use a backslash, you should use a raw
     docstring, which will preserve your backslashes exactly as you type
     them:

          >>> def f(x):
          ...     r'''Backslashes in a raw docstring: m\n'''
          >>> print(f.__doc__)
          Backslashes in a raw docstring: m\n

     Otherwise, the backslash will be interpreted as part of the string.
     For example, the ‘\n’ above would be interpreted as a newline
     character.  Alternatively, you can double each backslash in the
     doctest version (and not use a raw string):

          >>> def f(x):
          ...     '''Backslashes in a raw docstring: m\\n'''
          >>> print(f.__doc__)
          Backslashes in a raw docstring: m\n

   * The starting column doesn’t matter:

          >>> assert "Easy!"
                >>> import math
                    >>> math.floor(1.9)
                    1

     and as many leading whitespace characters are stripped from the
     expected output as appeared in the initial ‘'>>> '’ line that
     started the example.


File: python.info,  Node: What’s the Execution Context?,  Next: What About Exceptions?,  Prev: How are Docstring Examples Recognized?,  Up: How It Works

5.26.7.6 What’s the Execution Context?
......................................

By default, each time *note doctest: 66. finds a docstring to test, it
uses a `shallow copy' of ‘M’’s globals, so that running tests doesn’t
change the module’s real globals, and so that one test in ‘M’ can’t
leave behind crumbs that accidentally allow another test to work.  This
means examples can freely use any names defined at top-level in ‘M’, and
names defined earlier in the docstring being run.  Examples cannot see
names defined in other docstrings.

You can force use of your own dict as the execution context by passing
‘globs=your_dict’ to *note testmod(): e95. or *note testfile(): 3457.
instead.


File: python.info,  Node: What About Exceptions?,  Next: Option Flags,  Prev: What’s the Execution Context?,  Up: How It Works

5.26.7.7 What About Exceptions?
...............................

No problem, provided that the traceback is the only output produced by
the example: just paste in the traceback.  (1) Since tracebacks contain
details that are likely to change rapidly (for example, exact file paths
and line numbers), this is one case where doctest works hard to be
flexible in what it accepts.

Simple example:

     >>> [1, 2, 3].remove(42)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ValueError: list.remove(x): x not in list

That doctest succeeds if *note ValueError: 16d. is raised, with the
‘list.remove(x): x not in list’ detail as shown.

The expected output for an exception must start with a traceback header,
which may be either of the following two lines, indented the same as the
first line of the example:

     Traceback (most recent call last):
     Traceback (innermost last):

The traceback header is followed by an optional traceback stack, whose
contents are ignored by doctest.  The traceback stack is typically
omitted, or copied verbatim from an interactive session.

The traceback stack is followed by the most interesting part: the
line(s) containing the exception type and detail.  This is usually the
last line of a traceback, but can extend across multiple lines if the
exception has a multi-line detail:

     >>> raise ValueError('multi\n    line\ndetail')
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ValueError: multi
         line
     detail

The last three lines (starting with *note ValueError: 16d.) are compared
against the exception’s type and detail, and the rest are ignored.

Best practice is to omit the traceback stack, unless it adds significant
documentation value to the example.  So the last example is probably
better as:

     >>> raise ValueError('multi\n    line\ndetail')
     Traceback (most recent call last):
         ...
     ValueError: multi
         line
     detail

Note that tracebacks are treated very specially.  In particular, in the
rewritten example, the use of ‘...’ is independent of doctest’s *note
ELLIPSIS: e96. option.  The ellipsis in that example could be left out,
or could just as well be three (or three hundred) commas or digits, or
an indented transcript of a Monty Python skit.

Some details you should read once, but won’t need to remember:

   * Doctest can’t guess whether your expected output came from an
     exception traceback or from ordinary printing.  So, e.g., an
     example that expects ‘ValueError: 42 is prime’ will pass whether
     *note ValueError: 16d. is actually raised or if the example merely
     prints that traceback text.  In practice, ordinary output rarely
     begins with a traceback header line, so this doesn’t create real
     problems.

   * Each line of the traceback stack (if present) must be indented
     further than the first line of the example, `or' start with a
     non-alphanumeric character.  The first line following the traceback
     header indented the same and starting with an alphanumeric is taken
     to be the start of the exception detail.  Of course this does the
     right thing for genuine tracebacks.

   * When the *note IGNORE_EXCEPTION_DETAIL: 3465. doctest option is
     specified, everything following the leftmost colon and any module
     information in the exception name is ignored.

   * The interactive shell omits the traceback header line for some
     *note SyntaxError: 55a.s.  But doctest uses the traceback header
     line to distinguish exceptions from non-exceptions.  So in the rare
     case where you need to test a *note SyntaxError: 55a. that omits
     the traceback header, you will need to manually add the traceback
     header line to your test example.

   * For some *note SyntaxError: 55a.s, Python displays the character
     position of the syntax error, using a ‘^’ marker:

          >>> 1 1
            File "<stdin>", line 1
              1 1
                ^
          SyntaxError: invalid syntax

     Since the lines showing the position of the error come before the
     exception type and detail, they are not checked by doctest.  For
     example, the following test would pass, even though it puts the ‘^’
     marker in the wrong location:

          >>> 1 1
          Traceback (most recent call last):
            File "<stdin>", line 1
              1 1
              ^
          SyntaxError: invalid syntax

   ---------- Footnotes ----------

   (1) (1) Examples containing both expected output and an exception are
not supported.  Trying to guess where one ends and the other begins is
too error-prone, and that also makes for a confusing test.


File: python.info,  Node: Option Flags,  Next: Directives,  Prev: What About Exceptions?,  Up: How It Works

5.26.7.8 Option Flags
.....................

A number of option flags control various aspects of doctest’s behavior.
Symbolic names for the flags are supplied as module constants, which can
be *note bitwise ORed: 1676. together and passed to various functions.
The names can also be used in *note doctest directives: 345f, and may be
passed to the doctest command line interface via the ‘-o’ option.

New in version 3.4: The ‘-o’ command line option.

The first group of options define test semantics, controlling aspects of
how doctest decides whether actual output matches an example’s expected
output:

 -- Data: doctest.DONT_ACCEPT_TRUE_FOR_1

     By default, if an expected output block contains just ‘1’, an
     actual output block containing just ‘1’ or just ‘True’ is
     considered to be a match, and similarly for ‘0’ versus ‘False’.
     When *note DONT_ACCEPT_TRUE_FOR_1: 3468. is specified, neither
     substitution is allowed.  The default behavior caters to that
     Python changed the return type of many functions from integer to
     boolean; doctests expecting “little integer” output still work in
     these cases.  This option will probably go away, but not for
     several years.

 -- Data: doctest.DONT_ACCEPT_BLANKLINE

     By default, if an expected output block contains a line containing
     only the string ‘<BLANKLINE>’, then that line will match a blank
     line in the actual output.  Because a genuinely blank line delimits
     the expected output, this is the only way to communicate that a
     blank line is expected.  When *note DONT_ACCEPT_BLANKLINE: 3469. is
     specified, this substitution is not allowed.

 -- Data: doctest.NORMALIZE_WHITESPACE

     When specified, all sequences of whitespace (blanks and newlines)
     are treated as equal.  Any sequence of whitespace within the
     expected output will match any sequence of whitespace within the
     actual output.  By default, whitespace must match exactly.  *note
     NORMALIZE_WHITESPACE: 345e. is especially useful when a line of
     expected output is very long, and you want to wrap it across
     multiple lines in your source.

 -- Data: doctest.ELLIPSIS

     When specified, an ellipsis marker (‘...’) in the expected output
     can match any substring in the actual output.  This includes
     substrings that span line boundaries, and empty substrings, so it’s
     best to keep usage of this simple.  Complicated uses can lead to
     the same kinds of “oops, it matched too much!” surprises that ‘.*’
     is prone to in regular expressions.

 -- Data: doctest.IGNORE_EXCEPTION_DETAIL

     When specified, an example that expects an exception passes if an
     exception of the expected type is raised, even if the exception
     detail does not match.  For example, an example expecting
     ‘ValueError: 42’ will pass if the actual exception raised is
     ‘ValueError: 3*14’, but will fail, e.g., if *note TypeError: 1fe.
     is raised.

     It will also ignore the module name used in Python 3 doctest
     reports.  Hence both of these variations will work with the flag
     specified, regardless of whether the test is run under Python 2.7
     or Python 3.2 (or later versions):

          >>> raise CustomError('message')
          Traceback (most recent call last):
          CustomError: message

          >>> raise CustomError('message')
          Traceback (most recent call last):
          my_module.CustomError: message

     Note that *note ELLIPSIS: e96. can also be used to ignore the
     details of the exception message, but such a test may still fail
     based on whether or not the module details are printed as part of
     the exception name.  Using *note IGNORE_EXCEPTION_DETAIL: 3465. and
     the details from Python 2.3 is also the only clear way to write a
     doctest that doesn’t care about the exception detail yet continues
     to pass under Python 2.3 or earlier (those releases do not support
     *note doctest directives: 345f. and ignore them as irrelevant
     comments).  For example:

          >>> (1, 2)[3] = 'moo'
          Traceback (most recent call last):
            File "<stdin>", line 1, in <module>
          TypeError: object doesn't support item assignment

     passes under Python 2.3 and later Python versions with the flag
     specified, even though the detail changed in Python 2.4 to say
     “does not” instead of “doesn’t”.

     Changed in version 3.2: *note IGNORE_EXCEPTION_DETAIL: 3465. now
     also ignores any information relating to the module containing the
     exception under test.

 -- Data: doctest.SKIP

     When specified, do not run the example at all.  This can be useful
     in contexts where doctest examples serve as both documentation and
     test cases, and an example should be included for documentation
     purposes, but should not be checked.  E.g., the example’s output
     might be random; or the example might depend on resources which
     would be unavailable to the test driver.

     The SKIP flag can also be used for temporarily “commenting out”
     examples.

 -- Data: doctest.COMPARISON_FLAGS

     A bitmask or’ing together all the comparison flags above.

The second group of options controls how test failures are reported:

 -- Data: doctest.REPORT_UDIFF

     When specified, failures that involve multi-line expected and
     actual outputs are displayed using a unified diff.

 -- Data: doctest.REPORT_CDIFF

     When specified, failures that involve multi-line expected and
     actual outputs will be displayed using a context diff.

 -- Data: doctest.REPORT_NDIFF

     When specified, differences are computed by ‘difflib.Differ’, using
     the same algorithm as the popular ‘ndiff.py’ utility.  This is the
     only method that marks differences within lines as well as across
     lines.  For example, if a line of expected output contains digit
     ‘1’ where actual output contains letter ‘l’, a line is inserted
     with a caret marking the mismatching column positions.

 -- Data: doctest.REPORT_ONLY_FIRST_FAILURE

     When specified, display the first failing example in each doctest,
     but suppress output for all remaining examples.  This will prevent
     doctest from reporting correct examples that break because of
     earlier failures; but it might also hide incorrect examples that
     fail independently of the first failure.  When *note
     REPORT_ONLY_FIRST_FAILURE: 346c. is specified, the remaining
     examples are still run, and still count towards the total number of
     failures reported; only the output is suppressed.

 -- Data: doctest.FAIL_FAST

     When specified, exit after the first failing example and don’t
     attempt to run the remaining examples.  Thus, the number of
     failures reported will be at most 1.  This flag may be useful
     during debugging, since examples after the first failure won’t even
     produce debugging output.

     The doctest command line accepts the option ‘-f’ as a shorthand for
     ‘-o FAIL_FAST’.

     New in version 3.4.

 -- Data: doctest.REPORTING_FLAGS

     A bitmask or’ing together all the reporting flags above.

There is also a way to register new option flag names, though this isn’t
useful unless you intend to extend *note doctest: 66. internals via
subclassing:

 -- Function: doctest.register_optionflag (name)

     Create a new option flag with a given name, and return the new
     flag’s integer value.  *note register_optionflag(): 346e. can be
     used when subclassing *note OutputChecker: 346f. or *note
     DocTestRunner: 3470. to create new options that are supported by
     your subclasses.  *note register_optionflag(): 346e. should always
     be called using the following idiom:

          MY_FLAG = register_optionflag('MY_FLAG')


File: python.info,  Node: Directives,  Next: Warnings<2>,  Prev: Option Flags,  Up: How It Works

5.26.7.9 Directives
...................

Doctest directives may be used to modify the *note option flags: 929.
for an individual example.  Doctest directives are special Python
comments following an example’s source code:

     directive             ::= "#" "doctest:" directive_options
     directive_options     ::= directive_option ("," directive_option)\*
     directive_option      ::= on_or_off directive_option_name
     on_or_off             ::= "+" \| "-"
     directive_option_name ::= "DONT_ACCEPT_BLANKLINE" \| "NORMALIZE_WHITESPACE" \| ...

Whitespace is not allowed between the ‘+’ or ‘-’ and the directive
option name.  The directive option name can be any of the option flag
names explained above.

An example’s doctest directives modify doctest’s behavior for that
single example.  Use ‘+’ to enable the named behavior, or ‘-’ to disable
it.

For example, this test passes:

     >>> print(list(range(20)))
     [0,   1,  2,  3,  4,  5,  6,  7,  8,  9,
     10,  11, 12, 13, 14, 15, 16, 17, 18, 19]

Without the directive it would fail, both because the actual output
doesn’t have two blanks before the single-digit list elements, and
because the actual output is on a single line.  This test also passes,
and also requires a directive to do so:

     >>> print(list(range(20)))
     [0, 1, ..., 18, 19]

Multiple directives can be used on a single physical line, separated by
commas:

     >>> print(list(range(20)))
     [0,    1, ...,   18,    19]

If multiple directive comments are used for a single example, then they
are combined:

     >>> print(list(range(20)))
     ...
     [0,    1, ...,   18,    19]

As the previous example shows, you can add ‘...’ lines to your example
containing only directives.  This can be useful when an example is too
long for a directive to comfortably fit on the same line:

     >>> print(list(range(5)) + list(range(10, 20)) + list(range(30, 40)))
     ...
     [0, ..., 4, 10, ..., 19, 30, ..., 39]

Note that since all options are disabled by default, and directives
apply only to the example they appear in, enabling options (via ‘+’ in a
directive) is usually the only meaningful choice.  However, option flags
can also be passed to functions that run doctests, establishing
different defaults.  In such cases, disabling an option via ‘-’ in a
directive can be useful.


File: python.info,  Node: Warnings<2>,  Prev: Directives,  Up: How It Works

5.26.7.10 Warnings
..................

*note doctest: 66. is serious about requiring exact matches in expected
output.  If even a single character doesn’t match, the test fails.  This
will probably surprise you a few times, as you learn exactly what Python
does and doesn’t guarantee about output.  For example, when printing a
set, Python doesn’t guarantee that the element is printed in any
particular order, so a test like

     >>> foo()
     {"Hermione", "Harry"}

is vulnerable!  One workaround is to do

     >>> foo() == {"Hermione", "Harry"}
     True

instead.  Another is to do

     >>> d = sorted(foo())
     >>> d
     ['Harry', 'Hermione']

     Note: Before Python 3.6, when printing a dict, Python did not
     guarantee that the key-value pairs was printed in any particular
     order.

There are others, but you get the idea.

Another bad idea is to print things that embed an object address, like

     >>> id(1.0) # certain to fail some of the time
     7948648
     >>> class C: pass
     >>> C()   # the default repr() for instances embeds an address
     <__main__.C instance at 0x00AC18F0>

The *note ELLIPSIS: e96. directive gives a nice approach for the last
example:

     >>> C()
     <__main__.C instance at 0x...>

Floating-point numbers are also subject to small output variations
across platforms, because Python defers to the platform C library for
float formatting, and C libraries vary widely in quality here.

     >>> 1./7  # risky
     0.14285714285714285
     >>> print(1./7) # safer
     0.142857142857
     >>> print(round(1./7, 6)) # much safer
     0.142857

Numbers of the form ‘I/2.**J’ are safe across all platforms, and I often
contrive doctest examples to produce numbers of that form:

     >>> 3./4  # utterly safe
     0.75

Simple fractions are also easier for people to understand, and that
makes for better documentation.


File: python.info,  Node: Basic API,  Next: Unittest API,  Prev: How It Works,  Up: doctest — Test interactive Python examples

5.26.7.11 Basic API
...................

The functions *note testmod(): e95. and *note testfile(): 3457. provide
a simple interface to doctest that should be sufficient for most basic
uses.  For a less formal introduction to these two functions, see
sections *note Simple Usage; Checking Examples in Docstrings: 3452. and
*note Simple Usage; Checking Examples in a Text File: 3455.

 -- Function: doctest.testfile (filename, module_relative=True,
          name=None, package=None, globs=None, verbose=None,
          report=True, optionflags=0, extraglobs=None,
          raise_on_error=False, parser=DocTestParser(), encoding=None)

     All arguments except `filename' are optional, and should be
     specified in keyword form.

     Test examples in the file named `filename'.  Return
     ‘(failure_count, test_count)’.

     Optional argument `module_relative' specifies how the filename
     should be interpreted:

        * If `module_relative' is ‘True’ (the default), then `filename'
          specifies an OS-independent module-relative path.  By default,
          this path is relative to the calling module’s directory; but
          if the `package' argument is specified, then it is relative to
          that package.  To ensure OS-independence, `filename' should
          use ‘/’ characters to separate path segments, and may not be
          an absolute path (i.e., it may not begin with ‘/’).

        * If `module_relative' is ‘False’, then `filename' specifies an
          OS-specific path.  The path may be absolute or relative;
          relative paths are resolved with respect to the current
          working directory.

     Optional argument `name' gives the name of the test; by default, or
     if ‘None’, ‘os.path.basename(filename)’ is used.

     Optional argument `package' is a Python package or the name of a
     Python package whose directory should be used as the base directory
     for a module-relative filename.  If no package is specified, then
     the calling module’s directory is used as the base directory for
     module-relative filenames.  It is an error to specify `package' if
     `module_relative' is ‘False’.

     Optional argument `globs' gives a dict to be used as the globals
     when executing examples.  A new shallow copy of this dict is
     created for the doctest, so its examples start with a clean slate.
     By default, or if ‘None’, a new empty dict is used.

     Optional argument `extraglobs' gives a dict merged into the globals
     used to execute examples.  This works like *note dict.update():
     e8e.: if `globs' and `extraglobs' have a common key, the associated
     value in `extraglobs' appears in the combined dict.  By default, or
     if ‘None’, no extra globals are used.  This is an advanced feature
     that allows parameterization of doctests.  For example, a doctest
     can be written for a base class, using a generic name for the
     class, then reused to test any number of subclasses by passing an
     `extraglobs' dict mapping the generic name to the subclass to be
     tested.

     Optional argument `verbose' prints lots of stuff if true, and
     prints only failures if false; by default, or if ‘None’, it’s true
     if and only if ‘'-v'’ is in ‘sys.argv’.

     Optional argument `report' prints a summary at the end when true,
     else prints nothing at the end.  In verbose mode, the summary is
     detailed, else the summary is very brief (in fact, empty if all
     tests passed).

     Optional argument `optionflags' (default value 0) takes the *note
     bitwise OR: 1676. of option flags.  See section *note Option Flags:
     929.

     Optional argument `raise_on_error' defaults to false.  If true, an
     exception is raised upon the first failure or unexpected exception
     in an example.  This allows failures to be post-mortem debugged.
     Default behavior is to continue running examples.

     Optional argument `parser' specifies a *note DocTestParser: 3460.
     (or subclass) that should be used to extract tests from the files.
     It defaults to a normal parser (i.e., ‘DocTestParser()’).

     Optional argument `encoding' specifies an encoding that should be
     used to convert the file to unicode.

 -- Function: doctest.testmod (m=None, name=None, globs=None,
          verbose=None, report=True, optionflags=0, extraglobs=None,
          raise_on_error=False, exclude_empty=False)

     All arguments are optional, and all except for `m' should be
     specified in keyword form.

     Test examples in docstrings in functions and classes reachable from
     module `m' (or module *note __main__: 1. if `m' is not supplied or
     is ‘None’), starting with ‘m.__doc__’.

     Also test examples reachable from dict ‘m.__test__’, if it exists
     and is not ‘None’.  ‘m.__test__’ maps names (strings) to functions,
     classes and strings; function and class docstrings are searched for
     examples; strings are searched directly, as if they were
     docstrings.

     Only docstrings attached to objects belonging to module `m' are
     searched.

     Return ‘(failure_count, test_count)’.

     Optional argument `name' gives the name of the module; by default,
     or if ‘None’, ‘m.__name__’ is used.

     Optional argument `exclude_empty' defaults to false.  If true,
     objects for which no doctests are found are excluded from
     consideration.  The default is a backward compatibility hack, so
     that code still using ‘doctest.master.summarize()’ in conjunction
     with *note testmod(): e95. continues to get output for objects with
     no tests.  The `exclude_empty' argument to the newer *note
     DocTestFinder: 347a. constructor defaults to true.

     Optional arguments `extraglobs', `verbose', `report',
     `optionflags', `raise_on_error', and `globs' are the same as for
     function *note testfile(): 3457. above, except that `globs'
     defaults to ‘m.__dict__’.

 -- Function: doctest.run_docstring_examples (f, globs, verbose=False,
          name="NoName", compileflags=None, optionflags=0)

     Test examples associated with object `f'; for example, `f' may be a
     string, a module, a function, or a class object.

     A shallow copy of dictionary argument `globs' is used for the
     execution context.

     Optional argument `name' is used in failure messages, and defaults
     to ‘"NoName"’.

     If optional argument `verbose' is true, output is generated even if
     there are no failures.  By default, output is generated only in
     case of an example failure.

     Optional argument `compileflags' gives the set of flags that should
     be used by the Python compiler when running the examples.  By
     default, or if ‘None’, flags are deduced corresponding to the set
     of future features found in `globs'.

     Optional argument `optionflags' works as for function *note
     testfile(): 3457. above.


File: python.info,  Node: Unittest API,  Next: Advanced API,  Prev: Basic API,  Up: doctest — Test interactive Python examples

5.26.7.12 Unittest API
......................

As your collection of doctest’ed modules grows, you’ll want a way to run
all their doctests systematically.  *note doctest: 66. provides two
functions that can be used to create *note unittest: 124. test suites
from modules and text files containing doctests.  To integrate with
*note unittest: 124. test discovery, include a ‘load_tests()’ function
in your test module:

     import unittest
     import doctest
     import my_module_with_doctests

     def load_tests(loader, tests, ignore):
         tests.addTests(doctest.DocTestSuite(my_module_with_doctests))
         return tests

There are two main functions for creating *note unittest.TestSuite: 7c1.
instances from text files and modules with doctests:

 -- Function: doctest.DocFileSuite (*paths, module_relative=True,
          package=None, setUp=None, tearDown=None, globs=None,
          optionflags=0, parser=DocTestParser(), encoding=None)

     Convert doctest tests from one or more text files to a *note
     unittest.TestSuite: 7c1.

     The returned *note unittest.TestSuite: 7c1. is to be run by the
     unittest framework and runs the interactive examples in each file.
     If an example in any file fails, then the synthesized unit test
     fails, and a ‘failureException’ exception is raised showing the
     name of the file containing the test and a (sometimes approximate)
     line number.

     Pass one or more paths (as strings) to text files to be examined.

     Options may be provided as keyword arguments:

     Optional argument `module_relative' specifies how the filenames in
     `paths' should be interpreted:

        * If `module_relative' is ‘True’ (the default), then each
          filename in `paths' specifies an OS-independent
          module-relative path.  By default, this path is relative to
          the calling module’s directory; but if the `package' argument
          is specified, then it is relative to that package.  To ensure
          OS-independence, each filename should use ‘/’ characters to
          separate path segments, and may not be an absolute path (i.e.,
          it may not begin with ‘/’).

        * If `module_relative' is ‘False’, then each filename in `paths'
          specifies an OS-specific path.  The path may be absolute or
          relative; relative paths are resolved with respect to the
          current working directory.

     Optional argument `package' is a Python package or the name of a
     Python package whose directory should be used as the base directory
     for module-relative filenames in `paths'.  If no package is
     specified, then the calling module’s directory is used as the base
     directory for module-relative filenames.  It is an error to specify
     `package' if `module_relative' is ‘False’.

     Optional argument `setUp' specifies a set-up function for the test
     suite.  This is called before running the tests in each file.  The
     `setUp' function will be passed a *note DocTest: 347f. object.  The
     setUp function can access the test globals as the `globs' attribute
     of the test passed.

     Optional argument `tearDown' specifies a tear-down function for the
     test suite.  This is called after running the tests in each file.
     The `tearDown' function will be passed a *note DocTest: 347f.
     object.  The setUp function can access the test globals as the
     `globs' attribute of the test passed.

     Optional argument `globs' is a dictionary containing the initial
     global variables for the tests.  A new copy of this dictionary is
     created for each test.  By default, `globs' is a new empty
     dictionary.

     Optional argument `optionflags' specifies the default doctest
     options for the tests, created by or-ing together individual option
     flags.  See section *note Option Flags: 929.  See function *note
     set_unittest_reportflags(): 3480. below for a better way to set
     reporting options.

     Optional argument `parser' specifies a *note DocTestParser: 3460.
     (or subclass) that should be used to extract tests from the files.
     It defaults to a normal parser (i.e., ‘DocTestParser()’).

     Optional argument `encoding' specifies an encoding that should be
     used to convert the file to unicode.

     The global ‘__file__’ is added to the globals provided to doctests
     loaded from a text file using *note DocFileSuite(): 347e.

 -- Function: doctest.DocTestSuite (module=None, globs=None,
          extraglobs=None, test_finder=None, setUp=None, tearDown=None,
          checker=None)

     Convert doctest tests for a module to a *note unittest.TestSuite:
     7c1.

     The returned *note unittest.TestSuite: 7c1. is to be run by the
     unittest framework and runs each doctest in the module.  If any of
     the doctests fail, then the synthesized unit test fails, and a
     ‘failureException’ exception is raised showing the name of the file
     containing the test and a (sometimes approximate) line number.

     Optional argument `module' provides the module to be tested.  It
     can be a module object or a (possibly dotted) module name.  If not
     specified, the module calling this function is used.

     Optional argument `globs' is a dictionary containing the initial
     global variables for the tests.  A new copy of this dictionary is
     created for each test.  By default, `globs' is a new empty
     dictionary.

     Optional argument `extraglobs' specifies an extra set of global
     variables, which is merged into `globs'.  By default, no extra
     globals are used.

     Optional argument `test_finder' is the *note DocTestFinder: 347a.
     object (or a drop-in replacement) that is used to extract doctests
     from the module.

     Optional arguments `setUp', `tearDown', and `optionflags' are the
     same as for function *note DocFileSuite(): 347e. above.

     This function uses the same search technique as *note testmod():
     e95.

     Changed in version 3.5: *note DocTestSuite(): 7c0. returns an empty
     *note unittest.TestSuite: 7c1. if `module' contains no docstrings
     instead of raising *note ValueError: 16d.

Under the covers, *note DocTestSuite(): 7c0. creates a *note
unittest.TestSuite: 7c1. out of ‘doctest.DocTestCase’ instances, and
‘DocTestCase’ is a subclass of *note unittest.TestCase: 9e5.
‘DocTestCase’ isn’t documented here (it’s an internal detail), but
studying its code can answer questions about the exact details of *note
unittest: 124. integration.

Similarly, *note DocFileSuite(): 347e. creates a *note
unittest.TestSuite: 7c1. out of ‘doctest.DocFileCase’ instances, and
‘DocFileCase’ is a subclass of ‘DocTestCase’.

So both ways of creating a *note unittest.TestSuite: 7c1. run instances
of ‘DocTestCase’.  This is important for a subtle reason: when you run
*note doctest: 66. functions yourself, you can control the *note
doctest: 66. options in use directly, by passing option flags to *note
doctest: 66. functions.  However, if you’re writing a *note unittest:
124. framework, *note unittest: 124. ultimately controls when and how
tests get run.  The framework author typically wants to control *note
doctest: 66. reporting options (perhaps, e.g., specified by command line
options), but there’s no way to pass options through *note unittest:
124. to *note doctest: 66. test runners.

For this reason, *note doctest: 66. also supports a notion of *note
doctest: 66. reporting flags specific to *note unittest: 124. support,
via this function:

 -- Function: doctest.set_unittest_reportflags (flags)

     Set the *note doctest: 66. reporting flags to use.

     Argument `flags' takes the *note bitwise OR: 1676. of option flags.
     See section *note Option Flags: 929.  Only “reporting flags” can be
     used.

     This is a module-global setting, and affects all future doctests
     run by module *note unittest: 124.: the ‘runTest()’ method of
     ‘DocTestCase’ looks at the option flags specified for the test case
     when the ‘DocTestCase’ instance was constructed.  If no reporting
     flags were specified (which is the typical and expected case),
     *note doctest: 66.’s *note unittest: 124. reporting flags are *note
     bitwise ORed: 1676. into the option flags, and the option flags so
     augmented are passed to the *note DocTestRunner: 3470. instance
     created to run the doctest.  If any reporting flags were specified
     when the ‘DocTestCase’ instance was constructed, *note doctest:
     66.’s *note unittest: 124. reporting flags are ignored.

     The value of the *note unittest: 124. reporting flags in effect
     before the function was called is returned by the function.


File: python.info,  Node: Advanced API,  Next: Debugging,  Prev: Unittest API,  Up: doctest — Test interactive Python examples

5.26.7.13 Advanced API
......................

The basic API is a simple wrapper that’s intended to make doctest easy
to use.  It is fairly flexible, and should meet most users’ needs;
however, if you require more fine-grained control over testing, or wish
to extend doctest’s capabilities, then you should use the advanced API.

The advanced API revolves around two container classes, which are used
to store the interactive examples extracted from doctest cases:

   * *note Example: 3483.: A single Python *note statement: 1cef, paired
     with its expected output.

   * *note DocTest: 347f.: A collection of *note Example: 3483.s,
     typically extracted from a single docstring or text file.

Additional processing classes are defined to find, parse, and run, and
check doctest examples:

   * *note DocTestFinder: 347a.: Finds all docstrings in a given module,
     and uses a *note DocTestParser: 3460. to create a *note DocTest:
     347f. from every docstring that contains interactive examples.

   * *note DocTestParser: 3460.: Creates a *note DocTest: 347f. object
     from a string (such as an object’s docstring).

   * *note DocTestRunner: 3470.: Executes the examples in a *note
     DocTest: 347f, and uses an *note OutputChecker: 346f. to verify
     their output.

   * *note OutputChecker: 346f.: Compares the actual output from a
     doctest example with the expected output, and decides whether they
     match.

The relationships among these processing classes are summarized in the
following diagram:

                                 list of:
     +------+                   +---------+
     |module| --DocTestFinder-> | DocTest | --DocTestRunner-> results
     +------+    |        ^     +---------+     |       ^    (printed)
                 |        |     | Example |     |       |
                 v        |     |   ...   |     v       |
                DocTestParser   | Example |   OutputChecker
                                +---------+

* Menu:

* DocTest Objects::
* Example Objects::
* DocTestFinder objects::
* DocTestParser objects::
* DocTestRunner objects::
* OutputChecker objects::


File: python.info,  Node: DocTest Objects,  Next: Example Objects,  Up: Advanced API

5.26.7.14 DocTest Objects
.........................

 -- Class: doctest.DocTest (examples, globs, name, filename, lineno,
          docstring)

     A collection of doctest examples that should be run in a single
     namespace.  The constructor arguments are used to initialize the
     attributes of the same names.

     *note DocTest: 347f. defines the following attributes.  They are
     initialized by the constructor, and should not be modified
     directly.

      -- Attribute: examples

          A list of *note Example: 3483. objects encoding the individual
          interactive Python examples that should be run by this test.

      -- Attribute: globs

          The namespace (aka globals) that the examples should be run
          in.  This is a dictionary mapping names to values.  Any
          changes to the namespace made by the examples (such as binding
          new variables) will be reflected in *note globs: 3487. after
          the test is run.

      -- Attribute: name

          A string name identifying the *note DocTest: 347f.  Typically,
          this is the name of the object or file that the test was
          extracted from.

      -- Attribute: filename

          The name of the file that this *note DocTest: 347f. was
          extracted from; or ‘None’ if the filename is unknown, or if
          the *note DocTest: 347f. was not extracted from a file.

      -- Attribute: lineno

          The line number within *note filename: 3489. where this *note
          DocTest: 347f. begins, or ‘None’ if the line number is
          unavailable.  This line number is zero-based with respect to
          the beginning of the file.

      -- Attribute: docstring

          The string that the test was extracted from, or ‘None’ if the
          string is unavailable, or if the test was not extracted from a
          string.


File: python.info,  Node: Example Objects,  Next: DocTestFinder objects,  Prev: DocTest Objects,  Up: Advanced API

5.26.7.15 Example Objects
.........................

 -- Class: doctest.Example (source, want, exc_msg=None, lineno=0,
          indent=0, options=None)

     A single interactive example, consisting of a Python statement and
     its expected output.  The constructor arguments are used to
     initialize the attributes of the same names.

     *note Example: 3483. defines the following attributes.  They are
     initialized by the constructor, and should not be modified
     directly.

      -- Attribute: source

          A string containing the example’s source code.  This source
          code consists of a single Python statement, and always ends
          with a newline; the constructor adds a newline when necessary.

      -- Attribute: want

          The expected output from running the example’s source code
          (either from stdout, or a traceback in case of exception).
          *note want: 348f. ends with a newline unless no output is
          expected, in which case it’s an empty string.  The constructor
          adds a newline when necessary.

      -- Attribute: exc_msg

          The exception message generated by the example, if the example
          is expected to generate an exception; or ‘None’ if it is not
          expected to generate an exception.  This exception message is
          compared against the return value of *note
          traceback.format_exception_only(): 3491.  *note exc_msg: 3490.
          ends with a newline unless it’s ‘None’.  The constructor adds
          a newline if needed.

      -- Attribute: lineno

          The line number within the string containing this example
          where the example begins.  This line number is zero-based with
          respect to the beginning of the containing string.

      -- Attribute: indent

          The example’s indentation in the containing string, i.e., the
          number of space characters that precede the example’s first
          prompt.

      -- Attribute: options

          A dictionary mapping from option flags to ‘True’ or ‘False’,
          which is used to override default options for this example.
          Any option flags not contained in this dictionary are left at
          their default value (as specified by the *note DocTestRunner:
          3470.’s ‘optionflags’).  By default, no options are set.


File: python.info,  Node: DocTestFinder objects,  Next: DocTestParser objects,  Prev: Example Objects,  Up: Advanced API

5.26.7.16 DocTestFinder objects
...............................

 -- Class: doctest.DocTestFinder (verbose=False, parser=DocTestParser(),
          recurse=True, exclude_empty=True)

     A processing class used to extract the *note DocTest: 347f.s that
     are relevant to a given object, from its docstring and the
     docstrings of its contained objects.  *note DocTest: 347f.s can be
     extracted from modules, classes, functions, methods, staticmethods,
     classmethods, and properties.

     The optional argument `verbose' can be used to display the objects
     searched by the finder.  It defaults to ‘False’ (no output).

     The optional argument `parser' specifies the *note DocTestParser:
     3460. object (or a drop-in replacement) that is used to extract
     doctests from docstrings.

     If the optional argument `recurse' is false, then *note
     DocTestFinder.find(): 3497. will only examine the given object, and
     not any contained objects.

     If the optional argument `exclude_empty' is false, then *note
     DocTestFinder.find(): 3497. will include tests for objects with
     empty docstrings.

     *note DocTestFinder: 347a. defines the following method:

      -- Method: find (obj[, name][, module][, globs][, extraglobs])

          Return a list of the *note DocTest: 347f.s that are defined by
          `obj'’s docstring, or by any of its contained objects’
          docstrings.

          The optional argument `name' specifies the object’s name; this
          name will be used to construct names for the returned *note
          DocTest: 347f.s.  If `name' is not specified, then
          ‘obj.__name__’ is used.

          The optional parameter `module' is the module that contains
          the given object.  If the module is not specified or is
          ‘None’, then the test finder will attempt to automatically
          determine the correct module.  The object’s module is used:

             * As a default namespace, if `globs' is not specified.

             * To prevent the DocTestFinder from extracting DocTests
               from objects that are imported from other modules.
               (Contained objects with modules other than `module' are
               ignored.)

             * To find the name of the file containing the object.

             * To help find the line number of the object within its
               file.

          If `module' is ‘False’, no attempt to find the module will be
          made.  This is obscure, of use mostly in testing doctest
          itself: if `module' is ‘False’, or is ‘None’ but cannot be
          found automatically, then all objects are considered to belong
          to the (non-existent) module, so all contained objects will
          (recursively) be searched for doctests.

          The globals for each *note DocTest: 347f. is formed by
          combining `globs' and `extraglobs' (bindings in `extraglobs'
          override bindings in `globs').  A new shallow copy of the
          globals dictionary is created for each *note DocTest: 347f.
          If `globs' is not specified, then it defaults to the module’s
          `__dict__', if specified, or ‘{}’ otherwise.  If `extraglobs'
          is not specified, then it defaults to ‘{}’.


File: python.info,  Node: DocTestParser objects,  Next: DocTestRunner objects,  Prev: DocTestFinder objects,  Up: Advanced API

5.26.7.17 DocTestParser objects
...............................

 -- Class: doctest.DocTestParser

     A processing class used to extract interactive examples from a
     string, and use them to create a *note DocTest: 347f. object.

     *note DocTestParser: 3460. defines the following methods:

      -- Method: get_doctest (string, globs, name, filename, lineno)

          Extract all doctest examples from the given string, and
          collect them into a *note DocTest: 347f. object.

          `globs', `name', `filename', and `lineno' are attributes for
          the new *note DocTest: 347f. object.  See the documentation
          for *note DocTest: 347f. for more information.

      -- Method: get_examples (string, name='<string>')

          Extract all doctest examples from the given string, and return
          them as a list of *note Example: 3483. objects.  Line numbers
          are 0-based.  The optional argument `name' is a name
          identifying this string, and is only used for error messages.

      -- Method: parse (string, name='<string>')

          Divide the given string into examples and intervening text,
          and return them as a list of alternating *note Example: 3483.s
          and strings.  Line numbers for the *note Example: 3483.s are
          0-based.  The optional argument `name' is a name identifying
          this string, and is only used for error messages.


File: python.info,  Node: DocTestRunner objects,  Next: OutputChecker objects,  Prev: DocTestParser objects,  Up: Advanced API

5.26.7.18 DocTestRunner objects
...............................

 -- Class: doctest.DocTestRunner (checker=None, verbose=None,
          optionflags=0)

     A processing class used to execute and verify the interactive
     examples in a *note DocTest: 347f.

     The comparison between expected outputs and actual outputs is done
     by an *note OutputChecker: 346f.  This comparison may be customized
     with a number of option flags; see section *note Option Flags: 929.
     for more information.  If the option flags are insufficient, then
     the comparison may also be customized by passing a subclass of
     *note OutputChecker: 346f. to the constructor.

     The test runner’s display output can be controlled in two ways.
     First, an output function can be passed to ‘TestRunner.run()’; this
     function will be called with strings that should be displayed.  It
     defaults to ‘sys.stdout.write’.  If capturing the output is not
     sufficient, then the display output can be also customized by
     subclassing DocTestRunner, and overriding the methods *note
     report_start(): 349f, *note report_success(): 34a0, *note
     report_unexpected_exception(): 34a1, and *note report_failure():
     34a2.

     The optional keyword argument `checker' specifies the *note
     OutputChecker: 346f. object (or drop-in replacement) that should be
     used to compare the expected outputs to the actual outputs of
     doctest examples.

     The optional keyword argument `verbose' controls the *note
     DocTestRunner: 3470.’s verbosity.  If `verbose' is ‘True’, then
     information is printed about each example, as it is run.  If
     `verbose' is ‘False’, then only failures are printed.  If `verbose'
     is unspecified, or ‘None’, then verbose output is used iff the
     command-line switch ‘-v’ is used.

     The optional keyword argument `optionflags' can be used to control
     how the test runner compares expected output to actual output, and
     how it displays failures.  For more information, see section *note
     Option Flags: 929.

     *note DocTestParser: 3460. defines the following methods:

      -- Method: report_start (out, test, example)

          Report that the test runner is about to process the given
          example.  This method is provided to allow subclasses of *note
          DocTestRunner: 3470. to customize their output; it should not
          be called directly.

          `example' is the example about to be processed.  `test' is the
          test `containing example'.  `out' is the output function that
          was passed to *note DocTestRunner.run(): 34a3.

      -- Method: report_success (out, test, example, got)

          Report that the given example ran successfully.  This method
          is provided to allow subclasses of *note DocTestRunner: 3470.
          to customize their output; it should not be called directly.

          `example' is the example about to be processed.  `got' is the
          actual output from the example.  `test' is the test containing
          `example'.  `out' is the output function that was passed to
          *note DocTestRunner.run(): 34a3.

      -- Method: report_failure (out, test, example, got)

          Report that the given example failed.  This method is provided
          to allow subclasses of *note DocTestRunner: 3470. to customize
          their output; it should not be called directly.

          `example' is the example about to be processed.  `got' is the
          actual output from the example.  `test' is the test containing
          `example'.  `out' is the output function that was passed to
          *note DocTestRunner.run(): 34a3.

      -- Method: report_unexpected_exception (out, test, example,
               exc_info)

          Report that the given example raised an unexpected exception.
          This method is provided to allow subclasses of *note
          DocTestRunner: 3470. to customize their output; it should not
          be called directly.

          `example' is the example about to be processed.  `exc_info' is
          a tuple containing information about the unexpected exception
          (as returned by *note sys.exc_info(): d27.).  `test' is the
          test containing `example'.  `out' is the output function that
          was passed to *note DocTestRunner.run(): 34a3.

      -- Method: run (test, compileflags=None, out=None,
               clear_globs=True)

          Run the examples in `test' (a *note DocTest: 347f. object),
          and display the results using the writer function `out'.

          The examples are run in the namespace ‘test.globs’.  If
          `clear_globs' is true (the default), then this namespace will
          be cleared after the test runs, to help with garbage
          collection.  If you would like to examine the namespace after
          the test completes, then use `clear_globs=False'.

          `compileflags' gives the set of flags that should be used by
          the Python compiler when running the examples.  If not
          specified, then it will default to the set of future-import
          flags that apply to `globs'.

          The output of each example is checked using the *note
          DocTestRunner: 3470.’s output checker, and the results are
          formatted by the ‘DocTestRunner.report_*()’ methods.

      -- Method: summarize (verbose=None)

          Print a summary of all the test cases that have been run by
          this DocTestRunner, and return a *note named tuple: b7b.
          ‘TestResults(failed, attempted)’.

          The optional `verbose' argument controls how detailed the
          summary is.  If the verbosity is not specified, then the *note
          DocTestRunner: 3470.’s verbosity is used.


File: python.info,  Node: OutputChecker objects,  Prev: DocTestRunner objects,  Up: Advanced API

5.26.7.19 OutputChecker objects
...............................

 -- Class: doctest.OutputChecker

     A class used to check the whether the actual output from a doctest
     example matches the expected output.  *note OutputChecker: 346f.
     defines two methods: *note check_output(): 34a7, which compares a
     given pair of outputs, and returns ‘True’ if they match; and *note
     output_difference(): 34a8, which returns a string describing the
     differences between two outputs.

     *note OutputChecker: 346f. defines the following methods:

      -- Method: check_output (want, got, optionflags)

          Return ‘True’ iff the actual output from an example (`got')
          matches the expected output (`want').  These strings are
          always considered to match if they are identical; but
          depending on what option flags the test runner is using,
          several non-exact match types are also possible.  See section
          *note Option Flags: 929. for more information about option
          flags.

      -- Method: output_difference (example, got, optionflags)

          Return a string describing the differences between the
          expected output for a given example (`example') and the actual
          output (`got').  `optionflags' is the set of option flags used
          to compare `want' and `got'.


File: python.info,  Node: Debugging,  Next: Soapbox,  Prev: Advanced API,  Up: doctest — Test interactive Python examples

5.26.7.20 Debugging
...................

Doctest provides several mechanisms for debugging doctest examples:

   * Several functions convert doctests to executable Python programs,
     which can be run under the Python debugger, *note pdb: c9.

   * The *note DebugRunner: 34ab. class is a subclass of *note
     DocTestRunner: 3470. that raises an exception for the first failing
     example, containing information about that example.  This
     information can be used to perform post-mortem debugging on the
     example.

   * The *note unittest: 124. cases generated by *note DocTestSuite():
     7c0. support the *note debug(): 34ac. method defined by *note
     unittest.TestCase: 9e5.

   * You can add a call to *note pdb.set_trace(): 4c9. in a doctest
     example, and you’ll drop into the Python debugger when that line is
     executed.  Then you can inspect current values of variables, and so
     on.  For example, suppose ‘a.py’ contains just this module
     docstring:

          """
          >>> def f(x):
          ...     g(x*2)
          >>> def g(x):
          ...     print(x+3)
          ...     import pdb; pdb.set_trace()
          >>> f(3)
          9
          """

     Then an interactive Python session may look like this:

          >>> import a, doctest
          >>> doctest.testmod(a)
          --Return--
          > <doctest a[1]>(3)g()->None
          -> import pdb; pdb.set_trace()
          (Pdb) list
            1     def g(x):
            2         print(x+3)
            3  ->     import pdb; pdb.set_trace()
          [EOF]
          (Pdb) p x
          6
          (Pdb) step
          --Return--
          > <doctest a[0]>(2)f()->None
          -> g(x*2)
          (Pdb) list
            1     def f(x):
            2  ->     g(x*2)
          [EOF]
          (Pdb) p x
          3
          (Pdb) step
          --Return--
          > <doctest a[2]>(1)?()->None
          -> f(3)
          (Pdb) cont
          (0, 3)
          >>>

Functions that convert doctests to Python code, and possibly run the
synthesized code under the debugger:

 -- Function: doctest.script_from_examples (s)

     Convert text with examples to a script.

     Argument `s' is a string containing doctest examples.  The string
     is converted to a Python script, where doctest examples in `s' are
     converted to regular code, and everything else is converted to
     Python comments.  The generated script is returned as a string.
     For example,

          import doctest
          print(doctest.script_from_examples(r"""
              Set x and y to 1 and 2.
              >>> x, y = 1, 2

              Print their sum:
              >>> print(x+y)
              3
          """))

     displays:

          # Set x and y to 1 and 2.
          x, y = 1, 2
          #
          # Print their sum:
          print(x+y)
          # Expected:
          ## 3

     This function is used internally by other functions (see below),
     but can also be useful when you want to transform an interactive
     Python session into a Python script.

 -- Function: doctest.testsource (module, name)

     Convert the doctest for an object to a script.

     Argument `module' is a module object, or dotted name of a module,
     containing the object whose doctests are of interest.  Argument
     `name' is the name (within the module) of the object with the
     doctests of interest.  The result is a string, containing the
     object’s docstring converted to a Python script, as described for
     *note script_from_examples(): 34ad. above.  For example, if module
     ‘a.py’ contains a top-level function ‘f()’, then

          import a, doctest
          print(doctest.testsource(a, "a.f"))

     prints a script version of function ‘f()’’s docstring, with
     doctests converted to code, and the rest placed in comments.

 -- Function: doctest.debug (module, name, pm=False)

     Debug the doctests for an object.

     The `module' and `name' arguments are the same as for function
     *note testsource(): 34ae. above.  The synthesized Python script for
     the named object’s docstring is written to a temporary file, and
     then that file is run under the control of the Python debugger,
     *note pdb: c9.

     A shallow copy of ‘module.__dict__’ is used for both local and
     global execution context.

     Optional argument `pm' controls whether post-mortem debugging is
     used.  If `pm' has a true value, the script file is run directly,
     and the debugger gets involved only if the script terminates via
     raising an unhandled exception.  If it does, then post-mortem
     debugging is invoked, via *note pdb.post_mortem(): e0a, passing the
     traceback object from the unhandled exception.  If `pm' is not
     specified, or is false, the script is run under the debugger from
     the start, via passing an appropriate *note exec(): d0c. call to
     *note pdb.run(): 34af.

 -- Function: doctest.debug_src (src, pm=False, globs=None)

     Debug the doctests in a string.

     This is like function *note debug(): 34ac. above, except that a
     string containing doctest examples is specified directly, via the
     `src' argument.

     Optional argument `pm' has the same meaning as in function *note
     debug(): 34ac. above.

     Optional argument `globs' gives a dictionary to use as both local
     and global execution context.  If not specified, or ‘None’, an
     empty dictionary is used.  If specified, a shallow copy of the
     dictionary is used.

The *note DebugRunner: 34ab. class, and the special exceptions it may
raise, are of most interest to testing framework authors, and will only
be sketched here.  See the source code, and especially *note
DebugRunner: 34ab.’s docstring (which is a doctest!)  for more details:

 -- Class: doctest.DebugRunner (checker=None, verbose=None,
          optionflags=0)

     A subclass of *note DocTestRunner: 3470. that raises an exception
     as soon as a failure is encountered.  If an unexpected exception
     occurs, an *note UnexpectedException: 34b1. exception is raised,
     containing the test, the example, and the original exception.  If
     the output doesn’t match, then a *note DocTestFailure: 34b2.
     exception is raised, containing the test, the example, and the
     actual output.

     For information about the constructor parameters and methods, see
     the documentation for *note DocTestRunner: 3470. in section *note
     Advanced API: 3482.

There are two exceptions that may be raised by *note DebugRunner: 34ab.
instances:

 -- Exception: doctest.DocTestFailure (test, example, got)

     An exception raised by *note DocTestRunner: 3470. to signal that a
     doctest example’s actual output did not match its expected output.
     The constructor arguments are used to initialize the attributes of
     the same names.

*note DocTestFailure: 34b2. defines the following attributes:

 -- Attribute: DocTestFailure.test

     The *note DocTest: 347f. object that was being run when the example
     failed.

 -- Attribute: DocTestFailure.example

     The *note Example: 3483. that failed.

 -- Attribute: DocTestFailure.got

     The example’s actual output.

 -- Exception: doctest.UnexpectedException (test, example, exc_info)

     An exception raised by *note DocTestRunner: 3470. to signal that a
     doctest example raised an unexpected exception.  The constructor
     arguments are used to initialize the attributes of the same names.

*note UnexpectedException: 34b1. defines the following attributes:

 -- Attribute: UnexpectedException.test

     The *note DocTest: 347f. object that was being run when the example
     failed.

 -- Attribute: UnexpectedException.example

     The *note Example: 3483. that failed.

 -- Attribute: UnexpectedException.exc_info

     A tuple containing information about the unexpected exception, as
     returned by *note sys.exc_info(): d27.


File: python.info,  Node: Soapbox,  Prev: Debugging,  Up: doctest — Test interactive Python examples

5.26.7.21 Soapbox
.................

As mentioned in the introduction, *note doctest: 66. has grown to have
three primary uses:

  1. Checking examples in docstrings.

  2. Regression testing.

  3. Executable documentation / literate testing.

These uses have different requirements, and it is important to
distinguish them.  In particular, filling your docstrings with obscure
test cases makes for bad documentation.

When writing a docstring, choose docstring examples with care.  There’s
an art to this that needs to be learned—it may not be natural at first.
Examples should add genuine value to the documentation.  A good example
can often be worth many words.  If done with care, the examples will be
invaluable for your users, and will pay back the time it takes to
collect them many times over as the years go by and things change.  I’m
still amazed at how often one of my *note doctest: 66. examples stops
working after a “harmless” change.

Doctest also makes an excellent tool for regression testing, especially
if you don’t skimp on explanatory text.  By interleaving prose and
examples, it becomes much easier to keep track of what’s actually being
tested, and why.  When a test fails, good prose can make it much easier
to figure out what the problem is, and how it should be fixed.  It’s
true that you could write extensive comments in code-based testing, but
few programmers do.  Many have found that using doctest approaches
instead leads to much clearer tests.  Perhaps this is simply because
doctest makes writing prose a little easier than writing code, while
writing comments in code is a little harder.  I think it goes deeper
than just that: the natural attitude when writing a doctest-based test
is that you want to explain the fine points of your software, and
illustrate them with examples.  This in turn naturally leads to test
files that start with the simplest features, and logically progress to
complications and edge cases.  A coherent narrative is the result,
instead of a collection of isolated functions that test isolated bits of
functionality seemingly at random.  It’s a different attitude, and
produces different results, blurring the distinction between testing and
explaining.

Regression testing is best confined to dedicated objects or files.
There are several options for organizing tests:

   * Write text files containing test cases as interactive examples, and
     test the files using *note testfile(): 3457. or *note
     DocFileSuite(): 347e.  This is recommended, although is easiest to
     do for new projects, designed from the start to use doctest.

   * Define functions named ‘_regrtest_topic’ that consist of single
     docstrings, containing test cases for the named topics.  These
     functions can be included in the same file as the module, or
     separated out into a separate test file.

   * Define a ‘__test__’ dictionary mapping from regression test topics
     to docstrings containing test cases.

When you have placed your tests in a module, the module can itself be
the test runner.  When a test fails, you can arrange for your test
runner to re-run only the failing doctest while you debug the problem.
Here is a minimal example of such a test runner:

     if __name__ == '__main__':
         import doctest
         flags = doctest.REPORT_NDIFF|doctest.FAIL_FAST
         if len(sys.argv) > 1:
             name = sys.argv[1]
             if name in globals():
                 obj = globals()[name]
             else:
                 obj = __test__[name]
             doctest.run_docstring_examples(obj, globals(), name=name,
                                            optionflags=flags)
         else:
             fail, total = doctest.testmod(optionflags=flags)
             print("{} failures out of {} tests".format(fail, total))


File: python.info,  Node: unittest — Unit testing framework,  Next: unittest mock — mock object library,  Prev: doctest — Test interactive Python examples,  Up: Development Tools

5.26.8 ‘unittest’ — Unit testing framework
------------------------------------------

`Source code:' Lib/unittest/__init__.py(1)

__________________________________________________________________

(If you are already familiar with the basic concepts of testing, you
might want to skip to *note the list of assert methods: 34bd.)

The *note unittest: 124. unit testing framework was originally inspired
by JUnit and has a similar flavor as major unit testing frameworks in
other languages.  It supports test automation, sharing of setup and
shutdown code for tests, aggregation of tests into collections, and
independence of the tests from the reporting framework.

To achieve this, *note unittest: 124. supports some important concepts
in an object-oriented way:

test fixture

     A `test fixture' represents the preparation needed to perform one
     or more tests, and any associated cleanup actions.  This may
     involve, for example, creating temporary or proxy databases,
     directories, or starting a server process.

test case

     A `test case' is the individual unit of testing.  It checks for a
     specific response to a particular set of inputs.  *note unittest:
     124. provides a base class, *note TestCase: 9e5, which may be used
     to create new test cases.

test suite

     A `test suite' is a collection of test cases, test suites, or both.
     It is used to aggregate tests that should be executed together.

test runner

     A `test runner' is a component which orchestrates the execution of
     tests and provides the outcome to the user.  The runner may use a
     graphical interface, a textual interface, or return a special value
     to indicate the results of executing the tests.

See also
........

Module *note doctest: 66.

     Another test-support module with a very different flavor.

Simple Smalltalk Testing: With Patterns(2)

     Kent Beck’s original paper on testing frameworks using the pattern
     shared by *note unittest: 124.

pytest(3)

     Third-party unittest framework with a lighter-weight syntax for
     writing tests.  For example, ‘assert func(10) == 42’.

The Python Testing Tools Taxonomy(4)

     An extensive list of Python testing tools including functional
     testing frameworks and mock object libraries.

Testing in Python Mailing List(5)

     A special-interest-group for discussion of testing, and testing
     tools, in Python.

The script ‘Tools/unittestgui/unittestgui.py’ in the Python source
distribution is a GUI tool for test discovery and execution.  This is
intended largely for ease of use for those new to unit testing.  For
production environments it is recommended that tests be driven by a
continuous integration system such as Buildbot(6), Jenkins(7) or
Travis-CI(8), or AppVeyor(9).

* Menu:

* Basic example::
* Command-Line Interface: Command-Line Interface<3>.
* Test Discovery::
* Organizing test code::
* Re-using old test code::
* Skipping tests and expected failures::
* Distinguishing test iterations using subtests::
* Classes and functions::
* Class and Module Fixtures::
* Signal Handling::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/unittest/__init__.py

   (2) 
https://web.archive.org/web/20150315073817/http://www.xprogramming.com/testfram.htm

   (3) https://docs.pytest.org/

   (4) https://wiki.python.org/moin/PythonTestingToolsTaxonomy

   (5) http://lists.idyll.org/listinfo/testing-in-python

   (6) https://buildbot.net/

   (7) https://jenkins.io/

   (8) https://travis-ci.com

   (9) https://www.appveyor.com/


File: python.info,  Node: Basic example,  Next: Command-Line Interface<3>,  Up: unittest — Unit testing framework

5.26.8.1 Basic example
......................

The *note unittest: 124. module provides a rich set of tools for
constructing and running tests.  This section demonstrates that a small
subset of the tools suffice to meet the needs of most users.

Here is a short script to test three string methods:

     import unittest

     class TestStringMethods(unittest.TestCase):

         def test_upper(self):
             self.assertEqual('foo'.upper(), 'FOO')

         def test_isupper(self):
             self.assertTrue('FOO'.isupper())
             self.assertFalse('Foo'.isupper())

         def test_split(self):
             s = 'hello world'
             self.assertEqual(s.split(), ['hello', 'world'])
             # check that s.split fails when the separator is not a string
             with self.assertRaises(TypeError):
                 s.split(2)

     if __name__ == '__main__':
         unittest.main()

A testcase is created by subclassing *note unittest.TestCase: 9e5.  The
three individual tests are defined with methods whose names start with
the letters ‘test’.  This naming convention informs the test runner
about which methods represent tests.

The crux of each test is a call to *note assertEqual(): c85. to check
for an expected result; *note assertTrue(): c84. or *note assertFalse():
d8f. to verify a condition; or *note assertRaises(): b92. to verify that
a specific exception gets raised.  These methods are used instead of the
*note assert: 23f. statement so the test runner can accumulate all test
results and produce a report.

The *note setUp(): d93. and *note tearDown(): d94. methods allow you to
define instructions that will be executed before and after each test
method.  They are covered in more detail in the section *note Organizing
test code: 34c0.

The final block shows a simple way to run the tests.  *note
unittest.main(): 9e8. provides a command-line interface to the test
script.  When run from the command line, the above script produces an
output that looks like this:

     ...
     ----------------------------------------------------------------------
     Ran 3 tests in 0.000s

     OK

Passing the ‘-v’ option to your test script will instruct *note
unittest.main(): 9e8. to enable a higher level of verbosity, and produce
the following output:

     test_isupper (__main__.TestStringMethods) ... ok
     test_split (__main__.TestStringMethods) ... ok
     test_upper (__main__.TestStringMethods) ... ok

     ----------------------------------------------------------------------
     Ran 3 tests in 0.001s

     OK

The above examples show the most commonly used *note unittest: 124.
features which are sufficient to meet many everyday testing needs.  The
remainder of the documentation explores the full feature set from first
principles.


File: python.info,  Node: Command-Line Interface<3>,  Next: Test Discovery,  Prev: Basic example,  Up: unittest — Unit testing framework

5.26.8.2 Command-Line Interface
...............................

The unittest module can be used from the command line to run tests from
modules, classes or even individual test methods:

     python -m unittest test_module1 test_module2
     python -m unittest test_module.TestClass
     python -m unittest test_module.TestClass.test_method

You can pass in a list with any combination of module names, and fully
qualified class or method names.

Test modules can be specified by file path as well:

     python -m unittest tests/test_something.py

This allows you to use the shell filename completion to specify the test
module.  The file specified must still be importable as a module.  The
path is converted to a module name by removing the ‘.py’ and converting
path separators into ‘.’.  If you want to execute a test file that isn’t
importable as a module you should execute the file directly instead.

You can run tests with more detail (higher verbosity) by passing in the
-v flag:

     python -m unittest -v test_module

When executed without arguments *note Test Discovery: 34c3. is started:

     python -m unittest

For a list of all the command-line options:

     python -m unittest -h

Changed in version 3.2: In earlier versions it was only possible to run
individual test methods and not modules or classes.

* Menu:

* Command-line options: Command-line options<3>.


File: python.info,  Node: Command-line options<3>,  Up: Command-Line Interface<3>

5.26.8.3 Command-line options
.............................

‘unittest’ supports these command-line options:

 -- Program Option: -b, --buffer

     The standard output and standard error streams are buffered during
     the test run.  Output during a passing test is discarded.  Output
     is echoed normally on test fail or error and is added to the
     failure messages.

 -- Program Option: -c, --catch

     ‘Control-C’ during the test run waits for the current test to end
     and then reports all the results so far.  A second ‘Control-C’
     raises the normal *note KeyboardInterrupt: 2cc. exception.

     See *note Signal Handling: 34c5. for the functions that provide
     this functionality.

 -- Program Option: -f, --failfast

     Stop the test run on the first error or failure.

 -- Program Option: -k

     Only run test methods and classes that match the pattern or
     substring.  This option may be used multiple times, in which case
     all test cases that match any of the given patterns are included.

     Patterns that contain a wildcard character (‘*’) are matched
     against the test name using *note fnmatch.fnmatchcase(): 1dd9.;
     otherwise simple case-sensitive substring matching is used.

     Patterns are matched against the fully qualified test method name
     as imported by the test loader.

     For example, ‘-k foo’ matches ‘foo_tests.SomeTest.test_something’,
     ‘bar_tests.SomeTest.test_foo’, but not
     ‘bar_tests.FooTest.test_something’.

 -- Program Option: --locals

     Show local variables in tracebacks.

New in version 3.2: The command-line options ‘-b’, ‘-c’ and ‘-f’ were
added.

New in version 3.5: The command-line option ‘--locals’.

New in version 3.7: The command-line option ‘-k’.

The command line can also be used for test discovery, for running all of
the tests in a project or just a subset.


File: python.info,  Node: Test Discovery,  Next: Organizing test code,  Prev: Command-Line Interface<3>,  Up: unittest — Unit testing framework

5.26.8.4 Test Discovery
.......................

New in version 3.2.

Unittest supports simple test discovery.  In order to be compatible with
test discovery, all of the test files must be *note modules: 13b1. or
*note packages: 13be. (including *note namespace packages: 15ee.)
importable from the top-level directory of the project (this means that
their filenames must be valid *note identifiers: 1505.).

Test discovery is implemented in *note TestLoader.discover(): 9ea, but
can also be used from the command line.  The basic command-line usage
is:

     cd project_directory
     python -m unittest discover

     Note: As a shortcut, ‘python -m unittest’ is the equivalent of
     ‘python -m unittest discover’.  If you want to pass arguments to
     test discovery the ‘discover’ sub-command must be used explicitly.

The ‘discover’ sub-command has the following options:

 -- Program Option: -v, --verbose

     Verbose output

 -- Program Option: -s, --start-directory directory

     Directory to start discovery (‘.’ default)

 -- Program Option: -p, --pattern pattern

     Pattern to match test files (‘test*.py’ default)

 -- Program Option: -t, --top-level-directory directory

     Top level directory of project (defaults to start directory)

The *note -s: 34ca, *note -p: 34cb, and *note -t: 34cc. options can be
passed in as positional arguments in that order.  The following two
command lines are equivalent:

     python -m unittest discover -s project_directory -p "*_test.py"
     python -m unittest discover project_directory "*_test.py"

As well as being a path it is possible to pass a package name, for
example ‘myproject.subpackage.test’, as the start directory.  The
package name you supply will then be imported and its location on the
filesystem will be used as the start directory.

     Caution: Test discovery loads tests by importing them.  Once test
     discovery has found all the test files from the start directory you
     specify it turns the paths into package names to import.  For
     example ‘foo/bar/baz.py’ will be imported as ‘foo.bar.baz’.

     If you have a package installed globally and attempt test discovery
     on a different copy of the package then the import `could' happen
     from the wrong place.  If this happens test discovery will warn you
     and exit.

     If you supply the start directory as a package name rather than a
     path to a directory then discover assumes that whichever location
     it imports from is the location you intended, so you will not get
     the warning.

Test modules and packages can customize test loading and discovery by
through the *note load_tests protocol: 34cd.

Changed in version 3.4: Test discovery supports *note namespace
packages: 15ee. for the start directory.  Note that you need to specify
the top level directory too (e.g.  ‘python -m unittest discover -s
root/namespace -t root’).


File: python.info,  Node: Organizing test code,  Next: Re-using old test code,  Prev: Test Discovery,  Up: unittest — Unit testing framework

5.26.8.5 Organizing test code
.............................

The basic building blocks of unit testing are `test cases' — single
scenarios that must be set up and checked for correctness.  In *note
unittest: 124, test cases are represented by *note unittest.TestCase:
9e5. instances.  To make your own test cases you must write subclasses
of *note TestCase: 9e5. or use *note FunctionTestCase: 34cf.

The testing code of a *note TestCase: 9e5. instance should be entirely
self contained, such that it can be run either in isolation or in
arbitrary combination with any number of other test cases.

The simplest *note TestCase: 9e5. subclass will simply implement a test
method (i.e.  a method whose name starts with ‘test’) in order to
perform specific testing code:

     import unittest

     class DefaultWidgetSizeTestCase(unittest.TestCase):
         def test_default_widget_size(self):
             widget = Widget('The widget')
             self.assertEqual(widget.size(), (50, 50))

Note that in order to test something, we use one of the ‘assert*()’
methods provided by the *note TestCase: 9e5. base class.  If the test
fails, an exception will be raised with an explanatory message, and
*note unittest: 124. will identify the test case as a `failure'.  Any
other exceptions will be treated as `errors'.

Tests can be numerous, and their set-up can be repetitive.  Luckily, we
can factor out set-up code by implementing a method called *note
setUp(): d93, which the testing framework will automatically call for
every single test we run:

     import unittest

     class WidgetTestCase(unittest.TestCase):
         def setUp(self):
             self.widget = Widget('The widget')

         def test_default_widget_size(self):
             self.assertEqual(self.widget.size(), (50,50),
                              'incorrect default size')

         def test_widget_resize(self):
             self.widget.resize(100,150)
             self.assertEqual(self.widget.size(), (100,150),
                              'wrong size after resize')

     Note: The order in which the various tests will be run is
     determined by sorting the test method names with respect to the
     built-in ordering for strings.

If the *note setUp(): d93. method raises an exception while the test is
running, the framework will consider the test to have suffered an error,
and the test method will not be executed.

Similarly, we can provide a *note tearDown(): d94. method that tidies up
after the test method has been run:

     import unittest

     class WidgetTestCase(unittest.TestCase):
         def setUp(self):
             self.widget = Widget('The widget')

         def tearDown(self):
             self.widget.dispose()

If *note setUp(): d93. succeeded, *note tearDown(): d94. will be run
whether the test method succeeded or not.

Such a working environment for the testing code is called a `test
fixture'.  A new TestCase instance is created as a unique test fixture
used to execute each individual test method.  Thus *note setUp(): d93,
*note tearDown(): d94, and ‘__init__()’ will be called once per test.

It is recommended that you use TestCase implementations to group tests
together according to the features they test.  *note unittest: 124.
provides a mechanism for this: the `test suite', represented by *note
unittest: 124.’s *note TestSuite: 7c1. class.  In most cases, calling
*note unittest.main(): 9e8. will do the right thing and collect all the
module’s test cases for you and execute them.

However, should you want to customize the building of your test suite,
you can do it yourself:

     def suite():
         suite = unittest.TestSuite()
         suite.addTest(WidgetTestCase('test_default_widget_size'))
         suite.addTest(WidgetTestCase('test_widget_resize'))
         return suite

     if __name__ == '__main__':
         runner = unittest.TextTestRunner()
         runner.run(suite())

You can place the definitions of test cases and test suites in the same
modules as the code they are to test (such as ‘widget.py’), but there
are several advantages to placing the test code in a separate module,
such as ‘test_widget.py’:

   * The test module can be run standalone from the command line.

   * The test code can more easily be separated from shipped code.

   * There is less temptation to change test code to fit the code it
     tests without a good reason.

   * Test code should be modified much less frequently than the code it
     tests.

   * Tested code can be refactored more easily.

   * Tests for modules written in C must be in separate modules anyway,
     so why not be consistent?

   * If the testing strategy changes, there is no need to change the
     source code.


File: python.info,  Node: Re-using old test code,  Next: Skipping tests and expected failures,  Prev: Organizing test code,  Up: unittest — Unit testing framework

5.26.8.6 Re-using old test code
...............................

Some users will find that they have existing test code that they would
like to run from *note unittest: 124, without converting every old test
function to a *note TestCase: 9e5. subclass.

For this reason, *note unittest: 124. provides a *note FunctionTestCase:
34cf. class.  This subclass of *note TestCase: 9e5. can be used to wrap
an existing test function.  Set-up and tear-down functions can also be
provided.

Given the following test function:

     def testSomething():
         something = makeSomething()
         assert something.name is not None
         # ...

one can create an equivalent test case instance as follows, with
optional set-up and tear-down methods:

     testcase = unittest.FunctionTestCase(testSomething,
                                          setUp=makeSomethingDB,
                                          tearDown=deleteSomethingDB)

     Note: Even though *note FunctionTestCase: 34cf. can be used to
     quickly convert an existing test base over to a *note unittest:
     124.-based system, this approach is not recommended.  Taking the
     time to set up proper *note TestCase: 9e5. subclasses will make
     future test refactorings infinitely easier.

In some cases, the existing tests may have been written using the *note
doctest: 66. module.  If so, *note doctest: 66. provides a
‘DocTestSuite’ class that can automatically build *note
unittest.TestSuite: 7c1. instances from the existing *note doctest:
66.-based tests.


File: python.info,  Node: Skipping tests and expected failures,  Next: Distinguishing test iterations using subtests,  Prev: Re-using old test code,  Up: unittest — Unit testing framework

5.26.8.7 Skipping tests and expected failures
.............................................

New in version 3.1.

Unittest supports skipping individual test methods and even whole
classes of tests.  In addition, it supports marking a test as an
“expected failure,” a test that is broken and will fail, but shouldn’t
be counted as a failure on a *note TestResult: b97.

Skipping a test is simply a matter of using the *note skip(): 10e5.
*note decorator: 174. or one of its conditional variants, calling *note
TestCase.skipTest(): 34d4. within a *note setUp(): d93. or test method,
or raising *note SkipTest: 9e9. directly.

Basic skipping looks like this:

     class MyTestCase(unittest.TestCase):

         @unittest.skip("demonstrating skipping")
         def test_nothing(self):
             self.fail("shouldn't happen")

         @unittest.skipIf(mylib.__version__ < (1, 3),
                          "not supported in this library version")
         def test_format(self):
             # Tests that work for only a certain version of the library.
             pass

         @unittest.skipUnless(sys.platform.startswith("win"), "requires Windows")
         def test_windows_support(self):
             # windows specific testing code
             pass

         def test_maybe_skipped(self):
             if not external_resource_available():
                 self.skipTest("external resource not available")
             # test code that depends on the external resource
             pass

This is the output of running the example above in verbose mode:

     test_format (__main__.MyTestCase) ... skipped 'not supported in this library version'
     test_nothing (__main__.MyTestCase) ... skipped 'demonstrating skipping'
     test_maybe_skipped (__main__.MyTestCase) ... skipped 'external resource not available'
     test_windows_support (__main__.MyTestCase) ... skipped 'requires Windows'

     ----------------------------------------------------------------------
     Ran 4 tests in 0.005s

     OK (skipped=4)

Classes can be skipped just like methods:

     @unittest.skip("showing class skipping")
     class MySkippedTestCase(unittest.TestCase):
         def test_not_run(self):
             pass

*note TestCase.setUp(): d93. can also skip the test.  This is useful
when a resource that needs to be set up is not available.

Expected failures use the *note expectedFailure(): 34d5. decorator.

     class ExpectedFailureTestCase(unittest.TestCase):
         @unittest.expectedFailure
         def test_fail(self):
             self.assertEqual(1, 0, "broken")

It’s easy to roll your own skipping decorators by making a decorator
that calls *note skip(): 10e5. on the test when it wants it to be
skipped.  This decorator skips the test unless the passed object has a
certain attribute:

     def skipUnlessHasattr(obj, attr):
         if hasattr(obj, attr):
             return lambda func: func
         return unittest.skip("{!r} doesn't have {!r}".format(obj, attr))

The following decorators and exception implement test skipping and
expected failures:

 -- Function: @unittest.skip (reason)

     Unconditionally skip the decorated test.  `reason' should describe
     why the test is being skipped.

 -- Function: @unittest.skipIf (condition, reason)

     Skip the decorated test if `condition' is true.

 -- Function: @unittest.skipUnless (condition, reason)

     Skip the decorated test unless `condition' is true.

 -- Function: @unittest.expectedFailure

     Mark the test as an expected failure or error.  If the test fails
     or errors in the test function itself (rather than in one of the
     `test fixture' methods) then it will be considered a success.  If
     the test passes, it will be considered a failure.

 -- Exception: unittest.SkipTest (reason)

     This exception is raised to skip a test.

     Usually you can use *note TestCase.skipTest(): 34d4. or one of the
     skipping decorators instead of raising this directly.

Skipped tests will not have *note setUp(): d93. or *note tearDown():
d94. run around them.  Skipped classes will not have *note setUpClass():
376. or *note tearDownClass(): d91. run.  Skipped modules will not have
‘setUpModule()’ or ‘tearDownModule()’ run.


File: python.info,  Node: Distinguishing test iterations using subtests,  Next: Classes and functions,  Prev: Skipping tests and expected failures,  Up: unittest — Unit testing framework

5.26.8.8 Distinguishing test iterations using subtests
......................................................

New in version 3.4.

When there are very small differences among your tests, for instance
some parameters, unittest allows you to distinguish them inside the body
of a test method using the *note subTest(): 9e6. context manager.

For example, the following test:

     class NumbersTest(unittest.TestCase):

         def test_even(self):
             """
             Test that numbers between 0 and 5 are all even.
             """
             for i in range(0, 6):
                 with self.subTest(i=i):
                     self.assertEqual(i % 2, 0)

will produce the following output:

     ======================================================================
     FAIL: test_even (__main__.NumbersTest) (i=1)
     ----------------------------------------------------------------------
     Traceback (most recent call last):
       File "subtests.py", line 32, in test_even
         self.assertEqual(i % 2, 0)
     AssertionError: 1 != 0

     ======================================================================
     FAIL: test_even (__main__.NumbersTest) (i=3)
     ----------------------------------------------------------------------
     Traceback (most recent call last):
       File "subtests.py", line 32, in test_even
         self.assertEqual(i % 2, 0)
     AssertionError: 1 != 0

     ======================================================================
     FAIL: test_even (__main__.NumbersTest) (i=5)
     ----------------------------------------------------------------------
     Traceback (most recent call last):
       File "subtests.py", line 32, in test_even
         self.assertEqual(i % 2, 0)
     AssertionError: 1 != 0

Without using a subtest, execution would stop after the first failure,
and the error would be less easy to diagnose because the value of ‘i’
wouldn’t be displayed:

     ======================================================================
     FAIL: test_even (__main__.NumbersTest)
     ----------------------------------------------------------------------
     Traceback (most recent call last):
       File "subtests.py", line 32, in test_even
         self.assertEqual(i % 2, 0)
     AssertionError: 1 != 0


File: python.info,  Node: Classes and functions,  Next: Class and Module Fixtures,  Prev: Distinguishing test iterations using subtests,  Up: unittest — Unit testing framework

5.26.8.9 Classes and functions
..............................

This section describes in depth the API of *note unittest: 124.

* Menu:

* Test cases::
* Grouping tests::
* Loading and running tests::


File: python.info,  Node: Test cases,  Next: Grouping tests,  Up: Classes and functions

5.26.8.10 Test cases
....................

 -- Class: unittest.TestCase (methodName='runTest')

     Instances of the *note TestCase: 9e5. class represent the logical
     test units in the *note unittest: 124. universe.  This class is
     intended to be used as a base class, with specific tests being
     implemented by concrete subclasses.  This class implements the
     interface needed by the test runner to allow it to drive the tests,
     and methods that the test code can use to check for and report
     various kinds of failure.

     Each instance of *note TestCase: 9e5. will run a single base
     method: the method named `methodName'.  In most uses of *note
     TestCase: 9e5, you will neither change the `methodName' nor
     reimplement the default ‘runTest()’ method.

     Changed in version 3.2: *note TestCase: 9e5. can be instantiated
     successfully without providing a `methodName'.  This makes it
     easier to experiment with *note TestCase: 9e5. from the interactive
     interpreter.

     *note TestCase: 9e5. instances provide three groups of methods: one
     group used to run the test, another used by the test implementation
     to check conditions and report failures, and some inquiry methods
     allowing information about the test itself to be gathered.

     Methods in the first group (running the test) are:

      -- Method: setUp ()

          Method called to prepare the test fixture.  This is called
          immediately before calling the test method; other than *note
          AssertionError: 240. or *note SkipTest: 9e9, any exception
          raised by this method will be considered an error rather than
          a test failure.  The default implementation does nothing.

      -- Method: tearDown ()

          Method called immediately after the test method has been
          called and the result recorded.  This is called even if the
          test method raised an exception, so the implementation in
          subclasses may need to be particularly careful about checking
          internal state.  Any exception, other than *note
          AssertionError: 240. or *note SkipTest: 9e9, raised by this
          method will be considered an additional error rather than a
          test failure (thus increasing the total number of reported
          errors).  This method will only be called if the *note
          setUp(): d93. succeeds, regardless of the outcome of the test
          method.  The default implementation does nothing.

      -- Method: setUpClass ()

          A class method called before tests in an individual class are
          run.  ‘setUpClass’ is called with the class as the only
          argument and must be decorated as a *note classmethod(): 309.:

               @classmethod
               def setUpClass(cls):
                   ...

          See *note Class and Module Fixtures: 34dd. for more details.

          New in version 3.2.

      -- Method: tearDownClass ()

          A class method called after tests in an individual class have
          run.  ‘tearDownClass’ is called with the class as the only
          argument and must be decorated as a *note classmethod(): 309.:

               @classmethod
               def tearDownClass(cls):
                   ...

          See *note Class and Module Fixtures: 34dd. for more details.

          New in version 3.2.

      -- Method: run (result=None)

          Run the test, collecting the result into the *note TestResult:
          b97. object passed as `result'.  If `result' is omitted or
          ‘None’, a temporary result object is created (by calling the
          *note defaultTestResult(): 34de. method) and used.  The result
          object is returned to *note run(): b96.’s caller.

          The same effect may be had by simply calling the *note
          TestCase: 9e5. instance.

          Changed in version 3.3: Previous versions of ‘run’ did not
          return the result.  Neither did calling an instance.

      -- Method: skipTest (reason)

          Calling this during a test method or *note setUp(): d93. skips
          the current test.  See *note Skipping tests and expected
          failures: 34d3. for more information.

          New in version 3.1.

      -- Method: subTest (msg=None, **params)

          Return a context manager which executes the enclosed code
          block as a subtest.  `msg' and `params' are optional,
          arbitrary values which are displayed whenever a subtest fails,
          allowing you to identify them clearly.

          A test case can contain any number of subtest declarations,
          and they can be arbitrarily nested.

          See *note Distinguishing test iterations using subtests: 9e7.
          for more information.

          New in version 3.4.

      -- Method: debug ()

          Run the test without collecting the result.  This allows
          exceptions raised by the test to be propagated to the caller,
          and can be used to support running tests under a debugger.
     The *note TestCase: 9e5. class provides several assert methods to
     check for and report failures.  The following table lists the most
     commonly used methods (see the tables below for more assert
     methods):

     Method                                        Checks that                       New in
                                                                                     
     ----------------------------------------------------------------------------------------------------
                                                                                     
     *note assertEqual(a, b): c85.                 ‘a == b’
                                                   
                                                                                     
     *note assertNotEqual(a, b): c86.              ‘a != b’
                                                   
                                                                                     
     *note assertTrue(x): c84.                     ‘bool(x) is True’
                                                   
                                                                                     
     *note assertFalse(x): d8f.                    ‘bool(x) is False’
                                                   
                                                                                     
     *note assertIs(a, b): d97.                    ‘a is b’                          3.1
                                                                                     
                                                                                     
     *note assertIsNot(a, b): d98.                 ‘a is not b’                      3.1
                                                                                     
                                                                                     
     *note assertIsNone(x): d95.                   ‘x is None’                       3.1
                                                                                     
                                                                                     
     *note assertIsNotNone(x): d96.                ‘x is not None’                   3.1
                                                                                     
                                                                                     
     *note assertIn(a, b): da0.                    ‘a in b’                          3.1
                                                                                     
                                                                                     
     *note assertNotIn(a, b): da1.                 ‘a not in b’                      3.1
                                                                                     
                                                                                     
     *note assertIsInstance(a, b): d99.            ‘isinstance(a, b)’                3.2
                                                                                     
                                                                                     
     *note assertNotIsInstance(a, b): d9a.         ‘not isinstance(a, b)’            3.2
                                                                                     

     All the assert methods accept a `msg' argument that, if specified,
     is used as the error message on failure (see also *note
     longMessage: d90.).  Note that the `msg' keyword argument can be
     passed to *note assertRaises(): b92, *note assertRaisesRegex():
     b93, *note assertWarns(): b94, *note assertWarnsRegex(): b95. only
     when they are used as a context manager.

      -- Method: assertEqual (first, second, msg=None)

          Test that `first' and `second' are equal.  If the values do
          not compare equal, the test will fail.

          In addition, if `first' and `second' are the exact same type
          and one of list, tuple, dict, set, frozenset or str or any
          type that a subclass registers with *note
          addTypeEqualityFunc(): da9. the type-specific equality
          function will be called in order to generate a more useful
          default error message (see also the *note list of
          type-specific methods: 34df.).

          Changed in version 3.1: Added the automatic calling of
          type-specific equality function.

          Changed in version 3.2: *note assertMultiLineEqual(): d9f.
          added as the default type equality function for comparing
          strings.

      -- Method: assertNotEqual (first, second, msg=None)

          Test that `first' and `second' are not equal.  If the values
          do compare equal, the test will fail.

      -- Method: assertTrue (expr, msg=None)
      -- Method: assertFalse (expr, msg=None)

          Test that `expr' is true (or false).

          Note that this is equivalent to ‘bool(expr) is True’ and not
          to ‘expr is True’ (use ‘assertIs(expr, True)’ for the latter).
          This method should also be avoided when more specific methods
          are available (e.g.  ‘assertEqual(a, b)’ instead of
          ‘assertTrue(a == b)’), because they provide a better error
          message in case of failure.

      -- Method: assertIs (first, second, msg=None)
      -- Method: assertIsNot (first, second, msg=None)

          Test that `first' and `second' are (or are not) the same
          object.

          New in version 3.1.

      -- Method: assertIsNone (expr, msg=None)
      -- Method: assertIsNotNone (expr, msg=None)

          Test that `expr' is (or is not) ‘None’.

          New in version 3.1.

      -- Method: assertIn (member, container, msg=None)
      -- Method: assertNotIn (member, container, msg=None)

          Test that `member' is (or is not) in `container'.

          New in version 3.1.

      -- Method: assertIsInstance (obj, cls, msg=None)
      -- Method: assertNotIsInstance (obj, cls, msg=None)

          Test that `obj' is (or is not) an instance of `cls' (which can
          be a class or a tuple of classes, as supported by *note
          isinstance(): 552.).  To check for the exact type, use *note
          assertIs(type(obj), cls): d97.

          New in version 3.2.

     It is also possible to check the production of exceptions,
     warnings, and log messages using the following methods:

     Method                                                        Checks that                                New in
                                                                                                              
     --------------------------------------------------------------------------------------------------------------------------
                                                                                                              
     *note assertRaises(exc, fun, *args, **kwds): b92.             ‘fun(*args, **kwds)’ raises `exc'
                                                                   
                                                                                                              
     *note assertRaisesRegex(exc, r, fun, *args, **kwds): b93.     ‘fun(*args, **kwds)’ raises `exc' and      3.1
                                                                   the message matches regex `r'              
                                                                   
                                                                                                              
     *note assertWarns(warn, fun, *args, **kwds): b94.             ‘fun(*args, **kwds)’ raises `warn'         3.2
                                                                                                              
                                                                                                              
     *note assertWarnsRegex(warn, r, fun, *args, **kwds): b95.     ‘fun(*args, **kwds)’ raises `warn' and     3.2
                                                                   the message matches regex `r'              
                                                                   
                                                                                                              
     *note assertLogs(logger, level): 9eb.                         The ‘with’ block logs on `logger' with     3.4
                                                                   minimum `level'                            
                                                                   

      -- Method: assertRaises (exception, callable, *args, **kwds)

      -- Method: assertRaises (exception, *, msg=None)

          Test that an exception is raised when `callable' is called
          with any positional or keyword arguments that are also passed
          to *note assertRaises(): b92.  The test passes if `exception'
          is raised, is an error if another exception is raised, or
          fails if no exception is raised.  To catch any of a group of
          exceptions, a tuple containing the exception classes may be
          passed as `exception'.

          If only the `exception' and possibly the `msg' arguments are
          given, return a context manager so that the code under test
          can be written inline rather than as a function:

               with self.assertRaises(SomeException):
                   do_something()

          When used as a context manager, *note assertRaises(): b92.
          accepts the additional keyword argument `msg'.

          The context manager will store the caught exception object in
          its ‘exception’ attribute.  This can be useful if the
          intention is to perform additional checks on the exception
          raised:

               with self.assertRaises(SomeException) as cm:
                   do_something()

               the_exception = cm.exception
               self.assertEqual(the_exception.error_code, 3)

          Changed in version 3.1: Added the ability to use *note
          assertRaises(): b92. as a context manager.

          Changed in version 3.2: Added the ‘exception’ attribute.

          Changed in version 3.3: Added the `msg' keyword argument when
          used as a context manager.

      -- Method: assertRaisesRegex (exception, regex, callable, *args,
               **kwds)

      -- Method: assertRaisesRegex (exception, regex, *, msg=None)

          Like *note assertRaises(): b92. but also tests that `regex'
          matches on the string representation of the raised exception.
          `regex' may be a regular expression object or a string
          containing a regular expression suitable for use by *note
          re.search(): c82.  Examples:

               self.assertRaisesRegex(ValueError, "invalid literal for.*XYZ'$",
                                      int, 'XYZ')

          or:

               with self.assertRaisesRegex(ValueError, 'literal'):
                  int('XYZ')

          New in version 3.1: Added under the name ‘assertRaisesRegexp’.

          Changed in version 3.2: Renamed to *note assertRaisesRegex():
          b93.

          Changed in version 3.3: Added the `msg' keyword argument when
          used as a context manager.

      -- Method: assertWarns (warning, callable, *args, **kwds)

      -- Method: assertWarns (warning, *, msg=None)

          Test that a warning is triggered when `callable' is called
          with any positional or keyword arguments that are also passed
          to *note assertWarns(): b94.  The test passes if `warning' is
          triggered and fails if it isn’t.  Any exception is an error.
          To catch any of a group of warnings, a tuple containing the
          warning classes may be passed as `warnings'.

          If only the `warning' and possibly the `msg' arguments are
          given, return a context manager so that the code under test
          can be written inline rather than as a function:

               with self.assertWarns(SomeWarning):
                   do_something()

          When used as a context manager, *note assertWarns(): b94.
          accepts the additional keyword argument `msg'.

          The context manager will store the caught warning object in
          its ‘warning’ attribute, and the source line which triggered
          the warnings in the ‘filename’ and ‘lineno’ attributes.  This
          can be useful if the intention is to perform additional checks
          on the warning caught:

               with self.assertWarns(SomeWarning) as cm:
                   do_something()

               self.assertIn('myfile.py', cm.filename)
               self.assertEqual(320, cm.lineno)

          This method works regardless of the warning filters in place
          when it is called.

          New in version 3.2.

          Changed in version 3.3: Added the `msg' keyword argument when
          used as a context manager.

      -- Method: assertWarnsRegex (warning, regex, callable, *args,
               **kwds)

      -- Method: assertWarnsRegex (warning, regex, *, msg=None)

          Like *note assertWarns(): b94. but also tests that `regex'
          matches on the message of the triggered warning.  `regex' may
          be a regular expression object or a string containing a
          regular expression suitable for use by *note re.search(): c82.
          Example:

               self.assertWarnsRegex(DeprecationWarning,
                                     r'legacy_function\(\) is deprecated',
                                     legacy_function, 'XYZ')

          or:

               with self.assertWarnsRegex(RuntimeWarning, 'unsafe frobnicating'):
                   frobnicate('/etc/passwd')

          New in version 3.2.

          Changed in version 3.3: Added the `msg' keyword argument when
          used as a context manager.

      -- Method: assertLogs (logger=None, level=None)

          A context manager to test that at least one message is logged
          on the `logger' or one of its children, with at least the
          given `level'.

          If given, `logger' should be a *note logging.Logger: 4ae.
          object or a *note str: 205. giving the name of a logger.  The
          default is the root logger, which will catch all messages that
          were not blocked by a non-propagating descendent logger.

          If given, `level' should be either a numeric logging level or
          its string equivalent (for example either ‘"ERROR"’ or
          ‘logging.ERROR’).  The default is ‘logging.INFO’.

          The test passes if at least one message emitted inside the
          ‘with’ block matches the `logger' and `level' conditions,
          otherwise it fails.

          The object returned by the context manager is a recording
          helper which keeps tracks of the matching log messages.  It
          has two attributes:

           -- Attribute: records

               A list of *note logging.LogRecord: 9ec. objects of the
               matching log messages.

           -- Attribute: output

               A list of *note str: 205. objects with the formatted
               output of matching messages.

          Example:

               with self.assertLogs('foo', level='INFO') as cm:
                  logging.getLogger('foo').info('first message')
                  logging.getLogger('foo.bar').error('second message')
               self.assertEqual(cm.output, ['INFO:foo:first message',
                                            'ERROR:foo.bar:second message'])

          New in version 3.4.

     There are also other methods used to perform more specific checks,
     such as:

     Method                                      Checks that                          New in
                                                                                      
     ----------------------------------------------------------------------------------------------------
                                                                                      
     *note assertAlmostEqual(a, b): c87.         ‘round(a-b, 7) == 0’
                                                 
                                                                                      
     *note assertNotAlmostEqual(a, b): c88.      ‘round(a-b, 7) != 0’
                                                 
                                                                                      
     *note assertGreater(a, b): d9b.             ‘a > b’                              3.1
                                                                                      
                                                                                      
     *note assertGreaterEqual(a, b): d9c.        ‘a >= b’                             3.1
                                                                                      
                                                                                      
     *note assertLess(a, b): d9d.                ‘a < b’                              3.1
                                                                                      
                                                                                      
     *note assertLessEqual(a, b): d9e.           ‘a <= b’                             3.1
                                                                                      
                                                                                      
     *note assertRegex(s, r): c81.               ‘r.search(s)’                        3.1
                                                                                      
                                                                                      
     *note assertNotRegex(s, r): 34e2.           ‘not r.search(s)’                    3.2
                                                                                      
                                                                                      
     *note assertCountEqual(a, b): c7f.          `a' and `b' have the same elements   3.2
                                                 in the same number, regardless of    
                                                 their order.
                                                 

      -- Method: assertAlmostEqual (first, second, places=7, msg=None,
               delta=None)
      -- Method: assertNotAlmostEqual (first, second, places=7,
               msg=None, delta=None)

          Test that `first' and `second' are approximately (or not
          approximately) equal by computing the difference, rounding to
          the given number of decimal `places' (default 7), and
          comparing to zero.  Note that these methods round the values
          to the given number of `decimal places' (i.e.  like the *note
          round(): d35. function) and not `significant digits'.

          If `delta' is supplied instead of `places' then the difference
          between `first' and `second' must be less or equal to (or
          greater than) `delta'.

          Supplying both `delta' and `places' raises a *note TypeError:
          1fe.

          Changed in version 3.2: *note assertAlmostEqual(): c87.
          automatically considers almost equal objects that compare
          equal.  *note assertNotAlmostEqual(): c88. automatically fails
          if the objects compare equal.  Added the `delta' keyword
          argument.

      -- Method: assertGreater (first, second, msg=None)
      -- Method: assertGreaterEqual (first, second, msg=None)
      -- Method: assertLess (first, second, msg=None)
      -- Method: assertLessEqual (first, second, msg=None)

          Test that `first' is respectively >, >=, < or <= than `second'
          depending on the method name.  If not, the test will fail:

               >>> self.assertGreaterEqual(3, 4)
               AssertionError: "3" unexpectedly not greater than or equal to "4"

          New in version 3.1.

      -- Method: assertRegex (text, regex, msg=None)
      -- Method: assertNotRegex (text, regex, msg=None)

          Test that a `regex' search matches (or does not match) `text'.
          In case of failure, the error message will include the pattern
          and the `text' (or the pattern and the part of `text' that
          unexpectedly matched).  `regex' may be a regular expression
          object or a string containing a regular expression suitable
          for use by *note re.search(): c82.

          New in version 3.1: Added under the name
          ‘assertRegexpMatches’.

          Changed in version 3.2: The method ‘assertRegexpMatches()’ has
          been renamed to *note assertRegex(): c81.

          New in version 3.2: *note assertNotRegex(): 34e2.

          New in version 3.5: The name ‘assertNotRegexpMatches’ is a
          deprecated alias for *note assertNotRegex(): 34e2.

      -- Method: assertCountEqual (first, second, msg=None)

          Test that sequence `first' contains the same elements as
          `second', regardless of their order.  When they don’t, an
          error message listing the differences between the sequences
          will be generated.

          Duplicate elements are `not' ignored when comparing `first'
          and `second'.  It verifies whether each element has the same
          count in both sequences.  Equivalent to:
          ‘assertEqual(Counter(list(first)), Counter(list(second)))’ but
          works with sequences of unhashable objects as well.

          New in version 3.2.

     The *note assertEqual(): c85. method dispatches the equality check
     for objects of the same type to different type-specific methods.
     These methods are already implemented for most of the built-in
     types, but it’s also possible to register new methods using *note
     addTypeEqualityFunc(): da9.:

      -- Method: addTypeEqualityFunc (typeobj, function)

          Registers a type-specific method called by *note
          assertEqual(): c85. to check if two objects of exactly the
          same `typeobj' (not subclasses) compare equal.  `function'
          must take two positional arguments and a third msg=None
          keyword argument just as *note assertEqual(): c85. does.  It
          must raise *note self.failureException(msg): 34e3. when
          inequality between the first two parameters is detected –
          possibly providing useful information and explaining the
          inequalities in details in the error message.

          New in version 3.1.

     The list of type-specific methods automatically used by *note
     assertEqual(): c85. are summarized in the following table.  Note
     that it’s usually not necessary to invoke these methods directly.

     Method                                        Used to compare                   New in
                                                                                     
     ---------------------------------------------------------------------------------------------------
                                                                                     
     *note assertMultiLineEqual(a, b): d9f.        strings                           3.1
                                                                                     
                                                                                     
     *note assertSequenceEqual(a, b): da5.         sequences                         3.1
                                                                                     
                                                                                     
     *note assertListEqual(a, b): da3.             lists                             3.1
                                                                                     
                                                                                     
     *note assertTupleEqual(a, b): da4.            tuples                            3.1
                                                                                     
                                                                                     
     *note assertSetEqual(a, b): da2.              sets or frozensets                3.1
                                                                                     
                                                                                     
     *note assertDictEqual(a, b): da6.             dicts                             3.1
                                                                                     

      -- Method: assertMultiLineEqual (first, second, msg=None)

          Test that the multiline string `first' is equal to the string
          `second'.  When not equal a diff of the two strings
          highlighting the differences will be included in the error
          message.  This method is used by default when comparing
          strings with *note assertEqual(): c85.

          New in version 3.1.

      -- Method: assertSequenceEqual (first, second, msg=None,
               seq_type=None)

          Tests that two sequences are equal.  If a `seq_type' is
          supplied, both `first' and `second' must be instances of
          `seq_type' or a failure will be raised.  If the sequences are
          different an error message is constructed that shows the
          difference between the two.

          This method is not called directly by *note assertEqual():
          c85, but it’s used to implement *note assertListEqual(): da3.
          and *note assertTupleEqual(): da4.

          New in version 3.1.

      -- Method: assertListEqual (first, second, msg=None)
      -- Method: assertTupleEqual (first, second, msg=None)

          Tests that two lists or tuples are equal.  If not, an error
          message is constructed that shows only the differences between
          the two.  An error is also raised if either of the parameters
          are of the wrong type.  These methods are used by default when
          comparing lists or tuples with *note assertEqual(): c85.

          New in version 3.1.

      -- Method: assertSetEqual (first, second, msg=None)

          Tests that two sets are equal.  If not, an error message is
          constructed that lists the differences between the sets.  This
          method is used by default when comparing sets or frozensets
          with *note assertEqual(): c85.

          Fails if either of `first' or `second' does not have a
          ‘set.difference()’ method.

          New in version 3.1.

      -- Method: assertDictEqual (first, second, msg=None)

          Test that two dictionaries are equal.  If not, an error
          message is constructed that shows the differences in the
          dictionaries.  This method will be used by default to compare
          dictionaries in calls to *note assertEqual(): c85.

          New in version 3.1.

     Finally the *note TestCase: 9e5. provides the following methods and
     attributes:

      -- Method: fail (msg=None)

          Signals a test failure unconditionally, with `msg' or ‘None’
          for the error message.

      -- Attribute: failureException

          This class attribute gives the exception raised by the test
          method.  If a test framework needs to use a specialized
          exception, possibly to carry additional information, it must
          subclass this exception in order to “play fair” with the
          framework.  The initial value of this attribute is *note
          AssertionError: 240.

      -- Attribute: longMessage

          This class attribute determines what happens when a custom
          failure message is passed as the msg argument to an assertXYY
          call that fails.  ‘True’ is the default value.  In this case,
          the custom message is appended to the end of the standard
          failure message.  When set to ‘False’, the custom message
          replaces the standard message.

          The class setting can be overridden in individual test methods
          by assigning an instance attribute, self.longMessage, to
          ‘True’ or ‘False’ before calling the assert methods.

          The class setting gets reset before each test call.

          New in version 3.1.

      -- Attribute: maxDiff

          This attribute controls the maximum length of diffs output by
          assert methods that report diffs on failure.  It defaults to
          80*8 characters.  Assert methods affected by this attribute
          are *note assertSequenceEqual(): da5. (including all the
          sequence comparison methods that delegate to it), *note
          assertDictEqual(): da6. and *note assertMultiLineEqual(): d9f.

          Setting ‘maxDiff’ to ‘None’ means that there is no maximum
          length of diffs.

          New in version 3.2.

     Testing frameworks can use the following methods to collect
     information on the test:

      -- Method: countTestCases ()

          Return the number of tests represented by this test object.
          For *note TestCase: 9e5. instances, this will always be ‘1’.

      -- Method: defaultTestResult ()

          Return an instance of the test result class that should be
          used for this test case class (if no other result instance is
          provided to the *note run(): b96. method).

          For *note TestCase: 9e5. instances, this will always be an
          instance of *note TestResult: b97.; subclasses of *note
          TestCase: 9e5. should override this as necessary.

      -- Method: id ()

          Return a string identifying the specific test case.  This is
          usually the full name of the test method, including the module
          and class name.

      -- Method: shortDescription ()

          Returns a description of the test, or ‘None’ if no description
          has been provided.  The default implementation of this method
          returns the first line of the test method’s docstring, if
          available, or ‘None’.

          Changed in version 3.1: In 3.1 this was changed to add the
          test name to the short description even in the presence of a
          docstring.  This caused compatibility issues with unittest
          extensions and adding the test name was moved to the *note
          TextTestResult: f51. in Python 3.2.

      -- Method: addCleanup (function, /, *args, **kwargs)

          Add a function to be called after *note tearDown(): d94. to
          cleanup resources used during the test.  Functions will be
          called in reverse order to the order they are added (LIFO).
          They are called with any arguments and keyword arguments
          passed into *note addCleanup(): 3c5. when they are added.

          If *note setUp(): d93. fails, meaning that *note tearDown():
          d94. is not called, then any cleanup functions added will
          still be called.

          New in version 3.1.

      -- Method: doCleanups ()

          This method is called unconditionally after *note tearDown():
          d94, or after *note setUp(): d93. if *note setUp(): d93.
          raises an exception.

          It is responsible for calling all the cleanup functions added
          by *note addCleanup(): 3c5.  If you need cleanup functions to
          be called `prior' to *note tearDown(): d94. then you can call
          *note doCleanups(): d92. yourself.

          *note doCleanups(): d92. pops methods off the stack of cleanup
          functions one at a time, so it can be called at any time.

          New in version 3.1.

      -- Method: classmethod addClassCleanup (function, /, *args,
               **kwargs)

          Add a function to be called after *note tearDownClass(): d91.
          to cleanup resources used during the test class.  Functions
          will be called in reverse order to the order they are added
          (LIFO).  They are called with any arguments and keyword
          arguments passed into *note addClassCleanup(): 375. when they
          are added.

          If *note setUpClass(): 376. fails, meaning that *note
          tearDownClass(): d91. is not called, then any cleanup
          functions added will still be called.

          New in version 3.8.

      -- Method: classmethod doClassCleanups ()

          This method is called unconditionally after *note
          tearDownClass(): d91, or after *note setUpClass(): 376. if
          *note setUpClass(): 376. raises an exception.

          It is responsible for calling all the cleanup functions added
          by *note addClassCleanup(): 375.  If you need cleanup
          functions to be called `prior' to *note tearDownClass(): d91.
          then you can call *note doClassCleanups(): 34e9. yourself.

          *note doClassCleanups(): 34e9. pops methods off the stack of
          cleanup functions one at a time, so it can be called at any
          time.

          New in version 3.8.

 -- Class: unittest.IsolatedAsyncioTestCase (methodName='runTest')

     This class provides an API similar to *note TestCase: 9e5. and also
     accepts coroutines as test functions.

     New in version 3.8.

      -- Method: coroutine asyncSetUp ()

          Method called to prepare the test fixture.  This is called
          after ‘setUp()’.  This is called immediately before calling
          the test method; other than *note AssertionError: 240. or
          *note SkipTest: 9e9, any exception raised by this method will
          be considered an error rather than a test failure.  The
          default implementation does nothing.

      -- Method: coroutine asyncTearDown ()

          Method called immediately after the test method has been
          called and the result recorded.  This is called before
          ‘tearDown()’.  This is called even if the test method raised
          an exception, so the implementation in subclasses may need to
          be particularly careful about checking internal state.  Any
          exception, other than *note AssertionError: 240. or *note
          SkipTest: 9e9, raised by this method will be considered an
          additional error rather than a test failure (thus increasing
          the total number of reported errors).  This method will only
          be called if the *note asyncSetUp(): 34ea. succeeds,
          regardless of the outcome of the test method.  The default
          implementation does nothing.

      -- Method: addAsyncCleanup (function, /, *args, **kwargs)

          This method accepts a coroutine that can be used as a cleanup
          function.

      -- Method: run (result=None)

          Sets up a new event loop to run the test, collecting the
          result into the *note TestResult: b97. object passed as
          `result'.  If `result' is omitted or ‘None’, a temporary
          result object is created (by calling the ‘defaultTestResult()’
          method) and used.  The result object is returned to *note
          run(): 34ed.’s caller.  At the end of the test all the tasks
          in the event loop are cancelled.

     An example illustrating the order:

          from unittest import IsolatedAsyncioTestCase

          events = []


          class Test(IsolatedAsyncioTestCase):


              def setUp(self):
                  events.append("setUp")

              async def asyncSetUp(self):
                  self._async_connection = await AsyncConnection()
                  events.append("asyncSetUp")

              async def test_response(self):
                  events.append("test_response")
                  response = await self._async_connection.get("https://example.com")
                  self.assertEqual(response.status_code, 200)
                  self.addAsyncCleanup(self.on_cleanup)

              def tearDown(self):
                  events.append("tearDown")

              async def asyncTearDown(self):
                  await self._async_connection.close()
                  events.append("asyncTearDown")

              async def on_cleanup(self):
                  events.append("cleanup")

          if __name__ == "__main__":
              unittest.main()

     After running the test, ‘events’ would contain ‘["setUp",
     "asyncSetUp", "test_response", "asyncTearDown", "tearDown",
     "cleanup"]’.

 -- Class: unittest.FunctionTestCase (testFunc, setUp=None,
          tearDown=None, description=None)

     This class implements the portion of the *note TestCase: 9e5.
     interface which allows the test runner to drive the test, but does
     not provide the methods which test code can use to check and report
     errors.  This is used to create test cases using legacy test code,
     allowing it to be integrated into a *note unittest: 124.-based test
     framework.

* Menu:

* Deprecated aliases::


File: python.info,  Node: Deprecated aliases,  Up: Test cases

5.26.8.11 Deprecated aliases
............................

For historical reasons, some of the *note TestCase: 9e5. methods had one
or more aliases that are now deprecated.  The following table lists the
correct names along with their deprecated aliases:

     Method Name                        Deprecated alias           Deprecated alias
                                                                   
     ------------------------------------------------------------------------------------------
                                                                   
     *note assertEqual(): c85.          failUnlessEqual            assertEquals
                                                                   
                                                                   
     *note assertNotEqual(): c86.       failIfEqual                assertNotEquals
                                                                   
                                                                   
     *note assertTrue(): c84.           failUnless                 assert_
                                                                   
                                                                   
     *note assertFalse(): d8f.          failIf
                                        
                                                                   
     *note assertRaises(): b92.         failUnlessRaises
                                        
                                                                   
     *note assertAlmostEqual(): c87.    failUnlessAlmostEqual      assertAlmostEquals
                                                                   
                                                                   
     *note assertNotAlmostEqual(): c88. failIfAlmostEqual          assertNotAlmostEquals
                                                                   
                                                                   
     *note assertRegex(): c81.                                     assertRegexpMatches
                                                                   
                                                                   
     *note assertNotRegex(): 34e2.                                 assertNotRegexpMatches
                                                                   
                                                                   
     *note assertRaisesRegex(): b93.                               assertRaisesRegexp
                                                                   

     Deprecated since version 3.1: The fail* aliases listed in the
     second column have been deprecated.

     Deprecated since version 3.2: The assert* aliases listed in the
     third column have been deprecated.

     Deprecated since version 3.2: ‘assertRegexpMatches’ and
     ‘assertRaisesRegexp’ have been renamed to *note assertRegex(): c81.
     and *note assertRaisesRegex(): b93.

     Deprecated since version 3.5: The ‘assertNotRegexpMatches’ name is
     deprecated in favor of *note assertNotRegex(): 34e2.


File: python.info,  Node: Grouping tests,  Next: Loading and running tests,  Prev: Test cases,  Up: Classes and functions

5.26.8.12 Grouping tests
........................

 -- Class: unittest.TestSuite (tests=())

     This class represents an aggregation of individual test cases and
     test suites.  The class presents the interface needed by the test
     runner to allow it to be run as any other test case.  Running a
     *note TestSuite: 7c1. instance is the same as iterating over the
     suite, running each test individually.

     If `tests' is given, it must be an iterable of individual test
     cases or other test suites that will be used to build the suite
     initially.  Additional methods are provided to add test cases and
     suites to the collection later on.

     *note TestSuite: 7c1. objects behave much like *note TestCase: 9e5.
     objects, except they do not actually implement a test.  Instead,
     they are used to aggregate tests into groups of tests that should
     be run together.  Some additional methods are available to add
     tests to *note TestSuite: 7c1. instances:

      -- Method: addTest (test)

          Add a *note TestCase: 9e5. or *note TestSuite: 7c1. to the
          suite.

      -- Method: addTests (tests)

          Add all the tests from an iterable of *note TestCase: 9e5. and
          *note TestSuite: 7c1. instances to this test suite.

          This is equivalent to iterating over `tests', calling *note
          addTest(): 34f1. for each element.

     *note TestSuite: 7c1. shares the following methods with *note
     TestCase: 9e5.:

      -- Method: run (result)

          Run the tests associated with this suite, collecting the
          result into the test result object passed as `result'.  Note
          that unlike *note TestCase.run(): b96, *note TestSuite.run():
          34f3. requires the result object to be passed in.

      -- Method: debug ()

          Run the tests associated with this suite without collecting
          the result.  This allows exceptions raised by the test to be
          propagated to the caller and can be used to support running
          tests under a debugger.

      -- Method: countTestCases ()

          Return the number of tests represented by this test object,
          including all individual tests and sub-suites.

      -- Method: __iter__ ()

          Tests grouped by a *note TestSuite: 7c1. are always accessed
          by iteration.  Subclasses can lazily provide tests by
          overriding *note __iter__(): a43.  Note that this method may
          be called several times on a single suite (for example when
          counting tests or comparing for equality) so the tests
          returned by repeated iterations before *note TestSuite.run():
          34f3. must be the same for each call iteration.  After *note
          TestSuite.run(): 34f3, callers should not rely on the tests
          returned by this method unless the caller uses a subclass that
          overrides ‘TestSuite._removeTestAtIndex()’ to preserve test
          references.

          Changed in version 3.2: In earlier versions the *note
          TestSuite: 7c1. accessed tests directly rather than through
          iteration, so overriding *note __iter__(): a43. wasn’t
          sufficient for providing tests.

          Changed in version 3.4: In earlier versions the *note
          TestSuite: 7c1. held references to each *note TestCase: 9e5.
          after *note TestSuite.run(): 34f3.  Subclasses can restore
          that behavior by overriding ‘TestSuite._removeTestAtIndex()’.

     In the typical usage of a *note TestSuite: 7c1. object, the *note
     run(): 34f3. method is invoked by a ‘TestRunner’ rather than by the
     end-user test harness.


File: python.info,  Node: Loading and running tests,  Prev: Grouping tests,  Up: Classes and functions

5.26.8.13 Loading and running tests
...................................

 -- Class: unittest.TestLoader

     The *note TestLoader: 871. class is used to create test suites from
     classes and modules.  Normally, there is no need to create an
     instance of this class; the *note unittest: 124. module provides an
     instance that can be shared as *note unittest.defaultTestLoader:
     34f7.  Using a subclass or instance, however, allows customization
     of some configurable properties.

     *note TestLoader: 871. objects have the following attributes:

      -- Attribute: errors

          A list of the non-fatal errors encountered while loading
          tests.  Not reset by the loader at any point.  Fatal errors
          are signalled by the relevant a method raising an exception to
          the caller.  Non-fatal errors are also indicated by a
          synthetic test that will raise the original error when run.

          New in version 3.5.

     *note TestLoader: 871. objects have the following methods:

      -- Method: loadTestsFromTestCase (testCaseClass)

          Return a suite of all test cases contained in the *note
          TestCase: 9e5.-derived ‘testCaseClass’.

          A test case instance is created for each method named by *note
          getTestCaseNames(): 34f9.  By default these are the method
          names beginning with ‘test’.  If *note getTestCaseNames():
          34f9. returns no methods, but the ‘runTest()’ method is
          implemented, a single test case is created for that method
          instead.

      -- Method: loadTestsFromModule (module, pattern=None)

          Return a suite of all test cases contained in the given
          module.  This method searches `module' for classes derived
          from *note TestCase: 9e5. and creates an instance of the class
          for each test method defined for the class.

               Note: While using a hierarchy of *note TestCase:
               9e5.-derived classes can be convenient in sharing
               fixtures and helper functions, defining test methods on
               base classes that are not intended to be instantiated
               directly does not play well with this method.  Doing so,
               however, can be useful when the fixtures are different
               and defined in subclasses.

          If a module provides a ‘load_tests’ function it will be called
          to load the tests.  This allows modules to customize test
          loading.  This is the *note load_tests protocol: 34cd.  The
          `pattern' argument is passed as the third argument to
          ‘load_tests’.

          Changed in version 3.2: Support for ‘load_tests’ added.

          Changed in version 3.5: The undocumented and unofficial
          `use_load_tests' default argument is deprecated and ignored,
          although it is still accepted for backward compatibility.  The
          method also now accepts a keyword-only argument `pattern'
          which is passed to ‘load_tests’ as the third argument.

      -- Method: loadTestsFromName (name, module=None)

          Return a suite of all test cases given a string specifier.

          The specifier `name' is a “dotted name” that may resolve
          either to a module, a test case class, a test method within a
          test case class, a *note TestSuite: 7c1. instance, or a
          callable object which returns a *note TestCase: 9e5. or *note
          TestSuite: 7c1. instance.  These checks are applied in the
          order listed here; that is, a method on a possible test case
          class will be picked up as “a test method within a test case
          class”, rather than “a callable object”.

          For example, if you have a module ‘SampleTests’ containing a
          *note TestCase: 9e5.-derived class ‘SampleTestCase’ with three
          test methods (‘test_one()’, ‘test_two()’, and ‘test_three()’),
          the specifier ‘'SampleTests.SampleTestCase'’ would cause this
          method to return a suite which will run all three test
          methods.  Using the specifier
          ‘'SampleTests.SampleTestCase.test_two'’ would cause it to
          return a test suite which will run only the ‘test_two()’ test
          method.  The specifier can refer to modules and packages which
          have not been imported; they will be imported as a
          side-effect.

          The method optionally resolves `name' relative to the given
          `module'.

          Changed in version 3.5: If an *note ImportError: 16c. or *note
          AttributeError: 4a2. occurs while traversing `name' then a
          synthetic test that raises that error when run will be
          returned.  These errors are included in the errors accumulated
          by self.errors.

      -- Method: loadTestsFromNames (names, module=None)

          Similar to *note loadTestsFromName(): da7, but takes a
          sequence of names rather than a single name.  The return value
          is a test suite which supports all the tests defined for each
          name.

      -- Method: getTestCaseNames (testCaseClass)

          Return a sorted sequence of method names found within
          `testCaseClass'; this should be a subclass of *note TestCase:
          9e5.

      -- Method: discover (start_dir, pattern='test*.py',
               top_level_dir=None)

          Find all the test modules by recursing into subdirectories
          from the specified start directory, and return a TestSuite
          object containing them.  Only test files that match `pattern'
          will be loaded.  (Using shell style pattern matching.)  Only
          module names that are importable (i.e.  are valid Python
          identifiers) will be loaded.

          All test modules must be importable from the top level of the
          project.  If the start directory is not the top level
          directory then the top level directory must be specified
          separately.

          If importing a module fails, for example due to a syntax
          error, then this will be recorded as a single error and
          discovery will continue.  If the import failure is due to
          *note SkipTest: 9e9. being raised, it will be recorded as a
          skip instead of an error.

          If a package (a directory containing a file named
          ‘__init__.py’) is found, the package will be checked for a
          ‘load_tests’ function.  If this exists then it will be called
          ‘package.load_tests(loader, tests, pattern)’.  Test discovery
          takes care to ensure that a package is only checked for tests
          once during an invocation, even if the load_tests function
          itself calls ‘loader.discover’.

          If ‘load_tests’ exists then discovery does `not' recurse into
          the package, ‘load_tests’ is responsible for loading all tests
          in the package.

          The pattern is deliberately not stored as a loader attribute
          so that packages can continue discovery themselves.
          `top_level_dir' is stored so ‘load_tests’ does not need to
          pass this argument in to ‘loader.discover()’.

          `start_dir' can be a dotted module name as well as a
          directory.

          New in version 3.2.

          Changed in version 3.4: Modules that raise *note SkipTest:
          9e9. on import are recorded as skips, not errors.

          Changed in version 3.4: `start_dir' can be a *note namespace
          packages: 15ee.

          Changed in version 3.4: Paths are sorted before being imported
          so that execution order is the same even if the underlying
          file system’s ordering is not dependent on file name.

          Changed in version 3.5: Found packages are now checked for
          ‘load_tests’ regardless of whether their path matches
          `pattern', because it is impossible for a package name to
          match the default pattern.

     The following attributes of a *note TestLoader: 871. can be
     configured either by subclassing or assignment on an instance:

      -- Attribute: testMethodPrefix

          String giving the prefix of method names which will be
          interpreted as test methods.  The default value is ‘'test'’.

          This affects *note getTestCaseNames(): 34f9. and all the
          ‘loadTestsFrom*()’ methods.

      -- Attribute: sortTestMethodsUsing

          Function to be used to compare method names when sorting them
          in *note getTestCaseNames(): 34f9. and all the
          ‘loadTestsFrom*()’ methods.

      -- Attribute: suiteClass

          Callable object that constructs a test suite from a list of
          tests.  No methods on the resulting object are needed.  The
          default value is the *note TestSuite: 7c1. class.

          This affects all the ‘loadTestsFrom*()’ methods.

      -- Attribute: testNamePatterns

          List of Unix shell-style wildcard test name patterns that test
          methods have to match to be included in test suites (see ‘-v’
          option).

          If this attribute is not ‘None’ (the default), all test
          methods to be included in test suites must match one of the
          patterns in this list.  Note that matches are always performed
          using *note fnmatch.fnmatchcase(): 1dd9, so unlike patterns
          passed to the ‘-v’ option, simple substring patterns will have
          to be converted using ‘*’ wildcards.

          This affects all the ‘loadTestsFrom*()’ methods.

          New in version 3.7.

 -- Class: unittest.TestResult

     This class is used to compile information about which tests have
     succeeded and which have failed.

     A *note TestResult: b97. object stores the results of a set of
     tests.  The *note TestCase: 9e5. and *note TestSuite: 7c1. classes
     ensure that results are properly recorded; test authors do not need
     to worry about recording the outcome of tests.

     Testing frameworks built on top of *note unittest: 124. may want
     access to the *note TestResult: b97. object generated by running a
     set of tests for reporting purposes; a *note TestResult: b97.
     instance is returned by the ‘TestRunner.run()’ method for this
     purpose.

     *note TestResult: b97. instances have the following attributes that
     will be of interest when inspecting the results of running a set of
     tests:

      -- Attribute: errors

          A list containing 2-tuples of *note TestCase: 9e5. instances
          and strings holding formatted tracebacks.  Each tuple
          represents a test which raised an unexpected exception.

      -- Attribute: failures

          A list containing 2-tuples of *note TestCase: 9e5. instances
          and strings holding formatted tracebacks.  Each tuple
          represents a test where a failure was explicitly signalled
          using the ‘TestCase.assert*()’ methods.

      -- Attribute: skipped

          A list containing 2-tuples of *note TestCase: 9e5. instances
          and strings holding the reason for skipping the test.

          New in version 3.1.

      -- Attribute: expectedFailures

          A list containing 2-tuples of *note TestCase: 9e5. instances
          and strings holding formatted tracebacks.  Each tuple
          represents an expected failure or error of the test case.

      -- Attribute: unexpectedSuccesses

          A list containing *note TestCase: 9e5. instances that were
          marked as expected failures, but succeeded.

      -- Attribute: shouldStop

          Set to ‘True’ when the execution of tests should stop by *note
          stop(): 3504.

      -- Attribute: testsRun

          The total number of tests run so far.

      -- Attribute: buffer

          If set to true, ‘sys.stdout’ and ‘sys.stderr’ will be buffered
          in between *note startTest(): 3507. and *note stopTest():
          3508. being called.  Collected output will only be echoed onto
          the real ‘sys.stdout’ and ‘sys.stderr’ if the test fails or
          errors.  Any output is also attached to the failure / error
          message.

          New in version 3.2.

      -- Attribute: failfast

          If set to true *note stop(): 3504. will be called on the first
          failure or error, halting the test run.

          New in version 3.2.

      -- Attribute: tb_locals

          If set to true then local variables will be shown in
          tracebacks.

          New in version 3.5.

      -- Method: wasSuccessful ()

          Return ‘True’ if all tests run so far have passed, otherwise
          returns ‘False’.

          Changed in version 3.4: Returns ‘False’ if there were any
          *note unexpectedSuccesses: 3502. from tests marked with the
          *note expectedFailure(): 34d5. decorator.

      -- Method: stop ()

          This method can be called to signal that the set of tests
          being run should be aborted by setting the *note shouldStop:
          3503. attribute to ‘True’.  ‘TestRunner’ objects should
          respect this flag and return without running any additional
          tests.

          For example, this feature is used by the *note TextTestRunner:
          f52. class to stop the test framework when the user signals an
          interrupt from the keyboard.  Interactive tools which provide
          ‘TestRunner’ implementations can use this in a similar manner.

     The following methods of the *note TestResult: b97. class are used
     to maintain the internal data structures, and may be extended in
     subclasses to support additional reporting requirements.  This is
     particularly useful in building tools which support interactive
     reporting while tests are being run.

      -- Method: startTest (test)

          Called when the test case `test' is about to be run.

      -- Method: stopTest (test)

          Called after the test case `test' has been executed,
          regardless of the outcome.

      -- Method: startTestRun ()

          Called once before any tests are executed.

          New in version 3.1.

      -- Method: stopTestRun ()

          Called once after all tests are executed.

          New in version 3.1.

      -- Method: addError (test, err)

          Called when the test case `test' raises an unexpected
          exception.  `err' is a tuple of the form returned by *note
          sys.exc_info(): d27.: ‘(type, value, traceback)’.

          The default implementation appends a tuple ‘(test,
          formatted_err)’ to the instance’s *note errors: 34fe.
          attribute, where `formatted_err' is a formatted traceback
          derived from `err'.

      -- Method: addFailure (test, err)

          Called when the test case `test' signals a failure.  `err' is
          a tuple of the form returned by *note sys.exc_info(): d27.:
          ‘(type, value, traceback)’.

          The default implementation appends a tuple ‘(test,
          formatted_err)’ to the instance’s *note failures: 34ff.
          attribute, where `formatted_err' is a formatted traceback
          derived from `err'.

      -- Method: addSuccess (test)

          Called when the test case `test' succeeds.

          The default implementation does nothing.

      -- Method: addSkip (test, reason)

          Called when the test case `test' is skipped.  `reason' is the
          reason the test gave for skipping.

          The default implementation appends a tuple ‘(test, reason)’ to
          the instance’s *note skipped: 3500. attribute.

      -- Method: addExpectedFailure (test, err)

          Called when the test case `test' fails or errors, but was
          marked with the *note expectedFailure(): 34d5. decorator.

          The default implementation appends a tuple ‘(test,
          formatted_err)’ to the instance’s *note expectedFailures:
          3501. attribute, where `formatted_err' is a formatted
          traceback derived from `err'.

      -- Method: addUnexpectedSuccess (test)

          Called when the test case `test' was marked with the *note
          expectedFailure(): 34d5. decorator, but succeeded.

          The default implementation appends the test to the instance’s
          *note unexpectedSuccesses: 3502. attribute.

      -- Method: addSubTest (test, subtest, outcome)

          Called when a subtest finishes.  `test' is the test case
          corresponding to the test method.  `subtest' is a custom *note
          TestCase: 9e5. instance describing the subtest.

          If `outcome' is *note None: 203, the subtest succeeded.
          Otherwise, it failed with an exception where `outcome' is a
          tuple of the form returned by *note sys.exc_info(): d27.:
          ‘(type, value, traceback)’.

          The default implementation does nothing when the outcome is a
          success, and records subtest failures as normal failures.

          New in version 3.4.

 -- Class: unittest.TextTestResult (stream, descriptions, verbosity)

     A concrete implementation of *note TestResult: b97. used by the
     *note TextTestRunner: f52.

     New in version 3.2: This class was previously named
     ‘_TextTestResult’.  The old name still exists as an alias but is
     deprecated.

 -- Data: unittest.defaultTestLoader

     Instance of the *note TestLoader: 871. class intended to be shared.
     If no customization of the *note TestLoader: 871. is needed, this
     instance can be used instead of repeatedly creating new instances.

 -- Class: unittest.TextTestRunner (stream=None, descriptions=True,
          verbosity=1, failfast=False, buffer=False, resultclass=None,
          warnings=None, *, tb_locals=False)

     A basic test runner implementation that outputs results to a
     stream.  If `stream' is ‘None’, the default, *note sys.stderr: 1ea.
     is used as the output stream.  This class has a few configurable
     parameters, but is essentially very simple.  Graphical applications
     which run test suites should provide alternate implementations.
     Such implementations should accept ‘**kwargs’ as the interface to
     construct runners changes when features are added to unittest.

     By default this runner shows *note DeprecationWarning: 15a, *note
     PendingDeprecationWarning: 15c, *note ResourceWarning: 5cb. and
     *note ImportWarning: 6cf. even if they are *note ignored by
     default: 3513.  Deprecation warnings caused by *note deprecated
     unittest methods: c89. are also special-cased and, when the warning
     filters are ‘'default'’ or ‘'always'’, they will appear only once
     per-module, in order to avoid too many warning messages.  This
     behavior can be overridden using Python’s ‘-Wd’ or ‘-Wa’ options
     (see *note Warning control: 147d.) and leaving `warnings' to
     ‘None’.

     Changed in version 3.2: Added the ‘warnings’ argument.

     Changed in version 3.2: The default stream is set to *note
     sys.stderr: 1ea. at instantiation time rather than import time.

     Changed in version 3.5: Added the tb_locals parameter.

      -- Method: _makeResult ()

          This method returns the instance of ‘TestResult’ used by *note
          run(): 3515.  It is not intended to be called directly, but
          can be overridden in subclasses to provide a custom
          ‘TestResult’.

          ‘_makeResult()’ instantiates the class or callable passed in
          the ‘TextTestRunner’ constructor as the ‘resultclass’
          argument.  It defaults to *note TextTestResult: f51. if no
          ‘resultclass’ is provided.  The result class is instantiated
          with the following arguments:

               stream, descriptions, verbosity

      -- Method: run (test)

          This method is the main public interface to the
          ‘TextTestRunner’.  This method takes a *note TestSuite: 7c1.
          or *note TestCase: 9e5. instance.  A *note TestResult: b97. is
          created by calling *note _makeResult(): 3514. and the test(s)
          are run and the results printed to stdout.

 -- Function: unittest.main (module='__main__', defaultTest=None,
          argv=None, testRunner=None,
          testLoader=unittest.defaultTestLoader, exit=True, verbosity=1,
          failfast=None, catchbreak=None, buffer=None, warnings=None)

     A command-line program that loads a set of tests from `module' and
     runs them; this is primarily for making test modules conveniently
     executable.  The simplest use for this function is to include the
     following line at the end of a test script:

          if __name__ == '__main__':
              unittest.main()

     You can run tests with more detailed information by passing in the
     verbosity argument:

          if __name__ == '__main__':
              unittest.main(verbosity=2)

     The `defaultTest' argument is either the name of a single test or
     an iterable of test names to run if no test names are specified via
     `argv'.  If not specified or ‘None’ and no test names are provided
     via `argv', all tests found in `module' are run.

     The `argv' argument can be a list of options passed to the program,
     with the first element being the program name.  If not specified or
     ‘None’, the values of *note sys.argv: cc6. are used.

     The `testRunner' argument can either be a test runner class or an
     already created instance of it.  By default ‘main’ calls *note
     sys.exit(): daa. with an exit code indicating success or failure of
     the tests run.

     The `testLoader' argument has to be a *note TestLoader: 871.
     instance, and defaults to *note defaultTestLoader: 34f7.

     ‘main’ supports being used from the interactive interpreter by
     passing in the argument ‘exit=False’.  This displays the result on
     standard output without calling *note sys.exit(): daa.:

          >>> from unittest import main
          >>> main(module='test_module', exit=False)

     The `failfast', `catchbreak' and `buffer' parameters have the same
     effect as the same-name *note command-line options: 34c4.

     The `warnings' argument specifies the *note warning filter: 15d.
     that should be used while running the tests.  If it’s not
     specified, it will remain ‘None’ if a ‘-W’ option is passed to
     ‘python’ (see *note Warning control: 147d.), otherwise it will be
     set to ‘'default'’.

     Calling ‘main’ actually returns an instance of the ‘TestProgram’
     class.  This stores the result of the tests run as the ‘result’
     attribute.

     Changed in version 3.1: The `exit' parameter was added.

     Changed in version 3.2: The `verbosity', `failfast', `catchbreak',
     `buffer' and `warnings' parameters were added.

     Changed in version 3.4: The `defaultTest' parameter was changed to
     also accept an iterable of test names.

* Menu:

* load_tests Protocol::


File: python.info,  Node: load_tests Protocol,  Up: Loading and running tests

5.26.8.14 load_tests Protocol
.............................

New in version 3.2.

Modules or packages can customize how tests are loaded from them during
normal test runs or test discovery by implementing a function called
‘load_tests’.

If a test module defines ‘load_tests’ it will be called by *note
TestLoader.loadTestsFromModule(): 86f. with the following arguments:

     load_tests(loader, standard_tests, pattern)

where `pattern' is passed straight through from ‘loadTestsFromModule’.
It defaults to ‘None’.

It should return a *note TestSuite: 7c1.

`loader' is the instance of *note TestLoader: 871. doing the loading.
`standard_tests' are the tests that would be loaded by default from the
module.  It is common for test modules to only want to add or remove
tests from the standard set of tests.  The third argument is used when
loading packages as part of test discovery.

A typical ‘load_tests’ function that loads tests from a specific set of
*note TestCase: 9e5. classes may look like:

     test_cases = (TestCase1, TestCase2, TestCase3)

     def load_tests(loader, tests, pattern):
         suite = TestSuite()
         for test_class in test_cases:
             tests = loader.loadTestsFromTestCase(test_class)
             suite.addTests(tests)
         return suite

If discovery is started in a directory containing a package, either from
the command line or by calling *note TestLoader.discover(): 9ea, then
the package ‘__init__.py’ will be checked for ‘load_tests’.  If that
function does not exist, discovery will recurse into the package as
though it were just another directory.  Otherwise, discovery of the
package’s tests will be left up to ‘load_tests’ which is called with the
following arguments:

     load_tests(loader, standard_tests, pattern)

This should return a *note TestSuite: 7c1. representing all the tests
from the package.  (‘standard_tests’ will only contain tests collected
from ‘__init__.py’.)

Because the pattern is passed into ‘load_tests’ the package is free to
continue (and potentially modify) test discovery.  A ‘do nothing’
‘load_tests’ function for a test package would look like:

     def load_tests(loader, standard_tests, pattern):
         # top level directory cached on loader instance
         this_dir = os.path.dirname(__file__)
         package_tests = loader.discover(start_dir=this_dir, pattern=pattern)
         standard_tests.addTests(package_tests)
         return standard_tests

Changed in version 3.5: Discovery no longer checks package names for
matching `pattern' due to the impossibility of package names matching
the default pattern.


File: python.info,  Node: Class and Module Fixtures,  Next: Signal Handling,  Prev: Classes and functions,  Up: unittest — Unit testing framework

5.26.8.15 Class and Module Fixtures
...................................

Class and module level fixtures are implemented in *note TestSuite: 7c1.
When the test suite encounters a test from a new class then
‘tearDownClass()’ from the previous class (if there is one) is called,
followed by ‘setUpClass()’ from the new class.

Similarly if a test is from a different module from the previous test
then ‘tearDownModule’ from the previous module is run, followed by
‘setUpModule’ from the new module.

After all the tests have run the final ‘tearDownClass’ and
‘tearDownModule’ are run.

Note that shared fixtures do not play well with [potential] features
like test parallelization and they break test isolation.  They should be
used with care.

The default ordering of tests created by the unittest test loaders is to
group all tests from the same modules and classes together.  This will
lead to ‘setUpClass’ / ‘setUpModule’ (etc) being called exactly once per
class and module.  If you randomize the order, so that tests from
different modules and classes are adjacent to each other, then these
shared fixture functions may be called multiple times in a single test
run.

Shared fixtures are not intended to work with suites with non-standard
ordering.  A ‘BaseTestSuite’ still exists for frameworks that don’t want
to support shared fixtures.

If there are any exceptions raised during one of the shared fixture
functions the test is reported as an error.  Because there is no
corresponding test instance an ‘_ErrorHolder’ object (that has the same
interface as a *note TestCase: 9e5.) is created to represent the error.
If you are just using the standard unittest test runner then this detail
doesn’t matter, but if you are a framework author it may be relevant.

* Menu:

* setUpClass and tearDownClass::
* setUpModule and tearDownModule::


File: python.info,  Node: setUpClass and tearDownClass,  Next: setUpModule and tearDownModule,  Up: Class and Module Fixtures

5.26.8.16 setUpClass and tearDownClass
......................................

These must be implemented as class methods:

     import unittest

     class Test(unittest.TestCase):
         @classmethod
         def setUpClass(cls):
             cls._connection = createExpensiveConnectionObject()

         @classmethod
         def tearDownClass(cls):
             cls._connection.destroy()

If you want the ‘setUpClass’ and ‘tearDownClass’ on base classes called
then you must call up to them yourself.  The implementations in *note
TestCase: 9e5. are empty.

If an exception is raised during a ‘setUpClass’ then the tests in the
class are not run and the ‘tearDownClass’ is not run.  Skipped classes
will not have ‘setUpClass’ or ‘tearDownClass’ run.  If the exception is
a *note SkipTest: 9e9. exception then the class will be reported as
having been skipped instead of as an error.


File: python.info,  Node: setUpModule and tearDownModule,  Prev: setUpClass and tearDownClass,  Up: Class and Module Fixtures

5.26.8.17 setUpModule and tearDownModule
........................................

These should be implemented as functions:

     def setUpModule():
         createConnection()

     def tearDownModule():
         closeConnection()

If an exception is raised in a ‘setUpModule’ then none of the tests in
the module will be run and the ‘tearDownModule’ will not be run.  If the
exception is a *note SkipTest: 9e9. exception then the module will be
reported as having been skipped instead of as an error.

To add cleanup code that must be run even in the case of an exception,
use ‘addModuleCleanup’:

 -- Function: unittest.addModuleCleanup (function, /, *args, **kwargs)

     Add a function to be called after ‘tearDownModule()’ to cleanup
     resources used during the test class.  Functions will be called in
     reverse order to the order they are added (LIFO).  They are called
     with any arguments and keyword arguments passed into *note
     addModuleCleanup(): 374. when they are added.

     If ‘setUpModule()’ fails, meaning that ‘tearDownModule()’ is not
     called, then any cleanup functions added will still be called.

     New in version 3.8.

 -- Function: unittest.doModuleCleanups ()

     This function is called unconditionally after ‘tearDownModule()’,
     or after ‘setUpModule()’ if ‘setUpModule()’ raises an exception.

     It is responsible for calling all the cleanup functions added by
     ‘addCleanupModule()’.  If you need cleanup functions to be called
     `prior' to ‘tearDownModule()’ then you can call *note
     doModuleCleanups(): 3518. yourself.

     *note doModuleCleanups(): 3518. pops methods off the stack of
     cleanup functions one at a time, so it can be called at any time.

     New in version 3.8.


File: python.info,  Node: Signal Handling,  Prev: Class and Module Fixtures,  Up: unittest — Unit testing framework

5.26.8.18 Signal Handling
.........................

New in version 3.2.

The *note -c/–catch: d8c. command-line option to unittest, along with
the ‘catchbreak’ parameter to *note unittest.main(): 9e8, provide more
friendly handling of control-C during a test run.  With catch break
behavior enabled control-C will allow the currently running test to
complete, and the test run will then end and report all the results so
far.  A second control-c will raise a *note KeyboardInterrupt: 2cc. in
the usual way.

The control-c handling signal handler attempts to remain compatible with
code or tests that install their own *note signal.SIGINT: 2626. handler.
If the ‘unittest’ handler is called but `isn’t' the installed *note
signal.SIGINT: 2626. handler, i.e.  it has been replaced by the system
under test and delegated to, then it calls the default handler.  This
will normally be the expected behavior by code that replaces an
installed handler and delegates to it.  For individual tests that need
‘unittest’ control-c handling disabled the *note removeHandler(): d8d.
decorator can be used.

There are a few utility functions for framework authors to enable
control-c handling functionality within test frameworks.

 -- Function: unittest.installHandler ()

     Install the control-c handler.  When a *note signal.SIGINT: 2626.
     is received (usually in response to the user pressing control-c)
     all registered results have *note stop(): 3504. called.

 -- Function: unittest.registerResult (result)

     Register a *note TestResult: b97. object for control-c handling.
     Registering a result stores a weak reference to it, so it doesn’t
     prevent the result from being garbage collected.

     Registering a *note TestResult: b97. object has no side-effects if
     control-c handling is not enabled, so test frameworks can
     unconditionally register all results they create independently of
     whether or not handling is enabled.

 -- Function: unittest.removeResult (result)

     Remove a registered result.  Once a result has been removed then
     *note stop(): 3504. will no longer be called on that result object
     in response to a control-c.

 -- Function: unittest.removeHandler (function=None)

     When called without arguments this function removes the control-c
     handler if it has been installed.  This function can also be used
     as a test decorator to temporarily remove the handler while the
     test is being executed:

          @unittest.removeHandler
          def test_signal_handling(self):
              ...


File: python.info,  Node: unittest mock — mock object library,  Next: unittest mock — getting started,  Prev: unittest — Unit testing framework,  Up: Development Tools

5.26.9 ‘unittest.mock’ — mock object library
--------------------------------------------

New in version 3.3.

`Source code:' Lib/unittest/mock.py(1)

__________________________________________________________________

*note unittest.mock: 125. is a library for testing in Python.  It allows
you to replace parts of your system under test with mock objects and
make assertions about how they have been used.

*note unittest.mock: 125. provides a core *note Mock: 373. class
removing the need to create a host of stubs throughout your test suite.
After performing an action, you can make assertions about which methods
/ attributes were used and arguments they were called with.  You can
also specify return values and set needed attributes in the normal way.

Additionally, mock provides a *note patch(): 877. decorator that handles
patching module and class level attributes within the scope of a test,
along with *note sentinel: 50f. for creating unique objects.  See the
*note quick guide: 351e. for some examples of how to use *note Mock:
373, *note MagicMock: 874. and *note patch(): 877.

Mock is designed for use with *note unittest: 124. and is based on the
‘action -> assertion’ pattern instead of ‘record -> replay’ used by many
mocking frameworks.

There is a backport of *note unittest.mock: 125. for earlier versions of
Python, available as mock on PyPI(2).

* Menu:

* Quick Guide::
* The Mock Class::
* The patchers::
* MagicMock and magic method support::
* Helpers::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/unittest/mock.py

   (2) https://pypi.org/project/mock


File: python.info,  Node: Quick Guide,  Next: The Mock Class,  Up: unittest mock — mock object library

5.26.9.1 Quick Guide
....................

*note Mock: 373. and *note MagicMock: 874. objects create all attributes
and methods as you access them and store details of how they have been
used.  You can configure them, to specify return values or limit what
attributes are available, and then make assertions about how they have
been used:

     >>> from unittest.mock import MagicMock
     >>> thing = ProductionClass()
     >>> thing.method = MagicMock(return_value=3)
     >>> thing.method(3, 4, 5, key='value')
     3
     >>> thing.method.assert_called_with(3, 4, 5, key='value')

‘side_effect’ allows you to perform side effects, including raising an
exception when a mock is called:

     >>> mock = Mock(side_effect=KeyError('foo'))
     >>> mock()
     Traceback (most recent call last):
      ...
     KeyError: 'foo'

     >>> values = {'a': 1, 'b': 2, 'c': 3}
     >>> def side_effect(arg):
     ...     return values[arg]
     ...
     >>> mock.side_effect = side_effect
     >>> mock('a'), mock('b'), mock('c')
     (1, 2, 3)
     >>> mock.side_effect = [5, 4, 3, 2, 1]
     >>> mock(), mock(), mock()
     (5, 4, 3)

Mock has many other ways you can configure it and control its behaviour.
For example the `spec' argument configures the mock to take its
specification from another object.  Attempting to access attributes or
methods on the mock that don’t exist on the spec will fail with an *note
AttributeError: 4a2.

The *note patch(): 877. decorator / context manager makes it easy to
mock classes or objects in a module under test.  The object you specify
will be replaced with a mock (or other object) during the test and
restored when the test ends:

     >>> from unittest.mock import patch
     >>> @patch('module.ClassName2')
     ... @patch('module.ClassName1')
     ... def test(MockClass1, MockClass2):
     ...     module.ClassName1()
     ...     module.ClassName2()
     ...     assert MockClass1 is module.ClassName1
     ...     assert MockClass2 is module.ClassName2
     ...     assert MockClass1.called
     ...     assert MockClass2.called
     ...
     >>> test()

     Note: When you nest patch decorators the mocks are passed in to the
     decorated function in the same order they applied (the normal
     `Python' order that decorators are applied).  This means from the
     bottom up, so in the example above the mock for ‘module.ClassName1’
     is passed in first.

     With *note patch(): 877. it matters that you patch objects in the
     namespace where they are looked up.  This is normally
     straightforward, but for a quick guide read *note where to patch:
     351f.

As well as a decorator *note patch(): 877. can be used as a context
manager in a with statement:

     >>> with patch.object(ProductionClass, 'method', return_value=None) as mock_method:
     ...     thing = ProductionClass()
     ...     thing.method(1, 2, 3)
     ...
     >>> mock_method.assert_called_once_with(1, 2, 3)

There is also *note patch.dict(): 110a. for setting values in a
dictionary just during a scope and restoring the dictionary to its
original state when the test ends:

     >>> foo = {'key': 'value'}
     >>> original = foo.copy()
     >>> with patch.dict(foo, {'newkey': 'newvalue'}, clear=True):
     ...     assert foo == {'newkey': 'newvalue'}
     ...
     >>> assert foo == original

Mock supports the mocking of Python *note magic methods: 3520.  The
easiest way of using magic methods is with the *note MagicMock: 874.
class.  It allows you to do things like:

     >>> mock = MagicMock()
     >>> mock.__str__.return_value = 'foobarbaz'
     >>> str(mock)
     'foobarbaz'
     >>> mock.__str__.assert_called_with()

Mock allows you to assign functions (or other Mock instances) to magic
methods and they will be called appropriately.  The *note MagicMock:
874. class is just a Mock variant that has all of the magic methods
pre-created for you (well, all the useful ones anyway).

The following is an example of using magic methods with the ordinary
Mock class:

     >>> mock = Mock()
     >>> mock.__str__ = Mock(return_value='wheeeeee')
     >>> str(mock)
     'wheeeeee'

For ensuring that the mock objects in your tests have the same api as
the objects they are replacing, you can use *note auto-speccing: 3521.
Auto-speccing can be done through the `autospec' argument to patch, or
the *note create_autospec(): 1087. function.  Auto-speccing creates mock
objects that have the same attributes and methods as the objects they
are replacing, and any functions and methods (including constructors)
have the same call signature as the real object.

This ensures that your mocks will fail in the same way as your
production code if they are used incorrectly:

     >>> from unittest.mock import create_autospec
     >>> def function(a, b, c):
     ...     pass
     ...
     >>> mock_function = create_autospec(function, return_value='fishy')
     >>> mock_function(1, 2, 3)
     'fishy'
     >>> mock_function.assert_called_once_with(1, 2, 3)
     >>> mock_function('wrong arguments')
     Traceback (most recent call last):
      ...
     TypeError: <lambda>() takes exactly 3 arguments (1 given)

*note create_autospec(): 1087. can also be used on classes, where it
copies the signature of the ‘__init__’ method, and on callable objects
where it copies the signature of the ‘__call__’ method.


File: python.info,  Node: The Mock Class,  Next: The patchers,  Prev: Quick Guide,  Up: unittest mock — mock object library

5.26.9.2 The Mock Class
.......................

*note Mock: 373. is a flexible mock object intended to replace the use
of stubs and test doubles throughout your code.  Mocks are callable and
create attributes as new mocks when you access them (1).  Accessing the
same attribute will always return the same mock.  Mocks record how you
use them, allowing you to make assertions about what your code has done
to them.

*note MagicMock: 874. is a subclass of *note Mock: 373. with all the
magic methods pre-created and ready to use.  There are also non-callable
variants, useful when you are mocking out objects that aren’t callable:
*note NonCallableMock: 3523. and *note NonCallableMagicMock: 3524.

The *note patch(): 877. decorators makes it easy to temporarily replace
classes in a particular module with a *note Mock: 373. object.  By
default *note patch(): 877. will create a *note MagicMock: 874. for you.
You can specify an alternative class of *note Mock: 373. using the
`new_callable' argument to *note patch(): 877.

 -- Class: unittest.mock.Mock (spec=None, side_effect=None,
          return_value=DEFAULT, wraps=None, name=None, spec_set=None,
          unsafe=False, **kwargs)

     Create a new *note Mock: 373. object.  *note Mock: 373. takes
     several optional arguments that specify the behaviour of the Mock
     object:

        * `spec': This can be either a list of strings or an existing
          object (a class or instance) that acts as the specification
          for the mock object.  If you pass in an object then a list of
          strings is formed by calling dir on the object (excluding
          unsupported magic attributes and methods).  Accessing any
          attribute not in this list will raise an *note AttributeError:
          4a2.

          If `spec' is an object (rather than a list of strings) then
          *note __class__: ecc. returns the class of the spec object.
          This allows mocks to pass *note isinstance(): 552. tests.

        * `spec_set': A stricter variant of `spec'.  If used, attempting
          to `set' or get an attribute on the mock that isn’t on the
          object passed as `spec_set' will raise an *note
          AttributeError: 4a2.

        * `side_effect': A function to be called whenever the Mock is
          called.  See the *note side_effect: 3525. attribute.  Useful
          for raising exceptions or dynamically changing return values.
          The function is called with the same arguments as the mock,
          and unless it returns *note DEFAULT: 3526, the return value of
          this function is used as the return value.

          Alternatively `side_effect' can be an exception class or
          instance.  In this case the exception will be raised when the
          mock is called.

          If `side_effect' is an iterable then each call to the mock
          will return the next value from the iterable.

          A `side_effect' can be cleared by setting it to ‘None’.

        * `return_value': The value returned when the mock is called.
          By default this is a new Mock (created on first access).  See
          the *note return_value: 3527. attribute.

        * `unsafe': By default if any attribute starts with `assert' or
          `assret' will raise an *note AttributeError: 4a2.  Passing
          ‘unsafe=True’ will allow access to these attributes.

          New in version 3.5.

        * `wraps': Item for the mock object to wrap.  If `wraps' is not
          ‘None’ then calling the Mock will pass the call through to the
          wrapped object (returning the real result).  Attribute access
          on the mock will return a Mock object that wraps the
          corresponding attribute of the wrapped object (so attempting
          to access an attribute that doesn’t exist will raise an *note
          AttributeError: 4a2.).

          If the mock has an explicit `return_value' set then calls are
          not passed to the wrapped object and the `return_value' is
          returned instead.

        * `name': If the mock has a name then it will be used in the
          repr of the mock.  This can be useful for debugging.  The name
          is propagated to child mocks.

     Mocks can also be called with arbitrary keyword arguments.  These
     will be used to set attributes on the mock after it is created.
     See the *note configure_mock(): 3528. method for details.

      -- Method: assert_called ()

          Assert that the mock was called at least once.

               >>> mock = Mock()
               >>> mock.method()
               <Mock name='mock.method()' id='...'>
               >>> mock.method.assert_called()

          New in version 3.6.

      -- Method: assert_called_once ()

          Assert that the mock was called exactly once.

               >>> mock = Mock()
               >>> mock.method()
               <Mock name='mock.method()' id='...'>
               >>> mock.method.assert_called_once()
               >>> mock.method()
               <Mock name='mock.method()' id='...'>
               >>> mock.method.assert_called_once()
               Traceback (most recent call last):
               ...
               AssertionError: Expected 'method' to have been called once. Called 2 times.

          New in version 3.6.

      -- Method: assert_called_with (*args, **kwargs)

          This method is a convenient way of asserting that the last
          call has been made in a particular way:

               >>> mock = Mock()
               >>> mock.method(1, 2, 3, test='wow')
               <Mock name='mock.method()' id='...'>
               >>> mock.method.assert_called_with(1, 2, 3, test='wow')

      -- Method: assert_called_once_with (*args, **kwargs)

          Assert that the mock was called exactly once and that call was
          with the specified arguments.

               >>> mock = Mock(return_value=None)
               >>> mock('foo', bar='baz')
               >>> mock.assert_called_once_with('foo', bar='baz')
               >>> mock('other', bar='values')
               >>> mock.assert_called_once_with('other', bar='values')
               Traceback (most recent call last):
                 ...
               AssertionError: Expected 'mock' to be called once. Called 2 times.

      -- Method: assert_any_call (*args, **kwargs)

          assert the mock has been called with the specified arguments.

          The assert passes if the mock has `ever' been called, unlike
          *note assert_called_with(): 113a. and *note
          assert_called_once_with(): 3529. that only pass if the call is
          the most recent one, and in the case of *note
          assert_called_once_with(): 3529. it must also be the only
          call.

               >>> mock = Mock(return_value=None)
               >>> mock(1, 2, arg='thing')
               >>> mock('some', 'thing', 'else')
               >>> mock.assert_any_call(1, 2, arg='thing')

      -- Method: assert_has_calls (calls, any_order=False)

          assert the mock has been called with the specified calls.  The
          *note mock_calls: 352c. list is checked for the calls.

          If `any_order' is false then the calls must be sequential.
          There can be extra calls before or after the specified calls.

          If `any_order' is true then the calls can be in any order, but
          they must all appear in *note mock_calls: 352c.

               >>> mock = Mock(return_value=None)
               >>> mock(1)
               >>> mock(2)
               >>> mock(3)
               >>> mock(4)
               >>> calls = [call(2), call(3)]
               >>> mock.assert_has_calls(calls)
               >>> calls = [call(4), call(2), call(3)]
               >>> mock.assert_has_calls(calls, any_order=True)

      -- Method: assert_not_called ()

          Assert the mock was never called.

               >>> m = Mock()
               >>> m.hello.assert_not_called()
               >>> obj = m.hello()
               >>> m.hello.assert_not_called()
               Traceback (most recent call last):
                 ...
               AssertionError: Expected 'hello' to not have been called. Called 1 times.

          New in version 3.5.

      -- Method: reset_mock (*, return_value=False, side_effect=False)

          The reset_mock method resets all the call attributes on a mock
          object:

               >>> mock = Mock(return_value=None)
               >>> mock('hello')
               >>> mock.called
               True
               >>> mock.reset_mock()
               >>> mock.called
               False

          Changed in version 3.6: Added two keyword only argument to the
          reset_mock function.

          This can be useful where you want to make a series of
          assertions that reuse the same object.  Note that *note
          reset_mock(): 6a1. `doesn’t' clear the return value, *note
          side_effect: 3525. or any child attributes you have set using
          normal assignment by default.  In case you want to reset
          `return_value' or *note side_effect: 3525, then pass the
          corresponding parameter as ‘True’.  Child mocks and the return
          value mock (if any) are reset as well.

               Note: `return_value', and *note side_effect: 3525. are
               keyword only argument.

      -- Method: mock_add_spec (spec, spec_set=False)

          Add a spec to a mock.  `spec' can either be an object or a
          list of strings.  Only attributes on the `spec' can be fetched
          as attributes from the mock.

          If `spec_set' is true then only attributes on the spec can be
          set.

      -- Method: attach_mock (mock, attribute)

          Attach a mock as an attribute of this one, replacing its name
          and parent.  Calls to the attached mock will be recorded in
          the *note method_calls: 352f. and *note mock_calls: 352c.
          attributes of this one.

      -- Method: configure_mock (**kwargs)

          Set attributes on the mock through keyword arguments.

          Attributes plus return values and side effects can be set on
          child mocks using standard dot notation and unpacking a
          dictionary in the method call:

               >>> mock = Mock()
               >>> attrs = {'method.return_value': 3, 'other.side_effect': KeyError}
               >>> mock.configure_mock(**attrs)
               >>> mock.method()
               3
               >>> mock.other()
               Traceback (most recent call last):
                 ...
               KeyError

          The same thing can be achieved in the constructor call to
          mocks:

               >>> attrs = {'method.return_value': 3, 'other.side_effect': KeyError}
               >>> mock = Mock(some_attribute='eggs', **attrs)
               >>> mock.some_attribute
               'eggs'
               >>> mock.method()
               3
               >>> mock.other()
               Traceback (most recent call last):
                 ...
               KeyError

          *note configure_mock(): 3528. exists to make it easier to do
          configuration after the mock has been created.

      -- Method: __dir__ ()

          *note Mock: 373. objects limit the results of ‘dir(some_mock)’
          to useful results.  For mocks with a `spec' this includes all
          the permitted attributes for the mock.

          See *note FILTER_DIR: 3531. for what this filtering does, and
          how to switch it off.

      -- Method: _get_child_mock (**kw)

          Create the child mocks for attributes and return value.  By
          default child mocks will be the same type as the parent.
          Subclasses of Mock may want to override this to customize the
          way child mocks are made.

          For non-callable mocks the callable variant will be used
          (rather than any custom subclass).

      -- Attribute: called

          A boolean representing whether or not the mock object has been
          called:

               >>> mock = Mock(return_value=None)
               >>> mock.called
               False
               >>> mock()
               >>> mock.called
               True

      -- Attribute: call_count

          An integer telling you how many times the mock object has been
          called:

               >>> mock = Mock(return_value=None)
               >>> mock.call_count
               0
               >>> mock()
               >>> mock()
               >>> mock.call_count
               2

      -- Attribute: return_value

          Set this to configure the value returned by calling the mock:

               >>> mock = Mock()
               >>> mock.return_value = 'fish'
               >>> mock()
               'fish'

          The default return value is a mock object and you can
          configure it in the normal way:

               >>> mock = Mock()
               >>> mock.return_value.attribute = sentinel.Attribute
               >>> mock.return_value()
               <Mock name='mock()()' id='...'>
               >>> mock.return_value.assert_called_with()

          *note return_value: 3527. can also be set in the constructor:

               >>> mock = Mock(return_value=3)
               >>> mock.return_value
               3
               >>> mock()
               3

      -- Attribute: side_effect

          This can either be a function to be called when the mock is
          called, an iterable or an exception (class or instance) to be
          raised.

          If you pass in a function it will be called with same
          arguments as the mock and unless the function returns the
          *note DEFAULT: 3526. singleton the call to the mock will then
          return whatever the function returns.  If the function returns
          *note DEFAULT: 3526. then the mock will return its normal
          value (from the *note return_value: 3527.).

          If you pass in an iterable, it is used to retrieve an iterator
          which must yield a value on every call.  This value can either
          be an exception instance to be raised, or a value to be
          returned from the call to the mock (*note DEFAULT: 3526.
          handling is identical to the function case).

          An example of a mock that raises an exception (to test
          exception handling of an API):

               >>> mock = Mock()
               >>> mock.side_effect = Exception('Boom!')
               >>> mock()
               Traceback (most recent call last):
                 ...
               Exception: Boom!

          Using *note side_effect: 3525. to return a sequence of values:

               >>> mock = Mock()
               >>> mock.side_effect = [3, 2, 1]
               >>> mock(), mock(), mock()
               (3, 2, 1)

          Using a callable:

               >>> mock = Mock(return_value=3)
               >>> def side_effect(*args, **kwargs):
               ...     return DEFAULT
               ...
               >>> mock.side_effect = side_effect
               >>> mock()
               3

          *note side_effect: 3525. can be set in the constructor.
          Here’s an example that adds one to the value the mock is
          called with and returns it:

               >>> side_effect = lambda value: value + 1
               >>> mock = Mock(side_effect=side_effect)
               >>> mock(3)
               4
               >>> mock(-8)
               -7

          Setting *note side_effect: 3525. to ‘None’ clears it:

               >>> m = Mock(side_effect=KeyError, return_value=3)
               >>> m()
               Traceback (most recent call last):
                ...
               KeyError
               >>> m.side_effect = None
               >>> m()
               3

      -- Attribute: call_args

          This is either ‘None’ (if the mock hasn’t been called), or the
          arguments that the mock was last called with.  This will be in
          the form of a tuple: the first member, which can also be
          accessed through the ‘args’ property, is any ordered arguments
          the mock was called with (or an empty tuple) and the second
          member, which can also be accessed through the ‘kwargs’
          property, is any keyword arguments (or an empty dictionary).

               >>> mock = Mock(return_value=None)
               >>> print(mock.call_args)
               None
               >>> mock()
               >>> mock.call_args
               call()
               >>> mock.call_args == ()
               True
               >>> mock(3, 4)
               >>> mock.call_args
               call(3, 4)
               >>> mock.call_args == ((3, 4),)
               True
               >>> mock.call_args.args
               (3, 4)
               >>> mock.call_args.kwargs
               {}
               >>> mock(3, 4, 5, key='fish', next='w00t!')
               >>> mock.call_args
               call(3, 4, 5, key='fish', next='w00t!')
               >>> mock.call_args.args
               (3, 4, 5)
               >>> mock.call_args.kwargs
               {'key': 'fish', 'next': 'w00t!'}

          *note call_args: 106a, along with members of the lists *note
          call_args_list: 3535, *note method_calls: 352f. and *note
          mock_calls: 352c. are *note call: 10cc. objects.  These are
          tuples, so they can be unpacked to get at the individual
          arguments and make more complex assertions.  See *note calls
          as tuples: 3536.

          Changed in version 3.8: Added ‘args’ and ‘kwargs’ properties.

      -- Attribute: call_args_list

          This is a list of all the calls made to the mock object in
          sequence (so the length of the list is the number of times it
          has been called).  Before any calls have been made it is an
          empty list.  The *note call: 10cc. object can be used for
          conveniently constructing lists of calls to compare with *note
          call_args_list: 3535.

               >>> mock = Mock(return_value=None)
               >>> mock()
               >>> mock(3, 4)
               >>> mock(key='fish', next='w00t!')
               >>> mock.call_args_list
               [call(), call(3, 4), call(key='fish', next='w00t!')]
               >>> expected = [(), ((3, 4),), ({'key': 'fish', 'next': 'w00t!'},)]
               >>> mock.call_args_list == expected
               True

          Members of *note call_args_list: 3535. are *note call: 10cc.
          objects.  These can be unpacked as tuples to get at the
          individual arguments.  See *note calls as tuples: 3536.

      -- Attribute: method_calls

          As well as tracking calls to themselves, mocks also track
          calls to methods and attributes, and `their' methods and
          attributes:

               >>> mock = Mock()
               >>> mock.method()
               <Mock name='mock.method()' id='...'>
               >>> mock.property.method.attribute()
               <Mock name='mock.property.method.attribute()' id='...'>
               >>> mock.method_calls
               [call.method(), call.property.method.attribute()]

          Members of *note method_calls: 352f. are *note call: 10cc.
          objects.  These can be unpacked as tuples to get at the
          individual arguments.  See *note calls as tuples: 3536.

      -- Attribute: mock_calls

          *note mock_calls: 352c. records `all' calls to the mock
          object, its methods, magic methods `and' return value mocks.

               >>> mock = MagicMock()
               >>> result = mock(1, 2, 3)
               >>> mock.first(a=3)
               <MagicMock name='mock.first()' id='...'>
               >>> mock.second()
               <MagicMock name='mock.second()' id='...'>
               >>> int(mock)
               1
               >>> result(1)
               <MagicMock name='mock()()' id='...'>
               >>> expected = [call(1, 2, 3), call.first(a=3), call.second(),
               ... call.__int__(), call()(1)]
               >>> mock.mock_calls == expected
               True

          Members of *note mock_calls: 352c. are *note call: 10cc.
          objects.  These can be unpacked as tuples to get at the
          individual arguments.  See *note calls as tuples: 3536.

               Note: The way *note mock_calls: 352c. are recorded means
               that where nested calls are made, the parameters of
               ancestor calls are not recorded and so will always
               compare equal:

                    >>> mock = MagicMock()
                    >>> mock.top(a=3).bottom()
                    <MagicMock name='mock.top().bottom()' id='...'>
                    >>> mock.mock_calls
                    [call.top(a=3), call.top().bottom()]
                    >>> mock.mock_calls[-1] == call.top(a=-1).bottom()
                    True

      -- Attribute: __class__

          Normally the *note __class__: 3537. attribute of an object
          will return its type.  For a mock object with a ‘spec’,
          ‘__class__’ returns the spec class instead.  This allows mock
          objects to pass *note isinstance(): 552. tests for the object
          they are replacing / masquerading as:

               >>> mock = Mock(spec=3)
               >>> isinstance(mock, int)
               True

          *note __class__: 3537. is assignable to, this allows a mock to
          pass an *note isinstance(): 552. check without forcing you to
          use a spec:

               >>> mock = Mock()
               >>> mock.__class__ = dict
               >>> isinstance(mock, dict)
               True

 -- Class: unittest.mock.NonCallableMock (spec=None, wraps=None,
          name=None, spec_set=None, **kwargs)

     A non-callable version of *note Mock: 373.  The constructor
     parameters have the same meaning of *note Mock: 373, with the
     exception of `return_value' and `side_effect' which have no meaning
     on a non-callable mock.

Mock objects that use a class or an instance as a ‘spec’ or ‘spec_set’
are able to pass *note isinstance(): 552. tests:

     >>> mock = Mock(spec=SomeClass)
     >>> isinstance(mock, SomeClass)
     True
     >>> mock = Mock(spec_set=SomeClass())
     >>> isinstance(mock, SomeClass)
     True

The *note Mock: 373. classes have support for mocking magic methods.
See *note magic methods: 3520. for the full details.

The mock classes and the *note patch(): 877. decorators all take
arbitrary keyword arguments for configuration.  For the *note patch():
877. decorators the keywords are passed to the constructor of the mock
being created.  The keyword arguments are for configuring attributes of
the mock:

     >>> m = MagicMock(attribute=3, other='fish')
     >>> m.attribute
     3
     >>> m.other
     'fish'

The return value and side effect of child mocks can be set in the same
way, using dotted notation.  As you can’t use dotted names directly in a
call you have to create a dictionary and unpack it using ‘**’:

     >>> attrs = {'method.return_value': 3, 'other.side_effect': KeyError}
     >>> mock = Mock(some_attribute='eggs', **attrs)
     >>> mock.some_attribute
     'eggs'
     >>> mock.method()
     3
     >>> mock.other()
     Traceback (most recent call last):
       ...
     KeyError

A callable mock which was created with a `spec' (or a `spec_set') will
introspect the specification object’s signature when matching calls to
the mock.  Therefore, it can match the actual call’s arguments
regardless of whether they were passed positionally or by name:

     >>> def f(a, b, c): pass
     ...
     >>> mock = Mock(spec=f)
     >>> mock(1, 2, c=3)
     <Mock name='mock()' id='140161580456576'>
     >>> mock.assert_called_with(1, 2, 3)
     >>> mock.assert_called_with(a=1, b=2, c=3)

This applies to *note assert_called_with(): 113a, *note
assert_called_once_with(): 3529, *note assert_has_calls(): 352b. and
*note assert_any_call(): 352a.  When *note Autospeccing: 3521, it will
also apply to method calls on the mock object.

     Changed in version 3.4: Added signature introspection on specced
     and autospecced mock objects.

 -- Class: unittest.mock.PropertyMock (*args, **kwargs)

     A mock intended to be used as a property, or other descriptor, on a
     class.  *note PropertyMock: 3538. provides *note __get__(): 156e.
     and *note __set__(): 1572. methods so you can specify a return
     value when it is fetched.

     Fetching a *note PropertyMock: 3538. instance from an object calls
     the mock, with no args.  Setting it calls the mock with the value
     being set.

          >>> class Foo:
          ...     @property
          ...     def foo(self):
          ...         return 'something'
          ...     @foo.setter
          ...     def foo(self, value):
          ...         pass
          ...
          >>> with patch('__main__.Foo.foo', new_callable=PropertyMock) as mock_foo:
          ...     mock_foo.return_value = 'mockity-mock'
          ...     this_foo = Foo()
          ...     print(this_foo.foo)
          ...     this_foo.foo = 6
          ...
          mockity-mock
          >>> mock_foo.mock_calls
          [call(), call(6)]

Because of the way mock attributes are stored you can’t directly attach
a *note PropertyMock: 3538. to a mock object.  Instead you can attach it
to the mock type object:

     >>> m = MagicMock()
     >>> p = PropertyMock(return_value=3)
     >>> type(m).foo = p
     >>> m.foo
     3
     >>> p.assert_called_once_with()

 -- Class: unittest.mock.AsyncMock (spec=None, side_effect=None,
          return_value=DEFAULT, wraps=None, name=None, spec_set=None,
          unsafe=False, **kwargs)

     An asynchronous version of *note MagicMock: 874.  The *note
     AsyncMock: 372. object will behave so the object is recognized as
     an async function, and the result of a call is an awaitable.

          >>> mock = AsyncMock()
          >>> asyncio.iscoroutinefunction(mock)
          True
          >>> inspect.isawaitable(mock())
          True

     The result of ‘mock()’ is an async function which will have the
     outcome of ‘side_effect’ or ‘return_value’ after it has been
     awaited:

        - if ‘side_effect’ is a function, the async function will return
          the result of that function,

        - if ‘side_effect’ is an exception, the async function will
          raise the exception,

        - if ‘side_effect’ is an iterable, the async function will
          return the next value of the iterable, however, if the
          sequence of result is exhausted, ‘StopAsyncIteration’ is
          raised immediately,

        - if ‘side_effect’ is not defined, the async function will
          return the value defined by ‘return_value’, hence, by default,
          the async function returns a new *note AsyncMock: 372. object.

     Setting the `spec' of a *note Mock: 373. or *note MagicMock: 874.
     to an async function will result in a coroutine object being
     returned after calling.

          >>> async def async_func(): pass
          ...
          >>> mock = MagicMock(async_func)
          >>> mock
          <MagicMock spec='function' id='...'>
          >>> mock()
          <coroutine object AsyncMockMixin._mock_call at ...>

     Setting the `spec' of a *note Mock: 373, *note MagicMock: 874, or
     *note AsyncMock: 372. to a class with asynchronous and synchronous
     functions will automatically detect the synchronous functions and
     set them as *note MagicMock: 874. (if the parent mock is *note
     AsyncMock: 372. or *note MagicMock: 874.) or *note Mock: 373. (if
     the parent mock is *note Mock: 373.).  All asynchronous functions
     will be *note AsyncMock: 372.

          >>> class ExampleClass:
          ...     def sync_foo():
          ...         pass
          ...     async def async_foo():
          ...         pass
          ...
          >>> a_mock = AsyncMock(ExampleClass)
          >>> a_mock.sync_foo
          <MagicMock name='mock.sync_foo' id='...'>
          >>> a_mock.async_foo
          <AsyncMock name='mock.async_foo' id='...'>
          >>> mock = Mock(ExampleClass)
          >>> mock.sync_foo
          <Mock name='mock.sync_foo' id='...'>
          >>> mock.async_foo
          <AsyncMock name='mock.async_foo' id='...'>

     New in version 3.8.

      -- Method: assert_awaited ()

          Assert that the mock was awaited at least once.  Note that
          this is separate from the object having been called, the
          ‘await’ keyword must be used:

               >>> mock = AsyncMock()
               >>> async def main(coroutine_mock):
               ...     await coroutine_mock
               ...
               >>> coroutine_mock = mock()
               >>> mock.called
               True
               >>> mock.assert_awaited()
               Traceback (most recent call last):
               ...
               AssertionError: Expected mock to have been awaited.
               >>> asyncio.run(main(coroutine_mock))
               >>> mock.assert_awaited()

      -- Method: assert_awaited_once ()

          Assert that the mock was awaited exactly once.

               >>> mock = AsyncMock()
               >>> async def main():
               ...     await mock()
               ...
               >>> asyncio.run(main())
               >>> mock.assert_awaited_once()
               >>> asyncio.run(main())
               >>> mock.method.assert_awaited_once()
               Traceback (most recent call last):
               ...
               AssertionError: Expected mock to have been awaited once. Awaited 2 times.

      -- Method: assert_awaited_with (*args, **kwargs)

          Assert that the last await was with the specified arguments.

               >>> mock = AsyncMock()
               >>> async def main(*args, **kwargs):
               ...     await mock(*args, **kwargs)
               ...
               >>> asyncio.run(main('foo', bar='bar'))
               >>> mock.assert_awaited_with('foo', bar='bar')
               >>> mock.assert_awaited_with('other')
               Traceback (most recent call last):
               ...
               AssertionError: expected call not found.
               Expected: mock('other')
               Actual: mock('foo', bar='bar')

      -- Method: assert_awaited_once_with (*args, **kwargs)

          Assert that the mock was awaited exactly once and with the
          specified arguments.

               >>> mock = AsyncMock()
               >>> async def main(*args, **kwargs):
               ...     await mock(*args, **kwargs)
               ...
               >>> asyncio.run(main('foo', bar='bar'))
               >>> mock.assert_awaited_once_with('foo', bar='bar')
               >>> asyncio.run(main('foo', bar='bar'))
               >>> mock.assert_awaited_once_with('foo', bar='bar')
               Traceback (most recent call last):
               ...
               AssertionError: Expected mock to have been awaited once. Awaited 2 times.

      -- Method: assert_any_await (*args, **kwargs)

          Assert the mock has ever been awaited with the specified
          arguments.

               >>> mock = AsyncMock()
               >>> async def main(*args, **kwargs):
               ...     await mock(*args, **kwargs)
               ...
               >>> asyncio.run(main('foo', bar='bar'))
               >>> asyncio.run(main('hello'))
               >>> mock.assert_any_await('foo', bar='bar')
               >>> mock.assert_any_await('other')
               Traceback (most recent call last):
               ...
               AssertionError: mock('other') await not found

      -- Method: assert_has_awaits (calls, any_order=False)

          Assert the mock has been awaited with the specified calls.
          The *note await_args_list: 1069. list is checked for the
          awaits.

          If `any_order' is false then the awaits must be sequential.
          There can be extra calls before or after the specified awaits.

          If `any_order' is true then the awaits can be in any order,
          but they must all appear in *note await_args_list: 1069.

               >>> mock = AsyncMock()
               >>> async def main(*args, **kwargs):
               ...     await mock(*args, **kwargs)
               ...
               >>> calls = [call("foo"), call("bar")]
               >>> mock.assert_has_awaits(calls)
               Traceback (most recent call last):
               ...
               AssertionError: Awaits not found.
               Expected: [call('foo'), call('bar')]
               Actual: []
               >>> asyncio.run(main('foo'))
               >>> asyncio.run(main('bar'))
               >>> mock.assert_has_awaits(calls)

      -- Method: assert_not_awaited ()

          Assert that the mock was never awaited.

               >>> mock = AsyncMock()
               >>> mock.assert_not_awaited()

      -- Method: reset_mock (*args, **kwargs)

          See *note Mock.reset_mock(): 6a1.  Also sets *note
          await_count: 3541. to 0, *note await_args: 3542. to None, and
          clears the *note await_args_list: 1069.

      -- Attribute: await_count

          An integer keeping track of how many times the mock object has
          been awaited.

               >>> mock = AsyncMock()
               >>> async def main():
               ...     await mock()
               ...
               >>> asyncio.run(main())
               >>> mock.await_count
               1
               >>> asyncio.run(main())
               >>> mock.await_count
               2

      -- Attribute: await_args

          This is either ‘None’ (if the mock hasn’t been awaited), or
          the arguments that the mock was last awaited with.  Functions
          the same as *note Mock.call_args: 106a.

               >>> mock = AsyncMock()
               >>> async def main(*args):
               ...     await mock(*args)
               ...
               >>> mock.await_args
               >>> asyncio.run(main('foo'))
               >>> mock.await_args
               call('foo')
               >>> asyncio.run(main('bar'))
               >>> mock.await_args
               call('bar')

      -- Attribute: await_args_list

          This is a list of all the awaits made to the mock object in
          sequence (so the length of the list is the number of times it
          has been awaited).  Before any awaits have been made it is an
          empty list.

               >>> mock = AsyncMock()
               >>> async def main(*args):
               ...     await mock(*args)
               ...
               >>> mock.await_args_list
               []
               >>> asyncio.run(main('foo'))
               >>> mock.await_args_list
               [call('foo')]
               >>> asyncio.run(main('bar'))
               >>> mock.await_args_list
               [call('foo'), call('bar')]

* Menu:

* Calling::
* Deleting Attributes::
* Mock names and the name attribute::
* Attaching Mocks as Attributes::

   ---------- Footnotes ----------

   (1) (1) The only exceptions are magic methods and attributes (those
that have leading and trailing double underscores).  Mock doesn’t create
these but instead raises an *note AttributeError: 4a2.  This is because
the interpreter will often implicitly request these methods, and gets
`very' confused to get a new Mock object when it expects a magic method.
If you need magic method support see *note magic methods: 3520.


File: python.info,  Node: Calling,  Next: Deleting Attributes,  Up: The Mock Class

5.26.9.3 Calling
................

Mock objects are callable.  The call will return the value set as the
*note return_value: 3527. attribute.  The default return value is a new
Mock object; it is created the first time the return value is accessed
(either explicitly or by calling the Mock) - but it is stored and the
same one returned each time.

Calls made to the object will be recorded in the attributes like *note
call_args: 106a. and *note call_args_list: 3535.

If *note side_effect: 3525. is set then it will be called after the call
has been recorded, so if ‘side_effect’ raises an exception the call is
still recorded.

The simplest way to make a mock raise an exception when called is to
make *note side_effect: 3525. an exception class or instance:

     >>> m = MagicMock(side_effect=IndexError)
     >>> m(1, 2, 3)
     Traceback (most recent call last):
       ...
     IndexError
     >>> m.mock_calls
     [call(1, 2, 3)]
     >>> m.side_effect = KeyError('Bang!')
     >>> m('two', 'three', 'four')
     Traceback (most recent call last):
       ...
     KeyError: 'Bang!'
     >>> m.mock_calls
     [call(1, 2, 3), call('two', 'three', 'four')]

If ‘side_effect’ is a function then whatever that function returns is
what calls to the mock return.  The ‘side_effect’ function is called
with the same arguments as the mock.  This allows you to vary the return
value of the call dynamically, based on the input:

     >>> def side_effect(value):
     ...     return value + 1
     ...
     >>> m = MagicMock(side_effect=side_effect)
     >>> m(1)
     2
     >>> m(2)
     3
     >>> m.mock_calls
     [call(1), call(2)]

If you want the mock to still return the default return value (a new
mock), or any set return value, then there are two ways of doing this.
Either return ‘mock.return_value’ from inside ‘side_effect’, or return
*note DEFAULT: 3526.:

     >>> m = MagicMock()
     >>> def side_effect(*args, **kwargs):
     ...     return m.return_value
     ...
     >>> m.side_effect = side_effect
     >>> m.return_value = 3
     >>> m()
     3
     >>> def side_effect(*args, **kwargs):
     ...     return DEFAULT
     ...
     >>> m.side_effect = side_effect
     >>> m()
     3

To remove a ‘side_effect’, and return to the default behaviour, set the
‘side_effect’ to ‘None’:

     >>> m = MagicMock(return_value=6)
     >>> def side_effect(*args, **kwargs):
     ...     return 3
     ...
     >>> m.side_effect = side_effect
     >>> m()
     3
     >>> m.side_effect = None
     >>> m()
     6

The ‘side_effect’ can also be any iterable object.  Repeated calls to
the mock will return values from the iterable (until the iterable is
exhausted and a *note StopIteration: 582. is raised):

     >>> m = MagicMock(side_effect=[1, 2, 3])
     >>> m()
     1
     >>> m()
     2
     >>> m()
     3
     >>> m()
     Traceback (most recent call last):
       ...
     StopIteration

If any members of the iterable are exceptions they will be raised
instead of returned:

     >>> iterable = (33, ValueError, 66)
     >>> m = MagicMock(side_effect=iterable)
     >>> m()
     33
     >>> m()
     Traceback (most recent call last):
      ...
     ValueError
     >>> m()
     66


File: python.info,  Node: Deleting Attributes,  Next: Mock names and the name attribute,  Prev: Calling,  Up: The Mock Class

5.26.9.4 Deleting Attributes
............................

Mock objects create attributes on demand.  This allows them to pretend
to be objects of any type.

You may want a mock object to return ‘False’ to a *note hasattr(): 54a.
call, or raise an *note AttributeError: 4a2. when an attribute is
fetched.  You can do this by providing an object as a ‘spec’ for a mock,
but that isn’t always convenient.

You “block” attributes by deleting them.  Once deleted, accessing an
attribute will raise an *note AttributeError: 4a2.

     >>> mock = MagicMock()
     >>> hasattr(mock, 'm')
     True
     >>> del mock.m
     >>> hasattr(mock, 'm')
     False
     >>> del mock.f
     >>> mock.f
     Traceback (most recent call last):
         ...
     AttributeError: f


File: python.info,  Node: Mock names and the name attribute,  Next: Attaching Mocks as Attributes,  Prev: Deleting Attributes,  Up: The Mock Class

5.26.9.5 Mock names and the name attribute
..........................................

Since “name” is an argument to the *note Mock: 373. constructor, if you
want your mock object to have a “name” attribute you can’t just pass it
in at creation time.  There are two alternatives.  One option is to use
*note configure_mock(): 3528.:

     >>> mock = MagicMock()
     >>> mock.configure_mock(name='my_name')
     >>> mock.name
     'my_name'

A simpler option is to simply set the “name” attribute after mock
creation:

     >>> mock = MagicMock()
     >>> mock.name = "foo"


File: python.info,  Node: Attaching Mocks as Attributes,  Prev: Mock names and the name attribute,  Up: The Mock Class

5.26.9.6 Attaching Mocks as Attributes
......................................

When you attach a mock as an attribute of another mock (or as the return
value) it becomes a “child” of that mock.  Calls to the child are
recorded in the *note method_calls: 352f. and *note mock_calls: 352c.
attributes of the parent.  This is useful for configuring child mocks
and then attaching them to the parent, or for attaching mocks to a
parent that records all calls to the children and allows you to make
assertions about the order of calls between mocks:

     >>> parent = MagicMock()
     >>> child1 = MagicMock(return_value=None)
     >>> child2 = MagicMock(return_value=None)
     >>> parent.child1 = child1
     >>> parent.child2 = child2
     >>> child1(1)
     >>> child2(2)
     >>> parent.mock_calls
     [call.child1(1), call.child2(2)]

The exception to this is if the mock has a name.  This allows you to
prevent the “parenting” if for some reason you don’t want it to happen.

     >>> mock = MagicMock()
     >>> not_a_child = MagicMock(name='not-a-child')
     >>> mock.attribute = not_a_child
     >>> mock.attribute()
     <MagicMock name='not-a-child()' id='...'>
     >>> mock.mock_calls
     []

Mocks created for you by *note patch(): 877. are automatically given
names.  To attach mocks that have names to a parent you use the *note
attach_mock(): 352e. method:

     >>> thing1 = object()
     >>> thing2 = object()
     >>> parent = MagicMock()
     >>> with patch('__main__.thing1', return_value=None) as child1:
     ...     with patch('__main__.thing2', return_value=None) as child2:
     ...         parent.attach_mock(child1, 'child1')
     ...         parent.attach_mock(child2, 'child2')
     ...         child1('one')
     ...         child2('two')
     ...
     >>> parent.mock_calls
     [call.child1('one'), call.child2('two')]


File: python.info,  Node: The patchers,  Next: MagicMock and magic method support,  Prev: The Mock Class,  Up: unittest mock — mock object library

5.26.9.7 The patchers
.....................

The patch decorators are used for patching objects only within the scope
of the function they decorate.  They automatically handle the unpatching
for you, even if exceptions are raised.  All of these functions can also
be used in with statements or as class decorators.

* Menu:

* patch::
* patch.object: patch object.
* patch.dict: patch dict.
* patch.multiple: patch multiple.
* patch methods; start and stop: patch methods start and stop.
* patch builtins::
* TEST_PREFIX::
* Nesting Patch Decorators::
* Where to patch::
* Patching Descriptors and Proxy Objects::


File: python.info,  Node: patch,  Next: patch object,  Up: The patchers

5.26.9.8 patch
..............

     Note: The key is to do the patching in the right namespace.  See
     the section *note where to patch: 354a.

 -- Function: unittest.mock.patch (target, new=DEFAULT, spec=None,
          create=False, spec_set=None, autospec=None, new_callable=None,
          **kwargs)

     *note patch(): 877. acts as a function decorator, class decorator
     or a context manager.  Inside the body of the function or with
     statement, the `target' is patched with a `new' object.  When the
     function/with statement exits the patch is undone.

     If `new' is omitted, then the target is replaced with an *note
     AsyncMock: 372. if the patched object is an async function or a
     *note MagicMock: 874. otherwise.  If *note patch(): 877. is used as
     a decorator and `new' is omitted, the created mock is passed in as
     an extra argument to the decorated function.  If *note patch():
     877. is used as a context manager the created mock is returned by
     the context manager.

     `target' should be a string in the form
     ‘'package.module.ClassName'’.  The `target' is imported and the
     specified object replaced with the `new' object, so the `target'
     must be importable from the environment you are calling *note
     patch(): 877. from.  The target is imported when the decorated
     function is executed, not at decoration time.

     The `spec' and `spec_set' keyword arguments are passed to the *note
     MagicMock: 874. if patch is creating one for you.

     In addition you can pass ‘spec=True’ or ‘spec_set=True’, which
     causes patch to pass in the object being mocked as the
     spec/spec_set object.

     `new_callable' allows you to specify a different class, or callable
     object, that will be called to create the `new' object.  By default
     *note AsyncMock: 372. is used for async functions and *note
     MagicMock: 874. for the rest.

     A more powerful form of `spec' is `autospec'.  If you set
     ‘autospec=True’ then the mock will be created with a spec from the
     object being replaced.  All attributes of the mock will also have
     the spec of the corresponding attribute of the object being
     replaced.  Methods and functions being mocked will have their
     arguments checked and will raise a *note TypeError: 1fe. if they
     are called with the wrong signature.  For mocks replacing a class,
     their return value (the ‘instance’) will have the same spec as the
     class.  See the *note create_autospec(): 1087. function and *note
     Autospeccing: 3521.

     Instead of ‘autospec=True’ you can pass ‘autospec=some_object’ to
     use an arbitrary object as the spec instead of the one being
     replaced.

     By default *note patch(): 877. will fail to replace attributes that
     don’t exist.  If you pass in ‘create=True’, and the attribute
     doesn’t exist, patch will create the attribute for you when the
     patched function is called, and delete it again after the patched
     function has exited.  This is useful for writing tests against
     attributes that your production code creates at runtime.  It is off
     by default because it can be dangerous.  With it switched on you
     can write passing tests against APIs that don’t actually exist!

          Note: 
          Changed in version 3.5: If you are patching builtins in a
          module then you don’t need to pass ‘create=True’, it will be
          added by default.

     Patch can be used as a ‘TestCase’ class decorator.  It works by
     decorating each test method in the class.  This reduces the
     boilerplate code when your test methods share a common patchings
     set.  *note patch(): 877. finds tests by looking for method names
     that start with ‘patch.TEST_PREFIX’.  By default this is ‘'test'’,
     which matches the way *note unittest: 124. finds tests.  You can
     specify an alternative prefix by setting ‘patch.TEST_PREFIX’.

     Patch can be used as a context manager, with the with statement.
     Here the patching applies to the indented block after the with
     statement.  If you use “as” then the patched object will be bound
     to the name after the “as”; very useful if *note patch(): 877. is
     creating a mock object for you.

     *note patch(): 877. takes arbitrary keyword arguments.  These will
     be passed to *note AsyncMock: 372. if the patched object is
     asynchronous, to *note MagicMock: 874. otherwise or to
     `new_callable' if specified.

     ‘patch.dict(...)’, ‘patch.multiple(...)’ and ‘patch.object(...)’
     are available for alternate use-cases.

*note patch(): 877. as function decorator, creating the mock for you and
passing it into the decorated function:

     >>> @patch('__main__.SomeClass')
     ... def function(normal_argument, mock_class):
     ...     print(mock_class is SomeClass)
     ...
     >>> function(None)
     True

Patching a class replaces the class with a *note MagicMock: 874.
`instance'.  If the class is instantiated in the code under test then it
will be the *note return_value: 3527. of the mock that will be used.

If the class is instantiated multiple times you could use *note
side_effect: 3525. to return a new mock each time.  Alternatively you
can set the `return_value' to be anything you want.

To configure return values on methods of `instances' on the patched
class you must do this on the ‘return_value’.  For example:

     >>> class Class:
     ...     def method(self):
     ...         pass
     ...
     >>> with patch('__main__.Class') as MockClass:
     ...     instance = MockClass.return_value
     ...     instance.method.return_value = 'foo'
     ...     assert Class() is instance
     ...     assert Class().method() == 'foo'
     ...

If you use `spec' or `spec_set' and *note patch(): 877. is replacing a
`class', then the return value of the created mock will have the same
spec.

     >>> Original = Class
     >>> patcher = patch('__main__.Class', spec=True)
     >>> MockClass = patcher.start()
     >>> instance = MockClass()
     >>> assert isinstance(instance, Original)
     >>> patcher.stop()

The `new_callable' argument is useful where you want to use an
alternative class to the default *note MagicMock: 874. for the created
mock.  For example, if you wanted a *note NonCallableMock: 3523. to be
used:

     >>> thing = object()
     >>> with patch('__main__.thing', new_callable=NonCallableMock) as mock_thing:
     ...     assert thing is mock_thing
     ...     thing()
     ...
     Traceback (most recent call last):
       ...
     TypeError: 'NonCallableMock' object is not callable

Another use case might be to replace an object with an *note
io.StringIO: 91a. instance:

     >>> from io import StringIO
     >>> def foo():
     ...     print('Something')
     ...
     >>> @patch('sys.stdout', new_callable=StringIO)
     ... def test(mock_stdout):
     ...     foo()
     ...     assert mock_stdout.getvalue() == 'Something\n'
     ...
     >>> test()

When *note patch(): 877. is creating a mock for you, it is common that
the first thing you need to do is to configure the mock.  Some of that
configuration can be done in the call to patch.  Any arbitrary keywords
you pass into the call will be used to set attributes on the created
mock:

     >>> patcher = patch('__main__.thing', first='one', second='two')
     >>> mock_thing = patcher.start()
     >>> mock_thing.first
     'one'
     >>> mock_thing.second
     'two'

As well as attributes on the created mock attributes, like the *note
return_value: 3527. and *note side_effect: 3525, of child mocks can also
be configured.  These aren’t syntactically valid to pass in directly as
keyword arguments, but a dictionary with these as keys can still be
expanded into a *note patch(): 877. call using ‘**’:

     >>> config = {'method.return_value': 3, 'other.side_effect': KeyError}
     >>> patcher = patch('__main__.thing', **config)
     >>> mock_thing = patcher.start()
     >>> mock_thing.method()
     3
     >>> mock_thing.other()
     Traceback (most recent call last):
       ...
     KeyError

By default, attempting to patch a function in a module (or a method or
an attribute in a class) that does not exist will fail with *note
AttributeError: 4a2.:

     >>> @patch('sys.non_existing_attribute', 42)
     ... def test():
     ...     assert sys.non_existing_attribute == 42
     ...
     >>> test()
     Traceback (most recent call last):
       ...
     AttributeError: <module 'sys' (built-in)> does not have the attribute 'non_existing_attribute'

but adding ‘create=True’ in the call to *note patch(): 877. will make
the previous example work as expected:

     >>> @patch('sys.non_existing_attribute', 42, create=True)
     ... def test(mock_stdout):
     ...     assert sys.non_existing_attribute == 42
     ...
     >>> test()

Changed in version 3.8: *note patch(): 877. now returns an *note
AsyncMock: 372. if the target is an async function.


File: python.info,  Node: patch object,  Next: patch dict,  Prev: patch,  Up: The patchers

5.26.9.9 patch.object
.....................

 -- Function: patch.object (target, attribute, new=DEFAULT, spec=None,
          create=False, spec_set=None, autospec=None, new_callable=None,
          **kwargs)

     patch the named member (`attribute') on an object (`target') with a
     mock object.

     *note patch.object(): 10b4. can be used as a decorator, class
     decorator or a context manager.  Arguments `new', `spec', `create',
     `spec_set', `autospec' and `new_callable' have the same meaning as
     for *note patch(): 877.  Like *note patch(): 877, *note
     patch.object(): 10b4. takes arbitrary keyword arguments for
     configuring the mock object it creates.

     When used as a class decorator *note patch.object(): 10b4. honours
     ‘patch.TEST_PREFIX’ for choosing which methods to wrap.

You can either call *note patch.object(): 10b4. with three arguments or
two arguments.  The three argument form takes the object to be patched,
the attribute name and the object to replace the attribute with.

When calling with the two argument form you omit the replacement object,
and a mock is created for you and passed in as an extra argument to the
decorated function:

     >>> @patch.object(SomeClass, 'class_method')
     ... def test(mock_method):
     ...     SomeClass.class_method(3)
     ...     mock_method.assert_called_with(3)
     ...
     >>> test()

`spec', `create' and the other arguments to *note patch.object(): 10b4.
have the same meaning as they do for *note patch(): 877.


File: python.info,  Node: patch dict,  Next: patch multiple,  Prev: patch object,  Up: The patchers

5.26.9.10 patch.dict
....................

 -- Function: patch.dict (in_dict, values=(), clear=False, **kwargs)

     Patch a dictionary, or dictionary like object, and restore the
     dictionary to its original state after the test.

     `in_dict' can be a dictionary or a mapping like container.  If it
     is a mapping then it must at least support getting, setting and
     deleting items plus iterating over keys.

     `in_dict' can also be a string specifying the name of the
     dictionary, which will then be fetched by importing it.

     `values' can be a dictionary of values to set in the dictionary.
     `values' can also be an iterable of ‘(key, value)’ pairs.

     If `clear' is true then the dictionary will be cleared before the
     new values are set.

     *note patch.dict(): 110a. can also be called with arbitrary keyword
     arguments to set values in the dictionary.

     Changed in version 3.8: *note patch.dict(): 110a. now returns the
     patched dictionary when used as a context manager.

*note patch.dict(): 110a. can be used as a context manager, decorator or
class decorator:

     >>> foo = {}
     >>> @patch.dict(foo, {'newkey': 'newvalue'})
     ... def test():
     ...     assert foo == {'newkey': 'newvalue'}
     >>> test()
     >>> assert foo == {}

When used as a class decorator *note patch.dict(): 110a. honours
‘patch.TEST_PREFIX’ (default to ‘'test'’) for choosing which methods to
wrap:

     >>> import os
     >>> import unittest
     >>> from unittest.mock import patch
     >>> @patch.dict('os.environ', {'newkey': 'newvalue'})
     ... class TestSample(unittest.TestCase):
     ...     def test_sample(self):
     ...         self.assertEqual(os.environ['newkey'], 'newvalue')

If you want to use a different prefix for your test, you can inform the
patchers of the different prefix by setting ‘patch.TEST_PREFIX’.  For
more details about how to change the value of see *note TEST_PREFIX:
354d.

*note patch.dict(): 110a. can be used to add members to a dictionary, or
simply let a test change a dictionary, and ensure the dictionary is
restored when the test ends.

     >>> foo = {}
     >>> with patch.dict(foo, {'newkey': 'newvalue'}) as patched_foo:
     ...     assert foo == {'newkey': 'newvalue'}
     ...     assert patched_foo == {'newkey': 'newvalue'}
     ...     # You can add, update or delete keys of foo (or patched_foo, it's the same dict)
     ...     patched_foo['spam'] = 'eggs'
     ...
     >>> assert foo == {}
     >>> assert patched_foo == {}

     >>> import os
     >>> with patch.dict('os.environ', {'newkey': 'newvalue'}):
     ...     print(os.environ['newkey'])
     ...
     newvalue
     >>> assert 'newkey' not in os.environ

Keywords can be used in the *note patch.dict(): 110a. call to set values
in the dictionary:

     >>> mymodule = MagicMock()
     >>> mymodule.function.return_value = 'fish'
     >>> with patch.dict('sys.modules', mymodule=mymodule):
     ...     import mymodule
     ...     mymodule.function('some', 'args')
     ...
     'fish'

*note patch.dict(): 110a. can be used with dictionary like objects that
aren’t actually dictionaries.  At the very minimum they must support
item getting, setting, deleting and either iteration or membership test.
This corresponds to the magic methods *note __getitem__(): 3a2, *note
__setitem__(): d2a, *note __delitem__(): d2b. and either *note
__iter__(): 609. or *note __contains__(): dee.

     >>> class Container:
     ...     def __init__(self):
     ...         self.values = {}
     ...     def __getitem__(self, name):
     ...         return self.values[name]
     ...     def __setitem__(self, name, value):
     ...         self.values[name] = value
     ...     def __delitem__(self, name):
     ...         del self.values[name]
     ...     def __iter__(self):
     ...         return iter(self.values)
     ...
     >>> thing = Container()
     >>> thing['one'] = 1
     >>> with patch.dict(thing, one=2, two=3):
     ...     assert thing['one'] == 2
     ...     assert thing['two'] == 3
     ...
     >>> assert thing['one'] == 1
     >>> assert list(thing) == ['one']


File: python.info,  Node: patch multiple,  Next: patch methods start and stop,  Prev: patch dict,  Up: The patchers

5.26.9.11 patch.multiple
........................

 -- Function: patch.multiple (target, spec=None, create=False,
          spec_set=None, autospec=None, new_callable=None, **kwargs)

     Perform multiple patches in a single call.  It takes the object to
     be patched (either as an object or a string to fetch the object by
     importing) and keyword arguments for the patches:

          with patch.multiple(settings, FIRST_PATCH='one', SECOND_PATCH='two'):
              ...

     Use *note DEFAULT: 3526. as the value if you want *note
     patch.multiple(): 354f. to create mocks for you.  In this case the
     created mocks are passed into a decorated function by keyword, and
     a dictionary is returned when *note patch.multiple(): 354f. is used
     as a context manager.

     *note patch.multiple(): 354f. can be used as a decorator, class
     decorator or a context manager.  The arguments `spec', `spec_set',
     `create', `autospec' and `new_callable' have the same meaning as
     for *note patch(): 877.  These arguments will be applied to `all'
     patches done by *note patch.multiple(): 354f.

     When used as a class decorator *note patch.multiple(): 354f.
     honours ‘patch.TEST_PREFIX’ for choosing which methods to wrap.

If you want *note patch.multiple(): 354f. to create mocks for you, then
you can use *note DEFAULT: 3526. as the value.  If you use *note
patch.multiple(): 354f. as a decorator then the created mocks are passed
into the decorated function by keyword.

     >>> thing = object()
     >>> other = object()

     >>> @patch.multiple('__main__', thing=DEFAULT, other=DEFAULT)
     ... def test_function(thing, other):
     ...     assert isinstance(thing, MagicMock)
     ...     assert isinstance(other, MagicMock)
     ...
     >>> test_function()

*note patch.multiple(): 354f. can be nested with other ‘patch’
decorators, but put arguments passed by keyword `after' any of the
standard arguments created by *note patch(): 877.:

     >>> @patch('sys.exit')
     ... @patch.multiple('__main__', thing=DEFAULT, other=DEFAULT)
     ... def test_function(mock_exit, other, thing):
     ...     assert 'other' in repr(other)
     ...     assert 'thing' in repr(thing)
     ...     assert 'exit' in repr(mock_exit)
     ...
     >>> test_function()

If *note patch.multiple(): 354f. is used as a context manager, the value
returned by the context manager is a dictionary where created mocks are
keyed by name:

     >>> with patch.multiple('__main__', thing=DEFAULT, other=DEFAULT) as values:
     ...     assert 'other' in repr(values['other'])
     ...     assert 'thing' in repr(values['thing'])
     ...     assert values['thing'] is thing
     ...     assert values['other'] is other
     ...


File: python.info,  Node: patch methods start and stop,  Next: patch builtins,  Prev: patch multiple,  Up: The patchers

5.26.9.12 patch methods: start and stop
.......................................

All the patchers have ‘start()’ and ‘stop()’ methods.  These make it
simpler to do patching in ‘setUp’ methods or where you want to do
multiple patches without nesting decorators or with statements.

To use them call *note patch(): 877, *note patch.object(): 10b4. or
*note patch.dict(): 110a. as normal and keep a reference to the returned
‘patcher’ object.  You can then call ‘start()’ to put the patch in place
and ‘stop()’ to undo it.

If you are using *note patch(): 877. to create a mock for you then it
will be returned by the call to ‘patcher.start’.

     >>> patcher = patch('package.module.ClassName')
     >>> from package import module
     >>> original = module.ClassName
     >>> new_mock = patcher.start()
     >>> assert module.ClassName is not original
     >>> assert module.ClassName is new_mock
     >>> patcher.stop()
     >>> assert module.ClassName is original
     >>> assert module.ClassName is not new_mock

A typical use case for this might be for doing multiple patches in the
‘setUp’ method of a ‘TestCase’:

     >>> class MyTest(unittest.TestCase):
     ...     def setUp(self):
     ...         self.patcher1 = patch('package.module.Class1')
     ...         self.patcher2 = patch('package.module.Class2')
     ...         self.MockClass1 = self.patcher1.start()
     ...         self.MockClass2 = self.patcher2.start()
     ...
     ...     def tearDown(self):
     ...         self.patcher1.stop()
     ...         self.patcher2.stop()
     ...
     ...     def test_something(self):
     ...         assert package.module.Class1 is self.MockClass1
     ...         assert package.module.Class2 is self.MockClass2
     ...
     >>> MyTest('test_something').run()

     Caution: If you use this technique you must ensure that the
     patching is “undone” by calling ‘stop’.  This can be fiddlier than
     you might think, because if an exception is raised in the ‘setUp’
     then ‘tearDown’ is not called.  *note
     unittest.TestCase.addCleanup(): 3c5. makes this easier:

          >>> class MyTest(unittest.TestCase):
          ...     def setUp(self):
          ...         patcher = patch('package.module.Class')
          ...         self.MockClass = patcher.start()
          ...         self.addCleanup(patcher.stop)
          ...
          ...     def test_something(self):
          ...         assert package.module.Class is self.MockClass
          ...

     As an added bonus you no longer need to keep a reference to the
     ‘patcher’ object.

It is also possible to stop all patches which have been started by using
*note patch.stopall(): 3552.

 -- Function: patch.stopall ()

     Stop all active patches.  Only stops patches started with ‘start’.


File: python.info,  Node: patch builtins,  Next: TEST_PREFIX,  Prev: patch methods start and stop,  Up: The patchers

5.26.9.13 patch builtins
........................

You can patch any builtins within a module.  The following example
patches builtin *note ord(): 1559.:

     >>> @patch('__main__.ord')
     ... def test(mock_ord):
     ...     mock_ord.return_value = 101
     ...     print(ord('c'))
     ...
     >>> test()
     101


File: python.info,  Node: TEST_PREFIX,  Next: Nesting Patch Decorators,  Prev: patch builtins,  Up: The patchers

5.26.9.14 TEST_PREFIX
.....................

All of the patchers can be used as class decorators.  When used in this
way they wrap every test method on the class.  The patchers recognise
methods that start with ‘'test'’ as being test methods.  This is the
same way that the *note unittest.TestLoader: 871. finds test methods by
default.

It is possible that you want to use a different prefix for your tests.
You can inform the patchers of the different prefix by setting
‘patch.TEST_PREFIX’:

     >>> patch.TEST_PREFIX = 'foo'
     >>> value = 3
     >>>
     >>> @patch('__main__.value', 'not three')
     ... class Thing:
     ...     def foo_one(self):
     ...         print(value)
     ...     def foo_two(self):
     ...         print(value)
     ...
     >>>
     >>> Thing().foo_one()
     not three
     >>> Thing().foo_two()
     not three
     >>> value
     3


File: python.info,  Node: Nesting Patch Decorators,  Next: Where to patch,  Prev: TEST_PREFIX,  Up: The patchers

5.26.9.15 Nesting Patch Decorators
..................................

If you want to perform multiple patches then you can simply stack up the
decorators.

You can stack up multiple patch decorators using this pattern:

     >>> @patch.object(SomeClass, 'class_method')
     ... @patch.object(SomeClass, 'static_method')
     ... def test(mock1, mock2):
     ...     assert SomeClass.static_method is mock1
     ...     assert SomeClass.class_method is mock2
     ...     SomeClass.static_method('foo')
     ...     SomeClass.class_method('bar')
     ...     return mock1, mock2
     ...
     >>> mock1, mock2 = test()
     >>> mock1.assert_called_once_with('foo')
     >>> mock2.assert_called_once_with('bar')

Note that the decorators are applied from the bottom upwards.  This is
the standard way that Python applies decorators.  The order of the
created mocks passed into your test function matches this order.


File: python.info,  Node: Where to patch,  Next: Patching Descriptors and Proxy Objects,  Prev: Nesting Patch Decorators,  Up: The patchers

5.26.9.16 Where to patch
........................

*note patch(): 877. works by (temporarily) changing the object that a
`name' points to with another one.  There can be many names pointing to
any individual object, so for patching to work you must ensure that you
patch the name used by the system under test.

The basic principle is that you patch where an object is `looked up',
which is not necessarily the same place as where it is defined.  A
couple of examples will help to clarify this.

Imagine we have a project that we want to test with the following
structure:

     a.py
         -> Defines SomeClass

     b.py
         -> from a import SomeClass
         -> some_function instantiates SomeClass

Now we want to test ‘some_function’ but we want to mock out ‘SomeClass’
using *note patch(): 877.  The problem is that when we import module b,
which we will have to do then it imports ‘SomeClass’ from module a.  If
we use *note patch(): 877. to mock out ‘a.SomeClass’ then it will have
no effect on our test; module b already has a reference to the `real'
‘SomeClass’ and it looks like our patching had no effect.

The key is to patch out ‘SomeClass’ where it is used (or where it is
looked up).  In this case ‘some_function’ will actually look up
‘SomeClass’ in module b, where we have imported it.  The patching should
look like:

     @patch('b.SomeClass')

However, consider the alternative scenario where instead of ‘from a
import SomeClass’ module b does ‘import a’ and ‘some_function’ uses
‘a.SomeClass’.  Both of these import forms are common.  In this case the
class we want to patch is being looked up in the module and so we have
to patch ‘a.SomeClass’ instead:

     @patch('a.SomeClass')


File: python.info,  Node: Patching Descriptors and Proxy Objects,  Prev: Where to patch,  Up: The patchers

5.26.9.17 Patching Descriptors and Proxy Objects
................................................

Both *note patch: 3549. and *note patch.object: 354b. correctly patch
and restore descriptors: class methods, static methods and properties.
You should patch these on the `class' rather than an instance.  They
also work with `some' objects that proxy attribute access, like the
django settings object(1).

   ---------- Footnotes ----------

   (1) 
http://www.voidspace.org.uk/python/weblog/arch_d7_2010_12_04.shtml#e1198


File: python.info,  Node: MagicMock and magic method support,  Next: Helpers,  Prev: The patchers,  Up: unittest mock — mock object library

5.26.9.18 MagicMock and magic method support
............................................

* Menu:

* Mocking Magic Methods::
* Magic Mock::


File: python.info,  Node: Mocking Magic Methods,  Next: Magic Mock,  Up: MagicMock and magic method support

5.26.9.19 Mocking Magic Methods
...............................

*note Mock: 373. supports mocking the Python protocol methods, also
known as “magic methods”.  This allows mock objects to replace
containers or other objects that implement Python protocols.

Because magic methods are looked up differently from normal methods (1),
this support has been specially implemented.  This means that only
specific magic methods are supported.  The supported list includes
`almost' all of them.  If there are any missing that you need please let
us know.

You mock magic methods by setting the method you are interested in to a
function or a mock instance.  If you are using a function then it `must'
take ‘self’ as the first argument (2).

     >>> def __str__(self):
     ...     return 'fooble'
     ...
     >>> mock = Mock()
     >>> mock.__str__ = __str__
     >>> str(mock)
     'fooble'

     >>> mock = Mock()
     >>> mock.__str__ = Mock()
     >>> mock.__str__.return_value = 'fooble'
     >>> str(mock)
     'fooble'

     >>> mock = Mock()
     >>> mock.__iter__ = Mock(return_value=iter([]))
     >>> list(mock)
     []

One use case for this is for mocking objects used as context managers in
a *note with: 7da. statement:

     >>> mock = Mock()
     >>> mock.__enter__ = Mock(return_value='foo')
     >>> mock.__exit__ = Mock(return_value=False)
     >>> with mock as m:
     ...     assert m == 'foo'
     ...
     >>> mock.__enter__.assert_called_with()
     >>> mock.__exit__.assert_called_with(None, None, None)

Calls to magic methods do not appear in *note method_calls: 352f, but
they are recorded in *note mock_calls: 352c.

     Note: If you use the `spec' keyword argument to create a mock then
     attempting to set a magic method that isn’t in the spec will raise
     an *note AttributeError: 4a2.

The full list of supported magic methods is:

   * ‘__hash__’, ‘__sizeof__’, ‘__repr__’ and ‘__str__’

   * ‘__dir__’, ‘__format__’ and ‘__subclasses__’

   * ‘__round__’, ‘__floor__’, ‘__trunc__’ and ‘__ceil__’

   * Comparisons: ‘__lt__’, ‘__gt__’, ‘__le__’, ‘__ge__’, ‘__eq__’ and
     ‘__ne__’

   * Container methods: ‘__getitem__’, ‘__setitem__’, ‘__delitem__’,
     ‘__contains__’, ‘__len__’, ‘__iter__’, ‘__reversed__’ and
     ‘__missing__’

   * Context manager: ‘__enter__’, ‘__exit__’, ‘__aenter__’ and
     ‘__aexit__’

   * Unary numeric methods: ‘__neg__’, ‘__pos__’ and ‘__invert__’

   * The numeric methods (including right hand and in-place variants):
     ‘__add__’, ‘__sub__’, ‘__mul__’, ‘__matmul__’, ‘__div__’,
     ‘__truediv__’, ‘__floordiv__’, ‘__mod__’, ‘__divmod__’,
     ‘__lshift__’, ‘__rshift__’, ‘__and__’, ‘__xor__’, ‘__or__’, and
     ‘__pow__’

   * Numeric conversion methods: ‘__complex__’, ‘__int__’, ‘__float__’
     and ‘__index__’

   * Descriptor methods: ‘__get__’, ‘__set__’ and ‘__delete__’

   * Pickling: ‘__reduce__’, ‘__reduce_ex__’, ‘__getinitargs__’,
     ‘__getnewargs__’, ‘__getstate__’ and ‘__setstate__’

   * File system path representation: ‘__fspath__’

   * Asynchronous iteration methods: ‘__aiter__’ and ‘__anext__’

Changed in version 3.8: Added support for *note
os.PathLike.__fspath__(): 5e7.

Changed in version 3.8: Added support for ‘__aenter__’, ‘__aexit__’,
‘__aiter__’ and ‘__anext__’.

The following methods exist but are `not' supported as they are either
in use by mock, can’t be set dynamically, or can cause problems:

   * ‘__getattr__’, ‘__setattr__’, ‘__init__’ and ‘__new__’

   * ‘__prepare__’, ‘__instancecheck__’, ‘__subclasscheck__’, ‘__del__’

   ---------- Footnotes ----------

   (1) (2) Magic methods `should' be looked up on the class rather than
the instance.  Different versions of Python are inconsistent about
applying this rule.  The supported protocol methods should work with all
supported versions of Python.

   (2) (3) The function is basically hooked up to the class, but each
‘Mock’ instance is kept isolated from the others.


File: python.info,  Node: Magic Mock,  Prev: Mocking Magic Methods,  Up: MagicMock and magic method support

5.26.9.20 Magic Mock
....................

There are two ‘MagicMock’ variants: *note MagicMock: 874. and *note
NonCallableMagicMock: 3524.

 -- Class: unittest.mock.MagicMock (*args, **kw)

     ‘MagicMock’ is a subclass of *note Mock: 373. with default
     implementations of most of the magic methods.  You can use
     ‘MagicMock’ without having to configure the magic methods yourself.

     The constructor parameters have the same meaning as for *note Mock:
     373.

     If you use the `spec' or `spec_set' arguments then `only' magic
     methods that exist in the spec will be created.

 -- Class: unittest.mock.NonCallableMagicMock (*args, **kw)

     A non-callable version of *note MagicMock: 874.

     The constructor parameters have the same meaning as for *note
     MagicMock: 874, with the exception of `return_value' and
     `side_effect' which have no meaning on a non-callable mock.

The magic methods are setup with *note MagicMock: 874. objects, so you
can configure them and use them in the usual way:

     >>> mock = MagicMock()
     >>> mock[3] = 'fish'
     >>> mock.__setitem__.assert_called_with(3, 'fish')
     >>> mock.__getitem__.return_value = 'result'
     >>> mock[2]
     'result'

By default many of the protocol methods are required to return objects
of a specific type.  These methods are preconfigured with a default
return value, so that they can be used without you having to do anything
if you aren’t interested in the return value.  You can still `set' the
return value manually if you want to change the default.

Methods and their defaults:

   * ‘__lt__’: ‘NotImplemented’

   * ‘__gt__’: ‘NotImplemented’

   * ‘__le__’: ‘NotImplemented’

   * ‘__ge__’: ‘NotImplemented’

   * ‘__int__’: ‘1’

   * ‘__contains__’: ‘False’

   * ‘__len__’: ‘0’

   * ‘__iter__’: ‘iter([])’

   * ‘__exit__’: ‘False’

   * ‘__aexit__’: ‘False’

   * ‘__complex__’: ‘1j’

   * ‘__float__’: ‘1.0’

   * ‘__bool__’: ‘True’

   * ‘__index__’: ‘1’

   * ‘__hash__’: default hash for the mock

   * ‘__str__’: default str for the mock

   * ‘__sizeof__’: default sizeof for the mock

For example:

     >>> mock = MagicMock()
     >>> int(mock)
     1
     >>> len(mock)
     0
     >>> list(mock)
     []
     >>> object() in mock
     False

The two equality methods, *note __eq__(): 44b. and *note __ne__(): f18,
are special.  They do the default equality comparison on identity, using
the *note side_effect: 3525. attribute, unless you change their return
value to return something else:

     >>> MagicMock() == 3
     False
     >>> MagicMock() != 3
     True
     >>> mock = MagicMock()
     >>> mock.__eq__.return_value = True
     >>> mock == 3
     True

The return value of ‘MagicMock.__iter__()’ can be any iterable object
and isn’t required to be an iterator:

     >>> mock = MagicMock()
     >>> mock.__iter__.return_value = ['a', 'b', 'c']
     >>> list(mock)
     ['a', 'b', 'c']
     >>> list(mock)
     ['a', 'b', 'c']

If the return value `is' an iterator, then iterating over it once will
consume it and subsequent iterations will result in an empty list:

     >>> mock.__iter__.return_value = iter(['a', 'b', 'c'])
     >>> list(mock)
     ['a', 'b', 'c']
     >>> list(mock)
     []

‘MagicMock’ has all of the supported magic methods configured except for
some of the obscure and obsolete ones.  You can still set these up if
you want.

Magic methods that are supported but not setup by default in ‘MagicMock’
are:

   * ‘__subclasses__’

   * ‘__dir__’

   * ‘__format__’

   * ‘__get__’, ‘__set__’ and ‘__delete__’

   * ‘__reversed__’ and ‘__missing__’

   * ‘__reduce__’, ‘__reduce_ex__’, ‘__getinitargs__’, ‘__getnewargs__’,
     ‘__getstate__’ and ‘__setstate__’

   * ‘__getformat__’ and ‘__setformat__’


File: python.info,  Node: Helpers,  Prev: MagicMock and magic method support,  Up: unittest mock — mock object library

5.26.9.21 Helpers
.................

* Menu:

* sentinel::
* DEFAULT::
* call::
* create_autospec::
* ANY::
* FILTER_DIR::
* mock_open::
* Autospeccing::
* Sealing mocks::


File: python.info,  Node: sentinel,  Next: DEFAULT,  Up: Helpers

5.26.9.22 sentinel
..................

 -- Data: unittest.mock.sentinel

     The ‘sentinel’ object provides a convenient way of providing unique
     objects for your tests.

     Attributes are created on demand when you access them by name.
     Accessing the same attribute will always return the same object.
     The objects returned have a sensible repr so that test failure
     messages are readable.

     Changed in version 3.7: The ‘sentinel’ attributes now preserve
     their identity when they are *note copied: 25. or *note pickled:
     ca.

Sometimes when testing you need to test that a specific object is passed
as an argument to another method, or returned.  It can be common to
create named sentinel objects to test this.  *note sentinel: 50f.
provides a convenient way of creating and testing the identity of
objects like this.

In this example we monkey patch ‘method’ to return
‘sentinel.some_object’:

     >>> real = ProductionClass()
     >>> real.method = Mock(name="method")
     >>> real.method.return_value = sentinel.some_object
     >>> result = real.method()
     >>> assert result is sentinel.some_object
     >>> result
     sentinel.some_object


File: python.info,  Node: DEFAULT,  Next: call,  Prev: sentinel,  Up: Helpers

5.26.9.23 DEFAULT
.................

 -- Data: unittest.mock.DEFAULT

     The *note DEFAULT: 3526. object is a pre-created sentinel (actually
     ‘sentinel.DEFAULT’).  It can be used by *note side_effect: 3525.
     functions to indicate that the normal return value should be used.


File: python.info,  Node: call,  Next: create_autospec,  Prev: DEFAULT,  Up: Helpers

5.26.9.24 call
..............

 -- Function: unittest.mock.call (*args, **kwargs)

     *note call(): 10cc. is a helper object for making simpler
     assertions, for comparing with *note call_args: 106a, *note
     call_args_list: 3535, *note mock_calls: 352c. and *note
     method_calls: 352f.  *note call(): 10cc. can also be used with
     *note assert_has_calls(): 352b.

          >>> m = MagicMock(return_value=None)
          >>> m(1, 2, a='foo', b='bar')
          >>> m()
          >>> m.call_args_list == [call(1, 2, a='foo', b='bar'), call()]
          True

 -- Method: call.call_list ()

     For a call object that represents multiple calls, *note
     call_list(): 355f. returns a list of all the intermediate calls as
     well as the final call.

‘call_list’ is particularly useful for making assertions on “chained
calls”.  A chained call is multiple calls on a single line of code.
This results in multiple entries in *note mock_calls: 352c. on a mock.
Manually constructing the sequence of calls can be tedious.

*note call_list(): 355f. can construct the sequence of calls from the
same chained call:

     >>> m = MagicMock()
     >>> m(1).method(arg='foo').other('bar')(2.0)
     <MagicMock name='mock().method().other()()' id='...'>
     >>> kall = call(1).method(arg='foo').other('bar')(2.0)
     >>> kall.call_list()
     [call(1),
      call().method(arg='foo'),
      call().method().other('bar'),
      call().method().other()(2.0)]
     >>> m.mock_calls == kall.call_list()
     True
A ‘call’ object is either a tuple of (positional args, keyword args) or
(name, positional args, keyword args) depending on how it was
constructed.  When you construct them yourself this isn’t particularly
interesting, but the ‘call’ objects that are in the *note
Mock.call_args: 106a, *note Mock.call_args_list: 3535. and *note
Mock.mock_calls: 352c. attributes can be introspected to get at the
individual arguments they contain.

The ‘call’ objects in *note Mock.call_args: 106a. and *note
Mock.call_args_list: 3535. are two-tuples of (positional args, keyword
args) whereas the ‘call’ objects in *note Mock.mock_calls: 352c, along
with ones you construct yourself, are three-tuples of (name, positional
args, keyword args).

You can use their “tupleness” to pull out the individual arguments for
more complex introspection and assertions.  The positional arguments are
a tuple (an empty tuple if there are no positional arguments) and the
keyword arguments are a dictionary:

     >>> m = MagicMock(return_value=None)
     >>> m(1, 2, 3, arg='one', arg2='two')
     >>> kall = m.call_args
     >>> kall.args
     (1, 2, 3)
     >>> kall.kwargs
     {'arg': 'one', 'arg2': 'two'}
     >>> kall.args is kall[0]
     True
     >>> kall.kwargs is kall[1]
     True

     >>> m = MagicMock()
     >>> m.foo(4, 5, 6, arg='two', arg2='three')
     <MagicMock name='mock.foo()' id='...'>
     >>> kall = m.mock_calls[0]
     >>> name, args, kwargs = kall
     >>> name
     'foo'
     >>> args
     (4, 5, 6)
     >>> kwargs
     {'arg': 'two', 'arg2': 'three'}
     >>> name is m.mock_calls[0][0]
     True


File: python.info,  Node: create_autospec,  Next: ANY,  Prev: call,  Up: Helpers

5.26.9.25 create_autospec
.........................

 -- Function: unittest.mock.create_autospec (spec, spec_set=False,
          instance=False, **kwargs)

     Create a mock object using another object as a spec.  Attributes on
     the mock will use the corresponding attribute on the `spec' object
     as their spec.

     Functions or methods being mocked will have their arguments checked
     to ensure that they are called with the correct signature.

     If `spec_set' is ‘True’ then attempting to set attributes that
     don’t exist on the spec object will raise an *note AttributeError:
     4a2.

     If a class is used as a spec then the return value of the mock (the
     instance of the class) will have the same spec.  You can use a
     class as the spec for an instance object by passing
     ‘instance=True’.  The returned mock will only be callable if
     instances of the mock are callable.

     *note create_autospec(): 1087. also takes arbitrary keyword
     arguments that are passed to the constructor of the created mock.

See *note Autospeccing: 3521. for examples of how to use auto-speccing
with *note create_autospec(): 1087. and the `autospec' argument to *note
patch(): 877.

Changed in version 3.8: *note create_autospec(): 1087. now returns an
*note AsyncMock: 372. if the target is an async function.


File: python.info,  Node: ANY,  Next: FILTER_DIR,  Prev: create_autospec,  Up: Helpers

5.26.9.26 ANY
.............

 -- Data: unittest.mock.ANY

Sometimes you may need to make assertions about `some' of the arguments
in a call to mock, but either not care about some of the arguments or
want to pull them individually out of *note call_args: 106a. and make
more complex assertions on them.

To ignore certain arguments you can pass in objects that compare equal
to `everything'.  Calls to *note assert_called_with(): 113a. and *note
assert_called_once_with(): 3529. will then succeed no matter what was
passed in.

     >>> mock = Mock(return_value=None)
     >>> mock('foo', bar=object())
     >>> mock.assert_called_once_with('foo', bar=ANY)

*note ANY: 10d1. can also be used in comparisons with call lists like
*note mock_calls: 352c.:

     >>> m = MagicMock(return_value=None)
     >>> m(1)
     >>> m(1, 2)
     >>> m(object())
     >>> m.mock_calls == [call(1), call(1, 2), ANY]
     True


File: python.info,  Node: FILTER_DIR,  Next: mock_open,  Prev: ANY,  Up: Helpers

5.26.9.27 FILTER_DIR
....................

 -- Data: unittest.mock.FILTER_DIR

*note FILTER_DIR: 3531. is a module level variable that controls the way
mock objects respond to *note dir(): df9. (only for Python 2.6 or more
recent).  The default is ‘True’, which uses the filtering described
below, to only show useful members.  If you dislike this filtering, or
need to switch it off for diagnostic purposes, then set ‘mock.FILTER_DIR
= False’.

With filtering on, ‘dir(some_mock)’ shows only useful attributes and
will include any dynamically created attributes that wouldn’t normally
be shown.  If the mock was created with a `spec' (or `autospec' of
course) then all the attributes from the original are shown, even if
they haven’t been accessed yet:

     >>> dir(Mock())
     ['assert_any_call',
      'assert_called',
      'assert_called_once',
      'assert_called_once_with',
      'assert_called_with',
      'assert_has_calls',
      'assert_not_called',
      'attach_mock',
      ...
     >>> from urllib import request
     >>> dir(Mock(spec=request))
     ['AbstractBasicAuthHandler',
      'AbstractDigestAuthHandler',
      'AbstractHTTPHandler',
      'BaseHandler',
      ...

Many of the not-very-useful (private to *note Mock: 373. rather than the
thing being mocked) underscore and double underscore prefixed attributes
have been filtered from the result of calling *note dir(): df9. on a
*note Mock: 373.  If you dislike this behaviour you can switch it off by
setting the module level switch *note FILTER_DIR: 3531.:

     >>> from unittest import mock
     >>> mock.FILTER_DIR = False
     >>> dir(mock.Mock())
     ['_NonCallableMock__get_return_value',
      '_NonCallableMock__get_side_effect',
      '_NonCallableMock__return_value_doc',
      '_NonCallableMock__set_return_value',
      '_NonCallableMock__set_side_effect',
      '__call__',
      '__class__',
      ...

Alternatively you can just use ‘vars(my_mock)’ (instance members) and
‘dir(type(my_mock))’ (type members) to bypass the filtering irrespective
of ‘mock.FILTER_DIR’.


File: python.info,  Node: mock_open,  Next: Autospeccing,  Prev: FILTER_DIR,  Up: Helpers

5.26.9.28 mock_open
...................

 -- Function: unittest.mock.mock_open (mock=None, read_data=None)

     A helper function to create a mock to replace the use of *note
     open(): 16f.  It works for *note open(): 16f. called directly or
     used as a context manager.

     The `mock' argument is the mock object to configure.  If ‘None’
     (the default) then a *note MagicMock: 874. will be created for you,
     with the API limited to methods or attributes available on standard
     file handles.

     `read_data' is a string for the ‘read()’, *note readline(): 1849,
     and *note readlines(): 18d6. methods of the file handle to return.
     Calls to those methods will take data from `read_data' until it is
     depleted.  The mock of these methods is pretty simplistic: every
     time the `mock' is called, the `read_data' is rewound to the start.
     If you need more control over the data that you are feeding to the
     tested code you will need to customize this mock for yourself.
     When that is insufficient, one of the in-memory filesystem packages
     on PyPI(1) can offer a realistic filesystem for testing.

     Changed in version 3.4: Added *note readline(): 1849. and *note
     readlines(): 18d6. support.  The mock of ‘read()’ changed to
     consume `read_data' rather than returning it on each call.

     Changed in version 3.5: `read_data' is now reset on each call to
     the `mock'.

     Changed in version 3.8: Added *note __iter__(): 609. to
     implementation so that iteration (such as in for loops) correctly
     consumes `read_data'.

Using *note open(): 16f. as a context manager is a great way to ensure
your file handles are closed properly and is becoming common:

     with open('/some/path', 'w') as f:
         f.write('something')

The issue is that even if you mock out the call to *note open(): 16f. it
is the `returned object' that is used as a context manager (and has
*note __enter__(): d5d. and *note __exit__(): d5e. called).

Mocking context managers with a *note MagicMock: 874. is common enough
and fiddly enough that a helper function is useful.

     >>> m = mock_open()
     >>> with patch('__main__.open', m):
     ...     with open('foo', 'w') as h:
     ...         h.write('some stuff')
     ...
     >>> m.mock_calls
     [call('foo', 'w'),
      call().__enter__(),
      call().write('some stuff'),
      call().__exit__(None, None, None)]
     >>> m.assert_called_once_with('foo', 'w')
     >>> handle = m()
     >>> handle.write.assert_called_once_with('some stuff')

And for reading files:

     >>> with patch('__main__.open', mock_open(read_data='bibble')) as m:
     ...     with open('foo') as h:
     ...         result = h.read()
     ...
     >>> m.assert_called_once_with('foo')
     >>> assert result == 'bibble'

   ---------- Footnotes ----------

   (1) https://pypi.org


File: python.info,  Node: Autospeccing,  Next: Sealing mocks,  Prev: mock_open,  Up: Helpers

5.26.9.29 Autospeccing
......................

Autospeccing is based on the existing ‘spec’ feature of mock.  It limits
the api of mocks to the api of an original object (the spec), but it is
recursive (implemented lazily) so that attributes of mocks only have the
same api as the attributes of the spec.  In addition mocked functions /
methods have the same call signature as the original so they raise a
*note TypeError: 1fe. if they are called incorrectly.

Before I explain how auto-speccing works, here’s why it is needed.

*note Mock: 373. is a very powerful and flexible object, but it suffers
from two flaws when used to mock out objects from a system under test.
One of these flaws is specific to the *note Mock: 373. api and the other
is a more general problem with using mock objects.

First the problem specific to *note Mock: 373.  *note Mock: 373. has two
assert methods that are extremely handy: *note assert_called_with():
113a. and *note assert_called_once_with(): 3529.

     >>> mock = Mock(name='Thing', return_value=None)
     >>> mock(1, 2, 3)
     >>> mock.assert_called_once_with(1, 2, 3)
     >>> mock(1, 2, 3)
     >>> mock.assert_called_once_with(1, 2, 3)
     Traceback (most recent call last):
      ...
     AssertionError: Expected 'mock' to be called once. Called 2 times.

Because mocks auto-create attributes on demand, and allow you to call
them with arbitrary arguments, if you misspell one of these assert
methods then your assertion is gone:

     >>> mock = Mock(name='Thing', return_value=None)
     >>> mock(1, 2, 3)
     >>> mock.assret_called_once_with(4, 5, 6)

Your tests can pass silently and incorrectly because of the typo.

The second issue is more general to mocking.  If you refactor some of
your code, rename members and so on, any tests for code that is still
using the `old api' but uses mocks instead of the real objects will
still pass.  This means your tests can all pass even though your code is
broken.

Note that this is another reason why you need integration tests as well
as unit tests.  Testing everything in isolation is all fine and dandy,
but if you don’t test how your units are “wired together” there is still
lots of room for bugs that tests might have caught.

‘mock’ already provides a feature to help with this, called speccing.
If you use a class or instance as the ‘spec’ for a mock then you can
only access attributes on the mock that exist on the real class:

     >>> from urllib import request
     >>> mock = Mock(spec=request.Request)
     >>> mock.assret_called_with
     Traceback (most recent call last):
      ...
     AttributeError: Mock object has no attribute 'assret_called_with'

The spec only applies to the mock itself, so we still have the same
issue with any methods on the mock:

     >>> mock.has_data()
     <mock.Mock object at 0x...>
     >>> mock.has_data.assret_called_with()

Auto-speccing solves this problem.  You can either pass ‘autospec=True’
to *note patch(): 877. / *note patch.object(): 10b4. or use the *note
create_autospec(): 1087. function to create a mock with a spec.  If you
use the ‘autospec=True’ argument to *note patch(): 877. then the object
that is being replaced will be used as the spec object.  Because the
speccing is done “lazily” (the spec is created as attributes on the mock
are accessed) you can use it with very complex or deeply nested objects
(like modules that import modules that import modules) without a big
performance hit.

Here’s an example of it in use:

     >>> from urllib import request
     >>> patcher = patch('__main__.request', autospec=True)
     >>> mock_request = patcher.start()
     >>> request is mock_request
     True
     >>> mock_request.Request
     <MagicMock name='request.Request' spec='Request' id='...'>

You can see that ‘request.Request’ has a spec.  ‘request.Request’ takes
two arguments in the constructor (one of which is `self').  Here’s what
happens if we try to call it incorrectly:

     >>> req = request.Request()
     Traceback (most recent call last):
      ...
     TypeError: <lambda>() takes at least 2 arguments (1 given)

The spec also applies to instantiated classes (i.e.  the return value of
specced mocks):

     >>> req = request.Request('foo')
     >>> req
     <NonCallableMagicMock name='request.Request()' spec='Request' id='...'>

‘Request’ objects are not callable, so the return value of instantiating
our mocked out ‘request.Request’ is a non-callable mock.  With the spec
in place any typos in our asserts will raise the correct error:

     >>> req.add_header('spam', 'eggs')
     <MagicMock name='request.Request().add_header()' id='...'>
     >>> req.add_header.assret_called_with
     Traceback (most recent call last):
      ...
     AttributeError: Mock object has no attribute 'assret_called_with'
     >>> req.add_header.assert_called_with('spam', 'eggs')

In many cases you will just be able to add ‘autospec=True’ to your
existing *note patch(): 877. calls and then be protected against bugs
due to typos and api changes.

As well as using `autospec' through *note patch(): 877. there is a *note
create_autospec(): 1087. for creating autospecced mocks directly:

     >>> from urllib import request
     >>> mock_request = create_autospec(request)
     >>> mock_request.Request('foo', 'bar')
     <NonCallableMagicMock name='mock.Request()' spec='Request' id='...'>

This isn’t without caveats and limitations however, which is why it is
not the default behaviour.  In order to know what attributes are
available on the spec object, autospec has to introspect (access
attributes) the spec.  As you traverse attributes on the mock a
corresponding traversal of the original object is happening under the
hood.  If any of your specced objects have properties or descriptors
that can trigger code execution then you may not be able to use
autospec.  On the other hand it is much better to design your objects so
that introspection is safe (1).

A more serious problem is that it is common for instance attributes to
be created in the *note __init__(): e23. method and not to exist on the
class at all.  `autospec' can’t know about any dynamically created
attributes and restricts the api to visible attributes.

     >>> class Something:
     ...   def __init__(self):
     ...     self.a = 33
     ...
     >>> with patch('__main__.Something', autospec=True):
     ...   thing = Something()
     ...   thing.a
     ...
     Traceback (most recent call last):
       ...
     AttributeError: Mock object has no attribute 'a'

There are a few different ways of resolving this problem.  The easiest,
but not necessarily the least annoying, way is to simply set the
required attributes on the mock after creation.  Just because `autospec'
doesn’t allow you to fetch attributes that don’t exist on the spec it
doesn’t prevent you setting them:

     >>> with patch('__main__.Something', autospec=True):
     ...   thing = Something()
     ...   thing.a = 33
     ...

There is a more aggressive version of both `spec' and `autospec' that
`does' prevent you setting non-existent attributes.  This is useful if
you want to ensure your code only `sets' valid attributes too, but
obviously it prevents this particular scenario:

     >>> with patch('__main__.Something', autospec=True, spec_set=True):
     ...   thing = Something()
     ...   thing.a = 33
     ...
     Traceback (most recent call last):
      ...
     AttributeError: Mock object has no attribute 'a'

Probably the best way of solving the problem is to add class attributes
as default values for instance members initialised in *note __init__():
e23.  Note that if you are only setting default attributes in *note
__init__(): e23. then providing them via class attributes (shared
between instances of course) is faster too.  e.g.

     class Something:
         a = 33

This brings up another issue.  It is relatively common to provide a
default value of ‘None’ for members that will later be an object of a
different type.  ‘None’ would be useless as a spec because it wouldn’t
let you access `any' attributes or methods on it.  As ‘None’ is `never'
going to be useful as a spec, and probably indicates a member that will
normally of some other type, autospec doesn’t use a spec for members
that are set to ‘None’.  These will just be ordinary mocks (well -
MagicMocks):

     >>> class Something:
     ...     member = None
     ...
     >>> mock = create_autospec(Something)
     >>> mock.member.foo.bar.baz()
     <MagicMock name='mock.member.foo.bar.baz()' id='...'>

If modifying your production classes to add defaults isn’t to your
liking then there are more options.  One of these is simply to use an
instance as the spec rather than the class.  The other is to create a
subclass of the production class and add the defaults to the subclass
without affecting the production class.  Both of these require you to
use an alternative object as the spec.  Thankfully *note patch(): 877.
supports this - you can simply pass the alternative object as the
`autospec' argument:

     >>> class Something:
     ...   def __init__(self):
     ...     self.a = 33
     ...
     >>> class SomethingForTest(Something):
     ...   a = 33
     ...
     >>> p = patch('__main__.Something', autospec=SomethingForTest)
     >>> mock = p.start()
     >>> mock.a
     <NonCallableMagicMock name='Something.a' spec='int' id='...'>

   ---------- Footnotes ----------

   (1) (4) This only applies to classes or already instantiated objects.
Calling a mocked class to create a mock instance `does not' create a
real instance.  It is only attribute lookups - along with calls to *note
dir(): df9. - that are done.


File: python.info,  Node: Sealing mocks,  Prev: Autospeccing,  Up: Helpers

5.26.9.30 Sealing mocks
.......................

 -- Function: unittest.mock.seal (mock)

     Seal will disable the automatic creation of mocks when accessing an
     attribute of the mock being sealed or any of its attributes that
     are already mocks recursively.

     If a mock instance with a name or a spec is assigned to an
     attribute it won’t be considered in the sealing chain.  This allows
     one to prevent seal from fixing part of the mock object.

          >>> mock = Mock()
          >>> mock.submock.attribute1 = 2
          >>> mock.not_submock = mock.Mock(name="sample_name")
          >>> seal(mock)
          >>> mock.new_attribute  # This will raise AttributeError.
          >>> mock.submock.attribute2  # This will raise AttributeError.
          >>> mock.not_submock.attribute2  # This won't raise.

     New in version 3.7.


File: python.info,  Node: unittest mock — getting started,  Next: 2to3 - Automated Python 2 to 3 code translation,  Prev: unittest mock — mock object library,  Up: Development Tools

5.26.10 ‘unittest.mock’ — getting started
-----------------------------------------

New in version 3.3.

* Menu:

* Using Mock::
* Patch Decorators::
* Further Examples::


File: python.info,  Node: Using Mock,  Next: Patch Decorators,  Up: unittest mock — getting started

5.26.10.1 Using Mock
....................

* Menu:

* Mock Patching Methods::
* Mock for Method Calls on an Object::
* Mocking Classes::
* Naming your mocks::
* Tracking all Calls::
* Setting Return Values and Attributes::
* Raising exceptions with mocks::
* Side effect functions and iterables::
* Mocking asynchronous iterators::
* Mocking asynchronous context manager::
* Creating a Mock from an Existing Object::


File: python.info,  Node: Mock Patching Methods,  Next: Mock for Method Calls on an Object,  Up: Using Mock

5.26.10.2 Mock Patching Methods
...............................

Common uses for *note Mock: 373. objects include:

   * Patching methods

   * Recording method calls on objects

You might want to replace a method on an object to check that it is
called with the correct arguments by another part of the system:

     >>> real = SomeClass()
     >>> real.method = MagicMock(name='method')
     >>> real.method(3, 4, 5, key='value')
     <MagicMock name='method()' id='...'>

Once our mock has been used (‘real.method’ in this example) it has
methods and attributes that allow you to make assertions about how it
has been used.

     Note: In most of these examples the *note Mock: 373. and *note
     MagicMock: 874. classes are interchangeable.  As the ‘MagicMock’ is
     the more capable class it makes a sensible one to use by default.

Once the mock has been called its *note called: 3533. attribute is set
to ‘True’.  More importantly we can use the *note assert_called_with():
113a. or *note assert_called_once_with(): 3529. method to check that it
was called with the correct arguments.

This example tests that calling ‘ProductionClass().method’ results in a
call to the ‘something’ method:

     >>> class ProductionClass:
     ...     def method(self):
     ...         self.something(1, 2, 3)
     ...     def something(self, a, b, c):
     ...         pass
     ...
     >>> real = ProductionClass()
     >>> real.something = MagicMock()
     >>> real.method()
     >>> real.something.assert_called_once_with(1, 2, 3)


File: python.info,  Node: Mock for Method Calls on an Object,  Next: Mocking Classes,  Prev: Mock Patching Methods,  Up: Using Mock

5.26.10.3 Mock for Method Calls on an Object
............................................

In the last example we patched a method directly on an object to check
that it was called correctly.  Another common use case is to pass an
object into a method (or some part of the system under test) and then
check that it is used in the correct way.

The simple ‘ProductionClass’ below has a ‘closer’ method.  If it is
called with an object then it calls ‘close’ on it.

     >>> class ProductionClass:
     ...     def closer(self, something):
     ...         something.close()
     ...

So to test it we need to pass in an object with a ‘close’ method and
check that it was called correctly.

     >>> real = ProductionClass()
     >>> mock = Mock()
     >>> real.closer(mock)
     >>> mock.close.assert_called_with()

We don’t have to do any work to provide the ‘close’ method on our mock.
Accessing close creates it.  So, if ‘close’ hasn’t already been called
then accessing it in the test will create it, but *note
assert_called_with(): 113a. will raise a failure exception.


File: python.info,  Node: Mocking Classes,  Next: Naming your mocks,  Prev: Mock for Method Calls on an Object,  Up: Using Mock

5.26.10.4 Mocking Classes
.........................

A common use case is to mock out classes instantiated by your code under
test.  When you patch a class, then that class is replaced with a mock.
Instances are created by `calling the class'.  This means you access the
“mock instance” by looking at the return value of the mocked class.

In the example below we have a function ‘some_function’ that
instantiates ‘Foo’ and calls a method on it.  The call to *note patch():
877. replaces the class ‘Foo’ with a mock.  The ‘Foo’ instance is the
result of calling the mock, so it is configured by modifying the mock
*note return_value: 3527.

     >>> def some_function():
     ...     instance = module.Foo()
     ...     return instance.method()
     ...
     >>> with patch('module.Foo') as mock:
     ...     instance = mock.return_value
     ...     instance.method.return_value = 'the result'
     ...     result = some_function()
     ...     assert result == 'the result'


File: python.info,  Node: Naming your mocks,  Next: Tracking all Calls,  Prev: Mocking Classes,  Up: Using Mock

5.26.10.5 Naming your mocks
...........................

It can be useful to give your mocks a name.  The name is shown in the
repr of the mock and can be helpful when the mock appears in test
failure messages.  The name is also propagated to attributes or methods
of the mock:

     >>> mock = MagicMock(name='foo')
     >>> mock
     <MagicMock name='foo' id='...'>
     >>> mock.method
     <MagicMock name='foo.method' id='...'>


File: python.info,  Node: Tracking all Calls,  Next: Setting Return Values and Attributes,  Prev: Naming your mocks,  Up: Using Mock

5.26.10.6 Tracking all Calls
............................

Often you want to track more than a single call to a method.  The *note
mock_calls: 352c. attribute records all calls to child attributes of the
mock - and also to their children.

     >>> mock = MagicMock()
     >>> mock.method()
     <MagicMock name='mock.method()' id='...'>
     >>> mock.attribute.method(10, x=53)
     <MagicMock name='mock.attribute.method()' id='...'>
     >>> mock.mock_calls
     [call.method(), call.attribute.method(10, x=53)]

If you make an assertion about ‘mock_calls’ and any unexpected methods
have been called, then the assertion will fail.  This is useful because
as well as asserting that the calls you expected have been made, you are
also checking that they were made in the right order and with no
additional calls:

You use the *note call: 10cc. object to construct lists for comparing
with ‘mock_calls’:

     >>> expected = [call.method(), call.attribute.method(10, x=53)]
     >>> mock.mock_calls == expected
     True

However, parameters to calls that return mocks are not recorded, which
means it is not possible to track nested calls where the parameters used
to create ancestors are important:

     >>> m = Mock()
     >>> m.factory(important=True).deliver()
     <Mock name='mock.factory().deliver()' id='...'>
     >>> m.mock_calls[-1] == call.factory(important=False).deliver()
     True


File: python.info,  Node: Setting Return Values and Attributes,  Next: Raising exceptions with mocks,  Prev: Tracking all Calls,  Up: Using Mock

5.26.10.7 Setting Return Values and Attributes
..............................................

Setting the return values on a mock object is trivially easy:

     >>> mock = Mock()
     >>> mock.return_value = 3
     >>> mock()
     3

Of course you can do the same for methods on the mock:

     >>> mock = Mock()
     >>> mock.method.return_value = 3
     >>> mock.method()
     3

The return value can also be set in the constructor:

     >>> mock = Mock(return_value=3)
     >>> mock()
     3

If you need an attribute setting on your mock, just do it:

     >>> mock = Mock()
     >>> mock.x = 3
     >>> mock.x
     3

Sometimes you want to mock up a more complex situation, like for example
‘mock.connection.cursor().execute("SELECT 1")’.  If we wanted this call
to return a list, then we have to configure the result of the nested
call.

We can use *note call: 10cc. to construct the set of calls in a “chained
call” like this for easy assertion afterwards:

     >>> mock = Mock()
     >>> cursor = mock.connection.cursor.return_value
     >>> cursor.execute.return_value = ['foo']
     >>> mock.connection.cursor().execute("SELECT 1")
     ['foo']
     >>> expected = call.connection.cursor().execute("SELECT 1").call_list()
     >>> mock.mock_calls
     [call.connection.cursor(), call.connection.cursor().execute('SELECT 1')]
     >>> mock.mock_calls == expected
     True

It is the call to ‘.call_list()’ that turns our call object into a list
of calls representing the chained calls.


File: python.info,  Node: Raising exceptions with mocks,  Next: Side effect functions and iterables,  Prev: Setting Return Values and Attributes,  Up: Using Mock

5.26.10.8 Raising exceptions with mocks
.......................................

A useful attribute is *note side_effect: 3525.  If you set this to an
exception class or instance then the exception will be raised when the
mock is called.

     >>> mock = Mock(side_effect=Exception('Boom!'))
     >>> mock()
     Traceback (most recent call last):
       ...
     Exception: Boom!


File: python.info,  Node: Side effect functions and iterables,  Next: Mocking asynchronous iterators,  Prev: Raising exceptions with mocks,  Up: Using Mock

5.26.10.9 Side effect functions and iterables
.............................................

‘side_effect’ can also be set to a function or an iterable.  The use
case for ‘side_effect’ as an iterable is where your mock is going to be
called several times, and you want each call to return a different
value.  When you set ‘side_effect’ to an iterable every call to the mock
returns the next value from the iterable:

     >>> mock = MagicMock(side_effect=[4, 5, 6])
     >>> mock()
     4
     >>> mock()
     5
     >>> mock()
     6

For more advanced use cases, like dynamically varying the return values
depending on what the mock is called with, ‘side_effect’ can be a
function.  The function will be called with the same arguments as the
mock.  Whatever the function returns is what the call returns:

     >>> vals = {(1, 2): 1, (2, 3): 2}
     >>> def side_effect(*args):
     ...     return vals[args]
     ...
     >>> mock = MagicMock(side_effect=side_effect)
     >>> mock(1, 2)
     1
     >>> mock(2, 3)
     2


File: python.info,  Node: Mocking asynchronous iterators,  Next: Mocking asynchronous context manager,  Prev: Side effect functions and iterables,  Up: Using Mock

5.26.10.10 Mocking asynchronous iterators
.........................................

Since Python 3.8, ‘AsyncMock’ and ‘MagicMock’ have support to mock *note
Asynchronous Iterators: 739. through ‘__aiter__’.  The *note
return_value: 3527. attribute of ‘__aiter__’ can be used to set the
return values to be used for iteration.

     >>> mock = MagicMock()  # AsyncMock also works here
     >>> mock.__aiter__.return_value = [1, 2, 3]
     >>> async def main():
     ...     return [i async for i in mock]
     ...
     >>> asyncio.run(main())
     [1, 2, 3]


File: python.info,  Node: Mocking asynchronous context manager,  Next: Creating a Mock from an Existing Object,  Prev: Mocking asynchronous iterators,  Up: Using Mock

5.26.10.11 Mocking asynchronous context manager
...............................................

Since Python 3.8, ‘AsyncMock’ and ‘MagicMock’ have support to mock *note
Asynchronous Context Managers: 15d2. through ‘__aenter__’ and
‘__aexit__’.  By default, ‘__aenter__’ and ‘__aexit__’ are ‘AsyncMock’
instances that return an async function.

     >>> class AsyncContextManager:
     ...     async def __aenter__(self):
     ...         return self
     ...     async def __aexit__(self, exc_type, exc, tb):
     ...         pass
     ...
     >>> mock_instance = MagicMock(AsyncContextManager())  # AsyncMock also works here
     >>> async def main():
     ...     async with mock_instance as result:
     ...         pass
     ...
     >>> asyncio.run(main())
     >>> mock_instance.__aenter__.assert_awaited_once()
     >>> mock_instance.__aexit__.assert_awaited_once()


File: python.info,  Node: Creating a Mock from an Existing Object,  Prev: Mocking asynchronous context manager,  Up: Using Mock

5.26.10.12 Creating a Mock from an Existing Object
..................................................

One problem with over use of mocking is that it couples your tests to
the implementation of your mocks rather than your real code.  Suppose
you have a class that implements ‘some_method’.  In a test for another
class, you provide a mock of this object that `also' provides
‘some_method’.  If later you refactor the first class, so that it no
longer has ‘some_method’ - then your tests will continue to pass even
though your code is now broken!

*note Mock: 373. allows you to provide an object as a specification for
the mock, using the `spec' keyword argument.  Accessing methods /
attributes on the mock that don’t exist on your specification object
will immediately raise an attribute error.  If you change the
implementation of your specification, then tests that use that class
will start failing immediately without you having to instantiate the
class in those tests.

     >>> mock = Mock(spec=SomeClass)
     >>> mock.old_method()
     Traceback (most recent call last):
        ...
     AttributeError: object has no attribute 'old_method'

Using a specification also enables a smarter matching of calls made to
the mock, regardless of whether some parameters were passed as
positional or named arguments:

     >>> def f(a, b, c): pass
     ...
     >>> mock = Mock(spec=f)
     >>> mock(1, 2, 3)
     <Mock name='mock()' id='140161580456576'>
     >>> mock.assert_called_with(a=1, b=2, c=3)

If you want this smarter matching to also work with method calls on the
mock, you can use *note auto-speccing: 3521.

If you want a stronger form of specification that prevents the setting
of arbitrary attributes as well as the getting of them then you can use
`spec_set' instead of `spec'.


File: python.info,  Node: Patch Decorators,  Next: Further Examples,  Prev: Using Mock,  Up: unittest mock — getting started

5.26.10.13 Patch Decorators
...........................

     Note: With *note patch(): 877. it matters that you patch objects in
     the namespace where they are looked up.  This is normally
     straightforward, but for a quick guide read *note where to patch:
     351f.

A common need in tests is to patch a class attribute or a module
attribute, for example patching a builtin or patching a class in a
module to test that it is instantiated.  Modules and classes are
effectively global, so patching on them has to be undone after the test
or the patch will persist into other tests and cause hard to diagnose
problems.

mock provides three convenient decorators for this: *note patch(): 877,
*note patch.object(): 10b4. and *note patch.dict(): 110a.  ‘patch’ takes
a single string, of the form ‘package.module.Class.attribute’ to specify
the attribute you are patching.  It also optionally takes a value that
you want the attribute (or class or whatever) to be replaced with.
‘patch.object’ takes an object and the name of the attribute you would
like patched, plus optionally the value to patch it with.

‘patch.object’:

     >>> original = SomeClass.attribute
     >>> @patch.object(SomeClass, 'attribute', sentinel.attribute)
     ... def test():
     ...     assert SomeClass.attribute == sentinel.attribute
     ...
     >>> test()
     >>> assert SomeClass.attribute == original

     >>> @patch('package.module.attribute', sentinel.attribute)
     ... def test():
     ...     from package.module import attribute
     ...     assert attribute is sentinel.attribute
     ...
     >>> test()

If you are patching a module (including *note builtins: 12.) then use
*note patch(): 877. instead of *note patch.object(): 10b4.:

     >>> mock = MagicMock(return_value=sentinel.file_handle)
     >>> with patch('builtins.open', mock):
     ...     handle = open('filename', 'r')
     ...
     >>> mock.assert_called_with('filename', 'r')
     >>> assert handle == sentinel.file_handle, "incorrect file handle returned"

The module name can be ‘dotted’, in the form ‘package.module’ if needed:

     >>> @patch('package.module.ClassName.attribute', sentinel.attribute)
     ... def test():
     ...     from package.module import ClassName
     ...     assert ClassName.attribute == sentinel.attribute
     ...
     >>> test()

A nice pattern is to actually decorate test methods themselves:

     >>> class MyTest(unittest.TestCase):
     ...     @patch.object(SomeClass, 'attribute', sentinel.attribute)
     ...     def test_something(self):
     ...         self.assertEqual(SomeClass.attribute, sentinel.attribute)
     ...
     >>> original = SomeClass.attribute
     >>> MyTest('test_something').test_something()
     >>> assert SomeClass.attribute == original

If you want to patch with a Mock, you can use *note patch(): 877. with
only one argument (or *note patch.object(): 10b4. with two arguments).
The mock will be created for you and passed into the test function /
method:

     >>> class MyTest(unittest.TestCase):
     ...     @patch.object(SomeClass, 'static_method')
     ...     def test_something(self, mock_method):
     ...         SomeClass.static_method()
     ...         mock_method.assert_called_with()
     ...
     >>> MyTest('test_something').test_something()

You can stack up multiple patch decorators using this pattern:

     >>> class MyTest(unittest.TestCase):
     ...     @patch('package.module.ClassName1')
     ...     @patch('package.module.ClassName2')
     ...     def test_something(self, MockClass2, MockClass1):
     ...         self.assertIs(package.module.ClassName1, MockClass1)
     ...         self.assertIs(package.module.ClassName2, MockClass2)
     ...
     >>> MyTest('test_something').test_something()

When you nest patch decorators the mocks are passed in to the decorated
function in the same order they applied (the normal `Python' order that
decorators are applied).  This means from the bottom up, so in the
example above the mock for ‘test_module.ClassName2’ is passed in first.

There is also *note patch.dict(): 110a. for setting values in a
dictionary just during a scope and restoring the dictionary to its
original state when the test ends:

     >>> foo = {'key': 'value'}
     >>> original = foo.copy()
     >>> with patch.dict(foo, {'newkey': 'newvalue'}, clear=True):
     ...     assert foo == {'newkey': 'newvalue'}
     ...
     >>> assert foo == original

‘patch’, ‘patch.object’ and ‘patch.dict’ can all be used as context
managers.

Where you use *note patch(): 877. to create a mock for you, you can get
a reference to the mock using the “as” form of the with statement:

     >>> class ProductionClass:
     ...     def method(self):
     ...         pass
     ...
     >>> with patch.object(ProductionClass, 'method') as mock_method:
     ...     mock_method.return_value = None
     ...     real = ProductionClass()
     ...     real.method(1, 2, 3)
     ...
     >>> mock_method.assert_called_with(1, 2, 3)

As an alternative ‘patch’, ‘patch.object’ and ‘patch.dict’ can be used
as class decorators.  When used in this way it is the same as applying
the decorator individually to every method whose name starts with
“test”.


File: python.info,  Node: Further Examples,  Prev: Patch Decorators,  Up: unittest mock — getting started

5.26.10.14 Further Examples
...........................

Here are some more examples for some slightly more advanced scenarios.

* Menu:

* Mocking chained calls::
* Partial mocking::
* Mocking a Generator Method::
* Applying the same patch to every test method::
* Mocking Unbound Methods::
* Checking multiple calls with mock::
* Coping with mutable arguments::
* Nesting Patches::
* Mocking a dictionary with MagicMock::
* Mock subclasses and their attributes::
* Mocking imports with patch.dict: Mocking imports with patch dict.
* Tracking order of calls and less verbose call assertions::
* More complex argument matching::


File: python.info,  Node: Mocking chained calls,  Next: Partial mocking,  Up: Further Examples

5.26.10.15 Mocking chained calls
................................

Mocking chained calls is actually straightforward with mock once you
understand the *note return_value: 3527. attribute.  When a mock is
called for the first time, or you fetch its ‘return_value’ before it has
been called, a new *note Mock: 373. is created.

This means that you can see how the object returned from a call to a
mocked object has been used by interrogating the ‘return_value’ mock:

     >>> mock = Mock()
     >>> mock().foo(a=2, b=3)
     <Mock name='mock().foo()' id='...'>
     >>> mock.return_value.foo.assert_called_with(a=2, b=3)

From here it is a simple step to configure and then make assertions
about chained calls.  Of course another alternative is writing your code
in a more testable way in the first place…

So, suppose we have some code that looks a little bit like this:

     >>> class Something:
     ...     def __init__(self):
     ...         self.backend = BackendProvider()
     ...     def method(self):
     ...         response = self.backend.get_endpoint('foobar').create_call('spam', 'eggs').start_call()
     ...         # more code

Assuming that ‘BackendProvider’ is already well tested, how do we test
‘method()’?  Specifically, we want to test that the code section ‘# more
code’ uses the response object in the correct way.

As this chain of calls is made from an instance attribute we can monkey
patch the ‘backend’ attribute on a ‘Something’ instance.  In this
particular case we are only interested in the return value from the
final call to ‘start_call’ so we don’t have much configuration to do.
Let’s assume the object it returns is ‘file-like’, so we’ll ensure that
our response object uses the builtin *note open(): 16f. as its ‘spec’.

To do this we create a mock instance as our mock backend and create a
mock response object for it.  To set the response as the return value
for that final ‘start_call’ we could do this:

     mock_backend.get_endpoint.return_value.create_call.return_value.start_call.return_value = mock_response

We can do that in a slightly nicer way using the *note configure_mock():
3528. method to directly set the return value for us:

     >>> something = Something()
     >>> mock_response = Mock(spec=open)
     >>> mock_backend = Mock()
     >>> config = {'get_endpoint.return_value.create_call.return_value.start_call.return_value': mock_response}
     >>> mock_backend.configure_mock(**config)

With these we monkey patch the “mock backend” in place and can make the
real call:

     >>> something.backend = mock_backend
     >>> something.method()

Using *note mock_calls: 352c. we can check the chained call with a
single assert.  A chained call is several calls in one line of code, so
there will be several entries in ‘mock_calls’.  We can use *note
call.call_list(): 355f. to create this list of calls for us:

     >>> chained = call.get_endpoint('foobar').create_call('spam', 'eggs').start_call()
     >>> call_list = chained.call_list()
     >>> assert mock_backend.mock_calls == call_list


File: python.info,  Node: Partial mocking,  Next: Mocking a Generator Method,  Prev: Mocking chained calls,  Up: Further Examples

5.26.10.16 Partial mocking
..........................

In some tests I wanted to mock out a call to *note
datetime.date.today(): 19e8. to return a known date, but I didn’t want
to prevent the code under test from creating new date objects.
Unfortunately *note datetime.date: 19e. is written in C, and so I
couldn’t just monkey-patch out the static ‘date.today()’ method.

I found a simple way of doing this that involved effectively wrapping
the date class with a mock, but passing through calls to the constructor
to the real class (and returning real instances).

The *note patch decorator: 877. is used here to mock out the ‘date’
class in the module under test.  The ‘side_effect’ attribute on the mock
date class is then set to a lambda function that returns a real date.
When the mock date class is called a real date will be constructed and
returned by ‘side_effect’.

     >>> from datetime import date
     >>> with patch('mymodule.date') as mock_date:
     ...     mock_date.today.return_value = date(2010, 10, 8)
     ...     mock_date.side_effect = lambda *args, **kw: date(*args, **kw)
     ...
     ...     assert mymodule.date.today() == date(2010, 10, 8)
     ...     assert mymodule.date(2009, 6, 8) == date(2009, 6, 8)

Note that we don’t patch *note datetime.date: 19e. globally, we patch
‘date’ in the module that `uses' it.  See *note where to patch: 351f.

When ‘date.today()’ is called a known date is returned, but calls to the
‘date(...)’ constructor still return normal dates.  Without this you can
find yourself having to calculate an expected result using exactly the
same algorithm as the code under test, which is a classic testing
anti-pattern.

Calls to the date constructor are recorded in the ‘mock_date’ attributes
(‘call_count’ and friends) which may also be useful for your tests.

An alternative way of dealing with mocking dates, or other builtin
classes, is discussed in this blog entry(1).

   ---------- Footnotes ----------

   (1) 
https://williambert.online/2011/07/how-to-unit-testing-in-django-with-mocking-and-patching/


File: python.info,  Node: Mocking a Generator Method,  Next: Applying the same patch to every test method,  Prev: Partial mocking,  Up: Further Examples

5.26.10.17 Mocking a Generator Method
.....................................

A Python generator is a function or method that uses the *note yield:
2c7. statement to return a series of values when iterated over (1).

A generator method / function is called to return the generator object.
It is the generator object that is then iterated over.  The protocol
method for iteration is *note __iter__(): 175d, so we can mock this
using a *note MagicMock: 874.

Here’s an example class with an “iter” method implemented as a
generator:

     >>> class Foo:
     ...     def iter(self):
     ...         for i in [1, 2, 3]:
     ...             yield i
     ...
     >>> foo = Foo()
     >>> list(foo.iter())
     [1, 2, 3]

How would we mock this class, and in particular its “iter” method?

To configure the values returned from the iteration (implicit in the
call to *note list: 1f8.), we need to configure the object returned by
the call to ‘foo.iter()’.

     >>> mock_foo = MagicMock()
     >>> mock_foo.iter.return_value = iter([1, 2, 3])
     >>> list(mock_foo.iter())
     [1, 2, 3]

   ---------- Footnotes ----------

   (1) (1) There are also generator expressions and more advanced uses
(http://www.dabeaz.com/coroutines/index.html) of generators, but we
aren’t concerned about them here.  A very good introduction to
generators and how powerful they are is: Generator Tricks for Systems
Programmers (http://www.dabeaz.com/generators/).


File: python.info,  Node: Applying the same patch to every test method,  Next: Mocking Unbound Methods,  Prev: Mocking a Generator Method,  Up: Further Examples

5.26.10.18 Applying the same patch to every test method
.......................................................

If you want several patches in place for multiple test methods the
obvious way is to apply the patch decorators to every method.  This can
feel like unnecessary repetition.  For Python 2.6 or more recent you can
use *note patch(): 877. (in all its various forms) as a class decorator.
This applies the patches to all test methods on the class.  A test
method is identified by methods whose names start with ‘test’:

     >>> @patch('mymodule.SomeClass')
     ... class MyTest(unittest.TestCase):
     ...
     ...     def test_one(self, MockSomeClass):
     ...         self.assertIs(mymodule.SomeClass, MockSomeClass)
     ...
     ...     def test_two(self, MockSomeClass):
     ...         self.assertIs(mymodule.SomeClass, MockSomeClass)
     ...
     ...     def not_a_test(self):
     ...         return 'something'
     ...
     >>> MyTest('test_one').test_one()
     >>> MyTest('test_two').test_two()
     >>> MyTest('test_two').not_a_test()
     'something'

An alternative way of managing patches is to use the *note patch
methods; start and stop: 3551.  These allow you to move the patching
into your ‘setUp’ and ‘tearDown’ methods.

     >>> class MyTest(unittest.TestCase):
     ...     def setUp(self):
     ...         self.patcher = patch('mymodule.foo')
     ...         self.mock_foo = self.patcher.start()
     ...
     ...     def test_foo(self):
     ...         self.assertIs(mymodule.foo, self.mock_foo)
     ...
     ...     def tearDown(self):
     ...         self.patcher.stop()
     ...
     >>> MyTest('test_foo').run()

If you use this technique you must ensure that the patching is “undone”
by calling ‘stop’.  This can be fiddlier than you might think, because
if an exception is raised in the setUp then tearDown is not called.
*note unittest.TestCase.addCleanup(): 3c5. makes this easier:

     >>> class MyTest(unittest.TestCase):
     ...     def setUp(self):
     ...         patcher = patch('mymodule.foo')
     ...         self.addCleanup(patcher.stop)
     ...         self.mock_foo = patcher.start()
     ...
     ...     def test_foo(self):
     ...         self.assertIs(mymodule.foo, self.mock_foo)
     ...
     >>> MyTest('test_foo').run()


File: python.info,  Node: Mocking Unbound Methods,  Next: Checking multiple calls with mock,  Prev: Applying the same patch to every test method,  Up: Further Examples

5.26.10.19 Mocking Unbound Methods
..................................

Whilst writing tests today I needed to patch an `unbound method'
(patching the method on the class rather than on the instance).  I
needed self to be passed in as the first argument because I want to make
asserts about which objects were calling this particular method.  The
issue is that you can’t patch with a mock for this, because if you
replace an unbound method with a mock it doesn’t become a bound method
when fetched from the instance, and so it doesn’t get self passed in.
The workaround is to patch the unbound method with a real function
instead.  The *note patch(): 877. decorator makes it so simple to patch
out methods with a mock that having to create a real function becomes a
nuisance.

If you pass ‘autospec=True’ to patch then it does the patching with a
`real' function object.  This function object has the same signature as
the one it is replacing, but delegates to a mock under the hood.  You
still get your mock auto-created in exactly the same way as before.
What it means though, is that if you use it to patch out an unbound
method on a class the mocked function will be turned into a bound method
if it is fetched from an instance.  It will have ‘self’ passed in as the
first argument, which is exactly what I wanted:

     >>> class Foo:
     ...   def foo(self):
     ...     pass
     ...
     >>> with patch.object(Foo, 'foo', autospec=True) as mock_foo:
     ...   mock_foo.return_value = 'foo'
     ...   foo = Foo()
     ...   foo.foo()
     ...
     'foo'
     >>> mock_foo.assert_called_once_with(foo)

If we don’t use ‘autospec=True’ then the unbound method is patched out
with a Mock instance instead, and isn’t called with ‘self’.


File: python.info,  Node: Checking multiple calls with mock,  Next: Coping with mutable arguments,  Prev: Mocking Unbound Methods,  Up: Further Examples

5.26.10.20 Checking multiple calls with mock
............................................

mock has a nice API for making assertions about how your mock objects
are used.

     >>> mock = Mock()
     >>> mock.foo_bar.return_value = None
     >>> mock.foo_bar('baz', spam='eggs')
     >>> mock.foo_bar.assert_called_with('baz', spam='eggs')

If your mock is only being called once you can use the
‘assert_called_once_with()’ method that also asserts that the
‘call_count’ is one.

     >>> mock.foo_bar.assert_called_once_with('baz', spam='eggs')
     >>> mock.foo_bar()
     >>> mock.foo_bar.assert_called_once_with('baz', spam='eggs')
     Traceback (most recent call last):
         ...
     AssertionError: Expected to be called once. Called 2 times.

Both ‘assert_called_with’ and ‘assert_called_once_with’ make assertions
about the `most recent' call.  If your mock is going to be called
several times, and you want to make assertions about `all' those calls
you can use *note call_args_list: 3535.:

     >>> mock = Mock(return_value=None)
     >>> mock(1, 2, 3)
     >>> mock(4, 5, 6)
     >>> mock()
     >>> mock.call_args_list
     [call(1, 2, 3), call(4, 5, 6), call()]

The *note call: 10cc. helper makes it easy to make assertions about
these calls.  You can build up a list of expected calls and compare it
to ‘call_args_list’.  This looks remarkably similar to the repr of the
‘call_args_list’:

     >>> expected = [call(1, 2, 3), call(4, 5, 6), call()]
     >>> mock.call_args_list == expected
     True


File: python.info,  Node: Coping with mutable arguments,  Next: Nesting Patches,  Prev: Checking multiple calls with mock,  Up: Further Examples

5.26.10.21 Coping with mutable arguments
........................................

Another situation is rare, but can bite you, is when your mock is called
with mutable arguments.  ‘call_args’ and ‘call_args_list’ store
`references' to the arguments.  If the arguments are mutated by the code
under test then you can no longer make assertions about what the values
were when the mock was called.

Here’s some example code that shows the problem.  Imagine the following
functions defined in ‘mymodule’:

     def frob(val):
         pass

     def grob(val):
         "First frob and then clear val"
         frob(val)
         val.clear()

When we try to test that ‘grob’ calls ‘frob’ with the correct argument
look what happens:

     >>> with patch('mymodule.frob') as mock_frob:
     ...     val = {6}
     ...     mymodule.grob(val)
     ...
     >>> val
     set()
     >>> mock_frob.assert_called_with({6})
     Traceback (most recent call last):
         ...
     AssertionError: Expected: (({6},), {})
     Called with: ((set(),), {})

One possibility would be for mock to copy the arguments you pass in.
This could then cause problems if you do assertions that rely on object
identity for equality.

Here’s one solution that uses the ‘side_effect’ functionality.  If you
provide a ‘side_effect’ function for a mock then ‘side_effect’ will be
called with the same args as the mock.  This gives us an opportunity to
copy the arguments and store them for later assertions.  In this example
I’m using `another' mock to store the arguments so that I can use the
mock methods for doing the assertion.  Again a helper function sets this
up for me.

     >>> from copy import deepcopy
     >>> from unittest.mock import Mock, patch, DEFAULT
     >>> def copy_call_args(mock):
     ...     new_mock = Mock()
     ...     def side_effect(*args, **kwargs):
     ...         args = deepcopy(args)
     ...         kwargs = deepcopy(kwargs)
     ...         new_mock(*args, **kwargs)
     ...         return DEFAULT
     ...     mock.side_effect = side_effect
     ...     return new_mock
     ...
     >>> with patch('mymodule.frob') as mock_frob:
     ...     new_mock = copy_call_args(mock_frob)
     ...     val = {6}
     ...     mymodule.grob(val)
     ...
     >>> new_mock.assert_called_with({6})
     >>> new_mock.call_args
     call({6})

‘copy_call_args’ is called with the mock that will be called.  It
returns a new mock that we do the assertion on.  The ‘side_effect’
function makes a copy of the args and calls our ‘new_mock’ with the
copy.

     Note: If your mock is only going to be used once there is an easier
     way of checking arguments at the point they are called.  You can
     simply do the checking inside a ‘side_effect’ function.

          >>> def side_effect(arg):
          ...     assert arg == {6}
          ...
          >>> mock = Mock(side_effect=side_effect)
          >>> mock({6})
          >>> mock(set())
          Traceback (most recent call last):
              ...
          AssertionError

An alternative approach is to create a subclass of *note Mock: 373. or
*note MagicMock: 874. that copies (using *note copy.deepcopy(): 4d3.)
the arguments.  Here’s an example implementation:

     >>> from copy import deepcopy
     >>> class CopyingMock(MagicMock):
     ...     def __call__(self, /, *args, **kwargs):
     ...         args = deepcopy(args)
     ...         kwargs = deepcopy(kwargs)
     ...         return super().__call__(*args, **kwargs)
     ...
     >>> c = CopyingMock(return_value=None)
     >>> arg = set()
     >>> c(arg)
     >>> arg.add(1)
     >>> c.assert_called_with(set())
     >>> c.assert_called_with(arg)
     Traceback (most recent call last):
         ...
     AssertionError: Expected call: mock({1})
     Actual call: mock(set())
     >>> c.foo
     <CopyingMock name='mock.foo' id='...'>

When you subclass ‘Mock’ or ‘MagicMock’ all dynamically created
attributes, and the ‘return_value’ will use your subclass automatically.
That means all children of a ‘CopyingMock’ will also have the type
‘CopyingMock’.


File: python.info,  Node: Nesting Patches,  Next: Mocking a dictionary with MagicMock,  Prev: Coping with mutable arguments,  Up: Further Examples

5.26.10.22 Nesting Patches
..........................

Using patch as a context manager is nice, but if you do multiple patches
you can end up with nested with statements indenting further and further
to the right:

     >>> class MyTest(unittest.TestCase):
     ...
     ...     def test_foo(self):
     ...         with patch('mymodule.Foo') as mock_foo:
     ...             with patch('mymodule.Bar') as mock_bar:
     ...                 with patch('mymodule.Spam') as mock_spam:
     ...                     assert mymodule.Foo is mock_foo
     ...                     assert mymodule.Bar is mock_bar
     ...                     assert mymodule.Spam is mock_spam
     ...
     >>> original = mymodule.Foo
     >>> MyTest('test_foo').test_foo()
     >>> assert mymodule.Foo is original

With unittest ‘cleanup’ functions and the *note patch methods; start and
stop: 3551. we can achieve the same effect without the nested
indentation.  A simple helper method, ‘create_patch’, puts the patch in
place and returns the created mock for us:

     >>> class MyTest(unittest.TestCase):
     ...
     ...     def create_patch(self, name):
     ...         patcher = patch(name)
     ...         thing = patcher.start()
     ...         self.addCleanup(patcher.stop)
     ...         return thing
     ...
     ...     def test_foo(self):
     ...         mock_foo = self.create_patch('mymodule.Foo')
     ...         mock_bar = self.create_patch('mymodule.Bar')
     ...         mock_spam = self.create_patch('mymodule.Spam')
     ...
     ...         assert mymodule.Foo is mock_foo
     ...         assert mymodule.Bar is mock_bar
     ...         assert mymodule.Spam is mock_spam
     ...
     >>> original = mymodule.Foo
     >>> MyTest('test_foo').run()
     >>> assert mymodule.Foo is original


File: python.info,  Node: Mocking a dictionary with MagicMock,  Next: Mock subclasses and their attributes,  Prev: Nesting Patches,  Up: Further Examples

5.26.10.23 Mocking a dictionary with MagicMock
..............................................

You may want to mock a dictionary, or other container object, recording
all access to it whilst having it still behave like a dictionary.

We can do this with *note MagicMock: 874, which will behave like a
dictionary, and using *note side_effect: 3525. to delegate dictionary
access to a real underlying dictionary that is under our control.

When the *note __getitem__(): 3a2. and *note __setitem__(): d2a. methods
of our ‘MagicMock’ are called (normal dictionary access) then
‘side_effect’ is called with the key (and in the case of ‘__setitem__’
the value too).  We can also control what is returned.

After the ‘MagicMock’ has been used we can use attributes like *note
call_args_list: 3535. to assert about how the dictionary was used:

     >>> my_dict = {'a': 1, 'b': 2, 'c': 3}
     >>> def getitem(name):
     ...      return my_dict[name]
     ...
     >>> def setitem(name, val):
     ...     my_dict[name] = val
     ...
     >>> mock = MagicMock()
     >>> mock.__getitem__.side_effect = getitem
     >>> mock.__setitem__.side_effect = setitem

     Note: An alternative to using ‘MagicMock’ is to use ‘Mock’ and
     `only' provide the magic methods you specifically want:

          >>> mock = Mock()
          >>> mock.__getitem__ = Mock(side_effect=getitem)
          >>> mock.__setitem__ = Mock(side_effect=setitem)

     A `third' option is to use ‘MagicMock’ but passing in ‘dict’ as the
     `spec' (or `spec_set') argument so that the ‘MagicMock’ created
     only has dictionary magic methods available:

          >>> mock = MagicMock(spec_set=dict)
          >>> mock.__getitem__.side_effect = getitem
          >>> mock.__setitem__.side_effect = setitem

With these side effect functions in place, the ‘mock’ will behave like a
normal dictionary but recording the access.  It even raises a *note
KeyError: 3e9. if you try to access a key that doesn’t exist.

     >>> mock['a']
     1
     >>> mock['c']
     3
     >>> mock['d']
     Traceback (most recent call last):
         ...
     KeyError: 'd'
     >>> mock['b'] = 'fish'
     >>> mock['d'] = 'eggs'
     >>> mock['b']
     'fish'
     >>> mock['d']
     'eggs'

After it has been used you can make assertions about the access using
the normal mock methods and attributes:

     >>> mock.__getitem__.call_args_list
     [call('a'), call('c'), call('d'), call('b'), call('d')]
     >>> mock.__setitem__.call_args_list
     [call('b', 'fish'), call('d', 'eggs')]
     >>> my_dict
     {'a': 1, 'b': 'fish', 'c': 3, 'd': 'eggs'}


File: python.info,  Node: Mock subclasses and their attributes,  Next: Mocking imports with patch dict,  Prev: Mocking a dictionary with MagicMock,  Up: Further Examples

5.26.10.24 Mock subclasses and their attributes
...............................................

There are various reasons why you might want to subclass *note Mock:
373.  One reason might be to add helper methods.  Here’s a silly
example:

     >>> class MyMock(MagicMock):
     ...     def has_been_called(self):
     ...         return self.called
     ...
     >>> mymock = MyMock(return_value=None)
     >>> mymock
     <MyMock id='...'>
     >>> mymock.has_been_called()
     False
     >>> mymock()
     >>> mymock.has_been_called()
     True

The standard behaviour for ‘Mock’ instances is that attributes and the
return value mocks are of the same type as the mock they are accessed
on.  This ensures that ‘Mock’ attributes are ‘Mocks’ and ‘MagicMock’
attributes are ‘MagicMocks’ (1).  So if you’re subclassing to add helper
methods then they’ll also be available on the attributes and return
value mock of instances of your subclass.

     >>> mymock.foo
     <MyMock name='mock.foo' id='...'>
     >>> mymock.foo.has_been_called()
     False
     >>> mymock.foo()
     <MyMock name='mock.foo()' id='...'>
     >>> mymock.foo.has_been_called()
     True

Sometimes this is inconvenient.  For example, one user(2) is subclassing
mock to created a Twisted adaptor(3).  Having this applied to attributes
too actually causes errors.

‘Mock’ (in all its flavours) uses a method called ‘_get_child_mock’ to
create these “sub-mocks” for attributes and return values.  You can
prevent your subclass being used for attributes by overriding this
method.  The signature is that it takes arbitrary keyword arguments
(‘**kwargs’) which are then passed onto the mock constructor:

     >>> class Subclass(MagicMock):
     ...     def _get_child_mock(self, /, **kwargs):
     ...         return MagicMock(**kwargs)
     ...
     >>> mymock = Subclass()
     >>> mymock.foo
     <MagicMock name='mock.foo' id='...'>
     >>> assert isinstance(mymock, Subclass)
     >>> assert not isinstance(mymock.foo, Subclass)
     >>> assert not isinstance(mymock(), Subclass)

   ---------- Footnotes ----------

   (1) (2) An exception to this rule are the non-callable mocks.
Attributes use the callable variant because otherwise non-callable mocks
couldn’t have callable methods.

   (2) https://code.google.com/archive/p/mock/issues/105

   (3) 
https://twistedmatrix.com/documents/11.0.0/api/twisted.python.components.html


File: python.info,  Node: Mocking imports with patch dict,  Next: Tracking order of calls and less verbose call assertions,  Prev: Mock subclasses and their attributes,  Up: Further Examples

5.26.10.25 Mocking imports with patch.dict
..........................................

One situation where mocking can be hard is where you have a local import
inside a function.  These are harder to mock because they aren’t using
an object from the module namespace that we can patch out.

Generally local imports are to be avoided.  They are sometimes done to
prevent circular dependencies, for which there is `usually' a much
better way to solve the problem (refactor the code) or to prevent “up
front costs” by delaying the import.  This can also be solved in better
ways than an unconditional local import (store the module as a class or
module attribute and only do the import on first use).

That aside there is a way to use ‘mock’ to affect the results of an
import.  Importing fetches an `object' from the *note sys.modules: 1051.
dictionary.  Note that it fetches an `object', which need not be a
module.  Importing a module for the first time results in a module
object being put in ‘sys.modules’, so usually when you import something
you get a module back.  This need not be the case however.

This means you can use *note patch.dict(): 110a. to `temporarily' put a
mock in place in *note sys.modules: 1051.  Any imports whilst this patch
is active will fetch the mock.  When the patch is complete (the
decorated function exits, the with statement body is complete or
‘patcher.stop()’ is called) then whatever was there previously will be
restored safely.

Here’s an example that mocks out the ‘fooble’ module.

     >>> import sys
     >>> mock = Mock()
     >>> with patch.dict('sys.modules', {'fooble': mock}):
     ...    import fooble
     ...    fooble.blob()
     ...
     <Mock name='mock.blob()' id='...'>
     >>> assert 'fooble' not in sys.modules
     >>> mock.blob.assert_called_once_with()

As you can see the ‘import fooble’ succeeds, but on exit there is no
‘fooble’ left in *note sys.modules: 1051.

This also works for the ‘from module import name’ form:

     >>> mock = Mock()
     >>> with patch.dict('sys.modules', {'fooble': mock}):
     ...    from fooble import blob
     ...    blob.blip()
     ...
     <Mock name='mock.blob.blip()' id='...'>
     >>> mock.blob.blip.assert_called_once_with()

With slightly more work you can also mock package imports:

     >>> mock = Mock()
     >>> modules = {'package': mock, 'package.module': mock.module}
     >>> with patch.dict('sys.modules', modules):
     ...    from package.module import fooble
     ...    fooble()
     ...
     <Mock name='mock.module.fooble()' id='...'>
     >>> mock.module.fooble.assert_called_once_with()


File: python.info,  Node: Tracking order of calls and less verbose call assertions,  Next: More complex argument matching,  Prev: Mocking imports with patch dict,  Up: Further Examples

5.26.10.26 Tracking order of calls and less verbose call assertions
...................................................................

The *note Mock: 373. class allows you to track the `order' of method
calls on your mock objects through the *note method_calls: 352f.
attribute.  This doesn’t allow you to track the order of calls between
separate mock objects, however we can use *note mock_calls: 352c. to
achieve the same effect.

Because mocks track calls to child mocks in ‘mock_calls’, and accessing
an arbitrary attribute of a mock creates a child mock, we can create our
separate mocks from a parent one.  Calls to those child mock will then
all be recorded, in order, in the ‘mock_calls’ of the parent:

     >>> manager = Mock()
     >>> mock_foo = manager.foo
     >>> mock_bar = manager.bar

     >>> mock_foo.something()
     <Mock name='mock.foo.something()' id='...'>
     >>> mock_bar.other.thing()
     <Mock name='mock.bar.other.thing()' id='...'>

     >>> manager.mock_calls
     [call.foo.something(), call.bar.other.thing()]

We can then assert about the calls, including the order, by comparing
with the ‘mock_calls’ attribute on the manager mock:

     >>> expected_calls = [call.foo.something(), call.bar.other.thing()]
     >>> manager.mock_calls == expected_calls
     True

If ‘patch’ is creating, and putting in place, your mocks then you can
attach them to a manager mock using the *note attach_mock(): 352e.
method.  After attaching calls will be recorded in ‘mock_calls’ of the
manager.

     >>> manager = MagicMock()
     >>> with patch('mymodule.Class1') as MockClass1:
     ...     with patch('mymodule.Class2') as MockClass2:
     ...         manager.attach_mock(MockClass1, 'MockClass1')
     ...         manager.attach_mock(MockClass2, 'MockClass2')
     ...         MockClass1().foo()
     ...         MockClass2().bar()
     <MagicMock name='mock.MockClass1().foo()' id='...'>
     <MagicMock name='mock.MockClass2().bar()' id='...'>
     >>> manager.mock_calls
     [call.MockClass1(),
     call.MockClass1().foo(),
     call.MockClass2(),
     call.MockClass2().bar()]

If many calls have been made, but you’re only interested in a particular
sequence of them then an alternative is to use the *note
assert_has_calls(): 352b. method.  This takes a list of calls
(constructed with the *note call: 10cc. object).  If that sequence of
calls are in *note mock_calls: 352c. then the assert succeeds.

     >>> m = MagicMock()
     >>> m().foo().bar().baz()
     <MagicMock name='mock().foo().bar().baz()' id='...'>
     >>> m.one().two().three()
     <MagicMock name='mock.one().two().three()' id='...'>
     >>> calls = call.one().two().three().call_list()
     >>> m.assert_has_calls(calls)

Even though the chained call ‘m.one().two().three()’ aren’t the only
calls that have been made to the mock, the assert still succeeds.

Sometimes a mock may have several calls made to it, and you are only
interested in asserting about `some' of those calls.  You may not even
care about the order.  In this case you can pass ‘any_order=True’ to
‘assert_has_calls’:

     >>> m = MagicMock()
     >>> m(1), m.two(2, 3), m.seven(7), m.fifty('50')
     (...)
     >>> calls = [call.fifty('50'), call(1), call.seven(7)]
     >>> m.assert_has_calls(calls, any_order=True)


File: python.info,  Node: More complex argument matching,  Prev: Tracking order of calls and less verbose call assertions,  Up: Further Examples

5.26.10.27 More complex argument matching
.........................................

Using the same basic concept as *note ANY: 10d1. we can implement
matchers to do more complex assertions on objects used as arguments to
mocks.

Suppose we expect some object to be passed to a mock that by default
compares equal based on object identity (which is the Python default for
user defined classes).  To use *note assert_called_with(): 113a. we
would need to pass in the exact same object.  If we are only interested
in some of the attributes of this object then we can create a matcher
that will check these attributes for us.

You can see in this example how a ‘standard’ call to
‘assert_called_with’ isn’t sufficient:

     >>> class Foo:
     ...     def __init__(self, a, b):
     ...         self.a, self.b = a, b
     ...
     >>> mock = Mock(return_value=None)
     >>> mock(Foo(1, 2))
     >>> mock.assert_called_with(Foo(1, 2))
     Traceback (most recent call last):
         ...
     AssertionError: Expected: call(<__main__.Foo object at 0x...>)
     Actual call: call(<__main__.Foo object at 0x...>)

A comparison function for our ‘Foo’ class might look something like
this:

     >>> def compare(self, other):
     ...     if not type(self) == type(other):
     ...         return False
     ...     if self.a != other.a:
     ...         return False
     ...     if self.b != other.b:
     ...         return False
     ...     return True
     ...

And a matcher object that can use comparison functions like this for its
equality operation would look something like this:

     >>> class Matcher:
     ...     def __init__(self, compare, some_obj):
     ...         self.compare = compare
     ...         self.some_obj = some_obj
     ...     def __eq__(self, other):
     ...         return self.compare(self.some_obj, other)
     ...

Putting all this together:

     >>> match_foo = Matcher(compare, Foo(1, 2))
     >>> mock.assert_called_with(match_foo)

The ‘Matcher’ is instantiated with our compare function and the ‘Foo’
object we want to compare against.  In ‘assert_called_with’ the
‘Matcher’ equality method will be called, which compares the object the
mock was called with against the one we created our matcher with.  If
they match then ‘assert_called_with’ passes, and if they don’t an *note
AssertionError: 240. is raised:

     >>> match_wrong = Matcher(compare, Foo(3, 4))
     >>> mock.assert_called_with(match_wrong)
     Traceback (most recent call last):
         ...
     AssertionError: Expected: ((<Matcher object at 0x...>,), {})
     Called with: ((<Foo object at 0x...>,), {})

With a bit of tweaking you could have the comparison function raise the
*note AssertionError: 240. directly and provide a more useful failure
message.

As of version 1.5, the Python testing library PyHamcrest(1) provides
similar functionality, that may be useful here, in the form of its
equality matcher (hamcrest.library.integration.match_equality(2)).

   ---------- Footnotes ----------

   (1) https://pyhamcrest.readthedocs.io/

   (2) 
https://pyhamcrest.readthedocs.io/en/release-1.8/integration/#module-hamcrest.library.integration.match_equality


File: python.info,  Node: 2to3 - Automated Python 2 to 3 code translation,  Next: test — Regression tests package for Python,  Prev: unittest mock — getting started,  Up: Development Tools

5.26.11 2to3 - Automated Python 2 to 3 code translation
-------------------------------------------------------

2to3 is a Python program that reads Python 2.x source code and applies a
series of `fixers' to transform it into valid Python 3.x code.  The
standard library contains a rich set of fixers that will handle almost
all code.  2to3 supporting library *note lib2to3: a7. is, however, a
flexible and generic library, so it is possible to write your own fixers
for 2to3.

* Menu:

* Using 2to3::
* Fixers::
* lib2to3 - 2to3’s library::


File: python.info,  Node: Using 2to3,  Next: Fixers,  Up: 2to3 - Automated Python 2 to 3 code translation

5.26.11.1 Using 2to3
....................

2to3 will usually be installed with the Python interpreter as a script.
It is also located in the ‘Tools/scripts’ directory of the Python root.

2to3’s basic arguments are a list of files or directories to transform.
The directories are recursively traversed for Python sources.

Here is a sample Python 2.x source file, ‘example.py’:

     def greet(name):
         print "Hello, {0}!".format(name)
     print "What's your name?"
     name = raw_input()
     greet(name)

It can be converted to Python 3.x code via 2to3 on the command line:

     $ 2to3 example.py

A diff against the original source file is printed.  2to3 can also write
the needed modifications right back to the source file.  (A backup of
the original file is made unless ‘-n’ is also given.)  Writing the
changes back is enabled with the ‘-w’ flag:

     $ 2to3 -w example.py

After transformation, ‘example.py’ looks like this:

     def greet(name):
         print("Hello, {0}!".format(name))
     print("What's your name?")
     name = input()
     greet(name)

Comments and exact indentation are preserved throughout the translation
process.

By default, 2to3 runs a set of *note predefined fixers: 3589.  The ‘-l’
flag lists all available fixers.  An explicit set of fixers to run can
be given with ‘-f’.  Likewise the ‘-x’ explicitly disables a fixer.  The
following example runs only the ‘imports’ and ‘has_key’ fixers:

     $ 2to3 -f imports -f has_key example.py

This command runs every fixer except the ‘apply’ fixer:

     $ 2to3 -x apply example.py

Some fixers are `explicit', meaning they aren’t run by default and must
be listed on the command line to be run.  Here, in addition to the
default fixers, the ‘idioms’ fixer is run:

     $ 2to3 -f all -f idioms example.py

Notice how passing ‘all’ enables all default fixers.

Sometimes 2to3 will find a place in your source code that needs to be
changed, but 2to3 cannot fix automatically.  In this case, 2to3 will
print a warning beneath the diff for a file.  You should address the
warning in order to have compliant 3.x code.

2to3 can also refactor doctests.  To enable this mode, use the ‘-d’
flag.  Note that `only' doctests will be refactored.  This also doesn’t
require the module to be valid Python.  For example, doctest like
examples in a reST document could also be refactored with this option.

The ‘-v’ option enables output of more information on the translation
process.

Since some print statements can be parsed as function calls or
statements, 2to3 cannot always read files containing the print function.
When 2to3 detects the presence of the ‘from __future__ import
print_function’ compiler directive, it modifies its internal grammar to
interpret *note print(): 971. as a function.  This change can also be
enabled manually with the ‘-p’ flag.  Use ‘-p’ to run fixers on code
that already has had its print statements converted.  Also ‘-e’ can be
used to make *note exec(): d0c. a function.

The ‘-o’ or ‘--output-dir’ option allows specification of an alternate
directory for processed output files to be written to.  The ‘-n’ flag is
required when using this as backup files do not make sense when not
overwriting the input files.

New in version 3.2.3: The ‘-o’ option was added.

The ‘-W’ or ‘--write-unchanged-files’ flag tells 2to3 to always write
output files even if no changes were required to the file.  This is most
useful with ‘-o’ so that an entire Python source tree is copied with
translation from one directory to another.  This option implies the ‘-w’
flag as it would not make sense otherwise.

New in version 3.2.3: The ‘-W’ flag was added.

The ‘--add-suffix’ option specifies a string to append to all output
filenames.  The ‘-n’ flag is required when specifying this as backups
are not necessary when writing to different filenames.  Example:

     $ 2to3 -n -W --add-suffix=3 example.py

Will cause a converted file named ‘example.py3’ to be written.

New in version 3.2.3: The ‘--add-suffix’ option was added.

To translate an entire project from one directory tree to another use:

     $ 2to3 --output-dir=python3-version/mycode -W -n python2-version/mycode


File: python.info,  Node: Fixers,  Next: lib2to3 - 2to3’s library,  Prev: Using 2to3,  Up: 2to3 - Automated Python 2 to 3 code translation

5.26.11.2 Fixers
................

Each step of transforming code is encapsulated in a fixer.  The command
‘2to3 -l’ lists them.  As *note documented above: 3587, each can be
turned on and off individually.  They are described here in more detail.

 -- 2to3fixer: apply

     Removes usage of ‘apply()’.  For example ‘apply(function, *args,
     **kwargs)’ is converted to ‘function(*args, **kwargs)’.

 -- 2to3fixer: asserts

     Replaces deprecated *note unittest: 124. method names with the
     correct ones.

     From                                 To
                                          
     ------------------------------------------------------------------------------------
                                          
     ‘failUnlessEqual(a, b)’              *note assertEqual(a, b): c85.
                                          
                                          
     ‘assertEquals(a, b)’                 *note assertEqual(a, b): c85.
                                          
                                          
     ‘failIfEqual(a, b)’                  *note assertNotEqual(a, b): c86.
                                          
                                          
     ‘assertNotEquals(a, b)’              *note assertNotEqual(a, b): c86.
                                          
                                          
     ‘failUnless(a)’                      *note assertTrue(a): c84.
                                          
                                          
     ‘assert_(a)’                         *note assertTrue(a): c84.
                                          
                                          
     ‘failIf(a)’                          *note assertFalse(a): d8f.
                                          
                                          
     ‘failUnlessRaises(exc, cal)’         *note assertRaises(exc, cal): b92.
                                          
                                          
     ‘failUnlessAlmostEqual(a, b)’        *note assertAlmostEqual(a, b): c87.
                                          
                                          
     ‘assertAlmostEquals(a, b)’           *note assertAlmostEqual(a, b): c87.
                                          
                                          
     ‘failIfAlmostEqual(a, b)’            *note assertNotAlmostEqual(a, b): c88.
                                          
                                          
     ‘assertNotAlmostEquals(a, b)’        *note assertNotAlmostEqual(a, b): c88.
                                          

 -- 2to3fixer: basestring

     Converts ‘basestring’ to *note str: 205.

 -- 2to3fixer: buffer

     Converts ‘buffer’ to *note memoryview: 386.  This fixer is optional
     because the *note memoryview: 386. API is similar but not exactly
     the same as that of ‘buffer’.

 -- 2to3fixer: dict

     Fixes dictionary iteration methods.  ‘dict.iteritems()’ is
     converted to *note dict.items(): cf5, ‘dict.iterkeys()’ to *note
     dict.keys(): cf4, and ‘dict.itervalues()’ to *note dict.values():
     cf6.  Similarly, ‘dict.viewitems()’, ‘dict.viewkeys()’ and
     ‘dict.viewvalues()’ are converted respectively to *note
     dict.items(): cf5, *note dict.keys(): cf4. and *note dict.values():
     cf6.  It also wraps existing usages of *note dict.items(): cf5,
     *note dict.keys(): cf4, and *note dict.values(): cf6. in a call to
     *note list: 1f8.

 -- 2to3fixer: except

     Converts ‘except X, T’ to ‘except X as T’.

 -- 2to3fixer: exec

     Converts the ‘exec’ statement to the *note exec(): d0c. function.

 -- 2to3fixer: execfile

     Removes usage of ‘execfile()’.  The argument to ‘execfile()’ is
     wrapped in calls to *note open(): 16f, *note compile(): 2e7, and
     *note exec(): d0c.

 -- 2to3fixer: exitfunc

     Changes assignment of ‘sys.exitfunc’ to use of the *note atexit: b.
     module.

 -- 2to3fixer: filter

     Wraps *note filter(): cf8. usage in a *note list: 1f8. call.

 -- 2to3fixer: funcattrs

     Fixes function attributes that have been renamed.  For example,
     ‘my_function.func_closure’ is converted to
     ‘my_function.__closure__’.

 -- 2to3fixer: future

     Removes ‘from __future__ import new_feature’ statements.

 -- 2to3fixer: getcwdu

     Renames ‘os.getcwdu()’ to *note os.getcwd(): 1119.

 -- 2to3fixer: has_key

     Changes ‘dict.has_key(key)’ to ‘key in dict’.

 -- 2to3fixer: idioms

     This optional fixer performs several transformations that make
     Python code more idiomatic.  Type comparisons like ‘type(x) is
     SomeClass’ and ‘type(x) == SomeClass’ are converted to
     ‘isinstance(x, SomeClass)’.  ‘while 1’ becomes ‘while True’.  This
     fixer also tries to make use of *note sorted(): 547. in appropriate
     places.  For example, this block

          L = list(some_iterable)
          L.sort()

     is changed to

          L = sorted(some_iterable)

 -- 2to3fixer: import

     Detects sibling imports and converts them to relative imports.

 -- 2to3fixer: imports

     Handles module renames in the standard library.

 -- 2to3fixer: imports2

     Handles other modules renames in the standard library.  It is
     separate from the *note imports: 359a. fixer only because of
     technical limitations.

 -- 2to3fixer: input

     Converts ‘input(prompt)’ to ‘eval(input(prompt))’.

 -- 2to3fixer: intern

     Converts ‘intern()’ to *note sys.intern(): d36.

 -- 2to3fixer: isinstance

     Fixes duplicate types in the second argument of *note isinstance():
     552.  For example, ‘isinstance(x, (int, int))’ is converted to
     ‘isinstance(x, int)’ and ‘isinstance(x, (int, float, int))’ is
     converted to ‘isinstance(x, (int, float))’.

 -- 2to3fixer: itertools_imports

     Removes imports of ‘itertools.ifilter()’, ‘itertools.izip()’, and
     ‘itertools.imap()’.  Imports of ‘itertools.ifilterfalse()’ are also
     changed to *note itertools.filterfalse(): 1722.

 -- 2to3fixer: itertools

     Changes usage of ‘itertools.ifilter()’, ‘itertools.izip()’, and
     ‘itertools.imap()’ to their built-in equivalents.
     ‘itertools.ifilterfalse()’ is changed to *note
     itertools.filterfalse(): 1722.

 -- 2to3fixer: long

     Renames ‘long’ to *note int: 204.

 -- 2to3fixer: map

     Wraps *note map(): cf7. in a *note list: 1f8. call.  It also
     changes ‘map(None, x)’ to ‘list(x)’.  Using ‘from future_builtins
     import map’ disables this fixer.

 -- 2to3fixer: metaclass

     Converts the old metaclass syntax (‘__metaclass__ = Meta’ in the
     class body) to the new (‘class X(metaclass=Meta)’).

 -- 2to3fixer: methodattrs

     Fixes old method attribute names.  For example, ‘meth.im_func’ is
     converted to ‘meth.__func__’.

 -- 2to3fixer: ne

     Converts the old not-equal syntax, ‘<>’, to ‘!=’.

 -- 2to3fixer: next

     Converts the use of iterator’s ‘next()’ methods to the *note
     next(): 775. function.  It also renames *note next(): 775. methods
     to *note __next__(): d2c.

 -- 2to3fixer: nonzero

     Renames definitions of methods called ‘__nonzero__()’ to *note
     __bool__(): d30.

 -- 2to3fixer: numliterals

     Converts octal literals into the new syntax.

 -- 2to3fixer: operator

     Converts calls to various functions in the *note operator: c2.
     module to other, but equivalent, function calls.  When needed, the
     appropriate ‘import’ statements are added, e.g.  ‘import
     collections.abc’.  The following mapping are made:

     From                                   To
                                            
     -----------------------------------------------------------------------------------------
                                            
     ‘operator.isCallable(obj)’             ‘callable(obj)’
                                            
                                            
     ‘operator.sequenceIncludes(obj)’       ‘operator.contains(obj)’
                                            
                                            
     ‘operator.isSequenceType(obj)’         ‘isinstance(obj, collections.abc.Sequence)’
                                            
                                            
     ‘operator.isMappingType(obj)’          ‘isinstance(obj, collections.abc.Mapping)’
                                            
                                            
     ‘operator.isNumberType(obj)’           ‘isinstance(obj, numbers.Number)’
                                            
                                            
     ‘operator.repeat(obj, n)’              ‘operator.mul(obj, n)’
                                            
                                            
     ‘operator.irepeat(obj, n)’             ‘operator.imul(obj, n)’
                                            

 -- 2to3fixer: paren

     Add extra parenthesis where they are required in list
     comprehensions.  For example, ‘[x for x in 1, 2]’ becomes ‘[x for x
     in (1, 2)]’.

 -- 2to3fixer: print

     Converts the ‘print’ statement to the *note print(): 971. function.

 -- 2to3fixer: raise

     Converts ‘raise E, V’ to ‘raise E(V)’, and ‘raise E, V, T’ to
     ‘raise E(V).with_traceback(T)’.  If ‘E’ is a tuple, the translation
     will be incorrect because substituting tuples for exceptions has
     been removed in 3.0.

 -- 2to3fixer: raw_input

     Converts ‘raw_input()’ to *note input(): d33.

 -- 2to3fixer: reduce

     Handles the move of ‘reduce()’ to *note functools.reduce(): d37.

 -- 2to3fixer: reload

     Converts ‘reload()’ to *note importlib.reload(): 4a0.

 -- 2to3fixer: renames

     Changes ‘sys.maxint’ to *note sys.maxsize: c15.

 -- 2to3fixer: repr

     Replaces backtick repr with the *note repr(): 8b9. function.

 -- 2to3fixer: set_literal

     Replaces use of the *note set: 1f6. constructor with set literals.
     This fixer is optional.

 -- 2to3fixer: standarderror

     Renames ‘StandardError’ to *note Exception: 2dc.

 -- 2to3fixer: sys_exc

     Changes the deprecated ‘sys.exc_value’, ‘sys.exc_type’,
     ‘sys.exc_traceback’ to use *note sys.exc_info(): d27.

 -- 2to3fixer: throw

     Fixes the API change in generator’s ‘throw()’ method.

 -- 2to3fixer: tuple_params

     Removes implicit tuple parameter unpacking.  This fixer inserts
     temporary variables.

 -- 2to3fixer: types

     Fixes code broken from the removal of some members in the *note
     types: 121. module.

 -- 2to3fixer: unicode

     Renames ‘unicode’ to *note str: 205.

 -- 2to3fixer: urllib

     Handles the rename of *note urllib: 126. and ‘urllib2’ to the *note
     urllib: 126. package.

 -- 2to3fixer: ws_comma

     Removes excess whitespace from comma separated items.  This fixer
     is optional.

 -- 2to3fixer: xrange

     Renames ‘xrange()’ to *note range(): 1f5. and wraps existing *note
     range(): 1f5. calls with *note list: 1f8.

 -- 2to3fixer: xreadlines

     Changes ‘for x in file.xreadlines()’ to ‘for x in file’.

 -- 2to3fixer: zip

     Wraps *note zip(): cfc. usage in a *note list: 1f8. call.  This is
     disabled when ‘from future_builtins import zip’ appears.


File: python.info,  Node: lib2to3 - 2to3’s library,  Prev: Fixers,  Up: 2to3 - Automated Python 2 to 3 code translation

5.26.11.3 ‘lib2to3’ - 2to3’s library
....................................

`Source code:' Lib/lib2to3/(1)

__________________________________________________________________

Deprecated since version 3.10: Python 3.9 will switch to a PEG parser
(see PEP 617(2)), and Python 3.10 may include new language syntax that
is not parsable by lib2to3’s LL(1) parser.  The ‘lib2to3’ module may be
removed from the standard library in a future Python version.  Consider
third-party alternatives such as LibCST(3) or parso(4).

     Note: The *note lib2to3: a7. API should be considered unstable and
     may change drastically in the future.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/lib2to3/

   (2) https://www.python.org/dev/peps/pep-0617

   (3) https://libcst.readthedocs.io/

   (4) https://parso.readthedocs.io/


File: python.info,  Node: test — Regression tests package for Python,  Next: test support — Utilities for the Python test suite,  Prev: 2to3 - Automated Python 2 to 3 code translation,  Up: Development Tools

5.26.12 ‘test’ — Regression tests package for Python
----------------------------------------------------

     Note: The *note test: 105. package is meant for internal use by
     Python only.  It is documented for the benefit of the core
     developers of Python.  Any use of this package outside of Python’s
     standard library is discouraged as code mentioned here can change
     or be removed without notice between releases of Python.

__________________________________________________________________

The *note test: 105. package contains all regression tests for Python as
well as the modules *note test.support: 106. and ‘test.regrtest’.  *note
test.support: 106. is used to enhance your tests while ‘test.regrtest’
drives the testing suite.

Each module in the *note test: 105. package whose name starts with
‘test_’ is a testing suite for a specific module or feature.  All new
tests should be written using the *note unittest: 124. or *note doctest:
66. module.  Some older tests are written using a “traditional” testing
style that compares output printed to ‘sys.stdout’; this style of test
is considered deprecated.

See also
........

Module *note unittest: 124.

     Writing PyUnit regression tests.

Module *note doctest: 66.

     Tests embedded in documentation strings.

* Menu:

* Writing Unit Tests for the test package::
* Running tests using the command-line interface::


File: python.info,  Node: Writing Unit Tests for the test package,  Next: Running tests using the command-line interface,  Up: test — Regression tests package for Python

5.26.12.1 Writing Unit Tests for the ‘test’ package
...................................................

It is preferred that tests that use the *note unittest: 124. module
follow a few guidelines.  One is to name the test module by starting it
with ‘test_’ and end it with the name of the module being tested.  The
test methods in the test module should start with ‘test_’ and end with a
description of what the method is testing.  This is needed so that the
methods are recognized by the test driver as test methods.  Also, no
documentation string for the method should be included.  A comment (such
as ‘# Tests function returns only True or False’) should be used to
provide documentation for test methods.  This is done because
documentation strings get printed out if they exist and thus what test
is being run is not stated.

A basic boilerplate is often used:

     import unittest
     from test import support

     class MyTestCase1(unittest.TestCase):

         # Only use setUp() and tearDown() if necessary

         def setUp(self):
             ... code to execute in preparation for tests ...

         def tearDown(self):
             ... code to execute to clean up after tests ...

         def test_feature_one(self):
             # Test feature one.
             ... testing code ...

         def test_feature_two(self):
             # Test feature two.
             ... testing code ...

         ... more test methods ...

     class MyTestCase2(unittest.TestCase):
         ... same structure as MyTestCase1 ...

     ... more test classes ...

     if __name__ == '__main__':
         unittest.main()

This code pattern allows the testing suite to be run by ‘test.regrtest’,
on its own as a script that supports the *note unittest: 124. CLI, or
via the ‘python -m unittest’ CLI.

The goal for regression testing is to try to break code.  This leads to
a few guidelines to be followed:

   * The testing suite should exercise all classes, functions, and
     constants.  This includes not just the external API that is to be
     presented to the outside world but also “private” code.

   * Whitebox testing (examining the code being tested when the tests
     are being written) is preferred.  Blackbox testing (testing only
     the published user interface) is not complete enough to make sure
     all boundary and edge cases are tested.

   * Make sure all possible values are tested including invalid ones.
     This makes sure that not only all valid values are acceptable but
     also that improper values are handled correctly.

   * Exhaust as many code paths as possible.  Test where branching
     occurs and thus tailor input to make sure as many different paths
     through the code are taken.

   * Add an explicit test for any bugs discovered for the tested code.
     This will make sure that the error does not crop up again if the
     code is changed in the future.

   * Make sure to clean up after your tests (such as close and remove
     all temporary files).

   * If a test is dependent on a specific condition of the operating
     system then verify the condition already exists before attempting
     the test.

   * Import as few modules as possible and do it as soon as possible.
     This minimizes external dependencies of tests and also minimizes
     possible anomalous behavior from side-effects of importing a
     module.

   * Try to maximize code reuse.  On occasion, tests will vary by
     something as small as what type of input is used.  Minimize code
     duplication by subclassing a basic test class with a class that
     specifies the input:

          class TestFuncAcceptsSequencesMixin:

              func = mySuperWhammyFunction

              def test_func(self):
                  self.func(self.arg)

          class AcceptLists(TestFuncAcceptsSequencesMixin, unittest.TestCase):
              arg = [1, 2, 3]

          class AcceptStrings(TestFuncAcceptsSequencesMixin, unittest.TestCase):
              arg = 'abc'

          class AcceptTuples(TestFuncAcceptsSequencesMixin, unittest.TestCase):
              arg = (1, 2, 3)

     When using this pattern, remember that all classes that inherit
     from *note unittest.TestCase: 9e5. are run as tests.  The ‘Mixin’
     class in the example above does not have any data and so can’t be
     run by itself, thus it does not inherit from *note
     unittest.TestCase: 9e5.

See also
........

Test Driven Development

     A book by Kent Beck on writing tests before code.


File: python.info,  Node: Running tests using the command-line interface,  Prev: Writing Unit Tests for the test package,  Up: test — Regression tests package for Python

5.26.12.2 Running tests using the command-line interface
........................................................

The *note test: 105. package can be run as a script to drive Python’s
regression test suite, thanks to the *note -m: 443. option: ‘python -m
test’.  Under the hood, it uses ‘test.regrtest’; the call ‘python -m
test.regrtest’ used in previous Python versions still works.  Running
the script by itself automatically starts running all regression tests
in the *note test: 105. package.  It does this by finding all modules in
the package whose name starts with ‘test_’, importing them, and
executing the function ‘test_main()’ if present or loading the tests via
unittest.TestLoader.loadTestsFromModule if ‘test_main’ does not exist.
The names of tests to execute may also be passed to the script.
Specifying a single regression test (‘python -m test test_spam’) will
minimize output and only print whether the test passed or failed.

Running *note test: 105. directly allows what resources are available
for tests to use to be set.  You do this by using the ‘-u’ command-line
option.  Specifying ‘all’ as the value for the ‘-u’ option enables all
possible resources: ‘python -m test -uall’.  If all but one resource is
desired (a more common case), a comma-separated list of resources that
are not desired may be listed after ‘all’.  The command ‘python -m test
-uall,-audio,-largefile’ will run *note test: 105. with all resources
except the ‘audio’ and ‘largefile’ resources.  For a list of all
resources and more command-line options, run ‘python -m test -h’.

Some other ways to execute the regression tests depend on what platform
the tests are being executed on.  On Unix, you can run ‘make test’ at
the top-level directory where Python was built.  On Windows, executing
‘rt.bat’ from your ‘PCbuild’ directory will run all regression tests.


File: python.info,  Node: test support — Utilities for the Python test suite,  Next: test support socket_helper — Utilities for socket tests,  Prev: test — Regression tests package for Python,  Up: Development Tools

5.26.13 ‘test.support’ — Utilities for the Python test suite
------------------------------------------------------------

The *note test.support: 106. module provides support for Python’s
regression test suite.

     Note: *note test.support: 106. is not a public module.  It is
     documented here to help Python developers write tests.  The API of
     this module is subject to change without backwards compatibility
     concerns between releases.

This module defines the following exceptions:

 -- Exception: test.support.TestFailed

     Exception to be raised when a test fails.  This is deprecated in
     favor of *note unittest: 124.-based tests and *note
     unittest.TestCase: 9e5.’s assertion methods.

 -- Exception: test.support.ResourceDenied

     Subclass of *note unittest.SkipTest: 9e9.  Raised when a resource
     (such as a network connection) is not available.  Raised by the
     *note requires(): 35c7. function.

The *note test.support: 106. module defines the following constants:

 -- Data: test.support.verbose

     ‘True’ when verbose output is enabled.  Should be checked when more
     detailed information is desired about a running test.  `verbose' is
     set by ‘test.regrtest’.

 -- Data: test.support.is_jython

     ‘True’ if the running interpreter is Jython.

 -- Data: test.support.is_android

     ‘True’ if the system is Android.

 -- Data: test.support.unix_shell

     Path for shell if not on Windows; otherwise ‘None’.

 -- Data: test.support.FS_NONASCII

     A non-ASCII character encodable by *note os.fsencode(): 5ea.

 -- Data: test.support.TESTFN

     Set to a name that is safe to use as the name of a temporary file.
     Any temporary file that is created should be closed and unlinked
     (removed).

 -- Data: test.support.TESTFN_UNICODE

     Set to a non-ASCII name for a temporary file.

 -- Data: test.support.TESTFN_ENCODING

     Set to *note sys.getfilesystemencoding(): 5f0.

 -- Data: test.support.TESTFN_UNENCODABLE

     Set to a filename (str type) that should not be able to be encoded
     by file system encoding in strict mode.  It may be ‘None’ if it’s
     not possible to generate such a filename.

 -- Data: test.support.TESTFN_UNDECODABLE

     Set to a filename (bytes type) that should not be able to be
     decoded by file system encoding in strict mode.  It may be ‘None’
     if it’s not possible to generate such a filename.

 -- Data: test.support.TESTFN_NONASCII

     Set to a filename containing the *note FS_NONASCII: 35cc.
     character.

 -- Data: test.support.LOOPBACK_TIMEOUT

     Timeout in seconds for tests using a network server listening on
     the network local loopback interface like ‘127.0.0.1’.

     The timeout is long enough to prevent test failure: it takes into
     account that the client and the server can run in different threads
     or even different processes.

     The timeout should be long enough for *note connect(): 769, *note
     recv(): 76a. and *note send(): 76d. methods of *note socket.socket:
     767.

     Its default value is 5 seconds.

     See also *note INTERNET_TIMEOUT: 10b2.

 -- Data: test.support.INTERNET_TIMEOUT

     Timeout in seconds for network requests going to the Internet.

     The timeout is short enough to prevent a test to wait for too long
     if the Internet request is blocked for whatever reason.

     Usually, a timeout using *note INTERNET_TIMEOUT: 10b2. should not
     mark a test as failed, but skip the test instead: see *note
     transient_internet(): 35d2.

     Its default value is 1 minute.

     See also *note LOOPBACK_TIMEOUT: 10b1.

 -- Data: test.support.SHORT_TIMEOUT

     Timeout in seconds to mark a test as failed if the test takes “too
     long”.

     The timeout value depends on the regrtest ‘--timeout’ command line
     option.

     If a test using *note SHORT_TIMEOUT: f94. starts to fail randomly
     on slow buildbots, use *note LONG_TIMEOUT: 10b3. instead.

     Its default value is 30 seconds.

 -- Data: test.support.LONG_TIMEOUT

     Timeout in seconds to detect when a test hangs.

     It is long enough to reduce the risk of test failure on the slowest
     Python buildbots.  It should not be used to mark a test as failed
     if the test takes “too long”.  The timeout value depends on the
     regrtest ‘--timeout’ command line option.

     Its default value is 5 minutes.

     See also *note LOOPBACK_TIMEOUT: 10b1, *note INTERNET_TIMEOUT:
     10b2. and *note SHORT_TIMEOUT: f94.

 -- Data: test.support.SAVEDCWD

     Set to *note os.getcwd(): 1119.

 -- Data: test.support.PGO

     Set when tests can be skipped when they are not useful for PGO.

 -- Data: test.support.PIPE_MAX_SIZE

     A constant that is likely larger than the underlying OS pipe buffer
     size, to make writes blocking.

 -- Data: test.support.SOCK_MAX_SIZE

     A constant that is likely larger than the underlying OS socket
     buffer size, to make writes blocking.

 -- Data: test.support.TEST_SUPPORT_DIR

     Set to the top level directory that contains *note test.support:
     106.

 -- Data: test.support.TEST_HOME_DIR

     Set to the top level directory for the test package.

 -- Data: test.support.TEST_DATA_DIR

     Set to the ‘data’ directory within the test package.

 -- Data: test.support.MAX_Py_ssize_t

     Set to *note sys.maxsize: c15. for big memory tests.

 -- Data: test.support.max_memuse

     Set by *note set_memlimit(): 35dc. as the memory limit for big
     memory tests.  Limited by *note MAX_Py_ssize_t: 35da.

 -- Data: test.support.real_max_memuse

     Set by *note set_memlimit(): 35dc. as the memory limit for big
     memory tests.  Not limited by *note MAX_Py_ssize_t: 35da.

 -- Data: test.support.MISSING_C_DOCSTRINGS

     Return ‘True’ if running on CPython, not on Windows, and
     configuration not set with ‘WITH_DOC_STRINGS’.

 -- Data: test.support.HAVE_DOCSTRINGS

     Check for presence of docstrings.

 -- Data: test.support.TEST_HTTP_URL

     Define the URL of a dedicated HTTP server for the network tests.

 -- Data: test.support.ALWAYS_EQ

     Object that is equal to anything.  Used to test mixed type
     comparison.

 -- Data: test.support.NEVER_EQ

     Object that is not equal to anything (even to *note ALWAYS_EQ:
     35e1.).  Used to test mixed type comparison.

 -- Data: test.support.LARGEST

     Object that is greater than anything (except itself).  Used to test
     mixed type comparison.

 -- Data: test.support.SMALLEST

     Object that is less than anything (except itself).  Used to test
     mixed type comparison.

The *note test.support: 106. module defines the following functions:

 -- Function: test.support.forget (module_name)

     Remove the module named `module_name' from ‘sys.modules’ and delete
     any byte-compiled files of the module.

 -- Function: test.support.unload (name)

     Delete `name' from ‘sys.modules’.

 -- Function: test.support.unlink (filename)

     Call *note os.unlink(): b18. on `filename'.  On Windows platforms,
     this is wrapped with a wait loop that checks for the existence of
     the file.

 -- Function: test.support.rmdir (filename)

     Call *note os.rmdir(): b16. on `filename'.  On Windows platforms,
     this is wrapped with a wait loop that checks for the existence of
     the file.

 -- Function: test.support.rmtree (path)

     Call *note shutil.rmtree(): 349. on `path' or call *note
     os.lstat(): 322. and *note os.rmdir(): b16. to remove a path and
     its contents.  On Windows platforms, this is wrapped with a wait
     loop that checks for the existence of the files.

 -- Function: test.support.make_legacy_pyc (source)

     Move a PEP 3147(1)/ PEP 488(2) pyc file to its legacy pyc location
     and return the file system path to the legacy pyc file.  The
     `source' value is the file system path to the source file.  It does
     not need to exist, however the PEP 3147/488 pyc file must exist.

 -- Function: test.support.is_resource_enabled (resource)

     Return ‘True’ if `resource' is enabled and available.  The list of
     available resources is only set when ‘test.regrtest’ is executing
     the tests.

 -- Function: test.support.python_is_optimized ()

     Return ‘True’ if Python was not built with ‘-O0’ or ‘-Og’.

 -- Function: test.support.with_pymalloc ()

     Return ‘_testcapi.WITH_PYMALLOC’.

 -- Function: test.support.requires (resource, msg=None)

     Raise *note ResourceDenied: 35c6. if `resource' is not available.
     `msg' is the argument to *note ResourceDenied: 35c6. if it is
     raised.  Always returns ‘True’ if called by a function whose
     ‘__name__’ is ‘'__main__'’.  Used when tests are executed by
     ‘test.regrtest’.

 -- Function: test.support.system_must_validate_cert (f)

     Raise *note unittest.SkipTest: 9e9. on TLS certification validation
     failures.

 -- Function: test.support.sortdict (dict)

     Return a repr of `dict' with keys sorted.

 -- Function: test.support.findfile (filename, subdir=None)

     Return the path to the file named `filename'.  If no match is found
     `filename' is returned.  This does not equal a failure since it
     could be the path to the file.

     Setting `subdir' indicates a relative path to use to find the file
     rather than looking directly in the path directories.

 -- Function: test.support.create_empty_file (filename)

     Create an empty file with `filename'.  If it already exists,
     truncate it.

 -- Function: test.support.fd_count ()

     Count the number of open file descriptors.

 -- Function: test.support.match_test (test)

     Match `test' to patterns set in *note set_match_tests(): 35f4.

 -- Function: test.support.set_match_tests (patterns)

     Define match test with regular expression `patterns'.

 -- Function: test.support.run_unittest (*classes)

     Execute *note unittest.TestCase: 9e5. subclasses passed to the
     function.  The function scans the classes for methods starting with
     the prefix ‘test_’ and executes the tests individually.

     It is also legal to pass strings as parameters; these should be
     keys in ‘sys.modules’.  Each associated module will be scanned by
     ‘unittest.TestLoader.loadTestsFromModule()’.  This is usually seen
     in the following ‘test_main()’ function:

          def test_main():
              support.run_unittest(__name__)

     This will run all tests defined in the named module.

 -- Function: test.support.run_doctest (module, verbosity=None,
          optionflags=0)

     Run *note doctest.testmod(): e95. on the given `module'.  Return
     ‘(failure_count, test_count)’.

     If `verbosity' is ‘None’, *note doctest.testmod(): e95. is run with
     verbosity set to *note verbose: 35c8.  Otherwise, it is run with
     verbosity set to ‘None’.  `optionflags' is passed as ‘optionflags’
     to *note doctest.testmod(): e95.

 -- Function: test.support.setswitchinterval (interval)

     Set the *note sys.setswitchinterval(): 218. to the given
     `interval'.  Defines a minimum interval for Android systems to
     prevent the system from hanging.

 -- Function: test.support.check_impl_detail (**guards)

     Use this check to guard CPython’s implementation-specific tests or
     to run them only on the implementations guarded by the arguments:

          check_impl_detail()               # Only on CPython (default).
          check_impl_detail(jython=True)    # Only on Jython.
          check_impl_detail(cpython=False)  # Everywhere except CPython.

 -- Function: test.support.check_warnings (*filters, quiet=True)

     A convenience wrapper for *note warnings.catch_warnings(): 35f9.
     that makes it easier to test that a warning was correctly raised.
     It is approximately equivalent to calling
     ‘warnings.catch_warnings(record=True)’ with *note
     warnings.simplefilter(): 35fa. set to ‘always’ and with the option
     to automatically validate the results that are recorded.

     ‘check_warnings’ accepts 2-tuples of the form ‘("message regexp",
     WarningCategory)’ as positional arguments.  If one or more
     `filters' are provided, or if the optional keyword argument `quiet'
     is ‘False’, it checks to make sure the warnings are as expected:
     each specified filter must match at least one of the warnings
     raised by the enclosed code or the test fails, and if any warnings
     are raised that do not match any of the specified filters the test
     fails.  To disable the first of these checks, set `quiet' to
     ‘True’.

     If no arguments are specified, it defaults to:

          check_warnings(("", Warning), quiet=True)

     In this case all warnings are caught and no errors are raised.

     On entry to the context manager, a ‘WarningRecorder’ instance is
     returned.  The underlying warnings list from *note
     catch_warnings(): 35f9. is available via the recorder object’s
     *note warnings: 12f. attribute.  As a convenience, the attributes
     of the object representing the most recent warning can also be
     accessed directly through the recorder object (see example below).
     If no warning has been raised, then any of the attributes that
     would otherwise be expected on an object representing a warning
     will return ‘None’.

     The recorder object also has a ‘reset()’ method, which clears the
     warnings list.

     The context manager is designed to be used like this:

          with check_warnings(("assertion is always true", SyntaxWarning),
                              ("", UserWarning)):
              exec('assert(False, "Hey!")')
              warnings.warn(UserWarning("Hide me!"))

     In this case if either warning was not raised, or some other
     warning was raised, *note check_warnings(): 35f8. would raise an
     error.

     When a test needs to look more deeply into the warnings, rather
     than just checking whether or not they occurred, code like this can
     be used:

          with check_warnings(quiet=True) as w:
              warnings.warn("foo")
              assert str(w.args[0]) == "foo"
              warnings.warn("bar")
              assert str(w.args[0]) == "bar"
              assert str(w.warnings[0].args[0]) == "foo"
              assert str(w.warnings[1].args[0]) == "bar"
              w.reset()
              assert len(w.warnings) == 0

     Here all warnings will be caught, and the test code tests the
     captured warnings directly.

     Changed in version 3.2: New optional arguments `filters' and
     `quiet'.

 -- Function: test.support.check_no_resource_warning (testcase)

     Context manager to check that no *note ResourceWarning: 5cb. was
     raised.  You must remove the object which may emit *note
     ResourceWarning: 5cb. before the end of the context manager.

 -- Function: test.support.set_memlimit (limit)

     Set the values for *note max_memuse: 35db. and *note
     real_max_memuse: 35dd. for big memory tests.

 -- Function: test.support.record_original_stdout (stdout)

     Store the value from `stdout'.  It is meant to hold the stdout at
     the time the regrtest began.

 -- Function: test.support.get_original_stdout ()

     Return the original stdout set by *note record_original_stdout():
     35fc. or ‘sys.stdout’ if it’s not set.

 -- Function: test.support.args_from_interpreter_flags ()

     Return a list of command line arguments reproducing the current
     settings in ‘sys.flags’ and ‘sys.warnoptions’.

 -- Function: test.support.optim_args_from_interpreter_flags ()

     Return a list of command line arguments reproducing the current
     optimization settings in ‘sys.flags’.

 -- Function: test.support.captured_stdin ()
 -- Function: test.support.captured_stdout ()
 -- Function: test.support.captured_stderr ()

     A context managers that temporarily replaces the named stream with
     *note io.StringIO: 91a. object.

     Example use with output streams:

          with captured_stdout() as stdout, captured_stderr() as stderr:
              print("hello")
              print("error", file=sys.stderr)
          assert stdout.getvalue() == "hello\n"
          assert stderr.getvalue() == "error\n"

     Example use with input stream:

          with captured_stdin() as stdin:
              stdin.write('hello\n')
              stdin.seek(0)
              # call test code that consumes from sys.stdin
              captured = input()
          self.assertEqual(captured, "hello")

 -- Function: test.support.temp_dir (path=None, quiet=False)

     A context manager that creates a temporary directory at `path' and
     yields the directory.

     If `path' is ‘None’, the temporary directory is created using *note
     tempfile.mkdtemp(): 1dc5.  If `quiet' is ‘False’, the context
     manager raises an exception on error.  Otherwise, if `path' is
     specified and cannot be created, only a warning is issued.

 -- Function: test.support.change_cwd (path, quiet=False)

     A context manager that temporarily changes the current working
     directory to `path' and yields the directory.

     If `quiet' is ‘False’, the context manager raises an exception on
     error.  Otherwise, it issues only a warning and keeps the current
     working directory the same.

 -- Function: test.support.temp_cwd (name='tempcwd', quiet=False)

     A context manager that temporarily creates a new directory and
     changes the current working directory (CWD).

     The context manager creates a temporary directory in the current
     directory with name `name' before temporarily changing the current
     working directory.  If `name' is ‘None’, the temporary directory is
     created using *note tempfile.mkdtemp(): 1dc5.

     If `quiet' is ‘False’ and it is not possible to create or change
     the CWD, an error is raised.  Otherwise, only a warning is raised
     and the original CWD is used.

 -- Function: test.support.temp_umask (umask)

     A context manager that temporarily sets the process umask.

 -- Function: test.support.disable_faulthandler ()

     A context manager that replaces ‘sys.stderr’ with ‘sys.__stderr__’.

 -- Function: test.support.gc_collect ()

     Force as many objects as possible to be collected.  This is needed
     because timely deallocation is not guaranteed by the garbage
     collector.  This means that ‘__del__’ methods may be called later
     than expected and weakrefs may remain alive for longer than
     expected.

 -- Function: test.support.disable_gc ()

     A context manager that disables the garbage collector upon entry
     and reenables it upon exit.

 -- Function: test.support.swap_attr (obj, attr, new_val)

     Context manager to swap out an attribute with a new object.

     Usage:

          with swap_attr(obj, "attr", 5):
              ...

     This will set ‘obj.attr’ to 5 for the duration of the ‘with’ block,
     restoring the old value at the end of the block.  If ‘attr’ doesn’t
     exist on ‘obj’, it will be created and then deleted at the end of
     the block.

     The old value (or ‘None’ if it doesn’t exist) will be assigned to
     the target of the “as” clause, if there is one.

 -- Function: test.support.swap_item (obj, attr, new_val)

     Context manager to swap out an item with a new object.

     Usage:

          with swap_item(obj, "item", 5):
              ...

     This will set ‘obj["item"]’ to 5 for the duration of the ‘with’
     block, restoring the old value at the end of the block.  If ‘item’
     doesn’t exist on ‘obj’, it will be created and then deleted at the
     end of the block.

     The old value (or ‘None’ if it doesn’t exist) will be assigned to
     the target of the “as” clause, if there is one.

 -- Function: test.support.print_warning (msg)

     Print a warning into *note sys.__stderr__: 360c.  Format the
     message as: ‘f"Warning -- {msg}"’.  If `msg' is made of multiple
     lines, add ‘"Warning -- "’ prefix to each line.

     New in version 3.9.

 -- Function: test.support.wait_process (pid, *, exitcode, timeout=None)

     Wait until process `pid' completes and check that the process exit
     code is `exitcode'.

     Raise an *note AssertionError: 240. if the process exit code is not
     equal to `exitcode'.

     If the process runs longer than `timeout' seconds (*note
     SHORT_TIMEOUT: f94. by default), kill the process and raise an
     *note AssertionError: 240.  The timeout feature is not available on
     Windows.

     New in version 3.9.

 -- Function: test.support.wait_threads_exit (timeout=60.0)

     Context manager to wait until all threads created in the ‘with’
     statement exit.

 -- Function: test.support.start_threads (threads, unlock=None)

     Context manager to start `threads'.  It attempts to join the
     threads upon exit.

 -- Function: test.support.calcobjsize (fmt)

     Return *note struct.calcsize(): 10c5. for ‘nP{fmt}0n’ or, if
     ‘gettotalrefcount’ exists, ‘2PnP{fmt}0P’.

 -- Function: test.support.calcvobjsize (fmt)

     Return *note struct.calcsize(): 10c5. for ‘nPn{fmt}0n’ or, if
     ‘gettotalrefcount’ exists, ‘2PnPn{fmt}0P’.

 -- Function: test.support.checksizeof (test, o, size)

     For testcase `test', assert that the ‘sys.getsizeof’ for `o' plus
     the GC header size equals `size'.

 -- Function: test.support.can_symlink ()

     Return ‘True’ if the OS supports symbolic links, ‘False’ otherwise.

 -- Function: test.support.can_xattr ()

     Return ‘True’ if the OS supports xattr, ‘False’ otherwise.

 -- Function: @test.support.skip_unless_symlink

     A decorator for running tests that require support for symbolic
     links.

 -- Function: @test.support.skip_unless_xattr

     A decorator for running tests that require support for xattr.

 -- Function: @test.support.anticipate_failure (condition)

     A decorator to conditionally mark tests with *note
     unittest.expectedFailure(): 34d5.  Any use of this decorator should
     have an associated comment identifying the relevant tracker issue.

 -- Function: @test.support.run_with_locale (catstr, *locales)

     A decorator for running a function in a different locale, correctly
     resetting it after it has finished.  `catstr' is the locale
     category as a string (for example ‘"LC_ALL"’).  The `locales'
     passed will be tried sequentially, and the first valid locale will
     be used.

 -- Function: @test.support.run_with_tz (tz)

     A decorator for running a function in a specific timezone,
     correctly resetting it after it has finished.

 -- Function: @test.support.requires_freebsd_version (*min_version)

     Decorator for the minimum version when running test on FreeBSD. If
     the FreeBSD version is less than the minimum, raise *note
     unittest.SkipTest: 9e9.

 -- Function: @test.support.requires_linux_version (*min_version)

     Decorator for the minimum version when running test on Linux.  If
     the Linux version is less than the minimum, raise *note
     unittest.SkipTest: 9e9.

 -- Function: @test.support.requires_mac_version (*min_version)

     Decorator for the minimum version when running test on macOS. If
     the macOS version is less than the minimum, raise *note
     unittest.SkipTest: 9e9.

 -- Function: @test.support.requires_IEEE_754

     Decorator for skipping tests on non-IEEE 754 platforms.

 -- Function: @test.support.requires_zlib

     Decorator for skipping tests if *note zlib: 14d. doesn’t exist.

 -- Function: @test.support.requires_gzip

     Decorator for skipping tests if *note gzip: 8b. doesn’t exist.

 -- Function: @test.support.requires_bz2

     Decorator for skipping tests if *note bz2: 13. doesn’t exist.

 -- Function: @test.support.requires_lzma

     Decorator for skipping tests if *note lzma: ad. doesn’t exist.

 -- Function: @test.support.requires_resource (resource)

     Decorator for skipping tests if `resource' is not available.

 -- Function: @test.support.requires_docstrings

     Decorator for only running the test if *note HAVE_DOCSTRINGS: 35df.

 -- Function: @test.support.cpython_only (test)

     Decorator for tests only applicable to CPython.

 -- Function: @test.support.impl_detail (msg=None, **guards)

     Decorator for invoking *note check_impl_detail(): 35f7. on
     `guards'.  If that returns ‘False’, then uses `msg' as the reason
     for skipping the test.

 -- Function: @test.support.no_tracing (func)

     Decorator to temporarily turn off tracing for the duration of the
     test.

 -- Function: @test.support.refcount_test (test)

     Decorator for tests which involve reference counting.  The
     decorator does not run the test if it is not run by CPython.  Any
     trace function is unset for the duration of the test to prevent
     unexpected refcounts caused by the trace function.

 -- Function: @test.support.reap_threads (func)

     Decorator to ensure the threads are cleaned up even if the test
     fails.

 -- Function: @test.support.bigmemtest (size, memuse, dry_run=True)

     Decorator for bigmem tests.

     `size' is a requested size for the test (in arbitrary,
     test-interpreted units.)  `memuse' is the number of bytes per unit
     for the test, or a good estimate of it.  For example, a test that
     needs two byte buffers, of 4 GiB each, could be decorated with
     ‘@bigmemtest(size=_4G, memuse=2)’.

     The `size' argument is normally passed to the decorated test method
     as an extra argument.  If `dry_run' is ‘True’, the value passed to
     the test method may be less than the requested value.  If `dry_run'
     is ‘False’, it means the test doesn’t support dummy runs when ‘-M’
     is not specified.

 -- Function: @test.support.bigaddrspacetest (f)

     Decorator for tests that fill the address space.  `f' is the
     function to wrap.

 -- Function: test.support.make_bad_fd ()

     Create an invalid file descriptor by opening and closing a
     temporary file, and returning its descriptor.

 -- Function: test.support.check_syntax_error (testcase, statement,
          errtext='', *, lineno=None, offset=None)

     Test for syntax errors in `statement' by attempting to compile
     `statement'.  `testcase' is the *note unittest: 124. instance for
     the test.  `errtext' is the regular expression which should match
     the string representation of the raised *note SyntaxError: 55a.  If
     `lineno' is not ‘None’, compares to the line of the exception.  If
     `offset' is not ‘None’, compares to the offset of the exception.

 -- Function: test.support.check_syntax_warning (testcase, statement,
          errtext='', *, lineno=1, offset=None)

     Test for syntax warning in `statement' by attempting to compile
     `statement'.  Test also that the *note SyntaxWarning: 2c9. is
     emitted only once, and that it will be converted to a *note
     SyntaxError: 55a. when turned into error.  `testcase' is the *note
     unittest: 124. instance for the test.  `errtext' is the regular
     expression which should match the string representation of the
     emitted *note SyntaxWarning: 2c9. and raised *note SyntaxError:
     55a.  If `lineno' is not ‘None’, compares to the line of the
     warning and exception.  If `offset' is not ‘None’, compares to the
     offset of the exception.

     New in version 3.8.

 -- Function: test.support.open_urlresource (url, *args, **kw)

     Open `url'.  If open fails, raises *note TestFailed: 35c5.

 -- Function: test.support.import_module (name, deprecated=False, *,
          required_on())

     This function imports and returns the named module.  Unlike a
     normal import, this function raises *note unittest.SkipTest: 9e9.
     if the module cannot be imported.

     Module and package deprecation messages are suppressed during this
     import if `deprecated' is ‘True’.  If a module is required on a
     platform but optional for others, set `required_on' to an iterable
     of platform prefixes which will be compared against *note
     sys.platform: 3d3.

     New in version 3.1.

 -- Function: test.support.import_fresh_module (name, fresh=(),
          blocked=(), deprecated=False)

     This function imports and returns a fresh copy of the named Python
     module by removing the named module from ‘sys.modules’ before doing
     the import.  Note that unlike ‘reload()’, the original module is
     not affected by this operation.

     `fresh' is an iterable of additional module names that are also
     removed from the ‘sys.modules’ cache before doing the import.

     `blocked' is an iterable of module names that are replaced with
     ‘None’ in the module cache during the import to ensure that
     attempts to import them raise *note ImportError: 16c.

     The named module and any modules named in the `fresh' and `blocked'
     parameters are saved before starting the import and then reinserted
     into ‘sys.modules’ when the fresh import is complete.

     Module and package deprecation messages are suppressed during this
     import if `deprecated' is ‘True’.

     This function will raise *note ImportError: 16c. if the named
     module cannot be imported.

     Example use:

          # Get copies of the warnings module for testing without affecting the
          # version being used by the rest of the test suite. One copy uses the
          # C implementation, the other is forced to use the pure Python fallback
          # implementation
          py_warnings = import_fresh_module('warnings', blocked=['_warnings'])
          c_warnings = import_fresh_module('warnings', fresh=['_warnings'])

     New in version 3.1.

 -- Function: test.support.modules_setup ()

     Return a copy of *note sys.modules: 1051.

 -- Function: test.support.modules_cleanup (oldmodules)

     Remove modules except for `oldmodules' and ‘encodings’ in order to
     preserve internal cache.

 -- Function: test.support.threading_setup ()

     Return current thread count and copy of dangling threads.

 -- Function: test.support.threading_cleanup (*original_values)

     Cleanup up threads not specified in `original_values'.  Designed to
     emit a warning if a test leaves running threads in the background.

 -- Function: test.support.join_thread (thread, timeout=30.0)

     Join a `thread' within `timeout'.  Raise an *note AssertionError:
     240. if thread is still alive after `timeout' seconds.

 -- Function: test.support.reap_children ()

     Use this at the end of ‘test_main’ whenever sub-processes are
     started.  This will help ensure that no extra children (zombies)
     stick around to hog resources and create problems when looking for
     refleaks.

 -- Function: test.support.get_attribute (obj, name)

     Get an attribute, raising *note unittest.SkipTest: 9e9. if *note
     AttributeError: 4a2. is raised.

 -- Function: test.support.catch_threading_exception ()

     Context manager catching *note threading.Thread: 21a. exception
     using *note threading.excepthook(): 35e.

     Attributes set when an exception is caught:

        * ‘exc_type’

        * ‘exc_value’

        * ‘exc_traceback’

        * ‘thread’

     See *note threading.excepthook(): 35e. documentation.

     These attributes are deleted at the context manager exit.

     Usage:

          with support.catch_threading_exception() as cm:
              # code spawning a thread which raises an exception
              ...

              # check the thread exception, use cm attributes:
              # exc_type, exc_value, exc_traceback, thread
              ...

          # exc_type, exc_value, exc_traceback, thread attributes of cm no longer
          # exists at this point
          # (to avoid reference cycles)

     New in version 3.8.

 -- Function: test.support.catch_unraisable_exception ()

     Context manager catching unraisable exception using *note
     sys.unraisablehook(): 35a.

     Storing the exception value (‘cm.unraisable.exc_value’) creates a
     reference cycle.  The reference cycle is broken explicitly when the
     context manager exits.

     Storing the object (‘cm.unraisable.object’) can resurrect it if it
     is set to an object which is being finalized.  Exiting the context
     manager clears the stored object.

     Usage:

          with support.catch_unraisable_exception() as cm:
              # code creating an "unraisable exception"
              ...

              # check the unraisable exception: use cm.unraisable
              ...

          # cm.unraisable attribute no longer exists at this point
          # (to break a reference cycle)

     New in version 3.8.

 -- Function: test.support.load_package_tests (pkg_dir, loader,
          standard_tests, pattern)

     Generic implementation of the *note unittest: 124. ‘load_tests’
     protocol for use in test packages.  `pkg_dir' is the root directory
     of the package; `loader', `standard_tests', and `pattern' are the
     arguments expected by ‘load_tests’.  In simple cases, the test
     package’s ‘__init__.py’ can be the following:

          import os
          from test.support import load_package_tests

          def load_tests(*args):
              return load_package_tests(os.path.dirname(__file__), *args)

 -- Function: test.support.fs_is_case_insensitive (directory)

     Return ‘True’ if the file system for `directory' is
     case-insensitive.

 -- Function: test.support.detect_api_mismatch (ref_api, other_api, *,
          ignore=())

     Returns the set of attributes, functions or methods of `ref_api'
     not found on `other_api', except for a defined list of items to be
     ignored in this check specified in `ignore'.

     By default this skips private attributes beginning with ‘_’ but
     includes all magic methods, i.e.  those starting and ending in
     ‘__’.

     New in version 3.5.

 -- Function: test.support.patch (test_instance, object_to_patch,
          attr_name, new_value)

     Override `object_to_patch.attr_name' with `new_value'.  Also add
     cleanup procedure to `test_instance' to restore `object_to_patch'
     for `attr_name'.  The `attr_name' should be a valid attribute for
     `object_to_patch'.

 -- Function: test.support.run_in_subinterp (code)

     Run `code' in subinterpreter.  Raise *note unittest.SkipTest: 9e9.
     if *note tracemalloc: 11d. is enabled.

 -- Function: test.support.check_free_after_iterating (test, iter, cls,
          args=())

     Assert that `iter' is deallocated after iterating.

 -- Function: test.support.missing_compiler_executable (cmd_names=[])

     Check for the existence of the compiler executables whose names are
     listed in `cmd_names' or all the compiler executables when
     `cmd_names' is empty and return the first missing executable or
     ‘None’ when none is found missing.

 -- Function: test.support.check__all__ (test_case, module,
          name_of_module=None, extra=(), blacklist=())

     Assert that the ‘__all__’ variable of `module' contains all public
     names.

     The module’s public names (its API) are detected automatically
     based on whether they match the public name convention and were
     defined in `module'.

     The `name_of_module' argument can specify (as a string or tuple
     thereof) what module(s) an API could be defined in order to be
     detected as a public API. One case for this is when `module'
     imports part of its public API from other modules, possibly a C
     backend (like ‘csv’ and its ‘_csv’).

     The `extra' argument can be a set of names that wouldn’t otherwise
     be automatically detected as “public”, like objects without a
     proper ‘__module__’ attribute.  If provided, it will be added to
     the automatically detected ones.

     The `blacklist' argument can be a set of names that must not be
     treated as part of the public API even though their names indicate
     otherwise.

     Example use:

          import bar
          import foo
          import unittest
          from test import support

          class MiscTestCase(unittest.TestCase):
              def test__all__(self):
                  support.check__all__(self, foo)

          class OtherTestCase(unittest.TestCase):
              def test__all__(self):
                  extra = {'BAR_CONST', 'FOO_CONST'}
                  blacklist = {'baz'}  # Undocumented name.
                  # bar imports part of its API from _bar.
                  support.check__all__(self, bar, ('bar', '_bar'),
                                       extra=extra, blacklist=blacklist)

     New in version 3.6.

The *note test.support: 106. module defines the following classes:

 -- Class: test.support.TransientResource (exc, **kwargs)

     Instances are a context manager that raises *note ResourceDenied:
     35c6. if the specified exception type is raised.  Any keyword
     arguments are treated as attribute/value pairs to be compared
     against any exception raised within the *note with: 7da. statement.
     Only if all pairs match properly against attributes on the
     exception is *note ResourceDenied: 35c6. raised.

 -- Class: test.support.EnvironmentVarGuard

     Class used to temporarily set or unset environment variables.
     Instances can be used as a context manager and have a complete
     dictionary interface for querying/modifying the underlying
     ‘os.environ’.  After exit from the context manager all changes to
     environment variables done through this instance will be rolled
     back.

     Changed in version 3.1: Added dictionary interface.

 -- Method: EnvironmentVarGuard.set (envvar, value)

     Temporarily set the environment variable ‘envvar’ to the value of
     ‘value’.

 -- Method: EnvironmentVarGuard.unset (envvar)

     Temporarily unset the environment variable ‘envvar’.

 -- Class: test.support.SuppressCrashReport

     A context manager used to try to prevent crash dialog popups on
     tests that are expected to crash a subprocess.

     On Windows, it disables Windows Error Reporting dialogs using
     SetErrorMode(3).

     On UNIX, *note resource.setrlimit(): 3643. is used to set *note
     resource.RLIMIT_CORE: 3644.’s soft limit to 0 to prevent coredump
     file creation.

     On both platforms, the old value is restored by *note __exit__():
     d5e.

 -- Class: test.support.CleanImport (*module_names)

     A context manager to force import to return a new module reference.
     This is useful for testing module-level behaviors, such as the
     emission of a DeprecationWarning on import.  Example usage:

          with CleanImport('foo'):
              importlib.import_module('foo')  # New reference.

 -- Class: test.support.DirsOnSysPath (*paths)

     A context manager to temporarily add directories to sys.path.

     This makes a copy of *note sys.path: 260, appends any directories
     given as positional arguments, then reverts *note sys.path: 260. to
     the copied settings when the context ends.

     Note that `all' *note sys.path: 260. modifications in the body of
     the context manager, including replacement of the object, will be
     reverted at the end of the block.

 -- Class: test.support.SaveSignals

     Class to save and restore signal handlers registered by the Python
     signal handler.

 -- Class: test.support.Matcher

      -- Method: matches (self, d, **kwargs)

          Try to match a single dict with the supplied arguments.

      -- Method: match_value (self, k, dv, v)

          Try to match a single stored value (`dv') with a supplied
          value (`v').

 -- Class: test.support.WarningsRecorder

     Class used to record warnings for unit tests.  See documentation of
     *note check_warnings(): 35f8. above for more details.

 -- Class: test.support.BasicTestRunner

      -- Method: run (test)

          Run `test' and return the result.

 -- Class: test.support.FakePath (path)

     Simple *note path-like object: 472.  It implements the
     ‘__fspath__()’ method which just returns the `path' argument.  If
     `path' is an exception, it will be raised in ‘__fspath__()’.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3147

   (2) https://www.python.org/dev/peps/pep-0488

   (3) 
https://msdn.microsoft.com/en-us/library/windows/desktop/ms680621.aspx


File: python.info,  Node: test support socket_helper — Utilities for socket tests,  Next: test support script_helper — Utilities for the Python execution tests,  Prev: test support — Utilities for the Python test suite,  Up: Development Tools

5.26.14 ‘test.support.socket_helper’ — Utilities for socket tests
-----------------------------------------------------------------

The *note test.support.socket_helper: 109. module provides support for
socket tests.

New in version 3.9.

 -- Data: test.support.socket_helper.IPV6_ENABLED

     Set to ‘True’ if IPv6 is enabled on this host, ‘False’ otherwise.

 -- Function: test.support.socket_helper.find_unused_port
          (family=socket.AF_INET, socktype=socket.SOCK_STREAM)

     Returns an unused port that should be suitable for binding.  This
     is achieved by creating a temporary socket with the same family and
     type as the ‘sock’ parameter (default is *note AF_INET: 26f8, *note
     SOCK_STREAM: d52.), and binding it to the specified host address
     (defaults to ‘0.0.0.0’) with the port set to 0, eliciting an unused
     ephemeral port from the OS. The temporary socket is then closed and
     deleted, and the ephemeral port is returned.

     Either this method or *note bind_port(): 3652. should be used for
     any tests where a server socket needs to be bound to a particular
     port for the duration of the test.  Which one to use depends on
     whether the calling code is creating a Python socket, or if an
     unused port needs to be provided in a constructor or passed to an
     external program (i.e.  the ‘-accept’ argument to openssl’s
     s_server mode).  Always prefer *note bind_port(): 3652. over *note
     find_unused_port(): 3651. where possible.  Using a hard coded port
     is discouraged since it can make multiple instances of the test
     impossible to run simultaneously, which is a problem for buildbots.

 -- Function: test.support.socket_helper.bind_port (sock, host=HOST)

     Bind the socket to a free port and return the port number.  Relies
     on ephemeral ports in order to ensure we are using an unbound port.
     This is important as many tests may be running simultaneously,
     especially in a buildbot environment.  This method raises an
     exception if the ‘sock.family’ is *note AF_INET: 26f8. and
     ‘sock.type’ is *note SOCK_STREAM: d52, and the socket has
     ‘SO_REUSEADDR’ or ‘SO_REUSEPORT’ set on it.  Tests should never set
     these socket options for TCP/IP sockets.  The only case for setting
     these options is testing multicasting via multiple UDP sockets.

     Additionally, if the ‘SO_EXCLUSIVEADDRUSE’ socket option is
     available (i.e.  on Windows), it will be set on the socket.  This
     will prevent anyone else from binding to our host/port for the
     duration of the test.

 -- Function: test.support.socket_helper.bind_unix_socket (sock, addr)

     Bind a unix socket, raising *note unittest.SkipTest: 9e9. if *note
     PermissionError: 6f6. is raised.

 -- Function: @test.support.socket_helper.skip_unless_bind_unix_socket

     A decorator for running tests that require a functional ‘bind()’
     for Unix sockets.

 -- Function: test.support.socket_helper.transient_internet
          (resource_name, *, timeout=30.0, errnos=())

     A context manager that raises *note ResourceDenied: 35c6. when
     various issues with the internet connection manifest themselves as
     exceptions.


File: python.info,  Node: test support script_helper — Utilities for the Python execution tests,  Next: test support bytecode_helper — Support tools for testing correct bytecode generation,  Prev: test support socket_helper — Utilities for socket tests,  Up: Development Tools

5.26.15 ‘test.support.script_helper’ — Utilities for the Python execution tests
-------------------------------------------------------------------------------

The *note test.support.script_helper: 108. module provides support for
Python’s script execution tests.

 -- Function:
          test.support.script_helper.interpreter_requires_environment ()

     Return ‘True’ if ‘sys.executable interpreter’ requires environment
     variables in order to be able to run at all.

     This is designed to be used with ‘@unittest.skipIf()’ to annotate
     tests that need to use an ‘assert_python*()’ function to launch an
     isolated mode (‘-I’) or no environment mode (‘-E’) sub-interpreter
     process.

     A normal build & test does not run into this situation but it can
     happen when trying to run the standard library test suite from an
     interpreter that doesn’t have an obvious home with Python’s current
     home finding logic.

     Setting *note PYTHONHOME: 5d1. is one way to get most of the
     testsuite to run in that situation.  *note PYTHONPATH: a34. or
     ‘PYTHONUSERSITE’ are other common environment variables that might
     impact whether or not the interpreter can start.

 -- Function: test.support.script_helper.run_python_until_end (*args,
          **env_vars)

     Set up the environment based on `env_vars' for running the
     interpreter in a subprocess.  The values can include ‘__isolated’,
     ‘__cleanenv’, ‘__cwd’, and ‘TERM’.

     Changed in version 3.9: The function no longer strips whitespaces
     from `stderr'.

 -- Function: test.support.script_helper.assert_python_ok (*args,
          **env_vars)

     Assert that running the interpreter with `args' and optional
     environment variables `env_vars' succeeds (‘rc == 0’) and return a
     ‘(return code, stdout, stderr)’ tuple.

     If the ‘__cleanenv’ keyword is set, `env_vars' is used as a fresh
     environment.

     Python is started in isolated mode (command line option ‘-I’),
     except if the ‘__isolated’ keyword is set to ‘False’.

     Changed in version 3.9: The function no longer strips whitespaces
     from `stderr'.

 -- Function: test.support.script_helper.assert_python_failure (*args,
          **env_vars)

     Assert that running the interpreter with `args' and optional
     environment variables `env_vars' fails (‘rc != 0’) and return a
     ‘(return code, stdout, stderr)’ tuple.

     See *note assert_python_ok(): 3658. for more options.

     Changed in version 3.9: The function no longer strips whitespaces
     from `stderr'.

 -- Function: test.support.script_helper.spawn_python (*args,
          stdout=subprocess.PIPE, stderr=subprocess.STDOUT, **kw)

     Run a Python subprocess with the given arguments.

     `kw' is extra keyword args to pass to *note subprocess.Popen():
     3db.  Returns a *note subprocess.Popen: 3db. object.

 -- Function: test.support.script_helper.kill_python (p)

     Run the given *note subprocess.Popen: 3db. process until completion
     and return stdout.

 -- Function: test.support.script_helper.make_script (script_dir,
          script_basename, source, omit_suffix=False)

     Create script containing `source' in path `script_dir' and
     `script_basename'.  If `omit_suffix' is ‘False’, append ‘.py’ to
     the name.  Return the full script path.

 -- Function: test.support.script_helper.make_zip_script (zip_dir,
          zip_basename, script_name, name_in_zip=None)

     Create zip file at `zip_dir' and `zip_basename' with extension
     ‘zip’ which contains the files in `script_name'.  `name_in_zip' is
     the archive name.  Return a tuple containing ‘(full path, full path
     of archive name)’.

 -- Function: test.support.script_helper.make_pkg (pkg_dir,
          init_source='')

     Create a directory named `pkg_dir' containing an ‘__init__’ file
     with `init_source' as its contents.

 -- Function: test.support.script_helper.make_zip_pkg (zip_dir,
          zip_basename, pkg_name, script_basename, source, depth=1,
          compiled=False)

     Create a zip package directory with a path of `zip_dir' and
     `zip_basename' containing an empty ‘__init__’ file and a file
     `script_basename' containing the `source'.  If `compiled' is
     ‘True’, both source files will be compiled and added to the zip
     package.  Return a tuple of the full zip path and the archive name
     for the zip file.


File: python.info,  Node: test support bytecode_helper — Support tools for testing correct bytecode generation,  Prev: test support script_helper — Utilities for the Python execution tests,  Up: Development Tools

5.26.16 ‘test.support.bytecode_helper’ — Support tools for testing correct bytecode generation
----------------------------------------------------------------------------------------------

The *note test.support.bytecode_helper: 107. module provides support for
testing and inspecting bytecode generation.

New in version 3.9.

The module defines the following class:

 -- Class: test.support.bytecode_helper.BytecodeTestCase
          (unittest.TestCase)

     This class has custom assertion methods for inspecting bytecode.

 -- Method: BytecodeTestCase.get_disassembly_as_string (co)

     Return the disassembly of `co' as string.

 -- Method: BytecodeTestCase.assertInBytecode (x, opname,
          argval=_UNSPECIFIED)

     Return instr if `opname' is found, otherwise throws *note
     AssertionError: 240.

 -- Method: BytecodeTestCase.assertNotInBytecode (x, opname,
          argval=_UNSPECIFIED)

     Throws *note AssertionError: 240. if `opname' is found.


File: python.info,  Node: Debugging and Profiling,  Next: Software Packaging and Distribution,  Prev: Development Tools,  Up: The Python Standard Library

5.27 Debugging and Profiling
============================

These libraries help you with Python development: the debugger enables
you to step through code, analyze stack frames and set breakpoints etc.,
and the profilers run code and give you a detailed breakdown of
execution times, allowing you to identify bottlenecks in your programs.
Auditing events provide visibility into runtime behaviors that would
otherwise require intrusive debugging or patching.

* Menu:

* Audit events table::
* bdb — Debugger framework::
* faulthandler — Dump the Python traceback::
* pdb — The Python Debugger::
* The Python Profilers::
* timeit — Measure execution time of small code snippets::
* trace — Trace or track Python statement execution::
* tracemalloc — Trace memory allocations::


File: python.info,  Node: Audit events table,  Next: bdb — Debugger framework,  Up: Debugging and Profiling

5.27.1 Audit events table
-------------------------

This table contains all events raised by *note sys.audit(): 1056. or
*note PySys_Audit(): 1068. calls throughout the CPython runtime and the
standard library.  These calls were added in 3.8.0 or later (see PEP
578(1)).

See *note sys.addaudithook(): 366a. and *note PySys_AddAuditHook():
366b. for information on handling these events.

`CPython implementation detail:' This table is generated from the
CPython documentation, and may not represent events raised by other
implementations.  See your runtime specific documentation for actual
events raised.

Audit event                        Arguments                                                   References
                                                                                               
-------------------------------------------------------------------------------------------------------------------

The following events are raised internally and do not correspond to any
public API of CPython:

Audit event                    Arguments
                               
-------------------------------------------------------------------------------
                               
_winapi.CreateFile             ‘file_name’, ‘desired_access’, ‘share_mode’,
                               ‘creation_disposition’,
                               ‘flags_and_attributes’
                               
                               
_winapi.CreateJunction         ‘src_path’, ‘dst_path’
                               
                               
_winapi.CreateNamedPipe        ‘name’, ‘open_mode’, ‘pipe_mode’
                               
                               
_winapi.CreatePipe

_winapi.CreateProcess          ‘application_name’, ‘command_line’,
                               ‘current_directory’
                               
                               
_winapi.OpenProcess            ‘process_id’, ‘desired_access’
                               
                               
_winapi.TerminateProcess       ‘handle’, ‘exit_code’
                               
                               
ctypes.PyObj_FromPtr           ‘obj’
                               

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0578


File: python.info,  Node: bdb — Debugger framework,  Next: faulthandler — Dump the Python traceback,  Prev: Audit events table,  Up: Debugging and Profiling

5.27.2 ‘bdb’ — Debugger framework
---------------------------------

`Source code:' Lib/bdb.py(1)

__________________________________________________________________

The *note bdb: e. module handles basic debugger functions, like setting
breakpoints or managing execution via the debugger.

The following exception is defined:

 -- Exception: bdb.BdbQuit

     Exception raised by the *note Bdb: d60. class for quitting the
     debugger.

The *note bdb: e. module also defines two classes:

 -- Class: bdb.Breakpoint (self, file, line, temporary=0, cond=None,
          funcname=None)

     This class implements temporary breakpoints, ignore counts,
     disabling and (re-)enabling, and conditionals.

     Breakpoints are indexed by number through a list called
     ‘bpbynumber’ and by ‘(file, line)’ pairs through ‘bplist’.  The
     former points to a single instance of class *note Breakpoint: 366f.
     The latter points to a list of such instances since there may be
     more than one breakpoint per line.

     When creating a breakpoint, its associated filename should be in
     canonical form.  If a `funcname' is defined, a breakpoint hit will
     be counted when the first line of that function is executed.  A
     conditional breakpoint always counts a hit.

     *note Breakpoint: 366f. instances have the following methods:

      -- Method: deleteMe ()

          Delete the breakpoint from the list associated to a file/line.
          If it is the last breakpoint in that position, it also deletes
          the entry for the file/line.

      -- Method: enable ()

          Mark the breakpoint as enabled.

      -- Method: disable ()

          Mark the breakpoint as disabled.

      -- Method: bpformat ()

          Return a string with all the information about the breakpoint,
          nicely formatted:

             * The breakpoint number.

             * If it is temporary or not.

             * Its file,line position.

             * The condition that causes a break.

             * If it must be ignored the next N times.

             * The breakpoint hit count.

          New in version 3.2.

      -- Method: bpprint (out=None)

          Print the output of *note bpformat(): 3673. to the file `out',
          or if it is ‘None’, to standard output.

 -- Class: bdb.Bdb (skip=None)

     The *note Bdb: d60. class acts as a generic Python debugger base
     class.

     This class takes care of the details of the trace facility; a
     derived class should implement user interaction.  The standard
     debugger class (*note pdb.Pdb: 1d3.) is an example.

     The `skip' argument, if given, must be an iterable of glob-style
     module name patterns.  The debugger will not step into frames that
     originate in a module that matches one of these patterns.  Whether
     a frame is considered to originate in a certain module is
     determined by the ‘__name__’ in the frame globals.

     New in version 3.1: The `skip' argument.

     The following methods of *note Bdb: d60. normally don’t need to be
     overridden.

      -- Method: canonic (filename)

          Auxiliary method for getting a filename in a canonical form,
          that is, as a case-normalized (on case-insensitive
          filesystems) absolute path, stripped of surrounding angle
          brackets.

      -- Method: reset ()

          Set the ‘botframe’, ‘stopframe’, ‘returnframe’ and ‘quitting’
          attributes with values ready to start debugging.

      -- Method: trace_dispatch (frame, event, arg)

          This function is installed as the trace function of debugged
          frames.  Its return value is the new trace function (in most
          cases, that is, itself).

          The default implementation decides how to dispatch a frame,
          depending on the type of event (passed as a string) that is
          about to be executed.  `event' can be one of the following:

             * ‘"line"’: A new line of code is going to be executed.

             * ‘"call"’: A function is about to be called, or another
               code block entered.

             * ‘"return"’: A function or other code block is about to
               return.

             * ‘"exception"’: An exception has occurred.

             * ‘"c_call"’: A C function is about to be called.

             * ‘"c_return"’: A C function has returned.

             * ‘"c_exception"’: A C function has raised an exception.

          For the Python events, specialized functions (see below) are
          called.  For the C events, no action is taken.

          The `arg' parameter depends on the previous event.

          See the documentation for *note sys.settrace(): f00. for more
          information on the trace function.  For more information on
          code and frame objects, refer to *note The standard type
          hierarchy: 1553.

      -- Method: dispatch_line (frame)

          If the debugger should stop on the current line, invoke the
          *note user_line(): 3679. method (which should be overridden in
          subclasses).  Raise a *note BdbQuit: 366e. exception if the
          ‘Bdb.quitting’ flag is set (which can be set from *note
          user_line(): 3679.).  Return a reference to the *note
          trace_dispatch(): 3677. method for further tracing in that
          scope.

      -- Method: dispatch_call (frame, arg)

          If the debugger should stop on this function call, invoke the
          *note user_call(): 367b. method (which should be overridden in
          subclasses).  Raise a *note BdbQuit: 366e. exception if the
          ‘Bdb.quitting’ flag is set (which can be set from *note
          user_call(): 367b.).  Return a reference to the *note
          trace_dispatch(): 3677. method for further tracing in that
          scope.

      -- Method: dispatch_return (frame, arg)

          If the debugger should stop on this function return, invoke
          the *note user_return(): 367d. method (which should be
          overridden in subclasses).  Raise a *note BdbQuit: 366e.
          exception if the ‘Bdb.quitting’ flag is set (which can be set
          from *note user_return(): 367d.).  Return a reference to the
          *note trace_dispatch(): 3677. method for further tracing in
          that scope.

      -- Method: dispatch_exception (frame, arg)

          If the debugger should stop at this exception, invokes the
          *note user_exception(): 367f. method (which should be
          overridden in subclasses).  Raise a *note BdbQuit: 366e.
          exception if the ‘Bdb.quitting’ flag is set (which can be set
          from *note user_exception(): 367f.).  Return a reference to
          the *note trace_dispatch(): 3677. method for further tracing
          in that scope.

     Normally derived classes don’t override the following methods, but
     they may if they want to redefine the definition of stopping and
     breakpoints.

      -- Method: stop_here (frame)

          This method checks if the `frame' is somewhere below
          ‘botframe’ in the call stack.  ‘botframe’ is the frame in
          which debugging started.

      -- Method: break_here (frame)

          This method checks if there is a breakpoint in the filename
          and line belonging to `frame' or, at least, in the current
          function.  If the breakpoint is a temporary one, this method
          deletes it.

      -- Method: break_anywhere (frame)

          This method checks if there is a breakpoint in the filename of
          the current frame.

     Derived classes should override these methods to gain control over
     debugger operation.

      -- Method: user_call (frame, argument_list)

          This method is called from *note dispatch_call(): 367a. when
          there is the possibility that a break might be necessary
          anywhere inside the called function.

      -- Method: user_line (frame)

          This method is called from *note dispatch_line(): 3678. when
          either *note stop_here(): 3680. or *note break_here(): 3681.
          yields ‘True’.

      -- Method: user_return (frame, return_value)

          This method is called from *note dispatch_return(): 367c. when
          *note stop_here(): 3680. yields ‘True’.

      -- Method: user_exception (frame, exc_info)

          This method is called from *note dispatch_exception(): 367e.
          when *note stop_here(): 3680. yields ‘True’.

      -- Method: do_clear (arg)

          Handle how a breakpoint must be removed when it is a temporary
          one.

          This method must be implemented by derived classes.

     Derived classes and clients can call the following methods to
     affect the stepping state.

      -- Method: set_step ()

          Stop after one line of code.

      -- Method: set_next (frame)

          Stop on the next line in or below the given frame.

      -- Method: set_return (frame)

          Stop when returning from the given frame.

      -- Method: set_until (frame)

          Stop when the line with the line no greater than the current
          one is reached or when returning from current frame.

      -- Method: set_trace ([frame])

          Start debugging from `frame'.  If `frame' is not specified,
          debugging starts from caller’s frame.

      -- Method: set_continue ()

          Stop only at breakpoints or when finished.  If there are no
          breakpoints, set the system trace function to ‘None’.

      -- Method: set_quit ()

          Set the ‘quitting’ attribute to ‘True’.  This raises *note
          BdbQuit: 366e. in the next call to one of the ‘dispatch_*()’
          methods.

     Derived classes and clients can call the following methods to
     manipulate breakpoints.  These methods return a string containing
     an error message if something went wrong, or ‘None’ if all is well.

      -- Method: set_break (filename, lineno, temporary=0, cond,
               funcname)

          Set a new breakpoint.  If the `lineno' line doesn’t exist for
          the `filename' passed as argument, return an error message.
          The `filename' should be in canonical form, as described in
          the *note canonic(): 3675. method.

      -- Method: clear_break (filename, lineno)

          Delete the breakpoints in `filename' and `lineno'.  If none
          were set, an error message is returned.

      -- Method: clear_bpbynumber (arg)

          Delete the breakpoint which has the index `arg' in the
          ‘Breakpoint.bpbynumber’.  If `arg' is not numeric or out of
          range, return an error message.

      -- Method: clear_all_file_breaks (filename)

          Delete all breakpoints in `filename'.  If none were set, an
          error message is returned.

      -- Method: clear_all_breaks ()

          Delete all existing breakpoints.

      -- Method: get_bpbynumber (arg)

          Return a breakpoint specified by the given number.  If `arg'
          is a string, it will be converted to a number.  If `arg' is a
          non-numeric string, if the given breakpoint never existed or
          has been deleted, a *note ValueError: 16d. is raised.

          New in version 3.2.

      -- Method: get_break (filename, lineno)

          Check if there is a breakpoint for `lineno' of `filename'.

      -- Method: get_breaks (filename, lineno)

          Return all breakpoints for `lineno' in `filename', or an empty
          list if none are set.

      -- Method: get_file_breaks (filename)

          Return all breakpoints in `filename', or an empty list if none
          are set.

      -- Method: get_all_breaks ()

          Return all breakpoints that are set.

     Derived classes and clients can call the following methods to get a
     data structure representing a stack trace.

      -- Method: get_stack (f, t)

          Get a list of records for a frame and all higher (calling) and
          lower frames, and the size of the higher part.

      -- Method: format_stack_entry (frame_lineno, lprefix=': ')

          Return a string with information about a stack entry,
          identified by a ‘(frame, lineno)’ tuple:

             * The canonical form of the filename which contains the
               frame.

             * The function name, or ‘"<lambda>"’.

             * The input arguments.

             * The return value.

             * The line of code (if it exists).

     The following two methods can be called by clients to use a
     debugger to debug a *note statement: 1cef, given as a string.

      -- Method: run (cmd, globals=None, locals=None)

          Debug a statement executed via the *note exec(): d0c.
          function.  `globals' defaults to ‘__main__.__dict__’, `locals'
          defaults to `globals'.

      -- Method: runeval (expr, globals=None, locals=None)

          Debug an expression executed via the *note eval(): c61.
          function.  `globals' and `locals' have the same meaning as in
          *note run(): 3697.

      -- Method: runctx (cmd, globals, locals)

          For backwards compatibility.  Calls the *note run(): 3697.
          method.

      -- Method: runcall (func, /, *args, **kwds)

          Debug a single function call, and return its result.

Finally, the module defines the following functions:

 -- Function: bdb.checkfuncname (b, frame)

     Check whether we should break here, depending on the way the
     breakpoint `b' was set.

     If it was set via line number, it checks if ‘b.line’ is the same as
     the one in the frame also passed as argument.  If the breakpoint
     was set via function name, we have to check we are in the right
     frame (the right function) and if we are in its first executable
     line.

 -- Function: bdb.effective (file, line, frame)

     Determine if there is an effective (active) breakpoint at this line
     of code.  Return a tuple of the breakpoint and a boolean that
     indicates if it is ok to delete a temporary breakpoint.  Return
     ‘(None, None)’ if there is no matching breakpoint.

 -- Function: bdb.set_trace ()

     Start debugging with a *note Bdb: d60. instance from caller’s
     frame.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/bdb.py


File: python.info,  Node: faulthandler — Dump the Python traceback,  Next: pdb — The Python Debugger,  Prev: bdb — Debugger framework,  Up: Debugging and Profiling

5.27.3 ‘faulthandler’ — Dump the Python traceback
-------------------------------------------------

New in version 3.3.

__________________________________________________________________

This module contains functions to dump Python tracebacks explicitly, on
a fault, after a timeout, or on a user signal.  Call *note
faulthandler.enable(): 642. to install fault handlers for the ‘SIGSEGV’,
‘SIGFPE’, ‘SIGABRT’, ‘SIGBUS’, and ‘SIGILL’ signals.  You can also
enable them at startup by setting the *note PYTHONFAULTHANDLER: aa7.
environment variable or by using the *note -X: 290. ‘faulthandler’
command line option.

The fault handler is compatible with system fault handlers like Apport
or the Windows fault handler.  The module uses an alternative stack for
signal handlers if the ‘sigaltstack()’ function is available.  This
allows it to dump the traceback even on a stack overflow.

The fault handler is called on catastrophic cases and therefore can only
use signal-safe functions (e.g.  it cannot allocate memory on the heap).
Because of this limitation traceback dumping is minimal compared to
normal Python tracebacks:

   * Only ASCII is supported.  The ‘backslashreplace’ error handler is
     used on encoding.

   * Each string is limited to 500 characters.

   * Only the filename, the function name and the line number are
     displayed.  (no source code)

   * It is limited to 100 frames and 100 threads.

   * The order is reversed: the most recent call is shown first.

By default, the Python traceback is written to *note sys.stderr: 1ea.
To see tracebacks, applications must be run in the terminal.  A log file
can alternatively be passed to *note faulthandler.enable(): 642.

The module is implemented in C, so tracebacks can be dumped on a crash
or when Python is deadlocked.

The *note Python Development Mode: 160. calls *note
faulthandler.enable(): 642. at Python startup.

* Menu:

* Dumping the traceback::
* Fault handler state::
* Dumping the tracebacks after a timeout::
* Dumping the traceback on a user signal::
* Issue with file descriptors::
* Example: Example<15>.


File: python.info,  Node: Dumping the traceback,  Next: Fault handler state,  Up: faulthandler — Dump the Python traceback

5.27.3.1 Dumping the traceback
..............................

 -- Function: faulthandler.dump_traceback (file=sys.stderr,
          all_threads=True)

     Dump the tracebacks of all threads into `file'.  If `all_threads'
     is ‘False’, dump only the current thread.

     Changed in version 3.5: Added support for passing file descriptor
     to this function.


File: python.info,  Node: Fault handler state,  Next: Dumping the tracebacks after a timeout,  Prev: Dumping the traceback,  Up: faulthandler — Dump the Python traceback

5.27.3.2 Fault handler state
............................

 -- Function: faulthandler.enable (file=sys.stderr, all_threads=True)

     Enable the fault handler: install handlers for the ‘SIGSEGV’,
     ‘SIGFPE’, ‘SIGABRT’, ‘SIGBUS’ and ‘SIGILL’ signals to dump the
     Python traceback.  If `all_threads' is ‘True’, produce tracebacks
     for every running thread.  Otherwise, dump only the current thread.

     The `file' must be kept open until the fault handler is disabled:
     see *note issue with file descriptors: 36a1.

     Changed in version 3.5: Added support for passing file descriptor
     to this function.

     Changed in version 3.6: On Windows, a handler for Windows exception
     is also installed.

 -- Function: faulthandler.disable ()

     Disable the fault handler: uninstall the signal handlers installed
     by *note enable(): 642.

 -- Function: faulthandler.is_enabled ()

     Check if the fault handler is enabled.


File: python.info,  Node: Dumping the tracebacks after a timeout,  Next: Dumping the traceback on a user signal,  Prev: Fault handler state,  Up: faulthandler — Dump the Python traceback

5.27.3.3 Dumping the tracebacks after a timeout
...............................................

 -- Function: faulthandler.dump_traceback_later (timeout, repeat=False,
          file=sys.stderr, exit=False)

     Dump the tracebacks of all threads, after a timeout of `timeout'
     seconds, or every `timeout' seconds if `repeat' is ‘True’.  If
     `exit' is ‘True’, call ‘_exit()’ with status=1 after dumping the
     tracebacks.  (Note ‘_exit()’ exits the process immediately, which
     means it doesn’t do any cleanup like flushing file buffers.)  If
     the function is called twice, the new call replaces previous
     parameters and resets the timeout.  The timer has a sub-second
     resolution.

     The `file' must be kept open until the traceback is dumped or *note
     cancel_dump_traceback_later(): 36a5. is called: see *note issue
     with file descriptors: 36a1.

     This function is implemented using a watchdog thread.

     Changed in version 3.7: This function is now always available.

     Changed in version 3.5: Added support for passing file descriptor
     to this function.

 -- Function: faulthandler.cancel_dump_traceback_later ()

     Cancel the last call to *note dump_traceback_later(): 7cc.


File: python.info,  Node: Dumping the traceback on a user signal,  Next: Issue with file descriptors,  Prev: Dumping the tracebacks after a timeout,  Up: faulthandler — Dump the Python traceback

5.27.3.4 Dumping the traceback on a user signal
...............................................

 -- Function: faulthandler.register (signum, file=sys.stderr,
          all_threads=True, chain=False)

     Register a user signal: install a handler for the `signum' signal
     to dump the traceback of all threads, or of the current thread if
     `all_threads' is ‘False’, into `file'.  Call the previous handler
     if chain is ‘True’.

     The `file' must be kept open until the signal is unregistered by
     *note unregister(): 36a7.: see *note issue with file descriptors:
     36a1.

     Not available on Windows.

     Changed in version 3.5: Added support for passing file descriptor
     to this function.

 -- Function: faulthandler.unregister (signum)

     Unregister a user signal: uninstall the handler of the `signum'
     signal installed by *note register(): 7ca.  Return ‘True’ if the
     signal was registered, ‘False’ otherwise.

     Not available on Windows.


File: python.info,  Node: Issue with file descriptors,  Next: Example<15>,  Prev: Dumping the traceback on a user signal,  Up: faulthandler — Dump the Python traceback

5.27.3.5 Issue with file descriptors
....................................

*note enable(): 642, *note dump_traceback_later(): 7cc. and *note
register(): 7ca. keep the file descriptor of their `file' argument.  If
the file is closed and its file descriptor is reused by a new file, or
if *note os.dup2(): 4c5. is used to replace the file descriptor, the
traceback will be written into a different file.  Call these functions
again each time that the file is replaced.


File: python.info,  Node: Example<15>,  Prev: Issue with file descriptors,  Up: faulthandler — Dump the Python traceback

5.27.3.6 Example
................

Example of a segmentation fault on Linux with and without enabling the
fault handler:

     $ python3 -c "import ctypes; ctypes.string_at(0)"
     Segmentation fault

     $ python3 -q -X faulthandler
     >>> import ctypes
     >>> ctypes.string_at(0)
     Fatal Python error: Segmentation fault

     Current thread 0x00007fb899f39700 (most recent call first):
       File "/home/python/cpython/Lib/ctypes/__init__.py", line 486 in string_at
       File "<stdin>", line 1 in <module>
     Segmentation fault


File: python.info,  Node: pdb — The Python Debugger,  Next: The Python Profilers,  Prev: faulthandler — Dump the Python traceback,  Up: Debugging and Profiling

5.27.4 ‘pdb’ — The Python Debugger
----------------------------------

`Source code:' Lib/pdb.py(1)

__________________________________________________________________

The module *note pdb: c9. defines an interactive source code debugger
for Python programs.  It supports setting (conditional) breakpoints and
single stepping at the source line level, inspection of stack frames,
source code listing, and evaluation of arbitrary Python code in the
context of any stack frame.  It also supports post-mortem debugging and
can be called under program control.

The debugger is extensible – it is actually defined as the class *note
Pdb: 1d3.  This is currently undocumented but easily understood by
reading the source.  The extension interface uses the modules *note bdb:
e. and *note cmd: 19.

The debugger’s prompt is ‘(Pdb)’.  Typical usage to run a program under
control of the debugger is:

     >>> import pdb
     >>> import mymodule
     >>> pdb.run('mymodule.test()')
     > <string>(0)?()
     (Pdb) continue
     > <string>(1)?()
     (Pdb) continue
     NameError: 'spam'
     > <string>(1)?()
     (Pdb)

Changed in version 3.3: Tab-completion via the *note readline: de.
module is available for commands and command arguments, e.g.  the
current global and local names are offered as arguments of the ‘p’
command.

‘pdb.py’ can also be invoked as a script to debug other scripts.  For
example:

     python3 -m pdb myscript.py

When invoked as a script, pdb will automatically enter post-mortem
debugging if the program being debugged exits abnormally.  After
post-mortem debugging (or after normal exit of the program), pdb will
restart the program.  Automatic restarting preserves pdb’s state (such
as breakpoints) and in most cases is more useful than quitting the
debugger upon program’s exit.

New in version 3.2: ‘pdb.py’ now accepts a ‘-c’ option that executes
commands as if given in a ‘.pdbrc’ file, see *note Debugger Commands:
36ad.

New in version 3.7: ‘pdb.py’ now accepts a ‘-m’ option that execute
modules similar to the way ‘python3 -m’ does.  As with a script, the
debugger will pause execution just before the first line of the module.

The typical usage to break into the debugger is to insert:

     import pdb; pdb.set_trace()

at the location you want to break into the debugger, and then run the
program.  You can then step through the code following this statement,
and continue running without the debugger using the *note continue:
36ae. command.

New in version 3.7: The built-in *note breakpoint(): 40b, when called
with defaults, can be used instead of ‘import pdb; pdb.set_trace()’.

The typical usage to inspect a crashed program is:

     >>> import pdb
     >>> import mymodule
     >>> mymodule.test()
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
       File "./mymodule.py", line 4, in test
         test2()
       File "./mymodule.py", line 3, in test2
         print(spam)
     NameError: spam
     >>> pdb.pm()
     > ./mymodule.py(3)test2()
     -> print(spam)
     (Pdb)

The module defines the following functions; each enters the debugger in
a slightly different way:

 -- Function: pdb.run (statement, globals=None, locals=None)

     Execute the `statement' (given as a string or a code object) under
     debugger control.  The debugger prompt appears before any code is
     executed; you can set breakpoints and type *note continue: 36ae, or
     you can step through the statement using *note step: 36af. or *note
     next: 36b0. (all these commands are explained below).  The optional
     `globals' and `locals' arguments specify the environment in which
     the code is executed; by default the dictionary of the module *note
     __main__: 1. is used.  (See the explanation of the built-in *note
     exec(): d0c. or *note eval(): c61. functions.)

 -- Function: pdb.runeval (expression, globals=None, locals=None)

     Evaluate the `expression' (given as a string or a code object)
     under debugger control.  When *note runeval(): 36b1. returns, it
     returns the value of the expression.  Otherwise this function is
     similar to *note run(): 34af.

 -- Function: pdb.runcall (function, *args, **kwds)

     Call the `function' (a function or method object, not a string)
     with the given arguments.  When *note runcall(): 36b2. returns, it
     returns whatever the function call returned.  The debugger prompt
     appears as soon as the function is entered.

 -- Function: pdb.set_trace (*, header=None)

     Enter the debugger at the calling stack frame.  This is useful to
     hard-code a breakpoint at a given point in a program, even if the
     code is not otherwise being debugged (e.g.  when an assertion
     fails).  If given, `header' is printed to the console just before
     debugging begins.

     Changed in version 3.7: The keyword-only argument `header'.

 -- Function: pdb.post_mortem (traceback=None)

     Enter post-mortem debugging of the given `traceback' object.  If no
     `traceback' is given, it uses the one of the exception that is
     currently being handled (an exception must be being handled if the
     default is to be used).

 -- Function: pdb.pm ()

     Enter post-mortem debugging of the traceback found in *note
     sys.last_traceback: 36b4.

The ‘run*’ functions and *note set_trace(): 4c9. are aliases for
instantiating the *note Pdb: 1d3. class and calling the method of the
same name.  If you want to access further features, you have to do this
yourself:

 -- Class: pdb.Pdb (completekey='tab', stdin=None, stdout=None,
          skip=None, nosigint=False, readrc=True)

     *note Pdb: 1d3. is the debugger class.

     The `completekey', `stdin' and `stdout' arguments are passed to the
     underlying *note cmd.Cmd: 3276. class; see the description there.

     The `skip' argument, if given, must be an iterable of glob-style
     module name patterns.  The debugger will not step into frames that
     originate in a module that matches one of these patterns.  (2)

     By default, Pdb sets a handler for the SIGINT signal (which is sent
     when the user presses ‘Ctrl-C’ on the console) when you give a
     ‘continue’ command.  This allows you to break into the debugger
     again by pressing ‘Ctrl-C’.  If you want Pdb not to touch the
     SIGINT handler, set `nosigint' to true.

     The `readrc' argument defaults to true and controls whether Pdb
     will load .pdbrc files from the filesystem.

     Example call to enable tracing with `skip':

          import pdb; pdb.Pdb(skip=['django.*']).set_trace()

     Raises an *note auditing event: fa1. ‘pdb.Pdb’ with no arguments.

     New in version 3.1: The `skip' argument.

     New in version 3.2: The `nosigint' argument.  Previously, a SIGINT
     handler was never set by Pdb.

     Changed in version 3.6: The `readrc' argument.

      -- Method: run (statement, globals=None, locals=None)
      -- Method: runeval (expression, globals=None, locals=None)
      -- Method: runcall (function, *args, **kwds)
      -- Method: set_trace ()

          See the documentation for the functions explained above.

* Menu:

* Debugger Commands::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/pdb.py

   (2) (1) Whether a frame is considered to originate in a certain
module is determined by the ‘__name__’ in the frame globals.


File: python.info,  Node: Debugger Commands,  Up: pdb — The Python Debugger

5.27.4.1 Debugger Commands
..........................

The commands recognized by the debugger are listed below.  Most commands
can be abbreviated to one or two letters as indicated; e.g.  ‘h(elp)’
means that either ‘h’ or ‘help’ can be used to enter the help command
(but not ‘he’ or ‘hel’, nor ‘H’ or ‘Help’ or ‘HELP’).  Arguments to
commands must be separated by whitespace (spaces or tabs).  Optional
arguments are enclosed in square brackets (‘[]’) in the command syntax;
the square brackets must not be typed.  Alternatives in the command
syntax are separated by a vertical bar (‘|’).

Entering a blank line repeats the last command entered.  Exception: if
the last command was a *note list: 36ba. command, the next 11 lines are
listed.

Commands that the debugger doesn’t recognize are assumed to be Python
statements and are executed in the context of the program being
debugged.  Python statements can also be prefixed with an exclamation
point (‘!’).  This is a powerful way to inspect the program being
debugged; it is even possible to change a variable or call a function.
When an exception occurs in such a statement, the exception name is
printed but the debugger’s state is not changed.

The debugger supports *note aliases: 36bb.  Aliases can have parameters
which allows one a certain level of adaptability to the context under
examination.

Multiple commands may be entered on a single line, separated by ‘;;’.
(A single ‘;’ is not used as it is the separator for multiple commands
in a line that is passed to the Python parser.)  No intelligence is
applied to separating the commands; the input is split at the first ‘;;’
pair, even if it is in the middle of a quoted string.

If a file ‘.pdbrc’ exists in the user’s home directory or in the current
directory, it is read in and executed as if it had been typed at the
debugger prompt.  This is particularly useful for aliases.  If both
files exist, the one in the home directory is read first and aliases
defined there can be overridden by the local file.

Changed in version 3.2: ‘.pdbrc’ can now contain commands that continue
debugging, such as *note continue: 36ae. or *note next: 36b0.
Previously, these commands had no effect.

 -- Pdbcommand: h(elp) [command]

     Without argument, print the list of available commands.  With a
     `command' as argument, print help about that command.  ‘help pdb’
     displays the full documentation (the docstring of the *note pdb:
     c9. module).  Since the `command' argument must be an identifier,
     ‘help exec’ must be entered to get help on the ‘!’ command.

 -- Pdbcommand: w(here)

     Print a stack trace, with the most recent frame at the bottom.  An
     arrow indicates the current frame, which determines the context of
     most commands.

 -- Pdbcommand: d(own) [count]

     Move the current frame `count' (default one) levels down in the
     stack trace (to a newer frame).

 -- Pdbcommand: u(p) [count]

     Move the current frame `count' (default one) levels up in the stack
     trace (to an older frame).

 -- Pdbcommand: b(reak) [([filename:]lineno | function) [, condition]]

     With a `lineno' argument, set a break there in the current file.
     With a `function' argument, set a break at the first executable
     statement within that function.  The line number may be prefixed
     with a filename and a colon, to specify a breakpoint in another
     file (probably one that hasn’t been loaded yet).  The file is
     searched on *note sys.path: 260.  Note that each breakpoint is
     assigned a number to which all the other breakpoint commands refer.

     If a second argument is present, it is an expression which must
     evaluate to true before the breakpoint is honored.

     Without argument, list all breaks, including for each breakpoint,
     the number of times that breakpoint has been hit, the current
     ignore count, and the associated condition if any.

 -- Pdbcommand: tbreak [([filename:]lineno | function) [, condition]]

     Temporary breakpoint, which is removed automatically when it is
     first hit.  The arguments are the same as for *note break: 36c0.

 -- Pdbcommand: cl(ear) [filename:lineno | bpnumber ...]

     With a `filename:lineno' argument, clear all the breakpoints at
     this line.  With a space separated list of breakpoint numbers,
     clear those breakpoints.  Without argument, clear all breaks (but
     first ask confirmation).

 -- Pdbcommand: disable [bpnumber ...]

     Disable the breakpoints given as a space separated list of
     breakpoint numbers.  Disabling a breakpoint means it cannot cause
     the program to stop execution, but unlike clearing a breakpoint, it
     remains in the list of breakpoints and can be (re-)enabled.

 -- Pdbcommand: enable [bpnumber ...]

     Enable the breakpoints specified.

 -- Pdbcommand: ignore bpnumber [count]

     Set the ignore count for the given breakpoint number.  If count is
     omitted, the ignore count is set to 0.  A breakpoint becomes active
     when the ignore count is zero.  When non-zero, the count is
     decremented each time the breakpoint is reached and the breakpoint
     is not disabled and any associated condition evaluates to true.

 -- Pdbcommand: condition bpnumber [condition]

     Set a new `condition' for the breakpoint, an expression which must
     evaluate to true before the breakpoint is honored.  If `condition'
     is absent, any existing condition is removed; i.e., the breakpoint
     is made unconditional.

 -- Pdbcommand: commands [bpnumber]

     Specify a list of commands for breakpoint number `bpnumber'.  The
     commands themselves appear on the following lines.  Type a line
     containing just ‘end’ to terminate the commands.  An example:

          (Pdb) commands 1
          (com) p some_variable
          (com) end
          (Pdb)

     To remove all commands from a breakpoint, type ‘commands’ and
     follow it immediately with ‘end’; that is, give no commands.

     With no `bpnumber' argument, ‘commands’ refers to the last
     breakpoint set.

     You can use breakpoint commands to start your program up again.
     Simply use the *note continue: 36ae. command, or *note step: 36af,
     or any other command that resumes execution.

     Specifying any command resuming execution (currently *note
     continue: 36ae, *note step: 36af, *note next: 36b0, *note return:
     36c8, *note jump: 36c9, *note quit: 36ca. and their abbreviations)
     terminates the command list (as if that command was immediately
     followed by end).  This is because any time you resume execution
     (even with a simple next or step), you may encounter another
     breakpoint—which could have its own command list, leading to
     ambiguities about which list to execute.

     If you use the ‘silent’ command in the command list, the usual
     message about stopping at a breakpoint is not printed.  This may be
     desirable for breakpoints that are to print a specific message and
     then continue.  If none of the other commands print anything, you
     see no sign that the breakpoint was reached.

 -- Pdbcommand: s(tep)

     Execute the current line, stop at the first possible occasion
     (either in a function that is called or on the next line in the
     current function).

 -- Pdbcommand: n(ext)

     Continue execution until the next line in the current function is
     reached or it returns.  (The difference between *note next: 36b0.
     and *note step: 36af. is that *note step: 36af. stops inside a
     called function, while *note next: 36b0. executes called functions
     at (nearly) full speed, only stopping at the next line in the
     current function.)

 -- Pdbcommand: unt(il) [lineno]

     Without argument, continue execution until the line with a number
     greater than the current one is reached.

     With a line number, continue execution until a line with a number
     greater or equal to that is reached.  In both cases, also stop when
     the current frame returns.

     Changed in version 3.2: Allow giving an explicit line number.

 -- Pdbcommand: r(eturn)

     Continue execution until the current function returns.

 -- Pdbcommand: c(ont(inue))

     Continue execution, only stop when a breakpoint is encountered.

 -- Pdbcommand: j(ump) lineno

     Set the next line that will be executed.  Only available in the
     bottom-most frame.  This lets you jump back and execute code again,
     or jump forward to skip code that you don’t want to run.

     It should be noted that not all jumps are allowed – for instance it
     is not possible to jump into the middle of a *note for: cfa. loop
     or out of a *note finally: 2bc. clause.

 -- Pdbcommand: l(ist) [first[, last]]

     List source code for the current file.  Without arguments, list 11
     lines around the current line or continue the previous listing.
     With ‘.’ as argument, list 11 lines around the current line.  With
     one argument, list 11 lines around at that line.  With two
     arguments, list the given range; if the second argument is less
     than the first, it is interpreted as a count.

     The current line in the current frame is indicated by ‘->’.  If an
     exception is being debugged, the line where the exception was
     originally raised or propagated is indicated by ‘>>’, if it differs
     from the current line.

     New in version 3.2: The ‘>>’ marker.

 -- Pdbcommand: ll | longlist

     List all source code for the current function or frame.
     Interesting lines are marked as for *note list: 36ba.

     New in version 3.2.

 -- Pdbcommand: a(rgs)

     Print the argument list of the current function.

 -- Pdbcommand: p expression

     Evaluate the `expression' in the current context and print its
     value.

          Note: ‘print()’ can also be used, but is not a debugger
          command — this executes the Python *note print(): 971.
          function.

 -- Pdbcommand: pp expression

     Like the *note p: 972. command, except the value of the expression
     is pretty-printed using the *note pprint: d2. module.

 -- Pdbcommand: whatis expression

     Print the type of the `expression'.

 -- Pdbcommand: source expression

     Try to get source code for the given object and display it.

     New in version 3.2.

 -- Pdbcommand: display [expression]

     Display the value of the expression if it changed, each time
     execution stops in the current frame.

     Without expression, list all display expressions for the current
     frame.

     New in version 3.2.

 -- Pdbcommand: undisplay [expression]

     Do not display the expression any more in the current frame.
     Without expression, clear all display expressions for the current
     frame.

     New in version 3.2.

 -- Pdbcommand: interact

     Start an interactive interpreter (using the *note code: 1a. module)
     whose global namespace contains all the (global and local) names
     found in the current scope.

     New in version 3.2.

 -- Pdbcommand: alias [name [command]]

     Create an alias called `name' that executes `command'.  The command
     must `not' be enclosed in quotes.  Replaceable parameters can be
     indicated by ‘%1’, ‘%2’, and so on, while ‘%*’ is replaced by all
     the parameters.  If no command is given, the current alias for
     `name' is shown.  If no arguments are given, all aliases are
     listed.

     Aliases may be nested and can contain anything that can be legally
     typed at the pdb prompt.  Note that internal pdb commands `can' be
     overridden by aliases.  Such a command is then hidden until the
     alias is removed.  Aliasing is recursively applied to the first
     word of the command line; all other words in the line are left
     alone.

     As an example, here are two useful aliases (especially when placed
     in the ‘.pdbrc’ file):

          # Print instance variables (usage "pi classInst")
          alias pi for k in %1.__dict__.keys(): print("%1.",k,"=",%1.__dict__[k])
          # Print instance variables in self
          alias ps pi self

 -- Pdbcommand: unalias name

     Delete the specified alias.

 -- Pdbcommand: ! statement

     Execute the (one-line) `statement' in the context of the current
     stack frame.  The exclamation point can be omitted unless the first
     word of the statement resembles a debugger command.  To set a
     global variable, you can prefix the assignment command with a *note
     global: 1378. statement on the same line, e.g.:

          (Pdb) global list_options; list_options = ['-l']
          (Pdb)

 -- Pdbcommand: run [args ...]
 -- Pdbcommand: restart [args ...]

     Restart the debugged Python program.  If an argument is supplied,
     it is split with *note shlex: e8. and the result is used as the new
     *note sys.argv: cc6.  History, breakpoints, actions and debugger
     options are preserved.  *note restart: 36d8. is an alias for *note
     run: 36d7.

 -- Pdbcommand: q(uit)

     Quit from the debugger.  The program being executed is aborted.

 -- Pdbcommand: debug code

     Enter a recursive debugger that steps through the code argument
     (which is an arbitrary expression or statement to be executed in
     the current environment).

 -- Pdbcommand: retval

     Print the return value for the last return of a function.


File: python.info,  Node: The Python Profilers,  Next: timeit — Measure execution time of small code snippets,  Prev: pdb — The Python Debugger,  Up: Debugging and Profiling

5.27.5 The Python Profilers
---------------------------

`Source code:' Lib/profile.py(1) and Lib/pstats.py(2)

__________________________________________________________________

* Menu:

* Introduction to the profilers::
* Instant User’s Manual::
* profile and cProfile Module Reference::
* The Stats Class::
* What Is Deterministic Profiling?::
* Limitations::
* Calibration::
* Using a custom timer::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/profile.py

   (2) https://github.com/python/cpython/tree/3.9/Lib/pstats.py


File: python.info,  Node: Introduction to the profilers,  Next: Instant User’s Manual,  Up: The Python Profilers

5.27.5.1 Introduction to the profilers
......................................

*note cProfile: 27. and *note profile: d3. provide `deterministic
profiling' of Python programs.  A `profile' is a set of statistics that
describes how often and for how long various parts of the program
executed.  These statistics can be formatted into reports via the *note
pstats: d4. module.

The Python standard library provides two different implementations of
the same profiling interface:

  1. *note cProfile: 27. is recommended for most users; it’s a C
     extension with reasonable overhead that makes it suitable for
     profiling long-running programs.  Based on ‘lsprof’, contributed by
     Brett Rosen and Ted Czotter.

  2. *note profile: d3, a pure Python module whose interface is imitated
     by *note cProfile: 27, but which adds significant overhead to
     profiled programs.  If you’re trying to extend the profiler in some
     way, the task might be easier with this module.  Originally
     designed and written by Jim Roskind.

     Note: The profiler modules are designed to provide an execution
     profile for a given program, not for benchmarking purposes (for
     that, there is *note timeit: 10d. for reasonably accurate results).
     This particularly applies to benchmarking Python code against C
     code: the profilers introduce overhead for Python code, but not for
     C-level functions, and so the C code would seem faster than any
     Python one.


File: python.info,  Node: Instant User’s Manual,  Next: profile and cProfile Module Reference,  Prev: Introduction to the profilers,  Up: The Python Profilers

5.27.5.2 Instant User’s Manual
..............................

This section is provided for users that “don’t want to read the manual.”
It provides a very brief overview, and allows a user to rapidly perform
profiling on an existing application.

To profile a function that takes a single argument, you can do:

     import cProfile
     import re
     cProfile.run('re.compile("foo|bar")')

(Use *note profile: d3. instead of *note cProfile: 27. if the latter is
not available on your system.)

The above action would run *note re.compile(): 54d. and print profile
results like the following:

           197 function calls (192 primitive calls) in 0.002 seconds

     Ordered by: standard name

     ncalls  tottime  percall  cumtime  percall filename:lineno(function)
          1    0.000    0.000    0.001    0.001 <string>:1(<module>)
          1    0.000    0.000    0.001    0.001 re.py:212(compile)
          1    0.000    0.000    0.001    0.001 re.py:268(_compile)
          1    0.000    0.000    0.000    0.000 sre_compile.py:172(_compile_charset)
          1    0.000    0.000    0.000    0.000 sre_compile.py:201(_optimize_charset)
          4    0.000    0.000    0.000    0.000 sre_compile.py:25(_identityfunction)
        3/1    0.000    0.000    0.000    0.000 sre_compile.py:33(_compile)

The first line indicates that 197 calls were monitored.  Of those calls,
192 were `primitive', meaning that the call was not induced via
recursion.  The next line: ‘Ordered by: standard name’, indicates that
the text string in the far right column was used to sort the output.
The column headings include:

ncalls

     for the number of calls.

tottime

     for the total time spent in the given function (and excluding time
     made in calls to sub-functions)

percall

     is the quotient of ‘tottime’ divided by ‘ncalls’

cumtime

     is the cumulative time spent in this and all subfunctions (from
     invocation till exit).  This figure is accurate `even' for
     recursive functions.

percall

     is the quotient of ‘cumtime’ divided by primitive calls

filename:lineno(function)

     provides the respective data of each function

When there are two numbers in the first column (for example ‘3/1’), it
means that the function recursed.  The second value is the number of
primitive calls and the former is the total number of calls.  Note that
when the function does not recurse, these two values are the same, and
only the single figure is printed.

Instead of printing the output at the end of the profile run, you can
save the results to a file by specifying a filename to the ‘run()’
function:

     import cProfile
     import re
     cProfile.run('re.compile("foo|bar")', 'restats')

The *note pstats.Stats: 36e2. class reads profile results from a file
and formats them in various ways.

The files *note cProfile: 27. and *note profile: d3. can also be invoked
as a script to profile another script.  For example:

     python -m cProfile [-o output_file] [-s sort_order] (-m module | myscript.py)

‘-o’ writes the profile results to a file instead of to stdout

‘-s’ specifies one of the *note sort_stats(): 36e3. sort values to sort
the output by.  This only applies when ‘-o’ is not supplied.

‘-m’ specifies that a module is being profiled instead of a script.

     New in version 3.7: Added the ‘-m’ option to *note cProfile: 27.

     New in version 3.8: Added the ‘-m’ option to *note profile: d3.

The *note pstats: d4. module’s *note Stats: 36e2. class has a variety of
methods for manipulating and printing the data saved into a profile
results file:

     import pstats
     from pstats import SortKey
     p = pstats.Stats('restats')
     p.strip_dirs().sort_stats(-1).print_stats()

The *note strip_dirs(): 36e4. method removed the extraneous path from
all the module names.  The *note sort_stats(): 36e3. method sorted all
the entries according to the standard module/line/name string that is
printed.  The *note print_stats(): 36e5. method printed out all the
statistics.  You might try the following sort calls:

     p.sort_stats(SortKey.NAME)
     p.print_stats()

The first call will actually sort the list by function name, and the
second call will print out the statistics.  The following are some
interesting calls to experiment with:

     p.sort_stats(SortKey.CUMULATIVE).print_stats(10)

This sorts the profile by cumulative time in a function, and then only
prints the ten most significant lines.  If you want to understand what
algorithms are taking time, the above line is what you would use.

If you were looking to see what functions were looping a lot, and taking
a lot of time, you would do:

     p.sort_stats(SortKey.TIME).print_stats(10)

to sort according to time spent within each function, and then print the
statistics for the top ten functions.

You might also try:

     p.sort_stats(SortKey.FILENAME).print_stats('__init__')

This will sort all the statistics by file name, and then print out
statistics for only the class init methods (since they are spelled with
‘__init__’ in them).  As one final example, you could try:

     p.sort_stats(SortKey.TIME, SortKey.CUMULATIVE).print_stats(.5, 'init')

This line sorts statistics with a primary key of time, and a secondary
key of cumulative time, and then prints out some of the statistics.  To
be specific, the list is first culled down to 50% (re: ‘.5’) of its
original size, then only lines containing ‘init’ are maintained, and
that sub-sub-list is printed.

If you wondered what functions called the above functions, you could now
(‘p’ is still sorted according to the last criteria) do:

     p.print_callers(.5, 'init')

and you would get a list of callers for each of the listed functions.

If you want more functionality, you’re going to have to read the manual,
or guess what the following functions do:

     p.print_callees()
     p.add('restats')

Invoked as a script, the *note pstats: d4. module is a statistics
browser for reading and examining profile dumps.  It has a simple
line-oriented interface (implemented using *note cmd: 19.) and
interactive help.


File: python.info,  Node: profile and cProfile Module Reference,  Next: The Stats Class,  Prev: Instant User’s Manual,  Up: The Python Profilers

5.27.5.3 ‘profile’ and ‘cProfile’ Module Reference
..................................................

Both the *note profile: d3. and *note cProfile: 27. modules provide the
following functions:

 -- Function: profile.run (command, filename=None, sort=-1)

     This function takes a single argument that can be passed to the
     *note exec(): d0c. function, and an optional file name.  In all
     cases this routine executes:

          exec(command, __main__.__dict__, __main__.__dict__)

     and gathers profiling statistics from the execution.  If no file
     name is present, then this function automatically creates a *note
     Stats: 36e2. instance and prints a simple profiling report.  If the
     sort value is specified, it is passed to this *note Stats: 36e2.
     instance to control how the results are sorted.

 -- Function: profile.runctx (command, globals, locals, filename=None,
          sort=-1)

     This function is similar to *note run(): 36e7, with added arguments
     to supply the globals and locals dictionaries for the `command'
     string.  This routine executes:

          exec(command, globals, locals)

     and gathers profiling statistics as in the *note run(): 36e7.
     function above.

 -- Class: profile.Profile (timer=None, timeunit=0.0, subcalls=True,
          builtins=True)

     This class is normally only used if more precise control over
     profiling is needed than what the ‘cProfile.run()’ function
     provides.

     A custom timer can be supplied for measuring how long code takes to
     run via the `timer' argument.  This must be a function that returns
     a single number representing the current time.  If the number is an
     integer, the `timeunit' specifies a multiplier that specifies the
     duration of each unit of time.  For example, if the timer returns
     times measured in thousands of seconds, the time unit would be
     ‘.001’.

     Directly using the *note Profile: 2ec. class allows formatting
     profile results without writing the profile data to a file:

          import cProfile, pstats, io
          from pstats import SortKey
          pr = cProfile.Profile()
          pr.enable()
          # ... do something ...
          pr.disable()
          s = io.StringIO()
          sortby = SortKey.CUMULATIVE
          ps = pstats.Stats(pr, stream=s).sort_stats(sortby)
          ps.print_stats()
          print(s.getvalue())

     The *note Profile: 2ec. class can also be used as a context manager
     (supported only in *note cProfile: 27. module.  see *note Context
     Manager Types: 15c6.):

          import cProfile

          with cProfile.Profile() as pr:
              # ... do something ...

          pr.print_stats()

     Changed in version 3.8: Added context manager support.

      -- Method: enable ()

          Start collecting profiling data.  Only in *note cProfile: 27.

      -- Method: disable ()

          Stop collecting profiling data.  Only in *note cProfile: 27.

      -- Method: create_stats ()

          Stop collecting profiling data and record the results
          internally as the current profile.

      -- Method: print_stats (sort=-1)

          Create a *note Stats: 36e2. object based on the current
          profile and print the results to stdout.

      -- Method: dump_stats (filename)

          Write the results of the current profile to `filename'.

      -- Method: run (cmd)

          Profile the cmd via *note exec(): d0c.

      -- Method: runctx (cmd, globals, locals)

          Profile the cmd via *note exec(): d0c. with the specified
          global and local environment.

      -- Method: runcall (func, /, *args, **kwargs)

          Profile ‘func(*args, **kwargs)’

Note that profiling will only work if the called command/function
actually returns.  If the interpreter is terminated (e.g.  via a *note
sys.exit(): daa. call during the called command/function execution) no
profiling results will be printed.


File: python.info,  Node: The Stats Class,  Next: What Is Deterministic Profiling?,  Prev: profile and cProfile Module Reference,  Up: The Python Profilers

5.27.5.4 The ‘Stats’ Class
..........................

Analysis of the profiler data is done using the *note Stats: 36e2.
class.

 -- Class: pstats.Stats (*filenames or profile, stream=sys.stdout)

     This class constructor creates an instance of a “statistics object”
     from a `filename' (or list of filenames) or from a ‘Profile’
     instance.  Output will be printed to the stream specified by
     `stream'.

     The file selected by the above constructor must have been created
     by the corresponding version of *note profile: d3. or *note
     cProfile: 27.  To be specific, there is `no' file compatibility
     guaranteed with future versions of this profiler, and there is no
     compatibility with files produced by other profilers, or the same
     profiler run on a different operating system.  If several files are
     provided, all the statistics for identical functions will be
     coalesced, so that an overall view of several processes can be
     considered in a single report.  If additional files need to be
     combined with data in an existing *note Stats: 36e2. object, the
     *note add(): 36f2. method can be used.

     Instead of reading the profile data from a file, a
     ‘cProfile.Profile’ or *note profile.Profile: 2ec. object can be
     used as the profile data source.

     *note Stats: 36e2. objects have the following methods:

      -- Method: strip_dirs ()

          This method for the *note Stats: 36e2. class removes all
          leading path information from file names.  It is very useful
          in reducing the size of the printout to fit within (close to)
          80 columns.  This method modifies the object, and the stripped
          information is lost.  After performing a strip operation, the
          object is considered to have its entries in a “random” order,
          as it was just after object initialization and loading.  If
          *note strip_dirs(): 36e4. causes two function names to be
          indistinguishable (they are on the same line of the same
          filename, and have the same function name), then the
          statistics for these two entries are accumulated into a single
          entry.

      -- Method: add (*filenames)

          This method of the *note Stats: 36e2. class accumulates
          additional profiling information into the current profiling
          object.  Its arguments should refer to filenames created by
          the corresponding version of *note profile.run(): 36e7. or
          ‘cProfile.run()’.  Statistics for identically named (re: file,
          line, name) functions are automatically accumulated into
          single function statistics.

      -- Method: dump_stats (filename)

          Save the data loaded into the *note Stats: 36e2. object to a
          file named `filename'.  The file is created if it does not
          exist, and is overwritten if it already exists.  This is
          equivalent to the method of the same name on the *note
          profile.Profile: 2ec. and ‘cProfile.Profile’ classes.

      -- Method: sort_stats (*keys)

          This method modifies the *note Stats: 36e2. object by sorting
          it according to the supplied criteria.  The argument can be
          either a string or a SortKey enum identifying the basis of a
          sort (example: ‘'time'’, ‘'name'’, ‘SortKey.TIME’ or
          ‘SortKey.NAME’).  The SortKey enums argument have advantage
          over the string argument in that it is more robust and less
          error prone.

          When more than one key is provided, then additional keys are
          used as secondary criteria when there is equality in all keys
          selected before them.  For example, ‘sort_stats(SortKey.NAME,
          SortKey.FILE)’ will sort all the entries according to their
          function name, and resolve all ties (identical function names)
          by sorting by file name.

          For the string argument, abbreviations can be used for any key
          names, as long as the abbreviation is unambiguous.

          The following are the valid string and SortKey:

          Valid String Arg       Valid enum Arg            Meaning
                                                           
          ----------------------------------------------------------------------------
                                                           
          ‘'calls'’              SortKey.CALLS             call count
                                                           
                                                           
          ‘'cumulative'’         SortKey.CUMULATIVE        cumulative time
                                                           
                                                           
          ‘'cumtime'’            N/A                       cumulative time
                                                           
                                                           
          ‘'file'’               N/A                       file name
                                                           
                                                           
          ‘'filename'’           SortKey.FILENAME          file name
                                                           
                                                           
          ‘'module'’             N/A                       file name
                                                           
                                                           
          ‘'ncalls'’             N/A                       call count
                                                           
                                                           
          ‘'pcalls'’             SortKey.PCALLS            primitive call count
                                                           
                                                           
          ‘'line'’               SortKey.LINE              line number
                                                           
                                                           
          ‘'name'’               SortKey.NAME              function name
                                                           
                                                           
          ‘'nfl'’                SortKey.NFL               name/file/line
                                                           
                                                           
          ‘'stdname'’            SortKey.STDNAME           standard name
                                                           
                                                           
          ‘'time'’               SortKey.TIME              internal time
                                                           
                                                           
          ‘'tottime'’            N/A                       internal time
                                                           

          Note that all sorts on statistics are in descending order
          (placing most time consuming items first), where as name,
          file, and line number searches are in ascending order
          (alphabetical).  The subtle distinction between ‘SortKey.NFL’
          and ‘SortKey.STDNAME’ is that the standard name is a sort of
          the name as printed, which means that the embedded line
          numbers get compared in an odd way.  For example, lines 3, 20,
          and 40 would (if the file names were the same) appear in the
          string order 20, 3 and 40.  In contrast, ‘SortKey.NFL’ does a
          numeric compare of the line numbers.  In fact,
          ‘sort_stats(SortKey.NFL)’ is the same as
          ‘sort_stats(SortKey.NAME, SortKey.FILENAME, SortKey.LINE)’.

          For backward-compatibility reasons, the numeric arguments
          ‘-1’, ‘0’, ‘1’, and ‘2’ are permitted.  They are interpreted
          as ‘'stdname'’, ‘'calls'’, ‘'time'’, and ‘'cumulative'’
          respectively.  If this old style format (numeric) is used,
          only one sort key (the numeric key) will be used, and
          additional arguments will be silently ignored.

          New in version 3.7: Added the SortKey enum.

      -- Method: reverse_order ()

          This method for the *note Stats: 36e2. class reverses the
          ordering of the basic list within the object.  Note that by
          default ascending vs descending order is properly selected
          based on the sort key of choice.

      -- Method: print_stats (*restrictions)

          This method for the *note Stats: 36e2. class prints out a
          report as described in the *note profile.run(): 36e7.
          definition.

          The order of the printing is based on the last *note
          sort_stats(): 36e3. operation done on the object (subject to
          caveats in *note add(): 36f2. and *note strip_dirs(): 36e4.).

          The arguments provided (if any) can be used to limit the list
          down to the significant entries.  Initially, the list is taken
          to be the complete set of profiled functions.  Each
          restriction is either an integer (to select a count of lines),
          or a decimal fraction between 0.0 and 1.0 inclusive (to select
          a percentage of lines), or a string that will interpreted as a
          regular expression (to pattern match the standard name that is
          printed).  If several restrictions are provided, then they are
          applied sequentially.  For example:

               print_stats(.1, 'foo:')

          would first limit the printing to first 10% of list, and then
          only print functions that were part of filename ‘.*foo:’.  In
          contrast, the command:

               print_stats('foo:', .1)

          would limit the list to all functions having file names
          ‘.*foo:’, and then proceed to only print the first 10% of
          them.

      -- Method: print_callers (*restrictions)

          This method for the *note Stats: 36e2. class prints a list of
          all functions that called each function in the profiled
          database.  The ordering is identical to that provided by *note
          print_stats(): 36e5, and the definition of the restricting
          argument is also identical.  Each caller is reported on its
          own line.  The format differs slightly depending on the
          profiler that produced the stats:

             * With *note profile: d3, a number is shown in parentheses
               after each caller to show how many times this specific
               call was made.  For convenience, a second
               non-parenthesized number repeats the cumulative time
               spent in the function at the right.

             * With *note cProfile: 27, each caller is preceded by three
               numbers: the number of times this specific call was made,
               and the total and cumulative times spent in the current
               function while it was invoked by this specific caller.

      -- Method: print_callees (*restrictions)

          This method for the *note Stats: 36e2. class prints a list of
          all function that were called by the indicated function.
          Aside from this reversal of direction of calls (re: called vs
          was called by), the arguments and ordering are identical to
          the *note print_callers(): 36f5. method.

      -- Method: get_stats_profile ()

          This method returns an instance of StatsProfile, which
          contains a mapping of function names to instances of
          FunctionProfile.  Each FunctionProfile instance holds
          information related to the function’s profile such as how long
          the function took to run, how many times it was called, etc…

          New in version 3.9: Added the following dataclasses:
          StatsProfile, FunctionProfile.  Added the following function:
          get_stats_profile.


File: python.info,  Node: What Is Deterministic Profiling?,  Next: Limitations,  Prev: The Stats Class,  Up: The Python Profilers

5.27.5.5 What Is Deterministic Profiling?
.........................................

`Deterministic profiling' is meant to reflect the fact that all
`function call', `function return', and `exception' events are
monitored, and precise timings are made for the intervals between these
events (during which time the user’s code is executing).  In contrast,
`statistical profiling' (which is not done by this module) randomly
samples the effective instruction pointer, and deduces where time is
being spent.  The latter technique traditionally involves less overhead
(as the code does not need to be instrumented), but provides only
relative indications of where time is being spent.

In Python, since there is an interpreter active during execution, the
presence of instrumented code is not required in order to do
deterministic profiling.  Python automatically provides a `hook'
(optional callback) for each event.  In addition, the interpreted nature
of Python tends to add so much overhead to execution, that deterministic
profiling tends to only add small processing overhead in typical
applications.  The result is that deterministic profiling is not that
expensive, yet provides extensive run time statistics about the
execution of a Python program.

Call count statistics can be used to identify bugs in code (surprising
counts), and to identify possible inline-expansion points (high call
counts).  Internal time statistics can be used to identify “hot loops”
that should be carefully optimized.  Cumulative time statistics should
be used to identify high level errors in the selection of algorithms.
Note that the unusual handling of cumulative times in this profiler
allows statistics for recursive implementations of algorithms to be
directly compared to iterative implementations.


File: python.info,  Node: Limitations,  Next: Calibration,  Prev: What Is Deterministic Profiling?,  Up: The Python Profilers

5.27.5.6 Limitations
....................

One limitation has to do with accuracy of timing information.  There is
a fundamental problem with deterministic profilers involving accuracy.
The most obvious restriction is that the underlying “clock” is only
ticking at a rate (typically) of about .001 seconds.  Hence no
measurements will be more accurate than the underlying clock.  If enough
measurements are taken, then the “error” will tend to average out.
Unfortunately, removing this first error induces a second source of
error.

The second problem is that it “takes a while” from when an event is
dispatched until the profiler’s call to get the time actually `gets' the
state of the clock.  Similarly, there is a certain lag when exiting the
profiler event handler from the time that the clock’s value was obtained
(and then squirreled away), until the user’s code is once again
executing.  As a result, functions that are called many times, or call
many functions, will typically accumulate this error.  The error that
accumulates in this fashion is typically less than the accuracy of the
clock (less than one clock tick), but it `can' accumulate and become
very significant.

The problem is more important with *note profile: d3. than with the
lower-overhead *note cProfile: 27.  For this reason, *note profile: d3.
provides a means of calibrating itself for a given platform so that this
error can be probabilistically (on the average) removed.  After the
profiler is calibrated, it will be more accurate (in a least square
sense), but it will sometimes produce negative numbers (when call counts
are exceptionally low, and the gods of probability work against you :-).
)  Do `not' be alarmed by negative numbers in the profile.  They should
`only' appear if you have calibrated your profiler, and the results are
actually better than without calibration.


File: python.info,  Node: Calibration,  Next: Using a custom timer,  Prev: Limitations,  Up: The Python Profilers

5.27.5.7 Calibration
....................

The profiler of the *note profile: d3. module subtracts a constant from
each event handling time to compensate for the overhead of calling the
time function, and socking away the results.  By default, the constant
is 0.  The following procedure can be used to obtain a better constant
for a given platform (see *note Limitations: 36fb.).

     import profile
     pr = profile.Profile()
     for i in range(5):
         print(pr.calibrate(10000))

The method executes the number of Python calls given by the argument,
directly and again under the profiler, measuring the time for both.  It
then computes the hidden overhead per profiler event, and returns that
as a float.  For example, on a 1.8Ghz Intel Core i5 running macOS, and
using Python’s time.process_time() as the timer, the magical number is
about 4.04e-6.

The object of this exercise is to get a fairly consistent result.  If
your computer is `very' fast, or your timer function has poor
resolution, you might have to pass 100000, or even 1000000, to get
consistent results.

When you have a consistent answer, there are three ways you can use it:

     import profile

     # 1. Apply computed bias to all Profile instances created hereafter.
     profile.Profile.bias = your_computed_bias

     # 2. Apply computed bias to a specific Profile instance.
     pr = profile.Profile()
     pr.bias = your_computed_bias

     # 3. Specify computed bias in instance constructor.
     pr = profile.Profile(bias=your_computed_bias)

If you have a choice, you are better off choosing a smaller constant,
and then your results will “less often” show up as negative in profile
statistics.


File: python.info,  Node: Using a custom timer,  Prev: Calibration,  Up: The Python Profilers

5.27.5.8 Using a custom timer
.............................

If you want to change how current time is determined (for example, to
force use of wall-clock time or elapsed process time), pass the timing
function you want to the ‘Profile’ class constructor:

     pr = profile.Profile(your_time_func)

The resulting profiler will then call ‘your_time_func’.  Depending on
whether you are using *note profile.Profile: 2ec. or ‘cProfile.Profile’,
‘your_time_func’’s return value will be interpreted differently:

*note profile.Profile: 2ec.

     ‘your_time_func’ should return a single number, or a list of
     numbers whose sum is the current time (like what *note os.times():
     b37. returns).  If the function returns a single time number, or
     the list of returned numbers has length 2, then you will get an
     especially fast version of the dispatch routine.

     Be warned that you should calibrate the profiler class for the
     timer function that you choose (see *note Calibration: 36fd.).  For
     most machines, a timer that returns a lone integer value will
     provide the best results in terms of low overhead during profiling.
     (*note os.times(): b37. is `pretty' bad, as it returns a tuple of
     floating point values).  If you want to substitute a better timer
     in the cleanest fashion, derive a class and hardwire a replacement
     dispatch method that best handles your timer call, along with the
     appropriate calibration constant.

‘cProfile.Profile’

     ‘your_time_func’ should return a single number.  If it returns
     integers, you can also invoke the class constructor with a second
     argument specifying the real duration of one unit of time.  For
     example, if ‘your_integer_time_func’ returns times measured in
     thousands of seconds, you would construct the ‘Profile’ instance as
     follows:

          pr = cProfile.Profile(your_integer_time_func, 0.001)

     As the ‘cProfile.Profile’ class cannot be calibrated, custom timer
     functions should be used with care and should be as fast as
     possible.  For the best results with a custom timer, it might be
     necessary to hard-code it in the C source of the internal ‘_lsprof’
     module.

Python 3.3 adds several new functions in *note time: 10c. that can be
used to make precise measurements of process or wall-clock time.  For
example, see *note time.perf_counter(): 3cc.


File: python.info,  Node: timeit — Measure execution time of small code snippets,  Next: trace — Trace or track Python statement execution,  Prev: The Python Profilers,  Up: Debugging and Profiling

5.27.6 ‘timeit’ — Measure execution time of small code snippets
---------------------------------------------------------------

`Source code:' Lib/timeit.py(1)

__________________________________________________________________

This module provides a simple way to time small bits of Python code.  It
has both a *note Command-Line Interface: 3702. as well as a *note
callable: 3703. one.  It avoids a number of common traps for measuring
execution times.  See also Tim Peters’ introduction to the “Algorithms”
chapter in the second edition of `Python Cookbook', published by
O’Reilly.

* Menu:

* Basic Examples: Basic Examples<2>.
* Python Interface::
* Command-Line Interface: Command-Line Interface<4>.
* Examples: Examples<26>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/timeit.py


File: python.info,  Node: Basic Examples<2>,  Next: Python Interface,  Up: timeit — Measure execution time of small code snippets

5.27.6.1 Basic Examples
.......................

The following example shows how the *note Command-Line Interface: 3702.
can be used to compare three different expressions:

     $ python3 -m timeit '"-".join(str(n) for n in range(100))'
     10000 loops, best of 5: 30.2 usec per loop
     $ python3 -m timeit '"-".join([str(n) for n in range(100)])'
     10000 loops, best of 5: 27.5 usec per loop
     $ python3 -m timeit '"-".join(map(str, range(100)))'
     10000 loops, best of 5: 23.2 usec per loop

This can be achieved from the *note Python Interface: 3703. with:

     >>> import timeit
     >>> timeit.timeit('"-".join(str(n) for n in range(100))', number=10000)
     0.3018611848820001
     >>> timeit.timeit('"-".join([str(n) for n in range(100)])', number=10000)
     0.2727368790656328
     >>> timeit.timeit('"-".join(map(str, range(100)))', number=10000)
     0.23702679807320237

A callable can also be passed from the *note Python Interface: 3703.:

     >>> timeit.timeit(lambda: "-".join(map(str, range(100))), number=10000)
     0.19665591977536678

Note however that *note timeit(): 860. will automatically determine the
number of repetitions only when the command-line interface is used.  In
the *note Examples: 3705. section you can find more advanced examples.


File: python.info,  Node: Python Interface,  Next: Command-Line Interface<4>,  Prev: Basic Examples<2>,  Up: timeit — Measure execution time of small code snippets

5.27.6.2 Python Interface
.........................

The module defines three convenience functions and a public class:

 -- Function: timeit.timeit (stmt='pass', setup='pass', timer=<default
          timer>, number=1000000, globals=None)

     Create a *note Timer: 3707. instance with the given statement,
     `setup' code and `timer' function and run its *note timeit(): 693.
     method with `number' executions.  The optional `globals' argument
     specifies a namespace in which to execute the code.

     Changed in version 3.5: The optional `globals' parameter was added.

 -- Function: timeit.repeat (stmt='pass', setup='pass', timer=<default
          timer>, repeat=5, number=1000000, globals=None)

     Create a *note Timer: 3707. instance with the given statement,
     `setup' code and `timer' function and run its *note repeat(): 3709.
     method with the given `repeat' count and `number' executions.  The
     optional `globals' argument specifies a namespace in which to
     execute the code.

     Changed in version 3.5: The optional `globals' parameter was added.

     Changed in version 3.7: Default value of `repeat' changed from 3 to
     5.

 -- Function: timeit.default_timer ()

     The default timer, which is always *note time.perf_counter(): 3cc.

     Changed in version 3.3: *note time.perf_counter(): 3cc. is now the
     default timer.

 -- Class: timeit.Timer (stmt='pass', setup='pass', timer=<timer
          function>, globals=None)

     Class for timing execution speed of small code snippets.

     The constructor takes a statement to be timed, an additional
     statement used for setup, and a timer function.  Both statements
     default to ‘'pass'’; the timer function is platform-dependent (see
     the module doc string).  `stmt' and `setup' may also contain
     multiple statements separated by ‘;’ or newlines, as long as they
     don’t contain multi-line string literals.  The statement will by
     default be executed within timeit’s namespace; this behavior can be
     controlled by passing a namespace to `globals'.

     To measure the execution time of the first statement, use the *note
     timeit(): 693. method.  The *note repeat(): 3709. and *note
     autorange(): 692. methods are convenience methods to call *note
     timeit(): 693. multiple times.

     The execution time of `setup' is excluded from the overall timed
     execution run.

     The `stmt' and `setup' parameters can also take objects that are
     callable without arguments.  This will embed calls to them in a
     timer function that will then be executed by *note timeit(): 693.
     Note that the timing overhead is a little larger in this case
     because of the extra function calls.

     Changed in version 3.5: The optional `globals' parameter was added.

      -- Method: timeit (number=1000000)

          Time `number' executions of the main statement.  This executes
          the setup statement once, and then returns the time it takes
          to execute the main statement a number of times, measured in
          seconds as a float.  The argument is the number of times
          through the loop, defaulting to one million.  The main
          statement, the setup statement and the timer function to be
          used are passed to the constructor.

               Note: By default, *note timeit(): 693. temporarily turns
               off *note garbage collection: fc8. during the timing.
               The advantage of this approach is that it makes
               independent timings more comparable.  The disadvantage is
               that GC may be an important component of the performance
               of the function being measured.  If so, GC can be
               re-enabled as the first statement in the `setup' string.
               For example:

                    timeit.Timer('for i in range(10): oct(i)', 'gc.enable()').timeit()

      -- Method: autorange (callback=None)

          Automatically determine how many times to call *note timeit():
          693.

          This is a convenience function that calls *note timeit(): 693.
          repeatedly so that the total time >= 0.2 second, returning the
          eventual (number of loops, time taken for that number of
          loops).  It calls *note timeit(): 693. with increasing numbers
          from the sequence 1, 2, 5, 10, 20, 50, … until the time taken
          is at least 0.2 second.

          If `callback' is given and is not ‘None’, it will be called
          after each trial with two arguments: ‘callback(number,
          time_taken)’.

          New in version 3.6.

      -- Method: repeat (repeat=5, number=1000000)

          Call *note timeit(): 693. a few times.

          This is a convenience function that calls the *note timeit():
          693. repeatedly, returning a list of results.  The first
          argument specifies how many times to call *note timeit(): 693.
          The second argument specifies the `number' argument for *note
          timeit(): 693.

               Note: It’s tempting to calculate mean and standard
               deviation from the result vector and report these.
               However, this is not very useful.  In a typical case, the
               lowest value gives a lower bound for how fast your
               machine can run the given code snippet; higher values in
               the result vector are typically not caused by variability
               in Python’s speed, but by other processes interfering
               with your timing accuracy.  So the *note min(): 8f6. of
               the result is probably the only number you should be
               interested in.  After that, you should look at the entire
               vector and apply common sense rather than statistics.

          Changed in version 3.7: Default value of `repeat' changed from
          3 to 5.

      -- Method: print_exc (file=None)

          Helper to print a traceback from the timed code.

          Typical use:

               t = Timer(...)       # outside the try/except
               try:
                   t.timeit(...)    # or t.repeat(...)
               except Exception:
                   t.print_exc()

          The advantage over the standard traceback is that source lines
          in the compiled template will be displayed.  The optional
          `file' argument directs where the traceback is sent; it
          defaults to *note sys.stderr: 1ea.


File: python.info,  Node: Command-Line Interface<4>,  Next: Examples<26>,  Prev: Python Interface,  Up: timeit — Measure execution time of small code snippets

5.27.6.3 Command-Line Interface
...............................

When called as a program from the command line, the following form is
used:

     python -m timeit [-n N] [-r N] [-u U] [-s S] [-h] [statement ...]

Where the following options are understood:

 -- Program Option: -n N, --number=N

     how many times to execute ‘statement’

 -- Program Option: -r N, --repeat=N

     how many times to repeat the timer (default 5)

 -- Program Option: -s S, --setup=S

     statement to be executed once initially (default ‘pass’)

 -- Program Option: -p, --process

     measure process time, not wallclock time, using *note
     time.process_time(): 3cd. instead of *note time.perf_counter():
     3cc, which is the default

     New in version 3.3.

 -- Program Option: -u, --unit=U

     specify a time unit for timer output; can select nsec, usec, msec,
     or sec

     New in version 3.5.

 -- Program Option: -v, --verbose

     print raw timing results; repeat for more digits precision

 -- Program Option: -h, --help

     print a short usage message and exit

A multi-line statement may be given by specifying each line as a
separate statement argument; indented lines are possible by enclosing an
argument in quotes and using leading spaces.  Multiple *note -s: 370f.
options are treated similarly.

If *note -n: 370d. is not given, a suitable number of loops is
calculated by trying increasing numbers from the sequence 1, 2, 5, 10,
20, 50, … until the total time is at least 0.2 seconds.

*note default_timer(): 370a. measurements can be affected by other
programs running on the same machine, so the best thing to do when
accurate timing is necessary is to repeat the timing a few times and use
the best time.  The *note -r: 370e. option is good for this; the default
of 5 repetitions is probably enough in most cases.  You can use *note
time.process_time(): 3cd. to measure CPU time.

     Note: There is a certain baseline overhead associated with
     executing a pass statement.  The code here doesn’t try to hide it,
     but you should be aware of it.  The baseline overhead can be
     measured by invoking the program without arguments, and it might
     differ between Python versions.


File: python.info,  Node: Examples<26>,  Prev: Command-Line Interface<4>,  Up: timeit — Measure execution time of small code snippets

5.27.6.4 Examples
.................

It is possible to provide a setup statement that is executed only once
at the beginning:

     $ python -m timeit -s 'text = "sample string"; char = "g"'  'char in text'
     5000000 loops, best of 5: 0.0877 usec per loop
     $ python -m timeit -s 'text = "sample string"; char = "g"'  'text.find(char)'
     1000000 loops, best of 5: 0.342 usec per loop

     >>> import timeit
     >>> timeit.timeit('char in text', setup='text = "sample string"; char = "g"')
     0.41440500499993504
     >>> timeit.timeit('text.find(char)', setup='text = "sample string"; char = "g"')
     1.7246671520006203

The same can be done using the *note Timer: 3707. class and its methods:

     >>> import timeit
     >>> t = timeit.Timer('char in text', setup='text = "sample string"; char = "g"')
     >>> t.timeit()
     0.3955516149999312
     >>> t.repeat()
     [0.40183617287970225, 0.37027556854118704, 0.38344867356679524, 0.3712595970846668, 0.37866875250654886]

The following examples show how to time expressions that contain
multiple lines.  Here we compare the cost of using *note hasattr(): 54a.
vs.  *note try: e37./*note except: c10. to test for missing and present
object attributes:

     $ python -m timeit 'try:' '  str.__bool__' 'except AttributeError:' '  pass'
     20000 loops, best of 5: 15.7 usec per loop
     $ python -m timeit 'if hasattr(str, "__bool__"): pass'
     50000 loops, best of 5: 4.26 usec per loop

     $ python -m timeit 'try:' '  int.__bool__' 'except AttributeError:' '  pass'
     200000 loops, best of 5: 1.43 usec per loop
     $ python -m timeit 'if hasattr(int, "__bool__"): pass'
     100000 loops, best of 5: 2.23 usec per loop

     >>> import timeit
     >>> # attribute is missing
     >>> s = """\
     ... try:
     ...     str.__bool__
     ... except AttributeError:
     ...     pass
     ... """
     >>> timeit.timeit(stmt=s, number=100000)
     0.9138244460009446
     >>> s = "if hasattr(str, '__bool__'): pass"
     >>> timeit.timeit(stmt=s, number=100000)
     0.5829014980008651
     >>>
     >>> # attribute is present
     >>> s = """\
     ... try:
     ...     int.__bool__
     ... except AttributeError:
     ...     pass
     ... """
     >>> timeit.timeit(stmt=s, number=100000)
     0.04215312199994514
     >>> s = "if hasattr(int, '__bool__'): pass"
     >>> timeit.timeit(stmt=s, number=100000)
     0.08588060699912603

To give the *note timeit: 10d. module access to functions you define,
you can pass a `setup' parameter which contains an import statement:

     def test():
         """Stupid test function"""
         L = [i for i in range(100)]

     if __name__ == '__main__':
         import timeit
         print(timeit.timeit("test()", setup="from __main__ import test"))

Another option is to pass *note globals(): f55. to the `globals'
parameter, which will cause the code to be executed within your current
global namespace.  This can be more convenient than individually
specifying imports:

     def f(x):
         return x**2
     def g(x):
         return x**4
     def h(x):
         return x**8

     import timeit
     print(timeit.timeit('[func(42) for func in (f,g,h)]', globals=globals()))


File: python.info,  Node: trace — Trace or track Python statement execution,  Next: tracemalloc — Trace memory allocations,  Prev: timeit — Measure execution time of small code snippets,  Up: Debugging and Profiling

5.27.7 ‘trace’ — Trace or track Python statement execution
----------------------------------------------------------

`Source code:' Lib/trace.py(1)

__________________________________________________________________

The *note trace: 11b. module allows you to trace program execution,
generate annotated statement coverage listings, print caller/callee
relationships and list functions executed during a program run.  It can
be used in another program or from the command line.

See also
........

Coverage.py(2)

     A popular third-party coverage tool that provides HTML output along
     with advanced features such as branch coverage.

* Menu:

* Command-Line Usage::
* Programmatic Interface::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/trace.py

   (2) https://coverage.readthedocs.io/


File: python.info,  Node: Command-Line Usage,  Next: Programmatic Interface,  Up: trace — Trace or track Python statement execution

5.27.7.1 Command-Line Usage
...........................

The *note trace: 11b. module can be invoked from the command line.  It
can be as simple as

     python -m trace --count -C . somefile.py ...

The above will execute ‘somefile.py’ and generate annotated listings of
all Python modules imported during the execution into the current
directory.

 -- Program Option: --help

     Display usage and exit.

 -- Program Option: --version

     Display the version of the module and exit.

New in version 3.8: Added ‘--module’ option that allows to run an
executable module.

* Menu:

* Main options::
* Modifiers::
* Filters::


File: python.info,  Node: Main options,  Next: Modifiers,  Up: Command-Line Usage

5.27.7.2 Main options
.....................

At least one of the following options must be specified when invoking
*note trace: 11b.  The *note –listfuncs: 371c. option is mutually
exclusive with the *note –trace: 371d. and *note –count: 371e. options.
When *note –listfuncs: 371c. is provided, neither *note –count: 371e.
nor *note –trace: 371d. are accepted, and vice versa.

 -- Program Option: -c, --count

     Produce a set of annotated listing files upon program completion
     that shows how many times each statement was executed.  See also
     *note –coverdir: 371f, *note –file: 3720. and *note –no-report:
     3721. below.

 -- Program Option: -t, --trace

     Display lines as they are executed.

 -- Program Option: -l, --listfuncs

     Display the functions executed by running the program.

 -- Program Option: -r, --report

     Produce an annotated list from an earlier program run that used the
     *note –count: 371e. and *note –file: 3720. option.  This does not
     execute any code.

 -- Program Option: -T, --trackcalls

     Display the calling relationships exposed by running the program.


File: python.info,  Node: Modifiers,  Next: Filters,  Prev: Main options,  Up: Command-Line Usage

5.27.7.3 Modifiers
..................

 -- Program Option: -f, --file=<file>

     Name of a file to accumulate counts over several tracing runs.
     Should be used with the *note –count: 371e. option.

 -- Program Option: -C, --coverdir=<dir>

     Directory where the report files go.  The coverage report for
     ‘package.module’ is written to file
     ‘`dir'/`package'/`module'.cover’.

 -- Program Option: -m, --missing

     When generating annotated listings, mark lines which were not
     executed with ‘>>>>>>’.

 -- Program Option: -s, --summary

     When using *note –count: 371e. or *note –report: 3722, write a
     brief summary to stdout for each file processed.

 -- Program Option: -R, --no-report

     Do not generate annotated listings.  This is useful if you intend
     to make several runs with *note –count: 371e, and then produce a
     single set of annotated listings at the end.

 -- Program Option: -g, --timing

     Prefix each line with the time since the program started.  Only
     used while tracing.


File: python.info,  Node: Filters,  Prev: Modifiers,  Up: Command-Line Usage

5.27.7.4 Filters
................

These options may be repeated multiple times.

 -- Program Option: --ignore-module=<mod>

     Ignore each of the given module names and its submodules (if it is
     a package).  The argument can be a list of names separated by a
     comma.

 -- Program Option: --ignore-dir=<dir>

     Ignore all modules and packages in the named directory and
     subdirectories.  The argument can be a list of directories
     separated by *note os.pathsep: 1486.


File: python.info,  Node: Programmatic Interface,  Prev: Command-Line Usage,  Up: trace — Trace or track Python statement execution

5.27.7.5 Programmatic Interface
...............................

 -- Class: trace.Trace (count=1, trace=1, countfuncs=0, countcallers=0,
          ignoremods=(), ignoredirs=(), infile=None, outfile=None,
          timing=False)

     Create an object to trace execution of a single statement or
     expression.  All parameters are optional.  `count' enables counting
     of line numbers.  `trace' enables line execution tracing.
     `countfuncs' enables listing of the functions called during the
     run.  `countcallers' enables call relationship tracking.
     `ignoremods' is a list of modules or packages to ignore.
     `ignoredirs' is a list of directories whose modules or packages
     should be ignored.  `infile' is the name of the file from which to
     read stored count information.  `outfile' is the name of the file
     in which to write updated count information.  `timing' enables a
     timestamp relative to when tracing was started to be displayed.

      -- Method: run (cmd)

          Execute the command and gather statistics from the execution
          with the current tracing parameters.  `cmd' must be a string
          or code object, suitable for passing into *note exec(): d0c.

      -- Method: runctx (cmd, globals=None, locals=None)

          Execute the command and gather statistics from the execution
          with the current tracing parameters, in the defined global and
          local environments.  If not defined, `globals' and `locals'
          default to empty dictionaries.

      -- Method: runfunc (func, /, *args, **kwds)

          Call `func' with the given arguments under control of the
          *note Trace: 372d. object with the current tracing parameters.

      -- Method: results ()

          Return a *note CoverageResults: 3731. object that contains the
          cumulative results of all previous calls to ‘run’, ‘runctx’
          and ‘runfunc’ for the given *note Trace: 372d. instance.  Does
          not reset the accumulated trace results.

 -- Class: trace.CoverageResults

     A container for coverage results, created by *note Trace.results():
     3730.  Should not be created directly by the user.

      -- Method: update (other)

          Merge in data from another *note CoverageResults: 3731.
          object.

      -- Method: write_results (show_missing=True, summary=False,
               coverdir=None)

          Write coverage results.  Set `show_missing' to show lines that
          had no hits.  Set `summary' to include in the output the
          coverage summary per module.  `coverdir' specifies the
          directory into which the coverage result files will be output.
          If ‘None’, the results for each source file are placed in its
          directory.

A simple example demonstrating the use of the programmatic interface:

     import sys
     import trace

     # create a Trace object, telling it what to ignore, and whether to
     # do tracing or line-counting or both.
     tracer = trace.Trace(
         ignoredirs=[sys.prefix, sys.exec_prefix],
         trace=0,
         count=1)

     # run the new command using the given tracer
     tracer.run('main()')

     # make a report, placing output in the current directory
     r = tracer.results()
     r.write_results(show_missing=True, coverdir=".")


File: python.info,  Node: tracemalloc — Trace memory allocations,  Prev: trace — Trace or track Python statement execution,  Up: Debugging and Profiling

5.27.8 ‘tracemalloc’ — Trace memory allocations
-----------------------------------------------

New in version 3.4.

`Source code:' Lib/tracemalloc.py(1)

__________________________________________________________________

The tracemalloc module is a debug tool to trace memory blocks allocated
by Python.  It provides the following information:

   * Traceback where an object was allocated

   * Statistics on allocated memory blocks per filename and per line
     number: total size, number and average size of allocated memory
     blocks

   * Compute the differences between two snapshots to detect memory
     leaks

To trace most memory blocks allocated by Python, the module should be
started as early as possible by setting the *note PYTHONTRACEMALLOC:
148c. environment variable to ‘1’, or by using *note -X: 290.
‘tracemalloc’ command line option.  The *note tracemalloc.start(): 1481.
function can be called at runtime to start tracing Python memory
allocations.

By default, a trace of an allocated memory block only stores the most
recent frame (1 frame).  To store 25 frames at startup: set the *note
PYTHONTRACEMALLOC: 148c. environment variable to ‘25’, or use the *note
-X: 290. ‘tracemalloc=25’ command line option.

* Menu:

* Examples: Examples<27>.
* API::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/tracemalloc.py


File: python.info,  Node: Examples<27>,  Next: API,  Up: tracemalloc — Trace memory allocations

5.27.8.1 Examples
.................

* Menu:

* Display the top 10::
* Compute differences::
* Get the traceback of a memory block::
* Pretty top::


File: python.info,  Node: Display the top 10,  Next: Compute differences,  Up: Examples<27>

5.27.8.2 Display the top 10
...........................

Display the 10 files allocating the most memory:

     import tracemalloc

     tracemalloc.start()

     # ... run your application ...

     snapshot = tracemalloc.take_snapshot()
     top_stats = snapshot.statistics('lineno')

     print("[ Top 10 ]")
     for stat in top_stats[:10]:
         print(stat)

Example of output of the Python test suite:

     [ Top 10 ]
     <frozen importlib._bootstrap>:716: size=4855 KiB, count=39328, average=126 B
     <frozen importlib._bootstrap>:284: size=521 KiB, count=3199, average=167 B
     /usr/lib/python3.4/collections/__init__.py:368: size=244 KiB, count=2315, average=108 B
     /usr/lib/python3.4/unittest/case.py:381: size=185 KiB, count=779, average=243 B
     /usr/lib/python3.4/unittest/case.py:402: size=154 KiB, count=378, average=416 B
     /usr/lib/python3.4/abc.py:133: size=88.7 KiB, count=347, average=262 B
     <frozen importlib._bootstrap>:1446: size=70.4 KiB, count=911, average=79 B
     <frozen importlib._bootstrap>:1454: size=52.0 KiB, count=25, average=2131 B
     <string>:5: size=49.7 KiB, count=148, average=344 B
     /usr/lib/python3.4/sysconfig.py:411: size=48.0 KiB, count=1, average=48.0 KiB

We can see that Python loaded ‘4855 KiB’ data (bytecode and constants)
from modules and that the *note collections: 1d. module allocated ‘244
KiB’ to build *note namedtuple: 1a1. types.

See *note Snapshot.statistics(): 3738. for more options.


File: python.info,  Node: Compute differences,  Next: Get the traceback of a memory block,  Prev: Display the top 10,  Up: Examples<27>

5.27.8.3 Compute differences
............................

Take two snapshots and display the differences:

     import tracemalloc
     tracemalloc.start()
     # ... start your application ...

     snapshot1 = tracemalloc.take_snapshot()
     # ... call the function leaking memory ...
     snapshot2 = tracemalloc.take_snapshot()

     top_stats = snapshot2.compare_to(snapshot1, 'lineno')

     print("[ Top 10 differences ]")
     for stat in top_stats[:10]:
         print(stat)

Example of output before/after running some tests of the Python test
suite:

     [ Top 10 differences ]
     <frozen importlib._bootstrap>:716: size=8173 KiB (+4428 KiB), count=71332 (+39369), average=117 B
     /usr/lib/python3.4/linecache.py:127: size=940 KiB (+940 KiB), count=8106 (+8106), average=119 B
     /usr/lib/python3.4/unittest/case.py:571: size=298 KiB (+298 KiB), count=589 (+589), average=519 B
     <frozen importlib._bootstrap>:284: size=1005 KiB (+166 KiB), count=7423 (+1526), average=139 B
     /usr/lib/python3.4/mimetypes.py:217: size=112 KiB (+112 KiB), count=1334 (+1334), average=86 B
     /usr/lib/python3.4/http/server.py:848: size=96.0 KiB (+96.0 KiB), count=1 (+1), average=96.0 KiB
     /usr/lib/python3.4/inspect.py:1465: size=83.5 KiB (+83.5 KiB), count=109 (+109), average=784 B
     /usr/lib/python3.4/unittest/mock.py:491: size=77.7 KiB (+77.7 KiB), count=143 (+143), average=557 B
     /usr/lib/python3.4/urllib/parse.py:476: size=71.8 KiB (+71.8 KiB), count=969 (+969), average=76 B
     /usr/lib/python3.4/contextlib.py:38: size=67.2 KiB (+67.2 KiB), count=126 (+126), average=546 B

We can see that Python has loaded ‘8173 KiB’ of module data (bytecode
and constants), and that this is ‘4428 KiB’ more than had been loaded
before the tests, when the previous snapshot was taken.  Similarly, the
*note linecache: a8. module has cached ‘940 KiB’ of Python source code
to format tracebacks, all of it since the previous snapshot.

If the system has little free memory, snapshots can be written on disk
using the *note Snapshot.dump(): 373a. method to analyze the snapshot
offline.  Then use the *note Snapshot.load(): 373b. method reload the
snapshot.


File: python.info,  Node: Get the traceback of a memory block,  Next: Pretty top,  Prev: Compute differences,  Up: Examples<27>

5.27.8.4 Get the traceback of a memory block
............................................

Code to display the traceback of the biggest memory block:

     import tracemalloc

     # Store 25 frames
     tracemalloc.start(25)

     # ... run your application ...

     snapshot = tracemalloc.take_snapshot()
     top_stats = snapshot.statistics('traceback')

     # pick the biggest memory block
     stat = top_stats[0]
     print("%s memory blocks: %.1f KiB" % (stat.count, stat.size / 1024))
     for line in stat.traceback.format():
         print(line)

Example of output of the Python test suite (traceback limited to 25
frames):

     903 memory blocks: 870.1 KiB
       File "<frozen importlib._bootstrap>", line 716
       File "<frozen importlib._bootstrap>", line 1036
       File "<frozen importlib._bootstrap>", line 934
       File "<frozen importlib._bootstrap>", line 1068
       File "<frozen importlib._bootstrap>", line 619
       File "<frozen importlib._bootstrap>", line 1581
       File "<frozen importlib._bootstrap>", line 1614
       File "/usr/lib/python3.4/doctest.py", line 101
         import pdb
       File "<frozen importlib._bootstrap>", line 284
       File "<frozen importlib._bootstrap>", line 938
       File "<frozen importlib._bootstrap>", line 1068
       File "<frozen importlib._bootstrap>", line 619
       File "<frozen importlib._bootstrap>", line 1581
       File "<frozen importlib._bootstrap>", line 1614
       File "/usr/lib/python3.4/test/support/__init__.py", line 1728
         import doctest
       File "/usr/lib/python3.4/test/test_pickletools.py", line 21
         support.run_doctest(pickletools)
       File "/usr/lib/python3.4/test/regrtest.py", line 1276
         test_runner()
       File "/usr/lib/python3.4/test/regrtest.py", line 976
         display_failure=not verbose)
       File "/usr/lib/python3.4/test/regrtest.py", line 761
         match_tests=ns.match_tests)
       File "/usr/lib/python3.4/test/regrtest.py", line 1563
         main()
       File "/usr/lib/python3.4/test/__main__.py", line 3
         regrtest.main_in_temp_cwd()
       File "/usr/lib/python3.4/runpy.py", line 73
         exec(code, run_globals)
       File "/usr/lib/python3.4/runpy.py", line 160
         "__main__", fname, loader, pkg_name)

We can see that the most memory was allocated in the *note importlib:
9a. module to load data (bytecode and constants) from modules: ‘870.1
KiB’.  The traceback is where the *note importlib: 9a. loaded data most
recently: on the ‘import pdb’ line of the *note doctest: 66. module.
The traceback may change if a new module is loaded.


File: python.info,  Node: Pretty top,  Prev: Get the traceback of a memory block,  Up: Examples<27>

5.27.8.5 Pretty top
...................

Code to display the 10 lines allocating the most memory with a pretty
output, ignoring ‘<frozen importlib._bootstrap>’ and ‘<unknown>’ files:

     import linecache
     import os
     import tracemalloc

     def display_top(snapshot, key_type='lineno', limit=10):
         snapshot = snapshot.filter_traces((
             tracemalloc.Filter(False, "<frozen importlib._bootstrap>"),
             tracemalloc.Filter(False, "<unknown>"),
         ))
         top_stats = snapshot.statistics(key_type)

         print("Top %s lines" % limit)
         for index, stat in enumerate(top_stats[:limit], 1):
             frame = stat.traceback[0]
             print("#%s: %s:%s: %.1f KiB"
                   % (index, frame.filename, frame.lineno, stat.size / 1024))
             line = linecache.getline(frame.filename, frame.lineno).strip()
             if line:
                 print('    %s' % line)

         other = top_stats[limit:]
         if other:
             size = sum(stat.size for stat in other)
             print("%s other: %.1f KiB" % (len(other), size / 1024))
         total = sum(stat.size for stat in top_stats)
         print("Total allocated size: %.1f KiB" % (total / 1024))

     tracemalloc.start()

     # ... run your application ...

     snapshot = tracemalloc.take_snapshot()
     display_top(snapshot)

Example of output of the Python test suite:

     Top 10 lines
     #1: Lib/base64.py:414: 419.8 KiB
         _b85chars2 = [(a + b) for a in _b85chars for b in _b85chars]
     #2: Lib/base64.py:306: 419.8 KiB
         _a85chars2 = [(a + b) for a in _a85chars for b in _a85chars]
     #3: collections/__init__.py:368: 293.6 KiB
         exec(class_definition, namespace)
     #4: Lib/abc.py:133: 115.2 KiB
         cls = super().__new__(mcls, name, bases, namespace)
     #5: unittest/case.py:574: 103.1 KiB
         testMethod()
     #6: Lib/linecache.py:127: 95.4 KiB
         lines = fp.readlines()
     #7: urllib/parse.py:476: 71.8 KiB
         for a in _hexdig for b in _hexdig}
     #8: <string>:5: 62.0 KiB
     #9: Lib/_weakrefset.py:37: 60.0 KiB
         self.data = set()
     #10: Lib/base64.py:142: 59.8 KiB
         _b32tab2 = [a + b for a in _b32tab for b in _b32tab]
     6220 other: 3602.8 KiB
     Total allocated size: 5303.1 KiB

See *note Snapshot.statistics(): 3738. for more options.

* Menu:

* Record the current and peak size of all traced memory blocks::


File: python.info,  Node: Record the current and peak size of all traced memory blocks,  Up: Pretty top

5.27.8.6 Record the current and peak size of all traced memory blocks
.....................................................................

The following code computes two sums like ‘0 + 1 + 2 + ...’
inefficiently, by creating a list of those numbers.  This list consumes
a lot of memory temporarily.  We can use *note get_traced_memory():
373f. and *note reset_peak(): 1ec. to observe the small memory usage
after the sum is computed as well as the peak memory usage during the
computations:

     import tracemalloc

     tracemalloc.start()

     # Example code: compute a sum with a large temporary list
     large_sum = sum(list(range(100000)))

     first_size, first_peak = tracemalloc.get_traced_memory()

     tracemalloc.reset_peak()

     # Example code: compute a sum with a small temporary list
     small_sum = sum(list(range(1000)))

     second_size, second_peak = tracemalloc.get_traced_memory()

     print(f"{first_size=}, {first_peak=}")
     print(f"{second_size=}, {second_peak=}")

Output:

     first_size=664, first_peak=3592984
     second_size=804, second_peak=29704

Using *note reset_peak(): 1ec. ensured we could accurately record the
peak during the computation of ‘small_sum’, even though it is much
smaller than the overall peak size of memory blocks since the *note
start(): 1481. call.  Without the call to *note reset_peak(): 1ec,
‘second_peak’ would still be the peak from the computation ‘large_sum’
(that is, equal to ‘first_peak’).  In this case, both peaks are much
higher than the final memory usage, and which suggests we could optimise
(by removing the unnecessary call to *note list: 1f8, and writing
‘sum(range(...))’).


File: python.info,  Node: API,  Prev: Examples<27>,  Up: tracemalloc — Trace memory allocations

5.27.8.7 API
............

* Menu:

* Functions: Functions<10>.
* DomainFilter::
* Filter::
* Frame::
* Snapshot::
* Statistic::
* StatisticDiff::
* Trace::
* Traceback::


File: python.info,  Node: Functions<10>,  Next: DomainFilter,  Up: API

5.27.8.8 Functions
..................

 -- Function: tracemalloc.clear_traces ()

     Clear traces of memory blocks allocated by Python.

     See also *note stop(): 3743.

 -- Function: tracemalloc.get_object_traceback (obj)

     Get the traceback where the Python object `obj' was allocated.
     Return a *note Traceback: 504. instance, or ‘None’ if the *note
     tracemalloc: 11d. module is not tracing memory allocations or did
     not trace the allocation of the object.

     See also *note gc.get_referrers(): fb6. and *note sys.getsizeof():
     3744. functions.

 -- Function: tracemalloc.get_traceback_limit ()

     Get the maximum number of frames stored in the traceback of a
     trace.

     The *note tracemalloc: 11d. module must be tracing memory
     allocations to get the limit, otherwise an exception is raised.

     The limit is set by the *note start(): 1481. function.

 -- Function: tracemalloc.get_traced_memory ()

     Get the current size and peak size of memory blocks traced by the
     *note tracemalloc: 11d. module as a tuple: ‘(current: int, peak:
     int)’.

 -- Function: tracemalloc.reset_peak ()

     Set the peak size of memory blocks traced by the *note tracemalloc:
     11d. module to the current size.

     Do nothing if the *note tracemalloc: 11d. module is not tracing
     memory allocations.

     This function only modifies the recorded peak size, and does not
     modify or clear any traces, unlike *note clear_traces(): 3742.
     Snapshots taken with *note take_snapshot(): 3746. before a call to
     *note reset_peak(): 1ec. can be meaningfully compared to snapshots
     taken after the call.

     See also *note get_traced_memory(): 373f.

     New in version 3.9.

 -- Function: tracemalloc.get_tracemalloc_memory ()

     Get the memory usage in bytes of the *note tracemalloc: 11d. module
     used to store traces of memory blocks.  Return an *note int: 204.

 -- Function: tracemalloc.is_tracing ()

     ‘True’ if the *note tracemalloc: 11d. module is tracing Python
     memory allocations, ‘False’ otherwise.

     See also *note start(): 1481. and *note stop(): 3743. functions.

 -- Function: tracemalloc.start (nframe: int=1)

     Start tracing Python memory allocations: install hooks on Python
     memory allocators.  Collected tracebacks of traces will be limited
     to `nframe' frames.  By default, a trace of a memory block only
     stores the most recent frame: the limit is ‘1’.  `nframe' must be
     greater or equal to ‘1’.

     You can still read the original number of total frames that
     composed the traceback by looking at the *note
     Traceback.total_nframe: 3749. attribute.

     Storing more than ‘1’ frame is only useful to compute statistics
     grouped by ‘'traceback'’ or to compute cumulative statistics: see
     the *note Snapshot.compare_to(): 374a. and *note
     Snapshot.statistics(): 3738. methods.

     Storing more frames increases the memory and CPU overhead of the
     *note tracemalloc: 11d. module.  Use the *note
     get_tracemalloc_memory(): 3747. function to measure how much memory
     is used by the *note tracemalloc: 11d. module.

     The *note PYTHONTRACEMALLOC: 148c. environment variable
     (‘PYTHONTRACEMALLOC=NFRAME’) and the *note -X: 290.
     ‘tracemalloc=NFRAME’ command line option can be used to start
     tracing at startup.

     See also *note stop(): 3743, *note is_tracing(): 3748. and *note
     get_traceback_limit(): 3745. functions.

 -- Function: tracemalloc.stop ()

     Stop tracing Python memory allocations: uninstall hooks on Python
     memory allocators.  Also clears all previously collected traces of
     memory blocks allocated by Python.

     Call *note take_snapshot(): 3746. function to take a snapshot of
     traces before clearing them.

     See also *note start(): 1481, *note is_tracing(): 3748. and *note
     clear_traces(): 3742. functions.

 -- Function: tracemalloc.take_snapshot ()

     Take a snapshot of traces of memory blocks allocated by Python.
     Return a new *note Snapshot: 374b. instance.

     The snapshot does not include memory blocks allocated before the
     *note tracemalloc: 11d. module started to trace memory allocations.

     Tracebacks of traces are limited to *note get_traceback_limit():
     3745. frames.  Use the `nframe' parameter of the *note start():
     1481. function to store more frames.

     The *note tracemalloc: 11d. module must be tracing memory
     allocations to take a snapshot, see the *note start(): 1481.
     function.

     See also the *note get_object_traceback(): 129b. function.


File: python.info,  Node: DomainFilter,  Next: Filter,  Prev: Functions<10>,  Up: API

5.27.8.9 DomainFilter
.....................

 -- Class: tracemalloc.DomainFilter (inclusive: bool, domain: int)

     Filter traces of memory blocks by their address space (domain).

     New in version 3.6.

      -- Attribute: inclusive

          If `inclusive' is ‘True’ (include), match memory blocks
          allocated in the address space *note domain: 374e.

          If `inclusive' is ‘False’ (exclude), match memory blocks not
          allocated in the address space *note domain: 374e.

      -- Attribute: domain

          Address space of a memory block (‘int’).  Read-only property.


File: python.info,  Node: Filter,  Next: Frame,  Prev: DomainFilter,  Up: API

5.27.8.10 Filter
................

 -- Class: tracemalloc.Filter (inclusive: bool, filename_pattern: str,
          lineno: int=None, all_frames: bool=False, domain: int=None)

     Filter on traces of memory blocks.

     See the *note fnmatch.fnmatch(): 1dd3. function for the syntax of
     `filename_pattern'.  The ‘'.pyc'’ file extension is replaced with
     ‘'.py'’.

     Examples:

        * ‘Filter(True, subprocess.__file__)’ only includes traces of
          the *note subprocess: f9. module

        * ‘Filter(False, tracemalloc.__file__)’ excludes traces of the
          *note tracemalloc: 11d. module

        * ‘Filter(False, "<unknown>")’ excludes empty tracebacks

     Changed in version 3.5: The ‘'.pyo'’ file extension is no longer
     replaced with ‘'.py'’.

     Changed in version 3.6: Added the *note domain: 3751. attribute.

      -- Attribute: domain

          Address space of a memory block (‘int’ or ‘None’).

          tracemalloc uses the domain ‘0’ to trace memory allocations
          made by Python.  C extensions can use other domains to trace
          other resources.

      -- Attribute: inclusive

          If `inclusive' is ‘True’ (include), only match memory blocks
          allocated in a file with a name matching *note
          filename_pattern: 3753. at line number *note lineno: 3754.

          If `inclusive' is ‘False’ (exclude), ignore memory blocks
          allocated in a file with a name matching *note
          filename_pattern: 3753. at line number *note lineno: 3754.

      -- Attribute: lineno

          Line number (‘int’) of the filter.  If `lineno' is ‘None’, the
          filter matches any line number.

      -- Attribute: filename_pattern

          Filename pattern of the filter (‘str’).  Read-only property.

      -- Attribute: all_frames

          If `all_frames' is ‘True’, all frames of the traceback are
          checked.  If `all_frames' is ‘False’, only the most recent
          frame is checked.

          This attribute has no effect if the traceback limit is ‘1’.
          See the *note get_traceback_limit(): 3745. function and *note
          Snapshot.traceback_limit: 3756. attribute.


File: python.info,  Node: Frame,  Next: Snapshot,  Prev: Filter,  Up: API

5.27.8.11 Frame
...............

 -- Class: tracemalloc.Frame

     Frame of a traceback.

     The *note Traceback: 504. class is a sequence of *note Frame: 3758.
     instances.

      -- Attribute: filename

          Filename (‘str’).

      -- Attribute: lineno

          Line number (‘int’).


File: python.info,  Node: Snapshot,  Next: Statistic,  Prev: Frame,  Up: API

5.27.8.12 Snapshot
..................

 -- Class: tracemalloc.Snapshot

     Snapshot of traces of memory blocks allocated by Python.

     The *note take_snapshot(): 3746. function creates a snapshot
     instance.

      -- Method: compare_to (old_snapshot: Snapshot, key_type: str,
               cumulative: bool=False)

          Compute the differences with an old snapshot.  Get statistics
          as a sorted list of *note StatisticDiff: 375c. instances
          grouped by `key_type'.

          See the *note Snapshot.statistics(): 3738. method for
          `key_type' and `cumulative' parameters.

          The result is sorted from the biggest to the smallest by:
          absolute value of *note StatisticDiff.size_diff: 375d, *note
          StatisticDiff.size: 375e, absolute value of *note
          StatisticDiff.count_diff: 375f, *note Statistic.count: 3760.
          and then by *note StatisticDiff.traceback: 3761.

      -- Method: dump (filename)

          Write the snapshot into a file.

          Use *note load(): 373b. to reload the snapshot.

      -- Method: filter_traces (filters)

          Create a new *note Snapshot: 374b. instance with a filtered
          *note traces: 3763. sequence, `filters' is a list of *note
          DomainFilter: 697. and *note Filter: 3750. instances.  If
          `filters' is an empty list, return a new *note Snapshot: 374b.
          instance with a copy of the traces.

          All inclusive filters are applied at once, a trace is ignored
          if no inclusive filters match it.  A trace is ignored if at
          least one exclusive filter matches it.

          Changed in version 3.6: *note DomainFilter: 697. instances are
          now also accepted in `filters'.

      -- Method: classmethod load (filename)

          Load a snapshot from a file.

          See also *note dump(): 373a.

      -- Method: statistics (key_type: str, cumulative: bool=False)

          Get statistics as a sorted list of *note Statistic: 3764.
          instances grouped by `key_type':

          key_type                  description
                                    
          -------------------------------------------------------
                                    
          ‘'filename'’              filename
                                    
                                    
          ‘'lineno'’                filename and line number
                                    
                                    
          ‘'traceback'’             traceback
                                    

          If `cumulative' is ‘True’, cumulate size and count of memory
          blocks of all frames of the traceback of a trace, not only the
          most recent frame.  The cumulative mode can only be used with
          `key_type' equals to ‘'filename'’ and ‘'lineno'’.

          The result is sorted from the biggest to the smallest by:
          *note Statistic.size: 3765, *note Statistic.count: 3760. and
          then by *note Statistic.traceback: 3766.

      -- Attribute: traceback_limit

          Maximum number of frames stored in the traceback of *note
          traces: 3763.: result of the *note get_traceback_limit():
          3745. when the snapshot was taken.

      -- Attribute: traces

          Traces of all memory blocks allocated by Python: sequence of
          *note Trace: 3767. instances.

          The sequence has an undefined order.  Use the *note
          Snapshot.statistics(): 3738. method to get a sorted list of
          statistics.


File: python.info,  Node: Statistic,  Next: StatisticDiff,  Prev: Snapshot,  Up: API

5.27.8.13 Statistic
...................

 -- Class: tracemalloc.Statistic

     Statistic on memory allocations.

     *note Snapshot.statistics(): 3738. returns a list of *note
     Statistic: 3764. instances.

     See also the *note StatisticDiff: 375c. class.

      -- Attribute: count

          Number of memory blocks (‘int’).

      -- Attribute: size

          Total size of memory blocks in bytes (‘int’).

      -- Attribute: traceback

          Traceback where the memory block was allocated, *note
          Traceback: 504. instance.


File: python.info,  Node: StatisticDiff,  Next: Trace,  Prev: Statistic,  Up: API

5.27.8.14 StatisticDiff
.......................

 -- Class: tracemalloc.StatisticDiff

     Statistic difference on memory allocations between an old and a new
     *note Snapshot: 374b. instance.

     *note Snapshot.compare_to(): 374a. returns a list of *note
     StatisticDiff: 375c. instances.  See also the *note Statistic:
     3764. class.

      -- Attribute: count

          Number of memory blocks in the new snapshot (‘int’): ‘0’ if
          the memory blocks have been released in the new snapshot.

      -- Attribute: count_diff

          Difference of number of memory blocks between the old and the
          new snapshots (‘int’): ‘0’ if the memory blocks have been
          allocated in the new snapshot.

      -- Attribute: size

          Total size of memory blocks in bytes in the new snapshot
          (‘int’): ‘0’ if the memory blocks have been released in the
          new snapshot.

      -- Attribute: size_diff

          Difference of total size of memory blocks in bytes between the
          old and the new snapshots (‘int’): ‘0’ if the memory blocks
          have been allocated in the new snapshot.

      -- Attribute: traceback

          Traceback where the memory blocks were allocated, *note
          Traceback: 504. instance.


File: python.info,  Node: Trace,  Next: Traceback,  Prev: StatisticDiff,  Up: API

5.27.8.15 Trace
...............

 -- Class: tracemalloc.Trace

     Trace of a memory block.

     The *note Snapshot.traces: 3763. attribute is a sequence of *note
     Trace: 3767. instances.

     Changed in version 3.6: Added the *note domain: 376c. attribute.

      -- Attribute: domain

          Address space of a memory block (‘int’).  Read-only property.

          tracemalloc uses the domain ‘0’ to trace memory allocations
          made by Python.  C extensions can use other domains to trace
          other resources.

      -- Attribute: size

          Size of the memory block in bytes (‘int’).

      -- Attribute: traceback

          Traceback where the memory block was allocated, *note
          Traceback: 504. instance.


File: python.info,  Node: Traceback,  Prev: Trace,  Up: API

5.27.8.16 Traceback
...................

 -- Class: tracemalloc.Traceback

     Sequence of *note Frame: 3758. instances sorted from the oldest
     frame to the most recent frame.

     A traceback contains at least ‘1’ frame.  If the ‘tracemalloc’
     module failed to get a frame, the filename ‘"<unknown>"’ at line
     number ‘0’ is used.

     When a snapshot is taken, tracebacks of traces are limited to *note
     get_traceback_limit(): 3745. frames.  See the *note
     take_snapshot(): 3746. function.  The original number of frames of
     the traceback is stored in the *note Traceback.total_nframe: 3749.
     attribute.  That allows to know if a traceback has been truncated
     by the traceback limit.

     The *note Trace.traceback: 376e. attribute is an instance of *note
     Traceback: 504. instance.

     Changed in version 3.7: Frames are now sorted from the oldest to
     the most recent, instead of most recent to oldest.

      -- Attribute: total_nframe

          Total number of frames that composed the traceback before
          truncation.  This attribute can be set to ‘None’ if the
          information is not available.

     Changed in version 3.9: The *note Traceback.total_nframe: 3749.
     attribute was added.

      -- Method: format (limit=None, most_recent_first=False)

          Format the traceback as a list of lines.  Use the *note
          linecache: a8. module to retrieve lines from the source code.
          If `limit' is set, format the `limit' most recent frames if
          `limit' is positive.  Otherwise, format the ‘abs(limit)’
          oldest frames.  If `most_recent_first' is ‘True’, the order of
          the formatted frames is reversed, returning the most recent
          frame first instead of last.

          Similar to the *note traceback.format_tb(): 3770. function,
          except that *note format(): 505. does not include newlines.

          Example:

               print("Traceback (most recent call first):")
               for line in traceback:
                   print(line)

          Output:

               Traceback (most recent call first):
                 File "test.py", line 9
                   obj = Object()
                 File "test.py", line 12
                   tb = tracemalloc.get_object_traceback(f())


File: python.info,  Node: Software Packaging and Distribution,  Next: Python Runtime Services,  Prev: Debugging and Profiling,  Up: The Python Standard Library

5.28 Software Packaging and Distribution
========================================

These libraries help you with publishing and installing Python software.
While these modules are designed to work in conjunction with the Python
Package Index(1), they can also be used with a local index server, or
without any index server at all.

* Menu:

* distutils — Building and installing Python modules::
* ensurepip — Bootstrapping the pip installer::
* venv — Creation of virtual environments::
* zipapp — Manage executable Python zip archives::

   ---------- Footnotes ----------

   (1) https://pypi.org


File: python.info,  Node: distutils — Building and installing Python modules,  Next: ensurepip — Bootstrapping the pip installer,  Up: Software Packaging and Distribution

5.28.1 ‘distutils’ — Building and installing Python modules
-----------------------------------------------------------

__________________________________________________________________

The *note distutils: 38. package provides support for building and
installing additional modules into a Python installation.  The new
modules may be either 100%-pure Python, or may be extension modules
written in C, or may be collections of Python packages which include
modules coded in both Python and C.

Most Python users will `not' want to use this module directly, but
instead use the cross-version tools maintained by the Python Packaging
Authority.  In particular, setuptools(1) is an enhanced alternative to
*note distutils: 38. that provides:

   * support for declaring project dependencies

   * additional mechanisms for configuring which files to include in
     source releases (including plugins for integration with version
     control systems)

   * the ability to declare project “entry points”, which can be used as
     the basis for application plugin systems

   * the ability to automatically generate Windows command line
     executables at installation time rather than needing to prebuild
     them

   * consistent behaviour across all supported Python versions

The recommended pip(2) installer runs all ‘setup.py’ scripts with
‘setuptools’, even if the script itself only imports ‘distutils’.  Refer
to the Python Packaging User Guide(3) for more information.

For the benefits of packaging tool authors and users seeking a deeper
understanding of the details of the current packaging and distribution
system, the legacy *note distutils: 38. based user documentation and API
reference remain available:

   * *note Installing Python Modules (Legacy version): 8e4.

   * *note Distributing Python Modules (Legacy version): 8e5.

   ---------- Footnotes ----------

   (1) https://setuptools.readthedocs.io/en/latest/

   (2) https://pip.pypa.io/

   (3) https://packaging.python.org


File: python.info,  Node: ensurepip — Bootstrapping the pip installer,  Next: venv — Creation of virtual environments,  Prev: distutils — Building and installing Python modules,  Up: Software Packaging and Distribution

5.28.2 ‘ensurepip’ — Bootstrapping the ‘pip’ installer
------------------------------------------------------

New in version 3.4.

__________________________________________________________________

The *note ensurepip: 78. package provides support for bootstrapping the
‘pip’ installer into an existing Python installation or virtual
environment.  This bootstrapping approach reflects the fact that ‘pip’
is an independent project with its own release cycle, and the latest
available stable version is bundled with maintenance and feature
releases of the CPython reference interpreter.

In most cases, end users of Python shouldn’t need to invoke this module
directly (as ‘pip’ should be bootstrapped by default), but it may be
needed if installing ‘pip’ was skipped when installing Python (or when
creating a virtual environment) or after explicitly uninstalling ‘pip’.

     Note: This module `does not' access the internet.  All of the
     components needed to bootstrap ‘pip’ are included as internal parts
     of the package.

See also
........

*note Installing Python Modules: 8e2.

     The end user guide for installing Python packages

PEP 453(1): Explicit bootstrapping of pip in Python installations

     The original rationale and specification for this module.

* Menu:

* Command line interface::
* Module API::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0453


File: python.info,  Node: Command line interface,  Next: Module API,  Up: ensurepip — Bootstrapping the pip installer

5.28.2.1 Command line interface
...............................

The command line interface is invoked using the interpreter’s ‘-m’
switch.

The simplest possible invocation is:

     python -m ensurepip

This invocation will install ‘pip’ if it is not already installed, but
otherwise does nothing.  To ensure the installed version of ‘pip’ is at
least as recent as the one bundled with ‘ensurepip’, pass the
‘--upgrade’ option:

     python -m ensurepip --upgrade

By default, ‘pip’ is installed into the current virtual environment (if
one is active) or into the system site packages (if there is no active
virtual environment).  The installation location can be controlled
through two additional command line options:

   * ‘--root <dir>’: Installs ‘pip’ relative to the given root directory
     rather than the root of the currently active virtual environment
     (if any) or the default root for the current Python installation.

   * ‘--user’: Installs ‘pip’ into the user site packages directory
     rather than globally for the current Python installation (this
     option is not permitted inside an active virtual environment).

By default, the scripts ‘pipX’ and ‘pipX.Y’ will be installed (where X.Y
stands for the version of Python used to invoke ‘ensurepip’).  The
scripts installed can be controlled through two additional command line
options:

   * ‘--altinstall’: if an alternate installation is requested, the
     ‘pipX’ script will `not' be installed.

   * ‘--default-pip’: if a “default pip” installation is requested, the
     ‘pip’ script will be installed in addition to the two regular
     scripts.

Providing both of the script selection options will trigger an
exception.


File: python.info,  Node: Module API,  Prev: Command line interface,  Up: ensurepip — Bootstrapping the pip installer

5.28.2.2 Module API
...................

*note ensurepip: 78. exposes two functions for programmatic use:

 -- Function: ensurepip.version ()

     Returns a string specifying the bundled version of pip that will be
     installed when bootstrapping an environment.

 -- Function: ensurepip.bootstrap (root=None, upgrade=False, user=False,
          altinstall=False, default_pip=False, verbosity=0)

     Bootstraps ‘pip’ into the current or designated environment.

     `root' specifies an alternative root directory to install relative
     to.  If `root' is ‘None’, then installation uses the default
     install location for the current environment.

     `upgrade' indicates whether or not to upgrade an existing
     installation of an earlier version of ‘pip’ to the bundled version.

     `user' indicates whether to use the user scheme rather than
     installing globally.

     By default, the scripts ‘pipX’ and ‘pipX.Y’ will be installed
     (where X.Y stands for the current version of Python).

     If `altinstall' is set, then ‘pipX’ will `not' be installed.

     If `default_pip' is set, then ‘pip’ will be installed in addition
     to the two regular scripts.

     Setting both `altinstall' and `default_pip' will trigger *note
     ValueError: 16d.

     `verbosity' controls the level of output to *note sys.stdout: 41f.
     from the bootstrapping operation.

     Raises an *note auditing event: fa1. ‘ensurepip.bootstrap’ with
     argument ‘root’.

          Note: The bootstrapping process has side effects on both
          ‘sys.path’ and ‘os.environ’.  Invoking the command line
          interface in a subprocess instead allows these side effects to
          be avoided.

          Note: The bootstrapping process may install additional modules
          required by ‘pip’, but other software should not assume those
          dependencies will always be present by default (as the
          dependencies may be removed in a future version of ‘pip’).


File: python.info,  Node: venv — Creation of virtual environments,  Next: zipapp — Manage executable Python zip archives,  Prev: ensurepip — Bootstrapping the pip installer,  Up: Software Packaging and Distribution

5.28.3 ‘venv’ — Creation of virtual environments
------------------------------------------------

New in version 3.3.

`Source code:' Lib/venv/(1)

__________________________________________________________________

The *note venv: 12e. module provides support for creating lightweight
“virtual environments” with their own site directories, optionally
isolated from system site directories.  Each virtual environment has its
own Python binary (which matches the version of the binary that was used
to create this environment) and can have its own independent set of
installed Python packages in its site directories.

See PEP 405(2) for more information about Python virtual environments.

See also
........

Python Packaging User Guide: Creating and using virtual environments(3)

* Menu:

* Creating virtual environments::
* API: API<2>.
* An example of extending EnvBuilder::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/venv/

   (2) https://www.python.org/dev/peps/pep-0405

   (3) 
https://packaging.python.org/guides/installing-using-pip-and-virtual-environments/#creating-a-virtual-environment


File: python.info,  Node: Creating virtual environments,  Next: API<2>,  Up: venv — Creation of virtual environments

5.28.3.1 Creating virtual environments
......................................

Creation of *note virtual environments: 377e. is done by executing the
command ‘venv’:

     python3 -m venv /path/to/new/virtual/environment

Running this command creates the target directory (creating any parent
directories that don’t exist already) and places a ‘pyvenv.cfg’ file in
it with a ‘home’ key pointing to the Python installation from which the
command was run (a common name for the target directory is ‘.venv’).  It
also creates a ‘bin’ (or ‘Scripts’ on Windows) subdirectory containing a
copy/symlink of the Python binary/binaries (as appropriate for the
platform or arguments used at environment creation time).  It also
creates an (initially empty) ‘lib/pythonX.Y/site-packages’ subdirectory
(on Windows, this is ‘Lib\site-packages’).  If an existing directory is
specified, it will be re-used.

Deprecated since version 3.6: ‘pyvenv’ was the recommended tool for
creating virtual environments for Python 3.3 and 3.4, and is deprecated
in Python 3.6(1).

Changed in version 3.5: The use of ‘venv’ is now recommended for
creating virtual environments.

On Windows, invoke the ‘venv’ command as follows:

     c:\>c:\Python35\python -m venv c:\path\to\myenv

Alternatively, if you configured the ‘PATH’ and ‘PATHEXT’ variables for
your *note Python installation: 3f8.:

     c:\>python -m venv c:\path\to\myenv

The command, if run with ‘-h’, will show the available options:

     usage: venv [-h] [--system-site-packages] [--symlinks | --copies] [--clear]
                 [--upgrade] [--without-pip] [--prompt PROMPT] [--upgrade-deps]
                 ENV_DIR [ENV_DIR ...]

     Creates virtual Python environments in one or more target directories.

     positional arguments:
       ENV_DIR               A directory to create the environment in.

     optional arguments:
       -h, --help            show this help message and exit
       --system-site-packages
                             Give the virtual environment access to the system
                             site-packages dir.
       --symlinks            Try to use symlinks rather than copies, when symlinks
                             are not the default for the platform.
       --copies              Try to use copies rather than symlinks, even when
                             symlinks are the default for the platform.
       --clear               Delete the contents of the environment directory if it
                             already exists, before environment creation.
       --upgrade             Upgrade the environment directory to use this version
                             of Python, assuming Python has been upgraded in-place.
       --without-pip         Skips installing or upgrading pip in the virtual
                             environment (pip is bootstrapped by default)
       --prompt PROMPT       Provides an alternative prompt prefix for this
                             environment.
       --upgrade-deps        Upgrade core dependencies: pip setuptools to the
                             latest version in PyPI

     Once an environment has been created, you may wish to activate it, e.g. by
     sourcing an activate script in its bin directory.

Changed in version 3.9: Add ‘--upgrade-deps’ option to upgrade pip +
setuptools to the latest on PyPI

Changed in version 3.4: Installs pip by default, added the
‘--without-pip’ and ‘--copies’ options

Changed in version 3.4: In earlier versions, if the target directory
already existed, an error was raised, unless the ‘--clear’ or
‘--upgrade’ option was provided.

     Note: While symlinks are supported on Windows, they are not
     recommended.  Of particular note is that double-clicking
     ‘python.exe’ in File Explorer will resolve the symlink eagerly and
     ignore the virtual environment.

     Note: On Microsoft Windows, it may be required to enable the
     ‘Activate.ps1’ script by setting the execution policy for the user.
     You can do this by issuing the following PowerShell command:

     PS C:> Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope
     CurrentUser

     See About Execution Policies(2) for more information.

The created ‘pyvenv.cfg’ file also includes the
‘include-system-site-packages’ key, set to ‘true’ if ‘venv’ is run with
the ‘--system-site-packages’ option, ‘false’ otherwise.

Unless the ‘--without-pip’ option is given, *note ensurepip: 78. will be
invoked to bootstrap ‘pip’ into the virtual environment.

Multiple paths can be given to ‘venv’, in which case an identical
virtual environment will be created, according to the given options, at
each provided path.

Once a virtual environment has been created, it can be “activated” using
a script in the virtual environment’s binary directory.  The invocation
of the script is platform-specific (‘<venv>’ must be replaced by the
path of the directory containing the virtual environment):

Platform          Shell                 Command to activate virtual environment
                                        
--------------------------------------------------------------------------------------
                                        
POSIX             bash/zsh              $ source <venv>/bin/activate
                                        
                                        
                  fish                  $ source <venv>/bin/activate.fish
                                        
                                        
                  csh/tcsh              $ source <venv>/bin/activate.csh
                                        
                                        
                  PowerShell Core       $ <venv>/bin/Activate.ps1
                                        
                                        
Windows           cmd.exe               C:\> <venv>\Scripts\activate.bat
                                        
                                        
                  PowerShell            PS C:\> <venv>\Scripts\Activate.ps1
                                        

When a virtual environment is active, the ‘VIRTUAL_ENV’ environment
variable is set to the path of the virtual environment.  This can be
used to check if one is running inside a virtual environment.

You don’t specifically `need' to activate an environment; activation
just prepends the virtual environment’s binary directory to your path,
so that “python” invokes the virtual environment’s Python interpreter
and you can run installed scripts without having to use their full path.
However, all scripts installed in a virtual environment should be
runnable without activating it, and run with the virtual environment’s
Python automatically.

You can deactivate a virtual environment by typing “deactivate” in your
shell.  The exact mechanism is platform-specific and is an internal
implementation detail (typically a script or shell function will be
used).

New in version 3.4: ‘fish’ and ‘csh’ activation scripts.

New in version 3.8: PowerShell activation scripts installed under POSIX
for PowerShell Core support.

     Note: A virtual environment is a Python environment such that the
     Python interpreter, libraries and scripts installed into it are
     isolated from those installed in other virtual environments, and
     (by default) any libraries installed in a “system” Python, i.e.,
     one which is installed as part of your operating system.

     A virtual environment is a directory tree which contains Python
     executable files and other files which indicate that it is a
     virtual environment.

     Common installation tools such as setuptools(3) and pip(4) work as
     expected with virtual environments.  In other words, when a virtual
     environment is active, they install Python packages into the
     virtual environment without needing to be told to do so explicitly.

     When a virtual environment is active (i.e., the virtual
     environment’s Python interpreter is running), the attributes *note
     sys.prefix: 377f. and *note sys.exec_prefix: 3780. point to the
     base directory of the virtual environment, whereas *note
     sys.base_prefix: 3180. and *note sys.base_exec_prefix: 3781. point
     to the non-virtual environment Python installation which was used
     to create the virtual environment.  If a virtual environment is not
     active, then *note sys.prefix: 377f. is the same as *note
     sys.base_prefix: 3180. and *note sys.exec_prefix: 3780. is the same
     as *note sys.base_exec_prefix: 3781. (they all point to a
     non-virtual environment Python installation).

     When a virtual environment is active, any options that change the
     installation path will be ignored from all *note distutils: 38.
     configuration files to prevent projects being inadvertently
     installed outside of the virtual environment.

     When working in a command shell, users can make a virtual
     environment active by running an ‘activate’ script in the virtual
     environment’s executables directory (the precise filename and
     command to use the file is shell-dependent), which prepends the
     virtual environment’s directory for executables to the ‘PATH’
     environment variable for the running shell.  There should be no
     need in other circumstances to activate a virtual environment;
     scripts installed into virtual environments have a “shebang” line
     which points to the virtual environment’s Python interpreter.  This
     means that the script will run with that interpreter regardless of
     the value of ‘PATH’.  On Windows, “shebang” line processing is
     supported if you have the Python Launcher for Windows installed
     (this was added to Python in 3.3 - see PEP 397(5) for more
     details).  Thus, double-clicking an installed script in a Windows
     Explorer window should run the script with the correct interpreter
     without there needing to be any reference to its virtual
     environment in ‘PATH’.

   ---------- Footnotes ----------

   (1) https://docs.python.org/dev/whatsnew/3.6.html#deprecated-features

   (2) https://go.microsoft.com/fwlink/?LinkID=135170

   (3) https://pypi.org/project/setuptools/

   (4) https://pypi.org/project/pip/

   (5) https://www.python.org/dev/peps/pep-0397


File: python.info,  Node: API<2>,  Next: An example of extending EnvBuilder,  Prev: Creating virtual environments,  Up: venv — Creation of virtual environments

5.28.3.2 API
............

The high-level method described above makes use of a simple API which
provides mechanisms for third-party virtual environment creators to
customize environment creation according to their needs, the *note
EnvBuilder: 9ee. class.

 -- Class: venv.EnvBuilder (system_site_packages=False, clear=False,
          symlinks=False, upgrade=False, with_pip=False, prompt=None,
          upgrade_deps=False)

     The *note EnvBuilder: 9ee. class accepts the following keyword
     arguments on instantiation:

        * ‘system_site_packages’ – a Boolean value indicating that the
          system Python site-packages should be available to the
          environment (defaults to ‘False’).

        * ‘clear’ – a Boolean value which, if true, will delete the
          contents of any existing target directory, before creating the
          environment.

        * ‘symlinks’ – a Boolean value indicating whether to attempt to
          symlink the Python binary rather than copying.

        * ‘upgrade’ – a Boolean value which, if true, will upgrade an
          existing environment with the running Python - for use when
          that Python has been upgraded in-place (defaults to ‘False’).

        * ‘with_pip’ – a Boolean value which, if true, ensures pip is
          installed in the virtual environment.  This uses *note
          ensurepip: 78. with the ‘--default-pip’ option.

        * ‘prompt’ – a String to be used after virtual environment is
          activated (defaults to ‘None’ which means directory name of
          the environment would be used).  If the special string ‘"."’
          is provided, the basename of the current directory is used as
          the prompt.

        * ‘upgrade_deps’ – Update the base venv modules to the latest on
          PyPI

     Changed in version 3.4: Added the ‘with_pip’ parameter

     New in version 3.6: Added the ‘prompt’ parameter

     New in version 3.9: Added the ‘upgrade_deps’ parameter

     Creators of third-party virtual environment tools will be free to
     use the provided *note EnvBuilder: 9ee. class as a base class.

     The returned env-builder is an object which has a method, ‘create’:

      -- Method: create (env_dir)

          Create a virtual environment by specifying the target
          directory (absolute or relative to the current directory)
          which is to contain the virtual environment.  The ‘create’
          method will either create the environment in the specified
          directory, or raise an appropriate exception.

          The ‘create’ method of the *note EnvBuilder: 9ee. class
          illustrates the hooks available for subclass customization:

               def create(self, env_dir):
                   """
                   Create a virtualized Python environment in a directory.
                   env_dir is the target directory to create an environment in.
                   """
                   env_dir = os.path.abspath(env_dir)
                   context = self.ensure_directories(env_dir)
                   self.create_configuration(context)
                   self.setup_python(context)
                   self.setup_scripts(context)
                   self.post_setup(context)

          Each of the methods *note ensure_directories(): 3784, *note
          create_configuration(): 3785, *note setup_python(): 3786,
          *note setup_scripts(): 3787. and *note post_setup(): 3788. can
          be overridden.

      -- Method: ensure_directories (env_dir)

          Creates the environment directory and all necessary
          directories, and returns a context object.  This is just a
          holder for attributes (such as paths), for use by the other
          methods.  The directories are allowed to exist already, as
          long as either ‘clear’ or ‘upgrade’ were specified to allow
          operating on an existing environment directory.

      -- Method: create_configuration (context)

          Creates the ‘pyvenv.cfg’ configuration file in the
          environment.

      -- Method: setup_python (context)

          Creates a copy or symlink to the Python executable in the
          environment.  On POSIX systems, if a specific executable
          ‘python3.x’ was used, symlinks to ‘python’ and ‘python3’ will
          be created pointing to that executable, unless files with
          those names already exist.

      -- Method: setup_scripts (context)

          Installs activation scripts appropriate to the platform into
          the virtual environment.

      -- Method: upgrade_dependencies (context)

          Upgrades the core venv dependency packages (currently ‘pip’
          and ‘setuptools’) in the environment.  This is done by
          shelling out to the ‘pip’ executable in the environment.

          New in version 3.9.

      -- Method: post_setup (context)

          A placeholder method which can be overridden in third party
          implementations to pre-install packages in the virtual
          environment or perform other post-creation steps.

     Changed in version 3.7.2: Windows now uses redirector scripts for
     ‘python[w].exe’ instead of copying the actual binaries.  In 3.7.2
     only *note setup_python(): 3786. does nothing unless running from a
     build in the source tree.

     Changed in version 3.7.3: Windows copies the redirector scripts as
     part of *note setup_python(): 3786. instead of *note
     setup_scripts(): 3787.  This was not the case in 3.7.2.  When using
     symlinks, the original executables will be linked.

     In addition, *note EnvBuilder: 9ee. provides this utility method
     that can be called from *note setup_scripts(): 3787. or *note
     post_setup(): 3788. in subclasses to assist in installing custom
     scripts into the virtual environment.

      -- Method: install_scripts (context, path)

          `path' is the path to a directory that should contain
          subdirectories “common”, “posix”, “nt”, each containing
          scripts destined for the bin directory in the environment.
          The contents of “common” and the directory corresponding to
          *note os.name: 2040. are copied after some text replacement of
          placeholders:

             * ‘__VENV_DIR__’ is replaced with the absolute path of the
               environment directory.

             * ‘__VENV_NAME__’ is replaced with the environment name
               (final path segment of environment directory).

             * ‘__VENV_PROMPT__’ is replaced with the prompt (the
               environment name surrounded by parentheses and with a
               following space)

             * ‘__VENV_BIN_NAME__’ is replaced with the name of the bin
               directory (either ‘bin’ or ‘Scripts’).

             * ‘__VENV_PYTHON__’ is replaced with the absolute path of
               the environment’s executable.

          The directories are allowed to exist (for when an existing
          environment is being upgraded).

There is also a module-level convenience function:

 -- Function: venv.create (env_dir, system_site_packages=False,
          clear=False, symlinks=False, with_pip=False, prompt=None)

     Create an *note EnvBuilder: 9ee. with the given keyword arguments,
     and call its *note create(): 3783. method with the `env_dir'
     argument.

     New in version 3.3.

     Changed in version 3.4: Added the ‘with_pip’ parameter

     Changed in version 3.6: Added the ‘prompt’ parameter


File: python.info,  Node: An example of extending EnvBuilder,  Prev: API<2>,  Up: venv — Creation of virtual environments

5.28.3.3 An example of extending ‘EnvBuilder’
.............................................

The following script shows how to extend *note EnvBuilder: 9ee. by
implementing a subclass which installs setuptools and pip into a created
virtual environment:

     import os
     import os.path
     from subprocess import Popen, PIPE
     import sys
     from threading import Thread
     from urllib.parse import urlparse
     from urllib.request import urlretrieve
     import venv

     class ExtendedEnvBuilder(venv.EnvBuilder):
         """
         This builder installs setuptools and pip so that you can pip or
         easy_install other packages into the created virtual environment.

         :param nodist: If true, setuptools and pip are not installed into the
                        created virtual environment.
         :param nopip: If true, pip is not installed into the created
                       virtual environment.
         :param progress: If setuptools or pip are installed, the progress of the
                          installation can be monitored by passing a progress
                          callable. If specified, it is called with two
                          arguments: a string indicating some progress, and a
                          context indicating where the string is coming from.
                          The context argument can have one of three values:
                          'main', indicating that it is called from virtualize()
                          itself, and 'stdout' and 'stderr', which are obtained
                          by reading lines from the output streams of a subprocess
                          which is used to install the app.

                          If a callable is not specified, default progress
                          information is output to sys.stderr.
         """

         def __init__(self, *args, **kwargs):
             self.nodist = kwargs.pop('nodist', False)
             self.nopip = kwargs.pop('nopip', False)
             self.progress = kwargs.pop('progress', None)
             self.verbose = kwargs.pop('verbose', False)
             super().__init__(*args, **kwargs)

         def post_setup(self, context):
             """
             Set up any packages which need to be pre-installed into the
             virtual environment being created.

             :param context: The information for the virtual environment
                             creation request being processed.
             """
             os.environ['VIRTUAL_ENV'] = context.env_dir
             if not self.nodist:
                 self.install_setuptools(context)
             # Can't install pip without setuptools
             if not self.nopip and not self.nodist:
                 self.install_pip(context)

         def reader(self, stream, context):
             """
             Read lines from a subprocess' output stream and either pass to a progress
             callable (if specified) or write progress information to sys.stderr.
             """
             progress = self.progress
             while True:
                 s = stream.readline()
                 if not s:
                     break
                 if progress is not None:
                     progress(s, context)
                 else:
                     if not self.verbose:
                         sys.stderr.write('.')
                     else:
                         sys.stderr.write(s.decode('utf-8'))
                     sys.stderr.flush()
             stream.close()

         def install_script(self, context, name, url):
             _, _, path, _, _, _ = urlparse(url)
             fn = os.path.split(path)[-1]
             binpath = context.bin_path
             distpath = os.path.join(binpath, fn)
             # Download script into the virtual environment's binaries folder
             urlretrieve(url, distpath)
             progress = self.progress
             if self.verbose:
                 term = '\n'
             else:
                 term = ''
             if progress is not None:
                 progress('Installing %s ...%s' % (name, term), 'main')
             else:
                 sys.stderr.write('Installing %s ...%s' % (name, term))
                 sys.stderr.flush()
             # Install in the virtual environment
             args = [context.env_exe, fn]
             p = Popen(args, stdout=PIPE, stderr=PIPE, cwd=binpath)
             t1 = Thread(target=self.reader, args=(p.stdout, 'stdout'))
             t1.start()
             t2 = Thread(target=self.reader, args=(p.stderr, 'stderr'))
             t2.start()
             p.wait()
             t1.join()
             t2.join()
             if progress is not None:
                 progress('done.', 'main')
             else:
                 sys.stderr.write('done.\n')
             # Clean up - no longer needed
             os.unlink(distpath)

         def install_setuptools(self, context):
             """
             Install setuptools in the virtual environment.

             :param context: The information for the virtual environment
                             creation request being processed.
             """
             url = 'https://bitbucket.org/pypa/setuptools/downloads/ez_setup.py'
             self.install_script(context, 'setuptools', url)
             # clear up the setuptools archive which gets downloaded
             pred = lambda o: o.startswith('setuptools-') and o.endswith('.tar.gz')
             files = filter(pred, os.listdir(context.bin_path))
             for f in files:
                 f = os.path.join(context.bin_path, f)
                 os.unlink(f)

         def install_pip(self, context):
             """
             Install pip in the virtual environment.

             :param context: The information for the virtual environment
                             creation request being processed.
             """
             url = 'https://bootstrap.pypa.io/get-pip.py'
             self.install_script(context, 'pip', url)

     def main(args=None):
         compatible = True
         if sys.version_info < (3, 3):
             compatible = False
         elif not hasattr(sys, 'base_prefix'):
             compatible = False
         if not compatible:
             raise ValueError('This script is only for use with '
                              'Python 3.3 or later')
         else:
             import argparse

             parser = argparse.ArgumentParser(prog=__name__,
                                              description='Creates virtual Python '
                                                          'environments in one or '
                                                          'more target '
                                                          'directories.')
             parser.add_argument('dirs', metavar='ENV_DIR', nargs='+',
                                 help='A directory in which to create the '
                                      'virtual environment.')
             parser.add_argument('--no-setuptools', default=False,
                                 action='store_true', dest='nodist',
                                 help="Don't install setuptools or pip in the "
                                      "virtual environment.")
             parser.add_argument('--no-pip', default=False,
                                 action='store_true', dest='nopip',
                                 help="Don't install pip in the virtual "
                                      "environment.")
             parser.add_argument('--system-site-packages', default=False,
                                 action='store_true', dest='system_site',
                                 help='Give the virtual environment access to the '
                                      'system site-packages dir.')
             if os.name == 'nt':
                 use_symlinks = False
             else:
                 use_symlinks = True
             parser.add_argument('--symlinks', default=use_symlinks,
                                 action='store_true', dest='symlinks',
                                 help='Try to use symlinks rather than copies, '
                                      'when symlinks are not the default for '
                                      'the platform.')
             parser.add_argument('--clear', default=False, action='store_true',
                                 dest='clear', help='Delete the contents of the '
                                                    'virtual environment '
                                                    'directory if it already '
                                                    'exists, before virtual '
                                                    'environment creation.')
             parser.add_argument('--upgrade', default=False, action='store_true',
                                 dest='upgrade', help='Upgrade the virtual '
                                                      'environment directory to '
                                                      'use this version of '
                                                      'Python, assuming Python '
                                                      'has been upgraded '
                                                      'in-place.')
             parser.add_argument('--verbose', default=False, action='store_true',
                                 dest='verbose', help='Display the output '
                                                    'from the scripts which '
                                                    'install setuptools and pip.')
             options = parser.parse_args(args)
             if options.upgrade and options.clear:
                 raise ValueError('you cannot supply --upgrade and --clear together.')
             builder = ExtendedEnvBuilder(system_site_packages=options.system_site,
                                            clear=options.clear,
                                            symlinks=options.symlinks,
                                            upgrade=options.upgrade,
                                            nodist=options.nodist,
                                            nopip=options.nopip,
                                            verbose=options.verbose)
             for d in options.dirs:
                 builder.create(d)

     if __name__ == '__main__':
         rc = 1
         try:
             main()
             rc = 0
         except Exception as e:
             print('Error: %s' % e, file=sys.stderr)
         sys.exit(rc)

This script is also available for download online(1).

   ---------- Footnotes ----------

   (1) https://gist.github.com/vsajip/4673395


File: python.info,  Node: zipapp — Manage executable Python zip archives,  Prev: venv — Creation of virtual environments,  Up: Software Packaging and Distribution

5.28.4 ‘zipapp’ — Manage executable Python zip archives
-------------------------------------------------------

New in version 3.5.

`Source code:' Lib/zipapp.py(1)

__________________________________________________________________

This module provides tools to manage the creation of zip files
containing Python code, which can be *note executed directly by the
Python interpreter: 146e.  The module provides both a *note Command-Line
Interface: 378f. and a *note Python API: 3790.

* Menu:

* Basic Example::
* Command-Line Interface: Command-Line Interface<5>.
* Python API::
* Examples: Examples<28>.
* Specifying the Interpreter::
* Creating Standalone Applications with zipapp::
* The Python Zip Application Archive Format::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/zipapp.py


File: python.info,  Node: Basic Example,  Next: Command-Line Interface<5>,  Up: zipapp — Manage executable Python zip archives

5.28.4.1 Basic Example
......................

The following example shows how the *note Command-Line Interface: 378f.
can be used to create an executable archive from a directory containing
Python code.  When run, the archive will execute the ‘main’ function
from the module ‘myapp’ in the archive.

     $ python -m zipapp myapp -m "myapp:main"
     $ python myapp.pyz
     <output from myapp>


File: python.info,  Node: Command-Line Interface<5>,  Next: Python API,  Prev: Basic Example,  Up: zipapp — Manage executable Python zip archives

5.28.4.2 Command-Line Interface
...............................

When called as a program from the command line, the following form is
used:

     $ python -m zipapp source [options]

If `source' is a directory, this will create an archive from the
contents of `source'.  If `source' is a file, it should be an archive,
and it will be copied to the target archive (or the contents of its
shebang line will be displayed if the –info option is specified).

The following options are understood:

 -- Program Option: -o <output>, --output=<output>

     Write the output to a file named `output'.  If this option is not
     specified, the output filename will be the same as the input
     `source', with the extension ‘.pyz’ added.  If an explicit filename
     is given, it is used as is (so a ‘.pyz’ extension should be
     included if required).

     An output filename must be specified if the `source' is an archive
     (and in that case, `output' must not be the same as `source').

 -- Program Option: -p <interpreter>, --python=<interpreter>

     Add a ‘#!’ line to the archive specifying `interpreter' as the
     command to run.  Also, on POSIX, make the archive executable.  The
     default is to write no ‘#!’ line, and not make the file executable.

 -- Program Option: -m <mainfn>, --main=<mainfn>

     Write a ‘__main__.py’ file to the archive that executes `mainfn'.
     The `mainfn' argument should have the form “pkg.mod:fn”, where
     “pkg.mod” is a package/module in the archive, and “fn” is a
     callable in the given module.  The ‘__main__.py’ file will execute
     that callable.

     *note –main: 3795. cannot be specified when copying an archive.

 -- Program Option: -c, --compress

     Compress files with the deflate method, reducing the size of the
     output file.  By default, files are stored uncompressed in the
     archive.

     *note –compress: 3796. has no effect when copying an archive.

     New in version 3.7.

 -- Program Option: --info

     Display the interpreter embedded in the archive, for diagnostic
     purposes.  In this case, any other options are ignored and SOURCE
     must be an archive, not a directory.

 -- Program Option: -h, --help

     Print a short usage message and exit.


File: python.info,  Node: Python API,  Next: Examples<28>,  Prev: Command-Line Interface<5>,  Up: zipapp — Manage executable Python zip archives

5.28.4.3 Python API
...................

The module defines two convenience functions:

 -- Function: zipapp.create_archive (source, target=None,
          interpreter=None, main=None, filter=None, compressed=False)

     Create an application archive from `source'.  The source can be any
     of the following:

        * The name of a directory, or a *note path-like object: 472.
          referring to a directory, in which case a new application
          archive will be created from the content of that directory.

        * The name of an existing application archive file, or a *note
          path-like object: 472. referring to such a file, in which case
          the file is copied to the target (modifying it to reflect the
          value given for the `interpreter' argument).  The file name
          should include the ‘.pyz’ extension, if required.

        * A file object open for reading in bytes mode.  The content of
          the file should be an application archive, and the file object
          is assumed to be positioned at the start of the archive.

     The `target' argument determines where the resulting archive will
     be written:

        * If it is the name of a file, or a *note path-like object: 472,
          the archive will be written to that file.

        * If it is an open file object, the archive will be written to
          that file object, which must be open for writing in bytes
          mode.

        * If the target is omitted (or ‘None’), the source must be a
          directory and the target will be a file with the same name as
          the source, with a ‘.pyz’ extension added.

     The `interpreter' argument specifies the name of the Python
     interpreter with which the archive will be executed.  It is written
     as a “shebang” line at the start of the archive.  On POSIX, this
     will be interpreted by the OS, and on Windows it will be handled by
     the Python launcher.  Omitting the `interpreter' results in no
     shebang line being written.  If an interpreter is specified, and
     the target is a filename, the executable bit of the target file
     will be set.

     The `main' argument specifies the name of a callable which will be
     used as the main program for the archive.  It can only be specified
     if the source is a directory, and the source does not already
     contain a ‘__main__.py’ file.  The `main' argument should take the
     form “pkg.module:callable” and the archive will be run by importing
     “pkg.module” and executing the given callable with no arguments.
     It is an error to omit `main' if the source is a directory and does
     not contain a ‘__main__.py’ file, as otherwise the resulting
     archive would not be executable.

     The optional `filter' argument specifies a callback function that
     is passed a Path object representing the path to the file being
     added (relative to the source directory).  It should return ‘True’
     if the file is to be added.

     The optional `compressed' argument determines whether files are
     compressed.  If set to ‘True’, files in the archive are compressed
     with the deflate method; otherwise, files are stored uncompressed.
     This argument has no effect when copying an existing archive.

     If a file object is specified for `source' or `target', it is the
     caller’s responsibility to close it after calling create_archive.

     When copying an existing archive, file objects supplied only need
     ‘read’ and ‘readline’, or ‘write’ methods.  When creating an
     archive from a directory, if the target is a file object it will be
     passed to the ‘zipfile.ZipFile’ class, and must supply the methods
     needed by that class.

     New in version 3.7: Added the `filter' and `compressed' arguments.

 -- Function: zipapp.get_interpreter (archive)

     Return the interpreter specified in the ‘#!’ line at the start of
     the archive.  If there is no ‘#!’ line, return *note None: 203.
     The `archive' argument can be a filename or a file-like object open
     for reading in bytes mode.  It is assumed to be at the start of the
     archive.


File: python.info,  Node: Examples<28>,  Next: Specifying the Interpreter,  Prev: Python API,  Up: zipapp — Manage executable Python zip archives

5.28.4.4 Examples
.................

Pack up a directory into an archive, and run it.

     $ python -m zipapp myapp
     $ python myapp.pyz
     <output from myapp>

The same can be done using the *note create_archive(): 521. function:

     >>> import zipapp
     >>> zipapp.create_archive('myapp', 'myapp.pyz')

To make the application directly executable on POSIX, specify an
interpreter to use.

     $ python -m zipapp myapp -p "/usr/bin/env python"
     $ ./myapp.pyz
     <output from myapp>

To replace the shebang line on an existing archive, create a modified
archive using the *note create_archive(): 521. function:

     >>> import zipapp
     >>> zipapp.create_archive('old_archive.pyz', 'new_archive.pyz', '/usr/bin/python3')

To update the file in place, do the replacement in memory using a
‘BytesIO’ object, and then overwrite the source afterwards.  Note that
there is a risk when overwriting a file in place that an error will
result in the loss of the original file.  This code does not protect
against such errors, but production code should do so.  Also, this
method will only work if the archive fits in memory:

     >>> import zipapp
     >>> import io
     >>> temp = io.BytesIO()
     >>> zipapp.create_archive('myapp.pyz', temp, '/usr/bin/python2')
     >>> with open('myapp.pyz', 'wb') as f:
     >>>     f.write(temp.getvalue())


File: python.info,  Node: Specifying the Interpreter,  Next: Creating Standalone Applications with zipapp,  Prev: Examples<28>,  Up: zipapp — Manage executable Python zip archives

5.28.4.5 Specifying the Interpreter
...................................

Note that if you specify an interpreter and then distribute your
application archive, you need to ensure that the interpreter used is
portable.  The Python launcher for Windows supports most common forms of
POSIX ‘#!’ line, but there are other issues to consider:

   * If you use “/usr/bin/env python” (or other forms of the “python”
     command, such as “/usr/bin/python”), you need to consider that your
     users may have either Python 2 or Python 3 as their default, and
     write your code to work under both versions.

   * If you use an explicit version, for example “/usr/bin/env python3”
     your application will not work for users who do not have that
     version.  (This may be what you want if you have not made your code
     Python 2 compatible).

   * There is no way to say “python X.Y or later”, so be careful of
     using an exact version like “/usr/bin/env python3.4” as you will
     need to change your shebang line for users of Python 3.5, for
     example.

Typically, you should use an “/usr/bin/env python2” or “/usr/bin/env
python3”, depending on whether your code is written for Python 2 or 3.


File: python.info,  Node: Creating Standalone Applications with zipapp,  Next: The Python Zip Application Archive Format,  Prev: Specifying the Interpreter,  Up: zipapp — Manage executable Python zip archives

5.28.4.6 Creating Standalone Applications with zipapp
.....................................................

Using the *note zipapp: 14a. module, it is possible to create
self-contained Python programs, which can be distributed to end users
who only need to have a suitable version of Python installed on their
system.  The key to doing this is to bundle all of the application’s
dependencies into the archive, along with the application code.

The steps to create a standalone archive are as follows:

  1. Create your application in a directory as normal, so you have a
     ‘myapp’ directory containing a ‘__main__.py’ file, and any
     supporting application code.

  2. Install all of your application’s dependencies into the ‘myapp’
     directory, using pip:

          $ python -m pip install -r requirements.txt --target myapp

     (this assumes you have your project requirements in a
     ‘requirements.txt’ file - if not, you can just list the
     dependencies manually on the pip command line).

  3. Optionally, delete the ‘.dist-info’ directories created by pip in
     the ‘myapp’ directory.  These hold metadata for pip to manage the
     packages, and as you won’t be making any further use of pip they
     aren’t required - although it won’t do any harm if you leave them.

  4. Package the application using:

          $ python -m zipapp -p "interpreter" myapp

This will produce a standalone executable, which can be run on any
machine with the appropriate interpreter available.  See *note
Specifying the Interpreter: 379e. for details.  It can be shipped to
users as a single file.

On Unix, the ‘myapp.pyz’ file is executable as it stands.  You can
rename the file to remove the ‘.pyz’ extension if you prefer a “plain”
command name.  On Windows, the ‘myapp.pyz[w]’ file is executable by
virtue of the fact that the Python interpreter registers the ‘.pyz’ and
‘.pyzw’ file extensions when installed.

* Menu:

* Making a Windows executable::
* Caveats::


File: python.info,  Node: Making a Windows executable,  Next: Caveats,  Up: Creating Standalone Applications with zipapp

5.28.4.7 Making a Windows executable
....................................

On Windows, registration of the ‘.pyz’ extension is optional, and
furthermore, there are certain places that don’t recognise registered
extensions “transparently” (the simplest example is that
‘subprocess.run(['myapp'])’ won’t find your application - you need to
explicitly specify the extension).

On Windows, therefore, it is often preferable to create an executable
from the zipapp.  This is relatively easy, although it does require a C
compiler.  The basic approach relies on the fact that zipfiles can have
arbitrary data prepended, and Windows exe files can have arbitrary data
appended.  So by creating a suitable launcher and tacking the ‘.pyz’
file onto the end of it, you end up with a single-file executable that
runs your application.

A suitable launcher can be as simple as the following:

     #define Py_LIMITED_API 1
     #include "Python.h"

     #define WIN32_LEAN_AND_MEAN
     #include <windows.h>

     #ifdef WINDOWS
     int WINAPI wWinMain(
         HINSTANCE hInstance,      /* handle to current instance */
         HINSTANCE hPrevInstance,  /* handle to previous instance */
         LPWSTR lpCmdLine,         /* pointer to command line */
         int nCmdShow              /* show state of window */
     )
     #else
     int wmain()
     #endif
     {
         wchar_t **myargv = _alloca((__argc + 1) * sizeof(wchar_t*));
         myargv[0] = __wargv[0];
         memcpy(myargv + 1, __wargv, __argc * sizeof(wchar_t *));
         return Py_Main(__argc+1, myargv);
     }

If you define the ‘WINDOWS’ preprocessor symbol, this will generate a
GUI executable, and without it, a console executable.

To compile the executable, you can either just use the standard MSVC
command line tools, or you can take advantage of the fact that distutils
knows how to compile Python source:

     >>> from distutils.ccompiler import new_compiler
     >>> import distutils.sysconfig
     >>> import sys
     >>> import os
     >>> from pathlib import Path

     >>> def compile(src):
     >>>     src = Path(src)
     >>>     cc = new_compiler()
     >>>     exe = src.stem
     >>>     cc.add_include_dir(distutils.sysconfig.get_python_inc())
     >>>     cc.add_library_dir(os.path.join(sys.base_exec_prefix, 'libs'))
     >>>     # First the CLI executable
     >>>     objs = cc.compile([str(src)])
     >>>     cc.link_executable(objs, exe)
     >>>     # Now the GUI executable
     >>>     cc.define_macro('WINDOWS')
     >>>     objs = cc.compile([str(src)])
     >>>     cc.link_executable(objs, exe + 'w')

     >>> if __name__ == "__main__":
     >>>     compile("zastub.c")

The resulting launcher uses the “Limited ABI”, so it will run unchanged
with any version of Python 3.x.  All it needs is for Python
(‘python3.dll’) to be on the user’s ‘PATH’.

For a fully standalone distribution, you can distribute the launcher
with your application appended, bundled with the Python “embedded”
distribution.  This will run on any PC with the appropriate architecture
(32 bit or 64 bit).


File: python.info,  Node: Caveats,  Prev: Making a Windows executable,  Up: Creating Standalone Applications with zipapp

5.28.4.8 Caveats
................

There are some limitations to the process of bundling your application
into a single file.  In most, if not all, cases they can be addressed
without needing major changes to your application.

  1. If your application depends on a package that includes a C
     extension, that package cannot be run from a zip file (this is an
     OS limitation, as executable code must be present in the filesystem
     for the OS loader to load it).  In this case, you can exclude that
     dependency from the zipfile, and either require your users to have
     it installed, or ship it alongside your zipfile and add code to
     your ‘__main__.py’ to include the directory containing the unzipped
     module in ‘sys.path’.  In this case, you will need to make sure to
     ship appropriate binaries for your target architecture(s) (and
     potentially pick the correct version to add to ‘sys.path’ at
     runtime, based on the user’s machine).

  2. If you are shipping a Windows executable as described above, you
     either need to ensure that your users have ‘python3.dll’ on their
     PATH (which is not the default behaviour of the installer) or you
     should bundle your application with the embedded distribution.

  3. The suggested launcher above uses the Python embedding API. This
     means that in your application, ‘sys.executable’ will be your
     application, and `not' a conventional Python interpreter.  Your
     code and its dependencies need to be prepared for this possibility.
     For example, if your application uses the *note multiprocessing:
     b7. module, it will need to call *note
     multiprocessing.set_executable(): 2520. to let the module know
     where to find the standard Python interpreter.


File: python.info,  Node: The Python Zip Application Archive Format,  Prev: Creating Standalone Applications with zipapp,  Up: zipapp — Manage executable Python zip archives

5.28.4.9 The Python Zip Application Archive Format
..................................................

Python has been able to execute zip files which contain a ‘__main__.py’
file since version 2.6.  In order to be executed by Python, an
application archive simply has to be a standard zip file containing a
‘__main__.py’ file which will be run as the entry point for the
application.  As usual for any Python script, the parent of the script
(in this case the zip file) will be placed on *note sys.path: 260. and
thus further modules can be imported from the zip file.

The zip file format allows arbitrary data to be prepended to a zip file.
The zip application format uses this ability to prepend a standard POSIX
“shebang” line to the file (‘#!/path/to/interpreter’).

Formally, the Python zip application format is therefore:

  1. An optional shebang line, containing the characters ‘b'#!'’
     followed by an interpreter name, and then a newline (‘b'\n'’)
     character.  The interpreter name can be anything acceptable to the
     OS “shebang” processing, or the Python launcher on Windows.  The
     interpreter should be encoded in UTF-8 on Windows, and in *note
     sys.getfilesystemencoding(): 5f0. on POSIX.

  2. Standard zipfile data, as generated by the *note zipfile: 14b.
     module.  The zipfile content `must' include a file called
     ‘__main__.py’ (which must be in the “root” of the zipfile - i.e.,
     it cannot be in a subdirectory).  The zipfile data can be
     compressed or uncompressed.

If an application archive has a shebang line, it may have the executable
bit set on POSIX systems, to allow it to be executed directly.

There is no requirement that the tools in this module are used to create
application archives - the module is a convenience, but archives in the
above format created by any means are acceptable to Python.


File: python.info,  Node: Python Runtime Services,  Next: Custom Python Interpreters,  Prev: Software Packaging and Distribution,  Up: The Python Standard Library

5.29 Python Runtime Services
============================

The modules described in this chapter provide a wide range of services
related to the Python interpreter and its interaction with its
environment.  Here’s an overview:

* Menu:

* sys — System-specific parameters and functions::
* sysconfig — Provide access to Python’s configuration information::
* builtins — Built-in objects::
* __main__ — Top-level script environment::
* warnings — Warning control::
* dataclasses — Data Classes::
* contextlib — Utilities for with-statement contexts::
* abc — Abstract Base Classes::
* atexit — Exit handlers::
* traceback — Print or retrieve a stack traceback::
* __future__ — Future statement definitions::
* gc — Garbage Collector interface::
* inspect — Inspect live objects::
* site — Site-specific configuration hook::


File: python.info,  Node: sys — System-specific parameters and functions,  Next: sysconfig — Provide access to Python’s configuration information,  Up: Python Runtime Services

5.29.1 ‘sys’ — System-specific parameters and functions
-------------------------------------------------------

__________________________________________________________________

This module provides access to some variables used or maintained by the
interpreter and to functions that interact strongly with the
interpreter.  It is always available.

 -- Data: sys.abiflags

     On POSIX systems where Python was built with the standard
     ‘configure’ script, this contains the ABI flags as specified by PEP
     3149(1).

     Changed in version 3.8: Default flags became an empty string (‘m’
     flag for pymalloc has been removed).

     New in version 3.2.

 -- Function: sys.addaudithook (hook)

     Append the callable `hook' to the list of active auditing hooks for
     the current (sub)interpreter.

     When an auditing event is raised through the *note sys.audit():
     1056. function, each hook will be called in the order it was added
     with the event name and the tuple of arguments.  Native hooks added
     by *note PySys_AddAuditHook(): 366b. are called first, followed by
     hooks added in the current (sub)interpreter.  Hooks can then log
     the event, raise an exception to abort the operation, or terminate
     the process entirely.

     Calling *note sys.addaudithook(): 366a. will itself raise an
     auditing event named ‘sys.addaudithook’ with no arguments.  If any
     existing hooks raise an exception derived from *note RuntimeError:
     3dc, the new hook will not be added and the exception suppressed.
     As a result, callers cannot assume that their hook has been added
     unless they control all existing hooks.

     See the *note audit events table: 3667. for all events raised by
     CPython, and PEP 578(2) for the original design discussion.

     New in version 3.8.

     Changed in version 3.8.1: Exceptions derived from *note Exception:
     2dc. but not *note RuntimeError: 3dc. are no longer suppressed.

     `CPython implementation detail:' When tracing is enabled (see *note
     settrace(): f00.), Python hooks are only traced if the callable has
     a ‘__cantrace__’ member that is set to a true value.  Otherwise,
     trace functions will skip the hook.

 -- Data: sys.argv

     The list of command line arguments passed to a Python script.
     ‘argv[0]’ is the script name (it is operating system dependent
     whether this is a full pathname or not).  If the command was
     executed using the *note -c: 1340. command line option to the
     interpreter, ‘argv[0]’ is set to the string ‘'-c'’.  If no script
     name was passed to the Python interpreter, ‘argv[0]’ is the empty
     string.

     To loop over the standard input, or the list of files given on the
     command line, see the *note fileinput: 7e. module.

          Note: On Unix, command line arguments are passed by bytes from
          OS. Python decodes them with filesystem encoding and
          “surrogateescape” error handler.  When you need original
          bytes, you can get it by ‘[os.fsencode(arg) for arg in
          sys.argv]’.
 -- Function: sys.audit (event, *args)

     Raise an auditing event and trigger any active auditing hooks.
     `event' is a string identifying the event, and `args' may contain
     optional arguments with more information about the event.  The
     number and types of arguments for a given event are considered a
     public and stable API and should not be modified between releases.

     For example, one auditing event is named ‘os.chdir’.  This event
     has one argument called `path' that will contain the requested new
     working directory.

     *note sys.audit(): 1056. will call the existing auditing hooks,
     passing the event name and arguments, and will re-raise the first
     exception from any hook.  In general, if an exception is raised, it
     should not be handled and the process should be terminated as
     quickly as possible.  This allows hook implementations to decide
     how to respond to particular events: they can merely log the event
     or abort the operation by raising an exception.

     Hooks are added using the *note sys.addaudithook(): 366a. or *note
     PySys_AddAuditHook(): 366b. functions.

     The native equivalent of this function is *note PySys_Audit():
     1068.  Using the native function is preferred when possible.

     See the *note audit events table: 3667. for all events raised by
     CPython.

     New in version 3.8.

 -- Data: sys.base_exec_prefix

     Set during Python startup, before ‘site.py’ is run, to the same
     value as *note exec_prefix: 3780.  If not running in a *note
     virtual environment: 377e, the values will stay the same; if
     ‘site.py’ finds that a virtual environment is in use, the values of
     *note prefix: 377f. and *note exec_prefix: 3780. will be changed to
     point to the virtual environment, whereas *note base_prefix: 3180.
     and *note base_exec_prefix: 3781. will remain pointing to the base
     Python installation (the one which the virtual environment was
     created from).

     New in version 3.3.

 -- Data: sys.base_prefix

     Set during Python startup, before ‘site.py’ is run, to the same
     value as *note prefix: 377f.  If not running in a *note virtual
     environment: 377e, the values will stay the same; if ‘site.py’
     finds that a virtual environment is in use, the values of *note
     prefix: 377f. and *note exec_prefix: 3780. will be changed to point
     to the virtual environment, whereas *note base_prefix: 3180. and
     *note base_exec_prefix: 3781. will remain pointing to the base
     Python installation (the one which the virtual environment was
     created from).

     New in version 3.3.

 -- Data: sys.byteorder

     An indicator of the native byte order.  This will have the value
     ‘'big'’ on big-endian (most-significant byte first) platforms, and
     ‘'little'’ on little-endian (least-significant byte first)
     platforms.

 -- Data: sys.builtin_module_names

     A tuple of strings giving the names of all modules that are
     compiled into this Python interpreter.  (This information is not
     available in any other way — ‘modules.keys()’ only lists the
     imported modules.)

 -- Function: sys.call_tracing (func, args)

     Call ‘func(*args)’, while tracing is enabled.  The tracing state is
     saved, and restored afterwards.  This is intended to be called from
     a debugger from a checkpoint, to recursively debug some other code.

 -- Data: sys.copyright

     A string containing the copyright pertaining to the Python
     interpreter.

 -- Function: sys._clear_type_cache ()

     Clear the internal type cache.  The type cache is used to speed up
     attribute and method lookups.  Use the function `only' to drop
     unnecessary references during reference leak debugging.

     This function should be used for internal and specialized purposes
     only.

 -- Function: sys._current_frames ()

     Return a dictionary mapping each thread’s identifier to the topmost
     stack frame currently active in that thread at the time the
     function is called.  Note that functions in the *note traceback:
     11c. module can build the call stack given such a frame.

     This is most useful for debugging deadlock: this function does not
     require the deadlocked threads’ cooperation, and such threads’ call
     stacks are frozen for as long as they remain deadlocked.  The frame
     returned for a non-deadlocked thread may bear no relationship to
     that thread’s current activity by the time calling code examines
     the frame.

     This function should be used for internal and specialized purposes
     only.

     Raises an *note auditing event: fa1. ‘sys._current_frames’ with no
     arguments.

 -- Function: sys.breakpointhook ()

     This hook function is called by built-in *note breakpoint(): 40b.
     By default, it drops you into the *note pdb: c9. debugger, but it
     can be set to any other function so that you can choose which
     debugger gets used.

     The signature of this function is dependent on what it calls.  For
     example, the default binding (e.g.  ‘pdb.set_trace()’) expects no
     arguments, but you might bind it to a function that expects
     additional arguments (positional and/or keyword).  The built-in
     ‘breakpoint()’ function passes its ‘*args’ and ‘**kws’ straight
     through.  Whatever ‘breakpointhooks()’ returns is returned from
     ‘breakpoint()’.

     The default implementation first consults the environment variable
     *note PYTHONBREAKPOINT: 424.  If that is set to ‘"0"’ then this
     function returns immediately; i.e.  it is a no-op.  If the
     environment variable is not set, or is set to the empty string,
     ‘pdb.set_trace()’ is called.  Otherwise this variable should name a
     function to run, using Python’s dotted-import nomenclature, e.g.
     ‘package.subpackage.module.function’.  In this case,
     ‘package.subpackage.module’ would be imported and the resulting
     module must have a callable named ‘function()’.  This is run,
     passing in ‘*args’ and ‘**kws’, and whatever ‘function()’ returns,
     ‘sys.breakpointhook()’ returns to the built-in *note breakpoint():
     40b. function.

     Note that if anything goes wrong while importing the callable named
     by *note PYTHONBREAKPOINT: 424, a *note RuntimeWarning: 3e2. is
     reported and the breakpoint is ignored.

     Also note that if ‘sys.breakpointhook()’ is overridden
     programmatically, *note PYTHONBREAKPOINT: 424. is `not' consulted.

     New in version 3.7.

 -- Function: sys._debugmallocstats ()

     Print low-level information to stderr about the state of CPython’s
     memory allocator.

     If Python is configured –with-pydebug, it also performs some
     expensive internal consistency checks.

     New in version 3.3.

     `CPython implementation detail:' This function is specific to
     CPython.  The exact output format is not defined here, and may
     change.

 -- Data: sys.dllhandle

     Integer specifying the handle of the Python DLL.

     *note Availability: 1491.: Windows.

 -- Function: sys.displayhook (value)

     If `value' is not ‘None’, this function prints ‘repr(value)’ to
     ‘sys.stdout’, and saves `value' in ‘builtins._’.  If ‘repr(value)’
     is not encodable to ‘sys.stdout.encoding’ with ‘sys.stdout.errors’
     error handler (which is probably ‘'strict'’), encode it to
     ‘sys.stdout.encoding’ with ‘'backslashreplace'’ error handler.

     ‘sys.displayhook’ is called on the result of evaluating an *note
     expression: 158f. entered in an interactive Python session.  The
     display of these values can be customized by assigning another
     one-argument function to ‘sys.displayhook’.

     Pseudo-code:

          def displayhook(value):
              if value is None:
                  return
              # Set '_' to None to avoid recursion
              builtins._ = None
              text = repr(value)
              try:
                  sys.stdout.write(text)
              except UnicodeEncodeError:
                  bytes = text.encode(sys.stdout.encoding, 'backslashreplace')
                  if hasattr(sys.stdout, 'buffer'):
                      sys.stdout.buffer.write(bytes)
                  else:
                      text = bytes.decode(sys.stdout.encoding, 'strict')
                      sys.stdout.write(text)
              sys.stdout.write("\n")
              builtins._ = value

     Changed in version 3.2: Use ‘'backslashreplace'’ error handler on
     *note UnicodeEncodeError: 32a.

 -- Data: sys.dont_write_bytecode

     If this is true, Python won’t try to write ‘.pyc’ files on the
     import of source modules.  This value is initially set to ‘True’ or
     ‘False’ depending on the *note -B: dfe. command line option and the
     *note PYTHONDONTWRITEBYTECODE: dff. environment variable, but you
     can set it yourself to control bytecode file generation.

 -- Data: sys.pycache_prefix

     If this is set (not ‘None’), Python will write bytecode-cache
     ‘.pyc’ files to (and read them from) a parallel directory tree
     rooted at this directory, rather than from ‘__pycache__’
     directories in the source code tree.  Any ‘__pycache__’ directories
     in the source code tree will be ignored and new ‘.pyc’ files
     written within the pycache prefix.  Thus if you use *note
     compileall: 20. as a pre-build step, you must ensure you run it
     with the same pycache prefix (if any) that you will use at runtime.

     A relative path is interpreted relative to the current working
     directory.

     This value is initially set based on the value of the *note -X:
     290. ‘pycache_prefix=PATH’ command-line option or the *note
     PYTHONPYCACHEPREFIX: 28f. environment variable (command-line takes
     precedence).  If neither are set, it is ‘None’.

     New in version 3.8.

 -- Function: sys.excepthook (type, value, traceback)

     This function prints out a given traceback and exception to
     ‘sys.stderr’.

     When an exception is raised and uncaught, the interpreter calls
     ‘sys.excepthook’ with three arguments, the exception class,
     exception instance, and a traceback object.  In an interactive
     session this happens just before control is returned to the prompt;
     in a Python program this happens just before the program exits.
     The handling of such top-level exceptions can be customized by
     assigning another three-argument function to ‘sys.excepthook’.

     Raise an auditing event ‘sys.excepthook’ with arguments ‘hook’,
     ‘type’, ‘value’, ‘traceback’ when an uncaught exception occurs.  If
     no hook has been set, ‘hook’ may be ‘None’.  If any hook raises an
     exception derived from *note RuntimeError: 3dc. the call to the
     hook will be suppressed.  Otherwise, the audit hook exception will
     be reported as unraisable and ‘sys.excepthook’ will be called.

     See also
     ........

     The *note sys.unraisablehook(): 35a. function handles unraisable
     exceptions and the *note threading.excepthook(): 35e. function
     handles exception raised by *note threading.Thread.run(): 35f.

 -- Data: sys.__breakpointhook__
 -- Data: sys.__displayhook__
 -- Data: sys.__excepthook__
 -- Data: sys.__unraisablehook__

     These objects contain the original values of ‘breakpointhook’,
     ‘displayhook’, ‘excepthook’, and ‘unraisablehook’ at the start of
     the program.  They are saved so that ‘breakpointhook’,
     ‘displayhook’ and ‘excepthook’, ‘unraisablehook’ can be restored in
     case they happen to get replaced with broken or alternative
     objects.

     New in version 3.7: __breakpointhook__

     New in version 3.8: __unraisablehook__

 -- Function: sys.exc_info ()

     This function returns a tuple of three values that give information
     about the exception that is currently being handled.  The
     information returned is specific both to the current thread and to
     the current stack frame.  If the current stack frame is not
     handling an exception, the information is taken from the calling
     stack frame, or its caller, and so on until a stack frame is found
     that is handling an exception.  Here, “handling an exception” is
     defined as “executing an except clause.” For any stack frame, only
     information about the exception being currently handled is
     accessible.

     If no exception is being handled anywhere on the stack, a tuple
     containing three ‘None’ values is returned.  Otherwise, the values
     returned are ‘(type, value, traceback)’.  Their meaning is: `type'
     gets the type of the exception being handled (a subclass of *note
     BaseException: 2db.); `value' gets the exception instance (an
     instance of the exception type); `traceback' gets a *note traceback
     object: 442. which encapsulates the call stack at the point where
     the exception originally occurred.

 -- Data: sys.exec_prefix

     A string giving the site-specific directory prefix where the
     platform-dependent Python files are installed; by default, this is
     also ‘'/usr/local'’.  This can be set at build time with the
     ‘--exec-prefix’ argument to the ‘configure’ script.  Specifically,
     all configuration files (e.g.  the ‘pyconfig.h’ header file) are
     installed in the directory ‘`exec_prefix'/lib/python`X.Y'/config’,
     and shared library modules are installed in
     ‘`exec_prefix'/lib/python`X.Y'/lib-dynload’, where `X.Y' is the
     version number of Python, for example ‘3.2’.

          Note: If a *note virtual environment: 377e. is in effect, this
          value will be changed in ‘site.py’ to point to the virtual
          environment.  The value for the Python installation will still
          be available, via *note base_exec_prefix: 3781.

 -- Data: sys.executable

     A string giving the absolute path of the executable binary for the
     Python interpreter, on systems where this makes sense.  If Python
     is unable to retrieve the real path to its executable, *note
     sys.executable: 39d. will be an empty string or ‘None’.

 -- Function: sys.exit ([arg])

     Exit from Python.  This is implemented by raising the *note
     SystemExit: 6f3. exception, so cleanup actions specified by finally
     clauses of *note try: e37. statements are honored, and it is
     possible to intercept the exit attempt at an outer level.

     The optional argument `arg' can be an integer giving the exit
     status (defaulting to zero), or another type of object.  If it is
     an integer, zero is considered “successful termination” and any
     nonzero value is considered “abnormal termination” by shells and
     the like.  Most systems require it to be in the range 0–127, and
     produce undefined results otherwise.  Some systems have a
     convention for assigning specific meanings to specific exit codes,
     but these are generally underdeveloped; Unix programs generally use
     2 for command line syntax errors and 1 for all other kind of
     errors.  If another type of object is passed, ‘None’ is equivalent
     to passing zero, and any other object is printed to *note stderr:
     1ea. and results in an exit code of 1.  In particular,
     ‘sys.exit("some error message")’ is a quick way to exit a program
     when an error occurs.

     Since *note exit(): 1743. ultimately “only” raises an exception, it
     will only exit the process when called from the main thread, and
     the exception is not intercepted.

     Changed in version 3.6: If an error occurs in the cleanup after the
     Python interpreter has caught *note SystemExit: 6f3. (such as an
     error flushing buffered data in the standard streams), the exit
     status is changed to 120.

 -- Data: sys.flags

     The *note named tuple: b7b. `flags' exposes the status of command
     line flags.  The attributes are read only.

     attribute                         flag
                                       
     -------------------------------------------------------------------------------------------------------
                                       
     ‘debug’                           *note -d: 1476.
                                       
                                       
     *note inspect: a0.                *note -i: ee1.
                                       
                                       
     ‘interactive’                     *note -i: ee1.
                                       
                                       
     ‘isolated’                        *note -I: 232.
                                       
                                       
     ‘optimize’                        *note -O: 77e. or *note -OO: 77f.
                                       
                                       
     *note dont_write_bytecode: 37ae.  *note -B: dfe.
                                       
                                       
     ‘no_user_site’                    *note -s: ddb.
                                       
                                       
     ‘no_site’                         *note -S: bf7.
                                       
                                       
     ‘ignore_environment’              *note -E: 231.
                                       
                                       
     ‘verbose’                         *note -v: e4d.
                                       
                                       
     ‘bytes_warning’                   *note -b: 51a.
                                       
                                       
     ‘quiet’                           *note -q: 1479.
                                       
                                       
     ‘hash_randomization’              *note -R: 11c9.
                                       
                                       
     ‘dev_mode’                        *note -X dev: 290. (*note Python Development Mode: 160.)
                                       
                                       
     ‘utf8_mode’                       *note -X utf8: 290.
                                       

     Changed in version 3.2: Added ‘quiet’ attribute for the new *note
     -q: 1479. flag.

     New in version 3.2.3: The ‘hash_randomization’ attribute.

     Changed in version 3.3: Removed obsolete ‘division_warning’
     attribute.

     Changed in version 3.4: Added ‘isolated’ attribute for *note -I:
     232. ‘isolated’ flag.

     Changed in version 3.7: Added the ‘dev_mode’ attribute for the new
     *note Python Development Mode: 160. and the ‘utf8_mode’ attribute
     for the new *note -X: 290. ‘utf8’ flag.

 -- Data: sys.float_info

     A *note named tuple: b7b. holding information about the float type.
     It contains low level information about the precision and internal
     representation.  The values correspond to the various
     floating-point constants defined in the standard header file
     ‘float.h’ for the ‘C’ programming language; see section 5.2.4.2.2
     of the 1999 ISO/IEC C standard *note [C99]: 37b3, ‘Characteristics
     of floating types’, for details.

     attribute                 float.h macro        explanation
                                                    
     ------------------------------------------------------------------------------------------------------
                                                    
     ‘epsilon’                 DBL_EPSILON          difference between 1.0 and the least value greater
                                                    than 1.0 that is representable as a float
                                                    
                                                    See also *note math.ulp(): 1c1.
                                                    
                                                    
     ‘dig’                     DBL_DIG              maximum number of decimal digits that can be
                                                    faithfully represented in a float; see below
                                                    
                                                    
     ‘mant_dig’                DBL_MANT_DIG         float precision: the number of base-‘radix’ digits
                                                    in the significand of a float
                                                    
                                                    
     *note max: 8f7.           DBL_MAX              maximum representable positive finite float
                                                    
                                                    
     ‘max_exp’                 DBL_MAX_EXP          maximum integer `e' such that ‘radix**(e-1)’ is a
                                                    representable finite float
                                                    
                                                    
     ‘max_10_exp’              DBL_MAX_10_EXP       maximum integer `e' such that ‘10**e’ is in the
                                                    range of representable finite floats
                                                    
                                                    
     *note min: 8f6.           DBL_MIN              minimum representable positive `normalized' float
                                                    
                                                    Use *note math.ulp(0.0): 1c1. to get the smallest
                                                    positive `denormalized' representable float.
                                                    
                                                    
     ‘min_exp’                 DBL_MIN_EXP          minimum integer `e' such that ‘radix**(e-1)’ is a
                                                    normalized float
                                                    
                                                    
     ‘min_10_exp’              DBL_MIN_10_EXP       minimum integer `e' such that ‘10**e’ is a
                                                    normalized float
                                                    
                                                    
     ‘radix’                   FLT_RADIX            radix of exponent representation
                                                    
                                                    
     ‘rounds’                  FLT_ROUNDS           integer constant representing the rounding mode used
                                                    for arithmetic operations.  This reflects the value
                                                    of the system FLT_ROUNDS macro at interpreter
                                                    startup time.  See section 5.2.4.2.2 of the C99
                                                    standard for an explanation of the possible values
                                                    and their meanings.
                                                    

     The attribute ‘sys.float_info.dig’ needs further explanation.  If
     ‘s’ is any string representing a decimal number with at most
     ‘sys.float_info.dig’ significant digits, then converting ‘s’ to a
     float and back again will recover a string representing the same
     decimal value:

          >>> import sys
          >>> sys.float_info.dig
          15
          >>> s = '3.14159265358979'    # decimal string with 15 significant digits
          >>> format(float(s), '.15g')  # convert to float and back -> same value
          '3.14159265358979'

     But for strings with more than ‘sys.float_info.dig’ significant
     digits, this isn’t always true:

          >>> s = '9876543211234567'    # 16 significant digits is too many!
          >>> format(float(s), '.16g')  # conversion changes value
          '9876543211234568'

 -- Data: sys.float_repr_style

     A string indicating how the *note repr(): 8b9. function behaves for
     floats.  If the string has value ‘'short'’ then for a finite float
     ‘x’, ‘repr(x)’ aims to produce a short string with the property
     that ‘float(repr(x)) == x’.  This is the usual behaviour in Python
     3.1 and later.  Otherwise, ‘float_repr_style’ has value ‘'legacy'’
     and ‘repr(x)’ behaves in the same way as it did in versions of
     Python prior to 3.1.

     New in version 3.1.

 -- Function: sys.getallocatedblocks ()

     Return the number of memory blocks currently allocated by the
     interpreter, regardless of their size.  This function is mainly
     useful for tracking and debugging memory leaks.  Because of the
     interpreter’s internal caches, the result can vary from call to
     call; you may have to call *note _clear_type_cache(): 37ab. and
     *note gc.collect(): 35b. to get more predictable results.

     If a Python build or implementation cannot reasonably compute this
     information, *note getallocatedblocks(): 9c8. is allowed to return
     0 instead.

     New in version 3.4.

 -- Function: sys.getandroidapilevel ()

     Return the build time API version of Android as an integer.

     *note Availability: 1491.: Android.

     New in version 3.7.

 -- Function: sys.getdefaultencoding ()

     Return the name of the current default string encoding used by the
     Unicode implementation.

 -- Function: sys.getdlopenflags ()

     Return the current value of the flags that are used for ‘dlopen()’
     calls.  Symbolic names for the flag values can be found in the
     *note os: c4. module (‘RTLD_xxx’ constants, e.g.  *note
     os.RTLD_LAZY: b3a.).

     *note Availability: 1491.: Unix.

 -- Function: sys.getfilesystemencoding ()

     Return the name of the encoding used to convert between Unicode
     filenames and bytes filenames.  For best compatibility, str should
     be used for filenames in all cases, although representing filenames
     as bytes is also supported.  Functions accepting or returning
     filenames should support either str or bytes and internally convert
     to the system’s preferred representation.

     This encoding is always ASCII-compatible.

     *note os.fsencode(): 5ea. and *note os.fsdecode(): 5e9. should be
     used to ensure that the correct encoding and errors mode are used.

        * In the UTF-8 mode, the encoding is ‘utf-8’ on any platform.

        * On macOS, the encoding is ‘'utf-8'’.

        * On Unix, the encoding is the locale encoding.

        * On Windows, the encoding may be ‘'utf-8'’ or ‘'mbcs'’,
          depending on user configuration.

        * On Android, the encoding is ‘'utf-8'’.

        * On VxWorks, the encoding is ‘'utf-8'’.

     Changed in version 3.2: *note getfilesystemencoding(): 5f0. result
     cannot be ‘None’ anymore.

     Changed in version 3.6: Windows is no longer guaranteed to return
     ‘'mbcs'’.  See PEP 529(3) and *note
     _enablelegacywindowsfsencoding(): 5f2. for more information.

     Changed in version 3.7: Return ‘utf-8’ in the UTF-8 mode.

 -- Function: sys.getfilesystemencodeerrors ()

     Return the name of the error mode used to convert between Unicode
     filenames and bytes filenames.  The encoding name is returned from
     *note getfilesystemencoding(): 5f0.

     *note os.fsencode(): 5ea. and *note os.fsdecode(): 5e9. should be
     used to ensure that the correct encoding and errors mode are used.

     New in version 3.6.

 -- Function: sys.getrefcount (object)

     Return the reference count of the `object'.  The count returned is
     generally one higher than you might expect, because it includes the
     (temporary) reference as an argument to *note getrefcount(): 37b5.

 -- Function: sys.getrecursionlimit ()

     Return the current value of the recursion limit, the maximum depth
     of the Python interpreter stack.  This limit prevents infinite
     recursion from causing an overflow of the C stack and crashing
     Python.  It can be set by *note setrecursionlimit(): f3c.

 -- Function: sys.getsizeof (object[, default])

     Return the size of an object in bytes.  The object can be any type
     of object.  All built-in objects will return correct results, but
     this does not have to hold true for third-party extensions as it is
     implementation specific.

     Only the memory consumption directly attributed to the object is
     accounted for, not the memory consumption of objects it refers to.

     If given, `default' will be returned if the object does not provide
     means to retrieve the size.  Otherwise a *note TypeError: 1fe. will
     be raised.

     *note getsizeof(): 3744. calls the object’s ‘__sizeof__’ method and
     adds an additional garbage collector overhead if the object is
     managed by the garbage collector.

     See recursive sizeof recipe(4) for an example of using *note
     getsizeof(): 3744. recursively to find the size of containers and
     all their contents.

 -- Function: sys.getswitchinterval ()

     Return the interpreter’s “thread switch interval”; see *note
     setswitchinterval(): 218.

     New in version 3.2.

 -- Function: sys._getframe ([depth])

     Return a frame object from the call stack.  If optional integer
     `depth' is given, return the frame object that many calls below the
     top of the stack.  If that is deeper than the call stack, *note
     ValueError: 16d. is raised.  The default for `depth' is zero,
     returning the frame at the top of the call stack.

     Raises an *note auditing event: fa1. ‘sys._getframe’ with no
     arguments.

     `CPython implementation detail:' This function should be used for
     internal and specialized purposes only.  It is not guaranteed to
     exist in all implementations of Python.

 -- Function: sys.getprofile ()

     Get the profiler function as set by *note setprofile(): eff.

 -- Function: sys.gettrace ()

     Get the trace function as set by *note settrace(): f00.

     `CPython implementation detail:' The *note gettrace(): e0d.
     function is intended only for implementing debuggers, profilers,
     coverage tools and the like.  Its behavior is part of the
     implementation platform, rather than part of the language
     definition, and thus may not be available in all Python
     implementations.

 -- Function: sys.getwindowsversion ()

     Return a named tuple describing the Windows version currently
     running.  The named elements are `major', `minor', `build',
     `platform', `service_pack', `service_pack_minor',
     `service_pack_major', `suite_mask', `product_type' and
     `platform_version'.  `service_pack' contains a string,
     `platform_version' a 3-tuple and all other values are integers.
     The components can also be accessed by name, so
     ‘sys.getwindowsversion()[0]’ is equivalent to
     ‘sys.getwindowsversion().major’.  For compatibility with prior
     versions, only the first 5 elements are retrievable by indexing.

     `platform' will be ‘2 (VER_PLATFORM_WIN32_NT)’.

     `product_type' may be one of the following values:

     Constant                                    Meaning
                                                 
     ----------------------------------------------------------------------------------
                                                 
     ‘1 (VER_NT_WORKSTATION)’                    The system is a workstation.
                                                 
                                                 
     ‘2 (VER_NT_DOMAIN_CONTROLLER)’              The system is a domain controller.
                                                 
                                                 
     ‘3 (VER_NT_SERVER)’                         The system is a server, but not a
                                                 domain controller.
                                                 

     This function wraps the Win32 ‘GetVersionEx()’ function; see the
     Microsoft documentation on ‘OSVERSIONINFOEX()’ for more information
     about these fields.

     `platform_version' returns the major version, minor version and
     build number of the current operating system, rather than the
     version that is being emulated for the process.  It is intended for
     use in logging rather than for feature detection.

          Note: `platform_version' derives the version from kernel32.dll
          which can be of a different version than the OS version.
          Please use *note platform: ce. module for achieving accurate
          OS version.

     *note Availability: 1491.: Windows.

     Changed in version 3.2: Changed to a named tuple and added
     `service_pack_minor', `service_pack_major', `suite_mask', and
     `product_type'.

     Changed in version 3.6: Added `platform_version'

 -- Function: sys.get_asyncgen_hooks ()

     Returns an `asyncgen_hooks' object, which is similar to a *note
     namedtuple: 1a1. of the form ‘(firstiter, finalizer)’, where
     `firstiter' and `finalizer' are expected to be either ‘None’ or
     functions which take an *note asynchronous generator iterator:
     37b7. as an argument, and are used to schedule finalization of an
     asynchronous generator by an event loop.

     New in version 3.6: See PEP 525(5) for more details.

          Note: This function has been added on a provisional basis (see
          PEP 411(6) for details.)

 -- Function: sys.get_coroutine_origin_tracking_depth ()

     Get the current coroutine origin tracking depth, as set by *note
     set_coroutine_origin_tracking_depth(): 4f9.

     New in version 3.7.

          Note: This function has been added on a provisional basis (see
          PEP 411(7) for details.)  Use it only for debugging purposes.

 -- Data: sys.hash_info

     A *note named tuple: b7b. giving parameters of the numeric hash
     implementation.  For more details about hashing of numeric types,
     see *note Hashing of numeric types: 175b.

     attribute                 explanation
                               
     ---------------------------------------------------------------------------------
                               
     ‘width’                   width in bits used for hash values
                               
                               
     ‘modulus’                 prime modulus P used for numeric hash scheme
                               
                               
     ‘inf’                     hash value returned for a positive infinity
                               
                               
     ‘nan’                     hash value returned for a nan
                               
                               
     ‘imag’                    multiplier used for the imaginary part of a complex
                               number
                               
                               
     ‘algorithm’               name of the algorithm for hashing of str, bytes, and
                               memoryview
                               
                               
     ‘hash_bits’               internal output size of the hash algorithm
                               
                               
     ‘seed_bits’               size of the seed key of the hash algorithm
                               

     New in version 3.2.

     Changed in version 3.4: Added `algorithm', `hash_bits' and
     `seed_bits'

 -- Data: sys.hexversion

     The version number encoded as a single integer.  This is guaranteed
     to increase with each version, including proper support for
     non-production releases.  For example, to test that the Python
     interpreter is at least version 1.5.2, use:

          if sys.hexversion >= 0x010502F0:
              # use some advanced feature
              ...
          else:
              # use an alternative implementation or warn the user
              ...

     This is called ‘hexversion’ since it only really looks meaningful
     when viewed as the result of passing it to the built-in *note
     hex(): d2e. function.  The *note named tuple: b7b. *note
     sys.version_info: bed. may be used for a more human-friendly
     encoding of the same information.

     More details of ‘hexversion’ can be found at *note API and ABI
     Versioning: 37b9.

 -- Data: sys.implementation

     An object containing information about the implementation of the
     currently running Python interpreter.  The following attributes are
     required to exist in all Python implementations.

     `name' is the implementation’s identifier, e.g.  ‘'cpython'’.  The
     actual string is defined by the Python implementation, but it is
     guaranteed to be lower case.

     `version' is a named tuple, in the same format as *note
     sys.version_info: bed.  It represents the version of the Python
     `implementation'.  This has a distinct meaning from the specific
     version of the Python `language' to which the currently running
     interpreter conforms, which ‘sys.version_info’ represents.  For
     example, for PyPy 1.8 ‘sys.implementation.version’ might be
     ‘sys.version_info(1, 8, 0, 'final', 0)’, whereas ‘sys.version_info’
     would be ‘sys.version_info(2, 7, 2, 'final', 0)’.  For CPython they
     are the same value, since it is the reference implementation.

     `hexversion' is the implementation version in hexadecimal format,
     like *note sys.hexversion: 37b8.

     `cache_tag' is the tag used by the import machinery in the
     filenames of cached modules.  By convention, it would be a
     composite of the implementation’s name and version, like
     ‘'cpython-33'’.  However, a Python implementation may use some
     other value if appropriate.  If ‘cache_tag’ is set to ‘None’, it
     indicates that module caching should be disabled.

     *note sys.implementation: a8b. may contain additional attributes
     specific to the Python implementation.  These non-standard
     attributes must start with an underscore, and are not described
     here.  Regardless of its contents, *note sys.implementation: a8b.
     will not change during a run of the interpreter, nor between
     implementation versions.  (It may change between Python language
     versions, however.)  See PEP 421(8) for more information.

     New in version 3.3.

          Note: The addition of new required attributes must go through
          the normal PEP process.  See PEP 421(9) for more information.

 -- Data: sys.int_info

     A *note named tuple: b7b. that holds information about Python’s
     internal representation of integers.  The attributes are read only.

     Attribute                     Explanation
                                   
     ---------------------------------------------------------------------------------
                                   
     ‘bits_per_digit’              number of bits held in each digit.  Python
                                   integers are stored internally in base
                                   ‘2**int_info.bits_per_digit’
                                   
                                   
     ‘sizeof_digit’                size in bytes of the C type used to represent a
                                   digit
                                   

     New in version 3.1.

 -- Data: sys.__interactivehook__

     When this attribute exists, its value is automatically called (with
     no arguments) when the interpreter is launched in *note interactive
     mode: 9c9.  This is done after the *note PYTHONSTARTUP: 9cb. file
     is read, so that you can set this hook there.  The *note site: eb.
     module *note sets this: 9cc.

     Raises an *note auditing event: fa1. ‘cpython.run_interactivehook’
     with the hook object as the argument when the hook is called on
     startup.

     New in version 3.4.

 -- Function: sys.intern (string)

     Enter `string' in the table of “interned” strings and return the
     interned string – which is `string' itself or a copy.  Interning
     strings is useful to gain a little performance on dictionary lookup
     – if the keys in a dictionary are interned, and the lookup key is
     interned, the key comparisons (after hashing) can be done by a
     pointer compare instead of a string compare.  Normally, the names
     used in Python programs are automatically interned, and the
     dictionaries used to hold module, class or instance attributes have
     interned keys.

     Interned strings are not immortal; you must keep a reference to the
     return value of *note intern(): d36. around to benefit from it.

 -- Function: sys.is_finalizing ()

     Return *note True: 594. if the Python interpreter is *note shutting
     down: 852, *note False: 48f. otherwise.

     New in version 3.5.

 -- Data: sys.last_type
 -- Data: sys.last_value
 -- Data: sys.last_traceback

     These three variables are not always defined; they are set when an
     exception is not handled and the interpreter prints an error
     message and a stack traceback.  Their intended use is to allow an
     interactive user to import a debugger module and engage in
     post-mortem debugging without having to re-execute the command that
     caused the error.  (Typical use is ‘import pdb; pdb.pm()’ to enter
     the post-mortem debugger; see *note pdb: c9. module for more
     information.)

     The meaning of the variables is the same as that of the return
     values from *note exc_info(): d27. above.

 -- Data: sys.maxsize

     An integer giving the maximum value a variable of type ‘Py_ssize_t’
     can take.  It’s usually ‘2**31 - 1’ on a 32-bit platform and ‘2**63
     - 1’ on a 64-bit platform.

 -- Data: sys.maxunicode

     An integer giving the value of the largest Unicode code point, i.e.
     ‘1114111’ (‘0x10FFFF’ in hexadecimal).

     Changed in version 3.3: Before PEP 393(10), ‘sys.maxunicode’ used
     to be either ‘0xFFFF’ or ‘0x10FFFF’, depending on the configuration
     option that specified whether Unicode characters were stored as
     UCS-2 or UCS-4.

 -- Data: sys.meta_path

     A list of *note meta path finder: a91. objects that have their
     *note find_spec(): 565. methods called to see if one of the objects
     can find the module to be imported.  The *note find_spec(): 565.
     method is called with at least the absolute name of the module
     being imported.  If the module to be imported is contained in a
     package, then the parent package’s *note __path__: 13c3. attribute
     is passed in as a second argument.  The method returns a *note
     module spec: 37bb, or ‘None’ if the module cannot be found.

     See also
     ........

     *note importlib.abc.MetaPathFinder: a93.

          The abstract base class defining the interface of finder
          objects on *note meta_path: 6dd.

     *note importlib.machinery.ModuleSpec: 1601.

          The concrete class which *note find_spec(): 565. should return
          instances of.

     Changed in version 3.4: *note Module specs: 37bb. were introduced
     in Python 3.4, by PEP 451(11).  Earlier versions of Python looked
     for a method called *note find_module(): 564.  This is still called
     as a fallback if a *note meta_path: 6dd. entry doesn’t have a *note
     find_spec(): 565. method.

 -- Data: sys.modules

     This is a dictionary that maps module names to modules which have
     already been loaded.  This can be manipulated to force reloading of
     modules and other tricks.  However, replacing the dictionary will
     not necessarily work as expected and deleting essential items from
     the dictionary may cause Python to fail.

 -- Data: sys.path

     A list of strings that specifies the search path for modules.
     Initialized from the environment variable *note PYTHONPATH: a34,
     plus an installation-dependent default.

     As initialized upon program startup, the first item of this list,
     ‘path[0]’, is the directory containing the script that was used to
     invoke the Python interpreter.  If the script directory is not
     available (e.g.  if the interpreter is invoked interactively or if
     the script is read from standard input), ‘path[0]’ is the empty
     string, which directs Python to search modules in the current
     directory first.  Notice that the script directory is inserted
     `before' the entries inserted as a result of *note PYTHONPATH: a34.

     A program is free to modify this list for its own purposes.  Only
     strings and bytes should be added to *note sys.path: 260.; all
     other data types are ignored during import.

     See also
     ........

     Module *note site: eb. This describes how to use .pth files to
     extend *note sys.path: 260.

 -- Data: sys.path_hooks

     A list of callables that take a path argument to try to create a
     *note finder: 15f5. for the path.  If a finder can be created, it
     is to be returned by the callable, else raise *note ImportError:
     16c.

     Originally specified in PEP 302(12).

 -- Data: sys.path_importer_cache

     A dictionary acting as a cache for *note finder: 15f5. objects.
     The keys are paths that have been passed to *note sys.path_hooks:
     a3d. and the values are the finders that are found.  If a path is a
     valid file system path but no finder is found on *note
     sys.path_hooks: a3d. then ‘None’ is stored.

     Originally specified in PEP 302(13).

     Changed in version 3.3: ‘None’ is stored instead of *note
     imp.NullImporter: a9b. when no finder is found.

 -- Data: sys.platform

     This string contains a platform identifier that can be used to
     append platform-specific components to *note sys.path: 260, for
     instance.

     For Unix systems, except on Linux and AIX, this is the lowercased
     OS name as returned by ‘uname -s’ with the first part of the
     version as returned by ‘uname -r’ appended, e.g.  ‘'sunos5'’ or
     ‘'freebsd8'’, `at the time when Python was built'.  Unless you want
     to test for a specific system version, it is therefore recommended
     to use the following idiom:

          if sys.platform.startswith('freebsd'):
              # FreeBSD-specific code here...
          elif sys.platform.startswith('linux'):
              # Linux-specific code here...
          elif sys.platform.startswith('aix'):
              # AIX-specific code here...

     For other systems, the values are:

     System               ‘platform’ value
                          
     -----------------------------------------------------
                          
     AIX                  ‘'aix'’
                          
                          
     Linux                ‘'linux'’
                          
                          
     Windows              ‘'win32'’
                          
                          
     Windows/Cygwin       ‘'cygwin'’
                          
                          
     macOS                ‘'darwin'’
                          

     Changed in version 3.3: On Linux, *note sys.platform: 3d3. doesn’t
     contain the major version anymore.  It is always ‘'linux'’, instead
     of ‘'linux2'’ or ‘'linux3'’.  Since older Python versions include
     the version number, it is recommended to always use the
     ‘startswith’ idiom presented above.

     Changed in version 3.8: On AIX, *note sys.platform: 3d3. doesn’t
     contain the major version anymore.  It is always ‘'aix'’, instead
     of ‘'aix5'’ or ‘'aix7'’.  Since older Python versions include the
     version number, it is recommended to always use the ‘startswith’
     idiom presented above.

     See also
     ........

     *note os.name: 2040. has a coarser granularity.  *note os.uname():
     b38. gives system-dependent version information.

     The *note platform: ce. module provides detailed checks for the
     system’s identity.

 -- Data: sys.platlibdir

     Name of the platform-specific library directory.  It is used to
     build the path of standard library and the paths of installed
     extension modules.

     It is equal to ‘"lib"’ on most platforms.  On Fedora and SuSE, it
     is equal to ‘"lib64"’ on 64-bit platforms which gives the following
     ‘sys.path’ paths (where ‘X.Y’ is the Python ‘major.minor’ version):

        * ‘/usr/lib64/pythonX.Y/’: Standard library (like ‘os.py’ of the
          *note os: c4. module)

        * ‘/usr/lib64/pythonX.Y/lib-dynload/’: C extension modules of
          the standard library (like the *note errno: 7a. module, the
          exact filename is platform specific)

        * ‘/usr/lib/pythonX.Y/site-packages/’ (always use ‘lib’, not
          *note sys.platlibdir: 1e9.): Third-party modules

        * ‘/usr/lib64/pythonX.Y/site-packages/’: C extension modules of
          third-party packages

     New in version 3.9.

 -- Data: sys.prefix

     A string giving the site-specific directory prefix where the
     platform independent Python files are installed; on Unix, the
     default is ‘'/usr/local'’.  This can be set at build time with the
     ‘--prefix’ argument to the ‘configure’ script.  See *note
     Installation paths: 37bc. for derived paths.

          Note: If a *note virtual environment: 377e. is in effect, this
          value will be changed in ‘site.py’ to point to the virtual
          environment.  The value for the Python installation will still
          be available, via *note base_prefix: 3180.

 -- Data: sys.ps1
 -- Data: sys.ps2

     Strings specifying the primary and secondary prompt of the
     interpreter.  These are only defined if the interpreter is in
     interactive mode.  Their initial values in this case are ‘'>>> '’
     and ‘'... '’.  If a non-string object is assigned to either
     variable, its *note str(): 205. is re-evaluated each time the
     interpreter prepares to read a new interactive command; this can be
     used to implement a dynamic prompt.

 -- Function: sys.setdlopenflags (n)

     Set the flags used by the interpreter for ‘dlopen()’ calls, such as
     when the interpreter loads extension modules.  Among other things,
     this will enable a lazy resolving of symbols when importing a
     module, if called as ‘sys.setdlopenflags(0)’.  To share symbols
     across extension modules, call as
     ‘sys.setdlopenflags(os.RTLD_GLOBAL)’.  Symbolic names for the flag
     values can be found in the *note os: c4. module (‘RTLD_xxx’
     constants, e.g.  *note os.RTLD_LAZY: b3a.).

     *note Availability: 1491.: Unix.

 -- Function: sys.setprofile (profilefunc)

     Set the system’s profile function, which allows you to implement a
     Python source code profiler in Python.  See chapter *note The
     Python Profilers: 36dc. for more information on the Python
     profiler.  The system’s profile function is called similarly to the
     system’s trace function (see *note settrace(): f00.), but it is
     called with different events, for example it isn’t called for each
     executed line of code (only on call and return, but the return
     event is reported even when an exception has been set).  The
     function is thread-specific, but there is no way for the profiler
     to know about context switches between threads, so it does not make
     sense to use this in the presence of multiple threads.  Also, its
     return value is not used, so it can simply return ‘None’.  Error in
     the profile function will cause itself unset.

     Profile functions should have three arguments: `frame', `event',
     and `arg'.  `frame' is the current stack frame.  `event' is a
     string: ‘'call'’, ‘'return'’, ‘'c_call'’, ‘'c_return'’, or
     ‘'c_exception'’.  `arg' depends on the event type.

     Raises an *note auditing event: fa1. ‘sys.setprofile’ with no
     arguments.

     The events have the following meaning:

     ‘'call'’

          A function is called (or some other code block entered).  The
          profile function is called; `arg' is ‘None’.

     ‘'return'’

          A function (or other code block) is about to return.  The
          profile function is called; `arg' is the value that will be
          returned, or ‘None’ if the event is caused by an exception
          being raised.

     ‘'c_call'’

          A C function is about to be called.  This may be an extension
          function or a built-in.  `arg' is the C function object.

     ‘'c_return'’

          A C function has returned.  `arg' is the C function object.

     ‘'c_exception'’

          A C function has raised an exception.  `arg' is the C function
          object.

 -- Function: sys.setrecursionlimit (limit)

     Set the maximum depth of the Python interpreter stack to `limit'.
     This limit prevents infinite recursion from causing an overflow of
     the C stack and crashing Python.

     The highest possible limit is platform-dependent.  A user may need
     to set the limit higher when they have a program that requires deep
     recursion and a platform that supports a higher limit.  This should
     be done with care, because a too-high limit can lead to a crash.

     If the new limit is too low at the current recursion depth, a *note
     RecursionError: 727. exception is raised.

     Changed in version 3.5.1: A *note RecursionError: 727. exception is
     now raised if the new limit is too low at the current recursion
     depth.

 -- Function: sys.setswitchinterval (interval)

     Set the interpreter’s thread switch interval (in seconds).  This
     floating-point value determines the ideal duration of the
     “timeslices” allocated to concurrently running Python threads.
     Please note that the actual value can be higher, especially if
     long-running internal functions or methods are used.  Also, which
     thread becomes scheduled at the end of the interval is the
     operating system’s decision.  The interpreter doesn’t have its own
     scheduler.

     New in version 3.2.

 -- Function: sys.settrace (tracefunc)

     Set the system’s trace function, which allows you to implement a
     Python source code debugger in Python.  The function is
     thread-specific; for a debugger to support multiple threads, it
     must register a trace function using *note settrace(): f00. for
     each thread being debugged or use *note threading.settrace(): 24ab.

     Trace functions should have three arguments: `frame', `event', and
     `arg'.  `frame' is the current stack frame.  `event' is a string:
     ‘'call'’, ‘'line'’, ‘'return'’, ‘'exception'’ or ‘'opcode'’.  `arg'
     depends on the event type.

     The trace function is invoked (with `event' set to ‘'call'’)
     whenever a new local scope is entered; it should return a reference
     to a local trace function to be used for the new scope, or ‘None’
     if the scope shouldn’t be traced.

     The local trace function should return a reference to itself (or to
     another function for further tracing in that scope), or ‘None’ to
     turn off tracing in that scope.

     If there is any error occurred in the trace function, it will be
     unset, just like ‘settrace(None)’ is called.

     The events have the following meaning:

     ‘'call'’

          A function is called (or some other code block entered).  The
          global trace function is called; `arg' is ‘None’; the return
          value specifies the local trace function.

     ‘'line'’

          The interpreter is about to execute a new line of code or
          re-execute the condition of a loop.  The local trace function
          is called; `arg' is ‘None’; the return value specifies the new
          local trace function.  See ‘Objects/lnotab_notes.txt’ for a
          detailed explanation of how this works.  Per-line events may
          be disabled for a frame by setting ‘f_trace_lines’ to *note
          False: 48f. on that frame.

     ‘'return'’

          A function (or other code block) is about to return.  The
          local trace function is called; `arg' is the value that will
          be returned, or ‘None’ if the event is caused by an exception
          being raised.  The trace function’s return value is ignored.

     ‘'exception'’

          An exception has occurred.  The local trace function is
          called; `arg' is a tuple ‘(exception, value, traceback)’; the
          return value specifies the new local trace function.

     ‘'opcode'’

          The interpreter is about to execute a new opcode (see *note
          dis: 37. for opcode details).  The local trace function is
          called; `arg' is ‘None’; the return value specifies the new
          local trace function.  Per-opcode events are not emitted by
          default: they must be explicitly requested by setting
          ‘f_trace_opcodes’ to *note True: 594. on the frame.

     Note that as an exception is propagated down the chain of callers,
     an ‘'exception'’ event is generated at each level.

     For more fine-grained usage, it’s possible to set a trace function
     by assigning ‘frame.f_trace = tracefunc’ explicitly, rather than
     relying on it being set indirectly via the return value from an
     already installed trace function.  This is also required for
     activating the trace function on the current frame, which *note
     settrace(): f00. doesn’t do.  Note that in order for this to work,
     a global tracing function must have been installed with *note
     settrace(): f00. in order to enable the runtime tracing machinery,
     but it doesn’t need to be the same tracing function (e.g.  it could
     be a low overhead tracing function that simply returns ‘None’ to
     disable itself immediately on each frame).

     For more information on code and frame objects, refer to *note The
     standard type hierarchy: 1553.

     Raises an *note auditing event: fa1. ‘sys.settrace’ with no
     arguments.

     `CPython implementation detail:' The *note settrace(): f00.
     function is intended only for implementing debuggers, profilers,
     coverage tools and the like.  Its behavior is part of the
     implementation platform, rather than part of the language
     definition, and thus may not be available in all Python
     implementations.

     Changed in version 3.7: ‘'opcode'’ event type added;
     ‘f_trace_lines’ and ‘f_trace_opcodes’ attributes added to frames

 -- Function: sys.set_asyncgen_hooks (firstiter, finalizer)

     Accepts two optional keyword arguments which are callables that
     accept an *note asynchronous generator iterator: 37b7. as an
     argument.  The `firstiter' callable will be called when an
     asynchronous generator is iterated for the first time.  The
     `finalizer' will be called when an asynchronous generator is about
     to be garbage collected.

     Raises an *note auditing event: fa1.
     ‘sys.set_asyncgen_hooks_firstiter’ with no arguments.

     Raises an *note auditing event: fa1.
     ‘sys.set_asyncgen_hooks_finalizer’ with no arguments.

     Two auditing events are raised because the underlying API consists
     of two calls, each of which must raise its own event.

     New in version 3.6: See PEP 525(14) for more details, and for a
     reference example of a `finalizer' method see the implementation of
     ‘asyncio.Loop.shutdown_asyncgens’ in Lib/asyncio/base_events.py(15)

          Note: This function has been added on a provisional basis (see
          PEP 411(16) for details.)

 -- Function: sys.set_coroutine_origin_tracking_depth (depth)

     Allows enabling or disabling coroutine origin tracking.  When
     enabled, the ‘cr_origin’ attribute on coroutine objects will
     contain a tuple of (filename, line number, function name) tuples
     describing the traceback where the coroutine object was created,
     with the most recent call first.  When disabled, ‘cr_origin’ will
     be None.

     To enable, pass a `depth' value greater than zero; this sets the
     number of frames whose information will be captured.  To disable,
     pass set `depth' to zero.

     This setting is thread-specific.

     New in version 3.7.

          Note: This function has been added on a provisional basis (see
          PEP 411(17) for details.)  Use it only for debugging purposes.

 -- Function: sys._enablelegacywindowsfsencoding ()

     Changes the default filesystem encoding and errors mode to ‘mbcs’
     and ‘replace’ respectively, for consistency with versions of Python
     prior to 3.6.

     This is equivalent to defining the *note
     PYTHONLEGACYWINDOWSFSENCODING: 5f1. environment variable before
     launching Python.

     *note Availability: 1491.: Windows.

     New in version 3.6: See PEP 529(18) for more details.

 -- Data: sys.stdin
 -- Data: sys.stdout
 -- Data: sys.stderr

     *note File objects: c14. used by the interpreter for standard
     input, output and errors:

        * ‘stdin’ is used for all interactive input (including calls to
          *note input(): d33.);

        * ‘stdout’ is used for the output of *note print(): 971. and
          *note expression: 158f. statements and for the prompts of
          *note input(): d33.;

        * The interpreter’s own prompts and its error messages go to
          ‘stderr’.

     These streams are regular *note text files: 13d9. like those
     returned by the *note open(): 16f. function.  Their parameters are
     chosen as follows:

        * The character encoding is platform-dependent.  Non-Windows
          platforms use the locale encoding (see *note
          locale.getpreferredencoding(): 4ac.).

          On Windows, UTF-8 is used for the console device.
          Non-character devices such as disk files and pipes use the
          system locale encoding (i.e.  the ANSI codepage).  Non-console
          character devices such as NUL (i.e.  where ‘isatty()’ returns
          ‘True’) use the value of the console input and output
          codepages at startup, respectively for stdin and
          stdout/stderr.  This defaults to the system locale encoding if
          the process is not initially attached to a console.

          The special behaviour of the console can be overridden by
          setting the environment variable PYTHONLEGACYWINDOWSSTDIO
          before starting Python.  In that case, the console codepages
          are used as for any other character device.

          Under all platforms, you can override the character encoding
          by setting the *note PYTHONIOENCODING: a14. environment
          variable before starting Python or by using the new *note -X:
          290. ‘utf8’ command line option and *note PYTHONUTF8: 421.
          environment variable.  However, for the Windows console, this
          only applies when *note PYTHONLEGACYWINDOWSSTDIO: 5f4. is also
          set.

        * When interactive, the ‘stdout’ stream is line-buffered.
          Otherwise, it is block-buffered like regular text files.  The
          ‘stderr’ stream is line-buffered in both cases.  You can make
          both streams unbuffered by passing the *note -u: 109d.
          command-line option or setting the *note PYTHONUNBUFFERED:
          109e. environment variable.

     Changed in version 3.9: Non-interactive ‘stderr’ is now
     line-buffered instead of fully buffered.

          Note: To write or read binary data from/to the standard
          streams, use the underlying binary *note buffer: d02. object.
          For example, to write bytes to *note stdout: 41f, use
          ‘sys.stdout.buffer.write(b'abc')’.

          However, if you are writing a library (and do not control in
          which context its code will be executed), be aware that the
          standard streams may be replaced with file-like objects like
          *note io.StringIO: 91a. which do not support the ‘buffer’
          attribute.

 -- Data: sys.__stdin__
 -- Data: sys.__stdout__
 -- Data: sys.__stderr__

     These objects contain the original values of ‘stdin’, ‘stderr’ and
     ‘stdout’ at the start of the program.  They are used during
     finalization, and could be useful to print to the actual standard
     stream no matter if the ‘sys.std*’ object has been redirected.

     It can also be used to restore the actual files to known working
     file objects in case they have been overwritten with a broken
     object.  However, the preferred way to do this is to explicitly
     save the previous stream before replacing it, and restore the saved
     object.

          Note: Under some conditions ‘stdin’, ‘stdout’ and ‘stderr’ as
          well as the original values ‘__stdin__’, ‘__stdout__’ and
          ‘__stderr__’ can be ‘None’.  It is usually the case for
          Windows GUI apps that aren’t connected to a console and Python
          apps started with ‘pythonw’.

 -- Data: sys.thread_info

     A *note named tuple: b7b. holding information about the thread
     implementation.

     Attribute              Explanation
                            
     -------------------------------------------------------------------------------------
                            
     ‘name’                 Name of the thread implementation:
                            
                                    * ‘'nt'’: Windows threads
                            
                                    * ‘'pthread'’: POSIX threads
                            
                                    * ‘'solaris'’: Solaris threads
                            
                            
     ‘lock’                 Name of the lock implementation:
                            
                                    * ‘'semaphore'’: a lock uses a semaphore
                            
                                    * ‘'mutex+cond'’: a lock uses a mutex and a
                                      condition variable
                            
                                    * ‘None’ if this information is unknown
                            
                            
     *note version: 6ca.    Name and version of the thread library.  It is a string, or
                            ‘None’ if this information is unknown.
                            

     New in version 3.3.

 -- Data: sys.tracebacklimit

     When this variable is set to an integer value, it determines the
     maximum number of levels of traceback information printed when an
     unhandled exception occurs.  The default is ‘1000’.  When set to
     ‘0’ or less, all traceback information is suppressed and only the
     exception type and value are printed.

 -- Function: sys.unraisablehook (unraisable, /)

     Handle an unraisable exception.

     Called when an exception has occurred but there is no way for
     Python to handle it.  For example, when a destructor raises an
     exception or during garbage collection (*note gc.collect(): 35b.).

     The `unraisable' argument has the following attributes:

        * `exc_type': Exception type.

        * `exc_value': Exception value, can be ‘None’.

        * `exc_traceback': Exception traceback, can be ‘None’.

        * `err_msg': Error message, can be ‘None’.

        * `object': Object causing the exception, can be ‘None’.

     The default hook formats `err_msg' and `object' as: ‘f'{err_msg}:
     {object!r}'’; use “Exception ignored in” error message if `err_msg'
     is ‘None’.

     *note sys.unraisablehook(): 35a. can be overridden to control how
     unraisable exceptions are handled.

     Storing `exc_value' using a custom hook can create a reference
     cycle.  It should be cleared explicitly to break the reference
     cycle when the exception is no longer needed.

     Storing `object' using a custom hook can resurrect it if it is set
     to an object which is being finalized.  Avoid storing `object'
     after the custom hook completes to avoid resurrecting objects.

     See also *note excepthook(): f24. which handles uncaught
     exceptions.

     Raise an auditing event ‘sys.unraisablehook’ with arguments ‘hook’,
     ‘unraisable’ when an exception that cannot be handled occurs.  The
     ‘unraisable’ object is the same as what will be passed to the hook.
     If no hook has been set, ‘hook’ may be ‘None’.

     New in version 3.8.

 -- Data: sys.version

     A string containing the version number of the Python interpreter
     plus additional information on the build number and compiler used.
     This string is displayed when the interactive interpreter is
     started.  Do not extract version information out of it, rather, use
     *note version_info: bed. and the functions provided by the *note
     platform: ce. module.

 -- Data: sys.api_version

     The C API version for this interpreter.  Programmers may find this
     useful when debugging version conflicts between Python and
     extension modules.

 -- Data: sys.version_info

     A tuple containing the five components of the version number:
     `major', `minor', `micro', `releaselevel', and `serial'.  All
     values except `releaselevel' are integers; the release level is
     ‘'alpha'’, ‘'beta'’, ‘'candidate'’, or ‘'final'’.  The
     ‘version_info’ value corresponding to the Python version 2.0 is
     ‘(2, 0, 0, 'final', 0)’.  The components can also be accessed by
     name, so ‘sys.version_info[0]’ is equivalent to
     ‘sys.version_info.major’ and so on.

     Changed in version 3.1: Added named component attributes.

 -- Data: sys.warnoptions

     This is an implementation detail of the warnings framework; do not
     modify this value.  Refer to the *note warnings: 12f. module for
     more information on the warnings framework.

 -- Data: sys.winver

     The version number used to form registry keys on Windows platforms.
     This is stored as string resource 1000 in the Python DLL. The value
     is normally the first three characters of *note version: 6ca.  It
     is provided in the *note sys: fd. module for informational
     purposes; modifying this value has no effect on the registry keys
     used by Python.

     *note Availability: 1491.: Windows.

 -- Data: sys._xoptions

     A dictionary of the various implementation-specific flags passed
     through the *note -X: 290. command-line option.  Option names are
     either mapped to their values, if given explicitly, or to *note
     True: 594.  Example:

          $ ./python -Xa=b -Xc
          Python 3.2a3+ (py3k, Oct 16 2010, 20:14:50)
          [GCC 4.4.3] on linux2
          Type "help", "copyright", "credits" or "license" for more information.
          >>> import sys
          >>> sys._xoptions
          {'a': 'b', 'c': True}

     `CPython implementation detail:' This is a CPython-specific way of
     accessing options passed through *note -X: 290.  Other
     implementations may export them through other means, or not at all.

     New in version 3.2.

Citations
.........

(C99) ISO/IEC 9899:1999.  “Programming languages – C.” A public draft of
this standard is available at
‘http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf’.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3149

   (2) https://www.python.org/dev/peps/pep-0578

   (3) https://www.python.org/dev/peps/pep-0529

   (4) https://code.activestate.com/recipes/577504

   (5) https://www.python.org/dev/peps/pep-0525

   (6) https://www.python.org/dev/peps/pep-0411

   (7) https://www.python.org/dev/peps/pep-0411

   (8) https://www.python.org/dev/peps/pep-0421

   (9) https://www.python.org/dev/peps/pep-0421

   (10) https://www.python.org/dev/peps/pep-0393

   (11) https://www.python.org/dev/peps/pep-0451

   (12) https://www.python.org/dev/peps/pep-0302

   (13) https://www.python.org/dev/peps/pep-0302

   (14) https://www.python.org/dev/peps/pep-0525

   (15) 
https://github.com/python/cpython/tree/3.9/Lib/asyncio/base_events.py

   (16) https://www.python.org/dev/peps/pep-0411

   (17) https://www.python.org/dev/peps/pep-0411

   (18) https://www.python.org/dev/peps/pep-0529


File: python.info,  Node: sysconfig — Provide access to Python’s configuration information,  Next: builtins — Built-in objects,  Prev: sys — System-specific parameters and functions,  Up: Python Runtime Services

5.29.2 ‘sysconfig’ — Provide access to Python’s configuration information
-------------------------------------------------------------------------

New in version 3.2.

`Source code:' Lib/sysconfig.py(1)

__________________________________________________________________

The *note sysconfig: fe. module provides access to Python’s
configuration information like the list of installation paths and the
configuration variables relevant for the current platform.

* Menu:

* Configuration variables::
* Installation paths::
* Other functions: Other functions<3>.
* Using sysconfig as a script::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/sysconfig.py


File: python.info,  Node: Configuration variables,  Next: Installation paths,  Up: sysconfig — Provide access to Python’s configuration information

5.29.2.1 Configuration variables
................................

A Python distribution contains a ‘Makefile’ and a ‘pyconfig.h’ header
file that are necessary to build both the Python binary itself and
third-party C extensions compiled using *note distutils: 38.

*note sysconfig: fe. puts all variables found in these files in a
dictionary that can be accessed using *note get_config_vars(): a46. or
*note get_config_var(): a45.

Notice that on Windows, it’s a much smaller set.

 -- Function: sysconfig.get_config_vars (*args)

     With no arguments, return a dictionary of all configuration
     variables relevant for the current platform.

     With arguments, return a list of values that result from looking up
     each argument in the configuration variable dictionary.

     For each argument, if the value is not found, return ‘None’.

 -- Function: sysconfig.get_config_var (name)

     Return the value of a single variable `name'.  Equivalent to
     ‘get_config_vars().get(name)’.

     If `name' is not found, return ‘None’.

Example of usage:

     >>> import sysconfig
     >>> sysconfig.get_config_var('Py_ENABLE_SHARED')
     0
     >>> sysconfig.get_config_var('LIBDIR')
     '/usr/local/lib'
     >>> sysconfig.get_config_vars('AR', 'CXX')
     ['ar', 'g++']


File: python.info,  Node: Installation paths,  Next: Other functions<3>,  Prev: Configuration variables,  Up: sysconfig — Provide access to Python’s configuration information

5.29.2.2 Installation paths
...........................

Python uses an installation scheme that differs depending on the
platform and on the installation options.  These schemes are stored in
*note sysconfig: fe. under unique identifiers based on the value
returned by *note os.name: 2040.

Every new component that is installed using *note distutils: 38. or a
Distutils-based system will follow the same scheme to copy its file in
the right places.

Python currently supports six schemes:

   - `posix_prefix': scheme for POSIX platforms like Linux or macOS.
     This is the default scheme used when Python or a component is
     installed.

   - `posix_home': scheme for POSIX platforms used when a `home' option
     is used upon installation.  This scheme is used when a component is
     installed through Distutils with a specific home prefix.

   - `posix_user': scheme for POSIX platforms used when a component is
     installed through Distutils and the `user' option is used.  This
     scheme defines paths located under the user home directory.

   - `nt': scheme for NT platforms like Windows.

   - `nt_user': scheme for NT platforms, when the `user' option is used.

   - `osx_framework_user': scheme for macOS, when the `user' option is
     used.

Each scheme is itself composed of a series of paths and each path has a
unique identifier.  Python currently uses eight paths:

   - `stdlib': directory containing the standard Python library files
     that are not platform-specific.

   - `platstdlib': directory containing the standard Python library
     files that are platform-specific.

   - `platlib': directory for site-specific, platform-specific files.

   - `purelib': directory for site-specific, non-platform-specific
     files.

   - `include': directory for non-platform-specific header files.

   - `platinclude': directory for platform-specific header files.

   - `scripts': directory for script files.

   - `data': directory for data files.

*note sysconfig: fe. provides some functions to determine these paths.

 -- Function: sysconfig.get_scheme_names ()

     Return a tuple containing all schemes currently supported in *note
     sysconfig: fe.

 -- Function: sysconfig.get_path_names ()

     Return a tuple containing all path names currently supported in
     *note sysconfig: fe.

 -- Function: sysconfig.get_path (name[, scheme[, vars[, expand]]])

     Return an installation path corresponding to the path `name', from
     the install scheme named `scheme'.

     `name' has to be a value from the list returned by *note
     get_path_names(): 37c6.

     *note sysconfig: fe. stores installation paths corresponding to
     each path name, for each platform, with variables to be expanded.
     For instance the `stdlib' path for the `nt' scheme is:
     ‘{base}/Lib’.

     *note get_path(): d86. will use the variables returned by *note
     get_config_vars(): a46. to expand the path.  All variables have
     default values for each platform so one may call this function and
     get the default value.

     If `scheme' is provided, it must be a value from the list returned
     by *note get_scheme_names(): 37c5.  Otherwise, the default scheme
     for the current platform is used.

     If `vars' is provided, it must be a dictionary of variables that
     will update the dictionary return by *note get_config_vars(): a46.

     If `expand' is set to ‘False’, the path will not be expanded using
     the variables.

     If `name' is not found, raise a *note KeyError: 3e9.

 -- Function: sysconfig.get_paths ([scheme[, vars[, expand]]])

     Return a dictionary containing all installation paths corresponding
     to an installation scheme.  See *note get_path(): d86. for more
     information.

     If `scheme' is not provided, will use the default scheme for the
     current platform.

     If `vars' is provided, it must be a dictionary of variables that
     will update the dictionary used to expand the paths.

     If `expand' is set to false, the paths will not be expanded.

     If `scheme' is not an existing scheme, *note get_paths(): ca7. will
     raise a *note KeyError: 3e9.


File: python.info,  Node: Other functions<3>,  Next: Using sysconfig as a script,  Prev: Installation paths,  Up: sysconfig — Provide access to Python’s configuration information

5.29.2.3 Other functions
........................

 -- Function: sysconfig.get_python_version ()

     Return the ‘MAJOR.MINOR’ Python version number as a string.
     Similar to ‘'%d.%d' % sys.version_info[:2]’.

 -- Function: sysconfig.get_platform ()

     Return a string that identifies the current platform.

     This is used mainly to distinguish platform-specific build
     directories and platform-specific built distributions.  Typically
     includes the OS name and version and the architecture (as supplied
     by ‘os.uname()’), although the exact information included depends
     on the OS; e.g., on Linux, the kernel version isn’t particularly
     important.

     Examples of returned values:

        - linux-i586

        - linux-alpha (?)

        - solaris-2.6-sun4u

     Windows will return one of:

        - win-amd64 (64bit Windows on AMD64, aka x86_64, Intel64, and
          EM64T)

        - win32 (all others - specifically, sys.platform is returned)

     macOS can return:

        - macosx-10.6-ppc

        - macosx-10.4-ppc64

        - macosx-10.3-i386

        - macosx-10.4-fat

     For other non-POSIX platforms, currently just returns *note
     sys.platform: 3d3.

 -- Function: sysconfig.is_python_build ()

     Return ‘True’ if the running Python interpreter was built from
     source and is being run from its built location, and not from a
     location resulting from e.g.  running ‘make install’ or installing
     via a binary installer.

 -- Function: sysconfig.parse_config_h (fp[, vars])

     Parse a ‘config.h’-style file.

     `fp' is a file-like object pointing to the ‘config.h’-like file.

     A dictionary containing name/value pairs is returned.  If an
     optional dictionary is passed in as the second argument, it is used
     instead of a new dictionary, and updated with the values read in
     the file.

 -- Function: sysconfig.get_config_h_filename ()

     Return the path of ‘pyconfig.h’.

 -- Function: sysconfig.get_makefile_filename ()

     Return the path of ‘Makefile’.


File: python.info,  Node: Using sysconfig as a script,  Prev: Other functions<3>,  Up: sysconfig — Provide access to Python’s configuration information

5.29.2.4 Using ‘sysconfig’ as a script
......................................

You can use *note sysconfig: fe. as a script with Python’s `-m' option:

     $ python -m sysconfig
     Platform: "macosx-10.4-i386"
     Python version: "3.2"
     Current installation scheme: "posix_prefix"

     Paths:
             data = "/usr/local"
             include = "/Users/tarek/Dev/svn.python.org/py3k/Include"
             platinclude = "."
             platlib = "/usr/local/lib/python3.2/site-packages"
             platstdlib = "/usr/local/lib/python3.2"
             purelib = "/usr/local/lib/python3.2/site-packages"
             scripts = "/usr/local/bin"
             stdlib = "/usr/local/lib/python3.2"

     Variables:
             AC_APPLE_UNIVERSAL_BUILD = "0"
             AIX_GENUINE_CPLUSPLUS = "0"
             AR = "ar"
             ARFLAGS = "rc"
             ...

This call will print in the standard output the information returned by
*note get_platform(): ca5, *note get_python_version(): ca6, *note
get_path(): d86. and *note get_config_vars(): a46.


File: python.info,  Node: builtins — Built-in objects,  Next: __main__ — Top-level script environment,  Prev: sysconfig — Provide access to Python’s configuration information,  Up: Python Runtime Services

5.29.3 ‘builtins’ — Built-in objects
------------------------------------

__________________________________________________________________

This module provides direct access to all ‘built-in’ identifiers of
Python; for example, ‘builtins.open’ is the full name for the built-in
function *note open(): 16f.  See *note Built-in Functions: cbe. and
*note Built-in Constants: 173f. for documentation.

This module is not normally accessed explicitly by most applications,
but can be useful in modules that provide objects with the same name as
a built-in value, but in which the built-in of that name is also needed.
For example, in a module that wants to implement an *note open(): 16f.
function that wraps the built-in *note open(): 16f, this module can be
used directly:

     import builtins

     def open(path):
         f = builtins.open(path, 'r')
         return UpperCaser(f)

     class UpperCaser:
         '''Wrapper around a file that converts output to upper-case.'''

         def __init__(self, f):
             self._f = f

         def read(self, count=-1):
             return self._f.read(count).upper()

         # ...

As an implementation detail, most modules have the name ‘__builtins__’
made available as part of their globals.  The value of ‘__builtins__’ is
normally either this module or the value of this module’s *note
__dict__: 5f6. attribute.  Since this is an implementation detail, it
may not be used by alternate implementations of Python.


File: python.info,  Node: __main__ — Top-level script environment,  Next: warnings — Warning control,  Prev: builtins — Built-in objects,  Up: Python Runtime Services

5.29.4 ‘__main__’ — Top-level script environment
------------------------------------------------

__________________________________________________________________

‘'__main__'’ is the name of the scope in which top-level code executes.
A module’s __name__ is set equal to ‘'__main__'’ when read from standard
input, a script, or from an interactive prompt.

A module can discover whether or not it is running in the main scope by
checking its own ‘__name__’, which allows a common idiom for
conditionally executing code in a module when it is run as a script or
with ‘python -m’ but not when it is imported:

     if __name__ == "__main__":
         # execute only if run as a script
         main()

For a package, the same effect can be achieved by including a
‘__main__.py’ module, the contents of which will be executed when the
module is run with ‘-m’.


File: python.info,  Node: warnings — Warning control,  Next: dataclasses — Data Classes,  Prev: __main__ — Top-level script environment,  Up: Python Runtime Services

5.29.5 ‘warnings’ — Warning control
-----------------------------------

`Source code:' Lib/warnings.py(1)

__________________________________________________________________

Warning messages are typically issued in situations where it is useful
to alert the user of some condition in a program, where that condition
(normally) doesn’t warrant raising an exception and terminating the
program.  For example, one might want to issue a warning when a program
uses an obsolete module.

Python programmers issue warnings by calling the *note warn(): f1a.
function defined in this module.  (C programmers use *note
PyErr_WarnEx(): e76.; see *note Exception Handling: 37d2. for details).

Warning messages are normally written to *note sys.stderr: 1ea, but
their disposition can be changed flexibly, from ignoring all warnings to
turning them into exceptions.  The disposition of warnings can vary
based on the *note warning category: 185f, the text of the warning
message, and the source location where it is issued.  Repetitions of a
particular warning for the same source location are typically
suppressed.

There are two stages in warning control: first, each time a warning is
issued, a determination is made whether a message should be issued or
not; next, if a message is to be issued, it is formatted and printed
using a user-settable hook.

The determination whether to issue a warning message is controlled by
the *note warning filter: 15d, which is a sequence of matching rules and
actions.  Rules can be added to the filter by calling *note
filterwarnings(): eca. and reset to its default state by calling *note
resetwarnings(): 37d3.

The printing of warning messages is done by calling *note showwarning():
37d4, which may be overridden; the default implementation of this
function formats the message by calling *note formatwarning(): 112d,
which is also available for use by custom implementations.

See also
........

*note logging.captureWarnings(): 2228. allows you to handle all warnings
with the standard logging infrastructure.

* Menu:

* Warning Categories::
* The Warnings Filter::
* Temporarily Suppressing Warnings::
* Testing Warnings::
* Updating Code For New Versions of Dependencies::
* Available Functions::
* Available Context Managers::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/warnings.py


File: python.info,  Node: Warning Categories,  Next: The Warnings Filter,  Up: warnings — Warning control

5.29.5.1 Warning Categories
...........................

There are a number of built-in exceptions that represent warning
categories.  This categorization is useful to be able to filter out
groups of warnings.

While these are technically *note built-in exceptions: 185d, they are
documented here, because conceptually they belong to the warnings
mechanism.

User code can define additional warning categories by subclassing one of
the standard warning categories.  A warning category must always be a
subclass of the *note Warning: 1860. class.

The following warnings category classes are currently defined:

Class                                  Description
                                       
-------------------------------------------------------------------------------------------
                                       
*note Warning: 1860.                   This is the base class of all warning category
                                       classes.  It is a subclass of
                                       *note Exception: 2dc.
                                       
                                       
*note UserWarning: 1861.               The default category for *note warn(): f1a.
                                       
                                       
*note DeprecationWarning: 15a.         Base category for warnings about deprecated
                                       features when those warnings are intended for
                                       other Python developers (ignored by default,
                                       unless triggered by code in ‘__main__’).
                                       
                                       
*note SyntaxWarning: 2c9.              Base category for warnings about dubious
                                       syntactic features.
                                       
                                       
*note RuntimeWarning: 3e2.             Base category for warnings about dubious runtime
                                       features.
                                       
                                       
*note FutureWarning: 435.              Base category for warnings about deprecated
                                       features when those warnings are intended for end
                                       users of applications that are written in Python.
                                       
                                       
*note PendingDeprecationWarning: 15c.  Base category for warnings about features that
                                       will be deprecated in the future (ignored by
                                       default).
                                       
                                       
*note ImportWarning: 6cf.              Base category for warnings triggered during the
                                       process of importing a module (ignored by
                                       default).
                                       
                                       
*note UnicodeWarning: e4c.             Base category for warnings related to Unicode.
                                       
                                       
*note BytesWarning: 5b0.               Base category for warnings related to
                                       *note bytes: 172. and *note bytearray: 173.
                                       
                                       
*note ResourceWarning: 5cb.            Base category for warnings related to resource
                                       usage (ignored by default).
                                       

Changed in version 3.7: Previously *note DeprecationWarning: 15a. and
*note FutureWarning: 435. were distinguished based on whether a feature
was being removed entirely or changing its behaviour.  They are now
distinguished based on their intended audience and the way they’re
handled by the default warnings filters.


File: python.info,  Node: The Warnings Filter,  Next: Temporarily Suppressing Warnings,  Prev: Warning Categories,  Up: warnings — Warning control

5.29.5.2 The Warnings Filter
............................

The warnings filter controls whether warnings are ignored, displayed, or
turned into errors (raising an exception).

Conceptually, the warnings filter maintains an ordered list of filter
specifications; any specific warning is matched against each filter
specification in the list in turn until a match is found; the filter
determines the disposition of the match.  Each entry is a tuple of the
form (`action', `message', `category', `module', `lineno'), where:

   * `action' is one of the following strings:

     Value               Disposition
                         
     -----------------------------------------------------------------------
                         
     ‘"default"’         print the first occurrence of matching warnings
                         for each location (module + line number) where
                         the warning is issued
                         
                         
     ‘"error"’           turn matching warnings into exceptions
                         
                         
     ‘"ignore"’          never print matching warnings
                         
                         
     ‘"always"’          always print matching warnings
                         
                         
     ‘"module"’          print the first occurrence of matching warnings
                         for each module where the warning is issued
                         (regardless of line number)
                         
                         
     ‘"once"’            print only the first occurrence of matching
                         warnings, regardless of location
                         

   * `message' is a string containing a regular expression that the
     start of the warning message must match.  The expression is
     compiled to always be case-insensitive.

   * `category' is a class (a subclass of *note Warning: 1860.) of which
     the warning category must be a subclass in order to match.

   * `module' is a string containing a regular expression that the
     module name must match.  The expression is compiled to be
     case-sensitive.

   * `lineno' is an integer that the line number where the warning
     occurred must match, or ‘0’ to match all line numbers.

Since the *note Warning: 1860. class is derived from the built-in *note
Exception: 2dc. class, to turn a warning into an error we simply raise
‘category(message)’.

If a warning is reported and doesn’t match any registered filter then
the “default” action is applied (hence its name).

* Menu:

* Describing Warning Filters::
* Default Warning Filter::
* Overriding the default filter::


File: python.info,  Node: Describing Warning Filters,  Next: Default Warning Filter,  Up: The Warnings Filter

5.29.5.3 Describing Warning Filters
...................................

The warnings filter is initialized by *note -W: 15b. options passed to
the Python interpreter command line and the *note PYTHONWARNINGS: 51c.
environment variable.  The interpreter saves the arguments for all
supplied entries without interpretation in *note sys.warnoptions: 51b.;
the *note warnings: 12f. module parses these when it is first imported
(invalid options are ignored, after printing a message to *note
sys.stderr: 1ea.).

Individual warnings filters are specified as a sequence of fields
separated by colons:

     action:message:category:module:line

The meaning of each of these fields is as described in *note The
Warnings Filter: 15d.  When listing multiple filters on a single line
(as for *note PYTHONWARNINGS: 51c.), the individual filters are
separated by commas and the filters listed later take precedence over
those listed before them (as they’re applied left-to-right, and the most
recently applied filters take precedence over earlier ones).

Commonly used warning filters apply to either all warnings, warnings in
a particular category, or warnings raised by particular modules or
packages.  Some examples:

     default                      # Show all warnings (even those ignored by default)
     ignore                       # Ignore all warnings
     error                        # Convert all warnings to errors
     error::ResourceWarning       # Treat ResourceWarning messages as errors
     default::DeprecationWarning  # Show DeprecationWarning messages
     ignore,default:::mymodule    # Only report warnings triggered by "mymodule"
     error:::mymodule[.*]         # Convert warnings to errors in "mymodule"
                                  # and any subpackages of "mymodule"


File: python.info,  Node: Default Warning Filter,  Next: Overriding the default filter,  Prev: Describing Warning Filters,  Up: The Warnings Filter

5.29.5.4 Default Warning Filter
...............................

By default, Python installs several warning filters, which can be
overridden by the *note -W: 15b. command-line option, the *note
PYTHONWARNINGS: 51c. environment variable and calls to *note
filterwarnings(): eca.

In regular release builds, the default warning filter has the following
entries (in order of precedence):

     default::DeprecationWarning:__main__
     ignore::DeprecationWarning
     ignore::PendingDeprecationWarning
     ignore::ImportWarning
     ignore::ResourceWarning

In debug builds, the list of default warning filters is empty.

Changed in version 3.2: *note DeprecationWarning: 15a. is now ignored by
default in addition to *note PendingDeprecationWarning: 15c.

Changed in version 3.7: *note DeprecationWarning: 15a. is once again
shown by default when triggered directly by code in ‘__main__’.

Changed in version 3.7: *note BytesWarning: 5b0. no longer appears in
the default filter list and is instead configured via *note
sys.warnoptions: 51b. when *note -b: 51a. is specified twice.


File: python.info,  Node: Overriding the default filter,  Prev: Default Warning Filter,  Up: The Warnings Filter

5.29.5.5 Overriding the default filter
......................................

Developers of applications written in Python may wish to hide `all'
Python level warnings from their users by default, and only display them
when running tests or otherwise working on the application.  The *note
sys.warnoptions: 51b. attribute used to pass filter configurations to
the interpreter can be used as a marker to indicate whether or not
warnings should be disabled:

     import sys

     if not sys.warnoptions:
         import warnings
         warnings.simplefilter("ignore")

Developers of test runners for Python code are advised to instead ensure
that `all' warnings are displayed by default for the code under test,
using code like:

     import sys

     if not sys.warnoptions:
         import os, warnings
         warnings.simplefilter("default") # Change the filter in this process
         os.environ["PYTHONWARNINGS"] = "default" # Also affect subprocesses

Finally, developers of interactive shells that run user code in a
namespace other than ‘__main__’ are advised to ensure that *note
DeprecationWarning: 15a. messages are made visible by default, using
code like the following (where ‘user_ns’ is the module used to execute
code entered interactively):

     import warnings
     warnings.filterwarnings("default", category=DeprecationWarning,
                                        module=user_ns.get("__name__"))


File: python.info,  Node: Temporarily Suppressing Warnings,  Next: Testing Warnings,  Prev: The Warnings Filter,  Up: warnings — Warning control

5.29.5.6 Temporarily Suppressing Warnings
.........................................

If you are using code that you know will raise a warning, such as a
deprecated function, but do not want to see the warning (even when
warnings have been explicitly configured via the command line), then it
is possible to suppress the warning using the *note catch_warnings:
35f9. context manager:

     import warnings

     def fxn():
         warnings.warn("deprecated", DeprecationWarning)

     with warnings.catch_warnings():
         warnings.simplefilter("ignore")
         fxn()

While within the context manager all warnings will simply be ignored.
This allows you to use known-deprecated code without having to see the
warning while not suppressing the warning for other code that might not
be aware of its use of deprecated code.  Note: this can only be
guaranteed in a single-threaded application.  If two or more threads use
the *note catch_warnings: 35f9. context manager at the same time, the
behavior is undefined.


File: python.info,  Node: Testing Warnings,  Next: Updating Code For New Versions of Dependencies,  Prev: Temporarily Suppressing Warnings,  Up: warnings — Warning control

5.29.5.7 Testing Warnings
.........................

To test warnings raised by code, use the *note catch_warnings: 35f9.
context manager.  With it you can temporarily mutate the warnings filter
to facilitate your testing.  For instance, do the following to capture
all raised warnings to check:

     import warnings

     def fxn():
         warnings.warn("deprecated", DeprecationWarning)

     with warnings.catch_warnings(record=True) as w:
         # Cause all warnings to always be triggered.
         warnings.simplefilter("always")
         # Trigger a warning.
         fxn()
         # Verify some things
         assert len(w) == 1
         assert issubclass(w[-1].category, DeprecationWarning)
         assert "deprecated" in str(w[-1].message)

One can also cause all warnings to be exceptions by using ‘error’
instead of ‘always’.  One thing to be aware of is that if a warning has
already been raised because of a ‘once’/‘default’ rule, then no matter
what filters are set the warning will not be seen again unless the
warnings registry related to the warning has been cleared.

Once the context manager exits, the warnings filter is restored to its
state when the context was entered.  This prevents tests from changing
the warnings filter in unexpected ways between tests and leading to
indeterminate test results.  The *note showwarning(): 37d4. function in
the module is also restored to its original value.  Note: this can only
be guaranteed in a single-threaded application.  If two or more threads
use the *note catch_warnings: 35f9. context manager at the same time,
the behavior is undefined.

When testing multiple operations that raise the same kind of warning, it
is important to test them in a manner that confirms each operation is
raising a new warning (e.g.  set warnings to be raised as exceptions and
check the operations raise exceptions, check that the length of the
warning list continues to increase after each operation, or else delete
the previous entries from the warnings list before each new operation).


File: python.info,  Node: Updating Code For New Versions of Dependencies,  Next: Available Functions,  Prev: Testing Warnings,  Up: warnings — Warning control

5.29.5.8 Updating Code For New Versions of Dependencies
.......................................................

Warning categories that are primarily of interest to Python developers
(rather than end users of applications written in Python) are ignored by
default.

Notably, this “ignored by default” list includes *note
DeprecationWarning: 15a. (for every module except ‘__main__’), which
means developers should make sure to test their code with typically
ignored warnings made visible in order to receive timely notifications
of future breaking API changes (whether in the standard library or third
party packages).

In the ideal case, the code will have a suitable test suite, and the
test runner will take care of implicitly enabling all warnings when
running tests (the test runner provided by the *note unittest: 124.
module does this).

In less ideal cases, applications can be checked for use of deprecated
interfaces by passing *note -Wd: 15b. to the Python interpreter (this is
shorthand for ‘-W default’) or setting ‘PYTHONWARNINGS=default’ in the
environment.  This enables default handling for all warnings, including
those that are ignored by default.  To change what action is taken for
encountered warnings you can change what argument is passed to *note -W:
15b. (e.g.  ‘-W error’).  See the *note -W: 15b. flag for more details
on what is possible.


File: python.info,  Node: Available Functions,  Next: Available Context Managers,  Prev: Updating Code For New Versions of Dependencies,  Up: warnings — Warning control

5.29.5.9 Available Functions
............................

 -- Function: warnings.warn (message, category=None, stacklevel=1,
          source=None)

     Issue a warning, or maybe ignore it or raise an exception.  The
     `category' argument, if given, must be a *note warning category
     class: 185f.; it defaults to *note UserWarning: 1861.
     Alternatively, `message' can be a *note Warning: 1860. instance, in
     which case `category' will be ignored and ‘message.__class__’ will
     be used.  In this case, the message text will be ‘str(message)’.
     This function raises an exception if the particular warning issued
     is changed into an error by the *note warnings filter: 15d.  The
     `stacklevel' argument can be used by wrapper functions written in
     Python, like this:

          def deprecation(message):
              warnings.warn(message, DeprecationWarning, stacklevel=2)

     This makes the warning refer to ‘deprecation()’’s caller, rather
     than to the source of ‘deprecation()’ itself (since the latter
     would defeat the purpose of the warning message).

     `source', if supplied, is the destroyed object which emitted a
     *note ResourceWarning: 5cb.

     Changed in version 3.6: Added `source' parameter.

 -- Function: warnings.warn_explicit (message, category, filename,
          lineno, module=None, registry=None, module_globals=None,
          source=None)

     This is a low-level interface to the functionality of *note warn():
     f1a, passing in explicitly the message, category, filename and line
     number, and optionally the module name and the registry (which
     should be the ‘__warningregistry__’ dictionary of the module).  The
     module name defaults to the filename with ‘.py’ stripped; if no
     registry is passed, the warning is never suppressed.  `message'
     must be a string and `category' a subclass of *note Warning: 1860.
     or `message' may be a *note Warning: 1860. instance, in which case
     `category' will be ignored.

     `module_globals', if supplied, should be the global namespace in
     use by the code for which the warning is issued.  (This argument is
     used to support displaying source for modules found in zipfiles or
     other non-filesystem import sources).

     `source', if supplied, is the destroyed object which emitted a
     *note ResourceWarning: 5cb.

     Changed in version 3.6: Add the `source' parameter.

 -- Function: warnings.showwarning (message, category, filename, lineno,
          file=None, line=None)

     Write a warning to a file.  The default implementation calls
     ‘formatwarning(message, category, filename, lineno, line)’ and
     writes the resulting string to `file', which defaults to *note
     sys.stderr: 1ea.  You may replace this function with any callable
     by assigning to ‘warnings.showwarning’.  `line' is a line of source
     code to be included in the warning message; if `line' is not
     supplied, *note showwarning(): 37d4. will try to read the line
     specified by `filename' and `lineno'.

 -- Function: warnings.formatwarning (message, category, filename,
          lineno, line=None)

     Format a warning the standard way.  This returns a string which may
     contain embedded newlines and ends in a newline.  `line' is a line
     of source code to be included in the warning message; if `line' is
     not supplied, *note formatwarning(): 112d. will try to read the
     line specified by `filename' and `lineno'.

 -- Function: warnings.filterwarnings (action, message='',
          category=Warning, module='', lineno=0, append=False)

     Insert an entry into the list of *note warnings filter
     specifications: 15d.  The entry is inserted at the front by
     default; if `append' is true, it is inserted at the end.  This
     checks the types of the arguments, compiles the `message' and
     `module' regular expressions, and inserts them as a tuple in the
     list of warnings filters.  Entries closer to the front of the list
     override entries later in the list, if both match a particular
     warning.  Omitted arguments default to a value that matches
     everything.

 -- Function: warnings.simplefilter (action, category=Warning, lineno=0,
          append=False)

     Insert a simple entry into the list of *note warnings filter
     specifications: 15d.  The meaning of the function parameters is as
     for *note filterwarnings(): eca, but regular expressions are not
     needed as the filter inserted always matches any message in any
     module as long as the category and line number match.

 -- Function: warnings.resetwarnings ()

     Reset the warnings filter.  This discards the effect of all
     previous calls to *note filterwarnings(): eca, including that of
     the *note -W: 15b. command line options and calls to *note
     simplefilter(): 35fa.


File: python.info,  Node: Available Context Managers,  Prev: Available Functions,  Up: warnings — Warning control

5.29.5.10 Available Context Managers
....................................

 -- Class: warnings.catch_warnings (*, record=False, module=None)

     A context manager that copies and, upon exit, restores the warnings
     filter and the *note showwarning(): 37d4. function.  If the
     `record' argument is *note False: 48f. (the default) the context
     manager returns *note None: 203. on entry.  If `record' is *note
     True: 594, a list is returned that is progressively populated with
     objects as seen by a custom *note showwarning(): 37d4. function
     (which also suppresses output to ‘sys.stdout’).  Each object in the
     list has attributes with the same names as the arguments to *note
     showwarning(): 37d4.

     The `module' argument takes a module that will be used instead of
     the module returned when you import *note warnings: 12f. whose
     filter will be protected.  This argument exists primarily for
     testing the *note warnings: 12f. module itself.

          Note: The *note catch_warnings: 35f9. manager works by
          replacing and then later restoring the module’s *note
          showwarning(): 37d4. function and internal list of filter
          specifications.  This means the context manager is modifying
          global state and therefore is not thread-safe.


File: python.info,  Node: dataclasses — Data Classes,  Next: contextlib — Utilities for with-statement contexts,  Prev: warnings — Warning control,  Up: Python Runtime Services

5.29.6 ‘dataclasses’ — Data Classes
-----------------------------------

`Source code:' Lib/dataclasses.py(1)

__________________________________________________________________

This module provides a decorator and functions for automatically adding
generated *note special method: 37e6.s such as *note __init__(): e23.
and *note __repr__(): 44a. to user-defined classes.  It was originally
described in PEP 557(2).

The member variables to use in these generated methods are defined using
PEP 526(3) type annotations.  For example, this code:

     from dataclasses import dataclass

     @dataclass
     class InventoryItem:
         """Class for keeping track of an item in inventory."""
         name: str
         unit_price: float
         quantity_on_hand: int = 0

         def total_cost(self) -> float:
             return self.unit_price * self.quantity_on_hand

will add, among other things, a *note __init__(): e23. that looks like:

     def __init__(self, name: str, unit_price: float, quantity_on_hand: int = 0):
         self.name = name
         self.unit_price = unit_price
         self.quantity_on_hand = quantity_on_hand

Note that this method is automatically added to the class: it is not
directly specified in the ‘InventoryItem’ definition shown above.

New in version 3.7.

* Menu:

* Module-level decorators, classes, and functions: Module-level decorators classes and functions.
* Post-init processing::
* Class variables::
* Init-only variables::
* Frozen instances::
* Inheritance: Inheritance<2>.
* Default factory functions::
* Mutable default values::
* Exceptions: Exceptions<18>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/dataclasses.py

   (2) https://www.python.org/dev/peps/pep-0557

   (3) https://www.python.org/dev/peps/pep-0526


File: python.info,  Node: Module-level decorators classes and functions,  Next: Post-init processing,  Up: dataclasses — Data Classes

5.29.6.1 Module-level decorators, classes, and functions
........................................................

 -- Function: @dataclasses.dataclass (*, init=True, repr=True, eq=True,
          order=False, unsafe_hash=False, frozen=False)

     This function is a *note decorator: 174. that is used to add
     generated *note special method: 37e6.s to classes, as described
     below.

     The *note dataclass(): 449. decorator examines the class to find
     ‘field’s.  A ‘field’ is defined as a class variable that has a
     *note type annotation: 712.  With two exceptions described below,
     nothing in *note dataclass(): 449. examines the type specified in
     the variable annotation.

     The order of the fields in all of the generated methods is the
     order in which they appear in the class definition.

     The *note dataclass(): 449. decorator will add various “dunder”
     methods to the class, described below.  If any of the added methods
     already exist in the class, the behavior depends on the parameter,
     as documented below.  The decorator returns the same class that it
     is called on; no new class is created.

     If *note dataclass(): 449. is used just as a simple decorator with
     no parameters, it acts as if it has the default values documented
     in this signature.  That is, these three uses of *note dataclass():
     449. are equivalent:

          @dataclass
          class C:
              ...

          @dataclass()
          class C:
              ...

          @dataclass(init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False)
          class C:
             ...

     The parameters to *note dataclass(): 449. are:

        - ‘init’: If true (the default), a *note __init__(): e23. method
          will be generated.

          If the class already defines *note __init__(): e23, this
          parameter is ignored.

        - ‘repr’: If true (the default), a *note __repr__(): 44a. method
          will be generated.  The generated repr string will have the
          class name and the name and repr of each field, in the order
          they are defined in the class.  Fields that are marked as
          being excluded from the repr are not included.  For example:
          ‘InventoryItem(name='widget', unit_price=3.0,
          quantity_on_hand=10)’.

          If the class already defines *note __repr__(): 44a, this
          parameter is ignored.

        - ‘eq’: If true (the default), an *note __eq__(): 44b. method
          will be generated.  This method compares the class as if it
          were a tuple of its fields, in order.  Both instances in the
          comparison must be of the identical type.

          If the class already defines *note __eq__(): 44b, this
          parameter is ignored.

        - ‘order’: If true (the default is ‘False’), *note __lt__():
          cfe, *note __le__(): d68, *note __gt__(): d69, and *note
          __ge__(): d6a. methods will be generated.  These compare the
          class as if it were a tuple of its fields, in order.  Both
          instances in the comparison must be of the identical type.  If
          ‘order’ is true and ‘eq’ is false, a *note ValueError: 16d. is
          raised.

          If the class already defines any of *note __lt__(): cfe, *note
          __le__(): d68, *note __gt__(): d69, or *note __ge__(): d6a,
          then *note TypeError: 1fe. is raised.

        - ‘unsafe_hash’: If ‘False’ (the default), a *note __hash__():
          44c. method is generated according to how ‘eq’ and ‘frozen’
          are set.

          *note __hash__(): 44c. is used by built-in *note hash(): aa3,
          and when objects are added to hashed collections such as
          dictionaries and sets.  Having a *note __hash__(): 44c.
          implies that instances of the class are immutable.  Mutability
          is a complicated property that depends on the programmer’s
          intent, the existence and behavior of *note __eq__(): 44b, and
          the values of the ‘eq’ and ‘frozen’ flags in the *note
          dataclass(): 449. decorator.

          By default, *note dataclass(): 449. will not implicitly add a
          *note __hash__(): 44c. method unless it is safe to do so.
          Neither will it add or change an existing explicitly defined
          *note __hash__(): 44c. method.  Setting the class attribute
          ‘__hash__ = None’ has a specific meaning to Python, as
          described in the *note __hash__(): 44c. documentation.

          If *note __hash__(): 44c. is not explicitly defined, or if it
          is set to ‘None’, then *note dataclass(): 449. `may' add an
          implicit *note __hash__(): 44c. method.  Although not
          recommended, you can force *note dataclass(): 449. to create a
          *note __hash__(): 44c. method with ‘unsafe_hash=True’.  This
          might be the case if your class is logically immutable but can
          nonetheless be mutated.  This is a specialized use case and
          should be considered carefully.

          Here are the rules governing implicit creation of a *note
          __hash__(): 44c. method.  Note that you cannot both have an
          explicit *note __hash__(): 44c. method in your dataclass and
          set ‘unsafe_hash=True’; this will result in a *note TypeError:
          1fe.

          If ‘eq’ and ‘frozen’ are both true, by default *note
          dataclass(): 449. will generate a *note __hash__(): 44c.
          method for you.  If ‘eq’ is true and ‘frozen’ is false, *note
          __hash__(): 44c. will be set to ‘None’, marking it unhashable
          (which it is, since it is mutable).  If ‘eq’ is false, *note
          __hash__(): 44c. will be left untouched meaning the *note
          __hash__(): 44c. method of the superclass will be used (if the
          superclass is *note object: 3d2, this means it will fall back
          to id-based hashing).

        - ‘frozen’: If true (the default is ‘False’), assigning to
          fields will generate an exception.  This emulates read-only
          frozen instances.  If *note __setattr__(): eee. or *note
          __delattr__(): 1563. is defined in the class, then *note
          TypeError: 1fe. is raised.  See the discussion below.

     ‘field’s may optionally specify a default value, using normal
     Python syntax:

          @dataclass
          class C:
              a: int       # 'a' has no default value
              b: int = 0   # assign a default value for 'b'

     In this example, both ‘a’ and ‘b’ will be included in the added
     *note __init__(): e23. method, which will be defined as:

          def __init__(self, a: int, b: int = 0):

     *note TypeError: 1fe. will be raised if a field without a default
     value follows a field with a default value.  This is true whether
     this occurs in a single class, or as a result of class inheritance.

 -- Function: dataclasses.field (*, default=MISSING,
          default_factory=MISSING, repr=True, hash=None, init=True,
          compare=True, metadata=None)

     For common and simple use cases, no other functionality is
     required.  There are, however, some dataclass features that require
     additional per-field information.  To satisfy this need for
     additional information, you can replace the default field value
     with a call to the provided *note field(): 1139. function.  For
     example:

          @dataclass
          class C:
              mylist: list[int] = field(default_factory=list)

          c = C()
          c.mylist += [1, 2, 3]

     As shown above, the ‘MISSING’ value is a sentinel object used to
     detect if the ‘default’ and ‘default_factory’ parameters are
     provided.  This sentinel is used because ‘None’ is a valid value
     for ‘default’.  No code should directly use the ‘MISSING’ value.

     The parameters to *note field(): 1139. are:

        - ‘default’: If provided, this will be the default value for
          this field.  This is needed because the *note field(): 1139.
          call itself replaces the normal position of the default value.

        - ‘default_factory’: If provided, it must be a zero-argument
          callable that will be called when a default value is needed
          for this field.  Among other purposes, this can be used to
          specify fields with mutable default values, as discussed
          below.  It is an error to specify both ‘default’ and
          ‘default_factory’.

        - ‘init’: If true (the default), this field is included as a
          parameter to the generated *note __init__(): e23. method.

        - ‘repr’: If true (the default), this field is included in the
          string returned by the generated *note __repr__(): 44a.
          method.

        - ‘compare’: If true (the default), this field is included in
          the generated equality and comparison methods (*note __eq__():
          44b, *note __gt__(): d69, et al.).

        - ‘hash’: This can be a bool or ‘None’.  If true, this field is
          included in the generated *note __hash__(): 44c. method.  If
          ‘None’ (the default), use the value of ‘compare’: this would
          normally be the expected behavior.  A field should be
          considered in the hash if it’s used for comparisons.  Setting
          this value to anything other than ‘None’ is discouraged.

          One possible reason to set ‘hash=False’ but ‘compare=True’
          would be if a field is expensive to compute a hash value for,
          that field is needed for equality testing, and there are other
          fields that contribute to the type’s hash value.  Even if a
          field is excluded from the hash, it will still be used for
          comparisons.

        - ‘metadata’: This can be a mapping or None.  None is treated as
          an empty dict.  This value is wrapped in *note
          MappingProxyType(): b8e. to make it read-only, and exposed on
          the *note Field: 37e8. object.  It is not used at all by Data
          Classes, and is provided as a third-party extension mechanism.
          Multiple third-parties can each have their own key, to use as
          a namespace in the metadata.

     If the default value of a field is specified by a call to *note
     field(): 1139, then the class attribute for this field will be
     replaced by the specified ‘default’ value.  If no ‘default’ is
     provided, then the class attribute will be deleted.  The intent is
     that after the *note dataclass(): 449. decorator runs, the class
     attributes will all contain the default values for the fields, just
     as if the default value itself were specified.  For example, after:

          @dataclass
          class C:
              x: int
              y: int = field(repr=False)
              z: int = field(repr=False, default=10)
              t: int = 20

     The class attribute ‘C.z’ will be ‘10’, the class attribute ‘C.t’
     will be ‘20’, and the class attributes ‘C.x’ and ‘C.y’ will not be
     set.

 -- Class: dataclasses.Field

     *note Field: 37e8. objects describe each defined field.  These
     objects are created internally, and are returned by the *note
     fields(): 37e9. module-level method (see below).  Users should
     never instantiate a *note Field: 37e8. object directly.  Its
     documented attributes are:

             - ‘name’: The name of the field.

             - ‘type’: The type of the field.

             - ‘default’, ‘default_factory’, ‘init’, ‘repr’, ‘hash’,
               ‘compare’, and ‘metadata’ have the identical meaning and
               values as they do in the *note field(): 1139.
               declaration.

     Other attributes may exist, but they are private and must not be
     inspected or relied on.

 -- Function: dataclasses.fields (class_or_instance)

     Returns a tuple of *note Field: 37e8. objects that define the
     fields for this dataclass.  Accepts either a dataclass, or an
     instance of a dataclass.  Raises *note TypeError: 1fe. if not
     passed a dataclass or instance of one.  Does not return
     pseudo-fields which are ‘ClassVar’ or ‘InitVar’.

 -- Function: dataclasses.asdict (obj, *, dict_factory=dict)

     Converts the dataclass ‘obj’ to a dict (by using the factory
     function ‘dict_factory’).  Each dataclass is converted to a dict of
     its fields, as ‘name: value’ pairs.  dataclasses, dicts, lists, and
     tuples are recursed into.  Other objects are copied with *note
     copy.deepcopy(): 4d3.

     Example of using *note asdict(): f57. on nested dataclasses:

          @dataclass
          class Point:
               x: int
               y: int

          @dataclass
          class C:
               mylist: list[Point]

          p = Point(10, 20)
          assert asdict(p) == {'x': 10, 'y': 20}

          c = C([Point(0, 0), Point(10, 4)])
          assert asdict(c) == {'mylist': [{'x': 0, 'y': 0}, {'x': 10, 'y': 4}]}

     To create a shallow copy, the following workaround may be used:

          dict((field.name, getattr(obj, field.name)) for field in fields(obj))

     *note asdict(): f57. raises *note TypeError: 1fe. if ‘obj’ is not a
     dataclass instance.

 -- Function: dataclasses.astuple (obj, *, tuple_factory=tuple)

     Converts the dataclass ‘obj’ to a tuple (by using the factory
     function ‘tuple_factory’).  Each dataclass is converted to a tuple
     of its field values.  dataclasses, dicts, lists, and tuples are
     recursed into.  Other objects are copied with *note
     copy.deepcopy(): 4d3.

     Continuing from the previous example:

          assert astuple(p) == (10, 20)
          assert astuple(c) == ([(0, 0), (10, 4)],)

     To create a shallow copy, the following workaround may be used:

          tuple(getattr(obj, field.name) for field in dataclasses.fields(obj))

     *note astuple(): f56. raises *note TypeError: 1fe. if ‘obj’ is not
     a dataclass instance.

 -- Function: dataclasses.make_dataclass (cls_name, fields, *, bases=(),
          namespace=None, init=True, repr=True, eq=True, order=False,
          unsafe_hash=False, frozen=False)

     Creates a new dataclass with name ‘cls_name’, fields as defined in
     ‘fields’, base classes as given in ‘bases’, and initialized with a
     namespace as given in ‘namespace’.  ‘fields’ is an iterable whose
     elements are each either ‘name’, ‘(name, type)’, or ‘(name, type,
     Field)’.  If just ‘name’ is supplied, ‘typing.Any’ is used for
     ‘type’.  The values of ‘init’, ‘repr’, ‘eq’, ‘order’,
     ‘unsafe_hash’, and ‘frozen’ have the same meaning as they do in
     *note dataclass(): 449.

     This function is not strictly required, because any Python
     mechanism for creating a new class with ‘__annotations__’ can then
     apply the *note dataclass(): 449. function to convert that class to
     a dataclass.  This function is provided as a convenience.  For
     example:

          C = make_dataclass('C',
                             [('x', int),
                               'y',
                              ('z', int, field(default=5))],
                             namespace={'add_one': lambda self: self.x + 1})

     Is equivalent to:

          @dataclass
          class C:
              x: int
              y: 'typing.Any'
              z: int = 5

              def add_one(self):
                  return self.x + 1

 -- Function: dataclasses.replace (obj, /, **changes)

     Creates a new object of the same type as ‘obj’, replacing fields
     with values from ‘changes’.  If ‘obj’ is not a Data Class, raises
     *note TypeError: 1fe.  If values in ‘changes’ do not specify
     fields, raises *note TypeError: 1fe.

     The newly returned object is created by calling the *note
     __init__(): e23. method of the dataclass.  This ensures that
     ‘__post_init__()’, if present, is also called.

     Init-only variables without default values, if any exist, must be
     specified on the call to *note replace(): fa8. so that they can be
     passed to *note __init__(): e23. and ‘__post_init__()’.

     It is an error for ‘changes’ to contain any fields that are defined
     as having ‘init=False’.  A *note ValueError: 16d. will be raised in
     this case.

     Be forewarned about how ‘init=False’ fields work during a call to
     *note replace(): fa8.  They are not copied from the source object,
     but rather are initialized in ‘__post_init__()’, if they’re
     initialized at all.  It is expected that ‘init=False’ fields will
     be rarely and judiciously used.  If they are used, it might be wise
     to have alternate class constructors, or perhaps a custom
     ‘replace()’ (or similarly named) method which handles instance
     copying.

 -- Function: dataclasses.is_dataclass (obj)

     Return ‘True’ if its parameter is a dataclass or an instance of
     one, otherwise return ‘False’.

     If you need to know if a class is an instance of a dataclass (and
     not a dataclass itself), then add a further check for ‘not
     isinstance(obj, type)’:

          def is_dataclass_instance(obj):
              return is_dataclass(obj) and not isinstance(obj, type)


File: python.info,  Node: Post-init processing,  Next: Class variables,  Prev: Module-level decorators classes and functions,  Up: dataclasses — Data Classes

5.29.6.2 Post-init processing
.............................

The generated *note __init__(): e23. code will call a method named
‘__post_init__()’, if ‘__post_init__()’ is defined on the class.  It
will normally be called as ‘self.__post_init__()’.  However, if any
‘InitVar’ fields are defined, they will also be passed to
‘__post_init__()’ in the order they were defined in the class.  If no
*note __init__(): e23. method is generated, then ‘__post_init__()’ will
not automatically be called.

Among other uses, this allows for initializing field values that depend
on one or more other fields.  For example:

     @dataclass
     class C:
         a: float
         b: float
         c: float = field(init=False)

         def __post_init__(self):
             self.c = self.a + self.b

The *note __init__(): e23. method generated by *note dataclass(): 449.
does not call base class *note __init__(): e23. methods.  If the base
class has an *note __init__(): e23. method that has to be called, it is
common to call this method in a ‘__post_init__()’ method:

     @dataclass
     class Rectangle:
         height: float
         width: float

     @dataclass
     class Square(Rectangle):
         side: float

         def __post_init__(self):
             super().__init__(self.side, self.side)

Note, however, that in general the dataclass-generated *note __init__():
e23. methods don’t need to be called, since the derived dataclass will
take care of initializing all fields of any base class that is a
dataclass itself.

See the section below on init-only variables for ways to pass parameters
to ‘__post_init__()’.  Also see the warning about how *note replace():
fa8. handles ‘init=False’ fields.


File: python.info,  Node: Class variables,  Next: Init-only variables,  Prev: Post-init processing,  Up: dataclasses — Data Classes

5.29.6.3 Class variables
........................

One of two places where *note dataclass(): 449. actually inspects the
type of a field is to determine if a field is a class variable as
defined in PEP 526(1).  It does this by checking if the type of the
field is ‘typing.ClassVar’.  If a field is a ‘ClassVar’, it is excluded
from consideration as a field and is ignored by the dataclass
mechanisms.  Such ‘ClassVar’ pseudo-fields are not returned by the
module-level *note fields(): 37e9. function.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0526


File: python.info,  Node: Init-only variables,  Next: Frozen instances,  Prev: Class variables,  Up: dataclasses — Data Classes

5.29.6.4 Init-only variables
............................

The other place where *note dataclass(): 449. inspects a type annotation
is to determine if a field is an init-only variable.  It does this by
seeing if the type of a field is of type ‘dataclasses.InitVar’.  If a
field is an ‘InitVar’, it is considered a pseudo-field called an
init-only field.  As it is not a true field, it is not returned by the
module-level *note fields(): 37e9. function.  Init-only fields are added
as parameters to the generated *note __init__(): e23. method, and are
passed to the optional ‘__post_init__()’ method.  They are not otherwise
used by dataclasses.

For example, suppose a field will be initialized from a database, if a
value is not provided when creating the class:

     @dataclass
     class C:
         i: int
         j: int = None
         database: InitVar[DatabaseType] = None

         def __post_init__(self, database):
             if self.j is None and database is not None:
                 self.j = database.lookup('j')

     c = C(10, database=my_database)

In this case, *note fields(): 37e9. will return *note Field: 37e8.
objects for ‘i’ and ‘j’, but not for ‘database’.


File: python.info,  Node: Frozen instances,  Next: Inheritance<2>,  Prev: Init-only variables,  Up: dataclasses — Data Classes

5.29.6.5 Frozen instances
.........................

It is not possible to create truly immutable Python objects.  However,
by passing ‘frozen=True’ to the *note dataclass(): 449. decorator you
can emulate immutability.  In that case, dataclasses will add *note
__setattr__(): eee. and *note __delattr__(): 1563. methods to the class.
These methods will raise a *note FrozenInstanceError: 37ef. when
invoked.

There is a tiny performance penalty when using ‘frozen=True’: *note
__init__(): e23. cannot use simple assignment to initialize fields, and
must use *note object.__setattr__(): eee.


File: python.info,  Node: Inheritance<2>,  Next: Default factory functions,  Prev: Frozen instances,  Up: dataclasses — Data Classes

5.29.6.6 Inheritance
....................

When the dataclass is being created by the *note dataclass(): 449.
decorator, it looks through all of the class’s base classes in reverse
MRO (that is, starting at *note object: 3d2.) and, for each dataclass
that it finds, adds the fields from that base class to an ordered
mapping of fields.  After all of the base class fields are added, it
adds its own fields to the ordered mapping.  All of the generated
methods will use this combined, calculated ordered mapping of fields.
Because the fields are in insertion order, derived classes override base
classes.  An example:

     @dataclass
     class Base:
         x: Any = 15.0
         y: int = 0

     @dataclass
     class C(Base):
         z: int = 10
         x: int = 15

The final list of fields is, in order, ‘x’, ‘y’, ‘z’.  The final type of
‘x’ is ‘int’, as specified in class ‘C’.

The generated *note __init__(): e23. method for ‘C’ will look like:

     def __init__(self, x: int = 15, y: int = 0, z: int = 10):


File: python.info,  Node: Default factory functions,  Next: Mutable default values,  Prev: Inheritance<2>,  Up: dataclasses — Data Classes

5.29.6.7 Default factory functions
..................................

     If a *note field(): 1139. specifies a ‘default_factory’, it is
     called with zero arguments when a default value for the field is
     needed.  For example, to create a new instance of a list, use:

          mylist: list = field(default_factory=list)

     If a field is excluded from *note __init__(): e23. (using
     ‘init=False’) and the field also specifies ‘default_factory’, then
     the default factory function will always be called from the
     generated *note __init__(): e23. function.  This happens because
     there is no other way to give the field an initial value.


File: python.info,  Node: Mutable default values,  Next: Exceptions<18>,  Prev: Default factory functions,  Up: dataclasses — Data Classes

5.29.6.8 Mutable default values
...............................

     Python stores default member variable values in class attributes.
     Consider this example, not using dataclasses:

          class C:
              x = []
              def add(self, element):
                  self.x.append(element)

          o1 = C()
          o2 = C()
          o1.add(1)
          o2.add(2)
          assert o1.x == [1, 2]
          assert o1.x is o2.x

     Note that the two instances of class ‘C’ share the same class
     variable ‘x’, as expected.

     Using dataclasses, `if' this code was valid:

          @dataclass
          class D:
              x: List = []
              def add(self, element):
                  self.x += element

     it would generate code similar to:

          class D:
              x = []
              def __init__(self, x=x):
                  self.x = x
              def add(self, element):
                  self.x += element

          assert D().x is D().x

     This has the same issue as the original example using class ‘C’.
     That is, two instances of class ‘D’ that do not specify a value for
     ‘x’ when creating a class instance will share the same copy of ‘x’.
     Because dataclasses just use normal Python class creation they also
     share this behavior.  There is no general way for Data Classes to
     detect this condition.  Instead, dataclasses will raise a *note
     TypeError: 1fe. if it detects a default parameter of type ‘list’,
     ‘dict’, or ‘set’.  This is a partial solution, but it does protect
     against many common errors.

     Using default factory functions is a way to create new instances of
     mutable types as default values for fields:

          @dataclass
          class D:
              x: list = field(default_factory=list)

          assert D().x is not D().x


File: python.info,  Node: Exceptions<18>,  Prev: Mutable default values,  Up: dataclasses — Data Classes

5.29.6.9 Exceptions
...................

 -- Exception: dataclasses.FrozenInstanceError

     Raised when an implicitly defined *note __setattr__(): eee. or
     *note __delattr__(): 1563. is called on a dataclass which was
     defined with ‘frozen=True’.  It is a subclass of *note
     AttributeError: 4a2.


File: python.info,  Node: contextlib — Utilities for with-statement contexts,  Next: abc — Abstract Base Classes,  Prev: dataclasses — Data Classes,  Up: Python Runtime Services

5.29.7 ‘contextlib’ — Utilities for ‘with’-statement contexts
-------------------------------------------------------------

`Source code:' Lib/contextlib.py(1)

__________________________________________________________________

This module provides utilities for common tasks involving the *note
with: 7da. statement.  For more information see also *note Context
Manager Types: 15c6. and *note With Statement Context Managers: 15c4.

* Menu:

* Utilities::
* Examples and Recipes::
* Single use, reusable and reentrant context managers: Single use reusable and reentrant context managers.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/contextlib.py


File: python.info,  Node: Utilities,  Next: Examples and Recipes,  Up: contextlib — Utilities for with-statement contexts

5.29.7.1 Utilities
..................

Functions and classes provided:

 -- Class: contextlib.AbstractContextManager

     An *note abstract base class: c05. for classes that implement *note
     object.__enter__(): d5d. and *note object.__exit__(): d5e.  A
     default implementation for *note object.__enter__(): d5d. is
     provided which returns ‘self’ while *note object.__exit__(): d5e.
     is an abstract method which by default returns ‘None’.  See also
     the definition of *note Context Manager Types: 15c6.

     New in version 3.6.

 -- Class: contextlib.AbstractAsyncContextManager

     An *note abstract base class: c05. for classes that implement *note
     object.__aenter__(): 109a. and *note object.__aexit__(): 109b.  A
     default implementation for *note object.__aenter__(): 109a. is
     provided which returns ‘self’ while *note object.__aexit__(): 109b.
     is an abstract method which by default returns ‘None’.  See also
     the definition of *note Asynchronous Context Managers: 15d2.

     New in version 3.7.

 -- Function: @contextlib.contextmanager

     This function is a *note decorator: 174. that can be used to define
     a factory function for *note with: 7da. statement context managers,
     without needing to create a class or separate *note __enter__():
     d5d. and *note __exit__(): d5e. methods.

     While many objects natively support use in with statements,
     sometimes a resource needs to be managed that isn’t a context
     manager in its own right, and doesn’t implement a ‘close()’ method
     for use with ‘contextlib.closing’

     An abstract example would be the following to ensure correct
     resource management:

          from contextlib import contextmanager

          @contextmanager
          def managed_resource(*args, **kwds):
              # Code to acquire resource, e.g.:
              resource = acquire_resource(*args, **kwds)
              try:
                  yield resource
              finally:
                  # Code to release resource, e.g.:
                  release_resource(resource)

          >>> with managed_resource(timeout=3600) as resource:
          ...     # Resource is released at the end of this block,
          ...     # even if code in the block raises an exception

     The function being decorated must return a *note generator:
     a83.-iterator when called.  This iterator must yield exactly one
     value, which will be bound to the targets in the *note with: 7da.
     statement’s ‘as’ clause, if any.

     At the point where the generator yields, the block nested in the
     *note with: 7da. statement is executed.  The generator is then
     resumed after the block is exited.  If an unhandled exception
     occurs in the block, it is reraised inside the generator at the
     point where the yield occurred.  Thus, you can use a *note try:
     e37.…*note except: c10.…*note finally: 2bc. statement to trap the
     error (if any), or ensure that some cleanup takes place.  If an
     exception is trapped merely in order to log it or to perform some
     action (rather than to suppress it entirely), the generator must
     reraise that exception.  Otherwise the generator context manager
     will indicate to the ‘with’ statement that the exception has been
     handled, and execution will resume with the statement immediately
     following the ‘with’ statement.

     *note contextmanager(): c4f. uses *note ContextDecorator: c4e. so
     the context managers it creates can be used as decorators as well
     as in *note with: 7da. statements.  When used as a decorator, a new
     generator instance is implicitly created on each function call
     (this allows the otherwise “one-shot” context managers created by
     *note contextmanager(): c4f. to meet the requirement that context
     managers support multiple invocations in order to be used as
     decorators).

     Changed in version 3.2: Use of *note ContextDecorator: c4e.

 -- Function: @contextlib.asynccontextmanager

     Similar to *note contextmanager(): c4f, but creates an *note
     asynchronous context manager: 15d2.

     This function is a *note decorator: 174. that can be used to define
     a factory function for *note async with: 736. statement
     asynchronous context managers, without needing to create a class or
     separate *note __aenter__(): 109a. and *note __aexit__(): 109b.
     methods.  It must be applied to an *note asynchronous generator:
     1640. function.

     A simple example:

          from contextlib import asynccontextmanager

          @asynccontextmanager
          async def get_connection():
              conn = await acquire_db_connection()
              try:
                  yield conn
              finally:
                  await release_db_connection(conn)

          async def get_all_users():
              async with get_connection() as conn:
                  return conn.query('SELECT ...')

     New in version 3.7.

 -- Function: contextlib.closing (thing)

     Return a context manager that closes `thing' upon completion of the
     block.  This is basically equivalent to:

          from contextlib import contextmanager

          @contextmanager
          def closing(thing):
              try:
                  yield thing
              finally:
                  thing.close()

     And lets you write code like this:

          from contextlib import closing
          from urllib.request import urlopen

          with closing(urlopen('https://www.python.org')) as page:
              for line in page:
                  print(line)

     without needing to explicitly close ‘page’.  Even if an error
     occurs, ‘page.close()’ will be called when the *note with: 7da.
     block is exited.
 -- Function: contextlib.nullcontext (enter_result=None)

     Return a context manager that returns `enter_result' from
     ‘__enter__’, but otherwise does nothing.  It is intended to be used
     as a stand-in for an optional context manager, for example:

          def myfunction(arg, ignore_exceptions=False):
              if ignore_exceptions:
                  # Use suppress to ignore all exceptions.
                  cm = contextlib.suppress(Exception)
              else:
                  # Do not ignore any exceptions, cm has no effect.
                  cm = contextlib.nullcontext()
              with cm:
                  # Do something

     An example using `enter_result':

          def process_file(file_or_path):
              if isinstance(file_or_path, str):
                  # If string, open file
                  cm = open(file_or_path)
              else:
                  # Caller is responsible for closing file
                  cm = nullcontext(file_or_path)

              with cm as file:
                  # Perform processing on the file

     New in version 3.7.

 -- Function: contextlib.suppress (*exceptions)

     Return a context manager that suppresses any of the specified
     exceptions if they occur in the body of a ‘with’ statement and then
     resumes execution with the first statement following the end of the
     ‘with’ statement.

     As with any other mechanism that completely suppresses exceptions,
     this context manager should be used only to cover very specific
     errors where silently continuing with program execution is known to
     be the right thing to do.

     For example:

          from contextlib import suppress

          with suppress(FileNotFoundError):
              os.remove('somefile.tmp')

          with suppress(FileNotFoundError):
              os.remove('someotherfile.tmp')

     This code is equivalent to:

          try:
              os.remove('somefile.tmp')
          except FileNotFoundError:
              pass

          try:
              os.remove('someotherfile.tmp')
          except FileNotFoundError:
              pass

     This context manager is *note reentrant: 37f9.

     New in version 3.4.

 -- Function: contextlib.redirect_stdout (new_target)

     Context manager for temporarily redirecting *note sys.stdout: 41f.
     to another file or file-like object.

     This tool adds flexibility to existing functions or classes whose
     output is hardwired to stdout.

     For example, the output of *note help(): 175. normally is sent to
     `sys.stdout'.  You can capture that output in a string by
     redirecting the output to an *note io.StringIO: 91a. object.  The
     replacement stream is returned from the ‘__enter__’ method and so
     is available as the target of the *note with: 7da. statement:

          with redirect_stdout(io.StringIO()) as f:
              help(pow)
          s = f.getvalue()

     To send the output of *note help(): 175. to a file on disk,
     redirect the output to a regular file:

          with open('help.txt', 'w') as f:
              with redirect_stdout(f):
                  help(pow)

     To send the output of *note help(): 175. to `sys.stderr':

          with redirect_stdout(sys.stderr):
              help(pow)

     Note that the global side effect on *note sys.stdout: 41f. means
     that this context manager is not suitable for use in library code
     and most threaded applications.  It also has no effect on the
     output of subprocesses.  However, it is still a useful approach for
     many utility scripts.

     This context manager is *note reentrant: 37f9.

     New in version 3.4.

 -- Function: contextlib.redirect_stderr (new_target)

     Similar to *note redirect_stdout(): 7b5. but redirecting *note
     sys.stderr: 1ea. to another file or file-like object.

     This context manager is *note reentrant: 37f9.

     New in version 3.5.

 -- Class: contextlib.ContextDecorator

     A base class that enables a context manager to also be used as a
     decorator.

     Context managers inheriting from ‘ContextDecorator’ have to
     implement ‘__enter__’ and ‘__exit__’ as normal.  ‘__exit__’ retains
     its optional exception handling even when used as a decorator.

     ‘ContextDecorator’ is used by *note contextmanager(): c4f, so you
     get this functionality automatically.

     Example of ‘ContextDecorator’:

          from contextlib import ContextDecorator

          class mycontext(ContextDecorator):
              def __enter__(self):
                  print('Starting')
                  return self

              def __exit__(self, *exc):
                  print('Finishing')
                  return False

          >>> @mycontext()
          ... def function():
          ...     print('The bit in the middle')
          ...
          >>> function()
          Starting
          The bit in the middle
          Finishing

          >>> with mycontext():
          ...     print('The bit in the middle')
          ...
          Starting
          The bit in the middle
          Finishing

     This change is just syntactic sugar for any construct of the
     following form:

          def f():
              with cm():
                  # Do stuff

     ‘ContextDecorator’ lets you instead write:

          @cm()
          def f():
              # Do stuff

     It makes it clear that the ‘cm’ applies to the whole function,
     rather than just a piece of it (and saving an indentation level is
     nice, too).

     Existing context managers that already have a base class can be
     extended by using ‘ContextDecorator’ as a mixin class:

          from contextlib import ContextDecorator

          class mycontext(ContextBaseClass, ContextDecorator):
              def __enter__(self):
                  return self

              def __exit__(self, *exc):
                  return False

          Note: As the decorated function must be able to be called
          multiple times, the underlying context manager must support
          use in multiple *note with: 7da. statements.  If this is not
          the case, then the original construct with the explicit ‘with’
          statement inside the function should be used.

     New in version 3.2.

 -- Class: contextlib.ExitStack

     A context manager that is designed to make it easy to
     programmatically combine other context managers and cleanup
     functions, especially those that are optional or otherwise driven
     by input data.

     For example, a set of files may easily be handled in a single with
     statement as follows:

          with ExitStack() as stack:
              files = [stack.enter_context(open(fname)) for fname in filenames]
              # All opened files will automatically be closed at the end of
              # the with statement, even if attempts to open files later
              # in the list raise an exception

     Each instance maintains a stack of registered callbacks that are
     called in reverse order when the instance is closed (either
     explicitly or implicitly at the end of a *note with: 7da.
     statement).  Note that callbacks are `not' invoked implicitly when
     the context stack instance is garbage collected.

     This stack model is used so that context managers that acquire
     their resources in their ‘__init__’ method (such as file objects)
     can be handled correctly.

     Since registered callbacks are invoked in the reverse order of
     registration, this ends up behaving as if multiple nested *note
     with: 7da. statements had been used with the registered set of
     callbacks.  This even extends to exception handling - if an inner
     callback suppresses or replaces an exception, then outer callbacks
     will be passed arguments based on that updated state.

     This is a relatively low level API that takes care of the details
     of correctly unwinding the stack of exit callbacks.  It provides a
     suitable foundation for higher level context managers that
     manipulate the exit stack in application specific ways.

     New in version 3.3.

      -- Method: enter_context (cm)

          Enters a new context manager and adds its *note __exit__():
          d5e. method to the callback stack.  The return value is the
          result of the context manager’s own *note __enter__(): d5d.
          method.

          These context managers may suppress exceptions just as they
          normally would if used directly as part of a *note with: 7da.
          statement.

      -- Method: push (exit)

          Adds a context manager’s *note __exit__(): d5e. method to the
          callback stack.

          As ‘__enter__’ is `not' invoked, this method can be used to
          cover part of an *note __enter__(): d5d. implementation with a
          context manager’s own *note __exit__(): d5e. method.

          If passed an object that is not a context manager, this method
          assumes it is a callback with the same signature as a context
          manager’s *note __exit__(): d5e. method and adds it directly
          to the callback stack.

          By returning true values, these callbacks can suppress
          exceptions the same way context manager *note __exit__(): d5e.
          methods can.

          The passed in object is returned from the function, allowing
          this method to be used as a function decorator.

      -- Method: callback (callback, /, *args, **kwds)

          Accepts an arbitrary callback function and arguments and adds
          it to the callback stack.

          Unlike the other methods, callbacks added this way cannot
          suppress exceptions (as they are never passed the exception
          details).

          The passed in callback is returned from the function, allowing
          this method to be used as a function decorator.

      -- Method: pop_all ()

          Transfers the callback stack to a fresh *note ExitStack: 47e.
          instance and returns it.  No callbacks are invoked by this
          operation - instead, they will now be invoked when the new
          stack is closed (either explicitly or implicitly at the end of
          a *note with: 7da. statement).

          For example, a group of files can be opened as an “all or
          nothing” operation as follows:

               with ExitStack() as stack:
                   files = [stack.enter_context(open(fname)) for fname in filenames]
                   # Hold onto the close method, but don't call it yet.
                   close_files = stack.pop_all().close
                   # If opening any file fails, all previously opened files will be
                   # closed automatically. If all files are opened successfully,
                   # they will remain open even after the with statement ends.
                   # close_files() can then be invoked explicitly to close them all.

      -- Method: close ()

          Immediately unwinds the callback stack, invoking callbacks in
          the reverse order of registration.  For any context managers
          and exit callbacks registered, the arguments passed in will
          indicate that no exception occurred.

 -- Class: contextlib.AsyncExitStack

     An *note asynchronous context manager: 15d2, similar to *note
     ExitStack: 47e, that supports combining both synchronous and
     asynchronous context managers, as well as having coroutines for
     cleanup logic.

     The ‘close()’ method is not implemented, *note aclose(): 37fe. must
     be used instead.

      -- Method: coroutine enter_async_context (cm)

          Similar to ‘enter_context()’ but expects an asynchronous
          context manager.

      -- Method: push_async_exit (exit)

          Similar to ‘push()’ but expects either an asynchronous context
          manager or a coroutine function.

      -- Method: push_async_callback (callback, /, *args, **kwds)

          Similar to ‘callback()’ but expects a coroutine function.

      -- Method: coroutine aclose ()

          Similar to ‘close()’ but properly handles awaitables.

     Continuing the example for *note asynccontextmanager(): 47f.:

          async with AsyncExitStack() as stack:
              connections = [await stack.enter_async_context(get_connection())
                  for i in range(5)]
              # All opened connections will automatically be released at the end of
              # the async with statement, even if attempts to open a connection
              # later in the list raise an exception.

     New in version 3.7.


File: python.info,  Node: Examples and Recipes,  Next: Single use reusable and reentrant context managers,  Prev: Utilities,  Up: contextlib — Utilities for with-statement contexts

5.29.7.2 Examples and Recipes
.............................

This section describes some examples and recipes for making effective
use of the tools provided by *note contextlib: 23.

* Menu:

* Supporting a variable number of context managers::
* Catching exceptions from __enter__ methods::
* Cleaning up in an __enter__ implementation::
* Replacing any use of try-finally and flag variables::
* Using a context manager as a function decorator::


File: python.info,  Node: Supporting a variable number of context managers,  Next: Catching exceptions from __enter__ methods,  Up: Examples and Recipes

5.29.7.3 Supporting a variable number of context managers
.........................................................

The primary use case for *note ExitStack: 47e. is the one given in the
class documentation: supporting a variable number of context managers
and other cleanup operations in a single *note with: 7da. statement.
The variability may come from the number of context managers needed
being driven by user input (such as opening a user specified collection
of files), or from some of the context managers being optional:

     with ExitStack() as stack:
         for resource in resources:
             stack.enter_context(resource)
         if need_special_resource():
             special = acquire_special_resource()
             stack.callback(release_special_resource, special)
         # Perform operations that use the acquired resources

As shown, *note ExitStack: 47e. also makes it quite easy to use *note
with: 7da. statements to manage arbitrary resources that don’t natively
support the context management protocol.


File: python.info,  Node: Catching exceptions from __enter__ methods,  Next: Cleaning up in an __enter__ implementation,  Prev: Supporting a variable number of context managers,  Up: Examples and Recipes

5.29.7.4 Catching exceptions from ‘__enter__’ methods
.....................................................

It is occasionally desirable to catch exceptions from an ‘__enter__’
method implementation, `without' inadvertently catching exceptions from
the *note with: 7da. statement body or the context manager’s ‘__exit__’
method.  By using *note ExitStack: 47e. the steps in the context
management protocol can be separated slightly in order to allow this:

     stack = ExitStack()
     try:
         x = stack.enter_context(cm)
     except Exception:
         # handle __enter__ exception
     else:
         with stack:
             # Handle normal case

Actually needing to do this is likely to indicate that the underlying
API should be providing a direct resource management interface for use
with *note try: e37./*note except: c10./*note finally: 2bc. statements,
but not all APIs are well designed in that regard.  When a context
manager is the only resource management API provided, then *note
ExitStack: 47e. can make it easier to handle various situations that
can’t be handled directly in a *note with: 7da. statement.


File: python.info,  Node: Cleaning up in an __enter__ implementation,  Next: Replacing any use of try-finally and flag variables,  Prev: Catching exceptions from __enter__ methods,  Up: Examples and Recipes

5.29.7.5 Cleaning up in an ‘__enter__’ implementation
.....................................................

As noted in the documentation of *note ExitStack.push(): 37fb, this
method can be useful in cleaning up an already allocated resource if
later steps in the *note __enter__(): d5d. implementation fail.

Here’s an example of doing this for a context manager that accepts
resource acquisition and release functions, along with an optional
validation function, and maps them to the context management protocol:

     from contextlib import contextmanager, AbstractContextManager, ExitStack

     class ResourceManager(AbstractContextManager):

         def __init__(self, acquire_resource, release_resource, check_resource_ok=None):
             self.acquire_resource = acquire_resource
             self.release_resource = release_resource
             if check_resource_ok is None:
                 def check_resource_ok(resource):
                     return True
             self.check_resource_ok = check_resource_ok

         @contextmanager
         def _cleanup_on_error(self):
             with ExitStack() as stack:
                 stack.push(self)
                 yield
                 # The validation check passed and didn't raise an exception
                 # Accordingly, we want to keep the resource, and pass it
                 # back to our caller
                 stack.pop_all()

         def __enter__(self):
             resource = self.acquire_resource()
             with self._cleanup_on_error():
                 if not self.check_resource_ok(resource):
                     msg = "Failed validation for {!r}"
                     raise RuntimeError(msg.format(resource))
             return resource

         def __exit__(self, *exc_details):
             # We don't need to duplicate any of our resource release logic
             self.release_resource()


File: python.info,  Node: Replacing any use of try-finally and flag variables,  Next: Using a context manager as a function decorator,  Prev: Cleaning up in an __enter__ implementation,  Up: Examples and Recipes

5.29.7.6 Replacing any use of ‘try-finally’ and flag variables
..............................................................

A pattern you will sometimes see is a ‘try-finally’ statement with a
flag variable to indicate whether or not the body of the ‘finally’
clause should be executed.  In its simplest form (that can’t already be
handled just by using an ‘except’ clause instead), it looks something
like this:

     cleanup_needed = True
     try:
         result = perform_operation()
         if result:
             cleanup_needed = False
     finally:
         if cleanup_needed:
             cleanup_resources()

As with any ‘try’ statement based code, this can cause problems for
development and review, because the setup code and the cleanup code can
end up being separated by arbitrarily long sections of code.

*note ExitStack: 47e. makes it possible to instead register a callback
for execution at the end of a ‘with’ statement, and then later decide to
skip executing that callback:

     from contextlib import ExitStack

     with ExitStack() as stack:
         stack.callback(cleanup_resources)
         result = perform_operation()
         if result:
             stack.pop_all()

This allows the intended cleanup up behaviour to be made explicit up
front, rather than requiring a separate flag variable.

If a particular application uses this pattern a lot, it can be
simplified even further by means of a small helper class:

     from contextlib import ExitStack

     class Callback(ExitStack):
         def __init__(self, callback, /, *args, **kwds):
             super().__init__()
             self.callback(callback, *args, **kwds)

         def cancel(self):
             self.pop_all()

     with Callback(cleanup_resources) as cb:
         result = perform_operation()
         if result:
             cb.cancel()

If the resource cleanup isn’t already neatly bundled into a standalone
function, then it is still possible to use the decorator form of *note
ExitStack.callback(): 3c7. to declare the resource cleanup in advance:

     from contextlib import ExitStack

     with ExitStack() as stack:
         @stack.callback
         def cleanup_resources():
             ...
         result = perform_operation()
         if result:
             stack.pop_all()

Due to the way the decorator protocol works, a callback function
declared this way cannot take any parameters.  Instead, any resources to
be released must be accessed as closure variables.


File: python.info,  Node: Using a context manager as a function decorator,  Prev: Replacing any use of try-finally and flag variables,  Up: Examples and Recipes

5.29.7.7 Using a context manager as a function decorator
........................................................

*note ContextDecorator: c4e. makes it possible to use a context manager
in both an ordinary ‘with’ statement and also as a function decorator.

For example, it is sometimes useful to wrap functions or groups of
statements with a logger that can track the time of entry and time of
exit.  Rather than writing both a function decorator and a context
manager for the task, inheriting from *note ContextDecorator: c4e.
provides both capabilities in a single definition:

     from contextlib import ContextDecorator
     import logging

     logging.basicConfig(level=logging.INFO)

     class track_entry_and_exit(ContextDecorator):
         def __init__(self, name):
             self.name = name

         def __enter__(self):
             logging.info('Entering: %s', self.name)

         def __exit__(self, exc_type, exc, exc_tb):
             logging.info('Exiting: %s', self.name)

Instances of this class can be used as both a context manager:

     with track_entry_and_exit('widget loader'):
         print('Some time consuming activity goes here')
         load_widget()

And also as a function decorator:

     @track_entry_and_exit('widget loader')
     def activity():
         print('Some time consuming activity goes here')
         load_widget()

Note that there is one additional limitation when using context managers
as function decorators: there’s no way to access the return value of
*note __enter__(): d5d.  If that value is needed, then it is still
necessary to use an explicit ‘with’ statement.

See also
........

PEP 343(1) - The “with” statement

     The specification, background, and examples for the Python *note
     with: 7da. statement.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0343


File: python.info,  Node: Single use reusable and reentrant context managers,  Prev: Examples and Recipes,  Up: contextlib — Utilities for with-statement contexts

5.29.7.8 Single use, reusable and reentrant context managers
............................................................

Most context managers are written in a way that means they can only be
used effectively in a *note with: 7da. statement once.  These single use
context managers must be created afresh each time they’re used -
attempting to use them a second time will trigger an exception or
otherwise not work correctly.

This common limitation means that it is generally advisable to create
context managers directly in the header of the *note with: 7da.
statement where they are used (as shown in all of the usage examples
above).

Files are an example of effectively single use context managers, since
the first *note with: 7da. statement will close the file, preventing any
further IO operations using that file object.

Context managers created using *note contextmanager(): c4f. are also
single use context managers, and will complain about the underlying
generator failing to yield if an attempt is made to use them a second
time:

     >>> from contextlib import contextmanager
     >>> @contextmanager
     ... def singleuse():
     ...     print("Before")
     ...     yield
     ...     print("After")
     ...
     >>> cm = singleuse()
     >>> with cm:
     ...     pass
     ...
     Before
     After
     >>> with cm:
     ...     pass
     ...
     Traceback (most recent call last):
         ...
     RuntimeError: generator didn't yield

* Menu:

* Reentrant context managers::
* Reusable context managers::


File: python.info,  Node: Reentrant context managers,  Next: Reusable context managers,  Up: Single use reusable and reentrant context managers

5.29.7.9 Reentrant context managers
...................................

More sophisticated context managers may be “reentrant”.  These context
managers can not only be used in multiple *note with: 7da. statements,
but may also be used `inside' a ‘with’ statement that is already using
the same context manager.

*note threading.RLock: cba. is an example of a reentrant context
manager, as are *note suppress(): 919. and *note redirect_stdout(): 7b5.
Here’s a very simple example of reentrant use:

     >>> from contextlib import redirect_stdout
     >>> from io import StringIO
     >>> stream = StringIO()
     >>> write_to_stream = redirect_stdout(stream)
     >>> with write_to_stream:
     ...     print("This is written to the stream rather than stdout")
     ...     with write_to_stream:
     ...         print("This is also written to the stream")
     ...
     >>> print("This is written directly to stdout")
     This is written directly to stdout
     >>> print(stream.getvalue())
     This is written to the stream rather than stdout
     This is also written to the stream

Real world examples of reentrancy are more likely to involve multiple
functions calling each other and hence be far more complicated than this
example.

Note also that being reentrant is `not' the same thing as being thread
safe.  *note redirect_stdout(): 7b5, for example, is definitely not
thread safe, as it makes a global modification to the system state by
binding *note sys.stdout: 41f. to a different stream.


File: python.info,  Node: Reusable context managers,  Prev: Reentrant context managers,  Up: Single use reusable and reentrant context managers

5.29.7.10 Reusable context managers
...................................

Distinct from both single use and reentrant context managers are
“reusable” context managers (or, to be completely explicit, “reusable,
but not reentrant” context managers, since reentrant context managers
are also reusable).  These context managers support being used multiple
times, but will fail (or otherwise not work correctly) if the specific
context manager instance has already been used in a containing with
statement.

*note threading.Lock: 24bc. is an example of a reusable, but not
reentrant, context manager (for a reentrant lock, it is necessary to use
*note threading.RLock: cba. instead).

Another example of a reusable, but not reentrant, context manager is
*note ExitStack: 47e, as it invokes `all' currently registered callbacks
when leaving any with statement, regardless of where those callbacks
were added:

     >>> from contextlib import ExitStack
     >>> stack = ExitStack()
     >>> with stack:
     ...     stack.callback(print, "Callback: from first context")
     ...     print("Leaving first context")
     ...
     Leaving first context
     Callback: from first context
     >>> with stack:
     ...     stack.callback(print, "Callback: from second context")
     ...     print("Leaving second context")
     ...
     Leaving second context
     Callback: from second context
     >>> with stack:
     ...     stack.callback(print, "Callback: from outer context")
     ...     with stack:
     ...         stack.callback(print, "Callback: from inner context")
     ...         print("Leaving inner context")
     ...     print("Leaving outer context")
     ...
     Leaving inner context
     Callback: from inner context
     Callback: from outer context
     Leaving outer context

As the output from the example shows, reusing a single stack object
across multiple with statements works correctly, but attempting to nest
them will cause the stack to be cleared at the end of the innermost with
statement, which is unlikely to be desirable behaviour.

Using separate *note ExitStack: 47e. instances instead of reusing a
single instance avoids that problem:

     >>> from contextlib import ExitStack
     >>> with ExitStack() as outer_stack:
     ...     outer_stack.callback(print, "Callback: from outer context")
     ...     with ExitStack() as inner_stack:
     ...         inner_stack.callback(print, "Callback: from inner context")
     ...         print("Leaving inner context")
     ...     print("Leaving outer context")
     ...
     Leaving inner context
     Callback: from inner context
     Leaving outer context
     Callback: from outer context


File: python.info,  Node: abc — Abstract Base Classes,  Next: atexit — Exit handlers,  Prev: contextlib — Utilities for with-statement contexts,  Up: Python Runtime Services

5.29.8 ‘abc’ — Abstract Base Classes
------------------------------------

`Source code:' Lib/abc.py(1)

__________________________________________________________________

This module provides the infrastructure for defining *note abstract base
classes: c05. (ABCs) in Python, as outlined in PEP 3119(2); see the PEP
for why this was added to Python.  (See also PEP 3141(3) and the *note
numbers: c1. module regarding a type hierarchy for numbers based on
ABCs.)

The *note collections: 1d. module has some concrete classes that derive
from ABCs; these can, of course, be further derived.  In addition, the
*note collections.abc: 1e. submodule has some ABCs that can be used to
test whether a class or instance provides a particular interface, for
example, if it is hashable or if it is a mapping.

This module provides the metaclass *note ABCMeta: 906. for defining ABCs
and a helper class *note ABC: 905. to alternatively define ABCs through
inheritance:

 -- Class: abc.ABC

     A helper class that has *note ABCMeta: 906. as its metaclass.  With
     this class, an abstract base class can be created by simply
     deriving from *note ABC: 905. avoiding sometimes confusing
     metaclass usage, for example:

          from abc import ABC

          class MyABC(ABC):
              pass

     Note that the type of *note ABC: 905. is still *note ABCMeta: 906,
     therefore inheriting from *note ABC: 905. requires the usual
     precautions regarding metaclass usage, as multiple inheritance may
     lead to metaclass conflicts.  One may also define an abstract base
     class by passing the metaclass keyword and using *note ABCMeta:
     906. directly, for example:

          from abc import ABCMeta

          class MyABC(metaclass=ABCMeta):
              pass

     New in version 3.4.

 -- Class: abc.ABCMeta

     Metaclass for defining Abstract Base Classes (ABCs).

     Use this metaclass to create an ABC. An ABC can be subclassed
     directly, and then acts as a mix-in class.  You can also register
     unrelated concrete classes (even built-in classes) and unrelated
     ABCs as “virtual subclasses” – these and their descendants will be
     considered subclasses of the registering ABC by the built-in *note
     issubclass(): 553. function, but the registering ABC won’t show up
     in their MRO (Method Resolution Order) nor will method
     implementations defined by the registering ABC be callable (not
     even via *note super(): 5dd.).  (4)

     Classes created with a metaclass of *note ABCMeta: 906. have the
     following method:

      -- Method: register (subclass)

          Register `subclass' as a “virtual subclass” of this ABC. For
          example:

               from abc import ABC

               class MyABC(ABC):
                   pass

               MyABC.register(tuple)

               assert issubclass(tuple, MyABC)
               assert isinstance((), MyABC)

          Changed in version 3.3: Returns the registered subclass, to
          allow usage as a class decorator.

          Changed in version 3.4: To detect calls to *note register():
          ab0, you can use the *note get_cache_token(): 904. function.

     You can also override this method in an abstract base class:

      -- Method: __subclasshook__ (subclass)

          (Must be defined as a class method.)

          Check whether `subclass' is considered a subclass of this ABC.
          This means that you can customize the behavior of ‘issubclass’
          further without the need to call *note register(): ab0. on
          every class you want to consider a subclass of the ABC. (This
          class method is called from the ‘__subclasscheck__()’ method
          of the ABC.)

          This method should return ‘True’, ‘False’ or ‘NotImplemented’.
          If it returns ‘True’, the `subclass' is considered a subclass
          of this ABC. If it returns ‘False’, the `subclass' is not
          considered a subclass of this ABC, even if it would normally
          be one.  If it returns ‘NotImplemented’, the subclass check is
          continued with the usual mechanism.

     For a demonstration of these concepts, look at this example ABC
     definition:

          class Foo:
              def __getitem__(self, index):
                  ...
              def __len__(self):
                  ...
              def get_iterator(self):
                  return iter(self)

          class MyIterable(ABC):

              @abstractmethod
              def __iter__(self):
                  while False:
                      yield None

              def get_iterator(self):
                  return self.__iter__()

              @classmethod
              def __subclasshook__(cls, C):
                  if cls is MyIterable:
                      if any("__iter__" in B.__dict__ for B in C.__mro__):
                          return True
                  return NotImplemented

          MyIterable.register(Foo)

     The ABC ‘MyIterable’ defines the standard iterable method, *note
     __iter__(): 175e, as an abstract method.  The implementation given
     here can still be called from subclasses.  The ‘get_iterator()’
     method is also part of the ‘MyIterable’ abstract base class, but it
     does not have to be overridden in non-abstract derived classes.

     The *note __subclasshook__(): 380d. class method defined here says
     that any class that has an *note __iter__(): 175e. method in its
     *note __dict__: 5f6. (or in that of one of its base classes,
     accessed via the *note __mro__: 173a. list) is considered a
     ‘MyIterable’ too.

     Finally, the last line makes ‘Foo’ a virtual subclass of
     ‘MyIterable’, even though it does not define an *note __iter__():
     175e. method (it uses the old-style iterable protocol, defined in
     terms of *note __len__(): e90. and *note __getitem__(): 3a2.).
     Note that this will not make ‘get_iterator’ available as a method
     of ‘Foo’, so it is provided separately.

The *note abc: 3. module also provides the following decorator:

 -- Function: @abc.abstractmethod

     A decorator indicating abstract methods.

     Using this decorator requires that the class’s metaclass is *note
     ABCMeta: 906. or is derived from it.  A class that has a metaclass
     derived from *note ABCMeta: 906. cannot be instantiated unless all
     of its abstract methods and properties are overridden.  The
     abstract methods can be called using any of the normal ‘super’ call
     mechanisms.  *note abstractmethod(): aad. may be used to declare
     abstract methods for properties and descriptors.

     Dynamically adding abstract methods to a class, or attempting to
     modify the abstraction status of a method or class once it is
     created, are not supported.  The *note abstractmethod(): aad. only
     affects subclasses derived using regular inheritance; “virtual
     subclasses” registered with the ABC’s ‘register()’ method are not
     affected.

     When *note abstractmethod(): aad. is applied in combination with
     other method descriptors, it should be applied as the innermost
     decorator, as shown in the following usage examples:

          class C(ABC):
              @abstractmethod
              def my_abstract_method(self, ...):
                  ...
              @classmethod
              @abstractmethod
              def my_abstract_classmethod(cls, ...):
                  ...
              @staticmethod
              @abstractmethod
              def my_abstract_staticmethod(...):
                  ...

              @property
              @abstractmethod
              def my_abstract_property(self):
                  ...
              @my_abstract_property.setter
              @abstractmethod
              def my_abstract_property(self, val):
                  ...

              @abstractmethod
              def _get_x(self):
                  ...
              @abstractmethod
              def _set_x(self, val):
                  ...
              x = property(_get_x, _set_x)

     In order to correctly interoperate with the abstract base class
     machinery, the descriptor must identify itself as abstract using
     ‘__isabstractmethod__’.  In general, this attribute should be
     ‘True’ if any of the methods used to compose the descriptor are
     abstract.  For example, Python’s built-in *note property: 308. does
     the equivalent of:

          class Descriptor:
              ...
              @property
              def __isabstractmethod__(self):
                  return any(getattr(f, '__isabstractmethod__', False) for
                             f in (self._fget, self._fset, self._fdel))

          Note: Unlike Java abstract methods, these abstract methods may
          have an implementation.  This implementation can be called via
          the *note super(): 5dd. mechanism from the class that
          overrides it.  This could be useful as an end-point for a
          super-call in a framework that uses cooperative
          multiple-inheritance.

The *note abc: 3. module also supports the following legacy decorators:

 -- Function: @abc.abstractclassmethod

     New in version 3.2.

     Deprecated since version 3.3: It is now possible to use *note
     classmethod: 309. with *note abstractmethod(): aad, making this
     decorator redundant.

     A subclass of the built-in *note classmethod(): 309, indicating an
     abstract classmethod.  Otherwise it is similar to *note
     abstractmethod(): aad.

     This special case is deprecated, as the *note classmethod(): 309.
     decorator is now correctly identified as abstract when applied to
     an abstract method:

          class C(ABC):
              @classmethod
              @abstractmethod
              def my_abstract_classmethod(cls, ...):
                  ...

 -- Function: @abc.abstractstaticmethod

     New in version 3.2.

     Deprecated since version 3.3: It is now possible to use *note
     staticmethod: 30a. with *note abstractmethod(): aad, making this
     decorator redundant.

     A subclass of the built-in *note staticmethod(): 30a, indicating an
     abstract staticmethod.  Otherwise it is similar to *note
     abstractmethod(): aad.

     This special case is deprecated, as the *note staticmethod(): 30a.
     decorator is now correctly identified as abstract when applied to
     an abstract method:

          class C(ABC):
              @staticmethod
              @abstractmethod
              def my_abstract_staticmethod(...):
                  ...

 -- Function: @abc.abstractproperty

     Deprecated since version 3.3: It is now possible to use *note
     property: 308, ‘property.getter()’, ‘property.setter()’ and
     ‘property.deleter()’ with *note abstractmethod(): aad, making this
     decorator redundant.

     A subclass of the built-in *note property(): 308, indicating an
     abstract property.

     This special case is deprecated, as the *note property(): 308.
     decorator is now correctly identified as abstract when applied to
     an abstract method:

          class C(ABC):
              @property
              @abstractmethod
              def my_abstract_property(self):
                  ...

     The above example defines a read-only property; you can also define
     a read-write abstract property by appropriately marking one or more
     of the underlying methods as abstract:

          class C(ABC):
              @property
              def x(self):
                  ...

              @x.setter
              @abstractmethod
              def x(self, val):
                  ...

     If only some components are abstract, only those components need to
     be updated to create a concrete property in a subclass:

          class D(C):
              @C.x.setter
              def x(self, val):
                  ...

The *note abc: 3. module also provides the following functions:

 -- Function: abc.get_cache_token ()

     Returns the current abstract base class cache token.

     The token is an opaque object (that supports equality testing)
     identifying the current version of the abstract base class cache
     for virtual subclasses.  The token changes with every call to *note
     ABCMeta.register(): ab0. on any ABC.

     New in version 3.4.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/abc.py

   (2) https://www.python.org/dev/peps/pep-3119

   (3) https://www.python.org/dev/peps/pep-3141

   (4) (1) C++ programmers should note that Python’s virtual base class
concept is not the same as C++’s.


File: python.info,  Node: atexit — Exit handlers,  Next: traceback — Print or retrieve a stack traceback,  Prev: abc — Abstract Base Classes,  Up: Python Runtime Services

5.29.9 ‘atexit’ — Exit handlers
-------------------------------

__________________________________________________________________

The *note atexit: b. module defines functions to register and unregister
cleanup functions.  Functions thus registered are automatically executed
upon normal interpreter termination.  *note atexit: b. runs these
functions in the `reverse' order in which they were registered; if you
register ‘A’, ‘B’, and ‘C’, at interpreter termination time they will be
run in the order ‘C’, ‘B’, ‘A’.

`Note:' The functions registered via this module are not called when the
program is killed by a signal not handled by Python, when a Python fatal
internal error is detected, or when *note os._exit(): 1854. is called.

Changed in version 3.7: When used with C-API subinterpreters, registered
functions are local to the interpreter they were registered in.

 -- Function: atexit.register (func, *args, **kwargs)

     Register `func' as a function to be executed at termination.  Any
     optional arguments that are to be passed to `func' must be passed
     as arguments to *note register(): f46.  It is possible to register
     the same function and arguments more than once.

     At normal program termination (for instance, if *note sys.exit():
     daa. is called or the main module’s execution completes), all
     functions registered are called in last in, first out order.  The
     assumption is that lower level modules will normally be imported
     before higher level modules and thus must be cleaned up later.

     If an exception is raised during execution of the exit handlers, a
     traceback is printed (unless *note SystemExit: 6f3. is raised) and
     the exception information is saved.  After all exit handlers have
     had a chance to run, the last exception to be raised is re-raised.

     This function returns `func', which makes it possible to use it as
     a decorator.

 -- Function: atexit.unregister (func)

     Remove `func' from the list of functions to be run at interpreter
     shutdown.  *note unregister(): 3810. silently does nothing if
     `func' was not previously registered.  If `func' has been
     registered more than once, every occurrence of that function in the
     *note atexit: b. call stack will be removed.  Equality comparisons
     (‘==’) are used internally during unregistration, so function
     references do not need to have matching identities.

See also
........

Module *note readline: de.

     Useful example of *note atexit: b. to read and write *note
     readline: de. history files.

* Menu:

* atexit Example::


File: python.info,  Node: atexit Example,  Up: atexit — Exit handlers

5.29.9.1 ‘atexit’ Example
.........................

The following simple example demonstrates how a module can initialize a
counter from a file when it is imported and save the counter’s updated
value automatically when the program terminates without relying on the
application making an explicit call into this module at termination.

     try:
         with open('counterfile') as infile:
             _count = int(infile.read())
     except FileNotFoundError:
         _count = 0

     def incrcounter(n):
         global _count
         _count = _count + n

     def savecounter():
         with open('counterfile', 'w') as outfile:
             outfile.write('%d' % _count)

     import atexit

     atexit.register(savecounter)

Positional and keyword arguments may also be passed to *note register():
f46. to be passed along to the registered function when it is called:

     def goodbye(name, adjective):
         print('Goodbye %s, it was %s to meet you.' % (name, adjective))

     import atexit

     atexit.register(goodbye, 'Donny', 'nice')
     # or:
     atexit.register(goodbye, adjective='nice', name='Donny')

Usage as a *note decorator: 174.:

     import atexit

     @atexit.register
     def goodbye():
         print('You are now leaving the Python sector.')

This only works with functions that can be called without arguments.


File: python.info,  Node: traceback — Print or retrieve a stack traceback,  Next: __future__ — Future statement definitions,  Prev: atexit — Exit handlers,  Up: Python Runtime Services

5.29.10 ‘traceback’ — Print or retrieve a stack traceback
---------------------------------------------------------

`Source code:' Lib/traceback.py(1)

__________________________________________________________________

This module provides a standard interface to extract, format and print
stack traces of Python programs.  It exactly mimics the behavior of the
Python interpreter when it prints a stack trace.  This is useful when
you want to print stack traces under program control, such as in a
“wrapper” around the interpreter.

The module uses traceback objects — this is the object type that is
stored in the *note sys.last_traceback: 36b4. variable and returned as
the third item from *note sys.exc_info(): d27.

The module defines the following functions:

 -- Function: traceback.print_tb (tb, limit=None, file=None)

     Print up to `limit' stack trace entries from traceback object `tb'
     (starting from the caller’s frame) if `limit' is positive.
     Otherwise, print the last ‘abs(limit)’ entries.  If `limit' is
     omitted or ‘None’, all entries are printed.  If `file' is omitted
     or ‘None’, the output goes to ‘sys.stderr’; otherwise it should be
     an open file or file-like object to receive the output.

     Changed in version 3.5: Added negative `limit' support.

 -- Function: traceback.print_exception (etype, value, tb, limit=None,
          file=None, chain=True)

     Print exception information and stack trace entries from traceback
     object `tb' to `file'.  This differs from *note print_tb(): 868. in
     the following ways:

        * if `tb' is not ‘None’, it prints a header ‘Traceback (most
          recent call last):’

        * it prints the exception `etype' and `value' after the stack
          trace

        * if `type(value)' is *note SyntaxError: 55a. and `value' has
          the appropriate format, it prints the line where the syntax
          error occurred with a caret indicating the approximate
          position of the error.

     The optional `limit' argument has the same meaning as for *note
     print_tb(): 868.  If `chain' is true (the default), then chained
     exceptions (the ‘__cause__’ or ‘__context__’ attributes of the
     exception) will be printed as well, like the interpreter itself
     does when printing an unhandled exception.

     Changed in version 3.5: The `etype' argument is ignored and
     inferred from the type of `value'.

 -- Function: traceback.print_exc (limit=None, file=None, chain=True)

     This is a shorthand for ‘print_exception(*sys.exc_info(), limit,
     file, chain)’.

 -- Function: traceback.print_last (limit=None, file=None, chain=True)

     This is a shorthand for ‘print_exception(sys.last_type,
     sys.last_value, sys.last_traceback, limit, file, chain)’.  In
     general it will work only after an exception has reached an
     interactive prompt (see *note sys.last_type: d22.).

 -- Function: traceback.print_stack (f=None, limit=None, file=None)

     Print up to `limit' stack trace entries (starting from the
     invocation point) if `limit' is positive.  Otherwise, print the
     last ‘abs(limit)’ entries.  If `limit' is omitted or ‘None’, all
     entries are printed.  The optional `f' argument can be used to
     specify an alternate stack frame to start.  The optional `file'
     argument has the same meaning as for *note print_tb(): 868.

     Changed in version 3.5: Added negative `limit' support.

 -- Function: traceback.extract_tb (tb, limit=None)

     Return a *note StackSummary: 866. object representing a list of
     “pre-processed” stack trace entries extracted from the traceback
     object `tb'.  It is useful for alternate formatting of stack
     traces.  The optional `limit' argument has the same meaning as for
     *note print_tb(): 868.  A “pre-processed” stack trace entry is a
     *note FrameSummary: 867. object containing attributes ‘filename’,
     ‘lineno’, ‘name’, and ‘line’ representing the information that is
     usually printed for a stack trace.  The ‘line’ is a string with
     leading and trailing whitespace stripped; if the source is not
     available it is ‘None’.

 -- Function: traceback.extract_stack (f=None, limit=None)

     Extract the raw traceback from the current stack frame.  The return
     value has the same format as for *note extract_tb(): 3817.  The
     optional `f' and `limit' arguments have the same meaning as for
     *note print_stack(): 869.

 -- Function: traceback.format_list (extracted_list)

     Given a list of tuples or *note FrameSummary: 867. objects as
     returned by *note extract_tb(): 3817. or *note extract_stack():
     3818, return a list of strings ready for printing.  Each string in
     the resulting list corresponds to the item with the same index in
     the argument list.  Each string ends in a newline; the strings may
     contain internal newlines as well, for those items whose source
     text line is not ‘None’.

 -- Function: traceback.format_exception_only (etype, value)

     Format the exception part of a traceback.  The arguments are the
     exception type and value such as given by ‘sys.last_type’ and
     ‘sys.last_value’.  The return value is a list of strings, each
     ending in a newline.  Normally, the list contains a single string;
     however, for *note SyntaxError: 55a. exceptions, it contains
     several lines that (when printed) display detailed information
     about where the syntax error occurred.  The message indicating
     which exception occurred is the always last string in the list.

 -- Function: traceback.format_exception (etype, value, tb, limit=None,
          chain=True)

     Format a stack trace and the exception information.  The arguments
     have the same meaning as the corresponding arguments to *note
     print_exception(): 2208.  The return value is a list of strings,
     each ending in a newline and some containing internal newlines.
     When these lines are concatenated and printed, exactly the same
     text is printed as does *note print_exception(): 2208.

     Changed in version 3.5: The `etype' argument is ignored and
     inferred from the type of `value'.

 -- Function: traceback.format_exc (limit=None, chain=True)

     This is like ‘print_exc(limit)’ but returns a string instead of
     printing to a file.

 -- Function: traceback.format_tb (tb, limit=None)

     A shorthand for ‘format_list(extract_tb(tb, limit))’.

 -- Function: traceback.format_stack (f=None, limit=None)

     A shorthand for ‘format_list(extract_stack(f, limit))’.

 -- Function: traceback.clear_frames (tb)

     Clears the local variables of all the stack frames in a traceback
     `tb' by calling the ‘clear()’ method of each frame object.

     New in version 3.4.

 -- Function: traceback.walk_stack (f)

     Walk a stack following ‘f.f_back’ from the given frame, yielding
     the frame and line number for each frame.  If `f' is ‘None’, the
     current stack is used.  This helper is used with *note
     StackSummary.extract(): 381d.

     New in version 3.5.

 -- Function: traceback.walk_tb (tb)

     Walk a traceback following ‘tb_next’ yielding the frame and line
     number for each frame.  This helper is used with *note
     StackSummary.extract(): 381d.

     New in version 3.5.

The module also defines the following classes:

* Menu:

* TracebackException Objects::
* StackSummary Objects::
* FrameSummary Objects::
* Traceback Examples::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/traceback.py


File: python.info,  Node: TracebackException Objects,  Next: StackSummary Objects,  Up: traceback — Print or retrieve a stack traceback

5.29.10.1 ‘TracebackException’ Objects
......................................

New in version 3.5.

*note TracebackException: 865. objects are created from actual
exceptions to capture data for later printing in a lightweight fashion.

 -- Class: traceback.TracebackException (exc_type, exc_value,
          exc_traceback, *, limit=None, lookup_lines=True,
          capture_locals=False)

     Capture an exception for later rendering.  `limit', `lookup_lines'
     and `capture_locals' are as for the *note StackSummary: 866. class.

     Note that when locals are captured, they are also shown in the
     traceback.

      -- Attribute: __cause__

          A *note TracebackException: 865. of the original ‘__cause__’.

      -- Attribute: __context__

          A *note TracebackException: 865. of the original
          ‘__context__’.

      -- Attribute: __suppress_context__

          The ‘__suppress_context__’ value from the original exception.

      -- Attribute: stack

          A *note StackSummary: 866. representing the traceback.

      -- Attribute: exc_type

          The class of the original traceback.

      -- Attribute: filename

          For syntax errors - the file name where the error occurred.

      -- Attribute: lineno

          For syntax errors - the line number where the error occurred.

      -- Attribute: text

          For syntax errors - the text where the error occurred.

      -- Attribute: offset

          For syntax errors - the offset into the text where the error
          occurred.

      -- Attribute: msg

          For syntax errors - the compiler error message.

      -- Method: classmethod from_exception (exc, *, limit=None,
               lookup_lines=True, capture_locals=False)

          Capture an exception for later rendering.  `limit',
          `lookup_lines' and `capture_locals' are as for the *note
          StackSummary: 866. class.

          Note that when locals are captured, they are also shown in the
          traceback.

      -- Method: format (*, chain=True)

          Format the exception.

          If `chain' is not ‘True’, ‘__cause__’ and ‘__context__’ will
          not be formatted.

          The return value is a generator of strings, each ending in a
          newline and some containing internal newlines.  *note
          print_exception(): 2208. is a wrapper around this method which
          just prints the lines to a file.

          The message indicating which exception occurred is always the
          last string in the output.

      -- Method: format_exception_only ()

          Format the exception part of the traceback.

          The return value is a generator of strings, each ending in a
          newline.

          Normally, the generator emits a single string; however, for
          *note SyntaxError: 55a. exceptions, it emits several lines
          that (when printed) display detailed information about where
          the syntax error occurred.

          The message indicating which exception occurred is always the
          last string in the output.


File: python.info,  Node: StackSummary Objects,  Next: FrameSummary Objects,  Prev: TracebackException Objects,  Up: traceback — Print or retrieve a stack traceback

5.29.10.2 ‘StackSummary’ Objects
................................

New in version 3.5.

*note StackSummary: 866. objects represent a call stack ready for
formatting.

 -- Class: traceback.StackSummary

      -- Method: classmethod extract (frame_gen, *, limit=None,
               lookup_lines=True, capture_locals=False)

          Construct a *note StackSummary: 866. object from a frame
          generator (such as is returned by *note walk_stack(): 863. or
          *note walk_tb(): 864.).

          If `limit' is supplied, only this many frames are taken from
          `frame_gen'.  If `lookup_lines' is ‘False’, the returned *note
          FrameSummary: 867. objects will not have read their lines in
          yet, making the cost of creating the *note StackSummary: 866.
          cheaper (which may be valuable if it may not actually get
          formatted).  If `capture_locals' is ‘True’ the local variables
          in each *note FrameSummary: 867. are captured as object
          representations.

      -- Method: classmethod from_list (a_list)

          Construct a *note StackSummary: 866. object from a supplied
          list of *note FrameSummary: 867. objects or old-style list of
          tuples.  Each tuple should be a 4-tuple with filename, lineno,
          name, line as the elements.

      -- Method: format ()

          Returns a list of strings ready for printing.  Each string in
          the resulting list corresponds to a single frame from the
          stack.  Each string ends in a newline; the strings may contain
          internal newlines as well, for those items with source text
          lines.

          For long sequences of the same frame and line, the first few
          repetitions are shown, followed by a summary line stating the
          exact number of further repetitions.

          Changed in version 3.6: Long sequences of repeated frames are
          now abbreviated.


File: python.info,  Node: FrameSummary Objects,  Next: Traceback Examples,  Prev: StackSummary Objects,  Up: traceback — Print or retrieve a stack traceback

5.29.10.3 ‘FrameSummary’ Objects
................................

New in version 3.5.

*note FrameSummary: 867. objects represent a single frame in a
traceback.

 -- Class: traceback.FrameSummary (filename, lineno, name,
          lookup_line=True, locals=None, line=None)

     Represent a single frame in the traceback or stack that is being
     formatted or printed.  It may optionally have a stringified version
     of the frames locals included in it.  If `lookup_line' is ‘False’,
     the source code is not looked up until the *note FrameSummary: 867.
     has the ‘line’ attribute accessed (which also happens when casting
     it to a tuple).  ‘line’ may be directly provided, and will prevent
     line lookups happening at all.  `locals' is an optional local
     variable dictionary, and if supplied the variable representations
     are stored in the summary for later display.


File: python.info,  Node: Traceback Examples,  Prev: FrameSummary Objects,  Up: traceback — Print or retrieve a stack traceback

5.29.10.4 Traceback Examples
............................

This simple example implements a basic read-eval-print loop, similar to
(but less useful than) the standard Python interactive interpreter loop.
For a more complete implementation of the interpreter loop, refer to the
*note code: 1a. module.

     import sys, traceback

     def run_user_code(envdir):
         source = input(">>> ")
         try:
             exec(source, envdir)
         except Exception:
             print("Exception in user code:")
             print("-"*60)
             traceback.print_exc(file=sys.stdout)
             print("-"*60)

     envdir = {}
     while True:
         run_user_code(envdir)

The following example demonstrates the different ways to print and
format the exception and traceback:

     import sys, traceback

     def lumberjack():
         bright_side_of_death()

     def bright_side_of_death():
         return tuple()[0]

     try:
         lumberjack()
     except IndexError:
         exc_type, exc_value, exc_traceback = sys.exc_info()
         print("*** print_tb:")
         traceback.print_tb(exc_traceback, limit=1, file=sys.stdout)
         print("*** print_exception:")
         # exc_type below is ignored on 3.5 and later
         traceback.print_exception(exc_type, exc_value, exc_traceback,
                                   limit=2, file=sys.stdout)
         print("*** print_exc:")
         traceback.print_exc(limit=2, file=sys.stdout)
         print("*** format_exc, first and last line:")
         formatted_lines = traceback.format_exc().splitlines()
         print(formatted_lines[0])
         print(formatted_lines[-1])
         print("*** format_exception:")
         # exc_type below is ignored on 3.5 and later
         print(repr(traceback.format_exception(exc_type, exc_value,
                                               exc_traceback)))
         print("*** extract_tb:")
         print(repr(traceback.extract_tb(exc_traceback)))
         print("*** format_tb:")
         print(repr(traceback.format_tb(exc_traceback)))
         print("*** tb_lineno:", exc_traceback.tb_lineno)

The output for the example would look similar to this:

     *** print_tb:
       File "<doctest...>", line 10, in <module>
         lumberjack()
     *** print_exception:
     Traceback (most recent call last):
       File "<doctest...>", line 10, in <module>
         lumberjack()
       File "<doctest...>", line 4, in lumberjack
         bright_side_of_death()
     IndexError: tuple index out of range
     *** print_exc:
     Traceback (most recent call last):
       File "<doctest...>", line 10, in <module>
         lumberjack()
       File "<doctest...>", line 4, in lumberjack
         bright_side_of_death()
     IndexError: tuple index out of range
     *** format_exc, first and last line:
     Traceback (most recent call last):
     IndexError: tuple index out of range
     *** format_exception:
     ['Traceback (most recent call last):\n',
      '  File "<doctest...>", line 10, in <module>\n    lumberjack()\n',
      '  File "<doctest...>", line 4, in lumberjack\n    bright_side_of_death()\n',
      '  File "<doctest...>", line 7, in bright_side_of_death\n    return tuple()[0]\n',
      'IndexError: tuple index out of range\n']
     *** extract_tb:
     [<FrameSummary file <doctest...>, line 10 in <module>>,
      <FrameSummary file <doctest...>, line 4 in lumberjack>,
      <FrameSummary file <doctest...>, line 7 in bright_side_of_death>]
     *** format_tb:
     ['  File "<doctest...>", line 10, in <module>\n    lumberjack()\n',
      '  File "<doctest...>", line 4, in lumberjack\n    bright_side_of_death()\n',
      '  File "<doctest...>", line 7, in bright_side_of_death\n    return tuple()[0]\n']
     *** tb_lineno: 10

The following example shows the different ways to print and format the
stack:

     >>> import traceback
     >>> def another_function():
     ...     lumberstack()
     ...
     >>> def lumberstack():
     ...     traceback.print_stack()
     ...     print(repr(traceback.extract_stack()))
     ...     print(repr(traceback.format_stack()))
     ...
     >>> another_function()
       File "<doctest>", line 10, in <module>
         another_function()
       File "<doctest>", line 3, in another_function
         lumberstack()
       File "<doctest>", line 6, in lumberstack
         traceback.print_stack()
     [('<doctest>', 10, '<module>', 'another_function()'),
      ('<doctest>', 3, 'another_function', 'lumberstack()'),
      ('<doctest>', 7, 'lumberstack', 'print(repr(traceback.extract_stack()))')]
     ['  File "<doctest>", line 10, in <module>\n    another_function()\n',
      '  File "<doctest>", line 3, in another_function\n    lumberstack()\n',
      '  File "<doctest>", line 8, in lumberstack\n    print(repr(traceback.format_stack()))\n']

This last example demonstrates the final few formatting functions:

     >>> import traceback
     >>> traceback.format_list([('spam.py', 3, '<module>', 'spam.eggs()'),
     ...                        ('eggs.py', 42, 'eggs', 'return "bacon"')])
     ['  File "spam.py", line 3, in <module>\n    spam.eggs()\n',
      '  File "eggs.py", line 42, in eggs\n    return "bacon"\n']
     >>> an_error = IndexError('tuple index out of range')
     >>> traceback.format_exception_only(type(an_error), an_error)
     ['IndexError: tuple index out of range\n']


File: python.info,  Node: __future__ — Future statement definitions,  Next: gc — Garbage Collector interface,  Prev: traceback — Print or retrieve a stack traceback,  Up: Python Runtime Services

5.29.11 ‘__future__’ — Future statement definitions
---------------------------------------------------

`Source code:' Lib/__future__.py(1)

__________________________________________________________________

*note __future__: 0. is a real module, and serves three purposes:

   * To avoid confusing existing tools that analyze import statements
     and expect to find the modules they’re importing.

   * To ensure that *note future statements: 16c4. run under releases
     prior to 2.1 at least yield runtime exceptions (the import of *note
     __future__: 0. will fail, because there was no module of that name
     prior to 2.1).

   * To document when incompatible changes were introduced, and when
     they will be — or were — made mandatory.  This is a form of
     executable documentation, and can be inspected programmatically via
     importing *note __future__: 0. and examining its contents.

Each statement in ‘__future__.py’ is of the form:

     FeatureName = _Feature(OptionalRelease, MandatoryRelease,
                            CompilerFlag)

where, normally, `OptionalRelease' is less than `MandatoryRelease', and
both are 5-tuples of the same form as *note sys.version_info: bed.:

     (PY_MAJOR_VERSION, # the 2 in 2.1.0a3; an int
      PY_MINOR_VERSION, # the 1; an int
      PY_MICRO_VERSION, # the 0; an int
      PY_RELEASE_LEVEL, # "alpha", "beta", "candidate" or "final"; string
      PY_RELEASE_SERIAL # the 3; an int
     )

`OptionalRelease' records the first release in which the feature was
accepted.

In the case of a `MandatoryRelease' that has not yet occurred,
`MandatoryRelease' predicts the release in which the feature will become
part of the language.

Else `MandatoryRelease' records when the feature became part of the
language; in releases at or after that, modules no longer need a future
statement to use the feature in question, but may continue to use such
imports.

`MandatoryRelease' may also be ‘None’, meaning that a planned feature
got dropped.

Instances of class ‘_Feature’ have two corresponding methods,
‘getOptionalRelease()’ and ‘getMandatoryRelease()’.

`CompilerFlag' is the (bitfield) flag that should be passed in the
fourth argument to the built-in function *note compile(): 2e7. to enable
the feature in dynamically compiled code.  This flag is stored in the
‘compiler_flag’ attribute on ‘_Feature’ instances.

No feature description will ever be deleted from *note __future__: 0.
Since its introduction in Python 2.1 the following features have found
their way into the language using this mechanism:

feature                optional in       mandatory in       effect
                                                            
--------------------------------------------------------------------------------------------------------------
                                                            
nested_scopes          2.1.0b1           2.2                PEP 227(2): `Statically Nested Scopes'
                                                            
                                                            
generators             2.2.0a1           2.3                PEP 255(3): `Simple Generators'
                                                            
                                                            
division               2.2.0a2           3.0                PEP 238(4): `Changing the Division Operator'
                                                            
                                                            
absolute_import        2.5.0a1           3.0                PEP 328(5): `Imports: Multi-Line and
                                                            Absolute/Relative'
                                                            
                                                            
with_statement         2.5.0a1           2.6                PEP 343(6): `The “with” Statement'
                                                            
                                                            
print_function         2.6.0a2           3.0                PEP 3105(7): `Make print a function'
                                                            
                                                            
unicode_literals       2.6.0a2           3.0                PEP 3112(8): `Bytes literals in Python 3000'
                                                            
                                                            
generator_stop         3.5.0b1           3.7                PEP 479(9): `StopIteration handling inside
                                                            generators'
                                                            
                                                            
annotations            3.7.0b1           3.10               PEP 563(10): `Postponed evaluation of
                                                            annotations'
                                                            

See also
........

*note Future statements: 16c4.

     How the compiler treats future imports.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/__future__.py

   (2) https://www.python.org/dev/peps/pep-0227

   (3) https://www.python.org/dev/peps/pep-0255

   (4) https://www.python.org/dev/peps/pep-0238

   (5) https://www.python.org/dev/peps/pep-0328

   (6) https://www.python.org/dev/peps/pep-0343

   (7) https://www.python.org/dev/peps/pep-3105

   (8) https://www.python.org/dev/peps/pep-3112

   (9) https://www.python.org/dev/peps/pep-0479

   (10) https://www.python.org/dev/peps/pep-0563


File: python.info,  Node: gc — Garbage Collector interface,  Next: inspect — Inspect live objects,  Prev: __future__ — Future statement definitions,  Up: Python Runtime Services

5.29.12 ‘gc’ — Garbage Collector interface
------------------------------------------

__________________________________________________________________

This module provides an interface to the optional garbage collector.  It
provides the ability to disable the collector, tune the collection
frequency, and set debugging options.  It also provides access to
unreachable objects that the collector found but cannot free.  Since the
collector supplements the reference counting already used in Python, you
can disable the collector if you are sure your program does not create
reference cycles.  Automatic collection can be disabled by calling
‘gc.disable()’.  To debug a leaking program call
‘gc.set_debug(gc.DEBUG_LEAK)’.  Notice that this includes
‘gc.DEBUG_SAVEALL’, causing garbage-collected objects to be saved in
gc.garbage for inspection.

The *note gc: 84. module provides the following functions:

 -- Function: gc.enable ()

     Enable automatic garbage collection.

 -- Function: gc.disable ()

     Disable automatic garbage collection.

 -- Function: gc.isenabled ()

     Return ‘True’ if automatic collection is enabled.

 -- Function: gc.collect (generation=2)

     With no arguments, run a full collection.  The optional argument
     `generation' may be an integer specifying which generation to
     collect (from 0 to 2).  A *note ValueError: 16d. is raised if the
     generation number is invalid.  The number of unreachable objects
     found is returned.

     The free lists maintained for a number of built-in types are
     cleared whenever a full collection or collection of the highest
     generation (2) is run.  Not all items in some free lists may be
     freed due to the particular implementation, in particular *note
     float: 1fd.

 -- Function: gc.set_debug (flags)

     Set the garbage collection debugging flags.  Debugging information
     will be written to ‘sys.stderr’.  See below for a list of debugging
     flags which can be combined using bit operations to control
     debugging.

 -- Function: gc.get_debug ()

     Return the debugging flags currently set.

 -- Function: gc.get_objects (generation=None)

     Returns a list of all objects tracked by the collector, excluding
     the list returned.  If `generation' is not None, return only the
     objects tracked by the collector that are in that generation.

     Changed in version 3.8: New `generation' parameter.

     Raises an *note auditing event: fa1. ‘gc.get_objects’ with argument
     ‘generation’.

 -- Function: gc.get_stats ()

     Return a list of three per-generation dictionaries containing
     collection statistics since interpreter start.  The number of keys
     may change in the future, but currently each dictionary will
     contain the following items:

        * ‘collections’ is the number of times this generation was
          collected;

        * ‘collected’ is the total number of objects collected inside
          this generation;

        * ‘uncollectable’ is the total number of objects which were
          found to be uncollectable (and were therefore moved to the
          *note garbage: c12. list) inside this generation.

     New in version 3.4.

 -- Function: gc.set_threshold (threshold0[, threshold1[, threshold2]])

     Set the garbage collection thresholds (the collection frequency).
     Setting `threshold0' to zero disables collection.

     The GC classifies objects into three generations depending on how
     many collection sweeps they have survived.  New objects are placed
     in the youngest generation (generation ‘0’).  If an object survives
     a collection it is moved into the next older generation.  Since
     generation ‘2’ is the oldest generation, objects in that generation
     remain there after a collection.  In order to decide when to run,
     the collector keeps track of the number object allocations and
     deallocations since the last collection.  When the number of
     allocations minus the number of deallocations exceeds `threshold0',
     collection starts.  Initially only generation ‘0’ is examined.  If
     generation ‘0’ has been examined more than `threshold1' times since
     generation ‘1’ has been examined, then generation ‘1’ is examined
     as well.  With the third generation, things are a bit more
     complicated, see Collecting the oldest generation(1) for more
     information.

 -- Function: gc.get_count ()

     Return the current collection counts as a tuple of ‘(count0,
     count1, count2)’.

 -- Function: gc.get_threshold ()

     Return the current collection thresholds as a tuple of
     ‘(threshold0, threshold1, threshold2)’.

 -- Function: gc.get_referrers (*objs)

     Return the list of objects that directly refer to any of objs.
     This function will only locate those containers which support
     garbage collection; extension types which do refer to other objects
     but do not support garbage collection will not be found.

     Note that objects which have already been dereferenced, but which
     live in cycles and have not yet been collected by the garbage
     collector can be listed among the resulting referrers.  To get only
     currently live objects, call *note collect(): 35b. before calling
     *note get_referrers(): fb6.

          Warning: Care must be taken when using objects returned by
          *note get_referrers(): fb6. because some of them could still
          be under construction and hence in a temporarily invalid
          state.  Avoid using *note get_referrers(): fb6. for any
          purpose other than debugging.

     Raises an *note auditing event: fa1. ‘gc.get_referrers’ with
     argument ‘objs’.

 -- Function: gc.get_referents (*objs)

     Return a list of objects directly referred to by any of the
     arguments.  The referents returned are those objects visited by the
     arguments’ C-level *note tp_traverse: 23b. methods (if any), and
     may not be all objects actually directly reachable.  *note
     tp_traverse: 23b. methods are supported only by objects that
     support garbage collection, and are only required to visit objects
     that may be involved in a cycle.  So, for example, if an integer is
     directly reachable from an argument, that integer object may or may
     not appear in the result list.

     Raises an *note auditing event: fa1. ‘gc.get_referents’ with
     argument ‘objs’.

 -- Function: gc.is_tracked (obj)

     Returns ‘True’ if the object is currently tracked by the garbage
     collector, ‘False’ otherwise.  As a general rule, instances of
     atomic types aren’t tracked and instances of non-atomic types
     (containers, user-defined objects…) are.  However, some
     type-specific optimizations can be present in order to suppress the
     garbage collector footprint of simple instances (e.g.  dicts
     containing only atomic keys and values):

          >>> gc.is_tracked(0)
          False
          >>> gc.is_tracked("a")
          False
          >>> gc.is_tracked([])
          True
          >>> gc.is_tracked({})
          False
          >>> gc.is_tracked({"a": 1})
          False
          >>> gc.is_tracked({"a": []})
          True

     New in version 3.1.

 -- Function: gc.is_finalized (obj)

     Returns ‘True’ if the given object has been finalized by the
     garbage collector, ‘False’ otherwise.

          >>> x = None
          >>> class Lazarus:
          ...     def __del__(self):
          ...         global x
          ...         x = self
          ...
          >>> lazarus = Lazarus()
          >>> gc.is_finalized(lazarus)
          False
          >>> del lazarus
          >>> gc.is_finalized(x)
          True

     New in version 3.9.

 -- Function: gc.freeze ()

     Freeze all the objects tracked by gc - move them to a permanent
     generation and ignore all the future collections.  This can be used
     before a POSIX fork() call to make the gc copy-on-write friendly or
     to speed up collection.  Also collection before a POSIX fork() call
     may free pages for future allocation which can cause copy-on-write
     too so it’s advised to disable gc in parent process and freeze
     before fork and enable gc in child process.

     New in version 3.7.

 -- Function: gc.unfreeze ()

     Unfreeze the objects in the permanent generation, put them back
     into the oldest generation.

     New in version 3.7.

 -- Function: gc.get_freeze_count ()

     Return the number of objects in the permanent generation.

     New in version 3.7.

The following variables are provided for read-only access (you can
mutate the values but should not rebind them):

 -- Data: gc.garbage

     A list of objects which the collector found to be unreachable but
     could not be freed (uncollectable objects).  Starting with Python
     3.4, this list should be empty most of the time, except when using
     instances of C extension types with a non-‘NULL’ ‘tp_del’ slot.

     If *note DEBUG_SAVEALL: 383e. is set, then all unreachable objects
     will be added to this list rather than freed.

     Changed in version 3.2: If this list is non-empty at *note
     interpreter shutdown: 852, a *note ResourceWarning: 5cb. is
     emitted, which is silent by default.  If *note DEBUG_UNCOLLECTABLE:
     c13. is set, in addition all uncollectable objects are printed.

     Changed in version 3.4: Following PEP 442(2), objects with a *note
     __del__(): a04. method don’t end up in *note gc.garbage: c12.
     anymore.

 -- Data: gc.callbacks

     A list of callbacks that will be invoked by the garbage collector
     before and after collection.  The callbacks will be called with two
     arguments, `phase' and `info'.

     `phase' can be one of two values:

          “start”: The garbage collection is about to start.

          “stop”: The garbage collection has finished.

     `info' is a dict providing more information for the callback.  The
     following keys are currently defined:

          “generation”: The oldest generation being collected.

          “collected”: When `phase' is “stop”, the number of objects
          successfully collected.

          “uncollectable”: When `phase' is “stop”, the number of objects
          that could not be collected and were put in *note garbage:
          c12.

     Applications can add their own callbacks to this list.  The primary
     use cases are:

          Gathering statistics about garbage collection, such as how
          often various generations are collected, and how long the
          collection takes.

          Allowing applications to identify and clear their own
          uncollectable types when they appear in *note garbage: c12.

     New in version 3.3.

The following constants are provided for use with *note set_debug():
3839.:

 -- Data: gc.DEBUG_STATS

     Print statistics during collection.  This information can be useful
     when tuning the collection frequency.

 -- Data: gc.DEBUG_COLLECTABLE

     Print information on collectable objects found.

 -- Data: gc.DEBUG_UNCOLLECTABLE

     Print information of uncollectable objects found (objects which are
     not reachable but cannot be freed by the collector).  These objects
     will be added to the ‘garbage’ list.

     Changed in version 3.2: Also print the contents of the *note
     garbage: c12. list at *note interpreter shutdown: 852, if it isn’t
     empty.

 -- Data: gc.DEBUG_SAVEALL

     When set, all unreachable objects found will be appended to
     `garbage' rather than being freed.  This can be useful for
     debugging a leaking program.

 -- Data: gc.DEBUG_LEAK

     The debugging flags necessary for the collector to print
     information about a leaking program (equal to ‘DEBUG_COLLECTABLE |
     DEBUG_UNCOLLECTABLE | DEBUG_SAVEALL’).

   ---------- Footnotes ----------

   (1) 
https://devguide.python.org/garbage_collector/#collecting-the-oldest-generation

   (2) https://www.python.org/dev/peps/pep-0442


File: python.info,  Node: inspect — Inspect live objects,  Next: site — Site-specific configuration hook,  Prev: gc — Garbage Collector interface,  Up: Python Runtime Services

5.29.13 ‘inspect’ — Inspect live objects
----------------------------------------

`Source code:' Lib/inspect.py(1)

__________________________________________________________________

The *note inspect: a0. module provides several useful functions to help
get information about live objects such as modules, classes, methods,
functions, tracebacks, frame objects, and code objects.  For example, it
can help you examine the contents of a class, retrieve the source code
of a method, extract and format the argument list for a function, or get
all the information you need to display a detailed traceback.

There are four main kinds of services provided by this module: type
checking, getting source code, inspecting classes and functions, and
examining the interpreter stack.

* Menu:

* Types and members::
* Retrieving source code::
* Introspecting callables with the Signature object::
* Classes and functions: Classes and functions<2>.
* The interpreter stack::
* Fetching attributes statically::
* Current State of Generators and Coroutines::
* Code Objects Bit Flags::
* Command Line Interface: Command Line Interface<3>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/inspect.py


File: python.info,  Node: Types and members,  Next: Retrieving source code,  Up: inspect — Inspect live objects

5.29.13.1 Types and members
...........................

The *note getmembers(): 3846. function retrieves the members of an
object such as a class or module.  The functions whose names begin with
“is” are mainly provided as convenient choices for the second argument
to *note getmembers(): 3846.  They also help you determine when you can
expect to find the following special attributes:

Type            Attribute               Description
                                        
------------------------------------------------------------------------
                                        
module          __doc__                 documentation string
                                        
                                        
                __file__                filename (missing for
                                        built-in modules)
                                        
                                        
class           __doc__                 documentation string
                                        
                                        
                __name__                name with which this class
                                        was defined
                                        
                                        
                __qualname__            qualified name
                                        
                                        
                __module__              name of module in which this
                                        class was defined
                                        
                                        
method          __doc__                 documentation string
                                        
                                        
                __name__                name with which this method
                                        was defined
                                        
                                        
                __qualname__            qualified name
                                        
                                        
                __func__                function object containing
                                        implementation of method
                                        
                                        
                __self__                instance to which this method
                                        is bound, or ‘None’
                                        
                                        
                __module__              name of module in which this
                                        method was defined
                                        
                                        
function        __doc__                 documentation string
                                        
                                        
                __name__                name with which this function
                                        was defined
                                        
                                        
                __qualname__            qualified name
                                        
                                        
                __code__                code object containing
                                        compiled function
                                        *note bytecode: 709.
                                        
                                        
                __defaults__            tuple of any default values
                                        for positional or keyword
                                        parameters
                                        
                                        
                __kwdefaults__          mapping of any default values
                                        for keyword-only parameters
                                        
                                        
                __globals__             global namespace in which
                                        this function was defined
                                        
                                        
                __annotations__         mapping of parameters names
                                        to annotations; ‘"return"’
                                        key is reserved for return
                                        annotations.
                                        
                                        
                __module__              name of module in which this
                                        function was defined
                                        
                                        
traceback       tb_frame                frame object at this level
                                        
                                        
                tb_lasti                index of last attempted
                                        instruction in bytecode
                                        
                                        
                tb_lineno               current line number in Python
                                        source code
                                        
                                        
                tb_next                 next inner traceback object
                                        (called by this level)
                                        
                                        
frame           f_back                  next outer frame object (this
                                        frame’s caller)
                                        
                                        
                f_builtins              builtins namespace seen by
                                        this frame
                                        
                                        
                f_code                  code object being executed in
                                        this frame
                                        
                                        
                f_globals               global namespace seen by this
                                        frame
                                        
                                        
                f_lasti                 index of last attempted
                                        instruction in bytecode
                                        
                                        
                f_lineno                current line number in Python
                                        source code
                                        
                                        
                f_locals                local namespace seen by this
                                        frame
                                        
                                        
                f_trace                 tracing function for this
                                        frame, or ‘None’
                                        
                                        
code            co_argcount             number of arguments (not
                                        including keyword only
                                        arguments, * or ** args)
                                        
                                        
                co_code                 string of raw compiled
                                        bytecode
                                        
                                        
                co_cellvars             tuple of names of cell
                                        variables (referenced by
                                        containing scopes)
                                        
                                        
                co_consts               tuple of constants used in
                                        the bytecode
                                        
                                        
                co_filename             name of file in which this
                                        code object was created
                                        
                                        
                co_firstlineno          number of first line in
                                        Python source code
                                        
                                        
                co_flags                bitmap of ‘CO_*’ flags, read
                                        more *note here: 3847.
                                        
                                        
                co_lnotab               encoded mapping of line
                                        numbers to bytecode indices
                                        
                                        
                co_freevars             tuple of names of free
                                        variables (referenced via a
                                        function’s closure)
                                        
                                        
                co_posonlyargcount      number of positional only
                                        arguments
                                        
                                        
                co_kwonlyargcount       number of keyword only
                                        arguments (not including **
                                        arg)
                                        
                                        
                co_name                 name with which this code
                                        object was defined
                                        
                                        
                co_names                tuple of names of local
                                        variables
                                        
                                        
                co_nlocals              number of local variables
                                        
                                        
                co_stacksize            virtual machine stack space
                                        required
                                        
                                        
                co_varnames             tuple of names of arguments
                                        and local variables
                                        
                                        
generator       __name__                name
                                        
                                        
                __qualname__            qualified name
                                        
                                        
                gi_frame                frame
                                        
                                        
                gi_running              is the generator running?
                                        
                                        
                gi_code                 code
                                        
                                        
                gi_yieldfrom            object being iterated by
                                        ‘yield from’, or ‘None’
                                        
                                        
coroutine       __name__                name
                                        
                                        
                __qualname__            qualified name
                                        
                                        
                cr_await                object being awaited on, or
                                        ‘None’
                                        
                                        
                cr_frame                frame
                                        
                                        
                cr_running              is the coroutine running?
                                        
                                        
                cr_code                 code
                                        
                                        
                cr_origin               where coroutine was created,
                                        or ‘None’.  See
                                        *note sys.set_coroutine_origin_tracking_depth(): 4f9.
                                        
                                        
builtin         __doc__                 documentation string
                                        
                                        
                __name__                original name of this
                                        function or method
                                        
                                        
                __qualname__            qualified name
                                        
                                        
                __self__                instance to which a method is
                                        bound, or ‘None’
                                        

Changed in version 3.5: Add ‘__qualname__’ and ‘gi_yieldfrom’ attributes
to generators.

The ‘__name__’ attribute of generators is now set from the function
name, instead of the code name, and it can now be modified.

Changed in version 3.7: Add ‘cr_origin’ attribute to coroutines.

 -- Function: inspect.getmembers (object[, predicate])

     Return all the members of an object in a list of ‘(name, value)’
     pairs sorted by name.  If the optional `predicate' argument—which
     will be called with the ‘value’ object of each member—is supplied,
     only members for which the predicate returns a true value are
     included.

          Note: *note getmembers(): 3846. will only return class
          attributes defined in the metaclass when the argument is a
          class and those attributes have been listed in the metaclass’
          custom *note __dir__(): 42b.

 -- Function: inspect.getmodulename (path)

     Return the name of the module named by the file `path', without
     including the names of enclosing packages.  The file extension is
     checked against all of the entries in *note
     importlib.machinery.all_suffixes(): 3848.  If it matches, the final
     path component is returned with the extension removed.  Otherwise,
     ‘None’ is returned.

     Note that this function `only' returns a meaningful name for actual
     Python modules - paths that potentially refer to Python packages
     will still return ‘None’.

     Changed in version 3.3: The function is based directly on *note
     importlib: 9a.

 -- Function: inspect.ismodule (object)

     Return ‘True’ if the object is a module.

 -- Function: inspect.isclass (object)

     Return ‘True’ if the object is a class, whether built-in or created
     in Python code.

 -- Function: inspect.ismethod (object)

     Return ‘True’ if the object is a bound method written in Python.

 -- Function: inspect.isfunction (object)

     Return ‘True’ if the object is a Python function, which includes
     functions created by a *note lambda: 1ca8. expression.

 -- Function: inspect.isgeneratorfunction (object)

     Return ‘True’ if the object is a Python generator function.

     Changed in version 3.8: Functions wrapped in *note
     functools.partial(): 8b5. now return ‘True’ if the wrapped function
     is a Python generator function.

 -- Function: inspect.isgenerator (object)

     Return ‘True’ if the object is a generator.

 -- Function: inspect.iscoroutinefunction (object)

     Return ‘True’ if the object is a *note coroutine function: 732. (a
     function defined with an *note async def: 3a9. syntax).

     New in version 3.5.

     Changed in version 3.8: Functions wrapped in *note
     functools.partial(): 8b5. now return ‘True’ if the wrapped function
     is a *note coroutine function: 732.

 -- Function: inspect.iscoroutine (object)

     Return ‘True’ if the object is a *note coroutine: 18a. created by
     an *note async def: 3a9. function.

     New in version 3.5.

 -- Function: inspect.isawaitable (object)

     Return ‘True’ if the object can be used in *note await: 2d8.
     expression.

     Can also be used to distinguish generator-based coroutines from
     regular generators:

          def gen():
              yield
          @types.coroutine
          def gen_coro():
              yield

          assert not isawaitable(gen())
          assert isawaitable(gen_coro())

     New in version 3.5.

 -- Function: inspect.isasyncgenfunction (object)

     Return ‘True’ if the object is an *note asynchronous generator:
     1640. function, for example:

          >>> async def agen():
          ...     yield 1
          ...
          >>> inspect.isasyncgenfunction(agen)
          True

     New in version 3.6.

     Changed in version 3.8: Functions wrapped in *note
     functools.partial(): 8b5. now return ‘True’ if the wrapped function
     is a *note asynchronous generator: 1640. function.

 -- Function: inspect.isasyncgen (object)

     Return ‘True’ if the object is an *note asynchronous generator
     iterator: 37b7. created by an *note asynchronous generator: 1640.
     function.

     New in version 3.6.

 -- Function: inspect.istraceback (object)

     Return ‘True’ if the object is a traceback.

 -- Function: inspect.isframe (object)

     Return ‘True’ if the object is a frame.

 -- Function: inspect.iscode (object)

     Return ‘True’ if the object is a code.

 -- Function: inspect.isbuiltin (object)

     Return ‘True’ if the object is a built-in function or a bound
     built-in method.

 -- Function: inspect.isroutine (object)

     Return ‘True’ if the object is a user-defined or built-in function
     or method.

 -- Function: inspect.isabstract (object)

     Return ‘True’ if the object is an abstract base class.

 -- Function: inspect.ismethoddescriptor (object)

     Return ‘True’ if the object is a method descriptor, but not if
     *note ismethod(): 384b, *note isclass(): 384a, *note isfunction():
     384c. or *note isbuiltin(): 3852. are true.

     This, for example, is true of ‘int.__add__’.  An object passing
     this test has a *note __get__(): 156e. method but not a *note
     __set__(): 1572. method, but beyond that the set of attributes
     varies.  A *note __name__: d2f. attribute is usually sensible, and
     ‘__doc__’ often is.

     Methods implemented via descriptors that also pass one of the other
     tests return ‘False’ from the *note ismethoddescriptor(): 3855.
     test, simply because the other tests promise more – you can, e.g.,
     count on having the ‘__func__’ attribute (etc) when an object
     passes *note ismethod(): 384b.

 -- Function: inspect.isdatadescriptor (object)

     Return ‘True’ if the object is a data descriptor.

     Data descriptors have a *note __set__: 1572. or a *note __delete__:
     1573. method.  Examples are properties (defined in Python),
     getsets, and members.  The latter two are defined in C and there
     are more specific tests available for those types, which is robust
     across Python implementations.  Typically, data descriptors will
     also have *note __name__: d2f. and ‘__doc__’ attributes
     (properties, getsets, and members have both of these attributes),
     but this is not guaranteed.

 -- Function: inspect.isgetsetdescriptor (object)

     Return ‘True’ if the object is a getset descriptor.

     `CPython implementation detail:' getsets are attributes defined in
     extension modules via *note PyGetSetDef: 52b. structures.  For
     Python implementations without such types, this method will always
     return ‘False’.

 -- Function: inspect.ismemberdescriptor (object)

     Return ‘True’ if the object is a member descriptor.

     `CPython implementation detail:' Member descriptors are attributes
     defined in extension modules via *note PyMemberDef: 52a.
     structures.  For Python implementations without such types, this
     method will always return ‘False’.


File: python.info,  Node: Retrieving source code,  Next: Introspecting callables with the Signature object,  Prev: Types and members,  Up: inspect — Inspect live objects

5.29.13.2 Retrieving source code
................................

 -- Function: inspect.getdoc (object)

     Get the documentation string for an object, cleaned up with *note
     cleandoc(): 385b.  If the documentation string for an object is not
     provided and the object is a class, a method, a property or a
     descriptor, retrieve the documentation string from the inheritance
     hierarchy.

     Changed in version 3.5: Documentation strings are now inherited if
     not overridden.

 -- Function: inspect.getcomments (object)

     Return in a single string any lines of comments immediately
     preceding the object’s source code (for a class, function, or
     method), or at the top of the Python source file (if the object is
     a module).  If the object’s source code is unavailable, return
     ‘None’.  This could happen if the object has been defined in C or
     the interactive shell.

 -- Function: inspect.getfile (object)

     Return the name of the (text or binary) file in which an object was
     defined.  This will fail with a *note TypeError: 1fe. if the object
     is a built-in module, class, or function.

 -- Function: inspect.getmodule (object)

     Try to guess which module an object was defined in.

 -- Function: inspect.getsourcefile (object)

     Return the name of the Python source file in which an object was
     defined.  This will fail with a *note TypeError: 1fe. if the object
     is a built-in module, class, or function.

 -- Function: inspect.getsourcelines (object)

     Return a list of source lines and starting line number for an
     object.  The argument may be a module, class, method, function,
     traceback, frame, or code object.  The source code is returned as a
     list of the lines corresponding to the object and the line number
     indicates where in the original source file the first line of code
     was found.  An *note OSError: 304. is raised if the source code
     cannot be retrieved.

     Changed in version 3.3: *note OSError: 304. is raised instead of
     *note IOError: a73, now an alias of the former.

 -- Function: inspect.getsource (object)

     Return the text of the source code for an object.  The argument may
     be a module, class, method, function, traceback, frame, or code
     object.  The source code is returned as a single string.  An *note
     OSError: 304. is raised if the source code cannot be retrieved.

     Changed in version 3.3: *note OSError: 304. is raised instead of
     *note IOError: a73, now an alias of the former.

 -- Function: inspect.cleandoc (doc)

     Clean up indentation from docstrings that are indented to line up
     with blocks of code.

     All leading whitespace is removed from the first line.  Any leading
     whitespace that can be uniformly removed from the second line
     onwards is removed.  Empty lines at the beginning and end are
     subsequently removed.  Also, all tabs are expanded to spaces.


File: python.info,  Node: Introspecting callables with the Signature object,  Next: Classes and functions<2>,  Prev: Retrieving source code,  Up: inspect — Inspect live objects

5.29.13.3 Introspecting callables with the Signature object
...........................................................

New in version 3.3.

The Signature object represents the call signature of a callable object
and its return annotation.  To retrieve a Signature object, use the
*note signature(): 655. function.

 -- Function: inspect.signature (callable, *, follow_wrapped=True)

     Return a *note Signature: 7e4. object for the given ‘callable’:

          >>> from inspect import signature
          >>> def foo(a, *, b:int, **kwargs):
          ...     pass

          >>> sig = signature(foo)

          >>> str(sig)
          '(a, *, b:int, **kwargs)'

          >>> str(sig.parameters['b'])
          'b:int'

          >>> sig.parameters['b'].annotation
          <class 'int'>

     Accepts a wide range of Python callables, from plain functions and
     classes to *note functools.partial(): 8b5. objects.

     Raises *note ValueError: 16d. if no signature can be provided, and
     *note TypeError: 1fe. if that type of object is not supported.

     A slash(/) in the signature of a function denotes that the
     parameters prior to it are positional-only.  For more info, see
     *note the FAQ entry on positional-only parameters: 1729.

     New in version 3.5: ‘follow_wrapped’ parameter.  Pass ‘False’ to
     get a signature of ‘callable’ specifically (‘callable.__wrapped__’
     will not be used to unwrap decorated callables.)

          Note: Some callables may not be introspectable in certain
          implementations of Python.  For example, in CPython, some
          built-in functions defined in C provide no metadata about
          their arguments.

 -- Class: inspect.Signature (parameters=None, *,
          return_annotation=Signature.empty)

     A Signature object represents the call signature of a function and
     its return annotation.  For each parameter accepted by the function
     it stores a *note Parameter: 7e5. object in its *note parameters:
     1088. collection.

     The optional `parameters' argument is a sequence of *note
     Parameter: 7e5. objects, which is validated to check that there are
     no parameters with duplicate names, and that the parameters are in
     the right order, i.e.  positional-only first, then
     positional-or-keyword, and that parameters with defaults follow
     parameters without defaults.

     The optional `return_annotation' argument, can be an arbitrary
     Python object, is the “return” annotation of the callable.

     Signature objects are `immutable'.  Use *note Signature.replace():
     3860. to make a modified copy.

     Changed in version 3.5: Signature objects are picklable and
     hashable.

      -- Attribute: empty

          A special class-level marker to specify absence of a return
          annotation.

      -- Attribute: parameters

          An ordered mapping of parameters’ names to the corresponding
          *note Parameter: 7e5. objects.  Parameters appear in strict
          definition order, including keyword-only parameters.

          Changed in version 3.7: Python only explicitly guaranteed that
          it preserved the declaration order of keyword-only parameters
          as of version 3.7, although in practice this order had always
          been preserved in Python 3.

      -- Attribute: return_annotation

          The “return” annotation for the callable.  If the callable has
          no “return” annotation, this attribute is set to *note
          Signature.empty: 3861.

      -- Method: bind (*args, **kwargs)

          Create a mapping from positional and keyword arguments to
          parameters.  Returns *note BoundArguments: a89. if ‘*args’ and
          ‘**kwargs’ match the signature, or raises a *note TypeError:
          1fe.

      -- Method: bind_partial (*args, **kwargs)

          Works the same way as *note Signature.bind(): 3863, but allows
          the omission of some required arguments (mimics *note
          functools.partial(): 8b5. behavior.)  Returns *note
          BoundArguments: a89, or raises a *note TypeError: 1fe. if the
          passed arguments do not match the signature.

      -- Method: replace (*[, parameters][, return_annotation])

          Create a new Signature instance based on the instance replace
          was invoked on.  It is possible to pass different ‘parameters’
          and/or ‘return_annotation’ to override the corresponding
          properties of the base signature.  To remove return_annotation
          from the copied Signature, pass in *note Signature.empty:
          3861.

               >>> def test(a, b):
               ...     pass
               >>> sig = signature(test)
               >>> new_sig = sig.replace(return_annotation="new return anno")
               >>> str(new_sig)
               "(a, b) -> 'new return anno'"

      -- Method: classmethod from_callable (obj, *, follow_wrapped=True)

          Return a *note Signature: 7e4. (or its subclass) object for a
          given callable ‘obj’.  Pass ‘follow_wrapped=False’ to get a
          signature of ‘obj’ without unwrapping its ‘__wrapped__’ chain.

          This method simplifies subclassing of *note Signature: 7e4.:

               class MySignature(Signature):
                   pass
               sig = MySignature.from_callable(min)
               assert isinstance(sig, MySignature)

          New in version 3.5.

 -- Class: inspect.Parameter (name, kind, *, default=Parameter.empty,
          annotation=Parameter.empty)

     Parameter objects are `immutable'.  Instead of modifying a
     Parameter object, you can use *note Parameter.replace(): 3865. to
     create a modified copy.

     Changed in version 3.5: Parameter objects are picklable and
     hashable.

      -- Attribute: empty

          A special class-level marker to specify absence of default
          values and annotations.

      -- Attribute: name

          The name of the parameter as a string.  The name must be a
          valid Python identifier.

          `CPython implementation detail:' CPython generates implicit
          parameter names of the form ‘.0’ on the code objects used to
          implement comprehensions and generator expressions.

          Changed in version 3.6: These parameter names are exposed by
          this module as names like ‘implicit0’.

      -- Attribute: default

          The default value for the parameter.  If the parameter has no
          default value, this attribute is set to *note Parameter.empty:
          3866.

      -- Attribute: annotation

          The annotation for the parameter.  If the parameter has no
          annotation, this attribute is set to *note Parameter.empty:
          3866.

      -- Attribute: kind

          Describes how argument values are bound to the parameter.
          Possible values (accessible via *note Parameter: 7e5, like
          ‘Parameter.KEYWORD_ONLY’):

          Name                         Meaning
                                       
          --------------------------------------------------------------------------------
                                       
          `POSITIONAL_ONLY'            Value must be supplied as a positional argument.
                                       Positional only parameters are those which
                                       appear before a ‘/’ entry (if present) in a
                                       Python function definition.
                                       
                                       
          `POSITIONAL_OR_KEYWORD'      Value may be supplied as either a keyword or
                                       positional argument (this is the standard
                                       binding behaviour for functions implemented in
                                       Python.)
                                       
                                       
          `VAR_POSITIONAL'             A tuple of positional arguments that aren’t
                                       bound to any other parameter.  This corresponds
                                       to a ‘*args’ parameter in a Python function
                                       definition.
                                       
                                       
          `KEYWORD_ONLY'               Value must be supplied as a keyword argument.
                                       Keyword only parameters are those which appear
                                       after a ‘*’ or ‘*args’ entry in a Python
                                       function definition.
                                       
                                       
          `VAR_KEYWORD'                A dict of keyword arguments that aren’t bound to
                                       any other parameter.  This corresponds to a
                                       ‘**kwargs’ parameter in a Python function
                                       definition.
                                       

          Example: print all keyword-only arguments without default
          values:

               >>> def foo(a, b, *, c, d=10):
               ...     pass

               >>> sig = signature(foo)
               >>> for param in sig.parameters.values():
               ...     if (param.kind == param.KEYWORD_ONLY and
               ...                        param.default is param.empty):
               ...         print('Parameter:', param)
               Parameter: c

      -- Attribute: kind.description

          Describes a enum value of Parameter.kind.

          New in version 3.8.

          Example: print all descriptions of arguments:

               >>> def foo(a, b, *, c, d=10):
               ...     pass

               >>> sig = signature(foo)
               >>> for param in sig.parameters.values():
               ...     print(param.kind.description)
               positional or keyword
               positional or keyword
               keyword-only
               keyword-only

      -- Method: replace (*[, name][, kind][, default][, annotation])

          Create a new Parameter instance based on the instance replaced
          was invoked on.  To override a *note Parameter: 7e5.
          attribute, pass the corresponding argument.  To remove a
          default value or/and an annotation from a Parameter, pass
          *note Parameter.empty: 3866.

               >>> from inspect import Parameter
               >>> param = Parameter('foo', Parameter.KEYWORD_ONLY, default=42)
               >>> str(param)
               'foo=42'

               >>> str(param.replace()) # Will create a shallow copy of 'param'
               'foo=42'

               >>> str(param.replace(default=Parameter.empty, annotation='spam'))
               "foo:'spam'"

     Changed in version 3.4: In Python 3.3 Parameter objects were
     allowed to have ‘name’ set to ‘None’ if their ‘kind’ was set to
     ‘POSITIONAL_ONLY’.  This is no longer permitted.

 -- Class: inspect.BoundArguments

     Result of a *note Signature.bind(): 3863. or *note
     Signature.bind_partial(): 3864. call.  Holds the mapping of
     arguments to the function’s parameters.

      -- Attribute: arguments

          A mutable mapping of parameters’ names to arguments’ values.
          Contains only explicitly bound arguments.  Changes in *note
          arguments: 1b9. will reflect in *note args: 386c. and *note
          kwargs: 386d.

          Should be used in conjunction with *note Signature.parameters:
          1088. for any argument processing purposes.

               Note: Arguments for which *note Signature.bind(): 3863.
               or *note Signature.bind_partial(): 3864. relied on a
               default value are skipped.  However, if needed, use *note
               BoundArguments.apply_defaults(): 7e6. to add them.

          Changed in version 3.9: *note arguments: 1b9. is now of type
          *note dict: 164.  Formerly, it was of type *note
          collections.OrderedDict: 2ea.

      -- Attribute: args

          A tuple of positional arguments values.  Dynamically computed
          from the *note arguments: 1b9. attribute.

      -- Attribute: kwargs

          A dict of keyword arguments values.  Dynamically computed from
          the *note arguments: 1b9. attribute.

      -- Attribute: signature

          A reference to the parent *note Signature: 7e4. object.

      -- Method: apply_defaults ()

          Set default values for missing arguments.

          For variable-positional arguments (‘*args’) the default is an
          empty tuple.

          For variable-keyword arguments (‘**kwargs’) the default is an
          empty dict.

               >>> def foo(a, b='ham', *args): pass
               >>> ba = inspect.signature(foo).bind('spam')
               >>> ba.apply_defaults()
               >>> ba.arguments
               {'a': 'spam', 'b': 'ham', 'args': ()}

          New in version 3.5.

     The *note args: 386c. and *note kwargs: 386d. properties can be
     used to invoke functions:

          def test(a, *, b):
              ...

          sig = signature(test)
          ba = sig.bind(10, b=20)
          test(*ba.args, **ba.kwargs)

See also
........

PEP 362(1) - Function Signature Object.

     The detailed specification, implementation details and examples.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0362


File: python.info,  Node: Classes and functions<2>,  Next: The interpreter stack,  Prev: Introspecting callables with the Signature object,  Up: inspect — Inspect live objects

5.29.13.4 Classes and functions
...............................

 -- Function: inspect.getclasstree (classes, unique=False)

     Arrange the given list of classes into a hierarchy of nested lists.
     Where a nested list appears, it contains classes derived from the
     class whose entry immediately precedes the list.  Each entry is a
     2-tuple containing a class and a tuple of its base classes.  If the
     `unique' argument is true, exactly one entry appears in the
     returned structure for each class in the given list.  Otherwise,
     classes using multiple inheritance and their descendants will
     appear multiple times.

 -- Function: inspect.getargspec (func)

     Get the names and default values of a Python function’s parameters.
     A *note named tuple: b7b. ‘ArgSpec(args, varargs, keywords,
     defaults)’ is returned.  `args' is a list of the parameter names.
     `varargs' and `keywords' are the names of the ‘*’ and ‘**’
     parameters or ‘None’.  `defaults' is a tuple of default argument
     values or ‘None’ if there are no default arguments; if this tuple
     has `n' elements, they correspond to the last `n' elements listed
     in `args'.

     Deprecated since version 3.0: Use *note getfullargspec(): 657. for
     an updated API that is usually a drop-in replacement, but also
     correctly handles function annotations and keyword-only parameters.

     Alternatively, use *note signature(): 655. and *note Signature
     Object: 385e, which provide a more structured introspection API for
     callables.

 -- Function: inspect.getfullargspec (func)

     Get the names and default values of a Python function’s parameters.
     A *note named tuple: b7b. is returned:

     ‘FullArgSpec(args, varargs, varkw, defaults, kwonlyargs,
     kwonlydefaults, annotations)’

     `args' is a list of the positional parameter names.  `varargs' is
     the name of the ‘*’ parameter or ‘None’ if arbitrary positional
     arguments are not accepted.  `varkw' is the name of the ‘**’
     parameter or ‘None’ if arbitrary keyword arguments are not
     accepted.  `defaults' is an `n'-tuple of default argument values
     corresponding to the last `n' positional parameters, or ‘None’ if
     there are no such defaults defined.  `kwonlyargs' is a list of
     keyword-only parameter names in declaration order.
     `kwonlydefaults' is a dictionary mapping parameter names from
     `kwonlyargs' to the default values used if no argument is supplied.
     `annotations' is a dictionary mapping parameter names to
     annotations.  The special key ‘"return"’ is used to report the
     function return value annotation (if any).

     Note that *note signature(): 655. and *note Signature Object: 385e.
     provide the recommended API for callable introspection, and support
     additional behaviours (like positional-only arguments) that are
     sometimes encountered in extension module APIs.  This function is
     retained primarily for use in code that needs to maintain
     compatibility with the Python 2 ‘inspect’ module API.

     Changed in version 3.4: This function is now based on *note
     signature(): 655, but still ignores ‘__wrapped__’ attributes and
     includes the already bound first parameter in the signature output
     for bound methods.

     Changed in version 3.6: This method was previously documented as
     deprecated in favour of *note signature(): 655. in Python 3.5, but
     that decision has been reversed in order to restore a clearly
     supported standard interface for single-source Python 2/3 code
     migrating away from the legacy *note getargspec(): 656. API.

     Changed in version 3.7: Python only explicitly guaranteed that it
     preserved the declaration order of keyword-only parameters as of
     version 3.7, although in practice this order had always been
     preserved in Python 3.

 -- Function: inspect.getargvalues (frame)

     Get information about arguments passed into a particular frame.  A
     *note named tuple: b7b. ‘ArgInfo(args, varargs, keywords, locals)’
     is returned.  `args' is a list of the argument names.  `varargs'
     and `keywords' are the names of the ‘*’ and ‘**’ arguments or
     ‘None’.  `locals' is the locals dictionary of the given frame.

          Note: This function was inadvertently marked as deprecated in
          Python 3.5.

 -- Function: inspect.formatargspec (args[, varargs, varkw, defaults,
          kwonlyargs, kwonlydefaults, annotations[, formatarg,
          formatvarargs, formatvarkw, formatvalue, formatreturns,
          formatannotations]])

     Format a pretty argument spec from the values returned by *note
     getfullargspec(): 657.

     The first seven arguments are (‘args’, ‘varargs’, ‘varkw’,
     ‘defaults’, ‘kwonlyargs’, ‘kwonlydefaults’, ‘annotations’).

     The other six arguments are functions that are called to turn
     argument names, ‘*’ argument name, ‘**’ argument name, default
     values, return annotation and individual annotations into strings,
     respectively.

     For example:

          >>> from inspect import formatargspec, getfullargspec
          >>> def f(a: int, b: float):
          ...     pass
          ...
          >>> formatargspec(*getfullargspec(f))
          '(a: int, b: float)'

     Deprecated since version 3.5: Use *note signature(): 655. and *note
     Signature Object: 385e, which provide a better introspecting API
     for callables.

 -- Function: inspect.formatargvalues (args[, varargs, varkw, locals,
          formatarg, formatvarargs, formatvarkw, formatvalue])

     Format a pretty argument spec from the four values returned by
     *note getargvalues(): 8a6.  The format* arguments are the
     corresponding optional formatting functions that are called to turn
     names and values into strings.

          Note: This function was inadvertently marked as deprecated in
          Python 3.5.

 -- Function: inspect.getmro (cls)

     Return a tuple of class cls’s base classes, including cls, in
     method resolution order.  No class appears more than once in this
     tuple.  Note that the method resolution order depends on cls’s
     type.  Unless a very peculiar user-defined metatype is in use, cls
     will be the first element of the tuple.

 -- Function: inspect.getcallargs (func, /, *args, **kwds)

     Bind the `args' and `kwds' to the argument names of the Python
     function or method `func', as if it was called with them.  For
     bound methods, bind also the first argument (typically named
     ‘self’) to the associated instance.  A dict is returned, mapping
     the argument names (including the names of the ‘*’ and ‘**’
     arguments, if any) to their values from `args' and `kwds'.  In case
     of invoking `func' incorrectly, i.e.  whenever ‘func(*args,
     **kwds)’ would raise an exception because of incompatible
     signature, an exception of the same type and the same or similar
     message is raised.  For example:

          >>> from inspect import getcallargs
          >>> def f(a, b=1, *pos, **named):
          ...     pass
          >>> getcallargs(f, 1, 2, 3) == {'a': 1, 'named': {}, 'b': 2, 'pos': (3,)}
          True
          >>> getcallargs(f, a=2, x=4) == {'a': 2, 'named': {'x': 4}, 'b': 1, 'pos': ()}
          True
          >>> getcallargs(f)
          Traceback (most recent call last):
          ...
          TypeError: f() missing 1 required positional argument: 'a'

     New in version 3.2.

     Deprecated since version 3.5: Use *note Signature.bind(): 3863. and
     *note Signature.bind_partial(): 3864. instead.

 -- Function: inspect.getclosurevars (func)

     Get the mapping of external name references in a Python function or
     method `func' to their current values.  A *note named tuple: b7b.
     ‘ClosureVars(nonlocals, globals, builtins, unbound)’ is returned.
     `nonlocals' maps referenced names to lexical closure variables,
     `globals' to the function’s module globals and `builtins' to the
     builtins visible from the function body.  `unbound' is the set of
     names referenced in the function that could not be resolved at all
     given the current module globals and builtins.

     *note TypeError: 1fe. is raised if `func' is not a Python function
     or method.

     New in version 3.3.

 -- Function: inspect.unwrap (func, *, stop=None)

     Get the object wrapped by `func'.  It follows the chain of
     ‘__wrapped__’ attributes returning the last object in the chain.

     `stop' is an optional callback accepting an object in the wrapper
     chain as its sole argument that allows the unwrapping to be
     terminated early if the callback returns a true value.  If the
     callback never returns a true value, the last object in the chain
     is returned as usual.  For example, *note signature(): 655. uses
     this to stop unwrapping if any object in the chain has a
     ‘__signature__’ attribute defined.

     *note ValueError: 16d. is raised if a cycle is encountered.

     New in version 3.4.


File: python.info,  Node: The interpreter stack,  Next: Fetching attributes statically,  Prev: Classes and functions<2>,  Up: inspect — Inspect live objects

5.29.13.5 The interpreter stack
...............................

When the following functions return “frame records,” each record is a
*note named tuple: b7b. ‘FrameInfo(frame, filename, lineno, function,
code_context, index)’.  The tuple contains the frame object, the
filename, the line number of the current line, the function name, a list
of lines of context from the source code, and the index of the current
line within that list.

Changed in version 3.5: Return a named tuple instead of a tuple.

     Note: Keeping references to frame objects, as found in the first
     element of the frame records these functions return, can cause your
     program to create reference cycles.  Once a reference cycle has
     been created, the lifespan of all objects which can be accessed
     from the objects which form the cycle can become much longer even
     if Python’s optional cycle detector is enabled.  If such cycles
     must be created, it is important to ensure they are explicitly
     broken to avoid the delayed destruction of objects and increased
     memory consumption which occurs.

     Though the cycle detector will catch these, destruction of the
     frames (and local variables) can be made deterministic by removing
     the cycle in a *note finally: 2bc. clause.  This is also important
     if the cycle detector was disabled when Python was compiled or
     using *note gc.disable(): 3837.  For example:

          def handle_stackframe_without_leak():
              frame = inspect.currentframe()
              try:
                  # do something with the frame
              finally:
                  del frame

     If you want to keep the frame around (for example to print a
     traceback later), you can also break reference cycles by using the
     *note frame.clear(): 8f8. method.

The optional `context' argument supported by most of these functions
specifies the number of lines of context to return, which are centered
around the current line.

 -- Function: inspect.getframeinfo (frame, context=1)

     Get information about a frame or traceback object.  A *note named
     tuple: b7b. ‘Traceback(filename, lineno, function, code_context,
     index)’ is returned.

 -- Function: inspect.getouterframes (frame, context=1)

     Get a list of frame records for a frame and all outer frames.
     These frames represent the calls that lead to the creation of
     `frame'.  The first entry in the returned list represents `frame';
     the last entry represents the outermost call on `frame'’s stack.

     Changed in version 3.5: A list of *note named tuples: b7b.
     ‘FrameInfo(frame, filename, lineno, function, code_context, index)’
     is returned.

 -- Function: inspect.getinnerframes (traceback, context=1)

     Get a list of frame records for a traceback’s frame and all inner
     frames.  These frames represent calls made as a consequence of
     `frame'.  The first entry in the list represents `traceback'; the
     last entry represents where the exception was raised.

     Changed in version 3.5: A list of *note named tuples: b7b.
     ‘FrameInfo(frame, filename, lineno, function, code_context, index)’
     is returned.

 -- Function: inspect.currentframe ()

     Return the frame object for the caller’s stack frame.

     `CPython implementation detail:' This function relies on Python
     stack frame support in the interpreter, which isn’t guaranteed to
     exist in all implementations of Python.  If running in an
     implementation without Python stack frame support this function
     returns ‘None’.

 -- Function: inspect.stack (context=1)

     Return a list of frame records for the caller’s stack.  The first
     entry in the returned list represents the caller; the last entry
     represents the outermost call on the stack.

     Changed in version 3.5: A list of *note named tuples: b7b.
     ‘FrameInfo(frame, filename, lineno, function, code_context, index)’
     is returned.

 -- Function: inspect.trace (context=1)

     Return a list of frame records for the stack between the current
     frame and the frame in which an exception currently being handled
     was raised in.  The first entry in the list represents the caller;
     the last entry represents where the exception was raised.

     Changed in version 3.5: A list of *note named tuples: b7b.
     ‘FrameInfo(frame, filename, lineno, function, code_context, index)’
     is returned.


File: python.info,  Node: Fetching attributes statically,  Next: Current State of Generators and Coroutines,  Prev: The interpreter stack,  Up: inspect — Inspect live objects

5.29.13.6 Fetching attributes statically
........................................

Both *note getattr(): 54b. and *note hasattr(): 54a. can trigger code
execution when fetching or checking for the existence of attributes.
Descriptors, like properties, will be invoked and *note __getattr__():
42a. and *note __getattribute__(): 54c. may be called.

For cases where you want passive introspection, like documentation
tools, this can be inconvenient.  *note getattr_static(): c99. has the
same signature as *note getattr(): 54b. but avoids executing code when
it fetches attributes.

 -- Function: inspect.getattr_static (obj, attr, default=None)

     Retrieve attributes without triggering dynamic lookup via the
     descriptor protocol, *note __getattr__(): 42a. or *note
     __getattribute__(): 54c.

     Note: this function may not be able to retrieve all attributes that
     getattr can fetch (like dynamically created attributes) and may
     find attributes that getattr can’t (like descriptors that raise
     AttributeError).  It can also return descriptors objects instead of
     instance members.

     If the instance *note __dict__: 5f6. is shadowed by another member
     (for example a property) then this function will be unable to find
     instance members.

     New in version 3.2.

*note getattr_static(): c99. does not resolve descriptors, for example
slot descriptors or getset descriptors on objects implemented in C. The
descriptor object is returned instead of the underlying attribute.

You can handle these with code like the following.  Note that for
arbitrary getset descriptors invoking these may trigger code execution:

     # example code for resolving the builtin descriptor types
     class _foo:
         __slots__ = ['foo']

     slot_descriptor = type(_foo.foo)
     getset_descriptor = type(type(open(__file__)).name)
     wrapper_descriptor = type(str.__dict__['__add__'])
     descriptor_types = (slot_descriptor, getset_descriptor, wrapper_descriptor)

     result = getattr_static(some_object, 'foo')
     if type(result) in descriptor_types:
         try:
             result = result.__get__()
         except AttributeError:
             # descriptors can raise AttributeError to
             # indicate there is no underlying value
             # in which case the descriptor itself will
             # have to do
             pass


File: python.info,  Node: Current State of Generators and Coroutines,  Next: Code Objects Bit Flags,  Prev: Fetching attributes statically,  Up: inspect — Inspect live objects

5.29.13.7 Current State of Generators and Coroutines
....................................................

When implementing coroutine schedulers and for other advanced uses of
generators, it is useful to determine whether a generator is currently
executing, is waiting to start or resume or execution, or has already
terminated.  *note getgeneratorstate(): c98. allows the current state of
a generator to be determined easily.

 -- Function: inspect.getgeneratorstate (generator)

     Get current state of a generator-iterator.

     Possible states are:

             * GEN_CREATED: Waiting to start execution.

             * GEN_RUNNING: Currently being executed by the interpreter.

             * GEN_SUSPENDED: Currently suspended at a yield expression.

             * GEN_CLOSED: Execution has completed.

     New in version 3.2.

 -- Function: inspect.getcoroutinestate (coroutine)

     Get current state of a coroutine object.  The function is intended
     to be used with coroutine objects created by *note async def: 3a9.
     functions, but will accept any coroutine-like object that has
     ‘cr_running’ and ‘cr_frame’ attributes.

     Possible states are:

             * CORO_CREATED: Waiting to start execution.

             * CORO_RUNNING: Currently being executed by the
               interpreter.

             * CORO_SUSPENDED: Currently suspended at an await
               expression.

             * CORO_CLOSED: Execution has completed.

     New in version 3.5.

The current internal state of the generator can also be queried.  This
is mostly useful for testing purposes, to ensure that internal state is
being updated as expected:

 -- Function: inspect.getgeneratorlocals (generator)

     Get the mapping of live local variables in `generator' to their
     current values.  A dictionary is returned that maps from variable
     names to values.  This is the equivalent of calling *note locals():
     557. in the body of the generator, and all the same caveats apply.

     If `generator' is a *note generator: a83. with no currently
     associated frame, then an empty dictionary is returned.  *note
     TypeError: 1fe. is raised if `generator' is not a Python generator
     object.

     `CPython implementation detail:' This function relies on the
     generator exposing a Python stack frame for introspection, which
     isn’t guaranteed to be the case in all implementations of Python.
     In such cases, this function will always return an empty
     dictionary.

     New in version 3.3.

 -- Function: inspect.getcoroutinelocals (coroutine)

     This function is analogous to *note getgeneratorlocals(): af7, but
     works for coroutine objects created by *note async def: 3a9.
     functions.

     New in version 3.5.


File: python.info,  Node: Code Objects Bit Flags,  Next: Command Line Interface<3>,  Prev: Current State of Generators and Coroutines,  Up: inspect — Inspect live objects

5.29.13.8 Code Objects Bit Flags
................................

Python code objects have a ‘co_flags’ attribute, which is a bitmap of
the following flags:

 -- Data: inspect.CO_OPTIMIZED

     The code object is optimized, using fast locals.

 -- Data: inspect.CO_NEWLOCALS

     If set, a new dict will be created for the frame’s ‘f_locals’ when
     the code object is executed.

 -- Data: inspect.CO_VARARGS

     The code object has a variable positional parameter (‘*args’-like).

 -- Data: inspect.CO_VARKEYWORDS

     The code object has a variable keyword parameter (‘**kwargs’-like).

 -- Data: inspect.CO_NESTED

     The flag is set when the code object is a nested function.

 -- Data: inspect.CO_GENERATOR

     The flag is set when the code object is a generator function, i.e.
     a generator object is returned when the code object is executed.

 -- Data: inspect.CO_NOFREE

     The flag is set if there are no free or cell variables.

 -- Data: inspect.CO_COROUTINE

     The flag is set when the code object is a coroutine function.  When
     the code object is executed it returns a coroutine object.  See PEP
     492(1) for more details.

     New in version 3.5.

 -- Data: inspect.CO_ITERABLE_COROUTINE

     The flag is used to transform generators into generator-based
     coroutines.  Generator objects with this flag can be used in
     ‘await’ expression, and can ‘yield from’ coroutine objects.  See
     PEP 492(2) for more details.

     New in version 3.5.

 -- Data: inspect.CO_ASYNC_GENERATOR

     The flag is set when the code object is an asynchronous generator
     function.  When the code object is executed it returns an
     asynchronous generator object.  See PEP 525(3) for more details.

     New in version 3.6.

     Note: The flags are specific to CPython, and may not be defined in
     other Python implementations.  Furthermore, the flags are an
     implementation detail, and can be removed or deprecated in future
     Python releases.  It’s recommended to use public APIs from the
     *note inspect: a0. module for any introspection needs.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0492

   (2) https://www.python.org/dev/peps/pep-0492

   (3) https://www.python.org/dev/peps/pep-0525


File: python.info,  Node: Command Line Interface<3>,  Prev: Code Objects Bit Flags,  Up: inspect — Inspect live objects

5.29.13.9 Command Line Interface
................................

The *note inspect: a0. module also provides a basic introspection
capability from the command line.

By default, accepts the name of a module and prints the source of that
module.  A class or function within the module can be printed instead by
appended a colon and the qualified name of the target object.

 -- Program Option: --details

     Print information about the specified object rather than the source
     code


File: python.info,  Node: site — Site-specific configuration hook,  Prev: inspect — Inspect live objects,  Up: Python Runtime Services

5.29.14 ‘site’ — Site-specific configuration hook
-------------------------------------------------

`Source code:' Lib/site.py(1)

__________________________________________________________________

`This module is automatically imported during initialization.'  The
automatic import can be suppressed using the interpreter’s *note -S:
bf7. option.

Importing this module will append site-specific paths to the module
search path and add a few builtins, unless *note -S: bf7. was used.  In
that case, this module can be safely imported with no automatic
modifications to the module search path or additions to the builtins.
To explicitly trigger the usual site-specific additions, call the *note
site.main(): 147b. function.

Changed in version 3.3: Importing the module used to trigger paths
manipulation even when using *note -S: bf7.

It starts by constructing up to four directories from a head and a tail
part.  For the head part, it uses ‘sys.prefix’ and ‘sys.exec_prefix’;
empty heads are skipped.  For the tail part, it uses the empty string
and then ‘lib/site-packages’ (on Windows) or
‘lib/python`X.Y'/site-packages’ (on Unix and macOS). For each of the
distinct head-tail combinations, it sees if it refers to an existing
directory, and if so, adds it to ‘sys.path’ and also inspects the newly
added path for configuration files.

Changed in version 3.5: Support for the “site-python” directory has been
removed.

If a file named “pyvenv.cfg” exists one directory above sys.executable,
sys.prefix and sys.exec_prefix are set to that directory and it is also
checked for site-packages (sys.base_prefix and sys.base_exec_prefix will
always be the “real” prefixes of the Python installation).  If
“pyvenv.cfg” (a bootstrap configuration file) contains the key
“include-system-site-packages” set to anything other than “true”
(case-insensitive), the system-level prefixes will not be searched for
site-packages; otherwise they will.

A path configuration file is a file whose name has the form ‘`name'.pth’
and exists in one of the four directories mentioned above; its contents
are additional items (one per line) to be added to ‘sys.path’.
Non-existing items are never added to ‘sys.path’, and no check is made
that the item refers to a directory rather than a file.  No item is
added to ‘sys.path’ more than once.  Blank lines and lines beginning
with ‘#’ are skipped.  Lines starting with ‘import’ (followed by space
or tab) are executed.

     Note: An executable line in a ‘.pth’ file is run at every Python
     startup, regardless of whether a particular module is actually
     going to be used.  Its impact should thus be kept to a minimum.
     The primary intended purpose of executable lines is to make the
     corresponding module(s) importable (load 3rd-party import hooks,
     adjust ‘PATH’ etc).  Any other initialization is supposed to be
     done upon a module’s actual import, if and when it happens.
     Limiting a code chunk to a single line is a deliberate measure to
     discourage putting anything more complex here.

For example, suppose ‘sys.prefix’ and ‘sys.exec_prefix’ are set to
‘/usr/local’.  The Python X.Y library is then installed in
‘/usr/local/lib/python`X.Y'’.  Suppose this has a subdirectory
‘/usr/local/lib/python`X.Y'/site-packages’ with three subsubdirectories,
‘foo’, ‘bar’ and ‘spam’, and two path configuration files, ‘foo.pth’ and
‘bar.pth’.  Assume ‘foo.pth’ contains the following:

     # foo package configuration

     foo
     bar
     bletch

and ‘bar.pth’ contains:

     # bar package configuration

     bar

Then the following version-specific directories are added to ‘sys.path’,
in this order:

     /usr/local/lib/pythonX.Y/site-packages/bar
     /usr/local/lib/pythonX.Y/site-packages/foo

Note that ‘bletch’ is omitted because it doesn’t exist; the ‘bar’
directory precedes the ‘foo’ directory because ‘bar.pth’ comes
alphabetically before ‘foo.pth’; and ‘spam’ is omitted because it is not
mentioned in either path configuration file.

After these path manipulations, an attempt is made to import a module
named ‘sitecustomize’, which can perform arbitrary site-specific
customizations.  It is typically created by a system administrator in
the site-packages directory.  If this import fails with an *note
ImportError: 16c. or its subclass exception, and the exception’s ‘name’
attribute equals to ‘'sitecustomize'’, it is silently ignored.  If
Python is started without output streams available, as with
‘pythonw.exe’ on Windows (which is used by default to start IDLE),
attempted output from ‘sitecustomize’ is ignored.  Any other exception
causes a silent and perhaps mysterious failure of the process.

After this, an attempt is made to import a module named ‘usercustomize’,
which can perform arbitrary user-specific customizations, if *note
ENABLE_USER_SITE: 3888. is true.  This file is intended to be created in
the user site-packages directory (see below), which is part of
‘sys.path’ unless disabled by *note -s: ddb.  If this import fails with
an *note ImportError: 16c. or its subclass exception, and the
exception’s ‘name’ attribute equals to ‘'usercustomize'’, it is silently
ignored.

Note that for some non-Unix systems, ‘sys.prefix’ and ‘sys.exec_prefix’
are empty, and the path manipulations are skipped; however the import of
‘sitecustomize’ and ‘usercustomize’ is still attempted.

* Menu:

* Readline configuration::
* Module contents: Module contents<4>.
* Command Line Interface: Command Line Interface<4>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/site.py


File: python.info,  Node: Readline configuration,  Next: Module contents<4>,  Up: site — Site-specific configuration hook

5.29.14.1 Readline configuration
................................

On systems that support *note readline: de, this module will also import
and configure the *note rlcompleter: e1. module, if Python is started in
*note interactive mode: 9c9. and without the *note -S: bf7. option.  The
default behavior is enable tab-completion and to use ‘~/.python_history’
as the history save file.  To disable it, delete (or override) the *note
sys.__interactivehook__: 9ca. attribute in your ‘sitecustomize’ or
‘usercustomize’ module or your *note PYTHONSTARTUP: 9cb. file.

Changed in version 3.4: Activation of rlcompleter and history was made
automatic.


File: python.info,  Node: Module contents<4>,  Next: Command Line Interface<4>,  Prev: Readline configuration,  Up: site — Site-specific configuration hook

5.29.14.2 Module contents
.........................

 -- Data: site.PREFIXES

     A list of prefixes for site-packages directories.

 -- Data: site.ENABLE_USER_SITE

     Flag showing the status of the user site-packages directory.
     ‘True’ means that it is enabled and was added to ‘sys.path’.
     ‘False’ means that it was disabled by user request (with *note -s:
     ddb. or *note PYTHONNOUSERSITE: ddc.).  ‘None’ means it was
     disabled for security reasons (mismatch between user or group id
     and effective id) or by an administrator.

 -- Data: site.USER_SITE

     Path to the user site-packages for the running Python.  Can be
     ‘None’ if *note getusersitepackages(): ca3. hasn’t been called yet.
     Default value is ‘~/.local/lib/python`X.Y'/site-packages’ for UNIX
     and non-framework macOS builds,
     ‘~/Library/Python/`X.Y'/lib/python/site-packages’ for macOS
     framework builds, and ‘`%APPDATA%'\Python\Python`XY'\site-packages’
     on Windows.  This directory is a site directory, which means that
     ‘.pth’ files in it will be processed.

 -- Data: site.USER_BASE

     Path to the base directory for the user site-packages.  Can be
     ‘None’ if *note getuserbase(): ca2. hasn’t been called yet.
     Default value is ‘~/.local’ for UNIX and macOS non-framework
     builds, ‘~/Library/Python/`X.Y'’ for macOS framework builds, and
     ‘`%APPDATA%'\Python’ for Windows.  This value is used by Distutils
     to compute the installation directories for scripts, data files,
     Python modules, etc.  for the *note user installation scheme: 148a.
     See also *note PYTHONUSERBASE: dda.

 -- Function: site.main ()

     Adds all the standard site-specific directories to the module
     search path.  This function is called automatically when this
     module is imported, unless the Python interpreter was started with
     the *note -S: bf7. flag.

     Changed in version 3.3: This function used to be called
     unconditionally.

 -- Function: site.addsitedir (sitedir, known_paths=None)

     Add a directory to sys.path and process its ‘.pth’ files.
     Typically used in ‘sitecustomize’ or ‘usercustomize’ (see above).

 -- Function: site.getsitepackages ()

     Return a list containing all global site-packages directories.

     New in version 3.2.

 -- Function: site.getuserbase ()

     Return the path of the user base directory, *note USER_BASE: 1489.
     If it is not initialized yet, this function will also set it,
     respecting *note PYTHONUSERBASE: dda.

     New in version 3.2.

 -- Function: site.getusersitepackages ()

     Return the path of the user-specific site-packages directory, *note
     USER_SITE: 147a.  If it is not initialized yet, this function will
     also set it, respecting *note USER_BASE: 1489.  To determine if the
     user-specific site-packages was added to ‘sys.path’ *note
     ENABLE_USER_SITE: 3888. should be used.

     New in version 3.2.


File: python.info,  Node: Command Line Interface<4>,  Prev: Module contents<4>,  Up: site — Site-specific configuration hook

5.29.14.3 Command Line Interface
................................

The *note site: eb. module also provides a way to get the user
directories from the command line:

     $ python3 -m site --user-site
     /home/user/.local/lib/python3.3/site-packages

If it is called without arguments, it will print the contents of *note
sys.path: 260. on the standard output, followed by the value of *note
USER_BASE: 1489. and whether the directory exists, then the same thing
for *note USER_SITE: 147a, and finally the value of *note
ENABLE_USER_SITE: 3888.

 -- Program Option: --user-base

     Print the path to the user base directory.

 -- Program Option: --user-site

     Print the path to the user site-packages directory.

If both options are given, user base and user site will be printed
(always in this order), separated by *note os.pathsep: 1486.

If any option is given, the script will exit with one of these values:
‘0’ if the user site-packages directory is enabled, ‘1’ if it was
disabled by the user, ‘2’ if it is disabled for security reasons or by
an administrator, and a value greater than 2 if there is an error.

See also
........

PEP 370(1) – Per user site-packages directory

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0370


File: python.info,  Node: Custom Python Interpreters,  Next: Importing Modules,  Prev: Python Runtime Services,  Up: The Python Standard Library

5.30 Custom Python Interpreters
===============================

The modules described in this chapter allow writing interfaces similar
to Python’s interactive interpreter.  If you want a Python interpreter
that supports some special feature in addition to the Python language,
you should look at the *note code: 1a. module.  (The *note codeop: 1c.
module is lower-level, used to support compiling a possibly-incomplete
chunk of Python code.)

The full list of modules described in this chapter is:

* Menu:

* code — Interpreter base classes::
* codeop — Compile Python code::


File: python.info,  Node: code — Interpreter base classes,  Next: codeop — Compile Python code,  Up: Custom Python Interpreters

5.30.1 ‘code’ — Interpreter base classes
----------------------------------------

`Source code:' Lib/code.py(1)

__________________________________________________________________

The ‘code’ module provides facilities to implement read-eval-print loops
in Python.  Two classes and convenience functions are included which can
be used to build applications which provide an interactive interpreter
prompt.

 -- Class: code.InteractiveInterpreter (locals=None)

     This class deals with parsing and interpreter state (the user’s
     namespace); it does not deal with input buffering or prompting or
     input file naming (the filename is always passed in explicitly).
     The optional `locals' argument specifies the dictionary in which
     code will be executed; it defaults to a newly created dictionary
     with key ‘'__name__'’ set to ‘'__console__'’ and key ‘'__doc__'’
     set to ‘None’.

 -- Class: code.InteractiveConsole (locals=None, filename="<console>")

     Closely emulate the behavior of the interactive Python interpreter.
     This class builds on *note InteractiveInterpreter: 3896. and adds
     prompting using the familiar ‘sys.ps1’ and ‘sys.ps2’, and input
     buffering.

 -- Function: code.interact (banner=None, readfunc=None, local=None,
          exitmsg=None)

     Convenience function to run a read-eval-print loop.  This creates a
     new instance of *note InteractiveConsole: 1944. and sets `readfunc'
     to be used as the *note InteractiveConsole.raw_input(): 3898.
     method, if provided.  If `local' is provided, it is passed to the
     *note InteractiveConsole: 1944. constructor for use as the default
     namespace for the interpreter loop.  The *note interact(): 3897.
     method of the instance is then run with `banner' and `exitmsg'
     passed as the banner and exit message to use, if provided.  The
     console object is discarded after use.

     Changed in version 3.6: Added `exitmsg' parameter.

 -- Function: code.compile_command (source, filename="<input>",
          symbol="single")

     This function is useful for programs that want to emulate Python’s
     interpreter main loop (a.k.a.  the read-eval-print loop).  The
     tricky part is to determine when the user has entered an incomplete
     command that can be completed by entering more text (as opposed to
     a complete command or a syntax error).  This function `almost'
     always makes the same decision as the real interpreter main loop.

     `source' is the source string; `filename' is the optional filename
     from which source was read, defaulting to ‘'<input>'’; and `symbol'
     is the optional grammar start symbol, which should be ‘'single'’
     (the default), ‘'eval'’ or ‘'exec'’.

     Returns a code object (the same as ‘compile(source, filename,
     symbol)’) if the command is complete and valid; ‘None’ if the
     command is incomplete; raises *note SyntaxError: 55a. if the
     command is complete and contains a syntax error, or raises *note
     OverflowError: a41. or *note ValueError: 16d. if the command
     contains an invalid literal.

* Menu:

* Interactive Interpreter Objects::
* Interactive Console Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/code.py


File: python.info,  Node: Interactive Interpreter Objects,  Next: Interactive Console Objects,  Up: code — Interpreter base classes

5.30.1.1 Interactive Interpreter Objects
........................................

 -- Method: InteractiveInterpreter.runsource (source,
          filename="<input>", symbol="single")

     Compile and run some source in the interpreter.  Arguments are the
     same as for *note compile_command(): 3899.; the default for
     `filename' is ‘'<input>'’, and for `symbol' is ‘'single'’.  One of
     several things can happen:

        * The input is incorrect; *note compile_command(): 3899. raised
          an exception (*note SyntaxError: 55a. or *note OverflowError:
          a41.).  A syntax traceback will be printed by calling the
          *note showsyntaxerror(): 389d. method.  *note runsource():
          389c. returns ‘False’.

        * The input is incomplete, and more input is required; *note
          compile_command(): 3899. returned ‘None’.  *note runsource():
          389c. returns ‘True’.

        * The input is complete; *note compile_command(): 3899. returned
          a code object.  The code is executed by calling the *note
          runcode(): 389e. (which also handles run-time exceptions,
          except for *note SystemExit: 6f3.).  *note runsource(): 389c.
          returns ‘False’.

     The return value can be used to decide whether to use ‘sys.ps1’ or
     ‘sys.ps2’ to prompt the next line.

 -- Method: InteractiveInterpreter.runcode (code)

     Execute a code object.  When an exception occurs, *note
     showtraceback(): 79a. is called to display a traceback.  All
     exceptions are caught except *note SystemExit: 6f3, which is
     allowed to propagate.

     A note about *note KeyboardInterrupt: 2cc.: this exception may
     occur elsewhere in this code, and may not always be caught.  The
     caller should be prepared to deal with it.

 -- Method: InteractiveInterpreter.showsyntaxerror (filename=None)

     Display the syntax error that just occurred.  This does not display
     a stack trace because there isn’t one for syntax errors.  If
     `filename' is given, it is stuffed into the exception instead of
     the default filename provided by Python’s parser, because it always
     uses ‘'<string>'’ when reading from a string.  The output is
     written by the *note write(): 389f. method.

 -- Method: InteractiveInterpreter.showtraceback ()

     Display the exception that just occurred.  We remove the first
     stack item because it is within the interpreter object
     implementation.  The output is written by the *note write(): 389f.
     method.

     Changed in version 3.5: The full chained traceback is displayed
     instead of just the primary traceback.

 -- Method: InteractiveInterpreter.write (data)

     Write a string to the standard error stream (‘sys.stderr’).
     Derived classes should override this to provide the appropriate
     output handling as needed.


File: python.info,  Node: Interactive Console Objects,  Prev: Interactive Interpreter Objects,  Up: code — Interpreter base classes

5.30.1.2 Interactive Console Objects
....................................

The *note InteractiveConsole: 1944. class is a subclass of *note
InteractiveInterpreter: 3896, and so offers all the methods of the
interpreter objects as well as the following additions.

 -- Method: InteractiveConsole.interact (banner=None, exitmsg=None)

     Closely emulate the interactive Python console.  The optional
     `banner' argument specify the banner to print before the first
     interaction; by default it prints a banner similar to the one
     printed by the standard Python interpreter, followed by the class
     name of the console object in parentheses (so as not to confuse
     this with the real interpreter – since it’s so close!).

     The optional `exitmsg' argument specifies an exit message printed
     when exiting.  Pass the empty string to suppress the exit message.
     If `exitmsg' is not given or ‘None’, a default message is printed.

     Changed in version 3.4: To suppress printing any banner, pass an
     empty string.

     Changed in version 3.6: Print an exit message when exiting.

 -- Method: InteractiveConsole.push (line)

     Push a line of source text to the interpreter.  The line should not
     have a trailing newline; it may have internal newlines.  The line
     is appended to a buffer and the interpreter’s ‘runsource()’ method
     is called with the concatenated contents of the buffer as source.
     If this indicates that the command was executed or invalid, the
     buffer is reset; otherwise, the command is incomplete, and the
     buffer is left as it was after the line was appended.  The return
     value is ‘True’ if more input is required, ‘False’ if the line was
     dealt with in some way (this is the same as ‘runsource()’).

 -- Method: InteractiveConsole.resetbuffer ()

     Remove any unhandled source text from the input buffer.

 -- Method: InteractiveConsole.raw_input (prompt="")

     Write a prompt and read a line.  The returned line does not include
     the trailing newline.  When the user enters the EOF key sequence,
     *note EOFError: d34. is raised.  The base implementation reads from
     ‘sys.stdin’; a subclass may replace this with a different
     implementation.


File: python.info,  Node: codeop — Compile Python code,  Prev: code — Interpreter base classes,  Up: Custom Python Interpreters

5.30.2 ‘codeop’ — Compile Python code
-------------------------------------

`Source code:' Lib/codeop.py(1)

__________________________________________________________________

The *note codeop: 1c. module provides utilities upon which the Python
read-eval-print loop can be emulated, as is done in the *note code: 1a.
module.  As a result, you probably don’t want to use the module
directly; if you want to include such a loop in your program you
probably want to use the *note code: 1a. module instead.

There are two parts to this job:

  1. Being able to tell if a line of input completes a Python statement:
     in short, telling whether to print ‘‘>>>’’ or ‘‘...’’ next.

  2. Remembering which future statements the user has entered, so
     subsequent input can be compiled with these in effect.

The *note codeop: 1c. module provides a way of doing each of these
things, and a way of doing them both.

To do just the former:

 -- Function: codeop.compile_command (source, filename="<input>",
          symbol="single")

     Tries to compile `source', which should be a string of Python code
     and return a code object if `source' is valid Python code.  In that
     case, the filename attribute of the code object will be `filename',
     which defaults to ‘'<input>'’.  Returns ‘None’ if `source' is `not'
     valid Python code, but is a prefix of valid Python code.

     If there is a problem with `source', an exception will be raised.
     *note SyntaxError: 55a. is raised if there is invalid Python
     syntax, and *note OverflowError: a41. or *note ValueError: 16d. if
     there is an invalid literal.

     The `symbol' argument determines whether `source' is compiled as a
     statement (‘'single'’, the default), as a sequence of statements
     (‘'exec'’) or as an *note expression: 158f. (‘'eval'’).  Any other
     value will cause *note ValueError: 16d. to be raised.

          Note: It is possible (but not likely) that the parser stops
          parsing with a successful outcome before reaching the end of
          the source; in this case, trailing symbols may be ignored
          instead of causing an error.  For example, a backslash
          followed by two newlines may be followed by arbitrary garbage.
          This will be fixed once the API for the parser is better.

 -- Class: codeop.Compile

     Instances of this class have *note __call__(): 1560. methods
     identical in signature to the built-in function *note compile():
     2e7, but with the difference that if the instance compiles program
     text containing a *note __future__: 0. statement, the instance
     ‘remembers’ and compiles all subsequent program texts with the
     statement in force.

 -- Class: codeop.CommandCompiler

     Instances of this class have *note __call__(): 1560. methods
     identical in signature to *note compile_command(): 103c.; the
     difference is that if the instance compiles program text containing
     a ‘__future__’ statement, the instance ‘remembers’ and compiles all
     subsequent program texts with the statement in force.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/codeop.py


File: python.info,  Node: Importing Modules,  Next: Python Language Services,  Prev: Custom Python Interpreters,  Up: The Python Standard Library

5.31 Importing Modules
======================

The modules described in this chapter provide new ways to import other
Python modules and hooks for customizing the import process.

The full list of modules described in this chapter is:

* Menu:

* zipimport — Import modules from Zip archives::
* pkgutil — Package extension utility::
* modulefinder — Find modules used by a script::
* runpy — Locating and executing Python modules::
* importlib — The implementation of import::
* Using importlib.metadata: Using importlib metadata.


File: python.info,  Node: zipimport — Import modules from Zip archives,  Next: pkgutil — Package extension utility,  Up: Importing Modules

5.31.1 ‘zipimport’ — Import modules from Zip archives
-----------------------------------------------------

`Source code:' Lib/zipimport.py(1)

__________________________________________________________________

This module adds the ability to import Python modules (‘*.py’, ‘*.pyc’)
and packages from ZIP-format archives.  It is usually not needed to use
the *note zipimport: 14c. module explicitly; it is automatically used by
the built-in *note import: ce7. mechanism for *note sys.path: 260. items
that are paths to ZIP archives.

Typically, *note sys.path: 260. is a list of directory names as strings.
This module also allows an item of *note sys.path: 260. to be a string
naming a ZIP file archive.  The ZIP archive can contain a subdirectory
structure to support package imports, and a path within the archive can
be specified to only import from a subdirectory.  For example, the path
‘example.zip/lib/’ would only import from the ‘lib/’ subdirectory within
the archive.

Any files may be present in the ZIP archive, but importers are only
invoked for ‘.py’ and ‘.pyc’ files.  ZIP import of dynamic modules
(‘.pyd’, ‘.so’) is disallowed.  Note that if an archive only contains
‘.py’ files, Python will not attempt to modify the archive by adding the
corresponding ‘.pyc’ file, meaning that if a ZIP archive doesn’t contain
‘.pyc’ files, importing may be rather slow.

Changed in version 3.8: Previously, ZIP archives with an archive comment
were not supported.

See also
........

PKZIP Application Note(2)

     Documentation on the ZIP file format by Phil Katz, the creator of
     the format and algorithms used.

PEP 273(3) - Import Modules from Zip Archives

     Written by James C. Ahlstrom, who also provided an implementation.
     Python 2.3 follows the specification in PEP 273(4), but uses an
     implementation written by Just van Rossum that uses the import
     hooks described in PEP 302(5).

PEP 302(6) - New Import Hooks

     The PEP to add the import hooks that help this module work.

This module defines an exception:

 -- Exception: zipimport.ZipImportError

     Exception raised by zipimporter objects.  It’s a subclass of *note
     ImportError: 16c, so it can be caught as *note ImportError: 16c,
     too.

* Menu:

* zipimporter Objects::
* Examples: Examples<29>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/zipimport.py

   (2) https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT

   (3) https://www.python.org/dev/peps/pep-0273

   (4) https://www.python.org/dev/peps/pep-0273

   (5) https://www.python.org/dev/peps/pep-0302

   (6) https://www.python.org/dev/peps/pep-0302


File: python.info,  Node: zipimporter Objects,  Next: Examples<29>,  Up: zipimport — Import modules from Zip archives

5.31.1.1 zipimporter Objects
............................

*note zipimporter: 38b1. is the class for importing ZIP files.

 -- Class: zipimport.zipimporter (archivepath)

     Create a new zipimporter instance.  `archivepath' must be a path to
     a ZIP file, or to a specific path within a ZIP file.  For example,
     an `archivepath' of ‘foo/bar.zip/lib’ will look for modules in the
     ‘lib’ directory inside the ZIP file ‘foo/bar.zip’ (provided that it
     exists).

     *note ZipImportError: 38ae. is raised if `archivepath' doesn’t
     point to a valid ZIP archive.

      -- Method: find_module (fullname[, path])

          Search for a module specified by `fullname'.  `fullname' must
          be the fully qualified (dotted) module name.  It returns the
          zipimporter instance itself if the module was found, or *note
          None: 203. if it wasn’t.  The optional `path' argument is
          ignored—it’s there for compatibility with the importer
          protocol.

      -- Method: get_code (fullname)

          Return the code object for the specified module.  Raise *note
          ZipImportError: 38ae. if the module couldn’t be found.

      -- Method: get_data (pathname)

          Return the data associated with `pathname'.  Raise *note
          OSError: 304. if the file wasn’t found.

          Changed in version 3.3: *note IOError: a73. used to be raised
          instead of *note OSError: 304.

      -- Method: get_filename (fullname)

          Return the value ‘__file__’ would be set to if the specified
          module was imported.  Raise *note ZipImportError: 38ae. if the
          module couldn’t be found.

          New in version 3.1.

      -- Method: get_source (fullname)

          Return the source code for the specified module.  Raise *note
          ZipImportError: 38ae. if the module couldn’t be found, return
          *note None: 203. if the archive does contain the module, but
          has no source for it.

      -- Method: is_package (fullname)

          Return ‘True’ if the module specified by `fullname' is a
          package.  Raise *note ZipImportError: 38ae. if the module
          couldn’t be found.

      -- Method: load_module (fullname)

          Load the module specified by `fullname'.  `fullname' must be
          the fully qualified (dotted) module name.  It returns the
          imported module, or raises *note ZipImportError: 38ae. if it
          wasn’t found.

      -- Attribute: archive

          The file name of the importer’s associated ZIP file, without a
          possible subpath.

      -- Attribute: prefix

          The subpath within the ZIP file where modules are searched.
          This is the empty string for zipimporter objects which point
          to the root of the ZIP file.

     The *note archive: 38b8. and *note prefix: 38b9. attributes, when
     combined with a slash, equal the original `archivepath' argument
     given to the *note zipimporter: 38b1. constructor.


File: python.info,  Node: Examples<29>,  Prev: zipimporter Objects,  Up: zipimport — Import modules from Zip archives

5.31.1.2 Examples
.................

Here is an example that imports a module from a ZIP archive - note that
the *note zipimport: 14c. module is not explicitly used.

     $ unzip -l example.zip
     Archive:  example.zip
       Length     Date   Time    Name
      --------    ----   ----    ----
          8467  11-26-02 22:30   jwzthreading.py
      --------                   -------
          8467                   1 file
     $ ./python
     Python 2.3 (#1, Aug 1 2003, 19:54:32)
     >>> import sys
     >>> sys.path.insert(0, 'example.zip')  # Add .zip file to front of path
     >>> import jwzthreading
     >>> jwzthreading.__file__
     'example.zip/jwzthreading.py'


File: python.info,  Node: pkgutil — Package extension utility,  Next: modulefinder — Find modules used by a script,  Prev: zipimport — Import modules from Zip archives,  Up: Importing Modules

5.31.2 ‘pkgutil’ — Package extension utility
--------------------------------------------

`Source code:' Lib/pkgutil.py(1)

__________________________________________________________________

This module provides utilities for the import system, in particular
package support.

 -- Class: pkgutil.ModuleInfo (module_finder, name, ispkg)

     A namedtuple that holds a brief summary of a module’s info.

     New in version 3.6.

 -- Function: pkgutil.extend_path (path, name)

     Extend the search path for the modules which comprise a package.
     Intended use is to place the following code in a package’s
     ‘__init__.py’:

          from pkgutil import extend_path
          __path__ = extend_path(__path__, __name__)

     This will add to the package’s ‘__path__’ all subdirectories of
     directories on ‘sys.path’ named after the package.  This is useful
     if one wants to distribute different parts of a single logical
     package as multiple directories.

     It also looks for ‘*.pkg’ files beginning where ‘*’ matches the
     `name' argument.  This feature is similar to ‘*.pth’ files (see the
     *note site: eb. module for more information), except that it
     doesn’t special-case lines starting with ‘import’.  A ‘*.pkg’ file
     is trusted at face value: apart from checking for duplicates, all
     entries found in a ‘*.pkg’ file are added to the path, regardless
     of whether they exist on the filesystem.  (This is a feature.)

     If the input path is not a list (as is the case for frozen
     packages) it is returned unchanged.  The input path is not
     modified; an extended copy is returned.  Items are only appended to
     the copy at the end.

     It is assumed that *note sys.path: 260. is a sequence.  Items of
     *note sys.path: 260. that are not strings referring to existing
     directories are ignored.  Unicode items on *note sys.path: 260.
     that cause errors when used as filenames may cause this function to
     raise an exception (in line with *note os.path.isdir(): 327.
     behavior).

 -- Class: pkgutil.ImpImporter (dirname=None)

     PEP 302(2) Finder that wraps Python’s “classic” import algorithm.

     If `dirname' is a string, a PEP 302(3) finder is created that
     searches that directory.  If `dirname' is ‘None’, a PEP 302(4)
     finder is created that searches the current *note sys.path: 260,
     plus any modules that are frozen or built-in.

     Note that *note ImpImporter: 38bf. does not currently support being
     used by placement on *note sys.meta_path: 6dd.

     Deprecated since version 3.3: This emulation is no longer needed,
     as the standard import mechanism is now fully PEP 302(5) compliant
     and available in *note importlib: 9a.

 -- Class: pkgutil.ImpLoader (fullname, file, filename, etc)

     *note Loader: 15f6. that wraps Python’s “classic” import algorithm.

     Deprecated since version 3.3: This emulation is no longer needed,
     as the standard import mechanism is now fully PEP 302(6) compliant
     and available in *note importlib: 9a.

 -- Function: pkgutil.find_loader (fullname)

     Retrieve a module *note loader: 15f6. for the given `fullname'.

     This is a backwards compatibility wrapper around *note
     importlib.util.find_spec(): a1c. that converts most failures to
     *note ImportError: 16c. and only returns the loader rather than the
     full ‘ModuleSpec’.

     Changed in version 3.3: Updated to be based directly on *note
     importlib: 9a. rather than relying on the package internal PEP
     302(7) import emulation.

     Changed in version 3.4: Updated to be based on PEP 451(8)

 -- Function: pkgutil.get_importer (path_item)

     Retrieve a *note finder: 15f5. for the given `path_item'.

     The returned finder is cached in *note sys.path_importer_cache:
     598. if it was newly created by a path hook.

     The cache (or part of it) can be cleared manually if a rescan of
     *note sys.path_hooks: a3d. is necessary.

     Changed in version 3.3: Updated to be based directly on *note
     importlib: 9a. rather than relying on the package internal PEP
     302(9) import emulation.

 -- Function: pkgutil.get_loader (module_or_name)

     Get a *note loader: 15f6. object for `module_or_name'.

     If the module or package is accessible via the normal import
     mechanism, a wrapper around the relevant part of that machinery is
     returned.  Returns ‘None’ if the module cannot be found or
     imported.  If the named module is not already imported, its
     containing package (if any) is imported, in order to establish the
     package ‘__path__’.

     Changed in version 3.3: Updated to be based directly on *note
     importlib: 9a. rather than relying on the package internal PEP
     302(10) import emulation.

     Changed in version 3.4: Updated to be based on PEP 451(11)

 -- Function: pkgutil.iter_importers (fullname='')

     Yield *note finder: 15f5. objects for the given module name.

     If fullname contains a ‘.’, the finders will be for the package
     containing fullname, otherwise they will be all registered top
     level finders (i.e.  those on both sys.meta_path and
     sys.path_hooks).

     If the named module is in a package, that package is imported as a
     side effect of invoking this function.

     If no module name is specified, all top level finders are produced.

     Changed in version 3.3: Updated to be based directly on *note
     importlib: 9a. rather than relying on the package internal PEP
     302(12) import emulation.

 -- Function: pkgutil.iter_modules (path=None, prefix='')

     Yields *note ModuleInfo: 703. for all submodules on `path', or, if
     `path' is ‘None’, all top-level modules on ‘sys.path’.

     `path' should be either ‘None’ or a list of paths to look for
     modules in.

     `prefix' is a string to output on the front of every module name on
     output.

          Note: Only works for a *note finder: 15f5. which defines an
          ‘iter_modules()’ method.  This interface is non-standard, so
          the module also provides implementations for *note
          importlib.machinery.FileFinder: a96. and *note
          zipimport.zipimporter: 38b1.

     Changed in version 3.3: Updated to be based directly on *note
     importlib: 9a. rather than relying on the package internal PEP
     302(13) import emulation.

 -- Function: pkgutil.walk_packages (path=None, prefix='', onerror=None)

     Yields *note ModuleInfo: 703. for all modules recursively on
     `path', or, if `path' is ‘None’, all accessible modules.

     `path' should be either ‘None’ or a list of paths to look for
     modules in.

     `prefix' is a string to output on the front of every module name on
     output.

     Note that this function must import all `packages' (`not' all
     modules!)  on the given `path', in order to access the ‘__path__’
     attribute to find submodules.

     `onerror' is a function which gets called with one argument (the
     name of the package which was being imported) if any exception
     occurs while trying to import a package.  If no `onerror' function
     is supplied, *note ImportError: 16c.s are caught and ignored, while
     all other exceptions are propagated, terminating the search.

     Examples:

          # list all modules python can access
          walk_packages()

          # list all submodules of ctypes
          walk_packages(ctypes.__path__, ctypes.__name__ + '.')

          Note: Only works for a *note finder: 15f5. which defines an
          ‘iter_modules()’ method.  This interface is non-standard, so
          the module also provides implementations for *note
          importlib.machinery.FileFinder: a96. and *note
          zipimport.zipimporter: 38b1.

     Changed in version 3.3: Updated to be based directly on *note
     importlib: 9a. rather than relying on the package internal PEP
     302(14) import emulation.

 -- Function: pkgutil.get_data (package, resource)

     Get a resource from a package.

     This is a wrapper for the *note loader: 15f6. *note get_data: 38c4.
     API. The `package' argument should be the name of a package, in
     standard module format (‘foo.bar’).  The `resource' argument should
     be in the form of a relative filename, using ‘/’ as the path
     separator.  The parent directory name ‘..’ is not allowed, and nor
     is a rooted name (starting with a ‘/’).

     The function returns a binary string that is the contents of the
     specified resource.

     For packages located in the filesystem, which have already been
     imported, this is the rough equivalent of:

          d = os.path.dirname(sys.modules[package].__file__)
          data = open(os.path.join(d, resource), 'rb').read()

     If the package cannot be located or loaded, or it uses a *note
     loader: 15f6. which does not support *note get_data: 38c4, then
     ‘None’ is returned.  In particular, the *note loader: 15f6. for
     *note namespace packages: 15ee. does not support *note get_data:
     38c4.

 -- Function: pkgutil.resolve_name (name)

     Resolve a name to an object.

     This functionality is used in numerous places in the standard
     library (see bpo-12915(15)) - and equivalent functionality is also
     in widely used third-party packages such as setuptools, Django and
     Pyramid.

     It is expected that `name' will be a string in one of the following
     formats, where W is shorthand for a valid Python identifier and dot
     stands for a literal period in these pseudo-regexes:

        * ‘W(.W)*’

        * ‘W(.W)*:(W(.W)*)?’

     The first form is intended for backward compatibility only.  It
     assumes that some part of the dotted name is a package, and the
     rest is an object somewhere within that package, possibly nested
     inside other objects.  Because the place where the package stops
     and the object hierarchy starts can’t be inferred by inspection,
     repeated attempts to import must be done with this form.

     In the second form, the caller makes the division point clear
     through the provision of a single colon: the dotted name to the
     left of the colon is a package to be imported, and the dotted name
     to the right is the object hierarchy within that package.  Only one
     import is needed in this form.  If it ends with the colon, then a
     module object is returned.

     The function will return an object (which might be a module), or
     raise one of the following exceptions:

     *note ValueError: 16d. – if `name' isn’t in a recognised format.

     *note ImportError: 16c. – if an import failed when it shouldn’t
     have.

     *note AttributeError: 4a2. – If a failure occurred when traversing
     the object hierarchy within the imported package to get to the
     desired object.

     New in version 3.9.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/pkgutil.py

   (2) https://www.python.org/dev/peps/pep-0302

   (3) https://www.python.org/dev/peps/pep-0302

   (4) https://www.python.org/dev/peps/pep-0302

   (5) https://www.python.org/dev/peps/pep-0302

   (6) https://www.python.org/dev/peps/pep-0302

   (7) https://www.python.org/dev/peps/pep-0302

   (8) https://www.python.org/dev/peps/pep-0451

   (9) https://www.python.org/dev/peps/pep-0302

   (10) https://www.python.org/dev/peps/pep-0302

   (11) https://www.python.org/dev/peps/pep-0451

   (12) https://www.python.org/dev/peps/pep-0302

   (13) https://www.python.org/dev/peps/pep-0302

   (14) https://www.python.org/dev/peps/pep-0302

   (15) https://bugs.python.org/issue12915


File: python.info,  Node: modulefinder — Find modules used by a script,  Next: runpy — Locating and executing Python modules,  Prev: pkgutil — Package extension utility,  Up: Importing Modules

5.31.3 ‘modulefinder’ — Find modules used by a script
-----------------------------------------------------

`Source code:' Lib/modulefinder.py(1)

__________________________________________________________________

This module provides a *note ModuleFinder: 111b. class that can be used
to determine the set of modules imported by a script.  ‘modulefinder.py’
can also be run as a script, giving the filename of a Python script as
its argument, after which a report of the imported modules will be
printed.

 -- Function: modulefinder.AddPackagePath (pkg_name, path)

     Record that the package named `pkg_name' can be found in the
     specified `path'.

 -- Function: modulefinder.ReplacePackage (oldname, newname)

     Allows specifying that the module named `oldname' is in fact the
     package named `newname'.

 -- Class: modulefinder.ModuleFinder (path=None, debug=0, excludes=[],
          replace_paths=[])

     This class provides *note run_script(): 38ca. and *note report():
     38cb. methods to determine the set of modules imported by a script.
     `path' can be a list of directories to search for modules; if not
     specified, ‘sys.path’ is used.  `debug' sets the debugging level;
     higher values make the class print debugging messages about what
     it’s doing.  `excludes' is a list of module names to exclude from
     the analysis.  `replace_paths' is a list of ‘(oldpath, newpath)’
     tuples that will be replaced in module paths.

      -- Method: report ()

          Print a report to standard output that lists the modules
          imported by the script and their paths, as well as modules
          that are missing or seem to be missing.

      -- Method: run_script (pathname)

          Analyze the contents of the `pathname' file, which must
          contain Python code.

      -- Attribute: modules

          A dictionary mapping module names to modules.  See *note
          Example usage of ModuleFinder: 38cd.

* Menu:

* Example usage of ModuleFinder::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/modulefinder.py


File: python.info,  Node: Example usage of ModuleFinder,  Up: modulefinder — Find modules used by a script

5.31.3.1 Example usage of ‘ModuleFinder’
........................................

The script that is going to get analyzed later on (bacon.py):

     import re, itertools

     try:
         import baconhameggs
     except ImportError:
         pass

     try:
         import guido.python.ham
     except ImportError:
         pass

The script that will output the report of bacon.py:

     from modulefinder import ModuleFinder

     finder = ModuleFinder()
     finder.run_script('bacon.py')

     print('Loaded modules:')
     for name, mod in finder.modules.items():
         print('%s: ' % name, end='')
         print(','.join(list(mod.globalnames.keys())[:3]))

     print('-'*50)
     print('Modules not imported:')
     print('\n'.join(finder.badmodules.keys()))

Sample output (may vary depending on the architecture):

     Loaded modules:
     _types:
     copyreg:  _inverted_registry,_slotnames,__all__
     sre_compile:  isstring,_sre,_optimize_unicode
     _sre:
     sre_constants:  REPEAT_ONE,makedict,AT_END_LINE
     sys:
     re:  __module__,finditer,_expand
     itertools:
     __main__:  re,itertools,baconhameggs
     sre_parse:  _PATTERNENDERS,SRE_FLAG_UNICODE
     array:
     types:  __module__,IntType,TypeType
     ---------------------------------------------------
     Modules not imported:
     guido.python.ham
     baconhameggs


File: python.info,  Node: runpy — Locating and executing Python modules,  Next: importlib — The implementation of import,  Prev: modulefinder — Find modules used by a script,  Up: Importing Modules

5.31.4 ‘runpy’ — Locating and executing Python modules
------------------------------------------------------

`Source code:' Lib/runpy.py(1)

__________________________________________________________________

The *note runpy: e2. module is used to locate and run Python modules
without importing them first.  Its main use is to implement the *note
-m: 443. command line switch that allows scripts to be located using the
Python module namespace rather than the filesystem.

Note that this is `not' a sandbox module - all code is executed in the
current process, and any side effects (such as cached imports of other
modules) will remain in place after the functions have returned.

Furthermore, any functions and classes defined by the executed code are
not guaranteed to work correctly after a *note runpy: e2. function has
returned.  If that limitation is not acceptable for a given use case,
*note importlib: 9a. is likely to be a more suitable choice than this
module.

The *note runpy: e2. module provides two functions:

 -- Function: runpy.run_module (mod_name, init_globals=None,
          run_name=None, alter_sys=False)

     Execute the code of the specified module and return the resulting
     module globals dictionary.  The module’s code is first located
     using the standard import mechanism (refer to PEP 302(2) for
     details) and then executed in a fresh module namespace.

     The `mod_name' argument should be an absolute module name.  If the
     module name refers to a package rather than a normal module, then
     that package is imported and the ‘__main__’ submodule within that
     package is then executed and the resulting module globals
     dictionary returned.

     The optional dictionary argument `init_globals' may be used to
     pre-populate the module’s globals dictionary before the code is
     executed.  The supplied dictionary will not be modified.  If any of
     the special global variables below are defined in the supplied
     dictionary, those definitions are overridden by *note run_module():
     146f.

     The special global variables ‘__name__’, ‘__spec__’, ‘__file__’,
     ‘__cached__’, ‘__loader__’ and ‘__package__’ are set in the globals
     dictionary before the module code is executed (Note that this is a
     minimal set of variables - other variables may be set implicitly as
     an interpreter implementation detail).

     ‘__name__’ is set to `run_name' if this optional argument is not
     *note None: 203, to ‘mod_name + '.__main__'’ if the named module is
     a package and to the `mod_name' argument otherwise.

     ‘__spec__’ will be set appropriately for the `actually' imported
     module (that is, ‘__spec__.name’ will always be `mod_name' or
     ‘mod_name + '.__main__’, never `run_name').

     ‘__file__’, ‘__cached__’, ‘__loader__’ and ‘__package__’ are *note
     set as normal: 15fd. based on the module spec.

     If the argument `alter_sys' is supplied and evaluates to *note
     True: 594, then ‘sys.argv[0]’ is updated with the value of
     ‘__file__’ and ‘sys.modules[__name__]’ is updated with a temporary
     module object for the module being executed.  Both ‘sys.argv[0]’
     and ‘sys.modules[__name__]’ are restored to their original values
     before the function returns.

     Note that this manipulation of *note sys: fd. is not thread-safe.
     Other threads may see the partially initialised module, as well as
     the altered list of arguments.  It is recommended that the *note
     sys: fd. module be left alone when invoking this function from
     threaded code.

     See also
     ........

     The *note -m: 443. option offering equivalent functionality from
     the command line.

     Changed in version 3.1: Added ability to execute packages by
     looking for a ‘__main__’ submodule.

     Changed in version 3.2: Added ‘__cached__’ global variable (see PEP
     3147(3)).

     Changed in version 3.4: Updated to take advantage of the module
     spec feature added by PEP 451(4).  This allows ‘__cached__’ to be
     set correctly for modules run this way, as well as ensuring the
     real module name is always accessible as ‘__spec__.name’.

 -- Function: runpy.run_path (file_path, init_globals=None,
          run_name=None)

     Execute the code at the named filesystem location and return the
     resulting module globals dictionary.  As with a script name
     supplied to the CPython command line, the supplied path may refer
     to a Python source file, a compiled bytecode file or a valid
     sys.path entry containing a ‘__main__’ module (e.g.  a zipfile
     containing a top-level ‘__main__.py’ file).

     For a simple script, the specified code is simply executed in a
     fresh module namespace.  For a valid sys.path entry (typically a
     zipfile or directory), the entry is first added to the beginning of
     ‘sys.path’.  The function then looks for and executes a *note
     __main__: 1. module using the updated path.  Note that there is no
     special protection against invoking an existing *note __main__: 1.
     entry located elsewhere on ‘sys.path’ if there is no such module at
     the specified location.

     The optional dictionary argument `init_globals' may be used to
     pre-populate the module’s globals dictionary before the code is
     executed.  The supplied dictionary will not be modified.  If any of
     the special global variables below are defined in the supplied
     dictionary, those definitions are overridden by *note run_path():
     d79.

     The special global variables ‘__name__’, ‘__spec__’, ‘__file__’,
     ‘__cached__’, ‘__loader__’ and ‘__package__’ are set in the globals
     dictionary before the module code is executed (Note that this is a
     minimal set of variables - other variables may be set implicitly as
     an interpreter implementation detail).

     ‘__name__’ is set to `run_name' if this optional argument is not
     *note None: 203. and to ‘'<run_path>'’ otherwise.

     If the supplied path directly references a script file (whether as
     source or as precompiled byte code), then ‘__file__’ will be set to
     the supplied path, and ‘__spec__’, ‘__cached__’, ‘__loader__’ and
     ‘__package__’ will all be set to *note None: 203.

     If the supplied path is a reference to a valid sys.path entry, then
     ‘__spec__’ will be set appropriately for the imported ‘__main__’
     module (that is, ‘__spec__.name’ will always be ‘__main__’).
     ‘__file__’, ‘__cached__’, ‘__loader__’ and ‘__package__’ will be
     *note set as normal: 15fd. based on the module spec.

     A number of alterations are also made to the *note sys: fd. module.
     Firstly, ‘sys.path’ may be altered as described above.
     ‘sys.argv[0]’ is updated with the value of ‘file_path’ and
     ‘sys.modules[__name__]’ is updated with a temporary module object
     for the module being executed.  All modifications to items in *note
     sys: fd. are reverted before the function returns.

     Note that, unlike *note run_module(): 146f, the alterations made to
     *note sys: fd. are not optional in this function as these
     adjustments are essential to allowing the execution of sys.path
     entries.  As the thread-safety limitations still apply, use of this
     function in threaded code should be either serialised with the
     import lock or delegated to a separate process.

     See also
     ........

     *note Interface options: 146e. for equivalent functionality on the
     command line (‘python path/to/script’).

     New in version 3.2.

     Changed in version 3.4: Updated to take advantage of the module
     spec feature added by PEP 451(5).  This allows ‘__cached__’ to be
     set correctly in the case where ‘__main__’ is imported from a valid
     sys.path entry rather than being executed directly.

See also
........

PEP 338(6) – Executing modules as scripts

     PEP written and implemented by Nick Coghlan.

PEP 366(7) – Main module explicit relative imports

     PEP written and implemented by Nick Coghlan.

PEP 451(8) – A ModuleSpec Type for the Import System

     PEP written and implemented by Eric Snow

*note Command line and environment: 10bd. - CPython command line details

The *note importlib.import_module(): be6. function

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/runpy.py

   (2) https://www.python.org/dev/peps/pep-0302

   (3) https://www.python.org/dev/peps/pep-3147

   (4) https://www.python.org/dev/peps/pep-0451

   (5) https://www.python.org/dev/peps/pep-0451

   (6) https://www.python.org/dev/peps/pep-0338

   (7) https://www.python.org/dev/peps/pep-0366

   (8) https://www.python.org/dev/peps/pep-0451


File: python.info,  Node: importlib — The implementation of import,  Next: Using importlib metadata,  Prev: runpy — Locating and executing Python modules,  Up: Importing Modules

5.31.5 ‘importlib’ — The implementation of ‘import’
---------------------------------------------------

New in version 3.1.

`Source code:' Lib/importlib/__init__.py(1)

__________________________________________________________________

* Menu:

* Introduction: Introduction<12>.
* Functions: Functions<11>.
* importlib.abc – Abstract base classes related to import: importlib abc – Abstract base classes related to import.
* importlib.resources – Resources: importlib resources – Resources.
* importlib.machinery – Importers and path hooks: importlib machinery – Importers and path hooks.
* importlib.util – Utility code for importers: importlib util – Utility code for importers.
* Examples: Examples<30>.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/importlib/__init__.py


File: python.info,  Node: Introduction<12>,  Next: Functions<11>,  Up: importlib — The implementation of import

5.31.5.1 Introduction
.....................

The purpose of the *note importlib: 9a. package is two-fold.  One is to
provide the implementation of the *note import: ce7. statement (and
thus, by extension, the *note __import__(): 16b. function) in Python
source code.  This provides an implementation of ‘import’ which is
portable to any Python interpreter.  This also provides an
implementation which is easier to comprehend than one implemented in a
programming language other than Python.

Two, the components to implement *note import: ce7. are exposed in this
package, making it easier for users to create their own custom objects
(known generically as an *note importer: 15f7.) to participate in the
import process.

See also
........

*note The import statement: ce7.

     The language reference for the *note import: ce7. statement.

Packages specification(1)

     Original specification of packages.  Some semantics have changed
     since the writing of this document (e.g.  redirecting based on
     ‘None’ in *note sys.modules: 1051.).

The *note __import__(): a8e. function

     The *note import: ce7. statement is syntactic sugar for this
     function.

PEP 235(2)

     Import on Case-Insensitive Platforms

PEP 263(3)

     Defining Python Source Code Encodings

PEP 302(4)

     New Import Hooks

PEP 328(5)

     Imports: Multi-Line and Absolute/Relative

PEP 366(6)

     Main module explicit relative imports

PEP 420(7)

     Implicit namespace packages

PEP 451(8)

     A ModuleSpec Type for the Import System

PEP 488(9)

     Elimination of PYO files

PEP 489(10)

     Multi-phase extension module initialization

PEP 552(11)

     Deterministic pycs

PEP 3120(12)

     Using UTF-8 as the Default Source Encoding

PEP 3147(13)

     PYC Repository Directories

   ---------- Footnotes ----------

   (1) https://www.python.org/doc/essays/packages/

   (2) https://www.python.org/dev/peps/pep-0235

   (3) https://www.python.org/dev/peps/pep-0263

   (4) https://www.python.org/dev/peps/pep-0302

   (5) https://www.python.org/dev/peps/pep-0328

   (6) https://www.python.org/dev/peps/pep-0366

   (7) https://www.python.org/dev/peps/pep-0420

   (8) https://www.python.org/dev/peps/pep-0451

   (9) https://www.python.org/dev/peps/pep-0488

   (10) https://www.python.org/dev/peps/pep-0489

   (11) https://www.python.org/dev/peps/pep-0552

   (12) https://www.python.org/dev/peps/pep-3120

   (13) https://www.python.org/dev/peps/pep-3147


File: python.info,  Node: Functions<11>,  Next: importlib abc – Abstract base classes related to import,  Prev: Introduction<12>,  Up: importlib — The implementation of import

5.31.5.2 Functions
..................

 -- Function: importlib.__import__ (name, globals=None, locals=None,
          fromlist=(), level=0)

     An implementation of the built-in *note __import__(): 16b.
     function.

          Note: Programmatic importing of modules should use *note
          import_module(): be6. instead of this function.

 -- Function: importlib.import_module (name, package=None)

     Import a module.  The `name' argument specifies what module to
     import in absolute or relative terms (e.g.  either ‘pkg.mod’ or
     ‘..mod’).  If the name is specified in relative terms, then the
     `package' argument must be set to the name of the package which is
     to act as the anchor for resolving the package name (e.g.
     ‘import_module('..mod', 'pkg.subpkg')’ will import ‘pkg.mod’).

     The *note import_module(): be6. function acts as a simplifying
     wrapper around *note importlib.__import__(): a8e.  This means all
     semantics of the function are derived from *note
     importlib.__import__(): a8e.  The most important difference between
     these two functions is that *note import_module(): be6. returns the
     specified package or module (e.g.  ‘pkg.mod’), while *note
     __import__(): 16b. returns the top-level package or module (e.g.
     ‘pkg’).

     If you are dynamically importing a module that was created since
     the interpreter began execution (e.g., created a Python source
     file), you may need to call *note invalidate_caches(): 597. in
     order for the new module to be noticed by the import system.

     Changed in version 3.3: Parent packages are automatically imported.

 -- Function: importlib.find_loader (name, path=None)

     Find the loader for a module, optionally within the specified
     `path'.  If the module is in *note sys.modules: 1051, then
     ‘sys.modules[name].__loader__’ is returned (unless the loader would
     be ‘None’ or is not set, in which case *note ValueError: 16d. is
     raised).  Otherwise a search using *note sys.meta_path: 6dd. is
     done.  ‘None’ is returned if no loader is found.

     A dotted name does not have its parents implicitly imported as that
     requires loading them and that may not be desired.  To properly
     import a submodule you will need to import all parent packages of
     the submodule and use the correct argument to `path'.

     New in version 3.3.

     Changed in version 3.4: If ‘__loader__’ is not set, raise *note
     ValueError: 16d, just like when the attribute is set to ‘None’.

     Deprecated since version 3.4: Use *note importlib.util.find_spec():
     a1c. instead.

 -- Function: importlib.invalidate_caches ()

     Invalidate the internal caches of finders stored at *note
     sys.meta_path: 6dd.  If a finder implements ‘invalidate_caches()’
     then it will be called to perform the invalidation.  This function
     should be called if any modules are created/installed while your
     program is running to guarantee all finders will notice the new
     module’s existence.

     New in version 3.3.

 -- Function: importlib.reload (module)

     Reload a previously imported `module'.  The argument must be a
     module object, so it must have been successfully imported before.
     This is useful if you have edited the module source file using an
     external editor and want to try out the new version without leaving
     the Python interpreter.  The return value is the module object
     (which can be different if re-importing causes a different object
     to be placed in *note sys.modules: 1051.).

     When *note reload(): 4a0. is executed:

        * Python module’s code is recompiled and the module-level code
          re-executed, defining a new set of objects which are bound to
          names in the module’s dictionary by reusing the *note loader:
          15f6. which originally loaded the module.  The ‘init’ function
          of extension modules is not called a second time.

        * As with all other objects in Python the old objects are only
          reclaimed after their reference counts drop to zero.

        * The names in the module namespace are updated to point to any
          new or changed objects.

        * Other references to the old objects (such as names external to
          the module) are not rebound to refer to the new objects and
          must be updated in each namespace where they occur if that is
          desired.

     There are a number of other caveats:

     When a module is reloaded, its dictionary (containing the module’s
     global variables) is retained.  Redefinitions of names will
     override the old definitions, so this is generally not a problem.
     If the new version of a module does not define a name that was
     defined by the old version, the old definition remains.  This
     feature can be used to the module’s advantage if it maintains a
     global table or cache of objects — with a *note try: e37. statement
     it can test for the table’s presence and skip its initialization if
     desired:

          try:
              cache
          except NameError:
              cache = {}

     It is generally not very useful to reload built-in or dynamically
     loaded modules.  Reloading *note sys: fd, *note __main__: 1, *note
     builtins: 12. and other key modules is not recommended.  In many
     cases extension modules are not designed to be initialized more
     than once, and may fail in arbitrary ways when reloaded.

     If a module imports objects from another module using *note from:
     d0d. … *note import: ce7. …, calling *note reload(): 4a0. for the
     other module does not redefine the objects imported from it — one
     way around this is to re-execute the ‘from’ statement, another is
     to use ‘import’ and qualified names (`module.name') instead.

     If a module instantiates instances of a class, reloading the module
     that defines the class does not affect the method definitions of
     the instances — they continue to use the old class definition.  The
     same is true for derived classes.

     New in version 3.4.

     Changed in version 3.7: *note ModuleNotFoundError: 4a1. is raised
     when the module being reloaded lacks a ‘ModuleSpec’.


File: python.info,  Node: importlib abc – Abstract base classes related to import,  Next: importlib resources – Resources,  Prev: Functions<11>,  Up: importlib — The implementation of import

5.31.5.3 ‘importlib.abc’ – Abstract base classes related to import
..................................................................

`Source code:' Lib/importlib/abc.py(1)

__________________________________________________________________

The *note importlib.abc: 9b. module contains all of the core abstract
base classes used by *note import: ce7.  Some subclasses of the core
abstract base classes are also provided to help in implementing the core
ABCs.

ABC hierarchy:

     object
      +-- Finder (deprecated)
      |    +-- MetaPathFinder
      |    +-- PathEntryFinder
      +-- Loader
           +-- ResourceLoader --------+
           +-- InspectLoader          |
                +-- ExecutionLoader --+
                                      +-- FileLoader
                                      +-- SourceLoader

 -- Class: importlib.abc.Finder

     An abstract base class representing a *note finder: 15f5.

     Deprecated since version 3.3: Use *note MetaPathFinder: a93. or
     *note PathEntryFinder: a94. instead.

      -- Method: abstractmethod find_module (fullname, path=None)

          An abstract method for finding a *note loader: 15f6. for the
          specified module.  Originally specified in PEP 302(2), this
          method was meant for use in *note sys.meta_path: 6dd. and in
          the path-based import subsystem.

          Changed in version 3.4: Returns ‘None’ when called instead of
          raising *note NotImplementedError: 704.

 -- Class: importlib.abc.MetaPathFinder

     An abstract base class representing a *note meta path finder: a91.
     For compatibility, this is a subclass of *note Finder: a95.

     New in version 3.3.

      -- Method: find_spec (fullname, path, target=None)

          An abstract method for finding a *note spec: 37bb. for the
          specified module.  If this is a top-level import, `path' will
          be ‘None’.  Otherwise, this is a search for a subpackage or
          module and `path' will be the value of *note __path__: 13c3.
          from the parent package.  If a spec cannot be found, ‘None’ is
          returned.  When passed in, ‘target’ is a module object that
          the finder may use to make a more educated guess about what
          spec to return.  *note importlib.util.spec_from_loader():
          38d7. may be useful for implementing concrete
          ‘MetaPathFinders’.

          New in version 3.4.

      -- Method: find_module (fullname, path)

          A legacy method for finding a *note loader: 15f6. for the
          specified module.  If this is a top-level import, `path' will
          be ‘None’.  Otherwise, this is a search for a subpackage or
          module and `path' will be the value of *note __path__: 13c3.
          from the parent package.  If a loader cannot be found, ‘None’
          is returned.

          If *note find_spec(): 565. is defined, backwards-compatible
          functionality is provided.

          Changed in version 3.4: Returns ‘None’ when called instead of
          raising *note NotImplementedError: 704.  Can use *note
          find_spec(): 565. to provide functionality.

          Deprecated since version 3.4: Use *note find_spec(): 565.
          instead.

      -- Method: invalidate_caches ()

          An optional method which, when called, should invalidate any
          internal cache used by the finder.  Used by *note
          importlib.invalidate_caches(): 597. when invalidating the
          caches of all finders on *note sys.meta_path: 6dd.

          Changed in version 3.4: Returns ‘None’ when called instead of
          ‘NotImplemented’.

 -- Class: importlib.abc.PathEntryFinder

     An abstract base class representing a *note path entry finder: a92.
     Though it bears some similarities to *note MetaPathFinder: a93,
     ‘PathEntryFinder’ is meant for use only within the path-based
     import subsystem provided by ‘PathFinder’.  This ABC is a subclass
     of *note Finder: a95. for compatibility reasons only.

     New in version 3.3.

      -- Method: find_spec (fullname, target=None)

          An abstract method for finding a *note spec: 37bb. for the
          specified module.  The finder will search for the module only
          within the *note path entry: 160b. to which it is assigned.
          If a spec cannot be found, ‘None’ is returned.  When passed
          in, ‘target’ is a module object that the finder may use to
          make a more educated guess about what spec to return.  *note
          importlib.util.spec_from_loader(): 38d7. may be useful for
          implementing concrete ‘PathEntryFinders’.

          New in version 3.4.

      -- Method: find_loader (fullname)

          A legacy method for finding a *note loader: 15f6. for the
          specified module.  Returns a 2-tuple of ‘(loader, portion)’
          where ‘portion’ is a sequence of file system locations
          contributing to part of a namespace package.  The loader may
          be ‘None’ while specifying ‘portion’ to signify the
          contribution of the file system locations to a namespace
          package.  An empty list can be used for ‘portion’ to signify
          the loader is not part of a namespace package.  If ‘loader’ is
          ‘None’ and ‘portion’ is the empty list then no loader or
          location for a namespace package were found (i.e.  failure to
          find anything for the module).

          If *note find_spec(): 567. is defined then
          backwards-compatible functionality is provided.

          Changed in version 3.4: Returns ‘(None, [])’ instead of
          raising *note NotImplementedError: 704.  Uses *note
          find_spec(): 567. when available to provide functionality.

          Deprecated since version 3.4: Use *note find_spec(): 567.
          instead.

      -- Method: find_module (fullname)

          A concrete implementation of *note Finder.find_module(): 38d6.
          which is equivalent to ‘self.find_loader(fullname)[0]’.

          Deprecated since version 3.4: Use *note find_spec(): 567.
          instead.

      -- Method: invalidate_caches ()

          An optional method which, when called, should invalidate any
          internal cache used by the finder.  Used by
          ‘PathFinder.invalidate_caches()’ when invalidating the caches
          of all cached finders.

 -- Class: importlib.abc.Loader

     An abstract base class for a *note loader: 15f6.  See PEP 302(3)
     for the exact definition for a loader.

     Loaders that wish to support resource reading should implement a
     ‘get_resource_reader(fullname)’ method as specified by *note
     importlib.abc.ResourceReader: 44e.

     Changed in version 3.7: Introduced the optional
     ‘get_resource_reader()’ method.

      -- Method: create_module (spec)

          A method that returns the module object to use when importing
          a module.  This method may return ‘None’, indicating that
          default module creation semantics should take place.

          New in version 3.4.

          Changed in version 3.5: Starting in Python 3.6, this method
          will not be optional when *note exec_module(): 6db. is
          defined.

      -- Method: exec_module (module)

          An abstract method that executes the module in its own
          namespace when a module is imported or reloaded.  The module
          should already be initialized when ‘exec_module()’ is called.
          When this method exists, *note create_module(): 64e. must be
          defined.

          New in version 3.4.

          Changed in version 3.6: *note create_module(): 64e. must also
          be defined.

      -- Method: load_module (fullname)

          A legacy method for loading a module.  If the module cannot be
          loaded, *note ImportError: 16c. is raised, otherwise the
          loaded module is returned.

          If the requested module already exists in *note sys.modules:
          1051, that module should be used and reloaded.  Otherwise the
          loader should create a new module and insert it into *note
          sys.modules: 1051. before any loading begins, to prevent
          recursion from the import.  If the loader inserted a module
          and the load fails, it must be removed by the loader from
          *note sys.modules: 1051.; modules already in *note
          sys.modules: 1051. before the loader began execution should be
          left alone (see *note importlib.util.module_for_loader():
          a26.).

          The loader should set several attributes on the module.  (Note
          that some of these attributes can change when a module is
          reloaded):

             - 
               *note __name__: dd8.

                    The name of the module.

             - 
               *note __file__: 1562.

                    The path to where the module data is stored (not set
                    for built-in modules).

             - 
               *note __cached__: c04.

                    The path to where a compiled version of the module
                    is/should be stored (not set when the attribute
                    would be inappropriate).

             - 
               *note __path__: 13c3.

                    A list of strings specifying the search path within
                    a package.  This attribute is not set on modules.

             - 
               *note __package__: a36.

                    The fully-qualified name of the package under which
                    the module was loaded as a submodule (or the empty
                    string for top-level modules).  For packages, it is
                    the same as *note __name__: dd8.  The *note
                    importlib.util.module_for_loader(): a26. decorator
                    can handle the details for *note __package__: a36.

             - 
               *note __loader__: a37.

                    The loader used to load the module.  The *note
                    importlib.util.module_for_loader(): a26. decorator
                    can handle the details for *note __package__: a36.

          When *note exec_module(): 6db. is available then
          backwards-compatible functionality is provided.

          Changed in version 3.4: Raise *note ImportError: 16c. when
          called instead of *note NotImplementedError: 704.
          Functionality provided when *note exec_module(): 6db. is
          available.

          Deprecated since version 3.4: The recommended API for loading
          a module is *note exec_module(): 6db. (and *note
          create_module(): 64e.).  Loaders should implement it instead
          of load_module().  The import machinery takes care of all the
          other responsibilities of load_module() when exec_module() is
          implemented.

      -- Method: module_repr (module)

          A legacy method which when implemented calculates and returns
          the given module’s repr, as a string.  The module type’s
          default repr() will use the result of this method as
          appropriate.

          New in version 3.3.

          Changed in version 3.4: Made optional instead of an
          abstractmethod.

          Deprecated since version 3.4: The import machinery now takes
          care of this automatically.

 -- Class: importlib.abc.ResourceReader

     `Superseded by TraversableResources'

     An *note abstract base class: c05. to provide the ability to read
     `resources'.

     From the perspective of this ABC, a `resource' is a binary artifact
     that is shipped within a package.  Typically this is something like
     a data file that lives next to the ‘__init__.py’ file of the
     package.  The purpose of this class is to help abstract out the
     accessing of such data files so that it does not matter if the
     package and its data file(s) are stored in a e.g.  zip file versus
     on the file system.

     For any of methods of this class, a `resource' argument is expected
     to be a *note path-like object: 472. which represents conceptually
     just a file name.  This means that no subdirectory paths should be
     included in the `resource' argument.  This is because the location
     of the package the reader is for, acts as the “directory”.  Hence
     the metaphor for directories and file names is packages and
     resources, respectively.  This is also why instances of this class
     are expected to directly correlate to a specific package (instead
     of potentially representing multiple packages or a module).

     Loaders that wish to support resource reading are expected to
     provide a method called ‘get_resource_reader(fullname)’ which
     returns an object implementing this ABC’s interface.  If the module
     specified by fullname is not a package, this method should return
     *note None: 203.  An object compatible with this ABC should only be
     returned when the specified module is a package.

     New in version 3.7.

      -- Method: abstractmethod open_resource (resource)

          Returns an opened, *note file-like object: 1dc6. for binary
          reading of the `resource'.

          If the resource cannot be found, *note FileNotFoundError: 8ad.
          is raised.

      -- Method: abstractmethod resource_path (resource)

          Returns the file system path to the `resource'.

          If the resource does not concretely exist on the file system,
          raise *note FileNotFoundError: 8ad.

      -- Method: abstractmethod is_resource (name)

          Returns ‘True’ if the named `name' is considered a resource.
          *note FileNotFoundError: 8ad. is raised if `name' does not
          exist.

      -- Method: abstractmethod contents ()

          Returns an *note iterable: c7c. of strings over the contents
          of the package.  Do note that it is not required that all
          names returned by the iterator be actual resources, e.g.  it
          is acceptable to return names for which *note is_resource():
          38dc. would be false.

          Allowing non-resource names to be returned is to allow for
          situations where how a package and its resources are stored
          are known a priori and the non-resource names would be useful.
          For instance, returning subdirectory names is allowed so that
          when it is known that the package and resources are stored on
          the file system then those subdirectory names can be used
          directly.

          The abstract method returns an iterable of no items.

 -- Class: importlib.abc.ResourceLoader

     An abstract base class for a *note loader: 15f6. which implements
     the optional PEP 302(4) protocol for loading arbitrary resources
     from the storage back-end.

     Deprecated since version 3.7: This ABC is deprecated in favour of
     supporting resource loading through *note
     importlib.abc.ResourceReader: 44e.

      -- Method: abstractmethod get_data (path)

          An abstract method to return the bytes for the data located at
          `path'.  Loaders that have a file-like storage back-end that
          allows storing arbitrary data can implement this abstract
          method to give direct access to the data stored.  *note
          OSError: 304. is to be raised if the `path' cannot be found.
          The `path' is expected to be constructed using a module’s
          *note __file__: 1562. attribute or an item from a package’s
          *note __path__: 13c3.

          Changed in version 3.4: Raises *note OSError: 304. instead of
          *note NotImplementedError: 704.

 -- Class: importlib.abc.InspectLoader

     An abstract base class for a *note loader: 15f6. which implements
     the optional PEP 302(5) protocol for loaders that inspect modules.

      -- Method: get_code (fullname)

          Return the code object for a module, or ‘None’ if the module
          does not have a code object (as would be the case, for
          example, for a built-in module).  Raise an *note ImportError:
          16c. if loader cannot find the requested module.

               Note: While the method has a default implementation, it
               is suggested that it be overridden if possible for
               performance.

          Changed in version 3.4: No longer abstract and a concrete
          implementation is provided.

      -- Method: abstractmethod get_source (fullname)

          An abstract method to return the source of a module.  It is
          returned as a text string using *note universal newlines: 6eb,
          translating all recognized line separators into ‘'\n'’
          characters.  Returns ‘None’ if no source is available (e.g.  a
          built-in module).  Raises *note ImportError: 16c. if the
          loader cannot find the module specified.

          Changed in version 3.4: Raises *note ImportError: 16c. instead
          of *note NotImplementedError: 704.

      -- Method: is_package (fullname)

          An optional method to return a true value if the module is a
          package, a false value otherwise.  *note ImportError: 16c. is
          raised if the *note loader: 15f6. cannot find the module.

          Changed in version 3.4: Raises *note ImportError: 16c. instead
          of *note NotImplementedError: 704.

      -- Method: static source_to_code (data, path='<string>')

          Create a code object from Python source.

          The `data' argument can be whatever the *note compile(): 2e7.
          function supports (i.e.  string or bytes).  The `path'
          argument should be the “path” to where the source code
          originated from, which can be an abstract concept (e.g.
          location in a zip file).

          With the subsequent code object one can execute it in a module
          by running ‘exec(code, module.__dict__)’.

          New in version 3.4.

          Changed in version 3.5: Made the method static.

      -- Method: exec_module (module)

          Implementation of *note Loader.exec_module(): 6db.

          New in version 3.4.

      -- Method: load_module (fullname)

          Implementation of *note Loader.load_module(): 6da.

          Deprecated since version 3.4: use *note exec_module(): a23.
          instead.

 -- Class: importlib.abc.ExecutionLoader

     An abstract base class which inherits from *note InspectLoader:
     94b. that, when implemented, helps a module to be executed as a
     script.  The ABC represents an optional PEP 302(6) protocol.

      -- Method: abstractmethod get_filename (fullname)

          An abstract method that is to return the value of *note
          __file__: 1562. for the specified module.  If no path is
          available, *note ImportError: 16c. is raised.

          If source code is available, then the method should return the
          path to the source file, regardless of whether a bytecode was
          used to load the module.

          Changed in version 3.4: Raises *note ImportError: 16c. instead
          of *note NotImplementedError: 704.

 -- Class: importlib.abc.FileLoader (fullname, path)

     An abstract base class which inherits from *note ResourceLoader:
     568. and *note ExecutionLoader: 38de, providing concrete
     implementations of *note ResourceLoader.get_data(): 38c4. and *note
     ExecutionLoader.get_filename(): 38df.

     The `fullname' argument is a fully resolved name of the module the
     loader is to handle.  The `path' argument is the path to the file
     for the module.

     New in version 3.3.

      -- Attribute: name

          The name of the module the loader can handle.

      -- Attribute: path

          Path to the file of the module.

      -- Method: load_module (fullname)

          Calls super’s ‘load_module()’.

          Deprecated since version 3.4: Use *note Loader.exec_module():
          6db. instead.

      -- Method: abstractmethod get_filename (fullname)

          Returns *note path: 38e1.

      -- Method: abstractmethod get_data (path)

          Reads `path' as a binary file and returns the bytes from it.

 -- Class: importlib.abc.SourceLoader

     An abstract base class for implementing source (and optionally
     bytecode) file loading.  The class inherits from both *note
     ResourceLoader: 568. and *note ExecutionLoader: 38de, requiring the
     implementation of:

        * *note ResourceLoader.get_data(): 38c4.

        * 
          *note ExecutionLoader.get_filename(): 38df.

               Should only return the path to the source file;
               sourceless loading is not supported.

     The abstract methods defined by this class are to add optional
     bytecode file support.  Not implementing these optional methods (or
     causing them to raise *note NotImplementedError: 704.) causes the
     loader to only work with source code.  Implementing the methods
     allows the loader to work with source `and' bytecode files; it does
     not allow for `sourceless' loading where only bytecode is provided.
     Bytecode files are an optimization to speed up loading by removing
     the parsing step of Python’s compiler, and so no bytecode-specific
     API is exposed.

      -- Method: path_stats (path)

          Optional abstract method which returns a *note dict: 164.
          containing metadata about the specified path.  Supported
          dictionary keys are:

             - ‘'mtime'’ (mandatory): an integer or floating-point
               number representing the modification time of the source
               code;

             - ‘'size'’ (optional): the size in bytes of the source
               code.

          Any other keys in the dictionary are ignored, to allow for
          future extensions.  If the path cannot be handled, *note
          OSError: 304. is raised.

          New in version 3.3.

          Changed in version 3.4: Raise *note OSError: 304. instead of
          *note NotImplementedError: 704.

      -- Method: path_mtime (path)

          Optional abstract method which returns the modification time
          for the specified path.

          Deprecated since version 3.3: This method is deprecated in
          favour of *note path_stats(): bc3.  You don’t have to
          implement it, but it is still available for compatibility
          purposes.  Raise *note OSError: 304. if the path cannot be
          handled.

          Changed in version 3.4: Raise *note OSError: 304. instead of
          *note NotImplementedError: 704.

      -- Method: set_data (path, data)

          Optional abstract method which writes the specified bytes to a
          file path.  Any intermediate directories which do not exist
          are to be created automatically.

          When writing to the path fails because the path is read-only
          (*note errno.EACCES: 23a0./*note PermissionError: 6f6.), do
          not propagate the exception.

          Changed in version 3.4: No longer raises *note
          NotImplementedError: 704. when called.

      -- Method: get_code (fullname)

          Concrete implementation of *note InspectLoader.get_code():
          94c.

      -- Method: exec_module (module)

          Concrete implementation of *note Loader.exec_module(): 6db.

          New in version 3.4.

      -- Method: load_module (fullname)

          Concrete implementation of *note Loader.load_module(): 6da.

          Deprecated since version 3.4: Use *note exec_module(): a24.
          instead.

      -- Method: get_source (fullname)

          Concrete implementation of *note InspectLoader.get_source():
          950.

      -- Method: is_package (fullname)

          Concrete implementation of *note InspectLoader.is_package():
          38dd.  A module is determined to be a package if its file path
          (as provided by *note ExecutionLoader.get_filename(): 38df.)
          is a file named ‘__init__’ when the file extension is removed
          `and' the module name itself does not end in ‘__init__’.

 -- Class: importlib.abc.Traversable

     An object with a subset of pathlib.Path methods suitable for
     traversing directories and opening files.

     New in version 3.9.

      -- Method: abstractmethod name ()

          The base name of this object without any parent references.

      -- Method: abstractmethod iterdir ()

          Yield Traversable objects in self.

      -- Method: abstractmethod is_dir ()

          Return True if self is a directory.

      -- Method: abstractmethod is_file ()

          Return True if self is a file.

      -- Method: abstractmethod joinpath (child)

          Return Traversable child in self.

      -- Method: abstractmethod __truediv__ (child)

          Return Traversable child in self.

      -- Method: abstractmethod open (mode='r', *args, **kwargs)

          `mode' may be ‘r’ or ‘rb’ to open as text or binary.  Return a
          handle suitable for reading (same as *note pathlib.Path.open:
          1d3a.).

          When opening as text, accepts encoding parameters such as
          those accepted by *note io.TextIOWrapper: 6ea.

      -- Method: read_bytes ()

          Read contents of self as bytes.

      -- Method: read_text (encoding=None)

          Read contents of self as text.

 -- Class: importlib.abc.TraversableResources

     An abstract base class for resource readers capable of serving the
     ‘files’ interface.  Subclasses ResourceReader and provides concrete
     implementations of the ResourceReader’s abstract methods.
     Therefore, any loader supplying TraversableReader also supplies
     ResourceReader.

     New in version 3.9.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/importlib/abc.py

   (2) https://www.python.org/dev/peps/pep-0302

   (3) https://www.python.org/dev/peps/pep-0302

   (4) https://www.python.org/dev/peps/pep-0302

   (5) https://www.python.org/dev/peps/pep-0302

   (6) https://www.python.org/dev/peps/pep-0302


File: python.info,  Node: importlib resources – Resources,  Next: importlib machinery – Importers and path hooks,  Prev: importlib abc – Abstract base classes related to import,  Up: importlib — The implementation of import

5.31.5.4 ‘importlib.resources’ – Resources
..........................................

`Source code:' Lib/importlib/resources.py(1)

__________________________________________________________________

New in version 3.7.

This module leverages Python’s import system to provide access to
`resources' within `packages'.  If you can import a package, you can
access resources within that package.  Resources can be opened or read,
in either binary or text mode.

Resources are roughly akin to files inside directories, though it’s
important to keep in mind that this is just a metaphor.  Resources and
packages `do not' have to exist as physical files and directories on the
file system.

     Note: This module provides functionality similar to
     pkg_resources(2) Basic Resource Access(3) without the performance
     overhead of that package.  This makes reading resources included in
     packages easier, with more stable and consistent semantics.

     The standalone backport of this module provides more information on
     using importlib.resources(4) and migrating from pkg_resources to
     importlib.resources(5).

Loaders that wish to support resource reading should implement a
‘get_resource_reader(fullname)’ method as specified by *note
importlib.abc.ResourceReader: 44e.

The following types are defined.

 -- Data: importlib.resources.Package

     The ‘Package’ type is defined as ‘Union[str, ModuleType]’.  This
     means that where the function describes accepting a ‘Package’, you
     can pass in either a string or a module.  Module objects must have
     a resolvable ‘__spec__.submodule_search_locations’ that is not
     ‘None’.

 -- Data: importlib.resources.Resource

     This type describes the resource names passed into the various
     functions in this package.  This is defined as ‘Union[str,
     os.PathLike]’.

The following functions are available.

 -- Function: importlib.resources.files (package)

     Returns an ‘importlib.resources.abc.Traversable’ object
     representing the resource container for the package (think
     directory) and its resources (think files).  A Traversable may
     contain other containers (think subdirectories).

     `package' is either a name or a module object which conforms to the
     ‘Package’ requirements.

     New in version 3.9.

 -- Function: importlib.resources.as_file (traversable)

     Given a ‘importlib.resources.abc.Traversable’ object representing a
     file, typically from *note importlib.resources.files(): 1b7, return
     a context manager for use in a *note with: 7da. statement.  The
     context manager provides a *note pathlib.Path: 32f. object.

     Exiting the context manager cleans up any temporary file created
     when the resource was extracted from e.g.  a zip file.

     Use ‘as_file’ when the Traversable methods (‘read_text’, etc) are
     insufficient and an actual file on the file system is required.

     New in version 3.9.

 -- Function: importlib.resources.open_binary (package, resource)

     Open for binary reading the `resource' within `package'.

     `package' is either a name or a module object which conforms to the
     ‘Package’ requirements.  `resource' is the name of the resource to
     open within `package'; it may not contain path separators and it
     may not have sub-resources (i.e.  it cannot be a directory).  This
     function returns a ‘typing.BinaryIO’ instance, a binary I/O stream
     open for reading.

 -- Function: importlib.resources.open_text (package, resource,
          encoding='utf-8', errors='strict')

     Open for text reading the `resource' within `package'.  By default,
     the resource is opened for reading as UTF-8.

     `package' is either a name or a module object which conforms to the
     ‘Package’ requirements.  `resource' is the name of the resource to
     open within `package'; it may not contain path separators and it
     may not have sub-resources (i.e.  it cannot be a directory).
     `encoding' and `errors' have the same meaning as with built-in
     *note open(): 16f.

     This function returns a ‘typing.TextIO’ instance, a text I/O stream
     open for reading.

 -- Function: importlib.resources.read_binary (package, resource)

     Read and return the contents of the `resource' within `package' as
     ‘bytes’.

     `package' is either a name or a module object which conforms to the
     ‘Package’ requirements.  `resource' is the name of the resource to
     open within `package'; it may not contain path separators and it
     may not have sub-resources (i.e.  it cannot be a directory).  This
     function returns the contents of the resource as *note bytes: 172.

 -- Function: importlib.resources.read_text (package, resource,
          encoding='utf-8', errors='strict')

     Read and return the contents of `resource' within `package' as a
     ‘str’.  By default, the contents are read as strict UTF-8.

     `package' is either a name or a module object which conforms to the
     ‘Package’ requirements.  `resource' is the name of the resource to
     open within `package'; it may not contain path separators and it
     may not have sub-resources (i.e.  it cannot be a directory).
     `encoding' and `errors' have the same meaning as with built-in
     *note open(): 16f.  This function returns the contents of the
     resource as *note str: 205.

 -- Function: importlib.resources.path (package, resource)

     Return the path to the `resource' as an actual file system path.
     This function returns a context manager for use in a *note with:
     7da. statement.  The context manager provides a *note pathlib.Path:
     32f. object.

     Exiting the context manager cleans up any temporary file created
     when the resource needs to be extracted from e.g.  a zip file.

     `package' is either a name or a module object which conforms to the
     ‘Package’ requirements.  `resource' is the name of the resource to
     open within `package'; it may not contain path separators and it
     may not have sub-resources (i.e.  it cannot be a directory).

 -- Function: importlib.resources.is_resource (package, name)

     Return ‘True’ if there is a resource named `name' in the package,
     otherwise ‘False’.  Remember that directories are `not' resources!
     `package' is either a name or a module object which conforms to the
     ‘Package’ requirements.

 -- Function: importlib.resources.contents (package)

     Return an iterable over the named items within the package.  The
     iterable returns *note str: 205. resources (e.g.  files) and
     non-resources (e.g.  directories).  The iterable does not recurse
     into subdirectories.

     `package' is either a name or a module object which conforms to the
     ‘Package’ requirements.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/importlib/resources.py

   (2) https://setuptools.readthedocs.io/en/latest/pkg_resources.html

   (3) 
http://setuptools.readthedocs.io/en/latest/pkg_resources.html#basic-resource-access

   (4) http://importlib-resources.readthedocs.io/en/latest/using.html

   (5) 
http://importlib-resources.readthedocs.io/en/latest/migration.html


File: python.info,  Node: importlib machinery – Importers and path hooks,  Next: importlib util – Utility code for importers,  Prev: importlib resources – Resources,  Up: importlib — The implementation of import

5.31.5.5 ‘importlib.machinery’ – Importers and path hooks
.........................................................

`Source code:' Lib/importlib/machinery.py(1)

__________________________________________________________________

This module contains the various objects that help *note import: ce7.
find and load modules.

 -- Attribute: importlib.machinery.SOURCE_SUFFIXES

     A list of strings representing the recognized file suffixes for
     source modules.

     New in version 3.3.

 -- Attribute: importlib.machinery.DEBUG_BYTECODE_SUFFIXES

     A list of strings representing the file suffixes for non-optimized
     bytecode modules.

     New in version 3.3.

     Deprecated since version 3.5: Use *note BYTECODE_SUFFIXES: 38fe.
     instead.

 -- Attribute: importlib.machinery.OPTIMIZED_BYTECODE_SUFFIXES

     A list of strings representing the file suffixes for optimized
     bytecode modules.

     New in version 3.3.

     Deprecated since version 3.5: Use *note BYTECODE_SUFFIXES: 38fe.
     instead.

 -- Attribute: importlib.machinery.BYTECODE_SUFFIXES

     A list of strings representing the recognized file suffixes for
     bytecode modules (including the leading dot).

     New in version 3.3.

     Changed in version 3.5: The value is no longer dependent on
     ‘__debug__’.

 -- Attribute: importlib.machinery.EXTENSION_SUFFIXES

     A list of strings representing the recognized file suffixes for
     extension modules.

     New in version 3.3.

 -- Function: importlib.machinery.all_suffixes ()

     Returns a combined list of strings representing all file suffixes
     for modules recognized by the standard import machinery.  This is a
     helper for code which simply needs to know if a filesystem path
     potentially refers to a module without needing any details on the
     kind of module (for example, *note inspect.getmodulename(): 6e9.).

     New in version 3.3.

 -- Class: importlib.machinery.BuiltinImporter

     An *note importer: 15f7. for built-in modules.  All known built-in
     modules are listed in *note sys.builtin_module_names: 37a8.  This
     class implements the *note importlib.abc.MetaPathFinder: a93. and
     *note importlib.abc.InspectLoader: 94b. ABCs.

     Only class methods are defined by this class to alleviate the need
     for instantiation.

     Changed in version 3.5: As part of PEP 489(2), the builtin importer
     now implements ‘Loader.create_module()’ and ‘Loader.exec_module()’

 -- Class: importlib.machinery.FrozenImporter

     An *note importer: 15f7. for frozen modules.  This class implements
     the *note importlib.abc.MetaPathFinder: a93. and *note
     importlib.abc.InspectLoader: 94b. ABCs.

     Only class methods are defined by this class to alleviate the need
     for instantiation.

     Changed in version 3.4: Gained ‘create_module()’ and
     ‘exec_module()’ methods.

 -- Class: importlib.machinery.WindowsRegistryFinder

     *note Finder: 15f5. for modules declared in the Windows registry.
     This class implements the *note importlib.abc.MetaPathFinder: a93.
     ABC.

     Only class methods are defined by this class to alleviate the need
     for instantiation.

     New in version 3.3.

     Deprecated since version 3.6: Use *note site: eb. configuration
     instead.  Future versions of Python may not enable this finder by
     default.

 -- Class: importlib.machinery.PathFinder

     A *note Finder: 15f5. for *note sys.path: 260. and package
     ‘__path__’ attributes.  This class implements the *note
     importlib.abc.MetaPathFinder: a93. ABC.

     Only class methods are defined by this class to alleviate the need
     for instantiation.

      -- Method: classmethod find_spec (fullname, path=None,
               target=None)

          Class method that attempts to find a *note spec: 37bb. for the
          module specified by `fullname' on *note sys.path: 260. or, if
          defined, on `path'.  For each path entry that is searched,
          *note sys.path_importer_cache: 598. is checked.  If a
          non-false object is found then it is used as the *note path
          entry finder: a92. to look for the module being searched for.
          If no entry is found in *note sys.path_importer_cache: 598,
          then *note sys.path_hooks: a3d. is searched for a finder for
          the path entry and, if found, is stored in *note
          sys.path_importer_cache: 598. along with being queried about
          the module.  If no finder is ever found then ‘None’ is both
          stored in the cache and returned.

          New in version 3.4.

          Changed in version 3.5: If the current working directory –
          represented by an empty string – is no longer valid then
          ‘None’ is returned but no value is cached in *note
          sys.path_importer_cache: 598.

      -- Method: classmethod find_module (fullname, path=None)

          A legacy wrapper around *note find_spec(): a1e.

          Deprecated since version 3.4: Use *note find_spec(): a1e.
          instead.

      -- Method: classmethod invalidate_caches ()

          Calls *note importlib.abc.PathEntryFinder.invalidate_caches():
          38d9. on all finders stored in *note sys.path_importer_cache:
          598. that define the method.  Otherwise entries in *note
          sys.path_importer_cache: 598. set to ‘None’ are deleted.

          Changed in version 3.7: Entries of ‘None’ in *note
          sys.path_importer_cache: 598. are deleted.

     Changed in version 3.4: Calls objects in *note sys.path_hooks: a3d.
     with the current working directory for ‘''’ (i.e.  the empty
     string).

 -- Class: importlib.machinery.FileFinder (path, *loader_details)

     A concrete implementation of *note importlib.abc.PathEntryFinder:
     a94. which caches results from the file system.

     The `path' argument is the directory for which the finder is in
     charge of searching.

     The `loader_details' argument is a variable number of 2-item tuples
     each containing a loader and a sequence of file suffixes the loader
     recognizes.  The loaders are expected to be callables which accept
     two arguments of the module’s name and the path to the file found.

     The finder will cache the directory contents as necessary, making
     stat calls for each module search to verify the cache is not
     outdated.  Because cache staleness relies upon the granularity of
     the operating system’s state information of the file system, there
     is a potential race condition of searching for a module, creating a
     new file, and then searching for the module the new file
     represents.  If the operations happen fast enough to fit within the
     granularity of stat calls, then the module search will fail.  To
     prevent this from happening, when you create a module dynamically,
     make sure to call *note importlib.invalidate_caches(): 597.

     New in version 3.3.

      -- Attribute: path

          The path the finder will search in.

      -- Method: find_spec (fullname, target=None)

          Attempt to find the spec to handle `fullname' within *note
          path: 3901.

          New in version 3.4.

      -- Method: find_loader (fullname)

          Attempt to find the loader to handle `fullname' within *note
          path: 3901.

      -- Method: invalidate_caches ()

          Clear out the internal cache.

      -- Method: classmethod path_hook (*loader_details)

          A class method which returns a closure for use on *note
          sys.path_hooks: a3d.  An instance of *note FileFinder: a96. is
          returned by the closure using the path argument given to the
          closure directly and `loader_details' indirectly.

          If the argument to the closure is not an existing directory,
          *note ImportError: 16c. is raised.

 -- Class: importlib.machinery.SourceFileLoader (fullname, path)

     A concrete implementation of *note importlib.abc.SourceLoader:
     38e4. by subclassing *note importlib.abc.FileLoader: a97. and
     providing some concrete implementations of other methods.

     New in version 3.3.

      -- Attribute: name

          The name of the module that this loader will handle.

      -- Attribute: path

          The path to the source file.

      -- Method: is_package (fullname)

          Return ‘True’ if *note path: 3906. appears to be for a
          package.

      -- Method: path_stats (path)

          Concrete implementation of *note
          importlib.abc.SourceLoader.path_stats(): bc3.

      -- Method: set_data (path, data)

          Concrete implementation of *note
          importlib.abc.SourceLoader.set_data(): 38e5.

      -- Method: load_module (name=None)

          Concrete implementation of *note
          importlib.abc.Loader.load_module(): 6da. where specifying the
          name of the module to load is optional.

          Deprecated since version 3.6: Use *note
          importlib.abc.Loader.exec_module(): 6db. instead.

 -- Class: importlib.machinery.SourcelessFileLoader (fullname, path)

     A concrete implementation of *note importlib.abc.FileLoader: a97.
     which can import bytecode files (i.e.  no source code files exist).

     Please note that direct use of bytecode files (and thus not source
     code files) inhibits your modules from being usable by all Python
     implementations or new versions of Python which change the bytecode
     format.

     New in version 3.3.

      -- Attribute: name

          The name of the module the loader will handle.

      -- Attribute: path

          The path to the bytecode file.

      -- Method: is_package (fullname)

          Determines if the module is a package based on *note path:
          390b.

      -- Method: get_code (fullname)

          Returns the code object for *note name: 390a. created from
          *note path: 390b.

      -- Method: get_source (fullname)

          Returns ‘None’ as bytecode files have no source when this
          loader is used.

      -- Method: load_module (name=None)

     Concrete implementation of *note
     importlib.abc.Loader.load_module(): 6da. where specifying the name
     of the module to load is optional.

     Deprecated since version 3.6: Use *note
     importlib.abc.Loader.exec_module(): 6db. instead.

 -- Class: importlib.machinery.ExtensionFileLoader (fullname, path)

     A concrete implementation of *note importlib.abc.ExecutionLoader:
     38de. for extension modules.

     The `fullname' argument specifies the name of the module the loader
     is to support.  The `path' argument is the path to the extension
     module’s file.

     New in version 3.3.

      -- Attribute: name

          Name of the module the loader supports.

      -- Attribute: path

          Path to the extension module.

      -- Method: create_module (spec)

          Creates the module object from the given specification in
          accordance with PEP 489(3).

          New in version 3.5.

      -- Method: exec_module (module)

          Initializes the given module object in accordance with PEP
          489(4).

          New in version 3.5.

      -- Method: is_package (fullname)

          Returns ‘True’ if the file path points to a package’s
          ‘__init__’ module based on *note EXTENSION_SUFFIXES: 3900.

      -- Method: get_code (fullname)

          Returns ‘None’ as extension modules lack a code object.

      -- Method: get_source (fullname)

          Returns ‘None’ as extension modules do not have source code.

      -- Method: get_filename (fullname)

          Returns *note path: 3910.

          New in version 3.4.

 -- Class: importlib.machinery.ModuleSpec (name, loader, *, origin=None,
          loader_state=None, is_package=None)

     A specification for a module’s import-system-related state.  This
     is typically exposed as the module’s ‘__spec__’ attribute.  In the
     descriptions below, the names in parentheses give the corresponding
     attribute available directly on the module object.  E.g.
     ‘module.__spec__.origin == module.__file__’.  Note however that
     while the `values' are usually equivalent, they can differ since
     there is no synchronization between the two objects.  Thus it is
     possible to update the module’s ‘__path__’ at runtime, and this
     will not be automatically reflected in
     ‘__spec__.submodule_search_locations’.

     New in version 3.4.

      -- Attribute: name

     (‘__name__’)

     A string for the fully-qualified name of the module.

      -- Attribute: loader

     (‘__loader__’)

     The *note Loader: 15f6. that should be used when loading the
     module.  *note Finders: 15f5. should always set this.

      -- Attribute: origin

     (‘__file__’)

     Name of the place from which the module is loaded, e.g.  “builtin”
     for built-in modules and the filename for modules loaded from
     source.  Normally “origin” should be set, but it may be ‘None’ (the
     default) which indicates it is unspecified (e.g.  for namespace
     packages).

      -- Attribute: submodule_search_locations

     (‘__path__’)

     List of strings for where to find submodules, if a package (‘None’
     otherwise).

      -- Attribute: loader_state

     Container of extra module-specific data for use during loading (or
     ‘None’).

      -- Attribute: cached

     (‘__cached__’)

     String for where the compiled module should be stored (or ‘None’).

      -- Attribute: parent

     (‘__package__’)

     (Read-only) The fully-qualified name of the package under which the
     module should be loaded as a submodule (or the empty string for
     top-level modules).  For packages, it is the same as *note
     __name__: dd8.

      -- Attribute: has_location

     Boolean indicating whether or not the module’s “origin” attribute
     refers to a loadable location.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/importlib/machinery.py

   (2) https://www.python.org/dev/peps/pep-0489

   (3) https://www.python.org/dev/peps/pep-0489

   (4) https://www.python.org/dev/peps/pep-0489


File: python.info,  Node: importlib util – Utility code for importers,  Next: Examples<30>,  Prev: importlib machinery – Importers and path hooks,  Up: importlib — The implementation of import

5.31.5.6 ‘importlib.util’ – Utility code for importers
......................................................

`Source code:' Lib/importlib/util.py(1)

__________________________________________________________________

This module contains the various objects that help in the construction
of an *note importer: 15f7.

 -- Attribute: importlib.util.MAGIC_NUMBER

     The bytes which represent the bytecode version number.  If you need
     help with loading/writing bytecode then consider *note
     importlib.abc.SourceLoader: 38e4.

     New in version 3.4.

 -- Function: importlib.util.cache_from_source (path,
          debug_override=None, *, optimization=None)

     Return the PEP 3147(2)/ PEP 488(3) path to the byte-compiled file
     associated with the source `path'.  For example, if `path' is
     ‘/foo/bar/baz.py’ the return value would be
     ‘/foo/bar/__pycache__/baz.cpython-32.pyc’ for Python 3.2.  The
     ‘cpython-32’ string comes from the current magic tag (see
     ‘get_tag()’; if ‘sys.implementation.cache_tag’ is not defined then
     *note NotImplementedError: 704. will be raised).

     The `optimization' parameter is used to specify the optimization
     level of the bytecode file.  An empty string represents no
     optimization, so ‘/foo/bar/baz.py’ with an `optimization' of ‘''’
     will result in a bytecode path of
     ‘/foo/bar/__pycache__/baz.cpython-32.pyc’.  ‘None’ causes the
     interpreter’s optimization level to be used.  Any other value’s
     string representation is used, so ‘/foo/bar/baz.py’ with an
     `optimization' of ‘2’ will lead to the bytecode path of
     ‘/foo/bar/__pycache__/baz.cpython-32.opt-2.pyc’.  The string
     representation of `optimization' can only be alphanumeric, else
     *note ValueError: 16d. is raised.

     The `debug_override' parameter is deprecated and can be used to
     override the system’s value for ‘__debug__’.  A ‘True’ value is the
     equivalent of setting `optimization' to the empty string.  A
     ‘False’ value is the same as setting `optimization' to ‘1’.  If
     both `debug_override' an `optimization' are not ‘None’ then *note
     TypeError: 1fe. is raised.

     New in version 3.4.

     Changed in version 3.5: The `optimization' parameter was added and
     the `debug_override' parameter was deprecated.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: importlib.util.source_from_cache (path)

     Given the `path' to a PEP 3147(4) file name, return the associated
     source code file path.  For example, if `path' is
     ‘/foo/bar/__pycache__/baz.cpython-32.pyc’ the returned path would
     be ‘/foo/bar/baz.py’.  `path' need not exist, however if it does
     not conform to PEP 3147(5) or PEP 488(6) format, a *note
     ValueError: 16d. is raised.  If ‘sys.implementation.cache_tag’ is
     not defined, *note NotImplementedError: 704. is raised.

     New in version 3.4.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: importlib.util.decode_source (source_bytes)

     Decode the given bytes representing source code and return it as a
     string with universal newlines (as required by *note
     importlib.abc.InspectLoader.get_source(): 950.).

     New in version 3.4.

 -- Function: importlib.util.resolve_name (name, package)

     Resolve a relative module name to an absolute one.

     If `name' has no leading dots, then `name' is simply returned.
     This allows for usage such as ‘importlib.util.resolve_name('sys',
     __spec__.parent)’ without doing a check to see if the `package'
     argument is needed.

     *note ImportError: 16c. is raised if `name' is a relative module
     name but `package' is a false value (e.g.  ‘None’ or the empty
     string).  *note ImportError: 16c. is also raised a relative name
     would escape its containing package (e.g.  requesting ‘..bacon’
     from within the ‘spam’ package).

     New in version 3.3.

     Changed in version 3.9: To improve consistency with import
     statements, raise *note ImportError: 16c. instead of *note
     ValueError: 16d. for invalid relative import attempts.

 -- Function: importlib.util.find_spec (name, package=None)

     Find the *note spec: 37bb. for a module, optionally relative to the
     specified `package' name.  If the module is in *note sys.modules:
     1051, then ‘sys.modules[name].__spec__’ is returned (unless the
     spec would be ‘None’ or is not set, in which case *note ValueError:
     16d. is raised).  Otherwise a search using *note sys.meta_path:
     6dd. is done.  ‘None’ is returned if no spec is found.

     If `name' is for a submodule (contains a dot), the parent module is
     automatically imported.

     `name' and `package' work the same as for ‘import_module()’.

     New in version 3.4.

     Changed in version 3.7: Raises *note ModuleNotFoundError: 4a1.
     instead of *note AttributeError: 4a2. if `package' is in fact not a
     package (i.e.  lacks a *note __path__: 13c3. attribute).

 -- Function: importlib.util.module_from_spec (spec)

     Create a new module based on `spec' and *note
     spec.loader.create_module: 64e.

     If *note spec.loader.create_module: 64e. does not return ‘None’,
     then any pre-existing attributes will not be reset.  Also, no *note
     AttributeError: 4a2. will be raised if triggered while accessing
     `spec' or setting an attribute on the module.

     This function is preferred over using *note types.ModuleType: 7e2.
     to create a new module as `spec' is used to set as many
     import-controlled attributes on the module as possible.

     New in version 3.5.

 -- Function: @importlib.util.module_for_loader

     A *note decorator: 174. for *note
     importlib.abc.Loader.load_module(): 6da. to handle selecting the
     proper module object to load with.  The decorated method is
     expected to have a call signature taking two positional arguments
     (e.g.  ‘load_module(self, module)’) for which the second argument
     will be the module `object' to be used by the loader.  Note that
     the decorator will not work on static methods because of the
     assumption of two arguments.

     The decorated method will take in the `name' of the module to be
     loaded as expected for a *note loader: 15f6.  If the module is not
     found in *note sys.modules: 1051. then a new one is constructed.
     Regardless of where the module came from, *note __loader__: a37.
     set to `self' and *note __package__: a36. is set based on what
     *note importlib.abc.InspectLoader.is_package(): 38dd. returns (if
     available).  These attributes are set unconditionally to support
     reloading.

     If an exception is raised by the decorated method and a module was
     added to *note sys.modules: 1051, then the module will be removed
     to prevent a partially initialized module from being in left in
     *note sys.modules: 1051.  If the module was already in *note
     sys.modules: 1051. then it is left alone.

     Changed in version 3.3: *note __loader__: a37. and *note
     __package__: a36. are automatically set (when possible).

     Changed in version 3.4: Set *note __name__: dd8, *note __loader__:
     a37. *note __package__: a36. unconditionally to support reloading.

     Deprecated since version 3.4: The import machinery now directly
     performs all the functionality provided by this function.

 -- Function: @importlib.util.set_loader

     A *note decorator: 174. for *note
     importlib.abc.Loader.load_module(): 6da. to set the *note
     __loader__: a37. attribute on the returned module.  If the
     attribute is already set the decorator does nothing.  It is assumed
     that the first positional argument to the wrapped method (i.e.
     ‘self’) is what *note __loader__: a37. should be set to.

     Changed in version 3.4: Set ‘__loader__’ if set to ‘None’, as if
     the attribute does not exist.

     Deprecated since version 3.4: The import machinery takes care of
     this automatically.

 -- Function: @importlib.util.set_package

     A *note decorator: 174. for *note
     importlib.abc.Loader.load_module(): 6da. to set the *note
     __package__: a36. attribute on the returned module.  If *note
     __package__: a36. is set and has a value other than ‘None’ it will
     not be changed.

     Deprecated since version 3.4: The import machinery takes care of
     this automatically.

 -- Function: importlib.util.spec_from_loader (name, loader, *,
          origin=None, is_package=None)

     A factory function for creating a ‘ModuleSpec’ instance based on a
     loader.  The parameters have the same meaning as they do for
     ModuleSpec.  The function uses available *note loader: 15f6. APIs,
     such as ‘InspectLoader.is_package()’, to fill in any missing
     information on the spec.

     New in version 3.4.

 -- Function: importlib.util.spec_from_file_location (name, location, *,
          loader=None, submodule_search_locations=None)

     A factory function for creating a ‘ModuleSpec’ instance based on
     the path to a file.  Missing information will be filled in on the
     spec by making use of loader APIs and by the implication that the
     module will be file-based.

     New in version 3.4.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- Function: importlib.util.source_hash (source_bytes)

     Return the hash of `source_bytes' as bytes.  A hash-based ‘.pyc’
     file embeds the *note source_hash(): 391c. of the corresponding
     source file’s contents in its header.

     New in version 3.7.

 -- Class: importlib.util.LazyLoader (loader)

     A class which postpones the execution of the loader of a module
     until the module has an attribute accessed.

     This class `only' works with loaders that define *note
     exec_module(): 6db. as control over what module type is used for
     the module is required.  For those same reasons, the loader’s *note
     create_module(): 64e. method must return ‘None’ or a type for which
     its ‘__class__’ attribute can be mutated along with not using *note
     slots: 391d.  Finally, modules which substitute the object placed
     into *note sys.modules: 1051. will not work as there is no way to
     properly replace the module references throughout the interpreter
     safely; *note ValueError: 16d. is raised if such a substitution is
     detected.

          Note: For projects where startup time is critical, this class
          allows for potentially minimizing the cost of loading a module
          if it is never used.  For projects where startup time is not
          essential then use of this class is `heavily' discouraged due
          to error messages created during loading being postponed and
          thus occurring out of context.

     New in version 3.5.

     Changed in version 3.6: Began calling *note create_module(): 64e,
     removing the compatibility warning for *note
     importlib.machinery.BuiltinImporter: 64f. and *note
     importlib.machinery.ExtensionFileLoader: 650.

      -- Method: classmethod factory (loader)

          A static method which returns a callable that creates a lazy
          loader.  This is meant to be used in situations where the
          loader is passed by class instead of by instance.

               suffixes = importlib.machinery.SOURCE_SUFFIXES
               loader = importlib.machinery.SourceFileLoader
               lazy_loader = importlib.util.LazyLoader.factory(loader)
               finder = importlib.machinery.FileFinder(path, (lazy_loader, suffixes))

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/importlib/util.py

   (2) https://www.python.org/dev/peps/pep-3147

   (3) https://www.python.org/dev/peps/pep-0488

   (4) https://www.python.org/dev/peps/pep-3147

   (5) https://www.python.org/dev/peps/pep-3147

   (6) https://www.python.org/dev/peps/pep-0488


File: python.info,  Node: Examples<30>,  Prev: importlib util – Utility code for importers,  Up: importlib — The implementation of import

5.31.5.7 Examples
.................

* Menu:

* Importing programmatically::
* Checking if a module can be imported::
* Importing a source file directly::
* Setting up an importer::
* Approximating importlib.import_module(): Approximating importlib import_module.


File: python.info,  Node: Importing programmatically,  Next: Checking if a module can be imported,  Up: Examples<30>

5.31.5.8 Importing programmatically
...................................

To programmatically import a module, use *note
importlib.import_module(): be6.

     import importlib

     itertools = importlib.import_module('itertools')


File: python.info,  Node: Checking if a module can be imported,  Next: Importing a source file directly,  Prev: Importing programmatically,  Up: Examples<30>

5.31.5.9 Checking if a module can be imported
.............................................

If you need to find out if a module can be imported without actually
doing the import, then you should use *note importlib.util.find_spec():
a1c.

     import importlib.util
     import sys

     # For illustrative purposes.
     name = 'itertools'

     if name in sys.modules:
         print(f"{name!r} already in sys.modules")
     elif (spec := importlib.util.find_spec(name)) is not None:
         # If you chose to perform the actual import ...
         module = importlib.util.module_from_spec(spec)
         sys.modules[name] = module
         spec.loader.exec_module(module)
         print(f"{name!r} has been imported")
     else:
         print(f"can't find the {name!r} module")


File: python.info,  Node: Importing a source file directly,  Next: Setting up an importer,  Prev: Checking if a module can be imported,  Up: Examples<30>

5.31.5.10 Importing a source file directly
..........................................

To import a Python source file directly, use the following recipe
(Python 3.5 and newer only):

     import importlib.util
     import sys

     # For illustrative purposes.
     import tokenize
     file_path = tokenize.__file__
     module_name = tokenize.__name__

     spec = importlib.util.spec_from_file_location(module_name, file_path)
     module = importlib.util.module_from_spec(spec)
     sys.modules[module_name] = module
     spec.loader.exec_module(module)


File: python.info,  Node: Setting up an importer,  Next: Approximating importlib import_module,  Prev: Importing a source file directly,  Up: Examples<30>

5.31.5.11 Setting up an importer
................................

For deep customizations of import, you typically want to implement an
*note importer: 15f7.  This means managing both the *note finder: 15f5.
and *note loader: 15f6. side of things.  For finders there are two
flavours to choose from depending on your needs: a *note meta path
finder: a91. or a *note path entry finder: a92.  The former is what you
would put on *note sys.meta_path: 6dd. while the latter is what you
create using a *note path entry hook: 160d. on *note sys.path_hooks:
a3d. which works with *note sys.path: 260. entries to potentially create
a finder.  This example will show you how to register your own importers
so that import will use them (for creating an importer for yourself,
read the documentation for the appropriate classes defined within this
package):

     import importlib.machinery
     import sys

     # For illustrative purposes only.
     SpamMetaPathFinder = importlib.machinery.PathFinder
     SpamPathEntryFinder = importlib.machinery.FileFinder
     loader_details = (importlib.machinery.SourceFileLoader,
                       importlib.machinery.SOURCE_SUFFIXES)

     # Setting up a meta path finder.
     # Make sure to put the finder in the proper location in the list in terms of
     # priority.
     sys.meta_path.append(SpamMetaPathFinder)

     # Setting up a path entry finder.
     # Make sure to put the path hook in the proper location in the list in terms
     # of priority.
     sys.path_hooks.append(SpamPathEntryFinder.path_hook(loader_details))


File: python.info,  Node: Approximating importlib import_module,  Prev: Setting up an importer,  Up: Examples<30>

5.31.5.12 Approximating ‘importlib.import_module()’
...................................................

Import itself is implemented in Python code, making it possible to
expose most of the import machinery through importlib.  The following
helps illustrate the various APIs that importlib exposes by providing an
approximate implementation of *note importlib.import_module(): be6.
(Python 3.4 and newer for the importlib usage, Python 3.6 and newer for
other parts of the code).

     import importlib.util
     import sys

     def import_module(name, package=None):
         """An approximate implementation of import."""
         absolute_name = importlib.util.resolve_name(name, package)
         try:
             return sys.modules[absolute_name]
         except KeyError:
             pass

         path = None
         if '.' in absolute_name:
             parent_name, _, child_name = absolute_name.rpartition('.')
             parent_module = import_module(parent_name)
             path = parent_module.__spec__.submodule_search_locations
         for finder in sys.meta_path:
             spec = finder.find_spec(absolute_name, path)
             if spec is not None:
                 break
         else:
             msg = f'No module named {absolute_name!r}'
             raise ModuleNotFoundError(msg, name=absolute_name)
         module = importlib.util.module_from_spec(spec)
         sys.modules[absolute_name] = module
         spec.loader.exec_module(module)
         if path is not None:
             setattr(parent_module, child_name, module)
         return module


File: python.info,  Node: Using importlib metadata,  Prev: importlib — The implementation of import,  Up: Importing Modules

5.31.6 Using ‘importlib.metadata’
---------------------------------

`Source code:' Lib/importlib/metadata.py(1)

New in version 3.8.

     Note: This functionality is provisional and may deviate from the
     usual version semantics of the standard library.

‘importlib.metadata’ is a library that provides for access to installed
package metadata.  Built in part on Python’s import system, this library
intends to replace similar functionality in the entry point API(2) and
metadata API(3) of ‘pkg_resources’.  Along with *note
importlib.resources: 9e. in Python 3.7 and newer (backported as
importlib_resources(4) for older versions of Python), this can eliminate
the need to use the older and less efficient ‘pkg_resources’ package.

By “installed package” we generally mean a third-party package installed
into Python’s ‘site-packages’ directory via tools such as pip(5).
Specifically, it means a package with either a discoverable ‘dist-info’
or ‘egg-info’ directory, and metadata defined by PEP 566(6) or its older
specifications.  By default, package metadata can live on the file
system or in zip archives on *note sys.path: 260.  Through an extension
mechanism, the metadata can live almost anywhere.

* Menu:

* Overview: Overview<2>.
* Functional API: Functional API<2>.
* Distributions::
* Extending the search algorithm::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/importlib/metadata.py

   (2) 
https://setuptools.readthedocs.io/en/latest/pkg_resources.html#entry-points

   (3) 
https://setuptools.readthedocs.io/en/latest/pkg_resources.html#metadata-api

   (4) https://importlib-resources.readthedocs.io/en/latest/index.html

   (5) https://pypi.org/project/pip/

   (6) https://www.python.org/dev/peps/pep-0566


File: python.info,  Node: Overview<2>,  Next: Functional API<2>,  Up: Using importlib metadata

5.31.6.1 Overview
.................

Let’s say you wanted to get the version string for a package you’ve
installed using ‘pip’.  We start by creating a virtual environment and
installing something into it:

     $ python3 -m venv example
     $ source example/bin/activate
     (example) $ pip install wheel

You can get the version string for ‘wheel’ by running the following:

     (example) $ python
     >>> from importlib.metadata import version
     >>> version('wheel')
     '0.32.3'

You can also get the set of entry points keyed by group, such as
‘console_scripts’, ‘distutils.commands’ and others.  Each group contains
a sequence of *note EntryPoint: 392a. objects.

You can get the *note metadata for a distribution: 392b.:

     >>> list(metadata('wheel'))
     ['Metadata-Version', 'Name', 'Version', 'Summary', 'Home-page', 'Author', 'Author-email', 'Maintainer', 'Maintainer-email', 'License', 'Project-URL', 'Project-URL', 'Project-URL', 'Keywords', 'Platform', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Classifier', 'Requires-Python', 'Provides-Extra', 'Requires-Dist', 'Requires-Dist']

You can also get a *note distribution’s version number: 392c, list its
*note constituent files: 392d, and get a list of the distribution’s
*note Distribution requirements: 392e.


File: python.info,  Node: Functional API<2>,  Next: Distributions,  Prev: Overview<2>,  Up: Using importlib metadata

5.31.6.2 Functional API
.......................

This package provides the following functionality via its public API.

* Menu:

* Entry points::
* Distribution metadata::
* Distribution versions::
* Distribution files::
* Distribution requirements::


File: python.info,  Node: Entry points,  Next: Distribution metadata,  Up: Functional API<2>

5.31.6.3 Entry points
.....................

The ‘entry_points()’ function returns a dictionary of all entry points,
keyed by group.  Entry points are represented by ‘EntryPoint’ instances;
each ‘EntryPoint’ has a ‘.name’, ‘.group’, and ‘.value’ attributes and a
‘.load()’ method to resolve the value.  There are also ‘.module’,
‘.attr’, and ‘.extras’ attributes for getting the components of the
‘.value’ attribute:

     >>> eps = entry_points()
     >>> list(eps)
     ['console_scripts', 'distutils.commands', 'distutils.setup_keywords', 'egg_info.writers', 'setuptools.installation']
     >>> scripts = eps['console_scripts']
     >>> wheel = [ep for ep in scripts if ep.name == 'wheel'][0]
     >>> wheel
     EntryPoint(name='wheel', value='wheel.cli:main', group='console_scripts')
     >>> wheel.module
     'wheel.cli'
     >>> wheel.attr
     'main'
     >>> wheel.extras
     []
     >>> main = wheel.load()
     >>> main
     <function main at 0x103528488>

The ‘group’ and ‘name’ are arbitrary values defined by the package
author and usually a client will wish to resolve all entry points for a
particular group.  Read the setuptools docs(1) for more information on
entry points, their definition, and usage.

   ---------- Footnotes ----------

   (1) 
https://setuptools.readthedocs.io/en/latest/setuptools.html#dynamic-discovery-of-services-and-plugins


File: python.info,  Node: Distribution metadata,  Next: Distribution versions,  Prev: Entry points,  Up: Functional API<2>

5.31.6.4 Distribution metadata
..............................

Every distribution includes some metadata, which you can extract using
the ‘metadata()’ function:

     >>> wheel_metadata = metadata('wheel')

The keys of the returned data structure (1) name the metadata keywords,
and their values are returned unparsed from the distribution metadata:

     >>> wheel_metadata['Requires-Python']
     '>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*'

   ---------- Footnotes ----------

   (1) (1) Technically, the returned distribution metadata object is an
*note email.message.EmailMessage: 63c. instance, but this is an
implementation detail, and not part of the stable API. You should only
use dictionary-like methods and syntax to access the metadata contents.


File: python.info,  Node: Distribution versions,  Next: Distribution files,  Prev: Distribution metadata,  Up: Functional API<2>

5.31.6.5 Distribution versions
..............................

The ‘version()’ function is the quickest way to get a distribution’s
version number, as a string:

     >>> version('wheel')
     '0.32.3'


File: python.info,  Node: Distribution files,  Next: Distribution requirements,  Prev: Distribution versions,  Up: Functional API<2>

5.31.6.6 Distribution files
...........................

You can also get the full set of files contained within a distribution.
The ‘files()’ function takes a distribution package name and returns all
of the files installed by this distribution.  Each file object returned
is a ‘PackagePath’, a *note pathlib.PurePath: 235. derived object with
additional ‘dist’, ‘size’, and ‘hash’ properties as indicated by the
metadata.  For example:

     >>> util = [p for p in files('wheel') if 'util.py' in str(p)][0]
     >>> util
     PackagePath('wheel/util.py')
     >>> util.size
     859
     >>> util.dist
     <importlib.metadata._hooks.PathDistribution object at 0x101e0cef0>
     >>> util.hash
     <FileHash mode: sha256 value: bYkw5oMccfazVCoYQwKkkemoVyMAFoR34mmKBx8R1NI>

Once you have the file, you can also read its contents:

     >>> print(util.read_text())
     import base64
     import sys
     ...
     def as_bytes(s):
         if isinstance(s, text_type):
             return s.encode('utf-8')
         return s

You can also use the ‘locate’ method to get a the absolute path to the
file:

     >>> util.locate()
     PosixPath('/home/gustav/example/lib/site-packages/wheel/util.py')

In the case where the metadata file listing files (RECORD or
SOURCES.txt) is missing, ‘files()’ will return ‘None’.  The caller may
wish to wrap calls to ‘files()’ in always_iterable(1) or otherwise guard
against this condition if the target distribution is not known to have
the metadata present.

   ---------- Footnotes ----------

   (1) 
https://more-itertools.readthedocs.io/en/stable/api.html#more_itertools.always_iterable


File: python.info,  Node: Distribution requirements,  Prev: Distribution files,  Up: Functional API<2>

5.31.6.7 Distribution requirements
..................................

To get the full set of requirements for a distribution, use the
‘requires()’ function:

     >>> requires('wheel')
     ["pytest (>=3.0.0) ; extra == 'test'", "pytest-cov ; extra == 'test'"]


File: python.info,  Node: Distributions,  Next: Extending the search algorithm,  Prev: Functional API<2>,  Up: Using importlib metadata

5.31.6.8 Distributions
......................

While the above API is the most common and convenient usage, you can get
all of that information from the ‘Distribution’ class.  A ‘Distribution’
is an abstract object that represents the metadata for a Python package.
You can get the ‘Distribution’ instance:

     >>> from importlib.metadata import distribution
     >>> dist = distribution('wheel')

Thus, an alternative way to get the version number is through the
‘Distribution’ instance:

     >>> dist.version
     '0.32.3'

There are all kinds of additional metadata available on the
‘Distribution’ instance:

     >>> dist.metadata['Requires-Python']
     '>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*'
     >>> dist.metadata['License']
     'MIT'

The full set of available metadata is not described here.  See PEP
566(1) for additional details.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0566


File: python.info,  Node: Extending the search algorithm,  Prev: Distributions,  Up: Using importlib metadata

5.31.6.9 Extending the search algorithm
.......................................

Because package metadata is not available through *note sys.path: 260.
searches, or package loaders directly, the metadata for a package is
found through import system *note finders: 15f3.  To find a distribution
package’s metadata, ‘importlib.metadata’ queries the list of *note meta
path finders: a91. on *note sys.meta_path: 6dd.

The default ‘PathFinder’ for Python includes a hook that calls into
‘importlib.metadata.MetadataPathFinder’ for finding distributions loaded
from typical file-system-based paths.

The abstract class *note importlib.abc.MetaPathFinder: a93. defines the
interface expected of finders by Python’s import system.
‘importlib.metadata’ extends this protocol by looking for an optional
‘find_distributions’ callable on the finders from *note sys.meta_path:
6dd. and presents this extended interface as the ‘DistributionFinder’
abstract base class, which defines this abstract method:

     @abc.abstractmethod
     def find_distributions(context=DistributionFinder.Context()):
         """Return an iterable of all Distribution instances capable of
         loading the metadata for packages for the indicated ``context``.
         """

The ‘DistributionFinder.Context’ object provides ‘.path’ and ‘.name’
properties indicating the path to search and name to match and may
supply other relevant context.

What this means in practice is that to support finding distribution
package metadata in locations other than the file system, subclass
‘Distribution’ and implement the abstract methods.  Then from a custom
finder, return instances of this derived ‘Distribution’ in the
‘find_distributions()’ method.


File: python.info,  Node: Python Language Services,  Next: Miscellaneous Services,  Prev: Importing Modules,  Up: The Python Standard Library

5.32 Python Language Services
=============================

Python provides a number of modules to assist in working with the Python
language.  These modules support tokenizing, parsing, syntax analysis,
bytecode disassembly, and various other facilities.

These modules include:

* Menu:

* parser — Access Python parse trees::
* ast — Abstract Syntax Trees::
* symtable — Access to the compiler’s symbol tables::
* symbol — Constants used with Python parse trees::
* token — Constants used with Python parse trees::
* keyword — Testing for Python keywords::
* tokenize — Tokenizer for Python source::
* tabnanny — Detection of ambiguous indentation::
* pyclbr — Python module browser support::
* py_compile — Compile Python source files::
* compileall — Byte-compile Python libraries::
* dis — Disassembler for Python bytecode::
* pickletools — Tools for pickle developers::


File: python.info,  Node: parser — Access Python parse trees,  Next: ast — Abstract Syntax Trees,  Up: Python Language Services

5.32.1 ‘parser’ — Access Python parse trees
-------------------------------------------

__________________________________________________________________

The *note parser: c7. module provides an interface to Python’s internal
parser and byte-code compiler.  The primary purpose for this interface
is to allow Python code to edit the parse tree of a Python expression
and create executable code from this.  This is better than trying to
parse and modify an arbitrary Python code fragment as a string because
parsing is performed in a manner identical to the code forming the
application.  It is also faster.

     Warning: The parser module is deprecated and will be removed in
     future versions of Python.  For the majority of use cases you can
     leverage the Abstract Syntax Tree (AST) generation and compilation
     stage, using the *note ast: 7. module.

There are a few things to note about this module which are important to
making use of the data structures created.  This is not a tutorial on
editing the parse trees for Python code, but some examples of using the
*note parser: c7. module are presented.

Most importantly, a good understanding of the Python grammar processed
by the internal parser is required.  For full information on the
language syntax, refer to *note The Python Language Reference: 1331.
The parser itself is created from a grammar specification defined in the
file ‘Grammar/Grammar’ in the standard Python distribution.  The parse
trees stored in the ST objects created by this module are the actual
output from the internal parser when created by the *note expr(): 393c.
or *note suite(): 393d. functions, described below.  The ST objects
created by *note sequence2st(): 393e. faithfully simulate those
structures.  Be aware that the values of the sequences which are
considered “correct” will vary from one version of Python to another as
the formal grammar for the language is revised.  However, transporting
code from one Python version to another as source text will always allow
correct parse trees to be created in the target version, with the only
restriction being that migrating to an older version of the interpreter
will not support more recent language constructs.  The parse trees are
not typically compatible from one version to another, though source code
has usually been forward-compatible within a major release series.

Each element of the sequences returned by *note st2list(): 393f. or
*note st2tuple(): 3940. has a simple form.  Sequences representing
non-terminal elements in the grammar always have a length greater than
one.  The first element is an integer which identifies a production in
the grammar.  These integers are given symbolic names in the C header
file ‘Include/graminit.h’ and the Python module *note symbol: fb.  Each
additional element of the sequence represents a component of the
production as recognized in the input string: these are always sequences
which have the same form as the parent.  An important aspect of this
structure which should be noted is that keywords used to identify the
parent node type, such as the keyword *note if: eab. in an ‘if_stmt’,
are included in the node tree without any special treatment.  For
example, the ‘if’ keyword is represented by the tuple ‘(1, 'if')’, where
‘1’ is the numeric value associated with all ‘NAME’ tokens, including
variable and function names defined by the user.  In an alternate form
returned when line number information is requested, the same token might
be represented as ‘(1, 'if', 12)’, where the ‘12’ represents the line
number at which the terminal symbol was found.

Terminal elements are represented in much the same way, but without any
child elements and the addition of the source text which was identified.
The example of the *note if: eab. keyword above is representative.  The
various types of terminal symbols are defined in the C header file
‘Include/token.h’ and the Python module *note token: 119.

The ST objects are not required to support the functionality of this
module, but are provided for three purposes: to allow an application to
amortize the cost of processing complex parse trees, to provide a parse
tree representation which conserves memory space when compared to the
Python list or tuple representation, and to ease the creation of
additional modules in C which manipulate parse trees.  A simple
“wrapper” class may be created in Python to hide the use of ST objects.

The *note parser: c7. module defines functions for a few distinct
purposes.  The most important purposes are to create ST objects and to
convert ST objects to other representations such as parse trees and
compiled code objects, but there are also functions which serve to query
the type of parse tree represented by an ST object.

See also
........

Module *note symbol: fb.

     Useful constants representing internal nodes of the parse tree.

Module *note token: 119.

     Useful constants representing leaf nodes of the parse tree and
     functions for testing node values.

* Menu:

* Creating ST Objects::
* Converting ST Objects::
* Queries on ST Objects::
* Exceptions and Error Handling::
* ST Objects::
* Example; Emulation of compile(): Example Emulation of compile.


File: python.info,  Node: Creating ST Objects,  Next: Converting ST Objects,  Up: parser — Access Python parse trees

5.32.1.1 Creating ST Objects
............................

ST objects may be created from source code or from a parse tree.  When
creating an ST object from source, different functions are used to
create the ‘'eval'’ and ‘'exec'’ forms.

 -- Function: parser.expr (source)

     The *note expr(): 393c. function parses the parameter `source' as
     if it were an input to ‘compile(source, 'file.py', 'eval')’.  If
     the parse succeeds, an ST object is created to hold the internal
     parse tree representation, otherwise an appropriate exception is
     raised.

 -- Function: parser.suite (source)

     The *note suite(): 393d. function parses the parameter `source' as
     if it were an input to ‘compile(source, 'file.py', 'exec')’.  If
     the parse succeeds, an ST object is created to hold the internal
     parse tree representation, otherwise an appropriate exception is
     raised.

 -- Function: parser.sequence2st (sequence)

     This function accepts a parse tree represented as a sequence and
     builds an internal representation if possible.  If it can validate
     that the tree conforms to the Python grammar and all nodes are
     valid node types in the host version of Python, an ST object is
     created from the internal representation and returned to the
     called.  If there is a problem creating the internal
     representation, or if the tree cannot be validated, a *note
     ParserError: 3943. exception is raised.  An ST object created this
     way should not be assumed to compile correctly; normal exceptions
     raised by compilation may still be initiated when the ST object is
     passed to *note compilest(): 3944.  This may indicate problems not
     related to syntax (such as a *note MemoryError: f69. exception),
     but may also be due to constructs such as the result of parsing
     ‘del f(0)’, which escapes the Python parser but is checked by the
     bytecode compiler.

     Sequences representing terminal tokens may be represented as either
     two-element lists of the form ‘(1, 'name')’ or as three-element
     lists of the form ‘(1, 'name', 56)’.  If the third element is
     present, it is assumed to be a valid line number.  The line number
     may be specified for any subset of the terminal symbols in the
     input tree.

 -- Function: parser.tuple2st (sequence)

     This is the same function as *note sequence2st(): 393e.  This entry
     point is maintained for backward compatibility.


File: python.info,  Node: Converting ST Objects,  Next: Queries on ST Objects,  Prev: Creating ST Objects,  Up: parser — Access Python parse trees

5.32.1.2 Converting ST Objects
..............................

ST objects, regardless of the input used to create them, may be
converted to parse trees represented as list- or tuple- trees, or may be
compiled into executable code objects.  Parse trees may be extracted
with or without line numbering information.

 -- Function: parser.st2list (st, line_info=False, col_info=False)

     This function accepts an ST object from the caller in `st' and
     returns a Python list representing the equivalent parse tree.  The
     resulting list representation can be used for inspection or the
     creation of a new parse tree in list form.  This function does not
     fail so long as memory is available to build the list
     representation.  If the parse tree will only be used for
     inspection, *note st2tuple(): 3940. should be used instead to
     reduce memory consumption and fragmentation.  When the list
     representation is required, this function is significantly faster
     than retrieving a tuple representation and converting that to
     nested lists.

     If `line_info' is true, line number information will be included
     for all terminal tokens as a third element of the list representing
     the token.  Note that the line number provided specifies the line
     on which the token `ends'.  This information is omitted if the flag
     is false or omitted.

 -- Function: parser.st2tuple (st, line_info=False, col_info=False)

     This function accepts an ST object from the caller in `st' and
     returns a Python tuple representing the equivalent parse tree.
     Other than returning a tuple instead of a list, this function is
     identical to *note st2list(): 393f.

     If `line_info' is true, line number information will be included
     for all terminal tokens as a third element of the list representing
     the token.  This information is omitted if the flag is false or
     omitted.

 -- Function: parser.compilest (st, filename='<syntax-tree>')

     The Python byte compiler can be invoked on an ST object to produce
     code objects which can be used as part of a call to the built-in
     *note exec(): d0c. or *note eval(): c61. functions.  This function
     provides the interface to the compiler, passing the internal parse
     tree from `st' to the parser, using the source file name specified
     by the `filename' parameter.  The default value supplied for
     `filename' indicates that the source was an ST object.

     Compiling an ST object may result in exceptions related to
     compilation; an example would be a *note SyntaxError: 55a. caused
     by the parse tree for ‘del f(0)’: this statement is considered
     legal within the formal grammar for Python but is not a legal
     language construct.  The *note SyntaxError: 55a. raised for this
     condition is actually generated by the Python byte-compiler
     normally, which is why it can be raised at this point by the *note
     parser: c7. module.  Most causes of compilation failure can be
     diagnosed programmatically by inspection of the parse tree.


File: python.info,  Node: Queries on ST Objects,  Next: Exceptions and Error Handling,  Prev: Converting ST Objects,  Up: parser — Access Python parse trees

5.32.1.3 Queries on ST Objects
..............................

Two functions are provided which allow an application to determine if an
ST was created as an expression or a suite.  Neither of these functions
can be used to determine if an ST was created from source code via *note
expr(): 393c. or *note suite(): 393d. or from a parse tree via *note
sequence2st(): 393e.

 -- Function: parser.isexpr (st)

     When `st' represents an ‘'eval'’ form, this function returns
     ‘True’, otherwise it returns ‘False’.  This is useful, since code
     objects normally cannot be queried for this information using
     existing built-in functions.  Note that the code objects created by
     *note compilest(): 3944. cannot be queried like this either, and
     are identical to those created by the built-in *note compile():
     2e7. function.

 -- Function: parser.issuite (st)

     This function mirrors *note isexpr(): 394a. in that it reports
     whether an ST object represents an ‘'exec'’ form, commonly known as
     a “suite.” It is not safe to assume that this function is
     equivalent to ‘not isexpr(st)’, as additional syntactic fragments
     may be supported in the future.


File: python.info,  Node: Exceptions and Error Handling,  Next: ST Objects,  Prev: Queries on ST Objects,  Up: parser — Access Python parse trees

5.32.1.4 Exceptions and Error Handling
......................................

The parser module defines a single exception, but may also pass other
built-in exceptions from other portions of the Python runtime
environment.  See each function for information about the exceptions it
can raise.

 -- Exception: parser.ParserError

     Exception raised when a failure occurs within the parser module.
     This is generally produced for validation failures rather than the
     built-in *note SyntaxError: 55a. raised during normal parsing.  The
     exception argument is either a string describing the reason of the
     failure or a tuple containing a sequence causing the failure from a
     parse tree passed to *note sequence2st(): 393e. and an explanatory
     string.  Calls to *note sequence2st(): 393e. need to be able to
     handle either type of exception, while calls to other functions in
     the module will only need to be aware of the simple string values.

Note that the functions *note compilest(): 3944, *note expr(): 393c, and
*note suite(): 393d. may raise exceptions which are normally raised by
the parsing and compilation process.  These include the built in
exceptions *note MemoryError: f69, *note OverflowError: a41, *note
SyntaxError: 55a, and *note SystemError: 6f2.  In these cases, these
exceptions carry all the meaning normally associated with them.  Refer
to the descriptions of each function for detailed information.


File: python.info,  Node: ST Objects,  Next: Example Emulation of compile,  Prev: Exceptions and Error Handling,  Up: parser — Access Python parse trees

5.32.1.5 ST Objects
...................

Ordered and equality comparisons are supported between ST objects.
Pickling of ST objects (using the *note pickle: ca. module) is also
supported.

 -- Data: parser.STType

     The type of the objects returned by *note expr(): 393c, *note
     suite(): 393d. and *note sequence2st(): 393e.

ST objects have the following methods:

 -- Method: ST.compile (filename='<syntax-tree>')

     Same as ‘compilest(st, filename)’.

 -- Method: ST.isexpr ()

     Same as ‘isexpr(st)’.

 -- Method: ST.issuite ()

     Same as ‘issuite(st)’.

 -- Method: ST.tolist (line_info=False, col_info=False)

     Same as ‘st2list(st, line_info, col_info)’.

 -- Method: ST.totuple (line_info=False, col_info=False)

     Same as ‘st2tuple(st, line_info, col_info)’.


File: python.info,  Node: Example Emulation of compile,  Prev: ST Objects,  Up: parser — Access Python parse trees

5.32.1.6 Example: Emulation of ‘compile()’
..........................................

While many useful operations may take place between parsing and bytecode
generation, the simplest operation is to do nothing.  For this purpose,
using the *note parser: c7. module to produce an intermediate data
structure is equivalent to the code

     >>> code = compile('a + 5', 'file.py', 'eval')
     >>> a = 5
     >>> eval(code)
     10

The equivalent operation using the *note parser: c7. module is somewhat
longer, and allows the intermediate internal parse tree to be retained
as an ST object:

     >>> import parser
     >>> st = parser.expr('a + 5')
     >>> code = st.compile('file.py')
     >>> a = 5
     >>> eval(code)
     10

An application which needs both ST and code objects can package this
code into readily available functions:

     import parser

     def load_suite(source_string):
         st = parser.suite(source_string)
         return st, st.compile()

     def load_expression(source_string):
         st = parser.expr(source_string)
         return st, st.compile()


File: python.info,  Node: ast — Abstract Syntax Trees,  Next: symtable — Access to the compiler’s symbol tables,  Prev: parser — Access Python parse trees,  Up: Python Language Services

5.32.2 ‘ast’ — Abstract Syntax Trees
------------------------------------

`Source code:' Lib/ast.py(1)

__________________________________________________________________

The *note ast: 7. module helps Python applications to process trees of
the Python abstract syntax grammar.  The abstract syntax itself might
change with each Python release; this module helps to find out
programmatically what the current grammar looks like.

An abstract syntax tree can be generated by passing *note
ast.PyCF_ONLY_AST: 3959. as a flag to the *note compile(): 2e7. built-in
function, or using the *note parse(): 2d6. helper provided in this
module.  The result will be a tree of objects whose classes all inherit
from *note ast.AST: 187.  An abstract syntax tree can be compiled into a
Python code object using the built-in *note compile(): 2e7. function.

* Menu:

* Abstract Grammar::
* Node classes::
* ast Helpers::
* Compiler Flags::
* Command-Line Usage: Command-Line Usage<2>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/ast.py


File: python.info,  Node: Abstract Grammar,  Next: Node classes,  Up: ast — Abstract Syntax Trees

5.32.2.1 Abstract Grammar
.........................

The abstract grammar is currently defined as follows:

     -- ASDL's 4 builtin types are:
     -- identifier, int, string, constant

     module Python
     {
         mod = Module(stmt* body, type_ignore* type_ignores)
             | Interactive(stmt* body)
             | Expression(expr body)
             | FunctionType(expr* argtypes, expr returns)

         stmt = FunctionDef(identifier name, arguments args,
                            stmt* body, expr* decorator_list, expr? returns,
                            string? type_comment)
               | AsyncFunctionDef(identifier name, arguments args,
                                  stmt* body, expr* decorator_list, expr? returns,
                                  string? type_comment)

               | ClassDef(identifier name,
                  expr* bases,
                  keyword* keywords,
                  stmt* body,
                  expr* decorator_list)
               | Return(expr? value)

               | Delete(expr* targets)
               | Assign(expr* targets, expr value, string? type_comment)
               | AugAssign(expr target, operator op, expr value)
               -- 'simple' indicates that we annotate simple name without parens
               | AnnAssign(expr target, expr annotation, expr? value, int simple)

               -- use 'orelse' because else is a keyword in target languages
               | For(expr target, expr iter, stmt* body, stmt* orelse, string? type_comment)
               | AsyncFor(expr target, expr iter, stmt* body, stmt* orelse, string? type_comment)
               | While(expr test, stmt* body, stmt* orelse)
               | If(expr test, stmt* body, stmt* orelse)
               | With(withitem* items, stmt* body, string? type_comment)
               | AsyncWith(withitem* items, stmt* body, string? type_comment)

               | Raise(expr? exc, expr? cause)
               | Try(stmt* body, excepthandler* handlers, stmt* orelse, stmt* finalbody)
               | Assert(expr test, expr? msg)

               | Import(alias* names)
               | ImportFrom(identifier? module, alias* names, int? level)

               | Global(identifier* names)
               | Nonlocal(identifier* names)
               | Expr(expr value)
               | Pass | Break | Continue

               -- col_offset is the byte offset in the utf8 string the parser uses
               attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

               -- BoolOp() can use left & right?
         expr = BoolOp(boolop op, expr* values)
              | NamedExpr(expr target, expr value)
              | BinOp(expr left, operator op, expr right)
              | UnaryOp(unaryop op, expr operand)
              | Lambda(arguments args, expr body)
              | IfExp(expr test, expr body, expr orelse)
              | Dict(expr* keys, expr* values)
              | Set(expr* elts)
              | ListComp(expr elt, comprehension* generators)
              | SetComp(expr elt, comprehension* generators)
              | DictComp(expr key, expr value, comprehension* generators)
              | GeneratorExp(expr elt, comprehension* generators)
              -- the grammar constrains where yield expressions can occur
              | Await(expr value)
              | Yield(expr? value)
              | YieldFrom(expr value)
              -- need sequences for compare to distinguish between
              -- x < 4 < 3 and (x < 4) < 3
              | Compare(expr left, cmpop* ops, expr* comparators)
              | Call(expr func, expr* args, keyword* keywords)
              | FormattedValue(expr value, int? conversion, expr? format_spec)
              | JoinedStr(expr* values)
              | Constant(constant value, string? kind)

              -- the following expression can appear in assignment context
              | Attribute(expr value, identifier attr, expr_context ctx)
              | Subscript(expr value, expr slice, expr_context ctx)
              | Starred(expr value, expr_context ctx)
              | Name(identifier id, expr_context ctx)
              | List(expr* elts, expr_context ctx)
              | Tuple(expr* elts, expr_context ctx)

              -- can appear only in Subscript
              | Slice(expr? lower, expr? upper, expr? step)

               -- col_offset is the byte offset in the utf8 string the parser uses
               attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

         expr_context = Load | Store | Del

         boolop = And | Or

         operator = Add | Sub | Mult | MatMult | Div | Mod | Pow | LShift
                      | RShift | BitOr | BitXor | BitAnd | FloorDiv

         unaryop = Invert | Not | UAdd | USub

         cmpop = Eq | NotEq | Lt | LtE | Gt | GtE | Is | IsNot | In | NotIn

         comprehension = (expr target, expr iter, expr* ifs, int is_async)

         excepthandler = ExceptHandler(expr? type, identifier? name, stmt* body)
                         attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

         arguments = (arg* posonlyargs, arg* args, arg? vararg, arg* kwonlyargs,
                      expr* kw_defaults, arg? kwarg, expr* defaults)

         arg = (identifier arg, expr? annotation, string? type_comment)
                attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

         -- keyword arguments supplied to call (NULL identifier for **kwargs)
         keyword = (identifier? arg, expr value)
                    attributes (int lineno, int col_offset, int? end_lineno, int? end_col_offset)

         -- import name with optional 'as' alias.
         alias = (identifier name, identifier? asname)

         withitem = (expr context_expr, expr? optional_vars)

         type_ignore = TypeIgnore(int lineno, string tag)
     }


File: python.info,  Node: Node classes,  Next: ast Helpers,  Prev: Abstract Grammar,  Up: ast — Abstract Syntax Trees

5.32.2.2 Node classes
.....................

 -- Class: ast.AST

     This is the base of all AST node classes.  The actual node classes
     are derived from the ‘Parser/Python.asdl’ file, which is reproduced
     *note below: 395a.  They are defined in the ‘_ast’ C module and
     re-exported in *note ast: 7.

     There is one class defined for each left-hand side symbol in the
     abstract grammar (for example, ‘ast.stmt’ or ‘ast.expr’).  In
     addition, there is one class defined for each constructor on the
     right-hand side; these classes inherit from the classes for the
     left-hand side trees.  For example, *note ast.BinOp: 10d2. inherits
     from ‘ast.expr’.  For production rules with alternatives (aka
     “sums”), the left-hand side class is abstract: only instances of
     specific constructor nodes are ever created.

      -- Attribute: _fields

          Each concrete class has an attribute *note _fields: 395d.
          which gives the names of all child nodes.

          Each instance of a concrete class has one attribute for each
          child node, of the type as defined in the grammar.  For
          example, *note ast.BinOp: 10d2. instances have an attribute
          ‘left’ of type ‘ast.expr’.

          If these attributes are marked as optional in the grammar
          (using a question mark), the value might be ‘None’.  If the
          attributes can have zero-or-more values (marked with an
          asterisk), the values are represented as Python lists.  All
          possible attributes must be present and have valid values when
          compiling an AST with *note compile(): 2e7.

      -- Attribute: lineno
      -- Attribute: col_offset
      -- Attribute: end_lineno
      -- Attribute: end_col_offset

          Instances of ‘ast.expr’ and ‘ast.stmt’ subclasses have *note
          lineno: 395e, *note col_offset: 395f, *note end_lineno: 3960,
          and *note end_col_offset: 3961. attributes.  The *note lineno:
          395e. and *note end_lineno: 3960. are the first and last line
          numbers of the source text span (1-indexed so the first line
          is line 1), and the *note col_offset: 395f. and *note
          end_col_offset: 3961. are the corresponding UTF-8 byte offsets
          of the first and last tokens that generated the node.  The
          UTF-8 offset is recorded because the parser uses UTF-8
          internally.

          Note that the end positions are not required by the compiler
          and are therefore optional.  The end offset is `after' the
          last symbol, for example one can get the source segment of a
          one-line expression node using ‘source_line[node.col_offset :
          node.end_col_offset]’.

     The constructor of a class ‘ast.T’ parses its arguments as follows:

        * If there are positional arguments, there must be as many as
          there are items in ‘T._fields’; they will be assigned as
          attributes of these names.

        * If there are keyword arguments, they will set the attributes
          of the same names to the given values.

     For example, to create and populate an *note ast.UnaryOp: 3962.
     node, you could use

          node = ast.UnaryOp()
          node.op = ast.USub()
          node.operand = ast.Constant()
          node.operand.value = 5
          node.operand.lineno = 0
          node.operand.col_offset = 0
          node.lineno = 0
          node.col_offset = 0

     or the more compact

          node = ast.UnaryOp(ast.USub(), ast.Constant(5, lineno=0, col_offset=0),
                             lineno=0, col_offset=0)

Changed in version 3.8: Class *note ast.Constant: 3a6. is now used for
all constants.

Changed in version 3.9: Simple indices are represented by their value,
extended slices are represented as tuples.

Deprecated since version 3.8: Old classes ‘ast.Num’, ‘ast.Str’,
‘ast.Bytes’, ‘ast.NameConstant’ and ‘ast.Ellipsis’ are still available,
but they will be removed in future Python releases.  In the meantime,
instantiating them will return an instance of a different class.

Deprecated since version 3.9: Old classes ‘ast.Index’ and ‘ast.ExtSlice’
are still available, but they will be removed in future Python releases.
In the meantime, instantiating them will return an instance of a
different class.

     Note: The descriptions of the specific node classes displayed here
     were initially adapted from the fantastic Green Tree Snakes(1)
     project and all its contributors.

* Menu:

* Literals: Literals<3>.
* Variables::
* Expressions: Expressions<2>.
* Statements::
* Control flow::
* Function and class definitions::
* Async and await::

   ---------- Footnotes ----------

   (1) https://greentreesnakes.readthedocs.io/en/latest/


File: python.info,  Node: Literals<3>,  Next: Variables,  Up: Node classes

5.32.2.3 Literals
.................

 -- Class: ast.Constant (value)

     A constant value.  The ‘value’ attribute of the ‘Constant’ literal
     contains the Python object it represents.  The values represented
     can be simple types such as a number, string or ‘None’, but also
     immutable container types (tuples and frozensets) if all of their
     elements are constant.

          >>> print(ast.dump(ast.parse('123', mode='eval'), indent=4))
          Expression(
              body=Constant(value=123))

 -- Class: ast.FormattedValue (value, conversion, format_spec)

     Node representing a single formatting field in an f-string.  If the
     string contains a single formatting field and nothing else the node
     can be isolated otherwise it appears in *note JoinedStr: 3965.

        * ‘value’ is any expression node (such as a literal, a variable,
          or a function call).

        * ‘conversion’ is an integer:

             * -1: no formatting

             * 115: ‘!s’ string formatting

             * 114: ‘!r’ repr formatting

             * 97: ‘!a’ ascii formatting

        * ‘format_spec’ is a *note JoinedStr: 3965. node representing
          the formatting of the value, or ‘None’ if no format was
          specified.  Both ‘conversion’ and ‘format_spec’ can be set at
          the same time.

 -- Class: ast.JoinedStr (values)

     An f-string, comprising a series of *note FormattedValue: 3964. and
     *note Constant: 3a6. nodes.

          >>> print(ast.dump(ast.parse('f"sin({a}) is {sin(a):.3}"', mode='eval'), indent=4))
          Expression(
              body=JoinedStr(
                  values=[
                      Constant(value='sin('),
                      FormattedValue(
                          value=Name(id='a', ctx=Load()),
                          conversion=-1),
                      Constant(value=') is '),
                      FormattedValue(
                          value=Call(
                              func=Name(id='sin', ctx=Load()),
                              args=[
                                  Name(id='a', ctx=Load())],
                              keywords=[]),
                          conversion=-1,
                          format_spec=JoinedStr(
                              values=[
                                  Constant(value='.3')]))]))

 -- Class: ast.List (elts, ctx)
 -- Class: ast.Tuple (elts, ctx)

     A list or tuple.  ‘elts’ holds a list of nodes representing the
     elements.  ‘ctx’ is *note Store: 3968. if the container is an
     assignment target (i.e.  ‘(x,y)=something’), and *note Load: 3969.
     otherwise.

          >>> print(ast.dump(ast.parse('[1, 2, 3]', mode='eval'), indent=4))
          Expression(
              body=List(
                  elts=[
                      Constant(value=1),
                      Constant(value=2),
                      Constant(value=3)],
                  ctx=Load()))
          >>> print(ast.dump(ast.parse('(1, 2, 3)', mode='eval'), indent=4))
          Expression(
              body=Tuple(
                  elts=[
                      Constant(value=1),
                      Constant(value=2),
                      Constant(value=3)],
                  ctx=Load()))

 -- Class: ast.Set (elts)

     A set.  ‘elts’ holds a list of nodes representing the set’s
     elements.

          >>> print(ast.dump(ast.parse('{1, 2, 3}', mode='eval'), indent=4))
          Expression(
              body=Set(
                  elts=[
                      Constant(value=1),
                      Constant(value=2),
                      Constant(value=3)]))

 -- Class: ast.Dict (keys, values)

     A dictionary.  ‘keys’ and ‘values’ hold lists of nodes representing
     the keys and the values respectively, in matching order (what would
     be returned when calling ‘dictionary.keys()’ and
     ‘dictionary.values()’).

     When doing dictionary unpacking using dictionary literals the
     expression to be expanded goes in the ‘values’ list, with a ‘None’
     at the corresponding position in ‘keys’.

          >>> print(ast.dump(ast.parse('{"a":1, **d}', mode='eval'), indent=4))
          Expression(
              body=Dict(
                  keys=[
                      Constant(value='a'),
                      None],
                  values=[
                      Constant(value=1),
                      Name(id='d', ctx=Load())]))


File: python.info,  Node: Variables,  Next: Expressions<2>,  Prev: Literals<3>,  Up: Node classes

5.32.2.4 Variables
..................

 -- Class: ast.Name (id, ctx)

     A variable name.  ‘id’ holds the name as a string, and ‘ctx’ is one
     of the following types.

 -- Class: ast.Load
 -- Class: ast.Store
 -- Class: ast.Del

     Variable references can be used to load the value of a variable, to
     assign a new value to it, or to delete it.  Variable references are
     given a context to distinguish these cases.

          >>> print(ast.dump(ast.parse('a'), indent=4))
          Module(
              body=[
                  Expr(
                      value=Name(id='a', ctx=Load()))],
              type_ignores=[])

          >>> print(ast.dump(ast.parse('a = 1'), indent=4))
          Module(
              body=[
                  Assign(
                      targets=[
                          Name(id='a', ctx=Store())],
                      value=Constant(value=1))],
              type_ignores=[])

          >>> print(ast.dump(ast.parse('del a'), indent=4))
          Module(
              body=[
                  Delete(
                      targets=[
                          Name(id='a', ctx=Del())])],
              type_ignores=[])

 -- Class: ast.Starred (value, ctx)

     A ‘*var’ variable reference.  ‘value’ holds the variable, typically
     a *note Name: 102b. node.  This type must be used when building a
     *note Call: 396e. node with ‘*args’.

          >>> print(ast.dump(ast.parse('a, *b = it'), indent=4))
          Module(
              body=[
                  Assign(
                      targets=[
                          Tuple(
                              elts=[
                                  Name(id='a', ctx=Store()),
                                  Starred(
                                      value=Name(id='b', ctx=Store()),
                                      ctx=Store())],
                              ctx=Store())],
                      value=Name(id='it', ctx=Load()))],
              type_ignores=[])


File: python.info,  Node: Expressions<2>,  Next: Statements,  Prev: Variables,  Up: Node classes

5.32.2.5 Expressions
....................

 -- Class: ast.Expr (value)

     When an expression, such as a function call, appears as a statement
     by itself with its return value not used or stored, it is wrapped
     in this container.  ‘value’ holds one of the other nodes in this
     section, a *note Constant: 3a6, a *note Name: 102b, a *note Lambda:
     3971, a *note Yield: 3972. or *note YieldFrom: 3973. node.

          >>> print(ast.dump(ast.parse('-a'), indent=4))
          Module(
              body=[
                  Expr(
                      value=UnaryOp(
                          op=USub(),
                          operand=Name(id='a', ctx=Load())))],
              type_ignores=[])

 -- Class: ast.UnaryOp (op, operand)

     A unary operation.  ‘op’ is the operator, and ‘operand’ any
     expression node.

 -- Class: ast.UAdd
 -- Class: ast.USub
 -- Class: ast.Not
 -- Class: ast.Invert

     Unary operator tokens.  *note Not: 3976. is the ‘not’ keyword,
     *note Invert: 3977. is the ‘~’ operator.

          >>> print(ast.dump(ast.parse('not x', mode='eval'), indent=4))
          Expression(
              body=UnaryOp(
                  op=Not(),
                  operand=Name(id='x', ctx=Load())))

 -- Class: ast.BinOp (left, op, right)

     A binary operation (like addition or division).  ‘op’ is the
     operator, and ‘left’ and ‘right’ are any expression nodes.

          >>> print(ast.dump(ast.parse('x + y', mode='eval'), indent=4))
          Expression(
              body=BinOp(
                  left=Name(id='x', ctx=Load()),
                  op=Add(),
                  right=Name(id='y', ctx=Load())))

 -- Class: ast.Add
 -- Class: ast.Sub
 -- Class: ast.Mult
 -- Class: ast.Div
 -- Class: ast.FloorDiv
 -- Class: ast.Mod
 -- Class: ast.Pow
 -- Class: ast.LShift
 -- Class: ast.RShift
 -- Class: ast.BitOr
 -- Class: ast.BitXor
 -- Class: ast.BitAnd
 -- Class: ast.MatMult

     Binary operator tokens.

 -- Class: ast.BoolOp (op, values)

     A boolean operation, ‘or’ or ‘and’.  ‘op’ is *note Or: 3986. or
     *note And: 3987.  ‘values’ are the values involved.  Consecutive
     operations with the same operator, such as ‘a or b or c’, are
     collapsed into one node with several values.

     This doesn’t include ‘not’, which is a *note UnaryOp: 3962.

          >>> print(ast.dump(ast.parse('x or y', mode='eval'), indent=4))
          Expression(
              body=BoolOp(
                  op=Or(),
                  values=[
                      Name(id='x', ctx=Load()),
                      Name(id='y', ctx=Load())]))

 -- Class: ast.And
 -- Class: ast.Or

     Boolean operator tokens.

 -- Class: ast.Compare (left, ops, comparators)

     A comparison of two or more values.  ‘left’ is the first value in
     the comparison, ‘ops’ the list of operators, and ‘comparators’ the
     list of values after the first element in the comparison.

          >>> print(ast.dump(ast.parse('1 <= a < 10', mode='eval'), indent=4))
          Expression(
              body=Compare(
                  left=Constant(value=1),
                  ops=[
                      LtE(),
                      Lt()],
                  comparators=[
                      Name(id='a', ctx=Load()),
                      Constant(value=10)]))

 -- Class: ast.Eq
 -- Class: ast.NotEq
 -- Class: ast.Lt
 -- Class: ast.LtE
 -- Class: ast.Gt
 -- Class: ast.GtE
 -- Class: ast.Is
 -- Class: ast.IsNot
 -- Class: ast.In
 -- Class: ast.NotIn

     Comparison operator tokens.

 -- Class: ast.Call (func, args, keywords, starargs, kwargs)

     A function call.  ‘func’ is the function, which will often be a
     *note Name: 102b. or *note Attribute: 3993. object.  Of the
     arguments:

        * ‘args’ holds a list of the arguments passed by position.

        * ‘keywords’ holds a list of *note keyword: a6. objects
          representing arguments passed by keyword.

     When creating a ‘Call’ node, ‘args’ and ‘keywords’ are required,
     but they can be empty lists.  ‘starargs’ and ‘kwargs’ are optional.

          >>> print(ast.dump(ast.parse('func(a, b=c, *d, **e)', mode='eval'), indent=4))
          Expression(
              body=Call(
                  func=Name(id='func', ctx=Load()),
                  args=[
                      Name(id='a', ctx=Load()),
                      Starred(
                          value=Name(id='d', ctx=Load()),
                          ctx=Load())],
                  keywords=[
                      keyword(
                          arg='b',
                          value=Name(id='c', ctx=Load())),
                      keyword(
                          value=Name(id='e', ctx=Load()))]))

 -- Class: ast.keyword (arg, value)

     A keyword argument to a function call or class definition.  ‘arg’
     is a raw string of the parameter name, ‘value’ is a node to pass
     in.

 -- Class: ast.IfExp (test, body, orelse)

     An expression such as ‘a if b else c’.  Each field holds a single
     node, so in the following example, all three are *note Name: 102b.
     nodes.

          >>> print(ast.dump(ast.parse('a if b else c', mode='eval'), indent=4))
          Expression(
              body=IfExp(
                  test=Name(id='b', ctx=Load()),
                  body=Name(id='a', ctx=Load()),
                  orelse=Name(id='c', ctx=Load())))

 -- Class: ast.Attribute (value, attr, ctx)

     Attribute access, e.g.  ‘d.keys’.  ‘value’ is a node, typically a
     *note Name: 102b.  ‘attr’ is a bare string giving the name of the
     attribute, and ‘ctx’ is *note Load: 3969, *note Store: 3968. or
     *note Del: 396c. according to how the attribute is acted on.

          >>> print(ast.dump(ast.parse('snake.colour', mode='eval'), indent=4))
          Expression(
              body=Attribute(
                  value=Name(id='snake', ctx=Load()),
                  attr='colour',
                  ctx=Load()))

 -- Class: ast.NamedExpr (target, value)

          A named expression.  This AST node is produced by the
          assignment expressions operator (also known as the walrus
          operator).  As opposed to the *note Assign: 3997. node in
          which the first argument can be multiple nodes, in this case
          both ‘target’ and ‘value’ must be single nodes.

          >>> print(ast.dump(ast.parse('(x := 4)', mode='eval'), indent=4))
          Expression(
              body=NamedExpr(
                  target=Name(id='x', ctx=Store()),
                  value=Constant(value=4)))

* Menu:

* Subscripting::
* Comprehensions::


File: python.info,  Node: Subscripting,  Next: Comprehensions,  Up: Expressions<2>

5.32.2.6 Subscripting
.....................

 -- Class: ast.Subscript (value, slice, ctx)

     A subscript, such as ‘l[1]’.  ‘value’ is the subscripted object
     (usually sequence or mapping).  ‘slice’ is an index, slice or key.
     It can be a *note Tuple: 3967. and contain a *note Slice: 399a.
     ‘ctx’ is *note Load: 3969, *note Store: 3968. or *note Del: 396c.
     according to the action performed with the subscript.

          >>> print(ast.dump(ast.parse('l[1:2, 3]', mode='eval'), indent=4))
          Expression(
              body=Subscript(
                  value=Name(id='l', ctx=Load()),
                  slice=Tuple(
                      elts=[
                          Slice(
                              lower=Constant(value=1),
                              upper=Constant(value=2)),
                          Constant(value=3)],
                      ctx=Load()),
                  ctx=Load()))

 -- Class: ast.Slice (lower, upper, step)

     Regular slicing (on the form ‘lower:upper’ or ‘lower:upper:step’).
     Can occur only inside the `slice' field of *note Subscript: 3999,
     either directly or as an element of *note Tuple: 3967.

          >>> print(ast.dump(ast.parse('l[1:2]', mode='eval'), indent=4))
          Expression(
              body=Subscript(
                  value=Name(id='l', ctx=Load()),
                  slice=Slice(
                      lower=Constant(value=1),
                      upper=Constant(value=2)),
                  ctx=Load()))


File: python.info,  Node: Comprehensions,  Prev: Subscripting,  Up: Expressions<2>

5.32.2.7 Comprehensions
.......................

 -- Class: ast.ListComp (elt, generators)
 -- Class: ast.SetComp (elt, generators)
 -- Class: ast.GeneratorExp (elt, generators)
 -- Class: ast.DictComp (key, value, generators)

     List and set comprehensions, generator expressions, and dictionary
     comprehensions.  ‘elt’ (or ‘key’ and ‘value’) is a single node
     representing the part that will be evaluated for each item.

     ‘generators’ is a list of *note comprehension: 39a0. nodes.

          >>> print(ast.dump(ast.parse('[x for x in numbers]', mode='eval'), indent=4))
          Expression(
              body=ListComp(
                  elt=Name(id='x', ctx=Load()),
                  generators=[
                      comprehension(
                          target=Name(id='x', ctx=Store()),
                          iter=Name(id='numbers', ctx=Load()),
                          ifs=[],
                          is_async=0)]))
          >>> print(ast.dump(ast.parse('{x: x**2 for x in numbers}', mode='eval'), indent=4))
          Expression(
              body=DictComp(
                  key=Name(id='x', ctx=Load()),
                  value=BinOp(
                      left=Name(id='x', ctx=Load()),
                      op=Pow(),
                      right=Constant(value=2)),
                  generators=[
                      comprehension(
                          target=Name(id='x', ctx=Store()),
                          iter=Name(id='numbers', ctx=Load()),
                          ifs=[],
                          is_async=0)]))
          >>> print(ast.dump(ast.parse('{x for x in numbers}', mode='eval'), indent=4))
          Expression(
              body=SetComp(
                  elt=Name(id='x', ctx=Load()),
                  generators=[
                      comprehension(
                          target=Name(id='x', ctx=Store()),
                          iter=Name(id='numbers', ctx=Load()),
                          ifs=[],
                          is_async=0)]))

 -- Class: ast.comprehension (target, iter, ifs, is_async)

     One ‘for’ clause in a comprehension.  ‘target’ is the reference to
     use for each element - typically a *note Name: 102b. or *note
     Tuple: 3967. node.  ‘iter’ is the object to iterate over.  ‘ifs’ is
     a list of test expressions: each ‘for’ clause can have multiple
     ‘ifs’.

     ‘is_async’ indicates a comprehension is asynchronous (using an
     ‘async for’ instead of ‘for’).  The value is an integer (0 or 1).

          >>> print(ast.dump(ast.parse('[ord(c) for line in file for c in line]', mode='eval'),
          ...                indent=4)) # Multiple comprehensions in one.
          Expression(
              body=ListComp(
                  elt=Call(
                      func=Name(id='ord', ctx=Load()),
                      args=[
                          Name(id='c', ctx=Load())],
                      keywords=[]),
                  generators=[
                      comprehension(
                          target=Name(id='line', ctx=Store()),
                          iter=Name(id='file', ctx=Load()),
                          ifs=[],
                          is_async=0),
                      comprehension(
                          target=Name(id='c', ctx=Store()),
                          iter=Name(id='line', ctx=Load()),
                          ifs=[],
                          is_async=0)]))

          >>> print(ast.dump(ast.parse('(n**2 for n in it if n>5 if n<10)', mode='eval'),
          ...                indent=4)) # generator comprehension
          Expression(
              body=GeneratorExp(
                  elt=BinOp(
                      left=Name(id='n', ctx=Load()),
                      op=Pow(),
                      right=Constant(value=2)),
                  generators=[
                      comprehension(
                          target=Name(id='n', ctx=Store()),
                          iter=Name(id='it', ctx=Load()),
                          ifs=[
                              Compare(
                                  left=Name(id='n', ctx=Load()),
                                  ops=[
                                      Gt()],
                                  comparators=[
                                      Constant(value=5)]),
                              Compare(
                                  left=Name(id='n', ctx=Load()),
                                  ops=[
                                      Lt()],
                                  comparators=[
                                      Constant(value=10)])],
                          is_async=0)]))

          >>> print(ast.dump(ast.parse('[i async for i in soc]', mode='eval'),
          ...                indent=4)) # Async comprehension
          Expression(
              body=ListComp(
                  elt=Name(id='i', ctx=Load()),
                  generators=[
                      comprehension(
                          target=Name(id='i', ctx=Store()),
                          iter=Name(id='soc', ctx=Load()),
                          ifs=[],
                          is_async=1)]))


File: python.info,  Node: Statements,  Next: Control flow,  Prev: Expressions<2>,  Up: Node classes

5.32.2.8 Statements
...................

 -- Class: ast.Assign (targets, value, type_comment)

     An assignment.  ‘targets’ is a list of nodes, and ‘value’ is a
     single node.

     Multiple nodes in ‘targets’ represents assigning the same value to
     each.  Unpacking is represented by putting a *note Tuple: 3967. or
     *note List: 3966. within ‘targets’.

      -- Attribute: type_comment

          ‘type_comment’ is an optional string with the type annotation
          as a comment.

          >>> print(ast.dump(ast.parse('a = b = 1'), indent=4)) # Multiple assignment
          Module(
              body=[
                  Assign(
                      targets=[
                          Name(id='a', ctx=Store()),
                          Name(id='b', ctx=Store())],
                      value=Constant(value=1))],
              type_ignores=[])

          >>> print(ast.dump(ast.parse('a,b = c'), indent=4)) # Unpacking
          Module(
              body=[
                  Assign(
                      targets=[
                          Tuple(
                              elts=[
                                  Name(id='a', ctx=Store()),
                                  Name(id='b', ctx=Store())],
                              ctx=Store())],
                      value=Name(id='c', ctx=Load()))],
              type_ignores=[])

 -- Class: ast.AnnAssign (target, annotation, value, simple)

     An assignment with a type annotation.  ‘target’ is a single node
     and can be a *note Name: 102b, a *note Attribute: 3993. or a *note
     Subscript: 3999.  ‘annotation’ is the annotation, such as a *note
     Constant: 3a6. or *note Name: 102b. node.  ‘value’ is a single
     optional node.  ‘simple’ is a boolean integer set to True for a
     *note Name: 102b. node in ‘target’ that do not appear in between
     parenthesis and are hence pure names and not expressions.

          >>> print(ast.dump(ast.parse('c: int'), indent=4))
          Module(
              body=[
                  AnnAssign(
                      target=Name(id='c', ctx=Store()),
                      annotation=Name(id='int', ctx=Load()),
                      simple=1)],
              type_ignores=[])

          >>> print(ast.dump(ast.parse('(a): int = 1'), indent=4)) # Annotation with parenthesis
          Module(
              body=[
                  AnnAssign(
                      target=Name(id='a', ctx=Store()),
                      annotation=Name(id='int', ctx=Load()),
                      value=Constant(value=1),
                      simple=0)],
              type_ignores=[])

          >>> print(ast.dump(ast.parse('a.b: int'), indent=4)) # Attribute annotation
          Module(
              body=[
                  AnnAssign(
                      target=Attribute(
                          value=Name(id='a', ctx=Load()),
                          attr='b',
                          ctx=Store()),
                      annotation=Name(id='int', ctx=Load()),
                      simple=0)],
              type_ignores=[])

          >>> print(ast.dump(ast.parse('a[1]: int'), indent=4)) # Subscript annotation
          Module(
              body=[
                  AnnAssign(
                      target=Subscript(
                          value=Name(id='a', ctx=Load()),
                          slice=Constant(value=1),
                          ctx=Store()),
                      annotation=Name(id='int', ctx=Load()),
                      simple=0)],
              type_ignores=[])

 -- Class: ast.AugAssign (target, op, value)

     Augmented assignment, such as ‘a += 1’.  In the following example,
     ‘target’ is a *note Name: 102b. node for ‘x’ (with the *note Store:
     3968. context), ‘op’ is *note Add: 3978, and ‘value’ is a *note
     Constant: 3a6. with value for 1.

     The ‘target’ attribute connot be of class *note Tuple: 3967. or
     *note List: 3966, unlike the targets of *note Assign: 3997.

          >>> print(ast.dump(ast.parse('x += 2'), indent=4))
          Module(
              body=[
                  AugAssign(
                      target=Name(id='x', ctx=Store()),
                      op=Add(),
                      value=Constant(value=2))],
              type_ignores=[])

 -- Class: ast.Raise (exc, cause)

     A ‘raise’ statement.  ‘exc’ is the exception object to be raised,
     normally a *note Call: 396e. or *note Name: 102b, or ‘None’ for a
     standalone ‘raise’.  ‘cause’ is the optional part for ‘y’ in ‘raise
     x from y’.

          >>> print(ast.dump(ast.parse('raise x from y'), indent=4))
          Module(
              body=[
                  Raise(
                      exc=Name(id='x', ctx=Load()),
                      cause=Name(id='y', ctx=Load()))],
              type_ignores=[])

 -- Class: ast.Assert (test, msg)

     An assertion.  ‘test’ holds the condition, such as a *note Compare:
     3988. node.  ‘msg’ holds the failure message.

          >>> print(ast.dump(ast.parse('assert x,y'), indent=4))
          Module(
              body=[
                  Assert(
                      test=Name(id='x', ctx=Load()),
                      msg=Name(id='y', ctx=Load()))],
              type_ignores=[])

 -- Class: ast.Delete (targets)

     Represents a ‘del’ statement.  ‘targets’ is a list of nodes, such
     as *note Name: 102b, *note Attribute: 3993. or *note Subscript:
     3999. nodes.

          >>> print(ast.dump(ast.parse('del x,y,z'), indent=4))
          Module(
              body=[
                  Delete(
                      targets=[
                          Name(id='x', ctx=Del()),
                          Name(id='y', ctx=Del()),
                          Name(id='z', ctx=Del())])],
              type_ignores=[])

 -- Class: ast.Pass

     A ‘pass’ statement.

          >>> print(ast.dump(ast.parse('pass'), indent=4))
          Module(
              body=[
                  Pass()],
              type_ignores=[])

Other statements which are only applicable inside functions or loops are
described in other sections.

* Menu:

* Imports::


File: python.info,  Node: Imports,  Up: Statements

5.32.2.9 Imports
................

 -- Class: ast.Import (names)

     An import statement.  ‘names’ is a list of *note alias: 39ab.
     nodes.

          >>> print(ast.dump(ast.parse('import x,y,z'), indent=4))
          Module(
              body=[
                  Import(
                      names=[
                          alias(name='x'),
                          alias(name='y'),
                          alias(name='z')])],
              type_ignores=[])

 -- Class: ast.ImportFrom (module, names, level)

     Represents ‘from x import y’.  ‘module’ is a raw string of the
     ‘from’ name, without any leading dots, or ‘None’ for statements
     such as ‘from . import foo’.  ‘level’ is an integer holding the
     level of the relative import (0 means absolute import).

          >>> print(ast.dump(ast.parse('from y import x,y,z'), indent=4))
          Module(
              body=[
                  ImportFrom(
                      module='y',
                      names=[
                          alias(name='x'),
                          alias(name='y'),
                          alias(name='z')],
                      level=0)],
              type_ignores=[])

 -- Class: ast.alias (name, asname)

     Both parameters are raw strings of the names.  ‘asname’ can be
     ‘None’ if the regular name is to be used.

          >>> print(ast.dump(ast.parse('from ..foo.bar import a as b, c'), indent=4))
          Module(
              body=[
                  ImportFrom(
                      module='foo.bar',
                      names=[
                          alias(name='a', asname='b'),
                          alias(name='c')],
                      level=2)],
              type_ignores=[])


File: python.info,  Node: Control flow,  Next: Function and class definitions,  Prev: Statements,  Up: Node classes

5.32.2.10 Control flow
......................

     Note: Optional clauses such as ‘else’ are stored as an empty list
     if they’re not present.

 -- Class: ast.If (test, body, orelse)

     An ‘if’ statement.  ‘test’ holds a single node, such as a *note
     Compare: 3988. node.  ‘body’ and ‘orelse’ each hold a list of
     nodes.

     ‘elif’ clauses don’t have a special representation in the AST, but
     rather appear as extra *note If: 39ae. nodes within the ‘orelse’
     section of the previous one.

          >>> print(ast.dump(ast.parse("""
          ... if x:
          ...    ...
          ... elif y:
          ...    ...
          ... else:
          ...    ...
          ... """), indent=4))
          Module(
              body=[
                  If(
                      test=Name(id='x', ctx=Load()),
                      body=[
                          Expr(
                              value=Constant(value=Ellipsis))],
                      orelse=[
                          If(
                              test=Name(id='y', ctx=Load()),
                              body=[
                                  Expr(
                                      value=Constant(value=Ellipsis))],
                              orelse=[
                                  Expr(
                                      value=Constant(value=Ellipsis))])])],
              type_ignores=[])

 -- Class: ast.For (target, iter, body, orelse, type_comment)

     A ‘for’ loop.  ‘target’ holds the variable(s) the loop assigns to,
     as a single *note Name: 102b, *note Tuple: 3967. or *note List:
     3966. node.  ‘iter’ holds the item to be looped over, again as a
     single node.  ‘body’ and ‘orelse’ contain lists of nodes to
     execute.  Those in ‘orelse’ are executed if the loop finishes
     normally, rather than via a ‘break’ statement.

      -- Attribute: type_comment

          ‘type_comment’ is an optional string with the type annotation
          as a comment.

          >>> print(ast.dump(ast.parse("""
          ... for x in y:
          ...     ...
          ... else:
          ...     ...
          ... """), indent=4))
          Module(
              body=[
                  For(
                      target=Name(id='x', ctx=Store()),
                      iter=Name(id='y', ctx=Load()),
                      body=[
                          Expr(
                              value=Constant(value=Ellipsis))],
                      orelse=[
                          Expr(
                              value=Constant(value=Ellipsis))])],
              type_ignores=[])

 -- Class: ast.While (test, body, orelse)

     A ‘while’ loop.  ‘test’ holds the condition, such as a *note
     Compare: 3988. node.

          >> print(ast.dump(ast.parse("""
          ... while x:
          ...    ...
          ... else:
          ...    ...
          ... """), indent=4))
          Module(
              body=[
                  While(
                      test=Name(id='x', ctx=Load()),
                      body=[
                          Expr(
                              value=Constant(value=Ellipsis))],
                      orelse=[
                          Expr(
                              value=Constant(value=Ellipsis))])],
              type_ignores=[])

 -- Class: ast.Break
 -- Class: ast.Continue

     The ‘break’ and ‘continue’ statements.

          >>> print(ast.dump(ast.parse("""\
          ... for a in b:
          ...     if a > 5:
          ...         break
          ...     else:
          ...         continue
          ...
          ... """), indent=4))
          Module(
              body=[
                  For(
                      target=Name(id='a', ctx=Store()),
                      iter=Name(id='b', ctx=Load()),
                      body=[
                          If(
                              test=Compare(
                                  left=Name(id='a', ctx=Load()),
                                  ops=[
                                      Gt()],
                                  comparators=[
                                      Constant(value=5)]),
                              body=[
                                  Break()],
                              orelse=[
                                  Continue()])],
                      orelse=[])],
              type_ignores=[])

 -- Class: ast.Try (body, handlers, orelse, finalbody)

     ‘try’ blocks.  All attributes are list of nodes to execute, except
     for ‘handlers’, which is a list of *note ExceptHandler: 39b5.
     nodes.

          >>> print(ast.dump(ast.parse("""
          ... try:
          ...    ...
          ... except Exception:
          ...    ...
          ... except OtherException as e:
          ...    ...
          ... else:
          ...    ...
          ... finally:
          ...    ...
          ... """), indent=4))
          Module(
              body=[
                  Try(
                      body=[
                          Expr(
                              value=Constant(value=Ellipsis))],
                      handlers=[
                          ExceptHandler(
                              type=Name(id='Exception', ctx=Load()),
                              body=[
                                  Expr(
                                      value=Constant(value=Ellipsis))]),
                          ExceptHandler(
                              type=Name(id='OtherException', ctx=Load()),
                              name='e',
                              body=[
                                  Expr(
                                      value=Constant(value=Ellipsis))])],
                      orelse=[
                          Expr(
                              value=Constant(value=Ellipsis))],
                      finalbody=[
                          Expr(
                              value=Constant(value=Ellipsis))])],
              type_ignores=[])

 -- Class: ast.ExceptHandler (type, name, body)

     A single ‘except’ clause.  ‘type’ is the exception type it will
     match, typically a *note Name: 102b. node (or ‘None’ for a
     catch-all ‘except:’ clause).  ‘name’ is a raw string for the name
     to hold the exception, or ‘None’ if the clause doesn’t have ‘as
     foo’.  ‘body’ is a list of nodes.

          >>> print(ast.dump(ast.parse("""\
          ... try:
          ...     a + 1
          ... except TypeError:
          ...     pass
          ... """), indent=4))
          Module(
              body=[
                  Try(
                      body=[
                          Expr(
                              value=BinOp(
                                  left=Name(id='a', ctx=Load()),
                                  op=Add(),
                                  right=Constant(value=1)))],
                      handlers=[
                          ExceptHandler(
                              type=Name(id='TypeError', ctx=Load()),
                              body=[
                                  Pass()])],
                      orelse=[],
                      finalbody=[])],
              type_ignores=[])

 -- Class: ast.With (items, body, type_comment)

     A ‘with’ block.  ‘items’ is a list of *note withitem: 39b7. nodes
     representing the context managers, and ‘body’ is the indented block
     inside the context.

      -- Attribute: type_comment

          ‘type_comment’ is an optional string with the type annotation
          as a comment.

 -- Class: ast.withitem (context_expr, optional_vars)

     A single context manager in a ‘with’ block.  ‘context_expr’ is the
     context manager, often a *note Call: 396e. node.  ‘optional_vars’
     is a *note Name: 102b, *note Tuple: 3967. or *note List: 3966. for
     the ‘as foo’ part, or ‘None’ if that isn’t used.

          >>> print(ast.dump(ast.parse("""\
          ... with a as b, c as d:
          ...    something(b, d)
          ... """), indent=4))
          Module(
              body=[
                  With(
                      items=[
                          withitem(
                              context_expr=Name(id='a', ctx=Load()),
                              optional_vars=Name(id='b', ctx=Store())),
                          withitem(
                              context_expr=Name(id='c', ctx=Load()),
                              optional_vars=Name(id='d', ctx=Store()))],
                      body=[
                          Expr(
                              value=Call(
                                  func=Name(id='something', ctx=Load()),
                                  args=[
                                      Name(id='b', ctx=Load()),
                                      Name(id='d', ctx=Load())],
                                  keywords=[]))])],
              type_ignores=[])


File: python.info,  Node: Function and class definitions,  Next: Async and await,  Prev: Control flow,  Up: Node classes

5.32.2.11 Function and class definitions
........................................

 -- Class: ast.FunctionDef (name, args, body, decorator_list, returns,
          type_comment)

     A function definition.

        * ‘name’ is a raw string of the function name.

        * ‘args’ is an *note arguments: 39bb. node.

        * ‘body’ is the list of nodes inside the function.

        * ‘decorator_list’ is the list of decorators to be applied,
          stored outermost first (i.e.  the first in the list will be
          applied last).

        * ‘returns’ is the return annotation.

      -- Attribute: type_comment

          ‘type_comment’ is an optional string with the type annotation
          as a comment.

 -- Class: ast.Lambda (args, body)

     ‘lambda’ is a minimal function definition that can be used inside
     an expression.  Unlike *note FunctionDef: 39ba, ‘body’ holds a
     single node.

          >>> print(ast.dump(ast.parse('lambda x,y: ...'), indent=4))
          Module(
              body=[
                  Expr(
                      value=Lambda(
                          args=arguments(
                              posonlyargs=[],
                              args=[
                                  arg(arg='x'),
                                  arg(arg='y')],
                              kwonlyargs=[],
                              kw_defaults=[],
                              defaults=[]),
                          body=Constant(value=Ellipsis)))],
              type_ignores=[])

 -- Class: ast.arguments (posonlyargs, args, vararg, kwonlyargs,
          kw_defaults, kwarg, defaults)

     The arguments for a function.

        * ‘posonlyargs’, ‘args’ and ‘kwonlyargs’ are lists of *note arg:
          39bd. nodes.

        * ‘vararg’ and ‘kwarg’ are single *note arg: 39bd. nodes,
          referring to the ‘*args, **kwargs’ parameters.

        * ‘kw_defaults’ is a list of default values for keyword-only
          arguments.  If one is ‘None’, the corresponding argument is
          required.

        * ‘defaults’ is a list of default values for arguments that can
          be passed positionally.  If there are fewer defaults, they
          correspond to the last n arguments.

 -- Class: ast.arg (arg, annotation, type_comment)

     A single argument in a list.  ‘arg’ is a raw string of the argument
     name, ‘annotation’ is its annotation, such as a ‘Str’ or *note
     Name: 102b. node.

      -- Attribute: type_comment

          ‘type_comment’ is an optional string with the type annotation
          as a comment

          >>> print(ast.dump(ast.parse("""\
          ... @decorator1
          ... @decorator2
          ... def f(a: 'annotation', b=1, c=2, *d, e, f=3, **g) -> 'return annotation':
          ...     pass
          ... """), indent=4))
          Module(
              body=[
                  FunctionDef(
                      name='f',
                      args=arguments(
                          posonlyargs=[],
                          args=[
                              arg(
                                  arg='a',
                                  annotation=Constant(value='annotation')),
                              arg(arg='b'),
                              arg(arg='c')],
                          vararg=arg(arg='d'),
                          kwonlyargs=[
                              arg(arg='e'),
                              arg(arg='f')],
                          kw_defaults=[
                              None,
                              Constant(value=3)],
                          kwarg=arg(arg='g'),
                          defaults=[
                              Constant(value=1),
                              Constant(value=2)]),
                      body=[
                          Pass()],
                      decorator_list=[
                          Name(id='decorator1', ctx=Load()),
                          Name(id='decorator2', ctx=Load())],
                      returns=Constant(value='return annotation'))],
              type_ignores=[])

 -- Class: ast.Return (value)

     A ‘return’ statement.

          >>> print(ast.dump(ast.parse('return 4'), indent=4))
          Module(
              body=[
                  Return(
                      value=Constant(value=4))],
              type_ignores=[])

 -- Class: ast.Yield (value)
 -- Class: ast.YieldFrom (value)

     A ‘yield’ or ‘yield from’ expression.  Because these are
     expressions, they must be wrapped in a *note Expr: 3970. node if
     the value sent back is not used.

          >>> print(ast.dump(ast.parse('yield x'), indent=4))
          Module(
              body=[
                  Expr(
                      value=Yield(
                          value=Name(id='x', ctx=Load())))],
              type_ignores=[])

          >>> print(ast.dump(ast.parse('yield from x'), indent=4))
          Module(
              body=[
                  Expr(
                      value=YieldFrom(
                          value=Name(id='x', ctx=Load())))],
              type_ignores=[])

 -- Class: ast.Global (names)
 -- Class: ast.Nonlocal (names)

     ‘global’ and ‘nonlocal’ statements.  ‘names’ is a list of raw
     strings.

          >>> print(ast.dump(ast.parse('global x,y,z'), indent=4))
          Module(
              body=[
                  Global(
                      names=[
                          'x',
                          'y',
                          'z'])],
              type_ignores=[])

          >>> print(ast.dump(ast.parse('nonlocal x,y,z'), indent=4))
          Module(
              body=[
                  Nonlocal(
                      names=[
                          'x',
                          'y',
                          'z'])],
              type_ignores=[])

 -- Class: ast.ClassDef (name, bases, keywords, starargs, kwargs, body,
          decorator_list)

     A class definition.

        * ‘name’ is a raw string for the class name

        * ‘bases’ is a list of nodes for explicitly specified base
          classes.

        * ‘keywords’ is a list of *note keyword: a6. nodes, principally
          for ‘metaclass’.  Other keywords will be passed to the
          metaclass, as per PEP-3115(1).

        * ‘starargs’ and ‘kwargs’ are each a single node, as in a
          function call.  starargs will be expanded to join the list of
          base classes, and kwargs will be passed to the metaclass.

        * ‘body’ is a list of nodes representing the code within the
          class definition.

        * ‘decorator_list’ is a list of nodes, as in *note FunctionDef:
          39ba.

          >>> print(ast.dump(ast.parse("""\
          ... @decorator1
          ... @decorator2
          ... class Foo(base1, base2, metaclass=meta):
          ...     pass
          ... """), indent=4))
          Module(
              body=[
                  ClassDef(
                      name='Foo',
                      bases=[
                          Name(id='base1', ctx=Load()),
                          Name(id='base2', ctx=Load())],
                      keywords=[
                          keyword(
                              arg='metaclass',
                              value=Name(id='meta', ctx=Load()))],
                      body=[
                          Pass()],
                      decorator_list=[
                          Name(id='decorator1', ctx=Load()),
                          Name(id='decorator2', ctx=Load())])],
              type_ignores=[])

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3115/


File: python.info,  Node: Async and await,  Prev: Function and class definitions,  Up: Node classes

5.32.2.12 Async and await
.........................

 -- Class: ast.AsyncFunctionDef (name, args, body, decorator_list,
          returns, type_comment)

     An ‘async def’ function definition.  Has the same fields as *note
     FunctionDef: 39ba.

 -- Class: ast.Await (value)

     An ‘await’ expression.  ‘value’ is what it waits for.  Only valid
     in the body of an *note AsyncFunctionDef: 39c4.

     >>> print(ast.dump(ast.parse("""\
     ... async def f():
     ...     await other_func()
     ... """), indent=4))
     Module(
         body=[
             AsyncFunctionDef(
                 name='f',
                 args=arguments(
                     posonlyargs=[],
                     args=[],
                     kwonlyargs=[],
                     kw_defaults=[],
                     defaults=[]),
                 body=[
                     Expr(
                         value=Await(
                             value=Call(
                                 func=Name(id='other_func', ctx=Load()),
                                 args=[],
                                 keywords=[])))],
                 decorator_list=[])],
         type_ignores=[])

 -- Class: ast.AsyncFor (target, iter, body, orelse, type_comment)
 -- Class: ast.AsyncWith (items, body, type_comment)

     ‘async for’ loops and ‘async with’ context managers.  They have the
     same fields as *note For: 39af. and *note With: 39b6, respectively.
     Only valid in the body of an *note AsyncFunctionDef: 39c4.

     Note: When a string is parsed by *note ast.parse(): 2d6, operator
     nodes (subclasses of ‘ast.operator’, ‘ast.unaryop’, ‘ast.cmpop’,
     ‘ast.boolop’ and ‘ast.expr_context’) on the returned tree will be
     singletons.  Changes to one will be reflected in all other
     occurrences of the same value (e.g.  *note ast.Add: 3978.).


File: python.info,  Node: ast Helpers,  Next: Compiler Flags,  Prev: Node classes,  Up: ast — Abstract Syntax Trees

5.32.2.13 ‘ast’ Helpers
.......................

Apart from the node classes, the *note ast: 7. module defines these
utility functions and classes for traversing abstract syntax trees:

 -- Function: ast.parse (source, filename='<unknown>', mode='exec', *,
          type_comments=False, feature_version=None)

     Parse the source into an AST node.  Equivalent to ‘compile(source,
     filename, mode, ast.PyCF_ONLY_AST)’.

     If ‘type_comments=True’ is given, the parser is modified to check
     and return type comments as specified by PEP 484(1) and PEP 526(2).
     This is equivalent to adding *note ast.PyCF_TYPE_COMMENTS: 39c9. to
     the flags passed to *note compile(): 2e7.  This will report syntax
     errors for misplaced type comments.  Without this flag, type
     comments will be ignored, and the ‘type_comment’ field on selected
     AST nodes will always be ‘None’.  In addition, the locations of ‘#
     type: ignore’ comments will be returned as the ‘type_ignores’
     attribute of ‘Module’ (otherwise it is always an empty list).

     In addition, if ‘mode’ is ‘'func_type'’, the input syntax is
     modified to correspond to PEP 484(3) “signature type comments”,
     e.g.  ‘(str, int) -> List[str]’.

     Also, setting ‘feature_version’ to a tuple ‘(major, minor)’ will
     attempt to parse using that Python version’s grammar.  Currently
     ‘major’ must equal to ‘3’.  For example, setting
     ‘feature_version=(3, 4)’ will allow the use of ‘async’ and ‘await’
     as variable names.  The lowest supported version is ‘(3, 4)’; the
     highest is ‘sys.version_info[0:2]’.

     If source contains a null character (‘0’), *note ValueError: 16d.
     is raised.

               Warning: Note that successfully parsing source code into
               an AST object doesn’t guarantee that the source code
               provided is valid Python code that can be executed as the
               compilation step can raise further *note SyntaxError:
               55a. exceptions.  For instance, the source ‘return 42’
               generates a valid AST node for a return statement, but it
               cannot be compiled alone (it needs to be inside a
               function node).

               In particular, *note ast.parse(): 2d6. won’t do any
               scoping checks, which the compilation step does.

          Warning: It is possible to crash the Python interpreter with a
          sufficiently large/complex string due to stack depth
          limitations in Python’s AST compiler.

     Changed in version 3.8: Added ‘type_comments’, ‘mode='func_type'’
     and ‘feature_version’.

 -- Function: ast.unparse (ast_obj)

     Unparse an *note ast.AST: 187. object and generate a string with
     code that would produce an equivalent *note ast.AST: 187. object if
     parsed back with *note ast.parse(): 2d6.

          Warning: The produced code string will not necessarily be
          equal to the original code that generated the *note ast.AST:
          187. object (without any compiler optimizations, such as
          constant tuples/frozensets).

          Warning: Trying to unparse a highly complex expression would
          result with *note RecursionError: 727.

     New in version 3.9.

 -- Function: ast.literal_eval (node_or_string)

     Safely evaluate an expression node or a string containing a Python
     literal or container display.  The string or node provided may only
     consist of the following Python literal structures: strings, bytes,
     numbers, tuples, lists, dicts, sets, booleans, and ‘None’.

     This can be used for safely evaluating strings containing Python
     values from untrusted sources without the need to parse the values
     oneself.  It is not capable of evaluating arbitrarily complex
     expressions, for example involving operators or indexing.

          Warning: It is possible to crash the Python interpreter with a
          sufficiently large/complex string due to stack depth
          limitations in Python’s AST compiler.

     Changed in version 3.2: Now allows bytes and set literals.

     Changed in version 3.9: Now supports creating empty sets with
     ‘'set()'’.

 -- Function: ast.get_docstring (node, clean=True)

     Return the docstring of the given `node' (which must be a *note
     FunctionDef: 39ba, *note AsyncFunctionDef: 39c4, *note ClassDef:
     39c2, or ‘Module’ node), or ‘None’ if it has no docstring.  If
     `clean' is true, clean up the docstring’s indentation with *note
     inspect.cleandoc(): 385b.

     Changed in version 3.5: *note AsyncFunctionDef: 39c4. is now
     supported.

 -- Function: ast.get_source_segment (source, node, *, padded=False)

     Get source code segment of the `source' that generated `node'.  If
     some location information (‘lineno’, ‘end_lineno’, ‘col_offset’, or
     ‘end_col_offset’) is missing, return ‘None’.

     If `padded' is ‘True’, the first line of a multi-line statement
     will be padded with spaces to match its original position.

     New in version 3.8.

 -- Function: ast.fix_missing_locations (node)

     When you compile a node tree with *note compile(): 2e7, the
     compiler expects ‘lineno’ and ‘col_offset’ attributes for every
     node that supports them.  This is rather tedious to fill in for
     generated nodes, so this helper adds these attributes recursively
     where not already set, by setting them to the values of the parent
     node.  It works recursively starting at `node'.

 -- Function: ast.increment_lineno (node, n=1)

     Increment the line number and end line number of each node in the
     tree starting at `node' by `n'.  This is useful to “move code” to a
     different location in a file.

 -- Function: ast.copy_location (new_node, old_node)

     Copy source location (‘lineno’, ‘col_offset’, ‘end_lineno’, and
     ‘end_col_offset’) from `old_node' to `new_node' if possible, and
     return `new_node'.

 -- Function: ast.iter_fields (node)

     Yield a tuple of ‘(fieldname, value)’ for each field in
     ‘node._fields’ that is present on `node'.

 -- Function: ast.iter_child_nodes (node)

     Yield all direct child nodes of `node', that is, all fields that
     are nodes and all items of fields that are lists of nodes.

 -- Function: ast.walk (node)

     Recursively yield all descendant nodes in the tree starting at
     `node' (including `node' itself), in no specified order.  This is
     useful if you only want to modify nodes in place and don’t care
     about the context.

 -- Class: ast.NodeVisitor

     A node visitor base class that walks the abstract syntax tree and
     calls a visitor function for every node found.  This function may
     return a value which is forwarded by the *note visit(): 39cf.
     method.

     This class is meant to be subclassed, with the subclass adding
     visitor methods.

      -- Method: visit (node)

          Visit a node.  The default implementation calls the method
          called ‘self.visit_`classname'’ where `classname' is the name
          of the node class, or *note generic_visit(): 39d0. if that
          method doesn’t exist.

      -- Method: generic_visit (node)

          This visitor calls *note visit(): 39cf. on all children of the
          node.

          Note that child nodes of nodes that have a custom visitor
          method won’t be visited unless the visitor calls *note
          generic_visit(): 39d0. or visits them itself.

     Don’t use the *note NodeVisitor: 3a7. if you want to apply changes
     to nodes during traversal.  For this a special visitor exists
     (*note NodeTransformer: 39d1.) that allows modifications.

     Deprecated since version 3.8: Methods ‘visit_Num()’, ‘visit_Str()’,
     ‘visit_Bytes()’, ‘visit_NameConstant()’ and ‘visit_Ellipsis()’ are
     deprecated now and will not be called in future Python versions.
     Add the ‘visit_Constant()’ method to handle all constant nodes.

 -- Class: ast.NodeTransformer

     A *note NodeVisitor: 3a7. subclass that walks the abstract syntax
     tree and allows modification of nodes.

     The *note NodeTransformer: 39d1. will walk the AST and use the
     return value of the visitor methods to replace or remove the old
     node.  If the return value of the visitor method is ‘None’, the
     node will be removed from its location, otherwise it is replaced
     with the return value.  The return value may be the original node
     in which case no replacement takes place.

     Here is an example transformer that rewrites all occurrences of
     name lookups (‘foo’) to ‘data['foo']’:

          class RewriteName(NodeTransformer):

              def visit_Name(self, node):
                  return Subscript(
                      value=Name(id='data', ctx=Load()),
                      slice=Constant(value=node.id),
                      ctx=node.ctx
                  )

     Keep in mind that if the node you’re operating on has child nodes
     you must either transform the child nodes yourself or call the
     ‘generic_visit()’ method for the node first.

     For nodes that were part of a collection of statements (that
     applies to all statement nodes), the visitor may also return a list
     of nodes rather than just a single node.

     If *note NodeTransformer: 39d1. introduces new nodes (that weren’t
     part of original tree) without giving them location information
     (such as ‘lineno’), *note fix_missing_locations(): 39ca. should be
     called with the new sub-tree to recalculate the location
     information:

          tree = ast.parse('foo', mode='eval')
          new_tree = fix_missing_locations(RewriteName().visit(tree))

     Usually you use the transformer like this:

          node = YourTransformer().visit(node)

 -- Function: ast.dump (node, annotate_fields=True,
          include_attributes=False, *, indent=None)

     Return a formatted dump of the tree in `node'.  This is mainly
     useful for debugging purposes.  If `annotate_fields' is true (by
     default), the returned string will show the names and the values
     for fields.  If `annotate_fields' is false, the result string will
     be more compact by omitting unambiguous field names.  Attributes
     such as line numbers and column offsets are not dumped by default.
     If this is wanted, `include_attributes' can be set to true.

     If `indent' is a non-negative integer or string, then the tree will
     be pretty-printed with that indent level.  An indent level of 0,
     negative, or ‘""’ will only insert newlines.  ‘None’ (the default)
     selects the single line representation.  Using a positive integer
     indent indents that many spaces per level.  If `indent' is a string
     (such as ‘"\t"’), that string is used to indent each level.

     Changed in version 3.9: Added the `indent' option.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0484

   (2) https://www.python.org/dev/peps/pep-0526

   (3) https://www.python.org/dev/peps/pep-0484


File: python.info,  Node: Compiler Flags,  Next: Command-Line Usage<2>,  Prev: ast Helpers,  Up: ast — Abstract Syntax Trees

5.32.2.14 Compiler Flags
........................

The following flags may be passed to *note compile(): 2e7. in order to
change effects on the compilation of a program:

 -- Data: ast.PyCF_ALLOW_TOP_LEVEL_AWAIT

     Enables support for top-level ‘await’, ‘async for’, ‘async with’
     and async comprehensions.

     New in version 3.8.

 -- Data: ast.PyCF_ONLY_AST

     Generates and returns an abstract syntax tree instead of returning
     a compiled code object.

 -- Data: ast.PyCF_TYPE_COMMENTS

     Enables support for PEP 484(1) and PEP 526(2) style type comments
     (‘# type: <type>’, ‘# type: ignore <stuff>’).

     New in version 3.8.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0484

   (2) https://www.python.org/dev/peps/pep-0526


File: python.info,  Node: Command-Line Usage<2>,  Prev: Compiler Flags,  Up: ast — Abstract Syntax Trees

5.32.2.15 Command-Line Usage
............................

New in version 3.9.

The *note ast: 7. module can be executed as a script from the command
line.  It is as simple as:

     python -m ast [-m <mode>] [-a] [infile]

The following options are accepted:

 -- Program Option: -h, --help

     Show the help message and exit.

 -- Program Option: -m <mode>
 -- Program Option: --mode <mode>

     Specify what kind of code must be compiled, like the `mode'
     argument in *note parse(): 2d6.

 -- Program Option: --no-type-comments

     Don’t parse type comments.

 -- Program Option: -a, --include-attributes

     Include attributes such as line numbers and column offsets.

 -- Program Option: -i <indent>
 -- Program Option: --indent <indent>

     Indentation of nodes in AST (number of spaces).

If ‘infile’ is specified its contents are parsed to AST and dumped to
stdout.  Otherwise, the content is read from stdin.

See also
........

Green Tree Snakes(1), an external documentation resource, has good
details on working with Python ASTs.

ASTTokens(2) annotates Python ASTs with the positions of tokens and text
in the source code that generated them.  This is helpful for tools that
make source code transformations.

leoAst.py(3) unifies the token-based and parse-tree-based views of
python programs by inserting two-way links between tokens and ast nodes.

LibCST(4) parses code as a Concrete Syntax Tree that looks like an ast
tree and keeps all formatting details.  It’s useful for building
automated refactoring (codemod) applications and linters.

Parso(5) is a Python parser that supports error recovery and round-trip
parsing for different Python versions (in multiple Python versions).
Parso is also able to list multiple syntax errors in your python file.

   ---------- Footnotes ----------

   (1) https://greentreesnakes.readthedocs.io/

   (2) https://asttokens.readthedocs.io/en/latest/user-guide.html

   (3) http://leoeditor.com/appendices.html#leoast-py

   (4) https://libcst.readthedocs.io/

   (5) https://parso.readthedocs.io


File: python.info,  Node: symtable — Access to the compiler’s symbol tables,  Next: symbol — Constants used with Python parse trees,  Prev: ast — Abstract Syntax Trees,  Up: Python Language Services

5.32.3 ‘symtable’ — Access to the compiler’s symbol tables
----------------------------------------------------------

`Source code:' Lib/symtable.py(1)

__________________________________________________________________

Symbol tables are generated by the compiler from AST just before
bytecode is generated.  The symbol table is responsible for calculating
the scope of every identifier in the code.  *note symtable: fc. provides
an interface to examine these tables.

* Menu:

* Generating Symbol Tables::
* Examining Symbol Tables::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/symtable.py


File: python.info,  Node: Generating Symbol Tables,  Next: Examining Symbol Tables,  Up: symtable — Access to the compiler’s symbol tables

5.32.3.1 Generating Symbol Tables
.................................

 -- Function: symtable.symtable (code, filename, compile_type)

     Return the toplevel *note SymbolTable: 39e0. for the Python source
     `code'.  `filename' is the name of the file containing the code.
     `compile_type' is like the `mode' argument to *note compile(): 2e7.


File: python.info,  Node: Examining Symbol Tables,  Prev: Generating Symbol Tables,  Up: symtable — Access to the compiler’s symbol tables

5.32.3.2 Examining Symbol Tables
................................

 -- Class: symtable.SymbolTable

     A namespace table for a block.  The constructor is not public.

      -- Method: get_type ()

          Return the type of the symbol table.  Possible values are
          ‘'class'’, ‘'module'’, and ‘'function'’.

      -- Method: get_id ()

          Return the table’s identifier.

      -- Method: get_name ()

          Return the table’s name.  This is the name of the class if the
          table is for a class, the name of the function if the table is
          for a function, or ‘'top'’ if the table is global (*note
          get_type(): 39e2. returns ‘'module'’).

      -- Method: get_lineno ()

          Return the number of the first line in the block this table
          represents.

      -- Method: is_optimized ()

          Return ‘True’ if the locals in this table can be optimized.

      -- Method: is_nested ()

          Return ‘True’ if the block is a nested class or function.

      -- Method: has_children ()

          Return ‘True’ if the block has nested namespaces within it.
          These can be obtained with *note get_children(): 39e9.

      -- Method: get_identifiers ()

          Return a list of names of symbols in this table.

      -- Method: lookup (name)

          Lookup `name' in the table and return a *note Symbol: 39ec.
          instance.

      -- Method: get_symbols ()

          Return a list of *note Symbol: 39ec. instances for names in
          the table.

      -- Method: get_children ()

          Return a list of the nested symbol tables.

 -- Class: symtable.Function

     A namespace for a function or method.  This class inherits *note
     SymbolTable: 39e0.

      -- Method: get_parameters ()

          Return a tuple containing names of parameters to this
          function.

      -- Method: get_locals ()

          Return a tuple containing names of locals in this function.

      -- Method: get_globals ()

          Return a tuple containing names of globals in this function.

      -- Method: get_nonlocals ()

          Return a tuple containing names of nonlocals in this function.

      -- Method: get_frees ()

          Return a tuple containing names of free variables in this
          function.

 -- Class: symtable.Class

     A namespace of a class.  This class inherits *note SymbolTable:
     39e0.

      -- Method: get_methods ()

          Return a tuple containing the names of methods declared in the
          class.

 -- Class: symtable.Symbol

     An entry in a *note SymbolTable: 39e0. corresponding to an
     identifier in the source.  The constructor is not public.

      -- Method: get_name ()

          Return the symbol’s name.

      -- Method: is_referenced ()

          Return ‘True’ if the symbol is used in its block.

      -- Method: is_imported ()

          Return ‘True’ if the symbol is created from an import
          statement.

      -- Method: is_parameter ()

          Return ‘True’ if the symbol is a parameter.

      -- Method: is_global ()

          Return ‘True’ if the symbol is global.

      -- Method: is_nonlocal ()

          Return ‘True’ if the symbol is nonlocal.

      -- Method: is_declared_global ()

          Return ‘True’ if the symbol is declared global with a global
          statement.

      -- Method: is_local ()

          Return ‘True’ if the symbol is local to its block.

      -- Method: is_annotated ()

          Return ‘True’ if the symbol is annotated.

          New in version 3.6.

      -- Method: is_free ()

          Return ‘True’ if the symbol is referenced in its block, but
          not assigned to.

      -- Method: is_assigned ()

          Return ‘True’ if the symbol is assigned to in its block.

      -- Method: is_namespace ()

          Return ‘True’ if name binding introduces new namespace.

          If the name is used as the target of a function or class
          statement, this will be true.

          For example:

               >>> table = symtable.symtable("def some_func(): pass", "string", "exec")
               >>> table.lookup("some_func").is_namespace()
               True

          Note that a single name can be bound to multiple objects.  If
          the result is ‘True’, the name may also be bound to other
          objects, like an int or list, that does not introduce a new
          namespace.

      -- Method: get_namespaces ()

          Return a list of namespaces bound to this name.

      -- Method: get_namespace ()

          Return the namespace bound to this name.  If more than one
          namespace is bound, *note ValueError: 16d. is raised.


File: python.info,  Node: symbol — Constants used with Python parse trees,  Next: token — Constants used with Python parse trees,  Prev: symtable — Access to the compiler’s symbol tables,  Up: Python Language Services

5.32.4 ‘symbol’ — Constants used with Python parse trees
--------------------------------------------------------

`Source code:' Lib/symbol.py(1)

__________________________________________________________________

This module provides constants which represent the numeric values of
internal nodes of the parse tree.  Unlike most Python constants, these
use lower-case names.  Refer to the file ‘Grammar/Grammar’ in the Python
distribution for the definitions of the names in the context of the
language grammar.  The specific numeric values which the names map to
may change between Python versions.

     Warning: The symbol module is deprecated and will be removed in
     future versions of Python.

This module also provides one additional data object:

 -- Data: symbol.sym_name

     Dictionary mapping the numeric values of the constants defined in
     this module back to name strings, allowing more human-readable
     representation of parse trees to be generated.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/symbol.py


File: python.info,  Node: token — Constants used with Python parse trees,  Next: keyword — Testing for Python keywords,  Prev: symbol — Constants used with Python parse trees,  Up: Python Language Services

5.32.5 ‘token’ — Constants used with Python parse trees
-------------------------------------------------------

`Source code:' Lib/token.py(1)

__________________________________________________________________

This module provides constants which represent the numeric values of
leaf nodes of the parse tree (terminal tokens).  Refer to the file
‘Grammar/Grammar’ in the Python distribution for the definitions of the
names in the context of the language grammar.  The specific numeric
values which the names map to may change between Python versions.

The module also provides a mapping from numeric codes to names and some
functions.  The functions mirror definitions in the Python C header
files.

 -- Data: token.tok_name

     Dictionary mapping the numeric values of the constants defined in
     this module back to name strings, allowing more human-readable
     representation of parse trees to be generated.

 -- Function: token.ISTERMINAL (x)

     Return ‘True’ for terminal token values.

 -- Function: token.ISNONTERMINAL (x)

     Return ‘True’ for non-terminal token values.

 -- Function: token.ISEOF (x)

     Return ‘True’ if `x' is the marker indicating the end of input.

The token constants are:

 -- Data: token.ENDMARKER

 -- Data: token.NAME

 -- Data: token.NUMBER

 -- Data: token.STRING

 -- Data: token.NEWLINE

 -- Data: token.INDENT

 -- Data: token.DEDENT

 -- Data: token.LPAR

     Token value for ‘"("’.

 -- Data: token.RPAR

     Token value for ‘")"’.

 -- Data: token.LSQB

     Token value for ‘"["’.

 -- Data: token.RSQB

     Token value for ‘"]"’.

 -- Data: token.COLON

     Token value for ‘":"’.

 -- Data: token.COMMA

     Token value for ‘","’.

 -- Data: token.SEMI

     Token value for ‘";"’.

 -- Data: token.PLUS

     Token value for ‘"+"’.

 -- Data: token.MINUS

     Token value for ‘"-"’.

 -- Data: token.STAR

     Token value for ‘"*"’.

 -- Data: token.SLASH

     Token value for ‘"/"’.

 -- Data: token.VBAR

     Token value for ‘"|"’.

 -- Data: token.AMPER

     Token value for ‘"&"’.

 -- Data: token.LESS

     Token value for ‘"<"’.

 -- Data: token.GREATER

     Token value for ‘">"’.

 -- Data: token.EQUAL

     Token value for ‘"="’.

 -- Data: token.DOT

     Token value for ‘"."’.

 -- Data: token.PERCENT

     Token value for ‘"%"’.

 -- Data: token.LBRACE

     Token value for ‘"{"’.

 -- Data: token.RBRACE

     Token value for ‘"}"’.

 -- Data: token.EQEQUAL

     Token value for ‘"=="’.

 -- Data: token.NOTEQUAL

     Token value for ‘"!="’.

 -- Data: token.LESSEQUAL

     Token value for ‘"<="’.

 -- Data: token.GREATEREQUAL

     Token value for ‘">="’.

 -- Data: token.TILDE

     Token value for ‘"~"’.

 -- Data: token.CIRCUMFLEX

     Token value for ‘"^"’.

 -- Data: token.LEFTSHIFT

     Token value for ‘"<<"’.

 -- Data: token.RIGHTSHIFT

     Token value for ‘">>"’.

 -- Data: token.DOUBLESTAR

     Token value for ‘"**"’.

 -- Data: token.PLUSEQUAL

     Token value for ‘"+="’.

 -- Data: token.MINEQUAL

     Token value for ‘"-="’.

 -- Data: token.STAREQUAL

     Token value for ‘"*="’.

 -- Data: token.SLASHEQUAL

     Token value for ‘"/="’.

 -- Data: token.PERCENTEQUAL

     Token value for ‘"%="’.

 -- Data: token.AMPEREQUAL

     Token value for ‘"&="’.

 -- Data: token.VBAREQUAL

     Token value for ‘"|="’.

 -- Data: token.CIRCUMFLEXEQUAL

     Token value for ‘"^="’.

 -- Data: token.LEFTSHIFTEQUAL

     Token value for ‘"<<="’.

 -- Data: token.RIGHTSHIFTEQUAL

     Token value for ‘">>="’.

 -- Data: token.DOUBLESTAREQUAL

     Token value for ‘"**="’.

 -- Data: token.DOUBLESLASH

     Token value for ‘"//"’.

 -- Data: token.DOUBLESLASHEQUAL

     Token value for ‘"//="’.

 -- Data: token.AT

     Token value for ‘"@"’.

 -- Data: token.ATEQUAL

     Token value for ‘"@="’.

 -- Data: token.RARROW

     Token value for ‘"->"’.

 -- Data: token.ELLIPSIS

     Token value for ‘"..."’.

 -- Data: token.COLONEQUAL

     Token value for ‘":="’.

 -- Data: token.OP

 -- Data: token.AWAIT

 -- Data: token.ASYNC

 -- Data: token.TYPE_IGNORE

 -- Data: token.TYPE_COMMENT

 -- Data: token.ERRORTOKEN

 -- Data: token.N_TOKENS

 -- Data: token.NT_OFFSET

The following token type values aren’t used by the C tokenizer but are
needed for the *note tokenize: 11a. module.

 -- Data: token.COMMENT

     Token value used to indicate a comment.

 -- Data: token.NL

     Token value used to indicate a non-terminating newline.  The *note
     NEWLINE: 3a0f. token indicates the end of a logical line of Python
     code; ‘NL’ tokens are generated when a logical line of code is
     continued over multiple physical lines.

 -- Data: token.ENCODING

     Token value that indicates the encoding used to decode the source
     bytes into text.  The first token returned by *note
     tokenize.tokenize(): d23. will always be an ‘ENCODING’ token.

 -- Data: token.TYPE_COMMENT

     Token value indicating that a type comment was recognized.  Such
     tokens are only produced when *note ast.parse(): 2d6. is invoked
     with ‘type_comments=True’.

Changed in version 3.5: Added *note AWAIT: 3a42. and *note ASYNC: 3a43.
tokens.

Changed in version 3.7: Added *note COMMENT: 3a49, *note NL: 3a4a. and
*note ENCODING: 3a4b. tokens.

Changed in version 3.7: Removed *note AWAIT: 3a42. and *note ASYNC:
3a43. tokens.  “async” and “await” are now tokenized as *note NAME:
3a0c. tokens.

Changed in version 3.8: Added *note TYPE_COMMENT: 3a45, *note
TYPE_IGNORE: 3a44, *note COLONEQUAL: 3a40.  Added *note AWAIT: 3a42. and
*note ASYNC: 3a43. tokens back (they’re needed to support parsing older
Python versions for *note ast.parse(): 2d6. with ‘feature_version’ set
to 6 or lower).

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/token.py


File: python.info,  Node: keyword — Testing for Python keywords,  Next: tokenize — Tokenizer for Python source,  Prev: token — Constants used with Python parse trees,  Up: Python Language Services

5.32.6 ‘keyword’ — Testing for Python keywords
----------------------------------------------

`Source code:' Lib/keyword.py(1)

__________________________________________________________________

This module allows a Python program to determine if a string is a *note
keyword: 150d.

 -- Function: keyword.iskeyword (s)

     Return ‘True’ if `s' is a Python *note keyword: 150d.

 -- Data: keyword.kwlist

     Sequence containing all the *note keywords: 150d. defined for the
     interpreter.  If any keywords are defined to only be active when
     particular *note __future__: 0. statements are in effect, these
     will be included as well.

 -- Function: keyword.issoftkeyword (s)

     Return ‘True’ if `s' is a Python soft *note keyword: 150d.

     New in version 3.9.

 -- Data: keyword.softkwlist

     Sequence containing all the soft *note keywords: 150d. defined for
     the interpreter.  If any soft keywords are defined to only be
     active when particular *note __future__: 0. statements are in
     effect, these will be included as well.

     New in version 3.9.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/keyword.py


File: python.info,  Node: tokenize — Tokenizer for Python source,  Next: tabnanny — Detection of ambiguous indentation,  Prev: keyword — Testing for Python keywords,  Up: Python Language Services

5.32.7 ‘tokenize’ — Tokenizer for Python source
-----------------------------------------------

`Source code:' Lib/tokenize.py(1)

__________________________________________________________________

The *note tokenize: 11a. module provides a lexical scanner for Python
source code, implemented in Python.  The scanner in this module returns
comments as tokens as well, making it useful for implementing
“pretty-printers”, including colorizers for on-screen displays.

To simplify token stream handling, all *note operator: 154a. and *note
delimiter: 154b. tokens and *note Ellipsis: 1740. are returned using the
generic *note OP: 3a41. token type.  The exact type can be determined by
checking the ‘exact_type’ property on the *note named tuple: b7b.
returned from *note tokenize.tokenize(): d23.

* Menu:

* Tokenizing Input::
* Command-Line Usage: Command-Line Usage<3>.
* Examples: Examples<31>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/tokenize.py


File: python.info,  Node: Tokenizing Input,  Next: Command-Line Usage<3>,  Up: tokenize — Tokenizer for Python source

5.32.7.1 Tokenizing Input
.........................

The primary entry point is a *note generator: a83.:

 -- Function: tokenize.tokenize (readline)

     The *note tokenize(): d23. generator requires one argument,
     `readline', which must be a callable object which provides the same
     interface as the *note io.IOBase.readline(): 1849. method of file
     objects.  Each call to the function should return one line of input
     as bytes.

     The generator produces 5-tuples with these members: the token type;
     the token string; a 2-tuple ‘(srow, scol)’ of ints specifying the
     row and column where the token begins in the source; a 2-tuple
     ‘(erow, ecol)’ of ints specifying the row and column where the
     token ends in the source; and the line on which the token was
     found.  The line passed (the last tuple item) is the `physical'
     line.  The 5 tuple is returned as a *note named tuple: b7b. with
     the field names: ‘type string start end line’.

     The returned *note named tuple: b7b. has an additional property
     named ‘exact_type’ that contains the exact operator type for *note
     OP: 3a41. tokens.  For all other token types ‘exact_type’ equals
     the named tuple ‘type’ field.

     Changed in version 3.1: Added support for named tuples.

     Changed in version 3.3: Added support for ‘exact_type’.

     *note tokenize(): d23. determines the source encoding of the file
     by looking for a UTF-8 BOM or encoding cookie, according to PEP
     263(1).

 -- Function: tokenize.generate_tokens (readline)

     Tokenize a source reading unicode strings instead of bytes.

     Like *note tokenize(): d23, the `readline' argument is a callable
     returning a single line of input.  However, *note
     generate_tokens(): 116b. expects `readline' to return a str object
     rather than bytes.

     The result is an iterator yielding named tuples, exactly like *note
     tokenize(): d23.  It does not yield an *note ENCODING: 3a4b. token.

All constants from the *note token: 119. module are also exported from
*note tokenize: 11a.

Another function is provided to reverse the tokenization process.  This
is useful for creating tools that tokenize a script, modify the token
stream, and write back the modified script.

 -- Function: tokenize.untokenize (iterable)

     Converts tokens back into Python source code.  The `iterable' must
     return sequences with at least two elements, the token type and the
     token string.  Any additional sequence elements are ignored.

     The reconstructed script is returned as a single string.  The
     result is guaranteed to tokenize back to match the input so that
     the conversion is lossless and round-trips are assured.  The
     guarantee applies only to the token type and token string as the
     spacing between tokens (column positions) may change.

     It returns bytes, encoded using the *note ENCODING: 3a4b. token,
     which is the first token sequence output by *note tokenize(): d23.
     If there is no encoding token in the input, it returns a str
     instead.

*note tokenize(): d23. needs to detect the encoding of source files it
tokenizes.  The function it uses to do this is available:

 -- Function: tokenize.detect_encoding (readline)

     The *note detect_encoding(): 1ddd. function is used to detect the
     encoding that should be used to decode a Python source file.  It
     requires one argument, readline, in the same way as the *note
     tokenize(): d23. generator.

     It will call readline a maximum of twice, and return the encoding
     used (as a string) and a list of any lines (not decoded from bytes)
     it has read in.

     It detects the encoding from the presence of a UTF-8 BOM or an
     encoding cookie as specified in PEP 263(2).  If both a BOM and a
     cookie are present, but disagree, a *note SyntaxError: 55a. will be
     raised.  Note that if the BOM is found, ‘'utf-8-sig'’ will be
     returned as an encoding.

     If no encoding is specified, then the default of ‘'utf-8'’ will be
     returned.

     Use *note open(): 1ddc. to open Python source files: it uses *note
     detect_encoding(): 1ddd. to detect the file encoding.

 -- Function: tokenize.open (filename)

     Open a file in read only mode using the encoding detected by *note
     detect_encoding(): 1ddd.

     New in version 3.2.

 -- Exception: tokenize.TokenError

     Raised when either a docstring or expression that may be split over
     several lines is not completed anywhere in the file, for example:

          """Beginning of
          docstring

     or:

          [1,
           2,
           3

Note that unclosed single-quoted strings do not cause an error to be
raised.  They are tokenized as *note ERRORTOKEN: 3a46, followed by the
tokenization of their contents.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0263

   (2) https://www.python.org/dev/peps/pep-0263


File: python.info,  Node: Command-Line Usage<3>,  Next: Examples<31>,  Prev: Tokenizing Input,  Up: tokenize — Tokenizer for Python source

5.32.7.2 Command-Line Usage
...........................

New in version 3.3.

The *note tokenize: 11a. module can be executed as a script from the
command line.  It is as simple as:

     python -m tokenize [-e] [filename.py]

The following options are accepted:

 -- Program Option: -h, --help

     show this help message and exit

 -- Program Option: -e, --exact

     display token names using the exact type

If ‘filename.py’ is specified its contents are tokenized to stdout.
Otherwise, tokenization is performed on stdin.


File: python.info,  Node: Examples<31>,  Prev: Command-Line Usage<3>,  Up: tokenize — Tokenizer for Python source

5.32.7.3 Examples
.................

Example of a script rewriter that transforms float literals into Decimal
objects:

     from tokenize import tokenize, untokenize, NUMBER, STRING, NAME, OP
     from io import BytesIO

     def decistmt(s):
         """Substitute Decimals for floats in a string of statements.

         >>> from decimal import Decimal
         >>> s = 'print(+21.3e-5*-.1234/81.7)'
         >>> decistmt(s)
         "print (+Decimal ('21.3e-5')*-Decimal ('.1234')/Decimal ('81.7'))"

         The format of the exponent is inherited from the platform C library.
         Known cases are "e-007" (Windows) and "e-07" (not Windows).  Since
         we're only showing 12 digits, and the 13th isn't close to 5, the
         rest of the output should be platform-independent.

         >>> exec(s)  #doctest: +ELLIPSIS
         -3.21716034272e-0...7

         Output from calculations with Decimal should be identical across all
         platforms.

         >>> exec(decistmt(s))
         -3.217160342717258261933904529E-7
         """
         result = []
         g = tokenize(BytesIO(s.encode('utf-8')).readline)  # tokenize the string
         for toknum, tokval, _, _, _ in g:
             if toknum == NUMBER and '.' in tokval:  # replace NUMBER tokens
                 result.extend([
                     (NAME, 'Decimal'),
                     (OP, '('),
                     (STRING, repr(tokval)),
                     (OP, ')')
                 ])
             else:
                 result.append((toknum, tokval))
         return untokenize(result).decode('utf-8')

Example of tokenizing from the command line.  The script:

     def say_hello():
         print("Hello, World!")

     say_hello()

will be tokenized to the following output where the first column is the
range of the line/column coordinates where the token is found, the
second column is the name of the token, and the final column is the
value of the token (if any)

     $ python -m tokenize hello.py
     0,0-0,0:            ENCODING       'utf-8'
     1,0-1,3:            NAME           'def'
     1,4-1,13:           NAME           'say_hello'
     1,13-1,14:          OP             '('
     1,14-1,15:          OP             ')'
     1,15-1,16:          OP             ':'
     1,16-1,17:          NEWLINE        '\n'
     2,0-2,4:            INDENT         '    '
     2,4-2,9:            NAME           'print'
     2,9-2,10:           OP             '('
     2,10-2,25:          STRING         '"Hello, World!"'
     2,25-2,26:          OP             ')'
     2,26-2,27:          NEWLINE        '\n'
     3,0-3,1:            NL             '\n'
     4,0-4,0:            DEDENT         ''
     4,0-4,9:            NAME           'say_hello'
     4,9-4,10:           OP             '('
     4,10-4,11:          OP             ')'
     4,11-4,12:          NEWLINE        '\n'
     5,0-5,0:            ENDMARKER      ''

The exact token type names can be displayed using the *note -e: 3a59.
option:

     $ python -m tokenize -e hello.py
     0,0-0,0:            ENCODING       'utf-8'
     1,0-1,3:            NAME           'def'
     1,4-1,13:           NAME           'say_hello'
     1,13-1,14:          LPAR           '('
     1,14-1,15:          RPAR           ')'
     1,15-1,16:          COLON          ':'
     1,16-1,17:          NEWLINE        '\n'
     2,0-2,4:            INDENT         '    '
     2,4-2,9:            NAME           'print'
     2,9-2,10:           LPAR           '('
     2,10-2,25:          STRING         '"Hello, World!"'
     2,25-2,26:          RPAR           ')'
     2,26-2,27:          NEWLINE        '\n'
     3,0-3,1:            NL             '\n'
     4,0-4,0:            DEDENT         ''
     4,0-4,9:            NAME           'say_hello'
     4,9-4,10:           LPAR           '('
     4,10-4,11:          RPAR           ')'
     4,11-4,12:          NEWLINE        '\n'
     5,0-5,0:            ENDMARKER      ''

Example of tokenizing a file programmatically, reading unicode strings
instead of bytes with *note generate_tokens(): 116b.:

     import tokenize

     with tokenize.open('hello.py') as f:
         tokens = tokenize.generate_tokens(f.readline)
         for token in tokens:
             print(token)

Or reading bytes directly with *note tokenize(): d23.:

     import tokenize

     with open('hello.py', 'rb') as f:
         tokens = tokenize.tokenize(f.readline)
         for token in tokens:
             print(token)


File: python.info,  Node: tabnanny — Detection of ambiguous indentation,  Next: pyclbr — Python module browser support,  Prev: tokenize — Tokenizer for Python source,  Up: Python Language Services

5.32.8 ‘tabnanny’ — Detection of ambiguous indentation
------------------------------------------------------

`Source code:' Lib/tabnanny.py(1)

__________________________________________________________________

For the time being this module is intended to be called as a script.
However it is possible to import it into an IDE and use the function
*note check(): 3a5d. described below.

     Note: The API provided by this module is likely to change in future
     releases; such changes may not be backward compatible.

 -- Function: tabnanny.check (file_or_dir)

     If `file_or_dir' is a directory and not a symbolic link, then
     recursively descend the directory tree named by `file_or_dir',
     checking all ‘.py’ files along the way.  If `file_or_dir' is an
     ordinary Python source file, it is checked for whitespace related
     problems.  The diagnostic messages are written to standard output
     using the *note print(): 971. function.

 -- Data: tabnanny.verbose

     Flag indicating whether to print verbose messages.  This is
     incremented by the ‘-v’ option if called as a script.

 -- Data: tabnanny.filename_only

     Flag indicating whether to print only the filenames of files
     containing whitespace related problems.  This is set to true by the
     ‘-q’ option if called as a script.

 -- Exception: tabnanny.NannyNag

     Raised by *note process_tokens(): 3a61. if detecting an ambiguous
     indent.  Captured and handled in *note check(): 3a5d.

 -- Function: tabnanny.process_tokens (tokens)

     This function is used by *note check(): 3a5d. to process tokens
     generated by the *note tokenize: 11a. module.

See also
........

Module *note tokenize: 11a.

     Lexical scanner for Python source code.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/tabnanny.py


File: python.info,  Node: pyclbr — Python module browser support,  Next: py_compile — Compile Python source files,  Prev: tabnanny — Detection of ambiguous indentation,  Up: Python Language Services

5.32.9 ‘pyclbr’ — Python module browser support
-----------------------------------------------

`Source code:' Lib/pyclbr.py(1)

__________________________________________________________________

The *note pyclbr: d8. module provides limited information about the
functions, classes, and methods defined in a Python-coded module.  The
information is sufficient to implement a module browser.  The
information is extracted from the Python source code rather than by
importing the module, so this module is safe to use with untrusted code.
This restriction makes it impossible to use this module with modules not
implemented in Python, including all standard and optional extension
modules.

 -- Function: pyclbr.readmodule (module, path=None)

     Return a dictionary mapping module-level class names to class
     descriptors.  If possible, descriptors for imported base classes
     are included.  Parameter `module' is a string with the name of the
     module to read; it may be the name of a module within a package.
     If given, `path' is a sequence of directory paths prepended to
     ‘sys.path’, which is used to locate the module source code.

     This function is the original interface and is only kept for back
     compatibility.  It returns a filtered version of the following.

 -- Function: pyclbr.readmodule_ex (module, path=None)

     Return a dictionary-based tree containing a function or class
     descriptors for each function and class defined in the module with
     a ‘def’ or ‘class’ statement.  The returned dictionary maps
     module-level function and class names to their descriptors.  Nested
     objects are entered into the children dictionary of their parent.
     As with readmodule, `module' names the module to be read and `path'
     is prepended to sys.path.  If the module being read is a package,
     the returned dictionary has a key ‘'__path__'’ whose value is a
     list containing the package search path.

New in version 3.7: Descriptors for nested definitions.  They are
accessed through the new children attribute.  Each has a new parent
attribute.

The descriptors returned by these functions are instances of Function
and Class classes.  Users are not expected to create instances of these
classes.

* Menu:

* Function Objects::
* Class Objects: Class Objects<2>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/pyclbr.py


File: python.info,  Node: Function Objects,  Next: Class Objects<2>,  Up: pyclbr — Python module browser support

5.32.9.1 Function Objects
.........................

Class ‘Function’ instances describe functions defined by def statements.
They have the following attributes:

 -- Attribute: Function.file

     Name of the file in which the function is defined.

 -- Attribute: Function.module

     The name of the module defining the function described.

 -- Attribute: Function.name

     The name of the function.

 -- Attribute: Function.lineno

     The line number in the file where the definition starts.

 -- Attribute: Function.parent

     For top-level functions, None.  For nested functions, the parent.

     New in version 3.7.

 -- Attribute: Function.children

     A dictionary mapping names to descriptors for nested functions and
     classes.

     New in version 3.7.


File: python.info,  Node: Class Objects<2>,  Prev: Function Objects,  Up: pyclbr — Python module browser support

5.32.9.2 Class Objects
......................

Class ‘Class’ instances describe classes defined by class statements.
They have the same attributes as Functions and two more.

 -- Attribute: Class.file

     Name of the file in which the class is defined.

 -- Attribute: Class.module

     The name of the module defining the class described.

 -- Attribute: Class.name

     The name of the class.

 -- Attribute: Class.lineno

     The line number in the file where the definition starts.

 -- Attribute: Class.parent

     For top-level classes, None.  For nested classes, the parent.

     New in version 3.7.

 -- Attribute: Class.children

     A dictionary mapping names to descriptors for nested functions and
     classes.

     New in version 3.7.

 -- Attribute: Class.super

     A list of ‘Class’ objects which describe the immediate base classes
     of the class being described.  Classes which are named as
     superclasses but which are not discoverable by *note
     readmodule_ex(): 129f. are listed as a string with the class name
     instead of as ‘Class’ objects.

 -- Attribute: Class.methods

     A dictionary mapping method names to line numbers.  This can be
     derived from the newer children dictionary, but remains for
     back-compatibility.


File: python.info,  Node: py_compile — Compile Python source files,  Next: compileall — Byte-compile Python libraries,  Prev: pyclbr — Python module browser support,  Up: Python Language Services

5.32.10 ‘py_compile’ — Compile Python source files
--------------------------------------------------

`Source code:' Lib/py_compile.py(1)

__________________________________________________________________

The *note py_compile: d7. module provides a function to generate a
byte-code file from a source file, and another function used when the
module source file is invoked as a script.

Though not often needed, this function can be useful when installing
modules for shared use, especially if some of the users may not have
permission to write the byte-code cache files in the directory
containing the source code.

 -- Exception: py_compile.PyCompileError

     Exception raised when an error occurs while attempting to compile
     the file.

 -- Function: py_compile.compile (file, cfile=None, dfile=None,
          doraise=False, optimize=-1,
          invalidation_mode=PycInvalidationMode.TIMESTAMP, quiet=0)

     Compile a source file to byte-code and write out the byte-code
     cache file.  The source code is loaded from the file named `file'.
     The byte-code is written to `cfile', which defaults to the PEP
     3147(2)/ PEP 488(3) path, ending in ‘.pyc’.  For example, if `file'
     is ‘/foo/bar/baz.py’ `cfile' will default to
     ‘/foo/bar/__pycache__/baz.cpython-32.pyc’ for Python 3.2.  If
     `dfile' is specified, it is used as the name of the source file in
     error messages instead of `file'.  If `doraise' is true, a *note
     PyCompileError: 3a78. is raised when an error is encountered while
     compiling `file'.  If `doraise' is false (the default), an error
     string is written to ‘sys.stderr’, but no exception is raised.
     This function returns the path to byte-compiled file, i.e.
     whatever `cfile' value was used.

     The `doraise' and `quiet' arguments determine how errors are
     handled while compiling file.  If `quiet' is 0 or 1, and `doraise'
     is false, the default behaviour is enabled: an error string is
     written to ‘sys.stderr’, and the function returns ‘None’ instead of
     a path.  If `doraise' is true, a *note PyCompileError: 3a78. is
     raised instead.  However if `quiet' is 2, no message is written,
     and `doraise' has no effect.

     If the path that `cfile' becomes (either explicitly specified or
     computed) is a symlink or non-regular file, *note FileExistsError:
     a39. will be raised.  This is to act as a warning that import will
     turn those paths into regular files if it is allowed to write
     byte-compiled files to those paths.  This is a side-effect of
     import using file renaming to place the final byte-compiled file
     into place to prevent concurrent file writing issues.

     `optimize' controls the optimization level and is passed to the
     built-in *note compile(): 2e7. function.  The default of ‘-1’
     selects the optimization level of the current interpreter.

     `invalidation_mode' should be a member of the *note
     PycInvalidationMode: 3a79. enum and controls how the generated
     bytecode cache is invalidated at runtime.  The default is *note
     PycInvalidationMode.CHECKED_HASH: 3a7a. if the ‘SOURCE_DATE_EPOCH’
     environment variable is set, otherwise the default is *note
     PycInvalidationMode.TIMESTAMP: 3a7b.

     Changed in version 3.2: Changed default value of `cfile' to be PEP
     3147(4)-compliant.  Previous default was `file' + ‘'c'’ (‘'o'’ if
     optimization was enabled).  Also added the `optimize' parameter.

     Changed in version 3.4: Changed code to use *note importlib: 9a.
     for the byte-code cache file writing.  This means file
     creation/writing semantics now match what *note importlib: 9a.
     does, e.g.  permissions, write-and-move semantics, etc.  Also added
     the caveat that *note FileExistsError: a39. is raised if `cfile' is
     a symlink or non-regular file.

     Changed in version 3.7: The `invalidation_mode' parameter was added
     as specified in PEP 552(5).  If the ‘SOURCE_DATE_EPOCH’ environment
     variable is set, `invalidation_mode' will be forced to *note
     PycInvalidationMode.CHECKED_HASH: 3a7a.

     Changed in version 3.7.2: The ‘SOURCE_DATE_EPOCH’ environment
     variable no longer overrides the value of the `invalidation_mode'
     argument, and determines its default value instead.

     Changed in version 3.8: The `quiet' parameter was added.

 -- Class: py_compile.PycInvalidationMode

     A enumeration of possible methods the interpreter can use to
     determine whether a bytecode file is up to date with a source file.
     The ‘.pyc’ file indicates the desired invalidation mode in its
     header.  See *note Cached bytecode invalidation: 439. for more
     information on how Python invalidates ‘.pyc’ files at runtime.

     New in version 3.7.

      -- Attribute: TIMESTAMP

          The ‘.pyc’ file includes the timestamp and size of the source
          file, which Python will compare against the metadata of the
          source file at runtime to determine if the ‘.pyc’ file needs
          to be regenerated.

      -- Attribute: CHECKED_HASH

          The ‘.pyc’ file includes a hash of the source file content,
          which Python will compare against the source at runtime to
          determine if the ‘.pyc’ file needs to be regenerated.

      -- Attribute: UNCHECKED_HASH

          Like *note CHECKED_HASH: 3a7a, the ‘.pyc’ file includes a hash
          of the source file content.  However, Python will at runtime
          assume the ‘.pyc’ file is up to date and not validate the
          ‘.pyc’ against the source file at all.

          This option is useful when the ‘.pycs’ are kept up to date by
          some system external to Python like a build system.

 -- Function: py_compile.main (args=None)

     Compile several source files.  The files named in `args' (or on the
     command line, if `args' is ‘None’) are compiled and the resulting
     byte-code is cached in the normal manner.  This function does not
     search a directory structure to locate source files; it only
     compiles files named explicitly.  If ‘'-'’ is the only parameter in
     args, the list of files is taken from standard input.

     Changed in version 3.2: Added support for ‘'-'’.

When this module is run as a script, the *note main(): 3a7d. is used to
compile all the files named on the command line.  The exit status is
nonzero if one of the files could not be compiled.

See also
........

Module *note compileall: 20.

     Utilities to compile all Python source files in a directory tree.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/py_compile.py

   (2) https://www.python.org/dev/peps/pep-3147

   (3) https://www.python.org/dev/peps/pep-0488

   (4) https://www.python.org/dev/peps/pep-3147

   (5) https://www.python.org/dev/peps/pep-0552


File: python.info,  Node: compileall — Byte-compile Python libraries,  Next: dis — Disassembler for Python bytecode,  Prev: py_compile — Compile Python source files,  Up: Python Language Services

5.32.11 ‘compileall’ — Byte-compile Python libraries
----------------------------------------------------

`Source code:' Lib/compileall.py(1)

__________________________________________________________________

This module provides some utility functions to support installing Python
libraries.  These functions compile Python source files in a directory
tree.  This module can be used to create the cached byte-code files at
library installation time, which makes them available for use even by
users who don’t have write permission to the library directories.

* Menu:

* Command-line use::
* Public functions::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/compileall.py


File: python.info,  Node: Command-line use,  Next: Public functions,  Up: compileall — Byte-compile Python libraries

5.32.11.1 Command-line use
..........................

This module can work as a script (using ‘python -m compileall’) to
compile Python sources.

 -- Program Option: directory ...
 -- Program Option: file ...

     Positional arguments are files to compile or directories that
     contain source files, traversed recursively.  If no argument is
     given, behave as if the command line was ‘-l <directories from
     sys.path>’.

 -- Program Option: -l

     Do not recurse into subdirectories, only compile source code files
     directly contained in the named or implied directories.

 -- Program Option: -f

     Force rebuild even if timestamps are up-to-date.

 -- Program Option: -q

     Do not print the list of files compiled.  If passed once, error
     messages will still be printed.  If passed twice (‘-qq’), all
     output is suppressed.

 -- Program Option: -d destdir

     Directory prepended to the path to each file being compiled.  This
     will appear in compilation time tracebacks, and is also compiled in
     to the byte-code file, where it will be used in tracebacks and
     other messages in cases where the source file does not exist at the
     time the byte-code file is executed.

 -- Program Option: -s strip_prefix

 -- Program Option: -p prepend_prefix

     Remove (‘-s’) or append (‘-p’) the given prefix of paths recorded
     in the ‘.pyc’ files.  Cannot be combined with ‘-d’.

 -- Program Option: -x regex

     regex is used to search the full path to each file considered for
     compilation, and if the regex produces a match, the file is
     skipped.

 -- Program Option: -i list

     Read the file ‘list’ and add each line that it contains to the list
     of files and directories to compile.  If ‘list’ is ‘-’, read lines
     from ‘stdin’.

 -- Program Option: -b

     Write the byte-code files to their legacy locations and names,
     which may overwrite byte-code files created by another version of
     Python.  The default is to write files to their PEP 3147(1)
     locations and names, which allows byte-code files from multiple
     versions of Python to coexist.

 -- Program Option: -r

     Control the maximum recursion level for subdirectories.  If this is
     given, then ‘-l’ option will not be taken into account.  ‘python -m
     compileall <directory> -r 0’ is equivalent to ‘python -m compileall
     <directory> -l’.

 -- Program Option: -j N

     Use `N' workers to compile the files within the given directory.
     If ‘0’ is used, then the result of *note os.cpu_count(): 96a. will
     be used.

 -- Program Option: --invalidation-mode
          [timestamp|checked-hash|unchecked-hash]

     Control how the generated byte-code files are invalidated at
     runtime.  The ‘timestamp’ value, means that ‘.pyc’ files with the
     source timestamp and size embedded will be generated.  The
     ‘checked-hash’ and ‘unchecked-hash’ values cause hash-based pycs to
     be generated.  Hash-based pycs embed a hash of the source file
     contents rather than a timestamp.  See *note Cached bytecode
     invalidation: 439. for more information on how Python validates
     bytecode cache files at runtime.  The default is ‘timestamp’ if the
     ‘SOURCE_DATE_EPOCH’ environment variable is not set, and
     ‘checked-hash’ if the ‘SOURCE_DATE_EPOCH’ environment variable is
     set.

 -- Program Option: -o level

     Compile with the given optimization level.  May be used multiple
     times to compile for multiple levels at a time (for example,
     ‘compileall -o 1 -o 2’).

 -- Program Option: -e dir

     Ignore symlinks pointing outside the given directory.

 -- Program Option: --hardlink-dupes

     If two ‘.pyc’ files with different optimization level have the same
     content, use hard links to consolidate duplicate files.

Changed in version 3.2: Added the ‘-i’, ‘-b’ and ‘-h’ options.

Changed in version 3.5: Added the ‘-j’, ‘-r’, and ‘-qq’ options.  ‘-q’
option was changed to a multilevel value.  ‘-b’ will always produce a
byte-code file ending in ‘.pyc’, never ‘.pyo’.

Changed in version 3.7: Added the ‘--invalidation-mode’ option.

Changed in version 3.9: Added the ‘-s’, ‘-p’, ‘-e’ and
‘--hardlink-dupes’ options.  Raised the default recursion limit from 10
to *note sys.getrecursionlimit(): f3b.  Added the possibility to specify
the ‘-o’ option multiple times.

There is no command-line option to control the optimization level used
by the *note compile(): 2e7. function, because the Python interpreter
itself already provides the option: ‘python -O -m compileall’.

Similarly, the *note compile(): 2e7. function respects the *note
sys.pycache_prefix: 291. setting.  The generated bytecode cache will
only be useful if *note compile(): 2e7. is run with the same *note
sys.pycache_prefix: 291. (if any) that will be used at runtime.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3147


File: python.info,  Node: Public functions,  Prev: Command-line use,  Up: compileall — Byte-compile Python libraries

5.32.11.2 Public functions
..........................

 -- Function: compileall.compile_dir (dir,
          maxlevels=sys.getrecursionlimit(), ddir=None, force=False,
          rx=None, quiet=0, legacy=False, optimize=-1, workers=1,
          invalidation_mode=None, *, stripdir=None, prependdir=None,
          limit_sl_dest=None, hardlink_dupes=False)

     Recursively descend the directory tree named by `dir', compiling
     all ‘.py’ files along the way.  Return a true value if all the
     files compiled successfully, and a false value otherwise.

     The `maxlevels' parameter is used to limit the depth of the
     recursion; it defaults to ‘sys.getrecursionlimit()’.

     If `ddir' is given, it is prepended to the path to each file being
     compiled for use in compilation time tracebacks, and is also
     compiled in to the byte-code file, where it will be used in
     tracebacks and other messages in cases where the source file does
     not exist at the time the byte-code file is executed.

     If `force' is true, modules are re-compiled even if the timestamps
     are up to date.

     If `rx' is given, its ‘search’ method is called on the complete
     path to each file considered for compilation, and if it returns a
     true value, the file is skipped.  This can be used to exclude files
     matching a regular expression, given as a *note re.Pattern: 983.
     object.

     If `quiet' is ‘False’ or ‘0’ (the default), the filenames and other
     information are printed to standard out.  Set to ‘1’, only errors
     are printed.  Set to ‘2’, all output is suppressed.

     If `legacy' is true, byte-code files are written to their legacy
     locations and names, which may overwrite byte-code files created by
     another version of Python.  The default is to write files to their
     PEP 3147(1) locations and names, which allows byte-code files from
     multiple versions of Python to coexist.

     `optimize' specifies the optimization level for the compiler.  It
     is passed to the built-in *note compile(): 2e7. function.  Accepts
     also a sequence of optimization levels which lead to multiple
     compilations of one ‘.py’ file in one call.

     The argument `workers' specifies how many workers are used to
     compile files in parallel.  The default is to not use multiple
     workers.  If the platform can’t use multiple workers and `workers'
     argument is given, then sequential compilation will be used as a
     fallback.  If `workers' is 0, the number of cores in the system is
     used.  If `workers' is lower than ‘0’, a *note ValueError: 16d.
     will be raised.

     `invalidation_mode' should be a member of the *note
     py_compile.PycInvalidationMode: 3a79. enum and controls how the
     generated pycs are invalidated at runtime.

     The `stripdir', `prependdir' and `limit_sl_dest' arguments
     correspond to the ‘-s’, ‘-p’ and ‘-e’ options described above.
     They may be specified as ‘str’, ‘bytes’ or *note os.PathLike: 5e6.

     If `hardlink_dupes' is true and two ‘.pyc’ files with different
     optimization level have the same content, use hard links to
     consolidate duplicate files.

     Changed in version 3.2: Added the `legacy' and `optimize'
     parameter.

     Changed in version 3.5: Added the `workers' parameter.

     Changed in version 3.5: `quiet' parameter was changed to a
     multilevel value.

     Changed in version 3.5: The `legacy' parameter only writes out
     ‘.pyc’ files, not ‘.pyo’ files no matter what the value of
     `optimize' is.

     Changed in version 3.6: Accepts a *note path-like object: 472.

     Changed in version 3.7: The `invalidation_mode' parameter was
     added.

     Changed in version 3.7.2: The `invalidation_mode' parameter’s
     default value is updated to None.

     Changed in version 3.8: Setting `workers' to 0 now chooses the
     optimal number of cores.

     Changed in version 3.9: Added `stripdir', `prependdir',
     `limit_sl_dest' and `hardlink_dupes' arguments.  Default value of
     `maxlevels' was changed from ‘10’ to ‘sys.getrecursionlimit()’

 -- Function: compileall.compile_file (fullname, ddir=None, force=False,
          rx=None, quiet=0, legacy=False, optimize=-1,
          invalidation_mode=None, *, stripdir=None, prependdir=None,
          limit_sl_dest=None, hardlink_dupes=False)

     Compile the file with path `fullname'.  Return a true value if the
     file compiled successfully, and a false value otherwise.

     If `ddir' is given, it is prepended to the path to the file being
     compiled for use in compilation time tracebacks, and is also
     compiled in to the byte-code file, where it will be used in
     tracebacks and other messages in cases where the source file does
     not exist at the time the byte-code file is executed.

     If `rx' is given, its ‘search’ method is passed the full path name
     to the file being compiled, and if it returns a true value, the
     file is not compiled and ‘True’ is returned.  This can be used to
     exclude files matching a regular expression, given as a *note
     re.Pattern: 983. object.

     If `quiet' is ‘False’ or ‘0’ (the default), the filenames and other
     information are printed to standard out.  Set to ‘1’, only errors
     are printed.  Set to ‘2’, all output is suppressed.

     If `legacy' is true, byte-code files are written to their legacy
     locations and names, which may overwrite byte-code files created by
     another version of Python.  The default is to write files to their
     PEP 3147(2) locations and names, which allows byte-code files from
     multiple versions of Python to coexist.

     `optimize' specifies the optimization level for the compiler.  It
     is passed to the built-in *note compile(): 2e7. function.  Accepts
     also a sequence of optimization levels which lead to multiple
     compilations of one ‘.py’ file in one call.

     `invalidation_mode' should be a member of the *note
     py_compile.PycInvalidationMode: 3a79. enum and controls how the
     generated pycs are invalidated at runtime.

     The `stripdir', `prependdir' and `limit_sl_dest' arguments
     correspond to the ‘-s’, ‘-p’ and ‘-e’ options described above.
     They may be specified as ‘str’, ‘bytes’ or *note os.PathLike: 5e6.

     If `hardlink_dupes' is true and two ‘.pyc’ files with different
     optimization level have the same content, use hard links to
     consolidate duplicate files.

     New in version 3.2.

     Changed in version 3.5: `quiet' parameter was changed to a
     multilevel value.

     Changed in version 3.5: The `legacy' parameter only writes out
     ‘.pyc’ files, not ‘.pyo’ files no matter what the value of
     `optimize' is.

     Changed in version 3.7: The `invalidation_mode' parameter was
     added.

     Changed in version 3.7.2: The `invalidation_mode' parameter’s
     default value is updated to None.

     Changed in version 3.9: Added `stripdir', `prependdir',
     `limit_sl_dest' and `hardlink_dupes' arguments.

 -- Function: compileall.compile_path (skip_curdir=True, maxlevels=0,
          force=False, quiet=0, legacy=False, optimize=-1,
          invalidation_mode=None)

     Byte-compile all the ‘.py’ files found along ‘sys.path’.  Return a
     true value if all the files compiled successfully, and a false
     value otherwise.

     If `skip_curdir' is true (the default), the current directory is
     not included in the search.  All other parameters are passed to the
     *note compile_dir(): 47a. function.  Note that unlike the other
     compile functions, ‘maxlevels’ defaults to ‘0’.

     Changed in version 3.2: Added the `legacy' and `optimize'
     parameter.

     Changed in version 3.5: `quiet' parameter was changed to a
     multilevel value.

     Changed in version 3.5: The `legacy' parameter only writes out
     ‘.pyc’ files, not ‘.pyo’ files no matter what the value of
     `optimize' is.

     Changed in version 3.7: The `invalidation_mode' parameter was
     added.

     Changed in version 3.7.2: The `invalidation_mode' parameter’s
     default value is updated to None.

To force a recompile of all the ‘.py’ files in the ‘Lib/’ subdirectory
and all its subdirectories:

     import compileall

     compileall.compile_dir('Lib/', force=True)

     # Perform same compilation, excluding files in .svn directories.
     import re
     compileall.compile_dir('Lib/', rx=re.compile(r'[/\\][.]svn'), force=True)

     # pathlib.Path objects can also be used.
     import pathlib
     compileall.compile_dir(pathlib.Path('Lib/'), force=True)

See also
........

Module *note py_compile: d7.

     Byte-compile a single source file.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3147

   (2) https://www.python.org/dev/peps/pep-3147


File: python.info,  Node: dis — Disassembler for Python bytecode,  Next: pickletools — Tools for pickle developers,  Prev: compileall — Byte-compile Python libraries,  Up: Python Language Services

5.32.12 ‘dis’ — Disassembler for Python bytecode
------------------------------------------------

`Source code:' Lib/dis.py(1)

__________________________________________________________________

The *note dis: 37. module supports the analysis of CPython *note
bytecode: 709. by disassembling it.  The CPython bytecode which this
module takes as an input is defined in the file ‘Include/opcode.h’ and
used by the compiler and the interpreter.

`CPython implementation detail:' Bytecode is an implementation detail of
the CPython interpreter.  No guarantees are made that bytecode will not
be added, removed, or changed between versions of Python.  Use of this
module should not be considered to work across Python VMs or Python
releases.

Changed in version 3.6: Use 2 bytes for each instruction.  Previously
the number of bytes varied by instruction.

Example: Given the function ‘myfunc()’:

     def myfunc(alist):
         return len(alist)

the following command can be used to display the disassembly of
‘myfunc()’:

     >>> dis.dis(myfunc)
       2           0 LOAD_GLOBAL              0 (len)
                   2 LOAD_FAST                0 (alist)
                   4 CALL_FUNCTION            1
                   6 RETURN_VALUE

(The “2” is a line number).

* Menu:

* Bytecode analysis::
* Analysis functions::
* Python Bytecode Instructions::
* Opcode collections::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/dis.py


File: python.info,  Node: Bytecode analysis,  Next: Analysis functions,  Up: dis — Disassembler for Python bytecode

5.32.12.1 Bytecode analysis
...........................

New in version 3.4.

The bytecode analysis API allows pieces of Python code to be wrapped in
a *note Bytecode: 924. object that provides easy access to details of
the compiled code.

 -- Class: dis.Bytecode (x, *, first_line=None, current_offset=None)

     Analyse the bytecode corresponding to a function, generator,
     asynchronous generator, coroutine, method, string of source code,
     or a code object (as returned by *note compile(): 2e7.).

     This is a convenience wrapper around many of the functions listed
     below, most notably *note get_instructions(): 923, as iterating
     over a *note Bytecode: 924. instance yields the bytecode operations
     as *note Instruction: 922. instances.

     If `first_line' is not ‘None’, it indicates the line number that
     should be reported for the first source line in the disassembled
     code.  Otherwise, the source line information (if any) is taken
     directly from the disassembled code object.

     If `current_offset' is not ‘None’, it refers to an instruction
     offset in the disassembled code.  Setting this means *note dis():
     925. will display a “current instruction” marker against the
     specified opcode.

      -- Method: classmethod from_traceback (tb)

          Construct a *note Bytecode: 924. instance from the given
          traceback, setting `current_offset' to the instruction
          responsible for the exception.

      -- Data: codeobj

          The compiled code object.

      -- Data: first_line

          The first source line of the code object (if available)

      -- Method: dis ()

          Return a formatted view of the bytecode operations (the same
          as printed by *note dis.dis(): 48b, but returned as a
          multi-line string).

      -- Method: info ()

          Return a formatted multi-line string with detailed information
          about the code object, like *note code_info(): c9c.

     Changed in version 3.7: This can now handle coroutine and
     asynchronous generator objects.

Example:

     >>> bytecode = dis.Bytecode(myfunc)
     >>> for instr in bytecode:
     ...     print(instr.opname)
     ...
     LOAD_GLOBAL
     LOAD_FAST
     CALL_FUNCTION
     RETURN_VALUE


File: python.info,  Node: Analysis functions,  Next: Python Bytecode Instructions,  Prev: Bytecode analysis,  Up: dis — Disassembler for Python bytecode

5.32.12.2 Analysis functions
............................

The *note dis: 37. module also defines the following analysis functions
that convert the input directly to the desired output.  They can be
useful if only a single operation is being performed, so the
intermediate analysis object isn’t useful:

 -- Function: dis.code_info (x)

     Return a formatted multi-line string with detailed code object
     information for the supplied function, generator, asynchronous
     generator, coroutine, method, source code string or code object.

     Note that the exact contents of code info strings are highly
     implementation dependent and they may change arbitrarily across
     Python VMs or Python releases.

     New in version 3.2.

     Changed in version 3.7: This can now handle coroutine and
     asynchronous generator objects.

 -- Function: dis.show_code (x, *, file=None)

     Print detailed code object information for the supplied function,
     method, source code string or code object to `file' (or
     ‘sys.stdout’ if `file' is not specified).

     This is a convenient shorthand for ‘print(code_info(x),
     file=file)’, intended for interactive exploration at the
     interpreter prompt.

     New in version 3.2.

     Changed in version 3.4: Added `file' parameter.

 -- Function: dis.dis (x=None, *, file=None, depth=None)

     Disassemble the `x' object.  `x' can denote either a module, a
     class, a method, a function, a generator, an asynchronous
     generator, a coroutine, a code object, a string of source code or a
     byte sequence of raw bytecode.  For a module, it disassembles all
     functions.  For a class, it disassembles all methods (including
     class and static methods).  For a code object or sequence of raw
     bytecode, it prints one line per bytecode instruction.  It also
     recursively disassembles nested code objects (the code of
     comprehensions, generator expressions and nested functions, and the
     code used for building nested classes).  Strings are first compiled
     to code objects with the *note compile(): 2e7. built-in function
     before being disassembled.  If no object is provided, this function
     disassembles the last traceback.

     The disassembly is written as text to the supplied `file' argument
     if provided and to ‘sys.stdout’ otherwise.

     The maximal depth of recursion is limited by `depth' unless it is
     ‘None’.  ‘depth=0’ means no recursion.

     Changed in version 3.4: Added `file' parameter.

     Changed in version 3.7: Implemented recursive disassembling and
     added `depth' parameter.

     Changed in version 3.7: This can now handle coroutine and
     asynchronous generator objects.

 -- Function: dis.distb (tb=None, *, file=None)

     Disassemble the top-of-stack function of a traceback, using the
     last traceback if none was passed.  The instruction causing the
     exception is indicated.

     The disassembly is written as text to the supplied `file' argument
     if provided and to ‘sys.stdout’ otherwise.

     Changed in version 3.4: Added `file' parameter.

 -- Function: dis.disassemble (code, lasti=-1, *, file=None)
 -- Function: dis.disco (code, lasti=-1, *, file=None)

     Disassemble a code object, indicating the last instruction if
     `lasti' was provided.  The output is divided in the following
     columns:

       1. the line number, for the first instruction of each line

       2. the current instruction, indicated as ‘-->’,

       3. a labelled instruction, indicated with ‘>>’,

       4. the address of the instruction,

       5. the operation code name,

       6. operation parameters, and

       7. interpretation of the parameters in parentheses.

     The parameter interpretation recognizes local and global variable
     names, constant values, branch targets, and compare operators.

     The disassembly is written as text to the supplied `file' argument
     if provided and to ‘sys.stdout’ otherwise.

     Changed in version 3.4: Added `file' parameter.

 -- Function: dis.get_instructions (x, *, first_line=None)

     Return an iterator over the instructions in the supplied function,
     method, source code string or code object.

     The iterator generates a series of *note Instruction: 922. named
     tuples giving the details of each operation in the supplied code.

     If `first_line' is not ‘None’, it indicates the line number that
     should be reported for the first source line in the disassembled
     code.  Otherwise, the source line information (if any) is taken
     directly from the disassembled code object.

     New in version 3.4.

 -- Function: dis.findlinestarts (code)

     This generator function uses the ‘co_firstlineno’ and ‘co_lnotab’
     attributes of the code object `code' to find the offsets which are
     starts of lines in the source code.  They are generated as
     ‘(offset, lineno)’ pairs.  See Objects/lnotab_notes.txt(1) for the
     ‘co_lnotab’ format and how to decode it.

     Changed in version 3.6: Line numbers can be decreasing.  Before,
     they were always increasing.

 -- Function: dis.findlabels (code)

     Detect all offsets in the raw compiled bytecode string `code' which
     are jump targets, and return a list of these offsets.

 -- Function: dis.stack_effect (opcode, oparg=None, *, jump=None)

     Compute the stack effect of `opcode' with argument `oparg'.

     If the code has a jump target and `jump' is ‘True’, *note
     stack_effect(): 927. will return the stack effect of jumping.  If
     `jump' is ‘False’, it will return the stack effect of not jumping.
     And if `jump' is ‘None’ (default), it will return the maximal stack
     effect of both cases.

     New in version 3.4.

     Changed in version 3.8: Added `jump' parameter.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Objects/lnotab_notes.txt


File: python.info,  Node: Python Bytecode Instructions,  Next: Opcode collections,  Prev: Analysis functions,  Up: dis — Disassembler for Python bytecode

5.32.12.3 Python Bytecode Instructions
......................................

The *note get_instructions(): 923. function and *note Bytecode: 924.
class provide details of bytecode instructions as *note Instruction:
922. instances:

 -- Class: dis.Instruction

     Details for a bytecode operation

      -- Data: opcode

          numeric code for operation, corresponding to the opcode values
          listed below and the bytecode values in the *note Opcode
          collections: 3aa0.

      -- Data: opname

          human readable name for operation

      -- Data: arg

          numeric argument to operation (if any), otherwise ‘None’

      -- Data: argval

          resolved arg value (if known), otherwise same as arg

      -- Data: argrepr

          human readable description of operation argument

      -- Data: offset

          start index of operation within bytecode sequence

      -- Data: starts_line

          line started by this opcode (if any), otherwise ‘None’

      -- Data: is_jump_target

          ‘True’ if other code jumps to here, otherwise ‘False’

     New in version 3.4.

The Python compiler currently generates the following bytecode
instructions.

`General instructions'

 -- Opcode: NOP

     Do nothing code.  Used as a placeholder by the bytecode optimizer.

 -- Opcode: POP_TOP

     Removes the top-of-stack (TOS) item.

 -- Opcode: ROT_TWO

     Swaps the two top-most stack items.

 -- Opcode: ROT_THREE

     Lifts second and third stack item one position up, moves top down
     to position three.

 -- Opcode: ROT_FOUR

     Lifts second, third and fourth stack items one position up, moves
     top down to position four.

     New in version 3.8.

 -- Opcode: DUP_TOP

     Duplicates the reference on top of the stack.

     New in version 3.2.

 -- Opcode: DUP_TOP_TWO

     Duplicates the two references on top of the stack, leaving them in
     the same order.

     New in version 3.2.

`Unary operations'

Unary operations take the top of the stack, apply the operation, and
push the result back on the stack.

 -- Opcode: UNARY_POSITIVE

     Implements ‘TOS = +TOS’.

 -- Opcode: UNARY_NEGATIVE

     Implements ‘TOS = -TOS’.

 -- Opcode: UNARY_NOT

     Implements ‘TOS = not TOS’.

 -- Opcode: UNARY_INVERT

     Implements ‘TOS = ~TOS’.

 -- Opcode: GET_ITER

     Implements ‘TOS = iter(TOS)’.

 -- Opcode: GET_YIELD_FROM_ITER

     If ‘TOS’ is a *note generator iterator: 559. or *note coroutine:
     18a. object it is left as is.  Otherwise, implements ‘TOS =
     iter(TOS)’.

     New in version 3.5.

`Binary operations'

Binary operations remove the top of the stack (TOS) and the second
top-most stack item (TOS1) from the stack.  They perform the operation,
and put the result back on the stack.

 -- Opcode: BINARY_POWER

     Implements ‘TOS = TOS1 ** TOS’.

 -- Opcode: BINARY_MULTIPLY

     Implements ‘TOS = TOS1 * TOS’.

 -- Opcode: BINARY_MATRIX_MULTIPLY

     Implements ‘TOS = TOS1 @ TOS’.

     New in version 3.5.

 -- Opcode: BINARY_FLOOR_DIVIDE

     Implements ‘TOS = TOS1 // TOS’.

 -- Opcode: BINARY_TRUE_DIVIDE

     Implements ‘TOS = TOS1 / TOS’.

 -- Opcode: BINARY_MODULO

     Implements ‘TOS = TOS1 % TOS’.

 -- Opcode: BINARY_ADD

     Implements ‘TOS = TOS1 + TOS’.

 -- Opcode: BINARY_SUBTRACT

     Implements ‘TOS = TOS1 - TOS’.

 -- Opcode: BINARY_SUBSCR

     Implements ‘TOS = TOS1[TOS]’.

 -- Opcode: BINARY_LSHIFT

     Implements ‘TOS = TOS1 << TOS’.

 -- Opcode: BINARY_RSHIFT

     Implements ‘TOS = TOS1 >> TOS’.

 -- Opcode: BINARY_AND

     Implements ‘TOS = TOS1 & TOS’.

 -- Opcode: BINARY_XOR

     Implements ‘TOS = TOS1 ^ TOS’.

 -- Opcode: BINARY_OR

     Implements ‘TOS = TOS1 | TOS’.

`In-place operations'

In-place operations are like binary operations, in that they remove TOS
and TOS1, and push the result back on the stack, but the operation is
done in-place when TOS1 supports it, and the resulting TOS may be (but
does not have to be) the original TOS1.

 -- Opcode: INPLACE_POWER

     Implements in-place ‘TOS = TOS1 ** TOS’.

 -- Opcode: INPLACE_MULTIPLY

     Implements in-place ‘TOS = TOS1 * TOS’.

 -- Opcode: INPLACE_MATRIX_MULTIPLY

     Implements in-place ‘TOS = TOS1 @ TOS’.

     New in version 3.5.

 -- Opcode: INPLACE_FLOOR_DIVIDE

     Implements in-place ‘TOS = TOS1 // TOS’.

 -- Opcode: INPLACE_TRUE_DIVIDE

     Implements in-place ‘TOS = TOS1 / TOS’.

 -- Opcode: INPLACE_MODULO

     Implements in-place ‘TOS = TOS1 % TOS’.

 -- Opcode: INPLACE_ADD

     Implements in-place ‘TOS = TOS1 + TOS’.

 -- Opcode: INPLACE_SUBTRACT

     Implements in-place ‘TOS = TOS1 - TOS’.

 -- Opcode: INPLACE_LSHIFT

     Implements in-place ‘TOS = TOS1 << TOS’.

 -- Opcode: INPLACE_RSHIFT

     Implements in-place ‘TOS = TOS1 >> TOS’.

 -- Opcode: INPLACE_AND

     Implements in-place ‘TOS = TOS1 & TOS’.

 -- Opcode: INPLACE_XOR

     Implements in-place ‘TOS = TOS1 ^ TOS’.

 -- Opcode: INPLACE_OR

     Implements in-place ‘TOS = TOS1 | TOS’.

 -- Opcode: STORE_SUBSCR

     Implements ‘TOS1[TOS] = TOS2’.

 -- Opcode: DELETE_SUBSCR

     Implements ‘del TOS1[TOS]’.

`Coroutine opcodes'

 -- Opcode: GET_AWAITABLE

     Implements ‘TOS = get_awaitable(TOS)’, where ‘get_awaitable(o)’
     returns ‘o’ if ‘o’ is a coroutine object or a generator object with
     the CO_ITERABLE_COROUTINE flag, or resolves ‘o.__await__’.

     New in version 3.5.

 -- Opcode: GET_AITER

     Implements ‘TOS = TOS.__aiter__()’.

     New in version 3.5.

     Changed in version 3.7: Returning awaitable objects from
     ‘__aiter__’ is no longer supported.

 -- Opcode: GET_ANEXT

     Implements ‘PUSH(get_awaitable(TOS.__anext__()))’.  See
     ‘GET_AWAITABLE’ for details about ‘get_awaitable’

     New in version 3.5.

 -- Opcode: END_ASYNC_FOR

     Terminates an *note async for: 3fd. loop.  Handles an exception
     raised when awaiting a next item.  If TOS is *note
     StopAsyncIteration: 114a. pop 7 values from the stack and restore
     the exception state using the second three of them.  Otherwise
     re-raise the exception using the three values from the stack.  An
     exception handler block is removed from the block stack.

     New in version 3.8.

 -- Opcode: BEFORE_ASYNC_WITH

     Resolves ‘__aenter__’ and ‘__aexit__’ from the object on top of the
     stack.  Pushes ‘__aexit__’ and result of ‘__aenter__()’ to the
     stack.

     New in version 3.5.

 -- Opcode: SETUP_ASYNC_WITH

     Creates a new frame object.

     New in version 3.5.

`Miscellaneous opcodes'

 -- Opcode: PRINT_EXPR

     Implements the expression statement for the interactive mode.  TOS
     is removed from the stack and printed.  In non-interactive mode, an
     expression statement is terminated with *note POP_TOP: 3aa9.

 -- Opcode: SET_ADD (i)

     Calls ‘set.add(TOS1[-i], TOS)’.  Used to implement set
     comprehensions.

 -- Opcode: LIST_APPEND (i)

     Calls ‘list.append(TOS1[-i], TOS)’.  Used to implement list
     comprehensions.

 -- Opcode: MAP_ADD (i)

     Calls ‘dict.__setitem__(TOS1[-i], TOS1, TOS)’.  Used to implement
     dict comprehensions.

     New in version 3.1.

     Changed in version 3.8: Map value is TOS and map key is TOS1.
     Before, those were reversed.

For all of the *note SET_ADD: 3ad7, *note LIST_APPEND: 3ad8. and *note
MAP_ADD: 3fe. instructions, while the added value or key/value pair is
popped off, the container object remains on the stack so that it is
available for further iterations of the loop.

 -- Opcode: RETURN_VALUE

     Returns with TOS to the caller of the function.

 -- Opcode: YIELD_VALUE

     Pops TOS and yields it from a *note generator: a83.

 -- Opcode: YIELD_FROM

     Pops TOS and delegates to it as a subiterator from a *note
     generator: a83.

     New in version 3.3.

 -- Opcode: SETUP_ANNOTATIONS

     Checks whether ‘__annotations__’ is defined in ‘locals()’, if not
     it is set up to an empty ‘dict’.  This opcode is only emitted if a
     class or module body contains *note variable annotations: 712.
     statically.

     New in version 3.6.

 -- Opcode: IMPORT_STAR

     Loads all symbols not starting with ‘'_'’ directly from the module
     TOS to the local namespace.  The module is popped after loading all
     names.  This opcode implements ‘from module import *’.

 -- Opcode: POP_BLOCK

     Removes one block from the block stack.  Per frame, there is a
     stack of blocks, denoting *note try: e37. statements, and such.

 -- Opcode: POP_EXCEPT

     Removes one block from the block stack.  The popped block must be
     an exception handler block, as implicitly created when entering an
     except handler.  In addition to popping extraneous values from the
     frame stack, the last three popped values are used to restore the
     exception state.

 -- Opcode: RERAISE

     Re-raises the exception currently on top of the stack.

     New in version 3.9.

 -- Opcode: WITH_EXCEPT_START

     Calls the function in position 7 on the stack with the top three
     items on the stack as arguments.  Used to implement the call
     ‘context_manager.__exit__(*exc_info())’ when an exception has
     occurred in a *note with: 7da. statement.

     New in version 3.9.

 -- Opcode: LOAD_ASSERTION_ERROR

     Pushes *note AssertionError: 240. onto the stack.  Used by the
     *note assert: 23f. statement.

     New in version 3.9.

 -- Opcode: LOAD_BUILD_CLASS

     Pushes ‘builtins.__build_class__()’ onto the stack.  It is later
     called by *note CALL_FUNCTION: 70e. to construct a class.

 -- Opcode: SETUP_WITH (delta)

     This opcode performs several operations before a with block starts.
     First, it loads *note __exit__(): d5e. from the context manager and
     pushes it onto the stack for later use by *note WITH_EXCEPT_START:
     3ae0.  Then, *note __enter__(): d5d. is called, and a finally block
     pointing to `delta' is pushed.  Finally, the result of calling the
     ‘__enter__()’ method is pushed onto the stack.  The next opcode
     will either ignore it (*note POP_TOP: 3aa9.), or store it in (a)
     variable(s) (*note STORE_FAST: 3ae3, *note STORE_NAME: 3ae4, or
     *note UNPACK_SEQUENCE: 3ae5.).

     New in version 3.2.

All of the following opcodes use their arguments.

 -- Opcode: STORE_NAME (namei)

     Implements ‘name = TOS’.  `namei' is the index of `name' in the
     attribute ‘co_names’ of the code object.  The compiler tries to use
     *note STORE_FAST: 3ae3. or *note STORE_GLOBAL: 3ae6. if possible.

 -- Opcode: DELETE_NAME (namei)

     Implements ‘del name’, where `namei' is the index into ‘co_names’
     attribute of the code object.

 -- Opcode: UNPACK_SEQUENCE (count)

     Unpacks TOS into `count' individual values, which are put onto the
     stack right-to-left.

 -- Opcode: UNPACK_EX (counts)

     Implements assignment with a starred target: Unpacks an iterable in
     TOS into individual values, where the total number of values can be
     smaller than the number of items in the iterable: one of the new
     values will be a list of all leftover items.

     The low byte of `counts' is the number of values before the list
     value, the high byte of `counts' the number of values after it.
     The resulting values are put onto the stack right-to-left.

 -- Opcode: STORE_ATTR (namei)

     Implements ‘TOS.name = TOS1’, where `namei' is the index of name in
     ‘co_names’.

 -- Opcode: DELETE_ATTR (namei)

     Implements ‘del TOS.name’, using `namei' as index into ‘co_names’.

 -- Opcode: STORE_GLOBAL (namei)

     Works as *note STORE_NAME: 3ae4, but stores the name as a global.

 -- Opcode: DELETE_GLOBAL (namei)

     Works as *note DELETE_NAME: 3ae7, but deletes a global name.

 -- Opcode: LOAD_CONST (consti)

     Pushes ‘co_consts[consti]’ onto the stack.

 -- Opcode: LOAD_NAME (namei)

     Pushes the value associated with ‘co_names[namei]’ onto the stack.

 -- Opcode: BUILD_TUPLE (count)

     Creates a tuple consuming `count' items from the stack, and pushes
     the resulting tuple onto the stack.

 -- Opcode: BUILD_LIST (count)

     Works as *note BUILD_TUPLE: 3aee, but creates a list.

 -- Opcode: BUILD_SET (count)

     Works as *note BUILD_TUPLE: 3aee, but creates a set.

 -- Opcode: BUILD_MAP (count)

     Pushes a new dictionary object onto the stack.  Pops ‘2 * count’
     items so that the dictionary holds `count' entries: ‘{..., TOS3:
     TOS2, TOS1: TOS}’.

     Changed in version 3.5: The dictionary is created from stack items
     instead of creating an empty dictionary pre-sized to hold `count'
     items.

 -- Opcode: BUILD_CONST_KEY_MAP (count)

     The version of *note BUILD_MAP: 3af1. specialized for constant
     keys.  Pops the top element on the stack which contains a tuple of
     keys, then starting from ‘TOS1’, pops `count' values to form values
     in the built dictionary.

     New in version 3.6.

 -- Opcode: BUILD_STRING (count)

     Concatenates `count' strings from the stack and pushes the
     resulting string onto the stack.

     New in version 3.6.

 -- Opcode: LIST_TO_TUPLE

     Pops a list from the stack and pushes a tuple containing the same
     values.

     New in version 3.9.

 -- Opcode: LIST_EXTEND (i)

     Calls ‘list.extend(TOS1[-i], TOS)’.  Used to build lists.

     New in version 3.9.

 -- Opcode: SET_UPDATE (i)

     Calls ‘set.update(TOS1[-i], TOS)’.  Used to build sets.

     New in version 3.9.

 -- Opcode: DICT_UPDATE (i)

     Calls ‘dict.update(TOS1[-i], TOS)’.  Used to build dicts.

     New in version 3.9.

 -- Opcode: DICT_MERGE

     Like *note DICT_UPDATE: 3af5. but raises an exception for duplicate
     keys.

     New in version 3.9.

 -- Opcode: LOAD_ATTR (namei)

     Replaces TOS with ‘getattr(TOS, co_names[namei])’.

 -- Opcode: COMPARE_OP (opname)

     Performs a Boolean operation.  The operation name can be found in
     ‘cmp_op[opname]’.

 -- Opcode: IS_OP (invert)

     Performs ‘is’ comparison, or ‘is not’ if ‘invert’ is 1.

     New in version 3.9.

 -- Opcode: CONTAINS_OP (invert)

     Performs ‘in’ comparison, or ‘not in’ if ‘invert’ is 1.

     New in version 3.9.

 -- Opcode: IMPORT_NAME (namei)

     Imports the module ‘co_names[namei]’.  TOS and TOS1 are popped and
     provide the `fromlist' and `level' arguments of *note __import__():
     16b.  The module object is pushed onto the stack.  The current
     namespace is not affected: for a proper import statement, a
     subsequent *note STORE_FAST: 3ae3. instruction modifies the
     namespace.

 -- Opcode: IMPORT_FROM (namei)

     Loads the attribute ‘co_names[namei]’ from the module found in TOS.
     The resulting object is pushed onto the stack, to be subsequently
     stored by a *note STORE_FAST: 3ae3. instruction.

 -- Opcode: JUMP_FORWARD (delta)

     Increments bytecode counter by `delta'.

 -- Opcode: POP_JUMP_IF_TRUE (target)

     If TOS is true, sets the bytecode counter to `target'.  TOS is
     popped.

     New in version 3.1.

 -- Opcode: POP_JUMP_IF_FALSE (target)

     If TOS is false, sets the bytecode counter to `target'.  TOS is
     popped.

     New in version 3.1.

 -- Opcode: JUMP_IF_NOT_EXC_MATCH (target)

     Tests whether the second value on the stack is an exception
     matching TOS, and jumps if it is not.  Pops two values from the
     stack.

     New in version 3.9.

 -- Opcode: JUMP_IF_TRUE_OR_POP (target)

     If TOS is true, sets the bytecode counter to `target' and leaves
     TOS on the stack.  Otherwise (TOS is false), TOS is popped.

     New in version 3.1.

 -- Opcode: JUMP_IF_FALSE_OR_POP (target)

     If TOS is false, sets the bytecode counter to `target' and leaves
     TOS on the stack.  Otherwise (TOS is true), TOS is popped.

     New in version 3.1.

 -- Opcode: JUMP_ABSOLUTE (target)

     Set bytecode counter to `target'.

 -- Opcode: FOR_ITER (delta)

     TOS is an *note iterator: 1171.  Call its *note __next__(): d2c.
     method.  If this yields a new value, push it on the stack (leaving
     the iterator below it).  If the iterator indicates it is exhausted,
     TOS is popped, and the byte code counter is incremented by `delta'.

 -- Opcode: LOAD_GLOBAL (namei)

     Loads the global named ‘co_names[namei]’ onto the stack.

 -- Opcode: SETUP_FINALLY (delta)

     Pushes a try block from a try-finally or try-except clause onto the
     block stack.  `delta' points to the finally block or the first
     except block.

 -- Opcode: LOAD_FAST (var_num)

     Pushes a reference to the local ‘co_varnames[var_num]’ onto the
     stack.

 -- Opcode: STORE_FAST (var_num)

     Stores TOS into the local ‘co_varnames[var_num]’.

 -- Opcode: DELETE_FAST (var_num)

     Deletes local ‘co_varnames[var_num]’.

 -- Opcode: LOAD_CLOSURE (i)

     Pushes a reference to the cell contained in slot `i' of the cell
     and free variable storage.  The name of the variable is
     ‘co_cellvars[i]’ if `i' is less than the length of `co_cellvars'.
     Otherwise it is ‘co_freevars[i - len(co_cellvars)]’.

 -- Opcode: LOAD_DEREF (i)

     Loads the cell contained in slot `i' of the cell and free variable
     storage.  Pushes a reference to the object the cell contains on the
     stack.

 -- Opcode: LOAD_CLASSDEREF (i)

     Much like *note LOAD_DEREF: 3b09. but first checks the locals
     dictionary before consulting the cell.  This is used for loading
     free variables in class bodies.

     New in version 3.4.

 -- Opcode: STORE_DEREF (i)

     Stores TOS into the cell contained in slot `i' of the cell and free
     variable storage.

 -- Opcode: DELETE_DEREF (i)

     Empties the cell contained in slot `i' of the cell and free
     variable storage.  Used by the *note del: 13a2. statement.

     New in version 3.2.

 -- Opcode: RAISE_VARARGS (argc)

     Raises an exception using one of the 3 forms of the ‘raise’
     statement, depending on the value of `argc':

        * 0: ‘raise’ (re-raise previous exception)

        * 1: ‘raise TOS’ (raise exception instance or type at ‘TOS’)

        * 2: ‘raise TOS1 from TOS’ (raise exception instance or type at
          ‘TOS1’ with ‘__cause__’ set to ‘TOS’)

 -- Opcode: CALL_FUNCTION (argc)

     Calls a callable object with positional arguments.  `argc'
     indicates the number of positional arguments.  The top of the stack
     contains positional arguments, with the right-most argument on top.
     Below the arguments is a callable object to call.  ‘CALL_FUNCTION’
     pops all arguments and the callable object off the stack, calls the
     callable object with those arguments, and pushes the return value
     returned by the callable object.

     Changed in version 3.6: This opcode is used only for calls with
     positional arguments.

 -- Opcode: CALL_FUNCTION_KW (argc)

     Calls a callable object with positional (if any) and keyword
     arguments.  `argc' indicates the total number of positional and
     keyword arguments.  The top element on the stack contains a tuple
     with the names of the keyword arguments, which must be strings.
     Below that are the values for the keyword arguments, in the order
     corresponding to the tuple.  Below that are positional arguments,
     with the right-most parameter on top.  Below the arguments is a
     callable object to call.  ‘CALL_FUNCTION_KW’ pops all arguments and
     the callable object off the stack, calls the callable object with
     those arguments, and pushes the return value returned by the
     callable object.

     Changed in version 3.6: Keyword arguments are packed in a tuple
     instead of a dictionary, `argc' indicates the total number of
     arguments.

 -- Opcode: CALL_FUNCTION_EX (flags)

     Calls a callable object with variable set of positional and keyword
     arguments.  If the lowest bit of `flags' is set, the top of the
     stack contains a mapping object containing additional keyword
     arguments.  Before the callable is called, the mapping object and
     iterable object are each “unpacked” and their contents passed in as
     keyword and positional arguments respectively.  ‘CALL_FUNCTION_EX’
     pops all arguments and the callable object off the stack, calls the
     callable object with those arguments, and pushes the return value
     returned by the callable object.

     New in version 3.6.

 -- Opcode: LOAD_METHOD (namei)

     Loads a method named ‘co_names[namei]’ from the TOS object.  TOS is
     popped.  This bytecode distinguishes two cases: if TOS has a method
     with the correct name, the bytecode pushes the unbound method and
     TOS. TOS will be used as the first argument (‘self’) by *note
     CALL_METHOD: 5a9. when calling the unbound method.  Otherwise,
     ‘NULL’ and the object return by the attribute lookup are pushed.

     New in version 3.7.

 -- Opcode: CALL_METHOD (argc)

     Calls a method.  `argc' is the number of positional arguments.
     Keyword arguments are not supported.  This opcode is designed to be
     used with *note LOAD_METHOD: 5a8.  Positional arguments are on top
     of the stack.  Below them, the two items described in *note
     LOAD_METHOD: 5a8. are on the stack (either ‘self’ and an unbound
     method object or ‘NULL’ and an arbitrary callable).  All of them
     are popped and the return value is pushed.

     New in version 3.7.

 -- Opcode: MAKE_FUNCTION (flags)

     Pushes a new function object on the stack.  From bottom to top, the
     consumed stack must consist of values if the argument carries a
     specified flag value

        * ‘0x01’ a tuple of default values for positional-only and
          positional-or-keyword parameters in positional order

        * ‘0x02’ a dictionary of keyword-only parameters’ default values

        * ‘0x04’ an annotation dictionary

        * ‘0x08’ a tuple containing cells for free variables, making a
          closure

        * the code associated with the function (at TOS1)

        * the *note qualified name: 155c. of the function (at TOS)

 -- Opcode: BUILD_SLICE (argc)

     Pushes a slice object on the stack.  `argc' must be 2 or 3.  If it
     is 2, ‘slice(TOS1, TOS)’ is pushed; if it is 3, ‘slice(TOS2, TOS1,
     TOS)’ is pushed.  See the *note slice(): ec8. built-in function for
     more information.

 -- Opcode: EXTENDED_ARG (ext)

     Prefixes any opcode which has an argument too big to fit into the
     default one byte.  `ext' holds an additional byte which act as
     higher bits in the argument.  For each opcode, at most three
     prefixal ‘EXTENDED_ARG’ are allowed, forming an argument from
     two-byte to four-byte.

 -- Opcode: FORMAT_VALUE (flags)

     Used for implementing formatted literal strings (f-strings).  Pops
     an optional `fmt_spec' from the stack, then a required `value'.
     `flags' is interpreted as follows:

        * ‘(flags & 0x03) == 0x00’: `value' is formatted as-is.

        * ‘(flags & 0x03) == 0x01’: call *note str(): 205. on `value'
          before formatting it.

        * ‘(flags & 0x03) == 0x02’: call *note repr(): 8b9. on `value'
          before formatting it.

        * ‘(flags & 0x03) == 0x03’: call *note ascii(): e11. on `value'
          before formatting it.

        * ‘(flags & 0x04) == 0x04’: pop `fmt_spec' from the stack and
          use it, else use an empty `fmt_spec'.

     Formatting is performed using ‘PyObject_Format()’.  The result is
     pushed on the stack.

     New in version 3.6.

 -- Opcode: HAVE_ARGUMENT

     This is not really an opcode.  It identifies the dividing line
     between opcodes which don’t use their argument and those that do
     (‘< HAVE_ARGUMENT’ and ‘>= HAVE_ARGUMENT’, respectively).

     Changed in version 3.6: Now every instruction has an argument, but
     opcodes ‘< HAVE_ARGUMENT’ ignore it.  Before, only opcodes ‘>=
     HAVE_ARGUMENT’ had an argument.


File: python.info,  Node: Opcode collections,  Prev: Python Bytecode Instructions,  Up: dis — Disassembler for Python bytecode

5.32.12.4 Opcode collections
............................

These collections are provided for automatic introspection of bytecode
instructions:

 -- Data: dis.opname

     Sequence of operation names, indexable using the bytecode.

 -- Data: dis.opmap

     Dictionary mapping operation names to bytecodes.

 -- Data: dis.cmp_op

     Sequence of all compare operation names.

 -- Data: dis.hasconst

     Sequence of bytecodes that access a constant.

 -- Data: dis.hasfree

     Sequence of bytecodes that access a free variable (note that ‘free’
     in this context refers to names in the current scope that are
     referenced by inner scopes or names in outer scopes that are
     referenced from this scope.  It does `not' include references to
     global or builtin scopes).

 -- Data: dis.hasname

     Sequence of bytecodes that access an attribute by name.

 -- Data: dis.hasjrel

     Sequence of bytecodes that have a relative jump target.

 -- Data: dis.hasjabs

     Sequence of bytecodes that have an absolute jump target.

 -- Data: dis.haslocal

     Sequence of bytecodes that access a local variable.

 -- Data: dis.hascompare

     Sequence of bytecodes of Boolean operations.


File: python.info,  Node: pickletools — Tools for pickle developers,  Prev: dis — Disassembler for Python bytecode,  Up: Python Language Services

5.32.13 ‘pickletools’ — Tools for pickle developers
---------------------------------------------------

`Source code:' Lib/pickletools.py(1)

__________________________________________________________________

This module contains various constants relating to the intimate details
of the *note pickle: ca. module, some lengthy comments about the
implementation, and a few useful functions for analyzing pickled data.
The contents of this module are useful for Python core developers who
are working on the *note pickle: ca.; ordinary users of the *note
pickle: ca. module probably won’t find the *note pickletools: cb. module
relevant.

* Menu:

* Command line usage: Command line usage<2>.
* Programmatic Interface: Programmatic Interface<2>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/pickletools.py


File: python.info,  Node: Command line usage<2>,  Next: Programmatic Interface<2>,  Up: pickletools — Tools for pickle developers

5.32.13.1 Command line usage
............................

New in version 3.2.

When invoked from the command line, ‘python -m pickletools’ will
disassemble the contents of one or more pickle files.  Note that if you
want to see the Python object stored in the pickle rather than the
details of pickle format, you may want to use ‘-m pickle’ instead.
However, when the pickle file that you want to examine comes from an
untrusted source, ‘-m pickletools’ is a safer option because it does not
execute pickle bytecode.

For example, with a tuple ‘(1, 2)’ pickled in file ‘x.pickle’:

     $ python -m pickle x.pickle
     (1, 2)

     $ python -m pickletools x.pickle
         0: \x80 PROTO      3
         2: K    BININT1    1
         4: K    BININT1    2
         6: \x86 TUPLE2
         7: q    BINPUT     0
         9: .    STOP
     highest protocol among opcodes = 2

* Menu:

* Command line options: Command line options<3>.


File: python.info,  Node: Command line options<3>,  Up: Command line usage<2>

5.32.13.2 Command line options
..............................

 -- Program Option: -a, --annotate

     Annotate each line with a short opcode description.

 -- Program Option: -o, --output=<file>

     Name of a file where the output should be written.

 -- Program Option: -l, --indentlevel=<num>

     The number of blanks by which to indent a new MARK level.

 -- Program Option: -m, --memo

     When multiple objects are disassembled, preserve memo between
     disassemblies.

 -- Program Option: -p, --preamble=<preamble>

     When more than one pickle file are specified, print given preamble
     before each disassembly.


File: python.info,  Node: Programmatic Interface<2>,  Prev: Command line usage<2>,  Up: pickletools — Tools for pickle developers

5.32.13.3 Programmatic Interface
................................

 -- Function: pickletools.dis (pickle, out=None, memo=None,
          indentlevel=4, annotate=0)

     Outputs a symbolic disassembly of the pickle to the file-like
     object `out', defaulting to ‘sys.stdout’.  `pickle' can be a string
     or a file-like object.  `memo' can be a Python dictionary that will
     be used as the pickle’s memo; it can be used to perform
     disassemblies across multiple pickles created by the same pickler.
     Successive levels, indicated by ‘MARK’ opcodes in the stream, are
     indented by `indentlevel' spaces.  If a nonzero value is given to
     `annotate', each opcode in the output is annotated with a short
     description.  The value of `annotate' is used as a hint for the
     column where annotation should start.

     New in version 3.2: The `annotate' argument.

 -- Function: pickletools.genops (pickle)

     Provides an *note iterator: 1171. over all of the opcodes in a
     pickle, returning a sequence of ‘(opcode, arg, pos)’ triples.
     `opcode' is an instance of an ‘OpcodeInfo’ class; `arg' is the
     decoded value, as a Python object, of the opcode’s argument; `pos'
     is the position at which this opcode is located.  `pickle' can be a
     string or a file-like object.

 -- Function: pickletools.optimize (picklestring)

     Returns a new equivalent pickle string after eliminating unused
     ‘PUT’ opcodes.  The optimized pickle is shorter, takes less
     transmission time, requires less storage space, and unpickles more
     efficiently.


File: python.info,  Node: Miscellaneous Services,  Next: MS Windows Specific Services,  Prev: Python Language Services,  Up: The Python Standard Library

5.33 Miscellaneous Services
===========================

The modules described in this chapter provide miscellaneous services
that are available in all Python versions.  Here’s an overview:

* Menu:

* formatter — Generic output formatting::


File: python.info,  Node: formatter — Generic output formatting,  Up: Miscellaneous Services

5.33.1 ‘formatter’ — Generic output formatting
----------------------------------------------

Deprecated since version 3.4: Due to lack of usage, the formatter module
has been deprecated.

__________________________________________________________________

This module supports two interface definitions, each with multiple
implementations: The `formatter' interface, and the `writer' interface
which is required by the formatter interface.

Formatter objects transform an abstract flow of formatting events into
specific output events on writer objects.  Formatters manage several
stack structures to allow various properties of a writer object to be
changed and restored; writers need not be able to handle relative
changes nor any sort of “change back” operation.  Specific writer
properties which may be controlled via formatter objects are horizontal
alignment, font, and left margin indentations.  A mechanism is provided
which supports providing arbitrary, non-exclusive style settings to a
writer as well.  Additional interfaces facilitate formatting events
which are not reversible, such as paragraph separation.

Writer objects encapsulate device interfaces.  Abstract devices, such as
file formats, are supported as well as physical devices.  The provided
implementations all work with abstract devices.  The interface makes
available mechanisms for setting the properties which formatter objects
manage and inserting data into the output.

* Menu:

* The Formatter Interface::
* Formatter Implementations::
* The Writer Interface::
* Writer Implementations::


File: python.info,  Node: The Formatter Interface,  Next: Formatter Implementations,  Up: formatter — Generic output formatting

5.33.1.1 The Formatter Interface
................................

Interfaces to create formatters are dependent on the specific formatter
class being instantiated.  The interfaces described below are the
required interfaces which all formatters must support once initialized.

One data element is defined at the module level:

 -- Data: formatter.AS_IS

     Value which can be used in the font specification passed to the
     ‘push_font()’ method described below, or as the new value to any
     other ‘push_property()’ method.  Pushing the ‘AS_IS’ value allows
     the corresponding ‘pop_property()’ method to be called without
     having to track whether the property was changed.

The following attributes are defined for formatter instance objects:

 -- Attribute: formatter.writer

     The writer instance with which the formatter interacts.

 -- Method: formatter.end_paragraph (blanklines)

     Close any open paragraphs and insert at least `blanklines' before
     the next paragraph.

 -- Method: formatter.add_line_break ()

     Add a hard line break if one does not already exist.  This does not
     break the logical paragraph.

 -- Method: formatter.add_hor_rule (*args, **kw)

     Insert a horizontal rule in the output.  A hard break is inserted
     if there is data in the current paragraph, but the logical
     paragraph is not broken.  The arguments and keywords are passed on
     to the writer’s ‘send_line_break()’ method.

 -- Method: formatter.add_flowing_data (data)

     Provide data which should be formatted with collapsed whitespace.
     Whitespace from preceding and successive calls to *note
     add_flowing_data(): 3b32. is considered as well when the whitespace
     collapse is performed.  The data which is passed to this method is
     expected to be word-wrapped by the output device.  Note that any
     word-wrapping still must be performed by the writer object due to
     the need to rely on device and font information.

 -- Method: formatter.add_literal_data (data)

     Provide data which should be passed to the writer unchanged.
     Whitespace, including newline and tab characters, are considered
     legal in the value of `data'.

 -- Method: formatter.add_label_data (format, counter)

     Insert a label which should be placed to the left of the current
     left margin.  This should be used for constructing bulleted or
     numbered lists.  If the `format' value is a string, it is
     interpreted as a format specification for `counter', which should
     be an integer.  The result of this formatting becomes the value of
     the label; if `format' is not a string it is used as the label
     value directly.  The label value is passed as the only argument to
     the writer’s ‘send_label_data()’ method.  Interpretation of
     non-string label values is dependent on the associated writer.

     Format specifications are strings which, in combination with a
     counter value, are used to compute label values.  Each character in
     the format string is copied to the label value, with some
     characters recognized to indicate a transform on the counter value.
     Specifically, the character ‘'1'’ represents the counter value
     formatter as an Arabic number, the characters ‘'A'’ and ‘'a'’
     represent alphabetic representations of the counter value in upper
     and lower case, respectively, and ‘'I'’ and ‘'i'’ represent the
     counter value in Roman numerals, in upper and lower case.  Note
     that the alphabetic and roman transforms require that the counter
     value be greater than zero.

 -- Method: formatter.flush_softspace ()

     Send any pending whitespace buffered from a previous call to *note
     add_flowing_data(): 3b32. to the associated writer object.  This
     should be called before any direct manipulation of the writer
     object.

 -- Method: formatter.push_alignment (align)

     Push a new alignment setting onto the alignment stack.  This may be
     *note AS_IS: 3b2d. if no change is desired.  If the alignment value
     is changed from the previous setting, the writer’s
     ‘new_alignment()’ method is called with the `align' value.

 -- Method: formatter.pop_alignment ()

     Restore the previous alignment.

 -- Method: formatter.push_font ((size, italic, bold, teletype))

     Change some or all font properties of the writer object.
     Properties which are not set to *note AS_IS: 3b2d. are set to the
     values passed in while others are maintained at their current
     settings.  The writer’s ‘new_font()’ method is called with the
     fully resolved font specification.

 -- Method: formatter.pop_font ()

     Restore the previous font.

 -- Method: formatter.push_margin (margin)

     Increase the number of left margin indentations by one, associating
     the logical tag `margin' with the new indentation.  The initial
     margin level is ‘0’.  Changed values of the logical tag must be
     true values; false values other than *note AS_IS: 3b2d. are not
     sufficient to change the margin.

 -- Method: formatter.pop_margin ()

     Restore the previous margin.

 -- Method: formatter.push_style (*styles)

     Push any number of arbitrary style specifications.  All styles are
     pushed onto the styles stack in order.  A tuple representing the
     entire stack, including *note AS_IS: 3b2d. values, is passed to the
     writer’s ‘new_styles()’ method.

 -- Method: formatter.pop_style (n=1)

     Pop the last `n' style specifications passed to *note push_style():
     3b3c.  A tuple representing the revised stack, including *note
     AS_IS: 3b2d. values, is passed to the writer’s ‘new_styles()’
     method.

 -- Method: formatter.set_spacing (spacing)

     Set the spacing style for the writer.

 -- Method: formatter.assert_line_data (flag=1)

     Inform the formatter that data has been added to the current
     paragraph out-of-band.  This should be used when the writer has
     been manipulated directly.  The optional `flag' argument can be set
     to false if the writer manipulations produced a hard line break at
     the end of the output.


File: python.info,  Node: Formatter Implementations,  Next: The Writer Interface,  Prev: The Formatter Interface,  Up: formatter — Generic output formatting

5.33.1.2 Formatter Implementations
..................................

Two implementations of formatter objects are provided by this module.
Most applications may use one of these classes without modification or
subclassing.

 -- Class: formatter.NullFormatter (writer=None)

     A formatter which does nothing.  If `writer' is omitted, a *note
     NullWriter: 3b43. instance is created.  No methods of the writer
     are called by *note NullFormatter: 3b42. instances.
     Implementations should inherit from this class if implementing a
     writer interface but don’t need to inherit any implementation.

 -- Class: formatter.AbstractFormatter (writer)

     The standard formatter.  This implementation has demonstrated wide
     applicability to many writers, and may be used directly in most
     circumstances.  It has been used to implement a full-featured World
     Wide Web browser.


File: python.info,  Node: The Writer Interface,  Next: Writer Implementations,  Prev: Formatter Implementations,  Up: formatter — Generic output formatting

5.33.1.3 The Writer Interface
.............................

Interfaces to create writers are dependent on the specific writer class
being instantiated.  The interfaces described below are the required
interfaces which all writers must support once initialized.  Note that
while most applications can use the *note AbstractFormatter: 3b44. class
as a formatter, the writer must typically be provided by the
application.

 -- Method: writer.flush ()

     Flush any buffered output or device control events.

 -- Method: writer.new_alignment (align)

     Set the alignment style.  The `align' value can be any object, but
     by convention is a string or ‘None’, where ‘None’ indicates that
     the writer’s “preferred” alignment should be used.  Conventional
     `align' values are ‘'left'’, ‘'center'’, ‘'right'’, and
     ‘'justify'’.

 -- Method: writer.new_font (font)

     Set the font style.  The value of `font' will be ‘None’, indicating
     that the device’s default font should be used, or a tuple of the
     form ‘(size, italic, bold, teletype)’.  Size will be a string
     indicating the size of font that should be used; specific strings
     and their interpretation must be defined by the application.  The
     `italic', `bold', and `teletype' values are Boolean values
     specifying which of those font attributes should be used.

 -- Method: writer.new_margin (margin, level)

     Set the margin level to the integer `level' and the logical tag to
     `margin'.  Interpretation of the logical tag is at the writer’s
     discretion; the only restriction on the value of the logical tag is
     that it not be a false value for non-zero values of `level'.

 -- Method: writer.new_spacing (spacing)

     Set the spacing style to `spacing'.

 -- Method: writer.new_styles (styles)

     Set additional styles.  The `styles' value is a tuple of arbitrary
     values; the value *note AS_IS: 3b2d. should be ignored.  The
     `styles' tuple may be interpreted either as a set or as a stack
     depending on the requirements of the application and writer
     implementation.

 -- Method: writer.send_line_break ()

     Break the current line.

 -- Method: writer.send_paragraph (blankline)

     Produce a paragraph separation of at least `blankline' blank lines,
     or the equivalent.  The `blankline' value will be an integer.  Note
     that the implementation will receive a call to *note
     send_line_break(): 3b4d. before this call if a line break is
     needed; this method should not include ending the last line of the
     paragraph.  It is only responsible for vertical spacing between
     paragraphs.

 -- Method: writer.send_hor_rule (*args, **kw)

     Display a horizontal rule on the output device.  The arguments to
     this method are entirely application- and writer-specific, and
     should be interpreted with care.  The method implementation may
     assume that a line break has already been issued via *note
     send_line_break(): 3b4d.

 -- Method: writer.send_flowing_data (data)

     Output character data which may be word-wrapped and re-flowed as
     needed.  Within any sequence of calls to this method, the writer
     may assume that spans of multiple whitespace characters have been
     collapsed to single space characters.

 -- Method: writer.send_literal_data (data)

     Output character data which has already been formatted for display.
     Generally, this should be interpreted to mean that line breaks
     indicated by newline characters should be preserved and no new line
     breaks should be introduced.  The data may contain embedded newline
     and tab characters, unlike data provided to the
     ‘send_formatted_data()’ interface.

 -- Method: writer.send_label_data (data)

     Set `data' to the left of the current left margin, if possible.
     The value of `data' is not restricted; treatment of non-string
     values is entirely application- and writer-dependent.  This method
     will only be called at the beginning of a line.


File: python.info,  Node: Writer Implementations,  Prev: The Writer Interface,  Up: formatter — Generic output formatting

5.33.1.4 Writer Implementations
...............................

Three implementations of the writer object interface are provided as
examples by this module.  Most applications will need to derive new
writer classes from the *note NullWriter: 3b43. class.

 -- Class: formatter.NullWriter

     A writer which only provides the interface definition; no actions
     are taken on any methods.  This should be the base class for all
     writers which do not need to inherit any implementation methods.

 -- Class: formatter.AbstractWriter

     A writer which can be used in debugging formatters, but not much
     else.  Each method simply announces itself by printing its name and
     arguments on standard output.

 -- Class: formatter.DumbWriter (file=None, maxcol=72)

     Simple writer class which writes output on the *note file object:
     c14. passed in as `file' or, if `file' is omitted, on standard
     output.  The output is simply word-wrapped to the number of columns
     specified by `maxcol'.  This class is suitable for reflowing a
     sequence of paragraphs.


File: python.info,  Node: MS Windows Specific Services,  Next: Unix Specific Services,  Prev: Miscellaneous Services,  Up: The Python Standard Library

5.34 MS Windows Specific Services
=================================

This chapter describes modules that are only available on MS Windows
platforms.

* Menu:

* msilib — Read and write Microsoft Installer files::
* msvcrt — Useful routines from the MS VC++ runtime::
* winreg — Windows registry access::
* winsound — Sound-playing interface for Windows::


File: python.info,  Node: msilib — Read and write Microsoft Installer files,  Next: msvcrt — Useful routines from the MS VC++ runtime,  Up: MS Windows Specific Services

5.34.1 ‘msilib’ — Read and write Microsoft Installer files
----------------------------------------------------------

`Source code:' Lib/msilib/__init__.py(1)

__________________________________________________________________

The *note msilib: b5. supports the creation of Microsoft Installer
(‘.msi’) files.  Because these files often contain an embedded “cabinet”
file (‘.cab’), it also exposes an API to create CAB files.  Support for
reading ‘.cab’ files is currently not implemented; read support for the
‘.msi’ database is possible.

This package aims to provide complete access to all tables in an ‘.msi’
file, therefore, it is a fairly low-level API. Two primary applications
of this package are the *note distutils: 38. command ‘bdist_msi’, and
the creation of Python installer package itself (although that currently
uses a different version of ‘msilib’).

The package contents can be roughly split into four parts: low-level CAB
routines, low-level MSI routines, higher-level MSI routines, and
standard table structures.

 -- Function: msilib.FCICreate (cabname, files)

     Create a new CAB file named `cabname'.  `files' must be a list of
     tuples, each containing the name of the file on disk, and the name
     of the file inside the CAB file.

     The files are added to the CAB file in the order they appear in the
     list.  All files are added into a single CAB file, using the MSZIP
     compression algorithm.

     Callbacks to Python for the various steps of MSI creation are
     currently not exposed.

 -- Function: msilib.UuidCreate ()

     Return the string representation of a new unique identifier.  This
     wraps the Windows API functions ‘UuidCreate()’ and
     ‘UuidToString()’.

 -- Function: msilib.OpenDatabase (path, persist)

     Return a new database object by calling MsiOpenDatabase.  `path' is
     the file name of the MSI file; `persist' can be one of the
     constants ‘MSIDBOPEN_CREATEDIRECT’, ‘MSIDBOPEN_CREATE’,
     ‘MSIDBOPEN_DIRECT’, ‘MSIDBOPEN_READONLY’, or ‘MSIDBOPEN_TRANSACT’,
     and may include the flag ‘MSIDBOPEN_PATCHFILE’.  See the Microsoft
     documentation for the meaning of these flags; depending on the
     flags, an existing database is opened, or a new one created.

 -- Function: msilib.CreateRecord (count)

     Return a new record object by calling ‘MSICreateRecord()’.  `count'
     is the number of fields of the record.

 -- Function: msilib.init_database (name, schema, ProductName,
          ProductCode, ProductVersion, Manufacturer)

     Create and return a new database `name', initialize it with
     `schema', and set the properties `ProductName', `ProductCode',
     `ProductVersion', and `Manufacturer'.

     `schema' must be a module object containing ‘tables’ and
     ‘_Validation_records’ attributes; typically, *note msilib.schema:
     3b5e. should be used.

     The database will contain just the schema and the validation
     records when this function returns.

 -- Function: msilib.add_data (database, table, records)

     Add all `records' to the table named `table' in `database'.

     The `table' argument must be one of the predefined tables in the
     MSI schema, e.g.  ‘'Feature'’, ‘'File'’, ‘'Component'’, ‘'Dialog'’,
     ‘'Control'’, etc.

     `records' should be a list of tuples, each one containing all
     fields of a record according to the schema of the table.  For
     optional fields, ‘None’ can be passed.

     Field values can be ints, strings, or instances of the Binary
     class.

 -- Class: msilib.Binary (filename)

     Represents entries in the Binary table; inserting such an object
     using *note add_data(): 3b5f. reads the file named `filename' into
     the table.

 -- Function: msilib.add_tables (database, module)

     Add all table content from `module' to `database'.  `module' must
     contain an attribute `tables' listing all tables for which content
     should be added, and one attribute per table that has the actual
     content.

     This is typically used to install the sequence tables.

 -- Function: msilib.add_stream (database, name, path)

     Add the file `path' into the ‘_Stream’ table of `database', with
     the stream name `name'.

 -- Function: msilib.gen_uuid ()

     Return a new UUID, in the format that MSI typically requires (i.e.
     in curly braces, and with all hexdigits in upper-case).

See also
........

FCICreate(2) UuidCreate(3) UuidToString(4)

* Menu:

* Database Objects::
* View Objects::
* Summary Information Objects::
* Record Objects::
* Errors::
* CAB Objects::
* Directory Objects::
* Features: Features<3>.
* GUI classes::
* Precomputed tables::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/msilib/__init__.py

   (2) https://msdn.microsoft.com/en-us/library/bb432265.aspx

   (3) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa379205.aspx

   (4) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa379352.aspx


File: python.info,  Node: Database Objects,  Next: View Objects,  Up: msilib — Read and write Microsoft Installer files

5.34.1.1 Database Objects
.........................

 -- Method: Database.OpenView (sql)

     Return a view object, by calling ‘MSIDatabaseOpenView()’.  `sql' is
     the SQL statement to execute.

 -- Method: Database.Commit ()

     Commit the changes pending in the current transaction, by calling
     ‘MSIDatabaseCommit()’.

 -- Method: Database.GetSummaryInformation (count)

     Return a new summary information object, by calling
     ‘MsiGetSummaryInformation()’.  `count' is the maximum number of
     updated values.

 -- Method: Database.Close ()

     Close the database object, through ‘MsiCloseHandle()’.

     New in version 3.7.

See also
........

MSIDatabaseOpenView(1) MSIDatabaseCommit(2) MSIGetSummaryInformation(3)
MsiCloseHandle(4)

   ---------- Footnotes ----------

   (1) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370082.aspx

   (2) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370075.aspx

   (3) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370301.aspx

   (4) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370067.aspx


File: python.info,  Node: View Objects,  Next: Summary Information Objects,  Prev: Database Objects,  Up: msilib — Read and write Microsoft Installer files

5.34.1.2 View Objects
.....................

 -- Method: View.Execute (params)

     Execute the SQL query of the view, through ‘MSIViewExecute()’.  If
     `params' is not ‘None’, it is a record describing actual values of
     the parameter tokens in the query.

 -- Method: View.GetColumnInfo (kind)

     Return a record describing the columns of the view, through calling
     ‘MsiViewGetColumnInfo()’.  `kind' can be either ‘MSICOLINFO_NAMES’
     or ‘MSICOLINFO_TYPES’.

 -- Method: View.Fetch ()

     Return a result record of the query, through calling
     ‘MsiViewFetch()’.

 -- Method: View.Modify (kind, data)

     Modify the view, by calling ‘MsiViewModify()’.  `kind' can be one
     of ‘MSIMODIFY_SEEK’, ‘MSIMODIFY_REFRESH’, ‘MSIMODIFY_INSERT’,
     ‘MSIMODIFY_UPDATE’, ‘MSIMODIFY_ASSIGN’, ‘MSIMODIFY_REPLACE’,
     ‘MSIMODIFY_MERGE’, ‘MSIMODIFY_DELETE’,
     ‘MSIMODIFY_INSERT_TEMPORARY’, ‘MSIMODIFY_VALIDATE’,
     ‘MSIMODIFY_VALIDATE_NEW’, ‘MSIMODIFY_VALIDATE_FIELD’, or
     ‘MSIMODIFY_VALIDATE_DELETE’.

     `data' must be a record describing the new data.

 -- Method: View.Close ()

     Close the view, through ‘MsiViewClose()’.

See also
........

MsiViewExecute(1) MSIViewGetColumnInfo(2) MsiViewFetch(3)
MsiViewModify(4) MsiViewClose(5)

   ---------- Footnotes ----------

   (1) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370513.aspx

   (2) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370516.aspx

   (3) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370514.aspx

   (4) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370519.aspx

   (5) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370510.aspx


File: python.info,  Node: Summary Information Objects,  Next: Record Objects,  Prev: View Objects,  Up: msilib — Read and write Microsoft Installer files

5.34.1.3 Summary Information Objects
....................................

 -- Method: SummaryInformation.GetProperty (field)

     Return a property of the summary, through
     ‘MsiSummaryInfoGetProperty()’.  `field' is the name of the
     property, and can be one of the constants ‘PID_CODEPAGE’,
     ‘PID_TITLE’, ‘PID_SUBJECT’, ‘PID_AUTHOR’, ‘PID_KEYWORDS’,
     ‘PID_COMMENTS’, ‘PID_TEMPLATE’, ‘PID_LASTAUTHOR’, ‘PID_REVNUMBER’,
     ‘PID_LASTPRINTED’, ‘PID_CREATE_DTM’, ‘PID_LASTSAVE_DTM’,
     ‘PID_PAGECOUNT’, ‘PID_WORDCOUNT’, ‘PID_CHARCOUNT’, ‘PID_APPNAME’,
     or ‘PID_SECURITY’.

 -- Method: SummaryInformation.GetPropertyCount ()

     Return the number of summary properties, through
     ‘MsiSummaryInfoGetPropertyCount()’.

 -- Method: SummaryInformation.SetProperty (field, value)

     Set a property through ‘MsiSummaryInfoSetProperty()’.  `field' can
     have the same values as in *note GetProperty(): 10fe, `value' is
     the new value of the property.  Possible value types are integer
     and string.

 -- Method: SummaryInformation.Persist ()

     Write the modified properties to the summary information stream,
     using ‘MsiSummaryInfoPersist()’.

See also
........

MsiSummaryInfoGetProperty(1) MsiSummaryInfoGetPropertyCount(2)
MsiSummaryInfoSetProperty(3) MsiSummaryInfoPersist(4)

   ---------- Footnotes ----------

   (1) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370409.aspx

   (2) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370488.aspx

   (3) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370491.aspx

   (4) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370490.aspx


File: python.info,  Node: Record Objects,  Next: Errors,  Prev: Summary Information Objects,  Up: msilib — Read and write Microsoft Installer files

5.34.1.4 Record Objects
.......................

 -- Method: Record.GetFieldCount ()

     Return the number of fields of the record, through
     ‘MsiRecordGetFieldCount()’.

 -- Method: Record.GetInteger (field)

     Return the value of `field' as an integer where possible.  `field'
     must be an integer.

 -- Method: Record.GetString (field)

     Return the value of `field' as a string where possible.  `field'
     must be an integer.

 -- Method: Record.SetString (field, value)

     Set `field' to `value' through ‘MsiRecordSetString()’.  `field'
     must be an integer; `value' a string.

 -- Method: Record.SetStream (field, value)

     Set `field' to the contents of the file named `value', through
     ‘MsiRecordSetStream()’.  `field' must be an integer; `value' a
     string.

 -- Method: Record.SetInteger (field, value)

     Set `field' to `value' through ‘MsiRecordSetInteger()’.  Both
     `field' and `value' must be an integer.

 -- Method: Record.ClearData ()

     Set all fields of the record to 0, through ‘MsiRecordClearData()’.

See also
........

MsiRecordGetFieldCount(1) MsiRecordSetString(2) MsiRecordSetStream(3)
MsiRecordSetInteger(4) MsiRecordClearData(5)

   ---------- Footnotes ----------

   (1) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370366.aspx

   (2) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370373.aspx

   (3) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370372.aspx

   (4) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370371.aspx

   (5) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370364.aspx


File: python.info,  Node: Errors,  Next: CAB Objects,  Prev: Record Objects,  Up: msilib — Read and write Microsoft Installer files

5.34.1.5 Errors
...............

All wrappers around MSI functions raise ‘MSIError’; the string inside
the exception will contain more detail.


File: python.info,  Node: CAB Objects,  Next: Directory Objects,  Prev: Errors,  Up: msilib — Read and write Microsoft Installer files

5.34.1.6 CAB Objects
....................

 -- Class: msilib.CAB (name)

     The class *note CAB: 3b81. represents a CAB file.  During MSI
     construction, files will be added simultaneously to the ‘Files’
     table, and to a CAB file.  Then, when all files have been added,
     the CAB file can be written, then added to the MSI file.

     `name' is the name of the CAB file in the MSI file.

      -- Method: append (full, file, logical)

          Add the file with the pathname `full' to the CAB file, under
          the name `logical'.  If there is already a file named
          `logical', a new file name is created.

          Return the index of the file in the CAB file, and the new name
          of the file inside the CAB file.

      -- Method: commit (database)

          Generate a CAB file, add it as a stream to the MSI file, put
          it into the ‘Media’ table, and remove the generated file from
          the disk.


File: python.info,  Node: Directory Objects,  Next: Features<3>,  Prev: CAB Objects,  Up: msilib — Read and write Microsoft Installer files

5.34.1.7 Directory Objects
..........................

 -- Class: msilib.Directory (database, cab, basedir, physical, logical,
          default[, componentflags])

     Create a new directory in the Directory table.  There is a current
     component at each point in time for the directory, which is either
     explicitly created through *note start_component(): 10ff, or
     implicitly when files are added for the first time.  Files are
     added into the current component, and into the cab file.  To create
     a directory, a base directory object needs to be specified (can be
     ‘None’), the path to the physical directory, and a logical
     directory name.  `default' specifies the DefaultDir slot in the
     directory table.  `componentflags' specifies the default flags that
     new components get.

      -- Method: start_component (component=None, feature=None,
               flags=None, keyfile=None, uuid=None)

          Add an entry to the Component table, and make this component
          the current component for this directory.  If no component
          name is given, the directory name is used.  If no `feature' is
          given, the current feature is used.  If no `flags' are given,
          the directory’s default flags are used.  If no `keyfile' is
          given, the KeyPath is left null in the Component table.

      -- Method: add_file (file, src=None, version=None, language=None)

          Add a file to the current component of the directory, starting
          a new one if there is no current component.  By default, the
          file name in the source and the file table will be identical.
          If the `src' file is specified, it is interpreted relative to
          the current directory.  Optionally, a `version' and a
          `language' can be specified for the entry in the File table.

      -- Method: glob (pattern, exclude=None)

          Add a list of files to the current component as specified in
          the glob pattern.  Individual files can be excluded in the
          `exclude' list.

      -- Method: remove_pyc ()

          Remove ‘.pyc’ files on uninstall.

See also
........

Directory Table(1) File Table(2) Component Table(3) FeatureComponents
Table(4)

   ---------- Footnotes ----------

   (1) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa368295.aspx

   (2) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa368596.aspx

   (3) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa368007.aspx

   (4) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa368579.aspx


File: python.info,  Node: Features<3>,  Next: GUI classes,  Prev: Directory Objects,  Up: msilib — Read and write Microsoft Installer files

5.34.1.8 Features
.................

 -- Class: msilib.Feature (db, id, title, desc, display, level=1,
          parent=None, directory=None, attributes=0)

     Add a new record to the ‘Feature’ table, using the values `id',
     `parent.id', `title', `desc', `display', `level', `directory', and
     `attributes'.  The resulting feature object can be passed to the
     ‘start_component()’ method of *note Directory: 3b86.

      -- Method: set_current ()

          Make this feature the current feature of *note msilib: b5.
          New components are automatically added to the default feature,
          unless a feature is explicitly specified.

See also
........

Feature Table(1)

   ---------- Footnotes ----------

   (1) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa368585.aspx


File: python.info,  Node: GUI classes,  Next: Precomputed tables,  Prev: Features<3>,  Up: msilib — Read and write Microsoft Installer files

5.34.1.9 GUI classes
....................

*note msilib: b5. provides several classes that wrap the GUI tables in
an MSI database.  However, no standard user interface is provided; use
*note bdist_msi: 40. to create MSI files with a user-interface for
installing Python packages.

 -- Class: msilib.Control (dlg, name)

     Base class of the dialog controls.  `dlg' is the dialog object the
     control belongs to, and `name' is the control’s name.

      -- Method: event (event, argument, condition=1, ordering=None)

          Make an entry into the ‘ControlEvent’ table for this control.

      -- Method: mapping (event, attribute)

          Make an entry into the ‘EventMapping’ table for this control.

      -- Method: condition (action, condition)

          Make an entry into the ‘ControlCondition’ table for this
          control.

 -- Class: msilib.RadioButtonGroup (dlg, name, property)

     Create a radio button control named `name'.  `property' is the
     installer property that gets set when a radio button is selected.

      -- Method: add (name, x, y, width, height, text, value=None)

          Add a radio button named `name' to the group, at the
          coordinates `x', `y', `width', `height', and with the label
          `text'.  If `value' is ‘None’, it defaults to `name'.

 -- Class: msilib.Dialog (db, name, x, y, w, h, attr, title, first,
          default, cancel)

     Return a new *note Dialog: 3b96. object.  An entry in the ‘Dialog’
     table is made, with the specified coordinates, dialog attributes,
     title, name of the first, default, and cancel controls.

      -- Method: control (name, type, x, y, width, height, attributes,
               property, text, control_next, help)

          Return a new *note Control: 3b90. object.  An entry in the
          ‘Control’ table is made with the specified parameters.

          This is a generic method; for specific types, specialized
          methods are provided.

      -- Method: text (name, x, y, width, height, attributes, text)

          Add and return a ‘Text’ control.

      -- Method: bitmap (name, x, y, width, height, text)

          Add and return a ‘Bitmap’ control.

      -- Method: line (name, x, y, width, height)

          Add and return a ‘Line’ control.

      -- Method: pushbutton (name, x, y, width, height, attributes,
               text, next_control)

          Add and return a ‘PushButton’ control.

      -- Method: radiogroup (name, x, y, width, height, attributes,
               property, text, next_control)

          Add and return a ‘RadioButtonGroup’ control.

      -- Method: checkbox (name, x, y, width, height, attributes,
               property, text, next_control)

          Add and return a ‘CheckBox’ control.

See also
........

Dialog Table(1) Control Table(2) Control Types(3) ControlCondition
Table(4) ControlEvent Table(5) EventMapping Table(6) RadioButton
Table(7)

   ---------- Footnotes ----------

   (1) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa368286.aspx

   (2) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa368044.aspx

   (3) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa368039.aspx

   (4) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa368035.aspx

   (5) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa368037.aspx

   (6) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa368559.aspx

   (7) 
https://msdn.microsoft.com/en-us/library/windows/desktop/aa370962.aspx


File: python.info,  Node: Precomputed tables,  Prev: GUI classes,  Up: msilib — Read and write Microsoft Installer files

5.34.1.10 Precomputed tables
............................

*note msilib: b5. provides a few subpackages that contain only schema
and table definitions.  Currently, these definitions are based on MSI
version 2.0.

 -- Data: msilib.schema

     This is the standard MSI schema for MSI 2.0, with the `tables'
     variable providing a list of table definitions, and
     `_Validation_records' providing the data for MSI validation.

 -- Data: msilib.sequence

     This module contains table contents for the standard sequence
     tables: `AdminExecuteSequence', `AdminUISequence',
     `AdvtExecuteSequence', `InstallExecuteSequence', and
     `InstallUISequence'.

 -- Data: msilib.text

     This module contains definitions for the UIText and ActionText
     tables, for the standard installer actions.


File: python.info,  Node: msvcrt — Useful routines from the MS VC++ runtime,  Next: winreg — Windows registry access,  Prev: msilib — Read and write Microsoft Installer files,  Up: MS Windows Specific Services

5.34.2 ‘msvcrt’ — Useful routines from the MS VC++ runtime
----------------------------------------------------------

__________________________________________________________________

These functions provide access to some useful capabilities on Windows
platforms.  Some higher-level modules use these functions to build the
Windows implementations of their services.  For example, the *note
getpass: 86. module uses this in the implementation of the *note
getpass(): 86. function.

Further documentation on these functions can be found in the Platform
API documentation.

The module implements both the normal and wide char variants of the
console I/O api.  The normal API deals only with ASCII characters and is
of limited use for internationalized applications.  The wide char API
should be used where ever possible.

Changed in version 3.3: Operations in this module now raise *note
OSError: 304. where *note IOError: a73. was raised.

* Menu:

* File Operations::
* Console I/O::
* Other Functions::


File: python.info,  Node: File Operations,  Next: Console I/O,  Up: msvcrt — Useful routines from the MS VC++ runtime

5.34.2.1 File Operations
........................

 -- Function: msvcrt.locking (fd, mode, nbytes)

     Lock part of a file based on file descriptor `fd' from the C
     runtime.  Raises *note OSError: 304. on failure.  The locked region
     of the file extends from the current file position for `nbytes'
     bytes, and may continue beyond the end of the file.  `mode' must be
     one of the ‘LK_*’ constants listed below.  Multiple regions in a
     file may be locked at the same time, but may not overlap.  Adjacent
     regions are not merged; they must be unlocked individually.

     Raises an *note auditing event: fa1. ‘msvcrt.locking’ with
     arguments ‘fd’, ‘mode’, ‘nbytes’.

 -- Data: msvcrt.LK_LOCK
 -- Data: msvcrt.LK_RLCK

     Locks the specified bytes.  If the bytes cannot be locked, the
     program immediately tries again after 1 second.  If, after 10
     attempts, the bytes cannot be locked, *note OSError: 304. is
     raised.

 -- Data: msvcrt.LK_NBLCK
 -- Data: msvcrt.LK_NBRLCK

     Locks the specified bytes.  If the bytes cannot be locked, *note
     OSError: 304. is raised.

 -- Data: msvcrt.LK_UNLCK

     Unlocks the specified bytes, which must have been previously
     locked.

 -- Function: msvcrt.setmode (fd, flags)

     Set the line-end translation mode for the file descriptor `fd'.  To
     set it to text mode, `flags' should be *note os.O_TEXT: 2085.; for
     binary, it should be *note os.O_BINARY: 2076.

 -- Function: msvcrt.open_osfhandle (handle, flags)

     Create a C runtime file descriptor from the file handle `handle'.
     The `flags' parameter should be a bitwise OR of *note os.O_APPEND:
     2078, *note os.O_RDONLY: 2074, and *note os.O_TEXT: 2085.  The
     returned file descriptor may be used as a parameter to *note
     os.fdopen(): 1564. to create a file object.

     Raises an *note auditing event: fa1. ‘msvcrt.open_osfhandle’ with
     arguments ‘handle’, ‘flags’.

 -- Function: msvcrt.get_osfhandle (fd)

     Return the file handle for the file descriptor `fd'.  Raises *note
     OSError: 304. if `fd' is not recognized.

     Raises an *note auditing event: fa1. ‘msvcrt.get_osfhandle’ with
     argument ‘fd’.


File: python.info,  Node: Console I/O,  Next: Other Functions,  Prev: File Operations,  Up: msvcrt — Useful routines from the MS VC++ runtime

5.34.2.2 Console I/O
....................

 -- Function: msvcrt.kbhit ()

     Return ‘True’ if a keypress is waiting to be read.

 -- Function: msvcrt.getch ()

     Read a keypress and return the resulting character as a byte
     string.  Nothing is echoed to the console.  This call will block if
     a keypress is not already available, but will not wait for ‘Enter’
     to be pressed.  If the pressed key was a special function key, this
     will return ‘'\000'’ or ‘'\xe0'’; the next call will return the
     keycode.  The ‘Control-C’ keypress cannot be read with this
     function.

 -- Function: msvcrt.getwch ()

     Wide char variant of *note getch(): 3bb2, returning a Unicode
     value.

 -- Function: msvcrt.getche ()

     Similar to *note getch(): 3bb2, but the keypress will be echoed if
     it represents a printable character.

 -- Function: msvcrt.getwche ()

     Wide char variant of *note getche(): 3bb4, returning a Unicode
     value.

 -- Function: msvcrt.putch (char)

     Print the byte string `char' to the console without buffering.

 -- Function: msvcrt.putwch (unicode_char)

     Wide char variant of *note putch(): 3bb6, accepting a Unicode
     value.

 -- Function: msvcrt.ungetch (char)

     Cause the byte string `char' to be “pushed back” into the console
     buffer; it will be the next character read by *note getch(): 3bb2.
     or *note getche(): 3bb4.

 -- Function: msvcrt.ungetwch (unicode_char)

     Wide char variant of *note ungetch(): 3bb8, accepting a Unicode
     value.


File: python.info,  Node: Other Functions,  Prev: Console I/O,  Up: msvcrt — Useful routines from the MS VC++ runtime

5.34.2.3 Other Functions
........................

 -- Function: msvcrt.heapmin ()

     Force the ‘malloc()’ heap to clean itself up and return unused
     blocks to the operating system.  On failure, this raises *note
     OSError: 304.


File: python.info,  Node: winreg — Windows registry access,  Next: winsound — Sound-playing interface for Windows,  Prev: msvcrt — Useful routines from the MS VC++ runtime,  Up: MS Windows Specific Services

5.34.3 ‘winreg’ — Windows registry access
-----------------------------------------

__________________________________________________________________

These functions expose the Windows registry API to Python.  Instead of
using an integer as the registry handle, a *note handle object: 3bbf. is
used to ensure that the handles are closed correctly, even if the
programmer neglects to explicitly close them.

Changed in version 3.3: Several functions in this module used to raise a
*note WindowsError: a75, which is now an alias of *note OSError: 304.

* Menu:

* Functions: Functions<12>.
* Constants: Constants<10>.
* Registry Handle Objects::


File: python.info,  Node: Functions<12>,  Next: Constants<10>,  Up: winreg — Windows registry access

5.34.3.1 Functions
..................

This module offers the following functions:

 -- Function: winreg.CloseKey (hkey)

     Closes a previously opened registry key.  The `hkey' argument
     specifies a previously opened key.

          Note: If `hkey' is not closed using this method (or via *note
          hkey.Close(): 3bc4.), it is closed when the `hkey' object is
          destroyed by Python.

 -- Function: winreg.ConnectRegistry (computer_name, key)

     Establishes a connection to a predefined registry handle on another
     computer, and returns a *note handle object: 3bbf.

     `computer_name' is the name of the remote computer, of the form
     ‘r"\\computername"’.  If ‘None’, the local computer is used.

     `key' is the predefined handle to connect to.

     The return value is the handle of the opened key.  If the function
     fails, an *note OSError: 304. exception is raised.

     Raises an *note auditing event: fa1. ‘winreg.ConnectRegistry’ with
     arguments ‘computer_name’, ‘key’.

     Changed in version 3.3: See *note above: 3bc0.

 -- Function: winreg.CreateKey (key, sub_key)

     Creates or opens the specified key, returning a *note handle
     object: 3bbf.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `sub_key' is a string that names the key this method opens or
     creates.

     If `key' is one of the predefined keys, `sub_key' may be ‘None’.
     In that case, the handle returned is the same key handle passed in
     to the function.

     If the key already exists, this function opens the existing key.

     The return value is the handle of the opened key.  If the function
     fails, an *note OSError: 304. exception is raised.

     Raises an *note auditing event: fa1. ‘winreg.CreateKey’ with
     arguments ‘key’, ‘sub_key’, ‘access’.

     Raises an *note auditing event: fa1. ‘winreg.OpenKey/result’ with
     argument ‘key’.

     Changed in version 3.3: See *note above: 3bc0.

 -- Function: winreg.CreateKeyEx (key, sub_key, reserved=0,
          access=KEY_WRITE)

     Creates or opens the specified key, returning a *note handle
     object: 3bbf.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `sub_key' is a string that names the key this method opens or
     creates.

     `reserved' is a reserved integer, and must be zero.  The default is
     zero.

     `access' is an integer that specifies an access mask that describes
     the desired security access for the key.  Default is *note
     KEY_WRITE: 3bc9.  See *note Access Rights: 3bca. for other allowed
     values.

     If `key' is one of the predefined keys, `sub_key' may be ‘None’.
     In that case, the handle returned is the same key handle passed in
     to the function.

     If the key already exists, this function opens the existing key.

     The return value is the handle of the opened key.  If the function
     fails, an *note OSError: 304. exception is raised.

     Raises an *note auditing event: fa1. ‘winreg.CreateKey’ with
     arguments ‘key’, ‘sub_key’, ‘access’.

     Raises an *note auditing event: fa1. ‘winreg.OpenKey/result’ with
     argument ‘key’.

     New in version 3.2.

     Changed in version 3.3: See *note above: 3bc0.

 -- Function: winreg.DeleteKey (key, sub_key)

     Deletes the specified key.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `sub_key' is a string that must be a subkey of the key identified
     by the `key' parameter.  This value must not be ‘None’, and the key
     may not have subkeys.

     `This method can not delete keys with subkeys.'

     If the method succeeds, the entire key, including all of its
     values, is removed.  If the method fails, an *note OSError: 304.
     exception is raised.

     Raises an *note auditing event: fa1. ‘winreg.DeleteKey’ with
     arguments ‘key’, ‘sub_key’, ‘access’.

     Changed in version 3.3: See *note above: 3bc0.

 -- Function: winreg.DeleteKeyEx (key, sub_key, access=KEY_WOW64_64KEY,
          reserved=0)

     Deletes the specified key.

          Note: The *note DeleteKeyEx(): 3bcc. function is implemented
          with the RegDeleteKeyEx Windows API function, which is
          specific to 64-bit versions of Windows.  See the
          RegDeleteKeyEx documentation(1).

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `sub_key' is a string that must be a subkey of the key identified
     by the `key' parameter.  This value must not be ‘None’, and the key
     may not have subkeys.

     `reserved' is a reserved integer, and must be zero.  The default is
     zero.

     `access' is an integer that specifies an access mask that describes
     the desired security access for the key.  Default is *note
     KEY_WOW64_64KEY: 3bcd.  See *note Access Rights: 3bca. for other
     allowed values.

     `This method can not delete keys with subkeys.'

     If the method succeeds, the entire key, including all of its
     values, is removed.  If the method fails, an *note OSError: 304.
     exception is raised.

     On unsupported Windows versions, *note NotImplementedError: 704. is
     raised.

     Raises an *note auditing event: fa1. ‘winreg.DeleteKey’ with
     arguments ‘key’, ‘sub_key’, ‘access’.

     New in version 3.2.

     Changed in version 3.3: See *note above: 3bc0.

 -- Function: winreg.DeleteValue (key, value)

     Removes a named value from a registry key.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `value' is a string that identifies the value to remove.

     Raises an *note auditing event: fa1. ‘winreg.DeleteValue’ with
     arguments ‘key’, ‘value’.

 -- Function: winreg.EnumKey (key, index)

     Enumerates subkeys of an open registry key, returning a string.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `index' is an integer that identifies the index of the key to
     retrieve.

     The function retrieves the name of one subkey each time it is
     called.  It is typically called repeatedly until an *note OSError:
     304. exception is raised, indicating, no more values are available.

     Raises an *note auditing event: fa1. ‘winreg.EnumKey’ with
     arguments ‘key’, ‘index’.

     Changed in version 3.3: See *note above: 3bc0.

 -- Function: winreg.EnumValue (key, index)

     Enumerates values of an open registry key, returning a tuple.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `index' is an integer that identifies the index of the value to
     retrieve.

     The function retrieves the name of one subkey each time it is
     called.  It is typically called repeatedly, until an *note OSError:
     304. exception is raised, indicating no more values.

     The result is a tuple of 3 items:

     Index       Meaning
                 
     -------------------------------------------------------------
                 
     ‘0’         A string that identifies the value name
                 
                 
     ‘1’         An object that holds the value data, and whose
                 type depends on the underlying registry type
                 
                 
     ‘2’         An integer that identifies the type of the
                 value data (see table in docs for
                 *note SetValueEx(): 3bd1.)
                 

     Raises an *note auditing event: fa1. ‘winreg.EnumValue’ with
     arguments ‘key’, ‘index’.

     Changed in version 3.3: See *note above: 3bc0.

 -- Function: winreg.ExpandEnvironmentStrings (str)

     Expands environment variable placeholders ‘%NAME%’ in strings like
     *note REG_EXPAND_SZ: 3bd3.:

          >>> ExpandEnvironmentStrings('%windir%')
          'C:\\Windows'

     Raises an *note auditing event: fa1.
     ‘winreg.ExpandEnvironmentStrings’ with argument ‘str’.

 -- Function: winreg.FlushKey (key)

     Writes all the attributes of a key to the registry.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     It is not necessary to call *note FlushKey(): 3bd4. to change a
     key.  Registry changes are flushed to disk by the registry using
     its lazy flusher.  Registry changes are also flushed to disk at
     system shutdown.  Unlike *note CloseKey(): 3bc3, the *note
     FlushKey(): 3bd4. method returns only when all the data has been
     written to the registry.  An application should only call *note
     FlushKey(): 3bd4. if it requires absolute certainty that registry
     changes are on disk.

          Note: If you don’t know whether a *note FlushKey(): 3bd4. call
          is required, it probably isn’t.

 -- Function: winreg.LoadKey (key, sub_key, file_name)

     Creates a subkey under the specified key and stores registration
     information from a specified file into that subkey.

     `key' is a handle returned by *note ConnectRegistry(): 3bc5. or one
     of the constants *note HKEY_USERS: 3bd6. or *note
     HKEY_LOCAL_MACHINE: 3bd7.

     `sub_key' is a string that identifies the subkey to load.

     `file_name' is the name of the file to load registry data from.
     This file must have been created with the *note SaveKey(): 3bd8.
     function.  Under the file allocation table (FAT) file system, the
     filename may not have an extension.

     A call to *note LoadKey(): 3bd5. fails if the calling process does
     not have the ‘SE_RESTORE_PRIVILEGE’ privilege.  Note that
     privileges are different from permissions – see the RegLoadKey
     documentation(2) for more details.

     If `key' is a handle returned by *note ConnectRegistry(): 3bc5,
     then the path specified in `file_name' is relative to the remote
     computer.

     Raises an *note auditing event: fa1. ‘winreg.LoadKey’ with
     arguments ‘key’, ‘sub_key’, ‘file_name’.

 -- Function: winreg.OpenKey (key, sub_key, reserved=0, access=KEY_READ)
 -- Function: winreg.OpenKeyEx (key, sub_key, reserved=0,
          access=KEY_READ)

     Opens the specified key, returning a *note handle object: 3bbf.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `sub_key' is a string that identifies the sub_key to open.

     `reserved' is a reserved integer, and must be zero.  The default is
     zero.

     `access' is an integer that specifies an access mask that describes
     the desired security access for the key.  Default is *note
     KEY_READ: 3bdb.  See *note Access Rights: 3bca. for other allowed
     values.

     The result is a new handle to the specified key.

     If the function fails, *note OSError: 304. is raised.

     Raises an *note auditing event: fa1. ‘winreg.OpenKey’ with
     arguments ‘key’, ‘sub_key’, ‘access’.

     Raises an *note auditing event: fa1. ‘winreg.OpenKey/result’ with
     argument ‘key’.

     Changed in version 3.2: Allow the use of named arguments.

     Changed in version 3.3: See *note above: 3bc0.

 -- Function: winreg.QueryInfoKey (key)

     Returns information about a key, as a tuple.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     The result is a tuple of 3 items:

     Index       Meaning
                 
     --------------------------------------------------------------
                 
     ‘0’         An integer giving the number of sub keys this
                 key has.
                 
                 
     ‘1’         An integer giving the number of values this key
                 has.
                 
                 
     ‘2’         An integer giving when the key was last
                 modified (if available) as 100’s of nanoseconds
                 since Jan 1, 1601.
                 

     Raises an *note auditing event: fa1. ‘winreg.QueryInfoKey’ with
     argument ‘key’.

 -- Function: winreg.QueryValue (key, sub_key)

     Retrieves the unnamed value for a key, as a string.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `sub_key' is a string that holds the name of the subkey with which
     the value is associated.  If this parameter is ‘None’ or empty, the
     function retrieves the value set by the *note SetValue(): 3bde.
     method for the key identified by `key'.

     Values in the registry have name, type, and data components.  This
     method retrieves the data for a key’s first value that has a ‘NULL’
     name.  But the underlying API call doesn’t return the type, so
     always use *note QueryValueEx(): 3bdf. if possible.

     Raises an *note auditing event: fa1. ‘winreg.QueryValue’ with
     arguments ‘key’, ‘sub_key’, ‘value_name’.

 -- Function: winreg.QueryValueEx (key, value_name)

     Retrieves the type and data for a specified value name associated
     with an open registry key.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `value_name' is a string indicating the value to query.

     The result is a tuple of 2 items:

     Index       Meaning
                 
     ----------------------------------------------------------
                 
     ‘0’         The value of the registry item.
                 
                 
     ‘1’         An integer giving the registry type for
                 this value (see table in docs for
                 *note SetValueEx(): 3bd1.)
                 

     Raises an *note auditing event: fa1. ‘winreg.QueryValue’ with
     arguments ‘key’, ‘sub_key’, ‘value_name’.

 -- Function: winreg.SaveKey (key, file_name)

     Saves the specified key, and all its subkeys to the specified file.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `file_name' is the name of the file to save registry data to.  This
     file cannot already exist.  If this filename includes an extension,
     it cannot be used on file allocation table (FAT) file systems by
     the *note LoadKey(): 3bd5. method.

     If `key' represents a key on a remote computer, the path described
     by `file_name' is relative to the remote computer.  The caller of
     this method must possess the ‘SeBackupPrivilege’ security
     privilege.  Note that privileges are different than permissions –
     see the Conflicts Between User Rights and Permissions
     documentation(3) for more details.

     This function passes ‘NULL’ for `security_attributes' to the API.

     Raises an *note auditing event: fa1. ‘winreg.SaveKey’ with
     arguments ‘key’, ‘file_name’.

 -- Function: winreg.SetValue (key, sub_key, type, value)

     Associates a value with a specified key.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `sub_key' is a string that names the subkey with which the value is
     associated.

     `type' is an integer that specifies the type of the data.
     Currently this must be *note REG_SZ: 3be0, meaning only strings are
     supported.  Use the *note SetValueEx(): 3bd1. function for support
     for other data types.

     `value' is a string that specifies the new value.

     If the key specified by the `sub_key' parameter does not exist, the
     SetValue function creates it.

     Value lengths are limited by available memory.  Long values (more
     than 2048 bytes) should be stored as files with the filenames
     stored in the configuration registry.  This helps the registry
     perform efficiently.

     The key identified by the `key' parameter must have been opened
     with *note KEY_SET_VALUE: 3be1. access.

     Raises an *note auditing event: fa1. ‘winreg.SetValue’ with
     arguments ‘key’, ‘sub_key’, ‘type’, ‘value’.

 -- Function: winreg.SetValueEx (key, value_name, reserved, type, value)

     Stores data in the value field of an open registry key.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     `value_name' is a string that names the subkey with which the value
     is associated.

     `reserved' can be anything – zero is always passed to the API.

     `type' is an integer that specifies the type of the data.  See
     *note Value Types: 3be2. for the available types.

     `value' is a string that specifies the new value.

     This method can also set additional value and type information for
     the specified key.  The key identified by the key parameter must
     have been opened with *note KEY_SET_VALUE: 3be1. access.

     To open the key, use the *note CreateKey(): 3bc6. or *note
     OpenKey(): 3bd9. methods.

     Value lengths are limited by available memory.  Long values (more
     than 2048 bytes) should be stored as files with the filenames
     stored in the configuration registry.  This helps the registry
     perform efficiently.

     Raises an *note auditing event: fa1. ‘winreg.SetValue’ with
     arguments ‘key’, ‘sub_key’, ‘type’, ‘value’.

 -- Function: winreg.DisableReflectionKey (key)

     Disables registry reflection for 32-bit processes running on a
     64-bit operating system.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     Will generally raise *note NotImplementedError: 704. if executed on
     a 32-bit operating system.

     If the key is not on the reflection list, the function succeeds but
     has no effect.  Disabling reflection for a key does not affect
     reflection of any subkeys.

     Raises an *note auditing event: fa1. ‘winreg.DisableReflectionKey’
     with argument ‘key’.

 -- Function: winreg.EnableReflectionKey (key)

     Restores registry reflection for the specified disabled key.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     Will generally raise *note NotImplementedError: 704. if executed on
     a 32-bit operating system.

     Restoring reflection for a key does not affect reflection of any
     subkeys.

     Raises an *note auditing event: fa1. ‘winreg.EnableReflectionKey’
     with argument ‘key’.

 -- Function: winreg.QueryReflectionKey (key)

     Determines the reflection state for the specified key.

     `key' is an already open key, or one of the predefined *note HKEY_*
     constants: 3bc7.

     Returns ‘True’ if reflection is disabled.

     Will generally raise *note NotImplementedError: 704. if executed on
     a 32-bit operating system.

     Raises an *note auditing event: fa1. ‘winreg.QueryReflectionKey’
     with argument ‘key’.

   ---------- Footnotes ----------

   (1) https://msdn.microsoft.com/en-us/library/ms724847%28VS.85%29.aspx

   (2) 
https://msdn.microsoft.com/en-us/library/ms724889%28v=VS.85%29.aspx

   (3) 
https://msdn.microsoft.com/en-us/library/ms724878%28v=VS.85%29.aspx


File: python.info,  Node: Constants<10>,  Next: Registry Handle Objects,  Prev: Functions<12>,  Up: winreg — Windows registry access

5.34.3.2 Constants
..................

The following constants are defined for use in many ‘_winreg’ functions.

* Menu:

* HKEY_* Constants::
* Access Rights::
* Value Types::


File: python.info,  Node: HKEY_* Constants,  Next: Access Rights,  Up: Constants<10>

5.34.3.3 HKEY_* Constants
.........................

 -- Data: winreg.HKEY_CLASSES_ROOT

     Registry entries subordinate to this key define types (or classes)
     of documents and the properties associated with those types.  Shell
     and COM applications use the information stored under this key.

 -- Data: winreg.HKEY_CURRENT_USER

     Registry entries subordinate to this key define the preferences of
     the current user.  These preferences include the settings of
     environment variables, data about program groups, colors, printers,
     network connections, and application preferences.

 -- Data: winreg.HKEY_LOCAL_MACHINE

     Registry entries subordinate to this key define the physical state
     of the computer, including data about the bus type, system memory,
     and installed hardware and software.

 -- Data: winreg.HKEY_USERS

     Registry entries subordinate to this key define the default user
     configuration for new users on the local computer and the user
     configuration for the current user.

 -- Data: winreg.HKEY_PERFORMANCE_DATA

     Registry entries subordinate to this key allow you to access
     performance data.  The data is not actually stored in the registry;
     the registry functions cause the system to collect the data from
     its source.

 -- Data: winreg.HKEY_CURRENT_CONFIG

     Contains information about the current hardware profile of the
     local computer system.

 -- Data: winreg.HKEY_DYN_DATA

     This key is not used in versions of Windows after 98.


File: python.info,  Node: Access Rights,  Next: Value Types,  Prev: HKEY_* Constants,  Up: Constants<10>

5.34.3.4 Access Rights
......................

For more information, see Registry Key Security and Access(1).

 -- Data: winreg.KEY_ALL_ACCESS

     Combines the STANDARD_RIGHTS_REQUIRED, *note KEY_QUERY_VALUE: 3bf0,
     *note KEY_SET_VALUE: 3be1, *note KEY_CREATE_SUB_KEY: 3bf1, *note
     KEY_ENUMERATE_SUB_KEYS: 3bf2, *note KEY_NOTIFY: 3bf3, and *note
     KEY_CREATE_LINK: 3bf4. access rights.

 -- Data: winreg.KEY_WRITE

     Combines the STANDARD_RIGHTS_WRITE, *note KEY_SET_VALUE: 3be1, and
     *note KEY_CREATE_SUB_KEY: 3bf1. access rights.

 -- Data: winreg.KEY_READ

     Combines the STANDARD_RIGHTS_READ, *note KEY_QUERY_VALUE: 3bf0,
     *note KEY_ENUMERATE_SUB_KEYS: 3bf2, and *note KEY_NOTIFY: 3bf3.
     values.

 -- Data: winreg.KEY_EXECUTE

     Equivalent to *note KEY_READ: 3bdb.

 -- Data: winreg.KEY_QUERY_VALUE

     Required to query the values of a registry key.

 -- Data: winreg.KEY_SET_VALUE

     Required to create, delete, or set a registry value.

 -- Data: winreg.KEY_CREATE_SUB_KEY

     Required to create a subkey of a registry key.

 -- Data: winreg.KEY_ENUMERATE_SUB_KEYS

     Required to enumerate the subkeys of a registry key.

 -- Data: winreg.KEY_NOTIFY

     Required to request change notifications for a registry key or for
     subkeys of a registry key.

 -- Data: winreg.KEY_CREATE_LINK

     Reserved for system use.

* Menu:

* 64-bit Specific::

   ---------- Footnotes ----------

   (1) 
https://msdn.microsoft.com/en-us/library/ms724878%28v=VS.85%29.aspx


File: python.info,  Node: 64-bit Specific,  Up: Access Rights

5.34.3.5 64-bit Specific
........................

For more information, see Accessing an Alternate Registry View(1).

 -- Data: winreg.KEY_WOW64_64KEY

     Indicates that an application on 64-bit Windows should operate on
     the 64-bit registry view.

 -- Data: winreg.KEY_WOW64_32KEY

     Indicates that an application on 64-bit Windows should operate on
     the 32-bit registry view.

   ---------- Footnotes ----------

   (1) https://msdn.microsoft.com/en-us/library/aa384129(v=VS.85).aspx


File: python.info,  Node: Value Types,  Prev: Access Rights,  Up: Constants<10>

5.34.3.6 Value Types
....................

For more information, see Registry Value Types(1).

 -- Data: winreg.REG_BINARY

     Binary data in any form.

 -- Data: winreg.REG_DWORD

     32-bit number.

 -- Data: winreg.REG_DWORD_LITTLE_ENDIAN

     A 32-bit number in little-endian format.  Equivalent to *note
     REG_DWORD: 3bfb.

 -- Data: winreg.REG_DWORD_BIG_ENDIAN

     A 32-bit number in big-endian format.

 -- Data: winreg.REG_EXPAND_SZ

     Null-terminated string containing references to environment
     variables (‘%PATH%’).

 -- Data: winreg.REG_LINK

     A Unicode symbolic link.

 -- Data: winreg.REG_MULTI_SZ

     A sequence of null-terminated strings, terminated by two null
     characters.  (Python handles this termination automatically.)

 -- Data: winreg.REG_NONE

     No defined value type.

 -- Data: winreg.REG_QWORD

     A 64-bit number.

     New in version 3.6.

 -- Data: winreg.REG_QWORD_LITTLE_ENDIAN

     A 64-bit number in little-endian format.  Equivalent to *note
     REG_QWORD: 6a9.

     New in version 3.6.

 -- Data: winreg.REG_RESOURCE_LIST

     A device-driver resource list.

 -- Data: winreg.REG_FULL_RESOURCE_DESCRIPTOR

     A hardware setting.

 -- Data: winreg.REG_RESOURCE_REQUIREMENTS_LIST

     A hardware resource list.

 -- Data: winreg.REG_SZ

     A null-terminated string.

   ---------- Footnotes ----------

   (1) 
https://msdn.microsoft.com/en-us/library/ms724884%28v=VS.85%29.aspx


File: python.info,  Node: Registry Handle Objects,  Prev: Constants<10>,  Up: winreg — Windows registry access

5.34.3.7 Registry Handle Objects
................................

This object wraps a Windows HKEY object, automatically closing it when
the object is destroyed.  To guarantee cleanup, you can call either the
*note Close(): 3bc4. method on the object, or the *note CloseKey():
3bc3. function.

All registry functions in this module return one of these objects.

All registry functions in this module which accept a handle object also
accept an integer, however, use of the handle object is encouraged.

Handle objects provide semantics for *note __bool__(): d30. – thus

     if handle:
         print("Yes")

will print ‘Yes’ if the handle is currently valid (has not been closed
or detached).

The object also support comparison semantics, so handle objects will
compare true if they both reference the same underlying Windows handle
value.

Handle objects can be converted to an integer (e.g., using the built-in
*note int(): 204. function), in which case the underlying Windows handle
value is returned.  You can also use the *note Detach(): 3c05. method to
return the integer handle, and also disconnect the Windows handle from
the handle object.

 -- Method: PyHKEY.Close ()

     Closes the underlying Windows handle.

     If the handle is already closed, no error is raised.

 -- Method: PyHKEY.Detach ()

     Detaches the Windows handle from the handle object.

     The result is an integer that holds the value of the handle before
     it is detached.  If the handle is already detached or closed, this
     will return zero.

     After calling this function, the handle is effectively invalidated,
     but the handle is not closed.  You would call this function when
     you need the underlying Win32 handle to exist beyond the lifetime
     of the handle object.

     Raises an *note auditing event: fa1. ‘winreg.PyHKEY.Detach’ with
     argument ‘key’.

 -- Method: PyHKEY.__enter__ ()
 -- Method: PyHKEY.__exit__ (*exc_info)

     The HKEY object implements *note __enter__(): d5d. and *note
     __exit__(): d5e. and thus supports the context protocol for the
     *note with: 7da. statement:

          with OpenKey(HKEY_LOCAL_MACHINE, "foo") as key:
              ...  # work with key

     will automatically close `key' when control leaves the *note with:
     7da. block.


File: python.info,  Node: winsound — Sound-playing interface for Windows,  Prev: winreg — Windows registry access,  Up: MS Windows Specific Services

5.34.4 ‘winsound’ — Sound-playing interface for Windows
-------------------------------------------------------

__________________________________________________________________

The *note winsound: 134. module provides access to the basic
sound-playing machinery provided by Windows platforms.  It includes
functions and several constants.

 -- Function: winsound.Beep (frequency, duration)

     Beep the PC’s speaker.  The `frequency' parameter specifies
     frequency, in hertz, of the sound, and must be in the range 37
     through 32,767.  The `duration' parameter specifies the number of
     milliseconds the sound should last.  If the system is not able to
     beep the speaker, *note RuntimeError: 3dc. is raised.

 -- Function: winsound.PlaySound (sound, flags)

     Call the underlying ‘PlaySound()’ function from the Platform API.
     The `sound' parameter may be a filename, a system sound alias,
     audio data as a *note bytes-like object: 6df, or ‘None’.  Its
     interpretation depends on the value of `flags', which can be a
     bitwise ORed combination of the constants described below.  If the
     `sound' parameter is ‘None’, any currently playing waveform sound
     is stopped.  If the system indicates an error, *note RuntimeError:
     3dc. is raised.

 -- Function: winsound.MessageBeep (type=MB_OK)

     Call the underlying ‘MessageBeep()’ function from the Platform API.
     This plays a sound as specified in the registry.  The `type'
     argument specifies which sound to play; possible values are ‘-1’,
     ‘MB_ICONASTERISK’, ‘MB_ICONEXCLAMATION’, ‘MB_ICONHAND’,
     ‘MB_ICONQUESTION’, and ‘MB_OK’, all described below.  The value
     ‘-1’ produces a “simple beep”; this is the final fallback if a
     sound cannot be played otherwise.  If the system indicates an
     error, *note RuntimeError: 3dc. is raised.

 -- Data: winsound.SND_FILENAME

     The `sound' parameter is the name of a WAV file.  Do not use with
     *note SND_ALIAS: 3c0b.

 -- Data: winsound.SND_ALIAS

     The `sound' parameter is a sound association name from the
     registry.  If the registry contains no such name, play the system
     default sound unless *note SND_NODEFAULT: 3c0c. is also specified.
     If no default sound is registered, raise *note RuntimeError: 3dc.
     Do not use with *note SND_FILENAME: 3c0a.

     All Win32 systems support at least the following; most systems
     support many more:

     *note PlaySound(): 6ad.        Corresponding Control Panel Sound name
     `name'                         

     ----------------------------------------------------------------------------
                                    
     ‘'SystemAsterisk'’             Asterisk
                                    
                                    
     ‘'SystemExclamation'’          Exclamation
                                    
                                    
     ‘'SystemExit'’                 Exit Windows
                                    
                                    
     ‘'SystemHand'’                 Critical Stop
                                    
                                    
     ‘'SystemQuestion'’             Question
                                    

     For example:

          import winsound
          # Play Windows exit sound.
          winsound.PlaySound("SystemExit", winsound.SND_ALIAS)

          # Probably play Windows default sound, if any is registered (because
          # "*" probably isn't the registered name of any sound).
          winsound.PlaySound("*", winsound.SND_ALIAS)

 -- Data: winsound.SND_LOOP

     Play the sound repeatedly.  The *note SND_ASYNC: 3c0e. flag must
     also be used to avoid blocking.  Cannot be used with *note
     SND_MEMORY: 3c0f.

 -- Data: winsound.SND_MEMORY

     The `sound' parameter to *note PlaySound(): 6ad. is a memory image
     of a WAV file, as a *note bytes-like object: 6df.

          Note: This module does not support playing from a memory image
          asynchronously, so a combination of this flag and *note
          SND_ASYNC: 3c0e. will raise *note RuntimeError: 3dc.

 -- Data: winsound.SND_PURGE

     Stop playing all instances of the specified sound.

          Note: This flag is not supported on modern Windows platforms.

 -- Data: winsound.SND_ASYNC

     Return immediately, allowing sounds to play asynchronously.

 -- Data: winsound.SND_NODEFAULT

     If the specified sound cannot be found, do not play the system
     default sound.

 -- Data: winsound.SND_NOSTOP

     Do not interrupt sounds currently playing.

 -- Data: winsound.SND_NOWAIT

     Return immediately if the sound driver is busy.

          Note: This flag is not supported on modern Windows platforms.

 -- Data: winsound.MB_ICONASTERISK

     Play the ‘SystemDefault’ sound.

 -- Data: winsound.MB_ICONEXCLAMATION

     Play the ‘SystemExclamation’ sound.

 -- Data: winsound.MB_ICONHAND

     Play the ‘SystemHand’ sound.

 -- Data: winsound.MB_ICONQUESTION

     Play the ‘SystemQuestion’ sound.

 -- Data: winsound.MB_OK

     Play the ‘SystemDefault’ sound.


File: python.info,  Node: Unix Specific Services,  Next: Superseded Modules,  Prev: MS Windows Specific Services,  Up: The Python Standard Library

5.35 Unix Specific Services
===========================

The modules described in this chapter provide interfaces to features
that are unique to the Unix operating system, or in some cases to some
or many variants of it.  Here’s an overview:

* Menu:

* posix — The most common POSIX system calls::
* pwd — The password database::
* spwd — The shadow password database::
* grp — The group database::
* crypt — Function to check Unix passwords::
* termios — POSIX style tty control::
* tty — Terminal control functions::
* pty — Pseudo-terminal utilities::
* fcntl — The fcntl and ioctl system calls::
* pipes — Interface to shell pipelines::
* resource — Resource usage information::
* nis — Interface to Sun’s NIS (Yellow Pages): nis — Interface to Sun’s NIS Yellow Pages.
* syslog — Unix syslog library routines::


File: python.info,  Node: posix — The most common POSIX system calls,  Next: pwd — The password database,  Up: Unix Specific Services

5.35.1 ‘posix’ — The most common POSIX system calls
---------------------------------------------------

__________________________________________________________________

This module provides access to operating system functionality that is
standardized by the C Standard and the POSIX standard (a thinly
disguised Unix interface).

`Do not import this module directly.'  Instead, import the module *note
os: c4, which provides a `portable' version of this interface.  On Unix,
the *note os: c4. module provides a superset of the *note posix: d1.
interface.  On non-Unix operating systems the *note posix: d1. module is
not available, but a subset is always available through the *note os:
c4. interface.  Once *note os: c4. is imported, there is `no'
performance penalty in using it instead of *note posix: d1.  In
addition, *note os: c4. provides some additional functionality, such as
automatically calling *note putenv(): 1cd. when an entry in ‘os.environ’
is changed.

Errors are reported as exceptions; the usual exceptions are given for
type errors, while errors reported by the system calls raise *note
OSError: 304.

* Menu:

* Large File Support::
* Notable Module Contents::


File: python.info,  Node: Large File Support,  Next: Notable Module Contents,  Up: posix — The most common POSIX system calls

5.35.1.1 Large File Support
...........................

Several operating systems (including AIX, HP-UX, Irix and Solaris)
provide support for files that are larger than 2 GiB from a C
programming model where ‘int’ and ‘long’ are 32-bit values.  This is
typically accomplished by defining the relevant size and offset types as
64-bit values.  Such files are sometimes referred to as `large files'.

Large file support is enabled in Python when the size of an ‘off_t’ is
larger than a ‘long’ and the ‘long long’ is at least as large as an
‘off_t’.  It may be necessary to configure and compile Python with
certain compiler flags to enable this mode.  For example, it is enabled
by default with recent versions of Irix, but with Solaris 2.6 and 2.7
you need to do something like:

     CFLAGS="`getconf LFS_CFLAGS`" OPT="-g -O2 $CFLAGS" \
             ./configure

On large-file-capable Linux systems, this might work:

     CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \
             ./configure


File: python.info,  Node: Notable Module Contents,  Prev: Large File Support,  Up: posix — The most common POSIX system calls

5.35.1.2 Notable Module Contents
................................

In addition to many functions described in the *note os: c4. module
documentation, *note posix: d1. defines the following data item:

 -- Data: posix.environ

     A dictionary representing the string environment at the time the
     interpreter was started.  Keys and values are bytes on Unix and str
     on Windows.  For example, ‘environ[b'HOME']’ (‘environ['HOME']’ on
     Windows) is the pathname of your home directory, equivalent to
     ‘getenv("HOME")’ in C.

     Modifying this dictionary does not affect the string environment
     passed on by *note execv(): 2058, *note popen(): 3cb. or *note
     system(): e86.; if you need to change the environment, pass
     ‘environ’ to *note execve(): b1b. or add variable assignments and
     export statements to the command string for *note system(): e86. or
     *note popen(): 3cb.

     Changed in version 3.2: On Unix, keys and values are bytes.

          Note: The *note os: c4. module provides an alternate
          implementation of ‘environ’ which updates the environment on
          modification.  Note also that updating *note os.environ: c09.
          will render this dictionary obsolete.  Use of the *note os:
          c4. module version of this is recommended over direct access
          to the *note posix: d1. module.


File: python.info,  Node: pwd — The password database,  Next: spwd — The shadow password database,  Prev: posix — The most common POSIX system calls,  Up: Unix Specific Services

5.35.2 ‘pwd’ — The password database
------------------------------------

__________________________________________________________________

This module provides access to the Unix user account and password
database.  It is available on all Unix versions.

Password database entries are reported as a tuple-like object, whose
attributes correspond to the members of the ‘passwd’ structure
(Attribute field below, see ‘<pwd.h>’):

Index       Attribute           Meaning
                                
------------------------------------------------------------------
                                
0           ‘pw_name’           Login name
                                
                                
1           ‘pw_passwd’         Optional encrypted password
                                
                                
2           ‘pw_uid’            Numerical user ID
                                
                                
3           ‘pw_gid’            Numerical group ID
                                
                                
4           ‘pw_gecos’          User name or comment field
                                
                                
5           ‘pw_dir’            User home directory
                                
                                
6           ‘pw_shell’          User command interpreter
                                

The uid and gid items are integers, all others are strings.  *note
KeyError: 3e9. is raised if the entry asked for cannot be found.

     Note: 
     In traditional Unix the field ‘pw_passwd’ usually contains a
     password encrypted with a DES derived algorithm (see module *note
     crypt: 28.).  However most modern unices use a so-called `shadow
     password' system.  On those unices the `pw_passwd' field only
     contains an asterisk (‘'*'’) or the letter ‘'x'’ where the
     encrypted password is stored in a file ‘/etc/shadow’ which is not
     world readable.  Whether the `pw_passwd' field contains anything
     useful is system-dependent.  If available, the *note spwd: f1.
     module should be used where access to the encrypted password is
     required.

It defines the following items:

 -- Function: pwd.getpwuid (uid)

     Return the password database entry for the given numeric user ID.

 -- Function: pwd.getpwnam (name)

     Return the password database entry for the given user name.

 -- Function: pwd.getpwall ()

     Return a list of all available password database entries, in
     arbitrary order.

See also
........

Module *note grp: 8a.

     An interface to the group database, similar to this.

Module *note spwd: f1.

     An interface to the shadow password database, similar to this.


File: python.info,  Node: spwd — The shadow password database,  Next: grp — The group database,  Prev: pwd — The password database,  Up: Unix Specific Services

5.35.3 ‘spwd’ — The shadow password database
--------------------------------------------

__________________________________________________________________

This module provides access to the Unix shadow password database.  It is
available on various Unix versions.

You must have enough privileges to access the shadow password database
(this usually means you have to be root).

Shadow password database entries are reported as a tuple-like object,
whose attributes correspond to the members of the ‘spwd’ structure
(Attribute field below, see ‘<shadow.h>’):

Index       Attribute           Meaning
                                
----------------------------------------------------------------------
                                
0           ‘sp_namp’           Login name
                                
                                
1           ‘sp_pwdp’           Encrypted password
                                
                                
2           ‘sp_lstchg’         Date of last change
                                
                                
3           ‘sp_min’            Minimal number of days between
                                changes
                                
                                
4           ‘sp_max’            Maximum number of days between
                                changes
                                
                                
5           ‘sp_warn’           Number of days before password
                                expires to warn user about it
                                
                                
6           ‘sp_inact’          Number of days after password
                                expires until account is disabled
                                
                                
7           ‘sp_expire’         Number of days since 1970-01-01
                                when account expires
                                
                                
8           ‘sp_flag’           Reserved
                                

The sp_namp and sp_pwdp items are strings, all others are integers.
*note KeyError: 3e9. is raised if the entry asked for cannot be found.

The following functions are defined:

 -- Function: spwd.getspnam (name)

     Return the shadow password database entry for the given user name.

     Changed in version 3.6: Raises a *note PermissionError: 6f6.
     instead of *note KeyError: 3e9. if the user doesn’t have
     privileges.

 -- Function: spwd.getspall ()

     Return a list of all available shadow password database entries, in
     arbitrary order.

See also
........

Module *note grp: 8a.

     An interface to the group database, similar to this.

Module *note pwd: d6.

     An interface to the normal password database, similar to this.


File: python.info,  Node: grp — The group database,  Next: crypt — Function to check Unix passwords,  Prev: spwd — The shadow password database,  Up: Unix Specific Services

5.35.4 ‘grp’ — The group database
---------------------------------

__________________________________________________________________

This module provides access to the Unix group database.  It is available
on all Unix versions.

Group database entries are reported as a tuple-like object, whose
attributes correspond to the members of the ‘group’ structure (Attribute
field below, see ‘<pwd.h>’):

Index       Attribute       Meaning
                            
------------------------------------------------------------------
                            
0           gr_name         the name of the group
                            
                            
1           gr_passwd       the (encrypted) group password;
                            often empty
                            
                            
2           gr_gid          the numerical group ID
                            
                            
3           gr_mem          all the group member’s user names
                            

The gid is an integer, name and password are strings, and the member
list is a list of strings.  (Note that most users are not explicitly
listed as members of the group they are in according to the password
database.  Check both databases to get complete membership information.
Also note that a ‘gr_name’ that starts with a ‘+’ or ‘-’ is likely to be
a YP/NIS reference and may not be accessible via *note getgrnam(): 1162.
or *note getgrgid(): 6d6.)

It defines the following items:

 -- Function: grp.getgrgid (gid)

     Return the group database entry for the given numeric group ID.
     *note KeyError: 3e9. is raised if the entry asked for cannot be
     found.

     Deprecated since version 3.6: Since Python 3.6 the support of
     non-integer arguments like floats or strings in *note getgrgid():
     6d6. is deprecated.

 -- Function: grp.getgrnam (name)

     Return the group database entry for the given group name.  *note
     KeyError: 3e9. is raised if the entry asked for cannot be found.

 -- Function: grp.getgrall ()

     Return a list of all available group entries, in arbitrary order.

See also
........

Module *note pwd: d6.

     An interface to the user database, similar to this.

Module *note spwd: f1.

     An interface to the shadow password database, similar to this.


File: python.info,  Node: crypt — Function to check Unix passwords,  Next: termios — POSIX style tty control,  Prev: grp — The group database,  Up: Unix Specific Services

5.35.5 ‘crypt’ — Function to check Unix passwords
-------------------------------------------------

`Source code:' Lib/crypt.py(1)

__________________________________________________________________

This module implements an interface to the ‘crypt(3)’ routine, which is
a one-way hash function based upon a modified DES algorithm; see the
Unix man page for further details.  Possible uses include storing hashed
passwords so you can check passwords without storing the actual
password, or attempting to crack Unix passwords with a dictionary.

Notice that the behavior of this module depends on the actual
implementation of the ‘crypt(3)’ routine in the running system.
Therefore, any extensions available on the current implementation will
also be available on this module.

*note Availability: 1491.: Unix.  Not available on VxWorks.

* Menu:

* Hashing Methods::
* Module Attributes::
* Module Functions: Module Functions<2>.
* Examples: Examples<32>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/crypt.py


File: python.info,  Node: Hashing Methods,  Next: Module Attributes,  Up: crypt — Function to check Unix passwords

5.35.5.1 Hashing Methods
........................

New in version 3.3.

The *note crypt: 28. module defines the list of hashing methods (not all
methods are available on all platforms):

 -- Data: crypt.METHOD_SHA512

     A Modular Crypt Format method with 16 character salt and 86
     character hash based on the SHA-512 hash function.  This is the
     strongest method.

 -- Data: crypt.METHOD_SHA256

     Another Modular Crypt Format method with 16 character salt and 43
     character hash based on the SHA-256 hash function.

 -- Data: crypt.METHOD_BLOWFISH

     Another Modular Crypt Format method with 22 character salt and 31
     character hash based on the Blowfish cipher.

     New in version 3.7.

 -- Data: crypt.METHOD_MD5

     Another Modular Crypt Format method with 8 character salt and 22
     character hash based on the MD5 hash function.

 -- Data: crypt.METHOD_CRYPT

     The traditional method with a 2 character salt and 13 characters of
     hash.  This is the weakest method.


File: python.info,  Node: Module Attributes,  Next: Module Functions<2>,  Prev: Hashing Methods,  Up: crypt — Function to check Unix passwords

5.35.5.2 Module Attributes
..........................

New in version 3.3.

 -- Attribute: crypt.methods

     A list of available password hashing algorithms, as
     ‘crypt.METHOD_*’ objects.  This list is sorted from strongest to
     weakest.


File: python.info,  Node: Module Functions<2>,  Next: Examples<32>,  Prev: Module Attributes,  Up: crypt — Function to check Unix passwords

5.35.5.3 Module Functions
.........................

The *note crypt: 28. module defines the following functions:

 -- Function: crypt.crypt (word, salt=None)

     `word' will usually be a user’s password as typed at a prompt or in
     a graphical interface.  The optional `salt' is either a string as
     returned from *note mksalt(): 484, one of the ‘crypt.METHOD_*’
     values (though not all may be available on all platforms), or a
     full encrypted password including salt, as returned by this
     function.  If `salt' is not provided, the strongest method will be
     used (as returned by *note methods(): 3c33.).

     Checking a password is usually done by passing the plain-text
     password as `word' and the full results of a previous *note
     crypt(): 28. call, which should be the same as the results of this
     call.

     `salt' (either a random 2 or 16 character string, possibly prefixed
     with ‘$digit$’ to indicate the method) which will be used to
     perturb the encryption algorithm.  The characters in `salt' must be
     in the set ‘[./a-zA-Z0-9]’, with the exception of Modular Crypt
     Format which prefixes a ‘$digit$’.

     Returns the hashed password as a string, which will be composed of
     characters from the same alphabet as the salt.

     Since a few ‘crypt(3)’ extensions allow different values, with
     different sizes in the `salt', it is recommended to use the full
     crypted password as salt when checking for a password.

     Changed in version 3.3: Accept ‘crypt.METHOD_*’ values in addition
     to strings for `salt'.

 -- Function: crypt.mksalt (method=None, *, rounds=None)

     Return a randomly generated salt of the specified method.  If no
     `method' is given, the strongest method available as returned by
     *note methods(): 3c33. is used.

     The return value is a string suitable for passing as the `salt'
     argument to *note crypt(): 28.

     `rounds' specifies the number of rounds for ‘METHOD_SHA256’,
     ‘METHOD_SHA512’ and ‘METHOD_BLOWFISH’.  For ‘METHOD_SHA256’ and
     ‘METHOD_SHA512’ it must be an integer between ‘1000’ and
     ‘999_999_999’, the default is ‘5000’.  For ‘METHOD_BLOWFISH’ it
     must be a power of two between ‘16’ (2^4) and ‘2_147_483_648’
     (2^31), the default is ‘4096’ (2^12).

     New in version 3.3.

     Changed in version 3.7: Added the `rounds' parameter.


File: python.info,  Node: Examples<32>,  Prev: Module Functions<2>,  Up: crypt — Function to check Unix passwords

5.35.5.4 Examples
.................

A simple example illustrating typical use (a constant-time comparison
operation is needed to limit exposure to timing attacks.  *note
hmac.compare_digest(): aea. is suitable for this purpose):

     import pwd
     import crypt
     import getpass
     from hmac import compare_digest as compare_hash

     def login():
         username = input('Python login: ')
         cryptedpasswd = pwd.getpwnam(username)[1]
         if cryptedpasswd:
             if cryptedpasswd == 'x' or cryptedpasswd == '*':
                 raise ValueError('no support for shadow passwords')
             cleartext = getpass.getpass()
             return compare_hash(crypt.crypt(cleartext, cryptedpasswd), cryptedpasswd)
         else:
             return True

To generate a hash of a password using the strongest available method
and check it against the original:

     import crypt
     from hmac import compare_digest as compare_hash

     hashed = crypt.crypt(plaintext)
     if not compare_hash(hashed, crypt.crypt(plaintext, hashed)):
         raise ValueError("hashed version doesn't validate against original")


File: python.info,  Node: termios — POSIX style tty control,  Next: tty — Terminal control functions,  Prev: crypt — Function to check Unix passwords,  Up: Unix Specific Services

5.35.6 ‘termios’ — POSIX style tty control
------------------------------------------

__________________________________________________________________

This module provides an interface to the POSIX calls for tty I/O
control.  For a complete description of these calls, see ‘termios(3)’
Unix manual page.  It is only available for those Unix versions that
support POSIX `termios' style tty I/O control configured during
installation.

All functions in this module take a file descriptor `fd' as their first
argument.  This can be an integer file descriptor, such as returned by
‘sys.stdin.fileno()’, or a *note file object: c14, such as ‘sys.stdin’
itself.

This module also defines all the constants needed to work with the
functions provided here; these have the same name as their counterparts
in C. Please refer to your system documentation for more information on
using these terminal control interfaces.

The module defines the following functions:

 -- Function: termios.tcgetattr (fd)

     Return a list containing the tty attributes for file descriptor
     `fd', as follows: ‘[iflag, oflag, cflag, lflag, ispeed, ospeed,
     cc]’ where `cc' is a list of the tty special characters (each a
     string of length 1, except the items with indices ‘VMIN’ and
     ‘VTIME’, which are integers when these fields are defined).  The
     interpretation of the flags and the speeds as well as the indexing
     in the `cc' array must be done using the symbolic constants defined
     in the *note termios: 104. module.

 -- Function: termios.tcsetattr (fd, when, attributes)

     Set the tty attributes for file descriptor `fd' from the
     `attributes', which is a list like the one returned by *note
     tcgetattr(): 3c39.  The `when' argument determines when the
     attributes are changed: ‘TCSANOW’ to change immediately,
     ‘TCSADRAIN’ to change after transmitting all queued output, or
     ‘TCSAFLUSH’ to change after transmitting all queued output and
     discarding all queued input.

 -- Function: termios.tcsendbreak (fd, duration)

     Send a break on file descriptor `fd'.  A zero `duration' sends a
     break for 0.25–0.5 seconds; a nonzero `duration' has a system
     dependent meaning.

 -- Function: termios.tcdrain (fd)

     Wait until all output written to file descriptor `fd' has been
     transmitted.

 -- Function: termios.tcflush (fd, queue)

     Discard queued data on file descriptor `fd'.  The `queue' selector
     specifies which queue: ‘TCIFLUSH’ for the input queue, ‘TCOFLUSH’
     for the output queue, or ‘TCIOFLUSH’ for both queues.

 -- Function: termios.tcflow (fd, action)

     Suspend or resume input or output on file descriptor `fd'.  The
     `action' argument can be ‘TCOOFF’ to suspend output, ‘TCOON’ to
     restart output, ‘TCIOFF’ to suspend input, or ‘TCION’ to restart
     input.

See also
........

Module *note tty: 11e.

     Convenience functions for common terminal control operations.

* Menu:

* Example: Example<16>.


File: python.info,  Node: Example<16>,  Up: termios — POSIX style tty control

5.35.6.1 Example
................

Here’s a function that prompts for a password with echoing turned off.
Note the technique using a separate *note tcgetattr(): 3c39. call and a
*note try: e37. … *note finally: 2bc. statement to ensure that the old
tty attributes are restored exactly no matter what happens:

     def getpass(prompt="Password: "):
         import termios, sys
         fd = sys.stdin.fileno()
         old = termios.tcgetattr(fd)
         new = termios.tcgetattr(fd)
         new[3] = new[3] & ~termios.ECHO          # lflags
         try:
             termios.tcsetattr(fd, termios.TCSADRAIN, new)
             passwd = input(prompt)
         finally:
             termios.tcsetattr(fd, termios.TCSADRAIN, old)
         return passwd


File: python.info,  Node: tty — Terminal control functions,  Next: pty — Pseudo-terminal utilities,  Prev: termios — POSIX style tty control,  Up: Unix Specific Services

5.35.7 ‘tty’ — Terminal control functions
-----------------------------------------

`Source code:' Lib/tty.py(1)

__________________________________________________________________

The *note tty: 11e. module defines functions for putting the tty into
cbreak and raw modes.

Because it requires the *note termios: 104. module, it will work only on
Unix.

The *note tty: 11e. module defines the following functions:

 -- Function: tty.setraw (fd, when=termios.TCSAFLUSH)

     Change the mode of the file descriptor `fd' to raw.  If `when' is
     omitted, it defaults to ‘termios.TCSAFLUSH’, and is passed to *note
     termios.tcsetattr(): 3c3a.

 -- Function: tty.setcbreak (fd, when=termios.TCSAFLUSH)

     Change the mode of file descriptor `fd' to cbreak.  If `when' is
     omitted, it defaults to ‘termios.TCSAFLUSH’, and is passed to *note
     termios.tcsetattr(): 3c3a.

See also
........

Module *note termios: 104.

     Low-level terminal control interface.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/tty.py


File: python.info,  Node: pty — Pseudo-terminal utilities,  Next: fcntl — The fcntl and ioctl system calls,  Prev: tty — Terminal control functions,  Up: Unix Specific Services

5.35.8 ‘pty’ — Pseudo-terminal utilities
----------------------------------------

`Source code:' Lib/pty.py(1)

__________________________________________________________________

The *note pty: d5. module defines operations for handling the
pseudo-terminal concept: starting another process and being able to
write to and read from its controlling terminal programmatically.

Because pseudo-terminal handling is highly platform dependent, there is
code to do it only for Linux.  (The Linux code is supposed to work on
other platforms, but hasn’t been tested yet.)

The *note pty: d5. module defines the following functions:

 -- Function: pty.fork ()

     Fork.  Connect the child’s controlling terminal to a
     pseudo-terminal.  Return value is ‘(pid, fd)’.  Note that the child
     gets `pid' 0, and the `fd' is `invalid'.  The parent’s return value
     is the `pid' of the child, and `fd' is a file descriptor connected
     to the child’s controlling terminal (and also to the child’s
     standard input and output).

 -- Function: pty.openpty ()

     Open a new pseudo-terminal pair, using *note os.openpty(): 208b. if
     possible, or emulation code for generic Unix systems.  Return a
     pair of file descriptors ‘(master, slave)’, for the master and the
     slave end, respectively.

 -- Function: pty.spawn (argv[, master_read[, stdin_read]])

     Spawn a process, and connect its controlling terminal with the
     current process’s standard io.  This is often used to baffle
     programs which insist on reading from the controlling terminal.  It
     is expected that the process spawned behind the pty will eventually
     terminate, and when it does `spawn' will return.

     The functions `master_read' and `stdin_read' are passed a file
     descriptor which they should read from, and they should always
     return a byte string.  In order to force spawn to return before the
     child process exits an *note OSError: 304. should be thrown.

     The default implementation for both functions will read and return
     up to 1024 bytes each time the function is called.  The
     `master_read' callback is passed the pseudoterminal’s master file
     descriptor to read output from the child process, and `stdin_read'
     is passed file descriptor 0, to read from the parent process’s
     standard input.

     Returning an empty byte string from either callback is interpreted
     as an end-of-file (EOF) condition, and that callback will not be
     called after that.  If `stdin_read' signals EOF the controlling
     terminal can no longer communicate with the parent process OR the
     child process.  Unless the child process will quit without any
     input, `spawn' will then loop forever.  If `master_read' signals
     EOF the same behavior results (on linux at least).

     If both callbacks signal EOF then `spawn' will probably never
     return, unless `select' throws an error on your platform when
     passed three empty lists.  This is a bug, documented in issue
     26228(2).

     Return the exit status value from *note os.waitpid(): 760. on the
     child process.

     ‘waitstatus_to_exitcode()’ can be used to convert the exit status
     into an exit code.

     Raises an *note auditing event: fa1. ‘pty.spawn’ with argument
     ‘argv’.

     Changed in version 3.4: *note spawn(): 97f. now returns the status
     value from *note os.waitpid(): 760. on the child process.

* Menu:

* Example: Example<17>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/pty.py

   (2) https://bugs.python.org/issue26228


File: python.info,  Node: Example<17>,  Up: pty — Pseudo-terminal utilities

5.35.8.1 Example
................

The following program acts like the Unix command ‘script(1)’, using a
pseudo-terminal to record all input and output of a terminal session in
a “typescript”.

     import argparse
     import os
     import pty
     import sys
     import time

     parser = argparse.ArgumentParser()
     parser.add_argument('-a', dest='append', action='store_true')
     parser.add_argument('-p', dest='use_python', action='store_true')
     parser.add_argument('filename', nargs='?', default='typescript')
     options = parser.parse_args()

     shell = sys.executable if options.use_python else os.environ.get('SHELL', 'sh')
     filename = options.filename
     mode = 'ab' if options.append else 'wb'

     with open(filename, mode) as script:
         def read(fd):
             data = os.read(fd, 1024)
             script.write(data)
             return data

         print('Script started, file is', filename)
         script.write(('Script started on %s\n' % time.asctime()).encode())

         pty.spawn(shell, read)

         script.write(('Script done on %s\n' % time.asctime()).encode())
         print('Script done, file is', filename)


File: python.info,  Node: fcntl — The fcntl and ioctl system calls,  Next: pipes — Interface to shell pipelines,  Prev: pty — Pseudo-terminal utilities,  Up: Unix Specific Services

5.35.9 ‘fcntl’ — The ‘fcntl’ and ‘ioctl’ system calls
-----------------------------------------------------

__________________________________________________________________

This module performs file control and I/O control on file descriptors.
It is an interface to the ‘fcntl()’ and ‘ioctl()’ Unix routines.  For a
complete description of these calls, see ‘fcntl(2)’ and ‘ioctl(2)’ Unix
manual pages.

All functions in this module take a file descriptor `fd' as their first
argument.  This can be an integer file descriptor, such as returned by
‘sys.stdin.fileno()’, or an *note io.IOBase: 30c. object, such as
‘sys.stdin’ itself, which provides a *note fileno(): 2069. that returns
a genuine file descriptor.

Changed in version 3.3: Operations in this module used to raise an *note
IOError: a73. where they now raise an *note OSError: 304.

Changed in version 3.8: The fcntl module now contains ‘F_ADD_SEALS’,
‘F_GET_SEALS’, and ‘F_SEAL_*’ constants for sealing of *note
os.memfd_create(): 320. file descriptors.

Changed in version 3.9: On macOS, the fcntl module exposes the
‘F_GETPATH’ constant, which obtains the path of a file from a file
descriptor.  On Linux(>=3.15), the fcntl module exposes the
‘F_OFD_GETLK’, ‘F_OFD_SETLK’ and ‘F_OFD_SETLKW’ constants, which working
with open file description locks.

The module defines the following functions:

 -- Function: fcntl.fcntl (fd, cmd, arg=0)

     Perform the operation `cmd' on file descriptor `fd' (file objects
     providing a *note fileno(): 2069. method are accepted as well).
     The values used for `cmd' are operating system dependent, and are
     available as constants in the *note fcntl: 7c. module, using the
     same names as used in the relevant C header files.  The argument
     `arg' can either be an integer value, or a *note bytes: 172.
     object.  With an integer value, the return value of this function
     is the integer return value of the C ‘fcntl()’ call.  When the
     argument is bytes it represents a binary structure, e.g.  created
     by *note struct.pack(): cd6.  The binary data is copied to a buffer
     whose address is passed to the C ‘fcntl()’ call.  The return value
     after a successful call is the contents of the buffer, converted to
     a *note bytes: 172. object.  The length of the returned object will
     be the same as the length of the `arg' argument.  This is limited
     to 1024 bytes.  If the information returned in the buffer by the
     operating system is larger than 1024 bytes, this is most likely to
     result in a segmentation violation or a more subtle data
     corruption.

     If the ‘fcntl()’ fails, an *note OSError: 304. is raised.

     Raises an *note auditing event: fa1. ‘fcntl.fcntl’ with arguments
     ‘fd’, ‘cmd’, ‘arg’.

 -- Function: fcntl.ioctl (fd, request, arg=0, mutate_flag=True)

     This function is identical to the *note fcntl(): 27e8. function,
     except that the argument handling is even more complicated.

     The `request' parameter is limited to values that can fit in
     32-bits.  Additional constants of interest for use as the `request'
     argument can be found in the *note termios: 104. module, under the
     same names as used in the relevant C header files.

     The parameter `arg' can be one of an integer, an object supporting
     the read-only buffer interface (like *note bytes: 172.) or an
     object supporting the read-write buffer interface (like *note
     bytearray: 173.).

     In all but the last case, behaviour is as for the *note fcntl():
     27e8. function.

     If a mutable buffer is passed, then the behaviour is determined by
     the value of the `mutate_flag' parameter.

     If it is false, the buffer’s mutability is ignored and behaviour is
     as for a read-only buffer, except that the 1024 byte limit
     mentioned above is avoided – so long as the buffer you pass is at
     least as long as what the operating system wants to put there,
     things should work.

     If `mutate_flag' is true (the default), then the buffer is (in
     effect) passed to the underlying *note ioctl(): ea2. system call,
     the latter’s return code is passed back to the calling Python, and
     the buffer’s new contents reflect the action of the *note ioctl():
     ea2.  This is a slight simplification, because if the supplied
     buffer is less than 1024 bytes long it is first copied into a
     static buffer 1024 bytes long which is then passed to *note
     ioctl(): ea2. and copied back into the supplied buffer.

     If the ‘ioctl()’ fails, an *note OSError: 304. exception is raised.

     An example:

          >>> import array, fcntl, struct, termios, os
          >>> os.getpgrp()
          13341
          >>> struct.unpack('h', fcntl.ioctl(0, termios.TIOCGPGRP, "  "))[0]
          13341
          >>> buf = array.array('h', [0])
          >>> fcntl.ioctl(0, termios.TIOCGPGRP, buf, 1)
          0
          >>> buf
          array('h', [13341])

     Raises an *note auditing event: fa1. ‘fcntl.ioctl’ with arguments
     ‘fd’, ‘request’, ‘arg’.

 -- Function: fcntl.flock (fd, operation)

     Perform the lock operation `operation' on file descriptor `fd'
     (file objects providing a *note fileno(): 2069. method are accepted
     as well).  See the Unix manual ‘flock(2)’ for details.  (On some
     systems, this function is emulated using ‘fcntl()’.)

     If the ‘flock()’ fails, an *note OSError: 304. exception is raised.

     Raises an *note auditing event: fa1. ‘fcntl.flock’ with arguments
     ‘fd’, ‘operation’.

 -- Function: fcntl.lockf (fd, cmd, len=0, start=0, whence=0)

     This is essentially a wrapper around the *note fcntl(): 27e8.
     locking calls.  `fd' is the file descriptor (file objects providing
     a *note fileno(): 2069. method are accepted as well) of the file to
     lock or unlock, and `cmd' is one of the following values:

        * ‘LOCK_UN’ – unlock

        * ‘LOCK_SH’ – acquire a shared lock

        * ‘LOCK_EX’ – acquire an exclusive lock

     When `cmd' is ‘LOCK_SH’ or ‘LOCK_EX’, it can also be bitwise ORed
     with ‘LOCK_NB’ to avoid blocking on lock acquisition.  If ‘LOCK_NB’
     is used and the lock cannot be acquired, an *note OSError: 304.
     will be raised and the exception will have an `errno' attribute set
     to ‘EACCES’ or ‘EAGAIN’ (depending on the operating system; for
     portability, check for both values).  On at least some systems,
     ‘LOCK_EX’ can only be used if the file descriptor refers to a file
     opened for writing.

     `len' is the number of bytes to lock, `start' is the byte offset at
     which the lock starts, relative to `whence', and `whence' is as
     with *note io.IOBase.seek(): 1efb, specifically:

        * ‘0’ – relative to the start of the file (*note os.SEEK_SET:
          e59.)

        * ‘1’ – relative to the current buffer position (*note
          os.SEEK_CUR: e5a.)

        * ‘2’ – relative to the end of the file (*note os.SEEK_END:
          e5b.)

     The default for `start' is 0, which means to start at the beginning
     of the file.  The default for `len' is 0 which means to lock to the
     end of the file.  The default for `whence' is also 0.

     Raises an *note auditing event: fa1. ‘fcntl.lockf’ with arguments
     ‘fd’, ‘cmd’, ‘len’, ‘start’, ‘whence’.

Examples (all on a SVR4 compliant system):

     import struct, fcntl, os

     f = open(...)
     rv = fcntl.fcntl(f, fcntl.F_SETFL, os.O_NDELAY)

     lockdata = struct.pack('hhllhh', fcntl.F_WRLCK, 0, 0, 0, 0, 0)
     rv = fcntl.fcntl(f, fcntl.F_SETLKW, lockdata)

Note that in the first example the return value variable `rv' will hold
an integer value; in the second example it will hold a *note bytes: 172.
object.  The structure lay-out for the `lockdata' variable is system
dependent — therefore using the *note flock(): 3c4c. call may be better.

See also
........

Module *note os: c4.

     If the locking flags *note O_SHLOCK: e5c. and *note O_EXLOCK: e5d.
     are present in the *note os: c4. module (on BSD only), the *note
     os.open(): 758. function provides an alternative to the *note
     lockf(): e17. and *note flock(): 3c4c. functions.


File: python.info,  Node: pipes — Interface to shell pipelines,  Next: resource — Resource usage information,  Prev: fcntl — The fcntl and ioctl system calls,  Up: Unix Specific Services

5.35.10 ‘pipes’ — Interface to shell pipelines
----------------------------------------------

`Source code:' Lib/pipes.py(1)

__________________________________________________________________

The *note pipes: cc. module defines a class to abstract the concept of a
`pipeline' — a sequence of converters from one file to another.

Because the module uses ‘/bin/sh’ command lines, a POSIX or compatible
shell for *note os.system(): e86. and *note os.popen(): 3cb. is
required.

The *note pipes: cc. module defines the following class:

 -- Class: pipes.Template

     An abstraction of a pipeline.

Example:

     >>> import pipes
     >>> t = pipes.Template()
     >>> t.append('tr a-z A-Z', '--')
     >>> f = t.open('pipefile', 'w')
     >>> f.write('hello world')
     >>> f.close()
     >>> open('pipefile').read()
     'HELLO WORLD'

* Menu:

* Template Objects::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/pipes.py


File: python.info,  Node: Template Objects,  Up: pipes — Interface to shell pipelines

5.35.10.1 Template Objects
..........................

Template objects following methods:

 -- Method: Template.reset ()

     Restore a pipeline template to its initial state.

 -- Method: Template.clone ()

     Return a new, equivalent, pipeline template.

 -- Method: Template.debug (flag)

     If `flag' is true, turn debugging on.  Otherwise, turn debugging
     off.  When debugging is on, commands to be executed are printed,
     and the shell is given ‘set -x’ command to be more verbose.

 -- Method: Template.append (cmd, kind)

     Append a new action at the end.  The `cmd' variable must be a valid
     bourne shell command.  The `kind' variable consists of two letters.

     The first letter can be either of ‘'-'’ (which means the command
     reads its standard input), ‘'f'’ (which means the commands reads a
     given file on the command line) or ‘'.'’ (which means the commands
     reads no input, and hence must be first.)

     Similarly, the second letter can be either of ‘'-'’ (which means
     the command writes to standard output), ‘'f'’ (which means the
     command writes a file on the command line) or ‘'.'’ (which means
     the command does not write anything, and hence must be last.)

 -- Method: Template.prepend (cmd, kind)

     Add a new action at the beginning.  See *note append(): 3c55. for
     explanations of the arguments.

 -- Method: Template.open (file, mode)

     Return a file-like object, open to `file', but read from or written
     to by the pipeline.  Note that only one of ‘'r'’, ‘'w'’ may be
     given.

 -- Method: Template.copy (infile, outfile)

     Copy `infile' to `outfile' through the pipe.


File: python.info,  Node: resource — Resource usage information,  Next: nis — Interface to Sun’s NIS Yellow Pages,  Prev: pipes — Interface to shell pipelines,  Up: Unix Specific Services

5.35.11 ‘resource’ — Resource usage information
-----------------------------------------------

__________________________________________________________________

This module provides basic mechanisms for measuring and controlling
system resources utilized by a program.

Symbolic constants are used to specify particular system resources and
to request usage information about either the current process or its
children.

An *note OSError: 304. is raised on syscall failure.

 -- Exception: resource.error

     A deprecated alias of *note OSError: 304.

     Changed in version 3.3: Following PEP 3151(1), this class was made
     an alias of *note OSError: 304.

* Menu:

* Resource Limits::
* Resource Usage::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3151


File: python.info,  Node: Resource Limits,  Next: Resource Usage,  Up: resource — Resource usage information

5.35.11.1 Resource Limits
.........................

Resources usage can be limited using the *note setrlimit(): 3643.
function described below.  Each resource is controlled by a pair of
limits: a soft limit and a hard limit.  The soft limit is the current
limit, and may be lowered or raised by a process over time.  The soft
limit can never exceed the hard limit.  The hard limit can be lowered to
any value greater than the soft limit, but not raised.  (Only processes
with the effective UID of the super-user can raise a hard limit.)

The specific resources that can be limited are system dependent.  They
are described in the ‘getrlimit(2)’ man page.  The resources listed
below are supported when the underlying operating system supports them;
resources which cannot be checked or controlled by the operating system
are not defined in this module for those platforms.

 -- Data: resource.RLIM_INFINITY

     Constant used to represent the limit for an unlimited resource.

 -- Function: resource.getrlimit (resource)

     Returns a tuple ‘(soft, hard)’ with the current soft and hard
     limits of `resource'.  Raises *note ValueError: 16d. if an invalid
     resource is specified, or *note error: 3c5b. if the underlying
     system call fails unexpectedly.

 -- Function: resource.setrlimit (resource, limits)

     Sets new limits of consumption of `resource'.  The `limits'
     argument must be a tuple ‘(soft, hard)’ of two integers describing
     the new limits.  A value of *note RLIM_INFINITY: 3c5d. can be used
     to request a limit that is unlimited.

     Raises *note ValueError: 16d. if an invalid resource is specified,
     if the new soft limit exceeds the hard limit, or if a process tries
     to raise its hard limit.  Specifying a limit of *note
     RLIM_INFINITY: 3c5d. when the hard or system limit for that
     resource is not unlimited will result in a *note ValueError: 16d.
     A process with the effective UID of super-user can request any
     valid limit value, including unlimited, but *note ValueError: 16d.
     will still be raised if the requested limit exceeds the system
     imposed limit.

     ‘setrlimit’ may also raise *note error: 3c5b. if the underlying
     system call fails.

     VxWorks only supports setting *note RLIMIT_NOFILE: 3c5f.

     Raises an *note auditing event: fa1. ‘resource.setrlimit’ with
     arguments ‘resource’, ‘limits’.

 -- Function: resource.prlimit (pid, resource[, limits])

     Combines *note setrlimit(): 3643. and *note getrlimit(): 3c5e. in
     one function and supports to get and set the resources limits of an
     arbitrary process.  If `pid' is 0, then the call applies to the
     current process.  `resource' and `limits' have the same meaning as
     in *note setrlimit(): 3643, except that `limits' is optional.

     When `limits' is not given the function returns the `resource'
     limit of the process `pid'.  When `limits' is given the `resource'
     limit of the process is set and the former resource limit is
     returned.

     Raises *note ProcessLookupError: a7c. when `pid' can’t be found and
     *note PermissionError: 6f6. when the user doesn’t have
     ‘CAP_SYS_RESOURCE’ for the process.

     Raises an *note auditing event: fa1. ‘resource.prlimit’ with
     arguments ‘pid’, ‘resource’, ‘limits’.

     *note Availability: 1491.: Linux 2.6.36 or later with glibc 2.13 or
     later.

     New in version 3.4.

These symbols define resources whose consumption can be controlled using
the *note setrlimit(): 3643. and *note getrlimit(): 3c5e. functions
described below.  The values of these symbols are exactly the constants
used by C programs.

The Unix man page for ‘getrlimit(2)’ lists the available resources.
Note that not all systems use the same symbol or same value to denote
the same resource.  This module does not attempt to mask platform
differences — symbols not defined for a platform will not be available
from this module on that platform.

 -- Data: resource.RLIMIT_CORE

     The maximum size (in bytes) of a core file that the current process
     can create.  This may result in the creation of a partial core file
     if a larger core would be required to contain the entire process
     image.

 -- Data: resource.RLIMIT_CPU

     The maximum amount of processor time (in seconds) that a process
     can use.  If this limit is exceeded, a ‘SIGXCPU’ signal is sent to
     the process.  (See the *note signal: ea. module documentation for
     information about how to catch this signal and do something useful,
     e.g.  flush open files to disk.)

 -- Data: resource.RLIMIT_FSIZE

     The maximum size of a file which the process may create.

 -- Data: resource.RLIMIT_DATA

     The maximum size (in bytes) of the process’s heap.

 -- Data: resource.RLIMIT_STACK

     The maximum size (in bytes) of the call stack for the current
     process.  This only affects the stack of the main thread in a
     multi-threaded process.

 -- Data: resource.RLIMIT_RSS

     The maximum resident set size that should be made available to the
     process.

 -- Data: resource.RLIMIT_NPROC

     The maximum number of processes the current process may create.

 -- Data: resource.RLIMIT_NOFILE

     The maximum number of open file descriptors for the current
     process.

 -- Data: resource.RLIMIT_OFILE

     The BSD name for *note RLIMIT_NOFILE: 3c5f.

 -- Data: resource.RLIMIT_MEMLOCK

     The maximum address space which may be locked in memory.

 -- Data: resource.RLIMIT_VMEM

     The largest area of mapped memory which the process may occupy.

 -- Data: resource.RLIMIT_AS

     The maximum area (in bytes) of address space which may be taken by
     the process.

 -- Data: resource.RLIMIT_MSGQUEUE

     The number of bytes that can be allocated for POSIX message queues.

     *note Availability: 1491.: Linux 2.6.8 or later.

     New in version 3.4.

 -- Data: resource.RLIMIT_NICE

     The ceiling for the process’s nice level (calculated as 20 -
     rlim_cur).

     *note Availability: 1491.: Linux 2.6.12 or later.

     New in version 3.4.

 -- Data: resource.RLIMIT_RTPRIO

     The ceiling of the real-time priority.

     *note Availability: 1491.: Linux 2.6.12 or later.

     New in version 3.4.

 -- Data: resource.RLIMIT_RTTIME

     The time limit (in microseconds) on CPU time that a process can
     spend under real-time scheduling without making a blocking syscall.

     *note Availability: 1491.: Linux 2.6.25 or later.

     New in version 3.4.

 -- Data: resource.RLIMIT_SIGPENDING

     The number of signals which the process may queue.

     *note Availability: 1491.: Linux 2.6.8 or later.

     New in version 3.4.

 -- Data: resource.RLIMIT_SBSIZE

     The maximum size (in bytes) of socket buffer usage for this user.
     This limits the amount of network memory, and hence the amount of
     mbufs, that this user may hold at any time.

     *note Availability: 1491.: FreeBSD 9 or later.

     New in version 3.4.

 -- Data: resource.RLIMIT_SWAP

     The maximum size (in bytes) of the swap space that may be reserved
     or used by all of this user id’s processes.  This limit is enforced
     only if bit 1 of the vm.overcommit sysctl is set.  Please see
     tuning(7)(1) for a complete description of this sysctl.

     *note Availability: 1491.: FreeBSD 9 or later.

     New in version 3.4.

 -- Data: resource.RLIMIT_NPTS

     The maximum number of pseudo-terminals created by this user id.

     *note Availability: 1491.: FreeBSD 9 or later.

     New in version 3.4.

   ---------- Footnotes ----------

   (1) https://www.freebsd.org/cgi/man.cgi?query=tuning&sektion=7


File: python.info,  Node: Resource Usage,  Prev: Resource Limits,  Up: resource — Resource usage information

5.35.11.2 Resource Usage
........................

These functions are used to retrieve resource usage information:

 -- Function: resource.getrusage (who)

     This function returns an object that describes the resources
     consumed by either the current process or its children, as
     specified by the `who' parameter.  The `who' parameter should be
     specified using one of the ‘RUSAGE_*’ constants described below.

     A simple example:

          from resource import *
          import time

          # a non CPU-bound task
          time.sleep(3)
          print(getrusage(RUSAGE_SELF))

          # a CPU-bound task
          for i in range(10 ** 8):
             _ = 1 + 1
          print(getrusage(RUSAGE_SELF))

     The fields of the return value each describe how a particular
     system resource has been used, e.g.  amount of time spent running
     is user mode or number of times the process was swapped out of main
     memory.  Some values are dependent on the clock tick internal, e.g.
     the amount of memory the process is using.

     For backward compatibility, the return value is also accessible as
     a tuple of 16 elements.

     The fields ‘ru_utime’ and ‘ru_stime’ of the return value are
     floating point values representing the amount of time spent
     executing in user mode and the amount of time spent executing in
     system mode, respectively.  The remaining values are integers.
     Consult the ‘getrusage(2)’ man page for detailed information about
     these values.  A brief summary is presented here:

     Index        Field                     Resource
                                            
     -----------------------------------------------------------------------------------
                                            
     ‘0’          ‘ru_utime’                time in user mode (float seconds)
                                            
                                            
     ‘1’          ‘ru_stime’                time in system mode (float seconds)
                                            
                                            
     ‘2’          ‘ru_maxrss’               maximum resident set size
                                            
                                            
     ‘3’          ‘ru_ixrss’                shared memory size
                                            
                                            
     ‘4’          ‘ru_idrss’                unshared memory size
                                            
                                            
     ‘5’          ‘ru_isrss’                unshared stack size
                                            
                                            
     ‘6’          ‘ru_minflt’               page faults not requiring I/O
                                            
                                            
     ‘7’          ‘ru_majflt’               page faults requiring I/O
                                            
                                            
     ‘8’          ‘ru_nswap’                number of swap outs
                                            
                                            
     ‘9’          ‘ru_inblock’              block input operations
                                            
                                            
     ‘10’         ‘ru_oublock’              block output operations
                                            
                                            
     ‘11’         ‘ru_msgsnd’               messages sent
                                            
                                            
     ‘12’         ‘ru_msgrcv’               messages received
                                            
                                            
     ‘13’         ‘ru_nsignals’             signals received
                                            
                                            
     ‘14’         ‘ru_nvcsw’                voluntary context switches
                                            
                                            
     ‘15’         ‘ru_nivcsw’               involuntary context switches
                                            

     This function will raise a *note ValueError: 16d. if an invalid
     `who' parameter is specified.  It may also raise *note error: 3c5b.
     exception in unusual circumstances.

 -- Function: resource.getpagesize ()

     Returns the number of bytes in a system page.  (This need not be
     the same as the hardware page size.)

The following ‘RUSAGE_*’ symbols are passed to the *note getrusage():
e5e. function to specify which processes information should be provided
for.

 -- Data: resource.RUSAGE_SELF

     Pass to *note getrusage(): e5e. to request resources consumed by
     the calling process, which is the sum of resources used by all
     threads in the process.

 -- Data: resource.RUSAGE_CHILDREN

     Pass to *note getrusage(): e5e. to request resources consumed by
     child processes of the calling process which have been terminated
     and waited for.

 -- Data: resource.RUSAGE_BOTH

     Pass to *note getrusage(): e5e. to request resources consumed by
     both the current process and child processes.  May not be available
     on all systems.

 -- Data: resource.RUSAGE_THREAD

     Pass to *note getrusage(): e5e. to request resources consumed by
     the current thread.  May not be available on all systems.

     New in version 3.2.


File: python.info,  Node: nis — Interface to Sun’s NIS Yellow Pages,  Next: syslog — Unix syslog library routines,  Prev: resource — Resource usage information,  Up: Unix Specific Services

5.35.12 ‘nis’ — Interface to Sun’s NIS (Yellow Pages)
-----------------------------------------------------

__________________________________________________________________

The *note nis: bf. module gives a thin wrapper around the NIS library,
useful for central administration of several hosts.

Because NIS exists only on Unix systems, this module is only available
for Unix.

The *note nis: bf. module defines the following functions:

 -- Function: nis.match (key, mapname, domain=default_domain)

     Return the match for `key' in map `mapname', or raise an error
     (*note nis.error: 3c72.) if there is none.  Both should be strings,
     `key' is 8-bit clean.  Return value is an arbitrary array of bytes
     (may contain ‘NULL’ and other joys).

     Note that `mapname' is first checked if it is an alias to another
     name.

     The `domain' argument allows overriding the NIS domain used for the
     lookup.  If unspecified, lookup is in the default NIS domain.

 -- Function: nis.cat (mapname, domain=default_domain)

     Return a dictionary mapping `key' to `value' such that ‘match(key,
     mapname)==value’.  Note that both keys and values of the dictionary
     are arbitrary arrays of bytes.

     Note that `mapname' is first checked if it is an alias to another
     name.

     The `domain' argument allows overriding the NIS domain used for the
     lookup.  If unspecified, lookup is in the default NIS domain.

 -- Function: nis.maps (domain=default_domain)

     Return a list of all valid maps.

     The `domain' argument allows overriding the NIS domain used for the
     lookup.  If unspecified, lookup is in the default NIS domain.

 -- Function: nis.get_default_domain ()

     Return the system default NIS domain.

The *note nis: bf. module defines the following exception:

 -- Exception: nis.error

     An error raised when a NIS function returns an error code.


File: python.info,  Node: syslog — Unix syslog library routines,  Prev: nis — Interface to Sun’s NIS Yellow Pages,  Up: Unix Specific Services

5.35.13 ‘syslog’ — Unix syslog library routines
-----------------------------------------------

__________________________________________________________________

This module provides an interface to the Unix ‘syslog’ library routines.
Refer to the Unix manual pages for a detailed description of the
‘syslog’ facility.

This module wraps the system ‘syslog’ family of routines.  A pure Python
library that can speak to a syslog server is available in the *note
logging.handlers: ac. module as ‘SysLogHandler’.

The module defines the following functions:

 -- Function: syslog.syslog (message)

 -- Function: syslog.syslog (priority, message)

     Send the string `message' to the system logger.  A trailing newline
     is added if necessary.  Each message is tagged with a priority
     composed of a `facility' and a `level'.  The optional `priority'
     argument, which defaults to ‘LOG_INFO’, determines the message
     priority.  If the facility is not encoded in `priority' using
     logical-or (‘LOG_INFO | LOG_USER’), the value given in the *note
     openlog(): 10a6. call is used.

     If *note openlog(): 10a6. has not been called prior to the call to
     *note syslog(): ff, ‘openlog()’ will be called with no arguments.

     Raises an *note auditing event: fa1. ‘syslog.syslog’ with arguments
     ‘priority’, ‘message’.

 -- Function: syslog.openlog ([ident[, logoption[, facility]]])

     Logging options of subsequent *note syslog(): ff. calls can be set
     by calling *note openlog(): 10a6.  *note syslog(): ff. will call
     *note openlog(): 10a6. with no arguments if the log is not
     currently open.

     The optional `ident' keyword argument is a string which is
     prepended to every message, and defaults to ‘sys.argv[0]’ with
     leading path components stripped.  The optional `logoption' keyword
     argument (default is 0) is a bit field – see below for possible
     values to combine.  The optional `facility' keyword argument
     (default is ‘LOG_USER’) sets the default facility for messages
     which do not have a facility explicitly encoded.

     Raises an *note auditing event: fa1. ‘syslog.openlog’ with
     arguments ‘ident’, ‘logoption’, ‘facility’.

     Changed in version 3.2: In previous versions, keyword arguments
     were not allowed, and `ident' was required.  The default for
     `ident' was dependent on the system libraries, and often was
     ‘python’ instead of the name of the Python program file.

 -- Function: syslog.closelog ()

     Reset the syslog module values and call the system library
     ‘closelog()’.

     This causes the module to behave as it does when initially
     imported.  For example, *note openlog(): 10a6. will be called on
     the first *note syslog(): ff. call (if *note openlog(): 10a6.
     hasn’t already been called), and `ident' and other *note openlog():
     10a6. parameters are reset to defaults.

     Raises an *note auditing event: fa1. ‘syslog.closelog’ with no
     arguments.

 -- Function: syslog.setlogmask (maskpri)

     Set the priority mask to `maskpri' and return the previous mask
     value.  Calls to *note syslog(): ff. with a priority level not set
     in `maskpri' are ignored.  The default is to log all priorities.
     The function ‘LOG_MASK(pri)’ calculates the mask for the individual
     priority `pri'.  The function ‘LOG_UPTO(pri)’ calculates the mask
     for all priorities up to and including `pri'.

     Raises an *note auditing event: fa1. ‘syslog.setlogmask’ with
     argument ‘maskpri’.

The module defines the following constants:

Priority levels (high to low):

     ‘LOG_EMERG’, ‘LOG_ALERT’, ‘LOG_CRIT’, ‘LOG_ERR’, ‘LOG_WARNING’,
     ‘LOG_NOTICE’, ‘LOG_INFO’, ‘LOG_DEBUG’.

Facilities:

     ‘LOG_KERN’, ‘LOG_USER’, ‘LOG_MAIL’, ‘LOG_DAEMON’, ‘LOG_AUTH’,
     ‘LOG_LPR’, ‘LOG_NEWS’, ‘LOG_UUCP’, ‘LOG_CRON’, ‘LOG_SYSLOG’,
     ‘LOG_LOCAL0’ to ‘LOG_LOCAL7’, and, if defined in ‘<syslog.h>’,
     ‘LOG_AUTHPRIV’.

Log options:

     ‘LOG_PID’, ‘LOG_CONS’, ‘LOG_NDELAY’, and, if defined in
     ‘<syslog.h>’, ‘LOG_ODELAY’, ‘LOG_NOWAIT’, and ‘LOG_PERROR’.

* Menu:

* Examples: Examples<33>.


File: python.info,  Node: Examples<33>,  Up: syslog — Unix syslog library routines

5.35.13.1 Examples
..................

* Menu:

* Simple example::


File: python.info,  Node: Simple example,  Up: Examples<33>

5.35.13.2 Simple example
........................

A simple set of examples:

     import syslog

     syslog.syslog('Processing started')
     if error:
         syslog.syslog(syslog.LOG_ERR, 'Processing started')

An example of setting some log options, these would include the process
ID in logged messages, and write the messages to the destination
facility used for mail logging:

     syslog.openlog(logoption=syslog.LOG_PID, facility=syslog.LOG_MAIL)
     syslog.syslog('E-mail processing initiated...')


File: python.info,  Node: Superseded Modules,  Next: Undocumented Modules,  Prev: Unix Specific Services,  Up: The Python Standard Library

5.36 Superseded Modules
=======================

The modules described in this chapter are deprecated and only kept for
backwards compatibility.  They have been superseded by other modules.

* Menu:

* optparse — Parser for command line options::
* imp — Access the import internals::


File: python.info,  Node: optparse — Parser for command line options,  Next: imp — Access the import internals,  Up: Superseded Modules

5.36.1 ‘optparse’ — Parser for command line options
---------------------------------------------------

`Source code:' Lib/optparse.py(1)

Deprecated since version 3.2: The *note optparse: c3. module is
deprecated and will not be developed further; development will continue
with the *note argparse: 5. module.

__________________________________________________________________

*note optparse: c3. is a more convenient, flexible, and powerful library
for parsing command-line options than the old *note getopt: 85. module.
*note optparse: c3. uses a more declarative style of command-line
parsing: you create an instance of *note OptionParser: 3c81, populate it
with options, and parse the command line.  *note optparse: c3. allows
users to specify options in the conventional GNU/POSIX syntax, and
additionally generates usage and help messages for you.

Here’s an example of using *note optparse: c3. in a simple script:

     from optparse import OptionParser
     ...
     parser = OptionParser()
     parser.add_option("-f", "--file", dest="filename",
                       help="write report to FILE", metavar="FILE")
     parser.add_option("-q", "--quiet",
                       action="store_false", dest="verbose", default=True,
                       help="don't print status messages to stdout")

     (options, args) = parser.parse_args()

With these few lines of code, users of your script can now do the “usual
thing” on the command-line, for example:

     <yourscript> --file=outfile -q

As it parses the command line, *note optparse: c3. sets attributes of
the ‘options’ object returned by ‘parse_args()’ based on user-supplied
command-line values.  When ‘parse_args()’ returns from parsing this
command line, ‘options.filename’ will be ‘"outfile"’ and
‘options.verbose’ will be ‘False’.  *note optparse: c3. supports both
long and short options, allows short options to be merged together, and
allows options to be associated with their arguments in a variety of
ways.  Thus, the following command lines are all equivalent to the above
example:

     <yourscript> -f outfile --quiet
     <yourscript> --quiet --file outfile
     <yourscript> -q -foutfile
     <yourscript> -qfoutfile

Additionally, users can run one of the following

     <yourscript> -h
     <yourscript> --help

and *note optparse: c3. will print out a brief summary of your script’s
options:

     Usage: <yourscript> [options]

     Options:
       -h, --help            show this help message and exit
       -f FILE, --file=FILE  write report to FILE
       -q, --quiet           don't print status messages to stdout

where the value of `yourscript' is determined at runtime (normally from
‘sys.argv[0]’).

* Menu:

* Background::
* Tutorial: Tutorial<2>.
* Reference Guide::
* Option Callbacks::
* Extending optparse::

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/optparse.py


File: python.info,  Node: Background,  Next: Tutorial<2>,  Up: optparse — Parser for command line options

5.36.1.1 Background
...................

*note optparse: c3. was explicitly designed to encourage the creation of
programs with straightforward, conventional command-line interfaces.  To
that end, it supports only the most common command-line syntax and
semantics conventionally used under Unix.  If you are unfamiliar with
these conventions, read this section to acquaint yourself with them.

* Menu:

* Terminology::
* What are options for?::
* What are positional arguments for?::


File: python.info,  Node: Terminology,  Next: What are options for?,  Up: Background

5.36.1.2 Terminology
....................

argument

     a string entered on the command-line, and passed by the shell to
     ‘execl()’ or ‘execv()’.  In Python, arguments are elements of
     ‘sys.argv[1:]’ (‘sys.argv[0]’ is the name of the program being
     executed).  Unix shells also use the term “word”.

     It is occasionally desirable to substitute an argument list other
     than ‘sys.argv[1:]’, so you should read “argument” as “an element
     of ‘sys.argv[1:]’, or of some other list provided as a substitute
     for ‘sys.argv[1:]’”.

option

     an argument used to supply extra information to guide or customize
     the execution of a program.  There are many different syntaxes for
     options; the traditional Unix syntax is a hyphen (“-”) followed by
     a single letter, e.g.  ‘-x’ or ‘-F’.  Also, traditional Unix syntax
     allows multiple options to be merged into a single argument, e.g.
     ‘-x -F’ is equivalent to ‘-xF’.  The GNU project introduced ‘--’
     followed by a series of hyphen-separated words, e.g.  ‘--file’ or
     ‘--dry-run’.  These are the only two option syntaxes provided by
     *note optparse: c3.

     Some other option syntaxes that the world has seen include:

        * a hyphen followed by a few letters, e.g.  ‘-pf’ (this is `not'
          the same as multiple options merged into a single argument)

        * a hyphen followed by a whole word, e.g.  ‘-file’ (this is
          technically equivalent to the previous syntax, but they aren’t
          usually seen in the same program)

        * a plus sign followed by a single letter, or a few letters, or
          a word, e.g.  ‘+f’, ‘+rgb’

        * a slash followed by a letter, or a few letters, or a word,
          e.g.  ‘/f’, ‘/file’

     These option syntaxes are not supported by *note optparse: c3, and
     they never will be.  This is deliberate: the first three are
     non-standard on any environment, and the last only makes sense if
     you’re exclusively targeting VMS, MS-DOS, and/or Windows.

option argument

     an argument that follows an option, is closely associated with that
     option, and is consumed from the argument list when that option is.
     With *note optparse: c3, option arguments may either be in a
     separate argument from their option:

          -f foo
          --file foo

     or included in the same argument:

          -ffoo
          --file=foo

     Typically, a given option either takes an argument or it doesn’t.
     Lots of people want an “optional option arguments” feature, meaning
     that some options will take an argument if they see it, and won’t
     if they don’t.  This is somewhat controversial, because it makes
     parsing ambiguous: if ‘-a’ takes an optional argument and ‘-b’ is
     another option entirely, how do we interpret ‘-ab’?  Because of
     this ambiguity, *note optparse: c3. does not support this feature.

positional argument

     something leftover in the argument list after options have been
     parsed, i.e.  after options and their arguments have been parsed
     and removed from the argument list.

required option

     an option that must be supplied on the command-line; note that the
     phrase “required option” is self-contradictory in English.  *note
     optparse: c3. doesn’t prevent you from implementing required
     options, but doesn’t give you much help at it either.

For example, consider this hypothetical command-line:

     prog -v --report report.txt foo bar

‘-v’ and ‘--report’ are both options.  Assuming that ‘--report’ takes
one argument, ‘report.txt’ is an option argument.  ‘foo’ and ‘bar’ are
positional arguments.


File: python.info,  Node: What are options for?,  Next: What are positional arguments for?,  Prev: Terminology,  Up: Background

5.36.1.3 What are options for?
..............................

Options are used to provide extra information to tune or customize the
execution of a program.  In case it wasn’t clear, options are usually
`optional'.  A program should be able to run just fine with no options
whatsoever.  (Pick a random program from the Unix or GNU toolsets.  Can
it run without any options at all and still make sense?  The main
exceptions are ‘find’, ‘tar’, and ‘dd’—all of which are mutant oddballs
that have been rightly criticized for their non-standard syntax and
confusing interfaces.)

Lots of people want their programs to have “required options”.  Think
about it.  If it’s required, then it’s `not optional'!  If there is a
piece of information that your program absolutely requires in order to
run successfully, that’s what positional arguments are for.

As an example of good command-line interface design, consider the humble
‘cp’ utility, for copying files.  It doesn’t make much sense to try to
copy files without supplying a destination and at least one source.
Hence, ‘cp’ fails if you run it with no arguments.  However, it has a
flexible, useful syntax that does not require any options at all:

     cp SOURCE DEST
     cp SOURCE ... DEST-DIR

You can get pretty far with just that.  Most ‘cp’ implementations
provide a bunch of options to tweak exactly how the files are copied:
you can preserve mode and modification time, avoid following symlinks,
ask before clobbering existing files, etc.  But none of this distracts
from the core mission of ‘cp’, which is to copy either one file to
another, or several files to another directory.


File: python.info,  Node: What are positional arguments for?,  Prev: What are options for?,  Up: Background

5.36.1.4 What are positional arguments for?
...........................................

Positional arguments are for those pieces of information that your
program absolutely, positively requires to run.

A good user interface should have as few absolute requirements as
possible.  If your program requires 17 distinct pieces of information in
order to run successfully, it doesn’t much matter `how' you get that
information from the user—most people will give up and walk away before
they successfully run the program.  This applies whether the user
interface is a command-line, a configuration file, or a GUI: if you make
that many demands on your users, most of them will simply give up.

In short, try to minimize the amount of information that users are
absolutely required to supply—use sensible defaults whenever possible.
Of course, you also want to make your programs reasonably flexible.
That’s what options are for.  Again, it doesn’t matter if they are
entries in a config file, widgets in the “Preferences” dialog of a GUI,
or command-line options—the more options you implement, the more
flexible your program is, and the more complicated its implementation
becomes.  Too much flexibility has drawbacks as well, of course; too
many options can overwhelm users and make your code much harder to
maintain.


File: python.info,  Node: Tutorial<2>,  Next: Reference Guide,  Prev: Background,  Up: optparse — Parser for command line options

5.36.1.5 Tutorial
.................

While *note optparse: c3. is quite flexible and powerful, it’s also
straightforward to use in most cases.  This section covers the code
patterns that are common to any *note optparse: c3.-based program.

First, you need to import the OptionParser class; then, early in the
main program, create an OptionParser instance:

     from optparse import OptionParser
     ...
     parser = OptionParser()

Then you can start defining options.  The basic syntax is:

     parser.add_option(opt_str, ...,
                       attr=value, ...)

Each option has one or more option strings, such as ‘-f’ or ‘--file’,
and several option attributes that tell *note optparse: c3. what to
expect and what to do when it encounters that option on the command
line.

Typically, each option will have one short option string and one long
option string, e.g.:

     parser.add_option("-f", "--file", ...)

You’re free to define as many short option strings and as many long
option strings as you like (including zero), as long as there is at
least one option string overall.

The option strings passed to *note OptionParser.add_option(): 21cd. are
effectively labels for the option defined by that call.  For brevity, we
will frequently refer to `encountering an option' on the command line;
in reality, *note optparse: c3. encounters `option strings' and looks up
options from them.

Once all of your options are defined, instruct *note optparse: c3. to
parse your program’s command line:

     (options, args) = parser.parse_args()

(If you like, you can pass a custom argument list to ‘parse_args()’, but
that’s rarely necessary: by default it uses ‘sys.argv[1:]’.)

‘parse_args()’ returns two values:

   * ‘options’, an object containing values for all of your options—e.g.
     if ‘--file’ takes a single string argument, then ‘options.file’
     will be the filename supplied by the user, or ‘None’ if the user
     did not supply that option

   * ‘args’, the list of positional arguments leftover after parsing
     options

This tutorial section only covers the four most important option
attributes: *note action: 3c8c, *note type: 3c8d, *note dest: 3c8e.
(destination), and *note help: 3c8f.  Of these, *note action: 3c8c. is
the most fundamental.

* Menu:

* Understanding option actions::
* The store action::
* Handling boolean (flag) options: Handling boolean flag options.
* Other actions::
* Default values::
* Generating help::
* Printing a version string::
* How optparse handles errors::
* Putting it all together::


File: python.info,  Node: Understanding option actions,  Next: The store action,  Up: Tutorial<2>

5.36.1.6 Understanding option actions
.....................................

Actions tell *note optparse: c3. what to do when it encounters an option
on the command line.  There is a fixed set of actions hard-coded into
*note optparse: c3.; adding new actions is an advanced topic covered in
section *note Extending optparse: 3c92.  Most actions tell *note
optparse: c3. to store a value in some variable—for example, take a
string from the command line and store it in an attribute of ‘options’.

If you don’t specify an option action, *note optparse: c3. defaults to
‘store’.


File: python.info,  Node: The store action,  Next: Handling boolean flag options,  Prev: Understanding option actions,  Up: Tutorial<2>

5.36.1.7 The store action
.........................

The most common option action is ‘store’, which tells *note optparse:
c3. to take the next argument (or the remainder of the current
argument), ensure that it is of the correct type, and store it to your
chosen destination.

For example:

     parser.add_option("-f", "--file",
                       action="store", type="string", dest="filename")

Now let’s make up a fake command line and ask *note optparse: c3. to
parse it:

     args = ["-f", "foo.txt"]
     (options, args) = parser.parse_args(args)

When *note optparse: c3. sees the option string ‘-f’, it consumes the
next argument, ‘foo.txt’, and stores it in ‘options.filename’.  So,
after this call to ‘parse_args()’, ‘options.filename’ is ‘"foo.txt"’.

Some other option types supported by *note optparse: c3. are ‘int’ and
‘float’.  Here’s an option that expects an integer argument:

     parser.add_option("-n", type="int", dest="num")

Note that this option has no long option string, which is perfectly
acceptable.  Also, there’s no explicit action, since the default is
‘store’.

Let’s parse another fake command-line.  This time, we’ll jam the option
argument right up against the option: since ‘-n42’ (one argument) is
equivalent to ‘-n 42’ (two arguments), the code

     (options, args) = parser.parse_args(["-n42"])
     print(options.num)

will print ‘42’.

If you don’t specify a type, *note optparse: c3. assumes ‘string’.
Combined with the fact that the default action is ‘store’, that means
our first example can be a lot shorter:

     parser.add_option("-f", "--file", dest="filename")

If you don’t supply a destination, *note optparse: c3. figures out a
sensible default from the option strings: if the first long option
string is ‘--foo-bar’, then the default destination is ‘foo_bar’.  If
there are no long option strings, *note optparse: c3. looks at the first
short option string: the default destination for ‘-f’ is ‘f’.

*note optparse: c3. also includes the built-in ‘complex’ type.  Adding
types is covered in section *note Extending optparse: 3c92.


File: python.info,  Node: Handling boolean flag options,  Next: Other actions,  Prev: The store action,  Up: Tutorial<2>

5.36.1.8 Handling boolean (flag) options
........................................

Flag options—set a variable to true or false when a particular option is
seen—are quite common.  *note optparse: c3. supports them with two
separate actions, ‘store_true’ and ‘store_false’.  For example, you
might have a ‘verbose’ flag that is turned on with ‘-v’ and off with
‘-q’:

     parser.add_option("-v", action="store_true", dest="verbose")
     parser.add_option("-q", action="store_false", dest="verbose")

Here we have two different options with the same destination, which is
perfectly OK. (It just means you have to be a bit careful when setting
default values—see below.)

When *note optparse: c3. encounters ‘-v’ on the command line, it sets
‘options.verbose’ to ‘True’; when it encounters ‘-q’, ‘options.verbose’
is set to ‘False’.


File: python.info,  Node: Other actions,  Next: Default values,  Prev: Handling boolean flag options,  Up: Tutorial<2>

5.36.1.9 Other actions
......................

Some other actions supported by *note optparse: c3. are:

‘"store_const"’

     store a constant value

‘"append"’

     append this option’s argument to a list

‘"count"’

     increment a counter by one

‘"callback"’

     call a specified function

These are covered in section *note Reference Guide: 3c99, and section
*note Option Callbacks: 3c9a.


File: python.info,  Node: Default values,  Next: Generating help,  Prev: Other actions,  Up: Tutorial<2>

5.36.1.10 Default values
........................

All of the above examples involve setting some variable (the
“destination”) when certain command-line options are seen.  What happens
if those options are never seen?  Since we didn’t supply any defaults,
they are all set to ‘None’.  This is usually fine, but sometimes you
want more control.  *note optparse: c3. lets you supply a default value
for each destination, which is assigned before the command line is
parsed.

First, consider the verbose/quiet example.  If we want *note optparse:
c3. to set ‘verbose’ to ‘True’ unless ‘-q’ is seen, then we can do this:

     parser.add_option("-v", action="store_true", dest="verbose", default=True)
     parser.add_option("-q", action="store_false", dest="verbose")

Since default values apply to the `destination' rather than to any
particular option, and these two options happen to have the same
destination, this is exactly equivalent:

     parser.add_option("-v", action="store_true", dest="verbose")
     parser.add_option("-q", action="store_false", dest="verbose", default=True)

Consider this:

     parser.add_option("-v", action="store_true", dest="verbose", default=False)
     parser.add_option("-q", action="store_false", dest="verbose", default=True)

Again, the default value for ‘verbose’ will be ‘True’: the last default
value supplied for any particular destination is the one that counts.

A clearer way to specify default values is the ‘set_defaults()’ method
of OptionParser, which you can call at any time before calling
‘parse_args()’:

     parser.set_defaults(verbose=True)
     parser.add_option(...)
     (options, args) = parser.parse_args()

As before, the last value specified for a given option destination is
the one that counts.  For clarity, try to use one method or the other of
setting default values, not both.


File: python.info,  Node: Generating help,  Next: Printing a version string,  Prev: Default values,  Up: Tutorial<2>

5.36.1.11 Generating help
.........................

*note optparse: c3.’s ability to generate help and usage text
automatically is useful for creating user-friendly command-line
interfaces.  All you have to do is supply a *note help: 3c8f. value for
each option, and optionally a short usage message for your whole
program.  Here’s an OptionParser populated with user-friendly
(documented) options:

     usage = "usage: %prog [options] arg1 arg2"
     parser = OptionParser(usage=usage)
     parser.add_option("-v", "--verbose",
                       action="store_true", dest="verbose", default=True,
                       help="make lots of noise [default]")
     parser.add_option("-q", "--quiet",
                       action="store_false", dest="verbose",
                       help="be vewwy quiet (I'm hunting wabbits)")
     parser.add_option("-f", "--filename",
                       metavar="FILE", help="write output to FILE")
     parser.add_option("-m", "--mode",
                       default="intermediate",
                       help="interaction mode: novice, intermediate, "
                            "or expert [default: %default]")

If *note optparse: c3. encounters either ‘-h’ or ‘--help’ on the
command-line, or if you just call ‘parser.print_help()’, it prints the
following to standard output:

     Usage: <yourscript> [options] arg1 arg2

     Options:
       -h, --help            show this help message and exit
       -v, --verbose         make lots of noise [default]
       -q, --quiet           be vewwy quiet (I'm hunting wabbits)
       -f FILE, --filename=FILE
                             write output to FILE
       -m MODE, --mode=MODE  interaction mode: novice, intermediate, or
                             expert [default: intermediate]

(If the help output is triggered by a help option, *note optparse: c3.
exits after printing the help text.)

There’s a lot going on here to help *note optparse: c3. generate the
best possible help message:

   * the script defines its own usage message:

          usage = "usage: %prog [options] arg1 arg2"

     *note optparse: c3. expands ‘%prog’ in the usage string to the name
     of the current program, i.e.  ‘os.path.basename(sys.argv[0])’.  The
     expanded string is then printed before the detailed option help.

     If you don’t supply a usage string, *note optparse: c3. uses a
     bland but sensible default: ‘"Usage: %prog [options]"’, which is
     fine if your script doesn’t take any positional arguments.

   * every option defines a help string, and doesn’t worry about
     line-wrapping—*note optparse: c3. takes care of wrapping lines and
     making the help output look good.

   * options that take a value indicate this fact in their
     automatically-generated help message, e.g.  for the “mode” option:

          -m MODE, --mode=MODE

     Here, “MODE” is called the meta-variable: it stands for the
     argument that the user is expected to supply to ‘-m’/‘--mode’.  By
     default, *note optparse: c3. converts the destination variable name
     to uppercase and uses that for the meta-variable.  Sometimes,
     that’s not what you want—for example, the ‘--filename’ option
     explicitly sets ‘metavar="FILE"’, resulting in this
     automatically-generated option description:

          -f FILE, --filename=FILE

     This is important for more than just saving space, though: the
     manually written help text uses the meta-variable ‘FILE’ to clue
     the user in that there’s a connection between the semi-formal
     syntax ‘-f FILE’ and the informal semantic description “write
     output to FILE”.  This is a simple but effective way to make your
     help text a lot clearer and more useful for end users.

   * options that have a default value can include ‘%default’ in the
     help string—*note optparse: c3. will replace it with *note str():
     205. of the option’s default value.  If an option has no default
     value (or the default value is ‘None’), ‘%default’ expands to
     ‘none’.

* Menu:

* Grouping Options::


File: python.info,  Node: Grouping Options,  Up: Generating help

5.36.1.12 Grouping Options
..........................

When dealing with many options, it is convenient to group these options
for better help output.  An *note OptionParser: 3c81. can contain
several option groups, each of which can contain several options.

An option group is obtained using the class *note OptionGroup: 3ca0.:

 -- Class: optparse.OptionGroup (parser, title, description=None)

     where

        * parser is the *note OptionParser: 3c81. instance the group
          will be inserted in to

        * title is the group title

        * description, optional, is a long description of the group

*note OptionGroup: 3ca0. inherits from ‘OptionContainer’ (like *note
OptionParser: 3c81.) and so the ‘add_option()’ method can be used to add
an option to the group.

Once all the options are declared, using the *note OptionParser: 3c81.
method ‘add_option_group()’ the group is added to the previously defined
parser.

Continuing with the parser defined in the previous section, adding an
*note OptionGroup: 3ca0. to a parser is easy:

     group = OptionGroup(parser, "Dangerous Options",
                         "Caution: use these options at your own risk.  "
                         "It is believed that some of them bite.")
     group.add_option("-g", action="store_true", help="Group option.")
     parser.add_option_group(group)

This would result in the following help output:

     Usage: <yourscript> [options] arg1 arg2

     Options:
       -h, --help            show this help message and exit
       -v, --verbose         make lots of noise [default]
       -q, --quiet           be vewwy quiet (I'm hunting wabbits)
       -f FILE, --filename=FILE
                             write output to FILE
       -m MODE, --mode=MODE  interaction mode: novice, intermediate, or
                             expert [default: intermediate]

       Dangerous Options:
         Caution: use these options at your own risk.  It is believed that some
         of them bite.

         -g                  Group option.

A bit more complete example might involve using more than one group:
still extending the previous example:

     group = OptionGroup(parser, "Dangerous Options",
                         "Caution: use these options at your own risk.  "
                         "It is believed that some of them bite.")
     group.add_option("-g", action="store_true", help="Group option.")
     parser.add_option_group(group)

     group = OptionGroup(parser, "Debug Options")
     group.add_option("-d", "--debug", action="store_true",
                      help="Print debug information")
     group.add_option("-s", "--sql", action="store_true",
                      help="Print all SQL statements executed")
     group.add_option("-e", action="store_true", help="Print every action done")
     parser.add_option_group(group)

that results in the following output:

     Usage: <yourscript> [options] arg1 arg2

     Options:
       -h, --help            show this help message and exit
       -v, --verbose         make lots of noise [default]
       -q, --quiet           be vewwy quiet (I'm hunting wabbits)
       -f FILE, --filename=FILE
                             write output to FILE
       -m MODE, --mode=MODE  interaction mode: novice, intermediate, or expert
                             [default: intermediate]

       Dangerous Options:
         Caution: use these options at your own risk.  It is believed that some
         of them bite.

         -g                  Group option.

       Debug Options:
         -d, --debug         Print debug information
         -s, --sql           Print all SQL statements executed
         -e                  Print every action done

Another interesting method, in particular when working programmatically
with option groups is:

 -- Method: OptionParser.get_option_group (opt_str)

     Return the *note OptionGroup: 3ca0. to which the short or long
     option string `opt_str' (e.g.  ‘'-o'’ or ‘'--option'’) belongs.  If
     there’s no such *note OptionGroup: 3ca0, return ‘None’.


File: python.info,  Node: Printing a version string,  Next: How optparse handles errors,  Prev: Generating help,  Up: Tutorial<2>

5.36.1.13 Printing a version string
...................................

Similar to the brief usage string, *note optparse: c3. can also print a
version string for your program.  You have to supply the string as the
‘version’ argument to OptionParser:

     parser = OptionParser(usage="%prog [-f] [-q]", version="%prog 1.0")

‘%prog’ is expanded just like it is in ‘usage’.  Apart from that,
‘version’ can contain anything you like.  When you supply it, *note
optparse: c3. automatically adds a ‘--version’ option to your parser.
If it encounters this option on the command line, it expands your
‘version’ string (by replacing ‘%prog’), prints it to stdout, and exits.

For example, if your script is called ‘/usr/bin/foo’:

     $ /usr/bin/foo --version
     foo 1.0

The following two methods can be used to print and get the ‘version’
string:

 -- Method: OptionParser.print_version (file=None)

     Print the version message for the current program (‘self.version’)
     to `file' (default stdout).  As with *note print_usage(): 3ca5, any
     occurrence of ‘%prog’ in ‘self.version’ is replaced with the name
     of the current program.  Does nothing if ‘self.version’ is empty or
     undefined.

 -- Method: OptionParser.get_version ()

     Same as *note print_version(): 3ca4. but returns the version string
     instead of printing it.


File: python.info,  Node: How optparse handles errors,  Next: Putting it all together,  Prev: Printing a version string,  Up: Tutorial<2>

5.36.1.14 How ‘optparse’ handles errors
.......................................

There are two broad classes of errors that *note optparse: c3. has to
worry about: programmer errors and user errors.  Programmer errors are
usually erroneous calls to *note OptionParser.add_option(): 21cd, e.g.
invalid option strings, unknown option attributes, missing option
attributes, etc.  These are dealt with in the usual way: raise an
exception (either ‘optparse.OptionError’ or *note TypeError: 1fe.) and
let the program crash.

Handling user errors is much more important, since they are guaranteed
to happen no matter how stable your code is.  *note optparse: c3. can
automatically detect some user errors, such as bad option arguments
(passing ‘-n 4x’ where ‘-n’ takes an integer argument), missing
arguments (‘-n’ at the end of the command line, where ‘-n’ takes an
argument of any type).  Also, you can call ‘OptionParser.error()’ to
signal an application-defined error condition:

     (options, args) = parser.parse_args()
     ...
     if options.a and options.b:
         parser.error("options -a and -b are mutually exclusive")

In either case, *note optparse: c3. handles the error the same way: it
prints the program’s usage message and an error message to standard
error and exits with error status 2.

Consider the first example above, where the user passes ‘4x’ to an
option that takes an integer:

     $ /usr/bin/foo -n 4x
     Usage: foo [options]

     foo: error: option -n: invalid integer value: '4x'

Or, where the user fails to pass a value at all:

     $ /usr/bin/foo -n
     Usage: foo [options]

     foo: error: -n option requires an argument

*note optparse: c3.-generated error messages take care always to mention
the option involved in the error; be sure to do the same when calling
‘OptionParser.error()’ from your application code.

If *note optparse: c3.’s default error-handling behaviour does not suit
your needs, you’ll need to subclass OptionParser and override its
‘exit()’ and/or ‘error()’ methods.


File: python.info,  Node: Putting it all together,  Prev: How optparse handles errors,  Up: Tutorial<2>

5.36.1.15 Putting it all together
.................................

Here’s what *note optparse: c3.-based scripts usually look like:

     from optparse import OptionParser
     ...
     def main():
         usage = "usage: %prog [options] arg"
         parser = OptionParser(usage)
         parser.add_option("-f", "--file", dest="filename",
                           help="read data from FILENAME")
         parser.add_option("-v", "--verbose",
                           action="store_true", dest="verbose")
         parser.add_option("-q", "--quiet",
                           action="store_false", dest="verbose")
         ...
         (options, args) = parser.parse_args()
         if len(args) != 1:
             parser.error("incorrect number of arguments")
         if options.verbose:
             print("reading %s..." % options.filename)
         ...

     if __name__ == "__main__":
         main()


File: python.info,  Node: Reference Guide,  Next: Option Callbacks,  Prev: Tutorial<2>,  Up: optparse — Parser for command line options

5.36.1.16 Reference Guide
.........................

* Menu:

* Creating the parser::
* Populating the parser::
* Defining options::
* Option attributes::
* Standard option actions::
* Standard option types::
* Parsing arguments: Parsing arguments<2>.
* Querying and manipulating your option parser::
* Conflicts between options::
* Cleanup: Cleanup<2>.
* Other methods::


File: python.info,  Node: Creating the parser,  Next: Populating the parser,  Up: Reference Guide

5.36.1.17 Creating the parser
.............................

The first step in using *note optparse: c3. is to create an OptionParser
instance.

 -- Class: optparse.OptionParser (...)

     The OptionParser constructor has no required arguments, but a
     number of optional keyword arguments.  You should always pass them
     as keyword arguments, i.e.  do not rely on the order in which the
     arguments are declared.

     ‘usage’ (default: ‘"%prog [options]"’)

          The usage summary to print when your program is run
          incorrectly or with a help option.  When *note optparse: c3.
          prints the usage string, it expands ‘%prog’ to
          ‘os.path.basename(sys.argv[0])’ (or to ‘prog’ if you passed
          that keyword argument).  To suppress a usage message, pass the
          special value ‘optparse.SUPPRESS_USAGE’.

     ‘option_list’ (default: ‘[]’)

          A list of Option objects to populate the parser with.  The
          options in ‘option_list’ are added after any options in
          ‘standard_option_list’ (a class attribute that may be set by
          OptionParser subclasses), but before any version or help
          options.  Deprecated; use *note add_option(): 21cd. after
          creating the parser instead.

     ‘option_class’ (default: optparse.Option)

          Class to use when adding options to the parser in *note
          add_option(): 21cd.

     ‘version’ (default: ‘None’)

          A version string to print when the user supplies a version
          option.  If you supply a true value for ‘version’, *note
          optparse: c3. automatically adds a version option with the
          single option string ‘--version’.  The substring ‘%prog’ is
          expanded the same as for ‘usage’.

     ‘conflict_handler’ (default: ‘"error"’)

          Specifies what to do when options with conflicting option
          strings are added to the parser; see section *note Conflicts
          between options: 3cae.

     ‘description’ (default: ‘None’)

          A paragraph of text giving a brief overview of your program.
          *note optparse: c3. reformats this paragraph to fit the
          current terminal width and prints it when the user requests
          help (after ‘usage’, but before the list of options).

     ‘formatter’ (default: a new ‘IndentedHelpFormatter’)

          An instance of optparse.HelpFormatter that will be used for
          printing help text.  *note optparse: c3. provides two concrete
          classes for this purpose: IndentedHelpFormatter and
          TitledHelpFormatter.

     ‘add_help_option’ (default: ‘True’)

          If true, *note optparse: c3. will add a help option (with
          option strings ‘-h’ and ‘--help’) to the parser.

     ‘prog’

          The string to use when expanding ‘%prog’ in ‘usage’ and
          ‘version’ instead of ‘os.path.basename(sys.argv[0])’.

     ‘epilog’ (default: ‘None’)

          A paragraph of help text to print after the option help.


File: python.info,  Node: Populating the parser,  Next: Defining options,  Prev: Creating the parser,  Up: Reference Guide

5.36.1.18 Populating the parser
...............................

There are several ways to populate the parser with options.  The
preferred way is by using *note OptionParser.add_option(): 21cd, as
shown in section *note Tutorial: 3c8a.  ‘add_option()’ can be called in
one of two ways:

   * pass it an Option instance (as returned by ‘make_option()’)

   * pass it any combination of positional and keyword arguments that
     are acceptable to ‘make_option()’ (i.e., to the Option
     constructor), and it will create the Option instance for you

The other alternative is to pass a list of pre-constructed Option
instances to the OptionParser constructor, as in:

     option_list = [
         make_option("-f", "--filename",
                     action="store", type="string", dest="filename"),
         make_option("-q", "--quiet",
                     action="store_false", dest="verbose"),
         ]
     parser = OptionParser(option_list=option_list)

(‘make_option()’ is a factory function for creating Option instances;
currently it is an alias for the Option constructor.  A future version
of *note optparse: c3. may split Option into several classes, and
‘make_option()’ will pick the right class to instantiate.  Do not
instantiate Option directly.)


File: python.info,  Node: Defining options,  Next: Option attributes,  Prev: Populating the parser,  Up: Reference Guide

5.36.1.19 Defining options
..........................

Each Option instance represents a set of synonymous command-line option
strings, e.g.  ‘-f’ and ‘--file’.  You can specify any number of short
or long option strings, but you must specify at least one overall option
string.

The canonical way to create an ‘Option’ instance is with the
‘add_option()’ method of *note OptionParser: 3c81.

 -- Method: OptionParser.add_option (option)

 -- Method: OptionParser.add_option (*opt_str, attr=value, ...)

     To define an option with only a short option string:

          parser.add_option("-f", attr=value, ...)

     And to define an option with only a long option string:

          parser.add_option("--foo", attr=value, ...)

     The keyword arguments define attributes of the new Option object.
     The most important option attribute is *note action: 3c8c, and it
     largely determines which other attributes are relevant or required.
     If you pass irrelevant option attributes, or fail to pass required
     ones, *note optparse: c3. raises an ‘OptionError’ exception
     explaining your mistake.

     An option’s `action' determines what *note optparse: c3. does when
     it encounters this option on the command-line.  The standard option
     actions hard-coded into *note optparse: c3. are:

     ‘"store"’

          store this option’s argument (default)

     ‘"store_const"’

          store a constant value

     ‘"store_true"’

          store ‘True’

     ‘"store_false"’

          store ‘False’

     ‘"append"’

          append this option’s argument to a list

     ‘"append_const"’

          append a constant value to a list

     ‘"count"’

          increment a counter by one

     ‘"callback"’

          call a specified function

     ‘"help"’

          print a usage message including all options and the
          documentation for them

     (If you don’t supply an action, the default is ‘"store"’.  For this
     action, you may also supply *note type: 3c8d. and *note dest: 3c8e.
     option attributes; see *note Standard option actions: 3cb3.)

As you can see, most actions involve storing or updating a value
somewhere.  *note optparse: c3. always creates a special object for
this, conventionally called ‘options’ (it happens to be an instance of
‘optparse.Values’).  Option arguments (and various other values) are
stored as attributes of this object, according to the *note dest: 3c8e.
(destination) option attribute.

For example, when you call

     parser.parse_args()

one of the first things *note optparse: c3. does is create the ‘options’
object:

     options = Values()

If one of the options in this parser is defined with

     parser.add_option("-f", "--file", action="store", type="string", dest="filename")

and the command-line being parsed includes any of the following:

     -ffoo
     -f foo
     --file=foo
     --file foo

then *note optparse: c3, on seeing this option, will do the equivalent
of

     options.filename = "foo"

The *note type: 3c8d. and *note dest: 3c8e. option attributes are almost
as important as *note action: 3c8c, but *note action: 3c8c. is the only
one that makes sense for `all' options.


File: python.info,  Node: Option attributes,  Next: Standard option actions,  Prev: Defining options,  Up: Reference Guide

5.36.1.20 Option attributes
...........................

The following option attributes may be passed as keyword arguments to
*note OptionParser.add_option(): 21cd.  If you pass an option attribute
that is not relevant to a particular option, or fail to pass a required
option attribute, *note optparse: c3. raises ‘OptionError’.

 -- Attribute: Option.action

     (default: ‘"store"’)

     Determines *note optparse: c3.’s behaviour when this option is seen
     on the command line; the available options are documented *note
     here: 3cb3.

 -- Attribute: Option.type

     (default: ‘"string"’)

     The argument type expected by this option (e.g., ‘"string"’ or
     ‘"int"’); the available option types are documented *note here:
     3cb6.

 -- Attribute: Option.dest

     (default: derived from option strings)

     If the option’s action implies writing or modifying a value
     somewhere, this tells *note optparse: c3. where to write it: *note
     dest: 3c8e. names an attribute of the ‘options’ object that *note
     optparse: c3. builds as it parses the command line.

 -- Attribute: Option.default

     The value to use for this option’s destination if the option is not
     seen on the command line.  See also *note
     OptionParser.set_defaults(): 3cb8.

 -- Attribute: Option.nargs

     (default: 1)

     How many arguments of type *note type: 3c8d. should be consumed
     when this option is seen.  If > 1, *note optparse: c3. will store a
     tuple of values to *note dest: 3c8e.

 -- Attribute: Option.const

     For actions that store a constant value, the constant value to
     store.

 -- Attribute: Option.choices

     For options of type ‘"choice"’, the list of strings the user may
     choose from.

 -- Attribute: Option.callback

     For options with action ‘"callback"’, the callable to call when
     this option is seen.  See section *note Option Callbacks: 3c9a. for
     detail on the arguments passed to the callable.

 -- Attribute: Option.callback_args
 -- Attribute: Option.callback_kwargs

     Additional positional and keyword arguments to pass to ‘callback’
     after the four standard callback arguments.

 -- Attribute: Option.help

     Help text to print for this option when listing all available
     options after the user supplies a *note help: 3c8f. option (such as
     ‘--help’).  If no help text is supplied, the option will be listed
     without help text.  To hide this option, use the special value
     ‘optparse.SUPPRESS_HELP’.

 -- Attribute: Option.metavar

     (default: derived from option strings)

     Stand-in for the option argument(s) to use when printing help text.
     See section *note Tutorial: 3c8a. for an example.


File: python.info,  Node: Standard option actions,  Next: Standard option types,  Prev: Option attributes,  Up: Reference Guide

5.36.1.21 Standard option actions
.................................

The various option actions all have slightly different requirements and
effects.  Most actions have several relevant option attributes which you
may specify to guide *note optparse: c3.’s behaviour; a few have
required attributes, which you must specify for any option using that
action.

   * ‘"store"’ [relevant: *note type: 3c8d, *note dest: 3c8e, *note
     nargs: 3cb9, *note choices: 3cbb.]

     The option must be followed by an argument, which is converted to a
     value according to *note type: 3c8d. and stored in *note dest:
     3c8e.  If *note nargs: 3cb9. > 1, multiple arguments will be
     consumed from the command line; all will be converted according to
     *note type: 3c8d. and stored to *note dest: 3c8e. as a tuple.  See
     the *note Standard option types: 3cb6. section.

     If *note choices: 3cbb. is supplied (a list or tuple of strings),
     the type defaults to ‘"choice"’.

     If *note type: 3c8d. is not supplied, it defaults to ‘"string"’.

     If *note dest: 3c8e. is not supplied, *note optparse: c3. derives a
     destination from the first long option string (e.g., ‘--foo-bar’
     implies ‘foo_bar’).  If there are no long option strings, *note
     optparse: c3. derives a destination from the first short option
     string (e.g., ‘-f’ implies ‘f’).

     Example:

          parser.add_option("-f")
          parser.add_option("-p", type="float", nargs=3, dest="point")

     As it parses the command line

          -f foo.txt -p 1 -3.5 4 -fbar.txt

     *note optparse: c3. will set

          options.f = "foo.txt"
          options.point = (1.0, -3.5, 4.0)
          options.f = "bar.txt"

   * ‘"store_const"’ [required: *note const: 3cba.; relevant: *note
     dest: 3c8e.]

     The value *note const: 3cba. is stored in *note dest: 3c8e.

     Example:

          parser.add_option("-q", "--quiet",
                            action="store_const", const=0, dest="verbose")
          parser.add_option("-v", "--verbose",
                            action="store_const", const=1, dest="verbose")
          parser.add_option("--noisy",
                            action="store_const", const=2, dest="verbose")

     If ‘--noisy’ is seen, *note optparse: c3. will set

          options.verbose = 2

   * ‘"store_true"’ [relevant: *note dest: 3c8e.]

     A special case of ‘"store_const"’ that stores ‘True’ to *note dest:
     3c8e.

   * ‘"store_false"’ [relevant: *note dest: 3c8e.]

     Like ‘"store_true"’, but stores ‘False’.

     Example:

          parser.add_option("--clobber", action="store_true", dest="clobber")
          parser.add_option("--no-clobber", action="store_false", dest="clobber")

   * ‘"append"’ [relevant: *note type: 3c8d, *note dest: 3c8e, *note
     nargs: 3cb9, *note choices: 3cbb.]

     The option must be followed by an argument, which is appended to
     the list in *note dest: 3c8e.  If no default value for *note dest:
     3c8e. is supplied, an empty list is automatically created when
     *note optparse: c3. first encounters this option on the
     command-line.  If *note nargs: 3cb9. > 1, multiple arguments are
     consumed, and a tuple of length *note nargs: 3cb9. is appended to
     *note dest: 3c8e.

     The defaults for *note type: 3c8d. and *note dest: 3c8e. are the
     same as for the ‘"store"’ action.

     Example:

          parser.add_option("-t", "--tracks", action="append", type="int")

     If ‘-t3’ is seen on the command-line, *note optparse: c3. does the
     equivalent of:

          options.tracks = []
          options.tracks.append(int("3"))

     If, a little later on, ‘--tracks=4’ is seen, it does:

          options.tracks.append(int("4"))

     The ‘append’ action calls the ‘append’ method on the current value
     of the option.  This means that any default value specified must
     have an ‘append’ method.  It also means that if the default value
     is non-empty, the default elements will be present in the parsed
     value for the option, with any values from the command line
     appended after those default values:

          >>> parser.add_option("--files", action="append", default=['~/.mypkg/defaults'])
          >>> opts, args = parser.parse_args(['--files', 'overrides.mypkg'])
          >>> opts.files
          ['~/.mypkg/defaults', 'overrides.mypkg']

   * ‘"append_const"’ [required: *note const: 3cba.; relevant: *note
     dest: 3c8e.]

     Like ‘"store_const"’, but the value *note const: 3cba. is appended
     to *note dest: 3c8e.; as with ‘"append"’, *note dest: 3c8e.
     defaults to ‘None’, and an empty list is automatically created the
     first time the option is encountered.

   * ‘"count"’ [relevant: *note dest: 3c8e.]

     Increment the integer stored at *note dest: 3c8e.  If no default
     value is supplied, *note dest: 3c8e. is set to zero before being
     incremented the first time.

     Example:

          parser.add_option("-v", action="count", dest="verbosity")

     The first time ‘-v’ is seen on the command line, *note optparse:
     c3. does the equivalent of:

          options.verbosity = 0
          options.verbosity += 1

     Every subsequent occurrence of ‘-v’ results in

          options.verbosity += 1

   * ‘"callback"’ [required: *note callback: 3cbc.; relevant: *note
     type: 3c8d, *note nargs: 3cb9, *note callback_args: 3cbd, *note
     callback_kwargs: 3cbe.]

     Call the function specified by *note callback: 3cbc, which is
     called as

          func(option, opt_str, value, parser, *args, **kwargs)

     See section *note Option Callbacks: 3c9a. for more detail.

   * ‘"help"’

     Prints a complete help message for all the options in the current
     option parser.  The help message is constructed from the ‘usage’
     string passed to OptionParser’s constructor and the *note help:
     3c8f. string passed to every option.

     If no *note help: 3c8f. string is supplied for an option, it will
     still be listed in the help message.  To omit an option entirely,
     use the special value ‘optparse.SUPPRESS_HELP’.

     *note optparse: c3. automatically adds a *note help: 3c8f. option
     to all OptionParsers, so you do not normally need to create one.

     Example:

          from optparse import OptionParser, SUPPRESS_HELP

          # usually, a help option is added automatically, but that can
          # be suppressed using the add_help_option argument
          parser = OptionParser(add_help_option=False)

          parser.add_option("-h", "--help", action="help")
          parser.add_option("-v", action="store_true", dest="verbose",
                            help="Be moderately verbose")
          parser.add_option("--file", dest="filename",
                            help="Input file to read data from")
          parser.add_option("--secret", help=SUPPRESS_HELP)

     If *note optparse: c3. sees either ‘-h’ or ‘--help’ on the command
     line, it will print something like the following help message to
     stdout (assuming ‘sys.argv[0]’ is ‘"foo.py"’):

          Usage: foo.py [options]

          Options:
            -h, --help        Show this help message and exit
            -v                Be moderately verbose
            --file=FILENAME   Input file to read data from

     After printing the help message, *note optparse: c3. terminates
     your process with ‘sys.exit(0)’.

   * ‘"version"’

     Prints the version number supplied to the OptionParser to stdout
     and exits.  The version number is actually formatted and printed by
     the ‘print_version()’ method of OptionParser.  Generally only
     relevant if the ‘version’ argument is supplied to the OptionParser
     constructor.  As with *note help: 3c8f. options, you will rarely
     create ‘version’ options, since *note optparse: c3. automatically
     adds them when needed.


File: python.info,  Node: Standard option types,  Next: Parsing arguments<2>,  Prev: Standard option actions,  Up: Reference Guide

5.36.1.22 Standard option types
...............................

*note optparse: c3. has five built-in option types: ‘"string"’, ‘"int"’,
‘"choice"’, ‘"float"’ and ‘"complex"’.  If you need to add new option
types, see section *note Extending optparse: 3c92.

Arguments to string options are not checked or converted in any way: the
text on the command line is stored in the destination (or passed to the
callback) as-is.

Integer arguments (type ‘"int"’) are parsed as follows:

   * if the number starts with ‘0x’, it is parsed as a hexadecimal
     number

   * if the number starts with ‘0’, it is parsed as an octal number

   * if the number starts with ‘0b’, it is parsed as a binary number

   * otherwise, the number is parsed as a decimal number

The conversion is done by calling *note int(): 204. with the appropriate
base (2, 8, 10, or 16).  If this fails, so will *note optparse: c3,
although with a more useful error message.

‘"float"’ and ‘"complex"’ option arguments are converted directly with
*note float(): 1fd. and *note complex(): 2c1, with similar
error-handling.

‘"choice"’ options are a subtype of ‘"string"’ options.  The *note
choices: 3cbb. option attribute (a sequence of strings) defines the set
of allowed option arguments.  ‘optparse.check_choice()’ compares
user-supplied option arguments against this master list and raises
‘OptionValueError’ if an invalid string is given.


File: python.info,  Node: Parsing arguments<2>,  Next: Querying and manipulating your option parser,  Prev: Standard option types,  Up: Reference Guide

5.36.1.23 Parsing arguments
...........................

The whole point of creating and populating an OptionParser is to call
its ‘parse_args()’ method:

     (options, args) = parser.parse_args(args=None, values=None)

where the input parameters are

‘args’

     the list of arguments to process (default: ‘sys.argv[1:]’)

‘values’

     an ‘optparse.Values’ object to store option arguments in (default:
     a new instance of ‘Values’) – if you give an existing object, the
     option defaults will not be initialized on it

and the return values are

‘options’

     the same object that was passed in as ‘values’, or the
     optparse.Values instance created by *note optparse: c3.

‘args’

     the leftover positional arguments after all options have been
     processed

The most common usage is to supply neither keyword argument.  If you
supply ‘values’, it will be modified with repeated *note setattr():
1712. calls (roughly one for every option argument stored to an option
destination) and returned by ‘parse_args()’.

If ‘parse_args()’ encounters any errors in the argument list, it calls
the OptionParser’s ‘error()’ method with an appropriate end-user error
message.  This ultimately terminates your process with an exit status of
2 (the traditional Unix exit status for command-line errors).


File: python.info,  Node: Querying and manipulating your option parser,  Next: Conflicts between options,  Prev: Parsing arguments<2>,  Up: Reference Guide

5.36.1.24 Querying and manipulating your option parser
......................................................

The default behavior of the option parser can be customized slightly,
and you can also poke around your option parser and see what’s there.
OptionParser provides several methods to help you out:

 -- Method: OptionParser.disable_interspersed_args ()

     Set parsing to stop on the first non-option.  For example, if ‘-a’
     and ‘-b’ are both simple options that take no arguments, *note
     optparse: c3. normally accepts this syntax:

          prog -a arg1 -b arg2

     and treats it as equivalent to

          prog -a -b arg1 arg2

     To disable this feature, call *note disable_interspersed_args():
     21ce.  This restores traditional Unix syntax, where option parsing
     stops with the first non-option argument.

     Use this if you have a command processor which runs another command
     which has options of its own and you want to make sure these
     options don’t get confused.  For example, each command might have a
     different set of options.

 -- Method: OptionParser.enable_interspersed_args ()

     Set parsing to not stop on the first non-option, allowing
     interspersing switches with command arguments.  This is the default
     behavior.

 -- Method: OptionParser.get_option (opt_str)

     Returns the Option instance with the option string `opt_str', or
     ‘None’ if no options have that option string.

 -- Method: OptionParser.has_option (opt_str)

     Return ‘True’ if the OptionParser has an option with option string
     `opt_str' (e.g., ‘-q’ or ‘--verbose’).

 -- Method: OptionParser.remove_option (opt_str)

     If the *note OptionParser: 3c81. has an option corresponding to
     `opt_str', that option is removed.  If that option provided any
     other option strings, all of those option strings become invalid.
     If `opt_str' does not occur in any option belonging to this *note
     OptionParser: 3c81, raises *note ValueError: 16d.


File: python.info,  Node: Conflicts between options,  Next: Cleanup<2>,  Prev: Querying and manipulating your option parser,  Up: Reference Guide

5.36.1.25 Conflicts between options
...................................

If you’re not careful, it’s easy to define options with conflicting
option strings:

     parser.add_option("-n", "--dry-run", ...)
     ...
     parser.add_option("-n", "--noisy", ...)

(This is particularly true if you’ve defined your own OptionParser
subclass with some standard options.)

Every time you add an option, *note optparse: c3. checks for conflicts
with existing options.  If it finds any, it invokes the current
conflict-handling mechanism.  You can set the conflict-handling
mechanism either in the constructor:

     parser = OptionParser(..., conflict_handler=handler)

or with a separate call:

     parser.set_conflict_handler(handler)

The available conflict handlers are:

     ‘"error"’ (default)

          assume option conflicts are a programming error and raise
          ‘OptionConflictError’

     ‘"resolve"’

          resolve option conflicts intelligently (see below)

As an example, let’s define an *note OptionParser: 3c81. that resolves
conflicts intelligently and add conflicting options to it:

     parser = OptionParser(conflict_handler="resolve")
     parser.add_option("-n", "--dry-run", ..., help="do no harm")
     parser.add_option("-n", "--noisy", ..., help="be noisy")

At this point, *note optparse: c3. detects that a previously-added
option is already using the ‘-n’ option string.  Since
‘conflict_handler’ is ‘"resolve"’, it resolves the situation by removing
‘-n’ from the earlier option’s list of option strings.  Now ‘--dry-run’
is the only way for the user to activate that option.  If the user asks
for help, the help message will reflect that:

     Options:
       --dry-run     do no harm
       ...
       -n, --noisy   be noisy

It’s possible to whittle away the option strings for a previously-added
option until there are none left, and the user has no way of invoking
that option from the command-line.  In that case, *note optparse: c3.
removes that option completely, so it doesn’t show up in help text or
anywhere else.  Carrying on with our existing OptionParser:

     parser.add_option("--dry-run", ..., help="new dry-run option")

At this point, the original ‘-n’/‘--dry-run’ option is no longer
accessible, so *note optparse: c3. removes it, leaving this help text:

     Options:
       ...
       -n, --noisy   be noisy
       --dry-run     new dry-run option


File: python.info,  Node: Cleanup<2>,  Next: Other methods,  Prev: Conflicts between options,  Up: Reference Guide

5.36.1.26 Cleanup
.................

OptionParser instances have several cyclic references.  This should not
be a problem for Python’s garbage collector, but you may wish to break
the cyclic references explicitly by calling ‘destroy()’ on your
OptionParser once you are done with it.  This is particularly useful in
long-running applications where large object graphs are reachable from
your OptionParser.


File: python.info,  Node: Other methods,  Prev: Cleanup<2>,  Up: Reference Guide

5.36.1.27 Other methods
.......................

OptionParser supports several other public methods:

 -- Method: OptionParser.set_usage (usage)

     Set the usage string according to the rules described above for the
     ‘usage’ constructor keyword argument.  Passing ‘None’ sets the
     default usage string; use ‘optparse.SUPPRESS_USAGE’ to suppress a
     usage message.

 -- Method: OptionParser.print_usage (file=None)

     Print the usage message for the current program (‘self.usage’) to
     `file' (default stdout).  Any occurrence of the string ‘%prog’ in
     ‘self.usage’ is replaced with the name of the current program.
     Does nothing if ‘self.usage’ is empty or not defined.

 -- Method: OptionParser.get_usage ()

     Same as *note print_usage(): 3ca5. but returns the usage string
     instead of printing it.

 -- Method: OptionParser.set_defaults (dest=value, ...)

     Set default values for several option destinations at once.  Using
     *note set_defaults(): 3cb8. is the preferred way to set default
     values for options, since multiple options can share the same
     destination.  For example, if several “mode” options all set the
     same destination, any one of them can set the default, and the last
     one wins:

          parser.add_option("--advanced", action="store_const",
                            dest="mode", const="advanced",
                            default="novice")    # overridden below
          parser.add_option("--novice", action="store_const",
                            dest="mode", const="novice",
                            default="advanced")  # overrides above setting

     To avoid this confusion, use *note set_defaults(): 3cb8.:

          parser.set_defaults(mode="advanced")
          parser.add_option("--advanced", action="store_const",
                            dest="mode", const="advanced")
          parser.add_option("--novice", action="store_const",
                            dest="mode", const="novice")


File: python.info,  Node: Option Callbacks,  Next: Extending optparse,  Prev: Reference Guide,  Up: optparse — Parser for command line options

5.36.1.28 Option Callbacks
..........................

When *note optparse: c3.’s built-in actions and types aren’t quite
enough for your needs, you have two choices: extend *note optparse: c3.
or define a callback option.  Extending *note optparse: c3. is more
general, but overkill for a lot of simple cases.  Quite often a simple
callback is all you need.

There are two steps to defining a callback option:

   * define the option itself using the ‘"callback"’ action

   * write the callback; this is a function (or method) that takes at
     least four arguments, as described below

* Menu:

* Defining a callback option::
* How callbacks are called::
* Raising errors in a callback::
* Callback example 1; trivial callback: Callback example 1 trivial callback.
* Callback example 2; check option order: Callback example 2 check option order.
* Callback example 3; check option order (generalized): Callback example 3 check option order generalized.
* Callback example 4; check arbitrary condition: Callback example 4 check arbitrary condition.
* Callback example 5; fixed arguments: Callback example 5 fixed arguments.
* Callback example 6; variable arguments: Callback example 6 variable arguments.


File: python.info,  Node: Defining a callback option,  Next: How callbacks are called,  Up: Option Callbacks

5.36.1.29 Defining a callback option
....................................

As always, the easiest way to define a callback option is by using the
*note OptionParser.add_option(): 21cd. method.  Apart from *note action:
3c8c, the only option attribute you must specify is ‘callback’, the
function to call:

     parser.add_option("-c", action="callback", callback=my_callback)

‘callback’ is a function (or other callable object), so you must have
already defined ‘my_callback()’ when you create this callback option.
In this simple case, *note optparse: c3. doesn’t even know if ‘-c’ takes
any arguments, which usually means that the option takes no
arguments—the mere presence of ‘-c’ on the command-line is all it needs
to know.  In some circumstances, though, you might want your callback to
consume an arbitrary number of command-line arguments.  This is where
writing callbacks gets tricky; it’s covered later in this section.

*note optparse: c3. always passes four particular arguments to your
callback, and it will only pass additional arguments if you specify them
via *note callback_args: 3cbd. and *note callback_kwargs: 3cbe.  Thus,
the minimal callback function signature is:

     def my_callback(option, opt, value, parser):

The four arguments to a callback are described below.

There are several other option attributes that you can supply when you
define a callback option:

*note type: 3c8d.

     has its usual meaning: as with the ‘"store"’ or ‘"append"’ actions,
     it instructs *note optparse: c3. to consume one argument and
     convert it to *note type: 3c8d.  Rather than storing the converted
     value(s) anywhere, though, *note optparse: c3. passes it to your
     callback function.

*note nargs: 3cb9.

     also has its usual meaning: if it is supplied and > 1, *note
     optparse: c3. will consume *note nargs: 3cb9. arguments, each of
     which must be convertible to *note type: 3c8d.  It then passes a
     tuple of converted values to your callback.

*note callback_args: 3cbd.

     a tuple of extra positional arguments to pass to the callback

*note callback_kwargs: 3cbe.

     a dictionary of extra keyword arguments to pass to the callback


File: python.info,  Node: How callbacks are called,  Next: Raising errors in a callback,  Prev: Defining a callback option,  Up: Option Callbacks

5.36.1.30 How callbacks are called
..................................

All callbacks are called as follows:

     func(option, opt_str, value, parser, *args, **kwargs)

where

‘option’

     is the Option instance that’s calling the callback

‘opt_str’

     is the option string seen on the command-line that’s triggering the
     callback.  (If an abbreviated long option was used, ‘opt_str’ will
     be the full, canonical option string—e.g.  if the user puts ‘--foo’
     on the command-line as an abbreviation for ‘--foobar’, then
     ‘opt_str’ will be ‘"--foobar"’.)

‘value’

     is the argument to this option seen on the command-line.  *note
     optparse: c3. will only expect an argument if *note type: 3c8d. is
     set; the type of ‘value’ will be the type implied by the option’s
     type.  If *note type: 3c8d. for this option is ‘None’ (no argument
     expected), then ‘value’ will be ‘None’.  If *note nargs: 3cb9. > 1,
     ‘value’ will be a tuple of values of the appropriate type.

‘parser’

     is the OptionParser instance driving the whole thing, mainly useful
     because you can access some other interesting data through its
     instance attributes:

     ‘parser.largs’

          the current list of leftover arguments, ie.  arguments that
          have been consumed but are neither options nor option
          arguments.  Feel free to modify ‘parser.largs’, e.g.  by
          adding more arguments to it.  (This list will become ‘args’,
          the second return value of ‘parse_args()’.)

     ‘parser.rargs’

          the current list of remaining arguments, ie.  with ‘opt_str’
          and ‘value’ (if applicable) removed, and only the arguments
          following them still there.  Feel free to modify
          ‘parser.rargs’, e.g.  by consuming more arguments.

     ‘parser.values’

          the object where option values are by default stored (an
          instance of optparse.OptionValues).  This lets callbacks use
          the same mechanism as the rest of *note optparse: c3. for
          storing option values; you don’t need to mess around with
          globals or closures.  You can also access or modify the
          value(s) of any options already encountered on the
          command-line.

‘args’

     is a tuple of arbitrary positional arguments supplied via the *note
     callback_args: 3cbd. option attribute.

‘kwargs’

     is a dictionary of arbitrary keyword arguments supplied via *note
     callback_kwargs: 3cbe.


File: python.info,  Node: Raising errors in a callback,  Next: Callback example 1 trivial callback,  Prev: How callbacks are called,  Up: Option Callbacks

5.36.1.31 Raising errors in a callback
......................................

The callback function should raise ‘OptionValueError’ if there are any
problems with the option or its argument(s).  *note optparse: c3.
catches this and terminates the program, printing the error message you
supply to stderr.  Your message should be clear, concise, accurate, and
mention the option at fault.  Otherwise, the user will have a hard time
figuring out what they did wrong.


File: python.info,  Node: Callback example 1 trivial callback,  Next: Callback example 2 check option order,  Prev: Raising errors in a callback,  Up: Option Callbacks

5.36.1.32 Callback example 1: trivial callback
..............................................

Here’s an example of a callback option that takes no arguments, and
simply records that the option was seen:

     def record_foo_seen(option, opt_str, value, parser):
         parser.values.saw_foo = True

     parser.add_option("--foo", action="callback", callback=record_foo_seen)

Of course, you could do that with the ‘"store_true"’ action.


File: python.info,  Node: Callback example 2 check option order,  Next: Callback example 3 check option order generalized,  Prev: Callback example 1 trivial callback,  Up: Option Callbacks

5.36.1.33 Callback example 2: check option order
................................................

Here’s a slightly more interesting example: record the fact that ‘-a’ is
seen, but blow up if it comes after ‘-b’ in the command-line.

     def check_order(option, opt_str, value, parser):
         if parser.values.b:
             raise OptionValueError("can't use -a after -b")
         parser.values.a = 1
     ...
     parser.add_option("-a", action="callback", callback=check_order)
     parser.add_option("-b", action="store_true", dest="b")


File: python.info,  Node: Callback example 3 check option order generalized,  Next: Callback example 4 check arbitrary condition,  Prev: Callback example 2 check option order,  Up: Option Callbacks

5.36.1.34 Callback example 3: check option order (generalized)
..............................................................

If you want to re-use this callback for several similar options (set a
flag, but blow up if ‘-b’ has already been seen), it needs a bit of
work: the error message and the flag that it sets must be generalized.

     def check_order(option, opt_str, value, parser):
         if parser.values.b:
             raise OptionValueError("can't use %s after -b" % opt_str)
         setattr(parser.values, option.dest, 1)
     ...
     parser.add_option("-a", action="callback", callback=check_order, dest='a')
     parser.add_option("-b", action="store_true", dest="b")
     parser.add_option("-c", action="callback", callback=check_order, dest='c')


File: python.info,  Node: Callback example 4 check arbitrary condition,  Next: Callback example 5 fixed arguments,  Prev: Callback example 3 check option order generalized,  Up: Option Callbacks

5.36.1.35 Callback example 4: check arbitrary condition
.......................................................

Of course, you could put any condition in there—you’re not limited to
checking the values of already-defined options.  For example, if you
have options that should not be called when the moon is full, all you
have to do is this:

     def check_moon(option, opt_str, value, parser):
         if is_moon_full():
             raise OptionValueError("%s option invalid when moon is full"
                                    % opt_str)
         setattr(parser.values, option.dest, 1)
     ...
     parser.add_option("--foo",
                       action="callback", callback=check_moon, dest="foo")

(The definition of ‘is_moon_full()’ is left as an exercise for the
reader.)


File: python.info,  Node: Callback example 5 fixed arguments,  Next: Callback example 6 variable arguments,  Prev: Callback example 4 check arbitrary condition,  Up: Option Callbacks

5.36.1.36 Callback example 5: fixed arguments
.............................................

Things get slightly more interesting when you define callback options
that take a fixed number of arguments.  Specifying that a callback
option takes arguments is similar to defining a ‘"store"’ or ‘"append"’
option: if you define *note type: 3c8d, then the option takes one
argument that must be convertible to that type; if you further define
*note nargs: 3cb9, then the option takes *note nargs: 3cb9. arguments.

Here’s an example that just emulates the standard ‘"store"’ action:

     def store_value(option, opt_str, value, parser):
         setattr(parser.values, option.dest, value)
     ...
     parser.add_option("--foo",
                       action="callback", callback=store_value,
                       type="int", nargs=3, dest="foo")

Note that *note optparse: c3. takes care of consuming 3 arguments and
converting them to integers for you; all you have to do is store them.
(Or whatever; obviously you don’t need a callback for this example.)


File: python.info,  Node: Callback example 6 variable arguments,  Prev: Callback example 5 fixed arguments,  Up: Option Callbacks

5.36.1.37 Callback example 6: variable arguments
................................................

Things get hairy when you want an option to take a variable number of
arguments.  For this case, you must write a callback, as *note optparse:
c3. doesn’t provide any built-in capabilities for it.  And you have to
deal with certain intricacies of conventional Unix command-line parsing
that *note optparse: c3. normally handles for you.  In particular,
callbacks should implement the conventional rules for bare ‘--’ and ‘-’
arguments:

   * either ‘--’ or ‘-’ can be option arguments

   * bare ‘--’ (if not the argument to some option): halt command-line
     processing and discard the ‘--’

   * bare ‘-’ (if not the argument to some option): halt command-line
     processing but keep the ‘-’ (append it to ‘parser.largs’)

If you want an option that takes a variable number of arguments, there
are several subtle, tricky issues to worry about.  The exact
implementation you choose will be based on which trade-offs you’re
willing to make for your application (which is why *note optparse: c3.
doesn’t support this sort of thing directly).

Nevertheless, here’s a stab at a callback for an option with variable
arguments:

     def vararg_callback(option, opt_str, value, parser):
         assert value is None
         value = []

         def floatable(str):
             try:
                 float(str)
                 return True
             except ValueError:
                 return False

         for arg in parser.rargs:
             # stop on --foo like options
             if arg[:2] == "--" and len(arg) > 2:
                 break
             # stop on -a, but not on -3 or -3.0
             if arg[:1] == "-" and len(arg) > 1 and not floatable(arg):
                 break
             value.append(arg)

         del parser.rargs[:len(value)]
         setattr(parser.values, option.dest, value)

     ...
     parser.add_option("-c", "--callback", dest="vararg_attr",
                       action="callback", callback=vararg_callback)


File: python.info,  Node: Extending optparse,  Prev: Option Callbacks,  Up: optparse — Parser for command line options

5.36.1.38 Extending ‘optparse’
..............................

Since the two major controlling factors in how *note optparse: c3.
interprets command-line options are the action and type of each option,
the most likely direction of extension is to add new actions and new
types.

* Menu:

* Adding new types::
* Adding new actions::


File: python.info,  Node: Adding new types,  Next: Adding new actions,  Up: Extending optparse

5.36.1.39 Adding new types
..........................

To add new types, you need to define your own subclass of *note
optparse: c3.’s ‘Option’ class.  This class has a couple of attributes
that define *note optparse: c3.’s types: *note TYPES: 3ce7. and *note
TYPE_CHECKER: 3ce8.

 -- Attribute: Option.TYPES

     A tuple of type names; in your subclass, simply define a new tuple
     *note TYPES: 3ce7. that builds on the standard one.

 -- Attribute: Option.TYPE_CHECKER

     A dictionary mapping type names to type-checking functions.  A
     type-checking function has the following signature:

          def check_mytype(option, opt, value)

     where ‘option’ is an ‘Option’ instance, ‘opt’ is an option string
     (e.g., ‘-f’), and ‘value’ is the string from the command line that
     must be checked and converted to your desired type.
     ‘check_mytype()’ should return an object of the hypothetical type
     ‘mytype’.  The value returned by a type-checking function will wind
     up in the OptionValues instance returned by
     ‘OptionParser.parse_args()’, or be passed to a callback as the
     ‘value’ parameter.

     Your type-checking function should raise ‘OptionValueError’ if it
     encounters any problems.  ‘OptionValueError’ takes a single string
     argument, which is passed as-is to *note OptionParser: 3c81.’s
     ‘error()’ method, which in turn prepends the program name and the
     string ‘"error:"’ and prints everything to stderr before
     terminating the process.

Here’s a silly example that demonstrates adding a ‘"complex"’ option
type to parse Python-style complex numbers on the command line.  (This
is even sillier than it used to be, because *note optparse: c3. 1.3
added built-in support for complex numbers, but never mind.)

First, the necessary imports:

     from copy import copy
     from optparse import Option, OptionValueError

You need to define your type-checker first, since it’s referred to later
(in the *note TYPE_CHECKER: 3ce8. class attribute of your Option
subclass):

     def check_complex(option, opt, value):
         try:
             return complex(value)
         except ValueError:
             raise OptionValueError(
                 "option %s: invalid complex value: %r" % (opt, value))

Finally, the Option subclass:

     class MyOption (Option):
         TYPES = Option.TYPES + ("complex",)
         TYPE_CHECKER = copy(Option.TYPE_CHECKER)
         TYPE_CHECKER["complex"] = check_complex

(If we didn’t make a *note copy(): 25. of *note Option.TYPE_CHECKER:
3ce8, we would end up modifying the *note TYPE_CHECKER: 3ce8. attribute
of *note optparse: c3.’s Option class.  This being Python, nothing stops
you from doing that except good manners and common sense.)

That’s it!  Now you can write a script that uses the new option type
just like any other *note optparse: c3.-based script, except you have to
instruct your OptionParser to use MyOption instead of Option:

     parser = OptionParser(option_class=MyOption)
     parser.add_option("-c", type="complex")

Alternately, you can build your own option list and pass it to
OptionParser; if you don’t use ‘add_option()’ in the above way, you
don’t need to tell OptionParser which option class to use:

     option_list = [MyOption("-c", action="store", type="complex", dest="c")]
     parser = OptionParser(option_list=option_list)


File: python.info,  Node: Adding new actions,  Prev: Adding new types,  Up: Extending optparse

5.36.1.40 Adding new actions
............................

Adding new actions is a bit trickier, because you have to understand
that *note optparse: c3. has a couple of classifications for actions:

“store” actions

     actions that result in *note optparse: c3. storing a value to an
     attribute of the current OptionValues instance; these options
     require a *note dest: 3c8e. attribute to be supplied to the Option
     constructor.

“typed” actions

     actions that take a value from the command line and expect it to be
     of a certain type; or rather, a string that can be converted to a
     certain type.  These options require a *note type: 3c8d. attribute
     to the Option constructor.

These are overlapping sets: some default “store” actions are ‘"store"’,
‘"store_const"’, ‘"append"’, and ‘"count"’, while the default “typed”
actions are ‘"store"’, ‘"append"’, and ‘"callback"’.

When you add an action, you need to categorize it by listing it in at
least one of the following class attributes of Option (all are lists of
strings):

 -- Attribute: Option.ACTIONS

     All actions must be listed in ACTIONS.

 -- Attribute: Option.STORE_ACTIONS

     “store” actions are additionally listed here.

 -- Attribute: Option.TYPED_ACTIONS

     “typed” actions are additionally listed here.

 -- Attribute: Option.ALWAYS_TYPED_ACTIONS

     Actions that always take a type (i.e.  whose options always take a
     value) are additionally listed here.  The only effect of this is
     that *note optparse: c3. assigns the default type, ‘"string"’, to
     options with no explicit type whose action is listed in *note
     ALWAYS_TYPED_ACTIONS: 3cee.

In order to actually implement your new action, you must override
Option’s ‘take_action()’ method and add a case that recognizes your
action.

For example, let’s add an ‘"extend"’ action.  This is similar to the
standard ‘"append"’ action, but instead of taking a single value from
the command-line and appending it to an existing list, ‘"extend"’ will
take multiple values in a single comma-delimited string, and extend an
existing list with them.  That is, if ‘--names’ is an ‘"extend"’ option
of type ‘"string"’, the command line

     --names=foo,bar --names blah --names ding,dong

would result in a list

     ["foo", "bar", "blah", "ding", "dong"]

Again we define a subclass of Option:

     class MyOption(Option):

         ACTIONS = Option.ACTIONS + ("extend",)
         STORE_ACTIONS = Option.STORE_ACTIONS + ("extend",)
         TYPED_ACTIONS = Option.TYPED_ACTIONS + ("extend",)
         ALWAYS_TYPED_ACTIONS = Option.ALWAYS_TYPED_ACTIONS + ("extend",)

         def take_action(self, action, dest, opt, value, values, parser):
             if action == "extend":
                 lvalue = value.split(",")
                 values.ensure_value(dest, []).extend(lvalue)
             else:
                 Option.take_action(
                     self, action, dest, opt, value, values, parser)

Features of note:

   * ‘"extend"’ both expects a value on the command-line and stores that
     value somewhere, so it goes in both *note STORE_ACTIONS: 3cec. and
     *note TYPED_ACTIONS: 3ced.

   * to ensure that *note optparse: c3. assigns the default type of
     ‘"string"’ to ‘"extend"’ actions, we put the ‘"extend"’ action in
     *note ALWAYS_TYPED_ACTIONS: 3cee. as well.

   * ‘MyOption.take_action()’ implements just this one new action, and
     passes control back to ‘Option.take_action()’ for the standard
     *note optparse: c3. actions.

   * ‘values’ is an instance of the optparse_parser.Values class, which
     provides the very useful ‘ensure_value()’ method.  ‘ensure_value()’
     is essentially *note getattr(): 54b. with a safety valve; it is
     called as

          values.ensure_value(attr, value)

     If the ‘attr’ attribute of ‘values’ doesn’t exist or is ‘None’,
     then ensure_value() first sets it to ‘value’, and then returns
     ‘value.  This is very handy for actions like ‘"extend"’,
     ‘"append"’, and ‘"count"’, all of which accumulate data in a
     variable and expect that variable to be of a certain type (a list
     for the first two, an integer for the latter).  Using
     ‘ensure_value()’ means that scripts using your action don’t have to
     worry about setting a default value for the option destinations in
     question; they can just leave the default as ‘None’ and
     ‘ensure_value()’ will take care of getting it right when it’s
     needed.


File: python.info,  Node: imp — Access the import internals,  Prev: optparse — Parser for command line options,  Up: Superseded Modules

5.36.2 ‘imp’ — Access the import internals
------------------------------------------

`Source code:' Lib/imp.py(1)

Deprecated since version 3.4: The *note imp: 99. module is deprecated in
favor of *note importlib: 9a.

__________________________________________________________________

This module provides an interface to the mechanisms used to implement
the *note import: ce7. statement.  It defines the following constants
and functions:

 -- Function: imp.get_magic ()

     Return the magic string value used to recognize byte-compiled code
     files (‘.pyc’ files).  (This value may be different for each Python
     version.)

     Deprecated since version 3.4: Use *note
     importlib.util.MAGIC_NUMBER: 94d. instead.

 -- Function: imp.get_suffixes ()

     Return a list of 3-element tuples, each describing a particular
     type of module.  Each triple has the form ‘(suffix, mode, type)’,
     where `suffix' is a string to be appended to the module name to
     form the filename to search for, `mode' is the mode string to pass
     to the built-in *note open(): 16f. function to open the file (this
     can be ‘'r'’ for text files or ‘'rb'’ for binary files), and `type'
     is the file type, which has one of the values *note PY_SOURCE:
     3cf2, *note PY_COMPILED: 3cf3, or *note C_EXTENSION: 3cf4,
     described below.

     Deprecated since version 3.3: Use the constants defined on *note
     importlib.machinery: 9c. instead.

 -- Function: imp.find_module (name[, path])

     Try to find the module `name'.  If `path' is omitted or ‘None’, the
     list of directory names given by ‘sys.path’ is searched, but first
     a few special places are searched: the function tries to find a
     built-in module with the given name (*note C_BUILTIN: 3cf6.), then
     a frozen module (*note PY_FROZEN: 3cf7.), and on some systems some
     other places are looked in as well (on Windows, it looks in the
     registry which may point to a specific file).

     Otherwise, `path' must be a list of directory names; each directory
     is searched for files with any of the suffixes returned by *note
     get_suffixes(): 3cf1. above.  Invalid names in the list are
     silently ignored (but all list items must be strings).

     If search is successful, the return value is a 3-element tuple
     ‘(file, pathname, description)’:

     `file' is an open *note file object: c14. positioned at the
     beginning, `pathname' is the pathname of the file found, and
     `description' is a 3-element tuple as contained in the list
     returned by *note get_suffixes(): 3cf1. describing the kind of
     module found.

     If the module is built-in or frozen then `file' and `pathname' are
     both ‘None’ and the `description' tuple contains empty strings for
     its suffix and mode; the module type is indicated as given in
     parentheses above.  If the search is unsuccessful, *note
     ImportError: 16c. is raised.  Other exceptions indicate problems
     with the arguments or environment.

     If the module is a package, `file' is ‘None’, `pathname' is the
     package path and the last item in the `description' tuple is *note
     PKG_DIRECTORY: 3cf8.

     This function does not handle hierarchical module names (names
     containing dots).  In order to find `P.M', that is, submodule `M'
     of package `P', use *note find_module(): 3cf5. and *note
     load_module(): 3cf9. to find and load package `P', and then use
     *note find_module(): 3cf5. with the `path' argument set to
     ‘P.__path__’.  When `P' itself has a dotted name, apply this recipe
     recursively.

     Deprecated since version 3.3: Use *note importlib.util.find_spec():
     a1c. instead unless Python 3.3 compatibility is required, in which
     case use *note importlib.find_loader(): a1b.  For example usage of
     the former case, see the *note Examples: 3920. section of the *note
     importlib: 9a. documentation.

 -- Function: imp.load_module (name, file, pathname, description)

     Load a module that was previously found by *note find_module():
     3cf5. (or by an otherwise conducted search yielding compatible
     results).  This function does more than importing the module: if
     the module was already imported, it will reload the module!  The
     `name' argument indicates the full module name (including the
     package name, if this is a submodule of a package).  The `file'
     argument is an open file, and `pathname' is the corresponding file
     name; these can be ‘None’ and ‘''’, respectively, when the module
     is a package or not being loaded from a file.  The `description'
     argument is a tuple, as would be returned by *note get_suffixes():
     3cf1, describing what kind of module must be loaded.

     If the load is successful, the return value is the module object;
     otherwise, an exception (usually *note ImportError: 16c.) is
     raised.

     `Important:' the caller is responsible for closing the `file'
     argument, if it was not ‘None’, even when an exception is raised.
     This is best done using a *note try: e37. … *note finally: 2bc.
     statement.

     Deprecated since version 3.3: If previously used in conjunction
     with *note imp.find_module(): 3cf5. then consider using *note
     importlib.import_module(): be6, otherwise use the loader returned
     by the replacement you chose for *note imp.find_module(): 3cf5.  If
     you called *note imp.load_module(): 3cf9. and related functions
     directly with file path arguments then use a combination of *note
     importlib.util.spec_from_file_location(): 653. and *note
     importlib.util.module_from_spec(): 7e1.  See the *note Examples:
     3920. section of the *note importlib: 9a. documentation for details
     of the various approaches.

 -- Function: imp.new_module (name)

     Return a new empty module object called `name'.  This object is
     `not' inserted in ‘sys.modules’.

     Deprecated since version 3.4: Use *note
     importlib.util.module_from_spec(): 7e1. instead.

 -- Function: imp.reload (module)

     Reload a previously imported `module'.  The argument must be a
     module object, so it must have been successfully imported before.
     This is useful if you have edited the module source file using an
     external editor and want to try out the new version without leaving
     the Python interpreter.  The return value is the module object (the
     same as the `module' argument).

     When ‘reload(module)’ is executed:

        * Python modules’ code is recompiled and the module-level code
          reexecuted, defining a new set of objects which are bound to
          names in the module’s dictionary.  The ‘init’ function of
          extension modules is not called a second time.

        * As with all other objects in Python the old objects are only
          reclaimed after their reference counts drop to zero.

        * The names in the module namespace are updated to point to any
          new or changed objects.

        * Other references to the old objects (such as names external to
          the module) are not rebound to refer to the new objects and
          must be updated in each namespace where they occur if that is
          desired.

     There are a number of other caveats:

     When a module is reloaded, its dictionary (containing the module’s
     global variables) is retained.  Redefinitions of names will
     override the old definitions, so this is generally not a problem.
     If the new version of a module does not define a name that was
     defined by the old version, the old definition remains.  This
     feature can be used to the module’s advantage if it maintains a
     global table or cache of objects — with a *note try: e37. statement
     it can test for the table’s presence and skip its initialization if
     desired:

          try:
              cache
          except NameError:
              cache = {}

     It is legal though generally not very useful to reload built-in or
     dynamically loaded modules, except for *note sys: fd, *note
     __main__: 1. and *note builtins: 12.  In many cases, however,
     extension modules are not designed to be initialized more than
     once, and may fail in arbitrary ways when reloaded.

     If a module imports objects from another module using *note from:
     d0d. … *note import: ce7. …, calling *note reload(): d38. for the
     other module does not redefine the objects imported from it — one
     way around this is to re-execute the ‘from’ statement, another is
     to use ‘import’ and qualified names (`module'.*name*) instead.

     If a module instantiates instances of a class, reloading the module
     that defines the class does not affect the method definitions of
     the instances — they continue to use the old class definition.  The
     same is true for derived classes.

     Changed in version 3.3: Relies on both ‘__name__’ and ‘__loader__’
     being defined on the module being reloaded instead of just
     ‘__name__’.

     Deprecated since version 3.4: Use *note importlib.reload(): 4a0.
     instead.

The following functions are conveniences for handling PEP 3147(2)
byte-compiled file paths.

New in version 3.2.

 -- Function: imp.cache_from_source (path, debug_override=None)

     Return the PEP 3147(3) path to the byte-compiled file associated
     with the source `path'.  For example, if `path' is
     ‘/foo/bar/baz.py’ the return value would be
     ‘/foo/bar/__pycache__/baz.cpython-32.pyc’ for Python 3.2.  The
     ‘cpython-32’ string comes from the current magic tag (see *note
     get_tag(): 3cfc.; if ‘sys.implementation.cache_tag’ is not defined
     then *note NotImplementedError: 704. will be raised).  By passing
     in ‘True’ or ‘False’ for `debug_override' you can override the
     system’s value for ‘__debug__’, leading to optimized bytecode.

     `path' need not exist.

     Changed in version 3.3: If ‘sys.implementation.cache_tag’ is
     ‘None’, then *note NotImplementedError: 704. is raised.

     Deprecated since version 3.4: Use *note
     importlib.util.cache_from_source(): 651. instead.

     Changed in version 3.5: The `debug_override' parameter no longer
     creates a ‘.pyo’ file.

 -- Function: imp.source_from_cache (path)

     Given the `path' to a PEP 3147(4) file name, return the associated
     source code file path.  For example, if `path' is
     ‘/foo/bar/__pycache__/baz.cpython-32.pyc’ the returned path would
     be ‘/foo/bar/baz.py’.  `path' need not exist, however if it does
     not conform to PEP 3147(5) format, a *note ValueError: 16d. is
     raised.  If ‘sys.implementation.cache_tag’ is not defined, *note
     NotImplementedError: 704. is raised.

     Changed in version 3.3: Raise *note NotImplementedError: 704. when
     ‘sys.implementation.cache_tag’ is not defined.

     Deprecated since version 3.4: Use *note
     importlib.util.source_from_cache(): 652. instead.

 -- Function: imp.get_tag ()

     Return the PEP 3147(6) magic tag string matching this version of
     Python’s magic number, as returned by *note get_magic(): 94e.

     Deprecated since version 3.4: Use ‘sys.implementation.cache_tag’
     directly starting in Python 3.3.

The following functions help interact with the import system’s internal
locking mechanism.  Locking semantics of imports are an implementation
detail which may vary from release to release.  However, Python ensures
that circular imports work without any deadlocks.

 -- Function: imp.lock_held ()

     Return ‘True’ if the global import lock is currently held, else
     ‘False’.  On platforms without threads, always return ‘False’.

     On platforms with threads, a thread executing an import first holds
     a global import lock, then sets up a per-module lock for the rest
     of the import.  This blocks other threads from importing the same
     module until the original import completes, preventing other
     threads from seeing incomplete module objects constructed by the
     original thread.  An exception is made for circular imports, which
     by construction have to expose an incomplete module object at some
     point.

     Changed in version 3.3: The locking scheme has changed to
     per-module locks for the most part.  A global import lock is kept
     for some critical tasks, such as initializing the per-module locks.

     Deprecated since version 3.4.

 -- Function: imp.acquire_lock ()

     Acquire the interpreter’s global import lock for the current
     thread.  This lock should be used by import hooks to ensure
     thread-safety when importing modules.

     Once a thread has acquired the import lock, the same thread may
     acquire it again without blocking; the thread must release it once
     for each time it has acquired it.

     On platforms without threads, this function does nothing.

     Changed in version 3.3: The locking scheme has changed to
     per-module locks for the most part.  A global import lock is kept
     for some critical tasks, such as initializing the per-module locks.

     Deprecated since version 3.4.

 -- Function: imp.release_lock ()

     Release the interpreter’s global import lock.  On platforms without
     threads, this function does nothing.

     Changed in version 3.3: The locking scheme has changed to
     per-module locks for the most part.  A global import lock is kept
     for some critical tasks, such as initializing the per-module locks.

     Deprecated since version 3.4.

The following constants with integer values, defined in this module, are
used to indicate the search result of *note find_module(): 3cf5.

 -- Data: imp.PY_SOURCE

     The module was found as a source file.

     Deprecated since version 3.3.

 -- Data: imp.PY_COMPILED

     The module was found as a compiled code object file.

     Deprecated since version 3.3.

 -- Data: imp.C_EXTENSION

     The module was found as dynamically loadable shared library.

     Deprecated since version 3.3.

 -- Data: imp.PKG_DIRECTORY

     The module was found as a package directory.

     Deprecated since version 3.3.

 -- Data: imp.C_BUILTIN

     The module was found as a built-in module.

     Deprecated since version 3.3.

 -- Data: imp.PY_FROZEN

     The module was found as a frozen module.

     Deprecated since version 3.3.

 -- Class: imp.NullImporter (path_string)

     The *note NullImporter: a9b. type is a PEP 302(7) import hook that
     handles non-directory path strings by failing to find any modules.
     Calling this type with an existing directory or empty string raises
     *note ImportError: 16c.  Otherwise, a *note NullImporter: a9b.
     instance is returned.

     Instances have only one method:

      -- Method: find_module (fullname[, path])

          This method always returns ‘None’, indicating that the
          requested module could not be found.

     Changed in version 3.3: ‘None’ is inserted into
     ‘sys.path_importer_cache’ instead of an instance of *note
     NullImporter: a9b.

     Deprecated since version 3.4: Insert ‘None’ into
     ‘sys.path_importer_cache’ instead.

* Menu:

* Examples: Examples<34>.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Lib/imp.py

   (2) https://www.python.org/dev/peps/pep-3147

   (3) https://www.python.org/dev/peps/pep-3147

   (4) https://www.python.org/dev/peps/pep-3147

   (5) https://www.python.org/dev/peps/pep-3147

   (6) https://www.python.org/dev/peps/pep-3147

   (7) https://www.python.org/dev/peps/pep-0302


File: python.info,  Node: Examples<34>,  Up: imp — Access the import internals

5.36.2.1 Examples
.................

The following function emulates what was the standard import statement
up to Python 1.4 (no hierarchical module names).  (This `implementation'
wouldn’t work in that version, since *note find_module(): 3cf5. has been
extended and *note load_module(): 3cf9. has been added in 1.4.)

     import imp
     import sys

     def __import__(name, globals=None, locals=None, fromlist=None):
         # Fast path: see if the module has already been imported.
         try:
             return sys.modules[name]
         except KeyError:
             pass

         # If any of the following calls raises an exception,
         # there's a problem we can't handle -- let the caller handle it.

         fp, pathname, description = imp.find_module(name)

         try:
             return imp.load_module(name, fp, pathname, description)
         finally:
             # Since we may exit via an exception, close fp explicitly.
             if fp:
                 fp.close()


File: python.info,  Node: Undocumented Modules,  Next: Security Considerations<2>,  Prev: Superseded Modules,  Up: The Python Standard Library

5.37 Undocumented Modules
=========================

Here’s a quick listing of modules that are currently undocumented, but
that should be documented.  Feel free to contribute documentation for
them!  (Send via email to <docs@python.org>.)

The idea and original contents for this chapter were taken from a
posting by Fredrik Lundh; the specific contents of this chapter have
been substantially revised.

* Menu:

* Platform specific modules::


File: python.info,  Node: Platform specific modules,  Up: Undocumented Modules

5.37.1 Platform specific modules
--------------------------------

These modules are used to implement the *note os.path: c5. module, and
are not documented beyond this mention.  There’s little need to document
these.

‘ntpath’

     — Implementation of *note os.path: c5. on Win32 and Win64
     platforms.

‘posixpath’

     — Implementation of *note os.path: c5. on POSIX.


File: python.info,  Node: Security Considerations<2>,  Prev: Undocumented Modules,  Up: The Python Standard Library

5.38 Security Considerations
============================

The following modules have specific security considerations:

   * *note cgi: 15.: *note CGI security considerations: 2d28.

   * *note hashlib: 8c.: *note all constructors take a “usedforsecurity”
     keyword-only argument disabling known insecure and blocked
     algorithms: 200b.

   * *note http.server: 96. is not suitable for production use, only
     implementing basic security checks

   * *note logging: aa.: *note Logging configuration uses eval(): 2230.

   * *note multiprocessing: b7.: *note Connection.recv() uses pickle:
     252b.

   * *note pickle: ca.: *note Restricting globals in pickle: 1e1e.

   * *note random: dc. shouldn’t be used for security purposes, use
     *note secrets: e4. instead

   * *note shelve: e7.: *note shelve is based on pickle and thus
     unsuitable for dealing with untrusted sources: 1e3b.

   * *note ssl: f3.: *note SSL/TLS security considerations: 26fd.

   * *note subprocess: f9.: *note Subprocess security considerations:
     25d0.

   * *note tempfile: 103.: *note mktemp is deprecated due to
     vulnerability to race conditions: 1dd0.

   * *note xml: 13c.: *note XML vulnerabilities: 2b34.

   * *note zipfile: 14b.: *note maliciously prepared .zip files can
     cause disk volume exhaustion: 1f31.


File: python.info,  Node: Extending and Embedding the Python Interpreter,  Next: Python/C API Reference Manual,  Prev: The Python Standard Library,  Up: Top

6 Extending and Embedding the Python Interpreter
************************************************

This document describes how to write modules in C or C++ to extend the
Python interpreter with new modules.  Those modules can not only define
new functions but also new object types and their methods.  The document
also describes how to embed the Python interpreter in another
application, for use as an extension language.  Finally, it shows how to
compile and link extension modules so that they can be loaded
dynamically (at run time) into the interpreter, if the underlying
operating system supports this feature.

This document assumes basic knowledge about Python.  For an informal
introduction to the language, see *note The Python Tutorial: 132f.
*note The Python Language Reference: 1331. gives a more formal
definition of the language.  *note The Python Standard Library: 1330.
documents the existing object types, functions and modules (both
built-in and written in Python) that give the language its wide
application range.

For a detailed description of the whole Python/C API, see the separate
*note Python/C API Reference Manual: 1333.

* Menu:

* Recommended third party tools::
* Creating extensions without third party tools::
* Embedding the CPython runtime in a larger application::


File: python.info,  Node: Recommended third party tools,  Next: Creating extensions without third party tools,  Up: Extending and Embedding the Python Interpreter

6.1 Recommended third party tools
=================================

This guide only covers the basic tools for creating extensions provided
as part of this version of CPython.  Third party tools like Cython(1),
cffi(2), SWIG(3) and Numba(4) offer both simpler and more sophisticated
approaches to creating C and C++ extensions for Python.

See also
........

Python Packaging User Guide: Binary Extensions(5)

     The Python Packaging User Guide not only covers several available
     tools that simplify the creation of binary extensions, but also
     discusses the various reasons why creating an extension module may
     be desirable in the first place.

   ---------- Footnotes ----------

   (1) http://cython.org/

   (2) https://cffi.readthedocs.io

   (3) http://www.swig.org

   (4) https://numba.pydata.org/

   (5) https://packaging.python.org/guides/packaging-binary-extensions/


File: python.info,  Node: Creating extensions without third party tools,  Next: Embedding the CPython runtime in a larger application,  Prev: Recommended third party tools,  Up: Extending and Embedding the Python Interpreter

6.2 Creating extensions without third party tools
=================================================

This section of the guide covers creating C and C++ extensions without
assistance from third party tools.  It is intended primarily for
creators of those tools, rather than being a recommended way to create
your own C extensions.

* Menu:

* Extending Python with C or C++::
* Defining Extension Types; Tutorial: Defining Extension Types Tutorial.
* Defining Extension Types; Assorted Topics: Defining Extension Types Assorted Topics.
* Building C and C++ Extensions::
* Building C and C++ Extensions on Windows::


File: python.info,  Node: Extending Python with C or C++,  Next: Defining Extension Types Tutorial,  Up: Creating extensions without third party tools

6.2.1 Extending Python with C or C++
------------------------------------

It is quite easy to add new built-in modules to Python, if you know how
to program in C. Such `extension modules' can do two things that can’t
be done directly in Python: they can implement new built-in object
types, and they can call C library functions and system calls.

To support extensions, the Python API (Application Programmers
Interface) defines a set of functions, macros and variables that provide
access to most aspects of the Python run-time system.  The Python API is
incorporated in a C source file by including the header ‘"Python.h"’.

The compilation of an extension module depends on its intended use as
well as on your system setup; details are given in later chapters.

     Note: The C extension interface is specific to CPython, and
     extension modules do not work on other Python implementations.  In
     many cases, it is possible to avoid writing C extensions and
     preserve portability to other implementations.  For example, if
     your use case is calling C library functions or system calls, you
     should consider using the *note ctypes: 2a. module or the cffi(1)
     library rather than writing custom C code.  These modules let you
     write Python code to interface with C code and are more portable
     between implementations of Python than writing and compiling a C
     extension module.

* Menu:

* A Simple Example::
* Intermezzo; Errors and Exceptions: Intermezzo Errors and Exceptions.
* Back to the Example::
* The Module’s Method Table and Initialization Function::
* Compilation and Linkage::
* Calling Python Functions from C::
* Extracting Parameters in Extension Functions::
* Keyword Parameters for Extension Functions::
* Building Arbitrary Values::
* Reference Counts::
* Writing Extensions in C++::
* Providing a C API for an Extension Module::

   ---------- Footnotes ----------

   (1) https://cffi.readthedocs.io/


File: python.info,  Node: A Simple Example,  Next: Intermezzo Errors and Exceptions,  Up: Extending Python with C or C++

6.2.1.1 A Simple Example
........................

Let’s create an extension module called ‘spam’ (the favorite food of
Monty Python fans…) and let’s say we want to create a Python interface
to the C library function ‘system()’ (1).  This function takes a
null-terminated character string as argument and returns an integer.  We
want this function to be callable from Python as follows:

     >>> import spam
     >>> status = spam.system("ls -l")

Begin by creating a file ‘spammodule.c’.  (Historically, if a module is
called ‘spam’, the C file containing its implementation is called
‘spammodule.c’; if the module name is very long, like ‘spammify’, the
module name can be just ‘spammify.c’.)

The first two lines of our file can be:

     #define PY_SSIZE_T_CLEAN
     #include <Python.h>

which pulls in the Python API (you can add a comment describing the
purpose of the module and a copyright notice if you like).

     Note: Since Python may define some pre-processor definitions which
     affect the standard headers on some systems, you `must' include
     ‘Python.h’ before any standard headers are included.

     It is recommended to always define ‘PY_SSIZE_T_CLEAN’ before
     including ‘Python.h’.  See *note Extracting Parameters in Extension
     Functions: 3d14. for a description of this macro.

All user-visible symbols defined by ‘Python.h’ have a prefix of ‘Py’ or
‘PY’, except those defined in standard header files.  For convenience,
and since they are used extensively by the Python interpreter,
‘"Python.h"’ includes a few standard header files: ‘<stdio.h>’,
‘<string.h>’, ‘<errno.h>’, and ‘<stdlib.h>’.  If the latter header file
does not exist on your system, it declares the functions ‘malloc()’,
‘free()’ and ‘realloc()’ directly.

The next thing we add to our module file is the C function that will be
called when the Python expression ‘spam.system(string)’ is evaluated
(we’ll see shortly how it ends up being called):

     static PyObject *
     spam_system(PyObject *self, PyObject *args)
     {
         const char *command;
         int sts;

         if (!PyArg_ParseTuple(args, "s", &command))
             return NULL;
         sts = system(command);
         return PyLong_FromLong(sts);
     }

There is a straightforward translation from the argument list in Python
(for example, the single expression ‘"ls -l"’) to the arguments passed
to the C function.  The C function always has two arguments,
conventionally named `self' and `args'.

The `self' argument points to the module object for module-level
functions; for a method it would point to the object instance.

The `args' argument will be a pointer to a Python tuple object
containing the arguments.  Each item of the tuple corresponds to an
argument in the call’s argument list.  The arguments are Python objects
— in order to do anything with them in our C function we have to convert
them to C values.  The function *note PyArg_ParseTuple(): 393. in the
Python API checks the argument types and converts them to C values.  It
uses a template string to determine the required types of the arguments
as well as the types of the C variables into which to store the
converted values.  More about this later.

*note PyArg_ParseTuple(): 393. returns true (nonzero) if all arguments
have the right type and its components have been stored in the variables
whose addresses are passed.  It returns false (zero) if an invalid
argument list was passed.  In the latter case it also raises an
appropriate exception so the calling function can return ‘NULL’
immediately (as we saw in the example).

   ---------- Footnotes ----------

   (1) (1) An interface for this function already exists in the standard
module *note os: c4. — it was chosen as a simple and straightforward
example.


File: python.info,  Node: Intermezzo Errors and Exceptions,  Next: Back to the Example,  Prev: A Simple Example,  Up: Extending Python with C or C++

6.2.1.2 Intermezzo: Errors and Exceptions
.........................................

An important convention throughout the Python interpreter is the
following: when a function fails, it should set an exception condition
and return an error value (usually ‘-1’ or a ‘NULL’ pointer).  Exception
information is stored in three members of the interpreter’s thread
state.  These are ‘NULL’ if there is no exception.  Otherwise they are
the C equivalents of the members of the Python tuple returned by *note
sys.exc_info(): d27.  These are the exception type, exception instance,
and a traceback object.  It is important to know about them to
understand how errors are passed around.

The Python API defines a number of functions to set various types of
exceptions.

The most common one is *note PyErr_SetString(): 3d17.  Its arguments are
an exception object and a C string.  The exception object is usually a
predefined object like ‘PyExc_ZeroDivisionError’.  The C string
indicates the cause of the error and is converted to a Python string
object and stored as the “associated value” of the exception.

Another useful function is *note PyErr_SetFromErrno(): 3d18, which only
takes an exception argument and constructs the associated value by
inspection of the global variable ‘errno’.  The most general function is
*note PyErr_SetObject(): 3d19, which takes two object arguments, the
exception and its associated value.  You don’t need to *note
Py_INCREF(): 38e. the objects passed to any of these functions.

You can test non-destructively whether an exception has been set with
*note PyErr_Occurred(): 3d1a.  This returns the current exception
object, or ‘NULL’ if no exception has occurred.  You normally don’t need
to call *note PyErr_Occurred(): 3d1a. to see whether an error occurred
in a function call, since you should be able to tell from the return
value.

When a function `f' that calls another function `g' detects that the
latter fails, `f' should itself return an error value (usually ‘NULL’ or
‘-1’).  It should `not' call one of the ‘PyErr_*()’ functions — one has
already been called by `g'.  `f'’s caller is then supposed to also
return an error indication to `its' caller, again `without' calling
‘PyErr_*()’, and so on — the most detailed cause of the error was
already reported by the function that first detected it.  Once the error
reaches the Python interpreter’s main loop, this aborts the currently
executing Python code and tries to find an exception handler specified
by the Python programmer.

(There are situations where a module can actually give a more detailed
error message by calling another ‘PyErr_*()’ function, and in such cases
it is fine to do so.  As a general rule, however, this is not necessary,
and can cause information about the cause of the error to be lost: most
operations can fail for a variety of reasons.)

To ignore an exception set by a function call that failed, the exception
condition must be cleared explicitly by calling *note PyErr_Clear():
a4c.  The only time C code should call *note PyErr_Clear(): a4c. is if
it doesn’t want to pass the error on to the interpreter but wants to
handle it completely by itself (possibly by trying something else, or
pretending nothing went wrong).

Every failing ‘malloc()’ call must be turned into an exception — the
direct caller of ‘malloc()’ (or ‘realloc()’) must call *note
PyErr_NoMemory(): 3d1b. and return a failure indicator itself.  All the
object-creating functions (for example, *note PyLong_FromLong(): 3d1c.)
already do this, so this note is only relevant to those who call
‘malloc()’ directly.

Also note that, with the important exception of *note
PyArg_ParseTuple(): 393. and friends, functions that return an integer
status usually return a positive value or zero for success and ‘-1’ for
failure, like Unix system calls.

Finally, be careful to clean up garbage (by making *note Py_XDECREF():
391. or *note Py_DECREF(): 38f. calls for objects you have already
created) when you return an error indicator!

The choice of which exception to raise is entirely yours.  There are
predeclared C objects corresponding to all built-in Python exceptions,
such as ‘PyExc_ZeroDivisionError’, which you can use directly.  Of
course, you should choose exceptions wisely — don’t use
‘PyExc_TypeError’ to mean that a file couldn’t be opened (that should
probably be ‘PyExc_IOError’).  If something’s wrong with the argument
list, the *note PyArg_ParseTuple(): 393. function usually raises
‘PyExc_TypeError’.  If you have an argument whose value must be in a
particular range or must satisfy other conditions, ‘PyExc_ValueError’ is
appropriate.

You can also define a new exception that is unique to your module.  For
this, you usually declare a static object variable at the beginning of
your file:

     static PyObject *SpamError;

and initialize it in your module’s initialization function
(‘PyInit_spam()’) with an exception object:

     PyMODINIT_FUNC
     PyInit_spam(void)
     {
         PyObject *m;

         m = PyModule_Create(&spammodule);
         if (m == NULL)
             return NULL;

         SpamError = PyErr_NewException("spam.error", NULL, NULL);
         Py_XINCREF(SpamError);
         if (PyModule_AddObject(m, "error", SpamError) < 0) {
             Py_XDECREF(SpamError);
             Py_CLEAR(SpamError);
             Py_DECREF(m);
             return NULL;
         }

         return m;
     }

Note that the Python name for the exception object is ‘spam.error’.  The
*note PyErr_NewException(): ccb. function may create a class with the
base class being *note Exception: 2dc. (unless another class is passed
in instead of ‘NULL’), described in *note Built-in Exceptions: f73.

Note also that the ‘SpamError’ variable retains a reference to the newly
created exception class; this is intentional!  Since the exception could
be removed from the module by external code, an owned reference to the
class is needed to ensure that it will not be discarded, causing
‘SpamError’ to become a dangling pointer.  Should it become a dangling
pointer, C code which raises the exception could cause a core dump or
other unintended side effects.

We discuss the use of ‘PyMODINIT_FUNC’ as a function return type later
in this sample.

The ‘spam.error’ exception can be raised in your extension module using
a call to *note PyErr_SetString(): 3d17. as shown below:

     static PyObject *
     spam_system(PyObject *self, PyObject *args)
     {
         const char *command;
         int sts;

         if (!PyArg_ParseTuple(args, "s", &command))
             return NULL;
         sts = system(command);
         if (sts < 0) {
             PyErr_SetString(SpamError, "System command failed");
             return NULL;
         }
         return PyLong_FromLong(sts);
     }


File: python.info,  Node: Back to the Example,  Next: The Module’s Method Table and Initialization Function,  Prev: Intermezzo Errors and Exceptions,  Up: Extending Python with C or C++

6.2.1.3 Back to the Example
...........................

Going back to our example function, you should now be able to understand
this statement:

     if (!PyArg_ParseTuple(args, "s", &command))
         return NULL;

It returns ‘NULL’ (the error indicator for functions returning object
pointers) if an error is detected in the argument list, relying on the
exception set by *note PyArg_ParseTuple(): 393.  Otherwise the string
value of the argument has been copied to the local variable ‘command’.
This is a pointer assignment and you are not supposed to modify the
string to which it points (so in Standard C, the variable ‘command’
should properly be declared as ‘const char *command’).

The next statement is a call to the Unix function ‘system()’, passing it
the string we just got from *note PyArg_ParseTuple(): 393.:

     sts = system(command);

Our ‘spam.system()’ function must return the value of ‘sts’ as a Python
object.  This is done using the function *note PyLong_FromLong(): 3d1c.

     return PyLong_FromLong(sts);

In this case, it will return an integer object.  (Yes, even integers are
objects on the heap in Python!)

If you have a C function that returns no useful argument (a function
returning ‘void’), the corresponding Python function must return ‘None’.
You need this idiom to do so (which is implemented by the *note
Py_RETURN_NONE: e9b. macro):

     Py_INCREF(Py_None);
     return Py_None;

*note Py_None: 3d1f. is the C name for the special Python object ‘None’.
It is a genuine Python object rather than a ‘NULL’ pointer, which means
“error” in most contexts, as we have seen.


File: python.info,  Node: The Module’s Method Table and Initialization Function,  Next: Compilation and Linkage,  Prev: Back to the Example,  Up: Extending Python with C or C++

6.2.1.4 The Module’s Method Table and Initialization Function
.............................................................

I promised to show how ‘spam_system()’ is called from Python programs.
First, we need to list its name and address in a “method table”:

     static PyMethodDef SpamMethods[] = {
         ...
         {"system",  spam_system, METH_VARARGS,
          "Execute a shell command."},
         ...
         {NULL, NULL, 0, NULL}        /* Sentinel */
     };

Note the third entry (‘METH_VARARGS’).  This is a flag telling the
interpreter the calling convention to be used for the C function.  It
should normally always be ‘METH_VARARGS’ or ‘METH_VARARGS |
METH_KEYWORDS’; a value of ‘0’ means that an obsolete variant of *note
PyArg_ParseTuple(): 393. is used.

When using only ‘METH_VARARGS’, the function should expect the
Python-level parameters to be passed in as a tuple acceptable for
parsing via *note PyArg_ParseTuple(): 393.; more information on this
function is provided below.

The ‘METH_KEYWORDS’ bit may be set in the third field if keyword
arguments should be passed to the function.  In this case, the C
function should accept a third ‘PyObject *’ parameter which will be a
dictionary of keywords.  Use *note PyArg_ParseTupleAndKeywords(): 6c1.
to parse the arguments to such a function.

The method table must be referenced in the module definition structure:

     static struct PyModuleDef spammodule = {
         PyModuleDef_HEAD_INIT,
         "spam",   /* name of module */
         spam_doc, /* module documentation, may be NULL */
         -1,       /* size of per-interpreter state of the module,
                      or -1 if the module keeps state in global variables. */
         SpamMethods
     };

This structure, in turn, must be passed to the interpreter in the
module’s initialization function.  The initialization function must be
named ‘PyInit_name()’, where `name' is the name of the module, and
should be the only non-‘static’ item defined in the module file:

     PyMODINIT_FUNC
     PyInit_spam(void)
     {
         return PyModule_Create(&spammodule);
     }

Note that PyMODINIT_FUNC declares the function as ‘PyObject *’ return
type, declares any special linkage declarations required by the
platform, and for C++ declares the function as ‘extern "C"’.

When the Python program imports module ‘spam’ for the first time,
‘PyInit_spam()’ is called.  (See below for comments about embedding
Python.)  It calls *note PyModule_Create(): 3d22, which returns a module
object, and inserts built-in function objects into the newly created
module based upon the table (an array of *note PyMethodDef: edd.
structures) found in the module definition.  *note PyModule_Create():
3d22. returns a pointer to the module object that it creates.  It may
abort with a fatal error for certain errors, or return ‘NULL’ if the
module could not be initialized satisfactorily.  The init function must
return the module object to its caller, so that it then gets inserted
into ‘sys.modules’.

When embedding Python, the ‘PyInit_spam()’ function is not called
automatically unless there’s an entry in the ‘PyImport_Inittab’ table.
To add the module to the initialization table, use *note
PyImport_AppendInittab(): f9c, optionally followed by an import of the
module:

     int
     main(int argc, char *argv[])
     {
         wchar_t *program = Py_DecodeLocale(argv[0], NULL);
         if (program == NULL) {
             fprintf(stderr, "Fatal error: cannot decode argv[0]\n");
             exit(1);
         }

         /* Add a built-in module, before Py_Initialize */
         if (PyImport_AppendInittab("spam", PyInit_spam) == -1) {
             fprintf(stderr, "Error: could not extend in-built modules table\n");
             exit(1);
         }

         /* Pass argv[0] to the Python interpreter */
         Py_SetProgramName(program);

         /* Initialize the Python interpreter.  Required.
            If this step fails, it will be a fatal error. */
         Py_Initialize();

         /* Optionally import the module; alternatively,
            import can be deferred until the embedded script
            imports it. */
         PyObject *pmodule = PyImport_ImportModule("spam");
         if (!pmodule) {
             PyErr_Print();
             fprintf(stderr, "Error: could not import module 'spam'\n");
         }

         ...

         PyMem_RawFree(program);
         return 0;
     }

     Note: Removing entries from ‘sys.modules’ or importing compiled
     modules into multiple interpreters within a process (or following a
     ‘fork()’ without an intervening ‘exec()’) can create problems for
     some extension modules.  Extension module authors should exercise
     caution when initializing internal data structures.

A more substantial example module is included in the Python source
distribution as ‘Modules/xxmodule.c’.  This file may be used as a
template or simply read as an example.

     Note: Unlike our ‘spam’ example, ‘xxmodule’ uses `multi-phase
     initialization' (new in Python 3.5), where a PyModuleDef structure
     is returned from ‘PyInit_spam’, and creation of the module is left
     to the import machinery.  For details on multi-phase
     initialization, see PEP 489(1).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0489


File: python.info,  Node: Compilation and Linkage,  Next: Calling Python Functions from C,  Prev: The Module’s Method Table and Initialization Function,  Up: Extending Python with C or C++

6.2.1.5 Compilation and Linkage
...............................

There are two more things to do before you can use your new extension:
compiling and linking it with the Python system.  If you use dynamic
loading, the details may depend on the style of dynamic loading your
system uses; see the chapters about building extension modules (chapter
*note Building C and C++ Extensions: 3d25.) and additional information
that pertains only to building on Windows (chapter *note Building C and
C++ Extensions on Windows: 14cd.) for more information about this.

If you can’t use dynamic loading, or if you want to make your module a
permanent part of the Python interpreter, you will have to change the
configuration setup and rebuild the interpreter.  Luckily, this is very
simple on Unix: just place your file (‘spammodule.c’ for example) in the
‘Modules/’ directory of an unpacked source distribution, add a line to
the file ‘Modules/Setup.local’ describing your file:

     spam spammodule.o

and rebuild the interpreter by running ‘make’ in the toplevel directory.
You can also run ‘make’ in the ‘Modules/’ subdirectory, but then you
must first rebuild ‘Makefile’ there by running ‘‘make’ Makefile’.  (This
is necessary each time you change the ‘Setup’ file.)

If your module requires additional libraries to link with, these can be
listed on the line in the configuration file as well, for instance:

     spam spammodule.o -lX11


File: python.info,  Node: Calling Python Functions from C,  Next: Extracting Parameters in Extension Functions,  Prev: Compilation and Linkage,  Up: Extending Python with C or C++

6.2.1.6 Calling Python Functions from C
.......................................

So far we have concentrated on making C functions callable from Python.
The reverse is also useful: calling Python functions from C. This is
especially the case for libraries that support so-called “callback”
functions.  If a C interface makes use of callbacks, the equivalent
Python often needs to provide a callback mechanism to the Python
programmer; the implementation will require calling the Python callback
functions from a C callback.  Other uses are also imaginable.

Fortunately, the Python interpreter is easily called recursively, and
there is a standard interface to call a Python function.  (I won’t dwell
on how to call the Python parser with a particular string as input — if
you’re interested, have a look at the implementation of the *note -c:
1340. command line option in ‘Modules/main.c’ from the Python source
code.)

Calling a Python function is easy.  First, the Python program must
somehow pass you the Python function object.  You should provide a
function (or some other interface) to do this.  When this function is
called, save a pointer to the Python function object (be careful to
*note Py_INCREF(): 38e. it!)  in a global variable — or wherever you see
fit.  For example, the following function might be part of a module
definition:

     static PyObject *my_callback = NULL;

     static PyObject *
     my_set_callback(PyObject *dummy, PyObject *args)
     {
         PyObject *result = NULL;
         PyObject *temp;

         if (PyArg_ParseTuple(args, "O:set_callback", &temp)) {
             if (!PyCallable_Check(temp)) {
                 PyErr_SetString(PyExc_TypeError, "parameter must be callable");
                 return NULL;
             }
             Py_XINCREF(temp);         /* Add a reference to new callback */
             Py_XDECREF(my_callback);  /* Dispose of previous callback */
             my_callback = temp;       /* Remember new callback */
             /* Boilerplate to return "None" */
             Py_INCREF(Py_None);
             result = Py_None;
         }
         return result;
     }

This function must be registered with the interpreter using the *note
METH_VARARGS: f0a. flag; this is described in section *note The Module’s
Method Table and Initialization Function: 3d20.  The *note
PyArg_ParseTuple(): 393. function and its arguments are documented in
section *note Extracting Parameters in Extension Functions: 3d14.

The macros *note Py_XINCREF(): 390. and *note Py_XDECREF(): 391.
increment/decrement the reference count of an object and are safe in the
presence of ‘NULL’ pointers (but note that `temp' will not be ‘NULL’ in
this context).  More info on them in section *note Reference Counts:
3d28.

Later, when it is time to call the function, you call the C function
*note PyObject_CallObject(): 3d29.  This function has two arguments,
both pointers to arbitrary Python objects: the Python function, and the
argument list.  The argument list must always be a tuple object, whose
length is the number of arguments.  To call the Python function with no
arguments, pass in ‘NULL’, or an empty tuple; to call it with one
argument, pass a singleton tuple.  *note Py_BuildValue(): 3f0. returns a
tuple when its format string consists of zero or more format codes
between parentheses.  For example:

     int arg;
     PyObject *arglist;
     PyObject *result;
     ...
     arg = 123;
     ...
     /* Time to call the callback */
     arglist = Py_BuildValue("(i)", arg);
     result = PyObject_CallObject(my_callback, arglist);
     Py_DECREF(arglist);

*note PyObject_CallObject(): 3d29. returns a Python object pointer: this
is the return value of the Python function.  *note
PyObject_CallObject(): 3d29. is “reference-count-neutral” with respect
to its arguments.  In the example a new tuple was created to serve as
the argument list, which is *note Py_DECREF(): 38f.-ed immediately after
the *note PyObject_CallObject(): 3d29. call.

The return value of *note PyObject_CallObject(): 3d29. is “new”: either
it is a brand new object, or it is an existing object whose reference
count has been incremented.  So, unless you want to save it in a global
variable, you should somehow *note Py_DECREF(): 38f. the result, even
(especially!)  if you are not interested in its value.

Before you do this, however, it is important to check that the return
value isn’t ‘NULL’.  If it is, the Python function terminated by raising
an exception.  If the C code that called *note PyObject_CallObject():
3d29. is called from Python, it should now return an error indication to
its Python caller, so the interpreter can print a stack trace, or the
calling Python code can handle the exception.  If this is not possible
or desirable, the exception should be cleared by calling *note
PyErr_Clear(): a4c.  For example:

     if (result == NULL)
         return NULL; /* Pass error back */
     ...use result...
     Py_DECREF(result);

Depending on the desired interface to the Python callback function, you
may also have to provide an argument list to *note
PyObject_CallObject(): 3d29.  In some cases the argument list is also
provided by the Python program, through the same interface that
specified the callback function.  It can then be saved and used in the
same manner as the function object.  In other cases, you may have to
construct a new tuple to pass as the argument list.  The simplest way to
do this is to call *note Py_BuildValue(): 3f0.  For example, if you want
to pass an integral event code, you might use the following code:

     PyObject *arglist;
     ...
     arglist = Py_BuildValue("(l)", eventcode);
     result = PyObject_CallObject(my_callback, arglist);
     Py_DECREF(arglist);
     if (result == NULL)
         return NULL; /* Pass error back */
     /* Here maybe use the result */
     Py_DECREF(result);

Note the placement of ‘Py_DECREF(arglist)’ immediately after the call,
before the error check!  Also note that strictly speaking this code is
not complete: *note Py_BuildValue(): 3f0. may run out of memory, and
this should be checked.

You may also call a function with keyword arguments by using *note
PyObject_Call(): 23c, which supports arguments and keyword arguments.
As in the above example, we use *note Py_BuildValue(): 3f0. to construct
the dictionary.

     PyObject *dict;
     ...
     dict = Py_BuildValue("{s:i}", "name", val);
     result = PyObject_Call(my_callback, NULL, dict);
     Py_DECREF(dict);
     if (result == NULL)
         return NULL; /* Pass error back */
     /* Here maybe use the result */
     Py_DECREF(result);


File: python.info,  Node: Extracting Parameters in Extension Functions,  Next: Keyword Parameters for Extension Functions,  Prev: Calling Python Functions from C,  Up: Extending Python with C or C++

6.2.1.7 Extracting Parameters in Extension Functions
....................................................

The *note PyArg_ParseTuple(): 393. function is declared as follows:

     int PyArg_ParseTuple(PyObject *arg, const char *format, ...);

The `arg' argument must be a tuple object containing an argument list
passed from Python to a C function.  The `format' argument must be a
format string, whose syntax is explained in *note Parsing arguments and
building values: 3f2. in the Python/C API Reference Manual.  The
remaining arguments must be addresses of variables whose type is
determined by the format string.

Note that while *note PyArg_ParseTuple(): 393. checks that the Python
arguments have the required types, it cannot check the validity of the
addresses of C variables passed to the call: if you make mistakes there,
your code will probably crash or at least overwrite random bits in
memory.  So be careful!

Note that any Python object references which are provided to the caller
are `borrowed' references; do not decrement their reference count!

Some example calls:

     #define PY_SSIZE_T_CLEAN  /* Make "s#" use Py_ssize_t rather than int. */
     #include <Python.h>

     int ok;
     int i, j;
     long k, l;
     const char *s;
     Py_ssize_t size;

     ok = PyArg_ParseTuple(args, ""); /* No arguments */
         /* Python call: f() */

     ok = PyArg_ParseTuple(args, "s", &s); /* A string */
         /* Possible Python call: f('whoops!') */

     ok = PyArg_ParseTuple(args, "lls", &k, &l, &s); /* Two longs and a string */
         /* Possible Python call: f(1, 2, 'three') */

     ok = PyArg_ParseTuple(args, "(ii)s#", &i, &j, &s, &size);
         /* A pair of ints and a string, whose size is also returned */
         /* Possible Python call: f((1, 2), 'three') */

     {
         const char *file;
         const char *mode = "r";
         int bufsize = 0;
         ok = PyArg_ParseTuple(args, "s|si", &file, &mode, &bufsize);
         /* A string, and optionally another string and an integer */
         /* Possible Python calls:
            f('spam')
            f('spam', 'w')
            f('spam', 'wb', 100000) */
     }

     {
         int left, top, right, bottom, h, v;
         ok = PyArg_ParseTuple(args, "((ii)(ii))(ii)",
                  &left, &top, &right, &bottom, &h, &v);
         /* A rectangle and a point */
         /* Possible Python call:
            f(((0, 0), (400, 300)), (10, 10)) */
     }

     {
         Py_complex c;
         ok = PyArg_ParseTuple(args, "D:myfunction", &c);
         /* a complex, also providing a function name for errors */
         /* Possible Python call: myfunction(1+2j) */
     }


File: python.info,  Node: Keyword Parameters for Extension Functions,  Next: Building Arbitrary Values,  Prev: Extracting Parameters in Extension Functions,  Up: Extending Python with C or C++

6.2.1.8 Keyword Parameters for Extension Functions
..................................................

The *note PyArg_ParseTupleAndKeywords(): 6c1. function is declared as
follows:

     int PyArg_ParseTupleAndKeywords(PyObject *arg, PyObject *kwdict,
                                     const char *format, char *kwlist[], ...);

The `arg' and `format' parameters are identical to those of the *note
PyArg_ParseTuple(): 393. function.  The `kwdict' parameter is the
dictionary of keywords received as the third parameter from the Python
runtime.  The `kwlist' parameter is a ‘NULL’-terminated list of strings
which identify the parameters; the names are matched with the type
information from `format' from left to right.  On success, *note
PyArg_ParseTupleAndKeywords(): 6c1. returns true, otherwise it returns
false and raises an appropriate exception.

     Note: Nested tuples cannot be parsed when using keyword arguments!
     Keyword parameters passed in which are not present in the `kwlist'
     will cause *note TypeError: 1fe. to be raised.

Here is an example module which uses keywords, based on an example by
Geoff Philbrick (<philbrick@hks.com>):

     #define PY_SSIZE_T_CLEAN  /* Make "s#" use Py_ssize_t rather than int. */
     #include <Python.h>

     static PyObject *
     keywdarg_parrot(PyObject *self, PyObject *args, PyObject *keywds)
     {
         int voltage;
         const char *state = "a stiff";
         const char *action = "voom";
         const char *type = "Norwegian Blue";

         static char *kwlist[] = {"voltage", "state", "action", "type", NULL};

         if (!PyArg_ParseTupleAndKeywords(args, keywds, "i|sss", kwlist,
                                          &voltage, &state, &action, &type))
             return NULL;

         printf("-- This parrot wouldn't %s if you put %i Volts through it.\n",
                action, voltage);
         printf("-- Lovely plumage, the %s -- It's %s!\n", type, state);

         Py_RETURN_NONE;
     }

     static PyMethodDef keywdarg_methods[] = {
         /* The cast of the function is necessary since PyCFunction values
          * only take two PyObject* parameters, and keywdarg_parrot() takes
          * three.
          */
         {"parrot", (PyCFunction)(void(*)(void))keywdarg_parrot, METH_VARARGS | METH_KEYWORDS,
          "Print a lovely skit to standard output."},
         {NULL, NULL, 0, NULL}   /* sentinel */
     };

     static struct PyModuleDef keywdargmodule = {
         PyModuleDef_HEAD_INIT,
         "keywdarg",
         NULL,
         -1,
         keywdarg_methods
     };

     PyMODINIT_FUNC
     PyInit_keywdarg(void)
     {
         return PyModule_Create(&keywdargmodule);
     }


File: python.info,  Node: Building Arbitrary Values,  Next: Reference Counts,  Prev: Keyword Parameters for Extension Functions,  Up: Extending Python with C or C++

6.2.1.9 Building Arbitrary Values
.................................

This function is the counterpart to *note PyArg_ParseTuple(): 393.  It
is declared as follows:

     PyObject *Py_BuildValue(const char *format, ...);

It recognizes a set of format units similar to the ones recognized by
*note PyArg_ParseTuple(): 393, but the arguments (which are input to the
function, not output) must not be pointers, just values.  It returns a
new Python object, suitable for returning from a C function called from
Python.

One difference with *note PyArg_ParseTuple(): 393.: while the latter
requires its first argument to be a tuple (since Python argument lists
are always represented as tuples internally), *note Py_BuildValue():
3f0. does not always build a tuple.  It builds a tuple only if its
format string contains two or more format units.  If the format string
is empty, it returns ‘None’; if it contains exactly one format unit, it
returns whatever object is described by that format unit.  To force it
to return a tuple of size 0 or one, parenthesize the format string.

Examples (to the left the call, to the right the resulting Python
value):

     Py_BuildValue("")                        None
     Py_BuildValue("i", 123)                  123
     Py_BuildValue("iii", 123, 456, 789)      (123, 456, 789)
     Py_BuildValue("s", "hello")              'hello'
     Py_BuildValue("y", "hello")              b'hello'
     Py_BuildValue("ss", "hello", "world")    ('hello', 'world')
     Py_BuildValue("s#", "hello", 4)          'hell'
     Py_BuildValue("y#", "hello", 4)          b'hell'
     Py_BuildValue("()")                      ()
     Py_BuildValue("(i)", 123)                (123,)
     Py_BuildValue("(ii)", 123, 456)          (123, 456)
     Py_BuildValue("(i,i)", 123, 456)         (123, 456)
     Py_BuildValue("[i,i]", 123, 456)         [123, 456]
     Py_BuildValue("{s:i,s:i}",
                   "abc", 123, "def", 456)    {'abc': 123, 'def': 456}
     Py_BuildValue("((ii)(ii)) (ii)",
                   1, 2, 3, 4, 5, 6)          (((1, 2), (3, 4)), (5, 6))


File: python.info,  Node: Reference Counts,  Next: Writing Extensions in C++,  Prev: Building Arbitrary Values,  Up: Extending Python with C or C++

6.2.1.10 Reference Counts
.........................

In languages like C or C++, the programmer is responsible for dynamic
allocation and deallocation of memory on the heap.  In C, this is done
using the functions ‘malloc()’ and ‘free()’.  In C++, the operators
‘new’ and ‘delete’ are used with essentially the same meaning and we’ll
restrict the following discussion to the C case.

Every block of memory allocated with ‘malloc()’ should eventually be
returned to the pool of available memory by exactly one call to
‘free()’.  It is important to call ‘free()’ at the right time.  If a
block’s address is forgotten but ‘free()’ is not called for it, the
memory it occupies cannot be reused until the program terminates.  This
is called a `memory leak'.  On the other hand, if a program calls
‘free()’ for a block and then continues to use the block, it creates a
conflict with re-use of the block through another ‘malloc()’ call.  This
is called `using freed memory'.  It has the same bad consequences as
referencing uninitialized data — core dumps, wrong results, mysterious
crashes.

Common causes of memory leaks are unusual paths through the code.  For
instance, a function may allocate a block of memory, do some
calculation, and then free the block again.  Now a change in the
requirements for the function may add a test to the calculation that
detects an error condition and can return prematurely from the function.
It’s easy to forget to free the allocated memory block when taking this
premature exit, especially when it is added later to the code.  Such
leaks, once introduced, often go undetected for a long time: the error
exit is taken only in a small fraction of all calls, and most modern
machines have plenty of virtual memory, so the leak only becomes
apparent in a long-running process that uses the leaking function
frequently.  Therefore, it’s important to prevent leaks from happening
by having a coding convention or strategy that minimizes this kind of
errors.

Since Python makes heavy use of ‘malloc()’ and ‘free()’, it needs a
strategy to avoid memory leaks as well as the use of freed memory.  The
chosen method is called `reference counting'.  The principle is simple:
every object contains a counter, which is incremented when a reference
to the object is stored somewhere, and which is decremented when a
reference to it is deleted.  When the counter reaches zero, the last
reference to the object has been deleted and the object is freed.

An alternative strategy is called `automatic garbage collection'.
(Sometimes, reference counting is also referred to as a garbage
collection strategy, hence my use of “automatic” to distinguish the
two.)  The big advantage of automatic garbage collection is that the
user doesn’t need to call ‘free()’ explicitly.  (Another claimed
advantage is an improvement in speed or memory usage — this is no hard
fact however.)  The disadvantage is that for C, there is no truly
portable automatic garbage collector, while reference counting can be
implemented portably (as long as the functions ‘malloc()’ and ‘free()’
are available — which the C Standard guarantees).  Maybe some day a
sufficiently portable automatic garbage collector will be available for
C. Until then, we’ll have to live with reference counts.

While Python uses the traditional reference counting implementation, it
also offers a cycle detector that works to detect reference cycles.
This allows applications to not worry about creating direct or indirect
circular references; these are the weakness of garbage collection
implemented using only reference counting.  Reference cycles consist of
objects which contain (possibly indirect) references to themselves, so
that each object in the cycle has a reference count which is non-zero.
Typical reference counting implementations are not able to reclaim the
memory belonging to any objects in a reference cycle, or referenced from
the objects in the cycle, even though there are no further references to
the cycle itself.

The cycle detector is able to detect garbage cycles and can reclaim
them.  The *note gc: 84. module exposes a way to run the detector (the
*note collect(): 35b. function), as well as configuration interfaces and
the ability to disable the detector at runtime.  The cycle detector is
considered an optional component; though it is included by default, it
can be disabled at build time using the ‘--without-cycle-gc’ option to
the ‘configure’ script on Unix platforms (including Mac OS X). If the
cycle detector is disabled in this way, the *note gc: 84. module will
not be available.

* Menu:

* Reference Counting in Python::
* Ownership Rules::
* Thin Ice::
* NULL Pointers::


File: python.info,  Node: Reference Counting in Python,  Next: Ownership Rules,  Up: Reference Counts

6.2.1.11 Reference Counting in Python
.....................................

There are two macros, ‘Py_INCREF(x)’ and ‘Py_DECREF(x)’, which handle
the incrementing and decrementing of the reference count.  *note
Py_DECREF(): 38f. also frees the object when the count reaches zero.
For flexibility, it doesn’t call ‘free()’ directly — rather, it makes a
call through a function pointer in the object’s `type object'.  For this
purpose (and others), every object also contains a pointer to its type
object.

The big question now remains: when to use ‘Py_INCREF(x)’ and
‘Py_DECREF(x)’?  Let’s first introduce some terms.  Nobody “owns” an
object; however, you can `own a reference' to an object.  An object’s
reference count is now defined as the number of owned references to it.
The owner of a reference is responsible for calling *note Py_DECREF():
38f. when the reference is no longer needed.  Ownership of a reference
can be transferred.  There are three ways to dispose of an owned
reference: pass it on, store it, or call *note Py_DECREF(): 38f.
Forgetting to dispose of an owned reference creates a memory leak.

It is also possible to `borrow' (1) a reference to an object.  The
borrower of a reference should not call *note Py_DECREF(): 38f.  The
borrower must not hold on to the object longer than the owner from which
it was borrowed.  Using a borrowed reference after the owner has
disposed of it risks using freed memory and should be avoided completely
(2).

The advantage of borrowing over owning a reference is that you don’t
need to take care of disposing of the reference on all possible paths
through the code — in other words, with a borrowed reference you don’t
run the risk of leaking when a premature exit is taken.  The
disadvantage of borrowing over owning is that there are some subtle
situations where in seemingly correct code a borrowed reference can be
used after the owner from which it was borrowed has in fact disposed of
it.

A borrowed reference can be changed into an owned reference by calling
*note Py_INCREF(): 38e.  This does not affect the status of the owner
from which the reference was borrowed — it creates a new owned
reference, and gives full owner responsibilities (the new owner must
dispose of the reference properly, as well as the previous owner).

   ---------- Footnotes ----------

   (1) (2) The metaphor of “borrowing” a reference is not completely
correct: the owner still has a copy of the reference.

   (2) (3) Checking that the reference count is at least 1 `does not
work' — the reference count itself could be in freed memory and may thus
be reused for another object!


File: python.info,  Node: Ownership Rules,  Next: Thin Ice,  Prev: Reference Counting in Python,  Up: Reference Counts

6.2.1.12 Ownership Rules
........................

Whenever an object reference is passed into or out of a function, it is
part of the function’s interface specification whether ownership is
transferred with the reference or not.

Most functions that return a reference to an object pass on ownership
with the reference.  In particular, all functions whose function it is
to create a new object, such as *note PyLong_FromLong(): 3d1c. and *note
Py_BuildValue(): 3f0, pass ownership to the receiver.  Even if the
object is not actually new, you still receive ownership of a new
reference to that object.  For instance, *note PyLong_FromLong(): 3d1c.
maintains a cache of popular values and can return a reference to a
cached item.

Many functions that extract objects from other objects also transfer
ownership with the reference, for instance *note
PyObject_GetAttrString(): 3d34.  The picture is less clear, here,
however, since a few common routines are exceptions: *note
PyTuple_GetItem(): 3d35, *note PyList_GetItem(): 3d36, *note
PyDict_GetItem(): 3d37, and *note PyDict_GetItemString(): 3d38. all
return references that you borrow from the tuple, list or dictionary.

The function *note PyImport_AddModule(): 3d39. also returns a borrowed
reference, even though it may actually create the object it returns:
this is possible because an owned reference to the object is stored in
‘sys.modules’.

When you pass an object reference into another function, in general, the
function borrows the reference from you — if it needs to store it, it
will use *note Py_INCREF(): 38e. to become an independent owner.  There
are exactly two important exceptions to this rule: *note
PyTuple_SetItem(): 3d3a. and *note PyList_SetItem(): 3d3b.  These
functions take over ownership of the item passed to them — even if they
fail!  (Note that *note PyDict_SetItem(): 3d3c. and friends don’t take
over ownership — they are “normal.”)

When a C function is called from Python, it borrows references to its
arguments from the caller.  The caller owns a reference to the object,
so the borrowed reference’s lifetime is guaranteed until the function
returns.  Only when such a borrowed reference must be stored or passed
on, it must be turned into an owned reference by calling *note
Py_INCREF(): 38e.

The object reference returned from a C function that is called from
Python must be an owned reference — ownership is transferred from the
function to its caller.


File: python.info,  Node: Thin Ice,  Next: NULL Pointers,  Prev: Ownership Rules,  Up: Reference Counts

6.2.1.13 Thin Ice
.................

There are a few situations where seemingly harmless use of a borrowed
reference can lead to problems.  These all have to do with implicit
invocations of the interpreter, which can cause the owner of a reference
to dispose of it.

The first and most important case to know about is using *note
Py_DECREF(): 38f. on an unrelated object while borrowing a reference to
a list item.  For instance:

     void
     bug(PyObject *list)
     {
         PyObject *item = PyList_GetItem(list, 0);

         PyList_SetItem(list, 1, PyLong_FromLong(0L));
         PyObject_Print(item, stdout, 0); /* BUG! */
     }

This function first borrows a reference to ‘list[0]’, then replaces
‘list[1]’ with the value ‘0’, and finally prints the borrowed reference.
Looks harmless, right?  But it’s not!

Let’s follow the control flow into *note PyList_SetItem(): 3d3b.  The
list owns references to all its items, so when item 1 is replaced, it
has to dispose of the original item 1.  Now let’s suppose the original
item 1 was an instance of a user-defined class, and let’s further
suppose that the class defined a *note __del__(): a04. method.  If this
class instance has a reference count of 1, disposing of it will call its
*note __del__(): a04. method.

Since it is written in Python, the *note __del__(): a04. method can
execute arbitrary Python code.  Could it perhaps do something to
invalidate the reference to ‘item’ in ‘bug()’?  You bet!  Assuming that
the list passed into ‘bug()’ is accessible to the *note __del__(): a04.
method, it could execute a statement to the effect of ‘del list[0]’, and
assuming this was the last reference to that object, it would free the
memory associated with it, thereby invalidating ‘item’.

The solution, once you know the source of the problem, is easy:
temporarily increment the reference count.  The correct version of the
function reads:

     void
     no_bug(PyObject *list)
     {
         PyObject *item = PyList_GetItem(list, 0);

         Py_INCREF(item);
         PyList_SetItem(list, 1, PyLong_FromLong(0L));
         PyObject_Print(item, stdout, 0);
         Py_DECREF(item);
     }

This is a true story.  An older version of Python contained variants of
this bug and someone spent a considerable amount of time in a C debugger
to figure out why his *note __del__(): a04. methods would fail…

The second case of problems with a borrowed reference is a variant
involving threads.  Normally, multiple threads in the Python interpreter
can’t get in each other’s way, because there is a global lock protecting
Python’s entire object space.  However, it is possible to temporarily
release this lock using the macro *note Py_BEGIN_ALLOW_THREADS: 3d3f,
and to re-acquire it using *note Py_END_ALLOW_THREADS: 3d7.  This is
common around blocking I/O calls, to let other threads use the processor
while waiting for the I/O to complete.  Obviously, the following
function has the same problem as the previous one:

     void
     bug(PyObject *list)
     {
         PyObject *item = PyList_GetItem(list, 0);
         Py_BEGIN_ALLOW_THREADS
         ...some blocking I/O call...
         Py_END_ALLOW_THREADS
         PyObject_Print(item, stdout, 0); /* BUG! */
     }


File: python.info,  Node: NULL Pointers,  Prev: Thin Ice,  Up: Reference Counts

6.2.1.14 NULL Pointers
......................

In general, functions that take object references as arguments do not
expect you to pass them ‘NULL’ pointers, and will dump core (or cause
later core dumps) if you do so.  Functions that return object references
generally return ‘NULL’ only to indicate that an exception occurred.
The reason for not testing for ‘NULL’ arguments is that functions often
pass the objects they receive on to other function — if each function
were to test for ‘NULL’, there would be a lot of redundant tests and the
code would run more slowly.

It is better to test for ‘NULL’ only at the “source:” when a pointer
that may be ‘NULL’ is received, for example, from ‘malloc()’ or from a
function that may raise an exception.

The macros *note Py_INCREF(): 38e. and *note Py_DECREF(): 38f. do not
check for ‘NULL’ pointers — however, their variants *note Py_XINCREF():
390. and *note Py_XDECREF(): 391. do.

The macros for checking for a particular object type (‘Pytype_Check()’)
don’t check for ‘NULL’ pointers — again, there is much code that calls
several of these in a row to test an object against various different
expected types, and this would generate redundant tests.  There are no
variants with ‘NULL’ checking.

The C function calling mechanism guarantees that the argument list
passed to C functions (‘args’ in the examples) is never ‘NULL’ — in fact
it guarantees that it is always a tuple (1).

It is a severe error to ever let a ‘NULL’ pointer “escape” to the Python
user.

   ---------- Footnotes ----------

   (1) (4) These guarantees don’t hold when you use the “old” style
calling convention — this is still found in much existing code.


File: python.info,  Node: Writing Extensions in C++,  Next: Providing a C API for an Extension Module,  Prev: Reference Counts,  Up: Extending Python with C or C++

6.2.1.15 Writing Extensions in C++
..................................

It is possible to write extension modules in C++.  Some restrictions
apply.  If the main program (the Python interpreter) is compiled and
linked by the C compiler, global or static objects with constructors
cannot be used.  This is not a problem if the main program is linked by
the C++ compiler.  Functions that will be called by the Python
interpreter (in particular, module initialization functions) have to be
declared using ‘extern "C"’.  It is unnecessary to enclose the Python
header files in ‘extern "C" {...}’ — they use this form already if the
symbol ‘__cplusplus’ is defined (all recent C++ compilers define this
symbol).


File: python.info,  Node: Providing a C API for an Extension Module,  Prev: Writing Extensions in C++,  Up: Extending Python with C or C++

6.2.1.16 Providing a C API for an Extension Module
..................................................

Many extension modules just provide new functions and types to be used
from Python, but sometimes the code in an extension module can be useful
for other extension modules.  For example, an extension module could
implement a type “collection” which works like lists without order.
Just like the standard Python list type has a C API which permits
extension modules to create and manipulate lists, this new collection
type should have a set of C functions for direct manipulation from other
extension modules.

At first sight this seems easy: just write the functions (without
declaring them ‘static’, of course), provide an appropriate header file,
and document the C API. And in fact this would work if all extension
modules were always linked statically with the Python interpreter.  When
modules are used as shared libraries, however, the symbols defined in
one module may not be visible to another module.  The details of
visibility depend on the operating system; some systems use one global
namespace for the Python interpreter and all extension modules (Windows,
for example), whereas others require an explicit list of imported
symbols at module link time (AIX is one example), or offer a choice of
different strategies (most Unices).  And even if symbols are globally
visible, the module whose functions one wishes to call might not have
been loaded yet!

Portability therefore requires not to make any assumptions about symbol
visibility.  This means that all symbols in extension modules should be
declared ‘static’, except for the module’s initialization function, in
order to avoid name clashes with other extension modules (as discussed
in section *note The Module’s Method Table and Initialization Function:
3d20.).  And it means that symbols that `should' be accessible from
other extension modules must be exported in a different way.

Python provides a special mechanism to pass C-level information
(pointers) from one extension module to another one: Capsules.  A
Capsule is a Python data type which stores a pointer (‘void *’).
Capsules can only be created and accessed via their C API, but they can
be passed around like any other Python object.  In particular, they can
be assigned to a name in an extension module’s namespace.  Other
extension modules can then import this module, retrieve the value of
this name, and then retrieve the pointer from the Capsule.

There are many ways in which Capsules can be used to export the C API of
an extension module.  Each function could get its own Capsule, or all C
API pointers could be stored in an array whose address is published in a
Capsule.  And the various tasks of storing and retrieving the pointers
can be distributed in different ways between the module providing the
code and the client modules.

Whichever method you choose, it’s important to name your Capsules
properly.  The function *note PyCapsule_New(): 3d45. takes a name
parameter (‘const char *’); you’re permitted to pass in a ‘NULL’ name,
but we strongly encourage you to specify a name.  Properly named
Capsules provide a degree of runtime type-safety; there is no feasible
way to tell one unnamed Capsule from another.

In particular, Capsules used to expose C APIs should be given a name
following this convention:

     modulename.attributename

The convenience function *note PyCapsule_Import(): 3d46. makes it easy
to load a C API provided via a Capsule, but only if the Capsule’s name
matches this convention.  This behavior gives C API users a high degree
of certainty that the Capsule they load contains the correct C API.

The following example demonstrates an approach that puts most of the
burden on the writer of the exporting module, which is appropriate for
commonly used library modules.  It stores all C API pointers (just one
in the example!)  in an array of ‘void’ pointers which becomes the value
of a Capsule.  The header file corresponding to the module provides a
macro that takes care of importing the module and retrieving its C API
pointers; client modules only have to call this macro before accessing
the C API.

The exporting module is a modification of the ‘spam’ module from section
*note A Simple Example: 3d13.  The function ‘spam.system()’ does not
call the C library function ‘system()’ directly, but a function
‘PySpam_System()’, which would of course do something more complicated
in reality (such as adding “spam” to every command).  This function
‘PySpam_System()’ is also exported to other extension modules.

The function ‘PySpam_System()’ is a plain C function, declared ‘static’
like everything else:

     static int
     PySpam_System(const char *command)
     {
         return system(command);
     }

The function ‘spam_system()’ is modified in a trivial way:

     static PyObject *
     spam_system(PyObject *self, PyObject *args)
     {
         const char *command;
         int sts;

         if (!PyArg_ParseTuple(args, "s", &command))
             return NULL;
         sts = PySpam_System(command);
         return PyLong_FromLong(sts);
     }

In the beginning of the module, right after the line

     #include <Python.h>

two more lines must be added:

     #define SPAM_MODULE
     #include "spammodule.h"

The ‘#define’ is used to tell the header file that it is being included
in the exporting module, not a client module.  Finally, the module’s
initialization function must take care of initializing the C API pointer
array:

     PyMODINIT_FUNC
     PyInit_spam(void)
     {
         PyObject *m;
         static void *PySpam_API[PySpam_API_pointers];
         PyObject *c_api_object;

         m = PyModule_Create(&spammodule);
         if (m == NULL)
             return NULL;

         /* Initialize the C API pointer array */
         PySpam_API[PySpam_System_NUM] = (void *)PySpam_System;

         /* Create a Capsule containing the API pointer array's address */
         c_api_object = PyCapsule_New((void *)PySpam_API, "spam._C_API", NULL);

         if (PyModule_AddObject(m, "_C_API", c_api_object) < 0) {
             Py_XDECREF(c_api_object);
             Py_DECREF(m);
             return NULL;
         }

         return m;
     }

Note that ‘PySpam_API’ is declared ‘static’; otherwise the pointer array
would disappear when ‘PyInit_spam()’ terminates!

The bulk of the work is in the header file ‘spammodule.h’, which looks
like this:

     #ifndef Py_SPAMMODULE_H
     #define Py_SPAMMODULE_H
     #ifdef __cplusplus
     extern "C" {
     #endif

     /* Header file for spammodule */

     /* C API functions */
     #define PySpam_System_NUM 0
     #define PySpam_System_RETURN int
     #define PySpam_System_PROTO (const char *command)

     /* Total number of C API pointers */
     #define PySpam_API_pointers 1


     #ifdef SPAM_MODULE
     /* This section is used when compiling spammodule.c */

     static PySpam_System_RETURN PySpam_System PySpam_System_PROTO;

     #else
     /* This section is used in modules that use spammodule's API */

     static void **PySpam_API;

     #define PySpam_System \
      (*(PySpam_System_RETURN (*)PySpam_System_PROTO) PySpam_API[PySpam_System_NUM])

     /* Return -1 on error, 0 on success.
      * PyCapsule_Import will set an exception if there's an error.
      */
     static int
     import_spam(void)
     {
         PySpam_API = (void **)PyCapsule_Import("spam._C_API", 0);
         return (PySpam_API != NULL) ? 0 : -1;
     }

     #endif

     #ifdef __cplusplus
     }
     #endif

     #endif /* !defined(Py_SPAMMODULE_H) */

All that a client module must do in order to have access to the function
‘PySpam_System()’ is to call the function (or rather macro)
‘import_spam()’ in its initialization function:

     PyMODINIT_FUNC
     PyInit_client(void)
     {
         PyObject *m;

         m = PyModule_Create(&clientmodule);
         if (m == NULL)
             return NULL;
         if (import_spam() < 0)
             return NULL;
         /* additional initialization can happen here */
         return m;
     }

The main disadvantage of this approach is that the file ‘spammodule.h’
is rather complicated.  However, the basic structure is the same for
each function that is exported, so it has to be learned only once.

Finally it should be mentioned that Capsules offer additional
functionality, which is especially useful for memory allocation and
deallocation of the pointer stored in a Capsule.  The details are
described in the Python/C API Reference Manual in the section *note
Capsules: 3d47. and in the implementation of Capsules (files
‘Include/pycapsule.h’ and ‘Objects/pycapsule.c’ in the Python source
code distribution).


File: python.info,  Node: Defining Extension Types Tutorial,  Next: Defining Extension Types Assorted Topics,  Prev: Extending Python with C or C++,  Up: Creating extensions without third party tools

6.2.2 Defining Extension Types: Tutorial
----------------------------------------

Python allows the writer of a C extension module to define new types
that can be manipulated from Python code, much like the built-in *note
str: 205. and *note list: 1f8. types.  The code for all extension types
follows a pattern, but there are some details that you need to
understand before you can get started.  This document is a gentle
introduction to the topic.

* Menu:

* The Basics::
* Adding data and methods to the Basic example::
* Providing finer control over data attributes::
* Supporting cyclic garbage collection::
* Subclassing other types::


File: python.info,  Node: The Basics,  Next: Adding data and methods to the Basic example,  Up: Defining Extension Types Tutorial

6.2.2.1 The Basics
..................

The *note CPython: 1569. runtime sees all Python objects as variables of
type *note PyObject*: 5b5, which serves as a “base type” for all Python
objects.  The *note PyObject: 5b5. structure itself only contains the
object’s *note reference count: 3d4d. and a pointer to the object’s
“type object”.  This is where the action is; the type object determines
which (C) functions get called by the interpreter when, for instance, an
attribute gets looked up on an object, a method called, or it is
multiplied by another object.  These C functions are called “type
methods”.

So, if you want to define a new extension type, you need to create a new
type object.

This sort of thing can only be explained by example, so here’s a
minimal, but complete, module that defines a new type named ‘Custom’
inside a C extension module ‘custom’:

     Note: What we’re showing here is the traditional way of defining
     `static' extension types.  It should be adequate for most uses.
     The C API also allows defining heap-allocated extension types using
     the *note PyType_FromSpec(): 23a. function, which isn’t covered in
     this tutorial.

     #define PY_SSIZE_T_CLEAN
     #include <Python.h>

     typedef struct {
         PyObject_HEAD
         /* Type-specific fields go here. */
     } CustomObject;

     static PyTypeObject CustomType = {
         PyVarObject_HEAD_INIT(NULL, 0)
         .tp_name = "custom.Custom",
         .tp_doc = "Custom objects",
         .tp_basicsize = sizeof(CustomObject),
         .tp_itemsize = 0,
         .tp_flags = Py_TPFLAGS_DEFAULT,
         .tp_new = PyType_GenericNew,
     };

     static PyModuleDef custommodule = {
         PyModuleDef_HEAD_INIT,
         .m_name = "custom",
         .m_doc = "Example module that creates an extension type.",
         .m_size = -1,
     };

     PyMODINIT_FUNC
     PyInit_custom(void)
     {
         PyObject *m;
         if (PyType_Ready(&CustomType) < 0)
             return NULL;

         m = PyModule_Create(&custommodule);
         if (m == NULL)
             return NULL;

         Py_INCREF(&CustomType);
         if (PyModule_AddObject(m, "Custom", (PyObject *) &CustomType) < 0) {
             Py_DECREF(&CustomType);
             Py_DECREF(m);
             return NULL;
         }

         return m;
     }

Now that’s quite a bit to take in at once, but hopefully bits will seem
familiar from the previous chapter.  This file defines three things:

  1. What a ‘Custom’ `object' contains: this is the ‘CustomObject’
     struct, which is allocated once for each ‘Custom’ instance.

  2. How the ‘Custom’ `type' behaves: this is the ‘CustomType’ struct,
     which defines a set of flags and function pointers that the
     interpreter inspects when specific operations are requested.

  3. How to initialize the ‘custom’ module: this is the ‘PyInit_custom’
     function and the associated ‘custommodule’ struct.

The first bit is:

     typedef struct {
         PyObject_HEAD
     } CustomObject;

This is what a Custom object will contain.  ‘PyObject_HEAD’ is mandatory
at the start of each object struct and defines a field called ‘ob_base’
of type *note PyObject: 5b5, containing a pointer to a type object and a
reference count (these can be accessed using the macros *note Py_REFCNT:
3d4e. and *note Py_TYPE: 3d4f. respectively).  The reason for the macro
is to abstract away the layout and to enable additional fields in debug
builds.

     Note: There is no semicolon above after the *note PyObject_HEAD:
     d3a. macro.  Be wary of adding one by accident: some compilers will
     complain.

Of course, objects generally store additional data besides the standard
‘PyObject_HEAD’ boilerplate; for example, here is the definition for
standard Python floats:

     typedef struct {
         PyObject_HEAD
         double ob_fval;
     } PyFloatObject;

The second bit is the definition of the type object.

     static PyTypeObject CustomType = {
         PyVarObject_HEAD_INIT(NULL, 0)
         .tp_name = "custom.Custom",
         .tp_doc = "Custom objects",
         .tp_basicsize = sizeof(CustomObject),
         .tp_itemsize = 0,
         .tp_flags = Py_TPFLAGS_DEFAULT,
         .tp_new = PyType_GenericNew,
     };

     Note: We recommend using C99-style designated initializers as
     above, to avoid listing all the *note PyTypeObject: 3f5. fields
     that you don’t care about and also to avoid caring about the
     fields’ declaration order.

The actual definition of *note PyTypeObject: 3f5. in ‘object.h’ has many
more *note fields: 271. than the definition above.  The remaining fields
will be filled with zeros by the C compiler, and it’s common practice to
not specify them explicitly unless you need them.

We’re going to pick it apart, one field at a time:

     PyVarObject_HEAD_INIT(NULL, 0)

This line is mandatory boilerplate to initialize the ‘ob_base’ field
mentioned above.

     .tp_name = "custom.Custom",

The name of our type.  This will appear in the default textual
representation of our objects and in some error messages, for example:

     >>> "" + custom.Custom()
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: can only concatenate str (not "custom.Custom") to str

Note that the name is a dotted name that includes both the module name
and the name of the type within the module.  The module in this case is
‘custom’ and the type is ‘Custom’, so we set the type name to
‘custom.Custom’.  Using the real dotted import path is important to make
your type compatible with the *note pydoc: d9. and *note pickle: ca.
modules.

     .tp_basicsize = sizeof(CustomObject),
     .tp_itemsize = 0,

This is so that Python knows how much memory to allocate when creating
new ‘Custom’ instances.  *note tp_itemsize: 3d50. is only used for
variable-sized objects and should otherwise be zero.

     Note: If you want your type to be subclassable from Python, and
     your type has the same *note tp_basicsize: 26a. as its base type,
     you may have problems with multiple inheritance.  A Python subclass
     of your type will have to list your type first in its *note
     __bases__: ecb, or else it will not be able to call your type’s
     *note __new__(): 974. method without getting an error.  You can
     avoid this problem by ensuring that your type has a larger value
     for *note tp_basicsize: 26a. than its base type does.  Most of the
     time, this will be true anyway, because either your base type will
     be *note object: 3d2, or else you will be adding data members to
     your base type, and therefore increasing its size.

We set the class flags to *note Py_TPFLAGS_DEFAULT: 3d51.

     .tp_flags = Py_TPFLAGS_DEFAULT,

All types should include this constant in their flags.  It enables all
of the members defined until at least Python 3.3.  If you need further
members, you will need to OR the corresponding flags.

We provide a doc string for the type in *note tp_doc: 3d52.

     .tp_doc = "Custom objects",

To enable object creation, we have to provide a *note tp_new: 3d53.
handler.  This is the equivalent of the Python method *note __new__():
974, but has to be specified explicitly.  In this case, we can just use
the default implementation provided by the API function *note
PyType_GenericNew(): 3d54.

     .tp_new = PyType_GenericNew,

Everything else in the file should be familiar, except for some code in
‘PyInit_custom()’:

     if (PyType_Ready(&CustomType) < 0)
         return;

This initializes the ‘Custom’ type, filling in a number of members to
the appropriate default values, including ‘ob_type’ that we initially
set to ‘NULL’.

     Py_INCREF(&CustomType);
     if (PyModule_AddObject(m, "Custom", (PyObject *) &CustomType) < 0) {
         Py_DECREF(&CustomType);
         Py_DECREF(m);
         return NULL;
     }

This adds the type to the module dictionary.  This allows us to create
‘Custom’ instances by calling the ‘Custom’ class:

     >>> import custom
     >>> mycustom = custom.Custom()

That’s it!  All that remains is to build it; put the above code in a
file called ‘custom.c’ and:

     from distutils.core import setup, Extension
     setup(name="custom", version="1.0",
           ext_modules=[Extension("custom", ["custom.c"])])

in a file called ‘setup.py’; then typing

     $ python setup.py build

at a shell should produce a file ‘custom.so’ in a subdirectory; move to
that directory and fire up Python — you should be able to ‘import
custom’ and play around with Custom objects.

That wasn’t so hard, was it?

Of course, the current Custom type is pretty uninteresting.  It has no
data and doesn’t do anything.  It can’t even be subclassed.

     Note: While this documentation showcases the standard *note
     distutils: 38. module for building C extensions, it is recommended
     in real-world use cases to use the newer and better-maintained
     ‘setuptools’ library.  Documentation on how to do this is out of
     scope for this document and can be found in the Python Packaging
     User’s Guide(1).

   ---------- Footnotes ----------

   (1) https://packaging.python.org/tutorials/distributing-packages/


File: python.info,  Node: Adding data and methods to the Basic example,  Next: Providing finer control over data attributes,  Prev: The Basics,  Up: Defining Extension Types Tutorial

6.2.2.2 Adding data and methods to the Basic example
....................................................

Let’s extend the basic example to add some data and methods.  Let’s also
make the type usable as a base class.  We’ll create a new module,
‘custom2’ that adds these capabilities:

     #define PY_SSIZE_T_CLEAN
     #include <Python.h>
     #include "structmember.h"

     typedef struct {
         PyObject_HEAD
         PyObject *first; /* first name */
         PyObject *last;  /* last name */
         int number;
     } CustomObject;

     static void
     Custom_dealloc(CustomObject *self)
     {
         Py_XDECREF(self->first);
         Py_XDECREF(self->last);
         Py_TYPE(self)->tp_free((PyObject *) self);
     }

     static PyObject *
     Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     {
         CustomObject *self;
         self = (CustomObject *) type->tp_alloc(type, 0);
         if (self != NULL) {
             self->first = PyUnicode_FromString("");
             if (self->first == NULL) {
                 Py_DECREF(self);
                 return NULL;
             }
             self->last = PyUnicode_FromString("");
             if (self->last == NULL) {
                 Py_DECREF(self);
                 return NULL;
             }
             self->number = 0;
         }
         return (PyObject *) self;
     }

     static int
     Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
     {
         static char *kwlist[] = {"first", "last", "number", NULL};
         PyObject *first = NULL, *last = NULL, *tmp;

         if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OOi", kwlist,
                                          &first, &last,
                                          &self->number))
             return -1;

         if (first) {
             tmp = self->first;
             Py_INCREF(first);
             self->first = first;
             Py_XDECREF(tmp);
         }
         if (last) {
             tmp = self->last;
             Py_INCREF(last);
             self->last = last;
             Py_XDECREF(tmp);
         }
         return 0;
     }

     static PyMemberDef Custom_members[] = {
         {"first", T_OBJECT_EX, offsetof(CustomObject, first), 0,
          "first name"},
         {"last", T_OBJECT_EX, offsetof(CustomObject, last), 0,
          "last name"},
         {"number", T_INT, offsetof(CustomObject, number), 0,
          "custom number"},
         {NULL}  /* Sentinel */
     };

     static PyObject *
     Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
     {
         if (self->first == NULL) {
             PyErr_SetString(PyExc_AttributeError, "first");
             return NULL;
         }
         if (self->last == NULL) {
             PyErr_SetString(PyExc_AttributeError, "last");
             return NULL;
         }
         return PyUnicode_FromFormat("%S %S", self->first, self->last);
     }

     static PyMethodDef Custom_methods[] = {
         {"name", (PyCFunction) Custom_name, METH_NOARGS,
          "Return the name, combining the first and last name"
         },
         {NULL}  /* Sentinel */
     };

     static PyTypeObject CustomType = {
         PyVarObject_HEAD_INIT(NULL, 0)
         .tp_name = "custom2.Custom",
         .tp_doc = "Custom objects",
         .tp_basicsize = sizeof(CustomObject),
         .tp_itemsize = 0,
         .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
         .tp_new = Custom_new,
         .tp_init = (initproc) Custom_init,
         .tp_dealloc = (destructor) Custom_dealloc,
         .tp_members = Custom_members,
         .tp_methods = Custom_methods,
     };

     static PyModuleDef custommodule = {
         PyModuleDef_HEAD_INIT,
         .m_name = "custom2",
         .m_doc = "Example module that creates an extension type.",
         .m_size = -1,
     };

     PyMODINIT_FUNC
     PyInit_custom2(void)
     {
         PyObject *m;
         if (PyType_Ready(&CustomType) < 0)
             return NULL;

         m = PyModule_Create(&custommodule);
         if (m == NULL)
             return NULL;

         Py_INCREF(&CustomType);
         if (PyModule_AddObject(m, "Custom", (PyObject *) &CustomType) < 0) {
             Py_DECREF(&CustomType);
             Py_DECREF(m);
             return NULL;
         }

         return m;
     }

This version of the module has a number of changes.

We’ve added an extra include:

     #include <structmember.h>

This include provides declarations that we use to handle attributes, as
described a bit later.

The ‘Custom’ type now has three data attributes in its C struct,
`first', `last', and `number'.  The `first' and `last' variables are
Python strings containing first and last names.  The `number' attribute
is a C integer.

The object structure is updated accordingly:

     typedef struct {
         PyObject_HEAD
         PyObject *first; /* first name */
         PyObject *last;  /* last name */
         int number;
     } CustomObject;

Because we now have data to manage, we have to be more careful about
object allocation and deallocation.  At a minimum, we need a
deallocation method:

     static void
     Custom_dealloc(CustomObject *self)
     {
         Py_XDECREF(self->first);
         Py_XDECREF(self->last);
         Py_TYPE(self)->tp_free((PyObject *) self);
     }

which is assigned to the *note tp_dealloc: 3d56. member:

     .tp_dealloc = (destructor) Custom_dealloc,

This method first clears the reference counts of the two Python
attributes.  *note Py_XDECREF(): 391. correctly handles the case where
its argument is ‘NULL’ (which might happen here if ‘tp_new’ failed
midway).  It then calls the *note tp_free: 3d57. member of the object’s
type (computed by ‘Py_TYPE(self)’) to free the object’s memory.  Note
that the object’s type might not be ‘CustomType’, because the object may
be an instance of a subclass.

     Note: The explicit cast to ‘destructor’ above is needed because we
     defined ‘Custom_dealloc’ to take a ‘CustomObject *’ argument, but
     the ‘tp_dealloc’ function pointer expects to receive a ‘PyObject *’
     argument.  Otherwise, the compiler will emit a warning.  This is
     object-oriented polymorphism, in C!

We want to make sure that the first and last names are initialized to
empty strings, so we provide a ‘tp_new’ implementation:

     static PyObject *
     Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     {
         CustomObject *self;
         self = (CustomObject *) type->tp_alloc(type, 0);
         if (self != NULL) {
             self->first = PyUnicode_FromString("");
             if (self->first == NULL) {
                 Py_DECREF(self);
                 return NULL;
             }
             self->last = PyUnicode_FromString("");
             if (self->last == NULL) {
                 Py_DECREF(self);
                 return NULL;
             }
             self->number = 0;
         }
         return (PyObject *) self;
     }

and install it in the *note tp_new: 3d53. member:

     .tp_new = Custom_new,

The ‘tp_new’ handler is responsible for creating (as opposed to
initializing) objects of the type.  It is exposed in Python as the *note
__new__(): 974. method.  It is not required to define a ‘tp_new’ member,
and indeed many extension types will simply reuse *note
PyType_GenericNew(): 3d54. as done in the first version of the ‘Custom’
type above.  In this case, we use the ‘tp_new’ handler to initialize the
‘first’ and ‘last’ attributes to non-‘NULL’ default values.

‘tp_new’ is passed the type being instantiated (not necessarily
‘CustomType’, if a subclass is instantiated) and any arguments passed
when the type was called, and is expected to return the instance
created.  ‘tp_new’ handlers always accept positional and keyword
arguments, but they often ignore the arguments, leaving the argument
handling to initializer (a.k.a.  ‘tp_init’ in C or ‘__init__’ in Python)
methods.

     Note: ‘tp_new’ shouldn’t call ‘tp_init’ explicitly, as the
     interpreter will do it itself.

The ‘tp_new’ implementation calls the *note tp_alloc: 3d58. slot to
allocate memory:

     self = (CustomObject *) type->tp_alloc(type, 0);

Since memory allocation may fail, we must check the *note tp_alloc:
3d58. result against ‘NULL’ before proceeding.

     Note: We didn’t fill the *note tp_alloc: 3d58. slot ourselves.
     Rather *note PyType_Ready(): 3d59. fills it for us by inheriting it
     from our base class, which is *note object: 3d2. by default.  Most
     types use the default allocation strategy.

     Note: If you are creating a co-operative *note tp_new: 3d53. (one
     that calls a base type’s *note tp_new: 3d53. or *note __new__():
     974.), you must `not' try to determine what method to call using
     method resolution order at runtime.  Always statically determine
     what type you are going to call, and call its *note tp_new: 3d53.
     directly, or via ‘type->tp_base->tp_new’.  If you do not do this,
     Python subclasses of your type that also inherit from other
     Python-defined classes may not work correctly.  (Specifically, you
     may not be able to create instances of such subclasses without
     getting a *note TypeError: 1fe.)

We also define an initialization function which accepts arguments to
provide initial values for our instance:

     static int
     Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
     {
         static char *kwlist[] = {"first", "last", "number", NULL};
         PyObject *first = NULL, *last = NULL, *tmp;

         if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OOi", kwlist,
                                          &first, &last,
                                          &self->number))
             return -1;

         if (first) {
             tmp = self->first;
             Py_INCREF(first);
             self->first = first;
             Py_XDECREF(tmp);
         }
         if (last) {
             tmp = self->last;
             Py_INCREF(last);
             self->last = last;
             Py_XDECREF(tmp);
         }
         return 0;
     }

by filling the *note tp_init: 3d5a. slot.

     .tp_init = (initproc) Custom_init,

The *note tp_init: 3d5a. slot is exposed in Python as the *note
__init__(): e23. method.  It is used to initialize an object after it’s
created.  Initializers always accept positional and keyword arguments,
and they should return either ‘0’ on success or ‘-1’ on error.

Unlike the ‘tp_new’ handler, there is no guarantee that ‘tp_init’ is
called at all (for example, the *note pickle: ca. module by default
doesn’t call *note __init__(): e23. on unpickled instances).  It can
also be called multiple times.  Anyone can call the *note __init__():
e23. method on our objects.  For this reason, we have to be extra
careful when assigning the new attribute values.  We might be tempted,
for example to assign the ‘first’ member like this:

     if (first) {
         Py_XDECREF(self->first);
         Py_INCREF(first);
         self->first = first;
     }

But this would be risky.  Our type doesn’t restrict the type of the
‘first’ member, so it could be any kind of object.  It could have a
destructor that causes code to be executed that tries to access the
‘first’ member; or that destructor could release the *note Global
interpreter Lock: 20e. and let arbitrary code run in other threads that
accesses and modifies our object.

To be paranoid and protect ourselves against this possibility, we almost
always reassign members before decrementing their reference counts.
When don’t we have to do this?

   * when we absolutely know that the reference count is greater than 1;

   * when we know that deallocation of the object (1) will neither
     release the *note GIL: 20e. nor cause any calls back into our
     type’s code;

   * when decrementing a reference count in a *note tp_dealloc: 3d56.
     handler on a type which doesn’t support cyclic garbage collection
     (2).

We want to expose our instance variables as attributes.  There are a
number of ways to do that.  The simplest way is to define member
definitions:

     static PyMemberDef Custom_members[] = {
         {"first", T_OBJECT_EX, offsetof(CustomObject, first), 0,
          "first name"},
         {"last", T_OBJECT_EX, offsetof(CustomObject, last), 0,
          "last name"},
         {"number", T_INT, offsetof(CustomObject, number), 0,
          "custom number"},
         {NULL}  /* Sentinel */
     };

and put the definitions in the *note tp_members: 3d5b. slot:

     .tp_members = Custom_members,

Each member definition has a member name, type, offset, access flags and
documentation string.  See the *note Generic Attribute Management: 3d5c.
section below for details.

A disadvantage of this approach is that it doesn’t provide a way to
restrict the types of objects that can be assigned to the Python
attributes.  We expect the first and last names to be strings, but any
Python objects can be assigned.  Further, the attributes can be deleted,
setting the C pointers to ‘NULL’.  Even though we can make sure the
members are initialized to non-‘NULL’ values, the members can be set to
‘NULL’ if the attributes are deleted.

We define a single method, ‘Custom.name()’, that outputs the objects
name as the concatenation of the first and last names.

     static PyObject *
     Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
     {
         if (self->first == NULL) {
             PyErr_SetString(PyExc_AttributeError, "first");
             return NULL;
         }
         if (self->last == NULL) {
             PyErr_SetString(PyExc_AttributeError, "last");
             return NULL;
         }
         return PyUnicode_FromFormat("%S %S", self->first, self->last);
     }

The method is implemented as a C function that takes a ‘Custom’ (or
‘Custom’ subclass) instance as the first argument.  Methods always take
an instance as the first argument.  Methods often take positional and
keyword arguments as well, but in this case we don’t take any and don’t
need to accept a positional argument tuple or keyword argument
dictionary.  This method is equivalent to the Python method:

     def name(self):
         return "%s %s" % (self.first, self.last)

Note that we have to check for the possibility that our ‘first’ and
‘last’ members are ‘NULL’.  This is because they can be deleted, in
which case they are set to ‘NULL’.  It would be better to prevent
deletion of these attributes and to restrict the attribute values to be
strings.  We’ll see how to do that in the next section.

Now that we’ve defined the method, we need to create an array of method
definitions:

     static PyMethodDef Custom_methods[] = {
         {"name", (PyCFunction) Custom_name, METH_NOARGS,
          "Return the name, combining the first and last name"
         },
         {NULL}  /* Sentinel */
     };

(note that we used the *note METH_NOARGS: eda. flag to indicate that the
method is expecting no arguments other than `self')

and assign it to the *note tp_methods: 3d5d. slot:

     .tp_methods = Custom_methods,

Finally, we’ll make our type usable as a base class for subclassing.
We’ve written our methods carefully so far so that they don’t make any
assumptions about the type of the object being created or used, so all
we need to do is to add the *note Py_TPFLAGS_BASETYPE: 3d5e. to our
class flag definition:

     .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,

We rename ‘PyInit_custom()’ to ‘PyInit_custom2()’, update the module
name in the *note PyModuleDef: 25b. struct, and update the full class
name in the *note PyTypeObject: 3f5. struct.

Finally, we update our ‘setup.py’ file to build the new module:

     from distutils.core import setup, Extension
     setup(name="custom", version="1.0",
           ext_modules=[
              Extension("custom", ["custom.c"]),
              Extension("custom2", ["custom2.c"]),
              ])

   ---------- Footnotes ----------

   (1) (1) This is true when we know that the object is a basic type,
like a string or a float.

   (2) (2) We relied on this in the *note tp_dealloc: 3d56. handler in
this example, because our type doesn’t support garbage collection.


File: python.info,  Node: Providing finer control over data attributes,  Next: Supporting cyclic garbage collection,  Prev: Adding data and methods to the Basic example,  Up: Defining Extension Types Tutorial

6.2.2.3 Providing finer control over data attributes
....................................................

In this section, we’ll provide finer control over how the ‘first’ and
‘last’ attributes are set in the ‘Custom’ example.  In the previous
version of our module, the instance variables ‘first’ and ‘last’ could
be set to non-string values or even deleted.  We want to make sure that
these attributes always contain strings.

     #define PY_SSIZE_T_CLEAN
     #include <Python.h>
     #include "structmember.h"

     typedef struct {
         PyObject_HEAD
         PyObject *first; /* first name */
         PyObject *last;  /* last name */
         int number;
     } CustomObject;

     static void
     Custom_dealloc(CustomObject *self)
     {
         Py_XDECREF(self->first);
         Py_XDECREF(self->last);
         Py_TYPE(self)->tp_free((PyObject *) self);
     }

     static PyObject *
     Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     {
         CustomObject *self;
         self = (CustomObject *) type->tp_alloc(type, 0);
         if (self != NULL) {
             self->first = PyUnicode_FromString("");
             if (self->first == NULL) {
                 Py_DECREF(self);
                 return NULL;
             }
             self->last = PyUnicode_FromString("");
             if (self->last == NULL) {
                 Py_DECREF(self);
                 return NULL;
             }
             self->number = 0;
         }
         return (PyObject *) self;
     }

     static int
     Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
     {
         static char *kwlist[] = {"first", "last", "number", NULL};
         PyObject *first = NULL, *last = NULL, *tmp;

         if (!PyArg_ParseTupleAndKeywords(args, kwds, "|UUi", kwlist,
                                          &first, &last,
                                          &self->number))
             return -1;

         if (first) {
             tmp = self->first;
             Py_INCREF(first);
             self->first = first;
             Py_DECREF(tmp);
         }
         if (last) {
             tmp = self->last;
             Py_INCREF(last);
             self->last = last;
             Py_DECREF(tmp);
         }
         return 0;
     }

     static PyMemberDef Custom_members[] = {
         {"number", T_INT, offsetof(CustomObject, number), 0,
          "custom number"},
         {NULL}  /* Sentinel */
     };

     static PyObject *
     Custom_getfirst(CustomObject *self, void *closure)
     {
         Py_INCREF(self->first);
         return self->first;
     }

     static int
     Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
     {
         PyObject *tmp;
         if (value == NULL) {
             PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
             return -1;
         }
         if (!PyUnicode_Check(value)) {
             PyErr_SetString(PyExc_TypeError,
                             "The first attribute value must be a string");
             return -1;
         }
         tmp = self->first;
         Py_INCREF(value);
         self->first = value;
         Py_DECREF(tmp);
         return 0;
     }

     static PyObject *
     Custom_getlast(CustomObject *self, void *closure)
     {
         Py_INCREF(self->last);
         return self->last;
     }

     static int
     Custom_setlast(CustomObject *self, PyObject *value, void *closure)
     {
         PyObject *tmp;
         if (value == NULL) {
             PyErr_SetString(PyExc_TypeError, "Cannot delete the last attribute");
             return -1;
         }
         if (!PyUnicode_Check(value)) {
             PyErr_SetString(PyExc_TypeError,
                             "The last attribute value must be a string");
             return -1;
         }
         tmp = self->last;
         Py_INCREF(value);
         self->last = value;
         Py_DECREF(tmp);
         return 0;
     }

     static PyGetSetDef Custom_getsetters[] = {
         {"first", (getter) Custom_getfirst, (setter) Custom_setfirst,
          "first name", NULL},
         {"last", (getter) Custom_getlast, (setter) Custom_setlast,
          "last name", NULL},
         {NULL}  /* Sentinel */
     };

     static PyObject *
     Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
     {
         return PyUnicode_FromFormat("%S %S", self->first, self->last);
     }

     static PyMethodDef Custom_methods[] = {
         {"name", (PyCFunction) Custom_name, METH_NOARGS,
          "Return the name, combining the first and last name"
         },
         {NULL}  /* Sentinel */
     };

     static PyTypeObject CustomType = {
         PyVarObject_HEAD_INIT(NULL, 0)
         .tp_name = "custom3.Custom",
         .tp_doc = "Custom objects",
         .tp_basicsize = sizeof(CustomObject),
         .tp_itemsize = 0,
         .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
         .tp_new = Custom_new,
         .tp_init = (initproc) Custom_init,
         .tp_dealloc = (destructor) Custom_dealloc,
         .tp_members = Custom_members,
         .tp_methods = Custom_methods,
         .tp_getset = Custom_getsetters,
     };

     static PyModuleDef custommodule = {
         PyModuleDef_HEAD_INIT,
         .m_name = "custom3",
         .m_doc = "Example module that creates an extension type.",
         .m_size = -1,
     };

     PyMODINIT_FUNC
     PyInit_custom3(void)
     {
         PyObject *m;
         if (PyType_Ready(&CustomType) < 0)
             return NULL;

         m = PyModule_Create(&custommodule);
         if (m == NULL)
             return NULL;

         Py_INCREF(&CustomType);
         if (PyModule_AddObject(m, "Custom", (PyObject *) &CustomType) < 0) {
             Py_DECREF(&CustomType);
             Py_DECREF(m);
             return NULL;
         }

         return m;
     }

To provide greater control, over the ‘first’ and ‘last’ attributes,
we’ll use custom getter and setter functions.  Here are the functions
for getting and setting the ‘first’ attribute:

     static PyObject *
     Custom_getfirst(CustomObject *self, void *closure)
     {
         Py_INCREF(self->first);
         return self->first;
     }

     static int
     Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
     {
         PyObject *tmp;
         if (value == NULL) {
             PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
             return -1;
         }
         if (!PyUnicode_Check(value)) {
             PyErr_SetString(PyExc_TypeError,
                             "The first attribute value must be a string");
             return -1;
         }
         tmp = self->first;
         Py_INCREF(value);
         self->first = value;
         Py_DECREF(tmp);
         return 0;
     }

The getter function is passed a ‘Custom’ object and a “closure”, which
is a void pointer.  In this case, the closure is ignored.  (The closure
supports an advanced usage in which definition data is passed to the
getter and setter.  This could, for example, be used to allow a single
set of getter and setter functions that decide the attribute to get or
set based on data in the closure.)

The setter function is passed the ‘Custom’ object, the new value, and
the closure.  The new value may be ‘NULL’, in which case the attribute
is being deleted.  In our setter, we raise an error if the attribute is
deleted or if its new value is not a string.

We create an array of *note PyGetSetDef: 52b. structures:

     static PyGetSetDef Custom_getsetters[] = {
         {"first", (getter) Custom_getfirst, (setter) Custom_setfirst,
          "first name", NULL},
         {"last", (getter) Custom_getlast, (setter) Custom_setlast,
          "last name", NULL},
         {NULL}  /* Sentinel */
     };

and register it in the *note tp_getset: 3d60. slot:

     .tp_getset = Custom_getsetters,

The last item in a *note PyGetSetDef: 52b. structure is the “closure”
mentioned above.  In this case, we aren’t using a closure, so we just
pass ‘NULL’.

We also remove the member definitions for these attributes:

     static PyMemberDef Custom_members[] = {
         {"number", T_INT, offsetof(CustomObject, number), 0,
          "custom number"},
         {NULL}  /* Sentinel */
     };

We also need to update the *note tp_init: 3d5a. handler to only allow
strings (1) to be passed:

     static int
     Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
     {
         static char *kwlist[] = {"first", "last", "number", NULL};
         PyObject *first = NULL, *last = NULL, *tmp;

         if (!PyArg_ParseTupleAndKeywords(args, kwds, "|UUi", kwlist,
                                          &first, &last,
                                          &self->number))
             return -1;

         if (first) {
             tmp = self->first;
             Py_INCREF(first);
             self->first = first;
             Py_DECREF(tmp);
         }
         if (last) {
             tmp = self->last;
             Py_INCREF(last);
             self->last = last;
             Py_DECREF(tmp);
         }
         return 0;
     }

With these changes, we can assure that the ‘first’ and ‘last’ members
are never ‘NULL’ so we can remove checks for ‘NULL’ values in almost all
cases.  This means that most of the *note Py_XDECREF(): 391. calls can
be converted to *note Py_DECREF(): 38f. calls.  The only place we can’t
change these calls is in the ‘tp_dealloc’ implementation, where there is
the possibility that the initialization of these members failed in
‘tp_new’.

We also rename the module initialization function and module name in the
initialization function, as we did before, and we add an extra
definition to the ‘setup.py’ file.

   ---------- Footnotes ----------

   (1) (3) We now know that the first and last members are strings, so
perhaps we could be less careful about decrementing their reference
counts, however, we accept instances of string subclasses.  Even though
deallocating normal strings won’t call back into our objects, we can’t
guarantee that deallocating an instance of a string subclass won’t call
back into our objects.


File: python.info,  Node: Supporting cyclic garbage collection,  Next: Subclassing other types,  Prev: Providing finer control over data attributes,  Up: Defining Extension Types Tutorial

6.2.2.4 Supporting cyclic garbage collection
............................................

Python has a *note cyclic garbage collector (GC): fc8. that can identify
unneeded objects even when their reference counts are not zero.  This
can happen when objects are involved in cycles.  For example, consider:

     >>> l = []
     >>> l.append(l)
     >>> del l

In this example, we create a list that contains itself.  When we delete
it, it still has a reference from itself.  Its reference count doesn’t
drop to zero.  Fortunately, Python’s cyclic garbage collector will
eventually figure out that the list is garbage and free it.

In the second version of the ‘Custom’ example, we allowed any kind of
object to be stored in the ‘first’ or ‘last’ attributes (1).  Besides,
in the second and third versions, we allowed subclassing ‘Custom’, and
subclasses may add arbitrary attributes.  For any of those two reasons,
‘Custom’ objects can participate in cycles:

     >>> import custom3
     >>> class Derived(custom3.Custom): pass
     ...
     >>> n = Derived()
     >>> n.some_attribute = n

To allow a ‘Custom’ instance participating in a reference cycle to be
properly detected and collected by the cyclic GC, our ‘Custom’ type
needs to fill two additional slots and to enable a flag that enables
these slots:

     #define PY_SSIZE_T_CLEAN
     #include <Python.h>
     #include "structmember.h"

     typedef struct {
         PyObject_HEAD
         PyObject *first; /* first name */
         PyObject *last;  /* last name */
         int number;
     } CustomObject;

     static int
     Custom_traverse(CustomObject *self, visitproc visit, void *arg)
     {
         Py_VISIT(self->first);
         Py_VISIT(self->last);
         return 0;
     }

     static int
     Custom_clear(CustomObject *self)
     {
         Py_CLEAR(self->first);
         Py_CLEAR(self->last);
         return 0;
     }

     static void
     Custom_dealloc(CustomObject *self)
     {
         PyObject_GC_UnTrack(self);
         Custom_clear(self);
         Py_TYPE(self)->tp_free((PyObject *) self);
     }

     static PyObject *
     Custom_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     {
         CustomObject *self;
         self = (CustomObject *) type->tp_alloc(type, 0);
         if (self != NULL) {
             self->first = PyUnicode_FromString("");
             if (self->first == NULL) {
                 Py_DECREF(self);
                 return NULL;
             }
             self->last = PyUnicode_FromString("");
             if (self->last == NULL) {
                 Py_DECREF(self);
                 return NULL;
             }
             self->number = 0;
         }
         return (PyObject *) self;
     }

     static int
     Custom_init(CustomObject *self, PyObject *args, PyObject *kwds)
     {
         static char *kwlist[] = {"first", "last", "number", NULL};
         PyObject *first = NULL, *last = NULL, *tmp;

         if (!PyArg_ParseTupleAndKeywords(args, kwds, "|UUi", kwlist,
                                          &first, &last,
                                          &self->number))
             return -1;

         if (first) {
             tmp = self->first;
             Py_INCREF(first);
             self->first = first;
             Py_DECREF(tmp);
         }
         if (last) {
             tmp = self->last;
             Py_INCREF(last);
             self->last = last;
             Py_DECREF(tmp);
         }
         return 0;
     }

     static PyMemberDef Custom_members[] = {
         {"number", T_INT, offsetof(CustomObject, number), 0,
          "custom number"},
         {NULL}  /* Sentinel */
     };

     static PyObject *
     Custom_getfirst(CustomObject *self, void *closure)
     {
         Py_INCREF(self->first);
         return self->first;
     }

     static int
     Custom_setfirst(CustomObject *self, PyObject *value, void *closure)
     {
         if (value == NULL) {
             PyErr_SetString(PyExc_TypeError, "Cannot delete the first attribute");
             return -1;
         }
         if (!PyUnicode_Check(value)) {
             PyErr_SetString(PyExc_TypeError,
                             "The first attribute value must be a string");
             return -1;
         }
         Py_INCREF(value);
         Py_CLEAR(self->first);
         self->first = value;
         return 0;
     }

     static PyObject *
     Custom_getlast(CustomObject *self, void *closure)
     {
         Py_INCREF(self->last);
         return self->last;
     }

     static int
     Custom_setlast(CustomObject *self, PyObject *value, void *closure)
     {
         if (value == NULL) {
             PyErr_SetString(PyExc_TypeError, "Cannot delete the last attribute");
             return -1;
         }
         if (!PyUnicode_Check(value)) {
             PyErr_SetString(PyExc_TypeError,
                             "The last attribute value must be a string");
             return -1;
         }
         Py_INCREF(value);
         Py_CLEAR(self->last);
         self->last = value;
         return 0;
     }

     static PyGetSetDef Custom_getsetters[] = {
         {"first", (getter) Custom_getfirst, (setter) Custom_setfirst,
          "first name", NULL},
         {"last", (getter) Custom_getlast, (setter) Custom_setlast,
          "last name", NULL},
         {NULL}  /* Sentinel */
     };

     static PyObject *
     Custom_name(CustomObject *self, PyObject *Py_UNUSED(ignored))
     {
         return PyUnicode_FromFormat("%S %S", self->first, self->last);
     }

     static PyMethodDef Custom_methods[] = {
         {"name", (PyCFunction) Custom_name, METH_NOARGS,
          "Return the name, combining the first and last name"
         },
         {NULL}  /* Sentinel */
     };

     static PyTypeObject CustomType = {
         PyVarObject_HEAD_INIT(NULL, 0)
         .tp_name = "custom4.Custom",
         .tp_doc = "Custom objects",
         .tp_basicsize = sizeof(CustomObject),
         .tp_itemsize = 0,
         .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,
         .tp_new = Custom_new,
         .tp_init = (initproc) Custom_init,
         .tp_dealloc = (destructor) Custom_dealloc,
         .tp_traverse = (traverseproc) Custom_traverse,
         .tp_clear = (inquiry) Custom_clear,
         .tp_members = Custom_members,
         .tp_methods = Custom_methods,
         .tp_getset = Custom_getsetters,
     };

     static PyModuleDef custommodule = {
         PyModuleDef_HEAD_INIT,
         .m_name = "custom4",
         .m_doc = "Example module that creates an extension type.",
         .m_size = -1,
     };

     PyMODINIT_FUNC
     PyInit_custom4(void)
     {
         PyObject *m;
         if (PyType_Ready(&CustomType) < 0)
             return NULL;

         m = PyModule_Create(&custommodule);
         if (m == NULL)
             return NULL;

         Py_INCREF(&CustomType);
         if (PyModule_AddObject(m, "Custom", (PyObject *) &CustomType) < 0) {
             Py_DECREF(&CustomType);
             Py_DECREF(m);
             return NULL;
         }

         return m;
     }

First, the traversal method lets the cyclic GC know about subobjects
that could participate in cycles:

     static int
     Custom_traverse(CustomObject *self, visitproc visit, void *arg)
     {
         int vret;
         if (self->first) {
             vret = visit(self->first, arg);
             if (vret != 0)
                 return vret;
         }
         if (self->last) {
             vret = visit(self->last, arg);
             if (vret != 0)
                 return vret;
         }
         return 0;
     }

For each subobject that can participate in cycles, we need to call the
‘visit()’ function, which is passed to the traversal method.  The
‘visit()’ function takes as arguments the subobject and the extra
argument `arg' passed to the traversal method.  It returns an integer
value that must be returned if it is non-zero.

Python provides a *note Py_VISIT(): 3d62. macro that automates calling
visit functions.  With *note Py_VISIT(): 3d62, we can minimize the
amount of boilerplate in ‘Custom_traverse’:

     static int
     Custom_traverse(CustomObject *self, visitproc visit, void *arg)
     {
         Py_VISIT(self->first);
         Py_VISIT(self->last);
         return 0;
     }

     Note: The *note tp_traverse: 23b. implementation must name its
     arguments exactly `visit' and `arg' in order to use *note
     Py_VISIT(): 3d62.

Second, we need to provide a method for clearing any subobjects that can
participate in cycles:

     static int
     Custom_clear(CustomObject *self)
     {
         Py_CLEAR(self->first);
         Py_CLEAR(self->last);
         return 0;
     }

Notice the use of the *note Py_CLEAR(): 3d63. macro.  It is the
recommended and safe way to clear data attributes of arbitrary types
while decrementing their reference counts.  If you were to call *note
Py_XDECREF(): 391. instead on the attribute before setting it to ‘NULL’,
there is a possibility that the attribute’s destructor would call back
into code that reads the attribute again (`especially' if there is a
reference cycle).

     Note: You could emulate *note Py_CLEAR(): 3d63. by writing:

          PyObject *tmp;
          tmp = self->first;
          self->first = NULL;
          Py_XDECREF(tmp);

     Nevertheless, it is much easier and less error-prone to always use
     *note Py_CLEAR(): 3d63. when deleting an attribute.  Don’t try to
     micro-optimize at the expense of robustness!

The deallocator ‘Custom_dealloc’ may call arbitrary code when clearing
attributes.  It means the circular GC can be triggered inside the
function.  Since the GC assumes reference count is not zero, we need to
untrack the object from the GC by calling *note PyObject_GC_UnTrack():
f07. before clearing members.  Here is our reimplemented deallocator
using *note PyObject_GC_UnTrack(): f07. and ‘Custom_clear’:

     static void
     Custom_dealloc(CustomObject *self)
     {
         PyObject_GC_UnTrack(self);
         Custom_clear(self);
         Py_TYPE(self)->tp_free((PyObject *) self);
     }

Finally, we add the *note Py_TPFLAGS_HAVE_GC: 3d64. flag to the class
flags:

     .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,

That’s pretty much it.  If we had written custom *note tp_alloc: 3d58.
or *note tp_free: 3d57. handlers, we’d need to modify them for cyclic
garbage collection.  Most extensions will use the versions automatically
provided.

   ---------- Footnotes ----------

   (1) (4) Also, even with our attributes restricted to strings
instances, the user could pass arbitrary *note str: 205. subclasses and
therefore still create reference cycles.


File: python.info,  Node: Subclassing other types,  Prev: Supporting cyclic garbage collection,  Up: Defining Extension Types Tutorial

6.2.2.5 Subclassing other types
...............................

It is possible to create new extension types that are derived from
existing types.  It is easiest to inherit from the built in types, since
an extension can easily use the *note PyTypeObject: 3f5. it needs.  It
can be difficult to share these *note PyTypeObject: 3f5. structures
between extension modules.

In this example we will create a ‘SubList’ type that inherits from the
built-in *note list: 1f8. type.  The new type will be completely
compatible with regular lists, but will have an additional ‘increment()’
method that increases an internal counter:

     >>> import sublist
     >>> s = sublist.SubList(range(3))
     >>> s.extend(s)
     >>> print(len(s))
     6
     >>> print(s.increment())
     1
     >>> print(s.increment())
     2

     #define PY_SSIZE_T_CLEAN
     #include <Python.h>

     typedef struct {
         PyListObject list;
         int state;
     } SubListObject;

     static PyObject *
     SubList_increment(SubListObject *self, PyObject *unused)
     {
         self->state++;
         return PyLong_FromLong(self->state);
     }

     static PyMethodDef SubList_methods[] = {
         {"increment", (PyCFunction) SubList_increment, METH_NOARGS,
          PyDoc_STR("increment state counter")},
         {NULL},
     };

     static int
     SubList_init(SubListObject *self, PyObject *args, PyObject *kwds)
     {
         if (PyList_Type.tp_init((PyObject *) self, args, kwds) < 0)
             return -1;
         self->state = 0;
         return 0;
     }

     static PyTypeObject SubListType = {
         PyVarObject_HEAD_INIT(NULL, 0)
         .tp_name = "sublist.SubList",
         .tp_doc = "SubList objects",
         .tp_basicsize = sizeof(SubListObject),
         .tp_itemsize = 0,
         .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
         .tp_init = (initproc) SubList_init,
         .tp_methods = SubList_methods,
     };

     static PyModuleDef sublistmodule = {
         PyModuleDef_HEAD_INIT,
         .m_name = "sublist",
         .m_doc = "Example module that creates an extension type.",
         .m_size = -1,
     };

     PyMODINIT_FUNC
     PyInit_sublist(void)
     {
         PyObject *m;
         SubListType.tp_base = &PyList_Type;
         if (PyType_Ready(&SubListType) < 0)
             return NULL;

         m = PyModule_Create(&sublistmodule);
         if (m == NULL)
             return NULL;

         Py_INCREF(&SubListType);
         if (PyModule_AddObject(m, "SubList", (PyObject *) &SubListType) < 0) {
             Py_DECREF(&SubListType);
             Py_DECREF(m);
             return NULL;
         }

         return m;
     }

As you can see, the source code closely resembles the ‘Custom’ examples
in previous sections.  We will break down the main differences between
them.

     typedef struct {
         PyListObject list;
         int state;
     } SubListObject;

The primary difference for derived type objects is that the base type’s
object structure must be the first value.  The base type will already
include the *note PyObject_HEAD(): d3a. at the beginning of its
structure.

When a Python object is a ‘SubList’ instance, its ‘PyObject *’ pointer
can be safely cast to both ‘PyListObject *’ and ‘SubListObject *’:

     static int
     SubList_init(SubListObject *self, PyObject *args, PyObject *kwds)
     {
         if (PyList_Type.tp_init((PyObject *) self, args, kwds) < 0)
             return -1;
         self->state = 0;
         return 0;
     }

We see above how to call through to the *note __init__: e23. method of
the base type.

This pattern is important when writing a type with custom *note tp_new:
3d53. and *note tp_dealloc: 3d56. members.  The *note tp_new: 3d53.
handler should not actually create the memory for the object with its
*note tp_alloc: 3d58, but let the base class handle it by calling its
own *note tp_new: 3d53.

The *note PyTypeObject: 3f5. struct supports a *note tp_base: 3d66.
specifying the type’s concrete base class.  Due to cross-platform
compiler issues, you can’t fill that field directly with a reference to
*note PyList_Type: 3d67.; it should be done later in the module
initialization function:

     PyMODINIT_FUNC
     PyInit_sublist(void)
     {
         PyObject* m;
         SubListType.tp_base = &PyList_Type;
         if (PyType_Ready(&SubListType) < 0)
             return NULL;

         m = PyModule_Create(&sublistmodule);
         if (m == NULL)
             return NULL;

         Py_INCREF(&SubListType);
         if (PyModule_AddObject(m, "SubList", (PyObject *) &SubListType) < 0) {
             Py_DECREF(&SubListType);
             Py_DECREF(m);
             return NULL;
         }

         return m;
     }

Before calling *note PyType_Ready(): 3d59, the type structure must have
the *note tp_base: 3d66. slot filled in.  When we are deriving an
existing type, it is not necessary to fill out the *note tp_alloc: 3d58.
slot with *note PyType_GenericNew(): 3d54. – the allocation function
from the base type will be inherited.

After that, calling *note PyType_Ready(): 3d59. and adding the type
object to the module is the same as with the basic ‘Custom’ examples.


File: python.info,  Node: Defining Extension Types Assorted Topics,  Next: Building C and C++ Extensions,  Prev: Defining Extension Types Tutorial,  Up: Creating extensions without third party tools

6.2.3 Defining Extension Types: Assorted Topics
-----------------------------------------------

This section aims to give a quick fly-by on the various type methods you
can implement and what they do.

Here is the definition of *note PyTypeObject: 3f5, with some fields only
used in debug builds omitted:

     typedef struct _typeobject {
         PyObject_VAR_HEAD
         const char *tp_name; /* For printing, in format "<module>.<name>" */
         Py_ssize_t tp_basicsize, tp_itemsize; /* For allocation */

         /* Methods to implement standard operations */

         destructor tp_dealloc;
         Py_ssize_t tp_vectorcall_offset;
         getattrfunc tp_getattr;
         setattrfunc tp_setattr;
         PyAsyncMethods *tp_as_async; /* formerly known as tp_compare (Python 2)
                                         or tp_reserved (Python 3) */
         reprfunc tp_repr;

         /* Method suites for standard classes */

         PyNumberMethods *tp_as_number;
         PySequenceMethods *tp_as_sequence;
         PyMappingMethods *tp_as_mapping;

         /* More standard operations (here for binary compatibility) */

         hashfunc tp_hash;
         ternaryfunc tp_call;
         reprfunc tp_str;
         getattrofunc tp_getattro;
         setattrofunc tp_setattro;

         /* Functions to access object as input/output buffer */
         PyBufferProcs *tp_as_buffer;

         /* Flags to define presence of optional/expanded features */
         unsigned long tp_flags;

         const char *tp_doc; /* Documentation string */

         /* call function for all accessible objects */
         traverseproc tp_traverse;

         /* delete references to contained objects */
         inquiry tp_clear;

         /* rich comparisons */
         richcmpfunc tp_richcompare;

         /* weak reference enabler */
         Py_ssize_t tp_weaklistoffset;

         /* Iterators */
         getiterfunc tp_iter;
         iternextfunc tp_iternext;

         /* Attribute descriptor and subclassing stuff */
         struct PyMethodDef *tp_methods;
         struct PyMemberDef *tp_members;
         struct PyGetSetDef *tp_getset;
         struct _typeobject *tp_base;
         PyObject *tp_dict;
         descrgetfunc tp_descr_get;
         descrsetfunc tp_descr_set;
         Py_ssize_t tp_dictoffset;
         initproc tp_init;
         allocfunc tp_alloc;
         newfunc tp_new;
         freefunc tp_free; /* Low-level free-memory routine */
         inquiry tp_is_gc; /* For PyObject_IS_GC */
         PyObject *tp_bases;
         PyObject *tp_mro; /* method resolution order */
         PyObject *tp_cache;
         PyObject *tp_subclasses;
         PyObject *tp_weaklist;
         destructor tp_del;

         /* Type attribute cache version tag. Added in version 2.6 */
         unsigned int tp_version_tag;

         destructor tp_finalize;

     } PyTypeObject;

Now that’s a `lot' of methods.  Don’t worry too much though – if you
have a type you want to define, the chances are very good that you will
only implement a handful of these.

As you probably expect by now, we’re going to go over this and give more
information about the various handlers.  We won’t go in the order they
are defined in the structure, because there is a lot of historical
baggage that impacts the ordering of the fields.  It’s often easiest to
find an example that includes the fields you need and then change the
values to suit your new type.

     const char *tp_name; /* For printing */

The name of the type – as mentioned in the previous chapter, this will
appear in various places, almost entirely for diagnostic purposes.  Try
to choose something that will be helpful in such a situation!

     Py_ssize_t tp_basicsize, tp_itemsize; /* For allocation */

These fields tell the runtime how much memory to allocate when new
objects of this type are created.  Python has some built-in support for
variable length structures (think: strings, tuples) which is where the
*note tp_itemsize: 3d50. field comes in.  This will be dealt with later.

     const char *tp_doc;

Here you can put a string (or its address) that you want returned when
the Python script references ‘obj.__doc__’ to retrieve the doc string.

Now we come to the basic type methods – the ones most extension types
will implement.

* Menu:

* Finalization and De-allocation::
* Object Presentation::
* Attribute Management::
* Object Comparison::
* Abstract Protocol Support::
* Weak Reference Support::
* More Suggestions::


File: python.info,  Node: Finalization and De-allocation,  Next: Object Presentation,  Up: Defining Extension Types Assorted Topics

6.2.3.1 Finalization and De-allocation
......................................

     destructor tp_dealloc;

This function is called when the reference count of the instance of your
type is reduced to zero and the Python interpreter wants to reclaim it.
If your type has memory to free or other clean-up to perform, you can
put it here.  The object itself needs to be freed here as well.  Here is
an example of this function:

     static void
     newdatatype_dealloc(newdatatypeobject *obj)
     {
         free(obj->obj_UnderlyingDatatypePtr);
         Py_TYPE(obj)->tp_free((PyObject *)obj);
     }

If your type supports garbage collection, the destructor should call
*note PyObject_GC_UnTrack(): f07. before clearing any member fields:

     static void
     newdatatype_dealloc(newdatatypeobject *obj)
     {
         PyObject_GC_UnTrack(obj);
         Py_CLEAR(obj->other_obj);
         ...
         Py_TYPE(obj)->tp_free((PyObject *)obj);
     }

One important requirement of the deallocator function is that it leaves
any pending exceptions alone.  This is important since deallocators are
frequently called as the interpreter unwinds the Python stack; when the
stack is unwound due to an exception (rather than normal returns),
nothing is done to protect the deallocators from seeing that an
exception has already been set.  Any actions which a deallocator
performs which may cause additional Python code to be executed may
detect that an exception has been set.  This can lead to misleading
errors from the interpreter.  The proper way to protect against this is
to save a pending exception before performing the unsafe action, and
restoring it when done.  This can be done using the *note PyErr_Fetch():
a4b. and *note PyErr_Restore(): 3d6d. functions:

     static void
     my_dealloc(PyObject *obj)
     {
         MyObject *self = (MyObject *) obj;
         PyObject *cbresult;

         if (self->my_callback != NULL) {
             PyObject *err_type, *err_value, *err_traceback;

             /* This saves the current exception state */
             PyErr_Fetch(&err_type, &err_value, &err_traceback);

             cbresult = PyObject_CallNoArgs(self->my_callback);
             if (cbresult == NULL)
                 PyErr_WriteUnraisable(self->my_callback);
             else
                 Py_DECREF(cbresult);

             /* This restores the saved exception state */
             PyErr_Restore(err_type, err_value, err_traceback);

             Py_DECREF(self->my_callback);
         }
         Py_TYPE(obj)->tp_free((PyObject*)self);
     }

     Note: There are limitations to what you can safely do in a
     deallocator function.  First, if your type supports garbage
     collection (using *note tp_traverse: 23b. and/or *note tp_clear:
     3d6e.), some of the object’s members can have been cleared or
     finalized by the time *note tp_dealloc: 3d56. is called.  Second,
     in *note tp_dealloc: 3d56, your object is in an unstable state: its
     reference count is equal to zero.  Any call to a non-trivial object
     or API (as in the example above) might end up calling *note
     tp_dealloc: 3d56. again, causing a double free and a crash.

     Starting with Python 3.4, it is recommended not to put any complex
     finalization code in *note tp_dealloc: 3d56, and instead use the
     new *note tp_finalize: 3f6. type method.

     See also
     ........

     PEP 442(1) explains the new finalization scheme.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0442


File: python.info,  Node: Object Presentation,  Next: Attribute Management,  Prev: Finalization and De-allocation,  Up: Defining Extension Types Assorted Topics

6.2.3.2 Object Presentation
...........................

In Python, there are two ways to generate a textual representation of an
object: the *note repr(): 8b9. function, and the *note str(): 205.
function.  (The *note print(): 971. function just calls *note str():
205.)  These handlers are both optional.

     reprfunc tp_repr;
     reprfunc tp_str;

The *note tp_repr: 3d70. handler should return a string object
containing a representation of the instance for which it is called.
Here is a simple example:

     static PyObject *
     newdatatype_repr(newdatatypeobject * obj)
     {
         return PyUnicode_FromFormat("Repr-ified_newdatatype{{size:%d}}",
                                     obj->obj_UnderlyingDatatypePtr->size);
     }

If no *note tp_repr: 3d70. handler is specified, the interpreter will
supply a representation that uses the type’s *note tp_name: 3d71. and a
uniquely-identifying value for the object.

The *note tp_str: 3d72. handler is to *note str(): 205. what the *note
tp_repr: 3d70. handler described above is to *note repr(): 8b9.; that
is, it is called when Python code calls *note str(): 205. on an instance
of your object.  Its implementation is very similar to the *note
tp_repr: 3d70. function, but the resulting string is intended for human
consumption.  If *note tp_str: 3d72. is not specified, the *note
tp_repr: 3d70. handler is used instead.

Here is a simple example:

     static PyObject *
     newdatatype_str(newdatatypeobject * obj)
     {
         return PyUnicode_FromFormat("Stringified_newdatatype{{size:%d}}",
                                     obj->obj_UnderlyingDatatypePtr->size);
     }


File: python.info,  Node: Attribute Management,  Next: Object Comparison,  Prev: Object Presentation,  Up: Defining Extension Types Assorted Topics

6.2.3.3 Attribute Management
............................

For every object which can support attributes, the corresponding type
must provide the functions that control how the attributes are resolved.
There needs to be a function which can retrieve attributes (if any are
defined), and another to set attributes (if setting attributes is
allowed).  Removing an attribute is a special case, for which the new
value passed to the handler is ‘NULL’.

Python supports two pairs of attribute handlers; a type that supports
attributes only needs to implement the functions for one pair.  The
difference is that one pair takes the name of the attribute as a
‘char*’, while the other accepts a *note PyObject*: 5b5.  Each type can
use whichever pair makes more sense for the implementation’s
convenience.

     getattrfunc  tp_getattr;        /* char * version */
     setattrfunc  tp_setattr;
     /* ... */
     getattrofunc tp_getattro;       /* PyObject * version */
     setattrofunc tp_setattro;

If accessing attributes of an object is always a simple operation (this
will be explained shortly), there are generic implementations which can
be used to provide the *note PyObject*: 5b5. version of the attribute
management functions.  The actual need for type-specific attribute
handlers almost completely disappeared starting with Python 2.2, though
there are many examples which have not been updated to use some of the
new generic mechanism that is available.

* Menu:

* Generic Attribute Management::
* Type-specific Attribute Management::


File: python.info,  Node: Generic Attribute Management,  Next: Type-specific Attribute Management,  Up: Attribute Management

6.2.3.4 Generic Attribute Management
....................................

Most extension types only use `simple' attributes.  So, what makes the
attributes simple?  There are only a couple of conditions that must be
met:

  1. The name of the attributes must be known when *note PyType_Ready():
     3d59. is called.

  2. No special processing is needed to record that an attribute was
     looked up or set, nor do actions need to be taken based on the
     value.

Note that this list does not place any restrictions on the values of the
attributes, when the values are computed, or how relevant data is
stored.

When *note PyType_Ready(): 3d59. is called, it uses three tables
referenced by the type object to create *note descriptor: 1579.s which
are placed in the dictionary of the type object.  Each descriptor
controls access to one attribute of the instance object.  Each of the
tables is optional; if all three are ‘NULL’, instances of the type will
only have attributes that are inherited from their base type, and should
leave the *note tp_getattro: 3d75. and *note tp_setattro: 3d76. fields
‘NULL’ as well, allowing the base type to handle attributes.

The tables are declared as three fields of the type object:

     struct PyMethodDef *tp_methods;
     struct PyMemberDef *tp_members;
     struct PyGetSetDef *tp_getset;

If *note tp_methods: 3d5d. is not ‘NULL’, it must refer to an array of
*note PyMethodDef: edd. structures.  Each entry in the table is an
instance of this structure:

     typedef struct PyMethodDef {
         const char  *ml_name;       /* method name */
         PyCFunction  ml_meth;       /* implementation function */
         int          ml_flags;      /* flags */
         const char  *ml_doc;        /* docstring */
     } PyMethodDef;

One entry should be defined for each method provided by the type; no
entries are needed for methods inherited from a base type.  One
additional entry is needed at the end; it is a sentinel that marks the
end of the array.  The ‘ml_name’ field of the sentinel must be ‘NULL’.

The second table is used to define attributes which map directly to data
stored in the instance.  A variety of primitive C types are supported,
and access may be read-only or read-write.  The structures in the table
are defined as:

     typedef struct PyMemberDef {
         const char *name;
         int         type;
         int         offset;
         int         flags;
         const char *doc;
     } PyMemberDef;

For each entry in the table, a *note descriptor: 1579. will be
constructed and added to the type which will be able to extract a value
from the instance structure.  The *note type: 6ff. field should contain
one of the type codes defined in the ‘structmember.h’ header; the value
will be used to determine how to convert Python values to and from C
values.  The ‘flags’ field is used to store flags which control how the
attribute can be accessed.

The following flag constants are defined in ‘structmember.h’; they may
be combined using bitwise-OR.

Constant                        Meaning
                                
-----------------------------------------------------------------------------------
                                
‘READONLY’                      Never writable.
                                
                                
‘READ_RESTRICTED’               Not readable in restricted mode.
                                
                                
‘WRITE_RESTRICTED’              Not writable in restricted mode.
                                
                                
‘RESTRICTED’                    Not readable or writable in restricted mode.
                                

An interesting advantage of using the *note tp_members: 3d5b. table to
build descriptors that are used at runtime is that any attribute defined
this way can have an associated doc string simply by providing the text
in the table.  An application can use the introspection API to retrieve
the descriptor from the class object, and get the doc string using its
‘__doc__’ attribute.

As with the *note tp_methods: 3d5d. table, a sentinel entry with a
‘name’ value of ‘NULL’ is required.


File: python.info,  Node: Type-specific Attribute Management,  Prev: Generic Attribute Management,  Up: Attribute Management

6.2.3.5 Type-specific Attribute Management
..........................................

For simplicity, only the ‘char*’ version will be demonstrated here; the
type of the name parameter is the only difference between the ‘char*’
and *note PyObject*: 5b5. flavors of the interface.  This example
effectively does the same thing as the generic example above, but does
not use the generic support added in Python 2.2.  It explains how the
handler functions are called, so that if you do need to extend their
functionality, you’ll understand what needs to be done.

The *note tp_getattr: 3d78. handler is called when the object requires
an attribute look-up.  It is called in the same situations where the
*note __getattr__(): 42a. method of a class would be called.

Here is an example:

     static PyObject *
     newdatatype_getattr(newdatatypeobject *obj, char *name)
     {
         if (strcmp(name, "data") == 0)
         {
             return PyLong_FromLong(obj->data);
         }

         PyErr_Format(PyExc_AttributeError,
                      "'%.50s' object has no attribute '%.400s'",
                      tp->tp_name, name);
         return NULL;
     }

The *note tp_setattr: 3d79. handler is called when the *note
__setattr__(): eee. or *note __delattr__(): 1563. method of a class
instance would be called.  When an attribute should be deleted, the
third parameter will be ‘NULL’.  Here is an example that simply raises
an exception; if this were really all you wanted, the *note tp_setattr:
3d79. handler should be set to ‘NULL’.

     static int
     newdatatype_setattr(newdatatypeobject *obj, char *name, PyObject *v)
     {
         PyErr_Format(PyExc_RuntimeError, "Read-only attribute: %s", name);
         return -1;
     }


File: python.info,  Node: Object Comparison,  Next: Abstract Protocol Support,  Prev: Attribute Management,  Up: Defining Extension Types Assorted Topics

6.2.3.6 Object Comparison
.........................

     richcmpfunc tp_richcompare;

The *note tp_richcompare: 3d7b. handler is called when comparisons are
needed.  It is analogous to the *note rich comparison methods: 156b,
like *note __lt__(): cfe, and also called by *note
PyObject_RichCompare(): 3d7c. and *note PyObject_RichCompareBool():
109c.

This function is called with two Python objects and the operator as
arguments, where the operator is one of ‘Py_EQ’, ‘Py_NE’, ‘Py_LE’,
‘Py_GE’, ‘Py_LT’ or ‘Py_GT’.  It should compare the two objects with
respect to the specified operator and return ‘Py_True’ or ‘Py_False’ if
the comparison is successful, ‘Py_NotImplemented’ to indicate that
comparison is not implemented and the other object’s comparison method
should be tried, or ‘NULL’ if an exception was set.

Here is a sample implementation, for a datatype that is considered equal
if the size of an internal pointer is equal:

     static PyObject *
     newdatatype_richcmp(PyObject *obj1, PyObject *obj2, int op)
     {
         PyObject *result;
         int c, size1, size2;

         /* code to make sure that both arguments are of type
            newdatatype omitted */

         size1 = obj1->obj_UnderlyingDatatypePtr->size;
         size2 = obj2->obj_UnderlyingDatatypePtr->size;

         switch (op) {
         case Py_LT: c = size1 <  size2; break;
         case Py_LE: c = size1 <= size2; break;
         case Py_EQ: c = size1 == size2; break;
         case Py_NE: c = size1 != size2; break;
         case Py_GT: c = size1 >  size2; break;
         case Py_GE: c = size1 >= size2; break;
         }
         result = c ? Py_True : Py_False;
         Py_INCREF(result);
         return result;
      }


File: python.info,  Node: Abstract Protocol Support,  Next: Weak Reference Support,  Prev: Object Comparison,  Up: Defining Extension Types Assorted Topics

6.2.3.7 Abstract Protocol Support
.................................

Python supports a variety of `abstract' ‘protocols;’ the specific
interfaces provided to use these interfaces are documented in *note
Abstract Objects Layer: 3d7e.

A number of these abstract interfaces were defined early in the
development of the Python implementation.  In particular, the number,
mapping, and sequence protocols have been part of Python since the
beginning.  Other protocols have been added over time.  For protocols
which depend on several handler routines from the type implementation,
the older protocols have been defined as optional blocks of handlers
referenced by the type object.  For newer protocols there are additional
slots in the main type object, with a flag bit being set to indicate
that the slots are present and should be checked by the interpreter.
(The flag bit does not indicate that the slot values are non-‘NULL’.
The flag may be set to indicate the presence of a slot, but a slot may
still be unfilled.)

     PyNumberMethods   *tp_as_number;
     PySequenceMethods *tp_as_sequence;
     PyMappingMethods  *tp_as_mapping;

If you wish your object to be able to act like a number, a sequence, or
a mapping object, then you place the address of a structure that
implements the C type *note PyNumberMethods: e46, *note
PySequenceMethods: 3d7f, or *note PyMappingMethods: 3d80, respectively.
It is up to you to fill in this structure with appropriate values.  You
can find examples of the use of each of these in the ‘Objects’ directory
of the Python source distribution.

     hashfunc tp_hash;

This function, if you choose to provide it, should return a hash number
for an instance of your data type.  Here is a simple example:

     static Py_hash_t
     newdatatype_hash(newdatatypeobject *obj)
     {
         Py_hash_t result;
         result = obj->some_size + 32767 * obj->some_number;
         if (result == -1)
            result = -2;
         return result;
     }

‘Py_hash_t’ is a signed integer type with a platform-varying width.
Returning ‘-1’ from *note tp_hash: 3d81. indicates an error, which is
why you should be careful to avoid returning it when hash computation is
successful, as seen above.

     ternaryfunc tp_call;

This function is called when an instance of your data type is “called”,
for example, if ‘obj1’ is an instance of your data type and the Python
script contains ‘obj1('hello')’, the *note tp_call: 3d82. handler is
invoked.

This function takes three arguments:

  1. `self' is the instance of the data type which is the subject of the
     call.  If the call is ‘obj1('hello')’, then `self' is ‘obj1’.

  2. `args' is a tuple containing the arguments to the call.  You can
     use *note PyArg_ParseTuple(): 393. to extract the arguments.

  3. `kwds' is a dictionary of keyword arguments that were passed.  If
     this is non-‘NULL’ and you support keyword arguments, use *note
     PyArg_ParseTupleAndKeywords(): 6c1. to extract the arguments.  If
     you do not want to support keyword arguments and this is
     non-‘NULL’, raise a *note TypeError: 1fe. with a message saying
     that keyword arguments are not supported.

Here is a toy ‘tp_call’ implementation:

     static PyObject *
     newdatatype_call(newdatatypeobject *self, PyObject *args, PyObject *kwds)
     {
         PyObject *result;
         const char *arg1;
         const char *arg2;
         const char *arg3;

         if (!PyArg_ParseTuple(args, "sss:call", &arg1, &arg2, &arg3)) {
             return NULL;
         }
         result = PyUnicode_FromFormat(
             "Returning -- value: [%d] arg1: [%s] arg2: [%s] arg3: [%s]\n",
             obj->obj_UnderlyingDatatypePtr->size,
             arg1, arg2, arg3);
         return result;
     }

     /* Iterators */
     getiterfunc tp_iter;
     iternextfunc tp_iternext;

These functions provide support for the iterator protocol.  Both
handlers take exactly one parameter, the instance for which they are
being called, and return a new reference.  In the case of an error, they
should set an exception and return ‘NULL’.  *note tp_iter: ef2.
corresponds to the Python *note __iter__(): 609. method, while *note
tp_iternext: ef3. corresponds to the Python *note __next__(): d2c.
method.

Any *note iterable: c7c. object must implement the *note tp_iter: ef2.
handler, which must return an *note iterator: 1171. object.  Here the
same guidelines apply as for Python classes:

   * For collections (such as lists and tuples) which can support
     multiple independent iterators, a new iterator should be created
     and returned by each call to *note tp_iter: ef2.

   * Objects which can only be iterated over once (usually due to side
     effects of iteration, such as file objects) can implement *note
     tp_iter: ef2. by returning a new reference to themselves – and
     should also therefore implement the *note tp_iternext: ef3.
     handler.

Any *note iterator: 1171. object should implement both *note tp_iter:
ef2. and *note tp_iternext: ef3.  An iterator’s *note tp_iter: ef2.
handler should return a new reference to the iterator.  Its *note
tp_iternext: ef3. handler should return a new reference to the next
object in the iteration, if there is one.  If the iteration has reached
the end, *note tp_iternext: ef3. may return ‘NULL’ without setting an
exception, or it may set *note StopIteration: 582. `in addition' to
returning ‘NULL’; avoiding the exception can yield slightly better
performance.  If an actual error occurs, *note tp_iternext: ef3. should
always set an exception and return ‘NULL’.


File: python.info,  Node: Weak Reference Support,  Next: More Suggestions,  Prev: Abstract Protocol Support,  Up: Defining Extension Types Assorted Topics

6.2.3.8 Weak Reference Support
..............................

One of the goals of Python’s weak reference implementation is to allow
any type to participate in the weak reference mechanism without
incurring the overhead on performance-critical objects (such as
numbers).

See also
........

Documentation for the *note weakref: 131. module.

For an object to be weakly referencable, the extension type must do two
things:

  1. Include a *note PyObject*: 5b5. field in the C object structure
     dedicated to the weak reference mechanism.  The object’s
     constructor should leave it ‘NULL’ (which is automatic when using
     the default *note tp_alloc: 3d58.).

  2. Set the *note tp_weaklistoffset: 26b. type member to the offset of
     the aforementioned field in the C object structure, so that the
     interpreter knows how to access and modify that field.

Concretely, here is how a trivial object structure would be augmented
with the required field:

     typedef struct {
         PyObject_HEAD
         PyObject *weakreflist;  /* List of weak references */
     } TrivialObject;

And the corresponding member in the statically-declared type object:

     static PyTypeObject TrivialType = {
         PyVarObject_HEAD_INIT(NULL, 0)
         /* ... other members omitted for brevity ... */
         .tp_weaklistoffset = offsetof(TrivialObject, weakreflist),
     };

The only further addition is that ‘tp_dealloc’ needs to clear any weak
references (by calling ‘PyObject_ClearWeakRefs()’) if the field is
non-‘NULL’:

     static void
     Trivial_dealloc(TrivialObject *self)
     {
         /* Clear weakrefs first before calling any destructors */
         if (self->weakreflist != NULL)
             PyObject_ClearWeakRefs((PyObject *) self);
         /* ... remainder of destruction code omitted for brevity ... */
         Py_TYPE(self)->tp_free((PyObject *) self);
     }


File: python.info,  Node: More Suggestions,  Prev: Weak Reference Support,  Up: Defining Extension Types Assorted Topics

6.2.3.9 More Suggestions
........................

In order to learn how to implement any specific method for your new data
type, get the *note CPython: 1569. source code.  Go to the ‘Objects’
directory, then search the C source files for ‘tp_’ plus the function
you want (for example, ‘tp_richcompare’).  You will find examples of the
function you want to implement.

When you need to verify that an object is a concrete instance of the
type you are implementing, use the *note PyObject_TypeCheck(): 3d85.
function.  A sample of its use might be something like the following:

     if (!PyObject_TypeCheck(some_object, &MyType)) {
         PyErr_SetString(PyExc_TypeError, "arg #1 not a mything");
         return NULL;
     }

See also
........

Download CPython source releases.

     ‘https://www.python.org/downloads/source/’

The CPython project on GitHub, where the CPython source code is developed.

     ‘https://github.com/python/cpython’


File: python.info,  Node: Building C and C++ Extensions,  Next: Building C and C++ Extensions on Windows,  Prev: Defining Extension Types Assorted Topics,  Up: Creating extensions without third party tools

6.2.4 Building C and C++ Extensions
-----------------------------------

A C extension for CPython is a shared library (e.g.  a ‘.so’ file on
Linux, ‘.pyd’ on Windows), which exports an `initialization function'.

To be importable, the shared library must be available on *note
PYTHONPATH: a34, and must be named after the module name, with an
appropriate extension.  When using distutils, the correct filename is
generated automatically.

The initialization function has the signature:

 -- C Function: PyObject* PyInit_modulename (void)

It returns either a fully-initialized module, or a *note PyModuleDef:
25b. instance.  See *note Initializing C modules: 3d89. for details.

For modules with ASCII-only names, the function must be named
‘PyInit_<modulename>’, with ‘<modulename>’ replaced by the name of the
module.  When using *note Multi-phase initialization: 3d8a, non-ASCII
module names are allowed.  In this case, the initialization function
name is ‘PyInitU_<modulename>’, with ‘<modulename>’ encoded using
Python’s `punycode' encoding with hyphens replaced by underscores.  In
Python:

     def initfunc_name(name):
         try:
             suffix = b'_' + name.encode('ascii')
         except UnicodeEncodeError:
             suffix = b'U_' + name.encode('punycode').replace(b'-', b'_')
         return b'PyInit' + suffix

It is possible to export multiple modules from a single shared library
by defining multiple initialization functions.  However, importing them
requires using symbolic links or a custom importer, because by default
only the function corresponding to the filename is found.  See the
`“Multiple modules in one library”' section in PEP 489(1) for details.

* Menu:

* Building C and C++ Extensions with distutils::
* Distributing your extension modules::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0489


File: python.info,  Node: Building C and C++ Extensions with distutils,  Next: Distributing your extension modules,  Up: Building C and C++ Extensions

6.2.4.1 Building C and C++ Extensions with distutils
....................................................

Extension modules can be built using distutils, which is included in
Python.  Since distutils also supports creation of binary packages,
users don’t necessarily need a compiler and distutils to install the
extension.

A distutils package contains a driver script, ‘setup.py’.  This is a
plain Python file, which, in the most simple case, could look like this:

     from distutils.core import setup, Extension

     module1 = Extension('demo',
                         sources = ['demo.c'])

     setup (name = 'PackageName',
            version = '1.0',
            description = 'This is a demo package',
            ext_modules = [module1])

With this ‘setup.py’, and a file ‘demo.c’, running

     python setup.py build

will compile ‘demo.c’, and produce an extension module named ‘demo’ in
the ‘build’ directory.  Depending on the system, the module file will
end up in a subdirectory ‘build/lib.system’, and may have a name like
‘demo.so’ or ‘demo.pyd’.

In the ‘setup.py’, all execution is performed by calling the ‘setup’
function.  This takes a variable number of keyword arguments, of which
the example above uses only a subset.  Specifically, the example
specifies meta-information to build packages, and it specifies the
contents of the package.  Normally, a package will contain additional
modules, like Python source modules, documentation, subpackages, etc.
Please refer to the distutils documentation in *note Distributing Python
Modules (Legacy version): 8e5. to learn more about the features of
distutils; this section explains building extension modules only.

It is common to pre-compute arguments to ‘setup()’, to better structure
the driver script.  In the example above, the ‘ext_modules’ argument to
*note setup(): 3d8c. is a list of extension modules, each of which is an
instance of the ‘Extension’.  In the example, the instance defines an
extension named ‘demo’ which is build by compiling a single source file,
‘demo.c’.

In many cases, building an extension is more complex, since additional
preprocessor defines and libraries may be needed.  This is demonstrated
in the example below.

     from distutils.core import setup, Extension

     module1 = Extension('demo',
                         define_macros = [('MAJOR_VERSION', '1'),
                                          ('MINOR_VERSION', '0')],
                         include_dirs = ['/usr/local/include'],
                         libraries = ['tcl83'],
                         library_dirs = ['/usr/local/lib'],
                         sources = ['demo.c'])

     setup (name = 'PackageName',
            version = '1.0',
            description = 'This is a demo package',
            author = 'Martin v. Loewis',
            author_email = 'martin@v.loewis.de',
            url = 'https://docs.python.org/extending/building',
            long_description = '''
     This is really just a demo package.
     ''',
            ext_modules = [module1])

In this example, *note setup(): 3d8c. is called with additional
meta-information, which is recommended when distribution packages have
to be built.  For the extension itself, it specifies preprocessor
defines, include directories, library directories, and libraries.
Depending on the compiler, distutils passes this information in
different ways to the compiler.  For example, on Unix, this may result
in the compilation commands

     gcc -DNDEBUG -g -O3 -Wall -Wstrict-prototypes -fPIC -DMAJOR_VERSION=1 -DMINOR_VERSION=0 -I/usr/local/include -I/usr/local/include/python2.2 -c demo.c -o build/temp.linux-i686-2.2/demo.o

     gcc -shared build/temp.linux-i686-2.2/demo.o -L/usr/local/lib -ltcl83 -o build/lib.linux-i686-2.2/demo.so

These lines are for demonstration purposes only; distutils users should
trust that distutils gets the invocations right.


File: python.info,  Node: Distributing your extension modules,  Prev: Building C and C++ Extensions with distutils,  Up: Building C and C++ Extensions

6.2.4.2 Distributing your extension modules
...........................................

When an extension has been successfully built, there are three ways to
use it.

End-users will typically want to install the module, they do so by
running

     python setup.py install

Module maintainers should produce source packages; to do so, they run

     python setup.py sdist

In some cases, additional files need to be included in a source
distribution; this is done through a ‘MANIFEST.in’ file; see *note
Specifying the files to distribute: 3d8f. for details.

If the source distribution has been built successfully, maintainers can
also create binary distributions.  Depending on the platform, one of the
following commands can be used to do so.

     python setup.py bdist_wininst
     python setup.py bdist_rpm
     python setup.py bdist_dumb


File: python.info,  Node: Building C and C++ Extensions on Windows,  Prev: Building C and C++ Extensions,  Up: Creating extensions without third party tools

6.2.5 Building C and C++ Extensions on Windows
----------------------------------------------

This chapter briefly explains how to create a Windows extension module
for Python using Microsoft Visual C++, and follows with more detailed
background information on how it works.  The explanatory material is
useful for both the Windows programmer learning to build Python
extensions and the Unix programmer interested in producing software
which can be successfully built on both Unix and Windows.

Module authors are encouraged to use the distutils approach for building
extension modules, instead of the one described in this section.  You
will still need the C compiler that was used to build Python; typically
Microsoft Visual C++.

     Note: This chapter mentions a number of filenames that include an
     encoded Python version number.  These filenames are represented
     with the version number shown as ‘XY’; in practice, ‘'X'’ will be
     the major version number and ‘'Y'’ will be the minor version number
     of the Python release you’re working with.  For example, if you are
     using Python 2.2.1, ‘XY’ will actually be ‘22’.

* Menu:

* A Cookbook Approach::
* Differences Between Unix and Windows::
* Using DLLs in Practice::


File: python.info,  Node: A Cookbook Approach,  Next: Differences Between Unix and Windows,  Up: Building C and C++ Extensions on Windows

6.2.5.1 A Cookbook Approach
...........................

There are two approaches to building extension modules on Windows, just
as there are on Unix: use the *note distutils: 38. package to control
the build process, or do things manually.  The distutils approach works
well for most extensions; documentation on using *note distutils: 38. to
build and package extension modules is available in *note Distributing
Python Modules (Legacy version): 8e5.  If you find you really need to do
things manually, it may be instructive to study the project file for the
winsound(1) standard library module.

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/PCbuild/winsound.vcxproj


File: python.info,  Node: Differences Between Unix and Windows,  Next: Using DLLs in Practice,  Prev: A Cookbook Approach,  Up: Building C and C++ Extensions on Windows

6.2.5.2 Differences Between Unix and Windows
............................................

Unix and Windows use completely different paradigms for run-time loading
of code.  Before you try to build a module that can be dynamically
loaded, be aware of how your system works.

In Unix, a shared object (‘.so’) file contains code to be used by the
program, and also the names of functions and data that it expects to
find in the program.  When the file is joined to the program, all
references to those functions and data in the file’s code are changed to
point to the actual locations in the program where the functions and
data are placed in memory.  This is basically a link operation.

In Windows, a dynamic-link library (‘.dll’) file has no dangling
references.  Instead, an access to functions or data goes through a
lookup table.  So the DLL code does not have to be fixed up at runtime
to refer to the program’s memory; instead, the code already uses the
DLL’s lookup table, and the lookup table is modified at runtime to point
to the functions and data.

In Unix, there is only one type of library file (‘.a’) which contains
code from several object files (‘.o’).  During the link step to create a
shared object file (‘.so’), the linker may find that it doesn’t know
where an identifier is defined.  The linker will look for it in the
object files in the libraries; if it finds it, it will include all the
code from that object file.

In Windows, there are two types of library, a static library and an
import library (both called ‘.lib’).  A static library is like a Unix
‘.a’ file; it contains code to be included as necessary.  An import
library is basically used only to reassure the linker that a certain
identifier is legal, and will be present in the program when the DLL is
loaded.  So the linker uses the information from the import library to
build the lookup table for using identifiers that are not included in
the DLL. When an application or a DLL is linked, an import library may
be generated, which will need to be used for all future DLLs that depend
on the symbols in the application or DLL.

Suppose you are building two dynamic-load modules, B and C, which should
share another block of code A. On Unix, you would `not' pass ‘A.a’ to
the linker for ‘B.so’ and ‘C.so’; that would cause it to be included
twice, so that B and C would each have their own copy.  In Windows,
building ‘A.dll’ will also build ‘A.lib’.  You `do' pass ‘A.lib’ to the
linker for B and C. ‘A.lib’ does not contain code; it just contains
information which will be used at runtime to access A’s code.

In Windows, using an import library is sort of like using ‘import spam’;
it gives you access to spam’s names, but does not create a separate
copy.  On Unix, linking with a library is more like ‘from spam import
*’; it does create a separate copy.


File: python.info,  Node: Using DLLs in Practice,  Prev: Differences Between Unix and Windows,  Up: Building C and C++ Extensions on Windows

6.2.5.3 Using DLLs in Practice
..............................

Windows Python is built in Microsoft Visual C++; using other compilers
may or may not work (though Borland seems to).  The rest of this section
is MSVC++ specific.

When creating DLLs in Windows, you must pass ‘pythonXY.lib’ to the
linker.  To build two DLLs, spam and ni (which uses C functions found in
spam), you could use these commands:

     cl /LD /I/python/include spam.c ../libs/pythonXY.lib
     cl /LD /I/python/include ni.c spam.lib ../libs/pythonXY.lib

The first command created three files: ‘spam.obj’, ‘spam.dll’ and
‘spam.lib’.  ‘Spam.dll’ does not contain any Python functions (such as
*note PyArg_ParseTuple(): 393.), but it does know how to find the Python
code thanks to ‘pythonXY.lib’.

The second command created ‘ni.dll’ (and ‘.obj’ and ‘.lib’), which knows
how to find the necessary functions from spam, and also from the Python
executable.

Not every identifier is exported to the lookup table.  If you want any
other modules (including Python) to be able to see your identifiers, you
have to say ‘_declspec(dllexport)’, as in ‘void _declspec(dllexport)
initspam(void)’ or ‘PyObject _declspec(dllexport) *NiGetSpamData(void)’.

Developer Studio will throw in a lot of import libraries that you do not
really need, adding about 100K to your executable.  To get rid of them,
use the Project Settings dialog, Link tab, to specify `ignore default
libraries'.  Add the correct ‘msvcrtxx.lib’ to the list of libraries.


File: python.info,  Node: Embedding the CPython runtime in a larger application,  Prev: Creating extensions without third party tools,  Up: Extending and Embedding the Python Interpreter

6.3 Embedding the CPython runtime in a larger application
=========================================================

Sometimes, rather than creating an extension that runs inside the Python
interpreter as the main application, it is desirable to instead embed
the CPython runtime inside a larger application.  This section covers
some of the details involved in doing that successfully.

* Menu:

* Embedding Python in Another Application::


File: python.info,  Node: Embedding Python in Another Application,  Up: Embedding the CPython runtime in a larger application

6.3.1 Embedding Python in Another Application
---------------------------------------------

The previous chapters discussed how to extend Python, that is, how to
extend the functionality of Python by attaching a library of C functions
to it.  It is also possible to do it the other way around: enrich your
C/C++ application by embedding Python in it.  Embedding provides your
application with the ability to implement some of the functionality of
your application in Python rather than C or C++.  This can be used for
many purposes; one example would be to allow users to tailor the
application to their needs by writing some scripts in Python.  You can
also use it yourself if some of the functionality can be written in
Python more easily.

Embedding Python is similar to extending it, but not quite.  The
difference is that when you extend Python, the main program of the
application is still the Python interpreter, while if you embed Python,
the main program may have nothing to do with Python — instead, some
parts of the application occasionally call the Python interpreter to run
some Python code.

So if you are embedding Python, you are providing your own main program.
One of the things this main program has to do is initialize the Python
interpreter.  At the very least, you have to call the function *note
Py_Initialize(): 20f.  There are optional calls to pass command line
arguments to Python.  Then later you can call the interpreter from any
part of the application.

There are several different ways to call the interpreter: you can pass a
string containing Python statements to *note PyRun_SimpleString(): 3d9c,
or you can pass a stdio file pointer and a file name (for identification
in error messages only) to *note PyRun_SimpleFile(): 3d9d.  You can also
call the lower-level operations described in the previous chapters to
construct and use Python objects.

See also
........

*note Python/C API Reference Manual: 1333.

     The details of Python’s C interface are given in this manual.  A
     great deal of necessary information can be found here.

* Menu:

* Very High Level Embedding::
* Beyond Very High Level Embedding; An overview: Beyond Very High Level Embedding An overview.
* Pure Embedding::
* Extending Embedded Python::
* Embedding Python in C++::
* Compiling and Linking under Unix-like systems::


File: python.info,  Node: Very High Level Embedding,  Next: Beyond Very High Level Embedding An overview,  Up: Embedding Python in Another Application

6.3.1.1 Very High Level Embedding
.................................

The simplest form of embedding Python is the use of the very high level
interface.  This interface is intended to execute a Python script
without needing to interact with the application directly.  This can for
example be used to perform some operation on a file.

     #define PY_SSIZE_T_CLEAN
     #include <Python.h>

     int
     main(int argc, char *argv[])
     {
         wchar_t *program = Py_DecodeLocale(argv[0], NULL);
         if (program == NULL) {
             fprintf(stderr, "Fatal error: cannot decode argv[0]\n");
             exit(1);
         }
         Py_SetProgramName(program);  /* optional but recommended */
         Py_Initialize();
         PyRun_SimpleString("from time import time,ctime\n"
                            "print('Today is', ctime(time()))\n");
         if (Py_FinalizeEx() < 0) {
             exit(120);
         }
         PyMem_RawFree(program);
         return 0;
     }

The *note Py_SetProgramName(): 10f2. function should be called before
*note Py_Initialize(): 20f. to inform the interpreter about paths to
Python run-time libraries.  Next, the Python interpreter is initialized
with *note Py_Initialize(): 20f, followed by the execution of a
hard-coded Python script that prints the date and time.  Afterwards, the
*note Py_FinalizeEx(): 6c0. call shuts the interpreter down, followed by
the end of the program.  In a real program, you may want to get the
Python script from another source, perhaps a text-editor routine, a
file, or a database.  Getting the Python code from a file can better be
done by using the *note PyRun_SimpleFile(): 3d9d. function, which saves
you the trouble of allocating memory space and loading the file
contents.


File: python.info,  Node: Beyond Very High Level Embedding An overview,  Next: Pure Embedding,  Prev: Very High Level Embedding,  Up: Embedding Python in Another Application

6.3.1.2 Beyond Very High Level Embedding: An overview
.....................................................

The high level interface gives you the ability to execute arbitrary
pieces of Python code from your application, but exchanging data values
is quite cumbersome to say the least.  If you want that, you should use
lower level calls.  At the cost of having to write more C code, you can
achieve almost anything.

It should be noted that extending Python and embedding Python is quite
the same activity, despite the different intent.  Most topics discussed
in the previous chapters are still valid.  To show this, consider what
the extension code from Python to C really does:

  1. Convert data values from Python to C,

  2. Perform a function call to a C routine using the converted values,
     and

  3. Convert the data values from the call from C to Python.

When embedding Python, the interface code does:

  1. Convert data values from C to Python,

  2. Perform a function call to a Python interface routine using the
     converted values, and

  3. Convert the data values from the call from Python to C.

As you can see, the data conversion steps are simply swapped to
accommodate the different direction of the cross-language transfer.  The
only difference is the routine that you call between both data
conversions.  When extending, you call a C routine, when embedding, you
call a Python routine.

This chapter will not discuss how to convert data from Python to C and
vice versa.  Also, proper use of references and dealing with errors is
assumed to be understood.  Since these aspects do not differ from
extending the interpreter, you can refer to earlier chapters for the
required information.


File: python.info,  Node: Pure Embedding,  Next: Extending Embedded Python,  Prev: Beyond Very High Level Embedding An overview,  Up: Embedding Python in Another Application

6.3.1.3 Pure Embedding
......................

The first program aims to execute a function in a Python script.  Like
in the section about the very high level interface, the Python
interpreter does not directly interact with the application (but that
will change in the next section).

The code to run a function defined in a Python script is:

     #define PY_SSIZE_T_CLEAN
     #include <Python.h>

     int
     main(int argc, char *argv[])
     {
         PyObject *pName, *pModule, *pFunc;
         PyObject *pArgs, *pValue;
         int i;

         if (argc < 3) {
             fprintf(stderr,"Usage: call pythonfile funcname [args]\n");
             return 1;
         }

         Py_Initialize();
         pName = PyUnicode_DecodeFSDefault(argv[1]);
         /* Error checking of pName left out */

         pModule = PyImport_Import(pName);
         Py_DECREF(pName);

         if (pModule != NULL) {
             pFunc = PyObject_GetAttrString(pModule, argv[2]);
             /* pFunc is a new reference */

             if (pFunc && PyCallable_Check(pFunc)) {
                 pArgs = PyTuple_New(argc - 3);
                 for (i = 0; i < argc - 3; ++i) {
                     pValue = PyLong_FromLong(atoi(argv[i + 3]));
                     if (!pValue) {
                         Py_DECREF(pArgs);
                         Py_DECREF(pModule);
                         fprintf(stderr, "Cannot convert argument\n");
                         return 1;
                     }
                     /* pValue reference stolen here: */
                     PyTuple_SetItem(pArgs, i, pValue);
                 }
                 pValue = PyObject_CallObject(pFunc, pArgs);
                 Py_DECREF(pArgs);
                 if (pValue != NULL) {
                     printf("Result of call: %ld\n", PyLong_AsLong(pValue));
                     Py_DECREF(pValue);
                 }
                 else {
                     Py_DECREF(pFunc);
                     Py_DECREF(pModule);
                     PyErr_Print();
                     fprintf(stderr,"Call failed\n");
                     return 1;
                 }
             }
             else {
                 if (PyErr_Occurred())
                     PyErr_Print();
                 fprintf(stderr, "Cannot find function \"%s\"\n", argv[2]);
             }
             Py_XDECREF(pFunc);
             Py_DECREF(pModule);
         }
         else {
             PyErr_Print();
             fprintf(stderr, "Failed to load \"%s\"\n", argv[1]);
             return 1;
         }
         if (Py_FinalizeEx() < 0) {
             return 120;
         }
         return 0;
     }

This code loads a Python script using ‘argv[1]’, and calls the function
named in ‘argv[2]’.  Its integer arguments are the other values of the
‘argv’ array.  If you *note compile and link: 3da4. this program (let’s
call the finished executable ‘call’), and use it to execute a Python
script, such as:

     def multiply(a,b):
         print("Will compute", a, "times", b)
         c = 0
         for i in range(0, a):
             c = c + b
         return c

then the result should be:

     $ call multiply multiply 3 2
     Will compute 3 times 2
     Result of call: 6

Although the program is quite large for its functionality, most of the
code is for data conversion between Python and C, and for error
reporting.  The interesting part with respect to embedding Python starts
with

     Py_Initialize();
     pName = PyUnicode_DecodeFSDefault(argv[1]);
     /* Error checking of pName left out */
     pModule = PyImport_Import(pName);

After initializing the interpreter, the script is loaded using *note
PyImport_Import(): e24.  This routine needs a Python string as its
argument, which is constructed using the *note PyUnicode_FromString():
3da5. data conversion routine.

     pFunc = PyObject_GetAttrString(pModule, argv[2]);
     /* pFunc is a new reference */

     if (pFunc && PyCallable_Check(pFunc)) {
         ...
     }
     Py_XDECREF(pFunc);

Once the script is loaded, the name we’re looking for is retrieved using
*note PyObject_GetAttrString(): 3d34.  If the name exists, and the
object returned is callable, you can safely assume that it is a
function.  The program then proceeds by constructing a tuple of
arguments as normal.  The call to the Python function is then made with:

     pValue = PyObject_CallObject(pFunc, pArgs);

Upon return of the function, ‘pValue’ is either ‘NULL’ or it contains a
reference to the return value of the function.  Be sure to release the
reference after examining the value.


File: python.info,  Node: Extending Embedded Python,  Next: Embedding Python in C++,  Prev: Pure Embedding,  Up: Embedding Python in Another Application

6.3.1.4 Extending Embedded Python
.................................

Until now, the embedded Python interpreter had no access to
functionality from the application itself.  The Python API allows this
by extending the embedded interpreter.  That is, the embedded
interpreter gets extended with routines provided by the application.
While it sounds complex, it is not so bad.  Simply forget for a while
that the application starts the Python interpreter.  Instead, consider
the application to be a set of subroutines, and write some glue code
that gives Python access to those routines, just like you would write a
normal Python extension.  For example:

     static int numargs=0;

     /* Return the number of arguments of the application command line */
     static PyObject*
     emb_numargs(PyObject *self, PyObject *args)
     {
         if(!PyArg_ParseTuple(args, ":numargs"))
             return NULL;
         return PyLong_FromLong(numargs);
     }

     static PyMethodDef EmbMethods[] = {
         {"numargs", emb_numargs, METH_VARARGS,
          "Return the number of arguments received by the process."},
         {NULL, NULL, 0, NULL}
     };

     static PyModuleDef EmbModule = {
         PyModuleDef_HEAD_INIT, "emb", NULL, -1, EmbMethods,
         NULL, NULL, NULL, NULL
     };

     static PyObject*
     PyInit_emb(void)
     {
         return PyModule_Create(&EmbModule);
     }

Insert the above code just above the ‘main()’ function.  Also, insert
the following two statements before the call to *note Py_Initialize():
20f.:

     numargs = argc;
     PyImport_AppendInittab("emb", &PyInit_emb);

These two lines initialize the ‘numargs’ variable, and make the
‘emb.numargs()’ function accessible to the embedded Python interpreter.
With these extensions, the Python script can do things like

     import emb
     print("Number of arguments", emb.numargs())

In a real application, the methods will expose an API of the application
to Python.


File: python.info,  Node: Embedding Python in C++,  Next: Compiling and Linking under Unix-like systems,  Prev: Extending Embedded Python,  Up: Embedding Python in Another Application

6.3.1.5 Embedding Python in C++
...............................

It is also possible to embed Python in a C++ program; precisely how this
is done will depend on the details of the C++ system used; in general
you will need to write the main program in C++, and use the C++ compiler
to compile and link your program.  There is no need to recompile Python
itself using C++.


File: python.info,  Node: Compiling and Linking under Unix-like systems,  Prev: Embedding Python in C++,  Up: Embedding Python in Another Application

6.3.1.6 Compiling and Linking under Unix-like systems
.....................................................

It is not necessarily trivial to find the right flags to pass to your
compiler (and linker) in order to embed the Python interpreter into your
application, particularly because Python needs to load library modules
implemented as C dynamic extensions (‘.so’ files) linked against it.

To find out the required compiler and linker flags, you can execute the
‘python`X.Y'-config’ script which is generated as part of the
installation process (a ‘python3-config’ script may also be available).
This script has several options, of which the following will be directly
useful to you:

   * ‘pythonX.Y-config --cflags’ will give you the recommended flags
     when compiling:

          $ /opt/bin/python3.4-config --cflags
          -I/opt/include/python3.4m -I/opt/include/python3.4m -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes

   * ‘pythonX.Y-config --ldflags’ will give you the recommended flags
     when linking:

          $ /opt/bin/python3.4-config --ldflags
          -L/opt/lib/python3.4/config-3.4m -lpthread -ldl -lutil -lm -lpython3.4m -Xlinker -export-dynamic

     Note: To avoid confusion between several Python installations (and
     especially between the system Python and your own compiled Python),
     it is recommended that you use the absolute path to
     ‘python`X.Y'-config’, as in the above example.

If this procedure doesn’t work for you (it is not guaranteed to work for
all Unix-like platforms; however, we welcome *note bug reports: 3dab.)
you will have to read your system’s documentation about dynamic linking
and/or examine Python’s ‘Makefile’ (use *note
sysconfig.get_makefile_filename(): 37ca. to find its location) and
compilation options.  In this case, the *note sysconfig: fe. module is a
useful tool to programmatically extract the configuration values that
you will want to combine together.  For example:

     >>> import sysconfig
     >>> sysconfig.get_config_var('LIBS')
     '-lpthread -ldl  -lutil'
     >>> sysconfig.get_config_var('LINKFORSHARED')
     '-Xlinker -export-dynamic'


File: python.info,  Node: Python/C API Reference Manual,  Next: Distributing Python Modules,  Prev: Extending and Embedding the Python Interpreter,  Up: Top

7 Python/C API Reference Manual
*******************************

This manual documents the API used by C and C++ programmers who want to
write extension modules or embed Python.  It is a companion to *note
Extending and Embedding the Python Interpreter: 1332, which describes
the general principles of extension writing but does not document the
API functions in detail.

* Menu:

* Introduction: Introduction<13>.
* Stable Application Binary Interface::
* The Very High Level Layer::
* Reference Counting::
* Exception Handling::
* Utilities: Utilities<2>.
* Abstract Objects Layer::
* Concrete Objects Layer::
* Initialization, Finalization, and Threads: Initialization Finalization and Threads.
* Python Initialization Configuration::
* Memory Management::
* Object Implementation Support::
* API and ABI Versioning::


File: python.info,  Node: Introduction<13>,  Next: Stable Application Binary Interface,  Up: Python/C API Reference Manual

7.1 Introduction
================

The Application Programmer’s Interface to Python gives C and C++
programmers access to the Python interpreter at a variety of levels.
The API is equally usable from C++, but for brevity it is generally
referred to as the Python/C API. There are two fundamentally different
reasons for using the Python/C API. The first reason is to write
`extension modules' for specific purposes; these are C modules that
extend the Python interpreter.  This is probably the most common use.
The second reason is to use Python as a component in a larger
application; this technique is generally referred to as `embedding'
Python in an application.

Writing an extension module is a relatively well-understood process,
where a “cookbook” approach works well.  There are several tools that
automate the process to some extent.  While people have embedded Python
in other applications since its early existence, the process of
embedding Python is less straightforward than writing an extension.

Many API functions are useful independent of whether you’re embedding or
extending Python; moreover, most applications that embed Python will
need to provide a custom extension as well, so it’s probably a good idea
to become familiar with writing an extension before attempting to embed
Python in a real application.

* Menu:

* Coding standards::
* Include Files::
* Useful macros::
* Objects, Types and Reference Counts: Objects Types and Reference Counts.
* Exceptions: Exceptions<19>.
* Embedding Python: Embedding Python<2>.
* Debugging Builds::


File: python.info,  Node: Coding standards,  Next: Include Files,  Up: Introduction<13>

7.1.1 Coding standards
----------------------

If you’re writing C code for inclusion in CPython, you `must' follow the
guidelines and standards defined in PEP 7(1).  These guidelines apply
regardless of the version of Python you are contributing to.  Following
these conventions is not necessary for your own third party extension
modules, unless you eventually expect to contribute them to Python.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0007


File: python.info,  Node: Include Files,  Next: Useful macros,  Prev: Coding standards,  Up: Introduction<13>

7.1.2 Include Files
-------------------

All function, type and macro definitions needed to use the Python/C API
are included in your code by the following line:

     #define PY_SSIZE_T_CLEAN
     #include <Python.h>

This implies inclusion of the following standard headers: ‘<stdio.h>’,
‘<string.h>’, ‘<errno.h>’, ‘<limits.h>’, ‘<assert.h>’ and ‘<stdlib.h>’
(if available).

     Note: Since Python may define some pre-processor definitions which
     affect the standard headers on some systems, you `must' include
     ‘Python.h’ before any standard headers are included.

     It is recommended to always define ‘PY_SSIZE_T_CLEAN’ before
     including ‘Python.h’.  See *note Parsing arguments and building
     values: 3f2. for a description of this macro.

All user visible names defined by Python.h (except those defined by the
included standard headers) have one of the prefixes ‘Py’ or ‘_Py’.
Names beginning with ‘_Py’ are for internal use by the Python
implementation and should not be used by extension writers.  Structure
member names do not have a reserved prefix.

     Note: User code should never define names that begin with ‘Py’ or
     ‘_Py’.  This confuses the reader, and jeopardizes the portability
     of the user code to future Python versions, which may define
     additional names beginning with one of these prefixes.

The header files are typically installed with Python.  On Unix, these
are located in the directories ‘`prefix'/include/pythonversion/’ and
‘`exec_prefix'/include/pythonversion/’, where ‘prefix’ and ‘exec_prefix’
are defined by the corresponding parameters to Python’s ‘configure’
script and `version' is ‘'%d.%d' % sys.version_info[:2]’.  On Windows,
the headers are installed in ‘`prefix'/include’, where ‘prefix’ is the
installation directory specified to the installer.

To include the headers, place both directories (if different) on your
compiler’s search path for includes.  Do `not' place the parent
directories on the search path and then use ‘#include
<pythonX.Y/Python.h>’; this will break on multi-platform builds since
the platform independent headers under ‘prefix’ include the platform
specific headers from ‘exec_prefix’.

C++ users should note that although the API is defined entirely using C,
the header files properly declare the entry points to be ‘extern "C"’.
As a result, there is no need to do anything special to use the API from
C++.


File: python.info,  Node: Useful macros,  Next: Objects Types and Reference Counts,  Prev: Include Files,  Up: Introduction<13>

7.1.3 Useful macros
-------------------

Several useful macros are defined in the Python header files.  Many are
defined closer to where they are useful (e.g.  *note Py_RETURN_NONE:
e9b.).  Others of a more general utility are defined here.  This is not
necessarily a complete listing.

 -- C Macro: Py_UNREACHABLE ()

     Use this when you have a code path that cannot be reached by
     design.  For example, in the ‘default:’ clause in a ‘switch’
     statement for which all possible values are covered in ‘case’
     statements.  Use this in places where you might be tempted to put
     an ‘assert(0)’ or ‘abort()’ call.

     In release mode, the macro helps the compiler to optimize the code,
     and avoids a warning about unreachable code.  For example, the
     macro is implemented with ‘__builtin_unreachable()’ on GCC in
     release mode.

     A use for ‘Py_UNREACHABLE()’ is following a call a function that
     never returns but that is not declared ‘_Py_NO_RETURN’.

     If a code path is very unlikely code but can be reached under
     exceptional case, this macro must not be used.  For example, under
     low memory condition or if a system call returns a value out of the
     expected range.  In this case, it’s better to report the error to
     the caller.  If the error cannot be reported to caller, *note
     Py_FatalError(): 266. can be used.

     New in version 3.7.

 -- C Macro: Py_ABS (x)

     Return the absolute value of ‘x’.

     New in version 3.3.

 -- C Macro: Py_MIN (x, y)

     Return the minimum value between ‘x’ and ‘y’.

     New in version 3.3.

 -- C Macro: Py_MAX (x, y)

     Return the maximum value between ‘x’ and ‘y’.

     New in version 3.3.

 -- C Macro: Py_STRINGIFY (x)

     Convert ‘x’ to a C string.  E.g.  ‘Py_STRINGIFY(123)’ returns
     ‘"123"’.

     New in version 3.4.

 -- C Macro: Py_MEMBER_SIZE (type, member)

     Return the size of a structure (‘type’) ‘member’ in bytes.

     New in version 3.6.

 -- C Macro: Py_CHARMASK (c)

     Argument must be a character or an integer in the range [-128, 127]
     or [0, 255].  This macro returns ‘c’ cast to an ‘unsigned char’.

 -- C Macro: Py_GETENV (s)

     Like ‘getenv(s)’, but returns ‘NULL’ if *note -E: 231. was passed
     on the command line (i.e.  if ‘Py_IgnoreEnvironmentFlag’ is set).

 -- C Macro: Py_UNUSED (arg)

     Use this for unused arguments in a function definition to silence
     compiler warnings.  Example: ‘int func(int a, int Py_UNUSED(b)) {
     return a; }’.

     New in version 3.4.

 -- C Macro: Py_DEPRECATED (version)

     Use this for deprecated declarations.  The macro must be placed
     before the symbol name.

     Example:

          Py_DEPRECATED(3.8) PyAPI_FUNC(int) Py_OldFunction(void);

     Changed in version 3.8: MSVC support was added.

 -- C Macro: PyDoc_STRVAR (name, str)

     Creates a variable with name ‘name’ that can be used in docstrings.
     If Python is built without docstrings, the value will be empty.

     Use *note PyDoc_STRVAR: 105a. for docstrings to support building
     Python without docstrings, as specified in PEP 7(1).

     Example:

          PyDoc_STRVAR(pop_doc, "Remove and return the rightmost element.");

          static PyMethodDef deque_methods[] = {
              // ...
              {"pop", (PyCFunction)deque_pop, METH_NOARGS, pop_doc},
              // ...
          }

 -- C Macro: PyDoc_STR (str)

     Creates a docstring for the given input string or an empty string
     if docstrings are disabled.

     Use *note PyDoc_STR: 3dbe. in specifying docstrings to support
     building Python without docstrings, as specified in PEP 7(2).

     Example:

          static PyMethodDef pysqlite_row_methods[] = {
              {"keys", (PyCFunction)pysqlite_row_keys, METH_NOARGS,
                  PyDoc_STR("Returns the keys of the row.")},
              {NULL, NULL}
          };

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0007

   (2) https://www.python.org/dev/peps/pep-0007


File: python.info,  Node: Objects Types and Reference Counts,  Next: Exceptions<19>,  Prev: Useful macros,  Up: Introduction<13>

7.1.4 Objects, Types and Reference Counts
-----------------------------------------

Most Python/C API functions have one or more arguments as well as a
return value of type *note PyObject*: 5b5.  This type is a pointer to an
opaque data type representing an arbitrary Python object.  Since all
Python object types are treated the same way by the Python language in
most situations (e.g., assignments, scope rules, and argument passing),
it is only fitting that they should be represented by a single C type.
Almost all Python objects live on the heap: you never declare an
automatic or static variable of type *note PyObject: 5b5, only pointer
variables of type *note PyObject*: 5b5. can be declared.  The sole
exception are the type objects; since these must never be deallocated,
they are typically static *note PyTypeObject: 3f5. objects.

All Python objects (even Python integers) have a `type' and a `reference
count'.  An object’s type determines what kind of object it is (e.g., an
integer, a list, or a user-defined function; there are many more as
explained in *note The standard type hierarchy: 1553.).  For each of the
well-known types there is a macro to check whether an object is of that
type; for instance, ‘PyList_Check(a)’ is true if (and only if) the
object pointed to by `a' is a Python list.

* Menu:

* Reference Counts: Reference Counts<2>.
* Types::


File: python.info,  Node: Reference Counts<2>,  Next: Types,  Up: Objects Types and Reference Counts

7.1.4.1 Reference Counts
........................

The reference count is important because today’s computers have a finite
(and often severely limited) memory size; it counts how many different
places there are that have a reference to an object.  Such a place could
be another object, or a global (or static) C variable, or a local
variable in some C function.  When an object’s reference count becomes
zero, the object is deallocated.  If it contains references to other
objects, their reference count is decremented.  Those other objects may
be deallocated in turn, if this decrement makes their reference count
become zero, and so on.  (There’s an obvious problem with objects that
reference each other here; for now, the solution is “don’t do that.”)

Reference counts are always manipulated explicitly.  The normal way is
to use the macro *note Py_INCREF(): 38e. to increment an object’s
reference count by one, and *note Py_DECREF(): 38f. to decrement it by
one.  The *note Py_DECREF(): 38f. macro is considerably more complex
than the incref one, since it must check whether the reference count
becomes zero and then cause the object’s deallocator to be called.  The
deallocator is a function pointer contained in the object’s type
structure.  The type-specific deallocator takes care of decrementing the
reference counts for other objects contained in the object if this is a
compound object type, such as a list, as well as performing any
additional finalization that’s needed.  There’s no chance that the
reference count can overflow; at least as many bits are used to hold the
reference count as there are distinct memory locations in virtual memory
(assuming ‘sizeof(Py_ssize_t) >= sizeof(void*)’).  Thus, the reference
count increment is a simple operation.

It is not necessary to increment an object’s reference count for every
local variable that contains a pointer to an object.  In theory, the
object’s reference count goes up by one when the variable is made to
point to it and it goes down by one when the variable goes out of scope.
However, these two cancel each other out, so at the end the reference
count hasn’t changed.  The only real reason to use the reference count
is to prevent the object from being deallocated as long as our variable
is pointing to it.  If we know that there is at least one other
reference to the object that lives at least as long as our variable,
there is no need to increment the reference count temporarily.  An
important situation where this arises is in objects that are passed as
arguments to C functions in an extension module that are called from
Python; the call mechanism guarantees to hold a reference to every
argument for the duration of the call.

However, a common pitfall is to extract an object from a list and hold
on to it for a while without incrementing its reference count.  Some
other operation might conceivably remove the object from the list,
decrementing its reference count and possibly deallocating it.  The real
danger is that innocent-looking operations may invoke arbitrary Python
code which could do this; there is a code path which allows control to
flow back to the user from a *note Py_DECREF(): 38f, so almost any
operation is potentially dangerous.

A safe approach is to always use the generic operations (functions whose
name begins with ‘PyObject_’, ‘PyNumber_’, ‘PySequence_’ or
‘PyMapping_’).  These operations always increment the reference count of
the object they return.  This leaves the caller with the responsibility
to call *note Py_DECREF(): 38f. when they are done with the result; this
soon becomes second nature.

* Menu:

* Reference Count Details::


File: python.info,  Node: Reference Count Details,  Up: Reference Counts<2>

7.1.4.2 Reference Count Details
...............................

The reference count behavior of functions in the Python/C API is best
explained in terms of `ownership of references'.  Ownership pertains to
references, never to objects (objects are not owned: they are always
shared).  “Owning a reference” means being responsible for calling
Py_DECREF on it when the reference is no longer needed.  Ownership can
also be transferred, meaning that the code that receives ownership of
the reference then becomes responsible for eventually decref’ing it by
calling *note Py_DECREF(): 38f. or *note Py_XDECREF(): 391. when it’s no
longer needed—or passing on this responsibility (usually to its caller).
When a function passes ownership of a reference on to its caller, the
caller is said to receive a `new' reference.  When no ownership is
transferred, the caller is said to `borrow' the reference.  Nothing
needs to be done for a borrowed reference.

Conversely, when a calling function passes in a reference to an object,
there are two possibilities: the function `steals' a reference to the
object, or it does not.  `Stealing a reference' means that when you pass
a reference to a function, that function assumes that it now owns that
reference, and you are not responsible for it any longer.

Few functions steal references; the two notable exceptions are *note
PyList_SetItem(): 3d3b. and *note PyTuple_SetItem(): 3d3a, which steal a
reference to the item (but not to the tuple or list into which the item
is put!).  These functions were designed to steal a reference because of
a common idiom for populating a tuple or list with newly created
objects; for example, the code to create the tuple ‘(1, 2, "three")’
could look like this (forgetting about error handling for the moment; a
better way to code this is shown below):

     PyObject *t;

     t = PyTuple_New(3);
     PyTuple_SetItem(t, 0, PyLong_FromLong(1L));
     PyTuple_SetItem(t, 1, PyLong_FromLong(2L));
     PyTuple_SetItem(t, 2, PyUnicode_FromString("three"));

Here, *note PyLong_FromLong(): 3d1c. returns a new reference which is
immediately stolen by *note PyTuple_SetItem(): 3d3a.  When you want to
keep using an object although the reference to it will be stolen, use
*note Py_INCREF(): 38e. to grab another reference before calling the
reference-stealing function.

Incidentally, *note PyTuple_SetItem(): 3d3a. is the `only' way to set
tuple items; *note PySequence_SetItem(): 1184. and *note
PyObject_SetItem(): 3dc5. refuse to do this since tuples are an
immutable data type.  You should only use *note PyTuple_SetItem(): 3d3a.
for tuples that you are creating yourself.

Equivalent code for populating a list can be written using *note
PyList_New(): 3dc6. and *note PyList_SetItem(): 3d3b.

However, in practice, you will rarely use these ways of creating and
populating a tuple or list.  There’s a generic function, *note
Py_BuildValue(): 3f0, that can create most common objects from C values,
directed by a `format string'.  For example, the above two blocks of
code could be replaced by the following (which also takes care of the
error checking):

     PyObject *tuple, *list;

     tuple = Py_BuildValue("(iis)", 1, 2, "three");
     list = Py_BuildValue("[iis]", 1, 2, "three");

It is much more common to use *note PyObject_SetItem(): 3dc5. and
friends with items whose references you are only borrowing, like
arguments that were passed in to the function you are writing.  In that
case, their behaviour regarding reference counts is much saner, since
you don’t have to increment a reference count so you can give a
reference away (“have it be stolen”).  For example, this function sets
all items of a list (actually, any mutable sequence) to a given item:

     int
     set_all(PyObject *target, PyObject *item)
     {
         Py_ssize_t i, n;

         n = PyObject_Length(target);
         if (n < 0)
             return -1;
         for (i = 0; i < n; i++) {
             PyObject *index = PyLong_FromSsize_t(i);
             if (!index)
                 return -1;
             if (PyObject_SetItem(target, index, item) < 0) {
                 Py_DECREF(index);
                 return -1;
             }
             Py_DECREF(index);
         }
         return 0;
     }

The situation is slightly different for function return values.  While
passing a reference to most functions does not change your ownership
responsibilities for that reference, many functions that return a
reference to an object give you ownership of the reference.  The reason
is simple: in many cases, the returned object is created on the fly, and
the reference you get is the only reference to the object.  Therefore,
the generic functions that return object references, like *note
PyObject_GetItem(): 3dc7. and *note PySequence_GetItem(): 1183, always
return a new reference (the caller becomes the owner of the reference).

It is important to realize that whether you own a reference returned by
a function depends on which function you call only — `the plumage' (the
type of the object passed as an argument to the function) `doesn’t enter
into it!'  Thus, if you extract an item from a list using *note
PyList_GetItem(): 3d36, you don’t own the reference — but if you obtain
the same item from the same list using *note PySequence_GetItem(): 1183.
(which happens to take exactly the same arguments), you do own a
reference to the returned object.

Here is an example of how you could write a function that computes the
sum of the items in a list of integers; once using *note
PyList_GetItem(): 3d36, and once using *note PySequence_GetItem(): 1183.

     long
     sum_list(PyObject *list)
     {
         Py_ssize_t i, n;
         long total = 0, value;
         PyObject *item;

         n = PyList_Size(list);
         if (n < 0)
             return -1; /* Not a list */
         for (i = 0; i < n; i++) {
             item = PyList_GetItem(list, i); /* Can't fail */
             if (!PyLong_Check(item)) continue; /* Skip non-integers */
             value = PyLong_AsLong(item);
             if (value == -1 && PyErr_Occurred())
                 /* Integer too big to fit in a C long, bail out */
                 return -1;
             total += value;
         }
         return total;
     }

     long
     sum_sequence(PyObject *sequence)
     {
         Py_ssize_t i, n;
         long total = 0, value;
         PyObject *item;
         n = PySequence_Length(sequence);
         if (n < 0)
             return -1; /* Has no length */
         for (i = 0; i < n; i++) {
             item = PySequence_GetItem(sequence, i);
             if (item == NULL)
                 return -1; /* Not a sequence, or other failure */
             if (PyLong_Check(item)) {
                 value = PyLong_AsLong(item);
                 Py_DECREF(item);
                 if (value == -1 && PyErr_Occurred())
                     /* Integer too big to fit in a C long, bail out */
                     return -1;
                 total += value;
             }
             else {
                 Py_DECREF(item); /* Discard reference ownership */
             }
         }
         return total;
     }


File: python.info,  Node: Types,  Prev: Reference Counts<2>,  Up: Objects Types and Reference Counts

7.1.4.3 Types
.............

There are few other data types that play a significant role in the
Python/C API; most are simple C types such as ‘int’, ‘long’, ‘double’
and ‘char*’.  A few structure types are used to describe static tables
used to list the functions exported by a module or the data attributes
of a new object type, and another is used to describe the value of a
complex number.  These will be discussed together with the functions
that use them.


File: python.info,  Node: Exceptions<19>,  Next: Embedding Python<2>,  Prev: Objects Types and Reference Counts,  Up: Introduction<13>

7.1.5 Exceptions
----------------

The Python programmer only needs to deal with exceptions if specific
error handling is required; unhandled exceptions are automatically
propagated to the caller, then to the caller’s caller, and so on, until
they reach the top-level interpreter, where they are reported to the
user accompanied by a stack traceback.

For C programmers, however, error checking always has to be explicit.
All functions in the Python/C API can raise exceptions, unless an
explicit claim is made otherwise in a function’s documentation.  In
general, when a function encounters an error, it sets an exception,
discards any object references that it owns, and returns an error
indicator.  If not documented otherwise, this indicator is either ‘NULL’
or ‘-1’, depending on the function’s return type.  A few functions
return a Boolean true/false result, with false indicating an error.
Very few functions return no explicit error indicator or have an
ambiguous return value, and require explicit testing for errors with
*note PyErr_Occurred(): 3d1a.  These exceptions are always explicitly
documented.

Exception state is maintained in per-thread storage (this is equivalent
to using global storage in an unthreaded application).  A thread can be
in one of two states: an exception has occurred, or not.  The function
*note PyErr_Occurred(): 3d1a. can be used to check for this: it returns
a borrowed reference to the exception type object when an exception has
occurred, and ‘NULL’ otherwise.  There are a number of functions to set
the exception state: *note PyErr_SetString(): 3d17. is the most common
(though not the most general) function to set the exception state, and
*note PyErr_Clear(): a4c. clears the exception state.

The full exception state consists of three objects (all of which can be
‘NULL’): the exception type, the corresponding exception value, and the
traceback.  These have the same meanings as the Python result of
‘sys.exc_info()’; however, they are not the same: the Python objects
represent the last exception being handled by a Python *note try: e37. …
*note except: c10. statement, while the C level exception state only
exists while an exception is being passed on between C functions until
it reaches the Python bytecode interpreter’s main loop, which takes care
of transferring it to ‘sys.exc_info()’ and friends.

Note that starting with Python 1.5, the preferred, thread-safe way to
access the exception state from Python code is to call the function
*note sys.exc_info(): d27, which returns the per-thread exception state
for Python code.  Also, the semantics of both ways to access the
exception state have changed so that a function which catches an
exception will save and restore its thread’s exception state so as to
preserve the exception state of its caller.  This prevents common bugs
in exception handling code caused by an innocent-looking function
overwriting the exception being handled; it also reduces the often
unwanted lifetime extension for objects that are referenced by the stack
frames in the traceback.

As a general principle, a function that calls another function to
perform some task should check whether the called function raised an
exception, and if so, pass the exception state on to its caller.  It
should discard any object references that it owns, and return an error
indicator, but it should `not' set another exception — that would
overwrite the exception that was just raised, and lose important
information about the exact cause of the error.

A simple example of detecting exceptions and passing them on is shown in
the ‘sum_sequence()’ example above.  It so happens that this example
doesn’t need to clean up any owned references when it detects an error.
The following example function shows some error cleanup.  First, to
remind you why you like Python, we show the equivalent Python code:

     def incr_item(dict, key):
         try:
             item = dict[key]
         except KeyError:
             item = 0
         dict[key] = item + 1

Here is the corresponding C code, in all its glory:

     int
     incr_item(PyObject *dict, PyObject *key)
     {
         /* Objects all initialized to NULL for Py_XDECREF */
         PyObject *item = NULL, *const_one = NULL, *incremented_item = NULL;
         int rv = -1; /* Return value initialized to -1 (failure) */

         item = PyObject_GetItem(dict, key);
         if (item == NULL) {
             /* Handle KeyError only: */
             if (!PyErr_ExceptionMatches(PyExc_KeyError))
                 goto error;

             /* Clear the error and use zero: */
             PyErr_Clear();
             item = PyLong_FromLong(0L);
             if (item == NULL)
                 goto error;
         }
         const_one = PyLong_FromLong(1L);
         if (const_one == NULL)
             goto error;

         incremented_item = PyNumber_Add(item, const_one);
         if (incremented_item == NULL)
             goto error;

         if (PyObject_SetItem(dict, key, incremented_item) < 0)
             goto error;
         rv = 0; /* Success */
         /* Continue with cleanup code */

      error:
         /* Cleanup code, shared by success and failure path */

         /* Use Py_XDECREF() to ignore NULL references */
         Py_XDECREF(item);
         Py_XDECREF(const_one);
         Py_XDECREF(incremented_item);

         return rv; /* -1 for error, 0 for success */
     }

This example represents an endorsed use of the ‘goto’ statement in C! It
illustrates the use of *note PyErr_ExceptionMatches(): 3dcc. and *note
PyErr_Clear(): a4c. to handle specific exceptions, and the use of *note
Py_XDECREF(): 391. to dispose of owned references that may be ‘NULL’
(note the ‘'X'’ in the name; *note Py_DECREF(): 38f. would crash when
confronted with a ‘NULL’ reference).  It is important that the variables
used to hold owned references are initialized to ‘NULL’ for this to
work; likewise, the proposed return value is initialized to ‘-1’
(failure) and only set to success after the final call made is
successful.


File: python.info,  Node: Embedding Python<2>,  Next: Debugging Builds,  Prev: Exceptions<19>,  Up: Introduction<13>

7.1.6 Embedding Python
----------------------

The one important task that only embedders (as opposed to extension
writers) of the Python interpreter have to worry about is the
initialization, and possibly the finalization, of the Python
interpreter.  Most functionality of the interpreter can only be used
after the interpreter has been initialized.

The basic initialization function is *note Py_Initialize(): 20f.  This
initializes the table of loaded modules, and creates the fundamental
modules *note builtins: 12, *note __main__: 1, and *note sys: fd.  It
also initializes the module search path (‘sys.path’).

*note Py_Initialize(): 20f. does not set the “script argument list”
(‘sys.argv’).  If this variable is needed by Python code that will be
executed later, it must be set explicitly with a call to
‘PySys_SetArgvEx(argc, argv, updatepath)’ after the call to *note
Py_Initialize(): 20f.

On most systems (in particular, on Unix and Windows, although the
details are slightly different), *note Py_Initialize(): 20f. calculates
the module search path based upon its best guess for the location of the
standard Python interpreter executable, assuming that the Python library
is found in a fixed location relative to the Python interpreter
executable.  In particular, it looks for a directory named
‘lib/python`X.Y'’ relative to the parent directory where the executable
named ‘python’ is found on the shell command search path (the
environment variable ‘PATH’).

For instance, if the Python executable is found in
‘/usr/local/bin/python’, it will assume that the libraries are in
‘/usr/local/lib/python`X.Y'’.  (In fact, this particular path is also
the “fallback” location, used when no executable file named ‘python’ is
found along ‘PATH’.)  The user can override this behavior by setting the
environment variable *note PYTHONHOME: 5d1, or insert additional
directories in front of the standard path by setting *note PYTHONPATH:
a34.

The embedding application can steer the search by calling
‘Py_SetProgramName(file)’ `before' calling *note Py_Initialize(): 20f.
Note that *note PYTHONHOME: 5d1. still overrides this and *note
PYTHONPATH: a34. is still inserted in front of the standard path.  An
application that requires total control has to provide its own
implementation of *note Py_GetPath(): 3dcf, *note Py_GetPrefix(): 3dd0,
*note Py_GetExecPrefix(): 3dd1, and *note Py_GetProgramFullPath(): 39e.
(all defined in ‘Modules/getpath.c’).

Sometimes, it is desirable to “uninitialize” Python.  For instance, the
application may want to start over (make another call to *note
Py_Initialize(): 20f.) or the application is simply done with its use of
Python and wants to free memory allocated by Python.  This can be
accomplished by calling *note Py_FinalizeEx(): 6c0.  The function *note
Py_IsInitialized(): 3dd2. returns true if Python is currently in the
initialized state.  More information about these functions is given in a
later chapter.  Notice that *note Py_FinalizeEx(): 6c0. does `not' free
all memory allocated by the Python interpreter, e.g.  memory allocated
by extension modules currently cannot be released.


File: python.info,  Node: Debugging Builds,  Prev: Embedding Python<2>,  Up: Introduction<13>

7.1.7 Debugging Builds
----------------------

Python can be built with several macros to enable extra checks of the
interpreter and extension modules.  These checks tend to add a large
amount of overhead to the runtime so they are not enabled by default.

A full list of the various types of debugging builds is in the file
‘Misc/SpecialBuilds.txt’ in the Python source distribution.  Builds are
available that support tracing of reference counts, debugging the memory
allocator, or low-level profiling of the main interpreter loop.  Only
the most frequently-used builds will be described in the remainder of
this section.

Compiling the interpreter with the ‘Py_DEBUG’ macro defined produces
what is generally meant by “a debug build” of Python.  ‘Py_DEBUG’ is
enabled in the Unix build by adding ‘--with-pydebug’ to the
‘./configure’ command.  It is also implied by the presence of the
not-Python-specific ‘_DEBUG’ macro.  When ‘Py_DEBUG’ is enabled in the
Unix build, compiler optimization is disabled.

In addition to the reference count debugging described below, the
following extra checks are performed:

   * Extra checks are added to the object allocator.

   * Extra checks are added to the parser and compiler.

   * Downcasts from wide types to narrow types are checked for loss of
     information.

   * A number of assertions are added to the dictionary and set
     implementations.  In addition, the set object acquires a
     ‘test_c_api()’ method.

   * Sanity checks of the input arguments are added to frame creation.

   * The storage for ints is initialized with a known invalid pattern to
     catch reference to uninitialized digits.

   * Low-level tracing and extra exception checking are added to the
     runtime virtual machine.

   * Extra checks are added to the memory arena implementation.

   * Extra debugging is added to the thread module.

There may be additional checks not mentioned here.

Defining ‘Py_TRACE_REFS’ enables reference tracing.  When defined, a
circular doubly linked list of active objects is maintained by adding
two extra fields to every *note PyObject: 5b5.  Total allocations are
tracked as well.  Upon exit, all existing references are printed.  (In
interactive mode this happens after every statement run by the
interpreter.)  Implied by ‘Py_DEBUG’.

Please refer to ‘Misc/SpecialBuilds.txt’ in the Python source
distribution for more detailed information.


File: python.info,  Node: Stable Application Binary Interface,  Next: The Very High Level Layer,  Prev: Introduction<13>,  Up: Python/C API Reference Manual

7.2 Stable Application Binary Interface
=======================================

Traditionally, the C API of Python will change with every release.  Most
changes will be source-compatible, typically by only adding API, rather
than changing existing API or removing API (although some interfaces do
get removed after being deprecated first).

Unfortunately, the API compatibility does not extend to binary
compatibility (the ABI). The reason is primarily the evolution of struct
definitions, where addition of a new field, or changing the type of a
field, might not break the API, but can break the ABI. As a consequence,
extension modules need to be recompiled for every Python release
(although an exception is possible on Unix when none of the affected
interfaces are used).  In addition, on Windows, extension modules link
with a specific pythonXY.dll and need to be recompiled to link with a
newer one.

Since Python 3.2, a subset of the API has been declared to guarantee a
stable ABI. Extension modules wishing to use this API (called “limited
API”) need to define ‘Py_LIMITED_API’.  A number of interpreter details
then become hidden from the extension module; in return, a module is
built that works on any 3.x version (x>=2) without recompilation.

In some cases, the stable ABI needs to be extended with new functions.
Extension modules wishing to use these new APIs need to set
‘Py_LIMITED_API’ to the ‘PY_VERSION_HEX’ value (see *note API and ABI
Versioning: 37b9.) of the minimum Python version they want to support
(e.g.  ‘0x03030000’ for Python 3.3).  Such modules will work on all
subsequent Python releases, but fail to load (because of missing
symbols) on the older releases.

As of Python 3.2, the set of functions available to the limited API is
documented in PEP 384(1).  In the C API documentation, API elements that
are not part of the limited API are marked as “Not part of the limited
API.”

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0384


File: python.info,  Node: The Very High Level Layer,  Next: Reference Counting,  Prev: Stable Application Binary Interface,  Up: Python/C API Reference Manual

7.3 The Very High Level Layer
=============================

The functions in this chapter will let you execute Python source code
given in a file or a buffer, but they will not let you interact in a
more detailed way with the interpreter.

Several of these functions accept a start symbol from the grammar as a
parameter.  The available start symbols are ‘Py_eval_input’,
‘Py_file_input’, and ‘Py_single_input’.  These are described following
the functions which accept them as parameters.

Note also that several of these functions take ‘FILE*’ parameters.  One
particular issue which needs to be handled carefully is that the ‘FILE’
structure for different C libraries can be different and incompatible.
Under Windows (at least), it is possible for dynamically linked
extensions to actually use different libraries, so care should be taken
that ‘FILE*’ parameters are only passed to these functions if it is
certain that they were created by the same library that the Python
runtime is using.

 -- C Function: int Py_Main (int argc, wchar_t **argv)

     The main program for the standard interpreter.  This is made
     available for programs which embed Python.  The `argc' and `argv'
     parameters should be prepared exactly as those which are passed to
     a C program’s ‘main()’ function (converted to wchar_t according to
     the user’s locale).  It is important to note that the argument list
     may be modified (but the contents of the strings pointed to by the
     argument list are not).  The return value will be ‘0’ if the
     interpreter exits normally (i.e., without an exception), ‘1’ if the
     interpreter exits due to an exception, or ‘2’ if the parameter list
     does not represent a valid Python command line.

     Note that if an otherwise unhandled *note SystemExit: 6f3. is
     raised, this function will not return ‘1’, but exit the process, as
     long as ‘Py_InspectFlag’ is not set.

 -- C Function: int Py_BytesMain (int argc, char **argv)

     Similar to *note Py_Main(): 5b2. but `argv' is an array of bytes
     strings.

     New in version 3.8.

 -- C Function: int PyRun_AnyFile (FILE *fp, const char *filename)

     This is a simplified interface to *note PyRun_AnyFileExFlags():
     3ddc. below, leaving `closeit' set to ‘0’ and `flags' set to
     ‘NULL’.

 -- C Function: int PyRun_AnyFileFlags (FILE *fp, const char *filename,
          PyCompilerFlags *flags)

     This is a simplified interface to *note PyRun_AnyFileExFlags():
     3ddc. below, leaving the `closeit' argument set to ‘0’.

 -- C Function: int PyRun_AnyFileEx (FILE *fp, const char *filename,
          int closeit)

     This is a simplified interface to *note PyRun_AnyFileExFlags():
     3ddc. below, leaving the `flags' argument set to ‘NULL’.

 -- C Function: int PyRun_AnyFileExFlags (FILE *fp, const
          char *filename, int closeit, PyCompilerFlags *flags)

     If `fp' refers to a file associated with an interactive device
     (console or terminal input or Unix pseudo-terminal), return the
     value of *note PyRun_InteractiveLoop(): 3ddf, otherwise return the
     result of *note PyRun_SimpleFile(): 3d9d.  `filename' is decoded
     from the filesystem encoding (*note sys.getfilesystemencoding():
     5f0.).  If `filename' is ‘NULL’, this function uses ‘"???"’ as the
     filename.

 -- C Function: int PyRun_SimpleString (const char *command)

     This is a simplified interface to *note PyRun_SimpleStringFlags():
     3de0. below, leaving the *note PyCompilerFlags: 3ee.* argument set
     to ‘NULL’.

 -- C Function: int PyRun_SimpleStringFlags (const char *command,
          PyCompilerFlags *flags)

     Executes the Python source code from `command' in the *note
     __main__: 1. module according to the `flags' argument.  If *note
     __main__: 1. does not already exist, it is created.  Returns ‘0’ on
     success or ‘-1’ if an exception was raised.  If there was an error,
     there is no way to get the exception information.  For the meaning
     of `flags', see below.

     Note that if an otherwise unhandled *note SystemExit: 6f3. is
     raised, this function will not return ‘-1’, but exit the process,
     as long as ‘Py_InspectFlag’ is not set.

 -- C Function: int PyRun_SimpleFile (FILE *fp, const char *filename)

     This is a simplified interface to *note PyRun_SimpleFileExFlags():
     fc7. below, leaving `closeit' set to ‘0’ and `flags' set to ‘NULL’.

 -- C Function: int PyRun_SimpleFileEx (FILE *fp, const char *filename,
          int closeit)

     This is a simplified interface to *note PyRun_SimpleFileExFlags():
     fc7. below, leaving `flags' set to ‘NULL’.

 -- C Function: int PyRun_SimpleFileExFlags (FILE *fp, const
          char *filename, int closeit, PyCompilerFlags *flags)

     Similar to *note PyRun_SimpleStringFlags(): 3de0, but the Python
     source code is read from `fp' instead of an in-memory string.
     `filename' should be the name of the file, it is decoded from the
     filesystem encoding (*note sys.getfilesystemencoding(): 5f0.).  If
     `closeit' is true, the file is closed before
     PyRun_SimpleFileExFlags returns.

          Note: On Windows, `fp' should be opened as binary mode (e.g.
          ‘fopen(filename, "rb")’).  Otherwise, Python may not handle
          script file with LF line ending correctly.

 -- C Function: int PyRun_InteractiveOne (FILE *fp, const
          char *filename)

     This is a simplified interface to *note
     PyRun_InteractiveOneFlags(): 3de3. below, leaving `flags' set to
     ‘NULL’.

 -- C Function: int PyRun_InteractiveOneFlags (FILE *fp, const
          char *filename, PyCompilerFlags *flags)

     Read and execute a single statement from a file associated with an
     interactive device according to the `flags' argument.  The user
     will be prompted using ‘sys.ps1’ and ‘sys.ps2’.  `filename' is
     decoded from the filesystem encoding (*note
     sys.getfilesystemencoding(): 5f0.).

     Returns ‘0’ when the input was executed successfully, ‘-1’ if there
     was an exception, or an error code from the ‘errcode.h’ include
     file distributed as part of Python if there was a parse error.
     (Note that ‘errcode.h’ is not included by ‘Python.h’, so must be
     included specifically if needed.)

 -- C Function: int PyRun_InteractiveLoop (FILE *fp, const
          char *filename)

     This is a simplified interface to *note
     PyRun_InteractiveLoopFlags(): 3de4. below, leaving `flags' set to
     ‘NULL’.

 -- C Function: int PyRun_InteractiveLoopFlags (FILE *fp, const
          char *filename, PyCompilerFlags *flags)

     Read and execute statements from a file associated with an
     interactive device until EOF is reached.  The user will be prompted
     using ‘sys.ps1’ and ‘sys.ps2’.  `filename' is decoded from the
     filesystem encoding (*note sys.getfilesystemencoding(): 5f0.).
     Returns ‘0’ at EOF or a negative number upon failure.

 -- C Variable: int (*PyOS_InputHook) (void)

     Can be set to point to a function with the prototype ‘int
     func(void)’.  The function will be called when Python’s interpreter
     prompt is about to become idle and wait for user input from the
     terminal.  The return value is ignored.  Overriding this hook can
     be used to integrate the interpreter’s prompt with other event
     loops, as done in the ‘Modules/_tkinter.c’ in the Python source
     code.

 -- C Variable: char* (*PyOS_ReadlineFunctionPointer) (FILE *, FILE *,
          const char *)

     Can be set to point to a function with the prototype ‘char
     *func(FILE *stdin, FILE *stdout, char *prompt)’, overriding the
     default function used to read a single line of input at the
     interpreter’s prompt.  The function is expected to output the
     string `prompt' if it’s not ‘NULL’, and then read a line of input
     from the provided standard input file, returning the resulting
     string.  For example, The *note readline: de. module sets this hook
     to provide line-editing and tab-completion features.

     The result must be a string allocated by *note PyMem_RawMalloc():
     a4e. or *note PyMem_RawRealloc(): a4f, or ‘NULL’ if an error
     occurred.

     Changed in version 3.4: The result must be allocated by *note
     PyMem_RawMalloc(): a4e. or *note PyMem_RawRealloc(): a4f, instead
     of being allocated by *note PyMem_Malloc(): 5ff. or *note
     PyMem_Realloc(): a50.

 -- C Function: struct _node* PyParser_SimpleParseString (const
          char *str, int start)

     This is a simplified interface to *note
     PyParser_SimpleParseStringFlagsFilename(): 200. below, leaving
     `filename' set to ‘NULL’ and `flags' set to ‘0’.

     Deprecated since version 3.9, will be removed in version 3.10.

 -- C Function: struct _node* PyParser_SimpleParseStringFlags (const
          char *str, int start, int flags)

     This is a simplified interface to *note
     PyParser_SimpleParseStringFlagsFilename(): 200. below, leaving
     `filename' set to ‘NULL’.

     Deprecated since version 3.9, will be removed in version 3.10.

 -- C Function: struct _node* PyParser_SimpleParseStringFlagsFilename
          (const char *str, const char *filename, int start, int flags)

     Parse Python source code from `str' using the start token `start'
     according to the `flags' argument.  The result can be used to
     create a code object which can be evaluated efficiently.  This is
     useful if a code fragment must be evaluated many times.  `filename'
     is decoded from the filesystem encoding (*note
     sys.getfilesystemencoding(): 5f0.).

     Deprecated since version 3.9, will be removed in version 3.10.

 -- C Function: struct _node* PyParser_SimpleParseFile (FILE *fp, const
          char *filename, int start)

     This is a simplified interface to *note
     PyParser_SimpleParseFileFlags(): 201. below, leaving `flags' set to
     ‘0’.

     Deprecated since version 3.9, will be removed in version 3.10.

 -- C Function: struct _node* PyParser_SimpleParseFileFlags (FILE *fp,
          const char *filename, int start, int flags)

     Similar to *note PyParser_SimpleParseStringFlagsFilename(): 200,
     but the Python source code is read from `fp' instead of an
     in-memory string.

     Deprecated since version 3.9, will be removed in version 3.10.

 -- C Function: PyObject* PyRun_String (const char *str, int start,
          PyObject *globals, PyObject *locals)
     `Return value: New reference.'  This is a simplified interface to
     *note PyRun_StringFlags(): 3de8. below, leaving `flags' set to
     ‘NULL’.

 -- C Function: PyObject* PyRun_StringFlags (const char *str, int start,
          PyObject *globals, PyObject *locals, PyCompilerFlags *flags)
     `Return value: New reference.'  Execute Python source code from
     `str' in the context specified by the objects `globals' and
     `locals' with the compiler flags specified by `flags'.  `globals'
     must be a dictionary; `locals' can be any object that implements
     the mapping protocol.  The parameter `start' specifies the start
     token that should be used to parse the source code.

     Returns the result of executing the code as a Python object, or
     ‘NULL’ if an exception was raised.

 -- C Function: PyObject* PyRun_File (FILE *fp, const char *filename,
          int start, PyObject *globals, PyObject *locals)
     `Return value: New reference.'  This is a simplified interface to
     *note PyRun_FileExFlags(): 3dea. below, leaving `closeit' set to
     ‘0’ and `flags' set to ‘NULL’.

 -- C Function: PyObject* PyRun_FileEx (FILE *fp, const char *filename,
          int start, PyObject *globals, PyObject *locals, int closeit)
     `Return value: New reference.'  This is a simplified interface to
     *note PyRun_FileExFlags(): 3dea. below, leaving `flags' set to
     ‘NULL’.

 -- C Function: PyObject* PyRun_FileFlags (FILE *fp, const
          char *filename, int start, PyObject *globals,
          PyObject *locals, PyCompilerFlags *flags)
     `Return value: New reference.'  This is a simplified interface to
     *note PyRun_FileExFlags(): 3dea. below, leaving `closeit' set to
     ‘0’.

 -- C Function: PyObject* PyRun_FileExFlags (FILE *fp, const
          char *filename, int start, PyObject *globals,
          PyObject *locals, int closeit, PyCompilerFlags *flags)
     `Return value: New reference.'  Similar to *note
     PyRun_StringFlags(): 3de8, but the Python source code is read from
     `fp' instead of an in-memory string.  `filename' should be the name
     of the file, it is decoded from the filesystem encoding (*note
     sys.getfilesystemencoding(): 5f0.).  If `closeit' is true, the file
     is closed before *note PyRun_FileExFlags(): 3dea. returns.

 -- C Function: PyObject* Py_CompileString (const char *str, const
          char *filename, int start)
     `Return value: New reference.'  This is a simplified interface to
     *note Py_CompileStringFlags(): 3dee. below, leaving `flags' set to
     ‘NULL’.

 -- C Function: PyObject* Py_CompileStringFlags (const char *str, const
          char *filename, int start, PyCompilerFlags *flags)
     `Return value: New reference.'  This is a simplified interface to
     *note Py_CompileStringExFlags(): 3def. below, with `optimize' set
     to ‘-1’.

 -- C Function: PyObject* Py_CompileStringObject (const char *str,
          PyObject *filename, int start, PyCompilerFlags *flags,
          int optimize)
     `Return value: New reference.'  Parse and compile the Python source
     code in `str', returning the resulting code object.  The start
     token is given by `start'; this can be used to constrain the code
     which can be compiled and should be ‘Py_eval_input’,
     ‘Py_file_input’, or ‘Py_single_input’.  The filename specified by
     `filename' is used to construct the code object and may appear in
     tracebacks or *note SyntaxError: 55a. exception messages.  This
     returns ‘NULL’ if the code cannot be parsed or compiled.

     The integer `optimize' specifies the optimization level of the
     compiler; a value of ‘-1’ selects the optimization level of the
     interpreter as given by *note -O: 77e. options.  Explicit levels
     are ‘0’ (no optimization; ‘__debug__’ is true), ‘1’ (asserts are
     removed, ‘__debug__’ is false) or ‘2’ (docstrings are removed too).

     New in version 3.4.

 -- C Function: PyObject* Py_CompileStringExFlags (const char *str,
          const char *filename, int start, PyCompilerFlags *flags,
          int optimize)
     `Return value: New reference.'  Like *note
     Py_CompileStringObject(): 3df0, but `filename' is a byte string
     decoded from the filesystem encoding (*note os.fsdecode(): 5e9.).

     New in version 3.2.

 -- C Function: PyObject* PyEval_EvalCode (PyObject *co,
          PyObject *globals, PyObject *locals)
     `Return value: New reference.'  This is a simplified interface to
     *note PyEval_EvalCodeEx(): 3df2, with just the code object, and
     global and local variables.  The other arguments are set to ‘NULL’.

 -- C Function: PyObject* PyEval_EvalCodeEx (PyObject *co,
          PyObject *globals, PyObject *locals, PyObject *const *args,
          int argcount, PyObject *const *kws, int kwcount, PyObject
          *const *defs, int defcount, PyObject *kwdefs,
          PyObject *closure)
     `Return value: New reference.'  Evaluate a precompiled code object,
     given a particular environment for its evaluation.  This
     environment consists of a dictionary of global variables, a mapping
     object of local variables, arrays of arguments, keywords and
     defaults, a dictionary of default values for *note keyword-only:
     3ce. arguments and a closure tuple of cells.

 -- C Type: PyFrameObject

     The C structure of the objects used to describe frame objects.  The
     fields of this type are subject to change at any time.

 -- C Function: PyObject* PyEval_EvalFrame (PyFrameObject *f)
     `Return value: New reference.'  Evaluate an execution frame.  This
     is a simplified interface to *note PyEval_EvalFrameEx(): a48, for
     backward compatibility.

 -- C Function: PyObject* PyEval_EvalFrameEx (PyFrameObject *f,
          int throwflag)
     `Return value: New reference.'  This is the main, unvarnished
     function of Python interpretation.  The code object associated with
     the execution frame `f' is executed, interpreting bytecode and
     executing calls as needed.  The additional `throwflag' parameter
     can mostly be ignored - if true, then it causes an exception to
     immediately be thrown; this is used for the *note throw(): ff8.
     methods of generator objects.

     Changed in version 3.4: This function now includes a debug
     assertion to help ensure that it does not silently discard an
     active exception.

 -- C Function: int PyEval_MergeCompilerFlags (PyCompilerFlags *cf)

     This function changes the flags of the current evaluation frame,
     and returns true on success, false on failure.

 -- C Variable: int Py_eval_input

     The start symbol from the Python grammar for isolated expressions;
     for use with *note Py_CompileString(): 3ded.

 -- C Variable: int Py_file_input

     The start symbol from the Python grammar for sequences of
     statements as read from a file or other source; for use with *note
     Py_CompileString(): 3ded.  This is the symbol to use when compiling
     arbitrarily long Python source code.

 -- C Variable: int Py_single_input

     The start symbol from the Python grammar for a single statement;
     for use with *note Py_CompileString(): 3ded.  This is the symbol
     used for the interactive interpreter loop.

 -- C Type: struct PyCompilerFlags

     This is the structure used to hold compiler flags.  In cases where
     code is only being compiled, it is passed as ‘int flags’, and in
     cases where code is being executed, it is passed as
     ‘PyCompilerFlags *flags’.  In this case, ‘from __future__ import’
     can modify `flags'.

     Whenever ‘PyCompilerFlags *flags’ is ‘NULL’, ‘cf_flags’ is treated
     as equal to ‘0’, and any modification due to ‘from __future__
     import’ is discarded.

      -- C Member: int cf_flags

          Compiler flags.

      -- C Member: int cf_feature_version

          `cf_feature_version' is the minor Python version.  It should
          be initialized to ‘PY_MINOR_VERSION’.

          The field is ignored by default, it is used if and only if
          ‘PyCF_ONLY_AST’ flag is set in `cf_flags'.

     Changed in version 3.8: Added `cf_feature_version' field.

 -- C Variable: int CO_FUTURE_DIVISION

     This bit can be set in `flags' to cause division operator ‘/’ to be
     interpreted as “true division” according to PEP 238(1).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0238


File: python.info,  Node: Reference Counting,  Next: Exception Handling,  Prev: The Very High Level Layer,  Up: Python/C API Reference Manual

7.4 Reference Counting
======================

The macros in this section are used for managing reference counts of
Python objects.

 -- C Function: void Py_INCREF (PyObject *o)

     Increment the reference count for object `o'.  The object must not
     be ‘NULL’; if you aren’t sure that it isn’t ‘NULL’, use *note
     Py_XINCREF(): 390.

 -- C Function: void Py_XINCREF (PyObject *o)

     Increment the reference count for object `o'.  The object may be
     ‘NULL’, in which case the macro has no effect.

 -- C Function: void Py_DECREF (PyObject *o)

     Decrement the reference count for object `o'.  The object must not
     be ‘NULL’; if you aren’t sure that it isn’t ‘NULL’, use *note
     Py_XDECREF(): 391.  If the reference count reaches zero, the
     object’s type’s deallocation function (which must not be ‘NULL’) is
     invoked.

          Warning: The deallocation function can cause arbitrary Python
          code to be invoked (e.g.  when a class instance with a *note
          __del__(): a04. method is deallocated).  While exceptions in
          such code are not propagated, the executed code has free
          access to all Python global variables.  This means that any
          object that is reachable from a global variable should be in a
          consistent state before *note Py_DECREF(): 38f. is invoked.
          For example, code to delete an object from a list should copy
          a reference to the deleted object in a temporary variable,
          update the list data structure, and then call *note
          Py_DECREF(): 38f. for the temporary variable.

 -- C Function: void Py_XDECREF (PyObject *o)

     Decrement the reference count for object `o'.  The object may be
     ‘NULL’, in which case the macro has no effect; otherwise the effect
     is the same as for *note Py_DECREF(): 38f, and the same warning
     applies.

 -- C Function: void Py_CLEAR (PyObject *o)

     Decrement the reference count for object `o'.  The object may be
     ‘NULL’, in which case the macro has no effect; otherwise the effect
     is the same as for *note Py_DECREF(): 38f, except that the argument
     is also set to ‘NULL’.  The warning for *note Py_DECREF(): 38f.
     does not apply with respect to the object passed because the macro
     carefully uses a temporary variable and sets the argument to ‘NULL’
     before decrementing its reference count.

     It is a good idea to use this macro whenever decrementing the
     reference count of an object that might be traversed during garbage
     collection.

The following functions are for runtime dynamic embedding of Python:
‘Py_IncRef(PyObject *o)’, ‘Py_DecRef(PyObject *o)’.  They are simply
exported function versions of *note Py_XINCREF(): 390. and *note
Py_XDECREF(): 391, respectively.

The following functions or macros are only for use within the
interpreter core: ‘_Py_Dealloc()’, ‘_Py_ForgetReference()’,
‘_Py_NewReference()’, as well as the global variable ‘_Py_RefTotal’.


File: python.info,  Node: Exception Handling,  Next: Utilities<2>,  Prev: Reference Counting,  Up: Python/C API Reference Manual

7.5 Exception Handling
======================

The functions described in this chapter will let you handle and raise
Python exceptions.  It is important to understand some of the basics of
Python exception handling.  It works somewhat like the POSIX ‘errno’
variable: there is a global indicator (per thread) of the last error
that occurred.  Most C API functions don’t clear this on success, but
will set it to indicate the cause of the error on failure.  Most C API
functions also return an error indicator, usually ‘NULL’ if they are
supposed to return a pointer, or ‘-1’ if they return an integer
(exception: the ‘PyArg_*()’ functions return ‘1’ for success and ‘0’ for
failure).

Concretely, the error indicator consists of three object pointers: the
exception’s type, the exception’s value, and the traceback object.  Any
of those pointers can be ‘NULL’ if non-set (although some combinations
are forbidden, for example you can’t have a non-‘NULL’ traceback if the
exception type is ‘NULL’).

When a function must fail because some function it called failed, it
generally doesn’t set the error indicator; the function it called
already set it.  It is responsible for either handling the error and
clearing the exception or returning after cleaning up any resources it
holds (such as object references or memory allocations); it should `not'
continue normally if it is not prepared to handle the error.  If
returning due to an error, it is important to indicate to the caller
that an error has been set.  If the error is not handled or carefully
propagated, additional calls into the Python/C API may not behave as
intended and may fail in mysterious ways.

     Note: The error indicator is `not' the result of *note
     sys.exc_info(): d27.  The former corresponds to an exception that
     is not yet caught (and is therefore still propagating), while the
     latter returns an exception after it is caught (and has therefore
     stopped propagating).

* Menu:

* Printing and clearing::
* Raising exceptions::
* Issuing warnings::
* Querying the error indicator::
* Signal Handling: Signal Handling<2>.
* Exception Classes::
* Exception Objects::
* Unicode Exception Objects::
* Recursion Control::
* Standard Exceptions::
* Standard Warning Categories::


File: python.info,  Node: Printing and clearing,  Next: Raising exceptions,  Up: Exception Handling

7.5.1 Printing and clearing
---------------------------

 -- C Function: void PyErr_Clear ()

     Clear the error indicator.  If the error indicator is not set,
     there is no effect.

 -- C Function: void PyErr_PrintEx (int set_sys_last_vars)

     Print a standard traceback to ‘sys.stderr’ and clear the error
     indicator.  `Unless' the error is a ‘SystemExit’, in that case no
     traceback is printed and the Python process will exit with the
     error code specified by the ‘SystemExit’ instance.

     Call this function `only' when the error indicator is set.
     Otherwise it will cause a fatal error!

     If `set_sys_last_vars' is nonzero, the variables *note
     sys.last_type: d22, *note sys.last_value: 37ba. and *note
     sys.last_traceback: 36b4. will be set to the type, value and
     traceback of the printed exception, respectively.

 -- C Function: void PyErr_Print ()

     Alias for ‘PyErr_PrintEx(1)’.

 -- C Function: void PyErr_WriteUnraisable (PyObject *obj)

     Call *note sys.unraisablehook(): 35a. using the current exception
     and `obj' argument.

     This utility function prints a warning message to ‘sys.stderr’ when
     an exception has been set but it is impossible for the interpreter
     to actually raise the exception.  It is used, for example, when an
     exception occurs in an *note __del__(): a04. method.

     The function is called with a single argument `obj' that identifies
     the context in which the unraisable exception occurred.  If
     possible, the repr of `obj' will be printed in the warning message.

     An exception must be set when calling this function.


File: python.info,  Node: Raising exceptions,  Next: Issuing warnings,  Prev: Printing and clearing,  Up: Exception Handling

7.5.2 Raising exceptions
------------------------

These functions help you set the current thread’s error indicator.  For
convenience, some of these functions will always return a ‘NULL’ pointer
for use in a ‘return’ statement.

 -- C Function: void PyErr_SetString (PyObject *type, const
          char *message)

     This is the most common way to set the error indicator.  The first
     argument specifies the exception type; it is normally one of the
     standard exceptions, e.g.  ‘PyExc_RuntimeError’.  You need not
     increment its reference count.  The second argument is an error
     message; it is decoded from ‘'utf-8'’.

 -- C Function: void PyErr_SetObject (PyObject *type, PyObject *value)

     This function is similar to *note PyErr_SetString(): 3d17. but lets
     you specify an arbitrary Python object for the “value” of the
     exception.

 -- C Function: PyObject* PyErr_Format (PyObject *exception, const
          char *format, ...)
     `Return value: Always NULL.' This function sets the error indicator
     and returns ‘NULL’.  `exception' should be a Python exception
     class.  The `format' and subsequent parameters help format the
     error message; they have the same meaning and values as in *note
     PyUnicode_FromFormat(): 8b8.  `format' is an ASCII-encoded string.

 -- C Function: PyObject* PyErr_FormatV (PyObject *exception, const
          char *format, va_list vargs)
     `Return value: Always NULL.' Same as *note PyErr_Format(): 898, but
     taking a ‘va_list’ argument rather than a variable number of
     arguments.

     New in version 3.5.

 -- C Function: void PyErr_SetNone (PyObject *type)

     This is a shorthand for ‘PyErr_SetObject(type, Py_None)’.

 -- C Function: int PyErr_BadArgument ()

     This is a shorthand for ‘PyErr_SetString(PyExc_TypeError,
     message)’, where `message' indicates that a built-in operation was
     invoked with an illegal argument.  It is mostly for internal use.

 -- C Function: PyObject* PyErr_NoMemory ()
     `Return value: Always NULL.' This is a shorthand for
     ‘PyErr_SetNone(PyExc_MemoryError)’; it returns ‘NULL’ so an object
     allocation function can write ‘return PyErr_NoMemory();’ when it
     runs out of memory.

 -- C Function: PyObject* PyErr_SetFromErrno (PyObject *type)
     `Return value: Always NULL.'

     This is a convenience function to raise an exception when a C
     library function has returned an error and set the C variable
     ‘errno’.  It constructs a tuple object whose first item is the
     integer ‘errno’ value and whose second item is the corresponding
     error message (gotten from ‘strerror()’), and then calls
     ‘PyErr_SetObject(type, object)’.  On Unix, when the ‘errno’ value
     is ‘EINTR’, indicating an interrupted system call, this calls *note
     PyErr_CheckSignals(): 3e05, and if that set the error indicator,
     leaves it set to that.  The function always returns ‘NULL’, so a
     wrapper function around a system call can write ‘return
     PyErr_SetFromErrno(type);’ when the system call returns an error.

 -- C Function: PyObject* PyErr_SetFromErrnoWithFilenameObject
          (PyObject *type, PyObject *filenameObject)
     `Return value: Always NULL.' Similar to *note PyErr_SetFromErrno():
     3d18, with the additional behavior that if `filenameObject' is not
     ‘NULL’, it is passed to the constructor of `type' as a third
     parameter.  In the case of *note OSError: 304. exception, this is
     used to define the ‘filename’ attribute of the exception instance.

 -- C Function: PyObject* PyErr_SetFromErrnoWithFilenameObjects
          (PyObject *type, PyObject *filenameObject,
          PyObject *filenameObject2)
     `Return value: Always NULL.' Similar to *note
     PyErr_SetFromErrnoWithFilenameObject(): 3e06, but takes a second
     filename object, for raising errors when a function that takes two
     filenames fails.

     New in version 3.4.

 -- C Function: PyObject* PyErr_SetFromErrnoWithFilename
          (PyObject *type, const char *filename)
     `Return value: Always NULL.' Similar to *note
     PyErr_SetFromErrnoWithFilenameObject(): 3e06, but the filename is
     given as a C string.  `filename' is decoded from the filesystem
     encoding (*note os.fsdecode(): 5e9.).

 -- C Function: PyObject* PyErr_SetFromWindowsErr (int ierr)
     `Return value: Always NULL.' This is a convenience function to
     raise *note WindowsError: a75.  If called with `ierr' of ‘0’, the
     error code returned by a call to ‘GetLastError()’ is used instead.
     It calls the Win32 function ‘FormatMessage()’ to retrieve the
     Windows description of error code given by `ierr' or
     ‘GetLastError()’, then it constructs a tuple object whose first
     item is the `ierr' value and whose second item is the corresponding
     error message (gotten from ‘FormatMessage()’), and then calls
     ‘PyErr_SetObject(PyExc_WindowsError, object)’.  This function
     always returns ‘NULL’.

     *note Availability: 1491.: Windows.

 -- C Function: PyObject* PyErr_SetExcFromWindowsErr (PyObject *type,
          int ierr)
     `Return value: Always NULL.' Similar to *note
     PyErr_SetFromWindowsErr(): 3e09, with an additional parameter
     specifying the exception type to be raised.

     *note Availability: 1491.: Windows.

 -- C Function: PyObject* PyErr_SetFromWindowsErrWithFilename (int ierr,
          const char *filename)
     `Return value: Always NULL.' Similar to
     ‘PyErr_SetFromWindowsErrWithFilenameObject()’, but the filename is
     given as a C string.  `filename' is decoded from the filesystem
     encoding (*note os.fsdecode(): 5e9.).

     *note Availability: 1491.: Windows.

 -- C Function: PyObject* PyErr_SetExcFromWindowsErrWithFilenameObject
          (PyObject *type, int ierr, PyObject *filename)
     `Return value: Always NULL.' Similar to
     ‘PyErr_SetFromWindowsErrWithFilenameObject()’, with an additional
     parameter specifying the exception type to be raised.

     *note Availability: 1491.: Windows.

 -- C Function: PyObject* PyErr_SetExcFromWindowsErrWithFilenameObjects
          (PyObject *type, int ierr, PyObject *filename,
          PyObject *filename2)
     `Return value: Always NULL.' Similar to *note
     PyErr_SetExcFromWindowsErrWithFilenameObject(): 3e0c, but accepts a
     second filename object.

     *note Availability: 1491.: Windows.

     New in version 3.4.

 -- C Function: PyObject* PyErr_SetExcFromWindowsErrWithFilename
          (PyObject *type, int ierr, const char *filename)
     `Return value: Always NULL.' Similar to *note
     PyErr_SetFromWindowsErrWithFilename(): 3e0b, with an additional
     parameter specifying the exception type to be raised.

     *note Availability: 1491.: Windows.

 -- C Function: PyObject* PyErr_SetImportError (PyObject *msg,
          PyObject *name, PyObject *path)
     `Return value: Always NULL.' This is a convenience function to
     raise *note ImportError: 16c.  `msg' will be set as the exception’s
     message string.  `name' and `path', both of which can be ‘NULL’,
     will be set as the *note ImportError: 16c.’s respective ‘name’ and
     ‘path’ attributes.

     New in version 3.3.

 -- C Function: void PyErr_SyntaxLocationObject (PyObject *filename,
          int lineno, int col_offset)

     Set file, line, and offset information for the current exception.
     If the current exception is not a *note SyntaxError: 55a, then it
     sets additional attributes, which make the exception printing
     subsystem think the exception is a *note SyntaxError: 55a.

     New in version 3.4.

 -- C Function: void PyErr_SyntaxLocationEx (const char *filename,
          int lineno, int col_offset)

     Like *note PyErr_SyntaxLocationObject(): 3e0f, but `filename' is a
     byte string decoded from the filesystem encoding (*note
     os.fsdecode(): 5e9.).

     New in version 3.2.

 -- C Function: void PyErr_SyntaxLocation (const char *filename,
          int lineno)

     Like *note PyErr_SyntaxLocationEx(): 3e10, but the col_offset
     parameter is omitted.

 -- C Function: void PyErr_BadInternalCall ()

     This is a shorthand for ‘PyErr_SetString(PyExc_SystemError,
     message)’, where `message' indicates that an internal operation
     (e.g.  a Python/C API function) was invoked with an illegal
     argument.  It is mostly for internal use.


File: python.info,  Node: Issuing warnings,  Next: Querying the error indicator,  Prev: Raising exceptions,  Up: Exception Handling

7.5.3 Issuing warnings
----------------------

Use these functions to issue warnings from C code.  They mirror similar
functions exported by the Python *note warnings: 12f. module.  They
normally print a warning message to `sys.stderr'; however, it is also
possible that the user has specified that warnings are to be turned into
errors, and in that case they will raise an exception.  It is also
possible that the functions raise an exception because of a problem with
the warning machinery.  The return value is ‘0’ if no exception is
raised, or ‘-1’ if an exception is raised.  (It is not possible to
determine whether a warning message is actually printed, nor what the
reason is for the exception; this is intentional.)  If an exception is
raised, the caller should do its normal exception handling (for example,
*note Py_DECREF(): 38f. owned references and return an error value).

 -- C Function: int PyErr_WarnEx (PyObject *category, const
          char *message, Py_ssize_t stack_level)

     Issue a warning message.  The `category' argument is a warning
     category (see below) or ‘NULL’; the `message' argument is a UTF-8
     encoded string.  `stack_level' is a positive number giving a number
     of stack frames; the warning will be issued from the currently
     executing line of code in that stack frame.  A `stack_level' of 1
     is the function calling *note PyErr_WarnEx(): e76, 2 is the
     function above that, and so forth.

     Warning categories must be subclasses of ‘PyExc_Warning’;
     ‘PyExc_Warning’ is a subclass of ‘PyExc_Exception’; the default
     warning category is ‘PyExc_RuntimeWarning’.  The standard Python
     warning categories are available as global variables whose names
     are enumerated at *note Standard Warning Categories: 3e14.

     For information about warning control, see the documentation for
     the *note warnings: 12f. module and the *note -W: 15b. option in
     the command line documentation.  There is no C API for warning
     control.

 -- C Function: PyObject* PyErr_SetImportErrorSubclass
          (PyObject *exception, PyObject *msg, PyObject *name,
          PyObject *path)
     `Return value: Always NULL.' Much like *note
     PyErr_SetImportError(): 6ef. but this function allows for
     specifying a subclass of *note ImportError: 16c. to raise.

     New in version 3.6.

 -- C Function: int PyErr_WarnExplicitObject (PyObject *category,
          PyObject *message, PyObject *filename, int lineno,
          PyObject *module, PyObject *registry)

     Issue a warning message with explicit control over all warning
     attributes.  This is a straightforward wrapper around the Python
     function *note warnings.warn_explicit(): 6a7, see there for more
     information.  The `module' and `registry' arguments may be set to
     ‘NULL’ to get the default effect described there.

     New in version 3.4.

 -- C Function: int PyErr_WarnExplicit (PyObject *category, const
          char *message, const char *filename, int lineno, const
          char *module, PyObject *registry)

     Similar to *note PyErr_WarnExplicitObject(): 3e15. except that
     `message' and `module' are UTF-8 encoded strings, and `filename' is
     decoded from the filesystem encoding (*note os.fsdecode(): 5e9.).

 -- C Function: int PyErr_WarnFormat (PyObject *category,
          Py_ssize_t stack_level, const char *format, ...)

     Function similar to *note PyErr_WarnEx(): e76, but use *note
     PyUnicode_FromFormat(): 8b8. to format the warning message.
     `format' is an ASCII-encoded string.

     New in version 3.2.

 -- C Function: int PyErr_ResourceWarning (PyObject *source,
          Py_ssize_t stack_level, const char *format, ...)

     Function similar to *note PyErr_WarnFormat(): 3e17, but `category'
     is *note ResourceWarning: 5cb. and it passes `source' to
     ‘warnings.WarningMessage()’.

     New in version 3.6.


File: python.info,  Node: Querying the error indicator,  Next: Signal Handling<2>,  Prev: Issuing warnings,  Up: Exception Handling

7.5.4 Querying the error indicator
----------------------------------

 -- C Function: PyObject* PyErr_Occurred ()
     `Return value: Borrowed reference.'  Test whether the error
     indicator is set.  If set, return the exception `type' (the first
     argument to the last call to one of the ‘PyErr_Set*()’ functions or
     to *note PyErr_Restore(): 3d6d.).  If not set, return ‘NULL’.  You
     do not own a reference to the return value, so you do not need to
     *note Py_DECREF(): 38f. it.

     The caller must hold the GIL.

          Note: Do not compare the return value to a specific exception;
          use *note PyErr_ExceptionMatches(): 3dcc. instead, shown
          below.  (The comparison could easily fail since the exception
          may be an instance instead of a class, in the case of a class
          exception, or it may be a subclass of the expected exception.)

 -- C Function: int PyErr_ExceptionMatches (PyObject *exc)

     Equivalent to ‘PyErr_GivenExceptionMatches(PyErr_Occurred(), exc)’.
     This should only be called when an exception is actually set; a
     memory access violation will occur if no exception has been raised.

 -- C Function: int PyErr_GivenExceptionMatches (PyObject *given,
          PyObject *exc)

     Return true if the `given' exception matches the exception type in
     `exc'.  If `exc' is a class object, this also returns true when
     `given' is an instance of a subclass.  If `exc' is a tuple, all
     exception types in the tuple (and recursively in subtuples) are
     searched for a match.

 -- C Function: void PyErr_Fetch (PyObject **ptype, PyObject **pvalue,
          PyObject **ptraceback)

     Retrieve the error indicator into three variables whose addresses
     are passed.  If the error indicator is not set, set all three
     variables to ‘NULL’.  If it is set, it will be cleared and you own
     a reference to each object retrieved.  The value and traceback
     object may be ‘NULL’ even when the type object is not.

          Note: This function is normally only used by code that needs
          to catch exceptions or by code that needs to save and restore
          the error indicator temporarily, e.g.:

               {
                  PyObject *type, *value, *traceback;
                  PyErr_Fetch(&type, &value, &traceback);

                  /* ... code that might produce other errors ... */

                  PyErr_Restore(type, value, traceback);
               }

 -- C Function: void PyErr_Restore (PyObject *type, PyObject *value,
          PyObject *traceback)

     Set the error indicator from the three objects.  If the error
     indicator is already set, it is cleared first.  If the objects are
     ‘NULL’, the error indicator is cleared.  Do not pass a ‘NULL’ type
     and non-‘NULL’ value or traceback.  The exception type should be a
     class.  Do not pass an invalid exception type or value.  (Violating
     these rules will cause subtle problems later.)  This call takes
     away a reference to each object: you must own a reference to each
     object before the call and after the call you no longer own these
     references.  (If you don’t understand this, don’t use this
     function.  I warned you.)

          Note: This function is normally only used by code that needs
          to save and restore the error indicator temporarily.  Use
          *note PyErr_Fetch(): a4b. to save the current error indicator.

 -- C Function: void PyErr_NormalizeException (PyObject**exc,
          PyObject**val, PyObject**tb)

     Under certain circumstances, the values returned by *note
     PyErr_Fetch(): a4b. below can be “unnormalized”, meaning that
     ‘*exc’ is a class object but ‘*val’ is not an instance of the same
     class.  This function can be used to instantiate the class in that
     case.  If the values are already normalized, nothing happens.  The
     delayed normalization is implemented to improve performance.

          Note: This function `does not' implicitly set the
          ‘__traceback__’ attribute on the exception value.  If setting
          the traceback appropriately is desired, the following
          additional snippet is needed:

               if (tb != NULL) {
                 PyException_SetTraceback(val, tb);
               }

 -- C Function: void PyErr_GetExcInfo (PyObject **ptype,
          PyObject **pvalue, PyObject **ptraceback)

     Retrieve the exception info, as known from ‘sys.exc_info()’.  This
     refers to an exception that was `already caught', not to an
     exception that was freshly raised.  Returns new references for the
     three objects, any of which may be ‘NULL’.  Does not modify the
     exception info state.

          Note: This function is not normally used by code that wants to
          handle exceptions.  Rather, it can be used when code needs to
          save and restore the exception state temporarily.  Use *note
          PyErr_SetExcInfo(): 3e1b. to restore or clear the exception
          state.

     New in version 3.3.

 -- C Function: void PyErr_SetExcInfo (PyObject *type, PyObject *value,
          PyObject *traceback)

     Set the exception info, as known from ‘sys.exc_info()’.  This
     refers to an exception that was `already caught', not to an
     exception that was freshly raised.  This function steals the
     references of the arguments.  To clear the exception state, pass
     ‘NULL’ for all three arguments.  For general rules about the three
     arguments, see *note PyErr_Restore(): 3d6d.

          Note: This function is not normally used by code that wants to
          handle exceptions.  Rather, it can be used when code needs to
          save and restore the exception state temporarily.  Use *note
          PyErr_GetExcInfo(): 3e1a. to read the exception state.

     New in version 3.3.


File: python.info,  Node: Signal Handling<2>,  Next: Exception Classes,  Prev: Querying the error indicator,  Up: Exception Handling

7.5.5 Signal Handling
---------------------

 -- C Function: int PyErr_CheckSignals ()

     This function interacts with Python’s signal handling.  It checks
     whether a signal has been sent to the processes and if so, invokes
     the corresponding signal handler.  If the *note signal: ea. module
     is supported, this can invoke a signal handler written in Python.
     In all cases, the default effect for ‘SIGINT’ is to raise the *note
     KeyboardInterrupt: 2cc. exception.  If an exception is raised the
     error indicator is set and the function returns ‘-1’; otherwise the
     function returns ‘0’.  The error indicator may or may not be
     cleared if it was previously set.

 -- C Function: void PyErr_SetInterrupt ()

     Simulate the effect of a ‘SIGINT’ signal arriving.  The next time
     *note PyErr_CheckSignals(): 3e05. is called, the Python signal
     handler for ‘SIGINT’ will be called.

     If ‘SIGINT’ isn’t handled by Python (it was set to *note
     signal.SIG_DFL: 2627. or *note signal.SIG_IGN: 2628.), this
     function does nothing.

 -- C Function: int PySignal_SetWakeupFd (int fd)

     This utility function specifies a file descriptor to which the
     signal number is written as a single byte whenever a signal is
     received.  `fd' must be non-blocking.  It returns the previous such
     file descriptor.

     The value ‘-1’ disables the feature; this is the initial state.
     This is equivalent to *note signal.set_wakeup_fd(): 4d5. in Python,
     but without any error checking.  `fd' should be a valid file
     descriptor.  The function should only be called from the main
     thread.

     Changed in version 3.5: On Windows, the function now also supports
     socket handles.


File: python.info,  Node: Exception Classes,  Next: Exception Objects,  Prev: Signal Handling<2>,  Up: Exception Handling

7.5.6 Exception Classes
-----------------------

 -- C Function: PyObject* PyErr_NewException (const char *name,
          PyObject *base, PyObject *dict)
     `Return value: New reference.'  This utility function creates and
     returns a new exception class.  The `name' argument must be the
     name of the new exception, a C string of the form
     ‘module.classname’.  The `base' and `dict' arguments are normally
     ‘NULL’.  This creates a class object derived from *note Exception:
     2dc. (accessible in C as ‘PyExc_Exception’).

     The ‘__module__’ attribute of the new class is set to the first
     part (up to the last dot) of the `name' argument, and the class
     name is set to the last part (after the last dot).  The `base'
     argument can be used to specify alternate base classes; it can
     either be only one class or a tuple of classes.  The `dict'
     argument can be used to specify a dictionary of class variables and
     methods.

 -- C Function: PyObject* PyErr_NewExceptionWithDoc (const char *name,
          const char *doc, PyObject *base, PyObject *dict)
     `Return value: New reference.'  Same as *note PyErr_NewException():
     ccb, except that the new exception class can easily be given a
     docstring: If `doc' is non-‘NULL’, it will be used as the docstring
     for the exception class.

     New in version 3.2.


File: python.info,  Node: Exception Objects,  Next: Unicode Exception Objects,  Prev: Exception Classes,  Up: Exception Handling

7.5.7 Exception Objects
-----------------------

 -- C Function: PyObject* PyException_GetTraceback (PyObject *ex)
     `Return value: New reference.'  Return the traceback associated
     with the exception as a new reference, as accessible from Python
     through ‘__traceback__’.  If there is no traceback associated, this
     returns ‘NULL’.

 -- C Function: int PyException_SetTraceback (PyObject *ex,
          PyObject *tb)

     Set the traceback associated with the exception to `tb'.  Use
     ‘Py_None’ to clear it.

 -- C Function: PyObject* PyException_GetContext (PyObject *ex)
     `Return value: New reference.'  Return the context (another
     exception instance during whose handling `ex' was raised)
     associated with the exception as a new reference, as accessible
     from Python through ‘__context__’.  If there is no context
     associated, this returns ‘NULL’.

 -- C Function: void PyException_SetContext (PyObject *ex,
          PyObject *ctx)

     Set the context associated with the exception to `ctx'.  Use ‘NULL’
     to clear it.  There is no type check to make sure that `ctx' is an
     exception instance.  This steals a reference to `ctx'.

 -- C Function: PyObject* PyException_GetCause (PyObject *ex)
     `Return value: New reference.'  Return the cause (either an
     exception instance, or *note None: 203, set by ‘raise ... from
     ...’) associated with the exception as a new reference, as
     accessible from Python through ‘__cause__’.

 -- C Function: void PyException_SetCause (PyObject *ex,
          PyObject *cause)

     Set the cause associated with the exception to `cause'.  Use ‘NULL’
     to clear it.  There is no type check to make sure that `cause' is
     either an exception instance or *note None: 203.  This steals a
     reference to `cause'.

     ‘__suppress_context__’ is implicitly set to ‘True’ by this
     function.


File: python.info,  Node: Unicode Exception Objects,  Next: Recursion Control,  Prev: Exception Objects,  Up: Exception Handling

7.5.8 Unicode Exception Objects
-------------------------------

The following functions are used to create and modify Unicode exceptions
from C.

 -- C Function: PyObject* PyUnicodeDecodeError_Create (const
          char *encoding, const char *object, Py_ssize_t length,
          Py_ssize_t start, Py_ssize_t end, const char *reason)
     `Return value: New reference.'  Create a *note UnicodeDecodeError:
     32b. object with the attributes `encoding', `object', `length',
     `start', `end' and `reason'.  `encoding' and `reason' are UTF-8
     encoded strings.

 -- C Function: PyObject* PyUnicodeEncodeError_Create (const
          char *encoding, const Py_UNICODE *object, Py_ssize_t length,
          Py_ssize_t start, Py_ssize_t end, const char *reason)
     `Return value: New reference.'  Create a *note UnicodeEncodeError:
     32a. object with the attributes `encoding', `object', `length',
     `start', `end' and `reason'.  `encoding' and `reason' are UTF-8
     encoded strings.

     Deprecated since version 3.3: 3.11

     ‘Py_UNICODE’ is deprecated since Python 3.3.  Please migrate to
     ‘PyObject_CallFunction(PyExc_UnicodeEncodeError, "sOnns", ...)’.

 -- C Function: PyObject* PyUnicodeTranslateError_Create (const
          Py_UNICODE *object, Py_ssize_t length, Py_ssize_t start,
          Py_ssize_t end, const char *reason)
     `Return value: New reference.'  Create a *note
     UnicodeTranslateError: 185b. object with the attributes `object',
     `length', `start', `end' and `reason'.  `reason' is a UTF-8 encoded
     string.

     Deprecated since version 3.3: 3.11

     ‘Py_UNICODE’ is deprecated since Python 3.3.  Please migrate to
     ‘PyObject_CallFunction(PyExc_UnicodeTranslateError, "Onns", ...)’.

 -- C Function: PyObject* PyUnicodeDecodeError_GetEncoding
          (PyObject *exc)
 -- C Function: PyObject* PyUnicodeEncodeError_GetEncoding
          (PyObject *exc)
     `Return value: New reference.'  Return the `encoding' attribute of
     the given exception object.

 -- C Function: PyObject* PyUnicodeDecodeError_GetObject (PyObject *exc)
 -- C Function: PyObject* PyUnicodeEncodeError_GetObject (PyObject *exc)
 -- C Function: PyObject* PyUnicodeTranslateError_GetObject
          (PyObject *exc)
     `Return value: New reference.'  Return the `object' attribute of
     the given exception object.

 -- C Function: int PyUnicodeDecodeError_GetStart (PyObject *exc,
          Py_ssize_t *start)
 -- C Function: int PyUnicodeEncodeError_GetStart (PyObject *exc,
          Py_ssize_t *start)
 -- C Function: int PyUnicodeTranslateError_GetStart (PyObject *exc,
          Py_ssize_t *start)

     Get the `start' attribute of the given exception object and place
     it into `*start'.  `start' must not be ‘NULL’.  Return ‘0’ on
     success, ‘-1’ on failure.

 -- C Function: int PyUnicodeDecodeError_SetStart (PyObject *exc,
          Py_ssize_t start)
 -- C Function: int PyUnicodeEncodeError_SetStart (PyObject *exc,
          Py_ssize_t start)
 -- C Function: int PyUnicodeTranslateError_SetStart (PyObject *exc,
          Py_ssize_t start)

     Set the `start' attribute of the given exception object to `start'.
     Return ‘0’ on success, ‘-1’ on failure.

 -- C Function: int PyUnicodeDecodeError_GetEnd (PyObject *exc,
          Py_ssize_t *end)
 -- C Function: int PyUnicodeEncodeError_GetEnd (PyObject *exc,
          Py_ssize_t *end)
 -- C Function: int PyUnicodeTranslateError_GetEnd (PyObject *exc,
          Py_ssize_t *end)

     Get the `end' attribute of the given exception object and place it
     into `*end'.  `end' must not be ‘NULL’.  Return ‘0’ on success,
     ‘-1’ on failure.

 -- C Function: int PyUnicodeDecodeError_SetEnd (PyObject *exc,
          Py_ssize_t end)
 -- C Function: int PyUnicodeEncodeError_SetEnd (PyObject *exc,
          Py_ssize_t end)
 -- C Function: int PyUnicodeTranslateError_SetEnd (PyObject *exc,
          Py_ssize_t end)

     Set the `end' attribute of the given exception object to `end'.
     Return ‘0’ on success, ‘-1’ on failure.

 -- C Function: PyObject* PyUnicodeDecodeError_GetReason (PyObject *exc)
 -- C Function: PyObject* PyUnicodeEncodeError_GetReason (PyObject *exc)
 -- C Function: PyObject* PyUnicodeTranslateError_GetReason
          (PyObject *exc)
     `Return value: New reference.'  Return the `reason' attribute of
     the given exception object.

 -- C Function: int PyUnicodeDecodeError_SetReason (PyObject *exc, const
          char *reason)
 -- C Function: int PyUnicodeEncodeError_SetReason (PyObject *exc, const
          char *reason)
 -- C Function: int PyUnicodeTranslateError_SetReason (PyObject *exc,
          const char *reason)

     Set the `reason' attribute of the given exception object to
     `reason'.  Return ‘0’ on success, ‘-1’ on failure.


File: python.info,  Node: Recursion Control,  Next: Standard Exceptions,  Prev: Unicode Exception Objects,  Up: Exception Handling

7.5.9 Recursion Control
-----------------------

These two functions provide a way to perform safe recursive calls at the
C level, both in the core and in extension modules.  They are needed if
the recursive code does not necessarily invoke Python code (which tracks
its recursion depth automatically).  They are also not needed for
`tp_call' implementations because the *note call protocol: 3e43. takes
care of recursion handling.

 -- C Function: int Py_EnterRecursiveCall (const char *where)

     Marks a point where a recursive C-level call is about to be
     performed.

     If ‘USE_STACKCHECK’ is defined, this function checks if the OS
     stack overflowed using *note PyOS_CheckStack(): 3e44.  In this is
     the case, it sets a *note MemoryError: f69. and returns a nonzero
     value.

     The function then checks if the recursion limit is reached.  If
     this is the case, a *note RecursionError: 727. is set and a nonzero
     value is returned.  Otherwise, zero is returned.

     `where' should be a UTF-8 encoded string such as ‘" in instance
     check"’ to be concatenated to the *note RecursionError: 727.
     message caused by the recursion depth limit.

     Changed in version 3.9: This function is now also available in the
     limited API.

 -- C Function: void Py_LeaveRecursiveCall (void)

     Ends a *note Py_EnterRecursiveCall(): 251.  Must be called once for
     each `successful' invocation of *note Py_EnterRecursiveCall(): 251.

     Changed in version 3.9: This function is now also available in the
     limited API.

Properly implementing *note tp_repr: 3d70. for container types requires
special recursion handling.  In addition to protecting the stack, *note
tp_repr: 3d70. also needs to track objects to prevent cycles.  The
following two functions facilitate this functionality.  Effectively,
these are the C equivalent to *note reprlib.recursive_repr(): c41.

 -- C Function: int Py_ReprEnter (PyObject *object)

     Called at the beginning of the *note tp_repr: 3d70. implementation
     to detect cycles.

     If the object has already been processed, the function returns a
     positive integer.  In that case the *note tp_repr: 3d70.
     implementation should return a string object indicating a cycle.
     As examples, *note dict: 164. objects return ‘{...}’ and *note
     list: 1f8. objects return ‘[...]’.

     The function will return a negative integer if the recursion limit
     is reached.  In that case the *note tp_repr: 3d70. implementation
     should typically return ‘NULL’.

     Otherwise, the function returns zero and the *note tp_repr: 3d70.
     implementation can continue normally.

 -- C Function: void Py_ReprLeave (PyObject *object)

     Ends a *note Py_ReprEnter(): 3e45.  Must be called once for each
     invocation of *note Py_ReprEnter(): 3e45. that returns zero.


File: python.info,  Node: Standard Exceptions,  Next: Standard Warning Categories,  Prev: Recursion Control,  Up: Exception Handling

7.5.10 Standard Exceptions
--------------------------

All standard Python exceptions are available as global variables whose
names are ‘PyExc_’ followed by the Python exception name.  These have
the type *note PyObject*: 5b5.; they are all class objects.  For
completeness, here are all the variables:

C Name                                        Python Name                           Notes
                                                                                    
---------------------------------------------------------------------------------------------------
                                                                                    
‘PyExc_BaseException’                         *note BaseException: 2db.             (1)
                                                                                    
                                                                                    
‘PyExc_Exception’                             *note Exception: 2dc.                 (1)
                                                                                    
                                                                                    
‘PyExc_ArithmeticError’                       *note ArithmeticError: 1845.          (1)
                                                                                    
                                                                                    
‘PyExc_AssertionError’                        *note AssertionError: 240.
                                              
                                                                                    
‘PyExc_AttributeError’                        *note AttributeError: 4a2.
                                              
                                                                                    
‘PyExc_BlockingIOError’                       *note BlockingIOError: a78.
                                              
                                                                                    
‘PyExc_BrokenPipeError’                       *note BrokenPipeError: a7e.
                                              
                                                                                    
‘PyExc_BufferError’                           *note BufferError: 1847.
                                              
                                                                                    
‘PyExc_ChildProcessError’                     *note ChildProcessError: a79.
                                              
                                                                                    
‘PyExc_ConnectionAbortedError’                *note ConnectionAbortedError: a7f.
                                              
                                                                                    
‘PyExc_ConnectionError’                       *note ConnectionError: 7d7.
                                              
                                                                                    
‘PyExc_ConnectionRefusedError’                *note ConnectionRefusedError: a80.
                                              
                                                                                    
‘PyExc_ConnectionResetError’                  *note ConnectionResetError: a81.
                                              
                                                                                    
‘PyExc_EOFError’                              *note EOFError: d34.
                                              
                                                                                    
‘PyExc_FileExistsError’                       *note FileExistsError: a39.
                                              
                                                                                    
‘PyExc_FileNotFoundError’                     *note FileNotFoundError: 8ad.
                                              
                                                                                    
‘PyExc_FloatingPointError’                    *note FloatingPointError: 1846.
                                              
                                                                                    
‘PyExc_GeneratorExit’                         *note GeneratorExit: df8.
                                              
                                                                                    
‘PyExc_ImportError’                           *note ImportError: 16c.
                                              
                                                                                    
‘PyExc_IndentationError’                      *note IndentationError: f39.
                                              
                                                                                    
‘PyExc_IndexError’                            *note IndexError: f36.
                                              
                                                                                    
‘PyExc_InterruptedError’                      *note InterruptedError: 74c.
                                              
                                                                                    
‘PyExc_IsADirectoryError’                     *note IsADirectoryError: a7a.
                                              
                                                                                    
‘PyExc_KeyError’                              *note KeyError: 3e9.
                                              
                                                                                    
‘PyExc_KeyboardInterrupt’                     *note KeyboardInterrupt: 2cc.
                                              
                                                                                    
‘PyExc_LookupError’                           *note LookupError: 1790.              (1)
                                                                                    
                                                                                    
‘PyExc_MemoryError’                           *note MemoryError: f69.
                                              
                                                                                    
‘PyExc_ModuleNotFoundError’                   *note ModuleNotFoundError: 4a1.
                                              
                                                                                    
‘PyExc_NameError’                             *note NameError: e40.
                                              
                                                                                    
‘PyExc_NotADirectoryError’                    *note NotADirectoryError: a7b.
                                              
                                                                                    
‘PyExc_NotImplementedError’                   *note NotImplementedError: 704.
                                              
                                                                                    
‘PyExc_OSError’                               *note OSError: 304.                   (1)
                                                                                    
                                                                                    
‘PyExc_OverflowError’                         *note OverflowError: a41.
                                              
                                                                                    
‘PyExc_PermissionError’                       *note PermissionError: 6f6.
                                              
                                                                                    
‘PyExc_ProcessLookupError’                    *note ProcessLookupError: a7c.
                                              
                                                                                    
‘PyExc_RecursionError’                        *note RecursionError: 727.
                                              
                                                                                    
‘PyExc_ReferenceError’                        *note ReferenceError: f0f.            (2)
                                                                                    
                                                                                    
‘PyExc_RuntimeError’                          *note RuntimeError: 3dc.
                                              
                                                                                    
‘PyExc_StopAsyncIteration’                    *note StopAsyncIteration: 114a.
                                              
                                                                                    
‘PyExc_StopIteration’                         *note StopIteration: 582.
                                              
                                                                                    
‘PyExc_SyntaxError’                           *note SyntaxError: 55a.
                                              
                                                                                    
‘PyExc_SystemError’                           *note SystemError: 6f2.
                                              
                                                                                    
‘PyExc_SystemExit’                            *note SystemExit: 6f3.
                                              
                                                                                    
‘PyExc_TabError’                              *note TabError: f38.
                                              
                                                                                    
‘PyExc_TimeoutError’                          *note TimeoutError: a7d.
                                              
                                                                                    
‘PyExc_TypeError’                             *note TypeError: 1fe.
                                              
                                                                                    
‘PyExc_UnboundLocalError’                     *note UnboundLocalError: f37.
                                              
                                                                                    
‘PyExc_UnicodeDecodeError’                    *note UnicodeDecodeError: 32b.
                                              
                                                                                    
‘PyExc_UnicodeEncodeError’                    *note UnicodeEncodeError: 32a.
                                              
                                                                                    
‘PyExc_UnicodeError’                          *note UnicodeError: d03.
                                              
                                                                                    
‘PyExc_UnicodeTranslateError’                 *note UnicodeTranslateError: 185b.
                                              
                                                                                    
‘PyExc_ValueError’                            *note ValueError: 16d.
                                              
                                                                                    
‘PyExc_ZeroDivisionError’                     *note ZeroDivisionError: 1fa.
                                              

New in version 3.3: ‘PyExc_BlockingIOError’, ‘PyExc_BrokenPipeError’,
‘PyExc_ChildProcessError’, ‘PyExc_ConnectionError’,
‘PyExc_ConnectionAbortedError’, ‘PyExc_ConnectionRefusedError’,
‘PyExc_ConnectionResetError’, ‘PyExc_FileExistsError’,
‘PyExc_FileNotFoundError’, ‘PyExc_InterruptedError’,
‘PyExc_IsADirectoryError’, ‘PyExc_NotADirectoryError’,
‘PyExc_PermissionError’, ‘PyExc_ProcessLookupError’ and
‘PyExc_TimeoutError’ were introduced following PEP 3151(1).

New in version 3.5: ‘PyExc_StopAsyncIteration’ and
‘PyExc_RecursionError’.

New in version 3.6: ‘PyExc_ModuleNotFoundError’.

These are compatibility aliases to ‘PyExc_OSError’:

C Name                                    Notes
                                          
---------------------------------------------------------
                                          
‘PyExc_EnvironmentError’

‘PyExc_IOError’

‘PyExc_WindowsError’                      (3)
                                          

Changed in version 3.3: These aliases used to be separate exception
types.

Notes:

  1. This is a base class for other standard exceptions.

  2. Only defined on Windows; protect code that uses this by testing
     that the preprocessor macro ‘MS_WINDOWS’ is defined.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3151


File: python.info,  Node: Standard Warning Categories,  Prev: Standard Exceptions,  Up: Exception Handling

7.5.11 Standard Warning Categories
----------------------------------

All standard Python warning categories are available as global variables
whose names are ‘PyExc_’ followed by the Python exception name.  These
have the type *note PyObject*: 5b5.; they are all class objects.  For
completeness, here are all the variables:

C Name                                         Python Name                           Notes
                                                                                     
----------------------------------------------------------------------------------------------------
                                                                                     
‘PyExc_Warning’                                *note Warning: 1860.                  (1)
                                                                                     
                                                                                     
‘PyExc_BytesWarning’                           *note BytesWarning: 5b0.
                                               
                                                                                     
‘PyExc_DeprecationWarning’                     *note DeprecationWarning: 15a.
                                               
                                                                                     
‘PyExc_FutureWarning’                          *note FutureWarning: 435.
                                               
                                                                                     
‘PyExc_ImportWarning’                          *note ImportWarning: 6cf.
                                               
                                                                                     
‘PyExc_PendingDeprecationWarning’              *note PendingDeprecationWarning: 15c.
                                               
                                                                                     
‘PyExc_ResourceWarning’                        *note ResourceWarning: 5cb.
                                               
                                                                                     
‘PyExc_RuntimeWarning’                         *note RuntimeWarning: 3e2.
                                               
                                                                                     
‘PyExc_SyntaxWarning’                          *note SyntaxWarning: 2c9.
                                               
                                                                                     
‘PyExc_UnicodeWarning’                         *note UnicodeWarning: e4c.
                                               
                                                                                     
‘PyExc_UserWarning’                            *note UserWarning: 1861.
                                               

New in version 3.2: ‘PyExc_ResourceWarning’.

Notes:

  1. This is a base class for other standard warning categories.


File: python.info,  Node: Utilities<2>,  Next: Abstract Objects Layer,  Prev: Exception Handling,  Up: Python/C API Reference Manual

7.6 Utilities
=============

The functions in this chapter perform various utility tasks, ranging
from helping C code be more portable across platforms, using Python
modules from C, and parsing function arguments and constructing Python
values from C values.

* Menu:

* Operating System Utilities::
* System Functions::
* Process Control::
* Importing Modules: Importing Modules<2>.
* Data marshalling support::
* Parsing arguments and building values::
* String conversion and formatting::
* Reflection::
* Codec registry and support functions::


File: python.info,  Node: Operating System Utilities,  Next: System Functions,  Up: Utilities<2>

7.6.1 Operating System Utilities
--------------------------------

 -- C Function: PyObject* PyOS_FSPath (PyObject *path)
     `Return value: New reference.'  Return the file system
     representation for `path'.  If the object is a *note str: 205. or
     *note bytes: 172. object, then its reference count is incremented.
     If the object implements the *note os.PathLike: 5e6. interface,
     then *note __fspath__(): 5e7. is returned as long as it is a *note
     str: 205. or *note bytes: 172. object.  Otherwise *note TypeError:
     1fe. is raised and ‘NULL’ is returned.

     New in version 3.6.

 -- C Function: int Py_FdIsInteractive (FILE *fp, const char *filename)

     Return true (nonzero) if the standard I/O file `fp' with name
     `filename' is deemed interactive.  This is the case for files for
     which ‘isatty(fileno(fp))’ is true.  If the global flag *note
     Py_InteractiveFlag: 3e51. is true, this function also returns true
     if the `filename' pointer is ‘NULL’ or if the name is equal to one
     of the strings ‘'<stdin>'’ or ‘'???'’.

 -- C Function: void PyOS_BeforeFork ()

     Function to prepare some internal state before a process fork.
     This should be called before calling ‘fork()’ or any similar
     function that clones the current process.  Only available on
     systems where ‘fork()’ is defined.

          Warning: The C ‘fork()’ call should only be made from the
          *note “main” thread: 3e52. (of the *note “main” interpreter:
          3e53.).  The same is true for ‘PyOS_BeforeFork()’.

     New in version 3.7.

 -- C Function: void PyOS_AfterFork_Parent ()

     Function to update some internal state after a process fork.  This
     should be called from the parent process after calling ‘fork()’ or
     any similar function that clones the current process, regardless of
     whether process cloning was successful.  Only available on systems
     where ‘fork()’ is defined.

          Warning: The C ‘fork()’ call should only be made from the
          *note “main” thread: 3e52. (of the *note “main” interpreter:
          3e53.).  The same is true for ‘PyOS_AfterFork_Parent()’.

     New in version 3.7.

 -- C Function: void PyOS_AfterFork_Child ()

     Function to update internal interpreter state after a process fork.
     This must be called from the child process after calling ‘fork()’,
     or any similar function that clones the current process, if there
     is any chance the process will call back into the Python
     interpreter.  Only available on systems where ‘fork()’ is defined.

          Warning: The C ‘fork()’ call should only be made from the
          *note “main” thread: 3e52. (of the *note “main” interpreter:
          3e53.).  The same is true for ‘PyOS_AfterFork_Child()’.

     New in version 3.7.

     See also
     ........

     *note os.register_at_fork(): 4bd. allows registering custom Python
     functions to be called by *note PyOS_BeforeFork(): 536, *note
     PyOS_AfterFork_Parent(): 537. and *note PyOS_AfterFork_Child():
     3ef.

 -- C Function: void PyOS_AfterFork ()

     Function to update some internal state after a process fork; this
     should be called in the new process if the Python interpreter will
     continue to be used.  If a new executable is loaded into the new
     process, this function does not need to be called.

     Deprecated since version 3.7: This function is superseded by *note
     PyOS_AfterFork_Child(): 3ef.

 -- C Function: int PyOS_CheckStack ()

     Return true when the interpreter runs out of stack space.  This is
     a reliable check, but is only available when ‘USE_STACKCHECK’ is
     defined (currently on Windows using the Microsoft Visual C++
     compiler).  ‘USE_STACKCHECK’ will be defined automatically; you
     should never change the definition in your own code.

 -- C Function: PyOS_sighandler_t PyOS_getsig (int i)

     Return the current signal handler for signal `i'.  This is a thin
     wrapper around either ‘sigaction()’ or ‘signal()’.  Do not call
     those functions directly!  ‘PyOS_sighandler_t’ is a typedef alias
     for ‘void (*)(int)’.

 -- C Function: PyOS_sighandler_t PyOS_setsig (int i,
          PyOS_sighandler_t h)

     Set the signal handler for signal `i' to be `h'; return the old
     signal handler.  This is a thin wrapper around either ‘sigaction()’
     or ‘signal()’.  Do not call those functions directly!
     ‘PyOS_sighandler_t’ is a typedef alias for ‘void (*)(int)’.

 -- C Function: wchar_t* Py_DecodeLocale (const char* arg, size_t *size)

     Decode a byte string from the locale encoding with the *note
     surrogateescape error handler: 198a.: undecodable bytes are decoded
     as characters in range U+DC80..U+DCFF. If a byte sequence can be
     decoded as a surrogate character, escape the bytes using the
     surrogateescape error handler instead of decoding them.

     Encoding, highest priority to lowest priority:

        * ‘UTF-8’ on macOS, Android, and VxWorks;

        * ‘UTF-8’ on Windows if *note Py_LegacyWindowsFSEncodingFlag:
          3e56. is zero;

        * ‘UTF-8’ if the Python UTF-8 mode is enabled;

        * ‘ASCII’ if the ‘LC_CTYPE’ locale is ‘"C"’,
          ‘nl_langinfo(CODESET)’ returns the ‘ASCII’ encoding (or an
          alias), and ‘mbstowcs()’ and ‘wcstombs()’ functions uses the
          ‘ISO-8859-1’ encoding.

        * the current locale encoding.

     Return a pointer to a newly allocated wide character string, use
     *note PyMem_RawFree(): 3e57. to free the memory.  If size is not
     ‘NULL’, write the number of wide characters excluding the null
     character into ‘*size’

     Return ‘NULL’ on decoding error or memory allocation error.  If
     `size' is not ‘NULL’, ‘*size’ is set to ‘(size_t)-1’ on memory
     error or set to ‘(size_t)-2’ on decoding error.

     Decoding errors should never happen, unless there is a bug in the C
     library.

     Use the *note Py_EncodeLocale(): 540. function to encode the
     character string back to a byte string.

     See also
     ........

     The *note PyUnicode_DecodeFSDefaultAndSize(): 3e58. and *note
     PyUnicode_DecodeLocaleAndSize(): 541. functions.

     New in version 3.5.

     Changed in version 3.7: The function now uses the UTF-8 encoding in
     the UTF-8 mode.

     Changed in version 3.8: The function now uses the UTF-8 encoding on
     Windows if *note Py_LegacyWindowsFSEncodingFlag: 3e56. is zero;

 -- C Function: char* Py_EncodeLocale (const wchar_t *text,
          size_t *error_pos)

     Encode a wide character string to the locale encoding with the
     *note surrogateescape error handler: 198a.: surrogate characters in
     the range U+DC80..U+DCFF are converted to bytes 0x80..0xFF.

     Encoding, highest priority to lowest priority:

        * ‘UTF-8’ on macOS, Android, and VxWorks;

        * ‘UTF-8’ on Windows if *note Py_LegacyWindowsFSEncodingFlag:
          3e56. is zero;

        * ‘UTF-8’ if the Python UTF-8 mode is enabled;

        * ‘ASCII’ if the ‘LC_CTYPE’ locale is ‘"C"’,
          ‘nl_langinfo(CODESET)’ returns the ‘ASCII’ encoding (or an
          alias), and ‘mbstowcs()’ and ‘wcstombs()’ functions uses the
          ‘ISO-8859-1’ encoding.

        * the current locale encoding.

     The function uses the UTF-8 encoding in the Python UTF-8 mode.

     Return a pointer to a newly allocated byte string, use *note
     PyMem_Free(): e6e. to free the memory.  Return ‘NULL’ on encoding
     error or memory allocation error

     If error_pos is not ‘NULL’, ‘*error_pos’ is set to ‘(size_t)-1’ on
     success, or set to the index of the invalid character on encoding
     error.

     Use the *note Py_DecodeLocale(): 53f. function to decode the bytes
     string back to a wide character string.

     See also
     ........

     The *note PyUnicode_EncodeFSDefault(): 1180. and *note
     PyUnicode_EncodeLocale(): 542. functions.

     New in version 3.5.

     Changed in version 3.7: The function now uses the UTF-8 encoding in
     the UTF-8 mode.

     Changed in version 3.8: The function now uses the UTF-8 encoding on
     Windows if *note Py_LegacyWindowsFSEncodingFlag: 3e56. is zero;


File: python.info,  Node: System Functions,  Next: Process Control,  Prev: Operating System Utilities,  Up: Utilities<2>

7.6.2 System Functions
----------------------

These are utility functions that make functionality from the *note sys:
fd. module accessible to C code.  They all work with the current
interpreter thread’s *note sys: fd. module’s dict, which is contained in
the internal thread state structure.

 -- C Function: PyObject *PySys_GetObject (const char *name)
     `Return value: Borrowed reference.'  Return the object `name' from
     the *note sys: fd. module or ‘NULL’ if it does not exist, without
     setting an exception.

 -- C Function: int PySys_SetObject (const char *name, PyObject *v)

     Set `name' in the *note sys: fd. module to `v' unless `v' is
     ‘NULL’, in which case `name' is deleted from the sys module.
     Returns ‘0’ on success, ‘-1’ on error.

 -- C Function: void PySys_ResetWarnOptions ()

     Reset *note sys.warnoptions: 51b. to an empty list.  This function
     may be called prior to *note Py_Initialize(): 20f.

 -- C Function: void PySys_AddWarnOption (const wchar_t *s)

     Append `s' to *note sys.warnoptions: 51b.  This function must be
     called prior to *note Py_Initialize(): 20f. in order to affect the
     warnings filter list.

 -- C Function: void PySys_AddWarnOptionUnicode (PyObject *unicode)

     Append `unicode' to *note sys.warnoptions: 51b.

     Note: this function is not currently usable from outside the
     CPython implementation, as it must be called prior to the implicit
     import of *note warnings: 12f. in *note Py_Initialize(): 20f. to be
     effective, but can’t be called until enough of the runtime has been
     initialized to permit the creation of Unicode objects.

 -- C Function: void PySys_SetPath (const wchar_t *path)

     Set *note sys.path: 260. to a list object of paths found in `path'
     which should be a list of paths separated with the platform’s
     search path delimiter (‘:’ on Unix, ‘;’ on Windows).

 -- C Function: void PySys_WriteStdout (const char *format, ...)

     Write the output string described by `format' to *note sys.stdout:
     41f.  No exceptions are raised, even if truncation occurs (see
     below).

     `format' should limit the total size of the formatted output string
     to 1000 bytes or less – after 1000 bytes, the output string is
     truncated.  In particular, this means that no unrestricted “%s”
     formats should occur; these should be limited using “%.<N>s” where
     <N> is a decimal number calculated so that <N> plus the maximum
     size of other formatted text does not exceed 1000 bytes.  Also
     watch out for “%f”, which can print hundreds of digits for very
     large numbers.

     If a problem occurs, or *note sys.stdout: 41f. is unset, the
     formatted message is written to the real (C level) `stdout'.

 -- C Function: void PySys_WriteStderr (const char *format, ...)

     As *note PySys_WriteStdout(): 3e5f, but write to *note sys.stderr:
     1ea. or `stderr' instead.

 -- C Function: void PySys_FormatStdout (const char *format, ...)

     Function similar to PySys_WriteStdout() but format the message
     using *note PyUnicode_FromFormatV(): 3e62. and don’t truncate the
     message to an arbitrary length.

     New in version 3.2.

 -- C Function: void PySys_FormatStderr (const char *format, ...)

     As *note PySys_FormatStdout(): 3e61, but write to *note sys.stderr:
     1ea. or `stderr' instead.

     New in version 3.2.

 -- C Function: void PySys_AddXOption (const wchar_t *s)

     Parse `s' as a set of *note -X: 290. options and add them to the
     current options mapping as returned by *note PySys_GetXOptions():
     3e65.  This function may be called prior to *note Py_Initialize():
     20f.

     New in version 3.2.

 -- C Function: PyObject *PySys_GetXOptions ()
     `Return value: Borrowed reference.'  Return the current dictionary
     of *note -X: 290. options, similarly to *note sys._xoptions: 1482.
     On error, ‘NULL’ is returned and an exception is set.

     New in version 3.2.

 -- C Function: int PySys_Audit (const char *event, const char *format,
          ...)

     Raise an auditing event with any active hooks.  Return zero for
     success and non-zero with an exception set on failure.

     If any hooks have been added, `format' and other arguments will be
     used to construct a tuple to pass.  Apart from ‘N’, the same format
     characters as used in *note Py_BuildValue(): 3f0. are available.
     If the built value is not a tuple, it will be added into a
     single-element tuple.  (The ‘N’ format option consumes a reference,
     but since there is no way to know whether arguments to this
     function will be consumed, using it may cause reference leaks.)

     Note that ‘#’ format characters should always be treated as
     ‘Py_ssize_t’, regardless of whether ‘PY_SSIZE_T_CLEAN’ was defined.

     *note sys.audit(): 1056. performs the same function from Python
     code.

     New in version 3.8.

     Changed in version 3.8.2: Require ‘Py_ssize_t’ for ‘#’ format
     characters.  Previously, an unavoidable deprecation warning was
     raised.

 -- C Function: int PySys_AddAuditHook (Py_AuditHookFunction hook,
          void *userData)

     Append the callable `hook' to the list of active auditing hooks.
     Return zero for success and non-zero on failure.  If the runtime
     has been initialized, also set an error on failure.  Hooks added
     through this API are called for all interpreters created by the
     runtime.

     The `userData' pointer is passed into the hook function.  Since
     hook functions may be called from different runtimes, this pointer
     should not refer directly to Python state.

     This function is safe to call before *note Py_Initialize(): 20f.
     When called after runtime initialization, existing audit hooks are
     notified and may silently abort the operation by raising an error
     subclassed from *note Exception: 2dc. (other errors will not be
     silenced).

     The hook function is of type ‘int (*)(const char *event, PyObject
     *args, void *userData)’, where `args' is guaranteed to be a *note
     PyTupleObject: 3e66.  The hook function is always called with the
     GIL held by the Python interpreter that raised the event.

     See PEP 578(1) for a detailed description of auditing.  Functions
     in the runtime and standard library that raise events are listed in
     the *note audit events table: 3667.  Details are in each function’s
     documentation.

     If the interpreter is initialized, this function raises a auditing
     event ‘sys.addaudithook’ with no arguments.  If any existing hooks
     raise an exception derived from *note Exception: 2dc, the new hook
     will not be added and the exception is cleared.  As a result,
     callers cannot assume that their hook has been added unless they
     control all existing hooks.

     New in version 3.8.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0578


File: python.info,  Node: Process Control,  Next: Importing Modules<2>,  Prev: System Functions,  Up: Utilities<2>

7.6.3 Process Control
---------------------

 -- C Function: void Py_FatalError (const char *message)

     Print a fatal error message and kill the process.  No cleanup is
     performed.  This function should only be invoked when a condition
     is detected that would make it dangerous to continue using the
     Python interpreter; e.g., when the object administration appears to
     be corrupted.  On Unix, the standard C library function ‘abort()’
     is called which will attempt to produce a ‘core’ file.

     The ‘Py_FatalError()’ function is replaced with a macro which logs
     automatically the name of the current function, unless the
     ‘Py_LIMITED_API’ macro is defined.

     Changed in version 3.9: Log the function name automatically.

 -- C Function: void Py_Exit (int status)

     Exit the current process.  This calls *note Py_FinalizeEx(): 6c0.
     and then calls the standard C library function ‘exit(status)’.  If
     *note Py_FinalizeEx(): 6c0. indicates an error, the exit status is
     set to 120.

     Changed in version 3.6: Errors from finalization no longer ignored.

 -- C Function: int Py_AtExit (void (*func)())

     Register a cleanup function to be called by *note Py_FinalizeEx():
     6c0.  The cleanup function will be called with no arguments and
     should return no value.  At most 32 cleanup functions can be
     registered.  When the registration is successful, *note
     Py_AtExit(): 3e69. returns ‘0’; on failure, it returns ‘-1’.  The
     cleanup function registered last is called first.  Each cleanup
     function will be called at most once.  Since Python’s internal
     finalization will have completed before the cleanup function, no
     Python APIs should be called by `func'.


File: python.info,  Node: Importing Modules<2>,  Next: Data marshalling support,  Prev: Process Control,  Up: Utilities<2>

7.6.4 Importing Modules
-----------------------

 -- C Function: PyObject* PyImport_ImportModule (const char *name)
     `Return value: New reference.'

     This is a simplified interface to *note PyImport_ImportModuleEx():
     bf4. below, leaving the `globals' and `locals' arguments set to
     ‘NULL’ and `level' set to 0.  When the `name' argument contains a
     dot (when it specifies a submodule of a package), the `fromlist'
     argument is set to the list ‘['*']’ so that the return value is the
     named module rather than the top-level package containing it as
     would otherwise be the case.  (Unfortunately, this has an
     additional side effect when `name' in fact specifies a subpackage
     instead of a submodule: the submodules specified in the package’s
     ‘__all__’ variable are loaded.)  Return a new reference to the
     imported module, or ‘NULL’ with an exception set on failure.  A
     failing import of a module doesn’t leave the module in *note
     sys.modules: 1051.

     This function always uses absolute imports.

 -- C Function: PyObject* PyImport_ImportModuleNoBlock (const
          char *name)
     `Return value: New reference.'  This function is a deprecated alias
     of *note PyImport_ImportModule(): d3b.

     Changed in version 3.3: This function used to fail immediately when
     the import lock was held by another thread.  In Python 3.3 though,
     the locking scheme switched to per-module locks for most purposes,
     so this function’s special behaviour isn’t needed anymore.

 -- C Function: PyObject* PyImport_ImportModuleEx (const char *name,
          PyObject *globals, PyObject *locals, PyObject *fromlist)
     `Return value: New reference.'

     Import a module.  This is best described by referring to the
     built-in Python function *note __import__(): 16b.

     The return value is a new reference to the imported module or
     top-level package, or ‘NULL’ with an exception set on failure.
     Like for *note __import__(): 16b, the return value when a submodule
     of a package was requested is normally the top-level package,
     unless a non-empty `fromlist' was given.

     Failing imports remove incomplete module objects, like with *note
     PyImport_ImportModule(): d3b.

 -- C Function: PyObject* PyImport_ImportModuleLevelObject
          (PyObject *name, PyObject *globals, PyObject *locals,
          PyObject *fromlist, int level)
     `Return value: New reference.'  Import a module.  This is best
     described by referring to the built-in Python function *note
     __import__(): 16b, as the standard *note __import__(): 16b.
     function calls this function directly.

     The return value is a new reference to the imported module or
     top-level package, or ‘NULL’ with an exception set on failure.
     Like for *note __import__(): 16b, the return value when a submodule
     of a package was requested is normally the top-level package,
     unless a non-empty `fromlist' was given.

     New in version 3.3.

 -- C Function: PyObject* PyImport_ImportModuleLevel (const char *name,
          PyObject *globals, PyObject *locals, PyObject *fromlist,
          int level)
     `Return value: New reference.'  Similar to *note
     PyImport_ImportModuleLevelObject(): 3e6d, but the name is a UTF-8
     encoded string instead of a Unicode object.

     Changed in version 3.3: Negative values for `level' are no longer
     accepted.

 -- C Function: PyObject* PyImport_Import (PyObject *name)
     `Return value: New reference.'  This is a higher-level interface
     that calls the current “import hook function” (with an explicit
     `level' of 0, meaning absolute import).  It invokes the *note
     __import__(): 16b. function from the ‘__builtins__’ of the current
     globals.  This means that the import is done using whatever import
     hooks are installed in the current environment.

     This function always uses absolute imports.

 -- C Function: PyObject* PyImport_ReloadModule (PyObject *m)
     `Return value: New reference.'  Reload a module.  Return a new
     reference to the reloaded module, or ‘NULL’ with an exception set
     on failure (the module still exists in this case).

 -- C Function: PyObject* PyImport_AddModuleObject (PyObject *name)
     `Return value: Borrowed reference.'  Return the module object
     corresponding to a module name.  The `name' argument may be of the
     form ‘package.module’.  First check the modules dictionary if
     there’s one there, and if not, create a new one and insert it in
     the modules dictionary.  Return ‘NULL’ with an exception set on
     failure.

          Note: This function does not load or import the module; if the
          module wasn’t already loaded, you will get an empty module
          object.  Use *note PyImport_ImportModule(): d3b. or one of its
          variants to import a module.  Package structures implied by a
          dotted name for `name' are not created if not already present.

     New in version 3.3.

 -- C Function: PyObject* PyImport_AddModule (const char *name)
     `Return value: Borrowed reference.'  Similar to *note
     PyImport_AddModuleObject(): 3e6f, but the name is a UTF-8 encoded
     string instead of a Unicode object.

 -- C Function: PyObject* PyImport_ExecCodeModule (const char *name,
          PyObject *co)
     `Return value: New reference.'

     Given a module name (possibly of the form ‘package.module’) and a
     code object read from a Python bytecode file or obtained from the
     built-in function *note compile(): 2e7, load the module.  Return a
     new reference to the module object, or ‘NULL’ with an exception set
     if an error occurred.  `name' is removed from *note sys.modules:
     1051. in error cases, even if `name' was already in *note
     sys.modules: 1051. on entry to *note PyImport_ExecCodeModule():
     3e70.  Leaving incompletely initialized modules in *note
     sys.modules: 1051. is dangerous, as imports of such modules have no
     way to know that the module object is an unknown (and probably
     damaged with respect to the module author’s intents) state.

     The module’s *note __spec__: 1603. and *note __loader__: a37. will
     be set, if not set already, with the appropriate values.  The
     spec’s loader will be set to the module’s ‘__loader__’ (if set) and
     to an instance of ‘SourceFileLoader’ otherwise.

     The module’s *note __file__: 1562. attribute will be set to the
     code object’s ‘co_filename’.  If applicable, *note __cached__: c04.
     will also be set.

     This function will reload the module if it was already imported.
     See *note PyImport_ReloadModule(): 3e6e. for the intended way to
     reload a module.

     If `name' points to a dotted name of the form ‘package.module’, any
     package structures not already created will still not be created.

     See also *note PyImport_ExecCodeModuleEx(): 3e71. and *note
     PyImport_ExecCodeModuleWithPathnames(): 3e72.

 -- C Function: PyObject* PyImport_ExecCodeModuleEx (const char *name,
          PyObject *co, const char *pathname)
     `Return value: New reference.'  Like *note
     PyImport_ExecCodeModule(): 3e70, but the *note __file__: 1562.
     attribute of the module object is set to `pathname' if it is
     non-‘NULL’.

     See also *note PyImport_ExecCodeModuleWithPathnames(): 3e72.

 -- C Function: PyObject* PyImport_ExecCodeModuleObject (PyObject *name,
          PyObject *co, PyObject *pathname, PyObject *cpathname)
     `Return value: New reference.'  Like *note
     PyImport_ExecCodeModuleEx(): 3e71, but the *note __cached__: c04.
     attribute of the module object is set to `cpathname' if it is
     non-‘NULL’.  Of the three functions, this is the preferred one to
     use.

     New in version 3.3.

 -- C Function: PyObject* PyImport_ExecCodeModuleWithPathnames (const
          char *name, PyObject *co, const char *pathname, const
          char *cpathname)
     `Return value: New reference.'  Like *note
     PyImport_ExecCodeModuleObject(): 3e73, but `name', `pathname' and
     `cpathname' are UTF-8 encoded strings.  Attempts are also made to
     figure out what the value for `pathname' should be from `cpathname'
     if the former is set to ‘NULL’.

     New in version 3.2.

     Changed in version 3.3: Uses *note imp.source_from_cache(): 3cfd.
     in calculating the source path if only the bytecode path is
     provided.

 -- C Function: long PyImport_GetMagicNumber ()

     Return the magic number for Python bytecode files (a.k.a.  ‘.pyc’
     file).  The magic number should be present in the first four bytes
     of the bytecode file, in little-endian byte order.  Returns ‘-1’ on
     error.

     Changed in version 3.3: Return value of ‘-1’ upon failure.

 -- C Function: const char * PyImport_GetMagicTag ()

     Return the magic tag string for PEP 3147(1) format Python bytecode
     file names.  Keep in mind that the value at
     ‘sys.implementation.cache_tag’ is authoritative and should be used
     instead of this function.

     New in version 3.2.

 -- C Function: PyObject* PyImport_GetModuleDict ()
     `Return value: Borrowed reference.'  Return the dictionary used for
     the module administration (a.k.a.  ‘sys.modules’).  Note that this
     is a per-interpreter variable.

 -- C Function: PyObject* PyImport_GetModule (PyObject *name)
     `Return value: New reference.'  Return the already imported module
     with the given name.  If the module has not been imported yet then
     returns ‘NULL’ but does not set an error.  Returns ‘NULL’ and sets
     an error if the lookup failed.

     New in version 3.7.

 -- C Function: PyObject* PyImport_GetImporter (PyObject *path)
     `Return value: New reference.'  Return a finder object for a *note
     sys.path: 260./‘pkg.__path__’ item `path', possibly by fetching it
     from the *note sys.path_importer_cache: 598. dict.  If it wasn’t
     yet cached, traverse *note sys.path_hooks: a3d. until a hook is
     found that can handle the path item.  Return ‘None’ if no hook
     could; this tells our caller that the *note path based finder:
     15fb. could not find a finder for this path item.  Cache the result
     in *note sys.path_importer_cache: 598.  Return a new reference to
     the finder object.

 -- C Function: int PyImport_ImportFrozenModuleObject (PyObject *name)
     `Return value: New reference.'  Load a frozen module named `name'.
     Return ‘1’ for success, ‘0’ if the module is not found, and ‘-1’
     with an exception set if the initialization failed.  To access the
     imported module on a successful load, use *note
     PyImport_ImportModule(): d3b.  (Note the misnomer — this function
     would reload the module if it was already imported.)

     New in version 3.3.

     Changed in version 3.4: The ‘__file__’ attribute is no longer set
     on the module.

 -- C Function: int PyImport_ImportFrozenModule (const char *name)

     Similar to *note PyImport_ImportFrozenModuleObject(): 3e77, but the
     name is a UTF-8 encoded string instead of a Unicode object.

 -- C Type: struct _frozen

     This is the structure type definition for frozen module
     descriptors, as generated by the ‘freeze’ utility (see
     ‘Tools/freeze/’ in the Python source distribution).  Its
     definition, found in ‘Include/import.h’, is:

          struct _frozen {
              const char *name;
              const unsigned char *code;
              int size;
          };

 -- C Variable: const struct _frozen* PyImport_FrozenModules

     This pointer is initialized to point to an array of ‘struct
     _frozen’ records, terminated by one whose members are all ‘NULL’ or
     zero.  When a frozen module is imported, it is searched in this
     table.  Third-party code could play tricks with this to provide a
     dynamically created collection of frozen modules.

 -- C Function: int PyImport_AppendInittab (const char *name, PyObject*
          (*initfunc)(void))

     Add a single module to the existing table of built-in modules.
     This is a convenience wrapper around *note
     PyImport_ExtendInittab(): f9d, returning ‘-1’ if the table could
     not be extended.  The new module can be imported by the name
     `name', and uses the function `initfunc' as the initialization
     function called on the first attempted import.  This should be
     called before *note Py_Initialize(): 20f.

 -- C Type: struct _inittab

     Structure describing a single entry in the list of built-in
     modules.  Each of these structures gives the name and
     initialization function for a module built into the interpreter.
     The name is an ASCII encoded string.  Programs which embed Python
     may use an array of these structures in conjunction with *note
     PyImport_ExtendInittab(): f9d. to provide additional built-in
     modules.  The structure is defined in ‘Include/import.h’ as:

          struct _inittab {
              const char *name;           /* ASCII encoded string */
              PyObject* (*initfunc)(void);
          };

 -- C Function: int PyImport_ExtendInittab (struct _inittab *newtab)

     Add a collection of modules to the table of built-in modules.  The
     `newtab' array must end with a sentinel entry which contains ‘NULL’
     for the ‘name’ field; failure to provide the sentinel value can
     result in a memory fault.  Returns ‘0’ on success or ‘-1’ if
     insufficient memory could be allocated to extend the internal
     table.  In the event of failure, no modules are added to the
     internal table.  This must be called before *note Py_Initialize():
     20f.

     If Python is initialized multiple times, *note
     PyImport_AppendInittab(): f9c. or *note PyImport_ExtendInittab():
     f9d. must be called before each Python initialization.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3147


File: python.info,  Node: Data marshalling support,  Next: Parsing arguments and building values,  Prev: Importing Modules<2>,  Up: Utilities<2>

7.6.5 Data marshalling support
------------------------------

These routines allow C code to work with serialized objects using the
same data format as the *note marshal: b0. module.  There are functions
to write data into the serialization format, and additional functions
that can be used to read the data back.  Files used to store marshalled
data must be opened in binary mode.

Numeric values are stored with the least significant byte first.

The module supports two versions of the data format: version 0 is the
historical version, version 1 shares interned strings in the file, and
upon unmarshalling.  Version 2 uses a binary format for floating point
numbers.  ‘Py_MARSHAL_VERSION’ indicates the current file format
(currently 2).

 -- C Function: void PyMarshal_WriteLongToFile (long value, FILE *file,
          int version)

     Marshal a ‘long’ integer, `value', to `file'.  This will only write
     the least-significant 32 bits of `value'; regardless of the size of
     the native ‘long’ type.  `version' indicates the file format.

 -- C Function: void PyMarshal_WriteObjectToFile (PyObject *value,
          FILE *file, int version)

     Marshal a Python object, `value', to `file'.  `version' indicates
     the file format.

 -- C Function: PyObject* PyMarshal_WriteObjectToString
          (PyObject *value, int version)
     `Return value: New reference.'  Return a bytes object containing
     the marshalled representation of `value'.  `version' indicates the
     file format.

The following functions allow marshalled values to be read back in.

 -- C Function: long PyMarshal_ReadLongFromFile (FILE *file)

     Return a C ‘long’ from the data stream in a ‘FILE*’ opened for
     reading.  Only a 32-bit value can be read in using this function,
     regardless of the native size of ‘long’.

     On error, sets the appropriate exception (*note EOFError: d34.) and
     returns ‘-1’.

 -- C Function: int PyMarshal_ReadShortFromFile (FILE *file)

     Return a C ‘short’ from the data stream in a ‘FILE*’ opened for
     reading.  Only a 16-bit value can be read in using this function,
     regardless of the native size of ‘short’.

     On error, sets the appropriate exception (*note EOFError: d34.) and
     returns ‘-1’.

 -- C Function: PyObject* PyMarshal_ReadObjectFromFile (FILE *file)
     `Return value: New reference.'  Return a Python object from the
     data stream in a ‘FILE*’ opened for reading.

     On error, sets the appropriate exception (*note EOFError: d34,
     *note ValueError: 16d. or *note TypeError: 1fe.) and returns
     ‘NULL’.

 -- C Function: PyObject* PyMarshal_ReadLastObjectFromFile (FILE *file)
     `Return value: New reference.'  Return a Python object from the
     data stream in a ‘FILE*’ opened for reading.  Unlike *note
     PyMarshal_ReadObjectFromFile(): 3e83, this function assumes that no
     further objects will be read from the file, allowing it to
     aggressively load file data into memory so that the
     de-serialization can operate from data in memory rather than
     reading a byte at a time from the file.  Only use these variant if
     you are certain that you won’t be reading anything else from the
     file.

     On error, sets the appropriate exception (*note EOFError: d34,
     *note ValueError: 16d. or *note TypeError: 1fe.) and returns
     ‘NULL’.

 -- C Function: PyObject* PyMarshal_ReadObjectFromString (const
          char *data, Py_ssize_t len)
     `Return value: New reference.'  Return a Python object from the
     data stream in a byte buffer containing `len' bytes pointed to by
     `data'.

     On error, sets the appropriate exception (*note EOFError: d34,
     *note ValueError: 16d. or *note TypeError: 1fe.) and returns
     ‘NULL’.


File: python.info,  Node: Parsing arguments and building values,  Next: String conversion and formatting,  Prev: Data marshalling support,  Up: Utilities<2>

7.6.6 Parsing arguments and building values
-------------------------------------------

These functions are useful when creating your own extensions functions
and methods.  Additional information and examples are available in *note
Extending and Embedding the Python Interpreter: 1332.

The first three of these functions described, *note PyArg_ParseTuple():
393, *note PyArg_ParseTupleAndKeywords(): 6c1, and *note PyArg_Parse():
10f0, all use `format strings' which are used to tell the function about
the expected arguments.  The format strings use the same syntax for each
of these functions.

* Menu:

* Parsing arguments: Parsing arguments<3>.
* Building values::


File: python.info,  Node: Parsing arguments<3>,  Next: Building values,  Up: Parsing arguments and building values

7.6.6.1 Parsing arguments
.........................

A format string consists of zero or more “format units.” A format unit
describes one Python object; it is usually a single character or a
parenthesized sequence of format units.  With a few exceptions, a format
unit that is not a parenthesized sequence normally corresponds to a
single address argument to these functions.  In the following
description, the quoted form is the format unit; the entry in (round)
parentheses is the Python object type that matches the format unit; and
the entry in [square] brackets is the type of the C variable(s) whose
address should be passed.

* Menu:

* Strings and buffers::
* Numbers: Numbers<2>.
* Other objects::
* API Functions::


File: python.info,  Node: Strings and buffers,  Next: Numbers<2>,  Up: Parsing arguments<3>

7.6.6.2 Strings and buffers
...........................

These formats allow accessing an object as a contiguous chunk of memory.
You don’t have to provide raw storage for the returned unicode or bytes
area.

In general, when a format sets a pointer to a buffer, the buffer is
managed by the corresponding Python object, and the buffer shares the
lifetime of this object.  You won’t have to release any memory yourself.
The only exceptions are ‘es’, ‘es#’, ‘et’ and ‘et#’.

However, when a *note Py_buffer: bee. structure gets filled, the
underlying buffer is locked so that the caller can subsequently use the
buffer even inside a *note Py_BEGIN_ALLOW_THREADS: 3d3f. block without
the risk of mutable data being resized or destroyed.  As a result, `you
have to call' *note PyBuffer_Release(): e19. after you have finished
processing the data (or in any early abort case).

Unless otherwise stated, buffers are not NUL-terminated.

Some formats require a read-only *note bytes-like object: 6df, and set a
pointer instead of a buffer structure.  They work by checking that the
object’s *note PyBufferProcs.bf_releasebuffer: 3e8a. field is ‘NULL’,
which disallows mutable objects such as *note bytearray: 173.

     Note: For all ‘#’ variants of formats (‘s#’, ‘y#’, etc.), the type
     of the length argument (int or ‘Py_ssize_t’) is controlled by
     defining the macro ‘PY_SSIZE_T_CLEAN’ before including ‘Python.h’.
     If the macro was defined, length is a ‘Py_ssize_t’ rather than an
     ‘int’.  This behavior will change in a future Python version to
     only support ‘Py_ssize_t’ and drop ‘int’ support.  It is best to
     always define ‘PY_SSIZE_T_CLEAN’.

‘s’ (*note str: 205.) [const char *]

     Convert a Unicode object to a C pointer to a character string.  A
     pointer to an existing string is stored in the character pointer
     variable whose address you pass.  The C string is NUL-terminated.
     The Python string must not contain embedded null code points; if it
     does, a *note ValueError: 16d. exception is raised.  Unicode
     objects are converted to C strings using ‘'utf-8'’ encoding.  If
     this conversion fails, a *note UnicodeError: d03. is raised.

          Note: This format does not accept *note bytes-like objects:
          6df.  If you want to accept filesystem paths and convert them
          to C character strings, it is preferable to use the ‘O&’
          format with *note PyUnicode_FSConverter(): 6c5. as
          `converter'.

     Changed in version 3.5: Previously, *note TypeError: 1fe. was
     raised when embedded null code points were encountered in the
     Python string.

‘s*’ (*note str: 205. or *note bytes-like object: 6df.) [Py_buffer]

     This format accepts Unicode objects as well as bytes-like objects.
     It fills a *note Py_buffer: bee. structure provided by the caller.
     In this case the resulting C string may contain embedded NUL bytes.
     Unicode objects are converted to C strings using ‘'utf-8'’
     encoding.

‘s#’ (*note str: 205, read-only *note bytes-like object: 6df.) [const char *, int or ‘Py_ssize_t’]

     Like ‘s*’, except that it doesn’t accept mutable objects.  The
     result is stored into two C variables, the first one a pointer to a
     C string, the second one its length.  The string may contain
     embedded null bytes.  Unicode objects are converted to C strings
     using ‘'utf-8'’ encoding.

‘z’ (*note str: 205. or ‘None’) [const char *]

     Like ‘s’, but the Python object may also be ‘None’, in which case
     the C pointer is set to ‘NULL’.

‘z*’ (*note str: 205, *note bytes-like object: 6df. or ‘None’) [Py_buffer]

     Like ‘s*’, but the Python object may also be ‘None’, in which case
     the ‘buf’ member of the *note Py_buffer: bee. structure is set to
     ‘NULL’.

‘z#’ (*note str: 205, read-only *note bytes-like object: 6df. or ‘None’) [const char *, int or ‘Py_ssize_t’]

     Like ‘s#’, but the Python object may also be ‘None’, in which case
     the C pointer is set to ‘NULL’.

‘y’ (read-only *note bytes-like object: 6df.) [const char *]

     This format converts a bytes-like object to a C pointer to a
     character string; it does not accept Unicode objects.  The bytes
     buffer must not contain embedded null bytes; if it does, a *note
     ValueError: 16d. exception is raised.

     Changed in version 3.5: Previously, *note TypeError: 1fe. was
     raised when embedded null bytes were encountered in the bytes
     buffer.

‘y*’ (*note bytes-like object: 6df.) [Py_buffer]

     This variant on ‘s*’ doesn’t accept Unicode objects, only
     bytes-like objects.  `This is the recommended way to accept binary
     data.'

‘y#’ (read-only *note bytes-like object: 6df.) [const char *, int or ‘Py_ssize_t’]

     This variant on ‘s#’ doesn’t accept Unicode objects, only
     bytes-like objects.

‘S’ (*note bytes: 172.) [PyBytesObject *]

     Requires that the Python object is a *note bytes: 172. object,
     without attempting any conversion.  Raises *note TypeError: 1fe. if
     the object is not a bytes object.  The C variable may also be
     declared as *note PyObject*: 5b5.

‘Y’ (*note bytearray: 173.) [PyByteArrayObject *]

     Requires that the Python object is a *note bytearray: 173. object,
     without attempting any conversion.  Raises *note TypeError: 1fe. if
     the object is not a *note bytearray: 173. object.  The C variable
     may also be declared as *note PyObject*: 5b5.

‘u’ (*note str: 205.) [const Py_UNICODE *]

     Convert a Python Unicode object to a C pointer to a NUL-terminated
     buffer of Unicode characters.  You must pass the address of a *note
     Py_UNICODE: bc5. pointer variable, which will be filled with the
     pointer to an existing Unicode buffer.  Please note that the width
     of a *note Py_UNICODE: bc5. character depends on compilation
     options (it is either 16 or 32 bits).  The Python string must not
     contain embedded null code points; if it does, a *note ValueError:
     16d. exception is raised.

     Changed in version 3.5: Previously, *note TypeError: 1fe. was
     raised when embedded null code points were encountered in the
     Python string.

     Deprecated since version 3.3, will be removed in version 3.12: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsWideCharString(): 53c.

‘u#’ (*note str: 205.) [const Py_UNICODE *, int or ‘Py_ssize_t’]

     This variant on ‘u’ stores into two C variables, the first one a
     pointer to a Unicode data buffer, the second one its length.  This
     variant allows null code points.

     Deprecated since version 3.3, will be removed in version 3.12: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsWideCharString(): 53c.

‘Z’ (*note str: 205. or ‘None’) [const Py_UNICODE *]

     Like ‘u’, but the Python object may also be ‘None’, in which case
     the *note Py_UNICODE: bc5. pointer is set to ‘NULL’.

     Deprecated since version 3.3, will be removed in version 3.12: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsWideCharString(): 53c.

‘Z#’ (*note str: 205. or ‘None’) [const Py_UNICODE *, int or ‘Py_ssize_t’]

     Like ‘u#’, but the Python object may also be ‘None’, in which case
     the *note Py_UNICODE: bc5. pointer is set to ‘NULL’.

     Deprecated since version 3.3, will be removed in version 3.12: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsWideCharString(): 53c.

‘U’ (*note str: 205.) [PyObject *]

     Requires that the Python object is a Unicode object, without
     attempting any conversion.  Raises *note TypeError: 1fe. if the
     object is not a Unicode object.  The C variable may also be
     declared as *note PyObject*: 5b5.

‘w*’ (read-write *note bytes-like object: 6df.) [Py_buffer]

     This format accepts any object which implements the read-write
     buffer interface.  It fills a *note Py_buffer: bee. structure
     provided by the caller.  The buffer may contain embedded null
     bytes.  The caller have to call *note PyBuffer_Release(): e19. when
     it is done with the buffer.

‘es’ (*note str: 205.) [const char *encoding, char **buffer]

     This variant on ‘s’ is used for encoding Unicode into a character
     buffer.  It only works for encoded data without embedded NUL bytes.

     This format requires two arguments.  The first is only used as
     input, and must be a ‘const char*’ which points to the name of an
     encoding as a NUL-terminated string, or ‘NULL’, in which case
     ‘'utf-8'’ encoding is used.  An exception is raised if the named
     encoding is not known to Python.  The second argument must be a
     ‘char**’; the value of the pointer it references will be set to a
     buffer with the contents of the argument text.  The text will be
     encoded in the encoding specified by the first argument.

     *note PyArg_ParseTuple(): 393. will allocate a buffer of the needed
     size, copy the encoded data into this buffer and adjust `*buffer'
     to reference the newly allocated storage.  The caller is
     responsible for calling *note PyMem_Free(): e6e. to free the
     allocated buffer after use.

‘et’ (*note str: 205, *note bytes: 172. or *note bytearray: 173.) [const char *encoding, char **buffer]

     Same as ‘es’ except that byte string objects are passed through
     without recoding them.  Instead, the implementation assumes that
     the byte string object uses the encoding passed in as parameter.

‘es#’ (*note str: 205.) [const char *encoding, char **buffer, int or ‘Py_ssize_t’ *buffer_length]

     This variant on ‘s#’ is used for encoding Unicode into a character
     buffer.  Unlike the ‘es’ format, this variant allows input data
     which contains NUL characters.

     It requires three arguments.  The first is only used as input, and
     must be a ‘const char*’ which points to the name of an encoding as
     a NUL-terminated string, or ‘NULL’, in which case ‘'utf-8'’
     encoding is used.  An exception is raised if the named encoding is
     not known to Python.  The second argument must be a ‘char**’; the
     value of the pointer it references will be set to a buffer with the
     contents of the argument text.  The text will be encoded in the
     encoding specified by the first argument.  The third argument must
     be a pointer to an integer; the referenced integer will be set to
     the number of bytes in the output buffer.

     There are two modes of operation:

     If `*buffer' points a ‘NULL’ pointer, the function will allocate a
     buffer of the needed size, copy the encoded data into this buffer
     and set `*buffer' to reference the newly allocated storage.  The
     caller is responsible for calling *note PyMem_Free(): e6e. to free
     the allocated buffer after usage.

     If `*buffer' points to a non-‘NULL’ pointer (an already allocated
     buffer), *note PyArg_ParseTuple(): 393. will use this location as
     the buffer and interpret the initial value of `*buffer_length' as
     the buffer size.  It will then copy the encoded data into the
     buffer and NUL-terminate it.  If the buffer is not large enough, a
     *note ValueError: 16d. will be set.

     In both cases, `*buffer_length' is set to the length of the encoded
     data without the trailing NUL byte.

‘et#’ (*note str: 205, *note bytes: 172. or *note bytearray: 173.) [const char *encoding, char **buffer, int or ‘Py_ssize_t’ *buffer_length]

     Same as ‘es#’ except that byte string objects are passed through
     without recoding them.  Instead, the implementation assumes that
     the byte string object uses the encoding passed in as parameter.


File: python.info,  Node: Numbers<2>,  Next: Other objects,  Prev: Strings and buffers,  Up: Parsing arguments<3>

7.6.6.3 Numbers
...............

‘b’ (*note int: 204.) [unsigned char]

     Convert a nonnegative Python integer to an unsigned tiny int,
     stored in a C ‘unsigned char’.

‘B’ (*note int: 204.) [unsigned char]

     Convert a Python integer to a tiny int without overflow checking,
     stored in a C ‘unsigned char’.

‘h’ (*note int: 204.) [short int]

     Convert a Python integer to a C ‘short int’.

‘H’ (*note int: 204.) [unsigned short int]

     Convert a Python integer to a C ‘unsigned short int’, without
     overflow checking.

‘i’ (*note int: 204.) [int]

     Convert a Python integer to a plain C ‘int’.

‘I’ (*note int: 204.) [unsigned int]

     Convert a Python integer to a C ‘unsigned int’, without overflow
     checking.

‘l’ (*note int: 204.) [long int]

     Convert a Python integer to a C ‘long int’.

‘k’ (*note int: 204.) [unsigned long]

     Convert a Python integer to a C ‘unsigned long’ without overflow
     checking.

‘L’ (*note int: 204.) [long long]

     Convert a Python integer to a C ‘long long’.

‘K’ (*note int: 204.) [unsigned long long]

     Convert a Python integer to a C ‘unsigned long long’ without
     overflow checking.

‘n’ (*note int: 204.) [Py_ssize_t]

     Convert a Python integer to a C ‘Py_ssize_t’.

‘c’ (*note bytes: 172. or *note bytearray: 173. of length 1) [char]

     Convert a Python byte, represented as a *note bytes: 172. or *note
     bytearray: 173. object of length 1, to a C ‘char’.

     Changed in version 3.3: Allow *note bytearray: 173. objects.

‘C’ (*note str: 205. of length 1) [int]

     Convert a Python character, represented as a *note str: 205. object
     of length 1, to a C ‘int’.

‘f’ (*note float: 1fd.) [float]

     Convert a Python floating point number to a C ‘float’.

‘d’ (*note float: 1fd.) [double]

     Convert a Python floating point number to a C ‘double’.

‘D’ (*note complex: 2c1.) [Py_complex]

     Convert a Python complex number to a C *note Py_complex: 3e8c.
     structure.


File: python.info,  Node: Other objects,  Next: API Functions,  Prev: Numbers<2>,  Up: Parsing arguments<3>

7.6.6.4 Other objects
.....................

‘O’ (object) [PyObject *]

     Store a Python object (without any conversion) in a C object
     pointer.  The C program thus receives the actual object that was
     passed.  The object’s reference count is not increased.  The
     pointer stored is not ‘NULL’.

‘O!’ (object) [`typeobject', PyObject *]

     Store a Python object in a C object pointer.  This is similar to
     ‘O’, but takes two C arguments: the first is the address of a
     Python type object, the second is the address of the C variable (of
     type *note PyObject*: 5b5.) into which the object pointer is
     stored.  If the Python object does not have the required type,
     *note TypeError: 1fe. is raised.

‘O&’ (object) [`converter', `anything']

     Convert a Python object to a C variable through a `converter'
     function.  This takes two arguments: the first is a function, the
     second is the address of a C variable (of arbitrary type),
     converted to ‘void *’.  The `converter' function in turn is called
     as follows:

          status = converter(object, address);

     where `object' is the Python object to be converted and `address'
     is the ‘void*’ argument that was passed to the *note
     PyArg_Parse*(): 10f0. function.  The returned `status' should be
     ‘1’ for a successful conversion and ‘0’ if the conversion has
     failed.  When the conversion fails, the `converter' function should
     raise an exception and leave the content of `address' unmodified.

     If the `converter' returns ‘Py_CLEANUP_SUPPORTED’, it may get
     called a second time if the argument parsing eventually fails,
     giving the converter a chance to release any memory that it had
     already allocated.  In this second call, the `object' parameter
     will be ‘NULL’; `address' will have the same value as in the
     original call.

     Changed in version 3.1: ‘Py_CLEANUP_SUPPORTED’ was added.

‘p’ (*note bool: 2bd.) [int]

     Tests the value passed in for truth (a boolean `p'redicate) and
     converts the result to its equivalent C true/false integer value.
     Sets the int to ‘1’ if the expression was true and ‘0’ if it was
     false.  This accepts any valid Python value.  See *note Truth Value
     Testing: 1718. for more information about how Python tests values
     for truth.

     New in version 3.3.

‘(items)’ (*note tuple: 1a2.) [`matching-items']

     The object must be a Python sequence whose length is the number of
     format units in `items'.  The C arguments must correspond to the
     individual format units in `items'.  Format units for sequences may
     be nested.

It is possible to pass “long” integers (integers whose value exceeds the
platform’s ‘LONG_MAX’) however no proper range checking is done — the
most significant bits are silently truncated when the receiving field is
too small to receive the value (actually, the semantics are inherited
from downcasts in C — your mileage may vary).

A few other characters have a meaning in a format string.  These may not
occur inside nested parentheses.  They are:

‘|’

     Indicates that the remaining arguments in the Python argument list
     are optional.  The C variables corresponding to optional arguments
     should be initialized to their default value — when an optional
     argument is not specified, *note PyArg_ParseTuple(): 393. does not
     touch the contents of the corresponding C variable(s).

‘$’

     *note PyArg_ParseTupleAndKeywords(): 6c1. only: Indicates that the
     remaining arguments in the Python argument list are keyword-only.
     Currently, all keyword-only arguments must also be optional
     arguments, so ‘|’ must always be specified before ‘$’ in the format
     string.

     New in version 3.3.

‘:’

     The list of format units ends here; the string after the colon is
     used as the function name in error messages (the “associated value”
     of the exception that *note PyArg_ParseTuple(): 393. raises).

‘;’

     The list of format units ends here; the string after the semicolon
     is used as the error message `instead' of the default error
     message.  ‘:’ and ‘;’ mutually exclude each other.

Note that any Python object references which are provided to the caller
are `borrowed' references; do not decrement their reference count!

Additional arguments passed to these functions must be addresses of
variables whose type is determined by the format string; these are used
to store values from the input tuple.  There are a few cases, as
described in the list of format units above, where these parameters are
used as input values; they should match what is specified for the
corresponding format unit in that case.

For the conversion to succeed, the `arg' object must match the format
and the format must be exhausted.  On success, the *note PyArg_Parse*():
10f0. functions return true, otherwise they return false and raise an
appropriate exception.  When the *note PyArg_Parse*(): 10f0. functions
fail due to conversion failure in one of the format units, the variables
at the addresses corresponding to that and the following format units
are left untouched.


File: python.info,  Node: API Functions,  Prev: Other objects,  Up: Parsing arguments<3>

7.6.6.5 API Functions
.....................

 -- C Function: int PyArg_ParseTuple (PyObject *args, const
          char *format, ...)

     Parse the parameters of a function that takes only positional
     parameters into local variables.  Returns true on success; on
     failure, it returns false and raises the appropriate exception.

 -- C Function: int PyArg_VaParse (PyObject *args, const char *format,
          va_list vargs)

     Identical to *note PyArg_ParseTuple(): 393, except that it accepts
     a va_list rather than a variable number of arguments.

 -- C Function: int PyArg_ParseTupleAndKeywords (PyObject *args,
          PyObject *kw, const char *format, char *keywords[], ...)

     Parse the parameters of a function that takes both positional and
     keyword parameters into local variables.  The `keywords' argument
     is a ‘NULL’-terminated array of keyword parameter names.  Empty
     names denote *note positional-only parameters: 3c9.  Returns true
     on success; on failure, it returns false and raises the appropriate
     exception.

     Changed in version 3.6: Added support for *note positional-only
     parameters: 3c9.

 -- C Function: int PyArg_VaParseTupleAndKeywords (PyObject *args,
          PyObject *kw, const char *format, char *keywords[],
          va_list vargs)

     Identical to *note PyArg_ParseTupleAndKeywords(): 6c1, except that
     it accepts a va_list rather than a variable number of arguments.

 -- C Function: int PyArg_ValidateKeywordArguments (PyObject *)

     Ensure that the keys in the keywords argument dictionary are
     strings.  This is only needed if *note
     PyArg_ParseTupleAndKeywords(): 6c1. is not used, since the latter
     already does this check.

     New in version 3.2.

 -- C Function: int PyArg_Parse (PyObject *args, const char *format,
          ...)

     Function used to deconstruct the argument lists of “old-style”
     functions — these are functions which use the ‘METH_OLDARGS’
     parameter parsing method, which has been removed in Python 3.  This
     is not recommended for use in parameter parsing in new code, and
     most code in the standard interpreter has been modified to no
     longer use this for that purpose.  It does remain a convenient way
     to decompose other tuples, however, and may continue to be used for
     that purpose.

 -- C Function: int PyArg_UnpackTuple (PyObject *args, const char *name,
          Py_ssize_t min, Py_ssize_t max, ...)

     A simpler form of parameter retrieval which does not use a format
     string to specify the types of the arguments.  Functions which use
     this method to retrieve their parameters should be declared as
     *note METH_VARARGS: f0a. in function or method tables.  The tuple
     containing the actual parameters should be passed as `args'; it
     must actually be a tuple.  The length of the tuple must be at least
     `min' and no more than `max'; `min' and `max' may be equal.
     Additional arguments must be passed to the function, each of which
     should be a pointer to a *note PyObject*: 5b5. variable; these will
     be filled in with the values from `args'; they will contain
     borrowed references.  The variables which correspond to optional
     parameters not given by `args' will not be filled in; these should
     be initialized by the caller.  This function returns true on
     success and false if `args' is not a tuple or contains the wrong
     number of elements; an exception will be set if there was a
     failure.

     This is an example of the use of this function, taken from the
     sources for the ‘_weakref’ helper module for weak references:

          static PyObject *
          weakref_ref(PyObject *self, PyObject *args)
          {
              PyObject *object;
              PyObject *callback = NULL;
              PyObject *result = NULL;

              if (PyArg_UnpackTuple(args, "ref", 1, 2, &object, &callback)) {
                  result = PyWeakref_NewRef(object, callback);
              }
              return result;
          }

     The call to *note PyArg_UnpackTuple(): f08. in this example is
     entirely equivalent to this call to *note PyArg_ParseTuple(): 393.:

          PyArg_ParseTuple(args, "O|O:ref", &object, &callback)


File: python.info,  Node: Building values,  Prev: Parsing arguments<3>,  Up: Parsing arguments and building values

7.6.6.6 Building values
.......................

 -- C Function: PyObject* Py_BuildValue (const char *format, ...)
     `Return value: New reference.'  Create a new value based on a
     format string similar to those accepted by the *note
     PyArg_Parse*(): 10f0. family of functions and a sequence of values.
     Returns the value or ‘NULL’ in the case of an error; an exception
     will be raised if ‘NULL’ is returned.

     *note Py_BuildValue(): 3f0. does not always build a tuple.  It
     builds a tuple only if its format string contains two or more
     format units.  If the format string is empty, it returns ‘None’; if
     it contains exactly one format unit, it returns whatever object is
     described by that format unit.  To force it to return a tuple of
     size 0 or one, parenthesize the format string.

     When memory buffers are passed as parameters to supply data to
     build objects, as for the ‘s’ and ‘s#’ formats, the required data
     is copied.  Buffers provided by the caller are never referenced by
     the objects created by *note Py_BuildValue(): 3f0.  In other words,
     if your code invokes ‘malloc()’ and passes the allocated memory to
     *note Py_BuildValue(): 3f0, your code is responsible for calling
     ‘free()’ for that memory once *note Py_BuildValue(): 3f0. returns.

     In the following description, the quoted form is the format unit;
     the entry in (round) parentheses is the Python object type that the
     format unit will return; and the entry in [square] brackets is the
     type of the C value(s) to be passed.

     The characters space, tab, colon and comma are ignored in format
     strings (but not within format units such as ‘s#’).  This can be
     used to make long format strings a tad more readable.

     ‘s’ (*note str: 205. or ‘None’) [const char *]

          Convert a null-terminated C string to a Python *note str: 205.
          object using ‘'utf-8'’ encoding.  If the C string pointer is
          ‘NULL’, ‘None’ is used.

     ‘s#’ (*note str: 205. or ‘None’) [const char *, int or ‘Py_ssize_t’]

          Convert a C string and its length to a Python *note str: 205.
          object using ‘'utf-8'’ encoding.  If the C string pointer is
          ‘NULL’, the length is ignored and ‘None’ is returned.

     ‘y’ (*note bytes: 172.) [const char *]

          This converts a C string to a Python *note bytes: 172. object.
          If the C string pointer is ‘NULL’, ‘None’ is returned.

     ‘y#’ (*note bytes: 172.) [const char *, int or ‘Py_ssize_t’]

          This converts a C string and its lengths to a Python object.
          If the C string pointer is ‘NULL’, ‘None’ is returned.

     ‘z’ (*note str: 205. or ‘None’) [const char *]

          Same as ‘s’.

     ‘z#’ (*note str: 205. or ‘None’) [const char *, int or ‘Py_ssize_t’]

          Same as ‘s#’.

     ‘u’ (*note str: 205.) [const wchar_t *]

          Convert a null-terminated ‘wchar_t’ buffer of Unicode (UTF-16
          or UCS-4) data to a Python Unicode object.  If the Unicode
          buffer pointer is ‘NULL’, ‘None’ is returned.

     ‘u#’ (*note str: 205.) [const wchar_t *, int or ‘Py_ssize_t’]

          Convert a Unicode (UTF-16 or UCS-4) data buffer and its length
          to a Python Unicode object.  If the Unicode buffer pointer is
          ‘NULL’, the length is ignored and ‘None’ is returned.

     ‘U’ (*note str: 205. or ‘None’) [const char *]

          Same as ‘s’.

     ‘U#’ (*note str: 205. or ‘None’) [const char *, int or ‘Py_ssize_t’]

          Same as ‘s#’.

     ‘i’ (*note int: 204.) [int]

          Convert a plain C ‘int’ to a Python integer object.

     ‘b’ (*note int: 204.) [char]

          Convert a plain C ‘char’ to a Python integer object.

     ‘h’ (*note int: 204.) [short int]

          Convert a plain C ‘short int’ to a Python integer object.

     ‘l’ (*note int: 204.) [long int]

          Convert a C ‘long int’ to a Python integer object.

     ‘B’ (*note int: 204.) [unsigned char]

          Convert a C ‘unsigned char’ to a Python integer object.

     ‘H’ (*note int: 204.) [unsigned short int]

          Convert a C ‘unsigned short int’ to a Python integer object.

     ‘I’ (*note int: 204.) [unsigned int]

          Convert a C ‘unsigned int’ to a Python integer object.

     ‘k’ (*note int: 204.) [unsigned long]

          Convert a C ‘unsigned long’ to a Python integer object.

     ‘L’ (*note int: 204.) [long long]

          Convert a C ‘long long’ to a Python integer object.

     ‘K’ (*note int: 204.) [unsigned long long]

          Convert a C ‘unsigned long long’ to a Python integer object.

     ‘n’ (*note int: 204.) [Py_ssize_t]

          Convert a C ‘Py_ssize_t’ to a Python integer.

     ‘c’ (*note bytes: 172. of length 1) [char]

          Convert a C ‘int’ representing a byte to a Python *note bytes:
          172. object of length 1.

     ‘C’ (*note str: 205. of length 1) [int]

          Convert a C ‘int’ representing a character to Python *note
          str: 205. object of length 1.

     ‘d’ (*note float: 1fd.) [double]

          Convert a C ‘double’ to a Python floating point number.

     ‘f’ (*note float: 1fd.) [float]

          Convert a C ‘float’ to a Python floating point number.

     ‘D’ (*note complex: 2c1.) [Py_complex *]

          Convert a C *note Py_complex: 3e8c. structure to a Python
          complex number.

     ‘O’ (object) [PyObject *]

          Pass a Python object untouched (except for its reference
          count, which is incremented by one).  If the object passed in
          is a ‘NULL’ pointer, it is assumed that this was caused
          because the call producing the argument found an error and set
          an exception.  Therefore, *note Py_BuildValue(): 3f0. will
          return ‘NULL’ but won’t raise an exception.  If no exception
          has been raised yet, *note SystemError: 6f2. is set.

     ‘S’ (object) [PyObject *]

          Same as ‘O’.

     ‘N’ (object) [PyObject *]

          Same as ‘O’, except it doesn’t increment the reference count
          on the object.  Useful when the object is created by a call to
          an object constructor in the argument list.

     ‘O&’ (object) [`converter', `anything']

          Convert `anything' to a Python object through a `converter'
          function.  The function is called with `anything' (which
          should be compatible with ‘void*’) as its argument and should
          return a “new” Python object, or ‘NULL’ if an error occurred.

     ‘(items)’ (*note tuple: 1a2.) [`matching-items']

          Convert a sequence of C values to a Python tuple with the same
          number of items.

     ‘[items]’ (*note list: 1f8.) [`matching-items']

          Convert a sequence of C values to a Python list with the same
          number of items.

     ‘{items}’ (*note dict: 164.) [`matching-items']

          Convert a sequence of C values to a Python dictionary.  Each
          pair of consecutive C values adds one item to the dictionary,
          serving as key and value, respectively.

     If there is an error in the format string, the *note SystemError:
     6f2. exception is set and ‘NULL’ returned.

 -- C Function: PyObject* Py_VaBuildValue (const char *format,
          va_list vargs)
     `Return value: New reference.'  Identical to *note Py_BuildValue():
     3f0, except that it accepts a va_list rather than a variable number
     of arguments.


File: python.info,  Node: String conversion and formatting,  Next: Reflection,  Prev: Parsing arguments and building values,  Up: Utilities<2>

7.6.7 String conversion and formatting
--------------------------------------

Functions for number conversion and formatted string output.

 -- C Function: int PyOS_snprintf (char *str, size_t size, const
          char *format, ...)

     Output not more than `size' bytes to `str' according to the format
     string `format' and the extra arguments.  See the Unix man page
     ‘snprintf(3)’.

 -- C Function: int PyOS_vsnprintf (char *str, size_t size, const
          char *format, va_list va)

     Output not more than `size' bytes to `str' according to the format
     string `format' and the variable argument list `va'.  Unix man page
     ‘vsnprintf(3)’.

*note PyOS_snprintf(): f0b. and *note PyOS_vsnprintf(): f0c. wrap the
Standard C library functions ‘snprintf()’ and ‘vsnprintf()’.  Their
purpose is to guarantee consistent behavior in corner cases, which the
Standard C functions do not.

The wrappers ensure that ‘str[size-1]’ is always ‘'\0'’ upon return.
They never write more than `size' bytes (including the trailing ‘'\0'’)
into str.  Both functions require that ‘str != NULL’, ‘size > 0’ and
‘format != NULL’.

If the platform doesn’t have ‘vsnprintf()’ and the buffer size needed to
avoid truncation exceeds `size' by more than 512 bytes, Python aborts
with a *note Py_FatalError(): 266.

The return value (`rv') for these functions should be interpreted as
follows:

   * When ‘0 <= rv < size’, the output conversion was successful and
     `rv' characters were written to `str' (excluding the trailing
     ‘'\0'’ byte at ‘str[rv]’).

   * When ‘rv >= size’, the output conversion was truncated and a buffer
     with ‘rv + 1’ bytes would have been needed to succeed.
     ‘str[size-1]’ is ‘'\0'’ in this case.

   * When ‘rv < 0’, “something bad happened.” ‘str[size-1]’ is ‘'\0'’ in
     this case too, but the rest of `str' is undefined.  The exact cause
     of the error depends on the underlying platform.

The following functions provide locale-independent string to number
conversions.

 -- C Function: double PyOS_string_to_double (const char *s,
          char **endptr, PyObject *overflow_exception)

     Convert a string ‘s’ to a ‘double’, raising a Python exception on
     failure.  The set of accepted strings corresponds to the set of
     strings accepted by Python’s *note float(): 1fd. constructor,
     except that ‘s’ must not have leading or trailing whitespace.  The
     conversion is independent of the current locale.

     If ‘endptr’ is ‘NULL’, convert the whole string.  Raise *note
     ValueError: 16d. and return ‘-1.0’ if the string is not a valid
     representation of a floating-point number.

     If endptr is not ‘NULL’, convert as much of the string as possible
     and set ‘*endptr’ to point to the first unconverted character.  If
     no initial segment of the string is the valid representation of a
     floating-point number, set ‘*endptr’ to point to the beginning of
     the string, raise ValueError, and return ‘-1.0’.

     If ‘s’ represents a value that is too large to store in a float
     (for example, ‘"1e500"’ is such a string on many platforms) then if
     ‘overflow_exception’ is ‘NULL’ return ‘Py_HUGE_VAL’ (with an
     appropriate sign) and don’t set any exception.  Otherwise,
     ‘overflow_exception’ must point to a Python exception object; raise
     that exception and return ‘-1.0’.  In both cases, set ‘*endptr’ to
     point to the first character after the converted value.

     If any other error occurs during the conversion (for example an
     out-of-memory error), set the appropriate Python exception and
     return ‘-1.0’.

     New in version 3.1.

 -- C Function: char* PyOS_double_to_string (double val,
          char format_code, int precision, int flags, int *ptype)

     Convert a ‘double’ `val' to a string using supplied `format_code',
     `precision', and `flags'.

     `format_code' must be one of ‘'e'’, ‘'E'’, ‘'f'’, ‘'F'’, ‘'g'’,
     ‘'G'’ or ‘'r'’.  For ‘'r'’, the supplied `precision' must be 0 and
     is ignored.  The ‘'r'’ format code specifies the standard *note
     repr(): 8b9. format.

     `flags' can be zero or more of the values ‘Py_DTSF_SIGN’,
     ‘Py_DTSF_ADD_DOT_0’, or ‘Py_DTSF_ALT’, or-ed together:

        * ‘Py_DTSF_SIGN’ means to always precede the returned string
          with a sign character, even if `val' is non-negative.

        * ‘Py_DTSF_ADD_DOT_0’ means to ensure that the returned string
          will not look like an integer.

        * ‘Py_DTSF_ALT’ means to apply “alternate” formatting rules.
          See the documentation for the *note PyOS_snprintf(): f0b.
          ‘'#'’ specifier for details.

     If `ptype' is non-‘NULL’, then the value it points to will be set
     to one of ‘Py_DTST_FINITE’, ‘Py_DTST_INFINITE’, or ‘Py_DTST_NAN’,
     signifying that `val' is a finite number, an infinite number, or
     not a number, respectively.

     The return value is a pointer to `buffer' with the converted string
     or ‘NULL’ if the conversion failed.  The caller is responsible for
     freeing the returned string by calling *note PyMem_Free(): e6e.

     New in version 3.1.

 -- C Function: int PyOS_stricmp (const char *s1, const char *s2)

     Case insensitive comparison of strings.  The function works almost
     identically to ‘strcmp()’ except that it ignores the case.

 -- C Function: int PyOS_strnicmp (const char *s1, const char *s2,
          Py_ssize_t  size)

     Case insensitive comparison of strings.  The function works almost
     identically to ‘strncmp()’ except that it ignores the case.


File: python.info,  Node: Reflection,  Next: Codec registry and support functions,  Prev: String conversion and formatting,  Up: Utilities<2>

7.6.8 Reflection
----------------

 -- C Function: PyObject* PyEval_GetBuiltins (void)
     `Return value: Borrowed reference.'  Return a dictionary of the
     builtins in the current execution frame, or the interpreter of the
     thread state if no frame is currently executing.

 -- C Function: PyObject* PyEval_GetLocals (void)
     `Return value: Borrowed reference.'  Return a dictionary of the
     local variables in the current execution frame, or ‘NULL’ if no
     frame is currently executing.

 -- C Function: PyObject* PyEval_GetGlobals (void)
     `Return value: Borrowed reference.'  Return a dictionary of the
     global variables in the current execution frame, or ‘NULL’ if no
     frame is currently executing.

 -- C Function: PyFrameObject* PyEval_GetFrame (void)
     `Return value: Borrowed reference.'  Return the current thread
     state’s frame, which is ‘NULL’ if no frame is currently executing.

     See also *note PyThreadState_GetFrame(): 24e.

 -- C Function: int PyFrame_GetBack (PyFrameObject *frame)

     Get the `frame' next outer frame.

     Return a strong reference, or ‘NULL’ if `frame' has no outer frame.

     `frame' must not be ‘NULL’.

     New in version 3.9.

 -- C Function: int PyFrame_GetCode (PyFrameObject *frame)

     Get the `frame' code.

     Return a strong reference.

     `frame' must not be ‘NULL’.  The result (frame code) cannot be
     ‘NULL’.

     New in version 3.9.

 -- C Function: int PyFrame_GetLineNumber (PyFrameObject *frame)

     Return the line number that `frame' is currently executing.

     `frame' must not be ‘NULL’.

 -- C Function: const char* PyEval_GetFuncName (PyObject *func)

     Return the name of `func' if it is a function, class or instance
     object, else the name of `func's type.

 -- C Function: const char* PyEval_GetFuncDesc (PyObject *func)

     Return a description string, depending on the type of `func'.
     Return values include “()” for functions and methods, ”
     constructor”, ” instance”, and ” object”.  Concatenated with the
     result of *note PyEval_GetFuncName(): 3ea1, the result will be a
     description of `func'.


File: python.info,  Node: Codec registry and support functions,  Prev: Reflection,  Up: Utilities<2>

7.6.9 Codec registry and support functions
------------------------------------------

 -- C Function: int PyCodec_Register (PyObject *search_function)

     Register a new codec search function.

     As side effect, this tries to load the ‘encodings’ package, if not
     yet done, to make sure that it is always first in the list of
     search functions.

 -- C Function: int PyCodec_KnownEncoding (const char *encoding)

     Return ‘1’ or ‘0’ depending on whether there is a registered codec
     for the given `encoding'.  This function always succeeds.

 -- C Function: PyObject* PyCodec_Encode (PyObject *object, const
          char *encoding, const char *errors)
     `Return value: New reference.'  Generic codec based encoding API.

     `object' is passed through the encoder function found for the given
     `encoding' using the error handling method defined by `errors'.
     `errors' may be ‘NULL’ to use the default method defined for the
     codec.  Raises a *note LookupError: 1790. if no encoder can be
     found.

 -- C Function: PyObject* PyCodec_Decode (PyObject *object, const
          char *encoding, const char *errors)
     `Return value: New reference.'  Generic codec based decoding API.

     `object' is passed through the decoder function found for the given
     `encoding' using the error handling method defined by `errors'.
     `errors' may be ‘NULL’ to use the default method defined for the
     codec.  Raises a *note LookupError: 1790. if no encoder can be
     found.

* Menu:

* Codec lookup API::
* Registry API for Unicode encoding error handlers::


File: python.info,  Node: Codec lookup API,  Next: Registry API for Unicode encoding error handlers,  Up: Codec registry and support functions

7.6.9.1 Codec lookup API
........................

In the following functions, the `encoding' string is looked up converted
to all lower-case characters, which makes encodings looked up through
this mechanism effectively case-insensitive.  If no codec is found, a
*note KeyError: 3e9. is set and ‘NULL’ returned.

 -- C Function: PyObject* PyCodec_Encoder (const char *encoding)
     `Return value: New reference.'  Get an encoder function for the
     given `encoding'.

 -- C Function: PyObject* PyCodec_Decoder (const char *encoding)
     `Return value: New reference.'  Get a decoder function for the
     given `encoding'.

 -- C Function: PyObject* PyCodec_IncrementalEncoder (const
          char *encoding, const char *errors)
     `Return value: New reference.'  Get an *note IncrementalEncoder:
     196e. object for the given `encoding'.

 -- C Function: PyObject* PyCodec_IncrementalDecoder (const
          char *encoding, const char *errors)
     `Return value: New reference.'  Get an *note IncrementalDecoder:
     196f. object for the given `encoding'.

 -- C Function: PyObject* PyCodec_StreamReader (const char *encoding,
          PyObject *stream, const char *errors)
     `Return value: New reference.'  Get a *note StreamReader: 1973.
     factory function for the given `encoding'.

 -- C Function: PyObject* PyCodec_StreamWriter (const char *encoding,
          PyObject *stream, const char *errors)
     `Return value: New reference.'  Get a *note StreamWriter: 1972.
     factory function for the given `encoding'.


File: python.info,  Node: Registry API for Unicode encoding error handlers,  Prev: Codec lookup API,  Up: Codec registry and support functions

7.6.9.2 Registry API for Unicode encoding error handlers
........................................................

 -- C Function: int PyCodec_RegisterError (const char *name,
          PyObject *error)

     Register the error handling callback function `error' under the
     given `name'.  This callback function will be called by a codec
     when it encounters unencodable characters/undecodable bytes and
     `name' is specified as the error parameter in the call to the
     encode/decode function.

     The callback gets a single argument, an instance of *note
     UnicodeEncodeError: 32a, *note UnicodeDecodeError: 32b. or *note
     UnicodeTranslateError: 185b. that holds information about the
     problematic sequence of characters or bytes and their offset in the
     original string (see *note Unicode Exception Objects: 3e26. for
     functions to extract this information).  The callback must either
     raise the given exception, or return a two-item tuple containing
     the replacement for the problematic sequence, and an integer giving
     the offset in the original string at which encoding/decoding should
     be resumed.

     Return ‘0’ on success, ‘-1’ on error.

 -- C Function: PyObject* PyCodec_LookupError (const char *name)
     `Return value: New reference.'  Lookup the error handling callback
     function registered under `name'.  As a special case ‘NULL’ can be
     passed, in which case the error handling callback for “strict” will
     be returned.

 -- C Function: PyObject* PyCodec_StrictErrors (PyObject *exc)
     `Return value: Always NULL.' Raise `exc' as an exception.

 -- C Function: PyObject* PyCodec_IgnoreErrors (PyObject *exc)
     `Return value: New reference.'  Ignore the unicode error, skipping
     the faulty input.

 -- C Function: PyObject* PyCodec_ReplaceErrors (PyObject *exc)
     `Return value: New reference.'  Replace the unicode encode error
     with ‘?’ or ‘U+FFFD’.

 -- C Function: PyObject* PyCodec_XMLCharRefReplaceErrors
          (PyObject *exc)
     `Return value: New reference.'  Replace the unicode encode error
     with XML character references.

 -- C Function: PyObject* PyCodec_BackslashReplaceErrors (PyObject *exc)
     `Return value: New reference.'  Replace the unicode encode error
     with backslash escapes (‘\x’, ‘\u’ and ‘\U’).

 -- C Function: PyObject* PyCodec_NameReplaceErrors (PyObject *exc)
     `Return value: New reference.'  Replace the unicode encode error
     with ‘\N{...}’ escapes.

     New in version 3.5.


File: python.info,  Node: Abstract Objects Layer,  Next: Concrete Objects Layer,  Prev: Utilities<2>,  Up: Python/C API Reference Manual

7.7 Abstract Objects Layer
==========================

The functions in this chapter interact with Python objects regardless of
their type, or with wide classes of object types (e.g.  all numerical
types, or all sequence types).  When used on object types for which they
do not apply, they will raise a Python exception.

It is not possible to use these functions on objects that are not
properly initialized, such as a list object that has been created by
*note PyList_New(): 3dc6, but whose items have not been set to some
non-‘NULL’ value yet.

* Menu:

* Object Protocol::
* Call Protocol::
* Number Protocol::
* Sequence Protocol::
* Mapping Protocol::
* Iterator Protocol::
* Buffer Protocol::
* Old Buffer Protocol::


File: python.info,  Node: Object Protocol,  Next: Call Protocol,  Up: Abstract Objects Layer

7.7.1 Object Protocol
---------------------

 -- C Variable: PyObject* Py_NotImplemented

     The ‘NotImplemented’ singleton, used to signal that an operation is
     not implemented for the given type combination.

 -- C Macro: Py_RETURN_NOTIMPLEMENTED

     Properly handle returning *note Py_NotImplemented: 3ebd. from
     within a C function (that is, increment the reference count of
     NotImplemented and return it).

 -- C Function: int PyObject_Print (PyObject *o, FILE *fp, int flags)

     Print an object `o', on file `fp'.  Returns ‘-1’ on error.  The
     flags argument is used to enable certain printing options.  The
     only option currently supported is ‘Py_PRINT_RAW’; if given, the
     *note str(): 205. of the object is written instead of the *note
     repr(): 8b9.

 -- C Function: int PyObject_HasAttr (PyObject *o, PyObject *attr_name)

     Returns ‘1’ if `o' has the attribute `attr_name', and ‘0’
     otherwise.  This is equivalent to the Python expression ‘hasattr(o,
     attr_name)’.  This function always succeeds.

     Note that exceptions which occur while calling *note __getattr__():
     42a. and *note __getattribute__(): 54c. methods will get
     suppressed.  To get error reporting use *note PyObject_GetAttr():
     3ec0. instead.

 -- C Function: int PyObject_HasAttrString (PyObject *o, const
          char *attr_name)

     Returns ‘1’ if `o' has the attribute `attr_name', and ‘0’
     otherwise.  This is equivalent to the Python expression ‘hasattr(o,
     attr_name)’.  This function always succeeds.

     Note that exceptions which occur while calling *note __getattr__():
     42a. and *note __getattribute__(): 54c. methods and creating a
     temporary string object will get suppressed.  To get error
     reporting use *note PyObject_GetAttrString(): 3d34. instead.

 -- C Function: PyObject* PyObject_GetAttr (PyObject *o,
          PyObject *attr_name)
     `Return value: New reference.'  Retrieve an attribute named
     `attr_name' from object `o'.  Returns the attribute value on
     success, or ‘NULL’ on failure.  This is the equivalent of the
     Python expression ‘o.attr_name’.

 -- C Function: PyObject* PyObject_GetAttrString (PyObject *o, const
          char *attr_name)
     `Return value: New reference.'  Retrieve an attribute named
     `attr_name' from object `o'.  Returns the attribute value on
     success, or ‘NULL’ on failure.  This is the equivalent of the
     Python expression ‘o.attr_name’.

 -- C Function: PyObject* PyObject_GenericGetAttr (PyObject *o,
          PyObject *name)
     `Return value: New reference.'  Generic attribute getter function
     that is meant to be put into a type object’s ‘tp_getattro’ slot.
     It looks for a descriptor in the dictionary of classes in the
     object’s MRO as well as an attribute in the object’s *note
     __dict__: 5f6. (if present).  As outlined in *note Implementing
     Descriptors: 5e4, data descriptors take preference over instance
     attributes, while non-data descriptors don’t.  Otherwise, an *note
     AttributeError: 4a2. is raised.

 -- C Function: int PyObject_SetAttr (PyObject *o, PyObject *attr_name,
          PyObject *v)

     Set the value of the attribute named `attr_name', for object `o',
     to the value `v'.  Raise an exception and return ‘-1’ on failure;
     return ‘0’ on success.  This is the equivalent of the Python
     statement ‘o.attr_name = v’.

     If `v' is ‘NULL’, the attribute is deleted, however this feature is
     deprecated in favour of using *note PyObject_DelAttr(): 3ec4.

 -- C Function: int PyObject_SetAttrString (PyObject *o, const
          char *attr_name, PyObject *v)

     Set the value of the attribute named `attr_name', for object `o',
     to the value `v'.  Raise an exception and return ‘-1’ on failure;
     return ‘0’ on success.  This is the equivalent of the Python
     statement ‘o.attr_name = v’.

     If `v' is ‘NULL’, the attribute is deleted, however this feature is
     deprecated in favour of using *note PyObject_DelAttrString(): 3ec6.

 -- C Function: int PyObject_GenericSetAttr (PyObject *o,
          PyObject *name, PyObject *value)

     Generic attribute setter and deleter function that is meant to be
     put into a type object’s *note tp_setattro: 3d76. slot.  It looks
     for a data descriptor in the dictionary of classes in the object’s
     MRO, and if found it takes preference over setting or deleting the
     attribute in the instance dictionary.  Otherwise, the attribute is
     set or deleted in the object’s *note __dict__: 5f6. (if present).
     On success, ‘0’ is returned, otherwise an *note AttributeError:
     4a2. is raised and ‘-1’ is returned.

 -- C Function: int PyObject_DelAttr (PyObject *o, PyObject *attr_name)

     Delete attribute named `attr_name', for object `o'.  Returns ‘-1’
     on failure.  This is the equivalent of the Python statement ‘del
     o.attr_name’.

 -- C Function: int PyObject_DelAttrString (PyObject *o, const
          char *attr_name)

     Delete attribute named `attr_name', for object `o'.  Returns ‘-1’
     on failure.  This is the equivalent of the Python statement ‘del
     o.attr_name’.

 -- C Function: PyObject* PyObject_GenericGetDict (PyObject *o,
          void *context)
     `Return value: New reference.'  A generic implementation for the
     getter of a ‘__dict__’ descriptor.  It creates the dictionary if
     necessary.

     New in version 3.3.

 -- C Function: int PyObject_GenericSetDict (PyObject *o,
          PyObject *value, void *context)

     A generic implementation for the setter of a ‘__dict__’ descriptor.
     This implementation does not allow the dictionary to be deleted.

     New in version 3.3.

 -- C Function: PyObject* PyObject_RichCompare (PyObject *o1,
          PyObject *o2, int opid)
     `Return value: New reference.'  Compare the values of `o1' and `o2'
     using the operation specified by `opid', which must be one of
     ‘Py_LT’, ‘Py_LE’, ‘Py_EQ’, ‘Py_NE’, ‘Py_GT’, or ‘Py_GE’,
     corresponding to ‘<’, ‘<=’, ‘==’, ‘!=’, ‘>’, or ‘>=’ respectively.
     This is the equivalent of the Python expression ‘o1 op o2’, where
     ‘op’ is the operator corresponding to `opid'.  Returns the value of
     the comparison on success, or ‘NULL’ on failure.

 -- C Function: int PyObject_RichCompareBool (PyObject *o1,
          PyObject *o2, int opid)

     Compare the values of `o1' and `o2' using the operation specified
     by `opid', which must be one of ‘Py_LT’, ‘Py_LE’, ‘Py_EQ’, ‘Py_NE’,
     ‘Py_GT’, or ‘Py_GE’, corresponding to ‘<’, ‘<=’, ‘==’, ‘!=’, ‘>’,
     or ‘>=’ respectively.  Returns ‘-1’ on error, ‘0’ if the result is
     false, ‘1’ otherwise.  This is the equivalent of the Python
     expression ‘o1 op o2’, where ‘op’ is the operator corresponding to
     `opid'.

     Note: If `o1' and `o2' are the same object, *note
     PyObject_RichCompareBool(): 109c. will always return ‘1’ for
     ‘Py_EQ’ and ‘0’ for ‘Py_NE’.

 -- C Function: PyObject* PyObject_Repr (PyObject *o)
     `Return value: New reference.'

     Compute a string representation of object `o'.  Returns the string
     representation on success, ‘NULL’ on failure.  This is the
     equivalent of the Python expression ‘repr(o)’.  Called by the *note
     repr(): 8b9. built-in function.

     Changed in version 3.4: This function now includes a debug
     assertion to help ensure that it does not silently discard an
     active exception.

 -- C Function: PyObject* PyObject_ASCII (PyObject *o)
     `Return value: New reference.'

     As *note PyObject_Repr(): a49, compute a string representation of
     object `o', but escape the non-ASCII characters in the string
     returned by *note PyObject_Repr(): a49. with ‘\x’, ‘\u’ or ‘\U’
     escapes.  This generates a string similar to that returned by *note
     PyObject_Repr(): a49. in Python 2.  Called by the *note ascii():
     e11. built-in function.

 -- C Function: PyObject* PyObject_Str (PyObject *o)
     `Return value: New reference.'  Compute a string representation of
     object `o'.  Returns the string representation on success, ‘NULL’
     on failure.  This is the equivalent of the Python expression
     ‘str(o)’.  Called by the *note str(): 205. built-in function and,
     therefore, by the *note print(): 971. function.

     Changed in version 3.4: This function now includes a debug
     assertion to help ensure that it does not silently discard an
     active exception.

 -- C Function: PyObject* PyObject_Bytes (PyObject *o)
     `Return value: New reference.'

     Compute a bytes representation of object `o'.  ‘NULL’ is returned
     on failure and a bytes object on success.  This is equivalent to
     the Python expression ‘bytes(o)’, when `o' is not an integer.
     Unlike ‘bytes(o)’, a TypeError is raised when `o' is an integer
     instead of a zero-initialized bytes object.

 -- C Function: int PyObject_IsSubclass (PyObject *derived,
          PyObject *cls)

     Return ‘1’ if the class `derived' is identical to or derived from
     the class `cls', otherwise return ‘0’.  In case of an error, return
     ‘-1’.

     If `cls' is a tuple, the check will be done against every entry in
     `cls'.  The result will be ‘1’ when at least one of the checks
     returns ‘1’, otherwise it will be ‘0’.

     If `cls' has a *note __subclasscheck__(): 1585. method, it will be
     called to determine the subclass status as described in PEP
     3119(1).  Otherwise, `derived' is a subclass of `cls' if it is a
     direct or indirect subclass, i.e.  contained in ‘cls.__mro__’.

     Normally only class objects, i.e.  instances of *note type: 6ff. or
     a derived class, are considered classes.  However, objects can
     override this by having a ‘__bases__’ attribute (which must be a
     tuple of base classes).

 -- C Function: int PyObject_IsInstance (PyObject *inst, PyObject *cls)

     Return ‘1’ if `inst' is an instance of the class `cls' or a
     subclass of `cls', or ‘0’ if not.  On error, returns ‘-1’ and sets
     an exception.

     If `cls' is a tuple, the check will be done against every entry in
     `cls'.  The result will be ‘1’ when at least one of the checks
     returns ‘1’, otherwise it will be ‘0’.

     If `cls' has a *note __instancecheck__(): 1584. method, it will be
     called to determine the subclass status as described in PEP
     3119(2).  Otherwise, `inst' is an instance of `cls' if its class is
     a subclass of `cls'.

     An instance `inst' can override what is considered its class by
     having a ‘__class__’ attribute.

     An object `cls' can override if it is considered a class, and what
     its base classes are, by having a ‘__bases__’ attribute (which must
     be a tuple of base classes).

 -- C Function: Py_hash_t PyObject_Hash (PyObject *o)

     Compute and return the hash value of an object `o'.  On failure,
     return ‘-1’.  This is the equivalent of the Python expression
     ‘hash(o)’.

     Changed in version 3.2: The return type is now Py_hash_t.  This is
     a signed integer the same size as Py_ssize_t.

 -- C Function: Py_hash_t PyObject_HashNotImplemented (PyObject *o)

     Set a *note TypeError: 1fe. indicating that ‘type(o)’ is not
     hashable and return ‘-1’.  This function receives special treatment
     when stored in a ‘tp_hash’ slot, allowing a type to explicitly
     indicate to the interpreter that it is not hashable.

 -- C Function: int PyObject_IsTrue (PyObject *o)

     Returns ‘1’ if the object `o' is considered to be true, and ‘0’
     otherwise.  This is equivalent to the Python expression ‘not not
     o’.  On failure, return ‘-1’.

 -- C Function: int PyObject_Not (PyObject *o)

     Returns ‘0’ if the object `o' is considered to be true, and ‘1’
     otherwise.  This is equivalent to the Python expression ‘not o’.
     On failure, return ‘-1’.

 -- C Function: PyObject* PyObject_Type (PyObject *o)
     `Return value: New reference.'

     When `o' is non-‘NULL’, returns a type object corresponding to the
     object type of object `o'.  On failure, raises *note SystemError:
     6f2. and returns ‘NULL’.  This is equivalent to the Python
     expression ‘type(o)’.  This function increments the reference count
     of the return value.  There’s really no reason to use this function
     instead of the common expression ‘o->ob_type’, which returns a
     pointer of type *note PyTypeObject*: 3f5, except when the
     incremented reference count is needed.

 -- C Function: int PyObject_TypeCheck (PyObject *o, PyTypeObject *type)

     Return true if the object `o' is of type `type' or a subtype of
     `type'.  Both parameters must be non-‘NULL’.

 -- C Function: Py_ssize_t PyObject_Size (PyObject *o)
 -- C Function: Py_ssize_t PyObject_Length (PyObject *o)

     Return the length of object `o'.  If the object `o' provides either
     the sequence and mapping protocols, the sequence length is
     returned.  On error, ‘-1’ is returned.  This is the equivalent to
     the Python expression ‘len(o)’.

 -- C Function: Py_ssize_t PyObject_LengthHint (PyObject *o,
          Py_ssize_t defaultvalue)

     Return an estimated length for the object `o'.  First try to return
     its actual length, then an estimate using *note __length_hint__():
     8f9, and finally return the default value.  On error return ‘-1’.
     This is the equivalent to the Python expression
     ‘operator.length_hint(o, defaultvalue)’.

     New in version 3.4.

 -- C Function: PyObject* PyObject_GetItem (PyObject *o, PyObject *key)
     `Return value: New reference.'  Return element of `o' corresponding
     to the object `key' or ‘NULL’ on failure.  This is the equivalent
     of the Python expression ‘o[key]’.

 -- C Function: int PyObject_SetItem (PyObject *o, PyObject *key,
          PyObject *v)

     Map the object `key' to the value `v'.  Raise an exception and
     return ‘-1’ on failure; return ‘0’ on success.  This is the
     equivalent of the Python statement ‘o[key] = v’.  This function
     `does not' steal a reference to `v'.

 -- C Function: int PyObject_DelItem (PyObject *o, PyObject *key)

     Remove the mapping for the object `key' from the object `o'.
     Return ‘-1’ on failure.  This is equivalent to the Python statement
     ‘del o[key]’.

 -- C Function: PyObject* PyObject_Dir (PyObject *o)
     `Return value: New reference.'  This is equivalent to the Python
     expression ‘dir(o)’, returning a (possibly empty) list of strings
     appropriate for the object argument, or ‘NULL’ if there was an
     error.  If the argument is ‘NULL’, this is like the Python ‘dir()’,
     returning the names of the current locals; in this case, if no
     execution frame is active then ‘NULL’ is returned but *note
     PyErr_Occurred(): 3d1a. will return false.

 -- C Function: PyObject* PyObject_GetIter (PyObject *o)
     `Return value: New reference.'  This is equivalent to the Python
     expression ‘iter(o)’.  It returns a new iterator for the object
     argument, or the object itself if the object is already an
     iterator.  Raises *note TypeError: 1fe. and returns ‘NULL’ if the
     object cannot be iterated.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3119

   (2) https://www.python.org/dev/peps/pep-3119


File: python.info,  Node: Call Protocol,  Next: Number Protocol,  Prev: Object Protocol,  Up: Abstract Objects Layer

7.7.2 Call Protocol
-------------------

CPython supports two different calling protocols: `tp_call' and
vectorcall.

* Menu:

* The tp_call Protocol::
* The Vectorcall Protocol::
* Object Calling API::
* Call Support API::


File: python.info,  Node: The tp_call Protocol,  Next: The Vectorcall Protocol,  Up: Call Protocol

7.7.2.1 The `tp_call' Protocol
..............................

Instances of classes that set *note tp_call: 3d82. are callable.  The
signature of the slot is:

     PyObject *tp_call(PyObject *callable, PyObject *args, PyObject *kwargs);

A call is made using a tuple for the positional arguments and a dict for
the keyword arguments, similarly to ‘callable(*args, **kwargs)’ in
Python code.  `args' must be non-NULL (use an empty tuple if there are
no arguments) but `kwargs' may be `NULL' if there are no keyword
arguments.

This convention is not only used by `tp_call': *note tp_new: 3d53. and
*note tp_init: 3d5a. also pass arguments this way.

To call an object, use *note PyObject_Call(): 23c. or other *note call
API: 3ed8.


File: python.info,  Node: The Vectorcall Protocol,  Next: Object Calling API,  Prev: The tp_call Protocol,  Up: Call Protocol

7.7.2.2 The Vectorcall Protocol
...............................

New in version 3.9.

The vectorcall protocol was introduced in PEP 590(1) as an additional
protocol for making calls more efficient.

As rule of thumb, CPython will prefer the vectorcall for internal calls
if the callable supports it.  However, this is not a hard rule.
Additionally, some third-party extensions use `tp_call' directly (rather
than using *note PyObject_Call(): 23c.).  Therefore, a class supporting
vectorcall must also implement *note tp_call: 3d82.  Moreover, the
callable must behave the same regardless of which protocol is used.  The
recommended way to achieve this is by setting *note tp_call: 3d82. to
*note PyVectorcall_Call(): 3eda.  This bears repeating:

     Warning: A class supporting vectorcall `must' also implement *note
     tp_call: 3d82. with the same semantics.

A class should not implement vectorcall if that would be slower than
`tp_call'.  For example, if the callee needs to convert the arguments to
an args tuple and kwargs dict anyway, then there is no point in
implementing vectorcall.

Classes can implement the vectorcall protocol by enabling the *note
Py_TPFLAGS_HAVE_VECTORCALL: 3edb. flag and setting *note
tp_vectorcall_offset: 3edc. to the offset inside the object structure
where a `vectorcallfunc' appears.  This is a pointer to a function with
the following signature:

 -- C Type: PyObject *(*vectorcallfunc) (PyObject *callable, PyObject
          *const *args, size_t nargsf, PyObject *kwnames)

   - `callable' is the object being called.

   - 
     `args' is a C array consisting of the positional arguments followed by the

          values of the keyword arguments.  This can be `NULL' if there
          are no arguments.

   - 
     `nargsf' is the number of positional arguments plus possibly the

          ‘PY_VECTORCALL_ARGUMENTS_OFFSET’ flag.  To get the actual
          number of positional arguments from `nargsf', use *note
          PyVectorcall_NARGS(): 3ede.

   - 
     `kwnames' is a tuple containing the names of the keyword arguments;

          in other words, the keys of the kwargs dict.  These names must
          be strings (instances of ‘str’ or a subclass) and they must be
          unique.  If there are no keyword arguments, then `kwnames' can
          instead be `NULL'.

 -- C Macro: PY_VECTORCALL_ARGUMENTS_OFFSET

     If this flag is set in a vectorcall `nargsf' argument, the callee
     is allowed to temporarily change ‘args[-1]’.  In other words,
     `args' points to argument 1 (not 0) in the allocated vector.  The
     callee must restore the value of ‘args[-1]’ before returning.

     For *note PyObject_VectorcallMethod(): 3ee0, this flag means
     instead that ‘args[0]’ may be changed.

     Whenever they can do so cheaply (without additional allocation),
     callers are encouraged to use ‘PY_VECTORCALL_ARGUMENTS_OFFSET’.
     Doing so will allow callables such as bound methods to make their
     onward calls (which include a prepended `self' argument) very
     efficiently.

To call an object that implements vectorcall, use a *note call API:
3ed8. function as with any other callable.  *note PyObject_Vectorcall():
3ee1. will usually be most efficient.

     Note: In CPython 3.8, the vectorcall API and related functions were
     available provisionally under names with a leading underscore:
     ‘_PyObject_Vectorcall’, ‘_Py_TPFLAGS_HAVE_VECTORCALL’,
     ‘_PyObject_VectorcallMethod’, ‘_PyVectorcall_Function’,
     ‘_PyObject_CallOneArg’, ‘_PyObject_CallMethodNoArgs’,
     ‘_PyObject_CallMethodOneArg’.  Additionally,
     ‘PyObject_VectorcallDict’ was available as
     ‘_PyObject_FastCallDict’.  The old names are still defined as
     aliases of the new, non-underscored names.

* Menu:

* Recursion Control: Recursion Control<2>.
* Vectorcall Support API::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0590


File: python.info,  Node: Recursion Control<2>,  Next: Vectorcall Support API,  Up: The Vectorcall Protocol

7.7.2.3 Recursion Control
.........................

When using `tp_call', callees do not need to worry about *note
recursion: 3e41.: CPython uses *note Py_EnterRecursiveCall(): 251. and
*note Py_LeaveRecursiveCall(): 252. for calls made using `tp_call'.

For efficiency, this is not the case for calls done using vectorcall:
the callee should use `Py_EnterRecursiveCall' and
`Py_LeaveRecursiveCall' if needed.


File: python.info,  Node: Vectorcall Support API,  Prev: Recursion Control<2>,  Up: The Vectorcall Protocol

7.7.2.4 Vectorcall Support API
..............................

 -- C Function: Py_ssize_t PyVectorcall_NARGS (size_t nargsf)

     Given a vectorcall `nargsf' argument, return the actual number of
     arguments.  Currently equivalent to:

          (Py_ssize_t)(nargsf & ~PY_VECTORCALL_ARGUMENTS_OFFSET)

     However, the function ‘PyVectorcall_NARGS’ should be used to allow
     for future extensions.

     This function is not part of the *note limited API: 3dd6.

     New in version 3.8.

 -- C Function: vectorcallfunc PyVectorcall_Function (PyObject *op)

     If `op' does not support the vectorcall protocol (either because
     the type does not or because the specific instance does not),
     return `NULL'. Otherwise, return the vectorcall function pointer
     stored in `op'.  This function never raises an exception.

     This is mostly useful to check whether or not `op' supports
     vectorcall, which can be done by checking
     ‘PyVectorcall_Function(op) != NULL’.

     This function is not part of the *note limited API: 3dd6.

     New in version 3.8.

 -- C Function: PyObject* PyVectorcall_Call (PyObject *callable,
          PyObject *tuple, PyObject *dict)

     Call `callable'’s *note vectorcallfunc: 3edd. with positional and
     keyword arguments given in a tuple and dict, respectively.

     This is a specialized function, intended to be put in the *note
     tp_call: 3d82. slot or be used in an implementation of ‘tp_call’.
     It does not check the *note Py_TPFLAGS_HAVE_VECTORCALL: 3edb. flag
     and it does not fall back to ‘tp_call’.

     This function is not part of the *note limited API: 3dd6.

     New in version 3.8.


File: python.info,  Node: Object Calling API,  Next: Call Support API,  Prev: The Vectorcall Protocol,  Up: Call Protocol

7.7.2.5 Object Calling API
..........................

Various functions are available for calling a Python object.  Each
converts its arguments to a convention supported by the called object –
either `tp_call' or vectorcall.  In order to do as little conversion as
possible, pick one that best fits the format of data you have available.

The following table summarizes the available functions; please see
individual documentation for details.

Function                                       callable               args                     kwargs
                                                                                               
-------------------------------------------------------------------------------------------------------------------
                                                                                               
*note PyObject_Call(): 23c.                    ‘PyObject *’           tuple                    dict/‘NULL’
                                                                                               
                                                                                               
*note PyObject_CallNoArgs(): 250.              ‘PyObject *’           —                        —
                                                                                               
                                                                                               
*note PyObject_CallOneArg(): 256.              ‘PyObject *’           1 object                 —
                                                                                               
                                                                                               
*note PyObject_CallObject(): 3d29.             ‘PyObject *’           tuple/‘NULL’             —
                                                                                               
                                                                                               
*note PyObject_CallFunction(): 3f1.            ‘PyObject *’           format                   —
                                                                                               
                                                                                               
*note PyObject_CallMethod(): 3ee6.             obj + ‘char*’          format                   —
                                                                                               
                                                                                               
*note PyObject_CallFunctionObjArgs(): 3ee7.    ‘PyObject *’           variadic                 —
                                                                                               
                                                                                               
*note PyObject_CallMethodObjArgs(): 1114.      obj + name             variadic                 —
                                                                                               
                                                                                               
*note PyObject_CallMethodNoArgs(): 3ee8.       obj + name             —                        —
                                                                                               
                                                                                               
*note PyObject_CallMethodOneArg(): 3ee9.       obj + name             1 object                 —
                                                                                               
                                                                                               
*note PyObject_Vectorcall(): 3ee1.             ‘PyObject *’           vectorcall               vectorcall
                                                                                               
                                                                                               
*note PyObject_VectorcallDict(): 3eea.         ‘PyObject *’           vectorcall               dict/‘NULL’
                                                                                               
                                                                                               
*note PyObject_VectorcallMethod(): 3ee0.       arg + name             vectorcall               vectorcall
                                                                                               

 -- C Function: PyObject* PyObject_Call (PyObject *callable,
          PyObject *args, PyObject *kwargs)
     `Return value: New reference.'  Call a callable Python object
     `callable', with arguments given by the tuple `args', and named
     arguments given by the dictionary `kwargs'.

     `args' must not be `NULL'; use an empty tuple if no arguments are
     needed.  If no named arguments are needed, `kwargs' can be `NULL'.

     Return the result of the call on success, or raise an exception and
     return `NULL' on failure.

     This is the equivalent of the Python expression: ‘callable(*args,
     **kwargs)’.

 -- C Function: PyObject* PyObject_CallNoArgs (PyObject *callable)

     Call a callable Python object `callable' without any arguments.  It
     is the most efficient way to call a callable Python object without
     any argument.

     Return the result of the call on success, or raise an exception and
     return `NULL' on failure.

     New in version 3.9.

 -- C Function: PyObject* PyObject_CallOneArg (PyObject *callable,
          PyObject *arg)

     Call a callable Python object `callable' with exactly 1 positional
     argument `arg' and no keyword arguments.

     Return the result of the call on success, or raise an exception and
     return `NULL' on failure.

     This function is not part of the *note limited API: 3dd6.

     New in version 3.9.

 -- C Function: PyObject* PyObject_CallObject (PyObject *callable,
          PyObject *args)
     `Return value: New reference.'  Call a callable Python object
     `callable', with arguments given by the tuple `args'.  If no
     arguments are needed, then `args' can be `NULL'.

     Return the result of the call on success, or raise an exception and
     return `NULL' on failure.

     This is the equivalent of the Python expression: ‘callable(*args)’.

 -- C Function: PyObject* PyObject_CallFunction (PyObject *callable,
          const char *format, ...)
     `Return value: New reference.'  Call a callable Python object
     `callable', with a variable number of C arguments.  The C arguments
     are described using a *note Py_BuildValue(): 3f0. style format
     string.  The format can be `NULL', indicating that no arguments are
     provided.

     Return the result of the call on success, or raise an exception and
     return `NULL' on failure.

     This is the equivalent of the Python expression: ‘callable(*args)’.

     Note that if you only pass *note PyObject *: 5b5. args, *note
     PyObject_CallFunctionObjArgs(): 3ee7. is a faster alternative.

     Changed in version 3.4: The type of `format' was changed from ‘char
     *’.

 -- C Function: PyObject* PyObject_CallMethod (PyObject *obj, const
          char *name, const char *format, ...)
     `Return value: New reference.'  Call the method named `name' of
     object `obj' with a variable number of C arguments.  The C
     arguments are described by a *note Py_BuildValue(): 3f0. format
     string that should produce a tuple.

     The format can be `NULL', indicating that no arguments are
     provided.

     Return the result of the call on success, or raise an exception and
     return `NULL' on failure.

     This is the equivalent of the Python expression: ‘obj.name(arg1,
     arg2, ...)’.

     Note that if you only pass *note PyObject *: 5b5. args, *note
     PyObject_CallMethodObjArgs(): 1114. is a faster alternative.

     Changed in version 3.4: The types of `name' and `format' were
     changed from ‘char *’.

 -- C Function: PyObject* PyObject_CallFunctionObjArgs
          (PyObject *callable, ...)
     `Return value: New reference.'  Call a callable Python object
     `callable', with a variable number of *note PyObject *: 5b5.
     arguments.  The arguments are provided as a variable number of
     parameters followed by `NULL'.

     Return the result of the call on success, or raise an exception and
     return `NULL' on failure.

     This is the equivalent of the Python expression: ‘callable(arg1,
     arg2, ...)’.

 -- C Function: PyObject* PyObject_CallMethodObjArgs (PyObject *obj,
          PyObject *name, ...)
     `Return value: New reference.'  Call a method of the Python object
     `obj', where the name of the method is given as a Python string
     object in `name'.  It is called with a variable number of *note
     PyObject *: 5b5. arguments.  The arguments are provided as a
     variable number of parameters followed by `NULL'.

     Return the result of the call on success, or raise an exception and
     return `NULL' on failure.

 -- C Function: PyObject* PyObject_CallMethodNoArgs (PyObject *obj,
          PyObject *name)

     Call a method of the Python object `obj' without arguments, where
     the name of the method is given as a Python string object in
     `name'.

     Return the result of the call on success, or raise an exception and
     return `NULL' on failure.

     This function is not part of the *note limited API: 3dd6.

     New in version 3.9.

 -- C Function: PyObject* PyObject_CallMethodOneArg (PyObject *obj,
          PyObject *name, PyObject *arg)

     Call a method of the Python object `obj' with a single positional
     argument `arg', where the name of the method is given as a Python
     string object in `name'.

     Return the result of the call on success, or raise an exception and
     return `NULL' on failure.

     This function is not part of the *note limited API: 3dd6.

     New in version 3.9.

 -- C Function: PyObject* PyObject_Vectorcall (PyObject *callable,
          PyObject *const *args, size_t nargsf, PyObject *kwnames)

     Call a callable Python object `callable'.  The arguments are the
     same as for *note vectorcallfunc: 3edd.  If `callable' supports
     *note vectorcall: 2b8, this directly calls the vectorcall function
     stored in `callable'.

     Return the result of the call on success, or raise an exception and
     return `NULL' on failure.

     This function is not part of the *note limited API: 3dd6.

     New in version 3.9.

 -- C Function: PyObject* PyObject_VectorcallDict (PyObject *callable,
          PyObject *const *args, size_t nargsf, PyObject *kwdict)

     Call `callable' with positional arguments passed exactly as in the
     *note vectorcall: 2b8. protocol, but with keyword arguments passed
     as a dictionary `kwdict'.  The `args' array contains only the
     positional arguments.

     Regardless of which protocol is used internally, a conversion of
     arguments needs to be done.  Therefore, this function should only
     be used if the caller already has a dictionary ready to use for the
     keyword arguments, but not a tuple for the positional arguments.

     This function is not part of the *note limited API: 3dd6.

     New in version 3.9.

 -- C Function: PyObject* PyObject_VectorcallMethod (PyObject *name,
          PyObject *const *args, size_t nargsf, PyObject *kwnames)

     Call a method using the vectorcall calling convention.  The name of
     the method is given as a Python string `name'.  The object whose
     method is called is `args[0]', and the `args' array starting at
     `args[1]' represents the arguments of the call.  There must be at
     least one positional argument.  `nargsf' is the number of
     positional arguments including `args[0]', plus
     ‘PY_VECTORCALL_ARGUMENTS_OFFSET’ if the value of ‘args[0]’ may
     temporarily be changed.  Keyword arguments can be passed just like
     in *note PyObject_Vectorcall(): 3ee1.

     If the object has the *note Py_TPFLAGS_METHOD_DESCRIPTOR: 3eeb.
     feature, this will call the unbound method object with the full
     `args' vector as arguments.

     Return the result of the call on success, or raise an exception and
     return `NULL' on failure.

     This function is not part of the *note limited API: 3dd6.

     New in version 3.9.


File: python.info,  Node: Call Support API,  Prev: Object Calling API,  Up: Call Protocol

7.7.2.6 Call Support API
........................

 -- C Function: int PyCallable_Check (PyObject *o)

     Determine if the object `o' is callable.  Return ‘1’ if the object
     is callable and ‘0’ otherwise.  This function always succeeds.


File: python.info,  Node: Number Protocol,  Next: Sequence Protocol,  Prev: Call Protocol,  Up: Abstract Objects Layer

7.7.3 Number Protocol
---------------------

 -- C Function: int PyNumber_Check (PyObject *o)

     Returns ‘1’ if the object `o' provides numeric protocols, and false
     otherwise.  This function always succeeds.

     Changed in version 3.8: Returns ‘1’ if `o' is an index integer.

 -- C Function: PyObject* PyNumber_Add (PyObject *o1, PyObject *o2)
     `Return value: New reference.'  Returns the result of adding `o1'
     and `o2', or ‘NULL’ on failure.  This is the equivalent of the
     Python expression ‘o1 + o2’.

 -- C Function: PyObject* PyNumber_Subtract (PyObject *o1, PyObject *o2)
     `Return value: New reference.'  Returns the result of subtracting
     `o2' from `o1', or ‘NULL’ on failure.  This is the equivalent of
     the Python expression ‘o1 - o2’.

 -- C Function: PyObject* PyNumber_Multiply (PyObject *o1, PyObject *o2)
     `Return value: New reference.'  Returns the result of multiplying
     `o1' and `o2', or ‘NULL’ on failure.  This is the equivalent of the
     Python expression ‘o1 * o2’.

 -- C Function: PyObject* PyNumber_MatrixMultiply (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the result of matrix
     multiplication on `o1' and `o2', or ‘NULL’ on failure.  This is the
     equivalent of the Python expression ‘o1 @ o2’.

     New in version 3.5.

 -- C Function: PyObject* PyNumber_FloorDivide (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Return the floor of `o1' divided by
     `o2', or ‘NULL’ on failure.  This is equivalent to the “classic”
     division of integers.

 -- C Function: PyObject* PyNumber_TrueDivide (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Return a reasonable approximation
     for the mathematical value of `o1' divided by `o2', or ‘NULL’ on
     failure.  The return value is “approximate” because binary floating
     point numbers are approximate; it is not possible to represent all
     real numbers in base two.  This function can return a floating
     point value when passed two integers.

 -- C Function: PyObject* PyNumber_Remainder (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the remainder of dividing
     `o1' by `o2', or ‘NULL’ on failure.  This is the equivalent of the
     Python expression ‘o1 % o2’.

 -- C Function: PyObject* PyNumber_Divmod (PyObject *o1, PyObject *o2)
     `Return value: New reference.'

     See the built-in function *note divmod(): 28d.  Returns ‘NULL’ on
     failure.  This is the equivalent of the Python expression
     ‘divmod(o1, o2)’.

 -- C Function: PyObject* PyNumber_Power (PyObject *o1, PyObject *o2,
          PyObject *o3)
     `Return value: New reference.'

     See the built-in function *note pow(): 2cf.  Returns ‘NULL’ on
     failure.  This is the equivalent of the Python expression ‘pow(o1,
     o2, o3)’, where `o3' is optional.  If `o3' is to be ignored, pass
     *note Py_None: 3d1f. in its place (passing ‘NULL’ for `o3' would
     cause an illegal memory access).

 -- C Function: PyObject* PyNumber_Negative (PyObject *o)
     `Return value: New reference.'  Returns the negation of `o' on
     success, or ‘NULL’ on failure.  This is the equivalent of the
     Python expression ‘-o’.

 -- C Function: PyObject* PyNumber_Positive (PyObject *o)
     `Return value: New reference.'  Returns `o' on success, or ‘NULL’
     on failure.  This is the equivalent of the Python expression ‘+o’.

 -- C Function: PyObject* PyNumber_Absolute (PyObject *o)
     `Return value: New reference.'

     Returns the absolute value of `o', or ‘NULL’ on failure.  This is
     the equivalent of the Python expression ‘abs(o)’.

 -- C Function: PyObject* PyNumber_Invert (PyObject *o)
     `Return value: New reference.'  Returns the bitwise negation of `o'
     on success, or ‘NULL’ on failure.  This is the equivalent of the
     Python expression ‘~o’.

 -- C Function: PyObject* PyNumber_Lshift (PyObject *o1, PyObject *o2)
     `Return value: New reference.'  Returns the result of left shifting
     `o1' by `o2' on success, or ‘NULL’ on failure.  This is the
     equivalent of the Python expression ‘o1 << o2’.

 -- C Function: PyObject* PyNumber_Rshift (PyObject *o1, PyObject *o2)
     `Return value: New reference.'  Returns the result of right
     shifting `o1' by `o2' on success, or ‘NULL’ on failure.  This is
     the equivalent of the Python expression ‘o1 >> o2’.

 -- C Function: PyObject* PyNumber_And (PyObject *o1, PyObject *o2)
     `Return value: New reference.'  Returns the “bitwise and” of `o1'
     and `o2' on success and ‘NULL’ on failure.  This is the equivalent
     of the Python expression ‘o1 & o2’.

 -- C Function: PyObject* PyNumber_Xor (PyObject *o1, PyObject *o2)
     `Return value: New reference.'  Returns the “bitwise exclusive or”
     of `o1' by `o2' on success, or ‘NULL’ on failure.  This is the
     equivalent of the Python expression ‘o1 ^ o2’.

 -- C Function: PyObject* PyNumber_Or (PyObject *o1, PyObject *o2)
     `Return value: New reference.'  Returns the “bitwise or” of `o1'
     and `o2' on success, or ‘NULL’ on failure.  This is the equivalent
     of the Python expression ‘o1 | o2’.

 -- C Function: PyObject* PyNumber_InPlaceAdd (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the result of adding `o1'
     and `o2', or ‘NULL’ on failure.  The operation is done `in-place'
     when `o1' supports it.  This is the equivalent of the Python
     statement ‘o1 += o2’.

 -- C Function: PyObject* PyNumber_InPlaceSubtract (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the result of subtracting
     `o2' from `o1', or ‘NULL’ on failure.  The operation is done
     `in-place' when `o1' supports it.  This is the equivalent of the
     Python statement ‘o1 -= o2’.

 -- C Function: PyObject* PyNumber_InPlaceMultiply (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the result of multiplying
     `o1' and `o2', or ‘NULL’ on failure.  The operation is done
     `in-place' when `o1' supports it.  This is the equivalent of the
     Python statement ‘o1 *= o2’.

 -- C Function: PyObject* PyNumber_InPlaceMatrixMultiply (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the result of matrix
     multiplication on `o1' and `o2', or ‘NULL’ on failure.  The
     operation is done `in-place' when `o1' supports it.  This is the
     equivalent of the Python statement ‘o1 @= o2’.

     New in version 3.5.

 -- C Function: PyObject* PyNumber_InPlaceFloorDivide (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the mathematical floor of
     dividing `o1' by `o2', or ‘NULL’ on failure.  The operation is done
     `in-place' when `o1' supports it.  This is the equivalent of the
     Python statement ‘o1 //= o2’.

 -- C Function: PyObject* PyNumber_InPlaceTrueDivide (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Return a reasonable approximation
     for the mathematical value of `o1' divided by `o2', or ‘NULL’ on
     failure.  The return value is “approximate” because binary floating
     point numbers are approximate; it is not possible to represent all
     real numbers in base two.  This function can return a floating
     point value when passed two integers.  The operation is done
     `in-place' when `o1' supports it.

 -- C Function: PyObject* PyNumber_InPlaceRemainder (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the remainder of dividing
     `o1' by `o2', or ‘NULL’ on failure.  The operation is done
     `in-place' when `o1' supports it.  This is the equivalent of the
     Python statement ‘o1 %= o2’.

 -- C Function: PyObject* PyNumber_InPlacePower (PyObject *o1,
          PyObject *o2, PyObject *o3)
     `Return value: New reference.'

     See the built-in function *note pow(): 2cf.  Returns ‘NULL’ on
     failure.  The operation is done `in-place' when `o1' supports it.
     This is the equivalent of the Python statement ‘o1 **= o2’ when o3
     is *note Py_None: 3d1f, or an in-place variant of ‘pow(o1, o2, o3)’
     otherwise.  If `o3' is to be ignored, pass *note Py_None: 3d1f. in
     its place (passing ‘NULL’ for `o3' would cause an illegal memory
     access).

 -- C Function: PyObject* PyNumber_InPlaceLshift (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the result of left shifting
     `o1' by `o2' on success, or ‘NULL’ on failure.  The operation is
     done `in-place' when `o1' supports it.  This is the equivalent of
     the Python statement ‘o1 <<= o2’.

 -- C Function: PyObject* PyNumber_InPlaceRshift (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the result of right
     shifting `o1' by `o2' on success, or ‘NULL’ on failure.  The
     operation is done `in-place' when `o1' supports it.  This is the
     equivalent of the Python statement ‘o1 >>= o2’.

 -- C Function: PyObject* PyNumber_InPlaceAnd (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the “bitwise and” of `o1'
     and `o2' on success and ‘NULL’ on failure.  The operation is done
     `in-place' when `o1' supports it.  This is the equivalent of the
     Python statement ‘o1 &= o2’.

 -- C Function: PyObject* PyNumber_InPlaceXor (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the “bitwise exclusive or”
     of `o1' by `o2' on success, or ‘NULL’ on failure.  The operation is
     done `in-place' when `o1' supports it.  This is the equivalent of
     the Python statement ‘o1 ^= o2’.

 -- C Function: PyObject* PyNumber_InPlaceOr (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Returns the “bitwise or” of `o1'
     and `o2' on success, or ‘NULL’ on failure.  The operation is done
     `in-place' when `o1' supports it.  This is the equivalent of the
     Python statement ‘o1 |= o2’.

 -- C Function: PyObject* PyNumber_Long (PyObject *o)
     `Return value: New reference.'

     Returns the `o' converted to an integer object on success, or
     ‘NULL’ on failure.  This is the equivalent of the Python expression
     ‘int(o)’.

 -- C Function: PyObject* PyNumber_Float (PyObject *o)
     `Return value: New reference.'

     Returns the `o' converted to a float object on success, or ‘NULL’
     on failure.  This is the equivalent of the Python expression
     ‘float(o)’.

 -- C Function: PyObject* PyNumber_Index (PyObject *o)
     `Return value: New reference.'  Returns the `o' converted to a
     Python int on success or ‘NULL’ with a *note TypeError: 1fe.
     exception raised on failure.

 -- C Function: PyObject* PyNumber_ToBase (PyObject *n, int base)
     `Return value: New reference.'  Returns the integer `n' converted
     to base `base' as a string.  The `base' argument must be one of 2,
     8, 10, or 16.  For base 2, 8, or 16, the returned string is
     prefixed with a base marker of ‘'0b'’, ‘'0o'’, or ‘'0x'’,
     respectively.  If `n' is not a Python int, it is converted with
     *note PyNumber_Index(): 3f0e. first.

 -- C Function: Py_ssize_t PyNumber_AsSsize_t (PyObject *o,
          PyObject *exc)

     Returns `o' converted to a Py_ssize_t value if `o' can be
     interpreted as an integer.  If the call fails, an exception is
     raised and ‘-1’ is returned.

     If `o' can be converted to a Python int but the attempt to convert
     to a Py_ssize_t value would raise an *note OverflowError: a41, then
     the `exc' argument is the type of exception that will be raised
     (usually *note IndexError: f36. or *note OverflowError: a41.).  If
     `exc' is ‘NULL’, then the exception is cleared and the value is
     clipped to ‘PY_SSIZE_T_MIN’ for a negative integer or
     ‘PY_SSIZE_T_MAX’ for a positive integer.

 -- C Function: int PyIndex_Check (PyObject *o)

     Returns ‘1’ if `o' is an index integer (has the nb_index slot of
     the tp_as_number structure filled in), and ‘0’ otherwise.  This
     function always succeeds.


File: python.info,  Node: Sequence Protocol,  Next: Mapping Protocol,  Prev: Number Protocol,  Up: Abstract Objects Layer

7.7.4 Sequence Protocol
-----------------------

 -- C Function: int PySequence_Check (PyObject *o)

     Return ‘1’ if the object provides sequence protocol, and ‘0’
     otherwise.  Note that it returns ‘1’ for Python classes with a
     *note __getitem__(): 3a2. method unless they are *note dict: 164.
     subclasses since in general case it is impossible to determine what
     the type of keys it supports.  This function always succeeds.

 -- C Function: Py_ssize_t PySequence_Size (PyObject *o)
 -- C Function: Py_ssize_t PySequence_Length (PyObject *o)

     Returns the number of objects in sequence `o' on success, and ‘-1’
     on failure.  This is equivalent to the Python expression ‘len(o)’.

 -- C Function: PyObject* PySequence_Concat (PyObject *o1, PyObject *o2)
     `Return value: New reference.'  Return the concatenation of `o1'
     and `o2' on success, and ‘NULL’ on failure.  This is the equivalent
     of the Python expression ‘o1 + o2’.

 -- C Function: PyObject* PySequence_Repeat (PyObject *o,
          Py_ssize_t count)
     `Return value: New reference.'  Return the result of repeating
     sequence object `o' `count' times, or ‘NULL’ on failure.  This is
     the equivalent of the Python expression ‘o * count’.

 -- C Function: PyObject* PySequence_InPlaceConcat (PyObject *o1,
          PyObject *o2)
     `Return value: New reference.'  Return the concatenation of `o1'
     and `o2' on success, and ‘NULL’ on failure.  The operation is done
     `in-place' when `o1' supports it.  This is the equivalent of the
     Python expression ‘o1 += o2’.

 -- C Function: PyObject* PySequence_InPlaceRepeat (PyObject *o,
          Py_ssize_t count)
     `Return value: New reference.'  Return the result of repeating
     sequence object `o' `count' times, or ‘NULL’ on failure.  The
     operation is done `in-place' when `o' supports it.  This is the
     equivalent of the Python expression ‘o *= count’.

 -- C Function: PyObject* PySequence_GetItem (PyObject *o, Py_ssize_t i)
     `Return value: New reference.'  Return the `i'th element of `o', or
     ‘NULL’ on failure.  This is the equivalent of the Python expression
     ‘o[i]’.

 -- C Function: PyObject* PySequence_GetSlice (PyObject *o,
          Py_ssize_t i1, Py_ssize_t i2)
     `Return value: New reference.'  Return the slice of sequence object
     `o' between `i1' and `i2', or ‘NULL’ on failure.  This is the
     equivalent of the Python expression ‘o[i1:i2]’.

 -- C Function: int PySequence_SetItem (PyObject *o, Py_ssize_t i,
          PyObject *v)

     Assign object `v' to the `i'th element of `o'.  Raise an exception
     and return ‘-1’ on failure; return ‘0’ on success.  This is the
     equivalent of the Python statement ‘o[i] = v’.  This function `does
     not' steal a reference to `v'.

     If `v' is ‘NULL’, the element is deleted, however this feature is
     deprecated in favour of using *note PySequence_DelItem(): 1185.

 -- C Function: int PySequence_DelItem (PyObject *o, Py_ssize_t i)

     Delete the `i'th element of object `o'.  Returns ‘-1’ on failure.
     This is the equivalent of the Python statement ‘del o[i]’.

 -- C Function: int PySequence_SetSlice (PyObject *o, Py_ssize_t i1,
          Py_ssize_t i2, PyObject *v)

     Assign the sequence object `v' to the slice in sequence object `o'
     from `i1' to `i2'.  This is the equivalent of the Python statement
     ‘o[i1:i2] = v’.

 -- C Function: int PySequence_DelSlice (PyObject *o, Py_ssize_t i1,
          Py_ssize_t i2)

     Delete the slice in sequence object `o' from `i1' to `i2'.  Returns
     ‘-1’ on failure.  This is the equivalent of the Python statement
     ‘del o[i1:i2]’.

 -- C Function: Py_ssize_t PySequence_Count (PyObject *o,
          PyObject *value)

     Return the number of occurrences of `value' in `o', that is, return
     the number of keys for which ‘o[key] == value’.  On failure, return
     ‘-1’.  This is equivalent to the Python expression
     ‘o.count(value)’.

 -- C Function: int PySequence_Contains (PyObject *o, PyObject *value)

     Determine if `o' contains `value'.  If an item in `o' is equal to
     `value', return ‘1’, otherwise return ‘0’.  On error, return ‘-1’.
     This is equivalent to the Python expression ‘value in o’.

 -- C Function: Py_ssize_t PySequence_Index (PyObject *o,
          PyObject *value)

     Return the first index `i' for which ‘o[i] == value’.  On error,
     return ‘-1’.  This is equivalent to the Python expression
     ‘o.index(value)’.

 -- C Function: PyObject* PySequence_List (PyObject *o)
     `Return value: New reference.'  Return a list object with the same
     contents as the sequence or iterable `o', or ‘NULL’ on failure.
     The returned list is guaranteed to be new.  This is equivalent to
     the Python expression ‘list(o)’.

 -- C Function: PyObject* PySequence_Tuple (PyObject *o)
     `Return value: New reference.'

     Return a tuple object with the same contents as the sequence or
     iterable `o', or ‘NULL’ on failure.  If `o' is a tuple, a new
     reference will be returned, otherwise a tuple will be constructed
     with the appropriate contents.  This is equivalent to the Python
     expression ‘tuple(o)’.

 -- C Function: PyObject* PySequence_Fast (PyObject *o, const char *m)
     `Return value: New reference.'  Return the sequence or iterable `o'
     as an object usable by the other ‘PySequence_Fast*’ family of
     functions.  If the object is not a sequence or iterable, raises
     *note TypeError: 1fe. with `m' as the message text.  Returns ‘NULL’
     on failure.

     The ‘PySequence_Fast*’ functions are thus named because they assume
     `o' is a *note PyTupleObject: 3e66. or a *note PyListObject: 3f22.
     and access the data fields of `o' directly.

     As a CPython implementation detail, if `o' is already a sequence or
     list, it will be returned.

 -- C Function: Py_ssize_t PySequence_Fast_GET_SIZE (PyObject *o)

     Returns the length of `o', assuming that `o' was returned by *note
     PySequence_Fast(): 3f21. and that `o' is not ‘NULL’.  The size can
     also be gotten by calling *note PySequence_Size(): 1182. on `o',
     but *note PySequence_Fast_GET_SIZE(): 3f23. is faster because it
     can assume `o' is a list or tuple.

 -- C Function: PyObject* PySequence_Fast_GET_ITEM (PyObject *o,
          Py_ssize_t i)
     `Return value: Borrowed reference.'  Return the `i'th element of
     `o', assuming that `o' was returned by *note PySequence_Fast():
     3f21, `o' is not ‘NULL’, and that `i' is within bounds.

 -- C Function: PyObject** PySequence_Fast_ITEMS (PyObject *o)

     Return the underlying array of PyObject pointers.  Assumes that `o'
     was returned by *note PySequence_Fast(): 3f21. and `o' is not
     ‘NULL’.

     Note, if a list gets resized, the reallocation may relocate the
     items array.  So, only use the underlying array pointer in contexts
     where the sequence cannot change.

 -- C Function: PyObject* PySequence_ITEM (PyObject *o, Py_ssize_t i)
     `Return value: New reference.'  Return the `i'th element of `o' or
     ‘NULL’ on failure.  Faster form of *note PySequence_GetItem():
     1183. but without checking that *note PySequence_Check(): 3f13. on
     `o' is true and without adjustment for negative indices.


File: python.info,  Node: Mapping Protocol,  Next: Iterator Protocol,  Prev: Sequence Protocol,  Up: Abstract Objects Layer

7.7.5 Mapping Protocol
----------------------

See also *note PyObject_GetItem(): 3dc7, *note PyObject_SetItem(): 3dc5.
and *note PyObject_DelItem(): 3ed2.

 -- C Function: int PyMapping_Check (PyObject *o)

     Return ‘1’ if the object provides mapping protocol or supports
     slicing, and ‘0’ otherwise.  Note that it returns ‘1’ for Python
     classes with a *note __getitem__(): 3a2. method since in general
     case it is impossible to determine what type of keys it supports.
     This function always succeeds.

 -- C Function: Py_ssize_t PyMapping_Size (PyObject *o)
 -- C Function: Py_ssize_t PyMapping_Length (PyObject *o)

     Returns the number of keys in object `o' on success, and ‘-1’ on
     failure.  This is equivalent to the Python expression ‘len(o)’.

 -- C Function: PyObject* PyMapping_GetItemString (PyObject *o, const
          char *key)
     `Return value: New reference.'  Return element of `o' corresponding
     to the string `key' or ‘NULL’ on failure.  This is the equivalent
     of the Python expression ‘o[key]’.  See also *note
     PyObject_GetItem(): 3dc7.

 -- C Function: int PyMapping_SetItemString (PyObject *o, const
          char *key, PyObject *v)

     Map the string `key' to the value `v' in object `o'.  Returns ‘-1’
     on failure.  This is the equivalent of the Python statement ‘o[key]
     = v’.  See also *note PyObject_SetItem(): 3dc5.  This function
     `does not' steal a reference to `v'.

 -- C Function: int PyMapping_DelItem (PyObject *o, PyObject *key)

     Remove the mapping for the object `key' from the object `o'.
     Return ‘-1’ on failure.  This is equivalent to the Python statement
     ‘del o[key]’.  This is an alias of *note PyObject_DelItem(): 3ed2.

 -- C Function: int PyMapping_DelItemString (PyObject *o, const
          char *key)

     Remove the mapping for the string `key' from the object `o'.
     Return ‘-1’ on failure.  This is equivalent to the Python statement
     ‘del o[key]’.

 -- C Function: int PyMapping_HasKey (PyObject *o, PyObject *key)

     Return ‘1’ if the mapping object has the key `key' and ‘0’
     otherwise.  This is equivalent to the Python expression ‘key in o’.
     This function always succeeds.

     Note that exceptions which occur while calling the *note
     __getitem__(): 3a2. method will get suppressed.  To get error
     reporting use *note PyObject_GetItem(): 3dc7. instead.

 -- C Function: int PyMapping_HasKeyString (PyObject *o, const
          char *key)

     Return ‘1’ if the mapping object has the key `key' and ‘0’
     otherwise.  This is equivalent to the Python expression ‘key in o’.
     This function always succeeds.

     Note that exceptions which occur while calling the *note
     __getitem__(): 3a2. method and creating a temporary string object
     will get suppressed.  To get error reporting use *note
     PyMapping_GetItemString(): 3f2c. instead.

 -- C Function: PyObject* PyMapping_Keys (PyObject *o)
     `Return value: New reference.'  On success, return a list of the
     keys in object `o'.  On failure, return ‘NULL’.

     Changed in version 3.7: Previously, the function returned a list or
     a tuple.

 -- C Function: PyObject* PyMapping_Values (PyObject *o)
     `Return value: New reference.'  On success, return a list of the
     values in object `o'.  On failure, return ‘NULL’.

     Changed in version 3.7: Previously, the function returned a list or
     a tuple.

 -- C Function: PyObject* PyMapping_Items (PyObject *o)
     `Return value: New reference.'  On success, return a list of the
     items in object `o', where each item is a tuple containing a
     key-value pair.  On failure, return ‘NULL’.

     Changed in version 3.7: Previously, the function returned a list or
     a tuple.


File: python.info,  Node: Iterator Protocol,  Next: Buffer Protocol,  Prev: Mapping Protocol,  Up: Abstract Objects Layer

7.7.6 Iterator Protocol
-----------------------

There are two functions specifically for working with iterators.

 -- C Function: int PyIter_Check (PyObject *o)

     Return true if the object `o' supports the iterator protocol.  This
     function always succeeds.

 -- C Function: PyObject* PyIter_Next (PyObject *o)
     `Return value: New reference.'  Return the next value from the
     iteration `o'.  The object must be an iterator (it is up to the
     caller to check this).  If there are no remaining values, returns
     ‘NULL’ with no exception set.  If an error occurs while retrieving
     the item, returns ‘NULL’ and passes along the exception.

To write a loop which iterates over an iterator, the C code should look
something like this:

     PyObject *iterator = PyObject_GetIter(obj);
     PyObject *item;

     if (iterator == NULL) {
         /* propagate error */
     }

     while ((item = PyIter_Next(iterator))) {
         /* do something with item */
         ...
         /* release reference when done */
         Py_DECREF(item);
     }

     Py_DECREF(iterator);

     if (PyErr_Occurred()) {
         /* propagate error */
     }
     else {
         /* continue doing useful work */
     }


File: python.info,  Node: Buffer Protocol,  Next: Old Buffer Protocol,  Prev: Iterator Protocol,  Up: Abstract Objects Layer

7.7.7 Buffer Protocol
---------------------

Certain objects available in Python wrap access to an underlying memory
array or `buffer'.  Such objects include the built-in *note bytes: 172.
and *note bytearray: 173, and some extension types like *note
array.array: 216.  Third-party libraries may define their own types for
special purposes, such as image processing or numeric analysis.

While each of these types have their own semantics, they share the
common characteristic of being backed by a possibly large memory buffer.
It is then desirable, in some situations, to access that buffer directly
and without intermediate copying.

Python provides such a facility at the C level in the form of the *note
buffer protocol: 171c.  This protocol has two sides:

   - on the producer side, a type can export a “buffer interface” which
     allows objects of that type to expose information about their
     underlying buffer.  This interface is described in the section
     *note Buffer Object Structures: 3f38.;

   - on the consumer side, several means are available to obtain a
     pointer to the raw underlying data of an object (for example a
     method parameter).

Simple objects such as *note bytes: 172. and *note bytearray: 173.
expose their underlying buffer in byte-oriented form.  Other forms are
possible; for example, the elements exposed by an *note array.array:
216. can be multi-byte values.

An example consumer of the buffer interface is the *note write(): 680.
method of file objects: any object that can export a series of bytes
through the buffer interface can be written to a file.  While ‘write()’
only needs read-only access to the internal contents of the object
passed to it, other methods such as *note readinto(): 2150. need write
access to the contents of their argument.  The buffer interface allows
objects to selectively allow or reject exporting of read-write and
read-only buffers.

There are two ways for a consumer of the buffer interface to acquire a
buffer over a target object:

   * call *note PyObject_GetBuffer(): deb. with the right parameters;

   * call *note PyArg_ParseTuple(): 393. (or one of its siblings) with
     one of the ‘y*’, ‘w*’ or ‘s*’ *note format codes: 3f2.

In both cases, *note PyBuffer_Release(): e19. must be called when the
buffer isn’t needed anymore.  Failure to do so could lead to various
issues such as resource leaks.

* Menu:

* Buffer structure::
* Buffer request types::
* Complex arrays::
* Buffer-related functions::


File: python.info,  Node: Buffer structure,  Next: Buffer request types,  Up: Buffer Protocol

7.7.7.1 Buffer structure
........................

Buffer structures (or simply “buffers”) are useful as a way to expose
the binary data from another object to the Python programmer.  They can
also be used as a zero-copy slicing mechanism.  Using their ability to
reference a block of memory, it is possible to expose any data to the
Python programmer quite easily.  The memory could be a large, constant
array in a C extension, it could be a raw block of memory for
manipulation before passing to an operating system library, or it could
be used to pass around structured data in its native, in-memory format.

Contrary to most data types exposed by the Python interpreter, buffers
are not *note PyObject: 5b5. pointers but rather simple C structures.
This allows them to be created and copied very simply.  When a generic
wrapper around a buffer is needed, a *note memoryview: 3f3b. object can
be created.

For short instructions how to write an exporting object, see *note
Buffer Object Structures: 3f38.  For obtaining a buffer, see *note
PyObject_GetBuffer(): deb.

 -- C Type: Py_buffer

      -- C Member: void *buf

          A pointer to the start of the logical structure described by
          the buffer fields.  This can be any location within the
          underlying physical memory block of the exporter.  For
          example, with negative *note strides: 3f3d. the value may
          point to the end of the memory block.

          For *note contiguous: 17ec. arrays, the value points to the
          beginning of the memory block.

      -- C Member: void *obj

          A new reference to the exporting object.  The reference is
          owned by the consumer and automatically decremented and set to
          ‘NULL’ by *note PyBuffer_Release(): e19.  The field is the
          equivalent of the return value of any standard C-API function.

          As a special case, for `temporary' buffers that are wrapped by
          *note PyMemoryView_FromBuffer(): 3f3f. or *note
          PyBuffer_FillInfo(): 3f40. this field is ‘NULL’.  In general,
          exporting objects MUST NOT use this scheme.

      -- C Member: Py_ssize_t len

          ‘product(shape) * itemsize’.  For contiguous arrays, this is
          the length of the underlying memory block.  For non-contiguous
          arrays, it is the length that the logical structure would have
          if it were copied to a contiguous representation.

          Accessing ‘((char *)buf)[0] up to ((char *)buf)[len-1]’ is
          only valid if the buffer has been obtained by a request that
          guarantees contiguity.  In most cases such a request will be
          *note PyBUF_SIMPLE: 3f42. or *note PyBUF_WRITABLE: 3f43.

      -- C Member: int readonly

          An indicator of whether the buffer is read-only.  This field
          is controlled by the *note PyBUF_WRITABLE: 3f43. flag.

      -- C Member: Py_ssize_t itemsize

          Item size in bytes of a single element.  Same as the value of
          *note struct.calcsize(): 10c5. called on non-‘NULL’ *note
          format: 3f46. values.

          Important exception: If a consumer requests a buffer without
          the *note PyBUF_FORMAT: 3f47. flag, *note format: 3f46. will
          be set to ‘NULL’, but *note itemsize: 3f45. still has the
          value for the original format.

          If *note shape: 3f48. is present, the equality ‘product(shape)
          * itemsize == len’ still holds and the consumer can use *note
          itemsize: 3f45. to navigate the buffer.

          If *note shape: 3f48. is ‘NULL’ as a result of a *note
          PyBUF_SIMPLE: 3f42. or a *note PyBUF_WRITABLE: 3f43. request,
          the consumer must disregard *note itemsize: 3f45. and assume
          ‘itemsize == 1’.

      -- C Member: const char *format

          A `NUL' terminated string in *note struct: f8. module style
          syntax describing the contents of a single item.  If this is
          ‘NULL’, ‘"B"’ (unsigned bytes) is assumed.

          This field is controlled by the *note PyBUF_FORMAT: 3f47.
          flag.

      -- C Member: int ndim

          The number of dimensions the memory represents as an
          n-dimensional array.  If it is ‘0’, *note buf: 3f3c. points to
          a single item representing a scalar.  In this case, *note
          shape: 3f48, *note strides: 3f3d. and *note suboffsets: 3f4a.
          MUST be ‘NULL’.

          The macro ‘PyBUF_MAX_NDIM’ limits the maximum number of
          dimensions to 64.  Exporters MUST respect this limit,
          consumers of multi-dimensional buffers SHOULD be able to
          handle up to ‘PyBUF_MAX_NDIM’ dimensions.

      -- C Member: Py_ssize_t *shape

          An array of ‘Py_ssize_t’ of length *note ndim: 3f49.
          indicating the shape of the memory as an n-dimensional array.
          Note that ‘shape[0] * ... * shape[ndim-1] * itemsize’ MUST be
          equal to *note len: 3f41.

          Shape values are restricted to ‘shape[n] >= 0’.  The case
          ‘shape[n] == 0’ requires special attention.  See *note complex
          arrays: 3f4b. for further information.

          The shape array is read-only for the consumer.

      -- C Member: Py_ssize_t *strides

          An array of ‘Py_ssize_t’ of length *note ndim: 3f49. giving
          the number of bytes to skip to get to a new element in each
          dimension.

          Stride values can be any integer.  For regular arrays, strides
          are usually positive, but a consumer MUST be able to handle
          the case ‘strides[n] <= 0’.  See *note complex arrays: 3f4b.
          for further information.

          The strides array is read-only for the consumer.

      -- C Member: Py_ssize_t *suboffsets

          An array of ‘Py_ssize_t’ of length *note ndim: 3f49.  If
          ‘suboffsets[n] >= 0’, the values stored along the nth
          dimension are pointers and the suboffset value dictates how
          many bytes to add to each pointer after de-referencing.  A
          suboffset value that is negative indicates that no
          de-referencing should occur (striding in a contiguous memory
          block).

          If all suboffsets are negative (i.e.  no de-referencing is
          needed), then this field must be ‘NULL’ (the default value).

          This type of array representation is used by the Python
          Imaging Library (PIL). See *note complex arrays: 3f4b. for
          further information how to access elements of such an array.

          The suboffsets array is read-only for the consumer.

      -- C Member: void *internal

          This is for use internally by the exporting object.  For
          example, this might be re-cast as an integer by the exporter
          and used to store flags about whether or not the shape,
          strides, and suboffsets arrays must be freed when the buffer
          is released.  The consumer MUST NOT alter this value.


File: python.info,  Node: Buffer request types,  Next: Complex arrays,  Prev: Buffer structure,  Up: Buffer Protocol

7.7.7.2 Buffer request types
............................

Buffers are usually obtained by sending a buffer request to an exporting
object via *note PyObject_GetBuffer(): deb.  Since the complexity of the
logical structure of the memory can vary drastically, the consumer uses
the `flags' argument to specify the exact buffer type it can handle.

All *note Py_buffer: bee. fields are unambiguously defined by the
request type.

* Menu:

* request-independent fields::
* readonly, format: readonly format.
* shape, strides, suboffsets: shape strides suboffsets.
* contiguity requests::
* compound requests::


File: python.info,  Node: request-independent fields,  Next: readonly format,  Up: Buffer request types

7.7.7.3 request-independent fields
..................................

The following fields are not influenced by `flags' and must always be
filled in with the correct values: *note obj: 3f3e, *note buf: 3f3c,
*note len: 3f41, *note itemsize: 3f45, *note ndim: 3f49.


File: python.info,  Node: readonly format,  Next: shape strides suboffsets,  Prev: request-independent fields,  Up: Buffer request types

7.7.7.4 readonly, format
........................

      -- C Macro: PyBUF_WRITABLE

          Controls the *note readonly: 3f44. field.  If set, the
          exporter MUST provide a writable buffer or else report
          failure.  Otherwise, the exporter MAY provide either a
          read-only or writable buffer, but the choice MUST be
          consistent for all consumers.

      -- C Macro: PyBUF_FORMAT

          Controls the *note format: 3f46. field.  If set, this field
          MUST be filled in correctly.  Otherwise, this field MUST be
          ‘NULL’.

*note PyBUF_WRITABLE: 3f43. can be |’d to any of the flags in the next
section.  Since *note PyBUF_SIMPLE: 3f42. is defined as 0, *note
PyBUF_WRITABLE: 3f43. can be used as a stand-alone flag to request a
simple writable buffer.

*note PyBUF_FORMAT: 3f47. can be |’d to any of the flags except *note
PyBUF_SIMPLE: 3f42.  The latter already implies format ‘B’ (unsigned
bytes).


File: python.info,  Node: shape strides suboffsets,  Next: contiguity requests,  Prev: readonly format,  Up: Buffer request types

7.7.7.5 shape, strides, suboffsets
..................................

The flags that control the logical structure of the memory are listed in
decreasing order of complexity.  Note that each flag contains all bits
of the flags below it.

Request                           shape       strides       suboffsets
                                                            
-----------------------------------------------------------------------------
                                                            
 -- C Macro: PyBUF_INDIRECT       yes         yes           if needed
                                                            
                                                            
 -- C Macro: PyBUF_STRIDES        yes         yes           NULL
                                                            
                                                            
 -- C Macro: PyBUF_ND             yes         NULL          NULL
                                                            
                                                            
 -- C Macro: PyBUF_SIMPLE         NULL        NULL          NULL
                                                            


File: python.info,  Node: contiguity requests,  Next: compound requests,  Prev: shape strides suboffsets,  Up: Buffer request types

7.7.7.6 contiguity requests
...........................

C or Fortran *note contiguity: 17ec. can be explicitly requested, with
and without stride information.  Without stride information, the buffer
must be C-contiguous.

Request                                 shape       strides       suboffsets       contig
                                                                                   
------------------------------------------------------------------------------------------------
                                                                                   
 -- C Macro: PyBUF_C_CONTIGUOUS         yes         yes           NULL             C
                                                                                   
                                                                                   
 -- C Macro: PyBUF_F_CONTIGUOUS         yes         yes           NULL             F
                                                                                   
                                                                                   
 -- C Macro: PyBUF_ANY_CONTIGUOUS       yes         yes           NULL             C or F
                                                                                   
                                                                                   
*note PyBUF_ND: 3f54.                   yes         NULL          NULL             C
                                                                                   


File: python.info,  Node: compound requests,  Prev: contiguity requests,  Up: Buffer request types

7.7.7.7 compound requests
.........................

All possible requests are fully defined by some combination of the flags
in the previous section.  For convenience, the buffer protocol provides
frequently used combinations as single flags.

In the following table `U' stands for undefined contiguity.  The
consumer would have to call *note PyBuffer_IsContiguous(): 3f5a. to
determine contiguity.

Request                             shape       strides       suboffsets       contig       readonly       format
                                                                                                           
------------------------------------------------------------------------------------------------------------------------
                                                                                                           
 -- C Macro: PyBUF_FULL             yes         yes           if needed        U            0              yes
                                                                                                           
                                                                                                           
 -- C Macro: PyBUF_FULL_RO          yes         yes           if needed        U            1 or 0         yes
                                                                                                           
                                                                                                           
 -- C Macro: PyBUF_RECORDS          yes         yes           NULL             U            0              yes
                                                                                                           
                                                                                                           
 -- C Macro: PyBUF_RECORDS_RO       yes         yes           NULL             U            1 or 0         yes
                                                                                                           
                                                                                                           
 -- C Macro: PyBUF_STRIDED          yes         yes           NULL             U            0              NULL
                                                                                                           
                                                                                                           
 -- C Macro: PyBUF_STRIDED_RO       yes         yes           NULL             U            1 or 0         NULL
                                                                                                           
                                                                                                           
 -- C Macro: PyBUF_CONTIG           yes         NULL          NULL             C            0              NULL
                                                                                                           
                                                                                                           
 -- C Macro: PyBUF_CONTIG_RO        yes         NULL          NULL             C            1 or 0         NULL
                                                                                                           


File: python.info,  Node: Complex arrays,  Next: Buffer-related functions,  Prev: Buffer request types,  Up: Buffer Protocol

7.7.7.8 Complex arrays
......................

* Menu:

* NumPy-style; shape and strides: NumPy-style shape and strides.
* PIL-style; shape, strides and suboffsets: PIL-style shape strides and suboffsets.


File: python.info,  Node: NumPy-style shape and strides,  Next: PIL-style shape strides and suboffsets,  Up: Complex arrays

7.7.7.9 NumPy-style: shape and strides
......................................

The logical structure of NumPy-style arrays is defined by *note
itemsize: 3f45, *note ndim: 3f49, *note shape: 3f48. and *note strides:
3f3d.

If ‘ndim == 0’, the memory location pointed to by *note buf: 3f3c. is
interpreted as a scalar of size *note itemsize: 3f45.  In that case,
both *note shape: 3f48. and *note strides: 3f3d. are ‘NULL’.

If *note strides: 3f3d. is ‘NULL’, the array is interpreted as a
standard n-dimensional C-array.  Otherwise, the consumer must access an
n-dimensional array as follows:

     ptr = (char *)buf + indices[0] * strides[0] + ... + indices[n-1] * strides[n-1];
     item = *((typeof(item) *)ptr);

As noted above, *note buf: 3f3c. can point to any location within the
actual memory block.  An exporter can check the validity of a buffer
with this function:

     def verify_structure(memlen, itemsize, ndim, shape, strides, offset):
         """Verify that the parameters represent a valid array within
            the bounds of the allocated memory:
                char *mem: start of the physical memory block
                memlen: length of the physical memory block
                offset: (char *)buf - mem
         """
         if offset % itemsize:
             return False
         if offset < 0 or offset+itemsize > memlen:
             return False
         if any(v % itemsize for v in strides):
             return False

         if ndim <= 0:
             return ndim == 0 and not shape and not strides
         if 0 in shape:
             return True

         imin = sum(strides[j]*(shape[j]-1) for j in range(ndim)
                    if strides[j] <= 0)
         imax = sum(strides[j]*(shape[j]-1) for j in range(ndim)
                    if strides[j] > 0)

         return 0 <= offset+imin and offset+imax+itemsize <= memlen


File: python.info,  Node: PIL-style shape strides and suboffsets,  Prev: NumPy-style shape and strides,  Up: Complex arrays

7.7.7.10 PIL-style: shape, strides and suboffsets
.................................................

In addition to the regular items, PIL-style arrays can contain pointers
that must be followed in order to get to the next element in a
dimension.  For example, the regular three-dimensional C-array ‘char
v[2][2][3]’ can also be viewed as an array of 2 pointers to 2
two-dimensional arrays: ‘char (*v[2])[2][3]’.  In suboffsets
representation, those two pointers can be embedded at the start of *note
buf: 3f3c, pointing to two ‘char x[2][3]’ arrays that can be located
anywhere in memory.

Here is a function that returns a pointer to the element in an N-D array
pointed to by an N-dimensional index when there are both non-‘NULL’
strides and suboffsets:

     void *get_item_pointer(int ndim, void *buf, Py_ssize_t *strides,
                            Py_ssize_t *suboffsets, Py_ssize_t *indices) {
         char *pointer = (char*)buf;
         int i;
         for (i = 0; i < ndim; i++) {
             pointer += strides[i] * indices[i];
             if (suboffsets[i] >=0 ) {
                 pointer = *((char**)pointer) + suboffsets[i];
             }
         }
         return (void*)pointer;
     }


File: python.info,  Node: Buffer-related functions,  Prev: Complex arrays,  Up: Buffer Protocol

7.7.7.11 Buffer-related functions
.................................

 -- C Function: int PyObject_CheckBuffer (PyObject *obj)

     Return ‘1’ if `obj' supports the buffer interface otherwise ‘0’.
     When ‘1’ is returned, it doesn’t guarantee that *note
     PyObject_GetBuffer(): deb. will succeed.  This function always
     succeeds.

 -- C Function: int PyObject_GetBuffer (PyObject *exporter,
          Py_buffer *view, int flags)

     Send a request to `exporter' to fill in `view' as specified by
     `flags'.  If the exporter cannot provide a buffer of the exact
     type, it MUST raise ‘PyExc_BufferError’, set ‘view->obj’ to ‘NULL’
     and return ‘-1’.

     On success, fill in `view', set ‘view->obj’ to a new reference to
     `exporter' and return 0.  In the case of chained buffer providers
     that redirect requests to a single object, ‘view->obj’ MAY refer to
     this object instead of `exporter' (See *note Buffer Object
     Structures: 3f38.).

     Successful calls to *note PyObject_GetBuffer(): deb. must be paired
     with calls to *note PyBuffer_Release(): e19, similar to ‘malloc()’
     and ‘free()’.  Thus, after the consumer is done with the buffer,
     *note PyBuffer_Release(): e19. must be called exactly once.

 -- C Function: void PyBuffer_Release (Py_buffer *view)

     Release the buffer `view' and decrement the reference count for
     ‘view->obj’.  This function MUST be called when the buffer is no
     longer being used, otherwise reference leaks may occur.

     It is an error to call this function on a buffer that was not
     obtained via *note PyObject_GetBuffer(): deb.

 -- C Function: Py_ssize_t PyBuffer_SizeFromFormat (const char *format)

     Return the implied *note itemsize: 3f45. from *note format: 3f46.
     On error, raise an exception and return -1.

     New in version 3.9.

 -- C Function: int PyBuffer_IsContiguous (Py_buffer *view, char order)

     Return ‘1’ if the memory defined by the `view' is C-style (`order'
     is ‘'C'’) or Fortran-style (`order' is ‘'F'’) *note contiguous:
     17ec. or either one (`order' is ‘'A'’).  Return ‘0’ otherwise.
     This function always succeeds.

 -- C Function: void* PyBuffer_GetPointer (Py_buffer *view,
          Py_ssize_t *indices)

     Get the memory area pointed to by the `indices' inside the given
     `view'.  `indices' must point to an array of ‘view->ndim’ indices.

 -- C Function: int PyBuffer_FromContiguous (Py_buffer *view, void *buf,
          Py_ssize_t len, char fort)

     Copy contiguous `len' bytes from `buf' to `view'.  `fort' can be
     ‘'C'’ or ‘'F'’ (for C-style or Fortran-style ordering).  ‘0’ is
     returned on success, ‘-1’ on error.

 -- C Function: int PyBuffer_ToContiguous (void *buf, Py_buffer *src,
          Py_ssize_t len, char order)

     Copy `len' bytes from `src' to its contiguous representation in
     `buf'.  `order' can be ‘'C'’ or ‘'F'’ or ‘'A'’ (for C-style or
     Fortran-style ordering or either one).  ‘0’ is returned on success,
     ‘-1’ on error.

     This function fails if `len' != `src->len'.

 -- C Function: void PyBuffer_FillContiguousStrides (int ndims,
          Py_ssize_t *shape, Py_ssize_t *strides, int itemsize,
          char order)

     Fill the `strides' array with byte-strides of a *note contiguous:
     17ec. (C-style if `order' is ‘'C'’ or Fortran-style if `order' is
     ‘'F'’) array of the given shape with the given number of bytes per
     element.

 -- C Function: int PyBuffer_FillInfo (Py_buffer *view,
          PyObject *exporter, void *buf, Py_ssize_t len, int readonly,
          int flags)

     Handle buffer requests for an exporter that wants to expose `buf'
     of size `len' with writability set according to `readonly'.  `buf'
     is interpreted as a sequence of unsigned bytes.

     The `flags' argument indicates the request type.  This function
     always fills in `view' as specified by flags, unless `buf' has been
     designated as read-only and *note PyBUF_WRITABLE: 3f43. is set in
     `flags'.

     On success, set ‘view->obj’ to a new reference to `exporter' and
     return 0.  Otherwise, raise ‘PyExc_BufferError’, set ‘view->obj’ to
     ‘NULL’ and return ‘-1’;

     If this function is used as part of a *note getbufferproc: 3f38,
     `exporter' MUST be set to the exporting object and `flags' must be
     passed unmodified.  Otherwise, `exporter' MUST be ‘NULL’.


File: python.info,  Node: Old Buffer Protocol,  Prev: Buffer Protocol,  Up: Abstract Objects Layer

7.7.8 Old Buffer Protocol
-------------------------

Deprecated since version 3.0.

These functions were part of the “old buffer protocol” API in Python 2.
In Python 3, this protocol doesn’t exist anymore but the functions are
still exposed to ease porting 2.x code.  They act as a compatibility
wrapper around the *note new buffer protocol: 171c, but they don’t give
you control over the lifetime of the resources acquired when a buffer is
exported.

Therefore, it is recommended that you call *note PyObject_GetBuffer():
deb. (or the ‘y*’ or ‘w*’ *note format codes: 3f2. with the *note
PyArg_ParseTuple(): 393. family of functions) to get a buffer view over
an object, and *note PyBuffer_Release(): e19. when the buffer view can
be released.

 -- C Function: int PyObject_AsCharBuffer (PyObject *obj, const
          char **buffer, Py_ssize_t *buffer_len)

     Returns a pointer to a read-only memory location usable as
     character-based input.  The `obj' argument must support the
     single-segment character buffer interface.  On success, returns
     ‘0’, sets `buffer' to the memory location and `buffer_len' to the
     buffer length.  Returns ‘-1’ and sets a *note TypeError: 1fe. on
     error.

 -- C Function: int PyObject_AsReadBuffer (PyObject *obj, const
          void **buffer, Py_ssize_t *buffer_len)

     Returns a pointer to a read-only memory location containing
     arbitrary data.  The `obj' argument must support the single-segment
     readable buffer interface.  On success, returns ‘0’, sets `buffer'
     to the memory location and `buffer_len' to the buffer length.
     Returns ‘-1’ and sets a *note TypeError: 1fe. on error.

 -- C Function: int PyObject_CheckReadBuffer (PyObject *o)

     Returns ‘1’ if `o' supports the single-segment readable buffer
     interface.  Otherwise returns ‘0’.  This function always succeeds.

     Note that this function tries to get and release a buffer, and
     exceptions which occur while calling corresponding functions will
     get suppressed.  To get error reporting use *note
     PyObject_GetBuffer(): deb. instead.

 -- C Function: int PyObject_AsWriteBuffer (PyObject *obj,
          void **buffer, Py_ssize_t *buffer_len)

     Returns a pointer to a writable memory location.  The `obj'
     argument must support the single-segment, character buffer
     interface.  On success, returns ‘0’, sets `buffer' to the memory
     location and `buffer_len' to the buffer length.  Returns ‘-1’ and
     sets a *note TypeError: 1fe. on error.


File: python.info,  Node: Concrete Objects Layer,  Next: Initialization Finalization and Threads,  Prev: Abstract Objects Layer,  Up: Python/C API Reference Manual

7.8 Concrete Objects Layer
==========================

The functions in this chapter are specific to certain Python object
types.  Passing them an object of the wrong type is not a good idea; if
you receive an object from a Python program and you are not sure that it
has the right type, you must perform a type check first; for example, to
check that an object is a dictionary, use *note PyDict_Check(): 3f73.
The chapter is structured like the “family tree” of Python object types.

     Warning: While the functions described in this chapter carefully
     check the type of the objects which are passed in, many of them do
     not check for ‘NULL’ being passed instead of a valid object.
     Allowing ‘NULL’ to be passed in can cause memory access violations
     and immediate termination of the interpreter.

* Menu:

* Fundamental Objects::
* Numeric Objects::
* Sequence Objects::
* Container Objects::
* Function Objects: Function Objects<2>.
* Other Objects::


File: python.info,  Node: Fundamental Objects,  Next: Numeric Objects,  Up: Concrete Objects Layer

7.8.1 Fundamental Objects
-------------------------

This section describes Python type objects and the singleton object
‘None’.

* Menu:

* Type Objects: Type Objects<2>.
* The None Object::


File: python.info,  Node: Type Objects<2>,  Next: The None Object,  Up: Fundamental Objects

7.8.1.1 Type Objects
....................

 -- C Type: PyTypeObject

     The C structure of the objects used to describe built-in types.

 -- C Variable: PyTypeObject PyType_Type

     This is the type object for type objects; it is the same object as
     *note type: 6ff. in the Python layer.

 -- C Function: int PyType_Check (PyObject *o)

     Return non-zero if the object `o' is a type object, including
     instances of types derived from the standard type object.  Return 0
     in all other cases.  This function always succeeds.

 -- C Function: int PyType_CheckExact (PyObject *o)

     Return non-zero if the object `o' is a type object, but not a
     subtype of the standard type object.  Return 0 in all other cases.
     This function always succeeds.

 -- C Function: unsigned int PyType_ClearCache ()

     Clear the internal lookup cache.  Return the current version tag.

 -- C Function: unsigned long PyType_GetFlags (PyTypeObject* type)

     Return the *note tp_flags: 1011. member of `type'.  This function
     is primarily meant for use with ‘Py_LIMITED_API’; the individual
     flag bits are guaranteed to be stable across Python releases, but
     access to *note tp_flags: 1011. itself is not part of the limited
     API.

     New in version 3.2.

     Changed in version 3.4: The return type is now ‘unsigned long’
     rather than ‘long’.

 -- C Function: void PyType_Modified (PyTypeObject *type)

     Invalidate the internal lookup cache for the type and all of its
     subtypes.  This function must be called after any manual
     modification of the attributes or base classes of the type.

 -- C Function: int PyType_HasFeature (PyTypeObject *o, int feature)

     Return non-zero if the type object `o' sets the feature `feature'.
     Type features are denoted by single bit flags.

 -- C Function: int PyType_IS_GC (PyTypeObject *o)

     Return true if the type object includes support for the cycle
     detector; this tests the type flag *note Py_TPFLAGS_HAVE_GC: 3d64.

 -- C Function: int PyType_IsSubtype (PyTypeObject *a, PyTypeObject *b)

     Return true if `a' is a subtype of `b'.

     This function only checks for actual subtypes, which means that
     *note __subclasscheck__(): 1585. is not called on `b'.  Call *note
     PyObject_IsSubclass(): 88d. to do the same check that *note
     issubclass(): 553. would do.

 -- C Function: PyObject* PyType_GenericAlloc (PyTypeObject *type,
          Py_ssize_t nitems)
     `Return value: New reference.'  Generic handler for the *note
     tp_alloc: 3d58. slot of a type object.  Use Python’s default memory
     allocation mechanism to allocate a new instance and initialize all
     its contents to ‘NULL’.

 -- C Function: PyObject* PyType_GenericNew (PyTypeObject *type,
          PyObject *args, PyObject *kwds)
     `Return value: New reference.'  Generic handler for the *note
     tp_new: 3d53. slot of a type object.  Create a new instance using
     the type’s *note tp_alloc: 3d58. slot.

 -- C Function: int PyType_Ready (PyTypeObject *type)

     Finalize a type object.  This should be called on all type objects
     to finish their initialization.  This function is responsible for
     adding inherited slots from a type’s base class.  Return ‘0’ on
     success, or return ‘-1’ and sets an exception on error.

          Note: If some of the base classes implements the GC protocol
          and the provided type does not include the *note
          Py_TPFLAGS_HAVE_GC: 3d64. in its flags, then the GC protocol
          will be automatically implemented from its parents.  On the
          contrary, if the type being created does include *note
          Py_TPFLAGS_HAVE_GC: 3d64. in its flags then it `must'
          implement the GC protocol itself by at least implementing the
          *note tp_traverse: 23b. handle.

 -- C Function: void* PyType_GetSlot (PyTypeObject *type, int slot)

     Return the function pointer stored in the given slot.  If the
     result is ‘NULL’, this indicates that either the slot is ‘NULL’, or
     that the function was called with invalid parameters.  Callers will
     typically cast the result pointer into the appropriate function
     type.

     See ‘PyType_Slot.slot’ for possible values of the `slot' argument.

     An exception is raised if `type' is not a heap type.

     New in version 3.4.

 -- C Function: PyObject* PyType_GetModule (PyTypeObject *type)

     Return the module object associated with the given type when the
     type was created using *note PyType_FromModuleAndSpec(): 245.

     If no module is associated with the given type, sets *note
     TypeError: 1fe. and returns ‘NULL’.

     This function is usually used to get the module in which a method
     is defined.  Note that in such a method,
     ‘PyType_GetModule(Py_TYPE(self))’ may not return the intended
     result.  ‘Py_TYPE(self)’ may be a `subclass' of the intended class,
     and subclasses are not necessarily defined in the same module as
     their superclass.  See *note PyCMethod: 248. to get the class that
     defines the method.

     New in version 3.9.

 -- C Function: void* PyType_GetModuleState (PyTypeObject *type)

     Return the state of the module object associated with the given
     type.  This is a shortcut for calling *note PyModule_GetState():
     25e. on the result of *note PyType_GetModule(): 246.

     If no module is associated with the given type, sets *note
     TypeError: 1fe. and returns ‘NULL’.

     If the `type' has an associated module but its state is ‘NULL’,
     returns ‘NULL’ without setting an exception.

     New in version 3.9.

* Menu:

* Creating Heap-Allocated Types::


File: python.info,  Node: Creating Heap-Allocated Types,  Up: Type Objects<2>

7.8.1.2 Creating Heap-Allocated Types
.....................................

The following functions and structs are used to create *note heap types:
3f7f.

 -- C Function: PyObject* PyType_FromModuleAndSpec (PyObject *module,
          PyType_Spec *spec, PyObject *bases)
     `Return value: New reference.'  Creates and returns a heap type
     object from the `spec' (*note Py_TPFLAGS_HEAPTYPE: 3f80.).

     If `bases' is a tuple, the created heap type contains all types
     contained in it as base types.

     If `bases' is ‘NULL’, the `Py_tp_bases' slot is used instead.  If
     that also is ‘NULL’, the `Py_tp_base' slot is used instead.  If
     that also is ‘NULL’, the new type derives from *note object: 3d2.

     The `module' argument can be used to record the module in which the
     new class is defined.  It must be a module object or ‘NULL’.  If
     not ‘NULL’, the module is associated with the new type and can
     later be retrieved with *note PyType_GetModule(): 246.  The
     associated module is not inherited by subclasses; it must be
     specified for each class individually.

     This function calls *note PyType_Ready(): 3d59. on the new type.

     New in version 3.9.

 -- C Function: PyObject* PyType_FromSpecWithBases (PyType_Spec *spec,
          PyObject *bases)
     `Return value: New reference.'  Equivalent to
     ‘PyType_FromModuleAndSpec(NULL, spec, bases)’.

     New in version 3.3.

 -- C Function: PyObject* PyType_FromSpec (PyType_Spec *spec)
     `Return value: New reference.'  Equivalent to
     ‘PyType_FromSpecWithBases(spec, NULL)’.

 -- C Type: PyType_Spec

     Structure defining a type’s behavior.

      -- C Member: const char* PyType_Spec.name

          Name of the type, used to set *note PyTypeObject.tp_name:
          3d71.

      -- C Member: int PyType_Spec.basicsize

      -- C Member: int PyType_Spec.itemsize

          Size of the instance in bytes, used to set *note
          PyTypeObject.tp_basicsize: 26a. and *note
          PyTypeObject.tp_itemsize: 3d50.

      -- C Member: int PyType_Spec.flags

          Type flags, used to set *note PyTypeObject.tp_flags: 1011.

          If the ‘Py_TPFLAGS_HEAPTYPE’ flag is not set, *note
          PyType_FromSpecWithBases(): 102d. sets it automatically.

      -- C Member: PyType_Slot *PyType_Spec.slots

          Array of *note PyType_Slot: 3f87. structures.  Terminated by
          the special slot value ‘{0, NULL}’.

 -- C Type: PyType_Slot

     Structure defining optional functionality of a type, containing a
     slot ID and a value pointer.

      -- C Member: int PyType_Slot.slot

               A slot ID.

               Slot IDs are named like the field names of the structures
               *note PyTypeObject: 3f5, *note PyNumberMethods: e46,
               *note PySequenceMethods: 3d7f, *note PyMappingMethods:
               3d80. and *note PyAsyncMethods: 3f89. with an added ‘Py_’
               prefix.  For example, use:

                  * ‘Py_tp_dealloc’ to set *note
                    PyTypeObject.tp_dealloc: 3d56.

                  * ‘Py_nb_add’ to set *note PyNumberMethods.nb_add:
                    3f8a.

                  * ‘Py_sq_length’ to set *note
                    PySequenceMethods.sq_length: 3f8b.

               The following fields cannot be set at all using *note
               PyType_Spec: 3f81. and *note PyType_Slot: 3f87.:

                  * *note tp_dict: 3f8c.

                  * *note tp_mro: 3f8d.

                  * *note tp_cache: 3f8e.

                  * *note tp_subclasses: 3f8f.

                  * *note tp_weaklist: 3f90.

                  * *note tp_vectorcall: 3f91.

                  * *note tp_weaklistoffset: 26b. (see *note
                    PyMemberDef: 3f92.)

                  * *note tp_dictoffset: 3f93. (see *note PyMemberDef:
                    3f92.)

                  * *note tp_vectorcall_offset: 3edc. (see *note
                    PyMemberDef: 3f92.)

               The following fields cannot be set using *note
               PyType_Spec: 3f81. and *note PyType_Slot: 3f87. under the
               limited API:

                  * *note bf_getbuffer: 3f94.

                  * *note bf_releasebuffer: 3e8a.

               Setting ‘Py_tp_bases’ or ‘Py_tp_base’ may be problematic
               on some platforms.  To avoid issues, use the `bases'
               argument of ‘PyType_FromSpecWithBases()’ instead.

          Changed in version 3.9: Slots in *note PyBufferProcs: 3f95. in
          may be set in the unlimited API.

      -- C Member: void *PyType_Slot.pfunc

          The desired value of the slot.  In most cases, this is a
          pointer to a function.

          May not be ‘NULL’.


File: python.info,  Node: The None Object,  Prev: Type Objects<2>,  Up: Fundamental Objects

7.8.1.3 The ‘None’ Object
.........................

Note that the *note PyTypeObject: 3f5. for ‘None’ is not directly
exposed in the Python/C API. Since ‘None’ is a singleton, testing for
object identity (using ‘==’ in C) is sufficient.  There is no
‘PyNone_Check()’ function for the same reason.

 -- C Variable: PyObject* Py_None

     The Python ‘None’ object, denoting lack of value.  This object has
     no methods.  It needs to be treated just like any other object with
     respect to reference counts.

 -- C Macro: Py_RETURN_NONE

     Properly handle returning *note Py_None: 3d1f. from within a C
     function (that is, increment the reference count of ‘None’ and
     return it.)


File: python.info,  Node: Numeric Objects,  Next: Sequence Objects,  Prev: Fundamental Objects,  Up: Concrete Objects Layer

7.8.2 Numeric Objects
---------------------

* Menu:

* Integer Objects::
* Boolean Objects::
* Floating Point Objects::
* Complex Number Objects::


File: python.info,  Node: Integer Objects,  Next: Boolean Objects,  Up: Numeric Objects

7.8.2.1 Integer Objects
.......................

All integers are implemented as “long” integer objects of arbitrary
size.

On error, most ‘PyLong_As*’ APIs return ‘(return type)-1’ which cannot
be distinguished from a number.  Use *note PyErr_Occurred(): 3d1a. to
disambiguate.

 -- C Type: PyLongObject

     This subtype of *note PyObject: 5b5. represents a Python integer
     object.

 -- C Variable: PyTypeObject PyLong_Type

     This instance of *note PyTypeObject: 3f5. represents the Python
     integer type.  This is the same object as *note int: 204. in the
     Python layer.

 -- C Function: int PyLong_Check (PyObject *p)

     Return true if its argument is a *note PyLongObject: 3f9f. or a
     subtype of *note PyLongObject: 3f9f.  This function always
     succeeds.

 -- C Function: int PyLong_CheckExact (PyObject *p)

     Return true if its argument is a *note PyLongObject: 3f9f, but not
     a subtype of *note PyLongObject: 3f9f.  This function always
     succeeds.

 -- C Function: PyObject* PyLong_FromLong (long v)
     `Return value: New reference.'  Return a new *note PyLongObject:
     3f9f. object from `v', or ‘NULL’ on failure.

     The current implementation keeps an array of integer objects for
     all integers between ‘-5’ and ‘256’, when you create an int in that
     range you actually just get back a reference to the existing
     object.

 -- C Function: PyObject* PyLong_FromUnsignedLong (unsigned long v)
     `Return value: New reference.'  Return a new *note PyLongObject:
     3f9f. object from a C ‘unsigned long’, or ‘NULL’ on failure.

 -- C Function: PyObject* PyLong_FromSsize_t (Py_ssize_t v)
     `Return value: New reference.'  Return a new *note PyLongObject:
     3f9f. object from a C ‘Py_ssize_t’, or ‘NULL’ on failure.

 -- C Function: PyObject* PyLong_FromSize_t (size_t v)
     `Return value: New reference.'  Return a new *note PyLongObject:
     3f9f. object from a C ‘size_t’, or ‘NULL’ on failure.

 -- C Function: PyObject* PyLong_FromLongLong (long long v)
     `Return value: New reference.'  Return a new *note PyLongObject:
     3f9f. object from a C ‘long long’, or ‘NULL’ on failure.

 -- C Function: PyObject* PyLong_FromUnsignedLongLong (unsigned long
          long v)
     `Return value: New reference.'  Return a new *note PyLongObject:
     3f9f. object from a C ‘unsigned long long’, or ‘NULL’ on failure.

 -- C Function: PyObject* PyLong_FromDouble (double v)
     `Return value: New reference.'  Return a new *note PyLongObject:
     3f9f. object from the integer part of `v', or ‘NULL’ on failure.

 -- C Function: PyObject* PyLong_FromString (const char *str,
          char **pend, int base)
     `Return value: New reference.'  Return a new *note PyLongObject:
     3f9f. based on the string value in `str', which is interpreted
     according to the radix in `base'.  If `pend' is non-‘NULL’, `*pend'
     will point to the first character in `str' which follows the
     representation of the number.  If `base' is ‘0’, `str' is
     interpreted using the *note Integer literals: 1533. definition; in
     this case, leading zeros in a non-zero decimal number raises a
     *note ValueError: 16d.  If `base' is not ‘0’, it must be between
     ‘2’ and ‘36’, inclusive.  Leading spaces and single underscores
     after a base specifier and between digits are ignored.  If there
     are no digits, *note ValueError: 16d. will be raised.

 -- C Function: PyObject* PyLong_FromUnicode (Py_UNICODE *u,
          Py_ssize_t length, int base)
     `Return value: New reference.'  Convert a sequence of Unicode
     digits to a Python integer value.

     Deprecated since version 3.3, will be removed in version 3.10: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyLong_FromUnicodeObject(): 3fa7.

 -- C Function: PyObject* PyLong_FromUnicodeObject (PyObject *u,
          int base)
     `Return value: New reference.'  Convert a sequence of Unicode
     digits in the string `u' to a Python integer value.

     New in version 3.3.

 -- C Function: PyObject* PyLong_FromVoidPtr (void *p)
     `Return value: New reference.'  Create a Python integer from the
     pointer `p'.  The pointer value can be retrieved from the resulting
     value using *note PyLong_AsVoidPtr(): 3fa9.

 -- C Function: long PyLong_AsLong (PyObject *obj)

     Return a C ‘long’ representation of `obj'.  If `obj' is not an
     instance of *note PyLongObject: 3f9f, first call its *note
     __index__(): 2c2. or *note __int__(): 2c3. method (if present) to
     convert it to a *note PyLongObject: 3f9f.

     Raise *note OverflowError: a41. if the value of `obj' is out of
     range for a ‘long’.

     Returns ‘-1’ on error.  Use *note PyErr_Occurred(): 3d1a. to
     disambiguate.

     Changed in version 3.8: Use *note __index__(): 2c2. if available.

     Deprecated since version 3.8: Using *note __int__(): 2c3. is
     deprecated.

 -- C Function: long PyLong_AsLongAndOverflow (PyObject *obj,
          int *overflow)

     Return a C ‘long’ representation of `obj'.  If `obj' is not an
     instance of *note PyLongObject: 3f9f, first call its *note
     __index__(): 2c2. or *note __int__(): 2c3. method (if present) to
     convert it to a *note PyLongObject: 3f9f.

     If the value of `obj' is greater than ‘LONG_MAX’ or less than
     ‘LONG_MIN’, set `*overflow' to ‘1’ or ‘-1’, respectively, and
     return ‘-1’; otherwise, set `*overflow' to ‘0’.  If any other
     exception occurs set `*overflow' to ‘0’ and return ‘-1’ as usual.

     Returns ‘-1’ on error.  Use *note PyErr_Occurred(): 3d1a. to
     disambiguate.

     Changed in version 3.8: Use *note __index__(): 2c2. if available.

     Deprecated since version 3.8: Using *note __int__(): 2c3. is
     deprecated.

 -- C Function: long long PyLong_AsLongLong (PyObject *obj)

     Return a C ‘long long’ representation of `obj'.  If `obj' is not an
     instance of *note PyLongObject: 3f9f, first call its *note
     __index__(): 2c2. or *note __int__(): 2c3. method (if present) to
     convert it to a *note PyLongObject: 3f9f.

     Raise *note OverflowError: a41. if the value of `obj' is out of
     range for a ‘long long’.

     Returns ‘-1’ on error.  Use *note PyErr_Occurred(): 3d1a. to
     disambiguate.

     Changed in version 3.8: Use *note __index__(): 2c2. if available.

     Deprecated since version 3.8: Using *note __int__(): 2c3. is
     deprecated.

 -- C Function: long long PyLong_AsLongLongAndOverflow (PyObject *obj,
          int *overflow)

     Return a C ‘long long’ representation of `obj'.  If `obj' is not an
     instance of *note PyLongObject: 3f9f, first call its *note
     __index__(): 2c2. or *note __int__(): 2c3. method (if present) to
     convert it to a *note PyLongObject: 3f9f.

     If the value of `obj' is greater than ‘LLONG_MAX’ or less than
     ‘LLONG_MIN’, set `*overflow' to ‘1’ or ‘-1’, respectively, and
     return ‘-1’; otherwise, set `*overflow' to ‘0’.  If any other
     exception occurs set `*overflow' to ‘0’ and return ‘-1’ as usual.

     Returns ‘-1’ on error.  Use *note PyErr_Occurred(): 3d1a. to
     disambiguate.

     New in version 3.2.

     Changed in version 3.8: Use *note __index__(): 2c2. if available.

     Deprecated since version 3.8: Using *note __int__(): 2c3. is
     deprecated.

 -- C Function: Py_ssize_t PyLong_AsSsize_t (PyObject *pylong)

     Return a C ‘Py_ssize_t’ representation of `pylong'.  `pylong' must
     be an instance of *note PyLongObject: 3f9f.

     Raise *note OverflowError: a41. if the value of `pylong' is out of
     range for a ‘Py_ssize_t’.

     Returns ‘-1’ on error.  Use *note PyErr_Occurred(): 3d1a. to
     disambiguate.

 -- C Function: unsigned long PyLong_AsUnsignedLong (PyObject *pylong)

     Return a C ‘unsigned long’ representation of `pylong'.  `pylong'
     must be an instance of *note PyLongObject: 3f9f.

     Raise *note OverflowError: a41. if the value of `pylong' is out of
     range for a ‘unsigned long’.

     Returns ‘(unsigned long)-1’ on error.  Use *note PyErr_Occurred():
     3d1a. to disambiguate.

 -- C Function: size_t PyLong_AsSize_t (PyObject *pylong)

     Return a C ‘size_t’ representation of `pylong'.  `pylong' must be
     an instance of *note PyLongObject: 3f9f.

     Raise *note OverflowError: a41. if the value of `pylong' is out of
     range for a ‘size_t’.

     Returns ‘(size_t)-1’ on error.  Use *note PyErr_Occurred(): 3d1a.
     to disambiguate.

 -- C Function: unsigned long long PyLong_AsUnsignedLongLong
          (PyObject *pylong)

     Return a C ‘unsigned long long’ representation of `pylong'.
     `pylong' must be an instance of *note PyLongObject: 3f9f.

     Raise *note OverflowError: a41. if the value of `pylong' is out of
     range for an ‘unsigned long long’.

     Returns ‘(unsigned long long)-1’ on error.  Use *note
     PyErr_Occurred(): 3d1a. to disambiguate.

     Changed in version 3.1: A negative `pylong' now raises *note
     OverflowError: a41, not *note TypeError: 1fe.

 -- C Function: unsigned long PyLong_AsUnsignedLongMask (PyObject *obj)

     Return a C ‘unsigned long’ representation of `obj'.  If `obj' is
     not an instance of *note PyLongObject: 3f9f, first call its *note
     __index__(): 2c2. or *note __int__(): 2c3. method (if present) to
     convert it to a *note PyLongObject: 3f9f.

     If the value of `obj' is out of range for an ‘unsigned long’,
     return the reduction of that value modulo ‘ULONG_MAX + 1’.

     Returns ‘(unsigned long)-1’ on error.  Use *note PyErr_Occurred():
     3d1a. to disambiguate.

     Changed in version 3.8: Use *note __index__(): 2c2. if available.

     Deprecated since version 3.8: Using *note __int__(): 2c3. is
     deprecated.

 -- C Function: unsigned long long PyLong_AsUnsignedLongLongMask
          (PyObject *obj)

     Return a C ‘unsigned long long’ representation of `obj'.  If `obj'
     is not an instance of *note PyLongObject: 3f9f, first call its
     *note __index__(): 2c2. or *note __int__(): 2c3. method (if
     present) to convert it to a *note PyLongObject: 3f9f.

     If the value of `obj' is out of range for an ‘unsigned long long’,
     return the reduction of that value modulo ‘ULLONG_MAX + 1’.

     Returns ‘(unsigned long long)-1’ on error.  Use *note
     PyErr_Occurred(): 3d1a. to disambiguate.

     Changed in version 3.8: Use *note __index__(): 2c2. if available.

     Deprecated since version 3.8: Using *note __int__(): 2c3. is
     deprecated.

 -- C Function: double PyLong_AsDouble (PyObject *pylong)

     Return a C ‘double’ representation of `pylong'.  `pylong' must be
     an instance of *note PyLongObject: 3f9f.

     Raise *note OverflowError: a41. if the value of `pylong' is out of
     range for a ‘double’.

     Returns ‘-1.0’ on error.  Use *note PyErr_Occurred(): 3d1a. to
     disambiguate.

 -- C Function: void* PyLong_AsVoidPtr (PyObject *pylong)

     Convert a Python integer `pylong' to a C ‘void’ pointer.  If
     `pylong' cannot be converted, an *note OverflowError: a41. will be
     raised.  This is only assured to produce a usable ‘void’ pointer
     for values created with *note PyLong_FromVoidPtr(): 3fa8.

     Returns ‘NULL’ on error.  Use *note PyErr_Occurred(): 3d1a. to
     disambiguate.


File: python.info,  Node: Boolean Objects,  Next: Floating Point Objects,  Prev: Integer Objects,  Up: Numeric Objects

7.8.2.2 Boolean Objects
.......................

Booleans in Python are implemented as a subclass of integers.  There are
only two booleans, ‘Py_False’ and ‘Py_True’.  As such, the normal
creation and deletion functions don’t apply to booleans.  The following
macros are available, however.

 -- C Function: int PyBool_Check (PyObject *o)

     Return true if `o' is of type ‘PyBool_Type’.  This function always
     succeeds.

 -- C Variable: PyObject* Py_False

     The Python ‘False’ object.  This object has no methods.  It needs
     to be treated just like any other object with respect to reference
     counts.

 -- C Variable: PyObject* Py_True

     The Python ‘True’ object.  This object has no methods.  It needs to
     be treated just like any other object with respect to reference
     counts.

 -- C Macro: Py_RETURN_FALSE

     Return ‘Py_False’ from a function, properly incrementing its
     reference count.

 -- C Macro: Py_RETURN_TRUE

     Return ‘Py_True’ from a function, properly incrementing its
     reference count.

 -- C Function: PyObject* PyBool_FromLong (long v)
     `Return value: New reference.'  Return a new reference to ‘Py_True’
     or ‘Py_False’ depending on the truth value of `v'.


File: python.info,  Node: Floating Point Objects,  Next: Complex Number Objects,  Prev: Boolean Objects,  Up: Numeric Objects

7.8.2.3 Floating Point Objects
..............................

 -- C Type: PyFloatObject

     This subtype of *note PyObject: 5b5. represents a Python floating
     point object.

 -- C Variable: PyTypeObject PyFloat_Type

     This instance of *note PyTypeObject: 3f5. represents the Python
     floating point type.  This is the same object as *note float: 1fd.
     in the Python layer.

 -- C Function: int PyFloat_Check (PyObject *p)

     Return true if its argument is a *note PyFloatObject: 3fba. or a
     subtype of *note PyFloatObject: 3fba.  This function always
     succeeds.

 -- C Function: int PyFloat_CheckExact (PyObject *p)

     Return true if its argument is a *note PyFloatObject: 3fba, but not
     a subtype of *note PyFloatObject: 3fba.  This function always
     succeeds.

 -- C Function: PyObject* PyFloat_FromString (PyObject *str)
     `Return value: New reference.'  Create a *note PyFloatObject: 3fba.
     object based on the string value in `str', or ‘NULL’ on failure.

 -- C Function: PyObject* PyFloat_FromDouble (double v)
     `Return value: New reference.'  Create a *note PyFloatObject: 3fba.
     object from `v', or ‘NULL’ on failure.

 -- C Function: double PyFloat_AsDouble (PyObject *pyfloat)

     Return a C ‘double’ representation of the contents of `pyfloat'.
     If `pyfloat' is not a Python floating point object but has a *note
     __float__(): 2c4. method, this method will first be called to
     convert `pyfloat' into a float.  If ‘__float__()’ is not defined
     then it falls back to *note __index__(): 2c2.  This method returns
     ‘-1.0’ upon failure, so one should call *note PyErr_Occurred():
     3d1a. to check for errors.

     Changed in version 3.8: Use *note __index__(): 2c2. if available.

 -- C Function: double PyFloat_AS_DOUBLE (PyObject *pyfloat)

     Return a C ‘double’ representation of the contents of `pyfloat',
     but without error checking.

 -- C Function: PyObject* PyFloat_GetInfo (void)
     `Return value: New reference.'  Return a structseq instance which
     contains information about the precision, minimum and maximum
     values of a float.  It’s a thin wrapper around the header file
     ‘float.h’.

 -- C Function: double PyFloat_GetMax ()

     Return the maximum representable finite float `DBL_MAX' as C
     ‘double’.

 -- C Function: double PyFloat_GetMin ()

     Return the minimum normalized positive float `DBL_MIN' as C
     ‘double’.


File: python.info,  Node: Complex Number Objects,  Prev: Floating Point Objects,  Up: Numeric Objects

7.8.2.4 Complex Number Objects
..............................

Python’s complex number objects are implemented as two distinct types
when viewed from the C API: one is the Python object exposed to Python
programs, and the other is a C structure which represents the actual
complex number value.  The API provides functions for working with both.

* Menu:

* Complex Numbers as C Structures::
* Complex Numbers as Python Objects::


File: python.info,  Node: Complex Numbers as C Structures,  Next: Complex Numbers as Python Objects,  Up: Complex Number Objects

7.8.2.5 Complex Numbers as C Structures
.......................................

Note that the functions which accept these structures as parameters and
return them as results do so `by value' rather than dereferencing them
through pointers.  This is consistent throughout the API.

 -- C Type: Py_complex

     The C structure which corresponds to the value portion of a Python
     complex number object.  Most of the functions for dealing with
     complex number objects use structures of this type as input or
     output values, as appropriate.  It is defined as:

          typedef struct {
             double real;
             double imag;
          } Py_complex;

 -- C Function: Py_complex _Py_c_sum (Py_complex left, Py_complex right)

     Return the sum of two complex numbers, using the C *note
     Py_complex: 3e8c. representation.

 -- C Function: Py_complex _Py_c_diff (Py_complex left,
          Py_complex right)

     Return the difference between two complex numbers, using the C
     *note Py_complex: 3e8c. representation.

 -- C Function: Py_complex _Py_c_neg (Py_complex num)

     Return the negation of the complex number `num', using the C *note
     Py_complex: 3e8c. representation.

 -- C Function: Py_complex _Py_c_prod (Py_complex left,
          Py_complex right)

     Return the product of two complex numbers, using the C *note
     Py_complex: 3e8c. representation.

 -- C Function: Py_complex _Py_c_quot (Py_complex dividend,
          Py_complex divisor)

     Return the quotient of two complex numbers, using the C *note
     Py_complex: 3e8c. representation.

     If `divisor' is null, this method returns zero and sets ‘errno’ to
     ‘EDOM’.

 -- C Function: Py_complex _Py_c_pow (Py_complex num, Py_complex exp)

     Return the exponentiation of `num' by `exp', using the C *note
     Py_complex: 3e8c. representation.

     If `num' is null and `exp' is not a positive real number, this
     method returns zero and sets ‘errno’ to ‘EDOM’.


File: python.info,  Node: Complex Numbers as Python Objects,  Prev: Complex Numbers as C Structures,  Up: Complex Number Objects

7.8.2.6 Complex Numbers as Python Objects
.........................................

 -- C Type: PyComplexObject

     This subtype of *note PyObject: 5b5. represents a Python complex
     number object.

 -- C Variable: PyTypeObject PyComplex_Type

     This instance of *note PyTypeObject: 3f5. represents the Python
     complex number type.  It is the same object as *note complex: 2c1.
     in the Python layer.

 -- C Function: int PyComplex_Check (PyObject *p)

     Return true if its argument is a *note PyComplexObject: 3fcc. or a
     subtype of *note PyComplexObject: 3fcc.  This function always
     succeeds.

 -- C Function: int PyComplex_CheckExact (PyObject *p)

     Return true if its argument is a *note PyComplexObject: 3fcc, but
     not a subtype of *note PyComplexObject: 3fcc.  This function always
     succeeds.

 -- C Function: PyObject* PyComplex_FromCComplex (Py_complex v)
     `Return value: New reference.'  Create a new Python complex number
     object from a C *note Py_complex: 3e8c. value.

 -- C Function: PyObject* PyComplex_FromDoubles (double real,
          double imag)
     `Return value: New reference.'  Return a new *note PyComplexObject:
     3fcc. object from `real' and `imag'.

 -- C Function: double PyComplex_RealAsDouble (PyObject *op)

     Return the real part of `op' as a C ‘double’.

 -- C Function: double PyComplex_ImagAsDouble (PyObject *op)

     Return the imaginary part of `op' as a C ‘double’.

 -- C Function: Py_complex PyComplex_AsCComplex (PyObject *op)

     Return the *note Py_complex: 3e8c. value of the complex number
     `op'.

     If `op' is not a Python complex number object but has a *note
     __complex__(): 2c5. method, this method will first be called to
     convert `op' to a Python complex number object.  If ‘__complex__()’
     is not defined then it falls back to *note __float__(): 2c4.  If
     ‘__float__()’ is not defined then it falls back to *note
     __index__(): 2c2.  Upon failure, this method returns ‘-1.0’ as a
     real value.

     Changed in version 3.8: Use *note __index__(): 2c2. if available.


File: python.info,  Node: Sequence Objects,  Next: Container Objects,  Prev: Numeric Objects,  Up: Concrete Objects Layer

7.8.3 Sequence Objects
----------------------

Generic operations on sequence objects were discussed in the previous
chapter; this section deals with the specific kinds of sequence objects
that are intrinsic to the Python language.

* Menu:

* Bytes Objects: Bytes Objects<2>.
* Byte Array Objects::
* Unicode Objects and Codecs::
* Tuple Objects::
* Struct Sequence Objects::
* List Objects::


File: python.info,  Node: Bytes Objects<2>,  Next: Byte Array Objects,  Up: Sequence Objects

7.8.3.1 Bytes Objects
.....................

These functions raise *note TypeError: 1fe. when expecting a bytes
parameter and are called with a non-bytes parameter.

 -- C Type: PyBytesObject

     This subtype of *note PyObject: 5b5. represents a Python bytes
     object.

 -- C Variable: PyTypeObject PyBytes_Type

     This instance of *note PyTypeObject: 3f5. represents the Python
     bytes type; it is the same object as *note bytes: 172. in the
     Python layer.

 -- C Function: int PyBytes_Check (PyObject *o)

     Return true if the object `o' is a bytes object or an instance of a
     subtype of the bytes type.  This function always succeeds.

 -- C Function: int PyBytes_CheckExact (PyObject *o)

     Return true if the object `o' is a bytes object, but not an
     instance of a subtype of the bytes type.  This function always
     succeeds.

 -- C Function: PyObject* PyBytes_FromString (const char *v)
     `Return value: New reference.'  Return a new bytes object with a
     copy of the string `v' as value on success, and ‘NULL’ on failure.
     The parameter `v' must not be ‘NULL’; it will not be checked.

 -- C Function: PyObject* PyBytes_FromStringAndSize (const char *v,
          Py_ssize_t len)
     `Return value: New reference.'  Return a new bytes object with a
     copy of the string `v' as value and length `len' on success, and
     ‘NULL’ on failure.  If `v' is ‘NULL’, the contents of the bytes
     object are uninitialized.

 -- C Function: PyObject* PyBytes_FromFormat (const char *format, ...)
     `Return value: New reference.'  Take a C ‘printf()’-style `format'
     string and a variable number of arguments, calculate the size of
     the resulting Python bytes object and return a bytes object with
     the values formatted into it.  The variable arguments must be C
     types and must correspond exactly to the format characters in the
     `format' string.  The following format characters are allowed:

     Format Characters       Type                Comment
                                                 
     ---------------------------------------------------------------------------------
                                                 
     ‘%%’                    `n/a'               The literal % character.
                                                 
                                                 
     ‘%c’                    int                 A single byte, represented as a C
                                                 int.
                                                 
                                                 
     ‘%d’                    int                 Equivalent to ‘printf("%d")’.  (1)
                                                 
                                                 
     ‘%u’                    unsigned int        Equivalent to ‘printf("%u")’.  (2)
                                                 
                                                 
     ‘%ld’                   long                Equivalent to ‘printf("%ld")’.
                                                 (3)
                                                 
                                                 
     ‘%lu’                   unsigned long       Equivalent to ‘printf("%lu")’.
                                                 (4)
                                                 
                                                 
     ‘%zd’                   Py_ssize_t          Equivalent to ‘printf("%zd")’.
                                                 (5)
                                                 
                                                 
     ‘%zu’                   size_t              Equivalent to ‘printf("%zu")’.
                                                 (6)
                                                 
                                                 
     ‘%i’                    int                 Equivalent to ‘printf("%i")’.  (7)
                                                 
                                                 
     ‘%x’                    int                 Equivalent to ‘printf("%x")’.  (8)
                                                 
                                                 
     ‘%s’                    const char*         A null-terminated C character
                                                 array.
                                                 
                                                 
     ‘%p’                    const void*         The hex representation of a C
                                                 pointer.  Mostly equivalent to
                                                 ‘printf("%p")’ except that it is
                                                 guaranteed to start with the
                                                 literal ‘0x’ regardless of what
                                                 the platform’s ‘printf’ yields.
                                                 

     An unrecognized format character causes all the rest of the format
     string to be copied as-is to the result object, and any extra
     arguments discarded.

 -- C Function: PyObject* PyBytes_FromFormatV (const char *format,
          va_list vargs)
     `Return value: New reference.'  Identical to *note
     PyBytes_FromFormat(): 1144. except that it takes exactly two
     arguments.

 -- C Function: PyObject* PyBytes_FromObject (PyObject *o)
     `Return value: New reference.'  Return the bytes representation of
     object `o' that implements the buffer protocol.

 -- C Function: Py_ssize_t PyBytes_Size (PyObject *o)

     Return the length of the bytes in bytes object `o'.

 -- C Function: Py_ssize_t PyBytes_GET_SIZE (PyObject *o)

     Macro form of *note PyBytes_Size(): 3fde. but without error
     checking.

 -- C Function: char* PyBytes_AsString (PyObject *o)

     Return a pointer to the contents of `o'.  The pointer refers to the
     internal buffer of `o', which consists of ‘len(o) + 1’ bytes.  The
     last byte in the buffer is always null, regardless of whether there
     are any other null bytes.  The data must not be modified in any
     way, unless the object was just created using
     ‘PyBytes_FromStringAndSize(NULL, size)’.  It must not be
     deallocated.  If `o' is not a bytes object at all, *note
     PyBytes_AsString(): 3fe0. returns ‘NULL’ and raises *note
     TypeError: 1fe.

 -- C Function: char* PyBytes_AS_STRING (PyObject *string)

     Macro form of *note PyBytes_AsString(): 3fe0. but without error
     checking.

 -- C Function: int PyBytes_AsStringAndSize (PyObject *obj,
          char **buffer, Py_ssize_t *length)

     Return the null-terminated contents of the object `obj' through the
     output variables `buffer' and `length'.

     If `length' is ‘NULL’, the bytes object may not contain embedded
     null bytes; if it does, the function returns ‘-1’ and a *note
     ValueError: 16d. is raised.

     The buffer refers to an internal buffer of `obj', which includes an
     additional null byte at the end (not counted in `length').  The
     data must not be modified in any way, unless the object was just
     created using ‘PyBytes_FromStringAndSize(NULL, size)’.  It must not
     be deallocated.  If `obj' is not a bytes object at all, *note
     PyBytes_AsStringAndSize(): 3fe2. returns ‘-1’ and raises *note
     TypeError: 1fe.

     Changed in version 3.5: Previously, *note TypeError: 1fe. was
     raised when embedded null bytes were encountered in the bytes
     object.

 -- C Function: void PyBytes_Concat (PyObject **bytes,
          PyObject *newpart)

     Create a new bytes object in `*bytes' containing the contents of
     `newpart' appended to `bytes'; the caller will own the new
     reference.  The reference to the old value of `bytes' will be
     stolen.  If the new object cannot be created, the old reference to
     `bytes' will still be discarded and the value of `*bytes' will be
     set to ‘NULL’; the appropriate exception will be set.

 -- C Function: void PyBytes_ConcatAndDel (PyObject **bytes,
          PyObject *newpart)

     Create a new bytes object in `*bytes' containing the contents of
     `newpart' appended to `bytes'.  This version decrements the
     reference count of `newpart'.

 -- C Function: int _PyBytes_Resize (PyObject **bytes,
          Py_ssize_t newsize)

     A way to resize a bytes object even though it is “immutable”.  Only
     use this to build up a brand new bytes object; don’t use this if
     the bytes may already be known in other parts of the code.  It is
     an error to call this function if the refcount on the input bytes
     object is not one.  Pass the address of an existing bytes object as
     an lvalue (it may be written into), and the new size desired.  On
     success, `*bytes' holds the resized bytes object and ‘0’ is
     returned; the address in `*bytes' may differ from its input value.
     If the reallocation fails, the original bytes object at `*bytes' is
     deallocated, `*bytes' is set to ‘NULL’, *note MemoryError: f69. is
     set, and ‘-1’ is returned.

   ---------- Footnotes ----------

   (1) (1) For integer specifiers (d, u, ld, lu, zd, zu, i, x): the
0-conversion flag has effect even when a precision is given.

   (2) (1) For integer specifiers (d, u, ld, lu, zd, zu, i, x): the
0-conversion flag has effect even when a precision is given.

   (3) (1) For integer specifiers (d, u, ld, lu, zd, zu, i, x): the
0-conversion flag has effect even when a precision is given.

   (4) (1) For integer specifiers (d, u, ld, lu, zd, zu, i, x): the
0-conversion flag has effect even when a precision is given.

   (5) (1) For integer specifiers (d, u, ld, lu, zd, zu, i, x): the
0-conversion flag has effect even when a precision is given.

   (6) (1) For integer specifiers (d, u, ld, lu, zd, zu, i, x): the
0-conversion flag has effect even when a precision is given.

   (7) (1) For integer specifiers (d, u, ld, lu, zd, zu, i, x): the
0-conversion flag has effect even when a precision is given.

   (8) (1) For integer specifiers (d, u, ld, lu, zd, zu, i, x): the
0-conversion flag has effect even when a precision is given.


File: python.info,  Node: Byte Array Objects,  Next: Unicode Objects and Codecs,  Prev: Bytes Objects<2>,  Up: Sequence Objects

7.8.3.2 Byte Array Objects
..........................

 -- C Type: PyByteArrayObject

     This subtype of *note PyObject: 5b5. represents a Python bytearray
     object.

 -- C Variable: PyTypeObject PyByteArray_Type

     This instance of *note PyTypeObject: 3f5. represents the Python
     bytearray type; it is the same object as *note bytearray: 173. in
     the Python layer.

* Menu:

* Type check macros::
* Direct API functions::
* Macros::


File: python.info,  Node: Type check macros,  Next: Direct API functions,  Up: Byte Array Objects

7.8.3.3 Type check macros
.........................

 -- C Function: int PyByteArray_Check (PyObject *o)

     Return true if the object `o' is a bytearray object or an instance
     of a subtype of the bytearray type.  This function always succeeds.

 -- C Function: int PyByteArray_CheckExact (PyObject *o)

     Return true if the object `o' is a bytearray object, but not an
     instance of a subtype of the bytearray type.  This function always
     succeeds.


File: python.info,  Node: Direct API functions,  Next: Macros,  Prev: Type check macros,  Up: Byte Array Objects

7.8.3.4 Direct API functions
............................

 -- C Function: PyObject* PyByteArray_FromObject (PyObject *o)
     `Return value: New reference.'  Return a new bytearray object from
     any object, `o', that implements the *note buffer protocol: 171c.

 -- C Function: PyObject* PyByteArray_FromStringAndSize (const
          char *string, Py_ssize_t len)
     `Return value: New reference.'  Create a new bytearray object from
     `string' and its length, `len'.  On failure, ‘NULL’ is returned.

 -- C Function: PyObject* PyByteArray_Concat (PyObject *a, PyObject *b)
     `Return value: New reference.'  Concat bytearrays `a' and `b' and
     return a new bytearray with the result.

 -- C Function: Py_ssize_t PyByteArray_Size (PyObject *bytearray)

     Return the size of `bytearray' after checking for a ‘NULL’ pointer.

 -- C Function: char* PyByteArray_AsString (PyObject *bytearray)

     Return the contents of `bytearray' as a char array after checking
     for a ‘NULL’ pointer.  The returned array always has an extra null
     byte appended.

 -- C Function: int PyByteArray_Resize (PyObject *bytearray,
          Py_ssize_t len)

     Resize the internal buffer of `bytearray' to `len'.


File: python.info,  Node: Macros,  Prev: Direct API functions,  Up: Byte Array Objects

7.8.3.5 Macros
..............

These macros trade safety for speed and they don’t check pointers.

 -- C Function: char* PyByteArray_AS_STRING (PyObject *bytearray)

     Macro version of *note PyByteArray_AsString(): 3ff0.

 -- C Function: Py_ssize_t PyByteArray_GET_SIZE (PyObject *bytearray)

     Macro version of *note PyByteArray_Size(): 3fef.


File: python.info,  Node: Unicode Objects and Codecs,  Next: Tuple Objects,  Prev: Byte Array Objects,  Up: Sequence Objects

7.8.3.6 Unicode Objects and Codecs
..................................

* Menu:

* Unicode Objects::
* Built-in Codecs::
* Methods and Slot Functions::


File: python.info,  Node: Unicode Objects,  Next: Built-in Codecs,  Up: Unicode Objects and Codecs

7.8.3.7 Unicode Objects
.......................

Since the implementation of PEP 393(1) in Python 3.3, Unicode objects
internally use a variety of representations, in order to allow handling
the complete range of Unicode characters while staying memory efficient.
There are special cases for strings where all code points are below 128,
256, or 65536; otherwise, code points must be below 1114112 (which is
the full Unicode range).

*note Py_UNICODE*: bc5. and UTF-8 representations are created on demand
and cached in the Unicode object.  The *note Py_UNICODE*: bc5.
representation is deprecated and inefficient.

Due to the transition between the old APIs and the new APIs, Unicode
objects can internally be in two states depending on how they were
created:

   * “canonical” Unicode objects are all objects created by a
     non-deprecated Unicode API. They use the most efficient
     representation allowed by the implementation.

   * “legacy” Unicode objects have been created through one of the
     deprecated APIs (typically *note PyUnicode_FromUnicode(): 263.) and
     only bear the *note Py_UNICODE*: bc5. representation; you will have
     to call *note PyUnicode_READY(): bad. on them before calling any
     other API.

     Note: The “legacy” Unicode object will be removed in Python 3.12
     with deprecated APIs.  All Unicode objects will be “canonical”
     since then.  See PEP 623(2) for more information.

* Menu:

* Unicode Type::
* Unicode Character Properties::
* Creating and accessing Unicode strings::
* Deprecated Py_UNICODE APIs::
* Locale Encoding::
* File System Encoding::
* wchar_t Support::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0393

   (2) https://www.python.org/dev/peps/pep-0623


File: python.info,  Node: Unicode Type,  Next: Unicode Character Properties,  Up: Unicode Objects

7.8.3.8 Unicode Type
....................

These are the basic Unicode object types used for the Unicode
implementation in Python:

 -- C Type: Py_UCS4
 -- C Type: Py_UCS2
 -- C Type: Py_UCS1

     These types are typedefs for unsigned integer types wide enough to
     contain characters of 32 bits, 16 bits and 8 bits, respectively.
     When dealing with single Unicode characters, use *note Py_UCS4:
     baa.

     New in version 3.3.

 -- C Type: Py_UNICODE

     This is a typedef of ‘wchar_t’, which is a 16-bit type or 32-bit
     type depending on the platform.

     Changed in version 3.3: In previous versions, this was a 16-bit
     type or a 32-bit type depending on whether you selected a “narrow”
     or “wide” Unicode version of Python at build time.

 -- C Type: PyASCIIObject
 -- C Type: PyCompactUnicodeObject
 -- C Type: PyUnicodeObject

     These subtypes of *note PyObject: 5b5. represent a Python Unicode
     object.  In almost all cases, they shouldn’t be used directly,
     since all API functions that deal with Unicode objects take and
     return *note PyObject: 5b5. pointers.

     New in version 3.3.

 -- C Variable: PyTypeObject PyUnicode_Type

     This instance of *note PyTypeObject: 3f5. represents the Python
     Unicode type.  It is exposed to Python code as ‘str’.

The following APIs are really C macros and can be used to do fast checks
and to access internal read-only data of Unicode objects:

 -- C Function: int PyUnicode_Check (PyObject *o)

     Return true if the object `o' is a Unicode object or an instance of
     a Unicode subtype.  This function always succeeds.

 -- C Function: int PyUnicode_CheckExact (PyObject *o)

     Return true if the object `o' is a Unicode object, but not an
     instance of a subtype.  This function always succeeds.

 -- C Function: int PyUnicode_READY (PyObject *o)

     Ensure the string object `o' is in the “canonical” representation.
     This is required before using any of the access macros described
     below.

     Returns ‘0’ on success and ‘-1’ with an exception set on failure,
     which in particular happens if memory allocation fails.

     New in version 3.3.

     Deprecated since version 3.10, will be removed in version 3.12:
     This API will be removed with *note PyUnicode_FromUnicode(): 263.

 -- C Function: Py_ssize_t PyUnicode_GET_LENGTH (PyObject *o)

     Return the length of the Unicode string, in code points.  `o' has
     to be a Unicode object in the “canonical” representation (not
     checked).

     New in version 3.3.

 -- C Function: Py_UCS1* PyUnicode_1BYTE_DATA (PyObject *o)
 -- C Function: Py_UCS2* PyUnicode_2BYTE_DATA (PyObject *o)
 -- C Function: Py_UCS4* PyUnicode_4BYTE_DATA (PyObject *o)

     Return a pointer to the canonical representation cast to UCS1, UCS2
     or UCS4 integer types for direct character access.  No checks are
     performed if the canonical representation has the correct character
     size; use *note PyUnicode_KIND(): bb5. to select the right macro.
     Make sure *note PyUnicode_READY(): bad. has been called before
     accessing this.

     New in version 3.3.

 -- C Macro: PyUnicode_WCHAR_KIND
 -- C Macro: PyUnicode_1BYTE_KIND
 -- C Macro: PyUnicode_2BYTE_KIND
 -- C Macro: PyUnicode_4BYTE_KIND

     Return values of the *note PyUnicode_KIND(): bb5. macro.

     New in version 3.3.

     Deprecated since version 3.10, will be removed in version 3.12:
     ‘PyUnicode_WCHAR_KIND’ is deprecated.

 -- C Function: unsigned int PyUnicode_KIND (PyObject *o)

     Return one of the PyUnicode kind constants (see above) that
     indicate how many bytes per character this Unicode object uses to
     store its data.  `o' has to be a Unicode object in the “canonical”
     representation (not checked).

     New in version 3.3.

 -- C Function: void* PyUnicode_DATA (PyObject *o)

     Return a void pointer to the raw Unicode buffer.  `o' has to be a
     Unicode object in the “canonical” representation (not checked).

     New in version 3.3.

 -- C Function: void PyUnicode_WRITE (int kind, void *data,
          Py_ssize_t index, Py_UCS4 value)

     Write into a canonical representation `data' (as obtained with
     *note PyUnicode_DATA(): bb1.).  This macro does not do any sanity
     checks and is intended for usage in loops.  The caller should cache
     the `kind' value and `data' pointer as obtained from other macro
     calls.  `index' is the index in the string (starts at 0) and
     `value' is the new code point value which should be written to that
     location.

     New in version 3.3.

 -- C Function: Py_UCS4 PyUnicode_READ (int kind, void *data,
          Py_ssize_t index)

     Read a code point from a canonical representation `data' (as
     obtained with *note PyUnicode_DATA(): bb1.).  No checks or ready
     calls are performed.

     New in version 3.3.

 -- C Function: Py_UCS4 PyUnicode_READ_CHAR (PyObject *o,
          Py_ssize_t index)

     Read a character from a Unicode object `o', which must be in the
     “canonical” representation.  This is less efficient than *note
     PyUnicode_READ(): bba. if you do multiple consecutive reads.

     New in version 3.3.

 -- C Macro: PyUnicode_MAX_CHAR_VALUE (o)

     Return the maximum code point that is suitable for creating another
     string based on `o', which must be in the “canonical”
     representation.  This is always an approximation but more efficient
     than iterating over the string.

     New in version 3.3.

 -- C Function: Py_ssize_t PyUnicode_GET_SIZE (PyObject *o)

     Return the size of the deprecated *note Py_UNICODE: bc5.
     representation, in code units (this includes surrogate pairs as 2
     units).  `o' has to be a Unicode object (not checked).

     Deprecated since version 3.3, will be removed in version 3.12: Part
     of the old-style Unicode API, please migrate to using *note
     PyUnicode_GET_LENGTH(): ba3.

 -- C Function: Py_ssize_t PyUnicode_GET_DATA_SIZE (PyObject *o)

     Return the size of the deprecated *note Py_UNICODE: bc5.
     representation in bytes.  `o' has to be a Unicode object (not
     checked).

     Deprecated since version 3.3, will be removed in version 3.12: Part
     of the old-style Unicode API, please migrate to using *note
     PyUnicode_GET_LENGTH(): ba3.

 -- C Function: Py_UNICODE* PyUnicode_AS_UNICODE (PyObject *o)
 -- C Function: const char* PyUnicode_AS_DATA (PyObject *o)

     Return a pointer to a *note Py_UNICODE: bc5. representation of the
     object.  The returned buffer is always terminated with an extra
     null code point.  It may also contain embedded null code points,
     which would cause the string to be truncated when used in most C
     functions.  The ‘AS_DATA’ form casts the pointer to ‘const char *’.
     The `o' argument has to be a Unicode object (not checked).

     Changed in version 3.3: This macro is now inefficient – because in
     many cases the *note Py_UNICODE: bc5. representation does not exist
     and needs to be created – and can fail (return ‘NULL’ with an
     exception set).  Try to port the code to use the new
     ‘PyUnicode_nBYTE_DATA()’ macros or use *note PyUnicode_WRITE():
     bbc. or *note PyUnicode_READ(): bba.

     Deprecated since version 3.3, will be removed in version 3.12: Part
     of the old-style Unicode API, please migrate to using the
     ‘PyUnicode_nBYTE_DATA()’ family of macros.

 -- C Function: int PyUnicode_IsIdentifier (PyObject *o)

     Return ‘1’ if the string is a valid identifier according to the
     language definition, section *note Identifiers and keywords: 1505.
     Return ‘0’ otherwise.

     Changed in version 3.9: The function does not call *note
     Py_FatalError(): 266. anymore if the string is not ready.


File: python.info,  Node: Unicode Character Properties,  Next: Creating and accessing Unicode strings,  Prev: Unicode Type,  Up: Unicode Objects

7.8.3.9 Unicode Character Properties
....................................

Unicode provides many different character properties.  The most often
needed ones are available through these macros which are mapped to C
functions depending on the Python configuration.

 -- C Function: int Py_UNICODE_ISSPACE (Py_UCS4 ch)

     Return ‘1’ or ‘0’ depending on whether `ch' is a whitespace
     character.

 -- C Function: int Py_UNICODE_ISLOWER (Py_UCS4 ch)

     Return ‘1’ or ‘0’ depending on whether `ch' is a lowercase
     character.

 -- C Function: int Py_UNICODE_ISUPPER (Py_UCS4 ch)

     Return ‘1’ or ‘0’ depending on whether `ch' is an uppercase
     character.

 -- C Function: int Py_UNICODE_ISTITLE (Py_UCS4 ch)

     Return ‘1’ or ‘0’ depending on whether `ch' is a titlecase
     character.

 -- C Function: int Py_UNICODE_ISLINEBREAK (Py_UCS4 ch)

     Return ‘1’ or ‘0’ depending on whether `ch' is a linebreak
     character.

 -- C Function: int Py_UNICODE_ISDECIMAL (Py_UCS4 ch)

     Return ‘1’ or ‘0’ depending on whether `ch' is a decimal character.

 -- C Function: int Py_UNICODE_ISDIGIT (Py_UCS4 ch)

     Return ‘1’ or ‘0’ depending on whether `ch' is a digit character.

 -- C Function: int Py_UNICODE_ISNUMERIC (Py_UCS4 ch)

     Return ‘1’ or ‘0’ depending on whether `ch' is a numeric character.

 -- C Function: int Py_UNICODE_ISALPHA (Py_UCS4 ch)

     Return ‘1’ or ‘0’ depending on whether `ch' is an alphabetic
     character.

 -- C Function: int Py_UNICODE_ISALNUM (Py_UCS4 ch)

     Return ‘1’ or ‘0’ depending on whether `ch' is an alphanumeric
     character.

 -- C Function: int Py_UNICODE_ISPRINTABLE (Py_UCS4 ch)

     Return ‘1’ or ‘0’ depending on whether `ch' is a printable
     character.  Nonprintable characters are those characters defined in
     the Unicode character database as “Other” or “Separator”, excepting
     the ASCII space (0x20) which is considered printable.  (Note that
     printable characters in this context are those which should not be
     escaped when *note repr(): 8b9. is invoked on a string.  It has no
     bearing on the handling of strings written to *note sys.stdout:
     41f. or *note sys.stderr: 1ea.)

These APIs can be used for fast direct character conversions:

 -- C Function: Py_UCS4 Py_UNICODE_TOLOWER (Py_UCS4 ch)

     Return the character `ch' converted to lower case.

     Deprecated since version 3.3: This function uses simple case
     mappings.

 -- C Function: Py_UCS4 Py_UNICODE_TOUPPER (Py_UCS4 ch)

     Return the character `ch' converted to upper case.

     Deprecated since version 3.3: This function uses simple case
     mappings.

 -- C Function: Py_UCS4 Py_UNICODE_TOTITLE (Py_UCS4 ch)

     Return the character `ch' converted to title case.

     Deprecated since version 3.3: This function uses simple case
     mappings.

 -- C Function: int Py_UNICODE_TODECIMAL (Py_UCS4 ch)

     Return the character `ch' converted to a decimal positive integer.
     Return ‘-1’ if this is not possible.  This macro does not raise
     exceptions.

 -- C Function: int Py_UNICODE_TODIGIT (Py_UCS4 ch)

     Return the character `ch' converted to a single digit integer.
     Return ‘-1’ if this is not possible.  This macro does not raise
     exceptions.

 -- C Function: double Py_UNICODE_TONUMERIC (Py_UCS4 ch)

     Return the character `ch' converted to a double.  Return ‘-1.0’ if
     this is not possible.  This macro does not raise exceptions.

These APIs can be used to work with surrogates:

 -- C Macro: Py_UNICODE_IS_SURROGATE (ch)

     Check if `ch' is a surrogate (‘0xD800 <= ch <= 0xDFFF’).

 -- C Macro: Py_UNICODE_IS_HIGH_SURROGATE (ch)

     Check if `ch' is a high surrogate (‘0xD800 <= ch <= 0xDBFF’).

 -- C Macro: Py_UNICODE_IS_LOW_SURROGATE (ch)

     Check if `ch' is a low surrogate (‘0xDC00 <= ch <= 0xDFFF’).

 -- C Macro: Py_UNICODE_JOIN_SURROGATES (high, low)

     Join two surrogate characters and return a single Py_UCS4 value.
     `high' and `low' are respectively the leading and trailing
     surrogates in a surrogate pair.


File: python.info,  Node: Creating and accessing Unicode strings,  Next: Deprecated Py_UNICODE APIs,  Prev: Unicode Character Properties,  Up: Unicode Objects

7.8.3.10 Creating and accessing Unicode strings
...............................................

To create Unicode objects and access their basic sequence properties,
use these APIs:

 -- C Function: PyObject* PyUnicode_New (Py_ssize_t size,
          Py_UCS4 maxchar)
     `Return value: New reference.'  Create a new Unicode object.
     `maxchar' should be the true maximum code point to be placed in the
     string.  As an approximation, it can be rounded up to the nearest
     value in the sequence 127, 255, 65535, 1114111.

     This is the recommended way to allocate a new Unicode object.
     Objects created using this function are not resizable.

     New in version 3.3.

 -- C Function: PyObject* PyUnicode_FromKindAndData (int kind, const
          void *buffer, Py_ssize_t size)
     `Return value: New reference.'  Create a new Unicode object with
     the given `kind' (possible values are *note PyUnicode_1BYTE_KIND:
     bb7. etc., as returned by *note PyUnicode_KIND(): bb5.).  The
     `buffer' must point to an array of `size' units of 1, 2 or 4 bytes
     per character, as given by the kind.

     New in version 3.3.

 -- C Function: PyObject* PyUnicode_FromStringAndSize (const char *u,
          Py_ssize_t size)
     `Return value: New reference.'  Create a Unicode object from the
     char buffer `u'.  The bytes will be interpreted as being UTF-8
     encoded.  The buffer is copied into the new object.  If the buffer
     is not ‘NULL’, the return value might be a shared object, i.e.
     modification of the data is not allowed.

     If `u' is ‘NULL’, this function behaves like *note
     PyUnicode_FromUnicode(): 263. with the buffer set to ‘NULL’.  This
     usage is deprecated in favor of *note PyUnicode_New(): ba4, and
     will be removed in Python 3.12.

 -- C Function: PyObject *PyUnicode_FromString (const char *u)
     `Return value: New reference.'  Create a Unicode object from a
     UTF-8 encoded null-terminated char buffer `u'.

 -- C Function: PyObject* PyUnicode_FromFormat (const char *format, ...)
     `Return value: New reference.'  Take a C ‘printf()’-style `format'
     string and a variable number of arguments, calculate the size of
     the resulting Python Unicode string and return a string with the
     values formatted into it.  The variable arguments must be C types
     and must correspond exactly to the format characters in the
     `format' ASCII-encoded string.  The following format characters are
     allowed:

     Format Characters       Type                      Comment
                                                       
     -----------------------------------------------------------------------------------------
                                                       
     ‘%%’                    `n/a'                     The literal % character.
                                                       
                                                       
     ‘%c’                    int                       A single character, represented as a
                                                       C int.
                                                       
                                                       
     ‘%d’                    int                       Equivalent to ‘printf("%d")’.  (1)
                                                       
                                                       
     ‘%u’                    unsigned int              Equivalent to ‘printf("%u")’.  (2)
                                                       
                                                       
     ‘%ld’                   long                      Equivalent to ‘printf("%ld")’.  (3)
                                                       
                                                       
     ‘%li’                   long                      Equivalent to ‘printf("%li")’.  (4)
                                                       
                                                       
     ‘%lu’                   unsigned long             Equivalent to ‘printf("%lu")’.  (5)
                                                       
                                                       
     ‘%lld’                  long long                 Equivalent to ‘printf("%lld")’.  (6)
                                                       
                                                       
     ‘%lli’                  long long                 Equivalent to ‘printf("%lli")’.  (7)
                                                       
                                                       
     ‘%llu’                  unsigned long long        Equivalent to ‘printf("%llu")’.  (8)
                                                       
                                                       
     ‘%zd’                   Py_ssize_t                Equivalent to ‘printf("%zd")’.  (9)
                                                       
                                                       
     ‘%zi’                   Py_ssize_t                Equivalent to ‘printf("%zi")’.  (10)
                                                       
                                                       
     ‘%zu’                   size_t                    Equivalent to ‘printf("%zu")’.  (11)
                                                       
                                                       
     ‘%i’                    int                       Equivalent to ‘printf("%i")’.  (12)
                                                       
                                                       
     ‘%x’                    int                       Equivalent to ‘printf("%x")’.  (13)
                                                       
                                                       
     ‘%s’                    const char*               A null-terminated C character array.
                                                       
                                                       
     ‘%p’                    const void*               The hex representation of a C
                                                       pointer.  Mostly equivalent to
                                                       ‘printf("%p")’ except that it is
                                                       guaranteed to start with the literal
                                                       ‘0x’ regardless of what the
                                                       platform’s ‘printf’ yields.
                                                       
                                                       
     ‘%A’                    PyObject*                 The result of calling
                                                       *note ascii(): e11.
                                                       
                                                       
     ‘%U’                    PyObject*                 A Unicode object.
                                                       
                                                       
     ‘%V’                    PyObject*, const char*    A Unicode object (which may be
                                                       ‘NULL’) and a null-terminated C
                                                       character array as a second
                                                       parameter (which will be used, if
                                                       the first parameter is ‘NULL’).
                                                       
                                                       
     ‘%S’                    PyObject*                 The result of calling
                                                       *note PyObject_Str(): a4a.
                                                       
                                                       
     ‘%R’                    PyObject*                 The result of calling
                                                       *note PyObject_Repr(): a49.
                                                       

     An unrecognized format character causes all the rest of the format
     string to be copied as-is to the result string, and any extra
     arguments discarded.

          Note: The width formatter unit is number of characters rather
          than bytes.  The precision formatter unit is number of bytes
          for ‘"%s"’ and ‘"%V"’ (if the ‘PyObject*’ argument is ‘NULL’),
          and a number of characters for ‘"%A"’, ‘"%U"’, ‘"%S"’, ‘"%R"’
          and ‘"%V"’ (if the ‘PyObject*’ argument is not ‘NULL’).

     Changed in version 3.2: Support for ‘"%lld"’ and ‘"%llu"’ added.

     Changed in version 3.3: Support for ‘"%li"’, ‘"%lli"’ and ‘"%zi"’
     added.

     Changed in version 3.4: Support width and precision formatter for
     ‘"%s"’, ‘"%A"’, ‘"%U"’, ‘"%V"’, ‘"%S"’, ‘"%R"’ added.

 -- C Function: PyObject* PyUnicode_FromFormatV (const char *format,
          va_list vargs)
     `Return value: New reference.'  Identical to *note
     PyUnicode_FromFormat(): 8b8. except that it takes exactly two
     arguments.

 -- C Function: PyObject* PyUnicode_FromEncodedObject (PyObject *obj,
          const char *encoding, const char *errors)
     `Return value: New reference.'  Decode an encoded object `obj' to a
     Unicode object.

     *note bytes: 172, *note bytearray: 173. and other *note bytes-like
     objects: 6df. are decoded according to the given `encoding' and
     using the error handling defined by `errors'.  Both can be ‘NULL’
     to have the interface use the default values (see *note Built-in
     Codecs: 4015. for details).

     All other objects, including Unicode objects, cause a *note
     TypeError: 1fe. to be set.

     The API returns ‘NULL’ if there was an error.  The caller is
     responsible for decref’ing the returned objects.

 -- C Function: Py_ssize_t PyUnicode_GetLength (PyObject *unicode)

     Return the length of the Unicode object, in code points.

     New in version 3.3.

 -- C Function: Py_ssize_t PyUnicode_CopyCharacters (PyObject *to,
          Py_ssize_t to_start, PyObject *from, Py_ssize_t from_start,
          Py_ssize_t how_many)

     Copy characters from one Unicode object into another.  This
     function performs character conversion when necessary and falls
     back to ‘memcpy()’ if possible.  Returns ‘-1’ and sets an exception
     on error, otherwise returns the number of copied characters.

     New in version 3.3.

 -- C Function: Py_ssize_t PyUnicode_Fill (PyObject *unicode,
          Py_ssize_t start, Py_ssize_t length, Py_UCS4 fill_char)

     Fill a string with a character: write `fill_char' into
     ‘unicode[start:start+length]’.

     Fail if `fill_char' is bigger than the string maximum character, or
     if the string has more than 1 reference.

     Return the number of written character, or return ‘-1’ and raise an
     exception on error.

     New in version 3.3.

 -- C Function: int PyUnicode_WriteChar (PyObject *unicode,
          Py_ssize_t index, Py_UCS4 character)

     Write a character to a string.  The string must have been created
     through *note PyUnicode_New(): ba4.  Since Unicode strings are
     supposed to be immutable, the string must not be shared, or have
     been hashed yet.

     This function checks that `unicode' is a Unicode object, that the
     index is not out of bounds, and that the object can be modified
     safely (i.e.  that it its reference count is one).

     New in version 3.3.

 -- C Function: Py_UCS4 PyUnicode_ReadChar (PyObject *unicode,
          Py_ssize_t index)

     Read a character from a string.  This function checks that
     `unicode' is a Unicode object and the index is not out of bounds,
     in contrast to the macro version *note PyUnicode_READ_CHAR(): bbb.

     New in version 3.3.

 -- C Function: PyObject* PyUnicode_Substring (PyObject *str,
          Py_ssize_t start, Py_ssize_t end)
     `Return value: New reference.'  Return a substring of `str', from
     character index `start' (included) to character index `end'
     (excluded).  Negative indices are not supported.

     New in version 3.3.

 -- C Function: Py_UCS4* PyUnicode_AsUCS4 (PyObject *u, Py_UCS4 *buffer,
          Py_ssize_t buflen, int copy_null)

     Copy the string `u' into a UCS4 buffer, including a null character,
     if `copy_null' is set.  Returns ‘NULL’ and sets an exception on
     error (in particular, a *note SystemError: 6f2. if `buflen' is
     smaller than the length of `u').  `buffer' is returned on success.

     New in version 3.3.

 -- C Function: Py_UCS4* PyUnicode_AsUCS4Copy (PyObject *u)

     Copy the string `u' into a new UCS4 buffer that is allocated using
     *note PyMem_Malloc(): 5ff.  If this fails, ‘NULL’ is returned with
     a *note MemoryError: f69. set.  The returned buffer always has an
     extra null code point appended.

     New in version 3.3.

   ---------- Footnotes ----------

   (1) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.

   (2) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.

   (3) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.

   (4) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.

   (5) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.

   (6) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.

   (7) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.

   (8) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.

   (9) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.

   (10) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.

   (11) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.

   (12) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.

   (13) (1) For integer specifiers (d, u, ld, li, lu, lld, lli, llu, zd,
zi, zu, i, x): the 0-conversion flag has effect even when a precision is
given.


File: python.info,  Node: Deprecated Py_UNICODE APIs,  Next: Locale Encoding,  Prev: Creating and accessing Unicode strings,  Up: Unicode Objects

7.8.3.11 Deprecated Py_UNICODE APIs
...................................

Deprecated since version 3.3, will be removed in version 3.12.

These API functions are deprecated with the implementation of PEP
393(1).  Extension modules can continue using them, as they will not be
removed in Python 3.x, but need to be aware that their use can now cause
performance and memory hits.

 -- C Function: PyObject* PyUnicode_FromUnicode (const Py_UNICODE *u,
          Py_ssize_t size)
     `Return value: New reference.'  Create a Unicode object from the
     Py_UNICODE buffer `u' of the given size.  `u' may be ‘NULL’ which
     causes the contents to be undefined.  It is the user’s
     responsibility to fill in the needed data.  The buffer is copied
     into the new object.

     If the buffer is not ‘NULL’, the return value might be a shared
     object.  Therefore, modification of the resulting Unicode object is
     only allowed when `u' is ‘NULL’.

     If the buffer is ‘NULL’, *note PyUnicode_READY(): bad. must be
     called once the string content has been filled before using any of
     the access macros such as *note PyUnicode_KIND(): bb5.

     Deprecated since version 3.3, will be removed in version 3.12: Part
     of the old-style Unicode API, please migrate to using *note
     PyUnicode_FromKindAndData(): bae, *note PyUnicode_FromWideChar():
     bc6, or *note PyUnicode_New(): ba4.

 -- C Function: Py_UNICODE* PyUnicode_AsUnicode (PyObject *unicode)

     Return a read-only pointer to the Unicode object’s internal *note
     Py_UNICODE: bc5. buffer, or ‘NULL’ on error.  This will create the
     *note Py_UNICODE*: bc5. representation of the object if it is not
     yet available.  The buffer is always terminated with an extra null
     code point.  Note that the resulting *note Py_UNICODE: bc5. string
     may also contain embedded null code points, which would cause the
     string to be truncated when used in most C functions.

     Deprecated since version 3.3, will be removed in version 3.12: Part
     of the old-style Unicode API, please migrate to using *note
     PyUnicode_AsUCS4(): baf, *note PyUnicode_AsWideChar(): 1187, *note
     PyUnicode_ReadChar(): ba6. or similar new APIs.

     Deprecated since version 3.3, will be removed in version 3.10.

 -- C Function: PyObject* PyUnicode_TransformDecimalToASCII
          (Py_UNICODE *s, Py_ssize_t size)
     `Return value: New reference.'  Create a Unicode object by
     replacing all decimal digits in *note Py_UNICODE: bc5. buffer of
     the given `size' by ASCII digits 0–9 according to their decimal
     value.  Return ‘NULL’ if an exception occurs.

     Deprecated since version 3.3, will be removed in version 3.11: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note Py_UNICODE_TODECIMAL(): 400b.

 -- C Function: Py_UNICODE* PyUnicode_AsUnicodeAndSize
          (PyObject *unicode, Py_ssize_t *size)

     Like *note PyUnicode_AsUnicode(): 264, but also saves the *note
     Py_UNICODE(): bc5. array length (excluding the extra null
     terminator) in `size'.  Note that the resulting *note Py_UNICODE*:
     bc5. string may contain embedded null code points, which would
     cause the string to be truncated when used in most C functions.

     New in version 3.3.

     Deprecated since version 3.3, will be removed in version 3.12: Part
     of the old-style Unicode API, please migrate to using *note
     PyUnicode_AsUCS4(): baf, *note PyUnicode_AsWideChar(): 1187, *note
     PyUnicode_ReadChar(): ba6. or similar new APIs.

 -- C Function: Py_UNICODE* PyUnicode_AsUnicodeCopy (PyObject *unicode)

     Create a copy of a Unicode string ending with a null code point.
     Return ‘NULL’ and raise a *note MemoryError: f69. exception on
     memory allocation failure, otherwise return a new allocated buffer
     (use *note PyMem_Free(): e6e. to free the buffer).  Note that the
     resulting *note Py_UNICODE*: bc5. string may contain embedded null
     code points, which would cause the string to be truncated when used
     in most C functions.

     New in version 3.2.

     Please migrate to using *note PyUnicode_AsUCS4Copy(): bb0. or
     similar new APIs.

 -- C Function: Py_ssize_t PyUnicode_GetSize (PyObject *unicode)

     Return the size of the deprecated *note Py_UNICODE: bc5.
     representation, in code units (this includes surrogate pairs as 2
     units).

     Deprecated since version 3.3, will be removed in version 3.12: Part
     of the old-style Unicode API, please migrate to using *note
     PyUnicode_GET_LENGTH(): ba3.

 -- C Function: PyObject* PyUnicode_FromObject (PyObject *obj)
     `Return value: New reference.'  Copy an instance of a Unicode
     subtype to a new true Unicode object if necessary.  If `obj' is
     already a true Unicode object (not a subtype), return the reference
     with incremented refcount.

     Objects other than Unicode or its subtypes will cause a *note
     TypeError: 1fe.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0393


File: python.info,  Node: Locale Encoding,  Next: File System Encoding,  Prev: Deprecated Py_UNICODE APIs,  Up: Unicode Objects

7.8.3.12 Locale Encoding
........................

The current locale encoding can be used to decode text from the
operating system.

 -- C Function: PyObject* PyUnicode_DecodeLocaleAndSize (const
          char *str, Py_ssize_t len, const char *errors)
     `Return value: New reference.'  Decode a string from UTF-8 on
     Android and VxWorks, or from the current locale encoding on other
     platforms.  The supported error handlers are ‘"strict"’ and
     ‘"surrogateescape"’ ( PEP 383(1)).  The decoder uses ‘"strict"’
     error handler if `errors' is ‘NULL’.  `str' must end with a null
     character but cannot contain embedded null characters.

     Use *note PyUnicode_DecodeFSDefaultAndSize(): 3e58. to decode a
     string from ‘Py_FileSystemDefaultEncoding’ (the locale encoding
     read at Python startup).

     This function ignores the Python UTF-8 mode.

     See also
     ........

     The *note Py_DecodeLocale(): 53f. function.

     New in version 3.3.

     Changed in version 3.7: The function now also uses the current
     locale encoding for the ‘surrogateescape’ error handler, except on
     Android.  Previously, *note Py_DecodeLocale(): 53f. was used for
     the ‘surrogateescape’, and the current locale encoding was used for
     ‘strict’.

 -- C Function: PyObject* PyUnicode_DecodeLocale (const char *str, const
          char *errors)
     `Return value: New reference.'  Similar to *note
     PyUnicode_DecodeLocaleAndSize(): 541, but compute the string length
     using ‘strlen()’.

     New in version 3.3.

 -- C Function: PyObject* PyUnicode_EncodeLocale (PyObject *unicode,
          const char *errors)
     `Return value: New reference.'  Encode a Unicode object to UTF-8 on
     Android and VxWorks, or to the current locale encoding on other
     platforms.  The supported error handlers are ‘"strict"’ and
     ‘"surrogateescape"’ ( PEP 383(2)).  The encoder uses ‘"strict"’
     error handler if `errors' is ‘NULL’.  Return a *note bytes: 172.
     object.  `unicode' cannot contain embedded null characters.

     Use *note PyUnicode_EncodeFSDefault(): 1180. to encode a string to
     ‘Py_FileSystemDefaultEncoding’ (the locale encoding read at Python
     startup).

     This function ignores the Python UTF-8 mode.

     See also
     ........

     The *note Py_EncodeLocale(): 540. function.

     New in version 3.3.

     Changed in version 3.7: The function now also uses the current
     locale encoding for the ‘surrogateescape’ error handler, except on
     Android.  Previously, *note Py_EncodeLocale(): 540. was used for
     the ‘surrogateescape’, and the current locale encoding was used for
     ‘strict’.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0383

   (2) https://www.python.org/dev/peps/pep-0383


File: python.info,  Node: File System Encoding,  Next: wchar_t Support,  Prev: Locale Encoding,  Up: Unicode Objects

7.8.3.13 File System Encoding
.............................

To encode and decode file names and other environment strings,
‘Py_FileSystemDefaultEncoding’ should be used as the encoding, and
‘Py_FileSystemDefaultEncodeErrors’ should be used as the error handler (
PEP 383(1) and PEP 529(2)).  To encode file names to *note bytes: 172.
during argument parsing, the ‘"O&"’ converter should be used, passing
*note PyUnicode_FSConverter(): 6c5. as the conversion function:

 -- C Function: int PyUnicode_FSConverter (PyObject* obj, void* result)

     ParseTuple converter: encode *note str: 205. objects – obtained
     directly or through the *note os.PathLike: 5e6. interface – to
     *note bytes: 172. using *note PyUnicode_EncodeFSDefault(): 1180.;
     *note bytes: 172. objects are output as-is.  `result' must be a
     *note PyBytesObject*: de4. which must be released when it is no
     longer used.

     New in version 3.1.

     Changed in version 3.6: Accepts a *note path-like object: 472.

To decode file names to *note str: 205. during argument parsing, the
‘"O&"’ converter should be used, passing *note PyUnicode_FSDecoder():
6c6. as the conversion function:

 -- C Function: int PyUnicode_FSDecoder (PyObject* obj, void* result)

     ParseTuple converter: decode *note bytes: 172. objects – obtained
     either directly or indirectly through the *note os.PathLike: 5e6.
     interface – to *note str: 205. using *note
     PyUnicode_DecodeFSDefaultAndSize(): 3e58.; *note str: 205. objects
     are output as-is.  `result' must be a *note PyUnicodeObject*: 3ff9.
     which must be released when it is no longer used.

     New in version 3.2.

     Changed in version 3.6: Accepts a *note path-like object: 472.

 -- C Function: PyObject* PyUnicode_DecodeFSDefaultAndSize (const
          char *s, Py_ssize_t size)
     `Return value: New reference.'  Decode a string using
     ‘Py_FileSystemDefaultEncoding’ and the
     ‘Py_FileSystemDefaultEncodeErrors’ error handler.

     If ‘Py_FileSystemDefaultEncoding’ is not set, fall back to the
     locale encoding.

     ‘Py_FileSystemDefaultEncoding’ is initialized at startup from the
     locale encoding and cannot be modified later.  If you need to
     decode a string from the current locale encoding, use *note
     PyUnicode_DecodeLocaleAndSize(): 541.

     See also
     ........

     The *note Py_DecodeLocale(): 53f. function.

     Changed in version 3.6: Use ‘Py_FileSystemDefaultEncodeErrors’
     error handler.

 -- C Function: PyObject* PyUnicode_DecodeFSDefault (const char *s)
     `Return value: New reference.'  Decode a null-terminated string
     using ‘Py_FileSystemDefaultEncoding’ and the
     ‘Py_FileSystemDefaultEncodeErrors’ error handler.

     If ‘Py_FileSystemDefaultEncoding’ is not set, fall back to the
     locale encoding.

     Use *note PyUnicode_DecodeFSDefaultAndSize(): 3e58. if you know the
     string length.

     Changed in version 3.6: Use ‘Py_FileSystemDefaultEncodeErrors’
     error handler.

 -- C Function: PyObject* PyUnicode_EncodeFSDefault (PyObject *unicode)
     `Return value: New reference.'  Encode a Unicode object to
     ‘Py_FileSystemDefaultEncoding’ with the
     ‘Py_FileSystemDefaultEncodeErrors’ error handler, and return *note
     bytes: 172.  Note that the resulting *note bytes: 172. object may
     contain null bytes.

     If ‘Py_FileSystemDefaultEncoding’ is not set, fall back to the
     locale encoding.

     ‘Py_FileSystemDefaultEncoding’ is initialized at startup from the
     locale encoding and cannot be modified later.  If you need to
     encode a string to the current locale encoding, use *note
     PyUnicode_EncodeLocale(): 542.

     See also
     ........

     The *note Py_EncodeLocale(): 540. function.

     New in version 3.2.

     Changed in version 3.6: Use ‘Py_FileSystemDefaultEncodeErrors’
     error handler.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0383

   (2) https://www.python.org/dev/peps/pep-0529


File: python.info,  Node: wchar_t Support,  Prev: File System Encoding,  Up: Unicode Objects

7.8.3.14 wchar_t Support
........................

‘wchar_t’ support for platforms which support it:

 -- C Function: PyObject* PyUnicode_FromWideChar (const wchar_t *w,
          Py_ssize_t size)
     `Return value: New reference.'  Create a Unicode object from the
     ‘wchar_t’ buffer `w' of the given `size'.  Passing ‘-1’ as the
     `size' indicates that the function must itself compute the length,
     using wcslen.  Return ‘NULL’ on failure.

 -- C Function: Py_ssize_t PyUnicode_AsWideChar (PyObject *unicode,
          wchar_t *w, Py_ssize_t size)

     Copy the Unicode object contents into the ‘wchar_t’ buffer `w'.  At
     most `size' ‘wchar_t’ characters are copied (excluding a possibly
     trailing null termination character).  Return the number of
     ‘wchar_t’ characters copied or ‘-1’ in case of an error.  Note that
     the resulting ‘wchar_t*’ string may or may not be null-terminated.
     It is the responsibility of the caller to make sure that the
     ‘wchar_t*’ string is null-terminated in case this is required by
     the application.  Also, note that the ‘wchar_t*’ string might
     contain null characters, which would cause the string to be
     truncated when used with most C functions.

 -- C Function: wchar_t* PyUnicode_AsWideCharString (PyObject *unicode,
          Py_ssize_t *size)

     Convert the Unicode object to a wide character string.  The output
     string always ends with a null character.  If `size' is not ‘NULL’,
     write the number of wide characters (excluding the trailing null
     termination character) into `*size'.  Note that the resulting
     ‘wchar_t’ string might contain null characters, which would cause
     the string to be truncated when used with most C functions.  If
     `size' is ‘NULL’ and the ‘wchar_t*’ string contains null characters
     a *note ValueError: 16d. is raised.

     Returns a buffer allocated by ‘PyMem_Alloc()’ (use *note
     PyMem_Free(): e6e. to free it) on success.  On error, returns
     ‘NULL’ and `*size' is undefined.  Raises a *note MemoryError: f69.
     if memory allocation is failed.

     New in version 3.2.

     Changed in version 3.7: Raises a *note ValueError: 16d. if `size'
     is ‘NULL’ and the ‘wchar_t*’ string contains null characters.


File: python.info,  Node: Built-in Codecs,  Next: Methods and Slot Functions,  Prev: Unicode Objects,  Up: Unicode Objects and Codecs

7.8.3.15 Built-in Codecs
........................

Python provides a set of built-in codecs which are written in C for
speed.  All of these codecs are directly usable via the following
functions.

Many of the following APIs take two arguments encoding and errors, and
they have the same semantics as the ones of the built-in *note str():
205. string object constructor.

Setting encoding to ‘NULL’ causes the default encoding to be used which
is UTF-8.  The file system calls should use *note
PyUnicode_FSConverter(): 6c5. for encoding file names.  This uses the
variable ‘Py_FileSystemDefaultEncoding’ internally.  This variable
should be treated as read-only: on some systems, it will be a pointer to
a static string, on others, it will change at run-time (such as when the
application invokes setlocale).

Error handling is set by errors which may also be set to ‘NULL’ meaning
to use the default handling defined for the codec.  Default error
handling for all built-in codecs is “strict” (*note ValueError: 16d. is
raised).

The codecs all use a similar interface.  Only deviation from the
following generic ones are documented for simplicity.

* Menu:

* Generic Codecs::
* UTF-8 Codecs::
* UTF-32 Codecs::
* UTF-16 Codecs::
* UTF-7 Codecs::
* Unicode-Escape Codecs::
* Raw-Unicode-Escape Codecs::
* Latin-1 Codecs::
* ASCII Codecs::
* Character Map Codecs::
* MBCS codecs for Windows::
* Methods & Slots::


File: python.info,  Node: Generic Codecs,  Next: UTF-8 Codecs,  Up: Built-in Codecs

7.8.3.16 Generic Codecs
.......................

These are the generic codec APIs:

 -- C Function: PyObject* PyUnicode_Decode (const char *s,
          Py_ssize_t size, const char *encoding, const char *errors)
     `Return value: New reference.'  Create a Unicode object by decoding
     `size' bytes of the encoded string `s'.  `encoding' and `errors'
     have the same meaning as the parameters of the same name in the
     *note str(): 205. built-in function.  The codec to be used is
     looked up using the Python codec registry.  Return ‘NULL’ if an
     exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_AsEncodedString (PyObject *unicode,
          const char *encoding, const char *errors)
     `Return value: New reference.'  Encode a Unicode object and return
     the result as Python bytes object.  `encoding' and `errors' have
     the same meaning as the parameters of the same name in the Unicode
     *note encode(): 170. method.  The codec to be used is looked up
     using the Python codec registry.  Return ‘NULL’ if an exception was
     raised by the codec.

 -- C Function: PyObject* PyUnicode_Encode (const Py_UNICODE *s,
          Py_ssize_t size, const char *encoding, const char *errors)
     `Return value: New reference.'  Encode the *note Py_UNICODE: bc5.
     buffer `s' of the given `size' and return a Python bytes object.
     `encoding' and `errors' have the same meaning as the parameters of
     the same name in the Unicode *note encode(): 170. method.  The
     codec to be used is looked up using the Python codec registry.
     Return ‘NULL’ if an exception was raised by the codec.

     Deprecated since version 3.3, will be removed in version 3.11: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsEncodedString(): 401f.


File: python.info,  Node: UTF-8 Codecs,  Next: UTF-32 Codecs,  Prev: Generic Codecs,  Up: Built-in Codecs

7.8.3.17 UTF-8 Codecs
.....................

These are the UTF-8 codec APIs:

 -- C Function: PyObject* PyUnicode_DecodeUTF8 (const char *s,
          Py_ssize_t size, const char *errors)
     `Return value: New reference.'  Create a Unicode object by decoding
     `size' bytes of the UTF-8 encoded string `s'.  Return ‘NULL’ if an
     exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_DecodeUTF8Stateful (const char *s,
          Py_ssize_t size, const char *errors, Py_ssize_t *consumed)
     `Return value: New reference.'  If `consumed' is ‘NULL’, behave
     like *note PyUnicode_DecodeUTF8(): 4021.  If `consumed' is not
     ‘NULL’, trailing incomplete UTF-8 byte sequences will not be
     treated as an error.  Those bytes will not be decoded and the
     number of bytes that have been decoded will be stored in
     `consumed'.

 -- C Function: PyObject* PyUnicode_AsUTF8String (PyObject *unicode)
     `Return value: New reference.'  Encode a Unicode object using UTF-8
     and return the result as Python bytes object.  Error handling is
     “strict”.  Return ‘NULL’ if an exception was raised by the codec.

 -- C Function: const char* PyUnicode_AsUTF8AndSize (PyObject *unicode,
          Py_ssize_t *size)

     Return a pointer to the UTF-8 encoding of the Unicode object, and
     store the size of the encoded representation (in bytes) in `size'.
     The `size' argument can be ‘NULL’; in this case no size will be
     stored.  The returned buffer always has an extra null byte appended
     (not included in `size'), regardless of whether there are any other
     null code points.

     In the case of an error, ‘NULL’ is returned with an exception set
     and no `size' is stored.

     This caches the UTF-8 representation of the string in the Unicode
     object, and subsequent calls will return a pointer to the same
     buffer.  The caller is not responsible for deallocating the buffer.

     New in version 3.3.

     Changed in version 3.7: The return type is now ‘const char *’
     rather of ‘char *’.

 -- C Function: const char* PyUnicode_AsUTF8 (PyObject *unicode)

     As *note PyUnicode_AsUTF8AndSize(): 52e, but does not store the
     size.

     New in version 3.3.

     Changed in version 3.7: The return type is now ‘const char *’
     rather of ‘char *’.

 -- C Function: PyObject* PyUnicode_EncodeUTF8 (const Py_UNICODE *s,
          Py_ssize_t size, const char *errors)
     `Return value: New reference.'  Encode the *note Py_UNICODE: bc5.
     buffer `s' of the given `size' using UTF-8 and return a Python
     bytes object.  Return ‘NULL’ if an exception was raised by the
     codec.

     Deprecated since version 3.3, will be removed in version 3.11: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsUTF8String(): bd2, *note
     PyUnicode_AsUTF8AndSize(): 52e. or *note
     PyUnicode_AsEncodedString(): 401f.


File: python.info,  Node: UTF-32 Codecs,  Next: UTF-16 Codecs,  Prev: UTF-8 Codecs,  Up: Built-in Codecs

7.8.3.18 UTF-32 Codecs
......................

These are the UTF-32 codec APIs:

 -- C Function: PyObject* PyUnicode_DecodeUTF32 (const char *s,
          Py_ssize_t size, const char *errors, int *byteorder)
     `Return value: New reference.'  Decode `size' bytes from a UTF-32
     encoded buffer string and return the corresponding Unicode object.
     `errors' (if non-‘NULL’) defines the error handling.  It defaults
     to “strict”.

     If `byteorder' is non-‘NULL’, the decoder starts decoding using the
     given byte order:

          *byteorder == -1: little endian
          *byteorder == 0:  native order
          *byteorder == 1:  big endian

     If ‘*byteorder’ is zero, and the first four bytes of the input data
     are a byte order mark (BOM), the decoder switches to this byte
     order and the BOM is not copied into the resulting Unicode string.
     If ‘*byteorder’ is ‘-1’ or ‘1’, any byte order mark is copied to
     the output.

     After completion, `*byteorder' is set to the current byte order at
     the end of input data.

     If `byteorder' is ‘NULL’, the codec starts in native order mode.

     Return ‘NULL’ if an exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_DecodeUTF32Stateful (const char *s,
          Py_ssize_t size, const char *errors, int *byteorder,
          Py_ssize_t *consumed)
     `Return value: New reference.'  If `consumed' is ‘NULL’, behave
     like *note PyUnicode_DecodeUTF32(): 4024.  If `consumed' is not
     ‘NULL’, *note PyUnicode_DecodeUTF32Stateful(): 4025. will not treat
     trailing incomplete UTF-32 byte sequences (such as a number of
     bytes not divisible by four) as an error.  Those bytes will not be
     decoded and the number of bytes that have been decoded will be
     stored in `consumed'.

 -- C Function: PyObject* PyUnicode_AsUTF32String (PyObject *unicode)
     `Return value: New reference.'  Return a Python byte string using
     the UTF-32 encoding in native byte order.  The string always starts
     with a BOM mark.  Error handling is “strict”.  Return ‘NULL’ if an
     exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_EncodeUTF32 (const Py_UNICODE *s,
          Py_ssize_t size, const char *errors, int byteorder)
     `Return value: New reference.'  Return a Python bytes object
     holding the UTF-32 encoded value of the Unicode data in `s'.
     Output is written according to the following byte order:

          byteorder == -1: little endian
          byteorder == 0:  native byte order (writes a BOM mark)
          byteorder == 1:  big endian

     If byteorder is ‘0’, the output string will always start with the
     Unicode BOM mark (U+FEFF). In the other two modes, no BOM mark is
     prepended.

     If ‘Py_UNICODE_WIDE’ is not defined, surrogate pairs will be output
     as a single code point.

     Return ‘NULL’ if an exception was raised by the codec.

     Deprecated since version 3.3, will be removed in version 3.11: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsUTF32String(): 4026. or *note
     PyUnicode_AsEncodedString(): 401f.


File: python.info,  Node: UTF-16 Codecs,  Next: UTF-7 Codecs,  Prev: UTF-32 Codecs,  Up: Built-in Codecs

7.8.3.19 UTF-16 Codecs
......................

These are the UTF-16 codec APIs:

 -- C Function: PyObject* PyUnicode_DecodeUTF16 (const char *s,
          Py_ssize_t size, const char *errors, int *byteorder)
     `Return value: New reference.'  Decode `size' bytes from a UTF-16
     encoded buffer string and return the corresponding Unicode object.
     `errors' (if non-‘NULL’) defines the error handling.  It defaults
     to “strict”.

     If `byteorder' is non-‘NULL’, the decoder starts decoding using the
     given byte order:

          *byteorder == -1: little endian
          *byteorder == 0:  native order
          *byteorder == 1:  big endian

     If ‘*byteorder’ is zero, and the first two bytes of the input data
     are a byte order mark (BOM), the decoder switches to this byte
     order and the BOM is not copied into the resulting Unicode string.
     If ‘*byteorder’ is ‘-1’ or ‘1’, any byte order mark is copied to
     the output (where it will result in either a ‘\ufeff’ or a ‘\ufffe’
     character).

     After completion, `*byteorder' is set to the current byte order at
     the end of input data.

     If `byteorder' is ‘NULL’, the codec starts in native order mode.

     Return ‘NULL’ if an exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_DecodeUTF16Stateful (const char *s,
          Py_ssize_t size, const char *errors, int *byteorder,
          Py_ssize_t *consumed)
     `Return value: New reference.'  If `consumed' is ‘NULL’, behave
     like *note PyUnicode_DecodeUTF16(): 4028.  If `consumed' is not
     ‘NULL’, *note PyUnicode_DecodeUTF16Stateful(): 4029. will not treat
     trailing incomplete UTF-16 byte sequences (such as an odd number of
     bytes or a split surrogate pair) as an error.  Those bytes will not
     be decoded and the number of bytes that have been decoded will be
     stored in `consumed'.

 -- C Function: PyObject* PyUnicode_AsUTF16String (PyObject *unicode)
     `Return value: New reference.'  Return a Python byte string using
     the UTF-16 encoding in native byte order.  The string always starts
     with a BOM mark.  Error handling is “strict”.  Return ‘NULL’ if an
     exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_EncodeUTF16 (const Py_UNICODE *s,
          Py_ssize_t size, const char *errors, int byteorder)
     `Return value: New reference.'  Return a Python bytes object
     holding the UTF-16 encoded value of the Unicode data in `s'.
     Output is written according to the following byte order:

          byteorder == -1: little endian
          byteorder == 0:  native byte order (writes a BOM mark)
          byteorder == 1:  big endian

     If byteorder is ‘0’, the output string will always start with the
     Unicode BOM mark (U+FEFF). In the other two modes, no BOM mark is
     prepended.

     If ‘Py_UNICODE_WIDE’ is defined, a single *note Py_UNICODE: bc5.
     value may get represented as a surrogate pair.  If it is not
     defined, each *note Py_UNICODE: bc5. values is interpreted as a
     UCS-2 character.

     Return ‘NULL’ if an exception was raised by the codec.

     Deprecated since version 3.3, will be removed in version 3.11: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsUTF16String(): 402a. or *note
     PyUnicode_AsEncodedString(): 401f.


File: python.info,  Node: UTF-7 Codecs,  Next: Unicode-Escape Codecs,  Prev: UTF-16 Codecs,  Up: Built-in Codecs

7.8.3.20 UTF-7 Codecs
.....................

These are the UTF-7 codec APIs:

 -- C Function: PyObject* PyUnicode_DecodeUTF7 (const char *s,
          Py_ssize_t size, const char *errors)
     `Return value: New reference.'  Create a Unicode object by decoding
     `size' bytes of the UTF-7 encoded string `s'.  Return ‘NULL’ if an
     exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_DecodeUTF7Stateful (const char *s,
          Py_ssize_t size, const char *errors, Py_ssize_t *consumed)
     `Return value: New reference.'  If `consumed' is ‘NULL’, behave
     like *note PyUnicode_DecodeUTF7(): 402c.  If `consumed' is not
     ‘NULL’, trailing incomplete UTF-7 base-64 sections will not be
     treated as an error.  Those bytes will not be decoded and the
     number of bytes that have been decoded will be stored in
     `consumed'.

 -- C Function: PyObject* PyUnicode_EncodeUTF7 (const Py_UNICODE *s,
          Py_ssize_t size, int base64SetO, int base64WhiteSpace, const
          char *errors)
     `Return value: New reference.'  Encode the *note Py_UNICODE: bc5.
     buffer of the given size using UTF-7 and return a Python bytes
     object.  Return ‘NULL’ if an exception was raised by the codec.

     If `base64SetO' is nonzero, “Set O” (punctuation that has no
     otherwise special meaning) will be encoded in base-64.  If
     `base64WhiteSpace' is nonzero, whitespace will be encoded in
     base-64.  Both are set to zero for the Python “utf-7” codec.

     Deprecated since version 3.3, will be removed in version 3.11: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsEncodedString(): 401f.


File: python.info,  Node: Unicode-Escape Codecs,  Next: Raw-Unicode-Escape Codecs,  Prev: UTF-7 Codecs,  Up: Built-in Codecs

7.8.3.21 Unicode-Escape Codecs
..............................

These are the “Unicode Escape” codec APIs:

 -- C Function: PyObject* PyUnicode_DecodeUnicodeEscape (const char *s,
          Py_ssize_t size, const char *errors)
     `Return value: New reference.'  Create a Unicode object by decoding
     `size' bytes of the Unicode-Escape encoded string `s'.  Return
     ‘NULL’ if an exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_AsUnicodeEscapeString
          (PyObject *unicode)
     `Return value: New reference.'  Encode a Unicode object using
     Unicode-Escape and return the result as a bytes object.  Error
     handling is “strict”.  Return ‘NULL’ if an exception was raised by
     the codec.

 -- C Function: PyObject* PyUnicode_EncodeUnicodeEscape (const
          Py_UNICODE *s, Py_ssize_t size)
     `Return value: New reference.'  Encode the *note Py_UNICODE: bc5.
     buffer of the given `size' using Unicode-Escape and return a bytes
     object.  Return ‘NULL’ if an exception was raised by the codec.

     Deprecated since version 3.3, will be removed in version 3.11: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsUnicodeEscapeString(): bd6.


File: python.info,  Node: Raw-Unicode-Escape Codecs,  Next: Latin-1 Codecs,  Prev: Unicode-Escape Codecs,  Up: Built-in Codecs

7.8.3.22 Raw-Unicode-Escape Codecs
..................................

These are the “Raw Unicode Escape” codec APIs:

 -- C Function: PyObject* PyUnicode_DecodeRawUnicodeEscape (const
          char *s, Py_ssize_t size, const char *errors)
     `Return value: New reference.'  Create a Unicode object by decoding
     `size' bytes of the Raw-Unicode-Escape encoded string `s'.  Return
     ‘NULL’ if an exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_AsRawUnicodeEscapeString
          (PyObject *unicode)
     `Return value: New reference.'  Encode a Unicode object using
     Raw-Unicode-Escape and return the result as a bytes object.  Error
     handling is “strict”.  Return ‘NULL’ if an exception was raised by
     the codec.

 -- C Function: PyObject* PyUnicode_EncodeRawUnicodeEscape (const
          Py_UNICODE *s, Py_ssize_t size)
     `Return value: New reference.'  Encode the *note Py_UNICODE: bc5.
     buffer of the given `size' using Raw-Unicode-Escape and return a
     bytes object.  Return ‘NULL’ if an exception was raised by the
     codec.

     Deprecated since version 3.3, will be removed in version 3.11: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsRawUnicodeEscapeString(): bd8. or *note
     PyUnicode_AsEncodedString(): 401f.


File: python.info,  Node: Latin-1 Codecs,  Next: ASCII Codecs,  Prev: Raw-Unicode-Escape Codecs,  Up: Built-in Codecs

7.8.3.23 Latin-1 Codecs
.......................

These are the Latin-1 codec APIs: Latin-1 corresponds to the first 256
Unicode ordinals and only these are accepted by the codecs during
encoding.

 -- C Function: PyObject* PyUnicode_DecodeLatin1 (const char *s,
          Py_ssize_t size, const char *errors)
     `Return value: New reference.'  Create a Unicode object by decoding
     `size' bytes of the Latin-1 encoded string `s'.  Return ‘NULL’ if
     an exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_AsLatin1String (PyObject *unicode)
     `Return value: New reference.'  Encode a Unicode object using
     Latin-1 and return the result as Python bytes object.  Error
     handling is “strict”.  Return ‘NULL’ if an exception was raised by
     the codec.

 -- C Function: PyObject* PyUnicode_EncodeLatin1 (const Py_UNICODE *s,
          Py_ssize_t size, const char *errors)
     `Return value: New reference.'  Encode the *note Py_UNICODE: bc5.
     buffer of the given `size' using Latin-1 and return a Python bytes
     object.  Return ‘NULL’ if an exception was raised by the codec.

     Deprecated since version 3.3, will be removed in version 3.11: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsLatin1String(): bda. or *note
     PyUnicode_AsEncodedString(): 401f.


File: python.info,  Node: ASCII Codecs,  Next: Character Map Codecs,  Prev: Latin-1 Codecs,  Up: Built-in Codecs

7.8.3.24 ASCII Codecs
.....................

These are the ASCII codec APIs.  Only 7-bit ASCII data is accepted.  All
other codes generate errors.

 -- C Function: PyObject* PyUnicode_DecodeASCII (const char *s,
          Py_ssize_t size, const char *errors)
     `Return value: New reference.'  Create a Unicode object by decoding
     `size' bytes of the ASCII encoded string `s'.  Return ‘NULL’ if an
     exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_AsASCIIString (PyObject *unicode)
     `Return value: New reference.'  Encode a Unicode object using ASCII
     and return the result as Python bytes object.  Error handling is
     “strict”.  Return ‘NULL’ if an exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_EncodeASCII (const Py_UNICODE *s,
          Py_ssize_t size, const char *errors)
     `Return value: New reference.'  Encode the *note Py_UNICODE: bc5.
     buffer of the given `size' using ASCII and return a Python bytes
     object.  Return ‘NULL’ if an exception was raised by the codec.

     Deprecated since version 3.3, will be removed in version 3.11: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsASCIIString(): bdc. or *note
     PyUnicode_AsEncodedString(): 401f.


File: python.info,  Node: Character Map Codecs,  Next: MBCS codecs for Windows,  Prev: ASCII Codecs,  Up: Built-in Codecs

7.8.3.25 Character Map Codecs
.............................

This codec is special in that it can be used to implement many different
codecs (and this is in fact what was done to obtain most of the standard
codecs included in the ‘encodings’ package).  The codec uses mapping to
encode and decode characters.  The mapping objects provided must support
the *note __getitem__(): 3a2. mapping interface; dictionaries and
sequences work well.

These are the mapping codec APIs:

 -- C Function: PyObject* PyUnicode_DecodeCharmap (const char *data,
          Py_ssize_t size, PyObject *mapping, const char *errors)
     `Return value: New reference.'  Create a Unicode object by decoding
     `size' bytes of the encoded string `s' using the given `mapping'
     object.  Return ‘NULL’ if an exception was raised by the codec.

     If `mapping' is ‘NULL’, Latin-1 decoding will be applied.  Else
     `mapping' must map bytes ordinals (integers in the range from 0 to
     255) to Unicode strings, integers (which are then interpreted as
     Unicode ordinals) or ‘None’.  Unmapped data bytes – ones which
     cause a *note LookupError: 1790, as well as ones which get mapped
     to ‘None’, ‘0xFFFE’ or ‘'\ufffe'’, are treated as undefined
     mappings and cause an error.

 -- C Function: PyObject* PyUnicode_AsCharmapString (PyObject *unicode,
          PyObject *mapping)
     `Return value: New reference.'  Encode a Unicode object using the
     given `mapping' object and return the result as a bytes object.
     Error handling is “strict”.  Return ‘NULL’ if an exception was
     raised by the codec.

     The `mapping' object must map Unicode ordinal integers to bytes
     objects, integers in the range from 0 to 255 or ‘None’.  Unmapped
     character ordinals (ones which cause a *note LookupError: 1790.) as
     well as mapped to ‘None’ are treated as “undefined mapping” and
     cause an error.

 -- C Function: PyObject* PyUnicode_EncodeCharmap (const Py_UNICODE *s,
          Py_ssize_t size, PyObject *mapping, const char *errors)
     `Return value: New reference.'  Encode the *note Py_UNICODE: bc5.
     buffer of the given `size' using the given `mapping' object and
     return the result as a bytes object.  Return ‘NULL’ if an exception
     was raised by the codec.

     Deprecated since version 3.3, will be removed in version 3.11: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsCharmapString(): 4038. or *note
     PyUnicode_AsEncodedString(): 401f.

The following codec API is special in that maps Unicode to Unicode.

 -- C Function: PyObject* PyUnicode_Translate (PyObject *str,
          PyObject *table, const char *errors)
     `Return value: New reference.'  Translate a string by applying a
     character mapping table to it and return the resulting Unicode
     object.  Return ‘NULL’ if an exception was raised by the codec.

     The mapping table must map Unicode ordinal integers to Unicode
     ordinal integers or ‘None’ (causing deletion of the character).

     Mapping tables need only provide the *note __getitem__(): 3a2.
     interface; dictionaries and sequences work well.  Unmapped
     character ordinals (ones which cause a *note LookupError: 1790.)
     are left untouched and are copied as-is.

     `errors' has the usual meaning for codecs.  It may be ‘NULL’ which
     indicates to use the default error handling.

 -- C Function: PyObject* PyUnicode_TranslateCharmap (const
          Py_UNICODE *s, Py_ssize_t size, PyObject *mapping, const
          char *errors)
     `Return value: New reference.'  Translate a *note Py_UNICODE: bc5.
     buffer of the given `size' by applying a character `mapping' table
     to it and return the resulting Unicode object.  Return ‘NULL’ when
     an exception was raised by the codec.

     Deprecated since version 3.3, will be removed in version 3.11: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_Translate(): 4039.  or *note generic codec
     based API: 6e5.


File: python.info,  Node: MBCS codecs for Windows,  Next: Methods & Slots,  Prev: Character Map Codecs,  Up: Built-in Codecs

7.8.3.26 MBCS codecs for Windows
................................

These are the MBCS codec APIs.  They are currently only available on
Windows and use the Win32 MBCS converters to implement the conversions.
Note that MBCS (or DBCS) is a class of encodings, not just one.  The
target encoding is defined by the user settings on the machine running
the codec.

 -- C Function: PyObject* PyUnicode_DecodeMBCS (const char *s,
          Py_ssize_t size, const char *errors)
     `Return value: New reference.'  Create a Unicode object by decoding
     `size' bytes of the MBCS encoded string `s'.  Return ‘NULL’ if an
     exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_DecodeMBCSStateful (const char *s,
          Py_ssize_t size, const char *errors, Py_ssize_t *consumed)
     `Return value: New reference.'  If `consumed' is ‘NULL’, behave
     like *note PyUnicode_DecodeMBCS(): 403b.  If `consumed' is not
     ‘NULL’, *note PyUnicode_DecodeMBCSStateful(): 403c. will not decode
     trailing lead byte and the number of bytes that have been decoded
     will be stored in `consumed'.

 -- C Function: PyObject* PyUnicode_AsMBCSString (PyObject *unicode)
     `Return value: New reference.'  Encode a Unicode object using MBCS
     and return the result as Python bytes object.  Error handling is
     “strict”.  Return ‘NULL’ if an exception was raised by the codec.

 -- C Function: PyObject* PyUnicode_EncodeCodePage (int code_page,
          PyObject *unicode, const char *errors)
     `Return value: New reference.'  Encode the Unicode object using the
     specified code page and return a Python bytes object.  Return
     ‘NULL’ if an exception was raised by the codec.  Use ‘CP_ACP’ code
     page to get the MBCS encoder.

     New in version 3.3.

 -- C Function: PyObject* PyUnicode_EncodeMBCS (const Py_UNICODE *s,
          Py_ssize_t size, const char *errors)
     `Return value: New reference.'  Encode the *note Py_UNICODE: bc5.
     buffer of the given `size' using MBCS and return a Python bytes
     object.  Return ‘NULL’ if an exception was raised by the codec.

     Deprecated since version 3.3, will be removed in version 4.0: Part
     of the old-style *note Py_UNICODE: bc5. API; please migrate to
     using *note PyUnicode_AsMBCSString(): be0, *note
     PyUnicode_EncodeCodePage(): be1. or *note
     PyUnicode_AsEncodedString(): 401f.


File: python.info,  Node: Methods & Slots,  Prev: MBCS codecs for Windows,  Up: Built-in Codecs

7.8.3.27 Methods & Slots
........................


File: python.info,  Node: Methods and Slot Functions,  Prev: Built-in Codecs,  Up: Unicode Objects and Codecs

7.8.3.28 Methods and Slot Functions
...................................

The following APIs are capable of handling Unicode objects and strings
on input (we refer to them as strings in the descriptions) and return
Unicode objects or integers as appropriate.

They all return ‘NULL’ or ‘-1’ if an exception occurs.

 -- C Function: PyObject* PyUnicode_Concat (PyObject *left,
          PyObject *right)
     `Return value: New reference.'  Concat two strings giving a new
     Unicode string.

 -- C Function: PyObject* PyUnicode_Split (PyObject *s, PyObject *sep,
          Py_ssize_t maxsplit)
     `Return value: New reference.'  Split a string giving a list of
     Unicode strings.  If `sep' is ‘NULL’, splitting will be done at all
     whitespace substrings.  Otherwise, splits occur at the given
     separator.  At most `maxsplit' splits will be done.  If negative,
     no limit is set.  Separators are not included in the resulting
     list.

 -- C Function: PyObject* PyUnicode_Splitlines (PyObject *s,
          int keepend)
     `Return value: New reference.'  Split a Unicode string at line
     breaks, returning a list of Unicode strings.  CRLF is considered to
     be one line break.  If `keepend' is ‘0’, the Line break characters
     are not included in the resulting strings.

 -- C Function: PyObject* PyUnicode_Join (PyObject *separator,
          PyObject *seq)
     `Return value: New reference.'  Join a sequence of strings using
     the given `separator' and return the resulting Unicode string.

 -- C Function: Py_ssize_t PyUnicode_Tailmatch (PyObject *str,
          PyObject *substr, Py_ssize_t start, Py_ssize_t end,
          int direction)

     Return ‘1’ if `substr' matches ‘str[start:end]’ at the given tail
     end (`direction' == ‘-1’ means to do a prefix match, `direction' ==
     ‘1’ a suffix match), ‘0’ otherwise.  Return ‘-1’ if an error
     occurred.

 -- C Function: Py_ssize_t PyUnicode_Find (PyObject *str,
          PyObject *substr, Py_ssize_t start, Py_ssize_t end,
          int direction)

     Return the first position of `substr' in ‘str[start:end]’ using the
     given `direction' (`direction' == ‘1’ means to do a forward search,
     `direction' == ‘-1’ a backward search).  The return value is the
     index of the first match; a value of ‘-1’ indicates that no match
     was found, and ‘-2’ indicates that an error occurred and an
     exception has been set.

 -- C Function: Py_ssize_t PyUnicode_FindChar (PyObject *str,
          Py_UCS4 ch, Py_ssize_t start, Py_ssize_t end, int direction)

     Return the first position of the character `ch' in ‘str[start:end]’
     using the given `direction' (`direction' == ‘1’ means to do a
     forward search, `direction' == ‘-1’ a backward search).  The return
     value is the index of the first match; a value of ‘-1’ indicates
     that no match was found, and ‘-2’ indicates that an error occurred
     and an exception has been set.

     New in version 3.3.

     Changed in version 3.7: `start' and `end' are now adjusted to
     behave like ‘str[start:end]’.

 -- C Function: Py_ssize_t PyUnicode_Count (PyObject *str,
          PyObject *substr, Py_ssize_t start, Py_ssize_t end)

     Return the number of non-overlapping occurrences of `substr' in
     ‘str[start:end]’.  Return ‘-1’ if an error occurred.

 -- C Function: PyObject* PyUnicode_Replace (PyObject *str,
          PyObject *substr, PyObject *replstr, Py_ssize_t maxcount)
     `Return value: New reference.'  Replace at most `maxcount'
     occurrences of `substr' in `str' with `replstr' and return the
     resulting Unicode object.  `maxcount' == ‘-1’ means replace all
     occurrences.

 -- C Function: int PyUnicode_Compare (PyObject *left, PyObject *right)

     Compare two strings and return ‘-1’, ‘0’, ‘1’ for less than, equal,
     and greater than, respectively.

     This function returns ‘-1’ upon failure, so one should call *note
     PyErr_Occurred(): 3d1a. to check for errors.

 -- C Function: int PyUnicode_CompareWithASCIIString (PyObject *uni,
          const char *string)

     Compare a Unicode object, `uni', with `string' and return ‘-1’,
     ‘0’, ‘1’ for less than, equal, and greater than, respectively.  It
     is best to pass only ASCII-encoded strings, but the function
     interprets the input string as ISO-8859-1 if it contains non-ASCII
     characters.

     This function does not raise exceptions.

 -- C Function: PyObject* PyUnicode_RichCompare (PyObject *left,
          PyObject *right, int op)
     `Return value: New reference.'  Rich compare two Unicode strings
     and return one of the following:

        * ‘NULL’ in case an exception was raised

        * ‘Py_True’ or ‘Py_False’ for successful comparisons

        * ‘Py_NotImplemented’ in case the type combination is unknown

     Possible values for `op' are ‘Py_GT’, ‘Py_GE’, ‘Py_EQ’, ‘Py_NE’,
     ‘Py_LT’, and ‘Py_LE’.

 -- C Function: PyObject* PyUnicode_Format (PyObject *format,
          PyObject *args)
     `Return value: New reference.'  Return a new string object from
     `format' and `args'; this is analogous to ‘format % args’.

 -- C Function: int PyUnicode_Contains (PyObject *container,
          PyObject *element)

     Check whether `element' is contained in `container' and return true
     or false accordingly.

     `element' has to coerce to a one element Unicode string.  ‘-1’ is
     returned if there was an error.

 -- C Function: void PyUnicode_InternInPlace (PyObject **string)

     Intern the argument `*string' in place.  The argument must be the
     address of a pointer variable pointing to a Python Unicode string
     object.  If there is an existing interned string that is the same
     as `*string', it sets `*string' to it (decrementing the reference
     count of the old string object and incrementing the reference count
     of the interned string object), otherwise it leaves `*string' alone
     and interns it (incrementing its reference count).  (Clarification:
     even though there is a lot of talk about reference counts, think of
     this function as reference-count-neutral; you own the object after
     the call if and only if you owned it before the call.)

 -- C Function: PyObject* PyUnicode_InternFromString (const char *v)
     `Return value: New reference.'  A combination of *note
     PyUnicode_FromString(): 3da5. and *note PyUnicode_InternInPlace():
     4048, returning either a new Unicode string object that has been
     interned, or a new (“owned”) reference to an earlier interned
     string object with the same value.


File: python.info,  Node: Tuple Objects,  Next: Struct Sequence Objects,  Prev: Unicode Objects and Codecs,  Up: Sequence Objects

7.8.3.29 Tuple Objects
......................

 -- C Type: PyTupleObject

     This subtype of *note PyObject: 5b5. represents a Python tuple
     object.

 -- C Variable: PyTypeObject PyTuple_Type

     This instance of *note PyTypeObject: 3f5. represents the Python
     tuple type; it is the same object as *note tuple: 1a2. in the
     Python layer.

 -- C Function: int PyTuple_Check (PyObject *p)

     Return true if `p' is a tuple object or an instance of a subtype of
     the tuple type.  This function always succeeds.

 -- C Function: int PyTuple_CheckExact (PyObject *p)

     Return true if `p' is a tuple object, but not an instance of a
     subtype of the tuple type.  This function always succeeds.

 -- C Function: PyObject* PyTuple_New (Py_ssize_t len)
     `Return value: New reference.'  Return a new tuple object of size
     `len', or ‘NULL’ on failure.

 -- C Function: PyObject* PyTuple_Pack (Py_ssize_t n, ...)
     `Return value: New reference.'  Return a new tuple object of size
     `n', or ‘NULL’ on failure.  The tuple values are initialized to the
     subsequent `n' C arguments pointing to Python objects.
     ‘PyTuple_Pack(2, a, b)’ is equivalent to ‘Py_BuildValue("(OO)", a,
     b)’.

 -- C Function: Py_ssize_t PyTuple_Size (PyObject *p)

     Take a pointer to a tuple object, and return the size of that
     tuple.

 -- C Function: Py_ssize_t PyTuple_GET_SIZE (PyObject *p)

     Return the size of the tuple `p', which must be non-‘NULL’ and
     point to a tuple; no error checking is performed.

 -- C Function: PyObject* PyTuple_GetItem (PyObject *p, Py_ssize_t pos)
     `Return value: Borrowed reference.'  Return the object at position
     `pos' in the tuple pointed to by `p'.  If `pos' is out of bounds,
     return ‘NULL’ and set an *note IndexError: f36. exception.

 -- C Function: PyObject* PyTuple_GET_ITEM (PyObject *p, Py_ssize_t pos)
     `Return value: Borrowed reference.'  Like *note PyTuple_GetItem():
     3d35, but does no checking of its arguments.

 -- C Function: PyObject* PyTuple_GetSlice (PyObject *p, Py_ssize_t low,
          Py_ssize_t high)
     `Return value: New reference.'  Return the slice of the tuple
     pointed to by `p' between `low' and `high', or ‘NULL’ on failure.
     This is the equivalent of the Python expression ‘p[low:high]’.
     Indexing from the end of the list is not supported.

 -- C Function: int PyTuple_SetItem (PyObject *p, Py_ssize_t pos,
          PyObject *o)

     Insert a reference to object `o' at position `pos' of the tuple
     pointed to by `p'.  Return ‘0’ on success.  If `pos' is out of
     bounds, return ‘-1’ and set an *note IndexError: f36. exception.

          Note: This function “steals” a reference to `o' and discards a
          reference to an item already in the tuple at the affected
          position.

 -- C Function: void PyTuple_SET_ITEM (PyObject *p, Py_ssize_t pos,
          PyObject *o)

     Like *note PyTuple_SetItem(): 3d3a, but does no error checking, and
     should `only' be used to fill in brand new tuples.

          Note: This macro “steals” a reference to `o', and, unlike
          *note PyTuple_SetItem(): 3d3a, does `not' discard a reference
          to any item that is being replaced; any reference in the tuple
          at position `pos' will be leaked.

 -- C Function: int _PyTuple_Resize (PyObject **p, Py_ssize_t newsize)

     Can be used to resize a tuple.  `newsize' will be the new length of
     the tuple.  Because tuples are `supposed' to be immutable, this
     should only be used if there is only one reference to the object.
     Do `not' use this if the tuple may already be known to some other
     part of the code.  The tuple will always grow or shrink at the end.
     Think of this as destroying the old tuple and creating a new one,
     only more efficiently.  Returns ‘0’ on success.  Client code should
     never assume that the resulting value of ‘*p’ will be the same as
     before calling this function.  If the object referenced by ‘*p’ is
     replaced, the original ‘*p’ is destroyed.  On failure, returns ‘-1’
     and sets ‘*p’ to ‘NULL’, and raises *note MemoryError: f69. or
     *note SystemError: 6f2.


File: python.info,  Node: Struct Sequence Objects,  Next: List Objects,  Prev: Tuple Objects,  Up: Sequence Objects

7.8.3.30 Struct Sequence Objects
................................

Struct sequence objects are the C equivalent of *note namedtuple(): 1a1.
objects, i.e.  a sequence whose items can also be accessed through
attributes.  To create a struct sequence, you first have to create a
specific struct sequence type.

 -- C Function: PyTypeObject* PyStructSequence_NewType
          (PyStructSequence_Desc *desc)
     `Return value: New reference.'  Create a new struct sequence type
     from the data in `desc', described below.  Instances of the
     resulting type can be created with *note PyStructSequence_New():
     4058.

 -- C Function: void PyStructSequence_InitType (PyTypeObject *type,
          PyStructSequence_Desc *desc)

     Initializes a struct sequence type `type' from `desc' in place.

 -- C Function: int PyStructSequence_InitType2 (PyTypeObject *type,
          PyStructSequence_Desc *desc)

     The same as ‘PyStructSequence_InitType’, but returns ‘0’ on success
     and ‘-1’ on failure.

     New in version 3.4.

 -- C Type: PyStructSequence_Desc

     Contains the meta information of a struct sequence type to create.

     Field                   C Type                             Meaning
                                                                
     ------------------------------------------------------------------------------------------------------
                                                                
     ‘name’                  ‘const char *’                     name of the struct sequence type
                                                                
                                                                
     ‘doc’                   ‘const char *’                     pointer to docstring for the type or
                                                                ‘NULL’ to omit
                                                                
                                                                
     ‘fields’                ‘PyStructSequence_Field *’         pointer to ‘NULL’-terminated array with
                                                                field names of the new type
                                                                
                                                                
     ‘n_in_sequence’         ‘int’                              number of fields visible to the Python
                                                                side (if used as tuple)
                                                                

 -- C Type: PyStructSequence_Field

     Describes a field of a struct sequence.  As a struct sequence is
     modeled as a tuple, all fields are typed as *note PyObject*: 5b5.
     The index in the ‘fields’ array of the *note PyStructSequence_Desc:
     52d. determines which field of the struct sequence is described.

     Field           C Type                 Meaning
                                            
     -------------------------------------------------------------------------------------
                                            
     ‘name’          ‘const char *’         name for the field or ‘NULL’ to end the
                                            list of named fields, set to
                                            *note PyStructSequence_UnnamedField: 262.
                                            to leave unnamed
                                            
                                            
     ‘doc’           ‘const char *’         field docstring or ‘NULL’ to omit
                                            

 -- C Variable: const char * const PyStructSequence_UnnamedField

     Special value for a field name to leave it unnamed.

     Changed in version 3.9: The type was changed from ‘char *’.

 -- C Function: PyObject* PyStructSequence_New (PyTypeObject *type)
     `Return value: New reference.'  Creates an instance of `type',
     which must have been created with *note PyStructSequence_NewType():
     f9e.

 -- C Function: PyObject* PyStructSequence_GetItem (PyObject *p,
          Py_ssize_t pos)
     `Return value: Borrowed reference.'  Return the object at position
     `pos' in the struct sequence pointed to by `p'.  No bounds checking
     is performed.

 -- C Function: PyObject* PyStructSequence_GET_ITEM (PyObject *p,
          Py_ssize_t pos)
     `Return value: Borrowed reference.'  Macro equivalent of *note
     PyStructSequence_GetItem(): 4059.

 -- C Function: void PyStructSequence_SetItem (PyObject *p,
          Py_ssize_t pos, PyObject *o)

     Sets the field at index `pos' of the struct sequence `p' to value
     `o'.  Like *note PyTuple_SET_ITEM(): 4056, this should only be used
     to fill in brand new instances.

          Note: This function “steals” a reference to `o'.

 -- C Function: void PyStructSequence_SET_ITEM (PyObject *p,
          Py_ssize_t *pos, PyObject *o)

     Macro equivalent of *note PyStructSequence_SetItem(): 405b.

          Note: This function “steals” a reference to `o'.


File: python.info,  Node: List Objects,  Prev: Struct Sequence Objects,  Up: Sequence Objects

7.8.3.31 List Objects
.....................

 -- C Type: PyListObject

     This subtype of *note PyObject: 5b5. represents a Python list
     object.

 -- C Variable: PyTypeObject PyList_Type

     This instance of *note PyTypeObject: 3f5. represents the Python
     list type.  This is the same object as *note list: 1f8. in the
     Python layer.

 -- C Function: int PyList_Check (PyObject *p)

     Return true if `p' is a list object or an instance of a subtype of
     the list type.  This function always succeeds.

 -- C Function: int PyList_CheckExact (PyObject *p)

     Return true if `p' is a list object, but not an instance of a
     subtype of the list type.  This function always succeeds.

 -- C Function: PyObject* PyList_New (Py_ssize_t len)
     `Return value: New reference.'  Return a new list of length `len'
     on success, or ‘NULL’ on failure.

          Note: If `len' is greater than zero, the returned list
          object’s items are set to ‘NULL’.  Thus you cannot use
          abstract API functions such as *note PySequence_SetItem():
          1184. or expose the object to Python code before setting all
          items to a real object with *note PyList_SetItem(): 3d3b.

 -- C Function: Py_ssize_t PyList_Size (PyObject *list)

     Return the length of the list object in `list'; this is equivalent
     to ‘len(list)’ on a list object.

 -- C Function: Py_ssize_t PyList_GET_SIZE (PyObject *list)

     Macro form of *note PyList_Size(): e43. without error checking.

 -- C Function: PyObject* PyList_GetItem (PyObject *list,
          Py_ssize_t index)
     `Return value: Borrowed reference.'  Return the object at position
     `index' in the list pointed to by `list'.  The position must be
     non-negative; indexing from the end of the list is not supported.
     If `index' is out of bounds (<0 or >=len(list)), return ‘NULL’ and
     set an *note IndexError: f36. exception.

 -- C Function: PyObject* PyList_GET_ITEM (PyObject *list, Py_ssize_t i)
     `Return value: Borrowed reference.'  Macro form of *note
     PyList_GetItem(): 3d36. without error checking.

 -- C Function: int PyList_SetItem (PyObject *list, Py_ssize_t index,
          PyObject *item)

     Set the item at index `index' in list to `item'.  Return ‘0’ on
     success.  If `index' is out of bounds, return ‘-1’ and set an *note
     IndexError: f36. exception.

          Note: This function “steals” a reference to `item' and
          discards a reference to an item already in the list at the
          affected position.

 -- C Function: void PyList_SET_ITEM (PyObject *list, Py_ssize_t i,
          PyObject *o)

     Macro form of *note PyList_SetItem(): 3d3b. without error checking.
     This is normally only used to fill in new lists where there is no
     previous content.

          Note: This macro “steals” a reference to `item', and, unlike
          *note PyList_SetItem(): 3d3b, does `not' discard a reference
          to any item that is being replaced; any reference in `list' at
          position `i' will be leaked.

 -- C Function: int PyList_Insert (PyObject *list, Py_ssize_t index,
          PyObject *item)

     Insert the item `item' into list `list' in front of index `index'.
     Return ‘0’ if successful; return ‘-1’ and set an exception if
     unsuccessful.  Analogous to ‘list.insert(index, item)’.

 -- C Function: int PyList_Append (PyObject *list, PyObject *item)

     Append the object `item' at the end of list `list'.  Return ‘0’ if
     successful; return ‘-1’ and set an exception if unsuccessful.
     Analogous to ‘list.append(item)’.

 -- C Function: PyObject* PyList_GetSlice (PyObject *list,
          Py_ssize_t low, Py_ssize_t high)
     `Return value: New reference.'  Return a list of the objects in
     `list' containing the objects `between' `low' and `high'.  Return
     ‘NULL’ and set an exception if unsuccessful.  Analogous to
     ‘list[low:high]’.  Indexing from the end of the list is not
     supported.

 -- C Function: int PyList_SetSlice (PyObject *list, Py_ssize_t low,
          Py_ssize_t high, PyObject *itemlist)

     Set the slice of `list' between `low' and `high' to the contents of
     `itemlist'.  Analogous to ‘list[low:high] = itemlist’.  The
     `itemlist' may be ‘NULL’, indicating the assignment of an empty
     list (slice deletion).  Return ‘0’ on success, ‘-1’ on failure.
     Indexing from the end of the list is not supported.

 -- C Function: int PyList_Sort (PyObject *list)

     Sort the items of `list' in place.  Return ‘0’ on success, ‘-1’ on
     failure.  This is equivalent to ‘list.sort()’.

 -- C Function: int PyList_Reverse (PyObject *list)

     Reverse the items of `list' in place.  Return ‘0’ on success, ‘-1’
     on failure.  This is the equivalent of ‘list.reverse()’.

 -- C Function: PyObject* PyList_AsTuple (PyObject *list)
     `Return value: New reference.'

     Return a new tuple object containing the contents of `list';
     equivalent to ‘tuple(list)’.


File: python.info,  Node: Container Objects,  Next: Function Objects<2>,  Prev: Sequence Objects,  Up: Concrete Objects Layer

7.8.4 Container Objects
-----------------------

* Menu:

* Dictionary Objects::
* Set Objects::


File: python.info,  Node: Dictionary Objects,  Next: Set Objects,  Up: Container Objects

7.8.4.1 Dictionary Objects
..........................

 -- C Type: PyDictObject

     This subtype of *note PyObject: 5b5. represents a Python dictionary
     object.

 -- C Variable: PyTypeObject PyDict_Type

     This instance of *note PyTypeObject: 3f5. represents the Python
     dictionary type.  This is the same object as *note dict: 164. in
     the Python layer.

 -- C Function: int PyDict_Check (PyObject *p)

     Return true if `p' is a dict object or an instance of a subtype of
     the dict type.  This function always succeeds.

 -- C Function: int PyDict_CheckExact (PyObject *p)

     Return true if `p' is a dict object, but not an instance of a
     subtype of the dict type.  This function always succeeds.

 -- C Function: PyObject* PyDict_New ()
     `Return value: New reference.'  Return a new empty dictionary, or
     ‘NULL’ on failure.

 -- C Function: PyObject* PyDictProxy_New (PyObject *mapping)
     `Return value: New reference.'  Return a *note
     types.MappingProxyType: b8e. object for a mapping which enforces
     read-only behavior.  This is normally used to create a view to
     prevent modification of the dictionary for non-dynamic class types.

 -- C Function: void PyDict_Clear (PyObject *p)

     Empty an existing dictionary of all key-value pairs.

 -- C Function: int PyDict_Contains (PyObject *p, PyObject *key)

     Determine if dictionary `p' contains `key'.  If an item in `p' is
     matches `key', return ‘1’, otherwise return ‘0’.  On error, return
     ‘-1’.  This is equivalent to the Python expression ‘key in p’.

 -- C Function: PyObject* PyDict_Copy (PyObject *p)
     `Return value: New reference.'  Return a new dictionary that
     contains the same key-value pairs as `p'.

 -- C Function: int PyDict_SetItem (PyObject *p, PyObject *key,
          PyObject *val)

     Insert `val' into the dictionary `p' with a key of `key'.  `key'
     must be *note hashable: 276.; if it isn’t, *note TypeError: 1fe.
     will be raised.  Return ‘0’ on success or ‘-1’ on failure.  This
     function `does not' steal a reference to `val'.

 -- C Function: int PyDict_SetItemString (PyObject *p, const char *key,
          PyObject *val)

     Insert `val' into the dictionary `p' using `key' as a key.  `key'
     should be a ‘const char*’.  The key object is created using
     ‘PyUnicode_FromString(key)’.  Return ‘0’ on success or ‘-1’ on
     failure.  This function `does not' steal a reference to `val'.

 -- C Function: int PyDict_DelItem (PyObject *p, PyObject *key)

     Remove the entry in dictionary `p' with key `key'.  `key' must be
     hashable; if it isn’t, *note TypeError: 1fe. is raised.  If `key'
     is not in the dictionary, *note KeyError: 3e9. is raised.  Return
     ‘0’ on success or ‘-1’ on failure.

 -- C Function: int PyDict_DelItemString (PyObject *p, const char *key)

     Remove the entry in dictionary `p' which has a key specified by the
     string `key'.  If `key' is not in the dictionary, *note KeyError:
     3e9. is raised.  Return ‘0’ on success or ‘-1’ on failure.

 -- C Function: PyObject* PyDict_GetItem (PyObject *p, PyObject *key)
     `Return value: Borrowed reference.'  Return the object from
     dictionary `p' which has a key `key'.  Return ‘NULL’ if the key
     `key' is not present, but `without' setting an exception.

     Note that exceptions which occur while calling *note __hash__():
     44c. and *note __eq__(): 44b. methods will get suppressed.  To get
     error reporting use *note PyDict_GetItemWithError(): 407c. instead.

 -- C Function: PyObject* PyDict_GetItemWithError (PyObject *p,
          PyObject *key)
     `Return value: Borrowed reference.'  Variant of *note
     PyDict_GetItem(): 3d37. that does not suppress exceptions.  Return
     ‘NULL’ `with' an exception set if an exception occurred.  Return
     ‘NULL’ `without' an exception set if the key wasn’t present.

 -- C Function: PyObject* PyDict_GetItemString (PyObject *p, const
          char *key)
     `Return value: Borrowed reference.'  This is the same as *note
     PyDict_GetItem(): 3d37, but `key' is specified as a ‘const char*’,
     rather than a *note PyObject*: 5b5.

     Note that exceptions which occur while calling *note __hash__():
     44c. and *note __eq__(): 44b. methods and creating a temporary
     string object will get suppressed.  To get error reporting use
     *note PyDict_GetItemWithError(): 407c. instead.

 -- C Function: PyObject* PyDict_SetDefault (PyObject *p, PyObject *key,
          PyObject *defaultobj)
     `Return value: Borrowed reference.'  This is the same as the
     Python-level *note dict.setdefault(): a9e.  If present, it returns
     the value corresponding to `key' from the dictionary `p'.  If the
     key is not in the dict, it is inserted with value `defaultobj' and
     `defaultobj' is returned.  This function evaluates the hash
     function of `key' only once, instead of evaluating it independently
     for the lookup and the insertion.

     New in version 3.4.

 -- C Function: PyObject* PyDict_Items (PyObject *p)
     `Return value: New reference.'  Return a *note PyListObject: 3f22.
     containing all the items from the dictionary.

 -- C Function: PyObject* PyDict_Keys (PyObject *p)
     `Return value: New reference.'  Return a *note PyListObject: 3f22.
     containing all the keys from the dictionary.

 -- C Function: PyObject* PyDict_Values (PyObject *p)
     `Return value: New reference.'  Return a *note PyListObject: 3f22.
     containing all the values from the dictionary `p'.

 -- C Function: Py_ssize_t PyDict_Size (PyObject *p)

     Return the number of items in the dictionary.  This is equivalent
     to ‘len(p)’ on a dictionary.

 -- C Function: int PyDict_Next (PyObject *p, Py_ssize_t *ppos,
          PyObject **pkey, PyObject **pvalue)

     Iterate over all key-value pairs in the dictionary `p'.  The
     ‘Py_ssize_t’ referred to by `ppos' must be initialized to ‘0’ prior
     to the first call to this function to start the iteration; the
     function returns true for each pair in the dictionary, and false
     once all pairs have been reported.  The parameters `pkey' and
     `pvalue' should either point to *note PyObject*: 5b5. variables
     that will be filled in with each key and value, respectively, or
     may be ‘NULL’.  Any references returned through them are borrowed.
     `ppos' should not be altered during iteration.  Its value
     represents offsets within the internal dictionary structure, and
     since the structure is sparse, the offsets are not consecutive.

     For example:

          PyObject *key, *value;
          Py_ssize_t pos = 0;

          while (PyDict_Next(self->dict, &pos, &key, &value)) {
              /* do something interesting with the values... */
              ...
          }

     The dictionary `p' should not be mutated during iteration.  It is
     safe to modify the values of the keys as you iterate over the
     dictionary, but only so long as the set of keys does not change.
     For example:

          PyObject *key, *value;
          Py_ssize_t pos = 0;

          while (PyDict_Next(self->dict, &pos, &key, &value)) {
              long i = PyLong_AsLong(value);
              if (i == -1 && PyErr_Occurred()) {
                  return -1;
              }
              PyObject *o = PyLong_FromLong(i + 1);
              if (o == NULL)
                  return -1;
              if (PyDict_SetItem(self->dict, key, o) < 0) {
                  Py_DECREF(o);
                  return -1;
              }
              Py_DECREF(o);
          }

 -- C Function: int PyDict_Merge (PyObject *a, PyObject *b,
          int override)

     Iterate over mapping object `b' adding key-value pairs to
     dictionary `a'.  `b' may be a dictionary, or any object supporting
     *note PyMapping_Keys(): 530. and *note PyObject_GetItem(): 3dc7.
     If `override' is true, existing pairs in `a' will be replaced if a
     matching key is found in `b', otherwise pairs will only be added if
     there is not a matching key in `a'.  Return ‘0’ on success or ‘-1’
     if an exception was raised.

 -- C Function: int PyDict_Update (PyObject *a, PyObject *b)

     This is the same as ‘PyDict_Merge(a, b, 1)’ in C, and is similar to
     ‘a.update(b)’ in Python except that *note PyDict_Update(): 4084.
     doesn’t fall back to the iterating over a sequence of key value
     pairs if the second argument has no “keys” attribute.  Return ‘0’
     on success or ‘-1’ if an exception was raised.

 -- C Function: int PyDict_MergeFromSeq2 (PyObject *a, PyObject *seq2,
          int override)

     Update or merge into dictionary `a', from the key-value pairs in
     `seq2'.  `seq2' must be an iterable object producing iterable
     objects of length 2, viewed as key-value pairs.  In case of
     duplicate keys, the last wins if `override' is true, else the first
     wins.  Return ‘0’ on success or ‘-1’ if an exception was raised.
     Equivalent Python (except for the return value):

          def PyDict_MergeFromSeq2(a, seq2, override):
              for key, value in seq2:
                  if override or key not in a:
                      a[key] = value


File: python.info,  Node: Set Objects,  Prev: Dictionary Objects,  Up: Container Objects

7.8.4.2 Set Objects
...................

This section details the public API for *note set: 1f6. and *note
frozenset: 1f7. objects.  Any functionality not listed below is best
accessed using the either the abstract object protocol (including *note
PyObject_CallMethod(): 3ee6, *note PyObject_RichCompareBool(): 109c,
*note PyObject_Hash(): 3ecc, *note PyObject_Repr(): a49, *note
PyObject_IsTrue(): 3ecd, *note PyObject_Print(): 1181, and *note
PyObject_GetIter(): 3ed4.) or the abstract number protocol (including
*note PyNumber_And(): 3eff, *note PyNumber_Subtract(): 3ef2, *note
PyNumber_Or(): 3f01, *note PyNumber_Xor(): 3f00, *note
PyNumber_InPlaceAnd(): 3f0b, *note PyNumber_InPlaceSubtract(): 3f03,
*note PyNumber_InPlaceOr(): 3f0d, and *note PyNumber_InPlaceXor():
3f0c.).

 -- C Type: PySetObject

     This subtype of *note PyObject: 5b5. is used to hold the internal
     data for both *note set: 1f6. and *note frozenset: 1f7. objects.
     It is like a *note PyDictObject: 4071. in that it is a fixed size
     for small sets (much like tuple storage) and will point to a
     separate, variable sized block of memory for medium and large sized
     sets (much like list storage).  None of the fields of this
     structure should be considered public and are subject to change.
     All access should be done through the documented API rather than by
     manipulating the values in the structure.

 -- C Variable: PyTypeObject PySet_Type

     This is an instance of *note PyTypeObject: 3f5. representing the
     Python *note set: 1f6. type.

 -- C Variable: PyTypeObject PyFrozenSet_Type

     This is an instance of *note PyTypeObject: 3f5. representing the
     Python *note frozenset: 1f7. type.

The following type check macros work on pointers to any Python object.
Likewise, the constructor functions work with any iterable Python
object.

 -- C Function: int PySet_Check (PyObject *p)

     Return true if `p' is a *note set: 1f6. object or an instance of a
     subtype.  This function always succeeds.

 -- C Function: int PyFrozenSet_Check (PyObject *p)

     Return true if `p' is a *note frozenset: 1f7. object or an instance
     of a subtype.  This function always succeeds.

 -- C Function: int PyAnySet_Check (PyObject *p)

     Return true if `p' is a *note set: 1f6. object, a *note frozenset:
     1f7. object, or an instance of a subtype.  This function always
     succeeds.

 -- C Function: int PyAnySet_CheckExact (PyObject *p)

     Return true if `p' is a *note set: 1f6. object or a *note
     frozenset: 1f7. object but not an instance of a subtype.  This
     function always succeeds.

 -- C Function: int PyFrozenSet_CheckExact (PyObject *p)

     Return true if `p' is a *note frozenset: 1f7. object but not an
     instance of a subtype.  This function always succeeds.

 -- C Function: PyObject* PySet_New (PyObject *iterable)
     `Return value: New reference.'  Return a new *note set: 1f6.
     containing objects returned by the `iterable'.  The `iterable' may
     be ‘NULL’ to create a new empty set.  Return the new set on success
     or ‘NULL’ on failure.  Raise *note TypeError: 1fe. if `iterable' is
     not actually iterable.  The constructor is also useful for copying
     a set (‘c=set(s)’).

 -- C Function: PyObject* PyFrozenSet_New (PyObject *iterable)
     `Return value: New reference.'  Return a new *note frozenset: 1f7.
     containing objects returned by the `iterable'.  The `iterable' may
     be ‘NULL’ to create a new empty frozenset.  Return the new set on
     success or ‘NULL’ on failure.  Raise *note TypeError: 1fe. if
     `iterable' is not actually iterable.

The following functions and macros are available for instances of *note
set: 1f6. or *note frozenset: 1f7. or instances of their subtypes.

 -- C Function: Py_ssize_t PySet_Size (PyObject *anyset)

     Return the length of a *note set: 1f6. or *note frozenset: 1f7.
     object.  Equivalent to ‘len(anyset)’.  Raises a ‘PyExc_SystemError’
     if `anyset' is not a *note set: 1f6, *note frozenset: 1f7, or an
     instance of a subtype.

 -- C Function: Py_ssize_t PySet_GET_SIZE (PyObject *anyset)

     Macro form of *note PySet_Size(): e75. without error checking.

 -- C Function: int PySet_Contains (PyObject *anyset, PyObject *key)

     Return ‘1’ if found, ‘0’ if not found, and ‘-1’ if an error is
     encountered.  Unlike the Python *note __contains__(): dee. method,
     this function does not automatically convert unhashable sets into
     temporary frozensets.  Raise a *note TypeError: 1fe. if the `key'
     is unhashable.  Raise ‘PyExc_SystemError’ if `anyset' is not a
     *note set: 1f6, *note frozenset: 1f7, or an instance of a subtype.

 -- C Function: int PySet_Add (PyObject *set, PyObject *key)

     Add `key' to a *note set: 1f6. instance.  Also works with *note
     frozenset: 1f7. instances (like *note PyTuple_SetItem(): 3d3a. it
     can be used to fill-in the values of brand new frozensets before
     they are exposed to other code).  Return ‘0’ on success or ‘-1’ on
     failure.  Raise a *note TypeError: 1fe. if the `key' is unhashable.
     Raise a *note MemoryError: f69. if there is no room to grow.  Raise
     a *note SystemError: 6f2. if `set' is not an instance of *note set:
     1f6. or its subtype.

The following functions are available for instances of *note set: 1f6.
or its subtypes but not for instances of *note frozenset: 1f7. or its
subtypes.

 -- C Function: int PySet_Discard (PyObject *set, PyObject *key)

     Return ‘1’ if found and removed, ‘0’ if not found (no action
     taken), and ‘-1’ if an error is encountered.  Does not raise *note
     KeyError: 3e9. for missing keys.  Raise a *note TypeError: 1fe. if
     the `key' is unhashable.  Unlike the Python ‘discard()’ method,
     this function does not automatically convert unhashable sets into
     temporary frozensets.  Raise ‘PyExc_SystemError’ if `set' is not an
     instance of *note set: 1f6. or its subtype.

 -- C Function: PyObject* PySet_Pop (PyObject *set)
     `Return value: New reference.'  Return a new reference to an
     arbitrary object in the `set', and removes the object from the
     `set'.  Return ‘NULL’ on failure.  Raise *note KeyError: 3e9. if
     the set is empty.  Raise a *note SystemError: 6f2. if `set' is not
     an instance of *note set: 1f6. or its subtype.

 -- C Function: int PySet_Clear (PyObject *set)

     Empty an existing set of all elements.


File: python.info,  Node: Function Objects<2>,  Next: Other Objects,  Prev: Container Objects,  Up: Concrete Objects Layer

7.8.5 Function Objects
----------------------

* Menu:

* Function Objects: Function Objects<3>.
* Instance Method Objects::
* Method Objects: Method Objects<2>.
* Cell Objects::
* Code Objects: Code Objects<2>.


File: python.info,  Node: Function Objects<3>,  Next: Instance Method Objects,  Up: Function Objects<2>

7.8.5.1 Function Objects
........................

There are a few functions specific to Python functions.

 -- C Type: PyFunctionObject

     The C structure used for functions.

 -- C Variable: PyTypeObject PyFunction_Type

     This is an instance of *note PyTypeObject: 3f5. and represents the
     Python function type.  It is exposed to Python programmers as
     ‘types.FunctionType’.

 -- C Function: int PyFunction_Check (PyObject *o)

     Return true if `o' is a function object (has type *note
     PyFunction_Type: 409a.).  The parameter must not be ‘NULL’.  This
     function always succeeds.

 -- C Function: PyObject* PyFunction_New (PyObject *code,
          PyObject *globals)
     `Return value: New reference.'  Return a new function object
     associated with the code object `code'.  `globals' must be a
     dictionary with the global variables accessible to the function.

     The function’s docstring and name are retrieved from the code
     object.  `__module__' is retrieved from `globals'.  The argument
     defaults, annotations and closure are set to ‘NULL’.
     `__qualname__' is set to the same value as the function’s name.

 -- C Function: PyObject* PyFunction_NewWithQualName (PyObject *code,
          PyObject *globals, PyObject *qualname)
     `Return value: New reference.'  As *note PyFunction_New(): 409c,
     but also allows setting the function object’s ‘__qualname__’
     attribute.  `qualname' should be a unicode object or ‘NULL’; if
     ‘NULL’, the ‘__qualname__’ attribute is set to the same value as
     its ‘__name__’ attribute.

     New in version 3.3.

 -- C Function: PyObject* PyFunction_GetCode (PyObject *op)
     `Return value: Borrowed reference.'  Return the code object
     associated with the function object `op'.

 -- C Function: PyObject* PyFunction_GetGlobals (PyObject *op)
     `Return value: Borrowed reference.'  Return the globals dictionary
     associated with the function object `op'.

 -- C Function: PyObject* PyFunction_GetModule (PyObject *op)
     `Return value: Borrowed reference.'  Return the `__module__'
     attribute of the function object `op'.  This is normally a string
     containing the module name, but can be set to any other object by
     Python code.

 -- C Function: PyObject* PyFunction_GetDefaults (PyObject *op)
     `Return value: Borrowed reference.'  Return the argument default
     values of the function object `op'.  This can be a tuple of
     arguments or ‘NULL’.

 -- C Function: int PyFunction_SetDefaults (PyObject *op,
          PyObject *defaults)

     Set the argument default values for the function object `op'.
     `defaults' must be ‘Py_None’ or a tuple.

     Raises *note SystemError: 6f2. and returns ‘-1’ on failure.

 -- C Function: PyObject* PyFunction_GetClosure (PyObject *op)
     `Return value: Borrowed reference.'  Return the closure associated
     with the function object `op'.  This can be ‘NULL’ or a tuple of
     cell objects.

 -- C Function: int PyFunction_SetClosure (PyObject *op,
          PyObject *closure)

     Set the closure associated with the function object `op'.
     `closure' must be ‘Py_None’ or a tuple of cell objects.

     Raises *note SystemError: 6f2. and returns ‘-1’ on failure.

 -- C Function: PyObject *PyFunction_GetAnnotations (PyObject *op)
     `Return value: Borrowed reference.'  Return the annotations of the
     function object `op'.  This can be a mutable dictionary or ‘NULL’.

 -- C Function: int PyFunction_SetAnnotations (PyObject *op,
          PyObject *annotations)

     Set the annotations for the function object `op'.  `annotations'
     must be a dictionary or ‘Py_None’.

     Raises *note SystemError: 6f2. and returns ‘-1’ on failure.


File: python.info,  Node: Instance Method Objects,  Next: Method Objects<2>,  Prev: Function Objects<3>,  Up: Function Objects<2>

7.8.5.2 Instance Method Objects
...............................

An instance method is a wrapper for a *note PyCFunction: e9f. and the
new way to bind a *note PyCFunction: e9f. to a class object.  It
replaces the former call ‘PyMethod_New(func, NULL, class)’.

 -- C Variable: PyTypeObject PyInstanceMethod_Type

     This instance of *note PyTypeObject: 3f5. represents the Python
     instance method type.  It is not exposed to Python programs.

 -- C Function: int PyInstanceMethod_Check (PyObject *o)

     Return true if `o' is an instance method object (has type *note
     PyInstanceMethod_Type: 40aa.).  The parameter must not be ‘NULL’.
     This function always succeeds.

 -- C Function: PyObject* PyInstanceMethod_New (PyObject *func)
     `Return value: New reference.'  Return a new instance method
     object, with `func' being any callable object `func' is the
     function that will be called when the instance method is called.

 -- C Function: PyObject* PyInstanceMethod_Function (PyObject *im)
     `Return value: Borrowed reference.'  Return the function object
     associated with the instance method `im'.

 -- C Function: PyObject* PyInstanceMethod_GET_FUNCTION (PyObject *im)
     `Return value: Borrowed reference.'  Macro version of *note
     PyInstanceMethod_Function(): 40ad. which avoids error checking.


File: python.info,  Node: Method Objects<2>,  Next: Cell Objects,  Prev: Instance Method Objects,  Up: Function Objects<2>

7.8.5.3 Method Objects
......................

Methods are bound function objects.  Methods are always bound to an
instance of a user-defined class.  Unbound methods (methods bound to a
class object) are no longer available.

 -- C Variable: PyTypeObject PyMethod_Type

     This instance of *note PyTypeObject: 3f5. represents the Python
     method type.  This is exposed to Python programs as
     ‘types.MethodType’.

 -- C Function: int PyMethod_Check (PyObject *o)

     Return true if `o' is a method object (has type *note
     PyMethod_Type: 40b1.).  The parameter must not be ‘NULL’.  This
     function always succeeds.

 -- C Function: PyObject* PyMethod_New (PyObject *func, PyObject *self)
     `Return value: New reference.'  Return a new method object, with
     `func' being any callable object and `self' the instance the method
     should be bound.  `func' is the function that will be called when
     the method is called.  `self' must not be ‘NULL’.

 -- C Function: PyObject* PyMethod_Function (PyObject *meth)
     `Return value: Borrowed reference.'  Return the function object
     associated with the method `meth'.

 -- C Function: PyObject* PyMethod_GET_FUNCTION (PyObject *meth)
     `Return value: Borrowed reference.'  Macro version of *note
     PyMethod_Function(): 40b4. which avoids error checking.

 -- C Function: PyObject* PyMethod_Self (PyObject *meth)
     `Return value: Borrowed reference.'  Return the instance associated
     with the method `meth'.

 -- C Function: PyObject* PyMethod_GET_SELF (PyObject *meth)
     `Return value: Borrowed reference.'  Macro version of *note
     PyMethod_Self(): 40b6. which avoids error checking.


File: python.info,  Node: Cell Objects,  Next: Code Objects<2>,  Prev: Method Objects<2>,  Up: Function Objects<2>

7.8.5.4 Cell Objects
....................

“Cell” objects are used to implement variables referenced by multiple
scopes.  For each such variable, a cell object is created to store the
value; the local variables of each stack frame that references the value
contains a reference to the cells from outer scopes which also use that
variable.  When the value is accessed, the value contained in the cell
is used instead of the cell object itself.  This de-referencing of the
cell object requires support from the generated byte-code; these are not
automatically de-referenced when accessed.  Cell objects are not likely
to be useful elsewhere.

 -- C Type: PyCellObject

     The C structure used for cell objects.

 -- C Variable: PyTypeObject PyCell_Type

     The type object corresponding to cell objects.

 -- C Function: int PyCell_Check (ob)

     Return true if `ob' is a cell object; `ob' must not be ‘NULL’.
     This function always succeeds.

 -- C Function: PyObject* PyCell_New (PyObject *ob)
     `Return value: New reference.'  Create and return a new cell object
     containing the value `ob'.  The parameter may be ‘NULL’.

 -- C Function: PyObject* PyCell_Get (PyObject *cell)
     `Return value: New reference.'  Return the contents of the cell
     `cell'.

 -- C Function: PyObject* PyCell_GET (PyObject *cell)
     `Return value: Borrowed reference.'  Return the contents of the
     cell `cell', but without checking that `cell' is non-‘NULL’ and a
     cell object.

 -- C Function: int PyCell_Set (PyObject *cell, PyObject *value)

     Set the contents of the cell object `cell' to `value'.  This
     releases the reference to any current content of the cell.  `value'
     may be ‘NULL’.  `cell' must be non-‘NULL’; if it is not a cell
     object, ‘-1’ will be returned.  On success, ‘0’ will be returned.

 -- C Function: void PyCell_SET (PyObject *cell, PyObject *value)

     Sets the value of the cell object `cell' to `value'.  No reference
     counts are adjusted, and no checks are made for safety; `cell' must
     be non-‘NULL’ and must be a cell object.


File: python.info,  Node: Code Objects<2>,  Prev: Cell Objects,  Up: Function Objects<2>

7.8.5.5 Code Objects
....................

Code objects are a low-level detail of the CPython implementation.  Each
one represents a chunk of executable code that hasn’t yet been bound
into a function.

 -- C Type: PyCodeObject

     The C structure of the objects used to describe code objects.  The
     fields of this type are subject to change at any time.

 -- C Variable: PyTypeObject PyCode_Type

     This is an instance of *note PyTypeObject: 3f5. representing the
     Python *note code: 1a. type.

 -- C Function: int PyCode_Check (PyObject *co)

     Return true if `co' is a *note code: 1a. object.  This function
     always succeeds.

 -- C Function: int PyCode_GetNumFree (PyCodeObject *co)

     Return the number of free variables in `co'.

 -- C Function: PyCodeObject* PyCode_New (int argcount,
          int kwonlyargcount, int nlocals, int stacksize, int flags,
          PyObject *code, PyObject *consts, PyObject *names,
          PyObject *varnames, PyObject *freevars, PyObject *cellvars,
          PyObject *filename, PyObject *name, int firstlineno,
          PyObject *lnotab)
     `Return value: New reference.'  Return a new code object.  If you
     need a dummy code object to create a frame, use *note
     PyCode_NewEmpty(): db1. instead.  Calling *note PyCode_New(): 39b.
     directly can bind you to a precise Python version since the
     definition of the bytecode changes often.

 -- C Function: PyCodeObject* PyCode_NewWithPosOnlyArgs (int argcount,
          int posonlyargcount, int kwonlyargcount, int nlocals,
          int stacksize, int flags, PyObject *code, PyObject *consts,
          PyObject *names, PyObject *varnames, PyObject *freevars,
          PyObject *cellvars, PyObject *filename, PyObject *name,
          int firstlineno, PyObject *lnotab)
     `Return value: New reference.'  Similar to *note PyCode_New(): 39b,
     but with an extra “posonlyargcount” for positional-only arguments.

     New in version 3.8.

 -- C Function: PyCodeObject* PyCode_NewEmpty (const char *filename,
          const char *funcname, int firstlineno)
     `Return value: New reference.'  Return a new empty code object with
     the specified filename, function name, and first line number.  It
     is illegal to *note exec(): d0c. or *note eval(): c61. the
     resulting code object.


File: python.info,  Node: Other Objects,  Prev: Function Objects<2>,  Up: Concrete Objects Layer

7.8.6 Other Objects
-------------------

* Menu:

* File Objects::
* Module Objects::
* Iterator Objects::
* Descriptor Objects::
* Slice Objects::
* Ellipsis Object::
* MemoryView objects::
* Weak Reference Objects: Weak Reference Objects<2>.
* Capsules: Capsules<2>.
* Generator Objects::
* Coroutine Objects: Coroutine Objects<2>.
* Context Variables Objects::
* DateTime Objects: DateTime Objects<2>.
* Objects for Type Hinting::


File: python.info,  Node: File Objects,  Next: Module Objects,  Up: Other Objects

7.8.6.1 File Objects
....................

These APIs are a minimal emulation of the Python 2 C API for built-in
file objects, which used to rely on the buffered I/O (‘FILE*’) support
from the C standard library.  In Python 3, files and streams use the new
*note io: a1. module, which defines several layers over the low-level
unbuffered I/O of the operating system.  The functions described below
are convenience C wrappers over these new APIs, and meant mostly for
internal error reporting in the interpreter; third-party code is advised
to access the *note io: a1. APIs instead.

 -- C Function: PyObject* PyFile_FromFd (int fd, const char *name, const
          char *mode, int buffering, const char *encoding, const
          char *errors, const char *newline, int closefd)
     `Return value: New reference.'  Create a Python file object from
     the file descriptor of an already opened file `fd'.  The arguments
     `name', `encoding', `errors' and `newline' can be ‘NULL’ to use the
     defaults; `buffering' can be `-1' to use the default.  `name' is
     ignored and kept for backward compatibility.  Return ‘NULL’ on
     failure.  For a more comprehensive description of the arguments,
     please refer to the *note io.open(): 74d. function documentation.

          Warning: Since Python streams have their own buffering layer,
          mixing them with OS-level file descriptors can produce various
          issues (such as unexpected ordering of data).

     Changed in version 3.2: Ignore `name' attribute.

 -- C Function: int PyObject_AsFileDescriptor (PyObject *p)

     Return the file descriptor associated with `p' as an ‘int’.  If the
     object is an integer, its value is returned.  If not, the object’s
     *note fileno(): 2069. method is called if it exists; the method
     must return an integer, which is returned as the file descriptor
     value.  Sets an exception and returns ‘-1’ on failure.

 -- C Function: PyObject* PyFile_GetLine (PyObject *p, int n)
     `Return value: New reference.'

     Equivalent to ‘p.readline([n])’, this function reads one line from
     the object `p'.  `p' may be a file object or any object with a
     *note readline(): 1849. method.  If `n' is ‘0’, exactly one line is
     read, regardless of the length of the line.  If `n' is greater than
     ‘0’, no more than `n' bytes will be read from the file; a partial
     line can be returned.  In both cases, an empty string is returned
     if the end of the file is reached immediately.  If `n' is less than
     ‘0’, however, one line is read regardless of length, but *note
     EOFError: d34. is raised if the end of the file is reached
     immediately.

 -- C Function: int PyFile_SetOpenCodeHook
          (Py_OpenCodeHookFunction handler)

     Overrides the normal behavior of *note io.open_code(): 1050. to
     pass its parameter through the provided handler.

     The handler is a function of type ‘PyObject *(*)(PyObject *path,
     void *userData)’, where `path' is guaranteed to be *note
     PyUnicodeObject: 3ff9.

     The `userData' pointer is passed into the hook function.  Since
     hook functions may be called from different runtimes, this pointer
     should not refer directly to Python state.

     As this hook is intentionally used during import, avoid importing
     new modules during its execution unless they are known to be frozen
     or available in ‘sys.modules’.

     Once a hook has been set, it cannot be removed or replaced, and
     later calls to *note PyFile_SetOpenCodeHook(): 2144. will fail.  On
     failure, the function returns -1 and sets an exception if the
     interpreter has been initialized.

     This function is safe to call before *note Py_Initialize(): 20f.

     Raises an *note auditing event: fa1. ‘setopencodehook’ with no
     arguments.

     New in version 3.8.

 -- C Function: int PyFile_WriteObject (PyObject *obj, PyObject *p,
          int flags)

     Write object `obj' to file object `p'.  The only supported flag for
     `flags' is ‘Py_PRINT_RAW’; if given, the *note str(): 205. of the
     object is written instead of the *note repr(): 8b9.  Return ‘0’ on
     success or ‘-1’ on failure; the appropriate exception will be set.

 -- C Function: int PyFile_WriteString (const char *s, PyObject *p)

     Write string `s' to file object `p'.  Return ‘0’ on success or ‘-1’
     on failure; the appropriate exception will be set.


File: python.info,  Node: Module Objects,  Next: Iterator Objects,  Prev: File Objects,  Up: Other Objects

7.8.6.2 Module Objects
......................

 -- C Variable: PyTypeObject PyModule_Type

     This instance of *note PyTypeObject: 3f5. represents the Python
     module type.  This is exposed to Python programs as
     ‘types.ModuleType’.

 -- C Function: int PyModule_Check (PyObject *p)

     Return true if `p' is a module object, or a subtype of a module
     object.  This function always succeeds.

 -- C Function: int PyModule_CheckExact (PyObject *p)

     Return true if `p' is a module object, but not a subtype of *note
     PyModule_Type: 40d6.  This function always succeeds.

 -- C Function: PyObject* PyModule_NewObject (PyObject *name)
     `Return value: New reference.'

     Return a new module object with the *note __name__: dd8. attribute
     set to `name'.  The module’s *note __name__: dd8, ‘__doc__’, *note
     __package__: a36, and *note __loader__: a37. attributes are filled
     in (all but *note __name__: dd8. are set to ‘None’); the caller is
     responsible for providing a *note __file__: 1562. attribute.

     New in version 3.3.

     Changed in version 3.4: *note __package__: a36. and *note
     __loader__: a37. are set to ‘None’.

 -- C Function: PyObject* PyModule_New (const char *name)
     `Return value: New reference.'  Similar to *note
     PyModule_NewObject(): 40d9, but the name is a UTF-8 encoded string
     instead of a Unicode object.

 -- C Function: PyObject* PyModule_GetDict (PyObject *module)
     `Return value: Borrowed reference.'

     Return the dictionary object that implements `module'’s namespace;
     this object is the same as the *note __dict__: 5f6. attribute of
     the module object.  If `module' is not a module object (or a
     subtype of a module object), *note SystemError: 6f2. is raised and
     ‘NULL’ is returned.

     It is recommended extensions use other ‘PyModule_*()’ and
     ‘PyObject_*()’ functions rather than directly manipulate a module’s
     *note __dict__: 5f6.

 -- C Function: PyObject* PyModule_GetNameObject (PyObject *module)
     `Return value: New reference.'

     Return `module'’s *note __name__: dd8. value.  If the module does
     not provide one, or if it is not a string, *note SystemError: 6f2.
     is raised and ‘NULL’ is returned.

     New in version 3.3.

 -- C Function: const char* PyModule_GetName (PyObject *module)

     Similar to *note PyModule_GetNameObject(): 40dc. but return the
     name encoded to ‘'utf-8'’.

 -- C Function: void* PyModule_GetState (PyObject *module)

     Return the “state” of the module, that is, a pointer to the block
     of memory allocated at module creation time, or ‘NULL’.  See *note
     PyModuleDef.m_size: 25d.

 -- C Function: PyModuleDef* PyModule_GetDef (PyObject *module)

     Return a pointer to the *note PyModuleDef: 25b. struct from which
     the module was created, or ‘NULL’ if the module wasn’t created from
     a definition.

 -- C Function: PyObject* PyModule_GetFilenameObject (PyObject *module)
     `Return value: New reference.'

     Return the name of the file from which `module' was loaded using
     `module'’s *note __file__: 1562. attribute.  If this is not
     defined, or if it is not a unicode string, raise *note SystemError:
     6f2. and return ‘NULL’; otherwise return a reference to a Unicode
     object.

     New in version 3.2.

 -- C Function: const char* PyModule_GetFilename (PyObject *module)

     Similar to *note PyModule_GetFilenameObject(): 40df. but return the
     filename encoded to ‘utf-8’.

     Deprecated since version 3.2: *note PyModule_GetFilename(): 40e0.
     raises ‘UnicodeEncodeError’ on unencodable filenames, use *note
     PyModule_GetFilenameObject(): 40df. instead.

* Menu:

* Initializing C modules::
* Module lookup::


File: python.info,  Node: Initializing C modules,  Next: Module lookup,  Up: Module Objects

7.8.6.3 Initializing C modules
..............................

Modules objects are usually created from extension modules (shared
libraries which export an initialization function), or compiled-in
modules (where the initialization function is added using *note
PyImport_AppendInittab(): f9c.).  See *note Building C and C++
Extensions: 3d25. or *note Extending Embedded Python: 3da7. for details.

The initialization function can either pass a module definition instance
to *note PyModule_Create(): 3d22, and return the resulting module
object, or request “multi-phase initialization” by returning the
definition struct itself.

 -- C Type: PyModuleDef

     The module definition struct, which holds all information needed to
     create a module object.  There is usually only one statically
     initialized variable of this type for each module.

      -- C Member: PyModuleDef_Base m_base

          Always initialize this member to ‘PyModuleDef_HEAD_INIT’.

      -- C Member: const char *m_name

          Name for the new module.

      -- C Member: const char *m_doc

          Docstring for the module; usually a docstring variable created
          with *note PyDoc_STRVAR: 105a. is used.

      -- C Member: Py_ssize_t m_size

          Module state may be kept in a per-module memory area that can
          be retrieved with *note PyModule_GetState(): 25e, rather than
          in static globals.  This makes modules safe for use in
          multiple sub-interpreters.

          This memory area is allocated based on `m_size' on module
          creation, and freed when the module object is deallocated,
          after the ‘m_free’ function has been called, if present.

          Setting ‘m_size’ to ‘-1’ means that the module does not
          support sub-interpreters, because it has global state.

          Setting it to a non-negative value means that the module can
          be re-initialized and specifies the additional amount of
          memory it requires for its state.  Non-negative ‘m_size’ is
          required for multi-phase initialization.

          See PEP 3121(1) for more details.

      -- C Member: PyMethodDef* m_methods

          A pointer to a table of module-level functions, described by
          *note PyMethodDef: edd. values.  Can be ‘NULL’ if no functions
          are present.

      -- C Member: PyModuleDef_Slot* m_slots

          An array of slot definitions for multi-phase initialization,
          terminated by a ‘{0, NULL}’ entry.  When using single-phase
          initialization, `m_slots' must be ‘NULL’.

          Changed in version 3.5: Prior to version 3.5, this member was
          always set to ‘NULL’, and was defined as:

                -- C Member: inquiry m_reload

      -- C Member: traverseproc m_traverse

          A traversal function to call during GC traversal of the module
          object, or ‘NULL’ if not needed.

          This function is not called if the module state was requested
          but is not allocated yet.  This is the case immediately after
          the module is created and before the module is executed (*note
          Py_mod_exec: 25c. function).  More precisely, this function is
          not called if ‘m_size’ is greater than 0 and the module state
          (as returned by *note PyModule_GetState(): 25e.) is ‘NULL’.

          Changed in version 3.9: No longer called before the module
          state is allocated.

      -- C Member: inquiry m_clear

          A clear function to call during GC clearing of the module
          object, or ‘NULL’ if not needed.

          This function is not called if the module state was requested
          but is not allocated yet.  This is the case immediately after
          the module is created and before the module is executed (*note
          Py_mod_exec: 25c. function).  More precisely, this function is
          not called if ‘m_size’ is greater than 0 and the module state
          (as returned by *note PyModule_GetState(): 25e.) is ‘NULL’.

          Like *note PyTypeObject.tp_clear: 3d6e, this function is not
          `always' called before a module is deallocated.  For example,
          when reference counting is enough to determine that an object
          is no longer used, the cyclic garbage collector is not
          involved and *note m_free: 25a. is called directly.

          Changed in version 3.9: No longer called before the module
          state is allocated.

      -- C Member: freefunc m_free

          A function to call during deallocation of the module object,
          or ‘NULL’ if not needed.

          This function is not called if the module state was requested
          but is not allocated yet.  This is the case immediately after
          the module is created and before the module is executed (*note
          Py_mod_exec: 25c. function).  More precisely, this function is
          not called if ‘m_size’ is greater than 0 and the module state
          (as returned by *note PyModule_GetState(): 25e.) is ‘NULL’.

          Changed in version 3.9: No longer called before the module
          state is allocated.

* Menu:

* Single-phase initialization::
* Multi-phase initialization::
* Low-level module creation functions::
* Support functions::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3121


File: python.info,  Node: Single-phase initialization,  Next: Multi-phase initialization,  Up: Initializing C modules

7.8.6.4 Single-phase initialization
...................................

The module initialization function may create and return the module
object directly.  This is referred to as “single-phase initialization”,
and uses one of the following two module creation functions:

 -- C Function: PyObject* PyModule_Create (PyModuleDef *def)
     `Return value: New reference.'  Create a new module object, given
     the definition in `def'.  This behaves like *note
     PyModule_Create2(): 40e9. with `module_api_version' set to
     ‘PYTHON_API_VERSION’.

 -- C Function: PyObject* PyModule_Create2 (PyModuleDef *def,
          int module_api_version)
     `Return value: New reference.'  Create a new module object, given
     the definition in `def', assuming the API version
     `module_api_version'.  If that version does not match the version
     of the running interpreter, a *note RuntimeWarning: 3e2. is
     emitted.

          Note: Most uses of this function should be using *note
          PyModule_Create(): 3d22. instead; only use this if you are
          sure you need it.

Before it is returned from in the initialization function, the resulting
module object is typically populated using functions like *note
PyModule_AddObject(): 10dd.


File: python.info,  Node: Multi-phase initialization,  Next: Low-level module creation functions,  Prev: Single-phase initialization,  Up: Initializing C modules

7.8.6.5 Multi-phase initialization
..................................

An alternate way to specify extensions is to request “multi-phase
initialization”.  Extension modules created this way behave more like
Python modules: the initialization is split between the `creation
phase', when the module object is created, and the `execution phase',
when it is populated.  The distinction is similar to the *note
__new__(): 974. and *note __init__(): e23. methods of classes.

Unlike modules created using single-phase initialization, these modules
are not singletons: if the `sys.modules' entry is removed and the module
is re-imported, a new module object is created, and the old module is
subject to normal garbage collection – as with Python modules.  By
default, multiple modules created from the same definition should be
independent: changes to one should not affect the others.  This means
that all state should be specific to the module object (using e.g.
using *note PyModule_GetState(): 25e.), or its contents (such as the
module’s *note __dict__: 5f6. or individual classes created with *note
PyType_FromSpec(): 23a.).

All modules created using multi-phase initialization are expected to
support *note sub-interpreters: 3e53.  Making sure multiple modules are
independent is typically enough to achieve this.

To request multi-phase initialization, the initialization function
(PyInit_modulename) returns a *note PyModuleDef: 25b. instance with
non-empty *note m_slots: 40e6.  Before it is returned, the ‘PyModuleDef’
instance must be initialized with the following function:

 -- C Function: PyObject* PyModuleDef_Init (PyModuleDef *def)
     `Return value: Borrowed reference.'  Ensures a module definition is
     a properly initialized Python object that correctly reports its
     type and reference count.

     Returns `def' cast to ‘PyObject*’, or ‘NULL’ if an error occurred.

     New in version 3.5.

The `m_slots' member of the module definition must point to an array of
‘PyModuleDef_Slot’ structures:

 -- C Type: PyModuleDef_Slot

      -- C Member: int slot

          A slot ID, chosen from the available values explained below.

      -- C Member: void* value

          Value of the slot, whose meaning depends on the slot ID.

     New in version 3.5.

The `m_slots' array must be terminated by a slot with id 0.

The available slot types are:

 -- C Macro: Py_mod_create

     Specifies a function that is called to create the module object
     itself.  The `value' pointer of this slot must point to a function
     of the signature:

      -- C Function: PyObject* create_module (PyObject *spec,
               PyModuleDef *def)

     The function receives a *note ModuleSpec: 1601. instance, as
     defined in PEP 451(1), and the module definition.  It should return
     a new module object, or set an error and return ‘NULL’.

     This function should be kept minimal.  In particular, it should not
     call arbitrary Python code, as trying to import the same module
     again may result in an infinite loop.

     Multiple ‘Py_mod_create’ slots may not be specified in one module
     definition.

     If ‘Py_mod_create’ is not specified, the import machinery will
     create a normal module object using *note PyModule_New(): 40da.
     The name is taken from `spec', not the definition, to allow
     extension modules to dynamically adjust to their place in the
     module hierarchy and be imported under different names through
     symlinks, all while sharing a single module definition.

     There is no requirement for the returned object to be an instance
     of *note PyModule_Type: 40d6.  Any type can be used, as long as it
     supports setting and getting import-related attributes.  However,
     only ‘PyModule_Type’ instances may be returned if the ‘PyModuleDef’
     has non-‘NULL’ ‘m_traverse’, ‘m_clear’, ‘m_free’; non-zero
     ‘m_size’; or slots other than ‘Py_mod_create’.

 -- C Macro: Py_mod_exec

     Specifies a function that is called to `execute' the module.  This
     is equivalent to executing the code of a Python module: typically,
     this function adds classes and constants to the module.  The
     signature of the function is:

      -- C Function: int exec_module (PyObject* module)

     If multiple ‘Py_mod_exec’ slots are specified, they are processed
     in the order they appear in the `m_slots' array.

See PEP 489(2) for more details on multi-phase initialization.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0451

   (2) https://www.python.org/dev/peps/pep-0489


File: python.info,  Node: Low-level module creation functions,  Next: Support functions,  Prev: Multi-phase initialization,  Up: Initializing C modules

7.8.6.6 Low-level module creation functions
...........................................

The following functions are called under the hood when using multi-phase
initialization.  They can be used directly, for example when creating
module objects dynamically.  Note that both ‘PyModule_FromDefAndSpec’
and ‘PyModule_ExecDef’ must be called to fully initialize a module.

 -- C Function: PyObject * PyModule_FromDefAndSpec (PyModuleDef *def,
          PyObject *spec)
     `Return value: New reference.'  Create a new module object, given
     the definition in `module' and the ModuleSpec `spec'.  This behaves
     like *note PyModule_FromDefAndSpec2(): 89a. with
     `module_api_version' set to ‘PYTHON_API_VERSION’.

     New in version 3.5.

 -- C Function: PyObject * PyModule_FromDefAndSpec2 (PyModuleDef *def,
          PyObject *spec, int module_api_version)
     `Return value: New reference.'  Create a new module object, given
     the definition in `module' and the ModuleSpec `spec', assuming the
     API version `module_api_version'.  If that version does not match
     the version of the running interpreter, a *note RuntimeWarning:
     3e2. is emitted.

          Note: Most uses of this function should be using *note
          PyModule_FromDefAndSpec(): 899. instead; only use this if you
          are sure you need it.

     New in version 3.5.

 -- C Function: int PyModule_ExecDef (PyObject *module,
          PyModuleDef *def)

     Process any execution slots (*note Py_mod_exec: 25c.) given in
     `def'.

     New in version 3.5.

 -- C Function: int PyModule_SetDocString (PyObject *module, const
          char *docstring)

     Set the docstring for `module' to `docstring'.  This function is
     called automatically when creating a module from ‘PyModuleDef’,
     using either ‘PyModule_Create’ or ‘PyModule_FromDefAndSpec’.

     New in version 3.5.

 -- C Function: int PyModule_AddFunctions (PyObject *module,
          PyMethodDef *functions)

     Add the functions from the ‘NULL’ terminated `functions' array to
     `module'.  Refer to the *note PyMethodDef: edd. documentation for
     details on individual entries (due to the lack of a shared module
     namespace, module level “functions” implemented in C typically
     receive the module as their first parameter, making them similar to
     instance methods on Python classes).  This function is called
     automatically when creating a module from ‘PyModuleDef’, using
     either ‘PyModule_Create’ or ‘PyModule_FromDefAndSpec’.

     New in version 3.5.


File: python.info,  Node: Support functions,  Prev: Low-level module creation functions,  Up: Initializing C modules

7.8.6.7 Support functions
.........................

The module initialization function (if using single phase
initialization) or a function called from a module execution slot (if
using multi-phase initialization), can use the following functions to
help initialize the module state:

 -- C Function: int PyModule_AddObject (PyObject *module, const
          char *name, PyObject *value)

     Add an object to `module' as `name'.  This is a convenience
     function which can be used from the module’s initialization
     function.  This steals a reference to `value' on success.  Return
     ‘-1’ on error, ‘0’ on success.

          Note: Unlike other functions that steal references,
          ‘PyModule_AddObject()’ only decrements the reference count of
          `value' `on success'.

          This means that its return value must be checked, and calling
          code must *note Py_DECREF(): 38f. `value' manually on error.
          Example usage:

               Py_INCREF(spam);
               if (PyModule_AddObject(module, "spam", spam) < 0) {
                   Py_DECREF(module);
                   Py_DECREF(spam);
                   return NULL;
               }

 -- C Function: int PyModule_AddIntConstant (PyObject *module, const
          char *name, long value)

     Add an integer constant to `module' as `name'.  This convenience
     function can be used from the module’s initialization function.
     Return ‘-1’ on error, ‘0’ on success.

 -- C Function: int PyModule_AddStringConstant (PyObject *module, const
          char *name, const char *value)

     Add a string constant to `module' as `name'.  This convenience
     function can be used from the module’s initialization function.
     The string `value' must be ‘NULL’-terminated.  Return ‘-1’ on
     error, ‘0’ on success.

 -- C Function: int PyModule_AddIntMacro (PyObject *module, macro)

     Add an int constant to `module'.  The name and the value are taken
     from `macro'.  For example ‘PyModule_AddIntMacro(module, AF_INET)’
     adds the int constant `AF_INET' with the value of `AF_INET' to
     `module'.  Return ‘-1’ on error, ‘0’ on success.

 -- C Function: int PyModule_AddStringMacro (PyObject *module, macro)

     Add a string constant to `module'.

 -- C Function: int PyModule_AddType (PyObject *module,
          PyTypeObject *type)

     Add a type object to `module'.  The type object is finalized by
     calling internally *note PyType_Ready(): 3d59.  The name of the
     type object is taken from the last component of *note tp_name:
     3d71. after dot.  Return ‘-1’ on error, ‘0’ on success.

     New in version 3.9.


File: python.info,  Node: Module lookup,  Prev: Initializing C modules,  Up: Module Objects

7.8.6.8 Module lookup
.....................

Single-phase initialization creates singleton modules that can be looked
up in the context of the current interpreter.  This allows the module
object to be retrieved later with only a reference to the module
definition.

These functions will not work on modules created using multi-phase
initialization, since multiple such modules can be created from a single
definition.

 -- C Function: PyObject* PyState_FindModule (PyModuleDef *def)
     `Return value: Borrowed reference.'  Returns the module object that
     was created from `def' for the current interpreter.  This method
     requires that the module object has been attached to the
     interpreter state with *note PyState_AddModule(): 40fb. beforehand.
     In case the corresponding module object is not found or has not
     been attached to the interpreter state yet, it returns ‘NULL’.

 -- C Function: int PyState_AddModule (PyObject *module,
          PyModuleDef *def)

     Attaches the module object passed to the function to the
     interpreter state.  This allows the module object to be accessible
     via *note PyState_FindModule(): 40fa.

     Only effective on modules created using single-phase
     initialization.

     Python calls ‘PyState_AddModule’ automatically after importing a
     module, so it is unnecessary (but harmless) to call it from module
     initialization code.  An explicit call is needed only if the
     module’s own init code subsequently calls ‘PyState_FindModule’.
     The function is mainly intended for implementing alternative import
     mechanisms (either by calling it directly, or by referring to its
     implementation for details of the required state updates).

     The caller must hold the GIL.

     Return 0 on success or -1 on failure.

     New in version 3.3.

 -- C Function: int PyState_RemoveModule (PyModuleDef *def)

     Removes the module object created from `def' from the interpreter
     state.  Return 0 on success or -1 on failure.

     The caller must hold the GIL.

     New in version 3.3.


File: python.info,  Node: Iterator Objects,  Next: Descriptor Objects,  Prev: Module Objects,  Up: Other Objects

7.8.6.9 Iterator Objects
........................

Python provides two general-purpose iterator objects.  The first, a
sequence iterator, works with an arbitrary sequence supporting the *note
__getitem__(): 3a2. method.  The second works with a callable object and
a sentinel value, calling the callable for each item in the sequence,
and ending the iteration when the sentinel value is returned.

 -- C Variable: PyTypeObject PySeqIter_Type

     Type object for iterator objects returned by *note PySeqIter_New():
     4101. and the one-argument form of the *note iter(): ded. built-in
     function for built-in sequence types.

 -- C Function: int PySeqIter_Check (op)

     Return true if the type of `op' is *note PySeqIter_Type: 4100.
     This function always succeeds.

 -- C Function: PyObject* PySeqIter_New (PyObject *seq)
     `Return value: New reference.'  Return an iterator that works with
     a general sequence object, `seq'.  The iteration ends when the
     sequence raises *note IndexError: f36. for the subscripting
     operation.

 -- C Variable: PyTypeObject PyCallIter_Type

     Type object for iterator objects returned by *note
     PyCallIter_New(): 4104. and the two-argument form of the *note
     iter(): ded. built-in function.

 -- C Function: int PyCallIter_Check (op)

     Return true if the type of `op' is *note PyCallIter_Type: 4103.
     This function always succeeds.

 -- C Function: PyObject* PyCallIter_New (PyObject *callable,
          PyObject *sentinel)
     `Return value: New reference.'  Return a new iterator.  The first
     parameter, `callable', can be any Python callable object that can
     be called with no parameters; each call to it should return the
     next item in the iteration.  When `callable' returns a value equal
     to `sentinel', the iteration will be terminated.


File: python.info,  Node: Descriptor Objects,  Next: Slice Objects,  Prev: Iterator Objects,  Up: Other Objects

7.8.6.10 Descriptor Objects
...........................

“Descriptors” are objects that describe some attribute of an object.
They are found in the dictionary of type objects.

 -- C Variable: PyTypeObject PyProperty_Type

     The type object for the built-in descriptor types.

 -- C Function: PyObject* PyDescr_NewGetSet (PyTypeObject *type, struct
          PyGetSetDef *getset)
     `Return value: New reference.'

 -- C Function: PyObject* PyDescr_NewMember (PyTypeObject *type, struct
          PyMemberDef *meth)
     `Return value: New reference.'

 -- C Function: PyObject* PyDescr_NewMethod (PyTypeObject *type, struct
          PyMethodDef *meth)
     `Return value: New reference.'

 -- C Function: PyObject* PyDescr_NewWrapper (PyTypeObject *type, struct
          wrapperbase *wrapper, void *wrapped)
     `Return value: New reference.'

 -- C Function: PyObject* PyDescr_NewClassMethod (PyTypeObject *type,
          PyMethodDef *method)
     `Return value: New reference.'

 -- C Function: int PyDescr_IsData (PyObject *descr)

     Return true if the descriptor objects `descr' describes a data
     attribute, or false if it describes a method.  `descr' must be a
     descriptor object; there is no error checking.

 -- C Function: PyObject* PyWrapper_New (PyObject *, PyObject *)
     `Return value: New reference.'


File: python.info,  Node: Slice Objects,  Next: Ellipsis Object,  Prev: Descriptor Objects,  Up: Other Objects

7.8.6.11 Slice Objects
......................

 -- C Variable: PyTypeObject PySlice_Type

     The type object for slice objects.  This is the same as *note
     slice: ec8. in the Python layer.

 -- C Function: int PySlice_Check (PyObject *ob)

     Return true if `ob' is a slice object; `ob' must not be ‘NULL’.
     This function always succeeds.

 -- C Function: PyObject* PySlice_New (PyObject *start, PyObject *stop,
          PyObject *step)
     `Return value: New reference.'  Return a new slice object with the
     given values.  The `start', `stop', and `step' parameters are used
     as the values of the slice object attributes of the same names.
     Any of the values may be ‘NULL’, in which case the ‘None’ will be
     used for the corresponding attribute.  Return ‘NULL’ if the new
     object could not be allocated.

 -- C Function: int PySlice_GetIndices (PyObject *slice,
          Py_ssize_t length, Py_ssize_t *start, Py_ssize_t *stop,
          Py_ssize_t *step)

     Retrieve the start, stop and step indices from the slice object
     `slice', assuming a sequence of length `length'.  Treats indices
     greater than `length' as errors.

     Returns ‘0’ on success and ‘-1’ on error with no exception set
     (unless one of the indices was not *note None: 203. and failed to
     be converted to an integer, in which case ‘-1’ is returned with an
     exception set).

     You probably do not want to use this function.

     Changed in version 3.2: The parameter type for the `slice'
     parameter was ‘PySliceObject*’ before.

 -- C Function: int PySlice_GetIndicesEx (PyObject *slice,
          Py_ssize_t length, Py_ssize_t *start, Py_ssize_t *stop,
          Py_ssize_t *step, Py_ssize_t *slicelength)

     Usable replacement for *note PySlice_GetIndices(): 4116.  Retrieve
     the start, stop, and step indices from the slice object `slice'
     assuming a sequence of length `length', and store the length of the
     slice in `slicelength'.  Out of bounds indices are clipped in a
     manner consistent with the handling of normal slices.

     Returns ‘0’ on success and ‘-1’ on error with exception set.

          Note: This function is considered not safe for resizable
          sequences.  Its invocation should be replaced by a combination
          of *note PySlice_Unpack(): 533. and *note
          PySlice_AdjustIndices(): 534. where

               if (PySlice_GetIndicesEx(slice, length, &start, &stop, &step, &slicelength) < 0) {
                   // return error
               }

          is replaced by

               if (PySlice_Unpack(slice, &start, &stop, &step) < 0) {
                   // return error
               }
               slicelength = PySlice_AdjustIndices(length, &start, &stop, step);

     Changed in version 3.2: The parameter type for the `slice'
     parameter was ‘PySliceObject*’ before.

     Changed in version 3.6.1: If ‘Py_LIMITED_API’ is not set or set to
     the value between ‘0x03050400’ and ‘0x03060000’ (not including) or
     ‘0x03060100’ or higher ‘PySlice_GetIndicesEx()’ is implemented as a
     macro using ‘PySlice_Unpack()’ and ‘PySlice_AdjustIndices()’.
     Arguments `start', `stop' and `step' are evaluated more than once.

     Deprecated since version 3.6.1: If ‘Py_LIMITED_API’ is set to the
     value less than ‘0x03050400’ or between ‘0x03060000’ and
     ‘0x03060100’ (not including) ‘PySlice_GetIndicesEx()’ is a
     deprecated function.

 -- C Function: int PySlice_Unpack (PyObject *slice, Py_ssize_t *start,
          Py_ssize_t *stop, Py_ssize_t *step)

     Extract the start, stop and step data members from a slice object
     as C integers.  Silently reduce values larger than ‘PY_SSIZE_T_MAX’
     to ‘PY_SSIZE_T_MAX’, silently boost the start and stop values less
     than ‘PY_SSIZE_T_MIN’ to ‘PY_SSIZE_T_MIN’, and silently boost the
     step values less than ‘-PY_SSIZE_T_MAX’ to ‘-PY_SSIZE_T_MAX’.

     Return ‘-1’ on error, ‘0’ on success.

     New in version 3.6.1.

 -- C Function: Py_ssize_t PySlice_AdjustIndices (Py_ssize_t length,
          Py_ssize_t *start, Py_ssize_t *stop, Py_ssize_t step)

     Adjust start/end slice indices assuming a sequence of the specified
     length.  Out of bounds indices are clipped in a manner consistent
     with the handling of normal slices.

     Return the length of the slice.  Always successful.  Doesn’t call
     Python code.

     New in version 3.6.1.


File: python.info,  Node: Ellipsis Object,  Next: MemoryView objects,  Prev: Slice Objects,  Up: Other Objects

7.8.6.12 Ellipsis Object
........................

 -- C Variable: PyObject *Py_Ellipsis

     The Python ‘Ellipsis’ object.  This object has no methods.  It
     needs to be treated just like any other object with respect to
     reference counts.  Like *note Py_None: 3d1f. it is a singleton
     object.


File: python.info,  Node: MemoryView objects,  Next: Weak Reference Objects<2>,  Prev: Ellipsis Object,  Up: Other Objects

7.8.6.13 MemoryView objects
...........................

A *note memoryview: 386. object exposes the C level *note buffer
interface: 171c. as a Python object which can then be passed around like
any other object.

 -- C Function: PyObject *PyMemoryView_FromObject (PyObject *obj)
     `Return value: New reference.'  Create a memoryview object from an
     object that provides the buffer interface.  If `obj' supports
     writable buffer exports, the memoryview object will be read/write,
     otherwise it may be either read-only or read/write at the
     discretion of the exporter.

 -- C Function: PyObject *PyMemoryView_FromMemory (char *mem,
          Py_ssize_t size, int flags)
     `Return value: New reference.'  Create a memoryview object using
     `mem' as the underlying buffer.  `flags' can be one of ‘PyBUF_READ’
     or ‘PyBUF_WRITE’.

     New in version 3.3.

 -- C Function: PyObject *PyMemoryView_FromBuffer (Py_buffer *view)
     `Return value: New reference.'  Create a memoryview object wrapping
     the given buffer structure `view'.  For simple byte buffers, *note
     PyMemoryView_FromMemory(): ba0. is the preferred function.

 -- C Function: PyObject *PyMemoryView_GetContiguous (PyObject *obj,
          int buffertype, char order)
     `Return value: New reference.'  Create a memoryview object to a
     *note contiguous: 17ec. chunk of memory (in either ‘C’ or ‘F’ortran
     `order') from an object that defines the buffer interface.  If
     memory is contiguous, the memoryview object points to the original
     memory.  Otherwise, a copy is made and the memoryview points to a
     new bytes object.

 -- C Function: int PyMemoryView_Check (PyObject *obj)

     Return true if the object `obj' is a memoryview object.  It is not
     currently allowed to create subclasses of *note memoryview: 386.
     This function always succeeds.

 -- C Function: Py_buffer *PyMemoryView_GET_BUFFER (PyObject *mview)

     Return a pointer to the memoryview’s private copy of the exporter’s
     buffer.  `mview' `must' be a memoryview instance; this macro
     doesn’t check its type, you must do it yourself or you will risk
     crashes.

 -- C Function: Py_buffer *PyMemoryView_GET_BASE (PyObject *mview)

     Return either a pointer to the exporting object that the memoryview
     is based on or ‘NULL’ if the memoryview has been created by one of
     the functions *note PyMemoryView_FromMemory(): ba0. or *note
     PyMemoryView_FromBuffer(): 3f3f.  `mview' `must' be a memoryview
     instance.


File: python.info,  Node: Weak Reference Objects<2>,  Next: Capsules<2>,  Prev: MemoryView objects,  Up: Other Objects

7.8.6.14 Weak Reference Objects
...............................

Python supports `weak references' as first-class objects.  There are two
specific object types which directly implement weak references.  The
first is a simple reference object, and the second acts as a proxy for
the original object as much as it can.

 -- C Function: int PyWeakref_Check (ob)

     Return true if `ob' is either a reference or proxy object.  This
     function always succeeds.

 -- C Function: int PyWeakref_CheckRef (ob)

     Return true if `ob' is a reference object.  This function always
     succeeds.

 -- C Function: int PyWeakref_CheckProxy (ob)

     Return true if `ob' is a proxy object.  This function always
     succeeds.

 -- C Function: PyObject* PyWeakref_NewRef (PyObject *ob,
          PyObject *callback)
     `Return value: New reference.'  Return a weak reference object for
     the object `ob'.  This will always return a new reference, but is
     not guaranteed to create a new object; an existing reference object
     may be returned.  The second parameter, `callback', can be a
     callable object that receives notification when `ob' is garbage
     collected; it should accept a single parameter, which will be the
     weak reference object itself.  `callback' may also be ‘None’ or
     ‘NULL’.  If `ob' is not a weakly-referencable object, or if
     `callback' is not callable, ‘None’, or ‘NULL’, this will return
     ‘NULL’ and raise *note TypeError: 1fe.

 -- C Function: PyObject* PyWeakref_NewProxy (PyObject *ob,
          PyObject *callback)
     `Return value: New reference.'  Return a weak reference proxy
     object for the object `ob'.  This will always return a new
     reference, but is not guaranteed to create a new object; an
     existing proxy object may be returned.  The second parameter,
     `callback', can be a callable object that receives notification
     when `ob' is garbage collected; it should accept a single
     parameter, which will be the weak reference object itself.
     `callback' may also be ‘None’ or ‘NULL’.  If `ob' is not a
     weakly-referencable object, or if `callback' is not callable,
     ‘None’, or ‘NULL’, this will return ‘NULL’ and raise *note
     TypeError: 1fe.

 -- C Function: PyObject* PyWeakref_GetObject (PyObject *ref)
     `Return value: Borrowed reference.'  Return the referenced object
     from a weak reference, `ref'.  If the referent is no longer live,
     returns ‘Py_None’.

          Note: This function returns a `borrowed reference' to the
          referenced object.  This means that you should always call
          *note Py_INCREF(): 38e. on the object except if you know that
          it cannot be destroyed while you are still using it.

 -- C Function: PyObject* PyWeakref_GET_OBJECT (PyObject *ref)
     `Return value: Borrowed reference.'  Similar to *note
     PyWeakref_GetObject(): 4128, but implemented as a macro that does
     no error checking.


File: python.info,  Node: Capsules<2>,  Next: Generator Objects,  Prev: Weak Reference Objects<2>,  Up: Other Objects

7.8.6.15 Capsules
.................

Refer to *note Providing a C API for an Extension Module: db7. for more
information on using these objects.

New in version 3.1.

 -- C Type: PyCapsule

     This subtype of *note PyObject: 5b5. represents an opaque value,
     useful for C extension modules who need to pass an opaque value (as
     a ‘void*’ pointer) through Python code to other C code.  It is
     often used to make a C function pointer defined in one module
     available to other modules, so the regular import mechanism can be
     used to access C APIs defined in dynamically loaded modules.

 -- C Type: PyCapsule_Destructor

     The type of a destructor callback for a capsule.  Defined as:

          typedef void (*PyCapsule_Destructor)(PyObject *);

     See *note PyCapsule_New(): 3d45. for the semantics of
     PyCapsule_Destructor callbacks.

 -- C Function: int PyCapsule_CheckExact (PyObject *p)

     Return true if its argument is a *note PyCapsule: cd2.  This
     function always succeeds.

 -- C Function: PyObject* PyCapsule_New (void *pointer, const
          char *name, PyCapsule_Destructor destructor)
     `Return value: New reference.'  Create a *note PyCapsule: cd2.
     encapsulating the `pointer'.  The `pointer' argument may not be
     ‘NULL’.

     On failure, set an exception and return ‘NULL’.

     The `name' string may either be ‘NULL’ or a pointer to a valid C
     string.  If non-‘NULL’, this string must outlive the capsule.
     (Though it is permitted to free it inside the `destructor'.)

     If the `destructor' argument is not ‘NULL’, it will be called with
     the capsule as its argument when it is destroyed.

     If this capsule will be stored as an attribute of a module, the
     `name' should be specified as ‘modulename.attributename’.  This
     will enable other modules to import the capsule using *note
     PyCapsule_Import(): 3d46.

 -- C Function: void* PyCapsule_GetPointer (PyObject *capsule, const
          char *name)

     Retrieve the `pointer' stored in the capsule.  On failure, set an
     exception and return ‘NULL’.

     The `name' parameter must compare exactly to the name stored in the
     capsule.  If the name stored in the capsule is ‘NULL’, the `name'
     passed in must also be ‘NULL’.  Python uses the C function
     ‘strcmp()’ to compare capsule names.

 -- C Function: PyCapsule_Destructor PyCapsule_GetDestructor
          (PyObject *capsule)

     Return the current destructor stored in the capsule.  On failure,
     set an exception and return ‘NULL’.

     It is legal for a capsule to have a ‘NULL’ destructor.  This makes
     a ‘NULL’ return code somewhat ambiguous; use *note
     PyCapsule_IsValid(): db6. or *note PyErr_Occurred(): 3d1a. to
     disambiguate.

 -- C Function: void* PyCapsule_GetContext (PyObject *capsule)

     Return the current context stored in the capsule.  On failure, set
     an exception and return ‘NULL’.

     It is legal for a capsule to have a ‘NULL’ context.  This makes a
     ‘NULL’ return code somewhat ambiguous; use *note
     PyCapsule_IsValid(): db6. or *note PyErr_Occurred(): 3d1a. to
     disambiguate.

 -- C Function: const char* PyCapsule_GetName (PyObject *capsule)

     Return the current name stored in the capsule.  On failure, set an
     exception and return ‘NULL’.

     It is legal for a capsule to have a ‘NULL’ name.  This makes a
     ‘NULL’ return code somewhat ambiguous; use *note
     PyCapsule_IsValid(): db6. or *note PyErr_Occurred(): 3d1a. to
     disambiguate.

 -- C Function: void* PyCapsule_Import (const char *name, int no_block)

     Import a pointer to a C object from a capsule attribute in a
     module.  The `name' parameter should specify the full name to the
     attribute, as in ‘module.attribute’.  The `name' stored in the
     capsule must match this string exactly.  If `no_block' is true,
     import the module without blocking (using *note
     PyImport_ImportModuleNoBlock(): aa0.).  If `no_block' is false,
     import the module conventionally (using *note
     PyImport_ImportModule(): d3b.).

     Return the capsule’s internal `pointer' on success.  On failure,
     set an exception and return ‘NULL’.

 -- C Function: int PyCapsule_IsValid (PyObject *capsule, const
          char *name)

     Determines whether or not `capsule' is a valid capsule.  A valid
     capsule is non-‘NULL’, passes *note PyCapsule_CheckExact(): 412d,
     has a non-‘NULL’ pointer stored in it, and its internal name
     matches the `name' parameter.  (See *note PyCapsule_GetPointer():
     412e. for information on how capsule names are compared.)

     In other words, if *note PyCapsule_IsValid(): db6. returns a true
     value, calls to any of the accessors (any function starting with
     ‘PyCapsule_Get()’) are guaranteed to succeed.

     Return a nonzero value if the object is valid and matches the name
     passed in.  Return ‘0’ otherwise.  This function will not fail.

 -- C Function: int PyCapsule_SetContext (PyObject *capsule,
          void *context)

     Set the context pointer inside `capsule' to `context'.

     Return ‘0’ on success.  Return nonzero and set an exception on
     failure.

 -- C Function: int PyCapsule_SetDestructor (PyObject *capsule,
          PyCapsule_Destructor destructor)

     Set the destructor inside `capsule' to `destructor'.

     Return ‘0’ on success.  Return nonzero and set an exception on
     failure.

 -- C Function: int PyCapsule_SetName (PyObject *capsule, const
          char *name)

     Set the name inside `capsule' to `name'.  If non-‘NULL’, the name
     must outlive the capsule.  If the previous `name' stored in the
     capsule was not ‘NULL’, no attempt is made to free it.

     Return ‘0’ on success.  Return nonzero and set an exception on
     failure.

 -- C Function: int PyCapsule_SetPointer (PyObject *capsule,
          void *pointer)

     Set the void pointer inside `capsule' to `pointer'.  The pointer
     may not be ‘NULL’.

     Return ‘0’ on success.  Return nonzero and set an exception on
     failure.


File: python.info,  Node: Generator Objects,  Next: Coroutine Objects<2>,  Prev: Capsules<2>,  Up: Other Objects

7.8.6.16 Generator Objects
..........................

Generator objects are what Python uses to implement generator iterators.
They are normally created by iterating over a function that yields
values, rather than explicitly calling *note PyGen_New(): 4139. or *note
PyGen_NewWithQualName(): 413a.

 -- C Type: PyGenObject

     The C structure used for generator objects.

 -- C Variable: PyTypeObject PyGen_Type

     The type object corresponding to generator objects.

 -- C Function: int PyGen_Check (PyObject *ob)

     Return true if `ob' is a generator object; `ob' must not be ‘NULL’.
     This function always succeeds.

 -- C Function: int PyGen_CheckExact (PyObject *ob)

     Return true if `ob'’s type is *note PyGen_Type: 413c.; `ob' must
     not be ‘NULL’.  This function always succeeds.

 -- C Function: PyObject* PyGen_New (PyFrameObject *frame)
     `Return value: New reference.'  Create and return a new generator
     object based on the `frame' object.  A reference to `frame' is
     stolen by this function.  The argument must not be ‘NULL’.

 -- C Function: PyObject* PyGen_NewWithQualName (PyFrameObject *frame,
          PyObject *name, PyObject *qualname)
     `Return value: New reference.'  Create and return a new generator
     object based on the `frame' object, with ‘__name__’ and
     ‘__qualname__’ set to `name' and `qualname'.  A reference to
     `frame' is stolen by this function.  The `frame' argument must not
     be ‘NULL’.


File: python.info,  Node: Coroutine Objects<2>,  Next: Context Variables Objects,  Prev: Generator Objects,  Up: Other Objects

7.8.6.17 Coroutine Objects
..........................

New in version 3.5.

Coroutine objects are what functions declared with an ‘async’ keyword
return.

 -- C Type: PyCoroObject

     The C structure used for coroutine objects.

 -- C Variable: PyTypeObject PyCoro_Type

     The type object corresponding to coroutine objects.

 -- C Function: int PyCoro_CheckExact (PyObject *ob)

     Return true if `ob'’s type is *note PyCoro_Type: 4142.; `ob' must
     not be ‘NULL’.  This function always succeeds.

 -- C Function: PyObject* PyCoro_New (PyFrameObject *frame,
          PyObject *name, PyObject *qualname)
     `Return value: New reference.'  Create and return a new coroutine
     object based on the `frame' object, with ‘__name__’ and
     ‘__qualname__’ set to `name' and `qualname'.  A reference to
     `frame' is stolen by this function.  The `frame' argument must not
     be ‘NULL’.


File: python.info,  Node: Context Variables Objects,  Next: DateTime Objects<2>,  Prev: Coroutine Objects<2>,  Up: Other Objects

7.8.6.18 Context Variables Objects
..................................

     Note Changed in version 3.7.1:: In Python 3.7.1 the signatures of
     all context variables C APIs were `changed' to use *note PyObject:
     5b5. pointers instead of *note PyContext: 4147, *note PyContextVar:
     4148, and *note PyContextToken: 4149, e.g.:

          // in 3.7.0:
          PyContext *PyContext_New(void);

          // in 3.7.1+:
          PyObject *PyContext_New(void);

     See bpo-34762(1) for more details.

New in version 3.7.

This section details the public C API for the *note contextvars: 24.
module.

 -- C Type: PyContext

     The C structure used to represent a *note contextvars.Context:
     260f. object.

 -- C Type: PyContextVar

     The C structure used to represent a *note contextvars.ContextVar:
     260d. object.

 -- C Type: PyContextToken

     The C structure used to represent a *note contextvars.Token: 2614.
     object.

 -- C Variable: PyTypeObject PyContext_Type

     The type object representing the `context' type.

 -- C Variable: PyTypeObject PyContextVar_Type

     The type object representing the `context variable' type.

 -- C Variable: PyTypeObject PyContextToken_Type

     The type object representing the `context variable token' type.

Type-check macros:

 -- C Function: int PyContext_CheckExact (PyObject *o)

     Return true if `o' is of type *note PyContext_Type: 414a.  `o' must
     not be ‘NULL’.  This function always succeeds.

 -- C Function: int PyContextVar_CheckExact (PyObject *o)

     Return true if `o' is of type *note PyContextVar_Type: 414b.  `o'
     must not be ‘NULL’.  This function always succeeds.

 -- C Function: int PyContextToken_CheckExact (PyObject *o)

     Return true if `o' is of type *note PyContextToken_Type: 414c.  `o'
     must not be ‘NULL’.  This function always succeeds.

Context object management functions:

 -- C Function: PyObject *PyContext_New (void)
     `Return value: New reference.'  Create a new empty context object.
     Returns ‘NULL’ if an error has occurred.

 -- C Function: PyObject *PyContext_Copy (PyObject *ctx)
     `Return value: New reference.'  Create a shallow copy of the passed
     `ctx' context object.  Returns ‘NULL’ if an error has occurred.

 -- C Function: PyObject *PyContext_CopyCurrent (void)
     `Return value: New reference.'  Create a shallow copy of the
     current thread context.  Returns ‘NULL’ if an error has occurred.

 -- C Function: int PyContext_Enter (PyObject *ctx)

     Set `ctx' as the current context for the current thread.  Returns
     ‘0’ on success, and ‘-1’ on error.

 -- C Function: int PyContext_Exit (PyObject *ctx)

     Deactivate the `ctx' context and restore the previous context as
     the current context for the current thread.  Returns ‘0’ on
     success, and ‘-1’ on error.

Context variable functions:

 -- C Function: PyObject *PyContextVar_New (const char *name,
          PyObject *def)
     `Return value: New reference.'  Create a new ‘ContextVar’ object.
     The `name' parameter is used for introspection and debug purposes.
     The `def' parameter specifies a default value for the context
     variable, or ‘NULL’ for no default.  If an error has occurred, this
     function returns ‘NULL’.

 -- C Function: int PyContextVar_Get (PyObject *var,
          PyObject *default_value, PyObject **value)

     Get the value of a context variable.  Returns ‘-1’ if an error has
     occurred during lookup, and ‘0’ if no error occurred, whether or
     not a value was found.

     If the context variable was found, `value' will be a pointer to it.
     If the context variable was `not' found, `value' will point to:

        - `default_value', if not ‘NULL’;

        - the default value of `var', if not ‘NULL’;

        - ‘NULL’

     Except for ‘NULL’, the function returns a new reference.

 -- C Function: PyObject *PyContextVar_Set (PyObject *var,
          PyObject *value)
     `Return value: New reference.'  Set the value of `var' to `value'
     in the current context.  Returns a new token object for this
     change, or ‘NULL’ if an error has occurred.

 -- C Function: int PyContextVar_Reset (PyObject *var, PyObject *token)

     Reset the state of the `var' context variable to that it was in
     before *note PyContextVar_Set(): 4157. that returned the `token'
     was called.  This function returns ‘0’ on success and ‘-1’ on
     error.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue34762


File: python.info,  Node: DateTime Objects<2>,  Next: Objects for Type Hinting,  Prev: Context Variables Objects,  Up: Other Objects

7.8.6.19 DateTime Objects
.........................

Various date and time objects are supplied by the *note datetime: 30.
module.  Before using any of these functions, the header file
‘datetime.h’ must be included in your source (note that this is not
included by ‘Python.h’), and the macro ‘PyDateTime_IMPORT’ must be
invoked, usually as part of the module initialisation function.  The
macro puts a pointer to a C structure into a static variable,
‘PyDateTimeAPI’, that is used by the following macros.

Macro for access to the UTC singleton:

 -- C Variable: PyObject* PyDateTime_TimeZone_UTC

     Returns the time zone singleton representing UTC, the same object
     as *note datetime.timezone.utc: 1a28.

     New in version 3.7.

Type-check macros:

 -- C Function: int PyDate_Check (PyObject *ob)

     Return true if `ob' is of type ‘PyDateTime_DateType’ or a subtype
     of ‘PyDateTime_DateType’.  `ob' must not be ‘NULL’.  This function
     always succeeds.

 -- C Function: int PyDate_CheckExact (PyObject *ob)

     Return true if `ob' is of type ‘PyDateTime_DateType’.  `ob' must
     not be ‘NULL’.  This function always succeeds.

 -- C Function: int PyDateTime_Check (PyObject *ob)

     Return true if `ob' is of type ‘PyDateTime_DateTimeType’ or a
     subtype of ‘PyDateTime_DateTimeType’.  `ob' must not be ‘NULL’.
     This function always succeeds.

 -- C Function: int PyDateTime_CheckExact (PyObject *ob)

     Return true if `ob' is of type ‘PyDateTime_DateTimeType’.  `ob'
     must not be ‘NULL’.  This function always succeeds.

 -- C Function: int PyTime_Check (PyObject *ob)

     Return true if `ob' is of type ‘PyDateTime_TimeType’ or a subtype
     of ‘PyDateTime_TimeType’.  `ob' must not be ‘NULL’.  This function
     always succeeds.

 -- C Function: int PyTime_CheckExact (PyObject *ob)

     Return true if `ob' is of type ‘PyDateTime_TimeType’.  `ob' must
     not be ‘NULL’.  This function always succeeds.

 -- C Function: int PyDelta_Check (PyObject *ob)

     Return true if `ob' is of type ‘PyDateTime_DeltaType’ or a subtype
     of ‘PyDateTime_DeltaType’.  `ob' must not be ‘NULL’.  This function
     always succeeds.

 -- C Function: int PyDelta_CheckExact (PyObject *ob)

     Return true if `ob' is of type ‘PyDateTime_DeltaType’.  `ob' must
     not be ‘NULL’.  This function always succeeds.

 -- C Function: int PyTZInfo_Check (PyObject *ob)

     Return true if `ob' is of type ‘PyDateTime_TZInfoType’ or a subtype
     of ‘PyDateTime_TZInfoType’.  `ob' must not be ‘NULL’.  This
     function always succeeds.

 -- C Function: int PyTZInfo_CheckExact (PyObject *ob)

     Return true if `ob' is of type ‘PyDateTime_TZInfoType’.  `ob' must
     not be ‘NULL’.  This function always succeeds.

Macros to create objects:

 -- C Function: PyObject* PyDate_FromDate (int year, int month, int day)
     `Return value: New reference.'  Return a *note datetime.date: 19e.
     object with the specified year, month and day.

 -- C Function: PyObject* PyDateTime_FromDateAndTime (int year,
          int month, int day, int hour, int minute, int second,
          int usecond)
     `Return value: New reference.'  Return a *note datetime.datetime:
     1a0. object with the specified year, month, day, hour, minute,
     second and microsecond.

 -- C Function: PyObject* PyDateTime_FromDateAndTimeAndFold (int year,
          int month, int day, int hour, int minute, int second,
          int usecond, int fold)
     `Return value: New reference.'  Return a *note datetime.datetime:
     1a0. object with the specified year, month, day, hour, minute,
     second, microsecond and fold.

     New in version 3.6.

 -- C Function: PyObject* PyTime_FromTime (int hour, int minute,
          int second, int usecond)
     `Return value: New reference.'  Return a *note datetime.time: 5ed.
     object with the specified hour, minute, second and microsecond.

 -- C Function: PyObject* PyTime_FromTimeAndFold (int hour, int minute,
          int second, int usecond, int fold)
     `Return value: New reference.'  Return a *note datetime.time: 5ed.
     object with the specified hour, minute, second, microsecond and
     fold.

     New in version 3.6.

 -- C Function: PyObject* PyDelta_FromDSU (int days, int seconds,
          int useconds)
     `Return value: New reference.'  Return a *note datetime.timedelta:
     2ca. object representing the given number of days, seconds and
     microseconds.  Normalization is performed so that the resulting
     number of microseconds and seconds lie in the ranges documented for
     *note datetime.timedelta: 2ca. objects.

 -- C Function: PyObject* PyTimeZone_FromOffset
          (PyDateTime_DeltaType* offset)
     `Return value: New reference.'  Return a *note datetime.timezone:
     ae0. object with an unnamed fixed offset represented by the
     `offset' argument.

     New in version 3.7.

 -- C Function: PyObject* PyTimeZone_FromOffsetAndName
          (PyDateTime_DeltaType* offset, PyUnicode* name)
     `Return value: New reference.'  Return a *note datetime.timezone:
     ae0. object with a fixed offset represented by the `offset'
     argument and with tzname `name'.

     New in version 3.7.

Macros to extract fields from date objects.  The argument must be an
instance of ‘PyDateTime_Date’, including subclasses (such as
‘PyDateTime_DateTime’).  The argument must not be ‘NULL’, and the type
is not checked:

 -- C Function: int PyDateTime_GET_YEAR (PyDateTime_Date *o)

     Return the year, as a positive int.

 -- C Function: int PyDateTime_GET_MONTH (PyDateTime_Date *o)

     Return the month, as an int from 1 through 12.

 -- C Function: int PyDateTime_GET_DAY (PyDateTime_Date *o)

     Return the day, as an int from 1 through 31.

Macros to extract fields from datetime objects.  The argument must be an
instance of ‘PyDateTime_DateTime’, including subclasses.  The argument
must not be ‘NULL’, and the type is not checked:

 -- C Function: int PyDateTime_DATE_GET_HOUR (PyDateTime_DateTime *o)

     Return the hour, as an int from 0 through 23.

 -- C Function: int PyDateTime_DATE_GET_MINUTE (PyDateTime_DateTime *o)

     Return the minute, as an int from 0 through 59.

 -- C Function: int PyDateTime_DATE_GET_SECOND (PyDateTime_DateTime *o)

     Return the second, as an int from 0 through 59.

 -- C Function: int PyDateTime_DATE_GET_MICROSECOND
          (PyDateTime_DateTime *o)

     Return the microsecond, as an int from 0 through 999999.

Macros to extract fields from time objects.  The argument must be an
instance of ‘PyDateTime_Time’, including subclasses.  The argument must
not be ‘NULL’, and the type is not checked:

 -- C Function: int PyDateTime_TIME_GET_HOUR (PyDateTime_Time *o)

     Return the hour, as an int from 0 through 23.

 -- C Function: int PyDateTime_TIME_GET_MINUTE (PyDateTime_Time *o)

     Return the minute, as an int from 0 through 59.

 -- C Function: int PyDateTime_TIME_GET_SECOND (PyDateTime_Time *o)

     Return the second, as an int from 0 through 59.

 -- C Function: int PyDateTime_TIME_GET_MICROSECOND (PyDateTime_Time *o)

     Return the microsecond, as an int from 0 through 999999.

Macros to extract fields from time delta objects.  The argument must be
an instance of ‘PyDateTime_Delta’, including subclasses.  The argument
must not be ‘NULL’, and the type is not checked:

 -- C Function: int PyDateTime_DELTA_GET_DAYS (PyDateTime_Delta *o)

     Return the number of days, as an int from -999999999 to 999999999.

     New in version 3.3.

 -- C Function: int PyDateTime_DELTA_GET_SECONDS (PyDateTime_Delta *o)

     Return the number of seconds, as an int from 0 through 86399.

     New in version 3.3.

 -- C Function: int PyDateTime_DELTA_GET_MICROSECONDS
          (PyDateTime_Delta *o)

     Return the number of microseconds, as an int from 0 through 999999.

     New in version 3.3.

Macros for the convenience of modules implementing the DB API:

 -- C Function: PyObject* PyDateTime_FromTimestamp (PyObject *args)
     `Return value: New reference.'  Create and return a new *note
     datetime.datetime: 1a0. object given an argument tuple suitable for
     passing to *note datetime.datetime.fromtimestamp(): 11c0.

 -- C Function: PyObject* PyDate_FromTimestamp (PyObject *args)
     `Return value: New reference.'  Create and return a new *note
     datetime.date: 19e. object given an argument tuple suitable for
     passing to *note datetime.date.fromtimestamp(): 19e9.


File: python.info,  Node: Objects for Type Hinting,  Prev: DateTime Objects<2>,  Up: Other Objects

7.8.6.20 Objects for Type Hinting
.................................

Various built-in types for type hinting are provided.  Only *note
GenericAlias: fe5. is exposed to C.

 -- C Function: PyObject* Py_GenericAlias (PyObject *origin,
          PyObject *args)

     Create a *note GenericAlias: fe5. object.  Equivalent to calling
     the Python class *note types.GenericAlias: 27c.  The `origin' and
     `args' arguments set the ‘GenericAlias’’s ‘__origin__’ and
     ‘__args__’ attributes respectively.  `origin' should be a *note
     PyTypeObject*: 3f5, and `args' can be a *note PyTupleObject*: 3e66.
     or any ‘PyObject*’.  If `args' passed is not a tuple, a 1-tuple is
     automatically constructed and ‘__args__’ is set to ‘(args,)’.
     Minimal checking is done for the arguments, so the function will
     succeed even if `origin' is not a type.  The ‘GenericAlias’’s
     ‘__parameters__’ attribute is constructed lazily from ‘__args__’.
     On failure, an exception is raised and ‘NULL’ is returned.

     Here’s an example of how to make an extension type generic:

          ...
          static PyMethodDef my_obj_methods[] = {
              // Other methods.
              ...
              {"__class_getitem__", (PyCFunction)Py_GenericAlias, METH_O|METH_CLASS, "See PEP 585"}
              ...
          }

     See also
     ........

     The data model method *note __class_getitem__(): 437.

     New in version 3.9.

 -- C Variable: PyTypeObject Py_GenericAliasType

     The C type of the object returned by *note Py_GenericAlias(): 417e.
     Equivalent to *note types.GenericAlias: 27c. in Python.

     New in version 3.9.


File: python.info,  Node: Initialization Finalization and Threads,  Next: Python Initialization Configuration,  Prev: Concrete Objects Layer,  Up: Python/C API Reference Manual

7.9 Initialization, Finalization, and Threads
=============================================

See also *note Python Initialization Configuration: 2b6.

* Menu:

* Before Python Initialization::
* Global configuration variables::
* Initializing and finalizing the interpreter::
* Process-wide parameters::
* Thread State and the Global Interpreter Lock::
* Sub-interpreter support::
* Asynchronous Notifications::
* Profiling and Tracing::
* Advanced Debugger Support::
* Thread Local Storage Support::


File: python.info,  Node: Before Python Initialization,  Next: Global configuration variables,  Up: Initialization Finalization and Threads

7.9.1 Before Python Initialization
----------------------------------

In an application embedding Python, the *note Py_Initialize(): 20f.
function must be called before using any other Python/C API functions;
with the exception of a few functions and the *note global configuration
variables: 4184.

The following functions can be safely called before Python is
initialized:

   * Configuration functions:

        * *note PyImport_AppendInittab(): f9c.

        * *note PyImport_ExtendInittab(): f9d.

        * ‘PyInitFrozenExtensions()’

        * *note PyMem_SetAllocator(): 4185.

        * *note PyMem_SetupDebugHooks(): 604.

        * *note PyObject_SetArenaAllocator(): 4186.

        * *note Py_SetPath(): 39c.

        * *note Py_SetProgramName(): 10f2.

        * *note Py_SetPythonHome(): 10f1.

        * *note Py_SetStandardStreamEncoding(): a0a.

        * *note PySys_AddWarnOption(): 5ae.

        * *note PySys_AddXOption(): 3e64.

        * *note PySys_ResetWarnOptions(): 3e5d.

   * Informative functions:

        * *note Py_IsInitialized(): 3dd2.

        * *note PyMem_GetAllocator(): 4187.

        * *note PyObject_GetArenaAllocator(): 4188.

        * *note Py_GetBuildInfo(): e5f.

        * *note Py_GetCompiler(): 4189.

        * *note Py_GetCopyright(): 418a.

        * *note Py_GetPlatform(): 418b.

        * *note Py_GetVersion(): 418c.

   * Utilities:

        * *note Py_DecodeLocale(): 53f.

   * Memory allocators:

        * *note PyMem_RawMalloc(): a4e.

        * *note PyMem_RawRealloc(): a4f.

        * *note PyMem_RawCalloc(): 893.

        * *note PyMem_RawFree(): 3e57.

     Note: The following functions `should not be called' before *note
     Py_Initialize(): 20f.: *note Py_EncodeLocale(): 540, *note
     Py_GetPath(): 3dcf, *note Py_GetPrefix(): 3dd0, *note
     Py_GetExecPrefix(): 3dd1, *note Py_GetProgramFullPath(): 39e, *note
     Py_GetPythonHome(): 418d, *note Py_GetProgramName(): 39f. and *note
     PyEval_InitThreads(): 20c.


File: python.info,  Node: Global configuration variables,  Next: Initializing and finalizing the interpreter,  Prev: Before Python Initialization,  Up: Initialization Finalization and Threads

7.9.2 Global configuration variables
------------------------------------

Python has variables for the global configuration to control different
features and options.  By default, these flags are controlled by *note
command line options: 146e.

When a flag is set by an option, the value of the flag is the number of
times that the option was set.  For example, ‘-b’ sets *note
Py_BytesWarningFlag: 5af. to 1 and ‘-bb’ sets *note Py_BytesWarningFlag:
5af. to 2.

 -- C Variable: int Py_BytesWarningFlag

     Issue a warning when comparing *note bytes: 172. or *note
     bytearray: 173. with *note str: 205. or *note bytes: 172. with
     *note int: 204.  Issue an error if greater or equal to ‘2’.

     Set by the *note -b: 51a. option.

 -- C Variable: int Py_DebugFlag

     Turn on parser debugging output (for expert only, depending on
     compilation options).

     Set by the *note -d: 1476. option and the *note PYTHONDEBUG: 1477.
     environment variable.

 -- C Variable: int Py_DontWriteBytecodeFlag

     If set to non-zero, Python won’t try to write ‘.pyc’ files on the
     import of source modules.

     Set by the *note -B: dfe. option and the *note
     PYTHONDONTWRITEBYTECODE: dff. environment variable.

 -- C Variable: int Py_FrozenFlag

     Suppress error messages when calculating the module search path in
     *note Py_GetPath(): 3dcf.

     Private flag used by ‘_freeze_importlib’ and ‘frozenmain’ programs.

 -- C Variable: int Py_HashRandomizationFlag

     Set to ‘1’ if the *note PYTHONHASHSEED: aa4. environment variable
     is set to a non-empty string.

     If the flag is non-zero, read the *note PYTHONHASHSEED: aa4.
     environment variable to initialize the secret hash seed.

 -- C Variable: int Py_IgnoreEnvironmentFlag

     Ignore all ‘PYTHON*’ environment variables, e.g.  *note PYTHONPATH:
     a34. and *note PYTHONHOME: 5d1, that might be set.

     Set by the *note -E: 231. and *note -I: 232. options.

 -- C Variable: int Py_InspectFlag

     When a script is passed as first argument or the *note -c: 1340.
     option is used, enter interactive mode after executing the script
     or the command, even when *note sys.stdin: 41e. does not appear to
     be a terminal.

     Set by the *note -i: ee1. option and the *note PYTHONINSPECT: ee0.
     environment variable.

 -- C Variable: int Py_InteractiveFlag

     Set by the *note -i: ee1. option.

 -- C Variable: int Py_IsolatedFlag

     Run Python in isolated mode.  In isolated mode *note sys.path: 260.
     contains neither the script’s directory nor the user’s
     site-packages directory.

     Set by the *note -I: 232. option.

     New in version 3.4.

 -- C Variable: int Py_LegacyWindowsFSEncodingFlag

     If the flag is non-zero, use the ‘mbcs’ encoding instead of the
     UTF-8 encoding for the filesystem encoding.

     Set to ‘1’ if the *note PYTHONLEGACYWINDOWSFSENCODING: 5f1.
     environment variable is set to a non-empty string.

     See PEP 529(1) for more details.

     *note Availability: 1491.: Windows.

 -- C Variable: int Py_LegacyWindowsStdioFlag

     If the flag is non-zero, use *note io.FileIO: d6c. instead of
     ‘WindowsConsoleIO’ for *note sys: fd. standard streams.

     Set to ‘1’ if the *note PYTHONLEGACYWINDOWSSTDIO: 5f4. environment
     variable is set to a non-empty string.

     See PEP 528(2) for more details.

     *note Availability: 1491.: Windows.

 -- C Variable: int Py_NoSiteFlag

     Disable the import of the module *note site: eb. and the
     site-dependent manipulations of *note sys.path: 260. that it
     entails.  Also disable these manipulations if *note site: eb. is
     explicitly imported later (call *note site.main(): 147b. if you
     want them to be triggered).

     Set by the *note -S: bf7. option.

 -- C Variable: int Py_NoUserSiteDirectory

     Don’t add the *note user site-packages directory: 147a. to *note
     sys.path: 260.

     Set by the *note -s: ddb. and *note -I: 232. options, and the *note
     PYTHONNOUSERSITE: ddc. environment variable.

 -- C Variable: int Py_OptimizeFlag

     Set by the *note -O: 77e. option and the *note PYTHONOPTIMIZE:
     1478. environment variable.

 -- C Variable: int Py_QuietFlag

     Don’t display the copyright and version messages even in
     interactive mode.

     Set by the *note -q: 1479. option.

     New in version 3.2.

 -- C Variable: int Py_UnbufferedStdioFlag

     Force the stdout and stderr streams to be unbuffered.

     Set by the *note -u: 109d. option and the *note PYTHONUNBUFFERED:
     109e. environment variable.

 -- C Variable: int Py_VerboseFlag

     Print a message each time a module is initialized, showing the
     place (filename or built-in module) from which it is loaded.  If
     greater or equal to ‘2’, print a message for each file that is
     checked for when searching for a module.  Also provides information
     on module cleanup at exit.

     Set by the *note -v: e4d. option and the *note PYTHONVERBOSE: 147c.
     environment variable.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0529

   (2) https://www.python.org/dev/peps/pep-0528


File: python.info,  Node: Initializing and finalizing the interpreter,  Next: Process-wide parameters,  Prev: Global configuration variables,  Up: Initialization Finalization and Threads

7.9.3 Initializing and finalizing the interpreter
-------------------------------------------------

 -- C Function: void Py_Initialize ()

     Initialize the Python interpreter.  In an application embedding
     Python, this should be called before using any other Python/C API
     functions; see *note Before Python Initialization: 53d. for the few
     exceptions.

     This initializes the table of loaded modules (‘sys.modules’), and
     creates the fundamental modules *note builtins: 12, *note __main__:
     1. and *note sys: fd.  It also initializes the module search path
     (‘sys.path’).  It does not set ‘sys.argv’; use *note
     PySys_SetArgvEx(): cc5. for that.  This is a no-op when called for
     a second time (without calling *note Py_FinalizeEx(): 6c0. first).
     There is no return value; it is a fatal error if the initialization
     fails.

          Note: On Windows, changes the console mode from ‘O_TEXT’ to
          ‘O_BINARY’, which will also affect non-Python uses of the
          console using the C Runtime.

 -- C Function: void Py_InitializeEx (int initsigs)

     This function works like *note Py_Initialize(): 20f. if `initsigs'
     is ‘1’.  If `initsigs' is ‘0’, it skips initialization registration
     of signal handlers, which might be useful when Python is embedded.

 -- C Function: int Py_IsInitialized ()

     Return true (nonzero) when the Python interpreter has been
     initialized, false (zero) if not.  After *note Py_FinalizeEx():
     6c0. is called, this returns false until *note Py_Initialize():
     20f. is called again.

 -- C Function: int Py_FinalizeEx ()

     Undo all initializations made by *note Py_Initialize(): 20f. and
     subsequent use of Python/C API functions, and destroy all
     sub-interpreters (see *note Py_NewInterpreter(): 419d. below) that
     were created and not yet destroyed since the last call to *note
     Py_Initialize(): 20f.  Ideally, this frees all memory allocated by
     the Python interpreter.  This is a no-op when called for a second
     time (without calling *note Py_Initialize(): 20f. again first).
     Normally the return value is ‘0’.  If there were errors during
     finalization (flushing buffered data), ‘-1’ is returned.

     This function is provided for a number of reasons.  An embedding
     application might want to restart Python without having to restart
     the application itself.  An application that has loaded the Python
     interpreter from a dynamically loadable library (or DLL) might want
     to free all memory allocated by Python before unloading the DLL.
     During a hunt for memory leaks in an application a developer might
     want to free all memory allocated by Python before exiting from the
     application.

     `Bugs and caveats:' The destruction of modules and objects in
     modules is done in random order; this may cause destructors (*note
     __del__(): a04. methods) to fail when they depend on other objects
     (even functions) or modules.  Dynamically loaded extension modules
     loaded by Python are not unloaded.  Small amounts of memory
     allocated by the Python interpreter may not be freed (if you find a
     leak, please report it).  Memory tied up in circular references
     between objects is not freed.  Some memory allocated by extension
     modules may not be freed.  Some extensions may not work properly if
     their initialization routine is called more than once; this can
     happen if an application calls *note Py_Initialize(): 20f. and
     *note Py_FinalizeEx(): 6c0. more than once.

     Raises an *note auditing event: fa1.
     ‘cpython._PySys_ClearAuditHooks’ with no arguments.

     New in version 3.6.

 -- C Function: void Py_Finalize ()

     This is a backwards-compatible version of *note Py_FinalizeEx():
     6c0. that disregards the return value.


File: python.info,  Node: Process-wide parameters,  Next: Thread State and the Global Interpreter Lock,  Prev: Initializing and finalizing the interpreter,  Up: Initialization Finalization and Threads

7.9.4 Process-wide parameters
-----------------------------

 -- C Function: int Py_SetStandardStreamEncoding (const char *encoding,
          const char *errors)

     This function should be called before *note Py_Initialize(): 20f,
     if it is called at all.  It specifies which encoding and error
     handling to use with standard IO, with the same meanings as in
     *note str.encode(): 170.

     It overrides *note PYTHONIOENCODING: a14. values, and allows
     embedding code to control IO encoding when the environment variable
     does not work.

     `encoding' and/or `errors' may be ‘NULL’ to use *note
     PYTHONIOENCODING: a14. and/or default values (depending on other
     settings).

     Note that *note sys.stderr: 1ea. always uses the “backslashreplace”
     error handler, regardless of this (or any other) setting.

     If *note Py_FinalizeEx(): 6c0. is called, this function will need
     to be called again in order to affect subsequent calls to *note
     Py_Initialize(): 20f.

     Returns ‘0’ if successful, a nonzero value on error (e.g.  calling
     after the interpreter has already been initialized).

     New in version 3.4.

 -- C Function: void Py_SetProgramName (const wchar_t *name)

     This function should be called before *note Py_Initialize(): 20f.
     is called for the first time, if it is called at all.  It tells the
     interpreter the value of the ‘argv[0]’ argument to the ‘main()’
     function of the program (converted to wide characters).  This is
     used by *note Py_GetPath(): 3dcf. and some other functions below to
     find the Python run-time libraries relative to the interpreter
     executable.  The default value is ‘'python'’.  The argument should
     point to a zero-terminated wide character string in static storage
     whose contents will not change for the duration of the program’s
     execution.  No code in the Python interpreter will change the
     contents of this storage.

     Use *note Py_DecodeLocale(): 53f. to decode a bytes string to get a
     ‘wchar_*’ string.

 -- C Function: wchar* Py_GetProgramName ()

     Return the program name set with *note Py_SetProgramName(): 10f2,
     or the default.  The returned string points into static storage;
     the caller should not modify its value.

 -- C Function: wchar_t* Py_GetPrefix ()

     Return the `prefix' for installed platform-independent files.  This
     is derived through a number of complicated rules from the program
     name set with *note Py_SetProgramName(): 10f2. and some environment
     variables; for example, if the program name is
     ‘'/usr/local/bin/python'’, the prefix is ‘'/usr/local'’.  The
     returned string points into static storage; the caller should not
     modify its value.  This corresponds to the ‘prefix’ variable in the
     top-level ‘Makefile’ and the ‘--prefix’ argument to the ‘configure’
     script at build time.  The value is available to Python code as
     ‘sys.prefix’.  It is only useful on Unix.  See also the next
     function.

 -- C Function: wchar_t* Py_GetExecPrefix ()

     Return the `exec-prefix' for installed platform-`dependent' files.
     This is derived through a number of complicated rules from the
     program name set with *note Py_SetProgramName(): 10f2. and some
     environment variables; for example, if the program name is
     ‘'/usr/local/bin/python'’, the exec-prefix is ‘'/usr/local'’.  The
     returned string points into static storage; the caller should not
     modify its value.  This corresponds to the ‘exec_prefix’ variable
     in the top-level ‘Makefile’ and the ‘--exec-prefix’ argument to the
     ‘configure’ script at build time.  The value is available to Python
     code as ‘sys.exec_prefix’.  It is only useful on Unix.

     Background: The exec-prefix differs from the prefix when platform
     dependent files (such as executables and shared libraries) are
     installed in a different directory tree.  In a typical
     installation, platform dependent files may be installed in the
     ‘/usr/local/plat’ subtree while platform independent may be
     installed in ‘/usr/local’.

     Generally speaking, a platform is a combination of hardware and
     software families, e.g.  Sparc machines running the Solaris 2.x
     operating system are considered the same platform, but Intel
     machines running Solaris 2.x are another platform, and Intel
     machines running Linux are yet another platform.  Different major
     revisions of the same operating system generally also form
     different platforms.  Non-Unix operating systems are a different
     story; the installation strategies on those systems are so
     different that the prefix and exec-prefix are meaningless, and set
     to the empty string.  Note that compiled Python bytecode files are
     platform independent (but not independent from the Python version
     by which they were compiled!).

     System administrators will know how to configure the ‘mount’ or
     ‘automount’ programs to share ‘/usr/local’ between platforms while
     having ‘/usr/local/plat’ be a different filesystem for each
     platform.

 -- C Function: wchar_t* Py_GetProgramFullPath ()

     Return the full program name of the Python executable; this is
     computed as a side-effect of deriving the default module search
     path from the program name (set by *note Py_SetProgramName(): 10f2.
     above).  The returned string points into static storage; the caller
     should not modify its value.  The value is available to Python code
     as ‘sys.executable’.

 -- C Function: wchar_t* Py_GetPath ()

     Return the default module search path; this is computed from the
     program name (set by *note Py_SetProgramName(): 10f2. above) and
     some environment variables.  The returned string consists of a
     series of directory names separated by a platform dependent
     delimiter character.  The delimiter character is ‘':'’ on Unix and
     macOS, ‘';'’ on Windows.  The returned string points into static
     storage; the caller should not modify its value.  The list *note
     sys.path: 260. is initialized with this value on interpreter
     startup; it can be (and usually is) modified later to change the
     search path for loading modules.

 -- C Function: void Py_SetPath (const wchar_t *)

     Set the default module search path.  If this function is called
     before *note Py_Initialize(): 20f, then *note Py_GetPath(): 3dcf.
     won’t attempt to compute a default search path but uses the one
     provided instead.  This is useful if Python is embedded by an
     application that has full knowledge of the location of all modules.
     The path components should be separated by the platform dependent
     delimiter character, which is ‘':'’ on Unix and macOS, ‘';'’ on
     Windows.

     This also causes *note sys.executable: 39d. to be set to the
     program full path (see *note Py_GetProgramFullPath(): 39e.) and for
     *note sys.prefix: 377f. and *note sys.exec_prefix: 3780. to be
     empty.  It is up to the caller to modify these if required after
     calling *note Py_Initialize(): 20f.

     Use *note Py_DecodeLocale(): 53f. to decode a bytes string to get a
     ‘wchar_*’ string.

     The path argument is copied internally, so the caller may free it
     after the call completes.

     Changed in version 3.8: The program full path is now used for *note
     sys.executable: 39d, instead of the program name.

 -- C Function: const char* Py_GetVersion ()

     Return the version of this Python interpreter.  This is a string
     that looks something like

          "3.0a5+ (py3k:63103M, May 12 2008, 00:53:55) \n[GCC 4.2.3]"

     The first word (up to the first space character) is the current
     Python version; the first three characters are the major and minor
     version separated by a period.  The returned string points into
     static storage; the caller should not modify its value.  The value
     is available to Python code as *note sys.version: 6ca.

 -- C Function: const char* Py_GetPlatform ()

     Return the platform identifier for the current platform.  On Unix,
     this is formed from the “official” name of the operating system,
     converted to lower case, followed by the major revision number;
     e.g., for Solaris 2.x, which is also known as SunOS 5.x, the value
     is ‘'sunos5'’.  On macOS, it is ‘'darwin'’.  On Windows, it is
     ‘'win'’.  The returned string points into static storage; the
     caller should not modify its value.  The value is available to
     Python code as ‘sys.platform’.

 -- C Function: const char* Py_GetCopyright ()

     Return the official copyright string for the current Python
     version, for example

     ‘'Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam'’

     The returned string points into static storage; the caller should
     not modify its value.  The value is available to Python code as
     ‘sys.copyright’.

 -- C Function: const char* Py_GetCompiler ()

     Return an indication of the compiler used to build the current
     Python version, in square brackets, for example:

          "[GCC 2.7.2.2]"

     The returned string points into static storage; the caller should
     not modify its value.  The value is available to Python code as
     part of the variable ‘sys.version’.

 -- C Function: const char* Py_GetBuildInfo ()

     Return information about the sequence number and build date and
     time of the current Python interpreter instance, for example

          "#67, Aug  1 1997, 22:34:28"

     The returned string points into static storage; the caller should
     not modify its value.  The value is available to Python code as
     part of the variable ‘sys.version’.

 -- C Function: void PySys_SetArgvEx (int argc, wchar_t **argv,
          int updatepath)

     Set *note sys.argv: cc6. based on `argc' and `argv'.  These
     parameters are similar to those passed to the program’s ‘main()’
     function with the difference that the first entry should refer to
     the script file to be executed rather than the executable hosting
     the Python interpreter.  If there isn’t a script that will be run,
     the first entry in `argv' can be an empty string.  If this function
     fails to initialize *note sys.argv: cc6, a fatal condition is
     signalled using *note Py_FatalError(): 266.

     If `updatepath' is zero, this is all the function does.  If
     `updatepath' is non-zero, the function also modifies *note
     sys.path: 260. according to the following algorithm:

        - If the name of an existing script is passed in ‘argv[0]’, the
          absolute path of the directory where the script is located is
          prepended to *note sys.path: 260.

        - Otherwise (that is, if `argc' is ‘0’ or ‘argv[0]’ doesn’t
          point to an existing file name), an empty string is prepended
          to *note sys.path: 260, which is the same as prepending the
          current working directory (‘"."’).

     Use *note Py_DecodeLocale(): 53f. to decode a bytes string to get a
     ‘wchar_*’ string.

          Note: It is recommended that applications embedding the Python
          interpreter for purposes other than executing a single script
          pass ‘0’ as `updatepath', and update *note sys.path: 260.
          themselves if desired.  See CVE-2008-5983(1).

          On versions before 3.1.3, you can achieve the same effect by
          manually popping the first *note sys.path: 260. element after
          having called *note PySys_SetArgv(): db2, for example using:

               PyRun_SimpleString("import sys; sys.path.pop(0)\n");

     New in version 3.1.3.

 -- C Function: void PySys_SetArgv (int argc, wchar_t **argv)

     This function works like *note PySys_SetArgvEx(): cc5. with
     `updatepath' set to ‘1’ unless the ‘python’ interpreter was started
     with the *note -I: 232.

     Use *note Py_DecodeLocale(): 53f. to decode a bytes string to get a
     ‘wchar_*’ string.

     Changed in version 3.4: The `updatepath' value depends on *note -I:
     232.

 -- C Function: void Py_SetPythonHome (const wchar_t *home)

     Set the default “home” directory, that is, the location of the
     standard Python libraries.  See *note PYTHONHOME: 5d1. for the
     meaning of the argument string.

     The argument should point to a zero-terminated character string in
     static storage whose contents will not change for the duration of
     the program’s execution.  No code in the Python interpreter will
     change the contents of this storage.

     Use *note Py_DecodeLocale(): 53f. to decode a bytes string to get a
     ‘wchar_*’ string.

 -- C Function: w_char* Py_GetPythonHome ()

     Return the default “home”, that is, the value set by a previous
     call to *note Py_SetPythonHome(): 10f1, or the value of the *note
     PYTHONHOME: 5d1. environment variable if it is set.

   ---------- Footnotes ----------

   (1) https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-5983


File: python.info,  Node: Thread State and the Global Interpreter Lock,  Next: Sub-interpreter support,  Prev: Process-wide parameters,  Up: Initialization Finalization and Threads

7.9.5 Thread State and the Global Interpreter Lock
--------------------------------------------------

The Python interpreter is not fully thread-safe.  In order to support
multi-threaded Python programs, there’s a global lock, called the *note
global interpreter lock: 600. or *note GIL: 20e, that must be held by
the current thread before it can safely access Python objects.  Without
the lock, even the simplest operations could cause problems in a
multi-threaded program: for example, when two threads simultaneously
increment the reference count of the same object, the reference count
could end up being incremented only once instead of twice.

Therefore, the rule exists that only the thread that has acquired the
*note GIL: 20e. may operate on Python objects or call Python/C API
functions.  In order to emulate concurrency of execution, the
interpreter regularly tries to switch threads (see *note
sys.setswitchinterval(): 218.).  The lock is also released around
potentially blocking I/O operations like reading or writing a file, so
that other Python threads can run in the meantime.

The Python interpreter keeps some thread-specific bookkeeping
information inside a data structure called *note PyThreadState: 41a1.
There’s also one global variable pointing to the current *note
PyThreadState: 41a1.: it can be retrieved using *note
PyThreadState_Get(): 41a2.

* Menu:

* Releasing the GIL from extension code::
* Non-Python created threads::
* Cautions about fork(): Cautions about fork.
* High-level API::
* Low-level API::


File: python.info,  Node: Releasing the GIL from extension code,  Next: Non-Python created threads,  Up: Thread State and the Global Interpreter Lock

7.9.5.1 Releasing the GIL from extension code
.............................................

Most extension code manipulating the *note GIL: 20e. has the following
simple structure:

     Save the thread state in a local variable.
     Release the global interpreter lock.
     ... Do some blocking I/O operation ...
     Reacquire the global interpreter lock.
     Restore the thread state from the local variable.

This is so common that a pair of macros exists to simplify it:

     Py_BEGIN_ALLOW_THREADS
     ... Do some blocking I/O operation ...
     Py_END_ALLOW_THREADS

The *note Py_BEGIN_ALLOW_THREADS: 3d3f. macro opens a new block and
declares a hidden local variable; the *note Py_END_ALLOW_THREADS: 3d7.
macro closes the block.

The block above expands to the following code:

     PyThreadState *_save;

     _save = PyEval_SaveThread();
     ... Do some blocking I/O operation ...
     PyEval_RestoreThread(_save);

Here is how these functions work: the global interpreter lock is used to
protect the pointer to the current thread state.  When releasing the
lock and saving the thread state, the current thread state pointer must
be retrieved before the lock is released (since another thread could
immediately acquire the lock and store its own thread state in the
global variable).  Conversely, when acquiring the lock and restoring the
thread state, the lock must be acquired before storing the thread state
pointer.

     Note: Calling system I/O functions is the most common use case for
     releasing the GIL, but it can also be useful before calling
     long-running computations which don’t need access to Python
     objects, such as compression or cryptographic functions operating
     over memory buffers.  For example, the standard *note zlib: 14d.
     and *note hashlib: 8c. modules release the GIL when compressing or
     hashing data.


File: python.info,  Node: Non-Python created threads,  Next: Cautions about fork,  Prev: Releasing the GIL from extension code,  Up: Thread State and the Global Interpreter Lock

7.9.5.2 Non-Python created threads
..................................

When threads are created using the dedicated Python APIs (such as the
*note threading: 10b. module), a thread state is automatically
associated to them and the code showed above is therefore correct.
However, when threads are created from C (for example by a third-party
library with its own thread management), they don’t hold the GIL, nor is
there a thread state structure for them.

If you need to call Python code from these threads (often this will be
part of a callback API provided by the aforementioned third-party
library), you must first register these threads with the interpreter by
creating a thread state data structure, then acquiring the GIL, and
finally storing their thread state pointer, before you can start using
the Python/C API. When you are done, you should reset the thread state
pointer, release the GIL, and finally free the thread state data
structure.

The *note PyGILState_Ensure(): 3d8. and *note PyGILState_Release():
41a6. functions do all of the above automatically.  The typical idiom
for calling into Python from a C thread is:

     PyGILState_STATE gstate;
     gstate = PyGILState_Ensure();

     /* Perform Python actions here. */
     result = CallSomeFunction();
     /* evaluate result or handle exception */

     /* Release the thread. No Python API allowed beyond this point. */
     PyGILState_Release(gstate);

Note that the ‘PyGILState_*()’ functions assume there is only one global
interpreter (created automatically by *note Py_Initialize(): 20f.).
Python supports the creation of additional interpreters (using *note
Py_NewInterpreter(): 419d.), but mixing multiple interpreters and the
‘PyGILState_*()’ API is unsupported.


File: python.info,  Node: Cautions about fork,  Next: High-level API,  Prev: Non-Python created threads,  Up: Thread State and the Global Interpreter Lock

7.9.5.3 Cautions about fork()
.............................

Another important thing to note about threads is their behaviour in the
face of the C ‘fork()’ call.  On most systems with ‘fork()’, after a
process forks only the thread that issued the fork will exist.  This has
a concrete impact both on how locks must be handled and on all stored
state in CPython’s runtime.

The fact that only the “current” thread remains means any locks held by
other threads will never be released.  Python solves this for *note
os.fork(): a42. by acquiring the locks it uses internally before the
fork, and releasing them afterwards.  In addition, it resets any *note
Lock Objects: 24b9. in the child.  When extending or embedding Python,
there is no way to inform Python of additional (non-Python) locks that
need to be acquired before or reset after a fork.  OS facilities such as
‘pthread_atfork()’ would need to be used to accomplish the same thing.
Additionally, when extending or embedding Python, calling ‘fork()’
directly rather than through *note os.fork(): a42. (and returning to or
calling into Python) may result in a deadlock by one of Python’s
internal locks being held by a thread that is defunct after the fork.
*note PyOS_AfterFork_Child(): 3ef. tries to reset the necessary locks,
but is not always able to.

The fact that all other threads go away also means that CPython’s
runtime state there must be cleaned up properly, which *note os.fork():
a42. does.  This means finalizing all other *note PyThreadState: 41a1.
objects belonging to the current interpreter and all other *note
PyInterpreterState: 3e4. objects.  Due to this and the special nature of
the *note “main” interpreter: 3e53, ‘fork()’ should only be called in
that interpreter’s “main” thread, where the CPython global runtime was
originally initialized.  The only exception is if ‘exec()’ will be
called immediately after.


File: python.info,  Node: High-level API,  Next: Low-level API,  Prev: Cautions about fork,  Up: Thread State and the Global Interpreter Lock

7.9.5.4 High-level API
......................

These are the most commonly used types and functions when writing C
extension code, or when embedding the Python interpreter:

 -- C Type: PyInterpreterState

     This data structure represents the state shared by a number of
     cooperating threads.  Threads belonging to the same interpreter
     share their module administration and a few other internal items.
     There are no public members in this structure.

     Threads belonging to different interpreters initially share
     nothing, except process state like available memory, open file
     descriptors and such.  The global interpreter lock is also shared
     by all threads, regardless of to which interpreter they belong.

 -- C Type: PyThreadState

     This data structure represents the state of a single thread.  The
     only public data member is ‘interp’ (*note PyInterpreterState *:
     3e4.), which points to this thread’s interpreter state.

 -- C Function: void PyEval_InitThreads ()

     Deprecated function which does nothing.

     In Python 3.6 and older, this function created the GIL if it didn’t
     exist.

     Changed in version 3.9: The function now does nothing.

     Changed in version 3.7: This function is now called by *note
     Py_Initialize(): 20f, so you don’t have to call it yourself
     anymore.

     Changed in version 3.2: This function cannot be called before *note
     Py_Initialize(): 20f. anymore.

     Deprecated since version 3.9, will be removed in version 3.11.

 -- C Function: int PyEval_ThreadsInitialized ()

     Returns a non-zero value if *note PyEval_InitThreads(): 20c. has
     been called.  This function can be called without holding the GIL,
     and therefore can be used to avoid calls to the locking API when
     running single-threaded.

     Changed in version 3.7: The *note GIL: 20e. is now initialized by
     *note Py_Initialize(): 20f.

     Deprecated since version 3.9, will be removed in version 3.11.

 -- C Function: PyThreadState* PyEval_SaveThread ()

     Release the global interpreter lock (if it has been created) and
     reset the thread state to ‘NULL’, returning the previous thread
     state (which is not ‘NULL’).  If the lock has been created, the
     current thread must have acquired it.

 -- C Function: void PyEval_RestoreThread (PyThreadState *tstate)

     Acquire the global interpreter lock (if it has been created) and
     set the thread state to `tstate', which must not be ‘NULL’.  If the
     lock has been created, the current thread must not have acquired
     it, otherwise deadlock ensues.

          Note: Calling this function from a thread when the runtime is
          finalizing will terminate the thread, even if the thread was
          not created by Python.  You can use ‘_Py_IsFinalizing()’ or
          *note sys.is_finalizing(): 851. to check if the interpreter is
          in process of being finalized before calling this function to
          avoid unwanted termination.

 -- C Function: PyThreadState* PyThreadState_Get ()

     Return the current thread state.  The global interpreter lock must
     be held.  When the current thread state is ‘NULL’, this issues a
     fatal error (so that the caller needn’t check for ‘NULL’).

 -- C Function: PyThreadState* PyThreadState_Swap
          (PyThreadState *tstate)

     Swap the current thread state with the thread state given by the
     argument `tstate', which may be ‘NULL’.  The global interpreter
     lock must be held and is not released.

The following functions use thread-local storage, and are not compatible
with sub-interpreters:

 -- C Function: PyGILState_STATE PyGILState_Ensure ()

     Ensure that the current thread is ready to call the Python C API
     regardless of the current state of Python, or of the global
     interpreter lock.  This may be called as many times as desired by a
     thread as long as each call is matched with a call to *note
     PyGILState_Release(): 41a6.  In general, other thread-related APIs
     may be used between *note PyGILState_Ensure(): 3d8. and *note
     PyGILState_Release(): 41a6. calls as long as the thread state is
     restored to its previous state before the Release().  For example,
     normal usage of the *note Py_BEGIN_ALLOW_THREADS: 3d3f. and *note
     Py_END_ALLOW_THREADS: 3d7. macros is acceptable.

     The return value is an opaque “handle” to the thread state when
     *note PyGILState_Ensure(): 3d8. was called, and must be passed to
     *note PyGILState_Release(): 41a6. to ensure Python is left in the
     same state.  Even though recursive calls are allowed, these handles
     `cannot' be shared - each unique call to *note PyGILState_Ensure():
     3d8. must save the handle for its call to *note
     PyGILState_Release(): 41a6.

     When the function returns, the current thread will hold the GIL and
     be able to call arbitrary Python code.  Failure is a fatal error.

          Note: Calling this function from a thread when the runtime is
          finalizing will terminate the thread, even if the thread was
          not created by Python.  You can use ‘_Py_IsFinalizing()’ or
          *note sys.is_finalizing(): 851. to check if the interpreter is
          in process of being finalized before calling this function to
          avoid unwanted termination.

 -- C Function: void PyGILState_Release (PyGILState_STATE)

     Release any resources previously acquired.  After this call,
     Python’s state will be the same as it was prior to the
     corresponding *note PyGILState_Ensure(): 3d8. call (but generally
     this state will be unknown to the caller, hence the use of the
     GILState API).

     Every call to *note PyGILState_Ensure(): 3d8. must be matched by a
     call to *note PyGILState_Release(): 41a6. on the same thread.

 -- C Function: PyThreadState* PyGILState_GetThisThreadState ()

     Get the current thread state for this thread.  May return ‘NULL’ if
     no GILState API has been used on the current thread.  Note that the
     main thread always has such a thread-state, even if no
     auto-thread-state call has been made on the main thread.  This is
     mainly a helper/diagnostic function.

 -- C Function: int PyGILState_Check ()

     Return ‘1’ if the current thread is holding the GIL and ‘0’
     otherwise.  This function can be called from any thread at any
     time.  Only if it has had its Python thread state initialized and
     currently is holding the GIL will it return ‘1’.  This is mainly a
     helper/diagnostic function.  It can be useful for example in
     callback contexts or memory allocation functions when knowing that
     the GIL is locked can allow the caller to perform sensitive actions
     or otherwise behave differently.

     New in version 3.4.

The following macros are normally used without a trailing semicolon;
look for example usage in the Python source distribution.

 -- C Macro: Py_BEGIN_ALLOW_THREADS

     This macro expands to ‘{ PyThreadState *_save; _save =
     PyEval_SaveThread();’.  Note that it contains an opening brace; it
     must be matched with a following *note Py_END_ALLOW_THREADS: 3d7.
     macro.  See above for further discussion of this macro.

 -- C Macro: Py_END_ALLOW_THREADS

     This macro expands to ‘PyEval_RestoreThread(_save); }’.  Note that
     it contains a closing brace; it must be matched with an earlier
     *note Py_BEGIN_ALLOW_THREADS: 3d3f. macro.  See above for further
     discussion of this macro.

 -- C Macro: Py_BLOCK_THREADS

     This macro expands to ‘PyEval_RestoreThread(_save);’: it is
     equivalent to *note Py_END_ALLOW_THREADS: 3d7. without the closing
     brace.

 -- C Macro: Py_UNBLOCK_THREADS

     This macro expands to ‘_save = PyEval_SaveThread();’: it is
     equivalent to *note Py_BEGIN_ALLOW_THREADS: 3d3f. without the
     opening brace and variable declaration.


File: python.info,  Node: Low-level API,  Prev: High-level API,  Up: Thread State and the Global Interpreter Lock

7.9.5.5 Low-level API
.....................

All of the following functions must be called after *note
Py_Initialize(): 20f.

Changed in version 3.7: *note Py_Initialize(): 20f. now initializes the
*note GIL: 20e.

 -- C Function: PyInterpreterState* PyInterpreterState_New ()

     Create a new interpreter state object.  The global interpreter lock
     need not be held, but may be held if it is necessary to serialize
     calls to this function.

     Raises an *note auditing event: fa1.
     ‘cpython.PyInterpreterState_New’ with no arguments.

 -- C Function: void PyInterpreterState_Clear
          (PyInterpreterState *interp)

     Reset all information in an interpreter state object.  The global
     interpreter lock must be held.

     Raises an *note auditing event: fa1.
     ‘cpython.PyInterpreterState_Clear’ with no arguments.

 -- C Function: void PyInterpreterState_Delete
          (PyInterpreterState *interp)

     Destroy an interpreter state object.  The global interpreter lock
     need not be held.  The interpreter state must have been reset with
     a previous call to *note PyInterpreterState_Clear(): 41b0.

 -- C Function: PyThreadState* PyThreadState_New
          (PyInterpreterState *interp)

     Create a new thread state object belonging to the given interpreter
     object.  The global interpreter lock need not be held, but may be
     held if it is necessary to serialize calls to this function.

 -- C Function: void PyThreadState_Clear (PyThreadState *tstate)

     Reset all information in a thread state object.  The global
     interpreter lock must be held.

     Changed in version 3.9: This function now calls the
     ‘PyThreadState.on_delete’ callback.  Previously, that happened in
     *note PyThreadState_Delete(): 1097.

 -- C Function: void PyThreadState_Delete (PyThreadState *tstate)

     Destroy a thread state object.  The global interpreter lock need
     not be held.  The thread state must have been reset with a previous
     call to *note PyThreadState_Clear(): 104c.

 -- C Function: void PyThreadState_DeleteCurrent (void)

     Destroy the current thread state and release the global interpreter
     lock.  Like *note PyThreadState_Delete(): 1097, the global
     interpreter lock need not be held.  The thread state must have been
     reset with a previous call to *note PyThreadState_Clear(): 104c.

 -- C Function: PyFrameObject* PyThreadState_GetFrame
          (PyThreadState *tstate)

     Get the current frame of the Python thread state `tstate'.

     Return a strong reference.  Return ‘NULL’ if no frame is currently
     executing.

     See also *note PyEval_GetFrame(): 3ea0.

     `tstate' must not be ‘NULL’.

     New in version 3.9.

 -- C Function: uint64_t PyThreadState_GetID (PyThreadState *tstate)

     Get the unique thread state identifier of the Python thread state
     `tstate'.

     `tstate' must not be ‘NULL’.

     New in version 3.9.

 -- C Function: PyInterpreterState* PyThreadState_GetInterpreter
          (PyThreadState *tstate)

     Get the interpreter of the Python thread state `tstate'.

     `tstate' must not be ‘NULL’.

     New in version 3.9.

 -- C Function: PyInterpreterState* PyInterpreterState_Get (void)

     Get the current interpreter.

     Issue a fatal error if there no current Python thread state or no
     current interpreter.  It cannot return NULL.

     The caller must hold the GIL.

     New in version 3.9.

 -- C Function: int64_t PyInterpreterState_GetID
          (PyInterpreterState *interp)

     Return the interpreter’s unique ID. If there was any error in doing
     so then ‘-1’ is returned and an error is set.

     The caller must hold the GIL.

     New in version 3.7.

 -- C Function: PyObject* PyInterpreterState_GetDict
          (PyInterpreterState *interp)

     Return a dictionary in which interpreter-specific data may be
     stored.  If this function returns ‘NULL’ then no exception has been
     raised and the caller should assume no interpreter-specific dict is
     available.

     This is not a replacement for *note PyModule_GetState(): 25e, which
     extensions should use to store interpreter-specific state
     information.

     New in version 3.8.

 -- C Type: PyObject* (*_PyFrameEvalFunction) (PyThreadState *tstate,
          PyFrameObject *frame, int throwflag)

     Type of a frame evaluation function.

     The `throwflag' parameter is used by the ‘throw()’ method of
     generators: if non-zero, handle the current exception.

     Changed in version 3.9: The function now takes a `tstate'
     parameter.

 -- C Function: _PyFrameEvalFunction
          _PyInterpreterState_GetEvalFrameFunc
          (PyInterpreterState *interp)

     Get the frame evaluation function.

     See the PEP 523(1) “Adding a frame evaluation API to CPython”.

     New in version 3.9.

 -- C Function: void _PyInterpreterState_SetEvalFrameFunc
          (PyInterpreterState *interp, _PyFrameEvalFunction eval_frame)

     Set the frame evaluation function.

     See the PEP 523(2) “Adding a frame evaluation API to CPython”.

     New in version 3.9.

 -- C Function: PyObject* PyThreadState_GetDict ()
     `Return value: Borrowed reference.'  Return a dictionary in which
     extensions can store thread-specific state information.  Each
     extension should use a unique key to use to store state in the
     dictionary.  It is okay to call this function when no current
     thread state is available.  If this function returns ‘NULL’, no
     exception has been raised and the caller should assume no current
     thread state is available.

 -- C Function: int PyThreadState_SetAsyncExc (unsigned long id,
          PyObject *exc)

     Asynchronously raise an exception in a thread.  The `id' argument
     is the thread id of the target thread; `exc' is the exception
     object to be raised.  This function does not steal any references
     to `exc'.  To prevent naive misuse, you must write your own C
     extension to call this.  Must be called with the GIL held.  Returns
     the number of thread states modified; this is normally one, but
     will be zero if the thread id isn’t found.  If `exc' is ‘NULL’, the
     pending exception (if any) for the thread is cleared.  This raises
     no exceptions.

     Changed in version 3.7: The type of the `id' parameter changed from
     ‘long’ to ‘unsigned long’.

 -- C Function: void PyEval_AcquireThread (PyThreadState *tstate)

     Acquire the global interpreter lock and set the current thread
     state to `tstate', which must not be ‘NULL’.  The lock must have
     been created earlier.  If this thread already has the lock,
     deadlock ensues.

          Note: Calling this function from a thread when the runtime is
          finalizing will terminate the thread, even if the thread was
          not created by Python.  You can use ‘_Py_IsFinalizing()’ or
          *note sys.is_finalizing(): 851. to check if the interpreter is
          in process of being finalized before calling this function to
          avoid unwanted termination.

     Changed in version 3.8: Updated to be consistent with *note
     PyEval_RestoreThread(): 3d6, *note Py_END_ALLOW_THREADS(): 3d7, and
     *note PyGILState_Ensure(): 3d8, and terminate the current thread if
     called while the interpreter is finalizing.

     *note PyEval_RestoreThread(): 3d6. is a higher-level function which
     is always available (even when threads have not been initialized).

 -- C Function: void PyEval_ReleaseThread (PyThreadState *tstate)

     Reset the current thread state to ‘NULL’ and release the global
     interpreter lock.  The lock must have been created earlier and must
     be held by the current thread.  The `tstate' argument, which must
     not be ‘NULL’, is only used to check that it represents the current
     thread state — if it isn’t, a fatal error is reported.

     *note PyEval_SaveThread(): cdc. is a higher-level function which is
     always available (even when threads have not been initialized).

 -- C Function: void PyEval_AcquireLock ()

     Acquire the global interpreter lock.  The lock must have been
     created earlier.  If this thread already has the lock, a deadlock
     ensues.

     Deprecated since version 3.2: This function does not update the
     current thread state.  Please use *note PyEval_RestoreThread():
     3d6. or *note PyEval_AcquireThread(): 3d5. instead.

          Note: Calling this function from a thread when the runtime is
          finalizing will terminate the thread, even if the thread was
          not created by Python.  You can use ‘_Py_IsFinalizing()’ or
          *note sys.is_finalizing(): 851. to check if the interpreter is
          in process of being finalized before calling this function to
          avoid unwanted termination.

     Changed in version 3.8: Updated to be consistent with *note
     PyEval_RestoreThread(): 3d6, *note Py_END_ALLOW_THREADS(): 3d7, and
     *note PyGILState_Ensure(): 3d8, and terminate the current thread if
     called while the interpreter is finalizing.

 -- C Function: void PyEval_ReleaseLock ()

     Release the global interpreter lock.  The lock must have been
     created earlier.

     Deprecated since version 3.2: This function does not update the
     current thread state.  Please use *note PyEval_SaveThread(): cdc.
     or *note PyEval_ReleaseThread(): 41b5. instead.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0523

   (2) https://www.python.org/dev/peps/pep-0523


File: python.info,  Node: Sub-interpreter support,  Next: Asynchronous Notifications,  Prev: Thread State and the Global Interpreter Lock,  Up: Initialization Finalization and Threads

7.9.6 Sub-interpreter support
-----------------------------

While in most uses, you will only embed a single Python interpreter,
there are cases where you need to create several independent
interpreters in the same process and perhaps even in the same thread.
Sub-interpreters allow you to do that.

The “main” interpreter is the first one created when the runtime
initializes.  It is usually the only Python interpreter in a process.
Unlike sub-interpreters, the main interpreter has unique process-global
responsibilities like signal handling.  It is also responsible for
execution during runtime initialization and is usually the active
interpreter during runtime finalization.  The *note
PyInterpreterState_Main(): 41b7. function returns a pointer to its
state.

You can switch between sub-interpreters using the *note
PyThreadState_Swap(): 41a9. function.  You can create and destroy them
using the following functions:

 -- C Function: PyThreadState* Py_NewInterpreter ()

     Create a new sub-interpreter.  This is an (almost) totally separate
     environment for the execution of Python code.  In particular, the
     new interpreter has separate, independent versions of all imported
     modules, including the fundamental modules *note builtins: 12,
     *note __main__: 1. and *note sys: fd.  The table of loaded modules
     (‘sys.modules’) and the module search path (‘sys.path’) are also
     separate.  The new environment has no ‘sys.argv’ variable.  It has
     new standard I/O stream file objects ‘sys.stdin’, ‘sys.stdout’ and
     ‘sys.stderr’ (however these refer to the same underlying file
     descriptors).

     The return value points to the first thread state created in the
     new sub-interpreter.  This thread state is made in the current
     thread state.  Note that no actual thread is created; see the
     discussion of thread states below.  If creation of the new
     interpreter is unsuccessful, ‘NULL’ is returned; no exception is
     set since the exception state is stored in the current thread state
     and there may not be a current thread state.  (Like all other
     Python/C API functions, the global interpreter lock must be held
     before calling this function and is still held when it returns;
     however, unlike most other Python/C API functions, there needn’t be
     a current thread state on entry.)

     Extension modules are shared between (sub-)interpreters as follows:

        * For modules using multi-phase initialization, e.g.  *note
          PyModule_FromDefAndSpec(): 899, a separate module object is
          created and initialized for each interpreter.  Only C-level
          static and global variables are shared between these module
          objects.

        * For modules using single-phase initialization, e.g.  *note
          PyModule_Create(): 3d22, the first time a particular extension
          is imported, it is initialized normally, and a (shallow) copy
          of its module’s dictionary is squirreled away.  When the same
          extension is imported by another (sub-)interpreter, a new
          module is initialized and filled with the contents of this
          copy; the extension’s ‘init’ function is not called.  Objects
          in the module’s dictionary thus end up shared across
          (sub-)interpreters, which might cause unwanted behavior (see
          *note Bugs and caveats: 41b8. below).

          Note that this is different from what happens when an
          extension is imported after the interpreter has been
          completely re-initialized by calling *note Py_FinalizeEx():
          6c0. and *note Py_Initialize(): 20f.; in that case, the
          extension’s ‘initmodule’ function `is' called again.  As with
          multi-phase initialization, this means that only C-level
          static and global variables are shared between these modules.

 -- C Function: void Py_EndInterpreter (PyThreadState *tstate)

     Destroy the (sub-)interpreter represented by the given thread
     state.  The given thread state must be the current thread state.
     See the discussion of thread states below.  When the call returns,
     the current thread state is ‘NULL’.  All thread states associated
     with this interpreter are destroyed.  (The global interpreter lock
     must be held before calling this function and is still held when it
     returns.)  *note Py_FinalizeEx(): 6c0. will destroy all
     sub-interpreters that haven’t been explicitly destroyed at that
     point.

* Menu:

* Bugs and caveats::


File: python.info,  Node: Bugs and caveats,  Up: Sub-interpreter support

7.9.6.1 Bugs and caveats
........................

Because sub-interpreters (and the main interpreter) are part of the same
process, the insulation between them isn’t perfect — for example, using
low-level file operations like *note os.close(): 4d9. they can
(accidentally or maliciously) affect each other’s open files.  Because
of the way extensions are shared between (sub-)interpreters, some
extensions may not work properly; this is especially likely when using
single-phase initialization or (static) global variables.  It is
possible to insert objects created in one sub-interpreter into a
namespace of another (sub-)interpreter; this should be avoided if
possible.

Special care should be taken to avoid sharing user-defined functions,
methods, instances or classes between sub-interpreters, since import
operations executed by such objects may affect the wrong
(sub-)interpreter’s dictionary of loaded modules.  It is equally
important to avoid sharing objects from which the above are reachable.

Also note that combining this functionality with ‘PyGILState_*()’ APIs
is delicate, because these APIs assume a bijection between Python thread
states and OS-level threads, an assumption broken by the presence of
sub-interpreters.  It is highly recommended that you don’t switch
sub-interpreters between a pair of matching *note PyGILState_Ensure():
3d8. and *note PyGILState_Release(): 41a6. calls.  Furthermore,
extensions (such as *note ctypes: 2a.) using these APIs to allow calling
of Python code from non-Python created threads will probably be broken
when using sub-interpreters.


File: python.info,  Node: Asynchronous Notifications,  Next: Profiling and Tracing,  Prev: Sub-interpreter support,  Up: Initialization Finalization and Threads

7.9.7 Asynchronous Notifications
--------------------------------

A mechanism is provided to make asynchronous notifications to the main
interpreter thread.  These notifications take the form of a function
pointer and a void pointer argument.

 -- C Function: int Py_AddPendingCall (int (*func)(void *), void *arg)

     Schedule a function to be called from the main interpreter thread.
     On success, ‘0’ is returned and `func' is queued for being called
     in the main thread.  On failure, ‘-1’ is returned without setting
     any exception.

     When successfully queued, `func' will be `eventually' called from
     the main interpreter thread with the argument `arg'.  It will be
     called asynchronously with respect to normally running Python code,
     but with both these conditions met:

        * on a *note bytecode: 709. boundary;

        * with the main thread holding the *note global interpreter
          lock: 600. (`func' can therefore use the full C API).

     `func' must return ‘0’ on success, or ‘-1’ on failure with an
     exception set.  `func' won’t be interrupted to perform another
     asynchronous notification recursively, but it can still be
     interrupted to switch threads if the global interpreter lock is
     released.

     This function doesn’t need a current thread state to run, and it
     doesn’t need the global interpreter lock.

     To call this function in a subinterpreter, the caller must hold the
     GIL. Otherwise, the function `func' can be scheduled to be called
     from the wrong interpreter.

          Warning: This is a low-level function, only useful for very
          special cases.  There is no guarantee that `func' will be
          called as quick as possible.  If the main thread is busy
          executing a system call, `func' won’t be called before the
          system call returns.  This function is generally `not'
          suitable for calling Python code from arbitrary C threads.
          Instead, use the *note PyGILState API: 41a4.

     Changed in version 3.9: If this function is called in a
     subinterpreter, the function `func' is now scheduled to be called
     from the subinterpreter, rather than being called from the main
     interpreter.  Each subinterpreter now has its own list of scheduled
     calls.

     New in version 3.1.


File: python.info,  Node: Profiling and Tracing,  Next: Advanced Debugger Support,  Prev: Asynchronous Notifications,  Up: Initialization Finalization and Threads

7.9.8 Profiling and Tracing
---------------------------

The Python interpreter provides some low-level support for attaching
profiling and execution tracing facilities.  These are used for
profiling, debugging, and coverage analysis tools.

This C interface allows the profiling or tracing code to avoid the
overhead of calling through Python-level callable objects, making a
direct C function call instead.  The essential attributes of the
facility have not changed; the interface allows trace functions to be
installed per-thread, and the basic events reported to the trace
function are the same as had been reported to the Python-level trace
functions in previous versions.

 -- C Type: int (*Py_tracefunc) (PyObject *obj, PyFrameObject *frame,
          int what, PyObject *arg)

     The type of the trace function registered using *note
     PyEval_SetProfile(): efd. and *note PyEval_SetTrace(): efe.  The
     first parameter is the object passed to the registration function
     as `obj', `frame' is the frame object to which the event pertains,
     `what' is one of the constants ‘PyTrace_CALL’, ‘PyTrace_EXCEPTION’,
     ‘PyTrace_LINE’, ‘PyTrace_RETURN’, ‘PyTrace_C_CALL’,
     ‘PyTrace_C_EXCEPTION’, ‘PyTrace_C_RETURN’, or ‘PyTrace_OPCODE’, and
     `arg' depends on the value of `what':

     Value of `what'                    Meaning of `arg'
                                        
     --------------------------------------------------------------------------------
                                        
     ‘PyTrace_CALL’                     Always *note Py_None: 3d1f.
                                        
                                        
     ‘PyTrace_EXCEPTION’                Exception information as returned by
                                        *note sys.exc_info(): d27.
                                        
                                        
     ‘PyTrace_LINE’                     Always *note Py_None: 3d1f.
                                        
                                        
     ‘PyTrace_RETURN’                   Value being returned to the caller, or
                                        ‘NULL’ if caused by an exception.
                                        
                                        
     ‘PyTrace_C_CALL’                   Function object being called.
                                        
                                        
     ‘PyTrace_C_EXCEPTION’              Function object being called.
                                        
                                        
     ‘PyTrace_C_RETURN’                 Function object being called.
                                        
                                        
     ‘PyTrace_OPCODE’                   Always *note Py_None: 3d1f.
                                        

 -- C Variable: int PyTrace_CALL

     The value of the `what' parameter to a *note Py_tracefunc: 41bc.
     function when a new call to a function or method is being reported,
     or a new entry into a generator.  Note that the creation of the
     iterator for a generator function is not reported as there is no
     control transfer to the Python bytecode in the corresponding frame.

 -- C Variable: int PyTrace_EXCEPTION

     The value of the `what' parameter to a *note Py_tracefunc: 41bc.
     function when an exception has been raised.  The callback function
     is called with this value for `what' when after any bytecode is
     processed after which the exception becomes set within the frame
     being executed.  The effect of this is that as exception
     propagation causes the Python stack to unwind, the callback is
     called upon return to each frame as the exception propagates.  Only
     trace functions receives these events; they are not needed by the
     profiler.

 -- C Variable: int PyTrace_LINE

     The value passed as the `what' parameter to a *note Py_tracefunc:
     41bc. function (but not a profiling function) when a line-number
     event is being reported.  It may be disabled for a frame by setting
     ‘f_trace_lines’ to `0' on that frame.

 -- C Variable: int PyTrace_RETURN

     The value for the `what' parameter to *note Py_tracefunc: 41bc.
     functions when a call is about to return.

 -- C Variable: int PyTrace_C_CALL

     The value for the `what' parameter to *note Py_tracefunc: 41bc.
     functions when a C function is about to be called.

 -- C Variable: int PyTrace_C_EXCEPTION

     The value for the `what' parameter to *note Py_tracefunc: 41bc.
     functions when a C function has raised an exception.

 -- C Variable: int PyTrace_C_RETURN

     The value for the `what' parameter to *note Py_tracefunc: 41bc.
     functions when a C function has returned.

 -- C Variable: int PyTrace_OPCODE

     The value for the `what' parameter to *note Py_tracefunc: 41bc.
     functions (but not profiling functions) when a new opcode is about
     to be executed.  This event is not emitted by default: it must be
     explicitly requested by setting ‘f_trace_opcodes’ to `1' on the
     frame.

 -- C Function: void PyEval_SetProfile (Py_tracefunc func,
          PyObject *obj)

     Set the profiler function to `func'.  The `obj' parameter is passed
     to the function as its first parameter, and may be any Python
     object, or ‘NULL’.  If the profile function needs to maintain
     state, using a different value for `obj' for each thread provides a
     convenient and thread-safe place to store it.  The profile function
     is called for all monitored events except ‘PyTrace_LINE’
     ‘PyTrace_OPCODE’ and ‘PyTrace_EXCEPTION’.

     The caller must hold the *note GIL: 20e.

 -- C Function: void PyEval_SetTrace (Py_tracefunc func, PyObject *obj)

     Set the tracing function to `func'.  This is similar to *note
     PyEval_SetProfile(): efd, except the tracing function does receive
     line-number events and per-opcode events, but does not receive any
     event related to C function objects being called.  Any trace
     function registered using *note PyEval_SetTrace(): efe. will not
     receive ‘PyTrace_C_CALL’, ‘PyTrace_C_EXCEPTION’ or
     ‘PyTrace_C_RETURN’ as a value for the `what' parameter.

     The caller must hold the *note GIL: 20e.


File: python.info,  Node: Advanced Debugger Support,  Next: Thread Local Storage Support,  Prev: Profiling and Tracing,  Up: Initialization Finalization and Threads

7.9.9 Advanced Debugger Support
-------------------------------

These functions are only intended to be used by advanced debugging
tools.

 -- C Function: PyInterpreterState* PyInterpreterState_Head ()

     Return the interpreter state object at the head of the list of all
     such objects.

 -- C Function: PyInterpreterState* PyInterpreterState_Main ()

     Return the main interpreter state object.

 -- C Function: PyInterpreterState* PyInterpreterState_Next
          (PyInterpreterState *interp)

     Return the next interpreter state object after `interp' from the
     list of all such objects.

 -- C Function: PyThreadState * PyInterpreterState_ThreadHead
          (PyInterpreterState *interp)

     Return the pointer to the first *note PyThreadState: 41a1. object
     in the list of threads associated with the interpreter `interp'.

 -- C Function: PyThreadState* PyThreadState_Next
          (PyThreadState *tstate)

     Return the next thread state object after `tstate' from the list of
     all such objects belonging to the same *note PyInterpreterState:
     3e4. object.


File: python.info,  Node: Thread Local Storage Support,  Prev: Advanced Debugger Support,  Up: Initialization Finalization and Threads

7.9.10 Thread Local Storage Support
-----------------------------------

The Python interpreter provides low-level support for thread-local
storage (TLS) which wraps the underlying native TLS implementation to
support the Python-level thread local storage API (*note
threading.local: 244e.).  The CPython C level APIs are similar to those
offered by pthreads and Windows: use a thread key and functions to
associate a ‘void*’ value per thread.

The GIL does `not' need to be held when calling these functions; they
supply their own locking.

Note that ‘Python.h’ does not include the declaration of the TLS APIs,
you need to include ‘pythread.h’ to use thread-local storage.

     Note: None of these API functions handle memory management on
     behalf of the ‘void*’ values.  You need to allocate and deallocate
     them yourself.  If the ‘void*’ values happen to be *note PyObject*:
     5b5, these functions don’t do refcount operations on them either.

* Menu:

* Thread Specific Storage (TSS) API: Thread Specific Storage TSS API.
* Thread Local Storage (TLS) API: Thread Local Storage TLS API.


File: python.info,  Node: Thread Specific Storage TSS API,  Next: Thread Local Storage TLS API,  Up: Thread Local Storage Support

7.9.10.1 Thread Specific Storage (TSS) API
..........................................

TSS API is introduced to supersede the use of the existing TLS API
within the CPython interpreter.  This API uses a new type *note
Py_tss_t: 428. instead of ‘int’ to represent thread keys.

New in version 3.7.

See also
........

“A New C-API for Thread-Local Storage in CPython” ( PEP 539(1))

 -- C Type: Py_tss_t

     This data structure represents the state of a thread key, the
     definition of which may depend on the underlying TLS
     implementation, and it has an internal field representing the key’s
     initialization state.  There are no public members in this
     structure.

     When *note Py_LIMITED_API: 3dd6. is not defined, static allocation
     of this type by *note Py_tss_NEEDS_INIT: 41ca. is allowed.

 -- C Macro: Py_tss_NEEDS_INIT

     This macro expands to the initializer for *note Py_tss_t: 428.
     variables.  Note that this macro won’t be defined with *note
     Py_LIMITED_API: 3dd6.

* Menu:

* Dynamic Allocation::
* Methods: Methods<4>.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0539


File: python.info,  Node: Dynamic Allocation,  Next: Methods<4>,  Up: Thread Specific Storage TSS API

7.9.10.2 Dynamic Allocation
...........................

Dynamic allocation of the *note Py_tss_t: 428, required in extension
modules built with *note Py_LIMITED_API: 3dd6, where static allocation
of this type is not possible due to its implementation being opaque at
build time.

 -- C Function: Py_tss_t* PyThread_tss_alloc ()

     Return a value which is the same state as a value initialized with
     *note Py_tss_NEEDS_INIT: 41ca, or ‘NULL’ in the case of dynamic
     allocation failure.

 -- C Function: void PyThread_tss_free (Py_tss_t *key)

     Free the given `key' allocated by *note PyThread_tss_alloc(): 41cc,
     after first calling *note PyThread_tss_delete(): 41ce. to ensure
     any associated thread locals have been unassigned.  This is a no-op
     if the `key' argument is ‘NULL’.

          Note: A freed key becomes a dangling pointer, you should reset
          the key to ‘NULL’.


File: python.info,  Node: Methods<4>,  Prev: Dynamic Allocation,  Up: Thread Specific Storage TSS API

7.9.10.3 Methods
................

The parameter `key' of these functions must not be ‘NULL’.  Moreover,
the behaviors of *note PyThread_tss_set(): 41d0. and *note
PyThread_tss_get(): 41d1. are undefined if the given *note Py_tss_t:
428. has not been initialized by *note PyThread_tss_create(): 41d2.

 -- C Function: int PyThread_tss_is_created (Py_tss_t *key)

     Return a non-zero value if the given *note Py_tss_t: 428. has been
     initialized by *note PyThread_tss_create(): 41d2.

 -- C Function: int PyThread_tss_create (Py_tss_t *key)

     Return a zero value on successful initialization of a TSS key.  The
     behavior is undefined if the value pointed to by the `key' argument
     is not initialized by *note Py_tss_NEEDS_INIT: 41ca.  This function
     can be called repeatedly on the same key – calling it on an already
     initialized key is a no-op and immediately returns success.

 -- C Function: void PyThread_tss_delete (Py_tss_t *key)

     Destroy a TSS key to forget the values associated with the key
     across all threads, and change the key’s initialization state to
     uninitialized.  A destroyed key is able to be initialized again by
     *note PyThread_tss_create(): 41d2.  This function can be called
     repeatedly on the same key – calling it on an already destroyed key
     is a no-op.

 -- C Function: int PyThread_tss_set (Py_tss_t *key, void *value)

     Return a zero value to indicate successfully associating a ‘void*’
     value with a TSS key in the current thread.  Each thread has a
     distinct mapping of the key to a ‘void*’ value.

 -- C Function: void* PyThread_tss_get (Py_tss_t *key)

     Return the ‘void*’ value associated with a TSS key in the current
     thread.  This returns ‘NULL’ if no value is associated with the key
     in the current thread.


File: python.info,  Node: Thread Local Storage TLS API,  Prev: Thread Specific Storage TSS API,  Up: Thread Local Storage Support

7.9.10.4 Thread Local Storage (TLS) API
.......................................

Deprecated since version 3.7: This API is superseded by *note Thread
Specific Storage (TSS) API: 427.

     Note: This version of the API does not support platforms where the
     native TLS key is defined in a way that cannot be safely cast to
     ‘int’.  On such platforms, *note PyThread_create_key(): 41d5. will
     return immediately with a failure status, and the other TLS
     functions will all be no-ops on such platforms.

Due to the compatibility problem noted above, this version of the API
should not be used in new code.

 -- C Function: int PyThread_create_key ()

 -- C Function: void PyThread_delete_key (int key)

 -- C Function: int PyThread_set_key_value (int key, void *value)

 -- C Function: void* PyThread_get_key_value (int key)

 -- C Function: void PyThread_delete_key_value (int key)

 -- C Function: void PyThread_ReInitTLS ()


File: python.info,  Node: Python Initialization Configuration,  Next: Memory Management,  Prev: Initialization Finalization and Threads,  Up: Python/C API Reference Manual

7.10 Python Initialization Configuration
========================================

New in version 3.8.

Structures:

   * *note PyConfig: 226.

   * *note PyPreConfig: 299.

   * *note PyStatus: 29a.

   * *note PyWideStringList: 29b.

Functions:

   * *note PyConfig_Clear(): 29c.

   * *note PyConfig_InitIsolatedConfig(): 29d.

   * *note PyConfig_InitPythonConfig(): 29e.

   * *note PyConfig_Read(): 29f.

   * *note PyConfig_SetArgv(): 2a0.

   * *note PyConfig_SetBytesArgv(): 2a1.

   * *note PyConfig_SetBytesString(): 2a2.

   * *note PyConfig_SetString(): 2a3.

   * *note PyConfig_SetWideStringList(): 41dc.

   * *note PyPreConfig_InitIsolatedConfig(): 2a4.

   * *note PyPreConfig_InitPythonConfig(): 2a5.

   * *note PyStatus_Error(): 2a6.

   * *note PyStatus_Exception(): 2a7.

   * *note PyStatus_Exit(): 2a8.

   * *note PyStatus_IsError(): 2a9.

   * *note PyStatus_IsExit(): 2aa.

   * *note PyStatus_NoMemory(): 2ab.

   * *note PyStatus_Ok(): 2ac.

   * *note PyWideStringList_Append(): 2ad.

   * *note PyWideStringList_Insert(): 2ae.

   * *note Py_ExitStatusException(): 2b0.

   * *note Py_InitializeFromConfig(): 2b1.

   * *note Py_PreInitialize(): 2b2.

   * *note Py_PreInitializeFromArgs(): 2b3.

   * *note Py_PreInitializeFromBytesArgs(): 2b4.

   * *note Py_RunMain(): 2b5.

   * *note Py_GetArgcArgv(): 1037.

The preconfiguration (‘PyPreConfig’ type) is stored in
‘_PyRuntime.preconfig’ and the configuration (‘PyConfig’ type) is stored
in ‘PyInterpreterState.config’.

See also *note Initialization, Finalization, and Threads: 4181.

See also
........

PEP 587(1) “Python Initialization Configuration”.

* Menu:

* PyWideStringList::
* PyStatus::
* PyPreConfig::
* Preinitialization with PyPreConfig::
* PyConfig::
* Initialization with PyConfig::
* Isolated Configuration::
* Python Configuration::
* Path Configuration::
* Py_RunMain(): Py_RunMain.
* Py_GetArgcArgv(): Py_GetArgcArgv.
* Multi-Phase Initialization Private Provisional API::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0587


File: python.info,  Node: PyWideStringList,  Next: PyStatus,  Up: Python Initialization Configuration

7.10.1 PyWideStringList
-----------------------

 -- C Type: PyWideStringList

     List of ‘wchar_t*’ strings.

     If `length' is non-zero, `items' must be non-‘NULL’ and all strings
     must be non-‘NULL’.

     Methods:

      -- C Function: PyStatus PyWideStringList_Append
               (PyWideStringList *list, const wchar_t *item)

          Append `item' to `list'.

          Python must be preinitialized to call this function.

      -- C Function: PyStatus PyWideStringList_Insert
               (PyWideStringList *list, Py_ssize_t index, const
               wchar_t *item)

          Insert `item' into `list' at `index'.

          If `index' is greater than or equal to `list' length, append
          `item' to `list'.

          `index' must be greater than or equal to 0.

          Python must be preinitialized to call this function.

     Structure fields:

      -- C Member: Py_ssize_t length

          List length.

      -- C Member: wchar_t** items

          List items.


File: python.info,  Node: PyStatus,  Next: PyPreConfig,  Prev: PyWideStringList,  Up: Python Initialization Configuration

7.10.2 PyStatus
---------------

 -- C Type: PyStatus

     Structure to store an initialization function status: success,
     error or exit.

     For an error, it can store the C function name which created the
     error.

     Structure fields:

      -- C Member: int exitcode

          Exit code.  Argument passed to ‘exit()’.

      -- C Member: const char *err_msg

          Error message.

      -- C Member: const char *func

          Name of the function which created an error, can be ‘NULL’.

     Functions to create a status:

      -- C Function: PyStatus PyStatus_Ok (void)

          Success.

      -- C Function: PyStatus PyStatus_Error (const char *err_msg)

          Initialization error with a message.

      -- C Function: PyStatus PyStatus_NoMemory (void)

          Memory allocation failure (out of memory).

      -- C Function: PyStatus PyStatus_Exit (int exitcode)

          Exit Python with the specified exit code.

     Functions to handle a status:

      -- C Function: int PyStatus_Exception (PyStatus status)

          Is the status an error or an exit?  If true, the exception
          must be handled; by calling *note Py_ExitStatusException():
          2b0. for example.

      -- C Function: int PyStatus_IsError (PyStatus status)

          Is the result an error?

      -- C Function: int PyStatus_IsExit (PyStatus status)

          Is the result an exit?

      -- C Function: void Py_ExitStatusException (PyStatus status)

          Call ‘exit(exitcode)’ if `status' is an exit.  Print the error
          message and exit with a non-zero exit code if `status' is an
          error.  Must only be called if ‘PyStatus_Exception(status)’ is
          non-zero.

     Note: Internally, Python uses macros which set ‘PyStatus.func’,
     whereas functions to create a status set ‘func’ to ‘NULL’.

Example:

     PyStatus alloc(void **ptr, size_t size)
     {
         *ptr = PyMem_RawMalloc(size);
         if (*ptr == NULL) {
             return PyStatus_NoMemory();
         }
         return PyStatus_Ok();
     }

     int main(int argc, char **argv)
     {
         void *ptr;
         PyStatus status = alloc(&ptr, 16);
         if (PyStatus_Exception(status)) {
             Py_ExitStatusException(status);
         }
         PyMem_Free(ptr);
         return 0;
     }


File: python.info,  Node: PyPreConfig,  Next: Preinitialization with PyPreConfig,  Prev: PyStatus,  Up: Python Initialization Configuration

7.10.3 PyPreConfig
------------------

 -- C Type: PyPreConfig

     Structure used to preinitialize Python:

        * Set the Python memory allocator

        * Configure the LC_CTYPE locale

        * Set the UTF-8 mode

     Function to initialize a preconfiguration:

      -- C Function: void PyPreConfig_InitPythonConfig
               (PyPreConfig *preconfig)

          Initialize the preconfiguration with *note Python
          Configuration: 41e5.

      -- C Function: void PyPreConfig_InitIsolatedConfig
               (PyPreConfig *preconfig)

          Initialize the preconfiguration with *note Isolated
          Configuration: 41e6.

     Structure fields:

      -- C Member: int allocator

          Name of the memory allocator:

             * ‘PYMEM_ALLOCATOR_NOT_SET’ (‘0’): don’t change memory
               allocators (use defaults)

             * ‘PYMEM_ALLOCATOR_DEFAULT’ (‘1’): default memory
               allocators

             * ‘PYMEM_ALLOCATOR_DEBUG’ (‘2’): default memory allocators
               with debug hooks

             * ‘PYMEM_ALLOCATOR_MALLOC’ (‘3’): force usage of ‘malloc()’

             * ‘PYMEM_ALLOCATOR_MALLOC_DEBUG’ (‘4’): force usage of
               ‘malloc()’ with debug hooks

             * ‘PYMEM_ALLOCATOR_PYMALLOC’ (‘5’): *note Python pymalloc
               memory allocator: 6b8.

             * ‘PYMEM_ALLOCATOR_PYMALLOC_DEBUG’ (‘6’): *note Python
               pymalloc memory allocator: 6b8. with debug hooks

          ‘PYMEM_ALLOCATOR_PYMALLOC’ and
          ‘PYMEM_ALLOCATOR_PYMALLOC_DEBUG’ are not supported if Python
          is configured using ‘--without-pymalloc’

          See *note Memory Management: 41e8.

      -- C Member: int configure_locale

          Set the LC_CTYPE locale to the user preferred locale?  If
          equals to 0, set ‘coerce_c_locale’ and ‘coerce_c_locale_warn’
          to 0.

      -- C Member: int coerce_c_locale

          If equals to 2, coerce the C locale; if equals to 1, read the
          LC_CTYPE locale to decide if it should be coerced.

      -- C Member: int coerce_c_locale_warn

          If non-zero, emit a warning if the C locale is coerced.

      -- C Member: int dev_mode

          See *note PyConfig.dev_mode: 41ed.

      -- C Member: int isolated

          See *note PyConfig.isolated: 41ef.

      -- C Member: int legacy_windows_fs_encoding (Windows only)

          If non-zero, disable UTF-8 Mode, set the Python filesystem
          encoding to ‘mbcs’, set the filesystem error handler to
          ‘replace’.

          Only available on Windows.  ‘#ifdef MS_WINDOWS’ macro can be
          used for Windows specific code.

      -- C Member: int parse_argv

          If non-zero, *note Py_PreInitializeFromArgs(): 2b3. and *note
          Py_PreInitializeFromBytesArgs(): 2b4. parse their ‘argv’
          argument the same way the regular Python parses command line
          arguments: see *note Command Line Arguments: a10.

      -- C Member: int use_environment

          See *note PyConfig.use_environment: 261.

      -- C Member: int utf8_mode

          If non-zero, enable the UTF-8 mode.


File: python.info,  Node: Preinitialization with PyPreConfig,  Next: PyConfig,  Prev: PyPreConfig,  Up: Python Initialization Configuration

7.10.4 Preinitialization with PyPreConfig
-----------------------------------------

Functions to preinitialize Python:

 -- C Function: PyStatus Py_PreInitialize (const PyPreConfig *preconfig)

     Preinitialize Python from `preconfig' preconfiguration.

 -- C Function: PyStatus Py_PreInitializeFromBytesArgs (const
          PyPreConfig *preconfig, int argc, char * const *argv)

     Preinitialize Python from `preconfig' preconfiguration and command
     line arguments (bytes strings).

 -- C Function: PyStatus Py_PreInitializeFromArgs (const
          PyPreConfig *preconfig, int argc, wchar_t * const * argv)

     Preinitialize Python from `preconfig' preconfiguration and command
     line arguments (wide strings).

The caller is responsible to handle exceptions (error or exit) using
*note PyStatus_Exception(): 2a7. and *note Py_ExitStatusException():
2b0.

For *note Python Configuration: 41e5. (*note
PyPreConfig_InitPythonConfig(): 2a5.), if Python is initialized with
command line arguments, the command line arguments must also be passed
to preinitialize Python, since they have an effect on the
pre-configuration like encodings.  For example, the *note -X utf8: 290.
command line option enables the UTF-8 Mode.

‘PyMem_SetAllocator()’ can be called after *note Py_PreInitialize():
2b2. and before *note Py_InitializeFromConfig(): 2b1. to install a
custom memory allocator.  It can be called before *note
Py_PreInitialize(): 2b2. if *note PyPreConfig.allocator: 41e7. is set to
‘PYMEM_ALLOCATOR_NOT_SET’.

Python memory allocation functions like *note PyMem_RawMalloc(): a4e.
must not be used before Python preinitialization, whereas calling
directly ‘malloc()’ and ‘free()’ is always safe.  *note
Py_DecodeLocale(): 53f. must not be called before the preinitialization.

Example using the preinitialization to enable the UTF-8 Mode:

     PyStatus status;
     PyPreConfig preconfig;
     PyPreConfig_InitPythonConfig(&preconfig);

     preconfig.utf8_mode = 1;

     status = Py_PreInitialize(&preconfig);
     if (PyStatus_Exception(status)) {
         Py_ExitStatusException(status);
     }

     /* at this point, Python will speak UTF-8 */

     Py_Initialize();
     /* ... use Python API here ... */
     Py_Finalize();


File: python.info,  Node: PyConfig,  Next: Initialization with PyConfig,  Prev: Preinitialization with PyPreConfig,  Up: Python Initialization Configuration

7.10.5 PyConfig
---------------

 -- C Type: PyConfig

     Structure containing most parameters to configure Python.

     Structure methods:

      -- C Function: void PyConfig_InitPythonConfig (PyConfig *config)

          Initialize configuration with *note Python Configuration:
          41e5.

      -- C Function: void PyConfig_InitIsolatedConfig (PyConfig *config)

          Initialize configuration with *note Isolated Configuration:
          41e6.

      -- C Function: PyStatus PyConfig_SetString (PyConfig *config,
               wchar_t * const *config_str, const wchar_t *str)

          Copy the wide character string `str' into ‘*config_str’.

          Preinitialize Python if needed.

      -- C Function: PyStatus PyConfig_SetBytesString (PyConfig *config,
               wchar_t * const *config_str, const char *str)

          Decode `str' using ‘Py_DecodeLocale()’ and set the result into
          ‘*config_str’.

          Preinitialize Python if needed.

      -- C Function: PyStatus PyConfig_SetArgv (PyConfig *config,
               int argc, wchar_t * const *argv)

          Set command line arguments from wide character strings.

          Preinitialize Python if needed.

      -- C Function: PyStatus PyConfig_SetBytesArgv (PyConfig *config,
               int argc, char * const *argv)

          Set command line arguments: decode bytes using *note
          Py_DecodeLocale(): 53f.

          Preinitialize Python if needed.

      -- C Function: PyStatus PyConfig_SetWideStringList
               (PyConfig *config, PyWideStringList *list,
               Py_ssize_t length, wchar_t **items)

          Set the list of wide strings `list' to `length' and `items'.

          Preinitialize Python if needed.

      -- C Function: PyStatus PyConfig_Read (PyConfig *config)

          Read all Python configuration.

          Fields which are already initialized are left unchanged.

          Preinitialize Python if needed.

      -- C Function: void PyConfig_Clear (PyConfig *config)

          Release configuration memory.

     Most ‘PyConfig’ methods preinitialize Python if needed.  In that
     case, the Python preinitialization configuration in based on the
     *note PyConfig: 226.  If configuration fields which are in common
     with *note PyPreConfig: 299. are tuned, they must be set before
     calling a *note PyConfig: 226. method:

        * *note dev_mode: 41ed.

        * *note isolated: 41ef.

        * *note parse_argv: 41f6.

        * *note use_environment: 261.

     Moreover, if *note PyConfig_SetArgv(): 2a0. or *note
     PyConfig_SetBytesArgv(): 2a1. is used, this method must be called
     first, before other methods, since the preinitialization
     configuration depends on command line arguments (if ‘parse_argv’ is
     non-zero).

     The caller of these methods is responsible to handle exceptions
     (error or exit) using ‘PyStatus_Exception()’ and
     ‘Py_ExitStatusException()’.

     Structure fields:

      -- C Member: PyWideStringList argv

          Command line arguments, *note sys.argv: cc6.  See *note
          parse_argv: 41f6. to parse *note argv: 41f7. the same way the
          regular Python parses Python command line arguments.  If *note
          argv: 41f7. is empty, an empty string is added to ensure that
          *note sys.argv: cc6. always exists and is never empty.

      -- C Member: wchar_t* base_exec_prefix

          *note sys.base_exec_prefix: 3781.

      -- C Member: wchar_t* base_executable

          ‘sys._base_executable’: ‘__PYVENV_LAUNCHER__’ environment
          variable value, or copy of *note PyConfig.executable: 41fa.

      -- C Member: wchar_t* base_prefix

          *note sys.base_prefix: 3180.

      -- C Member: wchar_t* platlibdir

          *note sys.platlibdir: 1e9.: platform library directory name,
          set at configure time by ‘--with-platlibdir’, overrideable by
          the ‘PYTHONPLATLIBDIR’ environment variable.

          New in version 3.9.

      -- C Member: int buffered_stdio

          If equals to 0, enable unbuffered mode, making the stdout and
          stderr streams unbuffered.

          stdin is always opened in buffered mode.

      -- C Member: int bytes_warning

          If equals to 1, issue a warning when comparing *note bytes:
          172. or *note bytearray: 173. with *note str: 205, or
          comparing *note bytes: 172. with *note int: 204.  If equal or
          greater to 2, raise a *note BytesWarning: 5b0. exception.

      -- C Member: wchar_t* check_hash_pycs_mode

          Control the validation behavior of hash-based ‘.pyc’ files
          (see PEP 552(1)): *note –check-hash-based-pycs: 1475. command
          line option value.

          Valid values: ‘always’, ‘never’ and ‘default’.

          The default value is: ‘default’.

      -- C Member: int configure_c_stdio

          If non-zero, configure C standard streams (‘stdio’, ‘stdout’,
          ‘stdout’).  For example, set their mode to ‘O_BINARY’ on
          Windows.

      -- C Member: int dev_mode

          If non-zero, enable the *note Python Development Mode: 160.

      -- C Member: int dump_refs

          If non-zero, dump all objects which are still alive at exit.

          ‘Py_TRACE_REFS’ macro must be defined in build.

      -- C Member: wchar_t* exec_prefix

          *note sys.exec_prefix: 3780.

      -- C Member: wchar_t* executable

          *note sys.executable: 39d.

      -- C Member: int faulthandler

          If non-zero, call *note faulthandler.enable(): 642. at
          startup.

      -- C Member: wchar_t* filesystem_encoding

          Filesystem encoding, *note sys.getfilesystemencoding(): 5f0.

      -- C Member: wchar_t* filesystem_errors

          Filesystem encoding errors, *note
          sys.getfilesystemencodeerrors(): 68b.

      -- C Member: unsigned long hash_seed

      -- C Member: int use_hash_seed

          Randomized hash function seed.

          If *note use_hash_seed: 4206. is zero, a seed is chosen
          randomly at Pythonstartup, and *note hash_seed: 4205. is
          ignored.

      -- C Member: wchar_t* home

          Python home directory.

          Initialized from *note PYTHONHOME: 5d1. environment variable
          value by default.

      -- C Member: int import_time

          If non-zero, profile import time.

      -- C Member: int inspect

          Enter interactive mode after executing a script or a command.

      -- C Member: int install_signal_handlers

          Install signal handlers?

      -- C Member: int interactive

          Interactive mode.

      -- C Member: int isolated

          If greater than 0, enable isolated mode:

             * *note sys.path: 260. contains neither the script’s
               directory (computed from ‘argv[0]’ or the current
               directory) nor the user’s site-packages directory.

             * Python REPL doesn’t import *note readline: de. nor enable
               default readline configuration on interactive prompts.

             * Set *note use_environment: 261. and *note
               user_site_directory: 420b. to 0.

      -- C Member: int legacy_windows_stdio

          If non-zero, use *note io.FileIO: d6c. instead of
          ‘io.WindowsConsoleIO’ for *note sys.stdin: 41e, *note
          sys.stdout: 41f. and *note sys.stderr: 1ea.

          Only available on Windows.  ‘#ifdef MS_WINDOWS’ macro can be
          used for Windows specific code.

      -- C Member: int malloc_stats

          If non-zero, dump statistics on *note Python pymalloc memory
          allocator: 6b8. at exit.

          The option is ignored if Python is built using
          ‘--without-pymalloc’.

      -- C Member: wchar_t* pythonpath_env

          Module search paths as a string separated by ‘DELIM’
          (‘os.path.pathsep’).

          Initialized from *note PYTHONPATH: a34. environment variable
          value by default.

      -- C Member: PyWideStringList module_search_paths

      -- C Member: int module_search_paths_set

          *note sys.path: 260.  If *note module_search_paths_set: 4210.
          is equal to 0, the *note module_search_paths: 420f. is
          overridden by the function calculating the *note Path
          Configuration: 1016.

      -- C Member: int optimization_level

          Compilation optimization level:

             * 0: Peephole optimizer (and ‘__debug__’ is set to ‘True’)

             * 1: Remove assertions, set ‘__debug__’ to ‘False’

             * 2: Strip docstrings

      -- C Member: int parse_argv

          If non-zero, parse *note argv: 41f7. the same way the regular
          Python command line arguments, and strip Python arguments from
          *note argv: 41f7.: see *note Command Line Arguments: a10.

      -- C Member: int parser_debug

          If non-zero, turn on parser debugging output (for expert only,
          depending on compilation options).

      -- C Member: int pathconfig_warnings

          If equal to 0, suppress warnings when calculating the *note
          Path Configuration: 1016. (Unix only, Windows does not log any
          warning).  Otherwise, warnings are written into ‘stderr’.

      -- C Member: wchar_t* prefix

          *note sys.prefix: 377f.

      -- C Member: wchar_t* program_name

          Program name.  Used to initialize *note executable: 41fa, and
          in early error messages.

      -- C Member: wchar_t* pycache_prefix

          *note sys.pycache_prefix: 291.: ‘.pyc’ cache prefix.

          If ‘NULL’, *note sys.pycache_prefix: 291. is set to ‘None’.

      -- C Member: int quiet

          Quiet mode.  For example, don’t display the copyright and
          version messages in interactive mode.

      -- C Member: wchar_t* run_command

          ‘python3 -c COMMAND’ argument.  Used by *note Py_RunMain():
          2b5.

      -- C Member: wchar_t* run_filename

          ‘python3 FILENAME’ argument.  Used by *note Py_RunMain(): 2b5.

      -- C Member: wchar_t* run_module

          ‘python3 -m MODULE’ argument.  Used by *note Py_RunMain():
          2b5.

      -- C Member: int show_ref_count

          Show total reference count at exit?

          Set to 1 by *note -X showrefcount: 290. command line option.

          Need a debug build of Python (‘Py_REF_DEBUG’ macro must be
          defined).

      -- C Member: int site_import

          Import the *note site: eb. module at startup?

      -- C Member: int skip_source_first_line

          Skip the first line of the source?

      -- C Member: wchar_t* stdio_encoding

      -- C Member: wchar_t* stdio_errors

          Encoding and encoding errors of *note sys.stdin: 41e, *note
          sys.stdout: 41f. and *note sys.stderr: 1ea.

      -- C Member: int tracemalloc

          If non-zero, call *note tracemalloc.start(): 1481. at startup.

      -- C Member: int use_environment

          If greater than 0, use *note environment variables: 1485.

      -- C Member: int user_site_directory

          If non-zero, add user site directory to *note sys.path: 260.

      -- C Member: int verbose

          If non-zero, enable verbose mode.

      -- C Member: PyWideStringList warnoptions

          *note sys.warnoptions: 51b.: options of the *note warnings:
          12f. module to build warnings filters: lowest to highest
          priority.

          The *note warnings: 12f. module adds *note sys.warnoptions:
          51b. in the reverse order: the last *note
          PyConfig.warnoptions: 4222. item becomes the first item of
          ‘warnings.filters’ which is checked first (highest priority).

      -- C Member: int write_bytecode

          If non-zero, write ‘.pyc’ files.

          *note sys.dont_write_bytecode: 37ae. is initialized to the
          inverted value of *note write_bytecode: 4223.

      -- C Member: PyWideStringList xoptions

          *note sys._xoptions: 1482.

      -- C Member: int _use_peg_parser

          Enable PEG parser?  Default: 1.

          Set to 0 by *note -X oldparser: 290. and *note
          PYTHONOLDPARSER: 1480.

          See also PEP 617(2).

          Deprecated since version 3.9, will be removed in version 3.10.

If ‘parse_argv’ is non-zero, ‘argv’ arguments are parsed the same way
the regular Python parses command line arguments, and Python arguments
are stripped from ‘argv’: see *note Command Line Arguments: a10.

The ‘xoptions’ options are parsed to set other options: see *note -X:
290. option.

Changed in version 3.9: The ‘show_alloc_count’ field has been removed.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0552

   (2) https://www.python.org/dev/peps/pep-0617


File: python.info,  Node: Initialization with PyConfig,  Next: Isolated Configuration,  Prev: PyConfig,  Up: Python Initialization Configuration

7.10.6 Initialization with PyConfig
-----------------------------------

Function to initialize Python:

 -- C Function: PyStatus Py_InitializeFromConfig (const
          PyConfig *config)

     Initialize Python from `config' configuration.

The caller is responsible to handle exceptions (error or exit) using
*note PyStatus_Exception(): 2a7. and *note Py_ExitStatusException():
2b0.

If *note PyImport_FrozenModules(): 2452, *note PyImport_AppendInittab():
f9c. or *note PyImport_ExtendInittab(): f9d. are used, they must be set
or called after Python preinitialization and before the Python
initialization.  If Python is initialized multiple times, *note
PyImport_AppendInittab(): f9c. or *note PyImport_ExtendInittab(): f9d.
must be called before each Python initialization.

Example setting the program name:

     void init_python(void)
     {
         PyStatus status;

         PyConfig config;
         PyConfig_InitPythonConfig(&config);

         /* Set the program name. Implicitly preinitialize Python. */
         status = PyConfig_SetString(&config, &config.program_name,
                                     L"/path/to/my_program");
         if (PyStatus_Exception(status)) {
             goto fail;
         }

         status = Py_InitializeFromConfig(&config);
         if (PyStatus_Exception(status)) {
             goto fail;
         }
         PyConfig_Clear(&config);
         return;

     fail:
         PyConfig_Clear(&config);
         Py_ExitStatusException(status);
     }

More complete example modifying the default configuration, read the
configuration, and then override some parameters:

     PyStatus init_python(const char *program_name)
     {
         PyStatus status;

         PyConfig config;
         PyConfig_InitPythonConfig(&config);

         /* Set the program name before reading the configuration
            (decode byte string from the locale encoding).

            Implicitly preinitialize Python. */
         status = PyConfig_SetBytesString(&config, &config.program_name,
                                       program_name);
         if (PyStatus_Exception(status)) {
             goto done;
         }

         /* Read all configuration at once */
         status = PyConfig_Read(&config);
         if (PyStatus_Exception(status)) {
             goto done;
         }

         /* Append our custom search path to sys.path */
         status = PyWideStringList_Append(&config.module_search_paths,
                                          L"/path/to/more/modules");
         if (PyStatus_Exception(status)) {
             goto done;
         }

         /* Override executable computed by PyConfig_Read() */
         status = PyConfig_SetString(&config, &config.executable,
                                     L"/path/to/my_executable");
         if (PyStatus_Exception(status)) {
             goto done;
         }

         status = Py_InitializeFromConfig(&config);

     done:
         PyConfig_Clear(&config);
         return status;
     }


File: python.info,  Node: Isolated Configuration,  Next: Python Configuration,  Prev: Initialization with PyConfig,  Up: Python Initialization Configuration

7.10.7 Isolated Configuration
-----------------------------

*note PyPreConfig_InitIsolatedConfig(): 2a4. and *note
PyConfig_InitIsolatedConfig(): 29d. functions create a configuration to
isolate Python from the system.  For example, to embed Python into an
application.

This configuration ignores global configuration variables, environments
variables, command line arguments (*note PyConfig.argv: 41f7. is not
parsed) and user site directory.  The C standard streams (ex: ‘stdout’)
and the LC_CTYPE locale are left unchanged.  Signal handlers are not
installed.

Configuration files are still used with this configuration.  Set the
*note Path Configuration: 1016. (“output fields”) to ignore these
configuration files and avoid the function computing the default path
configuration.


File: python.info,  Node: Python Configuration,  Next: Path Configuration,  Prev: Isolated Configuration,  Up: Python Initialization Configuration

7.10.8 Python Configuration
---------------------------

*note PyPreConfig_InitPythonConfig(): 2a5. and *note
PyConfig_InitPythonConfig(): 29e. functions create a configuration to
build a customized Python which behaves as the regular Python.

Environments variables and command line arguments are used to configure
Python, whereas global configuration variables are ignored.

This function enables C locale coercion ( PEP 538(1)) and UTF-8 Mode (
PEP 540(2)) depending on the LC_CTYPE locale, *note PYTHONUTF8: 421. and
*note PYTHONCOERCECLOCALE: 41d. environment variables.

Example of customized Python always running in isolated mode:

     int main(int argc, char **argv)
     {
         PyStatus status;

         PyConfig config;
         PyConfig_InitPythonConfig(&config);
         config.isolated = 1;

         /* Decode command line arguments.
            Implicitly preinitialize Python (in isolated mode). */
         status = PyConfig_SetBytesArgv(&config, argc, argv);
         if (PyStatus_Exception(status)) {
             goto fail;
         }

         status = Py_InitializeFromConfig(&config);
         if (PyStatus_Exception(status)) {
             goto fail;
         }
         PyConfig_Clear(&config);

         return Py_RunMain();

     fail:
         PyConfig_Clear(&config);
         if (PyStatus_IsExit(status)) {
             return status.exitcode;
         }
         /* Display the error message and exit the process with
            non-zero exit code */
         Py_ExitStatusException(status);
     }

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0538

   (2) https://www.python.org/dev/peps/pep-0540


File: python.info,  Node: Path Configuration,  Next: Py_RunMain,  Prev: Python Configuration,  Up: Python Initialization Configuration

7.10.9 Path Configuration
-------------------------

*note PyConfig: 226. contains multiple fields for the path
configuration:

   * Path configuration inputs:

        * *note PyConfig.home: 4207.

        * *note PyConfig.platlibdir: 1017.

        * *note PyConfig.pathconfig_warnings: 4213.

        * *note PyConfig.program_name: 4215.

        * *note PyConfig.pythonpath_env: 420e.

        * current working directory: to get absolute paths

        * ‘PATH’ environment variable to get the program full path (from
          *note PyConfig.program_name: 4215.)

        * ‘__PYVENV_LAUNCHER__’ environment variable

        * (Windows only) Application paths in the registry under
          “SoftwarePythonPythonCoreX.YPythonPath” of HKEY_CURRENT_USER
          and HKEY_LOCAL_MACHINE (where X.Y is the Python version).

   * Path configuration output fields:

        * *note PyConfig.base_exec_prefix: 41f8.

        * *note PyConfig.base_executable: 41f9.

        * *note PyConfig.base_prefix: 41fb.

        * *note PyConfig.exec_prefix: 4201.

        * *note PyConfig.executable: 41fa.

        * *note PyConfig.module_search_paths_set: 4210, *note
          PyConfig.module_search_paths: 420f.

        * *note PyConfig.prefix: 4214.

If at least one “output field” is not set, Python calculates the path
configuration to fill unset fields.  If *note module_search_paths_set:
4210. is equal to 0, *note module_search_paths: 420f. is overridden and
*note module_search_paths_set: 4210. is set to 1.

It is possible to completely ignore the function calculating the default
path configuration by setting explicitly all path configuration output
fields listed above.  A string is considered as set even if it is
non-empty.  ‘module_search_paths’ is considered as set if
‘module_search_paths_set’ is set to 1.  In this case, path configuration
input fields are ignored as well.

Set *note pathconfig_warnings: 4213. to 0 to suppress warnings when
calculating the path configuration (Unix only, Windows does not log any
warning).

If *note base_prefix: 41fb. or *note base_exec_prefix: 41f8. fields are
not set, they inherit their value from *note prefix: 4214. and *note
exec_prefix: 4201. respectively.

*note Py_RunMain(): 2b5. and *note Py_Main(): 5b2. modify *note
sys.path: 260.:

   * If *note run_filename: 4219. is set and is a directory which
     contains a ‘__main__.py’ script, prepend *note run_filename: 4219.
     to *note sys.path: 260.

   * If *note isolated: 41ef. is zero:

        * If *note run_module: 421a. is set, prepend the current
          directory to *note sys.path: 260.  Do nothing if the current
          directory cannot be read.

        * If *note run_filename: 4219. is set, prepend the directory of
          the filename to *note sys.path: 260.

        * Otherwise, prepend an empty string to *note sys.path: 260.

If *note site_import: 421c. is non-zero, *note sys.path: 260. can be
modified by the *note site: eb. module.  If *note user_site_directory:
420b. is non-zero and the user’s site-package directory exists, the
*note site: eb. module appends the user’s site-package directory to
*note sys.path: 260.

The following configuration files are used by the path configuration:

   * ‘pyvenv.cfg’

   * ‘python._pth’ (Windows only)

   * ‘pybuilddir.txt’ (Unix only)

The ‘__PYVENV_LAUNCHER__’ environment variable is used to set *note
PyConfig.base_executable: 41f9.


File: python.info,  Node: Py_RunMain,  Next: Py_GetArgcArgv,  Prev: Path Configuration,  Up: Python Initialization Configuration

7.10.10 Py_RunMain()
--------------------

 -- C Function: int Py_RunMain (void)

     Execute the command (*note PyConfig.run_command: 4218.), the script
     (*note PyConfig.run_filename: 4219.) or the module (*note
     PyConfig.run_module: 421a.) specified on the command line or in the
     configuration.

     By default and when if *note -i: ee1. option is used, run the REPL.

     Finally, finalizes Python and returns an exit status that can be
     passed to the ‘exit()’ function.

See *note Python Configuration: 41e5. for an example of customized
Python always running in isolated mode using *note Py_RunMain(): 2b5.


File: python.info,  Node: Py_GetArgcArgv,  Next: Multi-Phase Initialization Private Provisional API,  Prev: Py_RunMain,  Up: Python Initialization Configuration

7.10.11 Py_GetArgcArgv()
------------------------

 -- C Function: void Py_GetArgcArgv (int *argc, wchar_t ***argv)

     Get the original command line arguments, before Python modified
     them.


File: python.info,  Node: Multi-Phase Initialization Private Provisional API,  Prev: Py_GetArgcArgv,  Up: Python Initialization Configuration

7.10.12 Multi-Phase Initialization Private Provisional API
----------------------------------------------------------

This section is a private provisional API introducing multi-phase
initialization, the core feature of the PEP 432(1):

   * “Core” initialization phase, “bare minimum Python”:

        * Builtin types;

        * Builtin exceptions;

        * Builtin and frozen modules;

        * The *note sys: fd. module is only partially initialized (ex:
          *note sys.path: 260. doesn’t exist yet).

   * “Main” initialization phase, Python is fully initialized:

        * Install and configure *note importlib: 9a.;

        * Apply the *note Path Configuration: 1016.;

        * Install signal handlers;

        * Finish *note sys: fd. module initialization (ex: create *note
          sys.stdout: 41f. and *note sys.path: 260.);

        * Enable optional features like *note faulthandler: 7b. and
          *note tracemalloc: 11d.;

        * Import the *note site: eb. module;

        * etc.

Private provisional API:

   * ‘PyConfig._init_main’: if set to 0, *note
     Py_InitializeFromConfig(): 2b1. stops at the “Core” initialization
     phase.

   * ‘PyConfig._isolated_interpreter’: if non-zero, disallow threads,
     subprocesses and fork.

 -- C Function: PyStatus _Py_InitializeMain (void)

     Move to the “Main” initialization phase, finish the Python
     initialization.

No module is imported during the “Core” phase and the ‘importlib’ module
is not configured: the *note Path Configuration: 1016. is only applied
during the “Main” phase.  It may allow to customize Python in Python to
override or tune the *note Path Configuration: 1016, maybe install a
custom *note sys.meta_path: 6dd. importer or an import hook, etc.

It may become possible to calculatin the *note Path Configuration: 1016.
in Python, after the Core phase and before the Main phase, which is one
of the PEP 432(2) motivation.

The “Core” phase is not properly defined: what should be and what should
not be available at this phase is not specified yet.  The API is marked
as private and provisional: the API can be modified or even be removed
anytime until a proper public API is designed.

Example running Python code between “Core” and “Main” initialization
phases:

     void init_python(void)
     {
         PyStatus status;

         PyConfig config;
         PyConfig_InitPythonConfig(&config);
         config._init_main = 0;

         /* ... customize 'config' configuration ... */

         status = Py_InitializeFromConfig(&config);
         PyConfig_Clear(&config);
         if (PyStatus_Exception(status)) {
             Py_ExitStatusException(status);
         }

         /* Use sys.stderr because sys.stdout is only created
            by _Py_InitializeMain() */
         int res = PyRun_SimpleString(
             "import sys; "
             "print('Run Python code before _Py_InitializeMain', "
                    "file=sys.stderr)");
         if (res < 0) {
             exit(1);
         }

         /* ... put more configuration code here ... */

         status = _Py_InitializeMain();
         if (PyStatus_Exception(status)) {
             Py_ExitStatusException(status);
         }
     }

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0432

   (2) https://www.python.org/dev/peps/pep-0432


File: python.info,  Node: Memory Management,  Next: Object Implementation Support,  Prev: Python Initialization Configuration,  Up: Python/C API Reference Manual

7.11 Memory Management
======================

* Menu:

* Overview: Overview<3>.
* Raw Memory Interface::
* Memory Interface::
* Object allocators::
* Default Memory Allocators::
* Customize Memory Allocators::
* The pymalloc allocator::
* tracemalloc C API::
* Examples: Examples<35>.


File: python.info,  Node: Overview<3>,  Next: Raw Memory Interface,  Up: Memory Management

7.11.1 Overview
---------------

Memory management in Python involves a private heap containing all
Python objects and data structures.  The management of this private heap
is ensured internally by the `Python memory manager'.  The Python memory
manager has different components which deal with various dynamic storage
management aspects, like sharing, segmentation, preallocation or
caching.

At the lowest level, a raw memory allocator ensures that there is enough
room in the private heap for storing all Python-related data by
interacting with the memory manager of the operating system.  On top of
the raw memory allocator, several object-specific allocators operate on
the same heap and implement distinct memory management policies adapted
to the peculiarities of every object type.  For example, integer objects
are managed differently within the heap than strings, tuples or
dictionaries because integers imply different storage requirements and
speed/space tradeoffs.  The Python memory manager thus delegates some of
the work to the object-specific allocators, but ensures that the latter
operate within the bounds of the private heap.

It is important to understand that the management of the Python heap is
performed by the interpreter itself and that the user has no control
over it, even if they regularly manipulate object pointers to memory
blocks inside that heap.  The allocation of heap space for Python
objects and other internal buffers is performed on demand by the Python
memory manager through the Python/C API functions listed in this
document.

To avoid memory corruption, extension writers should never try to
operate on Python objects with the functions exported by the C library:
‘malloc()’, ‘calloc()’, ‘realloc()’ and ‘free()’.  This will result in
mixed calls between the C allocator and the Python memory manager with
fatal consequences, because they implement different algorithms and
operate on different heaps.  However, one may safely allocate and
release memory blocks with the C library allocator for individual
purposes, as shown in the following example:

     PyObject *res;
     char *buf = (char *) malloc(BUFSIZ); /* for I/O */

     if (buf == NULL)
         return PyErr_NoMemory();
     ...Do some I/O operation involving buf...
     res = PyBytes_FromString(buf);
     free(buf); /* malloc'ed */
     return res;

In this example, the memory request for the I/O buffer is handled by the
C library allocator.  The Python memory manager is involved only in the
allocation of the bytes object returned as a result.

In most situations, however, it is recommended to allocate memory from
the Python heap specifically because the latter is under control of the
Python memory manager.  For example, this is required when the
interpreter is extended with new object types written in C. Another
reason for using the Python heap is the desire to `inform' the Python
memory manager about the memory needs of the extension module.  Even
when the requested memory is used exclusively for internal,
highly-specific purposes, delegating all memory requests to the Python
memory manager causes the interpreter to have a more accurate image of
its memory footprint as a whole.  Consequently, under certain
circumstances, the Python memory manager may or may not trigger
appropriate actions, like garbage collection, memory compaction or other
preventive procedures.  Note that by using the C library allocator as
shown in the previous example, the allocated memory for the I/O buffer
escapes completely the Python memory manager.

See also
........

The *note PYTHONMALLOC: 5fd. environment variable can be used to
configure the memory allocators used by Python.

The *note PYTHONMALLOCSTATS: 1297. environment variable can be used to
print statistics of the *note pymalloc memory allocator: 6b8. every time
a new pymalloc object arena is created, and on shutdown.


File: python.info,  Node: Raw Memory Interface,  Next: Memory Interface,  Prev: Overview<3>,  Up: Memory Management

7.11.2 Raw Memory Interface
---------------------------

The following function sets are wrappers to the system allocator.  These
functions are thread-safe, the *note GIL: 600. does not need to be held.

The *note default raw memory allocator: 148f. uses the following
functions: ‘malloc()’, ‘calloc()’, ‘realloc()’ and ‘free()’; call
‘malloc(1)’ (or ‘calloc(1, 1)’) when requesting zero bytes.

New in version 3.4.

 -- C Function: void* PyMem_RawMalloc (size_t n)

     Allocates `n' bytes and returns a pointer of type ‘void*’ to the
     allocated memory, or ‘NULL’ if the request fails.

     Requesting zero bytes returns a distinct non-‘NULL’ pointer if
     possible, as if ‘PyMem_RawMalloc(1)’ had been called instead.  The
     memory will not have been initialized in any way.

 -- C Function: void* PyMem_RawCalloc (size_t nelem, size_t elsize)

     Allocates `nelem' elements each whose size in bytes is `elsize' and
     returns a pointer of type ‘void*’ to the allocated memory, or
     ‘NULL’ if the request fails.  The memory is initialized to zeros.

     Requesting zero elements or elements of size zero bytes returns a
     distinct non-‘NULL’ pointer if possible, as if ‘PyMem_RawCalloc(1,
     1)’ had been called instead.

     New in version 3.5.

 -- C Function: void* PyMem_RawRealloc (void *p, size_t n)

     Resizes the memory block pointed to by `p' to `n' bytes.  The
     contents will be unchanged to the minimum of the old and the new
     sizes.

     If `p' is ‘NULL’, the call is equivalent to ‘PyMem_RawMalloc(n)’;
     else if `n' is equal to zero, the memory block is resized but is
     not freed, and the returned pointer is non-‘NULL’.

     Unless `p' is ‘NULL’, it must have been returned by a previous call
     to *note PyMem_RawMalloc(): a4e, *note PyMem_RawRealloc(): a4f. or
     *note PyMem_RawCalloc(): 893.

     If the request fails, *note PyMem_RawRealloc(): a4f. returns ‘NULL’
     and `p' remains a valid pointer to the previous memory area.

 -- C Function: void PyMem_RawFree (void *p)

     Frees the memory block pointed to by `p', which must have been
     returned by a previous call to *note PyMem_RawMalloc(): a4e, *note
     PyMem_RawRealloc(): a4f. or *note PyMem_RawCalloc(): 893.
     Otherwise, or if ‘PyMem_RawFree(p)’ has been called before,
     undefined behavior occurs.

     If `p' is ‘NULL’, no operation is performed.


File: python.info,  Node: Memory Interface,  Next: Object allocators,  Prev: Raw Memory Interface,  Up: Memory Management

7.11.3 Memory Interface
-----------------------

The following function sets, modeled after the ANSI C standard, but
specifying behavior when requesting zero bytes, are available for
allocating and releasing memory from the Python heap.

The *note default memory allocator: 148f. uses the *note pymalloc memory
allocator: 6b8.

     Warning: The *note GIL: 600. must be held when using these
     functions.

Changed in version 3.6: The default allocator is now pymalloc instead of
system ‘malloc()’.

 -- C Function: void* PyMem_Malloc (size_t n)

     Allocates `n' bytes and returns a pointer of type ‘void*’ to the
     allocated memory, or ‘NULL’ if the request fails.

     Requesting zero bytes returns a distinct non-‘NULL’ pointer if
     possible, as if ‘PyMem_Malloc(1)’ had been called instead.  The
     memory will not have been initialized in any way.

 -- C Function: void* PyMem_Calloc (size_t nelem, size_t elsize)

     Allocates `nelem' elements each whose size in bytes is `elsize' and
     returns a pointer of type ‘void*’ to the allocated memory, or
     ‘NULL’ if the request fails.  The memory is initialized to zeros.

     Requesting zero elements or elements of size zero bytes returns a
     distinct non-‘NULL’ pointer if possible, as if ‘PyMem_Calloc(1, 1)’
     had been called instead.

     New in version 3.5.

 -- C Function: void* PyMem_Realloc (void *p, size_t n)

     Resizes the memory block pointed to by `p' to `n' bytes.  The
     contents will be unchanged to the minimum of the old and the new
     sizes.

     If `p' is ‘NULL’, the call is equivalent to ‘PyMem_Malloc(n)’; else
     if `n' is equal to zero, the memory block is resized but is not
     freed, and the returned pointer is non-‘NULL’.

     Unless `p' is ‘NULL’, it must have been returned by a previous call
     to *note PyMem_Malloc(): 5ff, *note PyMem_Realloc(): a50. or *note
     PyMem_Calloc(): 894.

     If the request fails, *note PyMem_Realloc(): a50. returns ‘NULL’
     and `p' remains a valid pointer to the previous memory area.

 -- C Function: void PyMem_Free (void *p)

     Frees the memory block pointed to by `p', which must have been
     returned by a previous call to *note PyMem_Malloc(): 5ff, *note
     PyMem_Realloc(): a50. or *note PyMem_Calloc(): 894.  Otherwise, or
     if ‘PyMem_Free(p)’ has been called before, undefined behavior
     occurs.

     If `p' is ‘NULL’, no operation is performed.

The following type-oriented macros are provided for convenience.  Note
that `TYPE' refers to any C type.

 -- C Function: TYPE* PyMem_New (TYPE, size_t n)

     Same as *note PyMem_Malloc(): 5ff, but allocates ‘(n *
     sizeof(TYPE))’ bytes of memory.  Returns a pointer cast to ‘TYPE*’.
     The memory will not have been initialized in any way.

 -- C Function: TYPE* PyMem_Resize (void *p, TYPE, size_t n)

     Same as *note PyMem_Realloc(): a50, but the memory block is resized
     to ‘(n * sizeof(TYPE))’ bytes.  Returns a pointer cast to ‘TYPE*’.
     On return, `p' will be a pointer to the new memory area, or ‘NULL’
     in the event of failure.

     This is a C preprocessor macro; `p' is always reassigned.  Save the
     original value of `p' to avoid losing memory when handling errors.

 -- C Function: void PyMem_Del (void *p)

     Same as *note PyMem_Free(): e6e.

In addition, the following macro sets are provided for calling the
Python memory allocator directly, without involving the C API functions
listed above.  However, note that their use does not preserve binary
compatibility across Python versions and is therefore deprecated in
extension modules.

   * ‘PyMem_MALLOC(size)’

   * ‘PyMem_NEW(type, size)’

   * ‘PyMem_REALLOC(ptr, size)’

   * ‘PyMem_RESIZE(ptr, type, size)’

   * ‘PyMem_FREE(ptr)’

   * ‘PyMem_DEL(ptr)’


File: python.info,  Node: Object allocators,  Next: Default Memory Allocators,  Prev: Memory Interface,  Up: Memory Management

7.11.4 Object allocators
------------------------

The following function sets, modeled after the ANSI C standard, but
specifying behavior when requesting zero bytes, are available for
allocating and releasing memory from the Python heap.

The *note default object allocator: 148f. uses the *note pymalloc memory
allocator: 6b8.

     Warning: The *note GIL: 600. must be held when using these
     functions.

 -- C Function: void* PyObject_Malloc (size_t n)

     Allocates `n' bytes and returns a pointer of type ‘void*’ to the
     allocated memory, or ‘NULL’ if the request fails.

     Requesting zero bytes returns a distinct non-‘NULL’ pointer if
     possible, as if ‘PyObject_Malloc(1)’ had been called instead.  The
     memory will not have been initialized in any way.

 -- C Function: void* PyObject_Calloc (size_t nelem, size_t elsize)

     Allocates `nelem' elements each whose size in bytes is `elsize' and
     returns a pointer of type ‘void*’ to the allocated memory, or
     ‘NULL’ if the request fails.  The memory is initialized to zeros.

     Requesting zero elements or elements of size zero bytes returns a
     distinct non-‘NULL’ pointer if possible, as if ‘PyObject_Calloc(1,
     1)’ had been called instead.

     New in version 3.5.

 -- C Function: void* PyObject_Realloc (void *p, size_t n)

     Resizes the memory block pointed to by `p' to `n' bytes.  The
     contents will be unchanged to the minimum of the old and the new
     sizes.

     If `p' is ‘NULL’, the call is equivalent to ‘PyObject_Malloc(n)’;
     else if `n' is equal to zero, the memory block is resized but is
     not freed, and the returned pointer is non-‘NULL’.

     Unless `p' is ‘NULL’, it must have been returned by a previous call
     to *note PyObject_Malloc(): 602, *note PyObject_Realloc(): e6f. or
     *note PyObject_Calloc(): 895.

     If the request fails, *note PyObject_Realloc(): e6f. returns ‘NULL’
     and `p' remains a valid pointer to the previous memory area.

 -- C Function: void PyObject_Free (void *p)

     Frees the memory block pointed to by `p', which must have been
     returned by a previous call to *note PyObject_Malloc(): 602, *note
     PyObject_Realloc(): e6f. or *note PyObject_Calloc(): 895.
     Otherwise, or if ‘PyObject_Free(p)’ has been called before,
     undefined behavior occurs.

     If `p' is ‘NULL’, no operation is performed.


File: python.info,  Node: Default Memory Allocators,  Next: Customize Memory Allocators,  Prev: Object allocators,  Up: Memory Management

7.11.5 Default Memory Allocators
--------------------------------

Default memory allocators:

Configuration                       Name                     PyMem_RawMalloc        PyMem_Malloc              PyObject_Malloc
                                                                                                              
---------------------------------------------------------------------------------------------------------------------------------------
                                                                                                              
Release build                       ‘"pymalloc"’             ‘malloc’               ‘pymalloc’                ‘pymalloc’
                                                                                                              
                                                                                                              
Debug build                         ‘"pymalloc_debug"’       ‘malloc’ + debug       ‘pymalloc’ + debug        ‘pymalloc’ + debug
                                                                                                              
                                                                                                              
Release build, without pymalloc     ‘"malloc"’               ‘malloc’               ‘malloc’                  ‘malloc’
                                                                                                              
                                                                                                              
Debug build, without pymalloc       ‘"malloc_debug"’         ‘malloc’ + debug       ‘malloc’ + debug          ‘malloc’ + debug
                                                                                                              

Legend:

   * Name: value for *note PYTHONMALLOC: 5fd. environment variable

   * ‘malloc’: system allocators from the standard C library, C
     functions: ‘malloc()’, ‘calloc()’, ‘realloc()’ and ‘free()’

   * ‘pymalloc’: *note pymalloc memory allocator: 6b8.

   * “+ debug”: with debug hooks installed by *note
     PyMem_SetupDebugHooks(): 604.


File: python.info,  Node: Customize Memory Allocators,  Next: The pymalloc allocator,  Prev: Default Memory Allocators,  Up: Memory Management

7.11.6 Customize Memory Allocators
----------------------------------

New in version 3.4.

 -- C Type: PyMemAllocatorEx

     Structure used to describe a memory block allocator.  The structure
     has four fields:

     Field                                                          Meaning
                                                                    
     -----------------------------------------------------------------------------------------------------------
                                                                    
     ‘void *ctx’                                                    user context passed as first argument
                                                                    
                                                                    
     ‘void* malloc(void *ctx, size_t size)’                         allocate a memory block
                                                                    
                                                                    
     ‘void* calloc(void *ctx, size_t nelem, size_t elsize)’         allocate a memory block initialized with
                                                                    zeros
                                                                    
                                                                    
     ‘void* realloc(void *ctx, void *ptr, size_t new_size)’         allocate or resize a memory block
                                                                    
                                                                    
     ‘void free(void *ctx, void *ptr)’                              free a memory block
                                                                    

     Changed in version 3.5: The ‘PyMemAllocator’ structure was renamed
     to *note PyMemAllocatorEx: 8b7. and a new ‘calloc’ field was added.

 -- C Type: PyMemAllocatorDomain

     Enum used to identify an allocator domain.  Domains:

      -- C Macro: PYMEM_DOMAIN_RAW

          Functions:

             * *note PyMem_RawMalloc(): a4e.

             * *note PyMem_RawRealloc(): a4f.

             * *note PyMem_RawCalloc(): 893.

             * *note PyMem_RawFree(): 3e57.

      -- C Macro: PYMEM_DOMAIN_MEM

          Functions:

             * *note PyMem_Malloc(): 5ff,

             * *note PyMem_Realloc(): a50.

             * *note PyMem_Calloc(): 894.

             * *note PyMem_Free(): e6e.

      -- C Macro: PYMEM_DOMAIN_OBJ

          Functions:

             * *note PyObject_Malloc(): 602.

             * *note PyObject_Realloc(): e6f.

             * *note PyObject_Calloc(): 895.

             * *note PyObject_Free(): 5fe.

 -- C Function: void PyMem_GetAllocator (PyMemAllocatorDomain domain,
          PyMemAllocatorEx *allocator)

     Get the memory block allocator of the specified domain.

 -- C Function: void PyMem_SetAllocator (PyMemAllocatorDomain domain,
          PyMemAllocatorEx *allocator)

     Set the memory block allocator of the specified domain.

     The new allocator must return a distinct non-‘NULL’ pointer when
     requesting zero bytes.

     For the *note PYMEM_DOMAIN_RAW: 1490. domain, the allocator must be
     thread-safe: the *note GIL: 600. is not held when the allocator is
     called.

     If the new allocator is not a hook (does not call the previous
     allocator), the *note PyMem_SetupDebugHooks(): 604. function must
     be called to reinstall the debug hooks on top on the new allocator.

 -- C Function: void PyMem_SetupDebugHooks (void)

     Setup hooks to detect bugs in the Python memory allocator
     functions.

     Newly allocated memory is filled with the byte ‘0xCD’
     (‘CLEANBYTE’), freed memory is filled with the byte ‘0xDD’
     (‘DEADBYTE’).  Memory blocks are surrounded by “forbidden bytes”
     (‘FORBIDDENBYTE’: byte ‘0xFD’).

     Runtime checks:

        - Detect API violations, ex: *note PyObject_Free(): 5fe. called
          on a buffer allocated by *note PyMem_Malloc(): 5ff.

        - Detect write before the start of the buffer (buffer underflow)

        - Detect write after the end of the buffer (buffer overflow)

        - Check that the *note GIL: 600. is held when allocator
          functions of *note PYMEM_DOMAIN_OBJ: 601. (ex: *note
          PyObject_Malloc(): 602.) and *note PYMEM_DOMAIN_MEM: 603. (ex:
          *note PyMem_Malloc(): 5ff.) domains are called

     On error, the debug hooks use the *note tracemalloc: 11d. module to
     get the traceback where a memory block was allocated.  The
     traceback is only displayed if *note tracemalloc: 11d. is tracing
     Python memory allocations and the memory block was traced.

     These hooks are *note installed by default: 148f. if Python is
     compiled in debug mode.  The *note PYTHONMALLOC: 5fd. environment
     variable can be used to install debug hooks on a Python compiled in
     release mode.

     Changed in version 3.6: This function now also works on Python
     compiled in release mode.  On error, the debug hooks now use *note
     tracemalloc: 11d. to get the traceback where a memory block was
     allocated.  The debug hooks now also check if the GIL is held when
     functions of *note PYMEM_DOMAIN_OBJ: 601. and *note
     PYMEM_DOMAIN_MEM: 603. domains are called.

     Changed in version 3.8: Byte patterns ‘0xCB’ (‘CLEANBYTE’), ‘0xDB’
     (‘DEADBYTE’) and ‘0xFB’ (‘FORBIDDENBYTE’) have been replaced with
     ‘0xCD’, ‘0xDD’ and ‘0xFD’ to use the same values than Windows CRT
     debug ‘malloc()’ and ‘free()’.


File: python.info,  Node: The pymalloc allocator,  Next: tracemalloc C API,  Prev: Customize Memory Allocators,  Up: Memory Management

7.11.7 The pymalloc allocator
-----------------------------

Python has a `pymalloc' allocator optimized for small objects (smaller
or equal to 512 bytes) with a short lifetime.  It uses memory mappings
called “arenas” with a fixed size of 256 KiB. It falls back to *note
PyMem_RawMalloc(): a4e. and *note PyMem_RawRealloc(): a4f. for
allocations larger than 512 bytes.

`pymalloc' is the *note default allocator: 148f. of the *note
PYMEM_DOMAIN_MEM: 603. (ex: *note PyMem_Malloc(): 5ff.) and *note
PYMEM_DOMAIN_OBJ: 601. (ex: *note PyObject_Malloc(): 602.) domains.

The arena allocator uses the following functions:

   * ‘VirtualAlloc()’ and ‘VirtualFree()’ on Windows,

   * ‘mmap()’ and ‘munmap()’ if available,

   * ‘malloc()’ and ‘free()’ otherwise.

* Menu:

* Customize pymalloc Arena Allocator::


File: python.info,  Node: Customize pymalloc Arena Allocator,  Up: The pymalloc allocator

7.11.7.1 Customize pymalloc Arena Allocator
...........................................

New in version 3.4.

 -- C Type: PyObjectArenaAllocator

     Structure used to describe an arena allocator.  The structure has
     three fields:

     Field                                                  Meaning
                                                            
     ---------------------------------------------------------------------------------------------------
                                                            
     ‘void *ctx’                                            user context passed as first argument
                                                            
                                                            
     ‘void* alloc(void *ctx, size_t size)’                  allocate an arena of size bytes
                                                            
                                                            
     ‘void free(void *ctx, void *ptr, size_t size)’         free an arena
                                                            

 -- C Function: void PyObject_GetArenaAllocator
          (PyObjectArenaAllocator *allocator)

     Get the arena allocator.

 -- C Function: void PyObject_SetArenaAllocator
          (PyObjectArenaAllocator *allocator)

     Set the arena allocator.


File: python.info,  Node: tracemalloc C API,  Next: Examples<35>,  Prev: The pymalloc allocator,  Up: Memory Management

7.11.8 tracemalloc C API
------------------------

New in version 3.7.

 -- C Function: int PyTraceMalloc_Track (unsigned int domain,
          uintptr_t ptr, size_t size)

     Track an allocated memory block in the *note tracemalloc: 11d.
     module.

     Return ‘0’ on success, return ‘-1’ on error (failed to allocate
     memory to store the trace).  Return ‘-2’ if tracemalloc is
     disabled.

     If memory block is already tracked, update the existing trace.

 -- C Function: int PyTraceMalloc_Untrack (unsigned int domain,
          uintptr_t ptr)

     Untrack an allocated memory block in the *note tracemalloc: 11d.
     module.  Do nothing if the block was not tracked.

     Return ‘-2’ if tracemalloc is disabled, otherwise return ‘0’.


File: python.info,  Node: Examples<35>,  Prev: tracemalloc C API,  Up: Memory Management

7.11.9 Examples
---------------

Here is the example from section *note Overview: 4230, rewritten so that
the I/O buffer is allocated from the Python heap by using the first
function set:

     PyObject *res;
     char *buf = (char *) PyMem_Malloc(BUFSIZ); /* for I/O */

     if (buf == NULL)
         return PyErr_NoMemory();
     /* ...Do some I/O operation involving buf... */
     res = PyBytes_FromString(buf);
     PyMem_Free(buf); /* allocated with PyMem_Malloc */
     return res;

The same code using the type-oriented function set:

     PyObject *res;
     char *buf = PyMem_New(char, BUFSIZ); /* for I/O */

     if (buf == NULL)
         return PyErr_NoMemory();
     /* ...Do some I/O operation involving buf... */
     res = PyBytes_FromString(buf);
     PyMem_Del(buf); /* allocated with PyMem_New */
     return res;

Note that in the two examples above, the buffer is always manipulated
via functions belonging to the same set.  Indeed, it is required to use
the same memory API family for a given memory block, so that the risk of
mixing different allocators is reduced to a minimum.  The following code
sequence contains two errors, one of which is labeled as `fatal' because
it mixes two different allocators operating on different heaps.

     char *buf1 = PyMem_New(char, BUFSIZ);
     char *buf2 = (char *) malloc(BUFSIZ);
     char *buf3 = (char *) PyMem_Malloc(BUFSIZ);
     ...
     PyMem_Del(buf3);  /* Wrong -- should be PyMem_Free() */
     free(buf2);       /* Right -- allocated via malloc() */
     free(buf1);       /* Fatal -- should be PyMem_Del()  */

In addition to the functions aimed at handling raw memory blocks from
the Python heap, objects in Python are allocated and released with *note
PyObject_New(): 268, *note PyObject_NewVar(): 269. and *note
PyObject_Del(): ed8.

These will be explained in the next chapter on defining and implementing
new object types in C.


File: python.info,  Node: Object Implementation Support,  Next: API and ABI Versioning,  Prev: Memory Management,  Up: Python/C API Reference Manual

7.12 Object Implementation Support
==================================

This chapter describes the functions, types, and macros used when
defining new object types.

* Menu:

* Allocating Objects on the Heap::
* Common Object Structures::
* Type Objects: Type Objects<3>.
* Number Object Structures::
* Mapping Object Structures::
* Sequence Object Structures::
* Buffer Object Structures::
* Async Object Structures::
* Slot Type typedefs::
* Examples: Examples<36>.
* Supporting Cyclic Garbage Collection::


File: python.info,  Node: Allocating Objects on the Heap,  Next: Common Object Structures,  Up: Object Implementation Support

7.12.1 Allocating Objects on the Heap
-------------------------------------

 -- C Function: PyObject* _PyObject_New (PyTypeObject *type)
     `Return value: New reference.'

 -- C Function: PyVarObject* _PyObject_NewVar (PyTypeObject *type,
          Py_ssize_t size)
     `Return value: New reference.'

 -- C Function: PyObject* PyObject_Init (PyObject *op,
          PyTypeObject *type)
     `Return value: Borrowed reference.'  Initialize a newly-allocated
     object `op' with its type and initial reference.  Returns the
     initialized object.  If `type' indicates that the object
     participates in the cyclic garbage detector, it is added to the
     detector’s set of observed objects.  Other fields of the object are
     not affected.

 -- C Function: PyVarObject* PyObject_InitVar (PyVarObject *op,
          PyTypeObject *type, Py_ssize_t size)
     `Return value: Borrowed reference.'  This does everything *note
     PyObject_Init(): 398. does, and also initializes the length
     information for a variable-size object.

 -- C Function: TYPE* PyObject_New (TYPE, PyTypeObject *type)
     `Return value: New reference.'  Allocate a new Python object using
     the C structure type `TYPE' and the Python type object `type'.
     Fields not defined by the Python object header are not initialized;
     the object’s reference count will be one.  The size of the memory
     allocation is determined from the *note tp_basicsize: 26a. field of
     the type object.

 -- C Function: TYPE* PyObject_NewVar (TYPE, PyTypeObject *type,
          Py_ssize_t size)
     `Return value: New reference.'  Allocate a new Python object using
     the C structure type `TYPE' and the Python type object `type'.
     Fields not defined by the Python object header are not initialized.
     The allocated memory allows for the `TYPE' structure plus `size'
     fields of the size given by the *note tp_itemsize: 3d50. field of
     `type'.  This is useful for implementing objects like tuples, which
     are able to determine their size at construction time.  Embedding
     the array of fields into the same allocation decreases the number
     of allocations, improving the memory management efficiency.

 -- C Function: void PyObject_Del (void *op)

     Releases memory allocated to an object using *note PyObject_New():
     268. or *note PyObject_NewVar(): 269.  This is normally called from
     the *note tp_dealloc: 3d56. handler specified in the object’s type.
     The fields of the object should not be accessed after this call as
     the memory is no longer a valid Python object.

 -- C Variable: PyObject _Py_NoneStruct

     Object which is visible in Python as ‘None’.  This should only be
     accessed using the *note Py_None: 3d1f. macro, which evaluates to a
     pointer to this object.

See also
........

*note PyModule_Create(): 3d22.

     To allocate and create extension modules.


File: python.info,  Node: Common Object Structures,  Next: Type Objects<3>,  Prev: Allocating Objects on the Heap,  Up: Object Implementation Support

7.12.2 Common Object Structures
-------------------------------

There are a large number of structures which are used in the definition
of object types for Python.  This section describes these structures and
how they are used.

* Menu:

* Base object types and macros::
* Implementing functions and methods::
* Accessing attributes of extension types::


File: python.info,  Node: Base object types and macros,  Next: Implementing functions and methods,  Up: Common Object Structures

7.12.2.1 Base object types and macros
.....................................

All Python objects ultimately share a small number of fields at the
beginning of the object’s representation in memory.  These are
represented by the *note PyObject: 5b5. and *note PyVarObject: 424f.
types, which are defined, in turn, by the expansions of some macros also
used, whether directly or indirectly, in the definition of all other
Python objects.

 -- C Type: PyObject

     All object types are extensions of this type.  This is a type which
     contains the information Python needs to treat a pointer to an
     object as an object.  In a normal “release” build, it contains only
     the object’s reference count and a pointer to the corresponding
     type object.  Nothing is actually declared to be a *note PyObject:
     5b5, but every pointer to a Python object can be cast to a *note
     PyObject*: 5b5.  Access to the members must be done by using the
     macros *note Py_REFCNT: 3d4e. and *note Py_TYPE: 3d4f.

 -- C Type: PyVarObject

     This is an extension of *note PyObject: 5b5. that adds the
     ‘ob_size’ field.  This is only used for objects that have some
     notion of `length'.  This type does not often appear in the
     Python/C API. Access to the members must be done by using the
     macros *note Py_REFCNT: 3d4e, *note Py_TYPE: 3d4f, and *note
     Py_SIZE: 4250.

 -- C Macro: PyObject_HEAD

     This is a macro used when declaring new types which represent
     objects without a varying length.  The PyObject_HEAD macro expands
     to:

          PyObject ob_base;

     See documentation of *note PyObject: 5b5. above.

 -- C Macro: PyObject_VAR_HEAD

     This is a macro used when declaring new types which represent
     objects with a length that varies from instance to instance.  The
     PyObject_VAR_HEAD macro expands to:

          PyVarObject ob_base;

     See documentation of *note PyVarObject: 424f. above.

 -- C Macro: Py_TYPE (o)

     This macro is used to access the ‘ob_type’ member of a Python
     object.  It expands to:

          (((PyObject*)(o))->ob_type)

 -- C Function: int Py_IS_TYPE (PyObject *o, PyTypeObject *type)

     Return non-zero if the object `o' type is `type'.  Return zero
     otherwise.  Equivalent to: ‘Py_TYPE(o) == type’.

     New in version 3.9.

 -- C Function: void Py_SET_TYPE (PyObject *o, PyTypeObject *type)

     Set the object `o' type to `type'.

     New in version 3.9.

 -- C Macro: Py_REFCNT (o)

     This macro is used to access the ‘ob_refcnt’ member of a Python
     object.  It expands to:

          (((PyObject*)(o))->ob_refcnt)

 -- C Function: void Py_SET_REFCNT (PyObject *o, Py_ssize_t refcnt)

     Set the object `o' reference counter to `refcnt'.

     New in version 3.9.

 -- C Macro: Py_SIZE (o)

     This macro is used to access the ‘ob_size’ member of a Python
     object.  It expands to:

          (((PyVarObject*)(o))->ob_size)

 -- C Function: void Py_SET_SIZE (PyVarObject *o, Py_ssize_t size)

     Set the object `o' size to `size'.

     New in version 3.9.

 -- C Macro: PyObject_HEAD_INIT (type)

     This is a macro which expands to initialization values for a new
     *note PyObject: 5b5. type.  This macro expands to:

          _PyObject_EXTRA_INIT
          1, type,

 -- C Macro: PyVarObject_HEAD_INIT (type, size)

     This is a macro which expands to initialization values for a new
     *note PyVarObject: 424f. type, including the ‘ob_size’ field.  This
     macro expands to:

          _PyObject_EXTRA_INIT
          1, type, size,


File: python.info,  Node: Implementing functions and methods,  Next: Accessing attributes of extension types,  Prev: Base object types and macros,  Up: Common Object Structures

7.12.2.2 Implementing functions and methods
...........................................

 -- C Type: PyCFunction

     Type of the functions used to implement most Python callables in C.
     Functions of this type take two *note PyObject*: 5b5. parameters
     and return one such value.  If the return value is ‘NULL’, an
     exception shall have been set.  If not ‘NULL’, the return value is
     interpreted as the return value of the function as exposed in
     Python.  The function must return a new reference.

     The function signature is:

          PyObject *PyCFunction(PyObject *self,
                                PyObject *args);

 -- C Type: PyCFunctionWithKeywords

     Type of the functions used to implement Python callables in C with
     signature ‘METH_VARARGS | METH_KEYWORDS’.  The function signature
     is:

          PyObject *PyCFunctionWithKeywords(PyObject *self,
                                            PyObject *args,
                                            PyObject *kwargs);

 -- C Type: _PyCFunctionFast

     Type of the functions used to implement Python callables in C with
     signature *note METH_FASTCALL: 10f3.  The function signature is:

          PyObject *_PyCFunctionFast(PyObject *self,
                                     PyObject *const *args,
                                     Py_ssize_t nargs);

 -- C Type: _PyCFunctionFastWithKeywords

     Type of the functions used to implement Python callables in C with
     signature ‘METH_FASTCALL | METH_KEYWORDS’.  The function signature
     is:

          PyObject *_PyCFunctionFastWithKeywords(PyObject *self,
                                                 PyObject *const *args,
                                                 Py_ssize_t nargs,
                                                 PyObject *kwnames);

 -- C Type: PyCMethod

     Type of the functions used to implement Python callables in C with
     signature ‘METH_METHOD | METH_FASTCALL | METH_KEYWORDS’.  The
     function signature is:

          PyObject *PyCMethod(PyObject *self,
                              PyTypeObject *defining_class,
                              PyObject *const *args,
                              Py_ssize_t nargs,
                              PyObject *kwnames)

     New in version 3.9.

 -- C Type: PyMethodDef

     Structure used to describe a method of an extension type.  This
     structure has four fields:

     Field                  C Type              Meaning
                                                
     -------------------------------------------------------------------------------
                                                
     ‘ml_name’              const char *        name of the method
                                                
                                                
     ‘ml_meth’              PyCFunction         pointer to the C implementation
                                                
                                                
     ‘ml_flags’             int                 flag bits indicating how the call
                                                should be constructed
                                                
                                                
     ‘ml_doc’               const char *        points to the contents of the
                                                docstring
                                                

The ‘ml_meth’ is a C function pointer.  The functions may be of
different types, but they always return *note PyObject*: 5b5.  If the
function is not of the *note PyCFunction: e9f, the compiler will require
a cast in the method table.  Even though *note PyCFunction: e9f. defines
the first parameter as *note PyObject*: 5b5, it is common that the
method implementation uses the specific C type of the `self' object.

The ‘ml_flags’ field is a bitfield which can include the following
flags.  The individual flags indicate either a calling convention or a
binding convention.

There are these calling conventions:

 -- Data: METH_VARARGS

     This is the typical calling convention, where the methods have the
     type *note PyCFunction: e9f.  The function expects two *note
     PyObject*: 5b5. values.  The first one is the `self' object for
     methods; for module functions, it is the module object.  The second
     parameter (often called `args') is a tuple object representing all
     arguments.  This parameter is typically processed using *note
     PyArg_ParseTuple(): 393. or *note PyArg_UnpackTuple(): f08.

 -- Data: METH_VARARGS | METH_KEYWORDS

     Methods with these flags must be of type *note
     PyCFunctionWithKeywords: 4255.  The function expects three
     parameters: `self', `args', `kwargs' where `kwargs' is a dictionary
     of all the keyword arguments or possibly ‘NULL’ if there are no
     keyword arguments.  The parameters are typically processed using
     *note PyArg_ParseTupleAndKeywords(): 6c1.

 -- Data: METH_FASTCALL

     Fast calling convention supporting only positional arguments.  The
     methods have the type *note _PyCFunctionFast: 4256.  The first
     parameter is `self', the second parameter is a C array of *note
     PyObject*: 5b5. values indicating the arguments and the third
     parameter is the number of arguments (the length of the array).

     This is not part of the *note limited API: 3dd6.

     New in version 3.7.

 -- Data: METH_FASTCALL | METH_KEYWORDS

     Extension of *note METH_FASTCALL: 10f3. supporting also keyword
     arguments, with methods of type *note _PyCFunctionFastWithKeywords:
     4257.  Keyword arguments are passed the same way as in the *note
     vectorcall protocol: 2b8.: there is an additional fourth *note
     PyObject*: 5b5. parameter which is a tuple representing the names
     of the keyword arguments (which are guaranteed to be strings) or
     possibly ‘NULL’ if there are no keywords.  The values of the
     keyword arguments are stored in the `args' array, after the
     positional arguments.

     This is not part of the *note limited API: 3dd6.

     New in version 3.7.

 -- Data: METH_METHOD | METH_FASTCALL | METH_KEYWORDS

     Extension of ‘METH_FASTCALL | METH_KEYWORDS’ supporting the
     `defining class', that is, the class that contains the method in
     question.  The defining class might be a superclass of
     ‘Py_TYPE(self)’.

     The method needs to be of type *note PyCMethod: 248, the same as
     for ‘METH_FASTCALL | METH_KEYWORDS’ with ‘defining_class’ argument
     added after ‘self’.

     New in version 3.9.

 -- Data: METH_NOARGS

     Methods without parameters don’t need to check whether arguments
     are given if they are listed with the *note METH_NOARGS: eda. flag.
     They need to be of type *note PyCFunction: e9f.  The first
     parameter is typically named `self' and will hold a reference to
     the module or object instance.  In all cases the second parameter
     will be ‘NULL’.

 -- Data: METH_O

     Methods with a single object argument can be listed with the *note
     METH_O: f09. flag, instead of invoking *note PyArg_ParseTuple():
     393. with a ‘"O"’ argument.  They have the type *note PyCFunction:
     e9f, with the `self' parameter, and a *note PyObject*: 5b5.
     parameter representing the single argument.

These two constants are not used to indicate the calling convention but
the binding when use with methods of classes.  These may not be used for
functions defined for modules.  At most one of these flags may be set
for any given method.

 -- Data: METH_CLASS

     The method will be passed the type object as the first parameter
     rather than an instance of the type.  This is used to create `class
     methods', similar to what is created when using the *note
     classmethod(): 309. built-in function.

 -- Data: METH_STATIC

     The method will be passed ‘NULL’ as the first parameter rather than
     an instance of the type.  This is used to create `static methods',
     similar to what is created when using the *note staticmethod():
     30a. built-in function.

One other constant controls whether a method is loaded in place of
another definition with the same method name.

 -- Data: METH_COEXIST

     The method will be loaded in place of existing definitions.
     Without `METH_COEXIST', the default is to skip repeated
     definitions.  Since slot wrappers are loaded before the method
     table, the existence of a `sq_contains' slot, for example, would
     generate a wrapped method named *note __contains__(): dee. and
     preclude the loading of a corresponding PyCFunction with the same
     name.  With the flag defined, the PyCFunction will be loaded in
     place of the wrapper object and will co-exist with the slot.  This
     is helpful because calls to PyCFunctions are optimized more than
     wrapper object calls.


File: python.info,  Node: Accessing attributes of extension types,  Prev: Implementing functions and methods,  Up: Common Object Structures

7.12.2.3 Accessing attributes of extension types
................................................

 -- C Type: PyMemberDef

     Structure which describes an attribute of a type which corresponds
     to a C struct member.  Its fields are:

     Field                  C Type              Meaning
                                                
     -------------------------------------------------------------------------------
                                                
     ‘name’                 const char *        name of the member
                                                
                                                
     ‘type’                 int                 the type of the member in the C
                                                struct
                                                
                                                
     ‘offset’               Py_ssize_t          the offset in bytes that the
                                                member is located on the type’s
                                                object struct
                                                
                                                
     ‘flags’                int                 flag bits indicating if the field
                                                should be read-only or writable
                                                
                                                
     ‘doc’                  const char *        points to the contents of the
                                                docstring
                                                

     ‘type’ can be one of many ‘T_’ macros corresponding to various C
     types.  When the member is accessed in Python, it will be converted
     to the equivalent Python type.

     Macro name          C type
                         
     -------------------------------------------
                         
     T_SHORT             short
                         
                         
     T_INT               int
                         
                         
     T_LONG              long
                         
                         
     T_FLOAT             float
                         
                         
     T_DOUBLE            double
                         
                         
     T_STRING            const char *
                         
                         
     T_OBJECT            PyObject *
                         
                         
     T_OBJECT_EX         PyObject *
                         
                         
     T_CHAR              char
                         
                         
     T_BYTE              char
                         
                         
     T_UBYTE             unsigned char
                         
                         
     T_UINT              unsigned int
                         
                         
     T_USHORT            unsigned short
                         
                         
     T_ULONG             unsigned long
                         
                         
     T_BOOL              char
                         
                         
     T_LONGLONG          long long
                         
                         
     T_ULONGLONG         unsigned long long
                         
                         
     T_PYSSIZET          Py_ssize_t
                         

     ‘T_OBJECT’ and ‘T_OBJECT_EX’ differ in that ‘T_OBJECT’ returns
     ‘None’ if the member is ‘NULL’ and ‘T_OBJECT_EX’ raises an *note
     AttributeError: 4a2.  Try to use ‘T_OBJECT_EX’ over ‘T_OBJECT’
     because ‘T_OBJECT_EX’ handles use of the *note del: 13a2. statement
     on that attribute more correctly than ‘T_OBJECT’.

     ‘flags’ can be ‘0’ for write and read access or ‘READONLY’ for
     read-only access.  Using ‘T_STRING’ for *note type: 6ff. implies
     ‘READONLY’.  ‘T_STRING’ data is interpreted as UTF-8.  Only
     ‘T_OBJECT’ and ‘T_OBJECT_EX’ members can be deleted.  (They are set
     to ‘NULL’).  Heap allocated types (created using *note
     PyType_FromSpec(): 23a. or similar), ‘PyMemberDef’ may contain
     definitions for the special members ‘__dictoffset__’,
     ‘__weaklistoffset__’ and ‘__vectorcalloffset__’, corresponding to
     *note tp_dictoffset: 3f93, *note tp_weaklistoffset: 26b. and *note
     tp_vectorcall_offset: 3edc. in type objects.  These must be defined
     with ‘T_PYSSIZET’ and ‘READONLY’, for example:

          static PyMemberDef spam_type_members[] = {
              {"__dictoffset__", T_PYSSIZET, offsetof(Spam_object, dict), READONLY},
              {NULL}  /* Sentinel */
          };

 -- C Function: PyObject* PyMember_GetOne (const char *obj_addr, struct
          PyMemberDef *m)

     Get an attribute belonging to the object at address `obj_addr'.
     The attribute is described by ‘PyMemberDef’ `m'.  Returns ‘NULL’ on
     error.

 -- C Function: int PyMember_SetOne (char *obj_addr, struct
          PyMemberDef *m, PyObject *o)

     Set an attribute belonging to the object at address `obj_addr' to
     object `o'.  The attribute to set is described by ‘PyMemberDef’
     `m'.  Returns ‘0’ if successful and a negative value on failure.

 -- C Type: PyGetSetDef

     Structure to define property-like access for a type.  See also
     description of the *note PyTypeObject.tp_getset: 3d60. slot.

     Field             C Type                 Meaning
                                              
     ---------------------------------------------------------------------------------
                                              
     name              const char *           attribute name
                                              
                                              
     get               getter                 C Function to get the attribute
                                              
                                              
     set               setter                 optional C function to set or delete
                                              the attribute, if omitted the
                                              attribute is readonly
                                              
                                              
     doc               const char *           optional docstring
                                              
                                              
     closure           void *                 optional function pointer, providing
                                              additional data for getter and setter
                                              

     The ‘get’ function takes one *note PyObject*: 5b5. parameter (the
     instance) and a function pointer (the associated ‘closure’):

          typedef PyObject *(*getter)(PyObject *, void *);

     It should return a new reference on success or ‘NULL’ with a set
     exception on failure.

     ‘set’ functions take two *note PyObject*: 5b5. parameters (the
     instance and the value to be set) and a function pointer (the
     associated ‘closure’):

          typedef int (*setter)(PyObject *, PyObject *, void *);

     In case the attribute should be deleted the second parameter is
     ‘NULL’.  Should return ‘0’ on success or ‘-1’ with a set exception
     on failure.


File: python.info,  Node: Type Objects<3>,  Next: Number Object Structures,  Prev: Common Object Structures,  Up: Object Implementation Support

7.12.3 Type Objects
-------------------

Perhaps one of the most important structures of the Python object system
is the structure that defines a new type: the *note PyTypeObject: 3f5.
structure.  Type objects can be handled using any of the ‘PyObject_*()’
or ‘PyType_*()’ functions, but do not offer much that’s interesting to
most Python applications.  These objects are fundamental to how objects
behave, so they are very important to the interpreter itself and to any
extension module that implements new types.

Type objects are fairly large compared to most of the standard types.
The reason for the size is that each type object stores a large number
of values, mostly C function pointers, each of which implements a small
part of the type’s functionality.  The fields of the type object are
examined in detail in this section.  The fields will be described in the
order in which they occur in the structure.

In addition to the following quick reference, the *note Examples: 425e.
section provides at-a-glance insight into the meaning and use of *note
PyTypeObject: 3f5.

* Menu:

* Quick Reference::
* PyTypeObject Definition::
* PyObject Slots::
* PyVarObject Slots::
* PyTypeObject Slots::
* Heap Types::


File: python.info,  Node: Quick Reference,  Next: PyTypeObject Definition,  Up: Type Objects<3>

7.12.3.1 Quick Reference
........................

* Menu:

* “tp slots”::
* sub-slots::
* slot typedefs::


File: python.info,  Node: “tp slots”,  Next: sub-slots,  Up: Quick Reference

7.12.3.2 “tp slots”
...................

PyTypeObject Slot      *note Type: 4262.      special                Info
(1)                                           methods/attrs          (2)
                                                                     
---------------------------------------------------------------------------------------------
                                                                     
O                      T                      D                      I
                                                                     
                                                                                       
<R>                    const char *           __name__               X     X
*note tp_name: 3d71.                                                       

*note tp_basicsize: 26a.Py_ssize_t                                   X     X           X
                                                                                       
                                                                                       
*note tp_itemsize: 3d50.Py_ssize_t                                         X           X
                                                                                       
                                                                                       
*note tp_dealloc: 3d56.*note destructor: 4263.                       X     X           X
                                                                                       
                                                                                       
*note tp_vectorcall_offset: 3edc.Py_ssize_t                                X           X
                                                                                       
                                                                                       
(*note tp_getattr: 3d78.)*note getattrfunc: 4264.__getattribute__,                     G
                                              __getattr__                              
                                              
                                                                                       
(*note tp_setattr: 3d79.)*note setattrfunc: 4265.__setattr__,                          G
                                              __delattr__                              
                                              
                                                                                       
*note tp_as_async: 4266.*note PyAsyncMethods: 3f89.*note sub-slots: 4267.              %
                       *                                                               
                       
                                                                                       
*note tp_repr: 3d70.   *note reprfunc: 4268.  __repr__               X     X           X
                                                                                       
                                                                                       
*note tp_as_number: 26f.*note PyNumberMethods: e46.*note sub-slots: 4267.              %
                       *                                                               
                       
                                                                                       
*note tp_as_sequence: 4269.*note PySequenceMethods: 3d7f.*note sub-slots: 4267.        %
                       *                                                               
                       
                                                                                       
*note tp_as_mapping: 426a.*note PyMappingMethods: 3d80.*note sub-slots: 4267.          %
                       *                                                               
                       
                                                                                       
*note tp_hash: 3d81.   *note hashfunc: 426b.  __hash__               X                 G
                                                                                       
                                                                                       
*note tp_call: 3d82.   *note ternaryfunc: 426c.__call__                    X           X
                                                                                       
                                                                                       
*note tp_str: 3d72.    *note reprfunc: 4268.  __str__                X                 X
                                                                                       
                                                                                       
*note tp_getattro: 3d75.*note getattrofunc: 426d.__getattribute__,   X     X           G
                                              __getattr__                              
                                              
                                                                                       
*note tp_setattro: 3d76.*note setattrofunc: 426e.__setattr__,        X     X           G
                                              __delattr__                              
                                              
                                                                                       
*note tp_as_buffer: 26d.*note PyBufferProcs: 3f95.                                     %
                       *                                                               
                       
                                                                                       
*note tp_flags: 1011.  unsigned long                                 X     X           ?
                                                                                       
                                                                                       
*note tp_doc: 3d52.    const char *           __doc__                X     X
                                                                           
                                                                                       
*note tp_traverse: 23b.*note traverseproc: 426f.                           X           G
                                                                                       
                                                                                       
*note tp_clear: 3d6e.  *note inquiry: 4270.                                X           G
                                                                                       
                                                                                       
*note tp_richcompare: 3d7b.*note richcmpfunc: 4271.__lt__, __le__,   X                 G
                                              __eq__, __ne__,                          
                                              __gt__, __ge__
                                              
                                                                                       
*note tp_weaklistoffset: 26b.Py_ssize_t                                    X           ?
                                                                                       
                                                                                       
*note tp_iter: ef2.    *note getiterfunc: 4272.__iter__                                X
                                                                                       
                                                                                       
*note tp_iternext: ef3.*note iternextfunc: 4273.__next__                               X
                                                                                       
                                                                                       
*note tp_methods: 3d5d.*note PyMethodDef: edd.                       X     X
                       []                                                  
                       
                                                                                       
*note tp_members: 3d5b.*note PyMemberDef: 52a.                             X
                       []                                                  
                       
                                                                                       
*note tp_getset: 3d60. *note PyGetSetDef: 52b.                       X     X
                       []                                                  
                       
                                                                                       
*note tp_base: 3d66.   *note PyTypeObject: 3f5.__base__                          X
                       *                                                         
                       
                                                                                       
*note tp_dict: 3f8c.   *note PyObject: 5b5.   __dict__                           ?
                       *                                                         
                       
                                                                                       
*note tp_descr_get: 4274.*note descrgetfunc: 4275.__get__                              X
                                                                                       
                                                                                       
*note tp_descr_set: 4276.*note descrsetfunc: 4277.__set__, __delete__                  X
                                                                                       
                                                                                       
*note tp_dictoffset: 3f93.Py_ssize_t                                       X           ?
                                                                                       
                                                                                       
*note tp_init: 3d5a.   *note initproc: 4278.  __init__               X     X           X
                                                                                       
                                                                                       
*note tp_alloc: 3d58.  *note allocfunc: 4279.                        X           ?     ?
                                                                                       
                                                                                       
*note tp_new: 3d53.    *note newfunc: 427a.   __new__                X     X     ?     ?
                                                                                       
                                                                                       
*note tp_free: 3d57.   *note freefunc: 427b.                         X     X     ?     ?
                                                                                       
                                                                                       
*note tp_is_gc: 427c.  *note inquiry: 4270.                                X           X
                                                                                       
                                                                                       
<*note tp_bases: 427d.>*note PyObject: 5b5.   __bases__                          ~
                       *                                                         
                       
                                                                                       
<*note tp_mro: 3f8d.>  *note PyObject: 5b5.   __mro__                            ~
                       *                                                         
                       
                                                                                       
[*note tp_cache: 3f8e.]*note PyObject: 5b5.
                       *
                       
                                                                                       
[*note tp_subclasses: 3f8f.]*note PyObject: 5b5.__subclasses__
                       *                      
                       
                                                                                       
[*note tp_weaklist: 3f90.]*note PyObject: 5b5.
                       *
                       
                                                                                       
(*note tp_del: 427e.)  *note destructor: 4263.
                       
                                                                                       
[*note tp_version_tag: 427f.]unsigned int
                       
                                                                                       
*note tp_finalize: 3f6.*note destructor: 4263.__del__                                  X
                                                                                       
                                                                                       
*note tp_vectorcall: 3f91.*note vectorcallfunc: 3edd.
                       

   ---------- Footnotes ----------

   (1) (1) A slot name in parentheses indicates it is (effectively)
deprecated.  Names in angle brackets should be treated as read-only.
Names in square brackets are for internal use only.  “<R>” (as a prefix)
means the field is required (must be non-‘NULL’).

   (2) (2) Columns:

`“O”': set on ‘PyBaseObject_Type’

`“T”': set on *note PyType_Type: 3f79.

`“D”': default (if slot is set to ‘NULL’)

     X - PyType_Ready sets this value if it is NULL
     ~ - PyType_Ready always sets this value (it should be NULL)
     ? - PyType_Ready may set this value depending on other slots

     Also see the inheritance column ("I").

`“I”': inheritance

     X - type slot is inherited via *PyType_Ready* if defined with a *NULL* value
     % - the slots of the sub-struct are inherited individually
     G - inherited, but only in combination with other slots; see the slot's description
     ? - it's complicated; see the slot's description

Note that some slots are effectively inherited through the normal
attribute lookup chain.


File: python.info,  Node: sub-slots,  Next: slot typedefs,  Prev: “tp slots”,  Up: Quick Reference

7.12.3.3 sub-slots
..................

Slot                           *note Type: 4262.     special
                                                     methods
                                                     
----------------------------------------------------------------------
                                                     
*note am_await: 4281.          *note unaryfunc: 4282.__await__
                                                     
                                                     
*note am_aiter: 4283.          *note unaryfunc: 4282.__aiter__
                                                     
                                                     
*note am_anext: 4284.          *note unaryfunc: 4282.__anext__
                                                     
                                                     
                                                     
*note nb_add: 3f8a.            *note binaryfunc: 4285.__add__
                                                     __radd__
                                                     
                                                     
*note nb_inplace_add: 4286.    *note binaryfunc: 4285.__iadd__
                                                     
                                                     
*note nb_subtract: 4287.       *note binaryfunc: 4285.__sub__
                                                     __rsub__
                                                     
                                                     
*note nb_inplace_subtract: 4288.*note binaryfunc: 4285.__isub__
                                                     
                                                     
*note nb_multiply: 4289.       *note binaryfunc: 4285.__mul__
                                                     __rmul__
                                                     
                                                     
*note nb_inplace_multiply: 428a.*note binaryfunc: 4285.__imul__
                                                     
                                                     
*note nb_remainder: 428b.      *note binaryfunc: 4285.__mod__
                                                     __rmod__
                                                     
                                                     
*note nb_inplace_remainder: 428c.*note binaryfunc: 4285.__imod__
                                                     
                                                     
*note nb_divmod: 428d.         *note binaryfunc: 4285.__divmod__
                                                     __rdivmod__
                                                     
                                                     
*note nb_power: 428e.          *note ternaryfunc: 426c.__pow__
                                                     __rpow__
                                                     
                                                     
*note nb_inplace_power: 428f.  *note ternaryfunc: 426c.__ipow__
                                                     
                                                     
*note nb_negative: 4290.       *note unaryfunc: 4282.__neg__
                                                     
                                                     
*note nb_positive: 4291.       *note unaryfunc: 4282.__pos__
                                                     
                                                     
*note nb_absolute: 4292.       *note unaryfunc: 4282.__abs__
                                                     
                                                     
*note nb_bool: 4293.           *note inquiry: 4270.  __bool__
                                                     
                                                     
*note nb_invert: 4294.         *note unaryfunc: 4282.__invert__
                                                     
                                                     
*note nb_lshift: 4295.         *note binaryfunc: 4285.__lshift__
                                                     __rlshift__
                                                     
                                                     
*note nb_inplace_lshift: 4296. *note binaryfunc: 4285.__ilshift__
                                                     
                                                     
*note nb_rshift: 4297.         *note binaryfunc: 4285.__rshift__
                                                     __rrshift__
                                                     
                                                     
*note nb_inplace_rshift: 4298. *note binaryfunc: 4285.__irshift__
                                                     
                                                     
*note nb_and: 4299.            *note binaryfunc: 4285.__and__
                                                     __rand__
                                                     
                                                     
*note nb_inplace_and: 429a.    *note binaryfunc: 4285.__iand__
                                                     
                                                     
*note nb_xor: 429b.            *note binaryfunc: 4285.__xor__
                                                     __rxor__
                                                     
                                                     
*note nb_inplace_xor: 429c.    *note binaryfunc: 4285.__ixor__
                                                     
                                                     
*note nb_or: 429d.             *note binaryfunc: 4285.__or__ __ror__
                                                     
                                                     
*note nb_inplace_or: 429e.     *note binaryfunc: 4285.__ior__
                                                     
                                                     
*note nb_int: 429f.            *note unaryfunc: 4282.__int__
                                                     
                                                     
*note nb_reserved: 42a0.       void *
                               
                                                     
*note nb_float: 42a1.          *note unaryfunc: 4282.__float__
                                                     
                                                     
*note nb_floor_divide: 42a2.   *note binaryfunc: 4285.__floordiv__
                                                     
                                                     
*note nb_inplace_floor_divide: 42a3.*note binaryfunc: 4285.__ifloordiv__
                                                     
                                                     
*note nb_true_divide: 42a4.    *note binaryfunc: 4285.__truediv__
                                                     
                                                     
*note nb_inplace_true_divide: 42a5.*note binaryfunc: 4285.__itruediv__
                                                     
                                                     
*note nb_index: 42a6.          *note unaryfunc: 4282.__index__
                                                     
                                                     
*note nb_matrix_multiply: 42a7.*note binaryfunc: 4285.__matmul__
                                                     __rmatmul__
                                                     
                                                     
*note nb_inplace_matrix_multiply: 42a8.*note binaryfunc: 4285.__imatmul__
                                                     
                                                     
                                                     
*note mp_length: 42a9.         *note lenfunc: 42aa.  __len__
                                                     
                                                     
*note mp_subscript: 42ab.      *note binaryfunc: 4285.__getitem__
                                                     
                                                     
*note mp_ass_subscript: 42ac.  *note objobjargproc: 42ad.__setitem__,
                                                     __delitem__
                                                     
                                                     
                                                     
*note sq_length: 3f8b.         *note lenfunc: 42aa.  __len__
                                                     
                                                     
*note sq_concat: 42ae.         *note binaryfunc: 4285.__add__
                                                     
                                                     
*note sq_repeat: 42af.         *note ssizeargfunc: 42b0.__mul__
                                                     
                                                     
*note sq_item: 10bf.           *note ssizeargfunc: 42b0.__getitem__
                                                     
                                                     
*note sq_ass_item: 42b1.       *note ssizeobjargproc: 42b2.__setitem__
                                                     __delitem__
                                                     
                                                     
*note sq_contains: 42b3.       *note objobjproc: 42b4.__contains__
                                                     
                                                     
*note sq_inplace_concat: 42b5. *note binaryfunc: 4285.__iadd__
                                                     
                                                     
*note sq_inplace_repeat: 42b6. *note ssizeargfunc: 42b0.__imul__
                                                     
                                                     
                                                     
*note bf_getbuffer: 3f94.      *note getbufferproc(): 42b7.
                               
                                                     
*note bf_releasebuffer: 3e8a.  *note releasebufferproc(): 42b8.
                               


File: python.info,  Node: slot typedefs,  Prev: sub-slots,  Up: Quick Reference

7.12.3.4 slot typedefs
......................

typedef                           Parameter Types                   Return Type
                                                                    
-----------------------------------------------------------------------------------------------
                                                                    
*note allocfunc: 4279.                 *note PyTypeObject: 3f5. *   *note PyObject: 5b5. *
                                       Py_ssize_t                   
                                  
                                                                    
*note destructor: 4263.           void *                            void
                                                                    
                                                                    
*note freefunc: 427b.             void *                            void
                                                                    
                                                                    
*note traverseproc: 426f.              void *                       int
                                       *note visitproc: 42ba.       
                                       void * 
                                  
                                                                    
*note newfunc: 427a.                   *note PyObject: 5b5. *       *note PyObject: 5b5. *
                                       *note PyObject: 5b5. *       
                                       *note PyObject: 5b5. * 
                                  
                                                                    
*note initproc: 4278.                  *note PyObject: 5b5. *       int
                                       *note PyObject: 5b5. *       
                                       *note PyObject: 5b5. * 
                                  
                                                                    
*note reprfunc: 4268.             *note PyObject: 5b5. *            *note PyObject: 5b5. *
                                                                    
                                                                    
*note getattrfunc: 4264.               *note PyObject: 5b5. *       *note PyObject: 5b5. *
                                       const char *                 
                                  
                                                                    
*note setattrfunc: 4265.               *note PyObject: 5b5. *       int
                                       const char *                 
                                       *note PyObject: 5b5. * 
                                  
                                                                    
*note getattrofunc: 426d.              *note PyObject: 5b5. *       *note PyObject: 5b5. *
                                       *note PyObject: 5b5. *       
                                  
                                                                    
*note setattrofunc: 426e.              *note PyObject: 5b5. *       int
                                       *note PyObject: 5b5. *       
                                       *note PyObject: 5b5. * 
                                  
                                                                    
*note descrgetfunc: 4275.              *note PyObject: 5b5. *       *note PyObject: 5b5. *
                                       *note PyObject: 5b5. *       
                                       *note PyObject: 5b5. * 
                                  
                                                                    
*note descrsetfunc: 4277.              *note PyObject: 5b5. *       int
                                       *note PyObject: 5b5. *       
                                       *note PyObject: 5b5. * 
                                  
                                                                    
*note hashfunc: 426b.             *note PyObject: 5b5. *            Py_hash_t
                                                                    
                                                                    
*note richcmpfunc: 4271.               *note PyObject: 5b5. *       *note PyObject: 5b5. *
                                       *note PyObject: 5b5. *       
                                       int 
                                  
                                                                    
*note getiterfunc: 4272.          *note PyObject: 5b5. *            *note PyObject: 5b5. *
                                                                    
                                                                    
*note iternextfunc: 4273.         *note PyObject: 5b5. *            *note PyObject: 5b5. *
                                                                    
                                                                    
*note lenfunc: 42aa.              *note PyObject: 5b5. *            Py_ssize_t
                                                                    
                                                                    
*note getbufferproc: 42b7.             *note PyObject: 5b5. *       int
                                       *note Py_buffer: bee. *      
                                       int 
                                  
                                                                    
*note releasebufferproc: 42b8.         *note PyObject: 5b5. *       void
                                       *note Py_buffer: bee. *      
                                  
                                                                    
*note inquiry: 4270.              void *                            int
                                                                    
                                                                    
*note unaryfunc: 4282.                 *note PyObject: 5b5. *       *note PyObject: 5b5. *
                                                                    
                                                                    
*note binaryfunc: 4285.                *note PyObject: 5b5. *       *note PyObject: 5b5. *
                                       *note PyObject: 5b5. *       
                                  
                                                                    
*note ternaryfunc: 426c.               *note PyObject: 5b5. *       *note PyObject: 5b5. *
                                       *note PyObject: 5b5. *       
                                       *note PyObject: 5b5. * 
                                  
                                                                    
*note ssizeargfunc: 42b0.              *note PyObject: 5b5. *       *note PyObject: 5b5. *
                                       Py_ssize_t                   
                                  
                                                                    
*note ssizeobjargproc: 42b2.           *note PyObject: 5b5. *       int
                                       Py_ssize_t                   
                                  
                                                                    
*note objobjproc: 42b4.                *note PyObject: 5b5. *       int
                                       *note PyObject: 5b5. *       
                                  
                                                                    
*note objobjargproc: 42ad.             *note PyObject: 5b5. *       int
                                       *note PyObject: 5b5. *       
                                       *note PyObject: 5b5. * 
                                  

See *note Slot Type typedefs: 42bb. below for more detail.


File: python.info,  Node: PyTypeObject Definition,  Next: PyObject Slots,  Prev: Quick Reference,  Up: Type Objects<3>

7.12.3.5 PyTypeObject Definition
................................

The structure definition for *note PyTypeObject: 3f5. can be found in
‘Include/object.h’.  For convenience of reference, this repeats the
definition found there:

     typedef struct _typeobject {
         PyObject_VAR_HEAD
         const char *tp_name; /* For printing, in format "<module>.<name>" */
         Py_ssize_t tp_basicsize, tp_itemsize; /* For allocation */

         /* Methods to implement standard operations */

         destructor tp_dealloc;
         Py_ssize_t tp_vectorcall_offset;
         getattrfunc tp_getattr;
         setattrfunc tp_setattr;
         PyAsyncMethods *tp_as_async; /* formerly known as tp_compare (Python 2)
                                         or tp_reserved (Python 3) */
         reprfunc tp_repr;

         /* Method suites for standard classes */

         PyNumberMethods *tp_as_number;
         PySequenceMethods *tp_as_sequence;
         PyMappingMethods *tp_as_mapping;

         /* More standard operations (here for binary compatibility) */

         hashfunc tp_hash;
         ternaryfunc tp_call;
         reprfunc tp_str;
         getattrofunc tp_getattro;
         setattrofunc tp_setattro;

         /* Functions to access object as input/output buffer */
         PyBufferProcs *tp_as_buffer;

         /* Flags to define presence of optional/expanded features */
         unsigned long tp_flags;

         const char *tp_doc; /* Documentation string */

         /* call function for all accessible objects */
         traverseproc tp_traverse;

         /* delete references to contained objects */
         inquiry tp_clear;

         /* rich comparisons */
         richcmpfunc tp_richcompare;

         /* weak reference enabler */
         Py_ssize_t tp_weaklistoffset;

         /* Iterators */
         getiterfunc tp_iter;
         iternextfunc tp_iternext;

         /* Attribute descriptor and subclassing stuff */
         struct PyMethodDef *tp_methods;
         struct PyMemberDef *tp_members;
         struct PyGetSetDef *tp_getset;
         struct _typeobject *tp_base;
         PyObject *tp_dict;
         descrgetfunc tp_descr_get;
         descrsetfunc tp_descr_set;
         Py_ssize_t tp_dictoffset;
         initproc tp_init;
         allocfunc tp_alloc;
         newfunc tp_new;
         freefunc tp_free; /* Low-level free-memory routine */
         inquiry tp_is_gc; /* For PyObject_IS_GC */
         PyObject *tp_bases;
         PyObject *tp_mro; /* method resolution order */
         PyObject *tp_cache;
         PyObject *tp_subclasses;
         PyObject *tp_weaklist;
         destructor tp_del;

         /* Type attribute cache version tag. Added in version 2.6 */
         unsigned int tp_version_tag;

         destructor tp_finalize;

     } PyTypeObject;


File: python.info,  Node: PyObject Slots,  Next: PyVarObject Slots,  Prev: PyTypeObject Definition,  Up: Type Objects<3>

7.12.3.6 PyObject Slots
.......................

The type object structure extends the *note PyVarObject: 424f.
structure.  The ‘ob_size’ field is used for dynamic types (created by
‘type_new()’, usually called from a class statement).  Note that *note
PyType_Type: 3f79. (the metatype) initializes *note tp_itemsize: 3d50,
which means that its instances (i.e.  type objects) `must' have the
‘ob_size’ field.

 -- C Member: PyObject* PyObject._ob_next
 -- C Member: PyObject* PyObject._ob_prev

     These fields are only present when the macro ‘Py_TRACE_REFS’ is
     defined.  Their initialization to ‘NULL’ is taken care of by the
     ‘PyObject_HEAD_INIT’ macro.  For statically allocated objects,
     these fields always remain ‘NULL’.  For dynamically allocated
     objects, these two fields are used to link the object into a
     doubly-linked list of `all' live objects on the heap.  This could
     be used for various debugging purposes; currently the only use is
     to print the objects that are still alive at the end of a run when
     the environment variable *note PYTHONDUMPREFS: 293. is set.

     `Inheritance:'

     These fields are not inherited by subtypes.

 -- C Member: Py_ssize_t PyObject.ob_refcnt

     This is the type object’s reference count, initialized to ‘1’ by
     the ‘PyObject_HEAD_INIT’ macro.  Note that for statically allocated
     type objects, the type’s instances (objects whose ‘ob_type’ points
     back to the type) do `not' count as references.  But for
     dynamically allocated type objects, the instances `do' count as
     references.

     `Inheritance:'

     This field is not inherited by subtypes.

 -- C Member: PyTypeObject* PyObject.ob_type

     This is the type’s type, in other words its metatype.  It is
     initialized by the argument to the ‘PyObject_HEAD_INIT’ macro, and
     its value should normally be ‘&PyType_Type’.  However, for
     dynamically loadable extension modules that must be usable on
     Windows (at least), the compiler complains that this is not a valid
     initializer.  Therefore, the convention is to pass ‘NULL’ to the
     ‘PyObject_HEAD_INIT’ macro and to initialize this field explicitly
     at the start of the module’s initialization function, before doing
     anything else.  This is typically done like this:

          Foo_Type.ob_type = &PyType_Type;

     This should be done before any instances of the type are created.
     *note PyType_Ready(): 3d59. checks if ‘ob_type’ is ‘NULL’, and if
     so, initializes it to the ‘ob_type’ field of the base class.  *note
     PyType_Ready(): 3d59. will not change this field if it is non-zero.

     `Inheritance:'

     This field is inherited by subtypes.


File: python.info,  Node: PyVarObject Slots,  Next: PyTypeObject Slots,  Prev: PyObject Slots,  Up: Type Objects<3>

7.12.3.7 PyVarObject Slots
..........................

 -- C Member: Py_ssize_t PyVarObject.ob_size

     For statically allocated type objects, this should be initialized
     to zero.  For dynamically allocated type objects, this field has a
     special internal meaning.

     `Inheritance:'

     This field is not inherited by subtypes.


File: python.info,  Node: PyTypeObject Slots,  Next: Heap Types,  Prev: PyVarObject Slots,  Up: Type Objects<3>

7.12.3.8 PyTypeObject Slots
...........................

Each slot has a section describing inheritance.  If *note
PyType_Ready(): 3d59. may set a value when the field is set to ‘NULL’
then there will also be a “Default” section.  (Note that many fields set
on ‘PyBaseObject_Type’ and *note PyType_Type: 3f79. effectively act as
defaults.)

 -- C Member: const char* PyTypeObject.tp_name

     Pointer to a NUL-terminated string containing the name of the type.
     For types that are accessible as module globals, the string should
     be the full module name, followed by a dot, followed by the type
     name; for built-in types, it should be just the type name.  If the
     module is a submodule of a package, the full package name is part
     of the full module name.  For example, a type named ‘T’ defined in
     module ‘M’ in subpackage ‘Q’ in package ‘P’ should have the *note
     tp_name: 3d71. initializer ‘"P.Q.M.T"’.

     For dynamically allocated type objects, this should just be the
     type name, and the module name explicitly stored in the type dict
     as the value for key ‘'__module__'’.

     For statically allocated type objects, the tp_name field should
     contain a dot.  Everything before the last dot is made accessible
     as the ‘__module__’ attribute, and everything after the last dot is
     made accessible as the *note __name__: d2f. attribute.

     If no dot is present, the entire *note tp_name: 3d71. field is made
     accessible as the *note __name__: d2f. attribute, and the
     ‘__module__’ attribute is undefined (unless explicitly set in the
     dictionary, as explained above).  This means your type will be
     impossible to pickle.  Additionally, it will not be listed in
     module documentations created with pydoc.

     This field must not be ‘NULL’.  It is the only required field in
     *note PyTypeObject(): 3f5. (other than potentially *note
     tp_itemsize: 3d50.).

     `Inheritance:'

     This field is not inherited by subtypes.

 -- C Member: Py_ssize_t PyTypeObject.tp_basicsize
 -- C Member: Py_ssize_t PyTypeObject.tp_itemsize

     These fields allow calculating the size in bytes of instances of
     the type.

     There are two kinds of types: types with fixed-length instances
     have a zero *note tp_itemsize: 3d50. field, types with
     variable-length instances have a non-zero *note tp_itemsize: 3d50.
     field.  For a type with fixed-length instances, all instances have
     the same size, given in *note tp_basicsize: 26a.

     For a type with variable-length instances, the instances must have
     an ‘ob_size’ field, and the instance size is *note tp_basicsize:
     26a. plus N times *note tp_itemsize: 3d50, where N is the “length”
     of the object.  The value of N is typically stored in the
     instance’s ‘ob_size’ field.  There are exceptions: for example,
     ints use a negative ‘ob_size’ to indicate a negative number, and N
     is ‘abs(ob_size)’ there.  Also, the presence of an ‘ob_size’ field
     in the instance layout doesn’t mean that the instance structure is
     variable-length (for example, the structure for the list type has
     fixed-length instances, yet those instances have a meaningful
     ‘ob_size’ field).

     The basic size includes the fields in the instance declared by the
     macro *note PyObject_HEAD: d3a. or *note PyObject_VAR_HEAD: 4251.
     (whichever is used to declare the instance struct) and this in turn
     includes the ‘_ob_prev’ and ‘_ob_next’ fields if they are present.
     This means that the only correct way to get an initializer for the
     *note tp_basicsize: 26a. is to use the ‘sizeof’ operator on the
     struct used to declare the instance layout.  The basic size does
     not include the GC header size.

     A note about alignment: if the variable items require a particular
     alignment, this should be taken care of by the value of *note
     tp_basicsize: 26a.  Example: suppose a type implements an array of
     ‘double’.  *note tp_itemsize: 3d50. is ‘sizeof(double)’.  It is the
     programmer’s responsibility that *note tp_basicsize: 26a. is a
     multiple of ‘sizeof(double)’ (assuming this is the alignment
     requirement for ‘double’).

     For any type with variable-length instances, this field must not be
     ‘NULL’.

     `Inheritance:'

     These fields are inherited separately by subtypes.  If the base
     type has a non-zero *note tp_itemsize: 3d50, it is generally not
     safe to set *note tp_itemsize: 3d50. to a different non-zero value
     in a subtype (though this depends on the implementation of the base
     type).

 -- C Member: destructor PyTypeObject.tp_dealloc

     A pointer to the instance destructor function.  This function must
     be defined unless the type guarantees that its instances will never
     be deallocated (as is the case for the singletons ‘None’ and
     ‘Ellipsis’).  The function signature is:

          void tp_dealloc(PyObject *self);

     The destructor function is called by the *note Py_DECREF(): 38f.
     and *note Py_XDECREF(): 391. macros when the new reference count is
     zero.  At this point, the instance is still in existence, but there
     are no references to it.  The destructor function should free all
     references which the instance owns, free all memory buffers owned
     by the instance (using the freeing function corresponding to the
     allocation function used to allocate the buffer), and call the
     type’s *note tp_free: 3d57. function.  If the type is not
     subtypable (doesn’t have the *note Py_TPFLAGS_BASETYPE: 3d5e. flag
     bit set), it is permissible to call the object deallocator directly
     instead of via *note tp_free: 3d57.  The object deallocator should
     be the one used to allocate the instance; this is normally *note
     PyObject_Del(): ed8. if the instance was allocated using *note
     PyObject_New(): 268. or ‘PyObject_VarNew()’, or *note
     PyObject_GC_Del(): f05. if the instance was allocated using *note
     PyObject_GC_New(): 3f3. or *note PyObject_GC_NewVar(): 3f4.

     If the type supports garbage collection (has the *note
     Py_TPFLAGS_HAVE_GC: 3d64. flag bit set), the destructor should call
     *note PyObject_GC_UnTrack(): f07. before clearing any member
     fields.

          static void foo_dealloc(foo_object *self) {
              PyObject_GC_UnTrack(self);
              Py_CLEAR(self->ref);
              Py_TYPE(self)->tp_free((PyObject *)self);
          }

     Finally, if the type is heap allocated (*note Py_TPFLAGS_HEAPTYPE:
     3f80.), the deallocator should decrement the reference count for
     its type object after calling the type deallocator.  In order to
     avoid dangling pointers, the recommended way to achieve this is:

          static void foo_dealloc(foo_object *self) {
              PyTypeObject *tp = Py_TYPE(self);
              // free references and buffers here
              tp->tp_free(self);
              Py_DECREF(tp);
          }

     `Inheritance:'

     This field is inherited by subtypes.

 -- C Member: Py_ssize_t PyTypeObject.tp_vectorcall_offset

     An optional offset to a per-instance function that implements
     calling the object using the *note vectorcall protocol: 2b8, a more
     efficient alternative of the simpler *note tp_call: 3d82.

     This field is only used if the flag *note
     Py_TPFLAGS_HAVE_VECTORCALL: 3edb. is set.  If so, this must be a
     positive integer containing the offset in the instance of a *note
     vectorcallfunc: 3edd. pointer.

     The `vectorcallfunc' pointer may be ‘NULL’, in which case the
     instance behaves as if *note Py_TPFLAGS_HAVE_VECTORCALL: 3edb. was
     not set: calling the instance falls back to *note tp_call: 3d82.

     Any class that sets ‘Py_TPFLAGS_HAVE_VECTORCALL’ must also set
     *note tp_call: 3d82. and make sure its behaviour is consistent with
     the `vectorcallfunc' function.  This can be done by setting
     `tp_call' to *note PyVectorcall_Call(): 3eda.

          Warning: It is not recommended for *note heap types: 3f7f. to
          implement the vectorcall protocol.  When a user sets *note
          __call__: 1560. in Python code, only `tp_call' is updated,
          likely making it inconsistent with the vectorcall function.

          Note: The semantics of the ‘tp_vectorcall_offset’ slot are
          provisional and expected to be finalized in Python 3.9.  If
          you use vectorcall, plan for updating your code for Python
          3.9.

     Changed in version 3.8: Before version 3.8, this slot was named
     ‘tp_print’.  In Python 2.x, it was used for printing to a file.  In
     Python 3.0 to 3.7, it was unused.

     `Inheritance:'

     This field is always inherited.  However, the *note
     Py_TPFLAGS_HAVE_VECTORCALL: 3edb. flag is not always inherited.  If
     it’s not, then the subclass won’t use *note vectorcall: 2b8, except
     when *note PyVectorcall_Call(): 3eda. is explicitly called.  This
     is in particular the case for *note heap types: 42c5. (including
     subclasses defined in Python).

 -- C Member: getattrfunc PyTypeObject.tp_getattr

     An optional pointer to the get-attribute-string function.

     This field is deprecated.  When it is defined, it should point to a
     function that acts the same as the *note tp_getattro: 3d75.
     function, but taking a C string instead of a Python string object
     to give the attribute name.

     `Inheritance:'

     Group: ‘tp_getattr’, ‘tp_getattro’

     This field is inherited by subtypes together with *note
     tp_getattro: 3d75.: a subtype inherits both *note tp_getattr: 3d78.
     and *note tp_getattro: 3d75. from its base type when the subtype’s
     *note tp_getattr: 3d78. and *note tp_getattro: 3d75. are both
     ‘NULL’.

 -- C Member: setattrfunc PyTypeObject.tp_setattr

     An optional pointer to the function for setting and deleting
     attributes.

     This field is deprecated.  When it is defined, it should point to a
     function that acts the same as the *note tp_setattro: 3d76.
     function, but taking a C string instead of a Python string object
     to give the attribute name.

     `Inheritance:'

     Group: ‘tp_setattr’, ‘tp_setattro’

     This field is inherited by subtypes together with *note
     tp_setattro: 3d76.: a subtype inherits both *note tp_setattr: 3d79.
     and *note tp_setattro: 3d76. from its base type when the subtype’s
     *note tp_setattr: 3d79. and *note tp_setattro: 3d76. are both
     ‘NULL’.

 -- C Member: PyAsyncMethods* PyTypeObject.tp_as_async

     Pointer to an additional structure that contains fields relevant
     only to objects which implement *note awaitable: 613. and *note
     asynchronous iterator: 738. protocols at the C-level.  See *note
     Async Object Structures: 42c6. for details.

     New in version 3.5: Formerly known as ‘tp_compare’ and
     ‘tp_reserved’.

     `Inheritance:'

     The *note tp_as_async: 4266. field is not inherited, but the
     contained fields are inherited individually.

 -- C Member: reprfunc PyTypeObject.tp_repr

     An optional pointer to a function that implements the built-in
     function *note repr(): 8b9.

     The signature is the same as for *note PyObject_Repr(): a49.:

          PyObject *tp_repr(PyObject *self);

     The function must return a string or a Unicode object.  Ideally,
     this function should return a string that, when passed to *note
     eval(): c61, given a suitable environment, returns an object with
     the same value.  If this is not feasible, it should return a string
     starting with ‘'<'’ and ending with ‘'>'’ from which both the type
     and the value of the object can be deduced.

     `Inheritance:'

     This field is inherited by subtypes.

     `Default:'

     When this field is not set, a string of the form ‘<%s object at
     %p>’ is returned, where ‘%s’ is replaced by the type name, and ‘%p’
     by the object’s memory address.

 -- C Member: PyNumberMethods* PyTypeObject.tp_as_number

     Pointer to an additional structure that contains fields relevant
     only to objects which implement the number protocol.  These fields
     are documented in *note Number Object Structures: 42c7.

     `Inheritance:'

     The *note tp_as_number: 26f. field is not inherited, but the
     contained fields are inherited individually.

 -- C Member: PySequenceMethods* PyTypeObject.tp_as_sequence

     Pointer to an additional structure that contains fields relevant
     only to objects which implement the sequence protocol.  These
     fields are documented in *note Sequence Object Structures: 42c8.

     `Inheritance:'

     The *note tp_as_sequence: 4269. field is not inherited, but the
     contained fields are inherited individually.

 -- C Member: PyMappingMethods* PyTypeObject.tp_as_mapping

     Pointer to an additional structure that contains fields relevant
     only to objects which implement the mapping protocol.  These fields
     are documented in *note Mapping Object Structures: 42c9.

     `Inheritance:'

     The *note tp_as_mapping: 426a. field is not inherited, but the
     contained fields are inherited individually.

 -- C Member: hashfunc PyTypeObject.tp_hash

     An optional pointer to a function that implements the built-in
     function *note hash(): aa3.

     The signature is the same as for *note PyObject_Hash(): 3ecc.:

          Py_hash_t tp_hash(PyObject *);

     The value ‘-1’ should not be returned as a normal return value;
     when an error occurs during the computation of the hash value, the
     function should set an exception and return ‘-1’.

     When this field is not set (`and' ‘tp_richcompare’ is not set), an
     attempt to take the hash of the object raises *note TypeError: 1fe.
     This is the same as setting it to *note
     PyObject_HashNotImplemented(): df7.

     This field can be set explicitly to *note
     PyObject_HashNotImplemented(): df7. to block inheritance of the
     hash method from a parent type.  This is interpreted as the
     equivalent of ‘__hash__ = None’ at the Python level, causing
     ‘isinstance(o, collections.Hashable)’ to correctly return ‘False’.
     Note that the converse is also true - setting ‘__hash__ = None’ on
     a class at the Python level will result in the ‘tp_hash’ slot being
     set to *note PyObject_HashNotImplemented(): df7.

     `Inheritance:'

     Group: ‘tp_hash’, ‘tp_richcompare’

     This field is inherited by subtypes together with *note
     tp_richcompare: 3d7b.: a subtype inherits both of *note
     tp_richcompare: 3d7b. and *note tp_hash: 3d81, when the subtype’s
     *note tp_richcompare: 3d7b. and *note tp_hash: 3d81. are both
     ‘NULL’.

 -- C Member: ternaryfunc PyTypeObject.tp_call

     An optional pointer to a function that implements calling the
     object.  This should be ‘NULL’ if the object is not callable.  The
     signature is the same as for *note PyObject_Call(): 23c.:

          PyObject *tp_call(PyObject *self, PyObject *args, PyObject *kwargs);

     `Inheritance:'

     This field is inherited by subtypes.

 -- C Member: reprfunc PyTypeObject.tp_str

     An optional pointer to a function that implements the built-in
     operation *note str(): 205.  (Note that *note str: 205. is a type
     now, and *note str(): 205. calls the constructor for that type.
     This constructor calls *note PyObject_Str(): a4a. to do the actual
     work, and *note PyObject_Str(): a4a. will call this handler.)

     The signature is the same as for *note PyObject_Str(): a4a.:

          PyObject *tp_str(PyObject *self);

     The function must return a string or a Unicode object.  It should
     be a “friendly” string representation of the object, as this is the
     representation that will be used, among other things, by the *note
     print(): 971. function.

     `Inheritance:'

     This field is inherited by subtypes.

     `Default:'

     When this field is not set, *note PyObject_Repr(): a49. is called
     to return a string representation.

 -- C Member: getattrofunc PyTypeObject.tp_getattro

     An optional pointer to the get-attribute function.

     The signature is the same as for *note PyObject_GetAttr(): 3ec0.:

          PyObject *tp_getattro(PyObject *self, PyObject *attr);

     It is usually convenient to set this field to *note
     PyObject_GenericGetAttr(): 3ec2, which implements the normal way of
     looking for object attributes.

     `Inheritance:'

     Group: ‘tp_getattr’, ‘tp_getattro’

     This field is inherited by subtypes together with *note tp_getattr:
     3d78.: a subtype inherits both *note tp_getattr: 3d78. and *note
     tp_getattro: 3d75. from its base type when the subtype’s *note
     tp_getattr: 3d78. and *note tp_getattro: 3d75. are both ‘NULL’.

     `Default:'

     ‘PyBaseObject_Type’ uses *note PyObject_GenericGetAttr(): 3ec2.

 -- C Member: setattrofunc PyTypeObject.tp_setattro

     An optional pointer to the function for setting and deleting
     attributes.

     The signature is the same as for *note PyObject_SetAttr(): 3ec3.:

          int tp_setattro(PyObject *self, PyObject *attr, PyObject *value);

     In addition, setting `value' to ‘NULL’ to delete an attribute must
     be supported.  It is usually convenient to set this field to *note
     PyObject_GenericSetAttr(): 3ec7, which implements the normal way of
     setting object attributes.

     `Inheritance:'

     Group: ‘tp_setattr’, ‘tp_setattro’

     This field is inherited by subtypes together with *note tp_setattr:
     3d79.: a subtype inherits both *note tp_setattr: 3d79. and *note
     tp_setattro: 3d76. from its base type when the subtype’s *note
     tp_setattr: 3d79. and *note tp_setattro: 3d76. are both ‘NULL’.

     `Default:'

     ‘PyBaseObject_Type’ uses *note PyObject_GenericSetAttr(): 3ec7.

 -- C Member: PyBufferProcs* PyTypeObject.tp_as_buffer

     Pointer to an additional structure that contains fields relevant
     only to objects which implement the buffer interface.  These fields
     are documented in *note Buffer Object Structures: 3f38.

     `Inheritance:'

     The *note tp_as_buffer: 26d. field is not inherited, but the
     contained fields are inherited individually.

 -- C Member: unsigned long PyTypeObject.tp_flags

     This field is a bit mask of various flags.  Some flags indicate
     variant semantics for certain situations; others are used to
     indicate that certain fields in the type object (or in the
     extension structures referenced via *note tp_as_number: 26f, *note
     tp_as_sequence: 4269, *note tp_as_mapping: 426a, and *note
     tp_as_buffer: 26d.) that were historically not always present are
     valid; if such a flag bit is clear, the type fields it guards must
     not be accessed and must be considered to have a zero or ‘NULL’
     value instead.

     `Inheritance:'

     Inheritance of this field is complicated.  Most flag bits are
     inherited individually, i.e.  if the base type has a flag bit set,
     the subtype inherits this flag bit.  The flag bits that pertain to
     extension structures are strictly inherited if the extension
     structure is inherited, i.e.  the base type’s value of the flag bit
     is copied into the subtype together with a pointer to the extension
     structure.  The *note Py_TPFLAGS_HAVE_GC: 3d64. flag bit is
     inherited together with the *note tp_traverse: 23b. and *note
     tp_clear: 3d6e. fields, i.e.  if the *note Py_TPFLAGS_HAVE_GC:
     3d64. flag bit is clear in the subtype and the *note tp_traverse:
     23b. and *note tp_clear: 3d6e. fields in the subtype exist and have
     ‘NULL’ values.

     `Default:'

     ‘PyBaseObject_Type’ uses ‘Py_TPFLAGS_DEFAULT |
     Py_TPFLAGS_BASETYPE’.

     `Bit Masks:'

     The following bit masks are currently defined; these can be ORed
     together using the ‘|’ operator to form the value of the *note
     tp_flags: 1011. field.  The macro *note PyType_HasFeature(): 1010.
     takes a type and a flags value, `tp' and `f', and checks whether
     ‘tp->tp_flags & f’ is non-zero.

      -- Data: Py_TPFLAGS_HEAPTYPE

          This bit is set when the type object itself is allocated on
          the heap, for example, types created dynamically using *note
          PyType_FromSpec(): 23a.  In this case, the ‘ob_type’ field of
          its instances is considered a reference to the type, and the
          type object is INCREF’ed when a new instance is created, and
          DECREF’ed when an instance is destroyed (this does not apply
          to instances of subtypes; only the type referenced by the
          instance’s ob_type gets INCREF’ed or DECREF’ed).

          `Inheritance:'

          ???

      -- Data: Py_TPFLAGS_BASETYPE

          This bit is set when the type can be used as the base type of
          another type.  If this bit is clear, the type cannot be
          subtyped (similar to a “final” class in Java).

          `Inheritance:'

          ???

      -- Data: Py_TPFLAGS_READY

          This bit is set when the type object has been fully
          initialized by *note PyType_Ready(): 3d59.

          `Inheritance:'

          ???

      -- Data: Py_TPFLAGS_READYING

          This bit is set while *note PyType_Ready(): 3d59. is in the
          process of initializing the type object.

          `Inheritance:'

          ???

      -- Data: Py_TPFLAGS_HAVE_GC

          This bit is set when the object supports garbage collection.
          If this bit is set, instances must be created using *note
          PyObject_GC_New(): 3f3. and destroyed using *note
          PyObject_GC_Del(): f05.  More information in section *note
          Supporting Cyclic Garbage Collection: 42cc.  This bit also
          implies that the GC-related fields *note tp_traverse: 23b. and
          *note tp_clear: 3d6e. are present in the type object.

          `Inheritance:'

          Group: *note Py_TPFLAGS_HAVE_GC: 3d64, ‘tp_traverse’,
          ‘tp_clear’

          The *note Py_TPFLAGS_HAVE_GC: 3d64. flag bit is inherited
          together with the ‘tp_traverse’ and ‘tp_clear’ fields, i.e.
          if the *note Py_TPFLAGS_HAVE_GC: 3d64. flag bit is clear in
          the subtype and the ‘tp_traverse’ and ‘tp_clear’ fields in the
          subtype exist and have ‘NULL’ values.

      -- Data: Py_TPFLAGS_DEFAULT

          This is a bitmask of all the bits that pertain to the
          existence of certain fields in the type object and its
          extension structures.  Currently, it includes the following
          bits: ‘Py_TPFLAGS_HAVE_STACKLESS_EXTENSION’,
          ‘Py_TPFLAGS_HAVE_VERSION_TAG’.

          `Inheritance:'

          ???

      -- Data: Py_TPFLAGS_METHOD_DESCRIPTOR

          This bit indicates that objects behave like unbound methods.

          If this flag is set for ‘type(meth)’, then:

             - ‘meth.__get__(obj, cls)(*args, **kwds)’ (with ‘obj’ not
               None) must be equivalent to ‘meth(obj, *args, **kwds)’.

             - ‘meth.__get__(None, cls)(*args, **kwds)’ must be
               equivalent to ‘meth(*args, **kwds)’.

          This flag enables an optimization for typical method calls
          like ‘obj.meth()’: it avoids creating a temporary “bound
          method” object for ‘obj.meth’.

          New in version 3.8.

          `Inheritance:'

          This flag is never inherited by heap types.  For extension
          types, it is inherited whenever *note tp_descr_get: 4274. is
          inherited.

      -- Data: Py_TPFLAGS_LONG_SUBCLASS

      -- Data: Py_TPFLAGS_LIST_SUBCLASS

      -- Data: Py_TPFLAGS_TUPLE_SUBCLASS

      -- Data: Py_TPFLAGS_BYTES_SUBCLASS

      -- Data: Py_TPFLAGS_UNICODE_SUBCLASS

      -- Data: Py_TPFLAGS_DICT_SUBCLASS

      -- Data: Py_TPFLAGS_BASE_EXC_SUBCLASS

      -- Data: Py_TPFLAGS_TYPE_SUBCLASS

          These flags are used by functions such as *note
          PyLong_Check(): 3fa1. to quickly determine if a type is a
          subclass of a built-in type; such specific checks are faster
          than a generic check, like *note PyObject_IsInstance(): 88c.
          Custom types that inherit from built-ins should have their
          *note tp_flags: 1011. set appropriately, or the code that
          interacts with such types will behave differently depending on
          what kind of check is used.

      -- Data: Py_TPFLAGS_HAVE_FINALIZE

          This bit is set when the *note tp_finalize: 3f6. slot is
          present in the type structure.

          New in version 3.4.

          Deprecated since version 3.8: This flag isn’t necessary
          anymore, as the interpreter assumes the *note tp_finalize:
          3f6. slot is always present in the type structure.

      -- Data: Py_TPFLAGS_HAVE_VECTORCALL

          This bit is set when the class implements the *note vectorcall
          protocol: 2b8.  See *note tp_vectorcall_offset: 3edc. for
          details.

          `Inheritance:'

          This bit is inherited for `static' subtypes if *note tp_call:
          3d82. is also inherited.  *note Heap types: 42c5. do not
          inherit ‘Py_TPFLAGS_HAVE_VECTORCALL’.

          New in version 3.9.

 -- C Member: const char* PyTypeObject.tp_doc

     An optional pointer to a NUL-terminated C string giving the
     docstring for this type object.  This is exposed as the ‘__doc__’
     attribute on the type and instances of the type.

     `Inheritance:'

     This field is `not' inherited by subtypes.

 -- C Member: traverseproc PyTypeObject.tp_traverse

     An optional pointer to a traversal function for the garbage
     collector.  This is only used if the *note Py_TPFLAGS_HAVE_GC:
     3d64. flag bit is set.  The signature is:

          int tp_traverse(PyObject *self, visitproc visit, void *arg);

     More information about Python’s garbage collection scheme can be
     found in section *note Supporting Cyclic Garbage Collection: 42cc.

     The *note tp_traverse: 23b. pointer is used by the garbage
     collector to detect reference cycles.  A typical implementation of
     a *note tp_traverse: 23b. function simply calls *note Py_VISIT():
     3d62. on each of the instance’s members that are Python objects
     that the instance owns.  For example, this is function
     ‘local_traverse()’ from the *note _thread: 2. extension module:

          static int
          local_traverse(localobject *self, visitproc visit, void *arg)
          {
              Py_VISIT(self->args);
              Py_VISIT(self->kw);
              Py_VISIT(self->dict);
              return 0;
          }

     Note that *note Py_VISIT(): 3d62. is called only on those members
     that can participate in reference cycles.  Although there is also a
     ‘self->key’ member, it can only be ‘NULL’ or a Python string and
     therefore cannot be part of a reference cycle.

     On the other hand, even if you know a member can never be part of a
     cycle, as a debugging aid you may want to visit it anyway just so
     the *note gc: 84. module’s *note get_referents(): fb7. function
     will include it.

          Warning: When implementing *note tp_traverse: 23b, only the
          members that the instance `owns' (by having strong references
          to them) must be visited.  For instance, if an object supports
          weak references via the *note tp_weaklist: 3f90. slot, the
          pointer supporting the linked list (what `tp_weaklist' points
          to) must `not' be visited as the instance does not directly
          own the weak references to itself (the weakreference list is
          there to support the weak reference machinery, but the
          instance has no strong reference to the elements inside it, as
          they are allowed to be removed even if the instance is still
          alive).

     Note that *note Py_VISIT(): 3d62. requires the `visit' and `arg'
     parameters to ‘local_traverse()’ to have these specific names;
     don’t name them just anything.

     Heap-allocated types (*note Py_TPFLAGS_HEAPTYPE: 3f80, such as
     those created with *note PyType_FromSpec(): 23a. and similar APIs)
     hold a reference to their type.  Their traversal function must
     therefore either visit *note Py_TYPE(self): 3d4f, or delegate this
     responsibility by calling ‘tp_traverse’ of another heap-allocated
     type (such as a heap-allocated superclass).  If they do not, the
     type object may not be garbage-collected.

     Changed in version 3.9: Heap-allocated types are expected to visit
     ‘Py_TYPE(self)’ in ‘tp_traverse’.  In earlier versions of Python,
     due to bug 40217(1), doing this may lead to crashes in subclasses.

     `Inheritance:'

     Group: *note Py_TPFLAGS_HAVE_GC: 3d64, ‘tp_traverse’, ‘tp_clear’

     This field is inherited by subtypes together with *note tp_clear:
     3d6e. and the *note Py_TPFLAGS_HAVE_GC: 3d64. flag bit: the flag
     bit, *note tp_traverse: 23b, and *note tp_clear: 3d6e. are all
     inherited from the base type if they are all zero in the subtype.

 -- C Member: inquiry PyTypeObject.tp_clear

     An optional pointer to a clear function for the garbage collector.
     This is only used if the *note Py_TPFLAGS_HAVE_GC: 3d64. flag bit
     is set.  The signature is:

          int tp_clear(PyObject *);

     The *note tp_clear: 3d6e. member function is used to break
     reference cycles in cyclic garbage detected by the garbage
     collector.  Taken together, all *note tp_clear: 3d6e. functions in
     the system must combine to break all reference cycles.  This is
     subtle, and if in any doubt supply a *note tp_clear: 3d6e.
     function.  For example, the tuple type does not implement a *note
     tp_clear: 3d6e. function, because it’s possible to prove that no
     reference cycle can be composed entirely of tuples.  Therefore the
     *note tp_clear: 3d6e. functions of other types must be sufficient
     to break any cycle containing a tuple.  This isn’t immediately
     obvious, and there’s rarely a good reason to avoid implementing
     *note tp_clear: 3d6e.

     Implementations of *note tp_clear: 3d6e. should drop the instance’s
     references to those of its members that may be Python objects, and
     set its pointers to those members to ‘NULL’, as in the following
     example:

          static int
          local_clear(localobject *self)
          {
              Py_CLEAR(self->key);
              Py_CLEAR(self->args);
              Py_CLEAR(self->kw);
              Py_CLEAR(self->dict);
              return 0;
          }

     The *note Py_CLEAR(): 3d63. macro should be used, because clearing
     references is delicate: the reference to the contained object must
     not be decremented until after the pointer to the contained object
     is set to ‘NULL’.  This is because decrementing the reference count
     may cause the contained object to become trash, triggering a chain
     of reclamation activity that may include invoking arbitrary Python
     code (due to finalizers, or weakref callbacks, associated with the
     contained object).  If it’s possible for such code to reference
     `self' again, it’s important that the pointer to the contained
     object be ‘NULL’ at that time, so that `self' knows the contained
     object can no longer be used.  The *note Py_CLEAR(): 3d63. macro
     performs the operations in a safe order.

     Note that *note tp_clear: 3d6e. is not `always' called before an
     instance is deallocated.  For example, when reference counting is
     enough to determine that an object is no longer used, the cyclic
     garbage collector is not involved and *note tp_dealloc: 3d56. is
     called directly.

     Because the goal of *note tp_clear: 3d6e. functions is to break
     reference cycles, it’s not necessary to clear contained objects
     like Python strings or Python integers, which can’t participate in
     reference cycles.  On the other hand, it may be convenient to clear
     all contained Python objects, and write the type’s *note
     tp_dealloc: 3d56. function to invoke *note tp_clear: 3d6e.

     More information about Python’s garbage collection scheme can be
     found in section *note Supporting Cyclic Garbage Collection: 42cc.

     `Inheritance:'

     Group: *note Py_TPFLAGS_HAVE_GC: 3d64, ‘tp_traverse’, ‘tp_clear’

     This field is inherited by subtypes together with *note
     tp_traverse: 23b. and the *note Py_TPFLAGS_HAVE_GC: 3d64. flag bit:
     the flag bit, *note tp_traverse: 23b, and *note tp_clear: 3d6e. are
     all inherited from the base type if they are all zero in the
     subtype.

 -- C Member: richcmpfunc PyTypeObject.tp_richcompare

     An optional pointer to the rich comparison function, whose
     signature is:

          PyObject *tp_richcompare(PyObject *self, PyObject *other, int op);

     The first parameter is guaranteed to be an instance of the type
     that is defined by *note PyTypeObject: 3f5.

     The function should return the result of the comparison (usually
     ‘Py_True’ or ‘Py_False’).  If the comparison is undefined, it must
     return ‘Py_NotImplemented’, if another error occurred it must
     return ‘NULL’ and set an exception condition.

     The following constants are defined to be used as the third
     argument for *note tp_richcompare: 3d7b. and for *note
     PyObject_RichCompare(): 3d7c.:

     Constant             Comparison
                          
     --------------------------------------
                          
     ‘Py_LT’              ‘<’
                          
                          
     ‘Py_LE’              ‘<=’
                          
                          
     ‘Py_EQ’              ‘==’
                          
                          
     ‘Py_NE’              ‘!=’
                          
                          
     ‘Py_GT’              ‘>’
                          
                          
     ‘Py_GE’              ‘>=’
                          

     The following macro is defined to ease writing rich comparison
     functions:

      -- C Macro: Py_RETURN_RICHCOMPARE (VAL_A, VAL_B, op)

          Return ‘Py_True’ or ‘Py_False’ from the function, depending on
          the result of a comparison.  VAL_A and VAL_B must be orderable
          by C comparison operators (for example, they may be C ints or
          floats).  The third argument specifies the requested
          operation, as for *note PyObject_RichCompare(): 3d7c.

          The return value’s reference count is properly incremented.

          On error, sets an exception and returns ‘NULL’ from the
          function.

          New in version 3.7.

     `Inheritance:'

     Group: ‘tp_hash’, ‘tp_richcompare’

     This field is inherited by subtypes together with *note tp_hash:
     3d81.: a subtype inherits *note tp_richcompare: 3d7b. and *note
     tp_hash: 3d81. when the subtype’s *note tp_richcompare: 3d7b. and
     *note tp_hash: 3d81. are both ‘NULL’.

     `Default:'

     ‘PyBaseObject_Type’ provides a ‘tp_richcompare’ implementation,
     which may be inherited.  However, if only ‘tp_hash’ is defined, not
     even the inherited function is used and instances of the type will
     not be able to participate in any comparisons.

 -- C Member: Py_ssize_t PyTypeObject.tp_weaklistoffset

     If the instances of this type are weakly referenceable, this field
     is greater than zero and contains the offset in the instance
     structure of the weak reference list head (ignoring the GC header,
     if present); this offset is used by ‘PyObject_ClearWeakRefs()’ and
     the ‘PyWeakref_*()’ functions.  The instance structure needs to
     include a field of type *note PyObject*: 5b5. which is initialized
     to ‘NULL’.

     Do not confuse this field with *note tp_weaklist: 3f90.; that is
     the list head for weak references to the type object itself.

     `Inheritance:'

     This field is inherited by subtypes, but see the rules listed
     below.  A subtype may override this offset; this means that the
     subtype uses a different weak reference list head than the base
     type.  Since the list head is always found via *note
     tp_weaklistoffset: 26b, this should not be a problem.

     When a type defined by a class statement has no *note __slots__:
     eef. declaration, and none of its base types are weakly
     referenceable, the type is made weakly referenceable by adding a
     weak reference list head slot to the instance layout and setting
     the *note tp_weaklistoffset: 26b. of that slot’s offset.

     When a type’s *note __slots__: eef. declaration contains a slot
     named ‘__weakref__’, that slot becomes the weak reference list head
     for instances of the type, and the slot’s offset is stored in the
     type’s *note tp_weaklistoffset: 26b.

     When a type’s *note __slots__: eef. declaration does not contain a
     slot named ‘__weakref__’, the type inherits its *note
     tp_weaklistoffset: 26b. from its base type.

 -- C Member: getiterfunc PyTypeObject.tp_iter

     An optional pointer to a function that returns an iterator for the
     object.  Its presence normally signals that the instances of this
     type are iterable (although sequences may be iterable without this
     function).

     This function has the same signature as *note PyObject_GetIter():
     3ed4.:

          PyObject *tp_iter(PyObject *self);

     `Inheritance:'

     This field is inherited by subtypes.

 -- C Member: iternextfunc PyTypeObject.tp_iternext

     An optional pointer to a function that returns the next item in an
     iterator.  The signature is:

          PyObject *tp_iternext(PyObject *self);

     When the iterator is exhausted, it must return ‘NULL’; a *note
     StopIteration: 582. exception may or may not be set.  When another
     error occurs, it must return ‘NULL’ too.  Its presence signals that
     the instances of this type are iterators.

     Iterator types should also define the *note tp_iter: ef2. function,
     and that function should return the iterator instance itself (not a
     new iterator instance).

     This function has the same signature as *note PyIter_Next(): 3f35.

     `Inheritance:'

     This field is inherited by subtypes.

 -- C Member: struct PyMethodDef* PyTypeObject.tp_methods

     An optional pointer to a static ‘NULL’-terminated array of *note
     PyMethodDef: edd. structures, declaring regular methods of this
     type.

     For each entry in the array, an entry is added to the type’s
     dictionary (see *note tp_dict: 3f8c. below) containing a method
     descriptor.

     `Inheritance:'

     This field is not inherited by subtypes (methods are inherited
     through a different mechanism).

 -- C Member: struct PyMemberDef* PyTypeObject.tp_members

     An optional pointer to a static ‘NULL’-terminated array of *note
     PyMemberDef: 52a. structures, declaring regular data members
     (fields or slots) of instances of this type.

     For each entry in the array, an entry is added to the type’s
     dictionary (see *note tp_dict: 3f8c. below) containing a member
     descriptor.

     `Inheritance:'

     This field is not inherited by subtypes (members are inherited
     through a different mechanism).

 -- C Member: struct PyGetSetDef* PyTypeObject.tp_getset

     An optional pointer to a static ‘NULL’-terminated array of *note
     PyGetSetDef: 52b. structures, declaring computed attributes of
     instances of this type.

     For each entry in the array, an entry is added to the type’s
     dictionary (see *note tp_dict: 3f8c. below) containing a getset
     descriptor.

     `Inheritance:'

     This field is not inherited by subtypes (computed attributes are
     inherited through a different mechanism).

 -- C Member: PyTypeObject* PyTypeObject.tp_base

     An optional pointer to a base type from which type properties are
     inherited.  At this level, only single inheritance is supported;
     multiple inheritance require dynamically creating a type object by
     calling the metatype.

          Note: 
          Slot initialization is subject to the rules of initializing
          globals.  C99 requires the initializers to be “address
          constants”.  Function designators like *note
          PyType_GenericNew(): 3d54, with implicit conversion to a
          pointer, are valid C99 address constants.

          However, the unary ‘&’ operator applied to a non-static
          variable like ‘PyBaseObject_Type()’ is not required to produce
          an address constant.  Compilers may support this (gcc does),
          MSVC does not.  Both compilers are strictly standard
          conforming in this particular behavior.

          Consequently, *note tp_base: 3d66. should be set in the
          extension module’s init function.

     `Inheritance:'

     This field is not inherited by subtypes (obviously).

     `Default:'

     This field defaults to ‘&PyBaseObject_Type’ (which to Python
     programmers is known as the type *note object: 3d2.).

 -- C Member: PyObject* PyTypeObject.tp_dict

     The type’s dictionary is stored here by *note PyType_Ready(): 3d59.

     This field should normally be initialized to ‘NULL’ before
     PyType_Ready is called; it may also be initialized to a dictionary
     containing initial attributes for the type.  Once *note
     PyType_Ready(): 3d59. has initialized the type, extra attributes
     for the type may be added to this dictionary only if they don’t
     correspond to overloaded operations (like *note __add__(): 1595.).

     `Inheritance:'

     This field is not inherited by subtypes (though the attributes
     defined in here are inherited through a different mechanism).

     `Default:'

     If this field is ‘NULL’, *note PyType_Ready(): 3d59. will assign a
     new dictionary to it.

          Warning: It is not safe to use *note PyDict_SetItem(): 3d3c.
          on or otherwise modify *note tp_dict: 3f8c. with the
          dictionary C-API.

 -- C Member: descrgetfunc PyTypeObject.tp_descr_get

     An optional pointer to a “descriptor get” function.

     The function signature is:

          PyObject * tp_descr_get(PyObject *self, PyObject *obj, PyObject *type);

     `Inheritance:'

     This field is inherited by subtypes.

 -- C Member: descrsetfunc PyTypeObject.tp_descr_set

     An optional pointer to a function for setting and deleting a
     descriptor’s value.

     The function signature is:

          int tp_descr_set(PyObject *self, PyObject *obj, PyObject *value);

     The `value' argument is set to ‘NULL’ to delete the value.

     `Inheritance:'

     This field is inherited by subtypes.

 -- C Member: Py_ssize_t PyTypeObject.tp_dictoffset

     If the instances of this type have a dictionary containing instance
     variables, this field is non-zero and contains the offset in the
     instances of the type of the instance variable dictionary; this
     offset is used by *note PyObject_GenericGetAttr(): 3ec2.

     Do not confuse this field with *note tp_dict: 3f8c.; that is the
     dictionary for attributes of the type object itself.

     If the value of this field is greater than zero, it specifies the
     offset from the start of the instance structure.  If the value is
     less than zero, it specifies the offset from the `end' of the
     instance structure.  A negative offset is more expensive to use,
     and should only be used when the instance structure contains a
     variable-length part.  This is used for example to add an instance
     variable dictionary to subtypes of *note str: 205. or *note tuple:
     1a2.  Note that the *note tp_basicsize: 26a. field should account
     for the dictionary added to the end in that case, even though the
     dictionary is not included in the basic object layout.  On a system
     with a pointer size of 4 bytes, *note tp_dictoffset: 3f93. should
     be set to ‘-4’ to indicate that the dictionary is at the very end
     of the structure.

     The real dictionary offset in an instance can be computed from a
     negative *note tp_dictoffset: 3f93. as follows:

          dictoffset = tp_basicsize + abs(ob_size)*tp_itemsize + tp_dictoffset
          if dictoffset is not aligned on sizeof(void*):
              round up to sizeof(void*)

     where *note tp_basicsize: 26a, *note tp_itemsize: 3d50. and *note
     tp_dictoffset: 3f93. are taken from the type object, and ‘ob_size’
     is taken from the instance.  The absolute value is taken because
     ints use the sign of ‘ob_size’ to store the sign of the number.
     (There’s never a need to do this calculation yourself; it is done
     for you by ‘_PyObject_GetDictPtr()’.)

     `Inheritance:'

     This field is inherited by subtypes, but see the rules listed
     below.  A subtype may override this offset; this means that the
     subtype instances store the dictionary at a difference offset than
     the base type.  Since the dictionary is always found via *note
     tp_dictoffset: 3f93, this should not be a problem.

     When a type defined by a class statement has no *note __slots__:
     eef. declaration, and none of its base types has an instance
     variable dictionary, a dictionary slot is added to the instance
     layout and the *note tp_dictoffset: 3f93. is set to that slot’s
     offset.

     When a type defined by a class statement has a *note __slots__:
     eef. declaration, the type inherits its *note tp_dictoffset: 3f93.
     from its base type.

     (Adding a slot named *note __dict__: 5f6. to the *note __slots__:
     eef. declaration does not have the expected effect, it just causes
     confusion.  Maybe this should be added as a feature just like
     ‘__weakref__’ though.)

     `Default:'

     This slot has no default.  For static types, if the field is ‘NULL’
     then no *note __dict__: 5f6. gets created for instances.

 -- C Member: initproc PyTypeObject.tp_init

     An optional pointer to an instance initialization function.

     This function corresponds to the *note __init__(): e23. method of
     classes.  Like *note __init__(): e23, it is possible to create an
     instance without calling *note __init__(): e23, and it is possible
     to reinitialize an instance by calling its *note __init__(): e23.
     method again.

     The function signature is:

          int tp_init(PyObject *self, PyObject *args, PyObject *kwds);

     The self argument is the instance to be initialized; the `args' and
     `kwds' arguments represent positional and keyword arguments of the
     call to *note __init__(): e23.

     The *note tp_init: 3d5a. function, if not ‘NULL’, is called when an
     instance is created normally by calling its type, after the type’s
     *note tp_new: 3d53. function has returned an instance of the type.
     If the *note tp_new: 3d53. function returns an instance of some
     other type that is not a subtype of the original type, no *note
     tp_init: 3d5a. function is called; if *note tp_new: 3d53. returns
     an instance of a subtype of the original type, the subtype’s *note
     tp_init: 3d5a. is called.

     Returns ‘0’ on success, ‘-1’ and sets an exception on error.

     `Inheritance:'

     This field is inherited by subtypes.

     `Default:'

     For static types this field does not have a default.

 -- C Member: allocfunc PyTypeObject.tp_alloc

     An optional pointer to an instance allocation function.

     The function signature is:

          PyObject *tp_alloc(PyTypeObject *self, Py_ssize_t nitems);

     `Inheritance:'

     This field is inherited by static subtypes, but not by dynamic
     subtypes (subtypes created by a class statement).

     `Default:'

     For dynamic subtypes, this field is always set to *note
     PyType_GenericAlloc(): 399, to force a standard heap allocation
     strategy.

     For static subtypes, ‘PyBaseObject_Type’ uses *note
     PyType_GenericAlloc(): 399.  That is the recommended value for all
     statically defined types.

 -- C Member: newfunc PyTypeObject.tp_new

     An optional pointer to an instance creation function.

     The function signature is:

          PyObject *tp_new(PyTypeObject *subtype, PyObject *args, PyObject *kwds);

     The `subtype' argument is the type of the object being created; the
     `args' and `kwds' arguments represent positional and keyword
     arguments of the call to the type.  Note that `subtype' doesn’t
     have to equal the type whose *note tp_new: 3d53. function is
     called; it may be a subtype of that type (but not an unrelated
     type).

     The *note tp_new: 3d53. function should call
     ‘subtype->tp_alloc(subtype, nitems)’ to allocate space for the
     object, and then do only as much further initialization as is
     absolutely necessary.  Initialization that can safely be ignored or
     repeated should be placed in the *note tp_init: 3d5a. handler.  A
     good rule of thumb is that for immutable types, all initialization
     should take place in *note tp_new: 3d53, while for mutable types,
     most initialization should be deferred to *note tp_init: 3d5a.

     `Inheritance:'

     This field is inherited by subtypes, except it is not inherited by
     static types whose *note tp_base: 3d66. is ‘NULL’ or
     ‘&PyBaseObject_Type’.

     `Default:'

     For static types this field has no default.  This means if the slot
     is defined as ‘NULL’, the type cannot be called to create new
     instances; presumably there is some other way to create instances,
     like a factory function.

 -- C Member: freefunc PyTypeObject.tp_free

     An optional pointer to an instance deallocation function.  Its
     signature is:

          void tp_free(void *self);

     An initializer that is compatible with this signature is *note
     PyObject_Free(): 5fe.

     `Inheritance:'

     This field is inherited by static subtypes, but not by dynamic
     subtypes (subtypes created by a class statement)

     `Default:'

     In dynamic subtypes, this field is set to a deallocator suitable to
     match *note PyType_GenericAlloc(): 399. and the value of the *note
     Py_TPFLAGS_HAVE_GC: 3d64. flag bit.

     For static subtypes, ‘PyBaseObject_Type’ uses PyObject_Del.

 -- C Member: inquiry PyTypeObject.tp_is_gc

     An optional pointer to a function called by the garbage collector.

     The garbage collector needs to know whether a particular object is
     collectible or not.  Normally, it is sufficient to look at the
     object’s type’s *note tp_flags: 1011. field, and check the *note
     Py_TPFLAGS_HAVE_GC: 3d64. flag bit.  But some types have a mixture
     of statically and dynamically allocated instances, and the
     statically allocated instances are not collectible.  Such types
     should define this function; it should return ‘1’ for a collectible
     instance, and ‘0’ for a non-collectible instance.  The signature
     is:

          int tp_is_gc(PyObject *self);

     (The only example of this are types themselves.  The metatype,
     *note PyType_Type: 3f79, defines this function to distinguish
     between statically and dynamically allocated types.)

     `Inheritance:'

     This field is inherited by subtypes.

     `Default:'

     This slot has no default.  If this field is ‘NULL’, *note
     Py_TPFLAGS_HAVE_GC: 3d64. is used as the functional equivalent.

 -- C Member: PyObject* PyTypeObject.tp_bases

     Tuple of base types.

     This is set for types created by a class statement.  It should be
     ‘NULL’ for statically defined types.

     `Inheritance:'

     This field is not inherited.

 -- C Member: PyObject* PyTypeObject.tp_mro

     Tuple containing the expanded set of base types, starting with the
     type itself and ending with *note object: 3d2, in Method Resolution
     Order.

     `Inheritance:'

     This field is not inherited; it is calculated fresh by *note
     PyType_Ready(): 3d59.

 -- C Member: PyObject* PyTypeObject.tp_cache

     Unused.  Internal use only.

     `Inheritance:'

     This field is not inherited.

 -- C Member: PyObject* PyTypeObject.tp_subclasses

     List of weak references to subclasses.  Internal use only.

     `Inheritance:'

     This field is not inherited.

 -- C Member: PyObject* PyTypeObject.tp_weaklist

     Weak reference list head, for weak references to this type object.
     Not inherited.  Internal use only.

     `Inheritance:'

     This field is not inherited.

 -- C Member: destructor PyTypeObject.tp_del

     This field is deprecated.  Use *note tp_finalize: 3f6. instead.

 -- C Member: unsigned int PyTypeObject.tp_version_tag

     Used to index into the method cache.  Internal use only.

     `Inheritance:'

     This field is not inherited.

 -- C Member: destructor PyTypeObject.tp_finalize

     An optional pointer to an instance finalization function.  Its
     signature is:

          void tp_finalize(PyObject *self);

     If *note tp_finalize: 3f6. is set, the interpreter calls it once
     when finalizing an instance.  It is called either from the garbage
     collector (if the instance is part of an isolated reference cycle)
     or just before the object is deallocated.  Either way, it is
     guaranteed to be called before attempting to break reference
     cycles, ensuring that it finds the object in a sane state.

     *note tp_finalize: 3f6. should not mutate the current exception
     status; therefore, a recommended way to write a non-trivial
     finalizer is:

          static void
          local_finalize(PyObject *self)
          {
              PyObject *error_type, *error_value, *error_traceback;

              /* Save the current exception, if any. */
              PyErr_Fetch(&error_type, &error_value, &error_traceback);

              /* ... */

              /* Restore the saved exception. */
              PyErr_Restore(error_type, error_value, error_traceback);
          }

     For this field to be taken into account (even through inheritance),
     you must also set the *note Py_TPFLAGS_HAVE_FINALIZE: 3f7. flags
     bit.

     `Inheritance:'

     This field is inherited by subtypes.

     New in version 3.4.

     See also
     ........

     “Safe object finalization” ( PEP 442(2))

 -- C Member: vectorcallfunc PyTypeObject.tp_vectorcall

     Vectorcall function to use for calls of this type object.  In other
     words, it is used to implement *note vectorcall: 2b8. for
     ‘type.__call__’.  If ‘tp_vectorcall’ is ‘NULL’, the default call
     implementation using *note __new__: 974. and *note __init__: e23.
     is used.

     `Inheritance:'

     This field is never inherited.

     New in version 3.9: (the field exists since 3.8 but it’s only used
     since 3.9)

Also, note that, in a garbage collected Python, *note tp_dealloc: 3d56.
may be called from any Python thread, not just the thread which created
the object (if the object becomes part of a refcount cycle, that cycle
might be collected by a garbage collection on any thread).  This is not
a problem for Python API calls, since the thread on which tp_dealloc is
called will own the Global Interpreter Lock (GIL). However, if the
object being destroyed in turn destroys objects from some other C or C++
library, care should be taken to ensure that destroying those objects on
the thread which called tp_dealloc will not violate any assumptions of
the library.

   ---------- Footnotes ----------

   (1) https://bugs.python.org/issue40217

   (2) https://www.python.org/dev/peps/pep-0442


File: python.info,  Node: Heap Types,  Prev: PyTypeObject Slots,  Up: Type Objects<3>

7.12.3.9 Heap Types
...................

Traditionally, types defined in C code are `static', that is, a static
*note PyTypeObject: 3f5. structure is defined directly in code and
initialized using *note PyType_Ready(): 3d59.

This results in types that are limited relative to types defined in
Python:

   * Static types are limited to one base, i.e.  they cannot use
     multiple inheritance.

   * Static type objects (but not necessarily their instances) are
     immutable.  It is not possible to add or modify the type object’s
     attributes from Python.

   * Static type objects are shared across *note sub-interpreters: 3e53,
     so they should not include any subinterpreter-specific state.

Also, since *note PyTypeObject: 3f5. is not part of the *note stable
ABI: 3dd6, any extension modules using static types must be compiled for
a specific Python minor version.

An alternative to static types is `heap-allocated types', or `heap
types' for short, which correspond closely to classes created by
Python’s ‘class’ statement.

This is done by filling a *note PyType_Spec: 3f81. structure and calling
*note PyType_FromSpecWithBases(): 102d.


File: python.info,  Node: Number Object Structures,  Next: Mapping Object Structures,  Prev: Type Objects<3>,  Up: Object Implementation Support

7.12.4 Number Object Structures
-------------------------------

 -- C Type: PyNumberMethods

     This structure holds pointers to the functions which an object uses
     to implement the number protocol.  Each function is used by the
     function of similar name documented in the *note Number Protocol:
     3eef. section.

     Here is the structure definition:

          typedef struct {
               binaryfunc nb_add;
               binaryfunc nb_subtract;
               binaryfunc nb_multiply;
               binaryfunc nb_remainder;
               binaryfunc nb_divmod;
               ternaryfunc nb_power;
               unaryfunc nb_negative;
               unaryfunc nb_positive;
               unaryfunc nb_absolute;
               inquiry nb_bool;
               unaryfunc nb_invert;
               binaryfunc nb_lshift;
               binaryfunc nb_rshift;
               binaryfunc nb_and;
               binaryfunc nb_xor;
               binaryfunc nb_or;
               unaryfunc nb_int;
               void *nb_reserved;
               unaryfunc nb_float;

               binaryfunc nb_inplace_add;
               binaryfunc nb_inplace_subtract;
               binaryfunc nb_inplace_multiply;
               binaryfunc nb_inplace_remainder;
               ternaryfunc nb_inplace_power;
               binaryfunc nb_inplace_lshift;
               binaryfunc nb_inplace_rshift;
               binaryfunc nb_inplace_and;
               binaryfunc nb_inplace_xor;
               binaryfunc nb_inplace_or;

               binaryfunc nb_floor_divide;
               binaryfunc nb_true_divide;
               binaryfunc nb_inplace_floor_divide;
               binaryfunc nb_inplace_true_divide;

               unaryfunc nb_index;

               binaryfunc nb_matrix_multiply;
               binaryfunc nb_inplace_matrix_multiply;
          } PyNumberMethods;

          Note: Binary and ternary functions must check the type of all
          their operands, and implement the necessary conversions (at
          least one of the operands is an instance of the defined type).
          If the operation is not defined for the given operands, binary
          and ternary functions must return ‘Py_NotImplemented’, if
          another error occurred they must return ‘NULL’ and set an
          exception.

          Note: The ‘nb_reserved’ field should always be ‘NULL’.  It was
          previously called ‘nb_long’, and was renamed in Python 3.0.1.

 -- C Member: binaryfunc PyNumberMethods.nb_add

 -- C Member: binaryfunc PyNumberMethods.nb_subtract

 -- C Member: binaryfunc PyNumberMethods.nb_multiply

 -- C Member: binaryfunc PyNumberMethods.nb_remainder

 -- C Member: binaryfunc PyNumberMethods.nb_divmod

 -- C Member: ternaryfunc PyNumberMethods.nb_power

 -- C Member: unaryfunc PyNumberMethods.nb_negative

 -- C Member: unaryfunc PyNumberMethods.nb_positive

 -- C Member: unaryfunc PyNumberMethods.nb_absolute

 -- C Member: inquiry PyNumberMethods.nb_bool

 -- C Member: unaryfunc PyNumberMethods.nb_invert

 -- C Member: binaryfunc PyNumberMethods.nb_lshift

 -- C Member: binaryfunc PyNumberMethods.nb_rshift

 -- C Member: binaryfunc PyNumberMethods.nb_and

 -- C Member: binaryfunc PyNumberMethods.nb_xor

 -- C Member: binaryfunc PyNumberMethods.nb_or

 -- C Member: unaryfunc PyNumberMethods.nb_int

 -- C Member: void *PyNumberMethods.nb_reserved

 -- C Member: unaryfunc PyNumberMethods.nb_float

 -- C Member: binaryfunc PyNumberMethods.nb_inplace_add

 -- C Member: binaryfunc PyNumberMethods.nb_inplace_subtract

 -- C Member: binaryfunc PyNumberMethods.nb_inplace_multiply

 -- C Member: binaryfunc PyNumberMethods.nb_inplace_remainder

 -- C Member: ternaryfunc PyNumberMethods.nb_inplace_power

 -- C Member: binaryfunc PyNumberMethods.nb_inplace_lshift

 -- C Member: binaryfunc PyNumberMethods.nb_inplace_rshift

 -- C Member: binaryfunc PyNumberMethods.nb_inplace_and

 -- C Member: binaryfunc PyNumberMethods.nb_inplace_xor

 -- C Member: binaryfunc PyNumberMethods.nb_inplace_or

 -- C Member: binaryfunc PyNumberMethods.nb_floor_divide

 -- C Member: binaryfunc PyNumberMethods.nb_true_divide

 -- C Member: binaryfunc PyNumberMethods.nb_inplace_floor_divide

 -- C Member: binaryfunc PyNumberMethods.nb_inplace_true_divide

 -- C Member: unaryfunc PyNumberMethods.nb_index

 -- C Member: binaryfunc PyNumberMethods.nb_matrix_multiply

 -- C Member: binaryfunc PyNumberMethods.nb_inplace_matrix_multiply


File: python.info,  Node: Mapping Object Structures,  Next: Sequence Object Structures,  Prev: Number Object Structures,  Up: Object Implementation Support

7.12.5 Mapping Object Structures
--------------------------------

 -- C Type: PyMappingMethods

     This structure holds pointers to the functions which an object uses
     to implement the mapping protocol.  It has three members:

 -- C Member: lenfunc PyMappingMethods.mp_length

     This function is used by *note PyMapping_Size(): 1186. and *note
     PyObject_Size(): 3ed0, and has the same signature.  This slot may
     be set to ‘NULL’ if the object has no defined length.

 -- C Member: binaryfunc PyMappingMethods.mp_subscript

     This function is used by *note PyObject_GetItem(): 3dc7. and *note
     PySequence_GetSlice(): 3f19, and has the same signature as
     ‘PyObject_GetItem()’.  This slot must be filled for the *note
     PyMapping_Check(): 3f2a. function to return ‘1’, it can be ‘NULL’
     otherwise.

 -- C Member: objobjargproc PyMappingMethods.mp_ass_subscript

     This function is used by *note PyObject_SetItem(): 3dc5, *note
     PyObject_DelItem(): 3ed2, ‘PyObject_SetSlice()’ and
     ‘PyObject_DelSlice()’.  It has the same signature as
     ‘PyObject_SetItem()’, but `v' can also be set to ‘NULL’ to delete
     an item.  If this slot is ‘NULL’, the object does not support item
     assignment and deletion.


File: python.info,  Node: Sequence Object Structures,  Next: Buffer Object Structures,  Prev: Mapping Object Structures,  Up: Object Implementation Support

7.12.6 Sequence Object Structures
---------------------------------

 -- C Type: PySequenceMethods

     This structure holds pointers to the functions which an object uses
     to implement the sequence protocol.

 -- C Member: lenfunc PySequenceMethods.sq_length

     This function is used by *note PySequence_Size(): 1182. and *note
     PyObject_Size(): 3ed0, and has the same signature.  It is also used
     for handling negative indices via the *note sq_item: 10bf. and the
     *note sq_ass_item: 42b1. slots.

 -- C Member: binaryfunc PySequenceMethods.sq_concat

     This function is used by *note PySequence_Concat(): 3f15. and has
     the same signature.  It is also used by the ‘+’ operator, after
     trying the numeric addition via the *note nb_add: 3f8a. slot.

 -- C Member: ssizeargfunc PySequenceMethods.sq_repeat

     This function is used by *note PySequence_Repeat(): 3f16. and has
     the same signature.  It is also used by the ‘*’ operator, after
     trying numeric multiplication via the *note nb_multiply: 4289.
     slot.

 -- C Member: ssizeargfunc PySequenceMethods.sq_item

     This function is used by *note PySequence_GetItem(): 1183. and has
     the same signature.  It is also used by *note PyObject_GetItem():
     3dc7, after trying the subscription via the *note mp_subscript:
     42ab. slot.  This slot must be filled for the *note
     PySequence_Check(): 3f13. function to return ‘1’, it can be ‘NULL’
     otherwise.

     Negative indexes are handled as follows: if the ‘sq_length’ slot is
     filled, it is called and the sequence length is used to compute a
     positive index which is passed to ‘sq_item’.  If ‘sq_length’ is
     ‘NULL’, the index is passed as is to the function.

 -- C Member: ssizeobjargproc PySequenceMethods.sq_ass_item

     This function is used by *note PySequence_SetItem(): 1184. and has
     the same signature.  It is also used by *note PyObject_SetItem():
     3dc5. and *note PyObject_DelItem(): 3ed2, after trying the item
     assignment and deletion via the *note mp_ass_subscript: 42ac. slot.
     This slot may be left to ‘NULL’ if the object does not support item
     assignment and deletion.

 -- C Member: objobjproc PySequenceMethods.sq_contains

     This function may be used by *note PySequence_Contains(): 3f1d. and
     has the same signature.  This slot may be left to ‘NULL’, in this
     case ‘PySequence_Contains()’ simply traverses the sequence until it
     finds a match.

 -- C Member: binaryfunc PySequenceMethods.sq_inplace_concat

     This function is used by *note PySequence_InPlaceConcat(): 3f17.
     and has the same signature.  It should modify its first operand,
     and return it.  This slot may be left to ‘NULL’, in this case
     ‘PySequence_InPlaceConcat()’ will fall back to *note
     PySequence_Concat(): 3f15.  It is also used by the augmented
     assignment ‘+=’, after trying numeric in-place addition via the
     *note nb_inplace_add: 4286. slot.

 -- C Member: ssizeargfunc PySequenceMethods.sq_inplace_repeat

     This function is used by *note PySequence_InPlaceRepeat(): 3f18.
     and has the same signature.  It should modify its first operand,
     and return it.  This slot may be left to ‘NULL’, in this case
     ‘PySequence_InPlaceRepeat()’ will fall back to *note
     PySequence_Repeat(): 3f16.  It is also used by the augmented
     assignment ‘*=’, after trying numeric in-place multiplication via
     the *note nb_inplace_multiply: 428a. slot.


File: python.info,  Node: Buffer Object Structures,  Next: Async Object Structures,  Prev: Sequence Object Structures,  Up: Object Implementation Support

7.12.7 Buffer Object Structures
-------------------------------

 -- C Type: PyBufferProcs

     This structure holds pointers to the functions required by the
     *note Buffer protocol: 171c.  The protocol defines how an exporter
     object can expose its internal data to consumer objects.

 -- C Member: getbufferproc PyBufferProcs.bf_getbuffer

     The signature of this function is:

          int (PyObject *exporter, Py_buffer *view, int flags);

     Handle a request to `exporter' to fill in `view' as specified by
     `flags'.  Except for point (3), an implementation of this function
     MUST take these steps:

       1. Check if the request can be met.  If not, raise
          ‘PyExc_BufferError’, set ‘view->obj’ to ‘NULL’ and return
          ‘-1’.

       2. Fill in the requested fields.

       3. Increment an internal counter for the number of exports.

       4. Set ‘view->obj’ to `exporter' and increment ‘view->obj’.

       5. Return ‘0’.

     If `exporter' is part of a chain or tree of buffer providers, two
     main schemes can be used:

        * Re-export: Each member of the tree acts as the exporting
          object and sets ‘view->obj’ to a new reference to itself.

        * Redirect: The buffer request is redirected to the root object
          of the tree.  Here, ‘view->obj’ will be a new reference to the
          root object.

     The individual fields of `view' are described in section *note
     Buffer structure: 3f39, the rules how an exporter must react to
     specific requests are in section *note Buffer request types: 3f4d.

     All memory pointed to in the *note Py_buffer: bee. structure
     belongs to the exporter and must remain valid until there are no
     consumers left.  *note format: 3f46, *note shape: 3f48, *note
     strides: 3f3d, *note suboffsets: 3f4a. and *note internal: 3f4c.
     are read-only for the consumer.

     *note PyBuffer_FillInfo(): 3f40. provides an easy way of exposing a
     simple bytes buffer while dealing correctly with all request types.

     *note PyObject_GetBuffer(): deb. is the interface for the consumer
     that wraps this function.

 -- C Member: releasebufferproc PyBufferProcs.bf_releasebuffer

     The signature of this function is:

          void (PyObject *exporter, Py_buffer *view);

     Handle a request to release the resources of the buffer.  If no
     resources need to be released, *note
     PyBufferProcs.bf_releasebuffer: 3e8a. may be ‘NULL’.  Otherwise, a
     standard implementation of this function will take these optional
     steps:

       1. Decrement an internal counter for the number of exports.

       2. If the counter is ‘0’, free all memory associated with `view'.

     The exporter MUST use the *note internal: 3f4c. field to keep track
     of buffer-specific resources.  This field is guaranteed to remain
     constant, while a consumer MAY pass a copy of the original buffer
     as the `view' argument.

     This function MUST NOT decrement ‘view->obj’, since that is done
     automatically in *note PyBuffer_Release(): e19. (this scheme is
     useful for breaking reference cycles).

     *note PyBuffer_Release(): e19. is the interface for the consumer
     that wraps this function.


File: python.info,  Node: Async Object Structures,  Next: Slot Type typedefs,  Prev: Buffer Object Structures,  Up: Object Implementation Support

7.12.8 Async Object Structures
------------------------------

New in version 3.5.

 -- C Type: PyAsyncMethods

     This structure holds pointers to the functions required to
     implement *note awaitable: 613. and *note asynchronous iterator:
     738. objects.

     Here is the structure definition:

          typedef struct {
              unaryfunc am_await;
              unaryfunc am_aiter;
              unaryfunc am_anext;
          } PyAsyncMethods;

 -- C Member: unaryfunc PyAsyncMethods.am_await

     The signature of this function is:

          PyObject *am_await(PyObject *self);

     The returned object must be an iterator, i.e.  *note
     PyIter_Check(): 1149. must return ‘1’ for it.

     This slot may be set to ‘NULL’ if an object is not an *note
     awaitable: 613.

 -- C Member: unaryfunc PyAsyncMethods.am_aiter

     The signature of this function is:

          PyObject *am_aiter(PyObject *self);

     Must return an *note awaitable: 613. object.  See *note
     __anext__(): 155f. for details.

     This slot may be set to ‘NULL’ if an object does not implement
     asynchronous iteration protocol.

 -- C Member: unaryfunc PyAsyncMethods.am_anext

     The signature of this function is:

          PyObject *am_anext(PyObject *self);

     Must return an *note awaitable: 613. object.  See *note
     __anext__(): 155f. for details.  This slot may be set to ‘NULL’.


File: python.info,  Node: Slot Type typedefs,  Next: Examples<36>,  Prev: Async Object Structures,  Up: Object Implementation Support

7.12.9 Slot Type typedefs
-------------------------

 -- C Type: PyObject *(*allocfunc) (PyTypeObject *cls,
          Py_ssize_t nitems)

     The purpose of this function is to separate memory allocation from
     memory initialization.  It should return a pointer to a block of
     memory of adequate length for the instance, suitably aligned, and
     initialized to zeros, but with ‘ob_refcnt’ set to ‘1’ and ‘ob_type’
     set to the type argument.  If the type’s *note tp_itemsize: 3d50.
     is non-zero, the object’s ‘ob_size’ field should be initialized to
     `nitems' and the length of the allocated memory block should be
     ‘tp_basicsize + nitems*tp_itemsize’, rounded up to a multiple of
     ‘sizeof(void*)’; otherwise, `nitems' is not used and the length of
     the block should be *note tp_basicsize: 26a.

     This function should not do any other instance initialization, not
     even to allocate additional memory; that should be done by *note
     tp_new: 3d53.

 -- C Type: void (*destructor) (PyObject *)

 -- C Type: void (*freefunc) (void *)

     See *note tp_free: 3d57.

 -- C Type: PyObject *(*newfunc) (PyObject *, PyObject *, PyObject *)

     See *note tp_new: 3d53.

 -- C Type: int (*initproc) (PyObject *, PyObject *, PyObject *)

     See *note tp_init: 3d5a.

 -- C Type: PyObject *(*reprfunc) (PyObject *)

     See *note tp_repr: 3d70.

 -- C Type: PyObject *(*getattrfunc) (PyObject *self, char *attr)

     Return the value of the named attribute for the object.

 -- C Type: int (*setattrfunc) (PyObject *self, char *attr,
          PyObject *value)

     Set the value of the named attribute for the object.  The value
     argument is set to ‘NULL’ to delete the attribute.

 -- C Type: PyObject *(*getattrofunc) (PyObject *self, PyObject *attr)

     Return the value of the named attribute for the object.

     See *note tp_getattro: 3d75.

 -- C Type: int (*setattrofunc) (PyObject *self, PyObject *attr,
          PyObject *value)

     Set the value of the named attribute for the object.  The value
     argument is set to ‘NULL’ to delete the attribute.

     See *note tp_setattro: 3d76.

 -- C Type: PyObject *(*descrgetfunc) (PyObject *, PyObject *,
          PyObject *)

     See ‘tp_descrget’.

 -- C Type: int (*descrsetfunc) (PyObject *, PyObject *, PyObject *)

     See ‘tp_descrset’.

 -- C Type: Py_hash_t (*hashfunc) (PyObject *)

     See *note tp_hash: 3d81.

 -- C Type: PyObject *(*richcmpfunc) (PyObject *, PyObject *, int)

     See *note tp_richcompare: 3d7b.

 -- C Type: PyObject *(*getiterfunc) (PyObject *)

     See *note tp_iter: ef2.

 -- C Type: PyObject *(*iternextfunc) (PyObject *)

     See *note tp_iternext: ef3.

 -- C Type: Py_ssize_t (*lenfunc) (PyObject *)

 -- C Type: int (*getbufferproc) (PyObject *, Py_buffer *, int)

 -- C Type: void (*releasebufferproc) (PyObject *, Py_buffer *)

 -- C Type: PyObject *(*unaryfunc) (PyObject *)

 -- C Type: PyObject *(*binaryfunc) (PyObject *, PyObject *)

 -- C Type: PyObject *(*ternaryfunc) (PyObject *, PyObject *,
          PyObject *)

 -- C Type: PyObject *(*ssizeargfunc) (PyObject *, Py_ssize_t)

 -- C Type: int (*ssizeobjargproc) (PyObject *, Py_ssize_t)

 -- C Type: int (*objobjproc) (PyObject *, PyObject *)

 -- C Type: int (*objobjargproc) (PyObject *, PyObject *, PyObject *)


File: python.info,  Node: Examples<36>,  Next: Supporting Cyclic Garbage Collection,  Prev: Slot Type typedefs,  Up: Object Implementation Support

7.12.10 Examples
----------------

The following are simple examples of Python type definitions.  They
include common usage you may encounter.  Some demonstrate tricky corner
cases.  For more examples, practical info, and a tutorial, see *note
Defining Extension Types; Tutorial: 3d4a. and *note Defining Extension
Types; Assorted Topics: 3d6a.

A basic static type:

     typedef struct {
         PyObject_HEAD
         const char *data;
     } MyObject;

     static PyTypeObject MyObject_Type = {
         PyVarObject_HEAD_INIT(NULL, 0)
         .tp_name = "mymod.MyObject",
         .tp_basicsize = sizeof(MyObject),
         .tp_doc = "My objects",
         .tp_new = myobj_new,
         .tp_dealloc = (destructor)myobj_dealloc,
         .tp_repr = (reprfunc)myobj_repr,
     };

You may also find older code (especially in the CPython code base) with
a more verbose initializer:

     static PyTypeObject MyObject_Type = {
         PyVarObject_HEAD_INIT(NULL, 0)
         "mymod.MyObject",               /* tp_name */
         sizeof(MyObject),               /* tp_basicsize */
         0,                              /* tp_itemsize */
         (destructor)myobj_dealloc,      /* tp_dealloc */
         0,                              /* tp_vectorcall_offset */
         0,                              /* tp_getattr */
         0,                              /* tp_setattr */
         0,                              /* tp_as_async */
         (reprfunc)myobj_repr,           /* tp_repr */
         0,                              /* tp_as_number */
         0,                              /* tp_as_sequence */
         0,                              /* tp_as_mapping */
         0,                              /* tp_hash */
         0,                              /* tp_call */
         0,                              /* tp_str */
         0,                              /* tp_getattro */
         0,                              /* tp_setattro */
         0,                              /* tp_as_buffer */
         0,                              /* tp_flags */
         "My objects",                   /* tp_doc */
         0,                              /* tp_traverse */
         0,                              /* tp_clear */
         0,                              /* tp_richcompare */
         0,                              /* tp_weaklistoffset */
         0,                              /* tp_iter */
         0,                              /* tp_iternext */
         0,                              /* tp_methods */
         0,                              /* tp_members */
         0,                              /* tp_getset */
         0,                              /* tp_base */
         0,                              /* tp_dict */
         0,                              /* tp_descr_get */
         0,                              /* tp_descr_set */
         0,                              /* tp_dictoffset */
         0,                              /* tp_init */
         0,                              /* tp_alloc */
         myobj_new,                      /* tp_new */
     };

A type that supports weakrefs, instance dicts, and hashing:

     typedef struct {
         PyObject_HEAD
         const char *data;
         PyObject *inst_dict;
         PyObject *weakreflist;
     } MyObject;

     static PyTypeObject MyObject_Type = {
         PyVarObject_HEAD_INIT(NULL, 0)
         .tp_name = "mymod.MyObject",
         .tp_basicsize = sizeof(MyObject),
         .tp_doc = "My objects",
         .tp_weaklistoffset = offsetof(MyObject, weakreflist),
         .tp_dictoffset = offsetof(MyObject, inst_dict),
         .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,
         .tp_new = myobj_new,
         .tp_traverse = (traverseproc)myobj_traverse,
         .tp_clear = (inquiry)myobj_clear,
         .tp_alloc = PyType_GenericNew,
         .tp_dealloc = (destructor)myobj_dealloc,
         .tp_repr = (reprfunc)myobj_repr,
         .tp_hash = (hashfunc)myobj_hash,
         .tp_richcompare = PyBaseObject_Type.tp_richcompare,
     };

A str subclass that cannot be subclassed and cannot be called to create
instances (e.g.  uses a separate factory func):

     typedef struct {
         PyUnicodeObject raw;
         char *extra;
     } MyStr;

     static PyTypeObject MyStr_Type = {
         PyVarObject_HEAD_INIT(NULL, 0)
         .tp_name = "mymod.MyStr",
         .tp_basicsize = sizeof(MyStr),
         .tp_base = NULL,  // set to &PyUnicode_Type in module init
         .tp_doc = "my custom str",
         .tp_flags = Py_TPFLAGS_DEFAULT,
         .tp_new = NULL,
         .tp_repr = (reprfunc)myobj_repr,
     };

The simplest static type (with fixed-length instances):

     typedef struct {
         PyObject_HEAD
     } MyObject;

     static PyTypeObject MyObject_Type = {
         PyVarObject_HEAD_INIT(NULL, 0)
         .tp_name = "mymod.MyObject",
     };

The simplest static type (with variable-length instances):

     typedef struct {
         PyObject_VAR_HEAD
         const char *data[1];
     } MyObject;

     static PyTypeObject MyObject_Type = {
         PyVarObject_HEAD_INIT(NULL, 0)
         .tp_name = "mymod.MyObject",
         .tp_basicsize = sizeof(MyObject) - sizeof(char *),
         .tp_itemsize = sizeof(char *),
     };


File: python.info,  Node: Supporting Cyclic Garbage Collection,  Prev: Examples<36>,  Up: Object Implementation Support

7.12.11 Supporting Cyclic Garbage Collection
--------------------------------------------

Python’s support for detecting and collecting garbage which involves
circular references requires support from object types which are
“containers” for other objects which may also be containers.  Types
which do not store references to other objects, or which only store
references to atomic types (such as numbers or strings), do not need to
provide any explicit support for garbage collection.

To create a container type, the *note tp_flags: 1011. field of the type
object must include the *note Py_TPFLAGS_HAVE_GC: 3d64. and provide an
implementation of the *note tp_traverse: 23b. handler.  If instances of
the type are mutable, a *note tp_clear: 3d6e. implementation must also
be provided.

 -- Data: Py_TPFLAGS_HAVE_GC

     Objects with a type with this flag set must conform with the rules
     documented here.  For convenience these objects will be referred to
     as container objects.

Constructors for container types must conform to two rules:

  1. The memory for the object must be allocated using *note
     PyObject_GC_New(): 3f3. or *note PyObject_GC_NewVar(): 3f4.

  2. Once all the fields which may contain references to other
     containers are initialized, it must call *note PyObject_GC_Track():
     f06.

Similarly, the deallocator for the object must conform to a similar pair
of rules:

  1. Before fields which refer to other containers are invalidated,
     *note PyObject_GC_UnTrack(): f07. must be called.

  2. The object’s memory must be deallocated using *note
     PyObject_GC_Del(): f05.

          Warning: If a type adds the Py_TPFLAGS_HAVE_GC, then it `must'
          implement at least a *note tp_traverse: 23b. handler or
          explicitly use one from its subclass or subclasses.

          When calling *note PyType_Ready(): 3d59. or some of the APIs
          that indirectly call it like *note PyType_FromSpecWithBases():
          102d. or *note PyType_FromSpec(): 23a. the interpreter will
          automatically populate the *note tp_flags: 1011, *note
          tp_traverse: 23b. and *note tp_clear: 3d6e. fields if the type
          inherits from a class that implements the garbage collector
          protocol and the child class does `not' include the *note
          Py_TPFLAGS_HAVE_GC: 3d64. flag.

 -- C Function: TYPE* PyObject_GC_New (TYPE, PyTypeObject *type)

     Analogous to *note PyObject_New(): 268. but for container objects
     with the *note Py_TPFLAGS_HAVE_GC: 3d64. flag set.

 -- C Function: TYPE* PyObject_GC_NewVar (TYPE, PyTypeObject *type,
          Py_ssize_t size)

     Analogous to *note PyObject_NewVar(): 269. but for container
     objects with the *note Py_TPFLAGS_HAVE_GC: 3d64. flag set.

 -- C Function: TYPE* PyObject_GC_Resize (TYPE, PyVarObject *op,
          Py_ssize_t newsize)

     Resize an object allocated by *note PyObject_NewVar(): 269.
     Returns the resized object or ‘NULL’ on failure.  `op' must not be
     tracked by the collector yet.

 -- C Function: void PyObject_GC_Track (PyObject *op)

     Adds the object `op' to the set of container objects tracked by the
     collector.  The collector can run at unexpected times so objects
     must be valid while being tracked.  This should be called once all
     the fields followed by the *note tp_traverse: 23b. handler become
     valid, usually near the end of the constructor.

 -- C Function: int PyObject_IS_GC (PyObject *obj)

     Returns non-zero if the object implements the garbage collector
     protocol, otherwise returns 0.

     The object cannot be tracked by the garbage collector if this
     function returns 0.

 -- C Function: int PyObject_GC_IsTracked (PyObject *op)

     Returns 1 if the object type of `op' implements the GC protocol and
     `op' is being currently tracked by the garbage collector and 0
     otherwise.

     This is analogous to the Python function *note gc.is_tracked():
     d6b.

     New in version 3.9.

 -- C Function: int PyObject_GC_IsFinalized (PyObject *op)

     Returns 1 if the object type of `op' implements the GC protocol and
     `op' has been already finalized by the garbage collector and 0
     otherwise.

     This is analogous to the Python function *note gc.is_finalized():
     1a9.

     New in version 3.9.

 -- C Function: void PyObject_GC_Del (void *op)

     Releases memory allocated to an object using *note
     PyObject_GC_New(): 3f3. or *note PyObject_GC_NewVar(): 3f4.

 -- C Function: void PyObject_GC_UnTrack (void *op)

     Remove the object `op' from the set of container objects tracked by
     the collector.  Note that *note PyObject_GC_Track(): f06. can be
     called again on this object to add it back to the set of tracked
     objects.  The deallocator (*note tp_dealloc: 3d56. handler) should
     call this for the object before any of the fields used by the *note
     tp_traverse: 23b. handler become invalid.

Changed in version 3.8: The ‘_PyObject_GC_TRACK()’ and
‘_PyObject_GC_UNTRACK()’ macros have been removed from the public C API.

The *note tp_traverse: 23b. handler accepts a function parameter of this
type:

 -- C Type: int (*visitproc) (PyObject *object, void *arg)

     Type of the visitor function passed to the *note tp_traverse: 23b.
     handler.  The function should be called with an object to traverse
     as `object' and the third parameter to the *note tp_traverse: 23b.
     handler as `arg'.  The Python core uses several visitor functions
     to implement cyclic garbage detection; it’s not expected that users
     will need to write their own visitor functions.

The *note tp_traverse: 23b. handler must have the following type:

 -- C Type: int (*traverseproc) (PyObject *self, visitproc visit,
          void *arg)

     Traversal function for a container object.  Implementations must
     call the `visit' function for each object directly contained by
     `self', with the parameters to `visit' being the contained object
     and the `arg' value passed to the handler.  The `visit' function
     must not be called with a ‘NULL’ object argument.  If `visit'
     returns a non-zero value that value should be returned immediately.

To simplify writing *note tp_traverse: 23b. handlers, a *note
Py_VISIT(): 3d62. macro is provided.  In order to use this macro, the
*note tp_traverse: 23b. implementation must name its arguments exactly
`visit' and `arg':

 -- C Function: void Py_VISIT (PyObject *o)

     If `o' is not ‘NULL’, call the `visit' callback, with arguments `o'
     and `arg'.  If `visit' returns a non-zero value, then return it.
     Using this macro, *note tp_traverse: 23b. handlers look like:

          static int
          my_traverse(Noddy *self, visitproc visit, void *arg)
          {
              Py_VISIT(self->foo);
              Py_VISIT(self->bar);
              return 0;
          }

The *note tp_clear: 3d6e. handler must be of the *note inquiry: 4270.
type, or ‘NULL’ if the object is immutable.

 -- C Type: int (*inquiry) (PyObject *self)

     Drop references that may have created reference cycles.  Immutable
     objects do not have to define this method since they can never
     directly create reference cycles.  Note that the object must still
     be valid after calling this method (don’t just call *note
     Py_DECREF(): 38f. on a reference).  The collector will call this
     method if it detects that this object is involved in a reference
     cycle.


File: python.info,  Node: API and ABI Versioning,  Prev: Object Implementation Support,  Up: Python/C API Reference Manual

7.13 API and ABI Versioning
===========================

‘PY_VERSION_HEX’ is the Python version number encoded in a single
integer.

For example if the ‘PY_VERSION_HEX’ is set to ‘0x030401a2’, the
underlying version information can be found by treating it as a 32 bit
number in the following manner:

     Bytes       Bits (big endian order)       Meaning
                                               
     -----------------------------------------------------------------------------------------------
                                               
     ‘1’         ‘1-8’                         ‘PY_MAJOR_VERSION’ (the ‘3’ in ‘3.4.1a2’)
                                               
                                               
     ‘2’         ‘9-16’                        ‘PY_MINOR_VERSION’ (the ‘4’ in ‘3.4.1a2’)
                                               
                                               
     ‘3’         ‘17-24’                       ‘PY_MICRO_VERSION’ (the ‘1’ in ‘3.4.1a2’)
                                               
                                               
     ‘4’         ‘25-28’                       ‘PY_RELEASE_LEVEL’ (‘0xA’ for alpha, ‘0xB’ for
                                               beta, ‘0xC’ for release candidate and ‘0xF’ for
                                               final), in this case it is alpha.
                                               
                                               
                 ‘29-32’                       ‘PY_RELEASE_SERIAL’ (the ‘2’ in ‘3.4.1a2’, zero
                                               for final releases)
                                               

Thus ‘3.4.1a2’ is hexversion ‘0x030401a2’.

All the given macros are defined in Include/patchlevel.h(1).

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Include/patchlevel.h


File: python.info,  Node: Distributing Python Modules,  Next: Installing Python Modules,  Prev: Python/C API Reference Manual,  Up: Top

8 Distributing Python Modules
*****************************


Email: <distutils-sig@python.org>

As a popular open source development project, Python has an active
supporting community of contributors and users that also make their
software available for other Python developers to use under open source
license terms.

This allows Python users to share and collaborate effectively,
benefiting from the solutions others have already created to common (and
sometimes even rare!)  problems, as well as potentially contributing
their own solutions to the common pool.

This guide covers the distribution part of the process.  For a guide to
installing other Python projects, refer to the *note installation guide:
8e2.

     Note: For corporate and other institutional users, be aware that
     many organisations have their own policies around using and
     contributing to open source software.  Please take such policies
     into account when making use of the distribution and installation
     tools provided with Python.

* Menu:

* Key terms::
* Open source licensing and collaboration::
* Installing the tools::
* Reading the Python Packaging User Guide::
* How do I…?::


File: python.info,  Node: Key terms,  Next: Open source licensing and collaboration,  Up: Distributing Python Modules

8.1 Key terms
=============

   * the Python Package Index(1) is a public repository of open source
     licensed packages made available for use by other Python users

   * the Python Packaging Authority(2) are the group of developers and
     documentation authors responsible for the maintenance and evolution
     of the standard packaging tools and the associated metadata and
     file format standards.  They maintain a variety of tools,
     documentation and issue trackers on both GitHub(3) and
     Bitbucket(4).

   * *note distutils: 38. is the original build and distribution system
     first added to the Python standard library in 1998.  While direct
     use of *note distutils: 38. is being phased out, it still laid the
     foundation for the current packaging and distribution
     infrastructure, and it not only remains part of the standard
     library, but its name lives on in other ways (such as the name of
     the mailing list used to coordinate Python packaging standards
     development).

   * setuptools(5) is a (largely) drop-in replacement for *note
     distutils: 38. first published in 2004.  Its most notable addition
     over the unmodified *note distutils: 38. tools was the ability to
     declare dependencies on other packages.  It is currently
     recommended as a more regularly updated alternative to *note
     distutils: 38. that offers consistent support for more recent
     packaging standards across a wide range of Python versions.

   * wheel(6) (in this context) is a project that adds the ‘bdist_wheel’
     command to *note distutils: 38./setuptools(7).  This produces a
     cross platform binary packaging format (called “wheels” or “wheel
     files” and defined in PEP 427(8)) that allows Python libraries,
     even those including binary extensions, to be installed on a system
     without needing to be built locally.

   ---------- Footnotes ----------

   (1) https://pypi.org

   (2) https://www.pypa.io/

   (3) https://github.com/pypa

   (4) https://bitbucket.org/pypa/

   (5) https://setuptools.readthedocs.io/en/latest/

   (6) https://wheel.readthedocs.io/

   (7) https://setuptools.readthedocs.io/en/latest/

   (8) https://www.python.org/dev/peps/pep-0427


File: python.info,  Node: Open source licensing and collaboration,  Next: Installing the tools,  Prev: Key terms,  Up: Distributing Python Modules

8.2 Open source licensing and collaboration
===========================================

In most parts of the world, software is automatically covered by
copyright.  This means that other developers require explicit permission
to copy, use, modify and redistribute the software.

Open source licensing is a way of explicitly granting such permission in
a relatively consistent way, allowing developers to share and
collaborate efficiently by making common solutions to various problems
freely available.  This leaves many developers free to spend more time
focusing on the problems that are relatively unique to their specific
situation.

The distribution tools provided with Python are designed to make it
reasonably straightforward for developers to make their own
contributions back to that common pool of software if they choose to do
so.

The same distribution tools can also be used to distribute software
within an organisation, regardless of whether that software is published
as open source software or not.


File: python.info,  Node: Installing the tools,  Next: Reading the Python Packaging User Guide,  Prev: Open source licensing and collaboration,  Up: Distributing Python Modules

8.3 Installing the tools
========================

The standard library does not include build tools that support modern
Python packaging standards, as the core development team has found that
it is important to have standard tools that work consistently, even on
older versions of Python.

The currently recommended build and distribution tools can be installed
by invoking the ‘pip’ module at the command line:

     python -m pip install setuptools wheel twine

     Note: For POSIX users (including macOS and Linux users), these
     instructions assume the use of a *note virtual environment: 1446.

     For Windows users, these instructions assume that the option to
     adjust the system PATH environment variable was selected when
     installing Python.

The Python Packaging User Guide includes more details on the currently
recommended tools(1).

   ---------- Footnotes ----------

   (1) 
https://packaging.python.org/guides/tool-recommendations/#packaging-tool-recommendations


File: python.info,  Node: Reading the Python Packaging User Guide,  Next: How do I…?,  Prev: Installing the tools,  Up: Distributing Python Modules

8.4 Reading the Python Packaging User Guide
===========================================

The Python Packaging User Guide covers the various key steps and
elements involved in creating and publishing a project:

   * Project structure(1)

   * Building and packaging the project(2)

   * Uploading the project to the Python Package Index(3)

   * The .pypirc file(4)

   ---------- Footnotes ----------

   (1) 
https://packaging.python.org/tutorials/packaging-projects/#packaging-python-projects

   (2) 
https://packaging.python.org/tutorials/packaging-projects/#creating-the-package-files

   (3) 
https://packaging.python.org/tutorials/packaging-projects/#uploading-the-distribution-archives

   (4) https://packaging.python.org/specifications/pypirc/


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8.5 How do I…?
==============

These are quick answers or links for some common tasks.

* Menu:

* … choose a name for my project?::
* … create and distribute binary extensions?::


File: python.info,  Node: … choose a name for my project?,  Next: … create and distribute binary extensions?,  Up: How do I…?

8.5.1 … choose a name for my project?
-------------------------------------

This isn’t an easy topic, but here are a few tips:

   * check the Python Package Index to see if the name is already in use

   * check popular hosting sites like GitHub, Bitbucket, etc to see if
     there is already a project with that name

   * check what comes up in a web search for the name you’re considering

   * avoid particularly common words, especially ones with multiple
     meanings, as they can make it difficult for users to find your
     software when searching for it


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8.5.2 … create and distribute binary extensions?
------------------------------------------------

This is actually quite a complex topic, with a variety of alternatives
available depending on exactly what you’re aiming to achieve.  See the
Python Packaging User Guide for more information and recommendations.

See also
........

Python Packaging User Guide: Binary Extensions(1)

   ---------- Footnotes ----------

   (1) https://packaging.python.org/guides/packaging-binary-extensions/


File: python.info,  Node: Installing Python Modules,  Next: Python HOWTOs,  Prev: Distributing Python Modules,  Up: Top

9 Installing Python Modules
***************************


Email: <distutils-sig@python.org>

As a popular open source development project, Python has an active
supporting community of contributors and users that also make their
software available for other Python developers to use under open source
license terms.

This allows Python users to share and collaborate effectively,
benefiting from the solutions others have already created to common (and
sometimes even rare!)  problems, as well as potentially contributing
their own solutions to the common pool.

This guide covers the installation part of the process.  For a guide to
creating and sharing your own Python projects, refer to the *note
distribution guide: 8e3.

     Note: For corporate and other institutional users, be aware that
     many organisations have their own policies around using and
     contributing to open source software.  Please take such policies
     into account when making use of the distribution and installation
     tools provided with Python.

* Menu:

* Key terms: Key terms<2>.
* Basic usage::
* How do I …?::
* Common installation issues::


File: python.info,  Node: Key terms<2>,  Next: Basic usage,  Up: Installing Python Modules

9.1 Key terms
=============

   * ‘pip’ is the preferred installer program.  Starting with Python
     3.4, it is included by default with the Python binary installers.

   * A `virtual environment' is a semi-isolated Python environment that
     allows packages to be installed for use by a particular
     application, rather than being installed system wide.

   * ‘venv’ is the standard tool for creating virtual environments, and
     has been part of Python since Python 3.3.  Starting with Python
     3.4, it defaults to installing ‘pip’ into all created virtual
     environments.

   * ‘virtualenv’ is a third party alternative (and predecessor) to
     ‘venv’.  It allows virtual environments to be used on versions of
     Python prior to 3.4, which either don’t provide ‘venv’ at all, or
     aren’t able to automatically install ‘pip’ into created
     environments.

   * The Python Package Index(1) is a public repository of open source
     licensed packages made available for use by other Python users.

   * the Python Packaging Authority(2) is the group of developers and
     documentation authors responsible for the maintenance and evolution
     of the standard packaging tools and the associated metadata and
     file format standards.  They maintain a variety of tools,
     documentation, and issue trackers on both GitHub(3) and
     Bitbucket(4).

   * ‘distutils’ is the original build and distribution system first
     added to the Python standard library in 1998.  While direct use of
     ‘distutils’ is being phased out, it still laid the foundation for
     the current packaging and distribution infrastructure, and it not
     only remains part of the standard library, but its name lives on in
     other ways (such as the name of the mailing list used to coordinate
     Python packaging standards development).

Changed in version 3.5: The use of ‘venv’ is now recommended for
creating virtual environments.

See also
........

Python Packaging User Guide: Creating and using virtual environments(5)

   ---------- Footnotes ----------

   (1) https://pypi.org

   (2) https://www.pypa.io/

   (3) https://github.com/pypa

   (4) https://bitbucket.org/pypa/

   (5) 
https://packaging.python.org/installing/#creating-virtual-environments


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9.2 Basic usage
===============

The standard packaging tools are all designed to be used from the
command line.

The following command will install the latest version of a module and
its dependencies from the Python Package Index:

     python -m pip install SomePackage

     Note: For POSIX users (including macOS and Linux users), the
     examples in this guide assume the use of a *note virtual
     environment: 1446.

     For Windows users, the examples in this guide assume that the
     option to adjust the system PATH environment variable was selected
     when installing Python.

It’s also possible to specify an exact or minimum version directly on
the command line.  When using comparator operators such as ‘>’, ‘<’ or
some other special character which get interpreted by shell, the package
name and the version should be enclosed within double quotes:

     python -m pip install SomePackage==1.0.4    # specific version
     python -m pip install "SomePackage>=1.0.4"  # minimum version

Normally, if a suitable module is already installed, attempting to
install it again will have no effect.  Upgrading existing modules must
be requested explicitly:

     python -m pip install --upgrade SomePackage

More information and resources regarding ‘pip’ and its capabilities can
be found in the Python Packaging User Guide(1).

Creation of virtual environments is done through the *note venv: 12e.
module.  Installing packages into an active virtual environment uses the
commands shown above.

See also
........

Python Packaging User Guide: Installing Python Distribution Packages(2)

   ---------- Footnotes ----------

   (1) https://packaging.python.org

   (2) https://packaging.python.org/installing/


File: python.info,  Node: How do I …?,  Next: Common installation issues,  Prev: Basic usage,  Up: Installing Python Modules

9.3 How do I …?
===============

These are quick answers or links for some common tasks.

* Menu:

* … install pip in versions of Python prior to Python 3.4?: … install pip in versions of Python prior to Python 3 4?.
* … install packages just for the current user?::
* … install scientific Python packages?::
* … work with multiple versions of Python installed in parallel?::


File: python.info,  Node: … install pip in versions of Python prior to Python 3 4?,  Next: … install packages just for the current user?,  Up: How do I …?

9.3.1 … install ‘pip’ in versions of Python prior to Python 3.4?
----------------------------------------------------------------

Python only started bundling ‘pip’ with Python 3.4.  For earlier
versions, ‘pip’ needs to be “bootstrapped” as described in the Python
Packaging User Guide.

See also
........

Python Packaging User Guide: Requirements for Installing Packages(1)

   ---------- Footnotes ----------

   (1) 
https://packaging.python.org/installing/#requirements-for-installing-packages


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9.3.2 … install packages just for the current user?
---------------------------------------------------

Passing the ‘--user’ option to ‘python -m pip install’ will install a
package just for the current user, rather than for all users of the
system.


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9.3.3 … install scientific Python packages?
-------------------------------------------

A number of scientific Python packages have complex binary dependencies,
and aren’t currently easy to install using ‘pip’ directly.  At this
point in time, it will often be easier for users to install these
packages by other means(1) rather than attempting to install them with
‘pip’.

See also
........

Python Packaging User Guide: Installing Scientific Packages(2)

   ---------- Footnotes ----------

   (1) https://packaging.python.org/science/

   (2) https://packaging.python.org/science/


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9.3.4 … work with multiple versions of Python installed in parallel?
--------------------------------------------------------------------

On Linux, macOS, and other POSIX systems, use the versioned Python
commands in combination with the ‘-m’ switch to run the appropriate copy
of ‘pip’:

     python2   -m pip install SomePackage  # default Python 2
     python2.7 -m pip install SomePackage  # specifically Python 2.7
     python3   -m pip install SomePackage  # default Python 3
     python3.4 -m pip install SomePackage  # specifically Python 3.4

Appropriately versioned ‘pip’ commands may also be available.

On Windows, use the ‘py’ Python launcher in combination with the ‘-m’
switch:

     py -2   -m pip install SomePackage  # default Python 2
     py -2.7 -m pip install SomePackage  # specifically Python 2.7
     py -3   -m pip install SomePackage  # default Python 3
     py -3.4 -m pip install SomePackage  # specifically Python 3.4


File: python.info,  Node: Common installation issues,  Prev: How do I …?,  Up: Installing Python Modules

9.4 Common installation issues
==============================

* Menu:

* Installing into the system Python on Linux::
* Pip not installed::
* Installing binary extensions::


File: python.info,  Node: Installing into the system Python on Linux,  Next: Pip not installed,  Up: Common installation issues

9.4.1 Installing into the system Python on Linux
------------------------------------------------

On Linux systems, a Python installation will typically be included as
part of the distribution.  Installing into this Python installation
requires root access to the system, and may interfere with the operation
of the system package manager and other components of the system if a
component is unexpectedly upgraded using ‘pip’.

On such systems, it is often better to use a virtual environment or a
per-user installation when installing packages with ‘pip’.


File: python.info,  Node: Pip not installed,  Next: Installing binary extensions,  Prev: Installing into the system Python on Linux,  Up: Common installation issues

9.4.2 Pip not installed
-----------------------

It is possible that ‘pip’ does not get installed by default.  One
potential fix is:

     python -m ensurepip --default-pip

There are also additional resources for installing pip.(1)

   ---------- Footnotes ----------

   (1) 
https://packaging.python.org/tutorials/installing-packages/#install-pip-setuptools-and-wheel


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9.4.3 Installing binary extensions
----------------------------------

Python has typically relied heavily on source based distribution, with
end users being expected to compile extension modules from source as
part of the installation process.

With the introduction of support for the binary ‘wheel’ format, and the
ability to publish wheels for at least Windows and macOS through the
Python Package Index, this problem is expected to diminish over time, as
users are more regularly able to install pre-built extensions rather
than needing to build them themselves.

Some of the solutions for installing scientific software(1) that are not
yet available as pre-built ‘wheel’ files may also help with obtaining
other binary extensions without needing to build them locally.

See also
........

Python Packaging User Guide: Binary Extensions(2)

   ---------- Footnotes ----------

   (1) https://packaging.python.org/science/

   (2) https://packaging.python.org/extensions/


File: python.info,  Node: Python HOWTOs,  Next: Python Frequently Asked Questions,  Prev: Installing Python Modules,  Up: Top

10 Python HOWTOs
****************

Python HOWTOs are documents that cover a single, specific topic, and
attempt to cover it fairly completely.  Modelled on the Linux
Documentation Project’s HOWTO collection, this collection is an effort
to foster documentation that’s more detailed than the Python Library
Reference.

Currently, the HOWTOs are:

* Menu:

* Porting Python 2 Code to Python 3::
* Porting Extension Modules to Python 3::
* Curses Programming with Python::
* Descriptor HowTo Guide::
* Functional Programming HOWTO::
* Logging HOWTO::
* Logging Cookbook::
* Regular Expression HOWTO::
* Socket Programming HOWTO::
* Sorting HOW TO::
* Unicode HOWTO::
* HOWTO Fetch Internet Resources Using The urllib Package::
* Argparse Tutorial::
* An introduction to the ipaddress module::
* Argument Clinic How-To::
* Instrumenting CPython with DTrace and SystemTap::


File: python.info,  Node: Porting Python 2 Code to Python 3,  Next: Porting Extension Modules to Python 3,  Up: Python HOWTOs

10.1 Porting Python 2 Code to Python 3
======================================


author: Brett Cannon

Abstract
........

With Python 3 being the future of Python while Python 2 is still in
active use, it is good to have your project available for both major
releases of Python.  This guide is meant to help you figure out how best
to support both Python 2 & 3 simultaneously.

If you are looking to port an extension module instead of pure Python
code, please see *note Porting Extension Modules to Python 3: d3f.

If you would like to read one core Python developer’s take on why Python
3 came into existence, you can read Nick Coghlan’s Python 3 Q & A(1) or
Brett Cannon’s Why Python 3 exists(2).

For help with porting, you can view the archived python-porting(3)
mailing list.

* Menu:

* The Short Explanation::
* Details::

   ---------- Footnotes ----------

   (1) 
https://ncoghlan-devs-python-notes.readthedocs.io/en/latest/python3/questions_and_answers.html

   (2) https://snarky.ca/why-python-3-exists

   (3) https://mail.python.org/pipermail/python-porting/


File: python.info,  Node: The Short Explanation,  Next: Details,  Up: Porting Python 2 Code to Python 3

10.1.1 The Short Explanation
----------------------------

To make your project be single-source Python 2/3 compatible, the basic
steps are:

  1. Only worry about supporting Python 2.7

  2. Make sure you have good test coverage (coverage.py(1) can help;
     ‘python -m pip install coverage’)

  3. Learn the differences between Python 2 & 3

  4. Use Futurize(2) (or Modernize(3)) to update your code (e.g.
     ‘python -m pip install future’)

  5. Use Pylint(4) to help make sure you don’t regress on your Python 3
     support (‘python -m pip install pylint’)

  6. Use caniusepython3(5) to find out which of your dependencies are
     blocking your use of Python 3 (‘python -m pip install
     caniusepython3’)

  7. Once your dependencies are no longer blocking you, use continuous
     integration to make sure you stay compatible with Python 2 & 3
     (tox(6) can help test against multiple versions of Python; ‘python
     -m pip install tox’)

  8. Consider using optional static type checking to make sure your type
     usage works in both Python 2 & 3 (e.g.  use mypy(7) to check your
     typing under both Python 2 & Python 3; ‘python -m pip install
     mypy’).

     Note: Note: Using ‘python -m pip install’ guarantees that the ‘pip’
     you invoke is the one installed for the Python currently in use,
     whether it be a system-wide ‘pip’ or one installed within a *note
     virtual environment: 1443.

   ---------- Footnotes ----------

   (1) https://pypi.org/project/coverage

   (2) http://python-future.org/automatic_conversion.html

   (3) https://python-modernize.readthedocs.io/

   (4) https://pypi.org/project/pylint

   (5) https://pypi.org/project/caniusepython3

   (6) https://pypi.org/project/tox

   (7) http://mypy-lang.org/


File: python.info,  Node: Details,  Prev: The Short Explanation,  Up: Porting Python 2 Code to Python 3

10.1.2 Details
--------------

A key point about supporting Python 2 & 3 simultaneously is that you can
start `today'!  Even if your dependencies are not supporting Python 3
yet that does not mean you can’t modernize your code `now' to support
Python 3.  Most changes required to support Python 3 lead to cleaner
code using newer practices even in Python 2 code.

Another key point is that modernizing your Python 2 code to also support
Python 3 is largely automated for you.  While you might have to make
some API decisions thanks to Python 3 clarifying text data versus binary
data, the lower-level work is now mostly done for you and thus can at
least benefit from the automated changes immediately.

Keep those key points in mind while you read on about the details of
porting your code to support Python 2 & 3 simultaneously.

* Menu:

* Drop support for Python 2.6 and older: Drop support for Python 2 6 and older.
* Make sure you specify the proper version support in your setup.py file: Make sure you specify the proper version support in your setup py file.
* Have good test coverage::
* Learn the differences between Python 2 & 3::
* Update your code::
* Prevent compatibility regressions::
* Check which dependencies block your transition::
* Update your setup.py file to denote Python 3 compatibility: Update your setup py file to denote Python 3 compatibility.
* Use continuous integration to stay compatible::
* Consider using optional static type checking::


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10.1.2.1 Drop support for Python 2.6 and older
..............................................

While you can make Python 2.5 work with Python 3, it is `much' easier if
you only have to work with Python 2.7.  If dropping Python 2.5 is not an
option then the six(1) project can help you support Python 2.5 & 3
simultaneously (‘python -m pip install six’).  Do realize, though, that
nearly all the projects listed in this HOWTO will not be available to
you.

If you are able to skip Python 2.5 and older, then the required changes
to your code should continue to look and feel like idiomatic Python
code.  At worst you will have to use a function instead of a method in
some instances or have to import a function instead of using a built-in
one, but otherwise the overall transformation should not feel foreign to
you.

But you should aim for only supporting Python 2.7.  Python 2.6 is no
longer freely supported and thus is not receiving bugfixes.  This means
`you' will have to work around any issues you come across with Python
2.6.  There are also some tools mentioned in this HOWTO which do not
support Python 2.6 (e.g., Pylint(2)), and this will become more
commonplace as time goes on.  It will simply be easier for you if you
only support the versions of Python that you have to support.

   ---------- Footnotes ----------

   (1) https://pypi.org/project/six

   (2) https://pypi.org/project/pylint


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10.1.2.2 Make sure you specify the proper version support in your ‘setup.py’ file
.................................................................................

In your ‘setup.py’ file you should have the proper trove classifier(1)
specifying what versions of Python you support.  As your project does
not support Python 3 yet you should at least have ‘Programming Language
:: Python :: 2 :: Only’ specified.  Ideally you should also specify each
major/minor version of Python that you do support, e.g.  ‘Programming
Language :: Python :: 2.7’.

   ---------- Footnotes ----------

   (1) https://pypi.org/classifiers


File: python.info,  Node: Have good test coverage,  Next: Learn the differences between Python 2 & 3,  Prev: Make sure you specify the proper version support in your setup py file,  Up: Details

10.1.2.3 Have good test coverage
................................

Once you have your code supporting the oldest version of Python 2 you
want it to, you will want to make sure your test suite has good
coverage.  A good rule of thumb is that if you want to be confident
enough in your test suite that any failures that appear after having
tools rewrite your code are actual bugs in the tools and not in your
code.  If you want a number to aim for, try to get over 80% coverage
(and don’t feel bad if you find it hard to get better than 90%
coverage).  If you don’t already have a tool to measure test coverage
then coverage.py(1) is recommended.

   ---------- Footnotes ----------

   (1) https://pypi.org/project/coverage


File: python.info,  Node: Learn the differences between Python 2 & 3,  Next: Update your code,  Prev: Have good test coverage,  Up: Details

10.1.2.4 Learn the differences between Python 2 & 3
...................................................

Once you have your code well-tested you are ready to begin porting your
code to Python 3!  But to fully understand how your code is going to
change and what you want to look out for while you code, you will want
to learn what changes Python 3 makes in terms of Python 2.  Typically
the two best ways of doing that is reading the *note “What’s New”: 153.
doc for each release of Python 3 and the Porting to Python 3(1) book
(which is free online).  There is also a handy cheat sheet(2) from the
Python-Future project.

   ---------- Footnotes ----------

   (1) http://python3porting.com/

   (2) http://python-future.org/compatible_idioms.html


File: python.info,  Node: Update your code,  Next: Prevent compatibility regressions,  Prev: Learn the differences between Python 2 & 3,  Up: Details

10.1.2.5 Update your code
.........................

Once you feel like you know what is different in Python 3 compared to
Python 2, it’s time to update your code!  You have a choice between two
tools in porting your code automatically: Futurize(1) and Modernize(2).
Which tool you choose will depend on how much like Python 3 you want
your code to be.  Futurize(3) does its best to make Python 3 idioms and
practices exist in Python 2, e.g.  backporting the ‘bytes’ type from
Python 3 so that you have semantic parity between the major versions of
Python.  Modernize(4), on the other hand, is more conservative and
targets a Python 2/3 subset of Python, directly relying on six(5) to
help provide compatibility.  As Python 3 is the future, it might be best
to consider Futurize to begin adjusting to any new practices that Python
3 introduces which you are not accustomed to yet.

Regardless of which tool you choose, they will update your code to run
under Python 3 while staying compatible with the version of Python 2 you
started with.  Depending on how conservative you want to be, you may
want to run the tool over your test suite first and visually inspect the
diff to make sure the transformation is accurate.  After you have
transformed your test suite and verified that all the tests still pass
as expected, then you can transform your application code knowing that
any tests which fail is a translation failure.

Unfortunately the tools can’t automate everything to make your code work
under Python 3 and so there are a handful of things you will need to
update manually to get full Python 3 support (which of these steps are
necessary vary between the tools).  Read the documentation for the tool
you choose to use to see what it fixes by default and what it can do
optionally to know what will (not) be fixed for you and what you may
have to fix on your own (e.g.  using ‘io.open()’ over the built-in
‘open()’ function is off by default in Modernize).  Luckily, though,
there are only a couple of things to watch out for which can be
considered large issues that may be hard to debug if not watched for.

* Menu:

* Division::
* Text versus binary data::
* Use feature detection instead of version detection::

   ---------- Footnotes ----------

   (1) http://python-future.org/automatic_conversion.html

   (2) https://python-modernize.readthedocs.io/

   (3) http://python-future.org/automatic_conversion.html

   (4) https://python-modernize.readthedocs.io/

   (5) https://pypi.org/project/six


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10.1.2.6 Division
.................

In Python 3, ‘5 / 2 == 2.5’ and not ‘2’; all division between ‘int’
values result in a ‘float’.  This change has actually been planned since
Python 2.2 which was released in 2002.  Since then users have been
encouraged to add ‘from __future__ import division’ to any and all files
which use the ‘/’ and ‘//’ operators or to be running the interpreter
with the ‘-Q’ flag.  If you have not been doing this then you will need
to go through your code and do two things:

  1. Add ‘from __future__ import division’ to your files

  2. Update any division operator as necessary to either use ‘//’ to use
     floor division or continue using ‘/’ and expect a float

The reason that ‘/’ isn’t simply translated to ‘//’ automatically is
that if an object defines a ‘__truediv__’ method but not ‘__floordiv__’
then your code would begin to fail (e.g.  a user-defined class that uses
‘/’ to signify some operation but not ‘//’ for the same thing or at
all).


File: python.info,  Node: Text versus binary data,  Next: Use feature detection instead of version detection,  Prev: Division,  Up: Update your code

10.1.2.7 Text versus binary data
................................

In Python 2 you could use the ‘str’ type for both text and binary data.
Unfortunately this confluence of two different concepts could lead to
brittle code which sometimes worked for either kind of data, sometimes
not.  It also could lead to confusing APIs if people didn’t explicitly
state that something that accepted ‘str’ accepted either text or binary
data instead of one specific type.  This complicated the situation
especially for anyone supporting multiple languages as APIs wouldn’t
bother explicitly supporting ‘unicode’ when they claimed text data
support.

To make the distinction between text and binary data clearer and more
pronounced, Python 3 did what most languages created in the age of the
internet have done and made text and binary data distinct types that
cannot blindly be mixed together (Python predates widespread access to
the internet).  For any code that deals only with text or only binary
data, this separation doesn’t pose an issue.  But for code that has to
deal with both, it does mean you might have to now care about when you
are using text compared to binary data, which is why this cannot be
entirely automated.

To start, you will need to decide which APIs take text and which take
binary (it is `highly' recommended you don’t design APIs that can take
both due to the difficulty of keeping the code working; as stated
earlier it is difficult to do well).  In Python 2 this means making sure
the APIs that take text can work with ‘unicode’ and those that work with
binary data work with the ‘bytes’ type from Python 3 (which is a subset
of ‘str’ in Python 2 and acts as an alias for ‘bytes’ type in Python 2).
Usually the biggest issue is realizing which methods exist on which
types in Python 2 & 3 simultaneously (for text that’s ‘unicode’ in
Python 2 and ‘str’ in Python 3, for binary that’s ‘str’/‘bytes’ in
Python 2 and ‘bytes’ in Python 3).  The following table lists the
`unique' methods of each data type across Python 2 & 3 (e.g., the
‘decode()’ method is usable on the equivalent binary data type in either
Python 2 or 3, but it can’t be used by the textual data type
consistently between Python 2 and 3 because ‘str’ in Python 3 doesn’t
have the method).  Do note that as of Python 3.5 the ‘__mod__’ method
was added to the bytes type.

`Text data'                  `Binary data'
                             
                             
                             decode
                             
                             
encode

format

isdecimal

isnumeric

Making the distinction easier to handle can be accomplished by encoding
and decoding between binary data and text at the edge of your code.
This means that when you receive text in binary data, you should
immediately decode it.  And if your code needs to send text as binary
data then encode it as late as possible.  This allows your code to work
with only text internally and thus eliminates having to keep track of
what type of data you are working with.

The next issue is making sure you know whether the string literals in
your code represent text or binary data.  You should add a ‘b’ prefix to
any literal that presents binary data.  For text you should add a ‘u’
prefix to the text literal.  (there is a *note __future__: 0. import to
force all unspecified literals to be Unicode, but usage has shown it
isn’t as effective as adding a ‘b’ or ‘u’ prefix to all literals
explicitly)

As part of this dichotomy you also need to be careful about opening
files.  Unless you have been working on Windows, there is a chance you
have not always bothered to add the ‘b’ mode when opening a binary file
(e.g., ‘rb’ for binary reading).  Under Python 3, binary files and text
files are clearly distinct and mutually incompatible; see the *note io:
a1. module for details.  Therefore, you `must' make a decision of
whether a file will be used for binary access (allowing binary data to
be read and/or written) or textual access (allowing text data to be read
and/or written).  You should also use *note io.open(): 74d. for opening
files instead of the built-in *note open(): 16f. function as the *note
io: a1. module is consistent from Python 2 to 3 while the built-in *note
open(): 16f. function is not (in Python 3 it’s actually *note io.open():
74d.).  Do not bother with the outdated practice of using *note
codecs.open(): 10c3. as that’s only necessary for keeping compatibility
with Python 2.5.

The constructors of both ‘str’ and ‘bytes’ have different semantics for
the same arguments between Python 2 & 3.  Passing an integer to ‘bytes’
in Python 2 will give you the string representation of the integer:
‘bytes(3) == '3'’.  But in Python 3, an integer argument to ‘bytes’ will
give you a bytes object as long as the integer specified, filled with
null bytes: ‘bytes(3) == b'\x00\x00\x00'’.  A similar worry is necessary
when passing a bytes object to ‘str’.  In Python 2 you just get the
bytes object back: ‘str(b'3') == b'3'’.  But in Python 3 you get the
string representation of the bytes object: ‘str(b'3') == "b'3'"’.

Finally, the indexing of binary data requires careful handling (slicing
does `not' require any special handling).  In Python 2, ‘b'123'[1] ==
b'2'’ while in Python 3 ‘b'123'[1] == 50’.  Because binary data is
simply a collection of binary numbers, Python 3 returns the integer
value for the byte you index on.  But in Python 2 because ‘bytes ==
str’, indexing returns a one-item slice of bytes.  The six(1) project
has a function named ‘six.indexbytes()’ which will return an integer
like in Python 3: ‘six.indexbytes(b'123', 1)’.

To summarize:

  1. Decide which of your APIs take text and which take binary data

  2. Make sure that your code that works with text also works with
     ‘unicode’ and code for binary data works with ‘bytes’ in Python 2
     (see the table above for what methods you cannot use for each type)

  3. Mark all binary literals with a ‘b’ prefix, textual literals with a
     ‘u’ prefix

  4. Decode binary data to text as soon as possible, encode text as
     binary data as late as possible

  5. Open files using *note io.open(): 74d. and make sure to specify the
     ‘b’ mode when appropriate

  6. Be careful when indexing into binary data

   ---------- Footnotes ----------

   (1) https://pypi.org/project/six


File: python.info,  Node: Use feature detection instead of version detection,  Prev: Text versus binary data,  Up: Update your code

10.1.2.8 Use feature detection instead of version detection
...........................................................

Inevitably you will have code that has to choose what to do based on
what version of Python is running.  The best way to do this is with
feature detection of whether the version of Python you’re running under
supports what you need.  If for some reason that doesn’t work then you
should make the version check be against Python 2 and not Python 3.  To
help explain this, let’s look at an example.

Let’s pretend that you need access to a feature of *note importlib: 9a.
that is available in Python’s standard library since Python 3.3 and
available for Python 2 through importlib2(1) on PyPI. You might be
tempted to write code to access e.g.  the *note importlib.abc: 9b.
module by doing the following:

     import sys

     if sys.version_info[0] == 3:
         from importlib import abc
     else:
         from importlib2 import abc

The problem with this code is what happens when Python 4 comes out?  It
would be better to treat Python 2 as the exceptional case instead of
Python 3 and assume that future Python versions will be more compatible
with Python 3 than Python 2:

     import sys

     if sys.version_info[0] > 2:
         from importlib import abc
     else:
         from importlib2 import abc

The best solution, though, is to do no version detection at all and
instead rely on feature detection.  That avoids any potential issues of
getting the version detection wrong and helps keep you
future-compatible:

     try:
         from importlib import abc
     except ImportError:
         from importlib2 import abc

   ---------- Footnotes ----------

   (1) https://pypi.org/project/importlib2


File: python.info,  Node: Prevent compatibility regressions,  Next: Check which dependencies block your transition,  Prev: Update your code,  Up: Details

10.1.2.9 Prevent compatibility regressions
..........................................

Once you have fully translated your code to be compatible with Python 3,
you will want to make sure your code doesn’t regress and stop working
under Python 3.  This is especially true if you have a dependency which
is blocking you from actually running under Python 3 at the moment.

To help with staying compatible, any new modules you create should have
at least the following block of code at the top of it:

     from __future__ import absolute_import
     from __future__ import division
     from __future__ import print_function

You can also run Python 2 with the ‘-3’ flag to be warned about various
compatibility issues your code triggers during execution.  If you turn
warnings into errors with ‘-Werror’ then you can make sure that you
don’t accidentally miss a warning.

You can also use the Pylint(1) project and its ‘--py3k’ flag to lint
your code to receive warnings when your code begins to deviate from
Python 3 compatibility.  This also prevents you from having to run
Modernize(2) or Futurize(3) over your code regularly to catch
compatibility regressions.  This does require you only support Python
2.7 and Python 3.4 or newer as that is Pylint’s minimum Python version
support.

   ---------- Footnotes ----------

   (1) https://pypi.org/project/pylint

   (2) https://python-modernize.readthedocs.io/

   (3) http://python-future.org/automatic_conversion.html


File: python.info,  Node: Check which dependencies block your transition,  Next: Update your setup py file to denote Python 3 compatibility,  Prev: Prevent compatibility regressions,  Up: Details

10.1.2.10 Check which dependencies block your transition
........................................................

`After' you have made your code compatible with Python 3 you should
begin to care about whether your dependencies have also been ported.
The caniusepython3(1) project was created to help you determine which
projects – directly or indirectly – are blocking you from supporting
Python 3.  There is both a command-line tool as well as a web interface
at ‘https://caniusepython3.com’.

The project also provides code which you can integrate into your test
suite so that you will have a failing test when you no longer have
dependencies blocking you from using Python 3.  This allows you to avoid
having to manually check your dependencies and to be notified quickly
when you can start running on Python 3.

   ---------- Footnotes ----------

   (1) https://pypi.org/project/caniusepython3


File: python.info,  Node: Update your setup py file to denote Python 3 compatibility,  Next: Use continuous integration to stay compatible,  Prev: Check which dependencies block your transition,  Up: Details

10.1.2.11 Update your ‘setup.py’ file to denote Python 3 compatibility
......................................................................

Once your code works under Python 3, you should update the classifiers
in your ‘setup.py’ to contain ‘Programming Language :: Python :: 3’ and
to not specify sole Python 2 support.  This will tell anyone using your
code that you support Python 2 `and' 3.  Ideally you will also want to
add classifiers for each major/minor version of Python you now support.


File: python.info,  Node: Use continuous integration to stay compatible,  Next: Consider using optional static type checking,  Prev: Update your setup py file to denote Python 3 compatibility,  Up: Details

10.1.2.12 Use continuous integration to stay compatible
.......................................................

Once you are able to fully run under Python 3 you will want to make sure
your code always works under both Python 2 & 3.  Probably the best tool
for running your tests under multiple Python interpreters is tox(1).
You can then integrate tox with your continuous integration system so
that you never accidentally break Python 2 or 3 support.

You may also want to use the ‘-bb’ flag with the Python 3 interpreter to
trigger an exception when you are comparing bytes to strings or bytes to
an int (the latter is available starting in Python 3.5).  By default
type-differing comparisons simply return ‘False’, but if you made a
mistake in your separation of text/binary data handling or indexing on
bytes you wouldn’t easily find the mistake.  This flag will raise an
exception when these kinds of comparisons occur, making the mistake much
easier to track down.

And that’s mostly it!  At this point your code base is compatible with
both Python 2 and 3 simultaneously.  Your testing will also be set up so
that you don’t accidentally break Python 2 or 3 compatibility regardless
of which version you typically run your tests under while developing.

   ---------- Footnotes ----------

   (1) https://pypi.org/project/tox


File: python.info,  Node: Consider using optional static type checking,  Prev: Use continuous integration to stay compatible,  Up: Details

10.1.2.13 Consider using optional static type checking
......................................................

Another way to help port your code is to use a static type checker like
mypy(1) or pytype(2) on your code.  These tools can be used to analyze
your code as if it’s being run under Python 2, then you can run the tool
a second time as if your code is running under Python 3.  By running a
static type checker twice like this you can discover if you’re e.g.
misusing binary data type in one version of Python compared to another.
If you add optional type hints to your code you can also explicitly
state whether your APIs use textual or binary data, helping to make sure
everything functions as expected in both versions of Python.

   ---------- Footnotes ----------

   (1) http://mypy-lang.org/

   (2) https://github.com/google/pytype


File: python.info,  Node: Porting Extension Modules to Python 3,  Next: Curses Programming with Python,  Prev: Porting Python 2 Code to Python 3,  Up: Python HOWTOs

10.2 Porting Extension Modules to Python 3
==========================================

We recommend the following resources for porting extension modules to
Python 3:

   * The Migrating C extensions(1) chapter from `Supporting Python 3: An
     in-depth guide', a book on moving from Python 2 to Python 3 in
     general, guides the reader through porting an extension module.

   * The Porting guide(2) from the `py3c' project provides opinionated
     suggestions with supporting code.

   * The Cython(3) and CFFI(4) libraries offer abstractions over
     Python’s C API. Extensions generally need to be re-written to use
     one of them, but the library then handles differences between
     various Python versions and implementations.

   ---------- Footnotes ----------

   (1) http://python3porting.com/cextensions.html

   (2) https://py3c.readthedocs.io/en/latest/guide.html

   (3) http://cython.org/

   (4) https://cffi.readthedocs.io/en/latest/


File: python.info,  Node: Curses Programming with Python,  Next: Descriptor HowTo Guide,  Prev: Porting Extension Modules to Python 3,  Up: Python HOWTOs

10.3 Curses Programming with Python
===================================


Author: A.M. Kuchling, Eric S. Raymond


Release: 2.04

Abstract
........

This document describes how to use the *note curses: 2b. extension
module to control text-mode displays.

* Menu:

* What is curses?::
* Starting and ending a curses application::
* Windows and Pads::
* Displaying Text::
* User Input::
* For More Information::


File: python.info,  Node: What is curses?,  Next: Starting and ending a curses application,  Up: Curses Programming with Python

10.3.1 What is curses?
----------------------

The curses library supplies a terminal-independent screen-painting and
keyboard-handling facility for text-based terminals; such terminals
include VT100s, the Linux console, and the simulated terminal provided
by various programs.  Display terminals support various control codes to
perform common operations such as moving the cursor, scrolling the
screen, and erasing areas.  Different terminals use widely differing
codes, and often have their own minor quirks.

In a world of graphical displays, one might ask “why bother”?  It’s true
that character-cell display terminals are an obsolete technology, but
there are niches in which being able to do fancy things with them are
still valuable.  One niche is on small-footprint or embedded Unixes that
don’t run an X server.  Another is tools such as OS installers and
kernel configurators that may have to run before any graphical support
is available.

The curses library provides fairly basic functionality, providing the
programmer with an abstraction of a display containing multiple
non-overlapping windows of text.  The contents of a window can be
changed in various ways—adding text, erasing it, changing its
appearance—and the curses library will figure out what control codes
need to be sent to the terminal to produce the right output.  curses
doesn’t provide many user-interface concepts such as buttons,
checkboxes, or dialogs; if you need such features, consider a user
interface library such as Urwid(1).

The curses library was originally written for BSD Unix; the later System
V versions of Unix from AT&T added many enhancements and new functions.
BSD curses is no longer maintained, having been replaced by ncurses,
which is an open-source implementation of the AT&T interface.  If you’re
using an open-source Unix such as Linux or FreeBSD, your system almost
certainly uses ncurses.  Since most current commercial Unix versions are
based on System V code, all the functions described here will probably
be available.  The older versions of curses carried by some proprietary
Unixes may not support everything, though.

The Windows version of Python doesn’t include the *note curses: 2b.
module.  A ported version called UniCurses(2) is available.  You could
also try the Console module(3) written by Fredrik Lundh, which doesn’t
use the same API as curses but provides cursor-addressable text output
and full support for mouse and keyboard input.

* Menu:

* The Python curses module::

   ---------- Footnotes ----------

   (1) https://pypi.org/project/urwid/

   (2) https://pypi.org/project/UniCurses

   (3) http://effbot.org/zone/console-index.htm


File: python.info,  Node: The Python curses module,  Up: What is curses?

10.3.1.1 The Python curses module
.................................

The Python module is a fairly simple wrapper over the C functions
provided by curses; if you’re already familiar with curses programming
in C, it’s really easy to transfer that knowledge to Python.  The
biggest difference is that the Python interface makes things simpler by
merging different C functions such as ‘addstr()’, ‘mvaddstr()’, and
‘mvwaddstr()’ into a single *note addstr(): 22c1. method.  You’ll see
this covered in more detail later.

This HOWTO is an introduction to writing text-mode programs with curses
and Python.  It doesn’t attempt to be a complete guide to the curses
API; for that, see the Python library guide’s section on ncurses, and
the C manual pages for ncurses.  It will, however, give you the basic
ideas.


File: python.info,  Node: Starting and ending a curses application,  Next: Windows and Pads,  Prev: What is curses?,  Up: Curses Programming with Python

10.3.2 Starting and ending a curses application
-----------------------------------------------

Before doing anything, curses must be initialized.  This is done by
calling the *note initscr(): 22c7. function, which will determine the
terminal type, send any required setup codes to the terminal, and create
various internal data structures.  If successful, ‘initscr()’ returns a
window object representing the entire screen; this is usually called
‘stdscr’ after the name of the corresponding C variable.

     import curses
     stdscr = curses.initscr()

Usually curses applications turn off automatic echoing of keys to the
screen, in order to be able to read keys and only display them under
certain circumstances.  This requires calling the *note noecho(): 22e6.
function.

     curses.noecho()

Applications will also commonly need to react to keys instantly, without
requiring the Enter key to be pressed; this is called cbreak mode, as
opposed to the usual buffered input mode.

     curses.cbreak()

Terminals usually return special keys, such as the cursor keys or
navigation keys such as Page Up and Home, as a multibyte escape
sequence.  While you could write your application to expect such
sequences and process them accordingly, curses can do it for you,
returning a special value such as ‘curses.KEY_LEFT’.  To get curses to
do the job, you’ll have to enable keypad mode.

     stdscr.keypad(True)

Terminating a curses application is much easier than starting one.
You’ll need to call:

     curses.nocbreak()
     stdscr.keypad(False)
     curses.echo()

to reverse the curses-friendly terminal settings.  Then call the *note
endwin(): 22c4. function to restore the terminal to its original
operating mode.

     curses.endwin()

A common problem when debugging a curses application is to get your
terminal messed up when the application dies without restoring the
terminal to its previous state.  In Python this commonly happens when
your code is buggy and raises an uncaught exception.  Keys are no longer
echoed to the screen when you type them, for example, which makes using
the shell difficult.

In Python you can avoid these complications and make debugging much
easier by importing the *note curses.wrapper(): 3c4. function and using
it like this:

     from curses import wrapper

     def main(stdscr):
         # Clear screen
         stdscr.clear()

         # This raises ZeroDivisionError when i == 10.
         for i in range(0, 11):
             v = i-10
             stdscr.addstr(i, 0, '10 divided by {} is {}'.format(v, 10/v))

         stdscr.refresh()
         stdscr.getkey()

     wrapper(main)

The *note wrapper(): 3c4. function takes a callable object and does the
initializations described above, also initializing colors if color
support is present.  ‘wrapper()’ then runs your provided callable.  Once
the callable returns, ‘wrapper()’ will restore the original state of the
terminal.  The callable is called inside a *note try: e37.…*note except:
c10. that catches exceptions, restores the state of the terminal, and
then re-raises the exception.  Therefore your terminal won’t be left in
a funny state on exception and you’ll be able to read the exception’s
message and traceback.


File: python.info,  Node: Windows and Pads,  Next: Displaying Text,  Prev: Starting and ending a curses application,  Up: Curses Programming with Python

10.3.3 Windows and Pads
-----------------------

Windows are the basic abstraction in curses.  A window object represents
a rectangular area of the screen, and supports methods to display text,
erase it, allow the user to input strings, and so forth.

The ‘stdscr’ object returned by the *note initscr(): 22c7. function is a
window object that covers the entire screen.  Many programs may need
only this single window, but you might wish to divide the screen into
smaller windows, in order to redraw or clear them separately.  The *note
newwin(): 22e4. function creates a new window of a given size, returning
the new window object.

     begin_x = 20; begin_y = 7
     height = 5; width = 40
     win = curses.newwin(height, width, begin_y, begin_x)

Note that the coordinate system used in curses is unusual.  Coordinates
are always passed in the order `y,x', and the top-left corner of a
window is coordinate (0,0).  This breaks the normal convention for
handling coordinates where the `x' coordinate comes first.  This is an
unfortunate difference from most other computer applications, but it’s
been part of curses since it was first written, and it’s too late to
change things now.

Your application can determine the size of the screen by using the
‘curses.LINES’ and ‘curses.COLS’ variables to obtain the `y' and `x'
sizes.  Legal coordinates will then extend from ‘(0,0)’ to
‘(curses.LINES - 1, curses.COLS - 1)’.

When you call a method to display or erase text, the effect doesn’t
immediately show up on the display.  Instead you must call the *note
refresh(): 22c2. method of window objects to update the screen.

This is because curses was originally written with slow 300-baud
terminal connections in mind; with these terminals, minimizing the time
required to redraw the screen was very important.  Instead curses
accumulates changes to the screen and displays them in the most
efficient manner when you call ‘refresh()’.  For example, if your
program displays some text in a window and then clears the window,
there’s no need to send the original text because they’re never visible.

In practice, explicitly telling curses to redraw a window doesn’t really
complicate programming with curses much.  Most programs go into a flurry
of activity, and then pause waiting for a keypress or some other action
on the part of the user.  All you have to do is to be sure that the
screen has been redrawn before pausing to wait for user input, by first
calling ‘stdscr.refresh()’ or the ‘refresh()’ method of some other
relevant window.

A pad is a special case of a window; it can be larger than the actual
display screen, and only a portion of the pad displayed at a time.
Creating a pad requires the pad’s height and width, while refreshing a
pad requires giving the coordinates of the on-screen area where a
subsection of the pad will be displayed.

     pad = curses.newpad(100, 100)
     # These loops fill the pad with letters; addch() is
     # explained in the next section
     for y in range(0, 99):
         for x in range(0, 99):
             pad.addch(y,x, ord('a') + (x*x+y*y) % 26)

     # Displays a section of the pad in the middle of the screen.
     # (0,0) : coordinate of upper-left corner of pad area to display.
     # (5,5) : coordinate of upper-left corner of window area to be filled
     #         with pad content.
     # (20, 75) : coordinate of lower-right corner of window area to be
     #          : filled with pad content.
     pad.refresh( 0,0, 5,5, 20,75)

The ‘refresh()’ call displays a section of the pad in the rectangle
extending from coordinate (5,5) to coordinate (20,75) on the screen; the
upper left corner of the displayed section is coordinate (0,0) on the
pad.  Beyond that difference, pads are exactly like ordinary windows and
support the same methods.

If you have multiple windows and pads on screen there is a more
efficient way to update the screen and prevent annoying screen flicker
as each part of the screen gets updated.  ‘refresh()’ actually does two
things:

  1. Calls the *note noutrefresh(): 22c0. method of each window to
     update an underlying data structure representing the desired state
     of the screen.

  2. Calls the function *note doupdate(): 22bf. function to change the
     physical screen to match the desired state recorded in the data
     structure.

Instead you can call ‘noutrefresh()’ on a number of windows to update
the data structure, and then call ‘doupdate()’ to update the screen.


File: python.info,  Node: Displaying Text,  Next: User Input,  Prev: Windows and Pads,  Up: Curses Programming with Python

10.3.4 Displaying Text
----------------------

From a C programmer’s point of view, curses may sometimes look like a
twisty maze of functions, all subtly different.  For example, ‘addstr()’
displays a string at the current cursor location in the ‘stdscr’ window,
while ‘mvaddstr()’ moves to a given y,x coordinate first before
displaying the string.  ‘waddstr()’ is just like ‘addstr()’, but allows
specifying a window to use instead of using ‘stdscr’ by default.
‘mvwaddstr()’ allows specifying both a window and a coordinate.

Fortunately the Python interface hides all these details.  ‘stdscr’ is a
window object like any other, and methods such as *note addstr(): 22c1.
accept multiple argument forms.  Usually there are four different forms.

Form                                  Description
                                      
------------------------------------------------------------------------------------------
                                      
`str' or `ch'                         Display the string `str' or character `ch' at the
                                      current position
                                      
                                      
`str' or `ch', `attr'                 Display the string `str' or character `ch', using
                                      attribute `attr' at the current position
                                      
                                      
`y', `x', `str' or `ch'               Move to position `y,x' within the window, and
                                      display `str' or `ch'
                                      
                                      
`y', `x', `str' or `ch', `attr'       Move to position `y,x' within the window, and
                                      display `str' or `ch', using attribute `attr'
                                      

Attributes allow displaying text in highlighted forms such as boldface,
underline, reverse code, or in color.  They’ll be explained in more
detail in the next subsection.

The *note addstr(): 22c1. method takes a Python string or bytestring as
the value to be displayed.  The contents of bytestrings are sent to the
terminal as-is.  Strings are encoded to bytes using the value of the
window’s ‘encoding’ attribute; this defaults to the default system
encoding as returned by *note locale.getpreferredencoding(): 4ac.

The *note addch(): 22ff. methods take a character, which can be either a
string of length 1, a bytestring of length 1, or an integer.

Constants are provided for extension characters; these constants are
integers greater than 255.  For example, ‘ACS_PLMINUS’ is a +/- symbol,
and ‘ACS_ULCORNER’ is the upper left corner of a box (handy for drawing
borders).  You can also use the appropriate Unicode character.

Windows remember where the cursor was left after the last operation, so
if you leave out the `y,x' coordinates, the string or character will be
displayed wherever the last operation left off.  You can also move the
cursor with the ‘move(y,x)’ method.  Because some terminals always
display a flashing cursor, you may want to ensure that the cursor is
positioned in some location where it won’t be distracting; it can be
confusing to have the cursor blinking at some apparently random
location.

If your application doesn’t need a blinking cursor at all, you can call
‘curs_set(False)’ to make it invisible.  For compatibility with older
curses versions, there’s a ‘leaveok(bool)’ function that’s a synonym for
*note curs_set(): 22b9.  When `bool' is true, the curses library will
attempt to suppress the flashing cursor, and you won’t need to worry
about leaving it in odd locations.

* Menu:

* Attributes and Color::


File: python.info,  Node: Attributes and Color,  Up: Displaying Text

10.3.4.1 Attributes and Color
.............................

Characters can be displayed in different ways.  Status lines in a
text-based application are commonly shown in reverse video, or a text
viewer may need to highlight certain words.  curses supports this by
allowing you to specify an attribute for each cell on the screen.

An attribute is an integer, each bit representing a different attribute.
You can try to display text with multiple attribute bits set, but curses
doesn’t guarantee that all the possible combinations are available, or
that they’re all visually distinct.  That depends on the ability of the
terminal being used, so it’s safest to stick to the most commonly
available attributes, listed here.

Attribute                  Description
                           
----------------------------------------------------------------------
                           
‘A_BLINK’                  Blinking text
                           
                           
‘A_BOLD’                   Extra bright or bold text
                           
                           
‘A_DIM’                    Half bright text
                           
                           
‘A_REVERSE’                Reverse-video text
                           
                           
‘A_STANDOUT’               The best highlighting mode available
                           
                           
‘A_UNDERLINE’              Underlined text
                           

So, to display a reverse-video status line on the top line of the
screen, you could code:

     stdscr.addstr(0, 0, "Current mode: Typing mode",
                   curses.A_REVERSE)
     stdscr.refresh()

The curses library also supports color on those terminals that provide
it.  The most common such terminal is probably the Linux console,
followed by color xterms.

To use color, you must call the *note start_color(): 22f2. function soon
after calling *note initscr(): 22c7, to initialize the default color set
(the *note curses.wrapper(): 3c4. function does this automatically).
Once that’s done, the *note has_colors(): 22cf. function returns TRUE if
the terminal in use can actually display color.  (Note: curses uses the
American spelling ‘color’, instead of the Canadian/British spelling
‘colour’.  If you’re used to the British spelling, you’ll have to resign
yourself to misspelling it for the sake of these functions.)

The curses library maintains a finite number of color pairs, containing
a foreground (or text) color and a background color.  You can get the
attribute value corresponding to a color pair with the *note
color_pair(): 22b7. function; this can be bitwise-OR’ed with other
attributes such as ‘A_REVERSE’, but again, such combinations are not
guaranteed to work on all terminals.

An example, which displays a line of text using color pair 1:

     stdscr.addstr("Pretty text", curses.color_pair(1))
     stdscr.refresh()

As I said before, a color pair consists of a foreground and background
color.  The ‘init_pair(n, f, b)’ function changes the definition of
color pair `n', to foreground color f and background color b.  Color
pair 0 is hard-wired to white on black, and cannot be changed.

Colors are numbered, and ‘start_color()’ initializes 8 basic colors when
it activates color mode.  They are: 0:black, 1:red, 2:green, 3:yellow,
4:blue, 5:magenta, 6:cyan, and 7:white.  The *note curses: 2b. module
defines named constants for each of these colors: ‘curses.COLOR_BLACK’,
‘curses.COLOR_RED’, and so forth.

Let’s put all this together.  To change color 1 to red text on a white
background, you would call:

     curses.init_pair(1, curses.COLOR_RED, curses.COLOR_WHITE)

When you change a color pair, any text already displayed using that
color pair will change to the new colors.  You can also display new text
in this color with:

     stdscr.addstr(0,0, "RED ALERT!", curses.color_pair(1))

Very fancy terminals can change the definitions of the actual colors to
a given RGB value.  This lets you change color 1, which is usually red,
to purple or blue or any other color you like.  Unfortunately, the Linux
console doesn’t support this, so I’m unable to try it out, and can’t
provide any examples.  You can check if your terminal can do this by
calling *note can_change_color(): 22b3, which returns ‘True’ if the
capability is there.  If you’re lucky enough to have such a talented
terminal, consult your system’s man pages for more information.


File: python.info,  Node: User Input,  Next: For More Information,  Prev: Displaying Text,  Up: Curses Programming with Python

10.3.5 User Input
-----------------

The C curses library offers only very simple input mechanisms.  Python’s
*note curses: 2b. module adds a basic text-input widget.  (Other
libraries such as Urwid(1) have more extensive collections of widgets.)

There are two methods for getting input from a window:

   * *note getch(): 22cb. refreshes the screen and then waits for the
     user to hit a key, displaying the key if *note echo(): 22c3. has
     been called earlier.  You can optionally specify a coordinate to
     which the cursor should be moved before pausing.

   * *note getkey(): 2318. does the same thing but converts the integer
     to a string.  Individual characters are returned as 1-character
     strings, and special keys such as function keys return longer
     strings containing a key name such as ‘KEY_UP’ or ‘^G’.

It’s possible to not wait for the user using the *note nodelay(): 232e.
window method.  After ‘nodelay(True)’, ‘getch()’ and ‘getkey()’ for the
window become non-blocking.  To signal that no input is ready, ‘getch()’
returns ‘curses.ERR’ (a value of -1) and ‘getkey()’ raises an exception.
There’s also a *note halfdelay(): 22d3. function, which can be used to
(in effect) set a timer on each ‘getch()’; if no input becomes available
within a specified delay (measured in tenths of a second), curses raises
an exception.

The ‘getch()’ method returns an integer; if it’s between 0 and 255, it
represents the ASCII code of the key pressed.  Values greater than 255
are special keys such as Page Up, Home, or the cursor keys.  You can
compare the value returned to constants such as ‘curses.KEY_PPAGE’,
‘curses.KEY_HOME’, or ‘curses.KEY_LEFT’.  The main loop of your program
may look something like this:

     while True:
         c = stdscr.getch()
         if c == ord('p'):
             PrintDocument()
         elif c == ord('q'):
             break  # Exit the while loop
         elif c == curses.KEY_HOME:
             x = y = 0

The *note curses.ascii: 2c. module supplies ASCII class membership
functions that take either integer or 1-character string arguments;
these may be useful in writing more readable tests for such loops.  It
also supplies conversion functions that take either integer or
1-character-string arguments and return the same type.  For example,
*note curses.ascii.ctrl(): 2362. returns the control character
corresponding to its argument.

There’s also a method to retrieve an entire string, *note getstr():
231b.  It isn’t used very often, because its functionality is quite
limited; the only editing keys available are the backspace key and the
Enter key, which terminates the string.  It can optionally be limited to
a fixed number of characters.

     curses.echo()            # Enable echoing of characters

     # Get a 15-character string, with the cursor on the top line
     s = stdscr.getstr(0,0, 15)

The *note curses.textpad: 2e. module supplies a text box that supports
an Emacs-like set of keybindings.  Various methods of the *note Textbox:
2348. class support editing with input validation and gathering the edit
results either with or without trailing spaces.  Here’s an example:

     import curses
     from curses.textpad import Textbox, rectangle

     def main(stdscr):
         stdscr.addstr(0, 0, "Enter IM message: (hit Ctrl-G to send)")

         editwin = curses.newwin(5,30, 2,1)
         rectangle(stdscr, 1,0, 1+5+1, 1+30+1)
         stdscr.refresh()

         box = Textbox(editwin)

         # Let the user edit until Ctrl-G is struck.
         box.edit()

         # Get resulting contents
         message = box.gather()

See the library documentation on *note curses.textpad: 2e. for more
details.

   ---------- Footnotes ----------

   (1) https://pypi.org/project/urwid/


File: python.info,  Node: For More Information,  Prev: User Input,  Up: Curses Programming with Python

10.3.6 For More Information
---------------------------

This HOWTO doesn’t cover some advanced topics, such as reading the
contents of the screen or capturing mouse events from an xterm instance,
but the Python library page for the *note curses: 2b. module is now
reasonably complete.  You should browse it next.

If you’re in doubt about the detailed behavior of the curses functions,
consult the manual pages for your curses implementation, whether it’s
ncurses or a proprietary Unix vendor’s.  The manual pages will document
any quirks, and provide complete lists of all the functions, attributes,
and ‘ACS_*’ characters available to you.

Because the curses API is so large, some functions aren’t supported in
the Python interface.  Often this isn’t because they’re difficult to
implement, but because no one has needed them yet.  Also, Python doesn’t
yet support the menu library associated with ncurses.  Patches adding
support for these would be welcome; see the Python Developer’s Guide(1)
to learn more about submitting patches to Python.

   * Writing Programs with NCURSES(2): a lengthy tutorial for C
     programmers.

   * The ncurses man page(3)

   * The ncurses FAQ(4)

   * "Use curses...  don’t swear"(5): video of a PyCon 2013 talk on
     controlling terminals using curses or Urwid.

   * "Console Applications with Urwid"(6): video of a PyCon CA 2012 talk
     demonstrating some applications written using Urwid.

   ---------- Footnotes ----------

   (1) https://devguide.python.org/

   (2) http://invisible-island.net/ncurses/ncurses-intro.html

   (3) https://linux.die.net/man/3/ncurses

   (4) http://invisible-island.net/ncurses/ncurses.faq.html

   (5) https://www.youtube.com/watch?v=eN1eZtjLEnU

   (6) http://www.pyvideo.org/video/1568/console-applications-with-urwid


File: python.info,  Node: Descriptor HowTo Guide,  Next: Functional Programming HOWTO,  Prev: Curses Programming with Python,  Up: Python HOWTOs

10.4 Descriptor HowTo Guide
===========================


Author: Raymond Hettinger


Contact: <python at rcn dot com>

*note Descriptors: 1579. let objects customize attribute lookup,
storage, and deletion.

This guide has four major sections:

  1. The “primer” gives a basic overview, moving gently from simple
     examples, adding one feature at a time.  Start here if you’re new
     to descriptors.

  2. The second section shows a complete, practical descriptor example.
     If you already know the basics, start there.

  3. The third section provides a more technical tutorial that goes into
     the detailed mechanics of how descriptors work.  Most people don’t
     need this level of detail.

  4. The last section has pure Python equivalents for built-in
     descriptors that are written in C. Read this if you’re curious
     about how functions turn into bound methods or about the
     implementation of common tools like *note classmethod(): 309, *note
     staticmethod(): 30a, *note property(): 308, and *note __slots__:
     391d.

* Menu:

* Primer::
* Complete Practical Example::
* Technical Tutorial::
* Pure Python Equivalents::


File: python.info,  Node: Primer,  Next: Complete Practical Example,  Up: Descriptor HowTo Guide

10.4.1 Primer
-------------

In this primer, we start with the most basic possible example and then
we’ll add new capabilities one by one.

* Menu:

* Simple example; A descriptor that returns a constant: Simple example A descriptor that returns a constant.
* Dynamic lookups::
* Managed attributes::
* Customized names::
* Closing thoughts::


File: python.info,  Node: Simple example A descriptor that returns a constant,  Next: Dynamic lookups,  Up: Primer

10.4.1.1 Simple example: A descriptor that returns a constant
.............................................................

The ‘Ten’ class is a descriptor that always returns the constant ‘10’
from its *note __get__(): 156e. method:

     class Ten:
         def __get__(self, obj, objtype=None):
             return 10

To use the descriptor, it must be stored as a class variable in another
class:

     class A:
         x = 5                       # Regular class attribute
         y = Ten()                   # Descriptor instance

An interactive session shows the difference between normal attribute
lookup and descriptor lookup:

     >>> a = A()                     # Make an instance of class A
     >>> a.x                         # Normal attribute lookup
     5
     >>> a.y                         # Descriptor lookup
     10

In the ‘a.x’ attribute lookup, the dot operator finds the key ‘x’ and
the value ‘5’ in the class dictionary.  In the ‘a.y’ lookup, the dot
operator finds a descriptor instance, recognized by its ‘__get__’
method, and calls that method which returns ‘10’.

Note that the value ‘10’ is not stored in either the class dictionary or
the instance dictionary.  Instead, the value ‘10’ is computed on demand.

This example shows how a simple descriptor works, but it isn’t very
useful.  For retrieving constants, normal attribute lookup would be
better.

In the next section, we’ll create something more useful, a dynamic
lookup.


File: python.info,  Node: Dynamic lookups,  Next: Managed attributes,  Prev: Simple example A descriptor that returns a constant,  Up: Primer

10.4.1.2 Dynamic lookups
........................

Interesting descriptors typically run computations instead of returning
constants:

     import os

     class DirectorySize:

         def __get__(self, obj, objtype=None):
             return len(os.listdir(obj.dirname))

     class Directory:

         size = DirectorySize()              # Descriptor instance

         def __init__(self, dirname):
             self.dirname = dirname          # Regular instance attribute

An interactive session shows that the lookup is dynamic — it computes
different, updated answers each time:

     >>> s = Directory('songs')
     >>> g = Directory('games')
     >>> s.size                              # The songs directory has twenty files
     20
     >>> g.size                              # The games directory has three files
     3
     >>> os.remove('games/chess')            # Delete a game
     >>> g.size                              # File count is automatically updated
     2

Besides showing how descriptors can run computations, this example also
reveals the purpose of the parameters to *note __get__(): 156e.  The
`self' parameter is `size', an instance of `DirectorySize'.  The `obj'
parameter is either `g' or `s', an instance of `Directory'.  It is the
`obj' parameter that lets the *note __get__(): 156e. method learn the
target directory.  The `objtype' parameter is the class `Directory'.


File: python.info,  Node: Managed attributes,  Next: Customized names,  Prev: Dynamic lookups,  Up: Primer

10.4.1.3 Managed attributes
...........................

A popular use for descriptors is managing access to instance data.  The
descriptor is assigned to a public attribute in the class dictionary
while the actual data is stored as a private attribute in the instance
dictionary.  The descriptor’s *note __get__(): 156e. and *note
__set__(): 1572. methods are triggered when the public attribute is
accessed.

In the following example, `age' is the public attribute and `_age' is
the private attribute.  When the public attribute is accessed, the
descriptor logs the lookup or update:

     import logging

     logging.basicConfig(level=logging.INFO)

     class LoggedAgeAccess:

         def __get__(self, obj, objtype=None):
             value = obj._age
             logging.info('Accessing %r giving %r', 'age', value)
             return value

         def __set__(self, obj, value):
             logging.info('Updating %r to %r', 'age', value)
             obj._age = value

     class Person:

         age = LoggedAgeAccess()             # Descriptor instance

         def __init__(self, name, age):
             self.name = name                # Regular instance attribute
             self.age = age                  # Calls __set__()

         def birthday(self):
             self.age += 1                   # Calls both __get__() and __set__()

An interactive session shows that all access to the managed attribute
`age' is logged, but that the regular attribute `name' is not logged:

     >>> mary = Person('Mary M', 30)         # The initial age update is logged
     INFO:root:Updating 'age' to 30
     >>> dave = Person('David D', 40)
     INFO:root:Updating 'age' to 40

     >>> vars(mary)                          # The actual data is in a private attribute
     {'name': 'Mary M', '_age': 30}
     >>> vars(dave)
     {'name': 'David D', '_age': 40}

     >>> mary.age                            # Access the data and log the lookup
     INFO:root:Accessing 'age' giving 30
     30
     >>> mary.birthday()                     # Updates are logged as well
     INFO:root:Accessing 'age' giving 30
     INFO:root:Updating 'age' to 31

     >>> dave.name                           # Regular attribute lookup isn't logged
     'David D'
     >>> dave.age                            # Only the managed attribute is logged
     INFO:root:Accessing 'age' giving 40
     40

One major issue with this example is that the private name `_age' is
hardwired in the `LoggedAgeAccess' class.  That means that each instance
can only have one logged attribute and that its name is unchangeable.
In the next example, we’ll fix that problem.


File: python.info,  Node: Customized names,  Next: Closing thoughts,  Prev: Managed attributes,  Up: Primer

10.4.1.4 Customized names
.........................

When a class uses descriptors, it can inform each descriptor about which
variable name was used.

In this example, the ‘Person’ class has two descriptor instances, `name'
and `age'.  When the ‘Person’ class is defined, it makes a callback to
*note __set_name__(): 5e3. in `LoggedAccess' so that the field names can
be recorded, giving each descriptor its own `public_name' and
`private_name':

     import logging

     logging.basicConfig(level=logging.INFO)

     class LoggedAccess:

         def __set_name__(self, owner, name):
             self.public_name = name
             self.private_name = '_' + name

         def __get__(self, obj, objtype=None):
             value = getattr(obj, self.private_name)
             logging.info('Accessing %r giving %r', self.public_name, value)
             return value

         def __set__(self, obj, value):
             logging.info('Updating %r to %r', self.public_name, value)
             setattr(obj, self.private_name, value)

     class Person:

         name = LoggedAccess()                # First descriptor instance
         age = LoggedAccess()                 # Second descriptor instance

         def __init__(self, name, age):
             self.name = name                 # Calls the first descriptor
             self.age = age                   # Calls the second descriptor

         def birthday(self):
             self.age += 1

An interactive session shows that the ‘Person’ class has called *note
__set_name__(): 5e3. so that the field names would be recorded.  Here we
call *note vars(): 116d. to look up the descriptor without triggering
it:

     >>> vars(vars(Person)['name'])
     {'public_name': 'name', 'private_name': '_name'}
     >>> vars(vars(Person)['age'])
     {'public_name': 'age', 'private_name': '_age'}

The new class now logs access to both `name' and `age':

     >>> pete = Person('Peter P', 10)
     INFO:root:Updating 'name' to 'Peter P'
     INFO:root:Updating 'age' to 10
     >>> kate = Person('Catherine C', 20)
     INFO:root:Updating 'name' to 'Catherine C'
     INFO:root:Updating 'age' to 20

The two `Person' instances contain only the private names:

     >>> vars(pete)
     {'_name': 'Peter P', '_age': 10}
     >>> vars(kate)
     {'_name': 'Catherine C', '_age': 20}


File: python.info,  Node: Closing thoughts,  Prev: Customized names,  Up: Primer

10.4.1.5 Closing thoughts
.........................

A *note descriptor: 1579. is what we call any object that defines *note
__get__(): 156e, *note __set__(): 1572, or *note __delete__(): 1573.

Optionally, descriptors can have a *note __set_name__(): 5e3. method.
This is only used in cases where a descriptor needs to know either the
class where it was created or the name of class variable it was assigned
to.  (This method, if present, is called even if the class is not a
descriptor.)

Descriptors get invoked by the dot “operator” during attribute lookup.
If a descriptor is accessed indirectly with
‘vars(some_class)[descriptor_name]’, the descriptor instance is returned
without invoking it.

Descriptors only work when used as class variables.  When put in
instances, they have no effect.

The main motivation for descriptors is to provide a hook allowing
objects stored in class variables to control what happens during
attribute lookup.

Traditionally, the calling class controls what happens during lookup.
Descriptors invert that relationship and allow the data being looked-up
to have a say in the matter.

Descriptors are used throughout the language.  It is how functions turn
into bound methods.  Common tools like *note classmethod(): 309, *note
staticmethod(): 30a, *note property(): 308, and *note
functools.cached_property(): 2f9. are all implemented as descriptors.


File: python.info,  Node: Complete Practical Example,  Next: Technical Tutorial,  Prev: Primer,  Up: Descriptor HowTo Guide

10.4.2 Complete Practical Example
---------------------------------

In this example, we create a practical and powerful tool for locating
notoriously hard to find data corruption bugs.

* Menu:

* Validator class::
* Custom validators::
* Practical application::


File: python.info,  Node: Validator class,  Next: Custom validators,  Up: Complete Practical Example

10.4.2.1 Validator class
........................

A validator is a descriptor for managed attribute access.  Prior to
storing any data, it verifies that the new value meets various type and
range restrictions.  If those restrictions aren’t met, it raises an
exception to prevent data corruption at its source.

This ‘Validator’ class is both an *note abstract base class: c05. and a
managed attribute descriptor:

     from abc import ABC, abstractmethod

     class Validator(ABC):

         def __set_name__(self, owner, name):
             self.private_name = '_' + name

         def __get__(self, obj, objtype=None):
             return getattr(obj, self.private_name)

         def __set__(self, obj, value):
             self.validate(value)
             setattr(obj, self.private_name, value)

         @abstractmethod
         def validate(self, value):
             pass

Custom validators need to inherit from ‘Validator’ and must supply a
‘validate()’ method to test various restrictions as needed.


File: python.info,  Node: Custom validators,  Next: Practical application,  Prev: Validator class,  Up: Complete Practical Example

10.4.2.2 Custom validators
..........................

Here are three practical data validation utilities:

  1. ‘OneOf’ verifies that a value is one of a restricted set of
     options.

  2. ‘Number’ verifies that a value is either an *note int: 204. or
     *note float: 1fd.  Optionally, it verifies that a value is between
     a given minimum or maximum.

  3. ‘String’ verifies that a value is a *note str: 205.  Optionally, it
     validates a given minimum or maximum length.  It can validate a
     user-defined predicate(1) as well.

     class OneOf(Validator):

         def __init__(self, *options):
             self.options = set(options)

         def validate(self, value):
             if value not in self.options:
                 raise ValueError(f'Expected {value!r} to be one of {self.options!r}')

     class Number(Validator):

         def __init__(self, minvalue=None, maxvalue=None):
             self.minvalue = minvalue
             self.maxvalue = maxvalue

         def validate(self, value):
             if not isinstance(value, (int, float)):
                 raise TypeError(f'Expected {value!r} to be an int or float')
             if self.minvalue is not None and value < self.minvalue:
                 raise ValueError(
                     f'Expected {value!r} to be at least {self.minvalue!r}'
                 )
             if self.maxvalue is not None and value > self.maxvalue:
                 raise ValueError(
                     f'Expected {value!r} to be no more than {self.maxvalue!r}'
                 )

     class String(Validator):

         def __init__(self, minsize=None, maxsize=None, predicate=None):
             self.minsize = minsize
             self.maxsize = maxsize
             self.predicate = predicate

         def validate(self, value):
             if not isinstance(value, str):
                 raise TypeError(f'Expected {value!r} to be an str')
             if self.minsize is not None and len(value) < self.minsize:
                 raise ValueError(
                     f'Expected {value!r} to be no smaller than {self.minsize!r}'
                 )
             if self.maxsize is not None and len(value) > self.maxsize:
                 raise ValueError(
                     f'Expected {value!r} to be no bigger than {self.maxsize!r}'
                 )
             if self.predicate is not None and not self.predicate(value):
                 raise ValueError(
                     f'Expected {self.predicate} to be true for {value!r}'
                 )

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Predicate_(mathematical_logic)


File: python.info,  Node: Practical application,  Prev: Custom validators,  Up: Complete Practical Example

10.4.2.3 Practical application
..............................

Here’s how the data validators can be used in a real class:

     class Component:

         name = String(minsize=3, maxsize=10, predicate=str.isupper)
         kind = OneOf('wood', 'metal', 'plastic')
         quantity = Number(minvalue=0)

         def __init__(self, name, kind, quantity):
             self.name = name
             self.kind = kind
             self.quantity = quantity

The descriptors prevent invalid instances from being created:

     >>> Component('Widget', 'metal', 5)      # Blocked: 'Widget' is not all uppercase
     Traceback (most recent call last):
         ...
     ValueError: Expected <method 'isupper' of 'str' objects> to be true for 'Widget'

     >>> Component('WIDGET', 'metle', 5)      # Blocked: 'metle' is misspelled
     Traceback (most recent call last):
         ...
     ValueError: Expected 'metle' to be one of {'metal', 'plastic', 'wood'}

     >>> Component('WIDGET', 'metal', -5)     # Blocked: -5 is negative
     Traceback (most recent call last):
         ...
     ValueError: Expected -5 to be at least 0
     >>> Component('WIDGET', 'metal', 'V')    # Blocked: 'V' isn't a number
     Traceback (most recent call last):
         ...
     TypeError: Expected 'V' to be an int or float

     >>> c = Component('WIDGET', 'metal', 5)  # Allowed:  The inputs are valid


File: python.info,  Node: Technical Tutorial,  Next: Pure Python Equivalents,  Prev: Complete Practical Example,  Up: Descriptor HowTo Guide

10.4.3 Technical Tutorial
-------------------------

What follows is a more technical tutorial for the mechanics and details
of how descriptors work.

* Menu:

* Abstract::
* Definition and introduction::
* Descriptor protocol::
* Overview of descriptor invocation::
* Invocation from an instance::
* Invocation from a class::
* Invocation from super::
* Summary of invocation logic::
* Automatic name notification::
* ORM example::


File: python.info,  Node: Abstract,  Next: Definition and introduction,  Up: Technical Tutorial

10.4.3.1 Abstract
.................

Defines descriptors, summarizes the protocol, and shows how descriptors
are called.  Provides an example showing how object relational mappings
work.

Learning about descriptors not only provides access to a larger toolset,
it creates a deeper understanding of how Python works.


File: python.info,  Node: Definition and introduction,  Next: Descriptor protocol,  Prev: Abstract,  Up: Technical Tutorial

10.4.3.2 Definition and introduction
....................................

In general, a descriptor is an attribute value that has one of the
methods in the descriptor protocol.  Those methods are *note __get__():
156e, *note __set__(): 1572, and *note __delete__(): 1573.  If any of
those methods are defined for an attribute, it is said to be a *note
descriptor: 1579.

The default behavior for attribute access is to get, set, or delete the
attribute from an object’s dictionary.  For instance, ‘a.x’ has a lookup
chain starting with ‘a.__dict__['x']’, then ‘type(a).__dict__['x']’, and
continuing through the method resolution order of ‘type(a)’.  If the
looked-up value is an object defining one of the descriptor methods,
then Python may override the default behavior and invoke the descriptor
method instead.  Where this occurs in the precedence chain depends on
which descriptor methods were defined.

Descriptors are a powerful, general purpose protocol.  They are the
mechanism behind properties, methods, static methods, class methods, and
*note super(): 5dd.  They are used throughout Python itself.
Descriptors simplify the underlying C code and offer a flexible set of
new tools for everyday Python programs.


File: python.info,  Node: Descriptor protocol,  Next: Overview of descriptor invocation,  Prev: Definition and introduction,  Up: Technical Tutorial

10.4.3.3 Descriptor protocol
............................

‘descr.__get__(self, obj, type=None) -> value’

‘descr.__set__(self, obj, value) -> None’

‘descr.__delete__(self, obj) -> None’

That is all there is to it.  Define any of these methods and an object
is considered a descriptor and can override default behavior upon being
looked up as an attribute.

If an object defines *note __set__(): 1572. or *note __delete__(): 1573,
it is considered a data descriptor.  Descriptors that only define *note
__get__(): 156e. are called non-data descriptors (they are often used
for methods but other uses are possible).

Data and non-data descriptors differ in how overrides are calculated
with respect to entries in an instance’s dictionary.  If an instance’s
dictionary has an entry with the same name as a data descriptor, the
data descriptor takes precedence.  If an instance’s dictionary has an
entry with the same name as a non-data descriptor, the dictionary entry
takes precedence.

To make a read-only data descriptor, define both *note __get__(): 156e.
and *note __set__(): 1572. with the *note __set__(): 1572. raising an
*note AttributeError: 4a2. when called.  Defining the *note __set__():
1572. method with an exception raising placeholder is enough to make it
a data descriptor.


File: python.info,  Node: Overview of descriptor invocation,  Next: Invocation from an instance,  Prev: Descriptor protocol,  Up: Technical Tutorial

10.4.3.4 Overview of descriptor invocation
..........................................

A descriptor can be called directly with ‘desc.__get__(obj)’ or
‘desc.__get__(None, cls)’.

But it is more common for a descriptor to be invoked automatically from
attribute access.

The expression ‘obj.x’ looks up the attribute ‘x’ in the chain of
namespaces for ‘obj’.  If the search finds a descriptor outside of the
instance ‘__dict__’, its *note __get__(): 156e. method is invoked
according to the precedence rules listed below.

The details of invocation depend on whether ‘obj’ is an object, class,
or instance of super.


File: python.info,  Node: Invocation from an instance,  Next: Invocation from a class,  Prev: Overview of descriptor invocation,  Up: Technical Tutorial

10.4.3.5 Invocation from an instance
....................................

Instance lookup scans through a chain of namespaces giving data
descriptors the highest priority, followed by instance variables, then
non-data descriptors, then class variables, and lastly *note
__getattr__(): 42a. if it is provided.

If a descriptor is found for ‘a.x’, then it is invoked with:
‘desc.__get__(a, type(a))’.

The logic for a dotted lookup is in *note object.__getattribute__():
54c.  Here is a pure Python equivalent:

     def object_getattribute(obj, name):
         "Emulate PyObject_GenericGetAttr() in Objects/object.c"
         null = object()
         objtype = type(obj)
         cls_var = getattr(objtype, name, null)
         descr_get = getattr(type(cls_var), '__get__', null)
         if descr_get is not null:
             if (hasattr(type(cls_var), '__set__')
                 or hasattr(type(cls_var), '__delete__')):
                 return descr_get(cls_var, obj, objtype)     # data descriptor
         if hasattr(obj, '__dict__') and name in vars(obj):
             return vars(obj)[name]                          # instance variable
         if descr_get is not null:
             return descr_get(cls_var, obj, objtype)         # non-data descriptor
         if cls_var is not null:
             return cls_var                                  # class variable
         raise AttributeError(name)

Interestingly, attribute lookup doesn’t call *note
object.__getattribute__(): 54c. directly.  Instead, both the dot
operator and the *note getattr(): 54b. function perform attribute lookup
by way of a helper function:

     def getattr_hook(obj, name):
         "Emulate slot_tp_getattr_hook() in Objects/typeobject.c"
         try:
             return obj.__getattribute__(name)
         except AttributeError:
             if not hasattr(type(obj), '__getattr__'):
                 raise
         return type(obj).__getattr__(obj, name)             # __getattr__

So if *note __getattr__(): 42a. exists, it is called whenever *note
__getattribute__(): 54c. raises *note AttributeError: 4a2. (either
directly or in one of the descriptor calls).

Also, if a user calls *note object.__getattribute__(): 54c. directly,
the *note __getattr__(): 42a. hook is bypassed entirely.


File: python.info,  Node: Invocation from a class,  Next: Invocation from super,  Prev: Invocation from an instance,  Up: Technical Tutorial

10.4.3.6 Invocation from a class
................................

The logic for a dotted lookup such as ‘A.x’ is in
‘type.__getattribute__()’.  The steps are similar to those for *note
object.__getattribute__(): 54c. but the instance dictionary lookup is
replaced by a search through the class’s *note method resolution order:
1739.

If a descriptor is found, it is invoked with ‘desc.__get__(None, A)’.

The full C implementation can be found in ‘type_getattro()’ and
‘_PyType_Lookup()’ in Objects/typeobject.c(1).

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Objects/typeobject.c


File: python.info,  Node: Invocation from super,  Next: Summary of invocation logic,  Prev: Invocation from a class,  Up: Technical Tutorial

10.4.3.7 Invocation from super
..............................

The logic for super’s dotted lookup is in the *note __getattribute__():
54c. method for object returned by *note super(): 5dd.

A dotted lookup such as ‘super(A, obj).m’ searches
‘obj.__class__.__mro__’ for the base class ‘B’ immediately following ‘A’
and then returns ‘B.__dict__['m'].__get__(obj, A)’.  If not a
descriptor, ‘m’ is returned unchanged.

The full C implementation can be found in ‘super_getattro()’ in
Objects/typeobject.c(1).  A pure Python equivalent can be found in
Guido’s Tutorial(2).

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Objects/typeobject.c

   (2) 
https://www.python.org/download/releases/2.2.3/descrintro/#cooperation


File: python.info,  Node: Summary of invocation logic,  Next: Automatic name notification,  Prev: Invocation from super,  Up: Technical Tutorial

10.4.3.8 Summary of invocation logic
....................................

The mechanism for descriptors is embedded in the *note
__getattribute__(): 54c. methods for *note object: 3d2, *note type: 6ff,
and *note super(): 5dd.

The important points to remember are:

   * Descriptors are invoked by the *note __getattribute__(): 54c.
     method.

   * Classes inherit this machinery from *note object: 3d2, *note type:
     6ff, or *note super(): 5dd.

   * Overriding *note __getattribute__(): 54c. prevents automatic
     descriptor calls because all the descriptor logic is in that
     method.

   * *note object.__getattribute__(): 54c. and ‘type.__getattribute__()’
     make different calls to *note __get__(): 156e.  The first includes
     the instance and may include the class.  The second puts in ‘None’
     for the instance and always includes the class.

   * Data descriptors always override instance dictionaries.

   * Non-data descriptors may be overridden by instance dictionaries.


File: python.info,  Node: Automatic name notification,  Next: ORM example,  Prev: Summary of invocation logic,  Up: Technical Tutorial

10.4.3.9 Automatic name notification
....................................

Sometimes it is desirable for a descriptor to know what class variable
name it was assigned to.  When a new class is created, the *note type:
6ff. metaclass scans the dictionary of the new class.  If any of the
entries are descriptors and if they define *note __set_name__(): 5e3,
that method is called with two arguments.  The `owner' is the class
where the descriptor is used, and the `name' is the class variable the
descriptor was assigned to.

The implementation details are in ‘type_new()’ and ‘set_names()’ in
Objects/typeobject.c(1).

Since the update logic is in ‘type.__new__()’, notifications only take
place at the time of class creation.  If descriptors are added to the
class afterwards, *note __set_name__(): 5e3. will need to be called
manually.

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Objects/typeobject.c


File: python.info,  Node: ORM example,  Prev: Automatic name notification,  Up: Technical Tutorial

10.4.3.10 ORM example
.....................

The following code is simplified skeleton showing how data descriptors
could be used to implement an object relational mapping(1).

The essential idea is that the data is stored in an external database.
The Python instances only hold keys to the database’s tables.
Descriptors take care of lookups or updates:

     class Field:

         def __set_name__(self, owner, name):
             self.fetch = f'SELECT {name} FROM {owner.table} WHERE {owner.key}=?;'
             self.store = f'UPDATE {owner.table} SET {name}=? WHERE {owner.key}=?;'

         def __get__(self, obj, objtype=None):
             return conn.execute(self.fetch, [obj.key]).fetchone()[0]

         def __set__(self, obj, value):
             conn.execute(self.store, [value, obj.key])
             conn.commit()

We can use the ‘Field’ class to define models(2) that describe the
schema for each table in a database:

     class Movie:
         table = 'Movies'                    # Table name
         key = 'title'                       # Primary key
         director = Field()
         year = Field()

         def __init__(self, key):
             self.key = key

     class Song:
         table = 'Music'
         key = 'title'
         artist = Field()
         year = Field()
         genre = Field()

         def __init__(self, key):
             self.key = key

To use the models, first connect to the database:

     >>> import sqlite3
     >>> conn = sqlite3.connect('entertainment.db')

An interactive session shows how data is retrieved from the database and
how it can be updated:

     >>> Movie('Star Wars').director
     'George Lucas'
     >>> jaws = Movie('Jaws')
     >>> f'Released in {jaws.year} by {jaws.director}'
     'Released in 1975 by Steven Spielberg'

     >>> Song('Country Roads').artist
     'John Denver'

     >>> Movie('Star Wars').director = 'J.J. Abrams'
     >>> Movie('Star Wars').director
     'J.J. Abrams'

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Object%E2%80%93relational_mapping

   (2) https://en.wikipedia.org/wiki/Database_model


File: python.info,  Node: Pure Python Equivalents,  Prev: Technical Tutorial,  Up: Descriptor HowTo Guide

10.4.4 Pure Python Equivalents
------------------------------

The descriptor protocol is simple and offers exciting possibilities.
Several use cases are so common that they have been prepackaged into
built-in tools.  Properties, bound methods, static methods, class
methods, and __slots__ are all based on the descriptor protocol.

* Menu:

* Properties::
* Functions and methods::
* Kinds of methods::
* Static methods::
* Class methods::
* Member objects and __slots__::


File: python.info,  Node: Properties,  Next: Functions and methods,  Up: Pure Python Equivalents

10.4.4.1 Properties
...................

Calling *note property(): 308. is a succinct way of building a data
descriptor that triggers a function call upon access to an attribute.
Its signature is:

     property(fget=None, fset=None, fdel=None, doc=None) -> property

The documentation shows a typical use to define a managed attribute ‘x’:

     class C:
         def getx(self): return self.__x
         def setx(self, value): self.__x = value
         def delx(self): del self.__x
         x = property(getx, setx, delx, "I'm the 'x' property.")

To see how *note property(): 308. is implemented in terms of the
descriptor protocol, here is a pure Python equivalent:

     class Property:
         "Emulate PyProperty_Type() in Objects/descrobject.c"

         def __init__(self, fget=None, fset=None, fdel=None, doc=None):
             self.fget = fget
             self.fset = fset
             self.fdel = fdel
             if doc is None and fget is not None:
                 doc = fget.__doc__
             self.__doc__ = doc

         def __get__(self, obj, objtype=None):
             if obj is None:
                 return self
             if self.fget is None:
                 raise AttributeError("unreadable attribute")
             return self.fget(obj)

         def __set__(self, obj, value):
             if self.fset is None:
                 raise AttributeError("can't set attribute")
             self.fset(obj, value)

         def __delete__(self, obj):
             if self.fdel is None:
                 raise AttributeError("can't delete attribute")
             self.fdel(obj)

         def getter(self, fget):
             return type(self)(fget, self.fset, self.fdel, self.__doc__)

         def setter(self, fset):
             return type(self)(self.fget, fset, self.fdel, self.__doc__)

         def deleter(self, fdel):
             return type(self)(self.fget, self.fset, fdel, self.__doc__)

The *note property(): 308. builtin helps whenever a user interface has
granted attribute access and then subsequent changes require the
intervention of a method.

For instance, a spreadsheet class may grant access to a cell value
through ‘Cell('b10').value’.  Subsequent improvements to the program
require the cell to be recalculated on every access; however, the
programmer does not want to affect existing client code accessing the
attribute directly.  The solution is to wrap access to the value
attribute in a property data descriptor:

     class Cell:
         ...

         @property
         def value(self):
             "Recalculate the cell before returning value"
             self.recalc()
             return self._value

Either the built-in *note property(): 308. or our ‘Property()’
equivalent would work in this example.


File: python.info,  Node: Functions and methods,  Next: Kinds of methods,  Prev: Properties,  Up: Pure Python Equivalents

10.4.4.2 Functions and methods
..............................

Python’s object oriented features are built upon a function based
environment.  Using non-data descriptors, the two are merged seamlessly.

Functions stored in class dictionaries get turned into methods when
invoked.  Methods only differ from regular functions in that the object
instance is prepended to the other arguments.  By convention, the
instance is called `self' but could be called `this' or any other
variable name.

Methods can be created manually with *note types.MethodType: 1af8. which
is roughly equivalent to:

     class MethodType:
         "Emulate PyMethod_Type in Objects/classobject.c"

         def __init__(self, func, obj):
             self.__func__ = func
             self.__self__ = obj

         def __call__(self, *args, **kwargs):
             func = self.__func__
             obj = self.__self__
             return func(obj, *args, **kwargs)

To support automatic creation of methods, functions include the *note
__get__(): 156e. method for binding methods during attribute access.
This means that functions are non-data descriptors that return bound
methods during dotted lookup from an instance.  Here’s how it works:

     class Function:
         ...

         def __get__(self, obj, objtype=None):
             "Simulate func_descr_get() in Objects/funcobject.c"
             if obj is None:
                 return self
             return MethodType(self, obj)

Running the following class in the interpreter shows how the function
descriptor works in practice:

     class D:
         def f(self, x):
              return x

The function has a *note qualified name: 155c. attribute to support
introspection:

     >>> D.f.__qualname__
     'D.f'

Accessing the function through the class dictionary does not invoke
*note __get__(): 156e.  Instead, it just returns the underlying function
object:

     >>> D.__dict__['f']
     <function D.f at 0x00C45070>

Dotted access from a class calls *note __get__(): 156e. which just
returns the underlying function unchanged:

     >>> D.f
     <function D.f at 0x00C45070>

The interesting behavior occurs during dotted access from an instance.
The dotted lookup calls *note __get__(): 156e. which returns a bound
method object:

     >>> d = D()
     >>> d.f
     <bound method D.f of <__main__.D object at 0x00B18C90>>

Internally, the bound method stores the underlying function and the
bound instance:

     >>> d.f.__func__
     <function D.f at 0x00C45070>

     >>> d.f.__self__
     <__main__.D object at 0x1012e1f98>

If you have ever wondered where `self' comes from in regular methods or
where `cls' comes from in class methods, this is it!


File: python.info,  Node: Kinds of methods,  Next: Static methods,  Prev: Functions and methods,  Up: Pure Python Equivalents

10.4.4.3 Kinds of methods
.........................

Non-data descriptors provide a simple mechanism for variations on the
usual patterns of binding functions into methods.

To recap, functions have a *note __get__(): 156e. method so that they
can be converted to a method when accessed as attributes.  The non-data
descriptor transforms an ‘obj.f(*args)’ call into ‘f(obj, *args)’.
Calling ‘cls.f(*args)’ becomes ‘f(*args)’.

This chart summarizes the binding and its two most useful variants:

     Transformation        Called from an object      Called from a class
                                                      
     ------------------------------------------------------------------------
                                                      
     function              f(obj, *args)              f(*args)
                                                      
                                                      
     staticmethod          f(*args)                   f(*args)
                                                      
                                                      
     classmethod           f(type(obj), *args)        f(cls, *args)
                                                      


File: python.info,  Node: Static methods,  Next: Class methods,  Prev: Kinds of methods,  Up: Pure Python Equivalents

10.4.4.4 Static methods
.......................

Static methods return the underlying function without changes.  Calling
either ‘c.f’ or ‘C.f’ is the equivalent of a direct lookup into
‘object.__getattribute__(c, "f")’ or ‘object.__getattribute__(C, "f")’.
As a result, the function becomes identically accessible from either an
object or a class.

Good candidates for static methods are methods that do not reference the
‘self’ variable.

For instance, a statistics package may include a container class for
experimental data.  The class provides normal methods for computing the
average, mean, median, and other descriptive statistics that depend on
the data.  However, there may be useful functions which are conceptually
related but do not depend on the data.  For instance, ‘erf(x)’ is handy
conversion routine that comes up in statistical work but does not
directly depend on a particular dataset.  It can be called either from
an object or the class: ‘s.erf(1.5) --> .9332’ or ‘Sample.erf(1.5) -->
.9332’.

Since static methods return the underlying function with no changes, the
example calls are unexciting:

     class E:
         @staticmethod
         def f(x):
             return x * 10

     >>> E.f(3)
     30
     >>> E().f(3)
     30

Using the non-data descriptor protocol, a pure Python version of *note
staticmethod(): 30a. would look like this:

     class StaticMethod:
         "Emulate PyStaticMethod_Type() in Objects/funcobject.c"

         def __init__(self, f):
             self.f = f

         def __get__(self, obj, objtype=None):
             return self.f


File: python.info,  Node: Class methods,  Next: Member objects and __slots__,  Prev: Static methods,  Up: Pure Python Equivalents

10.4.4.5 Class methods
......................

Unlike static methods, class methods prepend the class reference to the
argument list before calling the function.  This format is the same for
whether the caller is an object or a class:

     class F:
         @classmethod
         def f(cls, x):
             return cls.__name__, x

     >>> F.f(3)
     ('F', 3)
     >>> F().f(3)
     ('F', 3)

This behavior is useful whenever the method only needs to have a class
reference and does not rely on data stored in a specific instance.  One
use for class methods is to create alternate class constructors.  For
example, the classmethod *note dict.fromkeys(): 180a. creates a new
dictionary from a list of keys.  The pure Python equivalent is:

     class Dict(dict):
         @classmethod
         def fromkeys(cls, iterable, value=None):
             "Emulate dict_fromkeys() in Objects/dictobject.c"
             d = cls()
             for key in iterable:
                 d[key] = value
             return d

Now a new dictionary of unique keys can be constructed like this:

     >>> d = Dict.fromkeys('abracadabra')
     >>> type(d) is Dict
     True
     >>> d
     {'a': None, 'b': None, 'r': None, 'c': None, 'd': None}

Using the non-data descriptor protocol, a pure Python version of *note
classmethod(): 309. would look like this:

     class ClassMethod:
         "Emulate PyClassMethod_Type() in Objects/funcobject.c"

         def __init__(self, f):
             self.f = f

         def __get__(self, obj, cls=None):
             if cls is None:
                 cls = type(obj)
             if hasattr(type(self.f), '__get__'):
                 return self.f.__get__(cls)
             return MethodType(self.f, cls)

The code path for ‘hasattr(type(self.f), '__get__')’ was added in Python
3.9 and makes it possible for *note classmethod(): 309. to support
chained decorators.  For example, a classmethod and property could be
chained together:

     class G:
         @classmethod
         @property
         def __doc__(cls):
             return f'A doc for {cls.__name__!r}'

     >>> G.__doc__
     "A doc for 'G'"


File: python.info,  Node: Member objects and __slots__,  Prev: Class methods,  Up: Pure Python Equivalents

10.4.4.6 Member objects and __slots__
.....................................

When a class defines ‘__slots__’, it replaces instance dictionaries with
a fixed-length array of slot values.  From a user point of view that has
several effects:

1.  Provides immediate detection of bugs due to misspelled attribute
assignments.  Only attribute names specified in ‘__slots__’ are allowed:

     class Vehicle:
         __slots__ = ('id_number', 'make', 'model')

     >>> auto = Vehicle()
     >>> auto.id_nubmer = 'VYE483814LQEX'
     Traceback (most recent call last):
         ...
     AttributeError: 'Vehicle' object has no attribute 'id_nubmer'

2.  Helps create immutable objects where descriptors manage access to
private attributes stored in ‘__slots__’:

     class Immutable:

         __slots__ = ('_dept', '_name')          # Replace the instance dictionary

         def __init__(self, dept, name):
             self._dept = dept                   # Store to private attribute
             self._name = name                   # Store to private attribute

         @property                               # Read-only descriptor
         def dept(self):
             return self._dept

         @property
         def name(self):                         # Read-only descriptor
             return self._name

     >>> mark = Immutable('Botany', 'Mark Watney')
     >>> mark.dept
     'Botany'
     >>> mark.dept = 'Space Pirate'
     Traceback (most recent call last):
         ...
     AttributeError: can't set attribute
     >>> mark.location = 'Mars'
     Traceback (most recent call last):
         ...
     AttributeError: 'Immutable' object has no attribute 'location'

3.  Saves memory.  On a 64-bit Linux build, an instance with two
attributes takes 48 bytes with ‘__slots__’ and 152 bytes without.  This
flyweight design pattern(1) likely only matters when a large number of
instances are going to be created.

4.  Blocks tools like *note functools.cached_property(): 2f9. which
require an instance dictionary to function correctly:

     from functools import cached_property

     class CP:
         __slots__ = ()                          # Eliminates the instance dict

         @cached_property                        # Requires an instance dict
         def pi(self):
             return 4 * sum((-1.0)**n / (2.0*n + 1.0)
                            for n in reversed(range(100_000)))

     >>> CP().pi
     Traceback (most recent call last):
       ...
     TypeError: No '__dict__' attribute on 'CP' instance to cache 'pi' property.

It is not possible to create an exact drop-in pure Python version of
‘__slots__’ because it requires direct access to C structures and
control over object memory allocation.  However, we can build a mostly
faithful simulation where the actual C structure for slots is emulated
by a private ‘_slotvalues’ list.  Reads and writes to that private
structure are managed by member descriptors:

     null = object()

     class Member:

         def __init__(self, name, clsname, offset):
             'Emulate PyMemberDef in Include/structmember.h'
             # Also see descr_new() in Objects/descrobject.c
             self.name = name
             self.clsname = clsname
             self.offset = offset

         def __get__(self, obj, objtype=None):
             'Emulate member_get() in Objects/descrobject.c'
             # Also see PyMember_GetOne() in Python/structmember.c
             value = obj._slotvalues[self.offset]
             if value is null:
                 raise AttributeError(self.name)
             return value

         def __set__(self, obj, value):
             'Emulate member_set() in Objects/descrobject.c'
             obj._slotvalues[self.offset] = value

         def __delete__(self, obj):
             'Emulate member_delete() in Objects/descrobject.c'
             value = obj._slotvalues[self.offset]
             if value is null:
                 raise AttributeError(self.name)
             obj._slotvalues[self.offset] = null

         def __repr__(self):
             'Emulate member_repr() in Objects/descrobject.c'
             return f'<Member {self.name!r} of {self.clsname!r}>'

The ‘type.__new__()’ method takes care of adding member objects to class
variables:

     class Type(type):
         'Simulate how the type metaclass adds member objects for slots'

         def __new__(mcls, clsname, bases, mapping):
             'Emuluate type_new() in Objects/typeobject.c'
             # type_new() calls PyTypeReady() which calls add_methods()
             slot_names = mapping.get('slot_names', [])
             for offset, name in enumerate(slot_names):
                 mapping[name] = Member(name, clsname, offset)
             return type.__new__(mcls, clsname, bases, mapping)

The *note object.__new__(): 974. method takes care of creating instances
that have slots instead of an instance dictionary.  Here is a rough
simulation in pure Python:

     class Object:
         'Simulate how object.__new__() allocates memory for __slots__'

         def __new__(cls, *args):
             'Emulate object_new() in Objects/typeobject.c'
             inst = super().__new__(cls)
             if hasattr(cls, 'slot_names'):
                 empty_slots = [null] * len(cls.slot_names)
                 object.__setattr__(inst, '_slotvalues', empty_slots)
             return inst

         def __setattr__(self, name, value):
             'Emulate _PyObject_GenericSetAttrWithDict() Objects/object.c'
             cls = type(self)
             if hasattr(cls, 'slot_names') and name not in cls.slot_names:
                 raise AttributeError(
                     f'{type(self).__name__!r} object has no attribute {name!r}'
                 )
             super().__setattr__(name, value)

         def __delattr__(self, name):
             'Emulate _PyObject_GenericSetAttrWithDict() Objects/object.c'
             cls = type(self)
             if hasattr(cls, 'slot_names') and name not in cls.slot_names:
                 raise AttributeError(
                     f'{type(self).__name__!r} object has no attribute {name!r}'
                 )
             super().__delattr__(name)

To use the simulation in a real class, just inherit from ‘Object’ and
set the *note metaclass: 1590. to ‘Type’:

     class H(Object, metaclass=Type):
         'Instance variables stored in slots'

         slot_names = ['x', 'y']

         def __init__(self, x, y):
             self.x = x
             self.y = y

At this point, the metaclass has loaded member objects for `x' and `y':

     >>> from pprint import pp
     >>> pp(dict(vars(H)))
     {'__module__': '__main__',
      '__doc__': 'Instance variables stored in slots',
      'slot_names': ['x', 'y'],
      '__init__': <function H.__init__ at 0x7fb5d302f9d0>,
      'x': <Member 'x' of 'H'>,
      'y': <Member 'y' of 'H'>}

When instances are created, they have a ‘slot_values’ list where the
attributes are stored:

     >>> h = H(10, 20)
     >>> vars(h)
     {'_slotvalues': [10, 20]}
     >>> h.x = 55
     >>> vars(h)
     {'_slotvalues': [55, 20]}

Misspelled or unassigned attributes will raise an exception:

     >>> h.xz
     Traceback (most recent call last):
         ...
     AttributeError: 'H' object has no attribute 'xz'

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Flyweight_pattern


File: python.info,  Node: Functional Programming HOWTO,  Next: Logging HOWTO,  Prev: Descriptor HowTo Guide,  Up: Python HOWTOs

10.5 Functional Programming HOWTO
=================================


Author: A. M. Kuchling


Release: 0.32

In this document, we’ll take a tour of Python’s features suitable for
implementing programs in a functional style.  After an introduction to
the concepts of functional programming, we’ll look at language features
such as *note iterator: 1171.s and *note generator: a83.s and relevant
library modules such as *note itertools: a3. and *note functools: 83.

* Menu:

* Introduction: Introduction<14>.
* Iterators: Iterators<2>.
* Generator expressions and list comprehensions::
* Generators: Generators<2>.
* Built-in functions::
* The itertools module::
* The functools module::
* Small functions and the lambda expression::
* Revision History and Acknowledgements::
* References: References<2>.


File: python.info,  Node: Introduction<14>,  Next: Iterators<2>,  Up: Functional Programming HOWTO

10.5.1 Introduction
-------------------

This section explains the basic concept of functional programming; if
you’re just interested in learning about Python language features, skip
to the next section on *note Iterators: 433d.

Programming languages support decomposing problems in several different
ways:

   * Most programming languages are `procedural': programs are lists of
     instructions that tell the computer what to do with the program’s
     input.  C, Pascal, and even Unix shells are procedural languages.

   * In `declarative' languages, you write a specification that
     describes the problem to be solved, and the language implementation
     figures out how to perform the computation efficiently.  SQL is the
     declarative language you’re most likely to be familiar with; a SQL
     query describes the data set you want to retrieve, and the SQL
     engine decides whether to scan tables or use indexes, which
     subclauses should be performed first, etc.

   * `Object-oriented' programs manipulate collections of objects.
     Objects have internal state and support methods that query or
     modify this internal state in some way.  Smalltalk and Java are
     object-oriented languages.  C++ and Python are languages that
     support object-oriented programming, but don’t force the use of
     object-oriented features.

   * `Functional' programming decomposes a problem into a set of
     functions.  Ideally, functions only take inputs and produce
     outputs, and don’t have any internal state that affects the output
     produced for a given input.  Well-known functional languages
     include the ML family (Standard ML, OCaml, and other variants) and
     Haskell.

The designers of some computer languages choose to emphasize one
particular approach to programming.  This often makes it difficult to
write programs that use a different approach.  Other languages are
multi-paradigm languages that support several different approaches.
Lisp, C++, and Python are multi-paradigm; you can write programs or
libraries that are largely procedural, object-oriented, or functional in
all of these languages.  In a large program, different sections might be
written using different approaches; the GUI might be object-oriented
while the processing logic is procedural or functional, for example.

In a functional program, input flows through a set of functions.  Each
function operates on its input and produces some output.  Functional
style discourages functions with side effects that modify internal state
or make other changes that aren’t visible in the function’s return
value.  Functions that have no side effects at all are called `purely
functional'.  Avoiding side effects means not using data structures that
get updated as a program runs; every function’s output must only depend
on its input.

Some languages are very strict about purity and don’t even have
assignment statements such as ‘a=3’ or ‘c = a + b’, but it’s difficult
to avoid all side effects, such as printing to the screen or writing to
a disk file.  Another example is a call to the *note print(): 971. or
*note time.sleep(): 773. function, neither of which returns a useful
value.  Both are called only for their side effects of sending some text
to the screen or pausing execution for a second.

Python programs written in functional style usually won’t go to the
extreme of avoiding all I/O or all assignments; instead, they’ll provide
a functional-appearing interface but will use non-functional features
internally.  For example, the implementation of a function will still
use assignments to local variables, but won’t modify global variables or
have other side effects.

Functional programming can be considered the opposite of object-oriented
programming.  Objects are little capsules containing some internal state
along with a collection of method calls that let you modify this state,
and programs consist of making the right set of state changes.
Functional programming wants to avoid state changes as much as possible
and works with data flowing between functions.  In Python you might
combine the two approaches by writing functions that take and return
instances representing objects in your application (e-mail messages,
transactions, etc.).

Functional design may seem like an odd constraint to work under.  Why
should you avoid objects and side effects?  There are theoretical and
practical advantages to the functional style:

   * Formal provability.

   * Modularity.

   * Composability.

   * Ease of debugging and testing.

* Menu:

* Formal provability::
* Modularity::
* Ease of debugging and testing::
* Composability::


File: python.info,  Node: Formal provability,  Next: Modularity,  Up: Introduction<14>

10.5.1.1 Formal provability
...........................

A theoretical benefit is that it’s easier to construct a mathematical
proof that a functional program is correct.

For a long time researchers have been interested in finding ways to
mathematically prove programs correct.  This is different from testing a
program on numerous inputs and concluding that its output is usually
correct, or reading a program’s source code and concluding that the code
looks right; the goal is instead a rigorous proof that a program
produces the right result for all possible inputs.

The technique used to prove programs correct is to write down
`invariants', properties of the input data and of the program’s
variables that are always true.  For each line of code, you then show
that if invariants X and Y are true `before' the line is executed, the
slightly different invariants X’ and Y’ are true `after' the line is
executed.  This continues until you reach the end of the program, at
which point the invariants should match the desired conditions on the
program’s output.

Functional programming’s avoidance of assignments arose because
assignments are difficult to handle with this technique; assignments can
break invariants that were true before the assignment without producing
any new invariants that can be propagated onward.

Unfortunately, proving programs correct is largely impractical and not
relevant to Python software.  Even trivial programs require proofs that
are several pages long; the proof of correctness for a moderately
complicated program would be enormous, and few or none of the programs
you use daily (the Python interpreter, your XML parser, your web
browser) could be proven correct.  Even if you wrote down or generated a
proof, there would then be the question of verifying the proof; maybe
there’s an error in it, and you wrongly believe you’ve proved the
program correct.


File: python.info,  Node: Modularity,  Next: Ease of debugging and testing,  Prev: Formal provability,  Up: Introduction<14>

10.5.1.2 Modularity
...................

A more practical benefit of functional programming is that it forces you
to break apart your problem into small pieces.  Programs are more
modular as a result.  It’s easier to specify and write a small function
that does one thing than a large function that performs a complicated
transformation.  Small functions are also easier to read and to check
for errors.


File: python.info,  Node: Ease of debugging and testing,  Next: Composability,  Prev: Modularity,  Up: Introduction<14>

10.5.1.3 Ease of debugging and testing
......................................

Testing and debugging a functional-style program is easier.

Debugging is simplified because functions are generally small and
clearly specified.  When a program doesn’t work, each function is an
interface point where you can check that the data are correct.  You can
look at the intermediate inputs and outputs to quickly isolate the
function that’s responsible for a bug.

Testing is easier because each function is a potential subject for a
unit test.  Functions don’t depend on system state that needs to be
replicated before running a test; instead you only have to synthesize
the right input and then check that the output matches expectations.


File: python.info,  Node: Composability,  Prev: Ease of debugging and testing,  Up: Introduction<14>

10.5.1.4 Composability
......................

As you work on a functional-style program, you’ll write a number of
functions with varying inputs and outputs.  Some of these functions will
be unavoidably specialized to a particular application, but others will
be useful in a wide variety of programs.  For example, a function that
takes a directory path and returns all the XML files in the directory,
or a function that takes a filename and returns its contents, can be
applied to many different situations.

Over time you’ll form a personal library of utilities.  Often you’ll
assemble new programs by arranging existing functions in a new
configuration and writing a few functions specialized for the current
task.


File: python.info,  Node: Iterators<2>,  Next: Generator expressions and list comprehensions,  Prev: Introduction<14>,  Up: Functional Programming HOWTO

10.5.2 Iterators
----------------

I’ll start by looking at a Python language feature that’s an important
foundation for writing functional-style programs: iterators.

An iterator is an object representing a stream of data; this object
returns the data one element at a time.  A Python iterator must support
a method called *note __next__(): d2c. that takes no arguments and
always returns the next element of the stream.  If there are no more
elements in the stream, *note __next__(): d2c. must raise the *note
StopIteration: 582. exception.  Iterators don’t have to be finite,
though; it’s perfectly reasonable to write an iterator that produces an
infinite stream of data.

The built-in *note iter(): ded. function takes an arbitrary object and
tries to return an iterator that will return the object’s contents or
elements, raising *note TypeError: 1fe. if the object doesn’t support
iteration.  Several of Python’s built-in data types support iteration,
the most common being lists and dictionaries.  An object is called *note
iterable: c7c. if you can get an iterator for it.

You can experiment with the iteration interface manually:

     >>> L = [1, 2, 3]
     >>> it = iter(L)
     >>> it
     <...iterator object at ...>
     >>> it.__next__()  # same as next(it)
     1
     >>> next(it)
     2
     >>> next(it)
     3
     >>> next(it)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     StopIteration
     >>>

Python expects iterable objects in several different contexts, the most
important being the *note for: cfa. statement.  In the statement ‘for X
in Y’, Y must be an iterator or some object for which *note iter(): ded.
can create an iterator.  These two statements are equivalent:

     for i in iter(obj):
         print(i)

     for i in obj:
         print(i)

Iterators can be materialized as lists or tuples by using the *note
list(): 1f8. or *note tuple(): 1a2. constructor functions:

     >>> L = [1, 2, 3]
     >>> iterator = iter(L)
     >>> t = tuple(iterator)
     >>> t
     (1, 2, 3)

Sequence unpacking also supports iterators: if you know an iterator will
return N elements, you can unpack them into an N-tuple:

     >>> L = [1, 2, 3]
     >>> iterator = iter(L)
     >>> a, b, c = iterator
     >>> a, b, c
     (1, 2, 3)

Built-in functions such as *note max(): 8f7. and *note min(): 8f6. can
take a single iterator argument and will return the largest or smallest
element.  The ‘"in"’ and ‘"not in"’ operators also support iterators: ‘X
in iterator’ is true if X is found in the stream returned by the
iterator.  You’ll run into obvious problems if the iterator is infinite;
*note max(): 8f7, *note min(): 8f6. will never return, and if the
element X never appears in the stream, the ‘"in"’ and ‘"not in"’
operators won’t return either.

Note that you can only go forward in an iterator; there’s no way to get
the previous element, reset the iterator, or make a copy of it.
Iterator objects can optionally provide these additional capabilities,
but the iterator protocol only specifies the *note __next__(): d2c.
method.  Functions may therefore consume all of the iterator’s output,
and if you need to do something different with the same stream, you’ll
have to create a new iterator.

* Menu:

* Data Types That Support Iterators::


File: python.info,  Node: Data Types That Support Iterators,  Up: Iterators<2>

10.5.2.1 Data Types That Support Iterators
..........................................

We’ve already seen how lists and tuples support iterators.  In fact, any
Python sequence type, such as strings, will automatically support
creation of an iterator.

Calling *note iter(): ded. on a dictionary returns an iterator that will
loop over the dictionary’s keys:

     >>> m = {'Jan': 1, 'Feb': 2, 'Mar': 3, 'Apr': 4, 'May': 5, 'Jun': 6,
     ...      'Jul': 7, 'Aug': 8, 'Sep': 9, 'Oct': 10, 'Nov': 11, 'Dec': 12}
     >>> for key in m:
     ...     print(key, m[key])
     Jan 1
     Feb 2
     Mar 3
     Apr 4
     May 5
     Jun 6
     Jul 7
     Aug 8
     Sep 9
     Oct 10
     Nov 11
     Dec 12

Note that starting with Python 3.7, dictionary iteration order is
guaranteed to be the same as the insertion order.  In earlier versions,
the behaviour was unspecified and could vary between implementations.

Applying *note iter(): ded. to a dictionary always loops over the keys,
but dictionaries have methods that return other iterators.  If you want
to iterate over values or key/value pairs, you can explicitly call the
*note values(): cf6. or *note items(): cf5. methods to get an
appropriate iterator.

The *note dict(): 164. constructor can accept an iterator that returns a
finite stream of ‘(key, value)’ tuples:

     >>> L = [('Italy', 'Rome'), ('France', 'Paris'), ('US', 'Washington DC')]
     >>> dict(iter(L))
     {'Italy': 'Rome', 'France': 'Paris', 'US': 'Washington DC'}

Files also support iteration by calling the *note readline(): 1d5b.
method until there are no more lines in the file.  This means you can
read each line of a file like this:

     for line in file:
         # do something for each line
         ...

Sets can take their contents from an iterable and let you iterate over
the set’s elements:

     S = {2, 3, 5, 7, 11, 13}
     for i in S:
         print(i)


File: python.info,  Node: Generator expressions and list comprehensions,  Next: Generators<2>,  Prev: Iterators<2>,  Up: Functional Programming HOWTO

10.5.3 Generator expressions and list comprehensions
----------------------------------------------------

Two common operations on an iterator’s output are 1) performing some
operation for every element, 2) selecting a subset of elements that meet
some condition.  For example, given a list of strings, you might want to
strip off trailing whitespace from each line or extract all the strings
containing a given substring.

List comprehensions and generator expressions (short form: “listcomps”
and “genexps”) are a concise notation for such operations, borrowed from
the functional programming language Haskell
(‘https://www.haskell.org/’).  You can strip all the whitespace from a
stream of strings with the following code:

     line_list = ['  line 1\n', 'line 2  \n', ...]

     # Generator expression -- returns iterator
     stripped_iter = (line.strip() for line in line_list)

     # List comprehension -- returns list
     stripped_list = [line.strip() for line in line_list]

You can select only certain elements by adding an ‘"if"’ condition:

     stripped_list = [line.strip() for line in line_list
                      if line != ""]

With a list comprehension, you get back a Python list; ‘stripped_list’
is a list containing the resulting lines, not an iterator.  Generator
expressions return an iterator that computes the values as necessary,
not needing to materialize all the values at once.  This means that list
comprehensions aren’t useful if you’re working with iterators that
return an infinite stream or a very large amount of data.  Generator
expressions are preferable in these situations.

Generator expressions are surrounded by parentheses (“()”) and list
comprehensions are surrounded by square brackets (“[]”).  Generator
expressions have the form:

     ( expression for expr in sequence1
                  if condition1
                  for expr2 in sequence2
                  if condition2
                  for expr3 in sequence3 ...
                  if condition3
                  for exprN in sequenceN
                  if conditionN )

Again, for a list comprehension only the outside brackets are different
(square brackets instead of parentheses).

The elements of the generated output will be the successive values of
‘expression’.  The ‘if’ clauses are all optional; if present,
‘expression’ is only evaluated and added to the result when ‘condition’
is true.

Generator expressions always have to be written inside parentheses, but
the parentheses signalling a function call also count.  If you want to
create an iterator that will be immediately passed to a function you can
write:

     obj_total = sum(obj.count for obj in list_all_objects())

The ‘for...in’ clauses contain the sequences to be iterated over.  The
sequences do not have to be the same length, because they are iterated
over from left to right, `not' in parallel.  For each element in
‘sequence1’, ‘sequence2’ is looped over from the beginning.  ‘sequence3’
is then looped over for each resulting pair of elements from ‘sequence1’
and ‘sequence2’.

To put it another way, a list comprehension or generator expression is
equivalent to the following Python code:

     for expr1 in sequence1:
         if not (condition1):
             continue   # Skip this element
         for expr2 in sequence2:
             if not (condition2):
                 continue   # Skip this element
             ...
             for exprN in sequenceN:
                 if not (conditionN):
                     continue   # Skip this element

                 # Output the value of
                 # the expression.

This means that when there are multiple ‘for...in’ clauses but no ‘if’
clauses, the length of the resulting output will be equal to the product
of the lengths of all the sequences.  If you have two lists of length 3,
the output list is 9 elements long:

     >>> seq1 = 'abc'
     >>> seq2 = (1, 2, 3)
     >>> [(x, y) for x in seq1 for y in seq2]
     [('a', 1), ('a', 2), ('a', 3),
      ('b', 1), ('b', 2), ('b', 3),
      ('c', 1), ('c', 2), ('c', 3)]

To avoid introducing an ambiguity into Python’s grammar, if ‘expression’
is creating a tuple, it must be surrounded with parentheses.  The first
list comprehension below is a syntax error, while the second one is
correct:

     # Syntax error
     [x, y for x in seq1 for y in seq2]
     # Correct
     [(x, y) for x in seq1 for y in seq2]


File: python.info,  Node: Generators<2>,  Next: Built-in functions,  Prev: Generator expressions and list comprehensions,  Up: Functional Programming HOWTO

10.5.4 Generators
-----------------

Generators are a special class of functions that simplify the task of
writing iterators.  Regular functions compute a value and return it, but
generators return an iterator that returns a stream of values.

You’re doubtless familiar with how regular function calls work in Python
or C. When you call a function, it gets a private namespace where its
local variables are created.  When the function reaches a ‘return’
statement, the local variables are destroyed and the value is returned
to the caller.  A later call to the same function creates a new private
namespace and a fresh set of local variables.  But, what if the local
variables weren’t thrown away on exiting a function?  What if you could
later resume the function where it left off?  This is what generators
provide; they can be thought of as resumable functions.

Here’s the simplest example of a generator function:

     >>> def generate_ints(N):
     ...    for i in range(N):
     ...        yield i

Any function containing a *note yield: 2c7. keyword is a generator
function; this is detected by Python’s *note bytecode: 709. compiler
which compiles the function specially as a result.

When you call a generator function, it doesn’t return a single value;
instead it returns a generator object that supports the iterator
protocol.  On executing the ‘yield’ expression, the generator outputs
the value of ‘i’, similar to a ‘return’ statement.  The big difference
between ‘yield’ and a ‘return’ statement is that on reaching a ‘yield’
the generator’s state of execution is suspended and local variables are
preserved.  On the next call to the generator’s *note __next__(): 140e.
method, the function will resume executing.

Here’s a sample usage of the ‘generate_ints()’ generator:

     >>> gen = generate_ints(3)
     >>> gen
     <generator object generate_ints at ...>
     >>> next(gen)
     0
     >>> next(gen)
     1
     >>> next(gen)
     2
     >>> next(gen)
     Traceback (most recent call last):
       File "stdin", line 1, in <module>
       File "stdin", line 2, in generate_ints
     StopIteration

You could equally write ‘for i in generate_ints(5)’, or ‘a, b, c =
generate_ints(3)’.

Inside a generator function, ‘return value’ causes
‘StopIteration(value)’ to be raised from the *note __next__(): 140e.
method.  Once this happens, or the bottom of the function is reached,
the procession of values ends and the generator cannot yield any further
values.

You could achieve the effect of generators manually by writing your own
class and storing all the local variables of the generator as instance
variables.  For example, returning a list of integers could be done by
setting ‘self.count’ to 0, and having the *note __next__(): d2c. method
increment ‘self.count’ and return it.  However, for a moderately
complicated generator, writing a corresponding class can be much
messier.

The test suite included with Python’s library,
Lib/test/test_generators.py(1), contains a number of more interesting
examples.  Here’s one generator that implements an in-order traversal of
a tree using generators recursively.

     # A recursive generator that generates Tree leaves in in-order.
     def inorder(t):
         if t:
             for x in inorder(t.left):
                 yield x

             yield t.label

             for x in inorder(t.right):
                 yield x

Two other examples in ‘test_generators.py’ produce solutions for the
N-Queens problem (placing N queens on an NxN chess board so that no
queen threatens another) and the Knight’s Tour (finding a route that
takes a knight to every square of an NxN chessboard without visiting any
square twice).

* Menu:

* Passing values into a generator::

   ---------- Footnotes ----------

   (1) 
https://github.com/python/cpython/tree/3.9/Lib/test/test_generators.py


File: python.info,  Node: Passing values into a generator,  Up: Generators<2>

10.5.4.1 Passing values into a generator
........................................

In Python 2.4 and earlier, generators only produced output.  Once a
generator’s code was invoked to create an iterator, there was no way to
pass any new information into the function when its execution is
resumed.  You could hack together this ability by making the generator
look at a global variable or by passing in some mutable object that
callers then modify, but these approaches are messy.

In Python 2.5 there’s a simple way to pass values into a generator.
*note yield: 2c7. became an expression, returning a value that can be
assigned to a variable or otherwise operated on:

     val = (yield i)

I recommend that you `always' put parentheses around a ‘yield’
expression when you’re doing something with the returned value, as in
the above example.  The parentheses aren’t always necessary, but it’s
easier to always add them instead of having to remember when they’re
needed.

( PEP 342(1) explains the exact rules, which are that a
‘yield’-expression must always be parenthesized except when it occurs at
the top-level expression on the right-hand side of an assignment.  This
means you can write ‘val = yield i’ but have to use parentheses when
there’s an operation, as in ‘val = (yield i) + 12’.)

Values are sent into a generator by calling its *note send(value): 15cd.
method.  This method resumes the generator’s code and the ‘yield’
expression returns the specified value.  If the regular *note
__next__(): 140e. method is called, the ‘yield’ returns ‘None’.

Here’s a simple counter that increments by 1 and allows changing the
value of the internal counter.

     def counter(maximum):
         i = 0
         while i < maximum:
             val = (yield i)
             # If value provided, change counter
             if val is not None:
                 i = val
             else:
                 i += 1

And here’s an example of changing the counter:

     >>> it = counter(10)
     >>> next(it)
     0
     >>> next(it)
     1
     >>> it.send(8)
     8
     >>> next(it)
     9
     >>> next(it)
     Traceback (most recent call last):
       File "t.py", line 15, in <module>
         it.next()
     StopIteration

Because ‘yield’ will often be returning ‘None’, you should always check
for this case.  Don’t just use its value in expressions unless you’re
sure that the *note send(): 15cd. method will be the only method used to
resume your generator function.

In addition to *note send(): 15cd, there are two other methods on
generators:

   * *note throw(type, value=None, traceback=None): ff8. is used to
     raise an exception inside the generator; the exception is raised by
     the ‘yield’ expression where the generator’s execution is paused.

   * *note close(): 15d0. raises a *note GeneratorExit: df8. exception
     inside the generator to terminate the iteration.  On receiving this
     exception, the generator’s code must either raise *note
     GeneratorExit: df8. or *note StopIteration: 582.; catching the
     exception and doing anything else is illegal and will trigger a
     *note RuntimeError: 3dc.  *note close(): 15d0. will also be called
     by Python’s garbage collector when the generator is
     garbage-collected.

     If you need to run cleanup code when a *note GeneratorExit: df8.
     occurs, I suggest using a ‘try: ... finally:’ suite instead of
     catching *note GeneratorExit: df8.

The cumulative effect of these changes is to turn generators from
one-way producers of information into both producers and consumers.

Generators also become `coroutines', a more generalized form of
subroutines.  Subroutines are entered at one point and exited at another
point (the top of the function, and a ‘return’ statement), but
coroutines can be entered, exited, and resumed at many different points
(the ‘yield’ statements).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0342


File: python.info,  Node: Built-in functions,  Next: The itertools module,  Prev: Generators<2>,  Up: Functional Programming HOWTO

10.5.5 Built-in functions
-------------------------

Let’s look in more detail at built-in functions often used with
iterators.

Two of Python’s built-in functions, *note map(): cf7. and *note
filter(): cf8. duplicate the features of generator expressions:

*note map(f, iterA, iterB, ...): cf7. returns an iterator over the sequence

     ‘f(iterA[0], iterB[0]), f(iterA[1], iterB[1]), f(iterA[2],
     iterB[2]), ...’.

          >>> def upper(s):
          ...     return s.upper()

          >>> list(map(upper, ['sentence', 'fragment']))
          ['SENTENCE', 'FRAGMENT']
          >>> [upper(s) for s in ['sentence', 'fragment']]
          ['SENTENCE', 'FRAGMENT']

You can of course achieve the same effect with a list comprehension.

*note filter(predicate, iter): cf8. returns an iterator over all the
sequence elements that meet a certain condition, and is similarly
duplicated by list comprehensions.  A `predicate' is a function that
returns the truth value of some condition; for use with *note filter():
cf8, the predicate must take a single value.

     >>> def is_even(x):
     ...     return (x % 2) == 0

     >>> list(filter(is_even, range(10)))
     [0, 2, 4, 6, 8]

This can also be written as a list comprehension:

     >>> list(x for x in range(10) if is_even(x))
     [0, 2, 4, 6, 8]

*note enumerate(iter, start=0): ea7. counts off the elements in the
iterable returning 2-tuples containing the count (from `start') and each
element.

     >>> for item in enumerate(['subject', 'verb', 'object']):
     ...     print(item)
     (0, 'subject')
     (1, 'verb')
     (2, 'object')

*note enumerate(): ea7. is often used when looping through a list and
recording the indexes at which certain conditions are met:

     f = open('data.txt', 'r')
     for i, line in enumerate(f):
         if line.strip() == '':
             print('Blank line at line #%i' % i)

*note sorted(iterable, key=None, reverse=False): 547. collects all the
elements of the iterable into a list, sorts the list, and returns the
sorted result.  The `key' and `reverse' arguments are passed through to
the constructed list’s *note sort(): 548. method.

     >>> import random
     >>> # Generate 8 random numbers between [0, 10000)
     >>> rand_list = random.sample(range(10000), 8)
     >>> rand_list
     [769, 7953, 9828, 6431, 8442, 9878, 6213, 2207]
     >>> sorted(rand_list)
     [769, 2207, 6213, 6431, 7953, 8442, 9828, 9878]
     >>> sorted(rand_list, reverse=True)
     [9878, 9828, 8442, 7953, 6431, 6213, 2207, 769]

(For a more detailed discussion of sorting, see the *note Sorting HOW
TO: 1737.)

The *note any(iter): e49. and *note all(iter): e4a. built-ins look at
the truth values of an iterable’s contents.  *note any(): e49. returns
‘True’ if any element in the iterable is a true value, and *note all():
e4a. returns ‘True’ if all of the elements are true values:

     >>> any([0, 1, 0])
     True
     >>> any([0, 0, 0])
     False
     >>> any([1, 1, 1])
     True
     >>> all([0, 1, 0])
     False
     >>> all([0, 0, 0])
     False
     >>> all([1, 1, 1])
     True

*note zip(iterA, iterB, ...): cfc. takes one element from each iterable
and returns them in a tuple:

     zip(['a', 'b', 'c'], (1, 2, 3)) =>
       ('a', 1), ('b', 2), ('c', 3)

It doesn’t construct an in-memory list and exhaust all the input
iterators before returning; instead tuples are constructed and returned
only if they’re requested.  (The technical term for this behaviour is
lazy evaluation(1).)

This iterator is intended to be used with iterables that are all of the
same length.  If the iterables are of different lengths, the resulting
stream will be the same length as the shortest iterable.

     zip(['a', 'b'], (1, 2, 3)) =>
       ('a', 1), ('b', 2)

You should avoid doing this, though, because an element may be taken
from the longer iterators and discarded.  This means you can’t go on to
use the iterators further because you risk skipping a discarded element.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Lazy_evaluation


File: python.info,  Node: The itertools module,  Next: The functools module,  Prev: Built-in functions,  Up: Functional Programming HOWTO

10.5.6 The itertools module
---------------------------

The *note itertools: a3. module contains a number of commonly-used
iterators as well as functions for combining several iterators.  This
section will introduce the module’s contents by showing small examples.

The module’s functions fall into a few broad classes:

   * Functions that create a new iterator based on an existing iterator.

   * Functions for treating an iterator’s elements as function
     arguments.

   * Functions for selecting portions of an iterator’s output.

   * A function for grouping an iterator’s output.

* Menu:

* Creating new iterators::
* Calling functions on elements::
* Selecting elements::
* Combinatoric functions::
* Grouping elements::


File: python.info,  Node: Creating new iterators,  Next: Calling functions on elements,  Up: The itertools module

10.5.6.1 Creating new iterators
...............................

*note itertools.count(start, step): ce5. returns an infinite stream of
evenly spaced values.  You can optionally supply the starting number,
which defaults to 0, and the interval between numbers, which defaults to
1:

     itertools.count() =>
       0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ...
     itertools.count(10) =>
       10, 11, 12, 13, 14, 15, 16, 17, 18, 19, ...
     itertools.count(10, 5) =>
       10, 15, 20, 25, 30, 35, 40, 45, 50, 55, ...

*note itertools.cycle(iter): 1c9a. saves a copy of the contents of a
provided iterable and returns a new iterator that returns its elements
from first to last.  The new iterator will repeat these elements
infinitely.

     itertools.cycle([1, 2, 3, 4, 5]) =>
       1, 2, 3, 4, 5, 1, 2, 3, 4, 5, ...

*note itertools.repeat(elem, [n]): 11e7. returns the provided element
`n' times, or returns the element endlessly if `n' is not provided.

     itertools.repeat('abc') =>
       abc, abc, abc, abc, abc, abc, abc, abc, abc, abc, ...
     itertools.repeat('abc', 5) =>
       abc, abc, abc, abc, abc

*note itertools.chain(iterA, iterB, ...): 1738. takes an arbitrary
number of iterables as input, and returns all the elements of the first
iterator, then all the elements of the second, and so on, until all of
the iterables have been exhausted.

     itertools.chain(['a', 'b', 'c'], (1, 2, 3)) =>
       a, b, c, 1, 2, 3

*note itertools.islice(iter, [start], stop, [step]): 4a9. returns a
stream that’s a slice of the iterator.  With a single `stop' argument,
it will return the first `stop' elements.  If you supply a starting
index, you’ll get `stop-start' elements, and if you supply a value for
`step', elements will be skipped accordingly.  Unlike Python’s string
and list slicing, you can’t use negative values for `start', `stop', or
`step'.

     itertools.islice(range(10), 8) =>
       0, 1, 2, 3, 4, 5, 6, 7
     itertools.islice(range(10), 2, 8) =>
       2, 3, 4, 5, 6, 7
     itertools.islice(range(10), 2, 8, 2) =>
       2, 4, 6

*note itertools.tee(iter, [n]): 1c9f. replicates an iterator; it returns
`n' independent iterators that will all return the contents of the
source iterator.  If you don’t supply a value for `n', the default is 2.
Replicating iterators requires saving some of the contents of the source
iterator, so this can consume significant memory if the iterator is
large and one of the new iterators is consumed more than the others.

     itertools.tee( itertools.count() ) =>
        iterA, iterB

     where iterA ->
        0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ...

     and   iterB ->
        0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ...


File: python.info,  Node: Calling functions on elements,  Next: Selecting elements,  Prev: Creating new iterators,  Up: The itertools module

10.5.6.2 Calling functions on elements
......................................

The *note operator: c2. module contains a set of functions corresponding
to Python’s operators.  Some examples are *note operator.add(a, b):
1cc2. (adds two values), *note operator.ne(a, b): 1cb2. (same as ‘a !=
b’), and *note operator.attrgetter(’id’): 80a. (returns a callable that
fetches the ‘.id’ attribute).

*note itertools.starmap(func, iter): b05. assumes that the iterable will
return a stream of tuples, and calls `func' using these tuples as the
arguments:

     itertools.starmap(os.path.join,
                       [('/bin', 'python'), ('/usr', 'bin', 'java'),
                        ('/usr', 'bin', 'perl'), ('/usr', 'bin', 'ruby')])
     =>
       /bin/python, /usr/bin/java, /usr/bin/perl, /usr/bin/ruby


File: python.info,  Node: Selecting elements,  Next: Combinatoric functions,  Prev: Calling functions on elements,  Up: The itertools module

10.5.6.3 Selecting elements
...........................

Another group of functions chooses a subset of an iterator’s elements
based on a predicate.

*note itertools.filterfalse(predicate, iter): 1722. is the opposite of
*note filter(): cf8, returning all elements for which the predicate
returns false:

     itertools.filterfalse(is_even, itertools.count()) =>
       1, 3, 5, 7, 9, 11, 13, 15, ...

*note itertools.takewhile(predicate, iter): 1c9e. returns elements for
as long as the predicate returns true.  Once the predicate returns
false, the iterator will signal the end of its results.

     def less_than_10(x):
         return x < 10

     itertools.takewhile(less_than_10, itertools.count()) =>
       0, 1, 2, 3, 4, 5, 6, 7, 8, 9

     itertools.takewhile(is_even, itertools.count()) =>
       0

*note itertools.dropwhile(predicate, iter): 1c9c. discards elements
while the predicate returns true, and then returns the rest of the
iterable’s results.

     itertools.dropwhile(less_than_10, itertools.count()) =>
       10, 11, 12, 13, 14, 15, 16, 17, 18, 19, ...

     itertools.dropwhile(is_even, itertools.count()) =>
       1, 2, 3, 4, 5, 6, 7, 8, 9, 10, ...

*note itertools.compress(data, selectors): ce4. takes two iterators and
returns only those elements of `data' for which the corresponding
element of `selectors' is true, stopping whenever either one is
exhausted:

     itertools.compress([1, 2, 3, 4, 5], [True, True, False, False, True]) =>
        1, 2, 5


File: python.info,  Node: Combinatoric functions,  Next: Grouping elements,  Prev: Selecting elements,  Up: The itertools module

10.5.6.4 Combinatoric functions
...............................

The *note itertools.combinations(iterable, r): d6e. returns an iterator
giving all possible `r'-tuple combinations of the elements contained in
`iterable'.

     itertools.combinations([1, 2, 3, 4, 5], 2) =>
       (1, 2), (1, 3), (1, 4), (1, 5),
       (2, 3), (2, 4), (2, 5),
       (3, 4), (3, 5),
       (4, 5)

     itertools.combinations([1, 2, 3, 4, 5], 3) =>
       (1, 2, 3), (1, 2, 4), (1, 2, 5), (1, 3, 4), (1, 3, 5), (1, 4, 5),
       (2, 3, 4), (2, 3, 5), (2, 4, 5),
       (3, 4, 5)

The elements within each tuple remain in the same order as `iterable'
returned them.  For example, the number 1 is always before 2, 3, 4, or 5
in the examples above.  A similar function, *note
itertools.permutations(iterable, r=None): fc9, removes this constraint
on the order, returning all possible arrangements of length `r':

     itertools.permutations([1, 2, 3, 4, 5], 2) =>
       (1, 2), (1, 3), (1, 4), (1, 5),
       (2, 1), (2, 3), (2, 4), (2, 5),
       (3, 1), (3, 2), (3, 4), (3, 5),
       (4, 1), (4, 2), (4, 3), (4, 5),
       (5, 1), (5, 2), (5, 3), (5, 4)

     itertools.permutations([1, 2, 3, 4, 5]) =>
       (1, 2, 3, 4, 5), (1, 2, 3, 5, 4), (1, 2, 4, 3, 5),
       ...
       (5, 4, 3, 2, 1)

If you don’t supply a value for `r' the length of the iterable is used,
meaning that all the elements are permuted.

Note that these functions produce all of the possible combinations by
position and don’t require that the contents of `iterable' are unique:

     itertools.permutations('aba', 3) =>
       ('a', 'b', 'a'), ('a', 'a', 'b'), ('b', 'a', 'a'),
       ('b', 'a', 'a'), ('a', 'a', 'b'), ('a', 'b', 'a')

The identical tuple ‘('a', 'a', 'b')’ occurs twice, but the two ‘a’
strings came from different positions.

The *note itertools.combinations_with_replacement(iterable, r): ce3.
function relaxes a different constraint: elements can be repeated within
a single tuple.  Conceptually an element is selected for the first
position of each tuple and then is replaced before the second element is
selected.

     itertools.combinations_with_replacement([1, 2, 3, 4, 5], 2) =>
       (1, 1), (1, 2), (1, 3), (1, 4), (1, 5),
       (2, 2), (2, 3), (2, 4), (2, 5),
       (3, 3), (3, 4), (3, 5),
       (4, 4), (4, 5),
       (5, 5)


File: python.info,  Node: Grouping elements,  Prev: Combinatoric functions,  Up: The itertools module

10.5.6.5 Grouping elements
..........................

The last function I’ll discuss, *note itertools.groupby(iter,
key_func=None): 1c9d, is the most complicated.  ‘key_func(elem)’ is a
function that can compute a key value for each element returned by the
iterable.  If you don’t supply a key function, the key is simply each
element itself.

*note groupby(): 1c9d. collects all the consecutive elements from the
underlying iterable that have the same key value, and returns a stream
of 2-tuples containing a key value and an iterator for the elements with
that key.

     city_list = [('Decatur', 'AL'), ('Huntsville', 'AL'), ('Selma', 'AL'),
                  ('Anchorage', 'AK'), ('Nome', 'AK'),
                  ('Flagstaff', 'AZ'), ('Phoenix', 'AZ'), ('Tucson', 'AZ'),
                  ...
                 ]

     def get_state(city_state):
         return city_state[1]

     itertools.groupby(city_list, get_state) =>
       ('AL', iterator-1),
       ('AK', iterator-2),
       ('AZ', iterator-3), ...

     where
     iterator-1 =>
       ('Decatur', 'AL'), ('Huntsville', 'AL'), ('Selma', 'AL')
     iterator-2 =>
       ('Anchorage', 'AK'), ('Nome', 'AK')
     iterator-3 =>
       ('Flagstaff', 'AZ'), ('Phoenix', 'AZ'), ('Tucson', 'AZ')

*note groupby(): 1c9d. assumes that the underlying iterable’s contents
will already be sorted based on the key.  Note that the returned
iterators also use the underlying iterable, so you have to consume the
results of iterator-1 before requesting iterator-2 and its corresponding
key.


File: python.info,  Node: The functools module,  Next: Small functions and the lambda expression,  Prev: The itertools module,  Up: Functional Programming HOWTO

10.5.7 The functools module
---------------------------

The *note functools: 83. module in Python 2.5 contains some higher-order
functions.  A `higher-order function' takes one or more functions as
input and returns a new function.  The most useful tool in this module
is the *note functools.partial(): 8b5. function.

For programs written in a functional style, you’ll sometimes want to
construct variants of existing functions that have some of the
parameters filled in.  Consider a Python function ‘f(a, b, c)’; you may
wish to create a new function ‘g(b, c)’ that’s equivalent to ‘f(1, b,
c)’; you’re filling in a value for one of ‘f()’’s parameters.  This is
called “partial function application”.

The constructor for *note partial(): 8b5. takes the arguments
‘(function, arg1, arg2, ..., kwarg1=value1, kwarg2=value2)’.  The
resulting object is callable, so you can just call it to invoke
‘function’ with the filled-in arguments.

Here’s a small but realistic example:

     import functools

     def log(message, subsystem):
         """Write the contents of 'message' to the specified subsystem."""
         print('%s: %s' % (subsystem, message))
         ...

     server_log = functools.partial(log, subsystem='server')
     server_log('Unable to open socket')

*note functools.reduce(func, iter, [initial_value]): d37. cumulatively
performs an operation on all the iterable’s elements and, therefore,
can’t be applied to infinite iterables.  `func' must be a function that
takes two elements and returns a single value.  *note
functools.reduce(): d37. takes the first two elements A and B returned
by the iterator and calculates ‘func(A, B)’.  It then requests the third
element, C, calculates ‘func(func(A, B), C)’, combines this result with
the fourth element returned, and continues until the iterable is
exhausted.  If the iterable returns no values at all, a *note TypeError:
1fe. exception is raised.  If the initial value is supplied, it’s used
as a starting point and ‘func(initial_value, A)’ is the first
calculation.

     >>> import operator, functools
     >>> functools.reduce(operator.concat, ['A', 'BB', 'C'])
     'ABBC'
     >>> functools.reduce(operator.concat, [])
     Traceback (most recent call last):
       ...
     TypeError: reduce() of empty sequence with no initial value
     >>> functools.reduce(operator.mul, [1, 2, 3], 1)
     6
     >>> functools.reduce(operator.mul, [], 1)
     1

If you use *note operator.add(): 1cc2. with *note functools.reduce():
d37, you’ll add up all the elements of the iterable.  This case is so
common that there’s a special built-in called *note sum(): 316. to
compute it:

     >>> import functools, operator
     >>> functools.reduce(operator.add, [1, 2, 3, 4], 0)
     10
     >>> sum([1, 2, 3, 4])
     10
     >>> sum([])
     0

For many uses of *note functools.reduce(): d37, though, it can be
clearer to just write the obvious *note for: cfa. loop:

     import functools
     # Instead of:
     product = functools.reduce(operator.mul, [1, 2, 3], 1)

     # You can write:
     product = 1
     for i in [1, 2, 3]:
         product *= i

A related function is *note itertools.accumulate(iterable,
func=operator.add): 30e.  It performs the same calculation, but instead
of returning only the final result, ‘accumulate()’ returns an iterator
that also yields each partial result:

     itertools.accumulate([1, 2, 3, 4, 5]) =>
       1, 3, 6, 10, 15

     itertools.accumulate([1, 2, 3, 4, 5], operator.mul) =>
       1, 2, 6, 24, 120

* Menu:

* The operator module::


File: python.info,  Node: The operator module,  Up: The functools module

10.5.7.1 The operator module
............................

The *note operator: c2. module was mentioned earlier.  It contains a set
of functions corresponding to Python’s operators.  These functions are
often useful in functional-style code because they save you from writing
trivial functions that perform a single operation.

Some of the functions in this module are:

   * Math operations: ‘add()’, ‘sub()’, ‘mul()’, ‘floordiv()’, ‘abs()’,
     …

   * Logical operations: ‘not_()’, ‘truth()’.

   * Bitwise operations: ‘and_()’, ‘or_()’, ‘invert()’.

   * Comparisons: ‘eq()’, ‘ne()’, ‘lt()’, ‘le()’, ‘gt()’, and ‘ge()’.

   * Object identity: ‘is_()’, ‘is_not()’.

Consult the operator module’s documentation for a complete list.


File: python.info,  Node: Small functions and the lambda expression,  Next: Revision History and Acknowledgements,  Prev: The functools module,  Up: Functional Programming HOWTO

10.5.8 Small functions and the lambda expression
------------------------------------------------

When writing functional-style programs, you’ll often need little
functions that act as predicates or that combine elements in some way.

If there’s a Python built-in or a module function that’s suitable, you
don’t need to define a new function at all:

     stripped_lines = [line.strip() for line in lines]
     existing_files = filter(os.path.exists, file_list)

If the function you need doesn’t exist, you need to write it.  One way
to write small functions is to use the *note lambda: cf9. expression.
‘lambda’ takes a number of parameters and an expression combining these
parameters, and creates an anonymous function that returns the value of
the expression:

     adder = lambda x, y: x+y

     print_assign = lambda name, value: name + '=' + str(value)

An alternative is to just use the ‘def’ statement and define a function
in the usual way:

     def adder(x, y):
         return x + y

     def print_assign(name, value):
         return name + '=' + str(value)

Which alternative is preferable?  That’s a style question; my usual
course is to avoid using ‘lambda’.

One reason for my preference is that ‘lambda’ is quite limited in the
functions it can define.  The result has to be computable as a single
expression, which means you can’t have multiway ‘if... elif... else’
comparisons or ‘try... except’ statements.  If you try to do too much in
a ‘lambda’ statement, you’ll end up with an overly complicated
expression that’s hard to read.  Quick, what’s the following code doing?

     import functools
     total = functools.reduce(lambda a, b: (0, a[1] + b[1]), items)[1]

You can figure it out, but it takes time to disentangle the expression
to figure out what’s going on.  Using a short nested ‘def’ statements
makes things a little bit better:

     import functools
     def combine(a, b):
         return 0, a[1] + b[1]

     total = functools.reduce(combine, items)[1]

But it would be best of all if I had simply used a ‘for’ loop:

     total = 0
     for a, b in items:
         total += b

Or the *note sum(): 316. built-in and a generator expression:

     total = sum(b for a, b in items)

Many uses of *note functools.reduce(): d37. are clearer when written as
‘for’ loops.

Fredrik Lundh once suggested the following set of rules for refactoring
uses of ‘lambda’:

  1. Write a lambda function.

  2. Write a comment explaining what the heck that lambda does.

  3. Study the comment for a while, and think of a name that captures
     the essence of the comment.

  4. Convert the lambda to a def statement, using that name.

  5. Remove the comment.

I really like these rules, but you’re free to disagree about whether
this lambda-free style is better.


File: python.info,  Node: Revision History and Acknowledgements,  Next: References<2>,  Prev: Small functions and the lambda expression,  Up: Functional Programming HOWTO

10.5.9 Revision History and Acknowledgements
--------------------------------------------

The author would like to thank the following people for offering
suggestions, corrections and assistance with various drafts of this
article: Ian Bicking, Nick Coghlan, Nick Efford, Raymond Hettinger, Jim
Jewett, Mike Krell, Leandro Lameiro, Jussi Salmela, Collin Winter, Blake
Winton.

Version 0.1: posted June 30 2006.

Version 0.11: posted July 1 2006.  Typo fixes.

Version 0.2: posted July 10 2006.  Merged genexp and listcomp sections
into one.  Typo fixes.

Version 0.21: Added more references suggested on the tutor mailing list.

Version 0.30: Adds a section on the ‘functional’ module written by
Collin Winter; adds short section on the operator module; a few other
edits.


File: python.info,  Node: References<2>,  Prev: Revision History and Acknowledgements,  Up: Functional Programming HOWTO

10.5.10 References
------------------

* Menu:

* General::
* Python-specific::
* Python documentation::


File: python.info,  Node: General,  Next: Python-specific,  Up: References<2>

10.5.10.1 General
.................

`Structure and Interpretation of Computer Programs', by Harold Abelson
and Gerald Jay Sussman with Julie Sussman.  Full text at
‘https://mitpress.mit.edu/sicp/’.  In this classic textbook of computer
science, chapters 2 and 3 discuss the use of sequences and streams to
organize the data flow inside a program.  The book uses Scheme for its
examples, but many of the design approaches described in these chapters
are applicable to functional-style Python code.

‘http://www.defmacro.org/ramblings/fp.html’: A general introduction to
functional programming that uses Java examples and has a lengthy
historical introduction.

‘https://en.wikipedia.org/wiki/Functional_programming’: General
Wikipedia entry describing functional programming.

‘https://en.wikipedia.org/wiki/Coroutine’: Entry for coroutines.

‘https://en.wikipedia.org/wiki/Currying’: Entry for the concept of
currying.


File: python.info,  Node: Python-specific,  Next: Python documentation,  Prev: General,  Up: References<2>

10.5.10.2 Python-specific
.........................

‘http://gnosis.cx/TPiP/’: The first chapter of David Mertz’s book ‘Text
Processing in Python’ discusses functional programming for text
processing, in the section titled “Utilizing Higher-Order Functions in
Text Processing”.

Mertz also wrote a 3-part series of articles on functional programming
for IBM’s DeveloperWorks site; see part 1(1), part 2(2), and part 3(3),

   ---------- Footnotes ----------

   (1) https://developer.ibm.com/articles/l-prog/

   (2) https://developer.ibm.com/tutorials/l-prog2/

   (3) https://developer.ibm.com/tutorials/l-prog3/


File: python.info,  Node: Python documentation,  Prev: Python-specific,  Up: References<2>

10.5.10.3 Python documentation
..............................

Documentation for the *note itertools: a3. module.

Documentation for the *note functools: 83. module.

Documentation for the *note operator: c2. module.

PEP 289(1): “Generator Expressions”

PEP 342(2): “Coroutines via Enhanced Generators” describes the new
generator features in Python 2.5.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0289

   (2) https://www.python.org/dev/peps/pep-0342


File: python.info,  Node: Logging HOWTO,  Next: Logging Cookbook,  Prev: Functional Programming HOWTO,  Up: Python HOWTOs

10.6 Logging HOWTO
==================


Author: Vinay Sajip <vinay_sajip at red-dove dot com>

* Menu:

* Basic Logging Tutorial::
* Advanced Logging Tutorial::
* Logging Levels: Logging Levels<2>.
* Useful Handlers::
* Exceptions raised during logging::
* Using arbitrary objects as messages::
* Optimization::


File: python.info,  Node: Basic Logging Tutorial,  Next: Advanced Logging Tutorial,  Up: Logging HOWTO

10.6.1 Basic Logging Tutorial
-----------------------------

Logging is a means of tracking events that happen when some software
runs.  The software’s developer adds logging calls to their code to
indicate that certain events have occurred.  An event is described by a
descriptive message which can optionally contain variable data (i.e.
data that is potentially different for each occurrence of the event).
Events also have an importance which the developer ascribes to the
event; the importance can also be called the `level' or `severity'.

* Menu:

* When to use logging::
* A simple example::
* Logging to a file::
* Logging from multiple modules::
* Logging variable data::
* Changing the format of displayed messages::
* Displaying the date/time in messages::
* Next Steps::


File: python.info,  Node: When to use logging,  Next: A simple example,  Up: Basic Logging Tutorial

10.6.1.1 When to use logging
............................

Logging provides a set of convenience functions for simple logging
usage.  These are *note debug(): 21e1, *note info(): 220c, *note
warning(): 221e, *note error(): 221f. and *note critical(): 2220.  To
determine when to use logging, see the table below, which states, for
each of a set of common tasks, the best tool to use for it.

Task you want to perform                  The best tool for the task
                                          
-------------------------------------------------------------------------------------
                                          
Display console output for ordinary       *note print(): 971.
usage of a command line script or         
program

Report events that occur during normal    *note logging.info(): 220c. (or
operation of a program (e.g.  for         *note logging.debug(): 21e1. for very
status monitoring or fault                detailed output for diagnostic purposes)
investigation)                            

Issue a warning regarding a particular    *note warnings.warn(): f1a. in library
runtime event                             code if the issue is avoidable and the
                                          client application should be modified to
                                          eliminate the warning
                                          
                                          *note logging.warning(): 221e. if there
                                          is nothing the client application can do
                                          about the situation, but the event
                                          should still be noted
                                          
                                          
Report an error regarding a particular    Raise an exception
runtime event                             

Report suppression of an error without    *note logging.error(): 221f,
raising an exception (e.g.  error         *note logging.exception(): 2221. or
handler in a long-running server          *note logging.critical(): 2220. as
process)                                  appropriate for the specific error and
                                          application domain
                                          

The logging functions are named after the level or severity of the
events they are used to track.  The standard levels and their
applicability are described below (in increasing order of severity):

Level              When it’s used
                   
---------------------------------------------------------------------
                   
‘DEBUG’            Detailed information, typically of interest
                   only when diagnosing problems.
                   
                   
‘INFO’             Confirmation that things are working as
                   expected.
                   
                   
‘WARNING’          An indication that something unexpected
                   happened, or indicative of some problem in the
                   near future (e.g.  ‘disk space low’).  The
                   software is still working as expected.
                   
                   
‘ERROR’            Due to a more serious problem, the software has
                   not been able to perform some function.
                   
                   
‘CRITICAL’         A serious error, indicating that the program
                   itself may be unable to continue running.
                   

The default level is ‘WARNING’, which means that only events of this
level and above will be tracked, unless the logging package is
configured to do otherwise.

Events that are tracked can be handled in different ways.  The simplest
way of handling tracked events is to print them to the console.  Another
common way is to write them to a disk file.


File: python.info,  Node: A simple example,  Next: Logging to a file,  Prev: When to use logging,  Up: Basic Logging Tutorial

10.6.1.2 A simple example
.........................

A very simple example is:

     import logging
     logging.warning('Watch out!')  # will print a message to the console
     logging.info('I told you so')  # will not print anything

If you type these lines into a script and run it, you’ll see:

     WARNING:root:Watch out!

printed out on the console.  The ‘INFO’ message doesn’t appear because
the default level is ‘WARNING’.  The printed message includes the
indication of the level and the description of the event provided in the
logging call, i.e.  ‘Watch out!’.  Don’t worry about the ‘root’ part for
now: it will be explained later.  The actual output can be formatted
quite flexibly if you need that; formatting options will also be
explained later.


File: python.info,  Node: Logging to a file,  Next: Logging from multiple modules,  Prev: A simple example,  Up: Basic Logging Tutorial

10.6.1.3 Logging to a file
..........................

A very common situation is that of recording logging events in a file,
so let’s look at that next.  Be sure to try the following in a
newly-started Python interpreter, and don’t just continue from the
session described above:

     import logging
     logging.basicConfig(filename='example.log', encoding='utf-8', level=logging.DEBUG)
     logging.debug('This message should go to the log file')
     logging.info('So should this')
     logging.warning('And this, too')
     logging.error('And non-ASCII stuff, too, like Øresund and Malmö')

Changed in version 3.9: The `encoding' argument was added.  In earlier
Python versions, or if not specified, the encoding used is the default
value used by *note open(): 16f.  While not shown in the above example,
an `errors' argument can also now be passed, which determines how
encoding errors are handled.  For available values and the default, see
the documentation for *note open(): 16f.

And now if we open the file and look at what we have, we should find the
log messages:

     DEBUG:root:This message should go to the log file
     INFO:root:So should this
     WARNING:root:And this, too
     ERROR:root:And non-ASCII stuff, too, like Øresund and Malmö

This example also shows how you can set the logging level which acts as
the threshold for tracking.  In this case, because we set the threshold
to ‘DEBUG’, all of the messages were printed.

If you want to set the logging level from a command-line option such as:

     --log=INFO

and you have the value of the parameter passed for ‘--log’ in some
variable `loglevel', you can use:

     getattr(logging, loglevel.upper())

to get the value which you’ll pass to *note basicConfig(): 311. via the
`level' argument.  You may want to error check any user input value,
perhaps as in the following example:

     # assuming loglevel is bound to the string value obtained from the
     # command line argument. Convert to upper case to allow the user to
     # specify --log=DEBUG or --log=debug
     numeric_level = getattr(logging, loglevel.upper(), None)
     if not isinstance(numeric_level, int):
         raise ValueError('Invalid log level: %s' % loglevel)
     logging.basicConfig(level=numeric_level, ...)

The call to *note basicConfig(): 311. should come `before' any calls to
*note debug(): 21e1, *note info(): 220c. etc.  As it’s intended as a
one-off simple configuration facility, only the first call will actually
do anything: subsequent calls are effectively no-ops.

If you run the above script several times, the messages from successive
runs are appended to the file `example.log'.  If you want each run to
start afresh, not remembering the messages from earlier runs, you can
specify the `filemode' argument, by changing the call in the above
example to:

     logging.basicConfig(filename='example.log', filemode='w', level=logging.DEBUG)

The output will be the same as before, but the log file is no longer
appended to, so the messages from earlier runs are lost.


File: python.info,  Node: Logging from multiple modules,  Next: Logging variable data,  Prev: Logging to a file,  Up: Basic Logging Tutorial

10.6.1.4 Logging from multiple modules
......................................

If your program consists of multiple modules, here’s an example of how
you could organize logging in it:

     # myapp.py
     import logging
     import mylib

     def main():
         logging.basicConfig(filename='myapp.log', level=logging.INFO)
         logging.info('Started')
         mylib.do_something()
         logging.info('Finished')

     if __name__ == '__main__':
         main()

     # mylib.py
     import logging

     def do_something():
         logging.info('Doing something')

If you run `myapp.py', you should see this in `myapp.log':

     INFO:root:Started
     INFO:root:Doing something
     INFO:root:Finished

which is hopefully what you were expecting to see.  You can generalize
this to multiple modules, using the pattern in `mylib.py'.  Note that
for this simple usage pattern, you won’t know, by looking in the log
file, `where' in your application your messages came from, apart from
looking at the event description.  If you want to track the location of
your messages, you’ll need to refer to the documentation beyond the
tutorial level – see *note Advanced Logging Tutorial: c44.


File: python.info,  Node: Logging variable data,  Next: Changing the format of displayed messages,  Prev: Logging from multiple modules,  Up: Basic Logging Tutorial

10.6.1.5 Logging variable data
..............................

To log variable data, use a format string for the event description
message and append the variable data as arguments.  For example:

     import logging
     logging.warning('%s before you %s', 'Look', 'leap!')

will display:

     WARNING:root:Look before you leap!

As you can see, merging of variable data into the event description
message uses the old, %-style of string formatting.  This is for
backwards compatibility: the logging package pre-dates newer formatting
options such as *note str.format(): 5d5. and *note string.Template: 4f1.
These newer formatting options `are' supported, but exploring them is
outside the scope of this tutorial: see *note Using particular
formatting styles throughout your application: 2204. for more
information.


File: python.info,  Node: Changing the format of displayed messages,  Next: Displaying the date/time in messages,  Prev: Logging variable data,  Up: Basic Logging Tutorial

10.6.1.6 Changing the format of displayed messages
..................................................

To change the format which is used to display messages, you need to
specify the format you want to use:

     import logging
     logging.basicConfig(format='%(levelname)s:%(message)s', level=logging.DEBUG)
     logging.debug('This message should appear on the console')
     logging.info('So should this')
     logging.warning('And this, too')

which would print:

     DEBUG:This message should appear on the console
     INFO:So should this
     WARNING:And this, too

Notice that the ‘root’ which appeared in earlier examples has
disappeared.  For a full set of things that can appear in format
strings, you can refer to the documentation for *note LogRecord
attributes: 2202, but for simple usage, you just need the `levelname'
(severity), `message' (event description, including variable data) and
perhaps to display when the event occurred.  This is described in the
next section.


File: python.info,  Node: Displaying the date/time in messages,  Next: Next Steps,  Prev: Changing the format of displayed messages,  Up: Basic Logging Tutorial

10.6.1.7 Displaying the date/time in messages
.............................................

To display the date and time of an event, you would place ‘%(asctime)s’
in your format string:

     import logging
     logging.basicConfig(format='%(asctime)s %(message)s')
     logging.warning('is when this event was logged.')

which should print something like this:

     2010-12-12 11:41:42,612 is when this event was logged.

The default format for date/time display (shown above) is like ISO8601
or RFC 3339(1).  If you need more control over the formatting of the
date/time, provide a `datefmt' argument to ‘basicConfig’, as in this
example:

     import logging
     logging.basicConfig(format='%(asctime)s %(message)s', datefmt='%m/%d/%Y %I:%M:%S %p')
     logging.warning('is when this event was logged.')

which would display something like this:

     12/12/2010 11:46:36 AM is when this event was logged.

The format of the `datefmt' argument is the same as supported by *note
time.strftime(): c37.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc3339.html


File: python.info,  Node: Next Steps,  Prev: Displaying the date/time in messages,  Up: Basic Logging Tutorial

10.6.1.8 Next Steps
...................

That concludes the basic tutorial.  It should be enough to get you up
and running with logging.  There’s a lot more that the logging package
offers, but to get the best out of it, you’ll need to invest a little
more of your time in reading the following sections.  If you’re ready
for that, grab some of your favourite beverage and carry on.

If your logging needs are simple, then use the above examples to
incorporate logging into your own scripts, and if you run into problems
or don’t understand something, please post a question on the
comp.lang.python Usenet group (available at
‘https://groups.google.com/forum/#!forum/comp.lang.python’) and you
should receive help before too long.

Still here?  You can carry on reading the next few sections, which
provide a slightly more advanced/in-depth tutorial than the basic one
above.  After that, you can take a look at the *note Logging Cookbook:
c45.


File: python.info,  Node: Advanced Logging Tutorial,  Next: Logging Levels<2>,  Prev: Basic Logging Tutorial,  Up: Logging HOWTO

10.6.2 Advanced Logging Tutorial
--------------------------------

The logging library takes a modular approach and offers several
categories of components: loggers, handlers, filters, and formatters.

   * Loggers expose the interface that application code directly uses.

   * Handlers send the log records (created by loggers) to the
     appropriate destination.

   * Filters provide a finer grained facility for determining which log
     records to output.

   * Formatters specify the layout of log records in the final output.

Log event information is passed between loggers, handlers, filters and
formatters in a *note LogRecord: 9ec. instance.

Logging is performed by calling methods on instances of the *note
Logger: 4ae. class (hereafter called `loggers').  Each instance has a
name, and they are conceptually arranged in a namespace hierarchy using
dots (periods) as separators.  For example, a logger named ‘scan’ is the
parent of loggers ‘scan.text’, ‘scan.html’ and ‘scan.pdf’.  Logger names
can be anything you want, and indicate the area of an application in
which a logged message originates.

A good convention to use when naming loggers is to use a module-level
logger, in each module which uses logging, named as follows:

     logger = logging.getLogger(__name__)

This means that logger names track the package/module hierarchy, and
it’s intuitively obvious where events are logged just from the logger
name.

The root of the hierarchy of loggers is called the root logger.  That’s
the logger used by the functions *note debug(): 21e1, *note info():
220c, *note warning(): 221e, *note error(): 221f. and *note critical():
2220, which just call the same-named method of the root logger.  The
functions and the methods have the same signatures.  The root logger’s
name is printed as ‘root’ in the logged output.

It is, of course, possible to log messages to different destinations.
Support is included in the package for writing log messages to files,
HTTP GET/POST locations, email via SMTP, generic sockets, queues, or
OS-specific logging mechanisms such as syslog or the Windows NT event
log.  Destinations are served by `handler' classes.  You can create your
own log destination class if you have special requirements not met by
any of the built-in handler classes.

By default, no destination is set for any logging messages.  You can
specify a destination (such as console or file) by using *note
basicConfig(): 311. as in the tutorial examples.  If you call the
functions *note debug(): 21e1, *note info(): 220c, *note warning():
221e, *note error(): 221f. and *note critical(): 2220, they will check
to see if no destination is set; and if one is not set, they will set a
destination of the console (‘sys.stderr’) and a default format for the
displayed message before delegating to the root logger to do the actual
message output.

The default format set by *note basicConfig(): 311. for messages is:

     severity:logger name:message

You can change this by passing a format string to *note basicConfig():
311. with the `format' keyword argument.  For all options regarding how
a format string is constructed, see *note Formatter Objects: 2200.

* Menu:

* Logging Flow::
* Loggers::
* Handlers::
* Formatters::
* Configuring Logging::
* What happens if no configuration is provided::
* Configuring Logging for a Library::


File: python.info,  Node: Logging Flow,  Next: Loggers,  Up: Advanced Logging Tutorial

10.6.2.1 Logging Flow
.....................

The flow of log event information in loggers and handlers is illustrated
in the following diagram.

[python-figures/logging_flow]

File: python.info,  Node: Loggers,  Next: Handlers,  Prev: Logging Flow,  Up: Advanced Logging Tutorial

10.6.2.2 Loggers
................

*note Logger: 4ae. objects have a threefold job.  First, they expose
several methods to application code so that applications can log
messages at runtime.  Second, logger objects determine which log
messages to act upon based upon severity (the default filtering
facility) or filter objects.  Third, logger objects pass along relevant
log messages to all interested log handlers.

The most widely used methods on logger objects fall into two categories:
configuration and message sending.

These are the most common configuration methods:

   * *note Logger.setLevel(): 21da. specifies the lowest-severity log
     message a logger will handle, where debug is the lowest built-in
     severity level and critical is the highest built-in severity.  For
     example, if the severity level is INFO, the logger will handle only
     INFO, WARNING, ERROR, and CRITICAL messages and will ignore DEBUG
     messages.

   * *note Logger.addHandler(): 21e7. and *note Logger.removeHandler():
     21e8. add and remove handler objects from the logger object.
     Handlers are covered in more detail in *note Handlers: 4365.

   * *note Logger.addFilter(): 21e4. and *note Logger.removeFilter():
     21e5. add and remove filter objects from the logger object.
     Filters are covered in more detail in *note Filter Objects: 2209.

You don’t need to always call these methods on every logger you create.
See the last two paragraphs in this section.

With the logger object configured, the following methods create log
messages:

   * *note Logger.debug(): 801, *note Logger.info(): 21e0, *note
     Logger.warning(): 21e2, *note Logger.error(): 21e3, and *note
     Logger.critical(): 800. all create log records with a message and a
     level that corresponds to their respective method names.  The
     message is actually a format string, which may contain the standard
     string substitution syntax of ‘%s’, ‘%d’, ‘%f’, and so on.  The
     rest of their arguments is a list of objects that correspond with
     the substitution fields in the message.  With regard to ‘**kwargs’,
     the logging methods care only about a keyword of ‘exc_info’ and use
     it to determine whether to log exception information.

   * *note Logger.exception(): 7ff. creates a log message similar to
     *note Logger.error(): 21e3.  The difference is that *note
     Logger.exception(): 7ff. dumps a stack trace along with it.  Call
     this method only from an exception handler.

   * *note Logger.log(): 7fe. takes a log level as an explicit argument.
     This is a little more verbose for logging messages than using the
     log level convenience methods listed above, but this is how to log
     at custom log levels.

*note getLogger(): 234. returns a reference to a logger instance with
the specified name if it is provided, or ‘root’ if not.  The names are
period-separated hierarchical structures.  Multiple calls to *note
getLogger(): 234. with the same name will return a reference to the same
logger object.  Loggers that are further down in the hierarchical list
are children of loggers higher up in the list.  For example, given a
logger with a name of ‘foo’, loggers with names of ‘foo.bar’,
‘foo.bar.baz’, and ‘foo.bam’ are all descendants of ‘foo’.

Loggers have a concept of `effective level'.  If a level is not
explicitly set on a logger, the level of its parent is used instead as
its effective level.  If the parent has no explicit level set, `its'
parent is examined, and so on - all ancestors are searched until an
explicitly set level is found.  The root logger always has an explicit
level set (‘WARNING’ by default).  When deciding whether to process an
event, the effective level of the logger is used to determine whether
the event is passed to the logger’s handlers.

Child loggers propagate messages up to the handlers associated with
their ancestor loggers.  Because of this, it is unnecessary to define
and configure handlers for all the loggers an application uses.  It is
sufficient to configure handlers for a top-level logger and create child
loggers as needed.  (You can, however, turn off propagation by setting
the `propagate' attribute of a logger to ‘False’.)


File: python.info,  Node: Handlers,  Next: Formatters,  Prev: Loggers,  Up: Advanced Logging Tutorial

10.6.2.3 Handlers
.................

*note Handler: 21df. objects are responsible for dispatching the
appropriate log messages (based on the log messages’ severity) to the
handler’s specified destination.  *note Logger: 4ae. objects can add
zero or more handler objects to themselves with an *note addHandler():
21e7. method.  As an example scenario, an application may want to send
all log messages to a log file, all log messages of error or higher to
stdout, and all messages of critical to an email address.  This scenario
requires three individual handlers where each handler is responsible for
sending messages of a specific severity to a specific location.

The standard library includes quite a few handler types (see *note
Useful Handlers: 4367.); the tutorials use mainly *note StreamHandler:
c46. and *note FileHandler: 2245. in its examples.

There are very few methods in a handler for application developers to
concern themselves with.  The only handler methods that seem relevant
for application developers who are using the built-in handler objects
(that is, not creating custom handlers) are the following configuration
methods:

   * The *note setLevel(): 21f4. method, just as in logger objects,
     specifies the lowest severity that will be dispatched to the
     appropriate destination.  Why are there two ‘setLevel()’ methods?
     The level set in the logger determines which severity of messages
     it will pass to its handlers.  The level set in each handler
     determines which messages that handler will send on.

   * *note setFormatter(): 21f5. selects a Formatter object for this
     handler to use.

   * *note addFilter(): 21f6. and *note removeFilter(): 21f7.
     respectively configure and deconfigure filter objects on handlers.

Application code should not directly instantiate and use instances of
*note Handler: 21df.  Instead, the *note Handler: 21df. class is a base
class that defines the interface that all handlers should have and
establishes some default behavior that child classes can use (or
override).


File: python.info,  Node: Formatters,  Next: Configuring Logging,  Prev: Handlers,  Up: Advanced Logging Tutorial

10.6.2.4 Formatters
...................

Formatter objects configure the final order, structure, and contents of
the log message.  Unlike the base *note logging.Handler: 21df. class,
application code may instantiate formatter classes, although you could
likely subclass the formatter if your application needs special
behavior.  The constructor takes three optional arguments – a message
format string, a date format string and a style indicator.

 -- Method: logging.Formatter.__init__ (fmt=None, datefmt=None,
          style='%')

If there is no message format string, the default is to use the raw
message.  If there is no date format string, the default date format is:

     %Y-%m-%d %H:%M:%S

with the milliseconds tacked on at the end.  The ‘style’ is one of ‘%’,
‘{’ or ‘$’.  If one of these is not specified, then ‘%’ will be used.

If the ‘style’ is ‘%’, the message format string uses ‘%(<dictionary
key>)s’ styled string substitution; the possible keys are documented in
*note LogRecord attributes: 2202.  If the style is ‘{’, the message
format string is assumed to be compatible with *note str.format(): 5d5.
(using keyword arguments), while if the style is ‘$’ then the message
format string should conform to what is expected by *note
string.Template.substitute(): 1433.

Changed in version 3.2: Added the ‘style’ parameter.

The following message format string will log the time in a
human-readable format, the severity of the message, and the contents of
the message, in that order:

     '%(asctime)s - %(levelname)s - %(message)s'

Formatters use a user-configurable function to convert the creation time
of a record to a tuple.  By default, *note time.localtime(): 1080. is
used; to change this for a particular formatter instance, set the
‘converter’ attribute of the instance to a function with the same
signature as *note time.localtime(): 1080. or *note time.gmtime(): c11.
To change it for all formatters, for example if you want all logging
times to be shown in GMT, set the ‘converter’ attribute in the Formatter
class (to ‘time.gmtime’ for GMT display).


File: python.info,  Node: Configuring Logging,  Next: What happens if no configuration is provided,  Prev: Formatters,  Up: Advanced Logging Tutorial

10.6.2.5 Configuring Logging
............................

Programmers can configure logging in three ways:

  1. Creating loggers, handlers, and formatters explicitly using Python
     code that calls the configuration methods listed above.

  2. Creating a logging config file and reading it using the *note
     fileConfig(): 4b0. function.

  3. Creating a dictionary of configuration information and passing it
     to the *note dictConfig(): bfe. function.

For the reference documentation on the last two options, see *note
Configuration functions: d50.  The following example configures a very
simple logger, a console handler, and a simple formatter using Python
code:

     import logging

     # create logger
     logger = logging.getLogger('simple_example')
     logger.setLevel(logging.DEBUG)

     # create console handler and set level to debug
     ch = logging.StreamHandler()
     ch.setLevel(logging.DEBUG)

     # create formatter
     formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')

     # add formatter to ch
     ch.setFormatter(formatter)

     # add ch to logger
     logger.addHandler(ch)

     # 'application' code
     logger.debug('debug message')
     logger.info('info message')
     logger.warning('warn message')
     logger.error('error message')
     logger.critical('critical message')

Running this module from the command line produces the following output:

     $ python simple_logging_module.py
     2005-03-19 15:10:26,618 - simple_example - DEBUG - debug message
     2005-03-19 15:10:26,620 - simple_example - INFO - info message
     2005-03-19 15:10:26,695 - simple_example - WARNING - warn message
     2005-03-19 15:10:26,697 - simple_example - ERROR - error message
     2005-03-19 15:10:26,773 - simple_example - CRITICAL - critical message

The following Python module creates a logger, handler, and formatter
nearly identical to those in the example listed above, with the only
difference being the names of the objects:

     import logging
     import logging.config

     logging.config.fileConfig('logging.conf')

     # create logger
     logger = logging.getLogger('simpleExample')

     # 'application' code
     logger.debug('debug message')
     logger.info('info message')
     logger.warning('warn message')
     logger.error('error message')
     logger.critical('critical message')

Here is the logging.conf file:

     [loggers]
     keys=root,simpleExample

     [handlers]
     keys=consoleHandler

     [formatters]
     keys=simpleFormatter

     [logger_root]
     level=DEBUG
     handlers=consoleHandler

     [logger_simpleExample]
     level=DEBUG
     handlers=consoleHandler
     qualname=simpleExample
     propagate=0

     [handler_consoleHandler]
     class=StreamHandler
     level=DEBUG
     formatter=simpleFormatter
     args=(sys.stdout,)

     [formatter_simpleFormatter]
     format=%(asctime)s - %(name)s - %(levelname)s - %(message)s
     datefmt=

The output is nearly identical to that of the non-config-file-based
example:

     $ python simple_logging_config.py
     2005-03-19 15:38:55,977 - simpleExample - DEBUG - debug message
     2005-03-19 15:38:55,979 - simpleExample - INFO - info message
     2005-03-19 15:38:56,054 - simpleExample - WARNING - warn message
     2005-03-19 15:38:56,055 - simpleExample - ERROR - error message
     2005-03-19 15:38:56,130 - simpleExample - CRITICAL - critical message

You can see that the config file approach has a few advantages over the
Python code approach, mainly separation of configuration and code and
the ability of noncoders to easily modify the logging properties.

     Warning: The *note fileConfig(): 4b0. function takes a default
     parameter, ‘disable_existing_loggers’, which defaults to ‘True’ for
     reasons of backward compatibility.  This may or may not be what you
     want, since it will cause any non-root loggers existing before the
     *note fileConfig(): 4b0. call to be disabled unless they (or an
     ancestor) are explicitly named in the configuration.  Please refer
     to the reference documentation for more information, and specify
     ‘False’ for this parameter if you wish.

     The dictionary passed to *note dictConfig(): bfe. can also specify
     a Boolean value with key ‘disable_existing_loggers’, which if not
     specified explicitly in the dictionary also defaults to being
     interpreted as ‘True’.  This leads to the logger-disabling
     behaviour described above, which may not be what you want - in
     which case, provide the key explicitly with a value of ‘False’.

Note that the class names referenced in config files need to be either
relative to the logging module, or absolute values which can be resolved
using normal import mechanisms.  Thus, you could use either *note
WatchedFileHandler: 2257. (relative to the logging module) or
‘mypackage.mymodule.MyHandler’ (for a class defined in package
‘mypackage’ and module ‘mymodule’, where ‘mypackage’ is available on the
Python import path).

In Python 3.2, a new means of configuring logging has been introduced,
using dictionaries to hold configuration information.  This provides a
superset of the functionality of the config-file-based approach outlined
above, and is the recommended configuration method for new applications
and deployments.  Because a Python dictionary is used to hold
configuration information, and since you can populate that dictionary
using different means, you have more options for configuration.  For
example, you can use a configuration file in JSON format, or, if you
have access to YAML processing functionality, a file in YAML format, to
populate the configuration dictionary.  Or, of course, you can construct
the dictionary in Python code, receive it in pickled form over a socket,
or use whatever approach makes sense for your application.

Here’s an example of the same configuration as above, in YAML format for
the new dictionary-based approach:

     version: 1
     formatters:
       simple:
         format: '%(asctime)s - %(name)s - %(levelname)s - %(message)s'
     handlers:
       console:
         class: logging.StreamHandler
         level: DEBUG
         formatter: simple
         stream: ext://sys.stdout
     loggers:
       simpleExample:
         level: DEBUG
         handlers: [console]
         propagate: no
     root:
       level: DEBUG
       handlers: [console]

For more information about logging using a dictionary, see *note
Configuration functions: d50.


File: python.info,  Node: What happens if no configuration is provided,  Next: Configuring Logging for a Library,  Prev: Configuring Logging,  Up: Advanced Logging Tutorial

10.6.2.6 What happens if no configuration is provided
.....................................................

If no logging configuration is provided, it is possible to have a
situation where a logging event needs to be output, but no handlers can
be found to output the event.  The behaviour of the logging package in
these circumstances is dependent on the Python version.

For versions of Python prior to 3.2, the behaviour is as follows:

   * If `logging.raiseExceptions' is ‘False’ (production mode), the
     event is silently dropped.

   * If `logging.raiseExceptions' is ‘True’ (development mode), a
     message ‘No handlers could be found for logger X.Y.Z’ is printed
     once.

In Python 3.2 and later, the behaviour is as follows:

   * The event is output using a ‘handler of last resort’, stored in
     ‘logging.lastResort’.  This internal handler is not associated with
     any logger, and acts like a *note StreamHandler: c46. which writes
     the event description message to the current value of ‘sys.stderr’
     (therefore respecting any redirections which may be in effect).  No
     formatting is done on the message - just the bare event description
     message is printed.  The handler’s level is set to ‘WARNING’, so
     all events at this and greater severities will be output.

To obtain the pre-3.2 behaviour, ‘logging.lastResort’ can be set to
‘None’.


File: python.info,  Node: Configuring Logging for a Library,  Prev: What happens if no configuration is provided,  Up: Advanced Logging Tutorial

10.6.2.7 Configuring Logging for a Library
..........................................

When developing a library which uses logging, you should take care to
document how the library uses logging - for example, the names of
loggers used.  Some consideration also needs to be given to its logging
configuration.  If the using application does not use logging, and
library code makes logging calls, then (as described in the previous
section) events of severity ‘WARNING’ and greater will be printed to
‘sys.stderr’.  This is regarded as the best default behaviour.

If for some reason you `don’t' want these messages printed in the
absence of any logging configuration, you can attach a do-nothing
handler to the top-level logger for your library.  This avoids the
message being printed, since a handler will always be found for the
library’s events: it just doesn’t produce any output.  If the library
user configures logging for application use, presumably that
configuration will add some handlers, and if levels are suitably
configured then logging calls made in library code will send output to
those handlers, as normal.

A do-nothing handler is included in the logging package: *note
NullHandler: ce6. (since Python 3.1).  An instance of this handler could
be added to the top-level logger of the logging namespace used by the
library (`if' you want to prevent your library’s logged events being
output to ‘sys.stderr’ in the absence of logging configuration).  If all
logging by a library `foo' is done using loggers with names matching
‘foo.x’, ‘foo.x.y’, etc.  then the code:

     import logging
     logging.getLogger('foo').addHandler(logging.NullHandler())

should have the desired effect.  If an organisation produces a number of
libraries, then the logger name specified can be ‘orgname.foo’ rather
than just ‘foo’.

     Note: It is strongly advised that you `do not add any handlers
     other than' *note NullHandler: ce6. `to your library’s loggers'.
     This is because the configuration of handlers is the prerogative of
     the application developer who uses your library.  The application
     developer knows their target audience and what handlers are most
     appropriate for their application: if you add handlers ‘under the
     hood’, you might well interfere with their ability to carry out
     unit tests and deliver logs which suit their requirements.


File: python.info,  Node: Logging Levels<2>,  Next: Useful Handlers,  Prev: Advanced Logging Tutorial,  Up: Logging HOWTO

10.6.3 Logging Levels
---------------------

The numeric values of logging levels are given in the following table.
These are primarily of interest if you want to define your own levels,
and need them to have specific values relative to the predefined levels.
If you define a level with the same numeric value, it overwrites the
predefined value; the predefined name is lost.

Level              Numeric value
                   
---------------------------------------
                   
‘CRITICAL’         50
                   
                   
‘ERROR’            40
                   
                   
‘WARNING’          30
                   
                   
‘INFO’             20
                   
                   
‘DEBUG’            10
                   
                   
‘NOTSET’           0
                   

Levels can also be associated with loggers, being set either by the
developer or through loading a saved logging configuration.  When a
logging method is called on a logger, the logger compares its own level
with the level associated with the method call.  If the logger’s level
is higher than the method call’s, no logging message is actually
generated.  This is the basic mechanism controlling the verbosity of
logging output.

Logging messages are encoded as instances of the *note LogRecord: 9ec.
class.  When a logger decides to actually log an event, a *note
LogRecord: 9ec. instance is created from the logging message.

Logging messages are subjected to a dispatch mechanism through the use
of `handlers', which are instances of subclasses of the *note Handler:
21df. class.  Handlers are responsible for ensuring that a logged
message (in the form of a *note LogRecord: 9ec.) ends up in a particular
location (or set of locations) which is useful for the target audience
for that message (such as end users, support desk staff, system
administrators, developers).  Handlers are passed *note LogRecord: 9ec.
instances intended for particular destinations.  Each logger can have
zero, one or more handlers associated with it (via the *note
addHandler(): 21e7. method of *note Logger: 4ae.).  In addition to any
handlers directly associated with a logger, `all handlers associated
with all ancestors of the logger' are called to dispatch the message
(unless the `propagate' flag for a logger is set to a false value, at
which point the passing to ancestor handlers stops).

Just as for loggers, handlers can have levels associated with them.  A
handler’s level acts as a filter in the same way as a logger’s level
does.  If a handler decides to actually dispatch an event, the *note
emit(): 21fe. method is used to send the message to its destination.
Most user-defined subclasses of *note Handler: 21df. will need to
override this *note emit(): 21fe.

* Menu:

* Custom Levels::


File: python.info,  Node: Custom Levels,  Up: Logging Levels<2>

10.6.3.1 Custom Levels
......................

Defining your own levels is possible, but should not be necessary, as
the existing levels have been chosen on the basis of practical
experience.  However, if you are convinced that you need custom levels,
great care should be exercised when doing this, and it is possibly `a
very bad idea to define custom levels if you are developing a library'.
That’s because if multiple library authors all define their own custom
levels, there is a chance that the logging output from such multiple
libraries used together will be difficult for the using developer to
control and/or interpret, because a given numeric value might mean
different things for different libraries.


File: python.info,  Node: Useful Handlers,  Next: Exceptions raised during logging,  Prev: Logging Levels<2>,  Up: Logging HOWTO

10.6.4 Useful Handlers
----------------------

In addition to the base *note Handler: 21df. class, many useful
subclasses are provided:

  1. *note StreamHandler: c46. instances send messages to streams
     (file-like objects).

  2. *note FileHandler: 2245. instances send messages to disk files.

  3. *note BaseRotatingHandler: 225b. is the base class for handlers
     that rotate log files at a certain point.  It is not meant to be
     instantiated directly.  Instead, use *note RotatingFileHandler:
     2236. or *note TimedRotatingFileHandler: 959.

  4. *note RotatingFileHandler: 2236. instances send messages to disk
     files, with support for maximum log file sizes and log file
     rotation.

  5. *note TimedRotatingFileHandler: 959. instances send messages to
     disk files, rotating the log file at certain timed intervals.

  6. *note SocketHandler: 95a. instances send messages to TCP/IP
     sockets.  Since 3.4, Unix domain sockets are also supported.

  7. *note DatagramHandler: 95b. instances send messages to UDP sockets.
     Since 3.4, Unix domain sockets are also supported.

  8. *note SMTPHandler: 2288. instances send messages to a designated
     email address.

  9. *note SysLogHandler: afb. instances send messages to a Unix syslog
     daemon, possibly on a remote machine.

  10. *note NTEventLogHandler: 2280. instances send messages to a
     Windows NT/2000/XP event log.

  11. *note MemoryHandler: 223f. instances send messages to a buffer in
     memory, which is flushed whenever specific criteria are met.

  12. *note HTTPHandler: 802. instances send messages to an HTTP server
     using either ‘GET’ or ‘POST’ semantics.

  13. *note WatchedFileHandler: 2257. instances watch the file they are
     logging to.  If the file changes, it is closed and reopened using
     the file name.  This handler is only useful on Unix-like systems;
     Windows does not support the underlying mechanism used.

  14. *note QueueHandler: 229b. instances send messages to a queue, such
     as those implemented in the *note queue: da. or *note
     multiprocessing: b7. modules.

  15. *note NullHandler: ce6. instances do nothing with error messages.
     They are used by library developers who want to use logging, but
     want to avoid the ‘No handlers could be found for logger XXX’
     message which can be displayed if the library user has not
     configured logging.  See *note Configuring Logging for a Library:
     2254. for more information.

New in version 3.1: The *note NullHandler: ce6. class.

New in version 3.2: The *note QueueHandler: 229b. class.

The *note NullHandler: ce6, *note StreamHandler: c46. and *note
FileHandler: 2245. classes are defined in the core logging package.  The
other handlers are defined in a sub-module, *note logging.handlers: ac.
(There is also another sub-module, *note logging.config: ab, for
configuration functionality.)

Logged messages are formatted for presentation through instances of the
*note Formatter: 21de. class.  They are initialized with a format string
suitable for use with the % operator and a dictionary.

For formatting multiple messages in a batch, instances of
‘BufferingFormatter’ can be used.  In addition to the format string
(which is applied to each message in the batch), there is provision for
header and trailer format strings.

When filtering based on logger level and/or handler level is not enough,
instances of *note Filter: c48. can be added to both *note Logger: 4ae.
and *note Handler: 21df. instances (through their *note addFilter():
21f6. method).  Before deciding to process a message further, both
loggers and handlers consult all their filters for permission.  If any
filter returns a false value, the message is not processed further.

The basic *note Filter: c48. functionality allows filtering by specific
logger name.  If this feature is used, messages sent to the named logger
and its children are allowed through the filter, and all others dropped.


File: python.info,  Node: Exceptions raised during logging,  Next: Using arbitrary objects as messages,  Prev: Useful Handlers,  Up: Logging HOWTO

10.6.5 Exceptions raised during logging
---------------------------------------

The logging package is designed to swallow exceptions which occur while
logging in production.  This is so that errors which occur while
handling logging events - such as logging misconfiguration, network or
other similar errors - do not cause the application using logging to
terminate prematurely.

*note SystemExit: 6f3. and *note KeyboardInterrupt: 2cc. exceptions are
never swallowed.  Other exceptions which occur during the *note emit():
21fe. method of a *note Handler: 21df. subclass are passed to its *note
handleError(): 21fd. method.

The default implementation of *note handleError(): 21fd. in *note
Handler: 21df. checks to see if a module-level variable,
‘raiseExceptions’, is set.  If set, a traceback is printed to *note
sys.stderr: 1ea.  If not set, the exception is swallowed.

     Note: The default value of ‘raiseExceptions’ is ‘True’.  This is
     because during development, you typically want to be notified of
     any exceptions that occur.  It’s advised that you set
     ‘raiseExceptions’ to ‘False’ for production usage.


File: python.info,  Node: Using arbitrary objects as messages,  Next: Optimization,  Prev: Exceptions raised during logging,  Up: Logging HOWTO

10.6.6 Using arbitrary objects as messages
------------------------------------------

In the preceding sections and examples, it has been assumed that the
message passed when logging the event is a string.  However, this is not
the only possibility.  You can pass an arbitrary object as a message,
and its *note __str__(): ef9. method will be called when the logging
system needs to convert it to a string representation.  In fact, if you
want to, you can avoid computing a string representation altogether -
for example, the *note SocketHandler: 95a. emits an event by pickling it
and sending it over the wire.


File: python.info,  Node: Optimization,  Prev: Using arbitrary objects as messages,  Up: Logging HOWTO

10.6.7 Optimization
-------------------

Formatting of message arguments is deferred until it cannot be avoided.
However, computing the arguments passed to the logging method can also
be expensive, and you may want to avoid doing it if the logger will just
throw away your event.  To decide what to do, you can call the *note
isEnabledFor(): 21dd. method which takes a level argument and returns
true if the event would be created by the Logger for that level of call.
You can write code like this:

     if logger.isEnabledFor(logging.DEBUG):
         logger.debug('Message with %s, %s', expensive_func1(),
                                             expensive_func2())

so that if the logger’s threshold is set above ‘DEBUG’, the calls to
‘expensive_func1()’ and ‘expensive_func2()’ are never made.

     Note: In some cases, *note isEnabledFor(): 21dd. can itself be more
     expensive than you’d like (e.g.  for deeply nested loggers where an
     explicit level is only set high up in the logger hierarchy).  In
     such cases (or if you want to avoid calling a method in tight
     loops), you can cache the result of a call to *note isEnabledFor():
     21dd. in a local or instance variable, and use that instead of
     calling the method each time.  Such a cached value would only need
     to be recomputed when the logging configuration changes dynamically
     while the application is running (which is not all that common).

There are other optimizations which can be made for specific
applications which need more precise control over what logging
information is collected.  Here’s a list of things you can do to avoid
processing during logging which you don’t need:

What you don’t want to collect                      How to avoid collecting it
                                                    
-------------------------------------------------------------------------------------------------
                                                    
Information about where calls were made from.       Set ‘logging._srcfile’ to ‘None’.  This
                                                    avoids calling *note sys._getframe(): f25,
                                                    which may help to speed up your code in
                                                    environments like PyPy (which can’t speed
                                                    up code that uses
                                                    *note sys._getframe(): f25.).
                                                    
                                                    
Threading information.                              Set ‘logging.logThreads’ to ‘0’.
                                                    
                                                    
Process information.                                Set ‘logging.logProcesses’ to ‘0’.
                                                    

Also note that the core logging module only includes the basic handlers.
If you don’t import *note logging.handlers: ac. and *note
logging.config: ab, they won’t take up any memory.

See also
........

Module *note logging: aa.

     API reference for the logging module.

Module *note logging.config: ab.

     Configuration API for the logging module.

Module *note logging.handlers: ac.

     Useful handlers included with the logging module.

*note A logging cookbook: c45.


File: python.info,  Node: Logging Cookbook,  Next: Regular Expression HOWTO,  Prev: Logging HOWTO,  Up: Python HOWTOs

10.7 Logging Cookbook
=====================


Author: Vinay Sajip <vinay_sajip at red-dove dot com>

This page contains a number of recipes related to logging, which have
been found useful in the past.

* Menu:

* Using logging in multiple modules::
* Logging from multiple threads::
* Multiple handlers and formatters::
* Logging to multiple destinations::
* Configuration server example::
* Dealing with handlers that block::
* Sending and receiving logging events across a network::
* Adding contextual information to your logging output::
* Logging to a single file from multiple processes::
* Using file rotation::
* Use of alternative formatting styles::
* Customizing LogRecord::
* Subclassing QueueHandler - a ZeroMQ example::
* Subclassing QueueListener - a ZeroMQ example::
* An example dictionary-based configuration::
* Using a rotator and namer to customize log rotation processing::
* A more elaborate multiprocessing example::
* Inserting a BOM into messages sent to a SysLogHandler::
* Implementing structured logging::
* Customizing handlers with dictConfig(): Customizing handlers with dictConfig.
* Using particular formatting styles throughout your application::
* Configuring filters with dictConfig(): Configuring filters with dictConfig.
* Customized exception formatting::
* Speaking logging messages::
* Buffering logging messages and outputting them conditionally::
* Formatting times using UTC (GMT) via configuration: Formatting times using UTC GMT via configuration.
* Using a context manager for selective logging::
* A CLI application starter template::
* A Qt GUI for logging::
* Patterns to avoid::


File: python.info,  Node: Using logging in multiple modules,  Next: Logging from multiple threads,  Up: Logging Cookbook

10.7.1 Using logging in multiple modules
----------------------------------------

Multiple calls to ‘logging.getLogger('someLogger')’ return a reference
to the same logger object.  This is true not only within the same
module, but also across modules as long as it is in the same Python
interpreter process.  It is true for references to the same object;
additionally, application code can define and configure a parent logger
in one module and create (but not configure) a child logger in a
separate module, and all logger calls to the child will pass up to the
parent.  Here is a main module:

     import logging
     import auxiliary_module

     # create logger with 'spam_application'
     logger = logging.getLogger('spam_application')
     logger.setLevel(logging.DEBUG)
     # create file handler which logs even debug messages
     fh = logging.FileHandler('spam.log')
     fh.setLevel(logging.DEBUG)
     # create console handler with a higher log level
     ch = logging.StreamHandler()
     ch.setLevel(logging.ERROR)
     # create formatter and add it to the handlers
     formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
     fh.setFormatter(formatter)
     ch.setFormatter(formatter)
     # add the handlers to the logger
     logger.addHandler(fh)
     logger.addHandler(ch)

     logger.info('creating an instance of auxiliary_module.Auxiliary')
     a = auxiliary_module.Auxiliary()
     logger.info('created an instance of auxiliary_module.Auxiliary')
     logger.info('calling auxiliary_module.Auxiliary.do_something')
     a.do_something()
     logger.info('finished auxiliary_module.Auxiliary.do_something')
     logger.info('calling auxiliary_module.some_function()')
     auxiliary_module.some_function()
     logger.info('done with auxiliary_module.some_function()')

Here is the auxiliary module:

     import logging

     # create logger
     module_logger = logging.getLogger('spam_application.auxiliary')

     class Auxiliary:
         def __init__(self):
             self.logger = logging.getLogger('spam_application.auxiliary.Auxiliary')
             self.logger.info('creating an instance of Auxiliary')

         def do_something(self):
             self.logger.info('doing something')
             a = 1 + 1
             self.logger.info('done doing something')

     def some_function():
         module_logger.info('received a call to "some_function"')

The output looks like this:

     2005-03-23 23:47:11,663 - spam_application - INFO -
        creating an instance of auxiliary_module.Auxiliary
     2005-03-23 23:47:11,665 - spam_application.auxiliary.Auxiliary - INFO -
        creating an instance of Auxiliary
     2005-03-23 23:47:11,665 - spam_application - INFO -
        created an instance of auxiliary_module.Auxiliary
     2005-03-23 23:47:11,668 - spam_application - INFO -
        calling auxiliary_module.Auxiliary.do_something
     2005-03-23 23:47:11,668 - spam_application.auxiliary.Auxiliary - INFO -
        doing something
     2005-03-23 23:47:11,669 - spam_application.auxiliary.Auxiliary - INFO -
        done doing something
     2005-03-23 23:47:11,670 - spam_application - INFO -
        finished auxiliary_module.Auxiliary.do_something
     2005-03-23 23:47:11,671 - spam_application - INFO -
        calling auxiliary_module.some_function()
     2005-03-23 23:47:11,672 - spam_application.auxiliary - INFO -
        received a call to 'some_function'
     2005-03-23 23:47:11,673 - spam_application - INFO -
        done with auxiliary_module.some_function()


File: python.info,  Node: Logging from multiple threads,  Next: Multiple handlers and formatters,  Prev: Using logging in multiple modules,  Up: Logging Cookbook

10.7.2 Logging from multiple threads
------------------------------------

Logging from multiple threads requires no special effort.  The following
example shows logging from the main (initial) thread and another thread:

     import logging
     import threading
     import time

     def worker(arg):
         while not arg['stop']:
             logging.debug('Hi from myfunc')
             time.sleep(0.5)

     def main():
         logging.basicConfig(level=logging.DEBUG, format='%(relativeCreated)6d %(threadName)s %(message)s')
         info = {'stop': False}
         thread = threading.Thread(target=worker, args=(info,))
         thread.start()
         while True:
             try:
                 logging.debug('Hello from main')
                 time.sleep(0.75)
             except KeyboardInterrupt:
                 info['stop'] = True
                 break
         thread.join()

     if __name__ == '__main__':
         main()

When run, the script should print something like the following:

        0 Thread-1 Hi from myfunc
        3 MainThread Hello from main
      505 Thread-1 Hi from myfunc
      755 MainThread Hello from main
     1007 Thread-1 Hi from myfunc
     1507 MainThread Hello from main
     1508 Thread-1 Hi from myfunc
     2010 Thread-1 Hi from myfunc
     2258 MainThread Hello from main
     2512 Thread-1 Hi from myfunc
     3009 MainThread Hello from main
     3013 Thread-1 Hi from myfunc
     3515 Thread-1 Hi from myfunc
     3761 MainThread Hello from main
     4017 Thread-1 Hi from myfunc
     4513 MainThread Hello from main
     4518 Thread-1 Hi from myfunc

This shows the logging output interspersed as one might expect.  This
approach works for more threads than shown here, of course.


File: python.info,  Node: Multiple handlers and formatters,  Next: Logging to multiple destinations,  Prev: Logging from multiple threads,  Up: Logging Cookbook

10.7.3 Multiple handlers and formatters
---------------------------------------

Loggers are plain Python objects.  The *note addHandler(): 21e7. method
has no minimum or maximum quota for the number of handlers you may add.
Sometimes it will be beneficial for an application to log all messages
of all severities to a text file while simultaneously logging errors or
above to the console.  To set this up, simply configure the appropriate
handlers.  The logging calls in the application code will remain
unchanged.  Here is a slight modification to the previous simple
module-based configuration example:

     import logging

     logger = logging.getLogger('simple_example')
     logger.setLevel(logging.DEBUG)
     # create file handler which logs even debug messages
     fh = logging.FileHandler('spam.log')
     fh.setLevel(logging.DEBUG)
     # create console handler with a higher log level
     ch = logging.StreamHandler()
     ch.setLevel(logging.ERROR)
     # create formatter and add it to the handlers
     formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
     ch.setFormatter(formatter)
     fh.setFormatter(formatter)
     # add the handlers to logger
     logger.addHandler(ch)
     logger.addHandler(fh)

     # 'application' code
     logger.debug('debug message')
     logger.info('info message')
     logger.warning('warn message')
     logger.error('error message')
     logger.critical('critical message')

Notice that the ‘application’ code does not care about multiple
handlers.  All that changed was the addition and configuration of a new
handler named `fh'.

The ability to create new handlers with higher- or lower-severity
filters can be very helpful when writing and testing an application.
Instead of using many ‘print’ statements for debugging, use
‘logger.debug’: Unlike the print statements, which you will have to
delete or comment out later, the logger.debug statements can remain
intact in the source code and remain dormant until you need them again.
At that time, the only change that needs to happen is to modify the
severity level of the logger and/or handler to debug.


File: python.info,  Node: Logging to multiple destinations,  Next: Configuration server example,  Prev: Multiple handlers and formatters,  Up: Logging Cookbook

10.7.4 Logging to multiple destinations
---------------------------------------

Let’s say you want to log to console and file with different message
formats and in differing circumstances.  Say you want to log messages
with levels of DEBUG and higher to file, and those messages at level
INFO and higher to the console.  Let’s also assume that the file should
contain timestamps, but the console messages should not.  Here’s how you
can achieve this:

     import logging

     # set up logging to file - see previous section for more details
     logging.basicConfig(level=logging.DEBUG,
                         format='%(asctime)s %(name)-12s %(levelname)-8s %(message)s',
                         datefmt='%m-%d %H:%M',
                         filename='/temp/myapp.log',
                         filemode='w')
     # define a Handler which writes INFO messages or higher to the sys.stderr
     console = logging.StreamHandler()
     console.setLevel(logging.INFO)
     # set a format which is simpler for console use
     formatter = logging.Formatter('%(name)-12s: %(levelname)-8s %(message)s')
     # tell the handler to use this format
     console.setFormatter(formatter)
     # add the handler to the root logger
     logging.getLogger('').addHandler(console)

     # Now, we can log to the root logger, or any other logger. First the root...
     logging.info('Jackdaws love my big sphinx of quartz.')

     # Now, define a couple of other loggers which might represent areas in your
     # application:

     logger1 = logging.getLogger('myapp.area1')
     logger2 = logging.getLogger('myapp.area2')

     logger1.debug('Quick zephyrs blow, vexing daft Jim.')
     logger1.info('How quickly daft jumping zebras vex.')
     logger2.warning('Jail zesty vixen who grabbed pay from quack.')
     logger2.error('The five boxing wizards jump quickly.')

When you run this, on the console you will see

     root        : INFO     Jackdaws love my big sphinx of quartz.
     myapp.area1 : INFO     How quickly daft jumping zebras vex.
     myapp.area2 : WARNING  Jail zesty vixen who grabbed pay from quack.
     myapp.area2 : ERROR    The five boxing wizards jump quickly.

and in the file you will see something like

     10-22 22:19 root         INFO     Jackdaws love my big sphinx of quartz.
     10-22 22:19 myapp.area1  DEBUG    Quick zephyrs blow, vexing daft Jim.
     10-22 22:19 myapp.area1  INFO     How quickly daft jumping zebras vex.
     10-22 22:19 myapp.area2  WARNING  Jail zesty vixen who grabbed pay from quack.
     10-22 22:19 myapp.area2  ERROR    The five boxing wizards jump quickly.

As you can see, the DEBUG message only shows up in the file.  The other
messages are sent to both destinations.

This example uses console and file handlers, but you can use any number
and combination of handlers you choose.


File: python.info,  Node: Configuration server example,  Next: Dealing with handlers that block,  Prev: Logging to multiple destinations,  Up: Logging Cookbook

10.7.5 Configuration server example
-----------------------------------

Here is an example of a module using the logging configuration server:

     import logging
     import logging.config
     import time
     import os

     # read initial config file
     logging.config.fileConfig('logging.conf')

     # create and start listener on port 9999
     t = logging.config.listen(9999)
     t.start()

     logger = logging.getLogger('simpleExample')

     try:
         # loop through logging calls to see the difference
         # new configurations make, until Ctrl+C is pressed
         while True:
             logger.debug('debug message')
             logger.info('info message')
             logger.warning('warn message')
             logger.error('error message')
             logger.critical('critical message')
             time.sleep(5)
     except KeyboardInterrupt:
         # cleanup
         logging.config.stopListening()
         t.join()

And here is a script that takes a filename and sends that file to the
server, properly preceded with the binary-encoded length, as the new
logging configuration:

     #!/usr/bin/env python
     import socket, sys, struct

     with open(sys.argv[1], 'rb') as f:
         data_to_send = f.read()

     HOST = 'localhost'
     PORT = 9999
     s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
     print('connecting...')
     s.connect((HOST, PORT))
     print('sending config...')
     s.send(struct.pack('>L', len(data_to_send)))
     s.send(data_to_send)
     s.close()
     print('complete')


File: python.info,  Node: Dealing with handlers that block,  Next: Sending and receiving logging events across a network,  Prev: Configuration server example,  Up: Logging Cookbook

10.7.6 Dealing with handlers that block
---------------------------------------

Sometimes you have to get your logging handlers to do their work without
blocking the thread you’re logging from.  This is common in Web
applications, though of course it also occurs in other scenarios.

A common culprit which demonstrates sluggish behaviour is the *note
SMTPHandler: 2288.: sending emails can take a long time, for a number of
reasons outside the developer’s control (for example, a poorly
performing mail or network infrastructure).  But almost any
network-based handler can block: Even a *note SocketHandler: 95a.
operation may do a DNS query under the hood which is too slow (and this
query can be deep in the socket library code, below the Python layer,
and outside your control).

One solution is to use a two-part approach.  For the first part, attach
only a *note QueueHandler: 229b. to those loggers which are accessed
from performance-critical threads.  They simply write to their queue,
which can be sized to a large enough capacity or initialized with no
upper bound to their size.  The write to the queue will typically be
accepted quickly, though you will probably need to catch the *note
queue.Full: 250c. exception as a precaution in your code.  If you are a
library developer who has performance-critical threads in their code, be
sure to document this (together with a suggestion to attach only
‘QueueHandlers’ to your loggers) for the benefit of other developers who
will use your code.

The second part of the solution is *note QueueListener: 803, which has
been designed as the counterpart to *note QueueHandler: 229b.  A *note
QueueListener: 803. is very simple: it’s passed a queue and some
handlers, and it fires up an internal thread which listens to its queue
for LogRecords sent from ‘QueueHandlers’ (or any other source of
‘LogRecords’, for that matter).  The ‘LogRecords’ are removed from the
queue and passed to the handlers for processing.

The advantage of having a separate *note QueueListener: 803. class is
that you can use the same instance to service multiple ‘QueueHandlers’.
This is more resource-friendly than, say, having threaded versions of
the existing handler classes, which would eat up one thread per handler
for no particular benefit.

An example of using these two classes follows (imports omitted):

     que = queue.Queue(-1)  # no limit on size
     queue_handler = QueueHandler(que)
     handler = logging.StreamHandler()
     listener = QueueListener(que, handler)
     root = logging.getLogger()
     root.addHandler(queue_handler)
     formatter = logging.Formatter('%(threadName)s: %(message)s')
     handler.setFormatter(formatter)
     listener.start()
     # The log output will display the thread which generated
     # the event (the main thread) rather than the internal
     # thread which monitors the internal queue. This is what
     # you want to happen.
     root.warning('Look out!')
     listener.stop()

which, when run, will produce:

     MainThread: Look out!

Changed in version 3.5: Prior to Python 3.5, the *note QueueListener:
803. always passed every message received from the queue to every
handler it was initialized with.  (This was because it was assumed that
level filtering was all done on the other side, where the queue is
filled.)  From 3.5 onwards, this behaviour can be changed by passing a
keyword argument ‘respect_handler_level=True’ to the listener’s
constructor.  When this is done, the listener compares the level of each
message with the handler’s level, and only passes a message to a handler
if it’s appropriate to do so.


File: python.info,  Node: Sending and receiving logging events across a network,  Next: Adding contextual information to your logging output,  Prev: Dealing with handlers that block,  Up: Logging Cookbook

10.7.7 Sending and receiving logging events across a network
------------------------------------------------------------

Let’s say you want to send logging events across a network, and handle
them at the receiving end.  A simple way of doing this is attaching a
*note SocketHandler: 95a. instance to the root logger at the sending
end:

     import logging, logging.handlers

     rootLogger = logging.getLogger('')
     rootLogger.setLevel(logging.DEBUG)
     socketHandler = logging.handlers.SocketHandler('localhost',
                         logging.handlers.DEFAULT_TCP_LOGGING_PORT)
     # don't bother with a formatter, since a socket handler sends the event as
     # an unformatted pickle
     rootLogger.addHandler(socketHandler)

     # Now, we can log to the root logger, or any other logger. First the root...
     logging.info('Jackdaws love my big sphinx of quartz.')

     # Now, define a couple of other loggers which might represent areas in your
     # application:

     logger1 = logging.getLogger('myapp.area1')
     logger2 = logging.getLogger('myapp.area2')

     logger1.debug('Quick zephyrs blow, vexing daft Jim.')
     logger1.info('How quickly daft jumping zebras vex.')
     logger2.warning('Jail zesty vixen who grabbed pay from quack.')
     logger2.error('The five boxing wizards jump quickly.')

At the receiving end, you can set up a receiver using the *note
socketserver: f0. module.  Here is a basic working example:

     import pickle
     import logging
     import logging.handlers
     import socketserver
     import struct


     class LogRecordStreamHandler(socketserver.StreamRequestHandler):
         """Handler for a streaming logging request.

         This basically logs the record using whatever logging policy is
         configured locally.
         """

         def handle(self):
             """
             Handle multiple requests - each expected to be a 4-byte length,
             followed by the LogRecord in pickle format. Logs the record
             according to whatever policy is configured locally.
             """
             while True:
                 chunk = self.connection.recv(4)
                 if len(chunk) < 4:
                     break
                 slen = struct.unpack('>L', chunk)[0]
                 chunk = self.connection.recv(slen)
                 while len(chunk) < slen:
                     chunk = chunk + self.connection.recv(slen - len(chunk))
                 obj = self.unPickle(chunk)
                 record = logging.makeLogRecord(obj)
                 self.handleLogRecord(record)

         def unPickle(self, data):
             return pickle.loads(data)

         def handleLogRecord(self, record):
             # if a name is specified, we use the named logger rather than the one
             # implied by the record.
             if self.server.logname is not None:
                 name = self.server.logname
             else:
                 name = record.name
             logger = logging.getLogger(name)
             # N.B. EVERY record gets logged. This is because Logger.handle
             # is normally called AFTER logger-level filtering. If you want
             # to do filtering, do it at the client end to save wasting
             # cycles and network bandwidth!
             logger.handle(record)

     class LogRecordSocketReceiver(socketserver.ThreadingTCPServer):
         """
         Simple TCP socket-based logging receiver suitable for testing.
         """

         allow_reuse_address = True

         def __init__(self, host='localhost',
                      port=logging.handlers.DEFAULT_TCP_LOGGING_PORT,
                      handler=LogRecordStreamHandler):
             socketserver.ThreadingTCPServer.__init__(self, (host, port), handler)
             self.abort = 0
             self.timeout = 1
             self.logname = None

         def serve_until_stopped(self):
             import select
             abort = 0
             while not abort:
                 rd, wr, ex = select.select([self.socket.fileno()],
                                            [], [],
                                            self.timeout)
                 if rd:
                     self.handle_request()
                 abort = self.abort

     def main():
         logging.basicConfig(
             format='%(relativeCreated)5d %(name)-15s %(levelname)-8s %(message)s')
         tcpserver = LogRecordSocketReceiver()
         print('About to start TCP server...')
         tcpserver.serve_until_stopped()

     if __name__ == '__main__':
         main()

First run the server, and then the client.  On the client side, nothing
is printed on the console; on the server side, you should see something
like:

     About to start TCP server...
        59 root            INFO     Jackdaws love my big sphinx of quartz.
        59 myapp.area1     DEBUG    Quick zephyrs blow, vexing daft Jim.
        69 myapp.area1     INFO     How quickly daft jumping zebras vex.
        69 myapp.area2     WARNING  Jail zesty vixen who grabbed pay from quack.
        69 myapp.area2     ERROR    The five boxing wizards jump quickly.

Note that there are some security issues with pickle in some scenarios.
If these affect you, you can use an alternative serialization scheme by
overriding the ‘makePickle()’ method and implementing your alternative
there, as well as adapting the above script to use your alternative
serialization.

* Menu:

* Running a logging socket listener in production::


File: python.info,  Node: Running a logging socket listener in production,  Up: Sending and receiving logging events across a network

10.7.7.1 Running a logging socket listener in production
........................................................

To run a logging listener in production, you may need to use a
process-management tool such as Supervisor(1).  Here(2) is a Gist which
provides the bare-bones files to run the above functionality using
Supervisor: you will need to change the ‘/path/to/’ parts in the Gist to
reflect the actual paths you want to use.

   ---------- Footnotes ----------

   (1) http://supervisord.org/

   (2) https://gist.github.com/vsajip/4b227eeec43817465ca835ca66f75e2b


File: python.info,  Node: Adding contextual information to your logging output,  Next: Logging to a single file from multiple processes,  Prev: Sending and receiving logging events across a network,  Up: Logging Cookbook

10.7.8 Adding contextual information to your logging output
-----------------------------------------------------------

Sometimes you want logging output to contain contextual information in
addition to the parameters passed to the logging call.  For example, in
a networked application, it may be desirable to log client-specific
information in the log (e.g.  remote client’s username, or IP address).
Although you could use the `extra' parameter to achieve this, it’s not
always convenient to pass the information in this way.  While it might
be tempting to create ‘Logger’ instances on a per-connection basis, this
is not a good idea because these instances are not garbage collected.
While this is not a problem in practice, when the number of ‘Logger’
instances is dependent on the level of granularity you want to use in
logging an application, it could be hard to manage if the number of
‘Logger’ instances becomes effectively unbounded.

* Menu:

* Using LoggerAdapters to impart contextual information::
* Using Filters to impart contextual information::


File: python.info,  Node: Using LoggerAdapters to impart contextual information,  Next: Using Filters to impart contextual information,  Up: Adding contextual information to your logging output

10.7.8.1 Using LoggerAdapters to impart contextual information
..............................................................

An easy way in which you can pass contextual information to be output
along with logging event information is to use the ‘LoggerAdapter’
class.  This class is designed to look like a ‘Logger’, so that you can
call ‘debug()’, ‘info()’, ‘warning()’, ‘error()’, ‘exception()’,
‘critical()’ and ‘log()’.  These methods have the same signatures as
their counterparts in ‘Logger’, so you can use the two types of
instances interchangeably.

When you create an instance of ‘LoggerAdapter’, you pass it a ‘Logger’
instance and a dict-like object which contains your contextual
information.  When you call one of the logging methods on an instance of
‘LoggerAdapter’, it delegates the call to the underlying instance of
‘Logger’ passed to its constructor, and arranges to pass the contextual
information in the delegated call.  Here’s a snippet from the code of
‘LoggerAdapter’:

     def debug(self, msg, /, *args, **kwargs):
         """
         Delegate a debug call to the underlying logger, after adding
         contextual information from this adapter instance.
         """
         msg, kwargs = self.process(msg, kwargs)
         self.logger.debug(msg, *args, **kwargs)

The ‘process()’ method of ‘LoggerAdapter’ is where the contextual
information is added to the logging output.  It’s passed the message and
keyword arguments of the logging call, and it passes back (potentially)
modified versions of these to use in the call to the underlying logger.
The default implementation of this method leaves the message alone, but
inserts an ‘extra’ key in the keyword argument whose value is the
dict-like object passed to the constructor.  Of course, if you had
passed an ‘extra’ keyword argument in the call to the adapter, it will
be silently overwritten.

The advantage of using ‘extra’ is that the values in the dict-like
object are merged into the ‘LogRecord’ instance’s __dict__, allowing you
to use customized strings with your ‘Formatter’ instances which know
about the keys of the dict-like object.  If you need a different method,
e.g.  if you want to prepend or append the contextual information to the
message string, you just need to subclass ‘LoggerAdapter’ and override
‘process()’ to do what you need.  Here is a simple example:

     class CustomAdapter(logging.LoggerAdapter):
         """
         This example adapter expects the passed in dict-like object to have a
         'connid' key, whose value in brackets is prepended to the log message.
         """
         def process(self, msg, kwargs):
             return '[%s] %s' % (self.extra['connid'], msg), kwargs

which you can use like this:

     logger = logging.getLogger(__name__)
     adapter = CustomAdapter(logger, {'connid': some_conn_id})

Then any events that you log to the adapter will have the value of
‘some_conn_id’ prepended to the log messages.

* Menu:

* Using objects other than dicts to pass contextual information::


File: python.info,  Node: Using objects other than dicts to pass contextual information,  Up: Using LoggerAdapters to impart contextual information

10.7.8.2 Using objects other than dicts to pass contextual information
......................................................................

You don’t need to pass an actual dict to a ‘LoggerAdapter’ - you could
pass an instance of a class which implements ‘__getitem__’ and
‘__iter__’ so that it looks like a dict to logging.  This would be
useful if you want to generate values dynamically (whereas the values in
a dict would be constant).


File: python.info,  Node: Using Filters to impart contextual information,  Prev: Using LoggerAdapters to impart contextual information,  Up: Adding contextual information to your logging output

10.7.8.3 Using Filters to impart contextual information
.......................................................

You can also add contextual information to log output using a
user-defined ‘Filter’.  ‘Filter’ instances are allowed to modify the
‘LogRecords’ passed to them, including adding additional attributes
which can then be output using a suitable format string, or if needed a
custom ‘Formatter’.

For example in a web application, the request being processed (or at
least, the interesting parts of it) can be stored in a threadlocal
(*note threading.local: 244e.) variable, and then accessed from a
‘Filter’ to add, say, information from the request - say, the remote IP
address and remote user’s username - to the ‘LogRecord’, using the
attribute names ‘ip’ and ‘user’ as in the ‘LoggerAdapter’ example above.
In that case, the same format string can be used to get similar output
to that shown above.  Here’s an example script:

     import logging
     from random import choice

     class ContextFilter(logging.Filter):
         """
         This is a filter which injects contextual information into the log.

         Rather than use actual contextual information, we just use random
         data in this demo.
         """

         USERS = ['jim', 'fred', 'sheila']
         IPS = ['123.231.231.123', '127.0.0.1', '192.168.0.1']

         def filter(self, record):

             record.ip = choice(ContextFilter.IPS)
             record.user = choice(ContextFilter.USERS)
             return True

     if __name__ == '__main__':
         levels = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR, logging.CRITICAL)
         logging.basicConfig(level=logging.DEBUG,
                             format='%(asctime)-15s %(name)-5s %(levelname)-8s IP: %(ip)-15s User: %(user)-8s %(message)s')
         a1 = logging.getLogger('a.b.c')
         a2 = logging.getLogger('d.e.f')

         f = ContextFilter()
         a1.addFilter(f)
         a2.addFilter(f)
         a1.debug('A debug message')
         a1.info('An info message with %s', 'some parameters')
         for x in range(10):
             lvl = choice(levels)
             lvlname = logging.getLevelName(lvl)
             a2.log(lvl, 'A message at %s level with %d %s', lvlname, 2, 'parameters')

which, when run, produces something like:

     2010-09-06 22:38:15,292 a.b.c DEBUG    IP: 123.231.231.123 User: fred     A debug message
     2010-09-06 22:38:15,300 a.b.c INFO     IP: 192.168.0.1     User: sheila   An info message with some parameters
     2010-09-06 22:38:15,300 d.e.f CRITICAL IP: 127.0.0.1       User: sheila   A message at CRITICAL level with 2 parameters
     2010-09-06 22:38:15,300 d.e.f ERROR    IP: 127.0.0.1       User: jim      A message at ERROR level with 2 parameters
     2010-09-06 22:38:15,300 d.e.f DEBUG    IP: 127.0.0.1       User: sheila   A message at DEBUG level with 2 parameters
     2010-09-06 22:38:15,300 d.e.f ERROR    IP: 123.231.231.123 User: fred     A message at ERROR level with 2 parameters
     2010-09-06 22:38:15,300 d.e.f CRITICAL IP: 192.168.0.1     User: jim      A message at CRITICAL level with 2 parameters
     2010-09-06 22:38:15,300 d.e.f CRITICAL IP: 127.0.0.1       User: sheila   A message at CRITICAL level with 2 parameters
     2010-09-06 22:38:15,300 d.e.f DEBUG    IP: 192.168.0.1     User: jim      A message at DEBUG level with 2 parameters
     2010-09-06 22:38:15,301 d.e.f ERROR    IP: 127.0.0.1       User: sheila   A message at ERROR level with 2 parameters
     2010-09-06 22:38:15,301 d.e.f DEBUG    IP: 123.231.231.123 User: fred     A message at DEBUG level with 2 parameters
     2010-09-06 22:38:15,301 d.e.f INFO     IP: 123.231.231.123 User: fred     A message at INFO level with 2 parameters


File: python.info,  Node: Logging to a single file from multiple processes,  Next: Using file rotation,  Prev: Adding contextual information to your logging output,  Up: Logging Cookbook

10.7.9 Logging to a single file from multiple processes
-------------------------------------------------------

Although logging is thread-safe, and logging to a single file from
multiple threads in a single process `is' supported, logging to a single
file from `multiple processes' is `not' supported, because there is no
standard way to serialize access to a single file across multiple
processes in Python.  If you need to log to a single file from multiple
processes, one way of doing this is to have all the processes log to a
‘SocketHandler’, and have a separate process which implements a socket
server which reads from the socket and logs to file.  (If you prefer,
you can dedicate one thread in one of the existing processes to perform
this function.)  *note This section: 437d. documents this approach in
more detail and includes a working socket receiver which can be used as
a starting point for you to adapt in your own applications.

You could also write your own handler which uses the *note Lock: 24ee.
class from the *note multiprocessing: b7. module to serialize access to
the file from your processes.  The existing ‘FileHandler’ and subclasses
do not make use of *note multiprocessing: b7. at present, though they
may do so in the future.  Note that at present, the *note
multiprocessing: b7. module does not provide working lock functionality
on all platforms (see ‘https://bugs.python.org/issue3770’).

Alternatively, you can use a ‘Queue’ and a *note QueueHandler: 229b. to
send all logging events to one of the processes in your multi-process
application.  The following example script demonstrates how you can do
this; in the example a separate listener process listens for events sent
by other processes and logs them according to its own logging
configuration.  Although the example only demonstrates one way of doing
it (for example, you may want to use a listener thread rather than a
separate listener process – the implementation would be analogous) it
does allow for completely different logging configurations for the
listener and the other processes in your application, and can be used as
the basis for code meeting your own specific requirements:

     # You'll need these imports in your own code
     import logging
     import logging.handlers
     import multiprocessing

     # Next two import lines for this demo only
     from random import choice, random
     import time

     #
     # Because you'll want to define the logging configurations for listener and workers, the
     # listener and worker process functions take a configurer parameter which is a callable
     # for configuring logging for that process. These functions are also passed the queue,
     # which they use for communication.
     #
     # In practice, you can configure the listener however you want, but note that in this
     # simple example, the listener does not apply level or filter logic to received records.
     # In practice, you would probably want to do this logic in the worker processes, to avoid
     # sending events which would be filtered out between processes.
     #
     # The size of the rotated files is made small so you can see the results easily.
     def listener_configurer():
         root = logging.getLogger()
         h = logging.handlers.RotatingFileHandler('mptest.log', 'a', 300, 10)
         f = logging.Formatter('%(asctime)s %(processName)-10s %(name)s %(levelname)-8s %(message)s')
         h.setFormatter(f)
         root.addHandler(h)

     # This is the listener process top-level loop: wait for logging events
     # (LogRecords)on the queue and handle them, quit when you get a None for a
     # LogRecord.
     def listener_process(queue, configurer):
         configurer()
         while True:
             try:
                 record = queue.get()
                 if record is None:  # We send this as a sentinel to tell the listener to quit.
                     break
                 logger = logging.getLogger(record.name)
                 logger.handle(record)  # No level or filter logic applied - just do it!
             except Exception:
                 import sys, traceback
                 print('Whoops! Problem:', file=sys.stderr)
                 traceback.print_exc(file=sys.stderr)

     # Arrays used for random selections in this demo

     LEVELS = [logging.DEBUG, logging.INFO, logging.WARNING,
               logging.ERROR, logging.CRITICAL]

     LOGGERS = ['a.b.c', 'd.e.f']

     MESSAGES = [
         'Random message #1',
         'Random message #2',
         'Random message #3',
     ]

     # The worker configuration is done at the start of the worker process run.
     # Note that on Windows you can't rely on fork semantics, so each process
     # will run the logging configuration code when it starts.
     def worker_configurer(queue):
         h = logging.handlers.QueueHandler(queue)  # Just the one handler needed
         root = logging.getLogger()
         root.addHandler(h)
         # send all messages, for demo; no other level or filter logic applied.
         root.setLevel(logging.DEBUG)

     # This is the worker process top-level loop, which just logs ten events with
     # random intervening delays before terminating.
     # The print messages are just so you know it's doing something!
     def worker_process(queue, configurer):
         configurer(queue)
         name = multiprocessing.current_process().name
         print('Worker started: %s' % name)
         for i in range(10):
             time.sleep(random())
             logger = logging.getLogger(choice(LOGGERS))
             level = choice(LEVELS)
             message = choice(MESSAGES)
             logger.log(level, message)
         print('Worker finished: %s' % name)

     # Here's where the demo gets orchestrated. Create the queue, create and start
     # the listener, create ten workers and start them, wait for them to finish,
     # then send a None to the queue to tell the listener to finish.
     def main():
         queue = multiprocessing.Queue(-1)
         listener = multiprocessing.Process(target=listener_process,
                                            args=(queue, listener_configurer))
         listener.start()
         workers = []
         for i in range(10):
             worker = multiprocessing.Process(target=worker_process,
                                              args=(queue, worker_configurer))
             workers.append(worker)
             worker.start()
         for w in workers:
             w.join()
         queue.put_nowait(None)
         listener.join()

     if __name__ == '__main__':
         main()

A variant of the above script keeps the logging in the main process, in
a separate thread:

     import logging
     import logging.config
     import logging.handlers
     from multiprocessing import Process, Queue
     import random
     import threading
     import time

     def logger_thread(q):
         while True:
             record = q.get()
             if record is None:
                 break
             logger = logging.getLogger(record.name)
             logger.handle(record)


     def worker_process(q):
         qh = logging.handlers.QueueHandler(q)
         root = logging.getLogger()
         root.setLevel(logging.DEBUG)
         root.addHandler(qh)
         levels = [logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR,
                   logging.CRITICAL]
         loggers = ['foo', 'foo.bar', 'foo.bar.baz',
                    'spam', 'spam.ham', 'spam.ham.eggs']
         for i in range(100):
             lvl = random.choice(levels)
             logger = logging.getLogger(random.choice(loggers))
             logger.log(lvl, 'Message no. %d', i)

     if __name__ == '__main__':
         q = Queue()
         d = {
             'version': 1,
             'formatters': {
                 'detailed': {
                     'class': 'logging.Formatter',
                     'format': '%(asctime)s %(name)-15s %(levelname)-8s %(processName)-10s %(message)s'
                 }
             },
             'handlers': {
                 'console': {
                     'class': 'logging.StreamHandler',
                     'level': 'INFO',
                 },
                 'file': {
                     'class': 'logging.FileHandler',
                     'filename': 'mplog.log',
                     'mode': 'w',
                     'formatter': 'detailed',
                 },
                 'foofile': {
                     'class': 'logging.FileHandler',
                     'filename': 'mplog-foo.log',
                     'mode': 'w',
                     'formatter': 'detailed',
                 },
                 'errors': {
                     'class': 'logging.FileHandler',
                     'filename': 'mplog-errors.log',
                     'mode': 'w',
                     'level': 'ERROR',
                     'formatter': 'detailed',
                 },
             },
             'loggers': {
                 'foo': {
                     'handlers': ['foofile']
                 }
             },
             'root': {
                 'level': 'DEBUG',
                 'handlers': ['console', 'file', 'errors']
             },
         }
         workers = []
         for i in range(5):
             wp = Process(target=worker_process, name='worker %d' % (i + 1), args=(q,))
             workers.append(wp)
             wp.start()
         logging.config.dictConfig(d)
         lp = threading.Thread(target=logger_thread, args=(q,))
         lp.start()
         # At this point, the main process could do some useful work of its own
         # Once it's done that, it can wait for the workers to terminate...
         for wp in workers:
             wp.join()
         # And now tell the logging thread to finish up, too
         q.put(None)
         lp.join()

This variant shows how you can e.g.  apply configuration for particular
loggers - e.g.  the ‘foo’ logger has a special handler which stores all
events in the ‘foo’ subsystem in a file ‘mplog-foo.log’.  This will be
used by the logging machinery in the main process (even though the
logging events are generated in the worker processes) to direct the
messages to the appropriate destinations.

* Menu:

* Using concurrent.futures.ProcessPoolExecutor: Using concurrent futures ProcessPoolExecutor.
* Deploying Web applications using Gunicorn and uWSGI::


File: python.info,  Node: Using concurrent futures ProcessPoolExecutor,  Next: Deploying Web applications using Gunicorn and uWSGI,  Up: Logging to a single file from multiple processes

10.7.9.1 Using concurrent.futures.ProcessPoolExecutor
.....................................................

If you want to use *note concurrent.futures.ProcessPoolExecutor: 196. to
start your worker processes, you need to create the queue slightly
differently.  Instead of

     queue = multiprocessing.Queue(-1)

you should use

     queue = multiprocessing.Manager().Queue(-1)  # also works with the examples above

and you can then replace the worker creation from this:

     workers = []
     for i in range(10):
         worker = multiprocessing.Process(target=worker_process,
                                          args=(queue, worker_configurer))
         workers.append(worker)
         worker.start()
     for w in workers:
         w.join()

to this (remembering to first import *note concurrent.futures: 21.):

     with concurrent.futures.ProcessPoolExecutor(max_workers=10) as executor:
         for i in range(10):
             executor.submit(worker_process, queue, worker_configurer)


File: python.info,  Node: Deploying Web applications using Gunicorn and uWSGI,  Prev: Using concurrent futures ProcessPoolExecutor,  Up: Logging to a single file from multiple processes

10.7.9.2 Deploying Web applications using Gunicorn and uWSGI
............................................................

When deploying Web applications using Gunicorn(1) or uWSGI(2) (or
similar), multiple worker processes are created to handle client
requests.  In such environments, avoid creating file-based handlers
directly in your web application.  Instead, use a *note SocketHandler:
95a. to log from the web application to a listener in a separate
process.  This can be set up using a process management tool such as
Supervisor - see *note Running a logging socket listener in production:
437f. for more details.

   ---------- Footnotes ----------

   (1) https://gunicorn.org/

   (2) https://uwsgi-docs.readthedocs.io/en/latest/


File: python.info,  Node: Using file rotation,  Next: Use of alternative formatting styles,  Prev: Logging to a single file from multiple processes,  Up: Logging Cookbook

10.7.10 Using file rotation
---------------------------

Sometimes you want to let a log file grow to a certain size, then open a
new file and log to that.  You may want to keep a certain number of
these files, and when that many files have been created, rotate the
files so that the number of files and the size of the files both remain
bounded.  For this usage pattern, the logging package provides a
‘RotatingFileHandler’:

     import glob
     import logging
     import logging.handlers

     LOG_FILENAME = 'logging_rotatingfile_example.out'

     # Set up a specific logger with our desired output level
     my_logger = logging.getLogger('MyLogger')
     my_logger.setLevel(logging.DEBUG)

     # Add the log message handler to the logger
     handler = logging.handlers.RotatingFileHandler(
                   LOG_FILENAME, maxBytes=20, backupCount=5)

     my_logger.addHandler(handler)

     # Log some messages
     for i in range(20):
         my_logger.debug('i = %d' % i)

     # See what files are created
     logfiles = glob.glob('%s*' % LOG_FILENAME)

     for filename in logfiles:
         print(filename)

The result should be 6 separate files, each with part of the log history
for the application:

     logging_rotatingfile_example.out
     logging_rotatingfile_example.out.1
     logging_rotatingfile_example.out.2
     logging_rotatingfile_example.out.3
     logging_rotatingfile_example.out.4
     logging_rotatingfile_example.out.5

The most current file is always ‘logging_rotatingfile_example.out’, and
each time it reaches the size limit it is renamed with the suffix ‘.1’.
Each of the existing backup files is renamed to increment the suffix
(‘.1’ becomes ‘.2’, etc.)  and the ‘.6’ file is erased.

Obviously this example sets the log length much too small as an extreme
example.  You would want to set `maxBytes' to an appropriate value.


File: python.info,  Node: Use of alternative formatting styles,  Next: Customizing LogRecord,  Prev: Using file rotation,  Up: Logging Cookbook

10.7.11 Use of alternative formatting styles
--------------------------------------------

When logging was added to the Python standard library, the only way of
formatting messages with variable content was to use the %-formatting
method.  Since then, Python has gained two new formatting approaches:
*note string.Template: 4f1. (added in Python 2.4) and *note
str.format(): 5d5. (added in Python 2.6).

Logging (as of 3.2) provides improved support for these two additional
formatting styles.  The ‘Formatter’ class been enhanced to take an
additional, optional keyword parameter named ‘style’.  This defaults to
‘'%'’, but other possible values are ‘'{'’ and ‘'$'’, which correspond
to the other two formatting styles.  Backwards compatibility is
maintained by default (as you would expect), but by explicitly
specifying a style parameter, you get the ability to specify format
strings which work with *note str.format(): 5d5. or *note
string.Template: 4f1.  Here’s an example console session to show the
possibilities:

     >>> import logging
     >>> root = logging.getLogger()
     >>> root.setLevel(logging.DEBUG)
     >>> handler = logging.StreamHandler()
     >>> bf = logging.Formatter('{asctime} {name} {levelname:8s} {message}',
     ...                        style='{')
     >>> handler.setFormatter(bf)
     >>> root.addHandler(handler)
     >>> logger = logging.getLogger('foo.bar')
     >>> logger.debug('This is a DEBUG message')
     2010-10-28 15:11:55,341 foo.bar DEBUG    This is a DEBUG message
     >>> logger.critical('This is a CRITICAL message')
     2010-10-28 15:12:11,526 foo.bar CRITICAL This is a CRITICAL message
     >>> df = logging.Formatter('$asctime $name ${levelname} $message',
     ...                        style='$')
     >>> handler.setFormatter(df)
     >>> logger.debug('This is a DEBUG message')
     2010-10-28 15:13:06,924 foo.bar DEBUG This is a DEBUG message
     >>> logger.critical('This is a CRITICAL message')
     2010-10-28 15:13:11,494 foo.bar CRITICAL This is a CRITICAL message
     >>>

Note that the formatting of logging messages for final output to logs is
completely independent of how an individual logging message is
constructed.  That can still use %-formatting, as shown here:

     >>> logger.error('This is an%s %s %s', 'other,', 'ERROR,', 'message')
     2010-10-28 15:19:29,833 foo.bar ERROR This is another, ERROR, message
     >>>

Logging calls (‘logger.debug()’, ‘logger.info()’ etc.)  only take
positional parameters for the actual logging message itself, with
keyword parameters used only for determining options for how to handle
the actual logging call (e.g.  the ‘exc_info’ keyword parameter to
indicate that traceback information should be logged, or the ‘extra’
keyword parameter to indicate additional contextual information to be
added to the log).  So you cannot directly make logging calls using
*note str.format(): 5d5. or *note string.Template: 4f1. syntax, because
internally the logging package uses %-formatting to merge the format
string and the variable arguments.  There would be no changing this
while preserving backward compatibility, since all logging calls which
are out there in existing code will be using %-format strings.

There is, however, a way that you can use {}- and $- formatting to
construct your individual log messages.  Recall that for a message you
can use an arbitrary object as a message format string, and that the
logging package will call ‘str()’ on that object to get the actual
format string.  Consider the following two classes:

     class BraceMessage:
         def __init__(self, fmt, /, *args, **kwargs):
             self.fmt = fmt
             self.args = args
             self.kwargs = kwargs

         def __str__(self):
             return self.fmt.format(*self.args, **self.kwargs)

     class DollarMessage:
         def __init__(self, fmt, /, **kwargs):
             self.fmt = fmt
             self.kwargs = kwargs

         def __str__(self):
             from string import Template
             return Template(self.fmt).substitute(**self.kwargs)

Either of these can be used in place of a format string, to allow {}- or
$-formatting to be used to build the actual “message” part which appears
in the formatted log output in place of “%(message)s” or “{message}” or
“$message”.  It’s a little unwieldy to use the class names whenever you
want to log something, but it’s quite palatable if you use an alias such
as __ (double underscore — not to be confused with _, the single
underscore used as a synonym/alias for *note gettext.gettext(): e92. or
its brethren).

The above classes are not included in Python, though they’re easy enough
to copy and paste into your own code.  They can be used as follows
(assuming that they’re declared in a module called ‘wherever’):

     >>> from wherever import BraceMessage as __
     >>> print(__('Message with {0} {name}', 2, name='placeholders'))
     Message with 2 placeholders
     >>> class Point: pass
     ...
     >>> p = Point()
     >>> p.x = 0.5
     >>> p.y = 0.5
     >>> print(__('Message with coordinates: ({point.x:.2f}, {point.y:.2f})',
     ...       point=p))
     Message with coordinates: (0.50, 0.50)
     >>> from wherever import DollarMessage as __
     >>> print(__('Message with $num $what', num=2, what='placeholders'))
     Message with 2 placeholders
     >>>

While the above examples use ‘print()’ to show how the formatting works,
you would of course use ‘logger.debug()’ or similar to actually log
using this approach.

One thing to note is that you pay no significant performance penalty
with this approach: the actual formatting happens not when you make the
logging call, but when (and if) the logged message is actually about to
be output to a log by a handler.  So the only slightly unusual thing
which might trip you up is that the parentheses go around the format
string and the arguments, not just the format string.  That’s because
the __ notation is just syntax sugar for a constructor call to one of
the XXXMessage classes.

If you prefer, you can use a ‘LoggerAdapter’ to achieve a similar effect
to the above, as in the following example:

     import logging

     class Message:
         def __init__(self, fmt, args):
             self.fmt = fmt
             self.args = args

         def __str__(self):
             return self.fmt.format(*self.args)

     class StyleAdapter(logging.LoggerAdapter):
         def __init__(self, logger, extra=None):
             super().__init__(logger, extra or {})

         def log(self, level, msg, /, *args, **kwargs):
             if self.isEnabledFor(level):
                 msg, kwargs = self.process(msg, kwargs)
                 self.logger._log(level, Message(msg, args), (), **kwargs)

     logger = StyleAdapter(logging.getLogger(__name__))

     def main():
         logger.debug('Hello, {}', 'world!')

     if __name__ == '__main__':
         logging.basicConfig(level=logging.DEBUG)
         main()

The above script should log the message ‘Hello, world!’ when run with
Python 3.2 or later.


File: python.info,  Node: Customizing LogRecord,  Next: Subclassing QueueHandler - a ZeroMQ example,  Prev: Use of alternative formatting styles,  Up: Logging Cookbook

10.7.12 Customizing ‘LogRecord’
-------------------------------

Every logging event is represented by a *note LogRecord: 9ec. instance.
When an event is logged and not filtered out by a logger’s level, a
*note LogRecord: 9ec. is created, populated with information about the
event and then passed to the handlers for that logger (and its
ancestors, up to and including the logger where further propagation up
the hierarchy is disabled).  Before Python 3.2, there were only two
places where this creation was done:

   * *note Logger.makeRecord(): 21eb, which is called in the normal
     process of logging an event.  This invoked *note LogRecord: 9ec.
     directly to create an instance.

   * *note makeLogRecord(): 2210, which is called with a dictionary
     containing attributes to be added to the LogRecord.  This is
     typically invoked when a suitable dictionary has been received over
     the network (e.g.  in pickle form via a *note SocketHandler: 95a,
     or in JSON form via an *note HTTPHandler: 802.).

This has usually meant that if you need to do anything special with a
*note LogRecord: 9ec, you’ve had to do one of the following.

   * Create your own *note Logger: 4ae. subclass, which overrides *note
     Logger.makeRecord(): 21eb, and set it using *note setLoggerClass():
     221d. before any loggers that you care about are instantiated.

   * Add a *note Filter: c48. to a logger or handler, which does the
     necessary special manipulation you need when its *note filter():
     220b. method is called.

The first approach would be a little unwieldy in the scenario where
(say) several different libraries wanted to do different things.  Each
would attempt to set its own *note Logger: 4ae. subclass, and the one
which did this last would win.

The second approach works reasonably well for many cases, but does not
allow you to e.g.  use a specialized subclass of *note LogRecord: 9ec.
Library developers can set a suitable filter on their loggers, but they
would have to remember to do this every time they introduced a new
logger (which they would do simply by adding new packages or modules and
doing

     logger = logging.getLogger(__name__)

at module level).  It’s probably one too many things to think about.
Developers could also add the filter to a *note NullHandler: ce6.
attached to their top-level logger, but this would not be invoked if an
application developer attached a handler to a lower-level library logger
— so output from that handler would not reflect the intentions of the
library developer.

In Python 3.2 and later, *note LogRecord: 9ec. creation is done through
a factory, which you can specify.  The factory is just a callable you
can set with *note setLogRecordFactory(): 2213, and interrogate with
*note getLogRecordFactory(): 2212.  The factory is invoked with the same
signature as the *note LogRecord: 9ec. constructor, as *note LogRecord:
9ec. is the default setting for the factory.

This approach allows a custom factory to control all aspects of
LogRecord creation.  For example, you could return a subclass, or just
add some additional attributes to the record once created, using a
pattern similar to this:

     old_factory = logging.getLogRecordFactory()

     def record_factory(*args, **kwargs):
         record = old_factory(*args, **kwargs)
         record.custom_attribute = 0xdecafbad
         return record

     logging.setLogRecordFactory(record_factory)

This pattern allows different libraries to chain factories together, and
as long as they don’t overwrite each other’s attributes or
unintentionally overwrite the attributes provided as standard, there
should be no surprises.  However, it should be borne in mind that each
link in the chain adds run-time overhead to all logging operations, and
the technique should only be used when the use of a *note Filter: c48.
does not provide the desired result.


File: python.info,  Node: Subclassing QueueHandler - a ZeroMQ example,  Next: Subclassing QueueListener - a ZeroMQ example,  Prev: Customizing LogRecord,  Up: Logging Cookbook

10.7.13 Subclassing QueueHandler - a ZeroMQ example
---------------------------------------------------

You can use a ‘QueueHandler’ subclass to send messages to other kinds of
queues, for example a ZeroMQ ‘publish’ socket.  In the example below,the
socket is created separately and passed to the handler (as its ‘queue’):

     import zmq   # using pyzmq, the Python binding for ZeroMQ
     import json  # for serializing records portably

     ctx = zmq.Context()
     sock = zmq.Socket(ctx, zmq.PUB)  # or zmq.PUSH, or other suitable value
     sock.bind('tcp://*:5556')        # or wherever

     class ZeroMQSocketHandler(QueueHandler):
         def enqueue(self, record):
             self.queue.send_json(record.__dict__)


     handler = ZeroMQSocketHandler(sock)

Of course there are other ways of organizing this, for example passing
in the data needed by the handler to create the socket:

     class ZeroMQSocketHandler(QueueHandler):
         def __init__(self, uri, socktype=zmq.PUB, ctx=None):
             self.ctx = ctx or zmq.Context()
             socket = zmq.Socket(self.ctx, socktype)
             socket.bind(uri)
             super().__init__(socket)

         def enqueue(self, record):
             self.queue.send_json(record.__dict__)

         def close(self):
             self.queue.close()


File: python.info,  Node: Subclassing QueueListener - a ZeroMQ example,  Next: An example dictionary-based configuration,  Prev: Subclassing QueueHandler - a ZeroMQ example,  Up: Logging Cookbook

10.7.14 Subclassing QueueListener - a ZeroMQ example
----------------------------------------------------

You can also subclass ‘QueueListener’ to get messages from other kinds
of queues, for example a ZeroMQ ‘subscribe’ socket.  Here’s an example:

     class ZeroMQSocketListener(QueueListener):
         def __init__(self, uri, /, *handlers, **kwargs):
             self.ctx = kwargs.get('ctx') or zmq.Context()
             socket = zmq.Socket(self.ctx, zmq.SUB)
             socket.setsockopt_string(zmq.SUBSCRIBE, '')  # subscribe to everything
             socket.connect(uri)
             super().__init__(socket, *handlers, **kwargs)

         def dequeue(self):
             msg = self.queue.recv_json()
             return logging.makeLogRecord(msg)

See also
........

Module *note logging: aa.

     API reference for the logging module.

Module *note logging.config: ab.

     Configuration API for the logging module.

Module *note logging.handlers: ac.

     Useful handlers included with the logging module.

*note A basic logging tutorial: c43.

*note A more advanced logging tutorial: c44.


File: python.info,  Node: An example dictionary-based configuration,  Next: Using a rotator and namer to customize log rotation processing,  Prev: Subclassing QueueListener - a ZeroMQ example,  Up: Logging Cookbook

10.7.15 An example dictionary-based configuration
-------------------------------------------------

Below is an example of a logging configuration dictionary - it’s taken
from the documentation on the Django project(1).  This dictionary is
passed to *note dictConfig(): bfe. to put the configuration into effect:

     LOGGING = {
         'version': 1,
         'disable_existing_loggers': True,
         'formatters': {
             'verbose': {
                 'format': '%(levelname)s %(asctime)s %(module)s %(process)d %(thread)d %(message)s'
             },
             'simple': {
                 'format': '%(levelname)s %(message)s'
             },
         },
         'filters': {
             'special': {
                 '()': 'project.logging.SpecialFilter',
                 'foo': 'bar',
             }
         },
         'handlers': {
             'null': {
                 'level':'DEBUG',
                 'class':'django.utils.log.NullHandler',
             },
             'console':{
                 'level':'DEBUG',
                 'class':'logging.StreamHandler',
                 'formatter': 'simple'
             },
             'mail_admins': {
                 'level': 'ERROR',
                 'class': 'django.utils.log.AdminEmailHandler',
                 'filters': ['special']
             }
         },
         'loggers': {
             'django': {
                 'handlers':['null'],
                 'propagate': True,
                 'level':'INFO',
             },
             'django.request': {
                 'handlers': ['mail_admins'],
                 'level': 'ERROR',
                 'propagate': False,
             },
             'myproject.custom': {
                 'handlers': ['console', 'mail_admins'],
                 'level': 'INFO',
                 'filters': ['special']
             }
         }
     }

For more information about this configuration, you can see the relevant
section(2) of the Django documentation.

   ---------- Footnotes ----------

   (1) 
https://docs.djangoproject.com/en/stable/topics/logging/#configuring-logging

   (2) 
https://docs.djangoproject.com/en/stable/topics/logging/#configuring-logging


File: python.info,  Node: Using a rotator and namer to customize log rotation processing,  Next: A more elaborate multiprocessing example,  Prev: An example dictionary-based configuration,  Up: Logging Cookbook

10.7.16 Using a rotator and namer to customize log rotation processing
----------------------------------------------------------------------

An example of how you can define a namer and rotator is given in the
following snippet, which shows zlib-based compression of the log file:

     def namer(name):
         return name + ".gz"

     def rotator(source, dest):
         with open(source, "rb") as sf:
             data = sf.read()
             compressed = zlib.compress(data, 9)
             with open(dest, "wb") as df:
                 df.write(compressed)
         os.remove(source)

     rh = logging.handlers.RotatingFileHandler(...)
     rh.rotator = rotator
     rh.namer = namer

These are not “true” .gz files, as they are bare compressed data, with
no “container” such as you’d find in an actual gzip file.  This snippet
is just for illustration purposes.


File: python.info,  Node: A more elaborate multiprocessing example,  Next: Inserting a BOM into messages sent to a SysLogHandler,  Prev: Using a rotator and namer to customize log rotation processing,  Up: Logging Cookbook

10.7.17 A more elaborate multiprocessing example
------------------------------------------------

The following working example shows how logging can be used with
multiprocessing using configuration files.  The configurations are
fairly simple, but serve to illustrate how more complex ones could be
implemented in a real multiprocessing scenario.

In the example, the main process spawns a listener process and some
worker processes.  Each of the main process, the listener and the
workers have three separate configurations (the workers all share the
same configuration).  We can see logging in the main process, how the
workers log to a QueueHandler and how the listener implements a
QueueListener and a more complex logging configuration, and arranges to
dispatch events received via the queue to the handlers specified in the
configuration.  Note that these configurations are purely illustrative,
but you should be able to adapt this example to your own scenario.

Here’s the script - the docstrings and the comments hopefully explain
how it works:

     import logging
     import logging.config
     import logging.handlers
     from multiprocessing import Process, Queue, Event, current_process
     import os
     import random
     import time

     class MyHandler:
         """
         A simple handler for logging events. It runs in the listener process and
         dispatches events to loggers based on the name in the received record,
         which then get dispatched, by the logging system, to the handlers
         configured for those loggers.
         """

         def handle(self, record):
             if record.name == "root":
                 logger = logging.getLogger()
             else:
                 logger = logging.getLogger(record.name)

             if logger.isEnabledFor(record.levelno):
                 # The process name is transformed just to show that it's the listener
                 # doing the logging to files and console
                 record.processName = '%s (for %s)' % (current_process().name, record.processName)
                 logger.handle(record)

     def listener_process(q, stop_event, config):
         """
         This could be done in the main process, but is just done in a separate
         process for illustrative purposes.

         This initialises logging according to the specified configuration,
         starts the listener and waits for the main process to signal completion
         via the event. The listener is then stopped, and the process exits.
         """
         logging.config.dictConfig(config)
         listener = logging.handlers.QueueListener(q, MyHandler())
         listener.start()
         if os.name == 'posix':
             # On POSIX, the setup logger will have been configured in the
             # parent process, but should have been disabled following the
             # dictConfig call.
             # On Windows, since fork isn't used, the setup logger won't
             # exist in the child, so it would be created and the message
             # would appear - hence the "if posix" clause.
             logger = logging.getLogger('setup')
             logger.critical('Should not appear, because of disabled logger ...')
         stop_event.wait()
         listener.stop()

     def worker_process(config):
         """
         A number of these are spawned for the purpose of illustration. In
         practice, they could be a heterogeneous bunch of processes rather than
         ones which are identical to each other.

         This initialises logging according to the specified configuration,
         and logs a hundred messages with random levels to randomly selected
         loggers.

         A small sleep is added to allow other processes a chance to run. This
         is not strictly needed, but it mixes the output from the different
         processes a bit more than if it's left out.
         """
         logging.config.dictConfig(config)
         levels = [logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR,
                   logging.CRITICAL]
         loggers = ['foo', 'foo.bar', 'foo.bar.baz',
                    'spam', 'spam.ham', 'spam.ham.eggs']
         if os.name == 'posix':
             # On POSIX, the setup logger will have been configured in the
             # parent process, but should have been disabled following the
             # dictConfig call.
             # On Windows, since fork isn't used, the setup logger won't
             # exist in the child, so it would be created and the message
             # would appear - hence the "if posix" clause.
             logger = logging.getLogger('setup')
             logger.critical('Should not appear, because of disabled logger ...')
         for i in range(100):
             lvl = random.choice(levels)
             logger = logging.getLogger(random.choice(loggers))
             logger.log(lvl, 'Message no. %d', i)
             time.sleep(0.01)

     def main():
         q = Queue()
         # The main process gets a simple configuration which prints to the console.
         config_initial = {
             'version': 1,
             'handlers': {
                 'console': {
                     'class': 'logging.StreamHandler',
                     'level': 'INFO'
                 }
             },
             'root': {
                 'handlers': ['console'],
                 'level': 'DEBUG'
             }
         }
         # The worker process configuration is just a QueueHandler attached to the
         # root logger, which allows all messages to be sent to the queue.
         # We disable existing loggers to disable the "setup" logger used in the
         # parent process. This is needed on POSIX because the logger will
         # be there in the child following a fork().
         config_worker = {
             'version': 1,
             'disable_existing_loggers': True,
             'handlers': {
                 'queue': {
                     'class': 'logging.handlers.QueueHandler',
                     'queue': q
                 }
             },
             'root': {
                 'handlers': ['queue'],
                 'level': 'DEBUG'
             }
         }
         # The listener process configuration shows that the full flexibility of
         # logging configuration is available to dispatch events to handlers however
         # you want.
         # We disable existing loggers to disable the "setup" logger used in the
         # parent process. This is needed on POSIX because the logger will
         # be there in the child following a fork().
         config_listener = {
             'version': 1,
             'disable_existing_loggers': True,
             'formatters': {
                 'detailed': {
                     'class': 'logging.Formatter',
                     'format': '%(asctime)s %(name)-15s %(levelname)-8s %(processName)-10s %(message)s'
                 },
                 'simple': {
                     'class': 'logging.Formatter',
                     'format': '%(name)-15s %(levelname)-8s %(processName)-10s %(message)s'
                 }
             },
             'handlers': {
                 'console': {
                     'class': 'logging.StreamHandler',
                     'formatter': 'simple',
                     'level': 'INFO'
                 },
                 'file': {
                     'class': 'logging.FileHandler',
                     'filename': 'mplog.log',
                     'mode': 'w',
                     'formatter': 'detailed'
                 },
                 'foofile': {
                     'class': 'logging.FileHandler',
                     'filename': 'mplog-foo.log',
                     'mode': 'w',
                     'formatter': 'detailed'
                 },
                 'errors': {
                     'class': 'logging.FileHandler',
                     'filename': 'mplog-errors.log',
                     'mode': 'w',
                     'formatter': 'detailed',
                     'level': 'ERROR'
                 }
             },
             'loggers': {
                 'foo': {
                     'handlers': ['foofile']
                 }
             },
             'root': {
                 'handlers': ['console', 'file', 'errors'],
                 'level': 'DEBUG'
             }
         }
         # Log some initial events, just to show that logging in the parent works
         # normally.
         logging.config.dictConfig(config_initial)
         logger = logging.getLogger('setup')
         logger.info('About to create workers ...')
         workers = []
         for i in range(5):
             wp = Process(target=worker_process, name='worker %d' % (i + 1),
                          args=(config_worker,))
             workers.append(wp)
             wp.start()
             logger.info('Started worker: %s', wp.name)
         logger.info('About to create listener ...')
         stop_event = Event()
         lp = Process(target=listener_process, name='listener',
                      args=(q, stop_event, config_listener))
         lp.start()
         logger.info('Started listener')
         # We now hang around for the workers to finish their work.
         for wp in workers:
             wp.join()
         # Workers all done, listening can now stop.
         # Logging in the parent still works normally.
         logger.info('Telling listener to stop ...')
         stop_event.set()
         lp.join()
         logger.info('All done.')

     if __name__ == '__main__':
         main()


File: python.info,  Node: Inserting a BOM into messages sent to a SysLogHandler,  Next: Implementing structured logging,  Prev: A more elaborate multiprocessing example,  Up: Logging Cookbook

10.7.18 Inserting a BOM into messages sent to a SysLogHandler
-------------------------------------------------------------

RFC 5424(1) requires that a Unicode message be sent to a syslog daemon
as a set of bytes which have the following structure: an optional
pure-ASCII component, followed by a UTF-8 Byte Order Mark (BOM),
followed by Unicode encoded using UTF-8.  (See the relevant section of
the specification(2).)

In Python 3.1, code was added to *note SysLogHandler: afb. to insert a
BOM into the message, but unfortunately, it was implemented incorrectly,
with the BOM appearing at the beginning of the message and hence not
allowing any pure-ASCII component to appear before it.

As this behaviour is broken, the incorrect BOM insertion code is being
removed from Python 3.2.4 and later.  However, it is not being replaced,
and if you want to produce RFC 5424(3)-compliant messages which include
a BOM, an optional pure-ASCII sequence before it and arbitrary Unicode
after it, encoded using UTF-8, then you need to do the following:

  1. Attach a *note Formatter: 21de. instance to your *note
     SysLogHandler: afb. instance, with a format string such as:

          'ASCII section\ufeffUnicode section'

     The Unicode code point U+FEFF, when encoded using UTF-8, will be
     encoded as a UTF-8 BOM – the byte-string ‘b'\xef\xbb\xbf'’.

  2. Replace the ASCII section with whatever placeholders you like, but
     make sure that the data that appears in there after substitution is
     always ASCII (that way, it will remain unchanged after UTF-8
     encoding).

  3. Replace the Unicode section with whatever placeholders you like; if
     the data which appears there after substitution contains characters
     outside the ASCII range, that’s fine – it will be encoded using
     UTF-8.

The formatted message `will' be encoded using UTF-8 encoding by
‘SysLogHandler’.  If you follow the above rules, you should be able to
produce RFC 5424(4)-compliant messages.  If you don’t, logging may not
complain, but your messages will not be RFC 5424-compliant, and your
syslog daemon may complain.

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc5424.html

   (2) https://tools.ietf.org/html/rfc5424.html#section-6

   (3) https://tools.ietf.org/html/rfc5424.html

   (4) https://tools.ietf.org/html/rfc5424.html


File: python.info,  Node: Implementing structured logging,  Next: Customizing handlers with dictConfig,  Prev: Inserting a BOM into messages sent to a SysLogHandler,  Up: Logging Cookbook

10.7.19 Implementing structured logging
---------------------------------------

Although most logging messages are intended for reading by humans, and
thus not readily machine-parseable, there might be circumstances where
you want to output messages in a structured format which `is' capable of
being parsed by a program (without needing complex regular expressions
to parse the log message).  This is straightforward to achieve using the
logging package.  There are a number of ways in which this could be
achieved, but the following is a simple approach which uses JSON to
serialise the event in a machine-parseable manner:

     import json
     import logging

     class StructuredMessage:
         def __init__(self, message, /, **kwargs):
             self.message = message
             self.kwargs = kwargs

         def __str__(self):
             return '%s >>> %s' % (self.message, json.dumps(self.kwargs))

     _ = StructuredMessage   # optional, to improve readability

     logging.basicConfig(level=logging.INFO, format='%(message)s')
     logging.info(_('message 1', foo='bar', bar='baz', num=123, fnum=123.456))

If the above script is run, it prints:

     message 1 >>> {"fnum": 123.456, "num": 123, "bar": "baz", "foo": "bar"}

Note that the order of items might be different according to the version
of Python used.

If you need more specialised processing, you can use a custom JSON
encoder, as in the following complete example:

     from __future__ import unicode_literals

     import json
     import logging

     # This next bit is to ensure the script runs unchanged on 2.x and 3.x
     try:
         unicode
     except NameError:
         unicode = str

     class Encoder(json.JSONEncoder):
         def default(self, o):
             if isinstance(o, set):
                 return tuple(o)
             elif isinstance(o, unicode):
                 return o.encode('unicode_escape').decode('ascii')
             return super().default(o)

     class StructuredMessage:
         def __init__(self, message, /, **kwargs):
             self.message = message
             self.kwargs = kwargs

         def __str__(self):
             s = Encoder().encode(self.kwargs)
             return '%s >>> %s' % (self.message, s)

     _ = StructuredMessage   # optional, to improve readability

     def main():
         logging.basicConfig(level=logging.INFO, format='%(message)s')
         logging.info(_('message 1', set_value={1, 2, 3}, snowman='\u2603'))

     if __name__ == '__main__':
         main()

When the above script is run, it prints:

     message 1 >>> {"snowman": "\u2603", "set_value": [1, 2, 3]}

Note that the order of items might be different according to the version
of Python used.


File: python.info,  Node: Customizing handlers with dictConfig,  Next: Using particular formatting styles throughout your application,  Prev: Implementing structured logging,  Up: Logging Cookbook

10.7.20 Customizing handlers with ‘dictConfig()’
------------------------------------------------

There are times when you want to customize logging handlers in
particular ways, and if you use *note dictConfig(): bfe. you may be able
to do this without subclassing.  As an example, consider that you may
want to set the ownership of a log file.  On POSIX, this is easily done
using *note shutil.chown(): b51, but the file handlers in the stdlib
don’t offer built-in support.  You can customize handler creation using
a plain function such as:

     def owned_file_handler(filename, mode='a', encoding=None, owner=None):
         if owner:
             if not os.path.exists(filename):
                 open(filename, 'a').close()
             shutil.chown(filename, *owner)
         return logging.FileHandler(filename, mode, encoding)

You can then specify, in a logging configuration passed to *note
dictConfig(): bfe, that a logging handler be created by calling this
function:

     LOGGING = {
         'version': 1,
         'disable_existing_loggers': False,
         'formatters': {
             'default': {
                 'format': '%(asctime)s %(levelname)s %(name)s %(message)s'
             },
         },
         'handlers': {
             'file':{
                 # The values below are popped from this dictionary and
                 # used to create the handler, set the handler's level and
                 # its formatter.
                 '()': owned_file_handler,
                 'level':'DEBUG',
                 'formatter': 'default',
                 # The values below are passed to the handler creator callable
                 # as keyword arguments.
                 'owner': ['pulse', 'pulse'],
                 'filename': 'chowntest.log',
                 'mode': 'w',
                 'encoding': 'utf-8',
             },
         },
         'root': {
             'handlers': ['file'],
             'level': 'DEBUG',
         },
     }

In this example I am setting the ownership using the ‘pulse’ user and
group, just for the purposes of illustration.  Putting it together into
a working script, ‘chowntest.py’:

     import logging, logging.config, os, shutil

     def owned_file_handler(filename, mode='a', encoding=None, owner=None):
         if owner:
             if not os.path.exists(filename):
                 open(filename, 'a').close()
             shutil.chown(filename, *owner)
         return logging.FileHandler(filename, mode, encoding)

     LOGGING = {
         'version': 1,
         'disable_existing_loggers': False,
         'formatters': {
             'default': {
                 'format': '%(asctime)s %(levelname)s %(name)s %(message)s'
             },
         },
         'handlers': {
             'file':{
                 # The values below are popped from this dictionary and
                 # used to create the handler, set the handler's level and
                 # its formatter.
                 '()': owned_file_handler,
                 'level':'DEBUG',
                 'formatter': 'default',
                 # The values below are passed to the handler creator callable
                 # as keyword arguments.
                 'owner': ['pulse', 'pulse'],
                 'filename': 'chowntest.log',
                 'mode': 'w',
                 'encoding': 'utf-8',
             },
         },
         'root': {
             'handlers': ['file'],
             'level': 'DEBUG',
         },
     }

     logging.config.dictConfig(LOGGING)
     logger = logging.getLogger('mylogger')
     logger.debug('A debug message')

To run this, you will probably need to run as ‘root’:

     $ sudo python3.3 chowntest.py
     $ cat chowntest.log
     2013-11-05 09:34:51,128 DEBUG mylogger A debug message
     $ ls -l chowntest.log
     -rw-r--r-- 1 pulse pulse 55 2013-11-05 09:34 chowntest.log

Note that this example uses Python 3.3 because that’s where *note
shutil.chown(): b51. makes an appearance.  This approach should work
with any Python version that supports *note dictConfig(): bfe. - namely,
Python 2.7, 3.2 or later.  With pre-3.3 versions, you would need to
implement the actual ownership change using e.g.  *note os.chown(): b10.

In practice, the handler-creating function may be in a utility module
somewhere in your project.  Instead of the line in the configuration:

     '()': owned_file_handler,

you could use e.g.:

     '()': 'ext://project.util.owned_file_handler',

where ‘project.util’ can be replaced with the actual name of the package
where the function resides.  In the above working script, using
‘'ext://__main__.owned_file_handler'’ should work.  Here, the actual
callable is resolved by *note dictConfig(): bfe. from the ‘ext://’
specification.

This example hopefully also points the way to how you could implement
other types of file change - e.g.  setting specific POSIX permission
bits - in the same way, using *note os.chmod(): b0f.

Of course, the approach could also be extended to types of handler other
than a *note FileHandler: 2245. - for example, one of the rotating file
handlers, or a different type of handler altogether.


File: python.info,  Node: Using particular formatting styles throughout your application,  Next: Configuring filters with dictConfig,  Prev: Customizing handlers with dictConfig,  Up: Logging Cookbook

10.7.21 Using particular formatting styles throughout your application
----------------------------------------------------------------------

In Python 3.2, the *note Formatter: 21de. gained a ‘style’ keyword
parameter which, while defaulting to ‘%’ for backward compatibility,
allowed the specification of ‘{’ or ‘$’ to support the formatting
approaches supported by *note str.format(): 5d5. and *note
string.Template: 4f1.  Note that this governs the formatting of logging
messages for final output to logs, and is completely orthogonal to how
an individual logging message is constructed.

Logging calls (*note debug(): 801, *note info(): 21e0. etc.)  only take
positional parameters for the actual logging message itself, with
keyword parameters used only for determining options for how to handle
the logging call (e.g.  the ‘exc_info’ keyword parameter to indicate
that traceback information should be logged, or the ‘extra’ keyword
parameter to indicate additional contextual information to be added to
the log).  So you cannot directly make logging calls using *note
str.format(): 5d5. or *note string.Template: 4f1. syntax, because
internally the logging package uses %-formatting to merge the format
string and the variable arguments.  There would no changing this while
preserving backward compatibility, since all logging calls which are out
there in existing code will be using %-format strings.

There have been suggestions to associate format styles with specific
loggers, but that approach also runs into backward compatibility
problems because any existing code could be using a given logger name
and using %-formatting.

For logging to work interoperably between any third-party libraries and
your code, decisions about formatting need to be made at the level of
the individual logging call.  This opens up a couple of ways in which
alternative formatting styles can be accommodated.

* Menu:

* Using LogRecord factories::
* Using custom message objects::


File: python.info,  Node: Using LogRecord factories,  Next: Using custom message objects,  Up: Using particular formatting styles throughout your application

10.7.21.1 Using LogRecord factories
...................................

In Python 3.2, along with the *note Formatter: 21de. changes mentioned
above, the logging package gained the ability to allow users to set
their own *note LogRecord: 9ec. subclasses, using the *note
setLogRecordFactory(): 2213. function.  You can use this to set your own
subclass of *note LogRecord: 9ec, which does the Right Thing by
overriding the *note getMessage(): 2211. method.  The base class
implementation of this method is where the ‘msg % args’ formatting
happens, and where you can substitute your alternate formatting;
however, you should be careful to support all formatting styles and
allow %-formatting as the default, to ensure interoperability with other
code.  Care should also be taken to call ‘str(self.msg)’, just as the
base implementation does.

Refer to the reference documentation on *note setLogRecordFactory():
2213. and *note LogRecord: 9ec. for more information.


File: python.info,  Node: Using custom message objects,  Prev: Using LogRecord factories,  Up: Using particular formatting styles throughout your application

10.7.21.2 Using custom message objects
......................................

There is another, perhaps simpler way that you can use {}- and $-
formatting to construct your individual log messages.  You may recall
(from *note Using arbitrary objects as messages: 2215.) that when
logging you can use an arbitrary object as a message format string, and
that the logging package will call *note str(): 205. on that object to
get the actual format string.  Consider the following two classes:

     class BraceMessage:
         def __init__(self, fmt, /, *args, **kwargs):
             self.fmt = fmt
             self.args = args
             self.kwargs = kwargs

         def __str__(self):
             return self.fmt.format(*self.args, **self.kwargs)

     class DollarMessage:
         def __init__(self, fmt, /, **kwargs):
             self.fmt = fmt
             self.kwargs = kwargs

         def __str__(self):
             from string import Template
             return Template(self.fmt).substitute(**self.kwargs)

Either of these can be used in place of a format string, to allow {}- or
$-formatting to be used to build the actual “message” part which appears
in the formatted log output in place of “%(message)s” or “{message}” or
“$message”.  If you find it a little unwieldy to use the class names
whenever you want to log something, you can make it more palatable if
you use an alias such as ‘M’ or ‘_’ for the message (or perhaps ‘__’, if
you are using ‘_’ for localization).

Examples of this approach are given below.  Firstly, formatting with
*note str.format(): 5d5.:

     >>> __ = BraceMessage
     >>> print(__('Message with {0} {1}', 2, 'placeholders'))
     Message with 2 placeholders
     >>> class Point: pass
     ...
     >>> p = Point()
     >>> p.x = 0.5
     >>> p.y = 0.5
     >>> print(__('Message with coordinates: ({point.x:.2f}, {point.y:.2f})', point=p))
     Message with coordinates: (0.50, 0.50)

Secondly, formatting with *note string.Template: 4f1.:

     >>> __ = DollarMessage
     >>> print(__('Message with $num $what', num=2, what='placeholders'))
     Message with 2 placeholders
     >>>

One thing to note is that you pay no significant performance penalty
with this approach: the actual formatting happens not when you make the
logging call, but when (and if) the logged message is actually about to
be output to a log by a handler.  So the only slightly unusual thing
which might trip you up is that the parentheses go around the format
string and the arguments, not just the format string.  That’s because
the __ notation is just syntax sugar for a constructor call to one of
the ‘XXXMessage’ classes shown above.


File: python.info,  Node: Configuring filters with dictConfig,  Next: Customized exception formatting,  Prev: Using particular formatting styles throughout your application,  Up: Logging Cookbook

10.7.22 Configuring filters with ‘dictConfig()’
-----------------------------------------------

You `can' configure filters using *note dictConfig(): bfe, though it
might not be obvious at first glance how to do it (hence this recipe).
Since *note Filter: c48. is the only filter class included in the
standard library, and it is unlikely to cater to many requirements (it’s
only there as a base class), you will typically need to define your own
*note Filter: c48. subclass with an overridden *note filter(): 220b.
method.  To do this, specify the ‘()’ key in the configuration
dictionary for the filter, specifying a callable which will be used to
create the filter (a class is the most obvious, but you can provide any
callable which returns a *note Filter: c48. instance).  Here is a
complete example:

     import logging
     import logging.config
     import sys

     class MyFilter(logging.Filter):
         def __init__(self, param=None):
             self.param = param

         def filter(self, record):
             if self.param is None:
                 allow = True
             else:
                 allow = self.param not in record.msg
             if allow:
                 record.msg = 'changed: ' + record.msg
             return allow

     LOGGING = {
         'version': 1,
         'filters': {
             'myfilter': {
                 '()': MyFilter,
                 'param': 'noshow',
             }
         },
         'handlers': {
             'console': {
                 'class': 'logging.StreamHandler',
                 'filters': ['myfilter']
             }
         },
         'root': {
             'level': 'DEBUG',
             'handlers': ['console']
         },
     }

     if __name__ == '__main__':
         logging.config.dictConfig(LOGGING)
         logging.debug('hello')
         logging.debug('hello - noshow')

This example shows how you can pass configuration data to the callable
which constructs the instance, in the form of keyword parameters.  When
run, the above script will print:

     changed: hello

which shows that the filter is working as configured.

A couple of extra points to note:

   * If you can’t refer to the callable directly in the configuration
     (e.g.  if it lives in a different module, and you can’t import it
     directly where the configuration dictionary is), you can use the
     form ‘ext://...’ as described in *note Access to external objects:
     223c.  For example, you could have used the text
     ‘'ext://__main__.MyFilter'’ instead of ‘MyFilter’ in the above
     example.

   * As well as for filters, this technique can also be used to
     configure custom handlers and formatters.  See *note User-defined
     objects: 2232. for more information on how logging supports using
     user-defined objects in its configuration, and see the other
     cookbook recipe *note Customizing handlers with dictConfig(): 4395.
     above.


File: python.info,  Node: Customized exception formatting,  Next: Speaking logging messages,  Prev: Configuring filters with dictConfig,  Up: Logging Cookbook

10.7.23 Customized exception formatting
---------------------------------------

There might be times when you want to do customized exception formatting
- for argument’s sake, let’s say you want exactly one line per logged
event, even when exception information is present.  You can do this with
a custom formatter class, as shown in the following example:

     import logging

     class OneLineExceptionFormatter(logging.Formatter):
         def formatException(self, exc_info):
             """
             Format an exception so that it prints on a single line.
             """
             result = super().formatException(exc_info)
             return repr(result)  # or format into one line however you want to

         def format(self, record):
             s = super().format(record)
             if record.exc_text:
                 s = s.replace('\n', '') + '|'
             return s

     def configure_logging():
         fh = logging.FileHandler('output.txt', 'w')
         f = OneLineExceptionFormatter('%(asctime)s|%(levelname)s|%(message)s|',
                                       '%d/%m/%Y %H:%M:%S')
         fh.setFormatter(f)
         root = logging.getLogger()
         root.setLevel(logging.DEBUG)
         root.addHandler(fh)

     def main():
         configure_logging()
         logging.info('Sample message')
         try:
             x = 1 / 0
         except ZeroDivisionError as e:
             logging.exception('ZeroDivisionError: %s', e)

     if __name__ == '__main__':
         main()

When run, this produces a file with exactly two lines:

     28/01/2015 07:21:23|INFO|Sample message|
     28/01/2015 07:21:23|ERROR|ZeroDivisionError: integer division or modulo by zero|'Traceback (most recent call last):\n  File "logtest7.py", line 30, in main\n    x = 1 / 0\nZeroDivisionError: integer division or modulo by zero'|

While the above treatment is simplistic, it points the way to how
exception information can be formatted to your liking.  The *note
traceback: 11c. module may be helpful for more specialized needs.


File: python.info,  Node: Speaking logging messages,  Next: Buffering logging messages and outputting them conditionally,  Prev: Customized exception formatting,  Up: Logging Cookbook

10.7.24 Speaking logging messages
---------------------------------

There might be situations when it is desirable to have logging messages
rendered in an audible rather than a visible format.  This is easy to do
if you have text-to-speech (TTS) functionality available in your system,
even if it doesn’t have a Python binding.  Most TTS systems have a
command line program you can run, and this can be invoked from a handler
using *note subprocess: f9.  It’s assumed here that TTS command line
programs won’t expect to interact with users or take a long time to
complete, and that the frequency of logged messages will be not so high
as to swamp the user with messages, and that it’s acceptable to have the
messages spoken one at a time rather than concurrently, The example
implementation below waits for one message to be spoken before the next
is processed, and this might cause other handlers to be kept waiting.
Here is a short example showing the approach, which assumes that the
‘espeak’ TTS package is available:

     import logging
     import subprocess
     import sys

     class TTSHandler(logging.Handler):
         def emit(self, record):
             msg = self.format(record)
             # Speak slowly in a female English voice
             cmd = ['espeak', '-s150', '-ven+f3', msg]
             p = subprocess.Popen(cmd, stdout=subprocess.PIPE,
                                  stderr=subprocess.STDOUT)
             # wait for the program to finish
             p.communicate()

     def configure_logging():
         h = TTSHandler()
         root = logging.getLogger()
         root.addHandler(h)
         # the default formatter just returns the message
         root.setLevel(logging.DEBUG)

     def main():
         logging.info('Hello')
         logging.debug('Goodbye')

     if __name__ == '__main__':
         configure_logging()
         sys.exit(main())

When run, this script should say “Hello” and then “Goodbye” in a female
voice.

The above approach can, of course, be adapted to other TTS systems and
even other systems altogether which can process messages via external
programs run from a command line.


File: python.info,  Node: Buffering logging messages and outputting them conditionally,  Next: Formatting times using UTC GMT via configuration,  Prev: Speaking logging messages,  Up: Logging Cookbook

10.7.25 Buffering logging messages and outputting them conditionally
--------------------------------------------------------------------

There might be situations where you want to log messages in a temporary
area and only output them if a certain condition occurs.  For example,
you may want to start logging debug events in a function, and if the
function completes without errors, you don’t want to clutter the log
with the collected debug information, but if there is an error, you want
all the debug information to be output as well as the error.

Here is an example which shows how you could do this using a decorator
for your functions where you want logging to behave this way.  It makes
use of the *note logging.handlers.MemoryHandler: 223f, which allows
buffering of logged events until some condition occurs, at which point
the buffered events are ‘flushed’ - passed to another handler (the
‘target’ handler) for processing.  By default, the ‘MemoryHandler’
flushed when its buffer gets filled up or an event whose level is
greater than or equal to a specified threshold is seen.  You can use
this recipe with a more specialised subclass of ‘MemoryHandler’ if you
want custom flushing behavior.

The example script has a simple function, ‘foo’, which just cycles
through all the logging levels, writing to ‘sys.stderr’ to say what
level it’s about to log at, and then actually logging a message at that
level.  You can pass a parameter to ‘foo’ which, if true, will log at
ERROR and CRITICAL levels - otherwise, it only logs at DEBUG, INFO and
WARNING levels.

The script just arranges to decorate ‘foo’ with a decorator which will
do the conditional logging that’s required.  The decorator takes a
logger as a parameter and attaches a memory handler for the duration of
the call to the decorated function.  The decorator can be additionally
parameterised using a target handler, a level at which flushing should
occur, and a capacity for the buffer (number of records buffered).
These default to a *note StreamHandler: c46. which writes to
‘sys.stderr’, ‘logging.ERROR’ and ‘100’ respectively.

Here’s the script:

     import logging
     from logging.handlers import MemoryHandler
     import sys

     logger = logging.getLogger(__name__)
     logger.addHandler(logging.NullHandler())

     def log_if_errors(logger, target_handler=None, flush_level=None, capacity=None):
         if target_handler is None:
             target_handler = logging.StreamHandler()
         if flush_level is None:
             flush_level = logging.ERROR
         if capacity is None:
             capacity = 100
         handler = MemoryHandler(capacity, flushLevel=flush_level, target=target_handler)

         def decorator(fn):
             def wrapper(*args, **kwargs):
                 logger.addHandler(handler)
                 try:
                     return fn(*args, **kwargs)
                 except Exception:
                     logger.exception('call failed')
                     raise
                 finally:
                     super(MemoryHandler, handler).flush()
                     logger.removeHandler(handler)
             return wrapper

         return decorator

     def write_line(s):
         sys.stderr.write('%s\n' % s)

     def foo(fail=False):
         write_line('about to log at DEBUG ...')
         logger.debug('Actually logged at DEBUG')
         write_line('about to log at INFO ...')
         logger.info('Actually logged at INFO')
         write_line('about to log at WARNING ...')
         logger.warning('Actually logged at WARNING')
         if fail:
             write_line('about to log at ERROR ...')
             logger.error('Actually logged at ERROR')
             write_line('about to log at CRITICAL ...')
             logger.critical('Actually logged at CRITICAL')
         return fail

     decorated_foo = log_if_errors(logger)(foo)

     if __name__ == '__main__':
         logger.setLevel(logging.DEBUG)
         write_line('Calling undecorated foo with False')
         assert not foo(False)
         write_line('Calling undecorated foo with True')
         assert foo(True)
         write_line('Calling decorated foo with False')
         assert not decorated_foo(False)
         write_line('Calling decorated foo with True')
         assert decorated_foo(True)

When this script is run, the following output should be observed:

     Calling undecorated foo with False
     about to log at DEBUG ...
     about to log at INFO ...
     about to log at WARNING ...
     Calling undecorated foo with True
     about to log at DEBUG ...
     about to log at INFO ...
     about to log at WARNING ...
     about to log at ERROR ...
     about to log at CRITICAL ...
     Calling decorated foo with False
     about to log at DEBUG ...
     about to log at INFO ...
     about to log at WARNING ...
     Calling decorated foo with True
     about to log at DEBUG ...
     about to log at INFO ...
     about to log at WARNING ...
     about to log at ERROR ...
     Actually logged at DEBUG
     Actually logged at INFO
     Actually logged at WARNING
     Actually logged at ERROR
     about to log at CRITICAL ...
     Actually logged at CRITICAL

As you can see, actual logging output only occurs when an event is
logged whose severity is ERROR or greater, but in that case, any
previous events at lower severities are also logged.

You can of course use the conventional means of decoration:

     @log_if_errors(logger)
     def foo(fail=False):
         ...


File: python.info,  Node: Formatting times using UTC GMT via configuration,  Next: Using a context manager for selective logging,  Prev: Buffering logging messages and outputting them conditionally,  Up: Logging Cookbook

10.7.26 Formatting times using UTC (GMT) via configuration
----------------------------------------------------------

Sometimes you want to format times using UTC, which can be done using a
class such as ‘UTCFormatter’, shown below:

     import logging
     import time

     class UTCFormatter(logging.Formatter):
         converter = time.gmtime

and you can then use the ‘UTCFormatter’ in your code instead of *note
Formatter: 21de.  If you want to do that via configuration, you can use
the *note dictConfig(): bfe. API with an approach illustrated by the
following complete example:

     import logging
     import logging.config
     import time

     class UTCFormatter(logging.Formatter):
         converter = time.gmtime

     LOGGING = {
         'version': 1,
         'disable_existing_loggers': False,
         'formatters': {
             'utc': {
                 '()': UTCFormatter,
                 'format': '%(asctime)s %(message)s',
             },
             'local': {
                 'format': '%(asctime)s %(message)s',
             }
         },
         'handlers': {
             'console1': {
                 'class': 'logging.StreamHandler',
                 'formatter': 'utc',
             },
             'console2': {
                 'class': 'logging.StreamHandler',
                 'formatter': 'local',
             },
         },
         'root': {
             'handlers': ['console1', 'console2'],
        }
     }

     if __name__ == '__main__':
         logging.config.dictConfig(LOGGING)
         logging.warning('The local time is %s', time.asctime())

When this script is run, it should print something like:

     2015-10-17 12:53:29,501 The local time is Sat Oct 17 13:53:29 2015
     2015-10-17 13:53:29,501 The local time is Sat Oct 17 13:53:29 2015

showing how the time is formatted both as local time and UTC, one for
each handler.


File: python.info,  Node: Using a context manager for selective logging,  Next: A CLI application starter template,  Prev: Formatting times using UTC GMT via configuration,  Up: Logging Cookbook

10.7.27 Using a context manager for selective logging
-----------------------------------------------------

There are times when it would be useful to temporarily change the
logging configuration and revert it back after doing something.  For
this, a context manager is the most obvious way of saving and restoring
the logging context.  Here is a simple example of such a context
manager, which allows you to optionally change the logging level and add
a logging handler purely in the scope of the context manager:

     import logging
     import sys

     class LoggingContext:
         def __init__(self, logger, level=None, handler=None, close=True):
             self.logger = logger
             self.level = level
             self.handler = handler
             self.close = close

         def __enter__(self):
             if self.level is not None:
                 self.old_level = self.logger.level
                 self.logger.setLevel(self.level)
             if self.handler:
                 self.logger.addHandler(self.handler)

         def __exit__(self, et, ev, tb):
             if self.level is not None:
                 self.logger.setLevel(self.old_level)
             if self.handler:
                 self.logger.removeHandler(self.handler)
             if self.handler and self.close:
                 self.handler.close()
             # implicit return of None => don't swallow exceptions

If you specify a level value, the logger’s level is set to that value in
the scope of the with block covered by the context manager.  If you
specify a handler, it is added to the logger on entry to the block and
removed on exit from the block.  You can also ask the manager to close
the handler for you on block exit - you could do this if you don’t need
the handler any more.

To illustrate how it works, we can add the following block of code to
the above:

     if __name__ == '__main__':
         logger = logging.getLogger('foo')
         logger.addHandler(logging.StreamHandler())
         logger.setLevel(logging.INFO)
         logger.info('1. This should appear just once on stderr.')
         logger.debug('2. This should not appear.')
         with LoggingContext(logger, level=logging.DEBUG):
             logger.debug('3. This should appear once on stderr.')
         logger.debug('4. This should not appear.')
         h = logging.StreamHandler(sys.stdout)
         with LoggingContext(logger, level=logging.DEBUG, handler=h, close=True):
             logger.debug('5. This should appear twice - once on stderr and once on stdout.')
         logger.info('6. This should appear just once on stderr.')
         logger.debug('7. This should not appear.')

We initially set the logger’s level to ‘INFO’, so message #1 appears and
message #2 doesn’t.  We then change the level to ‘DEBUG’ temporarily in
the following ‘with’ block, and so message #3 appears.  After the block
exits, the logger’s level is restored to ‘INFO’ and so message #4
doesn’t appear.  In the next ‘with’ block, we set the level to ‘DEBUG’
again but also add a handler writing to ‘sys.stdout’.  Thus, message #5
appears twice on the console (once via ‘stderr’ and once via ‘stdout’).
After the ‘with’ statement’s completion, the status is as it was before
so message #6 appears (like message #1) whereas message #7 doesn’t (just
like message #2).

If we run the resulting script, the result is as follows:

     $ python logctx.py
     1. This should appear just once on stderr.
     3. This should appear once on stderr.
     5. This should appear twice - once on stderr and once on stdout.
     5. This should appear twice - once on stderr and once on stdout.
     6. This should appear just once on stderr.

If we run it again, but pipe ‘stderr’ to ‘/dev/null’, we see the
following, which is the only message written to ‘stdout’:

     $ python logctx.py 2>/dev/null
     5. This should appear twice - once on stderr and once on stdout.

Once again, but piping ‘stdout’ to ‘/dev/null’, we get:

     $ python logctx.py >/dev/null
     1. This should appear just once on stderr.
     3. This should appear once on stderr.
     5. This should appear twice - once on stderr and once on stdout.
     6. This should appear just once on stderr.

In this case, the message #5 printed to ‘stdout’ doesn’t appear, as
expected.

Of course, the approach described here can be generalised, for example
to attach logging filters temporarily.  Note that the above code works
in Python 2 as well as Python 3.


File: python.info,  Node: A CLI application starter template,  Next: A Qt GUI for logging,  Prev: Using a context manager for selective logging,  Up: Logging Cookbook

10.7.28 A CLI application starter template
------------------------------------------

Here’s an example which shows how you can:

   * Use a logging level based on command-line arguments

   * Dispatch to multiple subcommands in separate files, all logging at
     the same level in a consistent way

   * Make use of simple, minimal configuration

Suppose we have a command-line application whose job is to stop, start
or restart some services.  This could be organised for the purposes of
illustration as a file ‘app.py’ that is the main script for the
application, with individual commands implemented in ‘start.py’,
‘stop.py’ and ‘restart.py’.  Suppose further that we want to control the
verbosity of the application via a command-line argument, defaulting to
‘logging.INFO’.  Here’s one way that ‘app.py’ could be written:

     import argparse
     import importlib
     import logging
     import os
     import sys

     def main(args=None):
         scriptname = os.path.basename(__file__)
         parser = argparse.ArgumentParser(scriptname)
         levels = ('DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL')
         parser.add_argument('--log-level', default='INFO', choices=levels)
         subparsers = parser.add_subparsers(dest='command',
                                            help='Available commands:')
         start_cmd = subparsers.add_parser('start', help='Start a service')
         start_cmd.add_argument('name', metavar='NAME',
                                help='Name of service to start')
         stop_cmd = subparsers.add_parser('stop',
                                          help='Stop one or more services')
         stop_cmd.add_argument('names', metavar='NAME', nargs='+',
                               help='Name of service to stop')
         restart_cmd = subparsers.add_parser('restart',
                                             help='Restart one or more services')
         restart_cmd.add_argument('names', metavar='NAME', nargs='+',
                                  help='Name of service to restart')
         options = parser.parse_args()
         # the code to dispatch commands could all be in this file. For the purposes
         # of illustration only, we implement each command in a separate module.
         try:
             mod = importlib.import_module(options.command)
             cmd = getattr(mod, 'command')
         except (ImportError, AttributeError):
             print('Unable to find the code for command \'%s\'' % options.command)
             return 1
         # Could get fancy here and load configuration from file or dictionary
         logging.basicConfig(level=options.log_level,
                             format='%(levelname)s %(name)s %(message)s')
         cmd(options)

     if __name__ == '__main__':
         sys.exit(main())

And the ‘start’, ‘stop’ and ‘restart’ commands can be implemented in
separate modules, like so for starting:

     # start.py
     import logging

     logger = logging.getLogger(__name__)

     def command(options):
         logger.debug('About to start %s', options.name)
         # actually do the command processing here ...
         logger.info('Started the \'%s\' service.', options.name)

and thus for stopping:

     # stop.py
     import logging

     logger = logging.getLogger(__name__)

     def command(options):
         n = len(options.names)
         if n == 1:
             plural = ''
             services = '\'%s\'' % options.names[0]
         else:
             plural = 's'
             services = ', '.join('\'%s\'' % name for name in options.names)
             i = services.rfind(', ')
             services = services[:i] + ' and ' + services[i + 2:]
         logger.debug('About to stop %s', services)
         # actually do the command processing here ...
         logger.info('Stopped the %s service%s.', services, plural)

and similarly for restarting:

     # restart.py
     import logging

     logger = logging.getLogger(__name__)

     def command(options):
         n = len(options.names)
         if n == 1:
             plural = ''
             services = '\'%s\'' % options.names[0]
         else:
             plural = 's'
             services = ', '.join('\'%s\'' % name for name in options.names)
             i = services.rfind(', ')
             services = services[:i] + ' and ' + services[i + 2:]
         logger.debug('About to restart %s', services)
         # actually do the command processing here ...
         logger.info('Restarted the %s service%s.', services, plural)

If we run this application with the default log level, we get output
like this:

     $ python app.py start foo
     INFO start Started the 'foo' service.

     $ python app.py stop foo bar
     INFO stop Stopped the 'foo' and 'bar' services.

     $ python app.py restart foo bar baz
     INFO restart Restarted the 'foo', 'bar' and 'baz' services.

The first word is the logging level, and the second word is the module
or package name of the place where the event was logged.

If we change the logging level, then we can change the information sent
to the log.  For example, if we want more information:

     $ python app.py --log-level DEBUG start foo
     DEBUG start About to start foo
     INFO start Started the 'foo' service.

     $ python app.py --log-level DEBUG stop foo bar
     DEBUG stop About to stop 'foo' and 'bar'
     INFO stop Stopped the 'foo' and 'bar' services.

     $ python app.py --log-level DEBUG restart foo bar baz
     DEBUG restart About to restart 'foo', 'bar' and 'baz'
     INFO restart Restarted the 'foo', 'bar' and 'baz' services.

And if we want less:

     $ python app.py --log-level WARNING start foo
     $ python app.py --log-level WARNING stop foo bar
     $ python app.py --log-level WARNING restart foo bar baz

In this case, the commands don’t print anything to the console, since
nothing at ‘WARNING’ level or above is logged by them.


File: python.info,  Node: A Qt GUI for logging,  Next: Patterns to avoid,  Prev: A CLI application starter template,  Up: Logging Cookbook

10.7.29 A Qt GUI for logging
----------------------------

A question that comes up from time to time is about how to log to a GUI
application.  The Qt(1) framework is a popular cross-platform UI
framework with Python bindings using PySide2(2) or PyQt5(3) libraries.

The following example shows how to log to a Qt GUI. This introduces a
simple ‘QtHandler’ class which takes a callable, which should be a slot
in the main thread that does GUI updates.  A worker thread is also
created to show how you can log to the GUI from both the UI itself (via
a button for manual logging) as well as a worker thread doing work in
the background (here, just logging messages at random levels with random
short delays in between).

The worker thread is implemented using Qt’s ‘QThread’ class rather than
the *note threading: 10b. module, as there are circumstances where one
has to use ‘QThread’, which offers better integration with other ‘Qt’
components.

The code should work with recent releases of either ‘PySide2’ or
‘PyQt5’.  You should be able to adapt the approach to earlier versions
of Qt.  Please refer to the comments in the code snippet for more
detailed information.

     import datetime
     import logging
     import random
     import sys
     import time

     # Deal with minor differences between PySide2 and PyQt5
     try:
         from PySide2 import QtCore, QtGui, QtWidgets
         Signal = QtCore.Signal
         Slot = QtCore.Slot
     except ImportError:
         from PyQt5 import QtCore, QtGui, QtWidgets
         Signal = QtCore.pyqtSignal
         Slot = QtCore.pyqtSlot


     logger = logging.getLogger(__name__)


     #
     # Signals need to be contained in a QObject or subclass in order to be correctly
     # initialized.
     #
     class Signaller(QtCore.QObject):
         signal = Signal(str, logging.LogRecord)

     #
     # Output to a Qt GUI is only supposed to happen on the main thread. So, this
     # handler is designed to take a slot function which is set up to run in the main
     # thread. In this example, the function takes a string argument which is a
     # formatted log message, and the log record which generated it. The formatted
     # string is just a convenience - you could format a string for output any way
     # you like in the slot function itself.
     #
     # You specify the slot function to do whatever GUI updates you want. The handler
     # doesn't know or care about specific UI elements.
     #
     class QtHandler(logging.Handler):
         def __init__(self, slotfunc, *args, **kwargs):
             super().__init__(*args, **kwargs)
             self.signaller = Signaller()
             self.signaller.signal.connect(slotfunc)

         def emit(self, record):
             s = self.format(record)
             self.signaller.signal.emit(s, record)

     #
     # This example uses QThreads, which means that the threads at the Python level
     # are named something like "Dummy-1". The function below gets the Qt name of the
     # current thread.
     #
     def ctname():
         return QtCore.QThread.currentThread().objectName()


     #
     # Used to generate random levels for logging.
     #
     LEVELS = (logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR,
               logging.CRITICAL)

     #
     # This worker class represents work that is done in a thread separate to the
     # main thread. The way the thread is kicked off to do work is via a button press
     # that connects to a slot in the worker.
     #
     # Because the default threadName value in the LogRecord isn't much use, we add
     # a qThreadName which contains the QThread name as computed above, and pass that
     # value in an "extra" dictionary which is used to update the LogRecord with the
     # QThread name.
     #
     # This example worker just outputs messages sequentially, interspersed with
     # random delays of the order of a few seconds.
     #
     class Worker(QtCore.QObject):
         @Slot()
         def start(self):
             extra = {'qThreadName': ctname() }
             logger.debug('Started work', extra=extra)
             i = 1
             # Let the thread run until interrupted. This allows reasonably clean
             # thread termination.
             while not QtCore.QThread.currentThread().isInterruptionRequested():
                 delay = 0.5 + random.random() * 2
                 time.sleep(delay)
                 level = random.choice(LEVELS)
                 logger.log(level, 'Message after delay of %3.1f: %d', delay, i, extra=extra)
                 i += 1

     #
     # Implement a simple UI for this cookbook example. This contains:
     #
     # * A read-only text edit window which holds formatted log messages
     # * A button to start work and log stuff in a separate thread
     # * A button to log something from the main thread
     # * A button to clear the log window
     #
     class Window(QtWidgets.QWidget):

         COLORS = {
             logging.DEBUG: 'black',
             logging.INFO: 'blue',
             logging.WARNING: 'orange',
             logging.ERROR: 'red',
             logging.CRITICAL: 'purple',
         }

         def __init__(self, app):
             super().__init__()
             self.app = app
             self.textedit = te = QtWidgets.QPlainTextEdit(self)
             # Set whatever the default monospace font is for the platform
             f = QtGui.QFont('nosuchfont')
             f.setStyleHint(f.Monospace)
             te.setFont(f)
             te.setReadOnly(True)
             PB = QtWidgets.QPushButton
             self.work_button = PB('Start background work', self)
             self.log_button = PB('Log a message at a random level', self)
             self.clear_button = PB('Clear log window', self)
             self.handler = h = QtHandler(self.update_status)
             # Remember to use qThreadName rather than threadName in the format string.
             fs = '%(asctime)s %(qThreadName)-12s %(levelname)-8s %(message)s'
             formatter = logging.Formatter(fs)
             h.setFormatter(formatter)
             logger.addHandler(h)
             # Set up to terminate the QThread when we exit
             app.aboutToQuit.connect(self.force_quit)

             # Lay out all the widgets
             layout = QtWidgets.QVBoxLayout(self)
             layout.addWidget(te)
             layout.addWidget(self.work_button)
             layout.addWidget(self.log_button)
             layout.addWidget(self.clear_button)
             self.setFixedSize(900, 400)

             # Connect the non-worker slots and signals
             self.log_button.clicked.connect(self.manual_update)
             self.clear_button.clicked.connect(self.clear_display)

             # Start a new worker thread and connect the slots for the worker
             self.start_thread()
             self.work_button.clicked.connect(self.worker.start)
             # Once started, the button should be disabled
             self.work_button.clicked.connect(lambda : self.work_button.setEnabled(False))

         def start_thread(self):
             self.worker = Worker()
             self.worker_thread = QtCore.QThread()
             self.worker.setObjectName('Worker')
             self.worker_thread.setObjectName('WorkerThread')  # for qThreadName
             self.worker.moveToThread(self.worker_thread)
             # This will start an event loop in the worker thread
             self.worker_thread.start()

         def kill_thread(self):
             # Just tell the worker to stop, then tell it to quit and wait for that
             # to happen
             self.worker_thread.requestInterruption()
             if self.worker_thread.isRunning():
                 self.worker_thread.quit()
                 self.worker_thread.wait()
             else:
                 print('worker has already exited.')

         def force_quit(self):
             # For use when the window is closed
             if self.worker_thread.isRunning():
                 self.kill_thread()

         # The functions below update the UI and run in the main thread because
         # that's where the slots are set up

         @Slot(str, logging.LogRecord)
         def update_status(self, status, record):
             color = self.COLORS.get(record.levelno, 'black')
             s = '<pre><font color="%s">%s</font></pre>' % (color, status)
             self.textedit.appendHtml(s)

         @Slot()
         def manual_update(self):
             # This function uses the formatted message passed in, but also uses
             # information from the record to format the message in an appropriate
             # color according to its severity (level).
             level = random.choice(LEVELS)
             extra = {'qThreadName': ctname() }
             logger.log(level, 'Manually logged!', extra=extra)

         @Slot()
         def clear_display(self):
             self.textedit.clear()


     def main():
         QtCore.QThread.currentThread().setObjectName('MainThread')
         logging.getLogger().setLevel(logging.DEBUG)
         app = QtWidgets.QApplication(sys.argv)
         example = Window(app)
         example.show()
         sys.exit(app.exec_())

     if __name__=='__main__':
         main()

   ---------- Footnotes ----------

   (1) https://www.qt.io/

   (2) https://pypi.org/project/PySide2/

   (3) https://pypi.org/project/PyQt5/


File: python.info,  Node: Patterns to avoid,  Prev: A Qt GUI for logging,  Up: Logging Cookbook

10.7.30 Patterns to avoid
-------------------------

Although the preceding sections have described ways of doing things you
might need to do or deal with, it is worth mentioning some usage
patterns which are `unhelpful', and which should therefore be avoided in
most cases.  The following sections are in no particular order.

* Menu:

* Opening the same log file multiple times::
* Using loggers as attributes in a class or passing them as parameters::
* Adding handlers other than NullHandler to a logger in a library::
* Creating a lot of loggers::


File: python.info,  Node: Opening the same log file multiple times,  Next: Using loggers as attributes in a class or passing them as parameters,  Up: Patterns to avoid

10.7.30.1 Opening the same log file multiple times
..................................................

On Windows, you will generally not be able to open the same file
multiple times as this will lead to a “file is in use by another
process” error.  However, on POSIX platforms you’ll not get any errors
if you open the same file multiple times.  This could be done
accidentally, for example by:

   * Adding a file handler more than once which references the same file
     (e.g.  by a copy/paste/forget-to-change error).

   * Opening two files that look different, as they have different
     names, but are the same because one is a symbolic link to the
     other.

   * Forking a process, following which both parent and child have a
     reference to the same file.  This might be through use of the *note
     multiprocessing: b7. module, for example.

Opening a file multiple times might `appear' to work most of the time,
but can lead to a number of problems in practice:

   * Logging output can be garbled because multiple threads or processes
     try to write to the same file.  Although logging guards against
     concurrent use of the same handler instance by multiple threads,
     there is no such protection if concurrent writes are attempted by
     two different threads using two different handler instances which
     happen to point to the same file.

   * An attempt to delete a file (e.g.  during file rotation) silently
     fails, because there is another reference pointing to it.  This can
     lead to confusion and wasted debugging time - log entries end up in
     unexpected places, or are lost altogether.

Use the techniques outlined in *note Logging to a single file from
multiple processes: 4385. to circumvent such issues.


File: python.info,  Node: Using loggers as attributes in a class or passing them as parameters,  Next: Adding handlers other than NullHandler to a logger in a library,  Prev: Opening the same log file multiple times,  Up: Patterns to avoid

10.7.30.2 Using loggers as attributes in a class or passing them as parameters
..............................................................................

While there might be unusual cases where you’ll need to do this, in
general there is no point because loggers are singletons.  Code can
always access a given logger instance by name using
‘logging.getLogger(name)’, so passing instances around and holding them
as instance attributes is pointless.  Note that in other languages such
as Java and C#, loggers are often static class attributes.  However,
this pattern doesn’t make sense in Python, where the module (and not the
class) is the unit of software decomposition.


File: python.info,  Node: Adding handlers other than NullHandler to a logger in a library,  Next: Creating a lot of loggers,  Prev: Using loggers as attributes in a class or passing them as parameters,  Up: Patterns to avoid

10.7.30.3 Adding handlers other than ‘NullHandler’ to a logger in a library
...........................................................................

Configuring logging by adding handlers, formatters and filters is the
responsibility of the application developer, not the library developer.
If you are maintaining a library, ensure that you don’t add handlers to
any of your loggers other than a *note NullHandler: ce6. instance.


File: python.info,  Node: Creating a lot of loggers,  Prev: Adding handlers other than NullHandler to a logger in a library,  Up: Patterns to avoid

10.7.30.4 Creating a lot of loggers
...................................

Loggers are singletons that are never freed during a script execution,
and so creating lots of loggers will use up memory which can’t then be
freed.  Rather than create a logger per e.g.  file processed or network
connection made, use the *note existing mechanisms: 2218. for passing
contextual information into your logs and restrict the loggers created
to those describing areas within your application (generally modules,
but occasionally slightly more fine-grained than that).


File: python.info,  Node: Regular Expression HOWTO,  Next: Socket Programming HOWTO,  Prev: Logging Cookbook,  Up: Python HOWTOs

10.8 Regular Expression HOWTO
=============================


Author: A.M. Kuchling <<amk@amk.ca>>

Abstract
........

This document is an introductory tutorial to using regular expressions
in Python with the *note re: dd. module.  It provides a gentler
introduction than the corresponding section in the Library Reference.

* Menu:

* Introduction: Introduction<15>.
* Simple Patterns::
* Using Regular Expressions::
* More Pattern Power::
* Modifying Strings::
* Common Problems::
* Feedback::


File: python.info,  Node: Introduction<15>,  Next: Simple Patterns,  Up: Regular Expression HOWTO

10.8.1 Introduction
-------------------

Regular expressions (called REs, or regexes, or regex patterns) are
essentially a tiny, highly specialized programming language embedded
inside Python and made available through the *note re: dd. module.
Using this little language, you specify the rules for the set of
possible strings that you want to match; this set might contain English
sentences, or e-mail addresses, or TeX commands, or anything you like.
You can then ask questions such as “Does this string match the
pattern?”, or “Is there a match for the pattern anywhere in this
string?”.  You can also use REs to modify a string or to split it apart
in various ways.

Regular expression patterns are compiled into a series of bytecodes
which are then executed by a matching engine written in C. For advanced
use, it may be necessary to pay careful attention to how the engine will
execute a given RE, and write the RE in a certain way in order to
produce bytecode that runs faster.  Optimization isn’t covered in this
document, because it requires that you have a good understanding of the
matching engine’s internals.

The regular expression language is relatively small and restricted, so
not all possible string processing tasks can be done using regular
expressions.  There are also tasks that `can' be done with regular
expressions, but the expressions turn out to be very complicated.  In
these cases, you may be better off writing Python code to do the
processing; while Python code will be slower than an elaborate regular
expression, it will also probably be more understandable.


File: python.info,  Node: Simple Patterns,  Next: Using Regular Expressions,  Prev: Introduction<15>,  Up: Regular Expression HOWTO

10.8.2 Simple Patterns
----------------------

We’ll start by learning about the simplest possible regular expressions.
Since regular expressions are used to operate on strings, we’ll begin
with the most common task: matching characters.

For a detailed explanation of the computer science underlying regular
expressions (deterministic and non-deterministic finite automata), you
can refer to almost any textbook on writing compilers.

* Menu:

* Matching Characters::
* Repeating Things::


File: python.info,  Node: Matching Characters,  Next: Repeating Things,  Up: Simple Patterns

10.8.2.1 Matching Characters
............................

Most letters and characters will simply match themselves.  For example,
the regular expression ‘test’ will match the string ‘test’ exactly.
(You can enable a case-insensitive mode that would let this RE match
‘Test’ or ‘TEST’ as well; more about this later.)

There are exceptions to this rule; some characters are special
`metacharacters', and don’t match themselves.  Instead, they signal that
some out-of-the-ordinary thing should be matched, or they affect other
portions of the RE by repeating them or changing their meaning.  Much of
this document is devoted to discussing various metacharacters and what
they do.

Here’s a complete list of the metacharacters; their meanings will be
discussed in the rest of this HOWTO.

     . ^ $ * + ? { } [ ] \ | ( )

The first metacharacters we’ll look at are ‘[’ and ‘]’.  They’re used
for specifying a character class, which is a set of characters that you
wish to match.  Characters can be listed individually, or a range of
characters can be indicated by giving two characters and separating them
by a ‘'-'’.  For example, ‘[abc]’ will match any of the characters ‘a’,
‘b’, or ‘c’; this is the same as ‘[a-c]’, which uses a range to express
the same set of characters.  If you wanted to match only lowercase
letters, your RE would be ‘[a-z]’.

Metacharacters are not active inside classes.  For example, ‘[akm$]’
will match any of the characters ‘'a'’, ‘'k'’, ‘'m'’, or ‘'$'’; ‘'$'’ is
usually a metacharacter, but inside a character class it’s stripped of
its special nature.

You can match the characters not listed within the class by
`complementing' the set.  This is indicated by including a ‘'^'’ as the
first character of the class.  For example, ‘[^5]’ will match any
character except ‘'5'’.  If the caret appears elsewhere in a character
class, it does not have special meaning.  For example: ‘[5^]’ will match
either a ‘'5'’ or a ‘'^'’.

Perhaps the most important metacharacter is the backslash, ‘\’.  As in
Python string literals, the backslash can be followed by various
characters to signal various special sequences.  It’s also used to
escape all the metacharacters so you can still match them in patterns;
for example, if you need to match a ‘[’ or ‘\’, you can precede them
with a backslash to remove their special meaning: ‘\[’ or ‘\\’.

Some of the special sequences beginning with ‘'\'’ represent predefined
sets of characters that are often useful, such as the set of digits, the
set of letters, or the set of anything that isn’t whitespace.

Let’s take an example: ‘\w’ matches any alphanumeric character.  If the
regex pattern is expressed in bytes, this is equivalent to the class
‘[a-zA-Z0-9_]’.  If the regex pattern is a string, ‘\w’ will match all
the characters marked as letters in the Unicode database provided by the
*note unicodedata: 123. module.  You can use the more restricted
definition of ‘\w’ in a string pattern by supplying the *note re.ASCII:
4cf. flag when compiling the regular expression.

The following list of special sequences isn’t complete.  For a complete
list of sequences and expanded class definitions for Unicode string
patterns, see the last part of *note Regular Expression Syntax: 1893. in
the Standard Library reference.  In general, the Unicode versions match
any character that’s in the appropriate category in the Unicode
database.

‘\d’

     Matches any decimal digit; this is equivalent to the class ‘[0-9]’.

‘\D’

     Matches any non-digit character; this is equivalent to the class
     ‘[^0-9]’.

‘\s’

     Matches any whitespace character; this is equivalent to the class
     ‘[ \t\n\r\f\v]’.

‘\S’

     Matches any non-whitespace character; this is equivalent to the
     class ‘[^ \t\n\r\f\v]’.

‘\w’

     Matches any alphanumeric character; this is equivalent to the class
     ‘[a-zA-Z0-9_]’.

‘\W’

     Matches any non-alphanumeric character; this is equivalent to the
     class ‘[^a-zA-Z0-9_]’.

These sequences can be included inside a character class.  For example,
‘[\s,.]’ is a character class that will match any whitespace character,
or ‘','’ or ‘'.'’.

The final metacharacter in this section is ‘.’.  It matches anything
except a newline character, and there’s an alternate mode (*note
re.DOTALL: 1897.) where it will match even a newline.  ‘.’ is often used
where you want to match “any character”.


File: python.info,  Node: Repeating Things,  Prev: Matching Characters,  Up: Simple Patterns

10.8.2.2 Repeating Things
.........................

Being able to match varying sets of characters is the first thing
regular expressions can do that isn’t already possible with the methods
available on strings.  However, if that was the only additional
capability of regexes, they wouldn’t be much of an advance.  Another
capability is that you can specify that portions of the RE must be
repeated a certain number of times.

The first metacharacter for repeating things that we’ll look at is ‘*’.
‘*’ doesn’t match the literal character ‘'*'’; instead, it specifies
that the previous character can be matched zero or more times, instead
of exactly once.

For example, ‘ca*t’ will match ‘'ct'’ (0 ‘'a'’ characters), ‘'cat'’ (1
‘'a'’), ‘'caaat'’ (3 ‘'a'’ characters), and so forth.

Repetitions such as ‘*’ are `greedy'; when repeating a RE, the matching
engine will try to repeat it as many times as possible.  If later
portions of the pattern don’t match, the matching engine will then back
up and try again with fewer repetitions.

A step-by-step example will make this more obvious.  Let’s consider the
expression ‘a[bcd]*b’.  This matches the letter ‘'a'’, zero or more
letters from the class ‘[bcd]’, and finally ends with a ‘'b'’.  Now
imagine matching this RE against the string ‘'abcbd'’.

Step       Matched         Explanation
                           
-----------------------------------------------------------------
                           
1          ‘a’             The ‘a’ in the RE matches.
                           
                           
2          ‘abcbd’         The engine matches ‘[bcd]*’, going
                           as far as it can, which is to the
                           end of the string.
                           
                           
3          `Failure'       The engine tries to match ‘b’, but
                           the current position is at the end
                           of the string, so it fails.
                           
                           
4          ‘abcb’          Back up, so that ‘[bcd]*’ matches
                           one less character.
                           
                           
5          `Failure'       Try ‘b’ again, but the current
                           position is at the last character,
                           which is a ‘'d'’.
                           
                           
6          ‘abc’           Back up again, so that ‘[bcd]*’ is
                           only matching ‘bc’.
                           
                           
6          ‘abcb’          Try ‘b’ again.  This time the
                           character at the current position
                           is ‘'b'’, so it succeeds.
                           

The end of the RE has now been reached, and it has matched ‘'abcb'’.
This demonstrates how the matching engine goes as far as it can at
first, and if no match is found it will then progressively back up and
retry the rest of the RE again and again.  It will back up until it has
tried zero matches for ‘[bcd]*’, and if that subsequently fails, the
engine will conclude that the string doesn’t match the RE at all.

Another repeating metacharacter is ‘+’, which matches one or more times.
Pay careful attention to the difference between ‘*’ and ‘+’; ‘*’ matches
`zero' or more times, so whatever’s being repeated may not be present at
all, while ‘+’ requires at least `one' occurrence.  To use a similar
example, ‘ca+t’ will match ‘'cat'’ (1 ‘'a'’), ‘'caaat'’ (3 ‘'a'’s), but
won’t match ‘'ct'’.

There are two more repeating qualifiers.  The question mark character,
‘?’, matches either once or zero times; you can think of it as marking
something as being optional.  For example, ‘home-?brew’ matches either
‘'homebrew'’ or ‘'home-brew'’.

The most complicated repeated qualifier is ‘{m,n}’, where `m' and `n'
are decimal integers.  This qualifier means there must be at least `m'
repetitions, and at most `n'.  For example, ‘a/{1,3}b’ will match
‘'a/b'’, ‘'a//b'’, and ‘'a///b'’.  It won’t match ‘'ab'’, which has no
slashes, or ‘'a////b'’, which has four.

You can omit either `m' or `n'; in that case, a reasonable value is
assumed for the missing value.  Omitting `m' is interpreted as a lower
limit of 0, while omitting `n' results in an upper bound of infinity.

Readers of a reductionist bent may notice that the three other
qualifiers can all be expressed using this notation.  ‘{0,}’ is the same
as ‘*’, ‘{1,}’ is equivalent to ‘+’, and ‘{0,1}’ is the same as ‘?’.
It’s better to use ‘*’, ‘+’, or ‘?’ when you can, simply because they’re
shorter and easier to read.


File: python.info,  Node: Using Regular Expressions,  Next: More Pattern Power,  Prev: Simple Patterns,  Up: Regular Expression HOWTO

10.8.3 Using Regular Expressions
--------------------------------

Now that we’ve looked at some simple regular expressions, how do we
actually use them in Python?  The *note re: dd. module provides an
interface to the regular expression engine, allowing you to compile REs
into objects and then perform matches with them.

* Menu:

* Compiling Regular Expressions::
* The Backslash Plague::
* Performing Matches::
* Module-Level Functions: Module-Level Functions<2>.
* Compilation Flags::


File: python.info,  Node: Compiling Regular Expressions,  Next: The Backslash Plague,  Up: Using Regular Expressions

10.8.3.1 Compiling Regular Expressions
......................................

Regular expressions are compiled into pattern objects, which have
methods for various operations such as searching for pattern matches or
performing string substitutions.

     >>> import re
     >>> p = re.compile('ab*')
     >>> p
     re.compile('ab*')

*note re.compile(): 54d. also accepts an optional `flags' argument, used
to enable various special features and syntax variations.  We’ll go over
the available settings later, but for now a single example will do:

     >>> p = re.compile('ab*', re.IGNORECASE)

The RE is passed to *note re.compile(): 54d. as a string.  REs are
handled as strings because regular expressions aren’t part of the core
Python language, and no special syntax was created for expressing them.
(There are applications that don’t need REs at all, so there’s no need
to bloat the language specification by including them.)  Instead, the
*note re: dd. module is simply a C extension module included with
Python, just like the *note socket: ef. or *note zlib: 14d. modules.

Putting REs in strings keeps the Python language simpler, but has one
disadvantage which is the topic of the next section.


File: python.info,  Node: The Backslash Plague,  Next: Performing Matches,  Prev: Compiling Regular Expressions,  Up: Using Regular Expressions

10.8.3.2 The Backslash Plague
.............................

As stated earlier, regular expressions use the backslash character
(‘'\'’) to indicate special forms or to allow special characters to be
used without invoking their special meaning.  This conflicts with
Python’s usage of the same character for the same purpose in string
literals.

Let’s say you want to write a RE that matches the string ‘\section’,
which might be found in a LaTeX file.  To figure out what to write in
the program code, start with the desired string to be matched.  Next,
you must escape any backslashes and other metacharacters by preceding
them with a backslash, resulting in the string ‘\\section’.  The
resulting string that must be passed to *note re.compile(): 54d. must be
‘\\section’.  However, to express this as a Python string literal, both
backslashes must be escaped `again'.

Characters              Stage
                        
-----------------------------------------------------------------------
                        
‘\section’              Text string to be matched
                        
                        
‘\\section’             Escaped backslash for
                        *note re.compile(): 54d.
                        
                        
‘"\\\\section"’         Escaped backslashes for a string literal
                        

In short, to match a literal backslash, one has to write ‘'\\\\'’ as the
RE string, because the regular expression must be ‘\\’, and each
backslash must be expressed as ‘\\’ inside a regular Python string
literal.  In REs that feature backslashes repeatedly, this leads to lots
of repeated backslashes and makes the resulting strings difficult to
understand.

The solution is to use Python’s raw string notation for regular
expressions; backslashes are not handled in any special way in a string
literal prefixed with ‘'r'’, so ‘r"\n"’ is a two-character string
containing ‘'\'’ and ‘'n'’, while ‘"\n"’ is a one-character string
containing a newline.  Regular expressions will often be written in
Python code using this raw string notation.

In addition, special escape sequences that are valid in regular
expressions, but not valid as Python string literals, now result in a
*note DeprecationWarning: 15a. and will eventually become a *note
SyntaxError: 55a, which means the sequences will be invalid if raw
string notation or escaping the backslashes isn’t used.

Regular String          Raw string
                        
-----------------------------------------------
                        
‘"ab*"’                 ‘r"ab*"’
                        
                        
‘"\\\\section"’         ‘r"\\section"’
                        
                        
‘"\\w+\\s+\\1"’         ‘r"\w+\s+\1"’
                        


File: python.info,  Node: Performing Matches,  Next: Module-Level Functions<2>,  Prev: The Backslash Plague,  Up: Using Regular Expressions

10.8.3.3 Performing Matches
...........................

Once you have an object representing a compiled regular expression, what
do you do with it?  Pattern objects have several methods and attributes.
Only the most significant ones will be covered here; consult the *note
re: dd. docs for a complete listing.

Method/Attribute       Purpose
                       
---------------------------------------------------------------------------
                       
‘match()’              Determine if the RE matches at the beginning of
                       the string.
                       
                       
‘search()’             Scan through a string, looking for any location
                       where this RE matches.
                       
                       
‘findall()’            Find all substrings where the RE matches, and
                       returns them as a list.
                       
                       
‘finditer()’           Find all substrings where the RE matches, and
                       returns them as an *note iterator: 1171.
                       

*note match(): 18a2. and *note search(): 18a3. return ‘None’ if no match
can be found.  If they’re successful, a *note match object: 984.
instance is returned, containing information about the match: where it
starts and ends, the substring it matched, and more.

You can learn about this by interactively experimenting with the *note
re: dd. module.  If you have *note tkinter: 10e. available, you may also
want to look at Tools/demo/redemo.py(1), a demonstration program
included with the Python distribution.  It allows you to enter REs and
strings, and displays whether the RE matches or fails.  ‘redemo.py’ can
be quite useful when trying to debug a complicated RE.

This HOWTO uses the standard Python interpreter for its examples.
First, run the Python interpreter, import the *note re: dd. module, and
compile a RE:

     >>> import re
     >>> p = re.compile('[a-z]+')
     >>> p
     re.compile('[a-z]+')

Now, you can try matching various strings against the RE ‘[a-z]+’.  An
empty string shouldn’t match at all, since ‘+’ means ‘one or more
repetitions’.  *note match(): 18a2. should return ‘None’ in this case,
which will cause the interpreter to print no output.  You can explicitly
print the result of ‘match()’ to make this clear.

     >>> p.match("")
     >>> print(p.match(""))
     None

Now, let’s try it on a string that it should match, such as ‘tempo’.  In
this case, *note match(): 18a2. will return a *note match object: 984,
so you should store the result in a variable for later use.

     >>> m = p.match('tempo')
     >>> m
     <re.Match object; span=(0, 5), match='tempo'>

Now you can query the *note match object: 984. for information about the
matching string.  Match object instances also have several methods and
attributes; the most important ones are:

Method/Attribute       Purpose
                       
------------------------------------------------------------------------
                       
‘group()’              Return the string matched by the RE
                       
                       
‘start()’              Return the starting position of the match
                       
                       
‘end()’                Return the ending position of the match
                       
                       
‘span()’               Return a tuple containing the (start, end)
                       positions of the match
                       

Trying these methods will soon clarify their meaning:

     >>> m.group()
     'tempo'
     >>> m.start(), m.end()
     (0, 5)
     >>> m.span()
     (0, 5)

*note group(): 18b7. returns the substring that was matched by the RE.
*note start(): 18bb. and *note end(): 18bc. return the starting and
ending index of the match.  *note span(): 18bd. returns both start and
end indexes in a single tuple.  Since the *note match(): 18a2. method
only checks if the RE matches at the start of a string, ‘start()’ will
always be zero.  However, the *note search(): 18a3. method of patterns
scans through the string, so the match may not start at zero in that
case.

     >>> print(p.match('::: message'))
     None
     >>> m = p.search('::: message'); print(m)
     <re.Match object; span=(4, 11), match='message'>
     >>> m.group()
     'message'
     >>> m.span()
     (4, 11)

In actual programs, the most common style is to store the *note match
object: 984. in a variable, and then check if it was ‘None’.  This
usually looks like:

     p = re.compile( ... )
     m = p.match( 'string goes here' )
     if m:
         print('Match found: ', m.group())
     else:
         print('No match')

Two pattern methods return all of the matches for a pattern.  *note
findall(): 18ad. returns a list of matching strings:

     >>> p = re.compile(r'\d+')
     >>> p.findall('12 drummers drumming, 11 pipers piping, 10 lords a-leaping')
     ['12', '11', '10']

The ‘r’ prefix, making the literal a raw string literal, is needed in
this example because escape sequences in a normal “cooked” string
literal that are not recognized by Python, as opposed to regular
expressions, now result in a *note DeprecationWarning: 15a. and will
eventually become a *note SyntaxError: 55a.  See *note The Backslash
Plague: 43b8.

*note findall(): 18ad. has to create the entire list before it can be
returned as the result.  The *note finditer(): 18ae. method returns a
sequence of *note match object: 984. instances as an *note iterator:
1171.:

     >>> iterator = p.finditer('12 drummers drumming, 11 ... 10 ...')
     >>> iterator
     <callable_iterator object at 0x...>
     >>> for match in iterator:
     ...     print(match.span())
     ...
     (0, 2)
     (22, 24)
     (29, 31)

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Tools/demo/redemo.py


File: python.info,  Node: Module-Level Functions<2>,  Next: Compilation Flags,  Prev: Performing Matches,  Up: Using Regular Expressions

10.8.3.4 Module-Level Functions
...............................

You don’t have to create a pattern object and call its methods; the
*note re: dd. module also provides top-level functions called *note
match(): c83, *note search(): c82, *note findall(): a44, *note sub():
57a, and so forth.  These functions take the same arguments as the
corresponding pattern method with the RE string added as the first
argument, and still return either ‘None’ or a *note match object: 984.
instance.

     >>> print(re.match(r'From\s+', 'Fromage amk'))
     None
     >>> re.match(r'From\s+', 'From amk Thu May 14 19:12:10 1998')
     <re.Match object; span=(0, 5), match='From '>

Under the hood, these functions simply create a pattern object for you
and call the appropriate method on it.  They also store the compiled
object in a cache, so future calls using the same RE won’t need to parse
the pattern again and again.

Should you use these module-level functions, or should you get the
pattern and call its methods yourself?  If you’re accessing a regex
within a loop, pre-compiling it will save a few function calls.  Outside
of loops, there’s not much difference thanks to the internal cache.


File: python.info,  Node: Compilation Flags,  Prev: Module-Level Functions<2>,  Up: Using Regular Expressions

10.8.3.5 Compilation Flags
..........................

Compilation flags let you modify some aspects of how regular expressions
work.  Flags are available in the *note re: dd. module under two names,
a long name such as ‘IGNORECASE’ and a short, one-letter form such as
‘I’.  (If you’re familiar with Perl’s pattern modifiers, the one-letter
forms use the same letters; the short form of *note re.VERBOSE: 18a6. is
*note re.X: 189e, for example.)  Multiple flags can be specified by
bitwise OR-ing them; ‘re.I | re.M’ sets both the ‘I’ and ‘M’ flags, for
example.

Here’s a table of the available flags, followed by a more detailed
explanation of each one.

Flag                                  Meaning
                                      
---------------------------------------------------------------------------------------
                                      
‘ASCII’, ‘A’                          Makes several escapes like ‘\w’, ‘\b’, ‘\s’
                                      and ‘\d’ match only on ASCII characters with
                                      the respective property.
                                      
                                      
‘DOTALL’, ‘S’                         Make ‘.’ match any character, including
                                      newlines.
                                      
                                      
‘IGNORECASE’, ‘I’                     Do case-insensitive matches.
                                      
                                      
‘LOCALE’, ‘L’                         Do a locale-aware match.
                                      
                                      
‘MULTILINE’, ‘M’                      Multi-line matching, affecting ‘^’ and ‘$’.
                                      
                                      
‘VERBOSE’, ‘X’ (for ‘extended’)       Enable verbose REs, which can be organized
                                      more cleanly and understandably.
                                      

 -- Data: I

 -- Data: IGNORECASE

     Perform case-insensitive matching; character class and literal
     strings will match letters by ignoring case.  For example, ‘[A-Z]’
     will match lowercase letters, too.  Full Unicode matching also
     works unless the ‘ASCII’ flag is used to disable non-ASCII matches.
     When the Unicode patterns ‘[a-z]’ or ‘[A-Z]’ are used in
     combination with the ‘IGNORECASE’ flag, they will match the 52
     ASCII letters and 4 additional non-ASCII letters: ‘İ’ (U+0130,
     Latin capital letter I with dot above), ‘ı’ (U+0131, Latin small
     letter dotless i), ‘ſ’ (U+017F, Latin small letter long s) and ‘K’
     (U+212A, Kelvin sign).  ‘Spam’ will match ‘'Spam'’, ‘'spam'’,
     ‘'spAM'’, or ‘'ſpam'’ (the latter is matched only in Unicode mode).
     This lowercasing doesn’t take the current locale into account; it
     will if you also set the ‘LOCALE’ flag.

 -- Data: L

 -- Data: LOCALE

     Make ‘\w’, ‘\W’, ‘\b’, ‘\B’ and case-insensitive matching dependent
     on the current locale instead of the Unicode database.

     Locales are a feature of the C library intended to help in writing
     programs that take account of language differences.  For example,
     if you’re processing encoded French text, you’d want to be able to
     write ‘\w+’ to match words, but ‘\w’ only matches the character
     class ‘[A-Za-z]’ in bytes patterns; it won’t match bytes
     corresponding to ‘é’ or ‘ç’.  If your system is configured properly
     and a French locale is selected, certain C functions will tell the
     program that the byte corresponding to ‘é’ should also be
     considered a letter.  Setting the ‘LOCALE’ flag when compiling a
     regular expression will cause the resulting compiled object to use
     these C functions for ‘\w’; this is slower, but also enables ‘\w+’
     to match French words as you’d expect.  The use of this flag is
     discouraged in Python 3 as the locale mechanism is very unreliable,
     it only handles one “culture” at a time, and it only works with
     8-bit locales.  Unicode matching is already enabled by default in
     Python 3 for Unicode (str) patterns, and it is able to handle
     different locales/languages.

 -- Data: M

 -- Data: MULTILINE

     (‘^’ and ‘$’ haven’t been explained yet; they’ll be introduced in
     section *note More Metacharacters: 43bc.)

     Usually ‘^’ matches only at the beginning of the string, and ‘$’
     matches only at the end of the string and immediately before the
     newline (if any) at the end of the string.  When this flag is
     specified, ‘^’ matches at the beginning of the string and at the
     beginning of each line within the string, immediately following
     each newline.  Similarly, the ‘$’ metacharacter matches either at
     the end of the string and at the end of each line (immediately
     preceding each newline).

 -- Data: S

 -- Data: DOTALL

     Makes the ‘'.'’ special character match any character at all,
     including a newline; without this flag, ‘'.'’ will match anything
     `except' a newline.

 -- Data: A

 -- Data: ASCII

     Make ‘\w’, ‘\W’, ‘\b’, ‘\B’, ‘\s’ and ‘\S’ perform ASCII-only
     matching instead of full Unicode matching.  This is only meaningful
     for Unicode patterns, and is ignored for byte patterns.

 -- Data: X

 -- Data: VERBOSE

     This flag allows you to write regular expressions that are more
     readable by granting you more flexibility in how you can format
     them.  When this flag has been specified, whitespace within the RE
     string is ignored, except when the whitespace is in a character
     class or preceded by an unescaped backslash; this lets you organize
     and indent the RE more clearly.  This flag also lets you put
     comments within a RE that will be ignored by the engine; comments
     are marked by a ‘'#'’ that’s neither in a character class or
     preceded by an unescaped backslash.

     For example, here’s a RE that uses *note re.VERBOSE: 18a6.; see how
     much easier it is to read?

          charref = re.compile(r"""
           &[#]                # Start of a numeric entity reference
           (
               0[0-7]+         # Octal form
             | [0-9]+          # Decimal form
             | x[0-9a-fA-F]+   # Hexadecimal form
           )
           ;                   # Trailing semicolon
          """, re.VERBOSE)

     Without the verbose setting, the RE would look like this:

          charref = re.compile("&#(0[0-7]+"
                               "|[0-9]+"
                               "|x[0-9a-fA-F]+);")

     In the above example, Python’s automatic concatenation of string
     literals has been used to break up the RE into smaller pieces, but
     it’s still more difficult to understand than the version using
     *note re.VERBOSE: 18a6.


File: python.info,  Node: More Pattern Power,  Next: Modifying Strings,  Prev: Using Regular Expressions,  Up: Regular Expression HOWTO

10.8.4 More Pattern Power
-------------------------

So far we’ve only covered a part of the features of regular expressions.
In this section, we’ll cover some new metacharacters, and how to use
groups to retrieve portions of the text that was matched.

* Menu:

* More Metacharacters::
* Grouping::
* Non-capturing and Named Groups::
* Lookahead Assertions::


File: python.info,  Node: More Metacharacters,  Next: Grouping,  Up: More Pattern Power

10.8.4.1 More Metacharacters
............................

There are some metacharacters that we haven’t covered yet.  Most of them
will be covered in this section.

Some of the remaining metacharacters to be discussed are `zero-width
assertions'.  They don’t cause the engine to advance through the string;
instead, they consume no characters at all, and simply succeed or fail.
For example, ‘\b’ is an assertion that the current position is located
at a word boundary; the position isn’t changed by the ‘\b’ at all.  This
means that zero-width assertions should never be repeated, because if
they match once at a given location, they can obviously be matched an
infinite number of times.

‘|’

     Alternation, or the “or” operator.  If `A' and `B' are regular
     expressions, ‘A|B’ will match any string that matches either `A' or
     `B'. ‘|’ has very low precedence in order to make it work
     reasonably when you’re alternating multi-character strings.
     ‘Crow|Servo’ will match either ‘'Crow'’ or ‘'Servo'’, not ‘'Cro'’,
     a ‘'w'’ or an ‘'S'’, and ‘'ervo'’.

     To match a literal ‘'|'’, use ‘\|’, or enclose it inside a
     character class, as in ‘[|]’.

‘^’

     Matches at the beginning of lines.  Unless the ‘MULTILINE’ flag has
     been set, this will only match at the beginning of the string.  In
     ‘MULTILINE’ mode, this also matches immediately after each newline
     within the string.

     For example, if you wish to match the word ‘From’ only at the
     beginning of a line, the RE to use is ‘^From’.

          >>> print(re.search('^From', 'From Here to Eternity'))
          <re.Match object; span=(0, 4), match='From'>
          >>> print(re.search('^From', 'Reciting From Memory'))
          None

     To match a literal ‘'^'’, use ‘\^’.

‘$’

     Matches at the end of a line, which is defined as either the end of
     the string, or any location followed by a newline character.

          >>> print(re.search('}$', '{block}'))
          <re.Match object; span=(6, 7), match='}'>
          >>> print(re.search('}$', '{block} '))
          None
          >>> print(re.search('}$', '{block}\n'))
          <re.Match object; span=(6, 7), match='}'>

     To match a literal ‘'$'’, use ‘\$’ or enclose it inside a character
     class, as in ‘[$]’.

‘\A’

     Matches only at the start of the string.  When not in ‘MULTILINE’
     mode, ‘\A’ and ‘^’ are effectively the same.  In ‘MULTILINE’ mode,
     they’re different: ‘\A’ still matches only at the beginning of the
     string, but ‘^’ may match at any location inside the string that
     follows a newline character.

‘\Z’

     Matches only at the end of the string.

‘\b’

     Word boundary.  This is a zero-width assertion that matches only at
     the beginning or end of a word.  A word is defined as a sequence of
     alphanumeric characters, so the end of a word is indicated by
     whitespace or a non-alphanumeric character.

     The following example matches ‘class’ only when it’s a complete
     word; it won’t match when it’s contained inside another word.

          >>> p = re.compile(r'\bclass\b')
          >>> print(p.search('no class at all'))
          <re.Match object; span=(3, 8), match='class'>
          >>> print(p.search('the declassified algorithm'))
          None
          >>> print(p.search('one subclass is'))
          None

     There are two subtleties you should remember when using this
     special sequence.  First, this is the worst collision between
     Python’s string literals and regular expression sequences.  In
     Python’s string literals, ‘\b’ is the backspace character, ASCII
     value 8.  If you’re not using raw strings, then Python will convert
     the ‘\b’ to a backspace, and your RE won’t match as you expect it
     to.  The following example looks the same as our previous RE, but
     omits the ‘'r'’ in front of the RE string.

          >>> p = re.compile('\bclass\b')
          >>> print(p.search('no class at all'))
          None
          >>> print(p.search('\b' + 'class' + '\b'))
          <re.Match object; span=(0, 7), match='\x08class\x08'>

     Second, inside a character class, where there’s no use for this
     assertion, ‘\b’ represents the backspace character, for
     compatibility with Python’s string literals.

‘\B’

     Another zero-width assertion, this is the opposite of ‘\b’, only
     matching when the current position is not at a word boundary.


File: python.info,  Node: Grouping,  Next: Non-capturing and Named Groups,  Prev: More Metacharacters,  Up: More Pattern Power

10.8.4.2 Grouping
.................

Frequently you need to obtain more information than just whether the RE
matched or not.  Regular expressions are often used to dissect strings
by writing a RE divided into several subgroups which match different
components of interest.  For example, an RFC-822 header line is divided
into a header name and a value, separated by a ‘':'’, like this:

     From: author@example.com
     User-Agent: Thunderbird 1.5.0.9 (X11/20061227)
     MIME-Version: 1.0
     To: editor@example.com

This can be handled by writing a regular expression which matches an
entire header line, and has one group which matches the header name, and
another group which matches the header’s value.

Groups are marked by the ‘'('’, ‘')'’ metacharacters.  ‘'('’ and ‘')'’
have much the same meaning as they do in mathematical expressions; they
group together the expressions contained inside them, and you can repeat
the contents of a group with a repeating qualifier, such as ‘*’, ‘+’,
‘?’, or ‘{m,n}’.  For example, ‘(ab)*’ will match zero or more
repetitions of ‘ab’.

     >>> p = re.compile('(ab)*')
     >>> print(p.match('ababababab').span())
     (0, 10)

Groups indicated with ‘'('’, ‘')'’ also capture the starting and ending
index of the text that they match; this can be retrieved by passing an
argument to *note group(): 18b7, *note start(): 18bb, *note end(): 18bc,
and *note span(): 18bd.  Groups are numbered starting with 0.  Group 0
is always present; it’s the whole RE, so *note match object: 984.
methods all have group 0 as their default argument.  Later we’ll see how
to express groups that don’t capture the span of text that they match.

     >>> p = re.compile('(a)b')
     >>> m = p.match('ab')
     >>> m.group()
     'ab'
     >>> m.group(0)
     'ab'

Subgroups are numbered from left to right, from 1 upward.  Groups can be
nested; to determine the number, just count the opening parenthesis
characters, going from left to right.

     >>> p = re.compile('(a(b)c)d')
     >>> m = p.match('abcd')
     >>> m.group(0)
     'abcd'
     >>> m.group(1)
     'abc'
     >>> m.group(2)
     'b'

*note group(): 18b7. can be passed multiple group numbers at a time, in
which case it will return a tuple containing the corresponding values
for those groups.

     >>> m.group(2,1,2)
     ('b', 'abc', 'b')

The *note groups(): 18b9. method returns a tuple containing the strings
for all the subgroups, from 1 up to however many there are.

     >>> m.groups()
     ('abc', 'b')

Backreferences in a pattern allow you to specify that the contents of an
earlier capturing group must also be found at the current location in
the string.  For example, ‘\1’ will succeed if the exact contents of
group 1 can be found at the current position, and fails otherwise.
Remember that Python’s string literals also use a backslash followed by
numbers to allow including arbitrary characters in a string, so be sure
to use a raw string when incorporating backreferences in a RE.

For example, the following RE detects doubled words in a string.

     >>> p = re.compile(r'\b(\w+)\s+\1\b')
     >>> p.search('Paris in the the spring').group()
     'the the'

Backreferences like this aren’t often useful for just searching through
a string — there are few text formats which repeat data in this way —
but you’ll soon find out that they’re `very' useful when performing
string substitutions.


File: python.info,  Node: Non-capturing and Named Groups,  Next: Lookahead Assertions,  Prev: Grouping,  Up: More Pattern Power

10.8.4.3 Non-capturing and Named Groups
.......................................

Elaborate REs may use many groups, both to capture substrings of
interest, and to group and structure the RE itself.  In complex REs, it
becomes difficult to keep track of the group numbers.  There are two
features which help with this problem.  Both of them use a common syntax
for regular expression extensions, so we’ll look at that first.

Perl 5 is well known for its powerful additions to standard regular
expressions.  For these new features the Perl developers couldn’t choose
new single-keystroke metacharacters or new special sequences beginning
with ‘\’ without making Perl’s regular expressions confusingly different
from standard REs.  If they chose ‘&’ as a new metacharacter, for
example, old expressions would be assuming that ‘&’ was a regular
character and wouldn’t have escaped it by writing ‘\&’ or ‘[&]’.

The solution chosen by the Perl developers was to use ‘(?...)’ as the
extension syntax.  ‘?’ immediately after a parenthesis was a syntax
error because the ‘?’ would have nothing to repeat, so this didn’t
introduce any compatibility problems.  The characters immediately after
the ‘?’ indicate what extension is being used, so ‘(?=foo)’ is one thing
(a positive lookahead assertion) and ‘(?:foo)’ is something else (a
non-capturing group containing the subexpression ‘foo’).

Python supports several of Perl’s extensions and adds an extension
syntax to Perl’s extension syntax.  If the first character after the
question mark is a ‘P’, you know that it’s an extension that’s specific
to Python.

Now that we’ve looked at the general extension syntax, we can return to
the features that simplify working with groups in complex REs.

Sometimes you’ll want to use a group to denote a part of a regular
expression, but aren’t interested in retrieving the group’s contents.
You can make this fact explicit by using a non-capturing group:
‘(?:...)’, where you can replace the ‘...’ with any other regular
expression.

     >>> m = re.match("([abc])+", "abc")
     >>> m.groups()
     ('c',)
     >>> m = re.match("(?:[abc])+", "abc")
     >>> m.groups()
     ()

Except for the fact that you can’t retrieve the contents of what the
group matched, a non-capturing group behaves exactly the same as a
capturing group; you can put anything inside it, repeat it with a
repetition metacharacter such as ‘*’, and nest it within other groups
(capturing or non-capturing).  ‘(?:...)’ is particularly useful when
modifying an existing pattern, since you can add new groups without
changing how all the other groups are numbered.  It should be mentioned
that there’s no performance difference in searching between capturing
and non-capturing groups; neither form is any faster than the other.

A more significant feature is named groups: instead of referring to them
by numbers, groups can be referenced by a name.

The syntax for a named group is one of the Python-specific extensions:
‘(?P<name>...)’.  `name' is, obviously, the name of the group.  Named
groups behave exactly like capturing groups, and additionally associate
a name with a group.  The *note match object: 984. methods that deal
with capturing groups all accept either integers that refer to the group
by number or strings that contain the desired group’s name.  Named
groups are still given numbers, so you can retrieve information about a
group in two ways:

     >>> p = re.compile(r'(?P<word>\b\w+\b)')
     >>> m = p.search( '(((( Lots of punctuation )))' )
     >>> m.group('word')
     'Lots'
     >>> m.group(1)
     'Lots'

Additionally, you can retrieve named groups as a dictionary with *note
groupdict(): 18ba.:

     >>> m = re.match(r'(?P<first>\w+) (?P<last>\w+)', 'Jane Doe')
     >>> m.groupdict()
     {'first': 'Jane', 'last': 'Doe'}

Named groups are handy because they let you use easily-remembered names,
instead of having to remember numbers.  Here’s an example RE from the
*note imaplib: 97. module:

     InternalDate = re.compile(r'INTERNALDATE "'
             r'(?P<day>[ 123][0-9])-(?P<mon>[A-Z][a-z][a-z])-'
             r'(?P<year>[0-9][0-9][0-9][0-9])'
             r' (?P<hour>[0-9][0-9]):(?P<min>[0-9][0-9]):(?P<sec>[0-9][0-9])'
             r' (?P<zonen>[-+])(?P<zoneh>[0-9][0-9])(?P<zonem>[0-9][0-9])'
             r'"')

It’s obviously much easier to retrieve ‘m.group('zonem')’, instead of
having to remember to retrieve group 9.

The syntax for backreferences in an expression such as ‘(...)\1’ refers
to the number of the group.  There’s naturally a variant that uses the
group name instead of the number.  This is another Python extension:
‘(?P=name)’ indicates that the contents of the group called `name'
should again be matched at the current point.  The regular expression
for finding doubled words, ‘\b(\w+)\s+\1\b’ can also be written as
‘\b(?P<word>\w+)\s+(?P=word)\b’:

     >>> p = re.compile(r'\b(?P<word>\w+)\s+(?P=word)\b')
     >>> p.search('Paris in the the spring').group()
     'the the'


File: python.info,  Node: Lookahead Assertions,  Prev: Non-capturing and Named Groups,  Up: More Pattern Power

10.8.4.4 Lookahead Assertions
.............................

Another zero-width assertion is the lookahead assertion.  Lookahead
assertions are available in both positive and negative form, and look
like this:

‘(?=...)’

     Positive lookahead assertion.  This succeeds if the contained
     regular expression, represented here by ‘...’, successfully matches
     at the current location, and fails otherwise.  But, once the
     contained expression has been tried, the matching engine doesn’t
     advance at all; the rest of the pattern is tried right where the
     assertion started.

‘(?!...)’

     Negative lookahead assertion.  This is the opposite of the positive
     assertion; it succeeds if the contained expression `doesn’t' match
     at the current position in the string.

To make this concrete, let’s look at a case where a lookahead is useful.
Consider a simple pattern to match a filename and split it apart into a
base name and an extension, separated by a ‘.’.  For example, in
‘news.rc’, ‘news’ is the base name, and ‘rc’ is the filename’s
extension.

The pattern to match this is quite simple:

‘.*[.].*$’

Notice that the ‘.’ needs to be treated specially because it’s a
metacharacter, so it’s inside a character class to only match that
specific character.  Also notice the trailing ‘$’; this is added to
ensure that all the rest of the string must be included in the
extension.  This regular expression matches ‘foo.bar’ and ‘autoexec.bat’
and ‘sendmail.cf’ and ‘printers.conf’.

Now, consider complicating the problem a bit; what if you want to match
filenames where the extension is not ‘bat’?  Some incorrect attempts:

‘.*[.][^b].*$’ The first attempt above tries to exclude ‘bat’ by
requiring that the first character of the extension is not a ‘b’.  This
is wrong, because the pattern also doesn’t match ‘foo.bar’.

‘.*[.]([^b]..|.[^a].|..[^t])$’

The expression gets messier when you try to patch up the first solution
by requiring one of the following cases to match: the first character of
the extension isn’t ‘b’; the second character isn’t ‘a’; or the third
character isn’t ‘t’.  This accepts ‘foo.bar’ and rejects ‘autoexec.bat’,
but it requires a three-letter extension and won’t accept a filename
with a two-letter extension such as ‘sendmail.cf’.  We’ll complicate the
pattern again in an effort to fix it.

‘.*[.]([^b].?.?|.[^a]?.?|..?[^t]?)$’

In the third attempt, the second and third letters are all made optional
in order to allow matching extensions shorter than three characters,
such as ‘sendmail.cf’.

The pattern’s getting really complicated now, which makes it hard to
read and understand.  Worse, if the problem changes and you want to
exclude both ‘bat’ and ‘exe’ as extensions, the pattern would get even
more complicated and confusing.

A negative lookahead cuts through all this confusion:

‘.*[.](?!bat$)[^.]*$’ The negative lookahead means: if the expression
‘bat’ doesn’t match at this point, try the rest of the pattern; if
‘bat$’ does match, the whole pattern will fail.  The trailing ‘$’ is
required to ensure that something like ‘sample.batch’, where the
extension only starts with ‘bat’, will be allowed.  The ‘[^.]*’ makes
sure that the pattern works when there are multiple dots in the
filename.

Excluding another filename extension is now easy; simply add it as an
alternative inside the assertion.  The following pattern excludes
filenames that end in either ‘bat’ or ‘exe’:

‘.*[.](?!bat$|exe$)[^.]*$’


File: python.info,  Node: Modifying Strings,  Next: Common Problems,  Prev: More Pattern Power,  Up: Regular Expression HOWTO

10.8.5 Modifying Strings
------------------------

Up to this point, we’ve simply performed searches against a static
string.  Regular expressions are also commonly used to modify strings in
various ways, using the following pattern methods:

Method/Attribute       Purpose
                       
---------------------------------------------------------------------------
                       
‘split()’              Split the string into a list, splitting it
                       wherever the RE matches
                       
                       
‘sub()’                Find all substrings where the RE matches, and
                       replace them with a different string
                       
                       
‘subn()’               Does the same thing as ‘sub()’, but returns the
                       new string and the number of replacements
                       

* Menu:

* Splitting Strings::
* Search and Replace::


File: python.info,  Node: Splitting Strings,  Next: Search and Replace,  Up: Modifying Strings

10.8.5.1 Splitting Strings
..........................

The *note split(): 18ac. method of a pattern splits a string apart
wherever the RE matches, returning a list of the pieces.  It’s similar
to the *note split(): 890. method of strings but provides much more
generality in the delimiters that you can split by; string ‘split()’
only supports splitting by whitespace or by a fixed string.  As you’d
expect, there’s a module-level *note re.split(): 4d1. function, too.

 -- Method: .split (string[, maxsplit=0])

     Split `string' by the matches of the regular expression.  If
     capturing parentheses are used in the RE, then their contents will
     also be returned as part of the resulting list.  If `maxsplit' is
     nonzero, at most `maxsplit' splits are performed.

You can limit the number of splits made, by passing a value for
`maxsplit'.  When `maxsplit' is nonzero, at most `maxsplit' splits will
be made, and the remainder of the string is returned as the final
element of the list.  In the following example, the delimiter is any
sequence of non-alphanumeric characters.

     >>> p = re.compile(r'\W+')
     >>> p.split('This is a test, short and sweet, of split().')
     ['This', 'is', 'a', 'test', 'short', 'and', 'sweet', 'of', 'split', '']
     >>> p.split('This is a test, short and sweet, of split().', 3)
     ['This', 'is', 'a', 'test, short and sweet, of split().']

Sometimes you’re not only interested in what the text between delimiters
is, but also need to know what the delimiter was.  If capturing
parentheses are used in the RE, then their values are also returned as
part of the list.  Compare the following calls:

     >>> p = re.compile(r'\W+')
     >>> p2 = re.compile(r'(\W+)')
     >>> p.split('This... is a test.')
     ['This', 'is', 'a', 'test', '']
     >>> p2.split('This... is a test.')
     ['This', '... ', 'is', ' ', 'a', ' ', 'test', '.', '']

The module-level function *note re.split(): 4d1. adds the RE to be used
as the first argument, but is otherwise the same.

     >>> re.split(r'[\W]+', 'Words, words, words.')
     ['Words', 'words', 'words', '']
     >>> re.split(r'([\W]+)', 'Words, words, words.')
     ['Words', ', ', 'words', ', ', 'words', '.', '']
     >>> re.split(r'[\W]+', 'Words, words, words.', 1)
     ['Words', 'words, words.']


File: python.info,  Node: Search and Replace,  Prev: Splitting Strings,  Up: Modifying Strings

10.8.5.2 Search and Replace
...........................

Another common task is to find all the matches for a pattern, and
replace them with a different string.  The *note sub(): 18af. method
takes a replacement value, which can be either a string or a function,
and the string to be processed.

 -- Method: .sub (replacement, string[, count=0])

     Returns the string obtained by replacing the leftmost
     non-overlapping occurrences of the RE in `string' by the
     replacement `replacement'.  If the pattern isn’t found, `string' is
     returned unchanged.

     The optional argument `count' is the maximum number of pattern
     occurrences to be replaced; `count' must be a non-negative integer.
     The default value of 0 means to replace all occurrences.

Here’s a simple example of using the *note sub(): 18af. method.  It
replaces colour names with the word ‘colour’:

     >>> p = re.compile('(blue|white|red)')
     >>> p.sub('colour', 'blue socks and red shoes')
     'colour socks and colour shoes'
     >>> p.sub('colour', 'blue socks and red shoes', count=1)
     'colour socks and red shoes'

The *note subn(): 18b0. method does the same work, but returns a 2-tuple
containing the new string value and the number of replacements that were
performed:

     >>> p = re.compile('(blue|white|red)')
     >>> p.subn('colour', 'blue socks and red shoes')
     ('colour socks and colour shoes', 2)
     >>> p.subn('colour', 'no colours at all')
     ('no colours at all', 0)

Empty matches are replaced only when they’re not adjacent to a previous
empty match.

     >>> p = re.compile('x*')
     >>> p.sub('-', 'abxd')
     '-a-b--d-'

If `replacement' is a string, any backslash escapes in it are processed.
That is, ‘\n’ is converted to a single newline character, ‘\r’ is
converted to a carriage return, and so forth.  Unknown escapes such as
‘\&’ are left alone.  Backreferences, such as ‘\6’, are replaced with
the substring matched by the corresponding group in the RE. This lets
you incorporate portions of the original text in the resulting
replacement string.

This example matches the word ‘section’ followed by a string enclosed in
‘{’, ‘}’, and changes ‘section’ to ‘subsection’:

     >>> p = re.compile('section{ ( [^}]* ) }', re.VERBOSE)
     >>> p.sub(r'subsection{\1}','section{First} section{second}')
     'subsection{First} subsection{second}'

There’s also a syntax for referring to named groups as defined by the
‘(?P<name>...)’ syntax.  ‘\g<name>’ will use the substring matched by
the group named ‘name’, and ‘\g<number>’ uses the corresponding group
number.  ‘\g<2>’ is therefore equivalent to ‘\2’, but isn’t ambiguous in
a replacement string such as ‘\g<2>0’.  (‘\20’ would be interpreted as a
reference to group 20, not a reference to group 2 followed by the
literal character ‘'0'’.)  The following substitutions are all
equivalent, but use all three variations of the replacement string.

     >>> p = re.compile('section{ (?P<name> [^}]* ) }', re.VERBOSE)
     >>> p.sub(r'subsection{\1}','section{First}')
     'subsection{First}'
     >>> p.sub(r'subsection{\g<1>}','section{First}')
     'subsection{First}'
     >>> p.sub(r'subsection{\g<name>}','section{First}')
     'subsection{First}'

`replacement' can also be a function, which gives you even more control.
If `replacement' is a function, the function is called for every
non-overlapping occurrence of `pattern'.  On each call, the function is
passed a *note match object: 984. argument for the match and can use
this information to compute the desired replacement string and return
it.

In the following example, the replacement function translates decimals
into hexadecimal:

     >>> def hexrepl(match):
     ...     "Return the hex string for a decimal number"
     ...     value = int(match.group())
     ...     return hex(value)
     ...
     >>> p = re.compile(r'\d+')
     >>> p.sub(hexrepl, 'Call 65490 for printing, 49152 for user code.')
     'Call 0xffd2 for printing, 0xc000 for user code.'

When using the module-level *note re.sub(): 57a. function, the pattern
is passed as the first argument.  The pattern may be provided as an
object or as a string; if you need to specify regular expression flags,
you must either use a pattern object as the first parameter, or use
embedded modifiers in the pattern string, e.g.  ‘sub("(?i)b+", "x",
"bbbb BBBB")’ returns ‘'x x'’.


File: python.info,  Node: Common Problems,  Next: Feedback,  Prev: Modifying Strings,  Up: Regular Expression HOWTO

10.8.6 Common Problems
----------------------

Regular expressions are a powerful tool for some applications, but in
some ways their behaviour isn’t intuitive and at times they don’t behave
the way you may expect them to.  This section will point out some of the
most common pitfalls.

* Menu:

* Use String Methods::
* match() versus search(): match versus search.
* Greedy versus Non-Greedy::
* Using re.VERBOSE: Using re VERBOSE.


File: python.info,  Node: Use String Methods,  Next: match versus search,  Up: Common Problems

10.8.6.1 Use String Methods
...........................

Sometimes using the *note re: dd. module is a mistake.  If you’re
matching a fixed string, or a single character class, and you’re not
using any *note re: dd. features such as the *note IGNORECASE: 18a5.
flag, then the full power of regular expressions may not be required.
Strings have several methods for performing operations with fixed
strings and they’re usually much faster, because the implementation is a
single small C loop that’s been optimized for the purpose, instead of
the large, more generalized regular expression engine.

One example might be replacing a single fixed string with another one;
for example, you might replace ‘word’ with ‘deed’.  *note re.sub(): 57a.
seems like the function to use for this, but consider the *note
replace(): 1787. method.  Note that ‘replace()’ will also replace ‘word’
inside words, turning ‘swordfish’ into ‘sdeedfish’, but the naive RE
‘word’ would have done that, too.  (To avoid performing the substitution
on parts of words, the pattern would have to be ‘\bword\b’, in order to
require that ‘word’ have a word boundary on either side.  This takes the
job beyond ‘replace()’’s abilities.)

Another common task is deleting every occurrence of a single character
from a string or replacing it with another single character.  You might
do this with something like ‘re.sub('\n', ' ', S)’, but *note
translate(): 1786. is capable of doing both tasks and will be faster
than any regular expression operation can be.

In short, before turning to the *note re: dd. module, consider whether
your problem can be solved with a faster and simpler string method.


File: python.info,  Node: match versus search,  Next: Greedy versus Non-Greedy,  Prev: Use String Methods,  Up: Common Problems

10.8.6.2 match() versus search()
................................

The *note match(): c83. function only checks if the RE matches at the
beginning of the string while *note search(): c82. will scan forward
through the string for a match.  It’s important to keep this distinction
in mind.  Remember, ‘match()’ will only report a successful match which
will start at 0; if the match wouldn’t start at zero, ‘match()’ will
`not' report it.

     >>> print(re.match('super', 'superstition').span())
     (0, 5)
     >>> print(re.match('super', 'insuperable'))
     None

On the other hand, *note search(): c82. will scan forward through the
string, reporting the first match it finds.

     >>> print(re.search('super', 'superstition').span())
     (0, 5)
     >>> print(re.search('super', 'insuperable').span())
     (2, 7)

Sometimes you’ll be tempted to keep using *note re.match(): c83, and
just add ‘.*’ to the front of your RE. Resist this temptation and use
*note re.search(): c82. instead.  The regular expression compiler does
some analysis of REs in order to speed up the process of looking for a
match.  One such analysis figures out what the first character of a
match must be; for example, a pattern starting with ‘Crow’ must match
starting with a ‘'C'’.  The analysis lets the engine quickly scan
through the string looking for the starting character, only trying the
full match if a ‘'C'’ is found.

Adding ‘.*’ defeats this optimization, requiring scanning to the end of
the string and then backtracking to find a match for the rest of the RE.
Use *note re.search(): c82. instead.


File: python.info,  Node: Greedy versus Non-Greedy,  Next: Using re VERBOSE,  Prev: match versus search,  Up: Common Problems

10.8.6.3 Greedy versus Non-Greedy
.................................

When repeating a regular expression, as in ‘a*’, the resulting action is
to consume as much of the pattern as possible.  This fact often bites
you when you’re trying to match a pair of balanced delimiters, such as
the angle brackets surrounding an HTML tag.  The naive pattern for
matching a single HTML tag doesn’t work because of the greedy nature of
‘.*’.

     >>> s = '<html><head><title>Title</title>'
     >>> len(s)
     32
     >>> print(re.match('<.*>', s).span())
     (0, 32)
     >>> print(re.match('<.*>', s).group())
     <html><head><title>Title</title>

The RE matches the ‘'<'’ in ‘'<html>'’, and the ‘.*’ consumes the rest
of the string.  There’s still more left in the RE, though, and the ‘>’
can’t match at the end of the string, so the regular expression engine
has to backtrack character by character until it finds a match for the
‘>’.  The final match extends from the ‘'<'’ in ‘'<html>'’ to the ‘'>'’
in ‘'</title>'’, which isn’t what you want.

In this case, the solution is to use the non-greedy qualifiers ‘*?’,
‘+?’, ‘??’, or ‘{m,n}?’, which match as `little' text as possible.  In
the above example, the ‘'>'’ is tried immediately after the first ‘'<'’
matches, and when it fails, the engine advances a character at a time,
retrying the ‘'>'’ at every step.  This produces just the right result:

     >>> print(re.match('<.*?>', s).group())
     <html>

(Note that parsing HTML or XML with regular expressions is painful.
Quick-and-dirty patterns will handle common cases, but HTML and XML have
special cases that will break the obvious regular expression; by the
time you’ve written a regular expression that handles all of the
possible cases, the patterns will be `very' complicated.  Use an HTML or
XML parser module for such tasks.)


File: python.info,  Node: Using re VERBOSE,  Prev: Greedy versus Non-Greedy,  Up: Common Problems

10.8.6.4 Using re.VERBOSE
.........................

By now you’ve probably noticed that regular expressions are a very
compact notation, but they’re not terribly readable.  REs of moderate
complexity can become lengthy collections of backslashes, parentheses,
and metacharacters, making them difficult to read and understand.

For such REs, specifying the *note re.VERBOSE: 18a6. flag when compiling
the regular expression can be helpful, because it allows you to format
the regular expression more clearly.

The ‘re.VERBOSE’ flag has several effects.  Whitespace in the regular
expression that `isn’t' inside a character class is ignored.  This means
that an expression such as ‘dog | cat’ is equivalent to the less
readable ‘dog|cat’, but ‘[a b]’ will still match the characters ‘'a'’,
‘'b'’, or a space.  In addition, you can also put comments inside a RE;
comments extend from a ‘#’ character to the next newline.  When used
with triple-quoted strings, this enables REs to be formatted more
neatly:

     pat = re.compile(r"""
      \s*                 # Skip leading whitespace
      (?P<header>[^:]+)   # Header name
      \s* :               # Whitespace, and a colon
      (?P<value>.*?)      # The header's value -- *? used to
                          # lose the following trailing whitespace
      \s*$                # Trailing whitespace to end-of-line
     """, re.VERBOSE)

This is far more readable than:

     pat = re.compile(r"\s*(?P<header>[^:]+)\s*:(?P<value>.*?)\s*$")


File: python.info,  Node: Feedback,  Prev: Common Problems,  Up: Regular Expression HOWTO

10.8.7 Feedback
---------------

Regular expressions are a complicated topic.  Did this document help you
understand them?  Were there parts that were unclear, or Problems you
encountered that weren’t covered here?  If so, please send suggestions
for improvements to the author.

The most complete book on regular expressions is almost certainly
Jeffrey Friedl’s Mastering Regular Expressions, published by O’Reilly.
Unfortunately, it exclusively concentrates on Perl and Java’s flavours
of regular expressions, and doesn’t contain any Python material at all,
so it won’t be useful as a reference for programming in Python.  (The
first edition covered Python’s now-removed ‘regex’ module, which won’t
help you much.)  Consider checking it out from your library.


File: python.info,  Node: Socket Programming HOWTO,  Next: Sorting HOW TO,  Prev: Regular Expression HOWTO,  Up: Python HOWTOs

10.9 Socket Programming HOWTO
=============================


Author: Gordon McMillan

Abstract
........

Sockets are used nearly everywhere, but are one of the most severely
misunderstood technologies around.  This is a 10,000 foot overview of
sockets.  It’s not really a tutorial - you’ll still have work to do in
getting things operational.  It doesn’t cover the fine points (and there
are a lot of them), but I hope it will give you enough background to
begin using them decently.

* Menu:

* Sockets::
* Creating a Socket::
* Using a Socket::
* Disconnecting::
* Non-blocking Sockets::


File: python.info,  Node: Sockets,  Next: Creating a Socket,  Up: Socket Programming HOWTO

10.9.1 Sockets
--------------

I’m only going to talk about INET (i.e.  IPv4) sockets, but they account
for at least 99% of the sockets in use.  And I’ll only talk about STREAM
(i.e.  TCP) sockets - unless you really know what you’re doing (in which
case this HOWTO isn’t for you!), you’ll get better behavior and
performance from a STREAM socket than anything else.  I will try to
clear up the mystery of what a socket is, as well as some hints on how
to work with blocking and non-blocking sockets.  But I’ll start by
talking about blocking sockets.  You’ll need to know how they work
before dealing with non-blocking sockets.

Part of the trouble with understanding these things is that “socket” can
mean a number of subtly different things, depending on context.  So
first, let’s make a distinction between a “client” socket - an endpoint
of a conversation, and a “server” socket, which is more like a
switchboard operator.  The client application (your browser, for
example) uses “client” sockets exclusively; the web server it’s talking
to uses both “server” sockets and “client” sockets.

* Menu:

* History::


File: python.info,  Node: History,  Up: Sockets

10.9.1.1 History
................

Of the various forms of IPC (Inter Process Communication), sockets are
by far the most popular.  On any given platform, there are likely to be
other forms of IPC that are faster, but for cross-platform
communication, sockets are about the only game in town.

They were invented in Berkeley as part of the BSD flavor of Unix.  They
spread like wildfire with the Internet.  With good reason — the
combination of sockets with INET makes talking to arbitrary machines
around the world unbelievably easy (at least compared to other schemes).


File: python.info,  Node: Creating a Socket,  Next: Using a Socket,  Prev: Sockets,  Up: Socket Programming HOWTO

10.9.2 Creating a Socket
------------------------

Roughly speaking, when you clicked on the link that brought you to this
page, your browser did something like the following:

     # create an INET, STREAMing socket
     s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
     # now connect to the web server on port 80 - the normal http port
     s.connect(("www.python.org", 80))

When the ‘connect’ completes, the socket ‘s’ can be used to send in a
request for the text of the page.  The same socket will read the reply,
and then be destroyed.  That’s right, destroyed.  Client sockets are
normally only used for one exchange (or a small set of sequential
exchanges).

What happens in the web server is a bit more complex.  First, the web
server creates a “server socket”:

     # create an INET, STREAMing socket
     serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
     # bind the socket to a public host, and a well-known port
     serversocket.bind((socket.gethostname(), 80))
     # become a server socket
     serversocket.listen(5)

A couple things to notice: we used ‘socket.gethostname()’ so that the
socket would be visible to the outside world.  If we had used
‘s.bind(('localhost', 80))’ or ‘s.bind(('127.0.0.1', 80))’ we would
still have a “server” socket, but one that was only visible within the
same machine.  ‘s.bind(('', 80))’ specifies that the socket is reachable
by any address the machine happens to have.

A second thing to note: low number ports are usually reserved for “well
known” services (HTTP, SNMP etc).  If you’re playing around, use a nice
high number (4 digits).

Finally, the argument to ‘listen’ tells the socket library that we want
it to queue up as many as 5 connect requests (the normal max) before
refusing outside connections.  If the rest of the code is written
properly, that should be plenty.

Now that we have a “server” socket, listening on port 80, we can enter
the mainloop of the web server:

     while True:
         # accept connections from outside
         (clientsocket, address) = serversocket.accept()
         # now do something with the clientsocket
         # in this case, we'll pretend this is a threaded server
         ct = client_thread(clientsocket)
         ct.run()

There’s actually 3 general ways in which this loop could work -
dispatching a thread to handle ‘clientsocket’, create a new process to
handle ‘clientsocket’, or restructure this app to use non-blocking
sockets, and multiplex between our “server” socket and any active
‘clientsocket’s using ‘select’.  More about that later.  The important
thing to understand now is this: this is `all' a “server” socket does.
It doesn’t send any data.  It doesn’t receive any data.  It just
produces “client” sockets.  Each ‘clientsocket’ is created in response
to some `other' “client” socket doing a ‘connect()’ to the host and port
we’re bound to.  As soon as we’ve created that ‘clientsocket’, we go
back to listening for more connections.  The two “clients” are free to
chat it up - they are using some dynamically allocated port which will
be recycled when the conversation ends.

* Menu:

* IPC::


File: python.info,  Node: IPC,  Up: Creating a Socket

10.9.2.1 IPC
............

If you need fast IPC between two processes on one machine, you should
look into pipes or shared memory.  If you do decide to use AF_INET
sockets, bind the “server” socket to ‘'localhost'’.  On most platforms,
this will take a shortcut around a couple of layers of network code and
be quite a bit faster.

See also
........

The *note multiprocessing: b7. integrates cross-platform IPC into a
higher-level API.


File: python.info,  Node: Using a Socket,  Next: Disconnecting,  Prev: Creating a Socket,  Up: Socket Programming HOWTO

10.9.3 Using a Socket
---------------------

The first thing to note, is that the web browser’s “client” socket and
the web server’s “client” socket are identical beasts.  That is, this is
a “peer to peer” conversation.  Or to put it another way, `as the
designer, you will have to decide what the rules of etiquette are for a
conversation'.  Normally, the ‘connect’ing socket starts the
conversation, by sending in a request, or perhaps a signon.  But that’s
a design decision - it’s not a rule of sockets.

Now there are two sets of verbs to use for communication.  You can use
‘send’ and ‘recv’, or you can transform your client socket into a
file-like beast and use ‘read’ and ‘write’.  The latter is the way Java
presents its sockets.  I’m not going to talk about it here, except to
warn you that you need to use ‘flush’ on sockets.  These are buffered
“files”, and a common mistake is to ‘write’ something, and then ‘read’
for a reply.  Without a ‘flush’ in there, you may wait forever for the
reply, because the request may still be in your output buffer.

Now we come to the major stumbling block of sockets - ‘send’ and ‘recv’
operate on the network buffers.  They do not necessarily handle all the
bytes you hand them (or expect from them), because their major focus is
handling the network buffers.  In general, they return when the
associated network buffers have been filled (‘send’) or emptied
(‘recv’).  They then tell you how many bytes they handled.  It is `your'
responsibility to call them again until your message has been completely
dealt with.

When a ‘recv’ returns 0 bytes, it means the other side has closed (or is
in the process of closing) the connection.  You will not receive any
more data on this connection.  Ever.  You may be able to send data
successfully; I’ll talk more about this later.

A protocol like HTTP uses a socket for only one transfer.  The client
sends a request, then reads a reply.  That’s it.  The socket is
discarded.  This means that a client can detect the end of the reply by
receiving 0 bytes.

But if you plan to reuse your socket for further transfers, you need to
realize that `there is no' EOT (End of Transfer) `on a socket.'  I
repeat: if a socket ‘send’ or ‘recv’ returns after handling 0 bytes, the
connection has been broken.  If the connection has `not' been broken,
you may wait on a ‘recv’ forever, because the socket will `not' tell you
that there’s nothing more to read (for now).  Now if you think about
that a bit, you’ll come to realize a fundamental truth of sockets:
`messages must either be fixed length' (yuck), `or be delimited'
(shrug), `or indicate how long they are' (much better), `or end by
shutting down the connection'.  The choice is entirely yours, (but some
ways are righter than others).

Assuming you don’t want to end the connection, the simplest solution is
a fixed length message:

     class MySocket:
         """demonstration class only
           - coded for clarity, not efficiency
         """

         def __init__(self, sock=None):
             if sock is None:
                 self.sock = socket.socket(
                                 socket.AF_INET, socket.SOCK_STREAM)
             else:
                 self.sock = sock

         def connect(self, host, port):
             self.sock.connect((host, port))

         def mysend(self, msg):
             totalsent = 0
             while totalsent < MSGLEN:
                 sent = self.sock.send(msg[totalsent:])
                 if sent == 0:
                     raise RuntimeError("socket connection broken")
                 totalsent = totalsent + sent

         def myreceive(self):
             chunks = []
             bytes_recd = 0
             while bytes_recd < MSGLEN:
                 chunk = self.sock.recv(min(MSGLEN - bytes_recd, 2048))
                 if chunk == b'':
                     raise RuntimeError("socket connection broken")
                 chunks.append(chunk)
                 bytes_recd = bytes_recd + len(chunk)
             return b''.join(chunks)

The sending code here is usable for almost any messaging scheme - in
Python you send strings, and you can use ‘len()’ to determine its length
(even if it has embedded ‘\0’ characters).  It’s mostly the receiving
code that gets more complex.  (And in C, it’s not much worse, except you
can’t use ‘strlen’ if the message has embedded ‘\0’s.)

The easiest enhancement is to make the first character of the message an
indicator of message type, and have the type determine the length.  Now
you have two ‘recv’s - the first to get (at least) that first character
so you can look up the length, and the second in a loop to get the rest.
If you decide to go the delimited route, you’ll be receiving in some
arbitrary chunk size, (4096 or 8192 is frequently a good match for
network buffer sizes), and scanning what you’ve received for a
delimiter.

One complication to be aware of: if your conversational protocol allows
multiple messages to be sent back to back (without some kind of reply),
and you pass ‘recv’ an arbitrary chunk size, you may end up reading the
start of a following message.  You’ll need to put that aside and hold
onto it, until it’s needed.

Prefixing the message with its length (say, as 5 numeric characters)
gets more complex, because (believe it or not), you may not get all 5
characters in one ‘recv’.  In playing around, you’ll get away with it;
but in high network loads, your code will very quickly break unless you
use two ‘recv’ loops - the first to determine the length, the second to
get the data part of the message.  Nasty.  This is also when you’ll
discover that ‘send’ does not always manage to get rid of everything in
one pass.  And despite having read this, you will eventually get bit by
it!

In the interests of space, building your character, (and preserving my
competitive position), these enhancements are left as an exercise for
the reader.  Lets move on to cleaning up.

* Menu:

* Binary Data::


File: python.info,  Node: Binary Data,  Up: Using a Socket

10.9.3.1 Binary Data
....................

It is perfectly possible to send binary data over a socket.  The major
problem is that not all machines use the same formats for binary data.
For example, a Motorola chip will represent a 16 bit integer with the
value 1 as the two hex bytes 00 01.  Intel and DEC, however, are
byte-reversed - that same 1 is 01 00.  Socket libraries have calls for
converting 16 and 32 bit integers - ‘ntohl, htonl, ntohs, htons’ where
“n” means `network' and “h” means `host', “s” means `short' and “l”
means `long'.  Where network order is host order, these do nothing, but
where the machine is byte-reversed, these swap the bytes around
appropriately.

In these days of 32 bit machines, the ascii representation of binary
data is frequently smaller than the binary representation.  That’s
because a surprising amount of the time, all those longs have the value
0, or maybe 1.  The string “0” would be two bytes, while binary is four.
Of course, this doesn’t fit well with fixed-length messages.  Decisions,
decisions.


File: python.info,  Node: Disconnecting,  Next: Non-blocking Sockets,  Prev: Using a Socket,  Up: Socket Programming HOWTO

10.9.4 Disconnecting
--------------------

Strictly speaking, you’re supposed to use ‘shutdown’ on a socket before
you ‘close’ it.  The ‘shutdown’ is an advisory to the socket at the
other end.  Depending on the argument you pass it, it can mean “I’m not
going to send anymore, but I’ll still listen”, or “I’m not listening,
good riddance!”.  Most socket libraries, however, are so used to
programmers neglecting to use this piece of etiquette that normally a
‘close’ is the same as ‘shutdown(); close()’.  So in most situations, an
explicit ‘shutdown’ is not needed.

One way to use ‘shutdown’ effectively is in an HTTP-like exchange.  The
client sends a request and then does a ‘shutdown(1)’.  This tells the
server “This client is done sending, but can still receive.” The server
can detect “EOF” by a receive of 0 bytes.  It can assume it has the
complete request.  The server sends a reply.  If the ‘send’ completes
successfully then, indeed, the client was still receiving.

Python takes the automatic shutdown a step further, and says that when a
socket is garbage collected, it will automatically do a ‘close’ if it’s
needed.  But relying on this is a very bad habit.  If your socket just
disappears without doing a ‘close’, the socket at the other end may hang
indefinitely, thinking you’re just being slow.  `Please' ‘close’ your
sockets when you’re done.

* Menu:

* When Sockets Die::


File: python.info,  Node: When Sockets Die,  Up: Disconnecting

10.9.4.1 When Sockets Die
.........................

Probably the worst thing about using blocking sockets is what happens
when the other side comes down hard (without doing a ‘close’).  Your
socket is likely to hang.  TCP is a reliable protocol, and it will wait
a long, long time before giving up on a connection.  If you’re using
threads, the entire thread is essentially dead.  There’s not much you
can do about it.  As long as you aren’t doing something dumb, like
holding a lock while doing a blocking read, the thread isn’t really
consuming much in the way of resources.  Do `not' try to kill the thread
- part of the reason that threads are more efficient than processes is
that they avoid the overhead associated with the automatic recycling of
resources.  In other words, if you do manage to kill the thread, your
whole process is likely to be screwed up.


File: python.info,  Node: Non-blocking Sockets,  Prev: Disconnecting,  Up: Socket Programming HOWTO

10.9.5 Non-blocking Sockets
---------------------------

If you’ve understood the preceding, you already know most of what you
need to know about the mechanics of using sockets.  You’ll still use the
same calls, in much the same ways.  It’s just that, if you do it right,
your app will be almost inside-out.

In Python, you use ‘socket.setblocking(False)’ to make it non-blocking.
In C, it’s more complex, (for one thing, you’ll need to choose between
the BSD flavor ‘O_NONBLOCK’ and the almost indistinguishable POSIX
flavor ‘O_NDELAY’, which is completely different from ‘TCP_NODELAY’),
but it’s the exact same idea.  You do this after creating the socket,
but before using it.  (Actually, if you’re nuts, you can switch back and
forth.)

The major mechanical difference is that ‘send’, ‘recv’, ‘connect’ and
‘accept’ can return without having done anything.  You have (of course)
a number of choices.  You can check return code and error codes and
generally drive yourself crazy.  If you don’t believe me, try it
sometime.  Your app will grow large, buggy and suck CPU. So let’s skip
the brain-dead solutions and do it right.

Use ‘select’.

In C, coding ‘select’ is fairly complex.  In Python, it’s a piece of
cake, but it’s close enough to the C version that if you understand
‘select’ in Python, you’ll have little trouble with it in C:

     ready_to_read, ready_to_write, in_error = \
                    select.select(
                       potential_readers,
                       potential_writers,
                       potential_errs,
                       timeout)

You pass ‘select’ three lists: the first contains all sockets that you
might want to try reading; the second all the sockets you might want to
try writing to, and the last (normally left empty) those that you want
to check for errors.  You should note that a socket can go into more
than one list.  The ‘select’ call is blocking, but you can give it a
timeout.  This is generally a sensible thing to do - give it a nice long
timeout (say a minute) unless you have good reason to do otherwise.

In return, you will get three lists.  They contain the sockets that are
actually readable, writable and in error.  Each of these lists is a
subset (possibly empty) of the corresponding list you passed in.

If a socket is in the output readable list, you can be
as-close-to-certain-as-we-ever-get-in-this-business that a ‘recv’ on
that socket will return `something'.  Same idea for the writable list.
You’ll be able to send `something'.  Maybe not all you want to, but
`something' is better than nothing.  (Actually, any reasonably healthy
socket will return as writable - it just means outbound network buffer
space is available.)

If you have a “server” socket, put it in the potential_readers list.  If
it comes out in the readable list, your ‘accept’ will (almost certainly)
work.  If you have created a new socket to ‘connect’ to someone else,
put it in the potential_writers list.  If it shows up in the writable
list, you have a decent chance that it has connected.

Actually, ‘select’ can be handy even with blocking sockets.  It’s one
way of determining whether you will block - the socket returns as
readable when there’s something in the buffers.  However, this still
doesn’t help with the problem of determining whether the other end is
done, or just busy with something else.

`Portability alert': On Unix, ‘select’ works both with the sockets and
files.  Don’t try this on Windows.  On Windows, ‘select’ works with
sockets only.  Also note that in C, many of the more advanced socket
options are done differently on Windows.  In fact, on Windows I usually
use threads (which work very, very well) with my sockets.


File: python.info,  Node: Sorting HOW TO,  Next: Unicode HOWTO,  Prev: Socket Programming HOWTO,  Up: Python HOWTOs

10.10 Sorting HOW TO
====================


Author: Andrew Dalke and Raymond Hettinger


Release: 0.1

Python lists have a built-in *note list.sort(): 548. method that
modifies the list in-place.  There is also a *note sorted(): 547.
built-in function that builds a new sorted list from an iterable.

In this document, we explore the various techniques for sorting data
using Python.

* Menu:

* Sorting Basics::
* Key Functions::
* Operator Module Functions::
* Ascending and Descending::
* Sort Stability and Complex Sorts::
* The Old Way Using Decorate-Sort-Undecorate::
* The Old Way Using the cmp Parameter::
* Odd and Ends::


File: python.info,  Node: Sorting Basics,  Next: Key Functions,  Up: Sorting HOW TO

10.10.1 Sorting Basics
----------------------

A simple ascending sort is very easy: just call the *note sorted(): 547.
function.  It returns a new sorted list:

     >>> sorted([5, 2, 3, 1, 4])
     [1, 2, 3, 4, 5]

You can also use the *note list.sort(): 548. method.  It modifies the
list in-place (and returns ‘None’ to avoid confusion).  Usually it’s
less convenient than *note sorted(): 547. - but if you don’t need the
original list, it’s slightly more efficient.

     >>> a = [5, 2, 3, 1, 4]
     >>> a.sort()
     >>> a
     [1, 2, 3, 4, 5]

Another difference is that the *note list.sort(): 548. method is only
defined for lists.  In contrast, the *note sorted(): 547. function
accepts any iterable.

     >>> sorted({1: 'D', 2: 'B', 3: 'B', 4: 'E', 5: 'A'})
     [1, 2, 3, 4, 5]


File: python.info,  Node: Key Functions,  Next: Operator Module Functions,  Prev: Sorting Basics,  Up: Sorting HOW TO

10.10.2 Key Functions
---------------------

Both *note list.sort(): 548. and *note sorted(): 547. have a `key'
parameter to specify a function (or other callable) to be called on each
list element prior to making comparisons.

For example, here’s a case-insensitive string comparison:

     >>> sorted("This is a test string from Andrew".split(), key=str.lower)
     ['a', 'Andrew', 'from', 'is', 'string', 'test', 'This']

The value of the `key' parameter should be a function (or other
callable) that takes a single argument and returns a key to use for
sorting purposes.  This technique is fast because the key function is
called exactly once for each input record.

A common pattern is to sort complex objects using some of the object’s
indices as keys.  For example:

     >>> student_tuples = [
     ...     ('john', 'A', 15),
     ...     ('jane', 'B', 12),
     ...     ('dave', 'B', 10),
     ... ]
     >>> sorted(student_tuples, key=lambda student: student[2])   # sort by age
     [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

The same technique works for objects with named attributes.  For
example:

     >>> class Student:
     ...     def __init__(self, name, grade, age):
     ...         self.name = name
     ...         self.grade = grade
     ...         self.age = age
     ...     def __repr__(self):
     ...         return repr((self.name, self.grade, self.age))

     >>> student_objects = [
     ...     Student('john', 'A', 15),
     ...     Student('jane', 'B', 12),
     ...     Student('dave', 'B', 10),
     ... ]
     >>> sorted(student_objects, key=lambda student: student.age)   # sort by age
     [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]


File: python.info,  Node: Operator Module Functions,  Next: Ascending and Descending,  Prev: Key Functions,  Up: Sorting HOW TO

10.10.3 Operator Module Functions
---------------------------------

The key-function patterns shown above are very common, so Python
provides convenience functions to make accessor functions easier and
faster.  The *note operator: c2. module has *note itemgetter(): 38b,
*note attrgetter(): 80a, and a *note methodcaller(): 80b. function.

Using those functions, the above examples become simpler and faster:

     >>> from operator import itemgetter, attrgetter

     >>> sorted(student_tuples, key=itemgetter(2))
     [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

     >>> sorted(student_objects, key=attrgetter('age'))
     [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

The operator module functions allow multiple levels of sorting.  For
example, to sort by `grade' then by `age':

     >>> sorted(student_tuples, key=itemgetter(1,2))
     [('john', 'A', 15), ('dave', 'B', 10), ('jane', 'B', 12)]

     >>> sorted(student_objects, key=attrgetter('grade', 'age'))
     [('john', 'A', 15), ('dave', 'B', 10), ('jane', 'B', 12)]


File: python.info,  Node: Ascending and Descending,  Next: Sort Stability and Complex Sorts,  Prev: Operator Module Functions,  Up: Sorting HOW TO

10.10.4 Ascending and Descending
--------------------------------

Both *note list.sort(): 548. and *note sorted(): 547. accept a `reverse'
parameter with a boolean value.  This is used to flag descending sorts.
For example, to get the student data in reverse `age' order:

     >>> sorted(student_tuples, key=itemgetter(2), reverse=True)
     [('john', 'A', 15), ('jane', 'B', 12), ('dave', 'B', 10)]

     >>> sorted(student_objects, key=attrgetter('age'), reverse=True)
     [('john', 'A', 15), ('jane', 'B', 12), ('dave', 'B', 10)]


File: python.info,  Node: Sort Stability and Complex Sorts,  Next: The Old Way Using Decorate-Sort-Undecorate,  Prev: Ascending and Descending,  Up: Sorting HOW TO

10.10.5 Sort Stability and Complex Sorts
----------------------------------------

Sorts are guaranteed to be stable(1).  That means that when multiple
records have the same key, their original order is preserved.

     >>> data = [('red', 1), ('blue', 1), ('red', 2), ('blue', 2)]
     >>> sorted(data, key=itemgetter(0))
     [('blue', 1), ('blue', 2), ('red', 1), ('red', 2)]

Notice how the two records for `blue' retain their original order so
that ‘('blue', 1)’ is guaranteed to precede ‘('blue', 2)’.

This wonderful property lets you build complex sorts in a series of
sorting steps.  For example, to sort the student data by descending
`grade' and then ascending `age', do the `age' sort first and then sort
again using `grade':

     >>> s = sorted(student_objects, key=attrgetter('age'))     # sort on secondary key
     >>> sorted(s, key=attrgetter('grade'), reverse=True)       # now sort on primary key, descending
     [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

This can be abstracted out into a wrapper function that can take a list
and tuples of field and order to sort them on multiple passes.

     >>> def multisort(xs, specs):
     ...     for key, reverse in reversed(specs):
     ...         xs.sort(key=attrgetter(key), reverse=reverse)
     ...     return xs

     >>> multisort(list(student_objects), (('grade', True), ('age', False)))
     [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

The Timsort(2) algorithm used in Python does multiple sorts efficiently
because it can take advantage of any ordering already present in a
dataset.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Sorting_algorithm#Stability

   (2) https://en.wikipedia.org/wiki/Timsort


File: python.info,  Node: The Old Way Using Decorate-Sort-Undecorate,  Next: The Old Way Using the cmp Parameter,  Prev: Sort Stability and Complex Sorts,  Up: Sorting HOW TO

10.10.6 The Old Way Using Decorate-Sort-Undecorate
--------------------------------------------------

This idiom is called Decorate-Sort-Undecorate after its three steps:

   * First, the initial list is decorated with new values that control
     the sort order.

   * Second, the decorated list is sorted.

   * Finally, the decorations are removed, creating a list that contains
     only the initial values in the new order.

For example, to sort the student data by `grade' using the DSU approach:

     >>> decorated = [(student.grade, i, student) for i, student in enumerate(student_objects)]
     >>> decorated.sort()
     >>> [student for grade, i, student in decorated]               # undecorate
     [('john', 'A', 15), ('jane', 'B', 12), ('dave', 'B', 10)]

This idiom works because tuples are compared lexicographically; the
first items are compared; if they are the same then the second items are
compared, and so on.

It is not strictly necessary in all cases to include the index `i' in
the decorated list, but including it gives two benefits:

   * The sort is stable – if two items have the same key, their order
     will be preserved in the sorted list.

   * The original items do not have to be comparable because the
     ordering of the decorated tuples will be determined by at most the
     first two items.  So for example the original list could contain
     complex numbers which cannot be sorted directly.

Another name for this idiom is Schwartzian transform(1), after Randal L.
Schwartz, who popularized it among Perl programmers.

Now that Python sorting provides key-functions, this technique is not
often needed.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Schwartzian_transform


File: python.info,  Node: The Old Way Using the cmp Parameter,  Next: Odd and Ends,  Prev: The Old Way Using Decorate-Sort-Undecorate,  Up: Sorting HOW TO

10.10.7 The Old Way Using the `cmp' Parameter
---------------------------------------------

Many constructs given in this HOWTO assume Python 2.4 or later.  Before
that, there was no *note sorted(): 547. builtin and *note list.sort():
548. took no keyword arguments.  Instead, all of the Py2.x versions
supported a `cmp' parameter to handle user specified comparison
functions.

In Py3.0, the `cmp' parameter was removed entirely (as part of a larger
effort to simplify and unify the language, eliminating the conflict
between rich comparisons and the ‘__cmp__()’ magic method).

In Py2.x, sort allowed an optional function which can be called for
doing the comparisons.  That function should take two arguments to be
compared and then return a negative value for less-than, return zero if
they are equal, or return a positive value for greater-than.  For
example, we can do:

     >>> def numeric_compare(x, y):
     ...     return x - y
     >>> sorted([5, 2, 4, 1, 3], cmp=numeric_compare)
     [1, 2, 3, 4, 5]

Or you can reverse the order of comparison with:

     >>> def reverse_numeric(x, y):
     ...     return y - x
     >>> sorted([5, 2, 4, 1, 3], cmp=reverse_numeric)
     [5, 4, 3, 2, 1]

When porting code from Python 2.x to 3.x, the situation can arise when
you have the user supplying a comparison function and you need to
convert that to a key function.  The following wrapper makes that easy
to do:

     def cmp_to_key(mycmp):
         'Convert a cmp= function into a key= function'
         class K:
             def __init__(self, obj, *args):
                 self.obj = obj
             def __lt__(self, other):
                 return mycmp(self.obj, other.obj) < 0
             def __gt__(self, other):
                 return mycmp(self.obj, other.obj) > 0
             def __eq__(self, other):
                 return mycmp(self.obj, other.obj) == 0
             def __le__(self, other):
                 return mycmp(self.obj, other.obj) <= 0
             def __ge__(self, other):
                 return mycmp(self.obj, other.obj) >= 0
             def __ne__(self, other):
                 return mycmp(self.obj, other.obj) != 0
         return K

To convert to a key function, just wrap the old comparison function:

     >>> sorted([5, 2, 4, 1, 3], key=cmp_to_key(reverse_numeric))
     [5, 4, 3, 2, 1]

In Python 3.2, the *note functools.cmp_to_key(): c28. function was added
to the *note functools: 83. module in the standard library.


File: python.info,  Node: Odd and Ends,  Prev: The Old Way Using the cmp Parameter,  Up: Sorting HOW TO

10.10.8 Odd and Ends
--------------------

   * For locale aware sorting, use *note locale.strxfrm(): 31c3. for a
     key function or *note locale.strcoll(): 31c1. for a comparison
     function.

   * The `reverse' parameter still maintains sort stability (so that
     records with equal keys retain the original order).  Interestingly,
     that effect can be simulated without the parameter by using the
     builtin *note reversed(): 2c6. function twice:

          >>> data = [('red', 1), ('blue', 1), ('red', 2), ('blue', 2)]
          >>> standard_way = sorted(data, key=itemgetter(0), reverse=True)
          >>> double_reversed = list(reversed(sorted(reversed(data), key=itemgetter(0))))
          >>> assert standard_way == double_reversed
          >>> standard_way
          [('red', 1), ('red', 2), ('blue', 1), ('blue', 2)]

   * The sort routines are guaranteed to use *note __lt__(): cfe. when
     making comparisons between two objects.  So, it is easy to add a
     standard sort order to a class by defining an *note __lt__(): cfe.
     method:

          >>> Student.__lt__ = lambda self, other: self.age < other.age
          >>> sorted(student_objects)
          [('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

   * Key functions need not depend directly on the objects being sorted.
     A key function can also access external resources.  For instance,
     if the student grades are stored in a dictionary, they can be used
     to sort a separate list of student names:

          >>> students = ['dave', 'john', 'jane']
          >>> newgrades = {'john': 'F', 'jane':'A', 'dave': 'C'}
          >>> sorted(students, key=newgrades.__getitem__)
          ['jane', 'dave', 'john']


File: python.info,  Node: Unicode HOWTO,  Next: HOWTO Fetch Internet Resources Using The urllib Package,  Prev: Sorting HOW TO,  Up: Python HOWTOs

10.11 Unicode HOWTO
===================


Release: 1.12

This HOWTO discusses Python’s support for the Unicode specification for
representing textual data, and explains various problems that people
commonly encounter when trying to work with Unicode.

* Menu:

* Introduction to Unicode::
* Python’s Unicode Support::
* Reading and Writing Unicode Data::
* Acknowledgements: Acknowledgements<10>.


File: python.info,  Node: Introduction to Unicode,  Next: Python’s Unicode Support,  Up: Unicode HOWTO

10.11.1 Introduction to Unicode
-------------------------------

* Menu:

* Definitions::
* Encodings::
* References: References<3>.


File: python.info,  Node: Definitions,  Next: Encodings,  Up: Introduction to Unicode

10.11.1.1 Definitions
.....................

Today’s programs need to be able to handle a wide variety of characters.
Applications are often internationalized to display messages and output
in a variety of user-selectable languages; the same program might need
to output an error message in English, French, Japanese, Hebrew, or
Russian.  Web content can be written in any of these languages and can
also include a variety of emoji symbols.  Python’s string type uses the
Unicode Standard for representing characters, which lets Python programs
work with all these different possible characters.

Unicode (‘https://www.unicode.org/’) is a specification that aims to
list every character used by human languages and give each character its
own unique code.  The Unicode specifications are continually revised and
updated to add new languages and symbols.

A `character' is the smallest possible component of a text.  ‘A’, ‘B’,
‘C’, etc., are all different characters.  So are ‘È’ and ‘Í’.
Characters vary depending on the language or context you’re talking
about.  For example, there’s a character for “Roman Numeral One”, ‘Ⅰ’,
that’s separate from the uppercase letter ‘I’.  They’ll usually look the
same, but these are two different characters that have different
meanings.

The Unicode standard describes how characters are represented by `code
points'.  A code point value is an integer in the range 0 to 0x10FFFF
(about 1.1 million values, the actual number assigned(1) is less than
that).  In the standard and in this document, a code point is written
using the notation ‘U+265E’ to mean the character with value ‘0x265e’
(9,822 in decimal).

The Unicode standard contains a lot of tables listing characters and
their corresponding code points:

     0061    'a'; LATIN SMALL LETTER A
     0062    'b'; LATIN SMALL LETTER B
     0063    'c'; LATIN SMALL LETTER C
     ...
     007B    '{'; LEFT CURLY BRACKET
     ...
     2167    'Ⅷ'; ROMAN NUMERAL EIGHT
     2168    'Ⅸ'; ROMAN NUMERAL NINE
     ...
     265E    '♞'; BLACK CHESS KNIGHT
     265F    '♟'; BLACK CHESS PAWN
     ...
     1F600   '😀'; GRINNING FACE
     1F609   '😉'; WINKING FACE
     ...

Strictly, these definitions imply that it’s meaningless to say ‘this is
character ‘U+265E’’.  ‘U+265E’ is a code point, which represents some
particular character; in this case, it represents the character ‘BLACK
CHESS KNIGHT’, ‘♞’.  In informal contexts, this distinction between code
points and characters will sometimes be forgotten.

A character is represented on a screen or on paper by a set of graphical
elements that’s called a `glyph'.  The glyph for an uppercase A, for
example, is two diagonal strokes and a horizontal stroke, though the
exact details will depend on the font being used.  Most Python code
doesn’t need to worry about glyphs; figuring out the correct glyph to
display is generally the job of a GUI toolkit or a terminal’s font
renderer.

   ---------- Footnotes ----------

   (1) https://www.unicode.org/versions/latest/#Summary


File: python.info,  Node: Encodings,  Next: References<3>,  Prev: Definitions,  Up: Introduction to Unicode

10.11.1.2 Encodings
...................

To summarize the previous section: a Unicode string is a sequence of
code points, which are numbers from 0 through ‘0x10FFFF’ (1,114,111
decimal).  This sequence of code points needs to be represented in
memory as a set of `code units', and `code units' are then mapped to
8-bit bytes.  The rules for translating a Unicode string into a sequence
of bytes are called a `character encoding', or just an `encoding'.

The first encoding you might think of is using 32-bit integers as the
code unit, and then using the CPU’s representation of 32-bit integers.
In this representation, the string “Python” might look like this:

        P           y           t           h           o           n
     0x50 00 00 00 79 00 00 00 74 00 00 00 68 00 00 00 6f 00 00 00 6e 00 00 00
        0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

This representation is straightforward but using it presents a number of
problems.

  1. It’s not portable; different processors order the bytes
     differently.

  2. It’s very wasteful of space.  In most texts, the majority of the
     code points are less than 127, or less than 255, so a lot of space
     is occupied by ‘0x00’ bytes.  The above string takes 24 bytes
     compared to the 6 bytes needed for an ASCII representation.
     Increased RAM usage doesn’t matter too much (desktop computers have
     gigabytes of RAM, and strings aren’t usually that large), but
     expanding our usage of disk and network bandwidth by a factor of 4
     is intolerable.

  3. It’s not compatible with existing C functions such as ‘strlen()’,
     so a new family of wide string functions would need to be used.

Therefore this encoding isn’t used very much, and people instead choose
other encodings that are more efficient and convenient, such as UTF-8.

UTF-8 is one of the most commonly used encodings, and Python often
defaults to using it.  UTF stands for “Unicode Transformation Format”,
and the ‘8’ means that 8-bit values are used in the encoding.  (There
are also UTF-16 and UTF-32 encodings, but they are less frequently used
than UTF-8.)  UTF-8 uses the following rules:

  1. If the code point is < 128, it’s represented by the corresponding
     byte value.

  2. If the code point is >= 128, it’s turned into a sequence of two,
     three, or four bytes, where each byte of the sequence is between
     128 and 255.

UTF-8 has several convenient properties:

  1. It can handle any Unicode code point.

  2. A Unicode string is turned into a sequence of bytes that contains
     embedded zero bytes only where they represent the null character
     (U+0000).  This means that UTF-8 strings can be processed by C
     functions such as ‘strcpy()’ and sent through protocols that can’t
     handle zero bytes for anything other than end-of-string markers.

  3. A string of ASCII text is also valid UTF-8 text.

  4. UTF-8 is fairly compact; the majority of commonly used characters
     can be represented with one or two bytes.

  5. If bytes are corrupted or lost, it’s possible to determine the
     start of the next UTF-8-encoded code point and resynchronize.  It’s
     also unlikely that random 8-bit data will look like valid UTF-8.

  6. UTF-8 is a byte oriented encoding.  The encoding specifies that
     each character is represented by a specific sequence of one or more
     bytes.  This avoids the byte-ordering issues that can occur with
     integer and word oriented encodings, like UTF-16 and UTF-32, where
     the sequence of bytes varies depending on the hardware on which the
     string was encoded.


File: python.info,  Node: References<3>,  Prev: Encodings,  Up: Introduction to Unicode

10.11.1.3 References
....................

The Unicode Consortium site(1) has character charts, a glossary, and PDF
versions of the Unicode specification.  Be prepared for some difficult
reading.  A chronology(2) of the origin and development of Unicode is
also available on the site.

On the Computerphile Youtube channel, Tom Scott briefly discusses the
history of Unicode and UTF-8(3) (9 minutes 36 seconds).

To help understand the standard, Jukka Korpela has written an
introductory guide(4) to reading the Unicode character tables.

Another good introductory article(5) was written by Joel Spolsky.  If
this introduction didn’t make things clear to you, you should try
reading this alternate article before continuing.

Wikipedia entries are often helpful; see the entries for “character
encoding(6)” and UTF-8(7), for example.

   ---------- Footnotes ----------

   (1) https://www.unicode.org

   (2) https://www.unicode.org/history/

   (3) https://www.youtube.com/watch?v=MijmeoH9LT4

   (4) http://jkorpela.fi/unicode/guide.html

   (5) 
https://www.joelonsoftware.com/2003/10/08/the-absolute-minimum-every-software-developer-absolutely-positively-must-know-about-unicode-and-character-sets-no-excuses/

   (6) https://en.wikipedia.org/wiki/Character_encoding

   (7) https://en.wikipedia.org/wiki/UTF-8


File: python.info,  Node: Python’s Unicode Support,  Next: Reading and Writing Unicode Data,  Prev: Introduction to Unicode,  Up: Unicode HOWTO

10.11.2 Python’s Unicode Support
--------------------------------

Now that you’ve learned the rudiments of Unicode, we can look at
Python’s Unicode features.

* Menu:

* The String Type::
* Converting to Bytes::
* Unicode Literals in Python Source Code::
* Unicode Properties::
* Comparing Strings::
* Unicode Regular Expressions::
* References: References<4>.


File: python.info,  Node: The String Type,  Next: Converting to Bytes,  Up: Python’s Unicode Support

10.11.2.1 The String Type
.........................

Since Python 3.0, the language’s *note str: 205. type contains Unicode
characters, meaning any string created using ‘"unicode rocks!"’,
‘'unicode rocks!'’, or the triple-quoted string syntax is stored as
Unicode.

The default encoding for Python source code is UTF-8, so you can simply
include a Unicode character in a string literal:

     try:
         with open('/tmp/input.txt', 'r') as f:
             ...
     except OSError:
         # 'File not found' error message.
         print("Fichier non trouvé")

Side note: Python 3 also supports using Unicode characters in
identifiers:

     répertoire = "/tmp/records.log"
     with open(répertoire, "w") as f:
         f.write("test\n")

If you can’t enter a particular character in your editor or want to keep
the source code ASCII-only for some reason, you can also use escape
sequences in string literals.  (Depending on your system, you may see
the actual capital-delta glyph instead of a u escape.)

     >>> "\N{GREEK CAPITAL LETTER DELTA}"  # Using the character name
     '\u0394'
     >>> "\u0394"                          # Using a 16-bit hex value
     '\u0394'
     >>> "\U00000394"                      # Using a 32-bit hex value
     '\u0394'

In addition, one can create a string using the *note decode(): 171.
method of *note bytes: 172.  This method takes an `encoding' argument,
such as ‘UTF-8’, and optionally an `errors' argument.

The `errors' argument specifies the response when the input string can’t
be converted according to the encoding’s rules.  Legal values for this
argument are ‘'strict'’ (raise a *note UnicodeDecodeError: 32b.
exception), ‘'replace'’ (use ‘U+FFFD’, ‘REPLACEMENT CHARACTER’),
‘'ignore'’ (just leave the character out of the Unicode result), or
‘'backslashreplace'’ (inserts a ‘\xNN’ escape sequence).  The following
examples show the differences:

     >>> b'\x80abc'.decode("utf-8", "strict")
     Traceback (most recent call last):
         ...
     UnicodeDecodeError: 'utf-8' codec can't decode byte 0x80 in position 0:
       invalid start byte
     >>> b'\x80abc'.decode("utf-8", "replace")
     '\ufffdabc'
     >>> b'\x80abc'.decode("utf-8", "backslashreplace")
     '\\x80abc'
     >>> b'\x80abc'.decode("utf-8", "ignore")
     'abc'

Encodings are specified as strings containing the encoding’s name.
Python comes with roughly 100 different encodings; see the Python
Library Reference at *note Standard Encodings: 782. for a list.  Some
encodings have multiple names; for example, ‘'latin-1'’, ‘'iso_8859_1'’
and ‘'8859’’ are all synonyms for the same encoding.

One-character Unicode strings can also be created with the *note chr():
155a. built-in function, which takes integers and returns a Unicode
string of length 1 that contains the corresponding code point.  The
reverse operation is the built-in *note ord(): 1559. function that takes
a one-character Unicode string and returns the code point value:

     >>> chr(57344)
     '\ue000'
     >>> ord('\ue000')
     57344


File: python.info,  Node: Converting to Bytes,  Next: Unicode Literals in Python Source Code,  Prev: The String Type,  Up: Python’s Unicode Support

10.11.2.2 Converting to Bytes
.............................

The opposite method of *note bytes.decode(): 171. is *note str.encode():
170, which returns a *note bytes: 172. representation of the Unicode
string, encoded in the requested `encoding'.

The `errors' parameter is the same as the parameter of the *note
decode(): 171. method but supports a few more possible handlers.  As
well as ‘'strict'’, ‘'ignore'’, and ‘'replace'’ (which in this case
inserts a question mark instead of the unencodable character), there is
also ‘'xmlcharrefreplace'’ (inserts an XML character reference),
‘backslashreplace’ (inserts a ‘\uNNNN’ escape sequence) and
‘namereplace’ (inserts a ‘\N{...}’ escape sequence).

The following example shows the different results:

     >>> u = chr(40960) + 'abcd' + chr(1972)
     >>> u.encode('utf-8')
     b'\xea\x80\x80abcd\xde\xb4'
     >>> u.encode('ascii')
     Traceback (most recent call last):
         ...
     UnicodeEncodeError: 'ascii' codec can't encode character '\ua000' in
       position 0: ordinal not in range(128)
     >>> u.encode('ascii', 'ignore')
     b'abcd'
     >>> u.encode('ascii', 'replace')
     b'?abcd?'
     >>> u.encode('ascii', 'xmlcharrefreplace')
     b'&#40960;abcd&#1972;'
     >>> u.encode('ascii', 'backslashreplace')
     b'\\ua000abcd\\u07b4'
     >>> u.encode('ascii', 'namereplace')
     b'\\N{YI SYLLABLE IT}abcd\\u07b4'

The low-level routines for registering and accessing the available
encodings are found in the *note codecs: 1b. module.  Implementing new
encodings also requires understanding the *note codecs: 1b. module.
However, the encoding and decoding functions returned by this module are
usually more low-level than is comfortable, and writing new encodings is
a specialized task, so the module won’t be covered in this HOWTO.


File: python.info,  Node: Unicode Literals in Python Source Code,  Next: Unicode Properties,  Prev: Converting to Bytes,  Up: Python’s Unicode Support

10.11.2.3 Unicode Literals in Python Source Code
................................................

In Python source code, specific Unicode code points can be written using
the ‘\u’ escape sequence, which is followed by four hex digits giving
the code point.  The ‘\U’ escape sequence is similar, but expects eight
hex digits, not four:

     >>> s = "a\xac\u1234\u20ac\U00008000"
     ... #     ^^^^ two-digit hex escape
     ... #         ^^^^^^ four-digit Unicode escape
     ... #                     ^^^^^^^^^^ eight-digit Unicode escape
     >>> [ord(c) for c in s]
     [97, 172, 4660, 8364, 32768]

Using escape sequences for code points greater than 127 is fine in small
doses, but becomes an annoyance if you’re using many accented
characters, as you would in a program with messages in French or some
other accent-using language.  You can also assemble strings using the
*note chr(): 155a. built-in function, but this is even more tedious.

Ideally, you’d want to be able to write literals in your language’s
natural encoding.  You could then edit Python source code with your
favorite editor which would display the accented characters naturally,
and have the right characters used at runtime.

Python supports writing source code in UTF-8 by default, but you can use
almost any encoding if you declare the encoding being used.  This is
done by including a special comment as either the first or second line
of the source file:

     #!/usr/bin/env python
     # -*- coding: latin-1 -*-

     u = 'abcdé'
     print(ord(u[-1]))

The syntax is inspired by Emacs’s notation for specifying variables
local to a file.  Emacs supports many different variables, but Python
only supports ‘coding’.  The ‘-*-’ symbols indicate to Emacs that the
comment is special; they have no significance to Python but are a
convention.  Python looks for ‘coding: name’ or ‘coding=name’ in the
comment.

If you don’t include such a comment, the default encoding used will be
UTF-8 as already mentioned.  See also PEP 263(1) for more information.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0263


File: python.info,  Node: Unicode Properties,  Next: Comparing Strings,  Prev: Unicode Literals in Python Source Code,  Up: Python’s Unicode Support

10.11.2.4 Unicode Properties
............................

The Unicode specification includes a database of information about code
points.  For each defined code point, the information includes the
character’s name, its category, the numeric value if applicable (for
characters representing numeric concepts such as the Roman numerals,
fractions such as one-third and four-fifths, etc.).  There are also
display-related properties, such as how to use the code point in
bidirectional text.

The following program displays some information about several
characters, and prints the numeric value of one particular character:

     import unicodedata

     u = chr(233) + chr(0x0bf2) + chr(3972) + chr(6000) + chr(13231)

     for i, c in enumerate(u):
         print(i, '%04x' % ord(c), unicodedata.category(c), end=" ")
         print(unicodedata.name(c))

     # Get numeric value of second character
     print(unicodedata.numeric(u[1]))

When run, this prints:

     0 00e9 Ll LATIN SMALL LETTER E WITH ACUTE
     1 0bf2 No TAMIL NUMBER ONE THOUSAND
     2 0f84 Mn TIBETAN MARK HALANTA
     3 1770 Lo TAGBANWA LETTER SA
     4 33af So SQUARE RAD OVER S SQUARED
     1000.0

The category codes are abbreviations describing the nature of the
character.  These are grouped into categories such as “Letter”,
“Number”, “Punctuation”, or “Symbol”, which in turn are broken up into
subcategories.  To take the codes from the above output, ‘'Ll'’ means
‘Letter, lowercase’, ‘'No'’ means “Number, other”, ‘'Mn'’ is “Mark,
nonspacing”, and ‘'So'’ is “Symbol, other”.  See the General Category
Values section of the Unicode Character Database documentation(1) for a
list of category codes.

   ---------- Footnotes ----------

   (1) https://www.unicode.org/reports/tr44/#General_Category_Values


File: python.info,  Node: Comparing Strings,  Next: Unicode Regular Expressions,  Prev: Unicode Properties,  Up: Python’s Unicode Support

10.11.2.5 Comparing Strings
...........................

Unicode adds some complication to comparing strings, because the same
set of characters can be represented by different sequences of code
points.  For example, a letter like ‘ê’ can be represented as a single
code point U+00EA, or as U+0065 U+0302, which is the code point for ‘e’
followed by a code point for ‘COMBINING CIRCUMFLEX ACCENT’.  These will
produce the same output when printed, but one is a string of length 1
and the other is of length 2.

One tool for a case-insensitive comparison is the *note casefold(): 7a3.
string method that converts a string to a case-insensitive form
following an algorithm described by the Unicode Standard.  This
algorithm has special handling for characters such as the German letter
‘ß’ (code point U+00DF), which becomes the pair of lowercase letters
‘ss’.

     >>> street = 'Gürzenichstraße'
     >>> street.casefold()
     'gürzenichstrasse'

A second tool is the *note unicodedata: 123. module’s *note normalize():
11e4. function that converts strings to one of several normal forms,
where letters followed by a combining character are replaced with single
characters.  ‘normalize()’ can be used to perform string comparisons
that won’t falsely report inequality if two strings use combining
characters differently:

     import unicodedata

     def compare_strs(s1, s2):
         def NFD(s):
             return unicodedata.normalize('NFD', s)

         return NFD(s1) == NFD(s2)

     single_char = 'ê'
     multiple_chars = '\N{LATIN SMALL LETTER E}\N{COMBINING CIRCUMFLEX ACCENT}'
     print('length of first string=', len(single_char))
     print('length of second string=', len(multiple_chars))
     print(compare_strs(single_char, multiple_chars))

When run, this outputs:

     $ python3 compare-strs.py
     length of first string= 1
     length of second string= 2
     True

The first argument to the *note normalize(): 11e4. function is a string
giving the desired normalization form, which can be one of ‘NFC’,
‘NFKC’, ‘NFD’, and ‘NFKD’.

The Unicode Standard also specifies how to do caseless comparisons:

     import unicodedata

     def compare_caseless(s1, s2):
         def NFD(s):
             return unicodedata.normalize('NFD', s)

         return NFD(NFD(s1).casefold()) == NFD(NFD(s2).casefold())

     # Example usage
     single_char = 'ê'
     multiple_chars = '\N{LATIN CAPITAL LETTER E}\N{COMBINING CIRCUMFLEX ACCENT}'

     print(compare_caseless(single_char, multiple_chars))

This will print ‘True’.  (Why is ‘NFD()’ invoked twice?  Because there
are a few characters that make ‘casefold()’ return a non-normalized
string, so the result needs to be normalized again.  See section 3.13 of
the Unicode Standard for a discussion and an example.)


File: python.info,  Node: Unicode Regular Expressions,  Next: References<4>,  Prev: Comparing Strings,  Up: Python’s Unicode Support

10.11.2.6 Unicode Regular Expressions
.....................................

The regular expressions supported by the *note re: dd. module can be
provided either as bytes or strings.  Some of the special character
sequences such as ‘\d’ and ‘\w’ have different meanings depending on
whether the pattern is supplied as bytes or a string.  For example, ‘\d’
will match the characters ‘[0-9]’ in bytes but in strings will match any
character that’s in the ‘'Nd'’ category.

The string in this example has the number 57 written in both Thai and
Arabic numerals:

     import re
     p = re.compile(r'\d+')

     s = "Over \u0e55\u0e57 57 flavours"
     m = p.search(s)
     print(repr(m.group()))

When executed, ‘\d+’ will match the Thai numerals and print them out.
If you supply the *note re.ASCII: 4cf. flag to *note compile(): 54d,
‘\d+’ will match the substring “57” instead.

Similarly, ‘\w’ matches a wide variety of Unicode characters but only
‘[a-zA-Z0-9_]’ in bytes or if *note re.ASCII: 4cf. is supplied, and ‘\s’
will match either Unicode whitespace characters or ‘[ \t\n\r\f\v]’.


File: python.info,  Node: References<4>,  Prev: Unicode Regular Expressions,  Up: Python’s Unicode Support

10.11.2.7 References
....................

Some good alternative discussions of Python’s Unicode support are:

   * Processing Text Files in Python 3(1), by Nick Coghlan.

   * Pragmatic Unicode(2), a PyCon 2012 presentation by Ned Batchelder.

The *note str: 205. type is described in the Python library reference at
*note Text Sequence Type — str: 1357.

The documentation for the *note unicodedata: 123. module.

The documentation for the *note codecs: 1b. module.

Marc-André Lemburg gave a presentation titled "Python and Unicode" (PDF
slides)(3) at EuroPython 2002.  The slides are an excellent overview of
the design of Python 2’s Unicode features (where the Unicode string type
is called ‘unicode’ and literals start with ‘u’).

   ---------- Footnotes ----------

   (1) 
http://python-notes.curiousefficiency.org/en/latest/python3/text_file_processing.html

   (2) https://nedbatchelder.com/text/unipain.html

   (3) https://downloads.egenix.com/python/Unicode-EPC2002-Talk.pdf


File: python.info,  Node: Reading and Writing Unicode Data,  Next: Acknowledgements<10>,  Prev: Python’s Unicode Support,  Up: Unicode HOWTO

10.11.3 Reading and Writing Unicode Data
----------------------------------------

Once you’ve written some code that works with Unicode data, the next
problem is input/output.  How do you get Unicode strings into your
program, and how do you convert Unicode into a form suitable for storage
or transmission?

It’s possible that you may not need to do anything depending on your
input sources and output destinations; you should check whether the
libraries used in your application support Unicode natively.  XML
parsers often return Unicode data, for example.  Many relational
databases also support Unicode-valued columns and can return Unicode
values from an SQL query.

Unicode data is usually converted to a particular encoding before it
gets written to disk or sent over a socket.  It’s possible to do all the
work yourself: open a file, read an 8-bit bytes object from it, and
convert the bytes with ‘bytes.decode(encoding)’.  However, the manual
approach is not recommended.

One problem is the multi-byte nature of encodings; one Unicode character
can be represented by several bytes.  If you want to read the file in
arbitrary-sized chunks (say, 1024 or 4096 bytes), you need to write
error-handling code to catch the case where only part of the bytes
encoding a single Unicode character are read at the end of a chunk.  One
solution would be to read the entire file into memory and then perform
the decoding, but that prevents you from working with files that are
extremely large; if you need to read a 2 GiB file, you need 2 GiB of
RAM. (More, really, since for at least a moment you’d need to have both
the encoded string and its Unicode version in memory.)

The solution would be to use the low-level decoding interface to catch
the case of partial coding sequences.  The work of implementing this has
already been done for you: the built-in *note open(): 16f. function can
return a file-like object that assumes the file’s contents are in a
specified encoding and accepts Unicode parameters for methods such as
*note read(): 2162. and *note write(): 2165.  This works through *note
open(): 16f.’s `encoding' and `errors' parameters which are interpreted
just like those in *note str.encode(): 170. and *note bytes.decode():
171.

Reading Unicode from a file is therefore simple:

     with open('unicode.txt', encoding='utf-8') as f:
         for line in f:
             print(repr(line))

It’s also possible to open files in update mode, allowing both reading
and writing:

     with open('test', encoding='utf-8', mode='w+') as f:
         f.write('\u4500 blah blah blah\n')
         f.seek(0)
         print(repr(f.readline()[:1]))

The Unicode character ‘U+FEFF’ is used as a byte-order mark (BOM), and
is often written as the first character of a file in order to assist
with autodetection of the file’s byte ordering.  Some encodings, such as
UTF-16, expect a BOM to be present at the start of a file; when such an
encoding is used, the BOM will be automatically written as the first
character and will be silently dropped when the file is read.  There are
variants of these encodings, such as ‘utf-16-le’ and ‘utf-16-be’ for
little-endian and big-endian encodings, that specify one particular byte
ordering and don’t skip the BOM.

In some areas, it is also convention to use a “BOM” at the start of
UTF-8 encoded files; the name is misleading since UTF-8 is not
byte-order dependent.  The mark simply announces that the file is
encoded in UTF-8.  For reading such files, use the ‘utf-8-sig’ codec to
automatically skip the mark if present.

* Menu:

* Unicode filenames::
* Tips for Writing Unicode-aware Programs::
* References: References<5>.


File: python.info,  Node: Unicode filenames,  Next: Tips for Writing Unicode-aware Programs,  Up: Reading and Writing Unicode Data

10.11.3.1 Unicode filenames
...........................

Most of the operating systems in common use today support filenames that
contain arbitrary Unicode characters.  Usually this is implemented by
converting the Unicode string into some encoding that varies depending
on the system.  Today Python is converging on using UTF-8: Python on
MacOS has used UTF-8 for several versions, and Python 3.6 switched to
using UTF-8 on Windows as well.  On Unix systems, there will only be a
filesystem encoding if you’ve set the ‘LANG’ or ‘LC_CTYPE’ environment
variables; if you haven’t, the default encoding is again UTF-8.

The *note sys.getfilesystemencoding(): 5f0. function returns the
encoding to use on your current system, in case you want to do the
encoding manually, but there’s not much reason to bother.  When opening
a file for reading or writing, you can usually just provide the Unicode
string as the filename, and it will be automatically converted to the
right encoding for you:

     filename = 'filename\u4500abc'
     with open(filename, 'w') as f:
         f.write('blah\n')

Functions in the *note os: c4. module such as *note os.stat(): 321. will
also accept Unicode filenames.

The *note os.listdir(): b1c. function returns filenames, which raises an
issue: should it return the Unicode version of filenames, or should it
return bytes containing the encoded versions?  *note os.listdir(): b1c.
can do both, depending on whether you provided the directory path as
bytes or a Unicode string.  If you pass a Unicode string as the path,
filenames will be decoded using the filesystem’s encoding and a list of
Unicode strings will be returned, while passing a byte path will return
the filenames as bytes.  For example, assuming the default filesystem
encoding is UTF-8, running the following program:

     fn = 'filename\u4500abc'
     f = open(fn, 'w')
     f.close()

     import os
     print(os.listdir(b'.'))
     print(os.listdir('.'))

will produce the following output:

     $ python listdir-test.py
     [b'filename\xe4\x94\x80abc', ...]
     ['filename\u4500abc', ...]

The first list contains UTF-8-encoded filenames, and the second list
contains the Unicode versions.

Note that on most occasions, you should can just stick with using
Unicode with these APIs.  The bytes APIs should only be used on systems
where undecodable file names can be present; that’s pretty much only
Unix systems now.


File: python.info,  Node: Tips for Writing Unicode-aware Programs,  Next: References<5>,  Prev: Unicode filenames,  Up: Reading and Writing Unicode Data

10.11.3.2 Tips for Writing Unicode-aware Programs
.................................................

This section provides some suggestions on writing software that deals
with Unicode.

The most important tip is:

     Software should only work with Unicode strings internally, decoding
     the input data as soon as possible and encoding the output only at
     the end.

If you attempt to write processing functions that accept both Unicode
and byte strings, you will find your program vulnerable to bugs wherever
you combine the two different kinds of strings.  There is no automatic
encoding or decoding: if you do e.g.  ‘str + bytes’, a *note TypeError:
1fe. will be raised.

When using data coming from a web browser or some other untrusted
source, a common technique is to check for illegal characters in a
string before using the string in a generated command line or storing it
in a database.  If you’re doing this, be careful to check the decoded
string, not the encoded bytes data; some encodings may have interesting
properties, such as not being bijective or not being fully
ASCII-compatible.  This is especially true if the input data also
specifies the encoding, since the attacker can then choose a clever way
to hide malicious text in the encoded bytestream.

* Menu:

* Converting Between File Encodings::
* Files in an Unknown Encoding::


File: python.info,  Node: Converting Between File Encodings,  Next: Files in an Unknown Encoding,  Up: Tips for Writing Unicode-aware Programs

10.11.3.3 Converting Between File Encodings
...........................................

The *note StreamRecoder: 1108. class can transparently convert between
encodings, taking a stream that returns data in encoding #1 and behaving
like a stream returning data in encoding #2.

For example, if you have an input file `f' that’s in Latin-1, you can
wrap it with a *note StreamRecoder: 1108. to return bytes encoded in
UTF-8:

     new_f = codecs.StreamRecoder(f,
         # en/decoder: used by read() to encode its results and
         # by write() to decode its input.
         codecs.getencoder('utf-8'), codecs.getdecoder('utf-8'),

         # reader/writer: used to read and write to the stream.
         codecs.getreader('latin-1'), codecs.getwriter('latin-1') )


File: python.info,  Node: Files in an Unknown Encoding,  Prev: Converting Between File Encodings,  Up: Tips for Writing Unicode-aware Programs

10.11.3.4 Files in an Unknown Encoding
......................................

What can you do if you need to make a change to a file, but don’t know
the file’s encoding?  If you know the encoding is ASCII-compatible and
only want to examine or modify the ASCII parts, you can open the file
with the ‘surrogateescape’ error handler:

     with open(fname, 'r', encoding="ascii", errors="surrogateescape") as f:
         data = f.read()

     # make changes to the string 'data'

     with open(fname + '.new', 'w',
               encoding="ascii", errors="surrogateescape") as f:
         f.write(data)

The ‘surrogateescape’ error handler will decode any non-ASCII bytes as
code points in a special range running from U+DC80 to U+DCFF. These code
points will then turn back into the same bytes when the
‘surrogateescape’ error handler is used to encode the data and write it
back out.


File: python.info,  Node: References<5>,  Prev: Tips for Writing Unicode-aware Programs,  Up: Reading and Writing Unicode Data

10.11.3.5 References
....................

One section of Mastering Python 3 Input/Output(1), a PyCon 2010 talk by
David Beazley, discusses text processing and binary data handling.

The PDF slides for Marc-André Lemburg’s presentation "Writing
Unicode-aware Applications in Python"(2) discuss questions of character
encodings as well as how to internationalize and localize an
application.  These slides cover Python 2.x only.

The Guts of Unicode in Python(3) is a PyCon 2013 talk by Benjamin
Peterson that discusses the internal Unicode representation in Python
3.3.

   ---------- Footnotes ----------

   (1) http://pyvideo.org/video/289/pycon-2010–mastering-python-3-i-o

   (2) 
https://downloads.egenix.com/python/LSM2005-Developing-Unicode-aware-applications-in-Python.pdf

   (3) http://pyvideo.org/video/1768/the-guts-of-unicode-in-python


File: python.info,  Node: Acknowledgements<10>,  Prev: Reading and Writing Unicode Data,  Up: Unicode HOWTO

10.11.4 Acknowledgements
------------------------

The initial draft of this document was written by Andrew Kuchling.  It
has since been revised further by Alexander Belopolsky, Georg Brandl,
Andrew Kuchling, and Ezio Melotti.

Thanks to the following people who have noted errors or offered
suggestions on this article: Éric Araujo, Nicholas Bastin, Nick Coghlan,
Marius Gedminas, Kent Johnson, Ken Krugler, Marc-André Lemburg, Martin
von Löwis, Terry J. Reedy, Serhiy Storchaka, Eryk Sun, Chad Whitacre,
Graham Wideman.


File: python.info,  Node: HOWTO Fetch Internet Resources Using The urllib Package,  Next: Argparse Tutorial,  Prev: Unicode HOWTO,  Up: Python HOWTOs

10.12 HOWTO Fetch Internet Resources Using The urllib Package
=============================================================


Author: Michael Foord(1)

     Note: There is a French translation of an earlier revision of this
     HOWTO, available at urllib2 - Le Manuel manquant(2).

* Menu:

* Introduction: Introduction<16>.
* Fetching URLs::
* Handling Exceptions: Handling Exceptions<2>.
* info and geturl::
* Openers and Handlers::
* Basic Authentication::
* Proxies::
* Sockets and Layers::
* Footnotes::

   ---------- Footnotes ----------

   (1) http://www.voidspace.org.uk/python/index.shtml

   (2) 
http://www.voidspace.org.uk/python/articles/urllib2_francais.shtml


File: python.info,  Node: Introduction<16>,  Next: Fetching URLs,  Up: HOWTO Fetch Internet Resources Using The urllib Package

10.12.1 Introduction
--------------------

Related Articles
................

You may also find useful the following article on fetching web resources
with Python:

   * Basic Authentication(1)

          A tutorial on `Basic Authentication', with examples in Python.

`urllib.request' is a Python module for fetching URLs (Uniform Resource
Locators).  It offers a very simple interface, in the form of the
`urlopen' function.  This is capable of fetching URLs using a variety of
different protocols.  It also offers a slightly more complex interface
for handling common situations - like basic authentication, cookies,
proxies and so on.  These are provided by objects called handlers and
openers.

urllib.request supports fetching URLs for many “URL schemes” (identified
by the string before the ‘":"’ in URL - for example ‘"ftp"’ is the URL
scheme of ‘"ftp://python.org/"’) using their associated network
protocols (e.g.  FTP, HTTP). This tutorial focuses on the most common
case, HTTP.

For straightforward situations `urlopen' is very easy to use.  But as
soon as you encounter errors or non-trivial cases when opening HTTP
URLs, you will need some understanding of the HyperText Transfer
Protocol.  The most comprehensive and authoritative reference to HTTP is
RFC 2616(2).  This is a technical document and not intended to be easy
to read.  This HOWTO aims to illustrate using `urllib', with enough
detail about HTTP to help you through.  It is not intended to replace
the *note urllib.request: 129. docs, but is supplementary to them.

   ---------- Footnotes ----------

   (1) http://www.voidspace.org.uk/python/articles/authentication.shtml

   (2) https://tools.ietf.org/html/rfc2616.html


File: python.info,  Node: Fetching URLs,  Next: Handling Exceptions<2>,  Prev: Introduction<16>,  Up: HOWTO Fetch Internet Resources Using The urllib Package

10.12.2 Fetching URLs
---------------------

The simplest way to use urllib.request is as follows:

     import urllib.request
     with urllib.request.urlopen('http://python.org/') as response:
        html = response.read()

If you wish to retrieve a resource via URL and store it in a temporary
location, you can do so via the *note shutil.copyfileobj(): 387. and
*note tempfile.NamedTemporaryFile(): e0e. functions:

     import shutil
     import tempfile
     import urllib.request

     with urllib.request.urlopen('http://python.org/') as response:
         with tempfile.NamedTemporaryFile(delete=False) as tmp_file:
             shutil.copyfileobj(response, tmp_file)

     with open(tmp_file.name) as html:
         pass

Many uses of urllib will be that simple (note that instead of an ‘http:’
URL we could have used a URL starting with ‘ftp:’, ‘file:’, etc.).
However, it’s the purpose of this tutorial to explain the more
complicated cases, concentrating on HTTP.

HTTP is based on requests and responses - the client makes requests and
servers send responses.  urllib.request mirrors this with a ‘Request’
object which represents the HTTP request you are making.  In its
simplest form you create a Request object that specifies the URL you
want to fetch.  Calling ‘urlopen’ with this Request object returns a
response object for the URL requested.  This response is a file-like
object, which means you can for example call ‘.read()’ on the response:

     import urllib.request

     req = urllib.request.Request('http://www.voidspace.org.uk')
     with urllib.request.urlopen(req) as response:
        the_page = response.read()

Note that urllib.request makes use of the same Request interface to
handle all URL schemes.  For example, you can make an FTP request like
so:

     req = urllib.request.Request('ftp://example.com/')

In the case of HTTP, there are two extra things that Request objects
allow you to do: First, you can pass data to be sent to the server.
Second, you can pass extra information (“metadata”) `about' the data or
about the request itself, to the server - this information is sent as
HTTP “headers”.  Let’s look at each of these in turn.

* Menu:

* Data::
* Headers::


File: python.info,  Node: Data,  Next: Headers,  Up: Fetching URLs

10.12.2.1 Data
..............

Sometimes you want to send data to a URL (often the URL will refer to a
CGI (Common Gateway Interface) script or other web application).  With
HTTP, this is often done using what’s known as a `POST' request.  This
is often what your browser does when you submit a HTML form that you
filled in on the web.  Not all POSTs have to come from forms: you can
use a POST to transmit arbitrary data to your own application.  In the
common case of HTML forms, the data needs to be encoded in a standard
way, and then passed to the Request object as the ‘data’ argument.  The
encoding is done using a function from the *note urllib.parse: 128.
library.

     import urllib.parse
     import urllib.request

     url = 'http://www.someserver.com/cgi-bin/register.cgi'
     values = {'name' : 'Michael Foord',
               'location' : 'Northampton',
               'language' : 'Python' }

     data = urllib.parse.urlencode(values)
     data = data.encode('ascii') # data should be bytes
     req = urllib.request.Request(url, data)
     with urllib.request.urlopen(req) as response:
        the_page = response.read()

Note that other encodings are sometimes required (e.g.  for file upload
from HTML forms - see HTML Specification, Form Submission(1) for more
details).

If you do not pass the ‘data’ argument, urllib uses a `GET' request.
One way in which GET and POST requests differ is that POST requests
often have “side-effects”: they change the state of the system in some
way (for example by placing an order with the website for a
hundredweight of tinned spam to be delivered to your door).  Though the
HTTP standard makes it clear that POSTs are intended to `always' cause
side-effects, and GET requests `never' to cause side-effects, nothing
prevents a GET request from having side-effects, nor a POST requests
from having no side-effects.  Data can also be passed in an HTTP GET
request by encoding it in the URL itself.

This is done as follows:

     >>> import urllib.request
     >>> import urllib.parse
     >>> data = {}
     >>> data['name'] = 'Somebody Here'
     >>> data['location'] = 'Northampton'
     >>> data['language'] = 'Python'
     >>> url_values = urllib.parse.urlencode(data)
     >>> print(url_values)  # The order may differ from below.
     name=Somebody+Here&language=Python&location=Northampton
     >>> url = 'http://www.example.com/example.cgi'
     >>> full_url = url + '?' + url_values
     >>> data = urllib.request.urlopen(full_url)

Notice that the full URL is created by adding a ‘?’ to the URL, followed
by the encoded values.

   ---------- Footnotes ----------

   (1) https://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13


File: python.info,  Node: Headers,  Prev: Data,  Up: Fetching URLs

10.12.2.2 Headers
.................

We’ll discuss here one particular HTTP header, to illustrate how to add
headers to your HTTP request.

Some websites (1) dislike being browsed by programs, or send different
versions to different browsers (2).  By default urllib identifies itself
as ‘Python-urllib/x.y’ (where ‘x’ and ‘y’ are the major and minor
version numbers of the Python release, e.g.  ‘Python-urllib/2.5’), which
may confuse the site, or just plain not work.  The way a browser
identifies itself is through the ‘User-Agent’ header (3).  When you
create a Request object you can pass a dictionary of headers in.  The
following example makes the same request as above, but identifies itself
as a version of Internet Explorer (4).

     import urllib.parse
     import urllib.request

     url = 'http://www.someserver.com/cgi-bin/register.cgi'
     user_agent = 'Mozilla/5.0 (Windows NT 6.1; Win64; x64)'
     values = {'name': 'Michael Foord',
               'location': 'Northampton',
               'language': 'Python' }
     headers = {'User-Agent': user_agent}

     data = urllib.parse.urlencode(values)
     data = data.encode('ascii')
     req = urllib.request.Request(url, data, headers)
     with urllib.request.urlopen(req) as response:
        the_page = response.read()

The response also has two useful methods.  See the section on *note info
and geturl: 43fb. which comes after we have a look at what happens when
things go wrong.

   ---------- Footnotes ----------

   (1) (1) Google for example.

   (2) (2) Browser sniffing is a very bad practice for website design -
building sites using web standards is much more sensible.  Unfortunately
a lot of sites still send different versions to different browsers.

   (3) (3) The user agent for MSIE 6 is `‘Mozilla/4.0 (compatible; MSIE
6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322)’'

   (4) (4) For details of more HTTP request headers, see Quick Reference
to HTTP Headers (http://jkorpela.fi/http.html).


File: python.info,  Node: Handling Exceptions<2>,  Next: info and geturl,  Prev: Fetching URLs,  Up: HOWTO Fetch Internet Resources Using The urllib Package

10.12.3 Handling Exceptions
---------------------------

`urlopen' raises ‘URLError’ when it cannot handle a response (though as
usual with Python APIs, built-in exceptions such as *note ValueError:
16d, *note TypeError: 1fe. etc.  may also be raised).

‘HTTPError’ is the subclass of ‘URLError’ raised in the specific case of
HTTP URLs.

The exception classes are exported from the *note urllib.error: 127.
module.

* Menu:

* URLError::
* HTTPError::
* Wrapping it Up::


File: python.info,  Node: URLError,  Next: HTTPError,  Up: Handling Exceptions<2>

10.12.3.1 URLError
..................

Often, URLError is raised because there is no network connection (no
route to the specified server), or the specified server doesn’t exist.
In this case, the exception raised will have a ‘reason’ attribute, which
is a tuple containing an error code and a text error message.

e.g.

     >>> req = urllib.request.Request('http://www.pretend_server.org')
     >>> try: urllib.request.urlopen(req)
     ... except urllib.error.URLError as e:
     ...     print(e.reason)
     ...
     (4, 'getaddrinfo failed')


File: python.info,  Node: HTTPError,  Next: Wrapping it Up,  Prev: URLError,  Up: Handling Exceptions<2>

10.12.3.2 HTTPError
...................

Every HTTP response from the server contains a numeric “status code”.
Sometimes the status code indicates that the server is unable to fulfil
the request.  The default handlers will handle some of these responses
for you (for example, if the response is a “redirection” that requests
the client fetch the document from a different URL, urllib will handle
that for you).  For those it can’t handle, urlopen will raise an
‘HTTPError’.  Typical errors include ‘404’ (page not found), ‘403’
(request forbidden), and ‘401’ (authentication required).

See section 10 of RFC 2616(1) for a reference on all the HTTP error
codes.

The ‘HTTPError’ instance raised will have an integer ‘code’ attribute,
which corresponds to the error sent by the server.

* Menu:

* Error Codes::

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2616.html


File: python.info,  Node: Error Codes,  Up: HTTPError

10.12.3.3 Error Codes
.....................

Because the default handlers handle redirects (codes in the 300 range),
and codes in the 100–299 range indicate success, you will usually only
see error codes in the 400–599 range.

*note http.server.BaseHTTPRequestHandler.responses: 2e15. is a useful
dictionary of response codes in that shows all the response codes used
by RFC 2616(1).  The dictionary is reproduced here for convenience

     # Table mapping response codes to messages; entries have the
     # form {code: (shortmessage, longmessage)}.
     responses = {
         100: ('Continue', 'Request received, please continue'),
         101: ('Switching Protocols',
               'Switching to new protocol; obey Upgrade header'),

         200: ('OK', 'Request fulfilled, document follows'),
         201: ('Created', 'Document created, URL follows'),
         202: ('Accepted',
               'Request accepted, processing continues off-line'),
         203: ('Non-Authoritative Information', 'Request fulfilled from cache'),
         204: ('No Content', 'Request fulfilled, nothing follows'),
         205: ('Reset Content', 'Clear input form for further input.'),
         206: ('Partial Content', 'Partial content follows.'),

         300: ('Multiple Choices',
               'Object has several resources -- see URI list'),
         301: ('Moved Permanently', 'Object moved permanently -- see URI list'),
         302: ('Found', 'Object moved temporarily -- see URI list'),
         303: ('See Other', 'Object moved -- see Method and URL list'),
         304: ('Not Modified',
               'Document has not changed since given time'),
         305: ('Use Proxy',
               'You must use proxy specified in Location to access this '
               'resource.'),
         307: ('Temporary Redirect',
               'Object moved temporarily -- see URI list'),

         400: ('Bad Request',
               'Bad request syntax or unsupported method'),
         401: ('Unauthorized',
               'No permission -- see authorization schemes'),
         402: ('Payment Required',
               'No payment -- see charging schemes'),
         403: ('Forbidden',
               'Request forbidden -- authorization will not help'),
         404: ('Not Found', 'Nothing matches the given URI'),
         405: ('Method Not Allowed',
               'Specified method is invalid for this server.'),
         406: ('Not Acceptable', 'URI not available in preferred format.'),
         407: ('Proxy Authentication Required', 'You must authenticate with '
               'this proxy before proceeding.'),
         408: ('Request Timeout', 'Request timed out; try again later.'),
         409: ('Conflict', 'Request conflict.'),
         410: ('Gone',
               'URI no longer exists and has been permanently removed.'),
         411: ('Length Required', 'Client must specify Content-Length.'),
         412: ('Precondition Failed', 'Precondition in headers is false.'),
         413: ('Request Entity Too Large', 'Entity is too large.'),
         414: ('Request-URI Too Long', 'URI is too long.'),
         415: ('Unsupported Media Type', 'Entity body in unsupported format.'),
         416: ('Requested Range Not Satisfiable',
               'Cannot satisfy request range.'),
         417: ('Expectation Failed',
               'Expect condition could not be satisfied.'),

         500: ('Internal Server Error', 'Server got itself in trouble'),
         501: ('Not Implemented',
               'Server does not support this operation'),
         502: ('Bad Gateway', 'Invalid responses from another server/proxy.'),
         503: ('Service Unavailable',
               'The server cannot process the request due to a high load'),
         504: ('Gateway Timeout',
               'The gateway server did not receive a timely response'),
         505: ('HTTP Version Not Supported', 'Cannot fulfill request.'),
         }

When an error is raised the server responds by returning an HTTP error
code `and' an error page.  You can use the ‘HTTPError’ instance as a
response on the page returned.  This means that as well as the code
attribute, it also has read, geturl, and info, methods as returned by
the ‘urllib.response’ module:

     >>> req = urllib.request.Request('http://www.python.org/fish.html')
     >>> try:
     ...     urllib.request.urlopen(req)
     ... except urllib.error.HTTPError as e:
     ...     print(e.code)
     ...     print(e.read())
     ...
     404
     b'<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
       "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">\n\n\n<html
       ...
       <title>Page Not Found</title>\n
       ...

   ---------- Footnotes ----------

   (1) https://tools.ietf.org/html/rfc2616.html


File: python.info,  Node: Wrapping it Up,  Prev: HTTPError,  Up: Handling Exceptions<2>

10.12.3.4 Wrapping it Up
........................

So if you want to be prepared for ‘HTTPError’ `or' ‘URLError’ there are
two basic approaches.  I prefer the second approach.

* Menu:

* Number 1::
* Number 2::


File: python.info,  Node: Number 1,  Next: Number 2,  Up: Wrapping it Up

10.12.3.5 Number 1
..................

     from urllib.request import Request, urlopen
     from urllib.error import URLError, HTTPError
     req = Request(someurl)
     try:
         response = urlopen(req)
     except HTTPError as e:
         print('The server couldn\'t fulfill the request.')
         print('Error code: ', e.code)
     except URLError as e:
         print('We failed to reach a server.')
         print('Reason: ', e.reason)
     else:
         # everything is fine

     Note: The ‘except HTTPError’ `must' come first, otherwise ‘except
     URLError’ will `also' catch an ‘HTTPError’.


File: python.info,  Node: Number 2,  Prev: Number 1,  Up: Wrapping it Up

10.12.3.6 Number 2
..................

     from urllib.request import Request, urlopen
     from urllib.error import URLError
     req = Request(someurl)
     try:
         response = urlopen(req)
     except URLError as e:
         if hasattr(e, 'reason'):
             print('We failed to reach a server.')
             print('Reason: ', e.reason)
         elif hasattr(e, 'code'):
             print('The server couldn\'t fulfill the request.')
             print('Error code: ', e.code)
     else:
         # everything is fine


File: python.info,  Node: info and geturl,  Next: Openers and Handlers,  Prev: Handling Exceptions<2>,  Up: HOWTO Fetch Internet Resources Using The urllib Package

10.12.4 info and geturl
-----------------------

The response returned by urlopen (or the ‘HTTPError’ instance) has two
useful methods ‘info()’ and ‘geturl()’ and is defined in the module
*note urllib.response: 12a..

`geturl' - this returns the real URL of the page fetched.  This is
useful because ‘urlopen’ (or the opener object used) may have followed a
redirect.  The URL of the page fetched may not be the same as the URL
requested.

`info' - this returns a dictionary-like object that describes the page
fetched, particularly the headers sent by the server.  It is currently
an ‘http.client.HTTPMessage’ instance.

Typical headers include ‘Content-length’, ‘Content-type’, and so on.
See the Quick Reference to HTTP Headers(1) for a useful listing of HTTP
headers with brief explanations of their meaning and use.

   ---------- Footnotes ----------

   (1) http://jkorpela.fi/http.html


File: python.info,  Node: Openers and Handlers,  Next: Basic Authentication,  Prev: info and geturl,  Up: HOWTO Fetch Internet Resources Using The urllib Package

10.12.5 Openers and Handlers
----------------------------

When you fetch a URL you use an opener (an instance of the perhaps
confusingly-named *note urllib.request.OpenerDirector: 2d72.).  Normally
we have been using the default opener - via ‘urlopen’ - but you can
create custom openers.  Openers use handlers.  All the “heavy lifting”
is done by the handlers.  Each handler knows how to open URLs for a
particular URL scheme (http, ftp, etc.), or how to handle an aspect of
URL opening, for example HTTP redirections or HTTP cookies.

You will want to create openers if you want to fetch URLs with specific
handlers installed, for example to get an opener that handles cookies,
or to get an opener that does not handle redirections.

To create an opener, instantiate an ‘OpenerDirector’, and then call
‘.add_handler(some_handler_instance)’ repeatedly.

Alternatively, you can use ‘build_opener’, which is a convenience
function for creating opener objects with a single function call.
‘build_opener’ adds several handlers by default, but provides a quick
way to add more and/or override the default handlers.

Other sorts of handlers you might want to can handle proxies,
authentication, and other common but slightly specialised situations.

‘install_opener’ can be used to make an ‘opener’ object the (global)
default opener.  This means that calls to ‘urlopen’ will use the opener
you have installed.

Opener objects have an ‘open’ method, which can be called directly to
fetch urls in the same way as the ‘urlopen’ function: there’s no need to
call ‘install_opener’, except as a convenience.


File: python.info,  Node: Basic Authentication,  Next: Proxies,  Prev: Openers and Handlers,  Up: HOWTO Fetch Internet Resources Using The urllib Package

10.12.6 Basic Authentication
----------------------------

To illustrate creating and installing a handler we will use the
‘HTTPBasicAuthHandler’.  For a more detailed discussion of this subject
– including an explanation of how Basic Authentication works - see the
Basic Authentication Tutorial(1).

When authentication is required, the server sends a header (as well as
the 401 error code) requesting authentication.  This specifies the
authentication scheme and a ‘realm’.  The header looks like:
‘WWW-Authenticate: SCHEME realm="REALM"’.

e.g.

     WWW-Authenticate: Basic realm="cPanel Users"

The client should then retry the request with the appropriate name and
password for the realm included as a header in the request.  This is
‘basic authentication’.  In order to simplify this process we can create
an instance of ‘HTTPBasicAuthHandler’ and an opener to use this handler.

The ‘HTTPBasicAuthHandler’ uses an object called a password manager to
handle the mapping of URLs and realms to passwords and usernames.  If
you know what the realm is (from the authentication header sent by the
server), then you can use a ‘HTTPPasswordMgr’.  Frequently one doesn’t
care what the realm is.  In that case, it is convenient to use
‘HTTPPasswordMgrWithDefaultRealm’.  This allows you to specify a default
username and password for a URL. This will be supplied in the absence of
you providing an alternative combination for a specific realm.  We
indicate this by providing ‘None’ as the realm argument to the
‘add_password’ method.

The top-level URL is the first URL that requires authentication.  URLs
“deeper” than the URL you pass to .add_password() will also match.

     # create a password manager
     password_mgr = urllib.request.HTTPPasswordMgrWithDefaultRealm()

     # Add the username and password.
     # If we knew the realm, we could use it instead of None.
     top_level_url = "http://example.com/foo/"
     password_mgr.add_password(None, top_level_url, username, password)

     handler = urllib.request.HTTPBasicAuthHandler(password_mgr)

     # create "opener" (OpenerDirector instance)
     opener = urllib.request.build_opener(handler)

     # use the opener to fetch a URL
     opener.open(a_url)

     # Install the opener.
     # Now all calls to urllib.request.urlopen use our opener.
     urllib.request.install_opener(opener)

     Note: In the above example we only supplied our
     ‘HTTPBasicAuthHandler’ to ‘build_opener’.  By default openers have
     the handlers for normal situations – ‘ProxyHandler’ (if a proxy
     setting such as an ‘http_proxy’ environment variable is set),
     ‘UnknownHandler’, ‘HTTPHandler’, ‘HTTPDefaultErrorHandler’,
     ‘HTTPRedirectHandler’, ‘FTPHandler’, ‘FileHandler’, ‘DataHandler’,
     ‘HTTPErrorProcessor’.

‘top_level_url’ is in fact `either' a full URL (including the ‘http:’
scheme component and the hostname and optionally the port number) e.g.
‘"http://example.com/"’ `or' an “authority” (i.e.  the hostname,
optionally including the port number) e.g.  ‘"example.com"’ or
‘"example.com:8080"’ (the latter example includes a port number).  The
authority, if present, must NOT contain the “userinfo” component - for
example ‘"joe:password@example.com"’ is not correct.

   ---------- Footnotes ----------

   (1) http://www.voidspace.org.uk/python/articles/authentication.shtml


File: python.info,  Node: Proxies,  Next: Sockets and Layers,  Prev: Basic Authentication,  Up: HOWTO Fetch Internet Resources Using The urllib Package

10.12.7 Proxies
---------------

`urllib' will auto-detect your proxy settings and use those.  This is
through the ‘ProxyHandler’, which is part of the normal handler chain
when a proxy setting is detected.  Normally that’s a good thing, but
there are occasions when it may not be helpful (1).  One way to do this
is to setup our own ‘ProxyHandler’, with no proxies defined.  This is
done using similar steps to setting up a Basic Authentication(2)
handler:

     >>> proxy_support = urllib.request.ProxyHandler({})
     >>> opener = urllib.request.build_opener(proxy_support)
     >>> urllib.request.install_opener(opener)

     Note: Currently ‘urllib.request’ `does not' support fetching of
     ‘https’ locations through a proxy.  However, this can be enabled by
     extending urllib.request as shown in the recipe (3).

     Note: ‘HTTP_PROXY’ will be ignored if a variable ‘REQUEST_METHOD’
     is set; see the documentation on *note getproxies(): 2d7f.

   ---------- Footnotes ----------

   (1) (5) In my case I have to use a proxy to access the internet at
work.  If you attempt to fetch `localhost' URLs through this proxy it
blocks them.  IE is set to use the proxy, which urllib picks up on.  In
order to test scripts with a localhost server, I have to prevent urllib
from using the proxy.

   (2) http://www.voidspace.org.uk/python/articles/authentication.shtml

   (3) (6) urllib opener for SSL proxy (CONNECT method): ASPN Cookbook
Recipe (https://code.activestate.com/recipes/456195/).


File: python.info,  Node: Sockets and Layers,  Next: Footnotes,  Prev: Proxies,  Up: HOWTO Fetch Internet Resources Using The urllib Package

10.12.8 Sockets and Layers
--------------------------

The Python support for fetching resources from the web is layered.
urllib uses the *note http.client: 93. library, which in turn uses the
socket library.

As of Python 2.3 you can specify how long a socket should wait for a
response before timing out.  This can be useful in applications which
have to fetch web pages.  By default the socket module has `no timeout'
and can hang.  Currently, the socket timeout is not exposed at the
http.client or urllib.request levels.  However, you can set the default
timeout globally for all sockets using

     import socket
     import urllib.request

     # timeout in seconds
     timeout = 10
     socket.setdefaulttimeout(timeout)

     # this call to urllib.request.urlopen now uses the default timeout
     # we have set in the socket module
     req = urllib.request.Request('http://www.voidspace.org.uk')
     response = urllib.request.urlopen(req)

__________________________________________________________________


File: python.info,  Node: Footnotes,  Prev: Sockets and Layers,  Up: HOWTO Fetch Internet Resources Using The urllib Package

10.12.9 Footnotes
-----------------

This document was reviewed and revised by John Lee.


File: python.info,  Node: Argparse Tutorial,  Next: An introduction to the ipaddress module,  Prev: HOWTO Fetch Internet Resources Using The urllib Package,  Up: Python HOWTOs

10.13 Argparse Tutorial
=======================


author: Tshepang Lekhonkhobe

This tutorial is intended to be a gentle introduction to *note argparse:
5, the recommended command-line parsing module in the Python standard
library.

     Note: There are two other modules that fulfill the same task,
     namely *note getopt: 85. (an equivalent for ‘getopt()’ from the C
     language) and the deprecated *note optparse: c3.  Note also that
     *note argparse: 5. is based on *note optparse: c3, and therefore
     very similar in terms of usage.

* Menu:

* Concepts::
* The basics::
* Introducing Positional arguments::
* Introducing Optional arguments::
* Combining Positional and Optional arguments::
* Getting a little more advanced::
* Conclusion::


File: python.info,  Node: Concepts,  Next: The basics,  Up: Argparse Tutorial

10.13.1 Concepts
----------------

Let’s show the sort of functionality that we are going to explore in
this introductory tutorial by making use of the ‘ls’ command:

     $ ls
     cpython  devguide  prog.py  pypy  rm-unused-function.patch
     $ ls pypy
     ctypes_configure  demo  dotviewer  include  lib_pypy  lib-python ...
     $ ls -l
     total 20
     drwxr-xr-x 19 wena wena 4096 Feb 18 18:51 cpython
     drwxr-xr-x  4 wena wena 4096 Feb  8 12:04 devguide
     -rwxr-xr-x  1 wena wena  535 Feb 19 00:05 prog.py
     drwxr-xr-x 14 wena wena 4096 Feb  7 00:59 pypy
     -rw-r--r--  1 wena wena  741 Feb 18 01:01 rm-unused-function.patch
     $ ls --help
     Usage: ls [OPTION]... [FILE]...
     List information about the FILEs (the current directory by default).
     Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.
     ...

A few concepts we can learn from the four commands:

   * The ‘ls’ command is useful when run without any options at all.  It
     defaults to displaying the contents of the current directory.

   * If we want beyond what it provides by default, we tell it a bit
     more.  In this case, we want it to display a different directory,
     ‘pypy’.  What we did is specify what is known as a positional
     argument.  It’s named so because the program should know what to do
     with the value, solely based on where it appears on the command
     line.  This concept is more relevant to a command like ‘cp’, whose
     most basic usage is ‘cp SRC DEST’.  The first position is `what you
     want copied,' and the second position is `where you want it copied
     to'.

   * Now, say we want to change behaviour of the program.  In our
     example, we display more info for each file instead of just showing
     the file names.  The ‘-l’ in that case is known as an optional
     argument.

   * That’s a snippet of the help text.  It’s very useful in that you
     can come across a program you have never used before, and can
     figure out how it works simply by reading its help text.


File: python.info,  Node: The basics,  Next: Introducing Positional arguments,  Prev: Concepts,  Up: Argparse Tutorial

10.13.2 The basics
------------------

Let us start with a very simple example which does (almost) nothing:

     import argparse
     parser = argparse.ArgumentParser()
     parser.parse_args()

Following is a result of running the code:

     $ python3 prog.py
     $ python3 prog.py --help
     usage: prog.py [-h]

     optional arguments:
       -h, --help  show this help message and exit
     $ python3 prog.py --verbose
     usage: prog.py [-h]
     prog.py: error: unrecognized arguments: --verbose
     $ python3 prog.py foo
     usage: prog.py [-h]
     prog.py: error: unrecognized arguments: foo

Here is what is happening:

   * Running the script without any options results in nothing displayed
     to stdout.  Not so useful.

   * The second one starts to display the usefulness of the *note
     argparse: 5. module.  We have done almost nothing, but already we
     get a nice help message.

   * The ‘--help’ option, which can also be shortened to ‘-h’, is the
     only option we get for free (i.e.  no need to specify it).
     Specifying anything else results in an error.  But even then, we do
     get a useful usage message, also for free.


File: python.info,  Node: Introducing Positional arguments,  Next: Introducing Optional arguments,  Prev: The basics,  Up: Argparse Tutorial

10.13.3 Introducing Positional arguments
----------------------------------------

An example:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("echo")
     args = parser.parse_args()
     print(args.echo)

And running the code:

     $ python3 prog.py
     usage: prog.py [-h] echo
     prog.py: error: the following arguments are required: echo
     $ python3 prog.py --help
     usage: prog.py [-h] echo

     positional arguments:
       echo

     optional arguments:
       -h, --help  show this help message and exit
     $ python3 prog.py foo
     foo

Here is what’s happening:

   * We’ve added the ‘add_argument()’ method, which is what we use to
     specify which command-line options the program is willing to
     accept.  In this case, I’ve named it ‘echo’ so that it’s in line
     with its function.

   * Calling our program now requires us to specify an option.

   * The ‘parse_args()’ method actually returns some data from the
     options specified, in this case, ‘echo’.

   * The variable is some form of ‘magic’ that *note argparse: 5.
     performs for free (i.e.  no need to specify which variable that
     value is stored in).  You will also notice that its name matches
     the string argument given to the method, ‘echo’.

Note however that, although the help display looks nice and all, it
currently is not as helpful as it can be.  For example we see that we
got ‘echo’ as a positional argument, but we don’t know what it does,
other than by guessing or by reading the source code.  So, let’s make it
a bit more useful:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("echo", help="echo the string you use here")
     args = parser.parse_args()
     print(args.echo)

And we get:

     $ python3 prog.py -h
     usage: prog.py [-h] echo

     positional arguments:
       echo        echo the string you use here

     optional arguments:
       -h, --help  show this help message and exit

Now, how about doing something even more useful:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("square", help="display a square of a given number")
     args = parser.parse_args()
     print(args.square**2)

Following is a result of running the code:

     $ python3 prog.py 4
     Traceback (most recent call last):
       File "prog.py", line 5, in <module>
         print(args.square**2)
     TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'int'

That didn’t go so well.  That’s because *note argparse: 5. treats the
options we give it as strings, unless we tell it otherwise.  So, let’s
tell *note argparse: 5. to treat that input as an integer:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("square", help="display a square of a given number",
                         type=int)
     args = parser.parse_args()
     print(args.square**2)

Following is a result of running the code:

     $ python3 prog.py 4
     16
     $ python3 prog.py four
     usage: prog.py [-h] square
     prog.py: error: argument square: invalid int value: 'four'

That went well.  The program now even helpfully quits on bad illegal
input before proceeding.


File: python.info,  Node: Introducing Optional arguments,  Next: Combining Positional and Optional arguments,  Prev: Introducing Positional arguments,  Up: Argparse Tutorial

10.13.4 Introducing Optional arguments
--------------------------------------

So far we have been playing with positional arguments.  Let us have a
look on how to add optional ones:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("--verbosity", help="increase output verbosity")
     args = parser.parse_args()
     if args.verbosity:
         print("verbosity turned on")

And the output:

     $ python3 prog.py --verbosity 1
     verbosity turned on
     $ python3 prog.py
     $ python3 prog.py --help
     usage: prog.py [-h] [--verbosity VERBOSITY]

     optional arguments:
       -h, --help            show this help message and exit
       --verbosity VERBOSITY
                             increase output verbosity
     $ python3 prog.py --verbosity
     usage: prog.py [-h] [--verbosity VERBOSITY]
     prog.py: error: argument --verbosity: expected one argument

Here is what is happening:

   * The program is written so as to display something when
     ‘--verbosity’ is specified and display nothing when not.

   * To show that the option is actually optional, there is no error
     when running the program without it.  Note that by default, if an
     optional argument isn’t used, the relevant variable, in this case
     ‘args.verbosity’, is given ‘None’ as a value, which is the reason
     it fails the truth test of the *note if: eab. statement.

   * The help message is a bit different.

   * When using the ‘--verbosity’ option, one must also specify some
     value, any value.

The above example accepts arbitrary integer values for ‘--verbosity’,
but for our simple program, only two values are actually useful, ‘True’
or ‘False’.  Let’s modify the code accordingly:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("--verbose", help="increase output verbosity",
                         action="store_true")
     args = parser.parse_args()
     if args.verbose:
         print("verbosity turned on")

And the output:

     $ python3 prog.py --verbose
     verbosity turned on
     $ python3 prog.py --verbose 1
     usage: prog.py [-h] [--verbose]
     prog.py: error: unrecognized arguments: 1
     $ python3 prog.py --help
     usage: prog.py [-h] [--verbose]

     optional arguments:
       -h, --help  show this help message and exit
       --verbose   increase output verbosity

Here is what is happening:

   * The option is now more of a flag than something that requires a
     value.  We even changed the name of the option to match that idea.
     Note that we now specify a new keyword, ‘action’, and give it the
     value ‘"store_true"’.  This means that, if the option is specified,
     assign the value ‘True’ to ‘args.verbose’.  Not specifying it
     implies ‘False’.

   * It complains when you specify a value, in true spirit of what flags
     actually are.

   * Notice the different help text.

* Menu:

* Short options::


File: python.info,  Node: Short options,  Up: Introducing Optional arguments

10.13.4.1 Short options
.......................

If you are familiar with command line usage, you will notice that I
haven’t yet touched on the topic of short versions of the options.  It’s
quite simple:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("-v", "--verbose", help="increase output verbosity",
                         action="store_true")
     args = parser.parse_args()
     if args.verbose:
         print("verbosity turned on")

And here goes:

     $ python3 prog.py -v
     verbosity turned on
     $ python3 prog.py --help
     usage: prog.py [-h] [-v]

     optional arguments:
       -h, --help     show this help message and exit
       -v, --verbose  increase output verbosity

Note that the new ability is also reflected in the help text.


File: python.info,  Node: Combining Positional and Optional arguments,  Next: Getting a little more advanced,  Prev: Introducing Optional arguments,  Up: Argparse Tutorial

10.13.5 Combining Positional and Optional arguments
---------------------------------------------------

Our program keeps growing in complexity:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("square", type=int,
                         help="display a square of a given number")
     parser.add_argument("-v", "--verbose", action="store_true",
                         help="increase output verbosity")
     args = parser.parse_args()
     answer = args.square**2
     if args.verbose:
         print("the square of {} equals {}".format(args.square, answer))
     else:
         print(answer)

And now the output:

     $ python3 prog.py
     usage: prog.py [-h] [-v] square
     prog.py: error: the following arguments are required: square
     $ python3 prog.py 4
     16
     $ python3 prog.py 4 --verbose
     the square of 4 equals 16
     $ python3 prog.py --verbose 4
     the square of 4 equals 16

   * We’ve brought back a positional argument, hence the complaint.

   * Note that the order does not matter.

How about we give this program of ours back the ability to have multiple
verbosity values, and actually get to use them:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("square", type=int,
                         help="display a square of a given number")
     parser.add_argument("-v", "--verbosity", type=int,
                         help="increase output verbosity")
     args = parser.parse_args()
     answer = args.square**2
     if args.verbosity == 2:
         print("the square of {} equals {}".format(args.square, answer))
     elif args.verbosity == 1:
         print("{}^2 == {}".format(args.square, answer))
     else:
         print(answer)

And the output:

     $ python3 prog.py 4
     16
     $ python3 prog.py 4 -v
     usage: prog.py [-h] [-v VERBOSITY] square
     prog.py: error: argument -v/--verbosity: expected one argument
     $ python3 prog.py 4 -v 1
     4^2 == 16
     $ python3 prog.py 4 -v 2
     the square of 4 equals 16
     $ python3 prog.py 4 -v 3
     16

These all look good except the last one, which exposes a bug in our
program.  Let’s fix it by restricting the values the ‘--verbosity’
option can accept:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("square", type=int,
                         help="display a square of a given number")
     parser.add_argument("-v", "--verbosity", type=int, choices=[0, 1, 2],
                         help="increase output verbosity")
     args = parser.parse_args()
     answer = args.square**2
     if args.verbosity == 2:
         print("the square of {} equals {}".format(args.square, answer))
     elif args.verbosity == 1:
         print("{}^2 == {}".format(args.square, answer))
     else:
         print(answer)

And the output:

     $ python3 prog.py 4 -v 3
     usage: prog.py [-h] [-v {0,1,2}] square
     prog.py: error: argument -v/--verbosity: invalid choice: 3 (choose from 0, 1, 2)
     $ python3 prog.py 4 -h
     usage: prog.py [-h] [-v {0,1,2}] square

     positional arguments:
       square                display a square of a given number

     optional arguments:
       -h, --help            show this help message and exit
       -v {0,1,2}, --verbosity {0,1,2}
                             increase output verbosity

Note that the change also reflects both in the error message as well as
the help string.

Now, let’s use a different approach of playing with verbosity, which is
pretty common.  It also matches the way the CPython executable handles
its own verbosity argument (check the output of ‘python --help’):

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("square", type=int,
                         help="display the square of a given number")
     parser.add_argument("-v", "--verbosity", action="count",
                         help="increase output verbosity")
     args = parser.parse_args()
     answer = args.square**2
     if args.verbosity == 2:
         print("the square of {} equals {}".format(args.square, answer))
     elif args.verbosity == 1:
         print("{}^2 == {}".format(args.square, answer))
     else:
         print(answer)

We have introduced another action, “count”, to count the number of
occurrences of a specific optional arguments:

     $ python3 prog.py 4
     16
     $ python3 prog.py 4 -v
     4^2 == 16
     $ python3 prog.py 4 -vv
     the square of 4 equals 16
     $ python3 prog.py 4 --verbosity --verbosity
     the square of 4 equals 16
     $ python3 prog.py 4 -v 1
     usage: prog.py [-h] [-v] square
     prog.py: error: unrecognized arguments: 1
     $ python3 prog.py 4 -h
     usage: prog.py [-h] [-v] square

     positional arguments:
       square           display a square of a given number

     optional arguments:
       -h, --help       show this help message and exit
       -v, --verbosity  increase output verbosity
     $ python3 prog.py 4 -vvv
     16

   * Yes, it’s now more of a flag (similar to ‘action="store_true"’) in
     the previous version of our script.  That should explain the
     complaint.

   * It also behaves similar to “store_true” action.

   * Now here’s a demonstration of what the “count” action gives.
     You’ve probably seen this sort of usage before.

   * And if you don’t specify the ‘-v’ flag, that flag is considered to
     have ‘None’ value.

   * As should be expected, specifying the long form of the flag, we
     should get the same output.

   * Sadly, our help output isn’t very informative on the new ability
     our script has acquired, but that can always be fixed by improving
     the documentation for our script (e.g.  via the ‘help’ keyword
     argument).

   * That last output exposes a bug in our program.

Let’s fix:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("square", type=int,
                         help="display a square of a given number")
     parser.add_argument("-v", "--verbosity", action="count",
                         help="increase output verbosity")
     args = parser.parse_args()
     answer = args.square**2

     # bugfix: replace == with >=
     if args.verbosity >= 2:
         print("the square of {} equals {}".format(args.square, answer))
     elif args.verbosity >= 1:
         print("{}^2 == {}".format(args.square, answer))
     else:
         print(answer)

And this is what it gives:

     $ python3 prog.py 4 -vvv
     the square of 4 equals 16
     $ python3 prog.py 4 -vvvv
     the square of 4 equals 16
     $ python3 prog.py 4
     Traceback (most recent call last):
       File "prog.py", line 11, in <module>
         if args.verbosity >= 2:
     TypeError: '>=' not supported between instances of 'NoneType' and 'int'

   * First output went well, and fixes the bug we had before.  That is,
     we want any value >= 2 to be as verbose as possible.

   * Third output not so good.

Let’s fix that bug:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("square", type=int,
                         help="display a square of a given number")
     parser.add_argument("-v", "--verbosity", action="count", default=0,
                         help="increase output verbosity")
     args = parser.parse_args()
     answer = args.square**2
     if args.verbosity >= 2:
         print("the square of {} equals {}".format(args.square, answer))
     elif args.verbosity >= 1:
         print("{}^2 == {}".format(args.square, answer))
     else:
         print(answer)

We’ve just introduced yet another keyword, ‘default’.  We’ve set it to
‘0’ in order to make it comparable to the other int values.  Remember
that by default, if an optional argument isn’t specified, it gets the
‘None’ value, and that cannot be compared to an int value (hence the
*note TypeError: 1fe. exception).

And:

     $ python3 prog.py 4
     16

You can go quite far just with what we’ve learned so far, and we have
only scratched the surface.  The *note argparse: 5. module is very
powerful, and we’ll explore a bit more of it before we end this
tutorial.


File: python.info,  Node: Getting a little more advanced,  Next: Conclusion,  Prev: Combining Positional and Optional arguments,  Up: Argparse Tutorial

10.13.6 Getting a little more advanced
--------------------------------------

What if we wanted to expand our tiny program to perform other powers,
not just squares:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("x", type=int, help="the base")
     parser.add_argument("y", type=int, help="the exponent")
     parser.add_argument("-v", "--verbosity", action="count", default=0)
     args = parser.parse_args()
     answer = args.x**args.y
     if args.verbosity >= 2:
         print("{} to the power {} equals {}".format(args.x, args.y, answer))
     elif args.verbosity >= 1:
         print("{}^{} == {}".format(args.x, args.y, answer))
     else:
         print(answer)

Output:

     $ python3 prog.py
     usage: prog.py [-h] [-v] x y
     prog.py: error: the following arguments are required: x, y
     $ python3 prog.py -h
     usage: prog.py [-h] [-v] x y

     positional arguments:
       x                the base
       y                the exponent

     optional arguments:
       -h, --help       show this help message and exit
       -v, --verbosity
     $ python3 prog.py 4 2 -v
     4^2 == 16

Notice that so far we’ve been using verbosity level to `change' the text
that gets displayed.  The following example instead uses verbosity level
to display `more' text instead:

     import argparse
     parser = argparse.ArgumentParser()
     parser.add_argument("x", type=int, help="the base")
     parser.add_argument("y", type=int, help="the exponent")
     parser.add_argument("-v", "--verbosity", action="count", default=0)
     args = parser.parse_args()
     answer = args.x**args.y
     if args.verbosity >= 2:
         print("Running '{}'".format(__file__))
     if args.verbosity >= 1:
         print("{}^{} == ".format(args.x, args.y), end="")
     print(answer)

Output:

     $ python3 prog.py 4 2
     16
     $ python3 prog.py 4 2 -v
     4^2 == 16
     $ python3 prog.py 4 2 -vv
     Running 'prog.py'
     4^2 == 16

* Menu:

* Conflicting options::


File: python.info,  Node: Conflicting options,  Up: Getting a little more advanced

10.13.6.1 Conflicting options
.............................

So far, we have been working with two methods of an *note
argparse.ArgumentParser: 788. instance.  Let’s introduce a third one,
‘add_mutually_exclusive_group()’.  It allows for us to specify options
that conflict with each other.  Let’s also change the rest of the
program so that the new functionality makes more sense: we’ll introduce
the ‘--quiet’ option, which will be the opposite of the ‘--verbose’ one:

     import argparse

     parser = argparse.ArgumentParser()
     group = parser.add_mutually_exclusive_group()
     group.add_argument("-v", "--verbose", action="store_true")
     group.add_argument("-q", "--quiet", action="store_true")
     parser.add_argument("x", type=int, help="the base")
     parser.add_argument("y", type=int, help="the exponent")
     args = parser.parse_args()
     answer = args.x**args.y

     if args.quiet:
         print(answer)
     elif args.verbose:
         print("{} to the power {} equals {}".format(args.x, args.y, answer))
     else:
         print("{}^{} == {}".format(args.x, args.y, answer))

Our program is now simpler, and we’ve lost some functionality for the
sake of demonstration.  Anyways, here’s the output:

     $ python3 prog.py 4 2
     4^2 == 16
     $ python3 prog.py 4 2 -q
     16
     $ python3 prog.py 4 2 -v
     4 to the power 2 equals 16
     $ python3 prog.py 4 2 -vq
     usage: prog.py [-h] [-v | -q] x y
     prog.py: error: argument -q/--quiet: not allowed with argument -v/--verbose
     $ python3 prog.py 4 2 -v --quiet
     usage: prog.py [-h] [-v | -q] x y
     prog.py: error: argument -q/--quiet: not allowed with argument -v/--verbose

That should be easy to follow.  I’ve added that last output so you can
see the sort of flexibility you get, i.e.  mixing long form options with
short form ones.

Before we conclude, you probably want to tell your users the main
purpose of your program, just in case they don’t know:

     import argparse

     parser = argparse.ArgumentParser(description="calculate X to the power of Y")
     group = parser.add_mutually_exclusive_group()
     group.add_argument("-v", "--verbose", action="store_true")
     group.add_argument("-q", "--quiet", action="store_true")
     parser.add_argument("x", type=int, help="the base")
     parser.add_argument("y", type=int, help="the exponent")
     args = parser.parse_args()
     answer = args.x**args.y

     if args.quiet:
         print(answer)
     elif args.verbose:
         print("{} to the power {} equals {}".format(args.x, args.y, answer))
     else:
         print("{}^{} == {}".format(args.x, args.y, answer))

Note that slight difference in the usage text.  Note the ‘[-v | -q]’,
which tells us that we can either use ‘-v’ or ‘-q’, but not both at the
same time:

     $ python3 prog.py --help
     usage: prog.py [-h] [-v | -q] x y

     calculate X to the power of Y

     positional arguments:
       x              the base
       y              the exponent

     optional arguments:
       -h, --help     show this help message and exit
       -v, --verbose
       -q, --quiet


File: python.info,  Node: Conclusion,  Prev: Getting a little more advanced,  Up: Argparse Tutorial

10.13.7 Conclusion
------------------

The *note argparse: 5. module offers a lot more than shown here.  Its
docs are quite detailed and thorough, and full of examples.  Having gone
through this tutorial, you should easily digest them without feeling
overwhelmed.


File: python.info,  Node: An introduction to the ipaddress module,  Next: Argument Clinic How-To,  Prev: Argparse Tutorial,  Up: Python HOWTOs

10.14 An introduction to the ipaddress module
=============================================


author: Peter Moody


author: Nick Coghlan

Overview
........

This document aims to provide a gentle introduction to the *note
ipaddress: a2. module.  It is aimed primarily at users that aren’t
already familiar with IP networking terminology, but may also be useful
to network engineers wanting an overview of how *note ipaddress: a2.
represents IP network addressing concepts.

* Menu:

* Creating Address/Network/Interface objects::
* Inspecting Address/Network/Interface Objects::
* Networks as lists of Addresses::
* Comparisons: Comparisons<4>.
* Using IP Addresses with other modules::
* Getting more detail when instance creation fails::


File: python.info,  Node: Creating Address/Network/Interface objects,  Next: Inspecting Address/Network/Interface Objects,  Up: An introduction to the ipaddress module

10.14.1 Creating Address/Network/Interface objects
--------------------------------------------------

Since *note ipaddress: a2. is a module for inspecting and manipulating
IP addresses, the first thing you’ll want to do is create some objects.
You can use *note ipaddress: a2. to create objects from strings and
integers.

* Menu:

* A Note on IP Versions::
* IP Host Addresses::
* Defining Networks::
* Host Interfaces::


File: python.info,  Node: A Note on IP Versions,  Next: IP Host Addresses,  Up: Creating Address/Network/Interface objects

10.14.1.1 A Note on IP Versions
...............................

For readers that aren’t particularly familiar with IP addressing, it’s
important to know that the Internet Protocol is currently in the process
of moving from version 4 of the protocol to version 6.  This transition
is occurring largely because version 4 of the protocol doesn’t provide
enough addresses to handle the needs of the whole world, especially
given the increasing number of devices with direct connections to the
internet.

Explaining the details of the differences between the two versions of
the protocol is beyond the scope of this introduction, but readers need
to at least be aware that these two versions exist, and it will
sometimes be necessary to force the use of one version or the other.


File: python.info,  Node: IP Host Addresses,  Next: Defining Networks,  Prev: A Note on IP Versions,  Up: Creating Address/Network/Interface objects

10.14.1.2 IP Host Addresses
...........................

Addresses, often referred to as “host addresses” are the most basic unit
when working with IP addressing.  The simplest way to create addresses
is to use the *note ipaddress.ip_address(): 3045. factory function,
which automatically determines whether to create an IPv4 or IPv6 address
based on the passed in value:

     >>> ipaddress.ip_address('192.0.2.1')
     IPv4Address('192.0.2.1')
     >>> ipaddress.ip_address('2001:DB8::1')
     IPv6Address('2001:db8::1')

Addresses can also be created directly from integers.  Values that will
fit within 32 bits are assumed to be IPv4 addresses:

     >>> ipaddress.ip_address(3221225985)
     IPv4Address('192.0.2.1')
     >>> ipaddress.ip_address(42540766411282592856903984951653826561)
     IPv6Address('2001:db8::1')

To force the use of IPv4 or IPv6 addresses, the relevant classes can be
invoked directly.  This is particularly useful to force creation of IPv6
addresses for small integers:

     >>> ipaddress.ip_address(1)
     IPv4Address('0.0.0.1')
     >>> ipaddress.IPv4Address(1)
     IPv4Address('0.0.0.1')
     >>> ipaddress.IPv6Address(1)
     IPv6Address('::1')


File: python.info,  Node: Defining Networks,  Next: Host Interfaces,  Prev: IP Host Addresses,  Up: Creating Address/Network/Interface objects

10.14.1.3 Defining Networks
...........................

Host addresses are usually grouped together into IP networks, so *note
ipaddress: a2. provides a way to create, inspect and manipulate network
definitions.  IP network objects are constructed from strings that
define the range of host addresses that are part of that network.  The
simplest form for that information is a “network address/network prefix”
pair, where the prefix defines the number of leading bits that are
compared to determine whether or not an address is part of the network
and the network address defines the expected value of those bits.

As for addresses, a factory function is provided that determines the
correct IP version automatically:

     >>> ipaddress.ip_network('192.0.2.0/24')
     IPv4Network('192.0.2.0/24')
     >>> ipaddress.ip_network('2001:db8::0/96')
     IPv6Network('2001:db8::/96')

Network objects cannot have any host bits set.  The practical effect of
this is that ‘192.0.2.1/24’ does not describe a network.  Such
definitions are referred to as interface objects since the
ip-on-a-network notation is commonly used to describe network interfaces
of a computer on a given network and are described further in the next
section.

By default, attempting to create a network object with host bits set
will result in *note ValueError: 16d. being raised.  To request that the
additional bits instead be coerced to zero, the flag ‘strict=False’ can
be passed to the constructor:

     >>> ipaddress.ip_network('192.0.2.1/24')
     Traceback (most recent call last):
        ...
     ValueError: 192.0.2.1/24 has host bits set
     >>> ipaddress.ip_network('192.0.2.1/24', strict=False)
     IPv4Network('192.0.2.0/24')

While the string form offers significantly more flexibility, networks
can also be defined with integers, just like host addresses.  In this
case, the network is considered to contain only the single address
identified by the integer, so the network prefix includes the entire
network address:

     >>> ipaddress.ip_network(3221225984)
     IPv4Network('192.0.2.0/32')
     >>> ipaddress.ip_network(42540766411282592856903984951653826560)
     IPv6Network('2001:db8::/128')

As with addresses, creation of a particular kind of network can be
forced by calling the class constructor directly instead of using the
factory function.


File: python.info,  Node: Host Interfaces,  Prev: Defining Networks,  Up: Creating Address/Network/Interface objects

10.14.1.4 Host Interfaces
.........................

As mentioned just above, if you need to describe an address on a
particular network, neither the address nor the network classes are
sufficient.  Notation like ‘192.0.2.1/24’ is commonly used by network
engineers and the people who write tools for firewalls and routers as
shorthand for “the host ‘192.0.2.1’ on the network ‘192.0.2.0/24’”,
Accordingly, *note ipaddress: a2. provides a set of hybrid classes that
associate an address with a particular network.  The interface for
creation is identical to that for defining network objects, except that
the address portion isn’t constrained to being a network address.

     >>> ipaddress.ip_interface('192.0.2.1/24')
     IPv4Interface('192.0.2.1/24')
     >>> ipaddress.ip_interface('2001:db8::1/96')
     IPv6Interface('2001:db8::1/96')

Integer inputs are accepted (as with networks), and use of a particular
IP version can be forced by calling the relevant constructor directly.


File: python.info,  Node: Inspecting Address/Network/Interface Objects,  Next: Networks as lists of Addresses,  Prev: Creating Address/Network/Interface objects,  Up: An introduction to the ipaddress module

10.14.2 Inspecting Address/Network/Interface Objects
----------------------------------------------------

You’ve gone to the trouble of creating an
IPv(4|6)(Address|Network|Interface) object, so you probably want to get
information about it.  *note ipaddress: a2. tries to make doing this
easy and intuitive.

Extracting the IP version:

     >>> addr4 = ipaddress.ip_address('192.0.2.1')
     >>> addr6 = ipaddress.ip_address('2001:db8::1')
     >>> addr6.version
     6
     >>> addr4.version
     4

Obtaining the network from an interface:

     >>> host4 = ipaddress.ip_interface('192.0.2.1/24')
     >>> host4.network
     IPv4Network('192.0.2.0/24')
     >>> host6 = ipaddress.ip_interface('2001:db8::1/96')
     >>> host6.network
     IPv6Network('2001:db8::/96')

Finding out how many individual addresses are in a network:

     >>> net4 = ipaddress.ip_network('192.0.2.0/24')
     >>> net4.num_addresses
     256
     >>> net6 = ipaddress.ip_network('2001:db8::0/96')
     >>> net6.num_addresses
     4294967296

Iterating through the “usable” addresses on a network:

     >>> net4 = ipaddress.ip_network('192.0.2.0/24')
     >>> for x in net4.hosts():
     ...     print(x)
     192.0.2.1
     192.0.2.2
     192.0.2.3
     192.0.2.4
     ...
     192.0.2.252
     192.0.2.253
     192.0.2.254

Obtaining the netmask (i.e.  set bits corresponding to the network
prefix) or the hostmask (any bits that are not part of the netmask):

     >>> net4 = ipaddress.ip_network('192.0.2.0/24')
     >>> net4.netmask
     IPv4Address('255.255.255.0')
     >>> net4.hostmask
     IPv4Address('0.0.0.255')
     >>> net6 = ipaddress.ip_network('2001:db8::0/96')
     >>> net6.netmask
     IPv6Address('ffff:ffff:ffff:ffff:ffff:ffff::')
     >>> net6.hostmask
     IPv6Address('::ffff:ffff')

Exploding or compressing the address:

     >>> addr6.exploded
     '2001:0db8:0000:0000:0000:0000:0000:0001'
     >>> addr6.compressed
     '2001:db8::1'
     >>> net6.exploded
     '2001:0db8:0000:0000:0000:0000:0000:0000/96'
     >>> net6.compressed
     '2001:db8::/96'

While IPv4 doesn’t support explosion or compression, the associated
objects still provide the relevant properties so that version neutral
code can easily ensure the most concise or most verbose form is used for
IPv6 addresses while still correctly handling IPv4 addresses.


File: python.info,  Node: Networks as lists of Addresses,  Next: Comparisons<4>,  Prev: Inspecting Address/Network/Interface Objects,  Up: An introduction to the ipaddress module

10.14.3 Networks as lists of Addresses
--------------------------------------

It’s sometimes useful to treat networks as lists.  This means it is
possible to index them like this:

     >>> net4[1]
     IPv4Address('192.0.2.1')
     >>> net4[-1]
     IPv4Address('192.0.2.255')
     >>> net6[1]
     IPv6Address('2001:db8::1')
     >>> net6[-1]
     IPv6Address('2001:db8::ffff:ffff')

It also means that network objects lend themselves to using the list
membership test syntax like this:

     if address in network:
         # do something

Containment testing is done efficiently based on the network prefix:

     >>> addr4 = ipaddress.ip_address('192.0.2.1')
     >>> addr4 in ipaddress.ip_network('192.0.2.0/24')
     True
     >>> addr4 in ipaddress.ip_network('192.0.3.0/24')
     False


File: python.info,  Node: Comparisons<4>,  Next: Using IP Addresses with other modules,  Prev: Networks as lists of Addresses,  Up: An introduction to the ipaddress module

10.14.4 Comparisons
-------------------

*note ipaddress: a2. provides some simple, hopefully intuitive ways to
compare objects, where it makes sense:

     >>> ipaddress.ip_address('192.0.2.1') < ipaddress.ip_address('192.0.2.2')
     True

A *note TypeError: 1fe. exception is raised if you try to compare
objects of different versions or different types.


File: python.info,  Node: Using IP Addresses with other modules,  Next: Getting more detail when instance creation fails,  Prev: Comparisons<4>,  Up: An introduction to the ipaddress module

10.14.5 Using IP Addresses with other modules
---------------------------------------------

Other modules that use IP addresses (such as *note socket: ef.) usually
won’t accept objects from this module directly.  Instead, they must be
coerced to an integer or string that the other module will accept:

     >>> addr4 = ipaddress.ip_address('192.0.2.1')
     >>> str(addr4)
     '192.0.2.1'
     >>> int(addr4)
     3221225985


File: python.info,  Node: Getting more detail when instance creation fails,  Prev: Using IP Addresses with other modules,  Up: An introduction to the ipaddress module

10.14.6 Getting more detail when instance creation fails
--------------------------------------------------------

When creating address/network/interface objects using the
version-agnostic factory functions, any errors will be reported as *note
ValueError: 16d. with a generic error message that simply says the
passed in value was not recognized as an object of that type.  The lack
of a specific error is because it’s necessary to know whether the value
is `supposed' to be IPv4 or IPv6 in order to provide more detail on why
it has been rejected.

To support use cases where it is useful to have access to this
additional detail, the individual class constructors actually raise the
*note ValueError: 16d. subclasses *note ipaddress.AddressValueError:
304d. and *note ipaddress.NetmaskValueError: 3074. to indicate exactly
which part of the definition failed to parse correctly.

The error messages are significantly more detailed when using the class
constructors directly.  For example:

     >>> ipaddress.ip_address("192.168.0.256")
     Traceback (most recent call last):
       ...
     ValueError: '192.168.0.256' does not appear to be an IPv4 or IPv6 address
     >>> ipaddress.IPv4Address("192.168.0.256")
     Traceback (most recent call last):
       ...
     ipaddress.AddressValueError: Octet 256 (> 255) not permitted in '192.168.0.256'

     >>> ipaddress.ip_network("192.168.0.1/64")
     Traceback (most recent call last):
       ...
     ValueError: '192.168.0.1/64' does not appear to be an IPv4 or IPv6 network
     >>> ipaddress.IPv4Network("192.168.0.1/64")
     Traceback (most recent call last):
       ...
     ipaddress.NetmaskValueError: '64' is not a valid netmask

However, both of the module specific exceptions have *note ValueError:
16d. as their parent class, so if you’re not concerned with the
particular type of error, you can still write code like the following:

     try:
         network = ipaddress.IPv4Network(address)
     except ValueError:
         print('address/netmask is invalid for IPv4:', address)


File: python.info,  Node: Argument Clinic How-To,  Next: Instrumenting CPython with DTrace and SystemTap,  Prev: An introduction to the ipaddress module,  Up: Python HOWTOs

10.15 Argument Clinic How-To
============================


author: Larry Hastings

Abstract
........

Argument Clinic is a preprocessor for CPython C files.  Its purpose is
to automate all the boilerplate involved with writing argument parsing
code for “builtins”.  This document shows you how to convert your first
C function to work with Argument Clinic, and then introduces some
advanced topics on Argument Clinic usage.

Currently Argument Clinic is considered internal-only for CPython.  Its
use is not supported for files outside CPython, and no guarantees are
made regarding backwards compatibility for future versions.  In other
words: if you maintain an external C extension for CPython, you’re
welcome to experiment with Argument Clinic in your own code.  But the
version of Argument Clinic that ships with the next version of CPython
`could' be totally incompatible and break all your code.

* Menu:

* The Goals Of Argument Clinic::
* Basic Concepts And Usage::
* Converting Your First Function::
* Advanced Topics::


File: python.info,  Node: The Goals Of Argument Clinic,  Next: Basic Concepts And Usage,  Up: Argument Clinic How-To

10.15.1 The Goals Of Argument Clinic
------------------------------------

Argument Clinic’s primary goal is to take over responsibility for all
argument parsing code inside CPython.  This means that, when you convert
a function to work with Argument Clinic, that function should no longer
do any of its own argument parsing—the code generated by Argument Clinic
should be a “black box” to you, where CPython calls in at the top, and
your code gets called at the bottom, with ‘PyObject *args’ (and maybe
‘PyObject *kwargs’) magically converted into the C variables and types
you need.

In order for Argument Clinic to accomplish its primary goal, it must be
easy to use.  Currently, working with CPython’s argument parsing library
is a chore, requiring maintaining redundant information in a surprising
number of places.  When you use Argument Clinic, you don’t have to
repeat yourself.

Obviously, no one would want to use Argument Clinic unless it’s solving
their problem—and without creating new problems of its own.  So it’s
paramount that Argument Clinic generate correct code.  It’d be nice if
the code was faster, too, but at the very least it should not introduce
a major speed regression.  (Eventually Argument Clinic `should' make a
major speedup possible—we could rewrite its code generator to produce
tailor-made argument parsing code, rather than calling the
general-purpose CPython argument parsing library.  That would make for
the fastest argument parsing possible!)

Additionally, Argument Clinic must be flexible enough to work with any
approach to argument parsing.  Python has some functions with some very
strange parsing behaviors; Argument Clinic’s goal is to support all of
them.

Finally, the original motivation for Argument Clinic was to provide
introspection “signatures” for CPython builtins.  It used to be, the
introspection query functions would throw an exception if you passed in
a builtin.  With Argument Clinic, that’s a thing of the past!

One idea you should keep in mind, as you work with Argument Clinic: the
more information you give it, the better job it’ll be able to do.
Argument Clinic is admittedly relatively simple right now.  But as it
evolves it will get more sophisticated, and it should be able to do many
interesting and smart things with all the information you give it.


File: python.info,  Node: Basic Concepts And Usage,  Next: Converting Your First Function,  Prev: The Goals Of Argument Clinic,  Up: Argument Clinic How-To

10.15.2 Basic Concepts And Usage
--------------------------------

Argument Clinic ships with CPython; you’ll find it in
‘Tools/clinic/clinic.py’.  If you run that script, specifying a C file
as an argument:

     $ python3 Tools/clinic/clinic.py foo.c

Argument Clinic will scan over the file looking for lines that look
exactly like this:

     /*[clinic input]

When it finds one, it reads everything up to a line that looks exactly
like this:

     [clinic start generated code]*/

Everything in between these two lines is input for Argument Clinic.  All
of these lines, including the beginning and ending comment lines, are
collectively called an Argument Clinic “block”.

When Argument Clinic parses one of these blocks, it generates output.
This output is rewritten into the C file immediately after the block,
followed by a comment containing a checksum.  The Argument Clinic block
now looks like this:

     /*[clinic input]
     ... clinic input goes here ...
     [clinic start generated code]*/
     ... clinic output goes here ...
     /*[clinic end generated code: checksum=...]*/

If you run Argument Clinic on the same file a second time, Argument
Clinic will discard the old output and write out the new output with a
fresh checksum line.  However, if the input hasn’t changed, the output
won’t change either.

You should never modify the output portion of an Argument Clinic block.
Instead, change the input until it produces the output you want.
(That’s the purpose of the checksum—to detect if someone changed the
output, as these edits would be lost the next time Argument Clinic
writes out fresh output.)

For the sake of clarity, here’s the terminology we’ll use with Argument
Clinic:

   * The first line of the comment (‘/*[clinic input]’) is the `start
     line'.

   * The last line of the initial comment (‘[clinic start generated
     code]*/’) is the `end line'.

   * The last line (‘/*[clinic end generated code: checksum=...]*/’) is
     the `checksum line'.

   * In between the start line and the end line is the `input'.

   * In between the end line and the checksum line is the `output'.

   * All the text collectively, from the start line to the checksum line
     inclusively, is the `block'.  (A block that hasn’t been
     successfully processed by Argument Clinic yet doesn’t have output
     or a checksum line, but it’s still considered a block.)


File: python.info,  Node: Converting Your First Function,  Next: Advanced Topics,  Prev: Basic Concepts And Usage,  Up: Argument Clinic How-To

10.15.3 Converting Your First Function
--------------------------------------

The best way to get a sense of how Argument Clinic works is to convert a
function to work with it.  Here, then, are the bare minimum steps you’d
need to follow to convert a function to work with Argument Clinic.  Note
that for code you plan to check in to CPython, you really should take
the conversion farther, using some of the advanced concepts you’ll see
later on in the document (like “return converters” and “self
converters”).  But we’ll keep it simple for this walkthrough so you can
learn.

Let’s dive in!

  0. Make sure you’re working with a freshly updated checkout of the
     CPython trunk.

  1. Find a Python builtin that calls either *note PyArg_ParseTuple():
     393. or *note PyArg_ParseTupleAndKeywords(): 6c1, and hasn’t been
     converted to work with Argument Clinic yet.  For my example I’m
     using ‘_pickle.Pickler.dump()’.

  2. If the call to the ‘PyArg_Parse’ function uses any of the following
     format units:

          O&
          O!
          es
          es#
          et
          et#

     or if it has multiple calls to *note PyArg_ParseTuple(): 393, you
     should choose a different function.  Argument Clinic `does' support
     all of these scenarios.  But these are advanced topics—let’s do
     something simpler for your first function.

     Also, if the function has multiple calls to *note
     PyArg_ParseTuple(): 393. or *note PyArg_ParseTupleAndKeywords():
     6c1. where it supports different types for the same argument, or if
     the function uses something besides PyArg_Parse functions to parse
     its arguments, it probably isn’t suitable for conversion to
     Argument Clinic.  Argument Clinic doesn’t support generic functions
     or polymorphic parameters.

  3. Add the following boilerplate above the function, creating our
     block:

          /*[clinic input]
          [clinic start generated code]*/

  4. Cut the docstring and paste it in between the ‘[clinic]’ lines,
     removing all the junk that makes it a properly quoted C string.
     When you’re done you should have just the text, based at the left
     margin, with no line wider than 80 characters.  (Argument Clinic
     will preserve indents inside the docstring.)

     If the old docstring had a first line that looked like a function
     signature, throw that line away.  (The docstring doesn’t need it
     anymore—when you use ‘help()’ on your builtin in the future, the
     first line will be built automatically based on the function’s
     signature.)

     Sample:

          /*[clinic input]
          Write a pickled representation of obj to the open file.
          [clinic start generated code]*/

  5. If your docstring doesn’t have a “summary” line, Argument Clinic
     will complain.  So let’s make sure it has one.  The “summary” line
     should be a paragraph consisting of a single 80-column line at the
     beginning of the docstring.

     (Our example docstring consists solely of a summary line, so the
     sample code doesn’t have to change for this step.)

  6. Above the docstring, enter the name of the function, followed by a
     blank line.  This should be the Python name of the function, and
     should be the full dotted path to the function—it should start with
     the name of the module, include any sub-modules, and if the
     function is a method on a class it should include the class name
     too.

     Sample:

          /*[clinic input]
          _pickle.Pickler.dump

          Write a pickled representation of obj to the open file.
          [clinic start generated code]*/

  7. If this is the first time that module or class has been used with
     Argument Clinic in this C file, you must declare the module and/or
     class.  Proper Argument Clinic hygiene prefers declaring these in a
     separate block somewhere near the top of the C file, in the same
     way that include files and statics go at the top.  (In our sample
     code we’ll just show the two blocks next to each other.)

     The name of the class and module should be the same as the one seen
     by Python.  Check the name defined in the *note PyModuleDef: 25b.
     or *note PyTypeObject: 3f5. as appropriate.

     When you declare a class, you must also specify two aspects of its
     type in C: the type declaration you’d use for a pointer to an
     instance of this class, and a pointer to the *note PyTypeObject:
     3f5. for this class.

     Sample:

          /*[clinic input]
          module _pickle
          class _pickle.Pickler "PicklerObject *" "&Pickler_Type"
          [clinic start generated code]*/

          /*[clinic input]
          _pickle.Pickler.dump

          Write a pickled representation of obj to the open file.
          [clinic start generated code]*/

  8. Declare each of the parameters to the function.  Each parameter
     should get its own line.  All the parameter lines should be
     indented from the function name and the docstring.

     The general form of these parameter lines is as follows:

          name_of_parameter: converter

     If the parameter has a default value, add that after the converter:

          name_of_parameter: converter = default_value

     Argument Clinic’s support for “default values” is quite
     sophisticated; please see *note the section below on default
     values: 4424. for more information.

     Add a blank line below the parameters.

     What’s a “converter”?  It establishes both the type of the variable
     used in C, and the method to convert the Python value into a C
     value at runtime.  For now you’re going to use what’s called a
     “legacy converter”—a convenience syntax intended to make porting
     old code into Argument Clinic easier.

     For each parameter, copy the “format unit” for that parameter from
     the ‘PyArg_Parse()’ format argument and specify `that' as its
     converter, as a quoted string.  (“format unit” is the formal name
     for the one-to-three character substring of the ‘format’ parameter
     that tells the argument parsing function what the type of the
     variable is and how to convert it.  For more on format units please
     see *note Parsing arguments and building values: 3f2.)

     For multicharacter format units like ‘z#’, use the entire
     two-or-three character string.

     Sample:

           /*[clinic input]
           module _pickle
           class _pickle.Pickler "PicklerObject *" "&Pickler_Type"
           [clinic start generated code]*/

           /*[clinic input]
           _pickle.Pickler.dump

              obj: 'O'

          Write a pickled representation of obj to the open file.
          [clinic start generated code]*/

  9. If your function has ‘|’ in the format string, meaning some
     parameters have default values, you can ignore it.  Argument Clinic
     infers which parameters are optional based on whether or not they
     have default values.

     If your function has ‘$’ in the format string, meaning it takes
     keyword-only arguments, specify ‘*’ on a line by itself before the
     first keyword-only argument, indented the same as the parameter
     lines.

     (‘_pickle.Pickler.dump’ has neither, so our sample is unchanged.)

  10. If the existing C function calls *note PyArg_ParseTuple(): 393.
     (as opposed to *note PyArg_ParseTupleAndKeywords(): 6c1.), then all
     its arguments are positional-only.

     To mark all parameters as positional-only in Argument Clinic, add a
     ‘/’ on a line by itself after the last parameter, indented the same
     as the parameter lines.

     Currently this is all-or-nothing; either all parameters are
     positional-only, or none of them are.  (In the future Argument
     Clinic may relax this restriction.)

     Sample:

          /*[clinic input]
          module _pickle
          class _pickle.Pickler "PicklerObject *" "&Pickler_Type"
          [clinic start generated code]*/

          /*[clinic input]
          _pickle.Pickler.dump

              obj: 'O'
              /

          Write a pickled representation of obj to the open file.
          [clinic start generated code]*/

  11. It’s helpful to write a per-parameter docstring for each
     parameter.  But per-parameter docstrings are optional; you can skip
     this step if you prefer.

     Here’s how to add a per-parameter docstring.  The first line of the
     per-parameter docstring must be indented further than the parameter
     definition.  The left margin of this first line establishes the
     left margin for the whole per-parameter docstring; all the text you
     write will be outdented by this amount.  You can write as much text
     as you like, across multiple lines if you wish.

     Sample:

          /*[clinic input]
          module _pickle
          class _pickle.Pickler "PicklerObject *" "&Pickler_Type"
          [clinic start generated code]*/

          /*[clinic input]
          _pickle.Pickler.dump

              obj: 'O'
                  The object to be pickled.
              /

          Write a pickled representation of obj to the open file.
          [clinic start generated code]*/

  12. Save and close the file, then run ‘Tools/clinic/clinic.py’ on it.
     With luck everything worked—your block now has output, and a ‘.c.h’
     file has been generated!  Reopen the file in your text editor to
     see:

          /*[clinic input]
          _pickle.Pickler.dump

              obj: 'O'
                  The object to be pickled.
              /

          Write a pickled representation of obj to the open file.
          [clinic start generated code]*/

          static PyObject *
          _pickle_Pickler_dump(PicklerObject *self, PyObject *obj)
          /*[clinic end generated code: output=87ecad1261e02ac7 input=552eb1c0f52260d9]*/

     Obviously, if Argument Clinic didn’t produce any output, it’s
     because it found an error in your input.  Keep fixing your errors
     and retrying until Argument Clinic processes your file without
     complaint.

     For readability, most of the glue code has been generated to a
     ‘.c.h’ file.  You’ll need to include that in your original ‘.c’
     file, typically right after the clinic module block:

          #include "clinic/_pickle.c.h"

  13. Double-check that the argument-parsing code Argument Clinic
     generated looks basically the same as the existing code.

     First, ensure both places use the same argument-parsing function.
     The existing code must call either *note PyArg_ParseTuple(): 393.
     or *note PyArg_ParseTupleAndKeywords(): 6c1.; ensure that the code
     generated by Argument Clinic calls the `exact' same function.

     Second, the format string passed in to *note PyArg_ParseTuple():
     393. or *note PyArg_ParseTupleAndKeywords(): 6c1. should be
     `exactly' the same as the hand-written one in the existing
     function, up to the colon or semi-colon.

     (Argument Clinic always generates its format strings with a ‘:’
     followed by the name of the function.  If the existing code’s
     format string ends with ‘;’, to provide usage help, this change is
     harmless—don’t worry about it.)

     Third, for parameters whose format units require two arguments
     (like a length variable, or an encoding string, or a pointer to a
     conversion function), ensure that the second argument is `exactly'
     the same between the two invocations.

     Fourth, inside the output portion of the block you’ll find a
     preprocessor macro defining the appropriate static *note
     PyMethodDef: edd. structure for this builtin:

          #define __PICKLE_PICKLER_DUMP_METHODDEF    \
          {"dump", (PyCFunction)__pickle_Pickler_dump, METH_O, __pickle_Pickler_dump__doc__},

     This static structure should be `exactly' the same as the existing
     static *note PyMethodDef: edd. structure for this builtin.

     If any of these items differ in `any way', adjust your Argument
     Clinic function specification and rerun ‘Tools/clinic/clinic.py’
     until they `are' the same.

  14. Notice that the last line of its output is the declaration of your
     “impl” function.  This is where the builtin’s implementation goes.
     Delete the existing prototype of the function you’re modifying, but
     leave the opening curly brace.  Now delete its argument parsing
     code and the declarations of all the variables it dumps the
     arguments into.  Notice how the Python arguments are now arguments
     to this impl function; if the implementation used different names
     for these variables, fix it.

     Let’s reiterate, just because it’s kind of weird.  Your code should
     now look like this:

          static return_type
          your_function_impl(...)
          /*[clinic end generated code: checksum=...]*/
          {
          ...

     Argument Clinic generated the checksum line and the function
     prototype just above it.  You should write the opening (and
     closing) curly braces for the function, and the implementation
     inside.

     Sample:

          /*[clinic input]
          module _pickle
          class _pickle.Pickler "PicklerObject *" "&Pickler_Type"
          [clinic start generated code]*/
          /*[clinic end generated code: checksum=da39a3ee5e6b4b0d3255bfef95601890afd80709]*/

          /*[clinic input]
          _pickle.Pickler.dump

              obj: 'O'
                  The object to be pickled.
              /

          Write a pickled representation of obj to the open file.
          [clinic start generated code]*/

          PyDoc_STRVAR(__pickle_Pickler_dump__doc__,
          "Write a pickled representation of obj to the open file.\n"
          "\n"
          ...
          static PyObject *
          _pickle_Pickler_dump_impl(PicklerObject *self, PyObject *obj)
          /*[clinic end generated code: checksum=3bd30745bf206a48f8b576a1da3d90f55a0a4187]*/
          {
              /* Check whether the Pickler was initialized correctly (issue3664).
                 Developers often forget to call __init__() in their subclasses, which
                 would trigger a segfault without this check. */
              if (self->write == NULL) {
                  PyErr_Format(PicklingError,
                               "Pickler.__init__() was not called by %s.__init__()",
                               Py_TYPE(self)->tp_name);
                  return NULL;
              }

              if (_Pickler_ClearBuffer(self) < 0)
                  return NULL;

              ...

  15. Remember the macro with the *note PyMethodDef: edd. structure for
     this function?  Find the existing *note PyMethodDef: edd. structure
     for this function and replace it with a reference to the macro.
     (If the builtin is at module scope, this will probably be very near
     the end of the file; if the builtin is a class method, this will
     probably be below but relatively near to the implementation.)

     Note that the body of the macro contains a trailing comma.  So when
     you replace the existing static *note PyMethodDef: edd. structure
     with the macro, `don’t' add a comma to the end.

     Sample:

          static struct PyMethodDef Pickler_methods[] = {
              __PICKLE_PICKLER_DUMP_METHODDEF
              __PICKLE_PICKLER_CLEAR_MEMO_METHODDEF
              {NULL, NULL}                /* sentinel */
          };

  16. Compile, then run the relevant portions of the regression-test
     suite.  This change should not introduce any new compile-time
     warnings or errors, and there should be no externally-visible
     change to Python’s behavior.

     Well, except for one difference: ‘inspect.signature()’ run on your
     function should now provide a valid signature!

     Congratulations, you’ve ported your first function to work with
     Argument Clinic!


File: python.info,  Node: Advanced Topics,  Prev: Converting Your First Function,  Up: Argument Clinic How-To

10.15.4 Advanced Topics
-----------------------

Now that you’ve had some experience working with Argument Clinic, it’s
time for some advanced topics.

* Menu:

* Symbolic default values::
* Renaming the C functions and variables generated by Argument Clinic::
* Converting functions using PyArg_UnpackTuple::
* Optional Groups::
* Using real Argument Clinic converters, instead of “legacy converters”: Using real Argument Clinic converters instead of “legacy converters”.
* Py_buffer::
* Advanced converters::
* Parameter default values::
* The NULL default value::
* Expressions specified as default values::
* Using a return converter::
* Cloning existing functions::
* Calling Python code::
* Using a “self converter”::
* Writing a custom converter::
* Writing a custom return converter::
* METH_O and METH_NOARGS::
* tp_new and tp_init functions::
* Changing and redirecting Clinic’s output::
* The #ifdef trick::
* Using Argument Clinic in Python files::


File: python.info,  Node: Symbolic default values,  Next: Renaming the C functions and variables generated by Argument Clinic,  Up: Advanced Topics

10.15.4.1 Symbolic default values
.................................

The default value you provide for a parameter can’t be any arbitrary
expression.  Currently the following are explicitly supported:

   * Numeric constants (integer and float)

   * String constants

   * ‘True’, ‘False’, and ‘None’

   * Simple symbolic constants like ‘sys.maxsize’, which must start with
     the name of the module

In case you’re curious, this is implemented in ‘from_builtin()’ in
‘Lib/inspect.py’.

(In the future, this may need to get even more elaborate, to allow full
expressions like ‘CONSTANT - 1’.)


File: python.info,  Node: Renaming the C functions and variables generated by Argument Clinic,  Next: Converting functions using PyArg_UnpackTuple,  Prev: Symbolic default values,  Up: Advanced Topics

10.15.4.2 Renaming the C functions and variables generated by Argument Clinic
.............................................................................

Argument Clinic automatically names the functions it generates for you.
Occasionally this may cause a problem, if the generated name collides
with the name of an existing C function.  There’s an easy solution:
override the names used for the C functions.  Just add the keyword
‘"as"’ to your function declaration line, followed by the function name
you wish to use.  Argument Clinic will use that function name for the
base (generated) function, then add ‘"_impl"’ to the end and use that
for the name of the impl function.

For example, if we wanted to rename the C function names generated for
‘pickle.Pickler.dump’, it’d look like this:

     /*[clinic input]
     pickle.Pickler.dump as pickler_dumper

     ...

The base function would now be named ‘pickler_dumper()’, and the impl
function would now be named ‘pickler_dumper_impl()’.

Similarly, you may have a problem where you want to give a parameter a
specific Python name, but that name may be inconvenient in C. Argument
Clinic allows you to give a parameter different names in Python and in
C, using the same ‘"as"’ syntax:

     /*[clinic input]
     pickle.Pickler.dump

         obj: object
         file as file_obj: object
         protocol: object = NULL
         *
         fix_imports: bool = True

Here, the name used in Python (in the signature and the ‘keywords’
array) would be ‘file’, but the C variable would be named ‘file_obj’.

You can use this to rename the ‘self’ parameter too!


File: python.info,  Node: Converting functions using PyArg_UnpackTuple,  Next: Optional Groups,  Prev: Renaming the C functions and variables generated by Argument Clinic,  Up: Advanced Topics

10.15.4.3 Converting functions using PyArg_UnpackTuple
......................................................

To convert a function parsing its arguments with *note
PyArg_UnpackTuple(): f08, simply write out all the arguments, specifying
each as an ‘object’.  You may specify the ‘type’ argument to cast the
type as appropriate.  All arguments should be marked positional-only
(add a ‘/’ on a line by itself after the last argument).

Currently the generated code will use *note PyArg_ParseTuple(): 393, but
this will change soon.


File: python.info,  Node: Optional Groups,  Next: Using real Argument Clinic converters instead of “legacy converters”,  Prev: Converting functions using PyArg_UnpackTuple,  Up: Advanced Topics

10.15.4.4 Optional Groups
.........................

Some legacy functions have a tricky approach to parsing their arguments:
they count the number of positional arguments, then use a ‘switch’
statement to call one of several different *note PyArg_ParseTuple():
393. calls depending on how many positional arguments there are.  (These
functions cannot accept keyword-only arguments.)  This approach was used
to simulate optional arguments back before *note
PyArg_ParseTupleAndKeywords(): 6c1. was created.

While functions using this approach can often be converted to use *note
PyArg_ParseTupleAndKeywords(): 6c1, optional arguments, and default
values, it’s not always possible.  Some of these legacy functions have
behaviors *note PyArg_ParseTupleAndKeywords(): 6c1. doesn’t directly
support.  The most obvious example is the builtin function ‘range()’,
which has an optional argument on the `left' side of its required
argument!  Another example is ‘curses.window.addch()’, which has a group
of two arguments that must always be specified together.  (The arguments
are called ‘x’ and ‘y’; if you call the function passing in ‘x’, you
must also pass in ‘y’—and if you don’t pass in ‘x’ you may not pass in
‘y’ either.)

In any case, the goal of Argument Clinic is to support argument parsing
for all existing CPython builtins without changing their semantics.
Therefore Argument Clinic supports this alternate approach to parsing,
using what are called `optional groups'.  Optional groups are groups of
arguments that must all be passed in together.  They can be to the left
or the right of the required arguments.  They can `only' be used with
positional-only parameters.

     Note: Optional groups are `only' intended for use when converting
     functions that make multiple calls to *note PyArg_ParseTuple():
     393.!  Functions that use `any' other approach for parsing
     arguments should `almost never' be converted to Argument Clinic
     using optional groups.  Functions using optional groups currently
     cannot have accurate signatures in Python, because Python just
     doesn’t understand the concept.  Please avoid using optional groups
     wherever possible.

To specify an optional group, add a ‘[’ on a line by itself before the
parameters you wish to group together, and a ‘]’ on a line by itself
after these parameters.  As an example, here’s how ‘curses.window.addch’
uses optional groups to make the first two parameters and the last
parameter optional:

     /*[clinic input]

     curses.window.addch

         [
         x: int
           X-coordinate.
         y: int
           Y-coordinate.
         ]

         ch: object
           Character to add.

         [
         attr: long
           Attributes for the character.
         ]
         /

     ...

Notes:

   * For every optional group, one additional parameter will be passed
     into the impl function representing the group.  The parameter will
     be an int named ‘group_{direction}_{number}’, where ‘{direction}’
     is either ‘right’ or ‘left’ depending on whether the group is
     before or after the required parameters, and ‘{number}’ is a
     monotonically increasing number (starting at 1) indicating how far
     away the group is from the required parameters.  When the impl is
     called, this parameter will be set to zero if this group was
     unused, and set to non-zero if this group was used.  (By used or
     unused, I mean whether or not the parameters received arguments in
     this invocation.)

   * If there are no required arguments, the optional groups will behave
     as if they’re to the right of the required arguments.

   * In the case of ambiguity, the argument parsing code favors
     parameters on the left (before the required parameters).

   * Optional groups can only contain positional-only parameters.

   * Optional groups are `only' intended for legacy code.  Please do not
     use optional groups for new code.


File: python.info,  Node: Using real Argument Clinic converters instead of “legacy converters”,  Next: Py_buffer,  Prev: Optional Groups,  Up: Advanced Topics

10.15.4.5 Using real Argument Clinic converters, instead of “legacy converters”
...............................................................................

To save time, and to minimize how much you need to learn to achieve your
first port to Argument Clinic, the walkthrough above tells you to use
“legacy converters”.  “Legacy converters” are a convenience, designed
explicitly to make porting existing code to Argument Clinic easier.  And
to be clear, their use is acceptable when porting code for Python 3.4.

However, in the long term we probably want all our blocks to use
Argument Clinic’s real syntax for converters.  Why?  A couple reasons:

   * The proper converters are far easier to read and clearer in their
     intent.

   * There are some format units that are unsupported as “legacy
     converters”, because they require arguments, and the legacy
     converter syntax doesn’t support specifying arguments.

   * In the future we may have a new argument parsing library that isn’t
     restricted to what *note PyArg_ParseTuple(): 393. supports; this
     flexibility won’t be available to parameters using legacy
     converters.

Therefore, if you don’t mind a little extra effort, please use the
normal converters instead of legacy converters.

In a nutshell, the syntax for Argument Clinic (non-legacy) converters
looks like a Python function call.  However, if there are no explicit
arguments to the function (all functions take their default values), you
may omit the parentheses.  Thus ‘bool’ and ‘bool()’ are exactly the same
converters.

All arguments to Argument Clinic converters are keyword-only.  All
Argument Clinic converters accept the following arguments:

     ‘c_default’

          The default value for this parameter when defined in C.
          Specifically, this will be the initializer for the variable
          declared in the “parse function”.  See *note the section on
          default values: 4424. for how to use this.  Specified as a
          string.

     ‘annotation’

          The annotation value for this parameter.  Not currently
          supported, because PEP 8(1) mandates that the Python library
          may not use annotations.

In addition, some converters accept additional arguments.  Here is a
list of these arguments, along with their meanings:

     ‘accept’

          A set of Python types (and possibly pseudo-types); this
          restricts the allowable Python argument to values of these
          types.  (This is not a general-purpose facility; as a rule it
          only supports specific lists of types as shown in the legacy
          converter table.)

          To accept ‘None’, add ‘NoneType’ to this set.

     ‘bitwise’

          Only supported for unsigned integers.  The native integer
          value of this Python argument will be written to the parameter
          without any range checking, even for negative values.

     ‘converter’

          Only supported by the ‘object’ converter.  Specifies the name
          of a *note C “converter function”: 3e8e. to use to convert
          this object to a native type.

     ‘encoding’

          Only supported for strings.  Specifies the encoding to use
          when converting this string from a Python str (Unicode) value
          into a C ‘char *’ value.

     ‘subclass_of’

          Only supported for the ‘object’ converter.  Requires that the
          Python value be a subclass of a Python type, as expressed in
          C.

     ‘type’

          Only supported for the ‘object’ and ‘self’ converters.
          Specifies the C type that will be used to declare the
          variable.  Default value is ‘"PyObject *"’.

     ‘zeroes’

          Only supported for strings.  If true, embedded NUL bytes
          (‘'\\0'’) are permitted inside the value.  The length of the
          string will be passed in to the impl function, just after the
          string parameter, as a parameter named
          ‘<parameter_name>_length’.

Please note, not every possible combination of arguments will work.
Usually these arguments are implemented by specific ‘PyArg_ParseTuple’
`format units', with specific behavior.  For example, currently you
cannot call ‘unsigned_short’ without also specifying ‘bitwise=True’.
Although it’s perfectly reasonable to think this would work, these
semantics don’t map to any existing format unit.  So Argument Clinic
doesn’t support it.  (Or, at least, not yet.)

Below is a table showing the mapping of legacy converters into real
Argument Clinic converters.  On the left is the legacy converter, on the
right is the text you’d replace it with.

‘'B'’         ‘unsigned_char(bitwise=True)’
              
              
‘'b'’         ‘unsigned_char’
              
              
‘'c'’         ‘char’
              
              
‘'C'’         ‘int(accept={str})’
              
              
‘'d'’         ‘double’
              
              
‘'D'’         ‘Py_complex’
              
              
‘'es'’        ‘str(encoding='name_of_encoding')’
              
              
‘'es#'’       ‘str(encoding='name_of_encoding', zeroes=True)’
              
              
‘'et'’        ‘str(encoding='name_of_encoding', accept={bytes, bytearray, str})’
              
              
‘'et#'’       ‘str(encoding='name_of_encoding', accept={bytes, bytearray, str}, zeroes=True)’
              
              
‘'f'’         ‘float’
              
              
‘'h'’         ‘short’
              
              
‘'H'’         ‘unsigned_short(bitwise=True)’
              
              
‘'i'’         ‘int’
              
              
‘'I'’         ‘unsigned_int(bitwise=True)’
              
              
‘'k'’         ‘unsigned_long(bitwise=True)’
              
              
‘'K'’         ‘unsigned_long_long(bitwise=True)’
              
              
‘'l'’         ‘long’
              
              
‘'L'’         ‘long long’
              
              
‘'n'’         ‘Py_ssize_t’
              
              
‘'O'’         ‘object’
              
              
‘'O!'’        ‘object(subclass_of='&PySomething_Type')’
              
              
‘'O&'’        ‘object(converter='name_of_c_function')’
              
              
‘'p'’         ‘bool’
              
              
‘'S'’         ‘PyBytesObject’
              
              
‘'s'’         ‘str’
              
              
‘'s#'’        ‘str(zeroes=True)’
              
              
‘'s*'’        ‘Py_buffer(accept={buffer, str})’
              
              
‘'U'’         ‘unicode’
              
              
‘'u'’         ‘Py_UNICODE’
              
              
‘'u#'’        ‘Py_UNICODE(zeroes=True)’
              
              
‘'w*'’        ‘Py_buffer(accept={rwbuffer})’
              
              
‘'Y'’         ‘PyByteArrayObject’
              
              
‘'y'’         ‘str(accept={bytes})’
              
              
‘'y#'’        ‘str(accept={robuffer}, zeroes=True)’
              
              
‘'y*'’        ‘Py_buffer’
              
              
‘'Z'’         ‘Py_UNICODE(accept={str, NoneType})’
              
              
‘'Z#'’        ‘Py_UNICODE(accept={str, NoneType}, zeroes=True)’
              
              
‘'z'’         ‘str(accept={str, NoneType})’
              
              
‘'z#'’        ‘str(accept={str, NoneType}, zeroes=True)’
              
              
‘'z*'’        ‘Py_buffer(accept={buffer, str, NoneType})’
              

As an example, here’s our sample ‘pickle.Pickler.dump’ using the proper
converter:

     /*[clinic input]
     pickle.Pickler.dump

         obj: object
             The object to be pickled.
         /

     Write a pickled representation of obj to the open file.
     [clinic start generated code]*/

One advantage of real converters is that they’re more flexible than
legacy converters.  For example, the ‘unsigned_int’ converter (and all
the ‘unsigned_’ converters) can be specified without ‘bitwise=True’.
Their default behavior performs range checking on the value, and they
won’t accept negative numbers.  You just can’t do that with a legacy
converter!

Argument Clinic will show you all the converters it has available.  For
each converter it’ll show you all the parameters it accepts, along with
the default value for each parameter.  Just run ‘Tools/clinic/clinic.py
--converters’ to see the full list.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0008


File: python.info,  Node: Py_buffer,  Next: Advanced converters,  Prev: Using real Argument Clinic converters instead of “legacy converters”,  Up: Advanced Topics

10.15.4.6 Py_buffer
...................

When using the ‘Py_buffer’ converter (or the ‘'s*'’, ‘'w*'’, ‘'*y'’, or
‘'z*'’ legacy converters), you `must' not call *note PyBuffer_Release():
e19. on the provided buffer.  Argument Clinic generates code that does
it for you (in the parsing function).


File: python.info,  Node: Advanced converters,  Next: Parameter default values,  Prev: Py_buffer,  Up: Advanced Topics

10.15.4.7 Advanced converters
.............................

Remember those format units you skipped for your first time because they
were advanced?  Here’s how to handle those too.

The trick is, all those format units take arguments—either conversion
functions, or types, or strings specifying an encoding.  (But “legacy
converters” don’t support arguments.  That’s why we skipped them for
your first function.)  The argument you specified to the format unit is
now an argument to the converter; this argument is either ‘converter’
(for ‘O&’), ‘subclass_of’ (for ‘O!’), or ‘encoding’ (for all the format
units that start with ‘e’).

When using ‘subclass_of’, you may also want to use the other custom
argument for ‘object()’: ‘type’, which lets you set the type actually
used for the parameter.  For example, if you want to ensure that the
object is a subclass of ‘PyUnicode_Type’, you probably want to use the
converter ‘object(type='PyUnicodeObject *',
subclass_of='&PyUnicode_Type')’.

One possible problem with using Argument Clinic: it takes away some
possible flexibility for the format units starting with ‘e’.  When
writing a ‘PyArg_Parse’ call by hand, you could theoretically decide at
runtime what encoding string to pass in to *note PyArg_ParseTuple():
393.  But now this string must be hard-coded at
Argument-Clinic-preprocessing-time.  This limitation is deliberate; it
made supporting this format unit much easier, and may allow for future
optimizations.  This restriction doesn’t seem unreasonable; CPython
itself always passes in static hard-coded encoding strings for
parameters whose format units start with ‘e’.


File: python.info,  Node: Parameter default values,  Next: The NULL default value,  Prev: Advanced converters,  Up: Advanced Topics

10.15.4.8 Parameter default values
..................................

Default values for parameters can be any of a number of values.  At
their simplest, they can be string, int, or float literals:

     foo: str = "abc"
     bar: int = 123
     bat: float = 45.6

They can also use any of Python’s built-in constants:

     yep:  bool = True
     nope: bool = False
     nada: object = None

There’s also special support for a default value of ‘NULL’, and for
simple expressions, documented in the following sections.


File: python.info,  Node: The NULL default value,  Next: Expressions specified as default values,  Prev: Parameter default values,  Up: Advanced Topics

10.15.4.9 The ‘NULL’ default value
..................................

For string and object parameters, you can set them to ‘None’ to indicate
that there’s no default.  However, that means the C variable will be
initialized to ‘Py_None’.  For convenience’s sakes, there’s a special
value called ‘NULL’ for just this reason: from Python’s perspective it
behaves like a default value of ‘None’, but the C variable is
initialized with ‘NULL’.


File: python.info,  Node: Expressions specified as default values,  Next: Using a return converter,  Prev: The NULL default value,  Up: Advanced Topics

10.15.4.10 Expressions specified as default values
..................................................

The default value for a parameter can be more than just a literal value.
It can be an entire expression, using math operators and looking up
attributes on objects.  However, this support isn’t exactly simple,
because of some non-obvious semantics.

Consider the following example:

     foo: Py_ssize_t = sys.maxsize - 1

‘sys.maxsize’ can have different values on different platforms.
Therefore Argument Clinic can’t simply evaluate that expression locally
and hard-code it in C. So it stores the default in such a way that it
will get evaluated at runtime, when the user asks for the function’s
signature.

What namespace is available when the expression is evaluated?  It’s
evaluated in the context of the module the builtin came from.  So, if
your module has an attribute called “‘max_widgets’”, you may simply use
it:

     foo: Py_ssize_t = max_widgets

If the symbol isn’t found in the current module, it fails over to
looking in ‘sys.modules’.  That’s how it can find ‘sys.maxsize’ for
example.  (Since you don’t know in advance what modules the user will
load into their interpreter, it’s best to restrict yourself to modules
that are preloaded by Python itself.)

Evaluating default values only at runtime means Argument Clinic can’t
compute the correct equivalent C default value.  So you need to tell it
explicitly.  When you use an expression, you must also specify the
equivalent expression in C, using the ‘c_default’ parameter to the
converter:

     foo: Py_ssize_t(c_default="PY_SSIZE_T_MAX - 1") = sys.maxsize - 1

Another complication: Argument Clinic can’t know in advance whether or
not the expression you supply is valid.  It parses it to make sure it
looks legal, but it can’t `actually' know.  You must be very careful
when using expressions to specify values that are guaranteed to be valid
at runtime!

Finally, because expressions must be representable as static C values,
there are many restrictions on legal expressions.  Here’s a list of
Python features you’re not permitted to use:

   * Function calls.

   * Inline if statements (‘3 if foo else 5’).

   * Automatic sequence unpacking (‘*[1, 2, 3]’).

   * List/set/dict comprehensions and generator expressions.

   * Tuple/list/set/dict literals.


File: python.info,  Node: Using a return converter,  Next: Cloning existing functions,  Prev: Expressions specified as default values,  Up: Advanced Topics

10.15.4.11 Using a return converter
...................................

By default the impl function Argument Clinic generates for you returns
‘PyObject *’.  But your C function often computes some C type, then
converts it into the ‘PyObject *’ at the last moment.  Argument Clinic
handles converting your inputs from Python types into native C types—why
not have it convert your return value from a native C type into a Python
type too?

That’s what a “return converter” does.  It changes your impl function to
return some C type, then adds code to the generated (non-impl) function
to handle converting that value into the appropriate ‘PyObject *’.

The syntax for return converters is similar to that of parameter
converters.  You specify the return converter like it was a return
annotation on the function itself.  Return converters behave much the
same as parameter converters; they take arguments, the arguments are all
keyword-only, and if you’re not changing any of the default arguments
you can omit the parentheses.

(If you use both ‘"as"’ `and' a return converter for your function, the
‘"as"’ should come before the return converter.)

There’s one additional complication when using return converters: how do
you indicate an error has occurred?  Normally, a function returns a
valid (non-‘NULL’) pointer for success, and ‘NULL’ for failure.  But if
you use an integer return converter, all integers are valid.  How can
Argument Clinic detect an error?  Its solution: each return converter
implicitly looks for a special value that indicates an error.  If you
return that value, and an error has been set (‘PyErr_Occurred()’ returns
a true value), then the generated code will propagate the error.
Otherwise it will encode the value you return like normal.

Currently Argument Clinic supports only a few return converters:

     bool
     int
     unsigned int
     long
     unsigned int
     size_t
     Py_ssize_t
     float
     double
     DecodeFSDefault

None of these take parameters.  For the first three, return -1 to
indicate error.  For ‘DecodeFSDefault’, the return type is ‘const char
*’; return a ‘NULL’ pointer to indicate an error.

(There’s also an experimental ‘NoneType’ converter, which lets you
return ‘Py_None’ on success or ‘NULL’ on failure, without having to
increment the reference count on ‘Py_None’.  I’m not sure it adds enough
clarity to be worth using.)

To see all the return converters Argument Clinic supports, along with
their parameters (if any), just run ‘Tools/clinic/clinic.py
--converters’ for the full list.


File: python.info,  Node: Cloning existing functions,  Next: Calling Python code,  Prev: Using a return converter,  Up: Advanced Topics

10.15.4.12 Cloning existing functions
.....................................

If you have a number of functions that look similar, you may be able to
use Clinic’s “clone” feature.  When you clone an existing function, you
reuse:

   * its parameters, including

        * their names,

        * their converters, with all parameters,

        * their default values,

        * their per-parameter docstrings,

        * their `kind' (whether they’re positional only, positional or
          keyword, or keyword only), and

   * its return converter.

The only thing not copied from the original function is its docstring;
the syntax allows you to specify a new docstring.

Here’s the syntax for cloning a function:

     /*[clinic input]
     module.class.new_function [as c_basename] = module.class.existing_function

     Docstring for new_function goes here.
     [clinic start generated code]*/

(The functions can be in different modules or classes.  I wrote
‘module.class’ in the sample just to illustrate that you must use the
full path to `both' functions.)

Sorry, there’s no syntax for partially-cloning a function, or cloning a
function then modifying it.  Cloning is an all-or nothing proposition.

Also, the function you are cloning from must have been previously
defined in the current file.


File: python.info,  Node: Calling Python code,  Next: Using a “self converter”,  Prev: Cloning existing functions,  Up: Advanced Topics

10.15.4.13 Calling Python code
..............................

The rest of the advanced topics require you to write Python code which
lives inside your C file and modifies Argument Clinic’s runtime state.
This is simple: you simply define a Python block.

A Python block uses different delimiter lines than an Argument Clinic
function block.  It looks like this:

     /*[python input]
     # python code goes here
     [python start generated code]*/

All the code inside the Python block is executed at the time it’s
parsed.  All text written to stdout inside the block is redirected into
the “output” after the block.

As an example, here’s a Python block that adds a static integer variable
to the C code:

     /*[python input]
     print('static int __ignored_unused_variable__ = 0;')
     [python start generated code]*/
     static int __ignored_unused_variable__ = 0;
     /*[python checksum:...]*/


File: python.info,  Node: Using a “self converter”,  Next: Writing a custom converter,  Prev: Calling Python code,  Up: Advanced Topics

10.15.4.14 Using a “self converter”
...................................

Argument Clinic automatically adds a “self” parameter for you using a
default converter.  It automatically sets the ‘type’ of this parameter
to the “pointer to an instance” you specified when you declared the
type.  However, you can override Argument Clinic’s converter and specify
one yourself.  Just add your own ‘self’ parameter as the first parameter
in a block, and ensure that its converter is an instance of
‘self_converter’ or a subclass thereof.

What’s the point?  This lets you override the type of ‘self’, or give it
a different default name.

How do you specify the custom type you want to cast ‘self’ to?  If you
only have one or two functions with the same type for ‘self’, you can
directly use Argument Clinic’s existing ‘self’ converter, passing in the
type you want to use as the ‘type’ parameter:

     /*[clinic input]

     _pickle.Pickler.dump

       self: self(type="PicklerObject *")
       obj: object
       /

     Write a pickled representation of the given object to the open file.
     [clinic start generated code]*/

On the other hand, if you have a lot of functions that will use the same
type for ‘self’, it’s best to create your own converter, subclassing
‘self_converter’ but overwriting the ‘type’ member:

     /*[python input]
     class PicklerObject_converter(self_converter):
         type = "PicklerObject *"
     [python start generated code]*/

     /*[clinic input]

     _pickle.Pickler.dump

       self: PicklerObject
       obj: object
       /

     Write a pickled representation of the given object to the open file.
     [clinic start generated code]*/


File: python.info,  Node: Writing a custom converter,  Next: Writing a custom return converter,  Prev: Using a “self converter”,  Up: Advanced Topics

10.15.4.15 Writing a custom converter
.....................................

As we hinted at in the previous section… you can write your own
converters!  A converter is simply a Python class that inherits from
‘CConverter’.  The main purpose of a custom converter is if you have a
parameter using the ‘O&’ format unit—parsing this parameter means
calling a *note PyArg_ParseTuple(): 393. “converter function”.

Your converter class should be named ‘*something*_converter’.  If the
name follows this convention, then your converter class will be
automatically registered with Argument Clinic; its name will be the name
of your class with the ‘_converter’ suffix stripped off.  (This is
accomplished with a metaclass.)

You shouldn’t subclass ‘CConverter.__init__’.  Instead, you should write
a ‘converter_init()’ function.  ‘converter_init()’ always accepts a
‘self’ parameter; after that, all additional parameters `must' be
keyword-only.  Any arguments passed in to the converter in Argument
Clinic will be passed along to your ‘converter_init()’.

There are some additional members of ‘CConverter’ you may wish to
specify in your subclass.  Here’s the current list:

‘type’

     The C type to use for this variable.  ‘type’ should be a Python
     string specifying the type, e.g.  ‘int’.  If this is a pointer
     type, the type string should end with ‘' *'’.

‘default’

     The Python default value for this parameter, as a Python value.  Or
     the magic value ‘unspecified’ if there is no default.

‘py_default’

     ‘default’ as it should appear in Python code, as a string.  Or
     ‘None’ if there is no default.

‘c_default’

     ‘default’ as it should appear in C code, as a string.  Or ‘None’ if
     there is no default.

‘c_ignored_default’

     The default value used to initialize the C variable when there is
     no default, but not specifying a default may result in an
     “uninitialized variable” warning.  This can easily happen when
     using option groups—although properly-written code will never
     actually use this value, the variable does get passed in to the
     impl, and the C compiler will complain about the “use” of the
     uninitialized value.  This value should always be a non-empty
     string.

‘converter’

     The name of the C converter function, as a string.

‘impl_by_reference’

     A boolean value.  If true, Argument Clinic will add a ‘&’ in front
     of the name of the variable when passing it into the impl function.

‘parse_by_reference’

     A boolean value.  If true, Argument Clinic will add a ‘&’ in front
     of the name of the variable when passing it into *note
     PyArg_ParseTuple(): 393.

Here’s the simplest example of a custom converter, from
‘Modules/zlibmodule.c’:

     /*[python input]

     class ssize_t_converter(CConverter):
         type = 'Py_ssize_t'
         converter = 'ssize_t_converter'

     [python start generated code]*/
     /*[python end generated code: output=da39a3ee5e6b4b0d input=35521e4e733823c7]*/

This block adds a converter to Argument Clinic named ‘ssize_t’.
Parameters declared as ‘ssize_t’ will be declared as type ‘Py_ssize_t’,
and will be parsed by the ‘'O&'’ format unit, which will call the
‘ssize_t_converter’ converter function.  ‘ssize_t’ variables
automatically support default values.

More sophisticated custom converters can insert custom C code to handle
initialization and cleanup.  You can see more examples of custom
converters in the CPython source tree; grep the C files for the string
‘CConverter’.


File: python.info,  Node: Writing a custom return converter,  Next: METH_O and METH_NOARGS,  Prev: Writing a custom converter,  Up: Advanced Topics

10.15.4.16 Writing a custom return converter
............................................

Writing a custom return converter is much like writing a custom
converter.  Except it’s somewhat simpler, because return converters are
themselves much simpler.

Return converters must subclass ‘CReturnConverter’.  There are no
examples yet of custom return converters, because they are not widely
used yet.  If you wish to write your own return converter, please read
‘Tools/clinic/clinic.py’, specifically the implementation of
‘CReturnConverter’ and all its subclasses.


File: python.info,  Node: METH_O and METH_NOARGS,  Next: tp_new and tp_init functions,  Prev: Writing a custom return converter,  Up: Advanced Topics

10.15.4.17 METH_O and METH_NOARGS
.................................

To convert a function using ‘METH_O’, make sure the function’s single
argument is using the ‘object’ converter, and mark the arguments as
positional-only:

     /*[clinic input]
     meth_o_sample

          argument: object
          /
     [clinic start generated code]*/

To convert a function using ‘METH_NOARGS’, just don’t specify any
arguments.

You can still use a self converter, a return converter, and specify a
‘type’ argument to the object converter for ‘METH_O’.


File: python.info,  Node: tp_new and tp_init functions,  Next: Changing and redirecting Clinic’s output,  Prev: METH_O and METH_NOARGS,  Up: Advanced Topics

10.15.4.18 tp_new and tp_init functions
.......................................

You can convert ‘tp_new’ and ‘tp_init’ functions.  Just name them
‘__new__’ or ‘__init__’ as appropriate.  Notes:

   * The function name generated for ‘__new__’ doesn’t end in ‘__new__’
     like it would by default.  It’s just the name of the class,
     converted into a valid C identifier.

   * No ‘PyMethodDef’ ‘#define’ is generated for these functions.

   * ‘__init__’ functions return ‘int’, not ‘PyObject *’.

   * Use the docstring as the class docstring.

   * Although ‘__new__’ and ‘__init__’ functions must always accept both
     the ‘args’ and ‘kwargs’ objects, when converting you may specify
     any signature for these functions that you like.  (If your function
     doesn’t support keywords, the parsing function generated will throw
     an exception if it receives any.)


File: python.info,  Node: Changing and redirecting Clinic’s output,  Next: The #ifdef trick,  Prev: tp_new and tp_init functions,  Up: Advanced Topics

10.15.4.19 Changing and redirecting Clinic’s output
...................................................

It can be inconvenient to have Clinic’s output interspersed with your
conventional hand-edited C code.  Luckily, Clinic is configurable: you
can buffer up its output for printing later (or earlier!), or write its
output to a separate file.  You can also add a prefix or suffix to every
line of Clinic’s generated output.

While changing Clinic’s output in this manner can be a boon to
readability, it may result in Clinic code using types before they are
defined, or your code attempting to use Clinic-generated code before it
is defined.  These problems can be easily solved by rearranging the
declarations in your file, or moving where Clinic’s generated code goes.
(This is why the default behavior of Clinic is to output everything into
the current block; while many people consider this hampers readability,
it will never require rearranging your code to fix definition-before-use
problems.)

Let’s start with defining some terminology:

`field'

     A field, in this context, is a subsection of Clinic’s output.  For
     example, the ‘#define’ for the ‘PyMethodDef’ structure is a field,
     called ‘methoddef_define’.  Clinic has seven different fields it
     can output per function definition:

          docstring_prototype
          docstring_definition
          methoddef_define
          impl_prototype
          parser_prototype
          parser_definition
          impl_definition

     All the names are of the form ‘"<a>_<b>"’, where ‘"<a>"’ is the
     semantic object represented (the parsing function, the impl
     function, the docstring, or the methoddef structure) and ‘"<b>"’
     represents what kind of statement the field is.  Field names that
     end in ‘"_prototype"’ represent forward declarations of that thing,
     without the actual body/data of the thing; field names that end in
     ‘"_definition"’ represent the actual definition of the thing, with
     the body/data of the thing.  (‘"methoddef"’ is special, it’s the
     only one that ends with ‘"_define"’, representing that it’s a
     preprocessor #define.)

`destination'

     A destination is a place Clinic can write output to.  There are
     five built-in destinations:

     ‘block’

          The default destination: printed in the output section of the
          current Clinic block.

     ‘buffer’

          A text buffer where you can save text for later.  Text sent
          here is appended to the end of any existing text.  It’s an
          error to have any text left in the buffer when Clinic finishes
          processing a file.

     ‘file’

          A separate “clinic file” that will be created automatically by
          Clinic.  The filename chosen for the file is
          ‘{basename}.clinic{extension}’, where ‘basename’ and
          ‘extension’ were assigned the output from ‘os.path.splitext()’
          run on the current file.  (Example: the ‘file’ destination for
          ‘_pickle.c’ would be written to ‘_pickle.clinic.c’.)

          `Important: When using a' ‘file’ `destination, you' `must
          check in' `the generated file!'

     ‘two-pass’

          A buffer like ‘buffer’.  However, a two-pass buffer can only
          be dumped once, and it prints out all text sent to it during
          all processing, even from Clinic blocks `after' the dumping
          point.

     ‘suppress’

          The text is suppressed—thrown away.

Clinic defines five new directives that let you reconfigure its output.

The first new directive is ‘dump’:

     dump <destination>

This dumps the current contents of the named destination into the output
of the current block, and empties it.  This only works with ‘buffer’ and
‘two-pass’ destinations.

The second new directive is ‘output’.  The most basic form of ‘output’
is like this:

     output <field> <destination>

This tells Clinic to output `field' to `destination'.  ‘output’ also
supports a special meta-destination, called ‘everything’, which tells
Clinic to output `all' fields to that `destination'.

‘output’ has a number of other functions:

     output push
     output pop
     output preset <preset>

‘output push’ and ‘output pop’ allow you to push and pop configurations
on an internal configuration stack, so that you can temporarily modify
the output configuration, then easily restore the previous
configuration.  Simply push before your change to save the current
configuration, then pop when you wish to restore the previous
configuration.

‘output preset’ sets Clinic’s output to one of several built-in preset
configurations, as follows:

     ‘block’

          Clinic’s original starting configuration.  Writes everything
          immediately after the input block.

          Suppress the ‘parser_prototype’ and ‘docstring_prototype’,
          write everything else to ‘block’.

     ‘file’

          Designed to write everything to the “clinic file” that it can.
          You then ‘#include’ this file near the top of your file.  You
          may need to rearrange your file to make this work, though
          usually this just means creating forward declarations for
          various ‘typedef’ and ‘PyTypeObject’ definitions.

          Suppress the ‘parser_prototype’ and ‘docstring_prototype’,
          write the ‘impl_definition’ to ‘block’, and write everything
          else to ‘file’.

          The default filename is ‘"{dirname}/clinic/{basename}.h"’.

     ‘buffer’

          Save up most of the output from Clinic, to be written into
          your file near the end.  For Python files implementing modules
          or builtin types, it’s recommended that you dump the buffer
          just above the static structures for your module or builtin
          type; these are normally very near the end.  Using ‘buffer’
          may require even more editing than ‘file’, if your file has
          static ‘PyMethodDef’ arrays defined in the middle of the file.

          Suppress the ‘parser_prototype’, ‘impl_prototype’, and
          ‘docstring_prototype’, write the ‘impl_definition’ to ‘block’,
          and write everything else to ‘file’.

     ‘two-pass’

          Similar to the ‘buffer’ preset, but writes forward
          declarations to the ‘two-pass’ buffer, and definitions to the
          ‘buffer’.  This is similar to the ‘buffer’ preset, but may
          require less editing than ‘buffer’.  Dump the ‘two-pass’
          buffer near the top of your file, and dump the ‘buffer’ near
          the end just like you would when using the ‘buffer’ preset.

          Suppresses the ‘impl_prototype’, write the ‘impl_definition’
          to ‘block’, write ‘docstring_prototype’, ‘methoddef_define’,
          and ‘parser_prototype’ to ‘two-pass’, write everything else to
          ‘buffer’.

     ‘partial-buffer’

          Similar to the ‘buffer’ preset, but writes more things to
          ‘block’, only writing the really big chunks of generated code
          to ‘buffer’.  This avoids the definition-before-use problem of
          ‘buffer’ completely, at the small cost of having slightly more
          stuff in the block’s output.  Dump the ‘buffer’ near the end,
          just like you would when using the ‘buffer’ preset.

          Suppresses the ‘impl_prototype’, write the
          ‘docstring_definition’ and ‘parser_definition’ to ‘buffer’,
          write everything else to ‘block’.

The third new directive is ‘destination’:

     destination <name> <command> [...]

This performs an operation on the destination named ‘name’.

There are two defined subcommands: ‘new’ and ‘clear’.

The ‘new’ subcommand works like this:

     destination <name> new <type>

This creates a new destination with name ‘<name>’ and type ‘<type>’.

There are five destination types:

     ‘suppress’

          Throws the text away.

     ‘block’

          Writes the text to the current block.  This is what Clinic
          originally did.

     ‘buffer’

          A simple text buffer, like the “buffer” builtin destination
          above.

     ‘file’

          A text file.  The file destination takes an extra argument, a
          template to use for building the filename, like so:

               destination <name> new <type> <file_template>

          The template can use three strings internally that will be
          replaced by bits of the filename:

               {path}

                    The full path to the file, including directory and
                    full filename.

               {dirname}

                    The name of the directory the file is in.

               {basename}

                    Just the name of the file, not including the
                    directory.

               {basename_root}

                    Basename with the extension clipped off (everything
                    up to but not including the last ‘.’).

               {basename_extension}

                    The last ‘.’ and everything after it.  If the
                    basename does not contain a period, this will be the
                    empty string.

          If there are no periods in the filename, {basename} and
          {filename} are the same, and {extension} is empty.
          “{basename}{extension}” is always exactly the same as
          “{filename}”.”

     ‘two-pass’

          A two-pass buffer, like the “two-pass” builtin destination
          above.

The ‘clear’ subcommand works like this:

     destination <name> clear

It removes all the accumulated text up to this point in the destination.
(I don’t know what you’d need this for, but I thought maybe it’d be
useful while someone’s experimenting.)

The fourth new directive is ‘set’:

     set line_prefix "string"
     set line_suffix "string"

‘set’ lets you set two internal variables in Clinic.  ‘line_prefix’ is a
string that will be prepended to every line of Clinic’s output;
‘line_suffix’ is a string that will be appended to every line of
Clinic’s output.

Both of these support two format strings:

     ‘{block comment start}’

          Turns into the string ‘/*’, the start-comment text sequence
          for C files.

     ‘{block comment end}’

          Turns into the string ‘*/’, the end-comment text sequence for
          C files.

The final new directive is one you shouldn’t need to use directly,
called ‘preserve’:

     preserve

This tells Clinic that the current contents of the output should be
kept, unmodified.  This is used internally by Clinic when dumping output
into ‘file’ files; wrapping it in a Clinic block lets Clinic use its
existing checksum functionality to ensure the file was not modified by
hand before it gets overwritten.


File: python.info,  Node: The #ifdef trick,  Next: Using Argument Clinic in Python files,  Prev: Changing and redirecting Clinic’s output,  Up: Advanced Topics

10.15.4.20 The #ifdef trick
...........................

If you’re converting a function that isn’t available on all platforms,
there’s a trick you can use to make life a little easier.  The existing
code probably looks like this:

     #ifdef HAVE_FUNCTIONNAME
     static module_functionname(...)
     {
     ...
     }
     #endif /* HAVE_FUNCTIONNAME */

And then in the ‘PyMethodDef’ structure at the bottom the existing code
will have:

     #ifdef HAVE_FUNCTIONNAME
     {'functionname', ... },
     #endif /* HAVE_FUNCTIONNAME */

In this scenario, you should enclose the body of your impl function
inside the ‘#ifdef’, like so:

     #ifdef HAVE_FUNCTIONNAME
     /*[clinic input]
     module.functionname
     ...
     [clinic start generated code]*/
     static module_functionname(...)
     {
     ...
     }
     #endif /* HAVE_FUNCTIONNAME */

Then, remove those three lines from the ‘PyMethodDef’ structure,
replacing them with the macro Argument Clinic generated:

     MODULE_FUNCTIONNAME_METHODDEF

(You can find the real name for this macro inside the generated code.
Or you can calculate it yourself: it’s the name of your function as
defined on the first line of your block, but with periods changed to
underscores, uppercased, and ‘"_METHODDEF"’ added to the end.)

Perhaps you’re wondering: what if ‘HAVE_FUNCTIONNAME’ isn’t defined?
The ‘MODULE_FUNCTIONNAME_METHODDEF’ macro won’t be defined either!

Here’s where Argument Clinic gets very clever.  It actually detects that
the Argument Clinic block might be deactivated by the ‘#ifdef’.  When
that happens, it generates a little extra code that looks like this:

     #ifndef MODULE_FUNCTIONNAME_METHODDEF
         #define MODULE_FUNCTIONNAME_METHODDEF
     #endif /* !defined(MODULE_FUNCTIONNAME_METHODDEF) */

That means the macro always works.  If the function is defined, this
turns into the correct structure, including the trailing comma.  If the
function is undefined, this turns into nothing.

However, this causes one ticklish problem: where should Argument Clinic
put this extra code when using the “block” output preset?  It can’t go
in the output block, because that could be deactivated by the ‘#ifdef’.
(That’s the whole point!)

In this situation, Argument Clinic writes the extra code to the “buffer”
destination.  This may mean that you get a complaint from Argument
Clinic:

     Warning in file "Modules/posixmodule.c" on line 12357:
     Destination buffer 'buffer' not empty at end of file, emptying.

When this happens, just open your file, find the ‘dump buffer’ block
that Argument Clinic added to your file (it’ll be at the very bottom),
then move it above the ‘PyMethodDef’ structure where that macro is used.


File: python.info,  Node: Using Argument Clinic in Python files,  Prev: The #ifdef trick,  Up: Advanced Topics

10.15.4.21 Using Argument Clinic in Python files
................................................

It’s actually possible to use Argument Clinic to preprocess Python
files.  There’s no point to using Argument Clinic blocks, of course, as
the output wouldn’t make any sense to the Python interpreter.  But using
Argument Clinic to run Python blocks lets you use Python as a Python
preprocessor!

Since Python comments are different from C comments, Argument Clinic
blocks embedded in Python files look slightly different.  They look like
this:

     #/*[python input]
     #print("def foo(): pass")
     #[python start generated code]*/
     def foo(): pass
     #/*[python checksum:...]*/


File: python.info,  Node: Instrumenting CPython with DTrace and SystemTap,  Prev: Argument Clinic How-To,  Up: Python HOWTOs

10.16 Instrumenting CPython with DTrace and SystemTap
=====================================================


author: David Malcolm


author: Łukasz Langa

DTrace and SystemTap are monitoring tools, each providing a way to
inspect what the processes on a computer system are doing.  They both
use domain-specific languages allowing a user to write scripts which:

        - filter which processes are to be observed

        - gather data from the processes of interest

        - generate reports on the data

As of Python 3.6, CPython can be built with embedded “markers”, also
known as “probes”, that can be observed by a DTrace or SystemTap script,
making it easier to monitor what the CPython processes on a system are
doing.

`CPython implementation detail:' DTrace markers are implementation
details of the CPython interpreter.  No guarantees are made about probe
compatibility between versions of CPython.  DTrace scripts can stop
working or work incorrectly without warning when changing CPython
versions.

* Menu:

* Enabling the static markers::
* Static DTrace probes::
* Static SystemTap markers::
* Available static markers::
* SystemTap Tapsets::
* Examples: Examples<37>.


File: python.info,  Node: Enabling the static markers,  Next: Static DTrace probes,  Up: Instrumenting CPython with DTrace and SystemTap

10.16.1 Enabling the static markers
-----------------------------------

macOS comes with built-in support for DTrace.  On Linux, in order to
build CPython with the embedded markers for SystemTap, the SystemTap
development tools must be installed.

On a Linux machine, this can be done via:

     $ yum install systemtap-sdt-devel

or:

     $ sudo apt-get install systemtap-sdt-dev

CPython must then be configured ‘--with-dtrace’:

     checking for --with-dtrace... yes

On macOS, you can list available DTrace probes by running a Python
process in the background and listing all probes made available by the
Python provider:

     $ python3.6 -q &
     $ sudo dtrace -l -P python$!  # or: dtrace -l -m python3.6

        ID   PROVIDER            MODULE                          FUNCTION NAME
     29564 python18035        python3.6          _PyEval_EvalFrameDefault function-entry
     29565 python18035        python3.6             dtrace_function_entry function-entry
     29566 python18035        python3.6          _PyEval_EvalFrameDefault function-return
     29567 python18035        python3.6            dtrace_function_return function-return
     29568 python18035        python3.6                           collect gc-done
     29569 python18035        python3.6                           collect gc-start
     29570 python18035        python3.6          _PyEval_EvalFrameDefault line
     29571 python18035        python3.6                 maybe_dtrace_line line

On Linux, you can verify if the SystemTap static markers are present in
the built binary by seeing if it contains a “.note.stapsdt” section.

     $ readelf -S ./python | grep .note.stapsdt
     [30] .note.stapsdt        NOTE         0000000000000000 00308d78

If you’ve built Python as a shared library (with –enable-shared), you
need to look instead within the shared library.  For example:

     $ readelf -S libpython3.3dm.so.1.0 | grep .note.stapsdt
     [29] .note.stapsdt        NOTE         0000000000000000 00365b68

Sufficiently modern readelf can print the metadata:

     $ readelf -n ./python

     Displaying notes found at file offset 0x00000254 with length 0x00000020:
         Owner                 Data size          Description
         GNU                  0x00000010          NT_GNU_ABI_TAG (ABI version tag)
             OS: Linux, ABI: 2.6.32

     Displaying notes found at file offset 0x00000274 with length 0x00000024:
         Owner                 Data size          Description
         GNU                  0x00000014          NT_GNU_BUILD_ID (unique build ID bitstring)
             Build ID: df924a2b08a7e89f6e11251d4602022977af2670

     Displaying notes found at file offset 0x002d6c30 with length 0x00000144:
         Owner                 Data size          Description
         stapsdt              0x00000031          NT_STAPSDT (SystemTap probe descriptors)
             Provider: python
             Name: gc__start
             Location: 0x00000000004371c3, Base: 0x0000000000630ce2, Semaphore: 0x00000000008d6bf6
             Arguments: -4@%ebx
         stapsdt              0x00000030          NT_STAPSDT (SystemTap probe descriptors)
             Provider: python
             Name: gc__done
             Location: 0x00000000004374e1, Base: 0x0000000000630ce2, Semaphore: 0x00000000008d6bf8
             Arguments: -8@%rax
         stapsdt              0x00000045          NT_STAPSDT (SystemTap probe descriptors)
             Provider: python
             Name: function__entry
             Location: 0x000000000053db6c, Base: 0x0000000000630ce2, Semaphore: 0x00000000008d6be8
             Arguments: 8@%rbp 8@%r12 -4@%eax
         stapsdt              0x00000046          NT_STAPSDT (SystemTap probe descriptors)
             Provider: python
             Name: function__return
             Location: 0x000000000053dba8, Base: 0x0000000000630ce2, Semaphore: 0x00000000008d6bea
             Arguments: 8@%rbp 8@%r12 -4@%eax

The above metadata contains information for SystemTap describing how it
can patch strategically-placed machine code instructions to enable the
tracing hooks used by a SystemTap script.


File: python.info,  Node: Static DTrace probes,  Next: Static SystemTap markers,  Prev: Enabling the static markers,  Up: Instrumenting CPython with DTrace and SystemTap

10.16.2 Static DTrace probes
----------------------------

The following example DTrace script can be used to show the call/return
hierarchy of a Python script, only tracing within the invocation of a
function called “start”.  In other words, import-time function
invocations are not going to be listed:

     self int indent;

     python$target:::function-entry
     /copyinstr(arg1) == "start"/
     {
             self->trace = 1;
     }

     python$target:::function-entry
     /self->trace/
     {
             printf("%d\t%*s:", timestamp, 15, probename);
             printf("%*s", self->indent, "");
             printf("%s:%s:%d\n", basename(copyinstr(arg0)), copyinstr(arg1), arg2);
             self->indent++;
     }

     python$target:::function-return
     /self->trace/
     {
             self->indent--;
             printf("%d\t%*s:", timestamp, 15, probename);
             printf("%*s", self->indent, "");
             printf("%s:%s:%d\n", basename(copyinstr(arg0)), copyinstr(arg1), arg2);
     }

     python$target:::function-return
     /copyinstr(arg1) == "start"/
     {
             self->trace = 0;
     }

It can be invoked like this:

     $ sudo dtrace -q -s call_stack.d -c "python3.6 script.py"

The output looks like this:

     156641360502280  function-entry:call_stack.py:start:23
     156641360518804  function-entry: call_stack.py:function_1:1
     156641360532797  function-entry:  call_stack.py:function_3:9
     156641360546807 function-return:  call_stack.py:function_3:10
     156641360563367 function-return: call_stack.py:function_1:2
     156641360578365  function-entry: call_stack.py:function_2:5
     156641360591757  function-entry:  call_stack.py:function_1:1
     156641360605556  function-entry:   call_stack.py:function_3:9
     156641360617482 function-return:   call_stack.py:function_3:10
     156641360629814 function-return:  call_stack.py:function_1:2
     156641360642285 function-return: call_stack.py:function_2:6
     156641360656770  function-entry: call_stack.py:function_3:9
     156641360669707 function-return: call_stack.py:function_3:10
     156641360687853  function-entry: call_stack.py:function_4:13
     156641360700719 function-return: call_stack.py:function_4:14
     156641360719640  function-entry: call_stack.py:function_5:18
     156641360732567 function-return: call_stack.py:function_5:21
     156641360747370 function-return:call_stack.py:start:28


File: python.info,  Node: Static SystemTap markers,  Next: Available static markers,  Prev: Static DTrace probes,  Up: Instrumenting CPython with DTrace and SystemTap

10.16.3 Static SystemTap markers
--------------------------------

The low-level way to use the SystemTap integration is to use the static
markers directly.  This requires you to explicitly state the binary file
containing them.

For example, this SystemTap script can be used to show the call/return
hierarchy of a Python script:

     probe process("python").mark("function__entry") {
          filename = user_string($arg1);
          funcname = user_string($arg2);
          lineno = $arg3;

          printf("%s => %s in %s:%d\\n",
                 thread_indent(1), funcname, filename, lineno);
     }

     probe process("python").mark("function__return") {
         filename = user_string($arg1);
         funcname = user_string($arg2);
         lineno = $arg3;

         printf("%s <= %s in %s:%d\\n",
                thread_indent(-1), funcname, filename, lineno);
     }

It can be invoked like this:

     $ stap \
       show-call-hierarchy.stp \
       -c "./python test.py"

The output looks like this:

     11408 python(8274):        => __contains__ in Lib/_abcoll.py:362
     11414 python(8274):         => __getitem__ in Lib/os.py:425
     11418 python(8274):          => encode in Lib/os.py:490
     11424 python(8274):          <= encode in Lib/os.py:493
     11428 python(8274):         <= __getitem__ in Lib/os.py:426
     11433 python(8274):        <= __contains__ in Lib/_abcoll.py:366

where the columns are:

        - time in microseconds since start of script

        - name of executable

        - PID of process

and the remainder indicates the call/return hierarchy as the script
executes.

For a ‘–enable-shared’ build of CPython, the markers are contained
within the libpython shared library, and the probe’s dotted path needs
to reflect this.  For example, this line from the above example:

     probe process("python").mark("function__entry") {

should instead read:

     probe process("python").library("libpython3.6dm.so.1.0").mark("function__entry") {

(assuming a debug build of CPython 3.6)


File: python.info,  Node: Available static markers,  Next: SystemTap Tapsets,  Prev: Static SystemTap markers,  Up: Instrumenting CPython with DTrace and SystemTap

10.16.4 Available static markers
--------------------------------

 -- Object: function__entry(str filename, str funcname, int lineno)

     This marker indicates that execution of a Python function has
     begun.  It is only triggered for pure-Python (bytecode) functions.

     The filename, function name, and line number are provided back to
     the tracing script as positional arguments, which must be accessed
     using ‘$arg1’, ‘$arg2’, ‘$arg3’:

             * ‘$arg1’ : ‘(const char *)’ filename, accessible using
               ‘user_string($arg1)’

             * ‘$arg2’ : ‘(const char *)’ function name, accessible
               using ‘user_string($arg2)’

             * ‘$arg3’ : ‘int’ line number

 -- Object: function__return(str filename, str funcname, int lineno)

     This marker is the converse of ‘function__entry()’, and indicates
     that execution of a Python function has ended (either via ‘return’,
     or via an exception).  It is only triggered for pure-Python
     (bytecode) functions.

     The arguments are the same as for ‘function__entry()’

 -- Object: line(str filename, str funcname, int lineno)

     This marker indicates a Python line is about to be executed.  It is
     the equivalent of line-by-line tracing with a Python profiler.  It
     is not triggered within C functions.

     The arguments are the same as for ‘function__entry()’.

 -- Object: gc__start(int generation)

     Fires when the Python interpreter starts a garbage collection
     cycle.  ‘arg0’ is the generation to scan, like *note gc.collect():
     35b.

 -- Object: gc__done(long collected)

     Fires when the Python interpreter finishes a garbage collection
     cycle.  ‘arg0’ is the number of collected objects.

 -- Object: import__find__load__start(str modulename)

     Fires before *note importlib: 9a. attempts to find and load the
     module.  ‘arg0’ is the module name.

     New in version 3.7.

 -- Object: import__find__load__done(str modulename, int found)

     Fires after *note importlib: 9a.’s find_and_load function is
     called.  ‘arg0’ is the module name, ‘arg1’ indicates if module was
     successfully loaded.

     New in version 3.7.

 -- Object: audit(str event, void *tuple)

     Fires when *note sys.audit(): 1056. or *note PySys_Audit(): 1068.
     is called.  ‘arg0’ is the event name as C string, ‘arg1’ is a *note
     PyObject: 5b5. pointer to a tuple object.

     New in version 3.8.


File: python.info,  Node: SystemTap Tapsets,  Next: Examples<37>,  Prev: Available static markers,  Up: Instrumenting CPython with DTrace and SystemTap

10.16.5 SystemTap Tapsets
-------------------------

The higher-level way to use the SystemTap integration is to use a
“tapset”: SystemTap’s equivalent of a library, which hides some of the
lower-level details of the static markers.

Here is a tapset file, based on a non-shared build of CPython:

     /*
        Provide a higher-level wrapping around the function__entry and
        function__return markers:
      \*/
     probe python.function.entry = process("python").mark("function__entry")
     {
         filename = user_string($arg1);
         funcname = user_string($arg2);
         lineno = $arg3;
         frameptr = $arg4
     }
     probe python.function.return = process("python").mark("function__return")
     {
         filename = user_string($arg1);
         funcname = user_string($arg2);
         lineno = $arg3;
         frameptr = $arg4
     }

If this file is installed in SystemTap’s tapset directory (e.g.
‘/usr/share/systemtap/tapset’), then these additional probepoints become
available:

 -- Object: python.function.entry(str filename, str funcname, int
          lineno, frameptr)

     This probe point indicates that execution of a Python function has
     begun.  It is only triggered for pure-Python (bytecode) functions.

 -- Object: python.function.return(str filename, str funcname, int
          lineno, frameptr)

     This probe point is the converse of ‘python.function.return’, and
     indicates that execution of a Python function has ended (either via
     ‘return’, or via an exception).  It is only triggered for
     pure-Python (bytecode) functions.


File: python.info,  Node: Examples<37>,  Prev: SystemTap Tapsets,  Up: Instrumenting CPython with DTrace and SystemTap

10.16.6 Examples
----------------

This SystemTap script uses the tapset above to more cleanly implement
the example given above of tracing the Python function-call hierarchy,
without needing to directly name the static markers:

     probe python.function.entry
     {
       printf("%s => %s in %s:%d\n",
              thread_indent(1), funcname, filename, lineno);
     }

     probe python.function.return
     {
       printf("%s <= %s in %s:%d\n",
              thread_indent(-1), funcname, filename, lineno);
     }

The following script uses the tapset above to provide a top-like view of
all running CPython code, showing the top 20 most frequently-entered
bytecode frames, each second, across the whole system:

     global fn_calls;

     probe python.function.entry
     {
         fn_calls[pid(), filename, funcname, lineno] += 1;
     }

     probe timer.ms(1000) {
         printf("\033[2J\033[1;1H") /* clear screen \*/
         printf("%6s %80s %6s %30s %6s\n",
                "PID", "FILENAME", "LINE", "FUNCTION", "CALLS")
         foreach ([pid, filename, funcname, lineno] in fn_calls- limit 20) {
             printf("%6d %80s %6d %30s %6d\n",
                 pid, filename, lineno, funcname,
                 fn_calls[pid, filename, funcname, lineno]);
         }
         delete fn_calls;
     }


File: python.info,  Node: Python Frequently Asked Questions,  Next: Glossary,  Prev: Python HOWTOs,  Up: Top

11 Python Frequently Asked Questions
************************************

* Menu:

* General Python FAQ::
* Programming FAQ::
* Design and History FAQ::
* Library and Extension FAQ::
* Extending/Embedding FAQ::
* Python on Windows FAQ::
* Graphic User Interface FAQ::
* “Why is Python Installed on my Computer?” FAQ::


File: python.info,  Node: General Python FAQ,  Next: Programming FAQ,  Up: Python Frequently Asked Questions

11.1 General Python FAQ
=======================

* Menu:

* General Information::
* Python in the real world::


File: python.info,  Node: General Information,  Next: Python in the real world,  Up: General Python FAQ

11.1.1 General Information
--------------------------

* Menu:

* What is Python?::
* What is the Python Software Foundation?::
* Are there copyright restrictions on the use of Python?::
* Why was Python created in the first place?::
* What is Python good for?::
* How does the Python version numbering scheme work?::
* How do I obtain a copy of the Python source?::
* How do I get documentation on Python?::
* I’ve never programmed before. Is there a Python tutorial?: I’ve never programmed before Is there a Python tutorial?.
* Is there a newsgroup or mailing list devoted to Python?::
* How do I get a beta test version of Python?::
* How do I submit bug reports and patches for Python?::
* Are there any published articles about Python that I can reference?::
* Are there any books on Python?::
* Where in the world is www.python.org located?: Where in the world is www python org located?.
* Why is it called Python?::
* Do I have to like “Monty Python’s Flying Circus”?::


File: python.info,  Node: What is Python?,  Next: What is the Python Software Foundation?,  Up: General Information

11.1.1.1 What is Python?
........................

Python is an interpreted, interactive, object-oriented programming
language.  It incorporates modules, exceptions, dynamic typing, very
high level dynamic data types, and classes.  It supports multiple
programming paradigms beyond object-oriented programming, such as
procedural and functional programming.  Python combines remarkable power
with very clear syntax.  It has interfaces to many system calls and
libraries, as well as to various window systems, and is extensible in C
or C++.  It is also usable as an extension language for applications
that need a programmable interface.  Finally, Python is portable: it
runs on many Unix variants including Linux and macOS, and on Windows.

To find out more, start with *note The Python Tutorial: 132f.  The
Beginner’s Guide to Python(1) links to other introductory tutorials and
resources for learning Python.

   ---------- Footnotes ----------

   (1) https://wiki.python.org/moin/BeginnersGuide


File: python.info,  Node: What is the Python Software Foundation?,  Next: Are there copyright restrictions on the use of Python?,  Prev: What is Python?,  Up: General Information

11.1.1.2 What is the Python Software Foundation?
................................................

The Python Software Foundation is an independent non-profit organization
that holds the copyright on Python versions 2.1 and newer.  The PSF’s
mission is to advance open source technology related to the Python
programming language and to publicize the use of Python.  The PSF’s home
page is at ‘https://www.python.org/psf/’.

Donations to the PSF are tax-exempt in the US. If you use Python and
find it helpful, please contribute via the PSF donation page(1).

   ---------- Footnotes ----------

   (1) https://www.python.org/psf/donations/


File: python.info,  Node: Are there copyright restrictions on the use of Python?,  Next: Why was Python created in the first place?,  Prev: What is the Python Software Foundation?,  Up: General Information

11.1.1.3 Are there copyright restrictions on the use of Python?
...............................................................

You can do anything you want with the source, as long as you leave the
copyrights in and display those copyrights in any documentation about
Python that you produce.  If you honor the copyright rules, it’s OK to
use Python for commercial use, to sell copies of Python in source or
binary form (modified or unmodified), or to sell products that
incorporate Python in some form.  We would still like to know about all
commercial use of Python, of course.

See the PSF license page(1) to find further explanations and a link to
the full text of the license.

The Python logo is trademarked, and in certain cases permission is
required to use it.  Consult the Trademark Usage Policy(2) for more
information.

   ---------- Footnotes ----------

   (1) https://www.python.org/psf/license/

   (2) https://www.python.org/psf/trademarks/


File: python.info,  Node: Why was Python created in the first place?,  Next: What is Python good for?,  Prev: Are there copyright restrictions on the use of Python?,  Up: General Information

11.1.1.4 Why was Python created in the first place?
...................................................

Here’s a `very' brief summary of what started it all, written by Guido
van Rossum:

     I had extensive experience with implementing an interpreted
     language in the ABC group at CWI, and from working with this group
     I had learned a lot about language design.  This is the origin of
     many Python features, including the use of indentation for
     statement grouping and the inclusion of very-high-level data types
     (although the details are all different in Python).

     I had a number of gripes about the ABC language, but also liked
     many of its features.  It was impossible to extend the ABC language
     (or its implementation) to remedy my complaints – in fact its lack
     of extensibility was one of its biggest problems.  I had some
     experience with using Modula-2+ and talked with the designers of
     Modula-3 and read the Modula-3 report.  Modula-3 is the origin of
     the syntax and semantics used for exceptions, and some other Python
     features.

     I was working in the Amoeba distributed operating system group at
     CWI. We needed a better way to do system administration than by
     writing either C programs or Bourne shell scripts, since Amoeba had
     its own system call interface which wasn’t easily accessible from
     the Bourne shell.  My experience with error handling in Amoeba made
     me acutely aware of the importance of exceptions as a programming
     language feature.

     It occurred to me that a scripting language with a syntax like ABC
     but with access to the Amoeba system calls would fill the need.  I
     realized that it would be foolish to write an Amoeba-specific
     language, so I decided that I needed a language that was generally
     extensible.

     During the 1989 Christmas holidays, I had a lot of time on my hand,
     so I decided to give it a try.  During the next year, while still
     mostly working on it in my own time, Python was used in the Amoeba
     project with increasing success, and the feedback from colleagues
     made me add many early improvements.

     In February 1991, after just over a year of development, I decided
     to post to USENET. The rest is in the ‘Misc/HISTORY’ file.


File: python.info,  Node: What is Python good for?,  Next: How does the Python version numbering scheme work?,  Prev: Why was Python created in the first place?,  Up: General Information

11.1.1.5 What is Python good for?
.................................

Python is a high-level general-purpose programming language that can be
applied to many different classes of problems.

The language comes with a large standard library that covers areas such
as string processing (regular expressions, Unicode, calculating
differences between files), Internet protocols (HTTP, FTP, SMTP,
XML-RPC, POP, IMAP, CGI programming), software engineering (unit
testing, logging, profiling, parsing Python code), and operating system
interfaces (system calls, filesystems, TCP/IP sockets).  Look at the
table of contents for *note The Python Standard Library: 1330. to get an
idea of what’s available.  A wide variety of third-party extensions are
also available.  Consult the Python Package Index(1) to find packages of
interest to you.

   ---------- Footnotes ----------

   (1) https://pypi.org


File: python.info,  Node: How does the Python version numbering scheme work?,  Next: How do I obtain a copy of the Python source?,  Prev: What is Python good for?,  Up: General Information

11.1.1.6 How does the Python version numbering scheme work?
...........................................................

Python versions are numbered A.B.C or A.B. A is the major version number
– it is only incremented for really major changes in the language.  B is
the minor version number, incremented for less earth-shattering changes.
C is the micro-level – it is incremented for each bugfix release.  See
PEP 6(1) for more information about bugfix releases.

Not all releases are bugfix releases.  In the run-up to a new major
release, a series of development releases are made, denoted as alpha,
beta, or release candidate.  Alphas are early releases in which
interfaces aren’t yet finalized; it’s not unexpected to see an interface
change between two alpha releases.  Betas are more stable, preserving
existing interfaces but possibly adding new modules, and release
candidates are frozen, making no changes except as needed to fix
critical bugs.

Alpha, beta and release candidate versions have an additional suffix.
The suffix for an alpha version is “aN” for some small number N, the
suffix for a beta version is “bN” for some small number N, and the
suffix for a release candidate version is “rcN” for some small number N.
In other words, all versions labeled 2.0aN precede the versions labeled
2.0bN, which precede versions labeled 2.0rcN, and `those' precede 2.0.

You may also find version numbers with a “+” suffix, e.g.  “2.2+”.
These are unreleased versions, built directly from the CPython
development repository.  In practice, after a final minor release is
made, the version is incremented to the next minor version, which
becomes the “a0” version, e.g.  “2.4a0”.

See also the documentation for *note sys.version: 6ca, *note
sys.hexversion: 37b8, and *note sys.version_info: bed.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0006


File: python.info,  Node: How do I obtain a copy of the Python source?,  Next: How do I get documentation on Python?,  Prev: How does the Python version numbering scheme work?,  Up: General Information

11.1.1.7 How do I obtain a copy of the Python source?
.....................................................

The latest Python source distribution is always available from
python.org, at ‘https://www.python.org/downloads/’.  The latest
development sources can be obtained at
‘https://github.com/python/cpython/’.

The source distribution is a gzipped tar file containing the complete C
source, Sphinx-formatted documentation, Python library modules, example
programs, and several useful pieces of freely distributable software.
The source will compile and run out of the box on most UNIX platforms.

Consult the Getting Started section of the Python Developer’s Guide(1)
for more information on getting the source code and compiling it.

   ---------- Footnotes ----------

   (1) https://devguide.python.org/setup/


File: python.info,  Node: How do I get documentation on Python?,  Next: I’ve never programmed before Is there a Python tutorial?,  Prev: How do I obtain a copy of the Python source?,  Up: General Information

11.1.1.8 How do I get documentation on Python?
..............................................

The standard documentation for the current stable version of Python is
available at ‘https://docs.python.org/3/’.  PDF, plain text, and
downloadable HTML versions are also available at
‘https://docs.python.org/3/download.html’.

The documentation is written in reStructuredText and processed by the
Sphinx documentation tool(1).  The reStructuredText source for the
documentation is part of the Python source distribution.

   ---------- Footnotes ----------

   (1) http://sphinx-doc.org/


File: python.info,  Node: I’ve never programmed before Is there a Python tutorial?,  Next: Is there a newsgroup or mailing list devoted to Python?,  Prev: How do I get documentation on Python?,  Up: General Information

11.1.1.9 I’ve never programmed before. Is there a Python tutorial?
..................................................................

There are numerous tutorials and books available.  The standard
documentation includes *note The Python Tutorial: 132f.

Consult the Beginner’s Guide(1) to find information for beginning Python
programmers, including lists of tutorials.

   ---------- Footnotes ----------

   (1) https://wiki.python.org/moin/BeginnersGuide


File: python.info,  Node: Is there a newsgroup or mailing list devoted to Python?,  Next: How do I get a beta test version of Python?,  Prev: I’ve never programmed before Is there a Python tutorial?,  Up: General Information

11.1.1.10 Is there a newsgroup or mailing list devoted to Python?
.................................................................

There is a newsgroup, ‘comp.lang.python’, and a mailing list,
python-list(1).  The newsgroup and mailing list are gatewayed into each
other – if you can read news it’s unnecessary to subscribe to the
mailing list.  ‘comp.lang.python’ is high-traffic, receiving hundreds of
postings every day, and Usenet readers are often more able to cope with
this volume.

Announcements of new software releases and events can be found in
comp.lang.python.announce, a low-traffic moderated list that receives
about five postings per day.  It’s available as the python-announce
mailing list(2).

More info about other mailing lists and newsgroups can be found at
‘https://www.python.org/community/lists/’.

   ---------- Footnotes ----------

   (1) https://mail.python.org/mailman/listinfo/python-list

   (2) https://mail.python.org/mailman/listinfo/python-announce-list


File: python.info,  Node: How do I get a beta test version of Python?,  Next: How do I submit bug reports and patches for Python?,  Prev: Is there a newsgroup or mailing list devoted to Python?,  Up: General Information

11.1.1.11 How do I get a beta test version of Python?
.....................................................

Alpha and beta releases are available from
‘https://www.python.org/downloads/’.  All releases are announced on the
comp.lang.python and comp.lang.python.announce newsgroups and on the
Python home page at ‘https://www.python.org/’; an RSS feed of news is
available.

You can also access the development version of Python through Git.  See
The Python Developer’s Guide(1) for details.

   ---------- Footnotes ----------

   (1) https://devguide.python.org/


File: python.info,  Node: How do I submit bug reports and patches for Python?,  Next: Are there any published articles about Python that I can reference?,  Prev: How do I get a beta test version of Python?,  Up: General Information

11.1.1.12 How do I submit bug reports and patches for Python?
.............................................................

To report a bug or submit a patch, please use the Roundup installation
at ‘https://bugs.python.org/’.

You must have a Roundup account to report bugs; this makes it possible
for us to contact you if we have follow-up questions.  It will also
enable Roundup to send you updates as we act on your bug.  If you had
previously used SourceForge to report bugs to Python, you can obtain
your Roundup password through Roundup’s password reset procedure(1).

For more information on how Python is developed, consult the Python
Developer’s Guide(2).

   ---------- Footnotes ----------

   (1) https://bugs.python.org/user?@template=forgotten

   (2) https://devguide.python.org/


File: python.info,  Node: Are there any published articles about Python that I can reference?,  Next: Are there any books on Python?,  Prev: How do I submit bug reports and patches for Python?,  Up: General Information

11.1.1.13 Are there any published articles about Python that I can reference?
.............................................................................

It’s probably best to cite your favorite book about Python.

The very first article about Python was written in 1991 and is now quite
outdated.

     Guido van Rossum and Jelke de Boer, “Interactively Testing Remote
     Servers Using the Python Programming Language”, CWI Quarterly,
     Volume 4, Issue 4 (December 1991), Amsterdam, pp 283–303.


File: python.info,  Node: Are there any books on Python?,  Next: Where in the world is www python org located?,  Prev: Are there any published articles about Python that I can reference?,  Up: General Information

11.1.1.14 Are there any books on Python?
........................................

Yes, there are many, and more are being published.  See the python.org
wiki at ‘https://wiki.python.org/moin/PythonBooks’ for a list.

You can also search online bookstores for “Python” and filter out the
Monty Python references; or perhaps search for “Python” and “language”.


File: python.info,  Node: Where in the world is www python org located?,  Next: Why is it called Python?,  Prev: Are there any books on Python?,  Up: General Information

11.1.1.15 Where in the world is www.python.org located?
.......................................................

The Python project’s infrastructure is located all over the world and is
managed by the Python Infrastructure Team.  Details here(1).

   ---------- Footnotes ----------

   (1) http://infra.psf.io


File: python.info,  Node: Why is it called Python?,  Next: Do I have to like “Monty Python’s Flying Circus”?,  Prev: Where in the world is www python org located?,  Up: General Information

11.1.1.16 Why is it called Python?
..................................

When he began implementing Python, Guido van Rossum was also reading the
published scripts from "Monty Python’s Flying Circus"(1), a BBC comedy
series from the 1970s.  Van Rossum thought he needed a name that was
short, unique, and slightly mysterious, so he decided to call the
language Python.

   ---------- Footnotes ----------

   (1) https://en.wikipedia.org/wiki/Monty_Python


File: python.info,  Node: Do I have to like “Monty Python’s Flying Circus”?,  Prev: Why is it called Python?,  Up: General Information

11.1.1.17 Do I have to like “Monty Python’s Flying Circus”?
...........................................................

No, but it helps.  :)


File: python.info,  Node: Python in the real world,  Prev: General Information,  Up: General Python FAQ

11.1.2 Python in the real world
-------------------------------

* Menu:

* How stable is Python?::
* How many people are using Python?::
* Have any significant projects been done in Python?::
* What new developments are expected for Python in the future?::
* Is it reasonable to propose incompatible changes to Python?::
* Is Python a good language for beginning programmers?::


File: python.info,  Node: How stable is Python?,  Next: How many people are using Python?,  Up: Python in the real world

11.1.2.1 How stable is Python?
..............................

Very stable.  New, stable releases have been coming out roughly every 6
to 18 months since 1991, and this seems likely to continue.  As of
version 3.9, Python will have a major new release every 12 months ( PEP
602(1)).

The developers issue “bugfix” releases of older versions, so the
stability of existing releases gradually improves.  Bugfix releases,
indicated by a third component of the version number (e.g.  3.5.3,
3.6.2), are managed for stability; only fixes for known problems are
included in a bugfix release, and it’s guaranteed that interfaces will
remain the same throughout a series of bugfix releases.

The latest stable releases can always be found on the Python download
page(2).  There are two production-ready versions of Python: 2.x and
3.x.  The recommended version is 3.x, which is supported by most widely
used libraries.  Although 2.x is still widely used, it is not maintained
anymore(3).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0602

   (2) https://www.python.org/downloads/

   (3) https://www.python.org/dev/peps/pep-0373/


File: python.info,  Node: How many people are using Python?,  Next: Have any significant projects been done in Python?,  Prev: How stable is Python?,  Up: Python in the real world

11.1.2.2 How many people are using Python?
..........................................

There are probably millions of users, though it’s difficult to obtain an
exact count.

Python is available for free download, so there are no sales figures,
and it’s available from many different sites and packaged with many
Linux distributions, so download statistics don’t tell the whole story
either.

The comp.lang.python newsgroup is very active, but not all Python users
post to the group or even read it.


File: python.info,  Node: Have any significant projects been done in Python?,  Next: What new developments are expected for Python in the future?,  Prev: How many people are using Python?,  Up: Python in the real world

11.1.2.3 Have any significant projects been done in Python?
...........................................................

See ‘https://www.python.org/about/success’ for a list of projects that
use Python.  Consulting the proceedings for past Python conferences(1)
will reveal contributions from many different companies and
organizations.

High-profile Python projects include the Mailman mailing list manager(2)
and the Zope application server(3).  Several Linux distributions, most
notably Red Hat(4), have written part or all of their installer and
system administration software in Python.  Companies that use Python
internally include Google, Yahoo, and Lucasfilm Ltd.

   ---------- Footnotes ----------

   (1) https://www.python.org/community/workshops/

   (2) http://www.list.org

   (3) http://www.zope.org

   (4) https://www.redhat.com


File: python.info,  Node: What new developments are expected for Python in the future?,  Next: Is it reasonable to propose incompatible changes to Python?,  Prev: Have any significant projects been done in Python?,  Up: Python in the real world

11.1.2.4 What new developments are expected for Python in the future?
.....................................................................

See ‘https://www.python.org/dev/peps/’ for the Python Enhancement
Proposals (PEPs).  PEPs are design documents describing a suggested new
feature for Python, providing a concise technical specification and a
rationale.  Look for a PEP titled “Python X.Y Release Schedule”, where
X.Y is a version that hasn’t been publicly released yet.

New development is discussed on the python-dev mailing list(1).

   ---------- Footnotes ----------

   (1) https://mail.python.org/mailman/listinfo/python-dev/


File: python.info,  Node: Is it reasonable to propose incompatible changes to Python?,  Next: Is Python a good language for beginning programmers?,  Prev: What new developments are expected for Python in the future?,  Up: Python in the real world

11.1.2.5 Is it reasonable to propose incompatible changes to Python?
....................................................................

In general, no.  There are already millions of lines of Python code
around the world, so any change in the language that invalidates more
than a very small fraction of existing programs has to be frowned upon.
Even if you can provide a conversion program, there’s still the problem
of updating all documentation; many books have been written about
Python, and we don’t want to invalidate them all at a single stroke.

Providing a gradual upgrade path is necessary if a feature has to be
changed.  PEP 5(1) describes the procedure followed for introducing
backward-incompatible changes while minimizing disruption for users.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0005


File: python.info,  Node: Is Python a good language for beginning programmers?,  Prev: Is it reasonable to propose incompatible changes to Python?,  Up: Python in the real world

11.1.2.6 Is Python a good language for beginning programmers?
.............................................................

Yes.

It is still common to start students with a procedural and statically
typed language such as Pascal, C, or a subset of C++ or Java.  Students
may be better served by learning Python as their first language.  Python
has a very simple and consistent syntax and a large standard library
and, most importantly, using Python in a beginning programming course
lets students concentrate on important programming skills such as
problem decomposition and data type design.  With Python, students can
be quickly introduced to basic concepts such as loops and procedures.
They can probably even work with user-defined objects in their very
first course.

For a student who has never programmed before, using a statically typed
language seems unnatural.  It presents additional complexity that the
student must master and slows the pace of the course.  The students are
trying to learn to think like a computer, decompose problems, design
consistent interfaces, and encapsulate data.  While learning to use a
statically typed language is important in the long term, it is not
necessarily the best topic to address in the students’ first programming
course.

Many other aspects of Python make it a good first language.  Like Java,
Python has a large standard library so that students can be assigned
programming projects very early in the course that `do' something.
Assignments aren’t restricted to the standard four-function calculator
and check balancing programs.  By using the standard library, students
can gain the satisfaction of working on realistic applications as they
learn the fundamentals of programming.  Using the standard library also
teaches students about code reuse.  Third-party modules such as PyGame
are also helpful in extending the students’ reach.

Python’s interactive interpreter enables students to test language
features while they’re programming.  They can keep a window with the
interpreter running while they enter their program’s source in another
window.  If they can’t remember the methods for a list, they can do
something like this:

     >>> L = []
     >>> dir(L)
     ['__add__', '__class__', '__contains__', '__delattr__', '__delitem__',
     '__dir__', '__doc__', '__eq__', '__format__', '__ge__',
     '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__',
     '__imul__', '__init__', '__iter__', '__le__', '__len__', '__lt__',
     '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__',
     '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__',
     '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear',
     'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove',
     'reverse', 'sort']
     >>> [d for d in dir(L) if '__' not in d]
     ['append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

     >>> help(L.append)
     Help on built-in function append:

     append(...)
         L.append(object) -> None -- append object to end

     >>> L.append(1)
     >>> L
     [1]

With the interpreter, documentation is never far from the student as
they are programming.

There are also good IDEs for Python.  IDLE is a cross-platform IDE for
Python that is written in Python using Tkinter.  PythonWin is a
Windows-specific IDE. Emacs users will be happy to know that there is a
very good Python mode for Emacs.  All of these programming environments
provide syntax highlighting, auto-indenting, and access to the
interactive interpreter while coding.  Consult the Python wiki(1) for a
full list of Python editing environments.

If you want to discuss Python’s use in education, you may be interested
in joining the edu-sig mailing list(2).

   ---------- Footnotes ----------

   (1) https://wiki.python.org/moin/PythonEditors

   (2) https://www.python.org/community/sigs/current/edu-sig


File: python.info,  Node: Programming FAQ,  Next: Design and History FAQ,  Prev: General Python FAQ,  Up: Python Frequently Asked Questions

11.2 Programming FAQ
====================

* Menu:

* General Questions::
* Core Language::
* Numbers and strings::
* Performance: Performance<4>.
* Sequences (Tuples/Lists): Sequences Tuples/Lists.
* Objects::
* Modules: Modules<3>.


File: python.info,  Node: General Questions,  Next: Core Language,  Up: Programming FAQ

11.2.1 General Questions
------------------------

* Menu:

* Is there a source code level debugger with breakpoints, single-stepping, etc.?: Is there a source code level debugger with breakpoints single-stepping etc ?.
* Are there tools to help find bugs or perform static analysis?::
* How can I create a stand-alone binary from a Python script?::
* Are there coding standards or a style guide for Python programs?::


File: python.info,  Node: Is there a source code level debugger with breakpoints single-stepping etc ?,  Next: Are there tools to help find bugs or perform static analysis?,  Up: General Questions

11.2.1.1 Is there a source code level debugger with breakpoints, single-stepping, etc.?
.......................................................................................

Yes.

Several debuggers for Python are described below, and the built-in
function *note breakpoint(): 40b. allows you to drop into any of them.

The pdb module is a simple but adequate console-mode debugger for
Python.  It is part of the standard Python library, and is *note
documented in the Library Reference Manual: c9.  You can also write your
own debugger by using the code for pdb as an example.

The IDLE interactive development environment, which is part of the
standard Python distribution (normally available as Tools/scripts/idle),
includes a graphical debugger.

PythonWin is a Python IDE that includes a GUI debugger based on pdb.
The PythonWin debugger colors breakpoints and has quite a few cool
features such as debugging non-PythonWin programs.  PythonWin is
available as part of pywin32(1) project and as a part of the
ActivePython(2) distribution.

Eric(3) is an IDE built on PyQt and the Scintilla editing component.

trepan3k(4) is a gdb-like debugger.

Visual Studio Code(5) is an IDE with debugging tools that integrates
with version-control software.

There are a number of commercial Python IDEs that include graphical
debuggers.  They include:

   * Wing IDE(6)

   * Komodo IDE(7)

   * PyCharm(8)

   ---------- Footnotes ----------

   (1) https://github.com/mhammond/pywin32

   (2) https://www.activestate.com/products/python/

   (3) http://eric-ide.python-projects.org/

   (4) https://github.com/rocky/python3-trepan/

   (5) https://code.visualstudio.com/

   (6) https://wingware.com/

   (7) https://www.activestate.com/products/komodo-ide/

   (8) https://www.jetbrains.com/pycharm/


File: python.info,  Node: Are there tools to help find bugs or perform static analysis?,  Next: How can I create a stand-alone binary from a Python script?,  Prev: Is there a source code level debugger with breakpoints single-stepping etc ?,  Up: General Questions

11.2.1.2 Are there tools to help find bugs or perform static analysis?
......................................................................

Yes.

Pylint(1) and Pyflakes(2) do basic checking that will help you catch
bugs sooner.

Static type checkers such as Mypy(3), Pyre(4), and Pytype(5) can check
type hints in Python source code.

   ---------- Footnotes ----------

   (1) https://www.pylint.org/

   (2) https://github.com/PyCQA/pyflakes

   (3) http://mypy-lang.org/

   (4) https://pyre-check.org/

   (5) https://github.com/google/pytype


File: python.info,  Node: How can I create a stand-alone binary from a Python script?,  Next: Are there coding standards or a style guide for Python programs?,  Prev: Are there tools to help find bugs or perform static analysis?,  Up: General Questions

11.2.1.3 How can I create a stand-alone binary from a Python script?
....................................................................

You don’t need the ability to compile Python to C code if all you want
is a stand-alone program that users can download and run without having
to install the Python distribution first.  There are a number of tools
that determine the set of modules required by a program and bind these
modules together with a Python binary to produce a single executable.

One is to use the freeze tool, which is included in the Python source
tree as ‘Tools/freeze’.  It converts Python byte code to C arrays; a C
compiler you can embed all your modules into a new program, which is
then linked with the standard Python modules.

It works by scanning your source recursively for import statements (in
both forms) and looking for the modules in the standard Python path as
well as in the source directory (for built-in modules).  It then turns
the bytecode for modules written in Python into C code (array
initializers that can be turned into code objects using the marshal
module) and creates a custom-made config file that only contains those
built-in modules which are actually used in the program.  It then
compiles the generated C code and links it with the rest of the Python
interpreter to form a self-contained binary which acts exactly like your
script.

The following packages can help with the creation of console and GUI
executables:

   * Nuitka(1) (Cross-platform)

   * PyInstaller(2) (Cross-platform)

   * PyOxidizer(3) (Cross-platform)

   * cx_Freeze(4) (Cross-platform)

   * py2app(5) (macOS only)

   * py2exe(6) (Windows only)

   ---------- Footnotes ----------

   (1) https://nuitka.net/

   (2) http://www.pyinstaller.org/

   (3) https://pyoxidizer.readthedocs.io/en/stable/

   (4) https://marcelotduarte.github.io/cx_Freeze/

   (5) https://github.com/ronaldoussoren/py2app

   (6) http://www.py2exe.org/


File: python.info,  Node: Are there coding standards or a style guide for Python programs?,  Prev: How can I create a stand-alone binary from a Python script?,  Up: General Questions

11.2.1.4 Are there coding standards or a style guide for Python programs?
.........................................................................

Yes.  The coding style required for standard library modules is
documented as PEP 8(1).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0008


File: python.info,  Node: Core Language,  Next: Numbers and strings,  Prev: General Questions,  Up: Programming FAQ

11.2.2 Core Language
--------------------

* Menu:

* Why am I getting an UnboundLocalError when the variable has a value?::
* What are the rules for local and global variables in Python?::
* Why do lambdas defined in a loop with different values all return the same result?::
* How do I share global variables across modules?::
* What are the “best practices” for using import in a module?::
* Why are default values shared between objects?::
* How can I pass optional or keyword parameters from one function to another?::
* What is the difference between arguments and parameters?::
* Why did changing list ‘y’ also change list ‘x’?::
* How do I write a function with output parameters (call by reference)?: How do I write a function with output parameters call by reference ?.
* How do you make a higher order function in Python?::
* How do I copy an object in Python?::
* How can I find the methods or attributes of an object?::
* How can my code discover the name of an object?::
* What’s up with the comma operator’s precedence?::
* Is there an equivalent of C’s “?;” ternary operator?: Is there an equivalent of C’s “? ” ternary operator?.
* Is it possible to write obfuscated one-liners in Python?::
* What does the slash(/) in the parameter list of a function mean?: What does the slash / in the parameter list of a function mean?.


File: python.info,  Node: Why am I getting an UnboundLocalError when the variable has a value?,  Next: What are the rules for local and global variables in Python?,  Up: Core Language

11.2.2.1 Why am I getting an UnboundLocalError when the variable has a value?
.............................................................................

It can be a surprise to get the UnboundLocalError in previously working
code when it is modified by adding an assignment statement somewhere in
the body of a function.

This code:

     >>> x = 10
     >>> def bar():
     ...     print(x)
     >>> bar()
     10

works, but this code:

     >>> x = 10
     >>> def foo():
     ...     print(x)
     ...     x += 1

results in an UnboundLocalError:

     >>> foo()
     Traceback (most recent call last):
       ...
     UnboundLocalError: local variable 'x' referenced before assignment

This is because when you make an assignment to a variable in a scope,
that variable becomes local to that scope and shadows any similarly
named variable in the outer scope.  Since the last statement in foo
assigns a new value to ‘x’, the compiler recognizes it as a local
variable.  Consequently when the earlier ‘print(x)’ attempts to print
the uninitialized local variable and an error results.

In the example above you can access the outer scope variable by
declaring it global:

     >>> x = 10
     >>> def foobar():
     ...     global x
     ...     print(x)
     ...     x += 1
     >>> foobar()
     10

This explicit declaration is required in order to remind you that
(unlike the superficially analogous situation with class and instance
variables) you are actually modifying the value of the variable in the
outer scope:

     >>> print(x)
     11

You can do a similar thing in a nested scope using the *note nonlocal:
d07. keyword:

     >>> def foo():
     ...    x = 10
     ...    def bar():
     ...        nonlocal x
     ...        print(x)
     ...        x += 1
     ...    bar()
     ...    print(x)
     >>> foo()
     10
     11


File: python.info,  Node: What are the rules for local and global variables in Python?,  Next: Why do lambdas defined in a loop with different values all return the same result?,  Prev: Why am I getting an UnboundLocalError when the variable has a value?,  Up: Core Language

11.2.2.2 What are the rules for local and global variables in Python?
.....................................................................

In Python, variables that are only referenced inside a function are
implicitly global.  If a variable is assigned a value anywhere within
the function’s body, it’s assumed to be a local unless explicitly
declared as global.

Though a bit surprising at first, a moment’s consideration explains
this.  On one hand, requiring *note global: 1378. for assigned variables
provides a bar against unintended side-effects.  On the other hand, if
‘global’ was required for all global references, you’d be using ‘global’
all the time.  You’d have to declare as global every reference to a
built-in function or to a component of an imported module.  This clutter
would defeat the usefulness of the ‘global’ declaration for identifying
side-effects.


File: python.info,  Node: Why do lambdas defined in a loop with different values all return the same result?,  Next: How do I share global variables across modules?,  Prev: What are the rules for local and global variables in Python?,  Up: Core Language

11.2.2.3 Why do lambdas defined in a loop with different values all return the same result?
...........................................................................................

Assume you use a for loop to define a few different lambdas (or even
plain functions), e.g.:

     >>> squares = []
     >>> for x in range(5):
     ...     squares.append(lambda: x**2)

This gives you a list that contains 5 lambdas that calculate ‘x**2’.
You might expect that, when called, they would return, respectively,
‘0’, ‘1’, ‘4’, ‘9’, and ‘16’.  However, when you actually try you will
see that they all return ‘16’:

     >>> squares[2]()
     16
     >>> squares[4]()
     16

This happens because ‘x’ is not local to the lambdas, but is defined in
the outer scope, and it is accessed when the lambda is called — not when
it is defined.  At the end of the loop, the value of ‘x’ is ‘4’, so all
the functions now return ‘4**2’, i.e.  ‘16’.  You can also verify this
by changing the value of ‘x’ and see how the results of the lambdas
change:

     >>> x = 8
     >>> squares[2]()
     64

In order to avoid this, you need to save the values in variables local
to the lambdas, so that they don’t rely on the value of the global ‘x’:

     >>> squares = []
     >>> for x in range(5):
     ...     squares.append(lambda n=x: n**2)

Here, ‘n=x’ creates a new variable ‘n’ local to the lambda and computed
when the lambda is defined so that it has the same value that ‘x’ had at
that point in the loop.  This means that the value of ‘n’ will be ‘0’ in
the first lambda, ‘1’ in the second, ‘2’ in the third, and so on.
Therefore each lambda will now return the correct result:

     >>> squares[2]()
     4
     >>> squares[4]()
     16

Note that this behaviour is not peculiar to lambdas, but applies to
regular functions too.


File: python.info,  Node: How do I share global variables across modules?,  Next: What are the “best practices” for using import in a module?,  Prev: Why do lambdas defined in a loop with different values all return the same result?,  Up: Core Language

11.2.2.4 How do I share global variables across modules?
........................................................

The canonical way to share information across modules within a single
program is to create a special module (often called config or cfg).
Just import the config module in all modules of your application; the
module then becomes available as a global name.  Because there is only
one instance of each module, any changes made to the module object get
reflected everywhere.  For example:

config.py:

     x = 0   # Default value of the 'x' configuration setting

mod.py:

     import config
     config.x = 1

main.py:

     import config
     import mod
     print(config.x)

Note that using a module is also the basis for implementing the
Singleton design pattern, for the same reason.


File: python.info,  Node: What are the “best practices” for using import in a module?,  Next: Why are default values shared between objects?,  Prev: How do I share global variables across modules?,  Up: Core Language

11.2.2.5 What are the “best practices” for using import in a module?
....................................................................

In general, don’t use ‘from modulename import *’.  Doing so clutters the
importer’s namespace, and makes it much harder for linters to detect
undefined names.

Import modules at the top of a file.  Doing so makes it clear what other
modules your code requires and avoids questions of whether the module
name is in scope.  Using one import per line makes it easy to add and
delete module imports, but using multiple imports per line uses less
screen space.

It’s good practice if you import modules in the following order:

  1. standard library modules – e.g.  ‘sys’, ‘os’, ‘getopt’, ‘re’

  2. third-party library modules (anything installed in Python’s
     site-packages directory) – e.g.  mx.DateTime, ZODB, PIL.Image, etc.

  3. locally-developed modules

It is sometimes necessary to move imports to a function or class to
avoid problems with circular imports.  Gordon McMillan says:

     Circular imports are fine where both modules use the “import
     <module>” form of import.  They fail when the 2nd module wants to
     grab a name out of the first (“from module import name”) and the
     import is at the top level.  That’s because names in the 1st are
     not yet available, because the first module is busy importing the
     2nd.

In this case, if the second module is only used in one function, then
the import can easily be moved into that function.  By the time the
import is called, the first module will have finished initializing, and
the second module can do its import.

It may also be necessary to move imports out of the top level of code if
some of the modules are platform-specific.  In that case, it may not
even be possible to import all of the modules at the top of the file.
In this case, importing the correct modules in the corresponding
platform-specific code is a good option.

Only move imports into a local scope, such as inside a function
definition, if it’s necessary to solve a problem such as avoiding a
circular import or are trying to reduce the initialization time of a
module.  This technique is especially helpful if many of the imports are
unnecessary depending on how the program executes.  You may also want to
move imports into a function if the modules are only ever used in that
function.  Note that loading a module the first time may be expensive
because of the one time initialization of the module, but loading a
module multiple times is virtually free, costing only a couple of
dictionary lookups.  Even if the module name has gone out of scope, the
module is probably available in *note sys.modules: 1051.


File: python.info,  Node: Why are default values shared between objects?,  Next: How can I pass optional or keyword parameters from one function to another?,  Prev: What are the “best practices” for using import in a module?,  Up: Core Language

11.2.2.6 Why are default values shared between objects?
.......................................................

This type of bug commonly bites neophyte programmers.  Consider this
function:

     def foo(mydict={}):  # Danger: shared reference to one dict for all calls
         ... compute something ...
         mydict[key] = value
         return mydict

The first time you call this function, ‘mydict’ contains a single item.
The second time, ‘mydict’ contains two items because when ‘foo()’ begins
executing, ‘mydict’ starts out with an item already in it.

It is often expected that a function call creates new objects for
default values.  This is not what happens.  Default values are created
exactly once, when the function is defined.  If that object is changed,
like the dictionary in this example, subsequent calls to the function
will refer to this changed object.

By definition, immutable objects such as numbers, strings, tuples, and
‘None’, are safe from change.  Changes to mutable objects such as
dictionaries, lists, and class instances can lead to confusion.

Because of this feature, it is good programming practice to not use
mutable objects as default values.  Instead, use ‘None’ as the default
value and inside the function, check if the parameter is ‘None’ and
create a new list/dictionary/whatever if it is.  For example, don’t
write:

     def foo(mydict={}):
         ...

but:

     def foo(mydict=None):
         if mydict is None:
             mydict = {}  # create a new dict for local namespace

This feature can be useful.  When you have a function that’s
time-consuming to compute, a common technique is to cache the parameters
and the resulting value of each call to the function, and return the
cached value if the same value is requested again.  This is called
“memoizing”, and can be implemented like this:

     # Callers can only provide two parameters and optionally pass _cache by keyword
     def expensive(arg1, arg2, *, _cache={}):
         if (arg1, arg2) in _cache:
             return _cache[(arg1, arg2)]

         # Calculate the value
         result = ... expensive computation ...
         _cache[(arg1, arg2)] = result           # Store result in the cache
         return result

You could use a global variable containing a dictionary instead of the
default value; it’s a matter of taste.


File: python.info,  Node: How can I pass optional or keyword parameters from one function to another?,  Next: What is the difference between arguments and parameters?,  Prev: Why are default values shared between objects?,  Up: Core Language

11.2.2.7 How can I pass optional or keyword parameters from one function to another?
....................................................................................

Collect the arguments using the ‘*’ and ‘**’ specifiers in the
function’s parameter list; this gives you the positional arguments as a
tuple and the keyword arguments as a dictionary.  You can then pass
these arguments when calling another function by using ‘*’ and ‘**’:

     def f(x, *args, **kwargs):
         ...
         kwargs['width'] = '14.3c'
         ...
         g(x, *args, **kwargs)


File: python.info,  Node: What is the difference between arguments and parameters?,  Next: Why did changing list ‘y’ also change list ‘x’?,  Prev: How can I pass optional or keyword parameters from one function to another?,  Up: Core Language

11.2.2.8 What is the difference between arguments and parameters?
.................................................................

*note Parameters: 1664. are defined by the names that appear in a
function definition, whereas *note arguments: 165c. are the values
actually passed to a function when calling it.  Parameters define what
types of arguments a function can accept.  For example, given the
function definition:

     def func(foo, bar=None, **kwargs):
         pass

`foo', `bar' and `kwargs' are parameters of ‘func’.  However, when
calling ‘func’, for example:

     func(42, bar=314, extra=somevar)

the values ‘42’, ‘314’, and ‘somevar’ are arguments.


File: python.info,  Node: Why did changing list ‘y’ also change list ‘x’?,  Next: How do I write a function with output parameters call by reference ?,  Prev: What is the difference between arguments and parameters?,  Up: Core Language

11.2.2.9 Why did changing list ‘y’ also change list ‘x’?
........................................................

If you wrote code like:

     >>> x = []
     >>> y = x
     >>> y.append(10)
     >>> y
     [10]
     >>> x
     [10]

you might be wondering why appending an element to ‘y’ changed ‘x’ too.

There are two factors that produce this result:

  1. Variables are simply names that refer to objects.  Doing ‘y = x’
     doesn’t create a copy of the list – it creates a new variable ‘y’
     that refers to the same object ‘x’ refers to.  This means that
     there is only one object (the list), and both ‘x’ and ‘y’ refer to
     it.

  2. Lists are *note mutable: 135e, which means that you can change
     their content.

After the call to ‘append()’, the content of the mutable object has
changed from ‘[]’ to ‘[10]’.  Since both the variables refer to the same
object, using either name accesses the modified value ‘[10]’.

If we instead assign an immutable object to ‘x’:

     >>> x = 5  # ints are immutable
     >>> y = x
     >>> x = x + 1  # 5 can't be mutated, we are creating a new object here
     >>> x
     6
     >>> y
     5

we can see that in this case ‘x’ and ‘y’ are not equal anymore.  This is
because integers are *note immutable: 1356, and when we do ‘x = x + 1’
we are not mutating the int ‘5’ by incrementing its value; instead, we
are creating a new object (the int ‘6’) and assigning it to ‘x’ (that
is, changing which object ‘x’ refers to).  After this assignment we have
two objects (the ints ‘6’ and ‘5’) and two variables that refer to them
(‘x’ now refers to ‘6’ but ‘y’ still refers to ‘5’).

Some operations (for example ‘y.append(10)’ and ‘y.sort()’) mutate the
object, whereas superficially similar operations (for example ‘y = y +
[10]’ and ‘sorted(y)’) create a new object.  In general in Python (and
in all cases in the standard library) a method that mutates an object
will return ‘None’ to help avoid getting the two types of operations
confused.  So if you mistakenly write ‘y.sort()’ thinking it will give
you a sorted copy of ‘y’, you’ll instead end up with ‘None’, which will
likely cause your program to generate an easily diagnosed error.

However, there is one class of operations where the same operation
sometimes has different behaviors with different types: the augmented
assignment operators.  For example, ‘+=’ mutates lists but not tuples or
ints (‘a_list += [1, 2, 3]’ is equivalent to ‘a_list.extend([1, 2, 3])’
and mutates ‘a_list’, whereas ‘some_tuple += (1, 2, 3)’ and ‘some_int +=
1’ create new objects).

In other words:

   * If we have a mutable object (*note list: 1f8, *note dict: 164,
     *note set: 1f6, etc.), we can use some specific operations to
     mutate it and all the variables that refer to it will see the
     change.

   * If we have an immutable object (*note str: 205, *note int: 204,
     *note tuple: 1a2, etc.), all the variables that refer to it will
     always see the same value, but operations that transform that value
     into a new value always return a new object.

If you want to know if two variables refer to the same object or not,
you can use the *note is: 1551. operator, or the built-in function *note
id(): e4b.


File: python.info,  Node: How do I write a function with output parameters call by reference ?,  Next: How do you make a higher order function in Python?,  Prev: Why did changing list ‘y’ also change list ‘x’?,  Up: Core Language

11.2.2.10 How do I write a function with output parameters (call by reference)?
...............................................................................

Remember that arguments are passed by assignment in Python.  Since
assignment just creates references to objects, there’s no alias between
an argument name in the caller and callee, and so no call-by-reference
per se.  You can achieve the desired effect in a number of ways.

  1. By returning a tuple of the results:

          >>> def func1(a, b):
          ...     a = 'new-value'        # a and b are local names
          ...     b = b + 1              # assigned to new objects
          ...     return a, b            # return new values
          ...
          >>> x, y = 'old-value', 99
          >>> func1(x, y)
          ('new-value', 100)

     This is almost always the clearest solution.

  2. By using global variables.  This isn’t thread-safe, and is not
     recommended.

  3. By passing a mutable (changeable in-place) object:

          >>> def func2(a):
          ...     a[0] = 'new-value'     # 'a' references a mutable list
          ...     a[1] = a[1] + 1        # changes a shared object
          ...
          >>> args = ['old-value', 99]
          >>> func2(args)
          >>> args
          ['new-value', 100]

  4. By passing in a dictionary that gets mutated:

          >>> def func3(args):
          ...     args['a'] = 'new-value'     # args is a mutable dictionary
          ...     args['b'] = args['b'] + 1   # change it in-place
          ...
          >>> args = {'a': 'old-value', 'b': 99}
          >>> func3(args)
          >>> args
          {'a': 'new-value', 'b': 100}

  5. Or bundle up values in a class instance:

          >>> class Namespace:
          ...     def __init__(self, /, **args):
          ...         for key, value in args.items():
          ...             setattr(self, key, value)
          ...
          >>> def func4(args):
          ...     args.a = 'new-value'        # args is a mutable Namespace
          ...     args.b = args.b + 1         # change object in-place
          ...
          >>> args = Namespace(a='old-value', b=99)
          >>> func4(args)
          >>> vars(args)
          {'a': 'new-value', 'b': 100}

     There’s almost never a good reason to get this complicated.

Your best choice is to return a tuple containing the multiple results.


File: python.info,  Node: How do you make a higher order function in Python?,  Next: How do I copy an object in Python?,  Prev: How do I write a function with output parameters call by reference ?,  Up: Core Language

11.2.2.11 How do you make a higher order function in Python?
............................................................

You have two choices: you can use nested scopes or you can use callable
objects.  For example, suppose you wanted to define ‘linear(a,b)’ which
returns a function ‘f(x)’ that computes the value ‘a*x+b’.  Using nested
scopes:

     def linear(a, b):
         def result(x):
             return a * x + b
         return result

Or using a callable object:

     class linear:

         def __init__(self, a, b):
             self.a, self.b = a, b

         def __call__(self, x):
             return self.a * x + self.b

In both cases,

     taxes = linear(0.3, 2)

gives a callable object where ‘taxes(10e6) == 0.3 * 10e6 + 2’.

The callable object approach has the disadvantage that it is a bit
slower and results in slightly longer code.  However, note that a
collection of callables can share their signature via inheritance:

     class exponential(linear):
         # __init__ inherited
         def __call__(self, x):
             return self.a * (x ** self.b)

Object can encapsulate state for several methods:

     class counter:

         value = 0

         def set(self, x):
             self.value = x

         def up(self):
             self.value = self.value + 1

         def down(self):
             self.value = self.value - 1

     count = counter()
     inc, dec, reset = count.up, count.down, count.set

Here ‘inc()’, ‘dec()’ and ‘reset()’ act like functions which share the
same counting variable.


File: python.info,  Node: How do I copy an object in Python?,  Next: How can I find the methods or attributes of an object?,  Prev: How do you make a higher order function in Python?,  Up: Core Language

11.2.2.12 How do I copy an object in Python?
............................................

In general, try *note copy.copy(): 4d2. or *note copy.deepcopy(): 4d3.
for the general case.  Not all objects can be copied, but most can.

Some objects can be copied more easily.  Dictionaries have a *note
copy(): 549. method:

     newdict = olddict.copy()

Sequences can be copied by slicing:

     new_l = l[:]


File: python.info,  Node: How can I find the methods or attributes of an object?,  Next: How can my code discover the name of an object?,  Prev: How do I copy an object in Python?,  Up: Core Language

11.2.2.13 How can I find the methods or attributes of an object?
................................................................

For an instance x of a user-defined class, ‘dir(x)’ returns an
alphabetized list of the names containing the instance attributes and
methods and attributes defined by its class.


File: python.info,  Node: How can my code discover the name of an object?,  Next: What’s up with the comma operator’s precedence?,  Prev: How can I find the methods or attributes of an object?,  Up: Core Language

11.2.2.14 How can my code discover the name of an object?
.........................................................

Generally speaking, it can’t, because objects don’t really have names.
Essentially, assignment always binds a name to a value; the same is true
of ‘def’ and ‘class’ statements, but in that case the value is a
callable.  Consider the following code:

     >>> class A:
     ...     pass
     ...
     >>> B = A
     >>> a = B()
     >>> b = a
     >>> print(b)
     <__main__.A object at 0x16D07CC>
     >>> print(a)
     <__main__.A object at 0x16D07CC>

Arguably the class has a name: even though it is bound to two names and
invoked through the name B the created instance is still reported as an
instance of class A. However, it is impossible to say whether the
instance’s name is a or b, since both names are bound to the same value.

Generally speaking it should not be necessary for your code to “know the
names” of particular values.  Unless you are deliberately writing
introspective programs, this is usually an indication that a change of
approach might be beneficial.

In comp.lang.python, Fredrik Lundh once gave an excellent analogy in
answer to this question:

     The same way as you get the name of that cat you found on your
     porch: the cat (object) itself cannot tell you its name, and it
     doesn’t really care – so the only way to find out what it’s called
     is to ask all your neighbours (namespaces) if it’s their cat
     (object)…

     ….and don’t be surprised if you’ll find that it’s known by many
     names, or no name at all!


File: python.info,  Node: What’s up with the comma operator’s precedence?,  Next: Is there an equivalent of C’s “? ” ternary operator?,  Prev: How can my code discover the name of an object?,  Up: Core Language

11.2.2.15 What’s up with the comma operator’s precedence?
.........................................................

Comma is not an operator in Python.  Consider this session:

     >>> "a" in "b", "a"
     (False, 'a')

Since the comma is not an operator, but a separator between expressions
the above is evaluated as if you had entered:

     ("a" in "b"), "a"

not:

     "a" in ("b", "a")

The same is true of the various assignment operators (‘=’, ‘+=’ etc).
They are not truly operators but syntactic delimiters in assignment
statements.


File: python.info,  Node: Is there an equivalent of C’s “? ” ternary operator?,  Next: Is it possible to write obfuscated one-liners in Python?,  Prev: What’s up with the comma operator’s precedence?,  Up: Core Language

11.2.2.16 Is there an equivalent of C’s “?:” ternary operator?
..............................................................

Yes, there is.  The syntax is as follows:

     [on_true] if [expression] else [on_false]

     x, y = 50, 25
     small = x if x < y else y

Before this syntax was introduced in Python 2.5, a common idiom was to
use logical operators:

     [expression] and [on_true] or [on_false]

However, this idiom is unsafe, as it can give wrong results when
`on_true' has a false boolean value.  Therefore, it is always better to
use the ‘... if ... else ...’ form.


File: python.info,  Node: Is it possible to write obfuscated one-liners in Python?,  Next: What does the slash / in the parameter list of a function mean?,  Prev: Is there an equivalent of C’s “? ” ternary operator?,  Up: Core Language

11.2.2.17 Is it possible to write obfuscated one-liners in Python?
..................................................................

Yes.  Usually this is done by nesting *note lambda: cf9. within
‘lambda’.  See the following three examples, due to Ulf Bartelt:

     from functools import reduce

     # Primes < 1000
     print(list(filter(None,map(lambda y:y*reduce(lambda x,y:x*y!=0,
     map(lambda x,y=y:y%x,range(2,int(pow(y,0.5)+1))),1),range(2,1000)))))

     # First 10 Fibonacci numbers
     print(list(map(lambda x,f=lambda x,f:(f(x-1,f)+f(x-2,f)) if x>1 else 1:
     f(x,f), range(10))))

     # Mandelbrot set
     print((lambda Ru,Ro,Iu,Io,IM,Sx,Sy:reduce(lambda x,y:x+y,map(lambda y,
     Iu=Iu,Io=Io,Ru=Ru,Ro=Ro,Sy=Sy,L=lambda yc,Iu=Iu,Io=Io,Ru=Ru,Ro=Ro,i=IM,
     Sx=Sx,Sy=Sy:reduce(lambda x,y:x+y,map(lambda x,xc=Ru,yc=yc,Ru=Ru,Ro=Ro,
     i=i,Sx=Sx,F=lambda xc,yc,x,y,k,f=lambda xc,yc,x,y,k,f:(k<=0)or (x*x+y*y
     >=4.0) or 1+f(xc,yc,x*x-y*y+xc,2.0*x*y+yc,k-1,f):f(xc,yc,x,y,k,f):chr(
     64+F(Ru+x*(Ro-Ru)/Sx,yc,0,0,i)),range(Sx))):L(Iu+y*(Io-Iu)/Sy),range(Sy
     ))))(-2.1, 0.7, -1.2, 1.2, 30, 80, 24))
     #    \___ ___/  \___ ___/  |   |   |__ lines on screen
     #        V          V      |   |______ columns on screen
     #        |          |      |__________ maximum of "iterations"
     #        |          |_________________ range on y axis
     #        |____________________________ range on x axis

Don’t try this at home, kids!


File: python.info,  Node: What does the slash / in the parameter list of a function mean?,  Prev: Is it possible to write obfuscated one-liners in Python?,  Up: Core Language

11.2.2.18 What does the slash(/) in the parameter list of a function mean?
..........................................................................

A slash in the argument list of a function denotes that the parameters
prior to it are positional-only.  Positional-only parameters are the
ones without an externally-usable name.  Upon calling a function that
accepts positional-only parameters, arguments are mapped to parameters
based solely on their position.  For example, *note divmod(): 28d. is a
function that accepts positional-only parameters.  Its documentation
looks like this:

     >>> help(divmod)
     Help on built-in function divmod in module builtins:

     divmod(x, y, /)
         Return the tuple (x//y, x%y).  Invariant: div*y + mod == x.

The slash at the end of the parameter list means that both parameters
are positional-only.  Thus, calling *note divmod(): 28d. with keyword
arguments would lead to an error:

     >>> divmod(x=3, y=4)
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: divmod() takes no keyword arguments


File: python.info,  Node: Numbers and strings,  Next: Performance<4>,  Prev: Core Language,  Up: Programming FAQ

11.2.3 Numbers and strings
--------------------------

* Menu:

* How do I specify hexadecimal and octal integers?::
* Why does -22 // 10 return -3?::
* How do I get int literal attribute instead of SyntaxError?::
* How do I convert a string to a number?::
* How do I convert a number to a string?::
* How do I modify a string in place?::
* How do I use strings to call functions/methods?::
* Is there an equivalent to Perl’s chomp() for removing trailing newlines from strings?: Is there an equivalent to Perl’s chomp for removing trailing newlines from strings?.
* Is there a scanf() or sscanf() equivalent?: Is there a scanf or sscanf equivalent?.
* What does ‘UnicodeDecodeError’ or ‘UnicodeEncodeError’ error mean?::


File: python.info,  Node: How do I specify hexadecimal and octal integers?,  Next: Why does -22 // 10 return -3?,  Up: Numbers and strings

11.2.3.1 How do I specify hexadecimal and octal integers?
.........................................................

To specify an octal digit, precede the octal value with a zero, and then
a lower or uppercase “o”.  For example, to set the variable “a” to the
octal value “10” (8 in decimal), type:

     >>> a = 0o10
     >>> a
     8

Hexadecimal is just as easy.  Simply precede the hexadecimal number with
a zero, and then a lower or uppercase “x”.  Hexadecimal digits can be
specified in lower or uppercase.  For example, in the Python
interpreter:

     >>> a = 0xa5
     >>> a
     165
     >>> b = 0XB2
     >>> b
     178


File: python.info,  Node: Why does -22 // 10 return -3?,  Next: How do I get int literal attribute instead of SyntaxError?,  Prev: How do I specify hexadecimal and octal integers?,  Up: Numbers and strings

11.2.3.2 Why does -22 // 10 return -3?
......................................

It’s primarily driven by the desire that ‘i % j’ have the same sign as
‘j’.  If you want that, and also want:

     i == (i // j) * j + (i % j)

then integer division has to return the floor.  C also requires that
identity to hold, and then compilers that truncate ‘i // j’ need to make
‘i % j’ have the same sign as ‘i’.

There are few real use cases for ‘i % j’ when ‘j’ is negative.  When ‘j’
is positive, there are many, and in virtually all of them it’s more
useful for ‘i % j’ to be ‘>= 0’.  If the clock says 10 now, what did it
say 200 hours ago?  ‘-190 % 12 == 2’ is useful; ‘-190 % 12 == -10’ is a
bug waiting to bite.


File: python.info,  Node: How do I get int literal attribute instead of SyntaxError?,  Next: How do I convert a string to a number?,  Prev: Why does -22 // 10 return -3?,  Up: Numbers and strings

11.2.3.3 How do I get int literal attribute instead of SyntaxError?
...................................................................

Trying to lookup an ‘int’ literal attribute in the normal manner gives a
syntax error because the period is seen as a decimal point:

     >>> 1.__class__
       File "<stdin>", line 1
       1.__class__
        ^
     SyntaxError: invalid decimal literal

The solution is to separate the literal from the period with either a
space or parentheses.

     >>> 1 .__class__
     <class 'int'>
     >>> (1).__class__
     <class 'int'>


File: python.info,  Node: How do I convert a string to a number?,  Next: How do I convert a number to a string?,  Prev: How do I get int literal attribute instead of SyntaxError?,  Up: Numbers and strings

11.2.3.4 How do I convert a string to a number?
...............................................

For integers, use the built-in *note int(): 204. type constructor, e.g.
‘int('144') == 144’.  Similarly, *note float(): 1fd. converts to
floating-point, e.g.  ‘float('144') == 144.0’.

By default, these interpret the number as decimal, so that ‘int('0144')
== 144’ holds true, and ‘int('0x144')’ raises *note ValueError: 16d.
‘int(string, base)’ takes the base to convert from as a second optional
argument, so ‘int( '0x144', 16) == 324’.  If the base is specified as 0,
the number is interpreted using Python’s rules: a leading ‘0o’ indicates
octal, and ‘0x’ indicates a hex number.

Do not use the built-in function *note eval(): c61. if all you need is
to convert strings to numbers.  *note eval(): c61. will be significantly
slower and it presents a security risk: someone could pass you a Python
expression that might have unwanted side effects.  For example, someone
could pass ‘__import__('os').system("rm -rf $HOME")’ which would erase
your home directory.

*note eval(): c61. also has the effect of interpreting numbers as Python
expressions, so that e.g.  ‘eval('09')’ gives a syntax error because
Python does not allow leading ‘0’ in a decimal number (except ‘0’).


File: python.info,  Node: How do I convert a number to a string?,  Next: How do I modify a string in place?,  Prev: How do I convert a string to a number?,  Up: Numbers and strings

11.2.3.5 How do I convert a number to a string?
...............................................

To convert, e.g., the number 144 to the string ‘144’, use the built-in
type constructor *note str(): 205.  If you want a hexadecimal or octal
representation, use the built-in functions *note hex(): d2e. or *note
oct(): d2d.  For fancy formatting, see the *note Formatted string
literals: 296. and *note Format String Syntax: de0. sections, e.g.
‘"{:04d}".format(144)’ yields ‘'0144'’ and ‘"{:.3f}".format(1.0/3.0)’
yields ‘'0.333'’.


File: python.info,  Node: How do I modify a string in place?,  Next: How do I use strings to call functions/methods?,  Prev: How do I convert a number to a string?,  Up: Numbers and strings

11.2.3.6 How do I modify a string in place?
...........................................

You can’t, because strings are immutable.  In most situations, you
should simply construct a new string from the various parts you want to
assemble it from.  However, if you need an object with the ability to
modify in-place unicode data, try using an *note io.StringIO: 91a.
object or the *note array: 6. module:

     >>> import io
     >>> s = "Hello, world"
     >>> sio = io.StringIO(s)
     >>> sio.getvalue()
     'Hello, world'
     >>> sio.seek(7)
     7
     >>> sio.write("there!")
     6
     >>> sio.getvalue()
     'Hello, there!'

     >>> import array
     >>> a = array.array('u', s)
     >>> print(a)
     array('u', 'Hello, world')
     >>> a[0] = 'y'
     >>> print(a)
     array('u', 'yello, world')
     >>> a.tounicode()
     'yello, world'


File: python.info,  Node: How do I use strings to call functions/methods?,  Next: Is there an equivalent to Perl’s chomp for removing trailing newlines from strings?,  Prev: How do I modify a string in place?,  Up: Numbers and strings

11.2.3.7 How do I use strings to call functions/methods?
........................................................

There are various techniques.

   * The best is to use a dictionary that maps strings to functions.
     The primary advantage of this technique is that the strings do not
     need to match the names of the functions.  This is also the primary
     technique used to emulate a case construct:

          def a():
              pass

          def b():
              pass

          dispatch = {'go': a, 'stop': b}  # Note lack of parens for funcs

          dispatch[get_input()]()  # Note trailing parens to call function

   * Use the built-in function *note getattr(): 54b.:

          import foo
          getattr(foo, 'bar')()

     Note that *note getattr(): 54b. works on any object, including
     classes, class instances, modules, and so on.

     This is used in several places in the standard library, like this:

          class Foo:
              def do_foo(self):
                  ...

              def do_bar(self):
                  ...

          f = getattr(foo_instance, 'do_' + opname)
          f()

   * Use *note locals(): 557. to resolve the function name:

          def myFunc():
              print("hello")

          fname = "myFunc"

          f = locals()[fname]
          f()


File: python.info,  Node: Is there an equivalent to Perl’s chomp for removing trailing newlines from strings?,  Next: Is there a scanf or sscanf equivalent?,  Prev: How do I use strings to call functions/methods?,  Up: Numbers and strings

11.2.3.8 Is there an equivalent to Perl’s chomp() for removing trailing newlines from strings?
..............................................................................................

You can use ‘S.rstrip("\r\n")’ to remove all occurrences of any line
terminator from the end of the string ‘S’ without removing other
trailing whitespace.  If the string ‘S’ represents more than one line,
with several empty lines at the end, the line terminators for all the
blank lines will be removed:

     >>> lines = ("line 1 \r\n"
     ...          "\r\n"
     ...          "\r\n")
     >>> lines.rstrip("\n\r")
     'line 1 '

Since this is typically only desired when reading text one line at a
time, using ‘S.rstrip()’ this way works well.


File: python.info,  Node: Is there a scanf or sscanf equivalent?,  Next: What does ‘UnicodeDecodeError’ or ‘UnicodeEncodeError’ error mean?,  Prev: Is there an equivalent to Perl’s chomp for removing trailing newlines from strings?,  Up: Numbers and strings

11.2.3.9 Is there a scanf() or sscanf() equivalent?
...................................................

Not as such.

For simple input parsing, the easiest approach is usually to split the
line into whitespace-delimited words using the *note split(): 890.
method of string objects and then convert decimal strings to numeric
values using *note int(): 204. or *note float(): 1fd.  ‘split()’
supports an optional “sep” parameter which is useful if the line uses
something other than whitespace as a separator.

For more complicated input parsing, regular expressions are more
powerful than C’s ‘sscanf()’ and better suited for the task.


File: python.info,  Node: What does ‘UnicodeDecodeError’ or ‘UnicodeEncodeError’ error mean?,  Prev: Is there a scanf or sscanf equivalent?,  Up: Numbers and strings

11.2.3.10 What does ‘UnicodeDecodeError’ or ‘UnicodeEncodeError’ error mean?
............................................................................

See the *note Unicode HOWTO: d04.


File: python.info,  Node: Performance<4>,  Next: Sequences Tuples/Lists,  Prev: Numbers and strings,  Up: Programming FAQ

11.2.4 Performance
------------------

* Menu:

* My program is too slow. How do I speed it up?: My program is too slow How do I speed it up?.
* What is the most efficient way to concatenate many strings together?::


File: python.info,  Node: My program is too slow How do I speed it up?,  Next: What is the most efficient way to concatenate many strings together?,  Up: Performance<4>

11.2.4.1 My program is too slow. How do I speed it up?
......................................................

That’s a tough one, in general.  First, here are a list of things to
remember before diving further:

   * Performance characteristics vary across Python implementations.
     This FAQ focuses on *note CPython: 1569.

   * Behaviour can vary across operating systems, especially when
     talking about I/O or multi-threading.

   * You should always find the hot spots in your program `before'
     attempting to optimize any code (see the *note profile: d3.
     module).

   * Writing benchmark scripts will allow you to iterate quickly when
     searching for improvements (see the *note timeit: 10d. module).

   * It is highly recommended to have good code coverage (through unit
     testing or any other technique) before potentially introducing
     regressions hidden in sophisticated optimizations.

That being said, there are many tricks to speed up Python code.  Here
are some general principles which go a long way towards reaching
acceptable performance levels:

   * Making your algorithms faster (or changing to faster ones) can
     yield much larger benefits than trying to sprinkle
     micro-optimization tricks all over your code.

   * Use the right data structures.  Study documentation for the *note
     Built-in Types: 1748. and the *note collections: 1d. module.

   * When the standard library provides a primitive for doing something,
     it is likely (although not guaranteed) to be faster than any
     alternative you may come up with.  This is doubly true for
     primitives written in C, such as builtins and some extension types.
     For example, be sure to use either the *note list.sort(): 548.
     built-in method or the related *note sorted(): 547. function to do
     sorting (and see the *note Sorting HOW TO: 1737. for examples of
     moderately advanced usage).

   * Abstractions tend to create indirections and force the interpreter
     to work more.  If the levels of indirection outweigh the amount of
     useful work done, your program will be slower.  You should avoid
     excessive abstraction, especially under the form of tiny functions
     or methods (which are also often detrimental to readability).

If you have reached the limit of what pure Python can allow, there are
tools to take you further away.  For example, Cython(1) can compile a
slightly modified version of Python code into a C extension, and can be
used on many different platforms.  Cython can take advantage of
compilation (and optional type annotations) to make your code
significantly faster than when interpreted.  If you are confident in
your C programming skills, you can also *note write a C extension
module: 1332. yourself.

See also
........

The wiki page devoted to performance tips(2).

   ---------- Footnotes ----------

   (1) http://cython.org

   (2) https://wiki.python.org/moin/PythonSpeed/PerformanceTips


File: python.info,  Node: What is the most efficient way to concatenate many strings together?,  Prev: My program is too slow How do I speed it up?,  Up: Performance<4>

11.2.4.2 What is the most efficient way to concatenate many strings together?
.............................................................................

*note str: 205. and *note bytes: 172. objects are immutable, therefore
concatenating many strings together is inefficient as each concatenation
creates a new object.  In the general case, the total runtime cost is
quadratic in the total string length.

To accumulate many *note str: 205. objects, the recommended idiom is to
place them into a list and call *note str.join(): 1766. at the end:

     chunks = []
     for s in my_strings:
         chunks.append(s)
     result = ''.join(chunks)

(another reasonably efficient idiom is to use *note io.StringIO: 91a.)

To accumulate many *note bytes: 172. objects, the recommended idiom is
to extend a *note bytearray: 173. object using in-place concatenation
(the ‘+=’ operator):

     result = bytearray()
     for b in my_bytes_objects:
         result += b


File: python.info,  Node: Sequences Tuples/Lists,  Next: Objects,  Prev: Performance<4>,  Up: Programming FAQ

11.2.5 Sequences (Tuples/Lists)
-------------------------------

* Menu:

* How do I convert between tuples and lists?::
* What’s a negative index?::
* How do I iterate over a sequence in reverse order?::
* How do you remove duplicates from a list?::
* How do you remove multiple items from a list::
* How do you make an array in Python?::
* How do I create a multidimensional list?::
* How do I apply a method to a sequence of objects?::
* Why does a_tuple[i] += [‘item’] raise an exception when the addition works?::
* I want to do a complicated sort; can you do a Schwartzian Transform in Python?: I want to do a complicated sort can you do a Schwartzian Transform in Python?.
* How can I sort one list by values from another list?::


File: python.info,  Node: How do I convert between tuples and lists?,  Next: What’s a negative index?,  Up: Sequences Tuples/Lists

11.2.5.1 How do I convert between tuples and lists?
...................................................

The type constructor ‘tuple(seq)’ converts any sequence (actually, any
iterable) into a tuple with the same items in the same order.

For example, ‘tuple([1, 2, 3])’ yields ‘(1, 2, 3)’ and ‘tuple('abc')’
yields ‘('a', 'b', 'c')’.  If the argument is a tuple, it does not make
a copy but returns the same object, so it is cheap to call *note
tuple(): 1a2. when you aren’t sure that an object is already a tuple.

The type constructor ‘list(seq)’ converts any sequence or iterable into
a list with the same items in the same order.  For example, ‘list((1, 2,
3))’ yields ‘[1, 2, 3]’ and ‘list('abc')’ yields ‘['a', 'b', 'c']’.  If
the argument is a list, it makes a copy just like ‘seq[:]’ would.


File: python.info,  Node: What’s a negative index?,  Next: How do I iterate over a sequence in reverse order?,  Prev: How do I convert between tuples and lists?,  Up: Sequences Tuples/Lists

11.2.5.2 What’s a negative index?
.................................

Python sequences are indexed with positive numbers and negative numbers.
For positive numbers 0 is the first index 1 is the second index and so
forth.  For negative indices -1 is the last index and -2 is the
penultimate (next to last) index and so forth.  Think of ‘seq[-n]’ as
the same as ‘seq[len(seq)-n]’.

Using negative indices can be very convenient.  For example ‘S[:-1]’ is
all of the string except for its last character, which is useful for
removing the trailing newline from a string.


File: python.info,  Node: How do I iterate over a sequence in reverse order?,  Next: How do you remove duplicates from a list?,  Prev: What’s a negative index?,  Up: Sequences Tuples/Lists

11.2.5.3 How do I iterate over a sequence in reverse order?
...........................................................

Use the *note reversed(): 2c6. built-in function:

     for x in reversed(sequence):
         ...  # do something with x ...

This won’t touch your original sequence, but build a new copy with
reversed order to iterate over.


File: python.info,  Node: How do you remove duplicates from a list?,  Next: How do you remove multiple items from a list,  Prev: How do I iterate over a sequence in reverse order?,  Up: Sequences Tuples/Lists

11.2.5.4 How do you remove duplicates from a list?
..................................................

See the Python Cookbook for a long discussion of many ways to do this:

     ‘https://code.activestate.com/recipes/52560/’

If you don’t mind reordering the list, sort it and then scan from the
end of the list, deleting duplicates as you go:

     if mylist:
         mylist.sort()
         last = mylist[-1]
         for i in range(len(mylist)-2, -1, -1):
             if last == mylist[i]:
                 del mylist[i]
             else:
                 last = mylist[i]

If all elements of the list may be used as set keys (i.e.  they are all
*note hashable: 276.) this is often faster

     mylist = list(set(mylist))

This converts the list into a set, thereby removing duplicates, and then
back into a list.


File: python.info,  Node: How do you remove multiple items from a list,  Next: How do you make an array in Python?,  Prev: How do you remove duplicates from a list?,  Up: Sequences Tuples/Lists

11.2.5.5 How do you remove multiple items from a list
.....................................................

As with removing duplicates, explicitly iterating in reverse with a
delete condition is one possibility.  However, it is easier and faster
to use slice replacement with an implicit or explicit forward iteration.
Here are three variations.:

     mylist[:] = filter(keep_function, mylist)
     mylist[:] = (x for x in mylist if keep_condition)
     mylist[:] = [x for x in mylist if keep_condition]

The list comprehension may be fastest.


File: python.info,  Node: How do you make an array in Python?,  Next: How do I create a multidimensional list?,  Prev: How do you remove multiple items from a list,  Up: Sequences Tuples/Lists

11.2.5.6 How do you make an array in Python?
............................................

Use a list:

     ["this", 1, "is", "an", "array"]

Lists are equivalent to C or Pascal arrays in their time complexity; the
primary difference is that a Python list can contain objects of many
different types.

The ‘array’ module also provides methods for creating arrays of fixed
types with compact representations, but they are slower to index than
lists.  Also note that NumPy and other third party packages define
array-like structures with various characteristics as well.

To get Lisp-style linked lists, you can emulate cons cells using tuples:

     lisp_list = ("like",  ("this",  ("example", None) ) )

If mutability is desired, you could use lists instead of tuples.  Here
the analogue of lisp car is ‘lisp_list[0]’ and the analogue of cdr is
‘lisp_list[1]’.  Only do this if you’re sure you really need to, because
it’s usually a lot slower than using Python lists.


File: python.info,  Node: How do I create a multidimensional list?,  Next: How do I apply a method to a sequence of objects?,  Prev: How do you make an array in Python?,  Up: Sequences Tuples/Lists

11.2.5.7 How do I create a multidimensional list?
.................................................

You probably tried to make a multidimensional array like this:

     >>> A = [[None] * 2] * 3

This looks correct if you print it:

     >>> A
     [[None, None], [None, None], [None, None]]

But when you assign a value, it shows up in multiple places:

     >>> A[0][0] = 5
     >>> A
     [[5, None], [5, None], [5, None]]

The reason is that replicating a list with ‘*’ doesn’t create copies, it
only creates references to the existing objects.  The ‘*3’ creates a
list containing 3 references to the same list of length two.  Changes to
one row will show in all rows, which is almost certainly not what you
want.

The suggested approach is to create a list of the desired length first
and then fill in each element with a newly created list:

     A = [None] * 3
     for i in range(3):
         A[i] = [None] * 2

This generates a list containing 3 different lists of length two.  You
can also use a list comprehension:

     w, h = 2, 3
     A = [[None] * w for i in range(h)]

Or, you can use an extension that provides a matrix datatype; NumPy(1)
is the best known.

   ---------- Footnotes ----------

   (1) http://www.numpy.org/


File: python.info,  Node: How do I apply a method to a sequence of objects?,  Next: Why does a_tuple[i] += [‘item’] raise an exception when the addition works?,  Prev: How do I create a multidimensional list?,  Up: Sequences Tuples/Lists

11.2.5.8 How do I apply a method to a sequence of objects?
..........................................................

Use a list comprehension:

     result = [obj.method() for obj in mylist]


File: python.info,  Node: Why does a_tuple[i] += [‘item’] raise an exception when the addition works?,  Next: I want to do a complicated sort can you do a Schwartzian Transform in Python?,  Prev: How do I apply a method to a sequence of objects?,  Up: Sequences Tuples/Lists

11.2.5.9 Why does a_tuple[i] += [‘item’] raise an exception when the addition works?
....................................................................................

This is because of a combination of the fact that augmented assignment
operators are `assignment' operators, and the difference between mutable
and immutable objects in Python.

This discussion applies in general when augmented assignment operators
are applied to elements of a tuple that point to mutable objects, but
we’ll use a ‘list’ and ‘+=’ as our exemplar.

If you wrote:

     >>> a_tuple = (1, 2)
     >>> a_tuple[0] += 1
     Traceback (most recent call last):
        ...
     TypeError: 'tuple' object does not support item assignment

The reason for the exception should be immediately clear: ‘1’ is added
to the object ‘a_tuple[0]’ points to (‘1’), producing the result object,
‘2’, but when we attempt to assign the result of the computation, ‘2’,
to element ‘0’ of the tuple, we get an error because we can’t change
what an element of a tuple points to.

Under the covers, what this augmented assignment statement is doing is
approximately this:

     >>> result = a_tuple[0] + 1
     >>> a_tuple[0] = result
     Traceback (most recent call last):
       ...
     TypeError: 'tuple' object does not support item assignment

It is the assignment part of the operation that produces the error,
since a tuple is immutable.

When you write something like:

     >>> a_tuple = (['foo'], 'bar')
     >>> a_tuple[0] += ['item']
     Traceback (most recent call last):
       ...
     TypeError: 'tuple' object does not support item assignment

The exception is a bit more surprising, and even more surprising is the
fact that even though there was an error, the append worked:

     >>> a_tuple[0]
     ['foo', 'item']

To see why this happens, you need to know that (a) if an object
implements an ‘__iadd__’ magic method, it gets called when the ‘+=’
augmented assignment is executed, and its return value is what gets used
in the assignment statement; and (b) for lists, ‘__iadd__’ is equivalent
to calling ‘extend’ on the list and returning the list.  That’s why we
say that for lists, ‘+=’ is a “shorthand” for ‘list.extend’:

     >>> a_list = []
     >>> a_list += [1]
     >>> a_list
     [1]

This is equivalent to:

     >>> result = a_list.__iadd__([1])
     >>> a_list = result

The object pointed to by a_list has been mutated, and the pointer to the
mutated object is assigned back to ‘a_list’.  The end result of the
assignment is a no-op, since it is a pointer to the same object that
‘a_list’ was previously pointing to, but the assignment still happens.

Thus, in our tuple example what is happening is equivalent to:

     >>> result = a_tuple[0].__iadd__(['item'])
     >>> a_tuple[0] = result
     Traceback (most recent call last):
       ...
     TypeError: 'tuple' object does not support item assignment

The ‘__iadd__’ succeeds, and thus the list is extended, but even though
‘result’ points to the same object that ‘a_tuple[0]’ already points to,
that final assignment still results in an error, because tuples are
immutable.


File: python.info,  Node: I want to do a complicated sort can you do a Schwartzian Transform in Python?,  Next: How can I sort one list by values from another list?,  Prev: Why does a_tuple[i] += [‘item’] raise an exception when the addition works?,  Up: Sequences Tuples/Lists

11.2.5.10 I want to do a complicated sort: can you do a Schwartzian Transform in Python?
........................................................................................

The technique, attributed to Randal Schwartz of the Perl community,
sorts the elements of a list by a metric which maps each element to its
“sort value”.  In Python, use the ‘key’ argument for the *note
list.sort(): 548. method:

     Isorted = L[:]
     Isorted.sort(key=lambda s: int(s[10:15]))


File: python.info,  Node: How can I sort one list by values from another list?,  Prev: I want to do a complicated sort can you do a Schwartzian Transform in Python?,  Up: Sequences Tuples/Lists

11.2.5.11 How can I sort one list by values from another list?
..............................................................

Merge them into an iterator of tuples, sort the resulting list, and then
pick out the element you want.

     >>> list1 = ["what", "I'm", "sorting", "by"]
     >>> list2 = ["something", "else", "to", "sort"]
     >>> pairs = zip(list1, list2)
     >>> pairs = sorted(pairs)
     >>> pairs
     [("I'm", 'else'), ('by', 'sort'), ('sorting', 'to'), ('what', 'something')]
     >>> result = [x[1] for x in pairs]
     >>> result
     ['else', 'sort', 'to', 'something']


File: python.info,  Node: Objects,  Next: Modules<3>,  Prev: Sequences Tuples/Lists,  Up: Programming FAQ

11.2.6 Objects
--------------

* Menu:

* What is a class?::
* What is a method?::
* What is self?::
* How do I check if an object is an instance of a given class or of a subclass of it?::
* What is delegation?::
* How do I call a method defined in a base class from a derived class that overrides it?::
* How can I organize my code to make it easier to change the base class?::
* How do I create static class data and static class methods?::
* How can I overload constructors (or methods) in Python?: How can I overload constructors or methods in Python?.
* I try to use __spam and I get an error about _SomeClassName__spam.: I try to use __spam and I get an error about _SomeClassName__spam.
* My class defines __del__ but it is not called when I delete the object.: My class defines __del__ but it is not called when I delete the object.
* How do I get a list of all instances of a given class?::
* Why does the result of id() appear to be not unique?: Why does the result of id appear to be not unique?.
* When can I rely on identity tests with the is operator?::
* How can a subclass control what data is stored in an immutable instance?::


File: python.info,  Node: What is a class?,  Next: What is a method?,  Up: Objects

11.2.6.1 What is a class?
.........................

A class is the particular object type created by executing a class
statement.  Class objects are used as templates to create instance
objects, which embody both the data (attributes) and code (methods)
specific to a datatype.

A class can be based on one or more other classes, called its base
class(es).  It then inherits the attributes and methods of its base
classes.  This allows an object model to be successively refined by
inheritance.  You might have a generic ‘Mailbox’ class that provides
basic accessor methods for a mailbox, and subclasses such as
‘MboxMailbox’, ‘MaildirMailbox’, ‘OutlookMailbox’ that handle various
specific mailbox formats.


File: python.info,  Node: What is a method?,  Next: What is self?,  Prev: What is a class?,  Up: Objects

11.2.6.2 What is a method?
..........................

A method is a function on some object ‘x’ that you normally call as
‘x.name(arguments...)’.  Methods are defined as functions inside the
class definition:

     class C:
         def meth(self, arg):
             return arg * 2 + self.attribute


File: python.info,  Node: What is self?,  Next: How do I check if an object is an instance of a given class or of a subclass of it?,  Prev: What is a method?,  Up: Objects

11.2.6.3 What is self?
......................

Self is merely a conventional name for the first argument of a method.
A method defined as ‘meth(self, a, b, c)’ should be called as ‘x.meth(a,
b, c)’ for some instance ‘x’ of the class in which the definition
occurs; the called method will think it is called as ‘meth(x, a, b, c)’.

See also *note Why must ‘self’ be used explicitly in method definitions
and calls?: 449b.


File: python.info,  Node: How do I check if an object is an instance of a given class or of a subclass of it?,  Next: What is delegation?,  Prev: What is self?,  Up: Objects

11.2.6.4 How do I check if an object is an instance of a given class or of a subclass of it?
............................................................................................

Use the built-in function ‘isinstance(obj, cls)’.  You can check if an
object is an instance of any of a number of classes by providing a tuple
instead of a single class, e.g.  ‘isinstance(obj, (class1, class2,
...))’, and can also check whether an object is one of Python’s built-in
types, e.g.  ‘isinstance(obj, str)’ or ‘isinstance(obj, (int, float,
complex))’.

Note that *note isinstance(): 552. also checks for virtual inheritance
from an *note abstract base class: c05.  So, the test will return ‘True’
for a registered class even if hasn’t directly or indirectly inherited
from it.  To test for “true inheritance”, scan the *note MRO: 29c7. of
the class:

     from collections.abc import Mapping

     class P:
          pass

     class C(P):
         pass

     Mapping.register(P)

     >>> c = C()
     >>> isinstance(c, C)        # direct
     True
     >>> isinstance(c, P)        # indirect
     True
     >>> isinstance(c, Mapping)  # virtual
     True

     # Actual inheritance chain
     >>> type(c).__mro__
     (<class 'C'>, <class 'P'>, <class 'object'>)

     # Test for "true inheritance"
     >>> Mapping in type(c).__mro__
     False

Note that most programs do not use *note isinstance(): 552. on
user-defined classes very often.  If you are developing the classes
yourself, a more proper object-oriented style is to define methods on
the classes that encapsulate a particular behaviour, instead of checking
the object’s class and doing a different thing based on what class it
is.  For example, if you have a function that does something:

     def search(obj):
         if isinstance(obj, Mailbox):
             ...  # code to search a mailbox
         elif isinstance(obj, Document):
             ...  # code to search a document
         elif ...

A better approach is to define a ‘search()’ method on all the classes
and just call it:

     class Mailbox:
         def search(self):
             ...  # code to search a mailbox

     class Document:
         def search(self):
             ...  # code to search a document

     obj.search()


File: python.info,  Node: What is delegation?,  Next: How do I call a method defined in a base class from a derived class that overrides it?,  Prev: How do I check if an object is an instance of a given class or of a subclass of it?,  Up: Objects

11.2.6.5 What is delegation?
............................

Delegation is an object oriented technique (also called a design
pattern).  Let’s say you have an object ‘x’ and want to change the
behaviour of just one of its methods.  You can create a new class that
provides a new implementation of the method you’re interested in
changing and delegates all other methods to the corresponding method of
‘x’.

Python programmers can easily implement delegation.  For example, the
following class implements a class that behaves like a file but converts
all written data to uppercase:

     class UpperOut:

         def __init__(self, outfile):
             self._outfile = outfile

         def write(self, s):
             self._outfile.write(s.upper())

         def __getattr__(self, name):
             return getattr(self._outfile, name)

Here the ‘UpperOut’ class redefines the ‘write()’ method to convert the
argument string to uppercase before calling the underlying
‘self._outfile.write()’ method.  All other methods are delegated to the
underlying ‘self._outfile’ object.  The delegation is accomplished via
the ‘__getattr__’ method; consult *note the language reference: 156c.
for more information about controlling attribute access.

Note that for more general cases delegation can get trickier.  When
attributes must be set as well as retrieved, the class must define a
*note __setattr__(): eee. method too, and it must do so carefully.  The
basic implementation of *note __setattr__(): eee. is roughly equivalent
to the following:

     class X:
         ...
         def __setattr__(self, name, value):
             self.__dict__[name] = value
         ...

Most *note __setattr__(): eee. implementations must modify
‘self.__dict__’ to store local state for self without causing an
infinite recursion.


File: python.info,  Node: How do I call a method defined in a base class from a derived class that overrides it?,  Next: How can I organize my code to make it easier to change the base class?,  Prev: What is delegation?,  Up: Objects

11.2.6.6 How do I call a method defined in a base class from a derived class that overrides it?
...............................................................................................

Use the built-in *note super(): 5dd. function:

     class Derived(Base):
         def meth(self):
             super(Derived, self).meth()

For version prior to 3.0, you may be using classic classes: For a class
definition such as ‘class Derived(Base): ...’ you can call method
‘meth()’ defined in ‘Base’ (or one of ‘Base’’s base classes) as
‘Base.meth(self, arguments...)’.  Here, ‘Base.meth’ is an unbound
method, so you need to provide the ‘self’ argument.


File: python.info,  Node: How can I organize my code to make it easier to change the base class?,  Next: How do I create static class data and static class methods?,  Prev: How do I call a method defined in a base class from a derived class that overrides it?,  Up: Objects

11.2.6.7 How can I organize my code to make it easier to change the base class?
...............................................................................

You could assign the base class to an alias and derive from the alias.
Then all you have to change is the value assigned to the alias.
Incidentally, this trick is also handy if you want to decide dynamically
(e.g.  depending on availability of resources) which base class to use.
Example:

     class Base:
         ...

     BaseAlias = Base

     class Derived(BaseAlias):
         ...


File: python.info,  Node: How do I create static class data and static class methods?,  Next: How can I overload constructors or methods in Python?,  Prev: How can I organize my code to make it easier to change the base class?,  Up: Objects

11.2.6.8 How do I create static class data and static class methods?
....................................................................

Both static data and static methods (in the sense of C++ or Java) are
supported in Python.

For static data, simply define a class attribute.  To assign a new value
to the attribute, you have to explicitly use the class name in the
assignment:

     class C:
         count = 0   # number of times C.__init__ called

         def __init__(self):
             C.count = C.count + 1

         def getcount(self):
             return C.count  # or return self.count

‘c.count’ also refers to ‘C.count’ for any ‘c’ such that ‘isinstance(c,
C)’ holds, unless overridden by ‘c’ itself or by some class on the
base-class search path from ‘c.__class__’ back to ‘C’.

Caution: within a method of C, an assignment like ‘self.count = 42’
creates a new and unrelated instance named “count” in ‘self’’s own dict.
Rebinding of a class-static data name must always specify the class
whether inside a method or not:

     C.count = 314

Static methods are possible:

     class C:
         @staticmethod
         def static(arg1, arg2, arg3):
             # No 'self' parameter!
             ...

However, a far more straightforward way to get the effect of a static
method is via a simple module-level function:

     def getcount():
         return C.count

If your code is structured so as to define one class (or tightly related
class hierarchy) per module, this supplies the desired encapsulation.


File: python.info,  Node: How can I overload constructors or methods in Python?,  Next: I try to use __spam and I get an error about _SomeClassName__spam,  Prev: How do I create static class data and static class methods?,  Up: Objects

11.2.6.9 How can I overload constructors (or methods) in Python?
................................................................

This answer actually applies to all methods, but the question usually
comes up first in the context of constructors.

In C++ you’d write

     class C {
         C() { cout << "No arguments\n"; }
         C(int i) { cout << "Argument is " << i << "\n"; }
     }

In Python you have to write a single constructor that catches all cases
using default arguments.  For example:

     class C:
         def __init__(self, i=None):
             if i is None:
                 print("No arguments")
             else:
                 print("Argument is", i)

This is not entirely equivalent, but close enough in practice.

You could also try a variable-length argument list, e.g.

     def __init__(self, *args):
         ...

The same approach works for all method definitions.


File: python.info,  Node: I try to use __spam and I get an error about _SomeClassName__spam,  Next: My class defines __del__ but it is not called when I delete the object,  Prev: How can I overload constructors or methods in Python?,  Up: Objects

11.2.6.10 I try to use __spam and I get an error about _SomeClassName__spam.
............................................................................

Variable names with double leading underscores are “mangled” to provide
a simple but effective way to define class private variables.  Any
identifier of the form ‘__spam’ (at least two leading underscores, at
most one trailing underscore) is textually replaced with
‘_classname__spam’, where ‘classname’ is the current class name with any
leading underscores stripped.

This doesn’t guarantee privacy: an outside user can still deliberately
access the “_classname__spam” attribute, and private values are visible
in the object’s ‘__dict__’.  Many Python programmers never bother to use
private variable names at all.


File: python.info,  Node: My class defines __del__ but it is not called when I delete the object,  Next: How do I get a list of all instances of a given class?,  Prev: I try to use __spam and I get an error about _SomeClassName__spam,  Up: Objects

11.2.6.11 My class defines __del__ but it is not called when I delete the object.
.................................................................................

There are several possible reasons for this.

The del statement does not necessarily call *note __del__(): a04. – it
simply decrements the object’s reference count, and if this reaches zero
*note __del__(): a04. is called.

If your data structures contain circular links (e.g.  a tree where each
child has a parent reference and each parent has a list of children) the
reference counts will never go back to zero.  Once in a while Python
runs an algorithm to detect such cycles, but the garbage collector might
run some time after the last reference to your data structure vanishes,
so your *note __del__(): a04. method may be called at an inconvenient
and random time.  This is inconvenient if you’re trying to reproduce a
problem.  Worse, the order in which object’s *note __del__(): a04.
methods are executed is arbitrary.  You can run *note gc.collect(): 35b.
to force a collection, but there `are' pathological cases where objects
will never be collected.

Despite the cycle collector, it’s still a good idea to define an
explicit ‘close()’ method on objects to be called whenever you’re done
with them.  The ‘close()’ method can then remove attributes that refer
to subobjects.  Don’t call *note __del__(): a04. directly – *note
__del__(): a04. should call ‘close()’ and ‘close()’ should make sure
that it can be called more than once for the same object.

Another way to avoid cyclical references is to use the *note weakref:
131. module, which allows you to point to objects without incrementing
their reference count.  Tree data structures, for instance, should use
weak references for their parent and sibling references (if they need
them!).

Finally, if your *note __del__(): a04. method raises an exception, a
warning message is printed to *note sys.stderr: 1ea.


File: python.info,  Node: How do I get a list of all instances of a given class?,  Next: Why does the result of id appear to be not unique?,  Prev: My class defines __del__ but it is not called when I delete the object,  Up: Objects

11.2.6.12 How do I get a list of all instances of a given class?
................................................................

Python does not keep track of all instances of a class (or of a built-in
type).  You can program the class’s constructor to keep track of all
instances by keeping a list of weak references to each instance.


File: python.info,  Node: Why does the result of id appear to be not unique?,  Next: When can I rely on identity tests with the is operator?,  Prev: How do I get a list of all instances of a given class?,  Up: Objects

11.2.6.13 Why does the result of ‘id()’ appear to be not unique?
................................................................

The *note id(): e4b. builtin returns an integer that is guaranteed to be
unique during the lifetime of the object.  Since in CPython, this is the
object’s memory address, it happens frequently that after an object is
deleted from memory, the next freshly created object is allocated at the
same position in memory.  This is illustrated by this example:

     >>> id(1000)
     13901272
     >>> id(2000)
     13901272

The two ids belong to different integer objects that are created before,
and deleted immediately after execution of the ‘id()’ call.  To be sure
that objects whose id you want to examine are still alive, create
another reference to the object:

     >>> a = 1000; b = 2000
     >>> id(a)
     13901272
     >>> id(b)
     13891296


File: python.info,  Node: When can I rely on identity tests with the is operator?,  Next: How can a subclass control what data is stored in an immutable instance?,  Prev: Why does the result of id appear to be not unique?,  Up: Objects

11.2.6.14 When can I rely on identity tests with the `is' operator?
...................................................................

The ‘is’ operator tests for object identity.  The test ‘a is b’ is
equivalent to ‘id(a) == id(b)’.

The most important property of an identity test is that an object is
always identical to itself, ‘a is a’ always returns ‘True’.  Identity
tests are usually faster than equality tests.  And unlike equality
tests, identity tests are guaranteed to return a boolean ‘True’ or
‘False’.

However, identity tests can `only' be substituted for equality tests
when object identity is assured.  Generally, there are three
circumstances where identity is guaranteed:

1) Assignments create new names but do not change object identity.
After the assignment ‘new = old’, it is guaranteed that ‘new is old’.

2) Putting an object in a container that stores object references does
not change object identity.  After the list assignment ‘s[0] = x’, it is
guaranteed that ‘s[0] is x’.

3) If an object is a singleton, it means that only one instance of that
object can exist.  After the assignments ‘a = None’ and ‘b = None’, it
is guaranteed that ‘a is b’ because ‘None’ is a singleton.

In most other circumstances, identity tests are inadvisable and equality
tests are preferred.  In particular, identity tests should not be used
to check constants such as *note int: 204. and *note str: 205. which
aren’t guaranteed to be singletons:

     >>> a = 1000
     >>> b = 500
     >>> c = b + 500
     >>> a is c
     False

     >>> a = 'Python'
     >>> b = 'Py'
     >>> c = b + 'thon'
     >>> a is c
     False

Likewise, new instances of mutable containers are never identical:

     >>> a = []
     >>> b = []
     >>> a is b
     False

In the standard library code, you will see several common patterns for
correctly using identity tests:

1) As recommended by PEP 8(1), an identity test is the preferred way to
check for ‘None’.  This reads like plain English in code and avoids
confusion with other objects that may have boolean values that evaluate
to false.

2) Detecting optional arguments can be tricky when ‘None’ is a valid
input value.  In those situations, you can create an singleton sentinel
object guaranteed to be distinct from other objects.  For example, here
is how to implement a method that behaves like *note dict.pop(): 180d.:

     _sentinel = object()

     def pop(self, key, default=_sentinel):
         if key in self:
             value = self[key]
             del self[key]
             return value
         if default is _sentinel:
             raise KeyError(key)
         return default

3) Container implementations sometimes need to augment equality tests
with identity tests.  This prevents the code from being confused by
objects such as ‘float('NaN')’ that are not equal to themselves.

For example, here is the implementation of
‘collections.abc.Sequence.__contains__()’:

     def __contains__(self, value):
         for v in self:
             if v is value or v == value:
                 return True
         return False

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0008


File: python.info,  Node: How can a subclass control what data is stored in an immutable instance?,  Prev: When can I rely on identity tests with the is operator?,  Up: Objects

11.2.6.15 How can a subclass control what data is stored in an immutable instance?
..................................................................................

When subclassing an immutable type, override the *note __new__(): 974.
method instead of the *note __init__(): e23. method.  The latter only
runs `after' an instance is created, which is too late to alter data in
an immutable instance.

All of these immutable classes have a different signature than their
parent class:

     from datetime import date

     class FirstOfMonthDate(date):
         "Always choose the first day of the month"
         def __new__(cls, year, month, day):
             return super().__new__(cls, year, month, 1)

     class NamedInt(int):
         "Allow text names for some numbers"
         xlat = {'zero': 0, 'one': 1, 'ten': 10}
         def __new__(cls, value):
             value = cls.xlat.get(value, value)
             return super().__new__(cls, value)

     class TitleStr(str):
         "Convert str to name suitable for a URL path"
         def __new__(cls, s):
             s = s.lower().replace(' ', '-')
             s = ''.join([c for c in s if c.isalnum() or c == '-'])
             return super().__new__(cls, s)

The classes can be used like this:

     >>> FirstOfMonthDate(2012, 2, 14)
     FirstOfMonthDate(2012, 2, 1)
     >>> NamedInt('ten')
     10
     >>> NamedInt(20)
     20
     >>> TitleStr('Blog: Why Python Rocks')
     'blog-why-python-rocks'


File: python.info,  Node: Modules<3>,  Prev: Objects,  Up: Programming FAQ

11.2.7 Modules
--------------

* Menu:

* How do I create a .pyc file?: How do I create a pyc file?.
* How do I find the current module name?::
* How can I have modules that mutually import each other?::
* __import__(‘x.y.z’) returns <module ‘x’>; how do I get z?: __import__ ‘x y z’ returns <module ‘x’>; how do I get z?.
* When I edit an imported module and reimport it, the changes don’t show up. Why does this happen?: When I edit an imported module and reimport it the changes don’t show up Why does this happen?.


File: python.info,  Node: How do I create a pyc file?,  Next: How do I find the current module name?,  Up: Modules<3>

11.2.7.1 How do I create a .pyc file?
.....................................

When a module is imported for the first time (or when the source file
has changed since the current compiled file was created) a ‘.pyc’ file
containing the compiled code should be created in a ‘__pycache__’
subdirectory of the directory containing the ‘.py’ file.  The ‘.pyc’
file will have a filename that starts with the same name as the ‘.py’
file, and ends with ‘.pyc’, with a middle component that depends on the
particular ‘python’ binary that created it.  (See PEP 3147(1) for
details.)

One reason that a ‘.pyc’ file may not be created is a permissions
problem with the directory containing the source file, meaning that the
‘__pycache__’ subdirectory cannot be created.  This can happen, for
example, if you develop as one user but run as another, such as if you
are testing with a web server.

Unless the *note PYTHONDONTWRITEBYTECODE: dff. environment variable is
set, creation of a .pyc file is automatic if you’re importing a module
and Python has the ability (permissions, free space, etc…) to create a
‘__pycache__’ subdirectory and write the compiled module to that
subdirectory.

Running Python on a top level script is not considered an import and no
‘.pyc’ will be created.  For example, if you have a top-level module
‘foo.py’ that imports another module ‘xyz.py’, when you run ‘foo’ (by
typing ‘python foo.py’ as a shell command), a ‘.pyc’ will be created for
‘xyz’ because ‘xyz’ is imported, but no ‘.pyc’ file will be created for
‘foo’ since ‘foo.py’ isn’t being imported.

If you need to create a ‘.pyc’ file for ‘foo’ – that is, to create a
‘.pyc’ file for a module that is not imported – you can, using the *note
py_compile: d7. and *note compileall: 20. modules.

The *note py_compile: d7. module can manually compile any module.  One
way is to use the ‘compile()’ function in that module interactively:

     >>> import py_compile
     >>> py_compile.compile('foo.py')

This will write the ‘.pyc’ to a ‘__pycache__’ subdirectory in the same
location as ‘foo.py’ (or you can override that with the optional
parameter ‘cfile’).

You can also automatically compile all files in a directory or
directories using the *note compileall: 20. module.  You can do it from
the shell prompt by running ‘compileall.py’ and providing the path of a
directory containing Python files to compile:

     python -m compileall .

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3147


File: python.info,  Node: How do I find the current module name?,  Next: How can I have modules that mutually import each other?,  Prev: How do I create a pyc file?,  Up: Modules<3>

11.2.7.2 How do I find the current module name?
...............................................

A module can find out its own module name by looking at the predefined
global variable ‘__name__’.  If this has the value ‘'__main__'’, the
program is running as a script.  Many modules that are usually used by
importing them also provide a command-line interface or a self-test, and
only execute this code after checking ‘__name__’:

     def main():
         print('Running test...')
         ...

     if __name__ == '__main__':
         main()


File: python.info,  Node: How can I have modules that mutually import each other?,  Next: __import__ ‘x y z’ returns <module ‘x’>; how do I get z?,  Prev: How do I find the current module name?,  Up: Modules<3>

11.2.7.3 How can I have modules that mutually import each other?
................................................................

Suppose you have the following modules:

foo.py:

     from bar import bar_var
     foo_var = 1

bar.py:

     from foo import foo_var
     bar_var = 2

The problem is that the interpreter will perform the following steps:

   * main imports foo

   * Empty globals for foo are created

   * foo is compiled and starts executing

   * foo imports bar

   * Empty globals for bar are created

   * bar is compiled and starts executing

   * bar imports foo (which is a no-op since there already is a module
     named foo)

   * bar.foo_var = foo.foo_var

The last step fails, because Python isn’t done with interpreting ‘foo’
yet and the global symbol dictionary for ‘foo’ is still empty.

The same thing happens when you use ‘import foo’, and then try to access
‘foo.foo_var’ in global code.

There are (at least) three possible workarounds for this problem.

Guido van Rossum recommends avoiding all uses of ‘from <module> import
...’, and placing all code inside functions.  Initializations of global
variables and class variables should use constants or built-in functions
only.  This means everything from an imported module is referenced as
‘<module>.<name>’.

Jim Roskind suggests performing steps in the following order in each
module:

   * exports (globals, functions, and classes that don’t need imported
     base classes)

   * ‘import’ statements

   * active code (including globals that are initialized from imported
     values).

Van Rossum doesn’t like this approach much because the imports appear in
a strange place, but it does work.

Matthias Urlichs recommends restructuring your code so that the
recursive import is not necessary in the first place.

These solutions are not mutually exclusive.


File: python.info,  Node: __import__ ‘x y z’ returns <module ‘x’>; how do I get z?,  Next: When I edit an imported module and reimport it the changes don’t show up Why does this happen?,  Prev: How can I have modules that mutually import each other?,  Up: Modules<3>

11.2.7.4 __import__(‘x.y.z’) returns <module ‘x’>; how do I get z?
..................................................................

Consider using the convenience function *note import_module(): be6. from
*note importlib: 9a. instead:

     z = importlib.import_module('x.y.z')


File: python.info,  Node: When I edit an imported module and reimport it the changes don’t show up Why does this happen?,  Prev: __import__ ‘x y z’ returns <module ‘x’>; how do I get z?,  Up: Modules<3>

11.2.7.5 When I edit an imported module and reimport it, the changes don’t show up. Why does this happen?
.........................................................................................................

For reasons of efficiency as well as consistency, Python only reads the
module file on the first time a module is imported.  If it didn’t, in a
program consisting of many modules where each one imports the same basic
module, the basic module would be parsed and re-parsed many times.  To
force re-reading of a changed module, do this:

     import importlib
     import modname
     importlib.reload(modname)

Warning: this technique is not 100% fool-proof.  In particular, modules
containing statements like

     from modname import some_objects

will continue to work with the old version of the imported objects.  If
the module contains class definitions, existing class instances will
`not' be updated to use the new class definition.  This can result in
the following paradoxical behaviour:

     >>> import importlib
     >>> import cls
     >>> c = cls.C()                # Create an instance of C
     >>> importlib.reload(cls)
     <module 'cls' from 'cls.py'>
     >>> isinstance(c, cls.C)       # isinstance is false?!?
     False

The nature of the problem is made clear if you print out the “identity”
of the class objects:

     >>> hex(id(c.__class__))
     '0x7352a0'
     >>> hex(id(cls.C))
     '0x4198d0'


File: python.info,  Node: Design and History FAQ,  Next: Library and Extension FAQ,  Prev: Programming FAQ,  Up: Python Frequently Asked Questions

11.3 Design and History FAQ
===========================

* Menu:

* Why does Python use indentation for grouping of statements?::
* Why am I getting strange results with simple arithmetic operations?::
* Why are floating-point calculations so inaccurate?::
* Why are Python strings immutable?::
* Why must ‘self’ be used explicitly in method definitions and calls?::
* Why can’t I use an assignment in an expression?::
* Why does Python use methods for some functionality (e.g. list.index()) but functions for other (e.g. len(list))?: Why does Python use methods for some functionality e g list index but functions for other e g len list ?.
* Why is join() a string method instead of a list or tuple method?: Why is join a string method instead of a list or tuple method?.
* How fast are exceptions?::
* Why isn’t there a switch or case statement in Python?::
* Can’t you emulate threads in the interpreter instead of relying on an OS-specific thread implementation?::
* Why can’t lambda expressions contain statements?::
* Can Python be compiled to machine code, C or some other language?: Can Python be compiled to machine code C or some other language?.
* How does Python manage memory?::
* Why doesn’t CPython use a more traditional garbage collection scheme?::
* Why isn’t all memory freed when CPython exits?::
* Why are there separate tuple and list data types?::
* How are lists implemented in CPython?::
* How are dictionaries implemented in CPython?::
* Why must dictionary keys be immutable?::
* Why doesn’t list.sort() return the sorted list?: Why doesn’t list sort return the sorted list?.
* How do you specify and enforce an interface spec in Python?::
* Why is there no goto?::
* Why can’t raw strings (r-strings) end with a backslash?: Why can’t raw strings r-strings end with a backslash?.
* Why doesn’t Python have a “with” statement for attribute assignments?::
* Why don’t generators support the with statement?::
* Why are colons required for the if/while/def/class statements?::
* Why does Python allow commas at the end of lists and tuples?::


File: python.info,  Node: Why does Python use indentation for grouping of statements?,  Next: Why am I getting strange results with simple arithmetic operations?,  Up: Design and History FAQ

11.3.1 Why does Python use indentation for grouping of statements?
------------------------------------------------------------------

Guido van Rossum believes that using indentation for grouping is
extremely elegant and contributes a lot to the clarity of the average
Python program.  Most people learn to love this feature after a while.

Since there are no begin/end brackets there cannot be a disagreement
between grouping perceived by the parser and the human reader.
Occasionally C programmers will encounter a fragment of code like this:

     if (x <= y)
             x++;
             y--;
     z++;

Only the ‘x++’ statement is executed if the condition is true, but the
indentation leads many to believe otherwise.  Even experienced C
programmers will sometimes stare at it a long time wondering as to why
‘y’ is being decremented even for ‘x > y’.

Because there are no begin/end brackets, Python is much less prone to
coding-style conflicts.  In C there are many different ways to place the
braces.  After becoming used to reading and writing code using a
particular style, it is normal to feel somewhat uneasy when reading (or
being required to write) in a different one.

Many coding styles place begin/end brackets on a line by themselves.
This makes programs considerably longer and wastes valuable screen
space, making it harder to get a good overview of a program.  Ideally, a
function should fit on one screen (say, 20–30 lines).  20 lines of
Python can do a lot more work than 20 lines of C. This is not solely due
to the lack of begin/end brackets – the lack of declarations and the
high-level data types are also responsible – but the indentation-based
syntax certainly helps.


File: python.info,  Node: Why am I getting strange results with simple arithmetic operations?,  Next: Why are floating-point calculations so inaccurate?,  Prev: Why does Python use indentation for grouping of statements?,  Up: Design and History FAQ

11.3.2 Why am I getting strange results with simple arithmetic operations?
--------------------------------------------------------------------------

See the next question.


File: python.info,  Node: Why are floating-point calculations so inaccurate?,  Next: Why are Python strings immutable?,  Prev: Why am I getting strange results with simple arithmetic operations?,  Up: Design and History FAQ

11.3.3 Why are floating-point calculations so inaccurate?
---------------------------------------------------------

Users are often surprised by results like this:

     >>> 1.2 - 1.0
     0.19999999999999996

and think it is a bug in Python.  It’s not.  This has little to do with
Python, and much more to do with how the underlying platform handles
floating-point numbers.

The *note float: 1fd. type in CPython uses a C ‘double’ for storage.  A
*note float: 1fd. object’s value is stored in binary floating-point with
a fixed precision (typically 53 bits) and Python uses C operations,
which in turn rely on the hardware implementation in the processor, to
perform floating-point operations.  This means that as far as
floating-point operations are concerned, Python behaves like many
popular languages including C and Java.

Many numbers that can be written easily in decimal notation cannot be
expressed exactly in binary floating-point.  For example, after:

     >>> x = 1.2

the value stored for ‘x’ is a (very good) approximation to the decimal
value ‘1.2’, but is not exactly equal to it.  On a typical machine, the
actual stored value is:

     1.0011001100110011001100110011001100110011001100110011 (binary)

which is exactly:

     1.1999999999999999555910790149937383830547332763671875 (decimal)

The typical precision of 53 bits provides Python floats with 15–16
decimal digits of accuracy.

For a fuller explanation, please see the *note floating point
arithmetic: 1456. chapter in the Python tutorial.


File: python.info,  Node: Why are Python strings immutable?,  Next: Why must ‘self’ be used explicitly in method definitions and calls?,  Prev: Why are floating-point calculations so inaccurate?,  Up: Design and History FAQ

11.3.4 Why are Python strings immutable?
----------------------------------------

There are several advantages.

One is performance: knowing that a string is immutable means we can
allocate space for it at creation time, and the storage requirements are
fixed and unchanging.  This is also one of the reasons for the
distinction between tuples and lists.

Another advantage is that strings in Python are considered as
“elemental” as numbers.  No amount of activity will change the value 8
to anything else, and in Python, no amount of activity will change the
string “eight” to anything else.


File: python.info,  Node: Why must ‘self’ be used explicitly in method definitions and calls?,  Next: Why can’t I use an assignment in an expression?,  Prev: Why are Python strings immutable?,  Up: Design and History FAQ

11.3.5 Why must ‘self’ be used explicitly in method definitions and calls?
--------------------------------------------------------------------------

The idea was borrowed from Modula-3.  It turns out to be very useful,
for a variety of reasons.

First, it’s more obvious that you are using a method or instance
attribute instead of a local variable.  Reading ‘self.x’ or
‘self.meth()’ makes it absolutely clear that an instance variable or
method is used even if you don’t know the class definition by heart.  In
C++, you can sort of tell by the lack of a local variable declaration
(assuming globals are rare or easily recognizable) – but in Python,
there are no local variable declarations, so you’d have to look up the
class definition to be sure.  Some C++ and Java coding standards call
for instance attributes to have an ‘m_’ prefix, so this explicitness is
still useful in those languages, too.

Second, it means that no special syntax is necessary if you want to
explicitly reference or call the method from a particular class.  In
C++, if you want to use a method from a base class which is overridden
in a derived class, you have to use the ‘::’ operator – in Python you
can write ‘baseclass.methodname(self, <argument list>)’.  This is
particularly useful for *note __init__(): e23. methods, and in general
in cases where a derived class method wants to extend the base class
method of the same name and thus has to call the base class method
somehow.

Finally, for instance variables it solves a syntactic problem with
assignment: since local variables in Python are (by definition!)  those
variables to which a value is assigned in a function body (and that
aren’t explicitly declared global), there has to be some way to tell the
interpreter that an assignment was meant to assign to an instance
variable instead of to a local variable, and it should preferably be
syntactic (for efficiency reasons).  C++ does this through declarations,
but Python doesn’t have declarations and it would be a pity having to
introduce them just for this purpose.  Using the explicit ‘self.var’
solves this nicely.  Similarly, for using instance variables, having to
write ‘self.var’ means that references to unqualified names inside a
method don’t have to search the instance’s directories.  To put it
another way, local variables and instance variables live in two
different namespaces, and you need to tell Python which namespace to
use.


File: python.info,  Node: Why can’t I use an assignment in an expression?,  Next: Why does Python use methods for some functionality e g list index but functions for other e g len list ?,  Prev: Why must ‘self’ be used explicitly in method definitions and calls?,  Up: Design and History FAQ

11.3.6 Why can’t I use an assignment in an expression?
------------------------------------------------------

Starting in Python 3.8, you can!

Assignment expressions using the walrus operator ‘:=’ assign a variable
in an expression:

     while chunk := fp.read(200):
        print(chunk)

See PEP 572(1) for more information.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0572


File: python.info,  Node: Why does Python use methods for some functionality e g list index but functions for other e g len list ?,  Next: Why is join a string method instead of a list or tuple method?,  Prev: Why can’t I use an assignment in an expression?,  Up: Design and History FAQ

11.3.7 Why does Python use methods for some functionality (e.g. list.index()) but functions for other (e.g. len(list))?
-----------------------------------------------------------------------------------------------------------------------

As Guido said:

     (a) For some operations, prefix notation just reads better than
     postfix – prefix (and infix!)  operations have a long tradition in
     mathematics which likes notations where the visuals help the
     mathematician thinking about a problem.  Compare the easy with
     which we rewrite a formula like x*(a+b) into x*a + x*b to the
     clumsiness of doing the same thing using a raw OO notation.

     (b) When I read code that says len(x) I `know' that it is asking
     for the length of something.  This tells me two things: the result
     is an integer, and the argument is some kind of container.  To the
     contrary, when I read x.len(), I have to already know that x is
     some kind of container implementing an interface or inheriting from
     a class that has a standard len().  Witness the confusion we
     occasionally have when a class that is not implementing a mapping
     has a get() or keys() method, or something that isn’t a file has a
     write() method.

— ‘https://mail.python.org/pipermail/python-3000/2006-November/004643.html’


File: python.info,  Node: Why is join a string method instead of a list or tuple method?,  Next: How fast are exceptions?,  Prev: Why does Python use methods for some functionality e g list index but functions for other e g len list ?,  Up: Design and History FAQ

11.3.8 Why is join() a string method instead of a list or tuple method?
-----------------------------------------------------------------------

Strings became much more like other standard types starting in Python
1.6, when methods were added which give the same functionality that has
always been available using the functions of the string module.  Most of
these new methods have been widely accepted, but the one which appears
to make some programmers feel uncomfortable is:

     ", ".join(['1', '2', '4', '8', '16'])

which gives the result:

     "1, 2, 4, 8, 16"

There are two common arguments against this usage.

The first runs along the lines of: “It looks really ugly using a method
of a string literal (string constant)”, to which the answer is that it
might, but a string literal is just a fixed value.  If the methods are
to be allowed on names bound to strings there is no logical reason to
make them unavailable on literals.

The second objection is typically cast as: “I am really telling a
sequence to join its members together with a string constant”.  Sadly,
you aren’t.  For some reason there seems to be much less difficulty with
having *note split(): 890. as a string method, since in that case it is
easy to see that

     "1, 2, 4, 8, 16".split(", ")

is an instruction to a string literal to return the substrings delimited
by the given separator (or, by default, arbitrary runs of white space).

*note join(): 1766. is a string method because in using it you are
telling the separator string to iterate over a sequence of strings and
insert itself between adjacent elements.  This method can be used with
any argument which obeys the rules for sequence objects, including any
new classes you might define yourself.  Similar methods exist for bytes
and bytearray objects.


File: python.info,  Node: How fast are exceptions?,  Next: Why isn’t there a switch or case statement in Python?,  Prev: Why is join a string method instead of a list or tuple method?,  Up: Design and History FAQ

11.3.9 How fast are exceptions?
-------------------------------

A try/except block is extremely efficient if no exceptions are raised.
Actually catching an exception is expensive.  In versions of Python
prior to 2.0 it was common to use this idiom:

     try:
         value = mydict[key]
     except KeyError:
         mydict[key] = getvalue(key)
         value = mydict[key]

This only made sense when you expected the dict to have the key almost
all the time.  If that wasn’t the case, you coded it like this:

     if key in mydict:
         value = mydict[key]
     else:
         value = mydict[key] = getvalue(key)

For this specific case, you could also use ‘value = dict.setdefault(key,
getvalue(key))’, but only if the ‘getvalue()’ call is cheap enough
because it is evaluated in all cases.


File: python.info,  Node: Why isn’t there a switch or case statement in Python?,  Next: Can’t you emulate threads in the interpreter instead of relying on an OS-specific thread implementation?,  Prev: How fast are exceptions?,  Up: Design and History FAQ

11.3.10 Why isn’t there a switch or case statement in Python?
-------------------------------------------------------------

You can do this easily enough with a sequence of ‘if... elif... elif...
else’.  There have been some proposals for switch statement syntax, but
there is no consensus (yet) on whether and how to do range tests.  See
PEP 275(1) for complete details and the current status.

For cases where you need to choose from a very large number of
possibilities, you can create a dictionary mapping case values to
functions to call.  For example:

     def function_1(...):
         ...

     functions = {'a': function_1,
                  'b': function_2,
                  'c': self.method_1, ...}

     func = functions[value]
     func()

For calling methods on objects, you can simplify yet further by using
the *note getattr(): 54b. built-in to retrieve methods with a particular
name:

     def visit_a(self, ...):
         ...
     ...

     def dispatch(self, value):
         method_name = 'visit_' + str(value)
         method = getattr(self, method_name)
         method()

It’s suggested that you use a prefix for the method names, such as
‘visit_’ in this example.  Without such a prefix, if values are coming
from an untrusted source, an attacker would be able to call any method
on your object.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0275


File: python.info,  Node: Can’t you emulate threads in the interpreter instead of relying on an OS-specific thread implementation?,  Next: Why can’t lambda expressions contain statements?,  Prev: Why isn’t there a switch or case statement in Python?,  Up: Design and History FAQ

11.3.11 Can’t you emulate threads in the interpreter instead of relying on an OS-specific thread implementation?
----------------------------------------------------------------------------------------------------------------

Answer 1: Unfortunately, the interpreter pushes at least one C stack
frame for each Python stack frame.  Also, extensions can call back into
Python at almost random moments.  Therefore, a complete threads
implementation requires thread support for C.

Answer 2: Fortunately, there is Stackless Python(1), which has a
completely redesigned interpreter loop that avoids the C stack.

   ---------- Footnotes ----------

   (1) https://github.com/stackless-dev/stackless/wiki


File: python.info,  Node: Why can’t lambda expressions contain statements?,  Next: Can Python be compiled to machine code C or some other language?,  Prev: Can’t you emulate threads in the interpreter instead of relying on an OS-specific thread implementation?,  Up: Design and History FAQ

11.3.12 Why can’t lambda expressions contain statements?
--------------------------------------------------------

Python lambda expressions cannot contain statements because Python’s
syntactic framework can’t handle statements nested inside expressions.
However, in Python, this is not a serious problem.  Unlike lambda forms
in other languages, where they add functionality, Python lambdas are
only a shorthand notation if you’re too lazy to define a function.

Functions are already first class objects in Python, and can be declared
in a local scope.  Therefore the only advantage of using a lambda
instead of a locally-defined function is that you don’t need to invent a
name for the function – but that’s just a local variable to which the
function object (which is exactly the same type of object that a lambda
expression yields) is assigned!


File: python.info,  Node: Can Python be compiled to machine code C or some other language?,  Next: How does Python manage memory?,  Prev: Why can’t lambda expressions contain statements?,  Up: Design and History FAQ

11.3.13 Can Python be compiled to machine code, C or some other language?
-------------------------------------------------------------------------

Cython(1) compiles a modified version of Python with optional
annotations into C extensions.  Nuitka(2) is an up-and-coming compiler
of Python into C++ code, aiming to support the full Python language.
For compiling to Java you can consider VOC(3).

   ---------- Footnotes ----------

   (1) http://cython.org/

   (2) http://www.nuitka.net/

   (3) https://voc.readthedocs.io


File: python.info,  Node: How does Python manage memory?,  Next: Why doesn’t CPython use a more traditional garbage collection scheme?,  Prev: Can Python be compiled to machine code C or some other language?,  Up: Design and History FAQ

11.3.14 How does Python manage memory?
--------------------------------------

The details of Python memory management depend on the implementation.
The standard implementation of Python, *note CPython: 1569, uses
reference counting to detect inaccessible objects, and another mechanism
to collect reference cycles, periodically executing a cycle detection
algorithm which looks for inaccessible cycles and deletes the objects
involved.  The *note gc: 84. module provides functions to perform a
garbage collection, obtain debugging statistics, and tune the
collector’s parameters.

Other implementations (such as Jython(1) or PyPy(2)), however, can rely
on a different mechanism such as a full-blown garbage collector.  This
difference can cause some subtle porting problems if your Python code
depends on the behavior of the reference counting implementation.

In some Python implementations, the following code (which is fine in
CPython) will probably run out of file descriptors:

     for file in very_long_list_of_files:
         f = open(file)
         c = f.read(1)

Indeed, using CPython’s reference counting and destructor scheme, each
new assignment to `f' closes the previous file.  With a traditional GC,
however, those file objects will only get collected (and closed) at
varying and possibly long intervals.

If you want to write code that will work with any Python implementation,
you should explicitly close the file or use the *note with: 7da.
statement; this will work regardless of memory management scheme:

     for file in very_long_list_of_files:
         with open(file) as f:
             c = f.read(1)

   ---------- Footnotes ----------

   (1) http://www.jython.org

   (2) http://www.pypy.org


File: python.info,  Node: Why doesn’t CPython use a more traditional garbage collection scheme?,  Next: Why isn’t all memory freed when CPython exits?,  Prev: How does Python manage memory?,  Up: Design and History FAQ

11.3.15 Why doesn’t CPython use a more traditional garbage collection scheme?
-----------------------------------------------------------------------------

For one thing, this is not a C standard feature and hence it’s not
portable.  (Yes, we know about the Boehm GC library.  It has bits of
assembler code for `most' common platforms, not for all of them, and
although it is mostly transparent, it isn’t completely transparent;
patches are required to get Python to work with it.)

Traditional GC also becomes a problem when Python is embedded into other
applications.  While in a standalone Python it’s fine to replace the
standard malloc() and free() with versions provided by the GC library,
an application embedding Python may want to have its `own' substitute
for malloc() and free(), and may not want Python’s.  Right now, CPython
works with anything that implements malloc() and free() properly.


File: python.info,  Node: Why isn’t all memory freed when CPython exits?,  Next: Why are there separate tuple and list data types?,  Prev: Why doesn’t CPython use a more traditional garbage collection scheme?,  Up: Design and History FAQ

11.3.16 Why isn’t all memory freed when CPython exits?
------------------------------------------------------

Objects referenced from the global namespaces of Python modules are not
always deallocated when Python exits.  This may happen if there are
circular references.  There are also certain bits of memory that are
allocated by the C library that are impossible to free (e.g.  a tool
like Purify will complain about these).  Python is, however, aggressive
about cleaning up memory on exit and does try to destroy every single
object.

If you want to force Python to delete certain things on deallocation use
the *note atexit: b. module to run a function that will force those
deletions.


File: python.info,  Node: Why are there separate tuple and list data types?,  Next: How are lists implemented in CPython?,  Prev: Why isn’t all memory freed when CPython exits?,  Up: Design and History FAQ

11.3.17 Why are there separate tuple and list data types?
---------------------------------------------------------

Lists and tuples, while similar in many respects, are generally used in
fundamentally different ways.  Tuples can be thought of as being similar
to Pascal records or C structs; they’re small collections of related
data which may be of different types which are operated on as a group.
For example, a Cartesian coordinate is appropriately represented as a
tuple of two or three numbers.

Lists, on the other hand, are more like arrays in other languages.  They
tend to hold a varying number of objects all of which have the same type
and which are operated on one-by-one.  For example, ‘os.listdir('.')’
returns a list of strings representing the files in the current
directory.  Functions which operate on this output would generally not
break if you added another file or two to the directory.

Tuples are immutable, meaning that once a tuple has been created, you
can’t replace any of its elements with a new value.  Lists are mutable,
meaning that you can always change a list’s elements.  Only immutable
elements can be used as dictionary keys, and hence only tuples and not
lists can be used as keys.


File: python.info,  Node: How are lists implemented in CPython?,  Next: How are dictionaries implemented in CPython?,  Prev: Why are there separate tuple and list data types?,  Up: Design and History FAQ

11.3.18 How are lists implemented in CPython?
---------------------------------------------

CPython’s lists are really variable-length arrays, not Lisp-style linked
lists.  The implementation uses a contiguous array of references to
other objects, and keeps a pointer to this array and the array’s length
in a list head structure.

This makes indexing a list ‘a[i]’ an operation whose cost is independent
of the size of the list or the value of the index.

When items are appended or inserted, the array of references is resized.
Some cleverness is applied to improve the performance of appending items
repeatedly; when the array must be grown, some extra space is allocated
so the next few times don’t require an actual resize.


File: python.info,  Node: How are dictionaries implemented in CPython?,  Next: Why must dictionary keys be immutable?,  Prev: How are lists implemented in CPython?,  Up: Design and History FAQ

11.3.19 How are dictionaries implemented in CPython?
----------------------------------------------------

CPython’s dictionaries are implemented as resizable hash tables.
Compared to B-trees, this gives better performance for lookup (the most
common operation by far) under most circumstances, and the
implementation is simpler.

Dictionaries work by computing a hash code for each key stored in the
dictionary using the *note hash(): aa3. built-in function.  The hash
code varies widely depending on the key and a per-process seed; for
example, “Python” could hash to -539294296 while “python”, a string that
differs by a single bit, could hash to 1142331976.  The hash code is
then used to calculate a location in an internal array where the value
will be stored.  Assuming that you’re storing keys that all have
different hash values, this means that dictionaries take constant time –
O(1), in Big-O notation – to retrieve a key.


File: python.info,  Node: Why must dictionary keys be immutable?,  Next: Why doesn’t list sort return the sorted list?,  Prev: How are dictionaries implemented in CPython?,  Up: Design and History FAQ

11.3.20 Why must dictionary keys be immutable?
----------------------------------------------

The hash table implementation of dictionaries uses a hash value
calculated from the key value to find the key.  If the key were a
mutable object, its value could change, and thus its hash could also
change.  But since whoever changes the key object can’t tell that it was
being used as a dictionary key, it can’t move the entry around in the
dictionary.  Then, when you try to look up the same object in the
dictionary it won’t be found because its hash value is different.  If
you tried to look up the old value it wouldn’t be found either, because
the value of the object found in that hash bin would be different.

If you want a dictionary indexed with a list, simply convert the list to
a tuple first; the function ‘tuple(L)’ creates a tuple with the same
entries as the list ‘L’.  Tuples are immutable and can therefore be used
as dictionary keys.

Some unacceptable solutions that have been proposed:

   - Hash lists by their address (object ID). This doesn’t work because
     if you construct a new list with the same value it won’t be found;
     e.g.:

          mydict = {[1, 2]: '12'}
          print(mydict[[1, 2]])

     would raise a *note KeyError: 3e9. exception because the id of the
     ‘[1, 2]’ used in the second line differs from that in the first
     line.  In other words, dictionary keys should be compared using
     ‘==’, not using *note is: 1551.

   - Make a copy when using a list as a key.  This doesn’t work because
     the list, being a mutable object, could contain a reference to
     itself, and then the copying code would run into an infinite loop.

   - Allow lists as keys but tell the user not to modify them.  This
     would allow a class of hard-to-track bugs in programs when you
     forgot or modified a list by accident.  It also invalidates an
     important invariant of dictionaries: every value in ‘d.keys()’ is
     usable as a key of the dictionary.

   - Mark lists as read-only once they are used as a dictionary key.
     The problem is that it’s not just the top-level object that could
     change its value; you could use a tuple containing a list as a key.
     Entering anything as a key into a dictionary would require marking
     all objects reachable from there as read-only – and again,
     self-referential objects could cause an infinite loop.

There is a trick to get around this if you need to, but use it at your
own risk: You can wrap a mutable structure inside a class instance which
has both a *note __eq__(): 44b. and a *note __hash__(): 44c. method.
You must then make sure that the hash value for all such wrapper objects
that reside in a dictionary (or other hash based structure), remain
fixed while the object is in the dictionary (or other structure).

     class ListWrapper:
         def __init__(self, the_list):
             self.the_list = the_list

         def __eq__(self, other):
             return self.the_list == other.the_list

         def __hash__(self):
             l = self.the_list
             result = 98767 - len(l)*555
             for i, el in enumerate(l):
                 try:
                     result = result + (hash(el) % 9999999) * 1001 + i
                 except Exception:
                     result = (result % 7777777) + i * 333
             return result

Note that the hash computation is complicated by the possibility that
some members of the list may be unhashable and also by the possibility
of arithmetic overflow.

Furthermore it must always be the case that if ‘o1 == o2’ (ie
‘o1.__eq__(o2) is True’) then ‘hash(o1) == hash(o2)’ (ie, ‘o1.__hash__()
== o2.__hash__()’), regardless of whether the object is in a dictionary
or not.  If you fail to meet these restrictions dictionaries and other
hash based structures will misbehave.

In the case of ListWrapper, whenever the wrapper object is in a
dictionary the wrapped list must not change to avoid anomalies.  Don’t
do this unless you are prepared to think hard about the requirements and
the consequences of not meeting them correctly.  Consider yourself
warned.


File: python.info,  Node: Why doesn’t list sort return the sorted list?,  Next: How do you specify and enforce an interface spec in Python?,  Prev: Why must dictionary keys be immutable?,  Up: Design and History FAQ

11.3.21 Why doesn’t list.sort() return the sorted list?
-------------------------------------------------------

In situations where performance matters, making a copy of the list just
to sort it would be wasteful.  Therefore, *note list.sort(): 548. sorts
the list in place.  In order to remind you of that fact, it does not
return the sorted list.  This way, you won’t be fooled into accidentally
overwriting a list when you need a sorted copy but also need to keep the
unsorted version around.

If you want to return a new list, use the built-in *note sorted(): 547.
function instead.  This function creates a new list from a provided
iterable, sorts it and returns it.  For example, here’s how to iterate
over the keys of a dictionary in sorted order:

     for key in sorted(mydict):
         ...  # do whatever with mydict[key]...


File: python.info,  Node: How do you specify and enforce an interface spec in Python?,  Next: Why is there no goto?,  Prev: Why doesn’t list sort return the sorted list?,  Up: Design and History FAQ

11.3.22 How do you specify and enforce an interface spec in Python?
-------------------------------------------------------------------

An interface specification for a module as provided by languages such as
C++ and Java describes the prototypes for the methods and functions of
the module.  Many feel that compile-time enforcement of interface
specifications helps in the construction of large programs.

Python 2.6 adds an *note abc: 3. module that lets you define Abstract
Base Classes (ABCs).  You can then use *note isinstance(): 552. and
*note issubclass(): 553. to check whether an instance or a class
implements a particular ABC. The *note collections.abc: 1e. module
defines a set of useful ABCs such as *note Iterable: 1818, *note
Container: 181a, and *note MutableMapping: ace.

For Python, many of the advantages of interface specifications can be
obtained by an appropriate test discipline for components.

A good test suite for a module can both provide a regression test and
serve as a module interface specification and a set of examples.  Many
Python modules can be run as a script to provide a simple “self test.”
Even modules which use complex external interfaces can often be tested
in isolation using trivial “stub” emulations of the external interface.
The *note doctest: 66. and *note unittest: 124. modules or third-party
test frameworks can be used to construct exhaustive test suites that
exercise every line of code in a module.

An appropriate testing discipline can help build large complex
applications in Python as well as having interface specifications would.
In fact, it can be better because an interface specification cannot test
certain properties of a program.  For example, the ‘append()’ method is
expected to add new elements to the end of some internal list; an
interface specification cannot test that your ‘append()’ implementation
will actually do this correctly, but it’s trivial to check this property
in a test suite.

Writing test suites is very helpful, and you might want to design your
code to make it easily tested.  One increasingly popular technique,
test-driven development, calls for writing parts of the test suite
first, before you write any of the actual code.  Of course Python allows
you to be sloppy and not write test cases at all.


File: python.info,  Node: Why is there no goto?,  Next: Why can’t raw strings r-strings end with a backslash?,  Prev: How do you specify and enforce an interface spec in Python?,  Up: Design and History FAQ

11.3.23 Why is there no goto?
-----------------------------

In the 1970s people realized that unrestricted goto could lead to messy
“spaghetti” code that was hard to understand and revise.  In a
high-level language, it is also unneeded as long as there are ways to
branch (in Python, with ‘if’ statements and ‘or’, ‘and’, and ‘if-else’
expressions) and loop (with ‘while’ and ‘for’ statements, possibly
containing ‘continue’ and ‘break’).

One can also use exceptions to provide a “structured goto” that works
even across function calls.  Many feel that exceptions can conveniently
emulate all reasonable uses of the “go” or “goto” constructs of C,
Fortran, and other languages.  For example:

     class label(Exception): pass  # declare a label

     try:
         ...
         if condition: raise label()  # goto label
         ...
     except label:  # where to goto
         pass
     ...

This doesn’t allow you to jump into the middle of a loop, but that’s
usually considered an abuse of goto anyway.  Use sparingly.


File: python.info,  Node: Why can’t raw strings r-strings end with a backslash?,  Next: Why doesn’t Python have a “with” statement for attribute assignments?,  Prev: Why is there no goto?,  Up: Design and History FAQ

11.3.24 Why can’t raw strings (r-strings) end with a backslash?
---------------------------------------------------------------

More precisely, they can’t end with an odd number of backslashes: the
unpaired backslash at the end escapes the closing quote character,
leaving an unterminated string.

Raw strings were designed to ease creating input for processors (chiefly
regular expression engines) that want to do their own backslash escape
processing.  Such processors consider an unmatched trailing backslash to
be an error anyway, so raw strings disallow that.  In return, they allow
you to pass on the string quote character by escaping it with a
backslash.  These rules work well when r-strings are used for their
intended purpose.

If you’re trying to build Windows pathnames, note that all Windows
system calls accept forward slashes too:

     f = open("/mydir/file.txt")  # works fine!

If you’re trying to build a pathname for a DOS command, try e.g.  one of

     dir = r"\this\is\my\dos\dir" "\\"
     dir = r"\this\is\my\dos\dir\ "[:-1]
     dir = "\\this\\is\\my\\dos\\dir\\"


File: python.info,  Node: Why doesn’t Python have a “with” statement for attribute assignments?,  Next: Why don’t generators support the with statement?,  Prev: Why can’t raw strings r-strings end with a backslash?,  Up: Design and History FAQ

11.3.25 Why doesn’t Python have a “with” statement for attribute assignments?
-----------------------------------------------------------------------------

Python has a ‘with’ statement that wraps the execution of a block,
calling code on the entrance and exit from the block.  Some languages
have a construct that looks like this:

     with obj:
         a = 1               # equivalent to obj.a = 1
         total = total + 1   # obj.total = obj.total + 1

In Python, such a construct would be ambiguous.

Other languages, such as Object Pascal, Delphi, and C++, use static
types, so it’s possible to know, in an unambiguous way, what member is
being assigned to.  This is the main point of static typing – the
compiler `always' knows the scope of every variable at compile time.

Python uses dynamic types.  It is impossible to know in advance which
attribute will be referenced at runtime.  Member attributes may be added
or removed from objects on the fly.  This makes it impossible to know,
from a simple reading, what attribute is being referenced: a local one,
a global one, or a member attribute?

For instance, take the following incomplete snippet:

     def foo(a):
         with a:
             print(x)

The snippet assumes that “a” must have a member attribute called “x”.
However, there is nothing in Python that tells the interpreter this.
What should happen if “a” is, let us say, an integer?  If there is a
global variable named “x”, will it be used inside the with block?  As
you see, the dynamic nature of Python makes such choices much harder.

The primary benefit of “with” and similar language features (reduction
of code volume) can, however, easily be achieved in Python by
assignment.  Instead of:

     function(args).mydict[index][index].a = 21
     function(args).mydict[index][index].b = 42
     function(args).mydict[index][index].c = 63

write this:

     ref = function(args).mydict[index][index]
     ref.a = 21
     ref.b = 42
     ref.c = 63

This also has the side-effect of increasing execution speed because name
bindings are resolved at run-time in Python, and the second version only
needs to perform the resolution once.


File: python.info,  Node: Why don’t generators support the with statement?,  Next: Why are colons required for the if/while/def/class statements?,  Prev: Why doesn’t Python have a “with” statement for attribute assignments?,  Up: Design and History FAQ

11.3.26 Why don’t generators support the with statement?
--------------------------------------------------------

For technical reasons, a generator used directly as a context manager
would not work correctly.  When, as is most common, a generator is used
as an iterator run to completion, no closing is needed.  When it is,
wrap it as “contextlib.closing(generator)” in the ‘with’ statement.


File: python.info,  Node: Why are colons required for the if/while/def/class statements?,  Next: Why does Python allow commas at the end of lists and tuples?,  Prev: Why don’t generators support the with statement?,  Up: Design and History FAQ

11.3.27 Why are colons required for the if/while/def/class statements?
----------------------------------------------------------------------

The colon is required primarily to enhance readability (one of the
results of the experimental ABC language).  Consider this:

     if a == b
         print(a)

versus

     if a == b:
         print(a)

Notice how the second one is slightly easier to read.  Notice further
how a colon sets off the example in this FAQ answer; it’s a standard
usage in English.

Another minor reason is that the colon makes it easier for editors with
syntax highlighting; they can look for colons to decide when indentation
needs to be increased instead of having to do a more elaborate parsing
of the program text.


File: python.info,  Node: Why does Python allow commas at the end of lists and tuples?,  Prev: Why are colons required for the if/while/def/class statements?,  Up: Design and History FAQ

11.3.28 Why does Python allow commas at the end of lists and tuples?
--------------------------------------------------------------------

Python lets you add a trailing comma at the end of lists, tuples, and
dictionaries:

     [1, 2, 3,]
     ('a', 'b', 'c',)
     d = {
         "A": [1, 5],
         "B": [6, 7],  # last trailing comma is optional but good style
     }

There are several reasons to allow this.

When you have a literal value for a list, tuple, or dictionary spread
across multiple lines, it’s easier to add more elements because you
don’t have to remember to add a comma to the previous line.  The lines
can also be reordered without creating a syntax error.

Accidentally omitting the comma can lead to errors that are hard to
diagnose.  For example:

     x = [
       "fee",
       "fie"
       "foo",
       "fum"
     ]

This list looks like it has four elements, but it actually contains
three: “fee”, “fiefoo” and “fum”.  Always adding the comma avoids this
source of error.

Allowing the trailing comma may also make programmatic code generation
easier.


File: python.info,  Node: Library and Extension FAQ,  Next: Extending/Embedding FAQ,  Prev: Design and History FAQ,  Up: Python Frequently Asked Questions

11.4 Library and Extension FAQ
==============================

* Menu:

* General Library Questions::
* Common tasks::
* Threads::
* Input and Output: Input and Output<2>.
* Network/Internet Programming::
* Databases::
* Mathematics and Numerics::


File: python.info,  Node: General Library Questions,  Next: Common tasks,  Up: Library and Extension FAQ

11.4.1 General Library Questions
--------------------------------

* Menu:

* How do I find a module or application to perform task X?::
* Where is the math.py (socket.py, regex.py, etc.) source file?: Where is the math py socket py regex py etc source file?.
* How do I make a Python script executable on Unix?::
* Is there a curses/termcap package for Python?::
* Is there an equivalent to C’s onexit() in Python?: Is there an equivalent to C’s onexit in Python?.
* Why don’t my signal handlers work?::


File: python.info,  Node: How do I find a module or application to perform task X?,  Next: Where is the math py socket py regex py etc source file?,  Up: General Library Questions

11.4.1.1 How do I find a module or application to perform task X?
.................................................................

Check *note the Library Reference: 1330. to see if there’s a relevant
standard library module.  (Eventually you’ll learn what’s in the
standard library and will be able to skip this step.)

For third-party packages, search the Python Package Index(1) or try
Google(2) or another Web search engine.  Searching for “Python” plus a
keyword or two for your topic of interest will usually find something
helpful.

   ---------- Footnotes ----------

   (1) https://pypi.org

   (2) https://www.google.com


File: python.info,  Node: Where is the math py socket py regex py etc source file?,  Next: How do I make a Python script executable on Unix?,  Prev: How do I find a module or application to perform task X?,  Up: General Library Questions

11.4.1.2 Where is the math.py (socket.py, regex.py, etc.) source file?
......................................................................

If you can’t find a source file for a module it may be a built-in or
dynamically loaded module implemented in C, C++ or other compiled
language.  In this case you may not have the source file or it may be
something like ‘mathmodule.c’, somewhere in a C source directory (not on
the Python Path).

There are (at least) three kinds of modules in Python:

  1. modules written in Python (.py);

  2. modules written in C and dynamically loaded (.dll, .pyd, .so, .sl,
     etc);

  3. modules written in C and linked with the interpreter; to get a list
     of these, type:

          import sys
          print(sys.builtin_module_names)


File: python.info,  Node: How do I make a Python script executable on Unix?,  Next: Is there a curses/termcap package for Python?,  Prev: Where is the math py socket py regex py etc source file?,  Up: General Library Questions

11.4.1.3 How do I make a Python script executable on Unix?
..........................................................

You need to do two things: the script file’s mode must be executable and
the first line must begin with ‘#!’ followed by the path of the Python
interpreter.

The first is done by executing ‘chmod +x scriptfile’ or perhaps ‘chmod
755 scriptfile’.

The second can be done in a number of ways.  The most straightforward
way is to write

     #!/usr/local/bin/python

as the very first line of your file, using the pathname for where the
Python interpreter is installed on your platform.

If you would like the script to be independent of where the Python
interpreter lives, you can use the ‘env’ program.  Almost all Unix
variants support the following, assuming the Python interpreter is in a
directory on the user’s ‘PATH’:

     #!/usr/bin/env python

`Don’t' do this for CGI scripts.  The ‘PATH’ variable for CGI scripts is
often very minimal, so you need to use the actual absolute pathname of
the interpreter.

Occasionally, a user’s environment is so full that the ‘/usr/bin/env’
program fails; or there’s no env program at all.  In that case, you can
try the following hack (due to Alex Rezinsky):

     #! /bin/sh
     """:"
     exec python $0 ${1+"$@"}
     """

The minor disadvantage is that this defines the script’s __doc__ string.
However, you can fix that by adding

     __doc__ = """...Whatever..."""


File: python.info,  Node: Is there a curses/termcap package for Python?,  Next: Is there an equivalent to C’s onexit in Python?,  Prev: How do I make a Python script executable on Unix?,  Up: General Library Questions

11.4.1.4 Is there a curses/termcap package for Python?
......................................................

For Unix variants: The standard Python source distribution comes with a
curses module in the Modules(1) subdirectory, though it’s not compiled
by default.  (Note that this is not available in the Windows
distribution – there is no curses module for Windows.)

The *note curses: 2b. module supports basic curses features as well as
many additional functions from ncurses and SYSV curses such as colour,
alternative character set support, pads, and mouse support.  This means
the module isn’t compatible with operating systems that only have BSD
curses, but there don’t seem to be any currently maintained OSes that
fall into this category.

For Windows: use the consolelib module(2).

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Modules

   (2) http://effbot.org/zone/console-index.htm


File: python.info,  Node: Is there an equivalent to C’s onexit in Python?,  Next: Why don’t my signal handlers work?,  Prev: Is there a curses/termcap package for Python?,  Up: General Library Questions

11.4.1.5 Is there an equivalent to C’s onexit() in Python?
..........................................................

The *note atexit: b. module provides a register function that is similar
to C’s ‘onexit()’.


File: python.info,  Node: Why don’t my signal handlers work?,  Prev: Is there an equivalent to C’s onexit in Python?,  Up: General Library Questions

11.4.1.6 Why don’t my signal handlers work?
...........................................

The most common problem is that the signal handler is declared with the
wrong argument list.  It is called as

     handler(signum, frame)

so it should be declared with two parameters:

     def handler(signum, frame):
         ...


File: python.info,  Node: Common tasks,  Next: Threads,  Prev: General Library Questions,  Up: Library and Extension FAQ

11.4.2 Common tasks
-------------------

* Menu:

* How do I test a Python program or component?::
* How do I create documentation from doc strings?::
* How do I get a single keypress at a time?::


File: python.info,  Node: How do I test a Python program or component?,  Next: How do I create documentation from doc strings?,  Up: Common tasks

11.4.2.1 How do I test a Python program or component?
.....................................................

Python comes with two testing frameworks.  The *note doctest: 66. module
finds examples in the docstrings for a module and runs them, comparing
the output with the expected output given in the docstring.

The *note unittest: 124. module is a fancier testing framework modelled
on Java and Smalltalk testing frameworks.

To make testing easier, you should use good modular design in your
program.  Your program should have almost all functionality encapsulated
in either functions or class methods – and this sometimes has the
surprising and delightful effect of making the program run faster
(because local variable accesses are faster than global accesses).
Furthermore the program should avoid depending on mutating global
variables, since this makes testing much more difficult to do.

The “global main logic” of your program may be as simple as

     if __name__ == "__main__":
         main_logic()

at the bottom of the main module of your program.

Once your program is organized as a tractable collection of function and
class behaviours, you should write test functions that exercise the
behaviours.  A test suite that automates a sequence of tests can be
associated with each module.  This sounds like a lot of work, but since
Python is so terse and flexible it’s surprisingly easy.  You can make
coding much more pleasant and fun by writing your test functions in
parallel with the “production code”, since this makes it easy to find
bugs and even design flaws earlier.

“Support modules” that are not intended to be the main module of a
program may include a self-test of the module.

     if __name__ == "__main__":
         self_test()

Even programs that interact with complex external interfaces may be
tested when the external interfaces are unavailable by using “fake”
interfaces implemented in Python.


File: python.info,  Node: How do I create documentation from doc strings?,  Next: How do I get a single keypress at a time?,  Prev: How do I test a Python program or component?,  Up: Common tasks

11.4.2.2 How do I create documentation from doc strings?
........................................................

The *note pydoc: d9. module can create HTML from the doc strings in your
Python source code.  An alternative for creating API documentation
purely from docstrings is epydoc(1).  Sphinx(2) can also include
docstring content.

   ---------- Footnotes ----------

   (1) http://epydoc.sourceforge.net/

   (2) http://sphinx-doc.org


File: python.info,  Node: How do I get a single keypress at a time?,  Prev: How do I create documentation from doc strings?,  Up: Common tasks

11.4.2.3 How do I get a single keypress at a time?
..................................................

For Unix variants there are several solutions.  It’s straightforward to
do this using curses, but curses is a fairly large module to learn.


File: python.info,  Node: Threads,  Next: Input and Output<2>,  Prev: Common tasks,  Up: Library and Extension FAQ

11.4.3 Threads
--------------

* Menu:

* How do I program using threads?::
* None of my threads seem to run; why?: None of my threads seem to run why?.
* How do I parcel out work among a bunch of worker threads?::
* What kinds of global value mutation are thread-safe?::
* Can’t we get rid of the Global Interpreter Lock?::


File: python.info,  Node: How do I program using threads?,  Next: None of my threads seem to run why?,  Up: Threads

11.4.3.1 How do I program using threads?
........................................

Be sure to use the *note threading: 10b. module and not the *note
_thread: 2. module.  The *note threading: 10b. module builds convenient
abstractions on top of the low-level primitives provided by the *note
_thread: 2. module.


File: python.info,  Node: None of my threads seem to run why?,  Next: How do I parcel out work among a bunch of worker threads?,  Prev: How do I program using threads?,  Up: Threads

11.4.3.2 None of my threads seem to run: why?
.............................................

As soon as the main thread exits, all threads are killed.  Your main
thread is running too quickly, giving the threads no time to do any
work.

A simple fix is to add a sleep to the end of the program that’s long
enough for all the threads to finish:

     import threading, time

     def thread_task(name, n):
         for i in range(n):
             print(name, i)

     for i in range(10):
         T = threading.Thread(target=thread_task, args=(str(i), i))
         T.start()

     time.sleep(10)  # <---------------------------!

But now (on many platforms) the threads don’t run in parallel, but
appear to run sequentially, one at a time!  The reason is that the OS
thread scheduler doesn’t start a new thread until the previous thread is
blocked.

A simple fix is to add a tiny sleep to the start of the run function:

     def thread_task(name, n):
         time.sleep(0.001)  # <--------------------!
         for i in range(n):
             print(name, i)

     for i in range(10):
         T = threading.Thread(target=thread_task, args=(str(i), i))
         T.start()

     time.sleep(10)

Instead of trying to guess a good delay value for *note time.sleep():
773, it’s better to use some kind of semaphore mechanism.  One idea is
to use the *note queue: da. module to create a queue object, let each
thread append a token to the queue when it finishes, and let the main
thread read as many tokens from the queue as there are threads.


File: python.info,  Node: How do I parcel out work among a bunch of worker threads?,  Next: What kinds of global value mutation are thread-safe?,  Prev: None of my threads seem to run why?,  Up: Threads

11.4.3.3 How do I parcel out work among a bunch of worker threads?
..................................................................

The easiest way is to use the *note concurrent.futures: 21. module,
especially the *note ThreadPoolExecutor: 18c. class.

Or, if you want fine control over the dispatching algorithm, you can
write your own logic manually.  Use the *note queue: da. module to
create a queue containing a list of jobs.  The *note Queue: dde. class
maintains a list of objects and has a ‘.put(obj)’ method that adds items
to the queue and a ‘.get()’ method to return them.  The class will take
care of the locking necessary to ensure that each job is handed out
exactly once.

Here’s a trivial example:

     import threading, queue, time

     # The worker thread gets jobs off the queue.  When the queue is empty, it
     # assumes there will be no more work and exits.
     # (Realistically workers will run until terminated.)
     def worker():
         print('Running worker')
         time.sleep(0.1)
         while True:
             try:
                 arg = q.get(block=False)
             except queue.Empty:
                 print('Worker', threading.currentThread(), end=' ')
                 print('queue empty')
                 break
             else:
                 print('Worker', threading.currentThread(), end=' ')
                 print('running with argument', arg)
                 time.sleep(0.5)

     # Create queue
     q = queue.Queue()

     # Start a pool of 5 workers
     for i in range(5):
         t = threading.Thread(target=worker, name='worker %i' % (i+1))
         t.start()

     # Begin adding work to the queue
     for i in range(50):
         q.put(i)

     # Give threads time to run
     print('Main thread sleeping')
     time.sleep(5)

When run, this will produce the following output:

     Running worker
     Running worker
     Running worker
     Running worker
     Running worker
     Main thread sleeping
     Worker <Thread(worker 1, started 130283832797456)> running with argument 0
     Worker <Thread(worker 2, started 130283824404752)> running with argument 1
     Worker <Thread(worker 3, started 130283816012048)> running with argument 2
     Worker <Thread(worker 4, started 130283807619344)> running with argument 3
     Worker <Thread(worker 5, started 130283799226640)> running with argument 4
     Worker <Thread(worker 1, started 130283832797456)> running with argument 5
     ...

Consult the module’s documentation for more details; the *note Queue:
dde. class provides a featureful interface.


File: python.info,  Node: What kinds of global value mutation are thread-safe?,  Next: Can’t we get rid of the Global Interpreter Lock?,  Prev: How do I parcel out work among a bunch of worker threads?,  Up: Threads

11.4.3.4 What kinds of global value mutation are thread-safe?
.............................................................

A *note global interpreter lock: 600. (GIL) is used internally to ensure
that only one thread runs in the Python VM at a time.  In general,
Python offers to switch among threads only between bytecode
instructions; how frequently it switches can be set via *note
sys.setswitchinterval(): 218.  Each bytecode instruction and therefore
all the C implementation code reached from each instruction is therefore
atomic from the point of view of a Python program.

In theory, this means an exact accounting requires an exact
understanding of the PVM bytecode implementation.  In practice, it means
that operations on shared variables of built-in data types (ints, lists,
dicts, etc) that “look atomic” really are.

For example, the following operations are all atomic (L, L1, L2 are
lists, D, D1, D2 are dicts, x, y are objects, i, j are ints):

     L.append(x)
     L1.extend(L2)
     x = L[i]
     x = L.pop()
     L1[i:j] = L2
     L.sort()
     x = y
     x.field = y
     D[x] = y
     D1.update(D2)
     D.keys()

These aren’t:

     i = i+1
     L.append(L[-1])
     L[i] = L[j]
     D[x] = D[x] + 1

Operations that replace other objects may invoke those other objects’
*note __del__(): a04. method when their reference count reaches zero,
and that can affect things.  This is especially true for the mass
updates to dictionaries and lists.  When in doubt, use a mutex!


File: python.info,  Node: Can’t we get rid of the Global Interpreter Lock?,  Prev: What kinds of global value mutation are thread-safe?,  Up: Threads

11.4.3.5 Can’t we get rid of the Global Interpreter Lock?
.........................................................

The *note global interpreter lock: 600. (GIL) is often seen as a
hindrance to Python’s deployment on high-end multiprocessor server
machines, because a multi-threaded Python program effectively only uses
one CPU, due to the insistence that (almost) all Python code can only
run while the GIL is held.

Back in the days of Python 1.5, Greg Stein actually implemented a
comprehensive patch set (the “free threading” patches) that removed the
GIL and replaced it with fine-grained locking.  Adam Olsen recently did
a similar experiment in his python-safethread(1) project.
Unfortunately, both experiments exhibited a sharp drop in single-thread
performance (at least 30% slower), due to the amount of fine-grained
locking necessary to compensate for the removal of the GIL.

This doesn’t mean that you can’t make good use of Python on multi-CPU
machines!  You just have to be creative with dividing the work up
between multiple `processes' rather than multiple `threads'.  The *note
ProcessPoolExecutor: 196. class in the new *note concurrent.futures: 21.
module provides an easy way of doing so; the *note multiprocessing: b7.
module provides a lower-level API in case you want more control over
dispatching of tasks.

Judicious use of C extensions will also help; if you use a C extension
to perform a time-consuming task, the extension can release the GIL
while the thread of execution is in the C code and allow other threads
to get some work done.  Some standard library modules such as *note
zlib: 14d. and *note hashlib: 8c. already do this.

It has been suggested that the GIL should be a per-interpreter-state
lock rather than truly global; interpreters then wouldn’t be able to
share objects.  Unfortunately, this isn’t likely to happen either.  It
would be a tremendous amount of work, because many object
implementations currently have global state.  For example, small
integers and short strings are cached; these caches would have to be
moved to the interpreter state.  Other object types have their own free
list; these free lists would have to be moved to the interpreter state.
And so on.

And I doubt that it can even be done in finite time, because the same
problem exists for 3rd party extensions.  It is likely that 3rd party
extensions are being written at a faster rate than you can convert them
to store all their global state in the interpreter state.

And finally, once you have multiple interpreters not sharing any state,
what have you gained over running each interpreter in a separate
process?

   ---------- Footnotes ----------

   (1) https://code.google.com/archive/p/python-safethread


File: python.info,  Node: Input and Output<2>,  Next: Network/Internet Programming,  Prev: Threads,  Up: Library and Extension FAQ

11.4.4 Input and Output
-----------------------

* Menu:

* How do I delete a file? (And other file questions…): How do I delete a file? And other file questions….
* How do I copy a file?::
* How do I read (or write) binary data?: How do I read or write binary data?.
* I can’t seem to use os.read() on a pipe created with os.popen(); why?: I can’t seem to use os read on a pipe created with os popen ; why?.
* How do I access the serial (RS232) port?: How do I access the serial RS232 port?.
* Why doesn’t closing sys.stdout (stdin, stderr) really close it?: Why doesn’t closing sys stdout stdin stderr really close it?.


File: python.info,  Node: How do I delete a file? And other file questions…,  Next: How do I copy a file?,  Up: Input and Output<2>

11.4.4.1 How do I delete a file? (And other file questions…)
............................................................

Use ‘os.remove(filename)’ or ‘os.unlink(filename)’; for documentation,
see the *note os: c4. module.  The two functions are identical; *note
unlink(): b18. is simply the name of the Unix system call for this
function.

To remove a directory, use *note os.rmdir(): b16.; use *note os.mkdir():
b12. to create one.  ‘os.makedirs(path)’ will create any intermediate
directories in ‘path’ that don’t exist.  ‘os.removedirs(path)’ will
remove intermediate directories as long as they’re empty; if you want to
delete an entire directory tree and its contents, use *note
shutil.rmtree(): 349.

To rename a file, use ‘os.rename(old_path, new_path)’.

To truncate a file, open it using ‘f = open(filename, "rb+")’, and use
‘f.truncate(offset)’; offset defaults to the current seek position.
There’s also ‘os.ftruncate(fd, offset)’ for files opened with *note
os.open(): 758, where `fd' is the file descriptor (a small integer).

The *note shutil: e9. module also contains a number of functions to work
on files including *note copyfile(): 382, *note copytree(): 347, and
*note rmtree(): 349.


File: python.info,  Node: How do I copy a file?,  Next: How do I read or write binary data?,  Prev: How do I delete a file? And other file questions…,  Up: Input and Output<2>

11.4.4.2 How do I copy a file?
..............................

The *note shutil: e9. module contains a *note copyfile(): 382. function.
Note that on MacOS 9 it doesn’t copy the resource fork and Finder info.


File: python.info,  Node: How do I read or write binary data?,  Next: I can’t seem to use os read on a pipe created with os popen ; why?,  Prev: How do I copy a file?,  Up: Input and Output<2>

11.4.4.3 How do I read (or write) binary data?
..............................................

To read or write complex binary data formats, it’s best to use the *note
struct: f8. module.  It allows you to take a string containing binary
data (usually numbers) and convert it to Python objects; and vice versa.

For example, the following code reads two 2-byte integers and one 4-byte
integer in big-endian format from a file:

     import struct

     with open(filename, "rb") as f:
         s = f.read(8)
         x, y, z = struct.unpack(">hhl", s)

The ‘>’ in the format string forces big-endian data; the letter ‘h’
reads one “short integer” (2 bytes), and ‘l’ reads one “long integer” (4
bytes) from the string.

For data that is more regular (e.g.  a homogeneous list of ints or
floats), you can also use the *note array: 6. module.

     Note: To read and write binary data, it is mandatory to open the
     file in binary mode (here, passing ‘"rb"’ to *note open(): 16f.).
     If you use ‘"r"’ instead (the default), the file will be open in
     text mode and ‘f.read()’ will return *note str: 205. objects rather
     than *note bytes: 172. objects.


File: python.info,  Node: I can’t seem to use os read on a pipe created with os popen ; why?,  Next: How do I access the serial RS232 port?,  Prev: How do I read or write binary data?,  Up: Input and Output<2>

11.4.4.4 I can’t seem to use os.read() on a pipe created with os.popen(); why?
..............................................................................

*note os.read(): 75b. is a low-level function which takes a file
descriptor, a small integer representing the opened file.  *note
os.popen(): 3cb. creates a high-level file object, the same type
returned by the built-in *note open(): 16f. function.  Thus, to read `n'
bytes from a pipe `p' created with *note os.popen(): 3cb, you need to
use ‘p.read(n)’.


File: python.info,  Node: How do I access the serial RS232 port?,  Next: Why doesn’t closing sys stdout stdin stderr really close it?,  Prev: I can’t seem to use os read on a pipe created with os popen ; why?,  Up: Input and Output<2>

11.4.4.5 How do I access the serial (RS232) port?
.................................................

For Win32, OSX, Linux, BSD, Jython, IronPython:

     ‘https://pypi.org/project/pyserial/’

For Unix, see a Usenet post by Mitch Chapman:

     ‘https://groups.google.com/groups?selm=34A04430.CF9@ohioee.com’


File: python.info,  Node: Why doesn’t closing sys stdout stdin stderr really close it?,  Prev: How do I access the serial RS232 port?,  Up: Input and Output<2>

11.4.4.6 Why doesn’t closing sys.stdout (stdin, stderr) really close it?
........................................................................

Python *note file objects: c14. are a high-level layer of abstraction on
low-level C file descriptors.

For most file objects you create in Python via the built-in *note
open(): 16f. function, ‘f.close()’ marks the Python file object as being
closed from Python’s point of view, and also arranges to close the
underlying C file descriptor.  This also happens automatically in ‘f’’s
destructor, when ‘f’ becomes garbage.

But stdin, stdout and stderr are treated specially by Python, because of
the special status also given to them by C. Running ‘sys.stdout.close()’
marks the Python-level file object as being closed, but does `not' close
the associated C file descriptor.

To close the underlying C file descriptor for one of these three, you
should first be sure that’s what you really want to do (e.g., you may
confuse extension modules trying to do I/O). If it is, use *note
os.close(): 4d9.:

     os.close(stdin.fileno())
     os.close(stdout.fileno())
     os.close(stderr.fileno())

Or you can use the numeric constants 0, 1 and 2, respectively.


File: python.info,  Node: Network/Internet Programming,  Next: Databases,  Prev: Input and Output<2>,  Up: Library and Extension FAQ

11.4.5 Network/Internet Programming
-----------------------------------

* Menu:

* What WWW tools are there for Python?::
* How can I mimic CGI form submission (METHOD=POST)?: How can I mimic CGI form submission METHOD=POST ?.
* What module should I use to help with generating HTML?::
* How do I send mail from a Python script?::
* How do I avoid blocking in the connect() method of a socket?: How do I avoid blocking in the connect method of a socket?.


File: python.info,  Node: What WWW tools are there for Python?,  Next: How can I mimic CGI form submission METHOD=POST ?,  Up: Network/Internet Programming

11.4.5.1 What WWW tools are there for Python?
.............................................

See the chapters titled *note Internet Protocols and Support: 2d07. and
*note Internet Data Handling: 291c. in the Library Reference Manual.
Python has many modules that will help you build server-side and
client-side web systems.

A summary of available frameworks is maintained by Paul Boddie at
‘https://wiki.python.org/moin/WebProgramming’.

Cameron Laird maintains a useful set of pages about Python web
technologies at ‘http://phaseit.net/claird/comp.lang.python/web_python’.


File: python.info,  Node: How can I mimic CGI form submission METHOD=POST ?,  Next: What module should I use to help with generating HTML?,  Prev: What WWW tools are there for Python?,  Up: Network/Internet Programming

11.4.5.2 How can I mimic CGI form submission (METHOD=POST)?
...........................................................

I would like to retrieve web pages that are the result of POSTing a
form.  Is there existing code that would let me do this easily?

Yes.  Here’s a simple example that uses *note urllib.request: 129.:

     #!/usr/local/bin/python

     import urllib.request

     # build the query string
     qs = "First=Josephine&MI=Q&Last=Public"

     # connect and send the server a path
     req = urllib.request.urlopen('http://www.some-server.out-there'
                                  '/cgi-bin/some-cgi-script', data=qs)
     with req:
         msg, hdrs = req.read(), req.info()

Note that in general for percent-encoded POST operations, query strings
must be quoted using *note urllib.parse.urlencode(): 87a.  For example,
to send ‘name=Guy Steele, Jr.’:

     >>> import urllib.parse
     >>> urllib.parse.urlencode({'name': 'Guy Steele, Jr.'})
     'name=Guy+Steele%2C+Jr.'

See also
........

*note HOWTO Fetch Internet Resources Using The urllib Package: 2deb. for
extensive examples.


File: python.info,  Node: What module should I use to help with generating HTML?,  Next: How do I send mail from a Python script?,  Prev: How can I mimic CGI form submission METHOD=POST ?,  Up: Network/Internet Programming

11.4.5.3 What module should I use to help with generating HTML?
...............................................................

You can find a collection of useful links on the Web Programming wiki
page(1).

   ---------- Footnotes ----------

   (1) https://wiki.python.org/moin/WebProgramming


File: python.info,  Node: How do I send mail from a Python script?,  Next: How do I avoid blocking in the connect method of a socket?,  Prev: What module should I use to help with generating HTML?,  Up: Network/Internet Programming

11.4.5.4 How do I send mail from a Python script?
.................................................

Use the standard library module *note smtplib: ed.

Here’s a very simple interactive mail sender that uses it.  This method
will work on any host that supports an SMTP listener.

     import sys, smtplib

     fromaddr = input("From: ")
     toaddrs  = input("To: ").split(',')
     print("Enter message, end with ^D:")
     msg = ''
     while True:
         line = sys.stdin.readline()
         if not line:
             break
         msg += line

     # The actual mail send
     server = smtplib.SMTP('localhost')
     server.sendmail(fromaddr, toaddrs, msg)
     server.quit()

A Unix-only alternative uses sendmail.  The location of the sendmail
program varies between systems; sometimes it is ‘/usr/lib/sendmail’,
sometimes ‘/usr/sbin/sendmail’.  The sendmail manual page will help you
out.  Here’s some sample code:

     import os

     SENDMAIL = "/usr/sbin/sendmail"  # sendmail location
     p = os.popen("%s -t -i" % SENDMAIL, "w")
     p.write("To: receiver@example.com\n")
     p.write("Subject: test\n")
     p.write("\n")  # blank line separating headers from body
     p.write("Some text\n")
     p.write("some more text\n")
     sts = p.close()
     if sts != 0:
         print("Sendmail exit status", sts)


File: python.info,  Node: How do I avoid blocking in the connect method of a socket?,  Prev: How do I send mail from a Python script?,  Up: Network/Internet Programming

11.4.5.5 How do I avoid blocking in the connect() method of a socket?
.....................................................................

The *note select: e5. module is commonly used to help with asynchronous
I/O on sockets.

To prevent the TCP connect from blocking, you can set the socket to
non-blocking mode.  Then when you do the ‘socket.connect()’, you will
either connect immediately (unlikely) or get an exception that contains
the error number as ‘.errno’.  ‘errno.EINPROGRESS’ indicates that the
connection is in progress, but hasn’t finished yet.  Different OSes will
return different values, so you’re going to have to check what’s
returned on your system.

You can use the ‘socket.connect_ex()’ method to avoid creating an
exception.  It will just return the errno value.  To poll, you can call
‘socket.connect_ex()’ again later – ‘0’ or ‘errno.EISCONN’ indicate that
you’re connected – or you can pass this socket to *note select.select():
766. to check if it’s writable.

     Note: The *note asyncio: 9. module provides a general purpose
     single-threaded and concurrent asynchronous library, which can be
     used for writing non-blocking network code.  The third-party
     Twisted(1) library is a popular and feature-rich alternative.

   ---------- Footnotes ----------

   (1) https://twistedmatrix.com/trac/


File: python.info,  Node: Databases,  Next: Mathematics and Numerics,  Prev: Network/Internet Programming,  Up: Library and Extension FAQ

11.4.6 Databases
----------------

* Menu:

* Are there any interfaces to database packages in Python?::
* How do you implement persistent objects in Python?::


File: python.info,  Node: Are there any interfaces to database packages in Python?,  Next: How do you implement persistent objects in Python?,  Up: Databases

11.4.6.1 Are there any interfaces to database packages in Python?
.................................................................

Yes.

Interfaces to disk-based hashes such as *note DBM: 34. and *note GDBM:
33. are also included with standard Python.  There is also the *note
sqlite3: f2. module, which provides a lightweight disk-based relational
database.

Support for most relational databases is available.  See the
DatabaseProgramming wiki page(1) for details.

   ---------- Footnotes ----------

   (1) https://wiki.python.org/moin/DatabaseProgramming


File: python.info,  Node: How do you implement persistent objects in Python?,  Prev: Are there any interfaces to database packages in Python?,  Up: Databases

11.4.6.2 How do you implement persistent objects in Python?
...........................................................

The *note pickle: ca. library module solves this in a very general way
(though you still can’t store things like open files, sockets or
windows), and the *note shelve: e7. library module uses pickle and
(g)dbm to create persistent mappings containing arbitrary Python
objects.


File: python.info,  Node: Mathematics and Numerics,  Prev: Databases,  Up: Library and Extension FAQ

11.4.7 Mathematics and Numerics
-------------------------------

* Menu:

* How do I generate random numbers in Python?::


File: python.info,  Node: How do I generate random numbers in Python?,  Up: Mathematics and Numerics

11.4.7.1 How do I generate random numbers in Python?
....................................................

The standard module *note random: dc. implements a random number
generator.  Usage is simple:

     import random
     random.random()

This returns a random floating point number in the range [0, 1).

There are also many other specialized generators in this module, such
as:

   * ‘randrange(a, b)’ chooses an integer in the range [a, b).

   * ‘uniform(a, b)’ chooses a floating point number in the range [a,
     b).

   * ‘normalvariate(mean, sdev)’ samples the normal (Gaussian)
     distribution.

Some higher-level functions operate on sequences directly, such as:

   * ‘choice(S)’ chooses a random element from a given sequence.

   * ‘shuffle(L)’ shuffles a list in-place, i.e.  permutes it randomly.

There’s also a ‘Random’ class you can instantiate to create independent
multiple random number generators.


File: python.info,  Node: Extending/Embedding FAQ,  Next: Python on Windows FAQ,  Prev: Library and Extension FAQ,  Up: Python Frequently Asked Questions

11.5 Extending/Embedding FAQ
============================

* Menu:

* Can I create my own functions in C?::
* Can I create my own functions in C++?::
* Writing C is hard; are there any alternatives?::
* How can I execute arbitrary Python statements from C?::
* How can I evaluate an arbitrary Python expression from C?::
* How do I extract C values from a Python object?::
* How do I use Py_BuildValue() to create a tuple of arbitrary length?: How do I use Py_BuildValue to create a tuple of arbitrary length?.
* How do I call an object’s method from C?::
* How do I catch the output from PyErr_Print() (or anything that prints to stdout/stderr)?: How do I catch the output from PyErr_Print or anything that prints to stdout/stderr ?.
* How do I access a module written in Python from C?::
* How do I interface to C++ objects from Python?::
* I added a module using the Setup file and the make fails; why?::
* How do I debug an extension?::
* I want to compile a Python module on my Linux system, but some files are missing. Why?: I want to compile a Python module on my Linux system but some files are missing Why?.
* How do I tell “incomplete input” from “invalid input”?::
* How do I find undefined g++ symbols __builtin_new or __pure_virtual?::
* Can I create an object class with some methods implemented in C and others in Python (e.g. through inheritance)?: Can I create an object class with some methods implemented in C and others in Python e g through inheritance ?.


File: python.info,  Node: Can I create my own functions in C?,  Next: Can I create my own functions in C++?,  Up: Extending/Embedding FAQ

11.5.1 Can I create my own functions in C?
------------------------------------------

Yes, you can create built-in modules containing functions, variables,
exceptions and even new types in C. This is explained in the document
*note Extending and Embedding the Python Interpreter: 1332.

Most intermediate or advanced Python books will also cover this topic.


File: python.info,  Node: Can I create my own functions in C++?,  Next: Writing C is hard; are there any alternatives?,  Prev: Can I create my own functions in C?,  Up: Extending/Embedding FAQ

11.5.2 Can I create my own functions in C++?
--------------------------------------------

Yes, using the C compatibility features found in C++.  Place ‘extern "C"
{ ... }’ around the Python include files and put ‘extern "C"’ before
each function that is going to be called by the Python interpreter.
Global or static C++ objects with constructors are probably not a good
idea.


File: python.info,  Node: Writing C is hard; are there any alternatives?,  Next: How can I execute arbitrary Python statements from C?,  Prev: Can I create my own functions in C++?,  Up: Extending/Embedding FAQ

11.5.3 Writing C is hard; are there any alternatives?
-----------------------------------------------------

There are a number of alternatives to writing your own C extensions,
depending on what you’re trying to do.

Cython(1) and its relative Pyrex(2) are compilers that accept a slightly
modified form of Python and generate the corresponding C code.  Cython
and Pyrex make it possible to write an extension without having to learn
Python’s C API.

If you need to interface to some C or C++ library for which no Python
extension currently exists, you can try wrapping the library’s data
types and functions with a tool such as SWIG(3). SIP(4), CXX(5)
Boost(6), or Weave(7) are also alternatives for wrapping C++ libraries.

   ---------- Footnotes ----------

   (1) http://cython.org

   (2) https://www.cosc.canterbury.ac.nz/greg.ewing/python/Pyrex/

   (3) http://www.swig.org

   (4) https://riverbankcomputing.com/software/sip/intro

   (5) http://cxx.sourceforge.net/

   (6) http://www.boost.org/libs/python/doc/index.html

   (7) https://github.com/scipy/weave


File: python.info,  Node: How can I execute arbitrary Python statements from C?,  Next: How can I evaluate an arbitrary Python expression from C?,  Prev: Writing C is hard; are there any alternatives?,  Up: Extending/Embedding FAQ

11.5.4 How can I execute arbitrary Python statements from C?
------------------------------------------------------------

The highest-level function to do this is *note PyRun_SimpleString():
3d9c. which takes a single string argument to be executed in the context
of the module ‘__main__’ and returns ‘0’ for success and ‘-1’ when an
exception occurred (including *note SyntaxError: 55a.).  If you want
more control, use *note PyRun_String(): 10e7.; see the source for *note
PyRun_SimpleString(): 3d9c. in ‘Python/pythonrun.c’.


File: python.info,  Node: How can I evaluate an arbitrary Python expression from C?,  Next: How do I extract C values from a Python object?,  Prev: How can I execute arbitrary Python statements from C?,  Up: Extending/Embedding FAQ

11.5.5 How can I evaluate an arbitrary Python expression from C?
----------------------------------------------------------------

Call the function *note PyRun_String(): 10e7. from the previous question
with the start symbol *note Py_eval_input: 3df5.; it parses an
expression, evaluates it and returns its value.


File: python.info,  Node: How do I extract C values from a Python object?,  Next: How do I use Py_BuildValue to create a tuple of arbitrary length?,  Prev: How can I evaluate an arbitrary Python expression from C?,  Up: Extending/Embedding FAQ

11.5.6 How do I extract C values from a Python object?
------------------------------------------------------

That depends on the object’s type.  If it’s a tuple, *note
PyTuple_Size(): 4052. returns its length and *note PyTuple_GetItem():
3d35. returns the item at a specified index.  Lists have similar
functions, ‘PyListSize()’ and *note PyList_GetItem(): 3d36.

For bytes, *note PyBytes_Size(): 3fde. returns its length and *note
PyBytes_AsStringAndSize(): 3fe2. provides a pointer to its value and its
length.  Note that Python bytes objects may contain null bytes so C’s
‘strlen()’ should not be used.

To test the type of an object, first make sure it isn’t ‘NULL’, and then
use *note PyBytes_Check(): de5, *note PyTuple_Check(): 404e, *note
PyList_Check(): 4060, etc.

There is also a high-level API to Python objects which is provided by
the so-called ‘abstract’ interface – read ‘Include/abstract.h’ for
further details.  It allows interfacing with any kind of Python sequence
using calls like *note PySequence_Length(): 3f14, *note
PySequence_GetItem(): 1183, etc.  as well as many other useful protocols
such as numbers (*note PyNumber_Index(): 3f0e. et al.)  and mappings in
the PyMapping APIs.


File: python.info,  Node: How do I use Py_BuildValue to create a tuple of arbitrary length?,  Next: How do I call an object’s method from C?,  Prev: How do I extract C values from a Python object?,  Up: Extending/Embedding FAQ

11.5.7 How do I use Py_BuildValue() to create a tuple of arbitrary length?
--------------------------------------------------------------------------

You can’t.  Use *note PyTuple_Pack(): 4051. instead.


File: python.info,  Node: How do I call an object’s method from C?,  Next: How do I catch the output from PyErr_Print or anything that prints to stdout/stderr ?,  Prev: How do I use Py_BuildValue to create a tuple of arbitrary length?,  Up: Extending/Embedding FAQ

11.5.8 How do I call an object’s method from C?
-----------------------------------------------

The *note PyObject_CallMethod(): 3ee6. function can be used to call an
arbitrary method of an object.  The parameters are the object, the name
of the method to call, a format string like that used with *note
Py_BuildValue(): 3f0, and the argument values:

     PyObject *
     PyObject_CallMethod(PyObject *object, const char *method_name,
                         const char *arg_format, ...);

This works for any object that has methods – whether built-in or
user-defined.  You are responsible for eventually *note Py_DECREF():
38f.’ing the return value.

To call, e.g., a file object’s “seek” method with arguments 10, 0
(assuming the file object pointer is “f”):

     res = PyObject_CallMethod(f, "seek", "(ii)", 10, 0);
     if (res == NULL) {
             ... an exception occurred ...
     }
     else {
             Py_DECREF(res);
     }

Note that since *note PyObject_CallObject(): 3d29. `always' wants a
tuple for the argument list, to call a function without arguments, pass
“()” for the format, and to call a function with one argument, surround
the argument in parentheses, e.g.  “(i)”.


File: python.info,  Node: How do I catch the output from PyErr_Print or anything that prints to stdout/stderr ?,  Next: How do I access a module written in Python from C?,  Prev: How do I call an object’s method from C?,  Up: Extending/Embedding FAQ

11.5.9 How do I catch the output from PyErr_Print() (or anything that prints to stdout/stderr)?
-----------------------------------------------------------------------------------------------

In Python code, define an object that supports the ‘write()’ method.
Assign this object to *note sys.stdout: 41f. and *note sys.stderr: 1ea.
Call print_error, or just allow the standard traceback mechanism to
work.  Then, the output will go wherever your ‘write()’ method sends it.

The easiest way to do this is to use the *note io.StringIO: 91a. class:

     >>> import io, sys
     >>> sys.stdout = io.StringIO()
     >>> print('foo')
     >>> print('hello world!')
     >>> sys.stderr.write(sys.stdout.getvalue())
     foo
     hello world!

A custom object to do the same would look like this:

     >>> import io, sys
     >>> class StdoutCatcher(io.TextIOBase):
     ...     def __init__(self):
     ...         self.data = []
     ...     def write(self, stuff):
     ...         self.data.append(stuff)
     ...
     >>> import sys
     >>> sys.stdout = StdoutCatcher()
     >>> print('foo')
     >>> print('hello world!')
     >>> sys.stderr.write(''.join(sys.stdout.data))
     foo
     hello world!


File: python.info,  Node: How do I access a module written in Python from C?,  Next: How do I interface to C++ objects from Python?,  Prev: How do I catch the output from PyErr_Print or anything that prints to stdout/stderr ?,  Up: Extending/Embedding FAQ

11.5.10 How do I access a module written in Python from C?
----------------------------------------------------------

You can get a pointer to the module object as follows:

     module = PyImport_ImportModule("<modulename>");

If the module hasn’t been imported yet (i.e.  it is not yet present in
*note sys.modules: 1051.), this initializes the module; otherwise it
simply returns the value of ‘sys.modules["<modulename>"]’.  Note that it
doesn’t enter the module into any namespace – it only ensures it has
been initialized and is stored in *note sys.modules: 1051.

You can then access the module’s attributes (i.e.  any name defined in
the module) as follows:

     attr = PyObject_GetAttrString(module, "<attrname>");

Calling *note PyObject_SetAttrString(): 3ec5. to assign to variables in
the module also works.


File: python.info,  Node: How do I interface to C++ objects from Python?,  Next: I added a module using the Setup file and the make fails; why?,  Prev: How do I access a module written in Python from C?,  Up: Extending/Embedding FAQ

11.5.11 How do I interface to C++ objects from Python?
------------------------------------------------------

Depending on your requirements, there are many approaches.  To do this
manually, begin by reading *note the “Extending and Embedding” document:
1332.  Realize that for the Python run-time system, there isn’t a whole
lot of difference between C and C++ – so the strategy of building a new
Python type around a C structure (pointer) type will also work for C++
objects.

For C++ libraries, see *note Writing C is hard; are there any
alternatives?: 44f5.


File: python.info,  Node: I added a module using the Setup file and the make fails; why?,  Next: How do I debug an extension?,  Prev: How do I interface to C++ objects from Python?,  Up: Extending/Embedding FAQ

11.5.12 I added a module using the Setup file and the make fails; why?
----------------------------------------------------------------------

Setup must end in a newline, if there is no newline there, the build
process fails.  (Fixing this requires some ugly shell script hackery,
and this bug is so minor that it doesn’t seem worth the effort.)


File: python.info,  Node: How do I debug an extension?,  Next: I want to compile a Python module on my Linux system but some files are missing Why?,  Prev: I added a module using the Setup file and the make fails; why?,  Up: Extending/Embedding FAQ

11.5.13 How do I debug an extension?
------------------------------------

When using GDB with dynamically loaded extensions, you can’t set a
breakpoint in your extension until your extension is loaded.

In your ‘.gdbinit’ file (or interactively), add the command:

     br _PyImport_LoadDynamicModule

Then, when you run GDB:

     $ gdb /local/bin/python
     gdb) run myscript.py
     gdb) continue # repeat until your extension is loaded
     gdb) finish   # so that your extension is loaded
     gdb) br myfunction.c:50
     gdb) continue


File: python.info,  Node: I want to compile a Python module on my Linux system but some files are missing Why?,  Next: How do I tell “incomplete input” from “invalid input”?,  Prev: How do I debug an extension?,  Up: Extending/Embedding FAQ

11.5.14 I want to compile a Python module on my Linux system, but some files are missing. Why?
----------------------------------------------------------------------------------------------

Most packaged versions of Python don’t include the
‘/usr/lib/python2.`x'/config/’ directory, which contains various files
required for compiling Python extensions.

For Red Hat, install the python-devel RPM to get the necessary files.

For Debian, run ‘apt-get install python-dev’.


File: python.info,  Node: How do I tell “incomplete input” from “invalid input”?,  Next: How do I find undefined g++ symbols __builtin_new or __pure_virtual?,  Prev: I want to compile a Python module on my Linux system but some files are missing Why?,  Up: Extending/Embedding FAQ

11.5.15 How do I tell “incomplete input” from “invalid input”?
--------------------------------------------------------------

Sometimes you want to emulate the Python interactive interpreter’s
behavior, where it gives you a continuation prompt when the input is
incomplete (e.g.  you typed the start of an “if” statement or you didn’t
close your parentheses or triple string quotes), but it gives you a
syntax error message immediately when the input is invalid.

In Python you can use the *note codeop: 1c. module, which approximates
the parser’s behavior sufficiently.  IDLE uses this, for example.

The easiest way to do it in C is to call *note PyRun_InteractiveLoop():
3ddf. (perhaps in a separate thread) and let the Python interpreter
handle the input for you.  You can also set the *note
PyOS_ReadlineFunctionPointer(): a4d. to point at your custom input
function.  See ‘Modules/readline.c’ and ‘Parser/myreadline.c’ for more
hints.

However sometimes you have to run the embedded Python interpreter in the
same thread as your rest application and you can’t allow the *note
PyRun_InteractiveLoop(): 3ddf. to stop while waiting for user input.
The one solution then is to call ‘PyParser_ParseString()’ and test for
‘e.error’ equal to ‘E_EOF’, which means the input is incomplete.  Here’s
a sample code fragment, untested, inspired by code from Alex Farber:

     #define PY_SSIZE_T_CLEAN
     #include <Python.h>
     #include <node.h>
     #include <errcode.h>
     #include <grammar.h>
     #include <parsetok.h>
     #include <compile.h>

     int testcomplete(char *code)
       /* code should end in \n */
       /* return -1 for error, 0 for incomplete, 1 for complete */
     {
       node *n;
       perrdetail e;

       n = PyParser_ParseString(code, &_PyParser_Grammar,
                                Py_file_input, &e);
       if (n == NULL) {
         if (e.error == E_EOF)
           return 0;
         return -1;
       }

       PyNode_Free(n);
       return 1;
     }

Another solution is trying to compile the received string with *note
Py_CompileString(): 3ded.  If it compiles without errors, try to execute
the returned code object by calling *note PyEval_EvalCode(): 3df1.
Otherwise save the input for later.  If the compilation fails, find out
if it’s an error or just more input is required - by extracting the
message string from the exception tuple and comparing it to the string
“unexpected EOF while parsing”.  Here is a complete example using the
GNU readline library (you may want to ignore `SIGINT' while calling
readline()):

     #include <stdio.h>
     #include <readline.h>

     #define PY_SSIZE_T_CLEAN
     #include <Python.h>
     #include <object.h>
     #include <compile.h>
     #include <eval.h>

     int main (int argc, char* argv[])
     {
       int i, j, done = 0;                          /* lengths of line, code */
       char ps1[] = ">>> ";
       char ps2[] = "... ";
       char *prompt = ps1;
       char *msg, *line, *code = NULL;
       PyObject *src, *glb, *loc;
       PyObject *exc, *val, *trb, *obj, *dum;

       Py_Initialize ();
       loc = PyDict_New ();
       glb = PyDict_New ();
       PyDict_SetItemString (glb, "__builtins__", PyEval_GetBuiltins ());

       while (!done)
       {
         line = readline (prompt);

         if (NULL == line)                          /* Ctrl-D pressed */
         {
           done = 1;
         }
         else
         {
           i = strlen (line);

           if (i > 0)
             add_history (line);                    /* save non-empty lines */

           if (NULL == code)                        /* nothing in code yet */
             j = 0;
           else
             j = strlen (code);

           code = realloc (code, i + j + 2);
           if (NULL == code)                        /* out of memory */
             exit (1);

           if (0 == j)                              /* code was empty, so */
             code[0] = '\0';                        /* keep strncat happy */

           strncat (code, line, i);                 /* append line to code */
           code[i + j] = '\n';                      /* append '\n' to code */
           code[i + j + 1] = '\0';

           src = Py_CompileString (code, "<stdin>", Py_single_input);

           if (NULL != src)                         /* compiled just fine - */
           {
             if (ps1  == prompt ||                  /* ">>> " or */
                 '\n' == code[i + j - 1])           /* "... " and double '\n' */
             {                                               /* so execute it */
               dum = PyEval_EvalCode (src, glb, loc);
               Py_XDECREF (dum);
               Py_XDECREF (src);
               free (code);
               code = NULL;
               if (PyErr_Occurred ())
                 PyErr_Print ();
               prompt = ps1;
             }
           }                                        /* syntax error or E_EOF? */
           else if (PyErr_ExceptionMatches (PyExc_SyntaxError))
           {
             PyErr_Fetch (&exc, &val, &trb);        /* clears exception! */

             if (PyArg_ParseTuple (val, "sO", &msg, &obj) &&
                 !strcmp (msg, "unexpected EOF while parsing")) /* E_EOF */
             {
               Py_XDECREF (exc);
               Py_XDECREF (val);
               Py_XDECREF (trb);
               prompt = ps2;
             }
             else                                   /* some other syntax error */
             {
               PyErr_Restore (exc, val, trb);
               PyErr_Print ();
               free (code);
               code = NULL;
               prompt = ps1;
             }
           }
           else                                     /* some non-syntax error */
           {
             PyErr_Print ();
             free (code);
             code = NULL;
             prompt = ps1;
           }

           free (line);
         }
       }

       Py_XDECREF(glb);
       Py_XDECREF(loc);
       Py_Finalize();
       exit(0);
     }


File: python.info,  Node: How do I find undefined g++ symbols __builtin_new or __pure_virtual?,  Next: Can I create an object class with some methods implemented in C and others in Python e g through inheritance ?,  Prev: How do I tell “incomplete input” from “invalid input”?,  Up: Extending/Embedding FAQ

11.5.16 How do I find undefined g++ symbols __builtin_new or __pure_virtual?
----------------------------------------------------------------------------

To dynamically load g++ extension modules, you must recompile Python,
relink it using g++ (change LINKCC in the Python Modules Makefile), and
link your extension module using g++ (e.g., ‘g++ -shared -o mymodule.so
mymodule.o’).


File: python.info,  Node: Can I create an object class with some methods implemented in C and others in Python e g through inheritance ?,  Prev: How do I find undefined g++ symbols __builtin_new or __pure_virtual?,  Up: Extending/Embedding FAQ

11.5.17 Can I create an object class with some methods implemented in C and others in Python (e.g. through inheritance)?
------------------------------------------------------------------------------------------------------------------------

Yes, you can inherit from built-in classes such as *note int: 204, *note
list: 1f8, *note dict: 164, etc.

The Boost Python Library (BPL,
‘http://www.boost.org/libs/python/doc/index.html’) provides a way of
doing this from C++ (i.e.  you can inherit from an extension class
written in C++ using the BPL).


File: python.info,  Node: Python on Windows FAQ,  Next: Graphic User Interface FAQ,  Prev: Extending/Embedding FAQ,  Up: Python Frequently Asked Questions

11.6 Python on Windows FAQ
==========================

* Menu:

* How do I run a Python program under Windows?::
* How do I make Python scripts executable?::
* Why does Python sometimes take so long to start?::
* How do I make an executable from a Python script?::
* Is a *.pyd file the same as a DLL?: Is a * pyd file the same as a DLL?.
* How can I embed Python into a Windows application?::
* How do I keep editors from inserting tabs into my Python source?::
* How do I check for a keypress without blocking?::


File: python.info,  Node: How do I run a Python program under Windows?,  Next: How do I make Python scripts executable?,  Up: Python on Windows FAQ

11.6.1 How do I run a Python program under Windows?
---------------------------------------------------

This is not necessarily a straightforward question.  If you are already
familiar with running programs from the Windows command line then
everything will seem obvious; otherwise, you might need a little more
guidance.

Unless you use some sort of integrated development environment, you will
end up `typing' Windows commands into what is variously referred to as a
“DOS window” or “Command prompt window”.  Usually you can create such a
window from your search bar by searching for ‘cmd’.  You should be able
to recognize when you have started such a window because you will see a
Windows “command prompt”, which usually looks like this:

     C:\>

The letter may be different, and there might be other things after it,
so you might just as easily see something like:

     D:\YourName\Projects\Python>

depending on how your computer has been set up and what else you have
recently done with it.  Once you have started such a window, you are
well on the way to running Python programs.

You need to realize that your Python scripts have to be processed by
another program called the Python `interpreter'.  The interpreter reads
your script, compiles it into bytecodes, and then executes the bytecodes
to run your program.  So, how do you arrange for the interpreter to
handle your Python?

First, you need to make sure that your command window recognises the
word “py” as an instruction to start the interpreter.  If you have
opened a command window, you should try entering the command ‘py’ and
hitting return:

     C:\Users\YourName> py

You should then see something like:

     Python 3.6.4 (v3.6.4:d48eceb, Dec 19 2017, 06:04:45) [MSC v.1900 32 bit (Intel)] on win32
     Type "help", "copyright", "credits" or "license" for more information.
     >>>

You have started the interpreter in “interactive mode”.  That means you
can enter Python statements or expressions interactively and have them
executed or evaluated while you wait.  This is one of Python’s strongest
features.  Check it by entering a few expressions of your choice and
seeing the results:

     >>> print("Hello")
     Hello
     >>> "Hello" * 3
     'HelloHelloHello'

Many people use the interactive mode as a convenient yet highly
programmable calculator.  When you want to end your interactive Python
session, call the *note exit(): 1743. function or hold the ‘Ctrl’ key
down while you enter a ‘Z’, then hit the “‘Enter’” key to get back to
your Windows command prompt.

You may also find that you have a Start-menu entry such as Start ‣
Programs ‣ Python 3.x ‣ Python (command line) that results in you seeing
the ‘>>>’ prompt in a new window.  If so, the window will disappear
after you call the *note exit(): 1743. function or enter the ‘Ctrl-Z’
character; Windows is running a single “python” command in the window,
and closes it when you terminate the interpreter.

Now that we know the ‘py’ command is recognized, you can give your
Python script to it.  You’ll have to give either an absolute or a
relative path to the Python script.  Let’s say your Python script is
located in your desktop and is named ‘hello.py’, and your command prompt
is nicely opened in your home directory so you’re seeing something
similar to:

     C:\Users\YourName>

So now you’ll ask the ‘py’ command to give your script to Python by
typing ‘py’ followed by your script path:

     C:\Users\YourName> py Desktop\hello.py
     hello


File: python.info,  Node: How do I make Python scripts executable?,  Next: Why does Python sometimes take so long to start?,  Prev: How do I run a Python program under Windows?,  Up: Python on Windows FAQ

11.6.2 How do I make Python scripts executable?
-----------------------------------------------

On Windows, the standard Python installer already associates the .py
extension with a file type (Python.File) and gives that file type an
open command that runs the interpreter (‘D:\Program
Files\Python\python.exe "%1" %*’).  This is enough to make scripts
executable from the command prompt as ‘foo.py’.  If you’d rather be able
to execute the script by simple typing ‘foo’ with no extension you need
to add .py to the PATHEXT environment variable.


File: python.info,  Node: Why does Python sometimes take so long to start?,  Next: How do I make an executable from a Python script?,  Prev: How do I make Python scripts executable?,  Up: Python on Windows FAQ

11.6.3 Why does Python sometimes take so long to start?
-------------------------------------------------------

Usually Python starts very quickly on Windows, but occasionally there
are bug reports that Python suddenly begins to take a long time to start
up.  This is made even more puzzling because Python will work fine on
other Windows systems which appear to be configured identically.

The problem may be caused by a misconfiguration of virus checking
software on the problem machine.  Some virus scanners have been known to
introduce startup overhead of two orders of magnitude when the scanner
is configured to monitor all reads from the filesystem.  Try checking
the configuration of virus scanning software on your systems to ensure
that they are indeed configured identically.  McAfee, when configured to
scan all file system read activity, is a particular offender.


File: python.info,  Node: How do I make an executable from a Python script?,  Next: Is a * pyd file the same as a DLL?,  Prev: Why does Python sometimes take so long to start?,  Up: Python on Windows FAQ

11.6.4 How do I make an executable from a Python script?
--------------------------------------------------------

See *note How can I create a stand-alone binary from a Python script?:
4465. for a list of tools that can be used to make executables.


File: python.info,  Node: Is a * pyd file the same as a DLL?,  Next: How can I embed Python into a Windows application?,  Prev: How do I make an executable from a Python script?,  Up: Python on Windows FAQ

11.6.5 Is a ‘*.pyd’ file the same as a DLL?
-------------------------------------------

Yes, .pyd files are dll’s, but there are a few differences.  If you have
a DLL named ‘foo.pyd’, then it must have a function ‘PyInit_foo()’.  You
can then write Python “import foo”, and Python will search for foo.pyd
(as well as foo.py, foo.pyc) and if it finds it, will attempt to call
‘PyInit_foo()’ to initialize it.  You do not link your .exe with
foo.lib, as that would cause Windows to require the DLL to be present.

Note that the search path for foo.pyd is PYTHONPATH, not the same as the
path that Windows uses to search for foo.dll.  Also, foo.pyd need not be
present to run your program, whereas if you linked your program with a
dll, the dll is required.  Of course, foo.pyd is required if you want to
say ‘import foo’.  In a DLL, linkage is declared in the source code with
‘__declspec(dllexport)’.  In a .pyd, linkage is defined in a list of
available functions.


File: python.info,  Node: How can I embed Python into a Windows application?,  Next: How do I keep editors from inserting tabs into my Python source?,  Prev: Is a * pyd file the same as a DLL?,  Up: Python on Windows FAQ

11.6.6 How can I embed Python into a Windows application?
---------------------------------------------------------

Embedding the Python interpreter in a Windows app can be summarized as
follows:

  1. Do _not_ build Python into your .exe file directly.  On Windows,
     Python must be a DLL to handle importing modules that are
     themselves DLL’s.  (This is the first key undocumented fact.)
     Instead, link to ‘python`NN'.dll’; it is typically installed in
     ‘C:\Windows\System’.  `NN' is the Python version, a number such as
     “33” for Python 3.3.

     You can link to Python in two different ways.  Load-time linking
     means linking against ‘python`NN'.lib’, while run-time linking
     means linking against ‘python`NN'.dll’.  (General note:
     ‘python`NN'.lib’ is the so-called “import lib” corresponding to
     ‘python`NN'.dll’.  It merely defines symbols for the linker.)

     Run-time linking greatly simplifies link options; everything
     happens at run time.  Your code must load ‘python`NN'.dll’ using
     the Windows ‘LoadLibraryEx()’ routine.  The code must also use
     access routines and data in ‘python`NN'.dll’ (that is, Python’s C
     API’s) using pointers obtained by the Windows ‘GetProcAddress()’
     routine.  Macros can make using these pointers transparent to any C
     code that calls routines in Python’s C API.

     Borland note: convert ‘python`NN'.lib’ to OMF format using
     Coff2Omf.exe first.

  2. If you use SWIG, it is easy to create a Python “extension module”
     that will make the app’s data and methods available to Python.
     SWIG will handle just about all the grungy details for you.  The
     result is C code that you link `into' your .exe file (!)  You do
     _not_ have to create a DLL file, and this also simplifies linking.

  3. SWIG will create an init function (a C function) whose name depends
     on the name of the extension module.  For example, if the name of
     the module is leo, the init function will be called initleo().  If
     you use SWIG shadow classes, as you should, the init function will
     be called initleoc().  This initializes a mostly hidden helper
     class used by the shadow class.

     The reason you can link the C code in step 2 into your .exe file is
     that calling the initialization function is equivalent to importing
     the module into Python!  (This is the second key undocumented
     fact.)

  4. In short, you can use the following code to initialize the Python
     interpreter with your extension module.

          #include "python.h"
          ...
          Py_Initialize();  // Initialize Python.
          initmyAppc();  // Initialize (import) the helper class.
          PyRun_SimpleString("import myApp");  // Import the shadow class.

  5. There are two problems with Python’s C API which will become
     apparent if you use a compiler other than MSVC, the compiler used
     to build pythonNN.dll.

     Problem 1: The so-called “Very High Level” functions that take FILE
     * arguments will not work in a multi-compiler environment because
     each compiler’s notion of a struct FILE will be different.  From an
     implementation standpoint these are very _low_ level functions.

     Problem 2: SWIG generates the following code when generating
     wrappers to void functions:

          Py_INCREF(Py_None);
          _resultobj = Py_None;
          return _resultobj;

     Alas, Py_None is a macro that expands to a reference to a complex
     data structure called _Py_NoneStruct inside pythonNN.dll.  Again,
     this code will fail in a mult-compiler environment.  Replace such
     code by:

          return Py_BuildValue("");

     It may be possible to use SWIG’s ‘%typemap’ command to make the
     change automatically, though I have not been able to get this to
     work (I’m a complete SWIG newbie).

  6. Using a Python shell script to put up a Python interpreter window
     from inside your Windows app is not a good idea; the resulting
     window will be independent of your app’s windowing system.  Rather,
     you (or the wxPythonWindow class) should create a “native”
     interpreter window.  It is easy to connect that window to the
     Python interpreter.  You can redirect Python’s i/o to _any_ object
     that supports read and write, so all you need is a Python object
     (defined in your extension module) that contains read() and write()
     methods.


File: python.info,  Node: How do I keep editors from inserting tabs into my Python source?,  Next: How do I check for a keypress without blocking?,  Prev: How can I embed Python into a Windows application?,  Up: Python on Windows FAQ

11.6.7 How do I keep editors from inserting tabs into my Python source?
-----------------------------------------------------------------------

The FAQ does not recommend using tabs, and the Python style guide, PEP
8(1), recommends 4 spaces for distributed Python code; this is also the
Emacs python-mode default.

Under any editor, mixing tabs and spaces is a bad idea.  MSVC is no
different in this respect, and is easily configured to use spaces: Take
Tools ‣ Options ‣ Tabs, and for file type “Default” set “Tab size” and
“Indent size” to 4, and select the “Insert spaces” radio button.

Python raises *note IndentationError: f39. or *note TabError: f38. if
mixed tabs and spaces are causing problems in leading whitespace.  You
may also run the *note tabnanny: 100. module to check a directory tree
in batch mode.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0008


File: python.info,  Node: How do I check for a keypress without blocking?,  Prev: How do I keep editors from inserting tabs into my Python source?,  Up: Python on Windows FAQ

11.6.8 How do I check for a keypress without blocking?
------------------------------------------------------

Use the *note msvcrt: b6. module.  This is a standard Windows-specific
extension module.  It defines a function ‘kbhit()’ which checks whether
a keyboard hit is present, and ‘getch()’ which gets one character
without echoing it.


File: python.info,  Node: Graphic User Interface FAQ,  Next: “Why is Python Installed on my Computer?” FAQ,  Prev: Python on Windows FAQ,  Up: Python Frequently Asked Questions

11.7 Graphic User Interface FAQ
===============================

* Menu:

* General GUI Questions::
* What GUI toolkits exist for Python?::
* Tkinter questions::


File: python.info,  Node: General GUI Questions,  Next: What GUI toolkits exist for Python?,  Up: Graphic User Interface FAQ

11.7.1 General GUI Questions
----------------------------


File: python.info,  Node: What GUI toolkits exist for Python?,  Next: Tkinter questions,  Prev: General GUI Questions,  Up: Graphic User Interface FAQ

11.7.2 What GUI toolkits exist for Python?
------------------------------------------

Standard builds of Python include an object-oriented interface to the
Tcl/Tk widget set, called *note tkinter: 32ac.  This is probably the
easiest to install (since it comes included with most binary
distributions(1) of Python) and use.  For more info about Tk, including
pointers to the source, see the Tcl/Tk home page(2).  Tcl/Tk is fully
portable to the macOS, Windows, and Unix platforms.

Depending on what platform(s) you are aiming at, there are also several
alternatives.  A list of cross-platform(3) and platform-specific(4) GUI
frameworks can be found on the python wiki.

   ---------- Footnotes ----------

   (1) https://www.python.org/downloads/

   (2) https://www.tcl.tk

   (3) 
https://wiki.python.org/moin/GuiProgramming#Cross-Platform_Frameworks

   (4) 
https://wiki.python.org/moin/GuiProgramming#Platform-specific_Frameworks


File: python.info,  Node: Tkinter questions,  Prev: What GUI toolkits exist for Python?,  Up: Graphic User Interface FAQ

11.7.3 Tkinter questions
------------------------

* Menu:

* How do I freeze Tkinter applications?::
* Can I have Tk events handled while waiting for I/O?::
* I can’t get key bindings to work in Tkinter; why?: I can’t get key bindings to work in Tkinter why?.


File: python.info,  Node: How do I freeze Tkinter applications?,  Next: Can I have Tk events handled while waiting for I/O?,  Up: Tkinter questions

11.7.3.1 How do I freeze Tkinter applications?
..............................................

Freeze is a tool to create stand-alone applications.  When freezing
Tkinter applications, the applications will not be truly stand-alone, as
the application will still need the Tcl and Tk libraries.

One solution is to ship the application with the Tcl and Tk libraries,
and point to them at run-time using the ‘TCL_LIBRARY’ and ‘TK_LIBRARY’
environment variables.

To get truly stand-alone applications, the Tcl scripts that form the
library have to be integrated into the application as well.  One tool
supporting that is SAM (stand-alone modules), which is part of the Tix
distribution (‘http://tix.sourceforge.net/’).

Build Tix with SAM enabled, perform the appropriate call to
‘Tclsam_init()’, etc.  inside Python’s ‘Modules/tkappinit.c’, and link
with libtclsam and libtksam (you might include the Tix libraries as
well).


File: python.info,  Node: Can I have Tk events handled while waiting for I/O?,  Next: I can’t get key bindings to work in Tkinter why?,  Prev: How do I freeze Tkinter applications?,  Up: Tkinter questions

11.7.3.2 Can I have Tk events handled while waiting for I/O?
............................................................

On platforms other than Windows, yes, and you don’t even need threads!
But you’ll have to restructure your I/O code a bit.  Tk has the
equivalent of Xt’s ‘XtAddInput()’ call, which allows you to register a
callback function which will be called from the Tk mainloop when I/O is
possible on a file descriptor.  See *note File Handlers: 32c6.


File: python.info,  Node: I can’t get key bindings to work in Tkinter why?,  Prev: Can I have Tk events handled while waiting for I/O?,  Up: Tkinter questions

11.7.3.3 I can’t get key bindings to work in Tkinter: why?
..........................................................

An often-heard complaint is that event handlers bound to events with the
‘bind()’ method don’t get handled even when the appropriate key is
pressed.

The most common cause is that the widget to which the binding applies
doesn’t have “keyboard focus”.  Check out the Tk documentation for the
focus command.  Usually a widget is given the keyboard focus by clicking
in it (but not for labels; see the takefocus option).


File: python.info,  Node: “Why is Python Installed on my Computer?” FAQ,  Prev: Graphic User Interface FAQ,  Up: Python Frequently Asked Questions

11.8 “Why is Python Installed on my Computer?” FAQ
==================================================

* Menu:

* What is Python?: What is Python?<2>.
* Why is Python installed on my machine?::
* Can I delete Python?::


File: python.info,  Node: What is Python?<2>,  Next: Why is Python installed on my machine?,  Up: “Why is Python Installed on my Computer?” FAQ

11.8.1 What is Python?
----------------------

Python is a programming language.  It’s used for many different
applications.  It’s used in some high schools and colleges as an
introductory programming language because Python is easy to learn, but
it’s also used by professional software developers at places such as
Google, NASA, and Lucasfilm Ltd.

If you wish to learn more about Python, start with the Beginner’s Guide
to Python(1).

   ---------- Footnotes ----------

   (1) https://wiki.python.org/moin/BeginnersGuide


File: python.info,  Node: Why is Python installed on my machine?,  Next: Can I delete Python?,  Prev: What is Python?<2>,  Up: “Why is Python Installed on my Computer?” FAQ

11.8.2 Why is Python installed on my machine?
---------------------------------------------

If you find Python installed on your system but don’t remember
installing it, there are several possible ways it could have gotten
there.

   * Perhaps another user on the computer wanted to learn programming
     and installed it; you’ll have to figure out who’s been using the
     machine and might have installed it.

   * A third-party application installed on the machine might have been
     written in Python and included a Python installation.  There are
     many such applications, from GUI programs to network servers and
     administrative scripts.

   * Some Windows machines also have Python installed.  At this writing
     we’re aware of computers from Hewlett-Packard and Compaq that
     include Python.  Apparently some of HP/Compaq’s administrative
     tools are written in Python.

   * Many Unix-compatible operating systems, such as macOS and some
     Linux distributions, have Python installed by default; it’s
     included in the base installation.


File: python.info,  Node: Can I delete Python?,  Prev: Why is Python installed on my machine?,  Up: “Why is Python Installed on my Computer?” FAQ

11.8.3 Can I delete Python?
---------------------------

That depends on where Python came from.

If someone installed it deliberately, you can remove it without hurting
anything.  On Windows, use the Add/Remove Programs icon in the Control
Panel.

If Python was installed by a third-party application, you can also
remove it, but that application will no longer work.  You should use
that application’s uninstaller rather than removing Python directly.

If Python came with your operating system, removing it is not
recommended.  If you remove it, whatever tools were written in Python
will no longer run, and some of them might be important to you.
Reinstalling the whole system would then be required to fix things
again.


File: python.info,  Node: Glossary,  Next: About these documents,  Prev: Python Frequently Asked Questions,  Up: Top

12 Glossary
***********

‘>>>’

     The default Python prompt of the interactive shell.  Often seen for
     code examples which can be executed interactively in the
     interpreter.

‘...’

     Can refer to:

        * The default Python prompt of the interactive shell when
          entering the code for an indented code block, when within a
          pair of matching left and right delimiters (parentheses,
          square brackets, curly braces or triple quotes), or after
          specifying a decorator.

        * The *note Ellipsis: 1740. built-in constant.

2to3

     A tool that tries to convert Python 2.x code to Python 3.x code by
     handling most of the incompatibilities which can be detected by
     parsing the source and traversing the parse tree.

     2to3 is available in the standard library as *note lib2to3: a7.; a
     standalone entry point is provided as ‘Tools/scripts/2to3’.  See
     *note 2to3 - Automated Python 2 to 3 code translation: d3e.

abstract base class

     Abstract base classes complement *note duck-typing: 4520. by
     providing a way to define interfaces when other techniques like
     *note hasattr(): 54a. would be clumsy or subtly wrong (for example
     with *note magic methods: 156f.).  ABCs introduce virtual
     subclasses, which are classes that don’t inherit from a class but
     are still recognized by *note isinstance(): 552. and *note
     issubclass(): 553.; see the *note abc: 3. module documentation.
     Python comes with many built-in ABCs for data structures (in the
     *note collections.abc: 1e. module), numbers (in the *note numbers:
     c1. module), streams (in the *note io: a1. module), import finders
     and loaders (in the *note importlib.abc: 9b. module).  You can
     create your own ABCs with the *note abc: 3. module.

annotation

     A label associated with a variable, a class attribute or a function
     parameter or return value, used by convention as a *note type hint:
     158b.

     Annotations of local variables cannot be accessed at runtime, but
     annotations of global variables, class attributes, and functions
     are stored in the ‘__annotations__’ special attribute of modules,
     classes, and functions, respectively.

     See *note variable annotation: 712, *note function annotation:
     1391, PEP 484(1) and PEP 526(2), which describe this functionality.

argument

     A value passed to a *note function: 165b. (or *note method: 4521.)
     when calling the function.  There are two kinds of argument:

        * `keyword argument': an argument preceded by an identifier
          (e.g.  ‘name=’) in a function call or passed as a value in a
          dictionary preceded by ‘**’.  For example, ‘3’ and ‘5’ are
          both keyword arguments in the following calls to *note
          complex(): 2c1.:

               complex(real=3, imag=5)
               complex(**{'real': 3, 'imag': 5})

        * `positional argument': an argument that is not a keyword
          argument.  Positional arguments can appear at the beginning of
          an argument list and/or be passed as elements of an *note
          iterable: c7c. preceded by ‘*’.  For example, ‘3’ and ‘5’ are
          both positional arguments in the following calls:

               complex(3, 5)
               complex(*(3, 5))

     Arguments are assigned to the named local variables in a function
     body.  See the *note Calls: 73f. section for the rules governing
     this assignment.  Syntactically, any expression can be used to
     represent an argument; the evaluated value is assigned to the local
     variable.

     See also the *note parameter: 1664. glossary entry, the FAQ
     question on *note the difference between arguments and parameters:
     4470, and PEP 362(3).

asynchronous context manager

     An object which controls the environment seen in an *note async
     with: 736. statement by defining *note __aenter__(): 109a. and
     *note __aexit__(): 109b. methods.  Introduced by PEP 492(4).

asynchronous generator

     A function which returns an *note asynchronous generator iterator:
     37b7.  It looks like a coroutine function defined with *note async
     def: 3a9. except that it contains *note yield: 2c7. expressions for
     producing a series of values usable in an *note async for: 3fd.
     loop.

     Usually refers to an asynchronous generator function, but may refer
     to an `asynchronous generator iterator' in some contexts.  In cases
     where the intended meaning isn’t clear, using the full terms avoids
     ambiguity.

     An asynchronous generator function may contain *note await: 2d8.
     expressions as well as *note async for: 3fd, and *note async with:
     736. statements.

asynchronous generator iterator

     An object created by a *note asynchronous generator: 1640.
     function.

     This is an *note asynchronous iterator: 738. which when called
     using the *note __anext__(): 155f. method returns an awaitable
     object which will execute the body of the asynchronous generator
     function until the next *note yield: 2c7. expression.

     Each *note yield: 2c7. temporarily suspends processing, remembering
     the location execution state (including local variables and pending
     try-statements).  When the `asynchronous generator iterator'
     effectively resumes with another awaitable returned by *note
     __anext__(): 155f, it picks up where it left off.  See PEP 492(5)
     and PEP 525(6).

asynchronous iterable

     An object, that can be used in an *note async for: 3fd. statement.
     Must return an *note asynchronous iterator: 738. from its *note
     __aiter__(): 583. method.  Introduced by PEP 492(7).

asynchronous iterator

     An object that implements the *note __aiter__(): 583. and *note
     __anext__(): 155f. methods.  ‘__anext__’ must return an *note
     awaitable: 613. object.  *note async for: 3fd. resolves the
     awaitables returned by an asynchronous iterator’s *note
     __anext__(): 155f. method until it raises a *note
     StopAsyncIteration: 114a. exception.  Introduced by PEP 492(8).

attribute

     A value associated with an object which is referenced by name using
     dotted expressions.  For example, if an object `o' has an attribute
     `a' it would be referenced as `o.a'.

awaitable

     An object that can be used in an *note await: 2d8. expression.  Can
     be a *note coroutine: 18a. or an object with an *note __await__():
     735. method.  See also PEP 492(9).

BDFL

     Benevolent Dictator For Life, a.k.a.  Guido van Rossum(10),
     Python’s creator.

binary file

     A *note file object: c14. able to read and write *note bytes-like
     objects: 6df.  Examples of binary files are files opened in binary
     mode (‘'rb'’, ‘'wb'’ or ‘'rb+'’), ‘sys.stdin.buffer’,
     ‘sys.stdout.buffer’, and instances of *note io.BytesIO: 88a. and
     *note gzip.GzipFile: 206.

     See also *note text file: 13d9. for a file object able to read and
     write *note str: 205. objects.

bytes-like object

     An object that supports the *note Buffer Protocol: 171c. and can
     export a C-*note contiguous: 17ec. buffer.  This includes all *note
     bytes: 172, *note bytearray: 173, and *note array.array: 216.
     objects, as well as many common *note memoryview: 386. objects.
     Bytes-like objects can be used for various operations that work
     with binary data; these include compression, saving to a binary
     file, and sending over a socket.

     Some operations need the binary data to be mutable.  The
     documentation often refers to these as “read-write bytes-like
     objects”.  Example mutable buffer objects include *note bytearray:
     173. and a *note memoryview: 386. of a *note bytearray: 173.  Other
     operations require the binary data to be stored in immutable
     objects (“read-only bytes-like objects”); examples of these include
     *note bytes: 172. and a *note memoryview: 386. of a *note bytes:
     172. object.

bytecode

     Python source code is compiled into bytecode, the internal
     representation of a Python program in the CPython interpreter.  The
     bytecode is also cached in ‘.pyc’ files so that executing the same
     file is faster the second time (recompilation from source to
     bytecode can be avoided).  This “intermediate language” is said to
     run on a *note virtual machine: 28d0. that executes the machine
     code corresponding to each bytecode.  Do note that bytecodes are
     not expected to work between different Python virtual machines, nor
     to be stable between Python releases.

     A list of bytecode instructions can be found in the documentation
     for *note the dis module: 3a9d.

callback

     A subroutine function which is passed as an argument to be executed
     at some point in the future.

class

     A template for creating user-defined objects.  Class definitions
     normally contain method definitions which operate on instances of
     the class.

class variable

     A variable defined in a class and intended to be modified only at
     class level (i.e., not in an instance of the class).

coercion

     The implicit conversion of an instance of one type to another
     during an operation which involves two arguments of the same type.
     For example, ‘int(3.15)’ converts the floating point number to the
     integer ‘3’, but in ‘3+4.5’, each argument is of a different type
     (one int, one float), and both must be converted to the same type
     before they can be added or it will raise a *note TypeError: 1fe.
     Without coercion, all arguments of even compatible types would have
     to be normalized to the same value by the programmer, e.g.,
     ‘float(3)+4.5’ rather than just ‘3+4.5’.

complex number

     An extension of the familiar real number system in which all
     numbers are expressed as a sum of a real part and an imaginary
     part.  Imaginary numbers are real multiples of the imaginary unit
     (the square root of ‘-1’), often written ‘i’ in mathematics or ‘j’
     in engineering.  Python has built-in support for complex numbers,
     which are written with this latter notation; the imaginary part is
     written with a ‘j’ suffix, e.g., ‘3+1j’.  To get access to complex
     equivalents of the *note math: b1. module, use *note cmath: 18.
     Use of complex numbers is a fairly advanced mathematical feature.
     If you’re not aware of a need for them, it’s almost certain you can
     safely ignore them.

context manager

     An object which controls the environment seen in a *note with: 7da.
     statement by defining *note __enter__(): d5d. and *note __exit__():
     d5e. methods.  See PEP 343(11).

context variable

     A variable which can have different values depending on its
     context.  This is similar to Thread-Local Storage in which each
     execution thread may have a different value for a variable.
     However, with context variables, there may be several contexts in
     one execution thread and the main usage for context variables is to
     keep track of variables in concurrent asynchronous tasks.  See
     *note contextvars: 24.

contiguous

     A buffer is considered contiguous exactly if it is either
     `C-contiguous' or `Fortran contiguous'.  Zero-dimensional buffers
     are C and Fortran contiguous.  In one-dimensional arrays, the items
     must be laid out in memory next to each other, in order of
     increasing indexes starting from zero.  In multidimensional
     C-contiguous arrays, the last index varies the fastest when
     visiting items in order of memory address.  However, in Fortran
     contiguous arrays, the first index varies the fastest.

coroutine

     Coroutines are a more generalized form of subroutines.  Subroutines
     are entered at one point and exited at another point.  Coroutines
     can be entered, exited, and resumed at many different points.  They
     can be implemented with the *note async def: 3a9. statement.  See
     also PEP 492(12).

coroutine function

     A function which returns a *note coroutine: 18a. object.  A
     coroutine function may be defined with the *note async def: 3a9.
     statement, and may contain *note await: 2d8, *note async for: 3fd,
     and *note async with: 736. keywords.  These were introduced by PEP
     492(13).

CPython

     The canonical implementation of the Python programming language, as
     distributed on python.org(14).  The term “CPython” is used when
     necessary to distinguish this implementation from others such as
     Jython or IronPython.

decorator

     A function returning another function, usually applied as a
     function transformation using the ‘@wrapper’ syntax.  Common
     examples for decorators are *note classmethod(): 309. and *note
     staticmethod(): 30a.

     The decorator syntax is merely syntactic sugar, the following two
     function definitions are semantically equivalent:

          def f(...):
              ...
          f = staticmethod(f)

          @staticmethod
          def f(...):
              ...

     The same concept exists for classes, but is less commonly used
     there.  See the documentation for *note function definitions: 1390.
     and *note class definitions: d32. for more about decorators.

descriptor

     Any object which defines the methods *note __get__(): 156e, *note
     __set__(): 1572, or *note __delete__(): 1573.  When a class
     attribute is a descriptor, its special binding behavior is
     triggered upon attribute lookup.  Normally, using `a.b' to get, set
     or delete an attribute looks up the object named `b' in the class
     dictionary for `a', but if `b' is a descriptor, the respective
     descriptor method gets called.  Understanding descriptors is a key
     to a deep understanding of Python because they are the basis for
     many features including functions, methods, properties, class
     methods, static methods, and reference to super classes.

     For more information about descriptors’ methods, see *note
     Implementing Descriptors: 5e4. or the *note Descriptor How To
     Guide: 431d.

dictionary

     An associative array, where arbitrary keys are mapped to values.
     The keys can be any object with *note __hash__(): 44c. and *note
     __eq__(): 44b. methods.  Called a hash in Perl.

dictionary comprehension

     A compact way to process all or part of the elements in an iterable
     and return a dictionary with the results.  ‘results = {n: n ** 2
     for n in range(10)}’ generates a dictionary containing key ‘n’
     mapped to value ‘n ** 2’.  See *note Displays for lists, sets and
     dictionaries: 1628.

dictionary view

     The objects returned from *note dict.keys(): cf4, *note
     dict.values(): cf6, and *note dict.items(): cf5. are called
     dictionary views.  They provide a dynamic view on the dictionary’s
     entries, which means that when the dictionary changes, the view
     reflects these changes.  To force the dictionary view to become a
     full list use ‘list(dictview)’.  See *note Dictionary view objects:
     180c.

docstring

     A string literal which appears as the first expression in a class,
     function or module.  While ignored when the suite is executed, it
     is recognized by the compiler and put into the ‘__doc__’ attribute
     of the enclosing class, function or module.  Since it is available
     via introspection, it is the canonical place for documentation of
     the object.

duck-typing

     A programming style which does not look at an object’s type to
     determine if it has the right interface; instead, the method or
     attribute is simply called or used (“If it looks like a duck and
     quacks like a duck, it must be a duck.”) By emphasizing interfaces
     rather than specific types, well-designed code improves its
     flexibility by allowing polymorphic substitution.  Duck-typing
     avoids tests using *note type(): 6ff. or *note isinstance(): 552.
     (Note, however, that duck-typing can be complemented with *note
     abstract base classes: c05.)  Instead, it typically employs *note
     hasattr(): 54a. tests or *note EAFP: 20a9. programming.

EAFP

     Easier to ask for forgiveness than permission.  This common Python
     coding style assumes the existence of valid keys or attributes and
     catches exceptions if the assumption proves false.  This clean and
     fast style is characterized by the presence of many *note try: e37.
     and *note except: c10. statements.  The technique contrasts with
     the *note LBYL: 4529. style common to many other languages such as
     C.

expression

     A piece of syntax which can be evaluated to some value.  In other
     words, an expression is an accumulation of expression elements like
     literals, names, attribute access, operators or function calls
     which all return a value.  In contrast to many other languages, not
     all language constructs are expressions.  There are also *note
     statement: 1cef.s which cannot be used as expressions, such as
     *note while: 1361.  Assignments are also statements, not
     expressions.

extension module

     A module written in C or C++, using Python’s C API to interact with
     the core and with user code.

f-string

     String literals prefixed with ‘'f'’ or ‘'F'’ are commonly called
     “f-strings” which is short for *note formatted string literals:
     296.  See also PEP 498(15).

file object

     An object exposing a file-oriented API (with methods such as
     ‘read()’ or ‘write()’) to an underlying resource.  Depending on the
     way it was created, a file object can mediate access to a real
     on-disk file or to another type of storage or communication device
     (for example standard input/output, in-memory buffers, sockets,
     pipes, etc.).  File objects are also called `file-like objects' or
     `streams'.

     There are actually three categories of file objects: raw *note
     binary files: 1e01, buffered *note binary files: 1e01. and *note
     text files: 13d9.  Their interfaces are defined in the *note io:
     a1. module.  The canonical way to create a file object is by using
     the *note open(): 16f. function.

file-like object

     A synonym for *note file object: c14.

finder

     An object that tries to find the *note loader: 15f6. for a module
     that is being imported.

     Since Python 3.3, there are two types of finder: *note meta path
     finders: a91. for use with *note sys.meta_path: 6dd, and *note path
     entry finders: a92. for use with *note sys.path_hooks: a3d.

     See PEP 302(16), PEP 420(17) and PEP 451(18) for much more detail.

floor division

     Mathematical division that rounds down to nearest integer.  The
     floor division operator is ‘//’.  For example, the expression ‘11
     // 4’ evaluates to ‘2’ in contrast to the ‘2.75’ returned by float
     true division.  Note that ‘(-11) // 4’ is ‘-3’ because that is
     ‘-2.75’ rounded `downward'.  See PEP 238(19).

function

     A series of statements which returns some value to a caller.  It
     can also be passed zero or more *note arguments: 165c. which may be
     used in the execution of the body.  See also *note parameter: 1664,
     *note method: 4521, and the *note Function definitions: 1390.
     section.

function annotation

     An *note annotation: 1587. of a function parameter or return value.

     Function annotations are usually used for *note type hints: 158b.:
     for example, this function is expected to take two *note int: 204.
     arguments and is also expected to have an *note int: 204. return
     value:

          def sum_two_numbers(a: int, b: int) -> int:
             return a + b

     Function annotation syntax is explained in section *note Function
     definitions: 1390.

     See *note variable annotation: 712. and PEP 484(20), which describe
     this functionality.

__future__

     A *note future statement: 16c4, ‘from __future__ import <feature>’,
     directs the compiler to compile the current module using syntax or
     semantics that will become standard in a future release of Python.
     The *note __future__: 0. module documents the possible values of
     `feature'.  By importing this module and evaluating its variables,
     you can see when a new feature was first added to the language and
     when it will (or did) become the default:

          >>> import __future__
          >>> __future__.division
          _Feature((2, 2, 0, 'alpha', 2), (3, 0, 0, 'alpha', 0), 8192)

garbage collection

     The process of freeing memory when it is not used anymore.  Python
     performs garbage collection via reference counting and a cyclic
     garbage collector that is able to detect and break reference
     cycles.  The garbage collector can be controlled using the *note
     gc: 84. module.

generator

     A function which returns a *note generator iterator: 559.  It looks
     like a normal function except that it contains *note yield: 2c7.
     expressions for producing a series of values usable in a for-loop
     or that can be retrieved one at a time with the *note next(): 775.
     function.

     Usually refers to a generator function, but may refer to a
     `generator iterator' in some contexts.  In cases where the intended
     meaning isn’t clear, using the full terms avoids ambiguity.

generator iterator

     An object created by a *note generator: a83. function.

     Each *note yield: 2c7. temporarily suspends processing, remembering
     the location execution state (including local variables and pending
     try-statements).  When the `generator iterator' resumes, it picks
     up where it left off (in contrast to functions which start fresh on
     every invocation).

generator expression

     An expression that returns an iterator.  It looks like a normal
     expression followed by a ‘for’ clause defining a loop variable,
     range, and an optional ‘if’ clause.  The combined expression
     generates values for an enclosing function:

          >>> sum(i*i for i in range(10))         # sum of squares 0, 1, 4, ... 81
          285

generic function

     A function composed of multiple functions implementing the same
     operation for different types.  Which implementation should be used
     during a call is determined by the dispatch algorithm.

     See also the *note single dispatch: 2fc. glossary entry, the *note
     functools.singledispatch(): 491. decorator, and PEP 443(21).

generic type

     A *note type: fe9. that can be parameterized; typically a *note
     container class: 1594. such as *note list: 1f8. or *note dict: 164.
     Used for *note type hints: 158b. and *note annotations: 1587.

     For more details, see *note generic alias types: fe5, PEP 483(22),
     PEP 484(23), PEP 585(24), and the *note typing: 122. module.

GIL

     See *note global interpreter lock: 600.

global interpreter lock

     The mechanism used by the *note CPython: 1569. interpreter to
     assure that only one thread executes Python *note bytecode: 709. at
     a time.  This simplifies the CPython implementation by making the
     object model (including critical built-in types such as *note dict:
     164.) implicitly safe against concurrent access.  Locking the
     entire interpreter makes it easier for the interpreter to be
     multi-threaded, at the expense of much of the parallelism afforded
     by multi-processor machines.

     However, some extension modules, either standard or third-party,
     are designed so as to release the GIL when doing
     computationally-intensive tasks such as compression or hashing.
     Also, the GIL is always released when doing I/O.

     Past efforts to create a “free-threaded” interpreter (one which
     locks shared data at a much finer granularity) have not been
     successful because performance suffered in the common
     single-processor case.  It is believed that overcoming this
     performance issue would make the implementation much more
     complicated and therefore costlier to maintain.

hash-based pyc

     A bytecode cache file that uses the hash rather than the
     last-modified time of the corresponding source file to determine
     its validity.  See *note Cached bytecode invalidation: 439.

hashable

     An object is `hashable' if it has a hash value which never changes
     during its lifetime (it needs a *note __hash__(): 44c. method), and
     can be compared to other objects (it needs an *note __eq__(): 44b.
     method).  Hashable objects which compare equal must have the same
     hash value.

     Hashability makes an object usable as a dictionary key and a set
     member, because these data structures use the hash value
     internally.

     Most of Python’s immutable built-in objects are hashable; mutable
     containers (such as lists or dictionaries) are not; immutable
     containers (such as tuples and frozensets) are only hashable if
     their elements are hashable.  Objects which are instances of
     user-defined classes are hashable by default.  They all compare
     unequal (except with themselves), and their hash value is derived
     from their *note id(): e4b.

IDLE

     An Integrated Development Environment for Python.  IDLE is a basic
     editor and interpreter environment which ships with the standard
     distribution of Python.

immutable

     An object with a fixed value.  Immutable objects include numbers,
     strings and tuples.  Such an object cannot be altered.  A new
     object has to be created if a different value has to be stored.
     They play an important role in places where a constant hash value
     is needed, for example as a key in a dictionary.

import path

     A list of locations (or *note path entries: 160b.) that are
     searched by the *note path based finder: 15fb. for modules to
     import.  During import, this list of locations usually comes from
     *note sys.path: 260, but for subpackages it may also come from the
     parent package’s ‘__path__’ attribute.

importing

     The process by which Python code in one module is made available to
     Python code in another module.

importer

     An object that both finds and loads a module; both a *note finder:
     15f5. and *note loader: 15f6. object.

interactive

     Python has an interactive interpreter which means you can enter
     statements and expressions at the interpreter prompt, immediately
     execute them and see their results.  Just launch ‘python’ with no
     arguments (possibly by selecting it from your computer’s main
     menu).  It is a very powerful way to test out new ideas or inspect
     modules and packages (remember ‘help(x)’).

interpreted

     Python is an interpreted language, as opposed to a compiled one,
     though the distinction can be blurry because of the presence of the
     bytecode compiler.  This means that source files can be run
     directly without explicitly creating an executable which is then
     run.  Interpreted languages typically have a shorter
     development/debug cycle than compiled ones, though their programs
     generally also run more slowly.  See also *note interactive: 452e.

interpreter shutdown

     When asked to shut down, the Python interpreter enters a special
     phase where it gradually releases all allocated resources, such as
     modules and various critical internal structures.  It also makes
     several calls to the *note garbage collector: fc8.  This can
     trigger the execution of code in user-defined destructors or
     weakref callbacks.  Code executed during the shutdown phase can
     encounter various exceptions as the resources it relies on may not
     function anymore (common examples are library modules or the
     warnings machinery).

     The main reason for interpreter shutdown is that the ‘__main__’
     module or the script being run has finished executing.

iterable

     An object capable of returning its members one at a time.  Examples
     of iterables include all sequence types (such as *note list: 1f8,
     *note str: 205, and *note tuple: 1a2.) and some non-sequence types
     like *note dict: 164, *note file objects: c14, and objects of any
     classes you define with an *note __iter__(): 609. method or with a
     *note __getitem__(): 3a2. method that implements *note Sequence:
     135c. semantics.

     Iterables can be used in a *note for: cfa. loop and in many other
     places where a sequence is needed (*note zip(): cfc, *note map():
     cf7, …).  When an iterable object is passed as an argument to the
     built-in function *note iter(): ded, it returns an iterator for the
     object.  This iterator is good for one pass over the set of values.
     When using iterables, it is usually not necessary to call *note
     iter(): ded. or deal with iterator objects yourself.  The ‘for’
     statement does that automatically for you, creating a temporary
     unnamed variable to hold the iterator for the duration of the loop.
     See also *note iterator: 1171, *note sequence: 135c, and *note
     generator: a83.

iterator

     An object representing a stream of data.  Repeated calls to the
     iterator’s *note __next__(): d2c. method (or passing it to the
     built-in function *note next(): 775.) return successive items in
     the stream.  When no more data are available a *note StopIteration:
     582. exception is raised instead.  At this point, the iterator
     object is exhausted and any further calls to its ‘__next__()’
     method just raise *note StopIteration: 582. again.  Iterators are
     required to have an *note __iter__(): 609. method that returns the
     iterator object itself so every iterator is also iterable and may
     be used in most places where other iterables are accepted.  One
     notable exception is code which attempts multiple iteration passes.
     A container object (such as a *note list: 1f8.) produces a fresh
     new iterator each time you pass it to the *note iter(): ded.
     function or use it in a *note for: cfa. loop.  Attempting this with
     an iterator will just return the same exhausted iterator object
     used in the previous iteration pass, making it appear like an empty
     container.

     More information can be found in *note Iterator Types: 159a.

key function

     A key function or collation function is a callable that returns a
     value used for sorting or ordering.  For example, *note
     locale.strxfrm(): 31c3. is used to produce a sort key that is aware
     of locale specific sort conventions.

     A number of tools in Python accept key functions to control how
     elements are ordered or grouped.  They include *note min(): 8f6,
     *note max(): 8f7, *note sorted(): 547, *note list.sort(): 548,
     *note heapq.merge(): 7d1, *note heapq.nsmallest(): 1ab3, *note
     heapq.nlargest(): 1ab2, and *note itertools.groupby(): 1c9d.

     There are several ways to create a key function.  For example.  the
     *note str.lower(): 1777. method can serve as a key function for
     case insensitive sorts.  Alternatively, a key function can be built
     from a *note lambda: cf9. expression such as ‘lambda r: (r[0],
     r[2])’.  Also, the *note operator: c2. module provides three key
     function constructors: *note attrgetter(): 80a, *note itemgetter():
     38b, and *note methodcaller(): 80b.  See the *note Sorting HOW TO:
     1737. for examples of how to create and use key functions.

keyword argument

     See *note argument: 165c.

lambda

     An anonymous inline function consisting of a single *note
     expression: 158f. which is evaluated when the function is called.
     The syntax to create a lambda function is ‘lambda [parameters]:
     expression’

LBYL

     Look before you leap.  This coding style explicitly tests for
     pre-conditions before making calls or lookups.  This style
     contrasts with the *note EAFP: 20a9. approach and is characterized
     by the presence of many *note if: eab. statements.

     In a multi-threaded environment, the LBYL approach can risk
     introducing a race condition between “the looking” and “the
     leaping”.  For example, the code, ‘if key in mapping: return
     mapping[key]’ can fail if another thread removes `key' from
     `mapping' after the test, but before the lookup.  This issue can be
     solved with locks or by using the EAFP approach.

list

     A built-in Python *note sequence: 135c.  Despite its name it is
     more akin to an array in other languages than to a linked list
     since access to elements is O(1).

list comprehension

     A compact way to process all or part of the elements in a sequence
     and return a list with the results.  ‘result = ['{:#04x}'.format(x)
     for x in range(256) if x % 2 == 0]’ generates a list of strings
     containing even hex numbers (0x..)  in the range from 0 to 255.
     The *note if: eab. clause is optional.  If omitted, all elements in
     ‘range(256)’ are processed.

loader

     An object that loads a module.  It must define a method named
     ‘load_module()’.  A loader is typically returned by a *note finder:
     15f5.  See PEP 302(25) for details and *note importlib.abc.Loader:
     8af. for an *note abstract base class: c05.

magic method

     An informal synonym for *note special method: 37e6.

mapping

     A container object that supports arbitrary key lookups and
     implements the methods specified in the *note Mapping: 15f. or
     *note MutableMapping: ace. *note abstract base classes: 15e.
     Examples include *note dict: 164, *note collections.defaultdict:
     c0c, *note collections.OrderedDict: 2ea. and *note
     collections.Counter: ab9.

meta path finder

     A *note finder: 15f5. returned by a search of *note sys.meta_path:
     6dd.  Meta path finders are related to, but different from *note
     path entry finders: a92.

     See *note importlib.abc.MetaPathFinder: a93. for the methods that
     meta path finders implement.

metaclass

     The class of a class.  Class definitions create a class name, a
     class dictionary, and a list of base classes.  The metaclass is
     responsible for taking those three arguments and creating the
     class.  Most object oriented programming languages provide a
     default implementation.  What makes Python special is that it is
     possible to create custom metaclasses.  Most users never need this
     tool, but when the need arises, metaclasses can provide powerful,
     elegant solutions.  They have been used for logging attribute
     access, adding thread-safety, tracking object creation,
     implementing singletons, and many other tasks.

     More information can be found in *note Metaclasses: 157c.

method

     A function which is defined inside a class body.  If called as an
     attribute of an instance of that class, the method will get the
     instance object as its first *note argument: 165c. (which is
     usually called ‘self’).  See *note function: 165b. and *note nested
     scope: 1721.

method resolution order

     Method Resolution Order is the order in which base classes are
     searched for a member during lookup.  See The Python 2.3 Method
     Resolution Order(26) for details of the algorithm used by the
     Python interpreter since the 2.3 release.

module

     An object that serves as an organizational unit of Python code.
     Modules have a namespace containing arbitrary Python objects.
     Modules are loaded into Python by the process of *note importing:
     15e8.

     See also *note package: 15eb.

module spec

     A namespace containing the import-related information used to load
     a module.  An instance of *note importlib.machinery.ModuleSpec:
     1601.

MRO

     See *note method resolution order: 1739.

mutable

     Mutable objects can change their value but keep their *note id():
     e4b.  See also *note immutable: 1356.

named tuple

     The term “named tuple” applies to any type or class that inherits
     from tuple and whose indexable elements are also accessible using
     named attributes.  The type or class may have other features as
     well.

     Several built-in types are named tuples, including the values
     returned by *note time.localtime(): 1080. and *note os.stat(): 321.
     Another example is *note sys.float_info: 10fc.:

          >>> sys.float_info[1]                   # indexed access
          1024
          >>> sys.float_info.max_exp              # named field access
          1024
          >>> isinstance(sys.float_info, tuple)   # kind of tuple
          True

     Some named tuples are built-in types (such as the above examples).
     Alternatively, a named tuple can be created from a regular class
     definition that inherits from *note tuple: 1a2. and that defines
     named fields.  Such a class can be written by hand or it can be
     created with the factory function *note collections.namedtuple():
     1a1.  The latter technique also adds some extra methods that may
     not be found in hand-written or built-in named tuples.

namespace

     The place where a variable is stored.  Namespaces are implemented
     as dictionaries.  There are the local, global and built-in
     namespaces as well as nested namespaces in objects (in methods).
     Namespaces support modularity by preventing naming conflicts.  For
     instance, the functions *note builtins.open: 16f. and *note
     os.open(): 758. are distinguished by their namespaces.  Namespaces
     also aid readability and maintainability by making it clear which
     module implements a function.  For instance, writing *note
     random.seed(): cd3. or *note itertools.islice(): 4a9. makes it
     clear that those functions are implemented by the *note random: dc.
     and *note itertools: a3. modules, respectively.

namespace package

     A PEP 420(27) *note package: 15eb. which serves only as a container
     for subpackages.  Namespace packages may have no physical
     representation, and specifically are not like a *note regular
     package: 15ed. because they have no ‘__init__.py’ file.

     See also *note module: 15e7.

nested scope

     The ability to refer to a variable in an enclosing definition.  For
     instance, a function defined inside another function can refer to
     variables in the outer function.  Note that nested scopes by
     default work only for reference and not for assignment.  Local
     variables both read and write in the innermost scope.  Likewise,
     global variables read and write to the global namespace.  The *note
     nonlocal: d07. allows writing to outer scopes.

new-style class

     Old name for the flavor of classes now used for all class objects.
     In earlier Python versions, only new-style classes could use
     Python’s newer, versatile features like *note __slots__: eef,
     descriptors, properties, *note __getattribute__(): 54c, class
     methods, and static methods.

object

     Any data with state (attributes or value) and defined behavior
     (methods).  Also the ultimate base class of any *note new-style
     class: 1e09.

package

     A Python *note module: 15e7. which can contain submodules or
     recursively, subpackages.  Technically, a package is a Python
     module with an ‘__path__’ attribute.

     See also *note regular package: 15ed. and *note namespace package:
     15ee.

parameter

     A named entity in a *note function: 165b. (or method) definition
     that specifies an *note argument: 165c. (or in some cases,
     arguments) that the function can accept.  There are five kinds of
     parameter:

        * `positional-or-keyword': specifies an argument that can be
          passed either *note positionally: 165c. or as a *note keyword
          argument: 165c.  This is the default kind of parameter, for
          example `foo' and `bar' in the following:

               def func(foo, bar=None): ...

        * `positional-only': specifies an argument that can be supplied
          only by position.  Positional-only parameters can be defined
          by including a ‘/’ character in the parameter list of the
          function definition after them, for example `posonly1' and
          `posonly2' in the following:

               def func(posonly1, posonly2, /, positional_or_keyword): ...

        * `keyword-only': specifies an argument that can be supplied
          only by keyword.  Keyword-only parameters can be defined by
          including a single var-positional parameter or bare ‘*’ in the
          parameter list of the function definition before them, for
          example `kw_only1' and `kw_only2' in the following:

               def func(arg, *, kw_only1, kw_only2): ...

        * `var-positional': specifies that an arbitrary sequence of
          positional arguments can be provided (in addition to any
          positional arguments already accepted by other parameters).
          Such a parameter can be defined by prepending the parameter
          name with ‘*’, for example `args' in the following:

               def func(*args, **kwargs): ...

        * `var-keyword': specifies that arbitrarily many keyword
          arguments can be provided (in addition to any keyword
          arguments already accepted by other parameters).  Such a
          parameter can be defined by prepending the parameter name with
          ‘**’, for example `kwargs' in the example above.

     Parameters can specify both optional and required arguments, as
     well as default values for some optional arguments.

     See also the *note argument: 165c. glossary entry, the FAQ question
     on *note the difference between arguments and parameters: 4470, the
     *note inspect.Parameter: 7e5. class, the *note Function
     definitions: 1390. section, and PEP 362(28).

path entry

     A single location on the *note import path: 15f8. which the *note
     path based finder: 15fb. consults to find modules for importing.

path entry finder

     A *note finder: 15f5. returned by a callable on *note
     sys.path_hooks: a3d. (i.e.  a *note path entry hook: 160d.) which
     knows how to locate modules given a *note path entry: 160b.

     See *note importlib.abc.PathEntryFinder: a94. for the methods that
     path entry finders implement.

path entry hook

     A callable on the ‘sys.path_hook’ list which returns a *note path
     entry finder: a92. if it knows how to find modules on a specific
     *note path entry: 160b.

path based finder

     One of the default *note meta path finders: a91. which searches an
     *note import path: 15f8. for modules.

path-like object

     An object representing a file system path.  A path-like object is
     either a *note str: 205. or *note bytes: 172. object representing a
     path, or an object implementing the *note os.PathLike: 5e6.
     protocol.  An object that supports the *note os.PathLike: 5e6.
     protocol can be converted to a *note str: 205. or *note bytes: 172.
     file system path by calling the *note os.fspath(): 5e8. function;
     *note os.fsdecode(): 5e9. and *note os.fsencode(): 5ea. can be used
     to guarantee a *note str: 205. or *note bytes: 172. result instead,
     respectively.  Introduced by PEP 519(29).

PEP

     Python Enhancement Proposal.  A PEP is a design document providing
     information to the Python community, or describing a new feature
     for Python or its processes or environment.  PEPs should provide a
     concise technical specification and a rationale for proposed
     features.

     PEPs are intended to be the primary mechanisms for proposing major
     new features, for collecting community input on an issue, and for
     documenting the design decisions that have gone into Python.  The
     PEP author is responsible for building consensus within the
     community and documenting dissenting opinions.

     See PEP 1(30).

portion

     A set of files in a single directory (possibly stored in a zip
     file) that contribute to a namespace package, as defined in PEP
     420(31).

positional argument

     See *note argument: 165c.

provisional API

     A provisional API is one which has been deliberately excluded from
     the standard library’s backwards compatibility guarantees.  While
     major changes to such interfaces are not expected, as long as they
     are marked provisional, backwards incompatible changes (up to and
     including removal of the interface) may occur if deemed necessary
     by core developers.  Such changes will not be made gratuitously –
     they will occur only if serious fundamental flaws are uncovered
     that were missed prior to the inclusion of the API.

     Even for provisional APIs, backwards incompatible changes are seen
     as a “solution of last resort” - every attempt will still be made
     to find a backwards compatible resolution to any identified
     problems.

     This process allows the standard library to continue to evolve over
     time, without locking in problematic design errors for extended
     periods of time.  See PEP 411(32) for more details.

provisional package

     See *note provisional API: 454.

Python 3000

     Nickname for the Python 3.x release line (coined long ago when the
     release of version 3 was something in the distant future.)  This is
     also abbreviated “Py3k”.

Pythonic

     An idea or piece of code which closely follows the most common
     idioms of the Python language, rather than implementing code using
     concepts common to other languages.  For example, a common idiom in
     Python is to loop over all elements of an iterable using a *note
     for: cfa. statement.  Many other languages don’t have this type of
     construct, so people unfamiliar with Python sometimes use a
     numerical counter instead:

          for i in range(len(food)):
              print(food[i])

     As opposed to the cleaner, Pythonic method:

          for piece in food:
              print(piece)

qualified name

     A dotted name showing the “path” from a module’s global scope to a
     class, function or method defined in that module, as defined in PEP
     3155(33).  For top-level functions and classes, the qualified name
     is the same as the object’s name:

          >>> class C:
          ...     class D:
          ...         def meth(self):
          ...             pass
          ...
          >>> C.__qualname__
          'C'
          >>> C.D.__qualname__
          'C.D'
          >>> C.D.meth.__qualname__
          'C.D.meth'

     When used to refer to modules, the `fully qualified name' means the
     entire dotted path to the module, including any parent packages,
     e.g.  ‘email.mime.text’:

          >>> import email.mime.text
          >>> email.mime.text.__name__
          'email.mime.text'

reference count

     The number of references to an object.  When the reference count of
     an object drops to zero, it is deallocated.  Reference counting is
     generally not visible to Python code, but it is a key element of
     the *note CPython: 1569. implementation.  The *note sys: fd. module
     defines a *note getrefcount(): 37b5. function that programmers can
     call to return the reference count for a particular object.

regular package

     A traditional *note package: 15eb, such as a directory containing
     an ‘__init__.py’ file.

     See also *note namespace package: 15ee.

__slots__

     A declaration inside a class that saves memory by pre-declaring
     space for instance attributes and eliminating instance
     dictionaries.  Though popular, the technique is somewhat tricky to
     get right and is best reserved for rare cases where there are large
     numbers of instances in a memory-critical application.

sequence

     An *note iterable: c7c. which supports efficient element access
     using integer indices via the *note __getitem__(): 3a2. special
     method and defines a *note __len__(): e90. method that returns the
     length of the sequence.  Some built-in sequence types are *note
     list: 1f8, *note str: 205, *note tuple: 1a2, and *note bytes: 172.
     Note that *note dict: 164. also supports *note __getitem__(): 3a2.
     and *note __len__(): e90, but is considered a mapping rather than a
     sequence because the lookups use arbitrary *note immutable: 1356.
     keys rather than integers.

     The *note collections.abc.Sequence: 1764. abstract base class
     defines a much richer interface that goes beyond just *note
     __getitem__(): 3a2. and *note __len__(): e90, adding ‘count()’,
     ‘index()’, *note __contains__(): dee, and *note __reversed__():
     629.  Types that implement this expanded interface can be
     registered explicitly using *note register(): ab0.

set comprehension

     A compact way to process all or part of the elements in an iterable
     and return a set with the results.  ‘results = {c for c in
     'abracadabra' if c not in 'abc'}’ generates the set of strings
     ‘{'r', 'd'}’.  See *note Displays for lists, sets and dictionaries:
     1628.

single dispatch

     A form of *note generic function: 2fb. dispatch where the
     implementation is chosen based on the type of a single argument.

slice

     An object usually containing a portion of a *note sequence: 135c.
     A slice is created using the subscript notation, ‘[]’ with colons
     between numbers when several are given, such as in
     ‘variable_name[1:3:5]’.  The bracket (subscript) notation uses
     *note slice: ec8. objects internally.

special method

     A method that is called implicitly by Python to execute a certain
     operation on a type, such as addition.  Such methods have names
     starting and ending with double underscores.  Special methods are
     documented in *note Special method names: 608.

statement

     A statement is part of a suite (a “block” of code).  A statement is
     either an *note expression: 158f. or one of several constructs with
     a keyword, such as *note if: eab, *note while: 1361. or *note for:
     cfa.

text encoding

     A codec which encodes Unicode strings to bytes.

text file

     A *note file object: c14. able to read and write *note str: 205.
     objects.  Often, a text file actually accesses a byte-oriented
     datastream and handles the *note text encoding: 1731.
     automatically.  Examples of text files are files opened in text
     mode (‘'r'’ or ‘'w'’), *note sys.stdin: 41e, *note sys.stdout: 41f,
     and instances of *note io.StringIO: 91a.

     See also *note binary file: 1e01. for a file object able to read
     and write *note bytes-like objects: 6df.

triple-quoted string

     A string which is bound by three instances of either a quotation
     mark (”) or an apostrophe (‘).  While they don’t provide any
     functionality not available with single-quoted strings, they are
     useful for a number of reasons.  They allow you to include
     unescaped single and double quotes within a string and they can
     span multiple lines without the use of the continuation character,
     making them especially useful when writing docstrings.

type

     The type of a Python object determines what kind of object it is;
     every object has a type.  An object’s type is accessible as its
     *note __class__: ecc. attribute or can be retrieved with
     ‘type(obj)’.

type alias

     A synonym for a type, created by assigning the type to an
     identifier.

     Type aliases are useful for simplifying *note type hints: 158b.
     For example:

          def remove_gray_shades(
                  colors: list[tuple[int, int, int]]) -> list[tuple[int, int, int]]:
              pass

     could be made more readable like this:

          Color = tuple[int, int, int]

          def remove_gray_shades(colors: list[Color]) -> list[Color]:
              pass

     See *note typing: 122. and PEP 484(34), which describe this
     functionality.

type hint

     An *note annotation: 1587. that specifies the expected type for a
     variable, a class attribute, or a function parameter or return
     value.

     Type hints are optional and are not enforced by Python but they are
     useful to static type analysis tools, and aid IDEs with code
     completion and refactoring.

     Type hints of global variables, class attributes, and functions,
     but not local variables, can be accessed using *note
     typing.get_type_hints(): 1ef.

     See *note typing: 122. and PEP 484(35), which describe this
     functionality.

universal newlines

     A manner of interpreting text streams in which all of the following
     are recognized as ending a line: the Unix end-of-line convention
     ‘'\n'’, the Windows convention ‘'\r\n'’, and the old Macintosh
     convention ‘'\r'’.  See PEP 278(36) and PEP 3116(37), as well as
     *note bytes.splitlines(): 17da. for an additional use.

variable annotation

     An *note annotation: 1587. of a variable or a class attribute.

     When annotating a variable or a class attribute, assignment is
     optional:

          class C:
              field: 'annotation'

     Variable annotations are usually used for *note type hints: 158b.:
     for example this variable is expected to take *note int: 204.
     values:

          count: int = 0

     Variable annotation syntax is explained in section *note Annotated
     assignment statements: 16ad.

     See *note function annotation: 1391, PEP 484(38) and PEP 526(39),
     which describe this functionality.

virtual environment

     A cooperatively isolated runtime environment that allows Python
     users and applications to install and upgrade Python distribution
     packages without interfering with the behaviour of other Python
     applications running on the same system.

     See also *note venv: 12e.

virtual machine

     A computer defined entirely in software.  Python’s virtual machine
     executes the *note bytecode: 709. emitted by the bytecode compiler.

Zen of Python

     Listing of Python design principles and philosophies that are
     helpful in understanding and using the language.  The listing can
     be found by typing “‘import this’” at the interactive prompt.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0484

   (2) https://www.python.org/dev/peps/pep-0526

   (3) https://www.python.org/dev/peps/pep-0362

   (4) https://www.python.org/dev/peps/pep-0492

   (5) https://www.python.org/dev/peps/pep-0492

   (6) https://www.python.org/dev/peps/pep-0525

   (7) https://www.python.org/dev/peps/pep-0492

   (8) https://www.python.org/dev/peps/pep-0492

   (9) https://www.python.org/dev/peps/pep-0492

   (10) https://gvanrossum.github.io/

   (11) https://www.python.org/dev/peps/pep-0343

   (12) https://www.python.org/dev/peps/pep-0492

   (13) https://www.python.org/dev/peps/pep-0492

   (14) https://www.python.org

   (15) https://www.python.org/dev/peps/pep-0498

   (16) https://www.python.org/dev/peps/pep-0302

   (17) https://www.python.org/dev/peps/pep-0420

   (18) https://www.python.org/dev/peps/pep-0451

   (19) https://www.python.org/dev/peps/pep-0238

   (20) https://www.python.org/dev/peps/pep-0484

   (21) https://www.python.org/dev/peps/pep-0443

   (22) https://www.python.org/dev/peps/pep-0483

   (23) https://www.python.org/dev/peps/pep-0484

   (24) https://www.python.org/dev/peps/pep-0585

   (25) https://www.python.org/dev/peps/pep-0302

   (26) https://www.python.org/download/releases/2.3/mro/

   (27) https://www.python.org/dev/peps/pep-0420

   (28) https://www.python.org/dev/peps/pep-0362

   (29) https://www.python.org/dev/peps/pep-0519

   (30) https://www.python.org/dev/peps/pep-0001

   (31) https://www.python.org/dev/peps/pep-0420

   (32) https://www.python.org/dev/peps/pep-0411

   (33) https://www.python.org/dev/peps/pep-3155

   (34) https://www.python.org/dev/peps/pep-0484

   (35) https://www.python.org/dev/peps/pep-0484

   (36) https://www.python.org/dev/peps/pep-0278

   (37) https://www.python.org/dev/peps/pep-3116

   (38) https://www.python.org/dev/peps/pep-0484

   (39) https://www.python.org/dev/peps/pep-0526


File: python.info,  Node: About these documents,  Next: Dealing with Bugs,  Prev: Glossary,  Up: Top

13 About these documents
************************

These documents are generated from reStructuredText(1) sources by
Sphinx(2), a document processor specifically written for the Python
documentation.

Development of the documentation and its toolchain is an entirely
volunteer effort, just like Python itself.  If you want to contribute,
please take a look at the *note Dealing with Bugs: 3dab. page for
information on how to do so.  New volunteers are always welcome!

Many thanks go to:

   * Fred L. Drake, Jr., the creator of the original Python
     documentation toolset and writer of much of the content;

   * the Docutils(3) project for creating reStructuredText and the
     Docutils suite;

   * Fredrik Lundh for his Alternative Python Reference(4) project from
     which Sphinx got many good ideas.

* Menu:

* Contributors to the Python Documentation::

   ---------- Footnotes ----------

   (1) http://docutils.sourceforge.net/rst.html

   (2) http://sphinx-doc.org/

   (3) http://docutils.sourceforge.net/

   (4) http://effbot.org/zone/pyref.htm


File: python.info,  Node: Contributors to the Python Documentation,  Up: About these documents

13.1 Contributors to the Python Documentation
=============================================

Many people have contributed to the Python language, the Python standard
library, and the Python documentation.  See Misc/ACKS(1) in the Python
source distribution for a partial list of contributors.

It is only with the input and contributions of the Python community that
Python has such wonderful documentation – Thank You!

   ---------- Footnotes ----------

   (1) https://github.com/python/cpython/tree/3.9/Misc/ACKS


File: python.info,  Node: Dealing with Bugs,  Next: Copyright,  Prev: About these documents,  Up: Top

14 Dealing with Bugs
********************

Python is a mature programming language which has established a
reputation for stability.  In order to maintain this reputation, the
developers would like to know of any deficiencies you find in Python.

It can be sometimes faster to fix bugs yourself and contribute patches
to Python as it streamlines the process and involves less people.  Learn
how to *note contribute: 4541.

* Menu:

* Documentation bugs::
* Using the Python issue tracker::
* Getting started contributing to Python yourself::


File: python.info,  Node: Documentation bugs,  Next: Using the Python issue tracker,  Up: Dealing with Bugs

14.1 Documentation bugs
=======================

If you find a bug in this documentation or would like to propose an
improvement, please submit a bug report on the *note tracker: 4543.  If
you have a suggestion on how to fix it, include that as well.

If you’re short on time, you can also email documentation bug reports to
<docs@python.org> (behavioral bugs can be sent to
<python-list@python.org>).  ‘docs@’ is a mailing list run by volunteers;
your request will be noticed, though it may take a while to be
processed.

See also
........

Documentation bugs(1)

     A list of documentation bugs that have been submitted to the Python
     issue tracker.

Issue Tracking(2)

     Overview of the process involved in reporting an improvement on the
     tracker.

Helping with Documentation(3)

     Comprehensive guide for individuals that are interested in
     contributing to Python documentation.

   ---------- Footnotes ----------

   (1) 
https://bugs.python.org/issue?@filter=status&@filter=components&components=4&status=1&@columns=id,activity,title,status&@sort=-activity

   (2) https://devguide.python.org/tracker/

   (3) 
https://devguide.python.org/docquality/#helping-with-documentation


File: python.info,  Node: Using the Python issue tracker,  Next: Getting started contributing to Python yourself,  Prev: Documentation bugs,  Up: Dealing with Bugs

14.2 Using the Python issue tracker
===================================

Bug reports for Python itself should be submitted via the Python Bug
Tracker (‘https://bugs.python.org/’).  The bug tracker offers a Web form
which allows pertinent information to be entered and submitted to the
developers.

The first step in filing a report is to determine whether the problem
has already been reported.  The advantage in doing so, aside from saving
the developers time, is that you learn what has been done to fix it; it
may be that the problem has already been fixed for the next release, or
additional information is needed (in which case you are welcome to
provide it if you can!).  To do this, search the bug database using the
search box on the top of the page.

If the problem you’re reporting is not already in the bug tracker, go
back to the Python Bug Tracker and log in.  If you don’t already have a
tracker account, select the “Register” link or, if you use OpenID, one
of the OpenID provider logos in the sidebar.  It is not possible to
submit a bug report anonymously.

Being now logged in, you can submit a bug.  Select the “Create New” link
in the sidebar to open the bug reporting form.

The submission form has a number of fields.  For the “Title” field,
enter a `very' short description of the problem; less than ten words is
good.  In the “Type” field, select the type of your problem; also select
the “Component” and “Versions” to which the bug relates.

In the “Comment” field, describe the problem in detail, including what
you expected to happen and what did happen.  Be sure to include whether
any extension modules were involved, and what hardware and software
platform you were using (including version information as appropriate).

Each bug report will be assigned to a developer who will determine what
needs to be done to correct the problem.  You will receive an update
each time action is taken on the bug.

See also
........

How to Report Bugs Effectively(1)

     Article which goes into some detail about how to create a useful
     bug report.  This describes what kind of information is useful and
     why it is useful.

Bug Writing Guidelines(2)

     Information about writing a good bug report.  Some of this is
     specific to the Mozilla project, but describes general good
     practices.

   ---------- Footnotes ----------

   (1) https://www.chiark.greenend.org.uk/~sgtatham/bugs.html

   (2) https://bugzilla.mozilla.org/page.cgi?id=bug-writing.html


File: python.info,  Node: Getting started contributing to Python yourself,  Prev: Using the Python issue tracker,  Up: Dealing with Bugs

14.3 Getting started contributing to Python yourself
====================================================

Beyond just reporting bugs that you find, you are also welcome to submit
patches to fix them.  You can find more information on how to get
started patching Python in the Python Developer’s Guide(1).  If you have
questions, the core-mentorship mailing list(2) is a friendly place to
get answers to any and all questions pertaining to the process of fixing
issues in Python.

   ---------- Footnotes ----------

   (1) https://devguide.python.org/

   (2) 
https://mail.python.org/mailman3/lists/core-mentorship.python.org/


File: python.info,  Node: Copyright,  Next: History and License,  Prev: Dealing with Bugs,  Up: Top

15 Copyright
************

Python and this documentation is:

Copyright © 2001-2022 Python Software Foundation.  All rights reserved.

Copyright © 2000 BeOpen.com.  All rights reserved.

Copyright © 1995-2000 Corporation for National Research Initiatives.
All rights reserved.

Copyright © 1991-1995 Stichting Mathematisch Centrum.  All rights
reserved.

__________________________________________________________________

See *note History and License: 4549. for complete license and
permissions information.


File: python.info,  Node: History and License,  Next: Distributing Python Modules Legacy version,  Prev: Copyright,  Up: Top

16 History and License
**********************

* Menu:

* History of the software::
* Terms and conditions for accessing or otherwise using Python::
* Licenses and Acknowledgements for Incorporated Software::


File: python.info,  Node: History of the software,  Next: Terms and conditions for accessing or otherwise using Python,  Up: History and License

16.1 History of the software
============================

Python was created in the early 1990s by Guido van Rossum at Stichting
Mathematisch Centrum (CWI, see ‘https://www.cwi.nl/’) in the Netherlands
as a successor of a language called ABC. Guido remains Python’s
principal author, although it includes many contributions from others.

In 1995, Guido continued his work on Python at the Corporation for
National Research Initiatives (CNRI, see
‘https://www.cnri.reston.va.us/’) in Reston, Virginia where he released
several versions of the software.

In May 2000, Guido and the Python core development team moved to
BeOpen.com to form the BeOpen PythonLabs team.  In October of the same
year, the PythonLabs team moved to Digital Creations (now Zope
Corporation; see ‘https://www.zope.org/’).  In 2001, the Python Software
Foundation (PSF, see ‘https://www.python.org/psf/’) was formed, a
non-profit organization created specifically to own Python-related
Intellectual Property.  Zope Corporation is a sponsoring member of the
PSF.

All Python releases are Open Source (see ‘https://opensource.org/’ for
the Open Source Definition).  Historically, most, but not all, Python
releases have also been GPL-compatible; the table below summarizes the
various releases.

Release              Derived from       Year             Owner            GPL compatible?
                                                                          
------------------------------------------------------------------------------------------------
                                                                          
0.9.0 thru 1.2       n/a                1991-1995        CWI              yes
                                                                          
                                                                          
1.3 thru 1.5.2       1.2                1995-1999        CNRI             yes
                                                                          
                                                                          
1.6                  1.5.2              2000             CNRI             no
                                                                          
                                                                          
2.0                  1.6                2000             BeOpen.com       no
                                                                          
                                                                          
1.6.1                1.6                2001             CNRI             no
                                                                          
                                                                          
2.1                  2.0+1.6.1          2001             PSF              no
                                                                          
                                                                          
2.0.1                2.0+1.6.1          2001             PSF              yes
                                                                          
                                                                          
2.1.1                2.1+2.0.1          2001             PSF              yes
                                                                          
                                                                          
2.1.2                2.1.1              2002             PSF              yes
                                                                          
                                                                          
2.1.3                2.1.2              2002             PSF              yes
                                                                          
                                                                          
2.2 and above        2.1.1              2001-now         PSF              yes
                                                                          

     Note: GPL-compatible doesn’t mean that we’re distributing Python
     under the GPL. All Python licenses, unlike the GPL, let you
     distribute a modified version without making your changes open
     source.  The GPL-compatible licenses make it possible to combine
     Python with other software that is released under the GPL; the
     others don’t.

Thanks to the many outside volunteers who have worked under Guido’s
direction to make these releases possible.


File: python.info,  Node: Terms and conditions for accessing or otherwise using Python,  Next: Licenses and Acknowledgements for Incorporated Software,  Prev: History of the software,  Up: History and License

16.2 Terms and conditions for accessing or otherwise using Python
=================================================================

Python software and documentation are licensed under the *note PSF
License Agreement: 454e.

Starting with Python 3.8.6, examples, recipes, and other code in the
documentation are dual licensed under the PSF License Agreement and the
*note Zero-Clause BSD license: 454f.

Some software incorporated into Python is under different licenses.  The
licenses are listed with code falling under that license.  See *note
Licenses and Acknowledgements for Incorporated Software: 4550. for an
incomplete list of these licenses.

* Menu:

* PSF LICENSE AGREEMENT FOR PYTHON 3.9.10: PSF LICENSE AGREEMENT FOR PYTHON 3 9 10.
* BEOPEN.COM LICENSE AGREEMENT FOR PYTHON 2.0: BEOPEN COM LICENSE AGREEMENT FOR PYTHON 2 0.
* CNRI LICENSE AGREEMENT FOR PYTHON 1.6.1: CNRI LICENSE AGREEMENT FOR PYTHON 1 6 1.
* CWI LICENSE AGREEMENT FOR PYTHON 0.9.0 THROUGH 1.2: CWI LICENSE AGREEMENT FOR PYTHON 0 9 0 THROUGH 1 2.
* ZERO-CLAUSE BSD LICENSE FOR CODE IN THE PYTHON 3.9.10 DOCUMENTATION: ZERO-CLAUSE BSD LICENSE FOR CODE IN THE PYTHON 3 9 10 DOCUMENTATION.


File: python.info,  Node: PSF LICENSE AGREEMENT FOR PYTHON 3 9 10,  Next: BEOPEN COM LICENSE AGREEMENT FOR PYTHON 2 0,  Up: Terms and conditions for accessing or otherwise using Python

16.2.1 PSF LICENSE AGREEMENT FOR PYTHON 3.9.10
----------------------------------------------

     1. This LICENSE AGREEMENT is between the Python Software Foundation ("PSF"), and
        the Individual or Organization ("Licensee") accessing and otherwise using Python
        3.9.10 software in source or binary form and its associated documentation.

     2. Subject to the terms and conditions of this License Agreement, PSF hereby
        grants Licensee a nonexclusive, royalty-free, world-wide license to reproduce,
        analyze, test, perform and/or display publicly, prepare derivative works,
        distribute, and otherwise use Python 3.9.10 alone or in any derivative
        version, provided, however, that PSF's License Agreement and PSF's notice of
        copyright, i.e., "Copyright © 2001-2022 Python Software Foundation; All Rights
        Reserved" are retained in Python 3.9.10 alone or in any derivative version
        prepared by Licensee.

     3. In the event Licensee prepares a derivative work that is based on or
        incorporates Python 3.9.10 or any part thereof, and wants to make the
        derivative work available to others as provided herein, then Licensee hereby
        agrees to include in any such work a brief summary of the changes made to Python
        3.9.10.

     4. PSF is making Python 3.9.10 available to Licensee on an "AS IS" basis.
        PSF MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED.  BY WAY OF
        EXAMPLE, BUT NOT LIMITATION, PSF MAKES NO AND DISCLAIMS ANY REPRESENTATION OR
        WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OR THAT THE
        USE OF PYTHON 3.9.10 WILL NOT INFRINGE ANY THIRD PARTY RIGHTS.

     5. PSF SHALL NOT BE LIABLE TO LICENSEE OR ANY OTHER USERS OF PYTHON 3.9.10
        FOR ANY INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES OR LOSS AS A RESULT OF
        MODIFYING, DISTRIBUTING, OR OTHERWISE USING PYTHON 3.9.10, OR ANY DERIVATIVE
        THEREOF, EVEN IF ADVISED OF THE POSSIBILITY THEREOF.

     6. This License Agreement will automatically terminate upon a material breach of
        its terms and conditions.

     7. Nothing in this License Agreement shall be deemed to create any relationship
        of agency, partnership, or joint venture between PSF and Licensee.  This License
        Agreement does not grant permission to use PSF trademarks or trade name in a
        trademark sense to endorse or promote products or services of Licensee, or any
        third party.

     8. By copying, installing or otherwise using Python 3.9.10, Licensee agrees
        to be bound by the terms and conditions of this License Agreement.


File: python.info,  Node: BEOPEN COM LICENSE AGREEMENT FOR PYTHON 2 0,  Next: CNRI LICENSE AGREEMENT FOR PYTHON 1 6 1,  Prev: PSF LICENSE AGREEMENT FOR PYTHON 3 9 10,  Up: Terms and conditions for accessing or otherwise using Python

16.2.2 BEOPEN.COM LICENSE AGREEMENT FOR PYTHON 2.0
--------------------------------------------------

BEOPEN PYTHON OPEN SOURCE LICENSE AGREEMENT VERSION 1

     1. This LICENSE AGREEMENT is between BeOpen.com ("BeOpen"), having an office at
        160 Saratoga Avenue, Santa Clara, CA 95051, and the Individual or Organization
        ("Licensee") accessing and otherwise using this software in source or binary
        form and its associated documentation ("the Software").

     2. Subject to the terms and conditions of this BeOpen Python License Agreement,
        BeOpen hereby grants Licensee a non-exclusive, royalty-free, world-wide license
        to reproduce, analyze, test, perform and/or display publicly, prepare derivative
        works, distribute, and otherwise use the Software alone or in any derivative
        version, provided, however, that the BeOpen Python License is retained in the
        Software, alone or in any derivative version prepared by Licensee.

     3. BeOpen is making the Software available to Licensee on an "AS IS" basis.
        BEOPEN MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED.  BY WAY OF
        EXAMPLE, BUT NOT LIMITATION, BEOPEN MAKES NO AND DISCLAIMS ANY REPRESENTATION OR
        WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OR THAT THE
        USE OF THE SOFTWARE WILL NOT INFRINGE ANY THIRD PARTY RIGHTS.

     4. BEOPEN SHALL NOT BE LIABLE TO LICENSEE OR ANY OTHER USERS OF THE SOFTWARE FOR
        ANY INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES OR LOSS AS A RESULT OF USING,
        MODIFYING OR DISTRIBUTING THE SOFTWARE, OR ANY DERIVATIVE THEREOF, EVEN IF
        ADVISED OF THE POSSIBILITY THEREOF.

     5. This License Agreement will automatically terminate upon a material breach of
        its terms and conditions.

     6. This License Agreement shall be governed by and interpreted in all respects
        by the law of the State of California, excluding conflict of law provisions.
        Nothing in this License Agreement shall be deemed to create any relationship of
        agency, partnership, or joint venture between BeOpen and Licensee.  This License
        Agreement does not grant permission to use BeOpen trademarks or trade names in a
        trademark sense to endorse or promote products or services of Licensee, or any
        third party.  As an exception, the "BeOpen Python" logos available at
        ‘http://www.pythonlabs.com/logos.html’ may be used according to the permissions
        granted on that web page.

     7. By copying, installing or otherwise using the software, Licensee agrees to be
        bound by the terms and conditions of this License Agreement.


File: python.info,  Node: CNRI LICENSE AGREEMENT FOR PYTHON 1 6 1,  Next: CWI LICENSE AGREEMENT FOR PYTHON 0 9 0 THROUGH 1 2,  Prev: BEOPEN COM LICENSE AGREEMENT FOR PYTHON 2 0,  Up: Terms and conditions for accessing or otherwise using Python

16.2.3 CNRI LICENSE AGREEMENT FOR PYTHON 1.6.1
----------------------------------------------

     1. This LICENSE AGREEMENT is between the Corporation for National Research
        Initiatives, having an office at 1895 Preston White Drive, Reston, VA 20191
        ("CNRI"), and the Individual or Organization ("Licensee") accessing and
        otherwise using Python 1.6.1 software in source or binary form and its
        associated documentation.

     2. Subject to the terms and conditions of this License Agreement, CNRI hereby
        grants Licensee a nonexclusive, royalty-free, world-wide license to reproduce,
        analyze, test, perform and/or display publicly, prepare derivative works,
        distribute, and otherwise use Python 1.6.1 alone or in any derivative version,
        provided, however, that CNRI's License Agreement and CNRI's notice of copyright,
        i.e., "Copyright © 1995-2001 Corporation for National Research Initiatives; All
        Rights Reserved" are retained in Python 1.6.1 alone or in any derivative version
        prepared by Licensee.  Alternately, in lieu of CNRI's License Agreement,
        Licensee may substitute the following text (omitting the quotes): "Python 1.6.1
        is made available subject to the terms and conditions in CNRI's License
        Agreement.  This Agreement together with Python 1.6.1 may be located on the
        Internet using the following unique, persistent identifier (known as a handle):
        1895.22/1013.  This Agreement may also be obtained from a proxy server on the
        Internet using the following URL: ‘http://hdl.handle.net/1895.22/1013’."

     3. In the event Licensee prepares a derivative work that is based on or
        incorporates Python 1.6.1 or any part thereof, and wants to make the derivative
        work available to others as provided herein, then Licensee hereby agrees to
        include in any such work a brief summary of the changes made to Python 1.6.1.

     4. CNRI is making Python 1.6.1 available to Licensee on an "AS IS" basis.  CNRI
        MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED.  BY WAY OF EXAMPLE,
        BUT NOT LIMITATION, CNRI MAKES NO AND DISCLAIMS ANY REPRESENTATION OR WARRANTY
        OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OR THAT THE USE OF
        PYTHON 1.6.1 WILL NOT INFRINGE ANY THIRD PARTY RIGHTS.

     5. CNRI SHALL NOT BE LIABLE TO LICENSEE OR ANY OTHER USERS OF PYTHON 1.6.1 FOR
        ANY INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES OR LOSS AS A RESULT OF
        MODIFYING, DISTRIBUTING, OR OTHERWISE USING PYTHON 1.6.1, OR ANY DERIVATIVE
        THEREOF, EVEN IF ADVISED OF THE POSSIBILITY THEREOF.

     6. This License Agreement will automatically terminate upon a material breach of
        its terms and conditions.

     7. This License Agreement shall be governed by the federal intellectual property
        law of the United States, including without limitation the federal copyright
        law, and, to the extent such U.S. federal law does not apply, by the law of the
        Commonwealth of Virginia, excluding Virginia's conflict of law provisions.
        Notwithstanding the foregoing, with regard to derivative works based on Python
        1.6.1 that incorporate non-separable material that was previously distributed
        under the GNU General Public License (GPL), the law of the Commonwealth of
        Virginia shall govern this License Agreement only as to issues arising under or
        with respect to Paragraphs 4, 5, and 7 of this License Agreement.  Nothing in
        this License Agreement shall be deemed to create any relationship of agency,
        partnership, or joint venture between CNRI and Licensee.  This License Agreement
        does not grant permission to use CNRI trademarks or trade name in a trademark
        sense to endorse or promote products or services of Licensee, or any third
        party.

     8. By clicking on the "ACCEPT" button where indicated, or by copying, installing
        or otherwise using Python 1.6.1, Licensee agrees to be bound by the terms and
        conditions of this License Agreement.


File: python.info,  Node: CWI LICENSE AGREEMENT FOR PYTHON 0 9 0 THROUGH 1 2,  Next: ZERO-CLAUSE BSD LICENSE FOR CODE IN THE PYTHON 3 9 10 DOCUMENTATION,  Prev: CNRI LICENSE AGREEMENT FOR PYTHON 1 6 1,  Up: Terms and conditions for accessing or otherwise using Python

16.2.4 CWI LICENSE AGREEMENT FOR PYTHON 0.9.0 THROUGH 1.2
---------------------------------------------------------

     Copyright © 1991 - 1995, Stichting Mathematisch Centrum Amsterdam, The
     Netherlands.  All rights reserved.

     Permission to use, copy, modify, and distribute this software and its
     documentation for any purpose and without fee is hereby granted, provided that
     the above copyright notice appear in all copies and that both that copyright
     notice and this permission notice appear in supporting documentation, and that
     the name of Stichting Mathematisch Centrum or CWI not be used in advertising or
     publicity pertaining to distribution of the software without specific, written
     prior permission.

     STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
     SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
     EVENT SHALL STICHTING MATHEMATISCH CENTRUM BE LIABLE FOR ANY SPECIAL, INDIRECT
     OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
     DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
     ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
     SOFTWARE.


File: python.info,  Node: ZERO-CLAUSE BSD LICENSE FOR CODE IN THE PYTHON 3 9 10 DOCUMENTATION,  Prev: CWI LICENSE AGREEMENT FOR PYTHON 0 9 0 THROUGH 1 2,  Up: Terms and conditions for accessing or otherwise using Python

16.2.5 ZERO-CLAUSE BSD LICENSE FOR CODE IN THE PYTHON 3.9.10 DOCUMENTATION
--------------------------------------------------------------------------

     Permission to use, copy, modify, and/or distribute this software for any
     purpose with or without fee is hereby granted.

     THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
     REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
     AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
     INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
     LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
     OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
     PERFORMANCE OF THIS SOFTWARE.


File: python.info,  Node: Licenses and Acknowledgements for Incorporated Software,  Prev: Terms and conditions for accessing or otherwise using Python,  Up: History and License

16.3 Licenses and Acknowledgements for Incorporated Software
============================================================

This section is an incomplete, but growing list of licenses and
acknowledgements for third-party software incorporated in the Python
distribution.

* Menu:

* Mersenne Twister::
* Sockets: Sockets<2>.
* Asynchronous socket services::
* Cookie management::
* Execution tracing::
* UUencode and UUdecode functions::
* XML Remote Procedure Calls::
* test_epoll::
* Select kqueue::
* SipHash24::
* strtod and dtoa::
* OpenSSL::
* expat::
* libffi::
* zlib: zlib<3>.
* cfuhash::
* libmpdec::
* W3C C14N test suite::


File: python.info,  Node: Mersenne Twister,  Next: Sockets<2>,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.1 Mersenne Twister
-----------------------

The ‘_random’ module includes code based on a download from
‘http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/emt19937ar.html’.
The following are the verbatim comments from the original code:

     A C-program for MT19937, with initialization improved 2002/1/26.
     Coded by Takuji Nishimura and Makoto Matsumoto.

     Before using, initialize the state by using init_genrand(seed)
     or init_by_array(init_key, key_length).

     Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura,
     All rights reserved.

     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
     are met:

      1. Redistributions of source code must retain the above copyright
         notice, this list of conditions and the following disclaimer.

      2. Redistributions in binary form must reproduce the above copyright
         notice, this list of conditions and the following disclaimer in the
         documentation and/or other materials provided with the distribution.

      3. The names of its contributors may not be used to endorse or promote
         products derived from this software without specific prior written
         permission.

     THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
     A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
     CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
     EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
     PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
     PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
     LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
     NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
     SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


     Any feedback is very welcome.
     http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
     email: m-mat @ math.sci.hiroshima-u.ac.jp (remove space)


File: python.info,  Node: Sockets<2>,  Next: Asynchronous socket services,  Prev: Mersenne Twister,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.2 Sockets
--------------

The *note socket: ef. module uses the functions, ‘getaddrinfo()’, and
‘getnameinfo()’, which are coded in separate source files from the WIDE
Project, ‘http://www.wide.ad.jp/’.

     Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
     All rights reserved.

     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
     are met:
     1. Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.
     2. Redistributions in binary form must reproduce the above copyright
        notice, this list of conditions and the following disclaimer in the
        documentation and/or other materials provided with the distribution.
     3. Neither the name of the project nor the names of its contributors
        may be used to endorse or promote products derived from this software
        without specific prior written permission.

     THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
     ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
     FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.


File: python.info,  Node: Asynchronous socket services,  Next: Cookie management,  Prev: Sockets<2>,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.3 Asynchronous socket services
-----------------------------------

The *note asynchat: 8. and *note asyncore: a. modules contain the
following notice:

     Copyright 1996 by Sam Rushing

                             All Rights Reserved

     Permission to use, copy, modify, and distribute this software and
     its documentation for any purpose and without fee is hereby
     granted, provided that the above copyright notice appear in all
     copies and that both that copyright notice and this permission
     notice appear in supporting documentation, and that the name of Sam
     Rushing not be used in advertising or publicity pertaining to
     distribution of the software without specific, written prior
     permission.

     SAM RUSHING DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
     INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
     NO EVENT SHALL SAM RUSHING BE LIABLE FOR ANY SPECIAL, INDIRECT OR
     CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
     OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
     NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
     CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.


File: python.info,  Node: Cookie management,  Next: Execution tracing,  Prev: Asynchronous socket services,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.4 Cookie management
------------------------

The *note http.cookies: 95. module contains the following notice:

     Copyright 2000 by Timothy O'Malley <timo@alum.mit.edu>

                    All Rights Reserved

     Permission to use, copy, modify, and distribute this software
     and its documentation for any purpose and without fee is hereby
     granted, provided that the above copyright notice appear in all
     copies and that both that copyright notice and this permission
     notice appear in supporting documentation, and that the name of
     Timothy O'Malley  not be used in advertising or publicity
     pertaining to distribution of the software without specific, written
     prior permission.

     Timothy O'Malley DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
     SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
     AND FITNESS, IN NO EVENT SHALL Timothy O'Malley BE LIABLE FOR
     ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
     WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
     WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
     ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
     PERFORMANCE OF THIS SOFTWARE.


File: python.info,  Node: Execution tracing,  Next: UUencode and UUdecode functions,  Prev: Cookie management,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.5 Execution tracing
------------------------

The *note trace: 11b. module contains the following notice:

     portions copyright 2001, Autonomous Zones Industries, Inc., all rights...
     err...  reserved and offered to the public under the terms of the
     Python 2.2 license.
     Author: Zooko O'Whielacronx
     http://zooko.com/
     mailto:zooko@zooko.com

     Copyright 2000, Mojam Media, Inc., all rights reserved.
     Author: Skip Montanaro

     Copyright 1999, Bioreason, Inc., all rights reserved.
     Author: Andrew Dalke

     Copyright 1995-1997, Automatrix, Inc., all rights reserved.
     Author: Skip Montanaro

     Copyright 1991-1995, Stichting Mathematisch Centrum, all rights reserved.


     Permission to use, copy, modify, and distribute this Python software and
     its associated documentation for any purpose without fee is hereby
     granted, provided that the above copyright notice appears in all copies,
     and that both that copyright notice and this permission notice appear in
     supporting documentation, and that the name of neither Automatrix,
     Bioreason or Mojam Media be used in advertising or publicity pertaining to
     distribution of the software without specific, written prior permission.


File: python.info,  Node: UUencode and UUdecode functions,  Next: XML Remote Procedure Calls,  Prev: Execution tracing,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.6 UUencode and UUdecode functions
--------------------------------------

The *note uu: 12c. module contains the following notice:

     Copyright 1994 by Lance Ellinghouse
     Cathedral City, California Republic, United States of America.
                            All Rights Reserved
     Permission to use, copy, modify, and distribute this software and its
     documentation for any purpose and without fee is hereby granted,
     provided that the above copyright notice appear in all copies and that
     both that copyright notice and this permission notice appear in
     supporting documentation, and that the name of Lance Ellinghouse
     not be used in advertising or publicity pertaining to distribution
     of the software without specific, written prior permission.
     LANCE ELLINGHOUSE DISCLAIMS ALL WARRANTIES WITH REGARD TO
     THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
     FITNESS, IN NO EVENT SHALL LANCE ELLINGHOUSE CENTRUM BE LIABLE
     FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
     WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
     ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
     OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

     Modified by Jack Jansen, CWI, July 1995:
     - Use binascii module to do the actual line-by-line conversion
       between ascii and binary. This results in a 1000-fold speedup. The C
       version is still 5 times faster, though.
     - Arguments more compliant with Python standard


File: python.info,  Node: XML Remote Procedure Calls,  Next: test_epoll,  Prev: UUencode and UUdecode functions,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.7 XML Remote Procedure Calls
---------------------------------

The *note xmlrpc.client: 148. module contains the following notice:

         The XML-RPC client interface is

     Copyright (c) 1999-2002 by Secret Labs AB
     Copyright (c) 1999-2002 by Fredrik Lundh

     By obtaining, using, and/or copying this software and/or its
     associated documentation, you agree that you have read, understood,
     and will comply with the following terms and conditions:

     Permission to use, copy, modify, and distribute this software and
     its associated documentation for any purpose and without fee is
     hereby granted, provided that the above copyright notice appears in
     all copies, and that both that copyright notice and this permission
     notice appear in supporting documentation, and that the name of
     Secret Labs AB or the author not be used in advertising or publicity
     pertaining to distribution of the software without specific, written
     prior permission.

     SECRET LABS AB AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD
     TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANT-
     ABILITY AND FITNESS.  IN NO EVENT SHALL SECRET LABS AB OR THE AUTHOR
     BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY
     DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
     WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
     ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
     OF THIS SOFTWARE.


File: python.info,  Node: test_epoll,  Next: Select kqueue,  Prev: XML Remote Procedure Calls,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.8 test_epoll
-----------------

The ‘test_epoll’ module contains the following notice:

     Copyright (c) 2001-2006 Twisted Matrix Laboratories.

     Permission is hereby granted, free of charge, to any person obtaining
     a copy of this software and associated documentation files (the
     "Software"), to deal in the Software without restriction, including
     without limitation the rights to use, copy, modify, merge, publish,
     distribute, sublicense, and/or sell copies of the Software, and to
     permit persons to whom the Software is furnished to do so, subject to
     the following conditions:

     The above copyright notice and this permission notice shall be
     included in all copies or substantial portions of the Software.

     THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
     EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
     MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
     NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
     LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
     OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
     WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


File: python.info,  Node: Select kqueue,  Next: SipHash24,  Prev: test_epoll,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.9 Select kqueue
--------------------

The *note select: e5. module contains the following notice for the
kqueue interface:

     Copyright (c) 2000 Doug White, 2006 James Knight, 2007 Christian Heimes
     All rights reserved.

     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
     are met:
     1. Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.
     2. Redistributions in binary form must reproduce the above copyright
        notice, this list of conditions and the following disclaimer in the
        documentation and/or other materials provided with the distribution.

     THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.


File: python.info,  Node: SipHash24,  Next: strtod and dtoa,  Prev: Select kqueue,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.10 SipHash24
-----------------

The file ‘Python/pyhash.c’ contains Marek Majkowski’ implementation of
Dan Bernstein’s SipHash24 algorithm.  It contains the following note:

     <MIT License>
     Copyright (c) 2013  Marek Majkowski <marek@popcount.org>

     Permission is hereby granted, free of charge, to any person obtaining a copy
     of this software and associated documentation files (the "Software"), to deal
     in the Software without restriction, including without limitation the rights
     to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     copies of the Software, and to permit persons to whom the Software is
     furnished to do so, subject to the following conditions:

     The above copyright notice and this permission notice shall be included in
     all copies or substantial portions of the Software.
     </MIT License>

     Original location:
        https://github.com/majek/csiphash/

     Solution inspired by code from:
        Samuel Neves (supercop/crypto_auth/siphash24/little)
        djb (supercop/crypto_auth/siphash24/little2)
        Jean-Philippe Aumasson (https://131002.net/siphash/siphash24.c)


File: python.info,  Node: strtod and dtoa,  Next: OpenSSL,  Prev: SipHash24,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.11 strtod and dtoa
-----------------------

The file ‘Python/dtoa.c’, which supplies C functions dtoa and strtod for
conversion of C doubles to and from strings, is derived from the file of
the same name by David M. Gay, currently available from
‘http://www.netlib.org/fp/’.  The original file, as retrieved on March
16, 2009, contains the following copyright and licensing notice:

     /****************************************************************
      *
      * The author of this software is David M. Gay.
      *
      * Copyright (c) 1991, 2000, 2001 by Lucent Technologies.
      *
      * Permission to use, copy, modify, and distribute this software for any
      * purpose without fee is hereby granted, provided that this entire notice
      * is included in all copies of any software which is or includes a copy
      * or modification of this software and in all copies of the supporting
      * documentation for such software.
      *
      * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
      * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHOR NOR LUCENT MAKES ANY
      * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
      * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
      *
      ***************************************************************/


File: python.info,  Node: OpenSSL,  Next: expat,  Prev: strtod and dtoa,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.12 OpenSSL
---------------

The modules *note hashlib: 8c, *note posix: d1, *note ssl: f3, *note
crypt: 28. use the OpenSSL library for added performance if made
available by the operating system.  Additionally, the Windows and macOS
installers for Python may include a copy of the OpenSSL libraries, so we
include a copy of the OpenSSL license here:

      LICENSE ISSUES
      ==============

      The OpenSSL toolkit stays under a dual license, i.e. both the conditions of
      the OpenSSL License and the original SSLeay license apply to the toolkit.
      See below for the actual license texts. Actually both licenses are BSD-style
      Open Source licenses. In case of any license issues related to OpenSSL
      please contact openssl-core@openssl.org.

      OpenSSL License
      ---------------

        /* ====================================================================
         * Copyright (c) 1998-2008 The OpenSSL Project.  All rights reserved.
         *
         * Redistribution and use in source and binary forms, with or without
         * modification, are permitted provided that the following conditions
         * are met:
         *
         * 1. Redistributions of source code must retain the above copyright
         *    notice, this list of conditions and the following disclaimer.
         *
         * 2. Redistributions in binary form must reproduce the above copyright
         *    notice, this list of conditions and the following disclaimer in
         *    the documentation and/or other materials provided with the
         *    distribution.
         *
         * 3. All advertising materials mentioning features or use of this
         *    software must display the following acknowledgment:
         *    "This product includes software developed by the OpenSSL Project
         *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
         *
         * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
         *    endorse or promote products derived from this software without
         *    prior written permission. For written permission, please contact
         *    openssl-core@openssl.org.
         *
         * 5. Products derived from this software may not be called "OpenSSL"
         *    nor may "OpenSSL" appear in their names without prior written
         *    permission of the OpenSSL Project.
         *
         * 6. Redistributions of any form whatsoever must retain the following
         *    acknowledgment:
         *    "This product includes software developed by the OpenSSL Project
         *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
         *
         * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
         * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
         * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
         * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
         * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
         * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
         * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
         * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
         * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
         * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
         * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
         * OF THE POSSIBILITY OF SUCH DAMAGE.
         * ====================================================================
         *
         * This product includes cryptographic software written by Eric Young
         * (eay@cryptsoft.com).  This product includes software written by Tim
         * Hudson (tjh@cryptsoft.com).
         *
         */

     Original SSLeay License
     -----------------------

        /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
         * All rights reserved.
         *
         * This package is an SSL implementation written
         * by Eric Young (eay@cryptsoft.com).
         * The implementation was written so as to conform with Netscapes SSL.
         *
         * This library is free for commercial and non-commercial use as long as
         * the following conditions are aheared to.  The following conditions
         * apply to all code found in this distribution, be it the RC4, RSA,
         * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
         * included with this distribution is covered by the same copyright terms
         * except that the holder is Tim Hudson (tjh@cryptsoft.com).
         *
         * Copyright remains Eric Young's, and as such any Copyright notices in
         * the code are not to be removed.
         * If this package is used in a product, Eric Young should be given attribution
         * as the author of the parts of the library used.
         * This can be in the form of a textual message at program startup or
         * in documentation (online or textual) provided with the package.
         *
         * Redistribution and use in source and binary forms, with or without
         * modification, are permitted provided that the following conditions
         * are met:
         * 1. Redistributions of source code must retain the copyright
         *    notice, this list of conditions and the following disclaimer.
         * 2. Redistributions in binary form must reproduce the above copyright
         *    notice, this list of conditions and the following disclaimer in the
         *    documentation and/or other materials provided with the distribution.
         * 3. All advertising materials mentioning features or use of this software
         *    must display the following acknowledgement:
         *    "This product includes cryptographic software written by
         *     Eric Young (eay@cryptsoft.com)"
         *    The word 'cryptographic' can be left out if the rouines from the library
         *    being used are not cryptographic related :-).
         * 4. If you include any Windows specific code (or a derivative thereof) from
         *    the apps directory (application code) you must include an acknowledgement:
         *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
         *
         * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
         * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
         * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
         * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
         * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
         * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
         * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
         * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
         * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
         * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
         * SUCH DAMAGE.
         *
         * The licence and distribution terms for any publically available version or
         * derivative of this code cannot be changed.  i.e. this code cannot simply be
         * copied and put under another distribution licence
         * [including the GNU Public Licence.]
         */


File: python.info,  Node: expat,  Next: libffi,  Prev: OpenSSL,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.13 expat
-------------

The ‘pyexpat’ extension is built using an included copy of the expat
sources unless the build is configured ‘--with-system-expat’:

     Copyright (c) 1998, 1999, 2000 Thai Open Source Software Center Ltd
                                    and Clark Cooper

     Permission is hereby granted, free of charge, to any person obtaining
     a copy of this software and associated documentation files (the
     "Software"), to deal in the Software without restriction, including
     without limitation the rights to use, copy, modify, merge, publish,
     distribute, sublicense, and/or sell copies of the Software, and to
     permit persons to whom the Software is furnished to do so, subject to
     the following conditions:

     The above copyright notice and this permission notice shall be included
     in all copies or substantial portions of the Software.

     THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
     EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
     MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
     IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
     CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
     TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
     SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


File: python.info,  Node: libffi,  Next: zlib<3>,  Prev: expat,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.14 libffi
--------------

The ‘_ctypes’ extension is built using an included copy of the libffi
sources unless the build is configured ‘--with-system-libffi’:

     Copyright (c) 1996-2008  Red Hat, Inc and others.

     Permission is hereby granted, free of charge, to any person obtaining
     a copy of this software and associated documentation files (the
     ``Software''), to deal in the Software without restriction, including
     without limitation the rights to use, copy, modify, merge, publish,
     distribute, sublicense, and/or sell copies of the Software, and to
     permit persons to whom the Software is furnished to do so, subject to
     the following conditions:

     The above copyright notice and this permission notice shall be included
     in all copies or substantial portions of the Software.

     THE SOFTWARE IS PROVIDED ``AS IS'', WITHOUT WARRANTY OF ANY KIND,
     EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
     MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
     NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
     HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
     WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
     OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
     DEALINGS IN THE SOFTWARE.


File: python.info,  Node: zlib<3>,  Next: cfuhash,  Prev: libffi,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.15 zlib
------------

The *note zlib: 14d. extension is built using an included copy of the
zlib sources if the zlib version found on the system is too old to be
used for the build:

     Copyright (C) 1995-2011 Jean-loup Gailly and Mark Adler

     This software is provided 'as-is', without any express or implied
     warranty.  In no event will the authors be held liable for any damages
     arising from the use of this software.

     Permission is granted to anyone to use this software for any purpose,
     including commercial applications, and to alter it and redistribute it
     freely, subject to the following restrictions:

     1. The origin of this software must not be misrepresented; you must not
        claim that you wrote the original software. If you use this software
        in a product, an acknowledgment in the product documentation would be
        appreciated but is not required.

     2. Altered source versions must be plainly marked as such, and must not be
        misrepresented as being the original software.

     3. This notice may not be removed or altered from any source distribution.

     Jean-loup Gailly        Mark Adler
     jloup@gzip.org          madler@alumni.caltech.edu


File: python.info,  Node: cfuhash,  Next: libmpdec,  Prev: zlib<3>,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.16 cfuhash
---------------

The implementation of the hash table used by the *note tracemalloc: 11d.
is based on the cfuhash project:

     Copyright (c) 2005 Don Owens
     All rights reserved.

     This code is released under the BSD license:

     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
     are met:

       * Redistributions of source code must retain the above copyright
         notice, this list of conditions and the following disclaimer.

       * Redistributions in binary form must reproduce the above
         copyright notice, this list of conditions and the following
         disclaimer in the documentation and/or other materials provided
         with the distribution.

       * Neither the name of the author nor the names of its
         contributors may be used to endorse or promote products derived
         from this software without specific prior written permission.

     THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
     FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
     COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
     INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
     (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
     SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
     STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
     OF THE POSSIBILITY OF SUCH DAMAGE.


File: python.info,  Node: libmpdec,  Next: W3C C14N test suite,  Prev: cfuhash,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.17 libmpdec
----------------

The ‘_decimal’ module is built using an included copy of the libmpdec
library unless the build is configured ‘--with-system-libmpdec’:

     Copyright (c) 2008-2020 Stefan Krah. All rights reserved.

     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
     are met:

     1. Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.

     2. Redistributions in binary form must reproduce the above copyright
        notice, this list of conditions and the following disclaimer in the
        documentation and/or other materials provided with the distribution.

     THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS" AND
     ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.


File: python.info,  Node: W3C C14N test suite,  Prev: libmpdec,  Up: Licenses and Acknowledgements for Incorporated Software

16.3.18 W3C C14N test suite
---------------------------

The C14N 2.0 test suite in the *note test: 105. package
(‘Lib/test/xmltestdata/c14n-20/’) was retrieved from the W3C website at
‘https://www.w3.org/TR/xml-c14n2-testcases/’ and is distributed under
the 3-clause BSD license:

     Copyright (c) 2013 W3C(R) (MIT, ERCIM, Keio, Beihang),
     All Rights Reserved.

     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
     are met:

     * Redistributions of works must retain the original copyright notice,
       this list of conditions and the following disclaimer.
     * Redistributions in binary form must reproduce the original copyright
       notice, this list of conditions and the following disclaimer in the
       documentation and/or other materials provided with the distribution.
     * Neither the name of the W3C nor the names of its contributors may be
       used to endorse or promote products derived from this work without
       specific prior written permission.

     THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
     A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
     OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
     SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
     LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
     OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


File: python.info,  Node: Distributing Python Modules Legacy version,  Next: Installing Python Modules Legacy version,  Prev: History and License,  Up: Top

17 Distributing Python Modules (Legacy version)
***********************************************


Authors: Greg Ward, Anthony Baxter


Email: <distutils-sig@python.org>

See also
........

*note Distributing Python Modules: 8e3.

     The up to date module distribution documentations

     Note: This document is being retained solely until the ‘setuptools’
     documentation at
     ‘https://setuptools.readthedocs.io/en/latest/setuptools.html’
     independently covers all of the relevant information currently
     included here.

     Note: This guide only covers the basic tools for building and
     distributing extensions that are provided as part of this version
     of Python.  Third party tools offer easier to use and more secure
     alternatives.  Refer to the quick recommendations section(1) in the
     Python Packaging User Guide for more information.

This document describes the Python Distribution Utilities (“Distutils”)
from the module developer’s point of view, describing the underlying
capabilities that ‘setuptools’ builds on to allow Python developers to
make Python modules and extensions readily available to a wider
audience.

* Menu:

* An Introduction to Distutils::
* Writing the Setup Script::
* Writing the Setup Configuration File::
* Creating a Source Distribution::
* Creating Built Distributions::
* Distutils Examples::
* Extending Distutils::
* Command Reference::
* API Reference::

   ---------- Footnotes ----------

   (1) https://packaging.python.org/guides/tool-recommendations/


File: python.info,  Node: An Introduction to Distutils,  Next: Writing the Setup Script,  Up: Distributing Python Modules Legacy version

17.1 An Introduction to Distutils
=================================

     Note: This document is being retained solely until the ‘setuptools’
     documentation at
     ‘https://setuptools.readthedocs.io/en/latest/setuptools.html’
     independently covers all of the relevant information currently
     included here.

This document covers using the Distutils to distribute your Python
modules, concentrating on the role of developer/distributor: if you’re
looking for information on installing Python modules, you should refer
to the *note Installing Python Modules (Legacy version): 8e4. chapter.

* Menu:

* Concepts & Terminology::
* A Simple Example: A Simple Example<2>.
* General Python terminology::
* Distutils-specific terminology::


File: python.info,  Node: Concepts & Terminology,  Next: A Simple Example<2>,  Up: An Introduction to Distutils

17.1.1 Concepts & Terminology
-----------------------------

Using the Distutils is quite simple, both for module developers and for
users/administrators installing third-party modules.  As a developer,
your responsibilities (apart from writing solid, well-documented and
well-tested code, of course!)  are:

   * write a setup script (‘setup.py’ by convention)

   * (optional) write a setup configuration file

   * create a source distribution

   * (optional) create one or more built (binary) distributions

Each of these tasks is covered in this document.

Not all module developers have access to a multitude of platforms, so
it’s not always feasible to expect them to create a multitude of built
distributions.  It is hoped that a class of intermediaries, called
`packagers', will arise to address this need.  Packagers will take
source distributions released by module developers, build them on one or
more platforms, and release the resulting built distributions.  Thus,
users on the most popular platforms will be able to install most popular
Python module distributions in the most natural way for their platform,
without having to run a single setup script or compile a line of code.


File: python.info,  Node: A Simple Example<2>,  Next: General Python terminology,  Prev: Concepts & Terminology,  Up: An Introduction to Distutils

17.1.2 A Simple Example
-----------------------

The setup script is usually quite simple, although since it’s written in
Python, there are no arbitrary limits to what you can do with it, though
you should be careful about putting arbitrarily expensive operations in
your setup script.  Unlike, say, Autoconf-style configure scripts, the
setup script may be run multiple times in the course of building and
installing your module distribution.

If all you want to do is distribute a module called ‘foo’, contained in
a file ‘foo.py’, then your setup script can be as simple as this:

     from distutils.core import setup
     setup(name='foo',
           version='1.0',
           py_modules=['foo'],
           )

Some observations:

   * most information that you supply to the Distutils is supplied as
     keyword arguments to the ‘setup()’ function

   * those keyword arguments fall into two categories: package metadata
     (name, version number) and information about what’s in the package
     (a list of pure Python modules, in this case)

   * modules are specified by module name, not filename (the same will
     hold true for packages and extensions)

   * it’s recommended that you supply a little more metadata, in
     particular your name, email address and a URL for the project (see
     section *note Writing the Setup Script: 4572. for an example)

To create a source distribution for this module, you would create a
setup script, ‘setup.py’, containing the above code, and run this
command from a terminal:

     python setup.py sdist

For Windows, open a command prompt window (Start ‣ Accessories) and
change the command to:

     setup.py sdist

‘sdist’ will create an archive file (e.g., tarball on Unix, ZIP file on
Windows) containing your setup script ‘setup.py’, and your module
‘foo.py’.  The archive file will be named ‘foo-1.0.tar.gz’ (or ‘.zip’),
and will unpack into a directory ‘foo-1.0’.

If an end-user wishes to install your ‘foo’ module, all they have to do
is download ‘foo-1.0.tar.gz’ (or ‘.zip’), unpack it, and—from the
‘foo-1.0’ directory—run

     python setup.py install

which will ultimately copy ‘foo.py’ to the appropriate directory for
third-party modules in their Python installation.

This simple example demonstrates some fundamental concepts of the
Distutils.  First, both developers and installers have the same basic
user interface, i.e.  the setup script.  The difference is which
Distutils `commands' they use: the ‘sdist’ command is almost exclusively
for module developers, while ‘install’ is more often for installers
(although most developers will want to install their own code
occasionally).

If you want to make things really easy for your users, you can create
one or more built distributions for them.  For instance, if you are
running on a Windows machine, and want to make things easy for other
Windows users, you can create an executable installer (the most
appropriate type of built distribution for this platform) with the
‘bdist_wininst’ command.  For example:

     python setup.py bdist_wininst

will create an executable installer, ‘foo-1.0.win32.exe’, in the current
directory.

Other useful built distribution formats are RPM, implemented by the
‘bdist_rpm’ command, Solaris ‘pkgtool’ (‘bdist_pkgtool’), and HP-UX
‘swinstall’ (‘bdist_sdux’).  For example, the following command will
create an RPM file called ‘foo-1.0.noarch.rpm’:

     python setup.py bdist_rpm

(The ‘bdist_rpm’ command uses the ‘rpm’ executable, therefore this has
to be run on an RPM-based system such as Red Hat Linux, SuSE Linux, or
Mandrake Linux.)

You can find out what distribution formats are available at any time by
running

     python setup.py bdist --help-formats


File: python.info,  Node: General Python terminology,  Next: Distutils-specific terminology,  Prev: A Simple Example<2>,  Up: An Introduction to Distutils

17.1.3 General Python terminology
---------------------------------

If you’re reading this document, you probably have a good idea of what
modules, extensions, and so forth are.  Nevertheless, just to be sure
that everyone is operating from a common starting point, we offer the
following glossary of common Python terms:

module

     the basic unit of code reusability in Python: a block of code
     imported by some other code.  Three types of modules concern us
     here: pure Python modules, extension modules, and packages.

pure Python module

     a module written in Python and contained in a single ‘.py’ file
     (and possibly associated ‘.pyc’ files).  Sometimes referred to as a
     “pure module.”

extension module

     a module written in the low-level language of the Python
     implementation: C/C++ for Python, Java for Jython.  Typically
     contained in a single dynamically loadable pre-compiled file, e.g.
     a shared object (‘.so’) file for Python extensions on Unix, a DLL
     (given the ‘.pyd’ extension) for Python extensions on Windows, or a
     Java class file for Jython extensions.  (Note that currently, the
     Distutils only handles C/C++ extensions for Python.)

package

     a module that contains other modules; typically contained in a
     directory in the filesystem and distinguished from other
     directories by the presence of a file ‘__init__.py’.

root package

     the root of the hierarchy of packages.  (This isn’t really a
     package, since it doesn’t have an ‘__init__.py’ file.  But we have
     to call it something.)  The vast majority of the standard library
     is in the root package, as are many small, standalone third-party
     modules that don’t belong to a larger module collection.  Unlike
     regular packages, modules in the root package can be found in many
     directories: in fact, every directory listed in ‘sys.path’
     contributes modules to the root package.


File: python.info,  Node: Distutils-specific terminology,  Prev: General Python terminology,  Up: An Introduction to Distutils

17.1.4 Distutils-specific terminology
-------------------------------------

The following terms apply more specifically to the domain of
distributing Python modules using the Distutils:

module distribution

     a collection of Python modules distributed together as a single
     downloadable resource and meant to be installed `en masse'.
     Examples of some well-known module distributions are NumPy, SciPy,
     Pillow, or mxBase.  (This would be called a `package', except that
     term is already taken in the Python context: a single module
     distribution may contain zero, one, or many Python packages.)

pure module distribution

     a module distribution that contains only pure Python modules and
     packages.  Sometimes referred to as a “pure distribution.”

non-pure module distribution

     a module distribution that contains at least one extension module.
     Sometimes referred to as a “non-pure distribution.”

distribution root

     the top-level directory of your source tree (or source
     distribution); the directory where ‘setup.py’ exists.  Generally
     ‘setup.py’ will be run from this directory.


File: python.info,  Node: Writing the Setup Script,  Next: Writing the Setup Configuration File,  Prev: An Introduction to Distutils,  Up: Distributing Python Modules Legacy version

17.2 Writing the Setup Script
=============================

     Note: This document is being retained solely until the ‘setuptools’
     documentation at
     ‘https://setuptools.readthedocs.io/en/latest/setuptools.html’
     independently covers all of the relevant information currently
     included here.

The setup script is the centre of all activity in building,
distributing, and installing modules using the Distutils.  The main
purpose of the setup script is to describe your module distribution to
the Distutils, so that the various commands that operate on your modules
do the right thing.  As we saw in section *note A Simple Example: 4571.
above, the setup script consists mainly of a call to ‘setup()’, and most
information supplied to the Distutils by the module developer is
supplied as keyword arguments to ‘setup()’.

Here’s a slightly more involved example, which we’ll follow for the next
couple of sections: the Distutils’ own setup script.  (Keep in mind that
although the Distutils are included with Python 1.6 and later, they also
have an independent existence so that Python 1.5.2 users can use them to
install other module distributions.  The Distutils’ own setup script,
shown here, is used to install the package into Python 1.5.2.)

     #!/usr/bin/env python

     from distutils.core import setup

     setup(name='Distutils',
           version='1.0',
           description='Python Distribution Utilities',
           author='Greg Ward',
           author_email='gward@python.net',
           url='https://www.python.org/sigs/distutils-sig/',
           packages=['distutils', 'distutils.command'],
          )

There are only two differences between this and the trivial one-file
distribution presented in section *note A Simple Example: 4571.: more
metadata, and the specification of pure Python modules by package,
rather than by module.  This is important since the Distutils consist of
a couple of dozen modules split into (so far) two packages; an explicit
list of every module would be tedious to generate and difficult to
maintain.  For more information on the additional meta-data, see section
*note Additional meta-data: 4579.

Note that any pathnames (files or directories) supplied in the setup
script should be written using the Unix convention, i.e.
slash-separated.  The Distutils will take care of converting this
platform-neutral representation into whatever is appropriate on your
current platform before actually using the pathname.  This makes your
setup script portable across operating systems, which of course is one
of the major goals of the Distutils.  In this spirit, all pathnames in
this document are slash-separated.

This, of course, only applies to pathnames given to Distutils functions.
If you, for example, use standard Python functions such as *note
glob.glob(): 6bd. or *note os.listdir(): b1c. to specify files, you
should be careful to write portable code instead of hardcoding path
separators:

     glob.glob(os.path.join('mydir', 'subdir', '*.html'))
     os.listdir(os.path.join('mydir', 'subdir'))

* Menu:

* Listing whole packages::
* Listing individual modules::
* Describing extension modules::
* Relationships between Distributions and Packages::
* Installing Scripts::
* Installing Package Data::
* Installing Additional Files::
* Additional meta-data::
* Debugging the setup script::


File: python.info,  Node: Listing whole packages,  Next: Listing individual modules,  Up: Writing the Setup Script

17.2.1 Listing whole packages
-----------------------------

The ‘packages’ option tells the Distutils to process (build, distribute,
install, etc.)  all pure Python modules found in each package mentioned
in the ‘packages’ list.  In order to do this, of course, there has to be
a correspondence between package names and directories in the
filesystem.  The default correspondence is the most obvious one, i.e.
package *note distutils: 38. is found in the directory ‘distutils’
relative to the distribution root.  Thus, when you say ‘packages =
['foo']’ in your setup script, you are promising that the Distutils will
find a file ‘foo/__init__.py’ (which might be spelled differently on
your system, but you get the idea) relative to the directory where your
setup script lives.  If you break this promise, the Distutils will issue
a warning but still process the broken package anyway.

If you use a different convention to lay out your source directory,
that’s no problem: you just have to supply the ‘package_dir’ option to
tell the Distutils about your convention.  For example, say you keep all
Python source under ‘lib’, so that modules in the “root package” (i.e.,
not in any package at all) are in ‘lib’, modules in the ‘foo’ package
are in ‘lib/foo’, and so forth.  Then you would put

     package_dir = {'': 'lib'}

in your setup script.  The keys to this dictionary are package names,
and an empty package name stands for the root package.  The values are
directory names relative to your distribution root.  In this case, when
you say ‘packages = ['foo']’, you are promising that the file
‘lib/foo/__init__.py’ exists.

Another possible convention is to put the ‘foo’ package right in ‘lib’,
the ‘foo.bar’ package in ‘lib/bar’, etc.  This would be written in the
setup script as

     package_dir = {'foo': 'lib'}

A ‘package: dir’ entry in the ‘package_dir’ dictionary implicitly
applies to all packages below `package', so the ‘foo.bar’ case is
automatically handled here.  In this example, having ‘packages = ['foo',
'foo.bar']’ tells the Distutils to look for ‘lib/__init__.py’ and
‘lib/bar/__init__.py’.  (Keep in mind that although ‘package_dir’
applies recursively, you must explicitly list all packages in
‘packages’: the Distutils will `not' recursively scan your source tree
looking for any directory with an ‘__init__.py’ file.)


File: python.info,  Node: Listing individual modules,  Next: Describing extension modules,  Prev: Listing whole packages,  Up: Writing the Setup Script

17.2.2 Listing individual modules
---------------------------------

For a small module distribution, you might prefer to list all modules
rather than listing packages—especially the case of a single module that
goes in the “root package” (i.e., no package at all).  This simplest
case was shown in section *note A Simple Example: 4571.; here is a
slightly more involved example:

     py_modules = ['mod1', 'pkg.mod2']

This describes two modules, one of them in the “root” package, the other
in the ‘pkg’ package.  Again, the default package/directory layout
implies that these two modules can be found in ‘mod1.py’ and
‘pkg/mod2.py’, and that ‘pkg/__init__.py’ exists as well.  And again,
you can override the package/directory correspondence using the
‘package_dir’ option.


File: python.info,  Node: Describing extension modules,  Next: Relationships between Distributions and Packages,  Prev: Listing individual modules,  Up: Writing the Setup Script

17.2.3 Describing extension modules
-----------------------------------

Just as writing Python extension modules is a bit more complicated than
writing pure Python modules, describing them to the Distutils is a bit
more complicated.  Unlike pure modules, it’s not enough just to list
modules or packages and expect the Distutils to go out and find the
right files; you have to specify the extension name, source file(s), and
any compile/link requirements (include directories, libraries to link
with, etc.).

All of this is done through another keyword argument to ‘setup()’, the
‘ext_modules’ option.  ‘ext_modules’ is just a list of *note Extension:
4580. instances, each of which describes a single extension module.
Suppose your distribution includes a single extension, called ‘foo’ and
implemented by ‘foo.c’.  If no additional instructions to the
compiler/linker are needed, describing this extension is quite simple:

     Extension('foo', ['foo.c'])

The ‘Extension’ class can be imported from *note distutils.core: 53.
along with ‘setup()’.  Thus, the setup script for a module distribution
that contains only this one extension and nothing else might be:

     from distutils.core import setup, Extension
     setup(name='foo',
           version='1.0',
           ext_modules=[Extension('foo', ['foo.c'])],
           )

The ‘Extension’ class (actually, the underlying extension-building
machinery implemented by the ‘build_ext’ command) supports a great deal
of flexibility in describing Python extensions, which is explained in
the following sections.

* Menu:

* Extension names and packages::
* Extension source files::
* Preprocessor options::
* Library options::
* Other options::


File: python.info,  Node: Extension names and packages,  Next: Extension source files,  Up: Describing extension modules

17.2.3.1 Extension names and packages
.....................................

The first argument to the *note Extension: 4580. constructor is always
the name of the extension, including any package names.  For example,

     Extension('foo', ['src/foo1.c', 'src/foo2.c'])

describes an extension that lives in the root package, while

     Extension('pkg.foo', ['src/foo1.c', 'src/foo2.c'])

describes the same extension in the ‘pkg’ package.  The source files and
resulting object code are identical in both cases; the only difference
is where in the filesystem (and therefore where in Python’s namespace
hierarchy) the resulting extension lives.

If you have a number of extensions all in the same package (or all under
the same base package), use the ‘ext_package’ keyword argument to
‘setup()’.  For example,

     setup(...,
           ext_package='pkg',
           ext_modules=[Extension('foo', ['foo.c']),
                        Extension('subpkg.bar', ['bar.c'])],
          )

will compile ‘foo.c’ to the extension ‘pkg.foo’, and ‘bar.c’ to
‘pkg.subpkg.bar’.


File: python.info,  Node: Extension source files,  Next: Preprocessor options,  Prev: Extension names and packages,  Up: Describing extension modules

17.2.3.2 Extension source files
...............................

The second argument to the *note Extension: 4580. constructor is a list
of source files.  Since the Distutils currently only support C, C++, and
Objective-C extensions, these are normally C/C++/Objective-C source
files.  (Be sure to use appropriate extensions to distinguish C++ source
files: ‘.cc’ and ‘.cpp’ seem to be recognized by both Unix and Windows
compilers.)

However, you can also include SWIG interface (‘.i’) files in the list;
the ‘build_ext’ command knows how to deal with SWIG extensions: it will
run SWIG on the interface file and compile the resulting C/C++ file into
your extension.

This warning notwithstanding, options to SWIG can be currently passed
like this:

     setup(...,
           ext_modules=[Extension('_foo', ['foo.i'],
                                  swig_opts=['-modern', '-I../include'])],
           py_modules=['foo'],
          )

Or on the commandline like this:

     > python setup.py build_ext --swig-opts="-modern -I../include"

On some platforms, you can include non-source files that are processed
by the compiler and included in your extension.  Currently, this just
means Windows message text (‘.mc’) files and resource definition (‘.rc’)
files for Visual C++.  These will be compiled to binary resource
(‘.res’) files and linked into the executable.


File: python.info,  Node: Preprocessor options,  Next: Library options,  Prev: Extension source files,  Up: Describing extension modules

17.2.3.3 Preprocessor options
.............................

Three optional arguments to *note Extension: 4580. will help if you need
to specify include directories to search or preprocessor macros to
define/undefine: ‘include_dirs’, ‘define_macros’, and ‘undef_macros’.

For example, if your extension requires header files in the ‘include’
directory under your distribution root, use the ‘include_dirs’ option:

     Extension('foo', ['foo.c'], include_dirs=['include'])

You can specify absolute directories there; if you know that your
extension will only be built on Unix systems with X11R6 installed to
‘/usr’, you can get away with

     Extension('foo', ['foo.c'], include_dirs=['/usr/include/X11'])

You should avoid this sort of non-portable usage if you plan to
distribute your code: it’s probably better to write C code like

     #include <X11/Xlib.h>

If you need to include header files from some other Python extension,
you can take advantage of the fact that header files are installed in a
consistent way by the Distutils ‘install_headers’ command.  For example,
the Numerical Python header files are installed (on a standard Unix
installation) to ‘/usr/local/include/python1.5/Numerical’.  (The exact
location will differ according to your platform and Python
installation.)  Since the Python include
directory—‘/usr/local/include/python1.5’ in this case—is always included
in the search path when building Python extensions, the best approach is
to write C code like

     #include <Numerical/arrayobject.h>

If you must put the ‘Numerical’ include directory right into your header
search path, though, you can find that directory using the Distutils
*note distutils.sysconfig: 61. module:

     from distutils.sysconfig import get_python_inc
     incdir = os.path.join(get_python_inc(plat_specific=1), 'Numerical')
     setup(...,
           Extension(..., include_dirs=[incdir]),
           )

Even though this is quite portable—it will work on any Python
installation, regardless of platform—it’s probably easier to just write
your C code in the sensible way.

You can define and undefine pre-processor macros with the
‘define_macros’ and ‘undef_macros’ options.  ‘define_macros’ takes a
list of ‘(name, value)’ tuples, where ‘name’ is the name of the macro to
define (a string) and ‘value’ is its value: either a string or ‘None’.
(Defining a macro ‘FOO’ to ‘None’ is the equivalent of a bare ‘#define
FOO’ in your C source: with most compilers, this sets ‘FOO’ to the
string ‘1’.)  ‘undef_macros’ is just a list of macros to undefine.

For example:

     Extension(...,
               define_macros=[('NDEBUG', '1'),
                              ('HAVE_STRFTIME', None)],
               undef_macros=['HAVE_FOO', 'HAVE_BAR'])

is the equivalent of having this at the top of every C source file:

     #define NDEBUG 1
     #define HAVE_STRFTIME
     #undef HAVE_FOO
     #undef HAVE_BAR


File: python.info,  Node: Library options,  Next: Other options,  Prev: Preprocessor options,  Up: Describing extension modules

17.2.3.4 Library options
........................

You can also specify the libraries to link against when building your
extension, and the directories to search for those libraries.  The
‘libraries’ option is a list of libraries to link against,
‘library_dirs’ is a list of directories to search for libraries at
link-time, and ‘runtime_library_dirs’ is a list of directories to search
for shared (dynamically loaded) libraries at run-time.

For example, if you need to link against libraries known to be in the
standard library search path on target systems

     Extension(...,
               libraries=['gdbm', 'readline'])

If you need to link with libraries in a non-standard location, you’ll
have to include the location in ‘library_dirs’:

     Extension(...,
               library_dirs=['/usr/X11R6/lib'],
               libraries=['X11', 'Xt'])

(Again, this sort of non-portable construct should be avoided if you
intend to distribute your code.)


File: python.info,  Node: Other options,  Prev: Library options,  Up: Describing extension modules

17.2.3.5 Other options
......................

There are still some other options which can be used to handle special
cases.

The ‘optional’ option is a boolean; if it is true, a build failure in
the extension will not abort the build process, but instead simply not
install the failing extension.

The ‘extra_objects’ option is a list of object files to be passed to the
linker.  These files must not have extensions, as the default extension
for the compiler is used.

‘extra_compile_args’ and ‘extra_link_args’ can be used to specify
additional command line options for the respective compiler and linker
command lines.

‘export_symbols’ is only useful on Windows.  It can contain a list of
symbols (functions or variables) to be exported.  This option is not
needed when building compiled extensions: Distutils will automatically
add ‘initmodule’ to the list of exported symbols.

The ‘depends’ option is a list of files that the extension depends on
(for example header files).  The build command will call the compiler on
the sources to rebuild extension if any on this files has been modified
since the previous build.


File: python.info,  Node: Relationships between Distributions and Packages,  Next: Installing Scripts,  Prev: Describing extension modules,  Up: Writing the Setup Script

17.2.4 Relationships between Distributions and Packages
-------------------------------------------------------

A distribution may relate to packages in three specific ways:

  1. It can require packages or modules.

  2. It can provide packages or modules.

  3. It can obsolete packages or modules.

These relationships can be specified using keyword arguments to the
*note distutils.core.setup(): 3d8c. function.

Dependencies on other Python modules and packages can be specified by
supplying the `requires' keyword argument to ‘setup()’.  The value must
be a list of strings.  Each string specifies a package that is required,
and optionally what versions are sufficient.

To specify that any version of a module or package is required, the
string should consist entirely of the module or package name.  Examples
include ‘'mymodule'’ and ‘'xml.parsers.expat'’.

If specific versions are required, a sequence of qualifiers can be
supplied in parentheses.  Each qualifier may consist of a comparison
operator and a version number.  The accepted comparison operators are:

     <    >    ==
     <=   >=   !=

These can be combined by using multiple qualifiers separated by commas
(and optional whitespace).  In this case, all of the qualifiers must be
matched; a logical AND is used to combine the evaluations.

Let’s look at a bunch of examples:

Requires Expression           Explanation
                              
---------------------------------------------------------------------------------
                              
‘==1.0’                       Only version ‘1.0’ is compatible
                              
                              
‘>1.0, !=1.5.1, <2.0’         Any version after ‘1.0’ and before ‘2.0’ is
                              compatible, except ‘1.5.1’
                              

Now that we can specify dependencies, we also need to be able to specify
what we provide that other distributions can require.  This is done
using the `provides' keyword argument to ‘setup()’.  The value for this
keyword is a list of strings, each of which names a Python module or
package, and optionally identifies the version.  If the version is not
specified, it is assumed to match that of the distribution.

Some examples:

Provides Expression       Explanation
                          
-----------------------------------------------------------------------------
                          
‘mypkg’                   Provide ‘mypkg’, using the distribution version
                          
                          
‘mypkg (1.1)’             Provide ‘mypkg’ version 1.1, regardless of the
                          distribution version
                          

A package can declare that it obsoletes other packages using the
`obsoletes' keyword argument.  The value for this is similar to that of
the `requires' keyword: a list of strings giving module or package
specifiers.  Each specifier consists of a module or package name
optionally followed by one or more version qualifiers.  Version
qualifiers are given in parentheses after the module or package name.

The versions identified by the qualifiers are those that are obsoleted
by the distribution being described.  If no qualifiers are given, all
versions of the named module or package are understood to be obsoleted.


File: python.info,  Node: Installing Scripts,  Next: Installing Package Data,  Prev: Relationships between Distributions and Packages,  Up: Writing the Setup Script

17.2.5 Installing Scripts
-------------------------

So far we have been dealing with pure and non-pure Python modules, which
are usually not run by themselves but imported by scripts.

Scripts are files containing Python source code, intended to be started
from the command line.  Scripts don’t require Distutils to do anything
very complicated.  The only clever feature is that if the first line of
the script starts with ‘#!’ and contains the word “python”, the
Distutils will adjust the first line to refer to the current interpreter
location.  By default, it is replaced with the current interpreter
location.  The ‘--executable’ (or ‘-e’) option will allow the
interpreter path to be explicitly overridden.

The ‘scripts’ option simply is a list of files to be handled in this
way.  From the PyXML setup script:

     setup(...,
           scripts=['scripts/xmlproc_parse', 'scripts/xmlproc_val']
           )

Changed in version 3.1: All the scripts will also be added to the
‘MANIFEST’ file if no template is provided.  See *note Specifying the
files to distribute: 3d8f.


File: python.info,  Node: Installing Package Data,  Next: Installing Additional Files,  Prev: Installing Scripts,  Up: Writing the Setup Script

17.2.6 Installing Package Data
------------------------------

Often, additional files need to be installed into a package.  These
files are often data that’s closely related to the package’s
implementation, or text files containing documentation that might be of
interest to programmers using the package.  These files are called
`package data'.

Package data can be added to packages using the ‘package_data’ keyword
argument to the ‘setup()’ function.  The value must be a mapping from
package name to a list of relative path names that should be copied into
the package.  The paths are interpreted as relative to the directory
containing the package (information from the ‘package_dir’ mapping is
used if appropriate); that is, the files are expected to be part of the
package in the source directories.  They may contain glob patterns as
well.

The path names may contain directory portions; any necessary directories
will be created in the installation.

For example, if a package should contain a subdirectory with several
data files, the files can be arranged like this in the source tree:

     setup.py
     src/
         mypkg/
             __init__.py
             module.py
             data/
                 tables.dat
                 spoons.dat
                 forks.dat

The corresponding call to ‘setup()’ might be:

     setup(...,
           packages=['mypkg'],
           package_dir={'mypkg': 'src/mypkg'},
           package_data={'mypkg': ['data/*.dat']},
           )

Changed in version 3.1: All the files that match ‘package_data’ will be
added to the ‘MANIFEST’ file if no template is provided.  See *note
Specifying the files to distribute: 3d8f.


File: python.info,  Node: Installing Additional Files,  Next: Additional meta-data,  Prev: Installing Package Data,  Up: Writing the Setup Script

17.2.7 Installing Additional Files
----------------------------------

The ‘data_files’ option can be used to specify additional files needed
by the module distribution: configuration files, message catalogs, data
files, anything which doesn’t fit in the previous categories.

‘data_files’ specifies a sequence of (`directory', `files') pairs in the
following way:

     setup(...,
           data_files=[('bitmaps', ['bm/b1.gif', 'bm/b2.gif']),
                       ('config', ['cfg/data.cfg'])],
          )

Each (`directory', `files') pair in the sequence specifies the
installation directory and the files to install there.

Each file name in `files' is interpreted relative to the ‘setup.py’
script at the top of the package source distribution.  Note that you can
specify the directory where the data files will be installed, but you
cannot rename the data files themselves.

The `directory' should be a relative path.  It is interpreted relative
to the installation prefix (Python’s ‘sys.prefix’ for system
installations; ‘site.USER_BASE’ for user installations).  Distutils
allows `directory' to be an absolute installation path, but this is
discouraged since it is incompatible with the wheel packaging format.
No directory information from `files' is used to determine the final
location of the installed file; only the name of the file is used.

You can specify the ‘data_files’ options as a simple sequence of files
without specifying a target directory, but this is not recommended, and
the ‘install’ command will print a warning in this case.  To install
data files directly in the target directory, an empty string should be
given as the directory.

Changed in version 3.1: All the files that match ‘data_files’ will be
added to the ‘MANIFEST’ file if no template is provided.  See *note
Specifying the files to distribute: 3d8f.


File: python.info,  Node: Additional meta-data,  Next: Debugging the setup script,  Prev: Installing Additional Files,  Up: Writing the Setup Script

17.2.8 Additional meta-data
---------------------------

The setup script may include additional meta-data beyond the name and
version.  This information includes:

Meta-Data                  Description                     Value                 Notes
                                                                                 
----------------------------------------------------------------------------------------------
                                                                                 
‘name’                     name of the package             short string          (1)
                                                                                 
                                                                                 
‘version’                  version of this release         short string          (1)(2)
                                                                                 
                                                                                 
‘author’                   package author’s name           short string          (3)
                                                                                 
                                                                                 
‘author_email’             email address of the package    email address         (3)
                           author                                                
                           
                                                                                 
‘maintainer’               package maintainer’s name       short string          (3)
                                                                                 
                                                                                 
‘maintainer_email’         email address of the package    email address         (3)
                           maintainer                                            
                           
                                                                                 
‘url’                      home page for the package       URL                   (1)
                                                                                 
                                                                                 
‘description’              short, summary description of   short string
                           the package                     
                           
                                                                                 
‘long_description’         longer description of the       long string           (4)
                           package                                               
                           
                                                                                 
‘download_url’             location where the package      URL
                           may be downloaded               
                           
                                                                                 
‘classifiers’              a list of classifiers           list of strings       (6)(7)
                                                                                 
                                                                                 
‘platforms’                a list of platforms             list of strings       (6)(8)
                                                                                 
                                                                                 
‘keywords’                 a list of keywords              list of strings       (6)(8)
                                                                                 
                                                                                 
‘license’                  license for the package         short string          (5)
                                                                                 

Notes:

  1. These fields are required.

  2. It is recommended that versions take the form
     `major.minor[.patch[.sub]]'.

  3. Either the author or the maintainer must be identified.  If
     maintainer is provided, distutils lists it as the author in
     ‘PKG-INFO’.

  4. The ‘long_description’ field is used by PyPI when you publish a
     package, to build its project page.

  5. The ‘license’ field is a text indicating the license covering the
     package where the license is not a selection from the “License”
     Trove classifiers.  See the ‘Classifier’ field.  Notice that
     there’s a ‘licence’ distribution option which is deprecated but
     still acts as an alias for ‘license’.

  6. This field must be a list.

  7. The valid classifiers are listed on PyPI(1).

  8. To preserve backward compatibility, this field also accepts a
     string.  If you pass a comma-separated string ‘'foo, bar'’, it will
     be converted to ‘['foo', 'bar']’, Otherwise, it will be converted
     to a list of one string.

‘short string’

     A single line of text, not more than 200 characters.

‘long string’

     Multiple lines of plain text in reStructuredText format (see
     ‘http://docutils.sourceforge.net/’).

‘list of strings’

     See below.

Encoding the version information is an art in itself.  Python packages
generally adhere to the version format `major.minor[.patch][sub]'.  The
major number is 0 for initial, experimental releases of software.  It is
incremented for releases that represent major milestones in a package.
The minor number is incremented when important new features are added to
the package.  The patch number increments when bug-fix releases are
made.  Additional trailing version information is sometimes used to
indicate sub-releases.  These are “a1,a2,…,aN” (for alpha releases,
where functionality and API may change), “b1,b2,…,bN” (for beta
releases, which only fix bugs) and “pr1,pr2,…,prN” (for final
pre-release release testing).  Some examples:

0.1.0

     the first, experimental release of a package

1.0.1a2

     the second alpha release of the first patch version of 1.0

‘classifiers’ must be specified in a list:

     setup(...,
           classifiers=[
               'Development Status :: 4 - Beta',
               'Environment :: Console',
               'Environment :: Web Environment',
               'Intended Audience :: End Users/Desktop',
               'Intended Audience :: Developers',
               'Intended Audience :: System Administrators',
               'License :: OSI Approved :: Python Software Foundation License',
               'Operating System :: MacOS :: MacOS X',
               'Operating System :: Microsoft :: Windows',
               'Operating System :: POSIX',
               'Programming Language :: Python',
               'Topic :: Communications :: Email',
               'Topic :: Office/Business',
               'Topic :: Software Development :: Bug Tracking',
               ],
           )

Changed in version 3.7: *note setup: 3d8c. now warns when ‘classifiers’,
‘keywords’ or ‘platforms’ fields are not specified as a list or a
string.

   ---------- Footnotes ----------

   (1) https://pypi.org/classifiers


File: python.info,  Node: Debugging the setup script,  Prev: Additional meta-data,  Up: Writing the Setup Script

17.2.9 Debugging the setup script
---------------------------------

Sometimes things go wrong, and the setup script doesn’t do what the
developer wants.

Distutils catches any exceptions when running the setup script, and
print a simple error message before the script is terminated.  The
motivation for this behaviour is to not confuse administrators who don’t
know much about Python and are trying to install a package.  If they get
a big long traceback from deep inside the guts of Distutils, they may
think the package or the Python installation is broken because they
don’t read all the way down to the bottom and see that it’s a permission
problem.

On the other hand, this doesn’t help the developer to find the cause of
the failure.  For this purpose, the ‘DISTUTILS_DEBUG’ environment
variable can be set to anything except an empty string, and distutils
will now print detailed information about what it is doing, dump the
full traceback when an exception occurs, and print the whole command
line when an external program (like a C compiler) fails.


File: python.info,  Node: Writing the Setup Configuration File,  Next: Creating a Source Distribution,  Prev: Writing the Setup Script,  Up: Distributing Python Modules Legacy version

17.3 Writing the Setup Configuration File
=========================================

     Note: This document is being retained solely until the ‘setuptools’
     documentation at
     ‘https://setuptools.readthedocs.io/en/latest/setuptools.html’
     independently covers all of the relevant information currently
     included here.

Often, it’s not possible to write down everything needed to build a
distribution `a priori': you may need to get some information from the
user, or from the user’s system, in order to proceed.  As long as that
information is fairly simple—a list of directories to search for C
header files or libraries, for example—then providing a configuration
file, ‘setup.cfg’, for users to edit is a cheap and easy way to solicit
it.  Configuration files also let you provide default values for any
command option, which the installer can then override either on the
command-line or by editing the config file.

The setup configuration file is a useful middle-ground between the setup
script—which, ideally, would be opaque to installers (1)—and the
command-line to the setup script, which is outside of your control and
entirely up to the installer.  In fact, ‘setup.cfg’ (and any other
Distutils configuration files present on the target system) are
processed after the contents of the setup script, but before the
command-line.  This has several useful consequences:

   * installers can override some of what you put in ‘setup.py’ by
     editing ‘setup.cfg’

   * you can provide non-standard defaults for options that are not
     easily set in ‘setup.py’

   * installers can override anything in ‘setup.cfg’ using the
     command-line options to ‘setup.py’

The basic syntax of the configuration file is simple:

     [command]
     option=value
     ...

where `command' is one of the Distutils commands (e.g.  ‘build_py’,
‘install’), and `option' is one of the options that command supports.
Any number of options can be supplied for each command, and any number
of command sections can be included in the file.  Blank lines are
ignored, as are comments, which run from a ‘'#'’ character until the end
of the line.  Long option values can be split across multiple lines
simply by indenting the continuation lines.

You can find out the list of options supported by a particular command
with the universal ‘--help’ option, e.g.

     $ python setup.py --help build_ext
     [...]
     Options for 'build_ext' command:
       --build-lib (-b)     directory for compiled extension modules
       --build-temp (-t)    directory for temporary files (build by-products)
       --inplace (-i)       ignore build-lib and put compiled extensions into the
                            source directory alongside your pure Python modules
       --include-dirs (-I)  list of directories to search for header files
       --define (-D)        C preprocessor macros to define
       --undef (-U)         C preprocessor macros to undefine
       --swig-opts          list of SWIG command line options
     [...]

Note that an option spelled ‘--foo-bar’ on the command-line is spelled
‘foo_bar’ in configuration files.  For example, say you want your
extensions to be built “in-place”—that is, you have an extension
‘pkg.ext’, and you want the compiled extension file (‘ext.so’ on Unix,
say) to be put in the same source directory as your pure Python modules
‘pkg.mod1’ and ‘pkg.mod2’.  You can always use the ‘--inplace’ option on
the command-line to ensure this:

     python setup.py build_ext --inplace

But this requires that you always specify the ‘build_ext’ command
explicitly, and remember to provide ‘--inplace’.  An easier way is to
“set and forget” this option, by encoding it in ‘setup.cfg’, the
configuration file for this distribution:

     [build_ext]
     inplace=1

This will affect all builds of this module distribution, whether or not
you explicitly specify ‘build_ext’.  If you include ‘setup.cfg’ in your
source distribution, it will also affect end-user builds—which is
probably a bad idea for this option, since always building extensions
in-place would break installation of the module distribution.  In
certain peculiar cases, though, modules are built right in their
installation directory, so this is conceivably a useful ability.
(Distributing extensions that expect to be built in their installation
directory is almost always a bad idea, though.)

Another example: certain commands take a lot of options that don’t
change from run to run; for example, ‘bdist_rpm’ needs to know
everything required to generate a “spec” file for creating an RPM
distribution.  Some of this information comes from the setup script, and
some is automatically generated by the Distutils (such as the list of
files installed).  But some of it has to be supplied as options to
‘bdist_rpm’, which would be very tedious to do on the command-line for
every run.  Hence, here is a snippet from the Distutils’ own
‘setup.cfg’:

     [bdist_rpm]
     release = 1
     packager = Greg Ward <gward@python.net>
     doc_files = CHANGES.txt
                 README.txt
                 USAGE.txt
                 doc/
                 examples/

Note that the ‘doc_files’ option is simply a whitespace-separated string
split across multiple lines for readability.

See also
........

*note Syntax of config files: 4594. in “Installing Python Modules”

     More information on the configuration files is available in the
     manual for system administrators.

   ---------- Footnotes ----------

   (1) (1) This ideal probably won’t be achieved until
auto-configuration is fully supported by the Distutils.


File: python.info,  Node: Creating a Source Distribution,  Next: Creating Built Distributions,  Prev: Writing the Setup Configuration File,  Up: Distributing Python Modules Legacy version

17.4 Creating a Source Distribution
===================================

     Note: This document is being retained solely until the ‘setuptools’
     documentation at
     ‘https://setuptools.readthedocs.io/en/latest/setuptools.html’
     independently covers all of the relevant information currently
     included here.

As shown in section *note A Simple Example: 4571, you use the ‘sdist’
command to create a source distribution.  In the simplest case,

     python setup.py sdist

(assuming you haven’t specified any ‘sdist’ options in the setup script
or config file), ‘sdist’ creates the archive of the default format for
the current platform.  The default format is a gzip’ed tar file
(‘.tar.gz’) on Unix, and ZIP file on Windows.

You can specify as many formats as you like using the ‘--formats’
option, for example:

     python setup.py sdist --formats=gztar,zip

to create a gzipped tarball and a zip file.  The available formats are:

Format          Description                   Notes
                                              
----------------------------------------------------------------
                                              
‘zip’           zip file (‘.zip’)             (1),(3)
                                              
                                              
‘gztar’         gzip’ed tar file              (2)
                (‘.tar.gz’)                   
                
                                              
‘bztar’         bzip2’ed tar file             (5)
                (‘.tar.bz2’)                  
                
                                              
‘xztar’         xz’ed tar file (‘.tar.xz’)    (5)
                                              
                                              
‘ztar’          compressed tar file           (4),(5)
                (‘.tar.Z’)                    
                
                                              
‘tar’           tar file (‘.tar’)             (5)
                                              

Changed in version 3.5: Added support for the ‘xztar’ format.

Notes:

  1. default on Windows

  2. default on Unix

  3. requires either external ‘zip’ utility or *note zipfile: 14b.
     module (part of the standard Python library since Python 1.6)

  4. requires the ‘compress’ program.  Notice that this format is now
     pending for deprecation and will be removed in the future versions
     of Python.

  5. deprecated by PEP 527(1); PyPI(2) only accepts ‘.zip’ and ‘.tar.gz’
     files.

When using any ‘tar’ format (‘gztar’, ‘bztar’, ‘xztar’, ‘ztar’ or
‘tar’), under Unix you can specify the ‘owner’ and ‘group’ names that
will be set for each member of the archive.

For example, if you want all files of the archive to be owned by root:

     python setup.py sdist --owner=root --group=root

* Menu:

* Specifying the files to distribute::
* Manifest-related options::

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0527/

   (2) https://pypi.org


File: python.info,  Node: Specifying the files to distribute,  Next: Manifest-related options,  Up: Creating a Source Distribution

17.4.1 Specifying the files to distribute
-----------------------------------------

If you don’t supply an explicit list of files (or instructions on how to
generate one), the ‘sdist’ command puts a minimal default set into the
source distribution:

   * all Python source files implied by the ‘py_modules’ and ‘packages’
     options

   * all C source files mentioned in the ‘ext_modules’ or ‘libraries’
     options

   * scripts identified by the ‘scripts’ option See *note Installing
     Scripts: 4587.

   * anything that looks like a test script: ‘test/test*.py’ (currently,
     the Distutils don’t do anything with test scripts except include
     them in source distributions, but in the future there will be a
     standard for testing Python module distributions)

   * Any of the standard README files (‘README’, ‘README.txt’, or
     ‘README.rst’), ‘setup.py’ (or whatever you called your setup
     script), and ‘setup.cfg’.

   * all files that matches the ‘package_data’ metadata.  See *note
     Installing Package Data: 4589.

   * all files that matches the ‘data_files’ metadata.  See *note
     Installing Additional Files: 458b.

Sometimes this is enough, but usually you will want to specify
additional files to distribute.  The typical way to do this is to write
a `manifest template', called ‘MANIFEST.in’ by default.  The manifest
template is just a list of instructions for how to generate your
manifest file, ‘MANIFEST’, which is the exact list of files to include
in your source distribution.  The ‘sdist’ command processes this
template and generates a manifest based on its instructions and what it
finds in the filesystem.

If you prefer to roll your own manifest file, the format is simple: one
filename per line, regular files (or symlinks to them) only.  If you do
supply your own ‘MANIFEST’, you must specify everything: the default set
of files described above does not apply in this case.

Changed in version 3.1: An existing generated ‘MANIFEST’ will be
regenerated without ‘sdist’ comparing its modification time to the one
of ‘MANIFEST.in’ or ‘setup.py’.

Changed in version 3.1.3: ‘MANIFEST’ files start with a comment
indicating they are generated.  Files without this comment are not
overwritten or removed.

Changed in version 3.2.2: ‘sdist’ will read a ‘MANIFEST’ file if no
‘MANIFEST.in’ exists, like it used to do.

Changed in version 3.7: ‘README.rst’ is now included in the list of
distutils standard READMEs.

The manifest template has one command per line, where each command
specifies a set of files to include or exclude from the source
distribution.  For an example, again we turn to the Distutils’ own
manifest template:

     include *.txt
     recursive-include examples *.txt *.py
     prune examples/sample?/build

The meanings should be fairly clear: include all files in the
distribution root matching ‘*.txt’, all files anywhere under the
‘examples’ directory matching ‘*.txt’ or ‘*.py’, and exclude all
directories matching ‘examples/sample?/build’.  All of this is done
`after' the standard include set, so you can exclude files from the
standard set with explicit instructions in the manifest template.  (Or,
you can use the ‘--no-defaults’ option to disable the standard set
entirely.)  There are several other commands available in the manifest
template mini-language; see section *note Creating a source
distribution; the sdist command: 4599.

The order of commands in the manifest template matters: initially, we
have the list of default files as described above, and each command in
the template adds to or removes from that list of files.  Once we have
fully processed the manifest template, we remove files that should not
be included in the source distribution:

   * all files in the Distutils “build” tree (default ‘build/’)

   * all files in directories named ‘RCS’, ‘CVS’, ‘.svn’, ‘.hg’, ‘.git’,
     ‘.bzr’ or ‘_darcs’

Now we have our complete list of files, which is written to the manifest
for future reference, and then used to build the source distribution
archive(s).

You can disable the default set of included files with the
‘--no-defaults’ option, and you can disable the standard exclude set
with ‘--no-prune’.

Following the Distutils’ own manifest template, let’s trace how the
‘sdist’ command builds the list of files to include in the Distutils
source distribution:

  1. include all Python source files in the ‘distutils’ and
     ‘distutils/command’ subdirectories (because packages corresponding
     to those two directories were mentioned in the ‘packages’ option in
     the setup script—see section *note Writing the Setup Script: 4572.)

  2. include ‘README.txt’, ‘setup.py’, and ‘setup.cfg’ (standard files)

  3. include ‘test/test*.py’ (standard files)

  4. include ‘*.txt’ in the distribution root (this will find
     ‘README.txt’ a second time, but such redundancies are weeded out
     later)

  5. include anything matching ‘*.txt’ or ‘*.py’ in the sub-tree under
     ‘examples’,

  6. exclude all files in the sub-trees starting at directories matching
     ‘examples/sample?/build’—this may exclude files included by the
     previous two steps, so it’s important that the ‘prune’ command in
     the manifest template comes after the ‘recursive-include’ command

  7. exclude the entire ‘build’ tree, and any ‘RCS’, ‘CVS’, ‘.svn’,
     ‘.hg’, ‘.git’, ‘.bzr’ and ‘_darcs’ directories

Just like in the setup script, file and directory names in the manifest
template should always be slash-separated; the Distutils will take care
of converting them to the standard representation on your platform.
That way, the manifest template is portable across operating systems.


File: python.info,  Node: Manifest-related options,  Prev: Specifying the files to distribute,  Up: Creating a Source Distribution

17.4.2 Manifest-related options
-------------------------------

The normal course of operations for the ‘sdist’ command is as follows:

   * if the manifest file (‘MANIFEST’ by default) exists and the first
     line does not have a comment indicating it is generated from
     ‘MANIFEST.in’, then it is used as is, unaltered

   * if the manifest file doesn’t exist or has been previously
     automatically generated, read ‘MANIFEST.in’ and create the manifest

   * if neither ‘MANIFEST’ nor ‘MANIFEST.in’ exist, create a manifest
     with just the default file set

   * use the list of files now in ‘MANIFEST’ (either just generated or
     read in) to create the source distribution archive(s)

There are a couple of options that modify this behaviour.  First, use
the ‘--no-defaults’ and ‘--no-prune’ to disable the standard “include”
and “exclude” sets.

Second, you might just want to (re)generate the manifest, but not create
a source distribution:

     python setup.py sdist --manifest-only

‘-o’ is a shortcut for ‘--manifest-only’.


File: python.info,  Node: Creating Built Distributions,  Next: Distutils Examples,  Prev: Creating a Source Distribution,  Up: Distributing Python Modules Legacy version

17.5 Creating Built Distributions
=================================

     Note: This document is being retained solely until the ‘setuptools’
     documentation at
     ‘https://setuptools.readthedocs.io/en/latest/setuptools.html’
     independently covers all of the relevant information currently
     included here.

A “built distribution” is what you’re probably used to thinking of
either as a “binary package” or an “installer” (depending on your
background).  It’s not necessarily binary, though, because it might
contain only Python source code and/or byte-code; and we don’t call it a
package, because that word is already spoken for in Python.  (And
“installer” is a term specific to the world of mainstream desktop
systems.)

A built distribution is how you make life as easy as possible for
installers of your module distribution: for users of RPM-based Linux
systems, it’s a binary RPM; for Windows users, it’s an executable
installer; for Debian-based Linux users, it’s a Debian package; and so
forth.  Obviously, no one person will be able to create built
distributions for every platform under the sun, so the Distutils are
designed to enable module developers to concentrate on their
specialty—writing code and creating source distributions—while an
intermediary species called `packagers' springs up to turn source
distributions into built distributions for as many platforms as there
are packagers.

Of course, the module developer could be their own packager; or the
packager could be a volunteer “out there” somewhere who has access to a
platform which the original developer does not; or it could be software
periodically grabbing new source distributions and turning them into
built distributions for as many platforms as the software has access to.
Regardless of who they are, a packager uses the setup script and the
‘bdist’ command family to generate built distributions.

As a simple example, if I run the following command in the Distutils
source tree:

     python setup.py bdist

then the Distutils builds my module distribution (the Distutils itself
in this case), does a “fake” installation (also in the ‘build’
directory), and creates the default type of built distribution for my
platform.  The default format for built distributions is a “dumb” tar
file on Unix, and a simple executable installer on Windows.  (That tar
file is considered “dumb” because it has to be unpacked in a specific
location to work.)

Thus, the above command on a Unix system creates
‘Distutils-1.0.`plat'.tar.gz’; unpacking this tarball from the right
place installs the Distutils just as though you had downloaded the
source distribution and run ‘python setup.py install’.  (The “right
place” is either the root of the filesystem or Python’s ‘`prefix'’
directory, depending on the options given to the ‘bdist_dumb’ command;
the default is to make dumb distributions relative to ‘`prefix'’.)

Obviously, for pure Python distributions, this isn’t any simpler than
just running ‘python setup.py install’—but for non-pure distributions,
which include extensions that would need to be compiled, it can mean the
difference between someone being able to use your extensions or not.
And creating “smart” built distributions, such as an RPM package or an
executable installer for Windows, is far more convenient for users even
if your distribution doesn’t include any extensions.

The ‘bdist’ command has a ‘--formats’ option, similar to the ‘sdist’
command, which you can use to select the types of built distribution to
generate: for example,

     python setup.py bdist --format=zip

would, when run on a Unix system, create
‘Distutils-1.0.`plat'.zip’—again, this archive would be unpacked from
the root directory to install the Distutils.

The available formats for built distributions are:

Format            Description                        Notes
                                                     
-------------------------------------------------------------------
                                                     
‘gztar’           gzipped tar file (‘.tar.gz’)       (1)
                                                     
                                                     
‘bztar’           bzipped tar file (‘.tar.bz2’)
                  
                                                     
‘xztar’           xzipped tar file (‘.tar.xz’)
                  
                                                     
‘ztar’            compressed tar file (‘.tar.Z’)     (3)
                                                     
                                                     
‘tar’             tar file (‘.tar’)
                  
                                                     
‘zip’             zip file (‘.zip’)                  (2),(4)
                                                     
                                                     
‘rpm’             RPM                                (5)
                                                     
                                                     
‘pkgtool’         Solaris ‘pkgtool’
                  
                                                     
‘sdux’            HP-UX ‘swinstall’
                  
                                                     
‘wininst’         self-extracting ZIP file for       (4)
                  Windows                            
                  
                                                     
‘msi’             Microsoft Installer.
                  

Changed in version 3.5: Added support for the ‘xztar’ format.

Notes:

  1. default on Unix

  2. default on Windows

  3. requires external ‘compress’ utility.

  4. requires either external ‘zip’ utility or *note zipfile: 14b.
     module (part of the standard Python library since Python 1.6)

  5. requires external ‘rpm’ utility, version 3.0.4 or better (use ‘rpm
     --version’ to find out which version you have)

You don’t have to use the ‘bdist’ command with the ‘--formats’ option;
you can also use the command that directly implements the format you’re
interested in.  Some of these ‘bdist’ “sub-commands” actually generate
several similar formats; for instance, the ‘bdist_dumb’ command
generates all the “dumb” archive formats (‘tar’, ‘gztar’, ‘bztar’,
‘xztar’, ‘ztar’, and ‘zip’), and ‘bdist_rpm’ generates both binary and
source RPMs.  The ‘bdist’ sub-commands, and the formats generated by
each, are:

Command                        Formats
                               
-------------------------------------------------------------------------
                               
‘bdist_dumb’                   tar, gztar, bztar, xztar, ztar, zip
                               
                               
‘bdist_rpm’                    rpm, srpm
                               
                               
‘bdist_wininst’                wininst
                               
                               
‘bdist_msi’                    msi
                               

     Note: bdist_wininst is deprecated since Python 3.8.

     Note: bdist_msi is deprecated since Python 3.9.

The following sections give details on the individual ‘bdist_*’
commands.

* Menu:

* Creating RPM packages::
* Creating Windows Installers::
* Cross-compiling on Windows::
* Vista User Access Control (UAC): Vista User Access Control UAC.


File: python.info,  Node: Creating RPM packages,  Next: Creating Windows Installers,  Up: Creating Built Distributions

17.5.1 Creating RPM packages
----------------------------

The RPM format is used by many popular Linux distributions, including
Red Hat, SuSE, and Mandrake.  If one of these (or any of the other
RPM-based Linux distributions) is your usual environment, creating RPM
packages for other users of that same distribution is trivial.
Depending on the complexity of your module distribution and differences
between Linux distributions, you may also be able to create RPMs that
work on different RPM-based distributions.

The usual way to create an RPM of your module distribution is to run the
‘bdist_rpm’ command:

     python setup.py bdist_rpm

or the ‘bdist’ command with the ‘--format’ option:

     python setup.py bdist --formats=rpm

The former allows you to specify RPM-specific options; the latter allows
you to easily specify multiple formats in one run.  If you need to do
both, you can explicitly specify multiple ‘bdist_*’ commands and their
options:

     python setup.py bdist_rpm --packager="John Doe <jdoe@example.org>" \
                     bdist_wininst --target-version="2.0"

Creating RPM packages is driven by a ‘.spec’ file, much as using the
Distutils is driven by the setup script.  To make your life easier, the
‘bdist_rpm’ command normally creates a ‘.spec’ file based on the
information you supply in the setup script, on the command line, and in
any Distutils configuration files.  Various options and sections in the
‘.spec’ file are derived from options in the setup script as follows:

RPM ‘.spec’ file option or section             Distutils setup script option
                                               
--------------------------------------------------------------------------------------------------
                                               
Name                                           ‘name’
                                               
                                               
Summary (in preamble)                          ‘description’
                                               
                                               
Version                                        ‘version’
                                               
                                               
Vendor                                         ‘author’ and ‘author_email’, or — & ‘maintainer’
                                               and ‘maintainer_email’
                                               
                                               
Copyright                                      ‘license’
                                               
                                               
Url                                            ‘url’
                                               
                                               
%description (section)                         ‘long_description’
                                               

Additionally, there are many options in ‘.spec’ files that don’t have
corresponding options in the setup script.  Most of these are handled
through options to the ‘bdist_rpm’ command as follows:

RPM ‘.spec’ file option or          ‘bdist_rpm’ option                default value
section                                                               

----------------------------------------------------------------------------------------------------
                                                                      
Release                             ‘release’                         “1”
                                                                      
                                                                      
Group                               ‘group’                           “Development/Libraries”
                                                                      
                                                                      
Vendor                              ‘vendor’                          (see above)
                                                                      
                                                                      
Packager                            ‘packager’                        (none)
                                                                      
                                                                      
Provides                            ‘provides’                        (none)
                                                                      
                                                                      
Requires                            ‘requires’                        (none)
                                                                      
                                                                      
Conflicts                           ‘conflicts’                       (none)
                                                                      
                                                                      
Obsoletes                           ‘obsoletes’                       (none)
                                                                      
                                                                      
Distribution                        ‘distribution_name’               (none)
                                                                      
                                                                      
BuildRequires                       ‘build_requires’                  (none)
                                                                      
                                                                      
Icon                                ‘icon’                            (none)
                                                                      

Obviously, supplying even a few of these options on the command-line
would be tedious and error-prone, so it’s usually best to put them in
the setup configuration file, ‘setup.cfg’—see section *note Writing the
Setup Configuration File: 4591.  If you distribute or package many
Python module distributions, you might want to put options that apply to
all of them in your personal Distutils configuration file
(‘~/.pydistutils.cfg’).  If you want to temporarily disable this file,
you can pass the ‘--no-user-cfg’ option to ‘setup.py’.

There are three steps to building a binary RPM package, all of which are
handled automatically by the Distutils:

  1. create a ‘.spec’ file, which describes the package (analogous to
     the Distutils setup script; in fact, much of the information in the
     setup script winds up in the ‘.spec’ file)

  2. create the source RPM

  3. create the “binary” RPM (which may or may not contain binary code,
     depending on whether your module distribution contains Python
     extensions)

Normally, RPM bundles the last two steps together; when you use the
Distutils, all three steps are typically bundled together.

If you wish, you can separate these three steps.  You can use the
‘--spec-only’ option to make ‘bdist_rpm’ just create the ‘.spec’ file
and exit; in this case, the ‘.spec’ file will be written to the
“distribution directory”—normally ‘dist/’, but customizable with the
‘--dist-dir’ option.  (Normally, the ‘.spec’ file winds up deep in the
“build tree,” in a temporary directory created by ‘bdist_rpm’.)


File: python.info,  Node: Creating Windows Installers,  Next: Cross-compiling on Windows,  Prev: Creating RPM packages,  Up: Creating Built Distributions

17.5.2 Creating Windows Installers
----------------------------------

     Warning: bdist_wininst is deprecated since Python 3.8.

     Warning: bdist_msi is deprecated since Python 3.9.

Executable installers are the natural format for binary distributions on
Windows.  They display a nice graphical user interface, display some
information about the module distribution to be installed taken from the
metadata in the setup script, let the user select a few options, and
start or cancel the installation.

Since the metadata is taken from the setup script, creating Windows
installers is usually as easy as running:

     python setup.py bdist_wininst

or the ‘bdist’ command with the ‘--formats’ option:

     python setup.py bdist --formats=wininst

If you have a pure module distribution (only containing pure Python
modules and packages), the resulting installer will be version
independent and have a name like ‘foo-1.0.win32.exe’.  Note that
creating ‘wininst’ binary distributions in only supported on Windows
systems.

If you have a non-pure distribution, the extensions can only be created
on a Windows platform, and will be Python version dependent.  The
installer filename will reflect this and now has the form
‘foo-1.0.win32-py2.0.exe’.  You have to create a separate installer for
every Python version you want to support.

The installer will try to compile pure modules into *note bytecode: 709.
after installation on the target system in normal and optimizing mode.
If you don’t want this to happen for some reason, you can run the
‘bdist_wininst’ command with the ‘--no-target-compile’ and/or the
‘--no-target-optimize’ option.

By default the installer will display the cool “Python Powered” logo
when it is run, but you can also supply your own 152x261 bitmap which
must be a Windows ‘.bmp’ file with the ‘--bitmap’ option.

The installer will also display a large title on the desktop background
window when it is run, which is constructed from the name of your
distribution and the version number.  This can be changed to another
text by using the ‘--title’ option.

The installer file will be written to the “distribution directory” —
normally ‘dist/’, but customizable with the ‘--dist-dir’ option.


File: python.info,  Node: Cross-compiling on Windows,  Next: Vista User Access Control UAC,  Prev: Creating Windows Installers,  Up: Creating Built Distributions

17.5.3 Cross-compiling on Windows
---------------------------------

Starting with Python 2.6, distutils is capable of cross-compiling
between Windows platforms.  In practice, this means that with the
correct tools installed, you can use a 32bit version of Windows to
create 64bit extensions and vice-versa.

To build for an alternate platform, specify the ‘--plat-name’ option to
the build command.  Valid values are currently ‘win32’, and ‘win-amd64’.
For example, on a 32bit version of Windows, you could execute:

     python setup.py build --plat-name=win-amd64

to build a 64bit version of your extension.  The Windows Installers also
support this option, so the command:

     python setup.py build --plat-name=win-amd64 bdist_wininst

would create a 64bit installation executable on your 32bit version of
Windows.

To cross-compile, you must download the Python source code and
cross-compile Python itself for the platform you are targeting - it is
not possible from a binary installation of Python (as the .lib etc file
for other platforms are not included.)  In practice, this means the user
of a 32 bit operating system will need to use Visual Studio 2008 to open
the ‘PCbuild/PCbuild.sln’ solution in the Python source tree and build
the “x64” configuration of the ‘pythoncore’ project before
cross-compiling extensions is possible.

Note that by default, Visual Studio 2008 does not install 64bit
compilers or tools.  You may need to reexecute the Visual Studio setup
process and select these tools (using Control Panel->[Add/Remove]
Programs is a convenient way to check or modify your existing install.)

* Menu:

* The Postinstallation script::


File: python.info,  Node: The Postinstallation script,  Up: Cross-compiling on Windows

17.5.3.1 The Postinstallation script
....................................

Starting with Python 2.3, a postinstallation script can be specified
with the ‘--install-script’ option.  The basename of the script must be
specified, and the script filename must also be listed in the scripts
argument to the setup function.

This script will be run at installation time on the target system after
all the files have been copied, with ‘argv[1]’ set to ‘-install’, and
again at uninstallation time before the files are removed with ‘argv[1]’
set to ‘-remove’.

The installation script runs embedded in the windows installer, every
output (‘sys.stdout’, ‘sys.stderr’) is redirected into a buffer and will
be displayed in the GUI after the script has finished.

Some functions especially useful in this context are available as
additional built-in functions in the installation script.

 -- Function: directory_created (path)
 -- Function: file_created (path)

     These functions should be called when a directory or file is
     created by the postinstall script at installation time.  It will
     register `path' with the uninstaller, so that it will be removed
     when the distribution is uninstalled.  To be safe, directories are
     only removed if they are empty.

 -- Function: get_special_folder_path (csidl_string)

     This function can be used to retrieve special folder locations on
     Windows like the Start Menu or the Desktop.  It returns the full
     path to the folder.  `csidl_string' must be one of the following
     strings:

          "CSIDL_APPDATA"

          "CSIDL_COMMON_STARTMENU"
          "CSIDL_STARTMENU"

          "CSIDL_COMMON_DESKTOPDIRECTORY"
          "CSIDL_DESKTOPDIRECTORY"

          "CSIDL_COMMON_STARTUP"
          "CSIDL_STARTUP"

          "CSIDL_COMMON_PROGRAMS"
          "CSIDL_PROGRAMS"

          "CSIDL_FONTS"

     If the folder cannot be retrieved, *note OSError: 304. is raised.

     Which folders are available depends on the exact Windows version,
     and probably also the configuration.  For details refer to
     Microsoft’s documentation of the ‘SHGetSpecialFolderPath()’
     function.

 -- Function: create_shortcut (target, description, filename[,
          arguments[, workdir[, iconpath[, iconindex]]]])

     This function creates a shortcut.  `target' is the path to the
     program to be started by the shortcut.  `description' is the
     description of the shortcut.  `filename' is the title of the
     shortcut that the user will see.  `arguments' specifies the command
     line arguments, if any.  `workdir' is the working directory for the
     program.  `iconpath' is the file containing the icon for the
     shortcut, and `iconindex' is the index of the icon in the file
     `iconpath'.  Again, for details consult the Microsoft documentation
     for the ‘IShellLink’ interface.


File: python.info,  Node: Vista User Access Control UAC,  Prev: Cross-compiling on Windows,  Up: Creating Built Distributions

17.5.4 Vista User Access Control (UAC)
--------------------------------------

Starting with Python 2.6, bdist_wininst supports a
‘--user-access-control’ option.  The default is ‘none’ (meaning no UAC
handling is done), and other valid values are ‘auto’ (meaning prompt for
UAC elevation if Python was installed for all users) and ‘force’
(meaning always prompt for elevation).

     Note: bdist_wininst is deprecated since Python 3.8.

     Note: bdist_msi is deprecated since Python 3.9.


File: python.info,  Node: Distutils Examples,  Next: Extending Distutils,  Prev: Creating Built Distributions,  Up: Distributing Python Modules Legacy version

17.6 Distutils Examples
=======================

     Note: This document is being retained solely until the ‘setuptools’
     documentation at
     ‘https://setuptools.readthedocs.io/en/latest/setuptools.html’
     independently covers all of the relevant information currently
     included here.

This chapter provides a number of basic examples to help get started
with distutils.  Additional information about using distutils can be
found in the Distutils Cookbook.

See also
........

Distutils Cookbook(1)

     Collection of recipes showing how to achieve more control over
     distutils.

* Menu:

* Pure Python distribution (by module): Pure Python distribution by module.
* Pure Python distribution (by package): Pure Python distribution by package.
* Single extension module::
* Checking a package::
* Reading the metadata::

   ---------- Footnotes ----------

   (1) https://wiki.python.org/moin/Distutils/Cookbook


File: python.info,  Node: Pure Python distribution by module,  Next: Pure Python distribution by package,  Up: Distutils Examples

17.6.1 Pure Python distribution (by module)
-------------------------------------------

If you’re just distributing a couple of modules, especially if they
don’t live in a particular package, you can specify them individually
using the ‘py_modules’ option in the setup script.

In the simplest case, you’ll have two files to worry about: a setup
script and the single module you’re distributing, ‘foo.py’ in this
example:

     <root>/
             setup.py
             foo.py

(In all diagrams in this section, `<root>' will refer to the
distribution root directory.)  A minimal setup script to describe this
situation would be:

     from distutils.core import setup
     setup(name='foo',
           version='1.0',
           py_modules=['foo'],
           )

Note that the name of the distribution is specified independently with
the ‘name’ option, and there’s no rule that says it has to be the same
as the name of the sole module in the distribution (although that’s
probably a good convention to follow).  However, the distribution name
is used to generate filenames, so you should stick to letters, digits,
underscores, and hyphens.

Since ‘py_modules’ is a list, you can of course specify multiple
modules, eg.  if you’re distributing modules ‘foo’ and ‘bar’, your setup
might look like this:

     <root>/
             setup.py
             foo.py
             bar.py

and the setup script might be

     from distutils.core import setup
     setup(name='foobar',
           version='1.0',
           py_modules=['foo', 'bar'],
           )

You can put module source files into another directory, but if you have
enough modules to do that, it’s probably easier to specify modules by
package rather than listing them individually.


File: python.info,  Node: Pure Python distribution by package,  Next: Single extension module,  Prev: Pure Python distribution by module,  Up: Distutils Examples

17.6.2 Pure Python distribution (by package)
--------------------------------------------

If you have more than a couple of modules to distribute, especially if
they are in multiple packages, it’s probably easier to specify whole
packages rather than individual modules.  This works even if your
modules are not in a package; you can just tell the Distutils to process
modules from the root package, and that works the same as any other
package (except that you don’t have to have an ‘__init__.py’ file).

The setup script from the last example could also be written as

     from distutils.core import setup
     setup(name='foobar',
           version='1.0',
           packages=[''],
           )

(The empty string stands for the root package.)

If those two files are moved into a subdirectory, but remain in the root
package, e.g.:

     <root>/
             setup.py
             src/      foo.py
                       bar.py

then you would still specify the root package, but you have to tell the
Distutils where source files in the root package live:

     from distutils.core import setup
     setup(name='foobar',
           version='1.0',
           package_dir={'': 'src'},
           packages=[''],
           )

More typically, though, you will want to distribute multiple modules in
the same package (or in sub-packages).  For example, if the ‘foo’ and
‘bar’ modules belong in package ‘foobar’, one way to layout your source
tree is

     <root>/
             setup.py
             foobar/
                      __init__.py
                      foo.py
                      bar.py

This is in fact the default layout expected by the Distutils, and the
one that requires the least work to describe in your setup script:

     from distutils.core import setup
     setup(name='foobar',
           version='1.0',
           packages=['foobar'],
           )

If you want to put modules in directories not named for their package,
then you need to use the ‘package_dir’ option again.  For example, if
the ‘src’ directory holds modules in the ‘foobar’ package:

     <root>/
             setup.py
             src/
                      __init__.py
                      foo.py
                      bar.py

an appropriate setup script would be

     from distutils.core import setup
     setup(name='foobar',
           version='1.0',
           package_dir={'foobar': 'src'},
           packages=['foobar'],
           )

Or, you might put modules from your main package right in the
distribution root:

     <root>/
             setup.py
             __init__.py
             foo.py
             bar.py

in which case your setup script would be

     from distutils.core import setup
     setup(name='foobar',
           version='1.0',
           package_dir={'foobar': ''},
           packages=['foobar'],
           )

(The empty string also stands for the current directory.)

If you have sub-packages, they must be explicitly listed in ‘packages’,
but any entries in ‘package_dir’ automatically extend to sub-packages.
(In other words, the Distutils does `not' scan your source tree, trying
to figure out which directories correspond to Python packages by looking
for ‘__init__.py’ files.)  Thus, if the default layout grows a
sub-package:

     <root>/
             setup.py
             foobar/
                      __init__.py
                      foo.py
                      bar.py
                      subfoo/
                                __init__.py
                                blah.py

then the corresponding setup script would be

     from distutils.core import setup
     setup(name='foobar',
           version='1.0',
           packages=['foobar', 'foobar.subfoo'],
           )


File: python.info,  Node: Single extension module,  Next: Checking a package,  Prev: Pure Python distribution by package,  Up: Distutils Examples

17.6.3 Single extension module
------------------------------

Extension modules are specified using the ‘ext_modules’ option.
‘package_dir’ has no effect on where extension source files are found;
it only affects the source for pure Python modules.  The simplest case,
a single extension module in a single C source file, is:

     <root>/
             setup.py
             foo.c

If the ‘foo’ extension belongs in the root package, the setup script for
this could be

     from distutils.core import setup
     from distutils.extension import Extension
     setup(name='foobar',
           version='1.0',
           ext_modules=[Extension('foo', ['foo.c'])],
           )

If the extension actually belongs in a package, say ‘foopkg’, then

With exactly the same source tree layout, this extension can be put in
the ‘foopkg’ package simply by changing the name of the extension:

     from distutils.core import setup
     from distutils.extension import Extension
     setup(name='foobar',
           version='1.0',
           ext_modules=[Extension('foopkg.foo', ['foo.c'])],
           )


File: python.info,  Node: Checking a package,  Next: Reading the metadata,  Prev: Single extension module,  Up: Distutils Examples

17.6.4 Checking a package
-------------------------

The ‘check’ command allows you to verify if your package meta-data meet
the minimum requirements to build a distribution.

To run it, just call it using your ‘setup.py’ script.  If something is
missing, ‘check’ will display a warning.

Let’s take an example with a simple script:

     from distutils.core import setup

     setup(name='foobar')

Running the ‘check’ command will display some warnings:

     $ python setup.py check
     running check
     warning: check: missing required meta-data: version, url
     warning: check: missing meta-data: either (author and author_email) or
              (maintainer and maintainer_email) should be supplied

If you use the reStructuredText syntax in the ‘long_description’ field
and docutils(1) is installed you can check if the syntax is fine with
the ‘check’ command, using the ‘restructuredtext’ option.

For example, if the ‘setup.py’ script is changed like this:

     from distutils.core import setup

     desc = """\
     My description
     ==============

     This is the description of the ``foobar`` package.
     """

     setup(name='foobar', version='1', author='tarek',
         author_email='tarek@ziade.org',
         url='http://example.com', long_description=desc)

Where the long description is broken, ‘check’ will be able to detect it
by using the ‘docutils’ parser:

     $ python setup.py check --restructuredtext
     running check
     warning: check: Title underline too short. (line 2)
     warning: check: Could not finish the parsing.

   ---------- Footnotes ----------

   (1) http://docutils.sourceforge.net


File: python.info,  Node: Reading the metadata,  Prev: Checking a package,  Up: Distutils Examples

17.6.5 Reading the metadata
---------------------------

The *note distutils.core.setup(): 3d8c. function provides a command-line
interface that allows you to query the metadata fields of a project
through the ‘setup.py’ script of a given project:

     $ python setup.py --name
     distribute

This call reads the ‘name’ metadata by running the *note
distutils.core.setup(): 3d8c. function.  Although, when a source or
binary distribution is created with Distutils, the metadata fields are
written in a static file called ‘PKG-INFO’.  When a Distutils-based
project is installed in Python, the ‘PKG-INFO’ file is copied alongside
the modules and packages of the distribution under
‘NAME-VERSION-pyX.X.egg-info’, where ‘NAME’ is the name of the project,
‘VERSION’ its version as defined in the Metadata, and ‘pyX.X’ the major
and minor version of Python like ‘2.7’ or ‘3.2’.

You can read back this static file, by using the
‘distutils.dist.DistributionMetadata’ class and its ‘read_pkg_file()’
method:

     >>> from distutils.dist import DistributionMetadata
     >>> metadata = DistributionMetadata()
     >>> metadata.read_pkg_file(open('distribute-0.6.8-py2.7.egg-info'))
     >>> metadata.name
     'distribute'
     >>> metadata.version
     '0.6.8'
     >>> metadata.description
     'Easily download, build, install, upgrade, and uninstall Python packages'

Notice that the class can also be instantiated with a metadata file path
to loads its values:

     >>> pkg_info_path = 'distribute-0.6.8-py2.7.egg-info'
     >>> DistributionMetadata(pkg_info_path).name
     'distribute'


File: python.info,  Node: Extending Distutils,  Next: Command Reference,  Prev: Distutils Examples,  Up: Distributing Python Modules Legacy version

17.7 Extending Distutils
========================

     Note: This document is being retained solely until the ‘setuptools’
     documentation at
     ‘https://setuptools.readthedocs.io/en/latest/setuptools.html’
     independently covers all of the relevant information currently
     included here.

Distutils can be extended in various ways.  Most extensions take the
form of new commands or replacements for existing commands.  New
commands may be written to support new types of platform-specific
packaging, for example, while replacements for existing commands may be
made to modify details of how the command operates on a package.

Most extensions of the distutils are made within ‘setup.py’ scripts that
want to modify existing commands; many simply add a few file extensions
that should be copied into packages in addition to ‘.py’ files as a
convenience.

Most distutils command implementations are subclasses of the *note
distutils.cmd.Command: 45ba. class.  New commands may directly inherit
from ‘Command’, while replacements often derive from ‘Command’
indirectly, directly subclassing the command they are replacing.
Commands are required to derive from ‘Command’.

* Menu:

* Integrating new commands::
* Adding new distribution types::


File: python.info,  Node: Integrating new commands,  Next: Adding new distribution types,  Up: Extending Distutils

17.7.1 Integrating new commands
-------------------------------

There are different ways to integrate new command implementations into
distutils.  The most difficult is to lobby for the inclusion of the new
features in distutils itself, and wait for (and require) a version of
Python that provides that support.  This is really hard for many
reasons.

The most common, and possibly the most reasonable for most needs, is to
include the new implementations with your ‘setup.py’ script, and cause
the *note distutils.core.setup(): 3d8c. function use them:

     from distutils.command.build_py import build_py as _build_py
     from distutils.core import setup

     class build_py(_build_py):
         """Specialized Python source builder."""

         # implement whatever needs to be different...

     setup(cmdclass={'build_py': build_py},
           ...)

This approach is most valuable if the new implementations must be used
to use a particular package, as everyone interested in the package will
need to have the new command implementation.

Beginning with Python 2.4, a third option is available, intended to
allow new commands to be added which can support existing ‘setup.py’
scripts without requiring modifications to the Python installation.
This is expected to allow third-party extensions to provide support for
additional packaging systems, but the commands can be used for anything
distutils commands can be used for.  A new configuration option,
‘command_packages’ (command-line option ‘--command-packages’), can be
used to specify additional packages to be searched for modules
implementing commands.  Like all distutils options, this can be
specified on the command line or in a configuration file.  This option
can only be set in the ‘[global]’ section of a configuration file, or
before any commands on the command line.  If set in a configuration
file, it can be overridden from the command line; setting it to an empty
string on the command line causes the default to be used.  This should
never be set in a configuration file provided with a package.

This new option can be used to add any number of packages to the list of
packages searched for command implementations; multiple package names
should be separated by commas.  When not specified, the search is only
performed in the *note distutils.command: 3d. package.  When ‘setup.py’
is run with the option ‘--command-packages distcmds,buildcmds’, however,
the packages *note distutils.command: 3d, ‘distcmds’, and ‘buildcmds’
will be searched in that order.  New commands are expected to be
implemented in modules of the same name as the command by classes
sharing the same name.  Given the example command line option above, the
command ‘bdist_openpkg’ could be implemented by the class
‘distcmds.bdist_openpkg.bdist_openpkg’ or
‘buildcmds.bdist_openpkg.bdist_openpkg’.


File: python.info,  Node: Adding new distribution types,  Prev: Integrating new commands,  Up: Extending Distutils

17.7.2 Adding new distribution types
------------------------------------

Commands that create distributions (files in the ‘dist/’ directory) need
to add ‘(command, filename)’ pairs to ‘self.distribution.dist_files’ so
that ‘upload’ can upload it to PyPI. The `filename' in the pair contains
no path information, only the name of the file itself.  In dry-run mode,
pairs should still be added to represent what would have been created.


File: python.info,  Node: Command Reference,  Next: API Reference,  Prev: Extending Distutils,  Up: Distributing Python Modules Legacy version

17.8 Command Reference
======================

     Note: This document is being retained solely until the ‘setuptools’
     documentation at
     ‘https://setuptools.readthedocs.io/en/latest/setuptools.html’
     independently covers all of the relevant information currently
     included here.

* Menu:

* Installing modules; the install command family: Installing modules the install command family.
* Creating a source distribution; the sdist command: Creating a source distribution the sdist command.


File: python.info,  Node: Installing modules the install command family,  Next: Creating a source distribution the sdist command,  Up: Command Reference

17.8.1 Installing modules: the ‘install’ command family
-------------------------------------------------------

The install command ensures that the build commands have been run and
then runs the subcommands ‘install_lib’, ‘install_data’ and
‘install_scripts’.

* Menu:

* install_data::
* install_scripts::


File: python.info,  Node: install_data,  Next: install_scripts,  Up: Installing modules the install command family

17.8.1.1 ‘install_data’
.......................

This command installs all data files provided with the distribution.


File: python.info,  Node: install_scripts,  Prev: install_data,  Up: Installing modules the install command family

17.8.1.2 ‘install_scripts’
..........................

This command installs all (Python) scripts in the distribution.


File: python.info,  Node: Creating a source distribution the sdist command,  Prev: Installing modules the install command family,  Up: Command Reference

17.8.2 Creating a source distribution: the ‘sdist’ command
----------------------------------------------------------

The manifest template commands are:

Command                                         Description
                                                
----------------------------------------------------------------------------------------------------
                                                
‘include pat1 pat2 ...’                         include all files matching any of the listed
                                                patterns
                                                
                                                
‘exclude pat1 pat2 ...’                         exclude all files matching any of the listed
                                                patterns
                                                
                                                
‘recursive-include dir pat1 pat2 ...’           include all files under `dir' matching any of the
                                                listed patterns
                                                
                                                
‘recursive-exclude dir pat1 pat2 ...’           exclude all files under `dir' matching any of the
                                                listed patterns
                                                
                                                
‘global-include pat1 pat2 ...’                  include all files anywhere in the source tree
                                                matching — & any of the listed patterns
                                                
                                                
‘global-exclude pat1 pat2 ...’                  exclude all files anywhere in the source tree
                                                matching — & any of the listed patterns
                                                
                                                
‘prune dir’                                     exclude all files under `dir'
                                                
                                                
‘graft dir’                                     include all files under `dir'
                                                

The patterns here are Unix-style “glob” patterns: ‘*’ matches any
sequence of regular filename characters, ‘?’ matches any single regular
filename character, and ‘[range]’ matches any of the characters in
`range' (e.g., ‘a-z’, ‘a-zA-Z’, ‘a-f0-9_.’).  The definition of “regular
filename character” is platform-specific: on Unix it is anything except
slash; on Windows anything except backslash or colon.


File: python.info,  Node: API Reference,  Prev: Command Reference,  Up: Distributing Python Modules Legacy version

17.9 API Reference
==================

See also
........

New and changed setup.py arguments in setuptools(1)

     The ‘setuptools’ project adds new capabilities to the ‘setup’
     function and other APIs, makes the API consistent across different
     Python versions, and is hence recommended over using ‘distutils’
     directly.

     Note: This document is being retained solely until the ‘setuptools’
     documentation at
     ‘https://setuptools.readthedocs.io/en/latest/setuptools.html’
     independently covers all of the relevant information currently
     included here.

* Menu:

* distutils.core — Core Distutils functionality: distutils core — Core Distutils functionality.
* distutils.ccompiler — CCompiler base class: distutils ccompiler — CCompiler base class.
* distutils.unixccompiler — Unix C Compiler: distutils unixccompiler — Unix C Compiler.
* distutils.msvccompiler — Microsoft Compiler: distutils msvccompiler — Microsoft Compiler.
* distutils.bcppcompiler — Borland Compiler: distutils bcppcompiler — Borland Compiler.
* distutils.cygwincompiler — Cygwin Compiler: distutils cygwincompiler — Cygwin Compiler.
* distutils.archive_util — Archiving utilities: distutils archive_util — Archiving utilities.
* distutils.dep_util — Dependency checking: distutils dep_util — Dependency checking.
* distutils.dir_util — Directory tree operations: distutils dir_util — Directory tree operations.
* distutils.file_util — Single file operations: distutils file_util — Single file operations.
* distutils.util — Miscellaneous other utility functions: distutils util — Miscellaneous other utility functions.
* distutils.dist — The Distribution class: distutils dist — The Distribution class.
* distutils.extension — The Extension class: distutils extension — The Extension class.
* distutils.debug — Distutils debug mode: distutils debug — Distutils debug mode.
* distutils.errors — Distutils exceptions: distutils errors — Distutils exceptions.
* distutils.fancy_getopt — Wrapper around the standard getopt module: distutils fancy_getopt — Wrapper around the standard getopt module.
* distutils.filelist — The FileList class: distutils filelist — The FileList class.
* distutils.log — Simple PEP 282-style logging: distutils log — Simple PEP 282-style logging.
* distutils.spawn — Spawn a sub-process: distutils spawn — Spawn a sub-process.
* distutils.sysconfig — System configuration information: distutils sysconfig — System configuration information.
* distutils.text_file — The TextFile class: distutils text_file — The TextFile class.
* distutils.version — Version number classes: distutils version — Version number classes.
* distutils.cmd — Abstract base class for Distutils commands: distutils cmd — Abstract base class for Distutils commands.
* Creating a new Distutils command::
* distutils.command — Individual Distutils commands: distutils command — Individual Distutils commands.
* distutils.command.bdist — Build a binary installer: distutils command bdist — Build a binary installer.
* distutils.command.bdist_packager — Abstract base class for packagers: distutils command bdist_packager — Abstract base class for packagers.
* distutils.command.bdist_dumb — Build a “dumb” installer: distutils command bdist_dumb — Build a “dumb” installer.
* distutils.command.bdist_msi — Build a Microsoft Installer binary package: distutils command bdist_msi — Build a Microsoft Installer binary package.
* distutils.command.bdist_rpm — Build a binary distribution as a Redhat RPM and SRPM: distutils command bdist_rpm — Build a binary distribution as a Redhat RPM and SRPM.
* distutils.command.bdist_wininst — Build a Windows installer: distutils command bdist_wininst — Build a Windows installer.
* distutils.command.sdist — Build a source distribution: distutils command sdist — Build a source distribution.
* distutils.command.build — Build all files of a package: distutils command build — Build all files of a package.
* distutils.command.build_clib — Build any C libraries in a package: distutils command build_clib — Build any C libraries in a package.
* distutils.command.build_ext — Build any extensions in a package: distutils command build_ext — Build any extensions in a package.
* distutils.command.build_py — Build the .py/.pyc files of a package: distutils command build_py — Build the py/ pyc files of a package.
* distutils.command.build_scripts — Build the scripts of a package: distutils command build_scripts — Build the scripts of a package.
* distutils.command.clean — Clean a package build area: distutils command clean — Clean a package build area.
* distutils.command.config — Perform package configuration: distutils command config — Perform package configuration.
* distutils.command.install — Install a package: distutils command install — Install a package.
* distutils.command.install_data — Install data files from a package: distutils command install_data — Install data files from a package.
* distutils.command.install_headers — Install C/C++ header files from a package: distutils command install_headers — Install C/C++ header files from a package.
* distutils.command.install_lib — Install library files from a package: distutils command install_lib — Install library files from a package.
* distutils.command.install_scripts — Install script files from a package: distutils command install_scripts — Install script files from a package.
* distutils.command.register — Register a module with the Python Package Index: distutils command register — Register a module with the Python Package Index.
* distutils.command.check — Check the meta-data of a package: distutils command check — Check the meta-data of a package.

   ---------- Footnotes ----------

   (1) 
https://setuptools.readthedocs.io/en/latest/setuptools.html#new-and-changed-setup-keywords


File: python.info,  Node: distutils core — Core Distutils functionality,  Next: distutils ccompiler — CCompiler base class,  Up: API Reference

17.9.1 ‘distutils.core’ — Core Distutils functionality
------------------------------------------------------

The *note distutils.core: 53. module is the only module that needs to be
installed to use the Distutils.  It provides the *note setup(): 3d8c.
(which is called from the setup script).  Indirectly provides the
‘distutils.dist.Distribution’ and *note distutils.cmd.Command: 45ba.
class.

 -- Function: distutils.core.setup (arguments)

     The basic do-everything function that does most everything you
     could ever ask for from a Distutils method.

     The setup function takes a large number of arguments.  These are
     laid out in the following table.

     argument name            value                                type
                                                                   
     --------------------------------------------------------------------------------------------------------------------------------
                                                                   
     `name'                   The name of the package              a string
                                                                   
                                                                   
     `version'                The version number of the package;   a string
                              see *note distutils.version: 65.     
                              
                                                                   
     `description'            A single line describing the         a string
                              package                              
                              
                                                                   
     `long_description'       Longer description of the package    a string
                                                                   
                                                                   
     `author'                 The name of the package author       a string
                                                                   
                                                                   
     `author_email'           The email address of the package     a string
                              author                               
                              
                                                                   
     `maintainer'             The name of the current              a string
                              maintainer, if different from the    
                              author.  Note that if the
                              maintainer is provided, distutils
                              will use it as the author in
                              ‘PKG-INFO’
                              
                                                                   
     `maintainer_email'       The email address of the current     a string
                              maintainer, if different from the    
                              author
                              
                                                                   
     `url'                    A URL for the package (homepage)     a string
                                                                   
                                                                   
     `download_url'           A URL to download the package        a string
                                                                   
                                                                   
     `packages'               A list of Python packages that       a list of strings
                              distutils will manipulate            
                              
                                                                   
     `py_modules'             A list of Python modules that        a list of strings
                              distutils will manipulate            
                              
                                                                   
     `scripts'                A list of standalone script files    a list of strings
                              to be built and installed            
                              
                                                                   
     `ext_modules'            A list of Python extensions to be    a list of instances of *note distutils.core.Extension: 4580.
                              built                                
                              
                                                                   
     `classifiers'            A list of categories for the         a list of strings; valid classifiers are listed on PyPI(1).
                              package                              
                              
                                                                   
     `distclass'              the *note Distribution: 45cb.        a subclass of *note distutils.core.Distribution: 45cb.
                              class to use                         
                              
                                                                   
     `script_name'            The name of the setup.py script -    a string
                              defaults to ‘sys.argv[0]’            
                              
                                                                   
     `script_args'            Arguments to supply to the setup     a list of strings
                              script                               
                              
                                                                   
     `options'                default options for the setup        a dictionary
                              script                               
                              
                                                                   
     `license'                The license for the package          a string
                                                                   
                                                                   
     `keywords'               Descriptive meta-data, see PEP       a list of strings or a comma-separated string
                              314(2)                               
                              
                                                                   
     `platforms'                                                   a list of strings or a comma-separated string
                                                                   
                                                                   
     `cmdclass'               A mapping of command names to        a dictionary
                              *note Command: 45cc. subclasses      
                              
                                                                   
     `data_files'             A list of data files to install      a list
                                                                   
                                                                   
     `package_dir'            A mapping of package to directory    a dictionary
                              names                                
                              

 -- Function: distutils.core.run_setup (script_name[, script_args=None,
          stop_after='run'])

     Run a setup script in a somewhat controlled environment, and return
     the ‘distutils.dist.Distribution’ instance that drives things.
     This is useful if you need to find out the distribution meta-data
     (passed as keyword args from `script' to *note setup(): 3d8c.), or
     the contents of the config files or command-line.

     `script_name' is a file that will be read and run with *note
     exec(): d0c.  ‘sys.argv[0]’ will be replaced with `script' for the
     duration of the call.  `script_args' is a list of strings; if
     supplied, ‘sys.argv[1:]’ will be replaced by `script_args' for the
     duration of the call.

     `stop_after' tells *note setup(): 3d8c. when to stop processing;
     possible values:

     value               description
                         
     ----------------------------------------------------------------------
                         
     `init'              Stop after the *note Distribution: 45cb.
                         instance has been created and populated with
                         the keyword arguments to *note setup(): 3d8c.
                         
                         
     `config'            Stop after config files have been parsed (and
                         their data stored in the
                         *note Distribution: 45cb. instance)
                         
                         
     `commandline'       Stop after the command-line (‘sys.argv[1:]’ or
                         `script_args') have been parsed (and the data
                         stored in the *note Distribution: 45cb.
                         instance.)
                         
                         
     `run'               Stop after all commands have been run (the same
                         as if *note setup(): 3d8c. had been called in
                         the usual way).  This is the default value.
                         

In addition, the *note distutils.core: 53. module exposed a number of
classes that live elsewhere.

   * ‘Extension’ from *note distutils.extension: 5a.

   * *note Command: 45ba. from *note distutils.cmd: 3c.

   * ‘Distribution’ from *note distutils.dist: 58.

A short description of each of these follows, but see the relevant
module for the full reference.

 -- Class: distutils.core.Extension

     The Extension class describes a single C or C++ extension module in
     a setup script.  It accepts the following keyword arguments in its
     constructor:

     argument name                value                                type
                                                                       
     --------------------------------------------------------------------------------------------------
                                                                       
     `name'                       the full name of the extension,      a string
                                  including any packages — ie.         
                                  `not' a filename or pathname, but
                                  Python dotted name
                                  
                                                                       
     `sources'                    list of source filenames, relative   a list of strings
                                  to the distribution root (where      
                                  the setup script lives), in Unix
                                  form (slash-separated) for
                                  portability.  Source files may be
                                  C, C++, SWIG (.i),
                                  platform-specific resource files,
                                  or whatever else is recognized by
                                  the ‘build_ext’ command as source
                                  for a Python extension.
                                  
                                                                       
     `include_dirs'               list of directories to search for    a list of strings
                                  C/C++ header files (in Unix form     
                                  for portability)
                                  
                                                                       
     `define_macros'              list of macros to define; each       a list of tuples
                                  macro is defined using a 2-tuple     
                                  ‘(name, value)’, where `value' is
                                  either the string to define it to
                                  or ‘None’ to define it without a
                                  particular value (equivalent of
                                  ‘#define FOO’ in source or ‘-DFOO’
                                  on Unix C compiler command line)
                                  
                                                                       
     `undef_macros'               list of macros to undefine           a list of strings
                                  explicitly                           
                                  
                                                                       
     `library_dirs'               list of directories to search for    a list of strings
                                  C/C++ libraries at link time         
                                  
                                                                       
     `libraries'                  list of library names (not           a list of strings
                                  filenames or paths) to link          
                                  against
                                  
                                                                       
     `runtime_library_dirs'       list of directories to search for    a list of strings
                                  C/C++ libraries at run time (for     
                                  shared extensions, this is when
                                  the extension is loaded)
                                  
                                                                       
     `extra_objects'              list of extra files to link with     a list of strings
                                  (eg.  object files not implied by    
                                  ‘sources’, static library that
                                  must be explicitly specified,
                                  binary resource files, etc.)
                                  
                                                                       
     `extra_compile_args'         any extra platform- and              a list of strings
                                  compiler-specific information to     
                                  use when compiling the source
                                  files in ‘sources’.  For platforms
                                  and compilers where a command line
                                  makes sense, this is typically a
                                  list of command-line arguments,
                                  but for other platforms it could
                                  be anything.
                                  
                                                                       
     `extra_link_args'            any extra platform- and              a list of strings
                                  compiler-specific information to     
                                  use when linking object files
                                  together to create the extension
                                  (or to create a new static Python
                                  interpreter).  Similar
                                  interpretation as for
                                  ‘extra_compile_args’.
                                  
                                                                       
     `export_symbols'             list of symbols to be exported       a list of strings
                                  from a shared extension.  Not used   
                                  on all platforms, and not
                                  generally necessary for Python
                                  extensions, which typically export
                                  exactly one symbol: ‘init’ +
                                  extension_name.
                                  
                                                                       
     `depends'                    list of files that the extension     a list of strings
                                  depends on                           
                                  
                                                                       
     `language'                   extension language (i.e.  ‘'c'’,     a string
                                  ‘'c++'’, ‘'objc'’).  Will be         
                                  detected from the source
                                  extensions if not provided.
                                  
                                                                       
     `optional'                   specifies that a build failure in    a boolean
                                  the extension should not abort the   
                                  build process, but simply skip the
                                  extension.
                                  

     Changed in version 3.8: On Unix, C extensions are no longer linked
     to libpython except on Android and Cygwin.

 -- Class: distutils.core.Distribution

     A *note Distribution: 45cb. describes how to build, install and
     package up a Python software package.

     See the *note setup(): 3d8c. function for a list of keyword
     arguments accepted by the Distribution constructor.  *note setup():
     3d8c. creates a Distribution instance.

     Changed in version 3.7: *note Distribution: 45cb. now warns if
     ‘classifiers’, ‘keywords’ and ‘platforms’ fields are not specified
     as a list or a string.

 -- Class: distutils.core.Command

     A *note Command: 45cc. class (or rather, an instance of one of its
     subclasses) implement a single distutils command.

   ---------- Footnotes ----------

   (1) https://pypi.org/classifiers

   (2) https://www.python.org/dev/peps/pep-0314


File: python.info,  Node: distutils ccompiler — CCompiler base class,  Next: distutils unixccompiler — Unix C Compiler,  Prev: distutils core — Core Distutils functionality,  Up: API Reference

17.9.2 ‘distutils.ccompiler’ — CCompiler base class
---------------------------------------------------

This module provides the abstract base class for the *note CCompiler:
45cf. classes.  A *note CCompiler: 45cf. instance can be used for all
the compile and link steps needed to build a single project.  Methods
are provided to set options for the compiler — macro definitions,
include directories, link path, libraries and the like.

This module provides the following functions.

 -- Function: distutils.ccompiler.gen_lib_options (compiler,
          library_dirs, runtime_library_dirs, libraries)

     Generate linker options for searching library directories and
     linking with specific libraries.  `libraries' and `library_dirs'
     are, respectively, lists of library names (not filenames!)  and
     search directories.  Returns a list of command-line options
     suitable for use with some compiler (depending on the two format
     strings passed in).

 -- Function: distutils.ccompiler.gen_preprocess_options (macros,
          include_dirs)

     Generate C pre-processor options (‘-D’, ‘-U’, ‘-I’) as used by at
     least two types of compilers: the typical Unix compiler and Visual
     C++.  `macros' is the usual thing, a list of 1- or 2-tuples, where
     ‘(name,)’ means undefine (‘-U’) macro `name', and ‘(name, value)’
     means define (‘-D’) macro `name' to `value'.  `include_dirs' is
     just a list of directory names to be added to the header file
     search path (‘-I’).  Returns a list of command-line options
     suitable for either Unix compilers or Visual C++.

 -- Function: distutils.ccompiler.get_default_compiler (osname,
          platform)

     Determine the default compiler to use for the given platform.

     `osname' should be one of the standard Python OS names (i.e.  the
     ones returned by ‘os.name’) and `platform' the common value
     returned by ‘sys.platform’ for the platform in question.

     The default values are ‘os.name’ and ‘sys.platform’ in case the
     parameters are not given.

 -- Function: distutils.ccompiler.new_compiler (plat=None,
          compiler=None, verbose=0, dry_run=0, force=0)

     Factory function to generate an instance of some CCompiler subclass
     for the supplied platform/compiler combination.  `plat' defaults to
     ‘os.name’ (eg.  ‘'posix'’, ‘'nt'’), and `compiler' defaults to the
     default compiler for that platform.  Currently only ‘'posix'’ and
     ‘'nt'’ are supported, and the default compilers are “traditional
     Unix interface” (‘UnixCCompiler’ class) and Visual C++
     (‘MSVCCompiler’ class).  Note that it’s perfectly possible to ask
     for a Unix compiler object under Windows, and a Microsoft compiler
     object under Unix—if you supply a value for `compiler', `plat' is
     ignored.

 -- Function: distutils.ccompiler.show_compilers ()

     Print list of available compilers (used by the ‘--help-compiler’
     options to ‘build’, ‘build_ext’, ‘build_clib’).

 -- Class: distutils.ccompiler.CCompiler ([verbose=0, dry_run=0,
          force=0])

     The abstract base class *note CCompiler: 45cf. defines the
     interface that must be implemented by real compiler classes.  The
     class also has some utility methods used by several compiler
     classes.

     The basic idea behind a compiler abstraction class is that each
     instance can be used for all the compile/link steps in building a
     single project.  Thus, attributes common to all of those compile
     and link steps — include directories, macros to define, libraries
     to link against, etc.  — are attributes of the compiler instance.
     To allow for variability in how individual files are treated, most
     of those attributes may be varied on a per-compilation or per-link
     basis.

     The constructor for each subclass creates an instance of the
     Compiler object.  Flags are `verbose' (show verbose output),
     `dry_run' (don’t actually execute the steps) and `force' (rebuild
     everything, regardless of dependencies).  All of these flags
     default to ‘0’ (off).  Note that you probably don’t want to
     instantiate *note CCompiler: 45cf. or one of its subclasses
     directly - use the ‘distutils.CCompiler.new_compiler()’ factory
     function instead.

     The following methods allow you to manually alter compiler options
     for the instance of the Compiler class.

      -- Method: add_include_dir (dir)

          Add `dir' to the list of directories that will be searched for
          header files.  The compiler is instructed to search
          directories in the order in which they are supplied by
          successive calls to *note add_include_dir(): 45d5.

      -- Method: set_include_dirs (dirs)

          Set the list of directories that will be searched to `dirs' (a
          list of strings).  Overrides any preceding calls to *note
          add_include_dir(): 45d5.; subsequent calls to *note
          add_include_dir(): 45d5. add to the list passed to *note
          set_include_dirs(): 45d6.  This does not affect any list of
          standard include directories that the compiler may search by
          default.

      -- Method: add_library (libname)

          Add `libname' to the list of libraries that will be included
          in all links driven by this compiler object.  Note that
          `libname' should *not* be the name of a file containing a
          library, but the name of the library itself: the actual
          filename will be inferred by the linker, the compiler, or the
          compiler class (depending on the platform).

          The linker will be instructed to link against libraries in the
          order they were supplied to *note add_library(): 45d7. and/or
          *note set_libraries(): 45d8.  It is perfectly valid to
          duplicate library names; the linker will be instructed to link
          against libraries as many times as they are mentioned.

      -- Method: set_libraries (libnames)

          Set the list of libraries to be included in all links driven
          by this compiler object to `libnames' (a list of strings).
          This does not affect any standard system libraries that the
          linker may include by default.

      -- Method: add_library_dir (dir)

          Add `dir' to the list of directories that will be searched for
          libraries specified to *note add_library(): 45d7. and *note
          set_libraries(): 45d8.  The linker will be instructed to
          search for libraries in the order they are supplied to *note
          add_library_dir(): 45d9. and/or *note set_library_dirs():
          45da.

      -- Method: set_library_dirs (dirs)

          Set the list of library search directories to `dirs' (a list
          of strings).  This does not affect any standard library search
          path that the linker may search by default.

      -- Method: add_runtime_library_dir (dir)

          Add `dir' to the list of directories that will be searched for
          shared libraries at runtime.

      -- Method: set_runtime_library_dirs (dirs)

          Set the list of directories to search for shared libraries at
          runtime to `dirs' (a list of strings).  This does not affect
          any standard search path that the runtime linker may search by
          default.

      -- Method: define_macro (name[, value=None])

          Define a preprocessor macro for all compilations driven by
          this compiler object.  The optional parameter `value' should
          be a string; if it is not supplied, then the macro will be
          defined without an explicit value and the exact outcome
          depends on the compiler used.

      -- Method: undefine_macro (name)

          Undefine a preprocessor macro for all compilations driven by
          this compiler object.  If the same macro is defined by *note
          define_macro(): 45dd. and undefined by *note undefine_macro():
          45de. the last call takes precedence (including multiple
          redefinitions or undefinitions).  If the macro is
          redefined/undefined on a per-compilation basis (ie.  in the
          call to *note compile(): 2e7.), then that takes precedence.

      -- Method: add_link_object (object)

          Add `object' to the list of object files (or analogues, such
          as explicitly named library files or the output of “resource
          compilers”) to be included in every link driven by this
          compiler object.

      -- Method: set_link_objects (objects)

          Set the list of object files (or analogues) to be included in
          every link to `objects'.  This does not affect any standard
          object files that the linker may include by default (such as
          system libraries).

     The following methods implement methods for autodetection of
     compiler options, providing some functionality similar to GNU
     ‘autoconf’.

      -- Method: detect_language (sources)

          Detect the language of a given file, or list of files.  Uses
          the instance attributes ‘language_map’ (a dictionary), and
          ‘language_order’ (a list) to do the job.

      -- Method: find_library_file (dirs, lib[, debug=0])

          Search the specified list of directories for a static or
          shared library file `lib' and return the full path to that
          file.  If `debug' is true, look for a debugging version (if
          that makes sense on the current platform).  Return ‘None’ if
          `lib' wasn’t found in any of the specified directories.

      -- Method: has_function (funcname[, includes=None,
               include_dirs=None, libraries=None, library_dirs=None])

          Return a boolean indicating whether `funcname' is supported on
          the current platform.  The optional arguments can be used to
          augment the compilation environment by providing additional
          include files and paths and libraries and paths.

      -- Method: library_dir_option (dir)

          Return the compiler option to add `dir' to the list of
          directories searched for libraries.

      -- Method: library_option (lib)

          Return the compiler option to add `lib' to the list of
          libraries linked into the shared library or executable.

      -- Method: runtime_library_dir_option (dir)

          Return the compiler option to add `dir' to the list of
          directories searched for runtime libraries.

      -- Method: set_executables (**args)

          Define the executables (and options for them) that will be run
          to perform the various stages of compilation.  The exact set
          of executables that may be specified here depends on the
          compiler class (via the ‘executables’ class attribute), but
          most will have:

          attribute          description
                             
          ------------------------------------------------------------------
                             
          `compiler'         the C/C++ compiler
                             
                             
          `linker_so'        linker used to create shared objects and
                             libraries
                             
                             
          `linker_exe'       linker used to create binary executables
                             
                             
          `archiver'         static library creator
                             

          On platforms with a command-line (Unix, DOS/Windows), each of
          these is a string that will be split into executable name and
          (optional) list of arguments.  (Splitting the string is done
          similarly to how Unix shells operate: words are delimited by
          spaces, but quotes and backslashes can override this.  See
          *note distutils.util.split_quoted(): 45e8.)

     The following methods invoke stages in the build process.

      -- Method: compile (sources[, output_dir=None, macros=None,
               include_dirs=None, debug=0, extra_preargs=None,
               extra_postargs=None, depends=None])

          Compile one or more source files.  Generates object files
          (e.g.  transforms a ‘.c’ file to a ‘.o’ file.)

          `sources' must be a list of filenames, most likely C/C++
          files, but in reality anything that can be handled by a
          particular compiler and compiler class (eg.  ‘MSVCCompiler’
          can handle resource files in `sources').  Return a list of
          object filenames, one per source filename in `sources'.
          Depending on the implementation, not all source files will
          necessarily be compiled, but all corresponding object
          filenames will be returned.

          If `output_dir' is given, object files will be put under it,
          while retaining their original path component.  That is,
          ‘foo/bar.c’ normally compiles to ‘foo/bar.o’ (for a Unix
          implementation); if `output_dir' is `build', then it would
          compile to ‘build/foo/bar.o’.

          `macros', if given, must be a list of macro definitions.  A
          macro definition is either a ‘(name, value)’ 2-tuple or a
          ‘(name,)’ 1-tuple.  The former defines a macro; if the value
          is ‘None’, the macro is defined without an explicit value.
          The 1-tuple case undefines a macro.  Later
          definitions/redefinitions/undefinitions take precedence.

          `include_dirs', if given, must be a list of strings, the
          directories to add to the default include file search path for
          this compilation only.

          `debug' is a boolean; if true, the compiler will be instructed
          to output debug symbols in (or alongside) the object file(s).

          `extra_preargs' and `extra_postargs' are
          implementation-dependent.  On platforms that have the notion
          of a command-line (e.g.  Unix, DOS/Windows), they are most
          likely lists of strings: extra command-line arguments to
          prepend/append to the compiler command line.  On other
          platforms, consult the implementation class documentation.  In
          any event, they are intended as an escape hatch for those
          occasions when the abstract compiler framework doesn’t cut the
          mustard.

          `depends', if given, is a list of filenames that all targets
          depend on.  If a source file is older than any file in
          depends, then the source file will be recompiled.  This
          supports dependency tracking, but only at a coarse
          granularity.

          Raises ‘CompileError’ on failure.

      -- Method: create_static_lib (objects, output_libname[,
               output_dir=None, debug=0, target_lang=None])

          Link a bunch of stuff together to create a static library
          file.  The “bunch of stuff” consists of the list of object
          files supplied as `objects', the extra object files supplied
          to *note add_link_object(): 45df. and/or *note
          set_link_objects(): 45e0, the libraries supplied to *note
          add_library(): 45d7. and/or *note set_libraries(): 45d8, and
          the libraries supplied as `libraries' (if any).

          `output_libname' should be a library name, not a filename; the
          filename will be inferred from the library name.  `output_dir'
          is the directory where the library file will be put.

          `debug' is a boolean; if true, debugging information will be
          included in the library (note that on most platforms, it is
          the compile step where this matters: the `debug' flag is
          included here just for consistency).

          `target_lang' is the target language for which the given
          objects are being compiled.  This allows specific linkage time
          treatment of certain languages.

          Raises ‘LibError’ on failure.

      -- Method: link (target_desc, objects, output_filename[,
               output_dir=None, libraries=None, library_dirs=None,
               runtime_library_dirs=None, export_symbols=None, debug=0,
               extra_preargs=None, extra_postargs=None, build_temp=None,
               target_lang=None])

          Link a bunch of stuff together to create an executable or
          shared library file.

          The “bunch of stuff” consists of the list of object files
          supplied as `objects'.  `output_filename' should be a
          filename.  If `output_dir' is supplied, `output_filename' is
          relative to it (i.e.  `output_filename' can provide directory
          components if needed).

          `libraries' is a list of libraries to link against.  These are
          library names, not filenames, since they’re translated into
          filenames in a platform-specific way (eg.  `foo' becomes
          ‘libfoo.a’ on Unix and ‘foo.lib’ on DOS/Windows).  However,
          they can include a directory component, which means the linker
          will look in that specific directory rather than searching all
          the normal locations.

          `library_dirs', if supplied, should be a list of directories
          to search for libraries that were specified as bare library
          names (ie.  no directory component).  These are on top of the
          system default and those supplied to *note add_library_dir():
          45d9. and/or *note set_library_dirs(): 45da.
          `runtime_library_dirs' is a list of directories that will be
          embedded into the shared library and used to search for other
          shared libraries that *it* depends on at run-time.  (This may
          only be relevant on Unix.)

          `export_symbols' is a list of symbols that the shared library
          will export.  (This appears to be relevant only on Windows.)

          `debug' is as for *note compile(): 2e7. and *note
          create_static_lib(): 45ea, with the slight distinction that it
          actually matters on most platforms (as opposed to *note
          create_static_lib(): 45ea, which includes a `debug' flag
          mostly for form’s sake).

          `extra_preargs' and `extra_postargs' are as for *note
          compile(): 2e7. (except of course that they supply
          command-line arguments for the particular linker being used).

          `target_lang' is the target language for which the given
          objects are being compiled.  This allows specific linkage time
          treatment of certain languages.

          Raises ‘LinkError’ on failure.

      -- Method: link_executable (objects, output_progname[,
               output_dir=None, libraries=None, library_dirs=None,
               runtime_library_dirs=None, debug=0, extra_preargs=None,
               extra_postargs=None, target_lang=None])

          Link an executable.  `output_progname' is the name of the file
          executable, while `objects' are a list of object filenames to
          link in.  Other arguments are as for the *note link(): 45eb.
          method.

      -- Method: link_shared_lib (objects, output_libname[,
               output_dir=None, libraries=None, library_dirs=None,
               runtime_library_dirs=None, export_symbols=None, debug=0,
               extra_preargs=None, extra_postargs=None, build_temp=None,
               target_lang=None])

          Link a shared library.  `output_libname' is the name of the
          output library, while `objects' is a list of object filenames
          to link in.  Other arguments are as for the *note link():
          45eb. method.

      -- Method: link_shared_object (objects, output_filename[,
               output_dir=None, libraries=None, library_dirs=None,
               runtime_library_dirs=None, export_symbols=None, debug=0,
               extra_preargs=None, extra_postargs=None, build_temp=None,
               target_lang=None])

          Link a shared object.  `output_filename' is the name of the
          shared object that will be created, while `objects' is a list
          of object filenames to link in.  Other arguments are as for
          the *note link(): 45eb. method.

      -- Method: preprocess (source[, output_file=None, macros=None,
               include_dirs=None, extra_preargs=None,
               extra_postargs=None])

          Preprocess a single C/C++ source file, named in `source'.
          Output will be written to file named `output_file', or
          `stdout' if `output_file' not supplied.  `macros' is a list of
          macro definitions as for *note compile(): 2e7, which will
          augment the macros set with *note define_macro(): 45dd. and
          *note undefine_macro(): 45de.  `include_dirs' is a list of
          directory names that will be added to the default list, in the
          same way as *note add_include_dir(): 45d5.

          Raises ‘PreprocessError’ on failure.

     The following utility methods are defined by the *note CCompiler:
     45cf. class, for use by the various concrete subclasses.

      -- Method: executable_filename (basename[, strip_dir=0,
               output_dir=''])

          Returns the filename of the executable for the given
          `basename'.  Typically for non-Windows platforms this is the
          same as the basename, while Windows will get a ‘.exe’ added.

      -- Method: library_filename (libname[, lib_type='static',
               strip_dir=0, output_dir=''])

          Returns the filename for the given library name on the current
          platform.  On Unix a library with `lib_type' of ‘'static'’
          will typically be of the form ‘liblibname.a’, while a
          `lib_type' of ‘'dynamic'’ will be of the form ‘liblibname.so’.

      -- Method: object_filenames (source_filenames[, strip_dir=0,
               output_dir=''])

          Returns the name of the object files for the given source
          files.  `source_filenames' should be a list of filenames.

      -- Method: shared_object_filename (basename[, strip_dir=0,
               output_dir=''])

          Returns the name of a shared object file for the given file
          name `basename'.

      -- Method: execute (func, args[, msg=None, level=1])

          Invokes *note distutils.util.execute(): 45f5.  This method
          invokes a Python function `func' with the given arguments
          `args', after logging and taking into account the `dry_run'
          flag.

      -- Method: spawn (cmd)

          Invokes ‘distutils.util.spawn()’.  This invokes an external
          process to run the given command.

      -- Method: mkpath (name[, mode=511])

          Invokes *note distutils.dir_util.mkpath(): 45f8.  This creates
          a directory and any missing ancestor directories.

      -- Method: move_file (src, dst)

          Invokes *note distutils.file_util.move_file(): 45fa.  Renames
          `src' to `dst'.

      -- Method: announce (msg[, level=1])

          Write a message using ‘distutils.log.debug()’.

      -- Method: warn (msg)

          Write a warning message `msg' to standard error.

      -- Method: debug_print (msg)

          If the `debug' flag is set on this *note CCompiler: 45cf.
          instance, print `msg' to standard output, otherwise do
          nothing.


File: python.info,  Node: distutils unixccompiler — Unix C Compiler,  Next: distutils msvccompiler — Microsoft Compiler,  Prev: distutils ccompiler — CCompiler base class,  Up: API Reference

17.9.3 ‘distutils.unixccompiler’ — Unix C Compiler
--------------------------------------------------

This module provides the ‘UnixCCompiler’ class, a subclass of
‘CCompiler’ that handles the typical Unix-style command-line C compiler:

   * macros defined with ‘-Dname[=value]’

   * macros undefined with ‘-Uname’

   * include search directories specified with ‘-Idir’

   * libraries specified with ‘-llib’

   * library search directories specified with ‘-Ldir’

   * compile handled by ‘cc’ (or similar) executable with ‘-c’ option:
     compiles ‘.c’ to ‘.o’

   * link static library handled by ‘ar’ command (possibly with
     ‘ranlib’)

   * link shared library handled by ‘cc’ ‘-shared’


File: python.info,  Node: distutils msvccompiler — Microsoft Compiler,  Next: distutils bcppcompiler — Borland Compiler,  Prev: distutils unixccompiler — Unix C Compiler,  Up: API Reference

17.9.4 ‘distutils.msvccompiler’ — Microsoft Compiler
----------------------------------------------------

This module provides ‘MSVCCompiler’, an implementation of the abstract
‘CCompiler’ class for Microsoft Visual Studio.  Typically, extension
modules need to be compiled with the same compiler that was used to
compile Python.  For Python 2.3 and earlier, the compiler was Visual
Studio 6.  For Python 2.4 and 2.5, the compiler is Visual Studio .NET
2003.

‘MSVCCompiler’ will normally choose the right compiler, linker etc.  on
its own.  To override this choice, the environment variables
`DISTUTILS_USE_SDK' and `MSSdk' must be both set.  `MSSdk' indicates
that the current environment has been setup by the SDK’s ‘SetEnv.Cmd’
script, or that the environment variables had been registered when the
SDK was installed; `DISTUTILS_USE_SDK' indicates that the distutils user
has made an explicit choice to override the compiler selection by
‘MSVCCompiler’.


File: python.info,  Node: distutils bcppcompiler — Borland Compiler,  Next: distutils cygwincompiler — Cygwin Compiler,  Prev: distutils msvccompiler — Microsoft Compiler,  Up: API Reference

17.9.5 ‘distutils.bcppcompiler’ — Borland Compiler
--------------------------------------------------

This module provides ‘BorlandCCompiler’, a subclass of the abstract
‘CCompiler’ class for the Borland C++ compiler.


File: python.info,  Node: distutils cygwincompiler — Cygwin Compiler,  Next: distutils archive_util — Archiving utilities,  Prev: distutils bcppcompiler — Borland Compiler,  Up: API Reference

17.9.6 ‘distutils.cygwincompiler’ — Cygwin Compiler
---------------------------------------------------

This module provides the ‘CygwinCCompiler’ class, a subclass of
‘UnixCCompiler’ that handles the Cygwin port of the GNU C compiler to
Windows.  It also contains the Mingw32CCompiler class which handles the
mingw32 port of GCC (same as cygwin in no-cygwin mode).


File: python.info,  Node: distutils archive_util — Archiving utilities,  Next: distutils dep_util — Dependency checking,  Prev: distutils cygwincompiler — Cygwin Compiler,  Up: API Reference

17.9.7 ‘distutils.archive_util’ — Archiving utilities
-----------------------------------------------------

This module provides a few functions for creating archive files, such as
tarballs or zipfiles.

 -- Function: distutils.archive_util.make_archive (base_name, format[,
          root_dir=None, base_dir=None, verbose=0, dry_run=0])

     Create an archive file (eg.  ‘zip’ or ‘tar’).  `base_name' is the
     name of the file to create, minus any format-specific extension;
     `format' is the archive format: one of ‘zip’, ‘tar’, ‘gztar’,
     ‘bztar’, ‘xztar’, or ‘ztar’.  `root_dir' is a directory that will
     be the root directory of the archive; ie.  we typically ‘chdir’
     into `root_dir' before creating the archive.  `base_dir' is the
     directory where we start archiving from; ie.  `base_dir' will be
     the common prefix of all files and directories in the archive.
     `root_dir' and `base_dir' both default to the current directory.
     Returns the name of the archive file.

     Changed in version 3.5: Added support for the ‘xztar’ format.

 -- Function: distutils.archive_util.make_tarball (base_name, base_dir[,
          compress='gzip', verbose=0, dry_run=0])

     ‘Create an (optional compressed) archive as a tar file from all
     files in and under `base_dir'.  `compress' must be ‘'gzip'’ (the
     default), ‘'bzip2'’, ‘'xz'’, ‘'compress'’, or ‘None’.  For the
     ‘'compress'’ method the compression utility named by ‘compress’
     must be on the default program search path, so this is probably
     Unix-specific.  The output tar file will be named ‘base_dir.tar’,
     possibly plus the appropriate compression extension (‘.gz’, ‘.bz2’,
     ‘.xz’ or ‘.Z’).  Return the output filename.

     Changed in version 3.5: Added support for the ‘xz’ compression.

 -- Function: distutils.archive_util.make_zipfile (base_name, base_dir[,
          verbose=0, dry_run=0])

     Create a zip file from all files in and under `base_dir'.  The
     output zip file will be named `base_name' + ‘.zip’.  Uses either
     the *note zipfile: 14b. Python module (if available) or the InfoZIP
     ‘zip’ utility (if installed and found on the default search path).
     If neither tool is available, raises ‘DistutilsExecError’.  Returns
     the name of the output zip file.


File: python.info,  Node: distutils dep_util — Dependency checking,  Next: distutils dir_util — Directory tree operations,  Prev: distutils archive_util — Archiving utilities,  Up: API Reference

17.9.8 ‘distutils.dep_util’ — Dependency checking
-------------------------------------------------

This module provides functions for performing simple, timestamp-based
dependency of files and groups of files; also, functions based entirely
on such timestamp dependency analysis.

 -- Function: distutils.dep_util.newer (source, target)

     Return true if `source' exists and is more recently modified than
     `target', or if `source' exists and `target' doesn’t.  Return false
     if both exist and `target' is the same age or newer than `source'.
     Raise ‘DistutilsFileError’ if `source' does not exist.

 -- Function: distutils.dep_util.newer_pairwise (sources, targets)

     Walk two filename lists in parallel, testing if each source is
     newer than its corresponding target.  Return a pair of lists
     (`sources', `targets') where source is newer than target, according
     to the semantics of *note newer(): 4607.

 -- Function: distutils.dep_util.newer_group (sources, target[,
          missing='error'])

     Return true if `target' is out-of-date with respect to any file
     listed in `sources'.  In other words, if `target' exists and is
     newer than every file in `sources', return false; otherwise return
     true.  `missing' controls what we do when a source file is missing;
     the default (‘'error'’) is to blow up with an *note OSError: 304.
     from inside *note os.stat(): 321.; if it is ‘'ignore'’, we silently
     drop any missing source files; if it is ‘'newer'’, any missing
     source files make us assume that `target' is out-of-date (this is
     handy in “dry-run” mode: it’ll make you pretend to carry out
     commands that wouldn’t work because inputs are missing, but that
     doesn’t matter because you’re not actually going to run the
     commands).


File: python.info,  Node: distutils dir_util — Directory tree operations,  Next: distutils file_util — Single file operations,  Prev: distutils dep_util — Dependency checking,  Up: API Reference

17.9.9 ‘distutils.dir_util’ — Directory tree operations
-------------------------------------------------------

This module provides functions for operating on directories and trees of
directories.

 -- Function: distutils.dir_util.mkpath (name[, mode=0o777, verbose=0,
          dry_run=0])

     Create a directory and any missing ancestor directories.  If the
     directory already exists (or if `name' is the empty string, which
     means the current directory, which of course exists), then do
     nothing.  Raise ‘DistutilsFileError’ if unable to create some
     directory along the way (eg.  some sub-path exists, but is a file
     rather than a directory).  If `verbose' is true, print a one-line
     summary of each mkdir to stdout.  Return the list of directories
     actually created.

 -- Function: distutils.dir_util.create_tree (base_dir, files[,
          mode=0o777, verbose=0, dry_run=0])

     Create all the empty directories under `base_dir' needed to put
     `files' there.  `base_dir' is just the name of a directory which
     doesn’t necessarily exist yet; `files' is a list of filenames to be
     interpreted relative to `base_dir'.  `base_dir' + the directory
     portion of every file in `files' will be created if it doesn’t
     already exist.  `mode', `verbose' and `dry_run' flags are as for
     *note mkpath(): 45f8.

 -- Function: distutils.dir_util.copy_tree (src, dst[, preserve_mode=1,
          preserve_times=1, preserve_symlinks=0, update=0, verbose=0,
          dry_run=0])

     Copy an entire directory tree `src' to a new location `dst'.  Both
     `src' and `dst' must be directory names.  If `src' is not a
     directory, raise ‘DistutilsFileError’.  If `dst' does not exist, it
     is created with *note mkpath(): 45f8.  The end result of the copy
     is that every file in `src' is copied to `dst', and directories
     under `src' are recursively copied to `dst'.  Return the list of
     files that were copied or might have been copied, using their
     output name.  The return value is unaffected by `update' or
     `dry_run': it is simply the list of all files under `src', with the
     names changed to be under `dst'.

     `preserve_mode' and `preserve_times' are the same as for *note
     distutils.file_util.copy_file(): 460d.; note that they only apply
     to regular files, not to directories.  If `preserve_symlinks' is
     true, symlinks will be copied as symlinks (on platforms that
     support them!); otherwise (the default), the destination of the
     symlink will be copied.  `update' and `verbose' are the same as for
     ‘copy_file()’.

     Files in `src' that begin with ‘.nfs’ are skipped (more information
     on these files is available in answer D2 of the NFS FAQ page(1)).

     Changed in version 3.3.1: NFS files are ignored.

 -- Function: distutils.dir_util.remove_tree (directory[, verbose=0,
          dry_run=0])

     Recursively remove `directory' and all files and directories
     underneath it.  Any errors are ignored (apart from being reported
     to ‘sys.stdout’ if `verbose' is true).

   ---------- Footnotes ----------

   (1) http://nfs.sourceforge.net/#section_d


File: python.info,  Node: distutils file_util — Single file operations,  Next: distutils util — Miscellaneous other utility functions,  Prev: distutils dir_util — Directory tree operations,  Up: API Reference

17.9.10 ‘distutils.file_util’ — Single file operations
------------------------------------------------------

This module contains some utility functions for operating on individual
files.

 -- Function: distutils.file_util.copy_file (src, dst[, preserve_mode=1,
          preserve_times=1, update=0, link=None, verbose=0, dry_run=0])

     Copy file `src' to `dst'.  If `dst' is a directory, then `src' is
     copied there with the same name; otherwise, it must be a filename.
     (If the file exists, it will be ruthlessly clobbered.)  If
     `preserve_mode' is true (the default), the file’s mode (type and
     permission bits, or whatever is analogous on the current platform)
     is copied.  If `preserve_times' is true (the default), the
     last-modified and last-access times are copied as well.  If
     `update' is true, `src' will only be copied if `dst' does not
     exist, or if `dst' does exist but is older than `src'.

     `link' allows you to make hard links (using *note os.link(): b11.)
     or symbolic links (using *note os.symlink(): b17.) instead of
     copying: set it to ‘'hard'’ or ‘'sym'’; if it is ‘None’ (the
     default), files are copied.  Don’t set `link' on systems that don’t
     support it: *note copy_file(): 460d. doesn’t check if hard or
     symbolic linking is available.  It uses ‘_copy_file_contents()’ to
     copy file contents.

     Return a tuple ‘(dest_name, copied)’: `dest_name' is the actual
     name of the output file, and `copied' is true if the file was
     copied (or would have been copied, if `dry_run' true).

 -- Function: distutils.file_util.move_file (src, dst[, verbose,
          dry_run])

     Move file `src' to `dst'.  If `dst' is a directory, the file will
     be moved into it with the same name; otherwise, `src' is just
     renamed to `dst'.  Returns the new full name of the file.

          Warning: Handles cross-device moves on Unix using *note
          copy_file(): 460d.  What about other systems?

 -- Function: distutils.file_util.write_file (filename, contents)

     Create a file called `filename' and write `contents' (a sequence of
     strings without line terminators) to it.


File: python.info,  Node: distutils util — Miscellaneous other utility functions,  Next: distutils dist — The Distribution class,  Prev: distutils file_util — Single file operations,  Up: API Reference

17.9.11 ‘distutils.util’ — Miscellaneous other utility functions
----------------------------------------------------------------

This module contains other assorted bits and pieces that don’t fit into
any other utility module.

 -- Function: distutils.util.get_platform ()

     Return a string that identifies the current platform.  This is used
     mainly to distinguish platform-specific build directories and
     platform-specific built distributions.  Typically includes the OS
     name and version and the architecture (as supplied by
     ‘os.uname()’), although the exact information included depends on
     the OS; e.g., on Linux, the kernel version isn’t particularly
     important.

     Examples of returned values:

        * ‘linux-i586’

        * ‘linux-alpha’

        * ‘solaris-2.6-sun4u’

     For non-POSIX platforms, currently just returns ‘sys.platform’.

     For macOS systems the OS version reflects the minimal version on
     which binaries will run (that is, the value of
     ‘MACOSX_DEPLOYMENT_TARGET’ during the build of Python), not the OS
     version of the current system.

     For universal binary builds on macOS the architecture value
     reflects the universal binary status instead of the architecture of
     the current processor.  For 32-bit universal binaries the
     architecture is ‘fat’, for 64-bit universal binaries the
     architecture is ‘fat64’, and for 4-way universal binaries the
     architecture is ‘universal’.  Starting from Python 2.7 and Python
     3.2 the architecture ‘fat3’ is used for a 3-way universal build
     (ppc, i386, x86_64) and ‘intel’ is used for a universal build with
     the i386 and x86_64 architectures

     Examples of returned values on macOS:

        * ‘macosx-10.3-ppc’

        * ‘macosx-10.3-fat’

        * ‘macosx-10.5-universal’

        * ‘macosx-10.6-intel’

     For AIX, Python 3.9 and later return a string starting with “aix”,
     followed by additional fields (separated by ‘'-'’) that represent
     the combined values of AIX Version, Release and Technology Level
     (first field), Build Date (second field), and bit-size (third
     field).  Python 3.8 and earlier returned only a single additional
     field with the AIX Version and Release.

     Examples of returned values on AIX:

        * ‘aix-5307-0747-32’ # 32-bit build on AIX ‘oslevel -s’:
          5300-07-00-0000

        * ‘aix-7105-1731-64’ # 64-bit build on AIX ‘oslevel -s’:
          7100-05-01-1731

        * ‘aix-7.2’ # Legacy form reported in Python 3.8 and earlier

     Changed in version 3.9: The AIX platform string format now also
     includes the technology level, build date, and ABI bit-size.

 -- Function: distutils.util.convert_path (pathname)

     Return ‘pathname’ as a name that will work on the native
     filesystem, i.e.  split it on ‘/’ and put it back together again
     using the current directory separator.  Needed because filenames in
     the setup script are always supplied in Unix style, and have to be
     converted to the local convention before we can actually use them
     in the filesystem.  Raises *note ValueError: 16d. on non-Unix-ish
     systems if `pathname' either starts or ends with a slash.

 -- Function: distutils.util.change_root (new_root, pathname)

     Return `pathname' with `new_root' prepended.  If `pathname' is
     relative, this is equivalent to ‘os.path.join(new_root,pathname)’
     Otherwise, it requires making `pathname' relative and then joining
     the two, which is tricky on DOS/Windows.

 -- Function: distutils.util.check_environ ()

     Ensure that ‘os.environ’ has all the environment variables we
     guarantee that users can use in config files, command-line options,
     etc.  Currently this includes:

        * ‘HOME’ - user’s home directory (Unix only)

        * ‘PLAT’ - description of the current platform, including
          hardware and OS (see *note get_platform(): 4612.)

 -- Function: distutils.util.subst_vars (s, local_vars)

     Perform shell/Perl-style variable substitution on `s'.  Every
     occurrence of ‘$’ followed by a name is considered a variable, and
     variable is substituted by the value found in the `local_vars'
     dictionary, or in ‘os.environ’ if it’s not in `local_vars'.
     `os.environ' is first checked/augmented to guarantee that it
     contains certain values: see *note check_environ(): 4615.  Raise
     *note ValueError: 16d. for any variables not found in either
     `local_vars' or ‘os.environ’.

     Note that this is not a fully-fledged string interpolation
     function.  A valid ‘$variable’ can consist only of upper and lower
     case letters, numbers and an underscore.  No { } or ( ) style
     quoting is available.

 -- Function: distutils.util.split_quoted (s)

     Split a string up according to Unix shell-like rules for quotes and
     backslashes.  In short: words are delimited by spaces, as long as
     those spaces are not escaped by a backslash, or inside a quoted
     string.  Single and double quotes are equivalent, and the quote
     characters can be backslash-escaped.  The backslash is stripped
     from any two-character escape sequence, leaving only the escaped
     character.  The quote characters are stripped from any quoted
     string.  Returns a list of words.

 -- Function: distutils.util.execute (func, args[, msg=None, verbose=0,
          dry_run=0])

     Perform some action that affects the outside world (for instance,
     writing to the filesystem).  Such actions are special because they
     are disabled by the `dry_run' flag.  This method takes care of all
     that bureaucracy for you; all you have to do is supply the function
     to call and an argument tuple for it (to embody the “external
     action” being performed), and an optional message to print.

 -- Function: distutils.util.strtobool (val)

     Convert a string representation of truth to true (1) or false (0).

     True values are ‘y’, ‘yes’, ‘t’, ‘true’, ‘on’ and ‘1’; false values
     are ‘n’, ‘no’, ‘f’, ‘false’, ‘off’ and ‘0’.  Raises *note
     ValueError: 16d. if `val' is anything else.

 -- Function: distutils.util.byte_compile (py_files[, optimize=0,
          force=0, prefix=None, base_dir=None, verbose=1, dry_run=0,
          direct=None])

     Byte-compile a collection of Python source files to ‘.pyc’ files in
     a ‘__pycache__’ subdirectory (see PEP 3147(1) and PEP 488(2)).
     `py_files' is a list of files to compile; any files that don’t end
     in ‘.py’ are silently skipped.  `optimize' must be one of the
     following:

        * ‘0’ - don’t optimize

        * ‘1’ - normal optimization (like ‘python -O’)

        * ‘2’ - extra optimization (like ‘python -OO’)

     If `force' is true, all files are recompiled regardless of
     timestamps.

     The source filename encoded in each *note bytecode: 709. file
     defaults to the filenames listed in `py_files'; you can modify
     these with `prefix' and `basedir'.  `prefix' is a string that will
     be stripped off of each source filename, and `base_dir' is a
     directory name that will be prepended (after `prefix' is stripped).
     You can supply either or both (or neither) of `prefix' and
     `base_dir', as you wish.

     If `dry_run' is true, doesn’t actually do anything that would
     affect the filesystem.

     Byte-compilation is either done directly in this interpreter
     process with the standard *note py_compile: d7. module, or
     indirectly by writing a temporary script and executing it.
     Normally, you should let *note byte_compile(): 4618. figure out to
     use direct compilation or not (see the source for details).  The
     `direct' flag is used by the script generated in indirect mode;
     unless you know what you’re doing, leave it set to ‘None’.

     Changed in version 3.2.3: Create ‘.pyc’ files with an *note import
     magic tag: 3cfc. in their name, in a ‘__pycache__’ subdirectory
     instead of files without tag in the current directory.

     Changed in version 3.5: Create ‘.pyc’ files according to PEP
     488(3).

 -- Function: distutils.util.rfc822_escape (header)

     Return a version of `header' escaped for inclusion in an RFC 822(4)
     header, by ensuring there are 8 spaces space after each newline.
     Note that it does no other modification of the string.

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-3147

   (2) https://www.python.org/dev/peps/pep-0488

   (3) https://www.python.org/dev/peps/pep-0488

   (4) https://tools.ietf.org/html/rfc822.html


File: python.info,  Node: distutils dist — The Distribution class,  Next: distutils extension — The Extension class,  Prev: distutils util — Miscellaneous other utility functions,  Up: API Reference

17.9.12 ‘distutils.dist’ — The Distribution class
-------------------------------------------------

This module provides the *note Distribution: 45cb. class, which
represents the module distribution being built/installed/distributed.


File: python.info,  Node: distutils extension — The Extension class,  Next: distutils debug — Distutils debug mode,  Prev: distutils dist — The Distribution class,  Up: API Reference

17.9.13 ‘distutils.extension’ — The Extension class
---------------------------------------------------

This module provides the ‘Extension’ class, used to describe C/C++
extension modules in setup scripts.


File: python.info,  Node: distutils debug — Distutils debug mode,  Next: distutils errors — Distutils exceptions,  Prev: distutils extension — The Extension class,  Up: API Reference

17.9.14 ‘distutils.debug’ — Distutils debug mode
------------------------------------------------

This module provides the DEBUG flag.


File: python.info,  Node: distutils errors — Distutils exceptions,  Next: distutils fancy_getopt — Wrapper around the standard getopt module,  Prev: distutils debug — Distutils debug mode,  Up: API Reference

17.9.15 ‘distutils.errors’ — Distutils exceptions
-------------------------------------------------

Provides exceptions used by the Distutils modules.  Note that Distutils
modules may raise standard exceptions; in particular, SystemExit is
usually raised for errors that are obviously the end-user’s fault (eg.
bad command-line arguments).

This module is safe to use in ‘from ... import *’ mode; it only exports
symbols whose names start with ‘Distutils’ and end with ‘Error’.


File: python.info,  Node: distutils fancy_getopt — Wrapper around the standard getopt module,  Next: distutils filelist — The FileList class,  Prev: distutils errors — Distutils exceptions,  Up: API Reference

17.9.16 ‘distutils.fancy_getopt’ — Wrapper around the standard getopt module
----------------------------------------------------------------------------

This module provides a wrapper around the standard *note getopt: 85.
module that provides the following additional features:

   * short and long options are tied together

   * options have help strings, so *note fancy_getopt(): 461f. could
     potentially create a complete usage summary

   * options set attributes of a passed-in object

   * boolean options can have “negative aliases” — eg.  if ‘--quiet’ is
     the “negative alias” of ‘--verbose’, then ‘--quiet’ on the command
     line sets `verbose' to false.

 -- Function: distutils.fancy_getopt.fancy_getopt (options,
          negative_opt, object, args)

     Wrapper function.  `options' is a list of ‘(long_option,
     short_option, help_string)’ 3-tuples as described in the
     constructor for *note FancyGetopt: 4620.  `negative_opt' should be
     a dictionary mapping option names to option names, both the key and
     value should be in the `options' list.  `object' is an object which
     will be used to store values (see the *note getopt(): 85. method of
     the *note FancyGetopt: 4620. class).  `args' is the argument list.
     Will use ‘sys.argv[1:]’ if you pass ‘None’ as `args'.

 -- Function: distutils.fancy_getopt.wrap_text (text, width)

     Wraps `text' to less than `width' wide.

 -- Class: distutils.fancy_getopt.FancyGetopt ([option_table=None])

     The option_table is a list of 3-tuples: ‘(long_option,
     short_option, help_string)’

     If an option takes an argument, its `long_option' should have ‘'='’
     appended; `short_option' should just be a single character, no
     ‘':'’ in any case.  `short_option' should be ‘None’ if a
     `long_option' doesn’t have a corresponding `short_option'.  All
     option tuples must have long options.

The *note FancyGetopt: 4620. class provides the following methods:

 -- Method: FancyGetopt.getopt ([args=None, object=None])

     Parse command-line options in args.  Store as attributes on
     `object'.

     If `args' is ‘None’ or not supplied, uses ‘sys.argv[1:]’.  If
     `object' is ‘None’ or not supplied, creates a new ‘OptionDummy’
     instance, stores option values there, and returns a tuple ‘(args,
     object)’.  If `object' is supplied, it is modified in place and
     *note getopt(): 85. just returns `args'; in both cases, the
     returned `args' is a modified copy of the passed-in `args' list,
     which is left untouched.

 -- Method: FancyGetopt.get_option_order ()

     Returns the list of ‘(option, value)’ tuples processed by the
     previous run of *note getopt(): 85. Raises *note RuntimeError: 3dc.
     if *note getopt(): 85. hasn’t been called yet.

 -- Method: FancyGetopt.generate_help ([header=None])

     Generate help text (a list of strings, one per suggested line of
     output) from the option table for this *note FancyGetopt: 4620.
     object.

     If supplied, prints the supplied `header' at the top of the help.


File: python.info,  Node: distutils filelist — The FileList class,  Next: distutils log — Simple PEP 282-style logging,  Prev: distutils fancy_getopt — Wrapper around the standard getopt module,  Up: API Reference

17.9.17 ‘distutils.filelist’ — The FileList class
-------------------------------------------------

This module provides the ‘FileList’ class, used for poking about the
filesystem and building lists of files.


File: python.info,  Node: distutils log — Simple PEP 282-style logging,  Next: distutils spawn — Spawn a sub-process,  Prev: distutils filelist — The FileList class,  Up: API Reference

17.9.18 ‘distutils.log’ — Simple `PEP 282'-style logging
--------------------------------------------------------


File: python.info,  Node: distutils spawn — Spawn a sub-process,  Next: distutils sysconfig — System configuration information,  Prev: distutils log — Simple PEP 282-style logging,  Up: API Reference

17.9.19 ‘distutils.spawn’ — Spawn a sub-process
-----------------------------------------------

This module provides the ‘spawn()’ function, a front-end to various
platform-specific functions for launching another program in a
sub-process.  Also provides ‘find_executable()’ to search the path for a
given executable name.


File: python.info,  Node: distutils sysconfig — System configuration information,  Next: distutils text_file — The TextFile class,  Prev: distutils spawn — Spawn a sub-process,  Up: API Reference

17.9.20 ‘distutils.sysconfig’ — System configuration information
----------------------------------------------------------------

The *note distutils.sysconfig: 61. module provides access to Python’s
low-level configuration information.  The specific configuration
variables available depend heavily on the platform and configuration.
The specific variables depend on the build process for the specific
version of Python being run; the variables are those found in the
‘Makefile’ and configuration header that are installed with Python on
Unix systems.  The configuration header is called ‘pyconfig.h’ for
Python versions starting with 2.2, and ‘config.h’ for earlier versions
of Python.

Some additional functions are provided which perform some useful
manipulations for other parts of the *note distutils: 38. package.

 -- Data: distutils.sysconfig.PREFIX

     The result of ‘os.path.normpath(sys.prefix)’.

 -- Data: distutils.sysconfig.EXEC_PREFIX

     The result of ‘os.path.normpath(sys.exec_prefix)’.

 -- Function: distutils.sysconfig.get_config_var (name)

     Return the value of a single variable.  This is equivalent to
     ‘get_config_vars().get(name)’.

 -- Function: distutils.sysconfig.get_config_vars (...)

     Return a set of variable definitions.  If there are no arguments,
     this returns a dictionary mapping names of configuration variables
     to values.  If arguments are provided, they should be strings, and
     the return value will be a sequence giving the associated values.
     If a given name does not have a corresponding value, ‘None’ will be
     included for that variable.

 -- Function: distutils.sysconfig.get_config_h_filename ()

     Return the full path name of the configuration header.  For Unix,
     this will be the header generated by the ‘configure’ script; for
     other platforms the header will have been supplied directly by the
     Python source distribution.  The file is a platform-specific text
     file.

 -- Function: distutils.sysconfig.get_makefile_filename ()

     Return the full path name of the ‘Makefile’ used to build Python.
     For Unix, this will be a file generated by the ‘configure’ script;
     the meaning for other platforms will vary.  The file is a
     platform-specific text file, if it exists.  This function is only
     useful on POSIX platforms.

 -- Function: distutils.sysconfig.get_python_inc ([plat_specific[,
          prefix]])

     Return the directory for either the general or platform-dependent C
     include files.  If `plat_specific' is true, the platform-dependent
     include directory is returned; if false or omitted, the
     platform-independent directory is returned.  If `prefix' is given,
     it is used as either the prefix instead of *note PREFIX: 4629, or
     as the exec-prefix instead of *note EXEC_PREFIX: 462a. if
     `plat_specific' is true.

 -- Function: distutils.sysconfig.get_python_lib ([plat_specific[,
          standard_lib[, prefix]]])

     Return the directory for either the general or platform-dependent
     library installation.  If `plat_specific' is true, the
     platform-dependent include directory is returned; if false or
     omitted, the platform-independent directory is returned.  If
     `prefix' is given, it is used as either the prefix instead of *note
     PREFIX: 4629, or as the exec-prefix instead of *note EXEC_PREFIX:
     462a. if `plat_specific' is true.  If `standard_lib' is true, the
     directory for the standard library is returned rather than the
     directory for the installation of third-party extensions.

The following function is only intended for use within the *note
distutils: 38. package.

 -- Function: distutils.sysconfig.customize_compiler (compiler)

     Do any platform-specific customization of a *note
     distutils.ccompiler.CCompiler: 45cf. instance.

     This function is only needed on Unix at this time, but should be
     called consistently to support forward-compatibility.  It inserts
     the information that varies across Unix flavors and is stored in
     Python’s ‘Makefile’.  This information includes the selected
     compiler, compiler and linker options, and the extension used by
     the linker for shared objects.

This function is even more special-purpose, and should only be used from
Python’s own build procedures.

 -- Function: distutils.sysconfig.set_python_build ()

     Inform the *note distutils.sysconfig: 61. module that it is being
     used as part of the build process for Python.  This changes a lot
     of relative locations for files, allowing them to be located in the
     build area rather than in an installed Python.


File: python.info,  Node: distutils text_file — The TextFile class,  Next: distutils version — Version number classes,  Prev: distutils sysconfig — System configuration information,  Up: API Reference

17.9.21 ‘distutils.text_file’ — The TextFile class
--------------------------------------------------

This module provides the *note TextFile: 4634. class, which gives an
interface to text files that (optionally) takes care of stripping
comments, ignoring blank lines, and joining lines with backslashes.

 -- Class: distutils.text_file.TextFile ([filename=None, file=None,
          **options])

     This class provides a file-like object that takes care of all the
     things you commonly want to do when processing a text file that has
     some line-by-line syntax: strip comments (as long as ‘#’ is your
     comment character), skip blank lines, join adjacent lines by
     escaping the newline (ie.  backslash at end of line), strip leading
     and/or trailing whitespace.  All of these are optional and
     independently controllable.

     The class provides a *note warn(): 4635. method so you can generate
     warning messages that report physical line number, even if the
     logical line in question spans multiple physical lines.  Also
     provides *note unreadline(): 4636. for implementing line-at-a-time
     lookahead.

     *note TextFile: 4634. instances are create with either `filename',
     `file', or both.  *note RuntimeError: 3dc. is raised if both are
     ‘None’.  `filename' should be a string, and `file' a file object
     (or something that provides *note readline(): de. and *note
     close(): 4637. methods).  It is recommended that you supply at
     least `filename', so that *note TextFile: 4634. can include it in
     warning messages.  If `file' is not supplied, *note TextFile: 4634.
     creates its own using the *note open(): 16f. built-in function.

     The options are all boolean, and affect the values returned by
     *note readline(): de.

     option name            description                          default
                                                                 
     --------------------------------------------------------------------------
                                                                 
     `strip_comments'       strip from ‘'#'’ to end-of-line,     true
                            as well as any whitespace leading    
                            up to the ‘'#'’—unless it is
                            escaped by a backslash
                            
                                                                 
     `lstrip_ws'            strip leading whitespace from each   false
                            line before returning it             
                            
                                                                 
     `rstrip_ws'            strip trailing whitespace            true
                            (including line terminator!)  from   
                            each line before returning it.
                            
                                                                 
     `skip_blanks'          skip lines that are empty *after*    true
                            stripping comments and whitespace.   
                            (If both lstrip_ws and rstrip_ws
                            are false, then some lines may
                            consist of solely whitespace:
                            these will *not* be skipped, even
                            if `skip_blanks' is true.)
                            
                                                                 
     `join_lines'           if a backslash is the last           false
                            non-newline character on a line      
                            after stripping comments and
                            whitespace, join the following
                            line to it to form one logical
                            line; if N consecutive lines end
                            with a backslash, then N+1
                            physical lines will be joined to
                            form one logical line.
                            
                                                                 
     `collapse_join'        strip leading whitespace from        false
                            lines that are joined to their       
                            predecessor; only matters if
                            ‘(join_lines and not lstrip_ws)’
                            

     Note that since `rstrip_ws' can strip the trailing newline, the
     semantics of *note readline(): de. must differ from those of the
     built-in file object’s *note readline(): de. method!  In
     particular, *note readline(): de. returns ‘None’ for end-of-file:
     an empty string might just be a blank line (or an all-whitespace
     line), if `rstrip_ws' is true but `skip_blanks' is not.

      -- Method: open (filename)

          Open a new file `filename'.  This overrides any `file' or
          `filename' constructor arguments.

      -- Method: close ()

          Close the current file and forget everything we know about it
          (including the filename and the current line number).

      -- Method: warn (msg[, line=None])

          Print (to stderr) a warning message tied to the current
          logical line in the current file.  If the current logical line
          in the file spans multiple physical lines, the warning refers
          to the whole range, such as ‘"lines 3-5"’.  If `line' is
          supplied, it overrides the current line number; it may be a
          list or tuple to indicate a range of physical lines, or an
          integer for a single physical line.

      -- Method: readline ()

          Read and return a single logical line from the current file
          (or from an internal buffer if lines have previously been
          “unread” with *note unreadline(): 4636.).  If the `join_lines'
          option is true, this may involve reading multiple physical
          lines concatenated into a single string.  Updates the current
          line number, so calling *note warn(): 4635. after *note
          readline(): de. emits a warning about the physical line(s)
          just read.  Returns ‘None’ on end-of-file, since the empty
          string can occur if `rstrip_ws' is true but `strip_blanks' is
          not.

      -- Method: readlines ()

          Read and return the list of all logical lines remaining in the
          current file.  This updates the current line number to the
          last line of the file.

      -- Method: unreadline (line)

          Push `line' (a string) onto an internal buffer that will be
          checked by future *note readline(): de. calls.  Handy for
          implementing a parser with line-at-a-time lookahead.  Note
          that lines that are “unread” with *note unreadline(): 4636.
          are not subsequently re-cleansed (whitespace stripped, or
          whatever) when read with *note readline(): de.  If multiple
          calls are made to *note unreadline(): 4636. before a call to
          *note readline(): de, the lines will be returned most in most
          recent first order.


File: python.info,  Node: distutils version — Version number classes,  Next: distutils cmd — Abstract base class for Distutils commands,  Prev: distutils text_file — The TextFile class,  Up: API Reference

17.9.22 ‘distutils.version’ — Version number classes
----------------------------------------------------


File: python.info,  Node: distutils cmd — Abstract base class for Distutils commands,  Next: Creating a new Distutils command,  Prev: distutils version — Version number classes,  Up: API Reference

17.9.23 ‘distutils.cmd’ — Abstract base class for Distutils commands
--------------------------------------------------------------------

This module supplies the abstract base class *note Command: 45ba.

 -- Class: distutils.cmd.Command (dist)

     Abstract base class for defining command classes, the “worker bees”
     of the Distutils.  A useful analogy for command classes is to think
     of them as subroutines with local variables called `options'.  The
     options are declared in *note initialize_options(): 463d. and
     defined (given their final values) in *note finalize_options():
     463e, both of which must be defined by every command class.  The
     distinction between the two is necessary because option values
     might come from the outside world (command line, config file, …),
     and any options dependent on other options must be computed after
     these outside influences have been processed — hence *note
     finalize_options(): 463e.  The body of the subroutine, where it
     does all its work based on the values of its options, is the *note
     run(): 463f. method, which must also be implemented by every
     command class.

     The class constructor takes a single argument `dist', a *note
     Distribution: 45cb. instance.


File: python.info,  Node: Creating a new Distutils command,  Next: distutils command — Individual Distutils commands,  Prev: distutils cmd — Abstract base class for Distutils commands,  Up: API Reference

17.9.24 Creating a new Distutils command
----------------------------------------

This section outlines the steps to create a new Distutils command.

A new command lives in a module in the *note distutils.command: 3d.
package.  There is a sample template in that directory called
‘command_template’.  Copy this file to a new module with the same name
as the new command you’re implementing.  This module should implement a
class with the same name as the module (and the command).  So, for
instance, to create the command ‘peel_banana’ (so that users can run
‘setup.py peel_banana’), you’d copy ‘command_template’ to
‘distutils/command/peel_banana.py’, then edit it so that it’s
implementing the class ‘peel_banana’, a subclass of *note
distutils.cmd.Command: 45ba.

Subclasses of *note Command: 45ba. must define the following methods.

 -- Method: Command.initialize_options ()

     Set default values for all the options that this command supports.
     Note that these defaults may be overridden by other commands, by
     the setup script, by config files, or by the command-line.  Thus,
     this is not the place to code dependencies between options;
     generally, *note initialize_options(): 463d. implementations are
     just a bunch of ‘self.foo = None’ assignments.

 -- Method: Command.finalize_options ()

     Set final values for all the options that this command supports.
     This is always called as late as possible, ie.  after any option
     assignments from the command-line or from other commands have been
     done.  Thus, this is the place to code option dependencies: if
     `foo' depends on `bar', then it is safe to set `foo' from `bar' as
     long as `foo' still has the same value it was assigned in *note
     initialize_options(): 463d.

 -- Method: Command.run ()

     A command’s raison d’etre: carry out the action it exists to
     perform, controlled by the options initialized in *note
     initialize_options(): 463d, customized by other commands, the setup
     script, the command-line, and config files, and finalized in *note
     finalize_options(): 463e.  All terminal output and filesystem
     interaction should be done by *note run(): 463f.

 -- Attribute: Command.sub_commands

     `sub_commands' formalizes the notion of a “family” of commands,
     e.g.  ‘install’ as the parent with sub-commands ‘install_lib’,
     ‘install_headers’, etc.  The parent of a family of commands defines
     `sub_commands' as a class attribute; it’s a list of 2-tuples
     ‘(command_name, predicate)’, with `command_name' a string and
     `predicate' a function, a string or ‘None’.  `predicate' is a
     method of the parent command that determines whether the
     corresponding command is applicable in the current situation.
     (E.g.  ‘install_headers’ is only applicable if we have any C header
     files to install.)  If `predicate' is ‘None’, that command is
     always applicable.

     `sub_commands' is usually defined at the `end' of a class, because
     predicates can be methods of the class, so they must already have
     been defined.  The canonical example is the ‘install’ command.


File: python.info,  Node: distutils command — Individual Distutils commands,  Next: distutils command bdist — Build a binary installer,  Prev: Creating a new Distutils command,  Up: API Reference

17.9.25 ‘distutils.command’ — Individual Distutils commands
-----------------------------------------------------------


File: python.info,  Node: distutils command bdist — Build a binary installer,  Next: distutils command bdist_packager — Abstract base class for packagers,  Prev: distutils command — Individual Distutils commands,  Up: API Reference

17.9.26 ‘distutils.command.bdist’ — Build a binary installer
------------------------------------------------------------


File: python.info,  Node: distutils command bdist_packager — Abstract base class for packagers,  Next: distutils command bdist_dumb — Build a “dumb” installer,  Prev: distutils command bdist — Build a binary installer,  Up: API Reference

17.9.27 ‘distutils.command.bdist_packager’ — Abstract base class for packagers
------------------------------------------------------------------------------


File: python.info,  Node: distutils command bdist_dumb — Build a “dumb” installer,  Next: distutils command bdist_msi — Build a Microsoft Installer binary package,  Prev: distutils command bdist_packager — Abstract base class for packagers,  Up: API Reference

17.9.28 ‘distutils.command.bdist_dumb’ — Build a “dumb” installer
-----------------------------------------------------------------


File: python.info,  Node: distutils command bdist_msi — Build a Microsoft Installer binary package,  Next: distutils command bdist_rpm — Build a binary distribution as a Redhat RPM and SRPM,  Prev: distutils command bdist_dumb — Build a “dumb” installer,  Up: API Reference

17.9.29 ‘distutils.command.bdist_msi’ — Build a Microsoft Installer binary package
----------------------------------------------------------------------------------

 -- Class: distutils.command.bdist_msi.bdist_msi

Deprecated since version 3.9: Use bdist_wheel (wheel packages) instead.

Builds a Windows Installer(1) (.msi) binary package.

In most cases, the ‘bdist_msi’ installer is a better choice than the
‘bdist_wininst’ installer, because it provides better support for Win64
platforms, allows administrators to perform non-interactive
installations, and allows installation through group policies.

   ---------- Footnotes ----------

   (1) https://msdn.microsoft.com/en-us/library/cc185688(VS.85).aspx


File: python.info,  Node: distutils command bdist_rpm — Build a binary distribution as a Redhat RPM and SRPM,  Next: distutils command bdist_wininst — Build a Windows installer,  Prev: distutils command bdist_msi — Build a Microsoft Installer binary package,  Up: API Reference

17.9.30 ‘distutils.command.bdist_rpm’ — Build a binary distribution as a Redhat RPM and SRPM
--------------------------------------------------------------------------------------------


File: python.info,  Node: distutils command bdist_wininst — Build a Windows installer,  Next: distutils command sdist — Build a source distribution,  Prev: distutils command bdist_rpm — Build a binary distribution as a Redhat RPM and SRPM,  Up: API Reference

17.9.31 ‘distutils.command.bdist_wininst’ — Build a Windows installer
---------------------------------------------------------------------

Deprecated since version 3.8: Use bdist_wheel (wheel packages) instead.


File: python.info,  Node: distutils command sdist — Build a source distribution,  Next: distutils command build — Build all files of a package,  Prev: distutils command bdist_wininst — Build a Windows installer,  Up: API Reference

17.9.32 ‘distutils.command.sdist’ — Build a source distribution
---------------------------------------------------------------


File: python.info,  Node: distutils command build — Build all files of a package,  Next: distutils command build_clib — Build any C libraries in a package,  Prev: distutils command sdist — Build a source distribution,  Up: API Reference

17.9.33 ‘distutils.command.build’ — Build all files of a package
----------------------------------------------------------------


File: python.info,  Node: distutils command build_clib — Build any C libraries in a package,  Next: distutils command build_ext — Build any extensions in a package,  Prev: distutils command build — Build all files of a package,  Up: API Reference

17.9.34 ‘distutils.command.build_clib’ — Build any C libraries in a package
---------------------------------------------------------------------------


File: python.info,  Node: distutils command build_ext — Build any extensions in a package,  Next: distutils command build_py — Build the py/ pyc files of a package,  Prev: distutils command build_clib — Build any C libraries in a package,  Up: API Reference

17.9.35 ‘distutils.command.build_ext’ — Build any extensions in a package
-------------------------------------------------------------------------


File: python.info,  Node: distutils command build_py — Build the py/ pyc files of a package,  Next: distutils command build_scripts — Build the scripts of a package,  Prev: distutils command build_ext — Build any extensions in a package,  Up: API Reference

17.9.36 ‘distutils.command.build_py’ — Build the .py/.pyc files of a package
----------------------------------------------------------------------------

 -- Class: distutils.command.build_py.build_py

 -- Class: distutils.command.build_py.build_py_2to3

     Alternative implementation of build_py which also runs the 2to3
     conversion library on each .py file that is going to be installed.
     To use this in a setup.py file for a distribution that is designed
     to run with both Python 2.x and 3.x, add:

          try:
              from distutils.command.build_py import build_py_2to3 as build_py
          except ImportError:
              from distutils.command.build_py import build_py

     to your setup.py, and later:

          cmdclass = {'build_py': build_py}

     to the invocation of setup().


File: python.info,  Node: distutils command build_scripts — Build the scripts of a package,  Next: distutils command clean — Clean a package build area,  Prev: distutils command build_py — Build the py/ pyc files of a package,  Up: API Reference

17.9.37 ‘distutils.command.build_scripts’ — Build the scripts of a package
--------------------------------------------------------------------------


File: python.info,  Node: distutils command clean — Clean a package build area,  Next: distutils command config — Perform package configuration,  Prev: distutils command build_scripts — Build the scripts of a package,  Up: API Reference

17.9.38 ‘distutils.command.clean’ — Clean a package build area
--------------------------------------------------------------

This command removes the temporary files created by ‘build’ and its
subcommands, like intermediary compiled object files.  With the ‘--all’
option, the complete build directory will be removed.

Extension modules built *note in place: 4593. will not be cleaned, as
they are not in the build directory.


File: python.info,  Node: distutils command config — Perform package configuration,  Next: distutils command install — Install a package,  Prev: distutils command clean — Clean a package build area,  Up: API Reference

17.9.39 ‘distutils.command.config’ — Perform package configuration
------------------------------------------------------------------


File: python.info,  Node: distutils command install — Install a package,  Next: distutils command install_data — Install data files from a package,  Prev: distutils command config — Perform package configuration,  Up: API Reference

17.9.40 ‘distutils.command.install’ — Install a package
-------------------------------------------------------


File: python.info,  Node: distutils command install_data — Install data files from a package,  Next: distutils command install_headers — Install C/C++ header files from a package,  Prev: distutils command install — Install a package,  Up: API Reference

17.9.41 ‘distutils.command.install_data’ — Install data files from a package
----------------------------------------------------------------------------


File: python.info,  Node: distutils command install_headers — Install C/C++ header files from a package,  Next: distutils command install_lib — Install library files from a package,  Prev: distutils command install_data — Install data files from a package,  Up: API Reference

17.9.42 ‘distutils.command.install_headers’ — Install C/C++ header files from a package
---------------------------------------------------------------------------------------


File: python.info,  Node: distutils command install_lib — Install library files from a package,  Next: distutils command install_scripts — Install script files from a package,  Prev: distutils command install_headers — Install C/C++ header files from a package,  Up: API Reference

17.9.43 ‘distutils.command.install_lib’ — Install library files from a package
------------------------------------------------------------------------------


File: python.info,  Node: distutils command install_scripts — Install script files from a package,  Next: distutils command register — Register a module with the Python Package Index,  Prev: distutils command install_lib — Install library files from a package,  Up: API Reference

17.9.44 ‘distutils.command.install_scripts’ — Install script files from a package
---------------------------------------------------------------------------------


File: python.info,  Node: distutils command register — Register a module with the Python Package Index,  Next: distutils command check — Check the meta-data of a package,  Prev: distutils command install_scripts — Install script files from a package,  Up: API Reference

17.9.45 ‘distutils.command.register’ — Register a module with the Python Package Index
--------------------------------------------------------------------------------------

The ‘register’ command registers the package with the Python Package
Index.  This is described in more detail in PEP 301(1).

   ---------- Footnotes ----------

   (1) https://www.python.org/dev/peps/pep-0301


File: python.info,  Node: distutils command check — Check the meta-data of a package,  Prev: distutils command register — Register a module with the Python Package Index,  Up: API Reference

17.9.46 ‘distutils.command.check’ — Check the meta-data of a package
--------------------------------------------------------------------

The ‘check’ command performs some tests on the meta-data of a package.
For example, it verifies that all required meta-data are provided as the
arguments passed to the ‘setup()’ function.


File: python.info,  Node: Installing Python Modules Legacy version,  Next: Python Module Index,  Prev: Distributing Python Modules Legacy version,  Up: Top

18 Installing Python Modules (Legacy version)
*********************************************


Author: Greg Ward

See also
........

*note Installing Python Modules: 8e2.

     The up to date module installation documentation.  For regular
     Python usage, you almost certainly want that document rather than
     this one.

     Note: This document is being retained solely until the ‘setuptools’
     documentation at
     ‘https://setuptools.readthedocs.io/en/latest/setuptools.html’
     independently covers all of the relevant information currently
     included here.

     Note: This guide only covers the basic tools for building and
     distributing extensions that are provided as part of this version
     of Python.  Third party tools offer easier to use and more secure
     alternatives.  Refer to the quick recommendations section(1) in the
     Python Packaging User Guide for more information.

* Menu:

* Introduction: Introduction<17>.
* Standard Build and Install::
* Alternate Installation::
* Custom Installation::
* Distutils Configuration Files::
* Building Extensions; Tips and Tricks: Building Extensions Tips and Tricks.

   ---------- Footnotes ----------

   (1) https://packaging.python.org/guides/tool-recommendations/


File: python.info,  Node: Introduction<17>,  Next: Standard Build and Install,  Up: Installing Python Modules Legacy version

18.1 Introduction
=================

In Python 2.0, the ‘distutils’ API was first added to the standard
library.  This provided Linux distro maintainers with a standard way of
converting Python projects into Linux distro packages, and system
administrators with a standard way of installing them directly onto
target systems.

In the many years since Python 2.0 was released, tightly coupling the
build system and package installer to the language runtime release cycle
has turned out to be problematic, and it is now recommended that
projects use the ‘pip’ package installer and the ‘setuptools’ build
system, rather than using ‘distutils’ directly.

See *note Installing Python Modules: 8e2. and *note Distributing Python
Modules: 8e3. for more details.

This legacy documentation is being retained only until we’re confident
that the ‘setuptools’ documentation covers everything needed.

* Menu:

* Distutils based source distributions::


File: python.info,  Node: Distutils based source distributions,  Up: Introduction<17>

18.1.1 Distutils based source distributions
-------------------------------------------

If you download a module source distribution, you can tell pretty
quickly if it was packaged and distributed in the standard way, i.e.
using the Distutils.  First, the distribution’s name and version number
will be featured prominently in the name of the downloaded archive, e.g.
‘foo-1.0.tar.gz’ or ‘widget-0.9.7.zip’.  Next, the archive will unpack
into a similarly-named directory: ‘foo-1.0’ or ‘widget-0.9.7’.
Additionally, the distribution will contain a setup script ‘setup.py’,
and a file named ‘README.txt’ or possibly just ‘README’, which should
explain that building and installing the module distribution is a simple
matter of running one command from a terminal:

     python setup.py install

For Windows, this command should be run from a command prompt window
(Start ‣ Accessories):

     setup.py install

If all these things are true, then you already know how to build and
install the modules you’ve just downloaded: Run the command above.
Unless you need to install things in a non-standard way or customize the
build process, you don’t really need this manual.  Or rather, the above
command is everything you need to get out of this manual.


File: python.info,  Node: Standard Build and Install,  Next: Alternate Installation,  Prev: Introduction<17>,  Up: Installing Python Modules Legacy version

18.2 Standard Build and Install
===============================

As described in section *note Distutils based source distributions:
4660, building and installing a module distribution using the Distutils
is usually one simple command to run from a terminal:

     python setup.py install

* Menu:

* Platform variations::
* Splitting the job up::
* How building works::
* How installation works::


File: python.info,  Node: Platform variations,  Next: Splitting the job up,  Up: Standard Build and Install

18.2.1 Platform variations
--------------------------

You should always run the setup command from the distribution root
directory, i.e.  the top-level subdirectory that the module source
distribution unpacks into.  For example, if you’ve just downloaded a
module source distribution ‘foo-1.0.tar.gz’ onto a Unix system, the
normal thing to do is:

     gunzip -c foo-1.0.tar.gz | tar xf -    # unpacks into directory foo-1.0
     cd foo-1.0
     python setup.py install

On Windows, you’d probably download ‘foo-1.0.zip’.  If you downloaded
the archive file to ‘C:\Temp’, then it would unpack into
‘C:\Temp\foo-1.0’; you can use either an archive manipulator with a
graphical user interface (such as WinZip) or a command-line tool (such
as ‘unzip’ or ‘pkunzip’) to unpack the archive.  Then, open a command
prompt window and run:

     cd c:\Temp\foo-1.0
     python setup.py install


File: python.info,  Node: Splitting the job up,  Next: How building works,  Prev: Platform variations,  Up: Standard Build and Install

18.2.2 Splitting the job up
---------------------------

Running ‘setup.py install’ builds and installs all modules in one run.
If you prefer to work incrementally—especially useful if you want to
customize the build process, or if things are going wrong—you can use
the setup script to do one thing at a time.  This is particularly
helpful when the build and install will be done by different users—for
example, you might want to build a module distribution and hand it off
to a system administrator for installation (or do it yourself, with
super-user privileges).

For example, you can build everything in one step, and then install
everything in a second step, by invoking the setup script twice:

     python setup.py build
     python setup.py install

If you do this, you will notice that running the ‘install’ command first
runs the ‘build’ command, which—in this case—quickly notices that it has
nothing to do, since everything in the ‘build’ directory is up-to-date.

You may not need this ability to break things down often if all you do
is install modules downloaded off the ‘net, but it’s very handy for more
advanced tasks.  If you get into distributing your own Python modules
and extensions, you’ll run lots of individual Distutils commands on
their own.


File: python.info,  Node: How building works,  Next: How installation works,  Prev: Splitting the job up,  Up: Standard Build and Install

18.2.3 How building works
-------------------------

As implied above, the ‘build’ command is responsible for putting the
files to install into a `build directory'.  By default, this is ‘build’
under the distribution root; if you’re excessively concerned with speed,
or want to keep the source tree pristine, you can change the build
directory with the ‘--build-base’ option.  For example:

     python setup.py build --build-base=/path/to/pybuild/foo-1.0

(Or you could do this permanently with a directive in your system or
personal Distutils configuration file; see section *note Distutils
Configuration Files: 4669.)  Normally, this isn’t necessary.

The default layout for the build tree is as follows:

     --- build/ --- lib/
     or
     --- build/ --- lib.<plat>/
                    temp.<plat>/

where ‘<plat>’ expands to a brief description of the current OS/hardware
platform and Python version.  The first form, with just a ‘lib’
directory, is used for “pure module distributions”—that is, module
distributions that include only pure Python modules.  If a module
distribution contains any extensions (modules written in C/C++), then
the second form, with two ‘<plat>’ directories, is used.  In that case,
the ‘temp.`plat'’ directory holds temporary files generated by the
compile/link process that don’t actually get installed.  In either case,
the ‘lib’ (or ‘lib.`plat'’) directory contains all Python modules (pure
Python and extensions) that will be installed.

In the future, more directories will be added to handle Python scripts,
documentation, binary executables, and whatever else is needed to handle
the job of installing Python modules and applications.


File: python.info,  Node: How installation works,  Prev: How building works,  Up: Standard Build and Install

18.2.4 How installation works
-----------------------------

After the ‘build’ command runs (whether you run it explicitly, or the
‘install’ command does it for you), the work of the ‘install’ command is
relatively simple: all it has to do is copy everything under ‘build/lib’
(or ‘build/lib.`plat'’) to your chosen installation directory.

If you don’t choose an installation directory—i.e., if you just run
‘setup.py install’—then the ‘install’ command installs to the standard
location for third-party Python modules.  This location varies by
platform and by how you built/installed Python itself.  On Unix (and
macOS, which is also Unix-based), it also depends on whether the module
distribution being installed is pure Python or contains extensions
(“non-pure”):

Platform              Standard installation location                            Default value                                          Notes
                                                                                                                                       
---------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                                       
Unix (pure)           ‘`prefix'/lib/python`X.Y'/site-packages’                  ‘/usr/local/lib/python`X.Y'/site-packages’             (1)
                                                                                                                                       
                                                                                                                                       
Unix (non-pure)       ‘`exec-prefix'/lib/python`X.Y'/site-packages’             ‘/usr/local/lib/python`X.Y'/site-packages’             (1)
                                                                                                                                       
                                                                                                                                       
Windows               ‘`prefix'\Lib\site-packages’                              ‘C:\Python`XY'\Lib\site-packages’                      (2)
                                                                                                                                       

Notes:

  1. Most Linux distributions include Python as a standard part of the
     system, so ‘`prefix'’ and ‘`exec-prefix'’ are usually both ‘/usr’
     on Linux.  If you build Python yourself on Linux (or any Unix-like
     system), the default ‘`prefix'’ and ‘`exec-prefix'’ are
     ‘/usr/local’.

  2. The default installation directory on Windows was ‘C:\Program
     Files\Python’ under Python 1.6a1, 1.5.2, and earlier.

‘`prefix'’ and ‘`exec-prefix'’ stand for the directories that Python is
installed to, and where it finds its libraries at run-time.  They are
always the same under Windows, and very often the same under Unix and
macOS. You can find out what your Python installation uses for
‘`prefix'’ and ‘`exec-prefix'’ by running Python in interactive mode and
typing a few simple commands.  Under Unix, just type ‘python’ at the
shell prompt.  Under Windows, choose Start ‣ Programs ‣ Python X.Y ‣
Python (command line).  Once the interpreter is started, you type Python
code at the prompt.  For example, on my Linux system, I type the three
Python statements shown below, and get the output as shown, to find out
my ‘`prefix'’ and ‘`exec-prefix'’:

     Python 2.4 (#26, Aug  7 2004, 17:19:02)
     Type "help", "copyright", "credits" or "license" for more information.
     >>> import sys
     >>> sys.prefix
     '/usr'
     >>> sys.exec_prefix
     '/usr'

A few other placeholders are used in this document: ‘`X.Y'’ stands for
the version of Python, for example ‘3.2’; ‘`abiflags'’ will be replaced
by the value of *note sys.abiflags: 38d. or the empty string for
platforms which don’t define ABI flags; ‘`distname'’ will be replaced by
the name of the module distribution being installed.  Dots and
capitalization are important in the paths; for example, a value that
uses ‘python3.2’ on UNIX will typically use ‘Python32’ on Windows.

If you don’t want to install modules to the standard location, or if you
don’t have permission to write there, then you need to read about
alternate installations in section *note Alternate Installation: 466c.
If you want to customize your installation directories more heavily, see
section *note Custom Installation: 466d. on custom installations.


File: python.info,  Node: Alternate Installation,  Next: Custom Installation,  Prev: Standard Build and Install,  Up: Installing Python Modules Legacy version

18.3 Alternate Installation
===========================

Often, it is necessary or desirable to install modules to a location
other than the standard location for third-party Python modules.  For
example, on a Unix system you might not have permission to write to the
standard third-party module directory.  Or you might wish to try out a
module before making it a standard part of your local Python
installation.  This is especially true when upgrading a distribution
already present: you want to make sure your existing base of scripts
still works with the new version before actually upgrading.

The Distutils ‘install’ command is designed to make installing module
distributions to an alternate location simple and painless.  The basic
idea is that you supply a base directory for the installation, and the
‘install’ command picks a set of directories (called an `installation
scheme') under this base directory in which to install files.  The
details differ across platforms, so read whichever of the following
sections applies to you.

Note that the various alternate installation schemes are mutually
exclusive: you can pass ‘--user’, or ‘--home’, or ‘--prefix’ and
‘--exec-prefix’, or ‘--install-base’ and ‘--install-platbase’, but you
can’t mix from these groups.

* Menu:

* Alternate installation; the user scheme: Alternate installation the user scheme.
* Alternate installation; the home scheme: Alternate installation the home scheme.
* Alternate installation; Unix (the prefix scheme): Alternate installation Unix the prefix scheme.
* Alternate installation; Windows (the prefix scheme): Alternate installation Windows the prefix scheme.


File: python.info,  Node: Alternate installation the user scheme,  Next: Alternate installation the home scheme,  Up: Alternate Installation

18.3.1 Alternate installation: the user scheme
----------------------------------------------

This scheme is designed to be the most convenient solution for users
that don’t have write permission to the global site-packages directory
or don’t want to install into it.  It is enabled with a simple option:

     python setup.py install --user

Files will be installed into subdirectories of *note site.USER_BASE:
1489. (written as ‘`userbase'’ hereafter).  This scheme installs pure
Python modules and extension modules in the same location (also known as
*note site.USER_SITE: 147a.).  Here are the values for UNIX, including
macOS:

Type of file        Installation directory
                    
------------------------------------------------------------------------------------
                    
modules             ‘`userbase'/lib/python`X.Y'/site-packages’
                    
                    
scripts             ‘`userbase'/bin’
                    
                    
data                ‘`userbase'’
                    
                    
C headers           ‘`userbase'/include/python`X.Y'`abiflags'/`distname'’
                    

And here are the values used on Windows:

Type of file        Installation directory
                    
------------------------------------------------------------------------------------
                    
modules             ‘`userbase'\Python`XY'\site-packages’
                    
                    
scripts             ‘`userbase'\Python`XY'\Scripts’
                    
                    
data                ‘`userbase'’
                    
                    
C headers           ‘`userbase'\Python`XY'\Include{distname}’
                    

The advantage of using this scheme compared to the other ones described
below is that the user site-packages directory is under normal
conditions always included in *note sys.path: 260. (see *note site: eb.
for more information), which means that there is no additional step to
perform after running the ‘setup.py’ script to finalize the
installation.

The ‘build_ext’ command also has a ‘--user’ option to add
‘`userbase'/include’ to the compiler search path for header files and
‘`userbase'/lib’ to the compiler search path for libraries as well as to
the runtime search path for shared C libraries (rpath).


File: python.info,  Node: Alternate installation the home scheme,  Next: Alternate installation Unix the prefix scheme,  Prev: Alternate installation the user scheme,  Up: Alternate Installation

18.3.2 Alternate installation: the home scheme
----------------------------------------------

The idea behind the “home scheme” is that you build and maintain a
personal stash of Python modules.  This scheme’s name is derived from
the idea of a “home” directory on Unix, since it’s not unusual for a
Unix user to make their home directory have a layout similar to ‘/usr/’
or ‘/usr/local/’.  This scheme can be used by anyone, regardless of the
operating system they are installing for.

Installing a new module distribution is as simple as

     python setup.py install --home=<dir>

where you can supply any directory you like for the ‘--home’ option.  On
Unix, lazy typists can just type a tilde (‘~’); the ‘install’ command
will expand this to your home directory:

     python setup.py install --home=~

To make Python find the distributions installed with this scheme, you
may have to *note modify Python’s search path: 4672. or edit
‘sitecustomize’ (see *note site: eb.) to call *note site.addsitedir():
388c. or edit *note sys.path: 260.

The ‘--home’ option defines the installation base directory.  Files are
installed to the following directories under the installation base as
follows:

Type of file        Installation directory
                    
------------------------------------------------------------------------------------
                    
modules             ‘`home'/lib/python’
                    
                    
scripts             ‘`home'/bin’
                    
                    
data                ‘`home'’
                    
                    
C headers           ‘`home'/include/python/`distname'’
                    

(Mentally replace slashes with backslashes if you’re on Windows.)


File: python.info,  Node: Alternate installation Unix the prefix scheme,  Next: Alternate installation Windows the prefix scheme,  Prev: Alternate installation the home scheme,  Up: Alternate Installation

18.3.3 Alternate installation: Unix (the prefix scheme)
-------------------------------------------------------

The “prefix scheme” is useful when you wish to use one Python
installation to perform the build/install (i.e., to run the setup
script), but install modules into the third-party module directory of a
different Python installation (or something that looks like a different
Python installation).  If this sounds a trifle unusual, it is—that’s why
the user and home schemes come before.  However, there are at least two
known cases where the prefix scheme will be useful.

First, consider that many Linux distributions put Python in ‘/usr’,
rather than the more traditional ‘/usr/local’.  This is entirely
appropriate, since in those cases Python is part of “the system” rather
than a local add-on.  However, if you are installing Python modules from
source, you probably want them to go in ‘/usr/local/lib/python2.`X'’
rather than ‘/usr/lib/python2.`X'’.  This can be done with

     /usr/bin/python setup.py install --prefix=/usr/local

Another possibility is a network filesystem where the name used to write
to a remote directory is different from the name used to read it: for
example, the Python interpreter accessed as ‘/usr/local/bin/python’
might search for modules in ‘/usr/local/lib/python2.`X'’, but those
modules would have to be installed to, say,
‘/mnt/`@server'/export/lib/python2.`X'’.  This could be done with

     /usr/local/bin/python setup.py install --prefix=/mnt/@server/export

In either case, the ‘--prefix’ option defines the installation base, and
the ‘--exec-prefix’ option defines the platform-specific installation
base, which is used for platform-specific files.  (Currently, this just
means non-pure module distributions, but could be expanded to C
libraries, binary executables, etc.)  If ‘--exec-prefix’ is not
supplied, it defaults to ‘--prefix’.  Files are installed as follows:

Type of file          Installation directory
                      
-------------------------------------------------------------------------------------
                      
Python modules        ‘`prefix'/lib/python`X.Y'/site-packages’
                      
                      
extension modules     ‘`exec-prefix'/lib/python`X.Y'/site-packages’
                      
                      
scripts               ‘`prefix'/bin’
                      
                      
data                  ‘`prefix'’
                      
                      
C headers             ‘`prefix'/include/python`X.Y'`abiflags'/`distname'’
                      

There is no requirement that ‘--prefix’ or ‘--exec-prefix’ actually
point to an alternate Python installation; if the directories listed
above do not already exist, they are created at installation time.

Incidentally, the real reason the prefix scheme is important is simply
that a standard Unix installation uses the prefix scheme, but with
‘--prefix’ and ‘--exec-prefix’ supplied by Python itself as ‘sys.prefix’
and ‘sys.exec_prefix’.  Thus, you might think you’ll never use the
prefix scheme, but every time you run ‘python setup.py install’ without
any other options, you’re using it.

Note that installing extensions to an alternate Python installation has
no effect on how those extensions are built: in particular, the Python
header files (‘Python.h’ and friends) installed with the Python
interpreter used to run the setup script will be used in compiling
extensions.  It is your responsibility to ensure that the interpreter
used to run extensions installed in this way is compatible with the
interpreter used to build them.  The best way to do this is to ensure
that the two interpreters are the same version of Python (possibly
different builds, or possibly copies of the same build).  (Of course, if
your ‘--prefix’ and ‘--exec-prefix’ don’t even point to an alternate
Python installation, this is immaterial.)


File: python.info,  Node: Alternate installation Windows the prefix scheme,  Prev: Alternate installation Unix the prefix scheme,  Up: Alternate Installation

18.3.4 Alternate installation: Windows (the prefix scheme)
----------------------------------------------------------

Windows has no concept of a user’s home directory, and since the
standard Python installation under Windows is simpler than under Unix,
the ‘--prefix’ option has traditionally been used to install additional
packages in separate locations on Windows.

     python setup.py install --prefix="\Temp\Python"

to install modules to the ‘\Temp\Python’ directory on the current drive.

The installation base is defined by the ‘--prefix’ option; the
‘--exec-prefix’ option is not supported under Windows, which means that
pure Python modules and extension modules are installed into the same
location.  Files are installed as follows:

Type of file        Installation directory
                    
-----------------------------------------------------------------------------------
                    
modules             ‘`prefix'\Lib\site-packages’
                    
                    
scripts             ‘`prefix'\Scripts’
                    
                    
data                ‘`prefix'’
                    
                    
C headers           ‘`prefix'\Include{distname}’
                    


File: python.info,  Node: Custom Installation,  Next: Distutils Configuration Files,  Prev: Alternate Installation,  Up: Installing Python Modules Legacy version

18.4 Custom Installation
========================

Sometimes, the alternate installation schemes described in section *note
Alternate Installation: 466c. just don’t do what you want.  You might
want to tweak just one or two directories while keeping everything under
the same base directory, or you might want to completely redefine the
installation scheme.  In either case, you’re creating a `custom
installation scheme'.

To create a custom installation scheme, you start with one of the
alternate schemes and override some of the installation directories used
for the various types of files, using these options:

Type of file               Override option
                           
-------------------------------------------------------
                           
Python modules             ‘--install-purelib’
                           
                           
extension modules          ‘--install-platlib’
                           
                           
all modules                ‘--install-lib’
                           
                           
scripts                    ‘--install-scripts’
                           
                           
data                       ‘--install-data’
                           
                           
C headers                  ‘--install-headers’
                           

These override options can be relative, absolute, or explicitly defined
in terms of one of the installation base directories.  (There are two
installation base directories, and they are normally the same—they only
differ when you use the Unix “prefix scheme” and supply different
‘--prefix’ and ‘--exec-prefix’ options; using ‘--install-lib’ will
override values computed or given for ‘--install-purelib’ and
‘--install-platlib’, and is recommended for schemes that don’t make a
difference between Python and extension modules.)

For example, say you’re installing a module distribution to your home
directory under Unix—but you want scripts to go in ‘~/scripts’ rather
than ‘~/bin’.  As you might expect, you can override this directory with
the ‘--install-scripts’ option; in this case, it makes most sense to
supply a relative path, which will be interpreted relative to the
installation base directory (your home directory, in this case):

     python setup.py install --home=~ --install-scripts=scripts

Another Unix example: suppose your Python installation was built and
installed with a prefix of ‘/usr/local/python’, so under a standard
installation scripts will wind up in ‘/usr/local/python/bin’.  If you
want them in ‘/usr/local/bin’ instead, you would supply this absolute
directory for the ‘--install-scripts’ option:

     python setup.py install --install-scripts=/usr/local/bin

(This performs an installation using the “prefix scheme”, where the
prefix is whatever your Python interpreter was installed with—
‘/usr/local/python’ in this case.)

If you maintain Python on Windows, you might want third-party modules to
live in a subdirectory of ‘`prefix'’, rather than right in ‘`prefix'’
itself.  This is almost as easy as customizing the script installation
directory—you just have to remember that there are two types of modules
to worry about, Python and extension modules, which can conveniently be
both controlled by one option:

     python setup.py install --install-lib=Site

The specified installation directory is relative to ‘`prefix'’.  Of
course, you also have to ensure that this directory is in Python’s
module search path, such as by putting a ‘.pth’ file in a site directory
(see *note site: eb.).  See section *note Modifying Python’s Search
Path: 4672. to find out how to modify Python’s search path.

If you want to define an entire installation scheme, you just have to
supply all of the installation directory options.  The recommended way
to do this is to supply relative paths; for example, if you want to
maintain all Python module-related files under ‘python’ in your home
directory, and you want a separate directory for each platform that you
use your home directory from, you might define the following
installation scheme:

     python setup.py install --home=~ \
                             --install-purelib=python/lib \
                             --install-platlib=python/lib.$PLAT \
                             --install-scripts=python/scripts
                             --install-data=python/data

or, equivalently,

     python setup.py install --home=~/python \
                             --install-purelib=lib \
                             --install-platlib='lib.$PLAT' \
                             --install-scripts=scripts
                             --install-data=data

‘$PLAT’ is not (necessarily) an environment variable—it will be expanded
by the Distutils as it parses your command line options, just as it does
when parsing your configuration file(s).

Obviously, specifying the entire installation scheme every time you
install a new module distribution would be very tedious.  Thus, you can
put these options into your Distutils config file (see section *note
Distutils Configuration Files: 4669.):

     [install]
     install-base=$HOME
     install-purelib=python/lib
     install-platlib=python/lib.$PLAT
     install-scripts=python/scripts
     install-data=python/data

or, equivalently,

     [install]
     install-base=$HOME/python
     install-purelib=lib
     install-platlib=lib.$PLAT
     install-scripts=scripts
     install-data=data

Note that these two are `not' equivalent if you supply a different
installation base directory when you run the setup script.  For example,

     python setup.py install --install-base=/tmp

would install pure modules to ‘/tmp/python/lib’ in the first case, and
to ‘/tmp/lib’ in the second case.  (For the second case, you probably
want to supply an installation base of ‘/tmp/python’.)

You probably noticed the use of ‘$HOME’ and ‘$PLAT’ in the sample
configuration file input.  These are Distutils configuration variables,
which bear a strong resemblance to environment variables.  In fact, you
can use environment variables in config files on platforms that have
such a notion but the Distutils additionally define a few extra
variables that may not be in your environment, such as ‘$PLAT’.  (And of
course, on systems that don’t have environment variables, such as Mac OS
9, the configuration variables supplied by the Distutils are the only
ones you can use.)  See section *note Distutils Configuration Files:
4669. for details.

     Note: When a *note virtual environment: 377e. is activated, any
     options that change the installation path will be ignored from all
     distutils configuration files to prevent inadvertently installing
     projects outside of the virtual environment.

* Menu:

* Modifying Python’s Search Path::


File: python.info,  Node: Modifying Python’s Search Path,  Up: Custom Installation

18.4.1 Modifying Python’s Search Path
-------------------------------------

When the Python interpreter executes an *note import: ce7. statement, it
searches for both Python code and extension modules along a search path.
A default value for the path is configured into the Python binary when
the interpreter is built.  You can determine the path by importing the
*note sys: fd. module and printing the value of ‘sys.path’.

     $ python
     Python 2.2 (#11, Oct  3 2002, 13:31:27)
     [GCC 2.96 20000731 (Red Hat Linux 7.3 2.96-112)] on linux2
     Type "help", "copyright", "credits" or "license" for more information.
     >>> import sys
     >>> sys.path
     ['', '/usr/local/lib/python2.3', '/usr/local/lib/python2.3/plat-linux2',
      '/usr/local/lib/python2.3/lib-tk', '/usr/local/lib/python2.3/lib-dynload',
      '/usr/local/lib/python2.3/site-packages']
     >>>

The null string in ‘sys.path’ represents the current working directory.

The expected convention for locally installed packages is to put them in
the ‘`…'/site-packages/’ directory, but you may want to install Python
modules into some arbitrary directory.  For example, your site may have
a convention of keeping all software related to the web server under
‘/www’.  Add-on Python modules might then belong in ‘/www/python’, and
in order to import them, this directory must be added to ‘sys.path’.
There are several different ways to add the directory.

The most convenient way is to add a path configuration file to a
directory that’s already on Python’s path, usually to the
‘.../site-packages/’ directory.  Path configuration files have an
extension of ‘.pth’, and each line must contain a single path that will
be appended to ‘sys.path’.  (Because the new paths are appended to
‘sys.path’, modules in the added directories will not override standard
modules.  This means you can’t use this mechanism for installing fixed
versions of standard modules.)

Paths can be absolute or relative, in which case they’re relative to the
directory containing the ‘.pth’ file.  See the documentation of the
*note site: eb. module for more information.

A slightly less convenient way is to edit the ‘site.py’ file in Python’s
standard library, and modify ‘sys.path’.  ‘site.py’ is automatically
imported when the Python interpreter is executed, unless the *note -S:
bf7. switch is supplied to suppress this behaviour.  So you could simply
edit ‘site.py’ and add two lines to it:

     import sys
     sys.path.append('/www/python/')

However, if you reinstall the same major version of Python (perhaps when
upgrading from 2.2 to 2.2.2, for example) ‘site.py’ will be overwritten
by the stock version.  You’d have to remember that it was modified and
save a copy before doing the installation.

There are two environment variables that can modify ‘sys.path’.  *note
PYTHONHOME: 5d1. sets an alternate value for the prefix of the Python
installation.  For example, if *note PYTHONHOME: 5d1. is set to
‘/www/python’, the search path will be set to ‘['',
'/www/python/lib/pythonX.Y/', '/www/python/lib/pythonX.Y/plat-linux2',
...]’.

The *note PYTHONPATH: a34. variable can be set to a list of paths that
will be added to the beginning of ‘sys.path’.  For example, if *note
PYTHONPATH: a34. is set to ‘/www/python:/opt/py’, the search path will
begin with ‘['/www/python', '/opt/py']’.  (Note that directories must
exist in order to be added to ‘sys.path’; the *note site: eb. module
removes paths that don’t exist.)

Finally, ‘sys.path’ is just a regular Python list, so any Python
application can modify it by adding or removing entries.


File: python.info,  Node: Distutils Configuration Files,  Next: Building Extensions Tips and Tricks,  Prev: Custom Installation,  Up: Installing Python Modules Legacy version

18.5 Distutils Configuration Files
==================================

As mentioned above, you can use Distutils configuration files to record
personal or site preferences for any Distutils options.  That is, any
option to any command can be stored in one of two or three (depending on
your platform) configuration files, which will be consulted before the
command-line is parsed.  This means that configuration files will
override default values, and the command-line will in turn override
configuration files.  Furthermore, if multiple configuration files
apply, values from “earlier” files are overridden by “later” files.

* Menu:

* Location and names of config files::
* Syntax of config files::


File: python.info,  Node: Location and names of config files,  Next: Syntax of config files,  Up: Distutils Configuration Files

18.5.1 Location and names of config files
-----------------------------------------

The names and locations of the configuration files vary slightly across
platforms.  On Unix and macOS, the three configuration files (in the
order they are processed) are:

Type of file       Location and filename                                          Notes
                                                                                  
----------------------------------------------------------------------------------------------
                                                                                  
system             ‘`prefix'/lib/python`ver'/distutils/distutils.cfg’             (1)
                                                                                  
                                                                                  
personal           ‘$HOME/.pydistutils.cfg’                                       (2)
                                                                                  
                                                                                  
local              ‘setup.cfg’                                                    (3)
                                                                                  

And on Windows, the configuration files are:

Type of file       Location and filename                                 Notes
                                                                         
-------------------------------------------------------------------------------------
                                                                         
system             ‘`prefix'\Lib\distutils\distutils.cfg’                (4)
                                                                         
                                                                         
personal           ‘%HOME%\pydistutils.cfg’                              (5)
                                                                         
                                                                         
local              ‘setup.cfg’                                           (3)
                                                                         

On all platforms, the “personal” file can be temporarily disabled by
passing the ‘–no-user-cfg’ option.

Notes:

  1. Strictly speaking, the system-wide configuration file lives in the
     directory where the Distutils are installed; under Python 1.6 and
     later on Unix, this is as shown.  For Python 1.5.2, the Distutils
     will normally be installed to
     ‘`prefix'/lib/python1.5/site-packages/distutils’, so the system
     configuration file should be put there under Python 1.5.2.

  2. On Unix, if the ‘HOME’ environment variable is not defined, the
     user’s home directory will be determined with the ‘getpwuid()’
     function from the standard *note pwd: d6. module.  This is done by
     the *note os.path.expanduser(): 32c. function used by Distutils.

  3. I.e., in the current directory (usually the location of the setup
     script).

  4. (See also note (1).)  Under Python 1.6 and later, Python’s default
     “installation prefix” is ‘C:\Python’, so the system configuration
     file is normally ‘C:\Python\Lib\distutils\distutils.cfg’.  Under
     Python 1.5.2, the default prefix was ‘C:\Program Files\Python’, and
     the Distutils were not part of the standard library—so the system
     configuration file would be ‘C:\Program
     Files\Python\distutils\distutils.cfg’ in a standard Python 1.5.2
     installation under Windows.

  5. On Windows, if the ‘HOME’ environment variable is not defined,
     ‘USERPROFILE’ then ‘HOMEDRIVE’ and ‘HOMEPATH’ will be tried.  This
     is done by the *note os.path.expanduser(): 32c. function used by
     Distutils.


File: python.info,  Node: Syntax of config files,  Prev: Location and names of config files,  Up: Distutils Configuration Files

18.5.2 Syntax of config files
-----------------------------

The Distutils configuration files all have the same syntax.  The config
files are grouped into sections.  There is one section for each
Distutils command, plus a ‘global’ section for global options that
affect every command.  Each section consists of one option per line,
specified as ‘option=value’.

For example, the following is a complete config file that just forces
all commands to run quietly by default:

     [global]
     verbose=0

If this is installed as the system config file, it will affect all
processing of any Python module distribution by any user on the current
system.  If it is installed as your personal config file (on systems
that support them), it will affect only module distributions processed
by you.  And if it is used as the ‘setup.cfg’ for a particular module
distribution, it affects only that distribution.

You could override the default “build base” directory and make the
‘build*’ commands always forcibly rebuild all files with the following:

     [build]
     build-base=blib
     force=1

which corresponds to the command-line arguments

     python setup.py build --build-base=blib --force

except that including the ‘build’ command on the command-line means that
command will be run.  Including a particular command in config files has
no such implication; it only means that if the command is run, the
options in the config file will apply.  (Or if other commands that
derive values from it are run, they will use the values in the config
file.)

You can find out the complete list of options for any command using the
‘--help’ option, e.g.:

     python setup.py build --help

and you can find out the complete list of global options by using
‘--help’ without a command:

     python setup.py --help

See also the “Reference” section of the “Distributing Python Modules”
manual.


File: python.info,  Node: Building Extensions Tips and Tricks,  Prev: Distutils Configuration Files,  Up: Installing Python Modules Legacy version

18.6 Building Extensions: Tips and Tricks
=========================================

Whenever possible, the Distutils try to use the configuration
information made available by the Python interpreter used to run the
‘setup.py’ script.  For example, the same compiler and linker flags used
to compile Python will also be used for compiling extensions.  Usually
this will work well, but in complicated situations this might be
inappropriate.  This section discusses how to override the usual
Distutils behaviour.

* Menu:

* Tweaking compiler/linker flags::
* Using non-Microsoft compilers on Windows::


File: python.info,  Node: Tweaking compiler/linker flags,  Next: Using non-Microsoft compilers on Windows,  Up: Building Extensions Tips and Tricks

18.6.1 Tweaking compiler/linker flags
-------------------------------------

Compiling a Python extension written in C or C++ will sometimes require
specifying custom flags for the compiler and linker in order to use a
particular library or produce a special kind of object code.  This is
especially true if the extension hasn’t been tested on your platform, or
if you’re trying to cross-compile Python.

In the most general case, the extension author might have foreseen that
compiling the extensions would be complicated, and provided a ‘Setup’
file for you to edit.  This will likely only be done if the module
distribution contains many separate extension modules, or if they often
require elaborate sets of compiler flags in order to work.

A ‘Setup’ file, if present, is parsed in order to get a list of
extensions to build.  Each line in a ‘Setup’ describes a single module.
Lines have the following structure:

     module ... [sourcefile ...] [cpparg ...] [library ...]

Let’s examine each of the fields in turn.

   * `module' is the name of the extension module to be built, and
     should be a valid Python identifier.  You can’t just change this in
     order to rename a module (edits to the source code would also be
     needed), so this should be left alone.

   * `sourcefile' is anything that’s likely to be a source code file, at
     least judging by the filename.  Filenames ending in ‘.c’ are
     assumed to be written in C, filenames ending in ‘.C’, ‘.cc’, and
     ‘.c++’ are assumed to be C++, and filenames ending in ‘.m’ or ‘.mm’
     are assumed to be in Objective C.

   * `cpparg' is an argument for the C preprocessor, and is anything
     starting with ‘-I’, ‘-D’, ‘-U’ or ‘-C’.

   * `library' is anything ending in ‘.a’ or beginning with ‘-l’ or
     ‘-L’.

If a particular platform requires a special library on your platform,
you can add it by editing the ‘Setup’ file and running ‘python setup.py
build’.  For example, if the module defined by the line

     foo foomodule.c

must be linked with the math library ‘libm.a’ on your platform, simply
add ‘-lm’ to the line:

     foo foomodule.c -lm

Arbitrary switches intended for the compiler or the linker can be
supplied with the ‘-Xcompiler’ `arg' and ‘-Xlinker’ `arg' options:

     foo foomodule.c -Xcompiler -o32 -Xlinker -shared -lm

The next option after ‘-Xcompiler’ and ‘-Xlinker’ will be appended to
the proper command line, so in the above example the compiler will be
passed the ‘-o32’ option, and the linker will be passed ‘-shared’.  If a
compiler option requires an argument, you’ll have to supply multiple
‘-Xcompiler’ options; for example, to pass ‘-x c++’ the ‘Setup’ file
would have to contain ‘-Xcompiler -x -Xcompiler c++’.

Compiler flags can also be supplied through setting the ‘CFLAGS’
environment variable.  If set, the contents of ‘CFLAGS’ will be added to
the compiler flags specified in the ‘Setup’ file.


File: python.info,  Node: Using non-Microsoft compilers on Windows,  Prev: Tweaking compiler/linker flags,  Up: Building Extensions Tips and Tricks

18.6.2 Using non-Microsoft compilers on Windows
-----------------------------------------------

* Menu:

* Borland/CodeGear C++::
* GNU C / Cygwin / MinGW::


File: python.info,  Node: Borland/CodeGear C++,  Next: GNU C / Cygwin / MinGW,  Up: Using non-Microsoft compilers on Windows

18.6.2.1 Borland/CodeGear C++
.............................

This subsection describes the necessary steps to use Distutils with the
Borland C++ compiler version 5.5.  First you have to know that Borland’s
object file format (OMF) is different from the format used by the Python
version you can download from the Python or ActiveState Web site.
(Python is built with Microsoft Visual C++, which uses COFF as the
object file format.)  For this reason you have to convert Python’s
library ‘python25.lib’ into the Borland format.  You can do this as
follows:

     coff2omf python25.lib python25_bcpp.lib

The ‘coff2omf’ program comes with the Borland compiler.  The file
‘python25.lib’ is in the ‘Libs’ directory of your Python installation.
If your extension uses other libraries (zlib, …) you have to convert
them too.

The converted files have to reside in the same directories as the normal
libraries.

How does Distutils manage to use these libraries with their changed
names?  If the extension needs a library (eg.  ‘foo’) Distutils checks
first if it finds a library with suffix ‘_bcpp’ (eg.  ‘foo_bcpp.lib’)
and then uses this library.  In the case it doesn’t find such a special
library it uses the default name (‘foo.lib’.)  (1)

To let Distutils compile your extension with Borland C++ you now have to
type:

     python setup.py build --compiler=bcpp

If you want to use the Borland C++ compiler as the default, you could
specify this in your personal or system-wide configuration file for
Distutils (see section *note Distutils Configuration Files: 4669.)

See also
........

C++Builder Compiler(2)

     Information about the free C++ compiler from Borland, including
     links to the download pages.

Creating Python Extensions Using Borland’s Free Compiler(3)

     Document describing how to use Borland’s free command-line C++
     compiler to build Python.

   ---------- Footnotes ----------

   (1) (1) This also means you could replace all existing COFF-libraries
with OMF-libraries of the same name.

   (2) https://www.embarcadero.com/products

   (3) http://www.cyberus.ca/~g_will/pyExtenDL.shtml


File: python.info,  Node: GNU C / Cygwin / MinGW,  Prev: Borland/CodeGear C++,  Up: Using non-Microsoft compilers on Windows

18.6.2.2 GNU C / Cygwin / MinGW
...............................

This section describes the necessary steps to use Distutils with the GNU
C/C++ compilers in their Cygwin and MinGW distributions.  (1) For a
Python interpreter that was built with Cygwin, everything should work
without any of these following steps.

Not all extensions can be built with MinGW or Cygwin, but many can.
Extensions most likely to not work are those that use C++ or depend on
Microsoft Visual C extensions.

To let Distutils compile your extension with Cygwin you have to type:

     python setup.py build --compiler=cygwin

and for Cygwin in no-cygwin mode (2) or for MinGW type:

     python setup.py build --compiler=mingw32

If you want to use any of these options/compilers as default, you should
consider writing it in your personal or system-wide configuration file
for Distutils (see section *note Distutils Configuration Files: 4669.)

* Menu:

* Older Versions of Python and MinGW::

   ---------- Footnotes ----------

   (1) (2) Check ‘https://www.sourceware.org/cygwin/’ for more
information

   (2) (3) Then you have no POSIX emulation available, but you also
don’t need ‘cygwin1.dll’.


File: python.info,  Node: Older Versions of Python and MinGW,  Up: GNU C / Cygwin / MinGW

18.6.2.3 Older Versions of Python and MinGW
...........................................

The following instructions only apply if you’re using a version of
Python inferior to 2.4.1 with a MinGW inferior to 3.0.0 (with
binutils-2.13.90-20030111-1).

These compilers require some special libraries.  This task is more
complex than for Borland’s C++, because there is no program to convert
the library.  First you have to create a list of symbols which the
Python DLL exports.  (You can find a good program for this task at
‘https://sourceforge.net/projects/mingw/files/MinGW/Extension/pexports/’).

     pexports python25.dll >python25.def

The location of an installed ‘python25.dll’ will depend on the
installation options and the version and language of Windows.  In a
“just for me” installation, it will appear in the root of the
installation directory.  In a shared installation, it will be located in
the system directory.

Then you can create from these information an import library for gcc.

     /cygwin/bin/dlltool --dllname python25.dll --def python25.def --output-lib libpython25.a

The resulting library has to be placed in the same directory as
‘python25.lib’.  (Should be the ‘libs’ directory under your Python
installation directory.)

If your extension uses other libraries (zlib,…) you might have to
convert them too.  The converted files have to reside in the same
directories as the normal libraries do.

See also
........

Building Python modules on MS Windows platform with MinGW(1)

     Information about building the required libraries for the MinGW
     environment.

   ---------- Footnotes ----------

   (1) http://old.zope.org/Members/als/tips/win32_mingw_modules


File: python.info,  Node: Python Module Index,  Next: Index,  Prev: Installing Python Modules Legacy version,  Up: Top

Python Module Index
*******************

* Menu:

* __future__: 0. Future statement definitions
* __main__: 1. The environment where the top-level script is run.
* _thread: 2. Low-level threading API.
* abc: 3. Abstract base classes according to :pep:‘3119‘.
* aifc: 4. Read and write audio files in AIFF or AIFC format.
* argparse: 5. Command-line option and argument parsing library.
* array: 6. Space efficient arrays of uniformly typed numeric
                        values.
* ast: 7. Abstract Syntax Tree classes and manipulation.
* asynchat: 8. Support for asynchronous command/response protocols.
* asyncio: 9. Asynchronous I/O.
* asyncore: a. A base class for developing asynchronous socket
                        handling services.
* atexit: b. Register and execute cleanup functions.
* audioop: c. Manipulate raw audio data.
* base64: d. RFC 3548: Base16, Base32, Base64 Data
                        Encodings; Base85 and Ascii85
* bdb: e. Debugger framework.
* binascii: f. Tools for converting between binary and various ASCII-
                        encoded binary representations.
* binhex: 10. Encode and decode files in binhex4 format.
* bisect: 11. Array bisection algorithms for binary searching.
* builtins: 12. The module that provides the built-in namespace.
* bz2: 13. Interfaces for bzip2 compression and decompression.
* calendar: 14. Functions for working with calendars, including
                        some emulation of the Unix cal program.
* cgi: 15. Helpers for running Python scripts via the Common
                        Gateway Interface.
* cgitb: 16. Configurable traceback handler for CGI scripts.
* chunk: 17. Module to read IFF chunks.
* cmath: 18. Mathematical functions for complex numbers.
* cmd: 19. Build line-oriented command interpreters.
* code: 1a. Facilities to implement read-eval-print loops.
* codecs: 1b. Encode and decode data and streams.
* codeop: 1c. Compile (possibly incomplete) Python code.
* collections: 1d. Container datatypes
* collections.abc: 1e. Abstract base classes for containers
* colorsys: 1f. Conversion functions between RGB and other color
                        systems.
* compileall: 20. Tools for byte-compiling all Python source files in a
                        directory tree.
* concurrent.futures: 21. Execute computations concurrently using threads or
                        processes.
* configparser: 22. Configuration file parser.
* contextlib: 23. Utilities for with-statement contexts.
* contextvars: 24. Context Variables
* copy: 25. Shallow and deep copy operations.
* copyreg: 26. Register pickle support functions.
* cProfile: 27.
* crypt: 28. The crypt() function used to check Unix passwords.
* csv: 29. Write and read tabular data to and from delimited
                        files.
* ctypes: 2a. A foreign function library for Python.
* curses: 2b. An interface to the curses library, providing
                        portable terminal handling.
* curses.ascii: 2c. Constants and set-membership functions for ASCII
                        characters.
* curses.panel: 2d. A panel stack extension that adds depth to curses
                        windows.
* curses.textpad: 2e. Emacs-like input editing in a curses window.
* dataclasses: 2f. Generate special methods on user-defined classes.
* datetime: 30. Basic date and time types.
* dbm: 31. Interfaces to various Unix "database" formats.
* dbm.dumb: 32. Portable implementation of the simple DBM interface.
* dbm.gnu: 33. GNU’s reinterpretation of dbm.
* dbm.ndbm: 34. The standard "database" interface, based on
                        ndbm.
* decimal: 35. Implementation of the General Decimal Arithmetic
                        Specification.
* difflib: 36. Helpers for computing differences between objects.
* dis: 37. Disassembler for Python bytecode.
* distutils: 38. Support for building and installing Python modules
                        into an existing Python installation.
* distutils.archive_util: 39. Utility functions for creating archive files
                          (tarballs, zip files, ...)
* distutils.bcppcompiler: 3a.
* distutils.ccompiler: 3b. Abstract CCompiler class
* distutils.cmd: 3c. Provides the abstract base class
                        :class:‘~distutils.cmd.Command‘. This class is
                        subclassed by the modules in the distutils.command
                        subpackage.
* distutils.command: 3d. Contains one module for each standard Distutils
                        command.
* distutils.command.bdist: 3e. Build a binary installer for a package
* distutils.command.bdist_dumb: 3f. Build a "dumb" installer - a simple archive of
                                files
* distutils.command.bdist_msi: 40. Build a binary distribution as a Windows MSI
                               file
* distutils.command.bdist_packager: 41. Abstract base class for packagers
* distutils.command.bdist_rpm: 42. Build a binary distribution as a Redhat RPM and
                               SRPM
* distutils.command.bdist_wininst: 43. Build a Windows installer
* distutils.command.build: 44. Build all files of a package
* distutils.command.build_clib: 45. Build any C libraries in a package
* distutils.command.build_ext: 46. Build any extensions in a package
* distutils.command.build_py: 47. Build the .py/.pyc files of a package
* distutils.command.build_scripts: 48. Build the scripts of a package
* distutils.command.check: 49. Check the meta-data of a package
* distutils.command.clean: 4a. Clean a package build area
* distutils.command.config: 4b. Perform package configuration
* distutils.command.install: 4c. Install a package
* distutils.command.install_data: 4d. Install data files from a package
* distutils.command.install_headers: 4e. Install C/C++ header files from a package
* distutils.command.install_lib: 4f. Install library files from a package
* distutils.command.install_scripts: 50. Install script files from a package
* distutils.command.register: 51. Register a module with the Python Package Index
* distutils.command.sdist: 52. Build a source distribution
* distutils.core: 53. The core Distutils functionality
* distutils.cygwinccompiler: 54.
* distutils.debug: 55. Provides the debug flag for distutils
* distutils.dep_util: 56. Utility functions for simple dependency checking
* distutils.dir_util: 57. Utility functions for operating on directories and
                        directory trees
* distutils.dist: 58. Provides the Distribution class, which
                        represents the module distribution being
                        built/installed/distributed
* distutils.errors: 59. Provides standard distutils exceptions
* distutils.extension: 5a. Provides the Extension class, used to describe
                        C/C++ extension modules in setup scripts
* distutils.fancy_getopt: 5b. Additional getopt functionality
* distutils.file_util: 5c. Utility functions for operating on single files
* distutils.filelist: 5d. The FileList class, used for poking about the
                        file system and building lists of files.
* distutils.log: 5e. A simple logging mechanism, :pep:‘282‘-style
* distutils.msvccompiler: 5f. Microsoft Compiler
* distutils.spawn: 60. Provides the spawn() function
* distutils.sysconfig: 61. Low-level access to configuration information of the
                        Python interpreter.
* distutils.text_file: 62. Provides the TextFile class, a simple interface
                        to text files
* distutils.unixccompiler: 63. UNIX C Compiler
* distutils.util: 64. Miscellaneous other utility functions
* distutils.version: 65. Implements classes that represent module version
                        numbers.
* doctest: 66. Test pieces of code within docstrings.
* email: 67. Package supporting the parsing,
                        manipulating, and generating email messages.
* email.charset: 68. Character Sets
* email.contentmanager: 69. Storing and Retrieving Content from MIME Parts
* email.encoders: 6a. Encoders for email message payloads.
* email.errors: 6b. The exception classes used by the email package.
* email.generator: 6c. Generate flat text email messages from a message
                        structure.
* email.header: 6d. Representing non-ASCII headers
* email.headerregistry: 6e. Automatic Parsing of headers based on the field name
* email.iterators: 6f. Iterate over a message object tree.
* email.message: 70. The base class representing email messages.
* email.mime: 71. Build MIME messages.
* email.parser: 72. Parse flat text email messages to produce a message
                        object structure.
* email.policy: 73. Controlling the parsing and generating of messages
* email.utils: 74. Miscellaneous email package utilities.
* encodings.idna: 75. Internationalized Domain Names implementation
* encodings.mbcs: 76. Windows ANSI codepage
* encodings.utf_8_sig: 77. UTF-8 codec with BOM signature
* ensurepip: 78. Bootstrapping the "pip" installer into an existing
                        Python installation or virtual environment.
* enum: 79. Implementation of an enumeration class.
* errno: 7a. Standard errno system symbols.
* faulthandler: 7b. Dump the Python traceback.
* fcntl: 7c. The fcntl() and ioctl() system calls.
* filecmp: 7d. Compare files efficiently.
* fileinput: 7e. Loop over standard input or a list of files.
* fnmatch: 7f. Unix shell style filename pattern matching.
* formatter: 80. Generic output formatter and device interface.
* fractions: 81. Rational numbers.
* ftplib: 82. FTP protocol client (requires sockets).
* functools: 83. Higher-order functions and operations on callable
                        objects.
* gc: 84. Interface to the cycle-detecting garbage collector.
* getopt: 85. Portable parser for command line options; support both
                        short and long option names.
* getpass: 86. Portable reading of passwords and retrieval of the
                        userid.
* gettext: 87. Multilingual internationalization services.
* glob: 88. Unix shell style pathname pattern expansion.
* graphlib: 89. Functionality to operate with graph-like structures
* grp: 8a. The group database (getgrnam() and friends).
* gzip: 8b. Interfaces for gzip compression and decompression
                        using file objects.
* hashlib: 8c. Secure hash and message digest algorithms.
* heapq: 8d. Heap queue algorithm (a.k.a. priority queue).
* hmac: 8e. Keyed-Hashing for Message Authentication (HMAC)
                        implementation
* html: 8f. Helpers for manipulating HTML.
* html.entities: 90. Definitions of HTML general entities.
* html.parser: 91. A simple parser that can handle HTML and XHTML.
* http: 92. HTTP status codes and messages
* http.client: 93. HTTP and HTTPS protocol client (requires sockets).
* http.cookiejar: 94. Classes for automatic handling of HTTP cookies.
* http.cookies: 95. Support for HTTP state management (cookies).
* http.server: 96. HTTP server and request handlers.
* imaplib: 97. IMAP4 protocol client (requires sockets).
* imghdr: 98. Determine the type of image contained in a file or
                        byte stream.
* imp: 99. Access the implementation of the import statement.
* importlib: 9a. The implementation of the import machinery.
* importlib.abc: 9b. Abstract base classes related to import
* importlib.machinery: 9c. Importers and path hooks
* importlib.metadata: 9d. The implementation of the importlib metadata.
* importlib.resources: 9e. Package resource reading, opening, and
                        access
* importlib.util: 9f. Utility code for importers
* inspect: a0. Extract information and source code from live objects.
* io: a1. Core tools for working with streams.
* ipaddress: a2. IPv4/IPv6 manipulation library.
* itertools: a3. Functions creating iterators for efficient looping.
* json: a4. Encode and decode the JSON format.
* json.tool: a5. A command line to validate and pretty-print JSON.
* keyword: a6. Test whether a string is a keyword in Python.
* lib2to3: a7. The 2to3 library
* linecache: a8. Provides random access to individual lines from text
                        files.
* locale: a9. Internationalization services.
* logging: aa. Flexible event logging system for applications.
* logging.config: ab. Configuration of the logging module.
* logging.handlers: ac. Handlers for the logging module.
* lzma: ad. A Python wrapper for the liblzma compression library.
* mailbox: ae. Manipulate mailboxes in various formats
* mailcap: af. Mailcap file handling.
* marshal: b0. Convert Python objects to streams of bytes and back
                        (with different constraints).
* math: b1. Mathematical functions (sin() etc.).
* mimetypes: b2. Mapping of filename extensions to MIME types.
* mmap: b3. Interface to memory-mapped files for Unix and Windows.
* modulefinder: b4. Find modules used by a script.
* msilib: b5. Creation of Microsoft Installer files, and CAB
                        files.
* msvcrt: b6. Miscellaneous useful routines from the MS VC++
                        runtime.
* multiprocessing: b7. Process-based parallelism.
* multiprocessing.connection: b8. API for dealing with sockets.
* multiprocessing.dummy: b9. Dumb wrapper around threading.
* multiprocessing.managers: ba. Share data between process with shared objects.
* multiprocessing.pool: bb. Create pools of processes.
* multiprocessing.shared_memory: bc. Provides shared memory for direct access
                                 across processes.
* multiprocessing.sharedctypes: bd. Allocate ctypes objects from shared memory.
* netrc: be. Loading of .netrc files.
* nis: bf. Interface to Sun’s NIS (Yellow Pages) library.
* nntplib: c0. NNTP protocol client (requires sockets).
* numbers: c1. Numeric abstract base classes (Complex,
                        Real, Integral, etc.).
* operator: c2. Functions corresponding to the standard operators.
* optparse: c3. Command-line option parsing library.
* os: c4. Miscellaneous operating system interfaces.
* os.path: c5. Operations on pathnames.
* ossaudiodev: c6. Access to OSS-compatible audio devices.
* parser: c7. Access parse trees for Python source code.
* pathlib: c8. Object-oriented filesystem paths
* pdb: c9. The Python debugger for interactive interpreters.
* pickle: ca. Convert Python objects to streams of bytes and back.
* pickletools: cb. Contains extensive comments about the pickle protocols
                        and pickle-machine opcodes, as well as some
                        useful functions.
* pipes: cc. A Python interface to Unix shell pipelines.
* pkgutil: cd. Utilities for the import system.
* platform: ce. Retrieves as much platform identifying data as
                        possible.
* plistlib: cf. Generate and parse Apple plist files.
* poplib: d0. POP3 protocol client (requires sockets).
* posix: d1. The most common POSIX system calls (normally used via
                        module os).
* pprint: d2. Data pretty printer.
* profile: d3. Python source profiler.
* pstats: d4. Statistics object for use with the profiler.
* pty: d5. Pseudo-Terminal Handling for Linux.
* pwd: d6. The password database (getpwnam() and friends).
* py_compile: d7. Generate byte-code files from Python source files.
* pyclbr: d8. Supports information extraction for a Python module
                        browser.
* pydoc: d9. Documentation generator and online help system.
* queue: da. A synchronized queue class.
* quopri: db. Encode and decode files using the MIME quoted-
                        printable encoding.
* random: dc. Generate pseudo-random numbers with various common
                        distributions.
* re: dd. Regular expression operations.
* readline: de. GNU readline support for Python.
* reprlib: df. Alternate repr() implementation with size limits.
* resource: e0. An interface to provide resource usage information on
                        the current process.
* rlcompleter: e1. Python identifier completion, suitable for the
                        GNU readline library.
* runpy: e2. Locate and run Python modules without importing them
                        first.
* sched: e3. General purpose event scheduler.
* secrets: e4. Generate secure random numbers for managing secrets.
* select: e5. Wait for I/O completion on multiple streams.
* selectors: e6. High-level I/O multiplexing.
* shelve: e7. Python object persistence.
* shlex: e8. Simple lexical analysis for Unix shell-like languages.
* shutil: e9. High-level file operations, including copying.
* signal: ea. Set handlers for asynchronous events.
* site: eb. Module responsible for site-specific configuration.
* smtpd: ec. A SMTP server implementation in Python.
* smtplib: ed. SMTP protocol client (requires sockets).
* sndhdr: ee. Determine type of a sound file.
* socket: ef. Low-level networking interface.
* socketserver: f0. A framework for network servers.
* spwd: f1. The shadow password database (getspnam() and friends).
* sqlite3: f2. A DB-API 2.0 implementation using SQLite 3.x.
* ssl: f3. TLS/SSL wrapper for socket objects
* stat: f4. Utilities for interpreting the results of
                        os.stat(), os.lstat() and os.fstat().
* statistics: f5. Mathematical statistics functions
* string: f6. Common string operations.
* stringprep: f7. String preparation, as per RFC 3453
* struct: f8. Interpret bytes as packed binary data.
* subprocess: f9. Subprocess management.
* sunau: fa. Provide an interface to the Sun AU sound format.
* symbol: fb. Constants representing internal nodes of the parse
                        tree.
* symtable: fc. Interface to the compiler’s internal symbol tables.
* sys: fd. Access system-specific parameters and functions.
* sysconfig: fe. Python’s configuration information
* syslog: ff. An interface to the Unix syslog library routines.
* tabnanny: 100. Tool for detecting white space related problems in
                        Python source files in a directory tree.
* tarfile: 101. Read and write tar-format archive files.
* telnetlib: 102. Telnet client class.
* tempfile: 103. Generate temporary files and directories.
* termios: 104. POSIX style tty control.
* test: 105. Regression tests package containing the testing suite
                        for Python.
* test.support: 106. Support for Python’s regression test suite.
* test.support.bytecode_helper: 107. Support tools for testing correct bytecode
                                generation.
* test.support.script_helper: 108. Support for Python’s script execution tests.
* test.support.socket_helper: 109. Support for socket tests.
* textwrap: 10a. Text wrapping and filling
* threading: 10b. Thread-based parallelism.
* time: 10c. Time access and conversions.
* timeit: 10d. Measure the execution time of small code snippets.
* tkinter: 10e. Interface to Tcl/Tk for graphical user interfaces
* tkinter.colorchooser: 10f. Color choosing dialog
* tkinter.commondialog: 110. Tkinter base class for dialogs
* tkinter.dnd: 111. Tkinter drag-and-drop interface
* tkinter.filedialog: 112. Dialog classes for file selection
* tkinter.font: 113. Tkinter font-wrapping class
* tkinter.messagebox: 114. Various types of alert dialogs
* tkinter.scrolledtext: 115. Text widget with a vertical scroll bar.
* tkinter.simpledialog: 116. Simple dialog windows
* tkinter.tix: 117. Tk Extension Widgets for Tkinter
* tkinter.ttk: 118. Tk themed widget set
* token: 119. Constants representing terminal nodes of the parse
                        tree.
* tokenize: 11a. Lexical scanner for Python source code.
* trace: 11b. Trace or track Python statement execution.
* traceback: 11c. Print or retrieve a stack traceback.
* tracemalloc: 11d. Trace memory allocations.
* tty: 11e. Utility functions that perform common terminal control
                        operations.
* turtle: 11f. An educational framework for simple graphics
                        applications
* turtledemo: 120. A viewer for example turtle scripts
* types: 121. Names for built-in types.
* typing: 122. Support for type hints (see :pep:‘484‘).
* unicodedata: 123. Access the Unicode Database.
* unittest: 124. Unit testing framework for Python.
* unittest.mock: 125. Mock object library.
* urllib: 126.
* urllib.error: 127. Exception classes raised by urllib.request.
* urllib.parse: 128. Parse URLs into or assemble them from components.
* urllib.request: 129. Extensible library for opening URLs.
* urllib.response: 12a. Response classes used by urllib.
* urllib.robotparser: 12b. Load a robots.txt file and answer questions about
                        fetchability of other URLs.
* uu: 12c. Encode and decode files in uuencode format.
* uuid: 12d. UUID objects (universally unique identifiers)
                        according to RFC 4122
* venv: 12e. Creation of virtual environments.
* warnings: 12f. Issue warning messages and control their disposition.
* wave: 130. Provide an interface to the WAV sound format.
* weakref: 131. Support for weak references and weak dictionaries.
* webbrowser: 132. Easy-to-use controller for Web browsers.
* winreg: 133. Routines and objects for manipulating the Windows
                        registry.
* winsound: 134. Access to the sound-playing machinery for Windows.
* wsgiref: 135. WSGI Utilities and Reference Implementation.
* wsgiref.handlers: 136. WSGI server/gateway base classes.
* wsgiref.headers: 137. WSGI response header tools.
* wsgiref.simple_server: 138. A simple WSGI HTTP server.
* wsgiref.util: 139. WSGI environment utilities.
* wsgiref.validate: 13a. WSGI conformance checker.
* xdrlib: 13b. Encoders and decoders for the External Data
                        Representation (XDR).
* xml: 13c. Package containing XML processing modules
* xml.dom: 13d. Document Object Model API for Python.
* xml.dom.minidom: 13e. Minimal Document Object Model (DOM) implementation.
* xml.dom.pulldom: 13f. Support for building partial DOM trees from SAX
                        events.
* xml.etree.ElementTree: 140. Implementation of the ElementTree API.
* xml.parsers.expat: 141. An interface to the Expat non-validating XML parser.
* xml.parsers.expat.errors: 142.
* xml.parsers.expat.model: 143.
* xml.sax: 144. Package containing SAX2 base classes and convenience
                        functions.
* xml.sax.handler: 145. Base classes for SAX event handlers.
* xml.sax.saxutils: 146. Convenience functions and classes for use with SAX.
* xml.sax.xmlreader: 147. Interface which SAX-compliant XML parsers must
                        implement.
* xmlrpc.client: 148. XML-RPC client access.
* xmlrpc.server: 149. Basic XML-RPC server implementations.
* zipapp: 14a. Manage executable Python zip archives
* zipfile: 14b. Read and write ZIP-format archive files.
* zipimport: 14c. Support for importing Python modules from ZIP
                        archives.
* zlib: 14d. Low-level interface to compression and decompression
                        routines compatible with gzip.
* zoneinfo: 14e. IANA time zone support


File: python.info,  Node: Index,  Prev: Python Module Index,  Up: Top

Index
*****

[index]
* Menu:

* ! (exclamation); in a command interpreter: Cmd Objects.    (line   27)
* ! (exclamation); in curses module:     curses ascii — Utilities for ASCII characters.
                                                             (line  226)
* ! (exclamation); in formatted string literal: String literal concatenation.
                                                             (line   24)
* ! (exclamation); in glob-style wildcards: glob — Unix style pathname pattern expansion.
                                                             (line   10)
* ! (exclamation); in glob-style wildcards <1>: fnmatch — Unix filename pattern matching.
                                                             (line   15)
* ! (exclamation); in string formatting: Format String Syntax.
                                                             (line   13)
* ! (exclamation); in struct format strings: Byte Order Size and Alignment.
                                                             (line   10)
* ! (pdb command):                       Debugger Commands.  (line  311)
* " (double quote); string literal:      Literals.           (line    8)
* """; string literal:                   String and Bytes literals.
                                                             (line   36)
* # (hash); comment:                     An Informal Introduction to Python.
                                                             (line   14)
* # (hash); comment <1>:                 Comments.           (line    6)
* # (hash); comment <2>:                 site — Site-specific configuration hook.
                                                             (line   45)
* # (hash); in doctests:                 Option Flags.       (line  183)
* # (hash); in printf-style formatting:  printf-style String Formatting.
                                                             (line   66)
* # (hash); in printf-style formatting <1>: printf-style Bytes Formatting.
                                                             (line   63)
* # (hash); in regular expressions:      Module Contents.    (line  123)
* # (hash); in string formatting:        Format Specification Mini-Language.
                                                             (line   87)
* # (hash); source encoding declaration: Encoding declarations.
                                                             (line    6)
* $ (dollar); environment variables expansion: os path — Common pathname manipulations.
                                                             (line  158)
* $ (dollar); in regular expressions:    Regular Expression Syntax.
                                                             (line   57)
* $ (dollar); in template strings:       Template strings.   (line   13)
* $ (dollar); interpolation in configuration files: Interpolation of values.
                                                             (line   40)
* % (percent); datetime format:          timezone Objects.   (line   71)
* % (percent); datetime format <1>:      Functions<3>.       (line  230)
* % (percent); datetime format <2>:      Functions<3>.       (line  362)
* % (percent); environment variables expansion (Windows): os path — Common pathname manipulations.
                                                             (line  158)
* % (percent); environment variables expansion (Windows) <1>: Functions<12>.
                                                             (line  233)
* % (percent); interpolation in configuration files: Interpolation of values.
                                                             (line   10)
* % (percent); printf-style formatting:  printf-style String Formatting.
                                                             (line    6)
* % (percent); printf-style formatting <1>: printf-style Bytes Formatting.
                                                             (line    6)
* %=; augmented assignment:              Augmented assignment statements.
                                                             (line    6)
* &=; augmented assignment:              Augmented assignment statements.
                                                             (line    6)
* ’ (single quote); string literal:      Literals.           (line    8)
* ’’’; string literal:                   String and Bytes literals.
                                                             (line   36)
* () (parentheses); call:                Slicings.           (line   38)
* () (parentheses); class definition:    Class definitions.  (line    6)
* () (parentheses); function definition: Function definitions.
                                                             (line    6)
* () (parentheses); generator expression: Generator expressions.
                                                             (line    6)
* () (parentheses); in assignment target list: Assignment statements.
                                                             (line   35)
* () (parentheses); in printf-style formatting: printf-style String Formatting.
                                                             (line   26)
* () (parentheses); in printf-style formatting <1>: printf-style Bytes Formatting.
                                                             (line   23)
* () (parentheses); in regular expressions: Regular Expression Syntax.
                                                             (line  199)
* () (parentheses); tuple display:       Parenthesized forms.
                                                             (line    6)
* (?!; in regular expressions:           Regular Expression Syntax.
                                                             (line  316)
* (?#; in regular expressions:           Regular Expression Syntax.
                                                             (line  305)
* (?; in regular expressions:            Regular Expression Syntax.
                                                             (line  208)
* (?;; in regular expressions:           Regular Expression Syntax.
                                                             (line  232)
* (?<!; in regular expressions:          Regular Expression Syntax.
                                                             (line  350)
* (?<=; in regular expressions:          Regular Expression Syntax.
                                                             (line  322)
* (?=; in regular expressions:           Regular Expression Syntax.
                                                             (line  309)
* (?P<; in regular expressions:          Regular Expression Syntax.
                                                             (line  267)
* (?P=; in regular expressions:          Regular Expression Syntax.
                                                             (line  300)
* * (asterisk); function definition:     Function definitions.
                                                             (line   81)
* * (asterisk); import statement:        The import statement.
                                                             (line   79)
* * (asterisk); in argparse module:      nargs.              (line   56)
* * (asterisk); in assignment target list: Assignment statements.
                                                             (line   35)
* * (asterisk); in AST grammar:          Node classes.       (line   22)
* * (asterisk); in expression lists:     Expression lists.   (line   16)
* * (asterisk); in function calls:       Arbitrary Argument Lists.
                                                             (line    6)
* * (asterisk); in function calls <1>:   Calls.              (line   74)
* * (asterisk); in glob-style wildcards: glob — Unix style pathname pattern expansion.
                                                             (line   10)
* * (asterisk); in glob-style wildcards <1>: fnmatch — Unix filename pattern matching.
                                                             (line   15)
* * (asterisk); in printf-style formatting: printf-style String Formatting.
                                                             (line   26)
* * (asterisk); in printf-style formatting <1>: printf-style Bytes Formatting.
                                                             (line   23)
* * (asterisk); in regular expressions:  Regular Expression Syntax.
                                                             (line   68)
* **; function definition:               Function definitions.
                                                             (line   81)
* **; in dictionary displays:            Dictionary displays.
                                                             (line   23)
* **; in function calls:                 Unpacking Argument Lists.
                                                             (line   19)
* **; in function calls <1>:             Calls.              (line  100)
* **; in glob-style wildcards:           glob — Unix style pathname pattern expansion.
                                                             (line   41)
* **=; augmented assignment:             Augmented assignment statements.
                                                             (line    6)
* *=; augmented assignment:              Augmented assignment statements.
                                                             (line    6)
* *?; in regular expressions:            Regular Expression Syntax.
                                                             (line   85)
* + (plus); binary operator:             Binary arithmetic operations.
                                                             (line   69)
* + (plus); binary operator <1>:         Numeric Types — int float complex.
                                                             (line   27)
* + (plus); in argparse module:          nargs.              (line   68)
* + (plus); in doctests:                 Option Flags.       (line  183)
* + (plus); in printf-style formatting:  printf-style String Formatting.
                                                             (line   66)
* + (plus); in printf-style formatting <1>: printf-style Bytes Formatting.
                                                             (line   63)
* + (plus); in regular expressions:      Regular Expression Syntax.
                                                             (line   74)
* + (plus); in string formatting:        Format Specification Mini-Language.
                                                             (line   71)
* + (plus); unary operator:              Unary arithmetic and bitwise operations.
                                                             (line   14)
* + (plus); unary operator <1>:          Numeric Types — int float complex.
                                                             (line   27)
* +=; augmented assignment:              Augmented assignment statements.
                                                             (line    6)
* +?; in regular expressions:            Regular Expression Syntax.
                                                             (line   85)
* , (comma):                             Parenthesized forms.
                                                             (line   20)
* , (comma); argument list:              Slicings.           (line   38)
* , (comma); expression list:            List displays.      (line    6)
* , (comma); expression list <1>:        Set displays.       (line    6)
* , (comma); expression list <2>:        Expression lists.   (line    6)
* , (comma); expression list <3>:        The assert statement.
                                                             (line    6)
* , (comma); expression list <4>:        Class definitions.  (line    6)
* , (comma); identifier list:            The global statement.
                                                             (line    6)
* , (comma); identifier list <1>:        The nonlocal statement.
                                                             (line    6)
* , (comma); import statement:           The import statement.
                                                             (line    6)
* , (comma); in dictionary displays:     Dictionary displays.
                                                             (line    6)
* , (comma); in string formatting:       Format Specification Mini-Language.
                                                             (line   99)
* , (comma); in target list:             Assignment statements.
                                                             (line   35)
* , (comma); parameter list:             Function definitions.
                                                             (line    6)
* , (comma); slicing:                    Slicings.           (line    6)
* , (comma); with statement:             The with statement. (line    6)
* - (minus); binary operator:            Binary arithmetic operations.
                                                             (line   78)
* - (minus); binary operator <1>:        Numeric Types — int float complex.
                                                             (line   27)
* - (minus); in doctests:                Option Flags.       (line  182)
* - (minus); in glob-style wildcards:    glob — Unix style pathname pattern expansion.
                                                             (line   10)
* - (minus); in glob-style wildcards <1>: fnmatch — Unix filename pattern matching.
                                                             (line   15)
* - (minus); in printf-style formatting: printf-style String Formatting.
                                                             (line   66)
* - (minus); in printf-style formatting <1>: printf-style Bytes Formatting.
                                                             (line   63)
* - (minus); in regular expressions:     Regular Expression Syntax.
                                                             (line  143)
* - (minus); in string formatting:       Format Specification Mini-Language.
                                                             (line   71)
* - (minus); unary operator:             Unary arithmetic and bitwise operations.
                                                             (line   10)
* - (minus); unary operator <1>:         Numeric Types — int float complex.
                                                             (line   27)
* -=; augmented assignment:              Augmented assignment statements.
                                                             (line    6)
* ->; function annotations:              Function Annotations.
                                                             (line    6)
* ->; function annotations <1>:          Function definitions.
                                                             (line   97)
* . (dot); attribute reference:          Attribute references.
                                                             (line    6)
* . (dot); in glob-style wildcards:      glob — Unix style pathname pattern expansion.
                                                             (line   10)
* . (dot); in numeric literal:           Integer literals.   (line   40)
* . (dot); in pathnames:                 Miscellaneous System Information.
                                                             (line   81)
* . (dot); in pathnames <1>:             Miscellaneous System Information.
                                                             (line  109)
* . (dot); in printf-style formatting:   printf-style String Formatting.
                                                             (line   26)
* . (dot); in printf-style formatting <1>: printf-style Bytes Formatting.
                                                             (line   23)
* . (dot); in regular expressions:       Regular Expression Syntax.
                                                             (line   46)
* . (dot); in string formatting:         Format String Syntax.
                                                             (line   13)
* . (dot); in Tkinter:                   A Very Quick Look at Tcl/Tk.
                                                             (line   44)
* ...:                                   Glossary.           (line   10)
* ...; ellipsis literal:                 The standard type hierarchy.
                                                             (line   46)
* ...; ellipsis literal <1>:             Built-in Constants. (line   57)
* ...; ellipsis literal <2>:             The Null Object.    (line   12)
* ...; in doctests:                      Option Flags.       (line   49)
* ...; interpreter prompt:               How are Docstring Examples Recognized?.
                                                             (line   26)
* ...; interpreter prompt <1>:           sys — System-specific parameters and functions.
                                                             (line 1210)
* ...; placeholder:                      textwrap — Text wrapping and filling.
                                                             (line  274)
* ...; placeholder <1>:                  pprint — Data pretty printer.
                                                             (line   30)
* ...; placeholder <2>:                  reprlib — Alternate repr implementation.
                                                             (line   41)
* ..; in pathnames:                      Miscellaneous System Information.
                                                             (line   87)
* .ini; file:                            configparser — Configuration file parser.
                                                             (line    8)
* .pdbrc; file:                          Debugger Commands.  (line   37)
* / (slash); function definition:        Function definitions.
                                                             (line   81)
* / (slash); in pathnames:               Miscellaneous System Information.
                                                             (line   93)
* / (slash); in pathnames <1>:           Miscellaneous System Information.
                                                             (line  102)
* //=; augmented assignment:             Augmented assignment statements.
                                                             (line    6)
* /=; augmented assignment:              Augmented assignment statements.
                                                             (line    6)
* 0b; integer literal:                   Numeric literals.   (line   14)
* 0o; integer literal:                   Numeric literals.   (line   14)
* 0x; integer literal:                   Numeric literals.   (line   14)
* 2-digit years:                         time — Time access and conversions.
                                                             (line   35)
* 2to3:                                  Glossary.           (line   23)
* ; (colon); annotated variable:         Annotated assignment statements.
                                                             (line    6)
* ; (colon); compound statement:         The if statement.   (line    6)
* ; (colon); compound statement <1>:     The while statement.
                                                             (line    6)
* ; (colon); compound statement <2>:     The for statement.  (line    6)
* ; (colon); compound statement <3>:     The try statement.  (line    6)
* ; (colon); compound statement <4>:     The with statement. (line    6)
* ; (colon); compound statement <5>:     Function definitions.
                                                             (line    6)
* ; (colon); compound statement <6>:     Class definitions.  (line    6)
* ; (colon); function annotations:       Function Annotations.
                                                             (line    6)
* ; (colon); function annotations <1>:   Function definitions.
                                                             (line   97)
* ; (colon); in dictionary expressions:  Dictionary displays.
                                                             (line    6)
* ; (colon); in formatted string literal: String literal concatenation.
                                                             (line   24)
* ; (colon); in SQL statements:          Cursor Objects.     (line   11)
* ; (colon); in string formatting:       Format String Syntax.
                                                             (line   13)
* ; (colon); lambda expression:          Lambdas.            (line    6)
* ; (colon); path separator (POSIX):     Miscellaneous System Information.
                                                             (line  115)
* ; (colon); slicing:                    Slicings.           (line    6)
* ; (semicolon):                         Compound statements.
                                                             (line   18)
* ; (semicolon) <1>:                     Miscellaneous System Information.
                                                             (line  115)
* < (less); in string formatting:        Format Specification Mini-Language.
                                                             (line   42)
* < (less); in struct format strings:    Byte Order Size and Alignment.
                                                             (line   10)
* <<=; augmented assignment:             Augmented assignment statements.
                                                             (line    6)
* <BLANKLINE>:                           Option Flags.       (line   30)
* = (equals); assignment statement:      Assignment statements.
                                                             (line    6)
* = (equals); class definition:          Metaclasses.        (line    6)
* = (equals); for help in debugging using string literals: String literal concatenation.
                                                             (line   23)
* = (equals); function definition:       Function definitions.
                                                             (line   56)
* = (equals); in function calls:         Slicings.           (line   37)
* = (equals); in string formatting:      Format Specification Mini-Language.
                                                             (line   42)
* = (equals); in struct format strings:  Byte Order Size and Alignment.
                                                             (line   10)
* > (greater); in string formatting:     Format Specification Mini-Language.
                                                             (line   42)
* > (greater); in struct format strings: Byte Order Size and Alignment.
                                                             (line   10)
* >>=; augmented assignment:             Augmented assignment statements.
                                                             (line    6)
* >>>:                                   Glossary.           (line    6)
* >>>; interpreter prompt:               How are Docstring Examples Recognized?.
                                                             (line   26)
* >>>; interpreter prompt <1>:           sys — System-specific parameters and functions.
                                                             (line 1210)
* ? (question mark); in a command interpreter: Cmd Objects.  (line   27)
* ? (question mark); in argparse module: nargs.              (line   23)
* ? (question mark); in AST grammar:     Node classes.       (line   22)
* ? (question mark); in glob-style wildcards: glob — Unix style pathname pattern expansion.
                                                             (line   10)
* ? (question mark); in glob-style wildcards <1>: fnmatch — Unix filename pattern matching.
                                                             (line   15)
* ? (question mark); in regular expressions: Regular Expression Syntax.
                                                             (line   80)
* ? (question mark); in SQL statements:  Cursor Objects.     (line   11)
* ? (question mark); in struct format strings: Format Characters.
                                                             (line   86)
* ? (question mark); in struct format strings <1>: Format Characters.
                                                             (line  161)
* ? (question mark); replacement character: Error Handlers.  (line   28)
* ??; in regular expressions:            Regular Expression Syntax.
                                                             (line   85)
* @ (at); class definition:              Class definitions.  (line   44)
* @ (at); function definition:           Function definitions.
                                                             (line   32)
* @ (at); in struct format strings:      Byte Order Size and Alignment.
                                                             (line   10)
* [] (square brackets); in assignment target list: Assignment statements.
                                                             (line   35)
* [] (square brackets); in glob-style wildcards: glob — Unix style pathname pattern expansion.
                                                             (line   10)
* [] (square brackets); in glob-style wildcards <1>: fnmatch — Unix filename pattern matching.
                                                             (line   15)
* [] (square brackets); in regular expressions: Regular Expression Syntax.
                                                             (line  136)
* [] (square brackets); in string formatting: Format String Syntax.
                                                             (line   13)
* [] (square brackets); list expression: List displays.      (line    6)
* [] (square brackets); subscription:    Subscriptions.      (line    6)
* \ (backslash); escape sequence:        String and Bytes literals.
                                                             (line   72)
* \ (backslash); escape sequence <1>:    Error Handlers.     (line   28)
* \ (backslash); in pathnames (Windows): Miscellaneous System Information.
                                                             (line   93)
* \ (backslash); in regular expressions: Regular Expression Syntax.
                                                             (line  121)
* \ (backslash); in regular expressions <1>: Regular Expression Syntax.
                                                             (line  155)
* \ (backslash); in regular expressions <2>: Regular Expression Syntax.
                                                             (line  374)
* \a; escape sequence:                   String and Bytes literals.
                                                             (line   72)
* \A; in regular expressions:            Regular Expression Syntax.
                                                             (line  386)
* \a; in regular expressions:            Regular Expression Syntax.
                                                             (line  486)
* \b; escape sequence:                   String and Bytes literals.
                                                             (line   72)
* \b; in regular expressions:            Regular Expression Syntax.
                                                             (line  390)
* \B; in regular expressions:            Regular Expression Syntax.
                                                             (line  407)
* \b; in regular expressions <1>:        Regular Expression Syntax.
                                                             (line  486)
* \d; in regular expressions:            Regular Expression Syntax.
                                                             (line  418)
* \D; in regular expressions:            Regular Expression Syntax.
                                                             (line  431)
* \f; escape sequence:                   String and Bytes literals.
                                                             (line   72)
* \f; in regular expressions:            Regular Expression Syntax.
                                                             (line  486)
* \g; in regular expressions:            Module Contents.    (line  292)
* \n; escape sequence:                   String and Bytes literals.
                                                             (line   72)
* \N; escape sequence:                   String and Bytes literals.
                                                             (line   72)
* \N; escape sequence <1>:               Error Handlers.     (line   28)
* \n; in regular expressions:            Regular Expression Syntax.
                                                             (line  486)
* \N; in regular expressions:            Regular Expression Syntax.
                                                             (line  486)
* \r; escape sequence:                   String and Bytes literals.
                                                             (line   72)
* \r; in regular expressions:            Regular Expression Syntax.
                                                             (line  486)
* \s; in regular expressions:            Regular Expression Syntax.
                                                             (line  437)
* \S; in regular expressions:            Regular Expression Syntax.
                                                             (line  452)
* \t; escape sequence:                   String and Bytes literals.
                                                             (line   72)
* \t; in regular expressions:            Regular Expression Syntax.
                                                             (line  486)
* \u; escape sequence:                   String and Bytes literals.
                                                             (line   72)
* \U; escape sequence:                   String and Bytes literals.
                                                             (line   72)
* \u; escape sequence <1>:               Error Handlers.     (line   28)
* \U; escape sequence <1>:               Error Handlers.     (line   28)
* \u; in regular expressions:            Regular Expression Syntax.
                                                             (line  486)
* \U; in regular expressions:            Regular Expression Syntax.
                                                             (line  486)
* \v; escape sequence:                   String and Bytes literals.
                                                             (line   72)
* \v; in regular expressions:            Regular Expression Syntax.
                                                             (line  486)
* \w; in regular expressions:            Regular Expression Syntax.
                                                             (line  458)
* \W; in regular expressions:            Regular Expression Syntax.
                                                             (line  474)
* \x; escape sequence:                   String and Bytes literals.
                                                             (line   72)
* \x; escape sequence <1>:               Error Handlers.     (line   28)
* \x; in regular expressions:            Regular Expression Syntax.
                                                             (line  486)
* \Z; in regular expressions:            Regular Expression Syntax.
                                                             (line  482)
* \\; escape sequence:                   String and Bytes literals.
                                                             (line   72)
* \\; in regular expressions:            Regular Expression Syntax.
                                                             (line  486)
* ^ (caret); in curses module:           curses ascii — Utilities for ASCII characters.
                                                             (line  226)
* ^ (caret); in regular expressions:     Regular Expression Syntax.
                                                             (line   52)
* ^ (caret); in regular expressions <1>: Regular Expression Syntax.
                                                             (line  160)
* ^ (caret); in string formatting:       Format Specification Mini-Language.
                                                             (line   42)
* ^ (caret); marker:                     What About Exceptions?.
                                                             (line   93)
* ^ (caret); marker <1>:                 traceback — Print or retrieve a stack traceback.
                                                             (line   46)
* ^=; augmented assignment:              Augmented assignment statements.
                                                             (line    6)
* _ (underscore); gettext:               GNU gettext API.    (line   42)
* _ (underscore); in numeric literal:    Numeric literals.   (line   13)
* _ (underscore); in numeric literal <1>: Integer literals.  (line   39)
* _ (underscore); in string formatting:  Format Specification Mini-Language.
                                                             (line  105)
* _, identifiers:                        Keywords.           (line   18)
* _anonymous_ (ctypes.Structure attribute): Structured data types.
                                                             (line   74)
* _asdict() (collections.somenamedtuple method): namedtuple Factory Function for Tuples with Named Fields.
                                                             (line  110)
* _b_base_ (ctypes._CData attribute):    Data types.         (line   71)
* _b_needsfree_ (ctypes._CData attribute): Data types.       (line   78)
* _callmethod() (multiprocessing.managers.BaseProxy method): Proxy Objects.
                                                             (line   96)
* _CData (class in ctypes):              Data types.         (line    6)
* _clear_type_cache() (in module sys):   sys — System-specific parameters and functions.
                                                             (line  158)
* _current_frames() (in module sys):     sys — System-specific parameters and functions.
                                                             (line  167)
* _debugmallocstats() (in module sys):   sys — System-specific parameters and functions.
                                                             (line  224)
* _enablelegacywindowsfsencoding() (in module sys): sys — System-specific parameters and functions.
                                                             (line 1455)
* _exit() (in module os):                Process Management. (line  120)
* _fields (ast.AST attribute):           Node classes.       (line   22)
* _fields (collections.somenamedtuple attribute): namedtuple Factory Function for Tuples with Named Fields.
                                                             (line  140)
* _fields_ (ctypes.Structure attribute): Structured data types.
                                                             (line   31)
* _field_defaults (collections.somenamedtuple attribute): namedtuple Factory Function for Tuples with Named Fields.
                                                             (line  153)
* _flush() (wsgiref.handlers.BaseHandler method): wsgiref handlers – server/gateway base classes.
                                                             (line  116)
* _frozen (C type):                      Importing Modules<2>.
                                                             (line  248)
* _FuncPtr (class in ctypes):            Foreign functions.  (line   12)
* _getframe() (in module sys):           sys — System-specific parameters and functions.
                                                             (line  720)
* _getvalue() (multiprocessing.managers.BaseProxy method): Proxy Objects.
                                                             (line  138)
* _get_child_mock() (unittest.mock.Mock method): The Mock Class.
                                                             (line  286)
* _handle (ctypes.PyDLL attribute):      Loading shared libraries.
                                                             (line  145)
* _inittab (C type):                     Importing Modules<2>.
                                                             (line  280)
* _length_ (ctypes.Array attribute):     Arrays and pointers.
                                                             (line   18)
* _make() (collections.somenamedtuple class method): namedtuple Factory Function for Tuples with Named Fields.
                                                             (line  101)
* _makeResult() (unittest.TextTestRunner method): Loading and running tests.
                                                             (line  466)
* _name (ctypes.PyDLL attribute):        Loading shared libraries.
                                                             (line  149)
* _objects (ctypes._CData attribute):    Data types.         (line   83)
* _pack_ (ctypes.Structure attribute):   Structured data types.
                                                             (line   67)
* _parse() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line   21)
* _Pointer (class in ctypes):            Arrays and pointers.
                                                             (line   31)
* _PyBytes_Resize (C function):          Bytes Objects<2>.   (line  183)
* _PyCFunctionFast (C type):             Implementing functions and methods.
                                                             (line   30)
* _PyCFunctionFastWithKeywords (C type): Implementing functions and methods.
                                                             (line   39)
* _PyFrameEvalFunction (C type):         Low-level API.      (line  135)
* _PyInterpreterState_GetEvalFrameFunc (C function): Low-level API.
                                                             (line  147)
* _PyInterpreterState_SetEvalFrameFunc (C function): Low-level API.
                                                             (line  157)
* _PyObject_New (C function):            Allocating Objects on the Heap.
                                                             (line    6)
* _PyObject_NewVar (C function):         Allocating Objects on the Heap.
                                                             (line    9)
* _PyTuple_Resize (C function):          Tuple Objects.      (line   88)
* _Py_c_diff (C function):               Complex Numbers as C Structures.
                                                             (line   27)
* _Py_c_neg (C function):                Complex Numbers as C Structures.
                                                             (line   33)
* _Py_c_pow (C function):                Complex Numbers as C Structures.
                                                             (line   53)
* _Py_c_prod (C function):               Complex Numbers as C Structures.
                                                             (line   38)
* _Py_c_quot (C function):               Complex Numbers as C Structures.
                                                             (line   44)
* _Py_c_sum (C function):                Complex Numbers as C Structures.
                                                             (line   22)
* _Py_InitializeMain (C function):       Multi-Phase Initialization Private Provisional API.
                                                             (line   47)
* _Py_NoneStruct (C variable):           Allocating Objects on the Heap.
                                                             (line   59)
* _replace() (collections.somenamedtuple method): namedtuple Factory Function for Tuples with Named Fields.
                                                             (line  128)
* _setroot() (xml.etree.ElementTree.ElementTree method): ElementTree Objects.
                                                             (line   15)
* _SimpleCData (class in ctypes):        Fundamental data types<2>.
                                                             (line    6)
* _structure() (in module email.iterators): email iterators Iterators.
                                                             (line   44)
* _thread (module):                      _thread — Low-level threading API.
                                                             (line    6)
* _type_ (ctypes.Array attribute):       Arrays and pointers.
                                                             (line   24)
* _type_ (ctypes._Pointer attribute):    Arrays and pointers.
                                                             (line   46)
* _write() (wsgiref.handlers.BaseHandler method): wsgiref handlers – server/gateway base classes.
                                                             (line  108)
* _xoptions (in module sys):             sys — System-specific parameters and functions.
                                                             (line 1690)
* __, identifiers:                       Keywords.           (line   17)
* __abs__() (in module operator):        operator — Standard operators as functions.
                                                             (line   73)
* __abs__() (object method):             Emulating numeric types.
                                                             (line  111)
* __add__() (in module operator):        operator — Standard operators as functions.
                                                             (line   78)
* __add__() (object method):             Emulating numeric types.
                                                             (line   11)
* __aenter__() (object method):          Asynchronous Context Managers.
                                                             (line   12)
* __aexit__() (object method):           Asynchronous Context Managers.
                                                             (line   17)
* __aiter__() (object method):           Asynchronous Iterators.
                                                             (line   12)
* __all__:                               Importing * From a Package.
                                                             (line    6)
* __all__ (optional module attribute):   The import statement.
                                                             (line   83)
* __all__ (package variable):            Importing Modules<2>.
                                                             (line    7)
* __and__() (in module operator):        operator — Standard operators as functions.
                                                             (line   83)
* __and__() (object method):             Emulating numeric types.
                                                             (line   11)
* __anext__() (agen method):             Asynchronous generator-iterator methods.
                                                             (line   10)
* __anext__() (object method):           Asynchronous Iterators.
                                                             (line   16)
* __annotations__ (class attribute):     The standard type hierarchy.
                                                             (line  593)
* __annotations__ (function attribute):  The standard type hierarchy.
                                                             (line  309)
* __annotations__ (module attribute):    The standard type hierarchy.
                                                             (line  541)
* __args__ (genericalias attribute):     Special Attributes of Generic Alias.
                                                             (line   15)
* __await__() (object method):           Awaitable Objects.  (line   15)
* __bases__ (class attribute):           The standard type hierarchy.
                                                             (line  593)
* __bases__ (class attribute) <1>:       Special Attributes. (line   19)
* __bool__() (object method):            Basic customization.
                                                             (line  301)
* __bool__() (object method) <1>:        Emulating container types.
                                                             (line   40)
* __breakpointhook__ (in module sys):    sys — System-specific parameters and functions.
                                                             (line  336)
* __bytes__() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  129)
* __bytes__() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  138)
* __bytes__() (object method):           Basic customization.
                                                             (line  143)
* __cached__:                            Import-related module attributes.
                                                             (line   69)
* __callback__ (weakref.ref attribute):  weakref — Weak references.
                                                             (line  126)
* __call__() (email.headerregistry.HeaderRegistry method): email headerregistry Custom Header Objects.
                                                             (line  389)
* __call__() (object method):            Emulating callable objects.
                                                             (line    6)
* __call__() (object method) <1>:        Calls.              (line  147)
* __call__() (weakref.finalize method):  weakref — Weak references.
                                                             (line  264)
* __cause__ (exception attribute):       The raise statement.
                                                             (line   30)
* __cause__ (traceback.TracebackException attribute): TracebackException Objects.
                                                             (line   21)
* __ceil__() (fractions.Fraction method): fractions — Rational numbers.
                                                             (line  163)
* __ceil__() (object method):            Emulating numeric types.
                                                             (line  141)
* __classcell__ (class namespace entry): Creating the class object.
                                                             (line    6)
* __class_getitem__() (object class method): Emulating generic types.
                                                             (line   32)
* __class__ (instance attribute):        The standard type hierarchy.
                                                             (line  630)
* __class__ (instance attribute) <1>:    Special Attributes. (line   15)
* __class__ (method cell):               Creating the class object.
                                                             (line    6)
* __class__ (module attribute):          Customizing module attribute access.
                                                             (line    6)
* __class__ (unittest.mock.Mock attribute): The Mock Class.  (line  537)
* __closure__ (function attribute):      The standard type hierarchy.
                                                             (line  309)
* __code__ (function attribute):         The standard type hierarchy.
                                                             (line  309)
* __code__ (function object attribute):  Code Objects.       (line    6)
* __complex__() (object method):         Emulating numeric types.
                                                             (line  119)
* __concat__() (in module operator):     operator — Standard operators as functions.
                                                             (line  172)
* __contains__() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  179)
* __contains__() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  300)
* __contains__() (in module operator):   operator — Standard operators as functions.
                                                             (line  177)
* __contains__() (mailbox.Mailbox method): Mailbox objects.  (line  195)
* __contains__() (object method):        Emulating container types.
                                                             (line  155)
* __context__ (exception attribute):     The raise statement.
                                                             (line   30)
* __context__ (traceback.TracebackException attribute): TracebackException Objects.
                                                             (line   25)
* __copy__() (copy protocol):            copy — Shallow and deep copy operations.
                                                             (line   73)
* __debug__:                             The assert statement.
                                                             (line   21)
* __debug__ (built-in variable):         Built-in Constants. (line   63)
* __deepcopy__() (copy protocol):        copy — Shallow and deep copy operations.
                                                             (line   73)
* __defaults__ (function attribute):     The standard type hierarchy.
                                                             (line  309)
* __delattr__() (object method):         Customizing attribute access.
                                                             (line   68)
* __delete__() (object method):          Implementing Descriptors.
                                                             (line   40)
* __delitem__() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  226)
* __delitem__() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  334)
* __delitem__() (in module operator):    operator — Standard operators as functions.
                                                             (line  187)
* __delitem__() (mailbox.Mailbox method): Mailbox objects.   (line   76)
* __delitem__() (mailbox.MH method):     MH.                 (line   76)
* __delitem__() (object method):         Emulating container types.
                                                             (line  109)
* __del__() (io.IOBase method):          I/O Base Classes.   (line  167)
* __del__() (object method):             Basic customization.
                                                             (line   53)
* __dict__ (class attribute):            The standard type hierarchy.
                                                             (line  593)
* __dict__ (function attribute):         The standard type hierarchy.
                                                             (line  309)
* __dict__ (instance attribute):         The standard type hierarchy.
                                                             (line  630)
* __dict__ (module attribute):           The standard type hierarchy.
                                                             (line  552)
* __dict__ (module attribute) <1>:       Module Objects.     (line   42)
* __dict__ (object attribute):           Special Attributes. (line   10)
* __dir__ (module attribute):            Customizing module attribute access.
                                                             (line    6)
* __dir__() (object method):             Customizing attribute access.
                                                             (line   77)
* __dir__() (unittest.mock.Mock method): The Mock Class.     (line  277)
* __displayhook__ (in module sys):       sys — System-specific parameters and functions.
                                                             (line  336)
* __divmod__() (object method):          Emulating numeric types.
                                                             (line   11)
* __doc__ (class attribute):             The standard type hierarchy.
                                                             (line  593)
* __doc__ (function attribute):          The standard type hierarchy.
                                                             (line  309)
* __doc__ (method attribute):            The standard type hierarchy.
                                                             (line  396)
* __doc__ (module attribute):            The standard type hierarchy.
                                                             (line  541)
* __doc__ (module attribute) <1>:        Module Objects.     (line   23)
* __doc__ (types.ModuleType attribute):  Standard Interpreter Types.
                                                             (line  126)
* __enter__() (contextmanager method):   Context Manager Types.
                                                             (line   12)
* __enter__() (object method):           With Statement Context Managers.
                                                             (line   21)
* __enter__() (winreg.PyHKEY method):    Registry Handle Objects.
                                                             (line   56)
* __eq__() (email.charset.Charset method): email charset Representing character sets.
                                                             (line  150)
* __eq__() (email.header.Header method): email header Internationalized headers.
                                                             (line  170)
* __eq__() (in module operator):         operator — Standard operators as functions.
                                                             (line   24)
* __eq__() (instance method):            Comparisons<2>.     (line   50)
* __eq__() (memoryview method):          Memory Views.       (line  109)
* __eq__() (object method):              Basic customization.
                                                             (line  172)
* __excepthook__ (in module sys):        sys — System-specific parameters and functions.
                                                             (line  336)
* __exit__() (contextmanager method):    Context Manager Types.
                                                             (line   32)
* __exit__() (object method):            With Statement Context Managers.
                                                             (line   27)
* __exit__() (winreg.PyHKEY method):     Registry Handle Objects.
                                                             (line   56)
* __file__:                              Import-related module attributes.
                                                             (line   67)
* __file__ (module attribute):           The standard type hierarchy.
                                                             (line  541)
* __file__ (module attribute) <1>:       Module Objects.     (line   23)
* __file__ (module attribute) <2>:       Module Objects.     (line   81)
* __float__() (object method):           Emulating numeric types.
                                                             (line  119)
* __floordiv__() (in module operator):   operator — Standard operators as functions.
                                                             (line   88)
* __floordiv__() (object method):        Emulating numeric types.
                                                             (line   11)
* __floor__() (fractions.Fraction method): fractions — Rational numbers.
                                                             (line  153)
* __floor__() (object method):           Emulating numeric types.
                                                             (line  141)
* __format__:                            Built-in Functions. (line  641)
* __format__() (datetime.date method):   date Objects.       (line  278)
* __format__() (datetime.datetime method): datetime Objects. (line  706)
* __format__() (datetime.time method):   time Objects.       (line  215)
* __format__() (ipaddress.IPv4Address method): Address objects.
                                                             (line  136)
* __format__() (ipaddress.IPv6Address method): Address objects.
                                                             (line  268)
* __format__() (object method):          Basic customization.
                                                             (line  149)
* __fspath__() (os.PathLike method):     Process Parameters. (line  121)
* __func__ (method attribute):           The standard type hierarchy.
                                                             (line  396)
* __future__:                            Glossary.           (line  485)
* __future__ (module):                   __future__ — Future statement definitions.
                                                             (line    6)
* __future__; future statement:          Future statements.  (line    6)
* __getattribute__() (object method):    Customizing attribute access.
                                                             (line   32)
* __getattr__ (module attribute):        Customizing module attribute access.
                                                             (line    6)
* __getattr__() (object method):         Customizing attribute access.
                                                             (line   10)
* __getitem__() (email.headerregistry.HeaderRegistry method): email headerregistry Custom Header Objects.
                                                             (line  384)
* __getitem__() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  189)
* __getitem__() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  309)
* __getitem__() (in module operator):    operator — Standard operators as functions.
                                                             (line  192)
* __getitem__() (mailbox.Mailbox method): Mailbox objects.   (line  140)
* __getitem__() (mapping object method): Special method names.
                                                             (line    6)
* __getitem__() (object method):         Emulating container types.
                                                             (line   77)
* __getitem__() (re.Match method):       Match Objects.      (line   83)
* __getnewargs_ex__() (object method):   Pickling Class Instances.
                                                             (line   29)
* __getnewargs__() (object method):      Pickling Class Instances.
                                                             (line   47)
* __getstate__() (copy protocol):        Handling Stateful Objects.
                                                             (line    6)
* __getstate__() (object method):        Pickling Class Instances.
                                                             (line   61)
* __get__() (object method):             Implementing Descriptors.
                                                             (line   13)
* __ge__() (in module operator):         operator — Standard operators as functions.
                                                             (line   24)
* __ge__() (instance method):            Comparisons<2>.     (line   50)
* __ge__() (object method):              Basic customization.
                                                             (line  172)
* __globals__ (function attribute):      The standard type hierarchy.
                                                             (line  309)
* __gt__() (in module operator):         operator — Standard operators as functions.
                                                             (line   24)
* __gt__() (instance method):            Comparisons<2>.     (line   50)
* __gt__() (object method):              Basic customization.
                                                             (line  172)
* __hash__() (object method):            Basic customization.
                                                             (line  220)
* __iadd__() (in module operator):       In-place Operators. (line   36)
* __iadd__() (object method):            Emulating numeric types.
                                                             (line   77)
* __iand__() (in module operator):       In-place Operators. (line   41)
* __iand__() (object method):            Emulating numeric types.
                                                             (line   77)
* __iconcat__() (in module operator):    In-place Operators. (line   46)
* __ifloordiv__() (in module operator):  In-place Operators. (line   52)
* __ifloordiv__() (object method):       Emulating numeric types.
                                                             (line   77)
* __ilshift__() (in module operator):    In-place Operators. (line   57)
* __ilshift__() (object method):         Emulating numeric types.
                                                             (line   77)
* __imatmul__() (in module operator):    In-place Operators. (line   72)
* __imatmul__() (object method):         Emulating numeric types.
                                                             (line   77)
* __imod__() (in module operator):       In-place Operators. (line   62)
* __imod__() (object method):            Emulating numeric types.
                                                             (line   77)
* __import__() (built-in function):      Built-in Functions. (line 1797)
* __import__() (in module importlib):    Functions<11>.      (line    6)
* __imul__() (in module operator):       In-place Operators. (line   67)
* __imul__() (object method):            Emulating numeric types.
                                                             (line   77)
* __index__() (in module operator):      operator — Standard operators as functions.
                                                             (line   93)
* __index__() (object method):           Emulating numeric types.
                                                             (line  127)
* __init_subclass__() (object class method): Customizing class creation.
                                                             (line   13)
* __init__() (difflib.HtmlDiff method):  difflib — Helpers for computing deltas.
                                                             (line   91)
* __init__() (logging.Handler method):   Handler Objects.    (line   13)
* __init__() (logging.logging.Formatter method): Formatters. (line   13)
* __init__() (object method):            Basic customization.
                                                             (line   37)
* __instancecheck__() (class method):    Customizing instance and subclass checks.
                                                             (line   15)
* __interactivehook__ (in module sys):   sys — System-specific parameters and functions.
                                                             (line  954)
* __int__() (object method):             Emulating numeric types.
                                                             (line  119)
* __invert__() (in module operator):     operator — Standard operators as functions.
                                                             (line   98)
* __invert__() (object method):          Emulating numeric types.
                                                             (line  111)
* __inv__() (in module operator):        operator — Standard operators as functions.
                                                             (line   98)
* __ior__() (in module operator):        In-place Operators. (line   79)
* __ior__() (object method):             Emulating numeric types.
                                                             (line   77)
* __ipow__() (in module operator):       In-place Operators. (line   84)
* __ipow__() (object method):            Emulating numeric types.
                                                             (line   77)
* __irshift__() (in module operator):    In-place Operators. (line   89)
* __irshift__() (object method):         Emulating numeric types.
                                                             (line   77)
* __isub__() (in module operator):       In-place Operators. (line   94)
* __isub__() (object method):            Emulating numeric types.
                                                             (line   77)
* __iter__() (container method):         Iterator Types.     (line   14)
* __iter__() (iterator method):          Iterator Types.     (line   29)
* __iter__() (mailbox.Mailbox method):   Mailbox objects.    (line  114)
* __iter__() (object method):            Emulating container types.
                                                             (line  123)
* __iter__() (unittest.TestSuite method): Grouping tests.    (line   60)
* __itruediv__() (in module operator):   In-place Operators. (line   99)
* __itruediv__() (object method):        Emulating numeric types.
                                                             (line   77)
* __ixor__() (in module operator):       In-place Operators. (line  104)
* __ixor__() (object method):            Emulating numeric types.
                                                             (line   77)
* __kwdefaults__ (function attribute):   The standard type hierarchy.
                                                             (line  309)
* __length_hint__() (object method):     Emulating container types.
                                                             (line   53)
* __len__() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  175)
* __len__() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  296)
* __len__() (mailbox.Mailbox method):    Mailbox objects.    (line  200)
* __len__() (mapping object method):     Basic customization.
                                                             (line  303)
* __len__() (object method):             Emulating container types.
                                                             (line   38)
* __le__() (in module operator):         operator — Standard operators as functions.
                                                             (line   24)
* __le__() (instance method):            Comparisons<2>.     (line   50)
* __le__() (object method):              Basic customization.
                                                             (line  172)
* __loader__:                            Import-related module attributes.
                                                             (line   16)
* __loader__ (module attribute):         Module Objects.     (line   23)
* __loader__ (types.ModuleType attribute): Standard Interpreter Types.
                                                             (line  130)
* __lshift__() (in module operator):     operator — Standard operators as functions.
                                                             (line  106)
* __lshift__() (object method):          Emulating numeric types.
                                                             (line   11)
* __lt__() (in module operator):         operator — Standard operators as functions.
                                                             (line   24)
* __lt__() (instance method):            Comparisons<2>.     (line   50)
* __lt__() (object method):              Basic customization.
                                                             (line  172)
* __main__ (module):                     __main__ — Top-level script environment.
                                                             (line    6)
* __matmul__() (in module operator):     operator — Standard operators as functions.
                                                             (line  121)
* __matmul__() (object method):          Emulating numeric types.
                                                             (line   11)
* __missing__():                         Mapping Types — dict.
                                                             (line   97)
* __missing__() (collections.defaultdict method): defaultdict objects.
                                                             (line   22)
* __missing__() (object method):         Emulating container types.
                                                             (line  118)
* __module__ (class attribute):          The standard type hierarchy.
                                                             (line  593)
* __module__ (function attribute):       The standard type hierarchy.
                                                             (line  309)
* __module__ (method attribute):         The standard type hierarchy.
                                                             (line  396)
* __mod__() (in module operator):        operator — Standard operators as functions.
                                                             (line  111)
* __mod__() (object method):             Emulating numeric types.
                                                             (line   11)
* __mro__ (class attribute):             Special Attributes. (line   35)
* __mul__() (in module operator):        operator — Standard operators as functions.
                                                             (line  116)
* __mul__() (object method):             Emulating numeric types.
                                                             (line   11)
* __name__:                              Import-related module attributes.
                                                             (line   10)
* __name__ (class attribute):            The standard type hierarchy.
                                                             (line  593)
* __name__ (definition attribute):       Special Attributes. (line   23)
* __name__ (function attribute):         The standard type hierarchy.
                                                             (line  309)
* __name__ (method attribute):           The standard type hierarchy.
                                                             (line  396)
* __name__ (module attribute):           The standard type hierarchy.
                                                             (line  541)
* __name__ (module attribute) <1>:       Module Objects.     (line   23)
* __name__ (module attribute) <2>:       Module Objects.     (line   55)
* __name__ (types.ModuleType attribute): Standard Interpreter Types.
                                                             (line  148)
* __neg__() (in module operator):        operator — Standard operators as functions.
                                                             (line  128)
* __neg__() (object method):             Emulating numeric types.
                                                             (line  111)
* __new__() (object method):             Basic customization.
                                                             (line    6)
* __next__() (csv.csvreader method):     Reader Objects.     (line    9)
* __next__() (generator method):         Generator-iterator methods.
                                                             (line   12)
* __next__() (iterator method):          Iterator Types.     (line   37)
* __ne__() (email.charset.Charset method): email charset Representing character sets.
                                                             (line  155)
* __ne__() (email.header.Header method): email header Internationalized headers.
                                                             (line  175)
* __ne__() (in module operator):         operator — Standard operators as functions.
                                                             (line   24)
* __ne__() (instance method):            Comparisons<2>.     (line   50)
* __ne__() (object method):              Basic customization.
                                                             (line  172)
* __not__() (in module operator):        operator — Standard operators as functions.
                                                             (line   49)
* __origin__ (genericalias attribute):   Special Attributes of Generic Alias.
                                                             (line    8)
* __or__() (in module operator):         operator — Standard operators as functions.
                                                             (line  133)
* __or__() (object method):              Emulating numeric types.
                                                             (line   11)
* __package__:                           Import-related module attributes.
                                                             (line   23)
* __package__ (module attribute):        Module Objects.     (line   23)
* __package__ (types.ModuleType attribute): Standard Interpreter Types.
                                                             (line  153)
* __parameters__ (genericalias attribute): Special Attributes of Generic Alias.
                                                             (line   24)
* __path__:                              Import-related module attributes.
                                                             (line   56)
* __pos__() (in module operator):        operator — Standard operators as functions.
                                                             (line  138)
* __pos__() (object method):             Emulating numeric types.
                                                             (line  111)
* __pow__() (in module operator):        operator — Standard operators as functions.
                                                             (line  143)
* __pow__() (object method):             Emulating numeric types.
                                                             (line   11)
* __prepare__ (metaclass method):        Preparing the class namespace.
                                                             (line    6)
* __qualname__ (definition attribute):   Special Attributes. (line   28)
* __radd__() (object method):            Emulating numeric types.
                                                             (line   41)
* __rand__() (object method):            Emulating numeric types.
                                                             (line   41)
* __rdivmod__() (object method):         Emulating numeric types.
                                                             (line   41)
* __reduce_ex__() (object method):       Pickling Class Instances.
                                                             (line  161)
* __reduce__() (object method):          Pickling Class Instances.
                                                             (line  106)
* __repr__() (multiprocessing.managers.BaseProxy method): Proxy Objects.
                                                             (line  145)
* __repr__() (netrc.netrc method):       netrc Objects.      (line   16)
* __repr__() (object method):            Basic customization.
                                                             (line  112)
* __reversed__() (object method):        Emulating container types.
                                                             (line  134)
* __rfloordiv__() (object method):       Emulating numeric types.
                                                             (line   41)
* __rlshift__() (object method):         Emulating numeric types.
                                                             (line   41)
* __rmatmul__() (object method):         Emulating numeric types.
                                                             (line   41)
* __rmod__() (object method):            Emulating numeric types.
                                                             (line   41)
* __rmul__() (object method):            Emulating numeric types.
                                                             (line   41)
* __ror__() (object method):             Emulating numeric types.
                                                             (line   41)
* __round__() (fractions.Fraction method): fractions — Rational numbers.
                                                             (line  168)
* __round__() (object method):           Emulating numeric types.
                                                             (line  141)
* __rpow__() (object method):            Emulating numeric types.
                                                             (line   41)
* __rrshift__() (object method):         Emulating numeric types.
                                                             (line   41)
* __rshift__() (in module operator):     operator — Standard operators as functions.
                                                             (line  148)
* __rshift__() (object method):          Emulating numeric types.
                                                             (line   11)
* __rsub__() (object method):            Emulating numeric types.
                                                             (line   41)
* __rtruediv__() (object method):        Emulating numeric types.
                                                             (line   41)
* __rxor__() (object method):            Emulating numeric types.
                                                             (line   41)
* __self__ (method attribute):           The standard type hierarchy.
                                                             (line  396)
* __setattr__() (object method):         Customizing attribute access.
                                                             (line   53)
* __setitem__() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  204)
* __setitem__() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  320)
* __setitem__() (in module operator):    operator — Standard operators as functions.
                                                             (line  201)
* __setitem__() (mailbox.Mailbox method): Mailbox objects.   (line   90)
* __setitem__() (mailbox.Maildir method): Maildir.           (line   91)
* __setitem__() (object method):         Emulating container types.
                                                             (line  100)
* __setstate__() (copy protocol):        Handling Stateful Objects.
                                                             (line    6)
* __setstate__() (object method):        Pickling Class Instances.
                                                             (line   70)
* __set_name__() (object method):        Implementing Descriptors.
                                                             (line   45)
* __set__() (object method):             Implementing Descriptors.
                                                             (line   31)
* __slots__:                             Glossary.           (line 1153)
* __spec__:                              Import-related module attributes.
                                                             (line   40)
* __spec__ (types.ModuleType attribute): Standard Interpreter Types.
                                                             (line  174)
* __stderr__ (in module sys):            sys — System-specific parameters and functions.
                                                             (line 1537)
* __stdin__ (in module sys):             sys — System-specific parameters and functions.
                                                             (line 1537)
* __stdout__ (in module sys):            sys — System-specific parameters and functions.
                                                             (line 1537)
* __str__() (datetime.date method):      date Objects.       (line  251)
* __str__() (datetime.datetime method):  datetime Objects.   (line  676)
* __str__() (datetime.time method):      time Objects.       (line  205)
* __str__() (email.charset.Charset method): email charset Representing character sets.
                                                             (line  145)
* __str__() (email.header.Header method): email header Internationalized headers.
                                                             (line  158)
* __str__() (email.headerregistry.Address method): email headerregistry Custom Header Objects.
                                                             (line  447)
* __str__() (email.headerregistry.Group method): email headerregistry Custom Header Objects.
                                                             (line  482)
* __str__() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line   95)
* __str__() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  101)
* __str__() (multiprocessing.managers.BaseProxy method): Proxy Objects.
                                                             (line  149)
* __str__() (object method):             Basic customization.
                                                             (line  128)
* __subclasscheck__() (class method):    Customizing instance and subclass checks.
                                                             (line   21)
* __subclasses__() (class method):       Special Attributes. (line   46)
* __subclasshook__() (abc.ABCMeta method): abc — Abstract Base Classes.
                                                             (line   92)
* __sub__() (in module operator):        operator — Standard operators as functions.
                                                             (line  153)
* __sub__() (object method):             Emulating numeric types.
                                                             (line   11)
* __suppress_context__ (traceback.TracebackException attribute): TracebackException Objects.
                                                             (line   30)
* __traceback__ (exception attribute):   The raise statement.
                                                             (line    6)
* __truediv__() (importlib.abc.Traversable method): importlib abc – Abstract base classes related to import.
                                                             (line  641)
* __truediv__() (in module operator):    operator — Standard operators as functions.
                                                             (line  158)
* __truediv__() (object method):         Emulating numeric types.
                                                             (line   11)
* __trunc__() (object method):           Emulating numeric types.
                                                             (line  141)
* __unraisablehook__ (in module sys):    sys — System-specific parameters and functions.
                                                             (line  336)
* __xor__() (in module operator):        operator — Standard operators as functions.
                                                             (line  164)
* __xor__() (object method):             Emulating numeric types.
                                                             (line   11)
* {} (curly brackets); dictionary expression: Dictionary displays.
                                                             (line    6)
* {} (curly brackets); in formatted string literal: String literal concatenation.
                                                             (line   24)
* {} (curly brackets); in regular expressions: Regular Expression Syntax.
                                                             (line   95)
* {} (curly brackets); in string formatting: Format String Syntax.
                                                             (line   13)
* {} (curly brackets); set expression:   Set displays.       (line    6)
* | (vertical bar); in regular expressions: Regular Expression Syntax.
                                                             (line  186)
* |=; augmented assignment:              Augmented assignment statements.
                                                             (line    6)
* ~ (tilde); home directory expansion:   os path — Common pathname manipulations.
                                                             (line  135)
* A (in module re):                      Module Contents.    (line   44)
* a-LAW:                                 audioop — Manipulate raw audio data.
                                                             (line   17)
* A-LAW:                                 aifc — Read and write AIFF and AIFC files.
                                                             (line  160)
* A-LAW <1>:                             sndhdr — Determine type of sound file.
                                                             (line    8)
* a2b_base64() (in module binascii):     binascii — Convert between binary and ASCII.
                                                             (line   41)
* a2b_hex() (in module binascii):        binascii — Convert between binary and ASCII.
                                                             (line  169)
* a2b_hqx() (in module binascii):        binascii — Convert between binary and ASCII.
                                                             (line   76)
* a2b_qp() (in module binascii):         binascii — Convert between binary and ASCII.
                                                             (line   55)
* a2b_uu() (in module binascii):         binascii — Convert between binary and ASCII.
                                                             (line   26)
* a85decode() (in module base64):        base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  163)
* a85encode() (in module base64):        base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  140)
* ABC (class in abc):                    abc — Abstract Base Classes.
                                                             (line   26)
* abc (module):                          abc — Abstract Base Classes.
                                                             (line    6)
* ABCMeta (class in abc):                abc — Abstract Base Classes.
                                                             (line   52)
* abiflags (in module sys):              sys — System-specific parameters and functions.
                                                             (line   12)
* abort():                               Process Control.    (line    8)
* abort() (asyncio.DatagramTransport method): Datagram Transports.
                                                             (line   15)
* abort() (asyncio.WriteTransport method): Write-only Transports.
                                                             (line    6)
* abort() (ftplib.FTP method):           FTP Objects.        (line   61)
* abort() (in module os):                Process Management. (line   16)
* abort() (threading.Barrier method):    Barrier Objects.    (line   82)
* above() (curses.panel.Panel method):   Panel Objects.      (line   13)
* ABOVE_NORMAL_PRIORITY_CLASS (in module subprocess): Windows Constants.
                                                             (line   52)
* abs() (built-in function):             Built-in Functions. (line   55)
* abs() (decimal.Context method):        Context objects.    (line  230)
* abs() (in module operator):            operator — Standard operators as functions.
                                                             (line   73)
* abspath() (in module os.path):         os path — Common pathname manipulations.
                                                             (line   54)
* abstract base class:                   Glossary.           (line   32)
* AbstractAsyncContextManager (class in contextlib): Utilities.
                                                             (line   19)
* AbstractBasicAuthHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  324)
* AbstractChildWatcher (class in asyncio): Process Watchers. (line   39)
* abstractclassmethod() (in module abc): abc — Abstract Base Classes.
                                                             (line  237)
* AbstractContextManager (class in contextlib): Utilities.   (line    8)
* AbstractDigestAuthHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  363)
* AbstractEventLoop (class in asyncio):  Event Loop Implementations.
                                                             (line   40)
* AbstractEventLoopPolicy (class in asyncio): Policy Objects.
                                                             (line    8)
* AbstractFormatter (class in formatter): Formatter Implementations.
                                                             (line   18)
* abstractmethod() (in module abc):      abc — Abstract Base Classes.
                                                             (line  161)
* abstractproperty() (in module abc):    abc — Abstract Base Classes.
                                                             (line  281)
* AbstractSet (class in typing):         Corresponding to collections in collections abc.
                                                             (line    6)
* abstractstaticmethod() (in module abc): abc — Abstract Base Classes.
                                                             (line  259)
* AbstractWriter (class in formatter):   Writer Implementations.
                                                             (line   16)
* accept() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  231)
* accept() (multiprocessing.connection.Listener method): Listeners and Clients.
                                                             (line   84)
* accept() (socket.socket method):       Socket Objects.     (line   13)
* access() (in module os):               Files and Directories.
                                                             (line   51)
* accumulate() (in module itertools):    Itertool functions. (line   10)
* aclose() (agen method):                Asynchronous generator-iterator methods.
                                                             (line   55)
* aclose() (contextlib.AsyncExitStack method): Utilities.    (line  478)
* acos() (in module cmath):              Trigonometric functions<2>.
                                                             (line    6)
* acos() (in module math):               Trigonometric functions.
                                                             (line    6)
* acosh() (in module cmath):             Hyperbolic functions<2>.
                                                             (line    6)
* acosh() (in module math):              Hyperbolic functions.
                                                             (line    9)
* acquire() (asyncio.Condition method):  Condition.          (line   48)
* acquire() (asyncio.Lock method):       Lock.               (line   36)
* acquire() (asyncio.Semaphore method):  Semaphore.          (line   43)
* acquire() (logging.Handler method):    Handler Objects.    (line   26)
* acquire() (multiprocessing.Lock method): Synchronization primitives.
                                                             (line   64)
* acquire() (multiprocessing.RLock method): Synchronization primitives.
                                                             (line  118)
* acquire() (threading.Condition method): Condition Objects. (line   85)
* acquire() (threading.Lock method):     Lock Objects.       (line   43)
* acquire() (threading.RLock method):    RLock Objects.      (line   35)
* acquire() (threading.Semaphore method): Semaphore Objects. (line   34)
* acquire() (_thread.lock method):       _thread — Low-level threading API.
                                                             (line  126)
* acquire_lock() (in module imp):        imp — Access the import internals.
                                                             (line  277)
* Action (class in argparse):            Action classes.     (line   11)
* action (optparse.Option attribute):    Option attributes.  (line   11)
* ACTIONS (optparse.Option attribute):   Adding new actions. (line   31)
* active_children() (in module multiprocessing): Miscellaneous<3>.
                                                             (line    6)
* active_count() (in module threading):  threading — Thread-based parallelism.
                                                             (line   33)
* actual() (tkinter.font.Font method):   tkinter font — Tkinter font wrapper.
                                                             (line   47)
* Add (class in ast):                    Expressions<2>.     (line   54)
* add() (decimal.Context method):        Context objects.    (line  234)
* add() (frozenset method):              Set Types — set frozenset.
                                                             (line  195)
* add() (graphlib.TopologicalSorter method): graphlib — Functionality to operate with graph-like structures.
                                                             (line   81)
* add() (in module audioop):             audioop — Manipulate raw audio data.
                                                             (line   31)
* add() (in module operator):            operator — Standard operators as functions.
                                                             (line   78)
* add() (mailbox.Mailbox method):        Mailbox objects.    (line   59)
* add() (mailbox.Maildir method):        Maildir.            (line   91)
* add() (msilib.RadioButtonGroup method): GUI classes.       (line   34)
* add() (pstats.Stats method):           The Stats Class.    (line   49)
* add() (tarfile.TarFile method):        TarFile Objects.    (line  202)
* add() (tkinter.ttk.Notebook method):   ttk Notebook.       (line    8)
* addAsyncCleanup() (unittest.IsolatedAsyncioTestCase method): Test cases.
                                                             (line  840)
* addaudithook() (in module sys):        sys — System-specific parameters and functions.
                                                             (line   23)
* addch() (curses.window method):        Window Objects.     (line    9)
* addClassCleanup() (unittest.TestCase class method): Test cases.
                                                             (line  776)
* addCleanup() (unittest.TestCase method): Test cases.       (line  746)
* addcomponent() (turtle.Shape method):  Public classes.     (line   66)
* addError() (unittest.TestResult method): Loading and running tests.
                                                             (line  351)
* addExpectedFailure() (unittest.TestResult method): Loading and running tests.
                                                             (line  387)
* addFailure() (unittest.TestResult method): Loading and running tests.
                                                             (line  362)
* addfile() (tarfile.TarFile method):    TarFile Objects.    (line  220)
* addFilter() (logging.Handler method):  Handler Objects.    (line   52)
* addFilter() (logging.Logger method):   Logger Objects.     (line  263)
* addHandler() (logging.Logger method):  Logger Objects.     (line  280)
* addinfourl (class in urllib.response): urllib response — Response classes used by urllib.
                                                             (line   12)
* addition:                              Binary arithmetic operations.
                                                             (line   69)
* addLevelName() (in module logging):    Module-Level Functions.
                                                             (line  190)
* addModuleCleanup() (in module unittest): setUpModule and tearDownModule.
                                                             (line   22)
* addnstr() (curses.window method):      Window Objects.     (line   23)
* AddPackagePath() (in module modulefinder): modulefinder — Find modules used by a script.
                                                             (line   16)
* addr (smtpd.SMTPChannel attribute):    SMTPChannel Objects.
                                                             (line   52)
* Address (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line  402)
* address (email.headerregistry.SingleAddressHeader attribute): email headerregistry Custom Header Objects.
                                                             (line  222)
* address (multiprocessing.connection.Listener attribute): Listeners and Clients.
                                                             (line   99)
* address (multiprocessing.managers.BaseManager attribute): Managers.
                                                             (line  120)
* addresses (email.headerregistry.AddressHeader attribute): email headerregistry Custom Header Objects.
                                                             (line  195)
* addresses (email.headerregistry.Group attribute): email headerregistry Custom Header Objects.
                                                             (line  477)
* AddressHeader (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line  180)
* addressof() (in module ctypes):        Utility functions.  (line    6)
* AddressValueError:                     Custom Exceptions.  (line    9)
* address_exclude() (ipaddress.IPv4Network method): Network objects.
                                                             (line  160)
* address_exclude() (ipaddress.IPv6Network method): Network objects.
                                                             (line  342)
* address_family (socketserver.BaseServer attribute): Server Objects<2>.
                                                             (line   65)
* address_string() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  326)
* addr_spec (email.headerregistry.Address attribute): email headerregistry Custom Header Objects.
                                                             (line  441)
* addshape() (in module turtle):         Settings and special methods.
                                                             (line   71)
* addsitedir() (in module site):         Module contents<4>. (line   51)
* addSkip() (unittest.TestResult method): Loading and running tests.
                                                             (line  379)
* addstr() (curses.window method):       Window Objects.     (line   31)
* addSubTest() (unittest.TestResult method): Loading and running tests.
                                                             (line  405)
* addSuccess() (unittest.TestResult method): Loading and running tests.
                                                             (line  373)
* addTest() (unittest.TestSuite method): Grouping tests.     (line   25)
* addTests() (unittest.TestSuite method): Grouping tests.    (line   30)
* addTypeEqualityFunc() (unittest.TestCase method): Test cases.
                                                             (line  564)
* addUnexpectedSuccess() (unittest.TestResult method): Loading and running tests.
                                                             (line  397)
* add_alias() (in module email.charset): email charset Representing character sets.
                                                             (line  193)
* add_alternative() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  640)
* add_argument() (argparse.ArgumentParser method): The add_argument method.
                                                             (line    6)
* add_argument_group() (argparse.ArgumentParser method): Argument groups.
                                                             (line    6)
* add_attachment() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  652)
* add_cgi_vars() (wsgiref.handlers.BaseHandler method): wsgiref handlers – server/gateway base classes.
                                                             (line  132)
* add_charset() (in module email.charset): email charset Representing character sets.
                                                             (line  164)
* add_child_handler() (asyncio.AbstractChildWatcher method): Process Watchers.
                                                             (line   41)
* add_codec() (in module email.charset): email charset Representing character sets.
                                                             (line  202)
* add_cookie_header() (http.cookiejar.CookieJar method): CookieJar and FileCookieJar Objects.
                                                             (line   11)
* add_data() (in module msilib):         msilib — Read and write Microsoft Installer files.
                                                             (line   74)
* add_dll_directory() (in module os):    Process Management. (line   24)
* add_done_callback() (asyncio.Future method): Future Object.
                                                             (line   77)
* add_done_callback() (asyncio.Task method): Task Object.    (line  151)
* add_done_callback() (concurrent.futures.Future method): Future Objects.
                                                             (line   70)
* add_fallback() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line   28)
* add_file() (msilib.Directory method):  Directory Objects.  (line   30)
* add_flag() (mailbox.MaildirMessage method): MaildirMessage.
                                                             (line   76)
* add_flag() (mailbox.mboxMessage method): mboxMessage.      (line   79)
* add_flag() (mailbox.MMDFMessage method): MMDFMessage.      (line   78)
* add_flowing_data() (formatter.formatter method): The Formatter Interface.
                                                             (line   43)
* add_folder() (mailbox.Maildir method): Maildir.            (line   71)
* add_folder() (mailbox.MH method):      MH.                 (line   42)
* add_get_handler() (email.contentmanager.ContentManager method): email contentmanager Managing MIME Content.
                                                             (line   75)
* add_handler() (urllib.request.OpenerDirector method): OpenerDirector Objects.
                                                             (line    8)
* add_header() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  260)
* add_header() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  368)
* add_header() (urllib.request.Request method): Request Objects.
                                                             (line   79)
* add_header() (wsgiref.headers.Headers method): wsgiref headers – WSGI response header tools.
                                                             (line   61)
* add_history() (in module readline):    History list.       (line   38)
* add_hor_rule() (formatter.formatter method): The Formatter Interface.
                                                             (line   36)
* add_include_dir() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line   96)
* add_label() (mailbox.BabylMessage method): BabylMessage.   (line   55)
* add_label_data() (formatter.formatter method): The Formatter Interface.
                                                             (line   59)
* add_library() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  113)
* add_library_dir() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  135)
* add_line_break() (formatter.formatter method): The Formatter Interface.
                                                             (line   31)
* add_link_object() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  180)
* add_literal_data() (formatter.formatter method): The Formatter Interface.
                                                             (line   53)
* add_mutually_exclusive_group() (argparse.ArgumentParser method): Mutual exclusion.
                                                             (line    6)
* add_option() (optparse.OptionParser method): Defining options.
                                                             (line   14)
* add_parent() (urllib.request.BaseHandler method): BaseHandler Objects.
                                                             (line   10)
* add_password() (urllib.request.HTTPPasswordMgr method): HTTPPasswordMgr Objects.
                                                             (line    9)
* add_password() (urllib.request.HTTPPasswordMgrWithPriorAuth method): HTTPPasswordMgrWithPriorAuth Objects.
                                                             (line   10)
* add_reader() (asyncio.loop method):    Watching file descriptors.
                                                             (line    6)
* add_related() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  627)
* add_runtime_library_dir() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  150)
* add_section() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line   86)
* add_section() (configparser.RawConfigParser method): RawConfigParser Objects.
                                                             (line   26)
* add_sequence() (mailbox.MHMessage method): MHMessage.      (line   41)
* add_set_handler() (email.contentmanager.ContentManager method): email contentmanager Managing MIME Content.
                                                             (line   80)
* add_signal_handler() (asyncio.loop method): Unix signals.  (line    6)
* add_stream() (in module msilib):       msilib — Read and write Microsoft Installer files.
                                                             (line  104)
* add_subparsers() (argparse.ArgumentParser method): Sub-commands.
                                                             (line    6)
* add_tables() (in module msilib):       msilib — Read and write Microsoft Installer files.
                                                             (line   95)
* add_type() (in module mimetypes):      mimetypes — Map filenames to MIME types.
                                                             (line  107)
* add_unredirected_header() (urllib.request.Request method): Request Objects.
                                                             (line   90)
* add_writer() (asyncio.loop method):    Watching file descriptors.
                                                             (line   16)
* adjusted() (decimal.Decimal method):   Decimal objects.    (line  114)
* adler32() (in module zlib):            zlib — Compression compatible with gzip.
                                                             (line   28)
* ADPCM, Intel/DVI:                      audioop — Manipulate raw audio data.
                                                             (line   17)
* adpcm2lin() (in module audioop):       audioop — Manipulate raw audio data.
                                                             (line   38)
* AF_ALG (in module socket):             Constants<8>.       (line  202)
* AF_CAN (in module socket):             Constants<8>.       (line   92)
* AF_INET (in module socket):            Constants<8>.       (line   11)
* AF_INET6 (in module socket):           Constants<8>.       (line   11)
* AF_LINK (in module socket):            Constants<8>.       (line  226)
* AF_PACKET (in module socket):          Constants<8>.       (line  163)
* AF_QIPCRTR (in module socket):         Constants<8>.       (line  254)
* AF_RDS (in module socket):             Constants<8>.       (line  173)
* AF_UNIX (in module socket):            Constants<8>.       (line   11)
* AF_VSOCK (in module socket):           Constants<8>.       (line  213)
* aifc (module):                         aifc — Read and write AIFF and AIFC files.
                                                             (line    6)
* aifc() (aifc.aifc method):             aifc — Read and write AIFF and AIFC files.
                                                             (line  134)
* AIFF:                                  aifc — Read and write AIFF and AIFC files.
                                                             (line    8)
* AIFF <1>:                              chunk — Read IFF chunked data.
                                                             (line    8)
* aiff() (aifc.aifc method):             aifc — Read and write AIFF and AIFC files.
                                                             (line  128)
* AIFF-C:                                aifc — Read and write AIFF and AIFC files.
                                                             (line    8)
* AIFF-C <1>:                            chunk — Read IFF chunked data.
                                                             (line    8)
* alarm() (in module signal):            Module contents<2>. (line  224)
* alaw2lin() (in module audioop):        audioop — Manipulate raw audio data.
                                                             (line   45)
* AlertDescription (class in ssl):       Constants<9>.       (line  494)
* ALERT_DESCRIPTION_HANDSHAKE_FAILURE (in module ssl): Constants<9>.
                                                             (line  480)
* ALERT_DESCRIPTION_INTERNAL_ERROR (in module ssl): Constants<9>.
                                                             (line  480)
* algorithms_available (in module hashlib): Hash algorithms. (line   91)
* algorithms_guaranteed (in module hashlib): Hash algorithms.
                                                             (line   82)
* alias (class in ast):                  Imports.            (line   40)
* alias (pdb command):                   Debugger Commands.  (line  283)
* alignment() (in module ctypes):        Utility functions.  (line   14)
* alive (weakref.finalize attribute):    weakref — Weak references.
                                                             (line  281)
* all() (built-in function):             Built-in Functions. (line   62)
* allocate_lock() (in module _thread):   _thread — Low-level threading API.
                                                             (line   68)
* allocfunc (C type):                    Slot Type typedefs. (line    6)
* allowed_domains() (http.cookiejar.DefaultCookiePolicy method): DefaultCookiePolicy Objects.
                                                             (line   65)
* allow_reuse_address (socketserver.BaseServer attribute): Server Objects<2>.
                                                             (line   92)
* all_errors (in module ftplib):         ftplib — FTP protocol client.
                                                             (line  152)
* all_features (in module xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line   90)
* all_frames (tracemalloc.Filter attribute): Filter.         (line   57)
* all_properties (in module xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line  122)
* all_suffixes() (in module importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line   57)
* all_tasks() (in module asyncio):       Introspection.      (line   16)
* alt() (in module curses.ascii):        curses ascii — Utilities for ASCII characters.
                                                             (line  218)
* altsep (in module os):                 Miscellaneous System Information.
                                                             (line  102)
* altzone (in module time):              Timezone Constants. (line    6)
* ALT_DIGITS (in module locale):         locale — Internationalization services.
                                                             (line  296)
* ALWAYS_EQ (in module test.support):    test support — Utilities for the Python test suite.
                                                             (line  200)
* ALWAYS_TYPED_ACTIONS (optparse.Option attribute): Adding new actions.
                                                             (line   43)
* AMPER (in module token):               token — Constants used with Python parse trees.
                                                             (line  102)
* AMPEREQUAL (in module token):          token — Constants used with Python parse trees.
                                                             (line  190)
* And (class in ast):                    Expressions<2>.     (line   87)
* and_() (in module operator):           operator — Standard operators as functions.
                                                             (line   83)
* AnnAssign (class in ast):              Statements.         (line   43)
* Annotated (in module typing):          Special forms.      (line  222)
* annotated; assignment:                 Annotated assignment statements.
                                                             (line    6)
* annotation:                            Glossary.           (line   47)
* annotation (inspect.Parameter attribute): Introspecting callables with the Signature object.
                                                             (line  175)
* announce() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  503)
* anonymous; function:                   Lambdas.            (line    6)
* answer_challenge() (in module multiprocessing.connection): Listeners and Clients.
                                                             (line   25)
* anticipate_failure() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  633)
* Any (in module typing):                Special types.      (line    8)
* ANY (in module unittest.mock):         ANY.                (line    6)
* any() (built-in function):             Built-in Functions. (line   73)
* AnyStr (in module typing):             Building generic types.
                                                             (line   73)
* apilevel (in module sqlite3):          Module functions and constants.
                                                             (line    6)
* api_version (in module sys):           sys — System-specific parameters and functions.
                                                             (line 1654)
* apop() (poplib.POP3 method):           POP3 Objects.       (line   41)
* APPDATA:                               PEP 370 Per-user site-packages Directory.
                                                             (line   26)
* append() (array.array method):         array — Efficient arrays of numeric values.
                                                             (line  113)
* append() (collections.deque method):   deque objects.      (line   35)
* append() (email.header.Header method): email header Internationalized headers.
                                                             (line   96)
* append() (imaplib.IMAP4 method):       IMAP4 Objects.      (line   33)
* append() (msilib.CAB method):          CAB Objects.        (line   15)
* append() (pipes.Template method):      Template Objects.   (line   22)
* append() (sequence method):            Mutable Sequence Types.
                                                             (line   16)
* append() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line   87)
* appendChild() (xml.dom.Node method):   Node Objects.       (line  115)
* appendleft() (collections.deque method): deque objects.    (line   39)
* append_history_file() (in module readline): History file.  (line   20)
* application_uri() (in module wsgiref.util): wsgiref util – WSGI environment utilities.
                                                             (line   32)
* apply (2to3 fixer):                    Fixers.             (line   10)
* apply() (multiprocessing.pool.Pool method): Process Pools. (line   63)
* apply_async() (multiprocessing.pool.Pool method): Process Pools.
                                                             (line   71)
* apply_defaults() (inspect.BoundArguments method): Introspecting callables with the Signature object.
                                                             (line  315)
* architecture() (in module platform):   Cross Platform.     (line    6)
* archive (zipimport.zipimporter attribute): zipimporter Objects.
                                                             (line   69)
* aRepr (in module reprlib):             reprlib — Alternate repr implementation.
                                                             (line   24)
* arg (class in ast):                    Function and class definitions.
                                                             (line   69)
* argparse (module):                     argparse — Parser for command-line options arguments and sub-commands.
                                                             (line    6)
* args (BaseException attribute):        Base classes.       (line   17)
* args (functools.partial attribute):    partial Objects.    (line   15)
* args (inspect.BoundArguments attribute): Introspecting callables with the Signature object.
                                                             (line  301)
* args (pdb command):                    Debugger Commands.  (line  229)
* args (subprocess.CompletedProcess attribute): Using the subprocess Module.
                                                             (line   96)
* args (subprocess.Popen attribute):     Popen Objects.      (line   99)
* args_from_interpreter_flags() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  446)
* argtypes (ctypes._FuncPtr attribute):  Foreign functions.  (line   36)
* argument:                              Glossary.           (line   62)
* argument; call semantics:              Slicings.           (line   38)
* argument; difference from parameter:   How can I pass optional or keyword parameters from one function to another?.
                                                             (line   17)
* argument; function definition:         Function definitions.
                                                             (line   56)
* ArgumentDefaultsHelpFormatter (class in argparse): formatter_class.
                                                             (line   10)
* ArgumentError:                         Foreign functions.  (line   83)
* ArgumentParser (class in argparse):    ArgumentParser objects.
                                                             (line    6)
* arguments (class in ast):              Function and class definitions.
                                                             (line   50)
* arguments (inspect.BoundArguments attribute): Introspecting callables with the Signature object.
                                                             (line  282)
* argv (in module sys):                  sys — System-specific parameters and functions.
                                                             (line   56)
* argv (in module sys) <1>:              Process-wide parameters.
                                                             (line  217)
* arithmetic:                            Numeric Types — int float complex.
                                                             (line   27)
* arithmetic; conversion:                Arithmetic conversions.
                                                             (line    6)
* ArithmeticError:                       Base classes.       (line   43)
* array (class in array):                array — Efficient arrays of numeric values.
                                                             (line   75)
* Array (class in ctypes):               Arrays and pointers.
                                                             (line    6)
* array (module):                        array — Efficient arrays of numeric values.
                                                             (line    6)
* Array() (in module multiprocessing):   Shared ctypes Objects.
                                                             (line   42)
* Array() (in module multiprocessing.sharedctypes): The multiprocessing sharedctypes module.
                                                             (line   51)
* Array() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  196)
* arrays:                                array — Efficient arrays of numeric values.
                                                             (line    6)
* arraysize (sqlite3.Cursor attribute):  Cursor Objects.     (line  201)
* article() (nntplib.NNTP method):       Methods<3>.         (line  241)
* as; except clause:                     The try statement.  (line   40)
* as; import statement:                  The import statement.
                                                             (line   38)
* as; with statement:                    The with statement. (line    6)
* ASCII:                                 Notation.           (line   31)
* ASCII <1>:                             Literals.           (line    8)
* ASCII (in module re):                  Module Contents.    (line   44)
* ascii() (built-in function):           Built-in Functions. (line   84)
* ascii() (in module curses.ascii):      curses ascii — Utilities for ASCII characters.
                                                             (line  209)
* ascii_letters (in module string):      String constants.   (line    8)
* ascii_lowercase (in module string):    String constants.   (line   14)
* ascii_uppercase (in module string):    String constants.   (line   19)
* asctime() (in module time):            Functions<3>.       (line    6)
* asdict() (in module dataclasses):      Module-level decorators classes and functions.
                                                             (line  268)
* asend() (agen method):                 Asynchronous generator-iterator methods.
                                                             (line   28)
* asin() (in module cmath):              Trigonometric functions<2>.
                                                             (line   13)
* asin() (in module math):               Trigonometric functions.
                                                             (line   11)
* asinh() (in module cmath):             Hyperbolic functions<2>.
                                                             (line   12)
* asinh() (in module math):              Hyperbolic functions.
                                                             (line   13)
* askcolor() (in module tkinter.colorchooser): tkinter colorchooser — Color choosing dialog.
                                                             (line   17)
* askdirectory() (in module tkinter.filedialog): Native Load/Save Dialogs.
                                                             (line   54)
* askfloat() (in module tkinter.simpledialog): tkinter simpledialog — Standard Tkinter input dialogs.
                                                             (line   14)
* askinteger() (in module tkinter.simpledialog): tkinter simpledialog — Standard Tkinter input dialogs.
                                                             (line   14)
* askokcancel() (in module tkinter.messagebox): tkinter messagebox — Tkinter message prompts.
                                                             (line   37)
* askopenfile() (in module tkinter.filedialog): Native Load/Save Dialogs.
                                                             (line   31)
* askopenfilename() (in module tkinter.filedialog): Native Load/Save Dialogs.
                                                             (line   42)
* askopenfilenames() (in module tkinter.filedialog): Native Load/Save Dialogs.
                                                             (line   42)
* askopenfiles() (in module tkinter.filedialog): Native Load/Save Dialogs.
                                                             (line   31)
* askquestion() (in module tkinter.messagebox): tkinter messagebox — Tkinter message prompts.
                                                             (line   37)
* askretrycancel() (in module tkinter.messagebox): tkinter messagebox — Tkinter message prompts.
                                                             (line   37)
* asksaveasfile() (in module tkinter.filedialog): Native Load/Save Dialogs.
                                                             (line   37)
* asksaveasfilename() (in module tkinter.filedialog): Native Load/Save Dialogs.
                                                             (line   49)
* askstring() (in module tkinter.simpledialog): tkinter simpledialog — Standard Tkinter input dialogs.
                                                             (line   14)
* askyesno() (in module tkinter.messagebox): tkinter messagebox — Tkinter message prompts.
                                                             (line   37)
* askyesnocancel() (in module tkinter.messagebox): tkinter messagebox — Tkinter message prompts.
                                                             (line   37)
* Assert (class in ast):                 Statements.         (line  130)
* assertAlmostEqual() (unittest.TestCase method): Test cases.
                                                             (line  484)
* assertCountEqual() (unittest.TestCase method): Test cases. (line  543)
* assertDictEqual() (unittest.TestCase method): Test cases.  (line  652)
* assertEqual() (unittest.TestCase method): Test cases.      (line  177)
* assertFalse() (unittest.TestCase method): Test cases.      (line  202)
* assertGreater() (unittest.TestCase method): Test cases.    (line  509)
* assertGreaterEqual() (unittest.TestCase method): Test cases.
                                                             (line  509)
* assertIn() (unittest.TestCase method): Test cases.         (line  229)
* assertInBytecode() (test.support.bytecode_helper.BytecodeTestCase method): test support bytecode_helper — Support tools for testing correct bytecode generation.
                                                             (line   22)
* AssertionError:                        Concrete exceptions.
                                                             (line    8)
* assertIs() (unittest.TestCase method): Test cases.         (line  214)
* assertIsInstance() (unittest.TestCase method): Test cases. (line  236)
* assertIsNone() (unittest.TestCase method): Test cases.     (line  222)
* assertIsNot() (unittest.TestCase method): Test cases.      (line  214)
* assertIsNotNone() (unittest.TestCase method): Test cases.  (line  222)
* assertLess() (unittest.TestCase method): Test cases.       (line  509)
* assertLessEqual() (unittest.TestCase method): Test cases.  (line  509)
* assertListEqual() (unittest.TestCase method): Test cases.  (line  629)
* assertLogs() (unittest.TestCase method): Test cases.       (line  405)
* assertMultiLineEqual() (unittest.TestCase method): Test cases.
                                                             (line  604)
* assertNotAlmostEqual() (unittest.TestCase method): Test cases.
                                                             (line  484)
* assertNotEqual() (unittest.TestCase method): Test cases.   (line  197)
* assertNotIn() (unittest.TestCase method): Test cases.      (line  229)
* assertNotInBytecode() (test.support.bytecode_helper.BytecodeTestCase method): test support bytecode_helper — Support tools for testing correct bytecode generation.
                                                             (line   28)
* assertNotIsInstance() (unittest.TestCase method): Test cases.
                                                             (line  236)
* assertNotRegex() (unittest.TestCase method): Test cases.   (line  522)
* assertRaises() (unittest.TestCase method): Test cases.     (line  271)
* assertRaisesRegex() (unittest.TestCase method): Test cases.
                                                             (line  312)
* assertRegex() (unittest.TestCase method): Test cases.      (line  522)
* asserts (2to3 fixer):                  Fixers.             (line   15)
* assertSequenceEqual() (unittest.TestCase method): Test cases.
                                                             (line  614)
* assertSetEqual() (unittest.TestCase method): Test cases.   (line  640)
* assertTrue() (unittest.TestCase method): Test cases.       (line  202)
* assertTupleEqual() (unittest.TestCase method): Test cases. (line  629)
* assertWarns() (unittest.TestCase method): Test cases.      (line  339)
* assertWarnsRegex() (unittest.TestCase method): Test cases. (line  380)
* assert_any_await() (unittest.mock.AsyncMock method): The Mock Class.
                                                             (line  809)
* assert_any_call() (unittest.mock.Mock method): The Mock Class.
                                                             (line  147)
* assert_awaited() (unittest.mock.AsyncMock method): The Mock Class.
                                                             (line  739)
* assert_awaited_once() (unittest.mock.AsyncMock method): The Mock Class.
                                                             (line  759)
* assert_awaited_once_with() (unittest.mock.AsyncMock method): The Mock Class.
                                                             (line  792)
* assert_awaited_with() (unittest.mock.AsyncMock method): The Mock Class.
                                                             (line  775)
* assert_called() (unittest.mock.Mock method): The Mock Class.
                                                             (line   95)
* assert_called_once() (unittest.mock.Mock method): The Mock Class.
                                                             (line  106)
* assert_called_once_with() (unittest.mock.Mock method): The Mock Class.
                                                             (line  133)
* assert_called_with() (unittest.mock.Mock method): The Mock Class.
                                                             (line  123)
* assert_has_awaits() (unittest.mock.AsyncMock method): The Mock Class.
                                                             (line  826)
* assert_has_calls() (unittest.mock.Mock method): The Mock Class.
                                                             (line  163)
* assert_line_data() (formatter.formatter method): The Formatter Interface.
                                                             (line  143)
* assert_not_awaited() (unittest.mock.AsyncMock method): The Mock Class.
                                                             (line  853)
* assert_not_called() (unittest.mock.Mock method): The Mock Class.
                                                             (line  184)
* assert_python_failure() (in module test.support.script_helper): test support script_helper — Utilities for the Python execution tests.
                                                             (line   56)
* assert_python_ok() (in module test.support.script_helper): test support script_helper — Utilities for the Python execution tests.
                                                             (line   40)
* Assign (class in ast):                 Statements.         (line    6)
* assignment; statement:                 The standard type hierarchy.
                                                             (line  197)
* assignment; statement <1>:             Assignment statements.
                                                             (line    6)
* AST (class in ast):                    Node classes.       (line    6)
* ast (module):                          ast — Abstract Syntax Trees.
                                                             (line    6)
* ast command line option; -a:           Command-Line Usage<2>.
                                                             (line   29)
* ast command line option; -h:           Command-Line Usage<2>.
                                                             (line   15)
* ast command line option; –help:        Command-Line Usage<2>.
                                                             (line   15)
* ast command line option; -i <indent>:  Command-Line Usage<2>.
                                                             (line   33)
* ast command line option; –include-attributes: Command-Line Usage<2>.
                                                             (line   29)
* ast command line option; –indent <indent>: Command-Line Usage<2>.
                                                             (line   33)
* ast command line option; -m <mode>:    Command-Line Usage<2>.
                                                             (line   19)
* ast command line option; –mode <mode>: Command-Line Usage<2>.
                                                             (line   19)
* ast command line option; –no-type-comments: Command-Line Usage<2>.
                                                             (line   25)
* astimezone() (datetime.datetime method): datetime Objects. (line  426)
* astuple() (in module dataclasses):     Module-level decorators classes and functions.
                                                             (line  300)
* ASYNC (in module token):               token — Constants used with Python parse trees.
                                                             (line  246)
* async for; in comprehensions:          Displays for lists sets and dictionaries.
                                                             (line   14)
* AsyncContextManager (class in typing): Context manager types.
                                                             (line   18)
* asynccontextmanager() (in module contextlib): Utilities.   (line   91)
* AsyncExitStack (class in contextlib):  Utilities.          (line  454)
* AsyncFor (class in ast):               Async and await.    (line   41)
* AsyncFunctionDef (class in ast):       Async and await.    (line    6)
* AsyncGenerator (class in collections.abc): Collections Abstract Base Classes.
                                                             (line  244)
* AsyncGenerator (class in typing):      Asynchronous programming.
                                                             (line   25)
* AsyncGeneratorType (in module types):  Standard Interpreter Types.
                                                             (line   43)
* asynchat (module):                     asynchat — Asynchronous socket command/response handler.
                                                             (line    6)
* asynchronous context manager:          Glossary.           (line   94)
* asynchronous generator:                Glossary.           (line  100)
* asynchronous generator iterator:       Glossary.           (line  117)
* asynchronous generator; asynchronous iterator: The standard type hierarchy.
                                                             (line  472)
* asynchronous generator; function:      The standard type hierarchy.
                                                             (line  472)
* asynchronous iterable:                 Glossary.           (line  134)
* asynchronous iterator:                 Glossary.           (line  140)
* asyncio (module):                      asyncio — Asynchronous I/O.
                                                             (line    6)
* asyncio.subprocess.DEVNULL (in module asyncio): Constants<7>.
                                                             (line   23)
* asyncio.subprocess.PIPE (in module asyncio): Constants<7>. (line    6)
* asyncio.subprocess.Process (class in asyncio): Interacting with Subprocesses.
                                                             (line   11)
* asyncio.subprocess.STDOUT (in module asyncio): Constants<7>.
                                                             (line   17)
* AsyncIterable (class in collections.abc): Collections Abstract Base Classes.
                                                             (line  230)
* AsyncIterable (class in typing):       Asynchronous programming.
                                                             (line   63)
* AsyncIterator (class in collections.abc): Collections Abstract Base Classes.
                                                             (line  237)
* AsyncIterator (class in typing):       Asynchronous programming.
                                                             (line   73)
* AsyncMock (class in unittest.mock):    The Mock Class.     (line  667)
* asyncore (module):                     asyncore — Asynchronous socket handler.
                                                             (line    6)
* AsyncResult (class in multiprocessing.pool): Process Pools.
                                                             (line  191)
* asyncSetUp() (unittest.IsolatedAsyncioTestCase method): Test cases.
                                                             (line  816)
* asyncTearDown() (unittest.IsolatedAsyncioTestCase method): Test cases.
                                                             (line  825)
* AsyncWith (class in ast):              Async and await.    (line   41)
* async_chat (class in asynchat):        asynchat — Asynchronous socket command/response handler.
                                                             (line   28)
* async_chat.ac_in_buffer_size (in module asynchat): asynchat — Asynchronous socket command/response handler.
                                                             (line   47)
* async_chat.ac_out_buffer_size (in module asynchat): asynchat — Asynchronous socket command/response handler.
                                                             (line   51)
* as_bytes() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  107)
* as_bytes() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  106)
* as_completed() (in module asyncio):    Waiting Primitives. (line   88)
* as_completed() (in module concurrent.futures): Module Functions.
                                                             (line   44)
* as_file() (in module importlib.resources): importlib resources – Resources.
                                                             (line   65)
* as_integer_ratio() (decimal.Decimal method): Decimal objects.
                                                             (line  122)
* as_integer_ratio() (float method):     Additional Methods on Float.
                                                             (line    9)
* as_integer_ratio() (fractions.Fraction method): fractions — Rational numbers.
                                                             (line  103)
* as_integer_ratio() (int method):       Additional Methods on Integer Types.
                                                             (line   98)
* AS_IS (in module formatter):           The Formatter Interface.
                                                             (line   12)
* as_posix() (pathlib.PurePath method):  Methods and properties.
                                                             (line  142)
* as_string() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line   61)
* as_string() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line   60)
* as_tuple() (decimal.Decimal method):   Decimal objects.    (line  136)
* as_uri() (pathlib.PurePath method):    Methods and properties.
                                                             (line  153)
* AT (in module token):                  token — Constants used with Python parse trees.
                                                             (line  222)
* atan() (in module cmath):              Trigonometric functions<2>.
                                                             (line   18)
* atan() (in module math):               Trigonometric functions.
                                                             (line   16)
* atan2() (in module math):              Trigonometric functions.
                                                             (line   21)
* atanh() (in module cmath):             Hyperbolic functions<2>.
                                                             (line   19)
* atanh() (in module math):              Hyperbolic functions.
                                                             (line   17)
* ATEQUAL (in module token):             token — Constants used with Python parse trees.
                                                             (line  226)
* atexit (module):                       atexit — Exit handlers.
                                                             (line    6)
* atexit (weakref.finalize attribute):   weakref — Weak references.
                                                             (line  286)
* athrow() (agen method):                Asynchronous generator-iterator methods.
                                                             (line   43)
* atof() (in module locale):             locale — Internationalization services.
                                                             (line  448)
* atoi() (in module locale):             locale — Internationalization services.
                                                             (line  453)
* atom:                                  Atoms.              (line    6)
* attach() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  167)
* attach_loop() (asyncio.AbstractChildWatcher method): Process Watchers.
                                                             (line   59)
* attach_mock() (unittest.mock.Mock method): The Mock Class. (line  235)
* AttlistDeclHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  208)
* attrgetter() (in module operator):     operator — Standard operators as functions.
                                                             (line  221)
* attrib (xml.etree.ElementTree.Element attribute): Element Objects.
                                                             (line   45)
* attribute:                             The standard type hierarchy.
                                                             (line   13)
* attribute <1>:                         Glossary.           (line  149)
* Attribute (class in ast):              Expressions<2>.     (line  171)
* attribute; assignment:                 Assignment statements.
                                                             (line    6)
* attribute; assignment <1>:             Assignment statements.
                                                             (line   78)
* attribute; deletion:                   The del statement<2>.
                                                             (line   20)
* attribute; reference:                  Attribute references.
                                                             (line    6)
* AttributeError:                        Concrete exceptions.
                                                             (line   12)
* attributes (xml.dom.Node attribute):   Node Objects.       (line   26)
* AttributesImpl (class in xml.sax.xmlreader): xml sax xmlreader — Interface for XML parsers.
                                                             (line   69)
* AttributesNSImpl (class in xml.sax.xmlreader): xml sax xmlreader — Interface for XML parsers.
                                                             (line   80)
* attroff() (curses.window method):      Window Objects.     (line   53)
* attron() (curses.window method):       Window Objects.     (line   58)
* attrset() (curses.window method):      Window Objects.     (line   63)
* at_eof() (asyncio.StreamReader method): StreamReader.      (line   64)
* Audio Interchange File Format:         aifc — Read and write AIFF and AIFC files.
                                                             (line    8)
* Audio Interchange File Format <1>:     chunk — Read IFF chunked data.
                                                             (line    8)
* AUDIODEV:                              ossaudiodev — Access to OSS-compatible audio devices.
                                                             (line   54)
* audioop (module):                      audioop — Manipulate raw audio data.
                                                             (line    6)
* AUDIO_FILE_ENCODING_ADPCM_G721 (in module sunau): sunau — Read and write Sun AU files.
                                                             (line   91)
* AUDIO_FILE_ENCODING_ADPCM_G722 (in module sunau): sunau — Read and write Sun AU files.
                                                             (line   91)
* AUDIO_FILE_ENCODING_ADPCM_G723_3 (in module sunau): sunau — Read and write Sun AU files.
                                                             (line   91)
* AUDIO_FILE_ENCODING_ADPCM_G723_5 (in module sunau): sunau — Read and write Sun AU files.
                                                             (line   91)
* AUDIO_FILE_ENCODING_ALAW_8 (in module sunau): sunau — Read and write Sun AU files.
                                                             (line   81)
* AUDIO_FILE_ENCODING_DOUBLE (in module sunau): sunau — Read and write Sun AU files.
                                                             (line   91)
* AUDIO_FILE_ENCODING_FLOAT (in module sunau): sunau — Read and write Sun AU files.
                                                             (line   91)
* AUDIO_FILE_ENCODING_LINEAR_16 (in module sunau): sunau — Read and write Sun AU files.
                                                             (line   81)
* AUDIO_FILE_ENCODING_LINEAR_24 (in module sunau): sunau — Read and write Sun AU files.
                                                             (line   81)
* AUDIO_FILE_ENCODING_LINEAR_32 (in module sunau): sunau — Read and write Sun AU files.
                                                             (line   81)
* AUDIO_FILE_ENCODING_LINEAR_8 (in module sunau): sunau — Read and write Sun AU files.
                                                             (line   81)
* AUDIO_FILE_ENCODING_MULAW_8 (in module sunau): sunau — Read and write Sun AU files.
                                                             (line   81)
* AUDIO_FILE_MAGIC (in module sunau):    sunau — Read and write Sun AU files.
                                                             (line   75)
* audit events:                          Debugging and Profiling.
                                                             (line   11)
* audit() (in module sys):               sys — System-specific parameters and functions.
                                                             (line   74)
* auditing:                              sys — System-specific parameters and functions.
                                                             (line   76)
* AugAssign (class in ast):              Statements.         (line   96)
* augmented; assignment:                 Augmented assignment statements.
                                                             (line    6)
* auth() (ftplib.FTP_TLS method):        FTP_TLS Objects.    (line   14)
* auth() (smtplib.SMTP method):          SMTP Objects.       (line  141)
* authenticate() (imaplib.IMAP4 method): IMAP4 Objects.      (line   37)
* AuthenticationError:                   Process and exceptions.
                                                             (line  216)
* authenticators() (netrc.netrc method): netrc Objects.      (line    8)
* authkey (multiprocessing.Process attribute): Process and exceptions.
                                                             (line  118)
* auto (class in enum):                  Module Contents<2>. (line   39)
* autorange() (timeit.Timer method):     Python Interface.   (line   90)
* available_timezones() (in module zoneinfo): Functions<2>.  (line    6)
* avg() (in module audioop):             audioop — Manipulate raw audio data.
                                                             (line   51)
* avgpp() (in module audioop):           audioop — Manipulate raw audio data.
                                                             (line   55)
* avoids_symlink_attacks (shutil.rmtree attribute): Directory and files operations.
                                                             (line  293)
* Await (class in ast):                  Async and await.    (line   12)
* AWAIT (in module token):               token — Constants used with Python parse trees.
                                                             (line  244)
* await; in comprehensions:              Displays for lists sets and dictionaries.
                                                             (line   45)
* awaitable:                             Glossary.           (line  155)
* Awaitable (class in collections.abc):  Collections Abstract Base Classes.
                                                             (line  194)
* Awaitable (class in typing):           Asynchronous programming.
                                                             (line   83)
* await_args (unittest.mock.AsyncMock attribute): The Mock Class.
                                                             (line  882)
* await_args_list (unittest.mock.AsyncMock attribute): The Mock Class.
                                                             (line  900)
* await_count (unittest.mock.AsyncMock attribute): The Mock Class.
                                                             (line  866)
* b"; bytes literal:                     String and Bytes literals.
                                                             (line   43)
* b’; bytes literal:                     String and Bytes literals.
                                                             (line   43)
* b16decode() (in module base64):        base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  128)
* b16encode() (in module base64):        base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  123)
* b2a_base64() (in module binascii):     binascii — Convert between binary and ASCII.
                                                             (line   46)
* b2a_hex() (in module binascii):        binascii — Convert between binary and ASCII.
                                                             (line  139)
* b2a_hqx() (in module binascii):        binascii — Convert between binary and ASCII.
                                                             (line  106)
* b2a_qp() (in module binascii):         binascii — Convert between binary and ASCII.
                                                             (line   62)
* b2a_uu() (in module binascii):         binascii — Convert between binary and ASCII.
                                                             (line   32)
* b32decode() (in module base64):        base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  103)
* b32encode() (in module base64):        base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line   98)
* b64decode() (in module base64):        base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line   55)
* b64encode() (in module base64):        base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line   43)
* b85decode() (in module base64):        base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  195)
* b85encode() (in module base64):        base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  184)
* Babyl (class in mailbox):              Babyl.              (line    6)
* BabylMessage (class in mailbox):       BabylMessage.       (line    6)
* back() (in module turtle):             Turtle motion.      (line   24)
* backslash character:                   Explicit line joining.
                                                             (line    6)
* backslashreplace_errors() (in module codecs): Error Handlers.
                                                             (line  151)
* backup() (sqlite3.Connection method):  Connection Objects. (line  410)
* backward() (in module turtle):         Turtle motion.      (line   24)
* BadGzipFile:                           gzip — Support for gzip files.
                                                             (line   63)
* BadStatusLine:                         http client — HTTP protocol client.
                                                             (line  174)
* BadZipFile:                            zipfile — Work with ZIP archives.
                                                             (line   24)
* BadZipfile:                            zipfile — Work with ZIP archives.
                                                             (line   30)
* Balloon (class in tkinter.tix):        Basic Widgets.      (line    6)
* Barrier (class in multiprocessing):    Synchronization primitives.
                                                             (line   13)
* Barrier (class in threading):          Barrier Objects.    (line   36)
* Barrier() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  143)
* base64 (module):                       base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line    6)
* base64; encoding:                      base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line    8)
* BaseCGIHandler (class in wsgiref.handlers): wsgiref handlers – server/gateway base classes.
                                                             (line   53)
* BaseCookie (class in http.cookies):    http cookies — HTTP state management.
                                                             (line   38)
* BaseException:                         Base classes.       (line    9)
* BaseHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  264)
* BaseHandler (class in wsgiref.handlers): wsgiref handlers – server/gateway base classes.
                                                             (line   88)
* BaseHeader (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line   37)
* BaseHTTPRequestHandler (class in http.server): http server — HTTP servers.
                                                             (line   46)
* BaseManager (class in multiprocessing.managers): Managers. (line   23)
* basename() (in module os.path):        os path — Common pathname manipulations.
                                                             (line   62)
* BaseProtocol (class in asyncio):       Base Protocols.     (line    6)
* BaseProxy (class in multiprocessing.managers): Proxy Objects.
                                                             (line   92)
* BaseRequestHandler (class in socketserver): Request Handler Objects.
                                                             (line    6)
* BaseRotatingHandler (class in logging.handlers): BaseRotatingHandler.
                                                             (line   12)
* BaseSelector (class in selectors):     Classes<3>.         (line   53)
* BaseServer (class in socketserver):    Server Objects<2>.  (line    6)
* basestring (2to3 fixer):               Fixers.             (line   60)
* BaseTransport (class in asyncio):      Transports Hierarchy.
                                                             (line    6)
* base_exec_prefix (in module sys):      sys — System-specific parameters and functions.
                                                             (line  105)
* base_prefix (in module sys):           sys — System-specific parameters and functions.
                                                             (line  119)
* basicConfig() (in module logging):     Module-Level Functions.
                                                             (line  244)
* BasicContext (class in decimal):       Context objects.    (line   47)
* BasicInterpolation (class in configparser): Interpolation of values.
                                                             (line   10)
* BasicTestRunner (class in test.support): test support — Utilities for the Python test suite.
                                                             (line 1123)
* baudrate() (in module curses):         Functions<4>.       (line   18)
* bbox() (tkinter.ttk.Treeview method):  ttk Treeview.       (line    8)
* BDADDR_ANY (in module socket):         Constants<8>.       (line  237)
* BDADDR_LOCAL (in module socket):       Constants<8>.       (line  237)
* Bdb (class in bdb):                    bdb — Debugger framework.
                                                             (line   79)
* bdb (module):                          bdb — Debugger framework.
                                                             (line    6)
* BdbQuit:                               bdb — Debugger framework.
                                                             (line   15)
* BDFL:                                  Glossary.           (line  161)
* bdist_msi (class in distutils.command.bdist_msi): distutils command bdist_msi — Build a Microsoft Installer binary package.
                                                             (line    6)
* beep() (in module curses):             Functions<4>.       (line   26)
* Beep() (in module winsound):           winsound — Sound-playing interface for Windows.
                                                             (line   12)
* BEFORE_ASYNC_WITH (opcode):            Python Bytecode Instructions.
                                                             (line  295)
* begin_fill() (in module turtle):       Filling.            (line   16)
* begin_poly() (in module turtle):       Special Turtle methods.
                                                             (line    6)
* below() (curses.panel.Panel method):   Panel Objects.      (line   17)
* BELOW_NORMAL_PRIORITY_CLASS (in module subprocess): Windows Constants.
                                                             (line   59)
* benchmarking:                          Functions<3>.       (line  182)
* benchmarking <1>:                      Functions<3>.       (line  200)
* benchmarking <2>:                      Functions<3>.       (line  479)
* Benchmarking:                          timeit — Measure execution time of small code snippets.
                                                             (line    8)
* betavariate() (in module random):      Real-valued distributions.
                                                             (line   33)
* bgcolor() (in module turtle):          Window control.     (line    6)
* bgpic() (in module turtle):            Window control.     (line   21)
* bias() (in module audioop):            audioop — Manipulate raw audio data.
                                                             (line   61)
* bidirectional() (in module unicodedata): unicodedata — Unicode Database.
                                                             (line   54)
* bigaddrspacetest() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  741)
* BigEndianStructure (class in ctypes):  Structured data types.
                                                             (line   10)
* bigmemtest() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  725)
* bin() (built-in function):             Built-in Functions. (line   92)
* Binary (class in msilib):              msilib — Read and write Microsoft Installer files.
                                                             (line   89)
* Binary (class in xmlrpc.client):       Binary Objects.     (line    6)
* binary file:                           Glossary.           (line  166)
* binary literal:                        Numeric literals.   (line    6)
* binary mode:                           Built-in Functions. (line 1223)
* binary semaphores:                     _thread — Low-level threading API.
                                                             (line    6)
* binary; arithmetic; operation:         Binary arithmetic operations.
                                                             (line    6)
* binary; bitwise; operation:            Binary bitwise operations.
                                                             (line    6)
* binary; literals:                      Numeric Types — int float complex.
                                                             (line   19)
* binaryfunc (C type):                   Slot Type typedefs. (line  100)
* BinaryIO (class in typing):            Other concrete types.
                                                             (line    6)
* BINARY_ADD (opcode):                   Python Bytecode Instructions.
                                                             (line  157)
* BINARY_AND (opcode):                   Python Bytecode Instructions.
                                                             (line  177)
* BINARY_FLOOR_DIVIDE (opcode):          Python Bytecode Instructions.
                                                             (line  145)
* BINARY_LSHIFT (opcode):                Python Bytecode Instructions.
                                                             (line  169)
* BINARY_MATRIX_MULTIPLY (opcode):       Python Bytecode Instructions.
                                                             (line  139)
* BINARY_MODULO (opcode):                Python Bytecode Instructions.
                                                             (line  153)
* BINARY_MULTIPLY (opcode):              Python Bytecode Instructions.
                                                             (line  135)
* BINARY_OR (opcode):                    Python Bytecode Instructions.
                                                             (line  185)
* BINARY_POWER (opcode):                 Python Bytecode Instructions.
                                                             (line  131)
* BINARY_RSHIFT (opcode):                Python Bytecode Instructions.
                                                             (line  173)
* BINARY_SUBSCR (opcode):                Python Bytecode Instructions.
                                                             (line  165)
* BINARY_SUBTRACT (opcode):              Python Bytecode Instructions.
                                                             (line  161)
* BINARY_TRUE_DIVIDE (opcode):           Python Bytecode Instructions.
                                                             (line  149)
* BINARY_XOR (opcode):                   Python Bytecode Instructions.
                                                             (line  181)
* binascii (module):                     binascii — Convert between binary and ASCII.
                                                             (line    6)
* bind (widgets):                        Bindings and Events.
                                                             (line    6)
* bind() (asyncore.dispatcher method):   asyncore — Asynchronous socket handler.
                                                             (line  222)
* bind() (inspect.Signature method):     Introspecting callables with the Signature object.
                                                             (line   96)
* bind() (socket.socket method):         Socket Objects.     (line   30)
* binding; name:                         Binding of names.   (line    6)
* binding; name <1>:                     Assignment statements.
                                                             (line    6)
* bindtextdomain() (in module gettext):  GNU gettext API.    (line   14)
* bindtextdomain() (in module locale):   Access to message catalogs.
                                                             (line   14)
* bind_partial() (inspect.Signature method): Introspecting callables with the Signature object.
                                                             (line  103)
* bind_port() (in module test.support.socket_helper): test support socket_helper — Utilities for socket tests.
                                                             (line   37)
* bind_textdomain_codeset() (in module gettext): GNU gettext API.
                                                             (line   26)
* bind_unix_socket() (in module test.support.socket_helper): test support socket_helper — Utilities for socket tests.
                                                             (line   54)
* binhex (module):                       binhex — Encode and decode binhex4 files.
                                                             (line    6)
* binhex() (in module binhex):           binhex — Encode and decode binhex4 files.
                                                             (line   18)
* BinOp (class in ast):                  Expressions<2>.     (line   42)
* bisect (module):                       bisect — Array bisection algorithm.
                                                             (line    6)
* bisect() (in module bisect):           bisect — Array bisection algorithm.
                                                             (line   34)
* bisect_left() (in module bisect):      bisect — Array bisection algorithm.
                                                             (line   20)
* bisect_right() (in module bisect):     bisect — Array bisection algorithm.
                                                             (line   34)
* BitAnd (class in ast):                 Expressions<2>.     (line   54)
* bitmap() (msilib.Dialog method):       GUI classes.        (line   60)
* BitOr (class in ast):                  Expressions<2>.     (line   54)
* bitwise; and:                          Binary bitwise operations.
                                                             (line   12)
* bitwise; operations:                   Bitwise Operations on Integer Types.
                                                             (line    6)
* bitwise; or:                           Binary bitwise operations.
                                                             (line   20)
* bitwise; xor:                          Binary bitwise operations.
                                                             (line   16)
* BitXor (class in ast):                 Expressions<2>.     (line   54)
* bit_length() (int method):             Additional Methods on Integer Types.
                                                             (line    9)
* bk() (in module turtle):               Turtle motion.      (line   24)
* bkgd() (curses.window method):         Window Objects.     (line   68)
* bkgdset() (curses.window method):      Window Objects.     (line   80)
* blake2b() (in module hashlib):         Creating hash objects.
                                                             (line    8)
* blake2b, blake2s:                      BLAKE2.             (line    6)
* blake2b.MAX_DIGEST_SIZE (in module hashlib): Constants<5>. (line   24)
* blake2b.MAX_KEY_SIZE (in module hashlib): Constants<5>.    (line   18)
* blake2b.PERSON_SIZE (in module hashlib): Constants<5>.     (line   12)
* blake2b.SALT_SIZE (in module hashlib): Constants<5>.       (line    6)
* blake2s() (in module hashlib):         Creating hash objects.
                                                             (line   14)
* blake2s.MAX_DIGEST_SIZE (in module hashlib): Constants<5>. (line   26)
* blake2s.MAX_KEY_SIZE (in module hashlib): Constants<5>.    (line   20)
* blake2s.PERSON_SIZE (in module hashlib): Constants<5>.     (line   14)
* blake2s.SALT_SIZE (in module hashlib): Constants<5>.       (line    8)
* blank line:                            Blank lines.        (line    6)
* block:                                 Structure of a program.
                                                             (line    6)
* blocked_domains() (http.cookiejar.DefaultCookiePolicy method): DefaultCookiePolicy Objects.
                                                             (line   52)
* BlockingIOError:                       OS exceptions.      (line    9)
* BlockingIOError <1>:                   High-level Module Interface.
                                                             (line   38)
* blocksize (http.client.HTTPConnection attribute): HTTPConnection Objects.
                                                             (line  115)
* block_size (hmac.HMAC attribute):      hmac — Keyed-Hashing for Message Authentication.
                                                             (line   94)
* BNF:                                   Notation.           (line    6)
* BNF <1>:                               Expressions.        (line    6)
* body() (nntplib.NNTP method):          Methods<3>.         (line  272)
* body() (tkinter.simpledialog.Dialog method): tkinter simpledialog — Standard Tkinter input dialogs.
                                                             (line   25)
* body_encode() (email.charset.Charset method): email charset Representing character sets.
                                                             (line  135)
* body_encoding (email.charset.Charset attribute): email charset Representing character sets.
                                                             (line   67)
* body_line_iterator() (in module email.iterators): email iterators Iterators.
                                                             (line   14)
* BOLD (in module tkinter.font):         tkinter font — Tkinter font wrapper.
                                                             (line   15)
* BOM (in module codecs):                codecs — Codec registry and base classes.
                                                             (line  244)
* BOM_BE (in module codecs):             codecs — Codec registry and base classes.
                                                             (line  244)
* BOM_LE (in module codecs):             codecs — Codec registry and base classes.
                                                             (line  244)
* BOM_UTF16 (in module codecs):          codecs — Codec registry and base classes.
                                                             (line  244)
* BOM_UTF16_BE (in module codecs):       codecs — Codec registry and base classes.
                                                             (line  244)
* BOM_UTF16_LE (in module codecs):       codecs — Codec registry and base classes.
                                                             (line  244)
* BOM_UTF32 (in module codecs):          codecs — Codec registry and base classes.
                                                             (line  244)
* BOM_UTF32_BE (in module codecs):       codecs — Codec registry and base classes.
                                                             (line  244)
* BOM_UTF32_LE (in module codecs):       codecs — Codec registry and base classes.
                                                             (line  244)
* BOM_UTF8 (in module codecs):           codecs — Codec registry and base classes.
                                                             (line  244)
* bool (built-in class):                 Built-in Functions. (line  114)
* Boolean; operation:                    Boolean operations. (line    6)
* Boolean; operations:                   Truth Value Testing.
                                                             (line    6)
* Boolean; operations <1>:               Boolean Operations — and or not.
                                                             (line    6)
* Boolean; type:                         Built-in Functions. (line  124)
* Boolean; values:                       Boolean Values.     (line   15)
* BOOLEAN_STATES (configparser.ConfigParser attribute): Customizing Parser Behaviour.
                                                             (line  245)
* BoolOp (class in ast):                 Expressions<2>.     (line   70)
* bootstrap() (in module ensurepip):     Module API.         (line   13)
* border() (curses.window method):       Window Objects.     (line   91)
* bottom() (curses.panel.Panel method):  Panel Objects.      (line   21)
* bottom_panel() (in module curses.panel): Functions<5>.     (line    8)
* BoundArguments (class in inspect):     Introspecting callables with the Signature object.
                                                             (line  276)
* BoundaryError:                         email errors Exception and Defect classes.
                                                             (line   38)
* BoundedSemaphore (class in asyncio):   BoundedSemaphore.   (line    6)
* BoundedSemaphore (class in multiprocessing): Synchronization primitives.
                                                             (line   19)
* BoundedSemaphore (class in threading): Semaphore Objects.  (line   73)
* BoundedSemaphore() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  150)
* box() (curses.window method):          Window Objects.     (line  130)
* bpformat() (bdb.Breakpoint method):    bdb — Debugger framework.
                                                             (line   55)
* bpprint() (bdb.Breakpoint method):     bdb — Debugger framework.
                                                             (line   74)
* Break (class in ast):                  Control flow.       (line  101)
* break (pdb command):                   Debugger Commands.  (line   71)
* Breakpoint (class in bdb):             bdb — Debugger framework.
                                                             (line   22)
* breakpoint() (built-in function):      Built-in Functions. (line  126)
* breakpointhook() (in module sys):      sys — System-specific parameters and functions.
                                                             (line  187)
* breakpoints:                           Help menu Shell and Editor.
                                                             (line   29)
* break_anywhere() (bdb.Bdb method):     bdb — Debugger framework.
                                                             (line  204)
* break_here() (bdb.Bdb method):         bdb — Debugger framework.
                                                             (line  197)
* break_long_words (textwrap.TextWrapper attribute): textwrap — Text wrapping and filling.
                                                             (line  246)
* break_on_hyphens (textwrap.TextWrapper attribute): textwrap — Text wrapping and filling.
                                                             (line  256)
* broadcast_address (ipaddress.IPv4Network attribute): Network objects.
                                                             (line   91)
* broadcast_address (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  311)
* broken (threading.Barrier attribute):  Barrier Objects.    (line  101)
* BrokenBarrierError:                    Barrier Objects.    (line  106)
* BrokenExecutor:                        Exception classes.  (line   14)
* BrokenPipeError:                       OS exceptions.      (line   37)
* BrokenProcessPool:                     Exception classes.  (line   37)
* BrokenThreadPool:                      Exception classes.  (line   29)
* BROWSER:                               webbrowser — Convenient Web-browser controller.
                                                             (line   20)
* BROWSER <1>:                           webbrowser — Convenient Web-browser controller.
                                                             (line   95)
* BsdDbShelf (class in shelve):          Restrictions.       (line   52)
* buf (multiprocessing.shared_memory.SharedMemory attribute): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line   87)
* buffer (2to3 fixer):                   Fixers.             (line   64)
* buffer (io.TextIOBase attribute):      Text I/O<2>.        (line   30)
* buffer (unittest.TestResult attribute): Loading and running tests.
                                                             (line  277)
* buffer interface; (see buffer protocol): Iterator Protocol.
                                                             (line   46)
* buffer object; (see buffer protocol):  Iterator Protocol.  (line   45)
* buffer protocol:                       Iterator Protocol.  (line   46)
* buffer protocol; binary sequence types: printf-style String Formatting.
                                                             (line  189)
* buffer protocol; str (built-in class): Text Sequence Type — str.
                                                             (line   60)
* buffer size, I/O:                      Built-in Functions. (line 1223)
* BufferedIOBase (class in io):          I/O Base Classes.   (line  227)
* BufferedProtocol (class in asyncio):   Base Protocols.     (line   15)
* BufferedRandom (class in io):          Buffered Streams.   (line  138)
* BufferedReader (class in io):          Buffered Streams.   (line   56)
* BufferedRWPair (class in io):          Buffered Streams.   (line  152)
* BufferedWriter (class in io):          Buffered Streams.   (line   97)
* BufferError:                           Base classes.       (line   49)
* BufferingHandler (class in logging.handlers): MemoryHandler.
                                                             (line   19)
* BufferTooShort:                        Process and exceptions.
                                                             (line  208)
* buffer_info() (array.array method):    array — Efficient arrays of numeric values.
                                                             (line  117)
* buffer_size (xml.parsers.expat.xmlparser attribute): XMLParser Objects<2>.
                                                             (line   84)
* buffer_text (xml.parsers.expat.xmlparser attribute): XMLParser Objects<2>.
                                                             (line   91)
* buffer_updated() (asyncio.BufferedProtocol method): Buffered Streaming Protocols.
                                                             (line   33)
* buffer_used (xml.parsers.expat.xmlparser attribute): XMLParser Objects<2>.
                                                             (line  100)
* bufsize() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line  214)
* BUILD_CONST_KEY_MAP (opcode):          Python Bytecode Instructions.
                                                             (line  503)
* BUILD_LIST (opcode):                   Python Bytecode Instructions.
                                                             (line  485)
* BUILD_MAP (opcode):                    Python Bytecode Instructions.
                                                             (line  493)
* build_opener() (in module urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  118)
* build_py (class in distutils.command.build_py): distutils command build_py — Build the py/ pyc files of a package.
                                                             (line    6)
* build_py_2to3 (class in distutils.command.build_py): distutils command build_py — Build the py/ pyc files of a package.
                                                             (line    8)
* BUILD_SET (opcode):                    Python Bytecode Instructions.
                                                             (line  489)
* BUILD_SLICE (opcode):                  Python Bytecode Instructions.
                                                             (line  794)
* BUILD_STRING (opcode):                 Python Bytecode Instructions.
                                                             (line  512)
* BUILD_TUPLE (opcode):                  Python Bytecode Instructions.
                                                             (line  480)
* built-in function; abs:                Emulating numeric types.
                                                             (line  116)
* built-in function; abs <1>:            Number Protocol.    (line   86)
* built-in function; ascii:              Object Protocol.    (line  177)
* built-in function; bytes:              Basic customization.
                                                             (line  145)
* built-in function; bytes <1>:          Object Protocol.    (line  198)
* built-in function; call:               Calls.              (line  132)
* built-in function; chr:                The standard type hierarchy.
                                                             (line  161)
* built-in function; classmethod:        Implementing functions and methods.
                                                             (line  184)
* built-in function; compile:            The global statement.
                                                             (line   27)
* built-in function; compile <1>:        Code Objects.       (line    6)
* built-in function; compile <2>:        Standard Interpreter Types.
                                                             (line   52)
* built-in function; compile <3>:        Queries on ST Objects.
                                                             (line   14)
* built-in function; compile <4>:        Importing Modules<2>.
                                                             (line  119)
* built-in function; complex:            Emulating numeric types.
                                                             (line  123)
* built-in function; complex <1>:        Numeric Types — int float complex.
                                                             (line   27)
* built-in function; divmod:             Emulating numeric types.
                                                             (line   26)
* built-in function; divmod <1>:         Emulating numeric types.
                                                             (line   56)
* built-in function; divmod <2>:         Number Protocol.    (line   59)
* built-in function; eval:               The global statement.
                                                             (line   27)
* built-in function; eval <1>:           Expression input.   (line    6)
* built-in function; eval <2>:           Code Objects.       (line   17)
* built-in function; eval <3>:           pprint — Data pretty printer.
                                                             (line  135)
* built-in function; eval <4>:           PrettyPrinter Objects.
                                                             (line   26)
* built-in function; eval <5>:           Converting ST Objects.
                                                             (line   45)
* built-in function; exec:               The global statement.
                                                             (line   27)
* built-in function; exec <1>:           Built-in Functions. (line  517)
* built-in function; exec <2>:           Code Objects.       (line   17)
* built-in function; exec <3>:           Converting ST Objects.
                                                             (line   45)
* built-in function; float:              Emulating numeric types.
                                                             (line  123)
* built-in function; float <1>:          Numeric Types — int float complex.
                                                             (line   27)
* built-in function; float <2>:          Number Protocol.    (line  238)
* built-in function; hash:               Basic customization.
                                                             (line  222)
* built-in function; hash <1>:           Immutable Sequence Types.
                                                             (line    6)
* built-in function; hash <2>:           Object Protocol.    (line  251)
* built-in function; hash <3>:           PyTypeObject Slots. (line  310)
* built-in function; help:               Operating System Interface.
                                                             (line   20)
* built-in function; id:                 Objects values and types.
                                                             (line   11)
* built-in function; int:                Emulating numeric types.
                                                             (line  123)
* built-in function; int <1>:            Numeric Types — int float complex.
                                                             (line   27)
* built-in function; int <2>:            Number Protocol.    (line  231)
* built-in function; len:                The standard type hierarchy.
                                                             (line  132)
* built-in function; len <1>:            The standard type hierarchy.
                                                             (line  224)
* built-in function; len <2>:            The standard type hierarchy.
                                                             (line  254)
* built-in function; len <3>:            Emulating container types.
                                                             (line   40)
* built-in function; len <4>:            Common Sequence Operations.
                                                             (line   21)
* built-in function; len <5>:            Mapping Types — dict.
                                                             (line    6)
* built-in function; len <6>:            Object Protocol.    (line  297)
* built-in function; len <7>:            Sequence Protocol.  (line   17)
* built-in function; len <8>:            Mapping Protocol.   (line   20)
* built-in function; len <9>:            List Objects.       (line   39)
* built-in function; len <10>:           Dictionary Objects. (line  136)
* built-in function; len <11>:           Set Objects.        (line   92)
* built-in function; max:                Common Sequence Operations.
                                                             (line   21)
* built-in function; min:                Common Sequence Operations.
                                                             (line   21)
* built-in function; open:               Reading and Writing Files.
                                                             (line    6)
* built-in function; open <1>:           The standard type hierarchy.
                                                             (line  635)
* built-in function; ord:                The standard type hierarchy.
                                                             (line  161)
* built-in function; pow:                Emulating numeric types.
                                                             (line   26)
* built-in function; pow <1>:            Emulating numeric types.
                                                             (line   26)
* built-in function; pow <2>:            Emulating numeric types.
                                                             (line   56)
* built-in function; pow <3>:            Emulating numeric types.
                                                             (line   66)
* built-in function; pow <4>:            Number Protocol.    (line   68)
* built-in function; pow <5>:            Number Protocol.    (line  183)
* built-in function; print:              Basic customization.
                                                             (line  149)
* built-in function; range:              The for statement.  (line   38)
* built-in function; repr:               Expression statements.
                                                             (line   17)
* built-in function; repr <1>:           Finalization and De-allocation.
                                                             (line   90)
* built-in function; repr <2>:           Object Protocol.    (line  165)
* built-in function; repr <3>:           PyTypeObject Slots. (line  251)
* built-in function; round:              Emulating numeric types.
                                                             (line  146)
* built-in function; slice:              The standard type hierarchy.
                                                             (line  810)
* built-in function; slice <1>:          Python Bytecode Instructions.
                                                             (line  796)
* built-in function; staticmethod:       Implementing functions and methods.
                                                             (line  191)
* built-in function; tuple:              Sequence Protocol.  (line  119)
* built-in function; tuple <1>:          List Objects.       (line  126)
* built-in function; type:               Objects values and types.
                                                             (line   11)
* built-in function; type <1>:           Metaclasses.        (line    6)
* built-in function; type <2>:           Type Objects.       (line    6)
* built-in function; type <3>:           Object Protocol.    (line  278)
* built-in function; __import__:         Importing Modules<2>.
                                                             (line   38)
* built-in method; call:                 Calls.              (line  132)
* built-in; method:                      The standard type hierarchy.
                                                             (line  503)
* built-in; types:                       Built-in Types.     (line    9)
* BuiltinFunctionType (in module types): Standard Interpreter Types.
                                                             (line   81)
* BuiltinImporter (class in importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line   67)
* BuiltinMethodType (in module types):   Standard Interpreter Types.
                                                             (line   81)
* builtins (module):                     builtins — Built-in objects.
                                                             (line    6)
* builtin_module_names (in module sys):  sys — System-specific parameters and functions.
                                                             (line  140)
* ButtonBox (class in tkinter.tix):      Basic Widgets.      (line   13)
* buttonbox() (tkinter.simpledialog.Dialog method): tkinter simpledialog — Standard Tkinter input dialogs.
                                                             (line   30)
* bye() (in module turtle):              Methods specific to Screen not inherited from TurtleScreen.
                                                             (line    6)
* byref() (in module ctypes):            Utility functions.  (line   19)
* byte:                                  The standard type hierarchy.
                                                             (line  188)
* bytearray:                             The standard type hierarchy.
                                                             (line  212)
* bytearray (built-in class):            Bytearray Objects.  (line    9)
* bytearray; formatting:                 printf-style Bytes Formatting.
                                                             (line    6)
* bytearray; interpolation:              printf-style Bytes Formatting.
                                                             (line    6)
* bytearray; methods:                    Bytes and Bytearray Operations.
                                                             (line    6)
* bytecode:                              The standard type hierarchy.
                                                             (line  654)
* bytecode <1>:                          Glossary.           (line  196)
* Bytecode (class in dis):               Bytecode analysis.  (line   12)
* Bytecode.codeobj (in module dis):      Bytecode analysis.  (line   39)
* Bytecode.first_line (in module dis):   Bytecode analysis.  (line   43)
* BytecodeTestCase (class in test.support.bytecode_helper): test support bytecode_helper — Support tools for testing correct bytecode generation.
                                                             (line   13)
* BYTECODE_SUFFIXES (in module importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line   40)
* byteorder (in module sys):             sys — System-specific parameters and functions.
                                                             (line  133)
* bytes:                                 The standard type hierarchy.
                                                             (line  188)
* bytes (built-in class):                Bytes Objects.      (line   12)
* bytes (uuid.UUID attribute):           uuid — UUID objects according to RFC 4122.
                                                             (line   84)
* bytes literal:                         Literals.           (line    8)
* bytes-like object:                     Glossary.           (line  177)
* bytes; formatting:                     printf-style Bytes Formatting.
                                                             (line    6)
* bytes; interpolation:                  printf-style Bytes Formatting.
                                                             (line    6)
* bytes; methods:                        Bytes and Bytearray Operations.
                                                             (line    6)
* bytes; str (built-in class):           Text Sequence Type — str.
                                                             (line   60)
* BytesFeedParser (class in email.parser): FeedParser API.   (line   28)
* BytesGenerator (class in email.generator): email generator Generating MIME documents.
                                                             (line   43)
* BytesHeaderParser (class in email.parser): Parser API.     (line   67)
* BytesIO (class in io):                 Buffered Streams.   (line    9)
* BytesParser (class in email.parser):   Parser API.         (line   17)
* ByteString (class in collections.abc): Collections Abstract Base Classes.
                                                             (line  159)
* ByteString (class in typing):          Corresponding to collections in collections abc.
                                                             (line   13)
* byteswap() (array.array method):       array — Efficient arrays of numeric values.
                                                             (line  136)
* byteswap() (in module audioop):        audioop — Manipulate raw audio data.
                                                             (line   66)
* BytesWarning:                          Warnings.           (line   68)
* bytes_le (uuid.UUID attribute):        uuid — UUID objects according to RFC 4122.
                                                             (line   89)
* byte_compile() (in module distutils.util): distutils util — Miscellaneous other utility functions.
                                                             (line  147)
* bz2 (module):                          bz2 — Support for bzip2 compression.
                                                             (line    6)
* BZ2Compressor (class in bz2):          Incremental de compression.
                                                             (line    6)
* BZ2Decompressor (class in bz2):        Incremental de compression.
                                                             (line   33)
* BZ2File (class in bz2):                De compression of files.
                                                             (line   40)
* C:                                     String and Bytes literals.
                                                             (line   72)
* C-contiguous:                          shape strides suboffsets.
                                                             (line   26)
* C-contiguous <1>:                      Glossary.           (line  273)
* C14NWriterTarget (class in xml.etree.ElementTree): TreeBuilder Objects.
                                                             (line   93)
* C; language:                           The standard type hierarchy.
                                                             (line    6)
* C; language <1>:                       The standard type hierarchy.
                                                             (line  112)
* C; language <2>:                       The standard type hierarchy.
                                                             (line  490)
* C; language <3>:                       Comparisons.        (line    6)
* C; language <4>:                       Numeric Types — int float complex.
                                                             (line    6)
* C; language <5>:                       Numeric Types — int float complex.
                                                             (line  104)
* C; structures:                         struct — Interpret bytes as packed binary data.
                                                             (line    8)
* CAB (class in msilib):                 CAB Objects.        (line    6)
* cache() (in module functools):         functools — Higher-order functions and operations on callable objects.
                                                             (line   16)
* cached (importlib.machinery.ModuleSpec attribute): importlib machinery – Importers and path hooks.
                                                             (line  403)
* cached_property() (in module functools): functools — Higher-order functions and operations on callable objects.
                                                             (line   41)
* CacheFTPHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  422)
* cache_from_source() (in module imp):   imp — Access the import internals.
                                                             (line  205)
* cache_from_source() (in module importlib.util): importlib util – Utility code for importers.
                                                             (line   21)
* calcobjsize() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  601)
* calcsize() (in module struct):         Functions and Exceptions.
                                                             (line   55)
* calcvobjsize() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  606)
* Calendar (class in calendar):          calendar — General calendar-related functions.
                                                             (line   27)
* calendar (module):                     calendar — General calendar-related functions.
                                                             (line    6)
* calendar() (in module calendar):       calendar — General calendar-related functions.
                                                             (line  349)
* call:                                  Slicings.           (line   38)
* Call (class in ast):                   Expressions<2>.     (line  122)
* call() (in module subprocess):         Older high-level API.
                                                             (line   10)
* call() (in module unittest.mock):      call.               (line    6)
* call; instance:                        Emulating callable objects.
                                                             (line    8)
* Callable (class in collections.abc):   Collections Abstract Base Classes.
                                                             (line  116)
* Callable (in module typing):           Special forms.      (line   80)
* callable() (built-in function):        Built-in Functions. (line  193)
* CallableProxyType (in module weakref): weakref — Weak references.
                                                             (line  309)
* callback:                              Glossary.           (line  211)
* callback (optparse.Option attribute):  Option attributes.  (line   60)
* callback() (contextlib.ExitStack method): Utilities.       (line  415)
* callbacks (in module gc):              gc — Garbage Collector interface.
                                                             (line  249)
* callback_args (optparse.Option attribute): Option attributes.
                                                             (line   66)
* callback_kwargs (optparse.Option attribute): Option attributes.
                                                             (line   66)
* called (unittest.mock.Mock attribute): The Mock Class.     (line  296)
* CalledProcessError:                    Using the subprocess Module.
                                                             (line  190)
* calloc():                              Overview<3>.        (line   33)
* call_args (unittest.mock.Mock attribute): The Mock Class.  (line  415)
* call_args_list (unittest.mock.Mock attribute): The Mock Class.
                                                             (line  459)
* call_at() (asyncio.loop method):       Scheduling delayed callbacks.
                                                             (line   37)
* call_count (unittest.mock.Mock attribute): The Mock Class. (line  308)
* call_exception_handler() (asyncio.loop method): Error Handling API.
                                                             (line   37)
* CALL_FUNCTION (opcode):                Python Bytecode Instructions.
                                                             (line  706)
* CALL_FUNCTION_EX (opcode):             Python Bytecode Instructions.
                                                             (line  737)
* CALL_FUNCTION_KW (opcode):             Python Bytecode Instructions.
                                                             (line  719)
* call_later() (asyncio.loop method):    Scheduling delayed callbacks.
                                                             (line   10)
* call_list() (unittest.mock.call method): call.             (line   20)
* CALL_METHOD (opcode):                  Python Bytecode Instructions.
                                                             (line  762)
* call_soon() (asyncio.loop method):     Scheduling callbacks.
                                                             (line    6)
* call_soon_threadsafe() (asyncio.loop method): Scheduling callbacks.
                                                             (line   23)
* call_tracing() (in module sys):        sys — System-specific parameters and functions.
                                                             (line  147)
* cancel() (asyncio.Future method):      Future Object.      (line  109)
* cancel() (asyncio.Handle method):      Callback Handles.   (line   11)
* cancel() (asyncio.Task method):        Task Object.        (line   52)
* cancel() (concurrent.futures.Future method): Future Objects.
                                                             (line   16)
* cancel() (sched.scheduler method):     Scheduler Objects.  (line   41)
* cancel() (threading.Timer method):     Timer Objects.      (line   35)
* cancel() (tkinter.dnd.DndHandler method): tkinter dnd — Drag and drop support.
                                                             (line   48)
* cancelled() (asyncio.Future method):   Future Object.      (line   67)
* cancelled() (asyncio.Handle method):   Callback Handles.   (line   16)
* cancelled() (asyncio.Task method):     Task Object.        (line  107)
* cancelled() (concurrent.futures.Future method): Future Objects.
                                                             (line   24)
* CancelledError:                        Exception classes.  (line    6)
* CancelledError <1>:                    Exceptions<10>.     (line   17)
* cancel_command() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line   82)
* cancel_dump_traceback_later() (in module faulthandler): Dumping the tracebacks after a timeout.
                                                             (line   29)
* cancel_join_thread() (multiprocessing.Queue method): Pipes and Queues.
                                                             (line  182)
* CannotSendHeader:                      http client — HTTP protocol client.
                                                             (line  166)
* CannotSendRequest:                     http client — HTTP protocol client.
                                                             (line  162)
* canonic() (bdb.Bdb method):            bdb — Debugger framework.
                                                             (line   99)
* canonical() (decimal.Context method):  Context objects.    (line  238)
* canonical() (decimal.Decimal method):  Decimal objects.    (line  141)
* canonicalize() (in module xml.etree.ElementTree): Functions<7>.
                                                             (line    6)
* CAN_BCM (in module socket):            Constants<8>.       (line  106)
* can_change_color() (in module curses): Functions<4>.       (line   30)
* can_fetch() (urllib.robotparser.RobotFileParser method): urllib robotparser — Parser for robots txt.
                                                             (line   33)
* CAN_ISOTP (in module socket):          Constants<8>.       (line  145)
* CAN_J1939 (in module socket):          Constants<8>.       (line  154)
* CAN_RAW_FD_FRAMES (in module socket):  Constants<8>.       (line  121)
* CAN_RAW_JOIN_FILTERS (in module socket): Constants<8>.     (line  134)
* can_symlink() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  616)
* can_write_eof() (asyncio.StreamWriter method): StreamWriter.
                                                             (line   47)
* can_write_eof() (asyncio.WriteTransport method): Write-only Transports.
                                                             (line   14)
* can_xattr() (in module test.support):  test support — Utilities for the Python test suite.
                                                             (line  620)
* capa() (poplib.POP3 method):           POP3 Objects.       (line   24)
* capitalize() (bytearray method):       Bytes and Bytearray Operations.
                                                             (line  465)
* capitalize() (bytes method):           Bytes and Bytearray Operations.
                                                             (line  465)
* capitalize() (str method):             String Methods<2>.  (line   22)
* captured_stderr() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  456)
* captured_stdin() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  456)
* captured_stdout() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  456)
* captureWarnings() (in module logging): Integration with the warnings module.
                                                             (line    9)
* capwords() (in module string):         Helper functions.   (line    6)
* casefold() (str method):               String Methods<2>.  (line   32)
* cast() (in module ctypes):             Utility functions.  (line   33)
* cast() (in module typing):             Functions and decorators.
                                                             (line    6)
* cast() (memoryview method):            Memory Views.       (line  270)
* cat() (in module nis):                 nis — Interface to Sun’s NIS Yellow Pages.
                                                             (line   29)
* catch_threading_exception() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  869)
* catch_unraisable_exception() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  904)
* catch_warnings (class in warnings):    Available Context Managers.
                                                             (line    6)
* category() (in module unicodedata):    unicodedata — Unicode Database.
                                                             (line   49)
* cbreak() (in module curses):           Functions<4>.       (line   35)
* CC:                                    New Improved and Deprecated Modules<4>.
                                                             (line   58)
* ccc() (ftplib.FTP_TLS method):         FTP_TLS Objects.    (line   23)
* CCompiler (class in distutils.ccompiler): distutils ccompiler — CCompiler base class.
                                                             (line   67)
* cdf() (statistics.NormalDist method):  NormalDist objects. (line   80)
* CDLL (class in ctypes):                Loading shared libraries.
                                                             (line    9)
* ceil() (in module math):               Numeric Types — int float complex.
                                                             (line  104)
* ceil() (in module math) <1>:           Number-theoretic and representation functions.
                                                             (line    6)
* CellType (in module types):            Standard Interpreter Types.
                                                             (line   70)
* center() (bytearray method):           Bytes and Bytearray Operations.
                                                             (line  284)
* center() (bytes method):               Bytes and Bytearray Operations.
                                                             (line  284)
* center() (str method):                 String Methods<2>.  (line   48)
* CertificateError:                      Exceptions<13>.     (line   94)
* certificates:                          SSL Contexts.       (line  673)
* CERT_NONE (in module ssl):             Constants<9>.       (line   11)
* CERT_OPTIONAL (in module ssl):         Constants<9>.       (line   25)
* CERT_REQUIRED (in module ssl):         Constants<9>.       (line   43)
* cert_store_stats() (ssl.SSLContext method): SSL Contexts.  (line   67)
* cert_time_to_seconds() (in module ssl): Certificate handling.
                                                             (line   48)
* CFLAGS:                                New Improved and Deprecated Modules<4>.
                                                             (line   58)
* CFLAGS <1>:                            Tweaking compiler/linker flags.
                                                             (line   66)
* CFLAGS <2>:                            Tweaking compiler/linker flags.
                                                             (line   67)
* CFUNCTYPE() (in module ctypes):        Function prototypes.
                                                             (line   15)
* cget() (tkinter.font.Font method):     tkinter font — Tkinter font wrapper.
                                                             (line   51)
* cgi (module):                          cgi — Common Gateway Interface support.
                                                             (line    6)
* CGI; debugging:                        Debugging CGI scripts.
                                                             (line    6)
* CGI; exceptions:                       cgitb — Traceback manager for CGI scripts.
                                                             (line    8)
* CGI; protocol:                         cgi — Common Gateway Interface support.
                                                             (line    8)
* CGI; security:                         Caring about security.
                                                             (line    6)
* CGI; tracebacks:                       cgitb — Traceback manager for CGI scripts.
                                                             (line    8)
* CGIHandler (class in wsgiref.handlers): wsgiref handlers – server/gateway base classes.
                                                             (line   11)
* CGIHTTPRequestHandler (class in http.server): http server — HTTP servers.
                                                             (line  456)
* cgitb (module):                        cgitb — Traceback manager for CGI scripts.
                                                             (line    6)
* CGIXMLRPCRequestHandler (class in xmlrpc.server): xmlrpc server — Basic XML-RPC servers.
                                                             (line   45)
* cgi_directories (http.server.CGIHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  482)
* chain() (in module itertools):         Itertool functions. (line   85)
* chaining; comparisons:                 Comparisons.        (line   19)
* chaining; comparisons <1>:             Comparisons<2>.     (line    6)
* ChainMap (class in collections):       ChainMap objects.   (line   16)
* ChainMap (class in typing):            Corresponding to types in collections.
                                                             (line   28)
* change_cwd() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  490)
* change_root() (in module distutils.util): distutils util — Miscellaneous other utility functions.
                                                             (line   84)
* channels() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line  133)
* CHANNEL_BINDING_TYPES (in module ssl): Constants<9>.       (line  441)
* channel_class (smtpd.SMTPServer attribute): SMTPServer Objects.
                                                             (line   80)
* character:                             The standard type hierarchy.
                                                             (line  161)
* character <1>:                         Subscriptions.      (line   38)
* character <2>:                         unicodedata — Unicode Database.
                                                             (line    6)
* CharacterDataHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  240)
* characters() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line  129)
* characters_written (BlockingIOError attribute): OS exceptions.
                                                             (line   18)
* Charset (class in email.charset):      email charset Representing character sets.
                                                             (line   24)
* charset() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line   83)
* CHAR_MAX (in module locale):           locale — Internationalization services.
                                                             (line  504)
* chdir() (in module os):                Files and Directories.
                                                             (line  115)
* check (lzma.LZMADecompressor attribute): Compressing and decompressing data in memory.
                                                             (line  159)
* check() (imaplib.IMAP4 method):        IMAP4 Objects.      (line   58)
* check() (in module tabnanny):          tabnanny — Detection of ambiguous indentation.
                                                             (line   17)
* checkbox() (msilib.Dialog method):     GUI classes.        (line   78)
* checkcache() (in module linecache):    linecache — Random access to text lines.
                                                             (line   43)
* CHECKED_HASH (py_compile.PycInvalidationMode attribute): py_compile — Compile Python source files.
                                                             (line  108)
* checkfuncname() (in module bdb):       bdb — Debugger framework.
                                                             (line  386)
* CheckList (class in tkinter.tix):      Hierarchical ListBox.
                                                             (line   13)
* checksizeof() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  611)
* checksum; Cyclic Redundancy Check:     zlib — Compression compatible with gzip.
                                                             (line  117)
* check_call() (in module subprocess):   Older high-level API.
                                                             (line   36)
* check_environ() (in module distutils.util): distutils util — Miscellaneous other utility functions.
                                                             (line   91)
* check_free_after_iterating() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  977)
* check_hostname (ssl.SSLContext attribute): SSL Contexts.   (line  492)
* check_impl_detail() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  347)
* check_no_resource_warning() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  425)
* check_output() (doctest.OutputChecker method): OutputChecker objects.
                                                             (line   17)
* check_output() (in module subprocess): Older high-level API.
                                                             (line   66)
* check_returncode() (subprocess.CompletedProcess method): Using the subprocess Module.
                                                             (line  125)
* check_syntax_error() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  751)
* check_syntax_warning() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  762)
* check_unused_args() (string.Formatter method): Custom String Formatting.
                                                             (line   91)
* check_warnings() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  356)
* check__all__() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  989)
* chflags() (in module os):              Files and Directories.
                                                             (line  134)
* chgat() (curses.window method):        Window Objects.     (line  136)
* childNodes (xml.dom.Node attribute):   Node Objects.       (line   49)
* ChildProcessError:                     OS exceptions.      (line   24)
* children (pyclbr.Class attribute):     Class Objects<2>.   (line   31)
* children (pyclbr.Function attribute):  Function Objects.   (line   31)
* chmod() (in module os):                Files and Directories.
                                                             (line  175)
* chmod() (pathlib.Path method):         Methods<2>.         (line   52)
* choice() (in module random):           Functions for sequences.
                                                             (line    6)
* choice() (in module secrets):          Random numbers.     (line   15)
* choices (optparse.Option attribute):   Option attributes.  (line   55)
* choices() (in module random):          Functions for sequences.
                                                             (line   11)
* Chooser (class in tkinter.colorchooser): tkinter colorchooser — Color choosing dialog.
                                                             (line   15)
* chown() (in module os):                Files and Directories.
                                                             (line  237)
* chown() (in module shutil):            Directory and files operations.
                                                             (line  357)
* chr() (built-in function):             Built-in Functions. (line  205)
* chroot() (in module os):               Files and Directories.
                                                             (line  260)
* Chunk (class in chunk):                chunk — Read IFF chunked data.
                                                             (line   49)
* chunk (module):                        chunk — Read IFF chunked data.
                                                             (line    6)
* cipher() (ssl.SSLSocket method):       SSL Sockets.        (line  209)
* cipher; DES:                           crypt — Function to check Unix passwords.
                                                             (line    8)
* circle() (in module turtle):           Turtle motion.      (line  177)
* CIRCUMFLEX (in module token):          token — Constants used with Python parse trees.
                                                             (line  154)
* CIRCUMFLEXEQUAL (in module token):     token — Constants used with Python parse trees.
                                                             (line  198)
* Clamped (class in decimal):            Signals.            (line   20)
* class:                                 Glossary.           (line  216)
* Class (class in symtable):             Examining Symbol Tables.
                                                             (line   89)
* Class browser:                         File menu Shell and Editor.
                                                             (line   22)
* class instance; attribute:             The standard type hierarchy.
                                                             (line  605)
* class instance; attribute; assignment: The standard type hierarchy.
                                                             (line  621)
* class instance; call:                  Calls.              (line  141)
* class object; call:                    The standard type hierarchy.
                                                             (line  578)
* class object; call <1>:                The standard type hierarchy.
                                                             (line  590)
* class object; call <2>:                Calls.              (line  137)
* class variable:                        Glossary.           (line  222)
* class; attribute:                      The standard type hierarchy.
                                                             (line  578)
* class; attribute; assignment:          The standard type hierarchy.
                                                             (line  587)
* class; body:                           Executing the class body.
                                                             (line    6)
* class; constructor:                    Basic customization.
                                                             (line   39)
* class; definition:                     The return statement.
                                                             (line    6)
* class; definition <1>:                 Class definitions.  (line    6)
* class; instance:                       The standard type hierarchy.
                                                             (line  605)
* class; name:                           Class definitions.  (line    6)
* ClassDef (class in ast):               Function and class definitions.
                                                             (line  177)
* classmethod() (built-in function):     Built-in Functions. (line  216)
* ClassMethodDescriptorType (in module types): Standard Interpreter Types.
                                                             (line  110)
* ClassVar (in module typing):           Special forms.      (line  175)
* clause:                                Compound statements.
                                                             (line   18)
* CLD_CONTINUED (in module os):          Process Management. (line  796)
* CLD_DUMPED (in module os):             Process Management. (line  796)
* CLD_EXITED (in module os):             Process Management. (line  796)
* CLD_KILLED (in module os):             Process Management. (line  796)
* CLD_STOPPED (in module os):            Process Management. (line  796)
* CLD_TRAPPED (in module os):            Process Management. (line  796)
* clean() (mailbox.Maildir method):      Maildir.            (line   82)
* cleandoc() (in module inspect):        Retrieving source code.
                                                             (line   65)
* CleanImport (class in test.support):   test support — Utilities for the Python test suite.
                                                             (line 1081)
* cleanup functions:                     Process Control.    (line   32)
* clear (pdb command):                   Debugger Commands.  (line   93)
* Clear Breakpoint:                      Help menu Shell and Editor.
                                                             (line   30)
* clear() (asyncio.Event method):        Event.              (line   59)
* clear() (collections.deque method):    deque objects.      (line   43)
* clear() (curses.window method):        Window Objects.     (line  152)
* clear() (dict method):                 Mapping Types — dict.
                                                             (line  143)
* clear() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  668)
* clear() (frame method):                The standard type hierarchy.
                                                             (line  749)
* clear() (frozenset method):            Set Types — set frozenset.
                                                             (line  213)
* clear() (http.cookiejar.CookieJar method): CookieJar and FileCookieJar Objects.
                                                             (line   77)
* clear() (in module turtle):            More drawing control.
                                                             (line   23)
* clear() (mailbox.Mailbox method):      Mailbox objects.    (line  204)
* clear() (sequence method):             Mutable Sequence Types.
                                                             (line   16)
* clear() (threading.Event method):      Event Objects.      (line   33)
* clear() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line   58)
* clearcache() (in module linecache):    linecache — Random access to text lines.
                                                             (line   38)
* ClearData() (msilib.Record method):    Record Objects.     (line   37)
* clearok() (curses.window method):      Window Objects.     (line  157)
* clearscreen() (in module turtle):      Window control.     (line   46)
* clearstamp() (in module turtle):       Turtle motion.      (line  249)
* clearstamps() (in module turtle):      Turtle motion.      (line  268)
* clear_all_breaks() (bdb.Bdb method):   bdb — Debugger framework.
                                                             (line  305)
* clear_all_file_breaks() (bdb.Bdb method): bdb — Debugger framework.
                                                             (line  300)
* clear_bpbynumber() (bdb.Bdb method):   bdb — Debugger framework.
                                                             (line  294)
* clear_break() (bdb.Bdb method):        bdb — Debugger framework.
                                                             (line  289)
* clear_cache() (in module filecmp):     filecmp — File and Directory Comparisons.
                                                             (line   56)
* clear_cache() (zoneinfo.ZoneInfo class method): The ZoneInfo class.
                                                             (line   58)
* clear_content() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  672)
* clear_flags() (decimal.Context method): Context objects.   (line  152)
* clear_frames() (in module traceback):  traceback — Print or retrieve a stack traceback.
                                                             (line  150)
* clear_history() (in module readline):  History list.       (line    8)
* clear_session_cookies() (http.cookiejar.CookieJar method): CookieJar and FileCookieJar Objects.
                                                             (line   89)
* clear_traces() (in module tracemalloc): Functions<10>.     (line    6)
* clear_traps() (decimal.Context method): Context objects.   (line  156)
* Client() (in module multiprocessing.connection): Listeners and Clients.
                                                             (line   34)
* client_address (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line   66)
* CLOCK_BOOTTIME (in module time):       Clock ID Constants. (line    9)
* clock_getres() (in module time):       Functions<3>.       (line   38)
* clock_gettime() (in module time):      Functions<3>.       (line   48)
* clock_gettime_ns() (in module time):   Functions<3>.       (line   58)
* CLOCK_HIGHRES (in module time):        Clock ID Constants. (line   23)
* CLOCK_MONOTONIC (in module time):      Clock ID Constants. (line   34)
* CLOCK_MONOTONIC_RAW (in module time):  Clock ID Constants. (line   43)
* CLOCK_PROCESS_CPUTIME_ID (in module time): Clock ID Constants.
                                                             (line   53)
* CLOCK_PROF (in module time):           Clock ID Constants. (line   61)
* CLOCK_REALTIME (in module time):       Clock ID Constants. (line  112)
* clock_settime() (in module time):      Functions<3>.       (line   67)
* clock_settime_ns() (in module time):   Functions<3>.       (line   76)
* CLOCK_TAI (in module time):            Clock ID Constants. (line   69)
* CLOCK_THREAD_CPUTIME_ID (in module time): Clock ID Constants.
                                                             (line   81)
* CLOCK_UPTIME (in module time):         Clock ID Constants. (line   89)
* CLOCK_UPTIME_RAW (in module time):     Clock ID Constants. (line   99)
* clone() (email.generator.BytesGenerator method): email generator Generating MIME documents.
                                                             (line  112)
* clone() (email.generator.Generator method): email generator Generating MIME documents.
                                                             (line  208)
* clone() (email.policy.Policy method):  email policy Policy Objects.
                                                             (line  207)
* clone() (in module turtle):            Special Turtle methods.
                                                             (line   32)
* clone() (pipes.Template method):       Template Objects.   (line   12)
* cloneNode() (xml.dom.Node method):     Node Objects.       (line  147)
* close() (aifc.aifc method):            aifc — Read and write AIFF and AIFC files.
                                                             (line  116)
* close() (asyncio.AbstractChildWatcher method): Process Watchers.
                                                             (line   77)
* close() (asyncio.BaseTransport method): Base Transport.    (line    6)
* close() (asyncio.loop method):         Running and stopping the loop.
                                                             (line   43)
* close() (asyncio.Server method):       Server Objects.     (line   29)
* close() (asyncio.StreamWriter method): StreamWriter.       (line   37)
* close() (asyncio.SubprocessTransport method): Subprocess Transports.
                                                             (line   59)
* close() (asyncore.dispatcher method):  asyncore — Asynchronous socket handler.
                                                             (line  243)
* close() (chunk.Chunk method):          chunk — Read IFF chunked data.
                                                             (line   78)
* close() (contextlib.ExitStack method): Utilities.          (line  447)
* close() (coroutine method):            Coroutine Objects.  (line   45)
* close() (dbm.dumb.dumbdbm method):     dbm dumb — Portable DBM implementation.
                                                             (line   83)
* close() (dbm.gnu.gdbm method):         dbm gnu — GNU’s reinterpretation of dbm.
                                                             (line  118)
* close() (dbm.ndbm.ndbm method):        dbm ndbm — Interface based on ndbm.
                                                             (line   66)
* close() (distutils.text_file.TextFile method): distutils text_file — The TextFile class.
                                                             (line   96)
* close() (email.parser.BytesFeedParser method): FeedParser API.
                                                             (line   65)
* close() (ftplib.FTP method):           FTP Objects.        (line  246)
* close() (generator method):            Generator-iterator methods.
                                                             (line   47)
* close() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line   15)
* close() (http.client.HTTPConnection method): HTTPConnection Objects.
                                                             (line  111)
* close() (imaplib.IMAP4 method):        IMAP4 Objects.      (line   62)
* close() (in module fileinput):         fileinput — Iterate over lines from multiple input streams.
                                                             (line  127)
* close() (in module os):                File Descriptor Operations.
                                                             (line   21)
* close() (in module os) <1>:            Sub-interpreter support.
                                                             (line   76)
* close() (in module socket):            Other functions<2>. (line    9)
* close() (io.IOBase method):            I/O Base Classes.   (line   49)
* close() (logging.FileHandler method):  FileHandler.        (line   27)
* close() (logging.Handler method):      Handler Objects.    (line   73)
* close() (logging.handlers.MemoryHandler method): MemoryHandler.
                                                             (line   55)
* close() (logging.handlers.NTEventLogHandler method): NTEventLogHandler.
                                                             (line   29)
* close() (logging.handlers.SocketHandler method): SocketHandler.
                                                             (line   20)
* close() (logging.handlers.SysLogHandler method): SysLogHandler.
                                                             (line   39)
* close() (mailbox.Mailbox method):      Mailbox objects.    (line  262)
* close() (mailbox.Maildir method):      Maildir.            (line  113)
* close() (mailbox.MH method):           MH.                 (line  104)
* close() (mmap.mmap method):            mmap — Memory-mapped file support.
                                                             (line  165)
* Close() (msilib.Database method):      Database Objects.   (line   22)
* Close() (msilib.View method):          View Objects.       (line   35)
* close() (multiprocessing.connection.Connection method): Connection Objects<2>.
                                                             (line   35)
* close() (multiprocessing.connection.Listener method): Listeners and Clients.
                                                             (line   91)
* close() (multiprocessing.pool.Pool method): Process Pools. (line  168)
* close() (multiprocessing.Process method): Process and exceptions.
                                                             (line  173)
* close() (multiprocessing.Queue method): Pipes and Queues.  (line  163)
* close() (multiprocessing.shared_memory.SharedMemory method): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line   65)
* close() (multiprocessing.SimpleQueue method): Pipes and Queues.
                                                             (line  209)
* close() (os.scandir method):           Files and Directories.
                                                             (line  783)
* close() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line   22)
* close() (ossaudiodev.oss_mixer_device method): Mixer Device Objects.
                                                             (line    8)
* close() (select.devpoll method):       /dev/poll Polling Objects.
                                                             (line   12)
* close() (select.epoll method):         Edge and Level Trigger Polling epoll Objects.
                                                             (line   65)
* close() (select.kqueue method):        Kqueue Objects.     (line    6)
* close() (selectors.BaseSelector method): Classes<3>.       (line  137)
* close() (shelve.Shelf method):         shelve — Python object persistence.
                                                             (line   71)
* close() (socket.socket method):        Socket Objects.     (line   39)
* close() (sqlite3.Connection method):   Connection Objects. (line   45)
* close() (sqlite3.Cursor method):       Cursor Objects.     (line  147)
* close() (sunau.AU_read method):        AU_read Objects.    (line    9)
* close() (sunau.AU_write method):       AU_write Objects.   (line   59)
* close() (tarfile.TarFile method):      TarFile Objects.    (line  250)
* close() (telnetlib.Telnet method):     Telnet Objects.     (line   89)
* close() (urllib.request.BaseHandler method): BaseHandler Objects.
                                                             (line   14)
* close() (wave.Wave_read method):       Wave_read Objects.  (line    9)
* close() (wave.Wave_write method):      Wave_write Objects. (line   23)
* Close() (winreg.PyHKEY method):        Registry Handle Objects.
                                                             (line   34)
* close() (xml.etree.ElementTree.TreeBuilder method): TreeBuilder Objects.
                                                             (line   28)
* close() (xml.etree.ElementTree.XMLParser method): XMLParser Objects.
                                                             (line   20)
* close() (xml.etree.ElementTree.XMLPullParser method): XMLPullParser Objects.
                                                             (line   22)
* close() (xml.sax.xmlreader.IncrementalParser method): IncrementalParser Objects.
                                                             (line   13)
* close() (zipfile.ZipFile method):      ZipFile Objects.    (line   86)
* closed (http.client.HTTPResponse attribute): HTTPResponse Objects.
                                                             (line   75)
* closed (io.IOBase attribute):          I/O Base Classes.   (line   59)
* closed (mmap.mmap attribute):          mmap — Memory-mapped file support.
                                                             (line  171)
* closed (ossaudiodev.oss_audio_device attribute): Audio Device Objects.
                                                             (line  230)
* closed (select.devpoll attribute):     /dev/poll Polling Objects.
                                                             (line   18)
* closed (select.epoll attribute):       Edge and Level Trigger Polling epoll Objects.
                                                             (line   69)
* closed (select.kqueue attribute):      Kqueue Objects.     (line   10)
* CloseKey() (in module winreg):         Functions<12>.      (line    8)
* closelog() (in module syslog):         syslog — Unix syslog library routines.
                                                             (line   59)
* closerange() (in module os):           File Descriptor Operations.
                                                             (line   32)
* close_connection (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line   75)
* close_when_done() (asynchat.async_chat method): asynchat — Asynchronous socket command/response handler.
                                                             (line   73)
* closing() (in module contextlib):      Utilities.          (line  121)
* clrtobot() (curses.window method):     Window Objects.     (line  162)
* clrtoeol() (curses.window method):     Window Objects.     (line  168)
* cmath (module):                        cmath — Mathematical functions for complex numbers.
                                                             (line    6)
* Cmd (class in cmd):                    cmd — Support for line-oriented command interpreters.
                                                             (line   15)
* cmd (module):                          cmd — Support for line-oriented command interpreters.
                                                             (line    6)
* cmd (subprocess.CalledProcessError attribute): Using the subprocess Module.
                                                             (line  201)
* cmd (subprocess.TimeoutExpired attribute): Using the subprocess Module.
                                                             (line  164)
* cmdloop() (cmd.Cmd method):            Cmd Objects.        (line    8)
* cmdqueue (cmd.Cmd attribute):          Cmd Objects.        (line  135)
* cmp() (in module filecmp):             filecmp — File and Directory Comparisons.
                                                             (line   16)
* cmpfiles() (in module filecmp):        filecmp — File and Directory Comparisons.
                                                             (line   36)
* cmp_op (in module dis):                Opcode collections. (line   17)
* cmp_to_key() (in module functools):    functools — Higher-order functions and operations on callable objects.
                                                             (line  102)
* CMSG_LEN() (in module socket):         Other functions<2>. (line  298)
* CMSG_SPACE() (in module socket):       Other functions<2>. (line  313)
* code (module):                         code — Interpreter base classes.
                                                             (line    6)
* code (SystemExit attribute):           Concrete exceptions.
                                                             (line  330)
* code (urllib.error.HTTPError attribute): urllib error — Exception classes raised by urllib request.
                                                             (line   38)
* code (urllib.response.addinfourl attribute): urllib response — Response classes used by urllib.
                                                             (line   40)
* code (xml.etree.ElementTree.ParseError attribute): Exceptions<16>.
                                                             (line   14)
* code (xml.parsers.expat.ExpatError attribute): ExpatError Exceptions.
                                                             (line    9)
* code object:                           The standard type hierarchy.
                                                             (line  654)
* code object <1>:                       Methods.            (line   42)
* code object <2>:                       marshal — Internal Python object serialization.
                                                             (line   30)
* code object <3>:                       Cell Objects.       (line   53)
* code; block:                           Execution model.    (line    6)
* CodecInfo (class in codecs):           codecs — Codec registry and base classes.
                                                             (line   58)
* Codecs:                                codecs — Codec registry and base classes.
                                                             (line    8)
* codecs (module):                       codecs — Codec registry and base classes.
                                                             (line    6)
* Codecs; decode:                        codecs — Codec registry and base classes.
                                                             (line    8)
* Codecs; encode:                        codecs — Codec registry and base classes.
                                                             (line    8)
* coded_value (http.cookies.Morsel attribute): Morsel Objects.
                                                             (line   56)
* codeop (module):                       codeop — Compile Python code.
                                                             (line    6)
* codepoint2name (in module html.entities): html entities — Definitions of HTML general entities.
                                                             (line   35)
* codes (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   16)
* CODESET (in module locale):            locale — Internationalization services.
                                                             (line  184)
* CodeType (class in types):             Standard Interpreter Types.
                                                             (line   50)
* code_info() (in module dis):           Analysis functions. (line   11)
* coding; style:                         Intermezzo Coding Style.
                                                             (line    6)
* coercion:                              Glossary.           (line  227)
* collapse_addresses() (in module ipaddress): Other Module Level Functions.
                                                             (line   43)
* collapse_rfc2231_value() (in module email.utils): email utils Miscellaneous utilities.
                                                             (line  187)
* collect() (in module gc):              gc — Garbage Collector interface.
                                                             (line   34)
* Collection (class in collections.abc): Collections Abstract Base Classes.
                                                             (line  131)
* Collection (class in typing):          Corresponding to collections in collections abc.
                                                             (line   27)
* collections (module):                  collections — Container datatypes.
                                                             (line    6)
* collections.abc (module):              collections abc — Abstract Base Classes for Containers.
                                                             (line    6)
* collect_incoming_data() (asynchat.async_chat method): asynchat — Asynchronous socket command/response handler.
                                                             (line   78)
* colno (json.JSONDecodeError attribute): Exceptions<14>.    (line   27)
* colno (re.error attribute):            Module Contents.    (line  389)
* COLON (in module token):               token — Constants used with Python parse trees.
                                                             (line   70)
* COLONEQUAL (in module token):          token — Constants used with Python parse trees.
                                                             (line  238)
* color() (in module turtle):            Color control.      (line  104)
* colormode() (in module turtle):        Settings and special methods.
                                                             (line   34)
* colorsys (module):                     colorsys — Conversions between color systems.
                                                             (line    6)
* color_content() (in module curses):    Functions<4>.       (line   45)
* color_pair() (in module curses):       Functions<4>.       (line   53)
* COLS:                                  curses<3>.          (line    7)
* COLS <1>:                              Functions<4>.       (line  555)
* column() (tkinter.ttk.Treeview method): ttk Treeview.      (line   35)
* COLUMNS:                               Functions<4>.       (line  579)
* COLUMNS <1>:                           Functions<4>.       (line  582)
* columns (os.terminal_size attribute):  Querying the size of a terminal.
                                                             (line   30)
* col_offset (ast.AST attribute):        Node classes.       (line   39)
* comb() (in module math):               Number-theoretic and representation functions.
                                                             (line   12)
* combinations() (in module itertools):  Itertool functions. (line  110)
* combinations_with_replacement() (in module itertools): Itertool functions.
                                                             (line  161)
* combine() (datetime.datetime class method): datetime Objects.
                                                             (line  170)
* combining() (in module unicodedata):   unicodedata — Unicode Database.
                                                             (line   59)
* ComboBox (class in tkinter.tix):       Basic Widgets.      (line   18)
* Combobox (class in tkinter.ttk):       ttk Combobox.       (line    6)
* comma:                                 Parenthesized forms.
                                                             (line   20)
* COMMA (in module token):               token — Constants used with Python parse trees.
                                                             (line   74)
* Command (class in distutils.cmd):      distutils cmd — Abstract base class for Distutils commands.
                                                             (line    8)
* Command (class in distutils.core):     distutils core — Core Distutils functionality.
                                                             (line  307)
* command (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line   88)
* command line:                          Complete Python programs.
                                                             (line   25)
* command line option; -?:               Generic options.    (line    6)
* command line option; -b:               Miscellaneous options.
                                                             (line    6)
* command line option; -B:               Miscellaneous options.
                                                             (line   16)
* command line option; -c <command>:     Interface options.  (line   36)
* command line option; –check-hash-based-pycs default|always|never: Miscellaneous options.
                                                             (line   21)
* command line option; -d:               Miscellaneous options.
                                                             (line   35)
* command line option; -E:               Miscellaneous options.
                                                             (line   40)
* command line option; -h:               Generic options.    (line    6)
* command line option; –help:            Generic options.    (line    6)
* command line option; -i:               Miscellaneous options.
                                                             (line   45)
* command line option; -I:               Miscellaneous options.
                                                             (line   56)
* command line option; -J:               Options you shouldn’t use.
                                                             (line    6)
* command line option; -m <module-name>: Interface options.  (line   50)
* command line option; -O:               Miscellaneous options.
                                                             (line   66)
* command line option; -OO:              Miscellaneous options.
                                                             (line   76)
* command line option; -q:               Miscellaneous options.
                                                             (line   85)
* command line option; -R:               Miscellaneous options.
                                                             (line   92)
* command line option; -s:               Miscellaneous options.
                                                             (line  117)
* command line option; -S:               Miscellaneous options.
                                                             (line  127)
* command line option; -u:               Miscellaneous options.
                                                             (line  135)
* command line option; -V:               Generic options.    (line   12)
* command line option; -v:               Miscellaneous options.
                                                             (line  145)
* command line option; –version:         Generic options.    (line   12)
* command line option; -W arg:           Miscellaneous options.
                                                             (line  152)
* command line option; -x:               Miscellaneous options.
                                                             (line  191)
* command line option; -X:               Miscellaneous options.
                                                             (line  196)
* CommandCompiler (class in codeop):     codeop — Compile Python code.
                                                             (line   64)
* commands (pdb command):                Debugger Commands.  (line  126)
* comment:                               Comments.           (line    6)
* comment (http.cookiejar.Cookie attribute): Cookie Objects<2>.
                                                             (line   58)
* COMMENT (in module token):             token — Constants used with Python parse trees.
                                                             (line  261)
* comment (zipfile.ZipFile attribute):   ZipFile Objects.    (line  312)
* comment (zipfile.ZipInfo attribute):   ZipInfo Objects.    (line   88)
* Comment() (in module xml.etree.ElementTree): Functions<7>. (line   72)
* comment() (xml.etree.ElementTree.TreeBuilder method): TreeBuilder Objects.
                                                             (line   49)
* commenters (shlex.shlex attribute):    shlex Objects.      (line   85)
* CommentHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  295)
* comment_url (http.cookiejar.Cookie attribute): Cookie Objects<2>.
                                                             (line   63)
* commit() (msilib.CAB method):          CAB Objects.        (line   24)
* Commit() (msilib.Database method):     Database Objects.   (line   11)
* commit() (sqlite3.Connection method):  Connection Objects. (line   32)
* common (filecmp.dircmp attribute):     The dircmp class.   (line   59)
* Common Gateway Interface:              cgi — Common Gateway Interface support.
                                                             (line    8)
* commonpath() (in module os.path):      os path — Common pathname manipulations.
                                                             (line   73)
* commonprefix() (in module os.path):    os path — Common pathname manipulations.
                                                             (line   88)
* common_dirs (filecmp.dircmp attribute): The dircmp class.  (line   71)
* common_files (filecmp.dircmp attribute): The dircmp class. (line   75)
* common_funny (filecmp.dircmp attribute): The dircmp class. (line   79)
* common_types (in module mimetypes):    mimetypes — Map filenames to MIME types.
                                                             (line  144)
* communicate() (asyncio.asyncio.subprocess.Process method): Interacting with Subprocesses.
                                                             (line   50)
* communicate() (subprocess.Popen method): Popen Objects.    (line   35)
* Compare (class in ast):                Expressions<2>.     (line   92)
* compare() (decimal.Context method):    Context objects.    (line  242)
* compare() (decimal.Decimal method):    Decimal objects.    (line  147)
* compare() (difflib.Differ method):     Differ Objects.     (line   38)
* compare_digest() (in module hmac):     hmac — Keyed-Hashing for Message Authentication.
                                                             (line  113)
* compare_digest() (in module secrets):  Other functions.    (line    6)
* compare_networks() (ipaddress.IPv4Network method): Network objects.
                                                             (line  237)
* compare_networks() (ipaddress.IPv6Network method): Network objects.
                                                             (line  352)
* COMPARE_OP (opcode):                   Python Bytecode Instructions.
                                                             (line  555)
* compare_signal() (decimal.Context method): Context objects.
                                                             (line  246)
* compare_signal() (decimal.Decimal method): Decimal objects.
                                                             (line  158)
* compare_to() (tracemalloc.Snapshot method): Snapshot.      (line   13)
* compare_total() (decimal.Context method): Context objects. (line  250)
* compare_total() (decimal.Decimal method): Decimal objects. (line  165)
* compare_total_mag() (decimal.Context method): Context objects.
                                                             (line  254)
* compare_total_mag() (decimal.Decimal method): Decimal objects.
                                                             (line  190)
* comparison:                            Comparisons.        (line    6)
* comparisons:                           Basic customization.
                                                             (line  179)
* COMPARISON_FLAGS (in module doctest):  Option Flags.       (line  115)
* Compat32 (class in email.policy):      email policy Policy Objects.
                                                             (line  547)
* compat32 (in module email.policy):     email policy Policy Objects.
                                                             (line  602)
* Compile (class in codeop):             codeop — Compile Python code.
                                                             (line   55)
* compile() (built-in function):         Built-in Functions. (line  245)
* compile() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  269)
* compile() (in module py_compile):      py_compile — Compile Python source files.
                                                             (line   24)
* compile() (in module re):              Module Contents.    (line   14)
* compile() (parser.ST method):          ST Objects.         (line   17)
* compileall (module):                   compileall — Byte-compile Python libraries.
                                                             (line    6)
* compileall command line option; -b:    Command-line use.   (line   59)
* compileall command line option; -d destdir: Command-line use.
                                                             (line   32)
* compileall command line option; -e dir: Command-line use.  (line  102)
* compileall command line option; -f:    Command-line use.   (line   22)
* compileall command line option; –hardlink-dupes: Command-line use.
                                                             (line  106)
* compileall command line option; -i list: Command-line use. (line   53)
* compileall command line option; –invalidation-mode [timestamp|checked-hash|unchecked-hash]: Command-line use.
                                                             (line   80)
* compileall command line option; -j N:  Command-line use.   (line   74)
* compileall command line option; -l:    Command-line use.   (line   17)
* compileall command line option; -o level: Command-line use.
                                                             (line   96)
* compileall command line option; -p prepend_prefix: Command-line use.
                                                             (line   42)
* compileall command line option; -q:    Command-line use.   (line   26)
* compileall command line option; -r:    Command-line use.   (line   67)
* compileall command line option; -s strip_prefix: Command-line use.
                                                             (line   40)
* compileall command line option; -x regex: Command-line use.
                                                             (line   47)
* compileall command line option; directory ...: Command-line use.
                                                             (line    9)
* compileall command line option; file ...: Command-line use.
                                                             (line    9)
* compilest() (in module parser):        Converting ST Objects.
                                                             (line   43)
* compile_command() (in module code):    code — Interpreter base classes.
                                                             (line   47)
* compile_command() (in module codeop):  codeop — Compile Python code.
                                                             (line   29)
* compile_dir() (in module compileall):  Public functions.   (line    6)
* compile_file() (in module compileall): Public functions.   (line   96)
* compile_path() (in module compileall): Public functions.   (line  161)
* complete() (rlcompleter.Completer method): Completer Objects.
                                                             (line    8)
* completedefault() (cmd.Cmd method):    Cmd Objects.        (line   80)
* CompletedProcess (class in subprocess): Using the subprocess Module.
                                                             (line   91)
* complete_statement() (in module sqlite3): Module functions and constants.
                                                             (line  182)
* complex (built-in class):              Built-in Functions. (line  324)
* Complex (class in numbers):            The numeric tower.  (line    6)
* complex literal:                       Numeric literals.   (line    6)
* complex number:                        Glossary.           (line  239)
* complex number; literals:              Numeric Types — int float complex.
                                                             (line   19)
* complex; number:                       The standard type hierarchy.
                                                             (line  124)
* compound; statement:                   Compound statements.
                                                             (line    6)
* comprehension (class in ast):          Comprehensions.     (line   52)
* comprehensions:                        Displays for lists sets and dictionaries.
                                                             (line    6)
* compress() (bz2.BZ2Compressor method): Incremental de compression.
                                                             (line   15)
* compress() (in module bz2):            One-shot de compression.
                                                             (line    6)
* compress() (in module gzip):           gzip — Support for gzip files.
                                                             (line  177)
* compress() (in module itertools):      Itertool functions. (line  212)
* compress() (in module lzma):           Compressing and decompressing data in memory.
                                                             (line  183)
* compress() (in module zlib):           zlib — Compression compatible with gzip.
                                                             (line   45)
* compress() (lzma.LZMACompressor method): Compressing and decompressing data in memory.
                                                             (line   81)
* compress() (zlib.Compress method):     zlib — Compression compatible with gzip.
                                                             (line  199)
* compressed (ipaddress.IPv4Address attribute): Address objects.
                                                             (line   64)
* compressed (ipaddress.IPv4Network attribute): Network objects.
                                                             (line  107)
* compressed (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  192)
* compressed (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  319)
* compression() (ssl.SSLSocket method):  SSL Sockets.        (line  227)
* CompressionError:                      tarfile — Read and write tar archive files.
                                                             (line  198)
* compressobj() (in module zlib):        zlib — Compression compatible with gzip.
                                                             (line   60)
* compress_size (zipfile.ZipInfo attribute): ZipInfo Objects.
                                                             (line  139)
* compress_type (zipfile.ZipInfo attribute): ZipInfo Objects.
                                                             (line   84)
* COMSPEC:                               Process Management. (line  681)
* COMSPEC <1>:                           Popen Constructor.  (line   91)
* concat() (in module operator):         operator — Standard operators as functions.
                                                             (line  172)
* concatenation; operation:              Common Sequence Operations.
                                                             (line   21)
* concurrent.futures (module):           concurrent futures — Launching parallel tasks.
                                                             (line    6)
* Condition (class in asyncio):          Condition.          (line    6)
* Condition (class in multiprocessing):  Synchronization primitives.
                                                             (line   32)
* Condition (class in threading):        Condition Objects.  (line   72)
* condition (pdb command):               Debugger Commands.  (line  119)
* condition() (msilib.Control method):   GUI classes.        (line   24)
* Condition() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  155)
* Conditional; expression:               Boolean operations. (line    6)
* conditional; expression:               Conditional expressions.
                                                             (line    6)
* config() (tkinter.font.Font method):   tkinter font — Tkinter font wrapper.
                                                             (line   55)
* ConfigParser (class in configparser):  ConfigParser Objects.
                                                             (line    6)
* configparser (module):                 configparser — Configuration file parser.
                                                             (line    6)
* configuration information:             sysconfig — Provide access to Python’s configuration information.
                                                             (line   10)
* configuration; file:                   configparser — Configuration file parser.
                                                             (line    8)
* configure() (tkinter.ttk.Style method): Ttk Styling.       (line   24)
* configure_mock() (unittest.mock.Mock method): The Mock Class.
                                                             (line  242)
* confstr() (in module os):              Miscellaneous System Information.
                                                             (line    6)
* confstr_names (in module os):          Miscellaneous System Information.
                                                             (line   28)
* conjugate() (complex number method):   Numeric Types — int float complex.
                                                             (line   94)
* conjugate() (decimal.Decimal method):  Decimal objects.    (line  202)
* conjugate() (numbers.Complex method):  The numeric tower.  (line   23)
* conn (smtpd.SMTPChannel attribute):    SMTPChannel Objects.
                                                             (line   48)
* connect() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  194)
* connect() (ftplib.FTP method):         FTP Objects.        (line   22)
* connect() (http.client.HTTPConnection method): HTTPConnection Objects.
                                                             (line  105)
* connect() (in module sqlite3):         Module functions and constants.
                                                             (line   90)
* connect() (multiprocessing.managers.BaseManager method): Managers.
                                                             (line   59)
* connect() (smtplib.SMTP method):       SMTP Objects.       (line   33)
* connect() (socket.socket method):      Socket Objects.     (line   60)
* Connection (class in multiprocessing.connection): Connection Objects<2>.
                                                             (line   13)
* Connection (class in sqlite3):         Connection Objects. (line    6)
* connection (sqlite3.Cursor attribute): Cursor Objects.     (line  217)
* ConnectionAbortedError:                OS exceptions.      (line   44)
* ConnectionError:                       OS exceptions.      (line   29)
* ConnectionRefusedError:                OS exceptions.      (line   50)
* ConnectionResetError:                  OS exceptions.      (line   56)
* connection_lost() (asyncio.BaseProtocol method): Base Protocol.
                                                             (line   23)
* connection_made() (asyncio.BaseProtocol method): Base Protocol.
                                                             (line   15)
* ConnectRegistry() (in module winreg):  Functions<12>.      (line   17)
* connect_accepted_socket() (asyncio.loop method): Creating network servers.
                                                             (line  122)
* connect_ex() (socket.socket method):   Socket Objects.     (line   82)
* connect_read_pipe() (asyncio.loop method): Working with pipes.
                                                             (line    6)
* connect_write_pipe() (asyncio.loop method): Working with pipes.
                                                             (line   22)
* const (optparse.Option attribute):     Option attributes.  (line   50)
* constant:                              Literals.           (line    6)
* Constant (class in ast):               Literals<3>.        (line    6)
* constructor() (in module copyreg):     copyreg — Register pickle support functions.
                                                             (line   17)
* consumed (asyncio.LimitOverrunError attribute): Exceptions<10>.
                                                             (line   65)
* container:                             Objects values and types.
                                                             (line   67)
* container <1>:                         The standard type hierarchy.
                                                             (line  578)
* Container (class in collections.abc):  Collections Abstract Base Classes.
                                                             (line  104)
* Container (class in typing):           Corresponding to collections in collections abc.
                                                             (line   37)
* container; iteration over:             Iterator Types.     (line    6)
* contains() (in module operator):       operator — Standard operators as functions.
                                                             (line  177)
* CONTAINS_OP (opcode):                  Python Bytecode Instructions.
                                                             (line  566)
* ContentDispositionHeader (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line  280)
* ContentHandler (class in xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line   18)
* ContentManager (class in email.contentmanager): email contentmanager Managing MIME Content.
                                                             (line   12)
* contents (ctypes._Pointer attribute):  Arrays and pointers.
                                                             (line   50)
* contents() (importlib.abc.ResourceReader method): importlib abc – Abstract base classes related to import.
                                                             (line  342)
* contents() (in module importlib.resources): importlib resources – Resources.
                                                             (line  154)
* ContentTooShortError:                  urllib error — Exception classes raised by urllib request.
                                                             (line   56)
* ContentTransferEncoding (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line  290)
* ContentTypeHeader (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line  267)
* content_disposition (email.headerregistry.ContentDispositionHeader attribute): email headerregistry Custom Header Objects.
                                                             (line  285)
* content_manager (email.policy.EmailPolicy attribute): email policy Policy Objects.
                                                             (line  402)
* content_type (email.headerregistry.ContentTypeHeader attribute): email headerregistry Custom Header Objects.
                                                             (line  272)
* Context (class in contextvars):        Manual Context Management.
                                                             (line   20)
* Context (class in decimal):            Context objects.    (line   96)
* context (ssl.SSLSocket attribute):     SSL Sockets.        (line  318)
* context management protocol:           Context Manager Types.
                                                             (line    6)
* context manager:                       With Statement Context Managers.
                                                             (line   14)
* context manager <1>:                   Context Manager Types.
                                                             (line    6)
* context manager <2>:                   Glossary.           (line  253)
* context variable:                      Glossary.           (line  259)
* ContextDecorator (class in contextlib): Utilities.         (line  265)
* contextlib (module):                   contextlib — Utilities for with-statement contexts.
                                                             (line    6)
* ContextManager (class in typing):      Context manager types.
                                                             (line    6)
* contextmanager() (in module contextlib): Utilities.        (line   30)
* ContextVar (class in contextvars):     Context Variables.  (line    6)
* contextvars (module):                  contextvars — Context Variables.
                                                             (line    6)
* context_diff() (in module difflib):    difflib — Helpers for computing deltas.
                                                             (line  157)
* contiguous:                            shape strides suboffsets.
                                                             (line   26)
* contiguous <1>:                        Glossary.           (line  269)
* contiguous (memoryview attribute):     Memory Views.       (line  483)
* Continue (class in ast):               Control flow.       (line  101)
* continue (pdb command):                Debugger Commands.  (line  192)
* Control (class in msilib):             GUI classes.        (line   11)
* Control (class in tkinter.tix):        Basic Widgets.      (line   24)
* control() (msilib.Dialog method):      GUI classes.        (line   47)
* control() (select.kqueue method):      Kqueue Objects.     (line   22)
* controlnames (in module curses.ascii): curses ascii — Utilities for ASCII characters.
                                                             (line  237)
* controls() (ossaudiodev.oss_mixer_device method): Mixer Device Objects.
                                                             (line   23)
* ConversionError:                       Exceptions<7>.      (line   13)
* convert_arg_line_to_args() (argparse.ArgumentParser method): Customizing file parsing.
                                                             (line    6)
* convert_field() (string.Formatter method): Custom String Formatting.
                                                             (line  108)
* convert_path() (in module distutils.util): distutils util — Miscellaneous other utility functions.
                                                             (line   74)
* Cookie (class in http.cookiejar):      http cookiejar — Cookie handling for HTTP clients.
                                                             (line  109)
* CookieError:                           http cookies — HTTP state management.
                                                             (line   33)
* CookieJar (class in http.cookiejar):   http cookiejar — Cookie handling for HTTP clients.
                                                             (line   45)
* cookiejar (urllib.request.HTTPCookieProcessor attribute): HTTPCookieProcessor Objects.
                                                             (line    8)
* CookiePolicy (class in http.cookiejar): http cookiejar — Cookie handling for HTTP clients.
                                                             (line   73)
* Coordinated Universal Time:            time — Time access and conversions.
                                                             (line   40)
* Copy:                                  Help menu Shell and Editor.
                                                             (line   30)
* copy (module):                         copy — Shallow and deep copy operations.
                                                             (line    6)
* copy() (collections.deque method):     deque objects.      (line   47)
* copy() (contextvars.Context method):   Manual Context Management.
                                                             (line   70)
* copy() (decimal.Context method):       Context objects.    (line  162)
* copy() (dict method):                  Mapping Types — dict.
                                                             (line  147)
* copy() (frozenset method):             Set Types — set frozenset.
                                                             (line  123)
* copy() (hashlib.hash method):          Hash algorithms.    (line  151)
* copy() (hmac.HMAC method):             hmac — Keyed-Hashing for Message Authentication.
                                                             (line   82)
* copy() (http.cookies.Morsel method):   Morsel Objects.     (line  102)
* copy() (imaplib.IMAP4 method):         IMAP4 Objects.      (line   68)
* copy() (in module copy):               copy — Shallow and deep copy operations.
                                                             (line   18)
* copy() (in module multiprocessing.sharedctypes): The multiprocessing sharedctypes module.
                                                             (line   83)
* copy() (in module shutil):             Directory and files operations.
                                                             (line  121)
* copy() (pipes.Template method):        Template Objects.   (line   48)
* copy() (sequence method):              Mutable Sequence Types.
                                                             (line   16)
* copy() (tkinter.font.Font method):     tkinter font — Tkinter font wrapper.
                                                             (line   59)
* copy() (types.MappingProxyType method): Standard Interpreter Types.
                                                             (line  268)
* copy() (zlib.Compress method):         zlib — Compression compatible with gzip.
                                                             (line  220)
* copy() (zlib.Decompress method):       zlib — Compression compatible with gzip.
                                                             (line  289)
* copy2() (in module shutil):            Directory and files operations.
                                                             (line  152)
* copy; protocol:                        Pickling Class Instances.
                                                             (line   93)
* copyfile() (in module shutil):         Directory and files operations.
                                                             (line   17)
* copyfileobj() (in module shutil):      Directory and files operations.
                                                             (line    6)
* copying files:                         shutil — High-level file operations.
                                                             (line    8)
* copymode() (in module shutil):         Directory and files operations.
                                                             (line   59)
* copyreg (module):                      copyreg — Register pickle support functions.
                                                             (line    6)
* copyright (built-in variable):         Constants added by the site module.
                                                             (line   18)
* copyright (in module sys):             sys — System-specific parameters and functions.
                                                             (line  153)
* copyright (in module sys) <1>:         Process-wide parameters.
                                                             (line  188)
* copysign() (in module math):           Number-theoretic and representation functions.
                                                             (line   30)
* copystat() (in module shutil):         Directory and files operations.
                                                             (line   77)
* copytree() (in module shutil):         Directory and files operations.
                                                             (line  191)
* copy_abs() (decimal.Context method):   Context objects.    (line  259)
* copy_abs() (decimal.Decimal method):   Decimal objects.    (line  207)
* copy_context() (in module contextvars): Manual Context Management.
                                                             (line    6)
* copy_decimal() (decimal.Context method): Context objects.  (line  166)
* copy_file() (in module distutils.file_util): distutils file_util — Single file operations.
                                                             (line    9)
* copy_file_range() (in module os):      File Descriptor Operations.
                                                             (line   44)
* copy_location() (in module ast):       ast Helpers.        (line  132)
* copy_negate() (decimal.Context method): Context objects.   (line  263)
* copy_negate() (decimal.Decimal method): Decimal objects.   (line  213)
* copy_sign() (decimal.Context method):  Context objects.    (line  267)
* copy_sign() (decimal.Decimal method):  Decimal objects.    (line  219)
* copy_tree() (in module distutils.dir_util): distutils dir_util — Directory tree operations.
                                                             (line   32)
* coroutine:                             Special method lookup.
                                                             (line   74)
* coroutine <1>:                         Yield expressions.  (line   52)
* coroutine <2>:                         Glossary.           (line  280)
* Coroutine (class in collections.abc):  Collections Abstract Base Classes.
                                                             (line  212)
* Coroutine (class in typing):           Asynchronous programming.
                                                             (line    6)
* coroutine function:                    Glossary.           (line  288)
* coroutine() (in module asyncio):       Generator-based Coroutines.
                                                             (line   16)
* coroutine() (in module types):         Coroutine Utility Functions.
                                                             (line    6)
* coroutine; function:                   The standard type hierarchy.
                                                             (line  463)
* CoroutineType (in module types):       Standard Interpreter Types.
                                                             (line   36)
* cos() (in module cmath):               Trigonometric functions<2>.
                                                             (line   25)
* cos() (in module math):                Trigonometric functions.
                                                             (line   31)
* cosh() (in module cmath):              Hyperbolic functions<2>.
                                                             (line   26)
* cosh() (in module math):               Hyperbolic functions.
                                                             (line   21)
* count (tracemalloc.Statistic attribute): Statistic.        (line   15)
* count (tracemalloc.StatisticDiff attribute): StatisticDiff.
                                                             (line   15)
* count() (array.array method):          array — Efficient arrays of numeric values.
                                                             (line  144)
* count() (bytearray method):            Bytes and Bytearray Operations.
                                                             (line   36)
* count() (bytes method):                Bytes and Bytearray Operations.
                                                             (line   36)
* count() (collections.deque method):    deque objects.      (line   53)
* count() (in module itertools):         Itertool functions. (line  225)
* count() (multiprocessing.shared_memory.ShareableList method): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line  264)
* count() (sequence method):             Common Sequence Operations.
                                                             (line   21)
* count() (str method):                  String Methods<2>.  (line   55)
* Counter (class in collections):        Counter objects.    (line   23)
* Counter (class in typing):             Corresponding to types in collections.
                                                             (line   40)
* countOf() (in module operator):        operator — Standard operators as functions.
                                                             (line  183)
* countTestCases() (unittest.TestCase method): Test cases.   (line  712)
* countTestCases() (unittest.TestSuite method): Grouping tests.
                                                             (line   55)
* count_diff (tracemalloc.StatisticDiff attribute): StatisticDiff.
                                                             (line   20)
* CoverageResults (class in trace):      Programmatic Interface.
                                                             (line   47)
* co_argcount (code object attribute):   The standard type hierarchy.
                                                             (line  667)
* CO_ASYNC_GENERATOR (in module inspect): Code Objects Bit Flags.
                                                             (line   56)
* co_cellvars (code object attribute):   The standard type hierarchy.
                                                             (line  667)
* co_code (code object attribute):       The standard type hierarchy.
                                                             (line  667)
* co_consts (code object attribute):     The standard type hierarchy.
                                                             (line  667)
* CO_COROUTINE (in module inspect):      Code Objects Bit Flags.
                                                             (line   39)
* co_filename (code object attribute):   The standard type hierarchy.
                                                             (line  667)
* co_firstlineno (code object attribute): The standard type hierarchy.
                                                             (line  667)
* co_flags (code object attribute):      The standard type hierarchy.
                                                             (line  667)
* co_freevars (code object attribute):   The standard type hierarchy.
                                                             (line  667)
* CO_FUTURE_DIVISION (C variable):       The Very High Level Layer.
                                                             (line  431)
* CO_GENERATOR (in module inspect):      Code Objects Bit Flags.
                                                             (line   30)
* CO_ITERABLE_COROUTINE (in module inspect): Code Objects Bit Flags.
                                                             (line   47)
* co_kwonlyargcount (code object attribute): The standard type hierarchy.
                                                             (line  667)
* co_lnotab (code object attribute):     The standard type hierarchy.
                                                             (line  667)
* co_name (code object attribute):       The standard type hierarchy.
                                                             (line  667)
* co_names (code object attribute):      The standard type hierarchy.
                                                             (line  667)
* CO_NESTED (in module inspect):         Code Objects Bit Flags.
                                                             (line   26)
* CO_NEWLOCALS (in module inspect):      Code Objects Bit Flags.
                                                             (line   13)
* co_nlocals (code object attribute):    The standard type hierarchy.
                                                             (line  667)
* CO_NOFREE (in module inspect):         Code Objects Bit Flags.
                                                             (line   35)
* CO_OPTIMIZED (in module inspect):      Code Objects Bit Flags.
                                                             (line    9)
* co_posonlyargcount (code object attribute): The standard type hierarchy.
                                                             (line  667)
* co_stacksize (code object attribute):  The standard type hierarchy.
                                                             (line  667)
* CO_VARARGS (in module inspect):        Code Objects Bit Flags.
                                                             (line   18)
* CO_VARKEYWORDS (in module inspect):    Code Objects Bit Flags.
                                                             (line   22)
* co_varnames (code object attribute):   The standard type hierarchy.
                                                             (line  667)
* CPP:                                   New Improved and Deprecated Modules<4>.
                                                             (line   59)
* CPPFLAGS:                              New Improved and Deprecated Modules<4>.
                                                             (line   59)
* cProfile (module):                     profile and cProfile Module Reference.
                                                             (line    6)
* CPU time:                              Functions<3>.       (line  200)
* CPU time <1>:                          Functions<3>.       (line  479)
* cpu_count() (in module multiprocessing): Miscellaneous<3>. (line   13)
* cpu_count() (in module os):            Miscellaneous System Information.
                                                             (line   37)
* CPython:                               Glossary.           (line  296)
* cpython_only() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  698)
* crawl_delay() (urllib.robotparser.RobotFileParser method): urllib robotparser — Parser for robots txt.
                                                             (line   50)
* CRC (zipfile.ZipInfo attribute):       ZipInfo Objects.    (line  135)
* crc32() (in module binascii):          binascii — Convert between binary and ASCII.
                                                             (line  121)
* crc32() (in module zlib):              zlib — Compression compatible with gzip.
                                                             (line  115)
* crc_hqx() (in module binascii):        binascii — Convert between binary and ASCII.
                                                             (line  114)
* create() (imaplib.IMAP4 method):       IMAP4 Objects.      (line   72)
* create() (in module venv):             API<2>.             (line  171)
* create() (venv.EnvBuilder method):     API<2>.             (line   57)
* createAttribute() (xml.dom.Document method): Document Objects.
                                                             (line   46)
* createAttributeNS() (xml.dom.Document method): Document Objects.
                                                             (line   53)
* createComment() (xml.dom.Document method): Document Objects.
                                                             (line   34)
* createDocument() (xml.dom.DOMImplementation method): DOMImplementation Objects.
                                                             (line   16)
* createDocumentType() (xml.dom.DOMImplementation method): DOMImplementation Objects.
                                                             (line   26)
* createElement() (xml.dom.Document method): Document Objects.
                                                             (line   14)
* createElementNS() (xml.dom.Document method): Document Objects.
                                                             (line   21)
* createfilehandler() (tkinter.Widget.tk method): File Handlers.
                                                             (line   27)
* CreateKey() (in module winreg):        Functions<12>.      (line   35)
* CreateKeyEx() (in module winreg):      Functions<12>.      (line   63)
* createLock() (logging.Handler method): Handler Objects.    (line   20)
* createLock() (logging.NullHandler method): NullHandler.    (line   24)
* createProcessingInstruction() (xml.dom.Document method): Document Objects.
                                                             (line   40)
* CreateRecord() (in module msilib):     msilib — Read and write Microsoft Installer files.
                                                             (line   55)
* createSocket() (logging.handlers.SocketHandler method): SocketHandler.
                                                             (line   72)
* createTextNode() (xml.dom.Document method): Document Objects.
                                                             (line   28)
* create_aggregate() (sqlite3.Connection method): Connection Objects.
                                                             (line  109)
* create_archive() (in module zipapp):   Python API.         (line    8)
* create_autospec() (in module unittest.mock): create_autospec.
                                                             (line    6)
* CREATE_BREAKAWAY_FROM_JOB (in module subprocess): Windows Constants.
                                                             (line  124)
* create_collation() (sqlite3.Connection method): Connection Objects.
                                                             (line  147)
* create_configuration() (venv.EnvBuilder method): API<2>.   (line   94)
* create_connection() (asyncio.loop method): Opening network connections.
                                                             (line    6)
* create_connection() (in module socket): Creating sockets.  (line   80)
* create_datagram_endpoint() (asyncio.loop method): Opening network connections.
                                                             (line  134)
* create_decimal() (decimal.Context method): Context objects.
                                                             (line  170)
* create_decimal_from_float() (decimal.Context method): Context objects.
                                                             (line  194)
* create_default_context() (in module ssl): Context creation.
                                                             (line    9)
* CREATE_DEFAULT_ERROR_MODE (in module subprocess): Windows Constants.
                                                             (line  114)
* create_empty_file() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  297)
* create_function() (sqlite3.Connection method): Connection Objects.
                                                             (line   73)
* create_future() (asyncio.loop method): Creating Futures and Tasks.
                                                             (line    6)
* create_module (C function):            Multi-phase initialization.
                                                             (line   67)
* create_module() (importlib.abc.Loader method): importlib abc – Abstract base classes related to import.
                                                             (line  170)
* create_module() (importlib.machinery.ExtensionFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  319)
* CREATE_NEW_CONSOLE (in module subprocess): Windows Constants.
                                                             (line   38)
* CREATE_NEW_PROCESS_GROUP (in module subprocess): Windows Constants.
                                                             (line   43)
* CREATE_NO_WINDOW (in module subprocess): Windows Constants.
                                                             (line   99)
* create_server() (asyncio.loop method): Creating network servers.
                                                             (line    6)
* create_server() (in module socket):    Creating sockets.   (line  104)
* create_shortcut() (built-in function): The Postinstallation script.
                                                             (line   62)
* create_socket() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  184)
* create_static_lib() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  323)
* create_stats() (profile.Profile method): profile and cProfile Module Reference.
                                                             (line   86)
* create_string_buffer() (in module ctypes): Utility functions.
                                                             (line   40)
* create_subprocess_exec() (in module asyncio): Creating Subprocesses.
                                                             (line    6)
* create_subprocess_shell() (in module asyncio): Creating Subprocesses.
                                                             (line   25)
* create_system (zipfile.ZipInfo attribute): ZipInfo Objects.
                                                             (line   99)
* create_task() (asyncio.loop method):   Creating Futures and Tasks.
                                                             (line   17)
* create_task() (in module asyncio):     Creating Tasks.     (line    6)
* create_tree() (in module distutils.dir_util): distutils dir_util — Directory tree operations.
                                                             (line   21)
* create_unicode_buffer() (in module ctypes): Utility functions.
                                                             (line   58)
* create_unix_connection() (asyncio.loop method): Opening network connections.
                                                             (line  212)
* create_unix_server() (asyncio.loop method): Creating network servers.
                                                             (line  100)
* create_version (zipfile.ZipInfo attribute): ZipInfo Objects.
                                                             (line  103)
* credits (built-in variable):           Constants added by the site module.
                                                             (line   18)
* critical() (in module logging):        Module-Level Functions.
                                                             (line  138)
* critical() (logging.Logger method):    Logger Objects.     (line  246)
* CRNCYSTR (in module locale):           locale — Internationalization services.
                                                             (line  257)
* cross() (in module audioop):           audioop — Manipulate raw audio data.
                                                             (line   74)
* crypt (module):                        crypt — Function to check Unix passwords.
                                                             (line    6)
* crypt() (in module crypt):             Module Functions<2>.
                                                             (line    8)
* crypt(3):                              crypt — Function to check Unix passwords.
                                                             (line    8)
* crypt(3) <1>:                          crypt — Function to check Unix passwords.
                                                             (line   16)
* crypt(3) <2>:                          Module Functions<2>.
                                                             (line   32)
* cryptography:                          Cryptographic Services.
                                                             (line    6)
* cssclasses (calendar.HTMLCalendar attribute): calendar — General calendar-related functions.
                                                             (line  193)
* cssclasses_weekday_head (calendar.HTMLCalendar attribute): calendar — General calendar-related functions.
                                                             (line  213)
* cssclass_month (calendar.HTMLCalendar attribute): calendar — General calendar-related functions.
                                                             (line  227)
* cssclass_month_head (calendar.HTMLCalendar attribute): calendar — General calendar-related functions.
                                                             (line  220)
* cssclass_noday (calendar.HTMLCalendar attribute): calendar — General calendar-related functions.
                                                             (line  206)
* cssclass_year (calendar.HTMLCalendar attribute): calendar — General calendar-related functions.
                                                             (line  234)
* cssclass_year_head (calendar.HTMLCalendar attribute): calendar — General calendar-related functions.
                                                             (line  241)
* csv:                                   csv — CSV File Reading and Writing.
                                                             (line    8)
* csv (module):                          csv — CSV File Reading and Writing.
                                                             (line    6)
* cte (email.headerregistry.ContentTransferEncoding attribute): email headerregistry Custom Header Objects.
                                                             (line  294)
* ctermid() (in module os):              Process Parameters. (line    9)
* cte_type (email.policy.Policy attribute): email policy Policy Objects.
                                                             (line  159)
* ctime() (datetime.date method):        date Objects.       (line  255)
* ctime() (datetime.datetime method):    datetime Objects.   (line  681)
* ctime() (in module time):              Functions<3>.       (line   85)
* ctrl() (in module curses.ascii):       curses ascii — Utilities for ASCII characters.
                                                             (line  213)
* CTRL_BREAK_EVENT (in module signal):   Module contents<2>. (line  155)
* CTRL_C_EVENT (in module signal):       Module contents<2>. (line  146)
* ctypes (module):                       ctypes — A foreign function library for Python.
                                                             (line    6)
* curdir (in module os):                 Miscellaneous System Information.
                                                             (line   81)
* currency() (in module locale):         locale — Internationalization services.
                                                             (line  420)
* current() (tkinter.ttk.Combobox method): ttk Combobox.     (line    8)
* CurrentByteIndex (xml.parsers.expat.xmlparser attribute): XMLParser Objects<2>.
                                                             (line  157)
* CurrentColumnNumber (xml.parsers.expat.xmlparser attribute): XMLParser Objects<2>.
                                                             (line  161)
* currentframe() (in module inspect):    The interpreter stack.
                                                             (line   74)
* CurrentLineNumber (xml.parsers.expat.xmlparser attribute): XMLParser Objects<2>.
                                                             (line  165)
* current_process() (in module multiprocessing): Miscellaneous<3>.
                                                             (line   29)
* current_task() (in module asyncio):    Introspection.      (line    6)
* current_thread() (in module threading): threading — Thread-based parallelism.
                                                             (line   39)
* curses (module):                       curses — Terminal handling for character-cell displays.
                                                             (line    6)
* curses.ascii (module):                 curses ascii — Utilities for ASCII characters.
                                                             (line    6)
* curses.panel (module):                 curses panel — A panel stack extension for curses.
                                                             (line    6)
* curses.textpad (module):               curses textpad — Text input widget for curses programs.
                                                             (line    6)
* Cursor (class in sqlite3):             Cursor Objects.     (line    6)
* cursor() (sqlite3.Connection method):  Connection Objects. (line   26)
* cursyncup() (curses.window method):    Window Objects.     (line  172)
* curs_set() (in module curses):         Functions<4>.       (line   61)
* customize_compiler() (in module distutils.sysconfig): distutils sysconfig — System configuration information.
                                                             (line   84)
* Cut:                                   Help menu Shell and Editor.
                                                             (line   30)
* cwd() (ftplib.FTP method):             FTP Objects.        (line  213)
* cwd() (pathlib.Path class method):     Methods<2>.         (line   17)
* cycle() (in module itertools):         Itertool functions. (line  247)
* CycleError:                            Exceptions<3>.      (line    8)
* Cyclic Redundancy Check:               zlib — Compression compatible with gzip.
                                                             (line  117)
* c_bool (class in ctypes):              Fundamental data types<2>.
                                                             (line  202)
* C_BUILTIN (in module imp):             imp — Access the import internals.
                                                             (line  333)
* c_byte (class in ctypes):              Fundamental data types<2>.
                                                             (line   45)
* c_char (class in ctypes):              Fundamental data types<2>.
                                                             (line   51)
* c_char_p (class in ctypes):            Fundamental data types<2>.
                                                             (line   58)
* c_contiguous (memoryview attribute):   Memory Views.       (line  469)
* c_double (class in ctypes):            Fundamental data types<2>.
                                                             (line   65)
* C_EXTENSION (in module imp):           imp — Access the import internals.
                                                             (line  321)
* c_float (class in ctypes):             Fundamental data types<2>.
                                                             (line   76)
* c_int (class in ctypes):               Fundamental data types<2>.
                                                             (line   81)
* c_int16 (class in ctypes):             Fundamental data types<2>.
                                                             (line   93)
* c_int32 (class in ctypes):             Fundamental data types<2>.
                                                             (line   98)
* c_int64 (class in ctypes):             Fundamental data types<2>.
                                                             (line  103)
* c_int8 (class in ctypes):              Fundamental data types<2>.
                                                             (line   88)
* c_long (class in ctypes):              Fundamental data types<2>.
                                                             (line  108)
* c_longdouble (class in ctypes):        Fundamental data types<2>.
                                                             (line   70)
* c_longlong (class in ctypes):          Fundamental data types<2>.
                                                             (line  113)
* c_short (class in ctypes):             Fundamental data types<2>.
                                                             (line  119)
* c_size_t (class in ctypes):            Fundamental data types<2>.
                                                             (line  124)
* c_ssize_t (class in ctypes):           Fundamental data types<2>.
                                                             (line  128)
* c_ubyte (class in ctypes):             Fundamental data types<2>.
                                                             (line  134)
* c_uint (class in ctypes):              Fundamental data types<2>.
                                                             (line  140)
* c_uint16 (class in ctypes):            Fundamental data types<2>.
                                                             (line  152)
* c_uint32 (class in ctypes):            Fundamental data types<2>.
                                                             (line  157)
* c_uint64 (class in ctypes):            Fundamental data types<2>.
                                                             (line  162)
* c_uint8 (class in ctypes):             Fundamental data types<2>.
                                                             (line  147)
* c_ulong (class in ctypes):             Fundamental data types<2>.
                                                             (line  167)
* c_ulonglong (class in ctypes):         Fundamental data types<2>.
                                                             (line  172)
* c_ushort (class in ctypes):            Fundamental data types<2>.
                                                             (line  178)
* c_void_p (class in ctypes):            Fundamental data types<2>.
                                                             (line  184)
* c_wchar (class in ctypes):             Fundamental data types<2>.
                                                             (line  189)
* c_wchar_p (class in ctypes):           Fundamental data types<2>.
                                                             (line  196)
* daemon (multiprocessing.Process attribute): Process and exceptions.
                                                             (line   87)
* daemon (threading.Thread attribute):   Thread Objects.     (line  184)
* dangling; else:                        Compound statements.
                                                             (line   54)
* data:                                  Objects values and types.
                                                             (line    6)
* data (collections.UserDict attribute): UserDict objects.   (line   24)
* data (collections.UserList attribute): UserList objects.   (line   29)
* data (collections.UserString attribute): UserString objects.
                                                             (line   24)
* data (select.kevent attribute):        Kevent Objects.     (line  175)
* data (selectors.SelectorKey attribute): Classes<3>.        (line   48)
* data (urllib.request.Request attribute): Request Objects.  (line   39)
* data (xml.dom.Comment attribute):      Comment Objects.    (line    9)
* data (xml.dom.ProcessingInstruction attribute): ProcessingInstruction Objects.
                                                             (line   14)
* data (xml.dom.Text attribute):         Text and CDATASection Objects.
                                                             (line   15)
* data (xmlrpc.client.Binary attribute): Binary Objects.     (line   12)
* data() (xml.etree.ElementTree.TreeBuilder method): TreeBuilder Objects.
                                                             (line   33)
* data; tabular:                         csv — CSV File Reading and Writing.
                                                             (line    8)
* data; type:                            The standard type hierarchy.
                                                             (line    6)
* DatabaseError:                         Exceptions<5>.      (line   15)
* databases:                             dbm dumb — Portable DBM implementation.
                                                             (line    8)
* dataclass() (in module dataclasses):   Module-level decorators classes and functions.
                                                             (line    6)
* dataclasses (module):                  dataclasses — Data Classes.
                                                             (line    6)
* DatagramHandler (class in logging.handlers): DatagramHandler.
                                                             (line   10)
* DatagramProtocol (class in asyncio):   Base Protocols.     (line   20)
* DatagramRequestHandler (class in socketserver): Request Handler Objects.
                                                             (line   42)
* DatagramTransport (class in asyncio):  Transports Hierarchy.
                                                             (line   43)
* datagram_received() (asyncio.DatagramProtocol method): Datagram Protocols.
                                                             (line    9)
* DataHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  412)
* data_open() (urllib.request.DataHandler method): DataHandler Objects.
                                                             (line    6)
* data_received() (asyncio.Protocol method): Streaming Protocols.
                                                             (line   13)
* date (class in datetime):              date Objects.       (line   13)
* date() (datetime.datetime method):     datetime Objects.   (line  391)
* date() (nntplib.NNTP method):          Methods<3>.         (line  298)
* DateHeader (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line  136)
* datetime (class in datetime):          datetime Objects.   (line   17)
* DateTime (class in xmlrpc.client):     DateTime Objects.   (line    6)
* datetime (email.headerregistry.DateHeader attribute): email headerregistry Custom Header Objects.
                                                             (line  145)
* datetime (module):                     datetime — Basic date and time types.
                                                             (line    6)
* date_time (zipfile.ZipInfo attribute): ZipInfo Objects.    (line   54)
* date_time_string() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  313)
* datum:                                 Dictionary displays.
                                                             (line    6)
* day (datetime.date attribute):         date Objects.       (line  110)
* day (datetime.datetime attribute):     datetime Objects.   (line  272)
* daylight (in module time):             Timezone Constants. (line   13)
* Daylight Saving Time:                  time — Time access and conversions.
                                                             (line   44)
* day_abbr (in module calendar):         calendar — General calendar-related functions.
                                                             (line  371)
* day_name (in module calendar):         calendar — General calendar-related functions.
                                                             (line  366)
* DbfilenameShelf (class in shelve):     Restrictions.       (line   64)
* dbm (module):                          dbm — Interfaces to Unix “databases”.
                                                             (line    6)
* dbm.dumb (module):                     dbm dumb — Portable DBM implementation.
                                                             (line    6)
* dbm.gnu (module):                      dbm gnu — GNU’s reinterpretation of dbm.
                                                             (line    6)
* dbm.ndbm (module):                     dbm ndbm — Interface based on ndbm.
                                                             (line    6)
* dcgettext() (in module locale):        Access to message catalogs.
                                                             (line   10)
* deallocation, object:                  Finalization and De-allocation.
                                                             (line    6)
* debug (imaplib.IMAP4 attribute):       IMAP4 Objects.      (line  397)
* DEBUG (in module re):                  Module Contents.    (line   58)
* debug (pdb command):                   Debugger Commands.  (line  335)
* debug (shlex.shlex attribute):         shlex Objects.      (line  162)
* debug (zipfile.ZipFile attribute):     ZipFile Objects.    (line  306)
* debug() (in module doctest):           Debugging.          (line  124)
* debug() (in module logging):           Module-Level Functions.
                                                             (line   44)
* debug() (logging.Logger method):       Logger Objects.     (line  130)
* debug() (pipes.Template method):       Template Objects.   (line   16)
* debug() (unittest.TestCase method):    Test cases.         (line  120)
* debug() (unittest.TestSuite method):   Grouping tests.     (line   48)
* debugger:                              Debug menu Shell window only.
                                                             (line   15)
* debugger <1>:                          sys — System-specific parameters and functions.
                                                             (line  741)
* debugger <2>:                          sys — System-specific parameters and functions.
                                                             (line 1316)
* debugger; configuration; file:         Debugger Commands.  (line   37)
* debugging:                             pdb — The Python Debugger.
                                                             (line    8)
* debugging; assertions:                 The assert statement.
                                                             (line    6)
* DebuggingServer (class in smtpd):      DebuggingServer Objects.
                                                             (line    6)
* debuglevel (http.client.HTTPResponse attribute): HTTPResponse Objects.
                                                             (line   69)
* DebugRunner (class in doctest):        Debugging.          (line  168)
* DEBUG_BYTECODE_SUFFIXES (in module importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line   20)
* DEBUG_COLLECTABLE (in module gc):      gc — Garbage Collector interface.
                                                             (line  293)
* DEBUG_LEAK (in module gc):             gc — Garbage Collector interface.
                                                             (line  313)
* debug_print() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  511)
* DEBUG_SAVEALL (in module gc):          gc — Garbage Collector interface.
                                                             (line  307)
* debug_src() (in module doctest):       Debugging.          (line  147)
* DEBUG_STATS (in module gc):            gc — Garbage Collector interface.
                                                             (line  288)
* DEBUG_UNCOLLECTABLE (in module gc):    gc — Garbage Collector interface.
                                                             (line  297)
* Decimal (class in decimal):            Decimal objects.    (line    6)
* decimal (module):                      decimal — Decimal fixed point and floating point arithmetic.
                                                             (line    6)
* decimal literal:                       Numeric literals.   (line    6)
* decimal() (in module unicodedata):     unicodedata — Unicode Database.
                                                             (line   31)
* DecimalException (class in decimal):   Signals.            (line   28)
* decode (codecs.CodecInfo attribute):   codecs — Codec registry and base classes.
                                                             (line   69)
* decode() (bytearray method):           Bytes and Bytearray Operations.
                                                             (line   89)
* decode() (bytes method):               Bytes and Bytearray Operations.
                                                             (line   89)
* decode() (codecs.Codec method):        Stateless Encoding and Decoding.
                                                             (line   26)
* decode() (codecs.IncrementalDecoder method): IncrementalDecoder Objects.
                                                             (line   28)
* decode() (in module base64):           base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  205)
* decode() (in module codecs):           codecs — Codec registry and base classes.
                                                             (line   34)
* decode() (in module quopri):           quopri — Encode and decode MIME quoted-printable data.
                                                             (line   19)
* decode() (in module uu):               uu — Encode and decode uuencode files.
                                                             (line   37)
* decode() (json.JSONDecoder method):    Encoders and Decoders.
                                                             (line   86)
* decode() (xmlrpc.client.Binary method): Binary Objects.    (line   20)
* decode() (xmlrpc.client.DateTime method): DateTime Objects.
                                                             (line   13)
* decodebytes() (in module base64):      base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  212)
* DecodedGenerator (class in email.generator): email generator Generating MIME documents.
                                                             (line  232)
* decodestring() (in module quopri):     quopri — Encode and decode MIME quoted-printable data.
                                                             (line   41)
* decode_header() (in module email.header): email header Internationalized headers.
                                                             (line  183)
* decode_header() (in module nntplib):   Utility functions<2>.
                                                             (line    8)
* decode_params() (in module email.utils): email utils Miscellaneous utilities.
                                                             (line  204)
* decode_rfc2231() (in module email.utils): email utils Miscellaneous utilities.
                                                             (line  174)
* decode_source() (in module importlib.util): importlib util – Utility code for importers.
                                                             (line   72)
* decomposition() (in module unicodedata): unicodedata — Unicode Database.
                                                             (line   75)
* decompress() (bz2.BZ2Decompressor method): Incremental de compression.
                                                             (line   45)
* decompress() (in module bz2):          One-shot de compression.
                                                             (line   16)
* decompress() (in module gzip):         gzip — Support for gzip files.
                                                             (line  188)
* decompress() (in module lzma):         Compressing and decompressing data in memory.
                                                             (line  192)
* decompress() (in module zlib):         zlib — Compression compatible with gzip.
                                                             (line  131)
* decompress() (lzma.LZMADecompressor method): Compressing and decompressing data in memory.
                                                             (line  132)
* decompress() (zlib.Decompress method): zlib — Compression compatible with gzip.
                                                             (line  258)
* decompressobj() (in module zlib):      zlib — Compression compatible with gzip.
                                                             (line  176)
* decorator:                             Glossary.           (line  303)
* DEDENT (in module token):              token — Constants used with Python parse trees.
                                                             (line   52)
* DEDENT token:                          Indentation.        (line   33)
* DEDENT token <1>:                      Compound statements.
                                                             (line   54)
* dedent() (in module textwrap):         textwrap — Text wrapping and filling.
                                                             (line   74)
* deepcopy() (in module copy):           copy — Shallow and deep copy operations.
                                                             (line   22)
* default (in module email.policy):      email policy Policy Objects.
                                                             (line  487)
* DEFAULT (in module unittest.mock):     DEFAULT.            (line    6)
* default (inspect.Parameter attribute): Introspecting callables with the Signature object.
                                                             (line  169)
* default (optparse.Option attribute):   Option attributes.  (line   36)
* default() (cmd.Cmd method):            Cmd Objects.        (line   74)
* default() (json.JSONEncoder method):   Encoders and Decoders.
                                                             (line  198)
* default; parameter; value:             Function definitions.
                                                             (line   56)
* DefaultContext (class in decimal):     Context objects.    (line   72)
* DefaultCookiePolicy (class in http.cookiejar): http cookiejar — Cookie handling for HTTP clients.
                                                             (line   78)
* defaultdict (class in collections):    defaultdict objects.
                                                             (line    6)
* DefaultDict (class in typing):         Corresponding to types in collections.
                                                             (line    6)
* DefaultEventLoopPolicy (class in asyncio): Policy Objects. (line   50)
* DefaultHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  310)
* DefaultHandlerExpand() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  317)
* defaults() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line   77)
* DefaultSelector (class in selectors):  Classes<3>.         (line  161)
* defaultTestLoader (in module unittest): Loading and running tests.
                                                             (line  430)
* defaultTestResult() (unittest.TestCase method): Test cases.
                                                             (line  717)
* DEFAULT_BUFFER_SIZE (in module io):    High-level Module Interface.
                                                             (line    6)
* default_bufsize (in module xml.dom.pulldom): xml dom pulldom — Support for building partial DOM trees.
                                                             (line  104)
* default_exception_handler() (asyncio.loop method): Error Handling API.
                                                             (line   26)
* default_factory (collections.defaultdict attribute): defaultdict objects.
                                                             (line   49)
* DEFAULT_FORMAT (in module tarfile):    tarfile — Read and write tar archive files.
                                                             (line  241)
* DEFAULT_IGNORES (in module filecmp):   The dircmp class.   (line  105)
* default_open() (urllib.request.BaseHandler method): BaseHandler Objects.
                                                             (line   30)
* DEFAULT_PROTOCOL (in module pickle):   Module Interface.   (line   21)
* default_timer() (in module timeit):    Python Interface.   (line   32)
* defects (email.headerregistry.BaseHeader attribute): email headerregistry Custom Header Objects.
                                                             (line   52)
* defects (email.message.EmailMessage attribute): email message Representing an email message.
                                                             (line  712)
* defects (email.message.Message attribute): email message Message Representing an email message using the compat32 API.
                                                             (line  724)
* define_macro() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  162)
* defpath (in module os):                Miscellaneous System Information.
                                                             (line  121)
* DefragResult (class in urllib.parse):  Structured Parse Results.
                                                             (line   40)
* DefragResultBytes (class in urllib.parse): Structured Parse Results.
                                                             (line   65)
* def_prog_mode() (in module curses):    Functions<4>.       (line   70)
* def_shell_mode() (in module curses):   Functions<4>.       (line   77)
* degrees() (in module math):            Angular conversion. (line    6)
* degrees() (in module turtle):          Settings for measurement.
                                                             (line    6)
* Del (class in ast):                    Variables.          (line   11)
* delattr() (built-in function):         Built-in Functions. (line  356)
* delay() (in module turtle):            Animation control.  (line    6)
* delayload (http.cookiejar.FileCookieJar attribute): CookieJar and FileCookieJar Objects.
                                                             (line  158)
* delay_output() (in module curses):     Functions<4>.       (line   85)
* delch() (curses.window method):        Window Objects.     (line  177)
* dele() (poplib.POP3 method):           POP3 Objects.       (line   67)
* Delete (class in ast):                 Statements.         (line  143)
* delete() (ftplib.FTP method):          FTP Objects.        (line  206)
* delete() (imaplib.IMAP4 method):       IMAP4 Objects.      (line   76)
* delete() (tkinter.ttk.Treeview method): ttk Treeview.      (line   79)
* deleteacl() (imaplib.IMAP4 method):    IMAP4 Objects.      (line   80)
* deletefilehandler() (tkinter.Widget.tk method): File Handlers.
                                                             (line   37)
* DeleteKey() (in module winreg):        Functions<12>.      (line  102)
* DeleteKeyEx() (in module winreg):      Functions<12>.      (line  124)
* deleteln() (curses.window method):     Window Objects.     (line  181)
* deleteMe() (bdb.Breakpoint method):    bdb — Debugger framework.
                                                             (line   41)
* DeleteValue() (in module winreg):      Functions<12>.      (line  165)
* DELETE_ATTR (opcode):                  Python Bytecode Instructions.
                                                             (line  460)
* DELETE_DEREF (opcode):                 Python Bytecode Instructions.
                                                             (line  687)
* DELETE_FAST (opcode):                  Python Bytecode Instructions.
                                                             (line  657)
* DELETE_GLOBAL (opcode):                Python Bytecode Instructions.
                                                             (line  468)
* DELETE_NAME (opcode):                  Python Bytecode Instructions.
                                                             (line  434)
* DELETE_SUBSCR (opcode):                Python Bytecode Instructions.
                                                             (line  254)
* deletion; target:                      The del statement<2>.
                                                             (line    6)
* deletion; target; list:                The del statement<2>.
                                                             (line    6)
* delimiter (csv.Dialect attribute):     Dialects and Formatting Parameters.
                                                             (line   19)
* delimiters:                            Delimiters.         (line    6)
* delitem() (in module operator):        operator — Standard operators as functions.
                                                             (line  187)
* deliver_challenge() (in module multiprocessing.connection): Listeners and Clients.
                                                             (line   15)
* delocalize() (in module locale):       locale — Internationalization services.
                                                             (line  441)
* del_param() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  383)
* del_param() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  543)
* demo_app() (in module wsgiref.simple_server): wsgiref simple_server – a simple WSGI HTTP server.
                                                             (line   36)
* denominator (fractions.Fraction attribute): fractions — Rational numbers.
                                                             (line   99)
* denominator (numbers.Rational attribute): The numeric tower.
                                                             (line   51)
* DeprecationWarning:                    Warnings.           (line   17)
* deque (class in collections):          deque objects.      (line    6)
* Deque (class in typing):               Corresponding to types in collections.
                                                             (line   51)
* dequeue() (logging.handlers.QueueListener method): QueueListener.
                                                             (line   46)
* derwin() (curses.window method):       Window Objects.     (line  186)
* DER_cert_to_PEM_cert() (in module ssl): Certificate handling.
                                                             (line   91)
* descrgetfunc (C type):                 Slot Type typedefs. (line   67)
* description (inspect.Parameter.kind attribute): Introspecting callables with the Signature object.
                                                             (line  234)
* description (sqlite3.Cursor attribute): Cursor Objects.    (line  207)
* description() (nntplib.NNTP method):   Methods<3>.         (line  149)
* descriptions() (nntplib.NNTP method):  Methods<3>.         (line  135)
* descriptor:                            Glossary.           (line  325)
* descrsetfunc (C type):                 Slot Type typedefs. (line   72)
* dest (optparse.Option attribute):      Option attributes.  (line   27)
* destructor:                            Basic customization.
                                                             (line   55)
* destructor <1>:                        Assignment statements.
                                                             (line   73)
* destructor (C type):                   Slot Type typedefs. (line   24)
* detach() (io.BufferedIOBase method):   I/O Base Classes.   (line  261)
* detach() (io.TextIOBase method):       Text I/O<2>.        (line   37)
* detach() (socket.socket method):       Socket Objects.     (line   94)
* detach() (tkinter.ttk.Treeview method): ttk Treeview.      (line   85)
* detach() (weakref.finalize method):    weakref — Weak references.
                                                             (line  270)
* Detach() (winreg.PyHKEY method):       Registry Handle Objects.
                                                             (line   40)
* DETACHED_PROCESS (in module subprocess): Windows Constants.
                                                             (line  106)
* detect_api_mismatch() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  951)
* detect_encoding() (in module tokenize): Tokenizing Input.  (line   77)
* detect_language() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  198)
* deterministic profiling:               Introduction to the profilers.
                                                             (line    6)
* device_encoding() (in module os):      File Descriptor Operations.
                                                             (line   67)
* devnull (in module os):                Miscellaneous System Information.
                                                             (line  136)
* DEVNULL (in module subprocess):        Using the subprocess Module.
                                                             (line  132)
* devpoll() (in module select):          select — Waiting for I/O completion.
                                                             (line   31)
* DevpollSelector (class in selectors):  Classes<3>.         (line  184)
* dgettext() (in module gettext):        GNU gettext API.    (line   49)
* dgettext() (in module locale):         Access to message catalogs.
                                                             (line    8)
* Dialect (class in csv):                Module Contents<3>. (line  177)
* dialect (csv.csvreader attribute):     Reader Objects.     (line   19)
* dialect (csv.csvwriter attribute):     Writer Objects.     (line   32)
* Dialog (class in msilib):              GUI classes.        (line   40)
* Dialog (class in tkinter.commondialog): tkinter commondialog — Dialog window templates.
                                                             (line   14)
* Dialog (class in tkinter.simpledialog): tkinter simpledialog — Standard Tkinter input dialogs.
                                                             (line   21)
* dict (2to3 fixer):                     Fixers.             (line   70)
* dict (built-in class):                 Mapping Types — dict.
                                                             (line   27)
* Dict (class in ast):                   Literals<3>.        (line  105)
* Dict (class in typing):                Corresponding to built-in types.
                                                             (line    6)
* dict() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  205)
* DictComp (class in ast):               Comprehensions.     (line    6)
* dictConfig() (in module logging.config): Configuration functions.
                                                             (line   13)
* dictionary:                            Glossary.           (line  342)
* dictionary comprehension:              Glossary.           (line  348)
* dictionary view:                       Glossary.           (line  356)
* dictionary; comprehensions:            Dictionary displays.
                                                             (line    6)
* dictionary; display:                   Dictionary displays.
                                                             (line    6)
* DictReader (class in csv):             Module Contents<3>. (line  103)
* DictWriter (class in csv):             Module Contents<3>. (line  144)
* DICT_MERGE (opcode):                   Python Bytecode Instructions.
                                                             (line  544)
* DICT_UPDATE (opcode):                  Python Bytecode Instructions.
                                                             (line  538)
* Differ (class in difflib):             difflib — Helpers for computing deltas.
                                                             (line   50)
* difference() (frozenset method):       Set Types — set frozenset.
                                                             (line  109)
* difference_update() (frozenset method): Set Types — set frozenset.
                                                             (line  182)
* difflib (module):                      difflib — Helpers for computing deltas.
                                                             (line    6)
* diff_bytes() (in module difflib):      difflib — Helpers for computing deltas.
                                                             (line  339)
* diff_files (filecmp.dircmp attribute): The dircmp class.   (line   90)
* digest() (hashlib.hash method):        Hash algorithms.    (line  138)
* digest() (hashlib.shake method):       SHAKE variable length digests.
                                                             (line   11)
* digest() (hmac.HMAC method):           hmac — Keyed-Hashing for Message Authentication.
                                                             (line   56)
* digest() (in module hmac):             hmac — Keyed-Hashing for Message Authentication.
                                                             (line   31)
* digest_size (hmac.HMAC attribute):     hmac — Keyed-Hashing for Message Authentication.
                                                             (line   90)
* digit() (in module unicodedata):       unicodedata — Unicode Database.
                                                             (line   37)
* digits (in module string):             String constants.   (line   24)
* dir() (built-in function):             Built-in Functions. (line  378)
* dir() (ftplib.FTP method):             FTP Objects.        (line  189)
* dircmp (class in filecmp):             The dircmp class.   (line    6)
* Directory (class in msilib):           Directory Objects.  (line    6)
* Directory (class in tkinter.filedialog): Native Load/Save Dialogs.
                                                             (line   71)
* directory; changing:                   Files and Directories.
                                                             (line  117)
* directory; creating:                   Files and Directories.
                                                             (line  453)
* directory; deleting:                   Directory and files operations.
                                                             (line  257)
* directory; deleting <1>:               Files and Directories.
                                                             (line  644)
* directory; traversal:                  Files and Directories.
                                                             (line 1493)
* directory; traversal <1>:              Files and Directories.
                                                             (line 1592)
* directory; walking:                    Files and Directories.
                                                             (line 1493)
* directory; walking <1>:                Files and Directories.
                                                             (line 1592)
* directory_created() (built-in function): The Postinstallation script.
                                                             (line   23)
* DirEntry (class in os):                Files and Directories.
                                                             (line  821)
* DirList (class in tkinter.tix):        File Selectors.     (line    6)
* dirname() (in module os.path):         os path — Common pathname manipulations.
                                                             (line  106)
* DirSelectBox (class in tkinter.tix):   File Selectors.     (line   26)
* DirSelectDialog (class in tkinter.tix): File Selectors.    (line   20)
* DirsOnSysPath (class in test.support): test support — Utilities for the Python test suite.
                                                             (line 1090)
* dirs_double_event() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line   86)
* dirs_select_event() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line   90)
* DirTree (class in tkinter.tix):        File Selectors.     (line   13)
* dis (module):                          dis — Disassembler for Python bytecode.
                                                             (line    6)
* dis() (dis.Bytecode method):           Bytecode analysis.  (line   47)
* dis() (in module dis):                 Analysis functions. (line   40)
* dis() (in module pickletools):         Programmatic Interface<2>.
                                                             (line    6)
* disable (pdb command):                 Debugger Commands.  (line  100)
* disable() (bdb.Breakpoint method):     bdb — Debugger framework.
                                                             (line   51)
* disable() (in module faulthandler):    Fault handler state.
                                                             (line   22)
* disable() (in module gc):              gc — Garbage Collector interface.
                                                             (line   26)
* disable() (in module logging):         Module-Level Functions.
                                                             (line  167)
* disable() (profile.Profile method):    profile and cProfile Module Reference.
                                                             (line   82)
* DisableReflectionKey() (in module winreg): Functions<12>.  (line  487)
* disable_faulthandler() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  517)
* disable_gc() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  529)
* disable_interspersed_args() (optparse.OptionParser method): Querying and manipulating your option parser.
                                                             (line   10)
* disassemble() (in module dis):         Analysis functions. (line   81)
* discard (http.cookiejar.Cookie attribute): Cookie Objects<2>.
                                                             (line   54)
* discard() (frozenset method):          Set Types — set frozenset.
                                                             (line  204)
* discard() (mailbox.Mailbox method):    Mailbox objects.    (line   76)
* discard() (mailbox.MH method):         MH.                 (line   76)
* discard_buffers() (asynchat.async_chat method): asynchat — Asynchronous socket command/response handler.
                                                             (line   84)
* disco() (in module dis):               Analysis functions. (line   81)
* discover() (unittest.TestLoader method): Loading and running tests.
                                                             (line  117)
* disk_usage() (in module shutil):       Directory and files operations.
                                                             (line  343)
* dispatcher (class in asyncore):        asyncore — Asynchronous socket handler.
                                                             (line   67)
* dispatcher_with_send (class in asyncore): asyncore — Asynchronous socket handler.
                                                             (line  250)
* dispatch_call() (bdb.Bdb method):      bdb — Debugger framework.
                                                             (line  157)
* dispatch_exception() (bdb.Bdb method): bdb — Debugger framework.
                                                             (line  177)
* dispatch_line() (bdb.Bdb method):      bdb — Debugger framework.
                                                             (line  147)
* dispatch_return() (bdb.Bdb method):    bdb — Debugger framework.
                                                             (line  167)
* dispatch_table (pickle.Pickler attribute): Module Interface.
                                                             (line  176)
* display (pdb command):                 Debugger Commands.  (line  257)
* displayhook() (in module sys):         sys — System-specific parameters and functions.
                                                             (line  244)
* display_name (email.headerregistry.Address attribute): email headerregistry Custom Header Objects.
                                                             (line  426)
* display_name (email.headerregistry.Group attribute): email headerregistry Custom Header Objects.
                                                             (line  471)
* dist() (in module math):               Trigonometric functions.
                                                             (line   35)
* distance() (in module turtle):         Tell Turtle’s state.
                                                             (line   68)
* distb() (in module dis):               Analysis functions. (line   70)
* Distribution (class in distutils.core): distutils core — Core Distutils functionality.
                                                             (line  294)
* distutils (module):                    distutils — Building and installing Python modules.
                                                             (line    6)
* distutils.archive_util (module):       distutils archive_util — Archiving utilities.
                                                             (line    6)
* distutils.bcppcompiler (module):       distutils bcppcompiler — Borland Compiler.
                                                             (line    6)
* distutils.ccompiler (module):          distutils ccompiler — CCompiler base class.
                                                             (line    6)
* distutils.cmd (module):                distutils cmd — Abstract base class for Distutils commands.
                                                             (line    6)
* distutils.command (module):            distutils command — Individual Distutils commands.
                                                             (line    5)
* distutils.command.bdist (module):      distutils command bdist — Build a binary installer.
                                                             (line    5)
* distutils.command.bdist_dumb (module): distutils command bdist_dumb — Build a “dumb” installer.
                                                             (line    5)
* distutils.command.bdist_msi (module):  distutils command bdist_msi — Build a Microsoft Installer binary package.
                                                             (line    6)
* distutils.command.bdist_packager (module): distutils command bdist_packager — Abstract base class for packagers.
                                                             (line    5)
* distutils.command.bdist_rpm (module):  distutils command bdist_rpm — Build a binary distribution as a Redhat RPM and SRPM.
                                                             (line    5)
* distutils.command.bdist_wininst (module): distutils command bdist_wininst — Build a Windows installer.
                                                             (line    6)
* distutils.command.build (module):      distutils command build — Build all files of a package.
                                                             (line    5)
* distutils.command.build_clib (module): distutils command build_clib — Build any C libraries in a package.
                                                             (line    5)
* distutils.command.build_ext (module):  distutils command build_ext — Build any extensions in a package.
                                                             (line    5)
* distutils.command.build_py (module):   distutils command build_py — Build the py/ pyc files of a package.
                                                             (line    6)
* distutils.command.build_scripts (module): distutils command build_scripts — Build the scripts of a package.
                                                             (line    5)
* distutils.command.check (module):      distutils command check — Check the meta-data of a package.
                                                             (line    6)
* distutils.command.clean (module):      distutils command clean — Clean a package build area.
                                                             (line    6)
* distutils.command.config (module):     distutils command config — Perform package configuration.
                                                             (line    5)
* distutils.command.install (module):    distutils command install — Install a package.
                                                             (line    5)
* distutils.command.install_data (module): distutils command install_data — Install data files from a package.
                                                             (line    5)
* distutils.command.install_headers (module): distutils command install_headers — Install C/C++ header files from a package.
                                                             (line    5)
* distutils.command.install_lib (module): distutils command install_lib — Install library files from a package.
                                                             (line    5)
* distutils.command.install_scripts (module): distutils command install_scripts — Install script files from a package.
                                                             (line    5)
* distutils.command.register (module):   distutils command register — Register a module with the Python Package Index.
                                                             (line    6)
* distutils.command.sdist (module):      distutils command sdist — Build a source distribution.
                                                             (line    5)
* distutils.core (module):               distutils core — Core Distutils functionality.
                                                             (line    6)
* distutils.cygwinccompiler (module):    distutils cygwincompiler — Cygwin Compiler.
                                                             (line    6)
* distutils.debug (module):              distutils debug — Distutils debug mode.
                                                             (line    6)
* distutils.dep_util (module):           distutils dep_util — Dependency checking.
                                                             (line    6)
* distutils.dir_util (module):           distutils dir_util — Directory tree operations.
                                                             (line    6)
* distutils.dist (module):               distutils dist — The Distribution class.
                                                             (line    6)
* distutils.errors (module):             distutils errors — Distutils exceptions.
                                                             (line    6)
* distutils.extension (module):          distutils extension — The Extension class.
                                                             (line    6)
* distutils.fancy_getopt (module):       distutils fancy_getopt — Wrapper around the standard getopt module.
                                                             (line    6)
* distutils.filelist (module):           distutils filelist — The FileList class.
                                                             (line    6)
* distutils.file_util (module):          distutils file_util — Single file operations.
                                                             (line    6)
* distutils.log (module):                distutils log — Simple PEP 282-style logging.
                                                             (line    5)
* distutils.msvccompiler (module):       distutils msvccompiler — Microsoft Compiler.
                                                             (line    6)
* distutils.spawn (module):              distutils spawn — Spawn a sub-process.
                                                             (line    6)
* distutils.sysconfig (module):          distutils sysconfig — System configuration information.
                                                             (line    6)
* distutils.text_file (module):          distutils text_file — The TextFile class.
                                                             (line    6)
* distutils.unixccompiler (module):      distutils unixccompiler — Unix C Compiler.
                                                             (line    6)
* distutils.util (module):               distutils util — Miscellaneous other utility functions.
                                                             (line    6)
* distutils.version (module):            distutils version — Version number classes.
                                                             (line    5)
* DISTUTILS_DEBUG:                       Debugging the setup script.
                                                             (line   19)
* Div (class in ast):                    Expressions<2>.     (line   54)
* divide() (decimal.Context method):     Context objects.    (line  271)
* divide_int() (decimal.Context method): Context objects.    (line  275)
* division:                              Binary arithmetic operations.
                                                             (line   31)
* DivisionByZero (class in decimal):     Signals.            (line   33)
* divmod() (built-in function):          Built-in Functions. (line  436)
* divmod() (decimal.Context method):     Context objects.    (line  279)
* DllCanUnloadNow() (in module ctypes):  Utility functions.  (line   76)
* DllGetClassObject() (in module ctypes): Utility functions. (line   82)
* dllhandle (in module sys):             sys — System-specific parameters and functions.
                                                             (line  238)
* DndHandler (class in tkinter.dnd):     tkinter dnd — Drag and drop support.
                                                             (line   43)
* dnd_start() (in module tkinter.dnd):   tkinter dnd — Drag and drop support.
                                                             (line   65)
* dngettext() (in module gettext):       GNU gettext API.    (line   68)
* dnpgettext() (in module gettext):      GNU gettext API.    (line   79)
* doc (json.JSONDecodeError attribute):  Exceptions<14>.     (line   15)
* DocCGIXMLRPCRequestHandler (class in xmlrpc.server): Documenting XMLRPC server.
                                                             (line   22)
* DocFileSuite() (in module doctest):    Unittest API.       (line   24)
* doClassCleanups() (unittest.TestCase class method): Test cases.
                                                             (line  792)
* doCleanups() (unittest.TestCase method): Test cases.       (line  760)
* docmd() (smtplib.SMTP method):         SMTP Objects.       (line   17)
* docstring:                             Class definitions.  (line    6)
* docstring <1>:                         Glossary.           (line  366)
* docstring (doctest.DocTest attribute): DocTest Objects.    (line   49)
* docstrings:                            Defining Functions. (line   21)
* docstrings <1>:                        Documentation Strings.
                                                             (line    6)
* DocTest (class in doctest):            DocTest Objects.    (line    6)
* doctest (module):                      doctest — Test interactive Python examples.
                                                             (line    6)
* DocTestFailure:                        Debugging.          (line  186)
* DocTestFinder (class in doctest):      DocTestFinder objects.
                                                             (line    6)
* DocTestParser (class in doctest):      DocTestParser objects.
                                                             (line    6)
* DocTestRunner (class in doctest):      DocTestRunner objects.
                                                             (line    6)
* DocTestSuite() (in module doctest):    Unittest API.       (line   99)
* doctype() (xml.etree.ElementTree.TreeBuilder method): TreeBuilder Objects.
                                                             (line   66)
* documentation string:                  The standard type hierarchy.
                                                             (line  708)
* documentation strings:                 Defining Functions. (line   21)
* documentation strings <1>:             Documentation Strings.
                                                             (line    6)
* documentation; generation:             pydoc — Documentation generator and online help system.
                                                             (line    8)
* documentation; online:                 pydoc — Documentation generator and online help system.
                                                             (line    8)
* documentElement (xml.dom.Document attribute): Document Objects.
                                                             (line   10)
* DocXMLRPCRequestHandler (class in xmlrpc.server): Documenting XMLRPC server.
                                                             (line   27)
* DocXMLRPCServer (class in xmlrpc.server): Documenting XMLRPC server.
                                                             (line   11)
* doc_header (cmd.Cmd attribute):        Cmd Objects.        (line  147)
* domain (email.headerregistry.Address attribute): email headerregistry Custom Header Objects.
                                                             (line  437)
* domain (tracemalloc.DomainFilter attribute): DomainFilter. (line   20)
* domain (tracemalloc.Filter attribute): Filter.             (line   30)
* domain (tracemalloc.Trace attribute):  Trace.              (line   15)
* DomainFilter (class in tracemalloc):   DomainFilter.       (line    6)
* DomainLiberal (http.cookiejar.DefaultCookiePolicy attribute): DefaultCookiePolicy Objects.
                                                             (line  156)
* DomainRFC2965Match (http.cookiejar.DefaultCookiePolicy attribute): DefaultCookiePolicy Objects.
                                                             (line  149)
* DomainStrict (http.cookiejar.DefaultCookiePolicy attribute): DefaultCookiePolicy Objects.
                                                             (line  161)
* DomainStrictNoDots (http.cookiejar.DefaultCookiePolicy attribute): DefaultCookiePolicy Objects.
                                                             (line  136)
* DomainStrictNonDomain (http.cookiejar.DefaultCookiePolicy attribute): DefaultCookiePolicy Objects.
                                                             (line  142)
* domain_initial_dot (http.cookiejar.Cookie attribute): Cookie Objects<2>.
                                                             (line   86)
* domain_return_ok() (http.cookiejar.CookiePolicy method): CookiePolicy Objects.
                                                             (line   27)
* domain_specified (http.cookiejar.Cookie attribute): Cookie Objects<2>.
                                                             (line   82)
* DOMEventStream (class in xml.dom.pulldom): DOMEventStream Objects.
                                                             (line    6)
* DOMException:                          Exceptions<17>.     (line   18)
* doModuleCleanups() (in module unittest): setUpModule and tearDownModule.
                                                             (line   35)
* DomstringSizeErr:                      Exceptions<17>.     (line   23)
* done() (asyncio.Future method):        Future Object.      (line   59)
* done() (asyncio.Task method):          Task Object.        (line  116)
* done() (concurrent.futures.Future method): Future Objects. (line   33)
* done() (graphlib.TopologicalSorter method): graphlib — Functionality to operate with graph-like structures.
                                                             (line  134)
* done() (in module turtle):             Using screen events.
                                                             (line  106)
* done() (xdrlib.Unpacker method):       Unpacker Objects.   (line   26)
* DONT_ACCEPT_BLANKLINE (in module doctest): Option Flags.   (line   30)
* DONT_ACCEPT_TRUE_FOR_1 (in module doctest): Option Flags.  (line   18)
* dont_write_bytecode (in module sys):   sys — System-specific parameters and functions.
                                                             (line  280)
* doRollover() (logging.handlers.RotatingFileHandler method): RotatingFileHandler.
                                                             (line   43)
* doRollover() (logging.handlers.TimedRotatingFileHandler method): TimedRotatingFileHandler.
                                                             (line  106)
* DOT (in module token):                 token — Constants used with Python parse trees.
                                                             (line  118)
* dot() (in module turtle):              Turtle motion.      (line  218)
* DOTALL (in module re):                 Module Contents.    (line  113)
* doublequote (csv.Dialect attribute):   Dialects and Formatting Parameters.
                                                             (line   24)
* DOUBLESLASH (in module token):         token — Constants used with Python parse trees.
                                                             (line  214)
* DOUBLESLASHEQUAL (in module token):    token — Constants used with Python parse trees.
                                                             (line  218)
* DOUBLESTAR (in module token):          token — Constants used with Python parse trees.
                                                             (line  166)
* DOUBLESTAREQUAL (in module token):     token — Constants used with Python parse trees.
                                                             (line  210)
* doupdate() (in module curses):         Functions<4>.       (line   89)
* down (pdb command):                    Debugger Commands.  (line   61)
* down() (in module turtle):             Drawing state.      (line    6)
* do_clear() (bdb.Bdb method):           bdb — Debugger framework.
                                                             (line  234)
* do_command() (curses.textpad.Textbox method): Textbox objects.
                                                             (line   30)
* do_GET() (http.server.SimpleHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  378)
* do_handshake() (ssl.SSLSocket method): SSL Sockets.        (line  121)
* do_HEAD() (http.server.SimpleHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  371)
* do_POST() (http.server.CGIHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  490)
* dpgettext() (in module gettext):       GNU gettext API.    (line   75)
* drain() (asyncio.StreamWriter method): StreamWriter.       (line   66)
* dropwhile() (in module itertools):     Itertool functions. (line  266)
* drop_whitespace (textwrap.TextWrapper attribute): textwrap — Text wrapping and filling.
                                                             (line  198)
* dst() (datetime.datetime method):      datetime Objects.   (line  485)
* dst() (datetime.time method):          time Objects.       (line  233)
* dst() (datetime.timezone method):      timezone Objects.   (line   57)
* dst() (datetime.tzinfo method):        tzinfo Objects.     (line   65)
* DTDHandler (class in xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line   24)
* duck-typing:                           Glossary.           (line  375)
* DumbWriter (class in formatter):       Writer Implementations.
                                                             (line   22)
* dump() (in module ast):                ast Helpers.        (line  235)
* dump() (in module json):               Basic Usage.        (line    6)
* dump() (in module marshal):            marshal — Internal Python object serialization.
                                                             (line   47)
* dump() (in module pickle):             Module Interface.   (line   35)
* dump() (in module plistlib):           plistlib — Generate and parse Apple plist files.
                                                             (line   81)
* dump() (in module xml.etree.ElementTree): Functions<7>.    (line   86)
* dump() (pickle.Pickler method):        Module Interface.   (line  155)
* dump() (tracemalloc.Snapshot method):  Snapshot.           (line   29)
* dumps() (in module json):              Basic Usage.        (line   78)
* dumps() (in module marshal):           marshal — Internal Python object serialization.
                                                             (line   82)
* dumps() (in module pickle):            Module Interface.   (line   47)
* dumps() (in module plistlib):          plistlib — Generate and parse Apple plist files.
                                                             (line  111)
* dumps() (in module xmlrpc.client):     Convenience Functions.
                                                             (line    6)
* dump_stats() (profile.Profile method): profile and cProfile Module Reference.
                                                             (line   96)
* dump_stats() (pstats.Stats method):    The Stats Class.    (line   59)
* dump_traceback() (in module faulthandler): Dumping the traceback.
                                                             (line    6)
* dump_traceback_later() (in module faulthandler): Dumping the tracebacks after a timeout.
                                                             (line    6)
* dup() (in module os):                  File Descriptor Operations.
                                                             (line   73)
* dup() (socket.socket method):          Socket Objects.     (line  102)
* dup2() (in module os):                 File Descriptor Operations.
                                                             (line   85)
* DuplicateOptionError:                  Exceptions<6>.      (line   24)
* DuplicateSectionError:                 Exceptions<6>.      (line   14)
* DUP_TOP (opcode):                      Python Bytecode Instructions.
                                                             (line   79)
* DUP_TOP_TWO (opcode):                  Python Bytecode Instructions.
                                                             (line   85)
* dwFlags (subprocess.STARTUPINFO attribute): Windows Popen Helpers.
                                                             (line   19)
* DynamicClassAttribute() (in module types): Additional Utility Classes and Functions.
                                                             (line   40)
* D_FMT (in module locale):              locale — Internationalization services.
                                                             (line  195)
* D_T_FMT (in module locale):            locale — Internationalization services.
                                                             (line  189)
* e (in module cmath):                   Constants<3>.       (line   10)
* e (in module math):                    Constants<2>.       (line   10)
* E2BIG (in module errno):               errno — Standard errno system symbols.
                                                             (line   55)
* e; in numeric literal:                 Integer literals.   (line   40)
* EACCES (in module errno):              errno — Standard errno system symbols.
                                                             (line   79)
* EADDRINUSE (in module errno):          errno — Standard errno system symbols.
                                                             (line  419)
* EADDRNOTAVAIL (in module errno):       errno — Standard errno system symbols.
                                                             (line  423)
* EADV (in module errno):                errno — Standard errno system symbols.
                                                             (line  299)
* EAFNOSUPPORT (in module errno):        errno — Standard errno system symbols.
                                                             (line  415)
* EAFP:                                  Glossary.           (line  388)
* EAGAIN (in module errno):              errno — Standard errno system symbols.
                                                             (line   71)
* EALREADY (in module errno):            errno — Standard errno system symbols.
                                                             (line  483)
* east_asian_width() (in module unicodedata): unicodedata — Unicode Database.
                                                             (line   64)
* EBADE (in module errno):               errno — Standard errno system symbols.
                                                             (line  235)
* EBADF (in module errno):               errno — Standard errno system symbols.
                                                             (line   63)
* EBADFD (in module errno):              errno — Standard errno system symbols.
                                                             (line  335)
* EBADMSG (in module errno):             errno — Standard errno system symbols.
                                                             (line  323)
* EBADR (in module errno):               errno — Standard errno system symbols.
                                                             (line  239)
* EBADRQC (in module errno):             errno — Standard errno system symbols.
                                                             (line  251)
* EBADSLT (in module errno):             errno — Standard errno system symbols.
                                                             (line  255)
* EBFONT (in module errno):              errno — Standard errno system symbols.
                                                             (line  263)
* EBUSY (in module errno):               errno — Standard errno system symbols.
                                                             (line   91)
* ECHILD (in module errno):              errno — Standard errno system symbols.
                                                             (line   67)
* echo() (in module curses):             Functions<4>.       (line  105)
* echochar() (curses.window method):     Window Objects.     (line  196)
* ECHRNG (in module errno):              errno — Standard errno system symbols.
                                                             (line  203)
* ECOMM (in module errno):               errno — Standard errno system symbols.
                                                             (line  307)
* ECONNABORTED (in module errno):        errno — Standard errno system symbols.
                                                             (line  439)
* ECONNREFUSED (in module errno):        errno — Standard errno system symbols.
                                                             (line  471)
* ECONNRESET (in module errno):          errno — Standard errno system symbols.
                                                             (line  443)
* EDEADLK (in module errno):             errno — Standard errno system symbols.
                                                             (line  167)
* EDEADLOCK (in module errno):           errno — Standard errno system symbols.
                                                             (line  259)
* EDESTADDRREQ (in module errno):        errno — Standard errno system symbols.
                                                             (line  383)
* edit() (curses.textpad.Textbox method): Textbox objects.   (line   19)
* EDOM (in module errno):                errno — Standard errno system symbols.
                                                             (line  159)
* EDOTDOT (in module errno):             errno — Standard errno system symbols.
                                                             (line  319)
* EDQUOT (in module errno):              errno — Standard errno system symbols.
                                                             (line  515)
* EEXIST (in module errno):              errno — Standard errno system symbols.
                                                             (line   95)
* EFAULT (in module errno):              errno — Standard errno system symbols.
                                                             (line   83)
* EFBIG (in module errno):               errno — Standard errno system symbols.
                                                             (line  135)
* effective() (in module bdb):           bdb — Debugger framework.
                                                             (line  397)
* ehlo() (smtplib.SMTP method):          SMTP Objects.       (line   58)
* ehlo_or_helo_if_needed() (smtplib.SMTP method): SMTP Objects.
                                                             (line   75)
* EHOSTDOWN (in module errno):           errno — Standard errno system symbols.
                                                             (line  475)
* EHOSTUNREACH (in module errno):        errno — Standard errno system symbols.
                                                             (line  479)
* EIDRM (in module errno):               errno — Standard errno system symbols.
                                                             (line  199)
* EILSEQ (in module errno):              errno — Standard errno system symbols.
                                                             (line  363)
* EINPROGRESS (in module errno):         errno — Standard errno system symbols.
                                                             (line  487)
* EINTR (in module errno):               errno — Standard errno system symbols.
                                                             (line   38)
* EINVAL (in module errno):              errno — Standard errno system symbols.
                                                             (line  115)
* EIO (in module errno):                 errno — Standard errno system symbols.
                                                             (line   47)
* EISCONN (in module errno):             errno — Standard errno system symbols.
                                                             (line  451)
* EISDIR (in module errno):              errno — Standard errno system symbols.
                                                             (line  111)
* EISNAM (in module errno):              errno — Standard errno system symbols.
                                                             (line  507)
* EL2HLT (in module errno):              errno — Standard errno system symbols.
                                                             (line  231)
* EL2NSYNC (in module errno):            errno — Standard errno system symbols.
                                                             (line  207)
* EL3HLT (in module errno):              errno — Standard errno system symbols.
                                                             (line  211)
* EL3RST (in module errno):              errno — Standard errno system symbols.
                                                             (line  215)
* Element (class in xml.etree.ElementTree): Element Objects. (line    6)
* ElementDeclHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  202)
* elements() (collections.Counter method): Counter objects.  (line   66)
* ElementTree (class in xml.etree.ElementTree): ElementTree Objects.
                                                             (line    6)
* element_create() (tkinter.ttk.Style method): Ttk Styling.  (line  131)
* element_names() (tkinter.ttk.Style method): Ttk Styling.   (line  183)
* element_options() (tkinter.ttk.Style method): Ttk Styling. (line  187)
* ELIBACC (in module errno):             errno — Standard errno system symbols.
                                                             (line  343)
* ELIBBAD (in module errno):             errno — Standard errno system symbols.
                                                             (line  347)
* ELIBEXEC (in module errno):            errno — Standard errno system symbols.
                                                             (line  359)
* ELIBMAX (in module errno):             errno — Standard errno system symbols.
                                                             (line  355)
* ELIBSCN (in module errno):             errno — Standard errno system symbols.
                                                             (line  351)
* Ellinghouse, Lance:                    uu — Encode and decode uuencode files.
                                                             (line   20)
* Ellipsis (built-in variable):          Built-in Constants. (line   57)
* ELLIPSIS (in module doctest):          Option Flags.       (line   49)
* ELLIPSIS (in module token):            token — Constants used with Python parse trees.
                                                             (line  234)
* ELNRNG (in module errno):              errno — Standard errno system symbols.
                                                             (line  219)
* ELOOP (in module errno):               errno — Standard errno system symbols.
                                                             (line  187)
* else; conditional expression:          Conditional expressions.
                                                             (line    6)
* email (module):                        email — An email and MIME handling package.
                                                             (line    6)
* email.charset (module):                email charset Representing character sets.
                                                             (line    6)
* email.contentmanager (module):         email contentmanager Managing MIME Content.
                                                             (line    6)
* email.encoders (module):               email encoders Encoders.
                                                             (line    6)
* email.errors (module):                 email errors Exception and Defect classes.
                                                             (line    6)
* email.generator (module):              email generator Generating MIME documents.
                                                             (line    6)
* email.header (module):                 email header Internationalized headers.
                                                             (line    6)
* email.headerregistry (module):         email headerregistry Custom Header Objects.
                                                             (line    6)
* email.iterators (module):              email iterators Iterators.
                                                             (line    6)
* email.message (module):                email message Representing an email message.
                                                             (line    6)
* email.mime (module):                   email mime Creating email and MIME objects from scratch.
                                                             (line    6)
* email.parser (module):                 email parser Parsing email messages.
                                                             (line    6)
* email.policy (module):                 email policy Policy Objects.
                                                             (line    6)
* email.utils (module):                  email utils Miscellaneous utilities.
                                                             (line    6)
* EmailMessage (class in email.message): email message Representing an email message.
                                                             (line   52)
* EmailPolicy (class in email.policy):   email policy Policy Objects.
                                                             (line  343)
* EMFILE (in module errno):              errno — Standard errno system symbols.
                                                             (line  123)
* emit() (logging.FileHandler method):   FileHandler.        (line   31)
* emit() (logging.Handler method):       Handler Objects.    (line  107)
* emit() (logging.handlers.BufferingHandler method): MemoryHandler.
                                                             (line   24)
* emit() (logging.handlers.DatagramHandler method): DatagramHandler.
                                                             (line   20)
* emit() (logging.handlers.HTTPHandler method): HTTPHandler. (line   36)
* emit() (logging.handlers.NTEventLogHandler method): NTEventLogHandler.
                                                             (line   38)
* emit() (logging.handlers.QueueHandler method): QueueHandler.
                                                             (line   31)
* emit() (logging.handlers.RotatingFileHandler method): RotatingFileHandler.
                                                             (line   47)
* emit() (logging.handlers.SMTPHandler method): SMTPHandler. (line   35)
* emit() (logging.handlers.SocketHandler method): SocketHandler.
                                                             (line   24)
* emit() (logging.handlers.SysLogHandler method): SysLogHandler.
                                                             (line   43)
* emit() (logging.handlers.TimedRotatingFileHandler method): TimedRotatingFileHandler.
                                                             (line  110)
* emit() (logging.handlers.WatchedFileHandler method): WatchedFileHandler.
                                                             (line   50)
* emit() (logging.NullHandler method):   NullHandler.        (line   16)
* emit() (logging.StreamHandler method): StreamHandler.      (line   17)
* EMLINK (in module errno):              errno — Standard errno system symbols.
                                                             (line  151)
* Empty:                                 queue — A synchronized queue class.
                                                             (line   82)
* empty (inspect.Parameter attribute):   Introspecting callables with the Signature object.
                                                             (line  152)
* empty (inspect.Signature attribute):   Introspecting callables with the Signature object.
                                                             (line   74)
* empty() (asyncio.Queue method):        Queue.              (line   28)
* empty() (multiprocessing.Queue method): Pipes and Queues.  (line  108)
* empty() (multiprocessing.SimpleQueue method): Pipes and Queues.
                                                             (line  219)
* empty() (queue.Queue method):          Queue Objects.      (line   15)
* empty() (queue.SimpleQueue method):    SimpleQueue Objects.
                                                             (line   14)
* empty() (sched.scheduler method):      Scheduler Objects.  (line   47)
* empty; list:                           List displays.      (line    6)
* empty; tuple:                          The standard type hierarchy.
                                                             (line  177)
* empty; tuple <1>:                      Parenthesized forms.
                                                             (line   16)
* emptyline() (cmd.Cmd method):          Cmd Objects.        (line   68)
* EMPTY_NAMESPACE (in module xml.dom):   Module Contents<4>. (line   35)
* EMSGSIZE (in module errno):            errno — Standard errno system symbols.
                                                             (line  387)
* EMULTIHOP (in module errno):           errno — Standard errno system symbols.
                                                             (line  315)
* enable (pdb command):                  Debugger Commands.  (line  107)
* enable() (bdb.Breakpoint method):      bdb — Debugger framework.
                                                             (line   47)
* enable() (imaplib.IMAP4 method):       IMAP4 Objects.      (line   84)
* enable() (in module cgitb):            cgitb — Traceback manager for CGI scripts.
                                                             (line   30)
* enable() (in module faulthandler):     Fault handler state.
                                                             (line    6)
* enable() (in module gc):               gc — Garbage Collector interface.
                                                             (line   22)
* enable() (profile.Profile method):     profile and cProfile Module Reference.
                                                             (line   78)
* EnableControlFlowGuard:                Build<4>.           (line    6)
* EnableReflectionKey() (in module winreg): Functions<12>.   (line  505)
* enable_callback_tracebacks() (in module sqlite3): Module functions and constants.
                                                             (line  224)
* enable_interspersed_args() (optparse.OptionParser method): Querying and manipulating your option parser.
                                                             (line   31)
* enable_load_extension() (sqlite3.Connection method): Connection Objects.
                                                             (line  256)
* enable_traversal() (tkinter.ttk.Notebook method): ttk Notebook.
                                                             (line   75)
* ENABLE_USER_SITE (in module site):     Module contents<4>. (line   10)
* ENAMETOOLONG (in module errno):        errno — Standard errno system symbols.
                                                             (line  171)
* ENAVAIL (in module errno):             errno — Standard errno system symbols.
                                                             (line  503)
* enclose() (curses.window method):      Window Objects.     (line  201)
* encode (codecs.CodecInfo attribute):   codecs — Codec registry and base classes.
                                                             (line   69)
* encode() (codecs.Codec method):        Stateless Encoding and Decoding.
                                                             (line    9)
* encode() (codecs.IncrementalEncoder method): IncrementalEncoder Objects.
                                                             (line   28)
* encode() (email.header.Header method): email header Internationalized headers.
                                                             (line  125)
* encode() (in module base64):           base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  220)
* encode() (in module codecs):           codecs — Codec registry and base classes.
                                                             (line   23)
* encode() (in module quopri):           quopri — Encode and decode MIME quoted-printable data.
                                                             (line   29)
* encode() (in module uu):               uu — Encode and decode uuencode files.
                                                             (line   25)
* encode() (json.JSONEncoder method):    Encoders and Decoders.
                                                             (line  217)
* encode() (str method):                 String Methods<2>.  (line   61)
* encode() (xmlrpc.client.Binary method): Binary Objects.    (line   25)
* encode() (xmlrpc.client.DateTime method): DateTime Objects.
                                                             (line   17)
* encodebytes() (in module base64):      base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  230)
* EncodedFile() (in module codecs):      codecs — Codec registry and base classes.
                                                             (line  197)
* encodePriority() (logging.handlers.SysLogHandler method): SysLogHandler.
                                                             (line   77)
* encodestring() (in module quopri):     quopri — Encode and decode MIME quoted-printable data.
                                                             (line   46)
* encode_7or8bit() (in module email.encoders): email encoders Encoders.
                                                             (line   57)
* encode_base64() (in module email.encoders): email encoders Encoders.
                                                             (line   49)
* encode_noop() (in module email.encoders): email encoders Encoders.
                                                             (line   63)
* encode_quopri() (in module email.encoders): email encoders Encoders.
                                                             (line   42)
* encode_rfc2231() (in module email.utils): email utils Miscellaneous utilities.
                                                             (line  178)
* encoding (curses.window attribute):    Window Objects.     (line  208)
* ENCODING (in module tarfile):          tarfile — Read and write tar archive files.
                                                             (line  220)
* ENCODING (in module token):            token — Constants used with Python parse trees.
                                                             (line  272)
* encoding (io.TextIOBase attribute):    Text I/O<2>.        (line   15)
* encoding (UnicodeError attribute):     Concrete exceptions.
                                                             (line  368)
* encoding declarations (source file):   Encoding declarations.
                                                             (line    6)
* encodings.idna (module):               encodings idna — Internationalized Domain Names in Applications.
                                                             (line    6)
* encodings.mbcs (module):               encodings mbcs — Windows ANSI codepage.
                                                             (line    6)
* encodings.utf_8_sig (module):          encodings utf_8_sig — UTF-8 codec with BOM signature.
                                                             (line    6)
* encodings_map (in module mimetypes):   mimetypes — Map filenames to MIME types.
                                                             (line  136)
* encodings_map (mimetypes.MimeTypes attribute): MimeTypes Objects.
                                                             (line   33)
* end (UnicodeError attribute):          Concrete exceptions.
                                                             (line  384)
* end() (re.Match method):               Match Objects.      (line  132)
* end() (xml.etree.ElementTree.TreeBuilder method): TreeBuilder Objects.
                                                             (line   38)
* EndCdataSectionHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  306)
* EndDoctypeDeclHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  197)
* endDocument() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line   40)
* endElement() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line   95)
* EndElementHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  232)
* endElementNS() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line  121)
* endheaders() (http.client.HTTPConnection method): HTTPConnection Objects.
                                                             (line  143)
* ENDMARKER (in module token):           token — Constants used with Python parse trees.
                                                             (line   40)
* EndNamespaceDeclHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  285)
* endpos (re.Match attribute):           Match Objects.      (line  171)
* endPrefixMapping() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line   73)
* endswith() (bytearray method):         Bytes and Bytearray Operations.
                                                             (line  115)
* endswith() (bytes method):             Bytes and Bytearray Operations.
                                                             (line  115)
* endswith() (str method):               String Methods<2>.  (line   83)
* endwin() (in module curses):           Functions<4>.       (line  110)
* END_ASYNC_FOR (opcode):                Python Bytecode Instructions.
                                                             (line  284)
* end_col_offset (ast.AST attribute):    Node classes.       (line   39)
* end_fill() (in module turtle):         Filling.            (line   20)
* end_headers() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  268)
* end_lineno (ast.AST attribute):        Node classes.       (line   39)
* end_ns() (xml.etree.ElementTree.TreeBuilder method): TreeBuilder Objects.
                                                             (line   85)
* end_paragraph() (formatter.formatter method): The Formatter Interface.
                                                             (line   26)
* end_poly() (in module turtle):         Special Turtle methods.
                                                             (line   11)
* ENETDOWN (in module errno):            errno — Standard errno system symbols.
                                                             (line  427)
* ENETRESET (in module errno):           errno — Standard errno system symbols.
                                                             (line  435)
* ENETUNREACH (in module errno):         errno — Standard errno system symbols.
                                                             (line  431)
* ENFILE (in module errno):              errno — Standard errno system symbols.
                                                             (line  119)
* ENOANO (in module errno):              errno — Standard errno system symbols.
                                                             (line  247)
* ENOBUFS (in module errno):             errno — Standard errno system symbols.
                                                             (line  447)
* ENOCSI (in module errno):              errno — Standard errno system symbols.
                                                             (line  227)
* ENODATA (in module errno):             errno — Standard errno system symbols.
                                                             (line  271)
* ENODEV (in module errno):              errno — Standard errno system symbols.
                                                             (line  103)
* ENOENT (in module errno):              errno — Standard errno system symbols.
                                                             (line   30)
* ENOEXEC (in module errno):             errno — Standard errno system symbols.
                                                             (line   59)
* ENOLCK (in module errno):              errno — Standard errno system symbols.
                                                             (line  175)
* ENOLINK (in module errno):             errno — Standard errno system symbols.
                                                             (line  295)
* ENOMEM (in module errno):              errno — Standard errno system symbols.
                                                             (line   75)
* ENOMSG (in module errno):              errno — Standard errno system symbols.
                                                             (line  195)
* ENONET (in module errno):              errno — Standard errno system symbols.
                                                             (line  283)
* ENOPKG (in module errno):              errno — Standard errno system symbols.
                                                             (line  287)
* ENOPROTOOPT (in module errno):         errno — Standard errno system symbols.
                                                             (line  395)
* ENOSPC (in module errno):              errno — Standard errno system symbols.
                                                             (line  139)
* ENOSR (in module errno):               errno — Standard errno system symbols.
                                                             (line  279)
* ENOSTR (in module errno):              errno — Standard errno system symbols.
                                                             (line  267)
* ENOSYS (in module errno):              errno — Standard errno system symbols.
                                                             (line  179)
* ENOTBLK (in module errno):             errno — Standard errno system symbols.
                                                             (line   87)
* ENOTCONN (in module errno):            errno — Standard errno system symbols.
                                                             (line  455)
* ENOTDIR (in module errno):             errno — Standard errno system symbols.
                                                             (line  107)
* ENOTEMPTY (in module errno):           errno — Standard errno system symbols.
                                                             (line  183)
* ENOTNAM (in module errno):             errno — Standard errno system symbols.
                                                             (line  499)
* ENOTSOCK (in module errno):            errno — Standard errno system symbols.
                                                             (line  379)
* ENOTTY (in module errno):              errno — Standard errno system symbols.
                                                             (line  127)
* ENOTUNIQ (in module errno):            errno — Standard errno system symbols.
                                                             (line  331)
* enqueue() (logging.handlers.QueueHandler method): QueueHandler.
                                                             (line   53)
* enqueue_sentinel() (logging.handlers.QueueListener method): QueueListener.
                                                             (line   87)
* ensurepip (module):                    ensurepip — Bootstrapping the pip installer.
                                                             (line    6)
* ensure_directories() (venv.EnvBuilder method): API<2>.     (line   85)
* ensure_future() (in module asyncio):   Future Functions.   (line   19)
* enter() (sched.scheduler method):      Scheduler Objects.  (line   30)
* enterabs() (sched.scheduler method):   Scheduler Objects.  (line    9)
* enter_async_context() (contextlib.AsyncExitStack method): Utilities.
                                                             (line  464)
* enter_context() (contextlib.ExitStack method): Utilities.  (line  383)
* entities (xml.dom.DocumentType attribute): DocumentType Objects.
                                                             (line   38)
* EntityDeclHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  258)
* entitydefs (in module html.entities):  html entities — Definitions of HTML general entities.
                                                             (line   25)
* EntityResolver (class in xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line   31)
* Enum (class in enum):                  Module Contents<2>. (line   11)
* enum (module):                         enum — Support for enumerations.
                                                             (line    6)
* enumerate() (built-in function):       Built-in Functions. (line  448)
* enumerate() (in module threading):     threading — Thread-based parallelism.
                                                             (line  108)
* EnumKey() (in module winreg):          Functions<12>.      (line  177)
* EnumValue() (in module winreg):        Functions<12>.      (line  196)
* enum_certificates() (in module ssl):   Certificate handling.
                                                             (line  129)
* enum_crls() (in module ssl):           Certificate handling.
                                                             (line  152)
* EnvBuilder (class in venv):            API<2>.             (line   11)
* environ (in module os):                Process Parameters. (line   16)
* environ (in module posix):             Notable Module Contents.
                                                             (line    9)
* environb (in module os):               Process Parameters. (line   52)
* environment:                           Resolution of names.
                                                             (line   12)
* environment variable; APPDATA:         PEP 370 Per-user site-packages Directory.
                                                             (line   26)
* environment variable; AUDIODEV:        ossaudiodev — Access to OSS-compatible audio devices.
                                                             (line   54)
* environment variable; BROWSER:         webbrowser — Convenient Web-browser controller.
                                                             (line   20)
* environment variable; BROWSER <1>:     webbrowser — Convenient Web-browser controller.
                                                             (line   95)
* environment variable; CC:              New Improved and Deprecated Modules<4>.
                                                             (line   58)
* environment variable; CFLAGS:          New Improved and Deprecated Modules<4>.
                                                             (line   58)
* environment variable; CFLAGS <1>:      Tweaking compiler/linker flags.
                                                             (line   66)
* environment variable; CFLAGS <2>:      Tweaking compiler/linker flags.
                                                             (line   67)
* environment variable; COLS:            curses<3>.          (line    7)
* environment variable; COLS <1>:        Functions<4>.       (line  555)
* environment variable; COLUMNS:         Functions<4>.       (line  579)
* environment variable; COLUMNS <1>:     Functions<4>.       (line  582)
* environment variable; COMSPEC:         Process Management. (line  681)
* environment variable; COMSPEC <1>:     Popen Constructor.  (line   91)
* environment variable; CPP:             New Improved and Deprecated Modules<4>.
                                                             (line   59)
* environment variable; CPPFLAGS:        New Improved and Deprecated Modules<4>.
                                                             (line   59)
* environment variable; DISTUTILS_DEBUG: Debugging the setup script.
                                                             (line   19)
* environment variable; EnableControlFlowGuard: Build<4>.    (line    6)
* environment variable; exec_prefix:     Python-related paths and files.
                                                             (line    7)
* environment variable; exec_prefix <1>: Include Files.      (line   37)
* environment variable; exec_prefix <2>: Include Files.      (line   48)
* environment variable; HOME:            os path.            (line   15)
* environment variable; HOME <1>:        Changes in the Python API<2>.
                                                             (line  117)
* environment variable; HOME <2>:        Windows<17>.        (line   15)
* environment variable; HOME <3>:        Windows<17>.        (line   18)
* environment variable; HOME <4>:        os path — Common pathname manipulations.
                                                             (line  140)
* environment variable; HOME <5>:        os path — Common pathname manipulations.
                                                             (line  156)
* environment variable; HOME <6>:        distutils util — Miscellaneous other utility functions.
                                                             (line   97)
* environment variable; HOME <7>:        Location and names of config files.
                                                             (line   50)
* environment variable; HOME <8>:        Location and names of config files.
                                                             (line   67)
* environment variable; HOMEDRIVE:       os path — Common pathname manipulations.
                                                             (line  147)
* environment variable; HOMEDRIVE <1>:   Location and names of config files.
                                                             (line   68)
* environment variable; HOMEPATH:        os path — Common pathname manipulations.
                                                             (line  147)
* environment variable; HOMEPATH <1>:    Location and names of config files.
                                                             (line   68)
* environment variable; http_proxy:      urllib request — Extensible library for opening URLs.
                                                             (line   78)
* environment variable; http_proxy <1>:  Examples<22>.       (line   97)
* environment variable; http_proxy <2>:  Basic Authentication.
                                                             (line   62)
* environment variable; IDLESTARTUP:     IDLE<24>.           (line  176)
* environment variable; IDLESTARTUP <1>: IDLE<28>.           (line    9)
* environment variable; IDLESTARTUP <2>: IDLE<34>.           (line    9)
* environment variable; IDLESTARTUP <3>: Startup and code execution.
                                                             (line    7)
* environment variable; KDEDIR:          webbrowser — Convenient Web-browser controller.
                                                             (line  184)
* environment variable; LANG:            GNU gettext API.    (line   21)
* environment variable; LANG <1>:        Class-based API.    (line   26)
* environment variable; LANG <2>:        locale — Internationalization services.
                                                             (line   49)
* environment variable; LANG <3>:        locale — Internationalization services.
                                                             (line  310)
* environment variable; LANG <4>:        locale — Internationalization services.
                                                             (line  314)
* environment variable; LANGUAGE:        GNU gettext API.    (line   20)
* environment variable; LANGUAGE <1>:    Class-based API.    (line   25)
* environment variable; LC_ALL:          GNU gettext API.    (line   20)
* environment variable; LC_ALL <1>:      Class-based API.    (line   25)
* environment variable; LC_MESSAGES:     GNU gettext API.    (line   20)
* environment variable; LC_MESSAGES <1>: Class-based API.    (line   26)
* environment variable; LDCXXSHARED:     Build and C API Changes<8>.
                                                             (line  153)
* environment variable; LDFLAGS:         New Improved and Deprecated Modules<4>.
                                                             (line   59)
* environment variable; LINES:           curses<3>.          (line    6)
* environment variable; LINES <1>:       Functions<4>.       (line  125)
* environment variable; LINES <2>:       Functions<4>.       (line  555)
* environment variable; LINES <3>:       Functions<4>.       (line  579)
* environment variable; LINES <4>:       Functions<4>.       (line  581)
* environment variable; LNAME:           getpass — Portable password input.
                                                             (line   38)
* environment variable; LOGNAME:         Process Parameters. (line  222)
* environment variable; LOGNAME <1>:     getpass — Portable password input.
                                                             (line   38)
* environment variable; MIXERDEV:        ossaudiodev — Access to OSS-compatible audio devices.
                                                             (line   74)
* environment variable; no_proxy:        urllib request — Extensible library for opening URLs.
                                                             (line  295)
* environment variable; PAGER:           pydoc — Documentation generator and online help system.
                                                             (line   47)
* environment variable; PATH:            Changes in the Python API<2>.
                                                             (line  144)
* environment variable; PATH <1>:        Changes in ‘python’ Command Behavior<2>.
                                                             (line    6)
* environment variable; PATH <2>:        Changes in ‘python’ Command Behavior<2>.
                                                             (line   11)
* environment variable; PATH <3>:        Changes in ‘python’ Command Behavior<2>.
                                                             (line   12)
* environment variable; PATH <4>:        Security<16>.       (line   16)
* environment variable; PATH <5>:        Security<16>.       (line   20)
* environment variable; PATH <6>:        The Module Search Path.
                                                             (line   16)
* environment variable; PATH <7>:        Executable Python Scripts.
                                                             (line   11)
* environment variable; PATH <8>:        Environment variables.
                                                             (line   27)
* environment variable; PATH <9>:        Miscellaneous.      (line   16)
* environment variable; PATH <10>:       Installation steps. (line   32)
* environment variable; PATH <11>:       Installation steps. (line   56)
* environment variable; PATH <12>:       Installing Without UI.
                                                             (line   57)
* environment variable; PATH <13>:       Excursus Setting environment variables.
                                                             (line   23)
* environment variable; PATH <14>:       Excursus Setting environment variables.
                                                             (line   35)
* environment variable; PATH <15>:       Finding the Python executable.
                                                             (line   14)
* environment variable; PATH <16>:       Finding the Python executable.
                                                             (line   21)
* environment variable; PATH <17>:       Finding the Python executable.
                                                             (line   22)
* environment variable; PATH <18>:       Python Launcher for Windows.
                                                             (line   13)
* environment variable; PATH <19>:       From the command-line.
                                                             (line    9)
* environment variable; PATH <20>:       From the command-line.
                                                             (line   38)
* environment variable; PATH <21>:       Shebang Lines.      (line   48)
* environment variable; PATH <22>:       Shebang Lines.      (line   50)
* environment variable; PATH <23>:       Process Management. (line   45)
* environment variable; PATH <24>:       Process Management. (line   86)
* environment variable; PATH <25>:       Process Management. (line   89)
* environment variable; PATH <26>:       Process Management. (line   92)
* environment variable; PATH <27>:       Process Management. (line  471)
* environment variable; PATH <28>:       Process Management. (line  557)
* environment variable; PATH <29>:       Process Management. (line  561)
* environment variable; PATH <30>:       Process Management. (line  563)
* environment variable; PATH <31>:       Miscellaneous System Information.
                                                             (line  118)
* environment variable; PATH <32>:       webbrowser — Convenient Web-browser controller.
                                                             (line  214)
* environment variable; PATH <33>:       Installing your CGI script on a Unix system.
                                                             (line   29)
* environment variable; PATH <34>:       Common problems and solutions.
                                                             (line   23)
* environment variable; PATH <35>:       site — Site-specific configuration hook.
                                                             (line   59)
* environment variable; PATH <36>:       Embedding Python<2>.
                                                             (line   31)
* environment variable; PATH <37>:       Embedding Python<2>.
                                                             (line   37)
* environment variable; PATH <38>:       How do I make a Python script executable on Unix?.
                                                             (line   24)
* environment variable; PATH <39>:       How do I make a Python script executable on Unix?.
                                                             (line   28)
* environment variable; PATHEXT:         Other Improvements<2>.
                                                             (line   30)
* environment variable; PATHEXT <1>:     Library<11>.        (line  105)
* environment variable; PATHEXT <2>:     Installing Without UI.
                                                             (line   58)
* environment variable; PIP_USER:        Windows<19>.        (line  102)
* environment variable; PLAT:            distutils util — Miscellaneous other utility functions.
                                                             (line   99)
* environment variable; POSIXLY_CORRECT: getopt — C-style parser for command line options.
                                                             (line   71)
* environment variable; prefix:          Python-related paths and files.
                                                             (line    7)
* environment variable; prefix <1>:      Include Files.      (line   37)
* environment variable; prefix <2>:      Include Files.      (line   40)
* environment variable; prefix <3>:      Include Files.      (line   47)
* environment variable; PYTHON*:         Other Improvements<2>.
                                                             (line    9)
* environment variable; PYTHON* <1>:     Interface options.  (line   80)
* environment variable; PYTHON* <2>:     Interface options.  (line  140)
* environment variable; PYTHON* <3>:     Miscellaneous options.
                                                             (line   42)
* environment variable; PYTHON* <4>:     Miscellaneous options.
                                                             (line   60)
* environment variable; PYTHON* <5>:     Global configuration variables.
                                                             (line   56)
* environment variable; PYTHONASYNCIODEBUG: Environment variables.
                                                             (line  254)
* environment variable; PYTHONASYNCIODEBUG <1>: Enabling debug mode.
                                                             (line   10)
* environment variable; PYTHONASYNCIODEBUG <2>: Debug Mode.  (line   11)
* environment variable; PYTHONASYNCIODEBUG <3>: Effects of the Python Development Mode.
                                                             (line   64)
* environment variable; PYTHONBREAKPOINT: PEP 553 Built-in breakpoint.
                                                             (line   13)
* environment variable; PYTHONBREAKPOINT <1>: Environment variables.
                                                             (line   73)
* environment variable; PYTHONBREAKPOINT <2>: sys — System-specific parameters and functions.
                                                             (line  202)
* environment variable; PYTHONBREAKPOINT <3>: sys — System-specific parameters and functions.
                                                             (line  216)
* environment variable; PYTHONBREAKPOINT <4>: sys — System-specific parameters and functions.
                                                             (line  220)
* environment variable; PYTHONCASEOK:    Changes in the Python API.
                                                             (line   29)
* environment variable; PYTHONCASEOK <1>: PEP 235 Importing Modules on Case-Insensitive Platforms.
                                                             (line   17)
* environment variable; PYTHONCASEOK <2>: Library<21>.       (line  144)
* environment variable; PYTHONCASEOK <3>: Environment variables.
                                                             (line  120)
* environment variable; PYTHONCASEOK <4>: Built-in Functions.
                                                             (line 1865)
* environment variable; PYTHONCOERCECLOCALE: PEP 538 Legacy C Locale Coercion.
                                                             (line   13)
* environment variable; PYTHONCOERCECLOCALE <1>: Environment variables.
                                                             (line  338)
* environment variable; PYTHONCOERCECLOCALE <2>: Environment variables.
                                                             (line  454)
* environment variable; PYTHONCOERCECLOCALE <3>: Python Configuration.
                                                             (line   15)
* environment variable; PYTHONDEBUG:     Miscellaneous options.
                                                             (line   38)
* environment variable; PYTHONDEBUG <1>: Environment variables.
                                                             (line   86)
* environment variable; PYTHONDEBUG <2>: Global configuration variables.
                                                             (line   28)
* environment variable; PYTHONDEVMODE:   Python Development Mode -X dev.
                                                             (line    6)
* environment variable; PYTHONDEVMODE <1>: Environment variables.
                                                             (line  394)
* environment variable; PYTHONDEVMODE <2>: Python Development Mode.
                                                             (line   14)
* environment variable; PYTHONDOCS:      pydoc — Documentation generator and online help system.
                                                             (line   85)
* environment variable; PYTHONDONTWRITEBYTECODE: Interpreter Changes<2>.
                                                             (line   16)
* environment variable; PYTHONDONTWRITEBYTECODE <1>: New and Improved Modules<2>.
                                                             (line  625)
* environment variable; PYTHONDONTWRITEBYTECODE <2>: Miscellaneous options.
                                                             (line   19)
* environment variable; PYTHONDONTWRITEBYTECODE <3>: Environment variables.
                                                             (line  125)
* environment variable; PYTHONDONTWRITEBYTECODE <4>: sys — System-specific parameters and functions.
                                                             (line  285)
* environment variable; PYTHONDONTWRITEBYTECODE <5>: Global configuration variables.
                                                             (line   36)
* environment variable; PYTHONDONTWRITEBYTECODE <6>: How do I create a pyc file?.
                                                             (line   21)
* environment variable; PYTHONDUMPREFS:  Debug build uses the same ABI as release build.
                                                             (line   14)
* environment variable; PYTHONDUMPREFS <1>: Build<21>.       (line   54)
* environment variable; PYTHONDUMPREFS <2>: Debug-mode variables.
                                                             (line   14)
* environment variable; PYTHONDUMPREFS <3>: PyObject Slots.  (line   24)
* environment variable; PYTHONEXECUTABLE: Environment variables.
                                                             (line  198)
* environment variable; PYTHONFAULTHANDLER: faulthandler<3>. (line   11)
* environment variable; PYTHONFAULTHANDLER <1>: Environment variables.
                                                             (line  225)
* environment variable; PYTHONFAULTHANDLER <2>: Effects of the Python Development Mode.
                                                             (line   58)
* environment variable; PYTHONFAULTHANDLER <3>: faulthandler — Dump the Python traceback.
                                                             (line   14)
* environment variable; PYTHONHASHSEED:  Builtin functions and types.
                                                             (line   17)
* environment variable; PYTHONHASHSEED <1>: Porting Python code.
                                                             (line    6)
* environment variable; PYTHONHASHSEED <2>: Core and Builtins<35>.
                                                             (line   30)
* environment variable; PYTHONHASHSEED <3>: Miscellaneous options.
                                                             (line   94)
* environment variable; PYTHONHASHSEED <4>: Miscellaneous options.
                                                             (line  110)
* environment variable; PYTHONHASHSEED <5>: Environment variables.
                                                             (line  140)
* environment variable; PYTHONHASHSEED <6>: Environment variables.
                                                             (line  145)
* environment variable; PYTHONHASHSEED <7>: Basic customization.
                                                             (line  297)
* environment variable; PYTHONHASHSEED <8>: Global configuration variables.
                                                             (line   48)
* environment variable; PYTHONHASHSEED <9>: Global configuration variables.
                                                             (line   51)
* environment variable; PYTHONHOME:      Summary – Release highlights<3>.
                                                             (line  107)
* environment variable; PYTHONHOME <1>:  Miscellaneous options.
                                                             (line   43)
* environment variable; PYTHONHOME <2>:  Environment variables.
                                                             (line   11)
* environment variable; PYTHONHOME <3>:  Environment variables.
                                                             (line   19)
* environment variable; PYTHONHOME <4>:  Environment variables.
                                                             (line   21)
* environment variable; PYTHONHOME <5>:  Environment variables.
                                                             (line   38)
* environment variable; PYTHONHOME <6>:  Finding modules.    (line   50)
* environment variable; PYTHONHOME <7>:  Finding modules.    (line   68)
* environment variable; PYTHONHOME <8>:  Finding modules.    (line  102)
* environment variable; PYTHONHOME <9>:  test support script_helper — Utilities for the Python execution tests.
                                                             (line   25)
* environment variable; PYTHONHOME <10>: Embedding Python<2>.
                                                             (line   38)
* environment variable; PYTHONHOME <11>: Embedding Python<2>.
                                                             (line   44)
* environment variable; PYTHONHOME <12>: Global configuration variables.
                                                             (line   57)
* environment variable; PYTHONHOME <13>: Process-wide parameters.
                                                             (line  270)
* environment variable; PYTHONHOME <14>: Process-wide parameters.
                                                             (line  284)
* environment variable; PYTHONHOME <15>: PyConfig.           (line  204)
* environment variable; PYTHONHOME <16>: Modifying Python’s Search Path.
                                                             (line   60)
* environment variable; PYTHONHOME <17>: Modifying Python’s Search Path.
                                                             (line   62)
* environment variable; PYTHONINSPECT:   Other Changes and Fixes<2>.
                                                             (line   13)
* environment variable; PYTHONINSPECT <1>: Miscellaneous options.
                                                             (line   53)
* environment variable; PYTHONINSPECT <2>: Environment variables.
                                                             (line  101)
* environment variable; PYTHONINSPECT <3>: Global configuration variables.
                                                             (line   68)
* environment variable; PYTHONIOENCODING: Other Improvements<2>.
                                                             (line   75)
* environment variable; PYTHONIOENCODING <1>: Interpreter Changes<2>.
                                                             (line   23)
* environment variable; PYTHONIOENCODING <2>: Environment variables.
                                                             (line  158)
* environment variable; PYTHONIOENCODING <3>: Environment variables.
                                                             (line  375)
* environment variable; PYTHONIOENCODING <4>: Environment variables.
                                                             (line  442)
* environment variable; PYTHONIOENCODING <5>: sys — System-specific parameters and functions.
                                                             (line 1509)
* environment variable; PYTHONIOENCODING <6>: Process-wide parameters.
                                                             (line   14)
* environment variable; PYTHONIOENCODING <7>: Process-wide parameters.
                                                             (line   18)
* environment variable; PYTHONLEGACYWINDOWSFSENCODING: PEP 529 Change Windows filesystem encoding to UTF-8.
                                                             (line   18)
* environment variable; PYTHONLEGACYWINDOWSFSENCODING <1>: Environment variables.
                                                             (line  311)
* environment variable; PYTHONLEGACYWINDOWSFSENCODING <2>: sys — System-specific parameters and functions.
                                                             (line 1461)
* environment variable; PYTHONLEGACYWINDOWSFSENCODING <3>: Global configuration variables.
                                                             (line   90)
* environment variable; PYTHONLEGACYWINDOWSSTDIO: PEP 528 Change Windows console encoding to UTF-8.
                                                             (line   12)
* environment variable; PYTHONLEGACYWINDOWSSTDIO <1>: Environment variables.
                                                             (line  172)
* environment variable; PYTHONLEGACYWINDOWSSTDIO <2>: Environment variables.
                                                             (line  325)
* environment variable; PYTHONLEGACYWINDOWSSTDIO <3>: sys — System-specific parameters and functions.
                                                             (line 1513)
* environment variable; PYTHONLEGACYWINDOWSSTDIO <4>: Global configuration variables.
                                                             (line  102)
* environment variable; PYTHONMALLOC:    PYTHONMALLOC environment variable.
                                                             (line    6)
* environment variable; PYTHONMALLOC <1>: Changes in the C API<4>.
                                                             (line    9)
* environment variable; PYTHONMALLOC <2>: Core and Builtins<55>.
                                                             (line   91)
* environment variable; PYTHONMALLOC <3>: Environment variables.
                                                             (line  261)
* environment variable; PYTHONMALLOC <4>: Environment variables.
                                                             (line  302)
* environment variable; PYTHONMALLOC <5>: Effects of the Python Development Mode.
                                                             (line   46)
* environment variable; PYTHONMALLOC <6>: Effects of the Python Development Mode.
                                                             (line   50)
* environment variable; PYTHONMALLOC <7>: Overview<3>.       (line   75)
* environment variable; PYTHONMALLOC <8>: Default Memory Allocators.
                                                             (line   26)
* environment variable; PYTHONMALLOC <9>: Customize Memory Allocators.
                                                             (line  129)
* environment variable; PYTHONMALLOCSTATS: Core and Builtins<55>.
                                                             (line   97)
* environment variable; PYTHONMALLOCSTATS <1>: Environment variables.
                                                             (line  296)
* environment variable; PYTHONMALLOCSTATS <2>: Overview<3>.  (line   78)
* environment variable; PYTHONNOUSERSITE: PEP 370 Per-user site-packages Directory.
                                                             (line   30)
* environment variable; PYTHONNOUSERSITE <1>: Environment variables.
                                                             (line  176)
* environment variable; PYTHONNOUSERSITE <2>: Module contents<4>.
                                                             (line   15)
* environment variable; PYTHONNOUSERSITE <3>: Global configuration variables.
                                                             (line  124)
* environment variable; PYTHONOLDPARSER: Miscellaneous options.
                                                             (line  204)
* environment variable; PYTHONOLDPARSER <1>: Environment variables.
                                                             (line   92)
* environment variable; PYTHONOLDPARSER <2>: PyConfig.       (line  398)
* environment variable; PYTHONOPTIMIZE:  Miscellaneous options.
                                                             (line   71)
* environment variable; PYTHONOPTIMIZE <1>: Environment variables.
                                                             (line   67)
* environment variable; PYTHONOPTIMIZE <2>: Global configuration variables.
                                                             (line  129)
* environment variable; PYTHONPATH:      Changes in ‘python’ Command Behavior<2>.
                                                             (line    8)
* environment variable; PYTHONPATH <1>:  Changes in ‘python’ Command Behavior<2>.
                                                             (line    9)
* environment variable; PYTHONPATH <2>:  The Module Search Path.
                                                             (line   15)
* environment variable; PYTHONPATH <3>:  Standard Modules.   (line   34)
* environment variable; PYTHONPATH <4>:  Standard Modules.   (line   35)
* environment variable; PYTHONPATH <5>:  Miscellaneous options.
                                                             (line   42)
* environment variable; PYTHONPATH <6>:  Environment variables.
                                                             (line   24)
* environment variable; PYTHONPATH <7>:  Environment variables.
                                                             (line   32)
* environment variable; PYTHONPATH <8>:  Environment variables.
                                                             (line   39)
* environment variable; PYTHONPATH <9>:  Environment variables.
                                                             (line   42)
* environment variable; PYTHONPATH <10>: Excursus Setting environment variables.
                                                             (line   38)
* environment variable; PYTHONPATH <11>: Finding modules.    (line   36)
* environment variable; PYTHONPATH <12>: Finding modules.    (line   59)
* environment variable; PYTHONPATH <13>: Finding modules.    (line  102)
* environment variable; PYTHONPATH <14>: Configuration.      (line    6)
* environment variable; PYTHONPATH <15>: Installing your CGI script on a Unix system.
                                                             (line   29)
* environment variable; PYTHONPATH <16>: test support script_helper — Utilities for the Python execution tests.
                                                             (line   26)
* environment variable; PYTHONPATH <17>: sys — System-specific parameters and functions.
                                                             (line 1063)
* environment variable; PYTHONPATH <18>: sys — System-specific parameters and functions.
                                                             (line 1073)
* environment variable; PYTHONPATH <19>: Building C and C++ Extensions.
                                                             (line    9)
* environment variable; PYTHONPATH <20>: Embedding Python<2>.
                                                             (line   39)
* environment variable; PYTHONPATH <21>: Embedding Python<2>.
                                                             (line   44)
* environment variable; PYTHONPATH <22>: Global configuration variables.
                                                             (line   56)
* environment variable; PYTHONPATH <23>: PyConfig.           (line  259)
* environment variable; PYTHONPATH <24>: Modifying Python’s Search Path.
                                                             (line   67)
* environment variable; PYTHONPATH <25>: Modifying Python’s Search Path.
                                                             (line   68)
* environment variable; PYTHONPLATLIBDIR: Core and Builtins<16>.
                                                             (line   25)
* environment variable; PYTHONPLATLIBDIR <1>: Environment variables.
                                                             (line   46)
* environment variable; PYTHONPROFILEIMPORTTIME: Other Language Changes<3>.
                                                             (line   47)
* environment variable; PYTHONPROFILEIMPORTTIME <1>: Core and Builtins<37>.
                                                             (line   67)
* environment variable; PYTHONPROFILEIMPORTTIME <2>: Miscellaneous options.
                                                             (line  222)
* environment variable; PYTHONPROFILEIMPORTTIME <3>: Environment variables.
                                                             (line  246)
* environment variable; PYTHONPYCACHEPREFIX: Parallel filesystem cache for compiled bytecode files.
                                                             (line    6)
* environment variable; PYTHONPYCACHEPREFIX <1>: Core and Builtins<28>.
                                                             (line  402)
* environment variable; PYTHONPYCACHEPREFIX <2>: Miscellaneous options.
                                                             (line  237)
* environment variable; PYTHONPYCACHEPREFIX <3>: Environment variables.
                                                             (line  131)
* environment variable; PYTHONPYCACHEPREFIX <4>: sys — System-specific parameters and functions.
                                                             (line  303)
* environment variable; PYTHONSHOWALLOCCOUNT: Two new environment variables for debug mode.
                                                             (line   11)
* environment variable; PYTHONSHOWREFCOUNT: Two new environment variables for debug mode.
                                                             (line    7)
* environment variable; PYTHONSTARTUP:   sys<7>.             (line   17)
* environment variable; PYTHONSTARTUP <1>: sys<7>.           (line   21)
* environment variable; PYTHONSTARTUP <2>: IDLE<24>.         (line  176)
* environment variable; PYTHONSTARTUP <3>: IDLE<28>.         (line    9)
* environment variable; PYTHONSTARTUP <4>: IDLE<34>.         (line    9)
* environment variable; PYTHONSTARTUP <5>: The Interactive Startup File.
                                                             (line    8)
* environment variable; PYTHONSTARTUP <6>: Miscellaneous options.
                                                             (line   50)
* environment variable; PYTHONSTARTUP <7>: Environment variables.
                                                             (line   53)
* environment variable; PYTHONSTARTUP <8>: Example.          (line   10)
* environment variable; PYTHONSTARTUP <9>: Startup and code execution.
                                                             (line    7)
* environment variable; PYTHONSTARTUP <10>: sys — System-specific parameters and functions.
                                                             (line  958)
* environment variable; PYTHONSTARTUP <11>: Readline configuration.
                                                             (line   12)
* environment variable; PYTHONTHREADDEBUG: Debug-mode variables.
                                                             (line    8)
* environment variable; PYTHONTRACEMALLOC: Environment variables.
                                                             (line  235)
* environment variable; PYTHONTRACEMALLOC <1>: tracemalloc — Trace memory allocations.
                                                             (line   25)
* environment variable; PYTHONTRACEMALLOC <2>: tracemalloc — Trace memory allocations.
                                                             (line   32)
* environment variable; PYTHONTRACEMALLOC <3>: Functions<10>.
                                                             (line   90)
* environment variable; PYTHONTZPATH:    Environment configuration.
                                                             (line   11)
* environment variable; PYTHONTZPATH <1>: Exceptions and warnings.
                                                             (line   14)
* environment variable; PYTHONUNBUFFERED: Core and Builtins<21>.
                                                             (line  107)
* environment variable; PYTHONUNBUFFERED <1>: Miscellaneous options.
                                                             (line  140)
* environment variable; PYTHONUNBUFFERED <2>: Environment variables.
                                                             (line  109)
* environment variable; PYTHONUNBUFFERED <3>: sys — System-specific parameters and functions.
                                                             (line 1520)
* environment variable; PYTHONUNBUFFERED <4>: Global configuration variables.
                                                             (line  145)
* environment variable; PYTHONUSERBASE:  PEP 370 Per-user site-packages Directory.
                                                             (line   23)
* environment variable; PYTHONUSERBASE <1>: Environment variables.
                                                             (line  186)
* environment variable; PYTHONUSERBASE <2>: Module contents<4>.
                                                             (line   39)
* environment variable; PYTHONUSERBASE <3>: Module contents<4>.
                                                             (line   66)
* environment variable; PYTHONUSERSITE:  test support script_helper — Utilities for the Python execution tests.
                                                             (line   26)
* environment variable; PYTHONUTF8:      PEP 540 Forced UTF-8 Runtime Mode.
                                                             (line    6)
* environment variable; PYTHONUTF8 <1>:  Miscellaneous options.
                                                             (line  232)
* environment variable; PYTHONUTF8 <2>:  Environment variables.
                                                             (line  385)
* environment variable; PYTHONUTF8 <3>:  Environment variables.
                                                             (line  402)
* environment variable; PYTHONUTF8 <4>:  UTF-8 mode.         (line   17)
* environment variable; PYTHONUTF8 <5>:  sys — System-specific parameters and functions.
                                                             (line 1511)
* environment variable; PYTHONUTF8 <6>:  Python Configuration.
                                                             (line   14)
* environment variable; PYTHONVERBOSE:   Miscellaneous options.
                                                             (line  151)
* environment variable; PYTHONVERBOSE <1>: Environment variables.
                                                             (line  114)
* environment variable; PYTHONVERBOSE <2>: Global configuration variables.
                                                             (line  156)
* environment variable; PYTHONWARNINGS:  warnings.           (line   21)
* environment variable; PYTHONWARNINGS <1>: Other Language Changes<8>.
                                                             (line  158)
* environment variable; PYTHONWARNINGS <2>: Changes to the Handling of Deprecation Warnings.
                                                             (line   25)
* environment variable; PYTHONWARNINGS <3>: Interpreter Changes.
                                                             (line    6)
* environment variable; PYTHONWARNINGS <4>: Miscellaneous options.
                                                             (line  169)
* environment variable; PYTHONWARNINGS <5>: Environment variables.
                                                             (line  204)
* environment variable; PYTHONWARNINGS <6>: Effects of the Python Development Mode.
                                                             (line   30)
* environment variable; PYTHONWARNINGS <7>: Describing Warning Filters.
                                                             (line    7)
* environment variable; PYTHONWARNINGS <8>: Describing Warning Filters.
                                                             (line   21)
* environment variable; PYTHONWARNINGS <9>: Default Warning Filter.
                                                             (line    7)
* environment variable; PYTHON_DOM:      Module Contents<4>. (line   23)
* environment variable; PY_PYTHON:       Customizing default Python versions.
                                                             (line   18)
* environment variable; SOURCE_DATE_EPOCH: py_compile<2>.    (line    7)
* environment variable; SOURCE_DATE_EPOCH <1>: Library<30>.  (line  453)
* environment variable; SOURCE_DATE_EPOCH <2>: Build<29>.    (line   15)
* environment variable; SOURCE_DATE_EPOCH <3>: py_compile — Compile Python source files.
                                                             (line   65)
* environment variable; SOURCE_DATE_EPOCH <4>: py_compile — Compile Python source files.
                                                             (line   81)
* environment variable; SOURCE_DATE_EPOCH <5>: py_compile — Compile Python source files.
                                                             (line   85)
* environment variable; SOURCE_DATE_EPOCH <6>: Command-line use.
                                                             (line   92)
* environment variable; SSLKEYLOGFILE:   Context creation.   (line   33)
* environment variable; SSLKEYLOGFILE <1>: Context creation. (line   67)
* environment variable; SSL_CERT_FILE:   LibreSSL support.   (line   15)
* environment variable; SSL_CERT_PATH:   LibreSSL support.   (line   15)
* environment variable; SystemRoot:      Popen Constructor.  (line  272)
* environment variable; TCL_LIBRARY:     How do I freeze Tkinter applications?.
                                                             (line   11)
* environment variable; TEMP:            tempfile — Generate temporary files and directories.
                                                             (line  239)
* environment variable; TERM:            Functions<4>.       (line  469)
* environment variable; TERM <1>:        Functions<4>.       (line  496)
* environment variable; TK_LIBRARY:      How do I freeze Tkinter applications?.
                                                             (line   11)
* environment variable; TMP:             tempfile — Generate temporary files and directories.
                                                             (line  241)
* environment variable; TMPDIR:          tempfile — Generate temporary files and directories.
                                                             (line  237)
* environment variable; TZ:              Functions<3>.       (line  508)
* environment variable; TZ <1>:          Functions<3>.       (line  509)
* environment variable; TZ <2>:          Functions<3>.       (line  517)
* environment variable; TZ <3>:          Functions<3>.       (line  522)
* environment variable; TZ <4>:          Functions<3>.       (line  524)
* environment variable; TZ <5>:          Functions<3>.       (line  584)
* environment variable; USER:            getpass — Portable password input.
                                                             (line   38)
* environment variable; USERNAME:        Process Parameters. (line  222)
* environment variable; USERNAME <1>:    getpass — Portable password input.
                                                             (line   39)
* environment variable; USERPROFILE:     os path.            (line   14)
* environment variable; USERPROFILE <1>: Changes in the Python API<2>.
                                                             (line  116)
* environment variable; USERPROFILE <2>: Windows<17>.        (line   15)
* environment variable; USERPROFILE <3>: os path — Common pathname manipulations.
                                                             (line  146)
* environment variable; USERPROFILE <4>: Location and names of config files.
                                                             (line   67)
* environment variable; USER_BASE:       New and Improved Modules.
                                                             (line  469)
* environment variable; VIRTUAL_ENV:     Creating virtual environments.
                                                             (line  134)
* environment variables; deleting:       Process Parameters. (line  501)
* environment variables; setting:        Process Parameters. (line  319)
* EnvironmentError:                      Concrete exceptions.
                                                             (line  420)
* Environments; virtual:                 venv — Creation of virtual environments.
                                                             (line   10)
* EnvironmentVarGuard (class in test.support): test support — Utilities for the Python test suite.
                                                             (line 1046)
* ENXIO (in module errno):               errno — Standard errno system symbols.
                                                             (line   51)
* eof (bz2.BZ2Decompressor attribute):   Incremental de compression.
                                                             (line   72)
* eof (lzma.LZMADecompressor attribute): Compressing and decompressing data in memory.
                                                             (line  165)
* eof (shlex.shlex attribute):           shlex Objects.      (line  178)
* eof (ssl.MemoryBIO attribute):         Memory BIO Support<2>.
                                                             (line  143)
* eof (zlib.Decompress attribute):       zlib — Compression compatible with gzip.
                                                             (line  248)
* EOFError:                              Concrete exceptions.
                                                             (line   19)
* EOFError (built-in exception):         File Objects.       (line   41)
* eof_received() (asyncio.BufferedProtocol method): Buffered Streaming Protocols.
                                                             (line   40)
* eof_received() (asyncio.Protocol method): Streaming Protocols.
                                                             (line   30)
* EOPNOTSUPP (in module errno):          errno — Standard errno system symbols.
                                                             (line  407)
* EOVERFLOW (in module errno):           errno — Standard errno system symbols.
                                                             (line  327)
* EPERM (in module errno):               errno — Standard errno system symbols.
                                                             (line   26)
* EPFNOSUPPORT (in module errno):        errno — Standard errno system symbols.
                                                             (line  411)
* epilogue (email.message.EmailMessage attribute): email message Representing an email message.
                                                             (line  704)
* epilogue (email.message.Message attribute): email message Message Representing an email message using the compat32 API.
                                                             (line  714)
* EPIPE (in module errno):               errno — Standard errno system symbols.
                                                             (line  155)
* epoch:                                 time — Time access and conversions.
                                                             (line   18)
* epoll() (in module select):            select — Waiting for I/O completion.
                                                             (line   50)
* EpollSelector (class in selectors):    Classes<3>.         (line  175)
* EPROTO (in module errno):              errno — Standard errno system symbols.
                                                             (line  311)
* EPROTONOSUPPORT (in module errno):     errno — Standard errno system symbols.
                                                             (line  399)
* EPROTOTYPE (in module errno):          errno — Standard errno system symbols.
                                                             (line  391)
* Eq (class in ast):                     Expressions<2>.     (line  109)
* eq() (in module operator):             operator — Standard operators as functions.
                                                             (line   24)
* EQEQUAL (in module token):             token — Constants used with Python parse trees.
                                                             (line  134)
* EQUAL (in module token):               token — Constants used with Python parse trees.
                                                             (line  114)
* ERA (in module locale):                locale — Internationalization services.
                                                             (line  264)
* ERANGE (in module errno):              errno — Standard errno system symbols.
                                                             (line  163)
* erase() (curses.window method):        Window Objects.     (line  218)
* erasechar() (in module curses):        Functions<4>.       (line  114)
* ERA_D_FMT (in module locale):          locale — Internationalization services.
                                                             (line  286)
* ERA_D_T_FMT (in module locale):        locale — Internationalization services.
                                                             (line  281)
* ERA_T_FMT (in module locale):          locale — Internationalization services.
                                                             (line  291)
* EREMCHG (in module errno):             errno — Standard errno system symbols.
                                                             (line  339)
* EREMOTE (in module errno):             errno — Standard errno system symbols.
                                                             (line  291)
* EREMOTEIO (in module errno):           errno — Standard errno system symbols.
                                                             (line  511)
* ERESTART (in module errno):            errno — Standard errno system symbols.
                                                             (line  367)
* erf() (in module math):                Special functions.  (line    6)
* erfc() (in module math):               Special functions.  (line   20)
* EROFS (in module errno):               errno — Standard errno system symbols.
                                                             (line  147)
* ERR (in module curses):                Constants<6>.       (line    8)
* errcheck (ctypes._FuncPtr attribute):  Foreign functions.  (line   59)
* errcode (xmlrpc.client.ProtocolError attribute): ProtocolError Objects.
                                                             (line   17)
* errmsg (xmlrpc.client.ProtocolError attribute): ProtocolError Objects.
                                                             (line   21)
* errno (module):                        errno — Standard errno system symbols.
                                                             (line    6)
* errno (OSError attribute):             Concrete exceptions.
                                                             (line  135)
* error:                                 Module Contents.    (line  363)
* error <1>:                             Functions and Exceptions.
                                                             (line    8)
* Error:                                 copy — Shallow and deep copy operations.
                                                             (line   26)
* Error <1>:                             Directory and files operations.
                                                             (line  403)
* error <2>:                             dbm — Interfaces to Unix “databases”.
                                                             (line   16)
* error <3>:                             dbm gnu — GNU’s reinterpretation of dbm.
                                                             (line   21)
* error <4>:                             dbm ndbm — Interface based on ndbm.
                                                             (line   21)
* error <5>:                             dbm dumb — Portable DBM implementation.
                                                             (line   24)
* Error <2>:                             Exceptions<5>.      (line   10)
* error <6>:                             zlib — Compression compatible with gzip.
                                                             (line   24)
* Error <3>:                             Module Contents<3>. (line  279)
* Error <4>:                             Exceptions<6>.      (line    6)
* Error <5>:                             Exceptions<7>.      (line    8)
* error <7>:                             os — Miscellaneous operating system interfaces.
                                                             (line   42)
* error <8>:                             getopt — C-style parser for command line options.
                                                             (line   85)
* error <9>:                             Functions<4>.       (line    8)
* error <10>:                            _thread — Low-level threading API.
                                                             (line   21)
* error <11>:                            Exceptions<12>.     (line    6)
* error <12>:                            select — Waiting for I/O completion.
                                                             (line   24)
* Error <6>:                             Exceptions<15>.     (line    9)
* Error <7>:                             binhex — Encode and decode binhex4 files.
                                                             (line   35)
* Error <8>:                             binascii — Convert between binary and ASCII.
                                                             (line  182)
* Error <9>:                             uu — Encode and decode uuencode files.
                                                             (line   51)
* error <13>:                            xml parsers expat — Fast XML parsing using Expat.
                                                             (line   31)
* Error <10>:                            webbrowser — Convenient Web-browser controller.
                                                             (line   44)
* error <14>:                            audioop — Manipulate raw audio data.
                                                             (line   26)
* Error <11>:                            sunau — Read and write Sun AU files.
                                                             (line   68)
* Error <12>:                            wave — Read and write WAV files.
                                                             (line   48)
* Error <13>:                            locale — Internationalization services.
                                                             (line   22)
* error <15>:                            resource — Resource usage information.
                                                             (line   17)
* error <16>:                            nis — Interface to Sun’s NIS Yellow Pages.
                                                             (line   54)
* error handling:                        Exceptions<2>.      (line    6)
* error() (argparse.ArgumentParser method): Exiting methods. (line   18)
* error() (in module logging):           Module-Level Functions.
                                                             (line  133)
* error() (logging.Logger method):       Logger Objects.     (line  241)
* error() (urllib.request.OpenerDirector method): OpenerDirector Objects.
                                                             (line   58)
* error() (xml.sax.handler.ErrorHandler method): ErrorHandler Objects.
                                                             (line   16)
* ErrorByteIndex (xml.parsers.expat.xmlparser attribute): XMLParser Objects<2>.
                                                             (line  132)
* errorcode (in module errno):           errno — Standard errno system symbols.
                                                             (line   13)
* ErrorCode (xml.parsers.expat.xmlparser attribute): XMLParser Objects<2>.
                                                             (line  136)
* ErrorColumnNumber (xml.parsers.expat.xmlparser attribute): XMLParser Objects<2>.
                                                             (line  142)
* ErrorHandler (class in xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line   38)
* ErrorLineNumber (xml.parsers.expat.xmlparser attribute): XMLParser Objects<2>.
                                                             (line  146)
* errors:                                Exceptions<2>.      (line    6)
* errors (io.TextIOBase attribute):      Text I/O<2>.        (line   20)
* errors (unittest.TestLoader attribute): Loading and running tests.
                                                             (line   17)
* errors (unittest.TestResult attribute): Loading and running tests.
                                                             (line  237)
* Errors; logging:                       logging — Logging facility for Python.
                                                             (line    8)
* ErrorString() (in module xml.parsers.expat): xml parsers expat — Fast XML parsing using Expat.
                                                             (line   42)
* ERRORTOKEN (in module token):          token — Constants used with Python parse trees.
                                                             (line  252)
* error_body (wsgiref.handlers.BaseHandler attribute): wsgiref handlers – server/gateway base classes.
                                                             (line  260)
* error_content_type (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  152)
* error_headers (wsgiref.handlers.BaseHandler attribute): wsgiref handlers – server/gateway base classes.
                                                             (line  253)
* error_leader() (shlex.shlex method):   shlex Objects.      (line   69)
* error_message_format (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  144)
* error_output() (wsgiref.handlers.BaseHandler method): wsgiref handlers – server/gateway base classes.
                                                             (line  225)
* error_perm:                            ftplib — FTP protocol client.
                                                             (line  141)
* error_proto:                           ftplib — FTP protocol client.
                                                             (line  146)
* error_proto <1>:                       poplib — POP3 protocol client.
                                                             (line   91)
* error_received() (asyncio.DatagramProtocol method): Datagram Protocols.
                                                             (line   15)
* error_reply:                           ftplib — FTP protocol client.
                                                             (line  131)
* error_status (wsgiref.handlers.BaseHandler attribute): wsgiref handlers – server/gateway base classes.
                                                             (line  247)
* error_temp:                            ftplib — FTP protocol client.
                                                             (line  136)
* escape (shlex.shlex attribute):        shlex Objects.      (line  110)
* escape sequence:                       String and Bytes literals.
                                                             (line   72)
* escape() (in module glob):             glob — Unix style pathname pattern expansion.
                                                             (line   62)
* escape() (in module html):             html — HyperText Markup Language support.
                                                             (line   12)
* escape() (in module re):               Module Contents.    (line  326)
* escape() (in module xml.sax.saxutils): xml sax saxutils — SAX Utilities.
                                                             (line   14)
* escapechar (csv.Dialect attribute):    Dialects and Formatting Parameters.
                                                             (line   35)
* escapedquotes (shlex.shlex attribute): shlex Objects.      (line  122)
* ESHUTDOWN (in module errno):           errno — Standard errno system symbols.
                                                             (line  459)
* ESOCKTNOSUPPORT (in module errno):     errno — Standard errno system symbols.
                                                             (line  403)
* ESPIPE (in module errno):              errno — Standard errno system symbols.
                                                             (line  143)
* ESRCH (in module errno):               errno — Standard errno system symbols.
                                                             (line   34)
* ESRMNT (in module errno):              errno — Standard errno system symbols.
                                                             (line  303)
* ESTALE (in module errno):              errno — Standard errno system symbols.
                                                             (line  491)
* ESTRPIPE (in module errno):            errno — Standard errno system symbols.
                                                             (line  371)
* ETIME (in module errno):               errno — Standard errno system symbols.
                                                             (line  275)
* ETIMEDOUT (in module errno):           errno — Standard errno system symbols.
                                                             (line  467)
* Etiny() (decimal.Context method):      Context objects.    (line  213)
* ETOOMANYREFS (in module errno):        errno — Standard errno system symbols.
                                                             (line  463)
* Etop() (decimal.Context method):       Context objects.    (line  219)
* ETXTBSY (in module errno):             errno — Standard errno system symbols.
                                                             (line  131)
* EUCLEAN (in module errno):             errno — Standard errno system symbols.
                                                             (line  495)
* EUNATCH (in module errno):             errno — Standard errno system symbols.
                                                             (line  223)
* EUSERS (in module errno):              errno — Standard errno system symbols.
                                                             (line  375)
* eval() (built-in function):            Built-in Functions. (line  471)
* evaluation; order:                     Evaluation order.   (line    6)
* Event (class in asyncio):              Event.              (line    6)
* Event (class in multiprocessing):      Synchronization primitives.
                                                             (line   42)
* Event (class in threading):            Event Objects.      (line   14)
* event scheduling:                      sched — Event scheduler.
                                                             (line    8)
* event() (msilib.Control method):       GUI classes.        (line   16)
* Event() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  166)
* events (selectors.SelectorKey attribute): Classes<3>.      (line   44)
* events (widgets):                      Bindings and Events.
                                                             (line    6)
* EWOULDBLOCK (in module errno):         errno — Standard errno system symbols.
                                                             (line  191)
* Example (class in doctest):            Example Objects.    (line    6)
* example (doctest.DocTestFailure attribute): Debugging.     (line  200)
* example (doctest.UnexpectedException attribute): Debugging.
                                                             (line  221)
* examples (doctest.DocTest attribute):  DocTest Objects.    (line   17)
* excel (class in csv):                  Module Contents<3>. (line  197)
* excel_tab (class in csv):              Module Contents<3>. (line  203)
* except (2to3 fixer):                   Fixers.             (line   82)
* ExceptHandler (class in ast):          Control flow.       (line  178)
* excepthook() (in module sys):          cgitb — Traceback manager for CGI scripts.
                                                             (line   33)
* excepthook() (in module sys) <1>:      sys — System-specific parameters and functions.
                                                             (line  309)
* excepthook() (in module threading):    threading — Thread-based parallelism.
                                                             (line   46)
* exception:                             Exceptions<2>.      (line    6)
* exception <1>:                         The raise statement.
                                                             (line    6)
* Exception:                             Base classes.       (line   37)
* EXCEPTION (in module tkinter):         File Handlers.      (line   41)
* exception handler:                     Exceptions<2>.      (line    6)
* exception() (asyncio.Future method):   Future Object.      (line  119)
* exception() (asyncio.Task method):     Task Object.        (line  137)
* exception() (concurrent.futures.Future method): Future Objects.
                                                             (line   54)
* exception() (in module logging):       Module-Level Functions.
                                                             (line  143)
* exception() (logging.Logger method):   Logger Objects.     (line  256)
* exception; AssertionError:             The assert statement.
                                                             (line   21)
* exception; AttributeError:             Attribute references.
                                                             (line   10)
* exception; chaining:                   The raise statement.
                                                             (line   30)
* exception; GeneratorExit:              Generator-iterator methods.
                                                             (line   47)
* exception; GeneratorExit <1>:          Asynchronous generator-iterator methods.
                                                             (line   55)
* exception; handler:                    The standard type hierarchy.
                                                             (line  765)
* exception; ImportError:                The import statement.
                                                             (line    6)
* exception; NameError:                  Identifiers Names.  (line   10)
* exception; StopAsyncIteration:         Asynchronous generator-iterator methods.
                                                             (line   10)
* exception; StopIteration:              Generator-iterator methods.
                                                             (line   12)
* exception; StopIteration <1>:          The yield statement.
                                                             (line    6)
* exception; TypeError:                  Unary arithmetic and bitwise operations.
                                                             (line   23)
* exception; ValueError:                 Shifting operations.
                                                             (line   18)
* exception; ZeroDivisionError:          Binary arithmetic operations.
                                                             (line   31)
* exceptions; in CGI scripts:            cgitb — Traceback manager for CGI scripts.
                                                             (line    8)
* exclusive; or:                         Binary bitwise operations.
                                                             (line   16)
* exc_info (doctest.UnexpectedException attribute): Debugging.
                                                             (line  225)
* exc_info (in module sys):              The standard type hierarchy.
                                                             (line  765)
* exc_info() (in module sys):            sys — System-specific parameters and functions.
                                                             (line  352)
* exc_info() (in module sys) <1>:        Exceptions<19>.     (line   45)
* exc_msg (doctest.Example attribute):   Example Objects.    (line   31)
* exc_type (traceback.TracebackException attribute): TracebackException Objects.
                                                             (line   38)
* EXDEV (in module errno):               errno — Standard errno system symbols.
                                                             (line   99)
* exec (2to3 fixer):                     Fixers.             (line   86)
* exec() (built-in function):            Built-in Functions. (line  517)
* execfile (2to3 fixer):                 Fixers.             (line   90)
* execl() (in module os):                Process Management. (line   53)
* execle() (in module os):               Process Management. (line   53)
* execlp() (in module os):               Process Management. (line   53)
* execlpe() (in module os):              Process Management. (line   53)
* executable (in module sys):            sys — System-specific parameters and functions.
                                                             (line  391)
* executable (in module sys) <1>:        Process-wide parameters.
                                                             (line  111)
* Executable Zip Files:                  zipapp — Manage executable Python zip archives.
                                                             (line   10)
* executable_filename() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  451)
* execute() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  481)
* execute() (in module distutils.util):  distutils util — Miscellaneous other utility functions.
                                                             (line  129)
* Execute() (msilib.View method):        View Objects.       (line    6)
* execute() (sqlite3.Connection method): Connection Objects. (line   52)
* execute() (sqlite3.Cursor method):     Cursor Objects.     (line   11)
* executemany() (sqlite3.Connection method): Connection Objects.
                                                             (line   59)
* executemany() (sqlite3.Cursor method): Cursor Objects.     (line   22)
* executescript() (sqlite3.Connection method): Connection Objects.
                                                             (line   66)
* executescript() (sqlite3.Cursor method): Cursor Objects.   (line   77)
* execution model:                       Execution model.    (line    6)
* execution; frame:                      Structure of a program.
                                                             (line   18)
* execution; frame <1>:                  Class definitions.  (line    6)
* execution; stack:                      The standard type hierarchy.
                                                             (line  765)
* ExecutionLoader (class in importlib.abc): importlib abc – Abstract base classes related to import.
                                                             (line  454)
* Executor (class in concurrent.futures): Executor Objects.  (line    6)
* execv() (in module os):                Process Management. (line   53)
* execve() (in module os):               Process Management. (line   53)
* execvp() (in module os):               Process Management. (line   53)
* execvpe() (in module os):              Process Management. (line   53)
* exec_module (C function):              Multi-phase initialization.
                                                             (line  103)
* exec_module() (importlib.abc.InspectLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  441)
* exec_module() (importlib.abc.Loader method): importlib abc – Abstract base classes related to import.
                                                             (line  182)
* exec_module() (importlib.abc.SourceLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  588)
* exec_module() (importlib.machinery.ExtensionFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  326)
* exec_prefix:                           Python-related paths and files.
                                                             (line    7)
* exec_prefix <1>:                       Include Files.      (line   37)
* exec_prefix <2>:                       Include Files.      (line   48)
* EXEC_PREFIX (in module distutils.sysconfig): distutils sysconfig — System configuration information.
                                                             (line   23)
* exec_prefix (in module sys):           sys — System-specific parameters and functions.
                                                             (line  374)
* ExFileSelectBox (class in tkinter.tix): File Selectors.    (line   34)
* EXFULL (in module errno):              errno — Standard errno system symbols.
                                                             (line  243)
* exists() (in module os.path):          os path — Common pathname manipulations.
                                                             (line  114)
* exists() (pathlib.Path method):        Methods<2>.         (line   63)
* exists() (tkinter.ttk.Treeview method): ttk Treeview.      (line   95)
* exists() (zipfile.Path method):        Path Objects.       (line   49)
* exit (built-in variable):              Constants added by the site module.
                                                             (line   11)
* exit():                                Process Control.    (line   23)
* exit() (argparse.ArgumentParser method): Exiting methods.  (line    6)
* exit() (in module sys):                sys — System-specific parameters and functions.
                                                             (line  398)
* exit() (in module _thread):            _thread — Low-level threading API.
                                                             (line   63)
* exitcode (multiprocessing.Process attribute): Process and exceptions.
                                                             (line  112)
* exitfunc (2to3 fixer):                 Fixers.             (line   96)
* exitonclick() (in module turtle):      Methods specific to Screen not inherited from TurtleScreen.
                                                             (line   10)
* ExitStack (class in contextlib):       Utilities.          (line  343)
* exp() (decimal.Context method):        Context objects.    (line  284)
* exp() (decimal.Decimal method):        Decimal objects.    (line  232)
* exp() (in module cmath):               Power and logarithmic functions<2>.
                                                             (line    6)
* exp() (in module math):                Power and logarithmic functions.
                                                             (line    6)
* expand() (re.Match method):            Match Objects.      (line   17)
* ExpandEnvironmentStrings() (in module winreg): Functions<12>.
                                                             (line  233)
* expandNode() (xml.dom.pulldom.DOMEventStream method): DOMEventStream Objects.
                                                             (line   21)
* expandtabs() (bytearray method):       Bytes and Bytearray Operations.
                                                             (line  476)
* expandtabs() (bytes method):           Bytes and Bytearray Operations.
                                                             (line  476)
* expandtabs() (str method):             String Methods<2>.  (line   90)
* expanduser() (in module os.path):      os path — Common pathname manipulations.
                                                             (line  135)
* expanduser() (pathlib.Path method):    Methods<2>.         (line   80)
* expandvars() (in module os.path):      os path — Common pathname manipulations.
                                                             (line  158)
* expand_tabs (textwrap.TextWrapper attribute): textwrap — Text wrapping and filling.
                                                             (line  164)
* Expat:                                 xml parsers expat — Fast XML parsing using Expat.
                                                             (line   12)
* ExpatError:                            xml parsers expat — Fast XML parsing using Expat.
                                                             (line   25)
* expect() (telnetlib.Telnet method):    Telnet Objects.     (line  121)
* expected (asyncio.IncompleteReadError attribute): Exceptions<10>.
                                                             (line   50)
* expectedFailure() (in module unittest): Skipping tests and expected failures.
                                                             (line   98)
* expectedFailures (unittest.TestResult attribute): Loading and running tests.
                                                             (line  257)
* expires (http.cookiejar.Cookie attribute): Cookie Objects<2>.
                                                             (line   49)
* exploded (ipaddress.IPv4Address attribute): Address objects.
                                                             (line   66)
* exploded (ipaddress.IPv4Network attribute): Network objects.
                                                             (line  109)
* exploded (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  200)
* exploded (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  321)
* expm1() (in module math):              Power and logarithmic functions.
                                                             (line   12)
* expovariate() (in module random):      Real-valued distributions.
                                                             (line   38)
* Expr (class in ast):                   Expressions<2>.     (line    6)
* expr() (in module parser):             Creating ST Objects.
                                                             (line   10)
* expression:                            Expressions.        (line    6)
* expression <1>:                        Glossary.           (line  398)
* expression; list:                      Expression lists.   (line    6)
* expression; list <1>:                  Expression statements.
                                                             (line    6)
* expression; list <2>:                  Expression statements.
                                                             (line    6)
* expression; statement:                 Expression statements.
                                                             (line    6)
* expunge() (imaplib.IMAP4 method):      IMAP4 Objects.      (line   93)
* extend() (array.array method):         array — Efficient arrays of numeric values.
                                                             (line  148)
* extend() (collections.deque method):   deque objects.      (line   59)
* extend() (sequence method):            Mutable Sequence Types.
                                                             (line   16)
* extend() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line   93)
* ExtendedContext (class in decimal):    Context objects.    (line   58)
* ExtendedInterpolation (class in configparser): Interpolation of values.
                                                             (line   40)
* EXTENDED_ARG (opcode):                 Python Bytecode Instructions.
                                                             (line  801)
* extendleft() (collections.deque method): deque objects.    (line   64)
* extend_path() (in module pkgutil):     pkgutil — Package extension utility.
                                                             (line   19)
* Extension (class in distutils.core):   distutils core — Core Distutils functionality.
                                                             (line  176)
* extension module:                      Glossary.           (line  409)
* extension; module:                     The standard type hierarchy.
                                                             (line    6)
* ExtensionFileLoader (class in importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line  300)
* extensions_map (http.server.SimpleHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  358)
* EXTENSION_SUFFIXES (in module importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line   50)
* External Data Representation:          Data stream format. (line    6)
* External Data Representation <1>:      xdrlib — Encode and decode XDR data.
                                                             (line    8)
* ExternalClashError:                    Exceptions<15>.     (line   25)
* ExternalEntityParserCreate() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line   44)
* ExternalEntityRefHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  333)
* external_attr (zipfile.ZipInfo attribute): ZipInfo Objects.
                                                             (line  127)
* extra (zipfile.ZipInfo attribute):     ZipInfo Objects.    (line   93)
* extract() (tarfile.TarFile method):    TarFile Objects.    (line  162)
* extract() (traceback.StackSummary class method): StackSummary Objects.
                                                             (line   13)
* extract() (zipfile.ZipFile method):    ZipFile Objects.    (line  158)
* extractall() (tarfile.TarFile method): TarFile Objects.    (line  136)
* extractall() (zipfile.ZipFile method): ZipFile Objects.    (line  185)
* ExtractError:                          tarfile — Read and write tar archive files.
                                                             (line  208)
* extractfile() (tarfile.TarFile method): TarFile Objects.   (line  190)
* extract_cookies() (http.cookiejar.CookieJar method): CookieJar and FileCookieJar Objects.
                                                             (line   30)
* extract_stack() (in module traceback): traceback — Print or retrieve a stack traceback.
                                                             (line   96)
* extract_tb() (in module traceback):    traceback — Print or retrieve a stack traceback.
                                                             (line   83)
* extract_version (zipfile.ZipInfo attribute): ZipInfo Objects.
                                                             (line  107)
* extsep (in module os):                 Miscellaneous System Information.
                                                             (line  109)
* EX_CANTCREAT (in module os):           Process Management. (line  202)
* EX_CONFIG (in module os):              Process Management. (line  238)
* EX_DATAERR (in module os):             Process Management. (line  151)
* EX_IOERR (in module os):               Process Management. (line  209)
* EX_NOHOST (in module os):              Process Management. (line  170)
* EX_NOINPUT (in module os):             Process Management. (line  157)
* EX_NOPERM (in module os):              Process Management. (line  231)
* EX_NOTFOUND (in module os):            Process Management. (line  245)
* EX_NOUSER (in module os):              Process Management. (line  164)
* EX_OK (in module os):                  Process Management. (line  138)
* EX_OSERR (in module os):               Process Management. (line  188)
* EX_OSFILE (in module os):              Process Management. (line  195)
* EX_PROTOCOL (in module os):            Process Management. (line  224)
* EX_SOFTWARE (in module os):            Process Management. (line  182)
* EX_TEMPFAIL (in module os):            Process Management. (line  216)
* EX_UNAVAILABLE (in module os):         Process Management. (line  176)
* EX_USAGE (in module os):               Process Management. (line  144)
* f"; formatted string literal:          String and Bytes literals.
                                                             (line   62)
* f’; formatted string literal:          String and Bytes literals.
                                                             (line   62)
* f-string:                              String literal concatenation.
                                                             (line   24)
* f-string <1>:                          Glossary.           (line  414)
* fabs() (in module math):               Number-theoretic and representation functions.
                                                             (line   36)
* factorial() (in module math):          Number-theoretic and representation functions.
                                                             (line   40)
* factory() (importlib.util.LazyLoader class method): importlib util – Utility code for importers.
                                                             (line  259)
* fail() (unittest.TestCase method):     Test cases.         (line  664)
* failfast (unittest.TestResult attribute): Loading and running tests.
                                                             (line  288)
* failureException (unittest.TestCase attribute): Test cases.
                                                             (line  669)
* failures (unittest.TestResult attribute): Loading and running tests.
                                                             (line  243)
* FAIL_FAST (in module doctest):         Option Flags.       (line  151)
* FakePath (class in test.support):      test support — Utilities for the Python test suite.
                                                             (line 1129)
* False:                                 The standard type hierarchy.
                                                             (line   98)
* false:                                 Truth Value Testing.
                                                             (line    6)
* False <1>:                             Truth Value Testing.
                                                             (line   23)
* False <2>:                             Boolean Values.     (line   15)
* False (Built-in object):               Truth Value Testing.
                                                             (line   15)
* False (built-in variable):             Built-in Constants. (line    8)
* families() (in module tkinter.font):   tkinter font — Tkinter font wrapper.
                                                             (line   88)
* family (socket.socket attribute):      Socket Objects.     (line  595)
* FancyGetopt (class in distutils.fancy_getopt): distutils fancy_getopt — Wrapper around the standard getopt module.
                                                             (line   36)
* FancyURLopener (class in urllib.request): Legacy interface.
                                                             (line  147)
* fancy_getopt() (in module distutils.fancy_getopt): distutils fancy_getopt — Wrapper around the standard getopt module.
                                                             (line   20)
* fast (pickle.Pickler attribute):       Module Interface.   (line  214)
* FastChildWatcher (class in asyncio):   Process Watchers.   (line  132)
* fatalError() (xml.sax.handler.ErrorHandler method): ErrorHandler Objects.
                                                             (line   24)
* Fault (class in xmlrpc.client):        Fault Objects.      (line    6)
* faultCode (xmlrpc.client.Fault attribute): Fault Objects.  (line   11)
* faulthandler (module):                 faulthandler — Dump the Python traceback.
                                                             (line    6)
* faultString (xmlrpc.client.Fault attribute): Fault Objects.
                                                             (line   15)
* fchdir() (in module os):               Files and Directories.
                                                             (line  268)
* fchmod() (in module os):               File Descriptor Operations.
                                                             (line   97)
* fchown() (in module os):               File Descriptor Operations.
                                                             (line  108)
* FCICreate() (in module msilib):        msilib — Read and write Microsoft Installer files.
                                                             (line   26)
* fcntl (module):                        fcntl — The fcntl and ioctl system calls.
                                                             (line    6)
* fcntl() (in module fcntl):             fcntl — The fcntl and ioctl system calls.
                                                             (line   34)
* fd (selectors.SelectorKey attribute):  Classes<3>.         (line   40)
* fd() (in module turtle):               Turtle motion.      (line    6)
* fdatasync() (in module os):            File Descriptor Operations.
                                                             (line  120)
* fdopen() (in module os):               File Object Creation.
                                                             (line    9)
* fd_count() (in module test.support):   test support — Utilities for the Python test suite.
                                                             (line  302)
* Feature (class in msilib):             Features<3>.        (line    6)
* feature_external_ges (in module xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line   76)
* feature_external_pes (in module xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line   83)
* feature_namespaces (in module xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line   48)
* feature_namespace_prefixes (in module xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line   55)
* feature_string_interning (in module xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line   62)
* feature_validation (in module xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line   69)
* feed() (email.parser.BytesFeedParser method): FeedParser API.
                                                             (line   56)
* feed() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line    8)
* feed() (xml.etree.ElementTree.XMLParser method): XMLParser Objects.
                                                             (line   27)
* feed() (xml.etree.ElementTree.XMLPullParser method): XMLPullParser Objects.
                                                             (line   18)
* feed() (xml.sax.xmlreader.IncrementalParser method): IncrementalParser Objects.
                                                             (line    9)
* FeedParser (class in email.parser):    FeedParser API.     (line   71)
* fetch() (imaplib.IMAP4 method):        IMAP4 Objects.      (line   99)
* Fetch() (msilib.View method):          View Objects.       (line   18)
* fetchall() (sqlite3.Cursor method):    Cursor Objects.     (line  140)
* fetchmany() (sqlite3.Cursor method):   Cursor Objects.     (line  120)
* fetchone() (sqlite3.Cursor method):    Cursor Objects.     (line  115)
* fflags (select.kevent attribute):      Kevent Objects.     (line   90)
* Field (class in dataclasses):          Module-level decorators classes and functions.
                                                             (line  240)
* field() (in module dataclasses):       Module-level decorators classes and functions.
                                                             (line  152)
* fieldnames (csv.csvreader attribute):  Reader Objects.     (line   31)
* fields (uuid.UUID attribute):          uuid — UUID objects according to RFC 4122.
                                                             (line   94)
* fields() (in module dataclasses):      Module-level decorators classes and functions.
                                                             (line  260)
* field_size_limit() (in module csv):    Module Contents<3>. (line   96)
* file (pyclbr.Class attribute):         Class Objects<2>.   (line    9)
* file (pyclbr.Function attribute):      Function Objects.   (line    9)
* file object:                           Glossary.           (line  420)
* file object; io module:                Overview.           (line    6)
* file object; open() built-in function: Built-in Functions. (line 1029)
* file-like object:                      Glossary.           (line  436)
* file; byte-code:                       py_compile — Compile Python source files.
                                                             (line    8)
* file; byte-code <1>:                   imp — Access the import internals.
                                                             (line   19)
* file; copying:                         shutil — High-level file operations.
                                                             (line    8)
* file; large files:                     Large File Support. (line    6)
* file; mime.types:                      mimetypes — Map filenames to MIME types.
                                                             (line  124)
* file; modes:                           Built-in Functions. (line 1053)
* filecmp (module):                      filecmp — File and Directory Comparisons.
                                                             (line    6)
* fileConfig() (in module logging.config): Configuration functions.
                                                             (line   61)
* FileCookieJar (class in http.cookiejar): http cookiejar — Cookie handling for HTTP clients.
                                                             (line   56)
* FileDialog (class in tkinter.filedialog): Native Load/Save Dialogs.
                                                             (line   78)
* FileEntry (class in tkinter.tix):      File Selectors.     (line   50)
* FileExistsError:                       OS exceptions.      (line   61)
* FileFinder (class in importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line  160)
* FileHandler (class in logging):        FileHandler.        (line   10)
* FileHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  408)
* FileInput (class in fileinput):        fileinput — Iterate over lines from multiple input streams.
                                                             (line  134)
* fileinput (module):                    fileinput — Iterate over lines from multiple input streams.
                                                             (line    6)
* FileIO (class in io):                  Raw File I/O.       (line    6)
* filelineno() (in module fileinput):    fileinput — Iterate over lines from multiple input streams.
                                                             (line   99)
* FileLoader (class in importlib.abc):   importlib abc – Abstract base classes related to import.
                                                             (line  473)
* filemode() (in module stat):           stat — Interpreting stat results.
                                                             (line  121)
* filename (doctest.DocTest attribute):  DocTest Objects.    (line   36)
* filename (http.cookiejar.FileCookieJar attribute): CookieJar and FileCookieJar Objects.
                                                             (line  153)
* filename (OSError attribute):          Concrete exceptions.
                                                             (line  157)
* filename (SyntaxError attribute):      Concrete exceptions.
                                                             (line  259)
* filename (traceback.TracebackException attribute): TracebackException Objects.
                                                             (line   42)
* filename (tracemalloc.Frame attribute): Frame.             (line   13)
* filename (zipfile.ZipFile attribute):  ZipFile Objects.    (line  302)
* filename (zipfile.ZipInfo attribute):  ZipInfo Objects.    (line   50)
* filename() (in module fileinput):      fileinput — Iterate over lines from multiple input streams.
                                                             (line   81)
* filename2 (OSError attribute):         Concrete exceptions.
                                                             (line  157)
* filenames; pathname expansion:         glob — Unix style pathname pattern expansion.
                                                             (line    8)
* filenames; wildcard expansion:         fnmatch — Unix filename pattern matching.
                                                             (line    8)
* filename_only (in module tabnanny):    tabnanny — Detection of ambiguous indentation.
                                                             (line   31)
* filename_pattern (tracemalloc.Filter attribute): Filter.   (line   53)
* fileno() (http.client.HTTPResponse method): HTTPResponse Objects.
                                                             (line   36)
* fileno() (in module fileinput):        fileinput — Iterate over lines from multiple input streams.
                                                             (line   86)
* fileno() (io.IOBase method):           I/O Base Classes.   (line   63)
* fileno() (multiprocessing.connection.Connection method): Connection Objects<2>.
                                                             (line   31)
* fileno() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line   28)
* fileno() (ossaudiodev.oss_mixer_device method): Mixer Device Objects.
                                                             (line   14)
* fileno() (select.devpoll method):      /dev/poll Polling Objects.
                                                             (line   24)
* fileno() (select.epoll method):        Edge and Level Trigger Polling epoll Objects.
                                                             (line   73)
* fileno() (select.kqueue method):       Kqueue Objects.     (line   14)
* fileno() (selectors.DevpollSelector method): Classes<3>.   (line  188)
* fileno() (selectors.EpollSelector method): Classes<3>.     (line  179)
* fileno() (selectors.KqueueSelector method): Classes<3>.    (line  199)
* fileno() (socket.socket method):       Socket Objects.     (line  110)
* fileno() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line   14)
* fileno() (telnetlib.Telnet method):    Telnet Objects.     (line   97)
* FileNotFoundError:                     OS exceptions.      (line   66)
* fileobj (selectors.SelectorKey attribute): Classes<3>.     (line   36)
* files() (in module importlib.resources): importlib resources – Resources.
                                                             (line   53)
* FileSelectBox (class in tkinter.tix):  File Selectors.     (line   42)
* files_double_event() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line   94)
* files_select_event() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line   98)
* FileType (class in argparse):          FileType objects.   (line    6)
* FileWrapper (class in wsgiref.util):   wsgiref util – WSGI environment utilities.
                                                             (line  114)
* FILE_ATTRIBUTE_ARCHIVE (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_COMPRESSED (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_DEVICE (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_DIRECTORY (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_ENCRYPTED (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_HIDDEN (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_INTEGRITY_STREAM (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_NORMAL (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_NOT_CONTENT_INDEXED (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_NO_SCRUB_DATA (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_OFFLINE (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_READONLY (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_REPARSE_POINT (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_SPARSE_FILE (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_SYSTEM (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_TEMPORARY (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* FILE_ATTRIBUTE_VIRTUAL (in module stat): stat — Interpreting stat results.
                                                             (line  394)
* file_created() (built-in function):    The Postinstallation script.
                                                             (line   23)
* file_dispatcher (class in asyncore):   asyncore — Asynchronous socket handler.
                                                             (line  256)
* file_open() (urllib.request.FileHandler method): FileHandler Objects.
                                                             (line    6)
* file_size (zipfile.ZipInfo attribute): ZipInfo Objects.    (line  143)
* file_wrapper (class in asyncore):      asyncore — Asynchronous socket handler.
                                                             (line  266)
* fill() (in module textwrap):           textwrap — Text wrapping and filling.
                                                             (line   32)
* fill() (textwrap.TextWrapper method):  textwrap — Text wrapping and filling.
                                                             (line  293)
* fillcolor() (in module turtle):        Color control.      (line   58)
* filling() (in module turtle):          Filling.            (line    6)
* filter (2to3 fixer):                   Fixers.             (line  101)
* Filter (class in logging):             Filter Objects.     (line   13)
* Filter (class in tracemalloc):         Filter.             (line    6)
* filter (select.kevent attribute):      Kevent Objects.     (line   15)
* filter() (built-in function):          Built-in Functions. (line  563)
* filter() (in module curses):           Functions<4>.       (line  121)
* filter() (in module fnmatch):          fnmatch — Unix filename pattern matching.
                                                             (line   65)
* filter() (logging.Filter method):      Filter Objects.     (line   20)
* filter() (logging.Handler method):     Handler Objects.    (line   60)
* filter() (logging.Logger method):      Logger Objects.     (line  271)
* filterfalse() (in module itertools):   Itertool functions. (line  284)
* filterwarnings() (in module warnings): Available Functions.
                                                             (line   77)
* filter_command() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line  102)
* FILTER_DIR (in module unittest.mock):  FILTER_DIR.         (line    6)
* filter_traces() (tracemalloc.Snapshot method): Snapshot.   (line   35)
* Final (in module typing):              Special forms.      (line  203)
* final() (in module typing):            Functions and decorators.
                                                             (line   45)
* finalization, of objects:              Finalization and De-allocation.
                                                             (line    6)
* finalize (class in weakref):           weakref — Weak references.
                                                             (line  237)
* finalizer:                             Basic customization.
                                                             (line   55)
* finalize_options() (distutils.cmd.Command method): Creating a new Distutils command.
                                                             (line   30)
* find() (bytearray method):             Bytes and Bytearray Operations.
                                                             (line  126)
* find() (bytes method):                 Bytes and Bytearray Operations.
                                                             (line  126)
* find() (doctest.DocTestFinder method): DocTestFinder objects.
                                                             (line   32)
* find() (in module gettext):            Class-based API.    (line   14)
* find() (mmap.mmap method):             mmap — Memory-mapped file support.
                                                             (line  177)
* find() (str method):                   String Methods<2>.  (line  111)
* find() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line  101)
* find() (xml.etree.ElementTree.ElementTree method): ElementTree Objects.
                                                             (line   21)
* findall() (in module re):              Module Contents.    (line  219)
* findall() (re.Pattern method):         Regular Expression Objects.
                                                             (line   79)
* findall() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line  110)
* findall() (xml.etree.ElementTree.ElementTree method): ElementTree Objects.
                                                             (line   26)
* findCaller() (logging.Logger method):  Logger Objects.     (line  288)
* finder:                                Finders and loaders.
                                                             (line    6)
* finder <1>:                            Glossary.           (line  440)
* Finder (class in importlib.abc):       importlib abc – Abstract base classes related to import.
                                                             (line   28)
* finder; find_spec:                     The meta path.      (line    6)
* findfactor() (in module audioop):      audioop — Manipulate raw audio data.
                                                             (line   79)
* findfile() (in module test.support):   test support — Utilities for the Python test suite.
                                                             (line  288)
* findfit() (in module audioop):         audioop — Manipulate raw audio data.
                                                             (line   88)
* finditer() (in module re):             Module Contents.    (line  241)
* finditer() (re.Pattern method):        Regular Expression Objects.
                                                             (line   85)
* findlabels() (in module dis):          Analysis functions. (line  136)
* findlinestarts() (in module dis):      Analysis functions. (line  125)
* findmatch() (in module mailcap):       mailcap — Mailcap file handling.
                                                             (line   24)
* findmax() (in module audioop):         audioop — Manipulate raw audio data.
                                                             (line   99)
* findtext() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line  119)
* findtext() (xml.etree.ElementTree.ElementTree method): ElementTree Objects.
                                                             (line   31)
* find_class() (pickle protocol):        Restricting Globals.
                                                             (line    6)
* find_class() (pickle.Unpickler method): Module Interface.  (line  286)
* find_library() (in module ctypes.util): Utility functions. (line   89)
* find_library_file() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  204)
* find_loader() (importlib.abc.PathEntryFinder method): importlib abc – Abstract base classes related to import.
                                                             (line  119)
* find_loader() (importlib.machinery.FileFinder method): importlib machinery – Importers and path hooks.
                                                             (line  197)
* find_loader() (in module importlib):   Functions<11>.      (line   40)
* find_loader() (in module pkgutil):     pkgutil — Package extension utility.
                                                             (line   77)
* find_longest_match() (difflib.SequenceMatcher method): SequenceMatcher Objects.
                                                             (line   64)
* find_module() (imp.NullImporter method): imp — Access the import internals.
                                                             (line  355)
* find_module() (importlib.abc.Finder method): importlib abc – Abstract base classes related to import.
                                                             (line   35)
* find_module() (importlib.abc.MetaPathFinder method): importlib abc – Abstract base classes related to import.
                                                             (line   67)
* find_module() (importlib.abc.PathEntryFinder method): importlib abc – Abstract base classes related to import.
                                                             (line  143)
* find_module() (importlib.machinery.PathFinder class method): importlib machinery – Importers and path hooks.
                                                             (line  139)
* find_module() (in module imp):         imp — Access the import internals.
                                                             (line   41)
* find_module() (zipimport.zipimporter method): zipimporter Objects.
                                                             (line   19)
* find_msvcrt() (in module ctypes.util): Utility functions.  (line   98)
* find_spec() (importlib.abc.MetaPathFinder method): importlib abc – Abstract base classes related to import.
                                                             (line   52)
* find_spec() (importlib.abc.PathEntryFinder method): importlib abc – Abstract base classes related to import.
                                                             (line  106)
* find_spec() (importlib.machinery.FileFinder method): importlib machinery – Importers and path hooks.
                                                             (line  190)
* find_spec() (importlib.machinery.PathFinder class method): importlib machinery – Importers and path hooks.
                                                             (line  116)
* find_spec() (in module importlib.util): importlib util – Utility code for importers.
                                                             (line  101)
* find_unused_port() (in module test.support.socket_helper): test support socket_helper — Utilities for socket tests.
                                                             (line   15)
* find_user_password() (urllib.request.HTTPPasswordMgr method): HTTPPasswordMgr Objects.
                                                             (line   16)
* find_user_password() (urllib.request.HTTPPasswordMgrWithPriorAuth method): HTTPPasswordMgrWithPriorAuth Objects.
                                                             (line   19)
* finish() (socketserver.BaseRequestHandler method): Request Handler Objects.
                                                             (line   35)
* finish() (tkinter.dnd.DndHandler method): tkinter dnd — Drag and drop support.
                                                             (line   52)
* finish_request() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line  125)
* firstChild (xml.dom.Node attribute):   Node Objects.       (line   54)
* firstkey() (dbm.gnu.gdbm method):      dbm gnu — GNU’s reinterpretation of dbm.
                                                             (line   85)
* firstweekday() (in module calendar):   calendar — General calendar-related functions.
                                                             (line  297)
* fix_missing_locations() (in module ast): ast Helpers.      (line  117)
* fix_sentence_endings (textwrap.TextWrapper attribute): textwrap — Text wrapping and filling.
                                                             (line  219)
* Flag (class in enum):                  Module Contents<2>. (line   28)
* flags (in module sys):                 sys — System-specific parameters and functions.
                                                             (line  429)
* flags (re.Pattern attribute):          Regular Expression Objects.
                                                             (line  101)
* flags (select.kevent attribute):       Kevent Objects.     (line   52)
* flag_bits (zipfile.ZipInfo attribute): ZipInfo Objects.    (line  115)
* flash() (in module curses):            Functions<4>.       (line  132)
* flatten() (email.generator.BytesGenerator method): email generator Generating MIME documents.
                                                             (line   80)
* flatten() (email.generator.Generator method): email generator Generating MIME documents.
                                                             (line  175)
* flattening; objects:                   pickle — Python object serialization.
                                                             (line    8)
* float (built-in class):                Built-in Functions. (line  580)
* floating point literal:                Numeric literals.   (line    6)
* floating point; literals:              Numeric Types — int float complex.
                                                             (line   19)
* floating point; number:                The standard type hierarchy.
                                                             (line  112)
* FloatingPointError:                    Concrete exceptions.
                                                             (line   26)
* FloatOperation (class in decimal):     Signals.            (line  100)
* float_info (in module sys):            sys — System-specific parameters and functions.
                                                             (line  498)
* float_repr_style (in module sys):      sys — System-specific parameters and functions.
                                                             (line  582)
* flock() (in module fcntl):             fcntl — The fcntl and ioctl system calls.
                                                             (line  114)
* floor division:                        Glossary.           (line  451)
* floor() (in module math):              Numeric Types — int float complex.
                                                             (line  104)
* floor() (in module math) <1>:          Number-theoretic and representation functions.
                                                             (line   48)
* FloorDiv (class in ast):               Expressions<2>.     (line   54)
* floordiv() (in module operator):       operator — Standard operators as functions.
                                                             (line   88)
* flush() (bz2.BZ2Compressor method):    Incremental de compression.
                                                             (line   25)
* flush() (formatter.writer method):     The Writer Interface.
                                                             (line   13)
* flush() (io.BufferedWriter method):    Buffered Streams.   (line  125)
* flush() (io.IOBase method):            I/O Base Classes.   (line   69)
* flush() (logging.Handler method):      Handler Objects.    (line   68)
* flush() (logging.handlers.BufferingHandler method): MemoryHandler.
                                                             (line   30)
* flush() (logging.handlers.MemoryHandler method): MemoryHandler.
                                                             (line   60)
* flush() (logging.StreamHandler method): StreamHandler.     (line   25)
* flush() (lzma.LZMACompressor method):  Compressing and decompressing data in memory.
                                                             (line   91)
* flush() (mailbox.Mailbox method):      Mailbox objects.    (line  242)
* flush() (mailbox.Maildir method):      Maildir.            (line  102)
* flush() (mailbox.MH method):           MH.                 (line   99)
* flush() (mmap.mmap method):            mmap — Memory-mapped file support.
                                                             (line  187)
* flush() (zlib.Compress method):        zlib — Compression compatible with gzip.
                                                             (line  207)
* flush() (zlib.Decompress method):      zlib — Compression compatible with gzip.
                                                             (line  279)
* flushinp() (in module curses):         Functions<4>.       (line  139)
* FlushKey() (in module winreg):         Functions<12>.      (line  244)
* flush_headers() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  277)
* flush_softspace() (formatter.formatter method): The Formatter Interface.
                                                             (line   83)
* fma() (decimal.Context method):        Context objects.    (line  288)
* fma() (decimal.Decimal method):        Decimal objects.    (line  270)
* fmean() (in module statistics):        Function details.   (line   49)
* fmod() (in module math):               Number-theoretic and representation functions.
                                                             (line   54)
* FMT_BINARY (in module plistlib):       plistlib — Generate and parse Apple plist files.
                                                             (line  141)
* FMT_XML (in module plistlib):          plistlib — Generate and parse Apple plist files.
                                                             (line  135)
* fnmatch (module):                      fnmatch — Unix filename pattern matching.
                                                             (line    6)
* fnmatch() (in module fnmatch):         fnmatch — Unix filename pattern matching.
                                                             (line   40)
* fnmatchcase() (in module fnmatch):     fnmatch — Unix filename pattern matching.
                                                             (line   59)
* focus() (tkinter.ttk.Treeview method): ttk Treeview.       (line   99)
* fold (datetime.datetime attribute):    datetime Objects.   (line  298)
* fold (datetime.time attribute):        time Objects.       (line   71)
* fold() (email.headerregistry.BaseHeader method): email headerregistry Custom Header Objects.
                                                             (line   72)
* fold() (email.policy.Compat32 method): email policy Policy Objects.
                                                             (line  584)
* fold() (email.policy.EmailPolicy method): email policy Policy Objects.
                                                             (line  450)
* fold() (email.policy.Policy method):   email policy Policy Objects.
                                                             (line  319)
* fold_binary() (email.policy.Compat32 method): email policy Policy Objects.
                                                             (line  592)
* fold_binary() (email.policy.EmailPolicy method): email policy Policy Objects.
                                                             (line  470)
* fold_binary() (email.policy.Policy method): email policy Policy Objects.
                                                             (line  334)
* Font (class in tkinter.font):          tkinter font — Tkinter font wrapper.
                                                             (line   20)
* For (class in ast):                    Control flow.       (line   45)
* for; in comprehensions:                Displays for lists sets and dictionaries.
                                                             (line   14)
* forget() (in module test.support):     test support — Utilities for the Python test suite.
                                                             (line  222)
* forget() (tkinter.ttk.Notebook method): ttk Notebook.      (line   18)
* fork() (in module os):                 Process Management. (line  251)
* fork() (in module pty):                pty — Pseudo-terminal utilities.
                                                             (line   20)
* ForkingMixIn (class in socketserver):  Server Creation Notes.
                                                             (line   28)
* ForkingTCPServer (class in socketserver): Server Creation Notes.
                                                             (line   62)
* ForkingUDPServer (class in socketserver): Server Creation Notes.
                                                             (line   62)
* forkpty() (in module os):              Process Management. (line  270)
* Form (class in tkinter.tix):           Form Geometry Manager.
                                                             (line    9)
* format (memoryview attribute):         Memory Views.       (line  417)
* format (multiprocessing.shared_memory.ShareableList attribute): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line  273)
* format (struct.Struct attribute):      Classes<2>.         (line   55)
* format() (built-in function):          Built-in Functions. (line  641)
* format() (built-in function); __str__() (object method): Basic customization.
                                                             (line  128)
* format() (in module locale):           locale — Internationalization services.
                                                             (line  407)
* format() (logging.Formatter method):   Formatter Objects.  (line   52)
* format() (logging.Handler method):     Handler Objects.    (line  102)
* format() (pprint.PrettyPrinter method): PrettyPrinter Objects.
                                                             (line   40)
* format() (str method):                 String Methods<2>.  (line  125)
* format() (string.Formatter method):    Custom String Formatting.
                                                             (line   17)
* format() (traceback.StackSummary method): StackSummary Objects.
                                                             (line   36)
* format() (traceback.TracebackException method): TracebackException Objects.
                                                             (line   73)
* format() (tracemalloc.Traceback method): Traceback.        (line   37)
* formataddr() (in module email.utils):  email utils Miscellaneous utilities.
                                                             (line   67)
* formatargspec() (in module inspect):   Classes and functions<2>.
                                                             (line   92)
* formatargvalues() (in module inspect): Classes and functions<2>.
                                                             (line  121)
* formatdate() (in module email.utils):  email utils Miscellaneous utilities.
                                                             (line  139)
* FormatError:                           Exceptions<15>.     (line   32)
* FormatError() (in module ctypes):      Utility functions.  (line  108)
* formatException() (logging.Formatter method): Formatter Objects.
                                                             (line  116)
* formatmonth() (calendar.HTMLCalendar method): calendar — General calendar-related functions.
                                                             (line  169)
* formatmonth() (calendar.TextCalendar method): calendar — General calendar-related functions.
                                                             (line  134)
* formatStack() (logging.Formatter method): Formatter Objects.
                                                             (line  124)
* formatted string literal:              String literal concatenation.
                                                             (line   24)
* FormattedValue (class in ast):         Literals<3>.        (line   18)
* Formatter (class in logging):          Formatter Objects.  (line   26)
* Formatter (class in string):           Custom String Formatting.
                                                             (line   13)
* formatter (module):                    formatter — Generic output formatting.
                                                             (line    6)
* formatTime() (logging.Formatter method): Formatter Objects.
                                                             (line   76)
* formatting, string (%):                printf-style String Formatting.
                                                             (line    6)
* formatting; bytearray (%):             printf-style Bytes Formatting.
                                                             (line    6)
* formatting; bytes (%):                 printf-style Bytes Formatting.
                                                             (line    6)
* formatwarning() (in module warnings):  Available Functions.
                                                             (line   68)
* formatyear() (calendar.HTMLCalendar method): calendar — General calendar-related functions.
                                                             (line  175)
* formatyear() (calendar.TextCalendar method): calendar — General calendar-related functions.
                                                             (line  148)
* formatyearpage() (calendar.HTMLCalendar method): calendar — General calendar-related functions.
                                                             (line  180)
* format_datetime() (in module email.utils): email utils Miscellaneous utilities.
                                                             (line  160)
* format_exc() (in module traceback):    traceback — Print or retrieve a stack traceback.
                                                             (line  137)
* format_exception() (in module traceback): traceback — Print or retrieve a stack traceback.
                                                             (line  124)
* format_exception_only() (in module traceback): traceback — Print or retrieve a stack traceback.
                                                             (line  113)
* format_exception_only() (traceback.TracebackException method): TracebackException Objects.
                                                             (line   88)
* format_field() (string.Formatter method): Custom String Formatting.
                                                             (line  102)
* format_help() (argparse.ArgumentParser method): Printing help.
                                                             (line   30)
* format_list() (in module traceback):   traceback — Print or retrieve a stack traceback.
                                                             (line  103)
* format_map() (str method):             String Methods<2>.  (line  155)
* format_stack() (in module traceback):  traceback — Print or retrieve a stack traceback.
                                                             (line  146)
* format_stack_entry() (bdb.Bdb method): bdb — Debugger framework.
                                                             (line  344)
* format_string() (in module locale):    locale — Internationalization services.
                                                             (line  390)
* format_tb() (in module traceback):     traceback — Print or retrieve a stack traceback.
                                                             (line  142)
* format_usage() (argparse.ArgumentParser method): Printing help.
                                                             (line   25)
* FORMAT_VALUE (opcode):                 Python Bytecode Instructions.
                                                             (line  809)
* Fortran contiguous:                    shape strides suboffsets.
                                                             (line   25)
* Fortran contiguous <1>:                Glossary.           (line  273)
* forward() (in module turtle):          Turtle motion.      (line    6)
* ForwardRef (class in typing):          Introspection helpers.
                                                             (line   60)
* FOR_ITER (opcode):                     Python Bytecode Instructions.
                                                             (line  631)
* found_terminator() (asynchat.async_chat method): asynchat — Asynchronous socket command/response handler.
                                                             (line   89)
* fpathconf() (in module os):            File Descriptor Operations.
                                                             (line  129)
* fqdn (smtpd.SMTPChannel attribute):    SMTPChannel Objects.
                                                             (line   90)
* Fraction (class in fractions):         fractions — Rational numbers.
                                                             (line   16)
* fractions (module):                    fractions — Rational numbers.
                                                             (line    6)
* Frame (class in tracemalloc):          Frame.              (line    6)
* frame (tkinter.scrolledtext.ScrolledText attribute): tkinter scrolledtext — Scrolled Text Widget.
                                                             (line   26)
* FrameSummary (class in traceback):     FrameSummary Objects.
                                                             (line   11)
* FrameType (in module types):           Standard Interpreter Types.
                                                             (line  209)
* free():                                Overview<3>.        (line   33)
* free; variable:                        Binding of names.   (line   26)
* freefunc (C type):                     Slot Type typedefs. (line   26)
* freeze utility:                        Importing Modules<2>.
                                                             (line  250)
* freeze() (in module gc):               gc — Garbage Collector interface.
                                                             (line  202)
* freeze_support() (in module multiprocessing): Miscellaneous<3>.
                                                             (line   44)
* frexp() (in module math):              Number-theoretic and representation functions.
                                                             (line   70)
* from; import statement:                Binding of names.   (line    9)
* from; import statement <1>:            The import statement.
                                                             (line   51)
* from; yield from expression:           Yield expressions.  (line   64)
* frombuf() (tarfile.TarInfo class method): TarInfo Objects. (line   19)
* frombytes() (array.array method):      array — Efficient arrays of numeric values.
                                                             (line  156)
* fromfd() (in module socket):           Creating sockets.   (line  147)
* fromfd() (select.epoll method):        Edge and Level Trigger Polling epoll Objects.
                                                             (line   77)
* fromfd() (select.kqueue method):       Kqueue Objects.     (line   18)
* fromfile() (array.array method):       array — Efficient arrays of numeric values.
                                                             (line  165)
* fromhex() (bytearray class method):    Bytearray Objects.  (line   36)
* fromhex() (bytes class method):        Bytes Objects.      (line   62)
* fromhex() (float class method):        Additional Methods on Float.
                                                             (line   39)
* fromisocalendar() (datetime.date class method): date Objects.
                                                             (line   77)
* fromisocalendar() (datetime.datetime class method): datetime Objects.
                                                             (line  222)
* fromisoformat() (datetime.date class method): date Objects.
                                                             (line   63)
* fromisoformat() (datetime.datetime class method): datetime Objects.
                                                             (line  187)
* fromisoformat() (datetime.time class method): time Objects.
                                                             (line  113)
* fromkeys() (collections.Counter method): Counter objects.  (line  106)
* fromkeys() (dict class method):        Mapping Types — dict.
                                                             (line  151)
* fromlist() (array.array method):       array — Efficient arrays of numeric values.
                                                             (line  172)
* fromordinal() (datetime.date class method): date Objects.  (line   54)
* fromordinal() (datetime.datetime class method): datetime Objects.
                                                             (line  161)
* fromshare() (in module socket):        Creating sockets.   (line  164)
* fromstring() (in module xml.etree.ElementTree): Functions<7>.
                                                             (line   99)
* fromstringlist() (in module xml.etree.ElementTree): Functions<7>.
                                                             (line  107)
* fromtarfile() (tarfile.TarInfo class method): TarInfo Objects.
                                                             (line   26)
* fromtimestamp() (datetime.date class method): date Objects.
                                                             (line   35)
* fromtimestamp() (datetime.datetime class method): datetime Objects.
                                                             (line   93)
* fromunicode() (array.array method):    array — Efficient arrays of numeric values.
                                                             (line  178)
* fromutc() (datetime.timezone method):  timezone Objects.   (line   61)
* fromutc() (datetime.tzinfo method):    tzinfo Objects.     (line  163)
* from_address() (ctypes._CData method): Data types.         (line   42)
* from_buffer() (ctypes._CData method):  Data types.         (line   19)
* from_buffer_copy() (ctypes._CData method): Data types.     (line   31)
* from_bytes() (int class method):       Additional Methods on Integer Types.
                                                             (line   67)
* from_callable() (inspect.Signature class method): Introspecting callables with the Signature object.
                                                             (line  127)
* from_decimal() (fractions.Fraction method): fractions — Rational numbers.
                                                             (line  121)
* from_exception() (traceback.TracebackException class method): TracebackException Objects.
                                                             (line   63)
* from_file() (zipfile.ZipInfo class method): ZipInfo Objects.
                                                             (line   14)
* from_file() (zoneinfo.ZoneInfo class method): The ZoneInfo class.
                                                             (line   28)
* from_float() (decimal.Decimal method): Decimal objects.    (line  243)
* from_float() (fractions.Fraction method): fractions — Rational numbers.
                                                             (line  110)
* from_iterable() (itertools.chain class method): Itertool functions.
                                                             (line   98)
* from_list() (traceback.StackSummary class method): StackSummary Objects.
                                                             (line   29)
* from_param() (ctypes._CData method):   Data types.         (line   51)
* from_samples() (statistics.NormalDist class method): NormalDist objects.
                                                             (line   45)
* from_traceback() (dis.Bytecode class method): Bytecode analysis.
                                                             (line   33)
* FrozenImporter (class in importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line   80)
* FrozenInstanceError:                   Exceptions<18>.     (line    6)
* frozenset (built-in class):            Set Types — set frozenset.
                                                             (line   33)
* FrozenSet (class in typing):           Corresponding to built-in types.
                                                             (line   49)
* fsdecode() (in module os):             Process Parameters. (line   89)
* fsencode() (in module os):             Process Parameters. (line   76)
* fspath() (in module os):               Process Parameters. (line  102)
* fstat() (in module os):                File Descriptor Operations.
                                                             (line  151)
* fstatvfs() (in module os):             File Descriptor Operations.
                                                             (line  163)
* fstring:                               String literal concatenation.
                                                             (line   24)
* fsum() (in module math):               Number-theoretic and representation functions.
                                                             (line   78)
* fsync() (in module os):                File Descriptor Operations.
                                                             (line  171)
* fs_is_case_insensitive() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  946)
* FS_NONASCII (in module test.support):  test support — Utilities for the Python test suite.
                                                             (line   48)
* FTP:                                   urllib request Restrictions.
                                                             (line   37)
* FTP (class in ftplib):                 ftplib — FTP protocol client.
                                                             (line   43)
* FTP; ftplib (standard module):         ftplib — FTP protocol client.
                                                             (line    8)
* FTP; protocol:                         urllib request Restrictions.
                                                             (line    6)
* FTP; protocol <1>:                     ftplib — FTP protocol client.
                                                             (line    8)
* FTPHandler (class in urllib.request):  urllib request — Extensible library for opening URLs.
                                                             (line  418)
* ftplib (module):                       ftplib — FTP protocol client.
                                                             (line    6)
* ftp_open() (urllib.request.FTPHandler method): FTPHandler Objects.
                                                             (line    6)
* FTP_TLS (class in ftplib):             ftplib — FTP protocol client.
                                                             (line   83)
* ftruncate() (in module os):            File Descriptor Operations.
                                                             (line  184)
* Full:                                  queue — A synchronized queue class.
                                                             (line   88)
* full() (asyncio.Queue method):         Queue.              (line   32)
* full() (multiprocessing.Queue method): Pipes and Queues.   (line  114)
* full() (queue.Queue method):           Queue Objects.      (line   22)
* fullmatch() (in module re):            Module Contents.    (line  167)
* fullmatch() (re.Pattern method):       Regular Expression Objects.
                                                             (line   56)
* full_url (urllib.request.Request attribute): Request Objects.
                                                             (line   11)
* func (functools.partial attribute):    partial Objects.    (line    9)
* funcattrs (2to3 fixer):                Fixers.             (line  105)
* function:                              Glossary.           (line  459)
* Function (class in symtable):          Examining Symbol Tables.
                                                             (line   62)
* function annotation:                   Glossary.           (line  467)
* function; annotations:                 Function Annotations.
                                                             (line    6)
* function; annotations <1>:             Function definitions.
                                                             (line   97)
* function; argument:                    The standard type hierarchy.
                                                             (line  297)
* function; call:                        The standard type hierarchy.
                                                             (line  297)
* function; call <1>:                    Calls.              (line  123)
* function; call <2>:                    Calls.              (line  132)
* function; definition:                  The return statement.
                                                             (line    6)
* function; definition <1>:              Function definitions.
                                                             (line    6)
* function; generator:                   The yield statement.
                                                             (line    6)
* function; name:                        Function definitions.
                                                             (line    6)
* function; name <1>:                    Function definitions.
                                                             (line    6)
* FunctionDef (class in ast):            Function and class definitions.
                                                             (line    6)
* FunctionTestCase (class in unittest):  Test cases.         (line  895)
* FunctionType (in module types):        Standard Interpreter Types.
                                                             (line   19)
* functools (module):                    functools — Higher-order functions and operations on callable objects.
                                                             (line    6)
* funny_files (filecmp.dircmp attribute): The dircmp class.  (line   95)
* future (2to3 fixer):                   Fixers.             (line  111)
* Future (class in asyncio):             Future Object.      (line    6)
* Future (class in concurrent.futures):  Future Objects.     (line   10)
* future; statement:                     Future statements.  (line    6)
* FutureWarning:                         Warnings.           (line   51)
* fwalk() (in module os):                Files and Directories.
                                                             (line 1589)
* f_back (frame attribute):              The standard type hierarchy.
                                                             (line  718)
* f_builtins (frame attribute):          The standard type hierarchy.
                                                             (line  718)
* f_code (frame attribute):              The standard type hierarchy.
                                                             (line  718)
* f_contiguous (memoryview attribute):   Memory Views.       (line  476)
* f_globals (frame attribute):           The standard type hierarchy.
                                                             (line  718)
* f_lasti (frame attribute):             The standard type hierarchy.
                                                             (line  718)
* f_lineno (frame attribute):            The standard type hierarchy.
                                                             (line  730)
* f_locals (frame attribute):            The standard type hierarchy.
                                                             (line  718)
* F_LOCK (in module os):                 File Descriptor Operations.
                                                             (line  229)
* F_OK (in module os):                   Files and Directories.
                                                             (line  106)
* F_TEST (in module os):                 File Descriptor Operations.
                                                             (line  229)
* F_TLOCK (in module os):                File Descriptor Operations.
                                                             (line  229)
* f_trace (frame attribute):             The standard type hierarchy.
                                                             (line  730)
* f_trace_lines (frame attribute):       The standard type hierarchy.
                                                             (line  730)
* f_trace_opcodes (frame attribute):     The standard type hierarchy.
                                                             (line  730)
* F_ULOCK (in module os):                File Descriptor Operations.
                                                             (line  229)
* G.722:                                 aifc — Read and write AIFF and AIFC files.
                                                             (line  160)
* gaierror:                              Exceptions<12>.     (line   27)
* gamma() (in module math):              Special functions.  (line   29)
* gammavariate() (in module random):     Real-valued distributions.
                                                             (line   46)
* garbage (in module gc):                gc — Garbage Collector interface.
                                                             (line  230)
* garbage collection:                    Objects values and types.
                                                             (line   37)
* garbage collection <1>:                Glossary.           (line  500)
* gather() (curses.textpad.Textbox method): Textbox objects. (line  109)
* gather() (in module asyncio):          Running Tasks Concurrently.
                                                             (line    6)
* gauss() (in module random):            Real-valued distributions.
                                                             (line   57)
* gc (module):                           gc — Garbage Collector interface.
                                                             (line    6)
* gcd() (in module math):                Number-theoretic and representation functions.
                                                             (line   98)
* gc_collect() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  521)
* ge() (in module operator):             operator — Standard operators as functions.
                                                             (line   24)
* generate_help() (distutils.fancy_getopt.FancyGetopt method): distutils fancy_getopt — Wrapper around the standard getopt module.
                                                             (line   68)
* generate_tokens() (in module tokenize): Tokenizing Input.  (line   38)
* generator:                             Glossary.           (line  509)
* generator <1>:                         Glossary.           (line  509)
* Generator (class in collections.abc):  Collections Abstract Base Classes.
                                                             (line  150)
* Generator (class in email.generator):  email generator Generating MIME documents.
                                                             (line  140)
* Generator (class in typing):           Corresponding to other types in collections abc.
                                                             (line   22)
* generator expression:                  Glossary.           (line  531)
* generator expression <1>:              Glossary.           (line  531)
* generator iterator:                    Glossary.           (line  519)
* generator; expression:                 Generator expressions.
                                                             (line    6)
* generator; function:                   The standard type hierarchy.
                                                             (line  449)
* generator; function <1>:               Yield expressions.  (line    6)
* generator; function <2>:               The yield statement.
                                                             (line    6)
* generator; iterator:                   The standard type hierarchy.
                                                             (line  449)
* generator; iterator <1>:               The yield statement.
                                                             (line    6)
* GeneratorExit:                         Concrete exceptions.
                                                             (line   30)
* GeneratorExp (class in ast):           Comprehensions.     (line    6)
* GeneratorType (in module types):       Standard Interpreter Types.
                                                             (line   31)
* Generic (class in typing):             Building generic types.
                                                             (line    9)
* generic function:                      Glossary.           (line  540)
* generic type:                          Glossary.           (line  548)
* Generic; Alias:                        Generic Alias Type. (line    6)
* generic; special; attribute:           The standard type hierarchy.
                                                             (line   13)
* GenericAlias (class in types):         Standard Interpreter Types.
                                                             (line  182)
* generic_visit() (ast.NodeVisitor method): ast Helpers.     (line  172)
* genops() (in module pickletools):      Programmatic Interface<2>.
                                                             (line   22)
* gen_lib_options() (in module distutils.ccompiler): distutils ccompiler — CCompiler base class.
                                                             (line   14)
* gen_preprocess_options() (in module distutils.ccompiler): distutils ccompiler — CCompiler base class.
                                                             (line   24)
* gen_uuid() (in module msilib):         msilib — Read and write Microsoft Installer files.
                                                             (line  109)
* geometric_mean() (in module statistics): Function details. (line   63)
* get() (asyncio.Queue method):          Queue.              (line   40)
* get() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  188)
* get() (contextvars.Context method):    Manual Context Management.
                                                             (line   85)
* get() (contextvars.ContextVar method): Context Variables.  (line   30)
* get() (dict method):                   Mapping Types — dict.
                                                             (line  163)
* get() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  245)
* get() (email.message.Message method):  email message Message Representing an email message using the compat32 API.
                                                             (line  353)
* get() (in module webbrowser):          webbrowser — Convenient Web-browser controller.
                                                             (line   77)
* get() (mailbox.Mailbox method):        Mailbox objects.    (line  140)
* get() (multiprocessing.pool.AsyncResult method): Process Pools.
                                                             (line  196)
* get() (multiprocessing.Queue method):  Pipes and Queues.   (line  140)
* get() (multiprocessing.SimpleQueue method): Pipes and Queues.
                                                             (line  223)
* get() (ossaudiodev.oss_mixer_device method): Mixer Device Objects.
                                                             (line   60)
* get() (queue.Queue method):            Queue Objects.      (line   44)
* get() (queue.SimpleQueue method):      SimpleQueue Objects.
                                                             (line   40)
* get() (tkinter.ttk.Combobox method):   ttk Combobox.       (line   15)
* get() (tkinter.ttk.Spinbox method):    ttk Spinbox.        (line    8)
* get() (types.MappingProxyType method): Standard Interpreter Types.
                                                             (line  272)
* get() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line   64)
* getacl() (imaplib.IMAP4 method):       IMAP4 Objects.      (line  106)
* getaddresses() (in module email.utils): email utils Miscellaneous utilities.
                                                             (line   81)
* getaddrinfo() (asyncio.loop method):   DNS.                (line    6)
* getaddrinfo() (in module socket):      Other functions<2>. (line   17)
* getallocatedblocks() (in module sys):  sys — System-specific parameters and functions.
                                                             (line  594)
* getandroidapilevel() (in module sys):  sys — System-specific parameters and functions.
                                                             (line  609)
* getannotation() (imaplib.IMAP4 method): IMAP4 Objects.     (line  111)
* getargspec() (in module inspect):      Classes and functions<2>.
                                                             (line   17)
* getargvalues() (in module inspect):    Classes and functions<2>.
                                                             (line   81)
* getatime() (in module os.path):        os path — Common pathname manipulations.
                                                             (line  170)
* getattr() (built-in function):         Built-in Functions. (line  674)
* getattrfunc (C type):                  Slot Type typedefs. (line   42)
* getAttribute() (xml.dom.Element method): Element Objects<2>.
                                                             (line   31)
* getAttributeNode() (xml.dom.Element method): Element Objects<2>.
                                                             (line   37)
* getAttributeNodeNS() (xml.dom.Element method): Element Objects<2>.
                                                             (line   47)
* getAttributeNS() (xml.dom.Element method): Element Objects<2>.
                                                             (line   41)
* getattrofunc (C type):                 Slot Type typedefs. (line   52)
* getattr_static() (in module inspect):  Fetching attributes statically.
                                                             (line   16)
* GetBase() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line   31)
* getbegyx() (curses.window method):     Window Objects.     (line  222)
* getbkgd() (curses.window method):      Window Objects.     (line  226)
* getblocking() (socket.socket method):  Socket Objects.     (line  153)
* getboolean() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  222)
* getbuffer() (io.BytesIO method):       Buffered Streams.   (line   21)
* getbufferproc (C type):                Slot Type typedefs. (line   94)
* getByteStream() (xml.sax.xmlreader.InputSource method): InputSource Objects.
                                                             (line   48)
* getcallargs() (in module inspect):     Classes and functions<2>.
                                                             (line  140)
* getcanvas() (in module turtle):        Settings and special methods.
                                                             (line   55)
* getcapabilities() (nntplib.NNTP method): Methods<3>.       (line   34)
* getcaps() (in module mailcap):         mailcap — Mailcap file handling.
                                                             (line   62)
* getch() (curses.window method):        Window Objects.     (line  231)
* getch() (in module msvcrt):            Console I/O.        (line   10)
* getCharacterStream() (xml.sax.xmlreader.InputSource method): InputSource Objects.
                                                             (line   64)
* getche() (in module msvcrt):           Console I/O.        (line   25)
* getChild() (logging.Logger method):    Logger Objects.     (line  118)
* getclasstree() (in module inspect):    Classes and functions<2>.
                                                             (line    6)
* getclosurevars() (in module inspect):  Classes and functions<2>.
                                                             (line  170)
* GetColumnInfo() (msilib.View method):  View Objects.       (line   12)
* getColumnNumber() (xml.sax.xmlreader.Locator method): Locator Objects.
                                                             (line    8)
* getcomments() (in module inspect):     Retrieving source code.
                                                             (line   17)
* getcompname() (aifc.aifc method):      aifc — Read and write AIFF and AIFC files.
                                                             (line   73)
* getcompname() (sunau.AU_read method):  AU_read Objects.    (line   35)
* getcompname() (wave.Wave_read method): Wave_read Objects.  (line   35)
* getcomptype() (aifc.aifc method):      aifc — Read and write AIFF and AIFC files.
                                                             (line   67)
* getcomptype() (sunau.AU_read method):  AU_read Objects.    (line   30)
* getcomptype() (wave.Wave_read method): Wave_read Objects.  (line   31)
* getContentHandler() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   21)
* getcontext() (in module decimal):      Context objects.    (line   14)
* getcoroutinelocals() (in module inspect): Current State of Generators and Coroutines.
                                                             (line   73)
* getcoroutinestate() (in module inspect): Current State of Generators and Coroutines.
                                                             (line   28)
* getctime() (in module os.path):        os path — Common pathname manipulations.
                                                             (line  186)
* getcwd() (in module os):               Files and Directories.
                                                             (line  280)
* getcwdb() (in module os):              Files and Directories.
                                                             (line  284)
* getcwdu (2to3 fixer):                  Fixers.             (line  115)
* getdecoder() (in module codecs):       codecs — Codec registry and base classes.
                                                             (line  107)
* getdefaultencoding() (in module sys):  sys — System-specific parameters and functions.
                                                             (line  617)
* getdefaultlocale() (in module locale): locale — Internationalization services.
                                                             (line  301)
* getdefaulttimeout() (in module socket): Other functions<2>.
                                                             (line  333)
* getdlopenflags() (in module sys):      sys — System-specific parameters and functions.
                                                             (line  622)
* getdoc() (in module inspect):          Retrieving source code.
                                                             (line    6)
* getDOMImplementation() (in module xml.dom): Module Contents<4>.
                                                             (line   17)
* getDTDHandler() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   30)
* getEffectiveLevel() (logging.Logger method): Logger Objects.
                                                             (line  109)
* getegid() (in module os):              Process Parameters. (line  164)
* getElementsByTagName() (xml.dom.Document method): Document Objects.
                                                             (line   61)
* getElementsByTagName() (xml.dom.Element method): Element Objects<2>.
                                                             (line   14)
* getElementsByTagNameNS() (xml.dom.Document method): Document Objects.
                                                             (line   66)
* getElementsByTagNameNS() (xml.dom.Element method): Element Objects<2>.
                                                             (line   18)
* getencoder() (in module codecs):       codecs — Codec registry and base classes.
                                                             (line   99)
* getEncoding() (xml.sax.xmlreader.InputSource method): InputSource Objects.
                                                             (line   32)
* getEntityResolver() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   39)
* getenv() (in module os):               Process Parameters. (line  129)
* getenvb() (in module os):              Process Parameters. (line  141)
* getErrorHandler() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   50)
* geteuid() (in module os):              Process Parameters. (line  172)
* getEvent() (xml.dom.pulldom.DOMEventStream method): DOMEventStream Objects.
                                                             (line   11)
* getEventCategory() (logging.handlers.NTEventLogHandler method): NTEventLogHandler.
                                                             (line   43)
* getEventType() (logging.handlers.NTEventLogHandler method): NTEventLogHandler.
                                                             (line   49)
* getException() (xml.sax.SAXException method): SAXException Objects.
                                                             (line   13)
* getFeature() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   69)
* GetFieldCount() (msilib.Record method): Record Objects.    (line    6)
* getfile() (in module inspect):         Retrieving source code.
                                                             (line   26)
* getFilesToDelete() (logging.handlers.TimedRotatingFileHandler method): TimedRotatingFileHandler.
                                                             (line  115)
* getfilesystemencodeerrors() (in module sys): sys — System-specific parameters and functions.
                                                             (line  667)
* getfilesystemencoding() (in module sys): sys — System-specific parameters and functions.
                                                             (line  631)
* getfirst() (cgi.FieldStorage method):  Higher Level Interface.
                                                             (line   56)
* getfloat() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  215)
* getfmts() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line   80)
* getfqdn() (in module socket):          Other functions<2>. (line   71)
* getframeinfo() (in module inspect):    The interpreter stack.
                                                             (line   46)
* getframerate() (aifc.aifc method):     aifc — Read and write AIFF and AIFC files.
                                                             (line   59)
* getframerate() (sunau.AU_read method): AU_read Objects.    (line   22)
* getframerate() (wave.Wave_read method): Wave_read Objects. (line   23)
* getfullargspec() (in module inspect):  Classes and functions<2>.
                                                             (line   36)
* getgeneratorlocals() (in module inspect): Current State of Generators and Coroutines.
                                                             (line   53)
* getgeneratorstate() (in module inspect): Current State of Generators and Coroutines.
                                                             (line   12)
* getgid() (in module os):               Process Parameters. (line  178)
* getgrall() (in module grp):            grp — The group database.
                                                             (line   57)
* getgrgid() (in module grp):            grp — The group database.
                                                             (line   42)
* getgrnam() (in module grp):            grp — The group database.
                                                             (line   52)
* getgrouplist() (in module os):         Process Parameters. (line  184)
* getgroups() (in module os):            Process Parameters. (line  194)
* getheader() (http.client.HTTPResponse method): HTTPResponse Objects.
                                                             (line   24)
* getheaders() (http.client.HTTPResponse method): HTTPResponse Objects.
                                                             (line   32)
* gethostbyaddr() (in module socket):    Process Parameters. (line  471)
* gethostbyaddr() (in module socket) <1>: Other functions<2>.
                                                             (line  122)
* gethostbyname() (in module socket):    Other functions<2>. (line   83)
* gethostbyname_ex() (in module socket): Other functions<2>. (line   96)
* gethostname() (in module socket):      Process Parameters. (line  471)
* gethostname() (in module socket) <1>:  Other functions<2>. (line  111)
* getincrementaldecoder() (in module codecs): codecs — Codec registry and base classes.
                                                             (line  123)
* getincrementalencoder() (in module codecs): codecs — Codec registry and base classes.
                                                             (line  115)
* getinfo() (zipfile.ZipFile method):    ZipFile Objects.    (line   91)
* getinnerframes() (in module inspect):  The interpreter stack.
                                                             (line   63)
* GetInputContext() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line   37)
* getint() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  208)
* GetInteger() (msilib.Record method):   Record Objects.     (line   11)
* getitem() (in module operator):        operator — Standard operators as functions.
                                                             (line  192)
* getiterfunc (C type):                  Slot Type typedefs. (line   84)
* getitimer() (in module signal):        Module contents<2>. (line  384)
* getkey() (curses.window method):       Window Objects.     (line  246)
* GetLastError() (in module ctypes):     Utility functions.  (line  114)
* getLength() (xml.sax.xmlreader.Attributes method): The Attributes Interface.
                                                             (line   11)
* getLevelName() (in module logging):    Module-Level Functions.
                                                             (line  203)
* getline() (in module linecache):       linecache — Random access to text lines.
                                                             (line   23)
* getLineNumber() (xml.sax.xmlreader.Locator method): Locator Objects.
                                                             (line   12)
* getlist() (cgi.FieldStorage method):   Higher Level Interface.
                                                             (line   67)
* getloadavg() (in module os):           Miscellaneous System Information.
                                                             (line   48)
* getlocale() (in module locale):        locale — Internationalization services.
                                                             (line  326)
* getLogger() (in module logging):       Module-Level Functions.
                                                             (line    9)
* getLoggerClass() (in module logging):  Module-Level Functions.
                                                             (line   21)
* getlogin() (in module os):             Process Parameters. (line  217)
* getLogRecordFactory() (in module logging): Module-Level Functions.
                                                             (line   32)
* getmark() (aifc.aifc method):          aifc — Read and write AIFF and AIFC files.
                                                             (line   92)
* getmark() (sunau.AU_read method):      AU_read Objects.    (line   77)
* getmark() (wave.Wave_read method):     Wave_read Objects.  (line   62)
* getmarkers() (aifc.aifc method):       aifc — Read and write AIFF and AIFC files.
                                                             (line   85)
* getmarkers() (sunau.AU_read method):   AU_read Objects.    (line   73)
* getmarkers() (wave.Wave_read method):  Wave_read Objects.  (line   58)
* getmaxyx() (curses.window method):     Window Objects.     (line  253)
* getmember() (tarfile.TarFile method):  TarFile Objects.    (line  101)
* getmembers() (in module inspect):      Types and members.  (line  276)
* getmembers() (tarfile.TarFile method): TarFile Objects.    (line  109)
* getMessage() (logging.LogRecord method): LogRecord Objects.
                                                             (line   56)
* getMessage() (xml.sax.SAXException method): SAXException Objects.
                                                             (line    9)
* getMessageID() (logging.handlers.NTEventLogHandler method): NTEventLogHandler.
                                                             (line   60)
* getmodule() (in module inspect):       Retrieving source code.
                                                             (line   32)
* getmodulename() (in module inspect):   Types and members.  (line  289)
* getmouse() (in module curses):         Functions<4>.       (line  145)
* getmro() (in module inspect):          Classes and functions<2>.
                                                             (line  132)
* getmtime() (in module os.path):        os path — Common pathname manipulations.
                                                             (line  177)
* getname() (chunk.Chunk method):        chunk — Read IFF chunked data.
                                                             (line   69)
* getName() (threading.Thread method):   Thread Objects.     (line  142)
* getNameByQName() (xml.sax.xmlreader.AttributesNS method): The AttributesNS Interface.
                                                             (line   16)
* getnameinfo() (asyncio.loop method):   DNS.                (line   11)
* getnameinfo() (in module socket):      Other functions<2>. (line  136)
* getnames() (tarfile.TarFile method):   TarFile Objects.    (line  115)
* getNames() (xml.sax.xmlreader.Attributes method): The Attributes Interface.
                                                             (line   15)
* getnchannels() (aifc.aifc method):     aifc — Read and write AIFF and AIFC files.
                                                             (line   51)
* getnchannels() (sunau.AU_read method): AU_read Objects.    (line   14)
* getnchannels() (wave.Wave_read method): Wave_read Objects. (line   15)
* getnframes() (aifc.aifc method):       aifc — Read and write AIFF and AIFC files.
                                                             (line   63)
* getnframes() (sunau.AU_read method):   AU_read Objects.    (line   26)
* getnframes() (wave.Wave_read method):  Wave_read Objects.  (line   27)
* getnode:                               uuid — UUID objects according to RFC 4122.
                                                             (line  178)
* getnode() (in module uuid):            uuid — UUID objects according to RFC 4122.
                                                             (line  160)
* getopt (module):                       getopt — C-style parser for command line options.
                                                             (line    6)
* getopt() (distutils.fancy_getopt.FancyGetopt method): distutils fancy_getopt — Wrapper around the standard getopt module.
                                                             (line   49)
* getopt() (in module getopt):           getopt — C-style parser for command line options.
                                                             (line   25)
* GetoptError:                           getopt — C-style parser for command line options.
                                                             (line   74)
* getouterframes() (in module inspect):  The interpreter stack.
                                                             (line   52)
* getoutput() (in module subprocess):    Legacy Shell Invocation Functions.
                                                             (line   41)
* getpagesize() (in module resource):    Resource Usage.     (line  101)
* getparams() (aifc.aifc method):        aifc — Read and write AIFF and AIFC files.
                                                             (line   79)
* getparams() (sunau.AU_read method):    AU_read Objects.    (line   41)
* getparams() (wave.Wave_read method):   Wave_read Objects.  (line   40)
* getparyx() (curses.window method):     Window Objects.     (line  257)
* getpass (module):                      getpass — Portable password input.
                                                             (line    6)
* getpass() (in module getpass):         getpass — Portable password input.
                                                             (line   12)
* GetPassWarning:                        getpass — Portable password input.
                                                             (line   29)
* getpeercert() (ssl.SSLSocket method):  SSL Sockets.        (line  139)
* getpeername() (socket.socket method):  Socket Objects.     (line  127)
* getpen() (in module turtle):           Special Turtle methods.
                                                             (line   40)
* getpgid() (in module os):              Process Parameters. (line  228)
* getpgrp() (in module os):              Process Parameters. (line  236)
* getpid() (in module os):               Process Parameters. (line  242)
* getpos() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line   28)
* getppid() (in module os):              Process Parameters. (line  246)
* getpreferredencoding() (in module locale): locale — Internationalization services.
                                                             (line  337)
* getpriority() (in module os):          Process Parameters. (line  257)
* getprofile() (in module sys):          sys — System-specific parameters and functions.
                                                             (line  735)
* GetProperty() (msilib.SummaryInformation method): Summary Information Objects.
                                                             (line    6)
* getProperty() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   83)
* GetPropertyCount() (msilib.SummaryInformation method): Summary Information Objects.
                                                             (line   17)
* getprotobyname() (in module socket):   Other functions<2>. (line  154)
* getproxies() (in module urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  153)
* getPublicId() (xml.sax.xmlreader.InputSource method): InputSource Objects.
                                                             (line   10)
* getPublicId() (xml.sax.xmlreader.Locator method): Locator Objects.
                                                             (line   16)
* getpwall() (in module pwd):            pwd — The password database.
                                                             (line   65)
* getpwnam() (in module pwd):            pwd — The password database.
                                                             (line   61)
* getpwuid() (in module pwd):            pwd — The password database.
                                                             (line   57)
* getQNameByName() (xml.sax.xmlreader.AttributesNS method): The AttributesNS Interface.
                                                             (line   20)
* getQNames() (xml.sax.xmlreader.AttributesNS method): The AttributesNS Interface.
                                                             (line   24)
* getquota() (imaplib.IMAP4 method):     IMAP4 Objects.      (line  116)
* getquotaroot() (imaplib.IMAP4 method): IMAP4 Objects.      (line  121)
* getrandbits() (in module random):      Functions for integers.
                                                             (line   28)
* getrandom() (in module os):            Random numbers<2>.  (line    6)
* getreader() (in module codecs):        codecs — Codec registry and base classes.
                                                             (line  131)
* getrecursionlimit() (in module sys):   sys — System-specific parameters and functions.
                                                             (line  684)
* getrefcount() (in module sys):         sys — System-specific parameters and functions.
                                                             (line  678)
* getresgid() (in module os):            Process Parameters. (line  292)
* getresponse() (http.client.HTTPConnection method): HTTPConnection Objects.
                                                             (line   59)
* getresuid() (in module os):            Process Parameters. (line  283)
* getrlimit() (in module resource):      Resource Limits.    (line   24)
* getroot() (xml.etree.ElementTree.ElementTree method): ElementTree Objects.
                                                             (line   36)
* getrusage() (in module resource):      Resource Usage.     (line    8)
* getsample() (in module audioop):       audioop — Manipulate raw audio data.
                                                             (line  108)
* getsampwidth() (aifc.aifc method):     aifc — Read and write AIFF and AIFC files.
                                                             (line   55)
* getsampwidth() (sunau.AU_read method): AU_read Objects.    (line   18)
* getsampwidth() (wave.Wave_read method): Wave_read Objects. (line   19)
* getscreen() (in module turtle):        Special Turtle methods.
                                                             (line   51)
* getservbyname() (in module socket):    Other functions<2>. (line  163)
* getservbyport() (in module socket):    Other functions<2>. (line  172)
* GetSetDescriptorType (in module types): Standard Interpreter Types.
                                                             (line  217)
* getshapes() (in module turtle):        Settings and special methods.
                                                             (line   64)
* getsid() (in module os):               Process Parameters. (line  432)
* getsignal() (in module signal):        Module contents<2>. (line  238)
* getsitepackages() (in module site):    Module contents<4>. (line   56)
* getsize() (chunk.Chunk method):        chunk — Read IFF chunked data.
                                                             (line   74)
* getsize() (in module os.path):         os path — Common pathname manipulations.
                                                             (line  197)
* getsizeof() (in module sys):           sys — System-specific parameters and functions.
                                                             (line  691)
* getsockname() (socket.socket method):  Socket Objects.     (line  135)
* getsockopt() (socket.socket method):   Socket Objects.     (line  141)
* getsource() (in module inspect):       Retrieving source code.
                                                             (line   55)
* getsourcefile() (in module inspect):   Retrieving source code.
                                                             (line   36)
* getsourcelines() (in module inspect):  Retrieving source code.
                                                             (line   42)
* getspall() (in module spwd):           spwd — The shadow password database.
                                                             (line   67)
* getspnam() (in module spwd):           spwd — The shadow password database.
                                                             (line   59)
* getstate() (codecs.IncrementalDecoder method): IncrementalDecoder Objects.
                                                             (line   44)
* getstate() (codecs.IncrementalEncoder method): IncrementalEncoder Objects.
                                                             (line   42)
* getstate() (in module random):         Bookkeeping functions.
                                                             (line   32)
* getstatus() (http.client.HTTPResponse method): HTTPResponse Objects.
                                                             (line   89)
* getstatus() (urllib.response.addinfourl method): urllib response — Response classes used by urllib.
                                                             (line   45)
* getstatusoutput() (in module subprocess): Legacy Shell Invocation Functions.
                                                             (line   11)
* getstr() (curses.window method):       Window Objects.     (line  263)
* GetString() (msilib.Record method):    Record Objects.     (line   16)
* getSubject() (logging.handlers.SMTPHandler method): SMTPHandler.
                                                             (line   39)
* GetSummaryInformation() (msilib.Database method): Database Objects.
                                                             (line   16)
* getswitchinterval() (in module sys):   sys — System-specific parameters and functions.
                                                             (line  713)
* getSystemId() (xml.sax.xmlreader.InputSource method): InputSource Objects.
                                                             (line   18)
* getSystemId() (xml.sax.xmlreader.Locator method): Locator Objects.
                                                             (line   20)
* getsyx() (in module curses):           Functions<4>.       (line  159)
* gettarinfo() (tarfile.TarFile method): TarFile Objects.    (line  228)
* gettempdir() (in module tempfile):     tempfile — Generate temporary files and directories.
                                                             (line  228)
* gettempdirb() (in module tempfile):    tempfile — Generate temporary files and directories.
                                                             (line  256)
* gettempprefix() (in module tempfile):  tempfile — Generate temporary files and directories.
                                                             (line  262)
* gettempprefixb() (in module tempfile): tempfile — Generate temporary files and directories.
                                                             (line  267)
* getTestCaseNames() (unittest.TestLoader method): Loading and running tests.
                                                             (line  111)
* gettext (module):                      gettext — Multilingual internationalization services.
                                                             (line    6)
* gettext() (gettext.GNUTranslations method): The GNUTranslations class.
                                                             (line   38)
* gettext() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line   35)
* gettext() (in module gettext):         GNU gettext API.    (line   42)
* gettext() (in module locale):          Access to message catalogs.
                                                             (line    6)
* gettimeout() (socket.socket method):   Socket Objects.     (line  162)
* gettrace() (in module sys):            sys — System-specific parameters and functions.
                                                             (line  739)
* getturtle() (in module turtle):        Special Turtle methods.
                                                             (line   40)
* getType() (xml.sax.xmlreader.Attributes method): The Attributes Interface.
                                                             (line   19)
* getuid() (in module os):               Process Parameters. (line  301)
* geturl() (http.client.HTTPResponse method): HTTPResponse Objects.
                                                             (line   79)
* geturl() (urllib.parse.urllib.parse.SplitResult method): Structured Parse Results.
                                                             (line   12)
* geturl() (urllib.response.addinfourl method): urllib response — Response classes used by urllib.
                                                             (line   30)
* getuser() (in module getpass):         getpass — Portable password input.
                                                             (line   34)
* getuserbase() (in module site):        Module contents<4>. (line   62)
* getusersitepackages() (in module site): Module contents<4>.
                                                             (line   70)
* getvalue() (io.BytesIO method):        Buffered Streams.   (line   38)
* getvalue() (io.StringIO method):       Text I/O<2>.        (line  215)
* getValue() (xml.sax.xmlreader.Attributes method): The Attributes Interface.
                                                             (line   24)
* getValueByQName() (xml.sax.xmlreader.AttributesNS method): The AttributesNS Interface.
                                                             (line   12)
* getwch() (in module msvcrt):           Console I/O.        (line   20)
* getwche() (in module msvcrt):          Console I/O.        (line   30)
* getweakrefcount() (in module weakref): weakref — Weak references.
                                                             (line  153)
* getweakrefs() (in module weakref):     weakref — Weak references.
                                                             (line  158)
* getwelcome() (ftplib.FTP method):      FTP Objects.        (line   42)
* getwelcome() (nntplib.NNTP method):    Methods<3>.         (line   28)
* getwelcome() (poplib.POP3 method):     POP3 Objects.       (line   20)
* getwin() (in module curses):           Functions<4>.       (line  165)
* getwindowsversion() (in module sys):   sys — System-specific parameters and functions.
                                                             (line  750)
* getwriter() (in module codecs):        codecs — Codec registry and base classes.
                                                             (line  139)
* getxattr() (in module os):             Linux extended attributes.
                                                             (line   10)
* getyx() (curses.window method):        Window Objects.     (line  274)
* GET_AITER (opcode):                    Python Bytecode Instructions.
                                                             (line  268)
* get_all() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  254)
* get_all() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  362)
* get_all() (wsgiref.headers.Headers method): wsgiref headers – WSGI response header tools.
                                                             (line   51)
* get_all_breaks() (bdb.Bdb method):     bdb — Debugger framework.
                                                             (line  332)
* get_all_start_methods() (in module multiprocessing): Miscellaneous<3>.
                                                             (line   71)
* GET_ANEXT (opcode):                    Python Bytecode Instructions.
                                                             (line  277)
* get_app() (wsgiref.simple_server.WSGIServer method): wsgiref simple_server – a simple WSGI HTTP server.
                                                             (line   66)
* get_archive_formats() (in module shutil): Archiving operations.
                                                             (line   59)
* get_args() (in module typing):         Introspection helpers.
                                                             (line   36)
* get_asyncgen_hooks() (in module sys):  sys — System-specific parameters and functions.
                                                             (line  803)
* get_attribute() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  864)
* GET_AWAITABLE (opcode):                Python Bytecode Instructions.
                                                             (line  260)
* get_begidx() (in module readline):     Completion.         (line   40)
* get_blocking() (in module os):         File Descriptor Operations.
                                                             (line  197)
* get_body() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  518)
* get_body_encoding() (email.charset.Charset method): email charset Representing character sets.
                                                             (line   96)
* get_boundary() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  403)
* get_boundary() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  579)
* get_bpbynumber() (bdb.Bdb method):     bdb — Debugger framework.
                                                             (line  309)
* get_break() (bdb.Bdb method):          bdb — Debugger framework.
                                                             (line  318)
* get_breaks() (bdb.Bdb method):         bdb — Debugger framework.
                                                             (line  322)
* get_buffer() (asyncio.BufferedProtocol method): Buffered Streaming Protocols.
                                                             (line   21)
* get_buffer() (xdrlib.Packer method):   Packer Objects.     (line    8)
* get_buffer() (xdrlib.Unpacker method): Unpacker Objects.   (line   22)
* get_bytes() (mailbox.Mailbox method):  Mailbox objects.    (line  159)
* get_cache_token() (in module abc):     abc — Abstract Base Classes.
                                                             (line  325)
* get_ca_certs() (ssl.SSLContext method): SSL Contexts.      (line  157)
* get_channel_binding() (ssl.SSLSocket method): SSL Sockets. (line  238)
* get_charset() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  265)
* get_charsets() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  431)
* get_charsets() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  613)
* get_children() (symtable.SymbolTable method): Examining Symbol Tables.
                                                             (line   58)
* get_children() (tkinter.ttk.Treeview method): ttk Treeview.
                                                             (line   19)
* get_child_watcher() (asyncio.AbstractEventLoopPolicy method): Policy Objects.
                                                             (line   33)
* get_child_watcher() (in module asyncio): Process Watchers. (line   25)
* get_ciphers() (ssl.SSLContext method): SSL Contexts.       (line  171)
* get_clock_info() (in module time):     Functions<3>.       (line   97)
* get_close_matches() (in module difflib): difflib — Helpers for computing deltas.
                                                             (line  204)
* get_code() (importlib.abc.InspectLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  389)
* get_code() (importlib.abc.SourceLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  583)
* get_code() (importlib.machinery.ExtensionFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  338)
* get_code() (importlib.machinery.SourcelessFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  281)
* get_code() (zipimport.zipimporter method): zipimporter Objects.
                                                             (line   28)
* get_completer() (in module readline):  Completion.         (line   29)
* get_completer_delims() (in module readline): Completion.   (line   48)
* get_completion_type() (in module readline): Completion.    (line   34)
* get_config_h_filename() (in module distutils.sysconfig): distutils sysconfig — System configuration information.
                                                             (line   41)
* get_config_h_filename() (in module sysconfig): Other functions<3>.
                                                             (line   68)
* get_config_var() (in module distutils.sysconfig): distutils sysconfig — System configuration information.
                                                             (line   27)
* get_config_var() (in module sysconfig): Configuration variables.
                                                             (line   26)
* get_config_vars() (in module distutils.sysconfig): distutils sysconfig — System configuration information.
                                                             (line   32)
* get_config_vars() (in module sysconfig): Configuration variables.
                                                             (line   16)
* get_content() (email.contentmanager.ContentManager method): email contentmanager Managing MIME Content.
                                                             (line   19)
* get_content() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  582)
* get_content() (in module email.contentmanager): Content Manager Instances.
                                                             (line   24)
* get_content_charset() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  424)
* get_content_charset() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  602)
* get_content_disposition() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  455)
* get_content_disposition() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  627)
* get_content_maintype() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  324)
* get_content_maintype() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  432)
* get_content_subtype() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  330)
* get_content_subtype() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  438)
* get_content_type() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  308)
* get_content_type() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  416)
* get_context() (in module multiprocessing): Miscellaneous<3>.
                                                             (line   81)
* get_coro() (asyncio.Task method):      Task Object.        (line  207)
* get_coroutine_origin_tracking_depth() (in module sys): sys — System-specific parameters and functions.
                                                             (line  817)
* get_count() (in module gc):            gc — Garbage Collector interface.
                                                             (line  110)
* get_current_history_length() (in module readline): History list.
                                                             (line   14)
* get_data() (importlib.abc.FileLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  505)
* get_data() (importlib.abc.ResourceLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  370)
* get_data() (in module pkgutil):        pkgutil — Package extension utility.
                                                             (line  201)
* get_data() (zipimport.zipimporter method): zipimporter Objects.
                                                             (line   33)
* get_date() (mailbox.MaildirMessage method): MaildirMessage.
                                                             (line   92)
* get_debug() (asyncio.loop method):     Enabling debug mode.
                                                             (line    6)
* get_debug() (in module gc):            gc — Garbage Collector interface.
                                                             (line   55)
* get_default() (argparse.ArgumentParser method): Parser defaults.
                                                             (line   33)
* get_default_compiler() (in module distutils.ccompiler): distutils ccompiler — CCompiler base class.
                                                             (line   36)
* get_default_domain() (in module nis):  nis — Interface to Sun’s NIS Yellow Pages.
                                                             (line   48)
* get_default_type() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  335)
* get_default_type() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  443)
* get_default_verify_paths() (in module ssl): Certificate handling.
                                                             (line  101)
* get_dialect() (in module csv):         Module Contents<3>. (line   86)
* get_disassembly_as_string() (test.support.bytecode_helper.BytecodeTestCase method): test support bytecode_helper — Support tools for testing correct bytecode generation.
                                                             (line   18)
* get_docstring() (in module ast):       ast Helpers.        (line   95)
* get_doctest() (doctest.DocTestParser method): DocTestParser objects.
                                                             (line   13)
* get_endidx() (in module readline):     Completion.         (line   40)
* get_environ() (wsgiref.simple_server.WSGIRequestHandler method): wsgiref simple_server – a simple WSGI HTTP server.
                                                             (line   88)
* get_errno() (in module ctypes):        Utility functions.  (line  121)
* get_escdelay() (in module curses):     Functions<4>.       (line  432)
* get_event_loop() (asyncio.AbstractEventLoopPolicy method): Policy Objects.
                                                             (line   12)
* get_event_loop() (in module asyncio):  Event Loop.         (line   39)
* get_event_loop_policy() (in module asyncio): Getting and Setting the Policy.
                                                             (line    9)
* get_examples() (doctest.DocTestParser method): DocTestParser objects.
                                                             (line   22)
* get_exception_handler() (asyncio.loop method): Error Handling API.
                                                             (line   19)
* get_exec_path() (in module os):        Process Parameters. (line  154)
* get_extra_info() (asyncio.BaseTransport method): Base Transport.
                                                             (line   20)
* get_extra_info() (asyncio.StreamWriter method): StreamWriter.
                                                             (line   61)
* get_field() (string.Formatter method): Custom String Formatting.
                                                             (line   55)
* get_file() (mailbox.Babyl method):     Babyl.              (line   49)
* get_file() (mailbox.Mailbox method):   Mailbox objects.    (line  175)
* get_file() (mailbox.Maildir method):   Maildir.            (line  119)
* get_file() (mailbox.mbox method):      mbox.               (line   33)
* get_file() (mailbox.MH method):        MH.                 (line   93)
* get_file() (mailbox.MMDF method):      MMDF.               (line   29)
* get_filename() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  393)
* get_filename() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  569)
* get_filename() (importlib.abc.ExecutionLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  460)
* get_filename() (importlib.abc.FileLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  501)
* get_filename() (importlib.machinery.ExtensionFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  346)
* get_filename() (zipimport.zipimporter method): zipimporter Objects.
                                                             (line   41)
* get_file_breaks() (bdb.Bdb method):    bdb — Debugger framework.
                                                             (line  327)
* get_filter() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line  106)
* get_flags() (mailbox.MaildirMessage method): MaildirMessage.
                                                             (line   63)
* get_flags() (mailbox.mboxMessage method): mboxMessage.     (line   64)
* get_flags() (mailbox.MMDFMessage method): MMDFMessage.     (line   63)
* get_folder() (mailbox.Maildir method): Maildir.            (line   65)
* get_folder() (mailbox.MH method):      MH.                 (line   36)
* get_frees() (symtable.Function method): Examining Symbol Tables.
                                                             (line   84)
* get_freeze_count() (in module gc):     gc — Garbage Collector interface.
                                                             (line  221)
* get_from() (mailbox.mboxMessage method): mboxMessage.      (line   47)
* get_from() (mailbox.MMDFMessage method): MMDFMessage.      (line   46)
* get_full_url() (urllib.request.Request method): Request Objects.
                                                             (line  106)
* get_globals() (symtable.Function method): Examining Symbol Tables.
                                                             (line   76)
* get_grouped_opcodes() (difflib.SequenceMatcher method): SequenceMatcher Objects.
                                                             (line  168)
* get_handle_inheritable() (in module os): Inheritance of File Descriptors.
                                                             (line   32)
* get_header() (urllib.request.Request method): Request Objects.
                                                             (line  120)
* get_history_item() (in module readline): History list.     (line   20)
* get_history_length() (in module readline): History file.   (line   30)
* get_id() (symtable.SymbolTable method): Examining Symbol Tables.
                                                             (line   15)
* get_ident() (in module threading):     threading — Thread-based parallelism.
                                                             (line   85)
* get_ident() (in module _thread):       _thread — Low-level threading API.
                                                             (line   73)
* get_identifiers() (symtable.SymbolTable method): Examining Symbol Tables.
                                                             (line   44)
* get_importer() (in module pkgutil):    pkgutil — Package extension utility.
                                                             (line   92)
* get_info() (mailbox.MaildirMessage method): MaildirMessage.
                                                             (line  102)
* get_inheritable() (in module os):      Inheritance of File Descriptors.
                                                             (line   23)
* get_inheritable() (socket.socket method): Socket Objects.  (line  119)
* get_instructions() (in module dis):    Analysis functions. (line  110)
* get_interpreter() (in module zipapp):  Python API.         (line   82)
* GET_ITER (opcode):                     Python Bytecode Instructions.
                                                             (line  113)
* get_key() (selectors.BaseSelector method): Classes<3>.     (line  145)
* get_labels() (mailbox.Babyl method):   Babyl.              (line   35)
* get_labels() (mailbox.BabylMessage method): BabylMessage.  (line   47)
* get_last_error() (in module ctypes):   Utility functions.  (line  129)
* get_lineno() (symtable.SymbolTable method): Examining Symbol Tables.
                                                             (line   26)
* get_line_buffer() (in module readline): Line buffer.       (line    8)
* get_loader() (in module pkgutil):      pkgutil — Package extension utility.
                                                             (line  106)
* get_locals() (symtable.Function method): Examining Symbol Tables.
                                                             (line   72)
* get_logger() (in module multiprocessing): Logging<2>.      (line   11)
* get_loop() (asyncio.Future method):    Future Object.      (line  132)
* get_loop() (asyncio.Server method):    Server Objects.     (line   41)
* get_magic() (in module imp):           imp — Access the import internals.
                                                             (line   17)
* get_makefile_filename() (in module distutils.sysconfig): distutils sysconfig — System configuration information.
                                                             (line   49)
* get_makefile_filename() (in module sysconfig): Other functions<3>.
                                                             (line   72)
* get_map() (selectors.BaseSelector method): Classes<3>.     (line  153)
* get_matching_blocks() (difflib.SequenceMatcher method): SequenceMatcher Objects.
                                                             (line  107)
* get_message() (mailbox.Mailbox method): Mailbox objects.   (line  152)
* get_method() (urllib.request.Request method): Request Objects.
                                                             (line   69)
* get_methods() (symtable.Class method): Examining Symbol Tables.
                                                             (line   94)
* get_mixed_type_key() (in module ipaddress): Other Module Level Functions.
                                                             (line   56)
* get_name() (asyncio.Task method):      Task Object.        (line  213)
* get_name() (symtable.Symbol method):   Examining Symbol Tables.
                                                             (line  104)
* get_name() (symtable.SymbolTable method): Examining Symbol Tables.
                                                             (line   19)
* get_namespace() (symtable.Symbol method): Examining Symbol Tables.
                                                             (line  175)
* get_namespaces() (symtable.Symbol method): Examining Symbol Tables.
                                                             (line  171)
* get_native_id() (in module threading): threading — Thread-based parallelism.
                                                             (line   95)
* get_native_id() (in module _thread):   _thread — Low-level threading API.
                                                             (line   81)
* get_nonlocals() (symtable.Function method): Examining Symbol Tables.
                                                             (line   80)
* get_nonstandard_attr() (http.cookiejar.Cookie method): Cookie Objects<2>.
                                                             (line   98)
* get_nowait() (asyncio.Queue method):   Queue.              (line   45)
* get_nowait() (multiprocessing.Queue method): Pipes and Queues.
                                                             (line  155)
* get_nowait() (queue.Queue method):     Queue Objects.      (line   61)
* get_nowait() (queue.SimpleQueue method): SimpleQueue Objects.
                                                             (line   51)
* get_objects() (in module gc):          gc — Garbage Collector interface.
                                                             (line   59)
* get_object_traceback() (in module tracemalloc): Functions<10>.
                                                             (line   12)
* get_opcodes() (difflib.SequenceMatcher method): SequenceMatcher Objects.
                                                             (line  125)
* get_option() (optparse.OptionParser method): Querying and manipulating your option parser.
                                                             (line   37)
* get_option_group() (optparse.OptionParser method): Grouping Options.
                                                             (line  103)
* get_option_order() (distutils.fancy_getopt.FancyGetopt method): distutils fancy_getopt — Wrapper around the standard getopt module.
                                                             (line   62)
* get_origin() (in module typing):       Introspection helpers.
                                                             (line   38)
* get_original_stdout() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  441)
* get_osfhandle() (in module msvcrt):    File Operations.    (line   55)
* get_output_charset() (email.charset.Charset method): email charset Representing character sets.
                                                             (line  111)
* get_param() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  478)
* get_parameters() (symtable.Function method): Examining Symbol Tables.
                                                             (line   67)
* get_params() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  457)
* get_path() (in module sysconfig):      Installation paths. (line   70)
* get_paths() (in module sysconfig):     Installation paths. (line  100)
* get_path_names() (in module sysconfig): Installation paths.
                                                             (line   65)
* get_payload() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  180)
* get_pid() (asyncio.SubprocessTransport method): Subprocess Transports.
                                                             (line    6)
* get_pipe_transport() (asyncio.SubprocessTransport method): Subprocess Transports.
                                                             (line   10)
* get_platform() (in module distutils.util): distutils util — Miscellaneous other utility functions.
                                                             (line    9)
* get_platform() (in module sysconfig):  Other functions<3>. (line   11)
* get_poly() (in module turtle):         Special Turtle methods.
                                                             (line   17)
* get_position() (xdrlib.Unpacker method): Unpacker Objects. (line   12)
* get_protocol() (asyncio.BaseTransport method): Base Transport.
                                                             (line   87)
* get_python_inc() (in module distutils.sysconfig): distutils sysconfig — System configuration information.
                                                             (line   57)
* get_python_lib() (in module distutils.sysconfig): distutils sysconfig — System configuration information.
                                                             (line   68)
* get_python_version() (in module sysconfig): Other functions<3>.
                                                             (line    6)
* get_ready() (graphlib.TopologicalSorter method): graphlib — Functionality to operate with graph-like structures.
                                                             (line  149)
* get_recsrc() (ossaudiodev.oss_mixer_device method): Mixer Device Objects.
                                                             (line   84)
* get_referents() (in module gc):        gc — Garbage Collector interface.
                                                             (line  142)
* get_referrers() (in module gc):        gc — Garbage Collector interface.
                                                             (line  120)
* get_request() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line  131)
* get_returncode() (asyncio.SubprocessTransport method): Subprocess Transports.
                                                             (line   29)
* get_running_loop() (in module asyncio): Event Loop.        (line   29)
* get_scheme() (wsgiref.handlers.BaseHandler method): wsgiref handlers – server/gateway base classes.
                                                             (line  188)
* get_scheme_names() (in module sysconfig): Installation paths.
                                                             (line   60)
* get_selection() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line  110)
* get_sequences() (mailbox.MH method):   MH.                 (line   53)
* get_sequences() (mailbox.MHMessage method): MHMessage.     (line   32)
* get_server() (multiprocessing.managers.BaseManager method): Managers.
                                                             (line   46)
* get_server_certificate() (in module ssl): Certificate handling.
                                                             (line   71)
* get_shapepoly() (in module turtle):    Appearance.         (line  189)
* get_socket() (telnetlib.Telnet method): Telnet Objects.    (line   93)
* get_source() (importlib.abc.InspectLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  403)
* get_source() (importlib.abc.SourceLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  601)
* get_source() (importlib.machinery.ExtensionFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  342)
* get_source() (importlib.machinery.SourcelessFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  286)
* get_source() (zipimport.zipimporter method): zipimporter Objects.
                                                             (line   49)
* get_source_segment() (in module ast):  ast Helpers.        (line  106)
* get_special_folder_path() (built-in function): The Postinstallation script.
                                                             (line   32)
* get_stack() (asyncio.Task method):     Task Object.        (line  171)
* get_stack() (bdb.Bdb method):          bdb — Debugger framework.
                                                             (line  339)
* get_starttag_text() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line   32)
* get_start_method() (in module multiprocessing): Miscellaneous<3>.
                                                             (line   93)
* get_stats() (in module gc):            gc — Garbage Collector interface.
                                                             (line   70)
* get_stats_profile() (pstats.Stats method): The Stats Class.
                                                             (line  225)
* get_stderr() (wsgiref.handlers.BaseHandler method): wsgiref handlers – server/gateway base classes.
                                                             (line  127)
* get_stderr() (wsgiref.simple_server.WSGIRequestHandler method): wsgiref simple_server – a simple WSGI HTTP server.
                                                             (line   98)
* get_stdin() (wsgiref.handlers.BaseHandler method): wsgiref handlers – server/gateway base classes.
                                                             (line  122)
* get_string() (mailbox.Mailbox method): Mailbox objects.    (line  167)
* get_subdir() (mailbox.MaildirMessage method): MaildirMessage.
                                                             (line   47)
* get_suffixes() (in module imp):        imp — Access the import internals.
                                                             (line   26)
* get_symbols() (symtable.SymbolTable method): Examining Symbol Tables.
                                                             (line   53)
* get_tabsize() (in module curses):      Functions<4>.       (line  447)
* get_tag() (in module imp):             imp — Access the import internals.
                                                             (line  244)
* get_task_factory() (asyncio.loop method): Creating Futures and Tasks.
                                                             (line   42)
* get_terminal_size() (in module os):    Querying the size of a terminal.
                                                             (line    8)
* get_terminal_size() (in module shutil): Querying the size of the output terminal.
                                                             (line    6)
* get_terminator() (asynchat.async_chat method): asynchat — Asynchronous socket command/response handler.
                                                             (line   97)
* get_threshold() (in module gc):        gc — Garbage Collector interface.
                                                             (line  115)
* get_token() (shlex.shlex method):      shlex Objects.      (line    8)
* get_traceback_limit() (in module tracemalloc): Functions<10>.
                                                             (line   22)
* get_traced_memory() (in module tracemalloc): Functions<10>.
                                                             (line   32)
* get_tracemalloc_memory() (in module tracemalloc): Functions<10>.
                                                             (line   56)
* get_type() (symtable.SymbolTable method): Examining Symbol Tables.
                                                             (line   10)
* get_type_hints() (in module typing):   Introspection helpers.
                                                             (line    6)
* get_unixfrom() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  152)
* get_unixfrom() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  162)
* get_unpack_formats() (in module shutil): Archiving operations.
                                                             (line  149)
* get_usage() (optparse.OptionParser method): Other methods. (line   22)
* get_value() (string.Formatter method): Custom String Formatting.
                                                             (line   65)
* get_version() (optparse.OptionParser method): Printing a version string.
                                                             (line   34)
* get_visible() (mailbox.BabylMessage method): BabylMessage. (line   63)
* get_wch() (curses.window method):      Window Objects.     (line  238)
* get_write_buffer_limits() (asyncio.WriteTransport method): Write-only Transports.
                                                             (line   23)
* get_write_buffer_size() (asyncio.WriteTransport method): Write-only Transports.
                                                             (line   19)
* GET_YIELD_FROM_ITER (opcode):          Python Bytecode Instructions.
                                                             (line  117)
* gid (tarfile.TarInfo attribute):       TarInfo Objects.    (line   76)
* GIL:                                   Glossary.           (line  557)
* glob (module):                         glob — Unix style pathname pattern expansion.
                                                             (line    6)
* glob() (in module glob):               glob — Unix style pathname pattern expansion.
                                                             (line   29)
* glob() (msilib.Directory method):      Directory Objects.  (line   39)
* glob() (pathlib.Path method):          Methods<2>.         (line   96)
* Global (class in ast):                 Function and class definitions.
                                                             (line  151)
* global interpreter lock:               Thread State and the Global Interpreter Lock.
                                                             (line    6)
* global interpreter lock <1>:           Glossary.           (line  561)
* global; name; binding:                 The global statement.
                                                             (line    6)
* global; namespace:                     The standard type hierarchy.
                                                             (line  309)
* globals() (built-in function):         Built-in Functions. (line  688)
* globs (doctest.DocTest attribute):     DocTest Objects.    (line   22)
* gmtime() (in module time):             Functions<3>.       (line  131)
* gname (tarfile.TarInfo attribute):     TarInfo Objects.    (line   84)
* GNOME:                                 The Catalog constructor.
                                                             (line    6)
* GNUTranslations (class in gettext):    The GNUTranslations class.
                                                             (line   33)
* GNU_FORMAT (in module tarfile):        tarfile — Read and write tar archive files.
                                                             (line  233)
* gnu_getopt() (in module getopt):       getopt — C-style parser for command line options.
                                                             (line   62)
* go() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line  114)
* got (doctest.DocTestFailure attribute): Debugging.         (line  204)
* goto() (in module turtle):             Turtle motion.      (line   74)
* grammar:                               Notation.           (line    6)
* Graphical User Interface:              Graphical User Interfaces with Tk.
                                                             (line    6)
* graphlib (module):                     graphlib — Functionality to operate with graph-like structures.
                                                             (line    6)
* GREATER (in module token):             token — Constants used with Python parse trees.
                                                             (line  110)
* GREATEREQUAL (in module token):        token — Constants used with Python parse trees.
                                                             (line  146)
* Greenwich Mean Time:                   time — Time access and conversions.
                                                             (line   40)
* GRND_NONBLOCK (in module os):          Random numbers<2>.  (line   73)
* GRND_RANDOM (in module os):            Random numbers<2>.  (line   86)
* Group (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line  457)
* group() (nntplib.NNTP method):         Methods<3>.         (line  158)
* group() (pathlib.Path method):         Methods<2>.         (line  122)
* group() (re.Match method):             Match Objects.      (line   29)
* groupby() (in module itertools):       Itertool functions. (line  298)
* groupdict() (re.Match method):         Match Objects.      (line  121)
* groupindex (re.Pattern attribute):     Regular Expression Objects.
                                                             (line  112)
* grouping:                              Indentation.        (line    6)
* groups (email.headerregistry.AddressHeader attribute): email headerregistry Custom Header Objects.
                                                             (line  188)
* groups (re.Pattern attribute):         Regular Expression Objects.
                                                             (line  108)
* groups() (re.Match method):            Match Objects.      (line   98)
* grp (module):                          grp — The group database.
                                                             (line    6)
* Gt (class in ast):                     Expressions<2>.     (line  109)
* gt() (in module operator):             operator — Standard operators as functions.
                                                             (line   24)
* GtE (class in ast):                    Expressions<2>.     (line  109)
* guess_all_extensions() (in module mimetypes): mimetypes — Map filenames to MIME types.
                                                             (line   51)
* guess_all_extensions() (mimetypes.MimeTypes method): MimeTypes Objects.
                                                             (line   65)
* guess_extension() (in module mimetypes): mimetypes — Map filenames to MIME types.
                                                             (line   63)
* guess_extension() (mimetypes.MimeTypes method): MimeTypes Objects.
                                                             (line   55)
* guess_scheme() (in module wsgiref.util): wsgiref util – WSGI environment utilities.
                                                             (line   12)
* guess_type() (in module mimetypes):    mimetypes — Map filenames to MIME types.
                                                             (line   24)
* guess_type() (mimetypes.MimeTypes method): MimeTypes Objects.
                                                             (line   60)
* GUI:                                   Graphical User Interfaces with Tk.
                                                             (line    6)
* gzip (module):                         gzip — Support for gzip files.
                                                             (line    6)
* gzip command line option; –best:       Command line options.
                                                             (line   14)
* gzip command line option; -d:          Command line options.
                                                             (line   18)
* gzip command line option; –decompress: Command line options.
                                                             (line   18)
* gzip command line option; –fast:       Command line options.
                                                             (line   10)
* gzip command line option; -h:          Command line options.
                                                             (line   22)
* gzip command line option; –help:       Command line options.
                                                             (line   22)
* gzip command line option; file:        Command line options.
                                                             (line    6)
* GzipFile (class in gzip):              gzip — Support for gzip files.
                                                             (line   71)
* halfdelay() (in module curses):        Functions<4>.       (line  195)
* Handle (class in asyncio):             Callback Handles.   (line    6)
* handle an exception:                   Exceptions<2>.      (line    6)
* handle() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  185)
* handle() (logging.Handler method):     Handler Objects.    (line   81)
* handle() (logging.handlers.QueueListener method): QueueListener.
                                                             (line   63)
* handle() (logging.Logger method):      Logger Objects.     (line  303)
* handle() (logging.NullHandler method): NullHandler.        (line   20)
* handle() (socketserver.BaseRequestHandler method): Request Handler Objects.
                                                             (line   20)
* handle() (wsgiref.simple_server.WSGIRequestHandler method): wsgiref simple_server – a simple WSGI HTTP server.
                                                             (line  103)
* handleError() (logging.Handler method): Handler Objects.   (line   88)
* handleError() (logging.handlers.SocketHandler method): SocketHandler.
                                                             (line   33)
* Handler (class in logging):            Handler Objects.    (line   11)
* handler() (in module cgitb):           cgitb — Traceback manager for CGI scripts.
                                                             (line   66)
* handle_accept() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  143)
* handle_accepted() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  153)
* handle_charref() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line   93)
* handle_close() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  134)
* handle_comment() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line  102)
* handle_connect() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  128)
* handle_data() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line   80)
* handle_decl() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line  115)
* handle_defect() (email.policy.Policy method): email policy Policy Objects.
                                                             (line  218)
* handle_endtag() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line   64)
* handle_entityref() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line   86)
* handle_error() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  138)
* handle_error() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line  137)
* handle_expect_100() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  198)
* handle_expt() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  122)
* handle_one_request() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  192)
* handle_pi() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line  123)
* handle_read() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  107)
* handle_request() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line   21)
* handle_request() (xmlrpc.server.CGIXMLRPCRequestHandler method): CGIXMLRPCRequestHandler.
                                                             (line   50)
* handle_startendtag() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line   71)
* handle_starttag() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line   45)
* handle_timeout() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line  147)
* handle_write() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  112)
* harmonic_mean() (in module statistics): Function details.  (line   83)
* hasattr() (built-in function):         Built-in Functions. (line  694)
* hasAttribute() (xml.dom.Element method): Element Objects<2>.
                                                             (line   22)
* hasAttributeNS() (xml.dom.Element method): Element Objects<2>.
                                                             (line   26)
* hasAttributes() (xml.dom.Node method): Node Objects.       (line   94)
* hasChildNodes() (xml.dom.Node method): Node Objects.       (line   98)
* hascompare (in module dis):            Opcode collections. (line   49)
* hasconst (in module dis):              Opcode collections. (line   21)
* hasFeature() (xml.dom.DOMImplementation method): DOMImplementation Objects.
                                                             (line   11)
* hasfree (in module dis):               Opcode collections. (line   25)
* hash character:                        Comments.           (line    6)
* hash() (built-in function):            Built-in Functions. (line  701)
* hash-based pyc:                        Glossary.           (line  584)
* hash.block_size (in module hashlib):   Hash algorithms.    (line  109)
* hash.digest_size (in module hashlib):  Hash algorithms.    (line  105)
* hashable:                              Dictionary displays.
                                                             (line   37)
* hashable <1>:                          Glossary.           (line  590)
* Hashable (class in collections.abc):   Collections Abstract Base Classes.
                                                             (line  108)
* Hashable (class in typing):            Corresponding to other types in collections abc.
                                                             (line   58)
* hasHandlers() (logging.Logger method): Logger Objects.     (line  318)
* hashfunc (C type):                     Slot Type typedefs. (line   76)
* hashlib (module):                      hashlib — Secure hashes and message digests.
                                                             (line    6)
* hash_info (in module sys):             sys — System-specific parameters and functions.
                                                             (line  827)
* hasjabs (in module dis):               Opcode collections. (line   41)
* hasjrel (in module dis):               Opcode collections. (line   37)
* haslocal (in module dis):              Opcode collections. (line   45)
* hasname (in module dis):               Opcode collections. (line   33)
* HAS_ALPN (in module ssl):              Constants<9>.       (line  358)
* has_children() (symtable.SymbolTable method): Examining Symbol Tables.
                                                             (line   39)
* has_colors() (in module curses):       Functions<4>.       (line  171)
* has_dualstack_ipv6() (in module socket): Creating sockets. (line  140)
* HAS_ECDH (in module ssl):              Constants<9>.       (line  374)
* has_extn() (smtplib.SMTP method):      SMTP Objects.       (line   85)
* has_function() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  212)
* has_header() (csv.Sniffer method):     Module Contents<3>. (line  232)
* has_header() (urllib.request.Request method): Request Objects.
                                                             (line   94)
* has_ic() (in module curses):           Functions<4>.       (line  176)
* has_il() (in module curses):           Functions<4>.       (line  183)
* has_ipv6 (in module socket):           Constants<8>.       (line  232)
* has_key (2to3 fixer):                  Fixers.             (line  119)
* has_key() (in module curses):          Functions<4>.       (line  190)
* has_location (importlib.machinery.ModuleSpec attribute): importlib machinery – Importers and path hooks.
                                                             (line  418)
* HAS_NEVER_CHECK_COMMON_NAME (in module ssl): Constants<9>. (line  366)
* has_nonstandard_attr() (http.cookiejar.Cookie method): Cookie Objects<2>.
                                                             (line   94)
* HAS_NPN (in module ssl):               Constants<9>.       (line  389)
* has_option() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  106)
* has_option() (optparse.OptionParser method): Querying and manipulating your option parser.
                                                             (line   42)
* has_section() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line   97)
* HAS_SNI (in module ssl):               Constants<9>.       (line  382)
* HAS_SSLv2 (in module ssl):             Constants<9>.       (line  399)
* HAS_SSLv3 (in module ssl):             Constants<9>.       (line  406)
* has_ticket (ssl.SSLSession attribute): SSL session.        (line   20)
* HAS_TLSv1 (in module ssl):             Constants<9>.       (line  413)
* HAS_TLSv1_1 (in module ssl):           Constants<9>.       (line  420)
* HAS_TLSv1_2 (in module ssl):           Constants<9>.       (line  427)
* HAS_TLSv1_3 (in module ssl):           Constants<9>.       (line  434)
* HAVE_ARGUMENT (opcode):                Python Bytecode Instructions.
                                                             (line  834)
* HAVE_CONTEXTVAR (in module decimal):   Constants<4>.       (line   32)
* HAVE_DOCSTRINGS (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  192)
* HAVE_THREADS (in module decimal):      Constants<4>.       (line   25)
* HCI_DATA_DIR (in module socket):       Constants<8>.       (line  245)
* HCI_FILTER (in module socket):         Constants<8>.       (line  245)
* HCI_TIME_STAMP (in module socket):     Constants<8>.       (line  245)
* head() (nntplib.NNTP method):          Methods<3>.         (line  266)
* Header (class in email.header):        email header Internationalized headers.
                                                             (line   60)
* HeaderError:                           tarfile — Read and write tar archive files.
                                                             (line  213)
* HeaderParseError:                      email errors Exception and Defect classes.
                                                             (line   26)
* HeaderParser (class in email.parser):  Parser API.         (line  106)
* HeaderRegistry (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line  299)
* Headers (class in wsgiref.headers):    wsgiref headers – WSGI response header tools.
                                                             (line    9)
* headers (http.client.HTTPResponse attribute): HTTPResponse Objects.
                                                             (line   56)
* headers (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  104)
* headers (urllib.error.HTTPError attribute): urllib error — Exception classes raised by urllib request.
                                                             (line   49)
* headers (urllib.response.addinfourl attribute): urllib response — Response classes used by urllib.
                                                             (line   19)
* headers (xmlrpc.client.ProtocolError attribute): ProtocolError Objects.
                                                             (line   25)
* header_encode() (email.charset.Charset method): email charset Representing character sets.
                                                             (line  118)
* header_encode_lines() (email.charset.Charset method): email charset Representing character sets.
                                                             (line  125)
* header_encoding (email.charset.Charset attribute): email charset Representing character sets.
                                                             (line   59)
* header_factory (email.policy.EmailPolicy attribute): email policy Policy Objects.
                                                             (line  391)
* header_fetch_parse() (email.policy.Compat32 method): email policy Policy Objects.
                                                             (line  578)
* header_fetch_parse() (email.policy.EmailPolicy method): email policy Policy Objects.
                                                             (line  441)
* header_fetch_parse() (email.policy.Policy method): email policy Policy Objects.
                                                             (line  302)
* header_items() (urllib.request.Request method): Request Objects.
                                                             (line  125)
* header_max_count() (email.policy.EmailPolicy method): email policy Policy Objects.
                                                             (line  418)
* header_max_count() (email.policy.Policy method): email policy Policy Objects.
                                                             (line  243)
* header_offset (zipfile.ZipInfo attribute): ZipInfo Objects.
                                                             (line  131)
* header_source_parse() (email.policy.Compat32 method): email policy Policy Objects.
                                                             (line  566)
* header_source_parse() (email.policy.EmailPolicy method): email policy Policy Objects.
                                                             (line  424)
* header_source_parse() (email.policy.Policy method): email policy Policy Objects.
                                                             (line  265)
* header_store_parse() (email.policy.Compat32 method): email policy Policy Objects.
                                                             (line  574)
* header_store_parse() (email.policy.EmailPolicy method): email policy Policy Objects.
                                                             (line  432)
* header_store_parse() (email.policy.Policy method): email policy Policy Objects.
                                                             (line  286)
* heading() (in module turtle):          Tell Turtle’s state.
                                                             (line   58)
* heading() (tkinter.ttk.Treeview method): ttk Treeview.     (line  105)
* heapify() (in module heapq):           heapq — Heap queue algorithm.
                                                             (line   56)
* heapmin() (in module msvcrt):          Other Functions.    (line    6)
* heappop() (in module heapq):           heapq — Heap queue algorithm.
                                                             (line   42)
* heappush() (in module heapq):          heapq — Heap queue algorithm.
                                                             (line   37)
* heappushpop() (in module heapq):       heapq — Heap queue algorithm.
                                                             (line   49)
* heapq (module):                        heapq — Heap queue algorithm.
                                                             (line    6)
* heapreplace() (in module heapq):       heapq — Heap queue algorithm.
                                                             (line   60)
* helo() (smtplib.SMTP method):          SMTP Objects.       (line   47)
* help (optparse.Option attribute):      Option attributes.  (line   72)
* help (pdb command):                    Debugger Commands.  (line   47)
* help() (built-in function):            Built-in Functions. (line  714)
* help() (nntplib.NNTP method):          Methods<3>.         (line  214)
* help; online:                          pydoc — Documentation generator and online help system.
                                                             (line    8)
* herror:                                Exceptions<12>.     (line   13)
* hex (uuid.UUID attribute):             uuid — UUID objects according to RFC 4122.
                                                             (line  127)
* hex() (built-in function):             Built-in Functions. (line  736)
* hex() (bytearray method):              Bytearray Objects.  (line   52)
* hex() (bytes method):                  Bytes Objects.      (line   78)
* hex() (float method):                  Additional Methods on Float.
                                                             (line   33)
* hex() (memoryview method):             Memory Views.       (line  185)
* hexadecimal literal:                   Numeric literals.   (line    6)
* hexadecimal; literals:                 Numeric Types — int float complex.
                                                             (line   19)
* hexbin() (in module binhex):           binhex — Encode and decode binhex4 files.
                                                             (line   25)
* hexdigest() (hashlib.hash method):     Hash algorithms.    (line  144)
* hexdigest() (hashlib.shake method):    SHAKE variable length digests.
                                                             (line   17)
* hexdigest() (hmac.HMAC method):        hmac — Keyed-Hashing for Message Authentication.
                                                             (line   69)
* hexdigits (in module string):          String constants.   (line   28)
* hexlify() (in module binascii):        binascii — Convert between binary and ASCII.
                                                             (line  139)
* hexversion (in module sys):            sys — System-specific parameters and functions.
                                                             (line  868)
* hidden() (curses.panel.Panel method):  Panel Objects.      (line   25)
* hide() (curses.panel.Panel method):    Panel Objects.      (line   30)
* hide() (tkinter.ttk.Notebook method):  ttk Notebook.       (line   23)
* hideturtle() (in module turtle):       Visibility.         (line    6)
* hide_cookie2 (http.cookiejar.CookiePolicy attribute): CookiePolicy Objects.
                                                             (line   76)
* HierarchyRequestErr:                   Exceptions<17>.     (line   29)
* HIGHEST_PROTOCOL (in module pickle):   Module Interface.   (line   14)
* HIGH_PRIORITY_CLASS (in module subprocess): Windows Constants.
                                                             (line   66)
* HKEY_CLASSES_ROOT (in module winreg):  HKEY_* Constants.   (line    6)
* HKEY_CURRENT_CONFIG (in module winreg): HKEY_* Constants.  (line   38)
* HKEY_CURRENT_USER (in module winreg):  HKEY_* Constants.   (line   12)
* HKEY_DYN_DATA (in module winreg):      HKEY_* Constants.   (line   43)
* HKEY_LOCAL_MACHINE (in module winreg): HKEY_* Constants.   (line   19)
* HKEY_PERFORMANCE_DATA (in module winreg): HKEY_* Constants.
                                                             (line   31)
* HKEY_USERS (in module winreg):         HKEY_* Constants.   (line   25)
* hline() (curses.window method):        Window Objects.     (line  279)
* HList (class in tkinter.tix):          Hierarchical ListBox.
                                                             (line    6)
* hls_to_rgb() (in module colorsys):     colorsys — Conversions between color systems.
                                                             (line   40)
* hmac (module):                         hmac — Keyed-Hashing for Message Authentication.
                                                             (line    6)
* HOME:                                  os path.            (line   15)
* HOME <1>:                              Changes in the Python API<2>.
                                                             (line  117)
* HOME <2>:                              Windows<17>.        (line   15)
* HOME <3>:                              Windows<17>.        (line   18)
* HOME <4>:                              os path — Common pathname manipulations.
                                                             (line  140)
* HOME <5>:                              os path — Common pathname manipulations.
                                                             (line  156)
* HOME <6>:                              distutils util — Miscellaneous other utility functions.
                                                             (line   97)
* HOME <7>:                              Location and names of config files.
                                                             (line   50)
* HOME <8>:                              Location and names of config files.
                                                             (line   67)
* home() (in module turtle):             Turtle motion.      (line  161)
* home() (pathlib.Path class method):    Methods<2>.         (line   25)
* HOMEDRIVE:                             os path — Common pathname manipulations.
                                                             (line  147)
* HOMEDRIVE <1>:                         Location and names of config files.
                                                             (line   68)
* HOMEPATH:                              os path — Common pathname manipulations.
                                                             (line  147)
* HOMEPATH <1>:                          Location and names of config files.
                                                             (line   68)
* hooks; import:                         Import hooks.       (line    6)
* hooks; meta:                           Import hooks.       (line    6)
* hooks; path:                           Import hooks.       (line    6)
* hook_compressed() (in module fileinput): fileinput — Iterate over lines from multiple input streams.
                                                             (line  188)
* hook_encoded() (in module fileinput):  fileinput — Iterate over lines from multiple input streams.
                                                             (line  199)
* host (urllib.request.Request attribute): Request Objects.  (line   25)
* hostmask (ipaddress.IPv4Network attribute): Network objects.
                                                             (line   97)
* hostmask (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  313)
* hostname_checks_common_name (ssl.SSLContext attribute): SSL Contexts.
                                                             (line  630)
* hosts (netrc.netrc attribute):         netrc Objects.      (line   23)
* hosts() (ipaddress.IPv4Network method): Network objects.   (line  136)
* hosts() (ipaddress.IPv6Network method): Network objects.   (line  331)
* hour (datetime.datetime attribute):    datetime Objects.   (line  277)
* hour (datetime.time attribute):        time Objects.       (line   50)
* HRESULT (class in ctypes):             Fundamental data types<2>.
                                                             (line  208)
* hStdError (subprocess.STARTUPINFO attribute): Windows Popen Helpers.
                                                             (line   42)
* hStdInput (subprocess.STARTUPINFO attribute): Windows Popen Helpers.
                                                             (line   27)
* hStdOutput (subprocess.STARTUPINFO attribute): Windows Popen Helpers.
                                                             (line   35)
* hsv_to_rgb() (in module colorsys):     colorsys — Conversions between color systems.
                                                             (line   48)
* ht() (in module turtle):               Visibility.         (line    6)
* HTML:                                  html parser — Simple HTML and XHTML parser.
                                                             (line    8)
* HTML <1>:                              urllib request Restrictions.
                                                             (line   29)
* html (module):                         html — HyperText Markup Language support.
                                                             (line    6)
* html() (in module cgitb):              cgitb — Traceback manager for CGI scripts.
                                                             (line   57)
* html.entities (module):                html entities — Definitions of HTML general entities.
                                                             (line    6)
* html.parser (module):                  html parser — Simple HTML and XHTML parser.
                                                             (line    6)
* html5 (in module html.entities):       html entities — Definitions of HTML general entities.
                                                             (line   14)
* HTMLCalendar (class in calendar):      calendar — General calendar-related functions.
                                                             (line  163)
* HtmlDiff (class in difflib):           difflib — Helpers for computing deltas.
                                                             (line   81)
* HTMLParser (class in html.parser):     html parser — Simple HTML and XHTML parser.
                                                             (line   14)
* htonl() (in module socket):            Other functions<2>. (line  201)
* htons() (in module socket):            Other functions<2>. (line  208)
* HTTP (in module email.policy):         email policy Policy Objects.
                                                             (line  508)
* http (module):                         http — HTTP modules.
                                                             (line    6)
* http.client (module):                  http client — HTTP protocol client.
                                                             (line    6)
* http.cookiejar (module):               http cookiejar — Cookie handling for HTTP clients.
                                                             (line    6)
* http.cookies (module):                 http cookies — HTTP state management.
                                                             (line    6)
* http.server (module):                  http server — HTTP servers.
                                                             (line    6)
* HTTP; http (standard module):          http — HTTP modules.
                                                             (line    8)
* HTTP; http.client (standard module):   http client — HTTP protocol client.
                                                             (line    8)
* HTTP; protocol:                        cgi — Common Gateway Interface support.
                                                             (line    8)
* HTTP; protocol <1>:                    urllib request Restrictions.
                                                             (line    6)
* HTTP; protocol <2>:                    urllib request Restrictions.
                                                             (line   29)
* HTTP; protocol <3>:                    http — HTTP modules.
                                                             (line    8)
* HTTP; protocol <4>:                    http client — HTTP protocol client.
                                                             (line    8)
* HTTP; protocol <5>:                    http server — HTTP servers.
                                                             (line    8)
* HTTPBasicAuthHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  347)
* HTTPConnection (class in http.client): http client — HTTP protocol client.
                                                             (line   26)
* HTTPCookieProcessor (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  278)
* httpd:                                 http server — HTTP servers.
                                                             (line    8)
* HTTPDefaultErrorHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  269)
* HTTPDigestAuthHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  371)
* HTTPError:                             urllib error — Exception classes raised by urllib request.
                                                             (line   30)
* HTTPErrorProcessor (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  431)
* HTTPException:                         http client — HTTP protocol client.
                                                             (line  128)
* HTTPHandler (class in logging.handlers): HTTPHandler.      (line   10)
* HTTPHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  395)
* HTTPPasswordMgr (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  304)
* HTTPPasswordMgrWithDefaultRealm (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  308)
* HTTPPasswordMgrWithPriorAuth (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  314)
* HTTPRedirectHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  274)
* HTTPResponse (class in http.client):   http client — HTTP protocol client.
                                                             (line   97)
* HTTPSConnection (class in http.client): http client — HTTP protocol client.
                                                             (line   57)
* HTTPServer (class in http.server):     http server — HTTP servers.
                                                             (line   25)
* HTTPSHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  399)
* HTTPStatus (class in http):            http — HTTP modules.
                                                             (line   28)
* https_open() (urllib.request.HTTPSHandler method): HTTPSHandler Objects.
                                                             (line    6)
* HTTPS_PORT (in module http.client):    http client — HTTP protocol client.
                                                             (line  201)
* https_response() (urllib.request.HTTPErrorProcessor method): HTTPErrorProcessor Objects.
                                                             (line   18)
* http_error_301() (urllib.request.HTTPRedirectHandler method): HTTPRedirectHandler Objects.
                                                             (line   35)
* http_error_302() (urllib.request.HTTPRedirectHandler method): HTTPRedirectHandler Objects.
                                                             (line   42)
* http_error_303() (urllib.request.HTTPRedirectHandler method): HTTPRedirectHandler Objects.
                                                             (line   48)
* http_error_307() (urllib.request.HTTPRedirectHandler method): HTTPRedirectHandler Objects.
                                                             (line   54)
* http_error_401() (urllib.request.HTTPBasicAuthHandler method): HTTPBasicAuthHandler Objects.
                                                             (line    6)
* http_error_401() (urllib.request.HTTPDigestAuthHandler method): HTTPDigestAuthHandler Objects.
                                                             (line    6)
* http_error_407() (urllib.request.ProxyBasicAuthHandler method): ProxyBasicAuthHandler Objects.
                                                             (line    6)
* http_error_407() (urllib.request.ProxyDigestAuthHandler method): ProxyDigestAuthHandler Objects.
                                                             (line    6)
* http_error_auth_reqed() (urllib.request.AbstractBasicAuthHandler method): AbstractBasicAuthHandler Objects.
                                                             (line    6)
* http_error_auth_reqed() (urllib.request.AbstractDigestAuthHandler method): AbstractDigestAuthHandler Objects.
                                                             (line    6)
* http_error_default() (urllib.request.BaseHandler method): BaseHandler Objects.
                                                             (line   65)
* http_open() (urllib.request.HTTPHandler method): HTTPHandler Objects.
                                                             (line    6)
* HTTP_PORT (in module http.client):     http client — HTTP protocol client.
                                                             (line  197)
* http_proxy:                            urllib request — Extensible library for opening URLs.
                                                             (line   78)
* http_proxy <1>:                        Examples<22>.       (line   97)
* http_proxy <2>:                        Basic Authentication.
                                                             (line   62)
* http_response() (urllib.request.HTTPErrorProcessor method): HTTPErrorProcessor Objects.
                                                             (line    6)
* http_version (wsgiref.handlers.BaseHandler attribute): wsgiref handlers – server/gateway base classes.
                                                             (line  300)
* hypot() (in module math):              Trigonometric functions.
                                                             (line   47)
* I (in module re):                      Module Contents.    (line   63)
* I/O control; buffering:                Built-in Functions. (line 1223)
* I/O control; buffering <1>:            Socket Objects.     (line  199)
* iadd() (in module operator):           In-place Operators. (line   36)
* iand() (in module operator):           In-place Operators. (line   41)
* iconcat() (in module operator):        In-place Operators. (line   46)
* id (ssl.SSLSession attribute):         SSL session.        (line   12)
* id() (built-in function):              Built-in Functions. (line  767)
* id() (unittest.TestCase method):       Test cases.         (line  727)
* idcok() (curses.window method):        Window Objects.     (line  286)
* ident (select.kevent attribute):       Kevent Objects.     (line    8)
* ident (threading.Thread attribute):    Thread Objects.     (line  148)
* identchars (cmd.Cmd attribute):        Cmd Objects.        (line  127)
* identifier:                            Identifiers and keywords.
                                                             (line    6)
* identifier <1>:                        Identifiers Names.  (line    6)
* identify() (tkinter.ttk.Notebook method): ttk Notebook.    (line   32)
* identify() (tkinter.ttk.Treeview method): ttk Treeview.    (line  143)
* identify() (tkinter.ttk.Widget method): ttk Widget.        (line   11)
* identify_column() (tkinter.ttk.Treeview method): ttk Treeview.
                                                             (line  153)
* identify_element() (tkinter.ttk.Treeview method): ttk Treeview.
                                                             (line  182)
* identify_region() (tkinter.ttk.Treeview method): ttk Treeview.
                                                             (line  160)
* identify_row() (tkinter.ttk.Treeview method): ttk Treeview.
                                                             (line  149)
* identity of an object:                 Objects values and types.
                                                             (line   11)
* identity; test:                        Membership test operations.
                                                             (line   40)
* idioms (2to3 fixer):                   Fixers.             (line  123)
* IDLE:                                  IDLE<51>.           (line    8)
* IDLE <1>:                              Glossary.           (line  610)
* IDLESTARTUP:                           IDLE<24>.           (line  176)
* IDLESTARTUP <1>:                       IDLE<28>.           (line    9)
* IDLESTARTUP <2>:                       IDLE<34>.           (line    9)
* IDLESTARTUP <3>:                       Startup and code execution.
                                                             (line    7)
* IDLE_PRIORITY_CLASS (in module subprocess): Windows Constants.
                                                             (line   73)
* idlok() (curses.window method):        Window Objects.     (line  294)
* If (class in ast):                     Control flow.       (line    9)
* if; conditional expression:            Conditional expressions.
                                                             (line    6)
* if; in comprehensions:                 Displays for lists sets and dictionaries.
                                                             (line   14)
* IfExp (class in ast):                  Expressions<2>.     (line  158)
* ifloordiv() (in module operator):      In-place Operators. (line   52)
* if_indextoname() (in module socket):   Other functions<2>. (line  402)
* if_nameindex() (in module socket):     Other functions<2>. (line  359)
* if_nametoindex() (in module socket):   Other functions<2>. (line  384)
* iglob() (in module glob):              glob — Unix style pathname pattern expansion.
                                                             (line   54)
* ignorableWhitespace() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line  150)
* ignore (pdb command):                  Debugger Commands.  (line  111)
* IGNORECASE (in module re):             Module Contents.    (line   63)
* ignore_errors() (in module codecs):    Error Handlers.     (line  140)
* IGNORE_EXCEPTION_DETAIL (in module doctest): Option Flags. (line   58)
* ignore_patterns() (in module shutil):  Directory and files operations.
                                                             (line  184)
* ihave() (nntplib.NNTP method):         Methods<3>.         (line  291)
* IISCGIHandler (class in wsgiref.handlers): wsgiref handlers – server/gateway base classes.
                                                             (line   24)
* ilshift() (in module operator):        In-place Operators. (line   57)
* imag (numbers.Complex attribute):      The numeric tower.  (line   19)
* imaginary literal:                     Numeric literals.   (line    6)
* imap() (multiprocessing.pool.Pool method): Process Pools.  (line  126)
* IMAP4 (class in imaplib):              imaplib — IMAP4 protocol client.
                                                             (line   20)
* IMAP4.abort:                           imaplib — IMAP4 protocol client.
                                                             (line   53)
* IMAP4.error:                           imaplib — IMAP4 protocol client.
                                                             (line   48)
* IMAP4.readonly:                        imaplib — IMAP4 protocol client.
                                                             (line   60)
* IMAP4; protocol:                       imaplib — IMAP4 protocol client.
                                                             (line    8)
* IMAP4_SSL (class in imaplib):          imaplib — IMAP4 protocol client.
                                                             (line   69)
* IMAP4_SSL; protocol:                   imaplib — IMAP4 protocol client.
                                                             (line    8)
* IMAP4_stream (class in imaplib):       imaplib — IMAP4 protocol client.
                                                             (line  109)
* IMAP4_stream; protocol:                imaplib — IMAP4 protocol client.
                                                             (line    8)
* imaplib (module):                      imaplib — IMAP4 protocol client.
                                                             (line    6)
* imap_unordered() (multiprocessing.pool.Pool method): Process Pools.
                                                             (line  141)
* imatmul() (in module operator):        In-place Operators. (line   72)
* imghdr (module):                       imghdr — Determine the type of an image.
                                                             (line    6)
* immedok() (curses.window method):      Window Objects.     (line  300)
* immutable:                             Glossary.           (line  616)
* immutable object:                      Objects values and types.
                                                             (line   11)
* immutable; data; type:                 Literals<2>.        (line   17)
* immutable; object:                     Literals<2>.        (line   17)
* immutable; object <1>:                 Dictionary displays.
                                                             (line   37)
* immutable; sequence; types:            Immutable Sequence Types.
                                                             (line    6)
* imod() (in module operator):           In-place Operators. (line   62)
* imp (module):                          imp — Access the import internals.
                                                             (line    6)
* ImpImporter (class in pkgutil):        pkgutil — Package extension utility.
                                                             (line   53)
* implementation (in module sys):        sys — System-specific parameters and functions.
                                                             (line  891)
* ImpLoader (class in pkgutil):          pkgutil — Package extension utility.
                                                             (line   69)
* impl_detail() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  702)
* import (2to3 fixer):                   Fixers.             (line  139)
* Import (class in ast):                 Imports.            (line    6)
* import hooks:                          Import hooks.       (line    6)
* import machinery:                      The import system.  (line    6)
* import path:                           Glossary.           (line  624)
* importer:                              Glossary.           (line  637)
* ImportError:                           Concrete exceptions.
                                                             (line   38)
* ImportFrom (class in ast):             Imports.            (line   21)
* importing:                             Glossary.           (line  632)
* importlib (module):                    importlib — The implementation of import.
                                                             (line    6)
* importlib.abc (module):                importlib abc – Abstract base classes related to import.
                                                             (line    6)
* importlib.machinery (module):          importlib machinery – Importers and path hooks.
                                                             (line    6)
* importlib.metadata (module):           Using importlib metadata.
                                                             (line    6)
* importlib.resources (module):          importlib resources – Resources.
                                                             (line    6)
* importlib.util (module):               importlib util – Utility code for importers.
                                                             (line    6)
* imports (2to3 fixer):                  Fixers.             (line  143)
* imports2 (2to3 fixer):                 Fixers.             (line  147)
* ImportWarning:                         Warnings.           (line   57)
* import_fresh_module() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  798)
* IMPORT_FROM (opcode):                  Python Bytecode Instructions.
                                                             (line  581)
* import_module() (in module importlib): Functions<11>.      (line   15)
* import_module() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  783)
* IMPORT_NAME (opcode):                  Python Bytecode Instructions.
                                                             (line  572)
* IMPORT_STAR (opcode):                  Python Bytecode Instructions.
                                                             (line  366)
* ImproperConnectionState:               http client — HTTP protocol client.
                                                             (line  158)
* imul() (in module operator):           In-place Operators. (line   67)
* In (class in ast):                     Expressions<2>.     (line  109)
* inch() (curses.window method):         Window Objects.     (line  308)
* inclusive (tracemalloc.DomainFilter attribute): DomainFilter.
                                                             (line   12)
* inclusive (tracemalloc.Filter attribute): Filter.          (line   38)
* inclusive; or:                         Binary bitwise operations.
                                                             (line   20)
* Incomplete:                            binascii — Convert between binary and ASCII.
                                                             (line  186)
* IncompleteRead:                        http client — HTTP protocol client.
                                                             (line  154)
* IncompleteReadError:                   Exceptions<10>.     (line   42)
* IncrementalDecoder (class in codecs):  IncrementalDecoder Objects.
                                                             (line   11)
* incrementaldecoder (codecs.CodecInfo attribute): codecs — Codec registry and base classes.
                                                             (line   78)
* IncrementalEncoder (class in codecs):  IncrementalEncoder Objects.
                                                             (line   11)
* incrementalencoder (codecs.CodecInfo attribute): codecs — Codec registry and base classes.
                                                             (line   78)
* IncrementalNewlineDecoder (class in io): Text I/O<2>.      (line  237)
* IncrementalParser (class in xml.sax.xmlreader): xml sax xmlreader — Interface for XML parsers.
                                                             (line   20)
* increment_lineno() (in module ast):    ast Helpers.        (line  126)
* incr_item():                           Exceptions<19>.     (line   78)
* incr_item() <1>:                       Exceptions<19>.     (line  123)
* indent (doctest.Example attribute):    Example Objects.    (line   47)
* INDENT (in module token):              token — Constants used with Python parse trees.
                                                             (line   50)
* INDENT token:                          Indentation.        (line   33)
* indent() (in module textwrap):         textwrap — Text wrapping and filling.
                                                             (line  100)
* indent() (in module xml.etree.ElementTree): Functions<7>.  (line  118)
* indentation:                           Indentation.        (line    6)
* IndentationError:                      Concrete exceptions.
                                                             (line  284)
* index operation:                       The standard type hierarchy.
                                                             (line  132)
* index() (array.array method):          array — Efficient arrays of numeric values.
                                                             (line  185)
* index() (bytearray method):            Bytes and Bytearray Operations.
                                                             (line  147)
* index() (bytes method):                Bytes and Bytearray Operations.
                                                             (line  147)
* index() (collections.deque method):    deque objects.      (line   70)
* index() (in module operator):          operator — Standard operators as functions.
                                                             (line   93)
* index() (multiprocessing.shared_memory.ShareableList method): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line  268)
* index() (sequence method):             Common Sequence Operations.
                                                             (line   21)
* index() (str method):                  String Methods<2>.  (line  170)
* index() (tkinter.ttk.Notebook method): ttk Notebook.       (line   37)
* index() (tkinter.ttk.Treeview method): ttk Treeview.       (line  188)
* IndexError:                            Concrete exceptions.
                                                             (line   59)
* indexOf() (in module operator):        operator — Standard operators as functions.
                                                             (line  197)
* IndexSizeErr:                          Exceptions<17>.     (line   34)
* indices() (slice method):              The standard type hierarchy.
                                                             (line  820)
* inet_aton() (in module socket):        Other functions<2>. (line  221)
* inet_ntoa() (in module socket):        Other functions<2>. (line  241)
* inet_ntop() (in module socket):        Other functions<2>. (line  276)
* inet_pton() (in module socket):        Other functions<2>. (line  258)
* Inexact (class in decimal):            Signals.            (line   42)
* inf (in module cmath):                 Constants<3>.       (line   20)
* inf (in module math):                  Constants<2>.       (line   24)
* infile (shlex.shlex attribute):        shlex Objects.      (line  140)
* Infinity:                              Built-in Functions. (line  582)
* infj (in module cmath):                Constants<3>.       (line   26)
* info() (dis.Bytecode method):          Bytecode analysis.  (line   53)
* info() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line   78)
* info() (http.client.HTTPResponse method): HTTPResponse Objects.
                                                             (line   84)
* info() (in module logging):            Module-Level Functions.
                                                             (line  119)
* info() (logging.Logger method):        Logger Objects.     (line  227)
* info() (urllib.response.addinfourl method): urllib response — Response classes used by urllib.
                                                             (line   35)
* infolist() (zipfile.ZipFile method):   ZipFile Objects.    (line   98)
* inheritance:                           Class definitions.  (line    6)
* ini file:                              configparser — Configuration file parser.
                                                             (line    8)
* init() (in module mimetypes):          mimetypes — Map filenames to MIME types.
                                                             (line   78)
* inited (in module mimetypes):          mimetypes — Map filenames to MIME types.
                                                             (line  117)
* initgroups() (in module os):           Process Parameters. (line  307)
* initialize_options() (distutils.cmd.Command method): Creating a new Distutils command.
                                                             (line   21)
* initial_indent (textwrap.TextWrapper attribute): textwrap — Text wrapping and filling.
                                                             (line  207)
* initproc (C type):                     Slot Type typedefs. (line   34)
* initscr() (in module curses):          Functions<4>.       (line  229)
* init_color() (in module curses):       Functions<4>.       (line  204)
* init_database() (in module msilib):    msilib — Read and write Microsoft Installer files.
                                                             (line   60)
* init_pair() (in module curses):        Functions<4>.       (line  216)
* inode() (os.DirEntry method):          Files and Directories.
                                                             (line  872)
* INPLACE_ADD (opcode):                  Python Bytecode Instructions.
                                                             (line  222)
* INPLACE_AND (opcode):                  Python Bytecode Instructions.
                                                             (line  238)
* INPLACE_FLOOR_DIVIDE (opcode):         Python Bytecode Instructions.
                                                             (line  210)
* INPLACE_LSHIFT (opcode):               Python Bytecode Instructions.
                                                             (line  230)
* INPLACE_MATRIX_MULTIPLY (opcode):      Python Bytecode Instructions.
                                                             (line  204)
* INPLACE_MODULO (opcode):               Python Bytecode Instructions.
                                                             (line  218)
* INPLACE_MULTIPLY (opcode):             Python Bytecode Instructions.
                                                             (line  200)
* INPLACE_OR (opcode):                   Python Bytecode Instructions.
                                                             (line  246)
* INPLACE_POWER (opcode):                Python Bytecode Instructions.
                                                             (line  196)
* INPLACE_RSHIFT (opcode):               Python Bytecode Instructions.
                                                             (line  234)
* INPLACE_SUBTRACT (opcode):             Python Bytecode Instructions.
                                                             (line  226)
* INPLACE_TRUE_DIVIDE (opcode):          Python Bytecode Instructions.
                                                             (line  214)
* INPLACE_XOR (opcode):                  Python Bytecode Instructions.
                                                             (line  242)
* input:                                 Expression input.   (line    6)
* input (2to3 fixer):                    Fixers.             (line  153)
* input() (built-in function):           Built-in Functions. (line  780)
* input() (in module fileinput):         fileinput — Iterate over lines from multiple input streams.
                                                             (line   54)
* InputOnly (class in tkinter.tix):      Miscellaneous Widgets.
                                                             (line    6)
* InputSource (class in xml.sax.xmlreader): xml sax xmlreader — Interface for XML parsers.
                                                             (line   51)
* input_charset (email.charset.Charset attribute): email charset Representing character sets.
                                                             (line   53)
* input_codec (email.charset.Charset attribute): email charset Representing character sets.
                                                             (line   82)
* inquiry (C type):                      Supporting Cyclic Garbage Collection.
                                                             (line  177)
* insch() (curses.window method):        Window Objects.     (line  314)
* insdelln() (curses.window method):     Window Objects.     (line  321)
* insert() (array.array method):         array — Efficient arrays of numeric values.
                                                             (line  190)
* insert() (collections.deque method):   deque objects.      (line   78)
* insert() (sequence method):            Mutable Sequence Types.
                                                             (line   16)
* insert() (tkinter.ttk.Notebook method): ttk Notebook.      (line   42)
* insert() (tkinter.ttk.Treeview method): ttk Treeview.      (line  193)
* insert() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line  130)
* insertBefore() (xml.dom.Node method):  Node Objects.       (line  121)
* insertln() (curses.window method):     Window Objects.     (line  329)
* insert_text() (in module readline):    Line buffer.        (line   13)
* insnstr() (curses.window method):      Window Objects.     (line  334)
* insort() (in module bisect):           bisect — Array bisection algorithm.
                                                             (line   52)
* insort_left() (in module bisect):      bisect — Array bisection algorithm.
                                                             (line   45)
* insort_right() (in module bisect):     bisect — Array bisection algorithm.
                                                             (line   52)
* inspect (module):                      inspect — Inspect live objects.
                                                             (line    6)
* inspect command line option; –details: Command Line Interface<3>.
                                                             (line   13)
* InspectLoader (class in importlib.abc): importlib abc – Abstract base classes related to import.
                                                             (line  384)
* insstr() (curses.window method):       Window Objects.     (line  345)
* install() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line  100)
* install() (in module gettext):         Class-based API.    (line   72)
* installHandler() (in module unittest): Signal Handling.    (line   29)
* install_opener() (in module urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  109)
* install_scripts() (venv.EnvBuilder method): API<2>.        (line  141)
* instance; call:                        Calls.              (line  147)
* instate() (tkinter.ttk.Widget method): ttk Widget.         (line   18)
* instr() (curses.window method):        Window Objects.     (line  355)
* instream (shlex.shlex attribute):      shlex Objects.      (line  146)
* Instruction (class in dis):            Python Bytecode Instructions.
                                                             (line   10)
* Instruction.arg (in module dis):       Python Bytecode Instructions.
                                                             (line   24)
* Instruction.argrepr (in module dis):   Python Bytecode Instructions.
                                                             (line   32)
* Instruction.argval (in module dis):    Python Bytecode Instructions.
                                                             (line   28)
* Instruction.is_jump_target (in module dis): Python Bytecode Instructions.
                                                             (line   44)
* Instruction.offset (in module dis):    Python Bytecode Instructions.
                                                             (line   36)
* Instruction.opcode (in module dis):    Python Bytecode Instructions.
                                                             (line   14)
* Instruction.opname (in module dis):    Python Bytecode Instructions.
                                                             (line   20)
* Instruction.starts_line (in module dis): Python Bytecode Instructions.
                                                             (line   40)
* int (built-in class):                  Built-in Functions. (line  803)
* int (uuid.UUID attribute):             uuid — UUID objects according to RFC 4122.
                                                             (line  131)
* Int2AP() (in module imaplib):          imaplib — IMAP4 protocol client.
                                                             (line  123)
* integer:                               The standard type hierarchy.
                                                             (line  161)
* integer literal:                       Numeric literals.   (line    6)
* integer; literals:                     Numeric Types — int float complex.
                                                             (line   19)
* integer; representation:               The standard type hierarchy.
                                                             (line  106)
* Integral (class in numbers):           The numeric tower.  (line   55)
* Integrated Development Environment:    IDLE<51>.           (line    8)
* IntegrityError:                        Exceptions<5>.      (line   19)
* Intel/DVI ADPCM:                       audioop — Manipulate raw audio data.
                                                             (line   17)
* IntEnum (class in enum):               Module Contents<2>. (line   16)
* interact (pdb command):                Debugger Commands.  (line  275)
* interact() (code.InteractiveConsole method): Interactive Console Objects.
                                                             (line   10)
* interact() (in module code):           code — Interpreter base classes.
                                                             (line   32)
* interact() (telnetlib.Telnet method):  Telnet Objects.     (line  113)
* interactive:                           Glossary.           (line  642)
* interactive mode:                      Complete Python programs.
                                                             (line   19)
* InteractiveConsole (class in code):    code — Interpreter base classes.
                                                             (line   25)
* InteractiveInterpreter (class in code): code — Interpreter base classes.
                                                             (line   15)
* intern (2to3 fixer):                   Fixers.             (line  157)
* intern() (in module sys):              sys — System-specific parameters and functions.
                                                             (line  968)
* internal type:                         The standard type hierarchy.
                                                             (line  650)
* Internaldate2tuple() (in module imaplib): imaplib — IMAP4 protocol client.
                                                             (line  117)
* internalSubset (xml.dom.DocumentType attribute): DocumentType Objects.
                                                             (line   27)
* internal_attr (zipfile.ZipInfo attribute): ZipInfo Objects.
                                                             (line  123)
* Internet:                              Internet Protocols and Support.
                                                             (line    6)
* INTERNET_TIMEOUT (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  100)
* interpolated string literal:           String literal concatenation.
                                                             (line   24)
* interpolation, string (%):             printf-style String Formatting.
                                                             (line    6)
* interpolation; bytearray (%):          printf-style Bytes Formatting.
                                                             (line    6)
* interpolation; bytes (%):              printf-style Bytes Formatting.
                                                             (line    6)
* InterpolationDepthError:               Exceptions<6>.      (line   42)
* InterpolationError:                    Exceptions<6>.      (line   37)
* InterpolationMissingOptionError:       Exceptions<6>.      (line   49)
* InterpolationSyntaxError:              Exceptions<6>.      (line   54)
* interpreted:                           Glossary.           (line  651)
* interpreter:                           Top-level components.
                                                             (line    6)
* interpreter lock:                      Thread State and the Global Interpreter Lock.
                                                             (line    6)
* interpreter prompts:                   sys — System-specific parameters and functions.
                                                             (line 1210)
* interpreter shutdown:                  Glossary.           (line  661)
* interpreter_requires_environment() (in module test.support.script_helper): test support script_helper — Utilities for the Python execution tests.
                                                             (line    9)
* interrupt() (sqlite3.Connection method): Connection Objects.
                                                             (line  188)
* InterruptedError:                      OS exceptions.      (line   71)
* interrupt_main() (in module _thread):  _thread — Low-level threading API.
                                                             (line   53)
* intersection() (frozenset method):     Set Types — set frozenset.
                                                             (line  102)
* intersection_update() (frozenset method): Set Types — set frozenset.
                                                             (line  175)
* IntFlag (class in enum):               Module Contents<2>. (line   21)
* intro (cmd.Cmd attribute):             Cmd Objects.        (line  142)
* int_info (in module sys):              sys — System-specific parameters and functions.
                                                             (line  934)
* InuseAttributeErr:                     Exceptions<17>.     (line   39)
* inv() (in module operator):            operator — Standard operators as functions.
                                                             (line   98)
* InvalidAccessErr:                      Exceptions<17>.     (line   44)
* invalidate_caches() (importlib.abc.MetaPathFinder method): importlib abc – Abstract base classes related to import.
                                                             (line   86)
* invalidate_caches() (importlib.abc.PathEntryFinder method): importlib abc – Abstract base classes related to import.
                                                             (line  151)
* invalidate_caches() (importlib.machinery.FileFinder method): importlib machinery – Importers and path hooks.
                                                             (line  202)
* invalidate_caches() (importlib.machinery.PathFinder class method): importlib machinery – Importers and path hooks.
                                                             (line  146)
* invalidate_caches() (in module importlib): Functions<11>.  (line   62)
* InvalidCharacterErr:                   Exceptions<17>.     (line   49)
* InvalidModificationErr:                Exceptions<17>.     (line   57)
* InvalidOperation (class in decimal):   Signals.            (line   50)
* InvalidStateErr:                       Exceptions<17>.     (line   61)
* InvalidStateError:                     Exception classes.  (line   22)
* InvalidStateError <1>:                 Exceptions<10>.     (line   28)
* InvalidTZPathWarning:                  Exceptions and warnings.
                                                             (line   12)
* InvalidURL:                            http client — HTTP protocol client.
                                                             (line  137)
* inversion:                             Unary arithmetic and bitwise operations.
                                                             (line   18)
* Invert (class in ast):                 Expressions<2>.     (line   28)
* invert() (in module operator):         operator — Standard operators as functions.
                                                             (line   98)
* invocation:                            The standard type hierarchy.
                                                             (line  297)
* inv_cdf() (statistics.NormalDist method): NormalDist objects.
                                                             (line   86)
* in_dll() (ctypes._CData method):       Data types.         (line   63)
* in_table_a1() (in module stringprep):  stringprep — Internet String Preparation.
                                                             (line   40)
* in_table_b1() (in module stringprep):  stringprep — Internet String Preparation.
                                                             (line   45)
* in_table_c11() (in module stringprep): stringprep — Internet String Preparation.
                                                             (line   60)
* in_table_c11_c12() (in module stringprep): stringprep — Internet String Preparation.
                                                             (line   69)
* in_table_c12() (in module stringprep): stringprep — Internet String Preparation.
                                                             (line   64)
* in_table_c21() (in module stringprep): stringprep — Internet String Preparation.
                                                             (line   74)
* in_table_c21_c22() (in module stringprep): stringprep — Internet String Preparation.
                                                             (line   84)
* in_table_c22() (in module stringprep): stringprep — Internet String Preparation.
                                                             (line   79)
* in_table_c3() (in module stringprep):  stringprep — Internet String Preparation.
                                                             (line   89)
* in_table_c4() (in module stringprep):  stringprep — Internet String Preparation.
                                                             (line   93)
* in_table_c5() (in module stringprep):  stringprep — Internet String Preparation.
                                                             (line   98)
* in_table_c6() (in module stringprep):  stringprep — Internet String Preparation.
                                                             (line  102)
* in_table_c7() (in module stringprep):  stringprep — Internet String Preparation.
                                                             (line  107)
* in_table_c8() (in module stringprep):  stringprep — Internet String Preparation.
                                                             (line  112)
* in_table_c9() (in module stringprep):  stringprep — Internet String Preparation.
                                                             (line  117)
* in_table_d1() (in module stringprep):  stringprep — Internet String Preparation.
                                                             (line  121)
* in_table_d2() (in module stringprep):  stringprep — Internet String Preparation.
                                                             (line  126)
* in_transaction (sqlite3.Connection attribute): Connection Objects.
                                                             (line   18)
* IO (class in typing):                  Other concrete types.
                                                             (line    6)
* io (module):                           io — Core tools for working with streams.
                                                             (line    6)
* IOBase (class in io):                  I/O Base Classes.   (line    6)
* ioctl() (in module fcntl):             fcntl — The fcntl and ioctl system calls.
                                                             (line   60)
* ioctl() (socket.socket method):        Socket Objects.     (line  168)
* IOCTL_VM_SOCKETS_GET_LOCAL_CID (in module socket): Constants<8>.
                                                             (line  213)
* IOError:                               Concrete exceptions.
                                                             (line  422)
* ior() (in module operator):            In-place Operators. (line   79)
* IO_REPARSE_TAG_APPEXECLINK (in module stat): stat — Interpreting stat results.
                                                             (line  418)
* IO_REPARSE_TAG_MOUNT_POINT (in module stat): stat — Interpreting stat results.
                                                             (line  418)
* IO_REPARSE_TAG_SYMLINK (in module stat): stat — Interpreting stat results.
                                                             (line  418)
* ip (ipaddress.IPv4Interface attribute): Interface objects. (line   19)
* ip (ipaddress.IPv6Interface attribute): Interface objects. (line   74)
* ipaddress (module):                    ipaddress — IPv4/IPv6 manipulation library.
                                                             (line    6)
* ipow() (in module operator):           In-place Operators. (line   84)
* IPv4Address (class in ipaddress):      Address objects.    (line   13)
* IPv4Interface (class in ipaddress):    Interface objects.  (line    9)
* IPv4Network (class in ipaddress):      Network objects.    (line   13)
* ipv4_mapped (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  240)
* IPv6Address (class in ipaddress):      Address objects.    (line  161)
* IPv6Interface (class in ipaddress):    Interface objects.  (line   64)
* IPv6Network (class in ipaddress):      Network objects.    (line  253)
* IPV6_ENABLED (in module test.support.socket_helper): test support socket_helper — Utilities for socket tests.
                                                             (line   11)
* ip_address() (in module ipaddress):    Convenience factory functions.
                                                             (line    9)
* ip_interface() (in module ipaddress):  Convenience factory functions.
                                                             (line   37)
* ip_network() (in module ipaddress):    Convenience factory functions.
                                                             (line   23)
* irshift() (in module operator):        In-place Operators. (line   89)
* Is (class in ast):                     Expressions<2>.     (line  109)
* isabs() (in module os.path):           os path — Common pathname manipulations.
                                                             (line  204)
* isabstract() (in module inspect):      Types and members.  (line  419)
* IsADirectoryError:                     OS exceptions.      (line   81)
* isalnum() (bytearray method):          Bytes and Bytearray Operations.
                                                             (line  503)
* isalnum() (bytes method):              Bytes and Bytearray Operations.
                                                             (line  503)
* isalnum() (in module curses.ascii):    curses ascii — Utilities for ASCII characters.
                                                             (line  131)
* isalnum() (str method):                String Methods<2>.  (line  175)
* isalpha() (bytearray method):          Bytes and Bytearray Operations.
                                                             (line  521)
* isalpha() (bytes method):              Bytes and Bytearray Operations.
                                                             (line  521)
* isalpha() (in module curses.ascii):    curses ascii — Utilities for ASCII characters.
                                                             (line  136)
* isalpha() (str method):                String Methods<2>.  (line  182)
* isascii() (bytearray method):          Bytes and Bytearray Operations.
                                                             (line  536)
* isascii() (bytes method):              Bytes and Bytearray Operations.
                                                             (line  536)
* isascii() (in module curses.ascii):    curses ascii — Utilities for ASCII characters.
                                                             (line  141)
* isascii() (str method):                String Methods<2>.  (line  192)
* isasyncgen() (in module inspect):      Types and members.  (line  389)
* isasyncgenfunction() (in module inspect): Types and members.
                                                             (line  372)
* isatty() (chunk.Chunk method):         chunk — Read IFF chunked data.
                                                             (line   88)
* isatty() (in module os):               File Descriptor Operations.
                                                             (line  209)
* isatty() (io.IOBase method):           I/O Base Classes.   (line   74)
* isawaitable() (in module inspect):     Types and members.  (line  353)
* isblank() (in module curses.ascii):    curses ascii — Utilities for ASCII characters.
                                                             (line  145)
* isblk() (tarfile.TarInfo method):      TarInfo Objects.    (line  120)
* isbuiltin() (in module inspect):       Types and members.  (line  409)
* ischr() (tarfile.TarInfo method):      TarInfo Objects.    (line  116)
* isclass() (in module inspect):         Types and members.  (line  309)
* isclose() (in module cmath):           Classification functions.
                                                             (line   23)
* isclose() (in module math):            Number-theoretic and representation functions.
                                                             (line  111)
* iscntrl() (in module curses.ascii):    curses ascii — Utilities for ASCII characters.
                                                             (line  149)
* iscode() (in module inspect):          Types and members.  (line  405)
* iscoroutine() (in module asyncio):     Generator-based Coroutines.
                                                             (line   36)
* iscoroutine() (in module inspect):     Types and members.  (line  346)
* iscoroutinefunction() (in module asyncio): Generator-based Coroutines.
                                                             (line   43)
* iscoroutinefunction() (in module inspect): Types and members.
                                                             (line  335)
* isctrl() (in module curses.ascii):     curses ascii — Utilities for ASCII characters.
                                                             (line  190)
* isDaemon() (threading.Thread method):  Thread Objects.     (line  197)
* isdatadescriptor() (in module inspect): Types and members. (line  441)
* isdecimal() (str method):              String Methods<2>.  (line  200)
* isdev() (tarfile.TarInfo method):      TarInfo Objects.    (line  128)
* isdigit() (bytearray method):          Bytes and Bytearray Operations.
                                                             (line  544)
* isdigit() (bytes method):              Bytes and Bytearray Operations.
                                                             (line  544)
* isdigit() (in module curses.ascii):    curses ascii — Utilities for ASCII characters.
                                                             (line  154)
* isdigit() (str method):                String Methods<2>.  (line  208)
* isdir() (in module os.path):           os path — Common pathname manipulations.
                                                             (line  220)
* isdir() (tarfile.TarInfo method):      TarInfo Objects.    (line  104)
* isdisjoint() (frozenset method):       Set Types — set frozenset.
                                                             (line   68)
* isdown() (in module turtle):           Drawing state.      (line   86)
* iselement() (in module xml.etree.ElementTree): Functions<7>.
                                                             (line  130)
* isenabled() (in module gc):            gc — Garbage Collector interface.
                                                             (line   30)
* isEnabledFor() (logging.Logger method): Logger Objects.    (line  101)
* isendwin() (in module curses):         Functions<4>.       (line  242)
* ISEOF() (in module token):             token — Constants used with Python parse trees.
                                                             (line   34)
* isexpr() (in module parser):           Queries on ST Objects.
                                                             (line   12)
* isexpr() (parser.ST method):           ST Objects.         (line   21)
* isfifo() (tarfile.TarInfo method):     TarInfo Objects.    (line  124)
* isfile() (in module os.path):          os path — Common pathname manipulations.
                                                             (line  212)
* isfile() (tarfile.TarInfo method):     TarInfo Objects.    (line   96)
* isfinite() (in module cmath):          Classification functions.
                                                             (line    6)
* isfinite() (in module math):           Number-theoretic and representation functions.
                                                             (line  144)
* isfirstline() (in module fileinput):   fileinput — Iterate over lines from multiple input streams.
                                                             (line  106)
* isframe() (in module inspect):         Types and members.  (line  401)
* isfunction() (in module inspect):      Types and members.  (line  318)
* isfuture() (in module asyncio):        Future Functions.   (line    6)
* isgenerator() (in module inspect):     Types and members.  (line  331)
* isgeneratorfunction() (in module inspect): Types and members.
                                                             (line  323)
* isgetsetdescriptor() (in module inspect): Types and members.
                                                             (line  454)
* isgraph() (in module curses.ascii):    curses ascii — Utilities for ASCII characters.
                                                             (line  159)
* isidentifier() (str method):           String Methods<2>.  (line  218)
* isinf() (in module cmath):             Classification functions.
                                                             (line   13)
* isinf() (in module math):              Number-theoretic and representation functions.
                                                             (line  151)
* isinstance (2to3 fixer):               Fixers.             (line  161)
* isinstance() (built-in function):      Built-in Functions. (line  845)
* iskeyword() (in module keyword):       keyword — Testing for Python keywords.
                                                             (line   13)
* isleap() (in module calendar):         calendar — General calendar-related functions.
                                                             (line  301)
* islice() (in module itertools):        Itertool functions. (line  355)
* islink() (in module os.path):          os path — Common pathname manipulations.
                                                             (line  228)
* islnk() (tarfile.TarInfo method):      TarInfo Objects.    (line  112)
* islower() (bytearray method):          Bytes and Bytearray Operations.
                                                             (line  558)
* islower() (bytes method):              Bytes and Bytearray Operations.
                                                             (line  558)
* islower() (in module curses.ascii):    curses ascii — Utilities for ASCII characters.
                                                             (line  163)
* islower() (str method):                String Methods<2>.  (line  236)
* ismemberdescriptor() (in module inspect): Types and members.
                                                             (line  463)
* ismeta() (in module curses.ascii):     curses ascii — Utilities for ASCII characters.
                                                             (line  194)
* ismethod() (in module inspect):        Types and members.  (line  314)
* ismethoddescriptor() (in module inspect): Types and members.
                                                             (line  423)
* ismodule() (in module inspect):        Types and members.  (line  305)
* ismount() (in module os.path):         os path — Common pathname manipulations.
                                                             (line  236)
* isnan() (in module cmath):             Classification functions.
                                                             (line   18)
* isnan() (in module math):              Number-theoretic and representation functions.
                                                             (line  156)
* ISNONTERMINAL() (in module token):     token — Constants used with Python parse trees.
                                                             (line   30)
* IsNot (class in ast):                  Expressions<2>.     (line  109)
* isnumeric() (str method):              String Methods<2>.  (line  242)
* isocalendar() (datetime.date method):  date Objects.       (line  213)
* isocalendar() (datetime.datetime method): datetime Objects.
                                                             (line  594)
* isoformat() (datetime.date method):    date Objects.       (line  240)
* isoformat() (datetime.datetime method): datetime Objects.  (line  599)
* isoformat() (datetime.time method):    time Objects.       (line  151)
* IsolatedAsyncioTestCase (class in unittest): Test cases.   (line  809)
* isolation_level (sqlite3.Connection attribute): Connection Objects.
                                                             (line   11)
* isoweekday() (datetime.date method):   date Objects.       (line  206)
* isoweekday() (datetime.datetime method): datetime Objects. (line  588)
* isprint() (in module curses.ascii):    curses ascii — Utilities for ASCII characters.
                                                             (line  167)
* isprintable() (str method):            String Methods<2>.  (line  252)
* ispunct() (in module curses.ascii):    curses ascii — Utilities for ASCII characters.
                                                             (line  171)
* isqrt() (in module math):              Number-theoretic and representation functions.
                                                             (line  161)
* isreadable() (in module pprint):       pprint — Data pretty printer.
                                                             (line  133)
* isreadable() (pprint.PrettyPrinter method): PrettyPrinter Objects.
                                                             (line   24)
* isrecursive() (in module pprint):      pprint — Data pretty printer.
                                                             (line  142)
* isrecursive() (pprint.PrettyPrinter method): PrettyPrinter Objects.
                                                             (line   32)
* isreg() (tarfile.TarInfo method):      TarInfo Objects.    (line  100)
* isReservedKey() (http.cookies.Morsel method): Morsel Objects.
                                                             (line   68)
* isroutine() (in module inspect):       Types and members.  (line  414)
* isSameNode() (xml.dom.Node method):    Node Objects.       (line  102)
* issoftkeyword() (in module keyword):   keyword — Testing for Python keywords.
                                                             (line   24)
* isspace() (bytearray method):          Bytes and Bytearray Operations.
                                                             (line  575)
* isspace() (bytes method):              Bytes and Bytearray Operations.
                                                             (line  575)
* isspace() (in module curses.ascii):    curses ascii — Utilities for ASCII characters.
                                                             (line  176)
* isspace() (str method):                String Methods<2>.  (line  264)
* isstdin() (in module fileinput):       fileinput — Iterate over lines from multiple input streams.
                                                             (line  111)
* issubclass() (built-in function):      Built-in Functions. (line  856)
* issubset() (frozenset method):         Set Types — set frozenset.
                                                             (line   74)
* issuite() (in module parser):          Queries on ST Objects.
                                                             (line   22)
* issuite() (parser.ST method):          ST Objects.         (line   25)
* issuperset() (frozenset method):       Set Types — set frozenset.
                                                             (line   85)
* issym() (tarfile.TarInfo method):      TarInfo Objects.    (line  108)
* ISTERMINAL() (in module token):        token — Constants used with Python parse trees.
                                                             (line   26)
* istitle() (bytearray method):          Bytes and Bytearray Operations.
                                                             (line  583)
* istitle() (bytes method):              Bytes and Bytearray Operations.
                                                             (line  583)
* istitle() (str method):                String Methods<2>.  (line  274)
* istraceback() (in module inspect):     Types and members.  (line  397)
* isub() (in module operator):           In-place Operators. (line   94)
* isupper() (bytearray method):          Bytes and Bytearray Operations.
                                                             (line  597)
* isupper() (bytes method):              Bytes and Bytearray Operations.
                                                             (line  597)
* isupper() (in module curses.ascii):    curses ascii — Utilities for ASCII characters.
                                                             (line  181)
* isupper() (str method):                String Methods<2>.  (line  281)
* isvisible() (in module turtle):        Visibility.         (line   22)
* isxdigit() (in module curses.ascii):   curses ascii — Utilities for ASCII characters.
                                                             (line  185)
* is_() (in module operator):            operator — Standard operators as functions.
                                                             (line   63)
* is_absolute() (pathlib.PurePath method): Methods and properties.
                                                             (line  165)
* is_active() (asyncio.AbstractChildWatcher method): Process Watchers.
                                                             (line   68)
* is_active() (graphlib.TopologicalSorter method): graphlib — Functionality to operate with graph-like structures.
                                                             (line  109)
* is_alive() (multiprocessing.Process method): Process and exceptions.
                                                             (line   79)
* is_alive() (threading.Thread method):  Thread Objects.     (line  175)
* is_android (in module test.support):   test support — Utilities for the Python test suite.
                                                             (line   40)
* is_annotated() (symtable.Symbol method): Examining Symbol Tables.
                                                             (line  138)
* is_assigned() (symtable.Symbol method): Examining Symbol Tables.
                                                             (line  149)
* is_attachment() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  445)
* is_authenticated() (urllib.request.HTTPPasswordMgrWithPriorAuth method): HTTPPasswordMgrWithPriorAuth Objects.
                                                             (line   30)
* is_blocked() (http.cookiejar.DefaultCookiePolicy method): DefaultCookiePolicy Objects.
                                                             (line   60)
* is_block_device() (pathlib.Path method): Methods<2>.       (line  182)
* is_canonical() (decimal.Context method): Context objects.  (line  292)
* is_canonical() (decimal.Decimal method): Decimal objects.  (line  278)
* IS_CHARACTER_JUNK() (in module difflib): difflib — Helpers for computing deltas.
                                                             (line  364)
* is_char_device() (pathlib.Path method): Methods<2>.        (line  191)
* is_check_supported() (in module lzma): Miscellaneous<2>.   (line    6)
* is_closed() (asyncio.loop method):     Running and stopping the loop.
                                                             (line   39)
* is_closing() (asyncio.BaseTransport method): Base Transport.
                                                             (line   16)
* is_closing() (asyncio.StreamWriter method): StreamWriter.  (line   81)
* is_dataclass() (in module dataclasses): Module-level decorators classes and functions.
                                                             (line  384)
* is_declared_global() (symtable.Symbol method): Examining Symbol Tables.
                                                             (line  129)
* is_dir() (importlib.abc.Traversable method): importlib abc – Abstract base classes related to import.
                                                             (line  629)
* is_dir() (os.DirEntry method):         Files and Directories.
                                                             (line  883)
* is_dir() (pathlib.Path method):        Methods<2>.         (line  127)
* is_dir() (zipfile.Path method):        Path Objects.       (line   41)
* is_dir() (zipfile.ZipInfo method):     ZipInfo Objects.    (line   42)
* is_enabled() (in module faulthandler): Fault handler state.
                                                             (line   27)
* is_expired() (http.cookiejar.Cookie method): Cookie Objects<2>.
                                                             (line  109)
* is_fifo() (pathlib.Path method):       Methods<2>.         (line  174)
* is_file() (importlib.abc.Traversable method): importlib abc – Abstract base classes related to import.
                                                             (line  633)
* is_file() (os.DirEntry method):        Files and Directories.
                                                             (line  912)
* is_file() (pathlib.Path method):       Methods<2>.         (line  136)
* is_file() (zipfile.Path method):       Path Objects.       (line   45)
* is_finalized() (in module gc):         gc — Garbage Collector interface.
                                                             (line  182)
* is_finalizing() (in module sys):       sys — System-specific parameters and functions.
                                                             (line  983)
* is_finite() (decimal.Context method):  Context objects.    (line  296)
* is_finite() (decimal.Decimal method):  Decimal objects.    (line  285)
* is_free() (symtable.Symbol method):    Examining Symbol Tables.
                                                             (line  144)
* is_global (ipaddress.IPv4Address attribute): Address objects.
                                                             (line  109)
* is_global (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  220)
* is_global() (symtable.Symbol method):  Examining Symbol Tables.
                                                             (line  121)
* is_hop_by_hop() (in module wsgiref.util): wsgiref util – WSGI environment utilities.
                                                             (line  109)
* is_imported() (symtable.Symbol method): Examining Symbol Tables.
                                                             (line  112)
* is_infinite() (decimal.Context method): Context objects.   (line  300)
* is_infinite() (decimal.Decimal method): Decimal objects.   (line  290)
* is_integer() (float method):           Additional Methods on Float.
                                                             (line   16)
* is_jython (in module test.support):    test support — Utilities for the Python test suite.
                                                             (line   36)
* is_linetouched() (curses.window method): Window Objects.   (line  365)
* IS_LINE_JUNK() (in module difflib):    difflib — Helpers for computing deltas.
                                                             (line  357)
* is_link_local (ipaddress.IPv4Address attribute): Address objects.
                                                             (line  131)
* is_link_local (ipaddress.IPv4Network attribute): Network objects.
                                                             (line   80)
* is_link_local (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  228)
* is_link_local (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  307)
* is_local() (symtable.Symbol method):   Examining Symbol Tables.
                                                             (line  134)
* is_loopback (ipaddress.IPv4Address attribute): Address objects.
                                                             (line  126)
* is_loopback (ipaddress.IPv4Network attribute): Network objects.
                                                             (line   78)
* is_loopback (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  226)
* is_loopback (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  305)
* is_mount() (pathlib.Path method):      Methods<2>.         (line  145)
* is_multicast (ipaddress.IPv4Address attribute): Address objects.
                                                             (line   98)
* is_multicast (ipaddress.IPv4Network attribute): Network objects.
                                                             (line   70)
* is_multicast (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  216)
* is_multicast (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  297)
* is_multipart() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  134)
* is_multipart() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  145)
* is_namespace() (symtable.Symbol method): Examining Symbol Tables.
                                                             (line  153)
* is_nan() (decimal.Context method):     Context objects.    (line  304)
* is_nan() (decimal.Decimal method):     Decimal objects.    (line  295)
* is_nested() (symtable.SymbolTable method): Examining Symbol Tables.
                                                             (line   35)
* is_nonlocal() (symtable.Symbol method): Examining Symbol Tables.
                                                             (line  125)
* is_normal() (decimal.Context method):  Context objects.    (line  309)
* is_normal() (decimal.Decimal method):  Decimal objects.    (line  300)
* is_normalized() (in module unicodedata): unicodedata — Unicode Database.
                                                             (line  117)
* is_not() (in module operator):         operator — Standard operators as functions.
                                                             (line   67)
* is_not_allowed() (http.cookiejar.DefaultCookiePolicy method): DefaultCookiePolicy Objects.
                                                             (line   74)
* IS_OP (opcode):                        Python Bytecode Instructions.
                                                             (line  560)
* is_optimized() (symtable.SymbolTable method): Examining Symbol Tables.
                                                             (line   31)
* is_package() (importlib.abc.InspectLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  415)
* is_package() (importlib.abc.SourceLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  606)
* is_package() (importlib.machinery.ExtensionFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  333)
* is_package() (importlib.machinery.SourceFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  232)
* is_package() (importlib.machinery.SourcelessFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  276)
* is_package() (zipimport.zipimporter method): zipimporter Objects.
                                                             (line   56)
* is_parameter() (symtable.Symbol method): Examining Symbol Tables.
                                                             (line  117)
* is_private (ipaddress.IPv4Address attribute): Address objects.
                                                             (line  103)
* is_private (ipaddress.IPv4Network attribute): Network objects.
                                                             (line   72)
* is_private (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  218)
* is_private (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  299)
* is_python_build() (in module sysconfig): Other functions<3>.
                                                             (line   50)
* is_qnan() (decimal.Context method):    Context objects.    (line  314)
* is_qnan() (decimal.Decimal method):    Decimal objects.    (line  306)
* is_reading() (asyncio.ReadTransport method): Read-only Transports.
                                                             (line    6)
* is_referenced() (symtable.Symbol method): Examining Symbol Tables.
                                                             (line  108)
* is_relative_to() (pathlib.PurePath method): Methods and properties.
                                                             (line  184)
* is_reserved (ipaddress.IPv4Address attribute): Address objects.
                                                             (line  122)
* is_reserved (ipaddress.IPv4Network attribute): Network objects.
                                                             (line   76)
* is_reserved (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  224)
* is_reserved (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  303)
* is_reserved() (pathlib.PurePath method): Methods and properties.
                                                             (line  196)
* is_resource() (importlib.abc.ResourceReader method): importlib abc – Abstract base classes related to import.
                                                             (line  336)
* is_resource() (in module importlib.resources): importlib resources – Resources.
                                                             (line  147)
* is_resource_enabled() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  257)
* is_running() (asyncio.loop method):    Running and stopping the loop.
                                                             (line   35)
* is_safe (uuid.UUID attribute):         uuid — UUID objects according to RFC 4122.
                                                             (line  151)
* is_serving() (asyncio.Server method):  Server Objects.     (line   89)
* is_set() (asyncio.Event method):       Event.              (line   66)
* is_set() (threading.Event method):     Event Objects.      (line   23)
* is_signed() (decimal.Context method):  Context objects.    (line  319)
* is_signed() (decimal.Decimal method):  Decimal objects.    (line  311)
* is_site_local (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  232)
* is_site_local (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  357)
* is_snan() (decimal.Context method):    Context objects.    (line  323)
* is_snan() (decimal.Decimal method):    Decimal objects.    (line  317)
* is_socket() (pathlib.Path method):     Methods<2>.         (line  165)
* is_subnormal() (decimal.Context method): Context objects.  (line  328)
* is_subnormal() (decimal.Decimal method): Decimal objects.  (line  322)
* is_symlink() (os.DirEntry method):     Files and Directories.
                                                             (line  928)
* is_symlink() (pathlib.Path method):    Methods<2>.         (line  157)
* is_tarfile() (in module tarfile):      tarfile — Read and write tar archive files.
                                                             (line  179)
* is_term_resized() (in module curses):  Functions<4>.       (line  237)
* is_tracing() (in module tracemalloc):  Functions<10>.      (line   61)
* is_tracked() (in module gc):           gc — Garbage Collector interface.
                                                             (line  157)
* is_unspecified (ipaddress.IPv4Address attribute): Address objects.
                                                             (line  117)
* is_unspecified (ipaddress.IPv4Network attribute): Network objects.
                                                             (line   74)
* is_unspecified (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  222)
* is_unspecified (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  301)
* is_wintouched() (curses.window method): Window Objects.    (line  372)
* is_zero() (decimal.Context method):    Context objects.    (line  332)
* is_zero() (decimal.Decimal method):    Decimal objects.    (line  327)
* is_zipfile() (in module zipfile):      zipfile — Work with ZIP archives.
                                                             (line   71)
* ITALIC (in module tkinter.font):       tkinter font — Tkinter font wrapper.
                                                             (line   15)
* item selection:                        The standard type hierarchy.
                                                             (line  132)
* item() (tkinter.ttk.Treeview method):  ttk Treeview.       (line  212)
* item() (xml.dom.NamedNodeMap method):  NamedNodeMap Objects.
                                                             (line   12)
* item() (xml.dom.NodeList method):      NodeList Objects.   (line   15)
* itemgetter() (in module operator):     operator — Standard operators as functions.
                                                             (line  258)
* items() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  235)
* items() (contextvars.Context method):  Manual Context Management.
                                                             (line  108)
* items() (dict method):                 Mapping Types — dict.
                                                             (line  169)
* items() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  240)
* items() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  348)
* items() (mailbox.Mailbox method):      Mailbox objects.    (line  129)
* items() (types.MappingProxyType method): Standard Interpreter Types.
                                                             (line  279)
* items() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line   71)
* itemsize (array.array attribute):      array — Efficient arrays of numeric values.
                                                             (line  108)
* itemsize (memoryview attribute):       Memory Views.       (line  429)
* ItemsView (class in collections.abc):  Collections Abstract Base Classes.
                                                             (line  187)
* ItemsView (class in typing):           Corresponding to collections in collections abc.
                                                             (line   45)
* iter() (built-in function):            Built-in Functions. (line  864)
* iter() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line  136)
* iter() (xml.etree.ElementTree.ElementTree method): ElementTree Objects.
                                                             (line   40)
* iterable:                              Glossary.           (line  676)
* Iterable (class in collections.abc):   Collections Abstract Base Classes.
                                                             (line  120)
* Iterable (class in typing):            Corresponding to other types in collections abc.
                                                             (line    6)
* iterable; unpacking:                   Expression lists.   (line   16)
* iterator:                              Glossary.           (line  698)
* Iterator (class in collections.abc):   Collections Abstract Base Classes.
                                                             (line  137)
* Iterator (class in typing):            Corresponding to other types in collections abc.
                                                             (line   14)
* iterator protocol:                     Iterator Types.     (line    6)
* iterdecode() (in module codecs):       codecs — Codec registry and base classes.
                                                             (line  228)
* iterdir() (importlib.abc.Traversable method): importlib abc – Abstract base classes related to import.
                                                             (line  625)
* iterdir() (pathlib.Path method):       Methods<2>.         (line  200)
* iterdir() (zipfile.Path method):       Path Objects.       (line   37)
* iterdump() (sqlite3.Connection method): Connection Objects.
                                                             (line  392)
* iterencode() (in module codecs):       codecs — Codec registry and base classes.
                                                             (line  216)
* iterencode() (json.JSONEncoder method): Encoders and Decoders.
                                                             (line  225)
* iterfind() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line  147)
* iterfind() (xml.etree.ElementTree.ElementTree method): ElementTree Objects.
                                                             (line   47)
* iteritems() (mailbox.Mailbox method):  Mailbox objects.    (line  129)
* iterkeys() (mailbox.Mailbox method):   Mailbox objects.    (line  107)
* itermonthdates() (calendar.Calendar method): calendar — General calendar-related functions.
                                                             (line   45)
* itermonthdays() (calendar.Calendar method): calendar — General calendar-related functions.
                                                             (line   53)
* itermonthdays2() (calendar.Calendar method): calendar — General calendar-related functions.
                                                             (line   61)
* itermonthdays3() (calendar.Calendar method): calendar — General calendar-related functions.
                                                             (line   69)
* itermonthdays4() (calendar.Calendar method): calendar — General calendar-related functions.
                                                             (line   79)
* iternextfunc (C type):                 Slot Type typedefs. (line   88)
* iterparse() (in module xml.etree.ElementTree): Functions<7>.
                                                             (line  136)
* itertext() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line  156)
* itertools (2to3 fixer):                Fixers.             (line  174)
* itertools (module):                    itertools — Functions creating iterators for efficient looping.
                                                             (line    6)
* itertools_imports (2to3 fixer):        Fixers.             (line  168)
* itervalues() (mailbox.Mailbox method): Mailbox objects.    (line  114)
* iterweekdays() (calendar.Calendar method): calendar — General calendar-related functions.
                                                             (line   39)
* iter_attachments() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  560)
* iter_child_nodes() (in module ast):    ast Helpers.        (line  143)
* iter_fields() (in module ast):         ast Helpers.        (line  138)
* iter_importers() (in module pkgutil):  pkgutil — Package extension utility.
                                                             (line  123)
* iter_modules() (in module pkgutil):    pkgutil — Package extension utility.
                                                             (line  141)
* iter_parts() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  576)
* iter_unpack() (in module struct):      Functions and Exceptions.
                                                             (line   42)
* iter_unpack() (struct.Struct method):  Classes<2>.         (line   47)
* ItimerError:                           Module contents<2>. (line  211)
* ITIMER_PROF (in module signal):        Module contents<2>. (line  178)
* ITIMER_REAL (in module signal):        Module contents<2>. (line  168)
* ITIMER_VIRTUAL (in module signal):     Module contents<2>. (line  173)
* itruediv() (in module operator):       In-place Operators. (line   99)
* ixor() (in module operator):           In-place Operators. (line  104)
* j; in numeric literal:                 Floating point literals.
                                                             (line   28)
* Jansen, Jack:                          uu — Encode and decode uuencode files.
                                                             (line   20)
* Java; language:                        The standard type hierarchy.
                                                             (line  112)
* java_ver() (in module platform):       Java Platform.      (line    6)
* join() (asyncio.Queue method):         Queue.              (line   50)
* join() (bytearray method):             Bytes and Bytearray Operations.
                                                             (line  159)
* join() (bytes method):                 Bytes and Bytearray Operations.
                                                             (line  159)
* join() (in module os.path):            os path — Common pathname manipulations.
                                                             (line  254)
* join() (in module shlex):              shlex — Simple lexical analysis.
                                                             (line   33)
* join() (multiprocessing.JoinableQueue method): Pipes and Queues.
                                                             (line  252)
* join() (multiprocessing.pool.Pool method): Process Pools.  (line  180)
* join() (multiprocessing.Process method): Process and exceptions.
                                                             (line   51)
* join() (queue.Queue method):           Queue Objects.      (line   83)
* join() (str method):                   String Methods<2>.  (line  296)
* join() (threading.Thread method):      Thread Objects.     (line  110)
* JoinableQueue (class in multiprocessing): Pipes and Queues.
                                                             (line  231)
* JoinedStr (class in ast):              Literals<3>.        (line   42)
* joinpath() (importlib.abc.Traversable method): importlib abc – Abstract base classes related to import.
                                                             (line  637)
* joinpath() (pathlib.PurePath method):  Methods and properties.
                                                             (line  210)
* join_thread() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  852)
* join_thread() (multiprocessing.Queue method): Pipes and Queues.
                                                             (line  170)
* json (module):                         json — JSON encoder and decoder.
                                                             (line    6)
* json.tool (module):                    Command Line Interface<2>.
                                                             (line    6)
* json.tool command line option; –compact: Command line options<2>.
                                                             (line   48)
* json.tool command line option; -h:     Command line options<2>.
                                                             (line   54)
* json.tool command line option; –help:  Command line options<2>.
                                                             (line   54)
* json.tool command line option; –indent: Command line options<2>.
                                                             (line   48)
* json.tool command line option; –json-lines: Command line options<2>.
                                                             (line   42)
* json.tool command line option; –no-ensure-ascii: Command line options<2>.
                                                             (line   35)
* json.tool command line option; –no-indent: Command line options<2>.
                                                             (line   48)
* json.tool command line option; –sort-keys: Command line options<2>.
                                                             (line   29)
* json.tool command line option; –tab:   Command line options<2>.
                                                             (line   48)
* json.tool command line option; infile: Command line options<2>.
                                                             (line    6)
* json.tool command line option; outfile: Command line options<2>.
                                                             (line   24)
* JSONDecodeError:                       Exceptions<14>.     (line    6)
* JSONDecoder (class in json):           Encoders and Decoders.
                                                             (line    6)
* JSONEncoder (class in json):           Encoders and Decoders.
                                                             (line  103)
* js_output() (http.cookies.BaseCookie method): Cookie Objects.
                                                             (line   32)
* js_output() (http.cookies.Morsel method): Morsel Objects.  (line   79)
* jump (pdb command):                    Debugger Commands.  (line  196)
* JUMP_ABSOLUTE (opcode):                Python Bytecode Instructions.
                                                             (line  627)
* JUMP_FORWARD (opcode):                 Python Bytecode Instructions.
                                                             (line  587)
* JUMP_IF_FALSE_OR_POP (opcode):         Python Bytecode Instructions.
                                                             (line  620)
* JUMP_IF_NOT_EXC_MATCH (opcode):        Python Bytecode Instructions.
                                                             (line  605)
* JUMP_IF_TRUE_OR_POP (opcode):          Python Bytecode Instructions.
                                                             (line  613)
* kbhit() (in module msvcrt):            Console I/O.        (line    6)
* KDEDIR:                                webbrowser — Convenient Web-browser controller.
                                                             (line  184)
* kevent() (in module select):           select — Waiting for I/O completion.
                                                             (line  103)
* key:                                   Dictionary displays.
                                                             (line    6)
* key (http.cookies.Morsel attribute):   Morsel Objects.     (line   60)
* key (zoneinfo.ZoneInfo attribute):     The ZoneInfo class. (line   75)
* key function:                          Glossary.           (line  720)
* key/datum pair:                        Dictionary displays.
                                                             (line    6)
* KeyboardInterrupt:                     Concrete exceptions.
                                                             (line   70)
* KeyboardInterrupt (built-in exception): Signal Handling<2>.
                                                             (line    8)
* KeyboardInterrupt (built-in exception) <1>: Signal Handling<2>.
                                                             (line   20)
* KeyError:                              Concrete exceptions.
                                                             (line   65)
* keylog_filename (ssl.SSLContext attribute): SSL Contexts.  (line  529)
* keyname() (in module curses):          Functions<4>.       (line  247)
* keypad() (curses.window method):       Window Objects.     (line  377)
* keyrefs() (weakref.WeakKeyDictionary method): weakref — Weak references.
                                                             (line  182)
* keys() (contextvars.Context method):   Manual Context Management.
                                                             (line  100)
* keys() (dict method):                  Mapping Types — dict.
                                                             (line  174)
* keys() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  232)
* keys() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  340)
* keys() (mailbox.Mailbox method):       Mailbox objects.    (line  107)
* keys() (sqlite3.Row method):           Row Objects.        (line   18)
* keys() (types.MappingProxyType method): Standard Interpreter Types.
                                                             (line  284)
* keys() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line   76)
* KeysView (class in collections.abc):   Collections Abstract Base Classes.
                                                             (line  187)
* KeysView (class in typing):            Corresponding to collections in collections abc.
                                                             (line   53)
* keyword:                               Keywords.           (line    6)
* keyword (class in ast):                Expressions<2>.     (line  152)
* keyword (module):                      keyword — Testing for Python keywords.
                                                             (line    6)
* keyword argument:                      Glossary.           (line  742)
* keyword; as:                           The import statement.
                                                             (line    6)
* keyword; as <1>:                       The try statement.  (line    6)
* keyword; as <2>:                       The with statement. (line    6)
* keyword; async:                        Coroutine function definition.
                                                             (line    9)
* keyword; await:                        Calls.              (line  149)
* keyword; await <1>:                    Coroutine function definition.
                                                             (line    9)
* keyword; elif:                         The if statement.   (line    6)
* keyword; else:                         The break statement.
                                                             (line   12)
* keyword; else <1>:                     The if statement.   (line    6)
* keyword; else <2>:                     The while statement.
                                                             (line    6)
* keyword; else <3>:                     The for statement.  (line    6)
* keyword; else <4>:                     The try statement.  (line    6)
* keyword; else <5>:                     The try statement.  (line   79)
* keyword; except:                       The try statement.  (line    6)
* keyword; finally:                      The return statement.
                                                             (line   17)
* keyword; finally <1>:                  The break statement.
                                                             (line   18)
* keyword; finally <2>:                  The continue statement.
                                                             (line    6)
* keyword; finally <3>:                  The try statement.  (line    6)
* keyword; finally <4>:                  The try statement.  (line   85)
* keyword; from:                         Yield expressions.  (line    6)
* keyword; from <1>:                     The import statement.
                                                             (line    6)
* keyword; in:                           The for statement.  (line    6)
* keyword; yield:                        Yield expressions.  (line    6)
* keywords (functools.partial attribute): partial Objects.   (line   20)
* KEY_ALL_ACCESS (in module winreg):     Access Rights.      (line    8)
* KEY_CREATE_LINK (in module winreg):    Access Rights.      (line   51)
* KEY_CREATE_SUB_KEY (in module winreg): Access Rights.      (line   38)
* KEY_ENUMERATE_SUB_KEYS (in module winreg): Access Rights.  (line   42)
* KEY_EXECUTE (in module winreg):        Access Rights.      (line   26)
* KEY_NOTIFY (in module winreg):         Access Rights.      (line   46)
* KEY_QUERY_VALUE (in module winreg):    Access Rights.      (line   30)
* KEY_READ (in module winreg):           Access Rights.      (line   20)
* KEY_SET_VALUE (in module winreg):      Access Rights.      (line   34)
* KEY_WOW64_32KEY (in module winreg):    64-bit Specific.    (line   13)
* KEY_WOW64_64KEY (in module winreg):    64-bit Specific.    (line    8)
* KEY_WRITE (in module winreg):          Access Rights.      (line   15)
* kill() (asyncio.asyncio.subprocess.Process method): Interacting with Subprocesses.
                                                             (line  100)
* kill() (asyncio.SubprocessTransport method): Subprocess Transports.
                                                             (line   35)
* kill() (in module os):                 Process Management. (line  287)
* kill() (multiprocessing.Process method): Process and exceptions.
                                                             (line  166)
* kill() (subprocess.Popen method):      Popen Objects.      (line   91)
* killchar() (in module curses):         Functions<4>.       (line  257)
* killpg() (in module os):               Process Management. (line  309)
* kill_python() (in module test.support.script_helper): test support script_helper — Utilities for the Python execution tests.
                                                             (line   76)
* kind (inspect.Parameter attribute):    Introspecting callables with the Signature object.
                                                             (line  181)
* knownfiles (in module mimetypes):      mimetypes — Map filenames to MIME types.
                                                             (line  122)
* kqueue() (in module select):           select — Waiting for I/O completion.
                                                             (line   92)
* KqueueSelector (class in selectors):   Classes<3>.         (line  195)
* kwargs (inspect.BoundArguments attribute): Introspecting callables with the Signature object.
                                                             (line  306)
* kwlist (in module keyword):            keyword — Testing for Python keywords.
                                                             (line   17)
* L (in module re):                      Module Contents.    (line   81)
* LabelEntry (class in tkinter.tix):     Basic Widgets.      (line   31)
* LabelFrame (class in tkinter.tix):     Basic Widgets.      (line   37)
* lambda:                                Glossary.           (line  746)
* Lambda (class in ast):                 Function and class definitions.
                                                             (line   28)
* lambda; expression:                    Lambdas.            (line    6)
* lambda; expression <1>:                Function definitions.
                                                             (line  112)
* lambda; form:                          Lambdas.            (line    6)
* LambdaType (in module types):          Standard Interpreter Types.
                                                             (line   19)
* LANG:                                  GNU gettext API.    (line   21)
* LANG <1>:                              Class-based API.    (line   26)
* LANG <2>:                              locale — Internationalization services.
                                                             (line   49)
* LANG <3>:                              locale — Internationalization services.
                                                             (line  310)
* LANG <4>:                              locale — Internationalization services.
                                                             (line  314)
* LANGUAGE:                              GNU gettext API.    (line   20)
* LANGUAGE <1>:                          Class-based API.    (line   25)
* large files:                           Large File Support. (line    6)
* LARGEST (in module test.support):      test support — Utilities for the Python test suite.
                                                             (line  210)
* LargeZipFile:                          zipfile — Work with ZIP archives.
                                                             (line   37)
* last() (nntplib.NNTP method):          Methods<3>.         (line  237)
* lastChild (xml.dom.Node attribute):    Node Objects.       (line   59)
* lastcmd (cmd.Cmd attribute):           Cmd Objects.        (line  131)
* lastgroup (re.Match attribute):        Match Objects.      (line  186)
* lastindex (re.Match attribute):        Match Objects.      (line  178)
* lastResort (in module logging):        Module-Level Attributes.
                                                             (line    6)
* lastrowid (sqlite3.Cursor attribute):  Cursor Objects.     (line  185)
* last_accepted (multiprocessing.connection.Listener attribute): Listeners and Clients.
                                                             (line  103)
* last_traceback (in module sys):        The standard type hierarchy.
                                                             (line  765)
* last_traceback (in module sys) <1>:    sys — System-specific parameters and functions.
                                                             (line  990)
* last_type (in module sys):             sys — System-specific parameters and functions.
                                                             (line  990)
* last_value (in module sys):            sys — System-specific parameters and functions.
                                                             (line  990)
* layout() (tkinter.ttk.Style method):   Ttk Styling.        (line   96)
* lazycache() (in module linecache):     linecache — Random access to text lines.
                                                             (line   50)
* LazyLoader (class in importlib.util):  importlib util – Utility code for importers.
                                                             (line  229)
* LBRACE (in module token):              token — Constants used with Python parse trees.
                                                             (line  126)
* LBYL:                                  Glossary.           (line  753)
* lchflags() (in module os):             Files and Directories.
                                                             (line  292)
* lchmod() (in module os):               Files and Directories.
                                                             (line  306)
* lchmod() (pathlib.Path method):        Methods<2>.         (line  221)
* lchown() (in module os):               Files and Directories.
                                                             (line  321)
* lcm() (in module math):                Number-theoretic and representation functions.
                                                             (line  174)
* LC_ALL:                                GNU gettext API.    (line   20)
* LC_ALL <1>:                            Class-based API.    (line   25)
* LC_ALL (in module locale):             locale — Internationalization services.
                                                             (line  495)
* LC_COLLATE (in module locale):         locale — Internationalization services.
                                                             (line  464)
* LC_CTYPE (in module locale):           locale — Internationalization services.
                                                             (line  458)
* LC_MESSAGES:                           GNU gettext API.    (line   20)
* LC_MESSAGES <1>:                       Class-based API.    (line   26)
* LC_MESSAGES (in module locale):        locale — Internationalization services.
                                                             (line  480)
* LC_MONETARY (in module locale):        locale — Internationalization services.
                                                             (line  475)
* LC_NUMERIC (in module locale):         locale — Internationalization services.
                                                             (line  487)
* LC_TIME (in module locale):            locale — Internationalization services.
                                                             (line  470)
* LDCXXSHARED:                           Build and C API Changes<8>.
                                                             (line  153)
* ldexp() (in module math):              Number-theoretic and representation functions.
                                                             (line  184)
* LDFLAGS:                               New Improved and Deprecated Modules<4>.
                                                             (line   59)
* ldgettext() (in module gettext):       GNU gettext API.    (line   90)
* ldngettext() (in module gettext):      GNU gettext API.    (line   94)
* le() (in module operator):             operator — Standard operators as functions.
                                                             (line   24)
* leading whitespace:                    Indentation.        (line    6)
* leapdays() (in module calendar):       calendar — General calendar-related functions.
                                                             (line  306)
* leaveok() (curses.window method):      Window Objects.     (line  384)
* left (filecmp.dircmp attribute):       The dircmp class.   (line   41)
* left() (in module turtle):             Turtle motion.      (line   57)
* LEFTSHIFT (in module token):           token — Constants used with Python parse trees.
                                                             (line  158)
* LEFTSHIFTEQUAL (in module token):      token — Constants used with Python parse trees.
                                                             (line  202)
* left_list (filecmp.dircmp attribute):  The dircmp class.   (line   49)
* left_only (filecmp.dircmp attribute):  The dircmp class.   (line   63)
* len() (built-in function):             Built-in Functions. (line  891)
* lenfunc (C type):                      Slot Type typedefs. (line   92)
* length (xml.dom.NamedNodeMap attribute): NamedNodeMap Objects.
                                                             (line    8)
* length (xml.dom.NodeList attribute):   NodeList Objects.   (line   21)
* length_hint() (in module operator):    operator — Standard operators as functions.
                                                             (line  206)
* LESS (in module token):                token — Constants used with Python parse trees.
                                                             (line  106)
* LESSEQUAL (in module token):           token — Constants used with Python parse trees.
                                                             (line  142)
* lexical analysis:                      Lexical analysis.   (line    6)
* lexical definitions:                   Notation.           (line   31)
* lexists() (in module os.path):         os path — Common pathname manipulations.
                                                             (line  127)
* lgamma() (in module math):             Special functions.  (line   35)
* lgettext() (gettext.GNUTranslations method): The GNUTranslations class.
                                                             (line   93)
* lgettext() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line   63)
* lgettext() (in module gettext):        GNU gettext API.    (line   88)
* lib2to3 (module):                      lib2to3 - 2to3’s library.
                                                             (line    6)
* libc_ver() (in module platform):       Unix Platforms.     (line    6)
* library (in module dbm.ndbm):          dbm ndbm — Interface based on ndbm.
                                                             (line   27)
* library (ssl.SSLError attribute):      Exceptions<13>.     (line   19)
* LibraryLoader (class in ctypes):       Loading shared libraries.
                                                             (line  158)
* library_dir_option() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  220)
* library_filename() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  459)
* library_option() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  225)
* license (built-in variable):           Constants added by the site module.
                                                             (line   24)
* LifoQueue (class in asyncio):          LIFO Queue.         (line    6)
* LifoQueue (class in queue):            queue — A synchronized queue class.
                                                             (line   42)
* light-weight processes:                _thread — Low-level threading API.
                                                             (line    6)
* LimitOverrunError:                     Exceptions<10>.     (line   59)
* limit_denominator() (fractions.Fraction method): fractions — Rational numbers.
                                                             (line  131)
* lin2adpcm() (in module audioop):       audioop — Manipulate raw audio data.
                                                             (line  112)
* lin2alaw() (in module audioop):        audioop — Manipulate raw audio data.
                                                             (line  126)
* lin2lin() (in module audioop):         audioop — Manipulate raw audio data.
                                                             (line  133)
* lin2ulaw() (in module audioop):        audioop — Manipulate raw audio data.
                                                             (line  148)
* line continuation:                     Explicit line joining.
                                                             (line    6)
* line joining:                          Logical lines.      (line    6)
* line joining <1>:                      Explicit line joining.
                                                             (line    6)
* line structure:                        Line structure.     (line    6)
* line() (msilib.Dialog method):         GUI classes.        (line   64)
* line-buffered I/O:                     Built-in Functions. (line 1223)
* linecache (module):                    linecache — Random access to text lines.
                                                             (line    6)
* lineno (ast.AST attribute):            Node classes.       (line   39)
* lineno (doctest.DocTest attribute):    DocTest Objects.    (line   42)
* lineno (doctest.Example attribute):    Example Objects.    (line   41)
* lineno (json.JSONDecodeError attribute): Exceptions<14>.   (line   23)
* lineno (pyclbr.Class attribute):       Class Objects<2>.   (line   21)
* lineno (pyclbr.Function attribute):    Function Objects.   (line   21)
* lineno (re.error attribute):           Module Contents.    (line  385)
* lineno (shlex.shlex attribute):        shlex Objects.      (line  169)
* lineno (SyntaxError attribute):        Concrete exceptions.
                                                             (line  263)
* lineno (traceback.TracebackException attribute): TracebackException Objects.
                                                             (line   46)
* lineno (tracemalloc.Filter attribute): Filter.             (line   48)
* lineno (tracemalloc.Frame attribute):  Frame.              (line   17)
* lineno (xml.parsers.expat.ExpatError attribute): ExpatError Exceptions.
                                                             (line   27)
* lineno() (in module fileinput):        fileinput — Iterate over lines from multiple input streams.
                                                             (line   92)
* LINES:                                 curses<3>.          (line    6)
* LINES <1>:                             Functions<4>.       (line  125)
* LINES <2>:                             Functions<4>.       (line  555)
* LINES <3>:                             Functions<4>.       (line  579)
* LINES <4>:                             Functions<4>.       (line  581)
* lines (os.terminal_size attribute):    Querying the size of a terminal.
                                                             (line   34)
* linesep (email.policy.Policy attribute): email policy Policy Objects.
                                                             (line  152)
* linesep (in module os):                Miscellaneous System Information.
                                                             (line  127)
* lineterminator (csv.Dialect attribute): Dialects and Formatting Parameters.
                                                             (line   43)
* LineTooLong:                           http client — HTTP protocol client.
                                                             (line  179)
* line_buffering (io.TextIOWrapper attribute): Text I/O<2>.  (line  164)
* line_num (csv.csvreader attribute):    Reader Objects.     (line   23)
* link() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  349)
* link() (in module os):                 Files and Directories.
                                                             (line  335)
* linkname (tarfile.TarInfo attribute):  TarInfo Objects.    (line   67)
* link_executable() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  401)
* link_shared_lib() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  411)
* link_shared_object() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  422)
* link_to() (pathlib.Path method):       Methods<2>.         (line  437)
* list:                                  Glossary.           (line  767)
* list (built-in class):                 Lists<2>.           (line   10)
* List (class in ast):                   Literals<3>.        (line   67)
* List (class in typing):                Corresponding to built-in types.
                                                             (line   20)
* list (pdb command):                    Debugger Commands.  (line  206)
* list comprehension:                    Glossary.           (line  773)
* list() (imaplib.IMAP4 method):         IMAP4 Objects.      (line  126)
* list() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  214)
* list() (nntplib.NNTP method):          Methods<3>.         (line  104)
* list() (poplib.POP3 method):           POP3 Objects.       (line   56)
* list() (tarfile.TarFile method):       TarFile Objects.    (line  120)
* list; comprehensions:                  List displays.      (line    6)
* list; display:                         List displays.      (line    6)
* ListComp (class in ast):               Comprehensions.     (line    6)
* listdir() (in module os):              Files and Directories.
                                                             (line  357)
* listen() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  215)
* listen() (in module logging.config):   Configuration functions.
                                                             (line  107)
* listen() (in module turtle):           Using screen events.
                                                             (line    6)
* listen() (socket.socket method):       Socket Objects.     (line  186)
* Listener (class in multiprocessing.connection): Listeners and Clients.
                                                             (line   50)
* listMethods() (xmlrpc.client.ServerProxy.system method): ServerProxy Objects.
                                                             (line   17)
* ListNoteBook (class in tkinter.tix):   Manager Widgets.    (line   13)
* listxattr() (in module os):            Linux extended attributes.
                                                             (line   26)
* LIST_APPEND (opcode):                  Python Bytecode Instructions.
                                                             (line  322)
* list_dialects() (in module csv):       Module Contents<3>. (line   92)
* LIST_EXTEND (opcode):                  Python Bytecode Instructions.
                                                             (line  526)
* list_folders() (mailbox.Maildir method): Maildir.          (line   61)
* list_folders() (mailbox.MH method):    MH.                 (line   32)
* LIST_TO_TUPLE (opcode):                Python Bytecode Instructions.
                                                             (line  519)
* literal:                               Literals.           (line    6)
* literal <1>:                           Literals<2>.        (line    6)
* Literal (in module typing):            Special forms.      (line  146)
* literal_eval() (in module ast):        ast Helpers.        (line   74)
* LittleEndianStructure (class in ctypes): Structured data types.
                                                             (line   14)
* ljust() (bytearray method):            Bytes and Bytearray Operations.
                                                             (line  296)
* ljust() (bytes method):                Bytes and Bytearray Operations.
                                                             (line  296)
* ljust() (str method):                  String Methods<2>.  (line  304)
* LK_LOCK (in module msvcrt):            File Operations.    (line   19)
* LK_NBLCK (in module msvcrt):           File Operations.    (line   27)
* LK_NBRLCK (in module msvcrt):          File Operations.    (line   27)
* LK_RLCK (in module msvcrt):            File Operations.    (line   19)
* LK_UNLCK (in module msvcrt):           File Operations.    (line   33)
* ll (pdb command):                      Debugger Commands.  (line  222)
* LMTP (class in smtplib):               smtplib — SMTP protocol client.
                                                             (line  108)
* ln() (decimal.Context method):         Context objects.    (line  336)
* ln() (decimal.Decimal method):         Decimal objects.    (line  332)
* LNAME:                                 getpass — Portable password input.
                                                             (line   38)
* lngettext() (gettext.GNUTranslations method): The GNUTranslations class.
                                                             (line   95)
* lngettext() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line   65)
* lngettext() (in module gettext):       GNU gettext API.    (line   92)
* Load (class in ast):                   Variables.          (line   11)
* load() (http.cookiejar.FileCookieJar method): CookieJar and FileCookieJar Objects.
                                                             (line  125)
* load() (http.cookies.BaseCookie method): Cookie Objects.   (line   40)
* load() (in module json):               Basic Usage.        (line   94)
* load() (in module marshal):            marshal — Internal Python object serialization.
                                                             (line   63)
* load() (in module pickle):             Module Interface.   (line   58)
* load() (in module plistlib):           plistlib — Generate and parse Apple plist files.
                                                             (line   46)
* load() (pickle.Unpickler method):      Module Interface.   (line  267)
* load() (tracemalloc.Snapshot class method): Snapshot.      (line   50)
* loader:                                Finders and loaders.
                                                             (line    6)
* loader <1>:                            Glossary.           (line  782)
* Loader (class in importlib.abc):       importlib abc – Abstract base classes related to import.
                                                             (line  158)
* loader (importlib.machinery.ModuleSpec attribute): importlib machinery – Importers and path hooks.
                                                             (line  374)
* LoadError:                             http cookiejar — Cookie handling for HTTP clients.
                                                             (line   34)
* loader_state (importlib.machinery.ModuleSpec attribute): importlib machinery – Importers and path hooks.
                                                             (line  398)
* LoadFileDialog (class in tkinter.filedialog): Native Load/Save Dialogs.
                                                             (line  135)
* LoadKey() (in module winreg):          Functions<12>.      (line  263)
* LoadLibrary() (ctypes.LibraryLoader method): Loading shared libraries.
                                                             (line  169)
* loads() (in module json):              Basic Usage.        (line  149)
* loads() (in module marshal):           marshal — Internal Python object serialization.
                                                             (line   95)
* loads() (in module pickle):            Module Interface.   (line   76)
* loads() (in module plistlib):          plistlib — Generate and parse Apple plist files.
                                                             (line   74)
* loads() (in module xmlrpc.client):     Convenience Functions.
                                                             (line   19)
* loadTestsFromModule() (unittest.TestLoader method): Loading and running tests.
                                                             (line   41)
* loadTestsFromName() (unittest.TestLoader method): Loading and running tests.
                                                             (line   70)
* loadTestsFromNames() (unittest.TestLoader method): Loading and running tests.
                                                             (line  104)
* loadTestsFromTestCase() (unittest.TestLoader method): Loading and running tests.
                                                             (line   29)
* LOAD_ASSERTION_ERROR (opcode):         Python Bytecode Instructions.
                                                             (line  400)
* LOAD_ATTR (opcode):                    Python Bytecode Instructions.
                                                             (line  551)
* LOAD_BUILD_CLASS (opcode):             Python Bytecode Instructions.
                                                             (line  407)
* load_cert_chain() (ssl.SSLContext method): SSL Contexts.   (line   80)
* LOAD_CLASSDEREF (opcode):              Python Bytecode Instructions.
                                                             (line  674)
* LOAD_CLOSURE (opcode):                 Python Bytecode Instructions.
                                                             (line  661)
* LOAD_CONST (opcode):                   Python Bytecode Instructions.
                                                             (line  472)
* load_default_certs() (ssl.SSLContext method): SSL Contexts.
                                                             (line  111)
* LOAD_DEREF (opcode):                   Python Bytecode Instructions.
                                                             (line  668)
* load_dh_params() (ssl.SSLContext method): SSL Contexts.    (line  355)
* load_extension() (sqlite3.Connection method): Connection Objects.
                                                             (line  297)
* LOAD_FAST (opcode):                    Python Bytecode Instructions.
                                                             (line  648)
* LOAD_GLOBAL (opcode):                  Python Bytecode Instructions.
                                                             (line  638)
* LOAD_METHOD (opcode):                  Python Bytecode Instructions.
                                                             (line  751)
* load_module() (importlib.abc.FileLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  494)
* load_module() (importlib.abc.InspectLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  447)
* load_module() (importlib.abc.Loader method): importlib abc – Abstract base classes related to import.
                                                             (line  195)
* load_module() (importlib.abc.SourceLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  594)
* load_module() (importlib.machinery.SourceFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  247)
* load_module() (importlib.machinery.SourcelessFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  291)
* load_module() (in module imp):         imp — Access the import internals.
                                                             (line   90)
* load_module() (zipimport.zipimporter method): zipimporter Objects.
                                                             (line   62)
* LOAD_NAME (opcode):                    Python Bytecode Instructions.
                                                             (line  476)
* load_package_tests() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  931)
* load_verify_locations() (ssl.SSLContext method): SSL Contexts.
                                                             (line  128)
* local (class in threading):            Thread-Local Data.  (line   15)
* localcontext() (in module decimal):    Context objects.    (line   25)
* LOCALE (in module re):                 Module Contents.    (line   81)
* locale (module):                       locale — Internationalization services.
                                                             (line    6)
* localeconv() (in module locale):       locale — Internationalization services.
                                                             (line   53)
* LocaleHTMLCalendar (class in calendar): calendar — General calendar-related functions.
                                                             (line  272)
* LocaleTextCalendar (class in calendar): calendar — General calendar-related functions.
                                                             (line  264)
* localName (xml.dom.Attr attribute):    Attr Objects.       (line   13)
* localName (xml.dom.Node attribute):    Node Objects.       (line   64)
* locals() (built-in function):          Built-in Functions. (line  907)
* localtime() (in module email.utils):   email utils Miscellaneous utilities.
                                                             (line   13)
* localtime() (in module time):          Functions<3>.       (line  141)
* Locator (class in xml.sax.xmlreader):  xml sax xmlreader — Interface for XML parsers.
                                                             (line   43)
* Lock (class in asyncio):               Lock.               (line    6)
* Lock (class in multiprocessing):       Synchronization primitives.
                                                             (line   46)
* Lock (class in threading):             Lock Objects.       (line   33)
* lock() (mailbox.Babyl method):         Babyl.              (line   59)
* lock() (mailbox.Mailbox method):       Mailbox objects.    (line  249)
* lock() (mailbox.Maildir method):       Maildir.            (line  107)
* lock() (mailbox.mbox method):          mbox.               (line   39)
* lock() (mailbox.MH method):            MH.                 (line   84)
* lock() (mailbox.MMDF method):          MMDF.               (line   35)
* Lock() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  171)
* lock, interpreter:                     Thread State and the Global Interpreter Lock.
                                                             (line    6)
* locked() (asyncio.Condition method):   Condition.          (line   64)
* locked() (asyncio.Lock method):        Lock.               (line   59)
* locked() (asyncio.Semaphore method):   Semaphore.          (line   51)
* locked() (threading.Lock method):      Lock Objects.       (line   87)
* locked() (_thread.lock method):        _thread — Low-level threading API.
                                                             (line  156)
* lockf() (in module fcntl):             fcntl — The fcntl and ioctl system calls.
                                                             (line  126)
* lockf() (in module os):                File Descriptor Operations.
                                                             (line  214)
* locking() (in module msvcrt):          File Operations.    (line    6)
* LockType (in module _thread):          _thread — Low-level threading API.
                                                             (line   28)
* lock_held() (in module imp):           imp — Access the import internals.
                                                             (line  257)
* log() (in module cmath):               Power and logarithmic functions<2>.
                                                             (line   11)
* log() (in module logging):             Module-Level Functions.
                                                             (line  150)
* log() (in module math):                Power and logarithmic functions.
                                                             (line   28)
* log() (logging.Logger method):         Logger Objects.     (line  251)
* log10() (decimal.Context method):      Context objects.    (line  340)
* log10() (decimal.Decimal method):      Decimal objects.    (line  338)
* log10() (in module cmath):             Power and logarithmic functions<2>.
                                                             (line   18)
* log10() (in module math):              Power and logarithmic functions.
                                                             (line   55)
* log1p() (in module math):              Power and logarithmic functions.
                                                             (line   36)
* log2() (in module math):               Power and logarithmic functions.
                                                             (line   41)
* logb() (decimal.Context method):       Context objects.    (line  344)
* logb() (decimal.Decimal method):       Decimal objects.    (line  344)
* Logger (class in logging):             Logger Objects.     (line   23)
* LoggerAdapter (class in logging):      LoggerAdapter Objects.
                                                             (line   11)
* logging (module):                      logging — Logging facility for Python.
                                                             (line    6)
* logging.config (module):               logging config — Logging configuration.
                                                             (line    6)
* logging.handlers (module):             logging handlers — Logging handlers.
                                                             (line    6)
* logical line:                          Logical lines.      (line    6)
* logical_and() (decimal.Context method): Context objects.   (line  348)
* logical_and() (decimal.Decimal method): Decimal objects.   (line  352)
* logical_invert() (decimal.Context method): Context objects.
                                                             (line  353)
* logical_invert() (decimal.Decimal method): Decimal objects.
                                                             (line  358)
* logical_or() (decimal.Context method): Context objects.    (line  357)
* logical_or() (decimal.Decimal method): Decimal objects.    (line  363)
* logical_xor() (decimal.Context method): Context objects.   (line  362)
* logical_xor() (decimal.Decimal method): Decimal objects.   (line  369)
* login() (ftplib.FTP method):           FTP Objects.        (line   48)
* login() (imaplib.IMAP4 method):        IMAP4 Objects.      (line  132)
* login() (nntplib.NNTP method):         Methods<3>.         (line   48)
* login() (smtplib.SMTP method):         SMTP Objects.       (line  102)
* login_cram_md5() (imaplib.IMAP4 method): IMAP4 Objects.    (line  137)
* LOGNAME:                               Process Parameters. (line  222)
* LOGNAME <1>:                           getpass — Portable password input.
                                                             (line   38)
* lognormvariate() (in module random):   Real-valued distributions.
                                                             (line   70)
* logout() (imaplib.IMAP4 method):       IMAP4 Objects.      (line  143)
* LogRecord (class in logging):          LogRecord Objects.  (line   11)
* log_date_time_string() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  322)
* log_error() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  291)
* log_exception() (wsgiref.handlers.BaseHandler method): wsgiref handlers – server/gateway base classes.
                                                             (line  209)
* log_message() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  297)
* log_request() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  284)
* log_to_stderr() (in module multiprocessing): Logging<2>.   (line   24)
* long (2to3 fixer):                     Fixers.             (line  181)
* longMessage (unittest.TestCase attribute): Test cases.     (line  678)
* longname() (in module curses):         Functions<4>.       (line  264)
* LONG_MAX:                              Integer Objects.    (line  108)
* LONG_TIMEOUT (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  128)
* lookup() (in module codecs):           codecs — Codec registry and base classes.
                                                             (line   47)
* lookup() (in module unicodedata):      unicodedata — Unicode Database.
                                                             (line   16)
* lookup() (symtable.SymbolTable method): Examining Symbol Tables.
                                                             (line   48)
* lookup() (tkinter.ttk.Style method):   Ttk Styling.        (line   81)
* LookupError:                           Base classes.       (line   54)
* lookup_error() (in module codecs):     Error Handlers.     (line  117)
* loop control; target:                  The break statement.
                                                             (line   12)
* loop() (in module asyncore):           asyncore — Asynchronous socket handler.
                                                             (line   49)
* loop; over mutable sequence:           The for statement.  (line   44)
* loop; statement:                       The break statement.
                                                             (line    6)
* loop; statement <1>:                   The continue statement.
                                                             (line    6)
* loop; statement <2>:                   The while statement.
                                                             (line    6)
* loop; statement <3>:                   The for statement.  (line    6)
* LOOPBACK_TIMEOUT (in module test.support): test support — Utilities for the Python test suite.
                                                             (line   83)
* lower() (bytearray method):            Bytes and Bytearray Operations.
                                                             (line  615)
* lower() (bytes method):                Bytes and Bytearray Operations.
                                                             (line  615)
* lower() (str method):                  String Methods<2>.  (line  311)
* LPAR (in module token):                token — Constants used with Python parse trees.
                                                             (line   54)
* lpAttributeList (subprocess.STARTUPINFO attribute): Windows Popen Helpers.
                                                             (line   60)
* lru_cache() (in module functools):     functools — Higher-order functions and operations on callable objects.
                                                             (line  127)
* lseek() (in module os):                File Descriptor Operations.
                                                             (line  240)
* LShift (class in ast):                 Expressions<2>.     (line   54)
* lshift() (in module operator):         operator — Standard operators as functions.
                                                             (line  106)
* LSQB (in module token):                token — Constants used with Python parse trees.
                                                             (line   62)
* lstat() (in module os):                Files and Directories.
                                                             (line  394)
* lstat() (pathlib.Path method):         Methods<2>.         (line  227)
* lstrip() (bytearray method):           Bytes and Bytearray Operations.
                                                             (line  308)
* lstrip() (bytes method):               Bytes and Bytearray Operations.
                                                             (line  308)
* lstrip() (str method):                 String Methods<2>.  (line  319)
* lsub() (imaplib.IMAP4 method):         IMAP4 Objects.      (line  150)
* Lt (class in ast):                     Expressions<2>.     (line  109)
* lt() (in module operator):             operator — Standard operators as functions.
                                                             (line   24)
* lt() (in module turtle):               Turtle motion.      (line   57)
* LtE (class in ast):                    Expressions<2>.     (line  109)
* LWPCookieJar (class in http.cookiejar): FileCookieJar subclasses and co-operation with web browsers.
                                                             (line   28)
* lzma (module):                         lzma — Compression using the LZMA algorithm.
                                                             (line    6)
* LZMACompressor (class in lzma):        Compressing and decompressing data in memory.
                                                             (line    6)
* LZMADecompressor (class in lzma):      Compressing and decompressing data in memory.
                                                             (line  100)
* LZMAError:                             lzma — Compression using the LZMA algorithm.
                                                             (line   24)
* LZMAFile (class in lzma):              Reading and writing compressed files.
                                                             (line   45)
* M (in module re):                      Module Contents.    (line  101)
* machine() (in module platform):        Cross Platform.     (line   35)
* macros (netrc.netrc attribute):        netrc Objects.      (line   29)
* mac_ver() (in module platform):        macOS Platform.     (line    6)
* madvise() (mmap.mmap method):          mmap — Memory-mapped file support.
                                                             (line  205)
* MADV_AUTOSYNC (in module mmap):        MADV_* Constants.   (line    6)
* MADV_CORE (in module mmap):            MADV_* Constants.   (line    6)
* MADV_DODUMP (in module mmap):          MADV_* Constants.   (line    6)
* MADV_DOFORK (in module mmap):          MADV_* Constants.   (line    6)
* MADV_DONTDUMP (in module mmap):        MADV_* Constants.   (line    6)
* MADV_DONTFORK (in module mmap):        MADV_* Constants.   (line    6)
* MADV_DONTNEED (in module mmap):        MADV_* Constants.   (line    6)
* MADV_FREE (in module mmap):            MADV_* Constants.   (line    6)
* MADV_HUGEPAGE (in module mmap):        MADV_* Constants.   (line    6)
* MADV_HWPOISON (in module mmap):        MADV_* Constants.   (line    6)
* MADV_MERGEABLE (in module mmap):       MADV_* Constants.   (line    6)
* MADV_NOCORE (in module mmap):          MADV_* Constants.   (line    6)
* MADV_NOHUGEPAGE (in module mmap):      MADV_* Constants.   (line    6)
* MADV_NORMAL (in module mmap):          MADV_* Constants.   (line    6)
* MADV_NOSYNC (in module mmap):          MADV_* Constants.   (line    6)
* MADV_PROTECT (in module mmap):         MADV_* Constants.   (line    6)
* MADV_RANDOM (in module mmap):          MADV_* Constants.   (line    6)
* MADV_REMOVE (in module mmap):          MADV_* Constants.   (line    6)
* MADV_SEQUENTIAL (in module mmap):      MADV_* Constants.   (line    6)
* MADV_SOFT_OFFLINE (in module mmap):    MADV_* Constants.   (line    6)
* MADV_UNMERGEABLE (in module mmap):     MADV_* Constants.   (line    6)
* MADV_WILLNEED (in module mmap):        MADV_* Constants.   (line    6)
* magic method:                          Glossary.           (line  789)
* magic; method:                         Glossary.           (line  793)
* MagicMock (class in unittest.mock):    Magic Mock.         (line    9)
* MAGIC_NUMBER (in module importlib.util): importlib util – Utility code for importers.
                                                             (line   13)
* Mailbox (class in mailbox):            Mailbox objects.    (line    6)
* mailbox (module):                      mailbox — Manipulate mailboxes in various formats.
                                                             (line    6)
* mailcap (module):                      mailcap — Mailcap file handling.
                                                             (line    6)
* Maildir (class in mailbox):            Maildir.            (line    6)
* MaildirMessage (class in mailbox):     MaildirMessage.     (line    6)
* mailfrom (smtpd.SMTPChannel attribute): SMTPChannel Objects.
                                                             (line   74)
* MailmanProxy (class in smtpd):         MailmanProxy Objects.
                                                             (line    6)
* main():                                Process-wide parameters.
                                                             (line    9)
* main() <1>:                            Process-wide parameters.
                                                             (line   36)
* main() <2>:                            Process-wide parameters.
                                                             (line  217)
* main() (in module py_compile):         py_compile — Compile Python source files.
                                                             (line  124)
* main() (in module site):               Module contents<4>. (line   41)
* main() (in module unittest):           Loading and running tests.
                                                             (line  489)
* mainloop() (in module turtle):         Using screen events.
                                                             (line  106)
* maintype (email.headerregistry.ContentTypeHeader attribute): email headerregistry Custom Header Objects.
                                                             (line  276)
* main_thread() (in module threading):   threading — Thread-based parallelism.
                                                             (line  116)
* major (email.headerregistry.MIMEVersionHeader attribute): email headerregistry Custom Header Objects.
                                                             (line  247)
* major() (in module os):                Files and Directories.
                                                             (line  532)
* makedev() (in module os):              Files and Directories.
                                                             (line  542)
* makedirs() (in module os):             Files and Directories.
                                                             (line  451)
* makeelement() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line  164)
* makefile() (socket method):            The standard type hierarchy.
                                                             (line  635)
* makefile() (socket.socket method):     Socket Objects.     (line  196)
* makeLogRecord() (in module logging):   Module-Level Functions.
                                                             (line  236)
* makePickle() (logging.handlers.SocketHandler method): SocketHandler.
                                                             (line   45)
* makeRecord() (logging.Logger method):  Logger Objects.     (line  312)
* makeSocket() (logging.handlers.DatagramHandler method): DatagramHandler.
                                                             (line   28)
* makeSocket() (logging.handlers.SocketHandler method): SocketHandler.
                                                             (line   39)
* maketrans() (bytearray static method): Bytes and Bytearray Operations.
                                                             (line  169)
* maketrans() (bytes static method):     Bytes and Bytearray Operations.
                                                             (line  169)
* maketrans() (str static method):       String Methods<2>.  (line  341)
* make_alternative() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  607)
* make_archive() (in module distutils.archive_util): distutils archive_util — Archiving utilities.
                                                             (line    9)
* make_archive() (in module shutil):     Archiving operations.
                                                             (line   14)
* make_bad_fd() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  746)
* make_cookies() (http.cookiejar.CookieJar method): CookieJar and FileCookieJar Objects.
                                                             (line   60)
* make_dataclass() (in module dataclasses): Module-level decorators classes and functions.
                                                             (line  320)
* make_file() (difflib.HtmlDiff method): difflib — Helpers for computing deltas.
                                                             (line  111)
* MAKE_FUNCTION (opcode):                Python Bytecode Instructions.
                                                             (line  774)
* make_header() (in module email.header): email header Internationalized headers.
                                                             (line  200)
* make_legacy_pyc() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  250)
* make_mixed() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  617)
* make_msgid() (in module email.utils):  email utils Miscellaneous utilities.
                                                             (line   29)
* make_parser() (in module xml.sax):     xml sax — Support for SAX2 parsers.
                                                             (line   28)
* make_pkg() (in module test.support.script_helper): test support script_helper — Utilities for the Python execution tests.
                                                             (line   96)
* make_related() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  598)
* make_script() (in module test.support.script_helper): test support script_helper — Utilities for the Python execution tests.
                                                             (line   81)
* make_server() (in module wsgiref.simple_server): wsgiref simple_server – a simple WSGI HTTP server.
                                                             (line   14)
* make_table() (difflib.HtmlDiff method): difflib — Helpers for computing deltas.
                                                             (line  143)
* make_tarball() (in module distutils.archive_util): distutils archive_util — Archiving utilities.
                                                             (line   25)
* make_zipfile() (in module distutils.archive_util): distutils archive_util — Archiving utilities.
                                                             (line   39)
* make_zip_pkg() (in module test.support.script_helper): test support script_helper — Utilities for the Python execution tests.
                                                             (line  103)
* make_zip_script() (in module test.support.script_helper): test support script_helper — Utilities for the Python execution tests.
                                                             (line   88)
* malloc():                              Overview<3>.        (line   33)
* mangle_from_ (email.policy.Compat32 attribute): email policy Policy Objects.
                                                             (line  559)
* mangle_from_ (email.policy.Policy attribute): email policy Policy Objects.
                                                             (line  186)
* map (2to3 fixer):                      Fixers.             (line  185)
* map() (built-in function):             Built-in Functions. (line  919)
* map() (concurrent.futures.Executor method): Executor Objects.
                                                             (line   22)
* map() (multiprocessing.pool.Pool method): Process Pools.   (line   90)
* map() (tkinter.ttk.Style method):      Ttk Styling.        (line   48)
* mapLogRecord() (logging.handlers.HTTPHandler method): HTTPHandler.
                                                             (line   27)
* mapping:                               Glossary.           (line  793)
* Mapping (class in collections.abc):    Collections Abstract Base Classes.
                                                             (line  182)
* Mapping (class in typing):             Corresponding to collections in collections abc.
                                                             (line   61)
* mapping() (msilib.Control method):     GUI classes.        (line   20)
* MappingProxyType (class in types):     Standard Interpreter Types.
                                                             (line  236)
* MappingView (class in collections.abc): Collections Abstract Base Classes.
                                                             (line  187)
* MappingView (class in typing):         Corresponding to collections in collections abc.
                                                             (line   73)
* mapPriority() (logging.handlers.SysLogHandler method): SysLogHandler.
                                                             (line  183)
* maps (collections.ChainMap attribute): ChainMap objects.   (line   39)
* maps() (in module nis):                nis — Interface to Sun’s NIS Yellow Pages.
                                                             (line   41)
* MAP_ADD (opcode):                      Python Bytecode Instructions.
                                                             (line  327)
* map_async() (multiprocessing.pool.Pool method): Process Pools.
                                                             (line  107)
* map_table_b2() (in module stringprep): stringprep — Internet String Preparation.
                                                             (line   50)
* map_table_b3() (in module stringprep): stringprep — Internet String Preparation.
                                                             (line   55)
* map_to_type() (email.headerregistry.HeaderRegistry method): email headerregistry Custom Header Objects.
                                                             (line  376)
* marshal (module):                      marshal — Internal Python object serialization.
                                                             (line    6)
* marshalling; objects:                  pickle — Python object serialization.
                                                             (line    8)
* masking; operations:                   Bitwise Operations on Integer Types.
                                                             (line    6)
* Match (class in typing):               Other concrete types.
                                                             (line   18)
* match() (in module nis):               nis — Interface to Sun’s NIS Yellow Pages.
                                                             (line   16)
* match() (in module re):                Module Contents.    (line  152)
* match() (pathlib.PurePath method):     Methods and properties.
                                                             (line  224)
* match() (re.Pattern method):           Regular Expression Objects.
                                                             (line   37)
* Matcher (class in test.support):       test support — Utilities for the Python test suite.
                                                             (line 1107)
* matches() (test.support.Matcher method): test support — Utilities for the Python test suite.
                                                             (line 1109)
* match_hostname() (in module ssl):      Certificate handling.
                                                             (line    6)
* match_test() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  306)
* match_value() (test.support.Matcher method): test support — Utilities for the Python test suite.
                                                             (line 1113)
* math (module):                         math — Mathematical functions.
                                                             (line    6)
* matmul() (in module operator):         operator — Standard operators as functions.
                                                             (line  121)
* MatMult (class in ast):                Expressions<2>.     (line   54)
* matrix multiplication:                 Binary arithmetic operations.
                                                             (line   26)
* max (datetime.date attribute):         date Objects.       (line   91)
* max (datetime.datetime attribute):     datetime Objects.   (line  252)
* max (datetime.time attribute):         time Objects.       (line   37)
* max (datetime.timedelta attribute):    timedelta Objects.  (line   78)
* max() (built-in function):             Built-in Functions. (line  929)
* max() (decimal.Context method):        Context objects.    (line  367)
* max() (decimal.Decimal method):        Decimal objects.    (line  375)
* max() (in module audioop):             audioop — Manipulate raw audio data.
                                                             (line  155)
* maxarray (reprlib.Repr attribute):     Repr Objects.       (line   15)
* maxdeque (reprlib.Repr attribute):     Repr Objects.       (line   15)
* maxdict (reprlib.Repr attribute):      Repr Objects.       (line   15)
* maxDiff (unittest.TestCase attribute): Test cases.         (line  695)
* maxfrozenset (reprlib.Repr attribute): Repr Objects.       (line   15)
* MAXIMUM_SUPPORTED (ssl.TLSVersion attribute): Constants<9>.
                                                             (line  535)
* maximum_version (ssl.SSLContext attribute): SSL Contexts.  (line  542)
* maxlen (collections.deque attribute):  deque objects.      (line  120)
* maxlevel (reprlib.Repr attribute):     Repr Objects.       (line   10)
* maxlist (reprlib.Repr attribute):      Repr Objects.       (line   15)
* maxlong (reprlib.Repr attribute):      Repr Objects.       (line   27)
* maxother (reprlib.Repr attribute):     Repr Objects.       (line   40)
* maxpp() (in module audioop):           audioop — Manipulate raw audio data.
                                                             (line  160)
* maxset (reprlib.Repr attribute):       Repr Objects.       (line   15)
* maxsize (asyncio.Queue attribute):     Queue.              (line   24)
* maxsize (in module sys):               sys — System-specific parameters and functions.
                                                             (line 1006)
* maxstring (reprlib.Repr attribute):    Repr Objects.       (line   32)
* maxtuple (reprlib.Repr attribute):     Repr Objects.       (line   15)
* maxunicode (in module sys):            sys — System-specific parameters and functions.
                                                             (line 1012)
* MAXYEAR (in module datetime):          Constants.          (line   13)
* max_count (email.headerregistry.BaseHeader attribute): email headerregistry Custom Header Objects.
                                                             (line   60)
* MAX_EMAX (in module decimal):          Constants<4>.       (line   16)
* MAX_INTERPOLATION_DEPTH (in module configparser): ConfigParser Objects.
                                                             (line  326)
* max_lines (textwrap.TextWrapper attribute): textwrap — Text wrapping and filling.
                                                             (line  266)
* max_line_length (email.policy.Policy attribute): email policy Policy Objects.
                                                             (line  145)
* max_mag() (decimal.Context method):    Context objects.    (line  371)
* max_mag() (decimal.Decimal method):    Decimal objects.    (line  382)
* max_memuse (in module test.support):   test support — Utilities for the Python test suite.
                                                             (line  177)
* MAX_PREC (in module decimal):          Constants<4>.       (line   13)
* max_prefixlen (ipaddress.IPv4Address attribute): Address objects.
                                                             (line   55)
* max_prefixlen (ipaddress.IPv4Network attribute): Network objects.
                                                             (line   65)
* max_prefixlen (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  214)
* max_prefixlen (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  295)
* MAX_Py_ssize_t (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  173)
* mbox (class in mailbox):               mbox.               (line    6)
* mboxMessage (class in mailbox):        mboxMessage.        (line    6)
* MB_ICONASTERISK (in module winsound):  winsound — Sound-playing interface for Windows.
                                                             (line  128)
* MB_ICONEXCLAMATION (in module winsound): winsound — Sound-playing interface for Windows.
                                                             (line  132)
* MB_ICONHAND (in module winsound):      winsound — Sound-playing interface for Windows.
                                                             (line  136)
* MB_ICONQUESTION (in module winsound):  winsound — Sound-playing interface for Windows.
                                                             (line  140)
* MB_OK (in module winsound):            winsound — Sound-playing interface for Windows.
                                                             (line  144)
* mean (statistics.NormalDist attribute): NormalDist objects.
                                                             (line   21)
* mean() (in module statistics):         Function details.   (line   10)
* measure() (tkinter.font.Font method):  tkinter font — Tkinter font wrapper.
                                                             (line   63)
* median (statistics.NormalDist attribute): NormalDist objects.
                                                             (line   26)
* median() (in module statistics):       Function details.   (line  120)
* median_grouped() (in module statistics): Function details. (line  183)
* median_high() (in module statistics):  Function details.   (line  165)
* median_low() (in module statistics):   Function details.   (line  147)
* MemberDescriptorType (in module types): Standard Interpreter Types.
                                                             (line  225)
* membership; test:                      Membership test operations.
                                                             (line   37)
* memfd_create() (in module os):         Files and Directories.
                                                             (line 1649)
* memmove() (in module ctypes):          Utility functions.  (line  137)
* MemoryBIO (class in ssl):              Memory BIO Support<2>.
                                                             (line  134)
* MemoryError:                           Concrete exceptions.
                                                             (line   78)
* MemoryHandler (class in logging.handlers): MemoryHandler.  (line   40)
* memoryview (built-in class):           Memory Views.       (line   10)
* memset() (in module ctypes):           Utility functions.  (line  143)
* merge() (in module heapq):             heapq — Heap queue algorithm.
                                                             (line   79)
* Message (class in email.message):      email message Message Representing an email message using the compat32 API.
                                                             (line   49)
* Message (class in mailbox):            Message objects.    (line    6)
* Message (class in tkinter.messagebox): tkinter messagebox — Tkinter message prompts.
                                                             (line   19)
* message digest, MD5:                   hashlib — Secure hashes and message digests.
                                                             (line    8)
* MessageBeep() (in module winsound):    winsound — Sound-playing interface for Windows.
                                                             (line   31)
* MessageClass (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  166)
* MessageError:                          email errors Exception and Defect classes.
                                                             (line   13)
* MessageParseError:                     email errors Exception and Defect classes.
                                                             (line   19)
* messages (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   22)
* message_factory (email.policy.Policy attribute): email policy Policy Objects.
                                                             (line  195)
* message_from_binary_file() (in module email): Parser API.  (line  129)
* message_from_bytes() (in module email): Parser API.        (line  116)
* message_from_file() (in module email): Parser API.         (line  152)
* message_from_string() (in module email): Parser API.       (line  142)
* meta hooks:                            Import hooks.       (line    6)
* meta path finder:                      Glossary.           (line  802)
* meta() (in module curses):             Functions<4>.       (line  271)
* metaclass:                             Metaclasses.        (line    6)
* metaclass <1>:                         Glossary.           (line  811)
* metaclass (2to3 fixer):                Fixers.             (line  191)
* metaclass hint:                        Determining the appropriate metaclass.
                                                             (line    6)
* MetaPathFinder (class in importlib.abc): importlib abc – Abstract base classes related to import.
                                                             (line   45)
* metavar (optparse.Option attribute):   Option attributes.  (line   80)
* MetavarTypeHelpFormatter (class in argparse): formatter_class.
                                                             (line   10)
* meta_path (in module sys):             sys — System-specific parameters and functions.
                                                             (line 1022)
* Meter (class in tkinter.tix):          Basic Widgets.      (line   44)
* method:                                Glossary.           (line  826)
* method (urllib.request.Request attribute): Request Objects.
                                                             (line   52)
* method resolution order:               Glossary.           (line  834)
* method; call:                          Calls.              (line  132)
* methodattrs (2to3 fixer):              Fixers.             (line  196)
* methodcaller() (in module operator):   operator — Standard operators as functions.
                                                             (line  307)
* MethodDescriptorType (in module types): Standard Interpreter Types.
                                                             (line  103)
* methodHelp() (xmlrpc.client.ServerProxy.system method): ServerProxy Objects.
                                                             (line   43)
* methods (in module crypt):             Module Attributes.  (line    8)
* methods (pyclbr.Class attribute):      Class Objects<2>.   (line   46)
* methodSignature() (xmlrpc.client.ServerProxy.system method): ServerProxy Objects.
                                                             (line   22)
* MethodType (in module types):          Standard Interpreter Types.
                                                             (line   77)
* MethodType (in module types) <1>:      Function Objects<3>.
                                                             (line   14)
* MethodType (in module types) <2>:      Method Objects<2>.  (line   12)
* MethodWrapperType (in module types):   Standard Interpreter Types.
                                                             (line   96)
* METHOD_BLOWFISH (in module crypt):     Hashing Methods.    (line   22)
* method_calls (unittest.mock.Mock attribute): The Mock Class.
                                                             (line  482)
* METHOD_CRYPT (in module crypt):        Hashing Methods.    (line   34)
* METHOD_MD5 (in module crypt):          Hashing Methods.    (line   29)
* METHOD_SHA256 (in module crypt):       Hashing Methods.    (line   17)
* METHOD_SHA512 (in module crypt):       Hashing Methods.    (line   11)
* METH_CLASS (built-in variable):        Implementing functions and methods.
                                                             (line  182)
* METH_COEXIST (built-in variable):      Implementing functions and methods.
                                                             (line  199)
* METH_FASTCALL (built-in variable):     Implementing functions and methods.
                                                             (line  119)
* METH_NOARGS (built-in variable):       Implementing functions and methods.
                                                             (line  160)
* METH_O (built-in variable):            Implementing functions and methods.
                                                             (line  169)
* METH_STATIC (built-in variable):       Implementing functions and methods.
                                                             (line  189)
* METH_VARARGS (built-in variable):      Implementing functions and methods.
                                                             (line  100)
* metrics() (tkinter.font.Font method):  tkinter font — Tkinter font wrapper.
                                                             (line   69)
* MFD_ALLOW_SEALING (in module os):      Files and Directories.
                                                             (line 1668)
* MFD_CLOEXEC (in module os):            Files and Directories.
                                                             (line 1668)
* MFD_HUGETLB (in module os):            Files and Directories.
                                                             (line 1668)
* MFD_HUGE_16GB (in module os):          Files and Directories.
                                                             (line 1668)
* MFD_HUGE_16MB (in module os):          Files and Directories.
                                                             (line 1668)
* MFD_HUGE_1GB (in module os):           Files and Directories.
                                                             (line 1668)
* MFD_HUGE_1MB (in module os):           Files and Directories.
                                                             (line 1668)
* MFD_HUGE_256MB (in module os):         Files and Directories.
                                                             (line 1668)
* MFD_HUGE_2GB (in module os):           Files and Directories.
                                                             (line 1668)
* MFD_HUGE_2MB (in module os):           Files and Directories.
                                                             (line 1668)
* MFD_HUGE_32MB (in module os):          Files and Directories.
                                                             (line 1668)
* MFD_HUGE_512KB (in module os):         Files and Directories.
                                                             (line 1668)
* MFD_HUGE_512MB (in module os):         Files and Directories.
                                                             (line 1668)
* MFD_HUGE_64KB (in module os):          Files and Directories.
                                                             (line 1668)
* MFD_HUGE_8MB (in module os):           Files and Directories.
                                                             (line 1668)
* MFD_HUGE_MASK (in module os):          Files and Directories.
                                                             (line 1668)
* MFD_HUGE_SHIFT (in module os):         Files and Directories.
                                                             (line 1668)
* MH (class in mailbox):                 MH.                 (line    6)
* MHMessage (class in mailbox):          MHMessage.          (line    6)
* microsecond (datetime.datetime attribute): datetime Objects.
                                                             (line  289)
* microsecond (datetime.time attribute): time Objects.       (line   62)
* MIME; base64 encoding:                 base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line    8)
* MIME; content type:                    mimetypes — Map filenames to MIME types.
                                                             (line    8)
* MIME; headers:                         mimetypes — Map filenames to MIME types.
                                                             (line   26)
* MIME; headers <1>:                     cgi — Common Gateway Interface support.
                                                             (line    8)
* MIME; quoted-printable encoding:       quopri — Encode and decode MIME quoted-printable data.
                                                             (line    8)
* MIMEApplication (class in email.mime.application): email mime Creating email and MIME objects from scratch.
                                                             (line   95)
* MIMEAudio (class in email.mime.audio): email mime Creating email and MIME objects from scratch.
                                                             (line  125)
* MIMEBase (class in email.mime.base):   email mime Creating email and MIME objects from scratch.
                                                             (line   30)
* MIMEImage (class in email.mime.image): email mime Creating email and MIME objects from scratch.
                                                             (line  158)
* MIMEMessage (class in email.mime.message): email mime Creating email and MIME objects from scratch.
                                                             (line  191)
* MIMEMultipart (class in email.mime.multipart): email mime Creating email and MIME objects from scratch.
                                                             (line   66)
* MIMENonMultipart (class in email.mime.nonmultipart): email mime Creating email and MIME objects from scratch.
                                                             (line   55)
* MIMEPart (class in email.message):     email message Representing an email message.
                                                             (line  718)
* MIMEText (class in email.mime.text):   email mime Creating email and MIME objects from scratch.
                                                             (line  209)
* MimeTypes (class in mimetypes):        MimeTypes Objects.  (line   10)
* mimetypes (module):                    mimetypes — Map filenames to MIME types.
                                                             (line    6)
* MIMEVersionHeader (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line  234)
* min (datetime.date attribute):         date Objects.       (line   87)
* min (datetime.datetime attribute):     datetime Objects.   (line  247)
* min (datetime.time attribute):         time Objects.       (line   33)
* min (datetime.timedelta attribute):    timedelta Objects.  (line   73)
* min() (built-in function):             Built-in Functions. (line  961)
* min() (decimal.Context method):        Context objects.    (line  375)
* min() (decimal.Decimal method):        Decimal objects.    (line  387)
* MINEQUAL (in module token):            token — Constants used with Python parse trees.
                                                             (line  174)
* MINIMUM_SUPPORTED (ssl.TLSVersion attribute): Constants<9>.
                                                             (line  533)
* minimum_version (ssl.SSLContext attribute): SSL Contexts.  (line  563)
* minmax() (in module audioop):          audioop — Manipulate raw audio data.
                                                             (line  164)
* minor (email.headerregistry.MIMEVersionHeader attribute): email headerregistry Custom Header Objects.
                                                             (line  251)
* minor() (in module os):                Files and Directories.
                                                             (line  537)
* minus:                                 Unary arithmetic and bitwise operations.
                                                             (line   10)
* MINUS (in module token):               token — Constants used with Python parse trees.
                                                             (line   86)
* minus() (decimal.Context method):      Context objects.    (line  383)
* minute (datetime.datetime attribute):  datetime Objects.   (line  281)
* minute (datetime.time attribute):      time Objects.       (line   54)
* MINYEAR (in module datetime):          Constants.          (line    8)
* MIN_EMIN (in module decimal):          Constants<4>.       (line   19)
* MIN_ETINY (in module decimal):         Constants<4>.       (line   22)
* min_mag() (decimal.Context method):    Context objects.    (line  379)
* min_mag() (decimal.Decimal method):    Decimal objects.    (line  394)
* mirrored() (in module unicodedata):    unicodedata — Unicode Database.
                                                             (line   69)
* misc_header (cmd.Cmd attribute):       Cmd Objects.        (line  152)
* MISSING (contextvars.Token attribute): Context Variables.  (line   94)
* MissingSectionHeaderError:             Exceptions<6>.      (line   60)
* missing_compiler_executable() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  982)
* MISSING_C_DOCSTRINGS (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  187)
* MIXERDEV:                              ossaudiodev — Access to OSS-compatible audio devices.
                                                             (line   74)
* mkd() (ftplib.FTP method):             FTP Objects.        (line  217)
* mkdir() (in module os):                Files and Directories.
                                                             (line  426)
* mkdir() (pathlib.Path method):         Methods<2>.         (line  233)
* mkdtemp() (in module tempfile):        tempfile — Generate temporary files and directories.
                                                             (line  200)
* mkfifo() (in module os):               Files and Directories.
                                                             (line  491)
* mknod() (in module os):                Files and Directories.
                                                             (line  512)
* mkpath() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  493)
* mkpath() (in module distutils.dir_util): distutils dir_util — Directory tree operations.
                                                             (line    9)
* mksalt() (in module crypt):            Module Functions<2>.
                                                             (line   39)
* mkstemp() (in module tempfile):        tempfile — Generate temporary files and directories.
                                                             (line  142)
* mktemp() (in module tempfile):         Deprecated functions and variables.
                                                             (line   15)
* mktime() (in module time):             Functions<3>.       (line  148)
* mktime_tz() (in module email.utils):   email utils Miscellaneous utilities.
                                                             (line  133)
* mlsd() (ftplib.FTP method):            FTP Objects.        (line  165)
* mmap (class in mmap):                  mmap — Memory-mapped file support.
                                                             (line   48)
* mmap (module):                         mmap — Memory-mapped file support.
                                                             (line    6)
* MMDF (class in mailbox):               MMDF.               (line    6)
* MMDFMessage (class in mailbox):        MMDFMessage.        (line    6)
* Mock (class in unittest.mock):         The Mock Class.     (line   24)
* mock_add_spec() (unittest.mock.Mock method): The Mock Class.
                                                             (line  226)
* mock_calls (unittest.mock.Mock attribute): The Mock Class. (line  500)
* mock_open() (in module unittest.mock): mock_open.          (line    6)
* Mod (class in ast):                    Expressions<2>.     (line   54)
* mod() (in module operator):            operator — Standard operators as functions.
                                                             (line  111)
* mode (io.FileIO attribute):            Raw File I/O.       (line   55)
* mode (ossaudiodev.oss_audio_device attribute): Audio Device Objects.
                                                             (line  238)
* mode (statistics.NormalDist attribute): NormalDist objects.
                                                             (line   31)
* mode (tarfile.TarInfo attribute):      TarInfo Objects.    (line   55)
* mode() (in module statistics):         Function details.   (line  228)
* mode() (in module turtle):             Settings and special methods.
                                                             (line    6)
* modf() (in module math):               Number-theoretic and representation functions.
                                                             (line  189)
* modified() (urllib.robotparser.RobotFileParser method): urllib robotparser — Parser for robots txt.
                                                             (line   45)
* Modify() (msilib.View method):         View Objects.       (line   23)
* modify() (select.devpoll method):      /dev/poll Polling Objects.
                                                             (line   49)
* modify() (select.epoll method):        Edge and Level Trigger Polling epoll Objects.
                                                             (line   85)
* modify() (select.poll method):         Polling Objects.    (line   60)
* modify() (selectors.BaseSelector method): Classes<3>.      (line   94)
* module:                                Glossary.           (line  841)
* module (pyclbr.Class attribute):       Class Objects<2>.   (line   13)
* module (pyclbr.Function attribute):    Function Objects.   (line   13)
* module spec:                           Finders and loaders.
                                                             (line    6)
* module spec <1>:                       Glossary.           (line  850)
* module; array:                         The standard type hierarchy.
                                                             (line  218)
* module; array <1>:                     Binary Sequence Types — bytes bytearray memoryview.
                                                             (line    6)
* module; base64:                        binascii — Convert between binary and ASCII.
                                                             (line    6)
* module; bdb:                           pdb — The Python Debugger.
                                                             (line   17)
* module; binhex:                        binascii — Convert between binary and ASCII.
                                                             (line    6)
* module; builtins:                      The dir Function.   (line   47)
* module; builtins <1>:                  Complete Python programs.
                                                             (line    6)
* module; builtins <2>:                  Embedding Python<2>.
                                                             (line   12)
* module; builtins <3>:                  Initializing and finalizing the interpreter.
                                                             (line    8)
* module; builtins <4>:                  Sub-interpreter support.
                                                             (line   26)
* module; cmd:                           pdb — The Python Debugger.
                                                             (line   17)
* module; copy:                          copyreg — Register pickle support functions.
                                                             (line    8)
* module; crypt:                         pwd — The password database.
                                                             (line   43)
* module; dbm.gnu:                       The standard type hierarchy.
                                                             (line  285)
* module; dbm.gnu <1>:                   Restrictions.       (line    6)
* module; dbm.ndbm:                      The standard type hierarchy.
                                                             (line  285)
* module; dbm.ndbm <1>:                  Restrictions.       (line    6)
* module; errno:                         Concrete exceptions.
                                                             (line  118)
* module; glob:                          fnmatch — Unix filename pattern matching.
                                                             (line   34)
* module; imp:                           Built-in Functions. (line 1800)
* module; importing:                     The import statement.
                                                             (line    6)
* module; io:                            The standard type hierarchy.
                                                             (line  635)
* module; json:                          Saving structured data with json.
                                                             (line    6)
* module; math:                          Numeric Types — int float complex.
                                                             (line  104)
* module; math <1>:                      Constants<3>.       (line   47)
* module; namespace:                     The standard type hierarchy.
                                                             (line  541)
* module; os:                            posix — The most common POSIX system calls.
                                                             (line   12)
* module; pickle:                        copy — Shallow and deep copy operations.
                                                             (line   68)
* module; pickle <1>:                    copyreg — Register pickle support functions.
                                                             (line    8)
* module; pickle <2>:                    shelve — Python object persistence.
                                                             (line    8)
* module; pickle <3>:                    marshal — Internal Python object serialization.
                                                             (line   15)
* module; pty:                           File Descriptor Operations.
                                                             (line  355)
* module; pwd:                           os path — Common pathname manipulations.
                                                             (line  140)
* module; pyexpat:                       xml parsers expat — Fast XML parsing using Expat.
                                                             (line   20)
* module; re:                            String Methods<2>.  (line    6)
* module; re <1>:                        fnmatch — Unix filename pattern matching.
                                                             (line    8)
* module; search; path:                  The Module Search Path.
                                                             (line    6)
* module; search; path <1>:              linecache — Random access to text lines.
                                                             (line   30)
* module; search; path <2>:              sys — System-specific parameters and functions.
                                                             (line 1062)
* module; search; path <3>:              site — Site-specific configuration hook.
                                                             (line   14)
* module; search; path <4>:              Embedding Python<2>.
                                                             (line   12)
* module; search; path <5>:              Initializing and finalizing the interpreter.
                                                             (line    8)
* module; search; path <6>:              Process-wide parameters.
                                                             (line  120)
* module; search; path <7>:              Process-wide parameters.
                                                             (line  133)
* module; shelve:                        marshal — Internal Python object serialization.
                                                             (line   15)
* module; signal:                        _thread — Low-level threading API.
                                                             (line  173)
* module; signal <1>:                    Signal Handling<2>. (line    8)
* module; sitecustomize:                 site — Site-specific configuration hook.
                                                             (line   94)
* module; socket:                        Internet Protocols and Support.
                                                             (line    6)
* module; stat:                          Files and Directories.
                                                             (line 1002)
* module; string:                        locale — Internationalization services.
                                                             (line  460)
* module; struct:                        Socket Objects.     (line  551)
* module; sys:                           Standard Modules.   (line    6)
* module; sys <1>:                       The try statement.  (line   69)
* module; sys <2>:                       Complete Python programs.
                                                             (line    6)
* module; sys <3>:                       Built-in Functions. (line 1223)
* module; sys <4>:                       Embedding Python<2>.
                                                             (line   12)
* module; sys <5>:                       Initializing and finalizing the interpreter.
                                                             (line    8)
* module; sys <6>:                       Sub-interpreter support.
                                                             (line   26)
* module; types:                         Type Objects.       (line    6)
* module; urllib.request:                http client — HTTP protocol client.
                                                             (line    8)
* module; usercustomize:                 site — Site-specific configuration hook.
                                                             (line  105)
* module; uu:                            binascii — Convert between binary and ASCII.
                                                             (line    6)
* module; _locale:                       locale — Internationalization services.
                                                             (line   16)
* module; _thread:                       High-level API.     (line   45)
* module; __main__:                      Resolution of names.
                                                             (line   51)
* module; __main__ <1>:                  Complete Python programs.
                                                             (line    6)
* module; __main__ <2>:                  Complete Python programs.
                                                             (line   19)
* module; __main__ <3>:                  runpy — Locating and executing Python modules.
                                                             (line   30)
* module; __main__ <4>:                  runpy — Locating and executing Python modules.
                                                             (line   98)
* module; __main__ <5>:                  Embedding Python<2>.
                                                             (line   12)
* module; __main__ <6>:                  Initializing and finalizing the interpreter.
                                                             (line    8)
* module; __main__ <7>:                  Sub-interpreter support.
                                                             (line   26)
* ModuleFinder (class in modulefinder):  modulefinder — Find modules used by a script.
                                                             (line   26)
* modulefinder (module):                 modulefinder — Find modules used by a script.
                                                             (line    6)
* ModuleInfo (class in pkgutil):         pkgutil — Package extension utility.
                                                             (line   13)
* ModuleNotFoundError:                   Concrete exceptions.
                                                             (line   51)
* modules (in module sys):               sys — System-specific parameters and functions.
                                                             (line 1052)
* modules (in module sys) <1>:           Importing Modules<2>.
                                                             (line    7)
* modules (in module sys) <2>:           Initializing and finalizing the interpreter.
                                                             (line    8)
* modules (modulefinder.ModuleFinder attribute): modulefinder — Find modules used by a script.
                                                             (line   49)
* ModuleSpec (class in importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line  352)
* modules_cleanup() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  838)
* modules_setup() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  834)
* ModuleType (class in types):           Standard Interpreter Types.
                                                             (line  117)
* ModuleType (in module types):          Module Objects.     (line    8)
* module_for_loader() (in module importlib.util): importlib util – Utility code for importers.
                                                             (line  137)
* module_from_spec() (in module importlib.util): importlib util – Utility code for importers.
                                                             (line  121)
* module_repr() (importlib.abc.Loader method): importlib abc – Abstract base classes related to import.
                                                             (line  272)
* modulo:                                Binary arithmetic operations.
                                                             (line   41)
* monotonic() (in module time):          Functions<3>.       (line  161)
* monotonic_ns() (in module time):       Functions<3>.       (line  174)
* month (datetime.date attribute):       date Objects.       (line  106)
* month (datetime.datetime attribute):   datetime Objects.   (line  268)
* month() (in module calendar):          calendar — General calendar-related functions.
                                                             (line  339)
* monthcalendar() (in module calendar):  calendar — General calendar-related functions.
                                                             (line  328)
* monthdatescalendar() (calendar.Calendar method): calendar — General calendar-related functions.
                                                             (line   89)
* monthdays2calendar() (calendar.Calendar method): calendar — General calendar-related functions.
                                                             (line   95)
* monthdayscalendar() (calendar.Calendar method): calendar — General calendar-related functions.
                                                             (line  101)
* monthrange() (in module calendar):     calendar — General calendar-related functions.
                                                             (line  323)
* month_abbr (in module calendar):       calendar — General calendar-related functions.
                                                             (line  383)
* month_name (in module calendar):       calendar — General calendar-related functions.
                                                             (line  376)
* Morsel (class in http.cookies):        Morsel Objects.     (line    6)
* most_common() (collections.Counter method): Counter objects.
                                                             (line   77)
* mouseinterval() (in module curses):    Functions<4>.       (line  276)
* mousemask() (in module curses):        Functions<4>.       (line  283)
* move() (curses.panel.Panel method):    Panel Objects.      (line   35)
* move() (curses.window method):         Window Objects.     (line  393)
* move() (in module shutil):             Directory and files operations.
                                                             (line  302)
* move() (mmap.mmap method):             mmap — Memory-mapped file support.
                                                             (line  218)
* move() (tkinter.ttk.Treeview method):  ttk Treeview.       (line  221)
* move_file() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  498)
* move_file() (in module distutils.file_util): distutils file_util — Single file operations.
                                                             (line   34)
* move_to_end() (collections.OrderedDict method): OrderedDict objects.
                                                             (line   53)
* MozillaCookieJar (class in http.cookiejar): FileCookieJar subclasses and co-operation with web browsers.
                                                             (line    9)
* MRO:                                   Glossary.           (line  856)
* mro() (class method):                  Special Attributes. (line   40)
* msg (http.client.HTTPResponse attribute): HTTPResponse Objects.
                                                             (line   40)
* msg (json.JSONDecodeError attribute):  Exceptions<14>.     (line   11)
* msg (re.error attribute):              Module Contents.    (line  372)
* msg (traceback.TracebackException attribute): TracebackException Objects.
                                                             (line   59)
* msg() (telnetlib.Telnet method):       Telnet Objects.     (line   78)
* msi:                                   msilib — Read and write Microsoft Installer files.
                                                             (line    8)
* msilib (module):                       msilib — Read and write Microsoft Installer files.
                                                             (line    6)
* msvcrt (module):                       msvcrt — Useful routines from the MS VC++ runtime.
                                                             (line    6)
* mtime (gzip.GzipFile attribute):       gzip — Support for gzip files.
                                                             (line  142)
* mtime (tarfile.TarInfo attribute):     TarInfo Objects.    (line   51)
* mtime() (urllib.robotparser.RobotFileParser method): urllib robotparser — Parser for robots txt.
                                                             (line   39)
* mt_interact() (telnetlib.Telnet method): Telnet Objects.   (line  117)
* mul() (in module audioop):             audioop — Manipulate raw audio data.
                                                             (line  169)
* mul() (in module operator):            operator — Standard operators as functions.
                                                             (line  116)
* Mult (class in ast):                   Expressions<2>.     (line   54)
* MultiCall (class in xmlrpc.client):    MultiCall Objects.  (line    9)
* MULTILINE (in module re):              Module Contents.    (line  101)
* MultiLoopChildWatcher (class in asyncio): Process Watchers.
                                                             (line  100)
* multimode() (in module statistics):    Function details.   (line  256)
* MultipartConversionError:              email errors Exception and Defect classes.
                                                             (line   42)
* multiplication:                        Binary arithmetic operations.
                                                             (line   16)
* multiply() (decimal.Context method):   Context objects.    (line  388)
* multiprocessing (module):              multiprocessing — Process-based parallelism.
                                                             (line    6)
* multiprocessing.connection (module):   Listeners and Clients.
                                                             (line    6)
* multiprocessing.dummy (module):        The multiprocessing dummy module.
                                                             (line    6)
* multiprocessing.Manager() (in module multiprocessing.sharedctypes): Managers.
                                                             (line   12)
* multiprocessing.managers (module):     Managers.           (line   18)
* multiprocessing.pool (module):         Process Pools.      (line    6)
* multiprocessing.sharedctypes (module): The multiprocessing sharedctypes module.
                                                             (line    6)
* multiprocessing.shared_memory (module): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line    6)
* mutable:                               Glossary.           (line  860)
* mutable object:                        Objects values and types.
                                                             (line   11)
* mutable sequence; loop over:           The for statement.  (line   44)
* mutable; sequence; types:              Mutable Sequence Types.
                                                             (line    6)
* MutableMapping (class in collections.abc): Collections Abstract Base Classes.
                                                             (line  182)
* MutableMapping (class in typing):      Corresponding to collections in collections abc.
                                                             (line   81)
* MutableSequence (class in collections.abc): Collections Abstract Base Classes.
                                                             (line  159)
* MutableSequence (class in typing):     Corresponding to collections in collections abc.
                                                             (line   89)
* MutableSet (class in collections.abc): Collections Abstract Base Classes.
                                                             (line  177)
* MutableSet (class in typing):          Corresponding to collections in collections abc.
                                                             (line   97)
* mvderwin() (curses.window method):     Window Objects.     (line  397)
* mvwin() (curses.window method):        Window Objects.     (line  404)
* myrights() (imaplib.IMAP4 method):     IMAP4 Objects.      (line  157)
* name:                                  Identifiers and keywords.
                                                             (line    6)
* name <1>:                              Binding of names.   (line    6)
* name <2>:                              Identifiers Names.  (line    6)
* Name (class in ast):                   Variables.          (line    6)
* name (codecs.CodecInfo attribute):     codecs — Codec registry and base classes.
                                                             (line   65)
* name (contextvars.ContextVar attribute): Context Variables.
                                                             (line   24)
* name (doctest.DocTest attribute):      DocTest Objects.    (line   30)
* name (email.headerregistry.BaseHeader attribute): email headerregistry Custom Header Objects.
                                                             (line   45)
* name (hashlib.hash attribute):         Hash algorithms.    (line  115)
* name (hmac.HMAC attribute):            hmac — Keyed-Hashing for Message Authentication.
                                                             (line  100)
* name (http.cookiejar.Cookie attribute): Cookie Objects<2>. (line   28)
* name (importlib.abc.FileLoader attribute): importlib abc – Abstract base classes related to import.
                                                             (line  486)
* name (importlib.machinery.ExtensionFileLoader attribute): importlib machinery – Importers and path hooks.
                                                             (line  311)
* name (importlib.machinery.ModuleSpec attribute): importlib machinery – Importers and path hooks.
                                                             (line  368)
* name (importlib.machinery.SourceFileLoader attribute): importlib machinery – Importers and path hooks.
                                                             (line  224)
* name (importlib.machinery.SourcelessFileLoader attribute): importlib machinery – Importers and path hooks.
                                                             (line  268)
* name (in module os):                   os — Miscellaneous operating system interfaces.
                                                             (line   46)
* NAME (in module token):                token — Constants used with Python parse trees.
                                                             (line   42)
* name (inspect.Parameter attribute):    Introspecting callables with the Signature object.
                                                             (line  157)
* name (io.FileIO attribute):            Raw File I/O.       (line   59)
* name (multiprocessing.Process attribute): Process and exceptions.
                                                             (line   67)
* name (multiprocessing.shared_memory.SharedMemory attribute): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line   91)
* name (os.DirEntry attribute):          Files and Directories.
                                                             (line  847)
* name (ossaudiodev.oss_audio_device attribute): Audio Device Objects.
                                                             (line  234)
* name (pyclbr.Class attribute):         Class Objects<2>.   (line   17)
* name (pyclbr.Function attribute):      Function Objects.   (line   17)
* name (tarfile.TarInfo attribute):      TarInfo Objects.    (line   43)
* name (threading.Thread attribute):     Thread Objects.     (line  136)
* name (xml.dom.Attr attribute):         Attr Objects.       (line    8)
* name (xml.dom.DocumentType attribute): DocumentType Objects.
                                                             (line   33)
* name (zipfile.Path attribute):         Path Objects.       (line   21)
* name() (importlib.abc.Traversable method): importlib abc – Abstract base classes related to import.
                                                             (line  621)
* name() (in module unicodedata):        unicodedata — Unicode Database.
                                                             (line   25)
* name2codepoint (in module html.entities): html entities — Definitions of HTML general entities.
                                                             (line   30)
* name; binding:                         The import statement.
                                                             (line    6)
* name; binding <1>:                     The import statement.
                                                             (line   51)
* name; binding <2>:                     Function definitions.
                                                             (line    6)
* name; binding <3>:                     Function definitions.
                                                             (line    6)
* name; binding <4>:                     Class definitions.  (line    6)
* name; mangling:                        Private Variables.  (line   13)
* name; mangling <1>:                    Identifiers Names.  (line   12)
* Named Shared Memory:                   multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line   10)
* named tuple:                           Glossary.           (line  865)
* NamedExpr (class in ast):              Expressions<2>.     (line  185)
* NamedTemporaryFile() (in module tempfile): tempfile — Generate temporary files and directories.
                                                             (line   71)
* NamedTuple (class in typing):          Other special directives.
                                                             (line    9)
* namedtuple() (in module collections):  namedtuple Factory Function for Tuples with Named Fields.
                                                             (line   11)
* NameError:                             Concrete exceptions.
                                                             (line   89)
* NameError (built-in exception):        Resolution of names.
                                                             (line   16)
* namelist() (zipfile.ZipFile method):   ZipFile Objects.    (line  105)
* nameprep() (in module encodings.idna): encodings idna — Internationalized Domain Names in Applications.
                                                             (line   50)
* namer (logging.handlers.BaseRotatingHandler attribute): BaseRotatingHandler.
                                                             (line   17)
* namereplace_errors() (in module codecs): Error Handlers.   (line  157)
* names() (in module tkinter.font):      tkinter font — Tkinter font wrapper.
                                                             (line   92)
* namespace:                             Naming and binding. (line    6)
* namespace <1>:                         Glossary.           (line  891)
* Namespace (class in argparse):         The Namespace object.
                                                             (line    6)
* Namespace (class in multiprocessing.managers): Managers.   (line  226)
* namespace package:                     Glossary.           (line  905)
* namespace() (imaplib.IMAP4 method):    IMAP4 Objects.      (line  162)
* Namespace() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  176)
* NamespaceErr:                          Exceptions<17>.     (line   66)
* namespaceURI (xml.dom.Node attribute): Node Objects.       (line   74)
* NAMESPACE_DNS (in module uuid):        uuid — UUID objects according to RFC 4122.
                                                             (line  203)
* NAMESPACE_OID (in module uuid):        uuid — UUID objects according to RFC 4122.
                                                             (line  212)
* NAMESPACE_URL (in module uuid):        uuid — UUID objects according to RFC 4122.
                                                             (line  208)
* NAMESPACE_X500 (in module uuid):       uuid — UUID objects according to RFC 4122.
                                                             (line  216)
* nametofont() (in module tkinter.font): tkinter font — Tkinter font wrapper.
                                                             (line   96)
* NaN:                                   Built-in Functions. (line  582)
* nan (in module cmath):                 Constants<3>.       (line   33)
* nan (in module math):                  Constants<2>.       (line   31)
* nanj (in module cmath):                Constants<3>.       (line   40)
* NannyNag:                              tabnanny — Detection of ambiguous indentation.
                                                             (line   37)
* napms() (in module curses):            Functions<4>.       (line  292)
* nargs (optparse.Option attribute):     Option attributes.  (line   42)
* native_id (threading.Thread attribute): Thread Objects.    (line  156)
* nbytes (memoryview attribute):         Memory Views.       (line  376)
* ncurses_version (in module curses):    Constants<6>.       (line   23)
* ndiff() (in module difflib):           difflib — Helpers for computing deltas.
                                                             (line  232)
* ndim (memoryview attribute):           Memory Views.       (line  442)
* ne (2to3 fixer):                       Fixers.             (line  201)
* ne() (in module operator):             operator — Standard operators as functions.
                                                             (line   24)
* needs_input (bz2.BZ2Decompressor attribute): Incremental de compression.
                                                             (line   85)
* needs_input (lzma.LZMADecompressor attribute): Compressing and decompressing data in memory.
                                                             (line  175)
* neg() (in module operator):            operator — Standard operators as functions.
                                                             (line  128)
* negation:                              Unary arithmetic and bitwise operations.
                                                             (line   10)
* nested scope:                          Glossary.           (line  914)
* netmask (ipaddress.IPv4Network attribute): Network objects.
                                                             (line  101)
* netmask (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  315)
* NetmaskValueError:                     Custom Exceptions.  (line   13)
* netrc (class in netrc):                netrc — netrc file processing.
                                                             (line   13)
* netrc (module):                        netrc — netrc file processing.
                                                             (line    6)
* NetrcParseError:                       netrc — netrc file processing.
                                                             (line   36)
* netscape (http.cookiejar.CookiePolicy attribute): CookiePolicy Objects.
                                                             (line   68)
* network (ipaddress.IPv4Interface attribute): Interface objects.
                                                             (line   28)
* network (ipaddress.IPv6Interface attribute): Interface objects.
                                                             (line   76)
* Network News Transfer Protocol:        nntplib — NNTP protocol client.
                                                             (line    8)
* network_address (ipaddress.IPv4Network attribute): Network objects.
                                                             (line   86)
* network_address (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  309)
* NEVER_EQ (in module test.support):     test support — Utilities for the Python test suite.
                                                             (line  205)
* new() (in module hashlib):             Hash algorithms.    (line   65)
* new() (in module hmac):                hmac — Keyed-Hashing for Message Authentication.
                                                             (line   12)
* new-style class:                       Glossary.           (line  924)
* newer() (in module distutils.dep_util): distutils dep_util — Dependency checking.
                                                             (line   10)
* newer_group() (in module distutils.dep_util): distutils dep_util — Dependency checking.
                                                             (line   24)
* newer_pairwise() (in module distutils.dep_util): distutils dep_util — Dependency checking.
                                                             (line   17)
* newfunc (C type):                      Slot Type typedefs. (line   30)
* newgroups() (nntplib.NNTP method):     Methods<3>.         (line   80)
* NEWLINE (in module token):             token — Constants used with Python parse trees.
                                                             (line   48)
* NEWLINE token:                         Logical lines.      (line    6)
* NEWLINE token <1>:                     Compound statements.
                                                             (line   54)
* newlines (io.TextIOBase attribute):    Text I/O<2>.        (line   24)
* newnews() (nntplib.NNTP method):       Methods<3>.         (line   95)
* newpad() (in module curses):           Functions<4>.       (line  296)
* NewType() (in module typing):          Other special directives.
                                                             (line   70)
* newwin() (in module curses):           Functions<4>.       (line  316)
* new_alignment() (formatter.writer method): The Writer Interface.
                                                             (line   17)
* new_child() (collections.ChainMap method): ChainMap objects.
                                                             (line   46)
* new_class() (in module types):         Dynamic Type Creation.
                                                             (line    6)
* new_compiler() (in module distutils.ccompiler): distutils ccompiler — CCompiler base class.
                                                             (line   48)
* new_event_loop() (asyncio.AbstractEventLoopPolicy method): Policy Objects.
                                                             (line   27)
* new_event_loop() (in module asyncio):  Event Loop.         (line   61)
* new_font() (formatter.writer method):  The Writer Interface.
                                                             (line   25)
* new_margin() (formatter.writer method): The Writer Interface.
                                                             (line   35)
* new_module() (in module imp):          imp — Access the import internals.
                                                             (line  124)
* new_panel() (in module curses.panel):  Functions<5>.       (line   12)
* new_spacing() (formatter.writer method): The Writer Interface.
                                                             (line   42)
* new_styles() (formatter.writer method): The Writer Interface.
                                                             (line   46)
* next (2to3 fixer):                     Fixers.             (line  205)
* next (pdb command):                    Debugger Commands.  (line  168)
* next() (built-in function):            Built-in Functions. (line  988)
* next() (nntplib.NNTP method):          Methods<3>.         (line  233)
* next() (tarfile.TarFile method):       TarFile Objects.    (line  130)
* next() (tkinter.ttk.Treeview method):  ttk Treeview.       (line  232)
* nextafter() (in module math):          Number-theoretic and representation functions.
                                                             (line  194)
* nextfile() (in module fileinput):      fileinput — Iterate over lines from multiple input streams.
                                                             (line  116)
* nextkey() (dbm.gnu.gdbm method):       dbm gnu — GNU’s reinterpretation of dbm.
                                                             (line   93)
* nextSibling (xml.dom.Node attribute):  Node Objects.       (line   42)
* next_minus() (decimal.Context method): Context objects.    (line  392)
* next_minus() (decimal.Decimal method): Decimal objects.    (line  399)
* next_plus() (decimal.Context method):  Context objects.    (line  396)
* next_plus() (decimal.Decimal method):  Decimal objects.    (line  405)
* next_toward() (decimal.Context method): Context objects.   (line  400)
* next_toward() (decimal.Decimal method): Decimal objects.   (line  411)
* ngettext() (gettext.GNUTranslations method): The GNUTranslations class.
                                                             (line   47)
* ngettext() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line   41)
* ngettext() (in module gettext):        GNU gettext API.    (line   54)
* nice() (in module os):                 Process Management. (line  318)
* nis (module):                          nis — Interface to Sun’s NIS Yellow Pages.
                                                             (line    6)
* NL (in module token):                  token — Constants used with Python parse trees.
                                                             (line  265)
* nl() (in module curses):               Functions<4>.       (line  326)
* nlargest() (in module heapq):          heapq — Heap queue algorithm.
                                                             (line  106)
* nlst() (ftplib.FTP method):            FTP Objects.        (line  179)
* nl_langinfo() (in module locale):      locale — Internationalization services.
                                                             (line  172)
* NNTP (class in nntplib):               nntplib — NNTP protocol client.
                                                             (line   54)
* NNTP; protocol:                        nntplib — NNTP protocol client.
                                                             (line    8)
* NNTPDataError:                         nntplib — NNTP protocol client.
                                                             (line  161)
* NNTPError:                             nntplib — NNTP protocol client.
                                                             (line  130)
* nntplib (module):                      nntplib — NNTP protocol client.
                                                             (line    6)
* NNTPPermanentError:                    nntplib — NNTP protocol client.
                                                             (line  151)
* NNTPProtocolError:                     nntplib — NNTP protocol client.
                                                             (line  156)
* NNTPReplyError:                        nntplib — NNTP protocol client.
                                                             (line  141)
* NNTPTemporaryError:                    nntplib — NNTP protocol client.
                                                             (line  146)
* nntp_implementation (nntplib.NNTP attribute): Attributes.  (line   14)
* NNTP_SSL (class in nntplib):           nntplib — NNTP protocol client.
                                                             (line   97)
* nntp_version (nntplib.NNTP attribute): Attributes.         (line    6)
* nocbreak() (in module curses):         Functions<4>.       (line  332)
* NoDataAllowedErr:                      Exceptions<17>.     (line   83)
* node() (in module platform):           Cross Platform.     (line   40)
* nodelay() (curses.window method):      Window Objects.     (line  408)
* nodeName (xml.dom.Node attribute):     Node Objects.       (line   79)
* NodeTransformer (class in ast):        ast Helpers.        (line  190)
* nodeType (xml.dom.Node attribute):     Node Objects.       (line    8)
* nodeValue (xml.dom.Node attribute):    Node Objects.       (line   88)
* NodeVisitor (class in ast):            ast Helpers.        (line  155)
* noecho() (in module curses):           Functions<4>.       (line  337)
* NOEXPR (in module locale):             locale — Internationalization services.
                                                             (line  251)
* NoModificationAllowedErr:              Exceptions<17>.     (line   88)
* nonblock() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line   75)
* NonCallableMagicMock (class in unittest.mock): Magic Mock. (line   21)
* NonCallableMock (class in unittest.mock): The Mock Class.  (line  558)
* None (Built-in object):                Truth Value Testing.
                                                             (line   15)
* None (built-in variable):              Built-in Constants. (line   18)
* nonl() (in module curses):             Functions<4>.       (line  341)
* Nonlocal (class in ast):               Function and class definitions.
                                                             (line  151)
* nonzero (2to3 fixer):                  Fixers.             (line  211)
* noop() (imaplib.IMAP4 method):         IMAP4 Objects.      (line  166)
* noop() (poplib.POP3 method):           POP3 Objects.       (line   78)
* NoOptionError:                         Exceptions<6>.      (line   32)
* NOP (opcode):                          Python Bytecode Instructions.
                                                             (line   55)
* noqiflush() (in module curses):        Functions<4>.       (line  351)
* noraw() (in module curses):            Functions<4>.       (line  359)
* NoReturn (in module typing):           Special types.      (line   16)
* NORMAL (in module tkinter.font):       tkinter font — Tkinter font wrapper.
                                                             (line   15)
* NormalDist (class in statistics):      NormalDist objects. (line   13)
* normalize() (decimal.Context method):  Context objects.    (line  404)
* normalize() (decimal.Decimal method):  Decimal objects.    (line  419)
* normalize() (in module locale):        locale — Internationalization services.
                                                             (line  356)
* normalize() (in module unicodedata):   unicodedata — Unicode Database.
                                                             (line   81)
* normalize() (xml.dom.Node method):     Node Objects.       (line  141)
* NORMALIZE_WHITESPACE (in module doctest): Option Flags.    (line   39)
* normalvariate() (in module random):    Real-valued distributions.
                                                             (line   77)
* NORMAL_PRIORITY_CLASS (in module subprocess): Windows Constants.
                                                             (line   80)
* normcase() (in module os.path):        os path — Common pathname manipulations.
                                                             (line  275)
* normpath() (in module os.path):        os path — Common pathname manipulations.
                                                             (line  284)
* NoSectionError:                        Exceptions<6>.      (line   10)
* NoSuchMailboxError:                    Exceptions<15>.     (line   13)
* Not (class in ast):                    Expressions<2>.     (line   28)
* NotADirectoryError:                    OS exceptions.      (line   86)
* notation:                              Notation.           (line    6)
* notationDecl() (xml.sax.handler.DTDHandler method): DTDHandler Objects.
                                                             (line    8)
* NotationDeclHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  272)
* notations (xml.dom.DocumentType attribute): DocumentType Objects.
                                                             (line   46)
* NotConnected:                          http client — HTTP protocol client.
                                                             (line  133)
* NoteBook (class in tkinter.tix):       Manager Widgets.    (line   22)
* Notebook (class in tkinter.ttk):       ttk Notebook.       (line    6)
* NotEmptyError:                         Exceptions<15>.     (line   20)
* NotEq (class in ast):                  Expressions<2>.     (line  109)
* NOTEQUAL (in module token):            token — Constants used with Python parse trees.
                                                             (line  138)
* NotFoundErr:                           Exceptions<17>.     (line   72)
* notify() (asyncio.Condition method):   Condition.          (line   55)
* notify() (threading.Condition method): Condition Objects.  (line  152)
* notify_all() (asyncio.Condition method): Condition.        (line   68)
* notify_all() (threading.Condition method): Condition Objects.
                                                             (line  172)
* notimeout() (curses.window method):    Window Objects.     (line  412)
* NotImplemented (built-in variable):    Built-in Constants. (line   25)
* NotImplementedError:                   Concrete exceptions.
                                                             (line   95)
* NotIn (class in ast):                  Expressions<2>.     (line  109)
* NotStandaloneHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  323)
* NotSupportedErr:                       Exceptions<17>.     (line   78)
* NotSupportedError:                     Exceptions<5>.      (line   40)
* not_() (in module operator):           operator — Standard operators as functions.
                                                             (line   49)
* noutrefresh() (curses.window method):  Window Objects.     (line  420)
* now() (datetime.datetime class method): datetime Objects.  (line   60)
* no_cache() (zoneinfo.ZoneInfo class method): The ZoneInfo class.
                                                             (line   41)
* no_proxy:                              urllib request — Extensible library for opening URLs.
                                                             (line  295)
* no_tracing() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  708)
* no_type_check() (in module typing):    Functions and decorators.
                                                             (line   70)
* no_type_check_decorator() (in module typing): Functions and decorators.
                                                             (line   80)
* npgettext() (gettext.GNUTranslations method): The GNUTranslations class.
                                                             (line   79)
* npgettext() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line   55)
* npgettext() (in module gettext):       GNU gettext API.    (line   77)
* NSIG (in module signal):               Module contents<2>. (line  164)
* nsmallest() (in module heapq):         heapq — Heap queue algorithm.
                                                             (line  114)
* NTEventLogHandler (class in logging.handlers): NTEventLogHandler.
                                                             (line   11)
* ntohl() (in module socket):            Other functions<2>. (line  181)
* ntohs() (in module socket):            Other functions<2>. (line  188)
* ntransfercmd() (ftplib.FTP method):    FTP Objects.        (line  157)
* NT_OFFSET (in module token):           token — Constants used with Python parse trees.
                                                             (line  256)
* null; operation:                       The pass statement. (line    6)
* null; operation <1>:                   The pass statement. (line    6)
* nullcontext() (in module contextlib):  Utilities.          (line  147)
* NullFormatter (class in formatter):    Formatter Implementations.
                                                             (line   10)
* NullHandler (class in logging):        NullHandler.        (line   12)
* NullImporter (class in imp):           imp — Access the import internals.
                                                             (line  345)
* NullTranslations (class in gettext):   The NullTranslations class.
                                                             (line   13)
* NullWriter (class in formatter):       Writer Implementations.
                                                             (line   10)
* number:                                Numeric literals.   (line    6)
* Number (class in numbers):             numbers — Numeric abstract base classes.
                                                             (line   15)
* NUMBER (in module token):              token — Constants used with Python parse trees.
                                                             (line   44)
* numbers (module):                      numbers — Numeric abstract base classes.
                                                             (line    6)
* number_class() (decimal.Context method): Context objects.  (line  408)
* number_class() (decimal.Decimal method): Decimal objects.  (line  428)
* numerator (fractions.Fraction attribute): fractions — Rational numbers.
                                                             (line   95)
* numerator (numbers.Rational attribute): The numeric tower. (line   47)
* numeric literal:                       Numeric literals.   (line    6)
* numeric() (in module unicodedata):     unicodedata — Unicode Database.
                                                             (line   43)
* numeric; conversions:                  Numeric Types — int float complex.
                                                             (line  104)
* numeric; literals:                     Numeric Types — int float complex.
                                                             (line   19)
* numinput() (in module turtle):         Input methods.      (line   22)
* numliterals (2to3 fixer):              Fixers.             (line  216)
* num_addresses (ipaddress.IPv4Network attribute): Network objects.
                                                             (line  128)
* num_addresses (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  327)
* num_tickets (ssl.SSLContext attribute): SSL Contexts.      (line  573)
* N_TOKENS (in module token):            token — Constants used with Python parse trees.
                                                             (line  254)
* n_waiting (threading.Barrier attribute): Barrier Objects.  (line   97)
* obj (memoryview attribute):            Memory Views.       (line  365)
* object:                                Objects values and types.
                                                             (line    6)
* object <1>:                            Glossary.           (line  932)
* object (built-in class):               Built-in Functions. (line  995)
* object (UnicodeError attribute):       Concrete exceptions.
                                                             (line  376)
* object.__slots__ (built-in variable):  __slots__.          (line   14)
* object; asynchronous-generator:        Asynchronous generator functions.
                                                             (line   55)
* object; Boolean:                       The standard type hierarchy.
                                                             (line   98)
* object; Boolean <1>:                   Numeric Types — int float complex.
                                                             (line    6)
* object; built-in function:             The standard type hierarchy.
                                                             (line  490)
* object; built-in function <1>:         Calls.              (line  132)
* object; built-in method:               The standard type hierarchy.
                                                             (line  503)
* object; built-in method <1>:           Calls.              (line  132)
* object; bytearray:                     Mutable Sequence Types.
                                                             (line    6)
* object; bytearray <1>:                 Binary Sequence Types — bytes bytearray memoryview.
                                                             (line    6)
* object; bytearray <2>:                 Bytearray Objects.  (line    6)
* object; bytearray <3>:                 Byte Array Objects. (line    6)
* object; bytes:                         Binary Sequence Types — bytes bytearray memoryview.
                                                             (line    6)
* object; bytes <1>:                     Bytes Objects.      (line    6)
* object; bytes <2>:                     Bytes Objects<2>.   (line    9)
* object; callable:                      The standard type hierarchy.
                                                             (line  297)
* object; callable <1>:                  Slicings.           (line   38)
* object; Capsule:                       Capsules<2>.        (line    6)
* object; class:                         The standard type hierarchy.
                                                             (line  578)
* object; class <1>:                     Calls.              (line  137)
* object; class <2>:                     Class definitions.  (line    6)
* object; class instance:                The standard type hierarchy.
                                                             (line  578)
* object; class instance <1>:            The standard type hierarchy.
                                                             (line  605)
* object; class instance <2>:            Calls.              (line  141)
* object; code:                          The standard type hierarchy.
                                                             (line  654)
* object; code <1>:                      Methods.            (line   43)
* object; code <2>:                      marshal — Internal Python object serialization.
                                                             (line   30)
* object; code <3>:                      Cell Objects.       (line   54)
* object; complex:                       The standard type hierarchy.
                                                             (line  124)
* object; complex number:                Numeric Types — int float complex.
                                                             (line    6)
* object; complex number <1>:            Complex Number Objects.
                                                             (line    6)
* object; deallocation:                  Finalization and De-allocation.
                                                             (line    6)
* object; dictionary:                    The standard type hierarchy.
                                                             (line  265)
* object; dictionary <1>:                The standard type hierarchy.
                                                             (line  578)
* object; dictionary <2>:                Basic customization.
                                                             (line  222)
* object; dictionary <3>:                Dictionary displays.
                                                             (line    6)
* object; dictionary <4>:                Subscriptions.      (line    6)
* object; dictionary <5>:                Assignment statements.
                                                             (line  116)
* object; dictionary <6>:                Mapping Types — dict.
                                                             (line    6)
* object; dictionary <7>:                Dictionary Objects. (line    6)
* object; Ellipsis:                      The standard type hierarchy.
                                                             (line   46)
* object; file:                          Reading and Writing Files.
                                                             (line    6)
* object; file <1>:                      File Objects.       (line    6)
* object; finalization:                  Finalization and De-allocation.
                                                             (line    6)
* object; floating point:                The standard type hierarchy.
                                                             (line  112)
* object; floating point <1>:            Numeric Types — int float complex.
                                                             (line    6)
* object; floating point <2>:            Floating Point Objects.
                                                             (line    6)
* object; frame:                         The standard type hierarchy.
                                                             (line  714)
* object; frozenset:                     The standard type hierarchy.
                                                             (line  247)
* object; frozenset <1>:                 Set Objects.        (line    6)
* object; function:                      The standard type hierarchy.
                                                             (line  302)
* object; function <1>:                  The standard type hierarchy.
                                                             (line  490)
* object; function <2>:                  Calls.              (line  123)
* object; function <3>:                  Calls.              (line  132)
* object; function <4>:                  Function definitions.
                                                             (line    6)
* object; function <5>:                  Function Objects<3>.
                                                             (line    6)
* object; generator:                     The standard type hierarchy.
                                                             (line  692)
* object; generator <1>:                 Generator expressions.
                                                             (line    6)
* object; generator <2>:                 Yield expressions.  (line  108)
* object; GenericAlias:                  Generic Alias Type. (line    6)
* object; immutable:                     The standard type hierarchy.
                                                             (line  151)
* object; immutable sequence:            The standard type hierarchy.
                                                             (line  151)
* object; instance:                      The standard type hierarchy.
                                                             (line  578)
* object; instance <1>:                  The standard type hierarchy.
                                                             (line  605)
* object; instance <2>:                  Calls.              (line  141)
* object; instancemethod:                Instance Method Objects.
                                                             (line    6)
* object; integer:                       The standard type hierarchy.
                                                             (line   82)
* object; integer <1>:                   Numeric Types — int float complex.
                                                             (line    6)
* object; integer <2>:                   Integer Objects.    (line    6)
* object; io.StringIO:                   Text Sequence Type — str.
                                                             (line   35)
* object; list:                          The standard type hierarchy.
                                                             (line  205)
* object; list <1>:                      List displays.      (line    6)
* object; list <2>:                      Attribute references.
                                                             (line   10)
* object; list <3>:                      Subscriptions.      (line    6)
* object; list <4>:                      Slicings.           (line    6)
* object; list <5>:                      Assignment statements.
                                                             (line  108)
* object; list <6>:                      Mutable Sequence Types.
                                                             (line    6)
* object; list <7>:                      Lists<2>.           (line    6)
* object; list <8>:                      List Objects.       (line    6)
* object; long integer:                  Integer Objects.    (line    6)
* object; mapping:                       The standard type hierarchy.
                                                             (line  254)
* object; mapping <1>:                   The standard type hierarchy.
                                                             (line  626)
* object; mapping <2>:                   Subscriptions.      (line    6)
* object; mapping <3>:                   Assignment statements.
                                                             (line  116)
* object; mapping <4>:                   Mapping Types — dict.
                                                             (line    6)
* object; mapping <5>:                   Container Objects.  (line    6)
* object; memoryview:                    Binary Sequence Types — bytes bytearray memoryview.
                                                             (line    6)
* object; memoryview <1>:                Ellipsis Object.    (line   11)
* object; method:                        Instance Objects.   (line   31)
* object; method <1>:                    The standard type hierarchy.
                                                             (line  393)
* object; method <2>:                    The standard type hierarchy.
                                                             (line  503)
* object; method <3>:                    Calls.              (line  132)
* object; method <4>:                    Methods.            (line    6)
* object; method <5>:                    Method Objects<2>.  (line    6)
* object; module:                        The standard type hierarchy.
                                                             (line  526)
* object; module <1>:                    Attribute references.
                                                             (line   10)
* object; module <2>:                    Module Objects.     (line    6)
* object; mutable:                       The standard type hierarchy.
                                                             (line  197)
* object; mutable <1>:                   Assignment statements.
                                                             (line    6)
* object; mutable <2>:                   Assignment statements.
                                                             (line  103)
* object; mutable sequence:              The standard type hierarchy.
                                                             (line  197)
* object; None:                          The standard type hierarchy.
                                                             (line   20)
* object; None <1>:                      Expression statements.
                                                             (line   17)
* object; None <2>:                      The None Object.    (line    6)
* object; NotImplemented:                The standard type hierarchy.
                                                             (line   28)
* object; numeric:                       The standard type hierarchy.
                                                             (line   52)
* object; numeric <1>:                   The standard type hierarchy.
                                                             (line  626)
* object; numeric <2>:                   Comparisons<2>.     (line   43)
* object; numeric <3>:                   Numeric Types — int float complex.
                                                             (line    6)
* object; numeric <4>:                   Numeric Objects.    (line    6)
* object; range:                         Ranges.             (line    6)
* object; sequence:                      The standard type hierarchy.
                                                             (line  132)
* object; sequence <1>:                  The standard type hierarchy.
                                                             (line  626)
* object; sequence <2>:                  Subscriptions.      (line    6)
* object; sequence <3>:                  Slicings.           (line    6)
* object; sequence <4>:                  Membership test operations.
                                                             (line   37)
* object; sequence <5>:                  Assignment statements.
                                                             (line  108)
* object; sequence <6>:                  The for statement.  (line    6)
* object; sequence <7>:                  Common Sequence Operations.
                                                             (line    6)
* object; sequence <8>:                  Sequence Objects.   (line    6)
* object; set:                           The standard type hierarchy.
                                                             (line  241)
* object; set <1>:                       Set displays.       (line    6)
* object; set <2>:                       Set Types — set frozenset.
                                                             (line    6)
* object; set <3>:                       Set Objects.        (line    6)
* object; set type:                      The standard type hierarchy.
                                                             (line  224)
* object; slice:                         Emulating container types.
                                                             (line   65)
* object; socket:                        socket — Low-level networking interface.
                                                             (line   17)
* object; string:                        Subscriptions.      (line    6)
* object; string <1>:                    Slicings.           (line    6)
* object; string <2>:                    Ranges.             (line  125)
* object; traceback:                     The standard type hierarchy.
                                                             (line  765)
* object; traceback <1>:                 The raise statement.
                                                             (line   21)
* object; traceback <2>:                 The try statement.  (line   69)
* object; traceback <3>:                 sys — System-specific parameters and functions.
                                                             (line  365)
* object; traceback <4>:                 traceback — Print or retrieve a stack traceback.
                                                             (line   16)
* object; tuple:                         The standard type hierarchy.
                                                             (line  177)
* object; tuple <1>:                     Subscriptions.      (line    6)
* object; tuple <2>:                     Slicings.           (line    6)
* object; tuple <3>:                     Expression lists.   (line   11)
* object; tuple <4>:                     Immutable Sequence Types.
                                                             (line    6)
* object; tuple <5>:                     Tuples.             (line    6)
* object; tuple <6>:                     Tuple Objects.      (line    6)
* object; type:                          Built-in Functions. (line 1691)
* object; type <1>:                      Objects Types and Reference Counts.
                                                             (line    6)
* object; type <2>:                      Type Objects<2>.    (line    6)
* object; user-defined function:         The standard type hierarchy.
                                                             (line  302)
* object; user-defined function <1>:     Calls.              (line  123)
* object; user-defined function <2>:     Function definitions.
                                                             (line    6)
* object; user-defined method:           The standard type hierarchy.
                                                             (line  393)
* objects; comparing:                    Comparisons<2>.     (line   43)
* object_filenames() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  467)
* objobjargproc (C type):                Slot Type typedefs. (line  111)
* objobjproc (C type):                   Slot Type typedefs. (line  109)
* obufcount() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line  218)
* obuffree() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line  223)
* oct() (built-in function):             Built-in Functions. (line 1005)
* octal literal:                         Numeric literals.   (line    6)
* octal; literals:                       Numeric Types — int float complex.
                                                             (line   19)
* octdigits (in module string):          String constants.   (line   32)
* offset (SyntaxError attribute):        Concrete exceptions.
                                                             (line  268)
* offset (traceback.TracebackException attribute): TracebackException Objects.
                                                             (line   54)
* offset (xml.parsers.expat.ExpatError attribute): ExpatError Exceptions.
                                                             (line   32)
* OK (in module curses):                 Constants<6>.       (line   13)
* ok_command() (tkinter.filedialog.LoadFileDialog method): Native Load/Save Dialogs.
                                                             (line  140)
* ok_command() (tkinter.filedialog.SaveFileDialog method): Native Load/Save Dialogs.
                                                             (line  150)
* ok_event() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line  119)
* old_value (contextvars.Token attribute): Context Variables.
                                                             (line   87)
* OleDLL (class in ctypes):              Loading shared libraries.
                                                             (line   32)
* onclick() (in module turtle):          Using screen events.
                                                             (line   56)
* ondrag() (in module turtle):           Using events.       (line   57)
* onecmd() (cmd.Cmd method):             Cmd Objects.        (line   57)
* onkey() (in module turtle):            Using screen events.
                                                             (line   12)
* onkeypress() (in module turtle):       Using screen events.
                                                             (line   35)
* onkeyrelease() (in module turtle):     Using screen events.
                                                             (line   12)
* onrelease() (in module turtle):        Using events.       (line   30)
* onscreenclick() (in module turtle):    Using screen events.
                                                             (line   56)
* ontimer() (in module turtle):          Using screen events.
                                                             (line   86)
* on_motion() (tkinter.dnd.DndHandler method): tkinter dnd — Drag and drop support.
                                                             (line   56)
* on_release() (tkinter.dnd.DndHandler method): tkinter dnd — Drag and drop support.
                                                             (line   61)
* OP (in module token):                  token — Constants used with Python parse trees.
                                                             (line  242)
* Open (class in tkinter.filedialog):    Native Load/Save Dialogs.
                                                             (line   60)
* open() (built-in function):            Built-in Functions. (line 1029)
* open() (distutils.text_file.TextFile method): distutils text_file — The TextFile class.
                                                             (line   91)
* open() (imaplib.IMAP4 method):         IMAP4 Objects.      (line  170)
* open() (importlib.abc.Traversable method): importlib abc – Abstract base classes related to import.
                                                             (line  645)
* open() (in module aifc):               aifc — Read and write AIFF and AIFC files.
                                                             (line   30)
* open() (in module bz2):                De compression of files.
                                                             (line    6)
* open() (in module codecs):             codecs — Codec registry and base classes.
                                                             (line  170)
* open() (in module dbm):                dbm — Interfaces to Unix “databases”.
                                                             (line   35)
* open() (in module dbm.dumb):           dbm dumb — Portable DBM implementation.
                                                             (line   30)
* open() (in module dbm.gnu):            dbm gnu — GNU’s reinterpretation of dbm.
                                                             (line   27)
* open() (in module dbm.ndbm):           dbm ndbm — Interface based on ndbm.
                                                             (line   31)
* open() (in module gzip):               gzip — Support for gzip files.
                                                             (line   28)
* open() (in module io):                 High-level Module Interface.
                                                             (line   12)
* open() (in module lzma):               Reading and writing compressed files.
                                                             (line    6)
* open() (in module os):                 File Descriptor Operations.
                                                             (line  259)
* open() (in module ossaudiodev):        ossaudiodev — Access to OSS-compatible audio devices.
                                                             (line   42)
* open() (in module shelve):             shelve — Python object persistence.
                                                             (line   17)
* open() (in module sunau):              sunau — Read and write Sun AU files.
                                                             (line   48)
* open() (in module tarfile):            tarfile — Read and write tar archive files.
                                                             (line   35)
* open() (in module tokenize):           Tokenizing Input.   (line  100)
* open() (in module wave):               wave — Read and write WAV files.
                                                             (line   17)
* open() (in module webbrowser):         webbrowser — Convenient Web-browser controller.
                                                             (line   50)
* open() (pathlib.Path method):          Methods<2>.         (line  258)
* open() (pipes.Template method):        Template Objects.   (line   42)
* open() (tarfile.TarFile class method): TarFile Objects.    (line   96)
* open() (telnetlib.Telnet method):      Telnet Objects.     (line   65)
* open() (urllib.request.OpenerDirector method): OpenerDirector Objects.
                                                             (line   46)
* open() (urllib.request.URLopener method): Legacy interface.
                                                             (line   98)
* open() (webbrowser.controller method): Browser Controller Objects.
                                                             (line    9)
* open() (zipfile.Path method):          Path Objects.       (line   25)
* open() (zipfile.ZipFile method):       ZipFile Objects.    (line  109)
* OpenDatabase() (in module msilib):     msilib — Read and write Microsoft Installer files.
                                                             (line   45)
* OpenerDirector (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  258)
* OpenKey() (in module winreg):          Functions<12>.      (line  291)
* OpenKeyEx() (in module winreg):        Functions<12>.      (line  291)
* openlog() (in module syslog):          syslog — Unix syslog library routines.
                                                             (line   36)
* openmixer() (in module ossaudiodev):   ossaudiodev — Access to OSS-compatible audio devices.
                                                             (line   70)
* openpty() (in module os):              File Descriptor Operations.
                                                             (line  353)
* openpty() (in module pty):             pty — Pseudo-terminal utilities.
                                                             (line   29)
* OpenSSL; (use in module hashlib):      Hash algorithms.    (line   21)
* OpenSSL; (use in module ssl):          ssl — TLS/SSL wrapper for socket objects.
                                                             (line    8)
* OPENSSL_VERSION (in module ssl):       Constants<9>.       (line  449)
* OPENSSL_VERSION_INFO (in module ssl):  Constants<9>.       (line  459)
* OPENSSL_VERSION_NUMBER (in module ssl): Constants<9>.      (line  469)
* OpenView() (msilib.Database method):   Database Objects.   (line    6)
* open_binary() (in module importlib.resources): importlib resources – Resources.
                                                             (line   80)
* open_code() (in module io):            High-level Module Interface.
                                                             (line   22)
* open_connection() (in module asyncio): Streams.            (line   42)
* open_new() (in module webbrowser):     webbrowser — Convenient Web-browser controller.
                                                             (line   67)
* open_new() (webbrowser.controller method): Browser Controller Objects.
                                                             (line   15)
* open_new_tab() (in module webbrowser): webbrowser — Convenient Web-browser controller.
                                                             (line   72)
* open_new_tab() (webbrowser.controller method): Browser Controller Objects.
                                                             (line   21)
* open_osfhandle() (in module msvcrt):   File Operations.    (line   44)
* open_resource() (importlib.abc.ResourceReader method): importlib abc – Abstract base classes related to import.
                                                             (line  321)
* open_text() (in module importlib.resources): importlib resources – Resources.
                                                             (line   91)
* open_unix_connection() (in module asyncio): Streams.       (line   98)
* open_unknown() (urllib.request.URLopener method): Legacy interface.
                                                             (line  109)
* open_urlresource() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  779)
* OperationalError:                      Exceptions<5>.      (line   32)
* operations on; dictionary; type:       Mapping Types — dict.
                                                             (line    6)
* operations on; integer; types:         Bitwise Operations on Integer Types.
                                                             (line    6)
* operations on; list; type:             Mutable Sequence Types.
                                                             (line   16)
* operations on; mapping; types:         Mapping Types — dict.
                                                             (line    6)
* operations on; numeric; types:         Numeric Types — int float complex.
                                                             (line   94)
* operations on; sequence; types:        Common Sequence Operations.
                                                             (line   21)
* operations on; sequence; types <1>:    Mutable Sequence Types.
                                                             (line   16)
* operator (2to3 fixer):                 Fixers.             (line  220)
* operator (module):                     operator — Standard operators as functions.
                                                             (line    6)
* operator; !=:                          Comparisons.        (line    6)
* operator; != <1>:                      Comparisons<2>.     (line    6)
* operator; % (percent):                 Binary arithmetic operations.
                                                             (line   41)
* operator; % (percent) <1>:             Numeric Types — int float complex.
                                                             (line   27)
* operator; & (ampersand):               Binary bitwise operations.
                                                             (line   12)
* operator; & (ampersand) <1>:           Bitwise Operations on Integer Types.
                                                             (line    6)
* operator; * (asterisk):                Binary arithmetic operations.
                                                             (line   16)
* operator; * (asterisk) <1>:            Numeric Types — int float complex.
                                                             (line   27)
* operator; **:                          The power operator. (line    6)
* operator; ** <1>:                      Numeric Types — int float complex.
                                                             (line   27)
* operator; + (plus):                    Unary arithmetic and bitwise operations.
                                                             (line   14)
* operator; + (plus) <1>:                Binary arithmetic operations.
                                                             (line   69)
* operator; + (plus) <2>:                Numeric Types — int float complex.
                                                             (line   27)
* operator; - (minus):                   Unary arithmetic and bitwise operations.
                                                             (line   10)
* operator; - (minus) <1>:               Binary arithmetic operations.
                                                             (line   78)
* operator; - (minus) <2>:               Numeric Types — int float complex.
                                                             (line   27)
* operator; / (slash):                   Binary arithmetic operations.
                                                             (line   31)
* operator; / (slash) <1>:               Numeric Types — int float complex.
                                                             (line   27)
* operator; //:                          Binary arithmetic operations.
                                                             (line   31)
* operator; // <1>:                      Numeric Types — int float complex.
                                                             (line   27)
* operator; < (less):                    Comparisons.        (line    6)
* operator; < (less) <1>:                Comparisons<2>.     (line    6)
* operator; <<:                          Shifting operations.
                                                             (line    6)
* operator; << <1>:                      Bitwise Operations on Integer Types.
                                                             (line    6)
* operator; <=:                          Comparisons.        (line    6)
* operator; <= <1>:                      Comparisons<2>.     (line    6)
* operator; ==:                          Comparisons.        (line    6)
* operator; == <1>:                      Comparisons<2>.     (line    6)
* operator; > (greater):                 Comparisons.        (line    6)
* operator; > (greater) <1>:             Comparisons<2>.     (line    6)
* operator; >=:                          Comparisons.        (line    6)
* operator; >= <1>:                      Comparisons<2>.     (line    6)
* operator; >>:                          Shifting operations.
                                                             (line    6)
* operator; >> <1>:                      Bitwise Operations on Integer Types.
                                                             (line    6)
* operator; @ (at):                      Binary arithmetic operations.
                                                             (line   26)
* operator; and:                         Boolean operations. (line   21)
* operator; and <1>:                     Truth Value Testing.
                                                             (line   23)
* operator; and <2>:                     Boolean Operations — and or not.
                                                             (line   22)
* operator; comparison:                  Comparisons<2>.     (line    6)
* operator; in:                          Membership test operations.
                                                             (line   37)
* operator; in <1>:                      Comparisons<2>.     (line   64)
* operator; in <2>:                      Common Sequence Operations.
                                                             (line   21)
* operator; is:                          Membership test operations.
                                                             (line   40)
* operator; is <1>:                      Comparisons<2>.     (line    6)
* operator; is not:                      Membership test operations.
                                                             (line   40)
* operator; is not <1>:                  Comparisons<2>.     (line    6)
* operator; not:                         Boolean operations. (line   18)
* operator; not <1>:                     Boolean Operations — and or not.
                                                             (line   22)
* operator; not in:                      Membership test operations.
                                                             (line   37)
* operator; not in <1>:                  Comparisons<2>.     (line   64)
* operator; not in <2>:                  Common Sequence Operations.
                                                             (line   21)
* operator; or:                          Boolean operations. (line   25)
* operator; or <1>:                      Truth Value Testing.
                                                             (line   23)
* operator; or <2>:                      Boolean Operations — and or not.
                                                             (line   22)
* operator; overloading:                 Special method names.
                                                             (line    6)
* operator; precedence:                  Operator precedence.
                                                             (line    6)
* operator; ^ (caret):                   Binary bitwise operations.
                                                             (line   16)
* operator; ^ (caret) <1>:               Bitwise Operations on Integer Types.
                                                             (line    6)
* operator; | (vertical bar):            Binary bitwise operations.
                                                             (line   20)
* operator; | (vertical bar) <1>:        Bitwise Operations on Integer Types.
                                                             (line    6)
* operator; ~ (tilde):                   Unary arithmetic and bitwise operations.
                                                             (line   18)
* operator; ~ (tilde) <1>:               Bitwise Operations on Integer Types.
                                                             (line    6)
* operators:                             Operators.          (line    6)
* opmap (in module dis):                 Opcode collections. (line   13)
* opname (in module dis):                Opcode collections. (line    9)
* optimize() (in module pickletools):    Programmatic Interface<2>.
                                                             (line   31)
* OPTIMIZED_BYTECODE_SUFFIXES (in module importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line   30)
* optim_args_from_interpreter_flags() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  451)
* Optional (in module typing):           Special forms.      (line   59)
* OptionGroup (class in optparse):       Grouping Options.   (line   12)
* OptionMenu (class in tkinter.tix):     Basic Widgets.      (line   49)
* OptionParser (class in optparse):      Creating the parser.
                                                             (line    9)
* Options (class in ssl):                Constants<9>.       (line  340)
* options (doctest.Example attribute):   Example Objects.    (line   53)
* options (ssl.SSLContext attribute):    SSL Contexts.       (line  584)
* options() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  102)
* optionxform() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  284)
* optparse (module):                     optparse — Parser for command line options.
                                                             (line    6)
* OP_ALL (in module ssl):                Constants<9>.       (line  209)
* OP_CIPHER_SERVER_PREFERENCE (in module ssl): Constants<9>. (line  298)
* OP_ENABLE_MIDDLEBOX_COMPAT (in module ssl): Constants<9>.  (line  322)
* OP_IGNORE_UNEXPECTED_EOF (in module ssl): Constants<9>.    (line  350)
* OP_NO_COMPRESSION (in module ssl):     Constants<9>.       (line  331)
* OP_NO_RENEGOTIATION (in module ssl):   Constants<9>.       (line  288)
* OP_NO_SSLv2 (in module ssl):           Constants<9>.       (line  217)
* OP_NO_SSLv3 (in module ssl):           Constants<9>.       (line  227)
* OP_NO_TICKET (in module ssl):          Constants<9>.       (line  344)
* OP_NO_TLSv1 (in module ssl):           Constants<9>.       (line  237)
* OP_NO_TLSv1_1 (in module ssl):         Constants<9>.       (line  249)
* OP_NO_TLSv1_2 (in module ssl):         Constants<9>.       (line  261)
* OP_NO_TLSv1_3 (in module ssl):         Constants<9>.       (line  273)
* OP_SINGLE_DH_USE (in module ssl):      Constants<9>.       (line  306)
* OP_SINGLE_ECDH_USE (in module ssl):    Constants<9>.       (line  314)
* Or (class in ast):                     Expressions<2>.     (line   87)
* ord() (built-in function):             Built-in Functions. (line 1270)
* OrderedDict (class in collections):    OrderedDict objects.
                                                             (line   39)
* OrderedDict (class in typing):         Corresponding to types in collections.
                                                             (line   17)
* ordered_attributes (xml.parsers.expat.xmlparser attribute): XMLParser Objects<2>.
                                                             (line  107)
* origin (importlib.machinery.ModuleSpec attribute): importlib machinery – Importers and path hooks.
                                                             (line  381)
* origin_req_host (urllib.request.Request attribute): Request Objects.
                                                             (line   30)
* origin_server (wsgiref.handlers.BaseHandler attribute): wsgiref handlers – server/gateway base classes.
                                                             (line  288)
* or_() (in module operator):            operator — Standard operators as functions.
                                                             (line  133)
* os (module):                           os — Miscellaneous operating system interfaces.
                                                             (line    6)
* os.path (module):                      os path — Common pathname manipulations.
                                                             (line    6)
* OSError:                               Concrete exceptions.
                                                             (line  113)
* ossaudiodev (module):                  ossaudiodev — Access to OSS-compatible audio devices.
                                                             (line    6)
* OSSAudioError:                         ossaudiodev — Access to OSS-compatible audio devices.
                                                             (line   29)
* os_environ (wsgiref.handlers.BaseHandler attribute): wsgiref handlers – server/gateway base classes.
                                                             (line  166)
* output:                                Expression statements.
                                                             (line   17)
* output (subprocess.CalledProcessError attribute): Using the subprocess Module.
                                                             (line  205)
* output (subprocess.TimeoutExpired attribute): Using the subprocess Module.
                                                             (line  172)
* output (unittest.TestCase attribute):  Test cases.         (line  433)
* output() (http.cookies.BaseCookie method): Cookie Objects. (line   24)
* output() (http.cookies.Morsel method): Morsel Objects.     (line   72)
* OutputChecker (class in doctest):      OutputChecker objects.
                                                             (line    6)
* OutputString() (http.cookies.Morsel method): Morsel Objects.
                                                             (line   87)
* output_charset (email.charset.Charset attribute): email charset Representing character sets.
                                                             (line   74)
* output_charset() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line   87)
* output_codec (email.charset.Charset attribute): email charset Representing character sets.
                                                             (line   88)
* output_difference() (doctest.OutputChecker method): OutputChecker objects.
                                                             (line   27)
* over() (nntplib.NNTP method):          Methods<3>.         (line  167)
* Overflow (class in decimal):           Signals.            (line   67)
* OverflowError:                         Concrete exceptions.
                                                             (line  177)
* OverflowError (built-in exception):    Integer Objects.    (line  108)
* OverflowError (built-in exception) <1>: Integer Objects.   (line  147)
* OverflowError (built-in exception) <2>: Integer Objects.   (line  189)
* OverflowError (built-in exception) <3>: Integer Objects.   (line  200)
* OverflowError (built-in exception) <4>: Integer Objects.   (line  211)
* OverflowError (built-in exception) <5>: Integer Objects.   (line  223)
* overlap() (statistics.NormalDist method): NormalDist objects.
                                                             (line   96)
* overlaps() (ipaddress.IPv4Network method): Network objects.
                                                             (line  155)
* overlaps() (ipaddress.IPv6Network method): Network objects.
                                                             (line  340)
* overlay() (curses.window method):      Window Objects.     (line  427)
* overload() (in module typing):         Functions and decorators.
                                                             (line   15)
* overwrite() (curses.window method):    Window Objects.     (line  440)
* owner() (pathlib.Path method):         Methods<2>.         (line  270)
* O_APPEND (in module os):               File Descriptor Operations.
                                                             (line  304)
* O_ASYNC (in module os):                File Descriptor Operations.
                                                             (line  336)
* O_BINARY (in module os):               File Descriptor Operations.
                                                             (line  326)
* O_CLOEXEC (in module os):              File Descriptor Operations.
                                                             (line  314)
* O_CREAT (in module os):                File Descriptor Operations.
                                                             (line  304)
* O_DIRECT (in module os):               File Descriptor Operations.
                                                             (line  336)
* O_DIRECTORY (in module os):            File Descriptor Operations.
                                                             (line  336)
* O_DSYNC (in module os):                File Descriptor Operations.
                                                             (line  314)
* O_EXCL (in module os):                 File Descriptor Operations.
                                                             (line  304)
* O_EXLOCK (in module os):               File Descriptor Operations.
                                                             (line  336)
* O_NDELAY (in module os):               File Descriptor Operations.
                                                             (line  314)
* O_NOATIME (in module os):              File Descriptor Operations.
                                                             (line  336)
* O_NOCTTY (in module os):               File Descriptor Operations.
                                                             (line  314)
* O_NOFOLLOW (in module os):             File Descriptor Operations.
                                                             (line  336)
* O_NOINHERIT (in module os):            File Descriptor Operations.
                                                             (line  326)
* O_NONBLOCK (in module os):             File Descriptor Operations.
                                                             (line  314)
* O_PATH (in module os):                 File Descriptor Operations.
                                                             (line  336)
* O_RANDOM (in module os):               File Descriptor Operations.
                                                             (line  326)
* O_RDONLY (in module os):               File Descriptor Operations.
                                                             (line  304)
* O_RDWR (in module os):                 File Descriptor Operations.
                                                             (line  304)
* O_RSYNC (in module os):                File Descriptor Operations.
                                                             (line  314)
* O_SEQUENTIAL (in module os):           File Descriptor Operations.
                                                             (line  326)
* O_SHLOCK (in module os):               File Descriptor Operations.
                                                             (line  336)
* O_SHORT_LIVED (in module os):          File Descriptor Operations.
                                                             (line  326)
* O_SYNC (in module os):                 File Descriptor Operations.
                                                             (line  314)
* O_TEMPORARY (in module os):            File Descriptor Operations.
                                                             (line  326)
* O_TEXT (in module os):                 File Descriptor Operations.
                                                             (line  326)
* O_TMPFILE (in module os):              File Descriptor Operations.
                                                             (line  336)
* O_TRUNC (in module os):                File Descriptor Operations.
                                                             (line  304)
* O_WRONLY (in module os):               File Descriptor Operations.
                                                             (line  304)
* p (pdb command):                       Debugger Commands.  (line  233)
* pack() (in module struct):             Functions and Exceptions.
                                                             (line   13)
* pack() (mailbox.MH method):            MH.                 (line   64)
* pack() (struct.Struct method):         Classes<2>.         (line   25)
* package:                               Packages<2>.        (line    6)
* package <1>:                           site — Site-specific configuration hook.
                                                             (line   64)
* package <2>:                           Glossary.           (line  938)
* Package (in module importlib.resources): importlib resources – Resources.
                                                             (line   37)
* package variable; __all__:             Importing Modules<2>.
                                                             (line    7)
* package; namespace:                    Namespace packages. (line    6)
* package; portion:                      Namespace packages. (line    6)
* package; regular:                      Regular packages.   (line    6)
* packed (ipaddress.IPv4Address attribute): Address objects. (line   77)
* packed (ipaddress.IPv6Address attribute): Address objects. (line  208)
* Packer (class in xdrlib):              xdrlib — Encode and decode XDR data.
                                                             (line   18)
* packing (widgets):                     The Packer.         (line    6)
* packing; binary; data:                 struct — Interpret bytes as packed binary data.
                                                             (line    8)
* pack_array() (xdrlib.Packer method):   Packer Objects.     (line   86)
* pack_bytes() (xdrlib.Packer method):   Packer Objects.     (line   54)
* pack_double() (xdrlib.Packer method):  Packer Objects.     (line   26)
* pack_farray() (xdrlib.Packer method):  Packer Objects.     (line   78)
* pack_float() (xdrlib.Packer method):   Packer Objects.     (line   22)
* pack_fopaque() (xdrlib.Packer method): Packer Objects.     (line   38)
* pack_fstring() (xdrlib.Packer method): Packer Objects.     (line   32)
* pack_into() (in module struct):        Functions and Exceptions.
                                                             (line   19)
* pack_into() (struct.Struct method):    Classes<2>.         (line   30)
* pack_list() (xdrlib.Packer method):    Packer Objects.     (line   61)
* pack_opaque() (xdrlib.Packer method):  Packer Objects.     (line   49)
* pack_string() (xdrlib.Packer method):  Packer Objects.     (line   43)
* PAGER:                                 pydoc — Documentation generator and online help system.
                                                             (line   47)
* pair_content() (in module curses):     Functions<4>.       (line  364)
* pair_number() (in module curses):      Functions<4>.       (line  370)
* PanedWindow (class in tkinter.tix):    Manager Widgets.    (line    6)
* parameter:                             Glossary.           (line  947)
* Parameter (class in inspect):          Introspecting callables with the Signature object.
                                                             (line  142)
* parameter; call semantics:             Calls.              (line   25)
* parameter; difference from argument:   How can I pass optional or keyword parameters from one function to another?.
                                                             (line   16)
* parameter; function definition:        The with statement. (line  103)
* ParameterizedMIMEHeader (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line  255)
* parameters (inspect.Signature attribute): Introspecting callables with the Signature object.
                                                             (line   79)
* params (email.headerregistry.ParameterizedMIMEHeader attribute): email headerregistry Custom Header Objects.
                                                             (line  263)
* paramstyle (in module sqlite3):        Module functions and constants.
                                                             (line   11)
* pardir (in module os):                 Miscellaneous System Information.
                                                             (line   87)
* paren (2to3 fixer):                    Fixers.             (line  252)
* parent (importlib.machinery.ModuleSpec attribute): importlib machinery – Importers and path hooks.
                                                             (line  409)
* parent (pyclbr.Class attribute):       Class Objects<2>.   (line   25)
* parent (pyclbr.Function attribute):    Function Objects.   (line   25)
* parent (urllib.request.BaseHandler attribute): BaseHandler Objects.
                                                             (line   25)
* parent() (tkinter.ttk.Treeview method): ttk Treeview.      (line  237)
* parenthesized form:                    Parenthesized forms.
                                                             (line    6)
* parentNode (xml.dom.Node attribute):   Node Objects.       (line   17)
* parents (collections.ChainMap attribute): ChainMap objects.
                                                             (line   59)
* parent_process() (in module multiprocessing): Miscellaneous<3>.
                                                             (line   36)
* paretovariate() (in module random):    Real-valued distributions.
                                                             (line   90)
* parse() (doctest.DocTestParser method): DocTestParser objects.
                                                             (line   29)
* parse() (email.parser.BytesParser method): Parser API.     (line   34)
* parse() (email.parser.Parser method):  Parser API.         (line   86)
* parse() (in module ast):               ast Helpers.        (line    9)
* parse() (in module cgi):               Functions<9>.       (line    9)
* parse() (in module xml.dom.minidom):   xml dom minidom — Minimal DOM implementation.
                                                             (line   37)
* parse() (in module xml.dom.pulldom):   xml dom pulldom — Support for building partial DOM trees.
                                                             (line   86)
* parse() (in module xml.etree.ElementTree): Functions<7>.   (line  172)
* parse() (in module xml.sax):           xml sax — Support for SAX2 parsers.
                                                             (line   39)
* parse() (string.Formatter method):     Custom String Formatting.
                                                             (line   40)
* parse() (urllib.robotparser.RobotFileParser method): urllib robotparser — Parser for robots txt.
                                                             (line   29)
* parse() (xml.etree.ElementTree.ElementTree method): ElementTree Objects.
                                                             (line   54)
* Parse() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line    8)
* parse() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line    8)
* parseaddr() (in module email.utils):   email utils Miscellaneous utilities.
                                                             (line   59)
* parsebytes() (email.parser.BytesParser method): Parser API.
                                                             (line   54)
* parsedate() (in module email.utils):   email utils Miscellaneous utilities.
                                                             (line   96)
* parsedate_to_datetime() (in module email.utils): email utils Miscellaneous utilities.
                                                             (line  119)
* parsedate_tz() (in module email.utils): email utils Miscellaneous utilities.
                                                             (line  108)
* ParseError (class in xml.etree.ElementTree): Exceptions<16>.
                                                             (line    6)
* ParseFile() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line   16)
* ParseFlags() (in module imaplib):      imaplib — IMAP4 protocol client.
                                                             (line  128)
* parser:                                Lexical analysis.   (line    6)
* Parser (class in email.parser):        Parser API.         (line   75)
* parser (module):                       parser — Access Python parse trees.
                                                             (line    6)
* ParserCreate() (in module xml.parsers.expat): xml parsers expat — Fast XML parsing using Expat.
                                                             (line   46)
* ParserError:                           Exceptions and Error Handling.
                                                             (line   11)
* ParseResult (class in urllib.parse):   Structured Parse Results.
                                                             (line   48)
* ParseResultBytes (class in urllib.parse): Structured Parse Results.
                                                             (line   73)
* parsestr() (email.parser.Parser method): Parser API.       (line   96)
* parseString() (in module xml.dom.minidom): xml dom minidom — Minimal DOM implementation.
                                                             (line   50)
* parseString() (in module xml.dom.pulldom): xml dom pulldom — Support for building partial DOM trees.
                                                             (line   99)
* parseString() (in module xml.sax):     xml sax — Support for SAX2 parsers.
                                                             (line   50)
* parse_and_bind() (in module readline): Init file.          (line    8)
* parse_args() (argparse.ArgumentParser method): The parse_args method.
                                                             (line    6)
* PARSE_COLNAMES (in module sqlite3):    Module functions and constants.
                                                             (line   73)
* parse_config_h() (in module sysconfig): Other functions<3>.
                                                             (line   57)
* PARSE_DECLTYPES (in module sqlite3):   Module functions and constants.
                                                             (line   60)
* parse_header() (in module cgi):        Functions<9>.       (line   39)
* parse_headers() (in module http.client): http client — HTTP protocol client.
                                                             (line  108)
* parse_intermixed_args() (argparse.ArgumentParser method): Intermixed parsing.
                                                             (line    6)
* parse_known_args() (argparse.ArgumentParser method): Partial parsing.
                                                             (line    6)
* parse_known_intermixed_args() (argparse.ArgumentParser method): Intermixed parsing.
                                                             (line    9)
* parse_multipart() (in module cgi):     Functions<9>.       (line   17)
* parse_qs() (in module urllib.parse):   URL Parsing.        (line  148)
* parse_qsl() (in module urllib.parse):  URL Parsing.        (line  194)
* parsing; Python source code:           parser — Access Python parse trees.
                                                             (line    6)
* ParsingError:                          Exceptions<6>.      (line   65)
* partial (asyncio.IncompleteReadError attribute): Exceptions<10>.
                                                             (line   54)
* partial() (imaplib.IMAP4 method):      IMAP4 Objects.      (line  188)
* partial() (in module functools):       functools — Higher-order functions and operations on callable objects.
                                                             (line  276)
* partialmethod (class in functools):    functools — Higher-order functions and operations on callable objects.
                                                             (line  307)
* parties (threading.Barrier attribute): Barrier Objects.    (line   93)
* partition() (bytearray method):        Bytes and Bytearray Operations.
                                                             (line  180)
* partition() (bytes method):            Bytes and Bytearray Operations.
                                                             (line  180)
* partition() (str method):              String Methods<2>.  (line  357)
* Pass (class in ast):                   Statements.         (line  159)
* pass_() (poplib.POP3 method):          POP3 Objects.       (line   36)
* Paste:                                 Help menu Shell and Editor.
                                                             (line   30)
* patch() (in module test.support):      test support — Utilities for the Python test suite.
                                                             (line  964)
* patch() (in module unittest.mock):     patch.              (line    9)
* patch.dict() (in module unittest.mock): patch dict.        (line    6)
* patch.multiple() (in module unittest.mock): patch multiple.
                                                             (line    6)
* patch.object() (in module unittest.mock): patch object.    (line    6)
* patch.stopall() (in module unittest.mock): patch methods start and stop.
                                                             (line   70)
* PATH:                                  Changes in the Python API<2>.
                                                             (line  144)
* PATH <1>:                              Changes in ‘python’ Command Behavior<2>.
                                                             (line    6)
* PATH <2>:                              Changes in ‘python’ Command Behavior<2>.
                                                             (line   11)
* PATH <3>:                              Changes in ‘python’ Command Behavior<2>.
                                                             (line   12)
* PATH <4>:                              Security<16>.       (line   16)
* PATH <5>:                              Security<16>.       (line   20)
* PATH <6>:                              The Module Search Path.
                                                             (line   16)
* PATH <7>:                              Executable Python Scripts.
                                                             (line   11)
* PATH <8>:                              Environment variables.
                                                             (line   27)
* PATH <9>:                              Miscellaneous.      (line   16)
* PATH <10>:                             Installation steps. (line   32)
* PATH <11>:                             Installation steps. (line   56)
* PATH <12>:                             Installing Without UI.
                                                             (line   57)
* PATH <13>:                             Excursus Setting environment variables.
                                                             (line   23)
* PATH <14>:                             Excursus Setting environment variables.
                                                             (line   35)
* PATH <15>:                             Finding the Python executable.
                                                             (line   14)
* PATH <16>:                             Finding the Python executable.
                                                             (line   21)
* PATH <17>:                             Finding the Python executable.
                                                             (line   22)
* PATH <18>:                             Python Launcher for Windows.
                                                             (line   13)
* PATH <19>:                             From the command-line.
                                                             (line    9)
* PATH <20>:                             From the command-line.
                                                             (line   38)
* PATH <21>:                             Shebang Lines.      (line   48)
* PATH <22>:                             Shebang Lines.      (line   50)
* PATH <23>:                             Process Management. (line   45)
* PATH <24>:                             Process Management. (line   86)
* PATH <25>:                             Process Management. (line   89)
* PATH <26>:                             Process Management. (line   92)
* PATH <27>:                             Process Management. (line  471)
* PATH <28>:                             Process Management. (line  557)
* PATH <29>:                             Process Management. (line  561)
* PATH <30>:                             Process Management. (line  563)
* PATH <31>:                             Miscellaneous System Information.
                                                             (line  118)
* PATH <32>:                             webbrowser — Convenient Web-browser controller.
                                                             (line  214)
* PATH <33>:                             Installing your CGI script on a Unix system.
                                                             (line   29)
* PATH <34>:                             Common problems and solutions.
                                                             (line   23)
* PATH <35>:                             site — Site-specific configuration hook.
                                                             (line   59)
* PATH <36>:                             Embedding Python<2>.
                                                             (line   31)
* PATH <37>:                             Embedding Python<2>.
                                                             (line   37)
* PATH <38>:                             How do I make a Python script executable on Unix?.
                                                             (line   24)
* PATH <39>:                             How do I make a Python script executable on Unix?.
                                                             (line   28)
* Path (class in pathlib):               Concrete paths.     (line   11)
* Path (class in zipfile):               Path Objects.       (line    6)
* path (http.cookiejar.Cookie attribute): Cookie Objects<2>. (line   41)
* path (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line   92)
* path (importlib.abc.FileLoader attribute): importlib abc – Abstract base classes related to import.
                                                             (line  490)
* path (importlib.machinery.ExtensionFileLoader attribute): importlib machinery – Importers and path hooks.
                                                             (line  315)
* path (importlib.machinery.FileFinder attribute): importlib machinery – Importers and path hooks.
                                                             (line  186)
* path (importlib.machinery.SourceFileLoader attribute): importlib machinery – Importers and path hooks.
                                                             (line  228)
* path (importlib.machinery.SourcelessFileLoader attribute): importlib machinery – Importers and path hooks.
                                                             (line  272)
* path (in module sys):                  sys — System-specific parameters and functions.
                                                             (line 1060)
* path (in module sys) <1>:              Embedding Python<2>.
                                                             (line   12)
* path (in module sys) <2>:              Initializing and finalizing the interpreter.
                                                             (line    8)
* path (in module sys) <3>:              Process-wide parameters.
                                                             (line  120)
* path (in module sys) <4>:              Process-wide parameters.
                                                             (line  133)
* path (os.DirEntry attribute):          Files and Directories.
                                                             (line  857)
* path based finder:                     The Path Based Finder.
                                                             (line    6)
* path based finder <1>:                 Glossary.           (line 1019)
* Path browser:                          File menu Shell and Editor.
                                                             (line   22)
* path entry:                            Glossary.           (line  999)
* path entry finder:                     Glossary.           (line 1004)
* path entry hook:                       Glossary.           (line 1013)
* path hooks:                            Import hooks.       (line    6)
* path() (in module importlib.resources): importlib resources – Resources.
                                                             (line  132)
* path-like object:                      Glossary.           (line 1024)
* path; configuration; file:             site — Site-specific configuration hook.
                                                             (line   64)
* path; operations:                      pathlib — Object-oriented filesystem paths.
                                                             (line   10)
* path; operations <1>:                  os path — Common pathname manipulations.
                                                             (line    9)
* pathconf() (in module os):             Files and Directories.
                                                             (line  547)
* pathconf_names (in module os):         Files and Directories.
                                                             (line  571)
* PathEntryFinder (class in importlib.abc): importlib abc – Abstract base classes related to import.
                                                             (line   96)
* PATHEXT:                               Other Improvements<2>.
                                                             (line   30)
* PATHEXT <1>:                           Library<11>.        (line  105)
* PATHEXT <2>:                           Installing Without UI.
                                                             (line   58)
* PathFinder (class in importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line  107)
* pathlib (module):                      pathlib — Object-oriented filesystem paths.
                                                             (line    6)
* PathLike (class in os):                Process Parameters. (line  114)
* pathname2url() (in module urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  140)
* pathsep (in module os):                Miscellaneous System Information.
                                                             (line  115)
* path_hook() (importlib.machinery.FileFinder class method): importlib machinery – Importers and path hooks.
                                                             (line  206)
* path_hooks (in module sys):            sys — System-specific parameters and functions.
                                                             (line 1085)
* path_importer_cache (in module sys):   sys — System-specific parameters and functions.
                                                             (line 1094)
* path_mtime() (importlib.abc.SourceLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  556)
* path_return_ok() (http.cookiejar.CookiePolicy method): CookiePolicy Objects.
                                                             (line   56)
* path_stats() (importlib.abc.SourceLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  534)
* path_stats() (importlib.machinery.SourceFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  237)
* Pattern (class in typing):             Other concrete types.
                                                             (line   18)
* pattern (re.error attribute):          Module Contents.    (line  376)
* pattern (re.Pattern attribute):        Regular Expression Objects.
                                                             (line  118)
* pause() (in module signal):            Module contents<2>. (line  265)
* pause_reading() (asyncio.ReadTransport method): Read-only Transports.
                                                             (line   12)
* pause_writing() (asyncio.BaseProtocol method): Base Protocol.
                                                             (line   40)
* PAX_FORMAT (in module tarfile):        tarfile — Read and write tar archive files.
                                                             (line  237)
* pax_headers (tarfile.TarFile attribute): TarFile Objects.  (line  255)
* pax_headers (tarfile.TarInfo attribute): TarInfo Objects.  (line   88)
* pbkdf2_hmac() (in module hashlib):     Key derivation.     (line   11)
* pd() (in module turtle):               Drawing state.      (line    6)
* Pdb (class in pdb):                    pdb — The Python Debugger.
                                                             (line   17)
* Pdb (class in pdb) <1>:                pdb — The Python Debugger.
                                                             (line  146)
* pdb (module):                          pdb — The Python Debugger.
                                                             (line    6)
* pdf() (statistics.NormalDist method):  NormalDist objects. (line   68)
* peek() (bz2.BZ2File method):           De compression of files.
                                                             (line   73)
* peek() (gzip.GzipFile method):         gzip — Support for gzip files.
                                                             (line  127)
* peek() (io.BufferedReader method):     Buffered Streams.   (line   75)
* peek() (lzma.LZMAFile method):         Reading and writing compressed files.
                                                             (line   85)
* peek() (weakref.finalize method):      weakref — Weak references.
                                                             (line  276)
* peer (smtpd.SMTPChannel attribute):    SMTPChannel Objects.
                                                             (line   95)
* PEM_cert_to_DER_cert() (in module ssl): Certificate handling.
                                                             (line   96)
* pen() (in module turtle):              Drawing state.      (line   33)
* pencolor() (in module turtle):         Color control.      (line    6)
* pending (ssl.MemoryBIO attribute):     Memory BIO Support<2>.
                                                             (line  139)
* pending() (ssl.SSLSocket method):      SSL Sockets.        (line  313)
* PendingDeprecationWarning:             Warnings.           (line   28)
* pendown() (in module turtle):          Drawing state.      (line    6)
* pensize() (in module turtle):          Drawing state.      (line   18)
* penup() (in module turtle):            Drawing state.      (line   12)
* PEP:                                   Glossary.           (line 1036)
* PERCENT (in module token):             token — Constants used with Python parse trees.
                                                             (line  122)
* PERCENTEQUAL (in module token):        token — Constants used with Python parse trees.
                                                             (line  186)
* Performance:                           timeit — Measure execution time of small code snippets.
                                                             (line    8)
* perf_counter() (in module time):       Functions<3>.       (line  180)
* perf_counter_ns() (in module time):    Functions<3>.       (line  191)
* perm() (in module math):               Number-theoretic and representation functions.
                                                             (line  217)
* PermissionError:                       OS exceptions.      (line   94)
* permutations() (in module itertools):  Itertool functions. (line  400)
* Persist() (msilib.SummaryInformation method): Summary Information Objects.
                                                             (line   29)
* persistence:                           pickle — Python object serialization.
                                                             (line    8)
* persistent; objects:                   pickle — Python object serialization.
                                                             (line    8)
* persistent_id (pickle protocol):       Persistence of External Objects.
                                                             (line    6)
* persistent_id() (pickle.Pickler method): Module Interface. (line  160)
* persistent_load (pickle protocol):     Persistence of External Objects.
                                                             (line    6)
* persistent_load() (pickle.Unpickler method): Module Interface.
                                                             (line  274)
* pformat() (in module pprint):          pprint — Data pretty printer.
                                                             (line   84)
* pformat() (pprint.PrettyPrinter method): PrettyPrinter Objects.
                                                             (line    8)
* PF_CAN (in module socket):             Constants<8>.       (line   92)
* PF_PACKET (in module socket):          Constants<8>.       (line  163)
* PF_RDS (in module socket):             Constants<8>.       (line  173)
* pgettext() (gettext.GNUTranslations method): The GNUTranslations class.
                                                             (line   68)
* pgettext() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line   47)
* pgettext() (in module gettext):        GNU gettext API.    (line   73)
* PGO (in module test.support):          test support — Utilities for the Python test suite.
                                                             (line  146)
* phase() (in module cmath):             Conversions to and from polar coordinates.
                                                             (line   22)
* Philbrick, Geoff:                      Keyword Parameters for Extension Functions.
                                                             (line   25)
* physical line:                         Logical lines.      (line    6)
* physical line <1>:                     Explicit line joining.
                                                             (line    6)
* physical line <2>:                     String and Bytes literals.
                                                             (line   72)
* pi (in module cmath):                  Constants<3>.       (line    6)
* pi (in module math):                   Constants<2>.       (line    6)
* pi() (xml.etree.ElementTree.TreeBuilder method): TreeBuilder Objects.
                                                             (line   56)
* pickle (module):                       pickle — Python object serialization.
                                                             (line    6)
* pickle() (in module copyreg):          copyreg — Register pickle support functions.
                                                             (line   23)
* PickleBuffer (class in pickle):        Module Interface.   (line  301)
* PickleError:                           Module Interface.   (line   95)
* Pickler (class in pickle):             Module Interface.   (line  121)
* pickletools (module):                  pickletools — Tools for pickle developers.
                                                             (line    6)
* pickletools command line option; -a:   Command line options<3>.
                                                             (line    6)
* pickletools command line option; –annotate: Command line options<3>.
                                                             (line    6)
* pickletools command line option; –indentlevel=<num>: Command line options<3>.
                                                             (line   14)
* pickletools command line option; -l:   Command line options<3>.
                                                             (line   14)
* pickletools command line option; -m:   Command line options<3>.
                                                             (line   18)
* pickletools command line option; –memo: Command line options<3>.
                                                             (line   18)
* pickletools command line option; -o:   Command line options<3>.
                                                             (line   10)
* pickletools command line option; –output=<file>: Command line options<3>.
                                                             (line   10)
* pickletools command line option; -p:   Command line options<3>.
                                                             (line   23)
* pickletools command line option; –preamble=<preamble>: Command line options<3>.
                                                             (line   23)
* pickling; objects:                     pickle — Python object serialization.
                                                             (line    8)
* PicklingError:                         Module Interface.   (line  100)
* pid (asyncio.asyncio.subprocess.Process attribute): Interacting with Subprocesses.
                                                             (line  132)
* pid (multiprocessing.Process attribute): Process and exceptions.
                                                             (line  107)
* pid (subprocess.Popen attribute):      Popen Objects.      (line  140)
* PidfdChildWatcher (class in asyncio):  Process Watchers.   (line  144)
* pidfd_open() (in module os):           Process Management. (line  325)
* pidfd_send_signal() (in module signal): Module contents<2>.
                                                             (line  282)
* PIPE (in module subprocess):           Using the subprocess Module.
                                                             (line  140)
* Pipe() (in module multiprocessing):    Pipes and Queues.   (line   74)
* pipe() (in module os):                 File Descriptor Operations.
                                                             (line  365)
* pipe2() (in module os):                File Descriptor Operations.
                                                             (line  376)
* pipes (module):                        pipes — Interface to shell pipelines.
                                                             (line    6)
* PIPE_BUF (in module select):           select — Waiting for I/O completion.
                                                             (line  157)
* pipe_connection_lost() (asyncio.SubprocessProtocol method): Subprocess Protocols.
                                                             (line   19)
* pipe_data_received() (asyncio.SubprocessProtocol method): Subprocess Protocols.
                                                             (line   10)
* PIPE_MAX_SIZE (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  150)
* PIP_USER:                              Windows<19>.        (line  102)
* pkgutil (module):                      pkgutil — Package extension utility.
                                                             (line    6)
* PKG_DIRECTORY (in module imp):         imp — Access the import internals.
                                                             (line  327)
* placeholder (textwrap.TextWrapper attribute): textwrap — Text wrapping and filling.
                                                             (line  274)
* PLAT:                                  distutils util — Miscellaneous other utility functions.
                                                             (line   99)
* platform (in module sys):              sys — System-specific parameters and functions.
                                                             (line 1107)
* platform (in module sys) <1>:          Process-wide parameters.
                                                             (line  172)
* platform (module):                     platform — Access to underlying platform’s identifying data.
                                                             (line    6)
* platform() (in module platform):       Cross Platform.     (line   45)
* platlibdir (in module sys):            sys — System-specific parameters and functions.
                                                             (line 1169)
* PlaySound() (in module winsound):      winsound — Sound-playing interface for Windows.
                                                             (line   20)
* plist; file:                           plistlib — Generate and parse Apple plist files.
                                                             (line    8)
* plistlib (module):                     plistlib — Generate and parse Apple plist files.
                                                             (line    6)
* plock() (in module os):                Process Management. (line  338)
* plus:                                  Unary arithmetic and bitwise operations.
                                                             (line   14)
* PLUS (in module token):                token — Constants used with Python parse trees.
                                                             (line   82)
* plus() (decimal.Context method):       Context objects.    (line  412)
* PLUSEQUAL (in module token):           token — Constants used with Python parse trees.
                                                             (line  170)
* pm() (in module pdb):                  pdb — The Python Debugger.
                                                             (line  136)
* POINTER() (in module ctypes):          Utility functions.  (line  149)
* pointer() (in module ctypes):          Utility functions.  (line  155)
* polar() (in module cmath):             Conversions to and from polar coordinates.
                                                             (line   42)
* Policy (class in email.policy):        email policy Policy Objects.
                                                             (line  128)
* poll() (in module select):             select — Waiting for I/O completion.
                                                             (line   84)
* poll() (multiprocessing.connection.Connection method): Connection Objects<2>.
                                                             (line   42)
* poll() (select.devpoll method):        /dev/poll Polling Objects.
                                                             (line   65)
* poll() (select.epoll method):          Edge and Level Trigger Polling epoll Objects.
                                                             (line   96)
* poll() (select.poll method):           Polling Objects.    (line   77)
* poll() (subprocess.Popen method):      Popen Objects.      (line    8)
* PollSelector (class in selectors):     Classes<3>.         (line  171)
* Pool (class in multiprocessing.pool):  Process Pools.      (line    9)
* pop() (array.array method):            array — Efficient arrays of numeric values.
                                                             (line  196)
* pop() (collections.deque method):      deque objects.      (line   87)
* pop() (dict method):                   Mapping Types — dict.
                                                             (line  179)
* pop() (frozenset method):              Set Types — set frozenset.
                                                             (line  208)
* pop() (mailbox.Mailbox method):        Mailbox objects.    (line  208)
* pop() (sequence method):               Mutable Sequence Types.
                                                             (line   16)
* POP3 (class in poplib):                poplib — POP3 protocol client.
                                                             (line   29)
* POP3; protocol:                        poplib — POP3 protocol client.
                                                             (line    8)
* POP3_SSL (class in poplib):            poplib — POP3 protocol client.
                                                             (line   49)
* Popen (class in subprocess):           Popen Constructor.  (line   11)
* popen() (in module os):                The standard type hierarchy.
                                                             (line  635)
* popen() (in module os) <1>:            Process Management. (line  345)
* popen() (in module os) <2>:            select — Waiting for I/O completion.
                                                             (line  138)
* popitem() (collections.OrderedDict method): OrderedDict objects.
                                                             (line   46)
* popitem() (dict method):               Mapping Types — dict.
                                                             (line  185)
* popitem() (mailbox.Mailbox method):    Mailbox objects.    (line  217)
* popleft() (collections.deque method):  deque objects.      (line   92)
* poplib (module):                       poplib — POP3 protocol client.
                                                             (line    6)
* PopupMenu (class in tkinter.tix):      Basic Widgets.      (line   53)
* pop_alignment() (formatter.formatter method): The Formatter Interface.
                                                             (line   97)
* pop_all() (contextlib.ExitStack method): Utilities.        (line  427)
* POP_BLOCK (opcode):                    Python Bytecode Instructions.
                                                             (line  372)
* POP_EXCEPT (opcode):                   Python Bytecode Instructions.
                                                             (line  377)
* pop_font() (formatter.formatter method): The Formatter Interface.
                                                             (line  109)
* POP_JUMP_IF_FALSE (opcode):            Python Bytecode Instructions.
                                                             (line  598)
* POP_JUMP_IF_TRUE (opcode):             Python Bytecode Instructions.
                                                             (line  591)
* pop_margin() (formatter.formatter method): The Formatter Interface.
                                                             (line  121)
* pop_source() (shlex.shlex method):     shlex Objects.      (line   63)
* pop_style() (formatter.formatter method): The Formatter Interface.
                                                             (line  132)
* POP_TOP (opcode):                      Python Bytecode Instructions.
                                                             (line   59)
* port (http.cookiejar.Cookie attribute): Cookie Objects<2>. (line   36)
* portion:                               Glossary.           (line 1052)
* port_specified (http.cookiejar.Cookie attribute): Cookie Objects<2>.
                                                             (line   77)
* pos (json.JSONDecodeError attribute):  Exceptions<14>.     (line   19)
* pos (re.error attribute):              Module Contents.    (line  380)
* pos (re.Match attribute):              Match Objects.      (line  164)
* pos() (in module operator):            operator — Standard operators as functions.
                                                             (line  138)
* pos() (in module turtle):              Tell Turtle’s state.
                                                             (line    6)
* position (xml.etree.ElementTree.ParseError attribute): Exceptions<16>.
                                                             (line   20)
* position() (in module turtle):         Tell Turtle’s state.
                                                             (line    6)
* positional argument:                   Glossary.           (line 1058)
* posix (module):                        posix — The most common POSIX system calls.
                                                             (line    6)
* POSIX Shared Memory:                   multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line   10)
* POSIX; I/O control:                    termios — POSIX style tty control.
                                                             (line    6)
* POSIXLY_CORRECT:                       getopt — C-style parser for command line options.
                                                             (line   71)
* PosixPath (class in pathlib):          Concrete paths.     (line   22)
* posix_fadvise() (in module os):        File Descriptor Operations.
                                                             (line  396)
* POSIX_FADV_DONTNEED (in module os):    File Descriptor Operations.
                                                             (line  410)
* POSIX_FADV_NOREUSE (in module os):     File Descriptor Operations.
                                                             (line  410)
* POSIX_FADV_NORMAL (in module os):      File Descriptor Operations.
                                                             (line  410)
* POSIX_FADV_RANDOM (in module os):      File Descriptor Operations.
                                                             (line  410)
* POSIX_FADV_SEQUENTIAL (in module os):  File Descriptor Operations.
                                                             (line  410)
* POSIX_FADV_WILLNEED (in module os):    File Descriptor Operations.
                                                             (line  410)
* posix_fallocate() (in module os):      File Descriptor Operations.
                                                             (line  387)
* posix_spawn() (in module os):          Process Management. (line  373)
* posix_spawnp() (in module os):         Process Management. (line  463)
* POSIX_SPAWN_CLOSE (in module os):      Process Management. (line  401)
* POSIX_SPAWN_DUP2 (in module os):       Process Management. (line  407)
* POSIX_SPAWN_OPEN (in module os):       Process Management. (line  395)
* post() (nntplib.NNTP method):          Methods<3>.         (line  278)
* post() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line  179)
* postcmd() (cmd.Cmd method):            Cmd Objects.        (line   96)
* postloop() (cmd.Cmd method):           Cmd Objects.        (line  114)
* post_handshake_auth (ssl.SSLContext attribute): SSL Contexts.
                                                             (line  602)
* post_mortem() (in module pdb):         pdb — The Python Debugger.
                                                             (line  129)
* post_setup() (venv.EnvBuilder method): API<2>.             (line  120)
* Pow (class in ast):                    Expressions<2>.     (line   54)
* pow() (built-in function):             Built-in Functions. (line 1277)
* pow() (in module math):                Power and logarithmic functions.
                                                             (line   60)
* pow() (in module operator):            operator — Standard operators as functions.
                                                             (line  143)
* power() (decimal.Context method):      Context objects.    (line  418)
* power; operation:                      The power operator. (line    6)
* pp (pdb command):                      Debugger Commands.  (line  242)
* pp() (in module pprint):               pprint — Data pretty printer.
                                                             (line   96)
* pprint (module):                       pprint — Data pretty printer.
                                                             (line    6)
* pprint() (in module pprint):           pprint — Data pretty printer.
                                                             (line  106)
* pprint() (pprint.PrettyPrinter method): PrettyPrinter Objects.
                                                             (line   14)
* prcal() (in module calendar):          calendar — General calendar-related functions.
                                                             (line  344)
* pread() (in module os):                File Descriptor Operations.
                                                             (line  424)
* preadv() (in module os):               File Descriptor Operations.
                                                             (line  437)
* preamble (email.message.EmailMessage attribute): email message Representing an email message.
                                                             (line  680)
* preamble (email.message.Message attribute): email message Message Representing an email message using the compat32 API.
                                                             (line  690)
* precmd() (cmd.Cmd method):             Cmd Objects.        (line   86)
* prefix:                                Python-related paths and files.
                                                             (line    7)
* prefix <1>:                            Include Files.      (line   37)
* prefix <2>:                            Include Files.      (line   40)
* prefix <3>:                            Include Files.      (line   47)
* PREFIX (in module distutils.sysconfig): distutils sysconfig — System configuration information.
                                                             (line   19)
* prefix (in module sys):                sys — System-specific parameters and functions.
                                                             (line 1194)
* prefix (xml.dom.Attr attribute):       Attr Objects.       (line   18)
* prefix (xml.dom.Node attribute):       Node Objects.       (line   69)
* prefix (zipimport.zipimporter attribute): zipimporter Objects.
                                                             (line   74)
* PREFIXES (in module site):             Module contents<4>. (line    6)
* prefixlen (ipaddress.IPv4Network attribute): Network objects.
                                                             (line  132)
* prefixlen (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  329)
* preloop() (cmd.Cmd method):            Cmd Objects.        (line  108)
* prepare() (graphlib.TopologicalSorter method): graphlib — Functionality to operate with graph-like structures.
                                                             (line   99)
* prepare() (logging.handlers.QueueHandler method): QueueHandler.
                                                             (line   40)
* prepare() (logging.handlers.QueueListener method): QueueListener.
                                                             (line   54)
* prepare_class() (in module types):     Dynamic Type Creation.
                                                             (line   23)
* prepare_input_source() (in module xml.sax.saxutils): xml sax saxutils — SAX Utilities.
                                                             (line   77)
* prepend() (pipes.Template method):     Template Objects.   (line   37)
* preprocess() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  433)
* PrettyPrinter (class in pprint):       pprint — Data pretty printer.
                                                             (line   30)
* prev() (tkinter.ttk.Treeview method):  ttk Treeview.       (line  242)
* previousSibling (xml.dom.Node attribute): Node Objects.    (line   32)
* primary:                               Primaries.          (line    6)
* print (2to3 fixer):                    Fixers.             (line  258)
* print() (built-in function):           Built-in Functions. (line 1315)
* print() (built-in function); __str__() (object method): Basic customization.
                                                             (line  128)
* printable (in module string):          String constants.   (line   41)
* printdir() (zipfile.ZipFile method):   ZipFile Objects.    (line  207)
* printf-style formatting:               printf-style String Formatting.
                                                             (line    6)
* printf-style formatting <1>:           printf-style Bytes Formatting.
                                                             (line    6)
* print_callees() (pstats.Stats method): The Stats Class.    (line  217)
* print_callers() (pstats.Stats method): The Stats Class.    (line  196)
* print_directory() (in module cgi):     Functions<9>.       (line   58)
* print_environ() (in module cgi):       Functions<9>.       (line   50)
* print_environ_usage() (in module cgi): Functions<9>.       (line   62)
* print_exc() (in module traceback):     traceback — Print or retrieve a stack traceback.
                                                             (line   60)
* print_exc() (timeit.Timer method):     Python Interface.   (line  133)
* print_exception() (in module traceback): traceback — Print or retrieve a stack traceback.
                                                             (line   33)
* PRINT_EXPR (opcode):                   Python Bytecode Instructions.
                                                             (line  311)
* print_form() (in module cgi):          Functions<9>.       (line   54)
* print_help() (argparse.ArgumentParser method): Printing help.
                                                             (line   16)
* print_last() (in module traceback):    traceback — Print or retrieve a stack traceback.
                                                             (line   65)
* print_stack() (asyncio.Task method):   Task Object.        (line  193)
* print_stack() (in module traceback):   traceback — Print or retrieve a stack traceback.
                                                             (line   72)
* print_stats() (profile.Profile method): profile and cProfile Module Reference.
                                                             (line   91)
* print_stats() (pstats.Stats method):   The Stats Class.    (line  164)
* print_tb() (in module traceback):      traceback — Print or retrieve a stack traceback.
                                                             (line   22)
* print_usage() (argparse.ArgumentParser method): Printing help.
                                                             (line   10)
* print_usage() (optparse.OptionParser method): Other methods.
                                                             (line   15)
* print_version() (optparse.OptionParser method): Printing a version string.
                                                             (line   26)
* print_warning() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  568)
* PriorityQueue (class in asyncio):      Priority Queue.     (line    6)
* PriorityQueue (class in queue):        queue — A synchronized queue class.
                                                             (line   50)
* PRIO_PGRP (in module os):              Process Parameters. (line  272)
* PRIO_PROCESS (in module os):           Process Parameters. (line  272)
* PRIO_USER (in module os):              Process Parameters. (line  272)
* private; names:                        Identifiers Names.  (line   12)
* prlimit() (in module resource):        Resource Limits.    (line   56)
* prmonth() (calendar.TextCalendar method): calendar — General calendar-related functions.
                                                             (line  143)
* prmonth() (in module calendar):        calendar — General calendar-related functions.
                                                             (line  335)
* ProactorEventLoop (class in asyncio):  Event Loop Implementations.
                                                             (line   29)
* procedure; call:                       Expression statements.
                                                             (line   17)
* Process (class in multiprocessing):    Process and exceptions.
                                                             (line    6)
* process() (logging.LoggerAdapter method): LoggerAdapter Objects.
                                                             (line   16)
* process; group:                        Process Parameters. (line  180)
* process; group <1>:                    Process Parameters. (line  238)
* process; id:                           Process Parameters. (line  244)
* process; id of parent:                 Process Parameters. (line  248)
* process; killing:                      Process Management. (line  289)
* process; killing <1>:                  Process Management. (line  311)
* process; scheduling priority:          Process Parameters. (line  259)
* process; scheduling priority <1>:      Process Parameters. (line  389)
* process; signalling:                   Process Management. (line  289)
* process; signalling <1>:               Process Management. (line  311)
* ProcessError:                          Process and exceptions.
                                                             (line  204)
* processes, light-weight:               _thread — Low-level threading API.
                                                             (line    6)
* ProcessingInstruction() (in module xml.etree.ElementTree): Functions<7>.
                                                             (line  179)
* processingInstruction() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line  164)
* ProcessingInstructionHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  236)
* ProcessLookupError:                    OS exceptions.      (line  100)
* processor time:                        Functions<3>.       (line  200)
* processor time <1>:                    Functions<3>.       (line  479)
* processor() (in module platform):      Cross Platform.     (line   66)
* ProcessPoolExecutor (class in concurrent.futures): ProcessPoolExecutor.
                                                             (line   21)
* process_exited() (asyncio.SubprocessProtocol method): Subprocess Protocols.
                                                             (line   26)
* process_message() (smtpd.SMTPServer method): SMTPServer Objects.
                                                             (line   41)
* process_request() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line  156)
* process_time() (in module time):       Functions<3>.       (line  198)
* process_time_ns() (in module time):    Functions<3>.       (line  208)
* process_tokens() (in module tabnanny): tabnanny — Detection of ambiguous indentation.
                                                             (line   42)
* prod() (in module math):               Number-theoretic and representation functions.
                                                             (line  234)
* product() (in module itertools):       Itertool functions. (line  461)
* Profile (class in profile):            profile and cProfile Module Reference.
                                                             (line   35)
* profile (module):                      profile and cProfile Module Reference.
                                                             (line    6)
* profile function:                      threading — Thread-based parallelism.
                                                             (line  133)
* profile function <1>:                  sys — System-specific parameters and functions.
                                                             (line  737)
* profile function <2>:                  sys — System-specific parameters and functions.
                                                             (line 1233)
* profiler:                              sys — System-specific parameters and functions.
                                                             (line  737)
* profiler <1>:                          sys — System-specific parameters and functions.
                                                             (line 1233)
* profiling, deterministic:              Introduction to the profilers.
                                                             (line    6)
* program:                               Complete Python programs.
                                                             (line    6)
* ProgrammingError:                      Exceptions<5>.      (line   25)
* Progressbar (class in tkinter.ttk):    ttk Progressbar.    (line    6)
* prompt (cmd.Cmd attribute):            Cmd Objects.        (line  123)
* prompts, interpreter:                  sys — System-specific parameters and functions.
                                                             (line 1210)
* prompt_user_passwd() (urllib.request.FancyURLopener method): Legacy interface.
                                                             (line  184)
* propagate (logging.Logger attribute):  Logger Objects.     (line   25)
* property (built-in class):             Built-in Functions. (line 1340)
* property list:                         plistlib — Generate and parse Apple plist files.
                                                             (line    8)
* PropertyMock (class in unittest.mock): The Mock Class.     (line  627)
* property_declaration_handler (in module xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line  101)
* property_dom_node (in module xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line  108)
* property_lexical_handler (in module xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line   94)
* property_xml_string (in module xml.sax.handler): xml sax handler — Base classes for SAX handlers.
                                                             (line  115)
* proto (socket.socket attribute):       Socket Objects.     (line  603)
* Protocol (class in asyncio):           Base Protocols.     (line   10)
* Protocol (class in typing):            Building generic types.
                                                             (line   89)
* protocol (ssl.SSLContext attribute):   SSL Contexts.       (line  625)
* protocol; context management:          Context Manager Types.
                                                             (line    6)
* protocol; iterator:                    Iterator Types.     (line    6)
* protocol; Telnet:                      telnetlib — Telnet client.
                                                             (line    8)
* ProtocolError (class in xmlrpc.client): ProtocolError Objects.
                                                             (line    6)
* PROTOCOL_SSLv2 (in module ssl):        Constants<9>.       (line  150)
* PROTOCOL_SSLv23 (in module ssl):       Constants<9>.       (line  143)
* PROTOCOL_SSLv3 (in module ssl):        Constants<9>.       (line  163)
* PROTOCOL_TLS (in module ssl):          Constants<9>.       (line  118)
* PROTOCOL_TLSv1 (in module ssl):        Constants<9>.       (line  177)
* PROTOCOL_TLSv1_1 (in module ssl):      Constants<9>.       (line  185)
* PROTOCOL_TLSv1_2 (in module ssl):      Constants<9>.       (line  196)
* PROTOCOL_TLS_CLIENT (in module ssl):   Constants<9>.       (line  126)
* PROTOCOL_TLS_SERVER (in module ssl):   Constants<9>.       (line  135)
* protocol_version (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  157)
* PROTOCOL_VERSION (imaplib.IMAP4 attribute): IMAP4 Objects. (line  392)
* prot_c() (ftplib.FTP_TLS method):      FTP_TLS Objects.    (line   35)
* prot_p() (ftplib.FTP_TLS method):      FTP_TLS Objects.    (line   31)
* provisional API:                       Glossary.           (line 1062)
* provisional package:                   Glossary.           (line 1082)
* proxy() (in module weakref):           weakref — Weak references.
                                                             (line  136)
* proxyauth() (imaplib.IMAP4 method):    IMAP4 Objects.      (line  193)
* ProxyBasicAuthHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  356)
* ProxyDigestAuthHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  388)
* ProxyHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  282)
* ProxyType (in module weakref):         weakref — Weak references.
                                                             (line  305)
* ProxyTypes (in module weakref):        weakref — Weak references.
                                                             (line  313)
* pryear() (calendar.TextCalendar method): calendar — General calendar-related functions.
                                                             (line  158)
* ps1 (in module sys):                   sys — System-specific parameters and functions.
                                                             (line 1207)
* ps2 (in module sys):                   sys — System-specific parameters and functions.
                                                             (line 1207)
* pstats (module):                       The Stats Class.    (line    7)
* pstdev() (in module statistics):       Function details.   (line  270)
* pthreads:                              _thread — Low-level threading API.
                                                             (line   16)
* pthread_getcpuclockid() (in module time): Functions<3>.    (line   21)
* pthread_kill() (in module signal):     Module contents<2>. (line  296)
* pthread_sigmask() (in module signal):  Module contents<2>. (line  325)
* pty (module):                          pty — Pseudo-terminal utilities.
                                                             (line    6)
* pu() (in module turtle):               Drawing state.      (line   12)
* publicId (xml.dom.DocumentType attribute): DocumentType Objects.
                                                             (line   17)
* PullDom (class in xml.dom.pulldom):    xml dom pulldom — Support for building partial DOM trees.
                                                             (line   78)
* punctuation (in module string):        String constants.   (line   36)
* punctuation_chars (shlex.shlex attribute): shlex Objects.  (line  183)
* PurePath (class in pathlib):           Pure paths.         (line   10)
* PurePath.anchor (in module pathlib):   Methods and properties.
                                                             (line   40)
* PurePath.drive (in module pathlib):    Methods and properties.
                                                             (line    8)
* PurePath.name (in module pathlib):     Methods and properties.
                                                             (line   94)
* PurePath.parent (in module pathlib):   Methods and properties.
                                                             (line   66)
* PurePath.parents (in module pathlib):  Methods and properties.
                                                             (line   53)
* PurePath.parts (in module pathlib):    Accessing individual parts.
                                                             (line    9)
* PurePath.root (in module pathlib):     Methods and properties.
                                                             (line   24)
* PurePath.stem (in module pathlib):     Methods and properties.
                                                             (line  131)
* PurePath.suffix (in module pathlib):   Methods and properties.
                                                             (line  109)
* PurePath.suffixes (in module pathlib): Methods and properties.
                                                             (line  120)
* PurePosixPath (class in pathlib):      Pure paths.         (line   68)
* PureProxy (class in smtpd):            PureProxy Objects.  (line    6)
* PureWindowsPath (class in pathlib):    Pure paths.         (line   78)
* purge() (in module re):                Module Contents.    (line  359)
* Purpose.CLIENT_AUTH (in module ssl):   Constants<9>.       (line  510)
* Purpose.SERVER_AUTH (in module ssl):   Constants<9>.       (line  501)
* push() (asynchat.async_chat method):   asynchat — Asynchronous socket command/response handler.
                                                             (line  101)
* push() (code.InteractiveConsole method): Interactive Console Objects.
                                                             (line   28)
* push() (contextlib.ExitStack method):  Utilities.          (line  394)
* pushbutton() (msilib.Dialog method):   GUI classes.        (line   68)
* push_alignment() (formatter.formatter method): The Formatter Interface.
                                                             (line   90)
* push_async_callback() (contextlib.AsyncExitStack method): Utilities.
                                                             (line  474)
* push_async_exit() (contextlib.AsyncExitStack method): Utilities.
                                                             (line  469)
* push_font() (formatter.formatter method): The Formatter Interface.
                                                             (line  101)
* push_margin() (formatter.formatter method): The Formatter Interface.
                                                             (line  113)
* push_source() (shlex.shlex method):    shlex Objects.      (line   56)
* push_style() (formatter.formatter method): The Formatter Interface.
                                                             (line  125)
* push_token() (shlex.shlex method):     shlex Objects.      (line   16)
* push_with_producer() (asynchat.async_chat method): asynchat — Asynchronous socket command/response handler.
                                                             (line  109)
* put() (asyncio.Queue method):          Queue.              (line   62)
* put() (multiprocessing.Queue method):  Pipes and Queues.   (line  120)
* put() (multiprocessing.SimpleQueue method): Pipes and Queues.
                                                             (line  227)
* put() (queue.Queue method):            Queue Objects.      (line   29)
* put() (queue.SimpleQueue method):      SimpleQueue Objects.
                                                             (line   20)
* putch() (in module msvcrt):            Console I/O.        (line   35)
* putenv() (in module os):               Process Parameters. (line  317)
* putheader() (http.client.HTTPConnection method): HTTPConnection Objects.
                                                             (line  136)
* putp() (in module curses):             Functions<4>.       (line  376)
* putrequest() (http.client.HTTPConnection method): HTTPConnection Objects.
                                                             (line  125)
* putwch() (in module msvcrt):           Console I/O.        (line   39)
* putwin() (curses.window method):       Window Objects.     (line  453)
* put_nowait() (asyncio.Queue method):   Queue.              (line   67)
* put_nowait() (multiprocessing.Queue method): Pipes and Queues.
                                                             (line  136)
* put_nowait() (queue.Queue method):     Queue Objects.      (line   40)
* put_nowait() (queue.SimpleQueue method): SimpleQueue Objects.
                                                             (line   35)
* pvariance() (in module statistics):    Function details.   (line  279)
* pwd (module):                          pwd — The password database.
                                                             (line    6)
* pwd() (ftplib.FTP method):             FTP Objects.        (line  221)
* pwrite() (in module os):               File Descriptor Operations.
                                                             (line  495)
* pwritev() (in module os):              File Descriptor Operations.
                                                             (line  506)
* PyAnySet_Check (C function):           Set Objects.        (line   55)
* PyAnySet_CheckExact (C function):      Set Objects.        (line   61)
* PyArg_Parse (C function):              API Functions.      (line   51)
* PyArg_ParseTuple (C function):         API Functions.      (line    6)
* PyArg_ParseTuple():                    Extracting Parameters in Extension Functions.
                                                             (line    6)
* PyArg_ParseTupleAndKeywords (C function): API Functions.   (line   20)
* PyArg_ParseTupleAndKeywords():         Keyword Parameters for Extension Functions.
                                                             (line    6)
* PyArg_UnpackTuple (C function):        API Functions.      (line   63)
* PyArg_ValidateKeywordArguments (C function): API Functions.
                                                             (line   42)
* PyArg_VaParse (C function):            API Functions.      (line   13)
* PyArg_VaParseTupleAndKeywords (C function): API Functions. (line   34)
* PyASCIIObject (C type):                Unicode Type.       (line   29)
* PyAsyncMethods (C type):               Async Object Structures.
                                                             (line    8)
* PyAsyncMethods.am_aiter (C member):    Async Object Structures.
                                                             (line   34)
* PyAsyncMethods.am_anext (C member):    Async Object Structures.
                                                             (line   46)
* PyAsyncMethods.am_await (C member):    Async Object Structures.
                                                             (line   22)
* PyBool_Check (C function):             Boolean Objects.    (line   11)
* PyBool_FromLong (C function):          Boolean Objects.    (line   38)
* PyBufferProcs:                         Buffer Protocol.    (line   20)
* PyBufferProcs (C type):                Buffer Object Structures.
                                                             (line    6)
* PyBufferProcs.bf_getbuffer (C member): Buffer Object Structures.
                                                             (line   12)
* PyBufferProcs.bf_releasebuffer (C member): Buffer Object Structures.
                                                             (line   60)
* PyBuffer_FillContiguousStrides (C function): Buffer-related functions.
                                                             (line   79)
* PyBuffer_FillInfo (C function):        Buffer-related functions.
                                                             (line   89)
* PyBuffer_FromContiguous (C function):  Buffer-related functions.
                                                             (line   61)
* PyBuffer_GetPointer (C function):      Buffer-related functions.
                                                             (line   55)
* PyBuffer_IsContiguous (C function):    Buffer-related functions.
                                                             (line   48)
* PyBuffer_Release (C function):         Buffer-related functions.
                                                             (line   32)
* PyBuffer_SizeFromFormat (C function):  Buffer-related functions.
                                                             (line   41)
* PyBuffer_ToContiguous (C function):    Buffer-related functions.
                                                             (line   68)
* PyBUF_ANY_CONTIGUOUS (C macro):        contiguity requests.
                                                             (line   20)
* PyBUF_CONTIG (C macro):                compound requests.  (line   36)
* PyBUF_CONTIG_RO (C macro):             compound requests.  (line   39)
* PyBUF_C_CONTIGUOUS (C macro):          contiguity requests.
                                                             (line   14)
* PyBUF_FORMAT (C macro):                readonly format.    (line   14)
* PyBUF_FULL (C macro):                  compound requests.  (line   18)
* PyBUF_FULL_RO (C macro):               compound requests.  (line   21)
* PyBUF_F_CONTIGUOUS (C macro):          contiguity requests.
                                                             (line   17)
* PyBUF_INDIRECT (C macro):              shape strides suboffsets.
                                                             (line   14)
* PyBUF_ND (C macro):                    shape strides suboffsets.
                                                             (line   20)
* PyBUF_RECORDS (C macro):               compound requests.  (line   24)
* PyBUF_RECORDS_RO (C macro):            compound requests.  (line   27)
* PyBUF_SIMPLE (C macro):                shape strides suboffsets.
                                                             (line   23)
* PyBUF_STRIDED (C macro):               compound requests.  (line   30)
* PyBUF_STRIDED_RO (C macro):            compound requests.  (line   33)
* PyBUF_STRIDES (C macro):               shape strides suboffsets.
                                                             (line   17)
* PyBUF_WRITABLE (C macro):              readonly format.    (line    6)
* PyByteArrayObject (C type):            Byte Array Objects. (line    6)
* PyByteArray_AsString (C function):     Direct API functions.
                                                             (line   23)
* PyByteArray_AS_STRING (C function):    Macros.             (line    8)
* PyByteArray_Check (C function):        Type check macros.  (line    6)
* PyByteArray_CheckExact (C function):   Type check macros.  (line   11)
* PyByteArray_Concat (C function):       Direct API functions.
                                                             (line   15)
* PyByteArray_FromObject (C function):   Direct API functions.
                                                             (line    6)
* PyByteArray_FromStringAndSize (C function): Direct API functions.
                                                             (line   10)
* PyByteArray_GET_SIZE (C function):     Macros.             (line   12)
* PyByteArray_Resize (C function):       Direct API functions.
                                                             (line   29)
* PyByteArray_Size (C function):         Direct API functions.
                                                             (line   19)
* PyByteArray_Type (C variable):         Byte Array Objects. (line   11)
* PyBytesObject (C type):                Bytes Objects<2>.   (line    9)
* PyBytes_AsString (C function):         Bytes Objects<2>.   (line  127)
* PyBytes_AsStringAndSize (C function):  Bytes Objects<2>.   (line  144)
* PyBytes_AS_STRING (C function):        Bytes Objects<2>.   (line  139)
* PyBytes_Check (C function):            Bytes Objects<2>.   (line   20)
* PyBytes_CheckExact (C function):       Bytes Objects<2>.   (line   25)
* PyBytes_Concat (C function):           Bytes Objects<2>.   (line  166)
* PyBytes_ConcatAndDel (C function):     Bytes Objects<2>.   (line  176)
* PyBytes_FromFormat (C function):       Bytes Objects<2>.   (line   44)
* PyBytes_FromFormatV (C function):      Bytes Objects<2>.   (line  107)
* PyBytes_FromObject (C function):       Bytes Objects<2>.   (line  114)
* PyBytes_FromString (C function):       Bytes Objects<2>.   (line   31)
* PyBytes_FromStringAndSize (C function): Bytes Objects<2>.  (line   36)
* PyBytes_GET_SIZE (C function):         Bytes Objects<2>.   (line  122)
* PyBytes_Size (C function):             Bytes Objects<2>.   (line  118)
* PyBytes_Type (C variable):             Bytes Objects<2>.   (line   14)
* pycache_prefix (in module sys):        sys — System-specific parameters and functions.
                                                             (line  288)
* PyCallable_Check (C function):         Call Support API.   (line    6)
* PyCallIter_Check (C function):         Iterator Objects.   (line   35)
* PyCallIter_New (C function):           Iterator Objects.   (line   40)
* PyCallIter_Type (C variable):          Iterator Objects.   (line   29)
* PyCapsule (C type):                    Capsules<2>.        (line   11)
* PyCapsule_CheckExact (C function):     Capsules<2>.        (line   29)
* PyCapsule_Destructor (C type):         Capsules<2>.        (line   20)
* PyCapsule_GetContext (C function):     Capsules<2>.        (line   77)
* PyCapsule_GetDestructor (C function):  Capsules<2>.        (line   66)
* PyCapsule_GetName (C function):        Capsules<2>.        (line   87)
* PyCapsule_GetPointer (C function):     Capsules<2>.        (line   54)
* PyCapsule_Import (C function):         Capsules<2>.        (line   97)
* PyCapsule_IsValid (C function):        Capsules<2>.        (line  111)
* PyCapsule_New (C function):            Capsules<2>.        (line   34)
* PyCapsule_SetContext (C function):     Capsules<2>.        (line  127)
* PyCapsule_SetDestructor (C function):  Capsules<2>.        (line  135)
* PyCapsule_SetName (C function):        Capsules<2>.        (line  144)
* PyCapsule_SetPointer (C function):     Capsules<2>.        (line  154)
* PyCellObject (C type):                 Cell Objects.       (line   16)
* PyCell_Check (C function):             Cell Objects.       (line   24)
* PyCell_Get (C function):               Cell Objects.       (line   33)
* PyCell_GET (C function):               Cell Objects.       (line   37)
* PyCell_New (C function):               Cell Objects.       (line   29)
* PyCell_Set (C function):               Cell Objects.       (line   42)
* PyCell_SET (C function):               Cell Objects.       (line   49)
* PyCell_Type (C variable):              Cell Objects.       (line   20)
* PyCFunction (C type):                  Implementing functions and methods.
                                                             (line    6)
* PyCFunctionWithKeywords (C type):      Implementing functions and methods.
                                                             (line   20)
* PyCF_ALLOW_TOP_LEVEL_AWAIT (in module ast): Compiler Flags.
                                                             (line    9)
* PyCF_ONLY_AST (in module ast):         Compiler Flags.     (line   16)
* PyCF_TYPE_COMMENTS (in module ast):    Compiler Flags.     (line   21)
* PycInvalidationMode (class in py_compile): py_compile — Compile Python source files.
                                                             (line   91)
* pyclbr (module):                       pyclbr — Python module browser support.
                                                             (line    6)
* PyCMethod (C type):                    Implementing functions and methods.
                                                             (line   50)
* PyCodec_BackslashReplaceErrors (C function): Registry API for Unicode encoding error handlers.
                                                             (line   50)
* PyCodec_Decode (C function):           Codec registry and support functions.
                                                             (line   29)
* PyCodec_Decoder (C function):          Codec lookup API.   (line   15)
* PyCodec_Encode (C function):           Codec registry and support functions.
                                                             (line   19)
* PyCodec_Encoder (C function):          Codec lookup API.   (line   11)
* PyCodec_IgnoreErrors (C function):     Registry API for Unicode encoding error handlers.
                                                             (line   37)
* PyCodec_IncrementalDecoder (C function): Codec lookup API. (line   24)
* PyCodec_IncrementalEncoder (C function): Codec lookup API. (line   19)
* PyCodec_KnownEncoding (C function):    Codec registry and support functions.
                                                             (line   14)
* PyCodec_LookupError (C function):      Registry API for Unicode encoding error handlers.
                                                             (line   28)
* PyCodec_NameReplaceErrors (C function): Registry API for Unicode encoding error handlers.
                                                             (line   54)
* PyCodec_Register (C function):         Codec registry and support functions.
                                                             (line    6)
* PyCodec_RegisterError (C function):    Registry API for Unicode encoding error handlers.
                                                             (line    6)
* PyCodec_ReplaceErrors (C function):    Registry API for Unicode encoding error handlers.
                                                             (line   41)
* PyCodec_StreamReader (C function):     Codec lookup API.   (line   29)
* PyCodec_StreamWriter (C function):     Codec lookup API.   (line   35)
* PyCodec_StrictErrors (C function):     Registry API for Unicode encoding error handlers.
                                                             (line   34)
* PyCodec_XMLCharRefReplaceErrors (C function): Registry API for Unicode encoding error handlers.
                                                             (line   45)
* PyCodeObject (C type):                 Code Objects<2>.    (line   10)
* PyCode_Check (C function):             Code Objects<2>.    (line   20)
* PyCode_GetNumFree (C function):        Code Objects<2>.    (line   25)
* PyCode_New (C function):               Code Objects<2>.    (line   29)
* PyCode_NewEmpty (C function):          Code Objects<2>.    (line   57)
* PyCode_NewWithPosOnlyArgs (C function): Code Objects<2>.   (line   43)
* PyCode_Type (C variable):              Code Objects<2>.    (line   15)
* PyCompactUnicodeObject (C type):       Unicode Type.       (line   29)
* PyCompileError:                        py_compile — Compile Python source files.
                                                             (line   19)
* PyCompilerFlags (C type):              The Very High Level Layer.
                                                             (line  405)
* PyCompilerFlags.cf_feature_version (C member): The Very High Level Layer.
                                                             (line  421)
* PyCompilerFlags.cf_flags (C member):   The Very High Level Layer.
                                                             (line  417)
* PyComplexObject (C type):              Complex Numbers as Python Objects.
                                                             (line    6)
* PyComplex_AsCComplex (C function):     Complex Numbers as Python Objects.
                                                             (line   46)
* PyComplex_Check (C function):          Complex Numbers as Python Objects.
                                                             (line   17)
* PyComplex_CheckExact (C function):     Complex Numbers as Python Objects.
                                                             (line   23)
* PyComplex_FromCComplex (C function):   Complex Numbers as Python Objects.
                                                             (line   29)
* PyComplex_FromDoubles (C function):    Complex Numbers as Python Objects.
                                                             (line   33)
* PyComplex_ImagAsDouble (C function):   Complex Numbers as Python Objects.
                                                             (line   42)
* PyComplex_RealAsDouble (C function):   Complex Numbers as Python Objects.
                                                             (line   38)
* PyComplex_Type (C variable):           Complex Numbers as Python Objects.
                                                             (line   11)
* PyConfig (C type):                     PyConfig.           (line    6)
* PyConfig.argv (C member):              PyConfig.           (line   99)
* PyConfig.base_executable (C member):   PyConfig.           (line  111)
* PyConfig.base_exec_prefix (C member):  PyConfig.           (line  107)
* PyConfig.base_prefix (C member):       PyConfig.           (line  116)
* PyConfig.buffered_stdio (C member):    PyConfig.           (line  128)
* PyConfig.bytes_warning (C member):     PyConfig.           (line  135)
* PyConfig.check_hash_pycs_mode (C member): PyConfig.        (line  142)
* PyConfig.configure_c_stdio (C member): PyConfig.           (line  152)
* PyConfig.dev_mode (C member):          PyConfig.           (line  158)
* PyConfig.dump_refs (C member):         PyConfig.           (line  162)
* PyConfig.executable (C member):        PyConfig.           (line  172)
* PyConfig.exec_prefix (C member):       PyConfig.           (line  168)
* PyConfig.faulthandler (C member):      PyConfig.           (line  176)
* PyConfig.filesystem_encoding (C member): PyConfig.         (line  181)
* PyConfig.filesystem_errors (C member): PyConfig.           (line  185)
* PyConfig.hash_seed (C member):         PyConfig.           (line  190)
* PyConfig.home (C member):              PyConfig.           (line  200)
* PyConfig.import_time (C member):       PyConfig.           (line  207)
* PyConfig.inspect (C member):           PyConfig.           (line  211)
* PyConfig.install_signal_handlers (C member): PyConfig.     (line  215)
* PyConfig.interactive (C member):       PyConfig.           (line  219)
* PyConfig.isolated (C member):          PyConfig.           (line  223)
* PyConfig.legacy_windows_stdio (C member): PyConfig.        (line  237)
* PyConfig.malloc_stats (C member):      PyConfig.           (line  246)
* PyConfig.module_search_paths (C member): PyConfig.         (line  262)
* PyConfig.module_search_paths_set (C member): PyConfig.     (line  264)
* PyConfig.optimization_level (C member): PyConfig.          (line  271)
* PyConfig.parser_debug (C member):      PyConfig.           (line  287)
* PyConfig.parse_argv (C member):        PyConfig.           (line  281)
* PyConfig.pathconfig_warnings (C member): PyConfig.         (line  292)
* PyConfig.platlibdir (C member):        PyConfig.           (line  120)
* PyConfig.prefix (C member):            PyConfig.           (line  298)
* PyConfig.program_name (C member):      PyConfig.           (line  302)
* PyConfig.pycache_prefix (C member):    PyConfig.           (line  307)
* PyConfig.pythonpath_env (C member):    PyConfig.           (line  254)
* PyConfig.quiet (C member):             PyConfig.           (line  313)
* PyConfig.run_command (C member):       PyConfig.           (line  318)
* PyConfig.run_filename (C member):      PyConfig.           (line  323)
* PyConfig.run_module (C member):        PyConfig.           (line  327)
* PyConfig.show_ref_count (C member):    PyConfig.           (line  332)
* PyConfig.site_import (C member):       PyConfig.           (line  341)
* PyConfig.skip_source_first_line (C member): PyConfig.      (line  345)
* PyConfig.stdio_encoding (C member):    PyConfig.           (line  349)
* PyConfig.stdio_errors (C member):      PyConfig.           (line  351)
* PyConfig.tracemalloc (C member):       PyConfig.           (line  356)
* PyConfig.user_site_directory (C member): PyConfig.         (line  364)
* PyConfig.use_environment (C member):   PyConfig.           (line  360)
* PyConfig.use_hash_seed (C member):     PyConfig.           (line  192)
* PyConfig.verbose (C member):           PyConfig.           (line  368)
* PyConfig.warnoptions (C member):       PyConfig.           (line  372)
* PyConfig.write_bytecode (C member):    PyConfig.           (line  383)
* PyConfig.xoptions (C member):          PyConfig.           (line  390)
* PyConfig._use_peg_parser (C member):   PyConfig.           (line  394)
* PyConfig_Clear (C function):           PyConfig.           (line   69)
* PyConfig_InitIsolatedConfig (C function): PyConfig.        (line   17)
* PyConfig_InitPythonConfig (C function): PyConfig.          (line   12)
* PyConfig_Read (C function):            PyConfig.           (line   61)
* PyConfig_SetArgv (C function):         PyConfig.           (line   37)
* PyConfig_SetBytesArgv (C function):    PyConfig.           (line   44)
* PyConfig_SetBytesString (C function):  PyConfig.           (line   29)
* PyConfig_SetString (C function):       PyConfig.           (line   22)
* PyConfig_SetWideStringList (C function): PyConfig.         (line   53)
* PyContext (C type):                    Context Variables Objects.
                                                             (line   24)
* PyContextToken (C type):               Context Variables Objects.
                                                             (line   34)
* PyContextToken_CheckExact (C function): Context Variables Objects.
                                                             (line   63)
* PyContextToken_Type (C variable):      Context Variables Objects.
                                                             (line   47)
* PyContextVar (C type):                 Context Variables Objects.
                                                             (line   29)
* PyContextVar_CheckExact (C function):  Context Variables Objects.
                                                             (line   58)
* PyContextVar_Get (C function):         Context Variables Objects.
                                                             (line  103)
* PyContextVar_New (C function):         Context Variables Objects.
                                                             (line   95)
* PyContextVar_Reset (C function):       Context Variables Objects.
                                                             (line  127)
* PyContextVar_Set (C function):         Context Variables Objects.
                                                             (line  121)
* PyContextVar_Type (C variable):        Context Variables Objects.
                                                             (line   43)
* PyContext_CheckExact (C function):     Context Variables Objects.
                                                             (line   53)
* PyContext_Copy (C function):           Context Variables Objects.
                                                             (line   74)
* PyContext_CopyCurrent (C function):    Context Variables Objects.
                                                             (line   78)
* PyContext_Enter (C function):          Context Variables Objects.
                                                             (line   82)
* PyContext_Exit (C function):           Context Variables Objects.
                                                             (line   87)
* PyContext_New (C function):            Context Variables Objects.
                                                             (line   70)
* PyContext_Type (C variable):           Context Variables Objects.
                                                             (line   39)
* PyCoroObject (C type):                 Coroutine Objects<2>.
                                                             (line   11)
* PyCoro_CheckExact (C function):        Coroutine Objects<2>.
                                                             (line   19)
* PyCoro_New (C function):               Coroutine Objects<2>.
                                                             (line   24)
* PyCoro_Type (C variable):              Coroutine Objects<2>.
                                                             (line   15)
* PyDateTime_Check (C function):         DateTime Objects<2>.
                                                             (line   36)
* PyDateTime_CheckExact (C function):    DateTime Objects<2>.
                                                             (line   42)
* PyDateTime_DATE_GET_HOUR (C function): DateTime Objects<2>.
                                                             (line  163)
* PyDateTime_DATE_GET_MICROSECOND (C function): DateTime Objects<2>.
                                                             (line  175)
* PyDateTime_DATE_GET_MINUTE (C function): DateTime Objects<2>.
                                                             (line  167)
* PyDateTime_DATE_GET_SECOND (C function): DateTime Objects<2>.
                                                             (line  171)
* PyDateTime_DELTA_GET_DAYS (C function): DateTime Objects<2>.
                                                             (line  205)
* PyDateTime_DELTA_GET_MICROSECONDS (C function): DateTime Objects<2>.
                                                             (line  217)
* PyDateTime_DELTA_GET_SECONDS (C function): DateTime Objects<2>.
                                                             (line  211)
* PyDateTime_FromDateAndTime (C function): DateTime Objects<2>.
                                                             (line   86)
* PyDateTime_FromDateAndTimeAndFold (C function): DateTime Objects<2>.
                                                             (line   93)
* PyDateTime_FromTimestamp (C function): DateTime Objects<2>.
                                                             (line  226)
* PyDateTime_GET_DAY (C function):       DateTime Objects<2>.
                                                             (line  155)
* PyDateTime_GET_MONTH (C function):     DateTime Objects<2>.
                                                             (line  151)
* PyDateTime_GET_YEAR (C function):      DateTime Objects<2>.
                                                             (line  147)
* PyDateTime_TimeZone_UTC (C variable):  DateTime Objects<2>.
                                                             (line   16)
* PyDateTime_TIME_GET_HOUR (C function): DateTime Objects<2>.
                                                             (line  185)
* PyDateTime_TIME_GET_MICROSECOND (C function): DateTime Objects<2>.
                                                             (line  197)
* PyDateTime_TIME_GET_MINUTE (C function): DateTime Objects<2>.
                                                             (line  189)
* PyDateTime_TIME_GET_SECOND (C function): DateTime Objects<2>.
                                                             (line  193)
* PyDate_Check (C function):             DateTime Objects<2>.
                                                             (line   25)
* PyDate_CheckExact (C function):        DateTime Objects<2>.
                                                             (line   31)
* PyDate_FromDate (C function):          DateTime Objects<2>.
                                                             (line   82)
* PyDate_FromTimestamp (C function):     DateTime Objects<2>.
                                                             (line  231)
* PyDelta_Check (C function):            DateTime Objects<2>.
                                                             (line   58)
* PyDelta_CheckExact (C function):       DateTime Objects<2>.
                                                             (line   64)
* PyDelta_FromDSU (C function):          DateTime Objects<2>.
                                                             (line  117)
* PyDescr_IsData (C function):           Descriptor Objects. (line   37)
* PyDescr_NewClassMethod (C function):   Descriptor Objects. (line   32)
* PyDescr_NewGetSet (C function):        Descriptor Objects. (line   13)
* PyDescr_NewMember (C function):        Descriptor Objects. (line   18)
* PyDescr_NewMethod (C function):        Descriptor Objects. (line   23)
* PyDescr_NewWrapper (C function):       Descriptor Objects. (line   28)
* PyDictObject (C type):                 Dictionary Objects. (line    6)
* PyDictProxy_New (C function):          Dictionary Objects. (line   31)
* PyDict_Check (C function):             Dictionary Objects. (line   17)
* PyDict_CheckExact (C function):        Dictionary Objects. (line   22)
* PyDict_Clear (C function):             Dictionary Objects. (line   37)
* PyDict_Contains (C function):          Dictionary Objects. (line   41)
* PyDict_Copy (C function):              Dictionary Objects. (line   47)
* PyDict_DelItem (C function):           Dictionary Objects. (line   69)
* PyDict_DelItemString (C function):     Dictionary Objects. (line   76)
* PyDict_GetItem (C function):           Dictionary Objects. (line   82)
* PyDict_GetItemString (C function):     Dictionary Objects. (line   99)
* PyDict_GetItemWithError (C function):  Dictionary Objects. (line   91)
* PyDict_Items (C function):             Dictionary Objects. (line  122)
* PyDict_Keys (C function):              Dictionary Objects. (line  126)
* PyDict_Merge (C function):             Dictionary Objects. (line  188)
* PyDict_MergeFromSeq2 (C function):     Dictionary Objects. (line  207)
* PyDict_New (C function):               Dictionary Objects. (line   27)
* PyDict_Next (C function):              Dictionary Objects. (line  139)
* PyDict_SetDefault (C function):        Dictionary Objects. (line  110)
* PyDict_SetItem (C function):           Dictionary Objects. (line   51)
* PyDict_SetItemString (C function):     Dictionary Objects. (line   60)
* PyDict_Size (C function):              Dictionary Objects. (line  134)
* PyDict_Type (C variable):              Dictionary Objects. (line   11)
* PyDict_Update (C function):            Dictionary Objects. (line  199)
* PyDict_Values (C function):            Dictionary Objects. (line  130)
* PyDLL (class in ctypes):               Loading shared libraries.
                                                             (line   61)
* pydoc (module):                        pydoc — Documentation generator and online help system.
                                                             (line    6)
* PyDoc_STR (C macro):                   Useful macros.      (line  114)
* PyDoc_STRVAR (C macro):                Useful macros.      (line   96)
* PyErr_BadArgument (C function):        Raising exceptions. (line   46)
* PyErr_BadInternalCall (C function):    Raising exceptions. (line  197)
* PyErr_CheckSignals (C function):       Signal Handling<2>. (line    6)
* PyErr_Clear (C function):              Printing and clearing.
                                                             (line    6)
* PyErr_Clear():                         Exceptions<19>.     (line   25)
* PyErr_Clear() <1>:                     Exceptions<19>.     (line  123)
* PyErr_ExceptionMatches (C function):   Querying the error indicator.
                                                             (line   22)
* PyErr_ExceptionMatches():              Exceptions<19>.     (line  123)
* PyErr_Fetch (C function):              Querying the error indicator.
                                                             (line   38)
* PyErr_Fetch():                         Finalization and De-allocation.
                                                             (line   33)
* PyErr_Format (C function):             Raising exceptions. (line   25)
* PyErr_FormatV (C function):            Raising exceptions. (line   33)
* PyErr_GetExcInfo (C function):         Querying the error indicator.
                                                             (line   99)
* PyErr_GivenExceptionMatches (C function): Querying the error indicator.
                                                             (line   28)
* PyErr_NewException (C function):       Exception Classes.  (line    6)
* PyErr_NewExceptionWithDoc (C function): Exception Classes. (line   24)
* PyErr_NoMemory (C function):           Raising exceptions. (line   52)
* PyErr_NormalizeException (C function): Querying the error indicator.
                                                             (line   80)
* PyErr_Occurred (C function):           Querying the error indicator.
                                                             (line    6)
* PyErr_Occurred():                      Exceptions<19>.     (line   12)
* PyErr_Print (C function):              Printing and clearing.
                                                             (line   26)
* PyErr_PrintEx (C function):            Printing and clearing.
                                                             (line   11)
* PyErr_ResourceWarning (C function):    Issuing warnings.   (line   80)
* PyErr_Restore (C function):            Querying the error indicator.
                                                             (line   61)
* PyErr_Restore():                       Finalization and De-allocation.
                                                             (line   33)
* PyErr_SetExcFromWindowsErr (C function): Raising exceptions.
                                                             (line  114)
* PyErr_SetExcFromWindowsErrWithFilename (C function): Raising exceptions.
                                                             (line  152)
* PyErr_SetExcFromWindowsErrWithFilenameObject (C function): Raising exceptions.
                                                             (line  132)
* PyErr_SetExcFromWindowsErrWithFilenameObjects (C function): Raising exceptions.
                                                             (line  141)
* PyErr_SetExcInfo (C function):         Querying the error indicator.
                                                             (line  116)
* PyErr_SetFromErrno (C function):       Raising exceptions. (line   58)
* PyErr_SetFromErrnoWithFilename (C function): Raising exceptions.
                                                             (line   93)
* PyErr_SetFromErrnoWithFilenameObject (C function): Raising exceptions.
                                                             (line   73)
* PyErr_SetFromErrnoWithFilenameObjects (C function): Raising exceptions.
                                                             (line   82)
* PyErr_SetFromWindowsErr (C function):  Raising exceptions. (line  100)
* PyErr_SetFromWindowsErrWithFilename (C function): Raising exceptions.
                                                             (line  123)
* PyErr_SetImportError (C function):     Raising exceptions. (line  161)
* PyErr_SetImportErrorSubclass (C function): Issuing warnings.
                                                             (line   41)
* PyErr_SetInterrupt (C function):       Signal Handling<2>. (line   18)
* PyErr_SetNone (C function):            Raising exceptions. (line   42)
* PyErr_SetObject (C function):          Raising exceptions. (line   19)
* PyErr_SetString (C function):          Raising exceptions. (line   10)
* PyErr_SetString():                     Exceptions<19>.     (line   25)
* PyErr_SyntaxLocation (C function):     Raising exceptions. (line  191)
* PyErr_SyntaxLocationEx (C function):   Raising exceptions. (line  182)
* PyErr_SyntaxLocationObject (C function): Raising exceptions.
                                                             (line  171)
* PyErr_WarnEx (C function):             Issuing warnings.   (line   19)
* PyErr_WarnExplicit (C function):       Issuing warnings.   (line   63)
* PyErr_WarnExplicitObject (C function): Issuing warnings.   (line   50)
* PyErr_WarnFormat (C function):         Issuing warnings.   (line   71)
* PyErr_WriteUnraisable (C function):    Printing and clearing.
                                                             (line   30)
* PyEval_AcquireLock (C function):       Low-level API.      (line  226)
* PyEval_AcquireThread (C function):     Low-level API.      (line  193)
* PyEval_AcquireThread():                High-level API.     (line   29)
* PyEval_EvalCode (C function):          The Very High Level Layer.
                                                             (line  338)
* PyEval_EvalCodeEx (C function):        The Very High Level Layer.
                                                             (line  344)
* PyEval_EvalFrame (C function):         The Very High Level Layer.
                                                             (line  363)
* PyEval_EvalFrameEx (C function):       The Very High Level Layer.
                                                             (line  368)
* PyEval_GetBuiltins (C function):       Reflection.         (line    6)
* PyEval_GetFrame (C function):          Reflection.         (line   21)
* PyEval_GetFuncDesc (C function):       Reflection.         (line   59)
* PyEval_GetFuncName (C function):       Reflection.         (line   54)
* PyEval_GetGlobals (C function):        Reflection.         (line   16)
* PyEval_GetLocals (C function):         Reflection.         (line   11)
* PyEval_InitThreads (C function):       High-level API.     (line   27)
* PyEval_InitThreads():                  Initializing and finalizing the interpreter.
                                                             (line    8)
* PyEval_MergeCompilerFlags (C function): The Very High Level Layer.
                                                             (line  382)
* PyEval_ReleaseLock (C function):       Low-level API.      (line  248)
* PyEval_ReleaseThread (C function):     Low-level API.      (line  215)
* PyEval_ReleaseThread():                High-level API.     (line   29)
* PyEval_RestoreThread (C function):     High-level API.     (line   64)
* PyEval_RestoreThread():                Releasing the GIL from extension code.
                                                             (line   33)
* PyEval_RestoreThread() <1>:            High-level API.     (line   29)
* PyEval_SaveThread (C function):        High-level API.     (line   57)
* PyEval_SaveThread():                   Releasing the GIL from extension code.
                                                             (line   33)
* PyEval_SaveThread() <1>:               High-level API.     (line   29)
* PyEval_SetProfile (C function):        Profiling and Tracing.
                                                             (line  116)
* PyEval_SetTrace (C function):          Profiling and Tracing.
                                                             (line  129)
* PyEval_ThreadsInitialized (C function): High-level API.    (line   45)
* PyException_GetCause (C function):     Exception Objects.  (line   32)
* PyException_GetContext (C function):   Exception Objects.  (line   18)
* PyException_GetTraceback (C function): Exception Objects.  (line    6)
* PyException_SetCause (C function):     Exception Objects.  (line   38)
* PyException_SetContext (C function):   Exception Objects.  (line   25)
* PyException_SetTraceback (C function): Exception Objects.  (line   12)
* PyExc_ArithmeticError:                 Standard Exceptions.
                                                             (line   11)
* PyExc_AssertionError:                  Standard Exceptions.
                                                             (line   11)
* PyExc_AttributeError:                  Standard Exceptions.
                                                             (line   11)
* PyExc_BaseException:                   Standard Exceptions.
                                                             (line   11)
* PyExc_BlockingIOError:                 Standard Exceptions.
                                                             (line   11)
* PyExc_BrokenPipeError:                 Standard Exceptions.
                                                             (line   11)
* PyExc_BufferError:                     Standard Exceptions.
                                                             (line   11)
* PyExc_BytesWarning:                    Standard Warning Categories.
                                                             (line   11)
* PyExc_ChildProcessError:               Standard Exceptions.
                                                             (line   11)
* PyExc_ConnectionAbortedError:          Standard Exceptions.
                                                             (line   11)
* PyExc_ConnectionError:                 Standard Exceptions.
                                                             (line   11)
* PyExc_ConnectionRefusedError:          Standard Exceptions.
                                                             (line   11)
* PyExc_ConnectionResetError:            Standard Exceptions.
                                                             (line   11)
* PyExc_DeprecationWarning:              Standard Warning Categories.
                                                             (line   11)
* PyExc_EnvironmentError:                Standard Exceptions.
                                                             (line  190)
* PyExc_EOFError:                        Standard Exceptions.
                                                             (line   11)
* PyExc_Exception:                       Standard Exceptions.
                                                             (line   11)
* PyExc_FileExistsError:                 Standard Exceptions.
                                                             (line   11)
* PyExc_FileNotFoundError:               Standard Exceptions.
                                                             (line   11)
* PyExc_FloatingPointError:              Standard Exceptions.
                                                             (line   11)
* PyExc_FutureWarning:                   Standard Warning Categories.
                                                             (line   11)
* PyExc_GeneratorExit:                   Standard Exceptions.
                                                             (line   11)
* PyExc_ImportError:                     Standard Exceptions.
                                                             (line   11)
* PyExc_ImportWarning:                   Standard Warning Categories.
                                                             (line   11)
* PyExc_IndentationError:                Standard Exceptions.
                                                             (line   11)
* PyExc_IndexError:                      Standard Exceptions.
                                                             (line   11)
* PyExc_InterruptedError:                Standard Exceptions.
                                                             (line   11)
* PyExc_IOError:                         Standard Exceptions.
                                                             (line  190)
* PyExc_IsADirectoryError:               Standard Exceptions.
                                                             (line   11)
* PyExc_KeyboardInterrupt:               Standard Exceptions.
                                                             (line   11)
* PyExc_KeyError:                        Standard Exceptions.
                                                             (line   11)
* PyExc_LookupError:                     Standard Exceptions.
                                                             (line   11)
* PyExc_MemoryError:                     Standard Exceptions.
                                                             (line   11)
* PyExc_ModuleNotFoundError:             Standard Exceptions.
                                                             (line   11)
* PyExc_NameError:                       Standard Exceptions.
                                                             (line   11)
* PyExc_NotADirectoryError:              Standard Exceptions.
                                                             (line   11)
* PyExc_NotImplementedError:             Standard Exceptions.
                                                             (line   11)
* PyExc_OSError:                         Standard Exceptions.
                                                             (line   11)
* PyExc_OverflowError:                   Standard Exceptions.
                                                             (line   11)
* PyExc_PendingDeprecationWarning:       Standard Warning Categories.
                                                             (line   11)
* PyExc_PermissionError:                 Standard Exceptions.
                                                             (line   11)
* PyExc_ProcessLookupError:              Standard Exceptions.
                                                             (line   11)
* PyExc_RecursionError:                  Standard Exceptions.
                                                             (line   11)
* PyExc_ReferenceError:                  Standard Exceptions.
                                                             (line   11)
* PyExc_ResourceWarning:                 Standard Warning Categories.
                                                             (line   11)
* PyExc_RuntimeError:                    Standard Exceptions.
                                                             (line   11)
* PyExc_RuntimeWarning:                  Standard Warning Categories.
                                                             (line   11)
* PyExc_StopAsyncIteration:              Standard Exceptions.
                                                             (line   11)
* PyExc_StopIteration:                   Standard Exceptions.
                                                             (line   11)
* PyExc_SyntaxError:                     Standard Exceptions.
                                                             (line   11)
* PyExc_SyntaxWarning:                   Standard Warning Categories.
                                                             (line   11)
* PyExc_SystemError:                     Standard Exceptions.
                                                             (line   11)
* PyExc_SystemExit:                      Standard Exceptions.
                                                             (line   11)
* PyExc_TabError:                        Standard Exceptions.
                                                             (line   11)
* PyExc_TimeoutError:                    Standard Exceptions.
                                                             (line   11)
* PyExc_TypeError:                       Standard Exceptions.
                                                             (line   11)
* PyExc_UnboundLocalError:               Standard Exceptions.
                                                             (line   11)
* PyExc_UnicodeDecodeError:              Standard Exceptions.
                                                             (line   11)
* PyExc_UnicodeEncodeError:              Standard Exceptions.
                                                             (line   11)
* PyExc_UnicodeError:                    Standard Exceptions.
                                                             (line   11)
* PyExc_UnicodeTranslateError:           Standard Exceptions.
                                                             (line   11)
* PyExc_UnicodeWarning:                  Standard Warning Categories.
                                                             (line   11)
* PyExc_UserWarning:                     Standard Warning Categories.
                                                             (line   11)
* PyExc_ValueError:                      Standard Exceptions.
                                                             (line   11)
* PyExc_Warning:                         Standard Warning Categories.
                                                             (line   11)
* PyExc_WindowsError:                    Standard Exceptions.
                                                             (line  190)
* PyExc_ZeroDivisionError:               Standard Exceptions.
                                                             (line   11)
* PyFile_FromFd (C function):            File Objects.       (line   15)
* PyFile_GetLine (C function):           File Objects.       (line   40)
* PyFile_SetOpenCodeHook (C function):   File Objects.       (line   54)
* PyFile_WriteObject (C function):       File Objects.       (line   84)
* PyFile_WriteString (C function):       File Objects.       (line   92)
* PyFloatObject (C type):                Floating Point Objects.
                                                             (line    6)
* PyFloat_AsDouble (C function):         Floating Point Objects.
                                                             (line   37)
* PyFloat_AS_DOUBLE (C function):        Floating Point Objects.
                                                             (line   49)
* PyFloat_Check (C function):            Floating Point Objects.
                                                             (line   17)
* PyFloat_CheckExact (C function):       Floating Point Objects.
                                                             (line   23)
* PyFloat_FromDouble (C function):       Floating Point Objects.
                                                             (line   33)
* PyFloat_FromString (C function):       Floating Point Objects.
                                                             (line   29)
* PyFloat_GetInfo (C function):          Floating Point Objects.
                                                             (line   54)
* PyFloat_GetMax (C function):           Floating Point Objects.
                                                             (line   60)
* PyFloat_GetMin (C function):           Floating Point Objects.
                                                             (line   65)
* PyFloat_Type (C variable):             Floating Point Objects.
                                                             (line   11)
* PyFrameObject (C type):                The Very High Level Layer.
                                                             (line  358)
* PyFrame_GetBack (C function):          Reflection.         (line   27)
* PyFrame_GetCode (C function):          Reflection.         (line   37)
* PyFrame_GetLineNumber (C function):    Reflection.         (line   48)
* PyFrozenSet_Check (C function):        Set Objects.        (line   50)
* PyFrozenSet_CheckExact (C function):   Set Objects.        (line   67)
* PyFrozenSet_New (C function):          Set Objects.        (line   80)
* PyFrozenSet_Type (C variable):         Set Objects.        (line   36)
* PyFunctionObject (C type):             Function Objects<3>.
                                                             (line    8)
* PyFunction_Check (C function):         Function Objects<3>.
                                                             (line   18)
* PyFunction_GetAnnotations (C function): Function Objects<3>.
                                                             (line   86)
* PyFunction_GetClosure (C function):    Function Objects<3>.
                                                             (line   73)
* PyFunction_GetCode (C function):       Function Objects<3>.
                                                             (line   46)
* PyFunction_GetDefaults (C function):   Function Objects<3>.
                                                             (line   60)
* PyFunction_GetGlobals (C function):    Function Objects<3>.
                                                             (line   50)
* PyFunction_GetModule (C function):     Function Objects<3>.
                                                             (line   54)
* PyFunction_New (C function):           Function Objects<3>.
                                                             (line   24)
* PyFunction_NewWithQualName (C function): Function Objects<3>.
                                                             (line   35)
* PyFunction_SetAnnotations (C function): Function Objects<3>.
                                                             (line   90)
* PyFunction_SetClosure (C function):    Function Objects<3>.
                                                             (line   78)
* PyFunction_SetDefaults (C function):   Function Objects<3>.
                                                             (line   65)
* PyFunction_Type (C variable):          Function Objects<3>.
                                                             (line   12)
* PYFUNCTYPE() (in module ctypes):       Function prototypes.
                                                             (line   34)
* PyGenObject (C type):                  Generator Objects.  (line   11)
* PyGen_Check (C function):              Generator Objects.  (line   19)
* PyGen_CheckExact (C function):         Generator Objects.  (line   24)
* PyGen_New (C function):                Generator Objects.  (line   29)
* PyGen_NewWithQualName (C function):    Generator Objects.  (line   34)
* PyGen_Type (C variable):               Generator Objects.  (line   15)
* PyGetSetDef (C type):                  Accessing attributes of extension types.
                                                             (line  135)
* PyGILState_Check (C function):         High-level API.     (line  144)
* PyGILState_Ensure (C function):        High-level API.     (line   94)
* PyGILState_GetThisThreadState (C function): High-level API.
                                                             (line  136)
* PyGILState_Release (C function):       High-level API.     (line  125)
* PyImport_AddModule (C function):       Importing Modules<2>.
                                                             (line  111)
* PyImport_AddModuleObject (C function): Importing Modules<2>.
                                                             (line   95)
* PyImport_AppendInittab (C function):   Importing Modules<2>.
                                                             (line  269)
* PyImport_ExecCodeModule (C function):  Importing Modules<2>.
                                                             (line  116)
* PyImport_ExecCodeModuleEx (C function): Importing Modules<2>.
                                                             (line  152)
* PyImport_ExecCodeModuleObject (C function): Importing Modules<2>.
                                                             (line  162)
* PyImport_ExecCodeModuleWithPathnames (C function): Importing Modules<2>.
                                                             (line  172)
* PyImport_ExtendInittab (C function):   Importing Modules<2>.
                                                             (line  295)
* PyImport_FrozenModules (C variable):   Importing Modules<2>.
                                                             (line  261)
* PyImport_GetImporter (C function):     Importing Modules<2>.
                                                             (line  219)
* PyImport_GetMagicNumber (C function):  Importing Modules<2>.
                                                             (line  188)
* PyImport_GetMagicTag (C function):     Importing Modules<2>.
                                                             (line  197)
* PyImport_GetModule (C function):       Importing Modules<2>.
                                                             (line  211)
* PyImport_GetModuleDict (C function):   Importing Modules<2>.
                                                             (line  206)
* PyImport_Import (C function):          Importing Modules<2>.
                                                             (line   80)
* PyImport_ImportFrozenModule (C function): Importing Modules<2>.
                                                             (line  243)
* PyImport_ImportFrozenModuleObject (C function): Importing Modules<2>.
                                                             (line  230)
* PyImport_ImportModule (C function):    Importing Modules<2>.
                                                             (line    6)
* PyImport_ImportModuleEx (C function):  Importing Modules<2>.
                                                             (line   35)
* PyImport_ImportModuleLevel (C function): Importing Modules<2>.
                                                             (line   69)
* PyImport_ImportModuleLevelObject (C function): Importing Modules<2>.
                                                             (line   52)
* PyImport_ImportModuleNoBlock (C function): Importing Modules<2>.
                                                             (line   25)
* PyImport_ReloadModule (C function):    Importing Modules<2>.
                                                             (line   90)
* PyIndex_Check (C function):            Number Protocol.    (line  272)
* PyInit_modulename (C function):        Building C and C++ Extensions.
                                                             (line   16)
* PyInstanceMethod_Check (C function):   Instance Method Objects.
                                                             (line   15)
* PyInstanceMethod_Function (C function): Instance Method Objects.
                                                             (line   26)
* PyInstanceMethod_GET_FUNCTION (C function): Instance Method Objects.
                                                             (line   30)
* PyInstanceMethod_New (C function):     Instance Method Objects.
                                                             (line   21)
* PyInstanceMethod_Type (C variable):    Instance Method Objects.
                                                             (line   10)
* PyInterpreterState (C type):           High-level API.     (line    9)
* PyInterpreterState_Clear (C function): Low-level API.      (line   21)
* PyInterpreterState_Delete (C function): Low-level API.     (line   30)
* PyInterpreterState_Get (C function):   Low-level API.      (line   99)
* PyInterpreterState_GetDict (C function): Low-level API.    (line  120)
* PyInterpreterState_GetID (C function): Low-level API.      (line  110)
* PyInterpreterState_Head (C function):  Advanced Debugger Support.
                                                             (line    9)
* PyInterpreterState_Main (C function):  Advanced Debugger Support.
                                                             (line   14)
* PyInterpreterState_New (C function):   Low-level API.      (line   12)
* PyInterpreterState_Next (C function):  Advanced Debugger Support.
                                                             (line   18)
* PyInterpreterState_ThreadHead (C function): Advanced Debugger Support.
                                                             (line   25)
* PyIter_Check (C function):             Iterator Protocol.  (line    8)
* PyIter_Next (C function):              Iterator Protocol.  (line   13)
* PyListObject (C type):                 List Objects.       (line    6)
* PyList_Append (C function):            List Objects.       (line   91)
* PyList_AsTuple (C function):           List Objects.       (line  125)
* PyList_Check (C function):             List Objects.       (line   17)
* PyList_CheckExact (C function):        List Objects.       (line   22)
* PyList_GetItem (C function):           List Objects.       (line   46)
* PyList_GetItem():                      Reference Count Details.
                                                             (line  117)
* PyList_GetSlice (C function):          List Objects.       (line   97)
* PyList_GET_ITEM (C function):          List Objects.       (line   54)
* PyList_GET_SIZE (C function):          List Objects.       (line   42)
* PyList_Insert (C function):            List Objects.       (line   83)
* PyList_New (C function):               List Objects.       (line   27)
* PyList_Reverse (C function):           List Objects.       (line  120)
* PyList_SetItem (C function):           List Objects.       (line   58)
* PyList_SetItem():                      Reference Count Details.
                                                             (line   26)
* PyList_SetSlice (C function):          List Objects.       (line  105)
* PyList_SET_ITEM (C function):          List Objects.       (line   70)
* PyList_Size (C function):              List Objects.       (line   37)
* PyList_Sort (C function):              List Objects.       (line  115)
* PyList_Type (C variable):              List Objects.       (line   11)
* PyLongObject (C type):                 Integer Objects.    (line   13)
* PyLong_AsDouble (C function):          Integer Objects.    (line  273)
* PyLong_AsLong (C function):            Integer Objects.    (line  106)
* PyLong_AsLongAndOverflow (C function): Integer Objects.    (line  124)
* PyLong_AsLongLong (C function):        Integer Objects.    (line  145)
* PyLong_AsLongLongAndOverflow (C function): Integer Objects.
                                                             (line  163)
* PyLong_AsSize_t (C function):          Integer Objects.    (line  209)
* PyLong_AsSsize_t (C function):         Integer Objects.    (line  187)
* PyLong_AsUnsignedLong (C function):    Integer Objects.    (line  198)
* PyLong_AsUnsignedLongLong (C function): Integer Objects.   (line  220)
* PyLong_AsUnsignedLongLongMask (C function): Integer Objects.
                                                             (line  253)
* PyLong_AsUnsignedLongMask (C function): Integer Objects.   (line  235)
* PyLong_AsVoidPtr (C function):         Integer Objects.    (line  284)
* PyLong_Check (C function):             Integer Objects.    (line   24)
* PyLong_CheckExact (C function):        Integer Objects.    (line   30)
* PyLong_FromDouble (C function):        Integer Objects.    (line   67)
* PyLong_FromLong (C function):          Integer Objects.    (line   36)
* PyLong_FromLongLong (C function):      Integer Objects.    (line   57)
* PyLong_FromSize_t (C function):        Integer Objects.    (line   53)
* PyLong_FromSsize_t (C function):       Integer Objects.    (line   49)
* PyLong_FromString (C function):        Integer Objects.    (line   71)
* PyLong_FromUnicode (C function):       Integer Objects.    (line   85)
* PyLong_FromUnicodeObject (C function): Integer Objects.    (line   94)
* PyLong_FromUnsignedLong (C function):  Integer Objects.    (line   45)
* PyLong_FromUnsignedLongLong (C function): Integer Objects. (line   61)
* PyLong_FromVoidPtr (C function):       Integer Objects.    (line  101)
* PyLong_Type (C variable):              Integer Objects.    (line   18)
* PyMappingMethods (C type):             Mapping Object Structures.
                                                             (line    6)
* PyMappingMethods.mp_ass_subscript (C member): Mapping Object Structures.
                                                             (line   25)
* PyMappingMethods.mp_length (C member): Mapping Object Structures.
                                                             (line   11)
* PyMappingMethods.mp_subscript (C member): Mapping Object Structures.
                                                             (line   17)
* PyMapping_Check (C function):          Mapping Protocol.   (line    9)
* PyMapping_DelItem (C function):        Mapping Protocol.   (line   39)
* PyMapping_DelItemString (C function):  Mapping Protocol.   (line   45)
* PyMapping_GetItemString (C function):  Mapping Protocol.   (line   23)
* PyMapping_HasKey (C function):         Mapping Protocol.   (line   52)
* PyMapping_HasKeyString (C function):   Mapping Protocol.   (line   62)
* PyMapping_Items (C function):          Mapping Protocol.   (line   88)
* PyMapping_Keys (C function):           Mapping Protocol.   (line   74)
* PyMapping_Length (C function):         Mapping Protocol.   (line   17)
* PyMapping_SetItemString (C function):  Mapping Protocol.   (line   31)
* PyMapping_Size (C function):           Mapping Protocol.   (line   17)
* PyMapping_Values (C function):         Mapping Protocol.   (line   81)
* PyMarshal_ReadLastObjectFromFile (C function): Data marshalling support.
                                                             (line   68)
* PyMarshal_ReadLongFromFile (C function): Data marshalling support.
                                                             (line   42)
* PyMarshal_ReadObjectFromFile (C function): Data marshalling support.
                                                             (line   60)
* PyMarshal_ReadObjectFromString (C function): Data marshalling support.
                                                             (line   83)
* PyMarshal_ReadShortFromFile (C function): Data marshalling support.
                                                             (line   51)
* PyMarshal_WriteLongToFile (C function): Data marshalling support.
                                                             (line   20)
* PyMarshal_WriteObjectToFile (C function): Data marshalling support.
                                                             (line   28)
* PyMarshal_WriteObjectToString (C function): Data marshalling support.
                                                             (line   34)
* PyMemAllocatorDomain (C type):         Customize Memory Allocators.
                                                             (line   36)
* PyMemAllocatorEx (C type):             Customize Memory Allocators.
                                                             (line    8)
* PyMemberDef (C type):                  Accessing attributes of extension types.
                                                             (line    6)
* PyMember_GetOne (C function):          Accessing attributes of extension types.
                                                             (line  120)
* PyMember_SetOne (C function):          Accessing attributes of extension types.
                                                             (line  128)
* PyMemoryView_Check (C function):       MemoryView objects. (line   41)
* PyMemoryView_FromBuffer (C function):  MemoryView objects. (line   26)
* PyMemoryView_FromMemory (C function):  MemoryView objects. (line   17)
* PyMemoryView_FromObject (C function):  MemoryView objects. (line   10)
* PyMemoryView_GetContiguous (C function): MemoryView objects.
                                                             (line   31)
* PyMemoryView_GET_BASE (C function):    MemoryView objects. (line   54)
* PyMemoryView_GET_BUFFER (C function):  MemoryView objects. (line   47)
* PyMem_Calloc (C function):             Memory Interface.   (line   28)
* PyMem_Del (C function):                Memory Interface.   (line   86)
* PYMEM_DOMAIN_MEM (C macro):            Customize Memory Allocators.
                                                             (line   52)
* PYMEM_DOMAIN_OBJ (C macro):            Customize Memory Allocators.
                                                             (line   64)
* PYMEM_DOMAIN_RAW (C macro):            Customize Memory Allocators.
                                                             (line   40)
* PyMem_Free (C function):               Memory Interface.   (line   57)
* PyMem_GetAllocator (C function):       Customize Memory Allocators.
                                                             (line   76)
* PyMem_Malloc (C function):             Memory Interface.   (line   19)
* PyMem_New (C function):                Memory Interface.   (line   70)
* PyMem_RawCalloc (C function):          Raw Memory Interface.
                                                             (line   24)
* PyMem_RawFree (C function):            Raw Memory Interface.
                                                             (line   53)
* PyMem_RawMalloc (C function):          Raw Memory Interface.
                                                             (line   15)
* PyMem_RawRealloc (C function):         Raw Memory Interface.
                                                             (line   36)
* PyMem_Realloc (C function):            Memory Interface.   (line   40)
* PyMem_Resize (C function):             Memory Interface.   (line   76)
* PyMem_SetAllocator (C function):       Customize Memory Allocators.
                                                             (line   82)
* PyMem_SetupDebugHooks (C function):    Customize Memory Allocators.
                                                             (line   99)
* PyMethodDef (C type):                  Implementing functions and methods.
                                                             (line   64)
* PyMethod_Check (C function):           Method Objects<2>.  (line   16)
* PyMethod_Function (C function):        Method Objects<2>.  (line   28)
* PyMethod_GET_FUNCTION (C function):    Method Objects<2>.  (line   32)
* PyMethod_GET_SELF (C function):        Method Objects<2>.  (line   40)
* PyMethod_New (C function):             Method Objects<2>.  (line   22)
* PyMethod_Self (C function):            Method Objects<2>.  (line   36)
* PyMethod_Type (C variable):            Method Objects<2>.  (line   10)
* PyModuleDef (C type):                  Initializing C modules.
                                                             (line   17)
* PyModuleDef.m_base (C member):         Initializing C modules.
                                                             (line   23)
* PyModuleDef.m_clear (C member):        Initializing C modules.
                                                             (line   89)
* PyModuleDef.m_doc (C member):          Initializing C modules.
                                                             (line   31)
* PyModuleDef.m_free (C member):         Initializing C modules.
                                                             (line  110)
* PyModuleDef.m_methods (C member):      Initializing C modules.
                                                             (line   57)
* PyModuleDef.m_name (C member):         Initializing C modules.
                                                             (line   27)
* PyModuleDef.m_reload (C member):       Initializing C modules.
                                                             (line   72)
* PyModuleDef.m_size (C member):         Initializing C modules.
                                                             (line   36)
* PyModuleDef.m_slots (C member):        Initializing C modules.
                                                             (line   63)
* PyModuleDef.m_traverse (C member):     Initializing C modules.
                                                             (line   74)
* PyModuleDef_Init (C function):         Multi-phase initialization.
                                                             (line   33)
* PyModuleDef_Slot (C type):             Multi-phase initialization.
                                                             (line   45)
* PyModuleDef_Slot.slot (C member):      Multi-phase initialization.
                                                             (line   47)
* PyModuleDef_Slot.value (C member):     Multi-phase initialization.
                                                             (line   51)
* PyModule_AddFunctions (C function):    Low-level module creation functions.
                                                             (line   53)
* PyModule_AddIntConstant (C function):  Support functions.  (line   34)
* PyModule_AddIntMacro (C function):     Support functions.  (line   51)
* PyModule_AddObject (C function):       Support functions.  (line   11)
* PyModule_AddStringConstant (C function): Support functions.
                                                             (line   42)
* PyModule_AddStringMacro (C function):  Support functions.  (line   58)
* PyModule_AddType (C function):         Support functions.  (line   62)
* PyModule_Check (C function):           Module Objects.     (line   12)
* PyModule_CheckExact (C function):      Module Objects.     (line   17)
* PyModule_Create (C function):          Single-phase initialization.
                                                             (line   10)
* PyModule_Create2 (C function):         Single-phase initialization.
                                                             (line   16)
* PyModule_ExecDef (C function):         Low-level module creation functions.
                                                             (line   36)
* PyModule_FromDefAndSpec (C function):  Low-level module creation functions.
                                                             (line   11)
* PyModule_FromDefAndSpec2 (C function): Low-level module creation functions.
                                                             (line   21)
* PyModule_GetDef (C function):          Module Objects.     (line   74)
* PyModule_GetDict (C function):         Module Objects.     (line   41)
* PyModule_GetFilename (C function):     Module Objects.     (line   91)
* PyModule_GetFilenameObject (C function): Module Objects.   (line   80)
* PyModule_GetName (C function):         Module Objects.     (line   63)
* PyModule_GetNameObject (C function):   Module Objects.     (line   54)
* PyModule_GetState (C function):        Module Objects.     (line   68)
* PyModule_New (C function):             Module Objects.     (line   36)
* PyModule_NewObject (C function):       Module Objects.     (line   22)
* PyModule_SetDocString (C function):    Low-level module creation functions.
                                                             (line   44)
* PyModule_Type (C variable):            Module Objects.     (line    6)
* PyNumberMethods (C type):              Number Object Structures.
                                                             (line    6)
* PyNumberMethods.nb_absolute (C member): Number Object Structures.
                                                             (line   85)
* PyNumberMethods.nb_add (C member):     Number Object Structures.
                                                             (line   69)
* PyNumberMethods.nb_and (C member):     Number Object Structures.
                                                             (line   95)
* PyNumberMethods.nb_bool (C member):    Number Object Structures.
                                                             (line   87)
* PyNumberMethods.nb_divmod (C member):  Number Object Structures.
                                                             (line   77)
* PyNumberMethods.nb_float (C member):   Number Object Structures.
                                                             (line  105)
* PyNumberMethods.nb_floor_divide (C member): Number Object Structures.
                                                             (line  127)
* PyNumberMethods.nb_index (C member):   Number Object Structures.
                                                             (line  135)
* PyNumberMethods.nb_inplace_add (C member): Number Object Structures.
                                                             (line  107)
* PyNumberMethods.nb_inplace_and (C member): Number Object Structures.
                                                             (line  121)
* PyNumberMethods.nb_inplace_floor_divide (C member): Number Object Structures.
                                                             (line  131)
* PyNumberMethods.nb_inplace_lshift (C member): Number Object Structures.
                                                             (line  117)
* PyNumberMethods.nb_inplace_matrix_multiply (C member): Number Object Structures.
                                                             (line  139)
* PyNumberMethods.nb_inplace_multiply (C member): Number Object Structures.
                                                             (line  111)
* PyNumberMethods.nb_inplace_or (C member): Number Object Structures.
                                                             (line  125)
* PyNumberMethods.nb_inplace_power (C member): Number Object Structures.
                                                             (line  115)
* PyNumberMethods.nb_inplace_remainder (C member): Number Object Structures.
                                                             (line  113)
* PyNumberMethods.nb_inplace_rshift (C member): Number Object Structures.
                                                             (line  119)
* PyNumberMethods.nb_inplace_subtract (C member): Number Object Structures.
                                                             (line  109)
* PyNumberMethods.nb_inplace_true_divide (C member): Number Object Structures.
                                                             (line  133)
* PyNumberMethods.nb_inplace_xor (C member): Number Object Structures.
                                                             (line  123)
* PyNumberMethods.nb_int (C member):     Number Object Structures.
                                                             (line  101)
* PyNumberMethods.nb_invert (C member):  Number Object Structures.
                                                             (line   89)
* PyNumberMethods.nb_lshift (C member):  Number Object Structures.
                                                             (line   91)
* PyNumberMethods.nb_matrix_multiply (C member): Number Object Structures.
                                                             (line  137)
* PyNumberMethods.nb_multiply (C member): Number Object Structures.
                                                             (line   73)
* PyNumberMethods.nb_negative (C member): Number Object Structures.
                                                             (line   81)
* PyNumberMethods.nb_or (C member):      Number Object Structures.
                                                             (line   99)
* PyNumberMethods.nb_positive (C member): Number Object Structures.
                                                             (line   83)
* PyNumberMethods.nb_power (C member):   Number Object Structures.
                                                             (line   79)
* PyNumberMethods.nb_remainder (C member): Number Object Structures.
                                                             (line   75)
* PyNumberMethods.nb_reserved (C member): Number Object Structures.
                                                             (line  103)
* PyNumberMethods.nb_rshift (C member):  Number Object Structures.
                                                             (line   93)
* PyNumberMethods.nb_subtract (C member): Number Object Structures.
                                                             (line   71)
* PyNumberMethods.nb_true_divide (C member): Number Object Structures.
                                                             (line  129)
* PyNumberMethods.nb_xor (C member):     Number Object Structures.
                                                             (line   97)
* PyNumber_Absolute (C function):        Number Protocol.    (line   85)
* PyNumber_Add (C function):             Number Protocol.    (line   13)
* PyNumber_And (C function):             Number Protocol.    (line  106)
* PyNumber_AsSsize_t (C function):       Number Protocol.    (line  257)
* PyNumber_Check (C function):           Number Protocol.    (line    6)
* PyNumber_Divmod (C function):          Number Protocol.    (line   58)
* PyNumber_Float (C function):           Number Protocol.    (line  237)
* PyNumber_FloorDivide (C function):     Number Protocol.    (line   37)
* PyNumber_Index (C function):           Number Protocol.    (line  244)
* PyNumber_InPlaceAdd (C function):      Number Protocol.    (line  121)
* PyNumber_InPlaceAnd (C function):      Number Protocol.    (line  209)
* PyNumber_InPlaceFloorDivide (C function): Number Protocol. (line  154)
* PyNumber_InPlaceLshift (C function):   Number Protocol.    (line  193)
* PyNumber_InPlaceMatrixMultiply (C function): Number Protocol.
                                                             (line  144)
* PyNumber_InPlaceMultiply (C function): Number Protocol.    (line  136)
* PyNumber_InPlaceOr (C function):       Number Protocol.    (line  223)
* PyNumber_InPlacePower (C function):    Number Protocol.    (line  181)
* PyNumber_InPlaceRemainder (C function): Number Protocol.   (line  173)
* PyNumber_InPlaceRshift (C function):   Number Protocol.    (line  201)
* PyNumber_InPlaceSubtract (C function): Number Protocol.    (line  128)
* PyNumber_InPlaceTrueDivide (C function): Number Protocol.  (line  162)
* PyNumber_InPlaceXor (C function):      Number Protocol.    (line  216)
* PyNumber_Invert (C function):          Number Protocol.    (line   91)
* PyNumber_Long (C function):            Number Protocol.    (line  230)
* PyNumber_Lshift (C function):          Number Protocol.    (line   96)
* PyNumber_MatrixMultiply (C function):  Number Protocol.    (line   28)
* PyNumber_Multiply (C function):        Number Protocol.    (line   23)
* PyNumber_Negative (C function):        Number Protocol.    (line   76)
* PyNumber_Or (C function):              Number Protocol.    (line  116)
* PyNumber_Positive (C function):        Number Protocol.    (line   81)
* PyNumber_Power (C function):           Number Protocol.    (line   65)
* PyNumber_Remainder (C function):       Number Protocol.    (line   52)
* PyNumber_Rshift (C function):          Number Protocol.    (line  101)
* PyNumber_Subtract (C function):        Number Protocol.    (line   18)
* PyNumber_ToBase (C function):          Number Protocol.    (line  249)
* PyNumber_TrueDivide (C function):      Number Protocol.    (line   43)
* PyNumber_Xor (C function):             Number Protocol.    (line  111)
* PyObject (C type):                     Base object types and macros.
                                                             (line   13)
* PyObject.ob_refcnt (C member):         PyObject Slots.     (line   30)
* PyObject.ob_type (C member):           PyObject Slots.     (line   43)
* PyObject._ob_next (C member):          PyObject Slots.     (line   13)
* PyObject._ob_prev (C member):          PyObject Slots.     (line   13)
* PyObjectArenaAllocator (C type):       Customize pymalloc Arena Allocator.
                                                             (line    8)
* PyObject_AsCharBuffer (C function):    Old Buffer Protocol.
                                                             (line   21)
* PyObject_ASCII (C function):           Object Protocol.    (line  176)
* PyObject_AsFileDescriptor (C function): File Objects.      (line   32)
* PyObject_AsReadBuffer (C function):    Old Buffer Protocol.
                                                             (line   31)
* PyObject_AsWriteBuffer (C function):   Old Buffer Protocol.
                                                             (line   50)
* PyObject_Bytes (C function):           Object Protocol.    (line  197)
* PyObject_Call (C function):            Object Calling API. (line   57)
* PyObject_CallFunction (C function):    Object Calling API. (line  109)
* PyObject_CallFunctionObjArgs (C function): Object Calling API.
                                                             (line  151)
* PyObject_CallMethod (C function):      Object Calling API. (line  128)
* PyObject_CallMethodNoArgs (C function): Object Calling API.
                                                             (line  176)
* PyObject_CallMethodObjArgs (C function): Object Calling API.
                                                             (line  164)
* PyObject_CallMethodOneArg (C function): Object Calling API.
                                                             (line  191)
* PyObject_CallNoArgs (C function):      Object Calling API. (line   72)
* PyObject_CallObject (C function):      Object Calling API. (line   97)
* PyObject_CallObject():                 Calling Python Functions from C.
                                                             (line   64)
* PyObject_Calloc (C function):          Object allocators.  (line   25)
* PyObject_CallOneArg (C function):      Object Calling API. (line   83)
* PyObject_CheckBuffer (C function):     Buffer-related functions.
                                                             (line    6)
* PyObject_CheckReadBuffer (C function): Old Buffer Protocol.
                                                             (line   40)
* PyObject_Del (C function):             Allocating Objects on the Heap.
                                                             (line   51)
* PyObject_DelAttr (C function):         Object Protocol.    (line  110)
* PyObject_DelAttrString (C function):   Object Protocol.    (line  116)
* PyObject_DelItem (C function):         Object Protocol.    (line  327)
* PyObject_Dir (C function):             Object Protocol.    (line  333)
* PyObject_Free (C function):            Object allocators.  (line   54)
* PyObject_GC_Del (C function):          Supporting Cyclic Garbage Collection.
                                                             (line  114)
* PyObject_GC_IsFinalized (C function):  Supporting Cyclic Garbage Collection.
                                                             (line  103)
* PyObject_GC_IsTracked (C function):    Supporting Cyclic Garbage Collection.
                                                             (line   92)
* PyObject_GC_New (C function):          Supporting Cyclic Garbage Collection.
                                                             (line   56)
* PyObject_GC_NewVar (C function):       Supporting Cyclic Garbage Collection.
                                                             (line   61)
* PyObject_GC_Resize (C function):       Supporting Cyclic Garbage Collection.
                                                             (line   68)
* PyObject_GC_Track (C function):        Supporting Cyclic Garbage Collection.
                                                             (line   76)
* PyObject_GC_UnTrack (C function):      Supporting Cyclic Garbage Collection.
                                                             (line  119)
* PyObject_GenericGetAttr (C function):  Object Protocol.    (line   63)
* PyObject_GenericGetDict (C function):  Object Protocol.    (line  123)
* PyObject_GenericSetAttr (C function):  Object Protocol.    (line   98)
* PyObject_GenericSetDict (C function):  Object Protocol.    (line  131)
* PyObject_GetArenaAllocator (C function): Customize pymalloc Arena Allocator.
                                                             (line   26)
* PyObject_GetAttr (C function):         Object Protocol.    (line   48)
* PyObject_GetAttrString (C function):   Object Protocol.    (line   55)
* PyObject_GetBuffer (C function):       Buffer-related functions.
                                                             (line   13)
* PyObject_GetItem (C function):         Object Protocol.    (line  313)
* PyObject_GetIter (C function):         Object Protocol.    (line  342)
* PyObject_HasAttr (C function):         Object Protocol.    (line   25)
* PyObject_HasAttrString (C function):   Object Protocol.    (line   36)
* PyObject_Hash (C function):            Object Protocol.    (line  249)
* PyObject_HashNotImplemented (C function): Object Protocol. (line  258)
* PyObject_HEAD (C macro):               Base object types and macros.
                                                             (line   33)
* PyObject_HEAD_INIT (C macro):          Base object types and macros.
                                                             (line   99)
* PyObject_Init (C function):            Allocating Objects on the Heap.
                                                             (line   14)
* PyObject_InitVar (C function):         Allocating Objects on the Heap.
                                                             (line   23)
* PyObject_IsInstance (C function):      Object Protocol.    (line  227)
* PyObject_IsSubclass (C function):      Object Protocol.    (line  206)
* PyObject_IsTrue (C function):          Object Protocol.    (line  265)
* PyObject_IS_GC (C function):           Supporting Cyclic Garbage Collection.
                                                             (line   84)
* PyObject_Length (C function):          Object Protocol.    (line  294)
* PyObject_LengthHint (C function):      Object Protocol.    (line  302)
* PyObject_Malloc (C function):          Object allocators.  (line   16)
* PyObject_New (C function):             Allocating Objects on the Heap.
                                                             (line   30)
* PyObject_NewVar (C function):          Allocating Objects on the Heap.
                                                             (line   38)
* PyObject_Not (C function):             Object Protocol.    (line  271)
* PyObject_Print (C function):           Object Protocol.    (line   17)
* PyObject_Realloc (C function):         Object allocators.  (line   37)
* PyObject_Repr (C function):            Object Protocol.    (line  164)
* PyObject_RichCompare (C function):     Object Protocol.    (line  139)
* PyObject_RichCompareBool (C function): Object Protocol.    (line  149)
* PyObject_SetArenaAllocator (C function): Customize pymalloc Arena Allocator.
                                                             (line   31)
* PyObject_SetAttr (C function):         Object Protocol.    (line   75)
* PyObject_SetAttrString (C function):   Object Protocol.    (line   87)
* PyObject_SetItem (C function):         Object Protocol.    (line  318)
* PyObject_Size (C function):            Object Protocol.    (line  294)
* PyObject_Str (C function):             Object Protocol.    (line  186)
* PyObject_Type (C function):            Object Protocol.    (line  277)
* PyObject_TypeCheck (C function):       Object Protocol.    (line  289)
* PyObject_VAR_HEAD (C macro):           Base object types and macros.
                                                             (line   43)
* PyObject_Vectorcall (C function):      Object Calling API. (line  206)
* PyObject_VectorcallDict (C function):  Object Calling API. (line  221)
* PyObject_VectorcallMethod (C function): Object Calling API.
                                                             (line  238)
* PyOS_AfterFork (C function):           Operating System Utilities.
                                                             (line   75)
* PyOS_AfterFork_Child (C function):     Operating System Utilities.
                                                             (line   53)
* PyOS_AfterFork_Parent (C function):    Operating System Utilities.
                                                             (line   39)
* PyOS_BeforeFork (C function):          Operating System Utilities.
                                                             (line   26)
* PyOS_CheckStack (C function):          Operating System Utilities.
                                                             (line   85)
* PyOS_double_to_string (C function):    String conversion and formatting.
                                                             (line   87)
* PyOS_FSPath (C function):              Operating System Utilities.
                                                             (line    6)
* PyOS_getsig (C function):              Operating System Utilities.
                                                             (line   93)
* PyOS_InputHook (C variable):           The Very High Level Layer.
                                                             (line  164)
* PyOS_ReadlineFunctionPointer (C variable): The Very High Level Layer.
                                                             (line  174)
* PyOS_setsig (C function):              Operating System Utilities.
                                                             (line  100)
* PyOS_snprintf (C function):            String conversion and formatting.
                                                             (line    8)
* PyOS_stricmp (C function):             String conversion and formatting.
                                                             (line  122)
* PyOS_string_to_double (C function):    String conversion and formatting.
                                                             (line   54)
* PyOS_strnicmp (C function):            String conversion and formatting.
                                                             (line  127)
* PyOS_vsnprintf (C function):           String conversion and formatting.
                                                             (line   15)
* PyParser_SimpleParseFile (C function): The Very High Level Layer.
                                                             (line  226)
* PyParser_SimpleParseFileFlags (C function): The Very High Level Layer.
                                                             (line  236)
* PyParser_SimpleParseString (C function): The Very High Level Layer.
                                                             (line  195)
* PyParser_SimpleParseStringFlags (C function): The Very High Level Layer.
                                                             (line  204)
* PyParser_SimpleParseStringFlagsFilename (C function): The Very High Level Layer.
                                                             (line  214)
* PyPI; (see Python Package Index (PyPI)): Installing the tools.
                                                             (line   25)
* PyPreConfig (C type):                  PyPreConfig.        (line    6)
* PyPreConfig.allocator (C member):      PyPreConfig.        (line   32)
* PyPreConfig.coerce_c_locale (C member): PyPreConfig.       (line   68)
* PyPreConfig.coerce_c_locale_warn (C member): PyPreConfig.  (line   73)
* PyPreConfig.configure_locale (C member): PyPreConfig.      (line   62)
* PyPreConfig.dev_mode (C member):       PyPreConfig.        (line   77)
* PyPreConfig.isolated (C member):       PyPreConfig.        (line   81)
* PyPreConfig.legacy_windows_fs_encoding (C member): PyPreConfig.
                                                             (line   85)
* PyPreConfig.parse_argv (C member):     PyPreConfig.        (line   94)
* PyPreConfig.use_environment (C member): PyPreConfig.       (line  101)
* PyPreConfig.utf8_mode (C member):      PyPreConfig.        (line  105)
* PyPreConfig_InitIsolatedConfig (C function): PyPreConfig.  (line   24)
* PyPreConfig_InitPythonConfig (C function): PyPreConfig.    (line   18)
* PyProperty_Type (C variable):          Descriptor Objects. (line    9)
* PyRun_AnyFile (C function):            The Very High Level Layer.
                                                             (line   48)
* PyRun_AnyFileEx (C function):          The Very High Level Layer.
                                                             (line   61)
* PyRun_AnyFileExFlags (C function):     The Very High Level Layer.
                                                             (line   68)
* PyRun_AnyFileFlags (C function):       The Very High Level Layer.
                                                             (line   54)
* PyRun_File (C function):               The Very High Level Layer.
                                                             (line  264)
* PyRun_FileEx (C function):             The Very High Level Layer.
                                                             (line  271)
* PyRun_FileExFlags (C function):        The Very High Level Layer.
                                                             (line  285)
* PyRun_FileFlags (C function):          The Very High Level Layer.
                                                             (line  278)
* PyRun_InteractiveLoop (C function):    The Very High Level Layer.
                                                             (line  148)
* PyRun_InteractiveLoopFlags (C function): The Very High Level Layer.
                                                             (line  155)
* PyRun_InteractiveOne (C function):     The Very High Level Layer.
                                                             (line  126)
* PyRun_InteractiveOneFlags (C function): The Very High Level Layer.
                                                             (line  133)
* PyRun_SimpleFile (C function):         The Very High Level Layer.
                                                             (line  100)
* PyRun_SimpleFileEx (C function):       The Very High Level Layer.
                                                             (line  105)
* PyRun_SimpleFileExFlags (C function):  The Very High Level Layer.
                                                             (line  112)
* PyRun_SimpleString (C function):       The Very High Level Layer.
                                                             (line   79)
* PyRun_SimpleStringFlags (C function):  The Very High Level Layer.
                                                             (line   85)
* PyRun_String (C function):             The Very High Level Layer.
                                                             (line  245)
* PyRun_StringFlags (C function):        The Very High Level Layer.
                                                             (line  252)
* PySeqIter_Check (C function):          Iterator Objects.   (line   18)
* PySeqIter_New (C function):            Iterator Objects.   (line   23)
* PySeqIter_Type (C variable):           Iterator Objects.   (line   12)
* PySequenceMethods (C type):            Sequence Object Structures.
                                                             (line    6)
* PySequenceMethods.sq_ass_item (C member): Sequence Object Structures.
                                                             (line   45)
* PySequenceMethods.sq_concat (C member): Sequence Object Structures.
                                                             (line   18)
* PySequenceMethods.sq_contains (C member): Sequence Object Structures.
                                                             (line   54)
* PySequenceMethods.sq_inplace_concat (C member): Sequence Object Structures.
                                                             (line   61)
* PySequenceMethods.sq_inplace_repeat (C member): Sequence Object Structures.
                                                             (line   71)
* PySequenceMethods.sq_item (C member):  Sequence Object Structures.
                                                             (line   31)
* PySequenceMethods.sq_length (C member): Sequence Object Structures.
                                                             (line   11)
* PySequenceMethods.sq_repeat (C member): Sequence Object Structures.
                                                             (line   24)
* PySequence_Check (C function):         Sequence Protocol.  (line    6)
* PySequence_Concat (C function):        Sequence Protocol.  (line   20)
* PySequence_Contains (C function):      Sequence Protocol.  (line   99)
* PySequence_Count (C function):         Sequence Protocol.  (line   91)
* PySequence_DelItem (C function):       Sequence Protocol.  (line   70)
* PySequence_DelSlice (C function):      Sequence Protocol.  (line   83)
* PySequence_Fast (C function):          Sequence Protocol.  (line  127)
* PySequence_Fast_GET_ITEM (C function): Sequence Protocol.  (line  149)
* PySequence_Fast_GET_SIZE (C function): Sequence Protocol.  (line  141)
* PySequence_Fast_ITEMS (C function):    Sequence Protocol.  (line  156)
* PySequence_GetItem (C function):       Sequence Protocol.  (line   47)
* PySequence_GetItem():                  Reference Count Details.
                                                             (line  117)
* PySequence_GetSlice (C function):      Sequence Protocol.  (line   52)
* PySequence_Index (C function):         Sequence Protocol.  (line  105)
* PySequence_InPlaceConcat (C function): Sequence Protocol.  (line   31)
* PySequence_InPlaceRepeat (C function): Sequence Protocol.  (line   39)
* PySequence_ITEM (C function):          Sequence Protocol.  (line  166)
* PySequence_Length (C function):        Sequence Protocol.  (line   14)
* PySequence_List (C function):          Sequence Protocol.  (line  112)
* PySequence_Repeat (C function):        Sequence Protocol.  (line   25)
* PySequence_SetItem (C function):       Sequence Protocol.  (line   58)
* PySequence_SetSlice (C function):      Sequence Protocol.  (line   75)
* PySequence_Size (C function):          Sequence Protocol.  (line   14)
* PySequence_Tuple (C function):         Sequence Protocol.  (line  118)
* PySetObject (C type):                  Set Objects.        (line   19)
* PySet_Add (C function):                Set Objects.        (line  110)
* PySet_Check (C function):              Set Objects.        (line   45)
* PySet_Clear (C function):              Set Objects.        (line  142)
* PySet_Contains (C function):           Set Objects.        (line  101)
* PySet_Discard (C function):            Set Objects.        (line  125)
* PySet_GET_SIZE (C function):           Set Objects.        (line   97)
* PySet_New (C function):                Set Objects.        (line   72)
* PySet_Pop (C function):                Set Objects.        (line  135)
* PySet_Size (C function):               Set Objects.        (line   90)
* PySet_Type (C variable):               Set Objects.        (line   31)
* PySignal_SetWakeupFd (C function):     Signal Handling<2>. (line   28)
* PySlice_AdjustIndices (C function):    Slice Objects.      (line  102)
* PySlice_Check (C function):            Slice Objects.      (line   11)
* PySlice_GetIndices (C function):       Slice Objects.      (line   26)
* PySlice_GetIndicesEx (C function):     Slice Objects.      (line   45)
* PySlice_New (C function):              Slice Objects.      (line   16)
* PySlice_Type (C variable):             Slice Objects.      (line    6)
* PySlice_Unpack (C function):           Slice Objects.      (line   88)
* PyState_AddModule (C function):        Module lookup.      (line   23)
* PyState_FindModule (C function):       Module lookup.      (line   15)
* PyState_RemoveModule (C function):     Module lookup.      (line   47)
* PyStatus (C type):                     PyStatus.           (line    6)
* PyStatus.err_msg (C member):           PyStatus.           (line   20)
* PyStatus.exitcode (C member):          PyStatus.           (line   16)
* PyStatus.func (C member):              PyStatus.           (line   24)
* PyStatus_Error (C function):           PyStatus.           (line   34)
* PyStatus_Exception (C function):       PyStatus.           (line   48)
* PyStatus_Exit (C function):            PyStatus.           (line   42)
* PyStatus_IsError (C function):         PyStatus.           (line   54)
* PyStatus_IsExit (C function):          PyStatus.           (line   58)
* PyStatus_NoMemory (C function):        PyStatus.           (line   38)
* PyStatus_Ok (C function):              PyStatus.           (line   30)
* PyStructSequence_Desc (C type):        Struct Sequence Objects.
                                                             (line   34)
* PyStructSequence_Field (C type):       Struct Sequence Objects.
                                                             (line   57)
* PyStructSequence_GetItem (C function): Struct Sequence Objects.
                                                             (line   88)
* PyStructSequence_GET_ITEM (C function): Struct Sequence Objects.
                                                             (line   95)
* PyStructSequence_InitType (C function): Struct Sequence Objects.
                                                             (line   19)
* PyStructSequence_InitType2 (C function): Struct Sequence Objects.
                                                             (line   25)
* PyStructSequence_New (C function):     Struct Sequence Objects.
                                                             (line   83)
* PyStructSequence_NewType (C function): Struct Sequence Objects.
                                                             (line   11)
* PyStructSequence_SetItem (C function): Struct Sequence Objects.
                                                             (line  101)
* PyStructSequence_SET_ITEM (C function): Struct Sequence Objects.
                                                             (line  110)
* PyStructSequence_UnnamedField (C variable): Struct Sequence Objects.
                                                             (line   77)
* PySys_AddAuditHook (C function):       System Functions.   (line  129)
* PySys_AddWarnOption (C function):      System Functions.   (line   27)
* PySys_AddWarnOptionUnicode (C function): System Functions. (line   33)
* PySys_AddXOption (C function):         System Functions.   (line   87)
* PySys_Audit (C function):              System Functions.   (line  103)
* PySys_FormatStderr (C function):       System Functions.   (line   80)
* PySys_FormatStdout (C function):       System Functions.   (line   72)
* PySys_GetObject (C function):          System Functions.   (line   11)
* PySys_GetXOptions (C function):        System Functions.   (line   96)
* PySys_ResetWarnOptions (C function):   System Functions.   (line   22)
* PySys_SetArgv (C function):            Process-wide parameters.
                                                             (line  255)
* PySys_SetArgv():                       Initializing and finalizing the interpreter.
                                                             (line    8)
* PySys_SetArgvEx (C function):          Process-wide parameters.
                                                             (line  214)
* PySys_SetArgvEx():                     Embedding Python<2>.
                                                             (line   17)
* PySys_SetArgvEx() <1>:                 Initializing and finalizing the interpreter.
                                                             (line    8)
* PySys_SetObject (C function):          System Functions.   (line   16)
* PySys_SetPath (C function):            System Functions.   (line   43)
* PySys_WriteStderr (C function):        System Functions.   (line   67)
* PySys_WriteStdout (C function):        System Functions.   (line   49)
* Python 3000:                           Glossary.           (line 1086)
* Python Editor:                         IDLE<51>.           (line    8)
* Python Enhancement Proposals; PEP 1:   New Development Process.
                                                             (line   67)
* Python Enhancement Proposals; PEP 1 <1>: New Development Process.
                                                             (line   82)
* Python Enhancement Proposals; PEP 1 <2>: Glossary.         (line 1052)
* Python Enhancement Proposals; PEP 100: Unicode<2>.         (line   15)
* Python Enhancement Proposals; PEP 11:  PEP 538 Legacy C Locale Coercion.
                                                             (line   19)
* Python Enhancement Proposals; PEP 11 <1>: Unsupported Operating Systems.
                                                             (line    6)
* Python Enhancement Proposals; PEP 11 <2>: Library Changes. (line   15)
* Python Enhancement Proposals; PEP 11 <3>: Build<32>.       (line   14)
* Python Enhancement Proposals; PEP 11 <4>: Using Python on Windows.
                                                             (line   18)
* Python Enhancement Proposals; PEP 11 <5>: Other Platforms. (line    8)
* Python Enhancement Proposals; PEP 201: New Development Process.
                                                             (line   86)
* Python Enhancement Proposals; PEP 205: PEP 205 Weak References.
                                                             (line   82)
* Python Enhancement Proposals; PEP 205 <1>: weakref — Weak references.
                                                             (line  322)
* Python Enhancement Proposals; PEP 207: PEP 207 Rich Comparisons.
                                                             (line   71)
* Python Enhancement Proposals; PEP 207 <1>: PEP 207 Rich Comparisons.
                                                             (line   77)
* Python Enhancement Proposals; PEP 208: PEP 208 New Coercion Model.
                                                             (line   30)
* Python Enhancement Proposals; PEP 217: PEP 217 Interactive Display Hook.
                                                             (line   27)
* Python Enhancement Proposals; PEP 218: PEP 218 Built-In Set Objects.
                                                             (line   50)
* Python Enhancement Proposals; PEP 218 <1>: Other Language Changes<13>.
                                                             (line   12)
* Python Enhancement Proposals; PEP 218 <2>: PEP 218 A Standard Set Datatype.
                                                             (line   80)
* Python Enhancement Proposals; PEP 227: PEP 227 Nested Scopes.
                                                             (line   96)
* Python Enhancement Proposals; PEP 227 <1>: PEP 227 Nested Scopes<2>.
                                                             (line   96)
* Python Enhancement Proposals; PEP 227 <2>: __future__ — Future statement definitions.
                                                             (line   71)
* Python Enhancement Proposals; PEP 229: PEP 229 New Build System.
                                                             (line   39)
* Python Enhancement Proposals; PEP 230: PEP 230 Warning Framework.
                                                             (line   73)
* Python Enhancement Proposals; PEP 232: PEP 232 Function Attributes.
                                                             (line   36)
* Python Enhancement Proposals; PEP 234: PEP 234 Iterators.  (line  124)
* Python Enhancement Proposals; PEP 235: Introduction<12>.   (line   37)
* Python Enhancement Proposals; PEP 236: PEP 227 Nested Scopes<2>.
                                                             (line   87)
* Python Enhancement Proposals; PEP 236 <1>: PEP 227 Nested Scopes<2>.
                                                             (line   88)
* Python Enhancement Proposals; PEP 236 <2>: PEP 236 __future__ Directives.
                                                             (line   29)
* Python Enhancement Proposals; PEP 236 <3>: Future statements.
                                                             (line   85)
* Python Enhancement Proposals; PEP 237: Integers.           (line    6)
* Python Enhancement Proposals; PEP 237 <1>: PEP 237 Unifying Long Integers and Integers.
                                                             (line   22)
* Python Enhancement Proposals; PEP 237 <2>: Other Language Changes<13>.
                                                             (line   18)
* Python Enhancement Proposals; PEP 237 <3>: PEP 237 Unifying Long Integers and Integers<2>.
                                                             (line   37)
* Python Enhancement Proposals; PEP 237 <4>: printf-style String Formatting.
                                                             (line  182)
* Python Enhancement Proposals; PEP 237 <5>: printf-style Bytes Formatting.
                                                             (line  189)
* Python Enhancement Proposals; PEP 238: Integers.           (line   10)
* Python Enhancement Proposals; PEP 238 <1>: PEP 238 Changing the Division Operator.
                                                             (line   21)
* Python Enhancement Proposals; PEP 238 <2>: PEP 238 Changing the Division Operator.
                                                             (line   27)
* Python Enhancement Proposals; PEP 238 <3>: PEP 238 Changing the Division Operator.
                                                             (line   68)
* Python Enhancement Proposals; PEP 238 <4>: __future__ — Future statement definitions.
                                                             (line   77)
* Python Enhancement Proposals; PEP 238 <5>: The Very High Level Layer.
                                                             (line  434)
* Python Enhancement Proposals; PEP 238 <6>: Glossary.       (line  459)
* Python Enhancement Proposals; PEP 241: PEP 241 Metadata in Python Packages.
                                                             (line   15)
* Python Enhancement Proposals; PEP 241 <1>: PEP 241 Metadata in Python Packages.
                                                             (line   28)
* Python Enhancement Proposals; PEP 241 <2>: PEP 241 Metadata in Python Packages.
                                                             (line   35)
* Python Enhancement Proposals; PEP 243: PEP 241 Metadata in Python Packages.
                                                             (line   39)
* Python Enhancement Proposals; PEP 247: hmac<2>.            (line   20)
* Python Enhancement Proposals; PEP 249: The sqlite3 package.
                                                             (line   18)
* Python Enhancement Proposals; PEP 249 <1>: The sqlite3 package.
                                                             (line  110)
* Python Enhancement Proposals; PEP 249 <2>: sqlite3 — DB-API 2 0 interface for SQLite databases.
                                                             (line   18)
* Python Enhancement Proposals; PEP 249 <3>: sqlite3 — DB-API 2 0 interface for SQLite databases.
                                                             (line  130)
* Python Enhancement Proposals; PEP 252: Related Links.      (line   17)
* Python Enhancement Proposals; PEP 252 <1>: Related Links.  (line   17)
* Python Enhancement Proposals; PEP 252 <2>: Implementing Descriptors.
                                                             (line   24)
* Python Enhancement Proposals; PEP 253: Old and New Classes.
                                                             (line   28)
* Python Enhancement Proposals; PEP 253 <1>: Multiple Inheritance The Diamond Rule.
                                                             (line    8)
* Python Enhancement Proposals; PEP 253 <2>: Related Links.  (line   17)
* Python Enhancement Proposals; PEP 253 <3>: Related Links.  (line   19)
* Python Enhancement Proposals; PEP 253 <4>: Related Links.  (line   21)
* Python Enhancement Proposals; PEP 255: PEP 255 Simple Generators.
                                                             (line   45)
* Python Enhancement Proposals; PEP 255 <1>: PEP 255 Simple Generators.
                                                             (line  131)
* Python Enhancement Proposals; PEP 255 <2>: PEP 255 Simple Generators<2>.
                                                             (line   43)
* Python Enhancement Proposals; PEP 255 <3>: PEP 255 Simple Generators<2>.
                                                             (line  129)
* Python Enhancement Proposals; PEP 255 <4>: Yield expressions.
                                                             (line   88)
* Python Enhancement Proposals; PEP 255 <5>: __future__ — Future statement definitions.
                                                             (line   74)
* Python Enhancement Proposals; PEP 261: Unicode Changes.    (line   18)
* Python Enhancement Proposals; PEP 261 <1>: Unicode Changes.
                                                             (line   61)
* Python Enhancement Proposals; PEP 263: Other Language Changes<12>.
                                                             (line   98)
* Python Enhancement Proposals; PEP 263 <1>: PEP 263 Source Code Encodings.
                                                             (line   29)
* Python Enhancement Proposals; PEP 263 <2>: Core and Builtins.
                                                             (line   32)
* Python Enhancement Proposals; PEP 263 <3>: Introduction<12>.
                                                             (line   41)
* Python Enhancement Proposals; PEP 263 <4>: Tokenizing Input.
                                                             (line   35)
* Python Enhancement Proposals; PEP 263 <5>: Tokenizing Input.
                                                             (line   89)
* Python Enhancement Proposals; PEP 263 <6>: Unicode Literals in Python Source Code.
                                                             (line   48)
* Python Enhancement Proposals; PEP 264: Other Changes and Fixes<3>.
                                                             (line   55)
* Python Enhancement Proposals; PEP 273: PEP 273 Importing Modules from ZIP Archives.
                                                             (line   41)
* Python Enhancement Proposals; PEP 273 <1>: PEP 273 Importing Modules from ZIP Archives.
                                                             (line   44)
* Python Enhancement Proposals; PEP 273 <2>: zipimport — Import modules from Zip archives.
                                                             (line   42)
* Python Enhancement Proposals; PEP 273 <3>: zipimport — Import modules from Zip archives.
                                                             (line   45)
* Python Enhancement Proposals; PEP 274: New Syntax.         (line   38)
* Python Enhancement Proposals; PEP 275: Why isn’t there a switch or case statement in Python?.
                                                             (line    8)
* Python Enhancement Proposals; PEP 277: PEP 277 Unicode file name support for Windows NT.
                                                             (line   32)
* Python Enhancement Proposals; PEP 278: PEP 278 Universal Newline Support.
                                                             (line   33)
* Python Enhancement Proposals; PEP 278 <1>: Glossary.       (line 1294)
* Python Enhancement Proposals; PEP 279: PEP 279 enumerate.  (line   27)
* Python Enhancement Proposals; PEP 282: PEP 282 The logging Package.
                                                             (line  101)
* Python Enhancement Proposals; PEP 282 <1>: PEP 282 The logging Package.
                                                             (line  107)
* Python Enhancement Proposals; PEP 282 <2>: Archiving operations.
                                                             (line   45)
* Python Enhancement Proposals; PEP 282 <3>: Integration with the warnings module.
                                                             (line   36)
* Python Enhancement Proposals; PEP 282 <4>: distutils log — Simple PEP 282-style logging.
                                                             (line    6)
* Python Enhancement Proposals; PEP 285: PEP 285 A Boolean Type.
                                                             (line   47)
* Python Enhancement Proposals; PEP 285 <1>: PEP 285 A Boolean Type.
                                                             (line   70)
* Python Enhancement Proposals; PEP 288: PEP 342 New Generator Features.
                                                             (line  146)
* Python Enhancement Proposals; PEP 289: PEP 289 Generator Expressions.
                                                             (line   56)
* Python Enhancement Proposals; PEP 289 <1>: Other Language Changes<13>.
                                                             (line   15)
* Python Enhancement Proposals; PEP 289 <2>: Python documentation.
                                                             (line   12)
* Python Enhancement Proposals; PEP 292: PEP 292 Simpler String Substitutions.
                                                             (line   45)
* Python Enhancement Proposals; PEP 292 <1>: Template strings.
                                                             (line    6)
* Python Enhancement Proposals; PEP 293: PEP 293 Codec Error Handling Callbacks.
                                                             (line   33)
* Python Enhancement Proposals; PEP 3000: Python 3 0.        (line   43)
* Python Enhancement Proposals; PEP 301: PEP 301 Package Index and Metadata for Distutils.
                                                             (line   45)
* Python Enhancement Proposals; PEP 301 <1>: distutils command register — Register a module with the Python Package Index.
                                                             (line    7)
* Python Enhancement Proposals; PEP 302: Using importlib as the Implementation of Import.
                                                             (line   13)
* Python Enhancement Proposals; PEP 302 <1>: Visible Changes.
                                                             (line   18)
* Python Enhancement Proposals; PEP 302 <2>: Porting Python code.
                                                             (line   71)
* Python Enhancement Proposals; PEP 302 <3>: New Improved and Deprecated Modules<2>.
                                                             (line  106)
* Python Enhancement Proposals; PEP 302 <4>: New Improved and Removed Modules.
                                                             (line  289)
* Python Enhancement Proposals; PEP 302 <5>: PEP 273 Importing Modules from ZIP Archives.
                                                             (line   46)
* Python Enhancement Proposals; PEP 302 <6>: PEP 302 New Import Hooks.
                                                             (line   13)
* Python Enhancement Proposals; PEP 302 <7>: PEP 302 New Import Hooks.
                                                             (line   38)
* Python Enhancement Proposals; PEP 302 <8>: PEP 302 New Import Hooks.
                                                             (line   62)
* Python Enhancement Proposals; PEP 302 <9>: The import system.
                                                             (line   42)
* Python Enhancement Proposals; PEP 302 <10>: References.    (line   10)
* Python Enhancement Proposals; PEP 302 <11>: Built-in Functions.
                                                             (line 1808)
* Python Enhancement Proposals; PEP 302 <12>: linecache — Random access to text lines.
                                                             (line   31)
* Python Enhancement Proposals; PEP 302 <13>: sys — System-specific parameters and functions.
                                                             (line 1092)
* Python Enhancement Proposals; PEP 302 <14>: sys — System-specific parameters and functions.
                                                             (line 1102)
* Python Enhancement Proposals; PEP 302 <15>: zipimport — Import modules from Zip archives.
                                                             (line   47)
* Python Enhancement Proposals; PEP 302 <16>: zipimport — Import modules from Zip archives.
                                                             (line   49)
* Python Enhancement Proposals; PEP 302 <17>: pkgutil — Package extension utility.
                                                             (line   55)
* Python Enhancement Proposals; PEP 302 <18>: pkgutil — Package extension utility.
                                                             (line   57)
* Python Enhancement Proposals; PEP 302 <19>: pkgutil — Package extension utility.
                                                             (line   58)
* Python Enhancement Proposals; PEP 302 <20>: pkgutil — Package extension utility.
                                                             (line   66)
* Python Enhancement Proposals; PEP 302 <21>: pkgutil — Package extension utility.
                                                             (line   74)
* Python Enhancement Proposals; PEP 302 <22>: pkgutil — Package extension utility.
                                                             (line   87)
* Python Enhancement Proposals; PEP 302 <23>: pkgutil — Package extension utility.
                                                             (line  103)
* Python Enhancement Proposals; PEP 302 <24>: pkgutil — Package extension utility.
                                                             (line  118)
* Python Enhancement Proposals; PEP 302 <25>: pkgutil — Package extension utility.
                                                             (line  138)
* Python Enhancement Proposals; PEP 302 <26>: pkgutil — Package extension utility.
                                                             (line  159)
* Python Enhancement Proposals; PEP 302 <27>: pkgutil — Package extension utility.
                                                             (line  198)
* Python Enhancement Proposals; PEP 302 <28>: runpy — Locating and executing Python modules.
                                                             (line   32)
* Python Enhancement Proposals; PEP 302 <29>: Introduction<12>.
                                                             (line   45)
* Python Enhancement Proposals; PEP 302 <30>: importlib abc – Abstract base classes related to import.
                                                             (line   38)
* Python Enhancement Proposals; PEP 302 <31>: importlib abc – Abstract base classes related to import.
                                                             (line  160)
* Python Enhancement Proposals; PEP 302 <32>: importlib abc – Abstract base classes related to import.
                                                             (line  363)
* Python Enhancement Proposals; PEP 302 <33>: importlib abc – Abstract base classes related to import.
                                                             (line  387)
* Python Enhancement Proposals; PEP 302 <34>: importlib abc – Abstract base classes related to import.
                                                             (line  458)
* Python Enhancement Proposals; PEP 302 <35>: imp — Access the import internals.
                                                             (line  347)
* Python Enhancement Proposals; PEP 302 <36>: Glossary.      (line  451)
* Python Enhancement Proposals; PEP 302 <37>: Glossary.      (line  788)
* Python Enhancement Proposals; PEP 305: PEP 305 Comma-separated Files.
                                                             (line   42)
* Python Enhancement Proposals; PEP 305 <1>: csv — CSV File Reading and Writing.
                                                             (line   38)
* Python Enhancement Proposals; PEP 307: PEP 307 Pickle Enhancements.
                                                             (line    8)
* Python Enhancement Proposals; PEP 307 <1>: PEP 307 Pickle Enhancements.
                                                             (line   30)
* Python Enhancement Proposals; PEP 307 <2>: PEP 307 Pickle Enhancements.
                                                             (line   42)
* Python Enhancement Proposals; PEP 307 <3>: Data stream format.
                                                             (line   32)
* Python Enhancement Proposals; PEP 308: PEP 308 Conditional Expressions.
                                                             (line   72)
* Python Enhancement Proposals; PEP 308 <1>: PEP 308 Conditional Expressions.
                                                             (line   78)
* Python Enhancement Proposals; PEP 308 <2>: Conditional expressions.
                                                             (line   16)
* Python Enhancement Proposals; PEP 309: PEP 309 Partial Function Application.
                                                             (line   73)
* Python Enhancement Proposals; PEP 3100: Python 3 0.        (line   44)
* Python Enhancement Proposals; PEP 3101: PEP 3101 A New Approach To String Formatting.
                                                             (line    6)
* Python Enhancement Proposals; PEP 3101 <1>: PEP 3101 A New Approach To String Formatting.
                                                             (line    9)
* Python Enhancement Proposals; PEP 3101 <2>: PEP 3101 Advanced String Formatting.
                                                             (line  162)
* Python Enhancement Proposals; PEP 3101 <3>: Custom String Formatting.
                                                             (line    8)
* Python Enhancement Proposals; PEP 3101 <4>: Custom String Formatting.
                                                             (line   60)
* Python Enhancement Proposals; PEP 3102: New Syntax.        (line   13)
* Python Enhancement Proposals; PEP 3104: New Syntax.        (line   24)
* Python Enhancement Proposals; PEP 3104 <1>: The nonlocal statement.
                                                             (line   26)
* Python Enhancement Proposals; PEP 3105: Print Is A Function.
                                                             (line    8)
* Python Enhancement Proposals; PEP 3105 <1>: PEP 3105 print As a Function.
                                                             (line   35)
* Python Enhancement Proposals; PEP 3105 <2>: __future__ — Future statement definitions.
                                                             (line   87)
* Python Enhancement Proposals; PEP 3106: PEP 3106 Dictionary Views.
                                                             (line   58)
* Python Enhancement Proposals; PEP 3107: PEP 563 Postponed Evaluation of Annotations.
                                                             (line    7)
* Python Enhancement Proposals; PEP 3107 <1>: PEP 484 - Type Hints.
                                                             (line    7)
* Python Enhancement Proposals; PEP 3107 <2>: New Syntax.    (line    6)
* Python Enhancement Proposals; PEP 3107 <3>: Function Annotations.
                                                             (line    7)
* Python Enhancement Proposals; PEP 3107 <4>: Function definitions.
                                                             (line  131)
* Python Enhancement Proposals; PEP 3108: Library Changes.   (line    7)
* Python Enhancement Proposals; PEP 3108 <1>: Library Changes.
                                                             (line   17)
* Python Enhancement Proposals; PEP 3108 <2>: Library Changes.
                                                             (line   95)
* Python Enhancement Proposals; PEP 3109: Changed Syntax.    (line    6)
* Python Enhancement Proposals; PEP 3109 <1>: Changes To Exceptions.
                                                             (line   29)
* Python Enhancement Proposals; PEP 3110: Changed Syntax.    (line   16)
* Python Enhancement Proposals; PEP 3110 <1>: Changes To Exceptions.
                                                             (line   35)
* Python Enhancement Proposals; PEP 3110 <2>: PEP 3110 Exception-Handling Changes.
                                                             (line   48)
* Python Enhancement Proposals; PEP 3111: Builtins.          (line   12)
* Python Enhancement Proposals; PEP 3112: PEP 3112 Byte Literals.
                                                             (line   75)
* Python Enhancement Proposals; PEP 3112 <1>: __future__ — Future statement definitions.
                                                             (line   90)
* Python Enhancement Proposals; PEP 3113: Removed Syntax.    (line    6)
* Python Enhancement Proposals; PEP 3114: Operators And Special Methods.
                                                             (line   19)
* Python Enhancement Proposals; PEP 3115: types<4>.          (line   10)
* Python Enhancement Proposals; PEP 3115 <1>: Changed Syntax.
                                                             (line   18)
* Python Enhancement Proposals; PEP 3115 <2>: Preparing the class namespace.
                                                             (line   21)
* Python Enhancement Proposals; PEP 3115 <3>: Class definitions.
                                                             (line   75)
* Python Enhancement Proposals; PEP 3115 <4>: Dynamic Type Creation.
                                                             (line   54)
* Python Enhancement Proposals; PEP 3116: Optimizations<8>.  (line    8)
* Python Enhancement Proposals; PEP 3116 <1>: PEP 3116 New I/O Library.
                                                             (line   69)
* Python Enhancement Proposals; PEP 3116 <2>: Glossary.      (line 1294)
* Python Enhancement Proposals; PEP 3118: Pickle protocol 5 with out-of-band data buffers.
                                                             (line   13)
* Python Enhancement Proposals; PEP 3118 <1>: PEP 3118 New memoryview implementation and buffer protocol documentation.
                                                             (line    6)
* Python Enhancement Proposals; PEP 3118 <2>: API changes.   (line   29)
* Python Enhancement Proposals; PEP 3118 <3>: Build and C API Changes<4>.
                                                             (line    8)
* Python Enhancement Proposals; PEP 3118 <4>: Build and C API Changes<7>.
                                                             (line   12)
* Python Enhancement Proposals; PEP 3118 <5>: PEP 3118 Revised Buffer Protocol.
                                                             (line   46)
* Python Enhancement Proposals; PEP 3118 <6>: Library<41>.   (line   99)
* Python Enhancement Proposals; PEP 3118 <7>: Library<46>.   (line   61)
* Python Enhancement Proposals; PEP 3118 <8>: Library<89>.   (line  956)
* Python Enhancement Proposals; PEP 3118 <9>: Memory Views.  (line  111)
* Python Enhancement Proposals; PEP 3119: PEP 3119 Abstract Base Classes.
                                                             (line  139)
* Python Enhancement Proposals; PEP 3119 <1>: Customizing instance and subclass checks.
                                                             (line   35)
* Python Enhancement Proposals; PEP 3119 <2>: Collections Abstract Base Classes.
                                                             (line  316)
* Python Enhancement Proposals; PEP 3119 <3>: abc — Abstract Base Classes.
                                                             (line   11)
* Python Enhancement Proposals; PEP 3119 <4>: Object Protocol.
                                                             (line  218)
* Python Enhancement Proposals; PEP 3119 <5>: Object Protocol.
                                                             (line  238)
* Python Enhancement Proposals; PEP 3120: Text Vs Data Instead Of Unicode Vs 8-bit.
                                                             (line  107)
* Python Enhancement Proposals; PEP 3120 <1>: Lexical analysis.
                                                             (line   12)
* Python Enhancement Proposals; PEP 3120 <2>: Introduction<12>.
                                                             (line   77)
* Python Enhancement Proposals; PEP 3121: Build and C API Changes<7>.
                                                             (line   14)
* Python Enhancement Proposals; PEP 3121 <1>: Initializing C modules.
                                                             (line   55)
* Python Enhancement Proposals; PEP 3123: Build and C API Changes<7>.
                                                             (line   16)
* Python Enhancement Proposals; PEP 3127: PEP 3127 Integer Literal Support and Syntax.
                                                             (line   47)
* Python Enhancement Proposals; PEP 3129: PEP 3129 Class Decorators.
                                                             (line   24)
* Python Enhancement Proposals; PEP 3129 <1>: Class definitions.
                                                             (line   81)
* Python Enhancement Proposals; PEP 3131: Text Vs Data Instead Of Unicode Vs 8-bit.
                                                             (line  109)
* Python Enhancement Proposals; PEP 3131 <1>: Identifiers and keywords.
                                                             (line   10)
* Python Enhancement Proposals; PEP 3131 <2>: Identifiers and keywords.
                                                             (line   19)
* Python Enhancement Proposals; PEP 3132: New Syntax.        (line   28)
* Python Enhancement Proposals; PEP 3132 <1>: Assignment statements.
                                                             (line  159)
* Python Enhancement Proposals; PEP 3134: Changed Syntax.    (line    6)
* Python Enhancement Proposals; PEP 3134 <1>: Changes To Exceptions.
                                                             (line   40)
* Python Enhancement Proposals; PEP 3134 <2>: Changes To Exceptions.
                                                             (line   60)
* Python Enhancement Proposals; PEP 3135: Builtins.          (line    6)
* Python Enhancement Proposals; PEP 3135 <1>: Creating the class object.
                                                             (line   54)
* Python Enhancement Proposals; PEP 3137: PEP 3137 The memoryview Object.
                                                             (line   49)
* Python Enhancement Proposals; PEP 3138: Text Vs Data Instead Of Unicode Vs 8-bit.
                                                             (line  103)
* Python Enhancement Proposals; PEP 314: PEP 314 Metadata for Python Software Packages v1 1.
                                                             (line   42)
* Python Enhancement Proposals; PEP 314 <1>: distutils core — Core Distutils functionality.
                                                             (line  103)
* Python Enhancement Proposals; PEP 3141: PEP 3141 A Type Hierarchy for Numbers.
                                                             (line   43)
* Python Enhancement Proposals; PEP 3141 <1>: numbers — Numeric abstract base classes.
                                                             (line   10)
* Python Enhancement Proposals; PEP 3141 <2>: abc — Abstract Base Classes.
                                                             (line   12)
* Python Enhancement Proposals; PEP 3144: ipaddress<5>.      (line   10)
* Python Enhancement Proposals; PEP 3147: PEP 421 Adding sys implementation.
                                                             (line   21)
* Python Enhancement Proposals; PEP 3147 <1>: PEP 3147 PYC Repository Directories.
                                                             (line   69)
* Python Enhancement Proposals; PEP 3147 <2>: “Compiled” Python files.
                                                             (line   47)
* Python Enhancement Proposals; PEP 3147 <3>: Import-related module attributes.
                                                             (line   79)
* Python Enhancement Proposals; PEP 3147 <4>: test support — Utilities for the Python test suite.
                                                             (line  252)
* Python Enhancement Proposals; PEP 3147 <5>: runpy — Locating and executing Python modules.
                                                             (line   87)
* Python Enhancement Proposals; PEP 3147 <6>: Introduction<12>.
                                                             (line   81)
* Python Enhancement Proposals; PEP 3147 <7>: importlib util – Utility code for importers.
                                                             (line   24)
* Python Enhancement Proposals; PEP 3147 <8>: importlib util – Utility code for importers.
                                                             (line   60)
* Python Enhancement Proposals; PEP 3147 <9>: importlib util – Utility code for importers.
                                                             (line   64)
* Python Enhancement Proposals; PEP 3147 <10>: py_compile — Compile Python source files.
                                                             (line   30)
* Python Enhancement Proposals; PEP 3147 <11>: py_compile — Compile Python source files.
                                                             (line   69)
* Python Enhancement Proposals; PEP 3147 <12>: Command-line use.
                                                             (line   63)
* Python Enhancement Proposals; PEP 3147 <13>: Public functions.
                                                             (line   40)
* Python Enhancement Proposals; PEP 3147 <14>: Public functions.
                                                             (line  122)
* Python Enhancement Proposals; PEP 3147 <15>: imp — Access the import internals.
                                                             (line  200)
* Python Enhancement Proposals; PEP 3147 <16>: imp — Access the import internals.
                                                             (line  207)
* Python Enhancement Proposals; PEP 3147 <17>: imp — Access the import internals.
                                                             (line  230)
* Python Enhancement Proposals; PEP 3147 <18>: imp — Access the import internals.
                                                             (line  234)
* Python Enhancement Proposals; PEP 3147 <19>: imp — Access the import internals.
                                                             (line  246)
* Python Enhancement Proposals; PEP 3147 <20>: Importing Modules<2>.
                                                             (line  199)
* Python Enhancement Proposals; PEP 3147 <21>: How do I create a pyc file?.
                                                             (line   12)
* Python Enhancement Proposals; PEP 3147 <22>: distutils util — Miscellaneous other utility functions.
                                                             (line  152)
* Python Enhancement Proposals; PEP 3148: PEP 3148 The concurrent futures module.
                                                             (line   51)
* Python Enhancement Proposals; PEP 3148 <1>: Module Functions.
                                                             (line   62)
* Python Enhancement Proposals; PEP 3149: PEP 3149 ABI Version Tagged so Files.
                                                             (line   33)
* Python Enhancement Proposals; PEP 3149 <1>: Core and Builtins<70>.
                                                             (line    9)
* Python Enhancement Proposals; PEP 3149 <2>: sys — System-specific parameters and functions.
                                                             (line   15)
* Python Enhancement Proposals; PEP 3151: PEP 3151 Reworking the OS and IO exception hierarchy.
                                                             (line   84)
* Python Enhancement Proposals; PEP 3151 <1>: OS exceptions. (line  116)
* Python Enhancement Proposals; PEP 3151 <2>: Exceptions<12>.
                                                             (line   10)
* Python Enhancement Proposals; PEP 3151 <3>: select — Waiting for I/O completion.
                                                             (line   28)
* Python Enhancement Proposals; PEP 3151 <4>: resource — Resource usage information.
                                                             (line   21)
* Python Enhancement Proposals; PEP 3151 <5>: Standard Exceptions.
                                                             (line  181)
* Python Enhancement Proposals; PEP 3154: Summary – Release Highlights<2>.
                                                             (line   57)
* Python Enhancement Proposals; PEP 3154 <1>: pickle<4>.     (line   16)
* Python Enhancement Proposals; PEP 3154 <2>: Library<30>.   (line 1283)
* Python Enhancement Proposals; PEP 3154 <3>: Data stream format.
                                                             (line   42)
* Python Enhancement Proposals; PEP 3155: PEP 3155 Qualified name for classes and functions.
                                                             (line   62)
* Python Enhancement Proposals; PEP 3155 <1>: Glossary.      (line 1115)
* Python Enhancement Proposals; PEP 3156: Summary – Release Highlights<2>.
                                                             (line   31)
* Python Enhancement Proposals; PEP 3156 <1>: Summary – Release Highlights<2>.
                                                             (line   44)
* Python Enhancement Proposals; PEP 3156 <2>: asyncio<7>.    (line    6)
* Python Enhancement Proposals; PEP 3156 <3>: asyncio<7>.    (line   17)
* Python Enhancement Proposals; PEP 3156 <4>: selectors<2>.  (line    6)
* Python Enhancement Proposals; PEP 318: PEP 318 Decorators for Functions and Methods.
                                                             (line  101)
* Python Enhancement Proposals; PEP 318 <1>: PEP 318 Decorators for Functions and Methods.
                                                             (line  125)
* Python Enhancement Proposals; PEP 318 <2>: Other Language Changes<13>.
                                                             (line    9)
* Python Enhancement Proposals; PEP 318 <3>: Class definitions.
                                                             (line   84)
* Python Enhancement Proposals; PEP 322: PEP 322 Reverse Iteration.
                                                             (line   35)
* Python Enhancement Proposals; PEP 322 <1>: Other Language Changes<13>.
                                                             (line   13)
* Python Enhancement Proposals; PEP 324: PEP 324 New subprocess Module.
                                                             (line   86)
* Python Enhancement Proposals; PEP 324 <1>: subprocess — Subprocess management.
                                                             (line   25)
* Python Enhancement Proposals; PEP 325: PEP 342 New Generator Features.
                                                             (line  147)
* Python Enhancement Proposals; PEP 327: The Context type.   (line   56)
* Python Enhancement Proposals; PEP 328: Porting Python code.
                                                             (line   36)
* Python Enhancement Proposals; PEP 328 <1>: Removed Syntax. (line   29)
* Python Enhancement Proposals; PEP 328 <2>: PEP 328 Absolute and Relative Imports.
                                                             (line    6)
* Python Enhancement Proposals; PEP 328 <3>: PEP 328 Absolute and Relative Imports.
                                                             (line   82)
* Python Enhancement Proposals; PEP 328 <4>: PEP 328 Multi-line Imports.
                                                             (line   35)
* Python Enhancement Proposals; PEP 328 <5>: Other Language Changes<13>.
                                                             (line   21)
* Python Enhancement Proposals; PEP 328 <6>: References.     (line   20)
* Python Enhancement Proposals; PEP 328 <7>: Built-in Functions.
                                                             (line 1826)
* Python Enhancement Proposals; PEP 328 <8>: __future__ — Future statement definitions.
                                                             (line   80)
* Python Enhancement Proposals; PEP 328 <9>: Introduction<12>.
                                                             (line   49)
* Python Enhancement Proposals; PEP 331: PEP 331 Locale-Independent Float/String Conversions.
                                                             (line   38)
* Python Enhancement Proposals; PEP 333: The wsgiref package.
                                                             (line    8)
* Python Enhancement Proposals; PEP 333 <1>: The wsgiref package.
                                                             (line   31)
* Python Enhancement Proposals; PEP 3333: PEP 3333 Python Web Server Gateway Interface v1 0 1.
                                                             (line   50)
* Python Enhancement Proposals; PEP 3333 <1>: wsgiref — WSGI Utilities and Reference Implementation.
                                                             (line   24)
* Python Enhancement Proposals; PEP 3333 <2>: wsgiref util – WSGI environment utilities.
                                                             (line    8)
* Python Enhancement Proposals; PEP 3333 <3>: wsgiref util – WSGI environment utilities.
                                                             (line   10)
* Python Enhancement Proposals; PEP 3333 <4>: wsgiref util – WSGI environment utilities.
                                                             (line   28)
* Python Enhancement Proposals; PEP 3333 <5>: wsgiref util – WSGI environment utilities.
                                                             (line   74)
* Python Enhancement Proposals; PEP 3333 <6>: wsgiref headers – WSGI response header tools.
                                                             (line   12)
* Python Enhancement Proposals; PEP 3333 <7>: wsgiref simple_server – a simple WSGI HTTP server.
                                                             (line   21)
* Python Enhancement Proposals; PEP 3333 <8>: wsgiref simple_server – a simple WSGI HTTP server.
                                                             (line   96)
* Python Enhancement Proposals; PEP 3333 <9>: wsgiref validate — WSGI conformance checker.
                                                             (line   13)
* Python Enhancement Proposals; PEP 3333 <10>: wsgiref validate — WSGI conformance checker.
                                                             (line   40)
* Python Enhancement Proposals; PEP 3333 <11>: wsgiref handlers – server/gateway base classes.
                                                             (line  234)
* Python Enhancement Proposals; PEP 3333 <12>: wsgiref handlers – server/gateway base classes.
                                                             (line  250)
* Python Enhancement Proposals; PEP 3333 <13>: wsgiref handlers – server/gateway base classes.
                                                             (line  257)
* Python Enhancement Proposals; PEP 3333 <14>: wsgiref handlers – server/gateway base classes.
                                                             (line  266)
* Python Enhancement Proposals; PEP 3333 <15>: wsgiref handlers – server/gateway base classes.
                                                             (line  308)
* Python Enhancement Proposals; PEP 338: PEP 338 Executing Modules as Scripts.
                                                             (line   21)
* Python Enhancement Proposals; PEP 338 <1>: Interface options.
                                                             (line  100)
* Python Enhancement Proposals; PEP 338 <2>: References.     (line   24)
* Python Enhancement Proposals; PEP 338 <3>: runpy — Locating and executing Python modules.
                                                             (line  171)
* Python Enhancement Proposals; PEP 339: Build and C API Changes<10>.
                                                             (line   45)
* Python Enhancement Proposals; PEP 341: PEP 341 Unified try/except/finally.
                                                             (line   44)
* Python Enhancement Proposals; PEP 342: PEP 342 New Generator Features.
                                                             (line   42)
* Python Enhancement Proposals; PEP 342 <1>: PEP 342 New Generator Features.
                                                             (line  140)
* Python Enhancement Proposals; PEP 342 <2>: Porting to Python 2 5.
                                                             (line   15)
* Python Enhancement Proposals; PEP 342 <3>: Yield expressions.
                                                             (line   93)
* Python Enhancement Proposals; PEP 342 <4>: Collections Abstract Base Classes.
                                                             (line  152)
* Python Enhancement Proposals; PEP 342 <5>: Passing values into a generator.
                                                             (line   25)
* Python Enhancement Proposals; PEP 342 <6>: Python documentation.
                                                             (line   14)
* Python Enhancement Proposals; PEP 343: The contextlib module.
                                                             (line   64)
* Python Enhancement Proposals; PEP 343 <1>: PEP 342 New Generator Features.
                                                             (line  129)
* Python Enhancement Proposals; PEP 343 <2>: The contextlib module<2>.
                                                             (line   64)
* Python Enhancement Proposals; PEP 343 <3>: With Statement Context Managers.
                                                             (line   45)
* Python Enhancement Proposals; PEP 343 <4>: The with statement.
                                                             (line   98)
* Python Enhancement Proposals; PEP 343 <5>: Using a context manager as a function decorator.
                                                             (line   51)
* Python Enhancement Proposals; PEP 343 <6>: __future__ — Future statement definitions.
                                                             (line   84)
* Python Enhancement Proposals; PEP 343 <7>: Glossary.       (line  259)
* Python Enhancement Proposals; PEP 347: Build and C API Changes<10>.
                                                             (line   10)
* Python Enhancement Proposals; PEP 352: Changes To Exceptions.
                                                             (line    9)
* Python Enhancement Proposals; PEP 352 <1>: Deprecations and Removals.
                                                             (line    9)
* Python Enhancement Proposals; PEP 352 <2>: PEP 352 Exceptions as New-Style Classes.
                                                             (line   57)
* Python Enhancement Proposals; PEP 353: PEP 353 Using ssize_t as the index type.
                                                             (line   48)
* Python Enhancement Proposals; PEP 353 <1>: PEP 353 Using ssize_t as the index type.
                                                             (line   54)
* Python Enhancement Proposals; PEP 353 <2>: Build and C API Changes<10>.
                                                             (line   20)
* Python Enhancement Proposals; PEP 356: What’s New in Python 2 5.
                                                             (line   10)
* Python Enhancement Proposals; PEP 357: PEP 357 The ‘__index__’ method.
                                                             (line   39)
* Python Enhancement Proposals; PEP 361: What’s New in Python 2 6.
                                                             (line   10)
* Python Enhancement Proposals; PEP 362: PEP 362 Function Signature Object.
                                                             (line   19)
* Python Enhancement Proposals; PEP 362 <1>: Introspecting callables with the Signature object.
                                                             (line  346)
* Python Enhancement Proposals; PEP 362 <2>: Glossary.       (line   94)
* Python Enhancement Proposals; PEP 362 <3>: Glossary.       (line  999)
* Python Enhancement Proposals; PEP 366: Visible Changes.    (line   24)
* Python Enhancement Proposals; PEP 366 <1>: Import-related module attributes.
                                                             (line   30)
* Python Enhancement Proposals; PEP 366 <2>: Import-related module attributes.
                                                             (line   34)
* Python Enhancement Proposals; PEP 366 <3>: References.     (line   17)
* Python Enhancement Proposals; PEP 366 <4>: References.     (line   21)
* Python Enhancement Proposals; PEP 366 <5>: runpy — Locating and executing Python modules.
                                                             (line  175)
* Python Enhancement Proposals; PEP 366 <6>: Introduction<12>.
                                                             (line   53)
* Python Enhancement Proposals; PEP 370: PEP 370 Per-user site-packages Directory.
                                                             (line   36)
* Python Enhancement Proposals; PEP 370 <1>: Miscellaneous options.
                                                             (line  125)
* Python Enhancement Proposals; PEP 370 <2>: Environment variables.
                                                             (line  184)
* Python Enhancement Proposals; PEP 370 <3>: Environment variables.
                                                             (line  196)
* Python Enhancement Proposals; PEP 370 <4>: Command Line Interface<4>.
                                                             (line   37)
* Python Enhancement Proposals; PEP 371: PEP 371 The multiprocessing Package.
                                                             (line  145)
* Python Enhancement Proposals; PEP 372: PEP 372 Ordered Dictionaries.
                                                             (line   31)
* Python Enhancement Proposals; PEP 372 <1>: PEP 372 Adding an Ordered Dictionary to collections.
                                                             (line   97)
* Python Enhancement Proposals; PEP 373: The Future for Python 2 x.
                                                             (line   23)
* Python Enhancement Proposals; PEP 378: PEP 378 Format Specifier for Thousands Separator.
                                                             (line   32)
* Python Enhancement Proposals; PEP 378 <1>: PEP 378 Format Specifier for Thousands Separator<2>.
                                                             (line   37)
* Python Enhancement Proposals; PEP 378 <2>: Format Specification Mini-Language.
                                                             (line  103)
* Python Enhancement Proposals; PEP 380: PEP 380 Syntax for Delegating to a Subgenerator.
                                                             (line   66)
* Python Enhancement Proposals; PEP 380 <1>: Yield expressions.
                                                             (line   98)
* Python Enhancement Proposals; PEP 383: Error Handlers.     (line   58)
* Python Enhancement Proposals; PEP 383 <1>: Socket families.
                                                             (line   15)
* Python Enhancement Proposals; PEP 383 <2>: Locale Encoding.
                                                             (line   14)
* Python Enhancement Proposals; PEP 383 <3>: Locale Encoding.
                                                             (line   50)
* Python Enhancement Proposals; PEP 383 <4>: File System Encoding.
                                                             (line    9)
* Python Enhancement Proposals; PEP 384: PEP 384 Defining a Stable ABI.
                                                             (line   24)
* Python Enhancement Proposals; PEP 384 <1>: Stable Application Binary Interface.
                                                             (line   36)
* Python Enhancement Proposals; PEP 385: Code Repository.    (line   13)
* Python Enhancement Proposals; PEP 387: Warnings.           (line   26)
* Python Enhancement Proposals; PEP 387 <1>: Warnings.       (line   41)
* Python Enhancement Proposals; PEP 389: PEP 389 Argparse Command Line Parsing Module.
                                                             (line   92)
* Python Enhancement Proposals; PEP 389 <1>: PEP 389 The argparse Module for Parsing Command Lines.
                                                             (line  100)
* Python Enhancement Proposals; PEP 391: PEP 391 Dictionary Based Configuration for Logging.
                                                             (line   52)
* Python Enhancement Proposals; PEP 391 <1>: PEP 391 Dictionary-Based Configuration For Logging.
                                                             (line   94)
* Python Enhancement Proposals; PEP 392: What’s New In Python 3 2.
                                                             (line   16)
* Python Enhancement Proposals; PEP 393: Porting to Python 3 9<2>.
                                                             (line   46)
* Python Enhancement Proposals; PEP 393 <1>: Removed<2>.     (line  101)
* Python Enhancement Proposals; PEP 393 <2>: PEP 393 Flexible String Representation.
                                                             (line   16)
* Python Enhancement Proposals; PEP 393 <3>: Functionality.  (line    6)
* Python Enhancement Proposals; PEP 393 <4>: Performance and resource usage.
                                                             (line   29)
* Python Enhancement Proposals; PEP 393 <5>: Optimizations<6>.
                                                             (line    8)
* Python Enhancement Proposals; PEP 393 <6>: Build and C API Changes<4>.
                                                             (line   12)
* Python Enhancement Proposals; PEP 393 <7>: Deprecated Python modules functions and methods<4>.
                                                             (line   10)
* Python Enhancement Proposals; PEP 393 <8>: Deprecated functions and types of the C API<3>.
                                                             (line    6)
* Python Enhancement Proposals; PEP 393 <9>: Porting C code. (line   17)
* Python Enhancement Proposals; PEP 393 <10>: Encodings and Unicode.
                                                             (line    7)
* Python Enhancement Proposals; PEP 393 <11>: sys — System-specific parameters and functions.
                                                             (line 1017)
* Python Enhancement Proposals; PEP 393 <12>: Unicode Objects.
                                                             (line    6)
* Python Enhancement Proposals; PEP 393 <13>: Deprecated Py_UNICODE APIs.
                                                             (line    8)
* Python Enhancement Proposals; PEP 395: Open issues.        (line   18)
* Python Enhancement Proposals; PEP 397: PEP 486 Make the Python Launcher aware of virtual environments.
                                                             (line    6)
* Python Enhancement Proposals; PEP 397 <1>: PEP 397 Python Launcher for Windows.
                                                             (line   31)
* Python Enhancement Proposals; PEP 397 <2>: Python Launcher for Windows.
                                                             (line   18)
* Python Enhancement Proposals; PEP 397 <3>: Creating virtual environments.
                                                             (line  200)
* Python Enhancement Proposals; PEP 398: What’s New In Python 3 3.
                                                             (line   13)
* Python Enhancement Proposals; PEP 4:   Library Changes.    (line   13)
* Python Enhancement Proposals; PEP 405: PEP 405 Virtual Environments.
                                                             (line   22)
* Python Enhancement Proposals; PEP 405 <1>: venv — Creation of virtual environments.
                                                             (line   19)
* Python Enhancement Proposals; PEP 409: PEP 409 Suppressing exception context.
                                                             (line   63)
* Python Enhancement Proposals; PEP 411: sys — System-specific parameters and functions.
                                                             (line  815)
* Python Enhancement Proposals; PEP 411 <1>: sys — System-specific parameters and functions.
                                                             (line  825)
* Python Enhancement Proposals; PEP 411 <2>: sys — System-specific parameters and functions.
                                                             (line 1433)
* Python Enhancement Proposals; PEP 411 <3>: sys — System-specific parameters and functions.
                                                             (line 1453)
* Python Enhancement Proposals; PEP 411 <4>: Glossary.       (line 1082)
* Python Enhancement Proposals; PEP 412: PEP 412 Key-Sharing Dictionary.
                                                             (line   15)
* Python Enhancement Proposals; PEP 412 <1>: functools — Higher-order functions and operations on callable objects.
                                                             (line   74)
* Python Enhancement Proposals; PEP 414: PEP 414 Explicit Unicode literals.
                                                             (line   17)
* Python Enhancement Proposals; PEP 414 <1>: String and Bytes literals.
                                                             (line   60)
* Python Enhancement Proposals; PEP 418: time<6>.            (line    6)
* Python Enhancement Proposals; PEP 420: PEP 420 Implicit Namespace Packages.
                                                             (line    9)
* Python Enhancement Proposals; PEP 420 <1>: PEP 420 Implicit Namespace Packages.
                                                             (line   14)
* Python Enhancement Proposals; PEP 420 <2>: Core and Builtins<55>.
                                                             (line   56)
* Python Enhancement Proposals; PEP 420 <3>: Core and Builtins<60>.
                                                             (line  114)
* Python Enhancement Proposals; PEP 420 <4>: The import system.
                                                             (line   45)
* Python Enhancement Proposals; PEP 420 <5>: Namespace packages.
                                                             (line   27)
* Python Enhancement Proposals; PEP 420 <6>: module __path__.
                                                             (line   21)
* Python Enhancement Proposals; PEP 420 <7>: module __path__.
                                                             (line   21)
* Python Enhancement Proposals; PEP 420 <8>: References.     (line   11)
* Python Enhancement Proposals; PEP 420 <9>: References.     (line   13)
* Python Enhancement Proposals; PEP 420 <10>: References.    (line   13)
* Python Enhancement Proposals; PEP 420 <11>: Introduction<12>.
                                                             (line   57)
* Python Enhancement Proposals; PEP 420 <12>: Glossary.      (line  451)
* Python Enhancement Proposals; PEP 420 <13>: Glossary.      (line  909)
* Python Enhancement Proposals; PEP 420 <14>: Glossary.      (line 1057)
* Python Enhancement Proposals; PEP 421: SimpleNamespace.    (line   16)
* Python Enhancement Proposals; PEP 421 <1>: sys — System-specific parameters and functions.
                                                             (line  927)
* Python Enhancement Proposals; PEP 421 <2>: sys — System-specific parameters and functions.
                                                             (line  932)
* Python Enhancement Proposals; PEP 424: Other Language Changes<6>.
                                                             (line   57)
* Python Enhancement Proposals; PEP 424 <1>: operator<2>.    (line    8)
* Python Enhancement Proposals; PEP 427: Key terms.          (line   36)
* Python Enhancement Proposals; PEP 428: Summary – Release Highlights<2>.
                                                             (line   39)
* Python Enhancement Proposals; PEP 428 <1>: pathlib<6>.     (line   17)
* Python Enhancement Proposals; PEP 428 <2>: pathlib — Object-oriented filesystem paths.
                                                             (line   39)
* Python Enhancement Proposals; PEP 429: What’s New In Python 3 4.
                                                             (line   16)
* Python Enhancement Proposals; PEP 432: Other CPython implementation changes.
                                                             (line    7)
* Python Enhancement Proposals; PEP 432 <1>: Core and Builtins<38>.
                                                             (line  313)
* Python Enhancement Proposals; PEP 432 <2>: Multi-Phase Initialization Private Provisional API.
                                                             (line    7)
* Python Enhancement Proposals; PEP 432 <3>: Multi-Phase Initialization Private Provisional API.
                                                             (line   60)
* Python Enhancement Proposals; PEP 434: PEP 434 IDLE Enhancement Exception for All Branches.
                                                             (line    6)
* Python Enhancement Proposals; PEP 435: Summary – Release Highlights<2>.
                                                             (line   36)
* Python Enhancement Proposals; PEP 435 <1>: enum<5>.        (line    6)
* Python Enhancement Proposals; PEP 435 <2>: enum<5>.        (line   15)
* Python Enhancement Proposals; PEP 436: Summary – Release Highlights<2>.
                                                             (line  120)
* Python Enhancement Proposals; PEP 436 <1>: PEP 436 Argument Clinic.
                                                             (line    6)
* Python Enhancement Proposals; PEP 436 <2>: PEP 436 Argument Clinic.
                                                             (line   28)
* Python Enhancement Proposals; PEP 441: zipapp<2>.          (line    6)
* Python Enhancement Proposals; PEP 441 <1>: zipapp<2>.      (line   24)
* Python Enhancement Proposals; PEP 442: Removed.            (line   69)
* Python Enhancement Proposals; PEP 442 <1>: Summary – Release Highlights<2>.
                                                             (line  113)
* Python Enhancement Proposals; PEP 442 <2>: Summary – Release Highlights<2>.
                                                             (line  115)
* Python Enhancement Proposals; PEP 442 <3>: PEP 442 Safe Object Finalization.
                                                             (line    6)
* Python Enhancement Proposals; PEP 442 <4>: PEP 442 Safe Object Finalization.
                                                             (line   21)
* Python Enhancement Proposals; PEP 442 <5>: C API<16>.      (line   57)
* Python Enhancement Proposals; PEP 442 <6>: gc — Garbage Collector interface.
                                                             (line  245)
* Python Enhancement Proposals; PEP 442 <7>: Finalization and De-allocation.
                                                             (line   89)
* Python Enhancement Proposals; PEP 442 <8>: PyTypeObject Slots.
                                                             (line 1392)
* Python Enhancement Proposals; PEP 443: Summary – Release Highlights<2>.
                                                             (line   55)
* Python Enhancement Proposals; PEP 443 <1>: functools<4>.   (line   22)
* Python Enhancement Proposals; PEP 443 <2>: Glossary.       (line  548)
* Python Enhancement Proposals; PEP 445: Summary – Release Highlights<2>.
                                                             (line  118)
* Python Enhancement Proposals; PEP 445 <1>: PEP 445 Customization of CPython Memory Allocators.
                                                             (line    6)
* Python Enhancement Proposals; PEP 445 <2>: PEP 445 Customization of CPython Memory Allocators.
                                                             (line   12)
* Python Enhancement Proposals; PEP 445 <3>: Other Improvements<2>.
                                                             (line   63)
* Python Enhancement Proposals; PEP 446: Summary – Release Highlights<2>.
                                                             (line   14)
* Python Enhancement Proposals; PEP 446 <1>: Summary – Release Highlights<2>.
                                                             (line   78)
* Python Enhancement Proposals; PEP 446 <2>: PEP 446 Newly Created File Descriptors Are Non-Inheritable.
                                                             (line    6)
* Python Enhancement Proposals; PEP 446 <3>: PEP 446 Newly Created File Descriptors Are Non-Inheritable.
                                                             (line   26)
* Python Enhancement Proposals; PEP 448: PEP 448 - Additional Unpacking Generalizations.
                                                             (line    6)
* Python Enhancement Proposals; PEP 448 <1>: PEP 448 - Additional Unpacking Generalizations.
                                                             (line   39)
* Python Enhancement Proposals; PEP 448 <2>: Documentation<45>.
                                                             (line   10)
* Python Enhancement Proposals; PEP 448 <3>: Documentation<49>.
                                                             (line    9)
* Python Enhancement Proposals; PEP 448 <4>: Core and Builtins<63>.
                                                             (line   12)
* Python Enhancement Proposals; PEP 448 <5>: Core and Builtins<66>.
                                                             (line    9)
* Python Enhancement Proposals; PEP 448 <6>: Dictionary displays.
                                                             (line   29)
* Python Enhancement Proposals; PEP 448 <7>: Calls.          (line  113)
* Python Enhancement Proposals; PEP 448 <8>: Expression lists.
                                                             (line   22)
* Python Enhancement Proposals; PEP 450: Summary – Release Highlights<2>.
                                                             (line   47)
* Python Enhancement Proposals; PEP 450 <1>: statistics<3>.  (line    6)
* Python Enhancement Proposals; PEP 450 <2>: statistics<3>.  (line   14)
* Python Enhancement Proposals; PEP 451: PEP 489 Multi-phase extension module initialization.
                                                             (line    7)
* Python Enhancement Proposals; PEP 451 <1>: Summary – Release Highlights<2>.
                                                             (line   22)
* Python Enhancement Proposals; PEP 451 <2>: PEP 451 A ModuleSpec Type for the Import System.
                                                             (line    6)
* Python Enhancement Proposals; PEP 451 <3>: Core and Builtins<55>.
                                                             (line   76)
* Python Enhancement Proposals; PEP 451 <4>: References.     (line   26)
* Python Enhancement Proposals; PEP 451 <5>: sys — System-specific parameters and functions.
                                                             (line 1047)
* Python Enhancement Proposals; PEP 451 <6>: pkgutil — Package extension utility.
                                                             (line   90)
* Python Enhancement Proposals; PEP 451 <7>: pkgutil — Package extension utility.
                                                             (line  121)
* Python Enhancement Proposals; PEP 451 <8>: runpy — Locating and executing Python modules.
                                                             (line   91)
* Python Enhancement Proposals; PEP 451 <9>: runpy — Locating and executing Python modules.
                                                             (line  164)
* Python Enhancement Proposals; PEP 451 <10>: runpy — Locating and executing Python modules.
                                                             (line  179)
* Python Enhancement Proposals; PEP 451 <11>: Introduction<12>.
                                                             (line   61)
* Python Enhancement Proposals; PEP 451 <12>: Multi-phase initialization.
                                                             (line   72)
* Python Enhancement Proposals; PEP 451 <13>: Glossary.      (line  451)
* Python Enhancement Proposals; PEP 453: Summary – Release Highlights<2>.
                                                             (line   12)
* Python Enhancement Proposals; PEP 453 <1>: Summary – Release Highlights<2>.
                                                             (line   34)
* Python Enhancement Proposals; PEP 453 <2>: Bootstrapping pip By Default.
                                                             (line    6)
* Python Enhancement Proposals; PEP 453 <3>: Documentation Changes.
                                                             (line   21)
* Python Enhancement Proposals; PEP 453 <4>: ensurepip.      (line    7)
* Python Enhancement Proposals; PEP 453 <5>: venv<5>.        (line   13)
* Python Enhancement Proposals; PEP 453 <6>: Other Improvements<2>.
                                                             (line   73)
* Python Enhancement Proposals; PEP 453 <7>: PEP 477 Backport ensurepip PEP 453 to Python 2 7.
                                                             (line    6)
* Python Enhancement Proposals; PEP 453 <8>: Bootstrapping pip By Default<2>.
                                                             (line    6)
* Python Enhancement Proposals; PEP 453 <9>: Documentation Changes<2>.
                                                             (line   21)
* Python Enhancement Proposals; PEP 453 <10>: ensurepip — Bootstrapping the pip installer.
                                                             (line   33)
* Python Enhancement Proposals; PEP 454: Summary – Release Highlights<2>.
                                                             (line   50)
* Python Enhancement Proposals; PEP 454 <1>: tracemalloc<4>. (line    6)
* Python Enhancement Proposals; PEP 454 <2>: tracemalloc<4>. (line   22)
* Python Enhancement Proposals; PEP 456: Summary – Release Highlights<2>.
                                                             (line   75)
* Python Enhancement Proposals; PEP 456 <1>: PEP 456 Secure and Interchangeable Hash Algorithm.
                                                             (line    6)
* Python Enhancement Proposals; PEP 461: PEP 461 - percent formatting support for bytes and bytearray.
                                                             (line    6)
* Python Enhancement Proposals; PEP 461 <1>: PEP 461 - percent formatting support for bytes and bytearray.
                                                             (line   41)
* Python Enhancement Proposals; PEP 461 <2>: printf-style Bytes Formatting.
                                                             (line  198)
* Python Enhancement Proposals; PEP 465: PEP 465 - A dedicated infix operator for matrix multiplication.
                                                             (line    6)
* Python Enhancement Proposals; PEP 465 <1>: PEP 465 - A dedicated infix operator for matrix multiplication.
                                                             (line   45)
* Python Enhancement Proposals; PEP 465 <2>: Build and C API Changes<3>.
                                                             (line   43)
* Python Enhancement Proposals; PEP 465 <3>: Tools/Demos<35>.
                                                             (line   39)
* Python Enhancement Proposals; PEP 466: PEP 466 Network Security Enhancements for Python 2 7.
                                                             (line    6)
* Python Enhancement Proposals; PEP 466 <1>: PEP 466 Network Security Enhancements for Python 2 7.
                                                             (line   11)
* Python Enhancement Proposals; PEP 466 <2>: PEP 466 Network Security Enhancements for Python 2 7.
                                                             (line   21)
* Python Enhancement Proposals; PEP 466 <3>: PEP 466 Network Security Enhancements for Python 2 7.
                                                             (line   32)
* Python Enhancement Proposals; PEP 468: PEP 468 Preserving Keyword Argument Order.
                                                             (line   12)
* Python Enhancement Proposals; PEP 468 <1>: Library<49>.    (line   87)
* Python Enhancement Proposals; PEP 468 <2>: OrderedDict objects.
                                                             (line   85)
* Python Enhancement Proposals; PEP 471: PEP 471 - os scandir function – a better and faster directory iterator.
                                                             (line    6)
* Python Enhancement Proposals; PEP 471 <1>: PEP 471 - os scandir function – a better and faster directory iterator.
                                                             (line   29)
* Python Enhancement Proposals; PEP 471 <2>: Library<88>.    (line    6)
* Python Enhancement Proposals; PEP 475: PEP 475 Retry system calls failing with EINTR.
                                                             (line   32)
* Python Enhancement Proposals; PEP 475 <1>: PEP 475 Retry system calls failing with EINTR.
                                                             (line   77)
* Python Enhancement Proposals; PEP 475 <2>: Changes in the Python API<5>.
                                                             (line    6)
* Python Enhancement Proposals; PEP 475 <3>: Library<39>.    (line  229)
* Python Enhancement Proposals; PEP 475 <4>: Library<86>.    (line  143)
* Python Enhancement Proposals; PEP 475 <5>: Built-in Functions.
                                                             (line 1257)
* Python Enhancement Proposals; PEP 475 <6>: OS exceptions.  (line   78)
* Python Enhancement Proposals; PEP 475 <7>: File Descriptor Operations.
                                                             (line  293)
* Python Enhancement Proposals; PEP 475 <8>: File Descriptor Operations.
                                                             (line  573)
* Python Enhancement Proposals; PEP 475 <9>: File Descriptor Operations.
                                                             (line  696)
* Python Enhancement Proposals; PEP 475 <10>: Process Management.
                                                             (line  850)
* Python Enhancement Proposals; PEP 475 <11>: Functions<3>.  (line  228)
* Python Enhancement Proposals; PEP 475 <12>: Socket Objects.
                                                             (line   28)
* Python Enhancement Proposals; PEP 475 <13>: Socket Objects.
                                                             (line   80)
* Python Enhancement Proposals; PEP 475 <14>: Socket Objects.
                                                             (line  234)
* Python Enhancement Proposals; PEP 475 <15>: Socket Objects.
                                                             (line  248)
* Python Enhancement Proposals; PEP 475 <16>: Socket Objects.
                                                             (line  323)
* Python Enhancement Proposals; PEP 475 <17>: Socket Objects.
                                                             (line  395)
* Python Enhancement Proposals; PEP 475 <18>: Socket Objects.
                                                             (line  414)
* Python Enhancement Proposals; PEP 475 <19>: Socket Objects.
                                                             (line  433)
* Python Enhancement Proposals; PEP 475 <20>: Socket Objects.
                                                             (line  475)
* Python Enhancement Proposals; PEP 475 <21>: select — Waiting for I/O completion.
                                                             (line  154)
* Python Enhancement Proposals; PEP 475 <22>: /dev/poll Polling Objects.
                                                             (line   82)
* Python Enhancement Proposals; PEP 475 <23>: Edge and Level Trigger Polling epoll Objects.
                                                             (line  102)
* Python Enhancement Proposals; PEP 475 <24>: Polling Objects.
                                                             (line   94)
* Python Enhancement Proposals; PEP 475 <25>: Kqueue Objects.
                                                             (line   36)
* Python Enhancement Proposals; PEP 475 <26>: Classes<3>.    (line  133)
* Python Enhancement Proposals; PEP 475 <27>: Module contents<2>.
                                                             (line  532)
* Python Enhancement Proposals; PEP 475 <28>: Module contents<2>.
                                                             (line  550)
* Python Enhancement Proposals; PEP 476: PEP 476 Enabling certificate verification by default for stdlib http clients<2>.
                                                             (line    6)
* Python Enhancement Proposals; PEP 477: PEP 477 Backport ensurepip PEP 453 to Python 2 7.
                                                             (line    6)
* Python Enhancement Proposals; PEP 478: What’s New In Python 3 5.
                                                             (line   17)
* Python Enhancement Proposals; PEP 479: Changes in Python Behavior.
                                                             (line   11)
* Python Enhancement Proposals; PEP 479 <1>: PEP 479 Change StopIteration handling inside generators.
                                                             (line   12)
* Python Enhancement Proposals; PEP 479 <2>: PEP 479 Change StopIteration handling inside generators.
                                                             (line   47)
* Python Enhancement Proposals; PEP 479 <3>: Library<30>.    (line 1271)
* Python Enhancement Proposals; PEP 479 <4>: Library<34>.    (line   52)
* Python Enhancement Proposals; PEP 479 <5>: Core and Builtins<34>.
                                                             (line   34)
* Python Enhancement Proposals; PEP 479 <6>: Library<42>.    (line   95)
* Python Enhancement Proposals; PEP 479 <7>: Library<56>.    (line   80)
* Python Enhancement Proposals; PEP 479 <8>: Library<69>.    (line  326)
* Python Enhancement Proposals; PEP 479 <9>: Concrete exceptions.
                                                             (line  234)
* Python Enhancement Proposals; PEP 479 <10>: Concrete exceptions.
                                                             (line  236)
* Python Enhancement Proposals; PEP 479 <11>: __future__ — Future statement definitions.
                                                             (line   93)
* Python Enhancement Proposals; PEP 483: PEP 484 - Type Hints.
                                                             (line   47)
* Python Enhancement Proposals; PEP 483 <1>: typing — Support for type hints.
                                                             (line   20)
* Python Enhancement Proposals; PEP 483 <2>: Relevant PEPs.  (line    6)
* Python Enhancement Proposals; PEP 483 <3>: Glossary.       (line  556)
* Python Enhancement Proposals; PEP 484: ast<2>.             (line   17)
* Python Enhancement Proposals; PEP 484 <1>: ast<2>.         (line   20)
* Python Enhancement Proposals; PEP 484 <2>: PEP 560 Core Support for typing module and Generic Types.
                                                             (line    6)
* Python Enhancement Proposals; PEP 484 <3>: PEP 526 Syntax for variable annotations.
                                                             (line    6)
* Python Enhancement Proposals; PEP 484 <4>: PEP 484 - Type Hints.
                                                             (line   16)
* Python Enhancement Proposals; PEP 484 <5>: PEP 484 - Type Hints.
                                                             (line   41)
* Python Enhancement Proposals; PEP 484 <6>: Function Annotations.
                                                             (line    8)
* Python Enhancement Proposals; PEP 484 <7>: Emulating generic types.
                                                             (line   15)
* Python Enhancement Proposals; PEP 484 <8>: Annotated assignment statements.
                                                             (line   45)
* Python Enhancement Proposals; PEP 484 <9>: Function definitions.
                                                             (line  135)
* Python Enhancement Proposals; PEP 484 <10>: typing — Support for type hints.
                                                             (line   19)
* Python Enhancement Proposals; PEP 484 <11>: Relevant PEPs. (line    6)
* Python Enhancement Proposals; PEP 484 <12>: NewType.       (line   64)
* Python Enhancement Proposals; PEP 484 <13>: Nominal vs structural subtyping.
                                                             (line    6)
* Python Enhancement Proposals; PEP 484 <14>: Nominal vs structural subtyping.
                                                             (line   14)
* Python Enhancement Proposals; PEP 484 <15>: Special forms. (line  130)
* Python Enhancement Proposals; PEP 484 <16>: Building generic types.
                                                             (line   66)
* Python Enhancement Proposals; PEP 484 <17>: Building generic types.
                                                             (line   71)
* Python Enhancement Proposals; PEP 484 <18>: Functions and decorators.
                                                             (line   42)
* Python Enhancement Proposals; PEP 484 <19>: ast Helpers.   (line   16)
* Python Enhancement Proposals; PEP 484 <20>: ast Helpers.   (line   26)
* Python Enhancement Proposals; PEP 484 <21>: Compiler Flags.
                                                             (line   23)
* Python Enhancement Proposals; PEP 484 <22>: Glossary.      (line   61)
* Python Enhancement Proposals; PEP 484 <23>: Glossary.      (line  484)
* Python Enhancement Proposals; PEP 484 <24>: Glossary.      (line  556)
* Python Enhancement Proposals; PEP 484 <25>: Glossary.      (line 1269)
* Python Enhancement Proposals; PEP 484 <26>: Glossary.      (line 1286)
* Python Enhancement Proposals; PEP 484 <27>: Glossary.      (line 1316)
* Python Enhancement Proposals; PEP 485: PEP 485 A function for testing approximate equality.
                                                             (line    6)
* Python Enhancement Proposals; PEP 485 <1>: PEP 485 A function for testing approximate equality.
                                                             (line   36)
* Python Enhancement Proposals; PEP 485 <2>: Library<84>.    (line   10)
* Python Enhancement Proposals; PEP 485 <3>: Number-theoretic and representation functions.
                                                             (line  142)
* Python Enhancement Proposals; PEP 485 <4>: Classification functions.
                                                             (line   54)
* Python Enhancement Proposals; PEP 486: PEP 486 Make the Python Launcher aware of virtual environments.
                                                             (line    6)
* Python Enhancement Proposals; PEP 486 <1>: PEP 486 Make the Python Launcher aware of virtual environments.
                                                             (line   14)
* Python Enhancement Proposals; PEP 486 <2>: Windows<53>.    (line    6)
* Python Enhancement Proposals; PEP 487: PEP 487 Simpler customization of class creation.
                                                             (line   32)
* Python Enhancement Proposals; PEP 487 <1>: PEP 487 Descriptor Protocol Enhancements.
                                                             (line    6)
* Python Enhancement Proposals; PEP 487 <2>: PEP 487 Descriptor Protocol Enhancements.
                                                             (line   33)
* Python Enhancement Proposals; PEP 487 <3>: Changes in the Python API<4>.
                                                             (line  104)
* Python Enhancement Proposals; PEP 487 <4>: Documentation<35>.
                                                             (line   52)
* Python Enhancement Proposals; PEP 487 <5>: Documentation<42>.
                                                             (line    8)
* Python Enhancement Proposals; PEP 487 <6>: Core and Builtins<52>.
                                                             (line   46)
* Python Enhancement Proposals; PEP 488: PEP 488 Elimination of PYO files.
                                                             (line    6)
* Python Enhancement Proposals; PEP 488 <1>: PEP 488 Elimination of PYO files.
                                                             (line   20)
* Python Enhancement Proposals; PEP 488 <2>: Changes in the Python API<5>.
                                                             (line   79)
* Python Enhancement Proposals; PEP 488 <3>: Core and Builtins<70>.
                                                             (line   15)
* Python Enhancement Proposals; PEP 488 <4>: Miscellaneous options.
                                                             (line   71)
* Python Enhancement Proposals; PEP 488 <5>: Miscellaneous options.
                                                             (line   73)
* Python Enhancement Proposals; PEP 488 <6>: Miscellaneous options.
                                                             (line   80)
* Python Enhancement Proposals; PEP 488 <7>: Miscellaneous options.
                                                             (line   82)
* Python Enhancement Proposals; PEP 488 <8>: test support — Utilities for the Python test suite.
                                                             (line  252)
* Python Enhancement Proposals; PEP 488 <9>: Introduction<12>.
                                                             (line   65)
* Python Enhancement Proposals; PEP 488 <10>: importlib util – Utility code for importers.
                                                             (line   24)
* Python Enhancement Proposals; PEP 488 <11>: importlib util – Utility code for importers.
                                                             (line   64)
* Python Enhancement Proposals; PEP 488 <12>: py_compile — Compile Python source files.
                                                             (line   31)
* Python Enhancement Proposals; PEP 488 <13>: distutils util — Miscellaneous other utility functions.
                                                             (line  152)
* Python Enhancement Proposals; PEP 488 <14>: distutils util — Miscellaneous other utility functions.
                                                             (line  189)
* Python Enhancement Proposals; PEP 489: PEP 489 Multi-phase extension module initialization.
                                                             (line    6)
* Python Enhancement Proposals; PEP 489 <1>: PEP 489 Multi-phase extension module initialization.
                                                             (line   18)
* Python Enhancement Proposals; PEP 489 <2>: Build and C API Changes<3>.
                                                             (line   37)
* Python Enhancement Proposals; PEP 489 <3>: Library<18>.    (line   65)
* Python Enhancement Proposals; PEP 489 <4>: Core and Builtins<17>.
                                                             (line   28)
* Python Enhancement Proposals; PEP 489 <5>: Core and Builtins<17>.
                                                             (line   35)
* Python Enhancement Proposals; PEP 489 <6>: Core and Builtins<17>.
                                                             (line   50)
* Python Enhancement Proposals; PEP 489 <7>: Core and Builtins<18>.
                                                             (line   46)
* Python Enhancement Proposals; PEP 489 <8>: Core and Builtins<18>.
                                                             (line   49)
* Python Enhancement Proposals; PEP 489 <9>: Core and Builtins<18>.
                                                             (line   51)
* Python Enhancement Proposals; PEP 489 <10>: Core and Builtins<18>.
                                                             (line   71)
* Python Enhancement Proposals; PEP 489 <11>: Core and Builtins<18>.
                                                             (line   75)
* Python Enhancement Proposals; PEP 489 <12>: Core and Builtins<19>.
                                                             (line   17)
* Python Enhancement Proposals; PEP 489 <13>: Core and Builtins<19>.
                                                             (line   20)
* Python Enhancement Proposals; PEP 489 <14>: Core and Builtins<19>.
                                                             (line   40)
* Python Enhancement Proposals; PEP 489 <15>: Core and Builtins<19>.
                                                             (line   54)
* Python Enhancement Proposals; PEP 489 <16>: Core and Builtins<19>.
                                                             (line  109)
* Python Enhancement Proposals; PEP 489 <17>: Core and Builtins<19>.
                                                             (line  118)
* Python Enhancement Proposals; PEP 489 <18>: Core and Builtins<20>.
                                                             (line   29)
* Python Enhancement Proposals; PEP 489 <19>: Core and Builtins<20>.
                                                             (line   32)
* Python Enhancement Proposals; PEP 489 <20>: Core and Builtins<20>.
                                                             (line   52)
* Python Enhancement Proposals; PEP 489 <21>: Core and Builtins<20>.
                                                             (line   55)
* Python Enhancement Proposals; PEP 489 <22>: Core and Builtins<20>.
                                                             (line   58)
* Python Enhancement Proposals; PEP 489 <23>: Core and Builtins<21>.
                                                             (line   62)
* Python Enhancement Proposals; PEP 489 <24>: Introduction<12>.
                                                             (line   69)
* Python Enhancement Proposals; PEP 489 <25>: importlib machinery – Importers and path hooks.
                                                             (line   77)
* Python Enhancement Proposals; PEP 489 <26>: importlib machinery – Importers and path hooks.
                                                             (line  322)
* Python Enhancement Proposals; PEP 489 <27>: importlib machinery – Importers and path hooks.
                                                             (line  328)
* Python Enhancement Proposals; PEP 489 <28>: The Module’s Method Table and Initialization Function.
                                                             (line  129)
* Python Enhancement Proposals; PEP 489 <29>: Building C and C++ Extensions.
                                                             (line   40)
* Python Enhancement Proposals; PEP 489 <30>: Multi-phase initialization.
                                                             (line  108)
* Python Enhancement Proposals; PEP 492: PEP 525 Asynchronous Generators.
                                                             (line    6)
* Python Enhancement Proposals; PEP 492 <1>: New Keywords.   (line    7)
* Python Enhancement Proposals; PEP 492 <2>: PEP 492 - Coroutines with async and await syntax.
                                                             (line    6)
* Python Enhancement Proposals; PEP 492 <3>: PEP 492 - Coroutines with async and await syntax.
                                                             (line   97)
* Python Enhancement Proposals; PEP 492 <4>: New Keywords<2>.
                                                             (line    7)
* Python Enhancement Proposals; PEP 492 <5>: Changes in the C API<5>.
                                                             (line   25)
* Python Enhancement Proposals; PEP 492 <6>: Core and Builtins<37>.
                                                             (line   99)
* Python Enhancement Proposals; PEP 492 <7>: Library<60>.    (line   36)
* Python Enhancement Proposals; PEP 492 <8>: Library<72>.    (line   16)
* Python Enhancement Proposals; PEP 492 <9>: Core and Builtins<67>.
                                                             (line   14)
* Python Enhancement Proposals; PEP 492 <10>: Awaitable Objects.
                                                             (line   27)
* Python Enhancement Proposals; PEP 492 <11>: Yield expressions.
                                                             (line  105)
* Python Enhancement Proposals; PEP 492 <12>: The async with statement.
                                                             (line   45)
* Python Enhancement Proposals; PEP 492 <13>: Collections Abstract Base Classes.
                                                             (line  247)
* Python Enhancement Proposals; PEP 492 <14>: Code Objects Bit Flags.
                                                             (line   42)
* Python Enhancement Proposals; PEP 492 <15>: Code Objects Bit Flags.
                                                             (line   51)
* Python Enhancement Proposals; PEP 492 <16>: Glossary.      (line  100)
* Python Enhancement Proposals; PEP 492 <17>: Glossary.      (line  133)
* Python Enhancement Proposals; PEP 492 <18>: Glossary.      (line  140)
* Python Enhancement Proposals; PEP 492 <19>: Glossary.      (line  149)
* Python Enhancement Proposals; PEP 492 <20>: Glossary.      (line  161)
* Python Enhancement Proposals; PEP 492 <21>: Glossary.      (line  288)
* Python Enhancement Proposals; PEP 492 <22>: Glossary.      (line  295)
* Python Enhancement Proposals; PEP 493: PEP 493 HTTPS verification migration tools for Python 2 7.
                                                             (line    6)
* Python Enhancement Proposals; PEP 494: What’s New In Python 3 6.
                                                             (line   17)
* Python Enhancement Proposals; PEP 495: PEP 495 Local Time Disambiguation.
                                                             (line   13)
* Python Enhancement Proposals; PEP 495 <1>: PEP 495 Local Time Disambiguation.
                                                             (line   36)
* Python Enhancement Proposals; PEP 495 <2>: Library<55>.    (line   96)
* Python Enhancement Proposals; PEP 495 <3>: Using ZoneInfo. (line   34)
* Python Enhancement Proposals; PEP 498: PEP 498 Formatted string literals.
                                                             (line    6)
* Python Enhancement Proposals; PEP 498 <1>: PEP 498 Formatted string literals.
                                                             (line   27)
* Python Enhancement Proposals; PEP 498 <2>: Core and Builtins<55>.
                                                             (line  284)
* Python Enhancement Proposals; PEP 498 <3>: Formatted string literals.
                                                             (line  141)
* Python Enhancement Proposals; PEP 498 <4>: Glossary.       (line  420)
* Python Enhancement Proposals; PEP 5:   PEP 230 Warning Framework.
                                                             (line   66)
* Python Enhancement Proposals; PEP 5 <1>: Is it reasonable to propose incompatible changes to Python?.
                                                             (line   14)
* Python Enhancement Proposals; PEP 506: secrets.            (line   19)
* Python Enhancement Proposals; PEP 506 <1>: Library<62>.    (line   60)
* Python Enhancement Proposals; PEP 506 <2>: secrets — Generate secure random numbers for managing secrets.
                                                             (line   24)
* Python Enhancement Proposals; PEP 511: Changes in the Python API<4>.
                                                             (line   32)
* Python Enhancement Proposals; PEP 514: Windows<43>.        (line    8)
* Python Enhancement Proposals; PEP 515: PEP 515 Underscores in Numeric Literals.
                                                             (line    6)
* Python Enhancement Proposals; PEP 515 <1>: PEP 515 Underscores in Numeric Literals.
                                                             (line   32)
* Python Enhancement Proposals; PEP 515 <2>: Core and Builtins<51>.
                                                             (line   15)
* Python Enhancement Proposals; PEP 515 <3>: Core and Builtins<51>.
                                                             (line   43)
* Python Enhancement Proposals; PEP 515 <4>: Format Specification Mini-Language.
                                                             (line  111)
* Python Enhancement Proposals; PEP 519: PEP 519 Adding a file system path protocol.
                                                             (line   62)
* Python Enhancement Proposals; PEP 519 <1>: Library<55>.    (line    6)
* Python Enhancement Proposals; PEP 519 <2>: Core and Builtins<54>.
                                                             (line   19)
* Python Enhancement Proposals; PEP 519 <3>: Library<60>.    (line   16)
* Python Enhancement Proposals; PEP 519 <4>: Library<60>.    (line   27)
* Python Enhancement Proposals; PEP 519 <5>: Library<60>.    (line   29)
* Python Enhancement Proposals; PEP 519 <6>: C API<37>.      (line    6)
* Python Enhancement Proposals; PEP 519 <7>: Glossary.       (line 1036)
* Python Enhancement Proposals; PEP 520: PEP 520 Preserving Class Attribute Definition Order.
                                                             (line   17)
* Python Enhancement Proposals; PEP 523: Porting to Python 3 9<2>.
                                                             (line    6)
* Python Enhancement Proposals; PEP 523 <1>: PEP 523 Adding a frame evaluation API to CPython.
                                                             (line   12)
* Python Enhancement Proposals; PEP 523 <2>: PEP 523 Adding a frame evaluation API to CPython.
                                                             (line   26)
* Python Enhancement Proposals; PEP 523 <3>: Tools/Demos<17>.
                                                             (line    7)
* Python Enhancement Proposals; PEP 523 <4>: Tools/Demos<21>.
                                                             (line    7)
* Python Enhancement Proposals; PEP 523 <5>: Core and Builtins<51>.
                                                             (line   83)
* Python Enhancement Proposals; PEP 523 <6>: Low-level API.  (line  153)
* Python Enhancement Proposals; PEP 523 <7>: Low-level API.  (line  163)
* Python Enhancement Proposals; PEP 524: Summary – Release highlights<3>.
                                                             (line   77)
* Python Enhancement Proposals; PEP 524 <1>: os<4>.          (line   20)
* Python Enhancement Proposals; PEP 524 <2>: os<4>.          (line   25)
* Python Enhancement Proposals; PEP 524 <3>: Library<54>.    (line  150)
* Python Enhancement Proposals; PEP 524 <4>: Library<54>.    (line  154)
* Python Enhancement Proposals; PEP 524 <5>: Random numbers<2>.
                                                             (line   42)
* Python Enhancement Proposals; PEP 525: PEP 525 Asynchronous Generators.
                                                             (line   23)
* Python Enhancement Proposals; PEP 525 <1>: Core and Builtins<51>.
                                                             (line   49)
* Python Enhancement Proposals; PEP 525 <2>: Yield expressions.
                                                             (line  103)
* Python Enhancement Proposals; PEP 525 <3>: Collections Abstract Base Classes.
                                                             (line  247)
* Python Enhancement Proposals; PEP 525 <4>: sys — System-specific parameters and functions.
                                                             (line  812)
* Python Enhancement Proposals; PEP 525 <5>: sys — System-specific parameters and functions.
                                                             (line 1428)
* Python Enhancement Proposals; PEP 525 <6>: Code Objects Bit Flags.
                                                             (line   60)
* Python Enhancement Proposals; PEP 525 <7>: Glossary.       (line  134)
* Python Enhancement Proposals; PEP 526: ast<2>.             (line   18)
* Python Enhancement Proposals; PEP 526 <1>: PEP 563 Postponed Evaluation of Annotations.
                                                             (line    8)
* Python Enhancement Proposals; PEP 526 <2>: PEP 526 Syntax for variable annotations.
                                                             (line   30)
* Python Enhancement Proposals; PEP 526 <3>: typing<4>.      (line   23)
* Python Enhancement Proposals; PEP 526 <4>: Core and Builtins<51>.
                                                             (line   51)
* Python Enhancement Proposals; PEP 526 <5>: Annotated assignment statements.
                                                             (line   39)
* Python Enhancement Proposals; PEP 526 <6>: Function definitions.
                                                             (line  139)
* Python Enhancement Proposals; PEP 526 <7>: Relevant PEPs.  (line   11)
* Python Enhancement Proposals; PEP 526 <8>: Special forms.  (line  179)
* Python Enhancement Proposals; PEP 526 <9>: Other special directives.
                                                             (line   56)
* Python Enhancement Proposals; PEP 526 <10>: Other special directives.
                                                             (line  104)
* Python Enhancement Proposals; PEP 526 <11>: dataclasses — Data Classes.
                                                             (line   16)
* Python Enhancement Proposals; PEP 526 <12>: Class variables.
                                                             (line    8)
* Python Enhancement Proposals; PEP 526 <13>: ast Helpers.   (line   16)
* Python Enhancement Proposals; PEP 526 <14>: Compiler Flags.
                                                             (line   23)
* Python Enhancement Proposals; PEP 526 <15>: Glossary.      (line   61)
* Python Enhancement Proposals; PEP 526 <16>: Glossary.      (line 1316)
* Python Enhancement Proposals; PEP 528: PEP 528 Change Windows console encoding to UTF-8.
                                                             (line   17)
* Python Enhancement Proposals; PEP 528 <1>: UTF-8 mode.     (line   42)
* Python Enhancement Proposals; PEP 528 <2>: Global configuration variables.
                                                             (line  105)
* Python Enhancement Proposals; PEP 529: Changes in the Python API<2>.
                                                             (line    7)
* Python Enhancement Proposals; PEP 529 <1>: PEP 529 Change Windows filesystem encoding to UTF-8.
                                                             (line   22)
* Python Enhancement Proposals; PEP 529 <2>: Library<25>.    (line  621)
* Python Enhancement Proposals; PEP 529 <3>: Windows<38>.    (line   14)
* Python Enhancement Proposals; PEP 529 <4>: Environment variables.
                                                             (line  323)
* Python Enhancement Proposals; PEP 529 <5>: UTF-8 mode.     (line   45)
* Python Enhancement Proposals; PEP 529 <6>: Files and Directories.
                                                             (line  289)
* Python Enhancement Proposals; PEP 529 <7>: sys — System-specific parameters and functions.
                                                             (line  662)
* Python Enhancement Proposals; PEP 529 <8>: sys — System-specific parameters and functions.
                                                             (line 1467)
* Python Enhancement Proposals; PEP 529 <9>: File System Encoding.
                                                             (line    9)
* Python Enhancement Proposals; PEP 529 <10>: Global configuration variables.
                                                             (line   93)
* Python Enhancement Proposals; PEP 530: PEP 530 Asynchronous Comprehensions.
                                                             (line    6)
* Python Enhancement Proposals; PEP 530 <1>: PEP 530 Asynchronous Comprehensions.
                                                             (line   19)
* Python Enhancement Proposals; PEP 530 <2>: Core and Builtins<51>.
                                                             (line  145)
* Python Enhancement Proposals; PEP 530 <3>: Displays for lists sets and dictionaries.
                                                             (line   53)
* Python Enhancement Proposals; PEP 538: PEP 538 Legacy C Locale Coercion.
                                                             (line   11)
* Python Enhancement Proposals; PEP 538 <1>: PEP 538 Legacy C Locale Coercion.
                                                             (line   36)
* Python Enhancement Proposals; PEP 538 <2>: PEP 538 Legacy C Locale Coercion.
                                                             (line   48)
* Python Enhancement Proposals; PEP 538 <3>: PEP 540 Forced UTF-8 Runtime Mode.
                                                             (line   27)
* Python Enhancement Proposals; PEP 538 <4>: Documentation<25>.
                                                             (line   68)
* Python Enhancement Proposals; PEP 538 <5>: Documentation<26>.
                                                             (line    6)
* Python Enhancement Proposals; PEP 538 <6>: Core and Builtins<38>.
                                                             (line  135)
* Python Enhancement Proposals; PEP 538 <7>: Environment variables.
                                                             (line  392)
* Python Enhancement Proposals; PEP 538 <8>: Python Configuration.
                                                             (line   13)
* Python Enhancement Proposals; PEP 539: PEP 539 New C API for Thread-Local Storage.
                                                             (line   12)
* Python Enhancement Proposals; PEP 539 <1>: PEP 539 New C API for Thread-Local Storage.
                                                             (line   30)
* Python Enhancement Proposals; PEP 539 <2>: C API<26>.      (line   13)
* Python Enhancement Proposals; PEP 539 <3>: Thread Specific Storage TSS API.
                                                             (line   15)
* Python Enhancement Proposals; PEP 540: PEP 540 Forced UTF-8 Runtime Mode.
                                                             (line   18)
* Python Enhancement Proposals; PEP 540 <1>: PEP 540 Forced UTF-8 Runtime Mode.
                                                             (line   35)
* Python Enhancement Proposals; PEP 540 <2>: Core and Builtins<35>.
                                                             (line   63)
* Python Enhancement Proposals; PEP 540 <3>: Environment variables.
                                                             (line  461)
* Python Enhancement Proposals; PEP 540 <4>: Python Configuration.
                                                             (line   13)
* Python Enhancement Proposals; PEP 544: typing<3>.          (line   32)
* Python Enhancement Proposals; PEP 544 <1>: Relevant PEPs.  (line   17)
* Python Enhancement Proposals; PEP 544 <2>: Nominal vs structural subtyping.
                                                             (line   23)
* Python Enhancement Proposals; PEP 544 <3>: Building generic types.
                                                             (line  110)
* Python Enhancement Proposals; PEP 545: PEP 545 Python Documentation Translations.
                                                             (line    6)
* Python Enhancement Proposals; PEP 545 <1>: PEP 545 Python Documentation Translations.
                                                             (line   20)
* Python Enhancement Proposals; PEP 552: PEP 552 Hash-based pyc Files.
                                                             (line   15)
* Python Enhancement Proposals; PEP 552 <1>: PEP 552 Hash-based pyc Files.
                                                             (line   35)
* Python Enhancement Proposals; PEP 552 <2>: Library<30>.    (line  797)
* Python Enhancement Proposals; PEP 552 <3>: Core and Builtins<35>.
                                                             (line   75)
* Python Enhancement Proposals; PEP 552 <4>: Introduction<12>.
                                                             (line   73)
* Python Enhancement Proposals; PEP 552 <5>: py_compile — Compile Python source files.
                                                             (line   81)
* Python Enhancement Proposals; PEP 552 <6>: PyConfig.       (line  145)
* Python Enhancement Proposals; PEP 553: PEP 553 Built-in breakpoint.
                                                             (line   20)
* Python Enhancement Proposals; PEP 553 <1>: Core and Builtins<37>.
                                                             (line   73)
* Python Enhancement Proposals; PEP 557: dataclasses.        (line   26)
* Python Enhancement Proposals; PEP 557 <1>: dataclasses — Data Classes.
                                                             (line   13)
* Python Enhancement Proposals; PEP 560: PEP 560 Core Support for typing module and Generic Types.
                                                             (line   19)
* Python Enhancement Proposals; PEP 560 <1>: types.          (line   12)
* Python Enhancement Proposals; PEP 560 <2>: Core and Builtins<35>.
                                                             (line   66)
* Python Enhancement Proposals; PEP 560 <3>: Resolving MRO entries.
                                                             (line   15)
* Python Enhancement Proposals; PEP 560 <4>: __class_getitem__ versus __getitem__.
                                                             (line   85)
* Python Enhancement Proposals; PEP 560 <5>: Generic Alias Type.
                                                             (line   18)
* Python Enhancement Proposals; PEP 560 <6>: Dynamic Type Creation.
                                                             (line   60)
* Python Enhancement Proposals; PEP 560 <7>: Dynamic Type Creation.
                                                             (line   74)
* Python Enhancement Proposals; PEP 562: PEP 562 Customization of Access to Module Attributes.
                                                             (line   16)
* Python Enhancement Proposals; PEP 562 <1>: Library<37>.    (line   63)
* Python Enhancement Proposals; PEP 562 <2>: Core and Builtins<35>.
                                                             (line   69)
* Python Enhancement Proposals; PEP 562 <3>: Customizing module attribute access.
                                                             (line   52)
* Python Enhancement Proposals; PEP 563: PEP 563 Postponed Evaluation of Annotations.
                                                             (line   51)
* Python Enhancement Proposals; PEP 563 <1>: Future statements.
                                                             (line   34)
* Python Enhancement Proposals; PEP 563 <2>: Function definitions.
                                                             (line  144)
* Python Enhancement Proposals; PEP 563 <3>: Constant.       (line   27)
* Python Enhancement Proposals; PEP 563 <4>: __future__ — Future statement definitions.
                                                             (line   97)
* Python Enhancement Proposals; PEP 564: PEP 564 New Time Functions With Nanosecond Resolution.
                                                             (line    8)
* Python Enhancement Proposals; PEP 564 <1>: PEP 564 New Time Functions With Nanosecond Resolution.
                                                             (line   33)
* Python Enhancement Proposals; PEP 564 <2>: time<3>.        (line    6)
* Python Enhancement Proposals; PEP 564 <3>: Library<39>.    (line  300)
* Python Enhancement Proposals; PEP 565: PEP 565 Show DeprecationWarning in __main__.
                                                             (line   41)
* Python Enhancement Proposals; PEP 565 <1>: Warnings.       (line   23)
* Python Enhancement Proposals; PEP 566: Using importlib metadata.
                                                             (line   24)
* Python Enhancement Proposals; PEP 566 <1>: Distributions.  (line   28)
* Python Enhancement Proposals; PEP 567: contextvars.        (line   20)
* Python Enhancement Proposals; PEP 567 <1>: asyncio<3>.     (line   19)
* Python Enhancement Proposals; PEP 567 <2>: Documentation<25>.
                                                             (line   86)
* Python Enhancement Proposals; PEP 567 <3>: Documentation<27>.
                                                             (line    9)
* Python Enhancement Proposals; PEP 567 <4>: Core and Builtins<34>.
                                                             (line   63)
* Python Enhancement Proposals; PEP 567 <5>: contextvars — Context Variables.
                                                             (line   18)
* Python Enhancement Proposals; PEP 567 <6>: Scheduling callbacks.
                                                             (line   36)
* Python Enhancement Proposals; PEP 567 <7>: Scheduling delayed callbacks.
                                                             (line   31)
* Python Enhancement Proposals; PEP 567 <8>: Scheduling delayed callbacks.
                                                             (line   49)
* Python Enhancement Proposals; PEP 567 <9>: Future Object.  (line  100)
* Python Enhancement Proposals; PEP 570: Positional-only parameters.
                                                             (line   70)
* Python Enhancement Proposals; PEP 570 <1>: Changes in the Python API<2>.
                                                             (line  160)
* Python Enhancement Proposals; PEP 570 <2>: Core and Builtins<25>.
                                                             (line   36)
* Python Enhancement Proposals; PEP 570 <3>: Function definitions.
                                                             (line   95)
* Python Enhancement Proposals; PEP 572: Assignment expressions.
                                                             (line   41)
* Python Enhancement Proposals; PEP 572 <1>: CPython bytecode changes<2>.
                                                             (line   27)
* Python Enhancement Proposals; PEP 572 <2>: Documentation<16>.
                                                             (line    6)
* Python Enhancement Proposals; PEP 572 <3>: Core and Builtins<23>.
                                                             (line  184)
* Python Enhancement Proposals; PEP 572 <4>: Core and Builtins<28>.
                                                             (line   92)
* Python Enhancement Proposals; PEP 572 <5>: Dictionary displays.
                                                             (line   47)
* Python Enhancement Proposals; PEP 572 <6>: Assignment expressions<2>.
                                                             (line   22)
* Python Enhancement Proposals; PEP 572 <7>: Why can’t I use an assignment in an expression?.
                                                             (line   14)
* Python Enhancement Proposals; PEP 573: Summary – Release highlights.
                                                             (line   27)
* Python Enhancement Proposals; PEP 573 <1>: New Features<2>.
                                                             (line    6)
* Python Enhancement Proposals; PEP 573 <2>: Core and Builtins<17>.
                                                             (line   19)
* Python Enhancement Proposals; PEP 573 <3>: C API<10>.      (line   57)
* Python Enhancement Proposals; PEP 574: Pickle protocol 5 with out-of-band data buffers.
                                                             (line   17)
* Python Enhancement Proposals; PEP 574 <1>: Data stream format.
                                                             (line   46)
* Python Enhancement Proposals; PEP 574 <2>: Example<4>.     (line   63)
* Python Enhancement Proposals; PEP 578: PEP 578 Python Runtime Audit Hooks.
                                                             (line   12)
* Python Enhancement Proposals; PEP 578 <1>: Audit events table.
                                                             (line    8)
* Python Enhancement Proposals; PEP 578 <2>: sys — System-specific parameters and functions.
                                                             (line   44)
* Python Enhancement Proposals; PEP 578 <3>: System Functions.
                                                             (line  153)
* Python Enhancement Proposals; PEP 584: Summary – Release highlights.
                                                             (line    8)
* Python Enhancement Proposals; PEP 584 <1>: Dictionary Merge & Update Operators.
                                                             (line   19)
* Python Enhancement Proposals; PEP 584 <2>: Library<20>.    (line  192)
* Python Enhancement Proposals; PEP 584 <3>: Library<20>.    (line  195)
* Python Enhancement Proposals; PEP 584 <4>: Library<20>.    (line  209)
* Python Enhancement Proposals; PEP 584 <5>: Library<21>.    (line   49)
* Python Enhancement Proposals; PEP 584 <6>: Library<21>.    (line   62)
* Python Enhancement Proposals; PEP 584 <7>: Library<21>.    (line  120)
* Python Enhancement Proposals; PEP 584 <8>: Library<21>.    (line  142)
* Python Enhancement Proposals; PEP 584 <9>: ChainMap objects.
                                                             (line   87)
* Python Enhancement Proposals; PEP 584 <10>: defaultdict objects.
                                                             (line   56)
* Python Enhancement Proposals; PEP 584 <11>: OrderedDict objects.
                                                             (line   90)
* Python Enhancement Proposals; PEP 584 <12>: weakref — Weak references.
                                                             (line  173)
* Python Enhancement Proposals; PEP 584 <13>: weakref — Weak references.
                                                             (line  193)
* Python Enhancement Proposals; PEP 584 <14>: Standard Interpreter Types.
                                                             (line  245)
* Python Enhancement Proposals; PEP 584 <15>: Process Parameters.
                                                             (line   49)
* Python Enhancement Proposals; PEP 584 <16>: Process Parameters.
                                                             (line   65)
* Python Enhancement Proposals; PEP 585: Summary – Release highlights.
                                                             (line   10)
* Python Enhancement Proposals; PEP 585 <1>: Type Hinting Generics in Standard Collections.
                                                             (line   18)
* Python Enhancement Proposals; PEP 585 <2>: Documentation<4>.
                                                             (line   25)
* Python Enhancement Proposals; PEP 585 <3>: Special Attributes of Generic Alias.
                                                             (line   38)
* Python Enhancement Proposals; PEP 585 <4>: collections abc — Abstract Base Classes for Containers.
                                                             (line   18)
* Python Enhancement Proposals; PEP 585 <5>: Relevant PEPs.  (line   23)
* Python Enhancement Proposals; PEP 585 <6>: Module contents<3>.
                                                             (line   21)
* Python Enhancement Proposals; PEP 585 <7>: Special forms.  (line   24)
* Python Enhancement Proposals; PEP 585 <8>: Special forms.  (line   98)
* Python Enhancement Proposals; PEP 585 <9>: Special forms.  (line  144)
* Python Enhancement Proposals; PEP 585 <10>: Corresponding to built-in types.
                                                             (line   18)
* Python Enhancement Proposals; PEP 585 <11>: Corresponding to built-in types.
                                                             (line   38)
* Python Enhancement Proposals; PEP 585 <12>: Corresponding to built-in types.
                                                             (line   47)
* Python Enhancement Proposals; PEP 585 <13>: Corresponding to built-in types.
                                                             (line   54)
* Python Enhancement Proposals; PEP 585 <14>: Corresponding to types in collections.
                                                             (line   14)
* Python Enhancement Proposals; PEP 585 <15>: Corresponding to types in collections.
                                                             (line   25)
* Python Enhancement Proposals; PEP 585 <16>: Corresponding to types in collections.
                                                             (line   38)
* Python Enhancement Proposals; PEP 585 <17>: Corresponding to types in collections.
                                                             (line   49)
* Python Enhancement Proposals; PEP 585 <18>: Corresponding to types in collections.
                                                             (line   60)
* Python Enhancement Proposals; PEP 585 <19>: Other concrete types.
                                                             (line   32)
* Python Enhancement Proposals; PEP 585 <20>: Corresponding to collections in collections abc.
                                                             (line   11)
* Python Enhancement Proposals; PEP 585 <21>: Corresponding to collections in collections abc.
                                                             (line   24)
* Python Enhancement Proposals; PEP 585 <22>: Corresponding to collections in collections abc.
                                                             (line   34)
* Python Enhancement Proposals; PEP 585 <23>: Corresponding to collections in collections abc.
                                                             (line   42)
* Python Enhancement Proposals; PEP 585 <24>: Corresponding to collections in collections abc.
                                                             (line   50)
* Python Enhancement Proposals; PEP 585 <25>: Corresponding to collections in collections abc.
                                                             (line   58)
* Python Enhancement Proposals; PEP 585 <26>: Corresponding to collections in collections abc.
                                                             (line   70)
* Python Enhancement Proposals; PEP 585 <27>: Corresponding to collections in collections abc.
                                                             (line   78)
* Python Enhancement Proposals; PEP 585 <28>: Corresponding to collections in collections abc.
                                                             (line   86)
* Python Enhancement Proposals; PEP 585 <29>: Corresponding to collections in collections abc.
                                                             (line   94)
* Python Enhancement Proposals; PEP 585 <30>: Corresponding to collections in collections abc.
                                                             (line  102)
* Python Enhancement Proposals; PEP 585 <31>: Corresponding to collections in collections abc.
                                                             (line  110)
* Python Enhancement Proposals; PEP 585 <32>: Corresponding to collections in collections abc.
                                                             (line  118)
* Python Enhancement Proposals; PEP 585 <33>: Corresponding to other types in collections abc.
                                                             (line   11)
* Python Enhancement Proposals; PEP 585 <34>: Corresponding to other types in collections abc.
                                                             (line   19)
* Python Enhancement Proposals; PEP 585 <35>: Corresponding to other types in collections abc.
                                                             (line   55)
* Python Enhancement Proposals; PEP 585 <36>: Corresponding to other types in collections abc.
                                                             (line   67)
* Python Enhancement Proposals; PEP 585 <37>: Asynchronous programming.
                                                             (line   22)
* Python Enhancement Proposals; PEP 585 <38>: Asynchronous programming.
                                                             (line   60)
* Python Enhancement Proposals; PEP 585 <39>: Asynchronous programming.
                                                             (line   70)
* Python Enhancement Proposals; PEP 585 <40>: Asynchronous programming.
                                                             (line   80)
* Python Enhancement Proposals; PEP 585 <41>: Asynchronous programming.
                                                             (line   90)
* Python Enhancement Proposals; PEP 585 <42>: Context manager types.
                                                             (line   15)
* Python Enhancement Proposals; PEP 585 <43>: Context manager types.
                                                             (line   29)
* Python Enhancement Proposals; PEP 585 <44>: Introspection helpers.
                                                             (line   68)
* Python Enhancement Proposals; PEP 585 <45>: Glossary.      (line  557)
* Python Enhancement Proposals; PEP 586: typing<2>.          (line    6)
* Python Enhancement Proposals; PEP 586 <1>: typing<3>.      (line   18)
* Python Enhancement Proposals; PEP 586 <2>: Relevant PEPs.  (line   29)
* Python Enhancement Proposals; PEP 586 <3>: Special forms.  (line  164)
* Python Enhancement Proposals; PEP 587: PEP 587 Python Initialization Configuration.
                                                             (line    6)
* Python Enhancement Proposals; PEP 587 <1>: PEP 587 Python Initialization Configuration.
                                                             (line   83)
* Python Enhancement Proposals; PEP 587 <2>: Core and Builtins<23>.
                                                             (line   76)
* Python Enhancement Proposals; PEP 587 <3>: C API<17>.      (line    6)
* Python Enhancement Proposals; PEP 587 <4>: Python Initialization Configuration.
                                                             (line   83)
* Python Enhancement Proposals; PEP 589: typing<3>.          (line    8)
* Python Enhancement Proposals; PEP 589 <1>: Relevant PEPs.  (line   34)
* Python Enhancement Proposals; PEP 589 <2>: Other special directives.
                                                             (line  123)
* Python Enhancement Proposals; PEP 590: Summary – Release highlights.
                                                             (line   33)
* Python Enhancement Proposals; PEP 590 <1>: Optimizations.  (line   37)
* Python Enhancement Proposals; PEP 590 <2>: PEP 590 Vectorcall a fast calling protocol for CPython.
                                                             (line   14)
* Python Enhancement Proposals; PEP 590 <3>: Core and Builtins<18>.
                                                             (line   39)
* Python Enhancement Proposals; PEP 590 <4>: Core and Builtins<18>.
                                                             (line   91)
* Python Enhancement Proposals; PEP 590 <5>: Core and Builtins<19>.
                                                             (line   42)
* Python Enhancement Proposals; PEP 590 <6>: Core and Builtins<19>.
                                                             (line   50)
* Python Enhancement Proposals; PEP 590 <7>: Core and Builtins<19>.
                                                             (line   67)
* Python Enhancement Proposals; PEP 590 <8>: C API<17>.      (line   17)
* Python Enhancement Proposals; PEP 590 <9>: The Vectorcall Protocol.
                                                             (line    8)
* Python Enhancement Proposals; PEP 591: typing<3>.          (line   25)
* Python Enhancement Proposals; PEP 591 <1>: Relevant PEPs.  (line   39)
* Python Enhancement Proposals; PEP 591 <2>: Special forms.  (line  217)
* Python Enhancement Proposals; PEP 591 <3>: Functions and decorators.
                                                             (line   65)
* Python Enhancement Proposals; PEP 593: Summary – Release highlights.
                                                             (line   20)
* Python Enhancement Proposals; PEP 593 <1>: typing.         (line    6)
* Python Enhancement Proposals; PEP 593 <2>: Library<22>.    (line   91)
* Python Enhancement Proposals; PEP 593 <3>: Relevant PEPs.  (line   45)
* Python Enhancement Proposals; PEP 593 <4>: Special forms.  (line  224)
* Python Enhancement Proposals; PEP 593 <5>: Introspection helpers.
                                                             (line   34)
* Python Enhancement Proposals; PEP 596: What’s New In Python 3 9.
                                                             (line   23)
* Python Enhancement Proposals; PEP 6:   How does the Python version numbering scheme work?.
                                                             (line    9)
* Python Enhancement Proposals; PEP 602: Summary – Release highlights.
                                                             (line   59)
* Python Enhancement Proposals; PEP 602 <1>: How stable is Python?.
                                                             (line    8)
* Python Enhancement Proposals; PEP 612: Core and Builtins<9>.
                                                             (line   65)
* Python Enhancement Proposals; PEP 614: Summary – Release highlights.
                                                             (line   12)
* Python Enhancement Proposals; PEP 614 <1>: Other Language Changes.
                                                             (line   37)
* Python Enhancement Proposals; PEP 614 <2>: Core and Builtins<19>.
                                                             (line  112)
* Python Enhancement Proposals; PEP 614 <3>: Function definitions.
                                                             (line   54)
* Python Enhancement Proposals; PEP 614 <4>: Class definitions.
                                                             (line   60)
* Python Enhancement Proposals; PEP 615: Summary – Release highlights.
                                                             (line   51)
* Python Enhancement Proposals; PEP 615 <1>: zoneinfo.       (line   37)
* Python Enhancement Proposals; PEP 615 <2>: Library<19>.    (line   54)
* Python Enhancement Proposals; PEP 615 <3>: zoneinfo — IANA time zone support.
                                                             (line   12)
* Python Enhancement Proposals; PEP 616: Summary – Release highlights.
                                                             (line   16)
* Python Enhancement Proposals; PEP 616 <1>: New String Methods to Remove Prefixes and Suffixes.
                                                             (line    9)
* Python Enhancement Proposals; PEP 616 <2>: Core and Builtins<18>.
                                                             (line   82)
* Python Enhancement Proposals; PEP 617: Summary – Release highlights.
                                                             (line   30)
* Python Enhancement Proposals; PEP 617 <1>: New Parser.     (line   21)
* Python Enhancement Proposals; PEP 617 <2>: Deprecated.     (line   97)
* Python Enhancement Proposals; PEP 617 <3>: Library<20>.    (line   35)
* Python Enhancement Proposals; PEP 617 <4>: Miscellaneous options.
                                                             (line  204)
* Python Enhancement Proposals; PEP 617 <5>: Environment variables.
                                                             (line   97)
* Python Enhancement Proposals; PEP 617 <6>: lib2to3 - 2to3’s library.
                                                             (line   11)
* Python Enhancement Proposals; PEP 617 <7>: PyConfig.       (line  401)
* Python Enhancement Proposals; PEP 623: Documentation<8>.   (line   19)
* Python Enhancement Proposals; PEP 623 <1>: Unicode Objects.
                                                             (line   33)
* Python Enhancement Proposals; PEP 628: cmath.              (line    7)
* Python Enhancement Proposals; PEP 628 <1>: math<4>.        (line    7)
* Python Enhancement Proposals; PEP 628 <2>: Library<55>.    (line   32)
* Python Enhancement Proposals; PEP 7:   Build and C API Changes<2>.
                                                             (line    9)
* Python Enhancement Proposals; PEP 7 <1>: Coding standards. (line    7)
* Python Enhancement Proposals; PEP 7 <2>: Useful macros.    (line  102)
* Python Enhancement Proposals; PEP 7 <3>: Useful macros.    (line  120)
* Python Enhancement Proposals; PEP 8:   Library Changes.    (line   26)
* Python Enhancement Proposals; PEP 8 <1>: Library<39>.      (line  125)
* Python Enhancement Proposals; PEP 8 <2>: IDLE<50>.         (line   81)
* Python Enhancement Proposals; PEP 8 <3>: Intermezzo Coding Style.
                                                             (line   13)
* Python Enhancement Proposals; PEP 8 <4>: Editors and IDEs. (line    7)
* Python Enhancement Proposals; PEP 8 <5>: Value comparisons.
                                                             (line   61)
* Python Enhancement Proposals; PEP 8 <6>: Built-in Functions.
                                                             (line 1537)
* Python Enhancement Proposals; PEP 8 <7>: Using real Argument Clinic converters instead of “legacy converters”.
                                                             (line   50)
* Python Enhancement Proposals; PEP 8 <8>: Are there coding standards or a style guide for Python programs?.
                                                             (line    7)
* Python Enhancement Proposals; PEP 8 <9>: When can I rely on identity tests with the is operator?.
                                                             (line   57)
* Python Enhancement Proposals; PEP 8 <10>: How do I keep editors from inserting tabs into my Python source?.
                                                             (line    6)
* Python Package Index (PyPI):           Installing the tools.
                                                             (line   26)
* PYTHON*:                               Other Improvements<2>.
                                                             (line    9)
* PYTHON* <1>:                           Interface options.  (line   80)
* PYTHON* <2>:                           Interface options.  (line  140)
* PYTHON* <3>:                           Miscellaneous options.
                                                             (line   42)
* PYTHON* <4>:                           Miscellaneous options.
                                                             (line   60)
* PYTHON* <5>:                           Global configuration variables.
                                                             (line   56)
* PYTHONASYNCIODEBUG:                    Enabling debug mode.
                                                             (line   10)
* PYTHONASYNCIODEBUG <1>:                Debug Mode.         (line   11)
* PYTHONASYNCIODEBUG <2>:                Effects of the Python Development Mode.
                                                             (line   64)
* PYTHONBREAKPOINT:                      PEP 553 Built-in breakpoint.
                                                             (line   13)
* PYTHONBREAKPOINT <1>:                  sys — System-specific parameters and functions.
                                                             (line  202)
* PYTHONBREAKPOINT <2>:                  sys — System-specific parameters and functions.
                                                             (line  216)
* PYTHONBREAKPOINT <3>:                  sys — System-specific parameters and functions.
                                                             (line  220)
* PYTHONCASEOK:                          Changes in the Python API.
                                                             (line   29)
* PYTHONCASEOK <1>:                      PEP 235 Importing Modules on Case-Insensitive Platforms.
                                                             (line   17)
* PYTHONCASEOK <2>:                      Library<21>.        (line  144)
* PYTHONCASEOK <3>:                      Built-in Functions. (line 1865)
* PYTHONCOERCECLOCALE:                   PEP 538 Legacy C Locale Coercion.
                                                             (line   13)
* PYTHONCOERCECLOCALE <1>:               Environment variables.
                                                             (line  454)
* PYTHONCOERCECLOCALE <2>:               Python Configuration.
                                                             (line   15)
* PYTHONDEBUG:                           Miscellaneous options.
                                                             (line   38)
* PYTHONDEBUG <1>:                       Global configuration variables.
                                                             (line   28)
* PYTHONDEVMODE:                         Python Development Mode -X dev.
                                                             (line    6)
* PYTHONDEVMODE <1>:                     Python Development Mode.
                                                             (line   14)
* PYTHONDOCS:                            pydoc — Documentation generator and online help system.
                                                             (line   85)
* PYTHONDONTWRITEBYTECODE:               Interpreter Changes<2>.
                                                             (line   16)
* PYTHONDONTWRITEBYTECODE <1>:           New and Improved Modules<2>.
                                                             (line  625)
* PYTHONDONTWRITEBYTECODE <2>:           Miscellaneous options.
                                                             (line   19)
* PYTHONDONTWRITEBYTECODE <3>:           sys — System-specific parameters and functions.
                                                             (line  285)
* PYTHONDONTWRITEBYTECODE <4>:           Global configuration variables.
                                                             (line   36)
* PYTHONDONTWRITEBYTECODE <5>:           How do I create a pyc file?.
                                                             (line   21)
* PYTHONDUMPREFS:                        Debug build uses the same ABI as release build.
                                                             (line   14)
* PYTHONDUMPREFS <1>:                    Build<21>.          (line   54)
* PYTHONDUMPREFS <2>:                    PyObject Slots.     (line   24)
* PYTHONFAULTHANDLER:                    faulthandler<3>.    (line   11)
* PYTHONFAULTHANDLER <1>:                Effects of the Python Development Mode.
                                                             (line   58)
* PYTHONFAULTHANDLER <2>:                faulthandler — Dump the Python traceback.
                                                             (line   14)
* PYTHONHASHSEED:                        Builtin functions and types.
                                                             (line   17)
* PYTHONHASHSEED <1>:                    Porting Python code.
                                                             (line    6)
* PYTHONHASHSEED <2>:                    Core and Builtins<35>.
                                                             (line   30)
* PYTHONHASHSEED <3>:                    Miscellaneous options.
                                                             (line   94)
* PYTHONHASHSEED <4>:                    Miscellaneous options.
                                                             (line  110)
* PYTHONHASHSEED <5>:                    Environment variables.
                                                             (line  145)
* PYTHONHASHSEED <6>:                    Basic customization.
                                                             (line  297)
* PYTHONHASHSEED <7>:                    Global configuration variables.
                                                             (line   48)
* PYTHONHASHSEED <8>:                    Global configuration variables.
                                                             (line   51)
* PYTHONHOME:                            Summary – Release highlights<3>.
                                                             (line  107)
* PYTHONHOME <1>:                        Miscellaneous options.
                                                             (line   43)
* PYTHONHOME <2>:                        Environment variables.
                                                             (line   19)
* PYTHONHOME <3>:                        Environment variables.
                                                             (line   21)
* PYTHONHOME <4>:                        Environment variables.
                                                             (line   38)
* PYTHONHOME <5>:                        Finding modules.    (line   50)
* PYTHONHOME <6>:                        Finding modules.    (line   68)
* PYTHONHOME <7>:                        Finding modules.    (line  102)
* PYTHONHOME <8>:                        test support script_helper — Utilities for the Python execution tests.
                                                             (line   25)
* PYTHONHOME <9>:                        Embedding Python<2>.
                                                             (line   38)
* PYTHONHOME <10>:                       Embedding Python<2>.
                                                             (line   44)
* PYTHONHOME <11>:                       Global configuration variables.
                                                             (line   57)
* PYTHONHOME <12>:                       Process-wide parameters.
                                                             (line  270)
* PYTHONHOME <13>:                       Process-wide parameters.
                                                             (line  284)
* PYTHONHOME <14>:                       PyConfig.           (line  204)
* PYTHONHOME <15>:                       Modifying Python’s Search Path.
                                                             (line   60)
* PYTHONHOME <16>:                       Modifying Python’s Search Path.
                                                             (line   62)
* Pythonic:                              Glossary.           (line 1092)
* PYTHONINSPECT:                         Other Changes and Fixes<2>.
                                                             (line   13)
* PYTHONINSPECT <1>:                     Miscellaneous options.
                                                             (line   53)
* PYTHONINSPECT <2>:                     Global configuration variables.
                                                             (line   68)
* PYTHONIOENCODING:                      Other Improvements<2>.
                                                             (line   75)
* PYTHONIOENCODING <1>:                  Interpreter Changes<2>.
                                                             (line   23)
* PYTHONIOENCODING <2>:                  Environment variables.
                                                             (line  375)
* PYTHONIOENCODING <3>:                  Environment variables.
                                                             (line  442)
* PYTHONIOENCODING <4>:                  sys — System-specific parameters and functions.
                                                             (line 1509)
* PYTHONIOENCODING <5>:                  Process-wide parameters.
                                                             (line   14)
* PYTHONIOENCODING <6>:                  Process-wide parameters.
                                                             (line   18)
* PYTHONLEGACYWINDOWSFSENCODING:         PEP 529 Change Windows filesystem encoding to UTF-8.
                                                             (line   18)
* PYTHONLEGACYWINDOWSFSENCODING <1>:     sys — System-specific parameters and functions.
                                                             (line 1461)
* PYTHONLEGACYWINDOWSFSENCODING <2>:     Global configuration variables.
                                                             (line   90)
* PYTHONLEGACYWINDOWSSTDIO:              PEP 528 Change Windows console encoding to UTF-8.
                                                             (line   12)
* PYTHONLEGACYWINDOWSSTDIO <1>:          Environment variables.
                                                             (line  172)
* PYTHONLEGACYWINDOWSSTDIO <2>:          sys — System-specific parameters and functions.
                                                             (line 1513)
* PYTHONLEGACYWINDOWSSTDIO <3>:          Global configuration variables.
                                                             (line  102)
* PYTHONMALLOC:                          PYTHONMALLOC environment variable.
                                                             (line    6)
* PYTHONMALLOC <1>:                      Changes in the C API<4>.
                                                             (line    9)
* PYTHONMALLOC <2>:                      Core and Builtins<55>.
                                                             (line   91)
* PYTHONMALLOC <3>:                      Environment variables.
                                                             (line  302)
* PYTHONMALLOC <4>:                      Effects of the Python Development Mode.
                                                             (line   46)
* PYTHONMALLOC <5>:                      Effects of the Python Development Mode.
                                                             (line   50)
* PYTHONMALLOC <6>:                      Overview<3>.        (line   75)
* PYTHONMALLOC <7>:                      Default Memory Allocators.
                                                             (line   26)
* PYTHONMALLOC <8>:                      Customize Memory Allocators.
                                                             (line  129)
* PYTHONMALLOCSTATS:                     Core and Builtins<55>.
                                                             (line   97)
* PYTHONMALLOCSTATS <1>:                 Overview<3>.        (line   78)
* PYTHONNOUSERSITE:                      PEP 370 Per-user site-packages Directory.
                                                             (line   30)
* PYTHONNOUSERSITE <1>:                  Module contents<4>. (line   15)
* PYTHONNOUSERSITE <2>:                  Global configuration variables.
                                                             (line  124)
* PYTHONOLDPARSER:                       Miscellaneous options.
                                                             (line  204)
* PYTHONOLDPARSER <1>:                   PyConfig.           (line  398)
* PYTHONOPTIMIZE:                        Miscellaneous options.
                                                             (line   71)
* PYTHONOPTIMIZE <1>:                    Global configuration variables.
                                                             (line  129)
* PYTHONPATH:                            Changes in ‘python’ Command Behavior<2>.
                                                             (line    8)
* PYTHONPATH <1>:                        Changes in ‘python’ Command Behavior<2>.
                                                             (line    9)
* PYTHONPATH <2>:                        The Module Search Path.
                                                             (line   15)
* PYTHONPATH <3>:                        Standard Modules.   (line   34)
* PYTHONPATH <4>:                        Standard Modules.   (line   35)
* PYTHONPATH <5>:                        Miscellaneous options.
                                                             (line   42)
* PYTHONPATH <6>:                        Environment variables.
                                                             (line   32)
* PYTHONPATH <7>:                        Environment variables.
                                                             (line   39)
* PYTHONPATH <8>:                        Environment variables.
                                                             (line   42)
* PYTHONPATH <9>:                        Excursus Setting environment variables.
                                                             (line   38)
* PYTHONPATH <10>:                       Finding modules.    (line   36)
* PYTHONPATH <11>:                       Finding modules.    (line   59)
* PYTHONPATH <12>:                       Finding modules.    (line  102)
* PYTHONPATH <13>:                       Configuration.      (line    6)
* PYTHONPATH <14>:                       Path entry finders. (line    6)
* PYTHONPATH <15>:                       Installing your CGI script on a Unix system.
                                                             (line   29)
* PYTHONPATH <16>:                       test support script_helper — Utilities for the Python execution tests.
                                                             (line   26)
* PYTHONPATH <17>:                       sys — System-specific parameters and functions.
                                                             (line 1063)
* PYTHONPATH <18>:                       sys — System-specific parameters and functions.
                                                             (line 1073)
* PYTHONPATH <19>:                       Building C and C++ Extensions.
                                                             (line    9)
* PYTHONPATH <20>:                       Embedding Python<2>.
                                                             (line   39)
* PYTHONPATH <21>:                       Embedding Python<2>.
                                                             (line   44)
* PYTHONPATH <22>:                       Global configuration variables.
                                                             (line   56)
* PYTHONPATH <23>:                       PyConfig.           (line  259)
* PYTHONPATH <24>:                       Modifying Python’s Search Path.
                                                             (line   67)
* PYTHONPATH <25>:                       Modifying Python’s Search Path.
                                                             (line   68)
* PYTHONPLATLIBDIR:                      Core and Builtins<16>.
                                                             (line   25)
* PYTHONPROFILEIMPORTTIME:               Other Language Changes<3>.
                                                             (line   47)
* PYTHONPROFILEIMPORTTIME <1>:           Core and Builtins<37>.
                                                             (line   67)
* PYTHONPROFILEIMPORTTIME <2>:           Miscellaneous options.
                                                             (line  222)
* PYTHONPYCACHEPREFIX:                   Parallel filesystem cache for compiled bytecode files.
                                                             (line    6)
* PYTHONPYCACHEPREFIX <1>:               Core and Builtins<28>.
                                                             (line  402)
* PYTHONPYCACHEPREFIX <2>:               Miscellaneous options.
                                                             (line  237)
* PYTHONPYCACHEPREFIX <3>:               sys — System-specific parameters and functions.
                                                             (line  303)
* PYTHONSHOWALLOCCOUNT:                  Two new environment variables for debug mode.
                                                             (line   11)
* PYTHONSHOWREFCOUNT:                    Two new environment variables for debug mode.
                                                             (line    7)
* PYTHONSTARTUP:                         sys<7>.             (line   17)
* PYTHONSTARTUP <1>:                     sys<7>.             (line   21)
* PYTHONSTARTUP <2>:                     IDLE<24>.           (line  176)
* PYTHONSTARTUP <3>:                     IDLE<28>.           (line    9)
* PYTHONSTARTUP <4>:                     IDLE<34>.           (line    9)
* PYTHONSTARTUP <5>:                     The Interactive Startup File.
                                                             (line    8)
* PYTHONSTARTUP <6>:                     Miscellaneous options.
                                                             (line   50)
* PYTHONSTARTUP <7>:                     Example.            (line   10)
* PYTHONSTARTUP <8>:                     Startup and code execution.
                                                             (line    7)
* PYTHONSTARTUP <9>:                     sys — System-specific parameters and functions.
                                                             (line  958)
* PYTHONSTARTUP <10>:                    Readline configuration.
                                                             (line   12)
* PYTHONTRACEMALLOC:                     tracemalloc — Trace memory allocations.
                                                             (line   25)
* PYTHONTRACEMALLOC <1>:                 tracemalloc — Trace memory allocations.
                                                             (line   32)
* PYTHONTRACEMALLOC <2>:                 Functions<10>.      (line   90)
* PYTHONTZPATH:                          Exceptions and warnings.
                                                             (line   14)
* PYTHONUNBUFFERED:                      Core and Builtins<21>.
                                                             (line  107)
* PYTHONUNBUFFERED <1>:                  Miscellaneous options.
                                                             (line  140)
* PYTHONUNBUFFERED <2>:                  sys — System-specific parameters and functions.
                                                             (line 1520)
* PYTHONUNBUFFERED <3>:                  Global configuration variables.
                                                             (line  145)
* PYTHONUSERBASE:                        PEP 370 Per-user site-packages Directory.
                                                             (line   23)
* PYTHONUSERBASE <1>:                    Module contents<4>. (line   39)
* PYTHONUSERBASE <2>:                    Module contents<4>. (line   66)
* PYTHONUSERSITE:                        test support script_helper — Utilities for the Python execution tests.
                                                             (line   26)
* PYTHONUTF8:                            PEP 540 Forced UTF-8 Runtime Mode.
                                                             (line    6)
* PYTHONUTF8 <1>:                        Miscellaneous options.
                                                             (line  232)
* PYTHONUTF8 <2>:                        Environment variables.
                                                             (line  385)
* PYTHONUTF8 <3>:                        UTF-8 mode.         (line   17)
* PYTHONUTF8 <4>:                        sys — System-specific parameters and functions.
                                                             (line 1511)
* PYTHONUTF8 <5>:                        Python Configuration.
                                                             (line   14)
* PYTHONVERBOSE:                         Miscellaneous options.
                                                             (line  151)
* PYTHONVERBOSE <1>:                     Global configuration variables.
                                                             (line  156)
* PYTHONWARNINGS:                        warnings.           (line   21)
* PYTHONWARNINGS <1>:                    Other Language Changes<8>.
                                                             (line  158)
* PYTHONWARNINGS <2>:                    Changes to the Handling of Deprecation Warnings.
                                                             (line   25)
* PYTHONWARNINGS <3>:                    Interpreter Changes.
                                                             (line    6)
* PYTHONWARNINGS <4>:                    Miscellaneous options.
                                                             (line  169)
* PYTHONWARNINGS <5>:                    Effects of the Python Development Mode.
                                                             (line   30)
* PYTHONWARNINGS <6>:                    Describing Warning Filters.
                                                             (line    7)
* PYTHONWARNINGS <7>:                    Describing Warning Filters.
                                                             (line   21)
* PYTHONWARNINGS <8>:                    Default Warning Filter.
                                                             (line    7)
* python_branch() (in module platform):  Cross Platform.     (line   85)
* python_build() (in module platform):   Cross Platform.     (line   75)
* python_compiler() (in module platform): Cross Platform.    (line   80)
* PYTHON_DOM:                            Module Contents<4>. (line   23)
* python_implementation() (in module platform): Cross Platform.
                                                             (line   89)
* python_is_optimized() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  263)
* python_revision() (in module platform): Cross Platform.    (line   94)
* python_version() (in module platform): Cross Platform.     (line   99)
* python_version_tuple() (in module platform): Cross Platform.
                                                             (line  106)
* PyThreadState:                         Thread State and the Global Interpreter Lock.
                                                             (line   23)
* PyThreadState <1>:                     Thread State and the Global Interpreter Lock.
                                                             (line   23)
* PyThreadState (C type):                High-level API.     (line   21)
* PyThreadState_Clear (C function):      Low-level API.      (line   44)
* PyThreadState_Delete (C function):     Low-level API.      (line   53)
* PyThreadState_DeleteCurrent (C function): Low-level API.   (line   59)
* PyThreadState_Get (C function):        High-level API.     (line   78)
* PyThreadState_GetDict (C function):    Low-level API.      (line  167)
* PyThreadState_GetFrame (C function):   Low-level API.      (line   66)
* PyThreadState_GetID (C function):      Low-level API.      (line   80)
* PyThreadState_GetInterpreter (C function): Low-level API.  (line   89)
* PyThreadState_New (C function):        Low-level API.      (line   37)
* PyThreadState_Next (C function):       Advanced Debugger Support.
                                                             (line   32)
* PyThreadState_SetAsyncExc (C function): Low-level API.     (line  176)
* PyThreadState_Swap (C function):       High-level API.     (line   84)
* PyThread_create_key (C function):      Thread Local Storage TLS API.
                                                             (line   18)
* PyThread_delete_key (C function):      Thread Local Storage TLS API.
                                                             (line   20)
* PyThread_delete_key_value (C function): Thread Local Storage TLS API.
                                                             (line   26)
* PyThread_get_key_value (C function):   Thread Local Storage TLS API.
                                                             (line   24)
* PyThread_ReInitTLS (C function):       Thread Local Storage TLS API.
                                                             (line   28)
* PyThread_set_key_value (C function):   Thread Local Storage TLS API.
                                                             (line   22)
* PyThread_tss_alloc (C function):       Dynamic Allocation. (line   11)
* PyThread_tss_create (C function):      Methods<4>.         (line   16)
* PyThread_tss_delete (C function):      Methods<4>.         (line   24)
* PyThread_tss_free (C function):        Dynamic Allocation. (line   17)
* PyThread_tss_get (C function):         Methods<4>.         (line   39)
* PyThread_tss_is_created (C function):  Methods<4>.         (line   11)
* PyThread_tss_set (C function):         Methods<4>.         (line   33)
* PyTimeZone_FromOffset (C function):    DateTime Objects<2>.
                                                             (line  125)
* PyTimeZone_FromOffsetAndName (C function): DateTime Objects<2>.
                                                             (line  133)
* PyTime_Check (C function):             DateTime Objects<2>.
                                                             (line   47)
* PyTime_CheckExact (C function):        DateTime Objects<2>.
                                                             (line   53)
* PyTime_FromTime (C function):          DateTime Objects<2>.
                                                             (line  103)
* PyTime_FromTimeAndFold (C function):   DateTime Objects<2>.
                                                             (line  108)
* PyTraceMalloc_Track (C function):      tracemalloc C API.  (line    8)
* PyTraceMalloc_Untrack (C function):    tracemalloc C API.  (line   20)
* PyTrace_CALL (C variable):             Profiling and Tracing.
                                                             (line   61)
* PyTrace_C_CALL (C variable):           Profiling and Tracing.
                                                             (line   93)
* PyTrace_C_EXCEPTION (C variable):      Profiling and Tracing.
                                                             (line   98)
* PyTrace_C_RETURN (C variable):         Profiling and Tracing.
                                                             (line  103)
* PyTrace_EXCEPTION (C variable):        Profiling and Tracing.
                                                             (line   69)
* PyTrace_LINE (C variable):             Profiling and Tracing.
                                                             (line   81)
* PyTrace_OPCODE (C variable):           Profiling and Tracing.
                                                             (line  108)
* PyTrace_RETURN (C variable):           Profiling and Tracing.
                                                             (line   88)
* PyTupleObject (C type):                Tuple Objects.      (line    6)
* PyTuple_Check (C function):            Tuple Objects.      (line   17)
* PyTuple_CheckExact (C function):       Tuple Objects.      (line   22)
* PyTuple_GetItem (C function):          Tuple Objects.      (line   48)
* PyTuple_GetSlice (C function):         Tuple Objects.      (line   57)
* PyTuple_GET_ITEM (C function):         Tuple Objects.      (line   53)
* PyTuple_GET_SIZE (C function):         Tuple Objects.      (line   43)
* PyTuple_New (C function):              Tuple Objects.      (line   27)
* PyTuple_Pack (C function):             Tuple Objects.      (line   31)
* PyTuple_SetItem (C function):          Tuple Objects.      (line   64)
* PyTuple_SetItem():                     Reference Count Details.
                                                             (line   26)
* PyTuple_SET_ITEM (C function):         Tuple Objects.      (line   76)
* PyTuple_Size (C function):             Tuple Objects.      (line   38)
* PyTuple_Type (C variable):             Tuple Objects.      (line   11)
* PyTypeObject (C type):                 Type Objects<2>.    (line    6)
* PyTypeObject.tp_alloc (C member):      PyTypeObject Slots. (line 1176)
* PyTypeObject.tp_as_async (C member):   PyTypeObject Slots. (line  234)
* PyTypeObject.tp_as_buffer (C member):  PyTypeObject Slots. (line  435)
* PyTypeObject.tp_as_mapping (C member): PyTypeObject Slots. (line  297)
* PyTypeObject.tp_as_number (C member):  PyTypeObject Slots. (line  275)
* PyTypeObject.tp_as_sequence (C member): PyTypeObject Slots.
                                                             (line  286)
* PyTypeObject.tp_base (C member):       PyTypeObject Slots. (line  989)
* PyTypeObject.tp_bases (C member):      PyTypeObject Slots. (line 1288)
* PyTypeObject.tp_basicsize (C member):  PyTypeObject Slots. (line   47)
* PyTypeObject.tp_cache (C member):      PyTypeObject Slots. (line 1310)
* PyTypeObject.tp_call (C member):       PyTypeObject Slots. (line  345)
* PyTypeObject.tp_clear (C member):      PyTypeObject Slots. (line  720)
* PyTypeObject.tp_dealloc (C member):    PyTypeObject Slots. (line   99)
* PyTypeObject.tp_del (C member):        PyTypeObject Slots. (line 1335)
* PyTypeObject.tp_descr_get (C member):  PyTypeObject Slots. (line 1046)
* PyTypeObject.tp_descr_set (C member):  PyTypeObject Slots. (line 1058)
* PyTypeObject.tp_dict (C member):       PyTypeObject Slots. (line 1021)
* PyTypeObject.tp_dictoffset (C member): PyTypeObject Slots. (line 1073)
* PyTypeObject.tp_doc (C member):        PyTypeObject Slots. (line  636)
* PyTypeObject.tp_finalize (C member):   PyTypeObject Slots. (line 1347)
* PyTypeObject.tp_flags (C member):      PyTypeObject Slots. (line  446)
* PyTypeObject.tp_free (C member):       PyTypeObject Slots. (line 1236)
* PyTypeObject.tp_getattr (C member):    PyTypeObject Slots. (line  195)
* PyTypeObject.tp_getattro (C member):   PyTypeObject Slots. (line  383)
* PyTypeObject.tp_getset (C member):     PyTypeObject Slots. (line  974)
* PyTypeObject.tp_hash (C member):       PyTypeObject Slots. (line  308)
* PyTypeObject.tp_init (C member):       PyTypeObject Slots. (line 1139)
* PyTypeObject.tp_is_gc (C member):      PyTypeObject Slots. (line 1259)
* PyTypeObject.tp_itemsize (C member):   PyTypeObject Slots. (line   47)
* PyTypeObject.tp_iter (C member):       PyTypeObject Slots. (line  906)
* PyTypeObject.tp_iternext (C member):   PyTypeObject Slots. (line  922)
* PyTypeObject.tp_members (C member):    PyTypeObject Slots. (line  959)
* PyTypeObject.tp_methods (C member):    PyTypeObject Slots. (line  944)
* PyTypeObject.tp_mro (C member):        PyTypeObject Slots. (line 1299)
* PyTypeObject.tp_name (C member):       PyTypeObject Slots. (line   12)
* PyTypeObject.tp_new (C member):        PyTypeObject Slots. (line 1199)
* PyTypeObject.tp_repr (C member):       PyTypeObject Slots. (line  249)
* PyTypeObject.tp_richcompare (C member): PyTypeObject Slots.
                                                             (line  795)
* PyTypeObject.tp_setattr (C member):    PyTypeObject Slots. (line  214)
* PyTypeObject.tp_setattro (C member):   PyTypeObject Slots. (line  408)
* PyTypeObject.tp_str (C member):        PyTypeObject Slots. (line  357)
* PyTypeObject.tp_subclasses (C member): PyTypeObject Slots. (line 1318)
* PyTypeObject.tp_traverse (C member):   PyTypeObject Slots. (line  646)
* PyTypeObject.tp_vectorcall (C member): PyTypeObject Slots. (line 1394)
* PyTypeObject.tp_vectorcall_offset (C member): PyTypeObject Slots.
                                                             (line  152)
* PyTypeObject.tp_version_tag (C member): PyTypeObject Slots.
                                                             (line 1339)
* PyTypeObject.tp_weaklist (C member):   PyTypeObject Slots. (line 1326)
* PyTypeObject.tp_weaklistoffset (C member): PyTypeObject Slots.
                                                             (line  870)
* PyType_Check (C function):             Type Objects<2>.    (line   15)
* PyType_CheckExact (C function):        Type Objects<2>.    (line   21)
* PyType_ClearCache (C function):        Type Objects<2>.    (line   27)
* PyType_FromModuleAndSpec (C function): Creating Heap-Allocated Types.
                                                             (line    9)
* PyType_FromSpec (C function):          Creating Heap-Allocated Types.
                                                             (line   41)
* PyType_FromSpecWithBases (C function): Creating Heap-Allocated Types.
                                                             (line   33)
* PyType_GenericAlloc (C function):      Type Objects<2>.    (line   69)
* PyType_GenericNew (C function):        Type Objects<2>.    (line   77)
* PyType_GetFlags (C function):          Type Objects<2>.    (line   31)
* PyType_GetModule (C function):         Type Objects<2>.    (line  114)
* PyType_GetModuleState (C function):    Type Objects<2>.    (line  132)
* PyType_GetSlot (C function):           Type Objects<2>.    (line  100)
* PyType_HasFeature (C function):        Type Objects<2>.    (line   50)
* PyType_IsSubtype (C function):         Type Objects<2>.    (line   60)
* PyType_IS_GC (C function):             Type Objects<2>.    (line   55)
* PyType_Modified (C function):          Type Objects<2>.    (line   44)
* PyType_Ready (C function):             Type Objects<2>.    (line   84)
* PyType_Slot (C type):                  Creating Heap-Allocated Types.
                                                             (line   74)
* PyType_Slot.PyType_Slot.pfunc (C member): Creating Heap-Allocated Types.
                                                             (line  137)
* PyType_Slot.PyType_Slot.slot (C member): Creating Heap-Allocated Types.
                                                             (line   79)
* PyType_Spec (C type):                  Creating Heap-Allocated Types.
                                                             (line   45)
* PyType_Spec.PyType_Spec.basicsize (C member): Creating Heap-Allocated Types.
                                                             (line   54)
* PyType_Spec.PyType_Spec.flags (C member): Creating Heap-Allocated Types.
                                                             (line   62)
* PyType_Spec.PyType_Spec.itemsize (C member): Creating Heap-Allocated Types.
                                                             (line   56)
* PyType_Spec.PyType_Spec.name (C member): Creating Heap-Allocated Types.
                                                             (line   49)
* PyType_Spec.PyType_Spec.slots (C member): Creating Heap-Allocated Types.
                                                             (line   69)
* PyType_Type (C variable):              Type Objects<2>.    (line   10)
* PyTZInfo_Check (C function):           DateTime Objects<2>.
                                                             (line   69)
* PyTZInfo_CheckExact (C function):      DateTime Objects<2>.
                                                             (line   75)
* PyUnicodeDecodeError_Create (C function): Unicode Exception Objects.
                                                             (line    9)
* PyUnicodeDecodeError_GetEncoding (C function): Unicode Exception Objects.
                                                             (line   47)
* PyUnicodeDecodeError_GetEnd (C function): Unicode Exception Objects.
                                                             (line   88)
* PyUnicodeDecodeError_GetObject (C function): Unicode Exception Objects.
                                                             (line   54)
* PyUnicodeDecodeError_GetReason (C function): Unicode Exception Objects.
                                                             (line  115)
* PyUnicodeDecodeError_GetStart (C function): Unicode Exception Objects.
                                                             (line   61)
* PyUnicodeDecodeError_SetEnd (C function): Unicode Exception Objects.
                                                             (line  102)
* PyUnicodeDecodeError_SetReason (C function): Unicode Exception Objects.
                                                             (line  122)
* PyUnicodeDecodeError_SetStart (C function): Unicode Exception Objects.
                                                             (line   75)
* PyUnicodeEncodeError_Create (C function): Unicode Exception Objects.
                                                             (line   18)
* PyUnicodeEncodeError_GetEncoding (C function): Unicode Exception Objects.
                                                             (line   47)
* PyUnicodeEncodeError_GetEnd (C function): Unicode Exception Objects.
                                                             (line   88)
* PyUnicodeEncodeError_GetObject (C function): Unicode Exception Objects.
                                                             (line   54)
* PyUnicodeEncodeError_GetReason (C function): Unicode Exception Objects.
                                                             (line  115)
* PyUnicodeEncodeError_GetStart (C function): Unicode Exception Objects.
                                                             (line   61)
* PyUnicodeEncodeError_SetEnd (C function): Unicode Exception Objects.
                                                             (line  102)
* PyUnicodeEncodeError_SetReason (C function): Unicode Exception Objects.
                                                             (line  122)
* PyUnicodeEncodeError_SetStart (C function): Unicode Exception Objects.
                                                             (line   75)
* PyUnicodeObject (C type):              Unicode Type.       (line   29)
* PyUnicodeTranslateError_Create (C function): Unicode Exception Objects.
                                                             (line   32)
* PyUnicodeTranslateError_GetEnd (C function): Unicode Exception Objects.
                                                             (line   88)
* PyUnicodeTranslateError_GetObject (C function): Unicode Exception Objects.
                                                             (line   54)
* PyUnicodeTranslateError_GetReason (C function): Unicode Exception Objects.
                                                             (line  115)
* PyUnicodeTranslateError_GetStart (C function): Unicode Exception Objects.
                                                             (line   61)
* PyUnicodeTranslateError_SetEnd (C function): Unicode Exception Objects.
                                                             (line  102)
* PyUnicodeTranslateError_SetReason (C function): Unicode Exception Objects.
                                                             (line  122)
* PyUnicodeTranslateError_SetStart (C function): Unicode Exception Objects.
                                                             (line   75)
* PyUnicode_1BYTE_DATA (C function):     Unicode Type.       (line   80)
* PyUnicode_1BYTE_KIND (C macro):        Unicode Type.       (line   93)
* PyUnicode_2BYTE_DATA (C function):     Unicode Type.       (line   80)
* PyUnicode_2BYTE_KIND (C macro):        Unicode Type.       (line   93)
* PyUnicode_4BYTE_DATA (C function):     Unicode Type.       (line   80)
* PyUnicode_4BYTE_KIND (C macro):        Unicode Type.       (line   93)
* PyUnicode_AsASCIIString (C function):  ASCII Codecs.       (line   16)
* PyUnicode_AsCharmapString (C function): Character Map Codecs.
                                                             (line   30)
* PyUnicode_AsEncodedString (C function): Generic Codecs.    (line   17)
* PyUnicode_AsLatin1String (C function): Latin-1 Codecs.     (line   17)
* PyUnicode_AsMBCSString (C function):   MBCS codecs for Windows.
                                                             (line   28)
* PyUnicode_AsRawUnicodeEscapeString (C function): Raw-Unicode-Escape Codecs.
                                                             (line   14)
* PyUnicode_AsUCS4 (C function):         Creating and accessing Unicode strings.
                                                             (line  251)
* PyUnicode_AsUCS4Copy (C function):     Creating and accessing Unicode strings.
                                                             (line  261)
* PyUnicode_AsUnicode (C function):      Deprecated Py_UNICODE APIs.
                                                             (line   35)
* PyUnicode_AsUnicodeAndSize (C function): Deprecated Py_UNICODE APIs.
                                                             (line   63)
* PyUnicode_AsUnicodeCopy (C function):  Deprecated Py_UNICODE APIs.
                                                             (line   79)
* PyUnicode_AsUnicodeEscapeString (C function): Unicode-Escape Codecs.
                                                             (line   15)
* PyUnicode_AsUTF16String (C function):  UTF-16 Codecs.      (line   50)
* PyUnicode_AsUTF32String (C function):  UTF-32 Codecs.      (line   49)
* PyUnicode_AsUTF8 (C function):         UTF-8 Codecs.       (line   53)
* PyUnicode_AsUTF8AndSize (C function):  UTF-8 Codecs.       (line   30)
* PyUnicode_AsUTF8String (C function):   UTF-8 Codecs.       (line   25)
* PyUnicode_AsWideChar (C function):     wchar_t Support.    (line   16)
* PyUnicode_AsWideCharString (C function): wchar_t Support.  (line   31)
* PyUnicode_AS_DATA (C function):        Unicode Type.       (line  182)
* PyUnicode_AS_UNICODE (C function):     Unicode Type.       (line  182)
* PyUnicode_Check (C function):          Unicode Type.       (line   48)
* PyUnicode_CheckExact (C function):     Unicode Type.       (line   53)
* PyUnicode_Compare (C function):        Methods and Slot Functions.
                                                             (line   87)
* PyUnicode_CompareWithASCIIString (C function): Methods and Slot Functions.
                                                             (line   95)
* PyUnicode_Concat (C function):         Methods and Slot Functions.
                                                             (line   12)
* PyUnicode_Contains (C function):       Methods and Slot Functions.
                                                             (line  126)
* PyUnicode_CopyCharacters (C function): Creating and accessing Unicode strings.
                                                             (line  190)
* PyUnicode_Count (C function):          Methods and Slot Functions.
                                                             (line   74)
* PyUnicode_DATA (C function):           Unicode Type.       (line  114)
* PyUnicode_Decode (C function):         Generic Codecs.     (line    8)
* PyUnicode_DecodeASCII (C function):    ASCII Codecs.       (line    9)
* PyUnicode_DecodeCharmap (C function):  Character Map Codecs.
                                                             (line   15)
* PyUnicode_DecodeFSDefault (C function): File System Encoding.
                                                             (line   65)
* PyUnicode_DecodeFSDefaultAndSize (C function): File System Encoding.
                                                             (line   43)
* PyUnicode_DecodeLatin1 (C function):   Latin-1 Codecs.     (line   10)
* PyUnicode_DecodeLocale (C function):   Locale Encoding.    (line   37)
* PyUnicode_DecodeLocaleAndSize (C function): Locale Encoding.
                                                             (line    9)
* PyUnicode_DecodeMBCS (C function):     MBCS codecs for Windows.
                                                             (line   12)
* PyUnicode_DecodeMBCSStateful (C function): MBCS codecs for Windows.
                                                             (line   19)
* PyUnicode_DecodeRawUnicodeEscape (C function): Raw-Unicode-Escape Codecs.
                                                             (line    8)
* PyUnicode_DecodeUnicodeEscape (C function): Unicode-Escape Codecs.
                                                             (line    8)
* PyUnicode_DecodeUTF16 (C function):    UTF-16 Codecs.      (line    8)
* PyUnicode_DecodeUTF16Stateful (C function): UTF-16 Codecs. (line   37)
* PyUnicode_DecodeUTF32 (C function):    UTF-32 Codecs.      (line    8)
* PyUnicode_DecodeUTF32Stateful (C function): UTF-32 Codecs. (line   36)
* PyUnicode_DecodeUTF7 (C function):     UTF-7 Codecs.       (line    8)
* PyUnicode_DecodeUTF7Stateful (C function): UTF-7 Codecs.   (line   15)
* PyUnicode_DecodeUTF8 (C function):     UTF-8 Codecs.       (line    8)
* PyUnicode_DecodeUTF8Stateful (C function): UTF-8 Codecs.   (line   15)
* PyUnicode_Encode (C function):         Generic Codecs.     (line   26)
* PyUnicode_EncodeASCII (C function):    ASCII Codecs.       (line   21)
* PyUnicode_EncodeCharmap (C function):  Character Map Codecs.
                                                             (line   44)
* PyUnicode_EncodeCodePage (C function): MBCS codecs for Windows.
                                                             (line   33)
* PyUnicode_EncodeFSDefault (C function): File System Encoding.
                                                             (line   79)
* PyUnicode_EncodeLatin1 (C function):   Latin-1 Codecs.     (line   23)
* PyUnicode_EncodeLocale (C function):   Locale Encoding.    (line   45)
* PyUnicode_EncodeMBCS (C function):     MBCS codecs for Windows.
                                                             (line   43)
* PyUnicode_EncodeRawUnicodeEscape (C function): Raw-Unicode-Escape Codecs.
                                                             (line   21)
* PyUnicode_EncodeUnicodeEscape (C function): Unicode-Escape Codecs.
                                                             (line   22)
* PyUnicode_EncodeUTF16 (C function):    UTF-16 Codecs.      (line   56)
* PyUnicode_EncodeUTF32 (C function):    UTF-32 Codecs.      (line   55)
* PyUnicode_EncodeUTF7 (C function):     UTF-7 Codecs.       (line   25)
* PyUnicode_EncodeUTF8 (C function):     UTF-8 Codecs.       (line   63)
* PyUnicode_Fill (C function):           Creating and accessing Unicode strings.
                                                             (line  203)
* PyUnicode_Find (C function):           Methods and Slot Functions.
                                                             (line   48)
* PyUnicode_FindChar (C function):       Methods and Slot Functions.
                                                             (line   59)
* PyUnicode_Format (C function):         Methods and Slot Functions.
                                                             (line  121)
* PyUnicode_FromEncodedObject (C function): Creating and accessing Unicode strings.
                                                             (line  167)
* PyUnicode_FromFormat (C function):     Creating and accessing Unicode strings.
                                                             (line   50)
* PyUnicode_FromFormatV (C function):    Creating and accessing Unicode strings.
                                                             (line  160)
* PyUnicode_FromKindAndData (C function): Creating and accessing Unicode strings.
                                                             (line   21)
* PyUnicode_FromObject (C function):     Deprecated Py_UNICODE APIs.
                                                             (line  104)
* PyUnicode_FromString (C function):     Creating and accessing Unicode strings.
                                                             (line   46)
* PyUnicode_FromString():                Dictionary Objects. (line   64)
* PyUnicode_FromStringAndSize (C function): Creating and accessing Unicode strings.
                                                             (line   32)
* PyUnicode_FromUnicode (C function):    Deprecated Py_UNICODE APIs.
                                                             (line   13)
* PyUnicode_FromWideChar (C function):   wchar_t Support.    (line    8)
* PyUnicode_FSConverter (C function):    File System Encoding.
                                                             (line   13)
* PyUnicode_FSDecoder (C function):      File System Encoding.
                                                             (line   30)
* PyUnicode_GetLength (C function):      Creating and accessing Unicode strings.
                                                             (line  184)
* PyUnicode_GetSize (C function):        Deprecated Py_UNICODE APIs.
                                                             (line   94)
* PyUnicode_GET_DATA_SIZE (C function):  Unicode Type.       (line  172)
* PyUnicode_GET_LENGTH (C function):     Unicode Type.       (line   72)
* PyUnicode_GET_SIZE (C function):       Unicode Type.       (line  162)
* PyUnicode_InternFromString (C function): Methods and Slot Functions.
                                                             (line  148)
* PyUnicode_InternInPlace (C function):  Methods and Slot Functions.
                                                             (line  135)
* PyUnicode_IsIdentifier (C function):   Unicode Type.       (line  203)
* PyUnicode_Join (C function):           Methods and Slot Functions.
                                                             (line   34)
* PyUnicode_KIND (C function):           Unicode Type.       (line  105)
* PyUnicode_MAX_CHAR_VALUE (C macro):    Unicode Type.       (line  153)
* PyUnicode_New (C function):            Creating and accessing Unicode strings.
                                                             (line    9)
* PyUnicode_READ (C function):           Unicode Type.       (line  134)
* PyUnicode_ReadChar (C function):       Creating and accessing Unicode strings.
                                                             (line  232)
* PyUnicode_READY (C function):          Unicode Type.       (line   58)
* PyUnicode_READ_CHAR (C function):      Unicode Type.       (line  144)
* PyUnicode_Replace (C function):        Methods and Slot Functions.
                                                             (line   80)
* PyUnicode_RichCompare (C function):    Methods and Slot Functions.
                                                             (line  106)
* PyUnicode_Split (C function):          Methods and Slot Functions.
                                                             (line   17)
* PyUnicode_Splitlines (C function):     Methods and Slot Functions.
                                                             (line   27)
* PyUnicode_Substring (C function):      Creating and accessing Unicode strings.
                                                             (line  242)
* PyUnicode_Tailmatch (C function):      Methods and Slot Functions.
                                                             (line   39)
* PyUnicode_TransformDecimalToASCII (C function): Deprecated Py_UNICODE APIs.
                                                             (line   52)
* PyUnicode_Translate (C function):      Character Map Codecs.
                                                             (line   59)
* PyUnicode_TranslateCharmap (C function): Character Map Codecs.
                                                             (line   76)
* PyUnicode_Type (C variable):           Unicode Type.       (line   40)
* PyUnicode_WCHAR_KIND (C macro):        Unicode Type.       (line   93)
* PyUnicode_WRITE (C function):          Unicode Type.       (line  121)
* PyUnicode_WriteChar (C function):      Creating and accessing Unicode strings.
                                                             (line  218)
* PyVarObject (C type):                  Base object types and macros.
                                                             (line   24)
* PyVarObject.ob_size (C member):        PyVarObject Slots.  (line    6)
* PyVarObject_HEAD_INIT (C macro):       Base object types and macros.
                                                             (line  107)
* PyVectorcall_Call (C function):        Vectorcall Support API.
                                                             (line   35)
* PyVectorcall_Function (C function):    Vectorcall Support API.
                                                             (line   20)
* PyVectorcall_NARGS (C function):       Vectorcall Support API.
                                                             (line    6)
* PyWeakref_Check (C function):          Weak Reference Objects<2>.
                                                             (line   11)
* PyWeakref_CheckProxy (C function):     Weak Reference Objects<2>.
                                                             (line   21)
* PyWeakref_CheckRef (C function):       Weak Reference Objects<2>.
                                                             (line   16)
* PyWeakref_GetObject (C function):      Weak Reference Objects<2>.
                                                             (line   53)
* PyWeakref_GET_OBJECT (C function):     Weak Reference Objects<2>.
                                                             (line   63)
* PyWeakref_NewProxy (C function):       Weak Reference Objects<2>.
                                                             (line   39)
* PyWeakref_NewRef (C function):         Weak Reference Objects<2>.
                                                             (line   26)
* PyWideStringList (C type):             PyWideStringList.   (line    6)
* PyWideStringList.items (C member):     PyWideStringList.   (line   41)
* PyWideStringList.length (C member):    PyWideStringList.   (line   37)
* PyWideStringList_Append (C function):  PyWideStringList.   (line   15)
* PyWideStringList_Insert (C function):  PyWideStringList.   (line   22)
* PyWrapper_New (C function):            Descriptor Objects. (line   43)
* PyZipFile (class in zipfile):          PyZipFile Objects.  (line   10)
* Py_ABS (C macro):                      Useful macros.      (line   36)
* Py_AddPendingCall (C function):        Asynchronous Notifications.
                                                             (line   10)
* Py_AddPendingCall():                   Asynchronous Notifications.
                                                             (line   12)
* Py_AtExit (C function):                Process Control.    (line   30)
* Py_BEGIN_ALLOW_THREADS:                Releasing the GIL from extension code.
                                                             (line   21)
* Py_BEGIN_ALLOW_THREADS (C macro):      High-level API.     (line  160)
* Py_BLOCK_THREADS (C macro):            High-level API.     (line  174)
* Py_buffer (C type):                    Buffer structure.   (line   25)
* Py_buffer.buf (C member):              Buffer structure.   (line   27)
* Py_buffer.format (C member):           Buffer structure.   (line   87)
* Py_buffer.internal (C member):         Buffer structure.   (line  154)
* Py_buffer.itemsize (C member):         Buffer structure.   (line   67)
* Py_buffer.len (C member):              Buffer structure.   (line   50)
* Py_buffer.ndim (C member):             Buffer structure.   (line   96)
* Py_buffer.obj (C member):              Buffer structure.   (line   38)
* Py_buffer.readonly (C member):         Buffer structure.   (line   62)
* Py_buffer.shape (C member):            Buffer structure.   (line  109)
* Py_buffer.strides (C member):          Buffer structure.   (line  122)
* Py_buffer.suboffsets (C member):       Buffer structure.   (line  135)
* Py_BuildValue (C function):            Building values.    (line    6)
* Py_BytesMain (C function):             The Very High Level Layer.
                                                             (line   41)
* Py_BytesWarningFlag (C variable):      Global configuration variables.
                                                             (line   15)
* Py_CHARMASK (C macro):                 Useful macros.      (line   67)
* Py_CLEAR (C function):                 Reference Counting. (line   47)
* py_compile (module):                   py_compile — Compile Python source files.
                                                             (line    6)
* PY_COMPILED (in module imp):           imp — Access the import internals.
                                                             (line  315)
* Py_CompileString (C function):         The Very High Level Layer.
                                                             (line  295)
* Py_CompileString():                    The Very High Level Layer.
                                                             (line  389)
* Py_CompileString() <1>:                The Very High Level Layer.
                                                             (line  394)
* Py_CompileString() <2>:                The Very High Level Layer.
                                                             (line  401)
* Py_CompileStringExFlags (C function):  The Very High Level Layer.
                                                             (line  329)
* Py_CompileStringFlags (C function):    The Very High Level Layer.
                                                             (line  301)
* Py_CompileStringObject (C function):   The Very High Level Layer.
                                                             (line  308)
* Py_complex (C type):                   Complex Numbers as C Structures.
                                                             (line   10)
* Py_DebugFlag (C variable):             Global configuration variables.
                                                             (line   23)
* Py_DecodeLocale (C function):          Operating System Utilities.
                                                             (line  108)
* Py_DECREF (C function):                Reference Counting. (line   20)
* Py_DECREF():                           Reference Counts<2>.
                                                             (line   17)
* Py_DEPRECATED (C macro):               Useful macros.      (line   85)
* Py_DontWriteBytecodeFlag (C variable): Global configuration variables.
                                                             (line   31)
* Py_Ellipsis (C variable):              Ellipsis Object.    (line    6)
* Py_EncodeLocale (C function):          Operating System Utilities.
                                                             (line  161)
* Py_EndInterpreter (C function):        Sub-interpreter support.
                                                             (line   76)
* Py_END_ALLOW_THREADS:                  Releasing the GIL from extension code.
                                                             (line   21)
* Py_END_ALLOW_THREADS (C macro):        High-level API.     (line  167)
* Py_EnterRecursiveCall (C function):    Recursion Control.  (line   13)
* Py_eval_input (C variable):            The Very High Level Layer.
                                                             (line  387)
* Py_Exit (C function):                  Process Control.    (line   21)
* Py_ExitStatusException (C function):   PyStatus.           (line   62)
* Py_False (C variable):                 Boolean Objects.    (line   16)
* Py_FatalError (C function):            Process Control.    (line    6)
* Py_FatalError():                       Process-wide parameters.
                                                             (line  217)
* Py_FdIsInteractive (C function):       Operating System Utilities.
                                                             (line   17)
* Py_file_input (C variable):            The Very High Level Layer.
                                                             (line  392)
* Py_Finalize (C function):              Initializing and finalizing the interpreter.
                                                             (line   78)
* Py_FinalizeEx (C function):            Initializing and finalizing the interpreter.
                                                             (line   39)
* Py_FinalizeEx():                       Process Control.    (line   23)
* Py_FinalizeEx() <1>:                   Process Control.    (line   32)
* Py_FinalizeEx() <2>:                   Initializing and finalizing the interpreter.
                                                             (line    8)
* Py_FinalizeEx() <3>:                   Sub-interpreter support.
                                                             (line   49)
* Py_FinalizeEx() <4>:                   Sub-interpreter support.
                                                             (line   78)
* PY_FROZEN (in module imp):             imp — Access the import internals.
                                                             (line  339)
* Py_FrozenFlag (C variable):            Global configuration variables.
                                                             (line   39)
* Py_GenericAlias (C function):          Objects for Type Hinting.
                                                             (line    9)
* Py_GenericAliasType (C variable):      Objects for Type Hinting.
                                                             (line   41)
* Py_GetArgcArgv (C function):           Py_GetArgcArgv.     (line    6)
* Py_GetBuildInfo (C function):          Process-wide parameters.
                                                             (line  203)
* Py_GetCompiler (C function):           Process-wide parameters.
                                                             (line  192)
* Py_GetCopyright (C function):          Process-wide parameters.
                                                             (line  181)
* Py_GETENV (C macro):                   Useful macros.      (line   72)
* Py_GetExecPrefix (C function):         Process-wide parameters.
                                                             (line   71)
* Py_GetExecPrefix():                    Embedding Python<2>.
                                                             (line   42)
* Py_GetPath (C function):               Process-wide parameters.
                                                             (line  118)
* Py_GetPath():                          Embedding Python<2>.
                                                             (line   42)
* Py_GetPath() <1>:                      Process-wide parameters.
                                                             (line   36)
* Py_GetPath() <2>:                      Process-wide parameters.
                                                             (line  133)
* Py_GetPlatform (C function):           Process-wide parameters.
                                                             (line  170)
* Py_GetPrefix (C function):             Process-wide parameters.
                                                             (line   57)
* Py_GetPrefix():                        Embedding Python<2>.
                                                             (line   42)
* Py_GetProgramFullPath (C function):    Process-wide parameters.
                                                             (line  109)
* Py_GetProgramFullPath():               Embedding Python<2>.
                                                             (line   42)
* Py_GetProgramName (C function):        Process-wide parameters.
                                                             (line   51)
* Py_GetPythonHome (C function):         Process-wide parameters.
                                                             (line  281)
* Py_GetVersion (C function):            Process-wide parameters.
                                                             (line  157)
* Py_HashRandomizationFlag (C variable): Global configuration variables.
                                                             (line   46)
* Py_IgnoreEnvironmentFlag (C variable): Global configuration variables.
                                                             (line   54)
* Py_INCREF (C function):                Reference Counting. (line    9)
* Py_INCREF():                           Reference Counts<2>.
                                                             (line   17)
* Py_Initialize (C function):            Initializing and finalizing the interpreter.
                                                             (line    6)
* Py_Initialize():                       Embedding Python<2>.
                                                             (line   12)
* Py_Initialize() <1>:                   Process-wide parameters.
                                                             (line    9)
* Py_Initialize() <2>:                   Process-wide parameters.
                                                             (line   36)
* Py_Initialize() <3>:                   Sub-interpreter support.
                                                             (line   49)
* Py_InitializeEx (C function):          Initializing and finalizing the interpreter.
                                                             (line   26)
* Py_InitializeFromConfig (C function):  Initialization with PyConfig.
                                                             (line    8)
* Py_InspectFlag (C variable):           Global configuration variables.
                                                             (line   61)
* Py_InteractiveFlag (C variable):       Global configuration variables.
                                                             (line   71)
* Py_IsInitialized (C function):         Initializing and finalizing the interpreter.
                                                             (line   32)
* Py_IsInitialized():                    Embedding Python<2>.
                                                             (line   51)
* Py_IsolatedFlag (C variable):          Global configuration variables.
                                                             (line   75)
* Py_IS_TYPE (C function):               Base object types and macros.
                                                             (line   60)
* Py_LeaveRecursiveCall (C function):    Recursion Control.  (line   34)
* Py_LegacyWindowsFSEncodingFlag (C variable): Global configuration variables.
                                                             (line   85)
* Py_LegacyWindowsStdioFlag (C variable): Global configuration variables.
                                                             (line   97)
* Py_Main (C function):                  The Very High Level Layer.
                                                             (line   24)
* Py_MAX (C macro):                      Useful macros.      (line   48)
* Py_MEMBER_SIZE (C macro):              Useful macros.      (line   61)
* Py_MIN (C macro):                      Useful macros.      (line   42)
* Py_mod_create (C macro):               Multi-phase initialization.
                                                             (line   61)
* Py_mod_exec (C macro):                 Multi-phase initialization.
                                                             (line   96)
* Py_NewInterpreter (C function):        Sub-interpreter support.
                                                             (line   24)
* Py_None (C variable):                  The None Object.    (line   11)
* Py_NoSiteFlag (C variable):            Global configuration variables.
                                                             (line  109)
* Py_NotImplemented (C variable):        Object Protocol.    (line    6)
* Py_NoUserSiteDirectory (C variable):   Global configuration variables.
                                                             (line  119)
* py_object (class in ctypes):           Fundamental data types<2>.
                                                             (line  213)
* Py_OptimizeFlag (C variable):          Global configuration variables.
                                                             (line  127)
* Py_PreInitialize (C function):         Preinitialization with PyPreConfig.
                                                             (line    8)
* Py_PreInitializeFromArgs (C function): Preinitialization with PyPreConfig.
                                                             (line   19)
* Py_PreInitializeFromBytesArgs (C function): Preinitialization with PyPreConfig.
                                                             (line   12)
* Py_PRINT_RAW:                          File Objects.       (line   87)
* PY_PYTHON:                             Customizing default Python versions.
                                                             (line   18)
* Py_QuietFlag (C variable):             Global configuration variables.
                                                             (line  132)
* Py_REFCNT (C macro):                   Base object types and macros.
                                                             (line   73)
* Py_ReprEnter (C function):             Recursion Control.  (line   48)
* Py_ReprLeave (C function):             Recursion Control.  (line   66)
* Py_RETURN_FALSE (C macro):             Boolean Objects.    (line   28)
* Py_RETURN_NONE (C macro):              The None Object.    (line   17)
* Py_RETURN_NOTIMPLEMENTED (C macro):    Object Protocol.    (line   11)
* Py_RETURN_RICHCOMPARE (C macro):       PyTypeObject Slots. (line  839)
* Py_RETURN_TRUE (C macro):              Boolean Objects.    (line   33)
* Py_RunMain (C function):               Py_RunMain.         (line    6)
* Py_SetPath (C function):               Process-wide parameters.
                                                             (line  131)
* Py_SetPath():                          Process-wide parameters.
                                                             (line  120)
* Py_SetProgramName (C function):        Process-wide parameters.
                                                             (line   34)
* Py_SetProgramName():                   Embedding Python<2>.
                                                             (line   42)
* Py_SetProgramName() <1>:               Initializing and finalizing the interpreter.
                                                             (line    8)
* Py_SetProgramName() <2>:               Process-wide parameters.
                                                             (line   53)
* Py_SetProgramName() <3>:               Process-wide parameters.
                                                             (line  111)
* Py_SetPythonHome (C function):         Process-wide parameters.
                                                             (line  267)
* Py_SetStandardStreamEncoding (C function): Process-wide parameters.
                                                             (line    6)
* Py_SET_REFCNT (C function):            Base object types and macros.
                                                             (line   80)
* Py_SET_SIZE (C function):              Base object types and macros.
                                                             (line   93)
* Py_SET_TYPE (C function):              Base object types and macros.
                                                             (line   67)
* Py_single_input (C variable):          The Very High Level Layer.
                                                             (line  399)
* Py_SIZE (C macro):                     Base object types and macros.
                                                             (line   86)
* PY_SOURCE (in module imp):             imp — Access the import internals.
                                                             (line  309)
* PY_SSIZE_T_MAX:                        Integer Objects.    (line  189)
* Py_STRINGIFY (C macro):                Useful macros.      (line   54)
* Py_TPFLAGS_BASETYPE (built-in variable): PyTypeObject Slots.
                                                             (line  501)
* Py_TPFLAGS_BASE_EXC_SUBCLASS (built-in variable): PyTypeObject Slots.
                                                             (line  598)
* Py_TPFLAGS_BYTES_SUBCLASS (built-in variable): PyTypeObject Slots.
                                                             (line  592)
* Py_TPFLAGS_DEFAULT (built-in variable): PyTypeObject Slots.
                                                             (line  550)
* Py_TPFLAGS_DICT_SUBCLASS (built-in variable): PyTypeObject Slots.
                                                             (line  596)
* Py_TPFLAGS_HAVE_FINALIZE (built-in variable): PyTypeObject Slots.
                                                             (line  611)
* Py_TPFLAGS_HAVE_GC (built-in variable): PyTypeObject Slots.
                                                             (line  529)
* Py_TPFLAGS_HAVE_VECTORCALL (built-in variable): PyTypeObject Slots.
                                                             (line  622)
* Py_TPFLAGS_HEAPTYPE (built-in variable): PyTypeObject Slots.
                                                             (line  486)
* Py_TPFLAGS_LIST_SUBCLASS (built-in variable): PyTypeObject Slots.
                                                             (line  588)
* Py_TPFLAGS_LONG_SUBCLASS (built-in variable): PyTypeObject Slots.
                                                             (line  586)
* Py_TPFLAGS_METHOD_DESCRIPTOR (built-in variable): PyTypeObject Slots.
                                                             (line  562)
* Py_TPFLAGS_READY (built-in variable):  PyTypeObject Slots. (line  511)
* Py_TPFLAGS_READYING (built-in variable): PyTypeObject Slots.
                                                             (line  520)
* Py_TPFLAGS_TUPLE_SUBCLASS (built-in variable): PyTypeObject Slots.
                                                             (line  590)
* Py_TPFLAGS_TYPE_SUBCLASS (built-in variable): PyTypeObject Slots.
                                                             (line  600)
* Py_TPFLAGS_UNICODE_SUBCLASS (built-in variable): PyTypeObject Slots.
                                                             (line  594)
* Py_tracefunc (C type):                 Profiling and Tracing.
                                                             (line   18)
* Py_True (C variable):                  Boolean Objects.    (line   22)
* Py_tss_NEEDS_INIT (C macro):           Thread Specific Storage TSS API.
                                                             (line   28)
* Py_tss_t (C type):                     Thread Specific Storage TSS API.
                                                             (line   17)
* Py_TYPE (C macro):                     Base object types and macros.
                                                             (line   53)
* Py_UCS1 (C type):                      Unicode Type.       (line    9)
* Py_UCS2 (C type):                      Unicode Type.       (line    9)
* Py_UCS4 (C type):                      Unicode Type.       (line    9)
* Py_UNBLOCK_THREADS (C macro):          High-level API.     (line  180)
* Py_UnbufferedStdioFlag (C variable):   Global configuration variables.
                                                             (line  141)
* Py_UNICODE (C type):                   Unicode Type.       (line   20)
* Py_UNICODE_ISALNUM (C function):       Unicode Character Properties.
                                                             (line   52)
* Py_UNICODE_ISALPHA (C function):       Unicode Character Properties.
                                                             (line   47)
* Py_UNICODE_ISDECIMAL (C function):     Unicode Character Properties.
                                                             (line   35)
* Py_UNICODE_ISDIGIT (C function):       Unicode Character Properties.
                                                             (line   39)
* Py_UNICODE_ISLINEBREAK (C function):   Unicode Character Properties.
                                                             (line   30)
* Py_UNICODE_ISLOWER (C function):       Unicode Character Properties.
                                                             (line   15)
* Py_UNICODE_ISNUMERIC (C function):     Unicode Character Properties.
                                                             (line   43)
* Py_UNICODE_ISPRINTABLE (C function):   Unicode Character Properties.
                                                             (line   57)
* Py_UNICODE_ISSPACE (C function):       Unicode Character Properties.
                                                             (line   10)
* Py_UNICODE_ISTITLE (C function):       Unicode Character Properties.
                                                             (line   25)
* Py_UNICODE_ISUPPER (C function):       Unicode Character Properties.
                                                             (line   20)
* Py_UNICODE_IS_HIGH_SURROGATE (C macro): Unicode Character Properties.
                                                             (line  114)
* Py_UNICODE_IS_LOW_SURROGATE (C macro): Unicode Character Properties.
                                                             (line  118)
* Py_UNICODE_IS_SURROGATE (C macro):     Unicode Character Properties.
                                                             (line  110)
* Py_UNICODE_JOIN_SURROGATES (C macro):  Unicode Character Properties.
                                                             (line  122)
* Py_UNICODE_TODECIMAL (C function):     Unicode Character Properties.
                                                             (line   91)
* Py_UNICODE_TODIGIT (C function):       Unicode Character Properties.
                                                             (line   97)
* Py_UNICODE_TOLOWER (C function):       Unicode Character Properties.
                                                             (line   70)
* Py_UNICODE_TONUMERIC (C function):     Unicode Character Properties.
                                                             (line  103)
* Py_UNICODE_TOTITLE (C function):       Unicode Character Properties.
                                                             (line   84)
* Py_UNICODE_TOUPPER (C function):       Unicode Character Properties.
                                                             (line   77)
* Py_UNREACHABLE (C macro):              Useful macros.      (line   11)
* Py_UNUSED (C macro):                   Useful macros.      (line   77)
* Py_VaBuildValue (C function):          Building values.    (line  200)
* PY_VECTORCALL_ARGUMENTS_OFFSET (C macro): The Vectorcall Protocol.
                                                             (line   61)
* Py_VerboseFlag (C variable):           Global configuration variables.
                                                             (line  148)
* Py_VISIT (C function):                 Supporting Cyclic Garbage Collection.
                                                             (line  160)
* Py_XDECREF (C function):               Reference Counting. (line   40)
* Py_XDECREF():                          Exceptions<19>.     (line  123)
* Py_XINCREF (C function):               Reference Counting. (line   15)
* P_ALL (in module os):                  Process Management. (line  765)
* P_DETACH (in module os):               Process Management. (line  617)
* P_NOWAIT (in module os):               Process Management. (line  597)
* P_NOWAITO (in module os):              Process Management. (line  597)
* P_OVERLAY (in module os):              Process Management. (line  617)
* P_PGID (in module os):                 Process Management. (line  765)
* P_PID (in module os):                  Process Management. (line  765)
* P_PIDFD (in module os):                Process Management. (line  776)
* P_WAIT (in module os):                 Process Management. (line  607)
* qiflush() (in module curses):          Functions<4>.       (line  382)
* QName (class in xml.etree.ElementTree): QName Objects.     (line    6)
* qsize() (asyncio.Queue method):        Queue.              (line   74)
* qsize() (multiprocessing.Queue method): Pipes and Queues.  (line   98)
* qsize() (queue.Queue method):          Queue Objects.      (line    9)
* qsize() (queue.SimpleQueue method):    SimpleQueue Objects.
                                                             (line    9)
* qualified name:                        Glossary.           (line 1111)
* quantiles() (in module statistics):    Function details.   (line  399)
* quantiles() (statistics.NormalDist method): NormalDist objects.
                                                             (line  103)
* quantize() (decimal.Context method):   Context objects.    (line  459)
* quantize() (decimal.Decimal method):   Decimal objects.    (line  462)
* QueryInfoKey() (in module winreg):     Functions<12>.      (line  324)
* QueryReflectionKey() (in module winreg): Functions<12>.    (line  521)
* QueryValue() (in module winreg):       Functions<12>.      (line  353)
* QueryValueEx() (in module winreg):     Functions<12>.      (line  373)
* Queue (class in asyncio):              Queue.              (line    6)
* Queue (class in multiprocessing):      Pipes and Queues.   (line   84)
* Queue (class in queue):                queue — A synchronized queue class.
                                                             (line   34)
* queue (module):                        queue — A synchronized queue class.
                                                             (line    6)
* queue (sched.scheduler attribute):     Scheduler Objects.  (line   74)
* Queue() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  181)
* QueueEmpty:                            Exceptions<9>.      (line    6)
* QueueFull:                             Exceptions<9>.      (line   11)
* QueueHandler (class in logging.handlers): QueueHandler.    (line   21)
* QueueListener (class in logging.handlers): QueueListener.  (line   25)
* quick_ratio() (difflib.SequenceMatcher method): SequenceMatcher Objects.
                                                             (line  204)
* quit (built-in variable):              Constants added by the site module.
                                                             (line   11)
* quit (pdb command):                    Debugger Commands.  (line  331)
* quit() (ftplib.FTP method):            FTP Objects.        (line  237)
* quit() (nntplib.NNTP method):          Methods<3>.         (line   22)
* quit() (poplib.POP3 method):           POP3 Objects.       (line   82)
* quit() (smtplib.SMTP method):          SMTP Objects.       (line  344)
* quit() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line  123)
* quopri (module):                       quopri — Encode and decode MIME quoted-printable data.
                                                             (line    6)
* quote() (in module email.utils):       email utils Miscellaneous utilities.
                                                             (line   47)
* quote() (in module shlex):             shlex — Simple lexical analysis.
                                                             (line   47)
* quote() (in module urllib.parse):      URL Quoting.        (line   13)
* quoteattr() (in module xml.sax.saxutils): xml sax saxutils — SAX Utilities.
                                                             (line   34)
* quotechar (csv.Dialect attribute):     Dialects and Formatting Parameters.
                                                             (line   52)
* quoted-printable; encoding:            quopri — Encode and decode MIME quoted-printable data.
                                                             (line    8)
* quotes (shlex.shlex attribute):        shlex Objects.      (line  115)
* QUOTE_ALL (in module csv):             Module Contents<3>. (line  248)
* quote_from_bytes() (in module urllib.parse): URL Quoting.  (line   53)
* QUOTE_MINIMAL (in module csv):         Module Contents<3>. (line  252)
* QUOTE_NONE (in module csv):            Module Contents<3>. (line  266)
* QUOTE_NONNUMERIC (in module csv):      Module Contents<3>. (line  258)
* quote_plus() (in module urllib.parse): URL Quoting.        (line   42)
* quoting (csv.Dialect attribute):       Dialects and Formatting Parameters.
                                                             (line   58)
* r"; raw string literal:                String and Bytes literals.
                                                             (line   48)
* r’; raw string literal:                String and Bytes literals.
                                                             (line   48)
* radians() (in module math):            Angular conversion. (line   10)
* radians() (in module turtle):          Settings for measurement.
                                                             (line   28)
* RadioButtonGroup (class in msilib):    GUI classes.        (line   29)
* radiogroup() (msilib.Dialog method):   GUI classes.        (line   73)
* radix() (decimal.Context method):      Context objects.    (line  464)
* radix() (decimal.Decimal method):      Decimal objects.    (line  490)
* RADIXCHAR (in module locale):          locale — Internationalization services.
                                                             (line  232)
* raise (2to3 fixer):                    Fixers.             (line  262)
* Raise (class in ast):                  Statements.         (line  115)
* raise an exception:                    Exceptions<2>.      (line    6)
* raise_on_defect (email.policy.Policy attribute): email policy Policy Objects.
                                                             (line  180)
* raise_signal() (in module signal):     Module contents<2>. (line  276)
* RAISE_VARARGS (opcode):                Python Bytecode Instructions.
                                                             (line  694)
* raising; exception:                    The raise statement.
                                                             (line    6)
* randbelow() (in module secrets):       Random numbers.     (line   19)
* randbits() (in module secrets):        Random numbers.     (line   23)
* randbytes() (in module random):        Functions for bytes.
                                                             (line    6)
* randint() (in module random):          Functions for integers.
                                                             (line   23)
* Random (class in random):              Alternative Generator.
                                                             (line    6)
* random (module):                       random — Generate pseudo-random numbers.
                                                             (line    6)
* random() (in module random):           Real-valued distributions.
                                                             (line   11)
* randrange() (in module random):        Functions for integers.
                                                             (line    6)
* RAND_add() (in module ssl):            Random generation.  (line   66)
* RAND_bytes() (in module ssl):          Random generation.  (line    6)
* RAND_egd() (in module ssl):            Random generation.  (line   50)
* RAND_pseudo_bytes() (in module ssl):   Random generation.  (line   23)
* RAND_status() (in module ssl):         Random generation.  (line   43)
* range (built-in class):                Ranges.             (line   10)
* RARROW (in module token):              token — Constants used with Python parse trees.
                                                             (line  230)
* ratecv() (in module audioop):          audioop — Manipulate raw audio data.
                                                             (line  175)
* ratio() (difflib.SequenceMatcher method): SequenceMatcher Objects.
                                                             (line  180)
* Rational (class in numbers):           The numeric tower.  (line   41)
* raw (io.BufferedIOBase attribute):     I/O Base Classes.   (line  254)
* raw string:                            String and Bytes literals.
                                                             (line   36)
* raw() (in module curses):              Functions<4>.       (line  389)
* raw() (pickle.PickleBuffer method):    Module Interface.   (line  317)
* RawArray() (in module multiprocessing.sharedctypes): The multiprocessing sharedctypes module.
                                                             (line   16)
* RawConfigParser (class in configparser): RawConfigParser Objects.
                                                             (line    6)
* RawDescriptionHelpFormatter (class in argparse): formatter_class.
                                                             (line   10)
* RawIOBase (class in io):               I/O Base Classes.   (line  173)
* RawPen (class in turtle):              Public classes.     (line    6)
* RawTextHelpFormatter (class in argparse): formatter_class. (line   10)
* RawTurtle (class in turtle):           Public classes.     (line    6)
* RawValue() (in module multiprocessing.sharedctypes): The multiprocessing sharedctypes module.
                                                             (line   33)
* raw_data_manager (in module email.contentmanager): Content Manager Instances.
                                                             (line   11)
* raw_decode() (json.JSONDecoder method): Encoders and Decoders.
                                                             (line   94)
* raw_input (2to3 fixer):                Fixers.             (line  269)
* raw_input() (code.InteractiveConsole method): Interactive Console Objects.
                                                             (line   44)
* RBRACE (in module token):              token — Constants used with Python parse trees.
                                                             (line  130)
* rcpttos (smtpd.SMTPChannel attribute): SMTPChannel Objects.
                                                             (line   79)
* re (module):                           re — Regular expression operations.
                                                             (line    6)
* re (re.Match attribute):               Match Objects.      (line  191)
* read() (asyncio.StreamReader method):  StreamReader.       (line   15)
* read() (chunk.Chunk method):           chunk — Read IFF chunked data.
                                                             (line  105)
* read() (codecs.StreamReader method):   StreamReader Objects.
                                                             (line   34)
* read() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  113)
* read() (http.client.HTTPResponse method): HTTPResponse Objects.
                                                             (line   13)
* read() (imaplib.IMAP4 method):         IMAP4 Objects.      (line  198)
* read() (in module os):                 File Descriptor Operations.
                                                             (line  555)
* read() (io.BufferedIOBase method):     I/O Base Classes.   (line  275)
* read() (io.BufferedReader method):     Buffered Streams.   (line   82)
* read() (io.RawIOBase method):          I/O Base Classes.   (line  187)
* read() (io.TextIOBase method):         Text I/O<2>.        (line   52)
* read() (mimetypes.MimeTypes method):   MimeTypes Objects.  (line   70)
* read() (mmap.mmap method):             mmap — Memory-mapped file support.
                                                             (line  225)
* read() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line   32)
* read() (ssl.MemoryBIO method):         Memory BIO Support<2>.
                                                             (line  148)
* read() (ssl.SSLSocket method):         SSL Sockets.        (line   71)
* read() (urllib.robotparser.RobotFileParser method): urllib robotparser — Parser for robots txt.
                                                             (line   25)
* read() (zipfile.ZipFile method):       ZipFile Objects.    (line  215)
* read1() (io.BufferedIOBase method):    I/O Base Classes.   (line  292)
* read1() (io.BufferedReader method):    Buffered Streams.   (line   88)
* read1() (io.BytesIO method):           Buffered Streams.   (line   43)
* READABLE (in module tkinter):          File Handlers.      (line   41)
* readable() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  164)
* readable() (io.IOBase method):         I/O Base Classes.   (line   79)
* readall() (io.RawIOBase method):       I/O Base Classes.   (line  202)
* reader() (in module csv):              Module Contents<3>. (line    8)
* ReadError:                             tarfile — Read and write tar archive files.
                                                             (line  193)
* readexactly() (asyncio.StreamReader method): StreamReader. (line   34)
* readfp() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  305)
* readfp() (mimetypes.MimeTypes method): MimeTypes Objects.  (line   78)
* readframes() (aifc.aifc method):       aifc — Read and write AIFF and AIFC files.
                                                             (line   97)
* readframes() (sunau.AU_read method):   AU_read Objects.    (line   47)
* readframes() (wave.Wave_read method):  Wave_read Objects.  (line   46)
* readinto() (http.client.HTTPResponse method): HTTPResponse Objects.
                                                             (line   17)
* readinto() (io.BufferedIOBase method): I/O Base Classes.   (line  303)
* readinto() (io.RawIOBase method):      I/O Base Classes.   (line  207)
* readinto1() (io.BufferedIOBase method): I/O Base Classes.  (line  316)
* readinto1() (io.BytesIO method):       Buffered Streams.   (line   49)
* readline (module):                     readline — GNU readline interface.
                                                             (line    6)
* readline() (asyncio.StreamReader method): StreamReader.    (line   23)
* readline() (codecs.StreamReader method): StreamReader Objects.
                                                             (line   60)
* readline() (distutils.text_file.TextFile method): distutils text_file — The TextFile class.
                                                             (line  111)
* readline() (imaplib.IMAP4 method):     IMAP4 Objects.      (line  203)
* readline() (io.IOBase method):         I/O Base Classes.   (line   84)
* readline() (io.TextIOBase method):     Text I/O<2>.        (line   58)
* readline() (mmap.mmap method):         mmap — Memory-mapped file support.
                                                             (line  240)
* readlines() (codecs.StreamReader method): StreamReader Objects.
                                                             (line   71)
* readlines() (distutils.text_file.TextFile method): distutils text_file — The TextFile class.
                                                             (line  124)
* readlines() (io.IOBase method):        I/O Base Classes.   (line   93)
* readlink() (in module os):             Files and Directories.
                                                             (line  580)
* readlink() (pathlib.Path method):      Methods<2>.         (line  303)
* readmodule() (in module pyclbr):       pyclbr — Python module browser support.
                                                             (line   19)
* readmodule_ex() (in module pyclbr):    pyclbr — Python module browser support.
                                                             (line   31)
* READONLY:                              Generic Attribute Management.
                                                             (line   92)
* readonly (memoryview attribute):       Memory Views.       (line  413)
* ReadTransport (class in asyncio):      Transports Hierarchy.
                                                             (line   20)
* readuntil() (asyncio.StreamReader method): StreamReader.   (line   43)
* readv() (in module os):                File Descriptor Operations.
                                                             (line  640)
* ready() (multiprocessing.pool.AsyncResult method): Process Pools.
                                                             (line  209)
* read_all() (telnetlib.Telnet method):  Telnet Objects.     (line   17)
* read_binary() (in module importlib.resources): importlib resources – Resources.
                                                             (line  107)
* read_byte() (mmap.mmap method):        mmap — Memory-mapped file support.
                                                             (line  235)
* read_bytes() (importlib.abc.Traversable method): importlib abc – Abstract base classes related to import.
                                                             (line  654)
* read_bytes() (pathlib.Path method):    Methods<2>.         (line  275)
* read_bytes() (zipfile.Path method):    Path Objects.       (line   60)
* read_dict() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  172)
* read_eager() (telnetlib.Telnet method): Telnet Objects.    (line   35)
* read_environ() (in module wsgiref.handlers): wsgiref handlers – server/gateway base classes.
                                                             (line  306)
* read_events() (xml.etree.ElementTree.XMLPullParser method): XMLPullParser Objects.
                                                             (line   29)
* read_file() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  150)
* read_history_file() (in module readline): History file.    (line    8)
* read_init_file() (in module readline): Init file.          (line   13)
* read_lazy() (telnetlib.Telnet method): Telnet Objects.     (line   43)
* read_mime_types() (in module mimetypes): mimetypes — Map filenames to MIME types.
                                                             (line   99)
* READ_RESTRICTED:                       Generic Attribute Management.
                                                             (line   92)
* read_sb_data() (telnetlib.Telnet method): Telnet Objects.  (line   59)
* read_some() (telnetlib.Telnet method): Telnet Objects.     (line   21)
* read_string() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  162)
* read_text() (importlib.abc.Traversable method): importlib abc – Abstract base classes related to import.
                                                             (line  658)
* read_text() (in module importlib.resources): importlib resources – Resources.
                                                             (line  118)
* read_text() (pathlib.Path method):     Methods<2>.         (line  288)
* read_text() (zipfile.Path method):     Path Objects.       (line   54)
* read_token() (shlex.shlex method):     shlex Objects.      (line   20)
* read_until() (telnetlib.Telnet method): Telnet Objects.    (line    8)
* read_very_eager() (telnetlib.Telnet method): Telnet Objects.
                                                             (line   27)
* read_very_lazy() (telnetlib.Telnet method): Telnet Objects.
                                                             (line   51)
* read_windows_registry() (mimetypes.MimeTypes method): MimeTypes Objects.
                                                             (line   86)
* Real (class in numbers):               The numeric tower.  (line   28)
* real (numbers.Complex attribute):      The numeric tower.  (line   15)
* Real Media File Format:                chunk — Read IFF chunked data.
                                                             (line    8)
* realloc():                             Overview<3>.        (line   33)
* realpath() (in module os.path):        os path — Common pathname manipulations.
                                                             (line  304)
* REALTIME_PRIORITY_CLASS (in module subprocess): Windows Constants.
                                                             (line   87)
* real_max_memuse (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  182)
* real_quick_ratio() (difflib.SequenceMatcher method): SequenceMatcher Objects.
                                                             (line  209)
* reap_children() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  857)
* reap_threads() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  720)
* reason (http.client.HTTPResponse attribute): HTTPResponse Objects.
                                                             (line   65)
* reason (ssl.SSLError attribute):       Exceptions<13>.     (line   27)
* reason (UnicodeError attribute):       Concrete exceptions.
                                                             (line  372)
* reason (urllib.error.HTTPError attribute): urllib error — Exception classes raised by urllib request.
                                                             (line   45)
* reason (urllib.error.URLError attribute): urllib error — Exception classes raised by urllib request.
                                                             (line   22)
* reattach() (tkinter.ttk.Treeview method): ttk Treeview.    (line  247)
* rebinding; name:                       Assignment statements.
                                                             (line    6)
* reccontrols() (ossaudiodev.oss_mixer_device method): Mixer Device Objects.
                                                             (line   54)
* received_data (smtpd.SMTPChannel attribute): SMTPChannel Objects.
                                                             (line   84)
* received_lines (smtpd.SMTPChannel attribute): SMTPChannel Objects.
                                                             (line   57)
* recent() (imaplib.IMAP4 method):       IMAP4 Objects.      (line  208)
* reconfigure() (io.TextIOWrapper method): Text I/O<2>.      (line  175)
* records (unittest.TestCase attribute): Test cases.         (line  428)
* record_original_stdout() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  436)
* rect() (in module cmath):              Conversions to and from polar coordinates.
                                                             (line   48)
* rectangle() (in module curses.textpad): curses textpad — Text input widget for curses programs.
                                                             (line   15)
* RecursionError:                        Concrete exceptions.
                                                             (line  187)
* recursive_repr() (in module reprlib):  reprlib — Alternate repr implementation.
                                                             (line   41)
* recv() (asyncore.dispatcher method):   asyncore — Asynchronous socket handler.
                                                             (line  204)
* recv() (multiprocessing.connection.Connection method): Connection Objects<2>.
                                                             (line   24)
* recv() (socket.socket method):         Socket Objects.     (line  219)
* recvfrom() (socket.socket method):     Socket Objects.     (line  236)
* recvfrom_into() (socket.socket method): Socket Objects.    (line  362)
* recvmsg() (socket.socket method):      Socket Objects.     (line  254)
* recvmsg_into() (socket.socket method): Socket Objects.     (line  325)
* recv_bytes() (multiprocessing.connection.Connection method): Connection Objects<2>.
                                                             (line   65)
* recv_bytes_into() (multiprocessing.connection.Connection method): Connection Objects<2>.
                                                             (line   79)
* recv_fds() (in module socket):         Other functions<2>. (line  432)
* recv_into() (socket.socket method):    Socket Objects.     (line  372)
* redirect_request() (urllib.request.HTTPRedirectHandler method): HTTPRedirectHandler Objects.
                                                             (line   15)
* redirect_stderr() (in module contextlib): Utilities.       (line  256)
* redirect_stdout() (in module contextlib): Utilities.       (line  216)
* redisplay() (in module readline):      Line buffer.        (line   19)
* redrawln() (curses.window method):     Window Objects.     (line  459)
* redrawwin() (curses.window method):    Window Objects.     (line  465)
* reduce (2to3 fixer):                   Fixers.             (line  273)
* reduce() (in module functools):        functools — Higher-order functions and operations on callable objects.
                                                             (line  352)
* reducer_override() (pickle.Pickler method): Module Interface.
                                                             (line  200)
* ref (class in weakref):                weakref — Weak references.
                                                             (line   90)
* refcount_test() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  713)
* reference count:                       Glossary.           (line 1138)
* reference counting:                    Objects values and types.
                                                             (line   37)
* ReferenceError:                        Concrete exceptions.
                                                             (line  196)
* ReferenceType (in module weakref):     weakref — Weak references.
                                                             (line  301)
* refold_source (email.policy.EmailPolicy attribute): email policy Policy Objects.
                                                             (line  371)
* refresh() (curses.window method):      Window Objects.     (line  470)
* register() (abc.ABCMeta method):       abc — Abstract Base Classes.
                                                             (line   69)
* register() (in module atexit):         atexit — Exit handlers.
                                                             (line   22)
* register() (in module codecs):         codecs — Codec registry and base classes.
                                                             (line  150)
* register() (in module faulthandler):   Dumping the traceback on a user signal.
                                                             (line    6)
* register() (in module webbrowser):     webbrowser — Convenient Web-browser controller.
                                                             (line   83)
* register() (multiprocessing.managers.BaseManager method): Managers.
                                                             (line   75)
* register() (select.devpoll method):    /dev/poll Polling Objects.
                                                             (line   30)
* register() (select.epoll method):      Edge and Level Trigger Polling epoll Objects.
                                                             (line   81)
* register() (select.poll method):       Polling Objects.    (line   15)
* register() (selectors.BaseSelector method): Classes<3>.    (line   65)
* registerDOMImplementation() (in module xml.dom): Module Contents<4>.
                                                             (line    8)
* registerResult() (in module unittest): Signal Handling.    (line   35)
* register_adapter() (in module sqlite3): Module functions and constants.
                                                             (line  175)
* register_archive_format() (in module shutil): Archiving operations.
                                                             (line   83)
* register_at_fork() (in module os):     Process Management. (line  482)
* register_converter() (in module sqlite3): Module functions and constants.
                                                             (line  166)
* register_defect() (email.policy.Policy method): email policy Policy Objects.
                                                             (line  229)
* register_dialect() (in module csv):    Module Contents<3>. (line   71)
* register_error() (in module codecs):   Error Handlers.     (line   88)
* register_function() (xmlrpc.server.CGIXMLRPCRequestHandler method): CGIXMLRPCRequestHandler.
                                                             (line    9)
* register_function() (xmlrpc.server.SimpleXMLRPCServer method): SimpleXMLRPCServer Objects.
                                                             (line   10)
* register_instance() (xmlrpc.server.CGIXMLRPCRequestHandler method): CGIXMLRPCRequestHandler.
                                                             (line   26)
* register_instance() (xmlrpc.server.SimpleXMLRPCServer method): SimpleXMLRPCServer Objects.
                                                             (line   27)
* register_introspection_functions() (xmlrpc.server.CGIXMLRPCRequestHandler method): CGIXMLRPCRequestHandler.
                                                             (line   41)
* register_introspection_functions() (xmlrpc.server.SimpleXMLRPCServer method): SimpleXMLRPCServer Objects.
                                                             (line   55)
* register_multicall_functions() (xmlrpc.server.CGIXMLRPCRequestHandler method): CGIXMLRPCRequestHandler.
                                                             (line   46)
* register_multicall_functions() (xmlrpc.server.SimpleXMLRPCServer method): SimpleXMLRPCServer Objects.
                                                             (line   60)
* register_namespace() (in module xml.etree.ElementTree): Functions<7>.
                                                             (line  194)
* register_optionflag() (in module doctest): Option Flags.   (line  172)
* register_shape() (in module turtle):   Settings and special methods.
                                                             (line   71)
* register_unpack_format() (in module shutil): Archiving operations.
                                                             (line  128)
* regular package:                       Glossary.           (line 1146)
* REG_BINARY (in module winreg):         Value Types.        (line    8)
* REG_DWORD (in module winreg):          Value Types.        (line   12)
* REG_DWORD_BIG_ENDIAN (in module winreg): Value Types.      (line   21)
* REG_DWORD_LITTLE_ENDIAN (in module winreg): Value Types.   (line   16)
* REG_EXPAND_SZ (in module winreg):      Value Types.        (line   25)
* REG_FULL_RESOURCE_DESCRIPTOR (in module winreg): Value Types.
                                                             (line   60)
* REG_LINK (in module winreg):           Value Types.        (line   30)
* REG_MULTI_SZ (in module winreg):       Value Types.        (line   34)
* REG_NONE (in module winreg):           Value Types.        (line   39)
* REG_QWORD (in module winreg):          Value Types.        (line   43)
* REG_QWORD_LITTLE_ENDIAN (in module winreg): Value Types.   (line   49)
* REG_RESOURCE_LIST (in module winreg):  Value Types.        (line   56)
* REG_RESOURCE_REQUIREMENTS_LIST (in module winreg): Value Types.
                                                             (line   64)
* REG_SZ (in module winreg):             Value Types.        (line   68)
* relative; import:                      The import statement.
                                                             (line   98)
* relative; URL:                         urllib parse — Parse URLs into components.
                                                             (line    8)
* relative_to() (pathlib.PurePath method): Methods and properties.
                                                             (line  254)
* release() (asyncio.Condition method):  Condition.          (line   79)
* release() (asyncio.Lock method):       Lock.               (line   50)
* release() (asyncio.Semaphore method):  Semaphore.          (line   55)
* release() (in module platform):        Cross Platform.     (line  114)
* release() (logging.Handler method):    Handler Objects.    (line   31)
* release() (memoryview method):         Memory Views.       (line  236)
* release() (multiprocessing.Lock method): Synchronization primitives.
                                                             (line   92)
* release() (multiprocessing.RLock method): Synchronization primitives.
                                                             (line  148)
* release() (pickle.PickleBuffer method): Module Interface.  (line  325)
* release() (threading.Condition method): Condition Objects. (line   91)
* release() (threading.Lock method):     Lock Objects.       (line   73)
* release() (threading.RLock method):    RLock Objects.      (line   66)
* release() (threading.Semaphore method): Semaphore Objects. (line   63)
* release() (_thread.lock method):       _thread — Low-level threading API.
                                                             (line  151)
* releasebufferproc (C type):            Slot Type typedefs. (line   96)
* release_lock() (in module imp):        imp — Access the import internals.
                                                             (line  295)
* reload (2to3 fixer):                   Fixers.             (line  277)
* reload() (in module imp):              imp — Access the import internals.
                                                             (line  132)
* reload() (in module importlib):        Functions<11>.      (line   73)
* relpath() (in module os.path):         os path — Common pathname manipulations.
                                                             (line  319)
* remainder() (decimal.Context method):  Context objects.    (line  468)
* remainder() (in module math):          Number-theoretic and representation functions.
                                                             (line  245)
* remainder_near() (decimal.Context method): Context objects.
                                                             (line  475)
* remainder_near() (decimal.Decimal method): Decimal objects.
                                                             (line  496)
* RemoteDisconnected:                    http client — HTTP protocol client.
                                                             (line  184)
* remove() (array.array method):         array — Efficient arrays of numeric values.
                                                             (line  202)
* remove() (collections.deque method):   deque objects.      (line   97)
* remove() (frozenset method):           Set Types — set frozenset.
                                                             (line  199)
* remove() (in module os):               Files and Directories.
                                                             (line  618)
* remove() (mailbox.Mailbox method):     Mailbox objects.    (line   76)
* remove() (mailbox.MH method):          MH.                 (line   76)
* remove() (sequence method):            Mutable Sequence Types.
                                                             (line   16)
* remove() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line  170)
* removeAttribute() (xml.dom.Element method): Element Objects<2>.
                                                             (line   52)
* removeAttributeNode() (xml.dom.Element method): Element Objects<2>.
                                                             (line   57)
* removeAttributeNS() (xml.dom.Element method): Element Objects<2>.
                                                             (line   62)
* removeChild() (xml.dom.Node method):   Node Objects.       (line  128)
* removedirs() (in module os):           Files and Directories.
                                                             (line  642)
* removeFilter() (logging.Handler method): Handler Objects.  (line   56)
* removeFilter() (logging.Logger method): Logger Objects.    (line  267)
* removeHandler() (in module unittest):  Signal Handling.    (line   52)
* removeHandler() (logging.Logger method): Logger Objects.   (line  284)
* removeprefix() (bytearray method):     Bytes and Bytearray Operations.
                                                             (line   49)
* removeprefix() (bytes method):         Bytes and Bytearray Operations.
                                                             (line   49)
* removeprefix() (str method):           String Methods<2>.  (line  365)
* removeResult() (in module unittest):   Signal Handling.    (line   46)
* removesuffix() (bytearray method):     Bytes and Bytearray Operations.
                                                             (line   69)
* removesuffix() (bytes method):         Bytes and Bytearray Operations.
                                                             (line   69)
* removesuffix() (str method):           String Methods<2>.  (line  378)
* removexattr() (in module os):          Linux extended attributes.
                                                             (line   41)
* remove_child_handler() (asyncio.AbstractChildWatcher method): Process Watchers.
                                                             (line   52)
* remove_done_callback() (asyncio.Future method): Future Object.
                                                             (line  102)
* remove_done_callback() (asyncio.Task method): Task Object. (line  161)
* remove_flag() (mailbox.MaildirMessage method): MaildirMessage.
                                                             (line   84)
* remove_flag() (mailbox.mboxMessage method): mboxMessage.   (line   85)
* remove_flag() (mailbox.MMDFMessage method): MMDFMessage.   (line   84)
* remove_folder() (mailbox.Maildir method): Maildir.         (line   76)
* remove_folder() (mailbox.MH method):   MH.                 (line   47)
* remove_header() (urllib.request.Request method): Request Objects.
                                                             (line   99)
* remove_history_item() (in module readline): History list.  (line   26)
* remove_label() (mailbox.BabylMessage method): BabylMessage.
                                                             (line   59)
* remove_option() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  271)
* remove_option() (optparse.OptionParser method): Querying and manipulating your option parser.
                                                             (line   47)
* remove_pyc() (msilib.Directory method): Directory Objects. (line   45)
* remove_reader() (asyncio.loop method): Watching file descriptors.
                                                             (line   12)
* remove_section() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  278)
* remove_sequence() (mailbox.MHMessage method): MHMessage.   (line   46)
* remove_signal_handler() (asyncio.loop method): Unix signals.
                                                             (line   26)
* remove_tree() (in module distutils.dir_util): distutils dir_util — Directory tree operations.
                                                             (line   60)
* remove_writer() (asyncio.loop method): Watching file descriptors.
                                                             (line   25)
* rename() (ftplib.FTP method):          FTP Objects.        (line  202)
* rename() (imaplib.IMAP4 method):       IMAP4 Objects.      (line  213)
* rename() (in module os):               Files and Directories.
                                                             (line  659)
* rename() (pathlib.Path method):        Methods<2>.         (line  315)
* renames (2to3 fixer):                  Fixers.             (line  281)
* renames() (in module os):              Files and Directories.
                                                             (line  693)
* reopenIfNeeded() (logging.handlers.WatchedFileHandler method): WatchedFileHandler.
                                                             (line   41)
* reorganize() (dbm.gnu.gdbm method):    dbm gnu — GNU’s reinterpretation of dbm.
                                                             (line  104)
* repeat() (in module itertools):        Itertool functions. (line  497)
* repeat() (in module timeit):           Python Interface.   (line   18)
* repeat() (timeit.Timer method):        Python Interface.   (line  108)
* repetition; operation:                 Common Sequence Operations.
                                                             (line   21)
* replace() (bytearray method):          Bytes and Bytearray Operations.
                                                             (line  193)
* replace() (bytes method):              Bytes and Bytearray Operations.
                                                             (line  193)
* replace() (curses.panel.Panel method): Panel Objects.      (line   39)
* replace() (datetime.date method):      date Objects.       (line  166)
* replace() (datetime.datetime method):  datetime Objects.   (line  413)
* replace() (datetime.time method):      time Objects.       (line  139)
* replace() (in module dataclasses):     Module-level decorators classes and functions.
                                                             (line  356)
* replace() (in module os):              Files and Directories.
                                                             (line  711)
* replace() (inspect.Parameter method):  Introspecting callables with the Signature object.
                                                             (line  253)
* replace() (inspect.Signature method):  Introspecting callables with the Signature object.
                                                             (line  111)
* replace() (pathlib.Path method):       Methods<2>.         (line  339)
* replace() (str method):                String Methods<2>.  (line  391)
* replace() (types.CodeType method):     Standard Interpreter Types.
                                                             (line   63)
* replaceChild() (xml.dom.Node method):  Node Objects.       (line  135)
* ReplacePackage() (in module modulefinder): modulefinder — Find modules used by a script.
                                                             (line   21)
* replace_errors() (in module codecs):   Error Handlers.     (line  133)
* replace_header() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  301)
* replace_header() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  409)
* replace_history_item() (in module readline): History list. (line   32)
* replace_whitespace (textwrap.TextWrapper attribute): textwrap — Text wrapping and filling.
                                                             (line  179)
* report() (filecmp.dircmp method):      The dircmp class.   (line   18)
* report() (modulefinder.ModuleFinder method): modulefinder — Find modules used by a script.
                                                             (line   38)
* REPORTING_FLAGS (in module doctest):   Option Flags.       (line  164)
* REPORT_CDIFF (in module doctest):      Option Flags.       (line  126)
* report_failure() (doctest.DocTestRunner method): DocTestRunner objects.
                                                             (line   70)
* report_full_closure() (filecmp.dircmp method): The dircmp class.
                                                             (line   28)
* REPORT_NDIFF (in module doctest):      Option Flags.       (line  131)
* REPORT_ONLY_FIRST_FAILURE (in module doctest): Option Flags.
                                                             (line  140)
* report_partial_closure() (filecmp.dircmp method): The dircmp class.
                                                             (line   23)
* report_start() (doctest.DocTestRunner method): DocTestRunner objects.
                                                             (line   48)
* report_success() (doctest.DocTestRunner method): DocTestRunner objects.
                                                             (line   59)
* REPORT_UDIFF (in module doctest):      Option Flags.       (line  121)
* report_unexpected_exception() (doctest.DocTestRunner method): DocTestRunner objects.
                                                             (line   81)
* repr (2to3 fixer):                     Fixers.             (line  285)
* Repr (class in reprlib):               reprlib — Alternate repr implementation.
                                                             (line   17)
* repr() (built-in function):            Built-in Functions. (line 1427)
* repr() (built-in function); __repr__() (object method): Basic customization.
                                                             (line  112)
* repr() (in module reprlib):            reprlib — Alternate repr implementation.
                                                             (line   31)
* repr() (reprlib.Repr method):          Repr Objects.       (line   47)
* repr1() (reprlib.Repr method):         Repr Objects.       (line   52)
* reprfunc (C type):                     Slot Type typedefs. (line   38)
* reprlib (module):                      reprlib — Alternate repr implementation.
                                                             (line    6)
* Request (class in urllib.request):     urllib request — Extensible library for opening URLs.
                                                             (line  174)
* request() (http.client.HTTPConnection method): HTTPConnection Objects.
                                                             (line    8)
* RequestHandlerClass (socketserver.BaseServer attribute): Server Objects<2>.
                                                             (line   71)
* requestline (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line   81)
* request_queue_size (socketserver.BaseServer attribute): Server Objects<2>.
                                                             (line   98)
* request_rate() (urllib.robotparser.RobotFileParser method): urllib robotparser — Parser for robots txt.
                                                             (line   60)
* request_uri() (in module wsgiref.util): wsgiref util – WSGI environment utilities.
                                                             (line   25)
* request_version (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line   99)
* requires() (in module test.support):   test support — Utilities for the Python test suite.
                                                             (line  271)
* requires_bz2() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  682)
* requires_docstrings() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  694)
* requires_freebsd_version() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  652)
* requires_gzip() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  678)
* requires_IEEE_754() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  670)
* requires_linux_version() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  658)
* requires_lzma() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  686)
* requires_mac_version() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  664)
* requires_resource() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  690)
* requires_zlib() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  674)
* RERAISE (opcode):                      Python Bytecode Instructions.
                                                             (line  385)
* reserved (zipfile.ZipInfo attribute):  ZipInfo Objects.    (line  111)
* reserved word:                         Keywords.           (line    6)
* RESERVED_FUTURE (in module uuid):      uuid — UUID objects according to RFC 4122.
                                                             (line  236)
* RESERVED_MICROSOFT (in module uuid):   uuid — UUID objects according to RFC 4122.
                                                             (line  232)
* RESERVED_NCS (in module uuid):         uuid — UUID objects according to RFC 4122.
                                                             (line  224)
* reset() (bdb.Bdb method):              bdb — Debugger framework.
                                                             (line  106)
* reset() (codecs.IncrementalDecoder method): IncrementalDecoder Objects.
                                                             (line   40)
* reset() (codecs.IncrementalEncoder method): IncrementalEncoder Objects.
                                                             (line   35)
* reset() (codecs.StreamReader method):  StreamReader Objects.
                                                             (line   83)
* reset() (codecs.StreamWriter method):  StreamWriter Objects.
                                                             (line   41)
* reset() (contextvars.ContextVar method): Context Variables.
                                                             (line   58)
* reset() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line   23)
* reset() (in module turtle):            More drawing control.
                                                             (line    6)
* reset() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line  172)
* reset() (pipes.Template method):       Template Objects.   (line    8)
* reset() (threading.Barrier method):    Barrier Objects.    (line   71)
* reset() (xdrlib.Packer method):        Packer Objects.     (line   12)
* reset() (xdrlib.Unpacker method):      Unpacker Objects.   (line    8)
* reset() (xml.dom.pulldom.DOMEventStream method): DOMEventStream Objects.
                                                             (line   37)
* reset() (xml.sax.xmlreader.IncrementalParser method): IncrementalParser Objects.
                                                             (line   19)
* resetbuffer() (code.InteractiveConsole method): Interactive Console Objects.
                                                             (line   40)
* resetlocale() (in module locale):      locale — Internationalization services.
                                                             (line  367)
* resetscreen() (in module turtle):      Window control.     (line   59)
* resetty() (in module curses):          Functions<4>.       (line  405)
* resetwarnings() (in module warnings):  Available Functions.
                                                             (line   99)
* reset_mock() (unittest.mock.AsyncMock method): The Mock Class.
                                                             (line  860)
* reset_mock() (unittest.mock.Mock method): The Mock Class.  (line  198)
* reset_peak() (in module tracemalloc):  Functions<10>.      (line   38)
* reset_prog_mode() (in module curses):  Functions<4>.       (line  395)
* reset_shell_mode() (in module curses): Functions<4>.       (line  400)
* reset_tzpath() (in module zoneinfo):   Functions<2>.       (line   27)
* resize() (curses.window method):       Window Objects.     (line  489)
* resize() (in module ctypes):           Utility functions.  (line  163)
* resize() (mmap.mmap method):           mmap — Memory-mapped file support.
                                                             (line  246)
* resizemode() (in module turtle):       Appearance.         (line   24)
* resizeterm() (in module curses):       Functions<4>.       (line  420)
* resize_term() (in module curses):      Functions<4>.       (line  410)
* resolution (datetime.date attribute):  date Objects.       (line   95)
* resolution (datetime.datetime attribute): datetime Objects.
                                                             (line  257)
* resolution (datetime.time attribute):  time Objects.       (line   42)
* resolution (datetime.timedelta attribute): timedelta Objects.
                                                             (line   84)
* resolve() (pathlib.Path method):       Methods<2>.         (line  352)
* resolveEntity() (xml.sax.handler.EntityResolver method): EntityResolver Objects.
                                                             (line    6)
* resolve_bases() (in module types):     Dynamic Type Creation.
                                                             (line   58)
* resolve_name() (in module importlib.util): importlib util – Utility code for importers.
                                                             (line   80)
* resolve_name() (in module pkgutil):    pkgutil — Package extension utility.
                                                             (line  227)
* Resource (in module importlib.resources): importlib resources – Resources.
                                                             (line   45)
* resource (module):                     resource — Resource usage information.
                                                             (line    6)
* ResourceDenied:                        test support — Utilities for the Python test suite.
                                                             (line   22)
* ResourceLoader (class in importlib.abc): importlib abc – Abstract base classes related to import.
                                                             (line  360)
* ResourceReader (class in importlib.abc): importlib abc – Abstract base classes related to import.
                                                             (line  287)
* ResourceWarning:                       Warnings.           (line   73)
* resource_path() (importlib.abc.ResourceReader method): importlib abc – Abstract base classes related to import.
                                                             (line  329)
* response (nntplib.NNTPError attribute): nntplib — NNTP protocol client.
                                                             (line  136)
* response() (imaplib.IMAP4 method):     IMAP4 Objects.      (line  217)
* ResponseNotReady:                      http client — HTTP protocol client.
                                                             (line  170)
* responses (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  172)
* responses (in module http.client):     http client — HTTP protocol client.
                                                             (line  205)
* restart (pdb command):                 Debugger Commands.  (line  322)
* restore() (in module difflib):         difflib — Helpers for computing deltas.
                                                             (line  273)
* RESTRICTED:                            Generic Attribute Management.
                                                             (line   92)
* restricted; execution:                 Builtins and restricted execution.
                                                             (line    6)
* restype (ctypes._FuncPtr attribute):   Foreign functions.  (line   22)
* result() (asyncio.Future method):      Future Object.      (line   28)
* result() (asyncio.Task method):        Task Object.        (line  123)
* result() (concurrent.futures.Future method): Future Objects.
                                                             (line   38)
* results() (trace.Trace method):        Programmatic Interface.
                                                             (line   40)
* resume_reading() (asyncio.ReadTransport method): Read-only Transports.
                                                             (line   21)
* resume_writing() (asyncio.BaseProtocol method): Base Protocol.
                                                             (line   44)
* retr() (poplib.POP3 method):           POP3 Objects.       (line   62)
* retrbinary() (ftplib.FTP method):      FTP Objects.        (line   84)
* retrieve() (urllib.request.URLopener method): Legacy interface.
                                                             (line  113)
* retrlines() (ftplib.FTP method):       FTP Objects.        (line   96)
* Return (class in ast):                 Function and class definitions.
                                                             (line  117)
* return (pdb command):                  Debugger Commands.  (line  188)
* returncode (asyncio.asyncio.subprocess.Process attribute): Interacting with Subprocesses.
                                                             (line  140)
* returncode (subprocess.CalledProcessError attribute): Using the subprocess Module.
                                                             (line  196)
* returncode (subprocess.CompletedProcess attribute): Using the subprocess Module.
                                                             (line  101)
* returncode (subprocess.Popen attribute): Popen Objects.    (line  147)
* return_annotation (inspect.Signature attribute): Introspecting callables with the Signature object.
                                                             (line   90)
* return_ok() (http.cookiejar.CookiePolicy method): CookiePolicy Objects.
                                                             (line   18)
* RETURN_VALUE (opcode):                 Python Bytecode Instructions.
                                                             (line  342)
* return_value (unittest.mock.Mock attribute): The Mock Class.
                                                             (line  321)
* retval (pdb command):                  Debugger Commands.  (line  341)
* reverse() (array.array method):        array — Efficient arrays of numeric values.
                                                             (line  206)
* reverse() (collections.deque method):  deque objects.      (line  102)
* reverse() (in module audioop):         audioop — Manipulate raw audio data.
                                                             (line  188)
* reverse() (sequence method):           Mutable Sequence Types.
                                                             (line   16)
* reversed() (built-in function):        Built-in Functions. (line 1439)
* reverse_order() (pstats.Stats method): The Stats Class.    (line  157)
* reverse_pointer (ipaddress.IPv4Address attribute): Address objects.
                                                             (line   83)
* reverse_pointer (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  210)
* Reversible (class in collections.abc): Collections Abstract Base Classes.
                                                             (line  143)
* Reversible (class in typing):          Corresponding to other types in collections abc.
                                                             (line   62)
* revert() (http.cookiejar.FileCookieJar method): CookieJar and FileCookieJar Objects.
                                                             (line  141)
* rewind() (aifc.aifc method):           aifc — Read and write AIFF and AIFC files.
                                                             (line  103)
* rewind() (sunau.AU_read method):       AU_read Objects.    (line   53)
* rewind() (wave.Wave_read method):      Wave_read Objects.  (line   51)
* rfc2109 (http.cookiejar.Cookie attribute): Cookie Objects<2>.
                                                             (line   68)
* rfc2109_as_netscape (http.cookiejar.DefaultCookiePolicy attribute): DefaultCookiePolicy Objects.
                                                             (line   83)
* rfc2965 (http.cookiejar.CookiePolicy attribute): CookiePolicy Objects.
                                                             (line   72)
* rfc822_escape() (in module distutils.util): distutils util — Miscellaneous other utility functions.
                                                             (line  192)
* RFC; RFC 1014:                         xdrlib — Encode and decode XDR data.
                                                             (line   11)
* RFC; RFC 1014 <1>:                     xdrlib — Encode and decode XDR data.
                                                             (line   32)
* RFC; RFC 1123:                         Functions<3>.       (line  615)
* RFC; RFC 1321:                         hashlib — Secure hashes and message digests.
                                                             (line   13)
* RFC; RFC 1422:                         Certificates.       (line   38)
* RFC; RFC 1422 <1>:                     LibreSSL support.   (line   29)
* RFC; RFC 1521:                         base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  258)
* RFC; RFC 1521 <1>:                     quopri — Encode and decode MIME quoted-printable data.
                                                             (line   11)
* RFC; RFC 1521 <2>:                     quopri — Encode and decode MIME quoted-printable data.
                                                             (line   37)
* RFC; RFC 1522:                         binascii — Convert between binary and ASCII.
                                                             (line   71)
* RFC; RFC 1522 <1>:                     quopri — Encode and decode MIME quoted-printable data.
                                                             (line   25)
* RFC; RFC 1522 <2>:                     quopri — Encode and decode MIME quoted-printable data.
                                                             (line   39)
* RFC; RFC 1524:                         mailcap — Mailcap file handling.
                                                             (line   19)
* RFC; RFC 1524 <1>:                     mailcap — Mailcap file handling.
                                                             (line   38)
* RFC; RFC 1730:                         imaplib — IMAP4 protocol client.
                                                             (line   14)
* RFC; RFC 1738:                         URL Quoting.        (line  187)
* RFC; RFC 1750:                         Random generation.  (line   70)
* RFC; RFC 1766:                         locale — Internationalization services.
                                                             (line  322)
* RFC; RFC 1766 <1>:                     locale — Internationalization services.
                                                             (line  333)
* RFC; RFC 1808:                         urllib.             (line   23)
* RFC; RFC 1808 <1>:                     URL Parsing.        (line   42)
* RFC; RFC 1808 <2>:                     URL Quoting.        (line  181)
* RFC; RFC 1832:                         xdrlib — Encode and decode XDR data.
                                                             (line   36)
* RFC; RFC 1832 <1>:                     xdrlib — Encode and decode XDR data.
                                                             (line   38)
* RFC; RFC 1869:                         smtplib — SMTP protocol client.
                                                             (line   13)
* RFC; RFC 1869 <1>:                     smtplib — SMTP protocol client.
                                                             (line  194)
* RFC; RFC 1870:                         smtpd<3>.           (line    7)
* RFC; RFC 1870 <1>:                     smtpd — SMTP Server.
                                                             (line   26)
* RFC; RFC 1870 <2>:                     SMTPChannel Objects.
                                                             (line  125)
* RFC; RFC 1939:                         poplib — POP3 protocol client.
                                                             (line   11)
* RFC; RFC 1939 <1>:                     poplib — POP3 protocol client.
                                                             (line   13)
* RFC; RFC 2033:                         New and Improved Modules<2>.
                                                             (line  569)
* RFC; RFC 2045:                         email — An email and MIME handling package.
                                                             (line   16)
* RFC; RFC 2045 <1>:                     email message Representing an email message.
                                                             (line  316)
* RFC; RFC 2045 <2>:                     email message Representing an email message.
                                                             (line  318)
* RFC; RFC 2045 <3>:                     email message Representing an email message.
                                                             (line  321)
* RFC; RFC 2045 <4>:                     email headerregistry Custom Header Objects.
                                                             (line  239)
* RFC; RFC 2045 <5>:                     email headerregistry Custom Header Objects.
                                                             (line  297)
* RFC; RFC 2045 <6>:                     email message Message Representing an email message using the compat32 API.
                                                             (line  422)
* RFC; RFC 2045 <7>:                     email message Message Representing an email message using the compat32 API.
                                                             (line  426)
* RFC; RFC 2045 <8>:                     email message Message Representing an email message using the compat32 API.
                                                             (line  429)
* RFC; RFC 2045 <9>:                     email message Message Representing an email message using the compat32 API.
                                                             (line  526)
* RFC; RFC 2045 <10>:                    email header Internationalized headers.
                                                             (line   31)
* RFC; RFC 2045 <11>:                    base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line   30)
* RFC; RFC 2045 <12>:                    base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line   31)
* RFC; RFC 2045 <13>:                    base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  228)
* RFC; RFC 2045 <14>:                    base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  236)
* RFC; RFC 2045#section-6.8:             Binary Objects.     (line   31)
* RFC; RFC 2046:                         email — An email and MIME handling package.
                                                             (line   16)
* RFC; RFC 2046 <1>:                     Content Manager Instances.
                                                             (line   85)
* RFC; RFC 2046 <2>:                     email header Internationalized headers.
                                                             (line   32)
* RFC; RFC 2047:                         PEP 3333 Python Web Server Gateway Interface v1 0 1.
                                                             (line   21)
* RFC; RFC 2047 <1>:                     email<5>.           (line   27)
* RFC; RFC 2047 <2>:                     email — An email and MIME handling package.
                                                             (line   16)
* RFC; RFC 2047 <3>:                     email policy Policy Objects.
                                                             (line  347)
* RFC; RFC 2047 <4>:                     email policy Policy Objects.
                                                             (line  353)
* RFC; RFC 2047 <5>:                     email headerregistry Custom Header Objects.
                                                             (line   78)
* RFC; RFC 2047 <6>:                     email headerregistry Custom Header Objects.
                                                             (line  123)
* RFC; RFC 2047 <7>:                     email headerregistry Custom Header Objects.
                                                             (line  128)
* RFC; RFC 2047 <8>:                     email header Internationalized headers.
                                                             (line   32)
* RFC; RFC 2047 <9>:                     email header Internationalized headers.
                                                             (line   55)
* RFC; RFC 2047 <10>:                    email header Internationalized headers.
                                                             (line  117)
* RFC; RFC 2047 <11>:                    email header Internationalized headers.
                                                             (line  141)
* RFC; RFC 2047 <12>:                    email utils Miscellaneous utilities.
                                                             (line   74)
* RFC; RFC 2060:                         imaplib — IMAP4 protocol client.
                                                             (line   13)
* RFC; RFC 2060 <1>:                     IMAP4 Objects.      (line  316)
* RFC; RFC 2068:                         http cookies — HTTP state management.
                                                             (line   16)
* RFC; RFC 2104:                         New and Improved Modules<3>.
                                                             (line   35)
* RFC; RFC 2104 <1>:                     hmac — Keyed-Hashing for Message Authentication.
                                                             (line   10)
* RFC; RFC 2109:                         http cookies — HTTP state management.
                                                             (line   15)
* RFC; RFC 2109 <1>:                     http cookies — HTTP state management.
                                                             (line   35)
* RFC; RFC 2109 <2>:                     http cookies — HTTP state management.
                                                             (line   65)
* RFC; RFC 2109 <3>:                     Morsel Objects.     (line    8)
* RFC; RFC 2109 <4>:                     Morsel Objects.     (line   11)
* RFC; RFC 2109 <5>:                     Morsel Objects.     (line   98)
* RFC; RFC 2109 <6>:                     Morsel Objects.     (line  110)
* RFC; RFC 2109 <7>:                     http cookiejar — Cookie handling for HTTP clients.
                                                             (line   17)
* RFC; RFC 2109 <8>:                     http cookiejar — Cookie handling for HTTP clients.
                                                             (line   99)
* RFC; RFC 2109 <9>:                     http cookiejar — Cookie handling for HTTP clients.
                                                             (line  111)
* RFC; RFC 2109 <10>:                    http cookiejar — Cookie handling for HTTP clients.
                                                             (line  138)
* RFC; RFC 2109 <11>:                    DefaultCookiePolicy Objects.
                                                             (line   86)
* RFC; RFC 2109 <12>:                    Cookie Objects<2>.  (line   11)
* RFC; RFC 2109 <13>:                    Cookie Objects<2>.  (line   23)
* RFC; RFC 2109 <14>:                    Cookie Objects<2>.  (line   70)
* RFC; RFC 2183:                         email — An email and MIME handling package.
                                                             (line   16)
* RFC; RFC 2183 <1>:                     email message Representing an email message.
                                                             (line  460)
* RFC; RFC 2183 <2>:                     email message Message Representing an email message using the compat32 API.
                                                             (line  632)
* RFC; RFC 2231:                         email — An email and MIME handling package.
                                                             (line   16)
* RFC; RFC 2231 <1>:                     email message Representing an email message.
                                                             (line  280)
* RFC; RFC 2231 <2>:                     email message Representing an email message.
                                                             (line  283)
* RFC; RFC 2231 <3>:                     email message Representing an email message.
                                                             (line  365)
* RFC; RFC 2231 <4>:                     email message Message Representing an email message using the compat32 API.
                                                             (line  385)
* RFC; RFC 2231 <5>:                     email message Message Representing an email message using the compat32 API.
                                                             (line  389)
* RFC; RFC 2231 <6>:                     email message Message Representing an email message using the compat32 API.
                                                             (line  491)
* RFC; RFC 2231 <7>:                     email message Message Representing an email message using the compat32 API.
                                                             (line  499)
* RFC; RFC 2231 <8>:                     email message Message Representing an email message using the compat32 API.
                                                             (line  533)
* RFC; RFC 2231 <9>:                     email header Internationalized headers.
                                                             (line   32)
* RFC; RFC 2231 <10>:                    email utils Miscellaneous utilities.
                                                             (line  176)
* RFC; RFC 2231 <11>:                    email utils Miscellaneous utilities.
                                                             (line  181)
* RFC; RFC 2231 <12>:                    email utils Miscellaneous utilities.
                                                             (line  190)
* RFC; RFC 2231 <13>:                    email utils Miscellaneous utilities.
                                                             (line  197)
* RFC; RFC 2231 <14>:                    email utils Miscellaneous utilities.
                                                             (line  206)
* RFC; RFC 2295:                         HTTP status codes.  (line  184)
* RFC; RFC 2324:                         HTTP status codes.  (line  133)
* RFC; RFC 2342:                         New and Improved Modules<3>.
                                                             (line   93)
* RFC; RFC 2342 <1>:                     IMAP4 Objects.      (line  164)
* RFC; RFC 2368:                         URL Quoting.        (line  177)
* RFC; RFC 2373:                         Address objects.    (line  101)
* RFC; RFC 2373 <1>:                     Address objects.    (line  120)
* RFC; RFC 2373 <2>:                     Address objects.    (line  129)
* RFC; RFC 2396:                         urllib parse<3>.    (line    6)
* RFC; RFC 2396 <1>:                     urllib.             (line   24)
* RFC; RFC 2396 <2>:                     URL Parsing.        (line  253)
* RFC; RFC 2396 <3>:                     URL Quoting.        (line   25)
* RFC; RFC 2396 <4>:                     URL Quoting.        (line  172)
* RFC; RFC 2397:                         DataHandler Objects.
                                                             (line    9)
* RFC; RFC 2449:                         POP3 Objects.       (line   26)
* RFC; RFC 2487:                         New and Improved Modules<3>.
                                                             (line   85)
* RFC; RFC 2518:                         HTTP status codes.  (line   19)
* RFC; RFC 2595:                         poplib — POP3 protocol client.
                                                             (line   14)
* RFC; RFC 2595 <1>:                     POP3 Objects.       (line  115)
* RFC; RFC 2616:                         PEP 3333 Python Web Server Gateway Interface v1 0 1.
                                                             (line   20)
* RFC; RFC 2616 <1>:                     wsgiref util – WSGI environment utilities.
                                                             (line  112)
* RFC; RFC 2616 <2>:                     wsgiref validate — WSGI conformance checker.
                                                             (line   27)
* RFC; RFC 2616 <3>:                     HTTPRedirectHandler Objects.
                                                             (line    8)
* RFC; RFC 2616 <4>:                     HTTPRedirectHandler Objects.
                                                             (line   28)
* RFC; RFC 2616 <5>:                     Legacy interface.   (line  164)
* RFC; RFC 2616 <6>:                     urllib error — Exception classes raised by urllib request.
                                                             (line   40)
* RFC; RFC 2616 <7>:                     Introduction<16>.   (line   34)
* RFC; RFC 2616 <8>:                     HTTPError.          (line   15)
* RFC; RFC 2616 <9>:                     Error Codes.        (line   12)
* RFC; RFC 2640:                         Changes in the Python API.
                                                             (line   36)
* RFC; RFC 2640 <1>:                     Tests<15>.          (line   22)
* RFC; RFC 2640 <2>:                     ftplib — FTP protocol client.
                                                             (line   18)
* RFC; RFC 2640 <3>:                     ftplib — FTP protocol client.
                                                             (line   80)
* RFC; RFC 2640 <4>:                     ftplib — FTP protocol client.
                                                             (line  118)
* RFC; RFC 2732:                         urllib parse<4>.    (line   10)
* RFC; RFC 2732 <1>:                     New and Improved Modules.
                                                             (line  638)
* RFC; RFC 2732 <2>:                     URL Quoting.        (line  168)
* RFC; RFC 2774:                         HTTP status codes.  (line  193)
* RFC; RFC 2818:                         ssl<9>.             (line   16)
* RFC; RFC 2818 <1>:                     Certificate handling.
                                                             (line   11)
* RFC; RFC 2821:                         email — An email and MIME handling package.
                                                             (line   12)
* RFC; RFC 2822:                         New and Improved Modules<3>.
                                                             (line   97)
* RFC; RFC 2822 <1>:                     Batteries Included. (line   16)
* RFC; RFC 2822 <2>:                     Functions<3>.       (line  346)
* RFC; RFC 2822 <3>:                     Functions<3>.       (line  616)
* RFC; RFC 2822 <4>:                     email message Message Representing an email message using the compat32 API.
                                                             (line  274)
* RFC; RFC 2822 <5>:                     email header Internationalized headers.
                                                             (line   20)
* RFC; RFC 2822 <6>:                     email header Internationalized headers.
                                                             (line   23)
* RFC; RFC 2822 <7>:                     email header Internationalized headers.
                                                             (line   31)
* RFC; RFC 2822 <8>:                     email header Internationalized headers.
                                                             (line   88)
* RFC; RFC 2822 <9>:                     email header Internationalized headers.
                                                             (line  116)
* RFC; RFC 2822 <10>:                    email header Internationalized headers.
                                                             (line  134)
* RFC; RFC 2822 <11>:                    email utils Miscellaneous utilities.
                                                             (line   31)
* RFC; RFC 2822 <12>:                    email utils Miscellaneous utilities.
                                                             (line   98)
* RFC; RFC 2822 <13>:                    email utils Miscellaneous utilities.
                                                             (line  101)
* RFC; RFC 2822 <14>:                    email utils Miscellaneous utilities.
                                                             (line  224)
* RFC; RFC 2822 <15>:                    email utils Miscellaneous utilities.
                                                             (line  142)
* RFC; RFC 2822 <16>:                    Message objects.    (line   17)
* RFC; RFC 2822 <17>:                    http client — HTTP protocol client.
                                                             (line  112)
* RFC; RFC 2822 <18>:                    http server — HTTP servers.
                                                             (line  111)
* RFC; RFC 2964:                         http cookiejar — Cookie handling for HTTP clients.
                                                             (line  151)
* RFC; RFC 2965:                         urllib request — Extensible library for opening URLs.
                                                             (line  217)
* RFC; RFC 2965 <1>:                     urllib request — Extensible library for opening URLs.
                                                             (line  225)
* RFC; RFC 2965 <2>:                     Request Objects.    (line   50)
* RFC; RFC 2965 <3>:                     http cookiejar — Cookie handling for HTTP clients.
                                                             (line   16)
* RFC; RFC 2965 <4>:                     http cookiejar — Cookie handling for HTTP clients.
                                                             (line   99)
* RFC; RFC 2965 <5>:                     http cookiejar — Cookie handling for HTTP clients.
                                                             (line  111)
* RFC; RFC 2965 <6>:                     http cookiejar — Cookie handling for HTTP clients.
                                                             (line  140)
* RFC; RFC 2965 <7>:                     http cookiejar — Cookie handling for HTTP clients.
                                                             (line  142)
* RFC; RFC 2965 <8>:                     http cookiejar — Cookie handling for HTTP clients.
                                                             (line  149)
* RFC; RFC 2965 <9>:                     FileCookieJar subclasses and co-operation with web browsers.
                                                             (line   16)
* RFC; RFC 2965 <10>:                    CookiePolicy Objects.
                                                             (line   74)
* RFC; RFC 2965 <11>:                    CookiePolicy Objects.
                                                             (line   79)
* RFC; RFC 2965 <12>:                    DefaultCookiePolicy Objects.
                                                             (line    8)
* RFC; RFC 2965 <13>:                    DefaultCookiePolicy Objects.
                                                             (line   90)
* RFC; RFC 2965 <14>:                    DefaultCookiePolicy Objects.
                                                             (line  101)
* RFC; RFC 2965 <15>:                    DefaultCookiePolicy Objects.
                                                             (line  105)
* RFC; RFC 2965 <16>:                    DefaultCookiePolicy Objects.
                                                             (line  114)
* RFC; RFC 2965 <17>:                    DefaultCookiePolicy Objects.
                                                             (line  151)
* RFC; RFC 2965 <18>:                    Cookie Objects<2>.  (line   23)
* RFC; RFC 2965 <19>:                    Examples<25>.       (line   25)
* RFC; RFC 2980:                         nntplib — NNTP protocol client.
                                                             (line   13)
* RFC; RFC 2980 <1>:                     Methods<3>.         (line  317)
* RFC; RFC 3056:                         Address objects.    (line  257)
* RFC; RFC 3171:                         Address objects.    (line  100)
* RFC; RFC 3207:                         New and Improved Modules<2>.
                                                             (line  574)
* RFC; RFC 3229:                         HTTP status codes.  (line   52)
* RFC; RFC 3280:                         SSL Sockets.        (line  152)
* RFC; RFC 3330:                         Address objects.    (line  128)
* RFC; RFC 3339:                         Displaying the date/time in messages.
                                                             (line   18)
* RFC; RFC 3454:                         stringprep — Internet String Preparation.
                                                             (line   17)
* RFC; RFC 3454 <1>:                     stringprep — Internet String Preparation.
                                                             (line   26)
* RFC; RFC 3490:                         Text Encodings.     (line   14)
* RFC; RFC 3490 <1>:                     encodings idna — Internationalized Domain Names in Applications.
                                                             (line    6)
* RFC; RFC 3490 <2>:                     encodings idna — Internationalized Domain Names in Applications.
                                                             (line   57)
* RFC; RFC 3490 <3>:                     encodings idna — Internationalized Domain Names in Applications.
                                                             (line   62)
* RFC; RFC 3490#section-3.1:             encodings idna — Internationalized Domain Names in Applications.
                                                             (line   27)
* RFC; RFC 3492:                         Text Encodings.     (line   36)
* RFC; RFC 3492 <1>:                     encodings idna — Internationalized Domain Names in Applications.
                                                             (line    7)
* RFC; RFC 3493:                         Example<8>.         (line  227)
* RFC; RFC 3501:                         IMAP4 Objects.      (line  327)
* RFC; RFC 3542:                         Library<30>.        (line  352)
* RFC; RFC 3542 <1>:                     Other functions<2>. (line  303)
* RFC; RFC 3548:                         New Improved and Deprecated Modules<3>.
                                                             (line   16)
* RFC; RFC 3548 <1>:                     base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line   12)
* RFC; RFC 3548 <2>:                     base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line   16)
* RFC; RFC 3548 <3>:                     base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line   24)
* RFC; RFC 3548 <4>:                     base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line  112)
* RFC; RFC 3548 <5>:                     binascii — Convert between binary and ASCII.
                                                             (line   50)
* RFC; RFC 3659:                         FTP Objects.        (line  168)
* RFC; RFC 3879:                         Address objects.    (line  235)
* RFC; RFC 3927:                         Address objects.    (line  133)
* RFC; RFC 3977:                         nntplib — NNTP protocol client.
                                                             (line   13)
* RFC; RFC 3977 <1>:                     Attributes.         (line   10)
* RFC; RFC 3977 <2>:                     Methods<3>.         (line   36)
* RFC; RFC 3977 <3>:                     Methods<3>.         (line  138)
* RFC; RFC 3977 <4>:                     Methods<3>.         (line  318)
* RFC; RFC 3986:                         urllib parse<2>.    (line    7)
* RFC; RFC 3986 <1>:                     urllib parse<3>.    (line    6)
* RFC; RFC 3986 <2>:                     urllib.             (line   22)
* RFC; RFC 3986 <3>:                     New and Improved Modules.
                                                             (line  617)
* RFC; RFC 3986 <4>:                     Porting to Python 2 7.
                                                             (line   80)
* RFC; RFC 3986 <5>:                     URL Parsing.        (line  138)
* RFC; RFC 3986 <6>:                     URL Parsing.        (line  356)
* RFC; RFC 3986 <7>:                     URL Quoting.        (line   25)
* RFC; RFC 3986 <8>:                     URL Quoting.        (line  160)
* RFC; RFC 3986 <9>:                     http server — HTTP servers.
                                                             (line   96)
* RFC; RFC 4007:                         Address objects.    (line  178)
* RFC; RFC 4007 <1>:                     Address objects.    (line  249)
* RFC; RFC 4086:                         LibreSSL support.   (line   33)
* RFC; RFC 4122:                         New Improved and Removed Modules.
                                                             (line  417)
* RFC; RFC 4122 <1>:                     New Improved and Removed Modules.
                                                             (line  422)
* RFC; RFC 4122 <2>:                     uuid — UUID objects according to RFC 4122.
                                                             (line    6)
* RFC; RFC 4122 <3>:                     uuid — UUID objects according to RFC 4122.
                                                             (line   13)
* RFC; RFC 4122 <4>:                     uuid — UUID objects according to RFC 4122.
                                                             (line   71)
* RFC; RFC 4122 <5>:                     uuid — UUID objects according to RFC 4122.
                                                             (line  137)
* RFC; RFC 4122 <6>:                     uuid — UUID objects according to RFC 4122.
                                                             (line  166)
* RFC; RFC 4122 <7>:                     uuid — UUID objects according to RFC 4122.
                                                             (line  230)
* RFC; RFC 4122 <8>:                     uuid — UUID objects according to RFC 4122.
                                                             (line  243)
* RFC; RFC 4180:                         csv — CSV File Reading and Writing.
                                                             (line   13)
* RFC; RFC 4193:                         Address objects.    (line  237)
* RFC; RFC 4217:                         ftplib — FTP protocol client.
                                                             (line   88)
* RFC; RFC 4291:                         Address objects.    (line  172)
* RFC; RFC 4380:                         Address objects.    (line  264)
* RFC; RFC 4627:                         json — JSON encoder and decoder.
                                                             (line   11)
* RFC; RFC 4627 <1>:                     Top-level Non-Object Non-Array Values.
                                                             (line    6)
* RFC; RFC 4642:                         nntplib — NNTP protocol client.
                                                             (line  109)
* RFC; RFC 4918:                         HTTP status codes.  (line   46)
* RFC; RFC 4918 <1>:                     HTTP status codes.  (line  139)
* RFC; RFC 4918 <2>:                     HTTP status codes.  (line  142)
* RFC; RFC 4918 <3>:                     HTTP status codes.  (line  145)
* RFC; RFC 4918 <4>:                     HTTP status codes.  (line  187)
* RFC; RFC 4954:                         SMTP Objects.       (line  135)
* RFC; RFC 4954 <1>:                     SMTP Objects.       (line  158)
* RFC; RFC 5161:                         imaplib<2>.         (line   11)
* RFC; RFC 5161 <1>:                     IMAP4 Objects.      (line   86)
* RFC; RFC 5246:                         Constants<9>.       (line  485)
* RFC; RFC 5246 <1>:                     LibreSSL support.   (line   41)
* RFC; RFC 5280:                         Other Changes.      (line   20)
* RFC; RFC 5280 <1>:                     Changes in the Python API<5>.
                                                             (line   95)
* RFC; RFC 5280 <2>:                     Certificate handling.
                                                             (line   11)
* RFC; RFC 5280 <3>:                     Certificate handling.
                                                             (line   64)
* RFC; RFC 5280 <4>:                     LibreSSL support.   (line   37)
* RFC; RFC 5321:                         smtpd<3>.           (line    6)
* RFC; RFC 5321 <1>:                     email headerregistry Custom Header Objects.
                                                             (line  453)
* RFC; RFC 5321 <2>:                     smtpd — SMTP Server.
                                                             (line   26)
* RFC; RFC 5321 <3>:                     SMTPServer Objects. (line   50)
* RFC; RFC 5321 <4>:                     SMTPServer Objects. (line   78)
* RFC; RFC 5322:                         email — An email and MIME handling package.
                                                             (line   15)
* RFC; RFC 5322 <1>:                     email message Representing an email message.
                                                             (line   20)
* RFC; RFC 5322 <2>:                     email message Representing an email message.
                                                             (line   31)
* RFC; RFC 5322 <3>:                     Parser API.         (line   41)
* RFC; RFC 5322 <4>:                     email generator Generating MIME documents.
                                                             (line  102)
* RFC; RFC 5322 <5>:                     email generator Generating MIME documents.
                                                             (line  195)
* RFC; RFC 5322 <6>:                     email policy Policy Objects.
                                                             (line  148)
* RFC; RFC 5322 <7>:                     email policy Policy Objects.
                                                             (line  326)
* RFC; RFC 5322 <8>:                     email policy Policy Objects.
                                                             (line  347)
* RFC; RFC 5322 <9>:                     email policy Policy Objects.
                                                             (line  353)
* RFC; RFC 5322 <10>:                    email policy Policy Objects.
                                                             (line  365)
* RFC; RFC 5322 <11>:                    email policy Policy Objects.
                                                             (line  398)
* RFC; RFC 5322 <12>:                    email errors Exception and Defect classes.
                                                             (line   28)
* RFC; RFC 5322 <13>:                    email headerregistry Custom Header Objects.
                                                             (line   16)
* RFC; RFC 5322 <14>:                    email headerregistry Custom Header Objects.
                                                             (line  117)
* RFC; RFC 5322 <15>:                    email headerregistry Custom Header Objects.
                                                             (line  122)
* RFC; RFC 5322 <16>:                    email headerregistry Custom Header Objects.
                                                             (line  123)
* RFC; RFC 5322 <17>:                    email headerregistry Custom Header Objects.
                                                             (line  138)
* RFC; RFC 5322 <18>:                    email headerregistry Custom Header Objects.
                                                             (line  159)
* RFC; RFC 5322 <19>:                    email headerregistry Custom Header Objects.
                                                             (line  416)
* RFC; RFC 5322 <20>:                    email headerregistry Custom Header Objects.
                                                             (line  450)
* RFC; RFC 5322 <21>:                    email headerregistry Custom Header Objects.
                                                             (line  484)
* RFC; RFC 5322 <22>:                    email message Message Representing an email message using the compat32 API.
                                                             (line   21)
* RFC; RFC 5322 <23>:                    SMTP Objects.       (line  317)
* RFC; RFC 5424:                         SysLogHandler.      (line   53)
* RFC; RFC 5424 <1>:                     Inserting a BOM into messages sent to a SysLogHandler.
                                                             (line    6)
* RFC; RFC 5424 <2>:                     Inserting a BOM into messages sent to a SysLogHandler.
                                                             (line   19)
* RFC; RFC 5424 <3>:                     Inserting a BOM into messages sent to a SysLogHandler.
                                                             (line   43)
* RFC; RFC 5424#section-6:               Inserting a BOM into messages sent to a SysLogHandler.
                                                             (line    9)
* RFC; RFC 5735:                         Address objects.    (line  119)
* RFC; RFC 5842:                         HTTP status codes.  (line   49)
* RFC; RFC 5842 <1>:                     HTTP status codes.  (line  190)
* RFC; RFC 5891:                         encodings idna — Internationalized Domain Names in Applications.
                                                             (line   11)
* RFC; RFC 5895:                         encodings idna — Internationalized Domain Names in Applications.
                                                             (line   11)
* RFC; RFC 5929:                         SSL Sockets.        (line  247)
* RFC; RFC 6066:                         Constants<9>.       (line  385)
* RFC; RFC 6066 <1>:                     SSL Contexts.       (line  293)
* RFC; RFC 6066 <2>:                     LibreSSL support.   (line   45)
* RFC; RFC 6125:                         Certificate handling.
                                                             (line   11)
* RFC; RFC 6125 <1>:                     Certificate handling.
                                                             (line   29)
* RFC; RFC 6152:                         smtpd.              (line   17)
* RFC; RFC 6152 <1>:                     SMTPServer Objects. (line   35)
* RFC; RFC 6531:                         email<2>.           (line   19)
* RFC; RFC 6531 <1>:                     smtpd.              (line   23)
* RFC; RFC 6531 <2>:                     smtplib<2>.         (line   15)
* RFC; RFC 6531 <3>:                     email message Representing an email message.
                                                             (line  103)
* RFC; RFC 6531 <4>:                     email policy Policy Objects.
                                                             (line  369)
* RFC; RFC 6531 <5>:                     smtplib — SMTP protocol client.
                                                             (line   63)
* RFC; RFC 6531 <6>:                     smtpd — SMTP Server.
                                                             (line   26)
* RFC; RFC 6531 <7>:                     SMTPServer Objects. (line   26)
* RFC; RFC 6531 <8>:                     SMTPChannel Objects.
                                                             (line   21)
* RFC; RFC 6532:                         email<2>.           (line   18)
* RFC; RFC 6532 <1>:                     email — An email and MIME handling package.
                                                             (line   15)
* RFC; RFC 6532 <2>:                     email message Representing an email message.
                                                             (line   20)
* RFC; RFC 6532 <3>:                     Parser API.         (line   42)
* RFC; RFC 6532 <4>:                     email policy Policy Objects.
                                                             (line  367)
* RFC; RFC 6585:                         HTTP status codes.  (line  154)
* RFC; RFC 6585 <1>:                     HTTP status codes.  (line  157)
* RFC; RFC 6585 <2>:                     HTTP status codes.  (line  160)
* RFC; RFC 6585 <3>:                     HTTP status codes.  (line  196)
* RFC; RFC 6855:                         imaplib<2>.         (line   12)
* RFC; RFC 6855 <1>:                     imaplib<2>.         (line   14)
* RFC; RFC 6855 <2>:                     IMAP4 Objects.      (line   88)
* RFC; RFC 6855 <3>:                     IMAP4 Objects.      (line   90)
* RFC; RFC 6856:                         poplib<2>.          (line    6)
* RFC; RFC 6856 <1>:                     POP3 Objects.       (line  108)
* RFC; RFC 7159:                         json — JSON encoder and decoder.
                                                             (line   10)
* RFC; RFC 7159 <1>:                     Standard Compliance and Interoperability.
                                                             (line    6)
* RFC; RFC 7159 <2>:                     Top-level Non-Object Non-Array Values.
                                                             (line    9)
* RFC; RFC 7230:                         urllib request — Extensible library for opening URLs.
                                                             (line  189)
* RFC; RFC 7230 <1>:                     HTTPConnection Objects.
                                                             (line  151)
* RFC; RFC 7231:                         HTTP status codes.  (line   13)
* RFC; RFC 7231 <1>:                     HTTP status codes.  (line   16)
* RFC; RFC 7231 <2>:                     HTTP status codes.  (line   25)
* RFC; RFC 7231 <3>:                     HTTP status codes.  (line   28)
* RFC; RFC 7231 <4>:                     HTTP status codes.  (line   31)
* RFC; RFC 7231 <5>:                     HTTP status codes.  (line   34)
* RFC; RFC 7231 <6>:                     HTTP status codes.  (line   37)
* RFC; RFC 7231 <7>:                     HTTP status codes.  (line   40)
* RFC; RFC 7231 <8>:                     HTTP status codes.  (line   55)
* RFC; RFC 7231 <9>:                     HTTP status codes.  (line   58)
* RFC; RFC 7231 <10>:                    HTTP status codes.  (line   61)
* RFC; RFC 7231 <11>:                    HTTP status codes.  (line   64)
* RFC; RFC 7231 <12>:                    HTTP status codes.  (line   70)
* RFC; RFC 7231 <13>:                    HTTP status codes.  (line   73)
* RFC; RFC 7231 <14>:                    HTTP status codes.  (line   79)
* RFC; RFC 7231 <15>:                    HTTP status codes.  (line   85)
* RFC; RFC 7231 <16>:                    HTTP status codes.  (line   88)
* RFC; RFC 7231 <17>:                    HTTP status codes.  (line   91)
* RFC; RFC 7231 <18>:                    HTTP status codes.  (line   94)
* RFC; RFC 7231 <19>:                    HTTP status codes.  (line   97)
* RFC; RFC 7231 <20>:                    HTTP status codes.  (line  103)
* RFC; RFC 7231 <21>:                    HTTP status codes.  (line  106)
* RFC; RFC 7231 <22>:                    HTTP status codes.  (line  109)
* RFC; RFC 7231 <23>:                    HTTP status codes.  (line  112)
* RFC; RFC 7231 <24>:                    HTTP status codes.  (line  118)
* RFC; RFC 7231 <25>:                    HTTP status codes.  (line  121)
* RFC; RFC 7231 <26>:                    HTTP status codes.  (line  124)
* RFC; RFC 7231 <27>:                    HTTP status codes.  (line  130)
* RFC; RFC 7231 <28>:                    HTTP status codes.  (line  151)
* RFC; RFC 7231 <29>:                    HTTP status codes.  (line  166)
* RFC; RFC 7231 <30>:                    HTTP status codes.  (line  169)
* RFC; RFC 7231 <31>:                    HTTP status codes.  (line  172)
* RFC; RFC 7231 <32>:                    HTTP status codes.  (line  175)
* RFC; RFC 7231 <33>:                    HTTP status codes.  (line  178)
* RFC; RFC 7231 <34>:                    HTTP status codes.  (line  181)
* RFC; RFC 7232:                         HTTP status codes.  (line   67)
* RFC; RFC 7232 <1>:                     HTTP status codes.  (line  115)
* RFC; RFC 7233:                         HTTP status codes.  (line   43)
* RFC; RFC 7233 <1>:                     HTTP status codes.  (line  127)
* RFC; RFC 7235:                         HTTP status codes.  (line   82)
* RFC; RFC 7235 <1>:                     HTTP status codes.  (line  100)
* RFC; RFC 7238:                         HTTP status codes.  (line   76)
* RFC; RFC 7301:                         Application-Layer Protocol Negotiation Support.
                                                             (line   10)
* RFC; RFC 7301 <1>:                     Constants<9>.       (line  362)
* RFC; RFC 7301 <2>:                     SSL Contexts.       (line  258)
* RFC; RFC 7525:                         LibreSSL support.   (line   53)
* RFC; RFC 7540:                         HTTP status codes.  (line  136)
* RFC; RFC 7693:                         BLAKE2.             (line    6)
* RFC; RFC 7725:                         HTTP status codes.  (line  163)
* RFC; RFC 7914:                         Key derivation.     (line   48)
* RFC; RFC 821:                          smtplib — SMTP protocol client.
                                                             (line   12)
* RFC; RFC 821 <1>:                      smtplib — SMTP protocol client.
                                                             (line  189)
* RFC; RFC 822:                          New and Improved Modules<3>.
                                                             (line   97)
* RFC; RFC 822 <1>:                      Functions<3>.       (line  610)
* RFC; RFC 822 <2>:                      Functions<3>.       (line  613)
* RFC; RFC 822 <3>:                      email Examples.     (line   36)
* RFC; RFC 822 <4>:                      email header Internationalized headers.
                                                             (line   21)
* RFC; RFC 822 <5>:                      HTTPConnection Objects.
                                                             (line  138)
* RFC; RFC 822 <6>:                      SMTP Objects.       (line   94)
* RFC; RFC 822 <7>:                      SMTP Objects.       (line  232)
* RFC; RFC 822 <8>:                      SMTP Objects.       (line  233)
* RFC; RFC 822 <9>:                      SMTP Example.       (line   10)
* RFC; RFC 822 <10>:                     The GNUTranslations class.
                                                             (line   13)
* RFC; RFC 822 <11>:                     distutils util — Miscellaneous other utility functions.
                                                             (line  194)
* RFC; RFC 8297:                         HTTP status codes.  (line   22)
* RFC; RFC 8305:                         Opening network connections.
                                                             (line   77)
* RFC; RFC 8305 <1>:                     Opening network connections.
                                                             (line   86)
* RFC; RFC 8470:                         HTTP status codes.  (line  148)
* RFC; RFC 854:                          telnetlib — Telnet client.
                                                             (line   11)
* RFC; RFC 854 <1>:                      telnetlib — Telnet client.
                                                             (line   58)
* RFC; RFC 959:                          ftplib — FTP protocol client.
                                                             (line   16)
* RFC; RFC 977:                          nntplib — NNTP protocol client.
                                                             (line   13)
* RFC_4122 (in module uuid):             uuid — UUID objects according to RFC 4122.
                                                             (line  228)
* rfile (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  113)
* rfind() (bytearray method):            Bytes and Bytearray Operations.
                                                             (line  207)
* rfind() (bytes method):                Bytes and Bytearray Operations.
                                                             (line  207)
* rfind() (mmap.mmap method):            mmap — Memory-mapped file support.
                                                             (line  252)
* rfind() (str method):                  String Methods<2>.  (line  397)
* rgb_to_hls() (in module colorsys):     colorsys — Conversions between color systems.
                                                             (line   36)
* rgb_to_hsv() (in module colorsys):     colorsys — Conversions between color systems.
                                                             (line   44)
* rgb_to_yiq() (in module colorsys):     colorsys — Conversions between color systems.
                                                             (line   28)
* rglob() (pathlib.Path method):         Methods<2>.         (line  380)
* richcmpfunc (C type):                  Slot Type typedefs. (line   80)
* right (filecmp.dircmp attribute):      The dircmp class.   (line   45)
* right() (in module turtle):            Turtle motion.      (line   40)
* RIGHTSHIFT (in module token):          token — Constants used with Python parse trees.
                                                             (line  162)
* RIGHTSHIFTEQUAL (in module token):     token — Constants used with Python parse trees.
                                                             (line  206)
* right_list (filecmp.dircmp attribute): The dircmp class.   (line   54)
* right_only (filecmp.dircmp attribute): The dircmp class.   (line   67)
* rindex() (bytearray method):           Bytes and Bytearray Operations.
                                                             (line  221)
* rindex() (bytes method):               Bytes and Bytearray Operations.
                                                             (line  221)
* rindex() (str method):                 String Methods<2>.  (line  404)
* rjust() (bytearray method):            Bytes and Bytearray Operations.
                                                             (line  338)
* rjust() (bytes method):                Bytes and Bytearray Operations.
                                                             (line  338)
* rjust() (str method):                  String Methods<2>.  (line  409)
* rlcompleter (module):                  rlcompleter — Completion function for GNU readline.
                                                             (line    6)
* rlecode_hqx() (in module binascii):    binascii — Convert between binary and ASCII.
                                                             (line   99)
* rledecode_hqx() (in module binascii):  binascii — Convert between binary and ASCII.
                                                             (line   85)
* RLIMIT_AS (in module resource):        Resource Limits.    (line  147)
* RLIMIT_CORE (in module resource):      Resource Limits.    (line   92)
* RLIMIT_CPU (in module resource):       Resource Limits.    (line   99)
* RLIMIT_DATA (in module resource):      Resource Limits.    (line  111)
* RLIMIT_FSIZE (in module resource):     Resource Limits.    (line  107)
* RLIMIT_MEMLOCK (in module resource):   Resource Limits.    (line  139)
* RLIMIT_MSGQUEUE (in module resource):  Resource Limits.    (line  152)
* RLIMIT_NICE (in module resource):      Resource Limits.    (line  160)
* RLIMIT_NOFILE (in module resource):    Resource Limits.    (line  130)
* RLIMIT_NPROC (in module resource):     Resource Limits.    (line  126)
* RLIMIT_NPTS (in module resource):      Resource Limits.    (line  215)
* RLIMIT_OFILE (in module resource):     Resource Limits.    (line  135)
* RLIMIT_RSS (in module resource):       Resource Limits.    (line  121)
* RLIMIT_RTPRIO (in module resource):    Resource Limits.    (line  169)
* RLIMIT_RTTIME (in module resource):    Resource Limits.    (line  177)
* RLIMIT_SBSIZE (in module resource):    Resource Limits.    (line  194)
* RLIMIT_SIGPENDING (in module resource): Resource Limits.   (line  186)
* RLIMIT_STACK (in module resource):     Resource Limits.    (line  115)
* RLIMIT_SWAP (in module resource):      Resource Limits.    (line  204)
* RLIMIT_VMEM (in module resource):      Resource Limits.    (line  143)
* RLIM_INFINITY (in module resource):    Resource Limits.    (line   20)
* RLock (class in multiprocessing):      Synchronization primitives.
                                                             (line  102)
* RLock (class in threading):            RLock Objects.      (line   23)
* RLock() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  186)
* rmd() (ftplib.FTP method):             FTP Objects.        (line  225)
* rmdir() (in module os):                Files and Directories.
                                                             (line  732)
* rmdir() (in module test.support):      test support — Utilities for the Python test suite.
                                                             (line  237)
* rmdir() (pathlib.Path method):         Methods<2>.         (line  395)
* RMFF:                                  chunk — Read IFF chunked data.
                                                             (line    8)
* rms() (in module audioop):             audioop — Manipulate raw audio data.
                                                             (line  193)
* rmtree() (in module shutil):           Directory and files operations.
                                                             (line  255)
* rmtree() (in module test.support):     test support — Utilities for the Python test suite.
                                                             (line  243)
* RobotFileParser (class in urllib.robotparser): urllib robotparser — Parser for robots txt.
                                                             (line   16)
* robots.txt:                            urllib robotparser — Parser for robots txt.
                                                             (line    8)
* rollback() (sqlite3.Connection method): Connection Objects.
                                                             (line   40)
* ROMAN (in module tkinter.font):        tkinter font — Tkinter font wrapper.
                                                             (line   15)
* rotate() (collections.deque method):   deque objects.      (line  109)
* rotate() (decimal.Context method):     Context objects.    (line  481)
* rotate() (decimal.Decimal method):     Decimal objects.    (line  515)
* rotate() (logging.handlers.BaseRotatingHandler method): BaseRotatingHandler.
                                                             (line   75)
* RotatingFileHandler (class in logging.handlers): RotatingFileHandler.
                                                             (line    9)
* rotation_filename() (logging.handlers.BaseRotatingHandler method): BaseRotatingHandler.
                                                             (line   58)
* rotator (logging.handlers.BaseRotatingHandler attribute): BaseRotatingHandler.
                                                             (line   49)
* ROT_FOUR (opcode):                     Python Bytecode Instructions.
                                                             (line   72)
* ROT_THREE (opcode):                    Python Bytecode Instructions.
                                                             (line   67)
* ROT_TWO (opcode):                      Python Bytecode Instructions.
                                                             (line   63)
* round() (built-in function):           Built-in Functions. (line 1446)
* Rounded (class in decimal):            Signals.            (line   77)
* ROUND_05UP (in module decimal):        Rounding modes.     (line   34)
* ROUND_CEILING (in module decimal):     Rounding modes.     (line    6)
* ROUND_DOWN (in module decimal):        Rounding modes.     (line   10)
* ROUND_FLOOR (in module decimal):       Rounding modes.     (line   14)
* ROUND_HALF_DOWN (in module decimal):   Rounding modes.     (line   18)
* ROUND_HALF_EVEN (in module decimal):   Rounding modes.     (line   22)
* ROUND_HALF_UP (in module decimal):     Rounding modes.     (line   26)
* ROUND_UP (in module decimal):          Rounding modes.     (line   30)
* Row (class in sqlite3):                Row Objects.        (line    6)
* rowcount (sqlite3.Cursor attribute):   Cursor Objects.     (line  164)
* row_factory (sqlite3.Connection attribute): Connection Objects.
                                                             (line  307)
* RPAR (in module token):                token — Constants used with Python parse trees.
                                                             (line   58)
* rpartition() (bytearray method):       Bytes and Bytearray Operations.
                                                             (line  233)
* rpartition() (bytes method):           Bytes and Bytearray Operations.
                                                             (line  233)
* rpartition() (str method):             String Methods<2>.  (line  416)
* rpc_paths (xmlrpc.server.SimpleXMLRPCRequestHandler attribute): SimpleXMLRPCServer Objects.
                                                             (line   64)
* rpop() (poplib.POP3 method):           POP3 Objects.       (line   46)
* rset() (poplib.POP3 method):           POP3 Objects.       (line   74)
* RShift (class in ast):                 Expressions<2>.     (line   54)
* rshift() (in module operator):         operator — Standard operators as functions.
                                                             (line  148)
* rsplit() (bytearray method):           Bytes and Bytearray Operations.
                                                             (line  350)
* rsplit() (bytes method):               Bytes and Bytearray Operations.
                                                             (line  350)
* rsplit() (str method):                 String Methods<2>.  (line  424)
* RSQB (in module token):                token — Constants used with Python parse trees.
                                                             (line   66)
* rstrip() (bytearray method):           Bytes and Bytearray Operations.
                                                             (line  361)
* rstrip() (bytes method):               Bytes and Bytearray Operations.
                                                             (line  361)
* rstrip() (str method):                 String Methods<2>.  (line  433)
* rt() (in module turtle):               Turtle motion.      (line   40)
* RTLD_DEEPBIND (in module os):          Miscellaneous System Information.
                                                             (line  141)
* RTLD_GLOBAL (in module os):            Miscellaneous System Information.
                                                             (line  141)
* RTLD_LAZY (in module os):              Miscellaneous System Information.
                                                             (line  141)
* RTLD_LOCAL (in module os):             Miscellaneous System Information.
                                                             (line  141)
* RTLD_NODELETE (in module os):          Miscellaneous System Information.
                                                             (line  141)
* RTLD_NOLOAD (in module os):            Miscellaneous System Information.
                                                             (line  141)
* RTLD_NOW (in module os):               Miscellaneous System Information.
                                                             (line  141)
* ruler (cmd.Cmd attribute):             Cmd Objects.        (line  164)
* run (pdb command):                     Debugger Commands.  (line  322)
* Run script:                            Format menu Editor window only.
                                                             (line   53)
* run() (bdb.Bdb method):                bdb — Debugger framework.
                                                             (line  363)
* run() (contextvars.Context method):    Manual Context Management.
                                                             (line   31)
* run() (distutils.cmd.Command method):  Creating a new Distutils command.
                                                             (line   40)
* run() (doctest.DocTestRunner method):  DocTestRunner objects.
                                                             (line   95)
* run() (in module asyncio):             Running an asyncio Program.
                                                             (line    6)
* run() (in module pdb):                 pdb — The Python Debugger.
                                                             (line   93)
* run() (in module profile):             profile and cProfile Module Reference.
                                                             (line    9)
* run() (in module subprocess):          Using the subprocess Module.
                                                             (line   15)
* run() (multiprocessing.Process method): Process and exceptions.
                                                             (line   33)
* run() (pdb.Pdb method):                pdb — The Python Debugger.
                                                             (line  180)
* run() (profile.Profile method):        profile and cProfile Module Reference.
                                                             (line  100)
* run() (sched.scheduler method):        Scheduler Objects.  (line   51)
* run() (test.support.BasicTestRunner method): test support — Utilities for the Python test suite.
                                                             (line 1125)
* run() (threading.Thread method):       Thread Objects.     (line  100)
* run() (trace.Trace method):            Programmatic Interface.
                                                             (line   22)
* run() (unittest.IsolatedAsyncioTestCase method): Test cases.
                                                             (line  845)
* run() (unittest.TestCase method):      Test cases.         (line   83)
* run() (unittest.TestSuite method):     Grouping tests.     (line   41)
* run() (unittest.TextTestRunner method): Loading and running tests.
                                                             (line  481)
* run() (wsgiref.handlers.BaseHandler method): wsgiref handlers – server/gateway base classes.
                                                             (line   98)
* runcall() (bdb.Bdb method):            bdb — Debugger framework.
                                                             (line  380)
* runcall() (in module pdb):             pdb — The Python Debugger.
                                                             (line  112)
* runcall() (pdb.Pdb method):            pdb — The Python Debugger.
                                                             (line  180)
* runcall() (profile.Profile method):    profile and cProfile Module Reference.
                                                             (line  109)
* runcode() (code.InteractiveInterpreter method): Interactive Interpreter Objects.
                                                             (line   33)
* runctx() (bdb.Bdb method):             bdb — Debugger framework.
                                                             (line  375)
* runctx() (in module profile):          profile and cProfile Module Reference.
                                                             (line   23)
* runctx() (profile.Profile method):     profile and cProfile Module Reference.
                                                             (line  104)
* runctx() (trace.Trace method):         Programmatic Interface.
                                                             (line   28)
* runeval() (bdb.Bdb method):            bdb — Debugger framework.
                                                             (line  369)
* runeval() (in module pdb):             pdb — The Python Debugger.
                                                             (line  105)
* runeval() (pdb.Pdb method):            pdb — The Python Debugger.
                                                             (line  180)
* runfunc() (trace.Trace method):        Programmatic Interface.
                                                             (line   35)
* running() (concurrent.futures.Future method): Future Objects.
                                                             (line   28)
* runpy (module):                        runpy — Locating and executing Python modules.
                                                             (line    6)
* runsource() (code.InteractiveInterpreter method): Interactive Interpreter Objects.
                                                             (line    6)
* RuntimeError:                          Concrete exceptions.
                                                             (line  204)
* RuntimeWarning:                        Warnings.           (line   47)
* runtime_checkable() (in module typing): Building generic types.
                                                             (line  123)
* runtime_library_dir_option() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  230)
* run_coroutine_threadsafe() (in module asyncio): Scheduling From Other Threads.
                                                             (line    6)
* run_docstring_examples() (in module doctest): Basic API.   (line  128)
* run_doctest() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  330)
* run_forever() (asyncio.loop method):   Running and stopping the loop.
                                                             (line   16)
* run_in_executor() (asyncio.loop method): Executing code in thread or process pools.
                                                             (line    6)
* run_in_subinterp() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  972)
* run_module() (in module runpy):        runpy — Locating and executing Python modules.
                                                             (line   27)
* run_path() (in module runpy):          runpy — Locating and executing Python modules.
                                                             (line   95)
* run_python_until_end() (in module test.support.script_helper): test support script_helper — Utilities for the Python execution tests.
                                                             (line   30)
* run_script() (modulefinder.ModuleFinder method): modulefinder — Find modules used by a script.
                                                             (line   44)
* run_setup() (in module distutils.core): distutils core — Core Distutils functionality.
                                                             (line  121)
* run_unittest() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  314)
* run_until_complete() (asyncio.loop method): Running and stopping the loop.
                                                             (line    6)
* run_with_locale() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  639)
* run_with_tz() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  647)
* RUSAGE_BOTH (in module resource):      Resource Usage.     (line  122)
* RUSAGE_CHILDREN (in module resource):  Resource Usage.     (line  116)
* RUSAGE_SELF (in module resource):      Resource Usage.     (line  110)
* RUSAGE_THREAD (in module resource):    Resource Usage.     (line  128)
* RWF_DSYNC (in module os):              File Descriptor Operations.
                                                             (line  535)
* RWF_HIPRI (in module os):              File Descriptor Operations.
                                                             (line  482)
* RWF_NOWAIT (in module os):             File Descriptor Operations.
                                                             (line  467)
* RWF_SYNC (in module os):               File Descriptor Operations.
                                                             (line  545)
* R_OK (in module os):                   Files and Directories.
                                                             (line  106)
* S (in module re):                      Module Contents.    (line  113)
* safe (uuid.SafeUUID attribute):        uuid — UUID objects according to RFC 4122.
                                                             (line   31)
* SafeChildWatcher (class in asyncio):   Process Watchers.   (line  118)
* saferepr() (in module pprint):         pprint — Data pretty printer.
                                                             (line  148)
* SafeUUID (class in uuid):              uuid — UUID objects according to RFC 4122.
                                                             (line   27)
* safe_substitute() (string.Template method): Template strings.
                                                             (line   50)
* samefile() (in module os.path):        os path — Common pathname manipulations.
                                                             (line  334)
* samefile() (pathlib.Path method):      Methods<2>.         (line  399)
* SameFileError:                         Directory and files operations.
                                                             (line   52)
* sameopenfile() (in module os.path):    os path — Common pathname manipulations.
                                                             (line  350)
* samestat() (in module os.path):        os path — Common pathname manipulations.
                                                             (line  361)
* same_files (filecmp.dircmp attribute): The dircmp class.   (line   85)
* same_quantum() (decimal.Context method): Context objects.  (line  485)
* same_quantum() (decimal.Decimal method): Decimal objects.  (line  527)
* sample() (in module random):           Functions for sequences.
                                                             (line   75)
* samples() (statistics.NormalDist method): NormalDist objects.
                                                             (line   58)
* save() (http.cookiejar.FileCookieJar method): CookieJar and FileCookieJar Objects.
                                                             (line  105)
* SaveAs (class in tkinter.filedialog):  Native Load/Save Dialogs.
                                                             (line   60)
* SAVEDCWD (in module test.support):     test support — Utilities for the Python test suite.
                                                             (line  142)
* SaveFileDialog (class in tkinter.filedialog): Native Load/Save Dialogs.
                                                             (line  145)
* SaveKey() (in module winreg):          Functions<12>.      (line  400)
* SaveSignals (class in test.support):   test support — Utilities for the Python test suite.
                                                             (line 1102)
* savetty() (in module curses):          Functions<4>.       (line  427)
* SAX2DOM (class in xml.dom.pulldom):    xml dom pulldom — Support for building partial DOM trees.
                                                             (line   82)
* SAXException:                          xml sax — Support for SAX2 parsers.
                                                             (line   86)
* SAXNotRecognizedException:             xml sax — Support for SAX2 parsers.
                                                             (line  111)
* SAXNotSupportedException:              xml sax — Support for SAX2 parsers.
                                                             (line  118)
* SAXParseException:                     xml sax — Support for SAX2 parsers.
                                                             (line  103)
* scaleb() (decimal.Context method):     Context objects.    (line  489)
* scaleb() (decimal.Decimal method):     Decimal objects.    (line  537)
* scandir() (in module os):              Files and Directories.
                                                             (line  749)
* scanf():                               Simulating scanf.   (line    6)
* sched (module):                        sched — Event scheduler.
                                                             (line    6)
* scheduler (class in sched):            sched — Event scheduler.
                                                             (line   13)
* SCHED_BATCH (in module os):            Interface to the scheduler.
                                                             (line   19)
* SCHED_FIFO (in module os):             Interface to the scheduler.
                                                             (line   32)
* sched_getaffinity() (in module os):    Interface to the scheduler.
                                                             (line  109)
* sched_getparam() (in module os):       Interface to the scheduler.
                                                             (line   87)
* sched_getscheduler() (in module os):   Interface to the scheduler.
                                                             (line   75)
* sched_get_priority_max() (in module os): Interface to the scheduler.
                                                             (line   63)
* sched_get_priority_min() (in module os): Interface to the scheduler.
                                                             (line   58)
* SCHED_IDLE (in module os):             Interface to the scheduler.
                                                             (line   24)
* SCHED_OTHER (in module os):            Interface to the scheduler.
                                                             (line   15)
* sched_param (class in os):             Interface to the scheduler.
                                                             (line   46)
* sched_priority (os.sched_param attribute): Interface to the scheduler.
                                                             (line   54)
* SCHED_RESET_ON_FORK (in module os):    Interface to the scheduler.
                                                             (line   40)
* SCHED_RR (in module os):               Interface to the scheduler.
                                                             (line   36)
* sched_rr_get_interval() (in module os): Interface to the scheduler.
                                                             (line   93)
* sched_setaffinity() (in module os):    Interface to the scheduler.
                                                             (line  102)
* sched_setparam() (in module os):       Interface to the scheduler.
                                                             (line   81)
* sched_setscheduler() (in module os):   Interface to the scheduler.
                                                             (line   68)
* SCHED_SPORADIC (in module os):         Interface to the scheduler.
                                                             (line   28)
* sched_yield() (in module os):          Interface to the scheduler.
                                                             (line   98)
* schema (in module msilib):             Precomputed tables. (line   10)
* scope:                                 Naming and binding. (line    6)
* scope <1>:                             Resolution of names.
                                                             (line    6)
* scope_id (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  247)
* Screen (class in turtle):              Public classes.     (line   30)
* screensize() (in module turtle):       Window control.     (line   63)
* script_from_examples() (in module doctest): Debugging.     (line   72)
* scroll() (curses.window method):       Window Objects.     (line  497)
* ScrolledCanvas (class in turtle):      Public classes.     (line   34)
* ScrolledText (class in tkinter.scrolledtext): tkinter scrolledtext — Scrolled Text Widget.
                                                             (line   24)
* scrollok() (curses.window method):     Window Objects.     (line  501)
* scrypt() (in module hashlib):          Key derivation.     (line   44)
* seal() (in module unittest.mock):      Sealing mocks.      (line    6)
* search() (imaplib.IMAP4 method):       IMAP4 Objects.      (line  222)
* search() (in module re):               Module Contents.    (line  143)
* search() (re.Pattern method):          Regular Expression Objects.
                                                             (line    9)
* second (datetime.datetime attribute):  datetime Objects.   (line  285)
* second (datetime.time attribute):      time Objects.       (line   58)
* seconds since the epoch:               time — Time access and conversions.
                                                             (line   25)
* secrets (module):                      secrets — Generate secure random numbers for managing secrets.
                                                             (line    6)
* SECTCRE (configparser.ConfigParser attribute): Customizing Parser Behaviour.
                                                             (line  300)
* sections() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line   81)
* secure (http.cookiejar.Cookie attribute): Cookie Objects<2>.
                                                             (line   45)
* secure hash algorithm, SHA1, SHA224, SHA256, SHA384, SHA512: hashlib — Secure hashes and message digests.
                                                             (line    8)
* Secure Sockets Layer:                  ssl — TLS/SSL wrapper for socket objects.
                                                             (line    8)
* security considerations:               Platform specific modules.
                                                             (line   17)
* see() (tkinter.ttk.Treeview method):   ttk Treeview.       (line  251)
* seed() (in module random):             Bookkeeping functions.
                                                             (line    6)
* seek() (chunk.Chunk method):           chunk — Read IFF chunked data.
                                                             (line   92)
* seek() (io.IOBase method):             I/O Base Classes.   (line  107)
* seek() (io.TextIOBase method):         Text I/O<2>.        (line   66)
* seek() (mmap.mmap method):             mmap — Memory-mapped file support.
                                                             (line  262)
* seekable() (io.IOBase method):         I/O Base Classes.   (line  132)
* SEEK_CUR (in module os):               File Descriptor Operations.
                                                             (line  249)
* SEEK_END (in module os):               File Descriptor Operations.
                                                             (line  249)
* SEEK_SET (in module os):               File Descriptor Operations.
                                                             (line  249)
* seen_greeting (smtpd.SMTPChannel attribute): SMTPChannel Objects.
                                                             (line   69)
* Select (class in tkinter.tix):         Basic Widgets.      (line   59)
* select (module):                       select — Waiting for I/O completion.
                                                             (line    6)
* select() (imaplib.IMAP4 method):       IMAP4 Objects.      (line  239)
* select() (in module select):           select — Waiting for I/O completion.
                                                             (line  110)
* select() (selectors.BaseSelector method): Classes<3>.      (line  108)
* select() (tkinter.ttk.Notebook method): ttk Notebook.      (line   53)
* selected_alpn_protocol() (ssl.SSLSocket method): SSL Sockets.
                                                             (line  253)
* selected_npn_protocol() (ssl.SSLSocket method): SSL Sockets.
                                                             (line  263)
* selection() (tkinter.ttk.Treeview method): ttk Treeview.   (line  259)
* selection_add() (tkinter.ttk.Treeview method): ttk Treeview.
                                                             (line  274)
* selection_remove() (tkinter.ttk.Treeview method): ttk Treeview.
                                                             (line  281)
* selection_set() (tkinter.ttk.Treeview method): ttk Treeview.
                                                             (line  267)
* selection_toggle() (tkinter.ttk.Treeview method): ttk Treeview.
                                                             (line  288)
* selector (urllib.request.Request attribute): Request Objects.
                                                             (line   34)
* SelectorEventLoop (class in asyncio):  Event Loop Implementations.
                                                             (line   12)
* SelectorKey (class in selectors):      Classes<3>.         (line   29)
* selectors (module):                    selectors — High-level I/O multiplexing.
                                                             (line    6)
* SelectSelector (class in selectors):   Classes<3>.         (line  167)
* Semaphore (class in asyncio):          Semaphore.          (line    6)
* Semaphore (class in multiprocessing):  Synchronization primitives.
                                                             (line  167)
* Semaphore (class in threading):        Semaphore Objects.  (line   19)
* Semaphore() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  191)
* semaphores, binary:                    _thread — Low-level threading API.
                                                             (line    6)
* SEMI (in module token):                token — Constants used with Python parse trees.
                                                             (line   78)
* send() (asyncore.dispatcher method):   asyncore — Asynchronous socket handler.
                                                             (line  200)
* send() (coroutine method):             Coroutine Objects.  (line   23)
* send() (generator method):             Generator-iterator methods.
                                                             (line   27)
* send() (http.client.HTTPConnection method): HTTPConnection Objects.
                                                             (line  170)
* send() (imaplib.IMAP4 method):         IMAP4 Objects.      (line  246)
* send() (logging.handlers.DatagramHandler method): DatagramHandler.
                                                             (line   34)
* send() (logging.handlers.SocketHandler method): SocketHandler.
                                                             (line   63)
* send() (multiprocessing.connection.Connection method): Connection Objects<2>.
                                                             (line   15)
* send() (socket.socket method):         Socket Objects.     (line  381)
* sendall() (socket.socket method):      Socket Objects.     (line  397)
* sendcmd() (ftplib.FTP method):         FTP Objects.        (line   66)
* sendfile() (asyncio.loop method):      Transferring files. (line    6)
* sendfile() (in module os):             File Descriptor Operations.
                                                             (line  576)
* sendfile() (socket.socket method):     Socket Objects.     (line  488)
* sendfile() (wsgiref.handlers.BaseHandler method): wsgiref handlers – server/gateway base classes.
                                                             (line  275)
* SendfileNotAvailableError:             Exceptions<10>.     (line   35)
* sendmail() (smtplib.SMTP method):      SMTP Objects.       (line  229)
* sendmsg() (socket.socket method):      Socket Objects.     (line  435)
* sendmsg_afalg() (socket.socket method): Socket Objects.    (line  477)
* sendto() (asyncio.DatagramTransport method): Datagram Transports.
                                                             (line    6)
* sendto() (socket.socket method):       Socket Objects.     (line  416)
* send_bytes() (multiprocessing.connection.Connection method): Connection Objects<2>.
                                                             (line   54)
* send_error() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  209)
* send_fds() (in module socket):         Other functions<2>. (line  420)
* send_flowing_data() (formatter.writer method): The Writer Interface.
                                                             (line   76)
* send_header() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  245)
* send_hor_rule() (formatter.writer method): The Writer Interface.
                                                             (line   68)
* send_label_data() (formatter.writer method): The Writer Interface.
                                                             (line   92)
* send_line_break() (formatter.writer method): The Writer Interface.
                                                             (line   54)
* send_literal_data() (formatter.writer method): The Writer Interface.
                                                             (line   83)
* send_message() (smtplib.SMTP method):  SMTP Objects.       (line  307)
* send_paragraph() (formatter.writer method): The Writer Interface.
                                                             (line   58)
* send_response() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  229)
* send_response_only() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  258)
* send_signal() (asyncio.asyncio.subprocess.Process method): Interacting with Subprocesses.
                                                             (line   81)
* send_signal() (asyncio.SubprocessTransport method): Subprocess Transports.
                                                             (line   44)
* send_signal() (subprocess.Popen method): Popen Objects.    (line   74)
* sentinel (in module unittest.mock):    sentinel.           (line    6)
* sentinel (multiprocessing.Process attribute): Process and exceptions.
                                                             (line  133)
* sep (in module os):                    Miscellaneous System Information.
                                                             (line   93)
* sequence:                              Glossary.           (line 1161)
* Sequence (class in collections.abc):   Collections Abstract Base Classes.
                                                             (line  159)
* Sequence (class in typing):            Corresponding to collections in collections abc.
                                                             (line  105)
* sequence (in module msilib):           Precomputed tables. (line   16)
* sequence2st() (in module parser):      Creating ST Objects.
                                                             (line   26)
* sequence; item:                        Subscriptions.      (line    6)
* sequence; iteration:                   Iterator Types.     (line    6)
* SequenceMatcher (class in difflib):    SequenceMatcher Objects.
                                                             (line    8)
* serializing; objects:                  pickle — Python object serialization.
                                                             (line    8)
* Server (class in asyncio):             Server Objects.     (line   12)
* server (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line   71)
* ServerProxy (class in xmlrpc.client):  xmlrpc client — XML-RPC client access.
                                                             (line   24)
* server_activate() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line  164)
* server_address (socketserver.BaseServer attribute): Server Objects<2>.
                                                             (line   76)
* server_bind() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line  170)
* server_close() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line   61)
* server_hostname (ssl.SSLSocket attribute): SSL Sockets.    (line  335)
* server_side (ssl.SSLSocket attribute): SSL Sockets.        (line  328)
* server_software (wsgiref.handlers.BaseHandler attribute): wsgiref handlers – server/gateway base classes.
                                                             (line  176)
* server_version (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  130)
* server_version (http.server.SimpleHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  353)
* serve_forever() (asyncio.Server method): Server Objects.   (line   63)
* serve_forever() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line   32)
* service_actions() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line   45)
* session (ssl.SSLSocket attribute):     SSL Sockets.        (line  348)
* session_reused (ssl.SSLSocket attribute): SSL Sockets.     (line  358)
* session_stats() (ssl.SSLContext method): SSL Contexts.     (line  480)
* set (built-in class):                  Set Types — set frozenset.
                                                             (line   33)
* Set (class in ast):                    Literals<3>.        (line   92)
* Set (class in collections.abc):        Collections Abstract Base Classes.
                                                             (line  177)
* Set (class in typing):                 Corresponding to built-in types.
                                                             (line   40)
* Set Breakpoint:                        Help menu Shell and Editor.
                                                             (line   30)
* set comprehension:                     Glossary.           (line 1180)
* set() (asyncio.Event method):          Event.              (line   52)
* set() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  250)
* set() (configparser.RawConfigParser method): RawConfigParser Objects.
                                                             (line   37)
* set() (contextvars.ContextVar method): Context Variables.  (line   46)
* set() (http.cookies.Morsel method):    Morsel Objects.     (line   64)
* set() (ossaudiodev.oss_mixer_device method): Mixer Device Objects.
                                                             (line   72)
* set() (test.support.EnvironmentVarGuard method): test support — Utilities for the Python test suite.
                                                             (line 1057)
* set() (threading.Event method):        Event Objects.      (line   27)
* set() (tkinter.ttk.Combobox method):   ttk Combobox.       (line   19)
* set() (tkinter.ttk.Spinbox method):    ttk Spinbox.        (line   12)
* set() (tkinter.ttk.Treeview method):   ttk Treeview.       (line  295)
* set() (xml.etree.ElementTree.Element method): Element Objects.
                                                             (line   81)
* set; comprehensions:                   Set displays.       (line    6)
* set; display:                          Set displays.       (line    6)
* setacl() (imaplib.IMAP4 method):       IMAP4 Objects.      (line  253)
* setannotation() (imaplib.IMAP4 method): IMAP4 Objects.     (line  258)
* setattr() (built-in function):         Built-in Functions. (line 1483)
* setattrfunc (C type):                  Slot Type typedefs. (line   46)
* setAttribute() (xml.dom.Element method): Element Objects<2>.
                                                             (line   67)
* setAttributeNode() (xml.dom.Element method): Element Objects<2>.
                                                             (line   71)
* setAttributeNodeNS() (xml.dom.Element method): Element Objects<2>.
                                                             (line   79)
* setAttributeNS() (xml.dom.Element method): Element Objects<2>.
                                                             (line   87)
* setattrofunc (C type):                 Slot Type typedefs. (line   58)
* SetBase() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line   22)
* setblocking() (socket.socket method):  Socket Objects.     (line  512)
* setByteStream() (xml.sax.xmlreader.InputSource method): InputSource Objects.
                                                             (line   36)
* setcbreak() (in module tty):           tty — Terminal control functions.
                                                             (line   24)
* setCharacterStream() (xml.sax.xmlreader.InputSource method): InputSource Objects.
                                                             (line   55)
* SetComp (class in ast):                Comprehensions.     (line    6)
* setcomptype() (aifc.aifc method):      aifc — Read and write AIFF and AIFC files.
                                                             (line  158)
* setcomptype() (sunau.AU_write method): AU_write Objects.   (line   28)
* setcomptype() (wave.Wave_write method): Wave_write Objects.
                                                             (line   51)
* setContentHandler() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   25)
* setcontext() (in module decimal):      Context objects.    (line   18)
* setDaemon() (threading.Thread method): Thread Objects.     (line  197)
* setdefault() (dict method):            Mapping Types — dict.
                                                             (line  206)
* setdefault() (http.cookies.Morsel method): Morsel Objects. (line  108)
* setdefaulttimeout() (in module socket): Other functions<2>.
                                                             (line  340)
* setdlopenflags() (in module sys):      sys — System-specific parameters and functions.
                                                             (line 1218)
* setDocumentLocator() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line   10)
* setDTDHandler() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   34)
* setegid() (in module os):              Process Parameters. (line  338)
* setEncoding() (xml.sax.xmlreader.InputSource method): InputSource Objects.
                                                             (line   22)
* setEntityResolver() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   43)
* setErrorHandler() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   54)
* seteuid() (in module os):              Process Parameters. (line  344)
* setFeature() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   76)
* setfirstweekday() (in module calendar): calendar — General calendar-related functions.
                                                             (line  287)
* setfmt() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line  125)
* setFormatter() (logging.Handler method): Handler Objects.  (line   48)
* setframerate() (aifc.aifc method):     aifc — Read and write AIFF and AIFC files.
                                                             (line  148)
* setframerate() (sunau.AU_write method): AU_write Objects.  (line   19)
* setframerate() (wave.Wave_write method): Wave_write Objects.
                                                             (line   38)
* setgid() (in module os):               Process Parameters. (line  350)
* setgroups() (in module os):            Process Parameters. (line  356)
* seth() (in module turtle):             Turtle motion.      (line  132)
* setheading() (in module turtle):       Turtle motion.      (line  132)
* sethostname() (in module socket):      Other functions<2>. (line  347)
* setinputsizes() (sqlite3.Cursor method): Cursor Objects.   (line  156)
* SetInteger() (msilib.Record method):   Record Objects.     (line   32)
* setitem() (in module operator):        operator — Standard operators as functions.
                                                             (line  201)
* setitimer() (in module signal):        Module contents<2>. (line  362)
* setLevel() (logging.Handler method):   Handler Objects.    (line   35)
* setLevel() (logging.Logger method):    Logger Objects.     (line   62)
* setlocale() (in module locale):        locale — Internationalization services.
                                                             (line   27)
* setLocale() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   60)
* setLoggerClass() (in module logging):  Module-Level Functions.
                                                             (line  362)
* setlogmask() (in module syslog):       syslog — Unix syslog library routines.
                                                             (line   73)
* setLogRecordFactory() (in module logging): Module-Level Functions.
                                                             (line  374)
* setmark() (aifc.aifc method):          aifc — Read and write AIFF and AIFC files.
                                                             (line  176)
* setMaxConns() (urllib.request.CacheFTPHandler method): CacheFTPHandler Objects.
                                                             (line   13)
* setmode() (in module msvcrt):          File Operations.    (line   38)
* setName() (threading.Thread method):   Thread Objects.     (line  142)
* setnchannels() (aifc.aifc method):     aifc — Read and write AIFF and AIFC files.
                                                             (line  140)
* setnchannels() (sunau.AU_write method): AU_write Objects.  (line    9)
* setnchannels() (wave.Wave_write method): Wave_write Objects.
                                                             (line   30)
* setnframes() (aifc.aifc method):       aifc — Read and write AIFF and AIFC files.
                                                             (line  152)
* setnframes() (sunau.AU_write method):  AU_write Objects.   (line   23)
* setnframes() (wave.Wave_write method): Wave_write Objects. (line   45)
* setoutputsize() (sqlite3.Cursor method): Cursor Objects.   (line  160)
* SetParamEntityParsing() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line   54)
* setparameters() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line  189)
* setparams() (aifc.aifc method):        aifc — Read and write AIFF and AIFC files.
                                                             (line  168)
* setparams() (sunau.AU_write method):   AU_write Objects.   (line   33)
* setparams() (wave.Wave_write method):  Wave_write Objects. (line   56)
* setpassword() (zipfile.ZipFile method): ZipFile Objects.   (line  211)
* setpgid() (in module os):              Process Parameters. (line  379)
* setpgrp() (in module os):              Process Parameters. (line  371)
* setpos() (aifc.aifc method):           aifc — Read and write AIFF and AIFC files.
                                                             (line  108)
* setpos() (in module turtle):           Turtle motion.      (line   74)
* setpos() (sunau.AU_read method):       AU_read Objects.    (line   60)
* setpos() (wave.Wave_read method):      Wave_read Objects.  (line   69)
* setposition() (in module turtle):      Turtle motion.      (line   74)
* setpriority() (in module os):          Process Parameters. (line  387)
* setprofile() (in module sys):          sys — System-specific parameters and functions.
                                                             (line 1231)
* setprofile() (in module threading):    threading — Thread-based parallelism.
                                                             (line  131)
* SetProperty() (msilib.SummaryInformation method): Summary Information Objects.
                                                             (line   22)
* setProperty() (xml.sax.xmlreader.XMLReader method): XMLReader Objects.
                                                             (line   90)
* setPublicId() (xml.sax.xmlreader.InputSource method): InputSource Objects.
                                                             (line    6)
* setquota() (imaplib.IMAP4 method):     IMAP4 Objects.      (line  263)
* setraw() (in module tty):              tty — Terminal control functions.
                                                             (line   18)
* setrecursionlimit() (in module sys):   sys — System-specific parameters and functions.
                                                             (line 1283)
* setregid() (in module os):             Process Parameters. (line  404)
* setresgid() (in module os):            Process Parameters. (line  410)
* setresuid() (in module os):            Process Parameters. (line  418)
* setreuid() (in module os):             Process Parameters. (line  426)
* setrlimit() (in module resource):      Resource Limits.    (line   31)
* setsampwidth() (aifc.aifc method):     aifc — Read and write AIFF and AIFC files.
                                                             (line  144)
* setsampwidth() (sunau.AU_write method): AU_write Objects.  (line   13)
* setsampwidth() (wave.Wave_write method): Wave_write Objects.
                                                             (line   34)
* setscrreg() (curses.window method):    Window Objects.     (line  511)
* setsid() (in module os):               Process Parameters. (line  439)
* setsockopt() (socket.socket method):   Socket Objects.     (line  545)
* setstate() (codecs.IncrementalDecoder method): IncrementalDecoder Objects.
                                                             (line   60)
* setstate() (codecs.IncrementalEncoder method): IncrementalEncoder Objects.
                                                             (line   51)
* setstate() (in module random):         Bookkeeping functions.
                                                             (line   38)
* setStream() (logging.StreamHandler method): StreamHandler. (line   32)
* SetStream() (msilib.Record method):    Record Objects.     (line   26)
* SetString() (msilib.Record method):    Record Objects.     (line   21)
* setswitchinterval() (in module sys):   sys — System-specific parameters and functions.
                                                             (line 1301)
* setswitchinterval() (in module sys) <1>: Thread State and the Global Interpreter Lock.
                                                             (line   15)
* setswitchinterval() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  341)
* setSystemId() (xml.sax.xmlreader.InputSource method): InputSource Objects.
                                                             (line   14)
* setsyx() (in module curses):           Functions<4>.       (line  461)
* setTarget() (logging.handlers.MemoryHandler method): MemoryHandler.
                                                             (line   67)
* settiltangle() (in module turtle):     Appearance.         (line  118)
* settimeout() (socket.socket method):   Socket Objects.     (line  529)
* setTimeout() (urllib.request.CacheFTPHandler method): CacheFTPHandler Objects.
                                                             (line    9)
* settrace() (in module sys):            sys — System-specific parameters and functions.
                                                             (line 1314)
* settrace() (in module threading):      threading — Thread-based parallelism.
                                                             (line  124)
* setuid() (in module os):               Process Parameters. (line  446)
* setundobuffer() (in module turtle):    Special Turtle methods.
                                                             (line   61)
* setup() (in module distutils.core):    distutils core — Core Distutils functionality.
                                                             (line   12)
* setup() (in module turtle):            Methods specific to Screen not inherited from TurtleScreen.
                                                             (line   20)
* setup() (socketserver.BaseRequestHandler method): Request Handler Objects.
                                                             (line   14)
* setUp() (unittest.TestCase method):    Test cases.         (line   33)
* setUpClass() (unittest.TestCase method): Test cases.       (line   55)
* setupterm() (in module curses):        Functions<4>.       (line  466)
* SETUP_ANNOTATIONS (opcode):            Python Bytecode Instructions.
                                                             (line  357)
* SETUP_ASYNC_WITH (opcode):             Python Bytecode Instructions.
                                                             (line  303)
* setup_environ() (wsgiref.handlers.BaseHandler method): wsgiref handlers – server/gateway base classes.
                                                             (line  196)
* SETUP_FINALLY (opcode):                Python Bytecode Instructions.
                                                             (line  642)
* setup_python() (venv.EnvBuilder method): API<2>.           (line   99)
* setup_scripts() (venv.EnvBuilder method): API<2>.          (line  107)
* setup_testing_defaults() (in module wsgiref.util): wsgiref util – WSGI environment utilities.
                                                             (line   68)
* SETUP_WITH (opcode):                   Python Bytecode Instructions.
                                                             (line  412)
* SetValue() (in module winreg):         Functions<12>.      (line  424)
* SetValueEx() (in module winreg):       Functions<12>.      (line  455)
* setworldcoordinates() (in module turtle): Window control.  (line   90)
* setx() (in module turtle):             Turtle motion.      (line  104)
* setxattr() (in module os):             Linux extended attributes.
                                                             (line   57)
* sety() (in module turtle):             Turtle motion.      (line  118)
* SET_ADD (opcode):                      Python Bytecode Instructions.
                                                             (line  317)
* set_all():                             Reference Count Details.
                                                             (line   98)
* set_allowed_domains() (http.cookiejar.DefaultCookiePolicy method): DefaultCookiePolicy Objects.
                                                             (line   70)
* set_alpn_protocols() (ssl.SSLContext method): SSL Contexts.
                                                             (line  252)
* set_app() (wsgiref.simple_server.WSGIServer method): wsgiref simple_server – a simple WSGI HTTP server.
                                                             (line   61)
* set_asyncgen_hooks() (in module sys):  sys — System-specific parameters and functions.
                                                             (line 1410)
* set_authorizer() (sqlite3.Connection method): Connection Objects.
                                                             (line  194)
* set_auto_history() (in module readline): History list.     (line   43)
* set_blocked_domains() (http.cookiejar.DefaultCookiePolicy method): DefaultCookiePolicy Objects.
                                                             (line   56)
* set_blocking() (in module os):         File Descriptor Operations.
                                                             (line  616)
* set_boundary() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  411)
* set_boundary() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  587)
* set_break() (bdb.Bdb method):          bdb — Debugger framework.
                                                             (line  281)
* set_charset() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  235)
* set_children() (tkinter.ttk.Treeview method): ttk Treeview.
                                                             (line   25)
* set_child_watcher() (asyncio.AbstractEventLoopPolicy method): Policy Objects.
                                                             (line   42)
* set_child_watcher() (in module asyncio): Process Watchers. (line   29)
* set_ciphers() (ssl.SSLContext method): SSL Contexts.       (line  238)
* set_completer() (in module readline):  Completion.         (line   14)
* set_completer_delims() (in module readline): Completion.   (line   48)
* set_completion_display_matches_hook() (in module readline): Completion.
                                                             (line   57)
* set_content() (email.contentmanager.ContentManager method): email contentmanager Managing MIME Content.
                                                             (line   40)
* set_content() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  590)
* set_content() (in module email.contentmanager): Content Manager Instances.
                                                             (line   35)
* set_continue() (bdb.Bdb method):       bdb — Debugger framework.
                                                             (line  266)
* set_cookie() (http.cookiejar.CookieJar method): CookieJar and FileCookieJar Objects.
                                                             (line   72)
* set_cookie_if_ok() (http.cookiejar.CookieJar method): CookieJar and FileCookieJar Objects.
                                                             (line   68)
* set_coroutine_origin_tracking_depth() (in module sys): sys — System-specific parameters and functions.
                                                             (line 1435)
* set_current() (msilib.Feature method): Features<3>.        (line   14)
* set_data() (importlib.abc.SourceLoader method): importlib abc – Abstract base classes related to import.
                                                             (line  570)
* set_data() (importlib.machinery.SourceFileLoader method): importlib machinery – Importers and path hooks.
                                                             (line  242)
* set_date() (mailbox.MaildirMessage method): MaildirMessage.
                                                             (line   97)
* set_debug() (asyncio.loop method):     Enabling debug mode.
                                                             (line   14)
* set_debug() (in module gc):            gc — Garbage Collector interface.
                                                             (line   48)
* set_debuglevel() (ftplib.FTP method):  FTP Objects.        (line   13)
* set_debuglevel() (http.client.HTTPConnection method): HTTPConnection Objects.
                                                             (line   71)
* set_debuglevel() (nntplib.NNTP method): Methods<3>.        (line  307)
* set_debuglevel() (poplib.POP3 method): POP3 Objects.       (line   11)
* set_debuglevel() (smtplib.SMTP method): SMTP Objects.      (line    8)
* set_debuglevel() (telnetlib.Telnet method): Telnet Objects.
                                                             (line   84)
* set_defaults() (argparse.ArgumentParser method): Parser defaults.
                                                             (line    6)
* set_defaults() (optparse.OptionParser method): Other methods.
                                                             (line   27)
* set_default_executor() (asyncio.loop method): Executing code in thread or process pools.
                                                             (line   65)
* set_default_type() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  342)
* set_default_type() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  450)
* set_default_verify_paths() (ssl.SSLContext method): SSL Contexts.
                                                             (line  229)
* set_ecdh_curve() (ssl.SSLContext method): SSL Contexts.    (line  368)
* set_errno() (in module ctypes):        Utility functions.  (line  171)
* set_escdelay() (in module curses):     Functions<4>.       (line  438)
* set_event_loop() (asyncio.AbstractEventLoopPolicy method): Policy Objects.
                                                             (line   23)
* set_event_loop() (in module asyncio):  Event Loop.         (line   57)
* set_event_loop_policy() (in module asyncio): Getting and Setting the Policy.
                                                             (line   13)
* set_exception() (asyncio.Future method): Future Object.    (line   52)
* set_exception() (concurrent.futures.Future method): Future Objects.
                                                             (line  123)
* set_exception_handler() (asyncio.loop method): Error Handling API.
                                                             (line    8)
* set_executable() (in module multiprocessing): Miscellaneous<3>.
                                                             (line  112)
* set_executables() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  235)
* set_filter() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line  127)
* set_flags() (mailbox.MaildirMessage method): MaildirMessage.
                                                             (line   72)
* set_flags() (mailbox.mboxMessage method): mboxMessage.     (line   72)
* set_flags() (mailbox.MMDFMessage method): MMDFMessage.     (line   71)
* set_from() (mailbox.mboxMessage method): mboxMessage.      (line   53)
* set_from() (mailbox.MMDFMessage method): MMDFMessage.      (line   52)
* set_handle_inheritable() (in module os): Inheritance of File Descriptors.
                                                             (line   38)
* set_history_length() (in module readline): History file.   (line   30)
* set_include_dirs() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  103)
* set_info() (mailbox.MaildirMessage method): MaildirMessage.
                                                             (line  108)
* set_inheritable() (in module os):      Inheritance of File Descriptors.
                                                             (line   28)
* set_inheritable() (socket.socket method): Socket Objects.  (line  505)
* set_labels() (mailbox.BabylMessage method): BabylMessage.  (line   51)
* set_last_error() (in module ctypes):   Utility functions.  (line  180)
* set_libraries() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  128)
* set_library_dirs() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  144)
* set_link_objects() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  187)
* set_literal (2to3 fixer):              Fixers.             (line  289)
* set_loader() (in module importlib.util): importlib util – Utility code for importers.
                                                             (line  172)
* set_match_tests() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  310)
* set_memlimit() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  431)
* set_name() (asyncio.Task method):      Task Object.        (line  223)
* set_next() (bdb.Bdb method):           bdb — Debugger framework.
                                                             (line  248)
* set_nonstandard_attr() (http.cookiejar.Cookie method): Cookie Objects<2>.
                                                             (line  103)
* set_npn_protocols() (ssl.SSLContext method): SSL Contexts. (line  272)
* set_ok() (http.cookiejar.CookiePolicy method): CookiePolicy Objects.
                                                             (line    9)
* set_option_negotiation_callback() (telnetlib.Telnet method): Telnet Objects.
                                                             (line  143)
* set_output_charset() (gettext.NullTranslations method): The NullTranslations class.
                                                             (line   94)
* set_package() (in module importlib.util): importlib util – Utility code for importers.
                                                             (line  187)
* set_param() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  351)
* set_param() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  518)
* set_pasv() (ftplib.FTP method):        FTP Objects.        (line  108)
* set_payload() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  225)
* set_policy() (http.cookiejar.CookieJar method): CookieJar and FileCookieJar Objects.
                                                             (line   56)
* set_position() (xdrlib.Unpacker method): Unpacker Objects. (line   16)
* set_pre_input_hook() (in module readline): Startup hooks.  (line   14)
* set_progress_handler() (sqlite3.Connection method): Connection Objects.
                                                             (line  218)
* set_protocol() (asyncio.BaseTransport method): Base Transport.
                                                             (line   80)
* set_proxy() (urllib.request.Request method): Request Objects.
                                                             (line  114)
* set_python_build() (in module distutils.sysconfig): distutils sysconfig — System configuration information.
                                                             (line   99)
* set_quit() (bdb.Bdb method):           bdb — Debugger framework.
                                                             (line  271)
* set_recsrc() (ossaudiodev.oss_mixer_device method): Mixer Device Objects.
                                                             (line   89)
* set_result() (asyncio.Future method):  Future Object.      (line   45)
* set_result() (concurrent.futures.Future method): Future Objects.
                                                             (line  111)
* set_return() (bdb.Bdb method):         bdb — Debugger framework.
                                                             (line  252)
* set_running_or_notify_cancel() (concurrent.futures.Future method): Future Objects.
                                                             (line   89)
* set_runtime_library_dirs() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  155)
* set_selection() (tkinter.filedialog.FileDialog method): Native Load/Save Dialogs.
                                                             (line  131)
* set_seq1() (difflib.SequenceMatcher method): SequenceMatcher Objects.
                                                             (line   54)
* set_seq2() (difflib.SequenceMatcher method): SequenceMatcher Objects.
                                                             (line   59)
* set_seqs() (difflib.SequenceMatcher method): SequenceMatcher Objects.
                                                             (line   44)
* set_sequences() (mailbox.MH method):   MH.                 (line   58)
* set_sequences() (mailbox.MHMessage method): MHMessage.     (line   37)
* set_servername_callback (ssl.SSLContext attribute): SSL Contexts.
                                                             (line  339)
* set_server_documentation() (xmlrpc.server.DocCGIXMLRPCRequestHandler method): DocCGIXMLRPCRequestHandler.
                                                             (line   24)
* set_server_documentation() (xmlrpc.server.DocXMLRPCServer method): DocXMLRPCServer Objects.
                                                             (line   24)
* set_server_name() (xmlrpc.server.DocCGIXMLRPCRequestHandler method): DocCGIXMLRPCRequestHandler.
                                                             (line   18)
* set_server_name() (xmlrpc.server.DocXMLRPCServer method): DocXMLRPCServer Objects.
                                                             (line   18)
* set_server_title() (xmlrpc.server.DocCGIXMLRPCRequestHandler method): DocCGIXMLRPCRequestHandler.
                                                             (line   13)
* set_server_title() (xmlrpc.server.DocXMLRPCServer method): DocXMLRPCServer Objects.
                                                             (line   13)
* set_spacing() (formatter.formatter method): The Formatter Interface.
                                                             (line  139)
* set_startup_hook() (in module readline): Startup hooks.    (line    6)
* set_start_method() (in module multiprocessing): Miscellaneous<3>.
                                                             (line  125)
* set_step() (bdb.Bdb method):           bdb — Debugger framework.
                                                             (line  244)
* set_subdir() (mailbox.MaildirMessage method): MaildirMessage.
                                                             (line   58)
* set_tabsize() (in module curses):      Functions<4>.       (line  453)
* set_task_factory() (asyncio.loop method): Creating Futures and Tasks.
                                                             (line   31)
* set_terminator() (asynchat.async_chat method): asynchat — Asynchronous socket command/response handler.
                                                             (line  117)
* set_threshold() (in module gc):        gc — Garbage Collector interface.
                                                             (line   89)
* set_trace() (bdb.Bdb method):          bdb — Debugger framework.
                                                             (line  261)
* set_trace() (in module bdb):           bdb — Debugger framework.
                                                             (line  404)
* set_trace() (in module pdb):           pdb — The Python Debugger.
                                                             (line  119)
* set_trace() (pdb.Pdb method):          pdb — The Python Debugger.
                                                             (line  180)
* set_trace_callback() (sqlite3.Connection method): Connection Objects.
                                                             (line  232)
* set_tunnel() (http.client.HTTPConnection method): HTTPConnection Objects.
                                                             (line   81)
* set_type() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  551)
* set_unittest_reportflags() (in module doctest): Unittest API.
                                                             (line  165)
* set_unixfrom() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  146)
* set_unixfrom() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  157)
* set_until() (bdb.Bdb method):          bdb — Debugger framework.
                                                             (line  256)
* SET_UPDATE (opcode):                   Python Bytecode Instructions.
                                                             (line  532)
* set_url() (urllib.robotparser.RobotFileParser method): urllib robotparser — Parser for robots txt.
                                                             (line   21)
* set_usage() (optparse.OptionParser method): Other methods. (line    8)
* set_userptr() (curses.panel.Panel method): Panel Objects.  (line   43)
* set_visible() (mailbox.BabylMessage method): BabylMessage. (line   68)
* set_wakeup_fd() (in module signal):    Module contents<2>. (line  391)
* set_write_buffer_limits() (asyncio.WriteTransport method): Write-only Transports.
                                                             (line   33)
* SF_APPEND (in module stat):            stat — Interpreting stat results.
                                                             (line  374)
* SF_ARCHIVED (in module stat):          stat — Interpreting stat results.
                                                             (line  366)
* SF_IMMUTABLE (in module stat):         stat — Interpreting stat results.
                                                             (line  370)
* SF_MNOWAIT (in module os):             File Descriptor Operations.
                                                             (line  629)
* SF_NODISKIO (in module os):            File Descriptor Operations.
                                                             (line  629)
* SF_NOUNLINK (in module stat):          stat — Interpreting stat results.
                                                             (line  378)
* SF_SNAPSHOT (in module stat):          stat — Interpreting stat results.
                                                             (line  382)
* SF_SYNC (in module os):                File Descriptor Operations.
                                                             (line  629)
* Shape (class in turtle):               Public classes.     (line   43)
* shape (memoryview attribute):          Memory Views.       (line  447)
* shape() (in module turtle):            Appearance.         (line    6)
* shapesize() (in module turtle):        Appearance.         (line   52)
* shapetransform() (in module turtle):   Appearance.         (line  157)
* share() (socket.socket method):        Socket Objects.     (line  575)
* ShareableList (class in multiprocessing.shared_memory): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line  243)
* ShareableList() (multiprocessing.managers.SharedMemoryManager method): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line  203)
* Shared Memory:                         multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line   10)
* SharedMemory (class in multiprocessing.shared_memory): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line   33)
* SharedMemory() (multiprocessing.managers.SharedMemoryManager method): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line  198)
* SharedMemoryManager (class in multiprocessing.managers): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line  171)
* shared_ciphers() (ssl.SSLSocket method): SSL Sockets.      (line  216)
* shared_object_filename() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  474)
* shearfactor() (in module turtle):      Appearance.         (line   84)
* Shelf (class in shelve):               Restrictions.       (line   23)
* shelve (module):                       shelve — Python object persistence.
                                                             (line    6)
* shield() (in module asyncio):          Shielding From Cancellation.
                                                             (line    6)
* shift() (decimal.Context method):      Context objects.    (line  494)
* shift() (decimal.Decimal method):      Decimal objects.    (line  543)
* shifting; operation:                   Shifting operations.
                                                             (line    6)
* shifting; operations:                  Bitwise Operations on Integer Types.
                                                             (line    6)
* shift_path_info() (in module wsgiref.util): wsgiref util – WSGI environment utilities.
                                                             (line   38)
* shlex (class in shlex):                shlex — Simple lexical analysis.
                                                             (line   85)
* shlex (module):                        shlex — Simple lexical analysis.
                                                             (line    6)
* shm (multiprocessing.shared_memory.ShareableList attribute): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line  278)
* shortDescription() (unittest.TestCase method): Test cases. (line  733)
* shorten() (in module textwrap):        textwrap — Text wrapping and filling.
                                                             (line   47)
* SHORT_TIMEOUT (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  115)
* shouldFlush() (logging.handlers.BufferingHandler method): MemoryHandler.
                                                             (line   35)
* shouldFlush() (logging.handlers.MemoryHandler method): MemoryHandler.
                                                             (line   71)
* shouldStop (unittest.TestResult attribute): Loading and running tests.
                                                             (line  268)
* show() (curses.panel.Panel method):    Panel Objects.      (line   49)
* show() (tkinter.commondialog.Dialog method): tkinter commondialog — Dialog window templates.
                                                             (line   16)
* showerror() (in module tkinter.messagebox): tkinter messagebox — Tkinter message prompts.
                                                             (line   30)
* showinfo() (in module tkinter.messagebox): tkinter messagebox — Tkinter message prompts.
                                                             (line   25)
* showsyntaxerror() (code.InteractiveInterpreter method): Interactive Interpreter Objects.
                                                             (line   44)
* showtraceback() (code.InteractiveInterpreter method): Interactive Interpreter Objects.
                                                             (line   53)
* showturtle() (in module turtle):       Visibility.         (line   15)
* showwarning() (in module tkinter.messagebox): tkinter messagebox — Tkinter message prompts.
                                                             (line   30)
* showwarning() (in module warnings):    Available Functions.
                                                             (line   56)
* show_code() (in module dis):           Analysis functions. (line   26)
* show_compilers() (in module distutils.ccompiler): distutils ccompiler — CCompiler base class.
                                                             (line   62)
* shuffle() (in module random):          Functions for sequences.
                                                             (line   54)
* shutdown() (concurrent.futures.Executor method): Executor Objects.
                                                             (line   56)
* shutdown() (imaplib.IMAP4 method):     IMAP4 Objects.      (line  268)
* shutdown() (in module logging):        Module-Level Functions.
                                                             (line  351)
* shutdown() (multiprocessing.managers.BaseManager method): Managers.
                                                             (line   67)
* shutdown() (socket.socket method):     Socket Objects.     (line  568)
* shutdown() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line   54)
* shutdown_asyncgens() (asyncio.loop method): Running and stopping the loop.
                                                             (line   56)
* shutdown_default_executor() (asyncio.loop method): Running and stopping the loop.
                                                             (line   77)
* shutil (module):                       shutil — High-level file operations.
                                                             (line    6)
* side_effect (unittest.mock.Mock attribute): The Mock Class.
                                                             (line  347)
* SIGABRT (in module signal):            Module contents<2>. (line   28)
* SIGALRM (in module signal):            Module contents<2>. (line   32)
* SIGBREAK (in module signal):           Module contents<2>. (line   38)
* SIGBUS (in module signal):             Module contents<2>. (line   44)
* SIGCHLD (in module signal):            Module contents<2>. (line   50)
* SIGCLD (in module signal):             Module contents<2>. (line   56)
* SIGCONT (in module signal):            Module contents<2>. (line   60)
* SIGFPE (in module signal):             Module contents<2>. (line   66)
* SIGHUP (in module signal):             Module contents<2>. (line   76)
* SIGILL (in module signal):             Module contents<2>. (line   83)
* SIGINT:                                Signal Handling<2>. (line    8)
* SIGINT <1>:                            Signal Handling<2>. (line   20)
* SIGINT (in module signal):             Module contents<2>. (line   87)
* siginterrupt() (in module signal):     Module contents<2>. (line  434)
* SIGKILL (in module signal):            Module contents<2>. (line   93)
* signal (module):                       signal — Set handlers for asynchronous events.
                                                             (line    6)
* signal() (in module signal):           Module contents<2>. (line  448)
* Signature (class in inspect):          Introspecting callables with the Signature object.
                                                             (line   50)
* signature (inspect.BoundArguments attribute): Introspecting callables with the Signature object.
                                                             (line  311)
* signature() (in module inspect):       Introspecting callables with the Signature object.
                                                             (line   12)
* sigpending() (in module signal):       Module contents<2>. (line  476)
* SIGPIPE (in module signal):            Module contents<2>. (line  101)
* SIGSEGV (in module signal):            Module contents<2>. (line  109)
* SIGTERM (in module signal):            Module contents<2>. (line  113)
* sigtimedwait() (in module signal):     Module contents<2>. (line  534)
* SIGUSR1 (in module signal):            Module contents<2>. (line  117)
* SIGUSR2 (in module signal):            Module contents<2>. (line  123)
* sigwait() (in module signal):          Module contents<2>. (line  490)
* sigwaitinfo() (in module signal):      Module contents<2>. (line  506)
* SIGWINCH (in module signal):           Module contents<2>. (line  129)
* SIG_BLOCK (in module signal):          Module contents<2>. (line  186)
* SIG_DFL (in module signal):            Module contents<2>. (line   15)
* SIG_IGN (in module signal):            Module contents<2>. (line   23)
* SIG_SETMASK (in module signal):        Module contents<2>. (line  201)
* SIG_UNBLOCK (in module signal):        Module contents<2>. (line  193)
* Simple Mail Transfer Protocol:         smtplib — SMTP protocol client.
                                                             (line    8)
* simple; statement:                     Simple statements.  (line    6)
* SimpleCookie (class in http.cookies):  http cookies — HTTP state management.
                                                             (line   48)
* simplefilter() (in module warnings):   Available Functions.
                                                             (line   90)
* SimpleHandler (class in wsgiref.handlers): wsgiref handlers – server/gateway base classes.
                                                             (line   70)
* SimpleHTTPRequestHandler (class in http.server): http server — HTTP servers.
                                                             (line  334)
* SimpleNamespace (class in types):      Additional Utility Classes and Functions.
                                                             (line    6)
* SimpleQueue (class in multiprocessing): Pipes and Queues.  (line  204)
* SimpleQueue (class in queue):          queue — A synchronized queue class.
                                                             (line   75)
* SimpleXMLRPCRequestHandler (class in xmlrpc.server): xmlrpc server — Basic XML-RPC servers.
                                                             (line   58)
* SimpleXMLRPCServer (class in xmlrpc.server): xmlrpc server — Basic XML-RPC servers.
                                                             (line   19)
* sin() (in module cmath):               Trigonometric functions<2>.
                                                             (line   29)
* sin() (in module math):                Trigonometric functions.
                                                             (line   60)
* single dispatch:                       Glossary.           (line 1188)
* SingleAddressHeader (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line  217)
* singledispatch() (in module functools): functools — Higher-order functions and operations on callable objects.
                                                             (line  380)
* singledispatchmethod (class in functools): functools — Higher-order functions and operations on callable objects.
                                                             (line  514)
* singleton; tuple:                      The standard type hierarchy.
                                                             (line  177)
* sinh() (in module cmath):              Hyperbolic functions<2>.
                                                             (line   30)
* sinh() (in module math):               Hyperbolic functions.
                                                             (line   25)
* SIO_KEEPALIVE_VALS (in module socket): Constants<8>.       (line  186)
* SIO_LOOPBACK_FAST_PATH (in module socket): Constants<8>.   (line  186)
* SIO_RCVALL (in module socket):         Constants<8>.       (line  186)
* site (module):                         site — Site-specific configuration hook.
                                                             (line    6)
* site command line option; –user-base:  Command Line Interface<4>.
                                                             (line   18)
* site command line option; –user-site:  Command Line Interface<4>.
                                                             (line   22)
* site-packages; directory:              site — Site-specific configuration hook.
                                                             (line   24)
* site_maps() (urllib.robotparser.RobotFileParser method): urllib robotparser — Parser for robots txt.
                                                             (line   71)
* sixtofour (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  254)
* size (multiprocessing.shared_memory.SharedMemory attribute): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line   96)
* size (struct.Struct attribute):        Classes<2>.         (line   62)
* size (tarfile.TarInfo attribute):      TarInfo Objects.    (line   47)
* size (tracemalloc.Statistic attribute): Statistic.         (line   19)
* size (tracemalloc.StatisticDiff attribute): StatisticDiff. (line   26)
* size (tracemalloc.Trace attribute):    Trace.              (line   23)
* size() (ftplib.FTP method):            FTP Objects.        (line  229)
* size() (mmap.mmap method):             mmap — Memory-mapped file support.
                                                             (line  270)
* Sized (class in collections.abc):      Collections Abstract Base Classes.
                                                             (line  112)
* Sized (class in typing):               Corresponding to other types in collections abc.
                                                             (line   70)
* sizeof() (in module ctypes):           Utility functions.  (line  189)
* size_diff (tracemalloc.StatisticDiff attribute): StatisticDiff.
                                                             (line   32)
* SIZE_MAX:                              Integer Objects.    (line  211)
* SKIP (in module doctest):              Option Flags.       (line  103)
* skip() (chunk.Chunk method):           chunk — Read IFF chunked data.
                                                             (line  113)
* skip() (in module unittest):           Skipping tests and expected failures.
                                                             (line   85)
* skipIf() (in module unittest):         Skipping tests and expected failures.
                                                             (line   90)
* skipinitialspace (csv.Dialect attribute): Dialects and Formatting Parameters.
                                                             (line   65)
* skipped (unittest.TestResult attribute): Loading and running tests.
                                                             (line  250)
* skippedEntity() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line  176)
* SkipTest:                              Skipping tests and expected failures.
                                                             (line  105)
* skipTest() (unittest.TestCase method): Test cases.         (line   97)
* skipUnless() (in module unittest):     Skipping tests and expected failures.
                                                             (line   94)
* skip_unless_bind_unix_socket() (in module test.support.socket_helper): test support socket_helper — Utilities for socket tests.
                                                             (line   59)
* skip_unless_symlink() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  624)
* skip_unless_xattr() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  629)
* SLASH (in module token):               token — Constants used with Python parse trees.
                                                             (line   94)
* SLASHEQUAL (in module token):          token — Constants used with Python parse trees.
                                                             (line  182)
* slave() (nntplib.NNTP method):         Methods<3>.         (line  303)
* sleep() (in module asyncio):           Sleeping.           (line    6)
* sleep() (in module time):              Functions<3>.       (line  215)
* slice:                                 Slicings.           (line    6)
* slice <1>:                             Glossary.           (line 1193)
* slice (built-in class):                Built-in Functions. (line 1497)
* Slice (class in ast):                  Subscripting.       (line   27)
* slice; assignment:                     Mutable Sequence Types.
                                                             (line   16)
* slice; operation:                      Common Sequence Operations.
                                                             (line   21)
* slicing:                               The standard type hierarchy.
                                                             (line  138)
* slicing <1>:                           The standard type hierarchy.
                                                             (line  197)
* slicing <2>:                           Slicings.           (line    6)
* slicing; assignment:                   Assignment statements.
                                                             (line  126)
* SMALLEST (in module test.support):     test support — Utilities for the Python test suite.
                                                             (line  215)
* SMTP (class in smtplib):               smtplib — SMTP protocol client.
                                                             (line   16)
* SMTP (in module email.policy):         email policy Policy Objects.
                                                             (line  493)
* SMTP; protocol:                        smtplib — SMTP protocol client.
                                                             (line    8)
* SMTPAuthenticationError:               smtplib — SMTP protocol client.
                                                             (line  181)
* SMTPChannel (class in smtpd):          SMTPChannel Objects.
                                                             (line    6)
* SMTPConnectError:                      smtplib — SMTP protocol client.
                                                             (line  166)
* smtpd (module):                        smtpd — SMTP Server.
                                                             (line    6)
* SMTPDataError:                         smtplib — SMTP protocol client.
                                                             (line  162)
* SMTPException:                         smtplib — SMTP protocol client.
                                                             (line  127)
* SMTPHandler (class in logging.handlers): SMTPHandler.      (line   10)
* SMTPHeloError:                         smtplib — SMTP protocol client.
                                                             (line  171)
* smtplib (module):                      smtplib — SMTP protocol client.
                                                             (line    6)
* SMTPNotSupportedError:                 smtplib — SMTP protocol client.
                                                             (line  175)
* SMTPRecipientsRefused:                 smtplib — SMTP protocol client.
                                                             (line  155)
* SMTPResponseException:                 smtplib — SMTP protocol client.
                                                             (line  141)
* SMTPSenderRefused:                     smtplib — SMTP protocol client.
                                                             (line  149)
* SMTPServer (class in smtpd):           SMTPServer Objects. (line    6)
* SMTPServerDisconnected:                smtplib — SMTP protocol client.
                                                             (line  135)
* SMTPUTF8 (in module email.policy):     email policy Policy Objects.
                                                             (line  499)
* smtp_server (smtpd.SMTPChannel attribute): SMTPChannel Objects.
                                                             (line   44)
* SMTP_SSL (class in smtplib):           smtplib — SMTP protocol client.
                                                             (line   70)
* smtp_state (smtpd.SMTPChannel attribute): SMTPChannel Objects.
                                                             (line   63)
* Snapshot (class in tracemalloc):       Snapshot.           (line    6)
* sndhdr (module):                       sndhdr — Determine type of sound file.
                                                             (line    6)
* SND_ALIAS (in module winsound):        winsound — Sound-playing interface for Windows.
                                                             (line   47)
* SND_ASYNC (in module winsound):        winsound — Sound-playing interface for Windows.
                                                             (line  109)
* SND_FILENAME (in module winsound):     winsound — Sound-playing interface for Windows.
                                                             (line   42)
* SND_LOOP (in module winsound):         winsound — Sound-playing interface for Windows.
                                                             (line   88)
* SND_MEMORY (in module winsound):       winsound — Sound-playing interface for Windows.
                                                             (line   94)
* SND_NODEFAULT (in module winsound):    winsound — Sound-playing interface for Windows.
                                                             (line  113)
* SND_NOSTOP (in module winsound):       winsound — Sound-playing interface for Windows.
                                                             (line  118)
* SND_NOWAIT (in module winsound):       winsound — Sound-playing interface for Windows.
                                                             (line  122)
* SND_PURGE (in module winsound):        winsound — Sound-playing interface for Windows.
                                                             (line  103)
* sniff() (csv.Sniffer method):          Module Contents<3>. (line  225)
* Sniffer (class in csv):                Module Contents<3>. (line  218)
* sni_callback (ssl.SSLContext attribute): SSL Contexts.     (line  288)
* socket (class in socket):              Creating sockets.   (line    8)
* socket (module):                       socket — Low-level networking interface.
                                                             (line    6)
* socket (socketserver.BaseServer attribute): Server Objects<2>.
                                                             (line   85)
* socket() (imaplib.IMAP4 method):       IMAP4 Objects.      (line  274)
* socket() (in module socket):           select — Waiting for I/O completion.
                                                             (line  138)
* SocketHandler (class in logging.handlers): SocketHandler.  (line   10)
* socketpair() (in module socket):       Creating sockets.   (line   62)
* sockets (asyncio.Server attribute):    Server Objects.     (line   99)
* socketserver (module):                 socketserver — A framework for network servers.
                                                             (line    6)
* SocketType (in module socket):         Creating sockets.   (line  174)
* socket_type (socketserver.BaseServer attribute): Server Objects<2>.
                                                             (line  108)
* sock_accept() (asyncio.loop method):   Working with socket objects directly.
                                                             (line   74)
* SOCK_CLOEXEC (in module socket):       Constants<8>.       (line   31)
* sock_connect() (asyncio.loop method):  Working with socket objects directly.
                                                             (line   55)
* SOCK_DGRAM (in module socket):         Constants<8>.       (line   20)
* SOCK_MAX_SIZE (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  155)
* SOCK_NONBLOCK (in module socket):      Constants<8>.       (line   31)
* SOCK_RAW (in module socket):           Constants<8>.       (line   20)
* SOCK_RDM (in module socket):           Constants<8>.       (line   20)
* sock_recv() (asyncio.loop method):     Working with socket objects directly.
                                                             (line   12)
* sock_recv_into() (asyncio.loop method): Working with socket objects directly.
                                                             (line   26)
* sock_sendall() (asyncio.loop method):  Working with socket objects directly.
                                                             (line   37)
* sock_sendfile() (asyncio.loop method): Working with socket objects directly.
                                                             (line   97)
* SOCK_SEQPACKET (in module socket):     Constants<8>.       (line   20)
* SOCK_STREAM (in module socket):        Constants<8>.       (line   20)
* softkwlist (in module keyword):        keyword — Testing for Python keywords.
                                                             (line   30)
* SOL_ALG (in module socket):            Constants<8>.       (line  202)
* SOL_RDS (in module socket):            Constants<8>.       (line  173)
* SOMAXCONN (in module socket):          Constants<8>.       (line   47)
* sort() (imaplib.IMAP4 method):         IMAP4 Objects.      (line  278)
* sort() (list method):                  Lists<2>.           (line   39)
* sortdict() (in module test.support):   test support — Utilities for the Python test suite.
                                                             (line  284)
* sorted() (built-in function):          Built-in Functions. (line 1512)
* sortTestMethodsUsing (unittest.TestLoader attribute): Loading and running tests.
                                                             (line  186)
* sort_stats() (pstats.Stats method):    The Stats Class.    (line   67)
* source (doctest.Example attribute):    Example Objects.    (line   17)
* source (pdb command):                  Debugger Commands.  (line  251)
* source (shlex.shlex attribute):        shlex Objects.      (line  151)
* source character set:                  Encoding declarations.
                                                             (line    6)
* SourceFileLoader (class in importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line  216)
* sourcehook() (shlex.shlex method):     shlex Objects.      (line   26)
* SourcelessFileLoader (class in importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line  256)
* SourceLoader (class in importlib.abc): importlib abc – Abstract base classes related to import.
                                                             (line  509)
* SOURCE_DATE_EPOCH:                     py_compile<2>.      (line    7)
* SOURCE_DATE_EPOCH <1>:                 Library<30>.        (line  453)
* SOURCE_DATE_EPOCH <2>:                 Build<29>.          (line   15)
* SOURCE_DATE_EPOCH <3>:                 py_compile — Compile Python source files.
                                                             (line   65)
* SOURCE_DATE_EPOCH <4>:                 py_compile — Compile Python source files.
                                                             (line   81)
* SOURCE_DATE_EPOCH <5>:                 py_compile — Compile Python source files.
                                                             (line   85)
* SOURCE_DATE_EPOCH <6>:                 Command-line use.   (line   92)
* source_from_cache() (in module imp):   imp — Access the import internals.
                                                             (line  228)
* source_from_cache() (in module importlib.util): importlib util – Utility code for importers.
                                                             (line   58)
* source_hash() (in module importlib.util): importlib util – Utility code for importers.
                                                             (line  221)
* SOURCE_SUFFIXES (in module importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line   13)
* source_to_code() (importlib.abc.InspectLoader static method): importlib abc – Abstract base classes related to import.
                                                             (line  424)
* space:                                 Indentation.        (line    6)
* space; in printf-style formatting:     printf-style String Formatting.
                                                             (line   66)
* space; in printf-style formatting <1>: printf-style Bytes Formatting.
                                                             (line   63)
* space; in string formatting:           Format Specification Mini-Language.
                                                             (line   71)
* span() (re.Match method):              Match Objects.      (line  157)
* spawn() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  488)
* spawn() (in module pty):               pty — Pseudo-terminal utilities.
                                                             (line   36)
* spawnl() (in module os):               Process Management. (line  518)
* spawnle() (in module os):              Process Management. (line  518)
* spawnlp() (in module os):              Process Management. (line  518)
* spawnlpe() (in module os):             Process Management. (line  518)
* spawnv() (in module os):               Process Management. (line  518)
* spawnve() (in module os):              Process Management. (line  518)
* spawnvp() (in module os):              Process Management. (line  518)
* spawnvpe() (in module os):             Process Management. (line  518)
* spawn_python() (in module test.support.script_helper): test support script_helper — Utilities for the Python execution tests.
                                                             (line   68)
* special method:                        Glossary.           (line 1201)
* special; attribute:                    The standard type hierarchy.
                                                             (line   13)
* special; method:                       Glossary.           (line 1205)
* specified_attributes (xml.parsers.expat.xmlparser attribute): XMLParser Objects<2>.
                                                             (line  117)
* spec_from_file_location() (in module importlib.util): importlib util – Utility code for importers.
                                                             (line  209)
* spec_from_loader() (in module importlib.util): importlib util – Utility code for importers.
                                                             (line  198)
* speed() (in module turtle):            Turtle motion.      (line  302)
* speed() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line  140)
* Spinbox (class in tkinter.ttk):        ttk Spinbox.        (line    6)
* split() (bytearray method):            Bytes and Bytearray Operations.
                                                             (line  391)
* split() (bytes method):                Bytes and Bytearray Operations.
                                                             (line  391)
* split() (in module os.path):           os path — Common pathname manipulations.
                                                             (line  375)
* split() (in module re):                Module Contents.    (line  176)
* split() (in module shlex):             shlex — Simple lexical analysis.
                                                             (line   17)
* split() (re.Pattern method):           Regular Expression Objects.
                                                             (line   74)
* split() (str method):                  String Methods<2>.  (line  455)
* splitdrive() (in module os.path):      os path — Common pathname manipulations.
                                                             (line  390)
* splitext() (in module os.path):        os path — Common pathname manipulations.
                                                             (line  414)
* splitlines() (bytearray method):       Bytes and Bytearray Operations.
                                                             (line  634)
* splitlines() (bytes method):           Bytes and Bytearray Operations.
                                                             (line  634)
* splitlines() (str method):             String Methods<2>.  (line  495)
* SplitResult (class in urllib.parse):   Structured Parse Results.
                                                             (line   55)
* SplitResultBytes (class in urllib.parse): Structured Parse Results.
                                                             (line   82)
* split_quoted() (in module distutils.util): distutils util — Miscellaneous other utility functions.
                                                             (line  118)
* SpooledTemporaryFile() (in module tempfile): tempfile — Generate temporary files and directories.
                                                             (line   93)
* sprintf-style formatting:              printf-style String Formatting.
                                                             (line    6)
* sprintf-style formatting <1>:          printf-style Bytes Formatting.
                                                             (line    6)
* spwd (module):                         spwd — The shadow password database.
                                                             (line    6)
* sqlite3 (module):                      sqlite3 — DB-API 2 0 interface for SQLite databases.
                                                             (line    6)
* sqlite_version (in module sqlite3):    Module functions and constants.
                                                             (line   32)
* sqlite_version_info (in module sqlite3): Module functions and constants.
                                                             (line   36)
* sqrt() (decimal.Context method):       Context objects.    (line  498)
* sqrt() (decimal.Decimal method):       Decimal objects.    (line  554)
* sqrt() (in module cmath):              Power and logarithmic functions<2>.
                                                             (line   23)
* sqrt() (in module math):               Power and logarithmic functions.
                                                             (line   74)
* ssizeargfunc (C type):                 Slot Type typedefs. (line  105)
* ssizeobjargproc (C type):              Slot Type typedefs. (line  107)
* SSL:                                   ssl — TLS/SSL wrapper for socket objects.
                                                             (line    8)
* ssl (module):                          ssl — TLS/SSL wrapper for socket objects.
                                                             (line    6)
* SSLCertVerificationError:              Exceptions<13>.     (line   79)
* SSLContext (class in ssl):             SSL Contexts.       (line   14)
* SSLEOFError:                           Exceptions<13>.     (line   71)
* SSLError:                              Exceptions<13>.     (line    6)
* SSLErrorNumber (class in ssl):         Constants<9>.       (line  519)
* SSLKEYLOGFILE:                         Context creation.   (line   33)
* SSLKEYLOGFILE <1>:                     Context creation.   (line   67)
* SSLObject (class in ssl):              Memory BIO Support<2>.
                                                             (line   30)
* sslobject_class (ssl.SSLContext attribute): SSL Contexts.  (line  471)
* SSLSession (class in ssl):             SSL session.        (line    8)
* SSLSocket (class in ssl):              SSL Sockets.        (line    6)
* sslsocket_class (ssl.SSLContext attribute): SSL Contexts.  (line  445)
* SSLSyscallError:                       Exceptions<13>.     (line   62)
* SSLv3 (ssl.TLSVersion attribute):      Constants<9>.       (line  541)
* SSLWantReadError:                      Exceptions<13>.     (line   44)
* SSLWantWriteError:                     Exceptions<13>.     (line   53)
* SSLZeroReturnError:                    Exceptions<13>.     (line   35)
* SSL_CERT_FILE:                         LibreSSL support.   (line   15)
* SSL_CERT_PATH:                         LibreSSL support.   (line   15)
* ssl_version (ftplib.FTP_TLS attribute): FTP_TLS Objects.   (line    9)
* st() (in module turtle):               Visibility.         (line   15)
* st2list() (in module parser):          Converting ST Objects.
                                                             (line   11)
* st2tuple() (in module parser):         Converting ST Objects.
                                                             (line   31)
* stack (traceback.TracebackException attribute): TracebackException Objects.
                                                             (line   34)
* stack viewer:                          Debug menu Shell window only.
                                                             (line   15)
* stack() (in module inspect):           The interpreter stack.
                                                             (line   84)
* stack; trace:                          The standard type hierarchy.
                                                             (line  765)
* stackable; streams:                    codecs — Codec registry and base classes.
                                                             (line    8)
* StackSummary (class in traceback):     StackSummary Objects.
                                                             (line   11)
* stack_effect() (in module dis):        Analysis functions. (line  141)
* stack_size() (in module threading):    threading — Thread-based parallelism.
                                                             (line  138)
* stack_size() (in module _thread):      _thread — Low-level threading API.
                                                             (line   94)
* stamp() (in module turtle):            Turtle motion.      (line  238)
* Standard C:                            String and Bytes literals.
                                                             (line   72)
* standard input:                        Complete Python programs.
                                                             (line   25)
* standard; output:                      Expression statements.
                                                             (line   17)
* standarderror (2to3 fixer):            Fixers.             (line  294)
* standard_b64decode() (in module base64): base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line   79)
* standard_b64encode() (in module base64): base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line   74)
* standend() (curses.window method):     Window Objects.     (line  516)
* standout() (curses.window method):     Window Objects.     (line  521)
* STAR (in module token):                token — Constants used with Python parse trees.
                                                             (line   90)
* STAREQUAL (in module token):           token — Constants used with Python parse trees.
                                                             (line  178)
* starmap() (in module itertools):       Itertool functions. (line  522)
* starmap() (multiprocessing.pool.Pool method): Process Pools.
                                                             (line  148)
* starmap_async() (multiprocessing.pool.Pool method): Process Pools.
                                                             (line  159)
* Starred (class in ast):                Variables.          (line   43)
* start (range attribute):               Ranges.             (line   61)
* start (slice object attribute):        The standard type hierarchy.
                                                             (line  814)
* start (slice object attribute) <1>:    Slicings.           (line   26)
* start (UnicodeError attribute):        Concrete exceptions.
                                                             (line  380)
* start() (in module tracemalloc):       Functions<10>.      (line   68)
* start() (logging.handlers.QueueListener method): QueueListener.
                                                             (line   71)
* start() (multiprocessing.managers.BaseManager method): Managers.
                                                             (line   40)
* start() (multiprocessing.Process method): Process and exceptions.
                                                             (line   43)
* start() (re.Match method):             Match Objects.      (line  132)
* start() (threading.Thread method):     Thread Objects.     (line   89)
* start() (tkinter.ttk.Progressbar method): ttk Progressbar. (line    8)
* start() (xml.etree.ElementTree.TreeBuilder method): TreeBuilder Objects.
                                                             (line   43)
* StartCdataSectionHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  300)
* StartDoctypeDeclHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  186)
* startDocument() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line   32)
* startElement() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line   82)
* StartElementHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  224)
* startElementNS() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line  102)
* startfile() (in module os):            Process Management. (line  629)
* STARTF_USESHOWWINDOW (in module subprocess): Windows Constants.
                                                             (line   33)
* STARTF_USESTDHANDLES (in module subprocess): Windows Constants.
                                                             (line   27)
* StartNamespaceDeclHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  279)
* startPrefixMapping() (xml.sax.handler.ContentHandler method): ContentHandler Objects.
                                                             (line   49)
* startswith() (bytearray method):       Bytes and Bytearray Operations.
                                                             (line  246)
* startswith() (bytes method):           Bytes and Bytearray Operations.
                                                             (line  246)
* startswith() (str method):             String Methods<2>.  (line  568)
* startTest() (unittest.TestResult method): Loading and running tests.
                                                             (line  330)
* startTestRun() (unittest.TestResult method): Loading and running tests.
                                                             (line  339)
* starttls() (imaplib.IMAP4 method):     IMAP4 Objects.      (line  296)
* starttls() (nntplib.NNTP method):      Methods<3>.         (line   62)
* starttls() (smtplib.SMTP method):      SMTP Objects.       (line  185)
* STARTUPINFO (class in subprocess):     Windows Popen Helpers.
                                                             (line    9)
* start_color() (in module curses):      Functions<4>.       (line  474)
* start_component() (msilib.Directory method): Directory Objects.
                                                             (line   20)
* start_new_thread() (in module _thread): _thread — Low-level threading API.
                                                             (line   32)
* start_ns() (xml.etree.ElementTree.TreeBuilder method): TreeBuilder Objects.
                                                             (line   75)
* start_server() (in module asyncio):    Streams.            (line   65)
* start_serving() (asyncio.Server method): Server Objects.   (line   47)
* start_threads() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  596)
* start_tls() (asyncio.loop method):     TLS Upgrade.        (line    6)
* start_unix_server() (in module asyncio): Streams.          (line  118)
* stat (module):                         stat — Interpreting stat results.
                                                             (line    6)
* stat() (in module os):                 Files and Directories.
                                                             (line  976)
* stat() (nntplib.NNTP method):          Methods<3>.         (line  219)
* stat() (os.DirEntry method):           Files and Directories.
                                                             (line  947)
* stat() (pathlib.Path method):          Methods<2>.         (line   40)
* stat() (poplib.POP3 method):           POP3 Objects.       (line   51)
* state() (tkinter.ttk.Widget method):   ttk Widget.         (line   25)
* statement:                             Glossary.           (line 1208)
* statement grouping:                    Indentation.        (line    6)
* statement; assert:                     The assert statement.
                                                             (line    6)
* statement; assert <1>:                 Concrete exceptions.
                                                             (line   10)
* statement; assignment, annotated:      Annotated assignment statements.
                                                             (line    6)
* statement; assignment, augmented:      Augmented assignment statements.
                                                             (line    6)
* statement; async def:                  Coroutines<2>.      (line    8)
* statement; async for:                  Coroutine function definition.
                                                             (line   26)
* statement; async with:                 The async for statement.
                                                             (line   43)
* statement; break:                      The break statement.
                                                             (line    6)
* statement; break <1>:                  The while statement.
                                                             (line   17)
* statement; break <2>:                  The for statement.  (line   22)
* statement; break <3>:                  The try statement.  (line   79)
* statement; break <4>:                  The try statement.  (line  108)
* statement; class:                      Class definitions.  (line    6)
* statement; continue:                   The continue statement.
                                                             (line    6)
* statement; continue <1>:               The while statement.
                                                             (line   17)
* statement; continue <2>:               The for statement.  (line   22)
* statement; continue <3>:               The try statement.  (line   79)
* statement; continue <4>:               The try statement.  (line  108)
* statement; def:                        Function definitions.
                                                             (line    6)
* statement; del:                        Basic customization.
                                                             (line   55)
* statement; del <1>:                    The del statement<2>.
                                                             (line    6)
* statement; del <2>:                    Mutable Sequence Types.
                                                             (line   16)
* statement; del <3>:                    Mapping Types — dict.
                                                             (line    6)
* statement; except:                     Built-in Exceptions.
                                                             (line    6)
* statement; for:                        for Statements.     (line    6)
* statement; for <1>:                    The break statement.
                                                             (line    6)
* statement; for <2>:                    The continue statement.
                                                             (line    6)
* statement; for <3>:                    The for statement.  (line    6)
* statement; global:                     The del statement<2>.
                                                             (line   15)
* statement; global <1>:                 The global statement.
                                                             (line    6)
* statement; if:                         The if statement.   (line    6)
* statement; if <1>:                     Truth Value Testing.
                                                             (line    6)
* statement; import:                     The standard type hierarchy.
                                                             (line  526)
* statement; import <1>:                 The import statement.
                                                             (line    6)
* statement; import <2>:                 Built-in Functions. (line 1800)
* statement; import <3>:                 site — Site-specific configuration hook.
                                                             (line   45)
* statement; import <4>:                 imp — Access the import internals.
                                                             (line   11)
* statement; nonlocal:                   The nonlocal statement.
                                                             (line    6)
* statement; pass:                       The pass statement. (line    6)
* statement; raise:                      The raise statement.
                                                             (line    6)
* statement; raise <1>:                  Built-in Exceptions.
                                                             (line   14)
* statement; return:                     The return statement.
                                                             (line    6)
* statement; return <1>:                 The try statement.  (line   79)
* statement; return <2>:                 The try statement.  (line  108)
* statement; try:                        The standard type hierarchy.
                                                             (line  788)
* statement; try <1>:                    The try statement.  (line    6)
* statement; try <2>:                    Built-in Exceptions.
                                                             (line    6)
* statement; while:                      The break statement.
                                                             (line    6)
* statement; while <1>:                  The continue statement.
                                                             (line    6)
* statement; while <2>:                  The while statement.
                                                             (line    6)
* statement; while <3>:                  Truth Value Testing.
                                                             (line    6)
* statement; with:                       With Statement Context Managers.
                                                             (line   14)
* statement; with <1>:                   The with statement. (line    6)
* statement; yield:                      The yield statement.
                                                             (line    6)
* staticmethod() (built-in function):    Built-in Functions. (line 1548)
* static_order() (graphlib.TopologicalSorter method): graphlib — Functionality to operate with graph-like structures.
                                                             (line  161)
* Statistic (class in tracemalloc):      Statistic.          (line    6)
* StatisticDiff (class in tracemalloc):  StatisticDiff.      (line    6)
* statistics (module):                   statistics — Mathematical statistics functions.
                                                             (line    6)
* statistics() (tracemalloc.Snapshot method): Snapshot.      (line   56)
* StatisticsError:                       Exceptions<4>.      (line    8)
* Stats (class in pstats):               The Stats Class.    (line    9)
* status (http.client.HTTPResponse attribute): HTTPResponse Objects.
                                                             (line   61)
* status (urllib.response.addinfourl attribute): urllib response — Response classes used by urllib.
                                                             (line   24)
* status() (imaplib.IMAP4 method):       IMAP4 Objects.      (line  309)
* statvfs() (in module os):              Files and Directories.
                                                             (line 1236)
* stat_result (class in os):             Files and Directories.
                                                             (line 1031)
* StdButtonBox (class in tkinter.tix):   Basic Widgets.      (line   65)
* stderr (asyncio.asyncio.subprocess.Process attribute): Interacting with Subprocesses.
                                                             (line  120)
* stderr (in module sys):                The standard type hierarchy.
                                                             (line  635)
* stderr (in module sys) <1>:            sys — System-specific parameters and functions.
                                                             (line 1469)
* stderr (in module sys) <2>:            Sub-interpreter support.
                                                             (line   26)
* stderr (subprocess.CalledProcessError attribute): Using the subprocess Module.
                                                             (line  214)
* stderr (subprocess.CompletedProcess attribute): Using the subprocess Module.
                                                             (line  119)
* stderr (subprocess.Popen attribute):   Popen Objects.      (line  125)
* stderr (subprocess.TimeoutExpired attribute): Using the subprocess Module.
                                                             (line  181)
* stdev (statistics.NormalDist attribute): NormalDist objects.
                                                             (line   35)
* stdev() (in module statistics):        Function details.   (line  334)
* stdin (asyncio.asyncio.subprocess.Process attribute): Interacting with Subprocesses.
                                                             (line  110)
* stdin (in module sys):                 The standard type hierarchy.
                                                             (line  635)
* stdin (in module sys) <1>:             sys — System-specific parameters and functions.
                                                             (line 1469)
* stdin (in module sys) <2>:             Sub-interpreter support.
                                                             (line   26)
* stdin (subprocess.Popen attribute):    Popen Objects.      (line  106)
* stdin; stdout; sdterr:                 Process-wide parameters.
                                                             (line    9)
* stdio:                                 The standard type hierarchy.
                                                             (line  635)
* stdout (asyncio.asyncio.subprocess.Process attribute): Interacting with Subprocesses.
                                                             (line  115)
* STDOUT (in module subprocess):         Using the subprocess Module.
                                                             (line  147)
* stdout (in module sys):                The standard type hierarchy.
                                                             (line  635)
* stdout (in module sys) <1>:            sys — System-specific parameters and functions.
                                                             (line 1469)
* stdout (in module sys) <2>:            Sub-interpreter support.
                                                             (line   26)
* stdout (subprocess.CalledProcessError attribute): Using the subprocess Module.
                                                             (line  210)
* stdout (subprocess.CompletedProcess attribute): Using the subprocess Module.
                                                             (line  109)
* stdout (subprocess.Popen attribute):   Popen Objects.      (line  115)
* stdout (subprocess.TimeoutExpired attribute): Using the subprocess Module.
                                                             (line  177)
* STD_ERROR_HANDLE (in module subprocess): Windows Constants.
                                                             (line   18)
* STD_INPUT_HANDLE (in module subprocess): Windows Constants.
                                                             (line    8)
* STD_OUTPUT_HANDLE (in module subprocess): Windows Constants.
                                                             (line   13)
* step (pdb command):                    Debugger Commands.  (line  162)
* step (range attribute):                Ranges.             (line   70)
* step (slice object attribute):         The standard type hierarchy.
                                                             (line  814)
* step (slice object attribute) <1>:     Slicings.           (line   26)
* step() (tkinter.ttk.Progressbar method): ttk Progressbar.  (line   15)
* stereocontrols() (ossaudiodev.oss_mixer_device method): Mixer Device Objects.
                                                             (line   44)
* stls() (poplib.POP3 method):           POP3 Objects.       (line  113)
* stop (range attribute):                Ranges.             (line   66)
* stop (slice object attribute):         The standard type hierarchy.
                                                             (line  814)
* stop (slice object attribute) <1>:     Slicings.           (line   26)
* stop() (asyncio.loop method):          Running and stopping the loop.
                                                             (line   31)
* stop() (in module tracemalloc):        Functions<10>.      (line   98)
* stop() (logging.handlers.QueueListener method): QueueListener.
                                                             (line   78)
* stop() (tkinter.ttk.Progressbar method): ttk Progressbar.  (line   21)
* stop() (unittest.TestResult method):   Loading and running tests.
                                                             (line  311)
* StopAsyncIteration:                    Concrete exceptions.
                                                             (line  240)
* StopIteration:                         Concrete exceptions.
                                                             (line  210)
* stopListening() (in module logging.config): Configuration functions.
                                                             (line  163)
* stopTest() (unittest.TestResult method): Loading and running tests.
                                                             (line  334)
* stopTestRun() (unittest.TestResult method): Loading and running tests.
                                                             (line  345)
* stop_here() (bdb.Bdb method):          bdb — Debugger framework.
                                                             (line  191)
* storbinary() (ftplib.FTP method):      FTP Objects.        (line  113)
* Store (class in ast):                  Variables.          (line   11)
* store() (imaplib.IMAP4 method):        IMAP4 Objects.      (line  313)
* STORE_ACTIONS (optparse.Option attribute): Adding new actions.
                                                             (line   35)
* STORE_ATTR (opcode):                   Python Bytecode Instructions.
                                                             (line  455)
* STORE_DEREF (opcode):                  Python Bytecode Instructions.
                                                             (line  682)
* STORE_FAST (opcode):                   Python Bytecode Instructions.
                                                             (line  653)
* STORE_GLOBAL (opcode):                 Python Bytecode Instructions.
                                                             (line  464)
* STORE_NAME (opcode):                   Python Bytecode Instructions.
                                                             (line  428)
* STORE_SUBSCR (opcode):                 Python Bytecode Instructions.
                                                             (line  250)
* storlines() (ftplib.FTP method):       FTP Objects.        (line  127)
* str (built-in class):                  Text Sequence Type — str.
                                                             (line   44)
* str (built-in class); (see also string): Ranges.           (line  126)
* str() (in module locale):              locale — Internationalization services.
                                                             (line  435)
* strcoll() (in module locale):          locale — Internationalization services.
                                                             (line  375)
* StreamError:                           tarfile — Read and write tar archive files.
                                                             (line  203)
* StreamHandler (class in logging):      StreamHandler.      (line   11)
* StreamReader (class in asyncio):       StreamReader.       (line    6)
* StreamReader (class in codecs):        StreamReader Objects.
                                                             (line   10)
* streamreader (codecs.CodecInfo attribute): codecs — Codec registry and base classes.
                                                             (line   87)
* StreamReaderWriter (class in codecs):  StreamReaderWriter Objects.
                                                             (line   12)
* StreamRecoder (class in codecs):       StreamRecoder Objects.
                                                             (line   13)
* StreamRequestHandler (class in socketserver): Request Handler Objects.
                                                             (line   42)
* streams:                               codecs — Codec registry and base classes.
                                                             (line    8)
* StreamWriter (class in asyncio):       StreamWriter.       (line    6)
* StreamWriter (class in codecs):        StreamWriter Objects.
                                                             (line   10)
* streamwriter (codecs.CodecInfo attribute): codecs — Codec registry and base classes.
                                                             (line   87)
* strerror (OSError attribute):          Concrete exceptions.
                                                             (line  151)
* strerror():                            Raising exceptions. (line   59)
* strerror() (in module os):             Process Parameters. (line  452)
* strftime() (datetime.date method):     date Objects.       (line  271)
* strftime() (datetime.datetime method): datetime Objects.   (line  700)
* strftime() (datetime.time method):     time Objects.       (line  209)
* strftime() (in module time):           Functions<3>.       (line  230)
* strict (csv.Dialect attribute):        Dialects and Formatting Parameters.
                                                             (line   70)
* strict (in module email.policy):       email policy Policy Objects.
                                                             (line  514)
* strict_domain (http.cookiejar.DefaultCookiePolicy attribute): DefaultCookiePolicy Objects.
                                                             (line   95)
* strict_errors() (in module codecs):    Error Handlers.     (line  128)
* strict_ns_domain (http.cookiejar.DefaultCookiePolicy attribute): DefaultCookiePolicy Objects.
                                                             (line  117)
* strict_ns_set_initial_dollar (http.cookiejar.DefaultCookiePolicy attribute): DefaultCookiePolicy Objects.
                                                             (line  122)
* strict_ns_set_path (http.cookiejar.DefaultCookiePolicy attribute): DefaultCookiePolicy Objects.
                                                             (line  127)
* strict_ns_unverifiable (http.cookiejar.DefaultCookiePolicy attribute): DefaultCookiePolicy Objects.
                                                             (line  112)
* strict_rfc2965_unverifiable (http.cookiejar.DefaultCookiePolicy attribute): DefaultCookiePolicy Objects.
                                                             (line  103)
* strides (memoryview attribute):        Memory Views.       (line  455)
* STRING (in module token):              token — Constants used with Python parse trees.
                                                             (line   46)
* string (module):                       string — Common string operations.
                                                             (line    6)
* string (re.Match attribute):           Match Objects.      (line  196)
* string literal:                        Literals.           (line    8)
* string; conversion:                    Basic customization.
                                                             (line  149)
* string; conversion <1>:                Expression statements.
                                                             (line   17)
* string; format() (built-in function):  Built-in Functions. (line  641)
* string; formatted literal:             String literal concatenation.
                                                             (line   24)
* string; formatting, printf:            printf-style String Formatting.
                                                             (line    6)
* string; immutable sequences:           The standard type hierarchy.
                                                             (line  159)
* string; interpolated literal:          String literal concatenation.
                                                             (line   24)
* string; interpolation, printf:         printf-style String Formatting.
                                                             (line    6)
* string; item:                          Subscriptions.      (line   38)
* string; methods:                       Text Sequence Type — str.
                                                             (line   85)
* string; object representation:         Finalization and De-allocation.
                                                             (line   91)
* string; PyObject_Str (C function):     Object Protocol.    (line  186)
* string; str (built-in class):          Text Sequence Type — str.
                                                             (line   44)
* string; str() (built-in function):     Built-in Functions. (line 1581)
* string; text sequence type:            Ranges.             (line  126)
* string; __format__() (object method):  Basic customization.
                                                             (line  149)
* string; __str__() (object method):     Basic customization.
                                                             (line  128)
* StringIO (class in io):                Text I/O<2>.        (line  195)
* stringprep (module):                   stringprep — Internet String Preparation.
                                                             (line    6)
* strings, documentation:                Defining Functions. (line   21)
* strings, documentation <1>:            Documentation Strings.
                                                             (line    6)
* string_at() (in module ctypes):        Utility functions.  (line  194)
* strip() (bytearray method):            Bytes and Bytearray Operations.
                                                             (line  437)
* strip() (bytes method):                Bytes and Bytearray Operations.
                                                             (line  437)
* strip() (str method):                  String Methods<2>.  (line  575)
* stripspaces (curses.textpad.Textbox attribute): Textbox objects.
                                                             (line  115)
* strip_dirs() (pstats.Stats method):    The Stats Class.    (line   34)
* strptime() (datetime.datetime class method): datetime Objects.
                                                             (line  231)
* strptime() (in module time):           Functions<3>.       (line  362)
* strsignal() (in module signal):        Module contents<2>. (line  249)
* strtobool() (in module distutils.util): distutils util — Miscellaneous other utility functions.
                                                             (line  139)
* Struct (class in struct):              Classes<2>.         (line    8)
* struct (module):                       struct — Interpret bytes as packed binary data.
                                                             (line    6)
* Structure (class in ctypes):           Structured data types.
                                                             (line   21)
* struct_time (class in time):           Functions<3>.       (line  396)
* strxfrm() (in module locale):          locale — Internationalization services.
                                                             (line  382)
* STType (in module parser):             ST Objects.         (line   10)
* Style (class in tkinter.ttk):          Ttk Styling.        (line   20)
* ST_ATIME (in module stat):             stat — Interpreting stat results.
                                                             (line  163)
* st_atime (os.stat_result attribute):   Files and Directories.
                                                             (line 1076)
* st_atime_ns (os.stat_result attribute): Files and Directories.
                                                             (line 1092)
* st_birthtime (os.stat_result attribute): Files and Directories.
                                                             (line 1160)
* st_blksize (os.stat_result attribute): Files and Directories.
                                                             (line 1138)
* st_blocks (os.stat_result attribute):  Files and Directories.
                                                             (line 1133)
* st_creator (os.stat_result attribute): Files and Directories.
                                                             (line 1178)
* ST_CTIME (in module stat):             stat — Interpreting stat results.
                                                             (line  171)
* st_ctime (os.stat_result attribute):   Files and Directories.
                                                             (line 1084)
* st_ctime_ns (os.stat_result attribute): Files and Directories.
                                                             (line 1102)
* ST_DEV (in module stat):               stat — Interpreting stat results.
                                                             (line  142)
* st_dev (os.stat_result attribute):     Files and Directories.
                                                             (line 1052)
* st_file_attributes (os.stat_result attribute): Files and Directories.
                                                             (line 1188)
* st_flags (os.stat_result attribute):   Files and Directories.
                                                             (line 1148)
* st_fstype (os.stat_result attribute):  Files and Directories.
                                                             (line 1167)
* st_gen (os.stat_result attribute):     Files and Directories.
                                                             (line 1156)
* ST_GID (in module stat):               stat — Interpreting stat results.
                                                             (line  154)
* st_gid (os.stat_result attribute):     Files and Directories.
                                                             (line 1064)
* ST_INO (in module stat):               stat — Interpreting stat results.
                                                             (line  138)
* st_ino (os.stat_result attribute):     Files and Directories.
                                                             (line 1043)
* ST_MODE (in module stat):              stat — Interpreting stat results.
                                                             (line  134)
* st_mode (os.stat_result attribute):    Files and Directories.
                                                             (line 1039)
* ST_MTIME (in module stat):             stat — Interpreting stat results.
                                                             (line  167)
* st_mtime (os.stat_result attribute):   Files and Directories.
                                                             (line 1080)
* st_mtime_ns (os.stat_result attribute): Files and Directories.
                                                             (line 1097)
* ST_NLINK (in module stat):             stat — Interpreting stat results.
                                                             (line  146)
* st_nlink (os.stat_result attribute):   Files and Directories.
                                                             (line 1056)
* st_rdev (os.stat_result attribute):    Files and Directories.
                                                             (line 1144)
* st_reparse_tag (os.stat_result attribute): Files and Directories.
                                                             (line 1195)
* st_rsize (os.stat_result attribute):   Files and Directories.
                                                             (line 1174)
* ST_SIZE (in module stat):              stat — Interpreting stat results.
                                                             (line  158)
* st_size (os.stat_result attribute):    Files and Directories.
                                                             (line 1068)
* st_type (os.stat_result attribute):    Files and Directories.
                                                             (line 1182)
* ST_UID (in module stat):               stat — Interpreting stat results.
                                                             (line  150)
* st_uid (os.stat_result attribute):     Files and Directories.
                                                             (line 1060)
* Sub (class in ast):                    Expressions<2>.     (line   54)
* sub() (in module operator):            operator — Standard operators as functions.
                                                             (line  153)
* sub() (in module re):                  Module Contents.    (line  251)
* sub() (re.Pattern method):             Regular Expression Objects.
                                                             (line   91)
* subclassing; immutable types:          Basic customization.
                                                             (line    8)
* subdirs (filecmp.dircmp attribute):    The dircmp class.   (line  100)
* SubElement() (in module xml.etree.ElementTree): Functions<7>.
                                                             (line  204)
* submit() (concurrent.futures.Executor method): Executor Objects.
                                                             (line   12)
* submodule_search_locations (importlib.machinery.ModuleSpec attribute): importlib machinery – Importers and path hooks.
                                                             (line  391)
* subn() (in module re):                 Module Contents.    (line  316)
* subn() (re.Pattern method):            Regular Expression Objects.
                                                             (line   96)
* subnets() (ipaddress.IPv4Network method): Network objects. (line  173)
* subnets() (ipaddress.IPv6Network method): Network objects. (line  344)
* subnet_of() (ipaddress.IPv4Network method): Network objects.
                                                             (line  215)
* subnet_of() (ipaddress.IPv6Network method): Network objects.
                                                             (line  348)
* Subnormal (class in decimal):          Signals.            (line   86)
* suboffsets (memoryview attribute):     Memory Views.       (line  464)
* subpad() (curses.window method):       Window Objects.     (line  525)
* subprocess (module):                   subprocess — Subprocess management.
                                                             (line    6)
* SubprocessError:                       Using the subprocess Module.
                                                             (line  153)
* SubprocessProtocol (class in asyncio): Base Protocols.     (line   24)
* SubprocessTransport (class in asyncio): Transports Hierarchy.
                                                             (line   50)
* subprocess_exec() (asyncio.loop method): Running Subprocesses.
                                                             (line   16)
* subprocess_shell() (asyncio.loop method): Running Subprocesses.
                                                             (line  113)
* subscribe() (imaplib.IMAP4 method):    IMAP4 Objects.      (line  337)
* Subscript (class in ast):              Subscripting.       (line    6)
* subscript; assignment:                 Mutable Sequence Types.
                                                             (line   16)
* subscript; operation:                  Common Sequence Operations.
                                                             (line   21)
* subscription:                          The standard type hierarchy.
                                                             (line  132)
* subscription <1>:                      The standard type hierarchy.
                                                             (line  197)
* subscription <2>:                      The standard type hierarchy.
                                                             (line  254)
* subscription <3>:                      Subscriptions.      (line    6)
* subscription; assignment:              Assignment statements.
                                                             (line  103)
* subsequent_indent (textwrap.TextWrapper attribute): textwrap — Text wrapping and filling.
                                                             (line  213)
* substitute() (string.Template method): Template strings.   (line   40)
* subst_vars() (in module distutils.util): distutils util — Miscellaneous other utility functions.
                                                             (line  102)
* subTest() (unittest.TestCase method):  Test cases.         (line  105)
* subtract() (collections.Counter method): Counter objects.  (line   88)
* subtract() (decimal.Context method):   Context objects.    (line  502)
* subtraction:                           Binary arithmetic operations.
                                                             (line   78)
* subtype (email.headerregistry.ContentTypeHeader attribute): email headerregistry Custom Header Objects.
                                                             (line  278)
* subwin() (curses.window method):       Window Objects.     (line  532)
* sub_commands (distutils.cmd.Command attribute): Creating a new Distutils command.
                                                             (line   49)
* successful() (multiprocessing.pool.AsyncResult method): Process Pools.
                                                             (line  213)
* suffix_map (in module mimetypes):      mimetypes — Map filenames to MIME types.
                                                             (line  128)
* suffix_map (mimetypes.MimeTypes attribute): MimeTypes Objects.
                                                             (line   23)
* suite:                                 Compound statements.
                                                             (line   18)
* suite() (in module parser):            Creating ST Objects.
                                                             (line   18)
* suiteClass (unittest.TestLoader attribute): Loading and running tests.
                                                             (line  192)
* sum() (built-in function):             Built-in Functions. (line 1592)
* summarize() (doctest.DocTestRunner method): DocTestRunner objects.
                                                             (line  116)
* summarize_address_range() (in module ipaddress): Other Module Level Functions.
                                                             (line   27)
* sum_list():                            Reference Count Details.
                                                             (line  143)
* sum_sequence():                        Reference Count Details.
                                                             (line  170)
* sum_sequence() <1>:                    Exceptions<19>.     (line   65)
* sunau (module):                        sunau — Read and write Sun AU files.
                                                             (line    6)
* super (pyclbr.Class attribute):        Class Objects<2>.   (line   38)
* super() (built-in function):           Built-in Functions. (line 1608)
* supernet() (ipaddress.IPv4Network method): Network objects.
                                                             (line  199)
* supernet() (ipaddress.IPv6Network method): Network objects.
                                                             (line  346)
* supernet_of() (ipaddress.IPv4Network method): Network objects.
                                                             (line  226)
* supernet_of() (ipaddress.IPv6Network method): Network objects.
                                                             (line  350)
* SupportsAbs (class in typing):         Protocols<3>.       (line    8)
* SupportsBytes (class in typing):       Protocols<3>.       (line   13)
* SupportsComplex (class in typing):     Protocols<3>.       (line   17)
* SupportsFloat (class in typing):       Protocols<3>.       (line   21)
* SupportsIndex (class in typing):       Protocols<3>.       (line   25)
* SupportsInt (class in typing):         Protocols<3>.       (line   31)
* SupportsRound (class in typing):       Protocols<3>.       (line   35)
* supports_bytes_environ (in module os): Process Parameters. (line  458)
* supports_dir_fd (in module os):        Files and Directories.
                                                             (line 1279)
* supports_effective_ids (in module os): Files and Directories.
                                                             (line 1304)
* supports_fd (in module os):            Files and Directories.
                                                             (line 1323)
* supports_follow_symlinks (in module os): Files and Directories.
                                                             (line 1342)
* supports_unicode_filenames (in module os.path): os path — Common pathname manipulations.
                                                             (line  444)
* suppress() (in module contextlib):     Utilities.          (line  178)
* SuppressCrashReport (class in test.support): test support — Utilities for the Python test suite.
                                                             (line 1066)
* swapcase() (bytearray method):         Bytes and Bytearray Operations.
                                                             (line  658)
* swapcase() (bytes method):             Bytes and Bytearray Operations.
                                                             (line  658)
* swapcase() (str method):               String Methods<2>.  (line  599)
* swap_attr() (in module test.support):  test support — Utilities for the Python test suite.
                                                             (line  534)
* swap_item() (in module test.support):  test support — Utilities for the Python test suite.
                                                             (line  551)
* SW_HIDE (in module subprocess):        Windows Constants.  (line   23)
* Symbol (class in symtable):            Examining Symbol Tables.
                                                             (line   99)
* symbol (module):                       symbol — Constants used with Python parse trees.
                                                             (line    6)
* SymbolTable (class in symtable):       Examining Symbol Tables.
                                                             (line    6)
* symlink() (in module os):              Files and Directories.
                                                             (line 1365)
* symlink_to() (pathlib.Path method):    Methods<2>.         (line  418)
* symmetric_difference() (frozenset method): Set Types — set frozenset.
                                                             (line  116)
* symmetric_difference_update() (frozenset method): Set Types — set frozenset.
                                                             (line  188)
* symtable (module):                     symtable — Access to the compiler’s symbol tables.
                                                             (line    6)
* symtable() (in module symtable):       Generating Symbol Tables.
                                                             (line    6)
* sym_name (in module symbol):           symbol — Constants used with Python parse trees.
                                                             (line   22)
* sync() (dbm.dumb.dumbdbm method):      dbm dumb — Portable DBM implementation.
                                                             (line   78)
* sync() (dbm.gnu.gdbm method):          dbm gnu — GNU’s reinterpretation of dbm.
                                                             (line  113)
* sync() (in module os):                 Files and Directories.
                                                             (line 1407)
* sync() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line  165)
* sync() (shelve.Shelf method):          shelve — Python object persistence.
                                                             (line   63)
* syncdown() (curses.window method):     Window Objects.     (line  542)
* synchronized() (in module multiprocessing.sharedctypes): The multiprocessing sharedctypes module.
                                                             (line   88)
* SyncManager (class in multiprocessing.managers): Managers. (line  133)
* syncok() (curses.window method):       Window Objects.     (line  548)
* syncup() (curses.window method):       Window Objects.     (line  553)
* syntax:                                Notation.           (line    6)
* SyntaxErr:                             Exceptions<17>.     (line   93)
* SyntaxError:                           Concrete exceptions.
                                                             (line  247)
* SyntaxWarning:                         Warnings.           (line   43)
* sys (module):                          sys — System-specific parameters and functions.
                                                             (line    6)
* sys.exc_info:                          The standard type hierarchy.
                                                             (line  765)
* sys.last_traceback:                    The standard type hierarchy.
                                                             (line  765)
* sys.meta_path:                         The meta path.      (line    6)
* sys.modules:                           The module cache.   (line    6)
* sys.path:                              Path entry finders. (line    6)
* sys.path_hooks:                        Path entry finders. (line    6)
* sys.path_importer_cache:               Path entry finders. (line    6)
* sys.stderr:                            The standard type hierarchy.
                                                             (line  635)
* sys.stdin:                             The standard type hierarchy.
                                                             (line  635)
* sys.stdout:                            The standard type hierarchy.
                                                             (line  635)
* sysconf() (in module os):              Miscellaneous System Information.
                                                             (line   56)
* sysconfig (module):                    sysconfig — Provide access to Python’s configuration information.
                                                             (line    6)
* sysconf_names (in module os):          Miscellaneous System Information.
                                                             (line   66)
* syslog (module):                       syslog — Unix syslog library routines.
                                                             (line    6)
* syslog() (in module syslog):           syslog — Unix syslog library routines.
                                                             (line   18)
* SysLogHandler (class in logging.handlers): SysLogHandler.  (line   10)
* system() (in module os):               Process Management. (line  665)
* system() (in module platform):         Cross Platform.     (line  119)
* SystemError:                           Concrete exceptions.
                                                             (line  294)
* SystemError (built-in exception):      Module Objects.     (line   55)
* SystemError (built-in exception) <1>:  Module Objects.     (line   81)
* SystemExit:                            Concrete exceptions.
                                                             (line  308)
* SystemExit (built-in exception):       Exceptions<2>.      (line   26)
* systemId (xml.dom.DocumentType attribute): DocumentType Objects.
                                                             (line   22)
* SystemRandom (class in random):        Alternative Generator.
                                                             (line   15)
* SystemRandom (class in secrets):       Random numbers.     (line    9)
* SystemRoot:                            Popen Constructor.  (line  272)
* system_alias() (in module platform):   Cross Platform.     (line  125)
* system_must_validate_cert() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  279)
* sys_exc (2to3 fixer):                  Fixers.             (line  298)
* sys_version (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  137)
* S_ENFMT (in module stat):              stat — Interpreting stat results.
                                                             (line  317)
* S_IEXEC (in module stat):              stat — Interpreting stat results.
                                                             (line  331)
* S_IFBLK (in module stat):              stat — Interpreting stat results.
                                                             (line  206)
* S_IFCHR (in module stat):              stat — Interpreting stat results.
                                                             (line  214)
* S_IFDIR (in module stat):              stat — Interpreting stat results.
                                                             (line  210)
* S_IFDOOR (in module stat):             stat — Interpreting stat results.
                                                             (line  222)
* S_IFIFO (in module stat):              stat — Interpreting stat results.
                                                             (line  218)
* S_IFLNK (in module stat):              stat — Interpreting stat results.
                                                             (line  198)
* S_IFMT() (in module stat):             stat — Interpreting stat results.
                                                             (line   78)
* S_IFPORT (in module stat):             stat — Interpreting stat results.
                                                             (line  228)
* S_IFREG (in module stat):              stat — Interpreting stat results.
                                                             (line  202)
* S_IFSOCK (in module stat):             stat — Interpreting stat results.
                                                             (line  194)
* S_IFWHT (in module stat):              stat — Interpreting stat results.
                                                             (line  234)
* S_IMODE() (in module stat):            stat — Interpreting stat results.
                                                             (line   71)
* S_IREAD (in module stat):              stat — Interpreting stat results.
                                                             (line  323)
* S_IRGRP (in module stat):              stat — Interpreting stat results.
                                                             (line  289)
* S_IROTH (in module stat):              stat — Interpreting stat results.
                                                             (line  305)
* S_IRUSR (in module stat):              stat — Interpreting stat results.
                                                             (line  273)
* S_IRWXG (in module stat):              stat — Interpreting stat results.
                                                             (line  285)
* S_IRWXO (in module stat):              stat — Interpreting stat results.
                                                             (line  301)
* S_IRWXU (in module stat):              stat — Interpreting stat results.
                                                             (line  269)
* S_ISBLK() (in module stat):            stat — Interpreting stat results.
                                                             (line   30)
* S_ISCHR() (in module stat):            stat — Interpreting stat results.
                                                             (line   25)
* S_ISDIR() (in module stat):            stat — Interpreting stat results.
                                                             (line   21)
* S_ISDOOR() (in module stat):           stat — Interpreting stat results.
                                                             (line   50)
* S_ISFIFO() (in module stat):           stat — Interpreting stat results.
                                                             (line   38)
* S_ISGID (in module stat):              stat — Interpreting stat results.
                                                             (line  251)
* S_ISLNK() (in module stat):            stat — Interpreting stat results.
                                                             (line   42)
* S_ISPORT() (in module stat):           stat — Interpreting stat results.
                                                             (line   56)
* S_ISREG() (in module stat):            stat — Interpreting stat results.
                                                             (line   34)
* S_ISSOCK() (in module stat):           stat — Interpreting stat results.
                                                             (line   46)
* S_ISUID (in module stat):              stat — Interpreting stat results.
                                                             (line  247)
* S_ISVTX (in module stat):              stat — Interpreting stat results.
                                                             (line  262)
* S_ISWHT() (in module stat):            stat — Interpreting stat results.
                                                             (line   62)
* S_IWGRP (in module stat):              stat — Interpreting stat results.
                                                             (line  293)
* S_IWOTH (in module stat):              stat — Interpreting stat results.
                                                             (line  309)
* S_IWRITE (in module stat):             stat — Interpreting stat results.
                                                             (line  327)
* S_IWUSR (in module stat):              stat — Interpreting stat results.
                                                             (line  277)
* S_IXGRP (in module stat):              stat — Interpreting stat results.
                                                             (line  297)
* S_IXOTH (in module stat):              stat — Interpreting stat results.
                                                             (line  313)
* S_IXUSR (in module stat):              stat — Interpreting stat results.
                                                             (line  281)
* tab:                                   Indentation.        (line    6)
* tab() (tkinter.ttk.Notebook method):   ttk Notebook.       (line   62)
* TabError:                              Concrete exceptions.
                                                             (line  289)
* tabnanny (module):                     tabnanny — Detection of ambiguous indentation.
                                                             (line    6)
* tabs() (tkinter.ttk.Notebook method):  ttk Notebook.       (line   71)
* tabsize (textwrap.TextWrapper attribute): textwrap — Text wrapping and filling.
                                                             (line  170)
* tag (xml.etree.ElementTree.Element attribute): Element Objects.
                                                             (line   16)
* tagName (xml.dom.Element attribute):   Element Objects<2>. (line    9)
* tag_bind() (tkinter.ttk.Treeview method): ttk Treeview.    (line  303)
* tag_configure() (tkinter.ttk.Treeview method): ttk Treeview.
                                                             (line  309)
* tag_has() (tkinter.ttk.Treeview method): ttk Treeview.     (line  319)
* tail (xml.etree.ElementTree.Element attribute): Element Objects.
                                                             (line   21)
* takewhile() (in module itertools):     Itertool functions. (line  537)
* take_snapshot() (in module tracemalloc): Functions<10>.    (line  110)
* tan() (in module cmath):               Trigonometric functions<2>.
                                                             (line   33)
* tan() (in module math):                Trigonometric functions.
                                                             (line   64)
* tanh() (in module cmath):              Hyperbolic functions<2>.
                                                             (line   34)
* tanh() (in module math):               Hyperbolic functions.
                                                             (line   29)
* TarError:                              tarfile — Read and write tar archive files.
                                                             (line  189)
* TarFile (class in tarfile):            TarFile Objects.    (line   22)
* tarfile (module):                      tarfile — Read and write tar archive files.
                                                             (line    6)
* tarfile command line option; -c <tarfile> <source1> ... <sourceN>: Command-line options<2>.
                                                             (line   11)
* tarfile command line option; –create <tarfile> <source1> ... <sourceN>: Command-line options<2>.
                                                             (line   11)
* tarfile command line option; -e <tarfile> [<output_dir>]: Command-line options<2>.
                                                             (line   16)
* tarfile command line option; –extract <tarfile> [<output_dir>]: Command-line options<2>.
                                                             (line   16)
* tarfile command line option; -l <tarfile>: Command-line options<2>.
                                                             (line    6)
* tarfile command line option; –list <tarfile>: Command-line options<2>.
                                                             (line    6)
* tarfile command line option; -t <tarfile>: Command-line options<2>.
                                                             (line   22)
* tarfile command line option; –test <tarfile>: Command-line options<2>.
                                                             (line   22)
* tarfile command line option; -v:       Command-line options<2>.
                                                             (line   27)
* tarfile command line option; –verbose: Command-line options<2>.
                                                             (line   27)
* target:                                Assignment statements.
                                                             (line   27)
* target (xml.dom.ProcessingInstruction attribute): ProcessingInstruction Objects.
                                                             (line    9)
* target; list:                          Assignment statements.
                                                             (line   27)
* target; list <1>:                      The for statement.  (line    6)
* target; list; assignment:              Assignment statements.
                                                             (line   35)
* TarInfo (class in tarfile):            TarInfo Objects.    (line   15)
* Task (class in asyncio):               Task Object.        (line    6)
* task_done() (asyncio.Queue method):    Queue.              (line   78)
* task_done() (multiprocessing.JoinableQueue method): Pipes and Queues.
                                                             (line  237)
* task_done() (queue.Queue method):      Queue Objects.      (line   68)
* tau (in module cmath):                 Constants<3>.       (line   14)
* tau (in module math):                  Constants<2>.       (line   14)
* tbreak (pdb command):                  Debugger Commands.  (line   88)
* tb_frame (traceback attribute):        The standard type hierarchy.
                                                             (line  788)
* tb_lasti (traceback attribute):        The standard type hierarchy.
                                                             (line  788)
* tb_lineno (traceback attribute):       The standard type hierarchy.
                                                             (line  788)
* tb_locals (unittest.TestResult attribute): Loading and running tests.
                                                             (line  295)
* tb_next (traceback attribute):         The standard type hierarchy.
                                                             (line  800)
* tcdrain() (in module termios):         termios — POSIX style tty control.
                                                             (line   53)
* tcflow() (in module termios):          termios — POSIX style tty control.
                                                             (line   64)
* tcflush() (in module termios):         termios — POSIX style tty control.
                                                             (line   58)
* tcgetattr() (in module termios):       termios — POSIX style tty control.
                                                             (line   26)
* tcgetpgrp() (in module os):            File Descriptor Operations.
                                                             (line  657)
* Tcl() (in module tkinter):             Tkinter Modules.    (line   22)
* TCL_LIBRARY:                           How do I freeze Tkinter applications?.
                                                             (line   11)
* TCPServer (class in socketserver):     socketserver — A framework for network servers.
                                                             (line   15)
* tcsendbreak() (in module termios):     termios — POSIX style tty control.
                                                             (line   47)
* tcsetattr() (in module termios):       termios — POSIX style tty control.
                                                             (line   37)
* tcsetpgrp() (in module os):            File Descriptor Operations.
                                                             (line  664)
* tearDown() (unittest.TestCase method): Test cases.         (line   41)
* tearDownClass() (unittest.TestCase method): Test cases.    (line   69)
* tee() (in module itertools):           Itertool functions. (line  550)
* tell() (aifc.aifc method):             aifc — Read and write AIFF and AIFC files.
                                                             (line  112)
* tell() (chunk.Chunk method):           chunk — Read IFF chunked data.
                                                             (line  101)
* tell() (io.IOBase method):             I/O Base Classes.   (line  138)
* tell() (io.TextIOBase method):         Text I/O<2>.        (line   88)
* tell() (mmap.mmap method):             mmap — Memory-mapped file support.
                                                             (line  275)
* tell() (sunau.AU_read method):         AU_read Objects.    (line   65)
* tell() (sunau.AU_write method):        AU_write Objects.   (line   39)
* tell() (wave.Wave_read method):        Wave_read Objects.  (line   73)
* tell() (wave.Wave_write method):       Wave_write Objects. (line   62)
* Telnet (class in telnetlib):           telnetlib — Telnet client.
                                                             (line   25)
* telnetlib (module):                    telnetlib — Telnet client.
                                                             (line    6)
* TEMP:                                  tempfile — Generate temporary files and directories.
                                                             (line  239)
* tempdir (in module tempfile):          tempfile — Generate temporary files and directories.
                                                             (line  281)
* tempfile (module):                     tempfile — Generate temporary files and directories.
                                                             (line    6)
* Template (class in pipes):             pipes — Interface to shell pipelines.
                                                             (line   19)
* Template (class in string):            Template strings.   (line   35)
* template (string.Template attribute):  Template strings.   (line   70)
* temporary; file:                       tempfile — Generate temporary files and directories.
                                                             (line    8)
* temporary; file name:                  tempfile — Generate temporary files and directories.
                                                             (line    8)
* TemporaryDirectory() (in module tempfile): tempfile — Generate temporary files and directories.
                                                             (line  119)
* TemporaryFile() (in module tempfile):  tempfile — Generate temporary files and directories.
                                                             (line   28)
* temp_cwd() (in module test.support):   test support — Utilities for the Python test suite.
                                                             (line  499)
* temp_dir() (in module test.support):   test support — Utilities for the Python test suite.
                                                             (line  480)
* temp_umask() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  513)
* teredo (ipaddress.IPv6Address attribute): Address objects. (line  261)
* TERM:                                  Functions<4>.       (line  469)
* TERM <1>:                              Functions<4>.       (line  496)
* termattrs() (in module curses):        Functions<4>.       (line  488)
* terminal_size (class in os):           Querying the size of a terminal.
                                                             (line   25)
* terminate() (asyncio.asyncio.subprocess.Process method): Interacting with Subprocesses.
                                                             (line   90)
* terminate() (asyncio.SubprocessTransport method): Subprocess Transports.
                                                             (line   49)
* terminate() (multiprocessing.pool.Pool method): Process Pools.
                                                             (line  174)
* terminate() (multiprocessing.Process method): Process and exceptions.
                                                             (line  149)
* terminate() (subprocess.Popen method): Popen Objects.      (line   85)
* termination model:                     Exceptions<2>.      (line   20)
* terminator (logging.StreamHandler attribute): StreamHandler.
                                                             (line   47)
* termios (module):                      termios — POSIX style tty control.
                                                             (line    6)
* termname() (in module curses):         Functions<4>.       (line  494)
* ternary; operator:                     Conditional expressions.
                                                             (line    6)
* ternaryfunc (C type):                  Slot Type typedefs. (line  102)
* test (doctest.DocTestFailure attribute): Debugging.        (line  195)
* test (doctest.UnexpectedException attribute): Debugging.   (line  216)
* test (module):                         test — Regression tests package for Python.
                                                             (line    6)
* test() (in module cgi):                Functions<9>.       (line   44)
* test.support (module):                 test support — Utilities for the Python test suite.
                                                             (line    6)
* test.support.bytecode_helper (module): test support bytecode_helper — Support tools for testing correct bytecode generation.
                                                             (line    6)
* test.support.script_helper (module):   test support script_helper — Utilities for the Python execution tests.
                                                             (line    6)
* test.support.socket_helper (module):   test support socket_helper — Utilities for socket tests.
                                                             (line    6)
* TestCase (class in unittest):          Test cases.         (line    6)
* TestFailed:                            test support — Utilities for the Python test suite.
                                                             (line   16)
* testfile() (in module doctest):        Basic API.          (line   12)
* TESTFN (in module test.support):       test support — Utilities for the Python test suite.
                                                             (line   52)
* TESTFN_ENCODING (in module test.support): test support — Utilities for the Python test suite.
                                                             (line   62)
* TESTFN_NONASCII (in module test.support): test support — Utilities for the Python test suite.
                                                             (line   78)
* TESTFN_UNDECODABLE (in module test.support): test support — Utilities for the Python test suite.
                                                             (line   72)
* TESTFN_UNENCODABLE (in module test.support): test support — Utilities for the Python test suite.
                                                             (line   66)
* TESTFN_UNICODE (in module test.support): test support — Utilities for the Python test suite.
                                                             (line   58)
* TestLoader (class in unittest):        Loading and running tests.
                                                             (line    6)
* testMethodPrefix (unittest.TestLoader attribute): Loading and running tests.
                                                             (line  178)
* testmod() (in module doctest):         Basic API.          (line   90)
* testNamePatterns (unittest.TestLoader attribute): Loading and running tests.
                                                             (line  200)
* TestResult (class in unittest):        Loading and running tests.
                                                             (line  217)
* tests (in module imghdr):              imghdr — Determine the type of an image.
                                                             (line   75)
* testsource() (in module doctest):      Debugging.          (line  106)
* testsRun (unittest.TestResult attribute): Loading and running tests.
                                                             (line  273)
* TestSuite (class in unittest):         Grouping tests.     (line    6)
* testzip() (zipfile.ZipFile method):    ZipFile Objects.    (line  232)
* TEST_DATA_DIR (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  169)
* TEST_HOME_DIR (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  165)
* TEST_HTTP_URL (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  196)
* TEST_SUPPORT_DIR (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  160)
* Text (class in typing):                Other concrete types.
                                                             (line   35)
* text (in module msilib):               Precomputed tables. (line   23)
* text (SyntaxError attribute):          Concrete exceptions.
                                                             (line  274)
* text (traceback.TracebackException attribute): TracebackException Objects.
                                                             (line   50)
* text (xml.etree.ElementTree.Element attribute): Element Objects.
                                                             (line   21)
* text encoding:                         Glossary.           (line 1215)
* text file:                             Glossary.           (line 1219)
* text mode:                             Built-in Functions. (line 1223)
* text() (in module cgitb):              cgitb — Traceback manager for CGI scripts.
                                                             (line   48)
* text() (msilib.Dialog method):         GUI classes.        (line   56)
* Textbox (class in curses.textpad):     Textbox objects.    (line    8)
* TextCalendar (class in calendar):      calendar — General calendar-related functions.
                                                             (line  128)
* textdomain() (in module gettext):      GNU gettext API.    (line   36)
* textdomain() (in module locale):       Access to message catalogs.
                                                             (line   12)
* TextFile (class in distutils.text_file): distutils text_file — The TextFile class.
                                                             (line   10)
* textinput() (in module turtle):        Input methods.      (line    6)
* TextIO (class in typing):              Other concrete types.
                                                             (line    6)
* TextIOBase (class in io):              Text I/O<2>.        (line    6)
* TextIOWrapper (class in io):           Text I/O<2>.        (line   99)
* TextTestResult (class in unittest):    Loading and running tests.
                                                             (line  421)
* TextTestRunner (class in unittest):    Loading and running tests.
                                                             (line  436)
* textwrap (module):                     textwrap — Text wrapping and filling.
                                                             (line    6)
* TextWrapper (class in textwrap):       textwrap — Text wrapping and filling.
                                                             (line  137)
* text_factory (sqlite3.Connection attribute): Connection Objects.
                                                             (line  342)
* theme_create() (tkinter.ttk.Style method): Ttk Styling.    (line  191)
* theme_names() (tkinter.ttk.Style method): Ttk Styling.     (line  239)
* theme_settings() (tkinter.ttk.Style method): Ttk Styling.  (line  201)
* theme_use() (tkinter.ttk.Style method): Ttk Styling.       (line  243)
* THOUSEP (in module locale):            locale — Internationalization services.
                                                             (line  236)
* Thread (class in threading):           Thread Objects.     (line   57)
* thread() (imaplib.IMAP4 method):       IMAP4 Objects.      (line  341)
* ThreadedChildWatcher (class in asyncio): Process Watchers. (line   84)
* threading (module):                    threading — Thread-based parallelism.
                                                             (line    6)
* ThreadingHTTPServer (class in http.server): http server — HTTP servers.
                                                             (line   32)
* ThreadingMixIn (class in socketserver): Server Creation Notes.
                                                             (line   28)
* ThreadingTCPServer (class in socketserver): Server Creation Notes.
                                                             (line   62)
* ThreadingUDPServer (class in socketserver): Server Creation Notes.
                                                             (line   62)
* threading_cleanup() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  847)
* threading_setup() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  843)
* ThreadPool (class in multiprocessing.pool): The multiprocessing dummy module.
                                                             (line   16)
* ThreadPoolExecutor (class in concurrent.futures): ThreadPoolExecutor.
                                                             (line   39)
* threads; POSIX:                        _thread — Low-level threading API.
                                                             (line   16)
* threadsafety (in module sqlite3):      Module functions and constants.
                                                             (line   41)
* thread_info (in module sys):           sys — System-specific parameters and functions.
                                                             (line 1558)
* thread_time() (in module time):        Functions<3>.       (line  477)
* thread_time_ns() (in module time):     Functions<3>.       (line  491)
* throw (2to3 fixer):                    Fixers.             (line  303)
* throw() (coroutine method):            Coroutine Objects.  (line   34)
* throw() (generator method):            Generator-iterator methods.
                                                             (line   38)
* ticket_lifetime_hint (ssl.SSLSession attribute): SSL session.
                                                             (line   18)
* tigetflag() (in module curses):        Functions<4>.       (line  499)
* tigetnum() (in module curses):         Functions<4>.       (line  506)
* tigetstr() (in module curses):         Functions<4>.       (line  513)
* TILDE (in module token):               token — Constants used with Python parse trees.
                                                             (line  150)
* tilt() (in module turtle):             Appearance.         (line  102)
* tiltangle() (in module turtle):        Appearance.         (line  137)
* time (class in datetime):              time Objects.       (line   10)
* time (module):                         time — Time access and conversions.
                                                             (line    6)
* time (ssl.SSLSession attribute):       SSL session.        (line   14)
* time() (asyncio.loop method):          Scheduling delayed callbacks.
                                                             (line   56)
* time() (datetime.datetime method):     datetime Objects.   (line  395)
* time() (in module time):               Functions<3>.       (line  454)
* Time2Internaldate() (in module imaplib): imaplib — IMAP4 protocol client.
                                                             (line  132)
* timedelta (class in datetime):         timedelta Objects.  (line    9)
* TimedRotatingFileHandler (class in logging.handlers): TimedRotatingFileHandler.
                                                             (line   10)
* timegm() (in module calendar):         calendar — General calendar-related functions.
                                                             (line  355)
* timeit (module):                       timeit — Measure execution time of small code snippets.
                                                             (line    6)
* timeit command line option; -h:        Command-Line Interface<4>.
                                                             (line   44)
* timeit command line option; –help:     Command-Line Interface<4>.
                                                             (line   44)
* timeit command line option; -n N:      Command-Line Interface<4>.
                                                             (line   13)
* timeit command line option; –number=N: Command-Line Interface<4>.
                                                             (line   13)
* timeit command line option; -p:        Command-Line Interface<4>.
                                                             (line   25)
* timeit command line option; –process:  Command-Line Interface<4>.
                                                             (line   25)
* timeit command line option; -r N:      Command-Line Interface<4>.
                                                             (line   17)
* timeit command line option; –repeat=N: Command-Line Interface<4>.
                                                             (line   17)
* timeit command line option; -s S:      Command-Line Interface<4>.
                                                             (line   21)
* timeit command line option; –setup=S:  Command-Line Interface<4>.
                                                             (line   21)
* timeit command line option; -u:        Command-Line Interface<4>.
                                                             (line   33)
* timeit command line option; –unit=U:   Command-Line Interface<4>.
                                                             (line   33)
* timeit command line option; -v:        Command-Line Interface<4>.
                                                             (line   40)
* timeit command line option; –verbose:  Command-Line Interface<4>.
                                                             (line   40)
* timeit() (in module timeit):           Python Interface.   (line    8)
* timeit() (timeit.Timer method):        Python Interface.   (line   69)
* timeout:                               Exceptions<12>.     (line   40)
* timeout (socketserver.BaseServer attribute): Server Objects<2>.
                                                             (line  114)
* timeout (ssl.SSLSession attribute):    SSL session.        (line   16)
* timeout (subprocess.TimeoutExpired attribute): Using the subprocess Module.
                                                             (line  168)
* timeout() (curses.window method):      Window Objects.     (line  558)
* TimeoutError:                          OS exceptions.      (line  105)
* TimeoutError <1>:                      Process and exceptions.
                                                             (line  220)
* TimeoutError <2>:                      Exception classes.  (line   10)
* TimeoutError <3>:                      Exceptions<10>.     (line   10)
* TimeoutExpired:                        Using the subprocess Module.
                                                             (line  159)
* TIMEOUT_MAX (in module threading):     threading — Thread-based parallelism.
                                                             (line  162)
* TIMEOUT_MAX (in module _thread):       _thread — Low-level threading API.
                                                             (line  116)
* Timer (class in threading):            Timer Objects.      (line   25)
* Timer (class in timeit):               Python Interface.   (line   39)
* TimerHandle (class in asyncio):        Callback Handles.   (line   22)
* times() (in module os):                Process Management. (line  701)
* TIMESTAMP (py_compile.PycInvalidationMode attribute): py_compile — Compile Python source files.
                                                             (line  101)
* timestamp() (datetime.datetime method): datetime Objects.  (line  546)
* timetuple() (datetime.date method):    date Objects.       (line  179)
* timetuple() (datetime.datetime method): datetime Objects.  (line  501)
* timetz() (datetime.datetime method):   datetime Objects.   (line  404)
* timezone (class in datetime):          timezone Objects.   (line   14)
* timezone (in module time):             Timezone Constants. (line   17)
* time_ns() (in module time):            Functions<3>.       (line  498)
* title() (bytearray method):            Bytes and Bytearray Operations.
                                                             (line  683)
* title() (bytes method):                Bytes and Bytearray Operations.
                                                             (line  683)
* title() (in module turtle):            Methods specific to Screen not inherited from TurtleScreen.
                                                             (line   49)
* title() (str method):                  String Methods<2>.  (line  605)
* Tix:                                   tkinter tix — Extension widgets for Tk.
                                                             (line    8)
* tixCommand (class in tkinter.tix):     Tix Commands.       (line    6)
* tix_addbitmapdir() (tkinter.tix.tixCommand method): Tix Commands.
                                                             (line   47)
* tix_cget() (tkinter.tix.tixCommand method): Tix Commands.  (line   32)
* tix_configure() (tkinter.tix.tixCommand method): Tix Commands.
                                                             (line   20)
* tix_filedialog() (tkinter.tix.tixCommand method): Tix Commands.
                                                             (line   57)
* tix_getbitmap() (tkinter.tix.tixCommand method): Tix Commands.
                                                             (line   37)
* tix_getimage() (tkinter.tix.tixCommand method): Tix Commands.
                                                             (line   68)
* tix_option_get() (tkinter.tix.tixCommand method): Tix Commands.
                                                             (line   82)
* tix_resetoptions() (tkinter.tix.tixCommand method): Tix Commands.
                                                             (line   86)
* Tk:                                    Graphical User Interfaces with Tk.
                                                             (line    6)
* Tk (class in tkinter):                 Tkinter Modules.    (line   14)
* Tk (class in tkinter.tix):             Using Tix.          (line    6)
* Tk Option Data Types:                  Tk Option Data Types.
                                                             (line    6)
* Tkinter:                               Graphical User Interfaces with Tk.
                                                             (line    6)
* tkinter (module):                      tkinter — Python interface to Tcl/Tk.
                                                             (line    6)
* tkinter.colorchooser (module):         tkinter colorchooser — Color choosing dialog.
                                                             (line    6)
* tkinter.commondialog (module):         tkinter commondialog — Dialog window templates.
                                                             (line    6)
* tkinter.dnd (module):                  tkinter dnd — Drag and drop support.
                                                             (line    6)
* tkinter.filedialog (module):           tkinter filedialog — File selection dialogs.
                                                             (line    6)
* tkinter.font (module):                 tkinter font — Tkinter font wrapper.
                                                             (line    6)
* tkinter.messagebox (module):           tkinter messagebox — Tkinter message prompts.
                                                             (line    6)
* tkinter.scrolledtext (module):         tkinter scrolledtext — Scrolled Text Widget.
                                                             (line    6)
* tkinter.simpledialog (module):         tkinter simpledialog — Standard Tkinter input dialogs.
                                                             (line    6)
* tkinter.tix (module):                  tkinter tix — Extension widgets for Tk.
                                                             (line    6)
* tkinter.ttk (module):                  tkinter ttk — Tk themed widgets.
                                                             (line    6)
* TK_LIBRARY:                            How do I freeze Tkinter applications?.
                                                             (line   11)
* TList (class in tkinter.tix):          Tabular ListBox.    (line    6)
* TLS:                                   ssl — TLS/SSL wrapper for socket objects.
                                                             (line    8)
* TLSv1 (ssl.TLSVersion attribute):      Constants<9>.       (line  543)
* TLSv1_1 (ssl.TLSVersion attribute):    Constants<9>.       (line  545)
* TLSv1_2 (ssl.TLSVersion attribute):    Constants<9>.       (line  547)
* TLSv1_3 (ssl.TLSVersion attribute):    Constants<9>.       (line  549)
* TLSVersion (class in ssl):             Constants<9>.       (line  525)
* TMP:                                   tempfile — Generate temporary files and directories.
                                                             (line  241)
* TMPDIR:                                tempfile — Generate temporary files and directories.
                                                             (line  237)
* ToASCII() (in module encodings.idna):  encodings idna — Internationalized Domain Names in Applications.
                                                             (line   55)
* tobuf() (tarfile.TarInfo method):      TarInfo Objects.    (line   31)
* tobytes() (array.array method):        array — Efficient arrays of numeric values.
                                                             (line  210)
* tobytes() (memoryview method):         Memory Views.       (line  160)
* today() (datetime.date class method):  date Objects.       (line   29)
* today() (datetime.datetime class method): datetime Objects.
                                                             (line   47)
* tofile() (array.array method):         array — Efficient arrays of numeric values.
                                                             (line  219)
* token:                                 Lexical analysis.   (line    6)
* Token (class in contextvars):          Context Variables.  (line   75)
* token (module):                        token — Constants used with Python parse trees.
                                                             (line    6)
* token (shlex.shlex attribute):         shlex Objects.      (line  173)
* TokenError:                            Tokenizing Input.   (line  107)
* tokenize (module):                     tokenize — Tokenizer for Python source.
                                                             (line    6)
* tokenize command line option; -e:      Command-Line Usage<3>.
                                                             (line   19)
* tokenize command line option; –exact:  Command-Line Usage<3>.
                                                             (line   19)
* tokenize command line option; -h:      Command-Line Usage<3>.
                                                             (line   15)
* tokenize command line option; –help:   Command-Line Usage<3>.
                                                             (line   15)
* tokenize() (in module tokenize):       Tokenizing Input.   (line    8)
* token_bytes() (in module secrets):     Generating tokens.  (line   10)
* token_hex() (in module secrets):       Generating tokens.  (line   19)
* token_urlsafe() (in module secrets):   Generating tokens.  (line   28)
* tok_name (in module token):            token — Constants used with Python parse trees.
                                                             (line   20)
* tolist() (array.array method):         array — Efficient arrays of numeric values.
                                                             (line  224)
* tolist() (memoryview method):          Memory Views.       (line  201)
* tolist() (parser.ST method):           ST Objects.         (line   29)
* tomono() (in module audioop):          audioop — Manipulate raw audio data.
                                                             (line  200)
* toordinal() (datetime.date method):    date Objects.       (line  194)
* toordinal() (datetime.datetime method): datetime Objects.  (line  541)
* top() (curses.panel.Panel method):     Panel Objects.      (line   53)
* top() (poplib.POP3 method):            POP3 Objects.       (line   86)
* TopologicalSorter (class in graphlib): graphlib — Functionality to operate with graph-like structures.
                                                             (line   10)
* toprettyxml() (xml.dom.minidom.Node method): DOM Objects.  (line   72)
* top_panel() (in module curses.panel):  Functions<5>.       (line   19)
* toreadonly() (memoryview method):      Memory Views.       (line  217)
* tostereo() (in module audioop):        audioop — Manipulate raw audio data.
                                                             (line  206)
* tostring() (in module xml.etree.ElementTree): Functions<7>.
                                                             (line  217)
* tostringlist() (in module xml.etree.ElementTree): Functions<7>.
                                                             (line  239)
* total_changes (sqlite3.Connection attribute): Connection Objects.
                                                             (line  386)
* total_nframe (tracemalloc.Traceback attribute): Traceback. (line   28)
* total_ordering() (in module functools): functools — Higher-order functions and operations on callable objects.
                                                             (line  233)
* total_seconds() (datetime.timedelta method): timedelta Objects.
                                                             (line  245)
* totuple() (parser.ST method):          ST Objects.         (line   33)
* touch() (pathlib.Path method):         Methods<2>.         (line  449)
* touchline() (curses.window method):    Window Objects.     (line  568)
* touchwin() (curses.window method):     Window Objects.     (line  575)
* tounicode() (array.array method):      array — Efficient arrays of numeric values.
                                                             (line  228)
* ToUnicode() (in module encodings.idna): encodings idna — Internationalized Domain Names in Applications.
                                                             (line   60)
* towards() (in module turtle):          Tell Turtle’s state.
                                                             (line   15)
* toxml() (xml.dom.minidom.Node method): DOM Objects.        (line   52)
* to_bytes() (int method):               Additional Methods on Integer Types.
                                                             (line   35)
* to_eng_string() (decimal.Context method): Context objects. (line  506)
* to_eng_string() (decimal.Decimal method): Decimal objects. (line  558)
* to_integral() (decimal.Decimal method): Decimal objects.   (line  571)
* to_integral_exact() (decimal.Context method): Context objects.
                                                             (line  516)
* to_integral_exact() (decimal.Decimal method): Decimal objects.
                                                             (line  577)
* to_integral_value() (decimal.Decimal method): Decimal objects.
                                                             (line  585)
* to_sci_string() (decimal.Context method): Context objects. (line  520)
* to_thread() (in module asyncio):       Running in Threads. (line    6)
* tparm() (in module curses):            Functions<4>.       (line  520)
* Trace (class in trace):                Programmatic Interface.
                                                             (line    6)
* Trace (class in tracemalloc):          Trace.              (line    6)
* trace (module):                        trace — Trace or track Python statement execution.
                                                             (line    6)
* trace command line option; -c:         Main options.       (line   12)
* trace command line option; -C:         Modifiers.          (line   11)
* trace command line option; –count:     Main options.       (line   12)
* trace command line option; –coverdir=<dir>: Modifiers.     (line   11)
* trace command line option; -f:         Modifiers.          (line    6)
* trace command line option; –file=<file>: Modifiers.        (line    6)
* trace command line option; -g:         Modifiers.          (line   33)
* trace command line option; –help:      Command-Line Usage. (line   15)
* trace command line option; –ignore-dir=<dir>: Filters.     (line   14)
* trace command line option; –ignore-module=<mod>: Filters.  (line    8)
* trace command line option; -l:         Main options.       (line   23)
* trace command line option; –listfuncs: Main options.       (line   23)
* trace command line option; -m:         Modifiers.          (line   17)
* trace command line option; –missing:   Modifiers.          (line   17)
* trace command line option; –no-report: Modifiers.          (line   27)
* trace command line option; -r:         Main options.       (line   27)
* trace command line option; -R:         Modifiers.          (line   27)
* trace command line option; –report:    Main options.       (line   27)
* trace command line option; -s:         Modifiers.          (line   22)
* trace command line option; –summary:   Modifiers.          (line   22)
* trace command line option; -t:         Main options.       (line   19)
* trace command line option; -T:         Main options.       (line   33)
* trace command line option; –timing:    Modifiers.          (line   33)
* trace command line option; –trace:     Main options.       (line   19)
* trace command line option; –trackcalls: Main options.      (line   33)
* trace command line option; –version:   Command-Line Usage. (line   19)
* trace function:                        threading — Thread-based parallelism.
                                                             (line  126)
* trace function <1>:                    sys — System-specific parameters and functions.
                                                             (line  741)
* trace function <2>:                    sys — System-specific parameters and functions.
                                                             (line 1316)
* trace() (in module inspect):           The interpreter stack.
                                                             (line   94)
* Traceback (class in tracemalloc):      Traceback.          (line    6)
* traceback (module):                    traceback — Print or retrieve a stack traceback.
                                                             (line    6)
* traceback (tracemalloc.Statistic attribute): Statistic.    (line   23)
* traceback (tracemalloc.StatisticDiff attribute): StatisticDiff.
                                                             (line   38)
* traceback (tracemalloc.Trace attribute): Trace.            (line   27)
* TracebackException (class in traceback): TracebackException Objects.
                                                             (line   11)
* tracebacklimit (in module sys):        sys — System-specific parameters and functions.
                                                             (line 1592)
* tracebacks; in CGI scripts:            cgitb — Traceback manager for CGI scripts.
                                                             (line    8)
* TracebackType (class in types):        Standard Interpreter Types.
                                                             (line  201)
* traceback_limit (tracemalloc.Snapshot attribute): Snapshot.
                                                             (line   83)
* traceback_limit (wsgiref.handlers.BaseHandler attribute): wsgiref handlers – server/gateway base classes.
                                                             (line  219)
* tracemalloc (module):                  tracemalloc — Trace memory allocations.
                                                             (line    6)
* tracer() (in module turtle):           Animation control.  (line   23)
* traces (tracemalloc.Snapshot attribute): Snapshot.         (line   89)
* trace_dispatch() (bdb.Bdb method):     bdb — Debugger framework.
                                                             (line  111)
* trailing; comma:                       Expression lists.   (line   24)
* transfercmd() (ftplib.FTP method):     FTP Objects.        (line  136)
* TransientResource (class in test.support): test support — Utilities for the Python test suite.
                                                             (line 1037)
* transient_internet() (in module test.support.socket_helper): test support socket_helper — Utilities for socket tests.
                                                             (line   64)
* translate() (bytearray method):        Bytes and Bytearray Operations.
                                                             (line  258)
* translate() (bytes method):            Bytes and Bytearray Operations.
                                                             (line  258)
* translate() (in module fnmatch):       fnmatch — Unix filename pattern matching.
                                                             (line   71)
* translate() (str method):              String Methods<2>.  (line  636)
* translation() (in module gettext):     Class-based API.    (line   44)
* transport (asyncio.StreamWriter attribute): StreamWriter.  (line   57)
* Transport (class in asyncio):          Transports Hierarchy.
                                                             (line   29)
* Transport Layer Security:              ssl — TLS/SSL wrapper for socket objects.
                                                             (line    8)
* Traversable (class in importlib.abc):  importlib abc – Abstract base classes related to import.
                                                             (line  614)
* TraversableResources (class in importlib.abc): importlib abc – Abstract base classes related to import.
                                                             (line  662)
* traverseproc (C type):                 Supporting Cyclic Garbage Collection.
                                                             (line  145)
* Tree (class in tkinter.tix):           Hierarchical ListBox.
                                                             (line   20)
* TreeBuilder (class in xml.etree.ElementTree): TreeBuilder Objects.
                                                             (line    6)
* Treeview (class in tkinter.ttk):       ttk Treeview.       (line    6)
* triangular() (in module random):       Real-valued distributions.
                                                             (line   25)
* triple-quoted string:                  String and Bytes literals.
                                                             (line   36)
* triple-quoted string <1>:              Glossary.           (line 1231)
* True:                                  The standard type hierarchy.
                                                             (line   98)
* true:                                  Truth Value Testing.
                                                             (line   10)
* True <1>:                              Truth Value Testing.
                                                             (line   23)
* True <2>:                              Boolean Values.     (line   15)
* True (built-in variable):              Built-in Constants. (line   13)
* truediv() (in module operator):        operator — Standard operators as functions.
                                                             (line  158)
* trunc() (in module math):              Numeric Types — int float complex.
                                                             (line  104)
* trunc() (in module math) <1>:          Number-theoretic and representation functions.
                                                             (line  267)
* truncate() (in module os):             Files and Directories.
                                                             (line 1415)
* truncate() (io.IOBase method):         I/O Base Classes.   (line  142)
* truth() (in module operator):          operator — Standard operators as functions.
                                                             (line   57)
* truth; value:                          Truth Value Testing.
                                                             (line    6)
* Try (class in ast):                    Control flow.       (line  134)
* ttk:                                   tkinter ttk — Tk themed widgets.
                                                             (line    8)
* tty (module):                          tty — Terminal control functions.
                                                             (line    6)
* tty; I/O control:                      termios — POSIX style tty control.
                                                             (line    6)
* ttyname() (in module os):              File Descriptor Operations.
                                                             (line  672)
* tuple (built-in class):                Tuples.             (line   12)
* Tuple (class in ast):                  Literals<3>.        (line   67)
* Tuple (in module typing):              Special forms.      (line    9)
* tuple2st() (in module parser):         Creating ST Objects.
                                                             (line   51)
* tuple_params (2to3 fixer):             Fixers.             (line  307)
* Turtle (class in turtle):              Public classes.     (line   16)
* turtle (module):                       turtle — Turtle graphics.
                                                             (line    6)
* turtledemo (module):                   turtledemo — Demo scripts.
                                                             (line    6)
* turtles() (in module turtle):          Settings and special methods.
                                                             (line   96)
* TurtleScreen (class in turtle):        Public classes.     (line   22)
* turtlesize() (in module turtle):       Appearance.         (line   52)
* type:                                  The standard type hierarchy.
                                                             (line    6)
* type <1>:                              Glossary.           (line 1241)
* type (built-in class):                 Built-in Functions. (line 1687)
* Type (class in typing):                Special forms.      (line  101)
* type (optparse.Option attribute):      Option attributes.  (line   19)
* type (socket.socket attribute):        Socket Objects.     (line  599)
* type (tarfile.TarInfo attribute):      TarInfo Objects.    (line   59)
* type (urllib.request.Request attribute): Request Objects.  (line   21)
* type alias:                            Glossary.           (line 1248)
* type hint:                             Glossary.           (line 1270)
* type of an object:                     Objects values and types.
                                                             (line   11)
* type; hierarchy:                       The standard type hierarchy.
                                                             (line    6)
* typeahead() (in module curses):        Functions<4>.       (line  528)
* typecode (array.array attribute):      array — Efficient arrays of numeric values.
                                                             (line  104)
* typecodes (in module array):           array — Efficient arrays of numeric values.
                                                             (line   91)
* TypedDict (class in typing):           Other special directives.
                                                             (line   81)
* TYPED_ACTIONS (optparse.Option attribute): Adding new actions.
                                                             (line   39)
* typed_subpart_iterator() (in module email.iterators): email iterators Iterators.
                                                             (line   26)
* TypeError:                             Concrete exceptions.
                                                             (line  335)
* types (2to3 fixer):                    Fixers.             (line  312)
* types (module):                        types — Dynamic type creation and names for built-in types.
                                                             (line    6)
* TYPES (optparse.Option attribute):     Adding new types.   (line   11)
* types, internal:                       The standard type hierarchy.
                                                             (line  650)
* types_map (in module mimetypes):       mimetypes — Map filenames to MIME types.
                                                             (line  140)
* types_map (mimetypes.MimeTypes attribute): MimeTypes Objects.
                                                             (line   39)
* types_map_inv (mimetypes.MimeTypes attribute): MimeTypes Objects.
                                                             (line   47)
* TypeVar (class in typing):             Building generic types.
                                                             (line   33)
* TYPE_CHECKER (optparse.Option attribute): Adding new types.
                                                             (line   16)
* TYPE_CHECKING (in module typing):      Constant.           (line    6)
* type_check_only() (in module typing):  Functions and decorators.
                                                             (line   88)
* type_comment (ast.arg attribute):      Function and class definitions.
                                                             (line   75)
* type_comment (ast.Assign attribute):   Statements.         (line   15)
* type_comment (ast.For attribute):      Control flow.       (line   54)
* type_comment (ast.FunctionDef attribute): Function and class definitions.
                                                             (line   23)
* type_comment (ast.With attribute):     Control flow.       (line  216)
* TYPE_COMMENT (in module token):        token — Constants used with Python parse trees.
                                                             (line  250)
* TYPE_IGNORE (in module token):         token — Constants used with Python parse trees.
                                                             (line  248)
* typing (module):                       typing — Support for type hints.
                                                             (line    6)
* TZ:                                    Functions<3>.       (line  508)
* TZ <1>:                                Functions<3>.       (line  509)
* TZ <2>:                                Functions<3>.       (line  517)
* TZ <3>:                                Functions<3>.       (line  522)
* TZ <4>:                                Functions<3>.       (line  524)
* TZ <5>:                                Functions<3>.       (line  584)
* tzinfo (class in datetime):            tzinfo Objects.     (line    6)
* tzinfo (datetime.datetime attribute):  datetime Objects.   (line  293)
* tzinfo (datetime.time attribute):      time Objects.       (line   66)
* tzname (in module time):               Timezone Constants. (line   23)
* tzname() (datetime.datetime method):   datetime Objects.   (line  495)
* tzname() (datetime.time method):       time Objects.       (line  243)
* tzname() (datetime.timezone method):   timezone Objects.   (line   42)
* tzname() (datetime.tzinfo method):     tzinfo Objects.     (line  123)
* TZPATH (in module zoneinfo):           Globals.            (line    6)
* tzset() (in module time):              Functions<3>.       (line  505)
* T_FMT (in module locale):              locale — Internationalization services.
                                                             (line  201)
* T_FMT_AMPM (in module locale):         locale — Internationalization services.
                                                             (line  207)
* u"; string literal:                    Literals.           (line    8)
* u’; string literal:                    Literals.           (line    8)
* u-LAW:                                 audioop — Manipulate raw audio data.
                                                             (line   17)
* u-LAW <1>:                             aifc — Read and write AIFF and AIFC files.
                                                             (line  160)
* u-LAW <2>:                             sndhdr — Determine type of sound file.
                                                             (line    8)
* UAdd (class in ast):                   Expressions<2>.     (line   28)
* ucd_3_2_0 (in module unicodedata):     unicodedata — Unicode Database.
                                                             (line  131)
* udata (select.kevent attribute):       Kevent Objects.     (line  179)
* UDPServer (class in socketserver):     socketserver — A framework for network servers.
                                                             (line   25)
* UF_APPEND (in module stat):            stat — Interpreting stat results.
                                                             (line  346)
* UF_COMPRESSED (in module stat):        stat — Interpreting stat results.
                                                             (line  358)
* UF_HIDDEN (in module stat):            stat — Interpreting stat results.
                                                             (line  362)
* UF_IMMUTABLE (in module stat):         stat — Interpreting stat results.
                                                             (line  342)
* UF_NODUMP (in module stat):            stat — Interpreting stat results.
                                                             (line  338)
* UF_NOUNLINK (in module stat):          stat — Interpreting stat results.
                                                             (line  354)
* UF_OPAQUE (in module stat):            stat — Interpreting stat results.
                                                             (line  350)
* UID (class in plistlib):               plistlib — Generate and parse Apple plist files.
                                                             (line  122)
* uid (tarfile.TarInfo attribute):       TarInfo Objects.    (line   72)
* uid() (imaplib.IMAP4 method):          IMAP4 Objects.      (line  364)
* uidl() (poplib.POP3 method):           POP3 Objects.       (line   98)
* ulaw2lin() (in module audioop):        audioop — Manipulate raw audio data.
                                                             (line  213)
* ULONG_MAX:                             Integer Objects.    (line  200)
* ulp() (in module math):                Number-theoretic and representation functions.
                                                             (line  273)
* umask() (in module os):                Process Parameters. (line  465)
* unalias (pdb command):                 Debugger Commands.  (line  307)
* uname (tarfile.TarInfo attribute):     TarInfo Objects.    (line   80)
* uname() (in module os):                Process Parameters. (line  469)
* uname() (in module platform):          Cross Platform.     (line  136)
* unary; arithmetic; operation:          Unary arithmetic and bitwise operations.
                                                             (line    6)
* unary; bitwise; operation:             Unary arithmetic and bitwise operations.
                                                             (line    6)
* unaryfunc (C type):                    Slot Type typedefs. (line   98)
* UnaryOp (class in ast):                Expressions<2>.     (line   23)
* UNARY_INVERT (opcode):                 Python Bytecode Instructions.
                                                             (line  109)
* UNARY_NEGATIVE (opcode):               Python Bytecode Instructions.
                                                             (line  101)
* UNARY_NOT (opcode):                    Python Bytecode Instructions.
                                                             (line  105)
* UNARY_POSITIVE (opcode):               Python Bytecode Instructions.
                                                             (line   97)
* unbinding; name:                       The del statement<2>.
                                                             (line   15)
* UnboundLocalError:                     Resolution of names.
                                                             (line   16)
* UnboundLocalError <1>:                 Concrete exceptions.
                                                             (line  353)
* unbuffered I/O:                        Built-in Functions. (line 1223)
* UNC paths; and os.makedirs():          Files and Directories.
                                                             (line  453)
* UNCHECKED_HASH (py_compile.PycInvalidationMode attribute): py_compile — Compile Python source files.
                                                             (line  114)
* unconsumed_tail (zlib.Decompress attribute): zlib — Compression compatible with gzip.
                                                             (line  239)
* unctrl() (in module curses):           Functions<4>.       (line  540)
* unctrl() (in module curses.ascii):     curses ascii — Utilities for ASCII characters.
                                                             (line  226)
* undefine_macro() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  170)
* Underflow (class in decimal):          Signals.            (line   93)
* undisplay (pdb command):               Debugger Commands.  (line  267)
* undo() (in module turtle):             Turtle motion.      (line  291)
* undobufferentries() (in module turtle): Special Turtle methods.
                                                             (line   74)
* undoc_header (cmd.Cmd attribute):      Cmd Objects.        (line  158)
* unescape() (in module html):           html — HyperText Markup Language support.
                                                             (line   23)
* unescape() (in module xml.sax.saxutils): xml sax saxutils — SAX Utilities.
                                                             (line   24)
* UnexpectedException:                   Debugging.          (line  208)
* unexpectedSuccesses (unittest.TestResult attribute): Loading and running tests.
                                                             (line  263)
* unfreeze() (in module gc):             gc — Garbage Collector interface.
                                                             (line  214)
* ungetch() (in module curses):          Functions<4>.       (line  547)
* ungetch() (in module msvcrt):          Console I/O.        (line   44)
* ungetmouse() (in module curses):       Functions<4>.       (line  569)
* ungetwch() (in module msvcrt):         Console I/O.        (line   50)
* unget_wch() (in module curses):        Functions<4>.       (line  560)
* unhexlify() (in module binascii):      binascii — Convert between binary and ASCII.
                                                             (line  169)
* Unicode:                               The standard type hierarchy.
                                                             (line  161)
* Unicode <1>:                           unicodedata — Unicode Database.
                                                             (line    6)
* Unicode <2>:                           codecs — Codec registry and base classes.
                                                             (line    8)
* unicode (2to3 fixer):                  Fixers.             (line  317)
* Unicode Consortium:                    String and Bytes literals.
                                                             (line   36)
* Unicode; database:                     unicodedata — Unicode Database.
                                                             (line    6)
* unicodedata (module):                  unicodedata — Unicode Database.
                                                             (line    6)
* UnicodeDecodeError:                    Concrete exceptions.
                                                             (line  393)
* UnicodeEncodeError:                    Concrete exceptions.
                                                             (line  388)
* UnicodeError:                          Concrete exceptions.
                                                             (line  359)
* UnicodeTranslateError:                 Concrete exceptions.
                                                             (line  398)
* UnicodeWarning:                        Warnings.           (line   64)
* unidata_version (in module unicodedata): unicodedata — Unicode Database.
                                                             (line  127)
* unified_diff() (in module difflib):    difflib — Helpers for computing deltas.
                                                             (line  295)
* uniform() (in module random):          Real-valued distributions.
                                                             (line   16)
* UnimplementedFileMode:                 http client — HTTP protocol client.
                                                             (line  150)
* Union (class in ctypes):               Structured data types.
                                                             (line    6)
* Union (in module typing):              Special forms.      (line   26)
* union() (frozenset method):            Set Types — set frozenset.
                                                             (line   96)
* unique() (in module enum):             Ensuring unique enumeration values.
                                                             (line   10)
* unittest (module):                     unittest — Unit testing framework.
                                                             (line    6)
* unittest command line option; -b:      Command-line options<3>.
                                                             (line    8)
* unittest command line option; –buffer: Command-line options<3>.
                                                             (line    8)
* unittest command line option; -c:      Command-line options<3>.
                                                             (line   15)
* unittest command line option; –catch:  Command-line options<3>.
                                                             (line   15)
* unittest command line option; -f:      Command-line options<3>.
                                                             (line   24)
* unittest command line option; –failfast: Command-line options<3>.
                                                             (line   24)
* unittest command line option; -k:      Command-line options<3>.
                                                             (line   28)
* unittest command line option; –locals: Command-line options<3>.
                                                             (line   45)
* unittest-discover command line option; -p: Test Discovery. (line   35)
* unittest-discover command line option; –pattern pattern: Test Discovery.
                                                             (line   35)
* unittest-discover command line option; -s: Test Discovery. (line   31)
* unittest-discover command line option; –start-directory directory: Test Discovery.
                                                             (line   31)
* unittest-discover command line option; -t: Test Discovery. (line   39)
* unittest-discover command line option; –top-level-directory directory: Test Discovery.
                                                             (line   39)
* unittest-discover command line option; -v: Test Discovery. (line   27)
* unittest-discover command line option; –verbose: Test Discovery.
                                                             (line   27)
* unittest.mock (module):                unittest mock — mock object library.
                                                             (line    6)
* universal newlines:                    Glossary.           (line 1287)
* universal newlines; bytearray.splitlines method: Bytes and Bytearray Operations.
                                                             (line  634)
* universal newlines; bytes.splitlines method: Bytes and Bytearray Operations.
                                                             (line  634)
* universal newlines; csv.reader function: Module Contents<3>.
                                                             (line    8)
* universal newlines; importlib.abc.InspectLoader.get_source method: importlib abc – Abstract base classes related to import.
                                                             (line  400)
* universal newlines; io.IncrementalNewlineDecoder class: Text I/O<2>.
                                                             (line  237)
* universal newlines; io.TextIOWrapper class: Text I/O<2>.   (line  124)
* universal newlines; open() built-in function: Built-in Functions.
                                                             (line 1161)
* universal newlines; str.splitlines method: String Methods<2>.
                                                             (line  495)
* universal newlines; subprocess module: Frequently Used Arguments.
                                                             (line   33)
* universal newlines; What’s new:        PEP 3116 New I/O Library.
                                                             (line   42)
* universal newlines; What’s new <1>:    New Improved and Removed Modules.
                                                             (line  138)
* universal newlines; What’s new <2>:    PEP 324 New subprocess Module.
                                                             (line   36)
* universal newlines; What’s new <3>:    PEP 277 Unicode file name support for Windows NT.
                                                             (line   36)
* UNIX:                                  Complete Python programs.
                                                             (line   25)
* UNIX; file control:                    fcntl — The fcntl and ioctl system calls.
                                                             (line    6)
* UNIX; I/O control:                     fcntl — The fcntl and ioctl system calls.
                                                             (line    6)
* UnixDatagramServer (class in socketserver): socketserver — A framework for network servers.
                                                             (line   32)
* UnixStreamServer (class in socketserver): socketserver — A framework for network servers.
                                                             (line   32)
* unix_dialect (class in csv):           Module Contents<3>. (line  209)
* unix_shell (in module test.support):   test support — Utilities for the Python test suite.
                                                             (line   44)
* unknown (uuid.SafeUUID attribute):     uuid — UUID objects according to RFC 4122.
                                                             (line   40)
* UnknownHandler (class in urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  427)
* UnknownProtocol:                       http client — HTTP protocol client.
                                                             (line  142)
* UnknownTransferEncoding:               http client — HTTP protocol client.
                                                             (line  146)
* unknown_decl() (html.parser.HTMLParser method): HTMLParser Methods.
                                                             (line  137)
* unknown_open() (urllib.request.BaseHandler method): BaseHandler Objects.
                                                             (line   55)
* unknown_open() (urllib.request.UnknownHandler method): UnknownHandler Objects.
                                                             (line    6)
* unlink() (in module os):               Files and Directories.
                                                             (line 1433)
* unlink() (in module test.support):     test support — Utilities for the Python test suite.
                                                             (line  231)
* unlink() (multiprocessing.shared_memory.SharedMemory method): multiprocessing shared_memory — Provides shared memory for direct access across processes.
                                                             (line   73)
* unlink() (pathlib.Path method):        Methods<2>.         (line  458)
* unlink() (xml.dom.minidom.Node method): DOM Objects.       (line   10)
* unload() (in module test.support):     test support — Utilities for the Python test suite.
                                                             (line  227)
* unlock() (mailbox.Babyl method):       Babyl.              (line   59)
* unlock() (mailbox.Mailbox method):     Mailbox objects.    (line  258)
* unlock() (mailbox.Maildir method):     Maildir.            (line  107)
* unlock() (mailbox.mbox method):        mbox.               (line   39)
* unlock() (mailbox.MH method):          MH.                 (line   84)
* unlock() (mailbox.MMDF method):        MMDF.               (line   35)
* unpack() (in module struct):           Functions and Exceptions.
                                                             (line   26)
* unpack() (struct.Struct method):       Classes<2>.         (line   35)
* Unpacker (class in xdrlib):            xdrlib — Encode and decode XDR data.
                                                             (line   24)
* unpacking; dictionary:                 Dictionary displays.
                                                             (line   23)
* unpacking; in function calls:          Calls.              (line   74)
* unpack_archive() (in module shutil):   Archiving operations.
                                                             (line  107)
* unpack_array() (xdrlib.Unpacker method): Unpacker Objects. (line   91)
* unpack_bytes() (xdrlib.Unpacker method): Unpacker Objects. (line   70)
* unpack_double() (xdrlib.Unpacker method): Unpacker Objects.
                                                             (line   40)
* UNPACK_EX (opcode):                    Python Bytecode Instructions.
                                                             (line  444)
* unpack_farray() (xdrlib.Unpacker method): Unpacker Objects.
                                                             (line   85)
* unpack_float() (xdrlib.Unpacker method): Unpacker Objects. (line   36)
* unpack_fopaque() (xdrlib.Unpacker method): Unpacker Objects.
                                                             (line   54)
* unpack_from() (in module struct):      Functions and Exceptions.
                                                             (line   34)
* unpack_from() (struct.Struct method):  Classes<2>.         (line   41)
* unpack_fstring() (xdrlib.Unpacker method): Unpacker Objects.
                                                             (line   48)
* unpack_list() (xdrlib.Unpacker method): Unpacker Objects.  (line   77)
* unpack_opaque() (xdrlib.Unpacker method): Unpacker Objects.
                                                             (line   65)
* UNPACK_SEQUENCE (opcode):              Python Bytecode Instructions.
                                                             (line  439)
* unpack_string() (xdrlib.Unpacker method): Unpacker Objects.
                                                             (line   59)
* unparse() (in module ast):             ast Helpers.        (line   58)
* unparsedEntityDecl() (xml.sax.handler.DTDHandler method): DTDHandler Objects.
                                                             (line   12)
* UnparsedEntityDeclHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  249)
* Unpickler (class in pickle):           Module Interface.   (line  226)
* UnpicklingError:                       Module Interface.   (line  108)
* unquote() (in module email.utils):     email utils Miscellaneous utilities.
                                                             (line   52)
* unquote() (in module urllib.parse):    URL Quoting.        (line   61)
* unquote_plus() (in module urllib.parse): URL Quoting.      (line   81)
* unquote_to_bytes() (in module urllib.parse): URL Quoting.  (line   91)
* unraisablehook() (in module sys):      sys — System-specific parameters and functions.
                                                             (line 1600)
* unreachable object:                    Objects values and types.
                                                             (line   37)
* unreadline() (distutils.text_file.TextFile method): distutils text_file — The TextFile class.
                                                             (line  130)
* unrecognized escape sequence:          String and Bytes literals.
                                                             (line  156)
* unregister() (in module atexit):       atexit — Exit handlers.
                                                             (line   43)
* unregister() (in module faulthandler): Dumping the traceback on a user signal.
                                                             (line   23)
* unregister() (select.devpoll method):  /dev/poll Polling Objects.
                                                             (line   55)
* unregister() (select.epoll method):    Edge and Level Trigger Polling epoll Objects.
                                                             (line   89)
* unregister() (select.poll method):     Polling Objects.    (line   67)
* unregister() (selectors.BaseSelector method): Classes<3>.  (line   80)
* unregister_archive_format() (in module shutil): Archiving operations.
                                                             (line  102)
* unregister_dialect() (in module csv):  Module Contents<3>. (line   80)
* unregister_unpack_format() (in module shutil): Archiving operations.
                                                             (line  145)
* unsafe (uuid.SafeUUID attribute):      uuid — UUID objects according to RFC 4122.
                                                             (line   36)
* unselect() (imaplib.IMAP4 method):     IMAP4 Objects.      (line  375)
* unset() (test.support.EnvironmentVarGuard method): test support — Utilities for the Python test suite.
                                                             (line 1062)
* unsetenv() (in module os):             Process Parameters. (line  499)
* UnstructuredHeader (class in email.headerregistry): email headerregistry Custom Header Objects.
                                                             (line  115)
* unsubscribe() (imaplib.IMAP4 method):  IMAP4 Objects.      (line  371)
* UnsupportedOperation:                  High-level Module Interface.
                                                             (line   43)
* until (pdb command):                   Debugger Commands.  (line  177)
* untokenize() (in module tokenize):     Tokenizing Input.   (line   57)
* untouchwin() (curses.window method):   Window Objects.     (line  580)
* unused_data (bz2.BZ2Decompressor attribute): Incremental de compression.
                                                             (line   78)
* unused_data (lzma.LZMADecompressor attribute): Compressing and decompressing data in memory.
                                                             (line  169)
* unused_data (zlib.Decompress attribute): zlib — Compression compatible with gzip.
                                                             (line  231)
* unverifiable (urllib.request.Request attribute): Request Objects.
                                                             (line   47)
* unwrap() (in module inspect):          Classes and functions<2>.
                                                             (line  186)
* unwrap() (in module urllib.parse):     URL Parsing.        (line  384)
* unwrap() (ssl.SSLSocket method):       SSL Sockets.        (line  272)
* up (pdb command):                      Debugger Commands.  (line   66)
* up() (in module turtle):               Drawing state.      (line   12)
* update() (collections.Counter method): Counter objects.    (line  111)
* update() (dict method):                Mapping Types — dict.
                                                             (line  212)
* update() (frozenset method):           Set Types — set frozenset.
                                                             (line  169)
* update() (hashlib.hash method):        Hash algorithms.    (line  127)
* update() (hmac.HMAC method):           hmac — Keyed-Hashing for Message Authentication.
                                                             (line   47)
* update() (http.cookies.Morsel method): Morsel Objects.     (line   94)
* update() (in module turtle):           Animation control.  (line   46)
* update() (mailbox.Mailbox method):     Mailbox objects.    (line  227)
* update() (mailbox.Maildir method):     Maildir.            (line   91)
* update() (trace.CoverageResults method): Programmatic Interface.
                                                             (line   52)
* update_authenticated() (urllib.request.HTTPPasswordMgrWithPriorAuth method): HTTPPasswordMgrWithPriorAuth Objects.
                                                             (line   24)
* update_lines_cols() (in module curses): Functions<4>.      (line  553)
* update_panels() (in module curses.panel): Functions<5>.    (line   23)
* update_visible() (mailbox.BabylMessage method): BabylMessage.
                                                             (line   76)
* update_wrapper() (in module functools): functools — Higher-order functions and operations on callable objects.
                                                             (line  564)
* upgrade_dependencies() (venv.EnvBuilder method): API<2>.   (line  112)
* upper() (bytearray method):            Bytes and Bytearray Operations.
                                                             (line  726)
* upper() (bytes method):                Bytes and Bytearray Operations.
                                                             (line  726)
* upper() (str method):                  String Methods<2>.  (line  654)
* urandom() (in module os):              Random numbers<2>.  (line   29)
* URL:                                   cgi — Common Gateway Interface support.
                                                             (line    8)
* URL <1>:                               urllib parse — Parse URLs into components.
                                                             (line    8)
* URL <2>:                               urllib robotparser — Parser for robots txt.
                                                             (line    8)
* URL <3>:                               http server — HTTP servers.
                                                             (line    8)
* url (http.client.HTTPResponse attribute): HTTPResponse Objects.
                                                             (line   51)
* url (urllib.response.addinfourl attribute): urllib response — Response classes used by urllib.
                                                             (line   14)
* url (xmlrpc.client.ProtocolError attribute): ProtocolError Objects.
                                                             (line   13)
* url2pathname() (in module urllib.request): urllib request — Extensible library for opening URLs.
                                                             (line  147)
* URL; parsing:                          urllib parse — Parse URLs into components.
                                                             (line    8)
* urlcleanup() (in module urllib.request): Legacy interface. (line   62)
* urldefrag() (in module urllib.parse):  URL Parsing.        (line  358)
* urlencode() (in module urllib.parse):  URL Quoting.        (line  104)
* URLError:                              urllib error — Exception classes raised by urllib request.
                                                             (line   17)
* urljoin() (in module urllib.parse):    URL Parsing.        (line  328)
* urllib (2to3 fixer):                   Fixers.             (line  321)
* urllib (module):                       urllib — URL handling modules.
                                                             (line    6)
* urllib.error (module):                 urllib error — Exception classes raised by urllib request.
                                                             (line    6)
* urllib.parse (module):                 urllib parse — Parse URLs into components.
                                                             (line    6)
* urllib.request (module):               urllib request — Extensible library for opening URLs.
                                                             (line    6)
* urllib.response (module):              urllib response — Response classes used by urllib.
                                                             (line    6)
* urllib.robotparser (module):           urllib robotparser — Parser for robots txt.
                                                             (line    6)
* urlopen() (in module urllib.request):  urllib request — Extensible library for opening URLs.
                                                             (line   22)
* URLopener (class in urllib.request):   Legacy interface.   (line   67)
* urlparse() (in module urllib.parse):   URL Parsing.        (line    9)
* urlretrieve() (in module urllib.request): Legacy interface.
                                                             (line   10)
* urlsafe_b64decode() (in module base64): base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line   91)
* urlsafe_b64encode() (in module base64): base64 — Base16 Base32 Base64 Base85 Data Encodings.
                                                             (line   84)
* urlsplit() (in module urllib.parse):   URL Parsing.        (line  246)
* urlunparse() (in module urllib.parse): URL Parsing.        (line  238)
* urlunsplit() (in module urllib.parse): URL Parsing.        (line  319)
* urn (uuid.UUID attribute):             uuid — UUID objects according to RFC 4122.
                                                             (line  135)
* UseForeignDTD() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line   63)
* USER:                                  getpass — Portable password input.
                                                             (line   38)
* user() (poplib.POP3 method):           POP3 Objects.       (line   31)
* user-defined; function:                The standard type hierarchy.
                                                             (line  302)
* user-defined; function; call:          Calls.              (line  123)
* user-defined; method:                  The standard type hierarchy.
                                                             (line  393)
* user; effective id:                    Process Parameters. (line  174)
* user; id:                              Process Parameters. (line  303)
* user; id, setting:                     Process Parameters. (line  448)
* UserDict (class in collections):       UserDict objects.   (line   12)
* UserList (class in collections):       UserList objects.   (line   16)
* USERNAME:                              Process Parameters. (line  222)
* USERNAME <1>:                          getpass — Portable password input.
                                                             (line   39)
* username (email.headerregistry.Address attribute): email headerregistry Custom Header Objects.
                                                             (line  432)
* USERPROFILE:                           os path.            (line   14)
* USERPROFILE <1>:                       Changes in the Python API<2>.
                                                             (line  116)
* USERPROFILE <2>:                       Windows<17>.        (line   15)
* USERPROFILE <3>:                       os path — Common pathname manipulations.
                                                             (line  146)
* USERPROFILE <4>:                       Location and names of config files.
                                                             (line   67)
* userptr() (curses.panel.Panel method): Panel Objects.      (line   57)
* UserString (class in collections):     UserString objects. (line   12)
* UserWarning:                           Warnings.           (line   13)
* USER_BASE:                             New and Improved Modules.
                                                             (line  469)
* USER_BASE (in module site):            Module contents<4>. (line   30)
* user_call() (bdb.Bdb method):          bdb — Debugger framework.
                                                             (line  212)
* user_exception() (bdb.Bdb method):     bdb — Debugger framework.
                                                             (line  229)
* user_line() (bdb.Bdb method):          bdb — Debugger framework.
                                                             (line  218)
* user_return() (bdb.Bdb method):        bdb — Debugger framework.
                                                             (line  224)
* USER_SITE (in module site):            Module contents<4>. (line   19)
* use_default_colors() (in module curses): Functions<4>.     (line  584)
* use_env() (in module curses):          Functions<4>.       (line  574)
* use_rawinput (cmd.Cmd attribute):      Cmd Objects.        (line  169)
* USTAR_FORMAT (in module tarfile):      tarfile — Read and write tar archive files.
                                                             (line  229)
* USub (class in ast):                   Expressions<2>.     (line   28)
* UTC:                                   time — Time access and conversions.
                                                             (line   40)
* utc (datetime.timezone attribute):     timezone Objects.   (line   68)
* utcfromtimestamp() (datetime.datetime class method): datetime Objects.
                                                             (line  124)
* utcnow() (datetime.datetime class method): datetime Objects.
                                                             (line   77)
* utcoffset() (datetime.datetime method): datetime Objects.  (line  475)
* utcoffset() (datetime.time method):    time Objects.       (line  223)
* utcoffset() (datetime.timezone method): timezone Objects.  (line   30)
* utcoffset() (datetime.tzinfo method):  tzinfo Objects.     (line   38)
* utctimetuple() (datetime.datetime method): datetime Objects.
                                                             (line  520)
* utf8 (email.policy.EmailPolicy attribute): email policy Policy Objects.
                                                             (line  363)
* utf8() (poplib.POP3 method):           POP3 Objects.       (line  105)
* utf8_enabled (imaplib.IMAP4 attribute): IMAP4 Objects.     (line  403)
* utime() (in module os):                Files and Directories.
                                                             (line 1447)
* uu (module):                           uu — Encode and decode uuencode files.
                                                             (line    6)
* UUID (class in uuid):                  uuid — UUID objects according to RFC 4122.
                                                             (line   45)
* uuid (module):                         uuid — UUID objects according to RFC 4122.
                                                             (line    6)
* uuid1:                                 uuid — UUID objects according to RFC 4122.
                                                             (line  186)
* uuid1() (in module uuid):              uuid — UUID objects according to RFC 4122.
                                                             (line  178)
* uuid3:                                 uuid — UUID objects according to RFC 4122.
                                                             (line  191)
* uuid3() (in module uuid):              uuid — UUID objects according to RFC 4122.
                                                             (line  186)
* uuid4:                                 uuid — UUID objects according to RFC 4122.
                                                             (line  195)
* uuid4() (in module uuid):              uuid — UUID objects according to RFC 4122.
                                                             (line  191)
* uuid5:                                 uuid — UUID objects according to RFC 4122.
                                                             (line  200)
* uuid5() (in module uuid):              uuid — UUID objects according to RFC 4122.
                                                             (line  195)
* UuidCreate() (in module msilib):       msilib — Read and write Microsoft Installer files.
                                                             (line   39)
* v4_int_to_packed() (in module ipaddress): Other Module Level Functions.
                                                             (line    8)
* v6_int_to_packed() (in module ipaddress): Other Module Level Functions.
                                                             (line   20)
* validator() (in module wsgiref.validate): wsgiref validate — WSGI conformance checker.
                                                             (line   22)
* valid_signals() (in module signal):    Module contents<2>. (line  257)
* value (ctypes._SimpleCData attribute): Fundamental data types<2>.
                                                             (line   17)
* value (http.cookiejar.Cookie attribute): Cookie Objects<2>.
                                                             (line   32)
* value (http.cookies.Morsel attribute): Morsel Objects.     (line   52)
* value (xml.dom.Attr attribute):        Attr Objects.       (line   23)
* value of an object:                    Objects values and types.
                                                             (line   11)
* Value() (in module multiprocessing):   Shared ctypes Objects.
                                                             (line    9)
* Value() (in module multiprocessing.sharedctypes): The multiprocessing sharedctypes module.
                                                             (line   67)
* Value() (multiprocessing.managers.SyncManager method): Managers.
                                                             (line  200)
* ValueError:                            Concrete exceptions.
                                                             (line  403)
* valuerefs() (weakref.WeakValueDictionary method): weakref — Weak references.
                                                             (line  199)
* values() (contextvars.Context method): Manual Context Management.
                                                             (line  104)
* values() (dict method):                Mapping Types — dict.
                                                             (line  223)
* values() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  236)
* values() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  344)
* values() (mailbox.Mailbox method):     Mailbox objects.    (line  114)
* values() (types.MappingProxyType method): Standard Interpreter Types.
                                                             (line  288)
* ValuesView (class in collections.abc): Collections Abstract Base Classes.
                                                             (line  187)
* ValuesView (class in typing):          Corresponding to collections in collections abc.
                                                             (line  113)
* value_decode() (http.cookies.BaseCookie method): Cookie Objects.
                                                             (line    6)
* value_encode() (http.cookies.BaseCookie method): Cookie Objects.
                                                             (line   13)
* var (contextvars.Token attribute):     Context Variables.  (line   82)
* variable annotation:                   Glossary.           (line 1295)
* variance (statistics.NormalDist attribute): NormalDist objects.
                                                             (line   40)
* variance() (in module statistics):     Function details.   (line  343)
* variant (uuid.UUID attribute):         uuid — UUID objects according to RFC 4122.
                                                             (line  139)
* vars() (built-in function):            Built-in Functions. (line 1728)
* VBAR (in module token):                token — Constants used with Python parse trees.
                                                             (line   98)
* vbar (tkinter.scrolledtext.ScrolledText attribute): tkinter scrolledtext — Scrolled Text Widget.
                                                             (line   30)
* VBAREQUAL (in module token):           token — Constants used with Python parse trees.
                                                             (line  194)
* Vec2D (class in turtle):               Public classes.     (line   86)
* vectorcallfunc (C type):               The Vectorcall Protocol.
                                                             (line   34)
* venv (module):                         venv — Creation of virtual environments.
                                                             (line    6)
* VERBOSE (in module re):                Module Contents.    (line  120)
* verbose (in module tabnanny):          tabnanny — Detection of ambiguous indentation.
                                                             (line   26)
* verbose (in module test.support):      test support — Utilities for the Python test suite.
                                                             (line   30)
* verify() (smtplib.SMTP method):        SMTP Objects.       (line   91)
* VerifyFlags (class in ssl):            Constants<9>.       (line  112)
* VerifyMode (class in ssl):             Constants<9>.       (line   64)
* verify_client_post_handshake() (ssl.SSLSocket method): SSL Sockets.
                                                             (line  281)
* verify_code (ssl.SSLCertVerificationError attribute): Exceptions<13>.
                                                             (line   86)
* VERIFY_CRL_CHECK_CHAIN (in module ssl): Constants<9>.      (line   89)
* VERIFY_CRL_CHECK_LEAF (in module ssl): Constants<9>.       (line   78)
* VERIFY_DEFAULT (in module ssl):        Constants<9>.       (line   70)
* verify_flags (ssl.SSLContext attribute): SSL Contexts.     (line  644)
* verify_message (ssl.SSLCertVerificationError attribute): Exceptions<13>.
                                                             (line   90)
* verify_mode (ssl.SSLContext attribute): SSL Contexts.      (line  660)
* verify_request() (socketserver.BaseServer method): Server Objects<2>.
                                                             (line  175)
* VERIFY_X509_STRICT (in module ssl):    Constants<9>.       (line   96)
* VERIFY_X509_TRUSTED_FIRST (in module ssl): Constants<9>.   (line  103)
* version (email.headerregistry.MIMEVersionHeader attribute): email headerregistry Custom Header Objects.
                                                             (line  242)
* version (http.client.HTTPResponse attribute): HTTPResponse Objects.
                                                             (line   46)
* version (http.cookiejar.Cookie attribute): Cookie Objects<2>.
                                                             (line   20)
* version (in module curses):            Constants<6>.       (line   18)
* version (in module marshal):           marshal — Internal Python object serialization.
                                                             (line  110)
* version (in module sqlite3):           Module functions and constants.
                                                             (line   22)
* version (in module sys):               sys — System-specific parameters and functions.
                                                             (line 1645)
* version (in module sys) <1>:           Process-wide parameters.
                                                             (line  164)
* version (in module sys) <2>:           Process-wide parameters.
                                                             (line  199)
* version (in module sys) <3>:           Process-wide parameters.
                                                             (line  210)
* version (ipaddress.IPv4Address attribute): Address objects.
                                                             (line   51)
* version (ipaddress.IPv4Network attribute): Network objects.
                                                             (line   63)
* version (ipaddress.IPv6Address attribute): Address objects.
                                                             (line  212)
* version (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  293)
* version (urllib.request.URLopener attribute): Legacy interface.
                                                             (line  139)
* version (uuid.UUID attribute):         uuid — UUID objects according to RFC 4122.
                                                             (line  146)
* version() (in module ensurepip):       Module API.         (line    8)
* version() (in module platform):        Cross Platform.     (line  131)
* version() (ssl.SSLSocket method):      SSL Sockets.        (line  303)
* version_info (in module sqlite3):      Module functions and constants.
                                                             (line   27)
* version_info (in module sys):          sys — System-specific parameters and functions.
                                                             (line 1660)
* version_string() (http.server.BaseHTTPRequestHandler method): http server — HTTP servers.
                                                             (line  307)
* vformat() (string.Formatter method):   Custom String Formatting.
                                                             (line   26)
* virtual environment:                   Glossary.           (line 1317)
* virtual machine:                       Glossary.           (line 1326)
* VIRTUAL_ENV:                           Creating virtual environments.
                                                             (line  134)
* visit() (ast.NodeVisitor method):      ast Helpers.        (line  165)
* visitproc (C type):                    Supporting Cyclic Garbage Collection.
                                                             (line  134)
* vline() (curses.window method):        Window Objects.     (line  585)
* voidcmd() (ftplib.FTP method):         FTP Objects.        (line   74)
* volume (zipfile.ZipInfo attribute):    ZipInfo Objects.    (line  119)
* vonmisesvariate() (in module random):  Real-valued distributions.
                                                             (line   82)
* wait() (asyncio.asyncio.subprocess.Process method): Interacting with Subprocesses.
                                                             (line   38)
* wait() (asyncio.Condition method):     Condition.          (line   86)
* wait() (asyncio.Event method):         Event.              (line   45)
* wait() (in module asyncio):            Waiting Primitives. (line    6)
* wait() (in module concurrent.futures): Module Functions.   (line    6)
* wait() (in module multiprocessing.connection): Listeners and Clients.
                                                             (line  113)
* wait() (in module os):                 Process Management. (line  729)
* wait() (multiprocessing.pool.AsyncResult method): Process Pools.
                                                             (line  204)
* wait() (subprocess.Popen method):      Popen Objects.      (line   13)
* wait() (threading.Barrier method):     Barrier Objects.    (line   43)
* wait() (threading.Condition method):   Condition Objects.  (line   97)
* wait() (threading.Event method):       Event Objects.      (line   39)
* wait3() (in module os):                Process Management. (line  853)
* wait4() (in module os):                Process Management. (line  867)
* waitid() (in module os):               Process Management. (line  748)
* waitpid() (in module os):              Process Management. (line  813)
* waitstatus_to_exitcode() (in module os): Process Management.
                                                             (line  881)
* wait_closed() (asyncio.Server method): Server Objects.     (line   95)
* wait_closed() (asyncio.StreamWriter method): StreamWriter. (line   88)
* wait_for() (asyncio.Condition method): Condition.          (line   98)
* wait_for() (in module asyncio):        Timeouts.           (line    6)
* wait_for() (threading.Condition method): Condition Objects.
                                                             (line  128)
* wait_process() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  576)
* wait_threads_exit() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  591)
* walk() (email.message.EmailMessage method): email message Representing an email message.
                                                             (line  467)
* walk() (email.message.Message method): email message Message Representing an email message using the compat32 API.
                                                             (line  636)
* walk() (in module ast):                ast Helpers.        (line  148)
* walk() (in module os):                 Files and Directories.
                                                             (line 1490)
* walk_packages() (in module pkgutil):   pkgutil — Package extension utility.
                                                             (line  162)
* walk_stack() (in module traceback):    traceback — Print or retrieve a stack traceback.
                                                             (line  157)
* walk_tb() (in module traceback):       traceback — Print or retrieve a stack traceback.
                                                             (line  166)
* want (doctest.Example attribute):      Example Objects.    (line   23)
* warn() (distutils.ccompiler.CCompiler method): distutils ccompiler — CCompiler base class.
                                                             (line  507)
* warn() (distutils.text_file.TextFile method): distutils text_file — The TextFile class.
                                                             (line  101)
* warn() (in module warnings):           Available Functions.
                                                             (line    6)
* Warning:                               Warnings.           (line    9)
* Warning <1>:                           Exceptions<5>.      (line    6)
* warning() (in module logging):         Module-Level Functions.
                                                             (line  124)
* warning() (logging.Logger method):     Logger Objects.     (line  232)
* warning() (xml.sax.handler.ErrorHandler method): ErrorHandler Objects.
                                                             (line   29)
* warnings:                              warnings — Warning control.
                                                             (line    8)
* warnings (module):                     warnings — Warning control.
                                                             (line    6)
* WarningsRecorder (class in test.support): test support — Utilities for the Python test suite.
                                                             (line 1118)
* warnoptions (in module sys):           sys — System-specific parameters and functions.
                                                             (line 1673)
* warn_explicit() (in module warnings):  Available Functions.
                                                             (line   32)
* wasSuccessful() (unittest.TestResult method): Loading and running tests.
                                                             (line  302)
* WatchedFileHandler (class in logging.handlers): WatchedFileHandler.
                                                             (line   24)
* wave (module):                         wave — Read and write WAV files.
                                                             (line    6)
* WCONTINUED (in module os):             Process Management. (line  922)
* WCOREDUMP() (in module os):            Process Management. (line  942)
* WeakKeyDictionary (class in weakref):  weakref — Weak references.
                                                             (line  163)
* WeakMethod (class in weakref):         weakref — Weak references.
                                                             (line  208)
* weakref (module):                      weakref — Weak references.
                                                             (line    6)
* WeakSet (class in weakref):            weakref — Weak references.
                                                             (line  203)
* WeakValueDictionary (class in weakref): weakref — Weak references.
                                                             (line  186)
* webbrowser (module):                   webbrowser — Convenient Web-browser controller.
                                                             (line    6)
* weekday() (datetime.date method):      date Objects.       (line  200)
* weekday() (datetime.datetime method):  datetime Objects.   (line  582)
* weekday() (in module calendar):        calendar — General calendar-related functions.
                                                             (line  313)
* weekheader() (in module calendar):     calendar — General calendar-related functions.
                                                             (line  318)
* weibullvariate() (in module random):   Real-valued distributions.
                                                             (line   94)
* WEXITED (in module os):                Process Management. (line  785)
* WEXITSTATUS() (in module os):          Process Management. (line  988)
* wfile (http.server.BaseHTTPRequestHandler attribute): http server — HTTP servers.
                                                             (line  118)
* what() (in module imghdr):             imghdr — Determine the type of an image.
                                                             (line   15)
* what() (in module sndhdr):             sndhdr — Determine type of sound file.
                                                             (line   25)
* whathdr() (in module sndhdr):          sndhdr — Determine type of sound file.
                                                             (line   34)
* whatis (pdb command):                  Debugger Commands.  (line  247)
* when() (asyncio.TimerHandle method):   Callback Handles.   (line   29)
* where (pdb command):                   Debugger Commands.  (line   55)
* which() (in module shutil):            Directory and files operations.
                                                             (line  373)
* whichdb() (in module dbm):             dbm — Interfaces to Unix “databases”.
                                                             (line   23)
* While (class in ast):                  Control flow.       (line   78)
* whitespace (in module string):         String constants.   (line   47)
* whitespace (shlex.shlex attribute):    shlex Objects.      (line  104)
* whitespace_split (shlex.shlex attribute): shlex Objects.   (line  128)
* Widget (class in tkinter.ttk):         ttk Widget.         (line    9)
* width (textwrap.TextWrapper attribute): textwrap — Text wrapping and filling.
                                                             (line  157)
* width() (in module turtle):            Drawing state.      (line   18)
* WIFCONTINUED() (in module os):         Process Management. (line  952)
* WIFEXITED() (in module os):            Process Management. (line  980)
* WIFSIGNALED() (in module os):          Process Management. (line  973)
* WIFSTOPPED() (in module os):           Process Management. (line  962)
* win32_edition() (in module platform):  Windows Platform.   (line   21)
* win32_is_iot() (in module platform):   Windows Platform.   (line   29)
* win32_ver() (in module platform):      Windows Platform.   (line    6)
* WinDLL (class in ctypes):              Loading shared libraries.
                                                             (line   46)
* window manager (widgets):              The Window Manager. (line    6)
* window() (curses.panel.Panel method):  Panel Objects.      (line   62)
* Windows:                               Complete Python programs.
                                                             (line   25)
* Windows ini file:                      configparser — Configuration file parser.
                                                             (line    8)
* WindowsError:                          Concrete exceptions.
                                                             (line  424)
* WindowsPath (class in pathlib):        Concrete paths.     (line   32)
* WindowsProactorEventLoopPolicy (class in asyncio): Policy Objects.
                                                             (line   68)
* WindowsRegistryFinder (class in importlib.machinery): importlib machinery – Importers and path hooks.
                                                             (line   92)
* WindowsSelectorEventLoopPolicy (class in asyncio): Policy Objects.
                                                             (line   61)
* window_height() (in module turtle):    Settings and special methods.
                                                             (line  103)
* window_width() (in module turtle):     Settings and special methods.
                                                             (line  110)
* winerror (OSError attribute):          Concrete exceptions.
                                                             (line  139)
* WinError() (in module ctypes):         Utility functions.  (line  203)
* WINFUNCTYPE() (in module ctypes):      Function prototypes.
                                                             (line   25)
* winreg (module):                       winreg — Windows registry access.
                                                             (line    6)
* WinSock:                               select — Waiting for I/O completion.
                                                             (line  146)
* winsound (module):                     winsound — Sound-playing interface for Windows.
                                                             (line    6)
* winver (in module sys):                sys — System-specific parameters and functions.
                                                             (line 1679)
* With (class in ast):                   Control flow.       (line  210)
* withitem (class in ast):               Control flow.       (line  221)
* WITH_EXCEPT_START (opcode):            Python Bytecode Instructions.
                                                             (line  391)
* with_hostmask (ipaddress.IPv4Interface attribute): Interface objects.
                                                             (line   55)
* with_hostmask (ipaddress.IPv4Network attribute): Network objects.
                                                             (line  123)
* with_hostmask (ipaddress.IPv6Interface attribute): Interface objects.
                                                             (line   82)
* with_hostmask (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  325)
* with_name() (pathlib.PurePath method): Methods and properties.
                                                             (line  275)
* with_netmask (ipaddress.IPv4Interface attribute): Interface objects.
                                                             (line   46)
* with_netmask (ipaddress.IPv4Network attribute): Network objects.
                                                             (line  118)
* with_netmask (ipaddress.IPv6Interface attribute): Interface objects.
                                                             (line   80)
* with_netmask (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  323)
* with_prefixlen (ipaddress.IPv4Interface attribute): Interface objects.
                                                             (line   37)
* with_prefixlen (ipaddress.IPv4Network attribute): Network objects.
                                                             (line  105)
* with_prefixlen (ipaddress.IPv6Interface attribute): Interface objects.
                                                             (line   78)
* with_prefixlen (ipaddress.IPv6Network attribute): Network objects.
                                                             (line  317)
* with_pymalloc() (in module test.support): test support — Utilities for the Python test suite.
                                                             (line  267)
* with_stem() (pathlib.PurePath method): Methods and properties.
                                                             (line  291)
* with_suffix() (pathlib.PurePath method): Methods and properties.
                                                             (line  314)
* with_traceback() (BaseException method): Base classes.     (line   25)
* WNOHANG (in module os):                Process Management. (line  914)
* WNOWAIT (in module os):                Process Management. (line  785)
* wordchars (shlex.shlex attribute):     shlex Objects.      (line   91)
* World Wide Web:                        Internet Protocols and Support.
                                                             (line    6)
* World Wide Web <1>:                    urllib parse — Parse URLs into components.
                                                             (line    8)
* World Wide Web <2>:                    urllib robotparser — Parser for robots txt.
                                                             (line    8)
* wrap() (in module textwrap):           textwrap — Text wrapping and filling.
                                                             (line   16)
* wrap() (textwrap.TextWrapper method):  textwrap — Text wrapping and filling.
                                                             (line  284)
* wrapper() (in module curses):          Functions<4>.       (line  593)
* WrapperDescriptorType (in module types): Standard Interpreter Types.
                                                             (line   88)
* wraps() (in module functools):         functools — Higher-order functions and operations on callable objects.
                                                             (line  612)
* wrap_bio() (ssl.SSLContext method):    SSL Contexts.       (line  454)
* wrap_future() (in module asyncio):     Future Functions.   (line   47)
* wrap_socket() (in module ssl):         Certificate handling.
                                                             (line  167)
* wrap_socket() (ssl.SSLContext method): SSL Contexts.       (line  390)
* wrap_text() (in module distutils.fancy_getopt): distutils fancy_getopt — Wrapper around the standard getopt module.
                                                             (line   32)
* WRITABLE (in module tkinter):          File Handlers.      (line   41)
* writable() (asyncore.dispatcher method): asyncore — Asynchronous socket handler.
                                                             (line  172)
* writable() (io.IOBase method):         I/O Base Classes.   (line  155)
* write() (asyncio.StreamWriter method): StreamWriter.       (line   15)
* write() (asyncio.WriteTransport method): Write-only Transports.
                                                             (line   60)
* write() (code.InteractiveInterpreter method): Interactive Interpreter Objects.
                                                             (line   63)
* write() (codecs.StreamWriter method):  StreamWriter Objects.
                                                             (line   31)
* write() (configparser.ConfigParser method): ConfigParser Objects.
                                                             (line  257)
* write() (email.generator.BytesGenerator method): email generator Generating MIME documents.
                                                             (line  118)
* write() (email.generator.Generator method): email generator Generating MIME documents.
                                                             (line  214)
* write() (in module os):                File Descriptor Operations.
                                                             (line  680)
* write() (in module turtle):            More drawing control.
                                                             (line   29)
* write() (io.BufferedIOBase method):    I/O Base Classes.   (line  329)
* write() (io.BufferedWriter method):    Buffered Streams.   (line  131)
* write() (io.RawIOBase method):         I/O Base Classes.   (line  215)
* write() (io.TextIOBase method):        Text I/O<2>.        (line   94)
* write() (mmap.mmap method):            mmap — Memory-mapped file support.
                                                             (line  279)
* write() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line   39)
* write() (ssl.MemoryBIO method):        Memory BIO Support<2>.
                                                             (line  153)
* write() (ssl.SSLSocket method):        SSL Sockets.        (line   91)
* write() (telnetlib.Telnet method):     Telnet Objects.     (line  101)
* write() (xml.etree.ElementTree.ElementTree method): ElementTree Objects.
                                                             (line   62)
* write() (zipfile.ZipFile method):      ZipFile Objects.    (line  242)
* writeall() (ossaudiodev.oss_audio_device method): Audio Device Objects.
                                                             (line   51)
* writeframes() (aifc.aifc method):      aifc — Read and write AIFF and AIFC files.
                                                             (line  187)
* writeframes() (sunau.AU_write method): AU_write Objects.   (line   52)
* writeframes() (wave.Wave_write method): Wave_write Objects.
                                                             (line   75)
* writeframesraw() (aifc.aifc method):   aifc — Read and write AIFF and AIFC files.
                                                             (line  195)
* writeframesraw() (sunau.AU_write method): AU_write Objects.
                                                             (line   45)
* writeframesraw() (wave.Wave_write method): Wave_write Objects.
                                                             (line   68)
* writeheader() (csv.DictWriter method): Writer Objects.     (line   38)
* writelines() (asyncio.StreamWriter method): StreamWriter.  (line   26)
* writelines() (asyncio.WriteTransport method): Write-only Transports.
                                                             (line   67)
* writelines() (codecs.StreamWriter method): StreamWriter Objects.
                                                             (line   35)
* writelines() (io.IOBase method):       I/O Base Classes.   (line  161)
* writepy() (zipfile.PyZipFile method):  PyZipFile Objects.  (line   20)
* writer (formatter.formatter attribute): The Formatter Interface.
                                                             (line   22)
* writer() (in module csv):              Module Contents<3>. (line   40)
* writerow() (csv.csvwriter method):     Writer Objects.     (line   15)
* writerows() (csv.csvwriter method):    Writer Objects.     (line   24)
* writestr() (zipfile.ZipFile method):   ZipFile Objects.    (line  270)
* WriteTransport (class in asyncio):     Transports Hierarchy.
                                                             (line   11)
* writev() (in module os):               File Descriptor Operations.
                                                             (line  699)
* writexml() (xml.dom.minidom.Node method): DOM Objects.     (line   27)
* write_byte() (mmap.mmap method):       mmap — Memory-mapped file support.
                                                             (line  295)
* write_bytes() (pathlib.Path method):   Methods<2>.         (line  471)
* write_docstringdict() (in module turtle): Translation of docstrings into different languages.
                                                             (line   10)
* write_eof() (asyncio.StreamWriter method): StreamWriter.   (line   52)
* write_eof() (asyncio.WriteTransport method): Write-only Transports.
                                                             (line   74)
* write_eof() (ssl.MemoryBIO method):    Memory BIO Support<2>.
                                                             (line  161)
* write_file() (in module distutils.file_util): distutils file_util — Single file operations.
                                                             (line   44)
* write_history_file() (in module readline): History file.   (line   14)
* WRITE_RESTRICTED:                      Generic Attribute Management.
                                                             (line   92)
* write_results() (trace.CoverageResults method): Programmatic Interface.
                                                             (line   57)
* write_text() (pathlib.Path method):    Methods<2>.         (line  486)
* write_through (io.TextIOWrapper attribute): Text I/O<2>.   (line  168)
* writing; values:                       Expression statements.
                                                             (line   17)
* WrongDocumentErr:                      Exceptions<17>.     (line   97)
* wsgiref (module):                      wsgiref — WSGI Utilities and Reference Implementation.
                                                             (line    6)
* wsgiref.handlers (module):             wsgiref handlers – server/gateway base classes.
                                                             (line    6)
* wsgiref.headers (module):              wsgiref headers – WSGI response header tools.
                                                             (line    6)
* wsgiref.simple_server (module):        wsgiref simple_server – a simple WSGI HTTP server.
                                                             (line    6)
* wsgiref.util (module):                 wsgiref util – WSGI environment utilities.
                                                             (line    6)
* wsgiref.validate (module):             wsgiref validate — WSGI conformance checker.
                                                             (line    6)
* WSGIRequestHandler (class in wsgiref.simple_server): wsgiref simple_server – a simple WSGI HTTP server.
                                                             (line   75)
* WSGIServer (class in wsgiref.simple_server): wsgiref simple_server – a simple WSGI HTTP server.
                                                             (line   45)
* wsgi_file_wrapper (wsgiref.handlers.BaseHandler attribute): wsgiref handlers – server/gateway base classes.
                                                             (line  269)
* wsgi_multiprocess (wsgiref.handlers.BaseHandler attribute): wsgiref handlers – server/gateway base classes.
                                                             (line  153)
* wsgi_multithread (wsgiref.handlers.BaseHandler attribute): wsgiref handlers – server/gateway base classes.
                                                             (line  146)
* wsgi_run_once (wsgiref.handlers.BaseHandler attribute): wsgiref handlers – server/gateway base classes.
                                                             (line  160)
* wShowWindow (subprocess.STARTUPINFO attribute): Windows Popen Helpers.
                                                             (line   49)
* WSTOPPED (in module os):               Process Management. (line  785)
* WSTOPSIG() (in module os):             Process Management. (line  997)
* wstring_at() (in module ctypes):       Utility functions.  (line  214)
* ws_comma (2to3 fixer):                 Fixers.             (line  326)
* WTERMSIG() (in module os):             Process Management. (line 1006)
* WUNTRACED (in module os):              Process Management. (line  930)
* WWW:                                   Internet Protocols and Support.
                                                             (line    6)
* WWW <1>:                               urllib parse — Parse URLs into components.
                                                             (line    8)
* WWW <2>:                               urllib robotparser — Parser for robots txt.
                                                             (line    8)
* WWW; server:                           cgi — Common Gateway Interface support.
                                                             (line    8)
* WWW; server <1>:                       http server — HTTP servers.
                                                             (line    8)
* W_OK (in module os):                   Files and Directories.
                                                             (line  106)
* X (in module re):                      Module Contents.    (line  120)
* X509 certificate:                      SSL Contexts.       (line  672)
* xatom() (imaplib.IMAP4 method):        IMAP4 Objects.      (line  385)
* XATTR_CREATE (in module os):           Linux extended attributes.
                                                             (line   87)
* XATTR_REPLACE (in module os):          Linux extended attributes.
                                                             (line   93)
* XATTR_SIZE_MAX (in module os):         Linux extended attributes.
                                                             (line   82)
* xcor() (in module turtle):             Tell Turtle’s state.
                                                             (line   34)
* XDR:                                   xdrlib — Encode and decode XDR data.
                                                             (line    8)
* xdrlib (module):                       xdrlib — Encode and decode XDR data.
                                                             (line    6)
* xhdr() (nntplib.NNTP method):          Methods<3>.         (line  320)
* XHTML:                                 html parser — Simple HTML and XHTML parser.
                                                             (line    8)
* XHTML_NAMESPACE (in module xml.dom):   Module Contents<4>. (line   53)
* xml (module):                          XML Processing Modules.
                                                             (line    6)
* XML() (in module xml.etree.ElementTree): Functions<7>.     (line  265)
* xml.dom (module):                      xml dom — The Document Object Model API.
                                                             (line    6)
* xml.dom.minidom (module):              xml dom minidom — Minimal DOM implementation.
                                                             (line    6)
* xml.dom.pulldom (module):              xml dom pulldom — Support for building partial DOM trees.
                                                             (line    6)
* xml.etree.ElementInclude.default_loader() (in module xml.etree.ElementTree): Functions<8>.
                                                             (line    6)
* xml.etree.ElementInclude.include() (in module xml.etree.ElementTree): Functions<8>.
                                                             (line   17)
* xml.etree.ElementTree (module):        xml etree ElementTree — The ElementTree XML API.
                                                             (line    6)
* xml.parsers.expat (module):            xml parsers expat — Fast XML parsing using Expat.
                                                             (line    6)
* xml.parsers.expat.errors (module):     Expat error constants.
                                                             (line    6)
* xml.parsers.expat.model (module):      Content Model Descriptions.
                                                             (line    6)
* xml.sax (module):                      xml sax — Support for SAX2 parsers.
                                                             (line    6)
* xml.sax.handler (module):              xml sax handler — Base classes for SAX handlers.
                                                             (line    6)
* xml.sax.saxutils (module):             xml sax saxutils — SAX Utilities.
                                                             (line    6)
* xml.sax.xmlreader (module):            xml sax xmlreader — Interface for XML parsers.
                                                             (line    6)
* xmlcharrefreplace_errors() (in module codecs): Error Handlers.
                                                             (line  145)
* XmlDeclHandler() (xml.parsers.expat.xmlparser method): XMLParser Objects<2>.
                                                             (line  175)
* XMLFilterBase (class in xml.sax.saxutils): xml sax saxutils — SAX Utilities.
                                                             (line   68)
* XMLGenerator (class in xml.sax.saxutils): xml sax saxutils — SAX Utilities.
                                                             (line   52)
* XMLID() (in module xml.etree.ElementTree): Functions<7>.   (line  273)
* XMLNS_NAMESPACE (in module xml.dom):   Module Contents<4>. (line   47)
* XMLParser (class in xml.etree.ElementTree): XMLParser Objects.
                                                             (line    6)
* XMLParserType (in module xml.parsers.expat): xml parsers expat — Fast XML parsing using Expat.
                                                             (line   35)
* XMLPullParser (class in xml.etree.ElementTree): XMLPullParser Objects.
                                                             (line    6)
* XMLReader (class in xml.sax.xmlreader): xml sax xmlreader — Interface for XML parsers.
                                                             (line   16)
* xmlrpc.client (module):                xmlrpc client — XML-RPC client access.
                                                             (line    6)
* xmlrpc.server (module):                xmlrpc server — Basic XML-RPC servers.
                                                             (line    6)
* XML_ERROR_ABORTED (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  180)
* XML_ERROR_ASYNC_ENTITY (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   29)
* XML_ERROR_ATTRIBUTE_EXTERNAL_ENTITY_REF (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   31)
* XML_ERROR_BAD_CHAR_REF (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   37)
* XML_ERROR_BINARY_ENTITY_REF (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   42)
* XML_ERROR_CANT_CHANGE_FEATURE_ONCE_PARSING (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  135)
* XML_ERROR_DUPLICATE_ATTRIBUTE (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   47)
* XML_ERROR_ENTITY_DECLARED_IN_PE (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  126)
* XML_ERROR_EXTERNAL_ENTITY_HANDLING (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  116)
* XML_ERROR_FEATURE_REQUIRES_XML_DTD (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  128)
* XML_ERROR_FINISHED (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  184)
* XML_ERROR_INCOMPLETE_PE (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  152)
* XML_ERROR_INCORRECT_ENCODING (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   51)
* XML_ERROR_INVALID_TOKEN (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   53)
* XML_ERROR_JUNK_AFTER_DOC_ELEMENT (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   59)
* XML_ERROR_MISPLACED_XML_PI (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   64)
* XML_ERROR_NOT_STANDALONE (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  118)
* XML_ERROR_NOT_SUSPENDED (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  175)
* XML_ERROR_NO_ELEMENTS (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   69)
* XML_ERROR_NO_MEMORY (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   74)
* XML_ERROR_PARAM_ENTITY_REF (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   78)
* XML_ERROR_PARTIAL_CHAR (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   82)
* XML_ERROR_PUBLICID (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  165)
* XML_ERROR_RECURSIVE_ENTITY_REF (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   86)
* XML_ERROR_SUSPENDED (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  169)
* XML_ERROR_SUSPEND_PE (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  190)
* XML_ERROR_SYNTAX (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   91)
* XML_ERROR_TAG_MISMATCH (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   95)
* XML_ERROR_TEXT_DECL (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  160)
* XML_ERROR_UNBOUND_PREFIX (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  142)
* XML_ERROR_UNCLOSED_CDATA_SECTION (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  112)
* XML_ERROR_UNCLOSED_TOKEN (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line   99)
* XML_ERROR_UNDECLARING_PREFIX (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  147)
* XML_ERROR_UNDEFINED_ENTITY (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  104)
* XML_ERROR_UNEXPECTED_STATE (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  124)
* XML_ERROR_UNKNOWN_ENCODING (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  108)
* XML_ERROR_XML_DECL (in module xml.parsers.expat.errors): Expat error constants.
                                                             (line  156)
* XML_NAMESPACE (in module xml.dom):     Module Contents<4>. (line   42)
* xor() (in module operator):            operator — Standard operators as functions.
                                                             (line  164)
* xover() (nntplib.NNTP method):         Methods<3>.         (line  336)
* xrange (2to3 fixer):                   Fixers.             (line  331)
* xreadlines (2to3 fixer):               Fixers.             (line  336)
* xview() (tkinter.ttk.Treeview method): ttk Treeview.       (line  327)
* X_OK (in module os):                   Files and Directories.
                                                             (line  106)
* ycor() (in module turtle):             Tell Turtle’s state.
                                                             (line   46)
* year (datetime.date attribute):        date Objects.       (line  102)
* year (datetime.datetime attribute):    datetime Objects.   (line  264)
* Year 2038:                             time — Time access and conversions.
                                                             (line   30)
* yeardatescalendar() (calendar.Calendar method): calendar — General calendar-related functions.
                                                             (line  106)
* yeardays2calendar() (calendar.Calendar method): calendar — General calendar-related functions.
                                                             (line  114)
* yeardayscalendar() (calendar.Calendar method): calendar — General calendar-related functions.
                                                             (line  121)
* YESEXPR (in module locale):            locale — Internationalization services.
                                                             (line  241)
* Yield (class in ast):                  Function and class definitions.
                                                             (line  128)
* yield; examples:                       Generator-iterator methods.
                                                             (line   57)
* yield; expression:                     Yield expressions.  (line    6)
* yield; yield from (in What’s New):     PEP 3151 Reworking the OS and IO exception hierarchy.
                                                             (line   87)
* YieldFrom (class in ast):              Function and class definitions.
                                                             (line  128)
* YIELD_FROM (opcode):                   Python Bytecode Instructions.
                                                             (line  350)
* YIELD_VALUE (opcode):                  Python Bytecode Instructions.
                                                             (line  346)
* yiq_to_rgb() (in module colorsys):     colorsys — Conversions between color systems.
                                                             (line   32)
* yview() (tkinter.ttk.Treeview method): ttk Treeview.       (line  331)
* Zen of Python:                         Glossary.           (line 1332)
* ZeroDivisionError:                     Concrete exceptions.
                                                             (line  410)
* zfill() (bytearray method):            Bytes and Bytearray Operations.
                                                             (line  745)
* zfill() (bytes method):                Bytes and Bytearray Operations.
                                                             (line  745)
* zfill() (str method):                  String Methods<2>.  (line  665)
* zip (2to3 fixer):                      Fixers.             (line  340)
* zip() (built-in function):             Built-in Functions. (line 1748)
* zipapp (module):                       zipapp — Manage executable Python zip archives.
                                                             (line    6)
* zipapp command line option; -c:        Command-Line Interface<5>.
                                                             (line   45)
* zipapp command line option; –compress: Command-Line Interface<5>.
                                                             (line   45)
* zipapp command line option; -h:        Command-Line Interface<5>.
                                                             (line   61)
* zipapp command line option; –help:     Command-Line Interface<5>.
                                                             (line   61)
* zipapp command line option; –info:     Command-Line Interface<5>.
                                                             (line   55)
* zipapp command line option; -m <mainfn>: Command-Line Interface<5>.
                                                             (line   35)
* zipapp command line option; –main=<mainfn>: Command-Line Interface<5>.
                                                             (line   35)
* zipapp command line option; -o <output>: Command-Line Interface<5>.
                                                             (line   18)
* zipapp command line option; –output=<output>: Command-Line Interface<5>.
                                                             (line   18)
* zipapp command line option; -p <interpreter>: Command-Line Interface<5>.
                                                             (line   29)
* zipapp command line option; –python=<interpreter>: Command-Line Interface<5>.
                                                             (line   29)
* ZipFile (class in zipfile):            ZipFile Objects.    (line    6)
* zipfile (module):                      zipfile — Work with ZIP archives.
                                                             (line    6)
* zipfile command line option; -c <zipfile> <source1> ... <sourceN>: Command-line options.
                                                             (line   11)
* zipfile command line option; –create <zipfile> <source1> ... <sourceN>: Command-line options.
                                                             (line   11)
* zipfile command line option; -e <zipfile> <output_dir>: Command-line options.
                                                             (line   16)
* zipfile command line option; –extract <zipfile> <output_dir>: Command-line options.
                                                             (line   16)
* zipfile command line option; -l <zipfile>: Command-line options.
                                                             (line    6)
* zipfile command line option; –list <zipfile>: Command-line options.
                                                             (line    6)
* zipfile command line option; -t <zipfile>: Command-line options.
                                                             (line   21)
* zipfile command line option; –test <zipfile>: Command-line options.
                                                             (line   21)
* zipimport (module):                    zipimport — Import modules from Zip archives.
                                                             (line    6)
* zipimporter (class in zipimport):      zipimporter Objects.
                                                             (line    8)
* ZipImportError:                        zipimport — Import modules from Zip archives.
                                                             (line   55)
* ZipInfo (class in zipfile):            zipfile — Work with ZIP archives.
                                                             (line   58)
* ZIP_BZIP2 (in module zipfile):         zipfile — Work with ZIP archives.
                                                             (line   88)
* ZIP_DEFLATED (in module zipfile):      zipfile — Work with ZIP archives.
                                                             (line   83)
* zip_longest() (in module itertools):   Itertool functions. (line  590)
* ZIP_LZMA (in module zipfile):          zipfile — Work with ZIP archives.
                                                             (line   95)
* ZIP_STORED (in module zipfile):        zipfile — Work with ZIP archives.
                                                             (line   79)
* zlib (module):                         zlib — Compression compatible with gzip.
                                                             (line    6)
* ZLIB_RUNTIME_VERSION (in module zlib): zlib — Compression compatible with gzip.
                                                             (line  309)
* ZLIB_VERSION (in module zlib):         zlib — Compression compatible with gzip.
                                                             (line  302)
* ZoneInfo (class in zoneinfo):          The ZoneInfo class. (line    6)
* zoneinfo (module):                     zoneinfo — IANA time zone support.
                                                             (line    6)
* ZoneInfoNotFoundError:                 Exceptions and warnings.
                                                             (line    6)
* zscore() (statistics.NormalDist method): NormalDist objects.
                                                             (line  114)



Tag Table:
Node: Top343
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Node: What’s New in Python195717
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Node: What’s New In Python 3 9197152
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Node: Summary – Release highlights198297
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Node: You should check for DeprecationWarning in your code200909
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Node: New Features202774
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Node: Dictionary Merge & Update Operators203150
Ref: whatsnew/3 9 dictionary-merge-update-operators203293
Ref: 163203293
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Node: New String Methods to Remove Prefixes and Suffixes204140
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Node: Type Hinting Generics in Standard Collections204940
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Node: New Parser205906
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Node: Other Language Changes207164
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Node: New Modules210861
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Node: zoneinfo211064
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Node: graphlib212335
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Node: Improved Modules212775
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Node: ast213412
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Node: compileall216353
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Node: concurrent futures217135
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Node: curses218248
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Node: datetime218668
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Node: distutils219124
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Node: fcntl219511
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Node: ftplib219834
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Node: gc220252
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Node: IDLE and idlelib222098
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Node: importlib223794
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Node: inspect224809
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Node: ipaddress225223
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Node: multiprocessing226995
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Node: smtplib231414
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Node: socket232004
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Node: Porting to Python 3 9256196
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Node: Changes in the Python API256578
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Node: New Features<2>267936
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Node: Notable changes in Python 3 9 1280625
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Node: macOS 11 0 Big Sur and Apple Silicon Mac support282413
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Node: Assignment expressions289294
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Node: Positional-only parameters291098
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Node: Parallel filesystem cache for compiled bytecode files294095
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Node: Debug build uses the same ABI as release build294975
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Node: f-strings support = for self-documenting expressions and debugging297717
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Node: PEP 590 Vectorcall a fast calling protocol for CPython302139
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Node: PEP 448 - Additional Unpacking Generalizations680356
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Node: PEP 485 A function for testing approximate equality693023
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Node: PEP 486 Make the Python Launcher aware of virtual environments694542
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Node: What’s New in Python 2 71271112
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Node: The Future for Python 2 x1273731
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Node: Changes to the Handling of Deprecation Warnings1277308
Ref: whatsnew/2 7 changes-to-the-handling-of-deprecation-warnings1277480
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Node: Python 3 1 Features1279097
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Node: PEP 372 Adding an Ordered Dictionary to collections1281214
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Node: PEP 378 Format Specifier for Thousands Separator<2>1285096
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Node: PEP 389 The argparse Module for Parsing Command Lines1286898
Ref: whatsnew/2 7 pep-389-the-argparse-module-for-parsing-command-lines1287133
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Ref: PEP 389 The argparse Module for Parsing Command Lines-Footnote-11291157
Node: PEP 391 Dictionary-Based Configuration For Logging1291206
Ref: whatsnew/2 7 pep-391-dictionary-based-configuration-for-logging1291415
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Node: PEP 3106 Dictionary Views1295332
Ref: whatsnew/2 7 pep-3106-dictionary-views1295518
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Node: PEP 3137 The memoryview Object1297726
Ref: whatsnew/2 7 pep-3137-the-memoryview-object1297888
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Node: Other Language Changes<10>1299644
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Node: Interpreter Changes1310790
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Node: Optimizations<9>1311593
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Node: New and Improved Modules1317139
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Node: New module importlib1356719
Ref: whatsnew/2 7 importlib-section1356829
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Node: New module sysconfig1358369
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Node: ttk Themed Widgets for Tk1359839
Ref: whatsnew/2 7 ttk-themed-widgets-for-tk1359986
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Node: Updated module unittest1361142
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Node: Updated module ElementTree 1 31370729
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Node: Build and C API Changes<8>1374849
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Node: Capsules1384675
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Node: Port-Specific Changes Windows1386825
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Node: Port-Specific Changes Mac OS X1388920
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Node: Port-Specific Changes FreeBSD1390219
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Node: Other Changes and Fixes1390752
Ref: whatsnew/2 7 other-changes-and-fixes1390903
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Node: Porting to Python 2 71393304
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Node: New Features Added to Python 2 7 Maintenance Releases1399649
Ref: whatsnew/2 7 new-features-added-to-python-2-7-maintenance-releases1399820
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Node: Two new environment variables for debug mode1401285
Ref: whatsnew/2 7 two-new-environment-variables-for-debug-mode1401479
Ref: dbf1401479
Ref: Two new environment variables for debug mode-Footnote-11402158
Ref: Two new environment variables for debug mode-Footnote-21402201
Node: PEP 434 IDLE Enhancement Exception for All Branches1402244
Ref: whatsnew/2 7 pep-434-idle-enhancement-exception-for-all-branches1402499
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Node: PEP 466 Network Security Enhancements for Python 2 71403068
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Node: PEP 477 Backport ensurepip PEP 453 to Python 2 71406055
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Node: Bootstrapping pip By Default<2>1406936
Ref: whatsnew/2 7 bootstrapping-pip-by-default1407085
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Node: Documentation Changes<2>1408900
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Node: PEP 476 Enabling certificate verification by default for stdlib http clients<2>1410089
Ref: whatsnew/2 7 pep-476-enabling-certificate-verification-by-default-for-stdlib-http-clients1410381
Ref: dc81410381
Ref: PEP 476 Enabling certificate verification by default for stdlib http clients<2>-Footnote-11411462
Node: PEP 493 HTTPS verification migration tools for Python 2 71411511
Ref: whatsnew/2 7 pep-493-https-verification-migration-tools-for-python-2-71411789
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Node: New make regen-all build target<3>1413002
Ref: whatsnew/2 7 new-make-regen-all-build-target1413238
Ref: dca1413238
Ref: New make regen-all build target<3>-Footnote-11414028
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Node: Removal of make touch build target<3>1414138
Ref: whatsnew/2 7 removal-of-make-touch-build-target1414308
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Node: Acknowledgements1414786
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Node: What’s New in Python 2 61415200
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Node: Python 3 01418467
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Node: Changes to the Development Process1420795
Ref: whatsnew/2 6 changes-to-the-development-process1420952
Ref: dd11420952
Node: New Issue Tracker Roundup1421470
Ref: whatsnew/2 6 new-issue-tracker-roundup1421629
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Node: New Documentation Format reStructuredText Using Sphinx1423872
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Ref: New Documentation Format reStructuredText Using Sphinx-Footnote-31426249
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Node: PEP 343 The ‘with’ statement1426320
Ref: whatsnew/2 6 pep-03431426519
Ref: d101426519
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Node: Writing Context Managers1429795
Ref: whatsnew/2 6 new-26-context-managers1429918
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Node: The contextlib module1434431
Ref: whatsnew/2 6 new-module-contextlib1434554
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Ref: The contextlib module-Footnote-11437056
Node: PEP 366 Explicit Relative Imports From a Main Module1437105
Ref: whatsnew/2 6 pep-03661437310
Ref: d131437310
Ref: whatsnew/2 6 pep-366-explicit-relative-imports-from-a-main-module1437310
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Node: PEP 370 Per-user site-packages Directory1438073
Ref: whatsnew/2 6 pep-03701438281
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Node: PEP 371 The multiprocessing Package1439789
Ref: whatsnew/2 6 pep-03711439980
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Ref: whatsnew/2 6 pep-371-the-multiprocessing-package1439980
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Node: PEP 3101 Advanced String Formatting1445168
Ref: whatsnew/2 6 pep-31011445347
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Node: PEP 3105 print As a Function1451109
Ref: whatsnew/2 6 pep-31051451288
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Node: PEP 3110 Exception-Handling Changes1452491
Ref: whatsnew/2 6 pep-31101452657
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Node: PEP 3112 Byte Literals1454307
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Node: PEP 3116 New I/O Library1457532
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Node: PEP 3118 Revised Buffer Protocol1461366
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Node: PEP 3119 Abstract Base Classes1463721
Ref: whatsnew/2 6 pep-31191463907
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Ref: whatsnew/2 6 pep-3119-abstract-base-classes1463907
Ref: dec1463907
Ref: PEP 3119 Abstract Base Classes-Footnote-11469276
Node: PEP 3127 Integer Literal Support and Syntax1469325
Ref: whatsnew/2 6 pep-31271469504
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Node: PEP 3129 Class Decorators1470918
Ref: whatsnew/2 6 pep-31291471104
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Ref: whatsnew/2 6 pep-3129-class-decorators1471104
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Node: PEP 3141 A Type Hierarchy for Numbers1471553
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Ref: PEP 3141 A Type Hierarchy for Numbers-Footnote-31474070
Node: The fractions Module1474155
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Ref: whatsnew/2 6 the-ast-module1535940
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Ref: whatsnew/2 6 the-future-builtins-module1538765
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Ref: whatsnew/2 6 the-json-module-javascript-object-notation1540072
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Ref: whatsnew/2 6 the-plistlib-module-a-property-list-parser1541269
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Ref: whatsnew/2 5 pep-309-partial-function-application1570927
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Ref: whatsnew/2 5 pep-314-metadata-for-python-software-packages-v1-11574027
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Ref: PEP 314 Metadata for Python Software Packages v1 1-Footnote-11575861
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Ref: whatsnew/2 5 pep-3281576114
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Ref: whatsnew/2 5 pep-328-absolute-and-relative-imports1576114
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Ref: PEP 328 Absolute and Relative Imports-Footnote-11579926
Ref: PEP 328 Absolute and Relative Imports-Footnote-21579975
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Ref: whatsnew/2 5 pep-3381580212
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Ref: whatsnew/2 5 pep-338-executing-modules-as-scripts1580212
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Ref: PEP 338 Executing Modules as Scripts-Footnote-11581107
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Ref: whatsnew/2 5 pep-341-unified-try-except-finally1581337
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Ref: whatsnew/2 5 pep-3421583333
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Ref: whatsnew/2 5 pep-342-new-generator-features1583333
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Ref: PEP 342 New Generator Features-Footnote-11589950
Ref: PEP 342 New Generator Features-Footnote-21589999
Ref: PEP 342 New Generator Features-Footnote-31590048
Ref: PEP 342 New Generator Features-Footnote-41590097
Ref: PEP 342 New Generator Features-Footnote-51590146
Node: PEP 343 The ‘with’ statement<2>1590195
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Ref: whatsnew/2 5 pep-343-the-with-statement1590380
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Ref: The contextlib module<2>-Footnote-11600553
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Ref: whatsnew/2 5 pep-353-using-ssize-t-as-the-index-type1603520
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Ref: whatsnew/2 5 module-ctypes1645424
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Ref: whatsnew/2 5 the-elementtree-package1648788
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Ref: whatsnew/2 5 module-wsgiref1660100
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Ref: The wsgiref package-Footnote-11661021
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Ref: whatsnew/2 5 ports1668531
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Ref: Port-Specific Changes-Footnote-11669208
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Ref: whatsnew/2 5 porting1669398
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Ref: e7a1669398
Ref: Porting to Python 2 5-Footnote-11672221
Node: Acknowledgements<3>1672270
Ref: whatsnew/2 5 acknowledgements1672382
Ref: e7b1672382
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Ref: whatsnew/2 4 doc1673031
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Ref: whatsnew/2 4 what-s-new-in-python-2-41673031
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Ref: whatsnew/2 4 pep-218-built-in-set-objects1675279
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Ref: PEP 218 Built-In Set Objects-Footnote-11677515
Node: PEP 237 Unifying Long Integers and Integers1677564
Ref: whatsnew/2 4 pep-237-unifying-long-integers-and-integers1677745
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Ref: whatsnew/2 4 pep-289-generator-expressions1679024
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Ref: PEP 289 Generator Expressions-Footnote-11681296
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Ref: whatsnew/2 4 pep-292-simpler-string-substitutions1681535
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Ref: whatsnew/2 4 pep-318-decorators-for-functions-and-methods1683569
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Ref: whatsnew/2 4 pep-322-reverse-iteration1688367
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Ref: PEP 322 Reverse Iteration-Footnote-11689329
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Ref: whatsnew/2 4 pep-324-new-subprocess-module1689538
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Ref: PEP 324 New subprocess Module-Footnote-11693302
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Ref: whatsnew/2 4 pep-327-decimal-data-type1693512
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Node: Why is Decimal needed?1694090
Ref: whatsnew/2 4 why-is-decimal-needed1694199
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Ref: whatsnew/2 4 the-decimal-type1696923
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Ref: whatsnew/2 4 the-context-type1700198
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Ref: The Context type-Footnote-11702807
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Ref: whatsnew/2 4 pep-328-multi-line-imports1703039
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Ref: PEP 328 Multi-line Imports-Footnote-11704533
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Ref: whatsnew/2 4 pep-331-locale-independent-float-string-conversions1704766
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Ref: whatsnew/2 4 other-language-changes1706751
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Ref: Other Language Changes<13>-Footnote-51713929
Ref: Other Language Changes<13>-Footnote-61713978
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Ref: whatsnew/2 4 optimizations1714107
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Ref: whatsnew/2 3 pep-218-a-standard-set-datatype1747151
Ref: ea81747151
Ref: PEP 218 A Standard Set Datatype-Footnote-11749642
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Ref: whatsnew/2 3 pep-255-simple-generators1749857
Ref: ea91749857
Ref: whatsnew/2 3 section-generators1749857
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Ref: PEP 255 Simple Generators-Footnote-11756039
Ref: PEP 255 Simple Generators-Footnote-21756088
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Ref: whatsnew/2 3 pep-263-source-code-encodings1756315
Ref: eac1756315
Ref: whatsnew/2 3 section-encodings1756315
Ref: ead1756315
Ref: PEP 263 Source Code Encodings-Footnote-11757527
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Ref: whatsnew/2 3 pep-273-importing-modules-from-zip-archives1757777
Ref: eae1757777
Ref: PEP 273 Importing Modules from ZIP Archives-Footnote-11759810
Ref: PEP 273 Importing Modules from ZIP Archives-Footnote-21759859
Ref: PEP 273 Importing Modules from ZIP Archives-Footnote-31759908
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Ref: whatsnew/2 3 pep-277-unicode-file-name-support-for-windows-nt1760162
Ref: eb01760162
Ref: PEP 277 Unicode file name support for Windows NT-Footnote-11761640
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Ref: whatsnew/2 3 pep-278-universal-newline-support1761868
Ref: eb21761868
Ref: PEP 278 Universal Newline Support-Footnote-11763383
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Ref: whatsnew/2 3 pep-279-enumerate1763590
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Ref: whatsnew/2 3 section-enumerate1763590
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Ref: whatsnew/2 3 pep-282-the-logging-package1764642
Ref: eb51764642
Ref: PEP 282 The logging Package-Footnote-11769336
Ref: PEP 282 The logging Package-Footnote-21769385
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Ref: whatsnew/2 3 pep-285-a-boolean-type1769602
Ref: eb61769602
Ref: whatsnew/2 3 section-bool1769602
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Ref: PEP 285 A Boolean Type-Footnote-11772051
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Node: PEP 293 Codec Error Handling Callbacks1772149
Ref: whatsnew/2 3 pep-293-codec-error-handling-callbacks1772338
Ref: eb81772338
Ref: PEP 293 Codec Error Handling Callbacks-Footnote-11773887
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Ref: whatsnew/2 3 pep-301-package-index-and-metadata-for-distutils1774127
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Ref: whatsnew/2 3 pep-302-new-import-hooks1776038
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Ref: PEP 302 New Import Hooks-Footnote-11778645
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Ref: whatsnew/2 3 pep-305-comma-separated-files1778953
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Ref: PEP 305 Comma-separated Files-Footnote-11780429
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Ref: whatsnew/2 3 pep-307-pickle-enhancements1780630
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Ref: whatsnew/2 3 extended-slices1782897
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Ref: whatsnew/2 3 other-language-changes1786449
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Ref: whatsnew/2 3 optimizations1797012
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Ref: whatsnew/2 3 new-improved-and-deprecated-modules1798643
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Ref: Emulating generic types-Footnote-14205339
Node: The purpose of __class_getitem__4205388
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Node: __class_getitem__ versus __getitem__4206416
Ref: reference/datamodel class-getitem-versus-getitem4206553
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Ref: reference/datamodel classgetitem-versus-getitem4206553
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Ref: __class_getitem__ versus __getitem__-Footnote-14209884
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Ref: reference/datamodel emulating-callable-objects4210082
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Ref: reference/datamodel object __call__4210155
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Ref: 15934210535
Ref: reference/datamodel sequence-types4210535
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Ref: reference/datamodel object __len__4212854
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Ref: reference/datamodel numeric-types4218842
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Ref: reference/datamodel object __add__4219157
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Ref: reference/datamodel object __itruediv__4222705
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Ref: reference/datamodel object __ilshift__4222892
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Ref: reference/datamodel object __irshift__4222937
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Ref: reference/datamodel object __iand__4222982
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Ref: reference/datamodel object __int__4224702
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Ref: reference/datamodel object __ceil__4225737
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Ref: Emulating numeric types-Footnote-14226333
Ref: Emulating numeric types-Footnote-24226652
Node: With Statement Context Managers4226881
Ref: reference/datamodel context-managers4227031
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Ref: reference/datamodel with-statement-context-managers4227031
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Ref: reference/datamodel object __enter__4227794
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Ref: With Statement Context Managers-Footnote-14228932
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Ref: Awaitable Objects-Footnote-14233041
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Ref: reference/datamodel id74233211
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Ref: reference/datamodel coroutine send4234081
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Ref: reference/datamodel coroutine throw4234620
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Ref: reference/datamodel coroutine close4235215
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Ref: reference/datamodel asynchronous-iterators4235970
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Ref: reference/datamodel async-context-managers4237289
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Ref: reference/datamodel asynchronous-context-managers4237289
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Ref: reference/datamodel object __aenter__4237594
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Ref: reference/datamodel object __aexit__4237753
Ref: 109b4237753
Node: Execution model4238228
Ref: reference/executionmodel doc4238354
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Ref: reference/executionmodel prog-structure4238585
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Ref: reference/executionmodel structure-of-a-program4238585
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Ref: reference/executionmodel naming-and-binding4239751
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Ref: reference/executionmodel binding-of-names4240032
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Ref: reference/executionmodel restrict-exec4245224
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Ref: Interaction with dynamic features-Footnote-14246991
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Ref: reference/executionmodel id24247225
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Node: The import system4249383
Ref: reference/import doc4249510
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Ref: reference/import importsystem4249510
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Ref: reference/import the-import-system4249510
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Ref: The import system-Footnote-14252160
Ref: The import system-Footnote-24252205
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Node: Packages<2>4252764
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Ref: Namespace packages-Footnote-14257077
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Ref: reference/import id24259815
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Ref: Loading-Footnote-14269046
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Ref: reference/import module-spec4274266
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Node: Import-related module attributes4275105
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Ref: 15fd4275225
Ref: reference/import import-related-module-attributes4275225
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Ref: reference/import __name__4275463
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Ref: reference/import __loader__4275661
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Ref: reference/import __package__4275977
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Ref: reference/import __spec__4276804
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Ref: reference/import __path__4277413
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Ref: Import-related module attributes-Footnote-14278919
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Ref: 16074279187
Ref: reference/import package-path-rules4279187
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Ref: module __path__-Footnote-14280369
Ref: module __path__-Footnote-24280418
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Ref: reference/import module-reprs4280584
Ref: 16084280584
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Ref: 16104295371
Ref: reference/import relativeimports4295371
Ref: 16114295371
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Ref: reference/import id54297408
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Ref: reference/import main-spec4297408
Ref: 16054297408
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Ref: reference/import open-issues4298934
Ref: 16144298934
Ref: Open issues-Footnote-14299570
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Ref: reference/import references4299703
Ref: 16154299703
Ref: References-Footnote-14300936
Ref: References-Footnote-24300988
Ref: References-Footnote-34301037
Ref: References-Footnote-44301086
Ref: References-Footnote-54301135
Ref: References-Footnote-64301184
Ref: References-Footnote-74301233
Ref: References-Footnote-84301282
Ref: References-Footnote-94301331
Ref: References-Footnote-104301380
Node: Expressions4301430
Ref: reference/expressions doc4301559
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Ref: reference/expressions expressions4301559
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Ref: reference/expressions id14301559
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Node: Arithmetic conversions4302419
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Ref: 161a4302503
Ref: reference/expressions conversions4302503
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Node: Atoms4303206
Ref: reference/expressions atoms4303308
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Ref: reference/expressions id24303308
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Ref: 161f4303607
Node: Identifiers Names4304034
Ref: reference/expressions atom-identifiers4304113
Ref: 15104304113
Ref: reference/expressions identifiers-names4304113
Ref: 16204304113
Ref: reference/expressions private-name-mangling4304550
Ref: 16214304550
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Ref: 16224305514
Ref: reference/expressions literals4305514
Ref: 16234305514
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Ref: 16244305622
Node: Parenthesized forms4306329
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Ref: reference/expressions parenthesized-forms4306459
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Ref: reference/expressions grammar-token-parenth-form4306594
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Node: Displays for lists sets and dictionaries4307358
Ref: reference/expressions comprehensions4307490
Ref: 16284307490
Ref: reference/expressions displays-for-lists-sets-and-dictionaries4307490
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Ref: reference/expressions grammar-token-comprehension4307936
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Ref: reference/expressions grammar-token-comp-for4307990
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Ref: reference/expressions grammar-token-comp-if4308108
Ref: 162d4308108
Ref: Displays for lists sets and dictionaries-Footnote-14310289
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Ref: reference/expressions list-displays4310463
Ref: 162e4310463
Ref: reference/expressions lists4310463
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Ref: reference/expressions set4311145
Ref: 16314311145
Ref: reference/expressions set-displays4311145
Ref: 16324311145
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Ref: reference/expressions dict4311969
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Ref: reference/expressions dictionary-displays4311969
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Ref: reference/expressions grammar-token-key-datum-list4312194
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Ref: reference/expressions grammar-token-dict-comprehension4312324
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Ref: Dictionary displays-Footnote-14314137
Ref: Dictionary displays-Footnote-24314186
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Ref: reference/expressions genexpr4314352
Ref: 163a4314352
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Ref: 163b4314485
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Ref: reference/expressions yieldexpr4316517
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Ref: 163f4316621
Ref: Yield expressions-Footnote-14321521
Ref: Yield expressions-Footnote-24321570
Ref: Yield expressions-Footnote-34321619
Ref: Yield expressions-Footnote-44321668
Ref: Yield expressions-Footnote-54321717
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Ref: reference/expressions generator-iterator-methods4321863
Ref: 16434321863
Ref: reference/expressions generator-methods4321863
Ref: 15cb4321863
Ref: reference/expressions generator __next__4322205
Ref: 140e4322205
Ref: reference/expressions generator send4322968
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Ref: reference/expressions generator throw4323550
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Ref: reference/expressions generator close4324036
Ref: 15d04324036
Node: Examples4324621
Ref: reference/expressions examples4324759
Ref: 16444324759
Node: Asynchronous generator functions4325818
Ref: reference/expressions asynchronous-generator-functions4325969
Ref: 16414325969
Ref: reference/expressions id34325969
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Ref: Asynchronous generator functions-Footnote-14329035
Node: Asynchronous generator-iterator methods4329114
Ref: reference/expressions asynchronous-generator-iterator-methods4329248
Ref: 16474329248
Ref: reference/expressions asynchronous-generator-methods4329248
Ref: 16484329248
Ref: reference/expressions agen __anext__4329490
Ref: 16464329490
Ref: reference/expressions agen asend4330421
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Ref: reference/expressions agen athrow4331284
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Ref: reference/expressions agen aclose4331972
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Node: Primaries4332986
Ref: reference/expressions id44333082
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Ref: reference/expressions primaries4333082
Ref: 164a4333082
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Ref: 164b4333204
Node: Attribute references4333350
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Ref: 164c4333438
Ref: reference/expressions id54333438
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Ref: 164e4333567
Node: Subscriptions4334146
Ref: reference/expressions id64334251
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Ref: reference/expressions subscriptions4334251
Ref: 158e4334251
Ref: reference/expressions grammar-token-subscription4334424
Ref: 16504334424
Node: Slicings4336172
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Ref: reference/expressions slicings4336262
Ref: 16524336262
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Ref: 16534336511
Ref: reference/expressions grammar-token-slice-list4336560
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Ref: reference/expressions grammar-token-slice-item4336617
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Ref: reference/expressions grammar-token-proper-slice4336665
Ref: 16564336665
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Ref: 16574336736
Ref: reference/expressions grammar-token-upper-bound4336769
Ref: 16584336769
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Ref: 16594336802
Node: Calls4338020
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Ref: reference/expressions id84338088
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Ref: reference/expressions grammar-token-starred-and-keywords4338723
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Ref: Calls-Footnote-14345029
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Ref: reference/expressions await4345187
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Ref: reference/expressions await-expression4345187
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Node: The power operator4345434
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Ref: 16694345770
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Ref: reference/expressions unary4347053
Ref: 166a4347053
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Ref: 166d4348127
Ref: reference/expressions binary-arithmetic-operations4348127
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Ref: reference/expressions grammar-token-a-expr4348627
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Ref: Binary arithmetic operations-Footnote-14351998
Ref: Binary arithmetic operations-Footnote-24352615
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Ref: reference/expressions shifting4353040
Ref: 16724353040
Ref: reference/expressions shifting-operations4353040
Ref: 16734353040
Ref: reference/expressions grammar-token-shift-expr4353170
Ref: 16744353170
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Ref: reference/expressions binary-bitwise-operations4353772
Ref: 16754353772
Ref: reference/expressions bitwise4353772
Ref: 16764353772
Ref: reference/expressions grammar-token-and-expr4353907
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Ref: reference/expressions grammar-token-xor-expr4353962
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Ref: reference/expressions grammar-token-or-expr4354013
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Node: Comparisons4354697
Ref: reference/expressions comparisons4354817
Ref: 167a4354817
Ref: reference/expressions id114354817
Ref: 167b4354817
Ref: reference/expressions grammar-token-comparison4355112
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Ref: reference/expressions grammar-token-comp-operator4355168
Ref: 167d4355168
Node: Value comparisons4356258
Ref: reference/expressions value-comparisons4356358
Ref: 167e4356358
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Ref: reference/expressions not-in4364207
Ref: 159b4364207
Ref: Value comparisons-Footnote-14364245
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Ref: 159c4365539
Ref: reference/expressions membership-test-operations4365539
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Ref: reference/expressions is4367433
Ref: 15514367433
Node: Identity comparisons4367433
Ref: reference/expressions identity-comparisons4367536
Ref: 16804367536
Ref: reference/expressions is-not4367536
Ref: 16814367536
Ref: reference/expressions booleans4367882
Ref: 16824367882
Ref: reference/expressions and4367882
Ref: 16834367882
Ref: reference/expressions or4367882
Ref: 16844367882
Ref: Identity comparisons-Footnote-14367920
Node: Boolean operations4368227
Ref: reference/expressions boolean-operations4368347
Ref: 16854368347
Ref: reference/expressions not4368347
Ref: 16864368347
Ref: reference/expressions grammar-token-or-test4368400
Ref: 16874368400
Ref: reference/expressions grammar-token-and-test4368451
Ref: 16884368451
Ref: reference/expressions grammar-token-not-test4368504
Ref: 16894368504
Node: Assignment expressions<2>4369947
Ref: reference/expressions assignment-expressions4370079
Ref: 168a4370079
Ref: reference/expressions grammar-token-assignment-expression4370140
Ref: 168b4370140
Ref: Assignment expressions<2>-Footnote-14370788
Node: Conditional expressions4370837
Ref: reference/expressions conditional-expressions4370958
Ref: 168d4370958
Ref: reference/expressions if-expr4370958
Ref: 168e4370958
Ref: reference/expressions grammar-token-conditional-expression4371021
Ref: 168f4371021
Ref: reference/expressions grammar-token-expression4371094
Ref: 168c4371094
Ref: reference/expressions lambdas4371550
Ref: 16904371550
Ref: Conditional expressions-Footnote-14371588
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Ref: reference/expressions id144371749
Ref: 16914371749
Ref: reference/expressions lambda4371749
Ref: cf94371749
Ref: reference/expressions grammar-token-lambda-expr4371780
Ref: 16924371780
Node: Expression lists4372314
Ref: reference/expressions expression-lists4372419
Ref: 16934372419
Ref: reference/expressions exprlists4372419
Ref: 7404372419
Ref: reference/expressions grammar-token-expression-list4372468
Ref: 16424372468
Ref: reference/expressions grammar-token-starred-list4372531
Ref: 16944372531
Ref: reference/expressions grammar-token-starred-expression4372598
Ref: 16954372598
Ref: reference/expressions grammar-token-starred-item4372674
Ref: 16964372674
Ref: Expression lists-Footnote-14373642
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Ref: reference/expressions evalorder4373808
Ref: 16974373808
Ref: reference/expressions evaluation-order4373808
Ref: 16984373808
Node: Operator precedence4374323
Ref: reference/expressions operator-precedence4374415
Ref: 16994374415
Ref: reference/expressions operator-summary4374415
Ref: 169a4374415
Ref: Operator precedence-Footnote-14378914
Ref: Operator precedence-Footnote-24379067
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Ref: reference/simple_stmts doc4379296
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Ref: reference/simple_stmts simple4379296
Ref: 169c4379296
Ref: reference/simple_stmts simple-statements4379296
Ref: 169d4379296
Ref: reference/simple_stmts grammar-token-simple-stmt4379520
Ref: 169e4379520
Node: Expression statements4380465
Ref: reference/simple_stmts expression-statements4380570
Ref: 169f4380570
Ref: reference/simple_stmts exprstmts4380570
Ref: 16a04380570
Ref: reference/simple_stmts grammar-token-expression-stmt4380960
Ref: 16a14380960
Node: Assignment statements4381387
Ref: reference/simple_stmts assignment4381521
Ref: 16a24381521
Ref: reference/simple_stmts assignment-statements4381521
Ref: 16a34381521
Ref: reference/simple_stmts grammar-token-assignment-stmt4381692
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Ref: reference/simple_stmts grammar-token-target-list4381776
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Ref: reference/simple_stmts grammar-token-target4381828
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Ref: reference/simple_stmts attr-target-note4385469
Ref: 16a74385469
Ref: Assignment statements-Footnote-14389526
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Ref: 16a84389704
Ref: reference/simple_stmts augmented-assignment-statements4389704
Ref: 16a94389704
Ref: reference/simple_stmts grammar-token-augmented-assignment-stmt4389901
Ref: 16aa4389901
Ref: reference/simple_stmts grammar-token-augtarget4389989
Ref: 16ab4389989
Ref: reference/simple_stmts grammar-token-augop4390075
Ref: 16ac4390075
Node: Annotated assignment statements4391817
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Ref: 16ad4391946
Ref: reference/simple_stmts annotated-assignment-statements4391946
Ref: 16ae4391946
Ref: reference/simple_stmts grammar-token-annotated-assignment-stmt4392181
Ref: 16af4392181
Ref: Annotated assignment statements-Footnote-14394128
Ref: Annotated assignment statements-Footnote-24394177
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Ref: reference/simple_stmts the-assert-statement4394357
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Ref: 16b14394507
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Ref: reference/simple_stmts the-pass-statement4395723
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Ref: reference/simple_stmts grammar-token-pass-stmt4395782
Ref: 16b34395782
Node: The del statement<2>4396133
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Ref: reference/simple_stmts grammar-token-del-stmt4396320
Ref: 16b54396320
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Ref: reference/simple_stmts the-return-statement4397372
Ref: 16b64397372
Ref: reference/simple_stmts grammar-token-return-stmt4397435
Ref: 16b74397435
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Ref: reference/simple_stmts yield4398690
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Ref: reference/simple_stmts grammar-token-yield-stmt4398751
Ref: 16b94398751
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Ref: 16bb4399776
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Ref: 16bd4403532
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Ref: 16bf4404328
Ref: reference/simple_stmts import4404794
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Ref: reference/simple_stmts grammar-token-relative-module4405515
Ref: 16c34405515
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Ref: reference/simple_stmts future-statements4410838
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Ref: reference/simple_stmts grammar-token-feature4411640
Ref: 16c74411640
Ref: Future statements-Footnote-14414357
Ref: Future statements-Footnote-24414406
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Ref: reference/simple_stmts the-global-statement4414589
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Ref: 16c94414654
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Ref: The nonlocal statement-Footnote-14417352
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Ref: reference/compound_stmts compound-statements4417541
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Ref: reference/compound_stmts grammar-token-compound-stmt4419311
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Ref: reference/compound_stmts grammar-token-stmt-list4419801
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Ref: 13674420327
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Ref: 13614421420
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Ref: cfa4422307
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Ref: reference/compound_stmts grammar-token-try2-stmt4425784
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Ref: 7da4431058
Ref: The try statement-Footnote-14431094
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Ref: reference/compound_stmts grammar-token-with-item4431857
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Ref: 13904434712
Ref: The with statement-Footnote-14434748
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Ref: reference/compound_stmts function-definitions4434926
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Ref: reference/compound_stmts grammar-token-parameter-list4435365
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Ref: reference/compound_stmts grammar-token-parameter-list-no-posonly4435540
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Ref: reference/compound_stmts grammar-token-parameter-list-starargs4435701
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Ref: reference/compound_stmts grammar-token-funcname4435984
Ref: 16ea4435984
Ref: Function definitions-Footnote-14442115
Ref: Function definitions-Footnote-24442313
Ref: Function definitions-Footnote-34442362
Ref: Function definitions-Footnote-44442411
Ref: Function definitions-Footnote-54442460
Ref: Function definitions-Footnote-64442509
Ref: Function definitions-Footnote-74442558
Node: Class definitions4442607
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Ref: reference/compound_stmts class-definitions4442731
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Ref: reference/compound_stmts grammar-token-inheritance4442955
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Ref: 16ef4443000
Ref: Class definitions-Footnote-14445897
Ref: Class definitions-Footnote-24446085
Ref: Class definitions-Footnote-34446134
Ref: Class definitions-Footnote-44446183
Ref: Class definitions-Footnote-54446232
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Ref: reference/compound_stmts grammar-token-async-for-stmt4447796
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Ref: The async with statement-Footnote-14450043
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Ref: Full Grammar specification-Footnote-14489362
Ref: Full Grammar specification-Footnote-24489433
Ref: Full Grammar specification-Footnote-34489505
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Ref: The Python Standard Library-Footnote-14492477
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Ref: 3044808402
Ref: library/exceptions OSError errno4809439
Ref: 184b4809439
Ref: library/exceptions OSError winerror4809531
Ref: 184c4809531
Ref: library/exceptions OSError strerror4810110
Ref: 184d4810110
Ref: library/exceptions OSError filename4810346
Ref: 184e4810346
Ref: library/exceptions OSError filename24810375
Ref: 184f4810375
Ref: library/exceptions OverflowError4811353
Ref: a414811353
Ref: library/exceptions RecursionError4811845
Ref: 7274811845
Ref: library/exceptions ReferenceError4812167
Ref: f0f4812167
Ref: library/exceptions RuntimeError4812493
Ref: 3dc4812493
Ref: library/exceptions StopIteration4812695
Ref: 5824812695
Ref: library/exceptions StopAsyncIteration4814026
Ref: 114a4814026
Ref: library/exceptions SyntaxError4814218
Ref: 55a4814218
Ref: library/exceptions SyntaxError filename4814740
Ref: 18504814740
Ref: library/exceptions SyntaxError lineno4814832
Ref: 18514814832
Ref: library/exceptions SyntaxError offset4815006
Ref: 18524815006
Ref: library/exceptions SyntaxError text4815192
Ref: 18534815192
Ref: library/exceptions IndentationError4815589
Ref: f394815589
Ref: library/exceptions TabError4815742
Ref: f384815742
Ref: library/exceptions SystemError4815903
Ref: 6f24815903
Ref: library/exceptions SystemExit4816546
Ref: 6f34816546
Ref: library/exceptions SystemExit code4817842
Ref: 18554817842
Ref: library/exceptions TypeError4817984
Ref: 1fe4817984
Ref: library/exceptions UnboundLocalError4818813
Ref: f374818813
Ref: library/exceptions UnicodeError4819031
Ref: d034819031
Ref: library/exceptions UnicodeError encoding4819392
Ref: 18564819392
Ref: library/exceptions UnicodeError reason4819481
Ref: 18574819481
Ref: library/exceptions UnicodeError object4819566
Ref: 18584819566
Ref: library/exceptions UnicodeError start4819662
Ref: 18594819662
Ref: library/exceptions UnicodeError end4819754
Ref: 185a4819754
Ref: library/exceptions UnicodeEncodeError4819850
Ref: 32a4819850
Ref: library/exceptions UnicodeDecodeError4820002
Ref: 32b4820002
Ref: library/exceptions UnicodeTranslateError4820154
Ref: 185b4820154
Ref: library/exceptions ValueError4820312
Ref: 16d4820312
Ref: library/exceptions ZeroDivisionError4820564
Ref: 1fa4820564
Ref: library/exceptions EnvironmentError4820921
Ref: a744820921
Ref: library/exceptions IOError4820954
Ref: a734820954
Ref: library/exceptions WindowsError4820978
Ref: a754820978
Ref: Concrete exceptions-Footnote-14821104
Ref: Concrete exceptions-Footnote-24821153
Node: OS exceptions4821202
Ref: library/exceptions os-exceptions4821271
Ref: 184a4821271
Ref: library/exceptions BlockingIOError4821432
Ref: a784821432
Ref: library/exceptions BlockingIOError characters_written4821788
Ref: 185c4821788
Ref: library/exceptions ChildProcessError4822043
Ref: a794822043
Ref: library/exceptions ConnectionError4822182
Ref: 7d74822182
Ref: library/exceptions BrokenPipeError4822430
Ref: a7e4822430
Ref: library/exceptions ConnectionAbortedError4822729
Ref: a7f4822729
Ref: library/exceptions ConnectionRefusedError4822931
Ref: a804822931
Ref: library/exceptions ConnectionResetError4823133
Ref: a814823133
Ref: library/exceptions FileExistsError4823316
Ref: a394823316
Ref: library/exceptions FileNotFoundError4823472
Ref: 8ad4823472
Ref: library/exceptions InterruptedError4823624
Ref: 74c4823624
Ref: library/exceptions IsADirectoryError4824030
Ref: a7a4824030
Ref: library/exceptions NotADirectoryError4824209
Ref: a7b4824209
Ref: library/exceptions PermissionError4824574
Ref: 6f64824574
Ref: library/exceptions ProcessLookupError4824792
Ref: a7c4824792
Ref: library/exceptions TimeoutError4824924
Ref: a7d4824924
Ref: OS exceptions-Footnote-14825261
Ref: OS exceptions-Footnote-24825310
Node: Warnings4825359
Ref: library/exceptions warning-categories-as-exceptions4825479
Ref: 185d4825479
Ref: library/exceptions warnings4825479
Ref: 185e4825479
Ref: library/exceptions Warning4825640
Ref: 18604825640
Ref: library/exceptions UserWarning4825705
Ref: 18614825705
Ref: library/exceptions DeprecationWarning4825787
Ref: 15a4825787
Ref: library/exceptions PendingDeprecationWarning4826179
Ref: 15c4826179
Ref: library/exceptions SyntaxWarning4826751
Ref: 2c94826751
Ref: library/exceptions RuntimeWarning4826833
Ref: 3e24826833
Ref: library/exceptions FutureWarning4826926
Ref: 4354826926
Ref: library/exceptions ImportWarning4827113
Ref: 6cf4827113
Ref: library/exceptions UnicodeWarning4827337
Ref: e4c4827337
Ref: library/exceptions BytesWarning4827418
Ref: 5b04827418
Ref: library/exceptions ResourceWarning4827537
Ref: 5cb4827537
Ref: Warnings-Footnote-14827809
Ref: Warnings-Footnote-24827858
Ref: Warnings-Footnote-34827907
Node: Exception hierarchy4827956
Ref: library/exceptions exception-hierarchy4828048
Ref: 18624828048
Ref: library/text stringservices4830292
Ref: 17724830292
Node: Text Processing Services4830293
Ref: library/text doc4830438
Ref: 18634830438
Ref: library/text text-processing-services4830438
Ref: 18644830438
Ref: library/text textservices4830438
Ref: 17754830438
Node: string — Common string operations4831226
Ref: library/string doc4831367
Ref: 18664831367
Ref: library/string module-string4831367
Ref: f64831367
Ref: library/string string-common-string-operations4831367
Ref: 18674831367
Ref: string — Common string operations-Footnote-14831811
Node: String constants4831876
Ref: library/string string-constants4831997
Ref: 18684831997
Ref: library/string string ascii_letters4832091
Ref: d244832091
Ref: library/string string ascii_lowercase4832290
Ref: 18694832290
Ref: library/string string ascii_uppercase4832450
Ref: 186a4832450
Ref: library/string string digits4832610
Ref: 186b4832610
Ref: library/string string hexdigits4832672
Ref: 186c4832672
Ref: library/string string octdigits4832749
Ref: 186d4832749
Ref: library/string string punctuation4832812
Ref: 186e4832812
Ref: library/string string printable4832987
Ref: 186f4832987
Ref: library/string string whitespace4833215
Ref: 18704833215
Node: Custom String Formatting4833421
Ref: library/string custom-string-formatting4833571
Ref: 18714833571
Ref: library/string string-formatting4833571
Ref: 17744833571
Ref: library/string string Formatter4834018
Ref: 8a34834018
Ref: library/string string Formatter format4834119
Ref: 5874834119
Ref: library/string string Formatter vformat4834480
Ref: 18724834480
Ref: library/string string Formatter parse4835191
Ref: 18734835191
Ref: library/string string Formatter get_field4835947
Ref: 18744835947
Ref: library/string string Formatter get_value4836496
Ref: 18754836496
Ref: library/string string Formatter check_unused_args4837732
Ref: 18764837732
Ref: library/string string Formatter format_field4838336
Ref: 18774838336
Ref: library/string string Formatter convert_field4838562
Ref: 18784838562
Ref: Custom String Formatting-Footnote-14838937
Ref: Custom String Formatting-Footnote-24838986
Node: Format String Syntax4839035
Ref: library/string format-string-syntax4839185
Ref: 18794839185
Ref: library/string formatstrings4839185
Ref: de04839185
Ref: library/string grammar-token-replacement-field4839986
Ref: 187a4839986
Ref: library/string grammar-token-field-name4840074
Ref: 187b4840074
Ref: library/string grammar-token-arg-name4840161
Ref: 187c4840161
Ref: library/string grammar-token-attribute-name4840215
Ref: 187d4840215
Ref: library/string grammar-token-element-index4840258
Ref: 187e4840258
Ref: library/string grammar-token-index-string4840312
Ref: 187f4840312
Ref: library/string grammar-token-conversion4840380
Ref: 18804840380
Ref: library/string grammar-token-format-spec4840428
Ref: 18814840428
Node: Format Specification Mini-Language4844425
Ref: library/string format-specification-mini-language4844540
Ref: 18834844540
Ref: library/string formatspec4844540
Ref: 5d94844540
Ref: library/string id14845437
Ref: 18844845437
Ref: library/string grammar-token-fill4845530
Ref: 18854845530
Ref: library/string grammar-token-align4845571
Ref: 18864845571
Ref: library/string grammar-token-sign4845618
Ref: 18874845618
Ref: library/string grammar-token-width4845659
Ref: 18884845659
Ref: library/string grammar-token-grouping-option4845691
Ref: 18894845691
Ref: library/string grammar-token-precision4845726
Ref: 188a4845726
Ref: library/string grammar-token-type4845758
Ref: 188b4845758
Ref: Format Specification Mini-Language-Footnote-14858638
Ref: Format Specification Mini-Language-Footnote-24858687
Node: Format examples4858736
Ref: library/string format-examples4858851
Ref: 188c4858851
Ref: library/string formatexamples4858851
Ref: 18824858851
Node: Template strings4863379
Ref: library/string id24863521
Ref: 188d4863521
Ref: library/string template-strings4863521
Ref: 17934863521
Ref: library/string string Template4864982
Ref: 4f14864982
Ref: library/string string Template substitute4865102
Ref: 14334865102
Ref: library/string string Template safe_substitute4865587
Ref: 14344865587
Ref: library/string string Template template4866624
Ref: 188e4866624
Ref: Template strings-Footnote-14870400
Ref: Template strings-Footnote-24870449
Node: Helper functions4870500
Ref: library/string helper-functions4870613
Ref: 188f4870613
Ref: library/string string capwords4870664
Ref: 18904870664
Node: re — Regular expression operations4871150
Ref: library/re doc4871340
Ref: 18914871340
Ref: library/re module-re4871340
Ref: dd4871340
Ref: library/re re-regular-expression-operations4871340
Ref: 18924871340
Ref: re — Regular expression operations-Footnote-14873914
Ref: re — Regular expression operations-Footnote-24873975
Node: Regular Expression Syntax4874015
Ref: library/re re-syntax4874137
Ref: 18934874137
Ref: library/re regular-expression-syntax4874137
Ref: 18944874137
Ref: Regular Expression Syntax-Footnote-14897750
Node: Module Contents4897792
Ref: library/re contents-of-module-re4897949
Ref: 189f4897949
Ref: library/re module-contents4897949
Ref: 18a04897949
Ref: library/re re compile4898364
Ref: 54d4898364
Ref: library/re re A4899492
Ref: 18994899492
Ref: library/re re ASCII4899507
Ref: 4cf4899507
Ref: library/re re DEBUG4900136
Ref: 18a44900136
Ref: library/re re I4900251
Ref: 189a4900251
Ref: library/re re IGNORECASE4900266
Ref: 18a54900266
Ref: library/re re L4901255
Ref: 189b4901255
Ref: library/re re LOCALE4901270
Ref: 4d04901270
Ref: library/re re M4902211
Ref: 189c4902211
Ref: library/re re MULTILINE4902226
Ref: 18984902226
Ref: library/re re S4902811
Ref: 189d4902811
Ref: library/re re DOTALL4902826
Ref: 18974902826
Ref: library/re re X4903062
Ref: 189e4903062
Ref: library/re re VERBOSE4903077
Ref: 18a64903077
Ref: library/re re search4904093
Ref: c824904093
Ref: library/re re match4904497
Ref: c834904497
Ref: library/re re fullmatch4905148
Ref: 9824905148
Ref: library/re re split4905477
Ref: 4d14905477
Ref: library/re re findall4907346
Ref: a444907346
Ref: library/re re finditer4908377
Ref: 18a84908377
Ref: library/re re sub4908815
Ref: 57a4908815
Ref: library/re re subn4911996
Ref: 8234911996
Ref: library/re re escape4912332
Ref: 5904912332
Ref: library/re re purge4913820
Ref: 18a94913820
Ref: library/re re error4913889
Ref: 8244913889
Ref: library/re re error msg4914322
Ref: 8254914322
Ref: library/re re error pattern4914389
Ref: 8264914389
Ref: library/re re error pos4914461
Ref: 8274914461
Ref: library/re re error lineno4914576
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Ref: library/re re error colno4914668
Ref: 8294914668
Node: Regular Expression Objects4914820
Ref: library/re re-objects4914965
Ref: 9834914965
Ref: library/re regular-expression-objects4914965
Ref: 18aa4914965
Ref: library/re re Pattern search4915119
Ref: 18a34915119
Ref: library/re re Pattern match4916583
Ref: 18a24916583
Ref: library/re re Pattern fullmatch4917442
Ref: 18ab4917442
Ref: library/re re Pattern split4918239
Ref: 18ac4918239
Ref: library/re re Pattern findall4918373
Ref: 18ad4918373
Ref: library/re re Pattern finditer4918634
Ref: 18ae4918634
Ref: library/re re Pattern sub4918898
Ref: 18af4918898
Ref: library/re re Pattern subn4919031
Ref: 18b04919031
Ref: library/re re Pattern flags4919166
Ref: 18b14919166
Ref: library/re re Pattern groups4919433
Ref: 18b24919433
Ref: library/re re Pattern groupindex4919517
Ref: 18b34919517
Ref: library/re re Pattern pattern4919731
Ref: 18b44919731
Node: Match Objects4919990
Ref: library/re id24920147
Ref: 18b54920147
Ref: library/re match-objects4920147
Ref: 9844920147
Ref: library/re re Match expand4920560
Ref: 18b64920560
Ref: library/re re Match group4921082
Ref: 18b74921082
Ref: library/re re Match __getitem__4923350
Ref: 18b84923350
Ref: library/re re Match groups4923825
Ref: 18b94923825
Ref: library/re re Match groupdict4924671
Ref: 18ba4924671
Ref: library/re re Match start4925138
Ref: 18bb4925138
Ref: library/re re Match end4925172
Ref: 18bc4925172
Ref: library/re re Match span4926219
Ref: 18bd4926219
Ref: library/re re Match pos4926472
Ref: 18be4926472
Ref: library/re re Match endpos4926732
Ref: 18bf4926732
Ref: library/re re Match lastindex4926986
Ref: 18c04926986
Ref: library/re re Match lastgroup4927385
Ref: 18c14927385
Ref: library/re re Match re4927558
Ref: 18c24927558
Ref: library/re re Match string4927725
Ref: 18c34927725
Node: Regular Expression Examples4927963
Ref: library/re re-examples4928085
Ref: cbf4928085
Ref: library/re regular-expression-examples4928085
Ref: 18c44928085
Node: Checking for a Pair4928429
Ref: library/re checking-for-a-pair4928537
Ref: 18c54928537
Node: Simulating scanf4930634
Ref: library/re simulating-scanf4930766
Ref: 18c64930766
Node: search vs match4932834
Ref: library/re id34932965
Ref: 18c74932965
Ref: library/re search-vs-match4932965
Ref: 18a74932965
Node: Making a Phonebook4934179
Ref: library/re making-a-phonebook4934306
Ref: 18c84934306
Node: Text Munging4936485
Ref: library/re text-munging4936616
Ref: 18c94936616
Node: Finding all Adverbs4937440
Ref: library/re finding-all-adverbs4937592
Ref: 18ca4937592
Node: Finding all Adverbs and their Positions4938049
Ref: library/re finding-all-adverbs-and-their-positions4938208
Ref: 18cb4938208
Node: Raw String Notation4938912
Ref: library/re raw-string-notation4939071
Ref: 18cc4939071
Node: Writing a Tokenizer4939998
Ref: library/re writing-a-tokenizer4940109
Ref: 18cd4940109
Ref: library/re frie094943480
Ref: 18954943480
Ref: Writing a Tokenizer-Footnote-14943760
Node: difflib — Helpers for computing deltas4943815
Ref: library/difflib doc4944008
Ref: 18ce4944008
Ref: library/difflib difflib-helpers-for-computing-deltas4944008
Ref: 18cf4944008
Ref: library/difflib module-difflib4944008
Ref: 364944008
Ref: library/difflib difflib Differ4946504
Ref: 18d04946504
Ref: library/difflib difflib HtmlDiff4947631
Ref: 18d14947631
Ref: library/difflib difflib HtmlDiff __init__4948001
Ref: 18d24948001
Ref: library/difflib difflib HtmlDiff make_file4948814
Ref: 7bc4948814
Ref: library/difflib difflib HtmlDiff make_table4950497
Ref: 18d44950497
Ref: library/difflib difflib context_diff4951079
Ref: 18d54951079
Ref: library/difflib difflib get_close_matches4953021
Ref: 18d94953021
Ref: library/difflib difflib ndiff4954185
Ref: 18d34954185
Ref: library/difflib difflib restore4955835
Ref: 18dc4955835
Ref: library/difflib difflib unified_diff4956578
Ref: 18de4956578
Ref: library/difflib difflib diff_bytes4958497
Ref: 7bd4958497
Ref: library/difflib difflib IS_LINE_JUNK4959389
Ref: 18da4959389
Ref: library/difflib difflib IS_CHARACTER_JUNK4959691
Ref: 18db4959691
Ref: difflib — Helpers for computing deltas-Footnote-14960351
Ref: difflib — Helpers for computing deltas-Footnote-24960417
Ref: difflib — Helpers for computing deltas-Footnote-34960506
Node: SequenceMatcher Objects4960538
Ref: library/difflib sequence-matcher4960671
Ref: 18df4960671
Ref: library/difflib sequencematcher-objects4960671
Ref: 18e04960671
Ref: library/difflib difflib SequenceMatcher4960797
Ref: a304960797
Ref: library/difflib difflib SequenceMatcher set_seqs4962320
Ref: 18e14962320
Ref: library/difflib difflib SequenceMatcher set_seq14962738
Ref: 18e34962738
Ref: library/difflib difflib SequenceMatcher set_seq24962881
Ref: 18e24962881
Ref: library/difflib difflib SequenceMatcher find_longest_match4963024
Ref: 10414963024
Ref: library/difflib difflib SequenceMatcher get_matching_blocks4965181
Ref: 18e44965181
Ref: library/difflib difflib SequenceMatcher get_opcodes4966098
Ref: 18e54966098
Ref: library/difflib difflib SequenceMatcher get_grouped_opcodes4968085
Ref: 18e64968085
Ref: library/difflib difflib SequenceMatcher ratio4968517
Ref: 18e74968517
Ref: library/difflib difflib SequenceMatcher quick_ratio4969540
Ref: 18e84969540
Ref: library/difflib difflib SequenceMatcher real_quick_ratio4969660
Ref: 18e94969660
Node: SequenceMatcher Examples4970171
Ref: library/difflib id14970327
Ref: 18ea4970327
Ref: library/difflib sequencematcher-examples4970327
Ref: 18eb4970327
Ref: SequenceMatcher Examples-Footnote-14972032
Node: Differ Objects4972085
Ref: library/difflib differ-objects4972232
Ref: 18ec4972232
Ref: library/difflib id24972232
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Ref: library/difflib difflib Differ compare4973638
Ref: 18dd4973638
Node: Differ Example4974162
Ref: library/difflib differ-example4974320
Ref: 18ee4974320
Ref: library/difflib differ-examples4974320
Ref: 18ef4974320
Node: A command-line interface to difflib4976578
Ref: library/difflib a-command-line-interface-to-difflib4976713
Ref: 18f04976713
Ref: library/difflib difflib-interface4976713
Ref: 18d84976713
Node: textwrap — Text wrapping and filling4979468
Ref: library/textwrap doc4979657
Ref: 18f14979657
Ref: library/textwrap module-textwrap4979657
Ref: 10a4979657
Ref: library/textwrap textwrap-text-wrapping-and-filling4979657
Ref: 18f24979657
Ref: library/textwrap textwrap wrap4980189
Ref: f864980189
Ref: library/textwrap textwrap fill4980893
Ref: f874980893
Ref: library/textwrap textwrap shorten4981490
Ref: 9d34981490
Ref: library/textwrap textwrap dedent4982733
Ref: 18f84982733
Ref: library/textwrap textwrap indent4983669
Ref: b804983669
Ref: library/textwrap textwrap TextWrapper4985001
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Ref: library/textwrap textwrap TextWrapper width4985677
Ref: 18fa4985677
Ref: library/textwrap textwrap TextWrapper expand_tabs4985999
Ref: 18f54985999
Ref: library/textwrap textwrap TextWrapper tabsize4986202
Ref: 18f44986202
Ref: library/textwrap textwrap TextWrapper replace_whitespace4986490
Ref: 18f74986490
Ref: library/textwrap textwrap TextWrapper drop_whitespace4987452
Ref: 18f64987452
Ref: library/textwrap textwrap TextWrapper initial_indent4987866
Ref: 18fb4987866
Ref: library/textwrap textwrap TextWrapper subsequent_indent4988101
Ref: 18fc4988101
Ref: library/textwrap textwrap TextWrapper fix_sentence_endings4988328
Ref: 18fd4988328
Ref: library/textwrap textwrap TextWrapper break_long_words4989549
Ref: 18f94989549
Ref: library/textwrap textwrap TextWrapper break_on_hyphens4990039
Ref: 18fe4990039
Ref: library/textwrap textwrap TextWrapper max_lines4990571
Ref: 9d14990571
Ref: library/textwrap textwrap TextWrapper placeholder4990816
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Ref: library/textwrap textwrap TextWrapper wrap4991130
Ref: 18f34991130
Ref: library/textwrap textwrap TextWrapper fill4991552
Ref: 18ff4991552
Ref: textwrap — Text wrapping and filling-Footnote-14991739
Node: unicodedata — Unicode Database4991806
Ref: library/unicodedata doc4991997
Ref: 19004991997
Ref: library/unicodedata module-unicodedata4991997
Ref: 1234991997
Ref: library/unicodedata unicodedata-unicode-database4991997
Ref: 19014991997
Ref: library/unicodedata unicodedata lookup4992519
Ref: a9d4992519
Ref: library/unicodedata unicodedata name4992836
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Ref: library/unicodedata unicodedata decimal4993062
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Ref: library/unicodedata unicodedata digit4993305
Ref: 19044993305
Ref: library/unicodedata unicodedata numeric4993543
Ref: cc44993543
Ref: library/unicodedata unicodedata category4993783
Ref: 19054993783
Ref: library/unicodedata unicodedata bidirectional4993908
Ref: 19064993908
Ref: library/unicodedata unicodedata combining4994100
Ref: 19074994100
Ref: library/unicodedata unicodedata east_asian_width4994287
Ref: 19084994287
Ref: library/unicodedata unicodedata mirrored4994420
Ref: 19094994420
Ref: library/unicodedata unicodedata decomposition4994678
Ref: 190a4994678
Ref: library/unicodedata unicodedata normalize4994893
Ref: 11e44994893
Ref: library/unicodedata unicodedata is_normalized4996755
Ref: 3704996755
Ref: library/unicodedata unicodedata unidata_version4997062
Ref: 190b4997062
Ref: library/unicodedata unicodedata ucd_3_2_04997164
Ref: e614997164
Ref: unicodedata — Unicode Database-Footnote-14997943
Ref: unicodedata — Unicode Database-Footnote-24997993
Ref: unicodedata — Unicode Database-Footnote-34998039
Ref: unicodedata — Unicode Database-Footnote-44998115
Node: stringprep — Internet String Preparation4998194
Ref: library/stringprep doc4998382
Ref: 190c4998382
Ref: library/stringprep module-stringprep4998382
Ref: f74998382
Ref: library/stringprep stringprep-internet-string-preparation4998382
Ref: 190d4998382
Ref: library/stringprep stringprep in_table_a15000304
Ref: 190e5000304
Ref: library/stringprep stringprep in_table_b15000441
Ref: 190f5000441
Ref: library/stringprep stringprep map_table_b25000567
Ref: 19105000567
Ref: library/stringprep stringprep map_table_b35000724
Ref: 19115000724
Ref: library/stringprep stringprep in_table_c115000893
Ref: 19125000893
Ref: library/stringprep stringprep in_table_c125001013
Ref: 19135001013
Ref: library/stringprep stringprep in_table_c11_c125001142
Ref: 19145001142
Ref: library/stringprep stringprep in_table_c215001289
Ref: 19155001289
Ref: library/stringprep stringprep in_table_c225001416
Ref: 19165001416
Ref: library/stringprep stringprep in_table_c21_c225001547
Ref: 19175001547
Ref: library/stringprep stringprep in_table_c35001696
Ref: 19185001696
Ref: library/stringprep stringprep in_table_c45001802
Ref: 19195001802
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Ref: 19655047105
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Ref: library/codecs codecs CodecInfo encode5047464
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Ref: library/codecs codecs CodecInfo decode5047491
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Ref: library/codecs codecs CodecInfo incrementalencoder5047869
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Ref: library/codecs codecs CodecInfo streamwriter5048247
Ref: 19705048247
Ref: library/codecs codecs CodecInfo streamreader5048280
Ref: 19715048280
Ref: library/codecs codecs getencoder5048733
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Ref: library/codecs codecs getdecoder5048945
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Ref: 19775049463
Ref: library/codecs codecs getreader5049769
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Ref: library/codecs codecs getwriter5050015
Ref: 19795050015
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Ref: 19805054663
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Ref: codecs — Codec registry and base classes-Footnote-15056028
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Ref: 19645056220
Ref: library/codecs id15056220
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Ref: Error Handlers-Footnote-15064452
Node: Stateless Encoding and Decoding5064501
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Ref: library/codecs codecs Codec encode5064863
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Ref: 19935066697
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Ref: 19965067668
Ref: library/codecs incrementalencoder-objects5067668
Ref: 19975067668
Ref: library/codecs codecs IncrementalEncoder5067967
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Ref: library/codecs codecs IncrementalEncoder encode5068752
Ref: 19945068752
Ref: library/codecs codecs IncrementalEncoder reset5069045
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Ref: library/codecs codecs IncrementalDecoder decode5071109
Ref: 19955071109
Ref: library/codecs codecs IncrementalDecoder reset5071738
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Ref: Encodings and Unicode-Footnote-15089126
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Node: encodings idna — Internationalized Domain Names in Applications5120669
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Ref: library/codecs module-encodings idna5120896
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Ref: library/codecs encodings idna nameprep5123548
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Ref: library/codecs encodings idna ToASCII5123736
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Ref: encodings idna — Internationalized Domain Names in Applications-Footnote-15124043
Ref: encodings idna — Internationalized Domain Names in Applications-Footnote-25124092
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Ref: encodings idna — Internationalized Domain Names in Applications-Footnote-45124190
Ref: encodings idna — Internationalized Domain Names in Applications-Footnote-55124239
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Node: encodings mbcs — Windows ANSI codepage5124398
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Ref: library/datetime datetime datetime __format__5187983
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Ref: datetime Objects-Footnote-15188461
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Ref: library/datetime examples-of-usage-datetime5188628
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Ref: library/datetime datetime time5193299
Ref: 5ed5193299
Ref: library/datetime datetime time min5193964
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Ref: library/datetime datetime time max5194063
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Ref: library/datetime datetime time resolution5194173
Ref: 1a185194173
Ref: library/datetime datetime time hour5194441
Ref: 19d15194441
Ref: library/datetime datetime time minute5194493
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Ref: library/datetime datetime time second5194547
Ref: 19d35194547
Ref: library/datetime datetime time microsecond5194601
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Ref: library/datetime datetime time tzinfo5194665
Ref: 19d55194665
Ref: library/datetime datetime time fold5194816
Ref: 1a195194816
Ref: library/datetime datetime time fromisoformat5196791
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Ref: library/datetime datetime time replace5197701
Ref: 1a1b5197701
Ref: library/datetime datetime time isoformat5198235
Ref: 1a1a5198235
Ref: library/datetime datetime time __str__5200246
Ref: 1a1d5200246
Ref: library/datetime datetime time strftime5200348
Ref: 1a1e5200348
Ref: library/datetime datetime time __format__5200579
Ref: 1a1f5200579
Ref: library/datetime datetime time utcoffset5200941
Ref: 1a1c5200941
Ref: library/datetime datetime time dst5201331
Ref: 1a205201331
Ref: library/datetime datetime time tzname5201710
Ref: 1a215201710
Ref: time Objects-Footnote-15202039
Node: Examples of Usage time5202082
Ref: library/datetime examples-of-usage-time5202153
Ref: 1a225202153
Node: tzinfo Objects5203035
Ref: library/datetime datetime-tzinfo5203170
Ref: 1a235203170
Ref: library/datetime tzinfo-objects5203170
Ref: 1a245203170
Ref: library/datetime datetime tzinfo5203227
Ref: 1805203227
Ref: library/datetime datetime tzinfo utcoffset5204869
Ref: 1a255204869
Ref: library/datetime datetime tzinfo dst5206099
Ref: 1a265206099
Ref: library/datetime datetime tzinfo tzname5208681
Ref: 1a275208681
Ref: library/datetime datetime tzinfo fromutc5210820
Ref: 1a095210820
Ref: tzinfo Objects-Footnote-15223355
Node: timezone Objects5223395
Ref: library/datetime datetime-timezone5223548
Ref: 1a295223548
Ref: library/datetime timezone-objects5223548
Ref: 1a2a5223548
Ref: library/datetime datetime timezone5223968
Ref: ae05223968
Ref: library/datetime datetime timezone utcoffset5224596
Ref: 1a2b5224596
Ref: library/datetime datetime timezone tzname5224986
Ref: 1a2c5224986
Ref: library/datetime datetime timezone dst5225668
Ref: 1a2d5225668
Ref: library/datetime datetime timezone fromutc5225732
Ref: 1a2e5225732
Ref: library/datetime datetime timezone utc5225927
Ref: 1a285225927
Node: strftime and strptime Behavior5226010
Ref: library/datetime strftime-and-strptime-behavior5226140
Ref: 1a2f5226140
Ref: library/datetime strftime-strptime-behavior5226140
Ref: 19f75226140
Node: strftime and strptime Format Codes5228325
Ref: library/datetime strftime-and-strptime-format-codes5228451
Ref: 1a305228451
Node: Technical Detail5238542
Ref: library/datetime technical-detail5238668
Ref: 1a315238668
Ref: Technical Detail-Footnote-15244755
Node: zoneinfo — IANA time zone support5244865
Ref: library/zoneinfo doc5245050
Ref: 1a335245050
Ref: library/zoneinfo module-zoneinfo5245050
Ref: 14e5245050
Ref: library/zoneinfo zoneinfo-iana-time-zone-support5245050
Ref: 1a345245050
Ref: zoneinfo — IANA time zone support-Footnote-15246085
Ref: zoneinfo — IANA time zone support-Footnote-25246134
Ref: zoneinfo — IANA time zone support-Footnote-35246175
Node: Using ZoneInfo5246216
Ref: library/zoneinfo using-zoneinfo5246323
Ref: 1a355246323
Ref: Using ZoneInfo-Footnote-15248271
Node: Data sources5248320
Ref: library/zoneinfo data-sources5248454
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Ref: Data sources-Footnote-15249138
Node: Configuring the data sources5249179
Ref: library/zoneinfo configuring-the-data-sources5249256
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Ref: library/zoneinfo zoneinfo-data-configuration5249256
Ref: 1a395249256
Node: Compile-time configuration5250009
Ref: library/zoneinfo compile-time-configuration5250134
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Ref: library/zoneinfo zoneinfo-data-compile-time-config5250134
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Node: Environment configuration5250868
Ref: library/zoneinfo environment-configuration5251023
Ref: 1a405251023
Ref: library/zoneinfo zoneinfo-data-environment-var5251023
Ref: 1a3c5251023
Ref: library/zoneinfo envvar-PYTHONTZPATH5251342
Ref: 1a415251342
Node: Runtime configuration5252003
Ref: library/zoneinfo runtime-configuration5252123
Ref: 1a435252123
Ref: library/zoneinfo zoneinfo-data-runtime-config5252123
Ref: 1a3d5252123
Node: The ZoneInfo class5252491
Ref: library/zoneinfo the-zoneinfo-class5252623
Ref: 1a445252623
Ref: library/zoneinfo zoneinfo ZoneInfo5252686
Ref: 17f5252686
Ref: library/zoneinfo zoneinfo ZoneInfo from_file5253566
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Ref: library/zoneinfo zoneinfo ZoneInfo no_cache5254095
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Ref: library/zoneinfo zoneinfo ZoneInfo clear_cache5254817
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Ref: library/zoneinfo zoneinfo ZoneInfo key5255627
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Node: String representations5256483
Ref: library/zoneinfo string-representations5256589
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Node: Pickle serialization5257398
Ref: library/zoneinfo pickle-serialization5257504
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Ref: library/zoneinfo pickling5257504
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Node: Functions<2>5259910
Ref: library/zoneinfo functions5260037
Ref: 1a4d5260037
Ref: library/zoneinfo zoneinfo available_timezones5260076
Ref: 103e5260076
Ref: library/zoneinfo zoneinfo reset_tzpath5261052
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Node: Globals5261749
Ref: library/zoneinfo globals5261881
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Ref: library/zoneinfo zoneinfo TZPATH5261916
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Node: Exceptions and warnings5262691
Ref: library/zoneinfo exceptions-and-warnings5262802
Ref: 1a4f5262802
Ref: library/zoneinfo zoneinfo ZoneInfoNotFoundError5262869
Ref: 1a375262869
Ref: library/zoneinfo zoneinfo InvalidTZPathWarning5263100
Ref: 1a425263100
Node: calendar — General calendar-related functions5263277
Ref: library/calendar doc5263459
Ref: 1a505263459
Ref: library/calendar calendar-general-calendar-related-functions5263459
Ref: 1a515263459
Ref: library/calendar module-calendar5263459
Ref: 145263459
Ref: library/calendar tzdata5263459
Ref: 1a525263459
Ref: library/calendar calendar Calendar5264662
Ref: 1a545264662
Ref: library/calendar calendar Calendar iterweekdays5265169
Ref: 1a555265169
Ref: library/calendar calendar Calendar itermonthdates5265418
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Ref: library/calendar calendar Calendar itermonthdays5265790
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Ref: library/calendar calendar Calendar itermonthdays25266175
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Ref: library/calendar calendar Calendar itermonthdays35266525
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Ref: library/calendar calendar Calendar itermonthdays45266905
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Ref: library/calendar calendar Calendar monthdatescalendar5267305
Ref: 1a595267305
Ref: library/calendar calendar Calendar monthdays2calendar5267525
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Ref: library/calendar calendar Calendar monthdayscalendar5267753
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Ref: library/calendar calendar Calendar yeardatescalendar5267940
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Ref: library/calendar calendar Calendar yeardays2calendar5268334
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Ref: library/calendar calendar Calendar yeardayscalendar5268650
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Ref: library/calendar calendar TextCalendar5268935
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Ref: library/calendar calendar TextCalendar formatmonth5269119
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Ref: library/calendar calendar TextCalendar prmonth5269568
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Ref: library/calendar calendar TextCalendar formatyear5269714
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Ref: library/calendar calendar TextCalendar pryear5270251
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Ref: library/calendar calendar HTMLCalendar5270406
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Ref: library/calendar calendar HTMLCalendar formatmonth5270577
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Ref: library/calendar calendar HTMLCalendar formatyear5270827
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Ref: library/calendar calendar HTMLCalendar formatyearpage5271008
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Ref: library/calendar calendar HTMLCalendar cssclasses5271648
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Ref: library/calendar calendar HTMLCalendar cssclass_noday5272062
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Ref: library/calendar calendar HTMLCalendar cssclasses_weekday_head5272221
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Ref: library/calendar calendar HTMLCalendar cssclass_month_head5272434
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Ref: library/calendar calendar HTMLCalendar cssclass_month5272628
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Ref: library/calendar calendar HTMLCalendar cssclass_year5272835
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Ref: library/calendar calendar HTMLCalendar cssclass_year_head5273048
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Ref: library/calendar calendar LocaleTextCalendar5273955
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Ref: library/calendar calendar LocaleHTMLCalendar5274319
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Ref: library/calendar calendar setfirstweekday5275007
Ref: 1a535275007
Ref: library/calendar calendar firstweekday5275433
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Ref: library/calendar calendar isleap5275543
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Ref: library/calendar calendar leapdays5275671
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Ref: library/calendar calendar weekday5275896
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Ref: library/calendar calendar weekheader5276095
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Ref: library/calendar calendar monthrange5276255
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Ref: library/calendar calendar monthcalendar5276424
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Ref: library/calendar calendar prmonth5276705
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Ref: library/calendar calendar month5276837
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Ref: library/calendar calendar prcal5277030
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Ref: library/calendar calendar calendar5277174
Ref: 1a795277174
Ref: library/calendar calendar timegm5277389
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Ref: library/calendar calendar day_name5277865
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Ref: library/calendar calendar day_abbr5277974
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Ref: library/calendar calendar month_name5278095
Ref: 1a7d5278095
Ref: library/calendar calendar month_abbr5278353
Ref: 1a7e5278353
Ref: calendar — General calendar-related functions-Footnote-15278886
Node: collections — Container datatypes5278953
Ref: library/collections doc5279156
Ref: 1a7f5279156
Ref: library/collections collections-container-datatypes5279156
Ref: 1a805279156
Ref: library/collections module-collections5279156
Ref: 1d5279156
Ref: collections — Container datatypes-Footnote-15281386
Node: ChainMap objects5281466
Ref: library/collections chainmap-objects5281578
Ref: 1a825281578
Ref: library/collections collections ChainMap5281965
Ref: 5a45281965
Ref: library/collections collections ChainMap maps5282998
Ref: 1a835282998
Ref: library/collections collections ChainMap new_child5283301
Ref: 9165283301
Ref: library/collections collections ChainMap parents5283939
Ref: 1a845283939
Ref: ChainMap objects-Footnote-15285902
Ref: ChainMap objects-Footnote-25285951
Ref: ChainMap objects-Footnote-35286046
Ref: ChainMap objects-Footnote-45286093
Ref: ChainMap objects-Footnote-55286172
Ref: ChainMap objects-Footnote-65286225
Node: ChainMap Examples and Recipes5286278
Ref: library/collections chainmap-examples-and-recipes5286360
Ref: 1a855286360
Node: Counter objects5289474
Ref: library/collections counter-objects5289608
Ref: 1a865289608
Ref: library/collections collections Counter5290313
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Ref: library/collections collections Counter elements5292283
Ref: d625292283
Ref: library/collections collections Counter most_common5292706
Ref: d615292706
Ref: library/collections collections Counter subtract5293166
Ref: c2c5293166
Ref: library/collections collections Counter fromkeys5293857
Ref: 1a875293857
Ref: library/collections collections Counter update5293986
Ref: 1a885293986
Ref: Counter objects-Footnote-15298372
Ref: Counter objects-Footnote-25298451
Ref: Counter objects-Footnote-35298498
Node: deque objects5298591
Ref: library/collections deque-objects5298728
Ref: 1a895298728
Ref: library/collections collections deque5298781
Ref: 62b5298781
Ref: library/collections collections deque append5300224
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Ref: library/collections collections deque appendleft5300304
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Ref: library/collections collections deque clear5300387
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Ref: library/collections collections deque copy5300486
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Ref: library/collections collections deque count5300590
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Ref: library/collections collections deque extend5300709
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Ref: library/collections collections deque index5301098
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Ref: library/collections collections deque insert5301370
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Ref: library/collections collections deque pop5301615
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Ref: library/collections collections deque popleft5301785
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Ref: library/collections collections deque remove5301958
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Ref: library/collections collections deque reverse5302099
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Ref: library/collections collections deque rotate5302251
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Ref: library/collections collections deque maxlen5302660
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Node: deque Recipes5305311
Ref: library/collections deque-recipes5305374
Ref: 1a935305374
Ref: deque Recipes-Footnote-15307837
Node: defaultdict objects5307898
Ref: library/collections defaultdict-objects5308076
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Ref: library/collections collections defaultdict5308141
Ref: c0c5308141
Ref: library/collections collections defaultdict __missing__5308927
Ref: 1a965308927
Ref: library/collections collections defaultdict default_factory5310116
Ref: 1a955310116
Ref: defaultdict objects-Footnote-15310538
Node: defaultdict Examples5310587
Ref: library/collections defaultdict-examples5310663
Ref: 1a975310663
Node: namedtuple Factory Function for Tuples with Named Fields5313326
Ref: library/collections namedtuple-factory-function-for-tuples-with-named-fields5313510
Ref: 1a985313510
Ref: library/collections collections namedtuple5313891
Ref: 1a15313891
Ref: library/collections collections somenamedtuple _make5317912
Ref: 1a995317912
Ref: library/collections collections somenamedtuple _asdict5318143
Ref: 2e95318143
Ref: library/collections collections somenamedtuple _replace5318829
Ref: 1a9a5318829
Ref: library/collections collections somenamedtuple _fields5319229
Ref: 1a9b5319229
Ref: library/collections collections somenamedtuple _field_defaults5319725
Ref: 1a9c5319725
Node: OrderedDict objects5322493
Ref: library/collections ordereddict-objects5322674
Ref: 1a9d5322674
Ref: library/collections collections OrderedDict5324097
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Ref: library/collections collections OrderedDict popitem5324293
Ref: d4c5324293
Ref: library/collections collections OrderedDict move_to_end5324573
Ref: c2d5324573
Ref: OrderedDict objects-Footnote-15326221
Ref: OrderedDict objects-Footnote-25326306
Ref: OrderedDict objects-Footnote-35326355
Node: OrderedDict Examples and Recipes5326404
Ref: library/collections ordereddict-examples-and-recipes5326492
Ref: 1a9f5326492
Node: UserDict objects5327720
Ref: library/collections userdict-objects5327861
Ref: 1aa05327861
Ref: library/collections collections UserDict5328227
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Ref: library/collections collections UserDict data5328820
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Node: UserList objects5328948
Ref: library/collections userlist-objects5329088
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Ref: library/collections collections UserList5329603
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Ref: library/collections collections UserList data5330208
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Node: UserString objects5331002
Ref: library/collections userstring-objects5331117
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Ref: library/collections collections UserString5331479
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Ref: library/collections collections UserString data5332073
Ref: 1aa55332073
Node: collections abc — Abstract Base Classes for Containers5332373
Ref: library/collections abc doc5332559
Ref: 1aa65332559
Ref: library/collections abc collections-abc-abstract-base-classes-for-containers5332559
Ref: 1aa75332559
Ref: library/collections abc module-collections abc5332559
Ref: 1e5332559
Ref: collections abc — Abstract Base Classes for Containers-Footnote-15333289
Ref: collections abc — Abstract Base Classes for Containers-Footnote-25333365
Node: Collections Abstract Base Classes5333414
Ref: library/collections abc collections-abstract-base-classes5333540
Ref: 15e5333540
Ref: library/collections abc id15333540
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Ref: library/collections abc collections abc Container5342499
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Ref: library/collections abc collections abc Hashable5342611
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Ref: library/collections abc collections abc Sized5342718
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Ref: library/collections abc collections abc Callable5342821
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Ref: library/collections abc collections abc Collection5343409
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Ref: library/collections abc collections abc Iterator5343522
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Ref: library/collections abc collections abc Reversible5343718
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Ref: library/collections abc collections abc Generator5343876
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Ref: library/collections abc collections abc Sequence5344193
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Ref: library/collections abc collections abc MutableSequence5344229
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Ref: library/collections abc collections abc ByteString5344272
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Ref: library/collections abc collections abc Set5345008
Ref: 18105345008
Ref: library/collections abc collections abc MutableSet5345039
Ref: 181b5345039
Ref: library/collections abc collections abc Mapping5345121
Ref: 15f5345121
Ref: library/collections abc collections abc MutableMapping5345156
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Ref: library/collections abc collections abc MappingView5345257
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Ref: library/collections abc collections abc ItemsView5345296
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Ref: library/collections abc collections abc KeysView5345333
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Ref: library/collections abc collections abc ValuesView5345369
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Ref: library/collections abc collections abc Awaitable5345475
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Ref: library/collections abc collections abc Coroutine5346251
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Ref: library/collections abc collections abc AsyncIterable5347145
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Ref: library/collections abc collections abc AsyncIterator5347339
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Ref: library/collections abc collections abc AsyncGenerator5347553
Ref: 62a5347553
Ref: Collections Abstract Base Classes-Footnote-15350612
Ref: Collections Abstract Base Classes-Footnote-25350661
Ref: Collections Abstract Base Classes-Footnote-35350710
Ref: Collections Abstract Base Classes-Footnote-45350759
Ref: Collections Abstract Base Classes-Footnote-55350812
Node: heapq — Heap queue algorithm5350861
Ref: library/heapq doc5351048
Ref: 1aab5351048
Ref: library/heapq heapq-heap-queue-algorithm5351048
Ref: 1aac5351048
Ref: library/heapq module-heapq5351048
Ref: 8d5351048
Ref: library/heapq heapq heappush5352603
Ref: 1aae5352603
Ref: library/heapq heapq heappop5352728
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Ref: library/heapq heapq heappushpop5352992
Ref: 1ab05352992
Ref: library/heapq heapq heapify5353265
Ref: 1aad5353265
Ref: library/heapq heapq heapreplace5353362
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Ref: library/heapq heapq merge5354209
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Ref: library/heapq heapq nlargest5355373
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Ref: library/heapq heapq nsmallest5355771
Ref: 1ab35355771
Ref: heapq — Heap queue algorithm-Footnote-15356640
Node: Basic Examples5356704
Ref: library/heapq basic-examples5356829
Ref: 1ab45356829
Ref: Basic Examples-Footnote-15357796
Node: Priority Queue Implementation Notes5357843
Ref: library/heapq priority-queue-implementation-notes5357983
Ref: 1ab55357983
Ref: Priority Queue Implementation Notes-Footnote-15360919
Node: Theory5360972
Ref: library/heapq theory5361089
Ref: 1ab65361089
Ref: Theory-Footnote-15365249
Node: bisect — Array bisection algorithm5365909
Ref: library/bisect doc5366084
Ref: 1ab75366084
Ref: library/bisect bisect-array-bisection-algorithm5366084
Ref: 1ab85366084
Ref: library/bisect module-bisect5366084
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Ref: library/bisect bisect bisect_left5366781
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Ref: library/bisect bisect bisect_right5367527
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Ref: bisect — Array bisection algorithm-Footnote-15368899
Ref: bisect — Array bisection algorithm-Footnote-25368964
Node: Searching Sorted Lists5369034
Ref: library/bisect searching-sorted-lists5369152
Ref: 1abf5369152
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Ref: library/bisect other-examples5370492
Ref: 1ac05370492
Ref: library/bisect bisect-example5370539
Ref: 1ac15370539
Node: array — Efficient arrays of numeric values5371864
Ref: library/array doc5372036
Ref: 1ac25372036
Ref: library/array array-efficient-arrays-of-numeric-values5372036
Ref: 1ac35372036
Ref: library/array module-array5372036
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Ref: library/array array array5376597
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Ref: library/array array typecodes5377317
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Ref: library/array array array typecode5377835
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Ref: library/array array array append5378033
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Ref: library/array array array frombytes5379933
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Ref: library/array array array index5381068
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Ref: library/array array array tolist5382212
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Ref: array — Efficient arrays of numeric values-Footnote-15383544
Node: weakref — Weak references5383571
Ref: library/weakref doc5383767
Ref: 1ad85383767
Ref: library/weakref module-weakref5383767
Ref: 1315383767
Ref: library/weakref weakref-weak-references5383767
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Ref: library/weakref weakref WeakKeyDictionary keyrefs5392073
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Ref: library/weakref weakref WeakValueDictionary5392176
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Ref: library/weakref weakref WeakValueDictionary valuerefs5392665
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Ref: library/weakref weakref WeakSet5392774
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Ref: library/weakref weakref WeakMethod5392958
Ref: 9f55392958
Ref: library/weakref weakref finalize5393893
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Node: NormalDist Examples and Recipes5697501
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Ref: functools — Higher-order functions and operations on callable objects-Footnote-15776188
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Ref: operator — Standard operators as functions-Footnote-15788580
Node: Mapping Operators to Functions5788647
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Ref: pathlib — Object-oriented filesystem paths-Footnote-15802548
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Ref: library/os path os path lexists5850165
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Ref: library/os path os path ismount5854603
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Ref: library/os path os path join5855491
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Ref: library/os path os path relpath5858436
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Ref: os path — Common pathname manipulations-Footnote-15863273
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Ref: os path — Common pathname manipulations-Footnote-35863406
Node: fileinput — Iterate over lines from multiple input streams5863497
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Ref: library/fileinput fileinput-iterate-over-lines-from-multiple-input-streams5863712
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Ref: library/fileinput fileinput FileInput5868878
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Ref: library/fileinput fileinput hook_compressed5871492
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Ref: library/fileinput fileinput hook_encoded5871989
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Ref: fileinput — Iterate over lines from multiple input streams-Footnote-15872409
Node: stat — Interpreting stat results5872477
Ref: library/stat doc5872693
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Ref: library/stat module-stat5872693
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Ref: library/stat stat-interpreting-stat-results5872693
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Ref: library/stat stat S_ISDIR5873371
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Ref: library/stat stat S_ISCHR5873461
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Ref: library/stat stat S_ISREG5873682
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Ref: library/stat stat S_ISFIFO5873775
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Ref: library/stat stat ST_ATIME5877126
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Ref: library/stat stat S_IRGRP5880190
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Ref: library/stat stat S_IRWXO5880365
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Ref: library/stat stat UF_HIDDEN5881587
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Ref: library/stat stat FILE_ATTRIBUTE_DIRECTORY5882452
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Ref: library/stat stat FILE_ATTRIBUTE_NOT_CONTENT_INDEXED5882653
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Ref: library/stat stat FILE_ATTRIBUTE_NO_SCRUB_DATA5882703
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Ref: library/stat stat FILE_ATTRIBUTE_READONLY5882785
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Ref: library/stat stat FILE_ATTRIBUTE_REPARSE_POINT5882824
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Ref: library/stat stat FILE_ATTRIBUTE_SPARSE_FILE5882868
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Ref: library/stat stat FILE_ATTRIBUTE_SYSTEM5882910
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Ref: library/stat stat FILE_ATTRIBUTE_TEMPORARY5882947
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Ref: library/stat stat FILE_ATTRIBUTE_VIRTUAL5882987
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Ref: library/stat stat IO_REPARSE_TAG_SYMLINK5883257
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Ref: library/stat stat IO_REPARSE_TAG_APPEXECLINK5883337
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Ref: stat — Interpreting stat results-Footnote-15883442
Ref: stat — Interpreting stat results-Footnote-25883505
Node: filecmp — File and Directory Comparisons5883585
Ref: library/filecmp doc5883794
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Ref: library/filecmp filecmp-file-and-directory-comparisons5883794
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Ref: library/filecmp module-filecmp5883794
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Ref: library/filecmp filecmp cmp5884263
Ref: f855884263
Ref: library/filecmp filecmp cmpfiles5885056
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Ref: library/filecmp filecmp clear_cache5886000
Ref: 9345886000
Ref: filecmp — File and Directory Comparisons-Footnote-15886315
Node: The dircmp class5886381
Ref: library/filecmp dircmp-objects5886476
Ref: 1dae5886476
Ref: library/filecmp the-dircmp-class5886476
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Ref: library/filecmp filecmp dircmp5886537
Ref: 9365886537
Ref: library/filecmp filecmp dircmp report5887071
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Ref: library/filecmp filecmp dircmp report_partial_closure5887188
Ref: 1db15887188
Ref: library/filecmp filecmp dircmp report_full_closure5887329
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Ref: library/filecmp filecmp dircmp left5887848
Ref: 1db35887848
Ref: library/filecmp filecmp dircmp right5887904
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Ref: library/filecmp filecmp dircmp left_list5887961
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Ref: library/filecmp filecmp dircmp right_list5888079
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Ref: library/filecmp filecmp dircmp common5888198
Ref: 1db75888198
Ref: library/filecmp filecmp dircmp left_only5888283
Ref: 1db85888283
Ref: library/filecmp filecmp dircmp right_only5888363
Ref: 1db95888363
Ref: library/filecmp filecmp dircmp common_dirs5888444
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Ref: library/filecmp filecmp dircmp common_files5888524
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Ref: library/filecmp filecmp dircmp common_funny5888596
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Ref: library/filecmp filecmp dircmp same_files5888799
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Ref: library/filecmp filecmp dircmp diff_files5888945
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Ref: library/filecmp filecmp dircmp funny_files5889110
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Ref: library/filecmp filecmp dircmp subdirs5889228
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Ref: library/filecmp filecmp DEFAULT_IGNORES5889364
Ref: 9355889364
Node: tempfile — Generate temporary files and directories5890048
Ref: library/tempfile doc5890269
Ref: 1dc15890269
Ref: library/tempfile module-tempfile5890269
Ref: 1035890269
Ref: library/tempfile tempfile-generate-temporary-files-and-directories5890269
Ref: 1dc25890269
Ref: library/tempfile tempfile TemporaryFile5891424
Ref: 1dc35891424
Ref: library/tempfile tempfile NamedTemporaryFile5893477
Ref: e0e5893477
Ref: library/tempfile tempfile SpooledTemporaryFile5894646
Ref: b7e5894646
Ref: library/tempfile tempfile TemporaryDirectory5895877
Ref: c965895877
Ref: library/tempfile tempfile mkstemp5896861
Ref: 1dc45896861
Ref: library/tempfile tempfile mkdtemp5899743
Ref: 1dc55899743
Ref: library/tempfile tempfile gettempdir5900857
Ref: 1dcb5900857
Ref: library/tempfile tempfile gettempdirb5901866
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Ref: library/tempfile tempfile gettempprefix5902005
Ref: 1dc95902005
Ref: library/tempfile tempfile gettempprefixb5902164
Ref: 1dca5902164
Ref: library/tempfile tempfile tempdir5902664
Ref: 1dcc5902664
Ref: tempfile — Generate temporary files and directories-Footnote-15903190
Node: Examples<4>5903257
Ref: library/tempfile examples5903401
Ref: 1dce5903401
Ref: library/tempfile tempfile-examples5903401
Ref: 1dc75903401
Node: Deprecated functions and variables5904319
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Ref: library/tempfile tempfile-mktemp-deprecated5904463
Ref: 1dd05904463
Ref: library/tempfile tempfile mktemp5905091
Ref: f7d5905091
Node: glob — Unix style pathname pattern expansion5906223
Ref: library/glob doc5906444
Ref: 1dd15906444
Ref: library/glob glob-unix-style-pathname-pattern-expansion5906444
Ref: 1dd25906444
Ref: library/glob module-glob5906444
Ref: 885906444
Ref: library/glob glob glob5907557
Ref: 6bd5907557
Ref: library/glob glob iglob5908826
Ref: 6be5908826
Ref: library/glob glob escape5909138
Ref: 93c5909138
Ref: glob — Unix style pathname pattern expansion-Footnote-15910592
Node: fnmatch — Unix filename pattern matching5910655
Ref: library/fnmatch doc5910864
Ref: 1dd65910864
Ref: library/fnmatch fnmatch-unix-filename-pattern-matching5910864
Ref: 1dd75910864
Ref: library/fnmatch module-fnmatch5910864
Ref: 7f5910864
Ref: library/fnmatch fnmatch fnmatch5912199
Ref: 1dd35912199
Ref: library/fnmatch fnmatch fnmatchcase5912886
Ref: 1dd95912886
Ref: library/fnmatch fnmatch filter5913133
Ref: 1dd85913133
Ref: library/fnmatch fnmatch translate5913381
Ref: 11735913381
Ref: fnmatch — Unix filename pattern matching-Footnote-15913961
Node: linecache — Random access to text lines5914027
Ref: library/linecache doc5914227
Ref: 1dda5914227
Ref: library/linecache linecache-random-access-to-text-lines5914227
Ref: 1ddb5914227
Ref: library/linecache module-linecache5914227
Ref: a85914227
Ref: library/linecache linecache getline5915057
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Ref: library/linecache linecache clearcache5915826
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Ref: library/linecache linecache checkcache5915995
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Ref: library/linecache linecache lazycache5916273
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Ref: linecache — Random access to text lines-Footnote-15916820
Ref: linecache — Random access to text lines-Footnote-25916888
Node: shutil — High-level file operations5916937
Ref: library/shutil doc5917086
Ref: 1de05917086
Ref: library/shutil module-shutil5917086
Ref: e95917086
Ref: library/shutil shutil-high-level-file-operations5917086
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Ref: shutil — High-level file operations-Footnote-15918189
Node: Directory and files operations5918254
Ref: library/shutil directory-and-files-operations5918387
Ref: 1de25918387
Ref: library/shutil file-operations5918387
Ref: 1de35918387
Ref: library/shutil shutil copyfileobj5918470
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Ref: library/shutil shutil copyfile5919053
Ref: 3825919053
Ref: library/shutil shutil SameFileError5920653
Ref: 99a5920653
Ref: library/shutil shutil copymode5920823
Ref: 1de45920823
Ref: library/shutil shutil copystat5921717
Ref: b525921717
Ref: library/shutil shutil copy5923823
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Ref: library/shutil shutil copy25925254
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Ref: library/shutil shutil ignore_patterns5926767
Ref: 1de65926767
Ref: library/shutil shutil copytree5927069
Ref: 3475927069
Ref: library/shutil shutil rmtree5930219
Ref: 3495930219
Ref: library/shutil shutil rmtree avoids_symlink_attacks5932143
Ref: 1de75932143
Ref: library/shutil shutil move5932483
Ref: 3855932483
Ref: library/shutil shutil disk_usage5934421
Ref: b505934421
Ref: library/shutil shutil chown5934869
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Ref: library/shutil shutil which5935355
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Ref: library/shutil shutil Error5936681
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Node: Platform-dependent efficient copy operations5937017
Ref: library/shutil platform-dependent-efficient-copy-operations5937153
Ref: 1de85937153
Ref: library/shutil shutil-platform-dependent-efficient-copy-operations5937153
Ref: 3885937153
Ref: Platform-dependent efficient copy operations-Footnote-15938277
Ref: Platform-dependent efficient copy operations-Footnote-25938320
Node: copytree example5938368
Ref: library/shutil copytree-example5938527
Ref: 1de95938527
Ref: library/shutil shutil-copytree-example5938527
Ref: 1dea5938527
Node: rmtree example5940605
Ref: library/shutil rmtree-example5940711
Ref: 1deb5940711
Ref: library/shutil shutil-rmtree-example5940711
Ref: 1dec5940711
Node: Archiving operations5941258
Ref: library/shutil archiving-operations5941440
Ref: c675941440
Ref: library/shutil id15941440
Ref: 1ded5941440
Ref: library/shutil shutil make_archive5941748
Ref: 3485941748
Ref: library/shutil shutil get_archive_formats5943772
Ref: 1def5943772
Ref: library/shutil shutil register_archive_format5944614
Ref: 1df05944614
Ref: library/shutil shutil unregister_archive_format5945460
Ref: 1df15945460
Ref: library/shutil shutil unpack_archive5945595
Ref: c685945595
Ref: library/shutil shutil register_unpack_format5946555
Ref: 1df25946555
Ref: library/shutil shutil unregister_unpack_format5947318
Ref: 1df45947318
Ref: library/shutil shutil get_unpack_formats5947442
Ref: 1df35947442
Ref: Archiving operations-Footnote-15948395
Node: Archiving example5948444
Ref: library/shutil archiving-example5948558
Ref: 1df55948558
Ref: library/shutil shutil-archiving-example5948558
Ref: 1df65948558
Node: Archiving example with base_dir5949651
Ref: library/shutil archiving-example-with-base-dir5949765
Ref: 1df75949765
Ref: library/shutil shutil-archiving-example-with-basedir5949765
Ref: 1dee5949765
Node: Querying the size of the output terminal5950869
Ref: library/shutil querying-the-size-of-the-output-terminal5951012
Ref: 1df85951012
Ref: library/shutil shutil get_terminal_size5951115
Ref: b255951115
Ref: Querying the size of the output terminal-Footnote-15952642
Node: Data Persistence5952724
Ref: library/persistence doc5952877
Ref: 1dfb5952877
Ref: library/persistence data-persistence5952877
Ref: 1dfc5952877
Ref: library/persistence other-environment-variables5952877
Ref: 1dfd5952877
Ref: library/persistence persistence5952877
Ref: 1dfe5952877
Node: pickle — Python object serialization5953708
Ref: library/pickle doc5953853
Ref: 1dff5953853
Ref: library/pickle module-pickle5953853
Ref: ca5953853
Ref: library/pickle pickle-python-object-serialization5953853
Ref: 1e005953853
Ref: pickle — Python object serialization-Footnote-15955688
Ref: pickle — Python object serialization-Footnote-25955753
Node: Relationship to other Python modules5955821
Ref: library/pickle relationship-to-other-python-modules5955959
Ref: 1e035955959
Node: Comparison with marshal5956115
Ref: library/pickle comparison-with-marshal5956240
Ref: 1e045956240
Node: Comparison with json5958468
Ref: library/pickle comparison-with-json5958593
Ref: 1e025958593
Ref: library/pickle id25958593
Ref: 1e055958593
Ref: Comparison with json-Footnote-15959758
Node: Data stream format5959782
Ref: library/pickle data-stream-format5959945
Ref: 1e075959945
Ref: library/pickle pickle-protocols5959945
Ref: 6665959945
Ref: Data stream format-Footnote-15962915
Ref: Data stream format-Footnote-25962964
Ref: Data stream format-Footnote-35963013
Node: Module Interface5963062
Ref: library/pickle module-interface5963223
Ref: 1e0a5963223
Ref: library/pickle pickle HIGHEST_PROTOCOL5963675
Ref: ec45963675
Ref: library/pickle pickle DEFAULT_PROTOCOL5963947
Ref: 1e0d5963947
Ref: library/pickle pickle dump5964455
Ref: 1e0c5964455
Ref: library/pickle pickle dumps5964953
Ref: ec35964953
Ref: library/pickle pickle load5965390
Ref: 6b95965390
Ref: library/pickle pickle loads5966138
Ref: 6ba5966138
Ref: library/pickle pickle PickleError5966874
Ref: 1e0e5966874
Ref: library/pickle pickle PicklingError5967008
Ref: 1e0f5967008
Ref: library/pickle pickle UnpicklingError5967287
Ref: 1e115967287
Ref: library/pickle pickle Pickler5967796
Ref: 33b5967796
Ref: library/pickle pickle Pickler dump5969350
Ref: 11725969350
Ref: library/pickle pickle Pickler persistent_id5969492
Ref: 1e145969492
Ref: library/pickle pickle Pickler dispatch_table5970168
Ref: b445970168
Ref: library/pickle pickle Pickler reducer_override5971332
Ref: 33c5971332
Ref: library/pickle pickle Pickler fast5971947
Ref: 1e1a5971947
Ref: library/pickle pickle Unpickler5972432
Ref: 1e0b5972432
Ref: library/pickle pickle Unpickler load5974536
Ref: 1e1c5974536
Ref: library/pickle pickle Unpickler persistent_load5974831
Ref: 1e155974831
Ref: library/pickle pickle Unpickler find_class5975278
Ref: 1e1d5975278
Ref: library/pickle pickle PickleBuffer5975957
Ref: 1e125975957
Ref: library/pickle pickle PickleBuffer raw5976575
Ref: 1e1f5976575
Ref: library/pickle pickle PickleBuffer release5976918
Ref: 1e205976918
Node: What can be pickled and unpickled?5977034
Ref: library/pickle pickle-picklable5977201
Ref: 1e105977201
Ref: library/pickle what-can-be-pickled-and-unpickled5977201
Ref: 1e215977201
Ref: What can be pickled and unpickled?-Footnote-15979929
Ref: What can be pickled and unpickled?-Footnote-25980065
Node: Pickling Class Instances5980205
Ref: library/pickle pickle-inst5980410
Ref: 1e065980410
Ref: library/pickle pickling-class-instances5980410
Ref: 1e225980410
Ref: library/pickle object __getnewargs_ex__5981342
Ref: 1e235981342
Ref: library/pickle object __getnewargs__5982174
Ref: 7a15982174
Ref: library/pickle object __getstate__5982740
Ref: ec55982740
Ref: library/pickle object __setstate__5983179
Ref: 2d15983179
Ref: library/pickle object __reduce__5985018
Ref: 2d05985018
Ref: library/pickle object __reduce_ex__5987883
Ref: 1b475987883
Ref: Pickling Class Instances-Footnote-15988544
Node: Persistence of External Objects5988643
Ref: library/pickle persistence-of-external-objects5988759
Ref: 1e255988759
Ref: library/pickle pickle-persistent5988759
Ref: 1e165988759
Ref: Persistence of External Objects-Footnote-15993427
Node: Dispatch Tables5993691
Ref: library/pickle dispatch-tables5993841
Ref: 1e265993841
Ref: library/pickle pickle-dispatch5993841
Ref: 1e185993841
Node: Handling Stateful Objects5995068
Ref: library/pickle handling-stateful-objects5995178
Ref: 1e275995178
Ref: library/pickle pickle-state5995178
Ref: 1e245995178
Node: Custom Reduction for Types Functions and Other Objects5997465
Ref: library/pickle custom-reduction-for-types-functions-and-other-objects5997655
Ref: 1e285997655
Ref: library/pickle reducer-override5997655
Ref: 1e195997655
Node: Out-of-band Buffers5999747
Ref: library/pickle out-of-band-buffers5999932
Ref: 1e295999932
Ref: library/pickle pickle-oob5999932
Ref: 1e135999932
Node: Provider API6000780
Ref: library/pickle provider-api6000869
Ref: 1e2a6000869
Node: Consumer API6001476
Ref: library/pickle consumer-api6001584
Ref: 1e2b6001584
Node: Example<4>6002886
Ref: library/pickle example6002973
Ref: 1e2c6002973
Ref: Example<4>-Footnote-16005357
Node: Restricting Globals6005406
Ref: library/pickle pickle-restrict6005551
Ref: 1e1e6005551
Ref: library/pickle restricting-globals6005551
Ref: 1e2d6005551
Node: Performance<2>6008327
Ref: library/pickle performance6008464
Ref: 1e2e6008464
Node: Examples<5>6008740
Ref: library/pickle examples6008849
Ref: 1e2f6008849
Ref: library/pickle pickle-example6008849
Ref: 1e306008849
Node: copyreg — Register pickle support functions6010067
Ref: library/copyreg doc6010257
Ref: 1e316010257
Ref: library/copyreg copyreg-register-pickle-support-functions6010257
Ref: 1e326010257
Ref: library/copyreg module-copyreg6010257
Ref: 266010257
Ref: library/copyreg copyreg constructor6010849
Ref: 1e336010849
Ref: library/copyreg copyreg pickle6011052
Ref: 1e176011052
Ref: copyreg — Register pickle support functions-Footnote-16012005
Node: Example<5>6012071
Ref: library/copyreg example6012163
Ref: 1e346012163
Node: shelve — Python object persistence6012707
Ref: library/shelve doc6012907
Ref: 1e356012907
Ref: library/shelve module-shelve6012907
Ref: e76012907
Ref: library/shelve shelve-python-object-persistence6012907
Ref: 1e366012907
Ref: library/shelve shelve open6013492
Ref: 1e376013492
Ref: library/shelve shelve-security6015292
Ref: 1e3b6015292
Ref: library/shelve shelve Shelf sync6015791
Ref: 1e396015791
Ref: library/shelve shelve Shelf close6016112
Ref: 1e3a6016112
Ref: shelve — Python object persistence-Footnote-16016494
Ref: shelve — Python object persistence-Footnote-26016559
Node: Restrictions6016612
Ref: library/shelve restrictions6016716
Ref: 1e3c6016716
Ref: library/shelve shelve Shelf6017741
Ref: 9976017741
Ref: library/shelve shelve BsdDbShelf6018977
Ref: 1e3d6018977
Ref: library/shelve shelve DbfilenameShelf6019683
Ref: 1e3e6019683
Ref: Restrictions-Footnote-16020298
Node: Example<6>6020351
Ref: library/shelve example6020455
Ref: 1e3f6020455
Ref: library/shelve shelve-example6020455
Ref: 1e386020455
Node: marshal — Internal Python object serialization6022134
Ref: library/marshal doc6022331
Ref: 1e406022331
Ref: library/marshal marshal-internal-python-object-serialization6022331
Ref: 1e416022331
Ref: library/marshal module-marshal6022331
Ref: b06022331
Ref: library/marshal marshal dump6024738
Ref: 1e426024738
Ref: library/marshal marshal load6025397
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Ref: library/marshal marshal dumps6026236
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Ref: library/marshal marshal loads6026747
Ref: 1e436026747
Ref: library/marshal marshal version6027345
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Ref: marshal — Internal Python object serialization-Footnote-16027699
Node: dbm — Interfaces to Unix “databases”6028083
Ref: library/dbm doc6028297
Ref: 1e456028297
Ref: library/dbm dbm-interfaces-to-unix-databases6028297
Ref: 1e466028297
Ref: library/dbm module-dbm6028297
Ref: 316028297
Ref: library/dbm dbm error6028807
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Ref: library/dbm dbm whichdb6029079
Ref: 1e486029079
Ref: library/dbm dbm open6029642
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Ref: dbm — Interfaces to Unix “databases”-Footnote-16033285
Ref: dbm — Interfaces to Unix “databases”-Footnote-26033356
Node: dbm gnu — GNU’s reinterpretation of dbm6033409
Ref: library/dbm dbm-gnu-gnu-s-reinterpretation-of-dbm6033576
Ref: 1e496033576
Ref: library/dbm module-dbm gnu6033576
Ref: 336033576
Ref: library/dbm dbm gnu error6034392
Ref: 3e76034392
Ref: library/dbm dbm gnu open6034596
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Ref: library/dbm dbm gnu gdbm firstkey6036674
Ref: 1e4a6036674
Ref: library/dbm dbm gnu gdbm nextkey6037018
Ref: 1e4b6037018
Ref: library/dbm dbm gnu gdbm reorganize6037403
Ref: 1e4c6037403
Ref: library/dbm dbm gnu gdbm sync6037846
Ref: 1e4d6037846
Ref: library/dbm dbm gnu gdbm close6038011
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Ref: dbm gnu — GNU’s reinterpretation of dbm-Footnote-16038121
Node: dbm ndbm — Interface based on ndbm6038187
Ref: library/dbm dbm-ndbm-interface-based-on-ndbm6038403
Ref: 1e4f6038403
Ref: library/dbm module-dbm ndbm6038403
Ref: 346038403
Ref: library/dbm dbm ndbm error6039159
Ref: 3e86039159
Ref: library/dbm dbm ndbm library6039365
Ref: 1e506039365
Ref: library/dbm dbm ndbm open6039451
Ref: 11686039451
Ref: library/dbm dbm ndbm ndbm close6040736
Ref: 1e516040736
Ref: dbm ndbm — Interface based on ndbm-Footnote-16040846
Node: dbm dumb — Portable DBM implementation6040913
Ref: library/dbm dbm-dumb-portable-dbm-implementation6041077
Ref: 1e526041077
Ref: library/dbm module-dbm dumb6041077
Ref: 326041077
Ref: library/dbm dbm dumb error6041902
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Ref: library/dbm dbm dumb open6042108
Ref: 3e16042108
Ref: library/dbm dbm dumb dumbdbm sync6044053
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Ref: library/dbm dbm dumb dumbdbm close6044216
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Ref: dbm dumb — Portable DBM implementation-Footnote-16044332
Node: sqlite3 — DB-API 2 0 interface for SQLite databases6044399
Ref: library/sqlite3 doc6044556
Ref: 1e556044556
Ref: library/sqlite3 module-sqlite36044556
Ref: f26044556
Ref: library/sqlite3 sqlite3-db-api-2-0-interface-for-sqlite-databases6044556
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Ref: library/sqlite3 sqlite3-placeholders6047091
Ref: 1e5b6047091
Ref: sqlite3 — DB-API 2 0 interface for SQLite databases-Footnote-16049590
Ref: sqlite3 — DB-API 2 0 interface for SQLite databases-Footnote-26049654
Ref: sqlite3 — DB-API 2 0 interface for SQLite databases-Footnote-36049703
Ref: sqlite3 — DB-API 2 0 interface for SQLite databases-Footnote-46049733
Node: Module functions and constants6049782
Ref: library/sqlite3 module-functions-and-constants6049929
Ref: 1e5c6049929
Ref: library/sqlite3 sqlite3-module-contents6049929
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Ref: library/sqlite3 sqlite3 apilevel6050010
Ref: 1e5e6050010
Ref: library/sqlite3 sqlite3 paramstyle6050153
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Ref: library/sqlite3 sqlite3 version6050655
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Ref: library/sqlite3 sqlite3 version_info6050789
Ref: 1e616050789
Ref: library/sqlite3 sqlite3 sqlite_version6050939
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Ref: library/sqlite3 sqlite3 sqlite_version_info6051043
Ref: 1e636051043
Ref: library/sqlite3 sqlite3 threadsafety6051168
Ref: 1e646051168
Ref: library/sqlite3 sqlite3 PARSE_DECLTYPES6051926
Ref: 1e656051926
Ref: library/sqlite3 sqlite3 PARSE_COLNAMES6052528
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Ref: library/sqlite3 sqlite3 connect6053421
Ref: 4e16053421
Ref: library/sqlite3 sqlite3 register_converter6057038
Ref: 1e696057038
Ref: library/sqlite3 sqlite3 register_adapter6057519
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Ref: library/sqlite3 sqlite3 complete_statement6057844
Ref: 1e6c6057844
Ref: library/sqlite3 sqlite3 enable_callback_tracebacks6059178
Ref: 1e6d6059178
Ref: Module functions and constants-Footnote-16059629
Ref: Module functions and constants-Footnote-26059680
Node: Connection Objects6059720
Ref: library/sqlite3 connection-objects6059890
Ref: 1e6e6059890
Ref: library/sqlite3 sqlite3-connection-objects6059890
Ref: 1e6f6059890
Ref: library/sqlite3 sqlite3 Connection6059947
Ref: 4df6059947
Ref: library/sqlite3 sqlite3 Connection isolation_level6060060
Ref: 1e686060060
Ref: library/sqlite3 sqlite3 Connection in_transaction6060370
Ref: 1e716060370
Ref: library/sqlite3 sqlite3 Connection cursor6060596
Ref: 1e726060596
Ref: library/sqlite3 sqlite3 Connection commit6060836
Ref: 1e736060836
Ref: library/sqlite3 sqlite3 Connection rollback6061229
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Ref: library/sqlite3 sqlite3 Connection close6061376
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Ref: library/sqlite3 sqlite3 Connection execute6061663
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Ref: library/sqlite3 sqlite3 Connection executemany6061959
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Ref: library/sqlite3 sqlite3 Connection executescript6062263
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Ref: library/sqlite3 sqlite3 Connection create_function6062564
Ref: 10d46062564
Ref: library/sqlite3 sqlite3 Connection create_aggregate6063976
Ref: 10d36063976
Ref: library/sqlite3 sqlite3 Connection create_collation6065308
Ref: 1e7c6065308
Ref: library/sqlite3 sqlite3 Connection interrupt6066918
Ref: 1e7d6066918
Ref: library/sqlite3 sqlite3 Connection set_authorizer6067158
Ref: 10d56067158
Ref: library/sqlite3 sqlite3 Connection set_progress_handler6068518
Ref: 10d66068518
Ref: library/sqlite3 sqlite3 Connection set_trace_callback6069176
Ref: b656069176
Ref: library/sqlite3 sqlite3 Connection enable_load_extension6070267
Ref: c6a6070267
Ref: library/sqlite3 sqlite3 Connection load_extension6072081
Ref: c6b6072081
Ref: library/sqlite3 sqlite3 Connection row_factory6072421
Ref: 1e7f6072421
Ref: library/sqlite3 sqlite3 Connection text_factory6073787
Ref: 1e806073787
Ref: library/sqlite3 sqlite3 Connection total_changes6075522
Ref: 1e816075522
Ref: library/sqlite3 sqlite3 Connection iterdump6075718
Ref: 1e826075718
Ref: library/sqlite3 sqlite3 Connection backup6076365
Ref: 4e06076365
Ref: Connection Objects-Footnote-16078778
Ref: Connection Objects-Footnote-26078824
Ref: Connection Objects-Footnote-36079120
Node: Cursor Objects6079416
Ref: library/sqlite3 cursor-objects6079567
Ref: 1e836079567
Ref: library/sqlite3 sqlite3-cursor-objects6079567
Ref: 1e846079567
Ref: library/sqlite3 sqlite3 Cursor6079616
Ref: 1e576079616
Ref: library/sqlite3 sqlite3 Cursor execute6079727
Ref: 1e586079727
Ref: library/sqlite3 sqlite3 Cursor executemany6080196
Ref: 1e786080196
Ref: library/sqlite3 sqlite3 Cursor executescript6082012
Ref: 1e7a6082012
Ref: library/sqlite3 sqlite3 Cursor fetchone6083238
Ref: 1e596083238
Ref: library/sqlite3 sqlite3 Cursor fetchmany6083414
Ref: 1e866083414
Ref: library/sqlite3 sqlite3 Cursor fetchall6084391
Ref: 1e5a6084391
Ref: library/sqlite3 sqlite3 Cursor close6084675
Ref: 1e876084675
Ref: library/sqlite3 sqlite3 Cursor setinputsizes6084979
Ref: 1e886084979
Ref: library/sqlite3 sqlite3 Cursor setoutputsize6085087
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Ref: library/sqlite3 sqlite3 Cursor rowcount6085204
Ref: 1e8a6085204
Ref: library/sqlite3 sqlite3 Cursor lastrowid6086198
Ref: 6756086198
Ref: library/sqlite3 sqlite3 Cursor arraysize6086898
Ref: 1e8b6086898
Ref: library/sqlite3 sqlite3 Cursor description6087127
Ref: 1e676087127
Ref: library/sqlite3 sqlite3 Cursor connection6087508
Ref: 1e8c6087508
Node: Row Objects6088004
Ref: library/sqlite3 row-objects6088150
Ref: 1e8d6088150
Ref: library/sqlite3 sqlite3-row-objects6088150
Ref: 1e8e6088150
Ref: library/sqlite3 sqlite3 Row6088193
Ref: 84d6088193
Ref: library/sqlite3 sqlite3 Row keys6088653
Ref: 1e8f6088653
Node: Exceptions<5>6089893
Ref: library/sqlite3 exceptions6090048
Ref: 1e906090048
Ref: library/sqlite3 sqlite3-exceptions6090048
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Ref: library/sqlite3 sqlite3 Warning6090089
Ref: 1e856090089
Ref: library/sqlite3 sqlite3 Error6090163
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Ref: library/sqlite3 sqlite3 DatabaseError6090302
Ref: 1e936090302
Ref: library/sqlite3 sqlite3 IntegrityError6090408
Ref: 1e946090408
Ref: library/sqlite3 sqlite3 ProgrammingError6090620
Ref: ff36090620
Ref: library/sqlite3 sqlite3 OperationalError6090890
Ref: 1e7e6090890
Ref: library/sqlite3 sqlite3 NotSupportedError6091254
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Node: SQLite and Python types6091600
Ref: library/sqlite3 sqlite-and-python-types6091768
Ref: 1e956091768
Ref: library/sqlite3 sqlite3-types6091768
Ref: 1e6a6091768
Node: Introduction<7>6092038
Ref: library/sqlite3 introduction6092189
Ref: 1e966092189
Node: Using adapters to store additional Python types in SQLite databases6094076
Ref: library/sqlite3 using-adapters-to-store-additional-python-types-in-sqlite-databases6094283
Ref: 1e976094283
Node: Letting your object adapt itself6094881
Ref: library/sqlite3 letting-your-object-adapt-itself6095057
Ref: 1e986095057
Node: Registering an adapter callable6096165
Ref: library/sqlite3 registering-an-adapter-callable6096341
Ref: 1e996096341
Node: Converting SQLite values to custom Python types6097657
Ref: library/sqlite3 converting-sqlite-values-to-custom-python-types6097880
Ref: 1e9a6097880
Node: Default adapters and converters6100509
Ref: library/sqlite3 default-adapters-and-converters6100656
Ref: 1e9b6100656
Node: Controlling Transactions6102536
Ref: library/sqlite3 controlling-transactions6102716
Ref: 1e9c6102716
Ref: library/sqlite3 sqlite3-controlling-transactions6102716
Ref: 1e706102716
Node: Using sqlite3 efficiently6104496
Ref: library/sqlite3 using-sqlite3-efficiently6104644
Ref: 1e9d6104644
Node: Using shortcut methods6104858
Ref: library/sqlite3 using-shortcut-methods6104996
Ref: 1e9e6104996
Node: Accessing columns by name instead of by index6106281
Ref: library/sqlite3 accessing-columns-by-name-instead-of-by-index6106469
Ref: 1e9f6106469
Node: Using the connection as a context manager6107193
Ref: library/sqlite3 using-the-connection-as-a-context-manager6107350
Ref: 1ea06107350
Node: Data Compression and Archiving6108449
Ref: library/archiving doc6108589
Ref: 1e086108589
Ref: library/archiving archiving6108589
Ref: 1ea16108589
Ref: library/archiving data-compression-and-archiving6108589
Ref: 1ea26108589
Node: zlib — Compression compatible with gzip6109181
Ref: library/zlib doc6109329
Ref: 1ea36109329
Ref: library/zlib module-zlib6109329
Ref: 14d6109329
Ref: library/zlib zlib-compression-compatible-with-gzip6109329
Ref: 1ea46109329
Ref: library/zlib zlib error6110298
Ref: 1ea56110298
Ref: library/zlib zlib adler326110389
Ref: 1ea66110389
Ref: library/zlib zlib compress6111302
Ref: 6b56111302
Ref: library/zlib zlib compressobj6112079
Ref: 1ea76112079
Ref: library/zlib zlib crc326114813
Ref: 1ea86114813
Ref: library/zlib zlib decompress6115641
Ref: 6b66115641
Ref: library/zlib decompress-wbits6116074
Ref: 1ea96116074
Ref: library/zlib zlib decompressobj6117809
Ref: 1eaa6117809
Ref: library/zlib zlib Compress compress6118808
Ref: 1eab6118808
Ref: library/zlib zlib Compress flush6119166
Ref: 1eac6119166
Ref: library/zlib zlib Compress copy6119921
Ref: 1ead6119921
Ref: library/zlib zlib Decompress unused_data6120289
Ref: 1eae6120289
Ref: library/zlib zlib Decompress unconsumed_tail6120635
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Ref: library/zlib zlib Decompress eof6121089
Ref: b9d6121089
Ref: library/zlib zlib Decompress decompress6121372
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Ref: library/zlib zlib Decompress flush6122399
Ref: 1eb16122399
Ref: library/zlib zlib Decompress copy6122804
Ref: 1eb26122804
Ref: library/zlib zlib ZLIB_VERSION6123282
Ref: 1eb36123282
Ref: library/zlib zlib ZLIB_RUNTIME_VERSION6123536
Ref: b9e6123536
Ref: zlib — Compression compatible with gzip-Footnote-16124010
Node: gzip — Support for gzip files6124055
Ref: library/gzip doc6124249
Ref: 1eb46124249
Ref: library/gzip gzip-support-for-gzip-files6124249
Ref: 1eb56124249
Ref: library/gzip module-gzip6124249
Ref: 8b6124249
Ref: library/gzip gzip open6125244
Ref: 1eb66125244
Ref: library/gzip gzip BadGzipFile6126775
Ref: 3036126775
Ref: library/gzip gzip GzipFile6127020
Ref: 2066127020
Ref: library/gzip gzip GzipFile peek6129970
Ref: c596129970
Ref: library/gzip gzip GzipFile mtime6130594
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Ref: library/gzip gzip compress6132065
Ref: 3026132065
Ref: library/gzip gzip decompress6132454
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Ref: gzip — Support for gzip files-Footnote-16132718
Node: Examples of usage6132781
Ref: library/gzip examples-of-usage6132897
Ref: 1ebc6132897
Ref: library/gzip gzip-usage-examples6132897
Ref: 1ebd6132897
Node: Command Line Interface6133815
Ref: library/gzip command-line-interface6133931
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Node: Command line options6134351
Ref: library/gzip command-line-options6134430
Ref: 1ebf6134430
Ref: library/gzip cmdoption-gzip-arg-file6134491
Ref: 1ec06134491
Ref: library/gzip cmdoption-gzip-fast6134583
Ref: 1ec16134583
Ref: library/gzip cmdoption-gzip-best6134678
Ref: 1ec26134678
Ref: library/gzip cmdoption-gzip-d6134773
Ref: 1ec36134773
Ref: library/gzip cmdoption-gzip-h6134844
Ref: 1ec46134844
Node: bz2 — Support for bzip2 compression6134905
Ref: library/bz2 doc6135103
Ref: 1ec56135103
Ref: library/bz2 bz2-support-for-bzip2-compression6135103
Ref: 1ec66135103
Ref: library/bz2 module-bz26135103
Ref: 136135103
Ref: bz2 — Support for bzip2 compression-Footnote-16136143
Node: De compression of files6136205
Ref: library/bz2 de-compression-of-files6136337
Ref: 1ec96136337
Ref: library/bz2 bz2 open6136406
Ref: ab56136406
Ref: library/bz2 bz2 BZ2File6137844
Ref: 2246137844
Ref: library/bz2 bz2 BZ2File peek6139282
Ref: 1eca6139282
Node: Incremental de compression6140887
Ref: library/bz2 incremental-de-compression6141051
Ref: 1ecb6141051
Ref: library/bz2 bz2 BZ2Compressor6141126
Ref: 1ec76141126
Ref: library/bz2 bz2 BZ2Compressor compress6141466
Ref: 1ecc6141466
Ref: library/bz2 bz2 BZ2Compressor flush6141814
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Ref: library/bz2 bz2 BZ2Decompressor6142043
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Ref: library/bz2 bz2 BZ2Decompressor decompress6142594
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Ref: library/bz2 bz2 BZ2Decompressor eof6143952
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Ref: library/bz2 bz2 BZ2Decompressor unused_data6144076
Ref: 1ecf6144076
Ref: library/bz2 bz2 BZ2Decompressor needs_input6144298
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Node: One-shot de compression6144520
Ref: library/bz2 one-shot-de-compression6144681
Ref: 1ed16144681
Ref: library/bz2 bz2 compress6144750
Ref: 19b66144750
Ref: library/bz2 bz2 decompress6145049
Ref: ab66145049
Node: Examples of usage<2>6145407
Ref: library/bz2 bz2-usage-examples6145533
Ref: 1ed26145533
Ref: library/bz2 examples-of-usage6145533
Ref: 1ed36145533
Node: lzma — Compression using the LZMA algorithm6148453
Ref: library/lzma doc6148654
Ref: 1ed46148654
Ref: library/lzma lzma-compression-using-the-lzma-algorithm6148654
Ref: 1ed56148654
Ref: library/lzma module-lzma6148654
Ref: ad6148654
Ref: library/lzma lzma LZMAError6149495
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Ref: lzma — Compression using the LZMA algorithm-Footnote-16149914
Node: Reading and writing compressed files6149977
Ref: library/lzma reading-and-writing-compressed-files6150148
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Ref: library/lzma lzma open6150241
Ref: 1ed86150241
Ref: library/lzma lzma LZMAFile6152008
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Ref: library/lzma lzma LZMAFile peek6153885
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Node: Compressing and decompressing data in memory6154766
Ref: library/lzma compressing-and-decompressing-data-in-memory6154962
Ref: 1edc6154962
Ref: library/lzma lzma LZMACompressor6155071
Ref: 1eda6155071
Ref: library/lzma lzma LZMACompressor compress6158149
Ref: 1edf6158149
Ref: library/lzma lzma LZMACompressor flush6158622
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Ref: library/lzma lzma LZMADecompressor6158902
Ref: 1ed96158902
Ref: library/lzma lzma LZMADecompressor decompress6160430
Ref: 8056160430
Ref: library/lzma lzma LZMADecompressor check6161791
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Ref: library/lzma lzma LZMADecompressor eof6162024
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Ref: library/lzma lzma LZMADecompressor unused_data6162117
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Ref: library/lzma lzma LZMADecompressor needs_input6162288
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Ref: library/lzma lzma compress6162510
Ref: 1edd6162510
Ref: library/lzma lzma decompress6162856
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Node: Miscellaneous<2>6163363
Ref: library/lzma miscellaneous6163554
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Ref: library/lzma lzma is_check_supported6163601
Ref: 1ee76163601
Node: Specifying custom filter chains6163963
Ref: library/lzma filter-chain-specs6164121
Ref: 1ede6164121
Ref: library/lzma specifying-custom-filter-chains6164121
Ref: 1ee86164121
Node: Examples<6>6166970
Ref: library/lzma examples6167103
Ref: 1ee96167103
Node: zipfile — Work with ZIP archives6168471
Ref: library/zipfile doc6168679
Ref: 1eea6168679
Ref: library/zipfile module-zipfile6168679
Ref: 14b6168679
Ref: library/zipfile zipfile-work-with-zip-archives6168679
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Ref: library/zipfile zipfile BadZipFile6169542
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Ref: library/zipfile zipfile BadZipfile6169645
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Ref: library/zipfile zipfile LargeZipFile6169806
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Ref: library/zipfile zipfile ZipInfo6170358
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Ref: library/zipfile zipfile is_zipfile6171056
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Ref: library/zipfile zipfile ZIP_STORED6171349
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Ref: library/zipfile zipfile ZIP_DEFLATED6171442
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Ref: library/zipfile zipfile ZIP_BZIP26171588
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Ref: library/zipfile zipfile ZIP_LZMA6171751
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Ref: zipfile — Work with ZIP archives-Footnote-16172757
Ref: zipfile — Work with ZIP archives-Footnote-26172823
Ref: zipfile — Work with ZIP archives-Footnote-36172891
Ref: zipfile — Work with ZIP archives-Footnote-46172959
Node: ZipFile Objects6172992
Ref: library/zipfile id16173099
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Ref: library/zipfile zipfile-objects6173099
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Ref: library/zipfile zipfile ZipFile6173150
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Ref: library/zipfile zipfile ZipFile close6177141
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Ref: library/zipfile zipfile ZipFile getinfo6177312
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Ref: library/zipfile zipfile ZipFile infolist6177571
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Ref: library/zipfile zipfile ZipFile namelist6177829
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Ref: library/zipfile zipfile ZipFile open6177910
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Ref: library/zipfile zipfile ZipFile extract6180297
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Ref: library/zipfile zipfile ZipFile extractall6181656
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Ref: library/zipfile zipfile ZipFile printdir6182674
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Ref: library/zipfile zipfile ZipFile setpassword6182776
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Ref: library/zipfile zipfile ZipFile read6182879
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Ref: library/zipfile zipfile ZipFile testzip6183781
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Ref: library/zipfile zipfile ZipFile write6184151
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Ref: library/zipfile zipfile ZipFile writestr6185476
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Ref: library/zipfile zipfile ZipFile filename6187116
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Ref: library/zipfile zipfile ZipFile debug6187177
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Ref: library/zipfile zipfile ZipFile comment6187397
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Node: Path Objects6187720
Ref: library/zipfile id26187853
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Ref: library/zipfile path-objects6187853
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Ref: library/zipfile zipfile Path6187898
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Ref: library/zipfile zipfile Path name6188444
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Ref: library/zipfile zipfile Path open6188502
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Ref: library/zipfile zipfile Path iterdir6189055
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Ref: library/zipfile zipfile Path is_dir6189139
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Ref: library/zipfile zipfile Path is_file6189238
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Ref: library/zipfile zipfile Path exists6189333
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Ref: library/zipfile zipfile Path read_text6189461
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Ref: library/zipfile zipfile Path read_bytes6189693
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Ref: library/zipfile id36189896
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Ref: library/zipfile pyzipfile-objects6189896
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Ref: library/zipfile zipfile PyZipFile6190098
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Ref: library/zipfile zipfile PyZipFile writepy6190422
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Node: ZipInfo Objects6193249
Ref: library/zipfile id46193392
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Ref: library/zipfile zipinfo-objects6193392
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Ref: library/zipfile zipfile ZipInfo from_file6193760
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Ref: library/zipfile zipfile ZipInfo is_dir6194827
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Ref: library/zipfile zipfile ZipInfo filename6195027
Ref: 1f126195027
Ref: library/zipfile zipfile ZipInfo date_time6195099
Ref: 1f136195099
Ref: library/zipfile zipfile ZipInfo compress_type6195881
Ref: 1f146195881
Ref: library/zipfile zipfile ZipInfo comment6195969
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Ref: library/zipfile zipfile ZipInfo extra6196085
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Ref: library/zipfile zipfile ZipInfo create_system6196289
Ref: 1f176196289
Ref: library/zipfile zipfile ZipInfo create_version6196367
Ref: 1f186196367
Ref: library/zipfile zipfile ZipInfo extract_version6196453
Ref: 1f196196453
Ref: library/zipfile zipfile ZipInfo reserved6196540
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Ref: library/zipfile zipfile ZipInfo flag_bits6196593
Ref: 1f1b6196593
Ref: library/zipfile zipfile ZipInfo volume6196648
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Ref: library/zipfile zipfile ZipInfo internal_attr6196715
Ref: 1f1d6196715
Ref: library/zipfile zipfile ZipInfo external_attr6196780
Ref: 1f1e6196780
Ref: library/zipfile zipfile ZipInfo header_offset6196850
Ref: 1f1f6196850
Ref: library/zipfile zipfile ZipInfo CRC6196926
Ref: 1f206196926
Ref: library/zipfile zipfile ZipInfo compress_size6196993
Ref: 1f216196993
Ref: library/zipfile zipfile ZipInfo file_size6197066
Ref: 1efd6197066
Ref: ZipInfo Objects-Footnote-16197173
Node: Command-Line Interface6197241
Ref: library/zipfile command-line-interface6197389
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Ref: library/zipfile zipfile-commandline6197389
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Node: Command-line options6198162
Ref: library/zipfile command-line-options6198241
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Ref: library/zipfile cmdoption-zipfile-list6198335
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Ref: library/zipfile cmdoption-zipfile-extract6198611
Ref: 1f2a6198611
Ref: library/zipfile cmdoption-zipfile-t6198710
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Ref: library/zipfile cmdoption-zipfile-test6198743
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Node: Decompression pitfalls6198829
Ref: library/zipfile decompression-pitfalls6198953
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Node: From file itself6199236
Ref: library/zipfile from-file-itself6199343
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Ref: library/zipfile file-system-limitations6199659
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Ref: Resources limitations-Footnote-16200381
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Node: Default behaviors of extraction6200775
Ref: library/zipfile default-behaviors-of-extraction6200886
Ref: 1f336200886
Node: tarfile — Read and write tar archive files6201151
Ref: library/tarfile doc6201305
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Ref: library/tarfile module-tarfile6201305
Ref: 1016201305
Ref: library/tarfile pkzip-application-note6201305
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Ref: library/tarfile tarfile-read-and-write-tar-archive-files6201305
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Ref: library/tarfile tarfile open6202567
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Ref: 1f3a6209377
Ref: library/tarfile tarfile ReadError6209467
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Ref: library/tarfile tarfile CompressionError6209639
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Ref: library/tarfile tarfile StreamError6209789
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Ref: library/tarfile tarfile ExtractError6209928
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Ref: library/tarfile tarfile HeaderError6210098
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Ref: library/tarfile tarfile GNU_FORMAT6210698
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Ref: library/tarfile tarfile DEFAULT_FORMAT6210813
Ref: 1f446210813
Ref: tarfile — Read and write tar archive files-Footnote-16211663
Ref: tarfile — Read and write tar archive files-Footnote-26211729
Node: TarFile Objects6211801
Ref: library/tarfile id16211921
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Ref: library/tarfile tarfile-objects6211921
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Ref: library/tarfile tarfile TarFile6212789
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Ref: library/tarfile tarfile TarFile open6216179
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Ref: library/tarfile tarfile TarFile getmember6216344
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Ref: library/tarfile tarfile TarFile getmembers6216667
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Ref: library/tarfile tarfile TarFile getnames6216854
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Ref: library/tarfile tarfile TarFile next6217465
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Ref: library/tarfile tarfile TarFile extractall6217685
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Ref: library/tarfile tarfile TarFile extract6218996
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Ref: library/tarfile tarfile TarFile gettarinfo6221988
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Ref: library/tarfile tarfile TarFile close6223129
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Ref: library/tarfile tarfile TarFile pax_headers6223271
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Ref: library/tarfile id26223530
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Ref: library/tarfile tarinfo-objects6223530
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Ref: library/tarfile tarfile TarInfo6224010
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Ref: library/tarfile tarfile TarInfo frombuf6224091
Ref: 1f3e6224091
Ref: library/tarfile tarfile TarInfo fromtarfile6224304
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Ref: library/tarfile tarfile TarInfo tobuf6224484
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Ref: library/tarfile tarfile TarInfo name6224923
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Ref: library/tarfile tarfile TarInfo size6224986
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Ref: library/tarfile tarfile TarInfo mtime6225036
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Ref: library/tarfile tarfile TarInfo mode6225099
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Ref: library/tarfile tarfile TarInfo type6225151
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Ref: library/tarfile tarfile TarInfo linkname6225529
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Ref: library/tarfile tarfile TarInfo uid6225697
Ref: 1f5b6225697
Ref: library/tarfile tarfile TarInfo gid6225786
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Ref: library/tarfile tarfile TarInfo uname6225876
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Ref: library/tarfile tarfile TarInfo gname6225923
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Ref: library/tarfile tarfile TarInfo pax_headers6225971
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Ref: library/tarfile tarfile TarInfo isfile6226171
Ref: 1f606226171
Ref: library/tarfile tarfile TarInfo isreg6226279
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Ref: library/tarfile tarfile TarInfo isdir6226345
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Ref: library/tarfile tarfile TarInfo issym6226427
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Ref: library/tarfile tarfile TarInfo isblk6226684
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Ref: library/tarfile tarfile TarInfo isfifo6226769
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Ref: library/tarfile tarfile TarInfo isdev6226847
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Node: Command-Line Interface<2>6226968
Ref: library/tarfile command-line-interface6227118
Ref: 1f696227118
Ref: library/tarfile tarfile-commandline6227118
Ref: 9ce6227118
Node: Command-line options<2>6228072
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Ref: library/tarfile cmdoption-tarfile-l6228218
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Ref: library/tarfile cmdoption-tarfile-c6228320
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Ref: library/tarfile cmdoption-tarfile-create6228377
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Ref: library/tarfile cmdoption-tarfile-e6228481
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Ref: library/tarfile cmdoption-tarfile-extract6228529
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Ref: library/tarfile cmdoption-tarfile-t6228673
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Ref: library/tarfile cmdoption-tarfile-test6228706
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Ref: library/tarfile cmdoption-tarfile-v6228792
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Node: Examples<7>6228849
Ref: library/tarfile examples6229005
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Ref: library/tarfile tar-examples6229005
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Node: Supported tar formats6230878
Ref: library/tarfile supported-tar-formats6231023
Ref: 1f756231023
Ref: library/tarfile tar-formats6231023
Ref: 1f406231023
Node: Unicode issues6233245
Ref: library/tarfile tar-unicode6233370
Ref: 1f476233370
Ref: library/tarfile unicode-issues6233370
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Node: File Formats6235343
Ref: library/fileformats doc6235489
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Ref: library/fileformats file-formats6235489
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Ref: library/fileformats fileformats6235489
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Node: csv — CSV File Reading and Writing6235949
Ref: library/csv doc6236085
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Ref: library/csv csv-csv-file-reading-and-writing6236085
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Ref: library/csv module-csv6236085
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Ref: csv — CSV File Reading and Writing-Footnote-16237995
Ref: csv — CSV File Reading and Writing-Footnote-26238057
Ref: csv — CSV File Reading and Writing-Footnote-36238106
Node: Module Contents<3>6238155
Ref: library/csv csv-contents6238289
Ref: 1f7d6238289
Ref: library/csv module-contents6238289
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Ref: library/csv csv reader6238400
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Ref: library/csv csv writer6240069
Ref: ec06240069
Ref: library/csv csv register_dialect6241833
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Ref: library/csv csv unregister_dialect6242302
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Ref: library/csv csv get_dialect6242509
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Ref: library/csv csv list_dialects6242739
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Ref: library/csv csv field_size_limit6242826
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Ref: library/csv csv DictReader6243061
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Ref: library/csv csv DictWriter6244663
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Ref: library/csv csv Dialect6246326
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Ref: library/csv csv excel6247206
Ref: 1f866247206
Ref: library/csv csv excel_tab6247389
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Ref: library/csv csv unix_dialect6247594
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Ref: library/csv csv Sniffer6247895
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Ref: library/csv csv Sniffer sniff6248064
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Ref: library/csv csv Sniffer has_header6248385
Ref: 1f8a6248385
Ref: library/csv csv QUOTE_ALL6248934
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Ref: library/csv csv QUOTE_MINIMAL6249023
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Ref: library/csv csv QUOTE_NONNUMERIC6249244
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Ref: library/csv csv QUOTE_NONE6249439
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Ref: library/csv csv Error6249939
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Ref: Module Contents<3>-Footnote-16250065
Ref: Module Contents<3>-Footnote-26250410
Node: Dialects and Formatting Parameters6250755
Ref: library/csv csv-fmt-params6250912
Ref: 1f806250912
Ref: library/csv dialects-and-formatting-parameters6250912
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Ref: library/csv csv Dialect delimiter6251702
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Ref: library/csv csv Dialect doublequote6251822
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Ref: library/csv csv Dialect escapechar6252294
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Ref: library/csv csv Dialect lineterminator6252674
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Ref: library/csv csv Dialect quotechar6253031
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Ref: library/csv csv Dialect quoting6253261
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Ref: library/csv csv Dialect skipinitialspace6253536
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Ref: library/csv csv Dialect strict6253705
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Node: Reader Objects6253845
Ref: library/csv reader-objects6253998
Ref: 1f986253998
Ref: library/csv csv csvreader __next__6254192
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Ref: library/csv csv csvreader dialect6254588
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Ref: library/csv csv csvreader line_num6254689
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Ref: library/csv csv csvreader fieldnames6254941
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Node: Writer Objects6255145
Ref: library/csv writer-objects6255275
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Ref: library/csv csv csvwriter writerow6255876
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Ref: library/csv csv csvwriter writerows6256205
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Ref: library/csv csv csvwriter dialect6256468
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Ref: library/csv csv DictWriter writeheader6256623
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Node: Examples<8>6257107
Ref: library/csv csv-examples6257214
Ref: 1fa06257214
Ref: library/csv examples6257214
Ref: 1fa16257214
Node: configparser — Configuration file parser6259226
Ref: library/configparser doc6259402
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Ref: library/configparser configparser-configuration-file-parser6259402
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Ref: library/configparser module-configparser6259402
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Ref: configparser — Configuration file parser-Footnote-16260696
Node: Quick Start6260767
Ref: library/configparser quick-start6260885
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Ref: Quick Start-Footnote-16263566
Ref: Quick Start-Footnote-26263772
Node: Supported Datatypes6263978
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Ref: Supported Datatypes-Footnote-16265442
Ref: Supported Datatypes-Footnote-26265648
Node: Fallback Values6265854
Ref: library/configparser fallback-values6266013
Ref: 1fac6266013
Node: Supported INI File Structure6267511
Ref: library/configparser supported-ini-file-structure6267674
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Ref: Supported INI File Structure-Footnote-16269994
Ref: Supported INI File Structure-Footnote-26270200
Ref: Supported INI File Structure-Footnote-36270406
Ref: Supported INI File Structure-Footnote-46270612
Ref: Supported INI File Structure-Footnote-56270818
Node: Interpolation of values6271024
Ref: library/configparser interpolation-of-values6271195
Ref: 1fad6271195
Ref: library/configparser configparser BasicInterpolation6271431
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Ref: library/configparser configparser ExtendedInterpolation6272710
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Ref: Interpolation of values-Footnote-16274191
Node: Mapping Protocol Access6274397
Ref: library/configparser mapping-protocol-access6274568
Ref: 1fa66274568
Ref: Mapping Protocol Access-Footnote-16277457
Node: Customizing Parser Behaviour6277663
Ref: library/configparser customizing-parser-behaviour6277830
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Ref: library/configparser configparser ConfigParser BOOLEAN_STATES6288573
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Ref: library/configparser configparser ConfigParser SECTCRE6290759
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Node: Legacy API Examples6292001
Ref: library/configparser legacy-api-examples6292165
Ref: 1fb26292165
Node: ConfigParser Objects6295983
Ref: library/configparser configparser-objects6296142
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Ref: library/configparser id126296142
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Ref: library/configparser configparser ConfigParser6296203
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Ref: library/configparser configparser ConfigParser defaults6300006
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Ref: library/configparser configparser ConfigParser sections6300106
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Ref: library/configparser configparser ConfigParser add_section6300249
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Ref: library/configparser configparser ConfigParser has_section6300738
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Ref: library/configparser configparser ConfigParser options6300914
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Ref: library/configparser configparser ConfigParser has_option6301024
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Ref: library/configparser configparser ConfigParser read6301324
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Ref: library/configparser configparser ConfigParser read_file6303049
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Ref: library/configparser configparser ConfigParser read_string6303530
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Ref: library/configparser configparser ConfigParser get6304572
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Ref: library/configparser configparser ConfigParser getfloat6305816
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Ref: library/configparser configparser ConfigParser getboolean6306119
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Ref: library/configparser configparser ConfigParser items6306849
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Ref: library/configparser configparser ConfigParser set6307487
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Ref: library/configparser configparser ConfigParser write6307772
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Ref: library/configparser configparser ConfigParser optionxform6308994
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Ref: library/configparser configparser ConfigParser readfp6309967
Ref: 1fbd6309967
Ref: library/configparser configparser MAX_INTERPOLATION_DEPTH6310735
Ref: 1fc36310735
Node: RawConfigParser Objects6310961
Ref: library/configparser id146311114
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Ref: library/configparser rawconfigparser-objects6311114
Ref: 1fc56311114
Ref: library/configparser configparser RawConfigParser6311183
Ref: 95c6311183
Ref: library/configparser configparser RawConfigParser add_section6312165
Ref: 1fc66312165
Ref: library/configparser configparser RawConfigParser set6312639
Ref: 1fc76312639
Node: Exceptions<6>6313466
Ref: library/configparser exceptions6313590
Ref: 1fc86313590
Ref: library/configparser configparser Error6313633
Ref: 1fc96313633
Ref: library/configparser configparser NoSectionError6313735
Ref: 1fc06313735
Ref: library/configparser configparser DuplicateSectionError6313841
Ref: cd06313841
Ref: library/configparser configparser DuplicateOptionError6314253
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Ref: library/configparser configparser NoOptionError6314613
Ref: 1fca6314613
Ref: library/configparser configparser InterpolationError6314747
Ref: 1fcb6314747
Ref: library/configparser configparser InterpolationDepthError6314892
Ref: 1fcc6314892
Ref: library/configparser configparser InterpolationMissingOptionError6315152
Ref: 1fcd6315152
Ref: library/configparser configparser InterpolationSyntaxError6315341
Ref: 1fce6315341
Ref: library/configparser configparser MissingSectionHeaderError6315569
Ref: 1fcf6315569
Ref: library/configparser configparser ParsingError6315714
Ref: 1fd06315714
Node: netrc — netrc file processing6315971
Ref: library/netrc doc6316148
Ref: 1fd16316148
Ref: library/netrc module-netrc6316148
Ref: be6316148
Ref: library/netrc netrc-netrc-file-processing6316148
Ref: 1fd26316148
Ref: library/netrc netrc netrc6316467
Ref: 11d56316467
Ref: library/netrc netrc NetrcParseError6317728
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Ref: netrc — netrc file processing-Footnote-16318198
Node: netrc Objects6318262
Ref: library/netrc id16318343
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Ref: library/netrc netrc-objects6318343
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Ref: library/netrc netrc netrc authenticators6318448
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Ref: library/netrc netrc netrc __repr__6318794
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Ref: library/netrc netrc netrc hosts6319018
Ref: 1fd86319018
Ref: library/netrc netrc netrc macros6319216
Ref: 1fd96319216
Node: xdrlib — Encode and decode XDR data6319622
Ref: library/xdrlib doc6319806
Ref: 1fda6319806
Ref: library/xdrlib module-xdrlib6319806
Ref: 13b6319806
Ref: library/xdrlib xdrlib-encode-and-decode-xdr-data6319806
Ref: 1fdb6319806
Ref: library/xdrlib xdrlib Packer6320411
Ref: 1fdc6320411
Ref: library/xdrlib xdrlib Unpacker6320594
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Ref: xdrlib — Encode and decode XDR data-Footnote-16321247
Ref: xdrlib — Encode and decode XDR data-Footnote-26321312
Ref: xdrlib — Encode and decode XDR data-Footnote-36321361
Ref: xdrlib — Encode and decode XDR data-Footnote-46321410
Ref: xdrlib — Encode and decode XDR data-Footnote-56321459
Node: Packer Objects6321508
Ref: library/xdrlib packer-objects6321621
Ref: 1fde6321621
Ref: library/xdrlib xdr-packer-objects6321621
Ref: 1fdf6321621
Ref: library/xdrlib xdrlib Packer get_buffer6321729
Ref: 1fe06321729
Ref: library/xdrlib xdrlib Packer reset6321814
Ref: 1fe16321814
Ref: library/xdrlib xdrlib Packer pack_float6322250
Ref: 1fe26322250
Ref: library/xdrlib xdrlib Packer pack_double6322353
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Ref: library/xdrlib xdrlib Packer pack_fstring6322529
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Ref: library/xdrlib xdrlib Packer pack_fopaque6322780
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Ref: library/xdrlib xdrlib Packer pack_string6322916
Ref: 1fe66322916
Ref: library/xdrlib xdrlib Packer pack_opaque6323135
Ref: 1fe76323135
Ref: library/xdrlib xdrlib Packer pack_bytes6323269
Ref: 1fe86323269
Ref: library/xdrlib xdrlib Packer pack_list6323453
Ref: 1fe96323453
Ref: library/xdrlib xdrlib Packer pack_farray6324143
Ref: 1fea6324143
Ref: library/xdrlib xdrlib Packer pack_array6324505
Ref: 1feb6324505
Node: Unpacker Objects6324756
Ref: library/xdrlib unpacker-objects6324891
Ref: 1fec6324891
Ref: library/xdrlib xdr-unpacker-objects6324891
Ref: 1fed6324891
Ref: library/xdrlib xdrlib Unpacker reset6325007
Ref: 1fee6325007
Ref: library/xdrlib xdrlib Unpacker get_position6325096
Ref: 1fef6325096
Ref: library/xdrlib xdrlib Unpacker set_position6325196
Ref: 1ff06325196
Ref: library/xdrlib xdrlib Unpacker get_buffer6325405
Ref: 1ff16325405
Ref: library/xdrlib xdrlib Unpacker done6325499
Ref: 1ff26325499
Ref: library/xdrlib xdrlib Unpacker unpack_float6325886
Ref: 1ff46325886
Ref: library/xdrlib xdrlib Unpacker unpack_double6325980
Ref: 1ff56325980
Ref: library/xdrlib xdrlib Unpacker unpack_fstring6326197
Ref: 1ff66326197
Ref: library/xdrlib xdrlib Unpacker unpack_fopaque6326408
Ref: 1ff76326408
Ref: library/xdrlib xdrlib Unpacker unpack_string6326558
Ref: 1ff86326558
Ref: library/xdrlib xdrlib Unpacker unpack_opaque6326795
Ref: 1ff96326795
Ref: library/xdrlib xdrlib Unpacker unpack_bytes6326945
Ref: 1ffa6326945
Ref: library/xdrlib xdrlib Unpacker unpack_list6327146
Ref: 1ffb6327146
Ref: library/xdrlib xdrlib Unpacker unpack_farray6327551
Ref: 1ffc6327551
Ref: library/xdrlib xdrlib Unpacker unpack_array6327822
Ref: 1ffd6327822
Node: Exceptions<7>6328097
Ref: library/xdrlib exceptions6328209
Ref: 1ffe6328209
Ref: library/xdrlib xdr-exceptions6328209
Ref: 1fff6328209
Ref: library/xdrlib xdrlib Error6328307
Ref: 1ff36328307
Ref: library/xdrlib xdrlib ConversionError6328474
Ref: 20006328474
Node: plistlib — Generate and parse Apple plist files6328865
Ref: library/plistlib doc6329009
Ref: 20016329009
Ref: library/plistlib module-plistlib6329009
Ref: cf6329009
Ref: library/plistlib plistlib-generate-and-parse-apple-plist-files6329009
Ref: 20026329009
Ref: library/plistlib plistlib load6330437
Ref: 21e6330437
Ref: library/plistlib plistlib loads6331389
Ref: 21f6331389
Ref: library/plistlib plistlib dump6331595
Ref: 2206331595
Ref: library/plistlib plistlib dumps6332693
Ref: 2216332693
Ref: library/plistlib plistlib UID6333027
Ref: 33e6333027
Ref: library/plistlib plistlib FMT_XML6333431
Ref: 9766333431
Ref: library/plistlib plistlib FMT_BINARY6333523
Ref: 9776333523
Ref: plistlib — Generate and parse Apple plist files-Footnote-16333691
Ref: plistlib — Generate and parse Apple plist files-Footnote-26333758
Node: Examples<9>6333857
Ref: library/plistlib examples6333954
Ref: 20036333954
Node: Cryptographic Services6334696
Ref: library/crypto doc6334845
Ref: 20046334845
Ref: library/crypto crypto6334845
Ref: 20056334845
Ref: library/crypto cryptographic-services6334845
Ref: 20066334845
Node: hashlib — Secure hashes and message digests6335330
Ref: library/hashlib doc6335492
Ref: 20076335492
Ref: library/hashlib hashlib-secure-hashes-and-message-digests6335492
Ref: 20086335492
Ref: library/hashlib module-hashlib6335492
Ref: 8c6335492
Ref: hashlib — Secure hashes and message digests-Footnote-16336513
Ref: hashlib — Secure hashes and message digests-Footnote-26336579
Node: Hash algorithms6336628
Ref: library/hashlib hash-algorithms6336763
Ref: 20096336763
Ref: library/hashlib id16336763
Ref: 200a6336763
Ref: library/hashlib hashlib-usedforsecurity6338429
Ref: 200b6338429
Ref: library/hashlib hashlib new6339457
Ref: 10306339457
Ref: library/hashlib hashlib algorithms_guaranteed6340181
Ref: dc26340181
Ref: library/hashlib hashlib algorithms_available6340514
Ref: dc36340514
Ref: library/hashlib hashlib hash digest_size6341050
Ref: 200c6341050
Ref: library/hashlib hashlib hash block_size6341125
Ref: 200d6341125
Ref: library/hashlib hashlib hash name6341259
Ref: 93e6341259
Ref: library/hashlib hashlib hash update6341680
Ref: 200e6341680
Ref: library/hashlib hashlib hash digest6342167
Ref: 200f6342167
Ref: library/hashlib hashlib hash hexdigest6342407
Ref: 20106342407
Ref: library/hashlib hashlib hash copy6342678
Ref: 20116342678
Node: SHAKE variable length digests6342865
Ref: library/hashlib shake-variable-length-digests6343023
Ref: 20126343023
Ref: library/hashlib hashlib shake digest6343352
Ref: 115d6343352
Ref: library/hashlib hashlib shake hexdigest6343576
Ref: 115e6343576
Node: Key derivation6343854
Ref: library/hashlib key-derivation6344003
Ref: 20136344003
Ref: library/hashlib hashlib pbkdf2_hmac6344314
Ref: 8d36344314
Ref: library/hashlib hashlib scrypt6345745
Ref: 5cd6345745
Ref: Key derivation-Footnote-16346514
Ref: Key derivation-Footnote-26346576
Node: BLAKE26346625
Ref: library/hashlib blake26346736
Ref: 20146346736
Ref: BLAKE2-Footnote-16347459
Ref: BLAKE2-Footnote-26347486
Ref: BLAKE2-Footnote-36347535
Node: Creating hash objects6347613
Ref: library/hashlib creating-hash-objects6347698
Ref: 20156347698
Ref: library/hashlib hashlib blake2b6347825
Ref: 6466347825
Ref: library/hashlib hashlib blake2s6348061
Ref: 6476348061
Ref: Creating hash objects-Footnote-16351043
Node: Constants<5>6351090
Ref: library/hashlib constants6351196
Ref: 20166351196
Ref: library/hashlib hashlib blake2b SALT_SIZE6351235
Ref: 20176351235
Ref: library/hashlib hashlib blake2s SALT_SIZE6351264
Ref: 20186351264
Ref: library/hashlib hashlib blake2b PERSON_SIZE6351349
Ref: 20196351349
Ref: library/hashlib hashlib blake2s PERSON_SIZE6351380
Ref: 201a6351380
Ref: library/hashlib hashlib blake2b MAX_KEY_SIZE6351485
Ref: 201b6351485
Ref: library/hashlib hashlib blake2s MAX_KEY_SIZE6351517
Ref: 201c6351517
Ref: library/hashlib hashlib blake2b MAX_DIGEST_SIZE6351568
Ref: 201d6351568
Ref: library/hashlib hashlib blake2s MAX_DIGEST_SIZE6351603
Ref: 201e6351603
Node: Examples<10>6351694
Ref: library/hashlib examples6351786
Ref: 201f6351786
Node: Simple hashing6351960
Ref: library/hashlib simple-hashing6352060
Ref: 20206352060
Node: Using different digest sizes6353482
Ref: library/hashlib using-different-digest-sizes6353604
Ref: 20216353604
Node: Keyed hashing6354745
Ref: library/hashlib keyed-hashing6354871
Ref: 20226354871
Ref: Keyed hashing-Footnote-16356882
Node: Randomized hashing6356925
Ref: library/hashlib randomized-hashing6357038
Ref: 20236357038
Ref: Randomized hashing-Footnote-16359642
Ref: Randomized hashing-Footnote-26359709
Node: Personalization6359740
Ref: library/hashlib personalization6359849
Ref: 20246359849
Ref: Personalization-Footnote-16361844
Node: Tree mode6361912
Ref: library/hashlib tree-mode6361994
Ref: 20256361994
Node: Credits6363245
Ref: library/hashlib credits6363316
Ref: 20266363316
Ref: Credits-Footnote-16365550
Ref: Credits-Footnote-26365577
Ref: Credits-Footnote-36365646
Ref: Credits-Footnote-46365680
Ref: Credits-Footnote-56365717
Ref: Credits-Footnote-66365760
Node: hmac — Keyed-Hashing for Message Authentication6365803
Ref: library/hmac doc6366037
Ref: 20276366037
Ref: library/hmac hmac-keyed-hashing-for-message-authentication6366037
Ref: 20286366037
Ref: library/hmac module-hmac6366037
Ref: 8e6366037
Ref: library/hmac hmac new6366329
Ref: 9406366329
Ref: library/hmac hmac digest6367256
Ref: 4976367256
Ref: library/hmac hmac HMAC update6367897
Ref: 9416367897
Ref: library/hmac hmac HMAC digest6368245
Ref: 20296368245
Ref: library/hmac hmac HMAC hexdigest6368854
Ref: 202a6368854
Ref: library/hmac hmac HMAC copy6369442
Ref: 202b6369442
Ref: library/hmac hmac HMAC digest_size6369680
Ref: 9446369680
Ref: library/hmac hmac HMAC block_size6369767
Ref: 9426369767
Ref: library/hmac hmac HMAC name6369887
Ref: 9436369887
Ref: library/hmac hmac compare_digest6370274
Ref: aea6370274
Ref: hmac — Keyed-Hashing for Message Authentication-Footnote-16371210
Ref: hmac — Keyed-Hashing for Message Authentication-Footnote-26371273
Node: secrets — Generate secure random numbers for managing secrets6371322
Ref: library/secrets doc6371502
Ref: 202c6371502
Ref: library/secrets module-secrets6371502
Ref: e46371502
Ref: library/secrets secrets-generate-secure-random-numbers-for-managing-secrets6371502
Ref: 202d6371502
Ref: secrets — Generate secure random numbers for managing secrets-Footnote-16372366
Ref: secrets — Generate secure random numbers for managing secrets-Footnote-26372432
Node: Random numbers6372481
Ref: library/secrets random-numbers6372621
Ref: 202e6372621
Ref: library/secrets secrets SystemRandom6372794
Ref: 202f6372794
Ref: library/secrets secrets choice6373011
Ref: 20306373011
Ref: library/secrets secrets randbelow6373118
Ref: 20316373118
Ref: library/secrets secrets randbits6373204
Ref: 20326373204
Node: Generating tokens6373282
Ref: library/secrets generating-tokens6373446
Ref: 20336373446
Ref: library/secrets secrets token_bytes6373665
Ref: 1c646373665
Ref: library/secrets secrets token_hex6373958
Ref: 20346373958
Ref: library/secrets secrets token_urlsafe6374294
Ref: 20356374294
Node: How many bytes should tokens use?6374724
Ref: library/secrets how-many-bytes-should-tokens-use6374811
Ref: 20366374811
Ref: How many bytes should tokens use?-Footnote-16375838
Node: Other functions6375895
Ref: library/secrets other-functions6376071
Ref: 20376376071
Ref: library/secrets secrets compare_digest6376122
Ref: 20386376122
Ref: Other functions-Footnote-16376415
Node: Recipes and best practices6376472
Ref: library/secrets recipes-and-best-practices6376622
Ref: 20396376622
Ref: Recipes and best practices-Footnote-16378362
Ref: Recipes and best practices-Footnote-26378417
Node: Generic Operating System Services6378447
Ref: library/allos doc6378604
Ref: 203a6378604
Ref: library/allos allos6378604
Ref: 203b6378604
Ref: library/allos generic-operating-system-services6378604
Ref: 203c6378604
Node: os — Miscellaneous operating system interfaces6380155
Ref: library/os doc6380324
Ref: 203d6380324
Ref: library/os module-os6380324
Ref: c46380324
Ref: library/os os-miscellaneous-operating-system-interfaces6380324
Ref: 203e6380324
Ref: library/os os error6382116
Ref: 203f6382116
Ref: library/os os name6382204
Ref: 20406382204
Ref: library/os os-filenames6382647
Ref: 1f776382647
Ref: os — Miscellaneous operating system interfaces-Footnote-16383052
Node: File Names Command Line Arguments and Environment Variables6383113
Ref: library/os file-names-command-line-arguments-and-environment-variables6383284
Ref: 20416383284
Ref: library/os filesystem-encoding6383284
Ref: 20426383284
Node: Process Parameters6384288
Ref: library/os os-procinfo6384488
Ref: 20436384488
Ref: library/os process-parameters6384488
Ref: 20446384488
Ref: library/os os ctermid6384642
Ref: 20456384642
Ref: library/os os environ6384799
Ref: c096384799
Ref: library/os os environb6386503
Ref: c656386503
Ref: library/os os fsencode6387264
Ref: 5ea6387264
Ref: library/os os fsdecode6387694
Ref: 5e96387694
Ref: library/os os fspath6388128
Ref: 5e86388128
Ref: library/os os PathLike6388539
Ref: 5e66388539
Ref: library/os os PathLike __fspath__6388715
Ref: 5e76388715
Ref: library/os os getenv6388985
Ref: 20476388985
Ref: library/os os getenvb6389465
Ref: c646389465
Ref: library/os os get_exec_path6389851
Ref: 20486389851
Ref: library/os os getegid6390230
Ref: 20496390230
Ref: library/os os geteuid6390461
Ref: 204a6390461
Ref: library/os os getgid6390585
Ref: 204b6390585
Ref: library/os os getgrouplist6390707
Ref: b366390707
Ref: library/os os getgroups6391021
Ref: 204c6391021
Ref: library/os os getlogin6392244
Ref: 204e6392244
Ref: library/os os getpgid6392726
Ref: 20506392726
Ref: library/os os getpgrp6392951
Ref: 20516392951
Ref: library/os os getpid6393069
Ref: 20526393069
Ref: library/os os getppid6393134
Ref: 20536393134
Ref: library/os os getpriority6393504
Ref: b216393504
Ref: library/os os PRIO_PROCESS6394136
Ref: 20546394136
Ref: library/os os PRIO_PGRP6394162
Ref: 20556394162
Ref: library/os os PRIO_USER6394185
Ref: 20566394185
Ref: library/os os getresuid6394371
Ref: d736394371
Ref: library/os os getresgid6394582
Ref: d726394582
Ref: library/os os getuid6394794
Ref: 20576394794
Ref: library/os os initgroups6394912
Ref: d766394912
Ref: library/os os putenv6395200
Ref: 1cd6395200
Ref: library/os os setegid6396118
Ref: 20596396118
Ref: library/os os seteuid6396244
Ref: 205a6396244
Ref: library/os os setgid6396369
Ref: 205b6396369
Ref: library/os os setgroups6396482
Ref: 204d6396482
Ref: library/os os setpgrp6397127
Ref: 205c6397127
Ref: library/os os setpgid6397363
Ref: 205d6397363
Ref: library/os os setpriority6397627
Ref: b226397627
Ref: library/os os setregid6398404
Ref: 205e6398404
Ref: library/os os setresgid6398547
Ref: d746398547
Ref: library/os os setresuid6398731
Ref: d756398731
Ref: library/os os setreuid6398914
Ref: 205f6398914
Ref: library/os os getsid6399056
Ref: 20606399056
Ref: library/os os setsid6399214
Ref: 10e06399214
Ref: library/os os setuid6399369
Ref: 20616399369
Ref: library/os os strerror6399482
Ref: 20626399482
Ref: library/os os supports_bytes_environ6399725
Ref: c636399725
Ref: library/os os umask6399890
Ref: 20636399890
Ref: library/os os uname6399988
Ref: b386399988
Ref: library/os os unsetenv6401040
Ref: 1cc6401040
Ref: Process Parameters-Footnote-16401817
Ref: Process Parameters-Footnote-26401866
Node: File Object Creation6401915
Ref: library/os file-object-creation6402082
Ref: 20656402082
Ref: library/os os-newstreams6402082
Ref: 20666402082
Ref: library/os os fdopen6402257
Ref: 15646402257
Node: File Descriptor Operations6402584
Ref: library/os file-descriptor-operations6402754
Ref: 20676402754
Ref: library/os os-fd-ops6402754
Ref: 20686402754
Ref: library/os os close6403595
Ref: 4d96403595
Ref: library/os os closerange6404041
Ref: 206b6404041
Ref: library/os os copy_file_range6404387
Ref: 206c6404387
Ref: library/os os device_encoding6405414
Ref: f676405414
Ref: library/os os dup6405607
Ref: 10e96405607
Ref: library/os os dup26405976
Ref: 4c56405976
Ref: library/os os fchmod6406435
Ref: 74f6406435
Ref: library/os os fchown6406841
Ref: 7506406841
Ref: library/os os fdatasync6407301
Ref: 7516407301
Ref: library/os os fpathconf6407532
Ref: 206e6407532
Ref: library/os os fstat6408562
Ref: 7526408562
Ref: library/os os fstatvfs6408822
Ref: 7536408822
Ref: library/os os fsync6409096
Ref: 7546409096
Ref: library/os os ftruncate6409581
Ref: 7556409581
Ref: library/os os get_blocking6410022
Ref: 8106410022
Ref: library/os os isatty6410362
Ref: f666410362
Ref: library/os os lockf6410513
Ref: b356410513
Ref: library/os os F_LOCK6411029
Ref: 20706411029
Ref: library/os os F_TLOCK6411049
Ref: 20716411049
Ref: library/os os F_ULOCK6411070
Ref: 20726411070
Ref: library/os os F_TEST6411091
Ref: 20736411091
Ref: library/os os lseek6411245
Ref: b396411245
Ref: library/os os SEEK_SET6411715
Ref: e596411715
Ref: library/os os SEEK_CUR6411737
Ref: e5a6411737
Ref: library/os os SEEK_END6411759
Ref: e5b6411759
Ref: library/os os open6412020
Ref: 7586412020
Ref: library/os os O_RDONLY6414085
Ref: 20746414085
Ref: library/os os O_WRONLY6414107
Ref: 20756414107
Ref: library/os os O_RDWR6414129
Ref: 20776414129
Ref: library/os os O_APPEND6414149
Ref: 20786414149
Ref: library/os os O_CREAT6414171
Ref: 20796414171
Ref: library/os os O_EXCL6414192
Ref: 1dc86414192
Ref: library/os os O_TRUNC6414212
Ref: 207a6414212
Ref: library/os os O_DSYNC6414295
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Ref: library/os os O_RSYNC6414316
Ref: 207c6414316
Ref: library/os os O_SYNC6414337
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Ref: library/os os O_NDELAY6414357
Ref: 207e6414357
Ref: library/os os O_NONBLOCK6414379
Ref: 8126414379
Ref: library/os os O_NOCTTY6414403
Ref: 207f6414403
Ref: library/os os O_CLOEXEC6414425
Ref: aa26414425
Ref: library/os os O_BINARY6414569
Ref: 20766414569
Ref: library/os os O_NOINHERIT6414591
Ref: 20806414591
Ref: library/os os O_SHORT_LIVED6414616
Ref: 20816414616
Ref: library/os os O_TEMPORARY6414643
Ref: 20826414643
Ref: library/os os O_RANDOM6414668
Ref: 20836414668
Ref: library/os os O_SEQUENTIAL6414690
Ref: 20846414690
Ref: library/os os O_TEXT6414716
Ref: 20856414716
Ref: library/os os O_ASYNC6414794
Ref: 20866414794
Ref: library/os os O_DIRECT6414815
Ref: 20876414815
Ref: library/os os O_DIRECTORY6414837
Ref: 20886414837
Ref: library/os os O_NOFOLLOW6414862
Ref: 20896414862
Ref: library/os os O_NOATIME6414886
Ref: 208a6414886
Ref: library/os os O_PATH6414909
Ref: 96e6414909
Ref: library/os os O_TMPFILE6414929
Ref: 96f6414929
Ref: library/os os O_SHLOCK6414952
Ref: e5c6414952
Ref: library/os os O_EXLOCK6414974
Ref: e5d6414974
Ref: library/os os openpty6415265
Ref: 208b6415265
Ref: library/os os pipe6415715
Ref: 206a6415715
Ref: library/os os pipe26416055
Ref: b0a6416055
Ref: library/os os posix_fallocate6416446
Ref: 75a6416446
Ref: library/os os posix_fadvise6416704
Ref: 7596416704
Ref: library/os os POSIX_FADV_NORMAL6417306
Ref: 208c6417306
Ref: library/os os POSIX_FADV_SEQUENTIAL6417337
Ref: 208d6417337
Ref: library/os os POSIX_FADV_RANDOM6417372
Ref: 208e6417372
Ref: library/os os POSIX_FADV_NOREUSE6417403
Ref: 208f6417403
Ref: library/os os POSIX_FADV_WILLNEED6417435
Ref: 20906417435
Ref: library/os os POSIX_FADV_DONTNEED6417468
Ref: 20916417468
Ref: library/os os pread6417703
Ref: 4c06417703
Ref: library/os os preadv6418090
Ref: 4be6418090
Ref: library/os os RWF_NOWAIT6419164
Ref: 20936419164
Ref: library/os os RWF_HIPRI6419673
Ref: 20926419673
Ref: library/os os pwrite6420071
Ref: 4c36420071
Ref: library/os os pwritev6420355
Ref: 4c16420355
Ref: library/os os RWF_DSYNC6421392
Ref: 20966421392
Ref: library/os os RWF_SYNC6421668
Ref: 20976421668
Ref: library/os os read6421942
Ref: 75b6421942
Ref: library/os os sendfile6422883
Ref: 4616422883
Ref: library/os os set_blocking6424378
Ref: 8116424378
Ref: library/os os SF_NODISKIO6424744
Ref: 20986424744
Ref: library/os os SF_MNOWAIT6424769
Ref: 20996424769
Ref: library/os os SF_SYNC6424793
Ref: 209a6424793
Ref: library/os os readv6424979
Ref: 4bf6424979
Ref: library/os os tcgetpgrp6425595
Ref: 209b6425595
Ref: library/os os tcsetpgrp6425810
Ref: 209c6425810
Ref: library/os os ttyname6426039
Ref: 209d6426039
Ref: library/os os write6426290
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Ref: library/os os writev6427138
Ref: 4c26427138
Ref: File Descriptor Operations-Footnote-16427832
Ref: File Descriptor Operations-Footnote-26427881
Ref: File Descriptor Operations-Footnote-36427944
Ref: File Descriptor Operations-Footnote-46427993
Node: Querying the size of a terminal6428042
Ref: library/os querying-the-size-of-a-terminal6428176
Ref: 209e6428176
Ref: library/os terminal-size6428176
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Ref: library/os os get_terminal_size6428280
Ref: b246428280
Ref: library/os os terminal_size6428917
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Ref: library/os os terminal_size columns6429038
Ref: 20a06429038
Ref: library/os os terminal_size lines6429122
Ref: 20a16429122
Node: Inheritance of File Descriptors6429205
Ref: library/os fd-inheritance6429339
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Ref: library/os inheritance-of-file-descriptors6429339
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Ref: library/os os get_inheritable6430302
Ref: 8e86430302
Ref: library/os os set_inheritable6430429
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Ref: library/os os get_handle_inheritable6430552
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Ref: library/os os set_handle_inheritable6430718
Ref: 8eb6430718
Node: Files and Directories6430885
Ref: library/os files-and-directories6431053
Ref: 20a46431053
Ref: library/os os-file-dir6431053
Ref: 20466431053
Ref: library/os path-fd6431202
Ref: 4bc6431202
Ref: library/os dir-fd6432146
Ref: b0b6432146
Ref: library/os follow-symlinks6432861
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Ref: library/os os access6433445
Ref: b0d6433445
Ref: library/os os F_OK6435993
Ref: 20a56435993
Ref: library/os os R_OK6436011
Ref: 20a66436011
Ref: library/os os W_OK6436029
Ref: 20a76436029
Ref: library/os os X_OK6436047
Ref: 20a86436047
Ref: library/os os chdir6436236
Ref: 16e6436236
Ref: library/os os chflags6436908
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Ref: library/os os chmod6437974
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Ref: library/os os chown6439730
Ref: b106439730
Ref: library/os os chroot6440623
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Ref: library/os os fchdir6440829
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Ref: library/os os getcwd6441233
Ref: 11196441233
Ref: library/os os getcwdb6441327
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Ref: library/os os lchflags6441635
Ref: 20aa6441635
Ref: library/os os lchmod6442114
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Ref: library/os os lchown6442684
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Ref: library/os os link6443196
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Ref: library/os os listdir6443975
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Ref: library/os os lstat6445451
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Ref: library/os os mkdir6446561
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Ref: library/os mkdir-modebits6446765
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Ref: library/os os makedirs6447613
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Ref: library/os os mkfifo6449332
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Ref: library/os os mknod6450218
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Ref: library/os os major6451089
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Ref: library/os os minor6451257
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Ref: library/os os makedev6451425
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Ref: library/os os pathconf6451546
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Ref: library/os os pathconf_names6452644
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Ref: library/os os readlink6452967
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Ref: library/os os remove6454466
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Ref: library/os os removedirs6455396
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Ref: library/os os rename6456238
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Ref: library/os os renames6457732
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Ref: library/os os replace6458519
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Ref: library/os os rmdir6459386
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Ref: library/os os scandir6460021
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Ref: library/os os scandir close6461797
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Ref: library/os os DirEntry6463321
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Ref: library/os os DirEntry name6464506
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Ref: Functions<3>-Footnote-16636397
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Ref: argparse — Parser for command-line options arguments and sub-commands-Footnote-16643942
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Ref: library/logging handlers logging handlers SocketHandler close6874894
Ref: 226c6874894
Ref: library/logging handlers logging handlers SocketHandler emit6874951
Ref: 226d6874951
Ref: library/logging handlers logging handlers SocketHandler handleError6875386
Ref: 226e6875386
Ref: library/logging handlers logging handlers SocketHandler makeSocket6875616
Ref: 226f6875616
Ref: library/logging handlers logging handlers SocketHandler makePickle6875859
Ref: 22706875859
Ref: library/logging handlers logging handlers SocketHandler send6876669
Ref: 22716876669
Ref: library/logging handlers logging handlers SocketHandler createSocket6876990
Ref: 22726876990
Node: DatagramHandler6878190
Ref: library/logging handlers datagram-handler6878323
Ref: 22736878323
Ref: library/logging handlers datagramhandler6878323
Ref: 22746878323
Ref: library/logging handlers logging handlers DatagramHandler6878559
Ref: 95b6878559
Ref: library/logging handlers logging handlers DatagramHandler emit6878970
Ref: 22756878970
Ref: library/logging handlers logging handlers DatagramHandler makeSocket6879324
Ref: 22766879324
Ref: library/logging handlers logging handlers DatagramHandler send6879510
Ref: 22776879510
Node: SysLogHandler6879725
Ref: library/logging handlers syslog-handler6879862
Ref: 22786879862
Ref: library/logging handlers sysloghandler6879862
Ref: 22796879862
Ref: library/logging handlers logging handlers SysLogHandler6880068
Ref: afb6880068
Ref: library/logging handlers logging handlers SysLogHandler close6881731
Ref: 227a6881731
Ref: library/logging handlers logging handlers SysLogHandler emit6881807
Ref: 227b6881807
Ref: library/logging handlers logging handlers SysLogHandler encodePriority6883689
Ref: 227c6883689
Ref: library/logging handlers logging handlers SysLogHandler mapPriority6887713
Ref: 227d6887713
Ref: SysLogHandler-Footnote-16888203
Ref: SysLogHandler-Footnote-26888246
Ref: SysLogHandler-Footnote-36888295
Node: NTEventLogHandler6888338
Ref: library/logging handlers nt-eventlog-handler6888471
Ref: 227e6888471
Ref: library/logging handlers nteventloghandler6888471
Ref: 227f6888471
Ref: library/logging handlers logging handlers NTEventLogHandler6888806
Ref: 22806888806
Ref: library/logging handlers logging handlers NTEventLogHandler close6889867
Ref: 22816889867
Ref: library/logging handlers logging handlers NTEventLogHandler emit6890269
Ref: 22826890269
Ref: library/logging handlers logging handlers NTEventLogHandler getEventCategory6890427
Ref: 22836890427
Ref: library/logging handlers logging handlers NTEventLogHandler getEventType6890629
Ref: 22846890629
Ref: library/logging handlers logging handlers NTEventLogHandler getMessageID6891222
Ref: 22856891222
Node: SMTPHandler6891652
Ref: library/logging handlers smtp-handler6891785
Ref: 22866891785
Ref: library/logging handlers smtphandler6891785
Ref: 22876891785
Ref: library/logging handlers logging handlers SMTPHandler6891982
Ref: 22886891982
Ref: library/logging handlers logging handlers SMTPHandler emit6893235
Ref: 22896893235
Ref: library/logging handlers logging handlers SMTPHandler getSubject6893339
Ref: 228a6893339
Node: MemoryHandler6893485
Ref: library/logging handlers memory-handler6893612
Ref: 228b6893612
Ref: library/logging handlers memoryhandler6893612
Ref: 228c6893612
Ref: library/logging handlers logging handlers BufferingHandler6894315
Ref: 228d6894315
Ref: library/logging handlers logging handlers BufferingHandler emit6894511
Ref: 228e6894511
Ref: library/logging handlers logging handlers BufferingHandler flush6894701
Ref: 22906894701
Ref: library/logging handlers logging handlers BufferingHandler shouldFlush6894854
Ref: 228f6894854
Ref: library/logging handlers logging handlers MemoryHandler6895037
Ref: 223f6895037
Ref: library/logging handlers logging handlers MemoryHandler close6895852
Ref: 22926895852
Ref: library/logging handlers logging handlers MemoryHandler flush6895980
Ref: 22936895980
Ref: library/logging handlers logging handlers MemoryHandler setTarget6896251
Ref: 22916896251
Ref: library/logging handlers logging handlers MemoryHandler shouldFlush6896341
Ref: 22946896341
Node: HTTPHandler6896467
Ref: library/logging handlers http-handler6896595
Ref: 22956896595
Ref: library/logging handlers httphandler6896595
Ref: 22966896595
Ref: library/logging handlers logging handlers HTTPHandler6896826
Ref: 8026896826
Ref: library/logging handlers logging handlers HTTPHandler mapLogRecord6897786
Ref: 22976897786
Ref: library/logging handlers logging handlers HTTPHandler emit6898242
Ref: 22986898242
Node: QueueHandler6898976
Ref: library/logging handlers queue-handler6899104
Ref: 22996899104
Ref: library/logging handlers queuehandler6899104
Ref: 229a6899104
Ref: library/logging handlers logging handlers QueueHandler6899843
Ref: 229b6899843
Ref: library/logging handlers logging handlers QueueHandler emit6900340
Ref: 229d6900340
Ref: library/logging handlers logging handlers QueueHandler prepare6900819
Ref: 229e6900819
Ref: library/logging handlers logging handlers QueueHandler enqueue6901366
Ref: 229c6901366
Node: QueueListener6901612
Ref: library/logging handlers queue-listener6901720
Ref: 229f6901720
Ref: library/logging handlers queuelistener6901720
Ref: 22a06901720
Ref: library/logging handlers logging handlers QueueListener6902740
Ref: 8036902740
Ref: library/logging handlers logging handlers QueueListener dequeue6903792
Ref: 22a16903792
Ref: library/logging handlers logging handlers QueueListener prepare6904073
Ref: 22a26904073
Ref: library/logging handlers logging handlers QueueListener handle6904390
Ref: 22a36904390
Ref: library/logging handlers logging handlers QueueListener start6904652
Ref: 22a46904652
Ref: library/logging handlers logging handlers QueueListener stop6904815
Ref: 22a56904815
Ref: library/logging handlers logging handlers QueueListener enqueue_sentinel6905126
Ref: 22a66905126
Node: getpass — Portable password input6905623
Ref: library/getpass doc6905839
Ref: 22a76905839
Ref: library/getpass getpass-portable-password-input6905839
Ref: 22a86905839
Ref: library/getpass module-getpass6905839
Ref: 866905839
Ref: library/getpass getpass getpass6906089
Ref: 22a96906089
Ref: library/getpass getpass GetPassWarning6906938
Ref: 22aa6906938
Ref: library/getpass getpass getuser6907066
Ref: 204f6907066
Ref: getpass — Portable password input-Footnote-16907653
Node: curses — Terminal handling for character-cell displays6907719
Ref: library/curses doc6907954
Ref: 22ab6907954
Ref: library/curses curses-terminal-handling-for-character-cell-displays6907954
Ref: 22ac6907954
Ref: library/curses module-curses6907954
Ref: 2b6907954
Ref: curses — Terminal handling for character-cell displays-Footnote-16910178
Node: Functions<4>6910241
Ref: library/curses curses-functions6910369
Ref: 22ae6910369
Ref: library/curses functions6910369
Ref: 22af6910369
Ref: library/curses curses error6910473
Ref: 22b06910473
Ref: library/curses curses baudrate6910835
Ref: 22b16910835
Ref: library/curses curses beep6911187
Ref: 22b26911187
Ref: library/curses curses can_change_color6911253
Ref: 22b36911253
Ref: library/curses curses cbreak6911425
Ref: 22b46911425
Ref: library/curses curses color_content6911903
Ref: 22b66911903
Ref: library/curses curses color_pair6912286
Ref: 22b76912286
Ref: library/curses curses curs_set6912661
Ref: 22b96912661
Ref: library/curses curses def_prog_mode6913089
Ref: 22ba6913089
Ref: library/curses curses def_shell_mode6913417
Ref: 22bc6913417
Ref: library/curses curses delay_output6913763
Ref: 22be6913763
Ref: library/curses curses doupdate6913853
Ref: 22bf6913853
Ref: library/curses curses echo6914678
Ref: 22c36914678
Ref: library/curses curses endwin6914814
Ref: 22c46914814
Ref: library/curses curses erasechar6914917
Ref: 22c56914917
Ref: library/curses curses filter6915185
Ref: 22c66915185
Ref: library/curses curses flash6915796
Ref: 22c86915796
Ref: library/curses curses flushinp6916059
Ref: 22c96916059
Ref: library/curses curses getmouse6916245
Ref: 22ca6916245
Ref: library/curses curses getsyx6917051
Ref: 22cc6917051
Ref: library/curses curses getwin6917262
Ref: 22ce6917262
Ref: library/curses curses has_colors6917498
Ref: 22cf6917498
Ref: library/curses curses has_ic6917630
Ref: 22d06917630
Ref: library/curses curses has_il6917886
Ref: 22d16917886
Ref: library/curses curses has_key6918183
Ref: 22d26918183
Ref: library/curses curses halfdelay6918337
Ref: 22d36918337
Ref: library/curses curses init_color6918775
Ref: 22d56918775
Ref: library/curses curses init_pair6919432
Ref: 22d66919432
Ref: library/curses curses initscr6920153
Ref: 22c76920153
Ref: library/curses curses is_term_resized6920428
Ref: 22d96920428
Ref: library/curses curses isendwin6920599
Ref: 22db6920599
Ref: library/curses curses keyname6920757
Ref: 22dc6920757
Ref: library/curses curses killchar6921288
Ref: 22dd6921288
Ref: library/curses curses longname6921559
Ref: 22de6921559
Ref: library/curses curses meta6921834
Ref: 22df6921834
Ref: library/curses curses mouseinterval6921991
Ref: 22e06921991
Ref: library/curses curses mousemask6922290
Ref: 22e16922290
Ref: library/curses curses napms6922710
Ref: 22e26922710
Ref: library/curses curses newpad6922778
Ref: 22e36922778
Ref: library/curses curses newwin6923866
Ref: 22e46923866
Ref: library/curses curses nl6924233
Ref: 22e56924233
Ref: library/curses curses nocbreak6924448
Ref: 22d46924448
Ref: library/curses curses noecho6924569
Ref: 22e66924569
Ref: library/curses curses nonl6924668
Ref: 22e76924668
Ref: library/curses curses noqiflush6925161
Ref: 22e86925161
Ref: library/curses curses noraw6925551
Ref: 22e96925551
Ref: library/curses curses pair_content6925666
Ref: 22ea6925666
Ref: library/curses curses pair_number6925892
Ref: 22b86925892
Ref: library/curses curses putp6926084
Ref: 22eb6926084
Ref: library/curses curses qiflush6926330
Ref: 22ec6926330
Ref: library/curses curses raw6926596
Ref: 22b56926596
Ref: library/curses curses reset_prog_mode6926838
Ref: 22bb6926838
Ref: library/curses curses reset_shell_mode6926986
Ref: 22bd6926986
Ref: library/curses curses resetty6927134
Ref: 22ed6927134
Ref: library/curses curses resize_term6927276
Ref: 22da6927276
Ref: library/curses curses resizeterm6927815
Ref: 22ef6927815
Ref: library/curses curses savetty6928088
Ref: 22ee6928088
Ref: library/curses curses get_escdelay6928223
Ref: 1986928223
Ref: library/curses curses set_escdelay6928347
Ref: 1996928347
Ref: library/curses curses get_tabsize6928643
Ref: 19a6928643
Ref: library/curses curses set_tabsize6928765
Ref: 19b6928765
Ref: library/curses curses setsyx6928976
Ref: 22f06928976
Ref: library/curses curses setupterm6929146
Ref: 22f16929146
Ref: library/curses curses start_color6929563
Ref: 22f26929563
Ref: library/curses curses termattrs6930243
Ref: 22f36930243
Ref: library/curses curses termname6930473
Ref: 22f46930473
Ref: library/curses curses tigetflag6930622
Ref: 22f56930622
Ref: library/curses curses tigetnum6930938
Ref: 22f66930938
Ref: library/curses curses tigetstr6931254
Ref: 22f76931254
Ref: library/curses curses tparm6931564
Ref: 22f86931564
Ref: library/curses curses typeahead6931901
Ref: 22f96931901
Ref: library/curses curses unctrl6932494
Ref: 22fa6932494
Ref: library/curses curses ungetch6932775
Ref: 22fb6932775
Ref: library/curses curses update_lines_cols6932952
Ref: 7b96932952
Ref: library/curses curses unget_wch6933111
Ref: abf6933111
Ref: library/curses curses ungetmouse6933329
Ref: 22fc6933329
Ref: library/curses curses use_env6933488
Ref: 22fd6933488
Ref: library/curses curses use_default_colors6933998
Ref: 22d76933998
Ref: library/curses curses wrapper6934431
Ref: 3c46934431
Node: Window Objects6935257
Ref: library/curses curses-window-objects6935406
Ref: 22d86935406
Ref: library/curses window-objects6935406
Ref: 22fe6935406
Ref: library/curses curses window addch6935588
Ref: 22ff6935588
Ref: library/curses curses window addnstr6936191
Ref: 23006936191
Ref: library/curses curses window addstr6936450
Ref: 22c16936450
Ref: library/curses curses window attroff6937450
Ref: 23016937450
Ref: library/curses curses window attron6937595
Ref: 23026937595
Ref: library/curses curses window attrset6937736
Ref: 23036937736
Ref: library/curses curses window bkgd6937884
Ref: 23046937884
Ref: library/curses curses window bkgdset6938329
Ref: 23056938329
Ref: library/curses curses window border6938895
Ref: 23066938895
Ref: library/curses curses window box6940847
Ref: 23076940847
Ref: library/curses curses window chgat6941075
Ref: 23086941075
Ref: library/curses curses window clear6941699
Ref: 230a6941699
Ref: library/curses curses window clearok6941854
Ref: 230c6941854
Ref: library/curses curses window clrtobot6941999
Ref: 230d6941999
Ref: library/curses curses window clrtoeol6942196
Ref: 230e6942196
Ref: library/curses curses window cursyncup6942276
Ref: 230f6942276
Ref: library/curses curses window delch6942444
Ref: 23106942444
Ref: library/curses curses window deleteln6942523
Ref: 23116942523
Ref: library/curses curses window derwin6942647
Ref: 23126942647
Ref: library/curses curses window echochar6943057
Ref: 23146943057
Ref: library/curses curses window enclose6943211
Ref: 23156943211
Ref: library/curses curses window encoding6943515
Ref: abd6943515
Ref: library/curses curses window erase6943899
Ref: 230b6943899
Ref: library/curses curses window getbegyx6943952
Ref: 23166943952
Ref: library/curses curses window getbkgd6944056
Ref: 23176944056
Ref: library/curses curses window getch6944171
Ref: 22cb6944171
Ref: library/curses curses window get_wch6944491
Ref: abe6944491
Ref: library/curses curses window getkey6944757
Ref: 23186944757
Ref: library/curses curses window getmaxyx6945065
Ref: 23196945065
Ref: library/curses curses window getparyx6945170
Ref: 231a6945170
Ref: library/curses curses window getstr6945374
Ref: 231b6945374
Ref: library/curses curses window getyx6945590
Ref: 231c6945590
Ref: library/curses curses window hline6945731
Ref: 231d6945731
Ref: library/curses curses window idcok6945917
Ref: 231e6945917
Ref: library/curses curses window idlok6946263
Ref: 231f6946263
Ref: library/curses curses window immedok6946456
Ref: 23206946456
Ref: library/curses curses window inch6946805
Ref: 23216946805
Ref: library/curses curses window insch6946993
Ref: 23226946993
Ref: library/curses curses window insdelln6947207
Ref: 23236947207
Ref: library/curses curses window insertln6947586
Ref: 23246947586
Ref: library/curses curses window insnstr6947716
Ref: 23256947716
Ref: library/curses curses window insstr6948229
Ref: 23266948229
Ref: library/curses curses window instr6948648
Ref: 23276948648
Ref: library/curses curses window is_linetouched6949044
Ref: 23286949044
Ref: library/curses curses window is_wintouched6949327
Ref: 23296949327
Ref: library/curses curses window keypad6949507
Ref: 232a6949507
Ref: library/curses curses window leaveok6949775
Ref: 22cd6949775
Ref: library/curses curses window move6950126
Ref: 232b6950126
Ref: library/curses curses window mvderwin6950209
Ref: 232c6950209
Ref: library/curses curses window mvwin6950486
Ref: 232d6950486
Ref: library/curses curses window nodelay6950602
Ref: 232e6950602
Ref: library/curses curses window notimeout6950711
Ref: 232f6950711
Ref: library/curses curses window noutrefresh6950975
Ref: 22c06950975
Ref: library/curses curses window overlay6951249
Ref: 23306951249
Ref: library/curses curses window overwrite6951898
Ref: 23316951898
Ref: library/curses curses window putwin6952550
Ref: 23326952550
Ref: library/curses curses window redrawln6952756
Ref: 23336952756
Ref: library/curses curses window redrawwin6952962
Ref: 23346952962
Ref: library/curses curses window refresh6953108
Ref: 22c26953108
Ref: library/curses curses window resize6954129
Ref: 23356954129
Ref: library/curses curses window scroll6954481
Ref: 23366954481
Ref: library/curses curses window scrollok6954589
Ref: 23376954589
Ref: library/curses curses window setscrreg6955125
Ref: 23386955125
Ref: library/curses curses window standend6955294
Ref: 23396955294
Ref: library/curses curses window standout6955445
Ref: 233a6955445
Ref: library/curses curses window subpad6955515
Ref: 233b6955515
Ref: library/curses curses window subwin6955754
Ref: 23136955754
Ref: library/curses curses window syncdown6956112
Ref: 233c6956112
Ref: library/curses curses window syncok6956358
Ref: 233d6956358
Ref: library/curses curses window syncup6956521
Ref: 233e6956521
Ref: library/curses curses window timeout6956647
Ref: 233f6956647
Ref: library/curses curses window touchline6957150
Ref: 23096957150
Ref: library/curses curses window touchwin6957458
Ref: 23406957458
Ref: library/curses curses window untouchwin6957583
Ref: 23416957583
Ref: library/curses curses window vline6957716
Ref: 23426957716
Ref: Window Objects-Footnote-16957936
Node: Constants<6>6957979
Ref: library/curses constants6958107
Ref: 23436958107
Ref: library/curses curses ERR6958214
Ref: 23446958214
Ref: library/curses curses OK6958359
Ref: 23456958359
Ref: library/curses curses version6958502
Ref: 23466958502
Ref: library/curses curses ncurses_version6958639
Ref: 2f06958639
Node: curses textpad — Text input widget for curses programs6977198
Ref: library/curses curses-textpad-text-input-widget-for-curses-programs6977445
Ref: 23476977445
Ref: library/curses module-curses textpad6977445
Ref: 2e6977445
Ref: library/curses curses textpad rectangle6978035
Ref: 23496978035
Node: Textbox objects6978758
Ref: library/curses curses-textpad-objects6978866
Ref: 234a6978866
Ref: library/curses textbox-objects6978866
Ref: 234b6978866
Ref: library/curses curses textpad Textbox6978982
Ref: 23486978982
Ref: library/curses curses textpad Textbox edit6979461
Ref: 234d6979461
Ref: library/curses curses textpad Textbox do_command6980032
Ref: 234e6980032
Ref: library/curses curses textpad Textbox gather6983556
Ref: 234f6983556
Ref: library/curses curses textpad Textbox stripspaces6983749
Ref: 234c6983749
Node: curses ascii — Utilities for ASCII characters6984160
Ref: library/curses ascii doc6984402
Ref: 23506984402
Ref: library/curses ascii curses-ascii-utilities-for-ascii-characters6984402
Ref: 23516984402
Ref: library/curses ascii module-curses ascii6984402
Ref: 2c6984402
Ref: library/curses ascii curses ascii isalnum6988084
Ref: 23526988084
Ref: library/curses ascii curses ascii isalpha6988231
Ref: 23536988231
Ref: library/curses ascii curses ascii isascii6988376
Ref: 23546988376
Ref: library/curses ascii curses ascii isblank6988485
Ref: 23556988485
Ref: library/curses ascii curses ascii iscntrl6988598
Ref: 23566988598
Ref: library/curses ascii curses ascii isdigit6988724
Ref: 23576988724
Ref: library/curses ascii curses ascii isgraph6988888
Ref: 23586988888
Ref: library/curses ascii curses ascii islower6988989
Ref: 23596988989
Ref: library/curses ascii curses ascii isprint6989077
Ref: 235a6989077
Ref: library/curses ascii curses ascii ispunct6989181
Ref: 235b6989181
Ref: library/curses ascii curses ascii isspace6989324
Ref: 235c6989324
Ref: library/curses ascii curses ascii isupper6989492
Ref: 235d6989492
Ref: library/curses ascii curses ascii isxdigit6989576
Ref: 235e6989576
Ref: library/curses ascii curses ascii isctrl6989719
Ref: 235f6989719
Ref: library/curses ascii curses ascii ismeta6989828
Ref: 23606989828
Ref: library/curses ascii curses ascii ascii6990428
Ref: 23616990428
Ref: library/curses ascii curses ascii ctrl6990535
Ref: 23626990535
Ref: library/curses ascii curses ascii alt6990703
Ref: 23636990703
Ref: library/curses ascii curses ascii unctrl6990975
Ref: 23646990975
Ref: library/curses ascii curses ascii controlnames6991530
Ref: 23656991530
Node: curses panel — A panel stack extension for curses6991776
Ref: library/curses panel doc6992025
Ref: 23666992025
Ref: library/curses panel curses-panel-a-panel-stack-extension-for-curses6992025
Ref: 23676992025
Ref: library/curses panel module-curses panel6992025
Ref: 2d6992025
Node: Functions<5>6992503
Ref: library/curses panel cursespanel-functions6992625
Ref: 23686992625
Ref: library/curses panel functions6992625
Ref: 23696992625
Ref: library/curses panel curses panel bottom_panel6992735
Ref: 236a6992735
Ref: library/curses panel curses panel new_panel6992830
Ref: 236b6992830
Ref: library/curses panel curses panel top_panel6993132
Ref: 236c6993132
Ref: library/curses panel curses panel update_panels6993221
Ref: 236d6993221
Node: Panel Objects6993432
Ref: library/curses panel curses-panel-objects6993554
Ref: 236e6993554
Ref: library/curses panel panel-objects6993554
Ref: 236f6993554
Ref: library/curses panel curses panel Panel above6993910
Ref: 23706993910
Ref: library/curses panel curses panel Panel below6993987
Ref: 23716993987
Ref: library/curses panel curses panel Panel bottom6994064
Ref: 23726994064
Ref: library/curses panel curses panel Panel hidden6994142
Ref: 23736994142
Ref: library/curses panel curses panel Panel hide6994262
Ref: 23746994262
Ref: library/curses panel curses panel Panel move6994396
Ref: 23756994396
Ref: library/curses panel curses panel Panel replace6994488
Ref: 23766994488
Ref: library/curses panel curses panel Panel set_userptr6994592
Ref: 23776994592
Ref: library/curses panel curses panel Panel show6994786
Ref: 23786994786
Ref: library/curses panel curses panel Panel top6994869
Ref: 23796994869
Ref: library/curses panel curses panel Panel userptr6994937
Ref: 237a6994937
Ref: library/curses panel curses panel Panel window6995052
Ref: 237b6995052
Node: platform — Access to underlying platform’s identifying data6995140
Ref: library/platform doc6995381
Ref: 237c6995381
Ref: library/platform module-platform6995381
Ref: ce6995381
Ref: library/platform platform-access-to-underlying-platform-s-identifying-data6995381
Ref: 237d6995381
Ref: platform — Access to underlying platform’s identifying data-Footnote-16995875
Node: Cross Platform6995942
Ref: library/platform cross-platform6996078
Ref: 237e6996078
Ref: library/platform platform architecture6996129
Ref: 114e6996129
Ref: library/platform platform machine6997457
Ref: 237f6997457
Ref: library/platform platform node6997613
Ref: 23806997613
Ref: library/platform platform platform6997788
Ref: 11536997788
Ref: library/platform platform processor6998723
Ref: 23826998723
Ref: library/platform platform python_build6999044
Ref: 23836999044
Ref: library/platform platform python_compiler6999191
Ref: 23846999191
Ref: library/platform platform python_branch6999314
Ref: 23856999314
Ref: library/platform platform python_implementation6999428
Ref: 23866999428
Ref: library/platform platform python_revision6999632
Ref: 23876999632
Ref: library/platform platform python_version6999755
Ref: 23886999755
Ref: library/platform platform python_version_tuple7000004
Ref: 23897000004
Ref: library/platform platform release7000284
Ref: 238a7000284
Ref: library/platform platform system7000459
Ref: 238b7000459
Ref: library/platform platform system_alias7000671
Ref: 23817000671
Ref: library/platform platform version7000954
Ref: 238c7000954
Ref: library/platform platform uname7001131
Ref: 11517001131
Node: Java Platform7001824
Ref: library/platform java-platform7001985
Ref: 238d7001985
Ref: library/platform platform java_ver7002034
Ref: 238e7002034
Node: Windows Platform7002505
Ref: library/platform windows-platform7002666
Ref: 238f7002666
Ref: library/platform platform win32_ver7002721
Ref: 10407002721
Ref: library/platform platform win32_edition7003420
Ref: 23907003420
Ref: library/platform platform win32_is_iot7003693
Ref: 23917003693
Node: macOS Platform7003885
Ref: library/platform macos-platform7004047
Ref: 23927004047
Ref: library/platform platform mac_ver7004098
Ref: 11547004098
Node: Unix Platforms7004479
Ref: library/platform unix-platforms7004616
Ref: 23937004616
Ref: library/platform platform libc_ver7004667
Ref: 11507004667
Node: errno — Standard errno system symbols7005284
Ref: library/errno doc7005522
Ref: 23947005522
Ref: library/errno errno-standard-errno-system-symbols7005522
Ref: 23957005522
Ref: library/errno module-errno7005522
Ref: 7a7005522
Ref: library/errno errno errorcode7005934
Ref: 23967005934
Ref: library/errno errno EPERM7006455
Ref: 23977006455
Ref: library/errno errno ENOENT7006508
Ref: 23987006508
Ref: library/errno errno ESRCH7006564
Ref: 23997006564
Ref: library/errno errno EINTR7006609
Ref: 74b7006609
Ref: library/errno errno EIO7006765
Ref: 239a7006765
Ref: library/errno errno ENXIO7006802
Ref: 239b7006802
Ref: library/errno errno E2BIG7006857
Ref: 239c7006857
Ref: library/errno errno ENOEXEC7006904
Ref: 239d7006904
Ref: library/errno errno EBADF7006953
Ref: 22f7006953
Ref: library/errno errno ECHILD7006998
Ref: 239e7006998
Ref: library/errno errno EAGAIN7007047
Ref: 20957007047
Ref: library/errno errno ENOMEM7007087
Ref: 239f7007087
Ref: library/errno errno EACCES7007131
Ref: 23a07007131
Ref: library/errno errno EFAULT7007179
Ref: 23a17007179
Ref: library/errno errno ENOTBLK7007221
Ref: 23a27007221
Ref: library/errno errno EBUSY7007274
Ref: 23a37007274
Ref: library/errno errno EEXIST7007327
Ref: 23a47007327
Ref: library/errno errno EXDEV7007369
Ref: 206d7007369
Ref: library/errno errno ENODEV7007416
Ref: 23a57007416
Ref: library/errno errno ENOTDIR7007461
Ref: 23a67007461
Ref: library/errno errno EISDIR7007508
Ref: 23a77007508
Ref: library/errno errno EINVAL7007553
Ref: 11047007553
Ref: library/errno errno ENFILE7007600
Ref: 23a87007600
Ref: library/errno errno EMFILE7007650
Ref: 23a97007650
Ref: library/errno errno ENOTTY7007700
Ref: 23aa7007700
Ref: library/errno errno ETXTBSY7007747
Ref: 23ab7007747
Ref: library/errno errno EFBIG7007793
Ref: 23ac7007793
Ref: library/errno errno ENOSPC7007837
Ref: 23ad7007837
Ref: library/errno errno ESPIPE7007891
Ref: 23ae7007891
Ref: library/errno errno EROFS7007934
Ref: 23af7007934
Ref: library/errno errno EMLINK7007985
Ref: 23b07007985
Ref: library/errno errno EPIPE7008030
Ref: 23b17008030
Ref: library/errno errno EDOM7008071
Ref: 23b27008071
Ref: library/errno errno ERANGE7008135
Ref: 23b37008135
Ref: library/errno errno EDEADLK7008195
Ref: 23b47008195
Ref: library/errno errno ENAMETOOLONG7008256
Ref: 23b57008256
Ref: library/errno errno ENOLCK7008311
Ref: 23b67008311
Ref: library/errno errno ENOSYS7008367
Ref: 23b77008367
Ref: library/errno errno ENOTEMPTY7008422
Ref: 23b87008422
Ref: library/errno errno ELOOP7008475
Ref: 23b97008475
Ref: library/errno errno EWOULDBLOCK7008540
Ref: 23ba7008540
Ref: library/errno errno ENOMSG7008597
Ref: 23bb7008597
Ref: library/errno errno EIDRM7008654
Ref: 23bc7008654
Ref: library/errno errno ECHRNG7008702
Ref: 23bd7008702
Ref: library/errno errno EL2NSYNC7008760
Ref: 23be7008760
Ref: library/errno errno EL3HLT7008817
Ref: 23bf7008817
Ref: library/errno errno EL3RST7008862
Ref: 23c07008862
Ref: library/errno errno ELNRNG7008906
Ref: 23c17008906
Ref: library/errno errno EUNATCH7008961
Ref: 23c27008961
Ref: library/errno errno ENOCSI7009021
Ref: 23c37009021
Ref: library/errno errno EL2HLT7009078
Ref: 23c47009078
Ref: library/errno errno EBADE7009123
Ref: 23c57009123
Ref: library/errno errno EBADR7009169
Ref: 23c67009169
Ref: library/errno errno EXFULL7009225
Ref: 23c77009225
Ref: library/errno errno ENOANO7009269
Ref: 23c87009269
Ref: library/errno errno EBADRQC7009308
Ref: 23c97009308
Ref: library/errno errno EBADSLT7009360
Ref: 23ca7009360
Ref: library/errno errno EDEADLOCK7009404
Ref: 23cb7009404
Ref: library/errno errno EBFONT7009465
Ref: 23cc7009465
Ref: library/errno errno ENOSTR7009516
Ref: 23cd7009516
Ref: library/errno errno ENODATA7009566
Ref: 23ce7009566
Ref: library/errno errno ETIME7009615
Ref: 23cf7009615
Ref: library/errno errno ENOSR7009658
Ref: 23d07009658
Ref: library/errno errno ENONET7009712
Ref: 23d17009712
Ref: library/errno errno ENOPKG7009772
Ref: 23d27009772
Ref: library/errno errno EREMOTE7009824
Ref: 23d37009824
Ref: library/errno errno ENOLINK7009872
Ref: 23d47009872
Ref: library/errno errno EADV7009925
Ref: 23d57009925
Ref: library/errno errno ESRMNT7009969
Ref: 23d67009969
Ref: library/errno errno ECOMM7010013
Ref: 23d77010013
Ref: library/errno errno EPROTO7010070
Ref: 23d87010070
Ref: library/errno errno EMULTIHOP7010115
Ref: 23d97010115
Ref: library/errno errno EDOTDOT7010167
Ref: 23da7010167
Ref: library/errno errno EBADMSG7010217
Ref: 23db7010217
Ref: library/errno errno EOVERFLOW7010267
Ref: 23dc7010267
Ref: library/errno errno ENOTUNIQ7010338
Ref: 23dd7010338
Ref: library/errno errno EBADFD7010397
Ref: 23de7010397
Ref: library/errno errno EREMCHG7010456
Ref: 23df7010456
Ref: library/errno errno ELIBACC7010510
Ref: 23e07010510
Ref: library/errno errno ELIBBAD7010580
Ref: 23e17010580
Ref: library/errno errno ELIBSCN7010648
Ref: 23e27010648
Ref: library/errno errno ELIBMAX7010711
Ref: 23e37010711
Ref: library/errno errno ELIBEXEC7010790
Ref: 23e47010790
Ref: library/errno errno EILSEQ7010860
Ref: 23e57010860
Ref: library/errno errno ERESTART7010912
Ref: 23e67010912
Ref: library/errno errno ESTRPIPE7010988
Ref: 23e77010988
Ref: library/errno errno EUSERS7011039
Ref: 23e87011039
Ref: library/errno errno ENOTSOCK7011084
Ref: 23e97011084
Ref: library/errno errno EDESTADDRREQ7011147
Ref: 23ea7011147
Ref: library/errno errno EMSGSIZE7011212
Ref: 23eb7011212
Ref: library/errno errno EPROTOTYPE7011261
Ref: 23ec7011261
Ref: library/errno errno ENOPROTOOPT7011326
Ref: 23ed7011326
Ref: library/errno errno EPROTONOSUPPORT7011384
Ref: 23ee7011384
Ref: library/errno errno ESOCKTNOSUPPORT7011446
Ref: 23ef7011446
Ref: library/errno errno EOPNOTSUPP7011511
Ref: 23f07011511
Ref: library/errno errno EPFNOSUPPORT7011591
Ref: 23f17011591
Ref: library/errno errno EAFNOSUPPORT7011657
Ref: 23f27011657
Ref: library/errno errno EADDRINUSE7011734
Ref: 23f37011734
Ref: library/errno errno EADDRNOTAVAIL7011791
Ref: 23f47011791
Ref: library/errno errno ENETDOWN7011860
Ref: 23f57011860
Ref: library/errno errno ENETUNREACH7011908
Ref: 111f7011908
Ref: library/errno errno ENETRESET7011966
Ref: 23f67011966
Ref: library/errno errno ECONNABORTED7012043
Ref: 23f77012043
Ref: library/errno errno ECONNRESET7012112
Ref: 23f87012112
Ref: library/errno errno ENOBUFS7012171
Ref: 23f97012171
Ref: library/errno errno EISCONN7012228
Ref: 23fa7012228
Ref: library/errno errno ENOTCONN7012299
Ref: 23fb7012299
Ref: library/errno errno ESHUTDOWN7012367
Ref: 23fc7012367
Ref: library/errno errno ETOOMANYREFS7012446
Ref: 23fd7012446
Ref: library/errno errno ETIMEDOUT7012517
Ref: 23fe7012517
Ref: library/errno errno ECONNREFUSED7012571
Ref: 23ff7012571
Ref: library/errno errno EHOSTDOWN7012626
Ref: 24007012626
Ref: library/errno errno EHOSTUNREACH7012672
Ref: 24017012672
Ref: library/errno errno EALREADY7012725
Ref: 24027012725
Ref: library/errno errno EINPROGRESS7012787
Ref: 24037012787
Ref: library/errno errno ESTALE7012848
Ref: 24047012848
Ref: library/errno errno EUCLEAN7012900
Ref: 24057012900
Ref: library/errno errno ENOTNAM7012956
Ref: 24067012956
Ref: library/errno errno ENAVAIL7013015
Ref: 24077013015
Ref: library/errno errno EISNAM7013076
Ref: 24087013076
Ref: library/errno errno EREMOTEIO7013127
Ref: 24097013127
Ref: library/errno errno EDQUOT7013177
Ref: 240a7013177
Node: ctypes — A foreign function library for Python7013222
Ref: library/ctypes doc7013388
Ref: 240b7013388
Ref: library/ctypes ctypes-a-foreign-function-library-for-python7013388
Ref: 240c7013388
Ref: library/ctypes module-ctypes7013388
Ref: 2a7013388
Node: ctypes tutorial7013841
Ref: library/ctypes ctypes-ctypes-tutorial7013966
Ref: 240d7013966
Ref: library/ctypes ctypes-tutorial7013966
Ref: 240e7013966
Node: Loading dynamic link libraries7015332
Ref: library/ctypes ctypes-loading-dynamic-link-libraries7015459
Ref: 24117015459
Ref: library/ctypes loading-dynamic-link-libraries7015459
Ref: 24127015459
Node: Accessing functions from loaded dlls7017505
Ref: library/ctypes accessing-functions-from-loaded-dlls7017658
Ref: 24137017658
Ref: library/ctypes ctypes-accessing-functions-from-loaded-dlls7017658
Ref: 24147017658
Node: Calling functions7019913
Ref: library/ctypes calling-functions7020058
Ref: 24157020058
Ref: library/ctypes ctypes-calling-functions7020058
Ref: 24167020058
Node: Fundamental data types7022530
Ref: library/ctypes ctypes-fundamental-data-types7022666
Ref: 24177022666
Ref: library/ctypes fundamental-data-types7022666
Ref: 24187022666
Node: Calling functions continued7030711
Ref: library/ctypes calling-functions-continued7030879
Ref: 24297030879
Ref: library/ctypes ctypes-calling-functions-continued7030879
Ref: 242a7030879
Node: Calling functions with your own custom data types7031963
Ref: library/ctypes calling-functions-with-your-own-custom-data-types7032167
Ref: 242b7032167
Ref: library/ctypes ctypes-calling-functions-with-own-custom-data-types7032167
Ref: 242c7032167
Node: Specifying the required argument types function prototypes7033010
Ref: library/ctypes ctypes-specifying-required-argument-types7033199
Ref: 242d7033199
Ref: library/ctypes specifying-the-required-argument-types-function-prototypes7033199
Ref: 242e7033199
Node: Return types7035025
Ref: library/ctypes ctypes-return-types7035216
Ref: 242f7035216
Ref: library/ctypes return-types7035216
Ref: 24307035216
Node: Passing pointers or passing parameters by reference7037845
Ref: library/ctypes ctypes-passing-pointers7037999
Ref: 24327037999
Ref: library/ctypes passing-pointers-or-passing-parameters-by-reference7037999
Ref: 24337037999
Node: Structures and unions7039093
Ref: library/ctypes ctypes-structures-unions7039275
Ref: 24367039275
Ref: library/ctypes structures-and-unions7039275
Ref: 24377039275
Ref: library/ctypes ctypes-structureunion-alignment-byte-order7041361
Ref: 243a7041361
Node: Structure/union alignment and byte order7041689
Ref: library/ctypes structure-union-alignment-and-byte-order7041855
Ref: 243b7041855
Node: Bit fields in structures and unions7042635
Ref: library/ctypes bit-fields-in-structures-and-unions7042786
Ref: 243e7042786
Ref: library/ctypes ctypes-bit-fields-in-structures-unions7042786
Ref: 243f7042786
Node: Arrays7043373
Ref: library/ctypes arrays7043492
Ref: 24407043492
Ref: library/ctypes ctypes-arrays7043492
Ref: 24417043492
Node: Pointers7044781
Ref: library/ctypes ctypes-pointers7044881
Ref: 24427044881
Ref: library/ctypes pointers7044881
Ref: 24437044881
Node: Type conversions7047544
Ref: library/ctypes ctypes-type-conversions7047654
Ref: 24467047654
Ref: library/ctypes type-conversions7047654
Ref: 24477047654
Node: Incomplete Types7050256
Ref: library/ctypes ctypes-incomplete-types7050376
Ref: 24487050376
Ref: library/ctypes incomplete-types7050376
Ref: 24497050376
Node: Callback functions7051985
Ref: library/ctypes callback-functions7052124
Ref: 244a7052124
Ref: library/ctypes ctypes-callback-functions7052124
Ref: 244b7052124
Node: Accessing values exported from dlls7055998
Ref: library/ctypes accessing-values-exported-from-dlls7056130
Ref: 244f7056130
Ref: library/ctypes ctypes-accessing-values-exported-from-dlls7056130
Ref: 24507056130
Node: Surprises7058933
Ref: library/ctypes ctypes-surprises7059072
Ref: 24537059072
Ref: library/ctypes surprises7059072
Ref: 24547059072
Node: Variable-sized data types7061247
Ref: library/ctypes ctypes-variable-sized-data-types7061342
Ref: 24557061342
Ref: library/ctypes variable-sized-data-types7061342
Ref: 24567061342
Node: ctypes reference7062745
Ref: library/ctypes ctypes-ctypes-reference7062870
Ref: 24587062870
Ref: library/ctypes ctypes-reference7062870
Ref: 24597062870
Node: Finding shared libraries7063181
Ref: library/ctypes ctypes-finding-shared-libraries7063291
Ref: 245a7063291
Ref: library/ctypes finding-shared-libraries7063291
Ref: 245b7063291
Node: Loading shared libraries7065817
Ref: library/ctypes ctypes-loading-shared-libraries7065953
Ref: 245c7065953
Ref: library/ctypes loading-shared-libraries7065953
Ref: 245d7065953
Ref: library/ctypes ctypes CDLL7066156
Ref: 2f27066156
Ref: library/ctypes ctypes OleDLL7067196
Ref: 245e7067196
Ref: library/ctypes ctypes WinDLL7067889
Ref: 24607067889
Ref: library/ctypes ctypes PyDLL7068563
Ref: 24617068563
Ref: library/ctypes ctypes PyDLL _handle7072286
Ref: 24667072286
Ref: library/ctypes ctypes PyDLL _name7072368
Ref: 24677072368
Ref: library/ctypes ctypes LibraryLoader7072710
Ref: 24687072710
Ref: library/ctypes ctypes LibraryLoader LoadLibrary7073175
Ref: 24697073175
Ref: Loading shared libraries-Footnote-17074750
Node: Foreign functions7074816
Ref: library/ctypes ctypes-foreign-functions7074947
Ref: 246a7074947
Ref: library/ctypes foreign-functions7074947
Ref: 246b7074947
Ref: library/ctypes ctypes _FuncPtr7075361
Ref: 246c7075361
Ref: library/ctypes ctypes _FuncPtr restype7075662
Ref: 246d7075662
Ref: library/ctypes ctypes _FuncPtr argtypes7076358
Ref: 246f7076358
Ref: library/ctypes ctypes _FuncPtr errcheck7077597
Ref: 246e7077597
Ref: library/ctypes ctypes ArgumentError7078583
Ref: 24707078583
Node: Function prototypes7079223
Ref: library/ctypes ctypes-function-prototypes7079347
Ref: 24717079347
Ref: library/ctypes function-prototypes7079347
Ref: 24727079347
Ref: library/ctypes ctypes CFUNCTYPE7079930
Ref: 244c7079930
Ref: library/ctypes ctypes WINFUNCTYPE7080441
Ref: 244d7080441
Ref: library/ctypes ctypes PYFUNCTYPE7080893
Ref: 24737080893
Node: Utility functions7086526
Ref: library/ctypes ctypes-utility-functions7086643
Ref: 24747086643
Ref: library/ctypes utility-functions7086643
Ref: 24757086643
Ref: library/ctypes ctypes addressof7086702
Ref: 24767086702
Ref: library/ctypes ctypes alignment7086945
Ref: 24777086945
Ref: library/ctypes ctypes byref7087105
Ref: 24347087105
Ref: library/ctypes ctypes cast7087619
Ref: 114b7087619
Ref: library/ctypes ctypes create_string_buffer7087913
Ref: 24287087913
Ref: library/ctypes ctypes create_unicode_buffer7088718
Ref: 10d77088718
Ref: library/ctypes ctypes DllCanUnloadNow7089537
Ref: 24787089537
Ref: library/ctypes ctypes DllGetClassObject7089782
Ref: 24797089782
Ref: library/ctypes ctypes util find_library7090042
Ref: 7017090042
Ref: library/ctypes ctypes util find_msvcrt7090434
Ref: 247a7090434
Ref: library/ctypes ctypes FormatError7090890
Ref: 247b7090890
Ref: library/ctypes ctypes GetLastError7091129
Ref: 24317091129
Ref: library/ctypes ctypes get_errno7091403
Ref: 24627091403
Ref: library/ctypes ctypes get_last_error7091655
Ref: 24647091655
Ref: library/ctypes ctypes memmove7091930
Ref: 247c7091930
Ref: library/ctypes ctypes memset7092174
Ref: 247d7092174
Ref: library/ctypes ctypes POINTER7092427
Ref: 24457092427
Ref: library/ctypes ctypes pointer7092675
Ref: 24357092675
Ref: library/ctypes ctypes resize7092995
Ref: 24577092995
Ref: library/ctypes ctypes set_errno7093333
Ref: 24637093333
Ref: library/ctypes ctypes set_last_error7093640
Ref: 24657093640
Ref: library/ctypes ctypes sizeof7093970
Ref: 247e7093970
Ref: library/ctypes ctypes string_at7094141
Ref: 247f7094141
Ref: library/ctypes ctypes WinError7094510
Ref: 24807094510
Ref: library/ctypes ctypes wstring_at7094991
Ref: 24817094991
Node: Data types7095410
Ref: library/ctypes ctypes-data-types7095533
Ref: 24827095533
Ref: library/ctypes data-types7095533
Ref: 24837095533
Ref: library/ctypes ctypes _CData7095578
Ref: 11e57095578
Ref: library/ctypes ctypes _CData from_buffer7096213
Ref: 24857096213
Ref: library/ctypes ctypes _CData from_buffer_copy7096799
Ref: 24867096799
Ref: library/ctypes ctypes _CData from_address7097343
Ref: 24877097343
Ref: library/ctypes ctypes _CData from_param7097688
Ref: 24887097688
Ref: library/ctypes ctypes _CData in_dll7098242
Ref: 24897098242
Ref: library/ctypes ctypes _CData _b_base_7098538
Ref: 248a7098538
Ref: library/ctypes ctypes _CData _b_needsfree_7098843
Ref: 248b7098843
Ref: library/ctypes ctypes _CData _objects7099017
Ref: 24847099017
Node: Fundamental data types<2>7099329
Ref: library/ctypes ctypes-fundamental-data-types-27099456
Ref: 248c7099456
Ref: library/ctypes id17099456
Ref: 248d7099456
Ref: library/ctypes ctypes _SimpleCData7099525
Ref: 248e7099525
Ref: library/ctypes ctypes _SimpleCData value7099998
Ref: 248f7099998
Ref: library/ctypes ctypes c_byte7101353
Ref: 241c7101353
Ref: library/ctypes ctypes c_char7101571
Ref: 241a7101571
Ref: library/ctypes ctypes c_char_p7101817
Ref: 24267101817
Ref: library/ctypes ctypes c_double7102118
Ref: fc47102118
Ref: library/ctypes ctypes c_longdouble7102253
Ref: fc57102253
Ref: library/ctypes ctypes c_float7102505
Ref: 24257102505
Ref: library/ctypes ctypes c_int7102638
Ref: 240f7102638
Ref: library/ctypes ctypes c_int87102908
Ref: 24907102908
Ref: library/ctypes ctypes c_int167103037
Ref: 24917103037
Ref: library/ctypes ctypes c_int327103169
Ref: 24927103169
Ref: library/ctypes ctypes c_int647103299
Ref: 24937103299
Ref: library/ctypes ctypes c_long7103434
Ref: 24107103434
Ref: library/ctypes ctypes c_longlong7103604
Ref: 24227103604
Ref: library/ctypes ctypes c_short7103788
Ref: 241e7103788
Ref: library/ctypes ctypes c_size_t7103960
Ref: 24247103960
Ref: library/ctypes ctypes c_ssize_t7104034
Ref: c9f7104034
Ref: library/ctypes ctypes c_ubyte7104136
Ref: 241d7104136
Ref: library/ctypes ctypes c_uint7104356
Ref: 24207104356
Ref: library/ctypes ctypes c_uint87104631
Ref: 24947104631
Ref: library/ctypes ctypes c_uint167104764
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Ref: library/ctypes ctypes c_uint327104900
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Ref: library/ctypes ctypes c_uint647105034
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Ref: library/ctypes ctypes c_ulong7105173
Ref: 24217105173
Ref: library/ctypes ctypes c_ulonglong7105346
Ref: 24237105346
Ref: library/ctypes ctypes c_ushort7105533
Ref: 241f7105533
Ref: library/ctypes ctypes c_void_p7105713
Ref: 24277105713
Ref: library/ctypes ctypes c_wchar7105884
Ref: 241b7105884
Ref: library/ctypes ctypes c_wchar_p7106149
Ref: fa97106149
Ref: library/ctypes ctypes c_bool7106363
Ref: 24197106363
Ref: library/ctypes ctypes HRESULT7106590
Ref: 245f7106590
Ref: library/ctypes ctypes py_object7106751
Ref: 24987106751
Node: Structured data types7107147
Ref: library/ctypes ctypes-structured-data-types7107283
Ref: 24997107283
Ref: library/ctypes structured-data-types7107283
Ref: 249a7107283
Ref: library/ctypes ctypes Union7107350
Ref: 24397107350
Ref: library/ctypes ctypes BigEndianStructure7107448
Ref: 243c7107448
Ref: library/ctypes ctypes LittleEndianStructure7107569
Ref: 243d7107569
Ref: library/ctypes ctypes Structure7107827
Ref: 24387107827
Ref: library/ctypes ctypes Structure _fields_7108251
Ref: 249b7108251
Ref: library/ctypes ctypes Structure _pack_7109845
Ref: 249c7109845
Ref: library/ctypes ctypes Structure _anonymous_7110133
Ref: 249d7110133
Node: Arrays and pointers7112489
Ref: library/ctypes arrays-and-pointers7112591
Ref: 249e7112591
Ref: library/ctypes ctypes-arrays-pointers7112591
Ref: 249f7112591
Ref: library/ctypes ctypes Array7112654
Ref: 11457112654
Ref: library/ctypes ctypes Array _length_7113164
Ref: 24a07113164
Ref: library/ctypes ctypes Array _type_7113392
Ref: 24a17113392
Ref: library/ctypes ctypes _Pointer7113590
Ref: 24a27113590
Ref: library/ctypes ctypes _Pointer _type_7114248
Ref: 24a37114248
Ref: library/ctypes ctypes _Pointer contents7114318
Ref: 24447114318
Node: Concurrent Execution7114508
Ref: library/concurrency doc7114684
Ref: 24a47114684
Ref: library/concurrency concurrency7114684
Ref: 24a57114684
Ref: library/concurrency concurrent-execution7114684
Ref: 24a67114684
Node: threading — Thread-based parallelism7115655
Ref: library/threading doc7115804
Ref: 24a77115804
Ref: library/threading module-threading7115804
Ref: 10b7115804
Ref: library/threading threading-thread-based-parallelism7115804
Ref: 24a87115804
Ref: library/threading threading active_count7117025
Ref: 24a97117025
Ref: library/threading threading current_thread7117237
Ref: 24aa7117237
Ref: library/threading threading excepthook7117555
Ref: 35e7117555
Ref: library/threading threading get_ident7118889
Ref: b877118889
Ref: library/threading threading get_native_id7119283
Ref: 3607119283
Ref: library/threading threading enumerate7119744
Ref: f907119744
Ref: library/threading threading main_thread7120129
Ref: 9d57120129
Ref: library/threading threading settrace7120354
Ref: 24ab7120354
Ref: library/threading threading setprofile7120621
Ref: 24ac7120621
Ref: library/threading threading stack_size7120894
Ref: 24ad7120894
Ref: library/threading threading TIMEOUT_MAX7122189
Ref: 24ae7122189
Ref: threading — Thread-based parallelism-Footnote-17123545
Node: Thread-Local Data7123613
Ref: library/threading thread-local-data7123728
Ref: 24af7123728
Ref: library/threading threading local7124080
Ref: 244e7124080
Node: Thread Objects7124276
Ref: library/threading id17124412
Ref: 24b07124412
Ref: library/threading thread-objects7124412
Ref: 24b17124412
Ref: library/threading threading Thread7127091
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Ref: library/threading threading Thread start7128325
Ref: 222e7128325
Ref: library/threading threading Thread run7128702
Ref: 35f7128702
Ref: library/threading threading Thread join7129114
Ref: c327129114
Ref: library/threading threading Thread name7130393
Ref: 24b27130393
Ref: library/threading threading Thread getName7130611
Ref: 24b47130611
Ref: library/threading threading Thread setName7130639
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Ref: library/threading threading Thread ident7130773
Ref: 21757130773
Ref: library/threading threading Thread native_id7131164
Ref: 3617131164
Ref: library/threading threading Thread is_alive7132024
Ref: 21b7132024
Ref: library/threading threading Thread daemon7132361
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Ref: library/threading threading Thread isDaemon7132944
Ref: 24b67132944
Ref: library/threading threading Thread setDaemon7132973
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Node: Lock Objects7133111
Ref: library/threading id27133243
Ref: 24b87133243
Ref: library/threading lock-objects7133243
Ref: 24b97133243
Ref: library/threading threading Lock7134660
Ref: 24bc7134660
Ref: library/threading threading Lock acquire7135062
Ref: 85b7135062
Ref: library/threading threading Lock release7136393
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Ref: library/threading threading Lock locked7136878
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Node: RLock Objects7136954
Ref: library/threading id37137089
Ref: 24be7137089
Ref: library/threading rlock-objects7137089
Ref: 24bf7137089
Ref: library/threading threading RLock7137999
Ref: cba7137999
Ref: library/threading threading RLock acquire7138521
Ref: 85c7138521
Ref: library/threading threading RLock release7140048
Ref: 24c07140048
Node: Condition Objects7140741
Ref: library/threading condition-objects7140881
Ref: 24c17140881
Ref: library/threading id47140881
Ref: 24c27140881
Ref: library/threading threading Condition7144001
Ref: b827144001
Ref: library/threading threading Condition acquire7144544
Ref: 24c37144544
Ref: library/threading threading Condition release7144756
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Ref: library/threading threading Condition wait7144939
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Ref: library/threading threading Condition wait_for7146470
Ref: 24c77146470
Ref: library/threading threading Condition notify7147440
Ref: 24c57147440
Ref: library/threading threading Condition notify_all7148341
Ref: 24c67148341
Node: Semaphore Objects7148680
Ref: library/threading id57148820
Ref: 24c87148820
Ref: library/threading semaphore-objects7148820
Ref: 24c97148820
Ref: library/threading threading Semaphore7149516
Ref: b837149516
Ref: library/threading threading Semaphore acquire7150205
Ref: cb87150205
Ref: library/threading threading Semaphore release7151494
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Ref: library/threading threading BoundedSemaphore7151871
Ref: b847151871
Node: Semaphore Example7152434
Ref: library/threading semaphore-example7152505
Ref: 24cb7152505
Ref: library/threading semaphore-examples7152505
Ref: 24cc7152505
Node: Event Objects7153374
Ref: library/threading event-objects7153510
Ref: 24cd7153510
Ref: library/threading id67153510
Ref: 24ce7153510
Ref: library/threading threading Event7153911
Ref: b857153911
Ref: library/threading threading Event is_set7154301
Ref: 24d17154301
Ref: library/threading threading Event set7154400
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Ref: library/threading threading Event clear7154627
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Ref: library/threading threading Event wait7154855
Ref: d7f7154855
Node: Timer Objects7155730
Ref: library/threading id77155864
Ref: 24d27155864
Ref: library/threading timer-objects7155864
Ref: 24d37155864
Ref: library/threading threading Timer7156613
Ref: b867156613
Ref: library/threading threading Timer cancel7157062
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Node: Barrier Objects7157252
Ref: library/threading barrier-objects7157432
Ref: 24d57157432
Ref: library/threading threading Barrier7158387
Ref: c317158387
Ref: library/threading threading Barrier wait7158731
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Ref: library/threading threading Barrier reset7159878
Ref: 24d77159878
Ref: library/threading threading Barrier abort7160314
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Ref: library/threading threading Barrier parties7160803
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Ref: library/threading threading Barrier n_waiting7160895
Ref: 24da7160895
Ref: library/threading threading Barrier broken7160993
Ref: 24db7160993
Ref: library/threading threading BrokenBarrierError7161110
Ref: c337161110
Node: Using locks conditions and semaphores in the with statement7161287
Ref: library/threading using-locks-conditions-and-semaphores-in-the-with-statement7161445
Ref: 24dc7161445
Ref: library/threading with-locks7161445
Ref: 24bb7161445
Node: multiprocessing — Process-based parallelism7162290
Ref: library/multiprocessing doc7162539
Ref: 24dd7162539
Ref: library/multiprocessing module-multiprocessing7162539
Ref: b77162539
Ref: library/multiprocessing multiprocessing-process-based-parallelism7162539
Ref: 24de7162539
Ref: multiprocessing — Process-based parallelism-Footnote-17162906
Node: Introduction<8>7162978
Ref: library/multiprocessing introduction7163093
Ref: 24df7163093
Node: The Process class7164626
Ref: library/multiprocessing the-process-class7164730
Ref: 24e07164730
Node: Contexts and start methods7165911
Ref: library/multiprocessing contexts-and-start-methods7166060
Ref: 24e37166060
Ref: library/multiprocessing multiprocessing-start-methods7166133
Ref: 9617166133
Ref: Contexts and start methods-Footnote-17170611
Node: Exchanging objects between processes7170654
Ref: library/multiprocessing exchanging-objects-between-processes7170819
Ref: 24e67170819
Node: Synchronization between processes7172537
Ref: library/multiprocessing synchronization-between-processes7172707
Ref: 24e97172707
Node: Sharing state between processes7173428
Ref: library/multiprocessing sharing-state-between-processes7173585
Ref: 24ea7173585
Node: Using a pool of workers7176670
Ref: library/multiprocessing using-a-pool-of-workers7176785
Ref: 24f57176785
Node: Reference7179902
Ref: library/multiprocessing reference7180048
Ref: 24f67180048
Node: Process and exceptions7180577
Ref: library/multiprocessing process-and-exceptions7180670
Ref: 24f77180670
Ref: library/multiprocessing multiprocessing Process7180743
Ref: 4b97180743
Ref: library/multiprocessing multiprocessing Process run7182112
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Ref: library/multiprocessing multiprocessing Process start7182524
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Ref: library/multiprocessing multiprocessing Process join7182773
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Ref: library/multiprocessing multiprocessing Process name7183495
Ref: 24f87183495
Ref: library/multiprocessing multiprocessing Process is_alive7183960
Ref: 24fc7183960
Ref: library/multiprocessing multiprocessing Process daemon7184196
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Ref: library/multiprocessing multiprocessing Process pid7185077
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Ref: library/multiprocessing multiprocessing Process exitcode7185202
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Ref: library/multiprocessing multiprocessing Process authkey7185430
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Ref: library/multiprocessing multiprocessing Process sentinel7185958
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Ref: library/multiprocessing multiprocessing Process terminate7186595
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Ref: library/multiprocessing multiprocessing Process kill7187397
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Ref: library/multiprocessing multiprocessing Process close7187552
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Ref: library/multiprocessing multiprocessing ProcessError7188790
Ref: 25017188790
Ref: library/multiprocessing multiprocessing BufferTooShort7188902
Ref: 25027188902
Ref: library/multiprocessing multiprocessing AuthenticationError7189211
Ref: 25037189211
Ref: library/multiprocessing multiprocessing TimeoutError7189315
Ref: 25047189315
Node: Pipes and Queues7189425
Ref: library/multiprocessing pipes-and-queues7189543
Ref: 25057189543
Ref: library/multiprocessing multiprocessing Pipe7192966
Ref: 24e87192966
Ref: library/multiprocessing multiprocessing Queue7193388
Ref: 24e77193388
Ref: library/multiprocessing multiprocessing Queue qsize7193986
Ref: 25127193986
Ref: library/multiprocessing multiprocessing Queue empty7194333
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Ref: library/multiprocessing multiprocessing Queue full7194530
Ref: 25137194530
Ref: library/multiprocessing multiprocessing Queue put7194725
Ref: 11637194725
Ref: library/multiprocessing multiprocessing Queue put_nowait7195552
Ref: 25147195552
Ref: library/multiprocessing multiprocessing Queue get7195635
Ref: 11647195635
Ref: library/multiprocessing multiprocessing Queue get_nowait7196423
Ref: 250e7196423
Ref: library/multiprocessing multiprocessing Queue close7196669
Ref: 25157196669
Ref: library/multiprocessing multiprocessing Queue join_thread7196965
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Ref: library/multiprocessing multiprocessing Queue cancel_join_thread7197516
Ref: 250f7197516
Ref: library/multiprocessing multiprocessing SimpleQueue7198661
Ref: 1c37198661
Ref: library/multiprocessing multiprocessing SimpleQueue close7198797
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Ref: library/multiprocessing multiprocessing SimpleQueue empty7199106
Ref: 25197199106
Ref: library/multiprocessing multiprocessing SimpleQueue get7199208
Ref: 25177199208
Ref: library/multiprocessing multiprocessing SimpleQueue put7199286
Ref: 25187199286
Ref: library/multiprocessing multiprocessing JoinableQueue7199353
Ref: 25067199353
Ref: library/multiprocessing multiprocessing JoinableQueue task_done7199573
Ref: 25097199573
Ref: library/multiprocessing multiprocessing JoinableQueue join7200261
Ref: 251a7200261
Ref: Pipes and Queues-Footnote-17200765
Node: Miscellaneous<3>7200807
Ref: library/multiprocessing miscellaneous7200924
Ref: 251b7200924
Ref: library/multiprocessing multiprocessing active_children7200973
Ref: 251c7200973
Ref: library/multiprocessing multiprocessing cpu_count7201190
Ref: 96b7201190
Ref: library/multiprocessing multiprocessing current_process7201624
Ref: 251d7201624
Ref: library/multiprocessing multiprocessing parent_process7201822
Ref: 251e7201822
Ref: library/multiprocessing multiprocessing freeze_support7202089
Ref: 251f7202089
Ref: library/multiprocessing multiprocessing get_all_start_methods7203125
Ref: 9627203125
Ref: library/multiprocessing multiprocessing get_context7203543
Ref: 9657203543
Ref: library/multiprocessing multiprocessing get_start_method7203977
Ref: 9637203977
Ref: library/multiprocessing multiprocessing set_executable7204780
Ref: 25207204780
Ref: library/multiprocessing multiprocessing set_start_method7205244
Ref: 9647205244
Ref: Miscellaneous<3>-Footnote-17205943
Node: Connection Objects<2>7205986
Ref: library/multiprocessing connection-objects7206113
Ref: 25217206113
Ref: library/multiprocessing multiprocessing connection Connection7206432
Ref: 25117206432
Ref: library/multiprocessing multiprocessing connection Connection send7206482
Ref: 25237206482
Ref: library/multiprocessing multiprocessing connection Connection recv7206809
Ref: 25247206809
Ref: library/multiprocessing multiprocessing connection Connection fileno7207101
Ref: 25257207101
Ref: library/multiprocessing multiprocessing connection Connection close7207201
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Ref: library/multiprocessing multiprocessing connection Connection poll7207353
Ref: 25277207353
Ref: library/multiprocessing multiprocessing connection Connection send_bytes7207839
Ref: 25287207839
Ref: library/multiprocessing multiprocessing connection Connection recv_bytes7208298
Ref: 25297208298
Ref: library/multiprocessing multiprocessing connection Connection recv_bytes_into7208938
Ref: 252a7208938
Ref: library/multiprocessing multiprocessing-recv-pickle-security7210766
Ref: 252b7210766
Node: Synchronization primitives7211452
Ref: library/multiprocessing synchronization-primitives7211584
Ref: 252c7211584
Ref: library/multiprocessing multiprocessing Barrier7211955
Ref: 24f47211955
Ref: library/multiprocessing multiprocessing BoundedSemaphore7212113
Ref: 24f17212113
Ref: library/multiprocessing multiprocessing Condition7212611
Ref: 24f27212611
Ref: library/multiprocessing multiprocessing Event7212945
Ref: 24f37212945
Ref: library/multiprocessing multiprocessing Lock7213024
Ref: 24ee7213024
Ref: library/multiprocessing multiprocessing Lock acquire7213867
Ref: 252d7213867
Ref: library/multiprocessing multiprocessing Lock release7215393
Ref: 252e7215393
Ref: library/multiprocessing multiprocessing RLock7215762
Ref: 24ef7215762
Ref: library/multiprocessing multiprocessing RLock acquire7216493
Ref: 252f7216493
Ref: library/multiprocessing multiprocessing RLock release7218142
Ref: 25307218142
Ref: library/multiprocessing multiprocessing Semaphore7219119
Ref: 24f07219119
Ref: Synchronization primitives-Footnote-17220541
Node: Shared ctypes Objects7220583
Ref: library/multiprocessing shared-ctypes-objects7220702
Ref: 25317220702
Ref: library/multiprocessing multiprocessing Value7220879
Ref: 24eb7220879
Ref: library/multiprocessing multiprocessing Array7222308
Ref: 24ec7222308
Node: The multiprocessing sharedctypes module7223751
Ref: library/multiprocessing module-multiprocessing sharedctypes7223848
Ref: bd7223848
Ref: library/multiprocessing the-multiprocessing-sharedctypes-module7223848
Ref: 25327223848
Ref: library/multiprocessing multiprocessing sharedctypes RawArray7224479
Ref: 25337224479
Ref: library/multiprocessing multiprocessing sharedctypes RawValue7225308
Ref: 25357225308
Ref: library/multiprocessing multiprocessing sharedctypes Array7226092
Ref: 25347226092
Ref: library/multiprocessing multiprocessing sharedctypes Value7226859
Ref: 25367226859
Ref: library/multiprocessing multiprocessing sharedctypes copy7227610
Ref: 25377227610
Ref: library/multiprocessing multiprocessing sharedctypes synchronized7227772
Ref: 8087227772
Node: Managers7230788
Ref: library/multiprocessing managers7230894
Ref: 25387230894
Ref: library/multiprocessing multiprocessing-managers7230894
Ref: 250a7230894
Ref: library/multiprocessing multiprocessing sharedctypes multiprocessing Manager7231244
Ref: 25397231244
Ref: library/multiprocessing module-multiprocessing managers7231564
Ref: ba7231564
Ref: library/multiprocessing multiprocessing managers BaseManager7231754
Ref: 253b7231754
Ref: library/multiprocessing multiprocessing managers BaseManager start7232473
Ref: 253c7232473
Ref: library/multiprocessing multiprocessing managers BaseManager get_server7232708
Ref: 253d7232708
Ref: library/multiprocessing multiprocessing managers BaseManager connect7233252
Ref: 253f7233252
Ref: library/multiprocessing multiprocessing managers BaseManager shutdown7233533
Ref: 25407233533
Ref: library/multiprocessing multiprocessing managers BaseManager register7233769
Ref: 25417233769
Ref: library/multiprocessing multiprocessing managers BaseManager address7236085
Ref: 253e7236085
Ref: library/multiprocessing multiprocessing managers SyncManager7236616
Ref: 253a7236616
Ref: library/multiprocessing multiprocessing managers SyncManager Barrier7237051
Ref: 25447237051
Ref: library/multiprocessing multiprocessing managers SyncManager BoundedSemaphore7237240
Ref: 25457237240
Ref: library/multiprocessing multiprocessing managers SyncManager Condition7237395
Ref: 25467237395
Ref: library/multiprocessing multiprocessing managers SyncManager Event7237768
Ref: 25477237768
Ref: library/multiprocessing multiprocessing managers SyncManager Lock7237894
Ref: 25487237894
Ref: library/multiprocessing multiprocessing managers SyncManager Namespace7238019
Ref: 25497238019
Ref: library/multiprocessing multiprocessing managers SyncManager Queue7238144
Ref: 254a7238144
Ref: library/multiprocessing multiprocessing managers SyncManager RLock7238275
Ref: 254b7238275
Ref: library/multiprocessing multiprocessing managers SyncManager Semaphore7238401
Ref: 254c7238401
Ref: library/multiprocessing multiprocessing managers SyncManager Array7238542
Ref: 254d7238542
Ref: library/multiprocessing multiprocessing managers SyncManager Value7238641
Ref: 254e7238641
Ref: library/multiprocessing multiprocessing managers SyncManager dict7238786
Ref: 254f7238786
Ref: library/multiprocessing multiprocessing managers SyncManager list7238967
Ref: 25507238967
Ref: library/multiprocessing multiprocessing managers Namespace7239373
Ref: 24ed7239373
Node: Customized managers7240154
Ref: library/multiprocessing customized-managers7240249
Ref: 25517240249
Node: Using a remote manager7241021
Ref: library/multiprocessing using-a-remote-manager7241116
Ref: 25527241116
Node: Proxy Objects7243257
Ref: library/multiprocessing multiprocessing-proxy-objects7243355
Ref: 65e7243355
Ref: library/multiprocessing proxy-objects7243355
Ref: 25537243355
Ref: library/multiprocessing multiprocessing managers BaseProxy7246614
Ref: 25427246614
Ref: library/multiprocessing multiprocessing managers BaseProxy _callmethod7246735
Ref: 25437246735
Ref: library/multiprocessing multiprocessing managers BaseProxy _getvalue7248316
Ref: 25547248316
Ref: library/multiprocessing multiprocessing managers BaseProxy __repr__7248476
Ref: 25557248476
Ref: library/multiprocessing multiprocessing managers BaseProxy __str__7248562
Ref: 25567248562
Node: Cleanup7248667
Ref: library/multiprocessing cleanup7248724
Ref: 25577248724
Node: Process Pools7249013
Ref: library/multiprocessing module-multiprocessing pool7249124
Ref: bb7249124
Ref: library/multiprocessing process-pools7249124
Ref: 25587249124
Ref: library/multiprocessing multiprocessing pool Pool7249285
Ref: 9667249285
Ref: library/multiprocessing multiprocessing pool Pool apply7251893
Ref: 255b7251893
Ref: library/multiprocessing multiprocessing pool Pool apply_async7252264
Ref: 255c7252264
Ref: library/multiprocessing multiprocessing pool Pool map7253116
Ref: b067253116
Ref: library/multiprocessing multiprocessing pool Pool map_async7253900
Ref: b077253900
Ref: library/multiprocessing multiprocessing pool Pool imap7254754
Ref: 255e7254754
Ref: library/multiprocessing multiprocessing pool Pool imap_unordered7255464
Ref: 255f7255464
Ref: library/multiprocessing multiprocessing pool Pool starmap7255790
Ref: b037255790
Ref: library/multiprocessing multiprocessing pool Pool starmap_async7256142
Ref: b047256142
Ref: library/multiprocessing multiprocessing pool Pool close7256493
Ref: 25597256493
Ref: library/multiprocessing multiprocessing pool Pool terminate7256680
Ref: 255a7256680
Ref: library/multiprocessing multiprocessing pool Pool join7256914
Ref: 25607256914
Ref: library/multiprocessing multiprocessing pool AsyncResult7257358
Ref: 255d7257358
Ref: library/multiprocessing multiprocessing pool AsyncResult get7257515
Ref: 25617257515
Ref: library/multiprocessing multiprocessing pool AsyncResult wait7257880
Ref: 25627257880
Ref: library/multiprocessing multiprocessing pool AsyncResult ready7258004
Ref: 25637258004
Ref: library/multiprocessing multiprocessing pool AsyncResult successful7258081
Ref: 25647258081
Node: Listeners and Clients7259374
Ref: library/multiprocessing listeners-and-clients7259491
Ref: 25657259491
Ref: library/multiprocessing module-multiprocessing connection7259491
Ref: b87259491
Ref: library/multiprocessing multiprocessing-listeners-clients7259491
Ref: 25227259491
Ref: library/multiprocessing multiprocessing connection deliver_challenge7260027
Ref: 25667260027
Ref: library/multiprocessing multiprocessing connection answer_challenge7260433
Ref: 25677260433
Ref: library/multiprocessing multiprocessing connection Client7260747
Ref: 25687260747
Ref: library/multiprocessing multiprocessing connection Listener7261501
Ref: 106b7261501
Ref: library/multiprocessing multiprocessing connection Listener accept7263261
Ref: 256a7263261
Ref: library/multiprocessing multiprocessing connection Listener close7263543
Ref: 256b7263543
Ref: library/multiprocessing multiprocessing connection Listener address7263843
Ref: 256c7263843
Ref: library/multiprocessing multiprocessing connection Listener last_accepted7263939
Ref: 256d7263939
Ref: library/multiprocessing multiprocessing connection wait7264355
Ref: b017264355
Node: Address Formats7268395
Ref: library/multiprocessing address-formats7268468
Ref: 256e7268468
Ref: library/multiprocessing multiprocessing-address-formats7268468
Ref: 25697268468
Node: Authentication keys7269189
Ref: library/multiprocessing authentication-keys7269303
Ref: 256f7269303
Ref: library/multiprocessing multiprocessing-auth-keys7269303
Ref: 24ff7269303
Node: Logging<2>7270487
Ref: library/multiprocessing logging7270612
Ref: 25707270612
Ref: library/multiprocessing multiprocessing get_logger7270880
Ref: 25717270880
Ref: library/multiprocessing multiprocessing log_to_stderr7271392
Ref: 25727271392
Node: The multiprocessing dummy module7272499
Ref: library/multiprocessing module-multiprocessing dummy7272596
Ref: b97272596
Ref: library/multiprocessing the-multiprocessing-dummy-module7272596
Ref: 25737272596
Ref: library/multiprocessing multiprocessing pool ThreadPool7273120
Ref: fce7273120
Node: Programming guidelines7274953
Ref: library/multiprocessing multiprocessing-programming7275096
Ref: 24e27275096
Ref: library/multiprocessing programming-guidelines7275096
Ref: 25747275096
Node: All start methods7275344
Ref: library/multiprocessing all-start-methods7275467
Ref: 25757275467
Ref: All start methods-Footnote-17281563
Ref: All start methods-Footnote-27281605
Ref: All start methods-Footnote-37281647
Node: The spawn and forkserver start methods7281689
Ref: library/multiprocessing the-spawn-and-forkserver-start-methods7281812
Ref: 25767281812
Node: Examples<11>7283889
Ref: library/multiprocessing examples7284014
Ref: 25777284014
Ref: library/multiprocessing multiprocessing-examples7284014
Ref: 25107284014
Node: multiprocessing shared_memory — Provides shared memory for direct access across processes7292925
Ref: library/multiprocessing shared_memory doc7293158
Ref: 25787293158
Ref: library/multiprocessing shared_memory module-multiprocessing shared_memory7293158
Ref: bc7293158
Ref: library/multiprocessing shared_memory multiprocessing-shared-memory-provides-shared-memory-for-direct-access-across-processes7293158
Ref: 25797293158
Ref: library/multiprocessing shared_memory multiprocessing shared_memory SharedMemory7294724
Ref: 24e57294724
Ref: library/multiprocessing shared_memory multiprocessing shared_memory SharedMemory close7296399
Ref: 257a7296399
Ref: library/multiprocessing shared_memory multiprocessing shared_memory SharedMemory unlink7296755
Ref: 257b7296755
Ref: library/multiprocessing shared_memory multiprocessing shared_memory SharedMemory buf7297535
Ref: 257c7297535
Ref: library/multiprocessing shared_memory multiprocessing shared_memory SharedMemory name7297624
Ref: 257d7297624
Ref: library/multiprocessing shared_memory multiprocessing shared_memory SharedMemory size7297735
Ref: 257e7297735
Ref: library/multiprocessing shared_memory multiprocessing managers SharedMemoryManager7300825
Ref: 257f7300825
Ref: library/multiprocessing shared_memory multiprocessing managers SharedMemoryManager SharedMemory7302240
Ref: 25807302240
Ref: library/multiprocessing shared_memory multiprocessing managers SharedMemoryManager ShareableList7302396
Ref: 25817302396
Ref: library/multiprocessing shared_memory multiprocessing shared_memory ShareableList7304242
Ref: 10557304242
Ref: library/multiprocessing shared_memory multiprocessing shared_memory ShareableList count7305417
Ref: 25827305417
Ref: library/multiprocessing shared_memory multiprocessing shared_memory ShareableList index7305510
Ref: 25837305510
Ref: library/multiprocessing shared_memory multiprocessing shared_memory ShareableList format7305670
Ref: 25847305670
Ref: library/multiprocessing shared_memory multiprocessing shared_memory ShareableList shm7305824
Ref: 25857305824
Ref: multiprocessing shared_memory — Provides shared memory for direct access across processes-Footnote-17307500
Ref: multiprocessing shared_memory — Provides shared memory for direct access across processes-Footnote-27307589
Node: The concurrent package7307620
Ref: library/concurrent doc7307855
Ref: 25867307855
Ref: library/concurrent the-concurrent-package7307855
Ref: 25877307855
Node: concurrent futures — Launching parallel tasks7308043
Ref: library/concurrent futures doc7308223
Ref: 25887308223
Ref: library/concurrent futures concurrent-futures-launching-parallel-tasks7308223
Ref: 25897308223
Ref: library/concurrent futures module-concurrent futures7308223
Ref: 217308223
Ref: concurrent futures — Launching parallel tasks-Footnote-17309067
Ref: concurrent futures — Launching parallel tasks-Footnote-27309152
Node: Executor Objects7309238
Ref: library/concurrent futures executor-objects7309365
Ref: 258b7309365
Ref: library/concurrent futures concurrent futures Executor7309418
Ref: 258a7309418
Ref: library/concurrent futures concurrent futures Executor submit7309617
Ref: 3c67309617
Ref: library/concurrent futures concurrent futures Executor map7310061
Ref: 7b17310061
Ref: library/concurrent futures concurrent futures Executor shutdown7311702
Ref: 1957311702
Node: ThreadPoolExecutor7314015
Ref: library/concurrent futures threadpoolexecutor7314170
Ref: 258d7314170
Ref: library/concurrent futures concurrent futures ThreadPoolExecutor7315238
Ref: 18c7315238
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Ref: library/concurrent futures id17317103
Ref: 258f7317103
Ref: library/concurrent futures threadpoolexecutor-example7317103
Ref: c017317103
Node: ProcessPoolExecutor7318302
Ref: library/concurrent futures processpoolexecutor7318455
Ref: 25907318455
Ref: library/concurrent futures concurrent futures ProcessPoolExecutor7319189
Ref: 1967319189
Node: ProcessPoolExecutor Example7321000
Ref: library/concurrent futures id27321083
Ref: 25927321083
Ref: library/concurrent futures processpoolexecutor-example7321083
Ref: c027321083
Node: Future Objects7321989
Ref: library/concurrent futures future-objects7322140
Ref: 25937322140
Ref: library/concurrent futures concurrent futures Future7322349
Ref: c007322349
Ref: library/concurrent futures concurrent futures Future cancel7322588
Ref: 25947322588
Ref: library/concurrent futures concurrent futures Future cancelled7322927
Ref: 25957322927
Ref: library/concurrent futures concurrent futures Future running7323037
Ref: 25967323037
Ref: library/concurrent futures concurrent futures Future done7323185
Ref: 25977323185
Ref: library/concurrent futures concurrent futures Future result7323325
Ref: 25987323325
Ref: library/concurrent futures concurrent futures Future exception7324072
Ref: 25997324072
Ref: library/concurrent futures concurrent futures Future add_done_callback7324811
Ref: 259a7324811
Ref: library/concurrent futures concurrent futures Future set_running_or_notify_cancel7325707
Ref: 259b7325707
Ref: library/concurrent futures concurrent futures Future set_result7326795
Ref: 259c7326795
Ref: library/concurrent futures concurrent futures Future set_exception7327251
Ref: 259d7327251
Node: Module Functions7327742
Ref: library/concurrent futures module-functions7327891
Ref: 259f7327891
Ref: library/concurrent futures concurrent futures wait7327944
Ref: f507327944
Ref: library/concurrent futures concurrent futures as_completed7329935
Ref: 12237329935
Ref: Module Functions-Footnote-17330992
Node: Exception classes7331041
Ref: library/concurrent futures exception-classes7331167
Ref: 25a07331167
Ref: library/concurrent futures concurrent futures CancelledError7331222
Ref: 2dd7331222
Ref: library/concurrent futures concurrent futures TimeoutError7331313
Ref: 258c7331313
Ref: library/concurrent futures concurrent futures BrokenExecutor7331425
Ref: 25a17331425
Ref: library/concurrent futures concurrent futures InvalidStateError7331681
Ref: 259e7331681
Ref: library/concurrent futures concurrent futures thread BrokenThreadPool7331863
Ref: 258e7331863
Ref: library/concurrent futures concurrent futures process BrokenProcessPool7332115
Ref: 25917332115
Node: subprocess — Subprocess management7332475
Ref: library/subprocess doc7332658
Ref: 25a27332658
Ref: library/subprocess module-subprocess7332658
Ref: f97332658
Ref: library/subprocess subprocess-subprocess-management7332658
Ref: 25a37332658
Ref: subprocess — Subprocess management-Footnote-17333599
Ref: subprocess — Subprocess management-Footnote-27333668
Node: Using the subprocess Module7333717
Ref: library/subprocess using-the-subprocess-module7333849
Ref: 25a47333849
Ref: library/subprocess subprocess run7334317
Ref: 4f37334317
Ref: library/subprocess subprocess CompletedProcess7338101
Ref: 84f7338101
Ref: library/subprocess subprocess CompletedProcess args7338234
Ref: 25a97338234
Ref: library/subprocess subprocess CompletedProcess returncode7338356
Ref: 25aa7338356
Ref: library/subprocess subprocess CompletedProcess stdout7338630
Ref: 25ab7338630
Ref: library/subprocess subprocess CompletedProcess stderr7339061
Ref: 25ac7339061
Ref: library/subprocess subprocess CompletedProcess check_returncode7339303
Ref: 25ad7339303
Ref: library/subprocess subprocess DEVNULL7339467
Ref: b787339467
Ref: library/subprocess subprocess PIPE7339711
Ref: 4f47339711
Ref: library/subprocess subprocess STDOUT7339975
Ref: 25ae7339975
Ref: library/subprocess subprocess SubprocessError7340182
Ref: 25af7340182
Ref: library/subprocess subprocess TimeoutExpired7340311
Ref: 25a87340311
Ref: library/subprocess subprocess TimeoutExpired cmd7340470
Ref: 25b07340470
Ref: library/subprocess subprocess TimeoutExpired timeout7340556
Ref: 25b17340556
Ref: library/subprocess subprocess TimeoutExpired output7340616
Ref: 25b27340616
Ref: library/subprocess subprocess TimeoutExpired stdout7340787
Ref: 25b37340787
Ref: library/subprocess subprocess TimeoutExpired stderr7340882
Ref: 25b47340882
Ref: library/subprocess subprocess CalledProcessError7341125
Ref: d7d7341125
Ref: library/subprocess subprocess CalledProcessError returncode7341345
Ref: 25b67341345
Ref: library/subprocess subprocess CalledProcessError cmd7341513
Ref: 25b77341513
Ref: library/subprocess subprocess CalledProcessError output7341599
Ref: 25b87341599
Ref: library/subprocess subprocess CalledProcessError stdout7341770
Ref: 25b97341770
Ref: library/subprocess subprocess CalledProcessError stderr7341865
Ref: 25ba7341865
Node: Frequently Used Arguments7342173
Ref: library/subprocess frequently-used-arguments7342288
Ref: 25a67342288
Ref: library/subprocess id17342288
Ref: 25bb7342288
Node: Popen Constructor7346457
Ref: library/subprocess popen-constructor7346594
Ref: 25c07346594
Ref: library/subprocess subprocess Popen7346889
Ref: 3db7346889
Ref: Popen Constructor-Footnote-17362243
Node: Exceptions<8>7362303
Ref: library/subprocess exceptions7362406
Ref: 25cf7362406
Node: Security Considerations7363672
Ref: library/subprocess security-considerations7363826
Ref: 25bf7363826
Ref: library/subprocess subprocess-security7363826
Ref: 25d07363826
Ref: Security Considerations-Footnote-17364554
Node: Popen Objects7364624
Ref: library/subprocess popen-objects7364772
Ref: 25d17364772
Ref: library/subprocess subprocess Popen poll7364889
Ref: 25d27364889
Ref: library/subprocess subprocess Popen wait7365049
Ref: 6897365049
Ref: library/subprocess subprocess Popen communicate7365978
Ref: 25a77365978
Ref: library/subprocess subprocess Popen send_signal7367729
Ref: 10a47367729
Ref: library/subprocess subprocess Popen terminate7368114
Ref: 25d37368114
Ref: library/subprocess subprocess Popen kill7368320
Ref: 25d47368320
Ref: library/subprocess subprocess Popen args7368554
Ref: 25d57368554
Ref: library/subprocess subprocess Popen stdin7368737
Ref: 25bc7368737
Ref: library/subprocess subprocess Popen stdout7369168
Ref: 25bd7369168
Ref: library/subprocess subprocess Popen stderr7369671
Ref: 25be7369671
Ref: library/subprocess subprocess Popen pid7370436
Ref: 25d67370436
Ref: library/subprocess subprocess Popen returncode7370618
Ref: 10a57370618
Node: Windows Popen Helpers7370969
Ref: library/subprocess windows-popen-helpers7371114
Ref: 25d77371114
Ref: library/subprocess subprocess STARTUPINFO7371268
Ref: 25c27371268
Ref: library/subprocess subprocess STARTUPINFO dwFlags7371687
Ref: 25d87371687
Ref: library/subprocess subprocess STARTUPINFO hStdInput7372001
Ref: 25d97372001
Ref: library/subprocess subprocess STARTUPINFO hStdOutput7372323
Ref: 25db7372323
Ref: library/subprocess subprocess STARTUPINFO hStdError7372634
Ref: 25dc7372634
Ref: library/subprocess subprocess STARTUPINFO wShowWindow7372942
Ref: 25dd7372942
Ref: library/subprocess subprocess STARTUPINFO lpAttributeList7373434
Ref: 5957373434
Ref: Windows Popen Helpers-Footnote-17374687
Ref: Windows Popen Helpers-Footnote-27374759
Ref: Windows Popen Helpers-Footnote-37374831
Node: Windows Constants7374920
Ref: library/subprocess windows-constants7374995
Ref: 25e07374995
Ref: library/subprocess subprocess STD_INPUT_HANDLE7375117
Ref: 25e17375117
Ref: library/subprocess subprocess STD_OUTPUT_HANDLE7375254
Ref: 25e27375254
Ref: library/subprocess subprocess STD_ERROR_HANDLE7375402
Ref: 25e37375402
Ref: library/subprocess subprocess SW_HIDE7375548
Ref: 25df7375548
Ref: library/subprocess subprocess STARTF_USESTDHANDLES7375637
Ref: 25da7375637
Ref: library/subprocess subprocess STARTF_USESHOWWINDOW7375868
Ref: 25de7375868
Ref: library/subprocess subprocess CREATE_NEW_CONSOLE7376021
Ref: 25c37376021
Ref: library/subprocess subprocess CREATE_NEW_PROCESS_GROUP7376168
Ref: 25c47376168
Ref: library/subprocess subprocess ABOVE_NORMAL_PRIORITY_CLASS7376490
Ref: 25c57376490
Ref: library/subprocess subprocess BELOW_NORMAL_PRIORITY_CLASS7376694
Ref: 25c67376694
Ref: library/subprocess subprocess HIGH_PRIORITY_CLASS7376897
Ref: 25c77376897
Ref: library/subprocess subprocess IDLE_PRIORITY_CLASS7377083
Ref: 25c87377083
Ref: library/subprocess subprocess NORMAL_PRIORITY_CLASS7377279
Ref: 25c97377279
Ref: library/subprocess subprocess REALTIME_PRIORITY_CLASS7377481
Ref: 25ca7377481
Ref: library/subprocess subprocess CREATE_NO_WINDOW7378015
Ref: 25cb7378015
Ref: library/subprocess subprocess DETACHED_PROCESS7378197
Ref: 25cc7378197
Ref: library/subprocess subprocess CREATE_DEFAULT_ERROR_MODE7378451
Ref: 25cd7378451
Ref: library/subprocess subprocess CREATE_BREAKAWAY_FROM_JOB7378851
Ref: 25ce7378851
Node: Older high-level API7379048
Ref: library/subprocess call-function-trio7379232
Ref: 25a57379232
Ref: library/subprocess older-high-level-api7379232
Ref: 25e47379232
Ref: library/subprocess subprocess call7379480
Ref: 4f57379480
Ref: library/subprocess subprocess check_call7380534
Ref: 25b57380534
Ref: library/subprocess subprocess check_output7381865
Ref: 9c17381865
Node: Replacing Older Functions with the subprocess Module7384096
Ref: library/subprocess replacing-older-functions-with-the-subprocess-module7384292
Ref: 25e57384292
Ref: library/subprocess subprocess-replacements7384292
Ref: bc17384292
Node: Replacing /bin/sh shell command substitution7385459
Ref: library/subprocess replacing-bin-sh-shell-command-substitution7385625
Ref: 25e67385625
Node: Replacing shell pipeline7385830
Ref: library/subprocess replacing-shell-pipeline7386024
Ref: 25e77386024
Node: Replacing os system7386673
Ref: library/subprocess replacing-os-system7386852
Ref: 25e87386852
Node: Replacing the os spawn family7387798
Ref: library/subprocess replacing-the-os-spawn-family7387991
Ref: 25e97387991
Node: Replacing os popen os popen2 os popen37388622
Ref: library/subprocess replacing-os-popen-os-popen2-os-popen37388838
Ref: 25ea7388838
Node: Replacing functions from the popen2 module7390133
Ref: library/subprocess replacing-functions-from-the-popen2-module7390311
Ref: 25eb7390311
Node: Legacy Shell Invocation Functions7391625
Ref: library/subprocess legacy-shell-invocation-functions7391806
Ref: 25ec7391806
Ref: library/subprocess subprocess getstatusoutput7392170
Ref: 9c27392170
Ref: library/subprocess subprocess getoutput7393349
Ref: 25ed7393349
Node: Notes7393796
Ref: library/subprocess notes7393916
Ref: 25ee7393916
Node: Converting an argument sequence to a string on Windows7394018
Ref: library/subprocess converting-an-argument-sequence-to-a-string-on-windows7394114
Ref: 25ef7394114
Ref: library/subprocess converting-argument-sequence7394114
Ref: 25c17394114
Node: sched — Event scheduler7395274
Ref: library/sched doc7395446
Ref: 25f07395446
Ref: library/sched module-sched7395446
Ref: e37395446
Ref: library/sched sched-event-scheduler7395446
Ref: 25f17395446
Ref: library/sched sched scheduler7395716
Ref: b497395716
Ref: sched — Event scheduler-Footnote-17397376
Node: Scheduler Objects7397440
Ref: library/sched id17397519
Ref: 25f27397519
Ref: library/sched scheduler-objects7397519
Ref: 25f37397519
Ref: library/sched sched scheduler enterabs7397650
Ref: b4b7397650
Ref: library/sched sched scheduler enter7398534
Ref: b4a7398534
Ref: library/sched sched scheduler cancel7398943
Ref: 25f47398943
Ref: library/sched sched scheduler empty7399130
Ref: 25f57399130
Ref: library/sched sched scheduler run7399215
Ref: b487399215
Ref: library/sched sched scheduler queue7400267
Ref: 25f67400267
Node: queue — A synchronized queue class7400526
Ref: library/queue doc7400695
Ref: 25f77400695
Ref: library/queue module-queue7400695
Ref: da7400695
Ref: library/queue queue-a-synchronized-queue-class7400695
Ref: 25f87400695
Ref: library/queue queue Queue7402018
Ref: dde7402018
Ref: library/queue queue LifoQueue7402382
Ref: 25f97402382
Ref: library/queue queue PriorityQueue7402750
Ref: 25fa7402750
Ref: library/queue queue SimpleQueue7403745
Ref: 4cd7403745
Ref: library/queue queue Empty7403919
Ref: 250b7403919
Ref: library/queue queue Full7404104
Ref: 250c7404104
Ref: queue — A synchronized queue class-Footnote-17404375
Node: Queue Objects7404439
Ref: library/queue queue-objects7404553
Ref: 25ff7404553
Ref: library/queue queueobjects7404553
Ref: 26007404553
Ref: library/queue queue Queue qsize7404732
Ref: 26017404732
Ref: library/queue queue Queue empty7404961
Ref: 26027404961
Ref: library/queue queue Queue full7405290
Ref: 26037405290
Ref: library/queue queue Queue put7405615
Ref: 25fd7405615
Ref: library/queue queue Queue put_nowait7406207
Ref: 25fe7406207
Ref: library/queue queue Queue get7406288
Ref: 25fb7406288
Ref: library/queue queue Queue get_nowait7407192
Ref: 25fc7407192
Ref: library/queue queue Queue task_done7407385
Ref: 25077407385
Ref: library/queue queue Queue join7408031
Ref: 25087408031
Node: SimpleQueue Objects7409080
Ref: library/queue simplequeue-objects7409194
Ref: 26047409194
Ref: library/queue queue SimpleQueue qsize7409330
Ref: 26057409330
Ref: library/queue queue SimpleQueue empty7409496
Ref: 26067409496
Ref: library/queue queue SimpleQueue put7409713
Ref: 26077409713
Ref: library/queue queue SimpleQueue put_nowait7410478
Ref: 26087410478
Ref: library/queue queue SimpleQueue get7410627
Ref: 26097410627
Ref: library/queue queue SimpleQueue get_nowait7411209
Ref: 260a7411209
Node: contextvars — Context Variables7411657
Ref: library/contextvars doc7411836
Ref: 260b7411836
Ref: library/contextvars contextvars-context-variables7411836
Ref: 260c7411836
Ref: library/contextvars module-contextvars7411836
Ref: 247411836
Ref: contextvars — Context Variables-Footnote-17412693
Node: Context Variables7412742
Ref: library/contextvars context-variables7412863
Ref: 26107412863
Ref: library/contextvars contextvars ContextVar7412918
Ref: 260d7412918
Ref: library/contextvars contextvars ContextVar name7413625
Ref: 26127413625
Ref: library/contextvars contextvars ContextVar get7413752
Ref: 26117413752
Ref: library/contextvars contextvars ContextVar set7414239
Ref: 26137414239
Ref: library/contextvars contextvars ContextVar reset7414635
Ref: 26157414635
Ref: library/contextvars contextvars Token7415156
Ref: 26147415156
Ref: library/contextvars contextvars Token var7415430
Ref: 26167415430
Ref: library/contextvars contextvars Token old_value7415568
Ref: 26177415568
Ref: library/contextvars contextvars Token MISSING7415860
Ref: 26187415860
Node: Manual Context Management7415953
Ref: library/contextvars manual-context-management7416098
Ref: 26197416098
Ref: library/contextvars contextvars copy_context7416169
Ref: 260e7416169
Ref: library/contextvars contextvars Context7416645
Ref: 260f7416645
Ref: library/contextvars contextvars Context run7416982
Ref: 261a7416982
Ref: library/contextvars contextvars Context copy7418409
Ref: 261b7418409
Ref: library/contextvars contextvars Context get7418852
Ref: 261c7418852
Ref: library/contextvars contextvars Context keys7419294
Ref: 261d7419294
Ref: library/contextvars contextvars Context values7419385
Ref: 261e7419385
Ref: library/contextvars contextvars Context items7419488
Ref: 261f7419488
Node: asyncio support7419627
Ref: library/contextvars asyncio-support7419746
Ref: 26207419746
Node: _thread — Low-level threading API7421321
Ref: library/_thread doc7421455
Ref: 26217421455
Ref: library/_thread module-_thread7421455
Ref: 27421455
Ref: library/_thread thread-low-level-threading-api7421455
Ref: 26227421455
Ref: library/_thread _thread error7422172
Ref: 26237422172
Ref: library/_thread _thread LockType7422340
Ref: 26247422340
Ref: library/_thread _thread start_new_thread7422408
Ref: 11007422408
Ref: library/_thread _thread interrupt_main7423300
Ref: 26257423300
Ref: library/_thread _thread exit7423683
Ref: 26297423683
Ref: library/_thread _thread allocate_lock7423832
Ref: 262a7423832
Ref: library/_thread _thread get_ident7423980
Ref: 262b7423980
Ref: library/_thread _thread get_native_id7424346
Ref: 262c7424346
Ref: library/_thread _thread stack_size7424805
Ref: 262d7424805
Ref: library/_thread _thread TIMEOUT_MAX7426048
Ref: 262e7426048
Ref: library/_thread _thread lock acquire7426328
Ref: 262f7426328
Ref: library/_thread _thread lock release7427411
Ref: 26307427411
Ref: library/_thread _thread lock locked7427553
Ref: 26317427553
Node: Networking and Interprocess Communication7428948
Ref: library/ipc doc7429113
Ref: 26327429113
Ref: library/ipc ipc7429113
Ref: 26337429113
Ref: library/ipc networking-and-interprocess-communication7429113
Ref: 26347429113
Node: asyncio — Asynchronous I/O7430017
Ref: library/asyncio doc7430173
Ref: 26357430173
Ref: library/asyncio asyncio-asynchronous-i-o7430173
Ref: 26367430173
Ref: library/asyncio module-asyncio7430173
Ref: 97430173
Node: Coroutines and Tasks7431978
Ref: library/asyncio-task doc7432079
Ref: 26407432079
Ref: library/asyncio-task coroutines-and-tasks7432079
Ref: 26417432079
Node: Coroutines<3>7432560
Ref: library/asyncio-task coroutine7432649
Ref: 26377432649
Ref: library/asyncio-task coroutines7432649
Ref: 26427432649
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Ref: library/asyncio-task asyncio-awaitables7435198
Ref: 26437435198
Ref: library/asyncio-task awaitables7435198
Ref: 26447435198
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Ref: library/asyncio-task running-an-asyncio-program7437959
Ref: 26467437959
Ref: library/asyncio-task asyncio run7438032
Ref: 18d7438032
Ref: Running an asyncio Program-Footnote-17439101
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Ref: library/asyncio-task creating-tasks7439298
Ref: 26477439298
Ref: library/asyncio-task asyncio create_task7439347
Ref: 2e17439347
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Ref: library/asyncio-task sleeping7440575
Ref: 26487440575
Ref: library/asyncio-task asyncio sleep7440612
Ref: 3aa7440612
Ref: library/asyncio-task asyncio-example-sleep7441214
Ref: 26497441214
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Ref: library/asyncio-task running-tasks-concurrently7441855
Ref: 264a7441855
Ref: library/asyncio-task asyncio gather7441928
Ref: 3ab7441928
Ref: library/asyncio-task asyncio-example-gather7443320
Ref: 264b7443320
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Ref: library/asyncio-task shielding-from-cancellation7445301
Ref: 264c7445301
Ref: library/asyncio-task asyncio shield7445376
Ref: 3ac7445376
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Ref: library/asyncio-task timeouts7446687
Ref: 264e7446687
Ref: library/asyncio-task asyncio wait_for7446724
Ref: 1917446724
Ref: library/asyncio-task asyncio-example-waitfor7447646
Ref: 26507447646
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Ref: library/asyncio-task waiting-primitives7448447
Ref: 26517448447
Ref: library/asyncio-task asyncio wait7448506
Ref: 2077448506
Ref: library/asyncio-task asyncio-example-wait-coroutine7450844
Ref: 26527450844
Ref: library/asyncio-task asyncio as_completed7451782
Ref: 3ad7451782
Node: Running in Threads7452417
Ref: library/asyncio-task running-in-threads7452557
Ref: 26537452557
Ref: library/asyncio-task asyncio to_thread7452616
Ref: 18f7452616
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Ref: library/asyncio-task scheduling-from-other-threads7454963
Ref: 26547454963
Ref: library/asyncio-task asyncio run_coroutine_threadsafe7455044
Ref: 6147455044
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Ref: library/asyncio-task introspection7456605
Ref: 26567456605
Ref: library/asyncio-task asyncio current_task7456654
Ref: 2287456654
Ref: library/asyncio-task asyncio all_tasks7456931
Ref: 2297456931
Node: Task Object7457189
Ref: library/asyncio-task task-object7457314
Ref: 26577457314
Ref: library/asyncio-task asyncio Task7457359
Ref: 2e07457359
Ref: library/asyncio-task asyncio Task cancel7459375
Ref: 264d7459375
Ref: library/asyncio-task asyncio-example-task-cancel7460160
Ref: 265c7460160
Ref: library/asyncio-task asyncio Task cancelled7461415
Ref: 26587461415
Ref: library/asyncio-task asyncio Task done7461725
Ref: 265d7461725
Ref: library/asyncio-task asyncio Task result7461941
Ref: 265e7461941
Ref: library/asyncio-task asyncio Task exception7462429
Ref: 26607462429
Ref: library/asyncio-task asyncio Task add_done_callback7462916
Ref: 26617462916
Ref: library/asyncio-task asyncio Task remove_done_callback7463231
Ref: 26627463231
Ref: library/asyncio-task asyncio Task get_stack7463529
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Ref: 76a7740578
Ref: library/socket socket socket recvfrom7741374
Ref: 76b7741374
Ref: library/socket socket socket recvmsg7742313
Ref: 76c7742313
Ref: library/socket socket socket recvmsg_into7746245
Ref: b5e7746245
Ref: library/socket socket socket recvfrom_into7747888
Ref: d7b7747888
Ref: library/socket socket socket recv_into7748422
Ref: d7a7748422
Ref: library/socket socket socket send7748869
Ref: 76d7748869
Ref: library/socket socket socket sendall7749682
Ref: 76e7749682
Ref: library/socket socket socket sendto7750656
Ref: 7707750656
Ref: library/socket socket socket sendmsg7751486
Ref: 76f7751486
Ref: library/socket socket socket sendmsg_afalg7753652
Ref: 67c7753652
Ref: library/socket socket socket sendfile7753990
Ref: 8397753990
Ref: library/socket socket socket set_inheritable7754894
Ref: 8ed7754894
Ref: library/socket socket socket setblocking7755074
Ref: 206f7755074
Ref: library/socket socket socket settimeout7755646
Ref: 27b97755646
Ref: library/socket socket socket setsockopt7756382
Ref: 67a7756382
Ref: library/socket socket socket shutdown7757460
Ref: 27e37757460
Ref: library/socket socket socket share7757756
Ref: 58f7757756
Ref: library/socket socket socket family7758622
Ref: 27eb7758622
Ref: library/socket socket socket type7758677
Ref: 5937758677
Ref: library/socket socket socket proto7758728
Ref: 27ec7758728
Ref: Socket Objects-Footnote-17758820
Ref: Socket Objects-Footnote-27758869
Ref: Socket Objects-Footnote-37758918
Ref: Socket Objects-Footnote-47758992
Ref: Socket Objects-Footnote-57759041
Ref: Socket Objects-Footnote-67759090
Ref: Socket Objects-Footnote-77759139
Ref: Socket Objects-Footnote-87759188
Ref: Socket Objects-Footnote-97759237
Ref: Socket Objects-Footnote-107759286
Node: Notes on socket timeouts7759336
Ref: library/socket notes-on-socket-timeouts7759480
Ref: 27ed7759480
Ref: library/socket socket-timeouts7759480
Ref: 27ea7759480
Node: Timeouts and the connect method7760837
Ref: library/socket timeouts-and-the-connect-method7760968
Ref: 27ee7760968
Node: Timeouts and the accept method7761443
Ref: library/socket timeouts-and-the-accept-method7761574
Ref: 27ef7761574
Node: Example<8>7762315
Ref: library/socket example7762436
Ref: 27f07762436
Ref: library/socket socket-example7762436
Ref: 27f17762436
Ref: Example<8>-Footnote-17770167
Node: ssl — TLS/SSL wrapper for socket objects7770216
Ref: library/ssl doc7770432
Ref: 27f27770432
Ref: library/ssl module-ssl7770432
Ref: f37770432
Ref: library/ssl ssl-tls-ssl-wrapper-for-socket-objects7770432
Ref: 27f37770432
Ref: ssl — TLS/SSL wrapper for socket objects-Footnote-17773063
Node: Functions Constants and Exceptions7773125
Ref: library/ssl functions-constants-and-exceptions7773258
Ref: 27f47773258
Node: Socket creation7773506
Ref: library/ssl socket-creation7773617
Ref: 27f57773617
Node: Context creation7775384
Ref: library/ssl context-creation7775518
Ref: 27f67775518
Ref: library/ssl ssl create_default_context7775660
Ref: 9a77775660
Ref: Context creation-Footnote-17778518
Node: Exceptions<13>7778563
Ref: library/ssl exceptions7778699
Ref: 27fc7778699
Ref: library/ssl ssl SSLError7778740
Ref: cda7778740
Ref: library/ssl ssl SSLError library7779312
Ref: b707779312
Ref: library/ssl ssl SSLError reason7779590
Ref: b717779590
Ref: library/ssl ssl SSLZeroReturnError7779849
Ref: 27fd7779849
Ref: library/ssl ssl SSLWantReadError7780143
Ref: 8457780143
Ref: library/ssl ssl SSLWantWriteError7780450
Ref: 8467780450
Ref: library/ssl ssl SSLSyscallError7780754
Ref: 27ff7780754
Ref: library/ssl ssl SSLEOFError7781043
Ref: 28007781043
Ref: library/ssl ssl SSLCertVerificationError7781311
Ref: 4e47781311
Ref: library/ssl ssl SSLCertVerificationError verify_code7781475
Ref: 28017781475
Ref: library/ssl ssl SSLCertVerificationError verify_message7781579
Ref: 28027781579
Ref: library/ssl ssl CertificateError7781677
Ref: 28037781677
Node: Random generation7781876
Ref: library/ssl random-generation7782016
Ref: 28047782016
Ref: library/ssl ssl RAND_bytes7782071
Ref: b677782071
Ref: library/ssl ssl RAND_pseudo_bytes7782750
Ref: b687782750
Ref: library/ssl ssl RAND_status7783600
Ref: 28057783600
Ref: library/ssl ssl RAND_egd7783927
Ref: 28077783927
Ref: library/ssl ssl RAND_add7784584
Ref: 28067784584
Ref: Random generation-Footnote-17785026
Ref: Random generation-Footnote-27785120
Node: Certificate handling7785169
Ref: library/ssl certificate-handling7785307
Ref: 28087785307
Ref: library/ssl ssl match_hostname7785368
Ref: 4e37785368
Ref: library/ssl ssl cert_time_to_seconds7787309
Ref: 8477787309
Ref: library/ssl ssl get_server_certificate7788219
Ref: b727788219
Ref: library/ssl ssl DER_cert_to_PEM_cert7789230
Ref: 280a7789230
Ref: library/ssl ssl PEM_cert_to_DER_cert7789412
Ref: 280b7789412
Ref: library/ssl ssl get_default_verify_paths7789592
Ref: 9a87789592
Ref: library/ssl ssl enum_certificates7790598
Ref: 9b47790598
Ref: library/ssl ssl enum_crls7791475
Ref: 9b57791475
Ref: library/ssl ssl wrap_socket7792006
Ref: 5717792006
Ref: Certificate handling-Footnote-17793499
Ref: Certificate handling-Footnote-27793548
Ref: Certificate handling-Footnote-37793597
Ref: Certificate handling-Footnote-47793646
Ref: Certificate handling-Footnote-57793695
Node: Constants<9>7793744
Ref: library/ssl constants7793856
Ref: 280e7793856
Ref: library/ssl ssl CERT_NONE7794021
Ref: 280f7794021
Ref: library/ssl ssl CERT_OPTIONAL7794638
Ref: 28117794638
Ref: library/ssl ssl CERT_REQUIRED7795543
Ref: 27fa7795543
Ref: library/ssl ssl VerifyMode7796668
Ref: 28137796668
Ref: library/ssl ssl VERIFY_DEFAULT7796784
Ref: 9ad7796784
Ref: library/ssl ssl VERIFY_CRL_CHECK_LEAF7797037
Ref: 9ae7797037
Ref: library/ssl ssl VERIFY_CRL_CHECK_CHAIN7797482
Ref: 9af7797482
Ref: library/ssl ssl VERIFY_X509_STRICT7797688
Ref: 9b07797688
Ref: library/ssl ssl VERIFY_X509_TRUSTED_FIRST7797868
Ref: 28147797868
Ref: library/ssl ssl VerifyFlags7798157
Ref: 28157798157
Ref: library/ssl ssl PROTOCOL_TLS7798277
Ref: 27f77798277
Ref: library/ssl ssl PROTOCOL_TLS_CLIENT7798507
Ref: 28107798507
Ref: library/ssl ssl PROTOCOL_TLS_SERVER7798821
Ref: 28167798821
Ref: library/ssl ssl PROTOCOL_SSLv237799037
Ref: 28177799037
Ref: library/ssl ssl PROTOCOL_SSLv27799190
Ref: 28187799190
Ref: library/ssl ssl PROTOCOL_SSLv37799555
Ref: 28097799555
Ref: library/ssl ssl PROTOCOL_TLSv17800047
Ref: 28197800047
Ref: library/ssl ssl PROTOCOL_TLSv1_17800346
Ref: 9a57800346
Ref: library/ssl ssl PROTOCOL_TLSv1_27800722
Ref: 9a67800722
Ref: library/ssl ssl OP_ALL7801224
Ref: 281a7801224
Ref: library/ssl ssl OP_NO_SSLv27801481
Ref: c717801481
Ref: library/ssl ssl OP_NO_SSLv37801782
Ref: 27f87801782
Ref: library/ssl ssl OP_NO_TLSv17802083
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Ref: library/ssl ssl OP_NO_TLSv1_17802522
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Ref: library/ssl ssl OP_NO_TLSv1_27802909
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Ref: library/ssl ssl OP_NO_TLSv1_37803296
Ref: 281e7803296
Ref: library/ssl ssl OP_NO_RENEGOTIATION7803887
Ref: 281f7803887
Ref: library/ssl ssl OP_CIPHER_SERVER_PREFERENCE7804168
Ref: b737804168
Ref: library/ssl ssl OP_SINGLE_DH_USE7804399
Ref: 28207804399
Ref: library/ssl ssl OP_SINGLE_ECDH_USE7804653
Ref: 28217804653
Ref: library/ssl ssl OP_ENABLE_MIDDLEBOX_COMPAT7804911
Ref: 28227804911
Ref: library/ssl ssl OP_NO_COMPRESSION7805188
Ref: b6e7805188
Ref: library/ssl ssl Options7805445
Ref: 28237805445
Ref: library/ssl ssl OP_NO_TICKET7805531
Ref: 28247805531
Ref: library/ssl ssl OP_IGNORE_UNEXPECTED_EOF7805645
Ref: fa57805645
Ref: library/ssl ssl HAS_ALPN7805831
Ref: 8427805831
Ref: library/ssl ssl HAS_NEVER_CHECK_COMMON_NAME7806038
Ref: 28257806038
Ref: library/ssl ssl HAS_ECDH7806274
Ref: 28267806274
Ref: library/ssl ssl HAS_SNI7806531
Ref: 28277806531
Ref: library/ssl ssl HAS_NPN7806712
Ref: 28287806712
Ref: library/ssl ssl HAS_SSLv27807063
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Ref: library/ssl ssl HAS_SSLv37807200
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Ref: library/ssl ssl HAS_TLSv17807337
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Ref: library/ssl ssl HAS_TLSv1_17807474
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Ref: library/ssl ssl HAS_TLSv1_27807613
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Ref: library/ssl ssl HAS_TLSv1_37807752
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Ref: library/ssl ssl CHANNEL_BINDING_TYPES7807891
Ref: 282e7807891
Ref: library/ssl ssl OPENSSL_VERSION7808109
Ref: c727808109
Ref: library/ssl ssl OPENSSL_VERSION_INFO7808321
Ref: c737808321
Ref: library/ssl ssl OPENSSL_VERSION_NUMBER7808547
Ref: c747808547
Ref: library/ssl ssl ALERT_DESCRIPTION_HANDSHAKE_FAILURE7808816
Ref: 282f7808816
Ref: library/ssl ssl ALERT_DESCRIPTION_INTERNAL_ERROR7808866
Ref: 28307808866
Ref: library/ssl ssl AlertDescription7809258
Ref: 28317809258
Ref: library/ssl ssl Purpose SERVER_AUTH7809398
Ref: 9b27809398
Ref: library/ssl ssl Purpose CLIENT_AUTH7809711
Ref: 9b37809711
Ref: library/ssl ssl SSLErrorNumber7810024
Ref: 28327810024
Ref: library/ssl ssl TLSVersion7810149
Ref: 28337810149
Ref: library/ssl ssl TLSVersion MINIMUM_SUPPORTED7810364
Ref: 28347810364
Ref: library/ssl ssl TLSVersion MAXIMUM_SUPPORTED7810409
Ref: 28357810409
Ref: library/ssl ssl TLSVersion SSLv37810632
Ref: 28367810632
Ref: library/ssl ssl TLSVersion TLSv17810665
Ref: 28377810665
Ref: library/ssl ssl TLSVersion TLSv1_17810698
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Ref: library/ssl ssl TLSVersion TLSv1_27810733
Ref: 28397810733
Ref: library/ssl ssl TLSVersion TLSv1_37810768
Ref: 283a7810768
Ref: Constants<9>-Footnote-17810865
Ref: Constants<9>-Footnote-27810914
Ref: Constants<9>-Footnote-37810963
Ref: Constants<9>-Footnote-47811041
Ref: Constants<9>-Footnote-57811090
Node: SSL Sockets7811183
Ref: library/ssl ssl-sockets7811337
Ref: 283b7811337
Ref: library/ssl ssl SSLSocket7811380
Ref: 1927811380
Ref: library/ssl ssl SSLSocket read7813556
Ref: 84a7813556
Ref: library/ssl ssl SSLSocket write7814376
Ref: 84b7814376
Ref: library/ssl ssl SSLSocket do_handshake7815606
Ref: 8497815606
Ref: library/ssl ssl SSLSocket getpeercert7816370
Ref: 9b77816370
Ref: library/ssl ssl SSLSocket cipher7819981
Ref: 27437819981
Ref: library/ssl ssl SSLSocket shared_ciphers7820265
Ref: 8487820265
Ref: library/ssl ssl SSLSocket compression7820746
Ref: b6d7820746
Ref: library/ssl ssl SSLSocket get_channel_binding7821091
Ref: b6c7821091
Ref: library/ssl ssl SSLSocket selected_alpn_protocol7821724
Ref: 8417821724
Ref: library/ssl ssl SSLSocket selected_npn_protocol7822135
Ref: 283e7822135
Ref: library/ssl ssl SSLSocket unwrap7822489
Ref: 283c7822489
Ref: library/ssl ssl SSLSocket verify_client_post_handshake7822912
Ref: 3527822912
Ref: library/ssl ssl SSLSocket version7823790
Ref: 8447823790
Ref: library/ssl ssl SSLSocket pending7824201
Ref: 283f7824201
Ref: library/ssl ssl SSLSocket context7824339
Ref: 283d7824339
Ref: library/ssl ssl SSLSocket server_side7824687
Ref: 28407824687
Ref: library/ssl ssl SSLSocket server_hostname7824857
Ref: 4e77824857
Ref: library/ssl ssl SSLSocket session7825360
Ref: 28417825360
Ref: library/ssl ssl SSLSocket session_reused7825716
Ref: 28427825716
Ref: SSL Sockets-Footnote-17825819
Ref: SSL Sockets-Footnote-27825868
Node: SSL Contexts7825917
Ref: library/ssl ssl-contexts7826049
Ref: 28437826049
Ref: library/ssl ssl SSLContext7826393
Ref: 4ea7826393
Ref: library/ssl ssl SSLContext cert_store_stats7830380
Ref: 9aa7830380
Ref: library/ssl ssl SSLContext load_cert_chain7830784
Ref: b697830784
Ref: library/ssl ssl SSLContext load_default_certs7832410
Ref: 9b17832410
Ref: library/ssl ssl SSLContext load_verify_locations7833232
Ref: 8d87833232
Ref: library/ssl ssl SSLContext get_ca_certs7834562
Ref: 9ab7834562
Ref: library/ssl ssl SSLContext get_ciphers7835197
Ref: 6837835197
Ref: library/ssl ssl SSLContext set_default_verify_paths7837339
Ref: 9a97837339
Ref: library/ssl ssl SSLContext set_ciphers7837808
Ref: 280d7837808
Ref: library/ssl ssl SSLContext set_alpn_protocols7838456
Ref: 8407838456
Ref: library/ssl ssl SSLContext set_npn_protocols7839344
Ref: b6f7839344
Ref: library/ssl ssl SSLContext sni_callback7840013
Ref: fba7840013
Ref: library/ssl ssl SSLContext set_servername_callback7842581
Ref: 9b67842581
Ref: library/ssl ssl SSLContext load_dh_params7843261
Ref: b6a7843261
Ref: library/ssl ssl SSLContext set_ecdh_curve7843804
Ref: b6b7843804
Ref: library/ssl ssl SSLContext wrap_socket7844531
Ref: 4eb7844531
Ref: library/ssl ssl SSLContext sslsocket_class7847318
Ref: 28457847318
Ref: library/ssl ssl SSLContext wrap_bio7847614
Ref: 4ec7847614
Ref: library/ssl ssl SSLContext sslobject_class7848353
Ref: 28467848353
Ref: library/ssl ssl SSLContext session_stats7848646
Ref: 28477848646
Ref: library/ssl ssl SSLContext check_hostname7849111
Ref: 28127849111
Ref: library/ssl ssl SSLContext keylog_filename7850702
Ref: 27fb7850702
Ref: library/ssl ssl SSLContext maximum_version7851210
Ref: 4ee7851210
Ref: library/ssl ssl SSLContext minimum_version7852193
Ref: 4ed7852193
Ref: library/ssl ssl SSLContext num_tickets7852527
Ref: 28487852527
Ref: library/ssl ssl SSLContext options7852874
Ref: 280c7852874
Ref: library/ssl ssl SSLContext post_handshake_auth7853621
Ref: 3517853621
Ref: library/ssl ssl SSLContext protocol7854604
Ref: 28497854604
Ref: library/ssl ssl SSLContext hostname_checks_common_name7854740
Ref: 4e57854740
Ref: library/ssl ssl SSLContext verify_flags7855236
Ref: 9ac7855236
Ref: library/ssl ssl SSLContext verify_mode7855820
Ref: 27f97855820
Ref: SSL Contexts-Footnote-17856326
Ref: SSL Contexts-Footnote-27856484
Ref: SSL Contexts-Footnote-37856575
Ref: SSL Contexts-Footnote-47856667
Ref: SSL Contexts-Footnote-57856825
Ref: SSL Contexts-Footnote-67856916
Ref: SSL Contexts-Footnote-77857008
Ref: SSL Contexts-Footnote-87857096
Ref: SSL Contexts-Footnote-97857161
Ref: SSL Contexts-Footnote-107857210
Ref: SSL Contexts-Footnote-117857289
Ref: SSL Contexts-Footnote-127857339
Ref: SSL Contexts-Footnote-137857416
Node: Certificates7857493
Ref: library/ssl certificates7857626
Ref: 284a7857626
Ref: library/ssl ssl-certificates7857626
Ref: 28447857626
Ref: Certificates-Footnote-17859975
Node: Certificate chains7860024
Ref: library/ssl certificate-chains7860115
Ref: 284b7860115
Node: CA certificates7861386
Ref: library/ssl ca-certificates7861514
Ref: 284c7861514
Node: Combined key and certificate7862104
Ref: library/ssl combined-key-and-certificate7862238
Ref: 284d7862238
Node: Self-signed certificates7862884
Ref: library/ssl self-signed-certificates7862994
Ref: 284e7862994
Node: Examples<17>7864692
Ref: library/ssl examples7864842
Ref: 284f7864842
Node: Testing for SSL support7864971
Ref: library/ssl testing-for-ssl-support7865073
Ref: 28507865073
Node: Client-side operation7865387
Ref: library/ssl client-side-operation7865519
Ref: 28517865519
Node: Server-side operation7870261
Ref: library/ssl server-side-operation7870361
Ref: 28527870361
Node: Notes on non-blocking sockets7872371
Ref: library/ssl notes-on-non-blocking-sockets7872530
Ref: 28537872530
Ref: library/ssl ssl-nonblocking7872530
Ref: 27fe7872530
Node: Memory BIO Support<2>7875418
Ref: library/ssl memory-bio-support7875576
Ref: 28557875576
Ref: library/ssl ssl SSLObject7876692
Ref: 4e97876692
Ref: library/ssl ssl MemoryBIO7880455
Ref: 83e7880455
Ref: library/ssl ssl MemoryBIO pending7880583
Ref: 28567880583
Ref: library/ssl ssl MemoryBIO eof7880682
Ref: 28577880682
Ref: library/ssl ssl MemoryBIO read7880812
Ref: 28587880812
Ref: library/ssl ssl MemoryBIO write7880970
Ref: 28597880970
Ref: library/ssl ssl MemoryBIO write_eof7881252
Ref: 285a7881252
Node: SSL session7881544
Ref: library/ssl ssl-session7881699
Ref: 285b7881699
Ref: library/ssl ssl SSLSession7881765
Ref: 6827881765
Ref: library/ssl ssl SSLSession id7881842
Ref: 285c7881842
Ref: library/ssl ssl SSLSession time7881866
Ref: 285d7881866
Ref: library/ssl ssl SSLSession timeout7881892
Ref: 285e7881892
Ref: library/ssl ssl SSLSession ticket_lifetime_hint7881921
Ref: 285f7881921
Ref: library/ssl ssl SSLSession has_ticket7881963
Ref: 28607881963
Node: Security considerations<2>7881995
Ref: library/ssl security-considerations7882136
Ref: 28617882136
Ref: library/ssl ssl-security7882136
Ref: 26fd7882136
Node: Best defaults7882274
Ref: library/ssl best-defaults7882374
Ref: 28627882374
Node: Manual settings7883535
Ref: library/ssl manual-settings7883660
Ref: 28637883660
Node: Verifying certificates7883793
Ref: library/ssl verifying-certificates7883893
Ref: 28647883893
Node: Protocol versions7885156
Ref: library/ssl protocol-versions7885281
Ref: 28657885281
Node: Cipher selection7886082
Ref: library/ssl cipher-selection7886176
Ref: 28667886176
Ref: Cipher selection-Footnote-17886832
Node: Multi-processing7886917
Ref: library/ssl multi-processing7887020
Ref: 28677887020
Node: TLS 1 37887575
Ref: library/ssl ssl-tlsv1-37887721
Ref: 4e87887721
Ref: library/ssl tls-1-37887721
Ref: 28687887721
Node: LibreSSL support7888892
Ref: library/ssl libressl-support7889003
Ref: 28697889003
Ref: library/ssl ssl-libressl7889003
Ref: 286a7889003
Ref: LibreSSL support-Footnote-17890627
Ref: LibreSSL support-Footnote-27890693
Ref: LibreSSL support-Footnote-37890742
Ref: LibreSSL support-Footnote-47890791
Ref: LibreSSL support-Footnote-57890840
Ref: LibreSSL support-Footnote-67890889
Ref: LibreSSL support-Footnote-77890938
Ref: LibreSSL support-Footnote-87891014
Ref: LibreSSL support-Footnote-97891063
Node: select — Waiting for I/O completion7891121
Ref: library/select doc7891337
Ref: 286b7891337
Ref: library/select module-select7891337
Ref: e57891337
Ref: library/select select-waiting-for-i-o-completion7891337
Ref: 286c7891337
Ref: library/select select error7892345
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Ref: library/select select devpoll7892532
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Ref: library/select select epoll7893252
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Ref: library/select select poll7894738
Ref: 28547894738
Ref: library/select select kqueue7895057
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Ref: library/select select kevent7895396
Ref: 28727895396
Ref: library/select select select7895673
Ref: 7667895673
Ref: library/select select PIPE_BUF7897942
Ref: c577897942
Ref: select — Waiting for I/O completion-Footnote-17898638
Ref: select — Waiting for I/O completion-Footnote-27898687
Node: /dev/poll Polling Objects7898736
Ref: library/select dev-poll-polling-objects7898888
Ref: 28747898888
Ref: library/select devpoll-objects7898888
Ref: 286d7898888
Ref: library/select select devpoll close7899242
Ref: 9947899242
Ref: library/select select devpoll closed7899353
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Ref: library/select select devpoll fileno7899460
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Ref: library/select select devpoll register7899580
Ref: 28757899580
Ref: library/select select devpoll modify7900564
Ref: 28767900564
Ref: library/select select devpoll unregister7900772
Ref: 28777900772
Ref: library/select select devpoll poll7901129
Ref: 7627901129
Ref: /dev/poll Polling Objects-Footnote-17902272
Node: Edge and Level Trigger Polling epoll Objects7902321
Ref: library/select edge-and-level-trigger-polling-epoll-objects7902497
Ref: 28787902497
Ref: library/select epoll-objects7902497
Ref: 286e7902497
Ref: library/select select epoll close7905365
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Ref: library/select select epoll closed7905454
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Ref: library/select select epoll register7905709
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Ref: library/select select epoll modify7905809
Ref: 287d7905809
Ref: library/select select epoll unregister7905894
Ref: 22e7905894
Ref: library/select select epoll poll7906087
Ref: 7637906087
Ref: Edge and Level Trigger Polling epoll Objects-Footnote-17906489
Node: Polling Objects7906538
Ref: library/select poll-objects7906703
Ref: 286f7906703
Ref: library/select polling-objects7906703
Ref: 287e7906703
Ref: library/select select poll register7907270
Ref: 287f7907270
Ref: library/select select poll modify7909247
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Ref: library/select select poll unregister7909548
Ref: 28817909548
Ref: library/select select poll poll7909937
Ref: 7657909937
Ref: Polling Objects-Footnote-17911083
Node: Kqueue Objects7911132
Ref: library/select id17911267
Ref: 28827911267
Ref: library/select kqueue-objects7911267
Ref: 28717911267
Ref: library/select select kqueue close7911316
Ref: 28837911316
Ref: library/select select kqueue closed7911407
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Ref: library/select select kqueue fileno7911486
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Ref: library/select select kqueue fromfd7911575
Ref: 28867911575
Ref: library/select select kqueue control7911666
Ref: 7647911666
Ref: Kqueue Objects-Footnote-17912317
Node: Kevent Objects7912366
Ref: library/select id27912477
Ref: 28877912477
Ref: library/select kevent-objects7912477
Ref: 28737912477
Ref: library/select select kevent ident7912592
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Ref: library/select select kevent filter7912894
Ref: 28897912894
Ref: library/select select kevent flags7914673
Ref: 288a7914673
Ref: library/select select kevent fflags7916334
Ref: 288b7916334
Ref: library/select select kevent data7920076
Ref: 288c7920076
Ref: library/select select kevent udata7920132
Ref: 288d7920132
Node: selectors — High-level I/O multiplexing7920187
Ref: library/selectors doc7920401
Ref: 288e7920401
Ref: library/selectors module-selectors7920401
Ref: e67920401
Ref: library/selectors selectors-high-level-i-o-multiplexing7920401
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Ref: selectors — High-level I/O multiplexing-Footnote-17920759
Node: Introduction<9>7920827
Ref: library/selectors introduction7920939
Ref: 28907920939
Node: Classes<3>7922106
Ref: library/selectors classes7922239
Ref: 28937922239
Ref: library/selectors selectors SelectorKey7923018
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Ref: library/selectors selectors SelectorKey fileobj7923296
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Ref: library/selectors selectors SelectorKey fd7923360
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Ref: library/selectors selectors SelectorKey events7923423
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Ref: library/selectors selectors SelectorKey data7923514
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Ref: library/selectors selectors BaseSelector7923680
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Ref: library/selectors selectors BaseSelector register7924356
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Ref: library/selectors selectors BaseSelector unregister7925010
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Ref: library/selectors selectors BaseSelector modify7925630
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Ref: library/selectors selectors BaseSelector select7926230
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Ref: library/selectors selectors BaseSelector close7927529
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Ref: library/selectors selectors BaseSelector get_key7927747
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Ref: library/selectors selectors BaseSelector get_map7928034
Ref: 289e7928034
Ref: library/selectors selectors DefaultSelector7928302
Ref: 28927928302
Ref: library/selectors selectors SelectSelector7928510
Ref: 27927928510
Ref: library/selectors selectors PollSelector7928597
Ref: 5507928597
Ref: library/selectors selectors EpollSelector7928681
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Ref: library/selectors selectors EpollSelector fileno7928766
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Ref: library/selectors selectors DevpollSelector7928906
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Ref: library/selectors selectors DevpollSelector fileno7928995
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Ref: library/selectors selectors KqueueSelector7929163
Ref: 27957929163
Ref: library/selectors selectors KqueueSelector fileno7929251
Ref: 28a17929251
Ref: Classes<3>-Footnote-17929429
Node: Examples<18>7929478
Ref: library/selectors examples7929587
Ref: 28a27929587
Node: asyncore — Asynchronous socket handler7930614
Ref: library/asyncore doc7930848
Ref: 28a37930848
Ref: library/asyncore asyncore-asynchronous-socket-handler7930848
Ref: 28a47930848
Ref: library/asyncore module-asyncore7930848
Ref: a7930848
Ref: library/asyncore asyncore loop7933148
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Ref: library/asyncore asyncore dispatcher7934178
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Ref: library/asyncore asyncore dispatcher handle_read7936097
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Ref: library/asyncore asyncore dispatcher handle_write7936258
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Ref: library/asyncore asyncore dispatcher handle_expt7936634
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Ref: library/asyncore asyncore dispatcher handle_connect7936846
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Ref: library/asyncore asyncore dispatcher handle_close7937093
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Ref: library/asyncore asyncore dispatcher handle_error7937172
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Ref: library/asyncore asyncore dispatcher handle_accept7937339
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Ref: library/asyncore asyncore dispatcher handle_accepted7937718
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Ref: library/asyncore asyncore dispatcher readable7938206
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Ref: library/asyncore asyncore dispatcher writable7938558
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Ref: library/asyncore asyncore dispatcher create_socket7939065
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Ref: library/asyncore asyncore dispatcher connect7939464
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Ref: library/asyncore asyncore dispatcher send7939665
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Ref: library/asyncore asyncore dispatcher recv7939757
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Ref: library/asyncore asyncore dispatcher listen7940204
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Ref: library/asyncore asyncore dispatcher bind7940475
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Ref: library/asyncore asyncore dispatcher accept7940914
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Ref: library/asyncore asyncore dispatcher close7941556
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Ref: library/asyncore asyncore dispatcher_with_send7941844
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Ref: library/asyncore asyncore file_dispatcher7942075
Ref: 28b67942075
Ref: library/asyncore asyncore file_wrapper7942505
Ref: 28b77942505
Ref: asyncore — Asynchronous socket handler-Footnote-17943022
Node: asyncore Example basic HTTP client7943089
Ref: library/asyncore asyncore-example-17943243
Ref: 28b87943243
Ref: library/asyncore asyncore-example-basic-http-client7943243
Ref: 28b97943243
Node: asyncore Example basic echo server7944253
Ref: library/asyncore asyncore-example-27944407
Ref: 28ba7944407
Ref: library/asyncore asyncore-example-basic-echo-server7944407
Ref: 28bb7944407
Node: asynchat — Asynchronous socket command/response handler7945334
Ref: library/asynchat doc7945574
Ref: 28bc7945574
Ref: library/asynchat asynchat-asynchronous-socket-command-response-handler7945574
Ref: 28bd7945574
Ref: library/asynchat module-asynchat7945574
Ref: 87945574
Ref: library/asynchat asynchat async_chat7946785
Ref: 99c7946785
Ref: library/asynchat asynchat async_chat ac_in_buffer_size7947700
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Ref: library/asynchat asynchat async_chat ac_out_buffer_size7947802
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Ref: library/asynchat asynchat async_chat close_when_done7948997
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Ref: library/asynchat asynchat async_chat collect_incoming_data7949177
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Ref: library/asynchat asynchat async_chat discard_buffers7949409
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Ref: library/asynchat asynchat async_chat found_terminator7949576
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Ref: library/asynchat asynchat async_chat get_terminator7949925
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Ref: library/asynchat asynchat async_chat push7950021
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Ref: library/asynchat asynchat async_chat push_with_producer7950358
Ref: 28c77950358
Ref: library/asynchat asynchat async_chat set_terminator7950707
Ref: 28c27950707
Ref: asynchat — Asynchronous socket command/response handler-Footnote-17951797
Node: asynchat Example7951864
Ref: library/asynchat asynchat-example7951974
Ref: 28c87951974
Ref: library/asynchat id17951974
Ref: 28c97951974
Node: signal — Set handlers for asynchronous events7954323
Ref: library/signal doc7954558
Ref: 28ca7954558
Ref: library/signal module-signal7954558
Ref: ea7954558
Ref: library/signal signal-set-handlers-for-asynchronous-events7954558
Ref: 28cb7954558
Node: General rules7954920
Ref: library/signal general-rules7955044
Ref: 28cc7955044
Node: Execution of Python signal handlers7955860
Ref: library/signal execution-of-python-signal-handlers7955973
Ref: 28cf7955973
Node: Signals and threads7957132
Ref: library/signal id17957245
Ref: 28d37957245
Ref: library/signal signals-and-threads7957245
Ref: 28d47957245
Node: Module contents<2>7957718
Ref: library/signal module-contents7957861
Ref: 28d57957861
Ref: library/signal signal SIG_DFL7958374
Ref: 26277958374
Ref: library/signal signal SIG_IGN7958706
Ref: 26287958706
Ref: library/signal signal SIGABRT7958827
Ref: 28da7958827
Ref: library/signal signal SIGALRM7958893
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Ref: library/signal signal SIGBREAK7958998
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Ref: library/signal signal SIGBUS7959113
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Ref: library/signal signal SIGCHLD7959214
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Ref: library/signal signal SIGCLD7959322
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Ref: library/signal signal SIGCONT7959383
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Ref: library/signal signal SIGFPE7959502
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Ref: library/signal signal SIGHUP7959739
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Ref: library/signal signal SIGILL7959887
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Ref: library/signal signal SIGINT7959939
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Ref: library/signal signal SIGKILL7960069
Ref: 28e17960069
Ref: library/signal signal SIGPIPE7960201
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Ref: library/signal signal SIGSEGV7960362
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Ref: library/signal signal SIGTERM7960440
Ref: 26be7960440
Ref: library/signal signal SIGUSR17960492
Ref: 28e27960492
Ref: library/signal signal SIGUSR27960586
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Ref: library/signal signal SIGWINCH7960680
Ref: 28e47960680
Ref: library/signal signal CTRL_C_EVENT7961337
Ref: 21007961337
Ref: library/signal signal CTRL_BREAK_EVENT7961566
Ref: 21017961566
Ref: library/signal signal NSIG7961803
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Ref: library/signal signal ITIMER_REAL7961887
Ref: 28e67961887
Ref: library/signal signal ITIMER_VIRTUAL7962019
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Ref: library/signal signal ITIMER_PROF7962165
Ref: 28e87962165
Ref: library/signal signal SIG_BLOCK7962504
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Ref: library/signal signal SIG_UNBLOCK7962686
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Ref: library/signal signal SIG_SETMASK7962877
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Ref: library/signal signal ItimerError7963127
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Ref: library/signal signal alarm7963650
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Ref: library/signal signal getsignal7964294
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Ref: library/signal signal strsignal7964866
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Ref: library/signal signal valid_signals7965124
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Ref: library/signal signal pause7965367
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Ref: library/signal signal raise_signal7965754
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Ref: library/signal signal pidfd_send_signal7965887
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Ref: library/signal signal pthread_kill7966387
Ref: b557966387
Ref: library/signal signal pthread_sigmask7967611
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Ref: library/signal signal setitimer7969031
Ref: 28ea7969031
Ref: library/signal signal getitimer7970050
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Ref: library/signal signal set_wakeup_fd7970210
Ref: 4d57970210
Ref: library/signal signal siginterrupt7972409
Ref: b597972409
Ref: library/signal signal signal7973013
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Ref: library/signal signal sigpending7974517
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Ref: library/signal signal sigwait7974976
Ref: b577974976
Ref: library/signal signal sigwaitinfo7975554
Ref: 7727975554
Ref: library/signal signal sigtimedwait7976818
Ref: 7717976818
Ref: Module contents<2>-Footnote-17977587
Ref: Module contents<2>-Footnote-27977636
Node: Example<9>7977685
Ref: library/signal example7977830
Ref: 28f07977830
Ref: library/signal signal-example7977830
Ref: 28f17977830
Node: Note on SIGPIPE7978729
Ref: library/signal note-on-sigpipe7978847
Ref: 28f27978847
Node: mmap — Memory-mapped file support7980261
Ref: library/mmap doc7980430
Ref: 28f37980430
Ref: library/mmap mmap-memory-mapped-file-support7980430
Ref: 28f47980430
Ref: library/mmap module-mmap7980430
Ref: b37980430
Ref: library/mmap mmap mmap7982866
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Ref: library/mmap mmap mmap close7987878
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Ref: library/mmap mmap mmap closed7988089
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Ref: library/mmap mmap mmap find7988193
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Ref: library/mmap mmap mmap flush7988623
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Ref: library/mmap mmap mmap madvise7989511
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Ref: library/mmap mmap mmap move7990077
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Ref: library/mmap mmap mmap read7990355
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Ref: library/mmap mmap mmap read_byte7990807
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Ref: library/mmap mmap mmap readline7990955
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Ref: library/mmap mmap mmap resize7991180
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Ref: library/mmap mmap mmap rfind7991428
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Ref: library/mmap mmap mmap seek7991860
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Ref: library/mmap mmap mmap size7992246
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Ref: library/mmap mmap mmap tell7992385
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Ref: library/mmap mmap mmap write7992472
Ref: 29017992472
Ref: library/mmap mmap mmap write_byte7993179
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Node: MADV_* Constants7993525
Ref: library/mmap madv-constants7993613
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Ref: library/mmap madvise-constants7993613
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Ref: library/mmap mmap MADV_NORMAL7993666
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Ref: library/mmap mmap MADV_SEQUENTIAL7993720
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Ref: library/mmap mmap MADV_REMOVE7993809
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Ref: library/mmap mmap MADV_DONTFORK7993836
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Ref: library/mmap mmap MADV_HWPOISON7993892
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Ref: library/mmap mmap MADV_MERGEABLE7993921
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Ref: library/mmap mmap MADV_UNMERGEABLE7993951
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Ref: library/mmap mmap MADV_SOFT_OFFLINE7993983
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Ref: library/mmap mmap MADV_HUGEPAGE7994016
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Ref: library/mmap mmap MADV_NOHUGEPAGE7994045
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Ref: library/mmap mmap MADV_DONTDUMP7994076
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Ref: library/mmap mmap MADV_NOCORE7994213
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Ref: library/mmap mmap MADV_CORE7994240
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Ref: library/mmap mmap MADV_PROTECT7994265
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Node: Internet Data Handling7994500
Ref: library/netdata doc7994679
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Ref: library/netdata internet-data-handling7994679
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Ref: library/netdata netdata7994679
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Node: email — An email and MIME handling package7995388
Ref: library/email doc7995533
Ref: 291d7995533
Ref: library/email email-an-email-and-mime-handling-package7995533
Ref: 291e7995533
Ref: library/email module-email7995533
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Ref: email — An email and MIME handling package-Footnote-18002293
Ref: email — An email and MIME handling package-Footnote-28002366
Ref: email — An email and MIME handling package-Footnote-38002415
Ref: email — An email and MIME handling package-Footnote-48002464
Ref: email — An email and MIME handling package-Footnote-58002513
Ref: email — An email and MIME handling package-Footnote-68002562
Ref: email — An email and MIME handling package-Footnote-78002611
Ref: email — An email and MIME handling package-Footnote-88002660
Ref: email — An email and MIME handling package-Footnote-98002709
Node: email message Representing an email message8002758
Ref: library/email message doc8002926
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Ref: library/email message email-message-representing-an-email-message8002926
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Ref: library/email message module-email message8002926
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Ref: library/email message email message EmailMessage as_string8005895
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Ref: library/email message email message EmailMessage __str__8007739
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Ref: library/email message email message EmailMessage as_bytes8008208
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Ref: library/email message email message EmailMessage is_multipart8009546
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Ref: library/email message email message EmailMessage set_unixfrom8010231
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Ref: library/email message email message EmailMessage get_unixfrom8010453
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Ref: library/email message email message EmailMessage __len__8011585
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Ref: library/email message email message EmailMessage keys8014049
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Ref: library/email message email message EmailMessage values8014143
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Ref: library/email message email message EmailMessage get8014364
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Ref: library/email message email message EmailMessage get_all8014713
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Ref: library/email message email message EmailMessage add_header8014950
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Ref: library/email message email message EmailMessage get_content_type8017220
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Ref: library/email message email message EmailMessage get_content_maintype8018104
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Ref: library/email message email message EmailMessage get_content_subtype8018310
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Ref: library/email message email message EmailMessage get_default_type8018503
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Ref: library/email message email message EmailMessage set_default_type8018823
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Ref: library/email message email message EmailMessage set_param8019265
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Ref: library/email message email message EmailMessage del_param8020879
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Ref: library/email message email message EmailMessage get_filename8021315
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Ref: library/email message email message EmailMessage get_boundary8021854
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Ref: library/email message email message EmailMessage set_boundary8022218
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Ref: library/email message email message EmailMessage get_content_charset8022886
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Ref: library/email message email message EmailMessage get_charsets8023188
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Ref: library/email message email message EmailMessage is_attachment8023881
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Ref: library/email message email message EmailMessage get_content_disposition8024248
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Ref: library/email message email message EmailMessage walk8024723
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Ref: library/email message email message EmailMessage get_body8026736
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Ref: library/email message email message EmailMessage get_content8030042
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Ref: library/email message email message EmailMessage make_related8030862
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Ref: library/email message email message EmailMessage clear8034837
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Ref: library/email message email message EmailMessage preamble8035178
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Ref: library/email message email message EmailMessage defects8036786
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Ref: library/email message email message MIMEPart8037028
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Ref: email message Representing an email message-Footnote-18037393
Ref: email message Representing an email message-Footnote-28037465
Ref: email message Representing an email message-Footnote-38037665
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Ref: email message Representing an email message-Footnote-118038058
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Ref: email message Representing an email message-Footnote-138038158
Node: email parser Parsing email messages8038208
Ref: library/email parser doc8038426
Ref: 295c8038426
Ref: library/email parser email-parser-parsing-email-messages8038426
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Ref: library/email parser module-email parser8038426
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Ref: email parser Parsing email messages-Footnote-18040810
Node: FeedParser API8040881
Ref: library/email parser feedparser-api8040986
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Ref: library/email parser email parser BytesFeedParser8042279
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Ref: library/email parser email parser BytesFeedParser feed8043478
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Node: Parser API8044611
Ref: library/email parser parser-api8044741
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Ref: library/email parser email parser BytesParser8045469
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Ref: library/email parser email parser BytesParser parse8046136
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Ref: library/email parser email parser HeaderParser8049112
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Ref: library/email parser email message_from_bytes8049509
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Ref: library/email parser email message_from_binary_file8049976
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Ref: Parser API-Footnote-18051574
Ref: Parser API-Footnote-28051623
Node: Additional notes8051672
Ref: library/email parser additional-notes8051779
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Node: email generator Generating MIME documents8053321
Ref: library/email generator doc8053523
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Ref: library/email generator email-generator-generating-mime-documents8053523
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Ref: library/email generator module-email generator8053523
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Ref: library/email generator email generator DecodedGenerator8065323
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Ref: email generator Generating MIME documents-Footnote-18066740
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Ref: email generator Generating MIME documents-Footnote-48067359
Ref: email generator Generating MIME documents-Footnote-58067408
Ref: email generator Generating MIME documents-Footnote-68067460
Node: email policy Policy Objects8067509
Ref: library/email policy doc8067717
Ref: 29738067717
Ref: library/email policy email-policy-policy-objects8067717
Ref: 29748067717
Ref: library/email policy module-email policy8067717
Ref: 738067717
Ref: library/email policy email policy Policy8073672
Ref: ad38073672
Ref: library/email policy email policy Policy max_line_length8074492
Ref: 29758074492
Ref: library/email policy email policy Policy linesep8074798
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Ref: library/email policy email policy Policy cte_type8075067
Ref: 296e8075067
Ref: library/email policy email policy Policy raise_on_defect8076178
Ref: 29788076178
Ref: library/email policy email policy Policy mangle_from_8076422
Ref: 7c38076422
Ref: library/email policy email policy Policy message_factory8076779
Ref: 6398076779
Ref: library/email policy email policy Policy clone8077216
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Ref: library/email policy email policy Policy handle_defect8077690
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Ref: library/email policy email policy Policy register_defect8078169
Ref: 29798078169
Ref: library/email policy email policy Policy header_max_count8078862
Ref: 297b8078862
Ref: library/email policy email policy Policy header_source_parse8079924
Ref: 297c8079924
Ref: library/email policy email policy Policy header_store_parse8080937
Ref: 297d8080937
Ref: library/email policy email policy Policy header_fetch_parse8081698
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Ref: library/email policy email policy Policy fold8082521
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Ref: library/email policy email policy Policy fold_binary8083237
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Ref: library/email policy email policy EmailPolicy8083571
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Ref: library/email policy email policy EmailPolicy utf88084401
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Ref: library/email policy email policy EmailPolicy refold_source8084797
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Ref: library/email policy email policy EmailPolicy header_factory8085592
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Ref: library/email policy email policy EmailPolicy content_manager8086203
Ref: 9318086203
Ref: library/email policy email policy EmailPolicy header_max_count8086911
Ref: 29838086911
Ref: library/email policy email policy EmailPolicy header_source_parse8087117
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Ref: library/email policy email policy EmailPolicy header_store_parse8087502
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Ref: library/email policy email policy EmailPolicy header_fetch_parse8087983
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Ref: library/email policy email policy EmailPolicy fold8088409
Ref: 29888088409
Ref: library/email policy email policy EmailPolicy fold_binary8089572
Ref: 29898089572
Ref: library/email policy email policy default8090391
Ref: 29228090391
Ref: library/email policy email policy SMTP8090601
Ref: 298a8090601
Ref: library/email policy email policy SMTPUTF88090803
Ref: 298b8090803
Ref: library/email policy email policy HTTP8091217
Ref: 298c8091217
Ref: library/email policy email policy strict8091409
Ref: 298d8091409
Ref: library/email policy email policy Compat328092836
Ref: ad48092836
Ref: library/email policy email policy Compat32 mangle_from_8093367
Ref: 298e8093367
Ref: library/email policy email policy Compat32 header_source_parse8093555
Ref: 298f8093555
Ref: library/email policy email policy Compat32 header_store_parse8093940
Ref: 29908093940
Ref: library/email policy email policy Compat32 header_fetch_parse8094046
Ref: 29918094046
Ref: library/email policy email policy Compat32 fold8094287
Ref: 29928094287
Ref: library/email policy email policy Compat32 fold_binary8094629
Ref: 29938094629
Ref: library/email policy email policy compat328095158
Ref: 63a8095158
Ref: email policy Policy Objects-Footnote-18095361
Ref: email policy Policy Objects-Footnote-28095432
Ref: email policy Policy Objects-Footnote-38095481
Ref: email policy Policy Objects-Footnote-48095530
Ref: email policy Policy Objects-Footnote-58095579
Ref: email policy Policy Objects-Footnote-68095628
Ref: email policy Policy Objects-Footnote-78095677
Ref: email policy Policy Objects-Footnote-88095726
Ref: email policy Policy Objects-Footnote-98095799
Ref: email policy Policy Objects-Footnote-108095848
Ref: email policy Policy Objects-Footnote-118095898
Ref: email policy Policy Objects-Footnote-128095948
Node: email errors Exception and Defect classes8095998
Ref: library/email errors doc8096207
Ref: 29948096207
Ref: library/email errors email-errors-exception-and-defect-classes8096207
Ref: 29958096207
Ref: library/email errors module-email errors8096207
Ref: 6b8096207
Ref: library/email errors email errors MessageError8096511
Ref: 29968096511
Ref: library/email errors email errors MessageParseError8096752
Ref: 29978096752
Ref: library/email errors email errors HeaderParseError8097028
Ref: 29438097028
Ref: library/email errors email errors BoundaryError8097670
Ref: 29988097670
Ref: library/email errors email errors MultipartConversionError8097750
Ref: 29998097750
Ref: email errors Exception and Defect classes-Footnote-18101076
Ref: email errors Exception and Defect classes-Footnote-28101147
Node: email headerregistry Custom Header Objects8101196
Ref: library/email headerregistry doc8101420
Ref: 299b8101420
Ref: library/email headerregistry email-headerregistry-custom-header-objects8101420
Ref: 299c8101420
Ref: library/email headerregistry module-email headerregistry8101420
Ref: 6e8101420
Ref: library/email headerregistry email headerregistry BaseHeader8103186
Ref: 29308103186
Ref: library/email headerregistry email headerregistry BaseHeader name8103499
Ref: 299f8103499
Ref: library/email headerregistry email headerregistry BaseHeader defects8103750
Ref: 29a08103750
Ref: library/email headerregistry email headerregistry BaseHeader max_count8104102
Ref: 29848104102
Ref: library/email headerregistry email headerregistry BaseHeader fold8104619
Ref: 29a18104619
Ref: library/email headerregistry email headerregistry UnstructuredHeader8106810
Ref: 299e8106810
Ref: library/email headerregistry email headerregistry DateHeader8107889
Ref: 29a28107889
Ref: library/email headerregistry email headerregistry DateHeader datetime8108252
Ref: 29a38108252
Ref: library/email headerregistry email headerregistry AddressHeader8109820
Ref: 29a48109820
Ref: library/email headerregistry email headerregistry AddressHeader groups8110104
Ref: 29a58110104
Ref: library/email headerregistry email headerregistry AddressHeader addresses8110419
Ref: 29a88110419
Ref: library/email headerregistry email headerregistry SingleAddressHeader8111581
Ref: 29aa8111581
Ref: library/email headerregistry email headerregistry SingleAddressHeader address8111722
Ref: 29ab8111722
Ref: library/email headerregistry email headerregistry MIMEVersionHeader8112254
Ref: 29ac8112254
Ref: library/email headerregistry email headerregistry MIMEVersionHeader version8112646
Ref: 29ad8112646
Ref: library/email headerregistry email headerregistry MIMEVersionHeader major8112773
Ref: 29ae8112773
Ref: library/email headerregistry email headerregistry MIMEVersionHeader minor8112850
Ref: 29af8112850
Ref: library/email headerregistry email headerregistry ParameterizedMIMEHeader8112927
Ref: 29b08112927
Ref: library/email headerregistry email headerregistry ParameterizedMIMEHeader params8113310
Ref: 29b18113310
Ref: library/email headerregistry email headerregistry ContentTypeHeader8113407
Ref: 29b28113407
Ref: library/email headerregistry email headerregistry ContentTypeHeader content_type8113558
Ref: 29b38113558
Ref: library/email headerregistry email headerregistry ContentTypeHeader maintype8113664
Ref: 29b48113664
Ref: library/email headerregistry email headerregistry ContentTypeHeader subtype8113694
Ref: 29b58113694
Ref: library/email headerregistry email headerregistry ContentDispositionHeader8113723
Ref: 29b68113723
Ref: library/email headerregistry email headerregistry ContentDispositionHeader content_disposition8113888
Ref: 29b78113888
Ref: library/email headerregistry email headerregistry ContentTransferEncoding8114025
Ref: 29b88114025
Ref: library/email headerregistry email headerregistry ContentTransferEncoding cte8114140
Ref: 29b98114140
Ref: library/email headerregistry email headerregistry HeaderRegistry8114309
Ref: 299d8114309
Ref: library/email headerregistry email headerregistry HeaderRegistry map_to_type8116029
Ref: 29ba8116029
Ref: library/email headerregistry email headerregistry HeaderRegistry __getitem__8116364
Ref: 29bb8116364
Ref: library/email headerregistry email headerregistry HeaderRegistry __call__8116487
Ref: 29bc8116487
Ref: library/email headerregistry email headerregistry Address8117129
Ref: 29a98117129
Ref: library/email headerregistry email headerregistry Address display_name8117968
Ref: 29bd8117968
Ref: library/email headerregistry email headerregistry Address username8118194
Ref: 29be8118194
Ref: library/email headerregistry email headerregistry Address domain8118314
Ref: 29bf8118314
Ref: library/email headerregistry email headerregistry Address addr_spec8118394
Ref: 29c08118394
Ref: library/email headerregistry email headerregistry Address __str__8118612
Ref: 29c18118612
Ref: library/email headerregistry email headerregistry Group8119051
Ref: 29a68119051
Ref: library/email headerregistry email headerregistry Group display_name8119600
Ref: 29a78119600
Ref: library/email headerregistry email headerregistry Group addresses8119855
Ref: 29c28119855
Ref: library/email headerregistry email headerregistry Group __str__8120003
Ref: 29c38120003
Ref: email headerregistry Custom Header Objects-Footnote-18120443
Ref: email headerregistry Custom Header Objects-Footnote-28120523
Ref: email headerregistry Custom Header Objects-Footnote-38120595
Ref: email headerregistry Custom Header Objects-Footnote-48120644
Ref: email headerregistry Custom Header Objects-Footnote-58120693
Ref: email headerregistry Custom Header Objects-Footnote-68120742
Ref: email headerregistry Custom Header Objects-Footnote-78120791
Ref: email headerregistry Custom Header Objects-Footnote-88120840
Ref: email headerregistry Custom Header Objects-Footnote-98120889
Ref: email headerregistry Custom Header Objects-Footnote-108120938
Ref: email headerregistry Custom Header Objects-Footnote-118120988
Ref: email headerregistry Custom Header Objects-Footnote-128121038
Ref: email headerregistry Custom Header Objects-Footnote-138121088
Ref: email headerregistry Custom Header Objects-Footnote-148121138
Ref: email headerregistry Custom Header Objects-Footnote-158121188
Ref: email headerregistry Custom Header Objects-Footnote-168121238
Ref: email headerregistry Custom Header Objects-Footnote-178121288
Node: email contentmanager Managing MIME Content8121338
Ref: library/email contentmanager doc8121535
Ref: 29c48121535
Ref: library/email contentmanager email-contentmanager-managing-mime-content8121535
Ref: 29c58121535
Ref: library/email contentmanager module-email contentmanager8121535
Ref: 698121535
Ref: library/email contentmanager email contentmanager ContentManager8121792
Ref: 29c68121792
Ref: library/email contentmanager email contentmanager ContentManager get_content8122081
Ref: 294e8122081
Ref: library/email contentmanager email contentmanager ContentManager set_content8122935
Ref: 294f8122935
Ref: library/email contentmanager email contentmanager ContentManager add_get_handler8124558
Ref: 29c88124558
Ref: library/email contentmanager email contentmanager ContentManager add_set_handler8124750
Ref: 29ca8124750
Ref: email contentmanager Managing MIME Content-Footnote-18125115
Ref: email contentmanager Managing MIME Content-Footnote-28125195
Node: Content Manager Instances8125267
Ref: library/email contentmanager content-manager-instances8125371
Ref: 29cc8125371
Ref: library/email contentmanager email contentmanager raw_data_manager8125711
Ref: 29828125711
Ref: library/email contentmanager email contentmanager get_content8126441
Ref: 29c98126441
Ref: library/email contentmanager email contentmanager set_content8127040
Ref: 29cb8127040
Ref: Content Manager Instances-Footnote-18131459
Node: email Examples8131508
Ref: library/email examples doc8131737
Ref: 29cd8131737
Ref: library/email examples email-examples8131737
Ref: 9328131737
Ref: library/email examples id18131737
Ref: 29ce8131737
Ref: email Examples-Footnote-18146402
Ref: email Examples-Footnote-28146450
Node: email message Message Representing an email message using the compat32 API8146536
Ref: library/email compat32-message doc8146778
Ref: 29cf8146778
Ref: library/email compat32-message compat32-message8146778
Ref: 29218146778
Ref: library/email compat32-message email-message-message-representing-an-email-message-using-the-compat32-api8146778
Ref: 29d08146778
Ref: library/email compat32-message email message Message8149335
Ref: 63b8149335
Ref: library/email compat32-message email message Message as_string8149868
Ref: 92c8149868
Ref: library/email compat32-message email message Message __str__8152016
Ref: 29d18152016
Ref: library/email compat32-message email message Message as_bytes8152181
Ref: 92d8152181
Ref: library/email compat32-message email message Message __bytes__8153737
Ref: 92e8153737
Ref: library/email compat32-message email message Message is_multipart8153942
Ref: 29478153942
Ref: library/email compat32-message email message Message set_unixfrom8154618
Ref: 29d28154618
Ref: library/email compat32-message email message Message get_unixfrom8154758
Ref: 29d38154758
Ref: library/email compat32-message email message Message attach8154915
Ref: 29548154915
Ref: library/email compat32-message email message Message get_payload8155532
Ref: c1d8155532
Ref: library/email compat32-message email message Message set_payload8158183
Ref: 29d48158183
Ref: library/email compat32-message email message Message set_charset8158650
Ref: 29d58158650
Ref: library/email compat32-message email message Message get_charset8160409
Ref: 29d68160409
Ref: library/email compat32-message email message Message __len__8161860
Ref: 29d88161860
Ref: library/email compat32-message email message Message __contains__8161958
Ref: 29d98161958
Ref: library/email compat32-message email message Message __getitem__8162328
Ref: 29da8162328
Ref: library/email compat32-message email message Message __setitem__8162863
Ref: 29dc8162863
Ref: library/email compat32-message email message Message __delitem__8163420
Ref: 29dd8163420
Ref: library/email compat32-message email message Message keys8163646
Ref: 29d78163646
Ref: library/email compat32-message email message Message values8163740
Ref: 29de8163740
Ref: library/email compat32-message email message Message items8163830
Ref: 29df8163830
Ref: library/email compat32-message email message Message get8163961
Ref: 29e08163961
Ref: library/email compat32-message email message Message get_all8164285
Ref: 29db8164285
Ref: library/email compat32-message email message Message add_header8164522
Ref: 29e18164522
Ref: library/email compat32-message email message Message replace_header8166488
Ref: 29e28166488
Ref: library/email compat32-message email message Message get_content_type8166777
Ref: 29e38166777
Ref: library/email compat32-message email message Message get_content_maintype8167635
Ref: 29e58167635
Ref: library/email compat32-message email message Message get_content_subtype8167841
Ref: 29e68167841
Ref: library/email compat32-message email message Message get_default_type8168034
Ref: 29e48168034
Ref: library/email compat32-message email message Message set_default_type8168354
Ref: 29e78168354
Ref: library/email compat32-message email message Message get_params8168641
Ref: 29e88168641
Ref: library/email compat32-message email message Message get_param8169697
Ref: 29e98169697
Ref: library/email compat32-message email message Message set_param8171699
Ref: 92f8171699
Ref: library/email compat32-message email message Message del_param8172966
Ref: 29eb8172966
Ref: library/email compat32-message email message Message set_type8173407
Ref: 29ec8173407
Ref: library/email compat32-message email message Message get_filename8174280
Ref: 29ed8174280
Ref: library/email compat32-message email message Message get_boundary8174819
Ref: 29ee8174819
Ref: library/email compat32-message email message Message set_boundary8175183
Ref: 29ef8175183
Ref: library/email compat32-message email message Message get_content_charset8175998
Ref: 29f08175998
Ref: library/email compat32-message email message Message get_charsets8176486
Ref: 29f18176486
Ref: library/email compat32-message email message Message get_content_disposition8177188
Ref: 7c48177188
Ref: library/email compat32-message email message Message walk8177551
Ref: 29f28177551
Ref: library/email compat32-message email message Message preamble8179671
Ref: 29f38179671
Ref: library/email compat32-message email message Message epilogue8180933
Ref: 29f48180933
Ref: library/email compat32-message email message Message defects8181331
Ref: 29f58181331
Ref: email message Message Representing an email message using the compat32 API-Footnote-18181609
Ref: email message Message Representing an email message using the compat32 API-Footnote-28181658
Ref: email message Message Representing an email message using the compat32 API-Footnote-38181707
Ref: email message Message Representing an email message using the compat32 API-Footnote-48181756
Ref: email message Message Representing an email message using the compat32 API-Footnote-58181805
Ref: email message Message Representing an email message using the compat32 API-Footnote-68181854
Ref: email message Message Representing an email message using the compat32 API-Footnote-78181903
Ref: email message Message Representing an email message using the compat32 API-Footnote-88181952
Ref: email message Message Representing an email message using the compat32 API-Footnote-98182001
Ref: email message Message Representing an email message using the compat32 API-Footnote-108182050
Ref: email message Message Representing an email message using the compat32 API-Footnote-118182100
Ref: email message Message Representing an email message using the compat32 API-Footnote-128182150
Node: email mime Creating email and MIME objects from scratch8182200
Ref: library/email mime doc8182466
Ref: 29f68182466
Ref: library/email mime email-mime-creating-email-and-mime-objects-from-scratch8182466
Ref: 29f78182466
Ref: library/email mime module-email mime8182466
Ref: 718182466
Ref: library/email mime email mime base MIMEBase8183702
Ref: 29f88183702
Ref: library/email mime email mime nonmultipart MIMENonMultipart8184845
Ref: f598184845
Ref: library/email mime email mime multipart MIMEMultipart8185337
Ref: 29f98185337
Ref: library/email mime email mime application MIMEApplication8186650
Ref: 29fa8186650
Ref: library/email mime email mime audio MIMEAudio8187991
Ref: 29fb8187991
Ref: library/email mime email mime image MIMEImage8189577
Ref: 299a8189577
Ref: library/email mime email mime message MIMEMessage8191174
Ref: 29fc8191174
Ref: library/email mime email mime text MIMEText8191857
Ref: 7c68191857
Ref: email mime Creating email and MIME objects from scratch-Footnote-18193494
Node: email header Internationalized headers8193561
Ref: library/email header doc8193794
Ref: 29fd8193794
Ref: library/email header email-header-internationalized-headers8193794
Ref: 29fe8193794
Ref: library/email header module-email header8193794
Ref: 6d8193794
Ref: library/email header email header Header8196486
Ref: f838196486
Ref: library/email header email header Header append8198358
Ref: 29ff8198358
Ref: library/email header email header Header encode8199692
Ref: 2a008199692
Ref: library/email header email header Header __str__8201332
Ref: 2a018201332
Ref: library/email header email header Header __eq__8201830
Ref: 2a028201830
Ref: library/email header email header Header __ne__8201965
Ref: 2a038201965
Ref: library/email header email header decode_header8202188
Ref: ad88202188
Ref: library/email header email header make_header8202844
Ref: ad98202844
Ref: email header Internationalized headers-Footnote-18203533
Ref: email header Internationalized headers-Footnote-28203604
Ref: email header Internationalized headers-Footnote-38203653
Ref: email header Internationalized headers-Footnote-48203701
Ref: email header Internationalized headers-Footnote-58203750
Ref: email header Internationalized headers-Footnote-68203799
Ref: email header Internationalized headers-Footnote-78203848
Ref: email header Internationalized headers-Footnote-88203897
Ref: email header Internationalized headers-Footnote-98203946
Ref: email header Internationalized headers-Footnote-108203995
Ref: email header Internationalized headers-Footnote-118204045
Ref: email header Internationalized headers-Footnote-128204095
Ref: email header Internationalized headers-Footnote-138204145
Ref: email header Internationalized headers-Footnote-148204195
Ref: email header Internationalized headers-Footnote-158204245
Node: email charset Representing character sets8204295
Ref: library/email charset doc8204496
Ref: 2a048204496
Ref: library/email charset email-charset-representing-character-sets8204496
Ref: 2a058204496
Ref: library/email charset module-email charset8204496
Ref: 688204496
Ref: library/email charset email charset Charset8205307
Ref: 7c78205307
Ref: library/email charset email charset Charset input_charset8206832
Ref: 2a068206832
Ref: library/email charset email charset Charset header_encoding8207088
Ref: 2a078207088
Ref: library/email charset email charset Charset body_encoding8207474
Ref: 2a088207474
Ref: library/email charset email charset Charset output_charset8207751
Ref: 2a098207751
Ref: library/email charset email charset Charset input_codec8208090
Ref: 2a0a8208090
Ref: library/email charset email charset Charset output_codec8208304
Ref: 2a0b8208304
Ref: library/email charset email charset Charset get_body_encoding8208616
Ref: 2a0c8208616
Ref: library/email charset email charset Charset get_output_charset8209333
Ref: 2a0d8209333
Ref: library/email charset email charset Charset header_encode8209537
Ref: 2a0e8209537
Ref: library/email charset email charset Charset header_encode_lines8209745
Ref: 2a0f8209745
Ref: library/email charset email charset Charset body_encode8210178
Ref: 2a108210178
Ref: library/email charset email charset Charset __str__8210510
Ref: 2a118210510
Ref: library/email charset email charset Charset __eq__8210681
Ref: 2a128210681
Ref: library/email charset email charset Charset __ne__8210817
Ref: 2a138210817
Ref: library/email charset email charset add_charset8211111
Ref: 2a148211111
Ref: library/email charset email charset add_alias8212436
Ref: 2a168212436
Ref: library/email charset email charset add_codec8212762
Ref: 2a158212762
Ref: email charset Representing character sets-Footnote-18213156
Node: email encoders Encoders8213228
Ref: library/email encoders doc8213426
Ref: 2a178213426
Ref: library/email encoders email-encoders-encoders8213426
Ref: 2a188213426
Ref: library/email encoders module-email encoders8213426
Ref: 6a8213426
Ref: library/email encoders email encoders encode_quopri8215112
Ref: 2a198215112
Ref: library/email encoders email encoders encode_base648215440
Ref: 2a1a8215440
Ref: library/email encoders email encoders encode_7or8bit8215836
Ref: 2a1b8215836
Ref: library/email encoders email encoders encode_noop8216096
Ref: 2a1c8216096
Ref: email encoders Encoders-Footnote-18216276
Ref: email encoders Encoders-Footnote-28216349
Node: email utils Miscellaneous utilities8216470
Ref: library/email utils doc8216652
Ref: 2a1d8216652
Ref: library/email utils email-utils-miscellaneous-utilities8216652
Ref: 2a1e8216652
Ref: library/email utils module-email utils8216652
Ref: 748216652
Ref: library/email utils email utils localtime8216948
Ref: adf8216948
Ref: library/email utils email utils make_msgid8217771
Ref: 2a1f8217771
Ref: library/email utils email utils quote8218668
Ref: 2a208218668
Ref: library/email utils email utils unquote8218847
Ref: 29408218847
Ref: library/email utils email utils parseaddr8219117
Ref: 2a218219117
Ref: library/email utils email utils formataddr8219476
Ref: be88219476
Ref: library/email utils email utils getaddresses8220157
Ref: f828220157
Ref: library/email utils email utils parsedate8220795
Ref: 2a228220795
Ref: library/email utils email utils parsedate_tz8221424
Ref: f6a8221424
Ref: library/email utils email utils parsedate_to_datetime8222003
Ref: ade8222003
Ref: library/email utils email utils mktime_tz8222714
Ref: 2a238222714
Ref: library/email utils email utils formatdate8222950
Ref: 2a248222950
Ref: library/email utils email utils format_datetime8223896
Ref: add8223896
Ref: library/email utils email utils decode_rfc22318224584
Ref: 2a258224584
Ref: library/email utils email utils encode_rfc22318224684
Ref: 2a268224684
Ref: library/email utils email utils collapse_rfc2231_value8225092
Ref: 29ea8225092
Ref: library/email utils email utils decode_params8225946
Ref: 2a278225946
Ref: email utils Miscellaneous utilities-Footnote-18226202
Ref: email utils Miscellaneous utilities-Footnote-28226272
Ref: email utils Miscellaneous utilities-Footnote-38226321
Ref: email utils Miscellaneous utilities-Footnote-48226370
Ref: email utils Miscellaneous utilities-Footnote-58226419
Ref: email utils Miscellaneous utilities-Footnote-68226468
Ref: email utils Miscellaneous utilities-Footnote-78226735
Ref: email utils Miscellaneous utilities-Footnote-88226784
Ref: email utils Miscellaneous utilities-Footnote-98226833
Ref: email utils Miscellaneous utilities-Footnote-108226882
Ref: email utils Miscellaneous utilities-Footnote-118226932
Ref: email utils Miscellaneous utilities-Footnote-128226982
Node: email iterators Iterators8227032
Ref: library/email iterators doc8227182
Ref: 2a288227182
Ref: library/email iterators email-iterators-iterators8227182
Ref: 2a298227182
Ref: library/email iterators module-email iterators8227182
Ref: 6f8227182
Ref: library/email iterators email iterators body_line_iterator8227582
Ref: 2a2a8227582
Ref: library/email iterators email iterators typed_subpart_iterator8228159
Ref: 2a2b8228159
Ref: library/email iterators email iterators _structure8228877
Ref: 2a2c8228877
Ref: email iterators Iterators-Footnote-18230457
Node: json — JSON encoder and decoder8230531
Ref: library/json doc8230718
Ref: 2a2d8230718
Ref: library/json json-json-encoder-and-decoder8230718
Ref: 2a2e8230718
Ref: library/json module-json8230718
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Ref: library/xml dom xml dom Document getElementsByTagName8488335
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Ref: library/xml dom xml dom NamedNodeMap length8493049
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Node: Text and CDATASection Objects8494133
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Ref: library/xml dom text-and-cdatasection-objects8494279
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Ref: library/xml dom xml dom Text data8494775
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Node: ProcessingInstruction Objects8495268
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Ref: library/xml dom xml dom ProcessingInstruction target8495625
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Ref: library/xml dom xml dom InvalidAccessErr8497579
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Ref: library/xml dom xml dom InvalidCharacterErr8497712
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Ref: library/xml dom xml dom InvalidModificationErr8498072
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Ref: library/xml dom xml dom InvalidStateErr8498186
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Ref: library/xml dom xml dom NamespaceErr8498329
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Ref: library/xml dom xml dom NotFoundErr8498538
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Ref: library/xml dom xml dom SyntaxErr8499205
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Ref: library/xml dom xml dom WrongDocumentErr8499300
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Ref: Exceptions<17>-Footnote-18502341
Node: Conformance8502386
Ref: library/xml dom conformance8502502
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Ref: library/xml dom dom-conformance8502502
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Node: Type Mapping8502759
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Ref: library/xml dom type-mapping8502844
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Node: Accessor Methods8503669
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Ref: DOM Objects-Footnote-18514398
Node: DOM Example8514805
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Ref: library/xml dom minidom id28514956
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Node: xml dom pulldom — Support for building partial DOM trees8519768
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Ref: xml dom pulldom — Support for building partial DOM trees-Footnote-18524051
Node: DOMEventStream Objects8524125
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Ref: library/xml dom pulldom xml dom pulldom DOMEventStream getEvent8524474
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Ref: library/xml dom pulldom xml dom pulldom DOMEventStream expandNode8524966
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Ref: library/xml dom pulldom xml dom pulldom DOMEventStream reset8525680
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Node: xml sax — Support for SAX2 parsers8525707
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Ref: xml sax — Support for SAX2 parsers-Footnote-18532647
Ref: xml sax — Support for SAX2 parsers-Footnote-28532723
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Ref: library/xml sax xml sax SAXException getException8533101
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Node: xml sax handler — Base classes for SAX handlers8533205
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Ref: library/xml sax handler xml sax handler EntityResolver8534525
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Ref: library/xml sax handler xml sax handler feature_namespaces8535204
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Ref: library/xml sax handler xml sax handler feature_string_interning8535965
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Ref: library/xml sax handler xml sax handler property_dom_node8538183
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Ref: xml sax handler — Base classes for SAX handlers-Footnote-18539080
Node: ContentHandler Objects8539154
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Ref: library/xml sax handler xml sax handler ContentHandler setDocumentLocator8539543
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Ref: library/xml sax handler xml sax handler DTDHandler unparsedEntityDecl8547991
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Node: EntityResolver Objects8548129
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Ref: library/xml sax handler xml sax handler EntityResolver resolveEntity8548360
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Node: xml sax saxutils — SAX Utilities8550312
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Ref: library/xml sax utils module-xml sax saxutils8550531
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Ref: library/xml sax utils xml-sax-saxutils-sax-utilities8550531
Ref: 2c678550531
Ref: library/xml sax utils xml sax saxutils escape8550918
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Ref: library/xml sax utils xml sax saxutils unescape8551372
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Ref: library/xml sax utils xml sax saxutils quoteattr8551839
Ref: 2c6a8551839
Ref: library/xml sax utils xml sax saxutils XMLGenerator8552748
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Ref: library/xml sax utils xml sax saxutils XMLFilterBase8553601
Ref: 2c6c8553601
Ref: library/xml sax utils xml sax saxutils prepare_input_source8554023
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Ref: xml sax saxutils — SAX Utilities-Footnote-18554512
Node: xml sax xmlreader — Interface for XML parsers8554588
Ref: library/xml sax reader doc8554808
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Ref: library/xml sax reader module-xml sax xmlreader8554808
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Ref: library/xml sax reader xml sax xmlreader XMLReader8555308
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Ref: library/xml sax reader xml sax xmlreader IncrementalParser8555404
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Ref: library/xml sax reader xml sax xmlreader Locator8556531
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Ref: library/xml sax reader xml sax xmlreader InputSource8556864
Ref: 8818556864
Ref: library/xml sax reader xml sax xmlreader AttributesImpl8557632
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Ref: library/xml sax reader xml sax xmlreader AttributesNSImpl8558231
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Ref: xml sax xmlreader — Interface for XML parsers-Footnote-18558988
Node: XMLReader Objects8559065
Ref: library/xml sax reader id18559200
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Ref: library/xml sax reader xml sax xmlreader XMLReader parse8559327
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Ref: library/xml sax reader xml sax xmlreader XMLReader getContentHandler8559916
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Ref: library/xml sax reader xml sax xmlreader XMLReader getDTDHandler8560196
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Ref: library/xml sax reader xml sax xmlreader XMLReader setDTDHandler8560285
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Ref: library/xml sax reader xml sax xmlreader XMLReader getEntityResolver8560452
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Ref: library/xml sax reader xml sax xmlreader XMLReader getErrorHandler8560841
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Ref: library/xml sax reader xml sax xmlreader XMLReader setErrorHandler8560934
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Ref: library/xml sax reader xml sax xmlreader XMLReader setLocale8561138
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Ref: library/xml sax reader xml sax xmlreader XMLReader getFeature8561504
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Ref: library/xml sax reader xml sax xmlreader IncrementalParser feed8562977
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Ref: library/xml sax reader xml sax xmlreader IncrementalParser close8563053
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Node: Locator Objects8563554
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Ref: library/xml sax reader xml sax xmlreader Locator getColumnNumber8563826
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Ref: library/xml sax reader xml sax xmlreader Locator getPublicId8564028
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Ref: library/xml sax reader xml sax xmlreader InputSource getPublicId8564544
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Ref: library/xml sax reader xml sax xmlreader InputSource getByteStream8565780
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Ref: library/xml sax reader xml sax xmlreader InputSource getCharacterStream8566302
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Node: The Attributes Interface8566403
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Node: The AttributesNS Interface8567265
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Ref: library/xml sax reader xml sax xmlreader AttributesNS getValueByQName8567741
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Ref: library/xml sax reader xml sax xmlreader AttributesNS getQNames8568079
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Node: xml parsers expat — Fast XML parsing using Expat8568170
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Ref: library/pyexpat xml-parsers-expat-fast-xml-parsing-using-expat8568347
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Ref: library/pyexpat xml parsers expat ParserCreate8570010
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Ref: xml parsers expat — Fast XML parsing using Expat-Footnote-18572446
Ref: xml parsers expat — Fast XML parsing using Expat-Footnote-28572759
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Ref: 2cab8572929
Ref: library/pyexpat xml parsers expat xmlparser Parse8573039
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Ref: library/pyexpat xml parsers expat xmlparser ParseFile8573417
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Ref: library/pyexpat xml parsers expat xmlparser SetBase8573637
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Ref: library/pyexpat xml parsers expat xmlparser GetBase8574053
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Ref: library/pyexpat xml parsers expat xmlparser GetInputContext8574251
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Ref: library/pyexpat xml parsers expat xmlparser ExternalEntityParserCreate8574534
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Ref: library/pyexpat xml parsers expat xmlparser SetParamEntityParsing8575051
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Ref: library/pyexpat xml parsers expat xmlparser UseForeignDTD8575416
Ref: 2cb88575416
Ref: library/pyexpat xml parsers expat xmlparser buffer_size8576458
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Ref: library/pyexpat xml parsers expat xmlparser specified_attributes8577937
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Ref: library/pyexpat xml parsers expat xmlparser ErrorByteIndex8578743
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Ref: library/pyexpat xml parsers expat xmlparser ErrorCode8578829
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Ref: library/pyexpat xml parsers expat xmlparser ErrorColumnNumber8579060
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Ref: library/pyexpat xml parsers expat xmlparser ErrorLineNumber8579152
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Ref: library/pyexpat xml parsers expat xmlparser CurrentByteIndex8579645
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Ref: library/pyexpat xml parsers expat xmlparser CurrentColumnNumber8579734
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Ref: library/pyexpat xml parsers expat xmlparser CurrentLineNumber8579829
Ref: 2cc58579829
Ref: library/pyexpat xml parsers expat xmlparser XmlDeclHandler8580242
Ref: 2cc68580242
Ref: library/pyexpat xml parsers expat xmlparser StartDoctypeDeclHandler8580855
Ref: 2cb98580855
Ref: library/pyexpat xml parsers expat xmlparser EndDoctypeDeclHandler8581408
Ref: 2cba8581408
Ref: library/pyexpat xml parsers expat xmlparser ElementDeclHandler8581574
Ref: 2cc78581574
Ref: library/pyexpat xml parsers expat xmlparser AttlistDeclHandler8581788
Ref: 2cc88581788
Ref: library/pyexpat xml parsers expat xmlparser StartElementHandler8582691
Ref: 2cc98582691
Ref: library/pyexpat xml parsers expat xmlparser EndElementHandler8583088
Ref: 2cca8583088
Ref: library/pyexpat xml parsers expat xmlparser ProcessingInstructionHandler8583179
Ref: 2ccb8583179
Ref: library/pyexpat xml parsers expat xmlparser CharacterDataHandler8583293
Ref: 2cbd8583293
Ref: library/pyexpat xml parsers expat xmlparser UnparsedEntityDeclHandler8583715
Ref: 2cb18583715
Ref: library/pyexpat xml parsers expat xmlparser EntityDeclHandler8584108
Ref: 2cce8584108
Ref: library/pyexpat xml parsers expat xmlparser NotationDeclHandler8584853
Ref: 2cb08584853
Ref: library/pyexpat xml parsers expat xmlparser StartNamespaceDeclHandler8585144
Ref: 2ccf8585144
Ref: library/pyexpat xml parsers expat xmlparser EndNamespaceDeclHandler8585422
Ref: 2cd08585422
Ref: library/pyexpat xml parsers expat xmlparser CommentHandler8585945
Ref: 2cd18585945
Ref: library/pyexpat xml parsers expat xmlparser StartCdataSectionHandler8586131
Ref: 2ccc8586131
Ref: library/pyexpat xml parsers expat xmlparser EndCdataSectionHandler8586368
Ref: 2ccd8586368
Ref: library/pyexpat xml parsers expat xmlparser DefaultHandler8586461
Ref: 2cd28586461
Ref: library/pyexpat xml parsers expat xmlparser DefaultHandlerExpand8586746
Ref: 2cd38586746
Ref: library/pyexpat xml parsers expat xmlparser NotStandaloneHandler8586986
Ref: 2cd48586986
Ref: library/pyexpat xml parsers expat xmlparser ExternalEntityRefHandler8587508
Ref: 2caf8587508
Node: ExpatError Exceptions8588564
Ref: library/pyexpat expaterror-exceptions8588721
Ref: 2cd58588721
Ref: library/pyexpat expaterror-objects8588721
Ref: 2ca58588721
Ref: library/pyexpat xml parsers expat ExpatError code8588862
Ref: 2cd68588862
Ref: library/pyexpat xml parsers expat ExpatError lineno8589511
Ref: 2cd98589511
Ref: library/pyexpat xml parsers expat ExpatError offset8589638
Ref: 2cda8589638
Node: Example<12>8589779
Ref: library/pyexpat example8589942
Ref: 2cdb8589942
Ref: library/pyexpat expat-example8589942
Ref: 2cdc8589942
Node: Content Model Descriptions8591040
Ref: library/pyexpat content-model-descriptions8591203
Ref: 2cdd8591203
Ref: library/pyexpat expat-content-models8591203
Ref: 2cde8591203
Ref: library/pyexpat module-xml parsers expat model8591203
Ref: 1438591203
Node: Expat error constants8593046
Ref: library/pyexpat expat-error-constants8593189
Ref: 2cdf8593189
Ref: library/pyexpat expat-errors8593189
Ref: 2ce08593189
Ref: library/pyexpat module-xml parsers expat errors8593189
Ref: 1428593189
Ref: library/pyexpat xml parsers expat errors codes8593781
Ref: 2cd88593781
Ref: library/pyexpat xml parsers expat errors messages8593918
Ref: 2cd78593918
Ref: library/pyexpat xml parsers expat errors XML_ERROR_ASYNC_ENTITY8594071
Ref: 2ce18594071
Ref: library/pyexpat xml parsers expat errors XML_ERROR_ATTRIBUTE_EXTERNAL_ENTITY_REF8594130
Ref: 2ce28594130
Ref: library/pyexpat xml parsers expat errors XML_ERROR_BAD_CHAR_REF8594331
Ref: 2ce38594331
Ref: library/pyexpat xml parsers expat errors XML_ERROR_BINARY_ENTITY_REF8594526
Ref: 2ce48594526
Ref: library/pyexpat xml parsers expat errors XML_ERROR_DUPLICATE_ATTRIBUTE8594700
Ref: 2ce58594700
Ref: library/pyexpat xml parsers expat errors XML_ERROR_INCORRECT_ENCODING8594825
Ref: 2ce68594825
Ref: library/pyexpat xml parsers expat errors XML_ERROR_INVALID_TOKEN8594890
Ref: 2ce78594890
Ref: library/pyexpat xml parsers expat errors XML_ERROR_JUNK_AFTER_DOC_ELEMENT8595104
Ref: 2ce88595104
Ref: library/pyexpat xml parsers expat errors XML_ERROR_MISPLACED_XML_PI8595253
Ref: 2ce98595253
Ref: library/pyexpat xml parsers expat errors XML_ERROR_NO_ELEMENTS8595406
Ref: 2cea8595406
Ref: library/pyexpat xml parsers expat errors XML_ERROR_NO_MEMORY8595581
Ref: 2ceb8595581
Ref: library/pyexpat xml parsers expat errors XML_ERROR_PARAM_ENTITY_REF8595693
Ref: 2cec8595693
Ref: library/pyexpat xml parsers expat errors XML_ERROR_PARTIAL_CHAR8595827
Ref: 2ced8595827
Ref: library/pyexpat xml parsers expat errors XML_ERROR_RECURSIVE_ENTITY_REF8595940
Ref: 2cee8595940
Ref: library/pyexpat xml parsers expat errors XML_ERROR_SYNTAX8596142
Ref: 2cef8596142
Ref: library/pyexpat xml parsers expat errors XML_ERROR_TAG_MISMATCH8596248
Ref: 2cf08596248
Ref: library/pyexpat xml parsers expat errors XML_ERROR_UNCLOSED_TOKEN8596368
Ref: 2cf18596368
Ref: library/pyexpat xml parsers expat errors XML_ERROR_UNDEFINED_ENTITY8596552
Ref: 2cf28596552
Ref: library/pyexpat xml parsers expat errors XML_ERROR_UNKNOWN_ENCODING8596678
Ref: 2cf38596678
Ref: library/pyexpat xml parsers expat errors XML_ERROR_UNCLOSED_CDATA_SECTION8596796
Ref: 2cf48596796
Ref: library/pyexpat xml parsers expat errors XML_ERROR_EXTERNAL_ENTITY_HANDLING8596910
Ref: 2cf58596910
Ref: library/pyexpat xml parsers expat errors XML_ERROR_NOT_STANDALONE8596981
Ref: 2cf68596981
Ref: library/pyexpat xml parsers expat errors XML_ERROR_UNEXPECTED_STATE8597244
Ref: 2cf78597244
Ref: library/pyexpat xml parsers expat errors XML_ERROR_ENTITY_DECLARED_IN_PE8597307
Ref: 2cf88597307
Ref: library/pyexpat xml parsers expat errors XML_ERROR_FEATURE_REQUIRES_XML_DTD8597375
Ref: 2cf98597375
Ref: library/pyexpat xml parsers expat errors XML_ERROR_CANT_CHANGE_FEATURE_ONCE_PARSING8597681
Ref: 2cfa8597681
Ref: library/pyexpat xml parsers expat errors XML_ERROR_UNBOUND_PREFIX8597954
Ref: 2cfb8597954
Ref: library/pyexpat xml parsers expat errors XML_ERROR_UNDECLARING_PREFIX8598096
Ref: 2cfc8598096
Ref: library/pyexpat xml parsers expat errors XML_ERROR_INCOMPLETE_PE8598257
Ref: 2cfd8598257
Ref: library/pyexpat xml parsers expat errors XML_ERROR_XML_DECL8598371
Ref: 2cfe8598371
Ref: library/pyexpat xml parsers expat errors XML_ERROR_TEXT_DECL8598483
Ref: 2cff8598483
Ref: library/pyexpat xml parsers expat errors XML_ERROR_PUBLICID8598619
Ref: 2d008598619
Ref: library/pyexpat xml parsers expat errors XML_ERROR_SUSPENDED8598741
Ref: 2d018598741
Ref: library/pyexpat xml parsers expat errors XML_ERROR_NOT_SUSPENDED8598965
Ref: 2d028598965
Ref: library/pyexpat xml parsers expat errors XML_ERROR_ABORTED8599117
Ref: 2d038599117
Ref: library/pyexpat xml parsers expat errors XML_ERROR_FINISHED8599229
Ref: 2d048599229
Ref: library/pyexpat xml parsers expat errors XML_ERROR_SUSPEND_PE8599475
Ref: 2d058599475
Node: Internet Protocols and Support8599532
Ref: library/internet doc8599697
Ref: 2d068599697
Ref: library/internet internet8599697
Ref: 2d078599697
Ref: library/internet internet-protocols-and-support8599697
Ref: 2d088599697
Node: webbrowser — Convenient Web-browser controller8601828
Ref: library/webbrowser doc8601992
Ref: 2d098601992
Ref: library/webbrowser module-webbrowser8601992
Ref: 1328601992
Ref: library/webbrowser webbrowser-convenient-web-browser-controller8601992
Ref: 2d0a8601992
Ref: library/webbrowser webbrowser Error8603942
Ref: 2d0c8603942
Ref: library/webbrowser webbrowser open8604073
Ref: 2d0b8604073
Ref: library/webbrowser webbrowser open_new8604880
Ref: 2d0d8604880
Ref: library/webbrowser webbrowser open_new_tab8605046
Ref: 2d0e8605046
Ref: library/webbrowser webbrowser get8605224
Ref: 2d0f8605224
Ref: library/webbrowser webbrowser register8605452
Ref: 2d108605452
Ref: webbrowser — Convenient Web-browser controller-Footnote-18611988
Ref: webbrowser — Convenient Web-browser controller-Footnote-28612057
Node: Browser Controller Objects8612194
Ref: library/webbrowser browser-controller-objects8612305
Ref: 2d118612305
Ref: library/webbrowser browser-controllers8612305
Ref: 2d128612305
Ref: library/webbrowser webbrowser controller open8612485
Ref: 2d138612485
Ref: library/webbrowser webbrowser controller open_new8612749
Ref: 2d148612749
Ref: library/webbrowser webbrowser controller open_new_tab8612968
Ref: 2d158612968
Node: cgi — Common Gateway Interface support8613168
Ref: library/cgi doc8613384
Ref: 2d168613384
Ref: library/cgi cgi-common-gateway-interface-support8613384
Ref: 2d178613384
Ref: library/cgi module-cgi8613384
Ref: 158613384
Ref: cgi — Common Gateway Interface support-Footnote-18614051
Node: Introduction<10>8614113
Ref: library/cgi introduction8614235
Ref: 2d188614235
Ref: library/cgi cgi-intro8614280
Ref: 2d198614280
Node: Using the cgi module8615949
Ref: library/cgi id18616102
Ref: 2d1a8616102
Ref: library/cgi using-the-cgi-module8616102
Ref: 2d1b8616102
Node: Higher Level Interface8622009
Ref: library/cgi higher-level-interface8622158
Ref: 2d1d8622158
Ref: library/cgi cgi FieldStorage getfirst8624472
Ref: 2d1e8624472
Ref: library/cgi cgi FieldStorage getlist8625046
Ref: 2d1c8625046
Ref: Higher Level Interface-Footnote-18625620
Node: Functions<9>8625878
Ref: library/cgi functions8626028
Ref: 2d1f8626028
Ref: library/cgi functions-in-cgi-module8626028
Ref: 2d208626028
Ref: library/cgi cgi parse8626210
Ref: 2818626210
Ref: library/cgi cgi parse_multipart8626577
Ref: 2828626577
Ref: library/cgi cgi parse_header8627555
Ref: 2d218627555
Ref: library/cgi cgi test8627706
Ref: 2d228627706
Ref: library/cgi cgi print_environ8627893
Ref: 2d238627893
Ref: library/cgi cgi print_form8627973
Ref: 2d248627973
Ref: library/cgi cgi print_directory8628039
Ref: 2d258628039
Ref: library/cgi cgi print_environ_usage8628121
Ref: 2d268628121
Node: Caring about security8628237
Ref: library/cgi caring-about-security8628408
Ref: 2d278628408
Ref: library/cgi cgi-security8628408
Ref: 2d288628408
Node: Installing your CGI script on a Unix system8629183
Ref: library/cgi installing-your-cgi-script-on-a-unix-system8629365
Ref: 2d298629365
Node: Testing your CGI script8631395
Ref: library/cgi testing-your-cgi-script8631577
Ref: 2d2a8631577
Node: Debugging CGI scripts8632191
Ref: library/cgi debugging-cgi-scripts8632359
Ref: 2d2b8632359
Node: Common problems and solutions8635511
Ref: library/cgi common-problems-and-solutions8635647
Ref: 2d2c8635647
Node: cgitb — Traceback manager for CGI scripts8636989
Ref: library/cgitb doc8637212
Ref: 2d2d8637212
Ref: library/cgitb cgitb-traceback-manager-for-cgi-scripts8637212
Ref: 2d2e8637212
Ref: library/cgitb module-cgitb8637212
Ref: 168637212
Ref: library/cgitb cgitb enable8638402
Ref: 2d2f8638402
Ref: library/cgitb cgitb text8639336
Ref: 2d308639336
Ref: library/cgitb cgitb html8639764
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Ref: library/cgitb cgitb handler8640192
Ref: 2d328640192
Ref: cgitb — Traceback manager for CGI scripts-Footnote-18640825
Node: wsgiref — WSGI Utilities and Reference Implementation8640889
Ref: library/wsgiref doc8641103
Ref: 2d338641103
Ref: library/wsgiref module-wsgiref8641103
Ref: 1358641103
Ref: library/wsgiref wsgiref-wsgi-utilities-and-reference-implementation8641103
Ref: 2d348641103
Ref: wsgiref — WSGI Utilities and Reference Implementation-Footnote-18642948
Ref: wsgiref — WSGI Utilities and Reference Implementation-Footnote-28642997
Node: wsgiref util – WSGI environment utilities8643034
Ref: library/wsgiref module-wsgiref util8643224
Ref: 1398643224
Ref: library/wsgiref wsgiref-util-wsgi-environment-utilities8643224
Ref: 2d358643224
Ref: library/wsgiref wsgiref util guess_scheme8643681
Ref: 2d368643681
Ref: library/wsgiref wsgiref util request_uri8644333
Ref: 2d378644333
Ref: library/wsgiref wsgiref util application_uri8644659
Ref: 2d388644659
Ref: library/wsgiref wsgiref util shift_path_info8644925
Ref: 2d398644925
Ref: library/wsgiref wsgiref util setup_testing_defaults8646593
Ref: 2d3a8646593
Ref: library/wsgiref wsgiref util is_hop_by_hop8648277
Ref: 2d3b8648277
Ref: library/wsgiref wsgiref util FileWrapper8648450
Ref: 3a48648450
Ref: wsgiref util – WSGI environment utilities-Footnote-18649723
Ref: wsgiref util – WSGI environment utilities-Footnote-28649772
Ref: wsgiref util – WSGI environment utilities-Footnote-38649821
Ref: wsgiref util – WSGI environment utilities-Footnote-48649870
Ref: wsgiref util – WSGI environment utilities-Footnote-58649919
Node: wsgiref headers – WSGI response header tools8649968
Ref: library/wsgiref module-wsgiref headers8650218
Ref: 1378650218
Ref: library/wsgiref wsgiref-headers-wsgi-response-header-tools8650218
Ref: 2d3c8650218
Ref: library/wsgiref wsgiref headers Headers8650480
Ref: 87e8650480
Ref: library/wsgiref wsgiref headers Headers get_all8652745
Ref: 2d3d8652745
Ref: library/wsgiref wsgiref headers Headers add_header8653182
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Ref: wsgiref headers – WSGI response header tools-Footnote-18654319
Node: wsgiref simple_server – a simple WSGI HTTP server8654368
Ref: library/wsgiref module-wsgiref simple_server8654620
Ref: 1388654620
Ref: library/wsgiref wsgiref-simple-server-a-simple-wsgi-http-server8654620
Ref: 2d3f8654620
Ref: library/wsgiref wsgiref simple_server make_server8655214
Ref: 2d408655214
Ref: library/wsgiref wsgiref simple_server demo_app8656054
Ref: 2d418656054
Ref: library/wsgiref wsgiref simple_server WSGIServer8656494
Ref: 2d428656494
Ref: library/wsgiref wsgiref simple_server WSGIServer set_app8657247
Ref: 2d448657247
Ref: library/wsgiref wsgiref simple_server WSGIServer get_app8657392
Ref: 2d458657392
Ref: library/wsgiref wsgiref simple_server WSGIRequestHandler8657735
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Ref: library/wsgiref wsgiref simple_server WSGIRequestHandler get_environ8658351
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Ref: library/wsgiref wsgiref simple_server WSGIRequestHandler get_stderr8658857
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Ref: library/wsgiref wsgiref simple_server WSGIRequestHandler handle8659040
Ref: 2d498659040
Ref: wsgiref simple_server – a simple WSGI HTTP server-Footnote-18659311
Ref: wsgiref simple_server – a simple WSGI HTTP server-Footnote-28659360
Node: wsgiref validate — WSGI conformance checker8659409
Ref: library/wsgiref module-wsgiref validate8659663
Ref: 13a8659663
Ref: library/wsgiref wsgiref-validate-wsgi-conformance-checker8659663
Ref: 2d4a8659663
Ref: library/wsgiref wsgiref validate validator8660570
Ref: 2d4b8660570
Ref: wsgiref validate — WSGI conformance checker-Footnote-18662783
Ref: wsgiref validate — WSGI conformance checker-Footnote-28662832
Ref: wsgiref validate — WSGI conformance checker-Footnote-38662881
Node: wsgiref handlers – server/gateway base classes8662930
Ref: library/wsgiref module-wsgiref handlers8663145
Ref: 1368663145
Ref: library/wsgiref wsgiref-handlers-server-gateway-base-classes8663145
Ref: 2d4c8663145
Ref: library/wsgiref wsgiref handlers CGIHandler8663536
Ref: 2d4d8663536
Ref: library/wsgiref wsgiref handlers IISCGIHandler8664185
Ref: 2d4f8664185
Ref: library/wsgiref wsgiref handlers BaseCGIHandler8665560
Ref: 2d4e8665560
Ref: library/wsgiref wsgiref handlers SimpleHandler8666427
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Ref: library/wsgiref wsgiref handlers BaseHandler8667344
Ref: 11078667344
Ref: library/wsgiref wsgiref handlers BaseHandler run8667703
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Ref: library/wsgiref wsgiref handlers BaseHandler _write8668042
Ref: 2d528668042
Ref: library/wsgiref wsgiref handlers BaseHandler _flush8668388
Ref: 2d538668388
Ref: library/wsgiref wsgiref handlers BaseHandler get_stdin8668597
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Ref: library/wsgiref wsgiref handlers BaseHandler get_stderr8668762
Ref: 2d558668762
Ref: library/wsgiref wsgiref handlers BaseHandler add_cgi_vars8668930
Ref: 2d568668930
Ref: library/wsgiref wsgiref handlers BaseHandler wsgi_multithread8669482
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Ref: library/wsgiref wsgiref handlers BaseHandler wsgi_multiprocess8669773
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Ref: library/wsgiref wsgiref handlers BaseHandler wsgi_run_once8670066
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Ref: library/wsgiref wsgiref handlers BaseHandler os_environ8670309
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Ref: library/wsgiref wsgiref handlers BaseHandler server_software8670815
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Ref: library/wsgiref wsgiref handlers BaseHandler get_scheme8671411
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Ref: library/wsgiref wsgiref handlers BaseHandler setup_environ8671772
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Ref: library/wsgiref wsgiref handlers BaseHandler log_exception8672432
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Ref: library/wsgiref wsgiref handlers BaseHandler traceback_limit8672932
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Ref: library/wsgiref wsgiref handlers BaseHandler error_output8673154
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Ref: library/wsgiref wsgiref handlers BaseHandler error_status8674226
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Ref: library/wsgiref wsgiref handlers BaseHandler error_headers8674431
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Ref: library/wsgiref wsgiref handlers BaseHandler error_body8674723
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Ref: library/wsgiref wsgiref handlers BaseHandler wsgi_file_wrapper8675069
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Ref: library/wsgiref wsgiref handlers BaseHandler sendfile8675277
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Ref: library/wsgiref wsgiref handlers BaseHandler origin_server8675853
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Ref: library/wsgiref wsgiref handlers BaseHandler http_version8676380
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Ref: library/wsgiref wsgiref handlers read_environ8676602
Ref: c088676602
Ref: wsgiref handlers – server/gateway base classes-Footnote-18677516
Ref: wsgiref handlers – server/gateway base classes-Footnote-28677565
Ref: wsgiref handlers – server/gateway base classes-Footnote-38677614
Ref: wsgiref handlers – server/gateway base classes-Footnote-48677663
Ref: wsgiref handlers – server/gateway base classes-Footnote-58677712
Node: Examples<21>8677761
Ref: library/wsgiref examples8677922
Ref: 2d688677922
Node: urllib — URL handling modules8680494
Ref: library/urllib doc8680719
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Ref: library/urllib module-urllib8680719
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Ref: library/urllib urllib-url-handling-modules8680719
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Ref: urllib — URL handling modules-Footnote-18681300
Node: urllib request — Extensible library for opening URLs8681363
Ref: library/urllib request doc8681584
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Ref: library/urllib request module-urllib request8681584
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Ref: library/urllib request urllib-request-extensible-library-for-opening-urls8681584
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Ref: library/urllib request urllib request urlopen8682195
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Ref: library/urllib request urllib request install_opener8686210
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Ref: library/urllib request urllib request build_opener8686663
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Ref: library/urllib request urllib request pathname2url8687781
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Ref: library/urllib request urllib request url2pathname8688080
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Ref: library/urllib request urllib request getproxies8688337
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Ref: library/urllib request urllib request Request8689480
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Ref: library/urllib request urllib request HTTPDefaultErrorHandler8694290
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Ref: library/urllib request urllib request HTTPRedirectHandler8694482
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Ref: library/urllib request urllib request HTTPCookieProcessor8694567
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Ref: library/urllib request urllib request HTTPPasswordMgr8695773
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Ref: library/urllib request urllib request HTTPPasswordMgrWithDefaultRealm8695890
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Ref: library/urllib request urllib request HTTPPasswordMgrWithPriorAuth8696131
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Ref: library/urllib request urllib request AbstractBasicAuthHandler8696517
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Ref: library/urllib request urllib request HTTPBasicAuthHandler8697859
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Ref: library/urllib request urllib request ProxyBasicAuthHandler8698323
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Ref: library/urllib request urllib request AbstractDigestAuthHandler8698663
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Ref: library/urllib request urllib request HTTPDigestAuthHandler8699073
Ref: 2d888699073
Ref: library/urllib request urllib request ProxyDigestAuthHandler8699935
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Ref: library/urllib request urllib request HTTPHandler8700276
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Ref: library/urllib request urllib request HTTPSHandler8700361
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Ref: library/urllib request urllib request FileHandler8700691
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Ref: library/urllib request urllib request CacheFTPHandler8700900
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Ref: library/urllib request urllib request UnknownHandler8701029
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Ref: library/urllib request urllib request HTTPErrorProcessor8701119
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Ref: urllib request — Extensible library for opening URLs-Footnote-18702000
Ref: urllib request — Extensible library for opening URLs-Footnote-28702073
Ref: urllib request — Extensible library for opening URLs-Footnote-38702124
Ref: urllib request — Extensible library for opening URLs-Footnote-48702173
Ref: urllib request — Extensible library for opening URLs-Footnote-58702222
Node: Request Objects8702271
Ref: library/urllib request id18702408
Ref: 2d8b8702408
Ref: library/urllib request request-objects8702408
Ref: 2d8c8702408
Ref: library/urllib request urllib request Request full_url8702679
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Ref: library/urllib request urllib request Request type8702974
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Ref: library/urllib request urllib request Request host8703025
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Ref: library/urllib request urllib request Request origin_req_host8703152
Ref: 2d8f8703152
Ref: library/urllib request urllib request Request selector8703247
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Ref: library/urllib request urllib request Request data8703411
Ref: 9df8703411
Ref: library/urllib request urllib request Request unverifiable8703674
Ref: 2d918703674
Ref: library/urllib request urllib request Request method8703804
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Ref: library/urllib request urllib request Request get_method8704510
Ref: b998704510
Ref: library/urllib request urllib request Request add_header8704932
Ref: 2d808704932
Ref: library/urllib request urllib request Request add_unredirected_header8705525
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Ref: library/urllib request urllib request Request has_header8705651
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Ref: library/urllib request urllib request Request remove_header8705792
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Ref: library/urllib request urllib request Request get_full_url8705965
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Ref: library/urllib request urllib request Request set_proxy8706122
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Ref: library/urllib request urllib request Request get_header8706375
Ref: 2d968706375
Ref: library/urllib request urllib request Request header_items8706541
Ref: 2d978706541
Ref: Request Objects-Footnote-18706900
Node: OpenerDirector Objects8706949
Ref: library/urllib request opener-director-objects8707114
Ref: 2d988707114
Ref: library/urllib request openerdirector-objects8707114
Ref: 2d998707114
Ref: library/urllib request urllib request OpenerDirector add_handler8707246
Ref: 2d9a8707246
Ref: library/urllib request urllib request OpenerDirector open8708804
Ref: 9e08708804
Ref: library/urllib request urllib request OpenerDirector error8709487
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Node: BaseHandler Objects8711263
Ref: library/urllib request base-handler-objects8711440
Ref: 2da08711440
Ref: library/urllib request basehandler-objects8711440
Ref: 2da18711440
Ref: library/urllib request urllib request BaseHandler add_parent8711680
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Ref: library/urllib request urllib request BaseHandler close8711759
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Ref: library/urllib request urllib request BaseHandler parent8712135
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Ref: library/urllib request urllib request BaseHandler default_open8712289
Ref: 2da58712289
Ref: library/urllib request protocol-open8712962
Ref: 2d9b8712962
Ref: library/urllib request urllib request BaseHandler unknown_open8713328
Ref: 2da68713328
Ref: library/urllib request urllib request BaseHandler http_error_default8713740
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Ref: library/urllib request http-error-nnn8714547
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Ref: library/urllib request protocol-request8715045
Ref: 2d9d8715045
Ref: library/urllib request protocol-response8715459
Ref: 2d9e8715459
Node: HTTPRedirectHandler Objects8716050
Ref: library/urllib request http-redirect-handler8716232
Ref: 2da88716232
Ref: library/urllib request httpredirecthandler-objects8716232
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Ref: library/urllib request urllib request HTTPRedirectHandler redirect_request8716729
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Ref: library/urllib request urllib request HTTPRedirectHandler http_error_3018717813
Ref: 2dab8717813
Ref: library/urllib request urllib request HTTPRedirectHandler http_error_3028718084
Ref: 2dac8718084
Ref: library/urllib request urllib request HTTPRedirectHandler http_error_3038718263
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Ref: library/urllib request urllib request HTTPRedirectHandler http_error_3078718446
Ref: 2dae8718446
Ref: HTTPRedirectHandler Objects-Footnote-18718674
Ref: HTTPRedirectHandler Objects-Footnote-28718723
Node: HTTPCookieProcessor Objects8718772
Ref: library/urllib request http-cookie-processor8718955
Ref: 2daf8718955
Ref: library/urllib request httpcookieprocessor-objects8718955
Ref: 2db08718955
Ref: library/urllib request urllib request HTTPCookieProcessor cookiejar8719094
Ref: 2db18719094
Node: ProxyHandler Objects8719222
Ref: library/urllib request proxy-handler8719401
Ref: 2db38719401
Ref: library/urllib request proxyhandler-objects8719401
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Node: HTTPPasswordMgr Objects8719879
Ref: library/urllib request http-password-mgr8720067
Ref: 2d848720067
Ref: library/urllib request httppasswordmgr-objects8720067
Ref: 2db58720067
Ref: library/urllib request urllib request HTTPPasswordMgr add_password8720253
Ref: 2db68720253
Ref: library/urllib request urllib request HTTPPasswordMgr find_user_password8720600
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Node: HTTPPasswordMgrWithPriorAuth Objects8720974
Ref: library/urllib request http-password-mgr-with-prior-auth8721174
Ref: 2d858721174
Ref: library/urllib request httppasswordmgrwithpriorauth-objects8721174
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Ref: library/urllib request urllib request HTTPPasswordMgrWithPriorAuth add_password8721428
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Ref: library/urllib request urllib request HTTPPasswordMgrWithPriorAuth find_user_password8721842
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Ref: library/urllib request urllib request HTTPPasswordMgrWithPriorAuth update_authenticated8722001
Ref: 2dbb8722001
Ref: library/urllib request urllib request HTTPPasswordMgrWithPriorAuth is_authenticated8722197
Ref: 2dbc8722197
Node: AbstractBasicAuthHandler Objects8722373
Ref: library/urllib request abstract-basic-auth-handler8722578
Ref: 2dbd8722578
Ref: library/urllib request abstractbasicauthhandler-objects8722578
Ref: 2dbe8722578
Ref: library/urllib request urllib request AbstractBasicAuthHandler http_error_auth_reqed8722663
Ref: 2dbf8722663
Node: HTTPBasicAuthHandler Objects8723483
Ref: library/urllib request http-basic-auth-handler8723681
Ref: 2dc08723681
Ref: library/urllib request httpbasicauthhandler-objects8723681
Ref: 2dc18723681
Ref: library/urllib request urllib request HTTPBasicAuthHandler http_error_4018723760
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Node: ProxyBasicAuthHandler Objects8723917
Ref: library/urllib request proxy-basic-auth-handler8724116
Ref: 2dc38724116
Ref: library/urllib request proxybasicauthhandler-objects8724116
Ref: 2dc48724116
Ref: library/urllib request urllib request ProxyBasicAuthHandler http_error_4078724197
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Node: AbstractDigestAuthHandler Objects8724355
Ref: library/urllib request abstract-digest-auth-handler8724555
Ref: 2dc68724555
Ref: library/urllib request abstractdigestauthhandler-objects8724555
Ref: 2dc78724555
Ref: library/urllib request urllib request AbstractDigestAuthHandler http_error_auth_reqed8724644
Ref: 2dc88724644
Node: HTTPDigestAuthHandler Objects8725021
Ref: library/urllib request http-digest-auth-handler8725222
Ref: 2dc98725222
Ref: library/urllib request httpdigestauthhandler-objects8725222
Ref: 2dca8725222
Ref: library/urllib request urllib request HTTPDigestAuthHandler http_error_4018725303
Ref: 2dcb8725303
Node: ProxyDigestAuthHandler Objects8725461
Ref: library/urllib request proxy-digest-auth-handler8725648
Ref: 2dcc8725648
Ref: library/urllib request proxydigestauthhandler-objects8725648
Ref: 2dcd8725648
Ref: library/urllib request urllib request ProxyDigestAuthHandler http_error_4078725731
Ref: 2dce8725731
Node: HTTPHandler Objects8725890
Ref: library/urllib request http-handler-objects8726068
Ref: 2dcf8726068
Ref: library/urllib request httphandler-objects8726068
Ref: 2dd08726068
Ref: library/urllib request urllib request HTTPHandler http_open8726129
Ref: 2dd18726129
Node: HTTPSHandler Objects8726271
Ref: library/urllib request https-handler-objects8726438
Ref: 2dd28726438
Ref: library/urllib request httpshandler-objects8726438
Ref: 2dd38726438
Ref: library/urllib request urllib request HTTPSHandler https_open8726501
Ref: 2dd48726501
Node: FileHandler Objects8726646
Ref: library/urllib request file-handler-objects8726813
Ref: 2dd58726813
Ref: library/urllib request filehandler-objects8726813
Ref: 2dd68726813
Ref: library/urllib request urllib request FileHandler file_open8726874
Ref: 2dd78726874
Node: DataHandler Objects8727176
Ref: library/urllib request data-handler-objects8727341
Ref: 2dd88727341
Ref: library/urllib request datahandler-objects8727341
Ref: 2dd98727341
Ref: library/urllib request urllib request DataHandler data_open8727402
Ref: 2dda8727402
Ref: DataHandler Objects-Footnote-18727961
Node: FTPHandler Objects8728010
Ref: library/urllib request ftp-handler-objects8728179
Ref: 2ddb8728179
Ref: library/urllib request ftphandler-objects8728179
Ref: 2ddc8728179
Ref: library/urllib request urllib request FTPHandler ftp_open8728238
Ref: 2ddd8728238
Node: CacheFTPHandler Objects8728386
Ref: library/urllib request cacheftp-handler-objects8728558
Ref: 2dde8728558
Ref: library/urllib request cacheftphandler-objects8728558
Ref: 2ddf8728558
Ref: library/urllib request urllib request CacheFTPHandler setTimeout8728740
Ref: 2de08728740
Ref: library/urllib request urllib request CacheFTPHandler setMaxConns8728833
Ref: 2de18728833
Node: UnknownHandler Objects8728933
Ref: library/urllib request unknown-handler-objects8729113
Ref: 2de28729113
Ref: library/urllib request unknownhandler-objects8729113
Ref: 2de38729113
Ref: library/urllib request urllib request UnknownHandler unknown_open8729180
Ref: 2de48729180
Node: HTTPErrorProcessor Objects8729271
Ref: library/urllib request http-error-processor-objects8729440
Ref: 2de58729440
Ref: library/urllib request httperrorprocessor-objects8729440
Ref: 2de68729440
Ref: library/urllib request urllib request HTTPErrorProcessor http_response8729515
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Ref: library/urllib request urllib request HTTPErrorProcessor https_response8729985
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Node: Examples<22>8730148
Ref: library/urllib request examples8730311
Ref: 2de98730311
Ref: library/urllib request urllib-request-examples8730311
Ref: 2dea8730311
Ref: library/urllib request urllib-examples8735879
Ref: 2dec8735879
Node: Legacy interface8737372
Ref: library/urllib request legacy-interface8737536
Ref: 2ded8737536
Ref: library/urllib request urllib request urlretrieve8737767
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Ref: library/urllib request urllib request urlcleanup8740429
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Ref: library/urllib request urllib request URLopener8740589
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Ref: library/urllib request urllib request URLopener open8742098
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Ref: library/urllib request urllib request URLopener open_unknown8742601
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Ref: library/urllib request urllib request URLopener retrieve8742713
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Ref: library/urllib request urllib request URLopener version8744261
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Ref: library/urllib request urllib request FancyURLopener8744582
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Ref: library/urllib request urllib request FancyURLopener prompt_user_passwd8746319
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Ref: Legacy interface-Footnote-18746859
Node: urllib request Restrictions8746908
Ref: library/urllib request urllib-request-restrictions8747051
Ref: 2df38747051
Node: urllib response — Response classes used by urllib8749619
Ref: library/urllib request module-urllib response8749852
Ref: 12a8749852
Ref: library/urllib request urllib-response-response-classes-used-by-urllib8749852
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Ref: library/urllib request urllib response addinfourl8750316
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Ref: library/urllib request urllib response addinfourl headers8750487
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Ref: library/urllib request urllib response addinfourl status8750626
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Ref: library/urllib request urllib response addinfourl geturl8750728
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Ref: library/urllib request urllib response addinfourl info8750847
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Ref: library/urllib request urllib response addinfourl code8750968
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Ref: library/urllib request urllib response addinfourl getstatus8751088
Ref: 2dfb8751088
Node: urllib parse — Parse URLs into components8751213
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Ref: library/urllib parse module-urllib parse8751451
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Ref: library/urllib parse urllib-parse-parse-urls-into-components8751451
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Ref: urllib parse — Parse URLs into components-Footnote-18752726
Node: URL Parsing8752797
Ref: library/urllib parse url-parsing8752924
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Ref: library/urllib parse urllib parse urlparse8753097
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Ref: library/urllib parse urllib parse parse_qs8760850
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Ref: library/urllib parse urllib parse parse_qsl8763033
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Ref: library/urllib parse urllib parse urlunparse8765066
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Ref: library/urllib parse urllib parse urlsplit8765468
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Ref: library/urllib parse urllib parse urljoin8770192
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Ref: library/urllib parse urllib parse urldefrag8771531
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Ref: library/urllib parse urllib parse unwrap8772876
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Ref: URL Parsing-Footnote-18773224
Ref: URL Parsing-Footnote-28773273
Ref: URL Parsing-Footnote-38773322
Ref: URL Parsing-Footnote-48773371
Ref: URL Parsing-Footnote-58773433
Node: Parsing ASCII Encoded Bytes8773482
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Ref: library/urllib parse parsing-ascii-encoded-bytes8773642
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Node: Structured Parse Results8775768
Ref: library/urllib parse structured-parse-results8775928
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Ref: library/urllib parse urlparse-result-object8775928
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Ref: library/urllib parse urllib parse urllib parse SplitResult geturl8776344
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Ref: library/urllib parse urllib parse DefragResult8777467
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Ref: library/urllib parse urllib parse ParseResult8777725
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Ref: library/urllib parse urllib parse SplitResult8777996
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Ref: library/urllib parse urllib parse DefragResultBytes8778401
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Ref: library/urllib parse urllib parse ParseResultBytes8778661
Ref: 2e098778661
Ref: library/urllib parse urllib parse SplitResultBytes8778960
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Node: URL Quoting8779251
Ref: library/urllib parse url-quoting8779375
Ref: 2e0c8779375
Ref: library/urllib parse urllib parse quote8779778
Ref: 5128779778
Ref: library/urllib parse urllib parse quote_plus8781153
Ref: cad8781153
Ref: library/urllib parse urllib parse quote_from_bytes8781646
Ref: 2e0d8781646
Ref: library/urllib parse urllib parse unquote8781939
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Ref: library/urllib parse urllib parse unquote_plus8782720
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Ref: library/urllib parse urllib parse unquote_to_bytes8783060
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Ref: library/urllib parse urllib parse urlencode8783493
Ref: 87a8783493
Ref: URL Quoting-Footnote-18787341
Ref: URL Quoting-Footnote-28787390
Ref: URL Quoting-Footnote-38787439
Ref: URL Quoting-Footnote-48787476
Ref: URL Quoting-Footnote-58787525
Ref: URL Quoting-Footnote-68787574
Ref: URL Quoting-Footnote-78787623
Ref: URL Quoting-Footnote-88787672
Ref: URL Quoting-Footnote-98787721
Node: urllib error — Exception classes raised by urllib request8787770
Ref: library/urllib error doc8788001
Ref: 2e108788001
Ref: library/urllib error module-urllib error8788001
Ref: 1278788001
Ref: library/urllib error urllib-error-exception-classes-raised-by-urllib-request8788001
Ref: 2e118788001
Ref: library/urllib error whatwg8788001
Ref: 2e128788001
Ref: library/urllib error urllib error URLError8788500
Ref: 2d718788500
Ref: library/urllib error urllib error URLError reason8788678
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Ref: library/urllib error urllib error HTTPError8788949
Ref: 9e28788949
Ref: library/urllib error urllib error HTTPError code8789306
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Ref: library/urllib error urllib error HTTPError reason8789566
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Ref: library/urllib error urllib error HTTPError headers8789668
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Ref: library/urllib error urllib error ContentTooShortError8789834
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Ref: urllib error — Exception classes raised by urllib request-Footnote-18790234
Ref: urllib error — Exception classes raised by urllib request-Footnote-28790305
Node: urllib robotparser — Parser for robots txt8790354
Ref: library/urllib robotparser doc8790563
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Ref: library/urllib robotparser module-urllib robotparser8790563
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Ref: library/urllib robotparser urllib-robotparser-parser-for-robots-txt8790563
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Ref: library/urllib robotparser urllib robotparser RobotFileParser8791106
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Ref: library/urllib robotparser urllib robotparser RobotFileParser set_url8791279
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Ref: library/urllib robotparser urllib robotparser RobotFileParser read8791373
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Ref: library/urllib robotparser urllib robotparser RobotFileParser parse8791469
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Ref: library/urllib robotparser urllib robotparser RobotFileParser can_fetch8791539
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Ref: library/urllib robotparser urllib robotparser RobotFileParser mtime8791753
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Ref: library/urllib robotparser urllib robotparser RobotFileParser modified8791981
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Ref: library/urllib robotparser urllib robotparser RobotFileParser crawl_delay8792110
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Ref: library/urllib robotparser urllib robotparser RobotFileParser request_rate8792512
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Ref: library/urllib robotparser urllib robotparser RobotFileParser site_maps8792963
Ref: 116c8792963
Ref: urllib robotparser — Parser for robots txt-Footnote-18793883
Node: http — HTTP modules8793961
Ref: library/http doc8794147
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Ref: library/http http-http-modules8794147
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Ref: library/http module-http8794147
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Ref: library/http http HTTPStatus8794970
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Ref: http — HTTP modules-Footnote-18795710
Node: HTTP status codes8795782
Ref: library/http http-status-codes8795857
Ref: 2e238795857
Ref: library/http id18795857
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Ref: HTTP status codes-Footnote-18809654
Ref: HTTP status codes-Footnote-28809738
Ref: HTTP status codes-Footnote-38809787
Ref: HTTP status codes-Footnote-48809836
Ref: HTTP status codes-Footnote-58809885
Ref: HTTP status codes-Footnote-68809934
Ref: HTTP status codes-Footnote-78809983
Ref: HTTP status codes-Footnote-88810032
Ref: HTTP status codes-Footnote-98810081
Ref: HTTP status codes-Footnote-108810130
Ref: HTTP status codes-Footnote-118810180
Ref: HTTP status codes-Footnote-128810230
Ref: HTTP status codes-Footnote-138810280
Ref: HTTP status codes-Footnote-148810330
Ref: HTTP status codes-Footnote-158810380
Ref: HTTP status codes-Footnote-168810430
Ref: HTTP status codes-Footnote-178810480
Ref: HTTP status codes-Footnote-188810530
Ref: HTTP status codes-Footnote-198810580
Ref: HTTP status codes-Footnote-208810630
Ref: HTTP status codes-Footnote-218810680
Ref: HTTP status codes-Footnote-228810730
Ref: HTTP status codes-Footnote-238810780
Ref: HTTP status codes-Footnote-248810830
Ref: HTTP status codes-Footnote-258810880
Ref: HTTP status codes-Footnote-268810930
Ref: HTTP status codes-Footnote-278810980
Ref: HTTP status codes-Footnote-288811030
Ref: HTTP status codes-Footnote-298811080
Ref: HTTP status codes-Footnote-308811130
Ref: HTTP status codes-Footnote-318811180
Ref: HTTP status codes-Footnote-328811230
Ref: HTTP status codes-Footnote-338811280
Ref: HTTP status codes-Footnote-348811330
Ref: HTTP status codes-Footnote-358811380
Ref: HTTP status codes-Footnote-368811430
Ref: HTTP status codes-Footnote-378811480
Ref: HTTP status codes-Footnote-388811530
Ref: HTTP status codes-Footnote-398811580
Ref: HTTP status codes-Footnote-408811630
Ref: HTTP status codes-Footnote-418811680
Ref: HTTP status codes-Footnote-428811730
Ref: HTTP status codes-Footnote-438811780
Ref: HTTP status codes-Footnote-448811830
Ref: HTTP status codes-Footnote-458811880
Ref: HTTP status codes-Footnote-468811930
Ref: HTTP status codes-Footnote-478811980
Ref: HTTP status codes-Footnote-488812030
Ref: HTTP status codes-Footnote-498812080
Ref: HTTP status codes-Footnote-508812130
Ref: HTTP status codes-Footnote-518812180
Ref: HTTP status codes-Footnote-528812230
Ref: HTTP status codes-Footnote-538812280
Ref: HTTP status codes-Footnote-548812330
Ref: HTTP status codes-Footnote-558812380
Ref: HTTP status codes-Footnote-568812430
Ref: HTTP status codes-Footnote-578812480
Ref: HTTP status codes-Footnote-588812530
Ref: HTTP status codes-Footnote-598812580
Ref: HTTP status codes-Footnote-608812630
Ref: HTTP status codes-Footnote-618812680
Ref: HTTP status codes-Footnote-628812730
Ref: HTTP status codes-Footnote-638812780
Node: http client — HTTP protocol client8812830
Ref: library/http client doc8813002
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Ref: library/http client http-client-http-protocol-client8813002
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Ref: library/http client module-http client8813002
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Ref: library/http client http client HTTPSConnection8815272
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Ref: library/http client http client UnknownProtocol8818815
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Ref: library/http client http client UnknownTransferEncoding8818906
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Ref: library/http client http client UnimplementedFileMode8819005
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Ref: library/http client http client IncompleteRead8819102
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Ref: library/http client http client ImproperConnectionState8819192
Ref: 2e308819192
Ref: library/http client http client CannotSendRequest8819291
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Ref: library/http client http client CannotSendHeader8819394
Ref: 2e328819394
Ref: library/http client http client ResponseNotReady8819496
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Ref: library/http client http client BadStatusLine8819598
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Ref: library/http client http client LineTooLong8819773
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Ref: library/http client http client RemoteDisconnected8819951
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Ref: library/http client http client HTTP_PORT8820430
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Ref: library/http client http client HTTPS_PORT8820527
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Ref: library/http client http client responses8820627
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Ref: http client — HTTP protocol client-Footnote-18821088
Ref: http client — HTTP protocol client-Footnote-28821158
Ref: http client — HTTP protocol client-Footnote-38821209
Node: HTTPConnection Objects8821258
Ref: library/http client httpconnection-objects8821382
Ref: 2e398821382
Ref: library/http client id18821382
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Ref: library/http client http client HTTPConnection request8821515
Ref: 6498821515
Ref: library/http client http client HTTPConnection getresponse8824297
Ref: 7d58824297
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Ref: library/http client http client HTTPConnection putrequest8826788
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Ref: library/http client http client HTTPConnection putheader8827337
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Ref: library/http client http client HTTPConnection endheaders8827672
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Ref: library/http client http client HTTPConnection send8829041
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Ref: HTTPConnection Objects-Footnote-18829299
Ref: HTTPConnection Objects-Footnote-28829347
Node: HTTPResponse Objects8829396
Ref: library/http client httpresponse-objects8829541
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Ref: library/http client id28829541
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Ref: library/http client http client HTTPResponse read8829955
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Ref: library/http client http client HTTPResponse readinto8830068
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Ref: library/http client http client HTTPResponse getheader8830255
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Ref: library/http client http client HTTPResponse url8831151
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Ref: library/http client http client HTTPResponse headers8831281
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Ref: library/http client http client HTTPResponse info8831963
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Ref: library/http client http client HTTPResponse getstatus8832082
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Node: Examples<23>8832205
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Node: HTTPMessage Objects8835263
Ref: library/http client httpmessage-objects8835376
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Ref: library/http client id38835376
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Node: ftplib — FTP protocol client8835591
Ref: library/ftplib doc8835773
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Ref: library/ftplib ftplib-ftp-protocol-client8835773
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Ref: library/ftplib module-ftplib8835773
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Ref: library/ftplib ftplib FTP8837426
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Ref: library/ftplib ftplib FTP_TLS8839323
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Ref: library/ftplib ftplib error_reply8841928
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Ref: library/ftplib ftplib error_temp8842045
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Ref: library/ftplib ftplib error_proto8842371
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Ref: library/ftplib ftplib all_errors8842602
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Ref: ftplib — FTP protocol client-Footnote-18843264
Ref: ftplib — FTP protocol client-Footnote-28843329
Ref: ftplib — FTP protocol client-Footnote-38843377
Ref: ftplib — FTP protocol client-Footnote-48843426
Ref: ftplib — FTP protocol client-Footnote-58843475
Ref: ftplib — FTP protocol client-Footnote-68843524
Node: FTP Objects8843573
Ref: library/ftplib ftp-objects8843675
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Ref: library/ftplib ftplib FTP set_debuglevel8844012
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Ref: library/ftplib ftplib FTP connect8844476
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Ref: library/ftplib ftplib FTP getwelcome8845487
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Ref: library/ftplib ftplib FTP login8845717
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Ref: library/ftplib ftplib FTP abort8846430
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Ref: library/ftplib ftplib FTP sendcmd8846568
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Ref: library/ftplib ftplib FTP voidcmd8846792
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Ref: library/ftplib ftplib FTP retrbinary8847165
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Ref: library/ftplib ftplib FTP retrlines8847845
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Ref: library/ftplib ftplib FTP set_pasv8848521
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Ref: library/ftplib ftplib FTP storbinary8848672
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Ref: library/ftplib ftplib FTP storlines8849372
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Ref: library/ftplib ftplib FTP transfercmd8849827
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Ref: library/ftplib ftplib FTP ntransfercmd8850985
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Ref: library/ftplib ftplib FTP mlsd8851335
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Ref: library/ftplib ftplib FTP dir8852438
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Ref: library/ftplib ftplib FTP rename8853073
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Ref: library/ftplib ftplib FTP delete8853172
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Ref: library/ftplib ftplib FTP cwd8853435
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Ref: library/ftplib ftplib FTP mkd8853514
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Ref: library/ftplib ftplib FTP pwd8853590
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Ref: library/ftplib ftplib FTP rmd8853680
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Ref: library/ftplib ftplib FTP size8853769
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Ref: library/ftplib ftplib FTP quit8854095
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Ref: library/ftplib ftplib FTP close8854505
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Ref: FTP Objects-Footnote-18854965
Node: FTP_TLS Objects8855014
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Ref: library/ftplib ftplib FTP_TLS ssl_version8855261
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Ref: library/ftplib ftplib FTP_TLS auth8855379
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Ref: library/ftplib ftplib FTP_TLS ccc8855737
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Ref: library/ftplib ftplib FTP_TLS prot_p8855977
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Ref: library/ftplib ftplib FTP_TLS prot_c8856045
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Node: poplib — POP3 protocol client8856117
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Ref: library/poplib module-poplib8856296
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Ref: library/poplib poplib-pop3-protocol-client8856296
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Ref: library/poplib poplib POP38857408
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Ref: library/poplib poplib POP3_SSL8858323
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Ref: library/poplib poplib error_proto8860268
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Ref: poplib — POP3 protocol client-Footnote-18860921
Ref: poplib — POP3 protocol client-Footnote-28860986
Ref: poplib — POP3 protocol client-Footnote-38861035
Ref: poplib — POP3 protocol client-Footnote-48861084
Ref: poplib — POP3 protocol client-Footnote-58861133
Node: POP3 Objects8861195
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Ref: library/poplib pop3-objects8861296
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Ref: library/poplib poplib POP3 set_debuglevel8861529
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Ref: library/poplib poplib POP3 getwelcome8861994
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Ref: library/poplib poplib POP3 capa8862085
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Ref: library/poplib poplib POP3 user8862274
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Ref: library/poplib poplib POP3 pass_8862392
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Ref: library/poplib poplib POP3 apop8862575
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Ref: library/poplib poplib POP3 rpop8862693
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Ref: library/poplib poplib POP3 stat8862812
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Ref: library/poplib poplib POP3 list8862944
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Ref: library/poplib poplib POP3 retr8863136
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Ref: library/poplib poplib POP3 dele8863299
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Ref: library/poplib poplib POP3 rset8863577
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Ref: library/poplib poplib POP3 quit8863728
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Ref: library/poplib poplib POP3 top8863818
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Ref: library/poplib poplib POP3 uidl8864355
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Ref: library/poplib poplib POP3 utf88864639
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Ref: library/poplib poplib POP3 stls8864846
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Ref: POP3 Objects-Footnote-18865645
Ref: POP3 Objects-Footnote-28865694
Ref: POP3 Objects-Footnote-38865743
Node: POP3 Example8865792
Ref: library/poplib id28865893
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Ref: library/poplib pop3-example8865893
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Node: imaplib — IMAP4 protocol client8866405
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Ref: library/imaplib imaplib-imap4-protocol-client8866586
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Ref: library/imaplib module-imaplib8866586
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Ref: library/imaplib imaplib IMAP48867250
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Ref: library/imaplib imaplib IMAP4 error8868454
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Ref: library/imaplib imaplib IMAP4 readonly8868859
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Ref: library/imaplib imaplib IMAP4_SSL8869216
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Ref: library/imaplib imaplib IMAP4_stream8871217
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Ref: library/imaplib imaplib Internaldate2tuple8871487
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Ref: library/imaplib imaplib Int2AP8871737
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Ref: library/imaplib imaplib ParseFlags8871885
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Ref: library/imaplib imaplib Time2Internaldate8872006
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Ref: imaplib — IMAP4 protocol client-Footnote-18873349
Ref: imaplib — IMAP4 protocol client-Footnote-28873415
Ref: imaplib — IMAP4 protocol client-Footnote-38873464
Node: IMAP4 Objects8873513
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Ref: library/imaplib imap4-objects8873618
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Ref: library/imaplib imaplib IMAP4 append8875122
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Ref: library/imaplib imaplib IMAP4 authenticate8875226
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Ref: library/imaplib imaplib IMAP4 check8876062
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Ref: library/imaplib imaplib IMAP4 close8876126
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Ref: library/imaplib imaplib IMAP4 copy8876311
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Ref: library/imaplib imaplib IMAP4 create8876423
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Ref: library/imaplib imaplib IMAP4 delete8876501
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Ref: library/imaplib imaplib IMAP4 deleteacl8876579
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Ref: library/imaplib imaplib IMAP4 enable8876689
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Ref: library/imaplib imaplib IMAP4 expunge8877006
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Ref: library/imaplib imaplib IMAP4 getacl8877534
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Ref: library/imaplib imaplib IMAP4 getannotation8877688
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Ref: library/imaplib imaplib IMAP4 getquota8877889
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Ref: library/imaplib imaplib IMAP4 getquotaroot8878063
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Ref: library/imaplib imaplib IMAP4 list8878251
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Ref: library/imaplib imaplib IMAP4 login8878520
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Ref: library/imaplib imaplib IMAP4 login_cram_md58878653
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Ref: library/imaplib imaplib IMAP4 logout8878913
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Ref: library/imaplib imaplib IMAP4 lsub8879110
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Ref: library/imaplib imaplib IMAP4 myrights8879400
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Ref: library/imaplib imaplib IMAP4 proxyauth8880779
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Ref: library/imaplib imaplib IMAP4 read8880931
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Ref: library/imaplib imaplib IMAP4 send8882550
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Ref: library/imaplib imaplib IMAP4 setquota8883115
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Ref: library/imaplib imaplib IMAP4 starttls8884506
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Ref: library/imaplib imaplib IMAP4 status8885033
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Ref: library/imaplib imaplib IMAP4 subscribe8886336
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Ref: library/imaplib imaplib IMAP4 thread8886407
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Ref: library/imaplib imaplib IMAP4 uid8887534
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Ref: library/imaplib imaplib IMAP4 unsubscribe8887852
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Ref: library/imaplib imaplib IMAP4 unselect8887929
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Ref: library/imaplib imaplib IMAP4 xatom8888326
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Ref: library/imaplib imaplib IMAP4 PROTOCOL_VERSION8888530
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Ref: IMAP4 Objects-Footnote-18889146
Ref: IMAP4 Objects-Footnote-28889195
Ref: IMAP4 Objects-Footnote-38889244
Ref: IMAP4 Objects-Footnote-48889293
Ref: IMAP4 Objects-Footnote-58889342
Ref: IMAP4 Objects-Footnote-68889391
Node: IMAP4 Example8889440
Ref: library/imaplib id28889545
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Ref: library/imaplib imap4-example8889545
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Node: nntplib — NNTP protocol client8890033
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Ref: library/nntplib module-nntplib8890215
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Ref: library/nntplib nntplib-nntp-protocol-client8890215
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Ref: library/nntplib nntplib NNTP8892067
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Ref: library/nntplib nntplib NNTP_SSL8894228
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Ref: nntplib — NNTP protocol client-Footnote-18896886
Ref: nntplib — NNTP protocol client-Footnote-28896952
Ref: nntplib — NNTP protocol client-Footnote-38897001
Ref: nntplib — NNTP protocol client-Footnote-48897049
Ref: nntplib — NNTP protocol client-Footnote-58897098
Node: NNTP Objects8897147
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Node: Attributes8897465
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Ref: Attributes-Footnote-18898089
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Ref: library/nntplib nntplib NNTP quit8899107
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Ref: library/nntplib nntplib NNTP getwelcome8899290
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Ref: library/nntplib nntplib NNTP getcapabilities8899521
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Ref: library/nntplib nntplib NNTP login8899982
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Ref: library/nntplib nntplib NNTP starttls8900600
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Ref: library/nntplib nntplib NNTP list8902438
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Ref: library/nntplib nntplib NNTP description8904372
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Ref: library/nntplib nntplib NNTP group8904739
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Ref: library/nntplib nntplib NNTP over8905173
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Ref: library/nntplib nntplib NNTP help8907335
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Ref: library/nntplib nntplib NNTP stat8907489
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Ref: library/nntplib nntplib NNTP next8908158
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Ref: library/nntplib nntplib NNTP last8908252
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Ref: library/nntplib nntplib NNTP article8908346
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Ref: library/nntplib nntplib NNTP head8909454
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Ref: library/nntplib nntplib NNTP body8909688
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Ref: library/nntplib nntplib NNTP post8909922
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Ref: library/nntplib nntplib NNTP ihave8910548
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Ref: library/nntplib nntplib NNTP date8910824
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Ref: library/nntplib nntplib NNTP slave8910992
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Ref: library/nntplib nntplib NNTP set_debuglevel8911088
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Ref: library/nntplib nntplib NNTP xhdr8911724
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Ref: library/nntplib nntplib NNTP xover8912662
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Ref: Methods<3>-Footnote-18913074
Ref: Methods<3>-Footnote-28913123
Ref: Methods<3>-Footnote-38913172
Ref: Methods<3>-Footnote-48913221
Node: Utility functions<2>8913270
Ref: library/nntplib utility-functions8913380
Ref: 2eee8913380
Ref: library/nntplib nntplib decode_header8913494
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Node: smtplib — SMTP protocol client8914085
Ref: library/smtplib doc8914255
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Ref: library/smtplib module-smtplib8914255
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Ref: library/smtplib smtplib-smtp-protocol-client8914255
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Ref: library/smtplib smtplib SMTP8914744
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Ref: library/smtplib smtplib SMTP_SSL8917320
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Ref: library/smtplib smtplib LMTP8919185
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Ref: library/smtplib smtplib SMTPException8920102
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Ref: library/smtplib smtplib SMTPServerDisconnected8920358
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Ref: library/smtplib smtplib SMTPResponseException8920586
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Ref: library/smtplib smtplib SMTPSenderRefused8920951
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Ref: library/smtplib smtplib SMTPRecipientsRefused8921192
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Ref: library/smtplib smtplib SMTPDataError8921465
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Ref: library/smtplib smtplib SMTPConnectError8921561
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Ref: library/smtplib smtplib SMTPHeloError8921682
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Ref: library/smtplib smtplib SMTPNotSupportedError8921769
Ref: 10cb8921769
Ref: library/smtplib smtplib SMTPAuthenticationError8921911
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Ref: smtplib — SMTP protocol client-Footnote-18922634
Ref: smtplib — SMTP protocol client-Footnote-28922700
Ref: smtplib — SMTP protocol client-Footnote-38922748
Ref: smtplib — SMTP protocol client-Footnote-48922797
Ref: smtplib — SMTP protocol client-Footnote-58922846
Ref: smtplib — SMTP protocol client-Footnote-68922894
Node: SMTP Objects8922943
Ref: library/smtplib id18923045
Ref: 2efa8923045
Ref: library/smtplib smtp-objects8923045
Ref: 2efb8923045
Ref: library/smtplib smtplib SMTP set_debuglevel8923149
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Ref: library/smtplib smtplib SMTP docmd8923500
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Ref: library/smtplib smtplib SMTP connect8924150
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Ref: library/smtplib smtplib SMTP helo8924835
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Ref: library/smtplib smtplib SMTP ehlo8925295
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Ref: library/smtplib smtplib SMTP ehlo_or_helo_if_needed8926188
Ref: 2f008926188
Ref: library/smtplib smtplib SMTP has_extn8926530
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Ref: library/smtplib smtplib SMTP verify8926725
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Ref: library/smtplib smtplib SMTP login8927144
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Ref: library/smtplib smtplib SMTP auth8928729
Ref: 8318928729
Ref: library/smtplib smtplib SMTP starttls8930972
Ref: b5c8930972
Ref: library/smtplib smtplib SMTP sendmail8932682
Ref: 8338932682
Ref: library/smtplib smtplib SMTP send_message8936163
Ref: 8348936163
Ref: library/smtplib smtplib SMTP quit8938231
Ref: 2ef28938231
Ref: SMTP Objects-Footnote-18938694
Ref: SMTP Objects-Footnote-28938742
Ref: SMTP Objects-Footnote-38938791
Ref: SMTP Objects-Footnote-48938840
Ref: SMTP Objects-Footnote-58938888
Ref: SMTP Objects-Footnote-68938936
Node: SMTP Example8938985
Ref: library/smtplib id28939087
Ref: 2f038939087
Ref: library/smtplib smtp-example8939087
Ref: 2f048939087
Ref: SMTP Example-Footnote-18940520
Node: smtpd — SMTP Server8940568
Ref: library/smtpd doc8940733
Ref: 2f058940733
Ref: library/smtpd module-smtpd8940733
Ref: ec8940733
Ref: library/smtpd smtpd-smtp-server8940733
Ref: 2f068940733
Ref: smtpd — SMTP Server-Footnote-18941736
Ref: smtpd — SMTP Server-Footnote-28941800
Ref: smtpd — SMTP Server-Footnote-38941840
Ref: smtpd — SMTP Server-Footnote-48941889
Ref: smtpd — SMTP Server-Footnote-58941938
Node: SMTPServer Objects8941987
Ref: library/smtpd smtpserver-objects8942095
Ref: 2f078942095
Ref: library/smtpd smtpd SMTPServer8942154
Ref: 6f98942154
Ref: library/smtpd smtpd SMTPServer process_message8944011
Ref: 6fa8944011
Ref: library/smtpd smtpd SMTPServer channel_class8945887
Ref: 2f088945887
Ref: SMTPServer Objects-Footnote-18946498
Ref: SMTPServer Objects-Footnote-28946547
Ref: SMTPServer Objects-Footnote-38946596
Ref: SMTPServer Objects-Footnote-48946645
Node: DebuggingServer Objects8946694
Ref: library/smtpd debuggingserver-objects8946828
Ref: 2f098946828
Ref: library/smtpd smtpd DebuggingServer8946897
Ref: 2f0a8946897
Node: PureProxy Objects8947099
Ref: library/smtpd pureproxy-objects8947235
Ref: 2f0b8947235
Ref: library/smtpd smtpd PureProxy8947292
Ref: 2f0c8947292
Node: MailmanProxy Objects8947583
Ref: library/smtpd mailmanproxy-objects8947715
Ref: 2f0d8947715
Ref: library/smtpd smtpd MailmanProxy8947778
Ref: 2118947778
Node: SMTPChannel Objects8948400
Ref: library/smtpd smtpchannel-objects8948506
Ref: 2f0e8948506
Ref: library/smtpd smtpd SMTPChannel8948567
Ref: 6f88948567
Ref: library/smtpd smtpd SMTPChannel smtp_server8950062
Ref: 2f0f8950062
Ref: library/smtpd smtpd SMTPChannel conn8950166
Ref: 2f108950166
Ref: library/smtpd smtpd SMTPChannel addr8950253
Ref: 2f118950253
Ref: library/smtpd smtpd SMTPChannel received_lines8950388
Ref: 2f128950388
Ref: library/smtpd smtpd SMTPChannel smtp_state8950609
Ref: 2f138950609
Ref: library/smtpd smtpd SMTPChannel seen_greeting8950819
Ref: 2f148950819
Ref: library/smtpd smtpd SMTPChannel mailfrom8950952
Ref: 2f158950952
Ref: library/smtpd smtpd SMTPChannel rcpttos8951098
Ref: 2f168951098
Ref: library/smtpd smtpd SMTPChannel received_data8951253
Ref: 2f178951253
Ref: library/smtpd smtpd SMTPChannel fqdn8951462
Ref: 2f188951462
Ref: library/smtpd smtpd SMTPChannel peer8951606
Ref: 2f198951606
Ref: SMTPChannel Objects-Footnote-18954062
Ref: SMTPChannel Objects-Footnote-28954111
Node: telnetlib — Telnet client8954160
Ref: library/telnetlib doc8954336
Ref: 2f1a8954336
Ref: library/telnetlib module-telnetlib8954336
Ref: 1028954336
Ref: library/telnetlib telnetlib-telnet-client8954336
Ref: 2f1b8954336
Ref: library/telnetlib telnetlib Telnet8955338
Ref: 68e8955338
Ref: telnetlib — Telnet client-Footnote-18956888
Ref: telnetlib — Telnet client-Footnote-28956956
Ref: telnetlib — Telnet client-Footnote-38957004
Node: Telnet Objects8957052
Ref: library/telnetlib id18957153
Ref: 2f1e8957153
Ref: library/telnetlib telnet-objects8957153
Ref: 2f1f8957153
Ref: library/telnetlib telnetlib Telnet read_until8957262
Ref: 2f208957262
Ref: library/telnetlib telnetlib Telnet read_all8957617
Ref: 2f218957617
Ref: library/telnetlib telnetlib Telnet read_some8957720
Ref: 2f228957720
Ref: library/telnetlib telnetlib Telnet read_very_eager8957898
Ref: 2f238957898
Ref: library/telnetlib telnetlib Telnet read_eager8958209
Ref: 2f248958209
Ref: library/telnetlib telnetlib Telnet read_lazy8958483
Ref: 2f258958483
Ref: library/telnetlib telnetlib Telnet read_very_lazy8958774
Ref: 2f268958774
Ref: library/telnetlib telnetlib Telnet read_sb_data8959047
Ref: 2f278959047
Ref: library/telnetlib telnetlib Telnet open8959280
Ref: 2f1c8959280
Ref: library/telnetlib telnetlib Telnet msg8959846
Ref: 2f288959846
Ref: library/telnetlib telnetlib Telnet set_debuglevel8960072
Ref: 2f298960072
Ref: library/telnetlib telnetlib Telnet close8960244
Ref: 2f1d8960244
Ref: library/telnetlib telnetlib Telnet get_socket8960301
Ref: 2f2a8960301
Ref: library/telnetlib telnetlib Telnet fileno8960383
Ref: 2f2b8960383
Ref: library/telnetlib telnetlib Telnet write8960484
Ref: 2f2c8960484
Ref: library/telnetlib telnetlib Telnet interact8960953
Ref: 2f2d8960953
Ref: library/telnetlib telnetlib Telnet mt_interact8961049
Ref: 2f2e8961049
Ref: library/telnetlib telnetlib Telnet expect8961139
Ref: 2f2f8961139
Ref: library/telnetlib telnetlib Telnet set_option_negotiation_callback8962145
Ref: 2f308962145
Node: Telnet Example8962460
Ref: library/telnetlib id28962561
Ref: 2f318962561
Ref: library/telnetlib telnet-example8962561
Ref: 2f328962561
Node: uuid — UUID objects according to RFC 41228963117
Ref: library/uuid doc8963320
Ref: 2f338963320
Ref: library/uuid module-uuid8963320
Ref: 12d8963320
Ref: library/uuid uuid-uuid-objects-according-to-rfc-41228963320
Ref: 2f348963320
Ref: library/uuid uuid SafeUUID8964446
Ref: 2f388964446
Ref: library/uuid uuid SafeUUID safe8964498
Ref: 2f398964498
Ref: library/uuid uuid SafeUUID unsafe8964615
Ref: 2f3a8964615
Ref: library/uuid uuid SafeUUID unknown8964712
Ref: 2f3b8964712
Ref: library/uuid uuid UUID8964853
Ref: 38a8964853
Ref: library/uuid uuid UUID bytes8966814
Ref: 2f3d8966814
Ref: library/uuid uuid UUID bytes_le8966943
Ref: 2f3e8966943
Ref: library/uuid uuid UUID fields8967095
Ref: 2f3f8967095
Ref: library/uuid uuid UUID hex8968655
Ref: 2f408968655
Ref: library/uuid uuid UUID int8968733
Ref: 2f3c8968733
Ref: library/uuid uuid UUID urn8968795
Ref: 2f418968795
Ref: library/uuid uuid UUID variant8968873
Ref: 2f428968873
Ref: library/uuid uuid UUID version8969137
Ref: 2f478969137
Ref: library/uuid uuid UUID is_safe8969275
Ref: 5168969275
Ref: library/uuid uuid getnode8969530
Ref: 5178969530
Ref: library/uuid uuid uuid18970500
Ref: 5188970500
Ref: library/uuid uuid uuid38970852
Ref: 2f358970852
Ref: library/uuid uuid uuid48971021
Ref: 2f368971021
Ref: library/uuid uuid uuid58971080
Ref: 2f378971080
Ref: library/uuid uuid NAMESPACE_DNS8971382
Ref: 2f488971382
Ref: library/uuid uuid NAMESPACE_URL8971509
Ref: 2f498971509
Ref: library/uuid uuid NAMESPACE_OID8971607
Ref: 2f4a8971607
Ref: library/uuid uuid NAMESPACE_X5008971710
Ref: 2f4b8971710
Ref: library/uuid uuid RESERVED_NCS8971968
Ref: 2f438971968
Ref: library/uuid uuid RFC_41228972035
Ref: 2f448972035
Ref: library/uuid uuid RESERVED_MICROSOFT8972114
Ref: 2f458972114
Ref: library/uuid uuid RESERVED_FUTURE8972193
Ref: 2f468972193
Ref: uuid — UUID objects according to RFC 4122-Footnote-18972571
Ref: uuid — UUID objects according to RFC 4122-Footnote-28972634
Ref: uuid — UUID objects according to RFC 4122-Footnote-38972683
Ref: uuid — UUID objects according to RFC 4122-Footnote-48972732
Ref: uuid — UUID objects according to RFC 4122-Footnote-58972781
Ref: uuid — UUID objects according to RFC 4122-Footnote-68972830
Ref: uuid — UUID objects according to RFC 4122-Footnote-78972879
Node: Example<13>8972928
Ref: library/uuid example8973019
Ref: 2f4c8973019
Ref: library/uuid uuid-example8973019
Ref: 2f4d8973019
Node: socketserver — A framework for network servers8974278
Ref: library/socketserver doc8974482
Ref: 2f4e8974482
Ref: library/socketserver module-socketserver8974482
Ref: f08974482
Ref: library/socketserver socketserver-a-framework-for-network-servers8974482
Ref: 2f4f8974482
Ref: library/socketserver socketserver TCPServer8974841
Ref: 2f508974841
Ref: library/socketserver socketserver UDPServer8975312
Ref: 2f538975312
Ref: library/socketserver socketserver UnixStreamServer8975615
Ref: 2f548975615
Ref: library/socketserver socketserver UnixDatagramServer8975728
Ref: 2f558975728
Ref: socketserver — A framework for network servers-Footnote-18978081
Node: Server Creation Notes8978152
Ref: library/socketserver server-creation-notes8978284
Ref: 2f5a8978284
Ref: library/socketserver socketserver ForkingMixIn8979118
Ref: 4dc8979118
Ref: library/socketserver socketserver ThreadingMixIn8979155
Ref: 4dd8979155
Ref: library/socketserver socketserver ForkingTCPServer8980645
Ref: 2f5c8980645
Ref: library/socketserver socketserver ForkingUDPServer8980686
Ref: 2f5d8980686
Ref: library/socketserver socketserver ThreadingTCPServer8980727
Ref: 2f5e8980727
Ref: library/socketserver socketserver ThreadingUDPServer8980770
Ref: 2f5b8980770
Node: Server Objects<2>8983061
Ref: library/socketserver server-objects8983225
Ref: 2f608983225
Ref: library/socketserver socketserver BaseServer8983276
Ref: b618983276
Ref: library/socketserver socketserver BaseServer fileno8983675
Ref: 2f638983675
Ref: library/socketserver socketserver BaseServer handle_request8983948
Ref: 2f588983948
Ref: library/socketserver socketserver BaseServer serve_forever8984550
Ref: b638984550
Ref: library/socketserver socketserver BaseServer service_actions8985201
Ref: b628985201
Ref: library/socketserver socketserver BaseServer shutdown8985501
Ref: 11558985501
Ref: library/socketserver socketserver BaseServer server_close8985781
Ref: 2f598985781
Ref: library/socketserver socketserver BaseServer address_family8985867
Ref: 2f698985867
Ref: library/socketserver socketserver BaseServer RequestHandlerClass8986078
Ref: 2f628986078
Ref: library/socketserver socketserver BaseServer server_address8986236
Ref: 2f618986236
Ref: library/socketserver socketserver BaseServer socket8986659
Ref: 2f6a8986659
Ref: library/socketserver socketserver BaseServer allow_reuse_address8986845
Ref: 2f6b8986845
Ref: library/socketserver socketserver BaseServer request_queue_size8987059
Ref: 2f6c8987059
Ref: library/socketserver socketserver BaseServer socket_type8987550
Ref: 2f6d8987550
Ref: library/socketserver socketserver BaseServer timeout8987741
Ref: 2f678987741
Ref: library/socketserver socketserver BaseServer finish_request8988247
Ref: 2f6e8988247
Ref: library/socketserver socketserver BaseServer get_request8988464
Ref: 2f648988464
Ref: library/socketserver socketserver BaseServer handle_error8988694
Ref: 6f48988694
Ref: library/socketserver socketserver BaseServer handle_timeout8989146
Ref: 2f688989146
Ref: library/socketserver socketserver BaseServer process_request8989585
Ref: 2f668989585
Ref: library/socketserver socketserver BaseServer server_activate8989956
Ref: 2f528989956
Ref: library/socketserver socketserver BaseServer server_bind8990203
Ref: 2f518990203
Ref: library/socketserver socketserver BaseServer verify_request8990357
Ref: 2f658990357
Node: Request Handler Objects8990942
Ref: library/socketserver request-handler-objects8991097
Ref: 2f6f8991097
Ref: library/socketserver socketserver BaseRequestHandler8991166
Ref: 2f568991166
Ref: library/socketserver socketserver BaseRequestHandler setup8991520
Ref: 2f708991520
Ref: library/socketserver socketserver BaseRequestHandler handle8991715
Ref: 2f578991715
Ref: library/socketserver socketserver BaseRequestHandler finish8992419
Ref: 2f718992419
Ref: library/socketserver socketserver StreamRequestHandler8992698
Ref: 67e8992698
Ref: library/socketserver socketserver DatagramRequestHandler8992743
Ref: 2f5f8992743
Node: Examples<24>8993507
Ref: library/socketserver examples8993636
Ref: 2f728993636
Node: socketserver TCPServer Example8993841
Ref: library/socketserver socketserver-tcpserver-example8993959
Ref: 2f738993959
Node: socketserver UDPServer Example8997115
Ref: library/socketserver socketserver-udpserver-example8997261
Ref: 2f748997261
Node: Asynchronous Mixins8998878
Ref: library/socketserver asynchronous-mixins8998985
Ref: 2f758998985
Node: http server — HTTP servers9001331
Ref: library/http server doc9001530
Ref: 2f769001530
Ref: library/http server http-server-http-servers9001530
Ref: 2f779001530
Ref: library/http server module-http server9001530
Ref: 969001530
Ref: library/http server http server HTTPServer9002340
Ref: 2d439002340
Ref: library/http server http server ThreadingHTTPServer9002695
Ref: 49d9002695
Ref: library/http server http server BaseHTTPRequestHandler9003243
Ref: aec9003243
Ref: library/http server http server BaseHTTPRequestHandler client_address9004233
Ref: 2f789004233
Ref: library/http server http server BaseHTTPRequestHandler server9004375
Ref: 2f799004375
Ref: library/http server http server BaseHTTPRequestHandler close_connection9004444
Ref: 2f7a9004444
Ref: library/http server http server BaseHTTPRequestHandler requestline9004679
Ref: 2f7c9004679
Ref: library/http server http server BaseHTTPRequestHandler command9004994
Ref: 2f7d9004994
Ref: library/http server http server BaseHTTPRequestHandler path9005098
Ref: 2f7e9005098
Ref: library/http server http server BaseHTTPRequestHandler request_version9005372
Ref: 2f7f9005372
Ref: library/http server http server BaseHTTPRequestHandler headers9005508
Ref: 2e289005508
Ref: library/http server http server BaseHTTPRequestHandler rfile9005935
Ref: 2f819005935
Ref: library/http server http server BaseHTTPRequestHandler wfile9006087
Ref: 2f829006087
Ref: library/http server http server BaseHTTPRequestHandler server_version9006535
Ref: 2f839006535
Ref: library/http server http server BaseHTTPRequestHandler sys_version9006822
Ref: 2f849006822
Ref: library/http server http server BaseHTTPRequestHandler error_message_format9007077
Ref: 2f869007077
Ref: library/http server http server BaseHTTPRequestHandler error_content_type9007438
Ref: 2f879007438
Ref: library/http server http server BaseHTTPRequestHandler protocol_version9007618
Ref: 2f889007618
Ref: library/http server http server BaseHTTPRequestHandler MessageClass9008081
Ref: 2f809008081
Ref: library/http server http server BaseHTTPRequestHandler responses9008313
Ref: 2e159008313
Ref: library/http server http server BaseHTTPRequestHandler handle9008878
Ref: 2f8b9008878
Ref: library/http server http server BaseHTTPRequestHandler handle_one_request9009178
Ref: 2f7b9009178
Ref: library/http server http server BaseHTTPRequestHandler handle_expect_1009009376
Ref: 2f8c9009376
Ref: library/http server http server BaseHTTPRequestHandler send_error9009883
Ref: 9479009883
Ref: library/http server http server BaseHTTPRequestHandler send_response9011011
Ref: 2f8d9011011
Ref: library/http server http server BaseHTTPRequestHandler send_header9011827
Ref: 2f899011827
Ref: library/http server http server BaseHTTPRequestHandler send_response_only9012407
Ref: 2f8a9012407
Ref: library/http server http server BaseHTTPRequestHandler end_headers9012827
Ref: aed9012827
Ref: library/http server http server BaseHTTPRequestHandler flush_headers9013126
Ref: aee9013126
Ref: library/http server http server BaseHTTPRequestHandler log_request9013298
Ref: 2f8f9013298
Ref: library/http server http server BaseHTTPRequestHandler log_error9013595
Ref: 2f909013595
Ref: library/http server http server BaseHTTPRequestHandler log_message9013840
Ref: 2f919013840
Ref: library/http server http server BaseHTTPRequestHandler version_string9014329
Ref: 2f859014329
Ref: library/http server http server BaseHTTPRequestHandler date_time_string9014543
Ref: 2f8e9014543
Ref: library/http server http server BaseHTTPRequestHandler log_date_time_string9014931
Ref: 2f929014931
Ref: library/http server http server BaseHTTPRequestHandler address_string9015042
Ref: 2f939015042
Ref: library/http server http server SimpleHTTPRequestHandler9015285
Ref: 49c9015285
Ref: library/http server http server SimpleHTTPRequestHandler server_version9016061
Ref: 2f969016061
Ref: library/http server http server SimpleHTTPRequestHandler extensions_map9016222
Ref: 2f979016222
Ref: library/http server http server SimpleHTTPRequestHandler do_HEAD9016724
Ref: 2f959016724
Ref: library/http server http server SimpleHTTPRequestHandler do_GET9017012
Ref: 2f949017012
Ref: library/http server http-server-cli9019439
Ref: 9489019439
Ref: library/http server http server CGIHTTPRequestHandler9020450
Ref: 2f989020450
Ref: library/http server http server CGIHTTPRequestHandler cgi_directories9021641
Ref: 2f999021641
Ref: library/http server http server CGIHTTPRequestHandler do_POST9021887
Ref: 2f9a9021887
Ref: http server — HTTP servers-Footnote-19022464
Ref: http server — HTTP servers-Footnote-29022534
Ref: http server — HTTP servers-Footnote-39022583
Node: http cookies — HTTP state management9022632
Ref: library/http cookies doc9022834
Ref: 2f9b9022834
Ref: library/http cookies http-cookies-http-state-management9022834
Ref: 2f9c9022834
Ref: library/http cookies module-http cookies9022834
Ref: 959022834
Ref: library/http cookies http cookies CookieError9024196
Ref: 2f9d9024196
Ref: library/http cookies http cookies BaseCookie9024363
Ref: 2f9e9024363
Ref: library/http cookies http cookies SimpleCookie9024752
Ref: 116e9024752
Ref: http cookies — HTTP state management-Footnote-19025582
Ref: http cookies — HTTP state management-Footnote-29025653
Ref: http cookies — HTTP state management-Footnote-39025702
Ref: http cookies — HTTP state management-Footnote-49025751
Ref: http cookies — HTTP state management-Footnote-59025800
Node: Cookie Objects9025849
Ref: library/http cookies cookie-objects9025961
Ref: 2fa09025961
Ref: library/http cookies id19025961
Ref: 2fa19025961
Ref: library/http cookies http cookies BaseCookie value_decode9026012
Ref: 2fa29026012
Ref: library/http cookies http cookies BaseCookie value_encode9026284
Ref: 2fa39026284
Ref: library/http cookies http cookies BaseCookie output9026736
Ref: 2fa49026736
Ref: library/http cookies http cookies BaseCookie js_output9027104
Ref: 2fa59027104
Ref: library/http cookies http cookies BaseCookie load9027383
Ref: 2f9f9027383
Node: Morsel Objects9027665
Ref: library/http cookies id29027797
Ref: 2fa69027797
Ref: library/http cookies morsel-objects9027797
Ref: 2fa79027797
Ref: library/http cookies http cookies Morsel9027848
Ref: 58b9027848
Ref: library/http cookies http cookies Morsel value9029200
Ref: 5899029200
Ref: library/http cookies http cookies Morsel coded_value9029260
Ref: 58a9029260
Ref: library/http cookies http cookies Morsel key9029366
Ref: 5889029366
Ref: library/http cookies http cookies Morsel set9029423
Ref: 58c9029423
Ref: library/http cookies http cookies Morsel isReservedKey9029532
Ref: 2fa89029532
Ref: library/http cookies http cookies Morsel output9029643
Ref: 2fa99029643
Ref: library/http cookies http cookies Morsel js_output9029983
Ref: 2faa9029983
Ref: library/http cookies http cookies Morsel OutputString9030257
Ref: 2fab9030257
Ref: library/http cookies http cookies Morsel update9030469
Ref: 8b19030469
Ref: library/http cookies http cookies Morsel copy9030769
Ref: 8b09030769
Ref: library/http cookies http cookies Morsel setdefault9030924
Ref: 2fac9030924
Ref: Morsel Objects-Footnote-19031139
Ref: Morsel Objects-Footnote-29031188
Ref: Morsel Objects-Footnote-39031237
Ref: Morsel Objects-Footnote-49031286
Node: Example<14>9031335
Ref: library/http cookies cookie-example9031444
Ref: 2fad9031444
Ref: library/http cookies example9031444
Ref: 2fae9031444
Node: http cookiejar — Cookie handling for HTTP clients9033096
Ref: library/http cookiejar doc9033313
Ref: 2faf9033313
Ref: library/http cookiejar http-cookiejar-cookie-handling-for-http-clients9033313
Ref: 2fb09033313
Ref: library/http cookiejar module-http cookiejar9033313
Ref: 949033313
Ref: library/http cookiejar http cookiejar LoadError9034881
Ref: 2fb19034881
Ref: library/http cookiejar http cookiejar CookieJar9035256
Ref: 2db29035256
Ref: library/http cookiejar http cookiejar FileCookieJar9035732
Ref: 2fb29035732
Ref: library/http cookiejar http cookiejar CookiePolicy9036476
Ref: 2fb39036476
Ref: library/http cookiejar http cookiejar DefaultCookiePolicy9036636
Ref: 11299036636
Ref: library/http cookiejar http cookiejar Cookie9038460
Ref: 2fb89038460
Ref: http cookiejar — Cookie handling for HTTP clients-Footnote-19040155
Ref: http cookiejar — Cookie handling for HTTP clients-Footnote-29040228
Ref: http cookiejar — Cookie handling for HTTP clients-Footnote-39040277
Ref: http cookiejar — Cookie handling for HTTP clients-Footnote-49040326
Ref: http cookiejar — Cookie handling for HTTP clients-Footnote-59040375
Ref: http cookiejar — Cookie handling for HTTP clients-Footnote-69040424
Ref: http cookiejar — Cookie handling for HTTP clients-Footnote-79040473
Ref: http cookiejar — Cookie handling for HTTP clients-Footnote-89040522
Ref: http cookiejar — Cookie handling for HTTP clients-Footnote-99040571
Ref: http cookiejar — Cookie handling for HTTP clients-Footnote-109040620
Ref: http cookiejar — Cookie handling for HTTP clients-Footnote-119040670
Ref: http cookiejar — Cookie handling for HTTP clients-Footnote-129040720
Node: CookieJar and FileCookieJar Objects9040770
Ref: library/http cookiejar cookie-jar-objects9040961
Ref: 2fb99040961
Ref: library/http cookiejar cookiejar-and-filecookiejar-objects9040961
Ref: 2fba9040961
Ref: library/http cookiejar http cookiejar CookieJar add_cookie_header9041238
Ref: 2fbb9041238
Ref: library/http cookiejar http cookiejar CookieJar extract_cookies9042156
Ref: 2fbc9042156
Ref: library/http cookiejar http cookiejar CookieJar set_policy9043391
Ref: 2fbe9043391
Ref: library/http cookiejar http cookiejar CookieJar make_cookies9043495
Ref: 2fbf9043495
Ref: library/http cookiejar http cookiejar CookieJar set_cookie_if_ok9043782
Ref: 2fc09043782
Ref: library/http cookiejar http cookiejar CookieJar set_cookie9043907
Ref: 2fc19043907
Ref: library/http cookiejar http cookiejar CookieJar clear9044056
Ref: 2fc29044056
Ref: library/http cookiejar http cookiejar CookieJar clear_session_cookies9044561
Ref: 2fc39044561
Ref: library/http cookiejar http cookiejar FileCookieJar save9045204
Ref: 2fc49045204
Ref: library/http cookiejar http cookiejar FileCookieJar load9046057
Ref: 2fb49046057
Ref: library/http cookiejar http cookiejar FileCookieJar revert9046624
Ref: 2fb59046624
Ref: library/http cookiejar http cookiejar FileCookieJar filename9047023
Ref: 2fc59047023
Ref: library/http cookiejar http cookiejar FileCookieJar delayload9047160
Ref: 2fc69047160
Node: FileCookieJar subclasses and co-operation with web browsers9047581
Ref: library/http cookiejar file-cookie-jar-classes9047801
Ref: 2fb69047801
Ref: library/http cookiejar filecookiejar-subclasses-and-co-operation-with-web-browsers9047801
Ref: 2fc79047801
Ref: library/http cookiejar http cookiejar MozillaCookieJar9048029
Ref: 2fc89048029
Ref: library/http cookiejar http cookiejar LWPCookieJar9048826
Ref: 2fc99048826
Ref: FileCookieJar subclasses and co-operation with web browsers-Footnote-19049304
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Ref: library/ipaddress ipaddress IPv6Interface with_prefixlen9148055
Ref: 30b69148055
Ref: library/ipaddress ipaddress IPv6Interface with_netmask9148091
Ref: 30b79148091
Ref: library/ipaddress ipaddress IPv6Interface with_hostmask9148125
Ref: 30b89148125
Node: Operators<5>9148299
Ref: library/ipaddress id29148365
Ref: 30b99148365
Node: Logical operators<2>9148627
Ref: library/ipaddress id39148696
Ref: 30ba9148696
Node: Other Module Level Functions9149353
Ref: library/ipaddress other-module-level-functions9149514
Ref: 30bb9149514
Ref: library/ipaddress ipaddress v4_int_to_packed9149659
Ref: 30bc9149659
Ref: library/ipaddress ipaddress v6_int_to_packed9150133
Ref: 30bd9150133
Ref: library/ipaddress ipaddress summarize_address_range9150442
Ref: 8889150442
Ref: library/ipaddress ipaddress collapse_addresses9151323
Ref: 8899151323
Ref: library/ipaddress ipaddress get_mixed_type_key9151891
Ref: 30be9151891
Node: Custom Exceptions9152490
Ref: library/ipaddress custom-exceptions9152625
Ref: 30bf9152625
Ref: library/ipaddress ipaddress AddressValueError9152796
Ref: 304d9152796
Ref: library/ipaddress ipaddress NetmaskValueError9152899
Ref: 30749152899
Node: Multimedia Services9153003
Ref: library/mm doc9153154
Ref: 30c09153154
Ref: library/mm mmedia9153154
Ref: 30c19153154
Ref: library/mm multimedia-services9153154
Ref: 30c29153154
Node: audioop — Manipulate raw audio data9153837
Ref: library/audioop doc9153982
Ref: 30c39153982
Ref: library/audioop audioop-manipulate-raw-audio-data9153982
Ref: 30c49153982
Ref: library/audioop module-audioop9153982
Ref: c9153982
Ref: library/audioop audioop error9154880
Ref: 30c59154880
Ref: library/audioop audioop add9155010
Ref: 30c69155010
Ref: library/audioop audioop adpcm2lin9155341
Ref: 30c79155341
Ref: library/audioop audioop alaw2lin9155660
Ref: 30c99155660
Ref: library/audioop audioop avg9155921
Ref: 30ca9155921
Ref: library/audioop audioop avgpp9156025
Ref: 30cb9156025
Ref: library/audioop audioop bias9156231
Ref: 30cc9156231
Ref: library/audioop audioop byteswap9156418
Ref: 90f9156418
Ref: library/audioop audioop cross9156648
Ref: 30cd9156648
Ref: library/audioop audioop findfactor9156781
Ref: 30ce9156781
Ref: library/audioop audioop findfit9157192
Ref: 30cf9157192
Ref: library/audioop audioop findmax9157802
Ref: 30d09157802
Ref: library/audioop audioop getsample9158159
Ref: 30d19158159
Ref: library/audioop audioop lin2adpcm9158277
Ref: 30c89158277
Ref: library/audioop audioop lin2alaw9159016
Ref: 30d29159016
Ref: library/audioop audioop lin2lin9159340
Ref: 30d39159340
Ref: library/audioop audioop lin2ulaw9159968
Ref: 30d49159968
Ref: library/audioop audioop max9160292
Ref: 30d59160292
Ref: library/audioop audioop maxpp9160421
Ref: 30d69160421
Ref: library/audioop audioop minmax9160532
Ref: 30d79160532
Ref: library/audioop audioop mul9160689
Ref: 30d89160689
Ref: library/audioop audioop ratecv9160915
Ref: 30d99160915
Ref: library/audioop audioop reverse9161493
Ref: 30da9161493
Ref: library/audioop audioop rms9161622
Ref: 30db9161622
Ref: library/audioop audioop tomono9161811
Ref: 30dc9161811
Ref: library/audioop audioop tostereo9162073
Ref: 30dd9162073
Ref: library/audioop audioop ulaw2lin9162388
Ref: 30de9162388
Node: aifc — Read and write AIFF and AIFC files9165123
Ref: library/aifc doc9165314
Ref: 30df9165314
Ref: library/aifc aifc-read-and-write-aiff-and-aifc-files9165314
Ref: 30e09165314
Ref: library/aifc module-aifc9165314
Ref: 49165314
Ref: library/aifc aifc open9166585
Ref: 55d9166585
Ref: library/aifc aifc aifc getnchannels9167644
Ref: 30e19167644
Ref: library/aifc aifc aifc getsampwidth9167748
Ref: 30e29167748
Ref: library/aifc aifc aifc getframerate9167836
Ref: 30e39167836
Ref: library/aifc aifc aifc getnframes9167938
Ref: 30e49167938
Ref: library/aifc aifc aifc getcomptype9168023
Ref: 30e59168023
Ref: library/aifc aifc aifc getcompname9168218
Ref: 30e69168218
Ref: library/aifc aifc aifc getparams9168447
Ref: 9089168447
Ref: library/aifc aifc aifc getmarkers9168649
Ref: 30e79168649
Ref: library/aifc aifc aifc getmark9168968
Ref: 30e89168968
Ref: library/aifc aifc aifc readframes9169103
Ref: 30e99169103
Ref: library/aifc aifc aifc rewind9169320
Ref: 30ea9169320
Ref: library/aifc aifc aifc setpos9169451
Ref: 30eb9169451
Ref: library/aifc aifc aifc tell9169524
Ref: 30ec9169524
Ref: library/aifc aifc aifc close9169589
Ref: 9099169589
Ref: library/aifc aifc aifc aiff9170141
Ref: 30ed9170141
Ref: library/aifc aifc aifc aifc9170345
Ref: 30ee9170345
Ref: library/aifc aifc aifc setnchannels9170551
Ref: 30ef9170551
Ref: library/aifc aifc aifc setsampwidth9170650
Ref: 30f09170650
Ref: library/aifc aifc aifc setframerate9170739
Ref: 30f19170739
Ref: library/aifc aifc aifc setnframes9170836
Ref: 30f29170836
Ref: library/aifc aifc aifc setcomptype9171050
Ref: 30f39171050
Ref: library/aifc aifc aifc setparams9171537
Ref: 30f49171537
Ref: library/aifc aifc aifc setmark9171875
Ref: 30f59171875
Ref: library/aifc aifc aifc writeframes9172229
Ref: 90b9172229
Ref: library/aifc aifc aifc writeframesraw9172473
Ref: 90a9172473
Ref: aifc — Read and write AIFF and AIFC files-Footnote-19172941
Node: sunau — Read and write Sun AU files9173004
Ref: library/sunau doc9173191
Ref: 30f69173191
Ref: library/sunau module-sunau9173191
Ref: fa9173191
Ref: library/sunau sunau-read-and-write-sun-au-files9173191
Ref: 30f79173191
Ref: library/sunau sunau open9174737
Ref: 5739174737
Ref: library/sunau sunau Error9175254
Ref: 30f89175254
Ref: library/sunau sunau AUDIO_FILE_MAGIC9175455
Ref: 30f99175455
Ref: library/sunau sunau AUDIO_FILE_ENCODING_MULAW_89175638
Ref: 30fa9175638
Ref: library/sunau sunau AUDIO_FILE_ENCODING_LINEAR_89175682
Ref: 30fb9175682
Ref: library/sunau sunau AUDIO_FILE_ENCODING_LINEAR_169175727
Ref: 30fc9175727
Ref: library/sunau sunau AUDIO_FILE_ENCODING_LINEAR_249175773
Ref: 30fd9175773
Ref: library/sunau sunau AUDIO_FILE_ENCODING_LINEAR_329175819
Ref: 30fe9175819
Ref: library/sunau sunau AUDIO_FILE_ENCODING_ALAW_89175865
Ref: 30ff9175865
Ref: library/sunau sunau AUDIO_FILE_ENCODING_FLOAT9176004
Ref: 31009176004
Ref: library/sunau sunau AUDIO_FILE_ENCODING_DOUBLE9176046
Ref: 31019176046
Ref: library/sunau sunau AUDIO_FILE_ENCODING_ADPCM_G7219176089
Ref: 31029176089
Ref: library/sunau sunau AUDIO_FILE_ENCODING_ADPCM_G7229176136
Ref: 31039176136
Ref: library/sunau sunau AUDIO_FILE_ENCODING_ADPCM_G723_39176183
Ref: 31049176183
Ref: library/sunau sunau AUDIO_FILE_ENCODING_ADPCM_G723_59176232
Ref: 31059176232
Ref: sunau — Read and write Sun AU files-Footnote-19176490
Node: AU_read Objects9176554
Ref: library/sunau au-read-objects9176668
Ref: 31069176668
Ref: library/sunau id19176668
Ref: 31079176668
Ref: library/sunau sunau AU_read close9176806
Ref: 31089176806
Ref: library/sunau sunau AU_read getnchannels9176942
Ref: 31099176942
Ref: library/sunau sunau AU_read getsampwidth9177046
Ref: 310a9177046
Ref: library/sunau sunau AU_read getframerate9177120
Ref: 310b9177120
Ref: library/sunau sunau AU_read getnframes9177191
Ref: 310c9177191
Ref: library/sunau sunau AU_read getcomptype9177264
Ref: 310d9177264
Ref: library/sunau sunau AU_read getcompname9177415
Ref: 310e9177415
Ref: library/sunau sunau AU_read getparams9177648
Ref: 310f9177648
Ref: library/sunau sunau AU_read readframes9177853
Ref: 31109177853
Ref: library/sunau sunau AU_read rewind9178092
Ref: 31119178092
Ref: library/sunau sunau AU_read setpos9178324
Ref: 31129178324
Ref: library/sunau sunau AU_read tell9178490
Ref: 31139178490
Ref: library/sunau sunau AU_read getmarkers9178774
Ref: 31149178774
Ref: library/sunau sunau AU_read getmark9178835
Ref: 31159178835
Node: AU_write Objects9178891
Ref: library/sunau au-write-objects9179005
Ref: 31169179005
Ref: library/sunau id29179005
Ref: 31179179005
Ref: library/sunau sunau AU_write setnchannels9179146
Ref: 31189179146
Ref: library/sunau sunau AU_write setsampwidth9179219
Ref: 9c49179219
Ref: library/sunau sunau AU_write setframerate9179361
Ref: 31199179361
Ref: library/sunau sunau AU_write setnframes9179426
Ref: 311a9179426
Ref: library/sunau sunau AU_write setcomptype9179565
Ref: 311b9179565
Ref: library/sunau sunau AU_write setparams9179726
Ref: 311c9179726
Ref: library/sunau sunau AU_write tell9179942
Ref: 311d9179942
Ref: library/sunau sunau AU_write writeframesraw9180129
Ref: 9c59180129
Ref: library/sunau sunau AU_write writeframes9180315
Ref: 9c69180315
Ref: library/sunau sunau AU_write close9180503
Ref: 311e9180503
Node: wave — Read and write WAV files9180743
Ref: library/wave doc9180918
Ref: 311f9180918
Ref: library/wave module-wave9180918
Ref: 1309180918
Ref: library/wave wave-read-and-write-wav-files9180918
Ref: 31209180918
Ref: library/wave wave open9181348
Ref: 2199181348
Ref: library/wave wave Error9182399
Ref: 31239182399
Ref: wave — Read and write WAV files-Footnote-19182653
Node: Wave_read Objects9182716
Ref: library/wave id19182830
Ref: 31249182830
Ref: library/wave wave-read-objects9182830
Ref: 31259182830
Ref: library/wave wave Wave_read close9182967
Ref: 31219182967
Ref: library/wave wave Wave_read getnchannels9183153
Ref: 31269183153
Ref: library/wave wave Wave_read getsampwidth9183271
Ref: 31279183271
Ref: library/wave wave Wave_read getframerate9183347
Ref: 31289183347
Ref: library/wave wave Wave_read getnframes9183420
Ref: 31299183420
Ref: library/wave wave Wave_read getcomptype9183495
Ref: 312a9183495
Ref: library/wave wave Wave_read getcompname9183607
Ref: 312b9183607
Ref: library/wave wave Wave_read getparams9183765
Ref: 312c9183765
Ref: library/wave wave Wave_read readframes9183972
Ref: 312d9183972
Ref: library/wave wave Wave_read rewind9184099
Ref: 312e9184099
Ref: library/wave wave Wave_read getmarkers9184326
Ref: 312f9184326
Ref: library/wave wave Wave_read getmark9184389
Ref: 31309184389
Ref: library/wave wave Wave_read setpos9184580
Ref: 31319184580
Ref: library/wave wave Wave_read tell9184670
Ref: 31329184670
Node: Wave_write Objects9184745
Ref: library/wave id29184859
Ref: 31339184859
Ref: library/wave wave-write-objects9184859
Ref: 9f19184859
Ref: library/wave wave Wave_write close9185800
Ref: 31229185800
Ref: library/wave wave Wave_write setnchannels9186121
Ref: 31369186121
Ref: library/wave wave Wave_write setsampwidth9186196
Ref: 31379186196
Ref: library/wave wave Wave_write setframerate9186278
Ref: 31389186278
Ref: library/wave wave Wave_write setnframes9186458
Ref: 31349186458
Ref: library/wave wave Wave_write setcomptype9186708
Ref: 31399186708
Ref: library/wave wave Wave_write setparams9186897
Ref: 31359186897
Ref: library/wave wave Wave_write tell9187116
Ref: 313a9187116
Ref: library/wave wave Wave_write writeframesraw9187309
Ref: 9f29187309
Ref: library/wave wave Wave_write writeframes9187497
Ref: 9f39187497
Node: chunk — Read IFF chunked data9188070
Ref: library/chunk doc9188254
Ref: 313b9188254
Ref: library/chunk chunk-read-iff-chunked-data9188254
Ref: 313c9188254
Ref: library/chunk module-chunk9188254
Ref: 179188254
Ref: library/chunk chunk Chunk9190084
Ref: 313d9190084
Ref: library/chunk chunk Chunk getname9191216
Ref: 313e9191216
Ref: library/chunk chunk Chunk getsize9191343
Ref: 313f9191343
Ref: library/chunk chunk Chunk close9191414
Ref: 31409191414
Ref: library/chunk chunk Chunk isatty9191778
Ref: 31419191778
Ref: library/chunk chunk Chunk seek9191838
Ref: 31429191838
Ref: library/chunk chunk Chunk tell9192280
Ref: 31439192280
Ref: library/chunk chunk Chunk read9192361
Ref: 31449192361
Ref: library/chunk chunk Chunk skip9192741
Ref: 31459192741
Ref: chunk — Read IFF chunked data-Footnote-19193095
Ref: chunk — Read IFF chunked data-Footnote-29193159
Node: colorsys — Conversions between color systems9193273
Ref: library/colorsys doc9193465
Ref: 31469193465
Ref: library/colorsys colorsys-conversions-between-color-systems9193465
Ref: 31479193465
Ref: library/colorsys module-colorsys9193465
Ref: 1f9193465
Ref: library/colorsys colorsys rgb_to_yiq9194452
Ref: 31489194452
Ref: library/colorsys colorsys yiq_to_rgb9194562
Ref: 31499194562
Ref: library/colorsys colorsys rgb_to_hls9194672
Ref: 314a9194672
Ref: library/colorsys colorsys hls_to_rgb9194782
Ref: 314b9194782
Ref: library/colorsys colorsys rgb_to_hsv9194892
Ref: 314c9194892
Ref: library/colorsys colorsys hsv_to_rgb9195002
Ref: 314d9195002
Ref: colorsys — Conversions between color systems-Footnote-19195314
Node: imghdr — Determine the type of an image9195381
Ref: library/imghdr doc9195581
Ref: 314e9195581
Ref: library/imghdr imghdr-determine-the-type-of-an-image9195581
Ref: 314f9195581
Ref: library/imghdr module-imghdr9195581
Ref: 989195581
Ref: library/imghdr imghdr what9195944
Ref: 7de9195944
Ref: library/imghdr imghdr tests9197665
Ref: 31509197665
Ref: imghdr — Determine the type of an image-Footnote-19198183
Node: sndhdr — Determine type of sound file9198248
Ref: library/sndhdr doc9198456
Ref: 31519198456
Ref: library/sndhdr module-sndhdr9198456
Ref: ee9198456
Ref: library/sndhdr sndhdr-determine-type-of-sound-file9198456
Ref: 31529198456
Ref: library/sndhdr sndhdr what9199700
Ref: 8369199700
Ref: library/sndhdr sndhdr whathdr9200018
Ref: 8379200018
Ref: sndhdr — Determine type of sound file-Footnote-19200401
Node: ossaudiodev — Access to OSS-compatible audio devices9200466
Ref: library/ossaudiodev doc9200624
Ref: 31539200624
Ref: library/ossaudiodev module-ossaudiodev9200624
Ref: c69200624
Ref: library/ossaudiodev ossaudiodev-access-to-oss-compatible-audio-devices9200624
Ref: 31549200624
Ref: library/ossaudiodev ossaudiodev OSSAudioError9201509
Ref: 31559201509
Ref: library/ossaudiodev ossaudiodev open9202028
Ref: 31569202028
Ref: library/ossaudiodev ossaudiodev openmixer9203427
Ref: 31579203427
Ref: ossaudiodev — Access to OSS-compatible audio devices-Footnote-19203865
Node: Audio Device Objects9203913
Ref: library/ossaudiodev audio-device-objects9204053
Ref: 31589204053
Ref: library/ossaudiodev ossaudio-device-objects9204053
Ref: 31599204053
Ref: library/ossaudiodev ossaudiodev oss_audio_device close9204645
Ref: 315a9204645
Ref: library/ossaudiodev ossaudiodev oss_audio_device fileno9204869
Ref: 315b9204869
Ref: library/ossaudiodev ossaudiodev oss_audio_device read9204970
Ref: 315c9204970
Ref: library/ossaudiodev ossaudiodev oss_audio_device write9205278
Ref: 315d9205278
Ref: library/ossaudiodev ossaudiodev oss_audio_device writeall9205798
Ref: 315e9205798
Ref: library/ossaudiodev ossaudiodev oss_audio_device nonblock9206960
Ref: 315f9206960
Ref: library/ossaudiodev ossaudiodev oss_audio_device getfmts9207127
Ref: 31609207127
Ref: library/ossaudiodev ossaudiodev oss_audio_device setfmt9209297
Ref: 31619209297
Ref: library/ossaudiodev ossaudiodev oss_audio_device channels9209668
Ref: 31629209668
Ref: library/ossaudiodev ossaudiodev oss_audio_device speed9209996
Ref: 31639209996
Ref: library/ossaudiodev ossaudiodev oss_audio_device sync9210741
Ref: 31649210741
Ref: library/ossaudiodev ossaudiodev oss_audio_device reset9211024
Ref: 31659211024
Ref: library/ossaudiodev ossaudiodev oss_audio_device post9211288
Ref: 31669211288
Ref: library/ossaudiodev ossaudiodev oss_audio_device setparameters9211701
Ref: 31679211701
Ref: library/ossaudiodev ossaudiodev oss_audio_device bufsize9212764
Ref: 31689212764
Ref: library/ossaudiodev ossaudiodev oss_audio_device obufcount9212864
Ref: 31699212864
Ref: library/ossaudiodev ossaudiodev oss_audio_device obuffree9212998
Ref: 316a9212998
Ref: library/ossaudiodev ossaudiodev oss_audio_device closed9213223
Ref: 316b9213223
Ref: library/ossaudiodev ossaudiodev oss_audio_device name9213324
Ref: 316c9213324
Ref: library/ossaudiodev ossaudiodev oss_audio_device mode9213415
Ref: 316d9213415
Node: Mixer Device Objects9213530
Ref: library/ossaudiodev id19213670
Ref: 316e9213670
Ref: library/ossaudiodev mixer-device-objects9213670
Ref: 316f9213670
Ref: library/ossaudiodev ossaudiodev oss_mixer_device close9213781
Ref: 31709213781
Ref: library/ossaudiodev ossaudiodev oss_mixer_device fileno9213982
Ref: 31719213982
Ref: library/ossaudiodev ossaudiodev oss_mixer_device controls9214228
Ref: 31729214228
Ref: library/ossaudiodev ossaudiodev oss_mixer_device stereocontrols9215206
Ref: 31739215206
Ref: library/ossaudiodev ossaudiodev oss_mixer_device reccontrols9215651
Ref: 31749215651
Ref: library/ossaudiodev ossaudiodev oss_mixer_device get9215880
Ref: 31759215880
Ref: library/ossaudiodev ossaudiodev oss_mixer_device set9216375
Ref: 31769216375
Ref: library/ossaudiodev ossaudiodev oss_mixer_device get_recsrc9216938
Ref: 31779216938
Ref: library/ossaudiodev ossaudiodev oss_mixer_device set_recsrc9217099
Ref: 31789217099
Node: Internationalization9217496
Ref: library/i18n doc9217635
Ref: 31799217635
Ref: library/i18n i18n9217635
Ref: 317a9217635
Ref: library/i18n internationalization9217635
Ref: 317b9217635
Node: gettext — Multilingual internationalization services9218090
Ref: library/gettext doc9218250
Ref: 317c9218250
Ref: library/gettext gettext-multilingual-internationalization-services9218250
Ref: 317d9218250
Ref: library/gettext module-gettext9218250
Ref: 879218250
Ref: gettext — Multilingual internationalization services-Footnote-19219227
Node: GNU gettext API9219293
Ref: library/gettext gnu-gettext-api9219423
Ref: 317e9219423
Ref: library/gettext gettext bindtextdomain9219967
Ref: 317f9219967
Ref: library/gettext gettext bind_textdomain_codeset9220539
Ref: 3ba9220539
Ref: library/gettext gettext textdomain9220965
Ref: 31819220965
Ref: library/gettext gettext gettext9221211
Ref: e929221211
Ref: library/gettext gettext dgettext9221480
Ref: 31829221480
Ref: library/gettext gettext ngettext9221619
Ref: 31839221619
Ref: library/gettext gettext dngettext9222329
Ref: 31849222329
Ref: library/gettext gettext pgettext9222483
Ref: 3009222483
Ref: library/gettext gettext dpgettext9222534
Ref: 31859222534
Ref: library/gettext gettext npgettext9222594
Ref: 31869222594
Ref: library/gettext gettext dnpgettext9222658
Ref: 31879222658
Ref: library/gettext gettext lgettext9223023
Ref: 3b69223023
Ref: library/gettext gettext ldgettext9223065
Ref: 3b79223065
Ref: library/gettext gettext lngettext9223116
Ref: 3b89223116
Ref: library/gettext gettext ldngettext9223171
Ref: 3b99223171
Ref: GNU gettext API-Footnote-19224616
Ref: GNU gettext API-Footnote-29225104
Node: Class-based API9225169
Ref: library/gettext class-based-api9225352
Ref: 31889225352
Ref: library/gettext gettext find9225882
Ref: 318a9225882
Ref: library/gettext gettext translation9227330
Ref: 3bd9227330
Ref: library/gettext gettext install9228766
Ref: 3be9228766
Ref: Class-based API-Footnote-19229861
Node: The NullTranslations class9229931
Ref: library/gettext the-nulltranslations-class9230043
Ref: 318f9230043
Ref: library/gettext gettext NullTranslations9230488
Ref: 318d9230488
Ref: library/gettext gettext NullTranslations _parse9230887
Ref: 31919230887
Ref: library/gettext gettext NullTranslations add_fallback9231198
Ref: 31909231198
Ref: library/gettext gettext NullTranslations gettext9231461
Ref: 31929231461
Ref: library/gettext gettext NullTranslations ngettext9231659
Ref: 31939231659
Ref: library/gettext gettext NullTranslations pgettext9231911
Ref: 31949231911
Ref: library/gettext gettext NullTranslations npgettext9232169
Ref: 31959232169
Ref: library/gettext gettext NullTranslations lgettext9232442
Ref: 318b9232442
Ref: library/gettext gettext NullTranslations lngettext9232479
Ref: 318c9232479
Ref: library/gettext gettext NullTranslations info9233055
Ref: 31969233055
Ref: library/gettext gettext NullTranslations charset9233223
Ref: 31979233223
Ref: library/gettext gettext NullTranslations output_charset9233312
Ref: 3bb9233312
Ref: library/gettext gettext NullTranslations set_output_charset9233554
Ref: 3bc9233554
Ref: library/gettext gettext NullTranslations install9233742
Ref: 318e9233742
Node: The GNUTranslations class9234981
Ref: library/gettext the-gnutranslations-class9235133
Ref: 31989235133
Ref: library/gettext gettext GNUTranslations9236643
Ref: 31899236643
Ref: library/gettext gettext GNUTranslations gettext9236763
Ref: 31999236763
Ref: library/gettext gettext GNUTranslations ngettext9237172
Ref: 319a9237172
Ref: library/gettext gettext GNUTranslations pgettext9238096
Ref: 319b9238096
Ref: library/gettext gettext GNUTranslations npgettext9238572
Ref: 319c9238572
Ref: library/gettext gettext GNUTranslations lgettext9239183
Ref: 319d9239183
Ref: library/gettext gettext GNUTranslations lngettext9239220
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Ref: tkinter — Python interface to Tcl/Tk-Footnote-19402605
Ref: tkinter — Python interface to Tcl/Tk-Footnote-29402681
Ref: tkinter — Python interface to Tcl/Tk-Footnote-39402708
Ref: tkinter — Python interface to Tcl/Tk-Footnote-49402748
Ref: tkinter — Python interface to Tcl/Tk-Footnote-59402805
Ref: tkinter — Python interface to Tcl/Tk-Footnote-69402832
Ref: tkinter — Python interface to Tcl/Tk-Footnote-79402869
Ref: tkinter — Python interface to Tcl/Tk-Footnote-89402961
Ref: tkinter — Python interface to Tcl/Tk-Footnote-99403012
Node: Tkinter Modules9403071
Ref: library/tkinter tkinter-modules9403192
Ref: 32af9403192
Ref: library/tkinter tkinter Tk9403521
Ref: 32b09403521
Ref: library/tkinter tkinter Tcl9403839
Ref: 32b19403839
Node: Tkinter Life Preserver9406542
Ref: library/tkinter tkinter-life-preserver9406699
Ref: 32b29406699
Node: How To Use This Section9407593
Ref: library/tkinter how-to-use-this-section9407712
Ref: 32b39407712
Node: A Simple Hello World Program9409152
Ref: library/tkinter a-simple-hello-world-program9409271
Ref: 32b49409271
Node: A Very Quick Look at Tcl/Tk9410143
Ref: library/tkinter a-very-quick-look-at-tcl-tk9410314
Ref: 32b59410314
Node: Mapping Basic Tk into Tkinter9413667
Ref: library/tkinter mapping-basic-tk-into-tkinter9413846
Ref: 32b79413846
Ref: library/tkinter tkinter-basic-mapping9413846
Ref: 32b69413846
Node: How Tk and Tkinter are Related9415668
Ref: library/tkinter how-tk-and-tkinter-are-related9415835
Ref: 32b99415835
Node: Handy Reference9417107
Ref: library/tkinter handy-reference9417258
Ref: 32ba9417258
Node: Setting Options9417510
Ref: library/tkinter setting-options9417596
Ref: 32bb9417596
Ref: library/tkinter tkinter-setting-options9417596
Ref: 32b89417596
Node: The Packer9420803
Ref: library/tkinter the-packer9420912
Ref: 32bc9420912
Node: Packer Options9422562
Ref: library/tkinter packer-options9422681
Ref: 32bd9422681
Node: Coupling Widget Variables9423381
Ref: library/tkinter coupling-widget-variables9423508
Ref: 32be9423508
Node: The Window Manager9425710
Ref: library/tkinter the-window-manager9425843
Ref: 32bf9425843
Node: Tk Option Data Types9427237
Ref: library/tkinter tk-option-data-types9427364
Ref: 32c09427364
Node: Bindings and Events9430427
Ref: library/tkinter bindings-and-events9430555
Ref: 32c19430555
Ref: library/tkinter id19430555
Ref: 32c29430555
Node: The index Parameter9433286
Ref: library/tkinter the-index-parameter9433400
Ref: 32c39433400
Node: Images9435335
Ref: library/tkinter images9435421
Ref: 32c49435421
Ref: Images-Footnote-19436355
Node: File Handlers9436389
Ref: library/tkinter file-handlers9436501
Ref: 32c59436501
Ref: library/tkinter tkinter-file-handlers9436501
Ref: 32c69436501
Ref: library/tkinter tkinter Widget tk createfilehandler9437443
Ref: 32c79437443
Ref: library/tkinter tkinter Widget tk deletefilehandler9437878
Ref: 32c89437878
Ref: library/tkinter tkinter READABLE9437960
Ref: 32c99437960
Ref: library/tkinter tkinter WRITABLE9437987
Ref: 32ca9437987
Ref: library/tkinter tkinter EXCEPTION9438014
Ref: 32cb9438014
Node: tkinter colorchooser — Color choosing dialog9438089
Ref: library/tkinter colorchooser doc9438298
Ref: 32cc9438298
Ref: library/tkinter colorchooser module-tkinter colorchooser9438298
Ref: 10f9438298
Ref: library/tkinter colorchooser tkinter-colorchooser-color-choosing-dialog9438298
Ref: 32cd9438298
Ref: library/tkinter colorchooser tkinter colorchooser Chooser9438797
Ref: 32ce9438797
Ref: library/tkinter colorchooser tkinter colorchooser askcolor9438863
Ref: 32d09438863
Ref: tkinter colorchooser — Color choosing dialog-Footnote-19439258
Node: tkinter font — Tkinter font wrapper9439338
Ref: library/tkinter font doc9439524
Ref: 32d19439524
Ref: library/tkinter font module-tkinter font9439524
Ref: 1139439524
Ref: library/tkinter font tkinter-font-tkinter-font-wrapper9439524
Ref: 32d29439524
Ref: library/tkinter font tkinter font NORMAL9439881
Ref: 32d39439881
Ref: library/tkinter font tkinter font BOLD9439911
Ref: 32d49439911
Ref: library/tkinter font tkinter font ITALIC9439939
Ref: 32d59439939
Ref: library/tkinter font tkinter font ROMAN9439969
Ref: 32d69439969
Ref: library/tkinter font tkinter font Font9439999
Ref: fcb9439999
Ref: library/tkinter font tkinter font Font actual9441316
Ref: 32d79441316
Ref: library/tkinter font tkinter font Font cget9441417
Ref: 32d89441417
Ref: library/tkinter font tkinter font Font config9441495
Ref: 32d99441495
Ref: library/tkinter font tkinter font Font copy9441574
Ref: 32da9441574
Ref: library/tkinter font tkinter font Font measure9441652
Ref: 32db9441652
Ref: library/tkinter font tkinter font Font metrics9441911
Ref: 32dc9441911
Ref: library/tkinter font tkinter font families9442488
Ref: 32dd9442488
Ref: library/tkinter font tkinter font names9442595
Ref: 32de9442595
Ref: library/tkinter font tkinter font nametofont9442682
Ref: 32df9442682
Ref: tkinter font — Tkinter font wrapper-Footnote-19442831
Node: Tkinter Dialogs9442902
Ref: library/dialog doc9443088
Ref: 32e09443088
Ref: library/dialog tkinter-dialogs9443088
Ref: 32e19443088
Node: tkinter simpledialog — Standard Tkinter input dialogs9443459
Ref: library/dialog module-tkinter simpledialog9443620
Ref: 1169443620
Ref: library/dialog tkinter-simpledialog-standard-tkinter-input-dialogs9443620
Ref: 32e29443620
Ref: library/dialog tkinter simpledialog askfloat9444024
Ref: 32e39444024
Ref: library/dialog tkinter simpledialog askinteger9444090
Ref: 32e49444090
Ref: library/dialog tkinter simpledialog askstring9444158
Ref: 32e59444158
Ref: library/dialog tkinter simpledialog Dialog9444338
Ref: 32e69444338
Ref: library/dialog tkinter simpledialog Dialog body9444440
Ref: 32e79444440
Ref: library/dialog tkinter simpledialog Dialog buttonbox9444609
Ref: 32e89444609
Ref: tkinter simpledialog — Standard Tkinter input dialogs-Footnote-19444795
Node: tkinter filedialog — File selection dialogs9444875
Ref: library/dialog module-tkinter filedialog9445093
Ref: 1129445093
Ref: library/dialog tkinter-filedialog-file-selection-dialogs9445093
Ref: 32e99445093
Ref: tkinter filedialog — File selection dialogs-Footnote-19445527
Node: Native Load/Save Dialogs9445605
Ref: library/dialog native-load-save-dialogs9445711
Ref: 32ea9445711
Ref: library/dialog tkinter filedialog askopenfile9446727
Ref: 32eb9446727
Ref: library/dialog tkinter filedialog askopenfiles9446794
Ref: 32ec9446794
Ref: library/dialog tkinter filedialog asksaveasfile9446989
Ref: 32ee9446989
Ref: library/dialog tkinter filedialog askopenfilename9447158
Ref: 32f09447158
Ref: library/dialog tkinter filedialog askopenfilenames9447219
Ref: 32f19447219
Ref: library/dialog tkinter filedialog asksaveasfilename9447430
Ref: 32f29447430
Ref: library/dialog tkinter filedialog askdirectory9447575
Ref: 32f39447575
Ref: library/dialog tkinter filedialog Open9447804
Ref: 32ed9447804
Ref: library/dialog tkinter filedialog SaveAs9447864
Ref: 32ef9447864
Ref: library/dialog tkinter filedialog Directory9448185
Ref: 32f49448185
Ref: library/dialog tkinter filedialog FileDialog9448417
Ref: 32f59448417
Ref: library/dialog tkinter filedialog FileDialog cancel_command9448524
Ref: 32f69448524
Ref: library/dialog tkinter filedialog FileDialog dirs_double_event9448627
Ref: 32f79448627
Ref: library/dialog tkinter filedialog FileDialog dirs_select_event9448733
Ref: 32f89448733
Ref: library/dialog tkinter filedialog FileDialog files_double_event9448832
Ref: 32f99448832
Ref: library/dialog tkinter filedialog FileDialog files_select_event9448934
Ref: 32fa9448934
Ref: library/dialog tkinter filedialog FileDialog filter_command9449036
Ref: 32fb9449036
Ref: library/dialog tkinter filedialog FileDialog get_filter9449124
Ref: 32fc9449124
Ref: library/dialog tkinter filedialog FileDialog get_selection9449210
Ref: 32fd9449210
Ref: library/dialog tkinter filedialog FileDialog go9449294
Ref: 32fe9449294
Ref: library/dialog tkinter filedialog FileDialog ok_event9449436
Ref: 32ff9449436
Ref: library/dialog tkinter filedialog FileDialog quit9449523
Ref: 33009449523
Ref: library/dialog tkinter filedialog FileDialog set_filter9449608
Ref: 33019449608
Ref: library/dialog tkinter filedialog FileDialog set_selection9449680
Ref: 33029449680
Ref: library/dialog tkinter filedialog LoadFileDialog9449775
Ref: 33039449775
Ref: library/dialog tkinter filedialog LoadFileDialog ok_command9449939
Ref: 33049449939
Ref: library/dialog tkinter filedialog SaveFileDialog9450080
Ref: 33059450080
Ref: library/dialog tkinter filedialog SaveFileDialog ok_command9450246
Ref: 33069450246
Node: tkinter commondialog — Dialog window templates9450458
Ref: library/dialog module-tkinter commondialog9450612
Ref: 1109450612
Ref: library/dialog tkinter-commondialog-dialog-window-templates9450612
Ref: 33079450612
Ref: library/dialog tkinter commondialog Dialog9451006
Ref: 32cf9451006
Ref: library/dialog tkinter commondialog Dialog show9451071
Ref: 33089451071
Ref: tkinter commondialog — Dialog window templates-Footnote-19451289
Node: tkinter messagebox — Tkinter message prompts9451369
Ref: library/tkinter messagebox doc9451563
Ref: 33099451563
Ref: library/tkinter messagebox module-tkinter messagebox9451563
Ref: 1149451563
Ref: library/tkinter messagebox tkinter-messagebox-tkinter-message-prompts9451563
Ref: 330a9451563
Ref: library/tkinter messagebox tkinter messagebox Message9452169
Ref: 330b9452169
Ref: library/tkinter messagebox tkinter messagebox showinfo9452308
Ref: 330c9452308
Ref: library/tkinter messagebox tkinter messagebox showwarning9452422
Ref: 330d9452422
Ref: library/tkinter messagebox tkinter messagebox showerror9452513
Ref: 330e9452513
Ref: library/tkinter messagebox tkinter messagebox askquestion9452629
Ref: 330f9452629
Ref: library/tkinter messagebox tkinter messagebox askokcancel9452720
Ref: 33109452720
Ref: library/tkinter messagebox tkinter messagebox askretrycancel9452811
Ref: 33119452811
Ref: library/tkinter messagebox tkinter messagebox askyesno9452905
Ref: 33129452905
Ref: library/tkinter messagebox tkinter messagebox askyesnocancel9452993
Ref: 33139452993
Ref: tkinter messagebox — Tkinter message prompts-Footnote-19453124
Node: tkinter scrolledtext — Scrolled Text Widget9453202
Ref: library/tkinter scrolledtext doc9453418
Ref: 33149453418
Ref: library/tkinter scrolledtext module-tkinter scrolledtext9453418
Ref: 1159453418
Ref: library/tkinter scrolledtext tkinter-scrolledtext-scrolled-text-widget9453418
Ref: 33159453418
Ref: library/tkinter scrolledtext tkinter scrolledtext ScrolledText9454332
Ref: 33169454332
Ref: library/tkinter scrolledtext tkinter scrolledtext ScrolledText frame9454398
Ref: 33179454398
Ref: library/tkinter scrolledtext tkinter scrolledtext ScrolledText vbar9454495
Ref: 33189454495
Ref: tkinter scrolledtext — Scrolled Text Widget-Footnote-19454591
Node: tkinter dnd — Drag and drop support9454671
Ref: library/tkinter dnd doc9454874
Ref: 33199454874
Ref: library/tkinter dnd module-tkinter dnd9454874
Ref: 1119454874
Ref: library/tkinter dnd tkinter-dnd-drag-and-drop-support9454874
Ref: 331a9454874
Ref: library/tkinter dnd tkinter dnd DndHandler9456366
Ref: 331c9456366
Ref: library/tkinter dnd tkinter dnd DndHandler cancel9456554
Ref: 331d9456554
Ref: library/tkinter dnd tkinter dnd DndHandler finish9456637
Ref: 331e9456637
Ref: library/tkinter dnd tkinter dnd DndHandler on_motion9456731
Ref: 331f9456731
Ref: library/tkinter dnd tkinter dnd DndHandler on_release9456857
Ref: 33209456857
Ref: library/tkinter dnd tkinter dnd dnd_start9456963
Ref: 331b9456963
Ref: tkinter dnd — Drag and drop support-Footnote-19457155
Node: tkinter ttk — Tk themed widgets9457225
Ref: library/tkinter ttk doc9457423
Ref: 33219457423
Ref: library/tkinter ttk module-tkinter ttk9457423
Ref: 1189457423
Ref: library/tkinter ttk tkinter-ttk-tk-themed-widgets9457423
Ref: 33229457423
Ref: tkinter ttk — Tk themed widgets-Footnote-19458485
Ref: tkinter ttk — Tk themed widgets-Footnote-29458555
Node: Using Ttk9458608
Ref: library/tkinter ttk using-ttk9458707
Ref: 33239458707
Ref: Using Ttk-Footnote-19459864
Node: Ttk Widgets9459927
Ref: library/tkinter ttk ttk-widgets9460041
Ref: 33249460041
Node: Widget9461150
Ref: library/tkinter ttk widget9461263
Ref: 332b9461263
Node: Standard Options9461580
Ref: library/tkinter ttk standard-options9461673
Ref: 332c9461673
Node: Scrollable Widget Options9463350
Ref: library/tkinter ttk scrollable-widget-options9463465
Ref: 332d9463465
Node: Label Options9464588
Ref: library/tkinter ttk label-options9464708
Ref: 332e9464708
Node: Compatibility Options9467266
Ref: library/tkinter ttk compatibility-options9467374
Ref: 332f9467374
Node: Widget States9467910
Ref: library/tkinter ttk widget-states9468015
Ref: 33319468015
Node: ttk Widget9469694
Ref: library/tkinter ttk ttk-widget9469769
Ref: 33329469769
Ref: library/tkinter ttk tkinter ttk Widget9469956
Ref: 33289469956
Ref: library/tkinter ttk tkinter ttk Widget identify9469987
Ref: 33339469987
Ref: library/tkinter ttk tkinter ttk Widget instate9470230
Ref: 33349470230
Ref: library/tkinter ttk tkinter ttk Widget state9470574
Ref: 33309470574
Node: Combobox9470962
Ref: library/tkinter ttk combobox9471071
Ref: 33359471071
Node: Options9471766
Ref: library/tkinter ttk options9471841
Ref: 33369471841
Node: Virtual events9474347
Ref: library/tkinter ttk virtual-events9474443
Ref: 33379474443
Node: ttk Combobox9474623
Ref: library/tkinter ttk ttk-combobox9474703
Ref: 33389474703
Ref: library/tkinter ttk tkinter ttk Combobox9474750
Ref: 33259474750
Ref: library/tkinter ttk tkinter ttk Combobox current9474783
Ref: 33399474783
Ref: library/tkinter ttk tkinter ttk Combobox get9475059
Ref: 333a9475059
Ref: library/tkinter ttk tkinter ttk Combobox set9475138
Ref: 333b9475138
Node: Spinbox9475222
Ref: library/tkinter ttk spinbox9475333
Ref: 333c9475333
Node: Options<2>9476093
Ref: library/tkinter ttk id19476173
Ref: 333d9476173
Node: Virtual events<2>9478559
Ref: library/tkinter ttk id29478659
Ref: 333e9478659
Node: ttk Spinbox9478867
Ref: library/tkinter ttk ttk-spinbox9478948
Ref: 333f9478948
Ref: library/tkinter ttk tkinter ttk Spinbox9478993
Ref: 5029478993
Ref: library/tkinter ttk tkinter ttk Spinbox get9479025
Ref: 33409479025
Ref: library/tkinter ttk tkinter ttk Spinbox set9479103
Ref: 33419479103
Node: Notebook9479186
Ref: library/tkinter ttk notebook9479300
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Node: Options<3>9479660
Ref: library/tkinter ttk id39479735
Ref: 33439479735
Node: Tab Options9480910
Ref: library/tkinter ttk tab-options9481009
Ref: 33449481009
Node: Tab Identifiers9483084
Ref: library/tkinter ttk tab-identifiers9483187
Ref: 33469483187
Node: Virtual Events9483721
Ref: library/tkinter ttk id49483825
Ref: 33489483825
Node: ttk Notebook9483969
Ref: library/tkinter ttk ttk-notebook9484049
Ref: 33499484049
Ref: library/tkinter ttk tkinter ttk Notebook9484096
Ref: 33269484096
Ref: library/tkinter ttk tkinter ttk Notebook add9484129
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Ref: library/tkinter ttk tkinter ttk Notebook forget9484414
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Ref: library/tkinter ttk tkinter ttk Notebook hide9484552
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Ref: library/tkinter ttk tkinter ttk Notebook index9485004
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Ref: library/tkinter ttk tkinter ttk Notebook insert9485183
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Ref: library/tkinter ttk tkinter ttk Notebook select9485568
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Ref: library/tkinter ttk tkinter ttk Notebook tabs9486228
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Ref: library/tkinter ttk tkinter ttk Notebook enable_traversal9486316
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Node: Progressbar9487143
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Ref: library/tkinter ttk tkinter ttk Progressbar start9489828
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Ref: library/tkinter ttk tkinter ttk Progressbar step9490096
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Ref: library/tkinter ttk tkinter ttk Progressbar stop9490243
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Node: Separator9490428
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Node: Platform-specific notes9491682
Ref: library/tkinter ttk platform-specific-notes9491763
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Node: Bugs9492019
Ref: library/tkinter ttk bugs9492100
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Node: Treeview9492373
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Node: Tag Options9497840
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Node: Column Identifiers9498674
Ref: library/tkinter ttk column-identifiers9498783
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Node: Virtual Events<2>9499655
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Ref: library/tkinter ttk tkinter ttk Treeview bbox9500830
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Ref: library/tkinter ttk tkinter ttk Treeview get_children9501267
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Ref: library/tkinter ttk tkinter ttk Treeview set_children9501433
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Ref: library/tkinter ttk tkinter ttk Treeview column9501825
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Ref: library/tkinter ttk tkinter ttk Treeview identify_element9506225
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Ref: library/tkinter ttk tkinter ttk Treeview index9506353
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Ref: library/tkinter ttk tkinter ttk Treeview next9508194
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Ref: library/tkinter ttk tkinter ttk Treeview parent9508349
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Ref: library/tkinter ttk tkinter ttk Treeview prev9508500
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Ref: library/tkinter ttk tkinter ttk Treeview reattach9508660
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Ref: library/tkinter ttk tkinter ttk Treeview see9508762
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Ref: library/tkinter ttk tkinter ttk Treeview selection_toggle9509879
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Ref: library/tkinter ttk tkinter ttk Treeview tag_bind9510469
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Ref: library/tkinter ttk tkinter ttk Treeview yview9511549
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Node: Ttk Styling9511643
Ref: library/tkinter ttk ttk-styling9511741
Ref: 33849511741
Ref: library/tkinter ttk ttkstyling9511741
Ref: 33299511741
Ref: library/tkinter ttk tkinter ttk Style9512335
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Ref: library/tkinter ttk tkinter ttk Style configure9512424
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Ref: library/tkinter ttk tkinter ttk Style map9513151
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Ref: library/tkinter ttk tkinter ttk Style lookup9514416
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Ref: library/tkinter ttk tkinter ttk Style layout9514937
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Ref: library/tkinter ttk tkinter ttk Style element_create9516249
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Ref: library/tkinter ttk tkinter ttk Style element_names9518371
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Ref: library/tkinter ttk tkinter ttk Style element_options9518476
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Ref: library/tkinter ttk tkinter ttk Style theme_create9518582
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Ref: library/tkinter ttk tkinter ttk Style theme_settings9518995
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Ref: library/tkinter ttk tkinter ttk Style theme_names9520471
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Ref: library/tkinter ttk tkinter ttk Style theme_use9520551
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Ref: Ttk Styling-Footnote-19520848
Node: Layouts9520909
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Node: Bad file descriptor error example9671340
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Ref: library/doctest module-doctest9673265
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Node: Simple Usage Checking Examples in Docstrings9677447
Ref: library/doctest doctest-simple-testmod9677626
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Ref: library/doctest simple-usage-checking-examples-in-docstrings9677626
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Node: Simple Usage Checking Examples in a Text File9679402
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Node: How It Works9681948
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Node: Which Docstrings Are Examined?9682768
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Node: How are Docstring Examples Recognized?9683741
Ref: library/doctest doctest-finding-examples9683907
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Ref: library/doctest how-are-docstring-examples-recognized9683907
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Node: What’s the Execution Context?9686995
Ref: library/doctest doctest-execution-context9687153
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Node: What About Exceptions?9687870
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Ref: library/doctest option-flags-and-directives9692510
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Ref: library/doctest doctest DONT_ACCEPT_TRUE_FOR_19693480
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Node: Directives9700790
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Node: Warnings<2>9703259
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Node: DocTestFinder objects9728127
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Ref: unittest — Unit testing framework-Footnote-79756341
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Node: Command-Line Interface<3>9759356
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Ref: test support — Utilities for the Python test suite-Footnote-110094859
Ref: test support — Utilities for the Python test suite-Footnote-210094908
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Ref: bdb — Debugger framework-Footnote-110122618
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Ref: pdb — The Python Debugger-Footnote-110138065
Ref: pdb — The Python Debugger-Footnote-210138127
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Ref: The Python Profilers-Footnote-110152486
Ref: The Python Profilers-Footnote-210152552
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Node: What Is Deterministic Profiling?10177091
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Node: timeit — Measure execution time of small code snippets10185390
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Ref: timeit — Measure execution time of small code snippets-Footnote-110186380
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Ref: library/timeit basic-examples10186580
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Node: Python Interface10187868
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Ref: library/timeit timeit timeit10188158
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Ref: library/timeit timeit repeat10188621
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Ref: library/timeit timeit default_timer10189211
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Ref: library/timeit timeit Timer autorange10191972
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Ref: library/timeit timeit Timer repeat10192699
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Ref: library/timeit timeit Timer print_exc10193974
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Ref: library/timeit timeit-command-line-interface10194718
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Ref: library/timeit examples10197082
Ref: 371410197082
Ref: library/timeit timeit-examples10197082
Ref: 370510197082
Node: trace — Trace or track Python statement execution10200298
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Ref: library/trace module-trace10200523
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Ref: library/trace trace-trace-or-track-python-statement-execution10200523
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Ref: trace — Trace or track Python statement execution-Footnote-110201268
Ref: trace — Trace or track Python statement execution-Footnote-210201332
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Ref: library/trace trace-cli10201510
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Ref: library/trace cmdoption-trace-help10201864
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Ref: library/trace cmdoption-trace-f10203517
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Ref: library/trace cmdoption-trace-coverdir10203684
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Ref: library/trace cmdoption-trace-g10204411
Ref: 372710204411
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Ref: library/trace filters10204620
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Ref: library/trace cmdoption-trace-ignore-module10204702
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Ref: library/trace cmdoption-trace-ignore-dir10204899
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Ref: library/trace programmatic-interface10205247
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Ref: library/trace trace-api10205247
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Ref: library/trace trace Trace10205312
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Ref: library/trace trace Trace run10206223
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Ref: library/trace trace Trace runctx10206465
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Ref: library/trace trace Trace runfunc10206779
Ref: 3c310206779
Ref: library/trace trace Trace results10206972
Ref: 373010206972
Ref: library/trace trace CoverageResults10207281
Ref: 373110207281
Ref: library/trace trace CoverageResults update10207445
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Ref: library/trace trace CoverageResults write_results10207563
Ref: 373310207563
Node: tracemalloc — Trace memory allocations10208593
Ref: library/tracemalloc doc10208753
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Ref: library/tracemalloc module-tracemalloc10208753
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Ref: library/tracemalloc tracemalloc-trace-memory-allocations10208753
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Ref: tracemalloc — Trace memory allocations-Footnote-110210093
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Ref: library/tracemalloc examples10210264
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Ref: library/tracemalloc display-the-top-1010210508
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Ref: library/tracemalloc pretty-top10217187
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Ref: library/tracemalloc record-the-current-and-peak-size-of-all-traced-memory-blocks10219756
Ref: 373e10219756
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Ref: library/tracemalloc api10221549
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Ref: library/tracemalloc functions10221795
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Ref: library/tracemalloc tracemalloc clear_traces10221834
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Ref: library/tracemalloc tracemalloc get_object_traceback10221969
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Ref: library/tracemalloc tracemalloc get_traceback_limit10222376
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Ref: library/tracemalloc tracemalloc get_traced_memory10222700
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Ref: library/tracemalloc tracemalloc reset_peak10222906
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Ref: library/tracemalloc tracemalloc get_tracemalloc_memory10223538
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Ref: library/tracemalloc tracemalloc is_tracing10223736
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Ref: library/tracemalloc tracemalloc start10223969
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Ref: library/tracemalloc tracemalloc stop10225333
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Ref: library/tracemalloc tracemalloc take_snapshot10225767
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Node: DomainFilter10226467
Ref: library/tracemalloc domainfilter10226556
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Ref: library/tracemalloc tracemalloc DomainFilter10226601
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Ref: library/tracemalloc tracemalloc DomainFilter inclusive10226765
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Ref: library/tracemalloc tracemalloc DomainFilter domain10227065
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Ref: library/tracemalloc filter10227251
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Ref: library/tracemalloc tracemalloc Filter10227286
Ref: 375010227286
Ref: library/tracemalloc tracemalloc Filter domain10228133
Ref: 375110228133
Ref: library/tracemalloc tracemalloc Filter inclusive10228404
Ref: 375210228404
Ref: library/tracemalloc tracemalloc Filter lineno10228836
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Ref: library/tracemalloc tracemalloc Filter filename_pattern10228988
Ref: 375310228988
Ref: library/tracemalloc tracemalloc Filter all_frames10229102
Ref: 375510229102
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Ref: library/tracemalloc frame10229586
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Ref: library/tracemalloc tracemalloc Frame10229619
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Ref: library/tracemalloc tracemalloc Frame filename10229767
Ref: 375910229767
Ref: library/tracemalloc tracemalloc Frame lineno10229830
Ref: 375a10229830
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Ref: library/tracemalloc snapshot10229974
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Ref: library/tracemalloc tracemalloc Snapshot10230013
Ref: 374b10230013
Ref: library/tracemalloc tracemalloc Snapshot compare_to10230191
Ref: 374a10230191
Ref: library/tracemalloc tracemalloc Snapshot dump10230917
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Ref: library/tracemalloc tracemalloc Snapshot filter_traces10231053
Ref: 376210231053
Ref: library/tracemalloc tracemalloc Snapshot load10231730
Ref: 373b10231730
Ref: library/tracemalloc tracemalloc Snapshot statistics10231856
Ref: 373810231856
Ref: library/tracemalloc tracemalloc Snapshot traceback_limit10233055
Ref: 375610233055
Ref: library/tracemalloc tracemalloc Snapshot traces10233274
Ref: 376310233274
Node: Statistic10233569
Ref: library/tracemalloc statistic10233657
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Ref: library/tracemalloc tracemalloc Statistic10233698
Ref: 376410233698
Ref: library/tracemalloc tracemalloc Statistic count10233922
Ref: 376010233922
Ref: library/tracemalloc tracemalloc Statistic size10233997
Ref: 376510233997
Ref: library/tracemalloc tracemalloc Statistic traceback10234084
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Ref: library/tracemalloc statisticdiff10234301
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Ref: library/tracemalloc tracemalloc StatisticDiff10234350
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Ref: library/tracemalloc tracemalloc StatisticDiff count10234650
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Ref: library/tracemalloc tracemalloc StatisticDiff count_diff10234824
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Ref: library/tracemalloc tracemalloc StatisticDiff size10235046
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Ref: library/tracemalloc tracemalloc StatisticDiff size_diff10235242
Ref: 375d10235242
Ref: library/tracemalloc tracemalloc StatisticDiff traceback10235476
Ref: 376110235476
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Ref: library/tracemalloc trace10235695
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Ref: library/tracemalloc tracemalloc Trace10235728
Ref: 376710235728
Ref: library/tracemalloc tracemalloc Trace domain10235961
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Ref: library/tracemalloc tracemalloc Trace size10236239
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Ref: library/tracemalloc tracemalloc Trace traceback10236323
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Ref: library/tracemalloc traceback10236518
Ref: 376f10236518
Ref: library/tracemalloc tracemalloc Traceback10236559
Ref: 50410236559
Ref: library/tracemalloc tracemalloc Traceback total_nframe10237486
Ref: 374910237486
Ref: library/tracemalloc tracemalloc Traceback format10237795
Ref: 50510237795
Node: Software Packaging and Distribution10238863
Ref: library/distribution doc10239026
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Ref: library/distribution software-packaging-and-distribution10239026
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Ref: Software Packaging and Distribution-Footnote-110239610
Node: distutils — Building and installing Python modules10239635
Ref: library/distutils doc10239813
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Ref: library/distutils distutils-building-and-installing-python-modules10239813
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Ref: library/distutils module-distutils10239813
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Ref: distutils — Building and installing Python modules-Footnote-110241720
Ref: distutils — Building and installing Python modules-Footnote-210241773
Ref: distutils — Building and installing Python modules-Footnote-310241802
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Ref: library/ensurepip ensurepip-bootstrapping-the-pip-installer10242067
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Ref: library/ensurepip module-ensurepip10242067
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Ref: ensurepip — Bootstrapping the pip installer-Footnote-110243472
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Ref: library/ensurepip command-line-interface10243644
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Ref: library/ensurepip ensurepip version10245655
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Ref: library/ensurepip ensurepip bootstrap10245815
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Ref: library/venv module-venv10247814
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Ref: library/venv venv-creation-of-virtual-environments10247814
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Ref: venv — Creation of virtual environments-Footnote-110248742
Ref: venv — Creation of virtual environments-Footnote-210248803
Ref: venv — Creation of virtual environments-Footnote-310248852
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Ref: 377d10249097
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Ref: Creating virtual environments-Footnote-110259336
Ref: Creating virtual environments-Footnote-210259410
Ref: Creating virtual environments-Footnote-310259465
Ref: Creating virtual environments-Footnote-410259510
Ref: Creating virtual environments-Footnote-510259548
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Ref: library/venv api10259762
Ref: 378210259762
Ref: library/venv venv-api10259762
Ref: 8df10259762
Ref: library/venv venv EnvBuilder10260019
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Ref: library/venv venv EnvBuilder create10262039
Ref: 378310262039
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Ref: library/venv venv EnvBuilder create_configuration10263788
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Ref: library/venv venv EnvBuilder setup_python10263926
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Ref: library/venv venv EnvBuilder setup_scripts10264292
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Ref: library/venv venv EnvBuilder upgrade_dependencies10264441
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Ref: An example of extending EnvBuilder-Footnote-110278320
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Ref: library/zipapp pip10278537
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Ref: zipapp — Manage executable Python zip archives-Footnote-110279314
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Ref: 52110282601
Ref: library/zipapp zipapp get_interpreter10286384
Ref: 379a10286384
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Ref: library/zipapp examples10286892
Ref: 379b10286892
Ref: library/zipapp zipapp-examples10286892
Ref: 379c10286892
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Ref: library/zipapp zipapp-specifying-the-interpreter10288442
Ref: 379e10288442
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Ref: library/zipapp caveats10295312
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Ref: sys — System-specific parameters and functions-Footnote-110376204
Ref: sys — System-specific parameters and functions-Footnote-210376253
Ref: sys — System-specific parameters and functions-Footnote-310376302
Ref: sys — System-specific parameters and functions-Footnote-410376351
Ref: sys — System-specific parameters and functions-Footnote-510376403
Ref: sys — System-specific parameters and functions-Footnote-610376452
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Ref: sys — System-specific parameters and functions-Footnote-1010376648
Ref: sys — System-specific parameters and functions-Footnote-1110376698
Ref: sys — System-specific parameters and functions-Footnote-1210376748
Ref: sys — System-specific parameters and functions-Footnote-1310376798
Ref: sys — System-specific parameters and functions-Footnote-1410376848
Ref: sys — System-specific parameters and functions-Footnote-1510376898
Ref: sys — System-specific parameters and functions-Footnote-1610376978
Ref: sys — System-specific parameters and functions-Footnote-1710377028
Ref: sys — System-specific parameters and functions-Footnote-1810377078
Node: sysconfig — Provide access to Python’s configuration information10377128
Ref: library/sysconfig doc10377351
Ref: 37c110377351
Ref: library/sysconfig module-sysconfig10377351
Ref: fe10377351
Ref: library/sysconfig sysconfig-provide-access-to-python-s-configuration-information10377351
Ref: 37c210377351
Ref: sysconfig — Provide access to Python’s configuration information-Footnote-110377993
Node: Configuration variables10378061
Ref: library/sysconfig configuration-variables10378216
Ref: 37c310378216
Ref: library/sysconfig sysconfig get_config_vars10378709
Ref: a4610378709
Ref: library/sysconfig sysconfig get_config_var10379080
Ref: a4510379080
Node: Installation paths10379523
Ref: library/sysconfig id110379705
Ref: 37c410379705
Ref: library/sysconfig installation-paths10379705
Ref: 37bc10379705
Ref: library/sysconfig sysconfig get_scheme_names10381758
Ref: 37c510381758
Ref: library/sysconfig sysconfig get_path_names10381896
Ref: 37c610381896
Ref: library/sysconfig sysconfig get_path10382035
Ref: d8610382035
Ref: library/sysconfig sysconfig get_paths10383254
Ref: ca710383254
Node: Other functions<3>10383877
Ref: library/sysconfig other-functions10384063
Ref: 37c710384063
Ref: library/sysconfig sysconfig get_python_version10384114
Ref: ca610384114
Ref: library/sysconfig sysconfig get_platform10384285
Ref: ca510384285
Ref: library/sysconfig sysconfig is_python_build10385288
Ref: d8710385288
Ref: library/sysconfig sysconfig parse_config_h10385579
Ref: 37c810385579
Ref: library/sysconfig sysconfig get_config_h_filename10385973
Ref: 37c910385973
Ref: library/sysconfig sysconfig get_makefile_filename10386066
Ref: 37ca10386066
Node: Using sysconfig as a script10386157
Ref: library/sysconfig using-sysconfig-as-a-script10386316
Ref: 37cb10386316
Node: builtins — Built-in objects10387389
Ref: library/builtins doc10387605
Ref: 37cc10387605
Ref: library/builtins builtins-built-in-objects10387605
Ref: 37cd10387605
Ref: library/builtins module-builtins10387605
Ref: 1210387605
Node: __main__ — Top-level script environment10389106
Ref: library/__main__ doc10389282
Ref: 37ce10389282
Ref: library/__main__ main-top-level-script-environment10389282
Ref: 37cf10389282
Ref: library/__main__ module-__main__10389282
Ref: 110389282
Node: warnings — Warning control10390176
Ref: library/warnings doc10390351
Ref: 37d010390351
Ref: library/warnings module-warnings10390351
Ref: 12f10390351
Ref: library/warnings warnings-warning-control10390351
Ref: 37d110390351
Ref: warnings — Warning control-Footnote-110392662
Node: Warning Categories10392729
Ref: library/warnings id110392840
Ref: 37d510392840
Ref: library/warnings warning-categories10392840
Ref: 185f10392840
Node: The Warnings Filter10396843
Ref: library/warnings the-warnings-filter10396995
Ref: 37d610396995
Ref: library/warnings warning-filter10396995
Ref: 15d10396995
Node: Describing Warning Filters10399730
Ref: library/warnings describing-warning-filters10399843
Ref: 147e10399843
Ref: library/warnings id210399843
Ref: 37d710399843
Node: Default Warning Filter10401638
Ref: library/warnings default-warning-filter10401789
Ref: 37d810401789
Ref: library/warnings id310401789
Ref: 37d910401789
Node: Overriding the default filter10402876
Ref: library/warnings overriding-the-default-filter10402992
Ref: 37da10402992
Ref: library/warnings warning-disable10402992
Ref: 37db10402992
Node: Temporarily Suppressing Warnings10404427
Ref: library/warnings temporarily-suppressing-warnings10404577
Ref: 37dc10404577
Ref: library/warnings warning-suppress10404577
Ref: 37dd10404577
Node: Testing Warnings10405595
Ref: library/warnings testing-warnings10405772
Ref: 37de10405772
Ref: library/warnings warning-testing10405772
Ref: 37df10405772
Node: Updating Code For New Versions of Dependencies10407836
Ref: library/warnings updating-code-for-new-versions-of-dependencies10408000
Ref: 37e010408000
Ref: library/warnings warning-ignored10408000
Ref: 351310408000
Node: Available Functions10409390
Ref: library/warnings available-functions10409564
Ref: 37e110409564
Ref: library/warnings warning-functions10409564
Ref: 37e210409564
Ref: library/warnings warnings warn10409623
Ref: f1a10409623
Ref: library/warnings warnings warn_explicit10410842
Ref: 6a710410842
Ref: library/warnings warnings showwarning10412030
Ref: 37d410412030
Ref: library/warnings warnings formatwarning10412668
Ref: 112d10412668
Ref: library/warnings warnings filterwarnings10413100
Ref: eca10413100
Ref: library/warnings warnings simplefilter10413776
Ref: 35fa10413776
Ref: library/warnings warnings resetwarnings10414211
Ref: 37d310414211
Node: Available Context Managers10414479
Ref: library/warnings available-context-managers10414598
Ref: 37e310414598
Ref: library/warnings warnings catch_warnings10414673
Ref: 35f910414673
Node: dataclasses — Data Classes10415922
Ref: library/dataclasses doc10416108
Ref: 37e410416108
Ref: library/dataclasses dataclasses-data-classes10416108
Ref: 37e510416108
Ref: library/dataclasses module-dataclasses10416108
Ref: 2f10416108
Ref: dataclasses — Data Classes-Footnote-110417772
Ref: dataclasses — Data Classes-Footnote-210417842
Ref: dataclasses — Data Classes-Footnote-310417891
Node: Module-level decorators classes and functions10417940
Ref: library/dataclasses module-level-decorators-classes-and-functions10418079
Ref: 37e710418079
Ref: library/dataclasses dataclasses dataclass10418194
Ref: 44910418194
Ref: library/dataclasses dataclasses field10425162
Ref: 113910425162
Ref: library/dataclasses dataclasses Field10429428
Ref: 37e810429428
Ref: library/dataclasses dataclasses fields10430221
Ref: 37e910430221
Ref: library/dataclasses dataclasses asdict10430600
Ref: f5710430600
Ref: library/dataclasses dataclasses astuple10431672
Ref: f5610431672
Ref: library/dataclasses dataclasses make_dataclass10432429
Ref: 37ea10432429
Ref: library/dataclasses dataclasses replace10433954
Ref: fa810433954
Ref: library/dataclasses dataclasses is_dataclass10435357
Ref: f5310435357
Node: Post-init processing10435798
Ref: library/dataclasses post-init-processing10435961
Ref: 37eb10435961
Node: Class variables10437706
Ref: library/dataclasses class-variables10437843
Ref: 37ec10437843
Ref: Class variables-Footnote-110438393
Node: Init-only variables10438442
Ref: library/dataclasses init-only-variables10438575
Ref: 37ed10438575
Node: Frozen instances10439786
Ref: library/dataclasses frozen-instances10439918
Ref: 37ee10439918
Node: Inheritance<2>10440519
Ref: library/dataclasses inheritance10440657
Ref: 37f010440657
Node: Default factory functions10441709
Ref: library/dataclasses default-factory-functions10441853
Ref: 37f110441853
Node: Mutable default values10442531
Ref: library/dataclasses mutable-default-values10442675
Ref: 37f210442675
Node: Exceptions<18>10444569
Ref: library/dataclasses exceptions10444679
Ref: 37f310444679
Ref: library/dataclasses dataclasses FrozenInstanceError10444720
Ref: 37ef10444720
Node: contextlib — Utilities for with-statement contexts10444994
Ref: library/contextlib doc10445181
Ref: 37f410445181
Ref: library/contextlib contextlib-utilities-for-with-statement-contexts10445181
Ref: 37f510445181
Ref: library/contextlib module-contextlib10445181
Ref: 2310445181
Ref: contextlib — Utilities for with-statement contexts-Footnote-110445819
Node: Utilities10445888
Ref: library/contextlib utilities10446015
Ref: 37f610446015
Ref: library/contextlib contextlib AbstractContextManager10446087
Ref: 62e10446087
Ref: library/contextlib contextlib AbstractAsyncContextManager10446573
Ref: 48010446573
Ref: library/contextlib contextlib contextmanager10447080
Ref: c4f10447080
Ref: library/contextlib contextlib asynccontextmanager10450048
Ref: 47f10450048
Ref: library/contextlib contextlib closing10451058
Ref: 37f710451058
Ref: library/contextlib simplifying-support-for-single-optional-context-managers10451854
Ref: 37f810451854
Ref: library/contextlib contextlib nullcontext10451854
Ref: 47d10451854
Ref: library/contextlib contextlib suppress10452966
Ref: 91910452966
Ref: library/contextlib contextlib redirect_stdout10454083
Ref: 7b510454083
Ref: library/contextlib contextlib redirect_stderr10455555
Ref: 7b410455555
Ref: library/contextlib contextlib ContextDecorator10455817
Ref: c4e10455817
Ref: library/contextlib contextlib ExitStack10458211
Ref: 47e10458211
Ref: library/contextlib contextlib ExitStack enter_context10460077
Ref: 37fa10460077
Ref: library/contextlib contextlib ExitStack push10460509
Ref: 37fb10460509
Ref: library/contextlib contextlib ExitStack callback10461397
Ref: 3c710461397
Ref: library/contextlib contextlib ExitStack pop_all10461853
Ref: 37fc10461853
Ref: library/contextlib contextlib ExitStack close10462905
Ref: 37fd10462905
Ref: library/contextlib contextlib AsyncExitStack10463193
Ref: 48110463193
Ref: library/contextlib contextlib AsyncExitStack enter_async_context10463554
Ref: 37ff10463554
Ref: library/contextlib contextlib AsyncExitStack push_async_exit10463706
Ref: 380010463706
Ref: library/contextlib contextlib AsyncExitStack push_async_callback10463868
Ref: 3c810463868
Ref: library/contextlib contextlib AsyncExitStack aclose10464008
Ref: 37fe10464008
Node: Examples and Recipes10464592
Ref: library/contextlib examples-and-recipes10464778
Ref: 380110464778
Node: Supporting a variable number of context managers10465226
Ref: library/contextlib supporting-a-variable-number-of-context-managers10465382
Ref: 380210465382
Node: Catching exceptions from __enter__ methods10466424
Ref: library/contextlib catching-exceptions-from-enter-methods10466631
Ref: 380310466631
Node: Cleaning up in an __enter__ implementation10467779
Ref: library/contextlib cleaning-up-in-an-enter-implementation10467989
Ref: 380410467989
Node: Replacing any use of try-finally and flag variables10469892
Ref: library/contextlib replacing-any-use-of-try-finally-and-flag-variables10470107
Ref: 380510470107
Node: Using a context manager as a function decorator10472622
Ref: library/contextlib using-a-context-manager-as-a-function-decorator10472786
Ref: 380610472786
Ref: Using a context manager as a function decorator-Footnote-110474620
Node: Single use reusable and reentrant context managers10474669
Ref: library/contextlib single-use-reusable-and-reentrant-cms10474837
Ref: 91b10474837
Ref: library/contextlib single-use-reusable-and-reentrant-context-managers10474837
Ref: 380710474837
Node: Reentrant context managers10476374
Ref: library/contextlib reentrant-cms10476521
Ref: 37f910476521
Ref: library/contextlib reentrant-context-managers10476521
Ref: 380810476521
Node: Reusable context managers10478037
Ref: library/contextlib reusable-cms10478184
Ref: 380910478184
Ref: library/contextlib reusable-context-managers10478184
Ref: 380a10478184
Node: abc — Abstract Base Classes10480862
Ref: library/abc doc10481045
Ref: 380b10481045
Ref: library/abc abc-abstract-base-classes10481045
Ref: 380c10481045
Ref: library/abc module-abc10481045
Ref: 310481045
Ref: library/abc abc ABC10482010
Ref: 90510482010
Ref: library/abc abc ABCMeta10482855
Ref: 90610482855
Ref: library/abc abc ABCMeta register10483635
Ref: ab010483635
Ref: library/abc abc ABCMeta __subclasshook__10484317
Ref: 380d10484317
Ref: library/abc abc abstractmethod10487214
Ref: aad10487214
Ref: library/abc abc abstractclassmethod10490314
Ref: aae10490314
Ref: library/abc abc abstractstaticmethod10491030
Ref: aaf10491030
Ref: library/abc abc abstractproperty10491748
Ref: aac10491748
Ref: library/abc abc get_cache_token10493135
Ref: 90410493135
Ref: abc — Abstract Base Classes-Footnote-110493548
Ref: abc — Abstract Base Classes-Footnote-210493610
Ref: abc — Abstract Base Classes-Footnote-310493659
Ref: abc — Abstract Base Classes-Footnote-410493708
Node: atexit — Exit handlers10493819
Ref: library/atexit doc10493999
Ref: 380e10493999
Ref: library/atexit atexit-exit-handlers10493999
Ref: 380f10493999
Ref: library/atexit module-atexit10493999
Ref: b10493999
Ref: library/atexit atexit register10494907
Ref: f4610494907
Ref: library/atexit atexit unregister10495959
Ref: 381010495959
Node: atexit Example10496649
Ref: library/atexit atexit-example10496724
Ref: 381110496724
Ref: library/atexit id110496724
Ref: 381210496724
Node: traceback — Print or retrieve a stack traceback10498085
Ref: library/traceback doc10498279
Ref: 381310498279
Ref: library/traceback module-traceback10498279
Ref: 11c10498279
Ref: library/traceback traceback-print-or-retrieve-a-stack-traceback10498279
Ref: 381410498279
Ref: library/traceback traceback print_tb10499059
Ref: 86810499059
Ref: library/traceback traceback print_exception10499610
Ref: 220810499610
Ref: library/traceback traceback print_exc10500759
Ref: 381510500759
Ref: library/traceback traceback print_last10500925
Ref: 381610500925
Ref: library/traceback traceback print_stack10501252
Ref: 86910501252
Ref: library/traceback traceback extract_tb10501797
Ref: 381710501797
Ref: library/traceback traceback extract_stack10502538
Ref: 381810502538
Ref: library/traceback traceback format_list10502841
Ref: 381910502841
Ref: library/traceback traceback format_exception_only10503350
Ref: 349110503350
Ref: library/traceback traceback format_exception10503969
Ref: 381a10503969
Ref: library/traceback traceback format_exc10504578
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Ref: library/traceback traceback format_tb10504738
Ref: 377010504738
Ref: library/traceback traceback format_stack10504854
Ref: 381c10504854
Ref: library/traceback traceback clear_frames10504979
Ref: 9d710504979
Ref: library/traceback traceback walk_stack10505188
Ref: 86310505188
Ref: library/traceback traceback walk_tb10505498
Ref: 86410505498
Ref: traceback — Print or retrieve a stack traceback-Footnote-110505930
Node: TracebackException Objects10505998
Ref: library/traceback tracebackexception-objects10506139
Ref: 381e10506139
Ref: library/traceback traceback TracebackException10506379
Ref: 86510506379
Ref: library/traceback traceback TracebackException __cause__10506764
Ref: 381f10506764
Ref: library/traceback traceback TracebackException __context__10506872
Ref: 382010506872
Ref: library/traceback traceback TracebackException __suppress_context__10506994
Ref: 382110506994
Ref: library/traceback traceback TracebackException stack10507113
Ref: 382210507113
Ref: library/traceback traceback TracebackException exc_type10507206
Ref: 382310507206
Ref: library/traceback traceback TracebackException filename10507284
Ref: 382410507284
Ref: library/traceback traceback TracebackException lineno10507385
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Ref: library/traceback traceback TracebackException text10507486
Ref: 382610507486
Ref: library/traceback traceback TracebackException offset10507578
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Ref: library/traceback traceback TracebackException msg10507698
Ref: 382810507698
Ref: library/traceback traceback TracebackException from_exception10507782
Ref: 382910507782
Ref: library/traceback traceback TracebackException format10508165
Ref: 382a10508165
Ref: library/traceback traceback TracebackException format_exception_only10508713
Ref: 382b10508713
Node: StackSummary Objects10509260
Ref: library/traceback stacksummary-objects10509430
Ref: 382c10509430
Ref: library/traceback traceback StackSummary10509601
Ref: 86610509601
Ref: library/traceback traceback StackSummary extract10509636
Ref: 381d10509636
Ref: library/traceback traceback StackSummary from_list10510461
Ref: 382d10510461
Ref: library/traceback traceback StackSummary format10510764
Ref: 382e10510764
Node: FrameSummary Objects10511384
Ref: library/traceback framesummary-objects10511546
Ref: 382f10511546
Ref: library/traceback traceback FrameSummary10511713
Ref: 86710511713
Node: Traceback Examples10512458
Ref: library/traceback traceback-example10512591
Ref: 383010512591
Ref: library/traceback traceback-examples10512591
Ref: 383110512591
Node: __future__ — Future statement definitions10517987
Ref: library/__future__ doc10518191
Ref: 383210518191
Ref: library/__future__ future-future-statement-definitions10518191
Ref: 383310518191
Ref: library/__future__ module-__future__10518191
Ref: 010518191
Ref: __future__ — Future statement definitions-Footnote-110523396
Ref: __future__ — Future statement definitions-Footnote-210523465
Ref: __future__ — Future statement definitions-Footnote-310523514
Ref: __future__ — Future statement definitions-Footnote-410523563
Ref: __future__ — Future statement definitions-Footnote-510523612
Ref: __future__ — Future statement definitions-Footnote-610523661
Ref: __future__ — Future statement definitions-Footnote-710523710
Ref: __future__ — Future statement definitions-Footnote-810523759
Ref: __future__ — Future statement definitions-Footnote-910523808
Ref: __future__ — Future statement definitions-Footnote-1010523857
Node: gc — Garbage Collector interface10523907
Ref: library/gc doc10524094
Ref: 383410524094
Ref: library/gc gc-garbage-collector-interface10524094
Ref: 383510524094
Ref: library/gc module-gc10524094
Ref: 8410524094
Ref: library/gc gc enable10525021
Ref: 383610525021
Ref: library/gc gc disable10525092
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Ref: library/gc gc isenabled10525165
Ref: 383810525165
Ref: library/gc gc collect10525256
Ref: 35b10525256
Ref: library/gc gc set_debug10525891
Ref: 383910525891
Ref: library/gc gc get_debug10526158
Ref: 383a10526158
Ref: library/gc gc get_objects10526237
Ref: 2fe10526237
Ref: library/gc gc get_stats10526653
Ref: 93a10526653
Ref: library/gc gc set_threshold10527347
Ref: 383b10527347
Ref: library/gc gc get_count10528573
Ref: 383c10528573
Ref: library/gc gc get_threshold10528698
Ref: 383d10528698
Ref: library/gc gc get_referrers10528843
Ref: fb610528843
Ref: library/gc gc get_referents10529881
Ref: fb710529881
Ref: library/gc gc is_tracked10530613
Ref: d6b10530613
Ref: library/gc gc is_finalized10531438
Ref: 1a910531438
Ref: library/gc gc freeze10531948
Ref: 49310531948
Ref: library/gc gc unfreeze10532482
Ref: 49410532482
Ref: library/gc gc get_freeze_count10532641
Ref: 49510532641
Ref: library/gc gc garbage10532884
Ref: c1210532884
Ref: library/gc gc callbacks10533750
Ref: ae810533750
Ref: library/gc gc DEBUG_STATS10535081
Ref: 383f10535081
Ref: library/gc gc DEBUG_COLLECTABLE10535224
Ref: 384010535224
Ref: library/gc gc DEBUG_UNCOLLECTABLE10535310
Ref: c1310535310
Ref: library/gc gc DEBUG_SAVEALL10535690
Ref: 383e10535690
Ref: library/gc gc DEBUG_LEAK10535882
Ref: 384110535882
Ref: gc — Garbage Collector interface-Footnote-110536126
Ref: gc — Garbage Collector interface-Footnote-210536215
Node: inspect — Inspect live objects10536264
Ref: library/inspect doc10536449
Ref: 384210536449
Ref: library/inspect inspect-inspect-live-objects10536449
Ref: 384310536449
Ref: library/inspect module-inspect10536449
Ref: a010536449
Ref: inspect — Inspect live objects-Footnote-110537621
Node: Types and members10537687
Ref: library/inspect inspect-types10537804
Ref: 384410537804
Ref: library/inspect types-and-members10537804
Ref: 384510537804
Ref: library/inspect inspect getmembers10551466
Ref: 384610551466
Ref: library/inspect inspect getmodulename10552078
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Ref: library/inspect inspect ismodule10552755
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Ref: library/inspect inspect isclass10552847
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Ref: library/inspect inspect ismethod10552986
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Ref: library/inspect inspect isfunction10553102
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Ref: library/inspect inspect isgeneratorfunction10553280
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Ref: library/inspect inspect isgenerator10553573
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Ref: library/inspect inspect iscoroutinefunction10553671
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Ref: library/inspect inspect iscoroutine10554062
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Ref: library/inspect inspect isawaitable10554248
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Ref: library/inspect inspect isasyncgenfunction10554698
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Ref: library/inspect inspect isasyncgen10555208
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Ref: library/inspect inspect istraceback10555436
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Ref: library/inspect inspect isframe10555534
Ref: 385010555534
Ref: library/inspect inspect iscode10555624
Ref: 385110555624
Ref: library/inspect inspect isbuiltin10555712
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Ref: library/inspect inspect isroutine10555848
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Ref: library/inspect inspect isabstract10555983
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Ref: library/inspect inspect ismethoddescriptor10556091
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Ref: library/inspect inspect isdatadescriptor10556974
Ref: 385610556974
Ref: library/inspect inspect isgetsetdescriptor10557603
Ref: 385710557603
Ref: library/inspect inspect ismemberdescriptor10557954
Ref: 385810557954
Node: Retrieving source code10558316
Ref: library/inspect inspect-source10558491
Ref: 385910558491
Ref: library/inspect retrieving-source-code10558491
Ref: 385a10558491
Ref: library/inspect inspect getdoc10558558
Ref: 30710558558
Ref: library/inspect inspect getcomments10558991
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Ref: library/inspect inspect getfile10559415
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Ref: library/inspect inspect getmodule10559649
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Ref: library/inspect inspect getsourcefile10559749
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Ref: library/inspect inspect getsourcelines10559986
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Ref: library/inspect inspect getsource10560605
Ref: fda10560605
Ref: library/inspect inspect cleandoc10561055
Ref: 385b10561055
Node: Introspecting callables with the Signature object10561466
Ref: library/inspect inspect-signature-object10561648
Ref: 385e10561648
Ref: library/inspect introspecting-callables-with-the-signature-object10561648
Ref: 385f10561648
Ref: library/inspect inspect signature10561965
Ref: 65510561965
Ref: library/inspect inspect Signature10563357
Ref: 7e410563357
Ref: library/inspect inspect Signature empty10564388
Ref: 386110564388
Ref: library/inspect inspect Signature parameters10564508
Ref: 108810564508
Ref: library/inspect inspect Signature return_annotation10565003
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Ref: library/inspect inspect Signature bind10565222
Ref: 386310565222
Ref: library/inspect inspect Signature bind_partial10565499
Ref: 386410565499
Ref: library/inspect inspect Signature replace10565875
Ref: 386010565875
Ref: library/inspect inspect Signature from_callable10566578
Ref: 7e710566578
Ref: library/inspect inspect Parameter10567160
Ref: 7e510567160
Ref: library/inspect inspect Parameter empty10567515
Ref: 386610567515
Ref: library/inspect inspect Parameter name10567646
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Ref: library/inspect inspect Parameter default10568110
Ref: 386810568110
Ref: library/inspect inspect Parameter annotation10568301
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Ref: library/inspect inspect Parameter kind10568489
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Ref: library/inspect inspect Parameter kind description10571313
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Ref: library/inspect inspect Parameter replace10571848
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Ref: library/inspect inspect BoundArguments10572836
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Ref: library/inspect inspect BoundArguments arguments10573040
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Ref: library/inspect inspect BoundArguments args10573889
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Ref: library/inspect inspect BoundArguments kwargs10574040
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Ref: library/inspect inspect BoundArguments signature10574189
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Ref: library/inspect inspect BoundArguments apply_defaults10574287
Ref: 7e610574287
Ref: Introspecting callables with the Signature object-Footnote-110575264
Node: Classes and functions<2>10575313
Ref: library/inspect classes-and-functions10575494
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Ref: library/inspect inspect getclosurevars10583262
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Node: The interpreter stack10584712
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Ref: library/inspect inspect stack10588491
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Node: Fetching attributes statically10589363
Ref: library/inspect fetching-attributes-statically10589543
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Ref: library/inspect inspect getattr_static10590125
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Node: Current State of Generators and Coroutines10591930
Ref: library/inspect current-state-of-generators-and-coroutines10592111
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Ref: library/inspect inspect getgeneratorstate10592540
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Node: Code Objects Bit Flags10594897
Ref: library/inspect code-objects-bit-flags10595073
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Ref: library/inspect inspect-module-co-flags10595073
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Ref: library/inspect inspect CO_OPTIMIZED10595236
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Ref: Code Objects Bit Flags-Footnote-110597241
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Node: Command Line Interface<3>10597388
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Ref: library/inspect inspect-module-cli10597513
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Node: site — Site-specific configuration hook10598003
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Node: Readline configuration10603972
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Node: Module contents<4>10604757
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Node: Command Line Interface<4>10607942
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Ref: Command Line Interface<4>-Footnote-110609314
Node: Custom Python Interpreters10609363
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Ref: library/custominterp custom-python-interpreters10609511
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Node: code — Interpreter base classes10610096
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Ref: library/code code interact10611472
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Ref: code — Interpreter base classes-Footnote-110613517
Node: Interactive Interpreter Objects10613580
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Node: Interactive Console Objects10616621
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Ref: library/code code InteractiveConsole resetbuffer10618570
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Node: codeop — Compile Python code10619039
Ref: library/codeop doc10619174
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Ref: library/codeop codeop-compile-python-code10619174
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Ref: 38a710621537
Ref: library/codeop codeop CommandCompiler10621938
Ref: 38a810621938
Ref: codeop — Compile Python code-Footnote-110622356
Node: Importing Modules10622421
Ref: library/modules doc10622570
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Ref: library/modules importing-modules10622570
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Node: zipimport — Import modules from Zip archives10623113
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Ref: zipimport — Import modules from Zip archives-Footnote-110625655
Ref: zipimport — Import modules from Zip archives-Footnote-210625723
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Ref: zipimport — Import modules from Zip archives-Footnote-410625840
Ref: zipimport — Import modules from Zip archives-Footnote-510625889
Ref: zipimport — Import modules from Zip archives-Footnote-610625938
Node: zipimporter Objects10625987
Ref: library/zipimport id110626110
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Ref: library/zipimport zipimporter-objects10626110
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Ref: library/zipimport zipimport zipimporter10626233
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Ref: library/zipimport zipimport zipimporter find_module10626704
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Ref: library/zipimport zipimport zipimporter get_code10627128
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Ref: library/zipimport zipimport zipimporter get_data10627306
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Ref: library/zipimport zipimport zipimporter get_filename10627578
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Ref: library/zipimport zipimport zipimporter get_source10627838
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Ref: library/zipimport zipimport zipimporter is_package10628128
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Ref: library/zipimport zipimport zipimporter load_module10628339
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Ref: library/zipimport zipimport zipimporter archive10628617
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Ref: library/zipimport zipimport zipimporter prefix10628750
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Node: Examples<29>10629157
Ref: library/zipimport examples10629280
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Ref: library/zipimport zipimport-examples10629280
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Node: pkgutil — Package extension utility10629960
Ref: library/pkgutil doc10630161
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Ref: library/pkgutil module-pkgutil10630161
Ref: cd10630161
Ref: library/pkgutil pkgutil-package-extension-utility10630161
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Ref: library/pkgutil pkgutil ModuleInfo10630446
Ref: 70310630446
Ref: library/pkgutil pkgutil extend_path10630600
Ref: 38be10630600
Ref: library/pkgutil pkgutil ImpImporter10632272
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Ref: library/pkgutil pkgutil ImpLoader10632971
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Ref: library/pkgutil pkgutil find_loader10633300
Ref: 38c110633300
Ref: library/pkgutil pkgutil get_importer10633877
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Ref: library/pkgutil pkgutil get_loader10634392
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Ref: library/pkgutil pkgutil iter_importers10635109
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Ref: library/pkgutil pkgutil iter_modules10635808
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Ref: library/pkgutil pkgutil walk_packages10636654
Ref: 58610636654
Ref: library/pkgutil pkgutil get_data10638232
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Ref: library/pkgutil pkgutil resolve_name10639366
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Ref: pkgutil — Package extension utility-Footnote-110641232
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Ref: pkgutil — Package extension utility-Footnote-1310641840
Ref: pkgutil — Package extension utility-Footnote-1410641890
Ref: pkgutil — Package extension utility-Footnote-1510641940
Node: modulefinder — Find modules used by a script10641984
Ref: library/modulefinder doc10642186
Ref: 38c610642186
Ref: library/modulefinder module-modulefinder10642186
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Ref: library/modulefinder modulefinder-find-modules-used-by-a-script10642186
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Ref: library/modulefinder modulefinder AddPackagePath10642705
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Ref: library/modulefinder modulefinder ModuleFinder10643018
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Ref: library/modulefinder modulefinder ModuleFinder report10643677
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Ref: library/modulefinder modulefinder ModuleFinder run_script10643892
Ref: 38ca10643892
Ref: library/modulefinder modulefinder ModuleFinder modules10644030
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Ref: modulefinder — Find modules used by a script-Footnote-110644254
Node: Example usage of ModuleFinder10644325
Ref: library/modulefinder example-usage-of-modulefinder10644437
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Ref: library/modulefinder modulefinder-example10644437
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Node: runpy — Locating and executing Python modules10645808
Ref: library/runpy doc10646015
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Ref: library/runpy runpy-locating-and-executing-python-modules10646015
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Ref: runpy — Locating and executing Python modules-Footnote-110654601
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Ref: runpy — Locating and executing Python modules-Footnote-610654861
Ref: runpy — Locating and executing Python modules-Footnote-710654910
Ref: runpy — Locating and executing Python modules-Footnote-810654959
Node: importlib — The implementation of import10655008
Ref: library/importlib doc10655193
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Ref: library/importlib module-importlib10655193
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Ref: importlib — The implementation of import-Footnote-110655966
Node: Introduction<12>10656044
Ref: library/importlib introduction10656161
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Ref: Introduction<12>-Footnote-110657996
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Ref: Introduction<12>-Footnote-1110658490
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Node: Functions<11>10658640
Ref: library/importlib functions10658823
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Ref: library/importlib importlib __import__10658862
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Ref: library/importlib importlib import_module10659170
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Ref: library/importlib importlib invalidate_caches10661502
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Node: importlib abc – Abstract base classes related to import10665183
Ref: library/importlib importlib-abc-abstract-base-classes-related-to-import10665383
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Ref: library/importlib module-importlib abc10665383
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Ref: library/importlib importlib abc PathEntryFinder invalidate_caches10671598
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Ref: library/importlib importlib abc Loader10671872
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Ref: library/importlib importlib abc ResourceReader10676870
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Ref: library/importlib importlib abc Traversable10689676
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Ref: importlib abc – Abstract base classes related to import-Footnote-110691364
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Ref: importlib abc – Abstract base classes related to import-Footnote-510691583
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Ref: importlib resources – Resources-Footnote-310699007
Ref: importlib resources – Resources-Footnote-410699100
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Node: importlib machinery – Importers and path hooks10699247
Ref: library/importlib importlib-machinery-importers-and-path-hooks10699470
Ref: 38fb10699470
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Ref: library/importlib importlib machinery OPTIMIZED_BYTECODE_SUFFIXES10700237
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Ref: library/importlib importlib machinery BYTECODE_SUFFIXES10700504
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Ref: library/importlib importlib machinery EXTENSION_SUFFIXES10700793
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Ref: library/importlib importlib machinery all_suffixes10700968
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Ref: library/importlib importlib machinery BuiltinImporter10701402
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Ref: library/importlib importlib machinery FrozenImporter10701967
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Ref: library/importlib importlib machinery WindowsRegistryFinder10702387
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Ref: library/importlib importlib machinery FileFinder10705188
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Ref: library/importlib importlib machinery FileFinder path10706493
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Ref: library/importlib importlib machinery FileFinder find_spec10706566
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Ref: library/importlib importlib machinery FileFinder find_loader10706741
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Ref: library/importlib importlib machinery FileFinder invalidate_caches10706876
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Ref: library/importlib importlib machinery FileFinder path_hook10706956
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Ref: library/importlib importlib machinery SourceFileLoader10707402
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Ref: library/importlib importlib machinery SourceFileLoader name10707693
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Ref: library/importlib importlib machinery SourceFileLoader path10707783
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Ref: library/importlib importlib machinery SourceFileLoader is_package10707849
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Ref: library/importlib importlib machinery SourceFileLoader path_stats10707978
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Ref: library/importlib importlib machinery SourceFileLoader set_data10708114
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Ref: library/importlib importlib machinery SourceFileLoader load_module10708253
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Ref: library/importlib importlib machinery SourcelessFileLoader10708572
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Ref: library/importlib importlib machinery SourcelessFileLoader name10709043
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Ref: library/importlib importlib machinery SourcelessFileLoader path10709127
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Ref: library/importlib importlib machinery SourcelessFileLoader is_package10709195
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Ref: library/importlib importlib machinery SourcelessFileLoader get_code10709321
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Ref: library/importlib importlib machinery SourcelessFileLoader get_source10709457
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Ref: library/importlib importlib machinery SourcelessFileLoader load_module10709596
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Ref: library/importlib importlib machinery ExtensionFileLoader10709890
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Ref: library/importlib importlib machinery ExtensionFileLoader name10710257
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Ref: library/importlib importlib machinery ExtensionFileLoader path10710334
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Ref: library/importlib importlib machinery ExtensionFileLoader create_module10710401
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Ref: library/importlib importlib machinery ExtensionFileLoader exec_module10710578
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Ref: library/importlib importlib machinery ExtensionFileLoader is_package10710736
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Ref: library/importlib importlib machinery ExtensionFileLoader get_code10710920
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Ref: library/importlib importlib machinery ExtensionFileLoader get_source10711029
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Ref: library/importlib importlib machinery ExtensionFileLoader get_filename10711145
Ref: 95110711145
Ref: library/importlib importlib machinery ModuleSpec10711255
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Ref: library/importlib importlib machinery ModuleSpec name10712068
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Ref: library/importlib importlib machinery ModuleSpec loader10712176
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Ref: library/importlib importlib machinery ModuleSpec origin10712355
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Ref: library/importlib importlib machinery ModuleSpec submodule_search_locations10712716
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Ref: library/importlib importlib machinery ModuleSpec loader_state10712881
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Ref: library/importlib importlib machinery ModuleSpec cached10713006
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Ref: library/importlib importlib machinery ModuleSpec parent10713136
Ref: 1b0110713136
Ref: library/importlib importlib machinery ModuleSpec has_location10713417
Ref: 391a10713417
Ref: importlib machinery – Importers and path hooks-Footnote-110713601
Ref: importlib machinery – Importers and path hooks-Footnote-210713680
Ref: importlib machinery – Importers and path hooks-Footnote-310713729
Ref: importlib machinery – Importers and path hooks-Footnote-410713778
Node: importlib util – Utility code for importers10713827
Ref: library/importlib importlib-util-utility-code-for-importers10714029
Ref: 391b10714029
Ref: library/importlib module-importlib util10714029
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Ref: library/importlib importlib util MAGIC_NUMBER10714355
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Ref: library/importlib importlib util cache_from_source10714598
Ref: 65110714598
Ref: library/importlib importlib util source_from_cache10716507
Ref: 65210716507
Ref: library/importlib importlib util decode_source10717132
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Ref: library/importlib importlib util resolve_name10717402
Ref: 1b610717402
Ref: library/importlib importlib util find_spec10718299
Ref: a1c10718299
Ref: library/importlib importlib util module_from_spec10719192
Ref: 7e110719192
Ref: library/importlib importlib util module_for_loader10719825
Ref: a2610719825
Ref: library/importlib importlib util set_loader10721602
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Ref: library/importlib importlib util set_package10722228
Ref: a2810722228
Ref: library/importlib importlib util spec_from_loader10722634
Ref: 38d710722634
Ref: library/importlib importlib util spec_from_file_location10723080
Ref: 65310723080
Ref: library/importlib importlib util source_hash10723554
Ref: 391c10723554
Ref: library/importlib importlib util LazyLoader10723826
Ref: 64d10723826
Ref: library/importlib importlib util LazyLoader factory10725309
Ref: 391e10725309
Ref: importlib util – Utility code for importers-Footnote-110725873
Ref: importlib util – Utility code for importers-Footnote-210725946
Ref: importlib util – Utility code for importers-Footnote-310725995
Ref: importlib util – Utility code for importers-Footnote-410726044
Ref: importlib util – Utility code for importers-Footnote-510726093
Ref: importlib util – Utility code for importers-Footnote-610726142
Node: Examples<30>10726191
Ref: library/importlib examples10726336
Ref: 391f10726336
Ref: library/importlib importlib-examples10726336
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Node: Importing programmatically10726601
Ref: library/importlib importing-programmatically10726721
Ref: 392110726721
Node: Checking if a module can be imported10726952
Ref: library/importlib checking-if-a-module-can-be-imported10727113
Ref: 392210727113
Node: Importing a source file directly10727898
Ref: library/importlib importing-a-source-file-directly10728055
Ref: 392310728055
Node: Setting up an importer10728614
Ref: library/importlib setting-up-an-importer10728772
Ref: 392410728772
Node: Approximating importlib import_module10730346
Ref: library/importlib approximating-importlib-import-module10730463
Ref: 392510730463
Node: Using importlib metadata10732060
Ref: library/importlib metadata doc10732189
Ref: 392610732189
Ref: library/importlib metadata module-importlib metadata10732189
Ref: 9d10732189
Ref: library/importlib metadata using10732189
Ref: 392710732189
Ref: library/importlib metadata using-importlib-metadata10732189
Ref: 392810732189
Ref: Using importlib metadata-Footnote-110733598
Ref: Using importlib metadata-Footnote-210733676
Ref: Using importlib metadata-Footnote-310733761
Ref: Using importlib metadata-Footnote-410733846
Ref: Using importlib metadata-Footnote-510733918
Ref: Using importlib metadata-Footnote-610733956
Node: Overview<2>10734005
Ref: library/importlib metadata overview10734103
Ref: 392910734103
Node: Functional API<2>10735525
Ref: library/importlib metadata functional-api10735645
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Node: Entry points10735897
Ref: library/importlib metadata entry-points10735993
Ref: 392a10735993
Ref: library/importlib metadata id110735993
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Ref: Entry points-Footnote-110737306
Node: Distribution metadata10737417
Ref: library/importlib metadata distribution-metadata10737543
Ref: 393110737543
Ref: library/importlib metadata metadata10737543
Ref: 392b10737543
Ref: Distribution metadata-Footnote-110738027
Node: Distribution versions10738307
Ref: library/importlib metadata distribution-versions10738439
Ref: 393210738439
Ref: library/importlib metadata version10738439
Ref: 392c10738439
Node: Distribution files10738648
Ref: library/importlib metadata distribution-files10738784
Ref: 393310738784
Ref: library/importlib metadata files10738784
Ref: 392d10738784
Ref: Distribution files-Footnote-110740355
Node: Distribution requirements10740452
Ref: library/importlib metadata distribution-requirements10740558
Ref: 393410740558
Ref: library/importlib metadata requirements10740558
Ref: 392e10740558
Node: Distributions10740825
Ref: library/importlib metadata distributions10740964
Ref: 393510740964
Ref: Distributions-Footnote-110741871
Node: Extending the search algorithm10741920
Ref: library/importlib metadata extending-the-search-algorithm10742033
Ref: 393610742033
Node: Python Language Services10743799
Ref: library/language doc10743944
Ref: 393710743944
Ref: library/language language10743944
Ref: 393810743944
Ref: library/language python-language-services10743944
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Node: parser — Access Python parse trees10744851
Ref: library/parser doc10744986
Ref: 393a10744986
Ref: library/parser module-parser10744986
Ref: c710744986
Ref: library/parser parser-access-python-parse-trees10744986
Ref: 393b10744986
Node: Creating ST Objects10750269
Ref: library/parser creating-st-objects10750391
Ref: 394110750391
Ref: library/parser creating-sts10750391
Ref: 394210750391
Ref: library/parser parser expr10750637
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Ref: library/parser parser suite10750972
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Ref: library/parser parser sequence2st10751309
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Ref: library/parser parser tuple2st10752723
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Node: Converting ST Objects10752892
Ref: library/parser converting-st-objects10753044
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Ref: library/parser converting-sts10753044
Ref: 394710753044
Ref: library/parser parser st2list10753358
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Ref: library/parser parser st2tuple10754432
Ref: 394010754432
Ref: library/parser parser compilest10754976
Ref: 394410754976
Node: Queries on ST Objects10756139
Ref: library/parser queries-on-st-objects10756301
Ref: 394810756301
Ref: library/parser querying-sts10756301
Ref: 394910756301
Ref: library/parser parser isexpr10756673
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Ref: library/parser parser issuite10757156
Ref: 394b10757156
Node: Exceptions and Error Handling10757516
Ref: library/parser exceptions-and-error-handling10757667
Ref: 394c10757667
Ref: library/parser st-errors10757667
Ref: 394d10757667
Ref: library/parser parser ParserError10757962
Ref: 394310757962
Node: ST Objects10759123
Ref: library/parser id110759281
Ref: 394e10759281
Ref: library/parser st-objects10759281
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Ref: library/parser parser STType10759469
Ref: 395010759469
Ref: library/parser parser ST compile10759653
Ref: 395110759653
Ref: library/parser parser ST isexpr10759749
Ref: 395210759749
Ref: library/parser parser ST issuite10759807
Ref: 395310759807
Ref: library/parser parser ST tolist10759867
Ref: 395410759867
Ref: library/parser parser ST totuple10759978
Ref: 395510759978
Node: Example Emulation of compile10760091
Ref: library/parser example-emulation-of-compile10760211
Ref: 395610760211
Node: ast — Abstract Syntax Trees10761305
Ref: library/ast doc10761502
Ref: 395710761502
Ref: library/ast ast-abstract-syntax-trees10761502
Ref: 395810761502
Ref: library/ast module-ast10761502
Ref: 710761502
Ref: ast — Abstract Syntax Trees-Footnote-110762518
Node: Abstract Grammar10762580
Ref: library/ast abstract-grammar10762683
Ref: 395a10762683
Ref: library/ast id110762683
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Node: Node classes10768611
Ref: library/ast node-classes10768734
Ref: 395c10768734
Ref: library/ast ast AST10768779
Ref: 18710768779
Ref: library/ast ast AST _fields10769609
Ref: 395d10769609
Ref: library/ast ast AST lineno10770418
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Ref: library/ast ast AST col_offset10770445
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Ref: library/ast ast AST end_lineno10770476
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Ref: library/ast ast AST end_col_offset10770507
Ref: 396110770507
Ref: Node classes-Footnote-110773538
Node: Literals<3>10773596
Ref: library/ast literals10773674
Ref: 396310773674
Ref: library/ast ast Constant10773711
Ref: 3a610773711
Ref: library/ast ast FormattedValue10774203
Ref: 396410774203
Ref: library/ast ast JoinedStr10775058
Ref: 396510775058
Ref: library/ast ast List10776076
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Ref: library/ast ast Tuple10776108
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Ref: library/ast ast Set10776989
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Ref: library/ast ast Dict10777377
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Node: Variables10778200
Ref: library/ast variables10778301
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Ref: library/ast ast Name10778340
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Ref: library/ast ast Load10778482
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Ref: library/ast ast Store10778502
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Ref: library/ast ast Del10778523
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Ref: library/ast ast Starred10779481
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Node: Expressions<2>10780311
Ref: library/ast expressions10780411
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Ref: library/ast ast Expr10780454
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Ref: library/ast ast UnaryOp10781128
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Ref: library/ast ast UAdd10781262
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Ref: library/ast ast USub10781282
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Ref: library/ast ast Not10781302
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Ref: library/ast ast Invert10781321
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Ref: library/ast ast BinOp10781672
Ref: 10d210781672
Ref: library/ast ast Add10782105
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Ref: library/ast ast Sub10782124
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Ref: library/ast ast Mult10782143
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Ref: library/ast ast Div10782163
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Ref: library/ast ast FloorDiv10782182
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Ref: library/ast ast Mod10782206
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Ref: library/ast ast Pow10782225
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Ref: library/ast ast LShift10782244
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Ref: library/ast ast RShift10782266
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Ref: library/ast ast BitOr10782288
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Ref: library/ast ast BitXor10782309
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Ref: library/ast ast BitAnd10782331
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Ref: library/ast ast MatMult10782353
Ref: 398410782353
Ref: library/ast ast BoolOp10782407
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Ref: library/ast ast And10783068
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Ref: library/ast ast Or10783087
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Ref: library/ast ast Compare10783137
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Ref: library/ast ast Eq10783783
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Ref: library/ast ast NotEq10783801
Ref: 398a10783801
Ref: library/ast ast Lt10783822
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Ref: library/ast ast LtE10783840
Ref: 398c10783840
Ref: library/ast ast Gt10783859
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Ref: library/ast ast GtE10783877
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Ref: library/ast ast Is10783896
Ref: 398f10783896
Ref: library/ast ast IsNot10783914
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Ref: library/ast ast In10783935
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Ref: library/ast ast NotIn10783953
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Ref: library/ast ast Call10784009
Ref: 396e10784009
Ref: library/ast ast keyword10785220
Ref: 399410785220
Ref: library/ast ast IfExp10785416
Ref: 399510785416
Ref: library/ast ast Attribute10785899
Ref: 399310785899
Ref: library/ast ast NamedExpr10786489
Ref: 399610786489
Node: Subscripting10787140
Ref: library/ast subscripting10787226
Ref: 399810787226
Ref: library/ast ast Subscript10787271
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Ref: library/ast ast Slice10788170
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Node: Comprehensions10788759
Ref: library/ast comprehensions10788845
Ref: 399b10788845
Ref: library/ast ast ListComp10788894
Ref: 399c10788894
Ref: library/ast ast SetComp10788936
Ref: 399d10788936
Ref: library/ast ast GeneratorExp10788977
Ref: 399e10788977
Ref: library/ast ast DictComp10789023
Ref: 399f10789023
Ref: library/ast ast comprehension10790890
Ref: 39a010790890
Node: Statements10794069
Ref: library/ast statements10794172
Ref: 39a110794172
Ref: library/ast ast Assign10794213
Ref: 399710794213
Ref: library/ast ast Assign type_comment10794556
Ref: 39a210794556
Ref: library/ast ast AnnAssign10795559
Ref: 39a310795559
Ref: library/ast ast AugAssign10797758
Ref: 39a410797758
Ref: library/ast ast Raise10798514
Ref: 39a510798514
Ref: library/ast ast Assert10799082
Ref: 39a610799082
Ref: library/ast ast Delete10799519
Ref: 39a710799519
Ref: library/ast ast Pass10800068
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Node: Imports10800401
Ref: library/ast imports10800455
Ref: 39a910800455
Ref: library/ast ast Import10800490
Ref: 39aa10800490
Ref: library/ast ast ImportFrom10800931
Ref: 39ac10800931
Ref: library/ast ast alias10801675
Ref: 39ab10801675
Node: Control flow10802225
Ref: library/ast control-flow10802344
Ref: 39ad10802344
Ref: library/ast ast If10802498
Ref: 39ae10802498
Ref: library/ast ast For10803786
Ref: 39af10803786
Ref: library/ast ast For type_comment10804273
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Ref: library/ast ast While10805029
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Ref: library/ast ast Break10805734
Ref: 39b210805734
Ref: library/ast ast Continue10805755
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Ref: library/ast ast Try10806826
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Ref: library/ast ast ExceptHandler10808434
Ref: 39b510808434
Ref: library/ast ast With10809668
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Ref: library/ast ast With type_comment10809899
Ref: 39b810809899
Ref: library/ast ast withitem10810034
Ref: 39b710810034
Node: Function and class definitions10811402
Ref: library/ast function-and-class-definitions10811526
Ref: 39b910811526
Ref: library/ast ast FunctionDef10811609
Ref: 39ba10811609
Ref: library/ast ast FunctionDef type_comment10812134
Ref: 39bc10812134
Ref: library/ast ast Lambda10812269
Ref: 397110812269
Ref: library/ast ast arguments10813089
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Ref: library/ast ast arg10813836
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Ref: library/ast ast arg type_comment10814065
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Ref: library/ast ast Return10815706
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Ref: library/ast ast Yield10815978
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Ref: library/ast ast YieldFrom10816007
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Ref: library/ast ast Global10816735
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Ref: library/ast ast Nonlocal10816765
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Ref: library/ast ast ClassDef10817476
Ref: 39c210817476
Ref: Function and class definitions-Footnote-110819273
Node: Async and await10819323
Ref: library/ast async-and-await10819426
Ref: 39c310819426
Ref: library/ast ast AsyncFunctionDef10819479
Ref: 39c410819479
Ref: library/ast ast Await10819680
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Ref: library/ast ast AsyncFor10820619
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Ref: library/ast ast AsyncWith10820686
Ref: 39c710820686
Node: ast Helpers10821321
Ref: library/ast ast-helpers10821442
Ref: 39c810821442
Ref: library/ast ast parse10821632
Ref: 2d610821632
Ref: library/ast ast unparse10824194
Ref: 18610824194
Ref: library/ast ast literal_eval10824814
Ref: 5a010824814
Ref: library/ast ast get_docstring10825763
Ref: 118a10825763
Ref: library/ast ast get_source_segment10826217
Ref: 2d510826217
Ref: library/ast ast fix_missing_locations10826667
Ref: 39ca10826667
Ref: library/ast ast increment_lineno10827123
Ref: 100310827123
Ref: library/ast ast copy_location10827355
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Ref: library/ast ast iter_fields10827589
Ref: 39cc10827589
Ref: library/ast ast iter_child_nodes10827744
Ref: 39cd10827744
Ref: library/ast ast walk10827922
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Ref: library/ast ast NodeVisitor10828188
Ref: 3a710828188
Ref: library/ast ast NodeVisitor visit10828530
Ref: 39cf10828530
Ref: library/ast ast NodeVisitor generic_visit10828810
Ref: 39d010828810
Ref: library/ast ast NodeTransformer10829645
Ref: 39d110829645
Ref: library/ast ast dump10831503
Ref: 18510831503
Ref: ast Helpers-Footnote-110832626
Ref: ast Helpers-Footnote-210832675
Ref: ast Helpers-Footnote-310832724
Node: Compiler Flags10832773
Ref: library/ast ast-compiler-flags10832903
Ref: 172010832903
Ref: library/ast compiler-flags10832903
Ref: 39d210832903
Ref: library/ast ast PyCF_ALLOW_TOP_LEVEL_AWAIT10833074
Ref: 39d310833074
Ref: library/ast ast PyCF_ONLY_AST10833256
Ref: 395910833256
Ref: library/ast ast PyCF_TYPE_COMMENTS10833387
Ref: 39c910833387
Ref: Compiler Flags-Footnote-110833614
Ref: Compiler Flags-Footnote-210833663
Node: Command-Line Usage<2>10833712
Ref: library/ast ast-cli10833822
Ref: 39d410833822
Ref: library/ast command-line-usage10833822
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Ref: library/ast cmdoption-ast-h10834083
Ref: 39d610834083
Ref: library/ast cmdoption-ast-m10834153
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Ref: library/ast cmdoption-ast-mode10834183
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Ref: library/ast cmdoption-ast-no-type-comments10834321
Ref: 39d910834321
Ref: library/ast cmdoption-ast-a10834396
Ref: 39da10834396
Ref: library/ast cmdoption-ast-i10834508
Ref: 39db10834508
Ref: library/ast cmdoption-ast-indent10834540
Ref: 39dc10834540
Ref: Command-Line Usage<2>-Footnote-110835651
Ref: Command-Line Usage<2>-Footnote-210835699
Ref: Command-Line Usage<2>-Footnote-310835766
Ref: Command-Line Usage<2>-Footnote-410835821
Ref: Command-Line Usage<2>-Footnote-510835860
Node: symtable — Access to the compiler’s symbol tables10835897
Ref: library/symtable doc10836107
Ref: 39dd10836107
Ref: library/symtable module-symtable10836107
Ref: fc10836107
Ref: library/symtable symtable-access-to-the-compiler-s-symbol-tables10836107
Ref: 39de10836107
Ref: symtable — Access to the compiler’s symbol tables-Footnote-110836689
Node: Generating Symbol Tables10836756
Ref: library/symtable generating-symbol-tables10836902
Ref: 39df10836902
Ref: library/symtable symtable symtable10836971
Ref: 110110836971
Node: Examining Symbol Tables10837251
Ref: library/symtable examining-symbol-tables10837397
Ref: 39e110837397
Ref: library/symtable symtable SymbolTable10837464
Ref: 39e010837464
Ref: library/symtable symtable SymbolTable get_type10837566
Ref: 39e210837566
Ref: library/symtable symtable SymbolTable get_id10837728
Ref: 39e310837728
Ref: library/symtable symtable SymbolTable get_name10837800
Ref: 39e410837800
Ref: library/symtable symtable SymbolTable get_lineno10838103
Ref: 39e510838103
Ref: library/symtable symtable SymbolTable is_optimized10838228
Ref: 39e610838228
Ref: library/symtable symtable SymbolTable is_nested10838337
Ref: 39e710838337
Ref: library/symtable symtable SymbolTable has_children10838441
Ref: 39e810838441
Ref: library/symtable symtable SymbolTable get_identifiers10838615
Ref: 39ea10838615
Ref: library/symtable symtable SymbolTable lookup10838712
Ref: 39eb10838712
Ref: library/symtable symtable SymbolTable get_symbols10838835
Ref: 39ed10838835
Ref: library/symtable symtable SymbolTable get_children10838960
Ref: 39e910838960
Ref: library/symtable symtable Function10839048
Ref: 39ee10839048
Ref: library/symtable symtable Function get_parameters10839173
Ref: 39ef10839173
Ref: library/symtable symtable Function get_locals10839294
Ref: 39f010839294
Ref: library/symtable symtable Function get_globals10839397
Ref: 39f110839397
Ref: library/symtable symtable Function get_nonlocals10839502
Ref: 39f210839502
Ref: library/symtable symtable Function get_frees10839611
Ref: 39f310839611
Ref: library/symtable symtable Class10839731
Ref: 39f410839731
Ref: library/symtable symtable Class get_methods10839839
Ref: 39f510839839
Ref: library/symtable symtable Symbol10839963
Ref: 39ec10839963
Ref: library/symtable symtable Symbol get_name10840119
Ref: 39f610840119
Ref: library/symtable symtable Symbol is_referenced10840188
Ref: 39f710840188
Ref: library/symtable symtable Symbol is_imported10840288
Ref: 39f810840288
Ref: library/symtable symtable Symbol is_parameter10840411
Ref: 39f910840411
Ref: library/symtable symtable Symbol is_global10840504
Ref: 39fa10840504
Ref: library/symtable symtable Symbol is_nonlocal10840589
Ref: 114610840589
Ref: library/symtable symtable Symbol is_declared_global10840678
Ref: d7e10840678
Ref: library/symtable symtable Symbol is_local10840815
Ref: 39fb10840815
Ref: library/symtable symtable Symbol is_annotated10840911
Ref: 39fc10840911
Ref: library/symtable symtable Symbol is_free10841033
Ref: 39fd10841033
Ref: library/symtable symtable Symbol is_assigned10841164
Ref: 39fe10841164
Ref: library/symtable symtable Symbol is_namespace10841269
Ref: 39ff10841269
Ref: library/symtable symtable Symbol get_namespaces10841911
Ref: 3a0010841911
Ref: library/symtable symtable Symbol get_namespace10842006
Ref: 3a0110842006
Node: symbol — Constants used with Python parse trees10842175
Ref: library/symbol doc10842404
Ref: 3a0210842404
Ref: library/symbol module-symbol10842404
Ref: fb10842404
Ref: library/symbol symbol-constants-used-with-python-parse-trees10842404
Ref: 3a0310842404
Ref: library/symbol symbol sym_name10843175
Ref: 3a0410843175
Ref: symbol — Constants used with Python parse trees-Footnote-110843430
Node: token — Constants used with Python parse trees10843495
Ref: library/token doc10843710
Ref: 3a0510843710
Ref: library/token module-token10843710
Ref: 11910843710
Ref: library/token token-constants-used-with-python-parse-trees10843710
Ref: 3a0610843710
Ref: library/token token tok_name10844424
Ref: 3a0710844424
Ref: library/token token ISTERMINAL10844642
Ref: 3a0810844642
Ref: library/token token ISNONTERMINAL10844729
Ref: 3a0910844729
Ref: library/token token ISEOF10844823
Ref: 3a0a10844823
Ref: library/token token ENDMARKER10844954
Ref: 3a0b10844954
Ref: library/token token NAME10844981
Ref: 3a0c10844981
Ref: library/token token NUMBER10845003
Ref: 3a0d10845003
Ref: library/token token STRING10845027
Ref: 3a0e10845027
Ref: library/token token NEWLINE10845051
Ref: 3a0f10845051
Ref: library/token token INDENT10845076
Ref: 3a1010845076
Ref: library/token token DEDENT10845100
Ref: 3a1110845100
Ref: library/token token LPAR10845124
Ref: 3a1210845124
Ref: library/token token RPAR10845179
Ref: 3a1310845179
Ref: library/token token LSQB10845234
Ref: 3a1410845234
Ref: library/token token RSQB10845289
Ref: 3a1510845289
Ref: library/token token COLON10845344
Ref: 3a1610845344
Ref: library/token token COMMA10845400
Ref: 3a1710845400
Ref: library/token token SEMI10845456
Ref: 3a1810845456
Ref: library/token token PLUS10845511
Ref: 3a1910845511
Ref: library/token token MINUS10845566
Ref: 3a1a10845566
Ref: library/token token STAR10845622
Ref: 3a1b10845622
Ref: library/token token SLASH10845677
Ref: 3a1c10845677
Ref: library/token token VBAR10845733
Ref: 3a1d10845733
Ref: library/token token AMPER10845788
Ref: 3a1e10845788
Ref: library/token token LESS10845844
Ref: 3a1f10845844
Ref: library/token token GREATER10845899
Ref: 3a2010845899
Ref: library/token token EQUAL10845957
Ref: 3a2110845957
Ref: library/token token DOT10846013
Ref: 3a2210846013
Ref: library/token token PERCENT10846067
Ref: 3a2310846067
Ref: library/token token LBRACE10846125
Ref: 3a2410846125
Ref: library/token token RBRACE10846182
Ref: 3a2510846182
Ref: library/token token EQEQUAL10846239
Ref: 3a2610846239
Ref: library/token token NOTEQUAL10846298
Ref: 3a2710846298
Ref: library/token token LESSEQUAL10846358
Ref: 3a2810846358
Ref: library/token token GREATEREQUAL10846419
Ref: 3a2910846419
Ref: library/token token TILDE10846483
Ref: 3a2a10846483
Ref: library/token token CIRCUMFLEX10846539
Ref: 3a2b10846539
Ref: library/token token LEFTSHIFT10846600
Ref: 3a2c10846600
Ref: library/token token RIGHTSHIFT10846661
Ref: 3a2d10846661
Ref: library/token token DOUBLESTAR10846723
Ref: 3a2e10846723
Ref: library/token token PLUSEQUAL10846785
Ref: 3a2f10846785
Ref: library/token token MINEQUAL10846846
Ref: 3a3010846846
Ref: library/token token STAREQUAL10846906
Ref: 3a3110846906
Ref: library/token token SLASHEQUAL10846967
Ref: 3a3210846967
Ref: library/token token PERCENTEQUAL10847029
Ref: 3a3310847029
Ref: library/token token AMPEREQUAL10847093
Ref: 3a3410847093
Ref: library/token token VBAREQUAL10847155
Ref: 3a3510847155
Ref: library/token token CIRCUMFLEXEQUAL10847216
Ref: 3a3610847216
Ref: library/token token LEFTSHIFTEQUAL10847283
Ref: 3a3710847283
Ref: library/token token RIGHTSHIFTEQUAL10847350
Ref: 3a3810847350
Ref: library/token token DOUBLESTAREQUAL10847418
Ref: 3a3910847418
Ref: library/token token DOUBLESLASH10847486
Ref: 3a3a10847486
Ref: library/token token DOUBLESLASHEQUAL10847549
Ref: 3a3b10847549
Ref: library/token token AT10847618
Ref: 3a3c10847618
Ref: library/token token ATEQUAL10847671
Ref: 3a3d10847671
Ref: library/token token RARROW10847730
Ref: 3a3e10847730
Ref: library/token token ELLIPSIS10847788
Ref: 3a3f10847788
Ref: library/token token COLONEQUAL10847849
Ref: 3a4010847849
Ref: library/token token OP10847911
Ref: 3a4110847911
Ref: library/token token AWAIT10847931
Ref: 3a4210847931
Ref: library/token token ASYNC10847954
Ref: 3a4310847954
Ref: library/token token TYPE_IGNORE10847977
Ref: 3a4410847977
Ref: library/token token TYPE_COMMENT10848006
Ref: 3a4510848006
Ref: library/token token ERRORTOKEN10848036
Ref: 3a4610848036
Ref: library/token token N_TOKENS10848064
Ref: 3a4710848064
Ref: library/token token NT_OFFSET10848090
Ref: 3a4810848090
Ref: library/token token COMMENT10848235
Ref: 3a4910848235
Ref: library/token token NL10848306
Ref: 3a4a10848306
Ref: library/token token ENCODING10848588
Ref: 3a4b10848588
Ref: token — Constants used with Python parse trees-Footnote-110849700
Node: keyword — Testing for Python keywords10849764
Ref: library/keyword doc10849970
Ref: 3a4c10849970
Ref: library/keyword keyword-testing-for-python-keywords10849970
Ref: 3a4d10849970
Ref: library/keyword module-keyword10849970
Ref: a610849970
Ref: library/keyword keyword iskeyword10850261
Ref: 177f10850261
Ref: library/keyword keyword kwlist10850362
Ref: 3a4e10850362
Ref: library/keyword keyword issoftkeyword10850630
Ref: 3a4f10850630
Ref: library/keyword keyword softkwlist10850766
Ref: 3a5010850766
Ref: keyword — Testing for Python keywords-Footnote-110851110
Node: tokenize — Tokenizer for Python source10851176
Ref: library/tokenize doc10851381
Ref: 3a5110851381
Ref: library/tokenize module-tokenize10851381
Ref: 11a10851381
Ref: library/tokenize tokenize-tokenizer-for-python-source10851381
Ref: 3a5210851381
Ref: tokenize — Tokenizer for Python source-Footnote-110852332
Node: Tokenizing Input10852399
Ref: library/tokenize tokenizing-input10852522
Ref: 3a5310852522
Ref: library/tokenize tokenize tokenize10852628
Ref: d2310852628
Ref: library/tokenize tokenize generate_tokens10854062
Ref: 116b10854062
Ref: library/tokenize tokenize untokenize10854829
Ref: 3a5410854829
Ref: library/tokenize tokenize detect_encoding10855773
Ref: 1ddd10855773
Ref: library/tokenize tokenize open10856769
Ref: 1ddc10856769
Ref: library/tokenize tokenize TokenError10856938
Ref: 3a5510856938
Ref: Tokenizing Input-Footnote-110857427
Ref: Tokenizing Input-Footnote-210857476
Node: Command-Line Usage<3>10857525
Ref: library/tokenize command-line-usage10857669
Ref: 3a5610857669
Ref: library/tokenize tokenize-cli10857669
Ref: 3a5710857669
Ref: library/tokenize cmdoption-tokenize-h10857933
Ref: 3a5810857933
Ref: library/tokenize cmdoption-tokenize-e10858003
Ref: 3a5910858003
Node: Examples<31>10858203
Ref: library/tokenize examples10858322
Ref: 3a5a10858322
Node: tabnanny — Detection of ambiguous indentation10862816
Ref: library/tabnanny doc10863022
Ref: 3a5b10863022
Ref: library/tabnanny module-tabnanny10863022
Ref: 10010863022
Ref: library/tabnanny tabnanny-detection-of-ambiguous-indentation10863022
Ref: 3a5c10863022
Ref: library/tabnanny tabnanny check10863553
Ref: 3a5d10863553
Ref: library/tabnanny tabnanny verbose10863993
Ref: 3a5e10863993
Ref: library/tabnanny tabnanny filename_only10864150
Ref: 3a5f10864150
Ref: library/tabnanny tabnanny NannyNag10864368
Ref: 3a6010864368
Ref: library/tabnanny tabnanny process_tokens10864533
Ref: 3a6110864533
Ref: tabnanny — Detection of ambiguous indentation-Footnote-110864832
Node: pyclbr — Python module browser support10864899
Ref: library/pyclbr doc10865107
Ref: 3a6210865107
Ref: library/pyclbr module-pyclbr10865107
Ref: d810865107
Ref: library/pyclbr pyclbr-python-module-browser-support10865107
Ref: 3a6310865107
Ref: library/pyclbr pyclbr readmodule10865805
Ref: 129e10865805
Ref: library/pyclbr pyclbr readmodule_ex10866416
Ref: 129f10866416
Ref: pyclbr — Python module browser support-Footnote-110867492
Node: Function Objects10867557
Ref: library/pyclbr function-objects10867675
Ref: 3a6410867675
Ref: library/pyclbr pyclbr-function-objects10867675
Ref: 3a6510867675
Ref: library/pyclbr pyclbr Function file10867842
Ref: 3a6610867842
Ref: library/pyclbr pyclbr Function module10867929
Ref: 3a6710867929
Ref: library/pyclbr pyclbr Function name10868023
Ref: 3a6810868023
Ref: library/pyclbr pyclbr Function lineno10868085
Ref: 3a6910868085
Ref: library/pyclbr pyclbr Function parent10868180
Ref: 3a6a10868180
Ref: library/pyclbr pyclbr Function children10868310
Ref: 3a6b10868310
Node: Class Objects<2>10868457
Ref: library/pyclbr class-objects10868575
Ref: 3a6c10868575
Ref: library/pyclbr pyclbr-class-objects10868575
Ref: 3a6d10868575
Ref: library/pyclbr pyclbr Class file10868754
Ref: 3a6e10868754
Ref: library/pyclbr pyclbr Class module10868835
Ref: 3a6f10868835
Ref: library/pyclbr pyclbr Class name10868923
Ref: 3a7010868923
Ref: library/pyclbr pyclbr Class lineno10868979
Ref: 3a7110868979
Ref: library/pyclbr pyclbr Class parent10869071
Ref: 3a7210869071
Ref: library/pyclbr pyclbr Class children10869194
Ref: 3a7310869194
Ref: library/pyclbr pyclbr Class super10869338
Ref: 3a7410869338
Ref: library/pyclbr pyclbr Class methods10869676
Ref: 3a7510869676
Node: py_compile — Compile Python source files10869866
Ref: library/py_compile doc10870071
Ref: 3a7610870071
Ref: library/py_compile module-py_compile10870071
Ref: d710870071
Ref: library/py_compile py-compile-compile-python-source-files10870071
Ref: 3a7710870071
Ref: library/py_compile py_compile PyCompileError10870696
Ref: 3a7810870696
Ref: library/py_compile py_compile compile10870825
Ref: 34310870825
Ref: library/py_compile py_compile PycInvalidationMode10874515
Ref: 3a7910874515
Ref: library/py_compile py_compile PycInvalidationMode TIMESTAMP10874936
Ref: 3a7b10874936
Ref: library/py_compile py_compile PycInvalidationMode CHECKED_HASH10875218
Ref: 3a7a10875218
Ref: library/py_compile py_compile PycInvalidationMode UNCHECKED_HASH10875464
Ref: 3a7c10875464
Ref: library/py_compile py_compile main10875913
Ref: 3a7d10875913
Ref: py_compile — Compile Python source files-Footnote-110876787
Ref: py_compile — Compile Python source files-Footnote-210876856
Ref: py_compile — Compile Python source files-Footnote-310876905
Ref: py_compile — Compile Python source files-Footnote-410876954
Ref: py_compile — Compile Python source files-Footnote-510877003
Node: compileall — Byte-compile Python libraries10877052
Ref: library/compileall doc10877257
Ref: 3a7e10877257
Ref: library/compileall compileall-byte-compile-python-libraries10877257
Ref: 3a7f10877257
Ref: library/compileall module-compileall10877257
Ref: 2010877257
Ref: compileall — Byte-compile Python libraries-Footnote-110877917
Node: Command-line use10877986
Ref: library/compileall command-line-use10878108
Ref: 3a8010878108
Ref: library/compileall cmdoption-compileall-arg-directory10878259
Ref: 3a8110878259
Ref: library/compileall cmdoption-compileall-arg-file10878293
Ref: 3a8210878293
Ref: library/compileall cmdoption-compileall-l10878549
Ref: 3a8310878549
Ref: library/compileall cmdoption-compileall-f10878707
Ref: 3a8410878707
Ref: library/compileall cmdoption-compileall-q10878786
Ref: 3a8510878786
Ref: library/compileall cmdoption-compileall-d10878978
Ref: 3a8610878978
Ref: library/compileall cmdoption-compileall-s10879339
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Ref: library/compileall cmdoption-compileall-p10879376
Ref: 3a8810879376
Ref: library/compileall cmdoption-compileall-x10879560
Ref: 3a8910879560
Ref: library/compileall cmdoption-compileall-i10879741
Ref: 3a8a10879741
Ref: library/compileall cmdoption-compileall-b10879951
Ref: 3a8b10879951
Ref: library/compileall cmdoption-compileall-r10880285
Ref: 3a8c10880285
Ref: library/compileall cmdoption-compileall-j10880563
Ref: 3a8d10880563
Ref: library/compileall cmdoption-compileall-invalidation-mode10880750
Ref: 3a8e10880750
Ref: library/compileall cmdoption-compileall-o10881567
Ref: 3a8f10881567
Ref: library/compileall cmdoption-compileall-e10881768
Ref: 3a9010881768
Ref: library/compileall cmdoption-compileall-hardlink-dupes10881856
Ref: 3a9110881856
Ref: Command-line use-Footnote-110883159
Node: Public functions10883208
Ref: library/compileall public-functions10883330
Ref: 3a9210883330
Ref: library/compileall compileall compile_dir10883385
Ref: 47a10883385
Ref: library/compileall compileall compile_file10887538
Ref: 7ae10887538
Ref: library/compileall compileall compile_path10890541
Ref: 7af10890541
Ref: Public functions-Footnote-110892269
Ref: Public functions-Footnote-210892318
Node: dis — Disassembler for Python bytecode10892367
Ref: library/dis doc10892573
Ref: 3a9310892573
Ref: library/dis dis-disassembler-for-python-bytecode10892573
Ref: 3a9410892573
Ref: library/dis module-dis10892573
Ref: 3710892573
Ref: dis — Disassembler for Python bytecode-Footnote-110894013
Node: Bytecode analysis10894075
Ref: library/dis bytecode-analysis10894196
Ref: 3a9510894196
Ref: library/dis dis Bytecode10894436
Ref: 92410894436
Ref: library/dis dis Bytecode from_traceback10895463
Ref: 92610895463
Ref: library/dis dis Bytecode codeobj10895687
Ref: 3a9610895687
Ref: library/dis dis Bytecode first_line10895748
Ref: 3a9710895748
Ref: library/dis dis Bytecode dis10895842
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Ref: library/dis dis Bytecode info10896033
Ref: 3a9810896033
Node: Analysis functions10896491
Ref: library/dis analysis-functions10896649
Ref: 3a9910896649
Ref: library/dis dis code_info10896955
Ref: c9c10896955
Ref: library/dis dis show_code10897494
Ref: 91f10897494
Ref: library/dis dis dis10897958
Ref: 48b10897958
Ref: library/dis dis distb10899394
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Ref: library/dis dis disassemble10899790
Ref: 92110899790
Ref: library/dis dis disco10899851
Ref: 3a9a10899851
Ref: library/dis dis get_instructions10900738
Ref: 92310900738
Ref: library/dis dis findlinestarts10901350
Ref: 3a9b10901350
Ref: library/dis dis findlabels10901838
Ref: 3a9c10901838
Ref: library/dis dis stack_effect10902008
Ref: 92710902008
Ref: Analysis functions-Footnote-110902576
Node: Python Bytecode Instructions10902653
Ref: library/dis bytecodes10902812
Ref: 3a9d10902812
Ref: library/dis python-bytecode-instructions10902812
Ref: 3a9e10902812
Ref: library/dis dis Instruction10903046
Ref: 92210903046
Ref: library/dis dis Instruction opcode10903113
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Ref: library/dis dis Instruction opname10903306
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Ref: library/dis dis Instruction arg10903374
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Ref: library/dis dis Instruction argval10903466
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Ref: library/dis dis Instruction argrepr10903553
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Ref: library/dis dis Instruction offset10903637
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Ref: library/dis dis Instruction starts_line10903721
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Ref: library/dis dis Instruction is_jump_target10903819
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Ref: library/dis opcode-NOP10904051
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Ref: library/dis opcode-POP_TOP10904141
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Ref: library/dis opcode-ROT_TWO10904205
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Ref: library/dis opcode-ROT_THREE10904268
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Ref: library/dis opcode-ROT_FOUR10904387
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Ref: library/dis opcode-DUP_TOP10904539
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Ref: library/dis opcode-DUP_TOP_TWO10904638
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Ref: library/dis opcode-UNARY_POSITIVE10904908
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Ref: library/dis opcode-UNARY_NEGATIVE10904971
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Ref: library/dis opcode-UNARY_NOT10905034
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Ref: library/dis opcode-UNARY_INVERT10905095
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Ref: library/dis opcode-GET_ITER10905156
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Ref: library/dis opcode-GET_YIELD_FROM_ITER10905218
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Ref: library/dis opcode-BINARY_POWER10905637
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Ref: library/dis opcode-BINARY_MULTIPLY10905705
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Ref: library/dis opcode-BINARY_MATRIX_MULTIPLY10905775
Ref: 3ab610905775
Ref: library/dis opcode-BINARY_FLOOR_DIVIDE10905878
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Ref: library/dis opcode-BINARY_TRUE_DIVIDE10905953
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Ref: library/dis opcode-BINARY_MODULO10906026
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Ref: library/dis opcode-BINARY_ADD10906094
Ref: 3aba10906094
Ref: library/dis opcode-BINARY_SUBTRACT10906159
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Ref: library/dis opcode-BINARY_SUBSCR10906229
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Ref: library/dis opcode-BINARY_LSHIFT10906296
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Ref: library/dis opcode-BINARY_RSHIFT10906365
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Ref: library/dis opcode-BINARY_AND10906434
Ref: 3abf10906434
Ref: library/dis opcode-BINARY_XOR10906499
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Ref: library/dis opcode-BINARY_OR10906564
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Ref: library/dis opcode-INPLACE_POWER10906905
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Ref: library/dis opcode-INPLACE_MULTIPLY10906983
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Ref: library/dis opcode-INPLACE_MATRIX_MULTIPLY10907063
Ref: 3ac410907063
Ref: library/dis opcode-INPLACE_FLOOR_DIVIDE10907176
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Ref: library/dis opcode-INPLACE_TRUE_DIVIDE10907261
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Ref: library/dis opcode-INPLACE_MODULO10907344
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Ref: library/dis opcode-INPLACE_ADD10907422
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Ref: library/dis opcode-INPLACE_SUBTRACT10907497
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Ref: library/dis opcode-INPLACE_LSHIFT10907577
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Ref: library/dis opcode-INPLACE_RSHIFT10907656
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Ref: library/dis opcode-INPLACE_AND10907735
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Ref: library/dis opcode-INPLACE_XOR10907810
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Ref: library/dis opcode-INPLACE_OR10907885
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Ref: library/dis opcode-STORE_SUBSCR10907959
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Ref: library/dis opcode-DELETE_SUBSCR10908026
Ref: 3ad010908026
Ref: library/dis opcode-GET_AWAITABLE10908112
Ref: 3ad110908112
Ref: library/dis opcode-GET_AITER10908392
Ref: 3ad210908392
Ref: library/dis opcode-GET_ANEXT10908595
Ref: 3ad310908595
Ref: library/dis opcode-END_ASYNC_FOR10908773
Ref: 3fc10908773
Ref: library/dis opcode-BEFORE_ASYNC_WITH10909224
Ref: 3ad410909224
Ref: library/dis opcode-SETUP_ASYNC_WITH10909451
Ref: 3ad510909451
Ref: library/dis opcode-PRINT_EXPR10909566
Ref: 3ad610909566
Ref: library/dis opcode-SET_ADD10909802
Ref: 3ad710909802
Ref: library/dis opcode-LIST_APPEND10909913
Ref: 3ad810909913
Ref: library/dis opcode-MAP_ADD10910033
Ref: 3fe10910033
Ref: library/dis opcode-RETURN_VALUE10910545
Ref: 3ad910910545
Ref: library/dis opcode-YIELD_VALUE10910625
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Ref: library/dis opcode-YIELD_FROM10910708
Ref: 3adb10910708
Ref: library/dis opcode-SETUP_ANNOTATIONS10910844
Ref: 71110910844
Ref: library/dis opcode-IMPORT_STAR10911142
Ref: 3adc10911142
Ref: library/dis opcode-POP_BLOCK10911381
Ref: 3add10911381
Ref: library/dis opcode-POP_EXCEPT10911542
Ref: 3ade10911542
Ref: library/dis opcode-RERAISE10911875
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Ref: library/dis opcode-WITH_EXCEPT_START10911983
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Ref: library/dis opcode-LOAD_ASSERTION_ERROR10912295
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Ref: library/dis opcode-LOAD_BUILD_CLASS10912459
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Ref: library/dis opcode-SETUP_WITH10912627
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Ref: library/dis opcode-STORE_NAME10913348
Ref: 3ae410913348
Ref: library/dis opcode-DELETE_NAME10913602
Ref: 3ae710913602
Ref: library/dis opcode-UNPACK_SEQUENCE10913750
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Ref: library/dis opcode-BUILD_MAP10915365
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Ref: library/dis opcode-BUILD_CONST_KEY_MAP10915725
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Ref: library/dis opcode-BUILD_STRING10916040
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Ref: library/dis opcode-LIST_EXTEND10916341
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Ref: library/dis opcode-DICT_UPDATE10916584
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Ref: library/dis opcode-DICT_MERGE10916707
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Ref: library/dis opcode-LOAD_ATTR10916842
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Ref: library/dis opcode-COMPARE_OP10916934
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Ref: library/dis opcode-IMPORT_FROM10917725
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Ref: library/dis opcode-JUMP_FORWARD10917961
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Ref: library/dis opcode-POP_JUMP_IF_TRUE10918041
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Ref: library/dis opcode-JUMP_IF_NOT_EXC_MATCH10918337
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Ref: library/dis opcode-JUMP_IF_TRUE_OR_POP10918554
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Ref: library/dis opcode-JUMP_IF_FALSE_OR_POP10918758
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Ref: library/dis opcode-JUMP_ABSOLUTE10918963
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Ref: library/dis opcode-SETUP_FINALLY10919458
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Ref: library/dis opcode-LOAD_FAST10919654
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Ref: library/dis opcode-STORE_FAST10919773
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Ref: library/dis opcode-DELETE_FAST10919867
Ref: 3b0710919867
Ref: library/dis opcode-LOAD_CLOSURE10919950
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Ref: library/dis opcode-LOAD_CLASSDEREF10920435
Ref: a1310920435
Ref: library/dis opcode-STORE_DEREF10920669
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Ref: library/dis opcode-DELETE_DEREF10920795
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Ref: library/dis opcode-RAISE_VARARGS10920981
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Ref: library/dis opcode-CALL_FUNCTION10921406
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Ref: 71010922919
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Ref: library/dis opcode-MAKE_FUNCTION10924626
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Ref: library/dis opcode-FORMAT_VALUE10925931
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Ref: library/dis opcode-HAVE_ARGUMENT10926791
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Ref: 3aa010927348
Ref: library/dis dis opname10927493
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Ref: library/dis dis opmap10927580
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Ref: library/dis dis cmp_op10927656
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Ref: library/dis dis hasfree10927801
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Ref: library/dis dis hasjrel10928222
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Ref: library/dis dis hasjabs10928307
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Ref: library/dis dis haslocal10928393
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Ref: library/dis dis hascompare10928475
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Node: pickletools — Tools for pickle developers10928552
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Ref: library/pickletools module-pickletools10928705
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Ref: library/pickletools pickletools-tools-for-pickle-developers10928705
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Ref: pickletools — Tools for pickle developers-Footnote-110929496
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Node: Command line options<3>10930654
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Ref: library/pickletools cmdoption-pickletools-a10930798
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Ref: library/pickletools cmdoption-pickletools-o10930892
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Ref: library/pickletools cmdoption-pickletools-m10931099
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Ref: library/pickletools cmdoption-pickletools-p10931219
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Node: Programmatic Interface<2>10931369
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Ref: library/pickletools pickletools dis10931571
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Ref: library/pickletools pickletools genops10932400
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Ref: library/pickletools pickletools optimize10932837
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Ref: library/misc misc10933273
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Ref: library/misc miscellaneous-services10933273
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Node: formatter — Generic output formatting10933520
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Ref: library/formatter formatter-generic-output-formatting10933618
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Ref: library/formatter module-formatter10933618
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Node: The Formatter Interface10935201
Ref: library/formatter formatter-interface10935334
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Ref: library/formatter the-formatter-interface10935334
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Ref: library/formatter formatter AS_IS10935662
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Ref: library/formatter formatter formatter writer10936109
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Ref: library/formatter formatter formatter end_paragraph10936204
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Ref: library/formatter formatter formatter add_hor_rule10936500
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Ref: library/formatter formatter formatter add_flowing_data10936813
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Ref: library/formatter formatter formatter add_literal_data10937333
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Ref: library/formatter formatter formatter add_label_data10937552
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Ref: library/formatter formatter formatter flush_softspace10938979
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Ref: library/formatter formatter formatter push_alignment10939244
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Ref: library/formatter formatter formatter pop_alignment10939563
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Ref: library/formatter formatter formatter pop_font10940022
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Ref: library/formatter formatter formatter pop_margin10940457
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Ref: library/formatter formatter formatter pop_style10940832
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Ref: library/formatter formatter formatter set_spacing10941099
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Ref: library/formatter formatter formatter assert_line_data10941188
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Node: Formatter Implementations10941546
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Ref: 3b4010941708
Ref: library/formatter formatter-impls10941708
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Ref: library/formatter formatter NullFormatter10941934
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Ref: library/formatter formatter AbstractFormatter10942322
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Node: The Writer Interface10942609
Ref: library/formatter the-writer-interface10942770
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Ref: library/formatter writer-interface10942770
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Ref: library/formatter formatter writer flush10943191
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Ref: library/formatter formatter writer new_alignment10943278
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Ref: library/formatter formatter writer new_margin10944168
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Ref: library/formatter formatter writer new_spacing10944498
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Ref: library/formatter formatter writer new_styles10944582
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Ref: library/formatter formatter writer send_line_break10944916
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Ref: library/formatter formatter writer send_paragraph10944985
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Ref: library/formatter formatter writer send_hor_rule10945461
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Ref: library/formatter formatter writer send_flowing_data10945812
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Ref: library/formatter formatter writer send_literal_data10946112
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Ref: library/formatter formatter writer send_label_data10946542
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Node: Writer Implementations10946848
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Ref: library/formatter writer-impls10946975
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Ref: library/formatter formatter AbstractWriter10947478
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Ref: library/formatter formatter DumbWriter10947694
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Node: MS Windows Specific Services10948060
Ref: library/windows doc10948214
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Ref: library/windows ms-windows-specific-services10948214
Ref: 3b5810948214
Ref: library/windows mswin-specific-services10948214
Ref: 14c710948214
Node: msilib — Read and write Microsoft Installer files10948578
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Ref: library/msilib module-msilib10948754
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Ref: library/msilib msilib-read-and-write-microsoft-installer-files10948754
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Ref: library/msilib msilib FCICreate10949828
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Ref: library/msilib msilib UuidCreate10950329
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Ref: library/msilib msilib OpenDatabase10950525
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Ref: library/msilib msilib CreateRecord10951077
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Ref: library/msilib msilib init_database10951242
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Ref: library/msilib msilib add_data10951813
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Ref: library/msilib msilib add_tables10952583
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Ref: library/msilib msilib add_stream10952924
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Ref: library/msilib msilib gen_uuid10953084
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Ref: msilib — Read and write Microsoft Installer files-Footnote-110953563
Ref: msilib — Read and write Microsoft Installer files-Footnote-210953637
Ref: msilib — Read and write Microsoft Installer files-Footnote-310953700
Ref: msilib — Read and write Microsoft Installer files-Footnote-410953780
Node: Database Objects10953860
Ref: library/msilib database-objects10953985
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Ref: library/msilib id110953985
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Ref: library/msilib msilib Database OpenView10954038
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Ref: library/msilib msilib Database Commit10954188
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Ref: library/msilib msilib Database GetSummaryInformation10954324
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Ref: library/msilib msilib Database Close10954528
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Ref: Database Objects-Footnote-210954876
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Node: View Objects10955116
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Ref: library/msilib view-objects10955277
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Ref: library/msilib msilib View Execute10955322
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Ref: library/msilib msilib View GetColumnInfo10955550
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Ref: library/msilib msilib View Fetch10955775
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Ref: library/msilib msilib View Modify10955888
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Ref: library/msilib msilib View Close10956439
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Ref: View Objects-Footnote-210956745
Ref: View Objects-Footnote-310956825
Ref: View Objects-Footnote-410956905
Ref: View Objects-Footnote-510956985
Node: Summary Information Objects10957065
Ref: library/msilib summary-information-objects10957224
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Ref: library/msilib summary-objects10957224
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Ref: library/msilib msilib SummaryInformation GetProperty10957299
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Ref: library/msilib msilib SummaryInformation GetPropertyCount10957890
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Ref: library/msilib msilib SummaryInformation SetProperty10958042
Ref: 3b7210958042
Ref: library/msilib msilib SummaryInformation Persist10958335
Ref: 3b7310958335
Ref: Summary Information Objects-Footnote-110958664
Ref: Summary Information Objects-Footnote-210958744
Ref: Summary Information Objects-Footnote-310958824
Ref: Summary Information Objects-Footnote-410958904
Node: Record Objects10958984
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Ref: library/msilib record-objects10959137
Ref: 3b7510959137
Ref: library/msilib msilib Record GetFieldCount10959186
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Ref: library/msilib msilib Record GetInteger10959317
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Ref: library/msilib msilib Record GetString10959454
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Ref: library/msilib msilib Record SetString10959588
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Ref: library/msilib msilib Record SetStream10959750
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Ref: library/msilib msilib Record SetInteger10959949
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Ref: library/msilib msilib Record ClearData10960112
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Ref: Record Objects-Footnote-110960393
Ref: Record Objects-Footnote-210960473
Ref: Record Objects-Footnote-310960553
Ref: Record Objects-Footnote-410960633
Ref: Record Objects-Footnote-510960713
Node: Errors10960793
Ref: library/msilib errors10960930
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Ref: library/msilib msi-errors10960930
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Node: CAB Objects10961078
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Ref: library/msilib cab-objects10961218
Ref: 3b8010961218
Ref: library/msilib msilib CAB10961261
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Ref: library/msilib msilib CAB append10961622
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Ref: library/msilib msilib CAB commit10961971
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Node: Directory Objects10962175
Ref: library/msilib directory-objects10962320
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Ref: library/msilib msi-directory10962320
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Ref: library/msilib msilib Directory10962375
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Ref: library/msilib msilib Directory start_component10963144
Ref: 10ff10963144
Ref: library/msilib msilib Directory add_file10963685
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Ref: library/msilib msilib Directory glob10964182
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Ref: library/msilib msilib Directory remove_pyc10964396
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Ref: Directory Objects-Footnote-110964612
Ref: Directory Objects-Footnote-210964692
Ref: Directory Objects-Footnote-310964772
Ref: Directory Objects-Footnote-410964852
Node: Features<3>10964932
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Ref: library/msilib id410965077
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Ref: library/msilib msilib Feature10965114
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Ref: library/msilib msilib Feature set_current10965512
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Ref: Features<3>-Footnote-110965813
Node: GUI classes10965893
Ref: library/msilib gui-classes10966039
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Ref: library/msilib msi-gui10966039
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Ref: library/msilib msilib Control10966320
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Ref: library/msilib msilib Control event10966493
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Ref: library/msilib msilib Control mapping10966640
Ref: 3b9210966640
Ref: library/msilib msilib Control condition10966762
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Ref: library/msilib msilib RadioButtonGroup10966901
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Ref: library/msilib msilib RadioButtonGroup add10967099
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Ref: library/msilib msilib Dialog10967369
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Ref: library/msilib msilib Dialog control10967674
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Ref: library/msilib msilib Dialog text10968037
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Ref: library/msilib msilib Dialog bitmap10968154
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Ref: library/msilib msilib Dialog line10968263
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Ref: library/msilib msilib Dialog pushbutton10968362
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Ref: library/msilib msilib Dialog radiogroup10968520
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Ref: library/msilib msilib Dialog checkbox10968694
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Ref: GUI classes-Footnote-110969055
Ref: GUI classes-Footnote-210969135
Ref: GUI classes-Footnote-310969215
Ref: GUI classes-Footnote-410969295
Ref: GUI classes-Footnote-510969375
Ref: GUI classes-Footnote-610969455
Ref: GUI classes-Footnote-710969535
Node: Precomputed tables10969615
Ref: library/msilib msi-tables10969741
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Ref: library/msilib precomputed-tables10969741
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Ref: library/msilib msilib schema10969954
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Ref: library/msilib msilib sequence10970171
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Ref: library/msilib msilib text10970406
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Node: msvcrt — Useful routines from the MS VC++ runtime10970547
Ref: library/msvcrt doc10970766
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Ref: library/msvcrt module-msvcrt10970766
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Ref: library/msvcrt msvcrt-useful-routines-from-the-ms-vc-runtime10970766
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Ref: library/msvcrt file-operations10971904
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Ref: library/msvcrt msvcrt-files10971904
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Ref: library/msvcrt msvcrt locking10971955
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Ref: library/msvcrt msvcrt LK_LOCK10972618
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Ref: library/msvcrt msvcrt LK_RLCK10972643
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Ref: library/msvcrt msvcrt LK_NBLCK10972884
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Ref: library/msvcrt msvcrt LK_NBRLCK10972910
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Ref: library/msvcrt msvcrt LK_UNLCK10973039
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Ref: library/msvcrt msvcrt setmode10973146
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Ref: library/msvcrt msvcrt open_osfhandle10973385
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Ref: library/msvcrt msvcrt get_osfhandle10973883
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Ref: library/msvcrt msvcrt-console10974289
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Ref: library/msvcrt msvcrt kbhit10974332
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Ref: library/msvcrt msvcrt getch10974424
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Ref: library/msvcrt msvcrt getwch10974905
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Ref: library/msvcrt msvcrt getche10975017
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Ref: library/msvcrt msvcrt getwche10975164
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Ref: library/msvcrt msvcrt putch10975278
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Ref: library/msvcrt msvcrt putwch10975382
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Ref: library/msvcrt msvcrt ungetch10975506
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Ref: library/msvcrt msvcrt ungetwch10975721
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Ref: library/msvcrt other-functions10975972
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Ref: library/msvcrt msvcrt heapmin10976023
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Node: winreg — Windows registry access10976216
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Ref: library/winreg module-winreg10976432
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Ref: library/winreg winreg-windows-registry-access10976432
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Ref: library/winreg exception-changed10976846
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Node: Functions<12>10977086
Ref: library/winreg functions10977192
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Ref: library/winreg id110977192
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Ref: library/winreg winreg CloseKey10977276
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Ref: library/winreg winreg ConnectRegistry10977597
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Ref: library/winreg winreg CreateKey10978288
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Ref: library/winreg winreg CreateKeyEx10979248
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Ref: library/winreg winreg DeleteKey10980584
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Ref: library/winreg winreg DeleteKeyEx10981332
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Ref: library/winreg winreg DeleteValue10982794
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Ref: library/winreg winreg EnumKey10983161
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Ref: library/winreg winreg EnumValue10983827
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Ref: library/winreg winreg ExpandEnvironmentStrings10985092
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Ref: library/winreg winreg FlushKey10985442
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Ref: library/winreg winreg LoadKey10986262
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Ref: library/winreg winreg OpenKey10987454
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Ref: library/winreg winreg OpenKeyEx10987527
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Ref: library/winreg winreg QueryInfoKey10988608
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Ref: library/winreg winreg QueryValue10989503
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Ref: library/winreg winreg QueryValueEx10990379
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Ref: library/winreg winreg SaveKey10991254
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Ref: library/winreg winreg SetValue10992299
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Ref: library/winreg winreg SetValueEx10993477
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Ref: library/winreg winreg DisableReflectionKey10994724
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Ref: library/winreg winreg EnableReflectionKey10995355
Ref: 3be410995355
Ref: library/winreg winreg QueryReflectionKey10995863
Ref: 3be510995863
Ref: Functions<12>-Footnote-110996366
Ref: Functions<12>-Footnote-210996440
Ref: Functions<12>-Footnote-310996517
Node: Constants<10>10996594
Ref: library/winreg constants10996732
Ref: 3be610996732
Ref: library/winreg id210996732
Ref: 3be710996732
Node: HKEY_* Constants10996914
Ref: library/winreg hkey-constants10997002
Ref: 3bc710997002
Ref: library/winreg id310997002
Ref: 3be810997002
Ref: library/winreg winreg HKEY_CLASSES_ROOT10997055
Ref: 3be910997055
Ref: library/winreg winreg HKEY_CURRENT_USER10997306
Ref: 3bea10997306
Ref: library/winreg winreg HKEY_LOCAL_MACHINE10997609
Ref: 3bd710997609
Ref: library/winreg winreg HKEY_USERS10997833
Ref: 3bd610997833
Ref: library/winreg winreg HKEY_PERFORMANCE_DATA10998042
Ref: 3beb10998042
Ref: library/winreg winreg HKEY_CURRENT_CONFIG10998309
Ref: 3bec10998309
Ref: library/winreg winreg HKEY_DYN_DATA10998444
Ref: 3bed10998444
Node: Access Rights10998536
Ref: library/winreg access-rights10998644
Ref: 3bca10998644
Ref: library/winreg id410998644
Ref: 3bee10998644
Ref: library/winreg winreg KEY_ALL_ACCESS10998755
Ref: 3bef10998755
Ref: library/winreg winreg KEY_WRITE10999044
Ref: 3bc910999044
Ref: library/winreg winreg KEY_READ10999197
Ref: 3bdb10999197
Ref: library/winreg winreg KEY_EXECUTE10999376
Ref: 3bf510999376
Ref: library/winreg winreg KEY_QUERY_VALUE10999448
Ref: 3bf010999448
Ref: library/winreg winreg KEY_SET_VALUE10999536
Ref: 3be110999536
Ref: library/winreg winreg KEY_CREATE_SUB_KEY10999627
Ref: 3bf110999627
Ref: library/winreg winreg KEY_ENUMERATE_SUB_KEYS10999717
Ref: 3bf210999717
Ref: library/winreg winreg KEY_NOTIFY10999817
Ref: 3bf310999817
Ref: library/winreg winreg KEY_CREATE_LINK10999951
Ref: 3bf410999951
Ref: Access Rights-Footnote-111000082
Node: 64-bit Specific11000159
Ref: library/winreg bit-access-rights11000224
Ref: 3bf611000224
Ref: library/winreg bit-specific11000224
Ref: 3bf711000224
Ref: library/winreg winreg KEY_WOW64_64KEY11000343
Ref: 3bcd11000343
Ref: library/winreg winreg KEY_WOW64_32KEY11000480
Ref: 3bf811000480
Ref: 64-bit Specific-Footnote-111000653
Node: Value Types11000725
Ref: library/winreg id511000808
Ref: 3bf911000808
Ref: library/winreg value-types11000808
Ref: 3be211000808
Ref: library/winreg winreg REG_BINARY11000903
Ref: 3bfa11000903
Ref: library/winreg winreg REG_DWORD11000963
Ref: 3bfb11000963
Ref: library/winreg winreg REG_DWORD_LITTLE_ENDIAN11001012
Ref: 3bfc11001012
Ref: library/winreg winreg REG_DWORD_BIG_ENDIAN11001144
Ref: 3bfd11001144
Ref: library/winreg winreg REG_EXPAND_SZ11001227
Ref: 3bd311001227
Ref: library/winreg winreg REG_LINK11001356
Ref: 3bfe11001356
Ref: library/winreg winreg REG_MULTI_SZ11001414
Ref: 10ea11001414
Ref: library/winreg winreg REG_NONE11001580
Ref: 3bff11001580
Ref: library/winreg winreg REG_QWORD11001636
Ref: 6a911001636
Ref: library/winreg winreg REG_QWORD_LITTLE_ENDIAN11001713
Ref: 3c0011001713
Ref: library/winreg winreg REG_RESOURCE_LIST11001870
Ref: 3c0111001870
Ref: library/winreg winreg REG_FULL_RESOURCE_DESCRIPTOR11001943
Ref: 3c0211001943
Ref: library/winreg winreg REG_RESOURCE_REQUIREMENTS_LIST11002016
Ref: 3c0311002016
Ref: library/winreg winreg REG_SZ11002097
Ref: 3be011002097
Ref: Value Types-Footnote-111002190
Node: Registry Handle Objects11002267
Ref: library/winreg handle-object11002383
Ref: 3bbf11002383
Ref: library/winreg registry-handle-objects11002383
Ref: 3c0411002383
Ref: library/winreg winreg PyHKEY Close11003543
Ref: 3bc411003543
Ref: library/winreg winreg PyHKEY Detach11003675
Ref: 3c0511003675
Ref: library/winreg winreg PyHKEY __enter__11004273
Ref: 3c0611004273
Ref: library/winreg winreg PyHKEY __exit__11004305
Ref: 3c0711004305
Node: winsound — Sound-playing interface for Windows11004699
Ref: library/winsound doc11004855
Ref: 3c0811004855
Ref: library/winsound module-winsound11004855
Ref: 13411004855
Ref: library/winsound winsound-sound-playing-interface-for-windows11004855
Ref: 3c0911004855
Ref: library/winsound winsound Beep11005205
Ref: 6ab11005205
Ref: library/winsound winsound PlaySound11005593
Ref: 6ad11005593
Ref: library/winsound winsound MessageBeep11006165
Ref: 6ac11006165
Ref: library/winsound winsound SND_FILENAME11006774
Ref: 3c0a11006774
Ref: library/winsound winsound SND_ALIAS11006907
Ref: 3c0b11006907
Ref: library/winsound winsound SND_LOOP11008525
Ref: 3c0d11008525
Ref: library/winsound winsound SND_MEMORY11008712
Ref: 3c0f11008712
Ref: library/winsound winsound SND_PURGE11009074
Ref: 3c1011009074
Ref: library/winsound winsound SND_ASYNC11009234
Ref: 3c0e11009234
Ref: library/winsound winsound SND_NODEFAULT11009330
Ref: 3c0c11009330
Ref: library/winsound winsound SND_NOSTOP11009453
Ref: 3c1111009453
Ref: library/winsound winsound SND_NOWAIT11009533
Ref: 3c1211009533
Ref: library/winsound winsound MB_ICONASTERISK11009691
Ref: 3c1311009691
Ref: library/winsound winsound MB_ICONEXCLAMATION11009769
Ref: 3c1411009769
Ref: library/winsound winsound MB_ICONHAND11009854
Ref: 3c1511009854
Ref: library/winsound winsound MB_ICONQUESTION11009925
Ref: 3c1611009925
Ref: library/winsound winsound MB_OK11010004
Ref: 3c1711010004
Node: Unix Specific Services11010072
Ref: library/unix doc11010222
Ref: 3c1811010222
Ref: library/unix unix11010222
Ref: 3c1911010222
Ref: library/unix unix-specific-services11010222
Ref: 3c1a11010222
Node: posix — The most common POSIX system calls11011073
Ref: library/posix doc11011214
Ref: 3c1b11011214
Ref: library/posix module-posix11011214
Ref: d111011214
Ref: library/posix posix-the-most-common-posix-system-calls11011214
Ref: 3c1c11011214
Node: Large File Support11012413
Ref: library/posix large-file-support11012544
Ref: 3c1d11012544
Ref: library/posix posix-large-files11012544
Ref: 3c1e11012544
Node: Notable Module Contents11013595
Ref: library/posix notable-module-contents11013726
Ref: 3c1f11013726
Ref: library/posix posix-contents11013726
Ref: 3c2011013726
Ref: library/posix posix environ11013927
Ref: 3c2111013927
Node: pwd — The password database11015113
Ref: library/pwd doc11015300
Ref: 3c2211015300
Ref: library/pwd module-pwd11015300
Ref: d611015300
Ref: library/pwd pwd-the-password-database11015300
Ref: 3c2311015300
Ref: library/pwd pwd getpwuid11017575
Ref: 114f11017575
Ref: library/pwd pwd getpwnam11017681
Ref: 116111017681
Ref: library/pwd pwd getpwall11017782
Ref: 3c2411017782
Node: spwd — The shadow password database11018096
Ref: library/spwd doc11018265
Ref: 3c2511018265
Ref: library/spwd module-spwd11018265
Ref: f111018265
Ref: library/spwd spwd-the-shadow-password-database11018265
Ref: 3c2611018265
Ref: library/spwd spwd getspnam11020559
Ref: 6f511020559
Ref: library/spwd spwd getspall11020816
Ref: 3c2711020816
Node: grp — The group database11021137
Ref: library/grp doc11021319
Ref: 3c2811021319
Ref: library/grp grp-the-group-database11021319
Ref: 3c2911021319
Ref: library/grp module-grp11021319
Ref: 8a11021319
Ref: library/grp grp getgrgid11022863
Ref: 6d611022863
Ref: library/grp grp getgrnam11023212
Ref: 116211023212
Ref: library/grp grp getgrall11023388
Ref: 3c2a11023388
Node: crypt — Function to check Unix passwords11023684
Ref: library/crypt doc11023864
Ref: 3c2b11023864
Ref: library/crypt crypt-function-to-check-unix-passwords11023864
Ref: 3c2c11023864
Ref: library/crypt module-crypt11023864
Ref: 2811023864
Ref: crypt — Function to check Unix passwords-Footnote-111024873
Node: Hashing Methods11024937
Ref: library/crypt hashing-methods11025057
Ref: 3c2d11025057
Ref: library/crypt crypt METHOD_SHA51211025244
Ref: 3c2e11025244
Ref: library/crypt crypt METHOD_SHA25611025433
Ref: 3c2f11025433
Ref: library/crypt crypt METHOD_BLOWFISH11025592
Ref: 3c3011025592
Ref: library/crypt crypt METHOD_MD511025773
Ref: 3c3111025773
Ref: library/crypt crypt METHOD_CRYPT11025924
Ref: 70011025924
Node: Module Attributes11026068
Ref: library/crypt module-attributes11026216
Ref: 3c3211026216
Ref: library/crypt crypt methods11026292
Ref: 3c3311026292
Node: Module Functions<2>11026468
Ref: library/crypt module-functions11026613
Ref: 3c3411026613
Ref: library/crypt crypt crypt11026728
Ref: 3c3511026728
Ref: library/crypt crypt mksalt11028232
Ref: 48411028232
Node: Examples<32>11029085
Ref: library/crypt examples11029204
Ref: 3c3611029204
Node: termios — POSIX style tty control11030345
Ref: library/termios doc11030533
Ref: 3c3711030533
Ref: library/termios module-termios11030533
Ref: 10411030533
Ref: library/termios termios-posix-style-tty-control11030533
Ref: 3c3811030533
Ref: library/termios termios tcgetattr11031510
Ref: 3c3911031510
Ref: library/termios termios tcsetattr11032089
Ref: 3c3a11032089
Ref: library/termios termios tcsendbreak11032583
Ref: 3c3b11032583
Ref: library/termios termios tcdrain11032797
Ref: 3c3c11032797
Ref: library/termios termios tcflush11032920
Ref: 3c3d11032920
Ref: library/termios termios tcflow11033178
Ref: 3c3e11033178
Node: Example<16>11033603
Ref: library/termios example11033686
Ref: 3c3f11033686
Ref: library/termios termios-example11033686
Ref: 3c4011033686
Node: tty — Terminal control functions11034444
Ref: library/tty doc11034623
Ref: 3c4111034623
Ref: library/tty module-tty11034623
Ref: 11e11034623
Ref: library/tty tty-terminal-control-functions11034623
Ref: 3c4211034623
Ref: library/tty tty setraw11035046
Ref: 3c4311035046
Ref: library/tty tty setcbreak11035282
Ref: 3c4411035282
Ref: tty — Terminal control functions-Footnote-111035647
Node: pty — Pseudo-terminal utilities11035709
Ref: library/pty doc11035895
Ref: 3c4511035895
Ref: library/pty module-pty11035895
Ref: d511035895
Ref: library/pty pty-pseudo-terminal-utilities11035895
Ref: 3c4611035895
Ref: library/pty pty fork11036530
Ref: 3c4711036530
Ref: library/pty pty openpty11036945
Ref: 3c4811036945
Ref: library/pty pty spawn11037224
Ref: 97f11037224
Ref: pty — Pseudo-terminal utilities-Footnote-111039450
Ref: pty — Pseudo-terminal utilities-Footnote-211039512
Node: Example<17>11039555
Ref: library/pty example11039636
Ref: 3c4911039636
Node: fcntl — The fcntl and ioctl system calls11040818
Ref: library/fcntl doc11041008
Ref: 3c4a11041008
Ref: library/fcntl fcntl-the-fcntl-and-ioctl-system-calls11041008
Ref: 3c4b11041008
Ref: library/fcntl module-fcntl11041008
Ref: 7c11041008
Ref: library/fcntl fcntl fcntl11042438
Ref: 27e811042438
Ref: library/fcntl fcntl ioctl11043882
Ref: ea211043882
Ref: library/fcntl fcntl flock11046212
Ref: 3c4c11046212
Ref: library/fcntl fcntl lockf11046719
Ref: e1711046719
Node: pipes — Interface to shell pipelines11049441
Ref: library/pipes doc11049637
Ref: 3c4d11049637
Ref: library/pipes module-pipes11049637
Ref: cc11049637
Ref: library/pipes pipes-interface-to-shell-pipelines11049637
Ref: 3c4e11049637
Ref: library/pipes pipes Template11050186
Ref: 3c4f11050186
Ref: pipes — Interface to shell pipelines-Footnote-111050557
Node: Template Objects11050621
Ref: library/pipes id111050712
Ref: 3c5011050712
Ref: library/pipes template-objects11050712
Ref: 3c5111050712
Ref: library/pipes pipes Template reset11050804
Ref: 3c5211050804
Ref: library/pipes pipes Template clone11050891
Ref: 3c5311050891
Ref: library/pipes pipes Template debug11050973
Ref: 3c5411050973
Ref: library/pipes pipes Template append11051218
Ref: 3c5511051218
Ref: library/pipes pipes Template prepend11051968
Ref: 3c5611051968
Ref: library/pipes pipes Template open11052118
Ref: 3c5711052118
Ref: library/pipes pipes Template copy11052320
Ref: 3c5811052320
Node: resource — Resource usage information11052416
Ref: library/resource doc11052615
Ref: 3c5911052615
Ref: library/resource module-resource11052615
Ref: e011052615
Ref: library/resource resource-resource-usage-information11052615
Ref: 3c5a11052615
Ref: library/resource resource error11053100
Ref: 3c5b11053100
Ref: resource — Resource usage information-Footnote-111053374
Node: Resource Limits11053423
Ref: library/resource resource-limits11053537
Ref: 3c5c11053537
Ref: library/resource resource RLIM_INFINITY11054416
Ref: 3c5d11054416
Ref: library/resource resource getrlimit11054520
Ref: 3c5e11054520
Ref: library/resource resource setrlimit11054814
Ref: 364311054814
Ref: library/resource resource prlimit11055972
Ref: 98611055972
Ref: library/resource resource RLIMIT_CORE11057578
Ref: 364411057578
Ref: library/resource resource RLIMIT_CPU11057839
Ref: 3c6011057839
Ref: library/resource resource RLIMIT_FSIZE11058199
Ref: 3c6111058199
Ref: library/resource resource RLIMIT_DATA11058295
Ref: 3c6211058295
Ref: library/resource resource RLIMIT_STACK11058386
Ref: 3c6311058386
Ref: library/resource resource RLIMIT_RSS11058583
Ref: 3c6411058583
Ref: library/resource resource RLIMIT_NPROC11058701
Ref: 3c6511058701
Ref: library/resource resource RLIMIT_NOFILE11058804
Ref: 3c5f11058804
Ref: library/resource resource RLIMIT_OFILE11058918
Ref: 3c6611058918
Ref: library/resource resource RLIMIT_MEMLOCK11059001
Ref: 3c6711059001
Ref: library/resource resource RLIMIT_VMEM11059099
Ref: 3c6811059099
Ref: library/resource resource RLIMIT_AS11059201
Ref: 3c6911059201
Ref: library/resource resource RLIMIT_MSGQUEUE11059322
Ref: 98711059322
Ref: library/resource resource RLIMIT_NICE11059513
Ref: 98811059513
Ref: library/resource resource RLIMIT_RTPRIO11059712
Ref: 98911059712
Ref: library/resource resource RLIMIT_RTTIME11059873
Ref: 98a11059873
Ref: library/resource resource RLIMIT_SIGPENDING11060132
Ref: 98b11060132
Ref: library/resource resource RLIMIT_SBSIZE11060308
Ref: 98c11060308
Ref: library/resource resource RLIMIT_SWAP11060613
Ref: 98d11060613
Ref: library/resource resource RLIMIT_NPTS11061000
Ref: 98e11061000
Ref: Resource Limits-Footnote-111061217
Node: Resource Usage11061284
Ref: library/resource resource-usage11061398
Ref: 3c6a11061398
Ref: library/resource resource getrusage11061515
Ref: e5e11061515
Ref: library/resource resource getpagesize11066008
Ref: 3c6b11066008
Ref: library/resource resource RUSAGE_SELF11066312
Ref: 3c6c11066312
Ref: library/resource resource RUSAGE_CHILDREN11066512
Ref: 3c6d11066512
Ref: library/resource resource RUSAGE_BOTH11066711
Ref: 3c6e11066711
Ref: library/resource resource RUSAGE_THREAD11066908
Ref: 3c6f11066908
Node: nis — Interface to Sun’s NIS Yellow Pages11067102
Ref: library/nis doc11067302
Ref: 3c7011067302
Ref: library/nis module-nis11067302
Ref: bf11067302
Ref: library/nis nis-interface-to-sun-s-nis-yellow-pages11067302
Ref: 3c7111067302
Ref: library/nis nis match11067753
Ref: e5711067753
Ref: library/nis nis cat11068300
Ref: 3c7311068300
Ref: library/nis nis maps11068766
Ref: e5811068766
Ref: library/nis nis get_default_domain11068994
Ref: 3c7411068994
Ref: library/nis nis error11069139
Ref: 3c7211069139
Node: syslog — Unix syslog library routines11069230
Ref: library/syslog doc11069382
Ref: 3c7511069382
Ref: library/syslog module-syslog11069382
Ref: ff11069382
Ref: library/syslog syslog-unix-syslog-library-routines11069382
Ref: 3c7611069382
Ref: library/syslog syslog syslog11069963
Ref: 3c7711069963
Ref: library/syslog syslog openlog11070774
Ref: 10a611070774
Ref: library/syslog syslog closelog11071938
Ref: 3c7811071938
Ref: library/syslog syslog setlogmask11072471
Ref: 3c7911072471
Node: Examples<33>11073750
Ref: library/syslog examples11073838
Ref: 3c7a11073838
Node: Simple example11073906
Ref: library/syslog simple-example11073969
Ref: 3c7b11073969
Node: Superseded Modules11074481
Ref: library/superseded doc11074623
Ref: 3c7c11074623
Ref: library/superseded superseded11074623
Ref: 3c7d11074623
Ref: library/superseded superseded-modules11074623
Ref: 3c7e11074623
Node: optparse — Parser for command line options11074913
Ref: library/optparse doc11075056
Ref: 3c7f11075056
Ref: library/optparse module-optparse11075056
Ref: c311075056
Ref: library/optparse optparse-parser-for-command-line-options11075056
Ref: 3c8011075056
Ref: optparse — Parser for command line options-Footnote-111077957
Node: Background11078024
Ref: library/optparse background11078135
Ref: 3c8211078135
Ref: library/optparse optparse-background11078135
Ref: 3c8311078135
Node: Terminology11078620
Ref: library/optparse optparse-terminology11078708
Ref: 3c8411078708
Ref: library/optparse terminology11078708
Ref: 3c8511078708
Node: What are options for?11082536
Ref: library/optparse optparse-what-options-for11082667
Ref: 3c8611082667
Ref: library/optparse what-are-options-for11082667
Ref: 3c8711082667
Node: What are positional arguments for?11084352
Ref: library/optparse optparse-what-positional-arguments-for11084463
Ref: 3c8811084463
Ref: library/optparse what-are-positional-arguments-for11084463
Ref: 3c8911084463
Node: Tutorial<2>11085798
Ref: library/optparse optparse-tutorial11085933
Ref: 3c8a11085933
Ref: library/optparse tutorial11085933
Ref: 3c8b11085933
Node: Understanding option actions11088539
Ref: library/optparse optparse-understanding-option-actions11088640
Ref: 3c9011088640
Ref: library/optparse understanding-option-actions11088640
Ref: 3c9111088640
Node: The store action11089231
Ref: library/optparse optparse-store-action11089370
Ref: 3c9311089370
Ref: library/optparse the-store-action11089370
Ref: 3c9411089370
Node: Handling boolean flag options11091560
Ref: library/optparse handling-boolean-flag-options11091684
Ref: 3c9511091684
Ref: library/optparse optparse-handling-boolean-options11091684
Ref: 3c9611091684
Node: Other actions11092567
Ref: library/optparse optparse-other-actions11092689
Ref: 3c9711092689
Ref: library/optparse other-actions11092689
Ref: 3c9811092689
Node: Default values11093107
Ref: library/optparse default-values11093215
Ref: 3c9b11093215
Ref: library/optparse optparse-default-values11093215
Ref: 3c9c11093215
Node: Generating help11095103
Ref: library/optparse generating-help11095223
Ref: 3c9d11095223
Ref: library/optparse optparse-generating-help11095223
Ref: 3c9e11095223
Node: Grouping Options11099397
Ref: library/optparse grouping-options11099465
Ref: 3c9f11099465
Ref: library/optparse optparse OptionGroup11099796
Ref: 3ca011099796
Ref: library/optparse optparse OptionParser get_option_group11103294
Ref: 3ca111103294
Node: Printing a version string11103564
Ref: library/optparse optparse-printing-version-string11103697
Ref: 3ca211103697
Ref: library/optparse printing-a-version-string11103697
Ref: 3ca311103697
Ref: library/optparse optparse OptionParser print_version11104581
Ref: 3ca411104581
Ref: library/optparse optparse OptionParser get_version11104955
Ref: 3ca611104955
Node: How optparse handles errors11105099
Ref: library/optparse how-optparse-handles-errors11105240
Ref: 3ca711105240
Ref: library/optparse optparse-how-optparse-handles-errors11105240
Ref: 3ca811105240
Node: Putting it all together11107323
Ref: library/optparse optparse-putting-it-all-together11107430
Ref: 3ca911107430
Ref: library/optparse putting-it-all-together11107430
Ref: 3caa11107430
Node: Reference Guide11108348
Ref: library/optparse optparse-reference-guide11108489
Ref: 3c9911108489
Ref: library/optparse reference-guide11108489
Ref: 3cab11108489
Node: Creating the parser11108862
Ref: library/optparse creating-the-parser11108963
Ref: 3cac11108963
Ref: library/optparse optparse-creating-parser11108963
Ref: 3cad11108963
Ref: library/optparse optparse OptionParser11109108
Ref: 3c8111109108
Node: Populating the parser11112114
Ref: library/optparse optparse-populating-parser11112240
Ref: 3caf11112240
Ref: library/optparse populating-the-parser11112240
Ref: 3cb011112240
Node: Defining options11113526
Ref: library/optparse defining-options11113650
Ref: 3cb111113650
Ref: library/optparse optparse-defining-options11113650
Ref: 3cb211113650
Ref: library/optparse optparse OptionParser add_option11114059
Ref: 21cd11114059
Node: Option attributes11116932
Ref: library/optparse option-attributes11117058
Ref: 3cb411117058
Ref: library/optparse optparse-option-attributes11117058
Ref: 3cb511117058
Ref: library/optparse optparse Option action11117394
Ref: 3c8c11117394
Ref: library/optparse optparse Option type11117617
Ref: 3c8d11117617
Ref: library/optparse optparse Option dest11117834
Ref: 3c8e11117834
Ref: library/optparse optparse Option default11118179
Ref: 3cb711118179
Ref: library/optparse optparse Option nargs11118373
Ref: 3cb911118373
Ref: library/optparse optparse Option const11118606
Ref: 3cba11118606
Ref: library/optparse optparse Option choices11118716
Ref: 3cbb11118716
Ref: library/optparse optparse Option callback11118840
Ref: 3cbc11118840
Ref: library/optparse optparse Option callback_args11119072
Ref: 3cbd11119072
Ref: library/optparse optparse Option callback_kwargs11119108
Ref: 3cbe11119108
Ref: library/optparse optparse Option help11119272
Ref: 3c8f11119272
Ref: library/optparse optparse Option metavar11119620
Ref: 3cbf11119620
Node: Standard option actions11119825
Ref: library/optparse optparse-standard-option-actions11119956
Ref: 3cb311119956
Ref: library/optparse standard-option-actions11119956
Ref: 3cc011119956
Node: Standard option types11128043
Ref: library/optparse optparse-standard-option-types11128177
Ref: 3cb611128177
Ref: library/optparse standard-option-types11128177
Ref: 3cc111128177
Node: Parsing arguments<2>11129648
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Node: Querying and manipulating your option parser11131173
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Ref: library/optparse querying-and-manipulating-your-option-parser11131332
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Ref: library/optparse optparse OptionParser disable_interspersed_args11131641
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Ref: library/optparse optparse OptionParser enable_interspersed_args11132431
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Ref: library/optparse optparse OptionParser get_option11132637
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Ref: library/optparse optparse OptionParser has_option11132810
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Ref: library/optparse optparse OptionParser remove_option11132986
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Node: Other methods11136516
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Ref: library/optparse other-methods11136600
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Ref: library/optparse optparse OptionParser set_usage11136702
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Ref: library/optparse optparse OptionParser print_usage11136991
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Ref: library/optparse optparse OptionParser get_usage11137327
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Ref: library/optparse raising-errors-in-a-callback11145252
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Ref: library/optparse optparse-callback-example-111145894
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Ref: library/optparse optparse-callback-example-211146534
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Ref: library/optparse optparse-callback-example-411148265
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Ref: library/optparse optparse Option TYPES11153406
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Ref: library/optparse optparse Option TYPE_CHECKER11153565
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Ref: library/optparse optparse Option ACTIONS11157777
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Ref: library/optparse optparse Option STORE_ACTIONS11157853
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Ref: library/optparse optparse Option TYPED_ACTIONS11157946
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Ref: library/optparse optparse Option ALWAYS_TYPED_ACTIONS11158039
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Ref: library/imp module-imp11161484
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Ref: library/imp imp get_magic11161935
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Ref: library/imp imp get_suffixes11162226
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Ref: library/imp imp load_module11165477
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Ref: library/imp imp reload11167597
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Ref: library/imp imp cache_from_source11170857
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Ref: imp — Access the import internals-Footnote-111176946
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Ref: imp — Access the import internals-Footnote-611177204
Ref: imp — Access the import internals-Footnote-711177253
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Node: Recommended third party tools11182372
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Ref: Reference Counting in Python-Footnote-111228997
Ref: Reference Counting in Python-Footnote-211229125
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Ref: 3d8411329130
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Ref: 3d8e11336499
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Ref: extending/windows building-on-windows11337510
Ref: 14cd11337510
Node: A Cookbook Approach11338779
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Ref: extending/windows win-cookbook11338920
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Ref: A Cookbook Approach-Footnote-111339555
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Ref: extending/windows win-dlls11342871
Ref: 3d9711342871
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Ref: c-api/veryhigh c PyRun_InteractiveLoop11405484
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Ref: c-api/veryhigh c PyRun_InteractiveLoopFlags11405704
Ref: 3de411405704
Ref: c-api/veryhigh c PyOS_InputHook11406164
Ref: 3de511406164
Ref: c-api/veryhigh c PyOS_ReadlineFunctionPointer11406647
Ref: a4d11406647
Ref: c-api/veryhigh c PyParser_SimpleParseString11407677
Ref: 3de611407677
Ref: c-api/veryhigh c PyParser_SimpleParseStringFlags11408019
Ref: 1ff11408019
Ref: c-api/veryhigh c PyParser_SimpleParseStringFlagsFilename11408350
Ref: 20011408350
Ref: c-api/veryhigh c PyParser_SimpleParseFile11408938
Ref: 3de711408938
Ref: c-api/veryhigh c PyParser_SimpleParseFileFlags11409250
Ref: 20111409250
Ref: c-api/veryhigh c PyRun_String11409603
Ref: 10e711409603
Ref: c-api/veryhigh c PyRun_StringFlags11409875
Ref: 3de811409875
Ref: c-api/veryhigh c PyRun_File11410536
Ref: 3de911410536
Ref: c-api/veryhigh c PyRun_FileEx11410850
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Ref: c-api/veryhigh c PyRun_FileFlags11411150
Ref: 3dec11411150
Ref: c-api/veryhigh c PyRun_FileExFlags11411473
Ref: 3dea11411473
Ref: c-api/veryhigh c Py_CompileString11412060
Ref: 3ded11412060
Ref: c-api/veryhigh c Py_CompileStringFlags11412325
Ref: 3dee11412325
Ref: c-api/veryhigh c Py_CompileStringObject11412619
Ref: 3df011412619
Ref: c-api/veryhigh c Py_CompileStringExFlags11413736
Ref: 3def11413736
Ref: c-api/veryhigh c PyEval_EvalCode11414110
Ref: 3df111414110
Ref: c-api/veryhigh c PyEval_EvalCodeEx11414432
Ref: 3df211414432
Ref: c-api/veryhigh c PyFrameObject11415109
Ref: a5211415109
Ref: c-api/veryhigh c PyEval_EvalFrame11415270
Ref: 3df311415270
Ref: c-api/veryhigh c PyEval_EvalFrameEx11415505
Ref: a4811415505
Ref: c-api/veryhigh c PyEval_MergeCompilerFlags11416201
Ref: 3df411416201
Ref: c-api/veryhigh c Py_eval_input11416393
Ref: 3df511416393
Ref: c-api/veryhigh c Py_file_input11416551
Ref: 3df611416551
Ref: c-api/veryhigh c Py_single_input11416837
Ref: 3df711416837
Ref: c-api/veryhigh c PyCompilerFlags11417063
Ref: 3ee11417063
Ref: c-api/veryhigh c PyCompilerFlags cf_flags11417594
Ref: 3df811417594
Ref: c-api/veryhigh c PyCompilerFlags cf_feature_version11417654
Ref: 3df911417654
Ref: c-api/veryhigh c CO_FUTURE_DIVISION11418012
Ref: 3dfa11418012
Ref: The Very High Level Layer-Footnote-111418231
Node: Reference Counting11418280
Ref: c-api/refcounting doc11418425
Ref: 3dfb11418425
Ref: c-api/refcounting countingrefs11418425
Ref: 3dfc11418425
Ref: c-api/refcounting reference-counting11418425
Ref: 3dfd11418425
Ref: c-api/refcounting c Py_INCREF11418558
Ref: 38e11418558
Ref: c-api/refcounting c Py_XINCREF11418780
Ref: 39011418780
Ref: c-api/refcounting c Py_DECREF11418954
Ref: 38f11418954
Ref: c-api/refcounting c Py_XDECREF11420067
Ref: 39111420067
Ref: c-api/refcounting c Py_CLEAR11420345
Ref: 3d6311420345
Node: Exception Handling11421490
Ref: c-api/exceptions doc11421622
Ref: 3dfe11421622
Ref: c-api/exceptions exception-handling11421622
Ref: 3dff11421622
Ref: c-api/exceptions exceptionhandling11421622
Ref: 37d211421622
Node: Printing and clearing11423936
Ref: c-api/exceptions printing-and-clearing11424039
Ref: 3e0011424039
Ref: c-api/exceptions c PyErr_Clear11424096
Ref: a4c11424096
Ref: c-api/exceptions c PyErr_PrintEx11424227
Ref: 3e0111424227
Ref: c-api/exceptions c PyErr_Print11424917
Ref: 102f11424917
Ref: c-api/exceptions c PyErr_WriteUnraisable11424994
Ref: 10f911424994
Node: Raising exceptions11425702
Ref: c-api/exceptions raising-exceptions11425830
Ref: 3e0211425830
Ref: c-api/exceptions c PyErr_SetString11426070
Ref: 3d1711426070
Ref: c-api/exceptions c PyErr_SetObject11426488
Ref: 3d1911426488
Ref: c-api/exceptions c PyErr_Format11426721
Ref: 89811426721
Ref: c-api/exceptions c PyErr_FormatV11427172
Ref: 89711427172
Ref: c-api/exceptions c PyErr_SetNone11427465
Ref: 3e0311427465
Ref: c-api/exceptions c PyErr_BadArgument11427586
Ref: 3e0411427586
Ref: c-api/exceptions c PyErr_NoMemory11427839
Ref: 3d1b11427839
Ref: c-api/exceptions c PyErr_SetFromErrno11428121
Ref: 3d1811428121
Ref: c-api/exceptions c PyErr_SetFromErrnoWithFilenameObject11429001
Ref: 3e0611429001
Ref: c-api/exceptions c PyErr_SetFromErrnoWithFilenameObjects11429480
Ref: 3e0711429480
Ref: c-api/exceptions c PyErr_SetFromErrnoWithFilename11429876
Ref: 3e0811429876
Ref: c-api/exceptions c PyErr_SetFromWindowsErr11430217
Ref: 3e0911430217
Ref: c-api/exceptions c PyErr_SetExcFromWindowsErr11430989
Ref: 3e0a11430989
Ref: c-api/exceptions c PyErr_SetFromWindowsErrWithFilename11431289
Ref: 3e0b11431289
Ref: c-api/exceptions c PyErr_SetExcFromWindowsErrWithFilenameObject11431670
Ref: 3e0c11431670
Ref: c-api/exceptions c PyErr_SetExcFromWindowsErrWithFilenameObjects11432020
Ref: 3e0d11432020
Ref: c-api/exceptions c PyErr_SetExcFromWindowsErrWithFilename11432402
Ref: 3e0e11432402
Ref: c-api/exceptions c PyErr_SetImportError11432748
Ref: 6ef11432748
Ref: c-api/exceptions c PyErr_SyntaxLocationObject11433203
Ref: 3e0f11433203
Ref: c-api/exceptions c PyErr_SyntaxLocationEx11433611
Ref: 3e1011433611
Ref: c-api/exceptions c PyErr_SyntaxLocation11433904
Ref: 3e1111433904
Ref: c-api/exceptions c PyErr_BadInternalCall11434087
Ref: 3e1211434087
Node: Issuing warnings11434385
Ref: c-api/exceptions issuing-warnings11434520
Ref: 3e1311434520
Ref: c-api/exceptions c PyErr_WarnEx11435416
Ref: e7611435416
Ref: c-api/exceptions c PyErr_SetImportErrorSubclass11436563
Ref: 6c211436563
Ref: c-api/exceptions c PyErr_WarnExplicitObject11436911
Ref: 3e1511436911
Ref: c-api/exceptions c PyErr_WarnExplicit11437452
Ref: 3e1611437452
Ref: c-api/exceptions c PyErr_WarnFormat11437841
Ref: 3e1711437841
Ref: c-api/exceptions c PyErr_ResourceWarning11438159
Ref: 6c311438159
Node: Querying the error indicator11438479
Ref: c-api/exceptions querying-the-error-indicator11438614
Ref: 3e1811438614
Ref: c-api/exceptions c PyErr_Occurred11438685
Ref: 3d1a11438685
Ref: c-api/exceptions c PyErr_ExceptionMatches11439517
Ref: 3dcc11439517
Ref: c-api/exceptions c PyErr_GivenExceptionMatches11439797
Ref: 3e1911439797
Ref: c-api/exceptions c PyErr_Fetch11440196
Ref: a4b11440196
Ref: c-api/exceptions c PyErr_Restore11441116
Ref: 3d6d11441116
Ref: c-api/exceptions c PyErr_NormalizeException11442109
Ref: 10fa11442109
Ref: c-api/exceptions c PyErr_GetExcInfo11442980
Ref: 3e1a11442980
Ref: c-api/exceptions c PyErr_SetExcInfo11443734
Ref: 3e1b11443734
Node: Signal Handling<2>11444544
Ref: c-api/exceptions signal-handling11444680
Ref: 3e1c11444680
Ref: c-api/exceptions c PyErr_CheckSignals11444725
Ref: 3e0511444725
Ref: c-api/exceptions c PyErr_SetInterrupt11445391
Ref: 3e1d11445391
Ref: c-api/exceptions c PySignal_SetWakeupFd11445787
Ref: e0b11445787
Node: Exception Classes11446457
Ref: c-api/exceptions exception-classes11446582
Ref: 3e1e11446582
Ref: c-api/exceptions c PyErr_NewException11446631
Ref: ccb11446631
Ref: c-api/exceptions c PyErr_NewExceptionWithDoc11447569
Ref: cca11447569
Node: Exception Objects11447974
Ref: c-api/exceptions exception-objects11448106
Ref: 3e1f11448106
Ref: c-api/exceptions c PyException_GetTraceback11448155
Ref: 3e2011448155
Ref: c-api/exceptions c PyException_SetTraceback11448463
Ref: 10fb11448463
Ref: c-api/exceptions c PyException_GetContext11448648
Ref: 3e2111448648
Ref: c-api/exceptions c PyException_SetContext11449020
Ref: 3e2211449020
Ref: c-api/exceptions c PyException_GetCause11449315
Ref: 3e2311449315
Ref: c-api/exceptions c PyException_SetCause11449632
Ref: 3e2411449632
Node: Unicode Exception Objects11450050
Ref: c-api/exceptions unicode-exception-objects11450182
Ref: 3e2511450182
Ref: c-api/exceptions unicodeexceptions11450182
Ref: 3e2611450182
Ref: c-api/exceptions c PyUnicodeDecodeError_Create11450329
Ref: 3e2711450329
Ref: c-api/exceptions c PyUnicodeEncodeError_Create11450752
Ref: 3e2811450752
Ref: c-api/exceptions c PyUnicodeTranslateError_Create11451370
Ref: 3e2911451370
Ref: c-api/exceptions c PyUnicodeDecodeError_GetEncoding11451948
Ref: 3e2a11451948
Ref: c-api/exceptions c PyUnicodeEncodeError_GetEncoding11452033
Ref: 3e2b11452033
Ref: c-api/exceptions c PyUnicodeDecodeError_GetObject11452224
Ref: 3e2c11452224
Ref: c-api/exceptions c PyUnicodeEncodeError_GetObject11452297
Ref: 3e2d11452297
Ref: c-api/exceptions c PyUnicodeTranslateError_GetObject11452370
Ref: 3e2e11452370
Ref: c-api/exceptions c PyUnicodeDecodeError_GetStart11452560
Ref: 3e2f11452560
Ref: c-api/exceptions c PyUnicodeEncodeError_GetStart11452655
Ref: 3e3011452655
Ref: c-api/exceptions c PyUnicodeTranslateError_GetStart11452750
Ref: 3e3111452750
Ref: c-api/exceptions c PyUnicodeDecodeError_SetStart11453031
Ref: 3e3211453031
Ref: c-api/exceptions c PyUnicodeEncodeError_SetStart11453125
Ref: 3e3311453125
Ref: c-api/exceptions c PyUnicodeTranslateError_SetStart11453219
Ref: 3e3411453219
Ref: c-api/exceptions c PyUnicodeDecodeError_GetEnd11453444
Ref: 3e3511453444
Ref: c-api/exceptions c PyUnicodeEncodeError_GetEnd11453535
Ref: 3e3611453535
Ref: c-api/exceptions c PyUnicodeTranslateError_GetEnd11453626
Ref: 3e3711453626
Ref: c-api/exceptions c PyUnicodeDecodeError_SetEnd11453897
Ref: 3e3811453897
Ref: c-api/exceptions c PyUnicodeEncodeError_SetEnd11453987
Ref: 3e3911453987
Ref: c-api/exceptions c PyUnicodeTranslateError_SetEnd11454077
Ref: 3e3a11454077
Ref: c-api/exceptions c PyUnicodeDecodeError_GetReason11454294
Ref: 3e3b11454294
Ref: c-api/exceptions c PyUnicodeEncodeError_GetReason11454367
Ref: 3e3c11454367
Ref: c-api/exceptions c PyUnicodeTranslateError_GetReason11454440
Ref: 3e3d11454440
Ref: c-api/exceptions c PyUnicodeDecodeError_SetReason11454630
Ref: 3e3e11454630
Ref: c-api/exceptions c PyUnicodeEncodeError_SetReason11454727
Ref: 3e3f11454727
Ref: c-api/exceptions c PyUnicodeTranslateError_SetReason11454824
Ref: 3e4011454824
Node: Recursion Control11455055
Ref: c-api/exceptions recursion11455189
Ref: 3e4111455189
Ref: c-api/exceptions recursion-control11455189
Ref: 3e4211455189
Ref: c-api/exceptions c Py_EnterRecursiveCall11455622
Ref: 25111455622
Ref: c-api/exceptions c Py_LeaveRecursiveCall11456472
Ref: 25211456472
Ref: c-api/exceptions c Py_ReprEnter11457109
Ref: 3e4511457109
Ref: c-api/exceptions c Py_ReprLeave11457877
Ref: 3e4611457877
Node: Standard Exceptions11458068
Ref: c-api/exceptions standard-exceptions11458204
Ref: 3e4711458204
Ref: c-api/exceptions standardexceptions11458204
Ref: 3e4811458204
Ref: Standard Exceptions-Footnote-111471581
Node: Standard Warning Categories11471630
Ref: c-api/exceptions standard-warning-categories11471740
Ref: 3e4911471740
Ref: c-api/exceptions standardwarningcategories11471740
Ref: 3e1411471740
Node: Utilities<2>11474869
Ref: c-api/utilities doc11475005
Ref: 3e4a11475005
Ref: c-api/utilities id111475005
Ref: 3e4b11475005
Ref: c-api/utilities utilities11475005
Ref: 3e4c11475005
Node: Operating System Utilities11475554
Ref: c-api/sys doc11475654
Ref: 3e4d11475654
Ref: c-api/sys operating-system-utilities11475654
Ref: 3e4e11475654
Ref: c-api/sys os11475654
Ref: 3e4f11475654
Ref: c-api/sys c PyOS_FSPath11475721
Ref: 6c411475721
Ref: c-api/sys c Py_FdIsInteractive11476267
Ref: 3e5011476267
Ref: c-api/sys c PyOS_BeforeFork11476750
Ref: 53611476750
Ref: c-api/sys c PyOS_AfterFork_Parent11477283
Ref: 53711477283
Ref: c-api/sys c PyOS_AfterFork_Child11477909
Ref: 3ef11477909
Ref: c-api/sys c PyOS_AfterFork11478810
Ref: 53511478810
Ref: c-api/sys c PyOS_CheckStack11479227
Ref: 3e4411479227
Ref: c-api/sys c PyOS_getsig11479611
Ref: 3e5411479611
Ref: c-api/sys c PyOS_setsig11479920
Ref: 3e5511479920
Ref: c-api/sys c Py_DecodeLocale11480289
Ref: 53f11480289
Ref: c-api/sys c Py_EncodeLocale11482338
Ref: 54011482338
Node: System Functions11484138
Ref: c-api/sys system-functions11484262
Ref: 3e5911484262
Ref: c-api/sys systemfunctions11484262
Ref: 3e5a11484262
Ref: c-api/sys c PySys_GetObject11484561
Ref: 3e5b11484561
Ref: c-api/sys c PySys_SetObject11484797
Ref: 3e5c11484797
Ref: c-api/sys c PySys_ResetWarnOptions11485055
Ref: 3e5d11485055
Ref: c-api/sys c PySys_AddWarnOption11485232
Ref: 5ae11485232
Ref: c-api/sys c PySys_AddWarnOptionUnicode11485463
Ref: 5ad11485463
Ref: c-api/sys c PySys_SetPath11485933
Ref: 3e5e11485933
Ref: c-api/sys c PySys_WriteStdout11486199
Ref: 3e5f11486199
Ref: c-api/sys c PySys_WriteStderr11487075
Ref: 3e6011487075
Ref: c-api/sys c PySys_FormatStdout11487245
Ref: 3e6111487245
Ref: c-api/sys c PySys_FormatStderr11487517
Ref: 3e6311487517
Ref: c-api/sys c PySys_AddXOption11487715
Ref: 3e6411487715
Ref: c-api/sys c PySys_GetXOptions11488023
Ref: 3e6511488023
Ref: c-api/sys c PySys_Audit11488304
Ref: 106811488304
Ref: c-api/sys c PySys_AddAuditHook11489433
Ref: 366b11489433
Ref: System Functions-Footnote-111491284
Node: Process Control11491333
Ref: c-api/sys process-control11491451
Ref: 3e6711491451
Ref: c-api/sys processcontrol11491451
Ref: 3e6811491451
Ref: c-api/sys c Py_FatalError11491496
Ref: 26611491496
Ref: c-api/sys c Py_Exit11492228
Ref: 70711492228
Ref: c-api/sys c Py_AtExit11492582
Ref: 3e6911492582
Node: Importing Modules<2>11493232
Ref: c-api/import doc11493358
Ref: 3e6a11493358
Ref: c-api/import importing11493358
Ref: 3e6b11493358
Ref: c-api/import importing-modules11493358
Ref: 3e6c11493358
Ref: c-api/import c PyImport_ImportModule11493407
Ref: d3b11493407
Ref: c-api/import c PyImport_ImportModuleNoBlock11494438
Ref: aa011494438
Ref: c-api/import c PyImport_ImportModuleEx11494926
Ref: bf411494926
Ref: c-api/import c PyImport_ImportModuleLevelObject11495654
Ref: 3e6d11495654
Ref: c-api/import c PyImport_ImportModuleLevel11496414
Ref: bf311496414
Ref: c-api/import c PyImport_Import11496836
Ref: e2411496836
Ref: c-api/import c PyImport_ReloadModule11497357
Ref: 3e6e11497357
Ref: c-api/import c PyImport_AddModuleObject11497619
Ref: 3e6f11497619
Ref: c-api/import c PyImport_AddModule11498446
Ref: 3d3911498446
Ref: c-api/import c PyImport_ExecCodeModule11498682
Ref: 3e7011498682
Ref: c-api/import c PyImport_ExecCodeModuleEx11500463
Ref: 3e7111500463
Ref: c-api/import c PyImport_ExecCodeModuleObject11500851
Ref: 3e7311500851
Ref: c-api/import c PyImport_ExecCodeModuleWithPathnames11501287
Ref: 3e7211501287
Ref: c-api/import c PyImport_GetMagicNumber11501931
Ref: bf211501931
Ref: c-api/import c PyImport_GetMagicTag11502286
Ref: 3e7411502286
Ref: c-api/import c PyImport_GetModuleDict11502595
Ref: 3e7511502595
Ref: c-api/import c PyImport_GetModule11502833
Ref: 52511502833
Ref: c-api/import c PyImport_GetImporter11503182
Ref: 3e7611503182
Ref: c-api/import c PyImport_ImportFrozenModuleObject11503844
Ref: 3e7711503844
Ref: c-api/import c PyImport_ImportFrozenModule11504448
Ref: 3e7811504448
Ref: c-api/import c _frozen11504655
Ref: 3e7911504655
Ref: c-api/import c PyImport_FrozenModules11505067
Ref: 245211505067
Ref: c-api/import c PyImport_AppendInittab11505471
Ref: f9c11505471
Ref: c-api/import c _inittab11506013
Ref: 3e7a11506013
Ref: c-api/import c PyImport_ExtendInittab11506667
Ref: f9d11506667
Ref: Importing Modules<2>-Footnote-111507469
Node: Data marshalling support11507518
Ref: c-api/marshal doc11507666
Ref: 3e7b11507666
Ref: c-api/marshal data-marshalling-support11507666
Ref: 3e7c11507666
Ref: c-api/marshal marshalling-utils11507666
Ref: 3e7d11507666
Ref: c-api/marshal c PyMarshal_WriteLongToFile11508413
Ref: 3e7e11508413
Ref: c-api/marshal c PyMarshal_WriteObjectToFile11508731
Ref: 3e7f11508731
Ref: c-api/marshal c PyMarshal_WriteObjectToString11508928
Ref: 3e8011508928
Ref: c-api/marshal c PyMarshal_ReadLongFromFile11509255
Ref: 3e8111509255
Ref: c-api/marshal c PyMarshal_ReadShortFromFile11509612
Ref: 3e8211509612
Ref: c-api/marshal c PyMarshal_ReadObjectFromFile11509971
Ref: 3e8311509971
Ref: c-api/marshal c PyMarshal_ReadLastObjectFromFile11510315
Ref: 3e8411510315
Ref: c-api/marshal c PyMarshal_ReadObjectFromString11511092
Ref: 3e8511511092
Node: Parsing arguments and building values11511500
Ref: c-api/arg doc11511660
Ref: 3e8611511660
Ref: c-api/arg arg-parsing11511660
Ref: 3f211511660
Ref: c-api/arg parsing-arguments-and-building-values11511660
Ref: 3e8711511660
Node: Parsing arguments<3>11512332
Ref: c-api/arg parsing-arguments11512450
Ref: 3e8811512450
Node: Strings and buffers11513180
Ref: c-api/arg strings-and-buffers11513275
Ref: 3e8911513275
Node: Numbers<2>11525463
Ref: c-api/arg numbers11525580
Ref: 3e8b11525580
Node: Other objects11527698
Ref: c-api/arg other-objects11527809
Ref: 3e8d11527809
Ref: c-api/arg o-ampersand11528561
Ref: 3e8e11528561
Node: API Functions11533103
Ref: c-api/arg api-functions11533195
Ref: 3e8f11533195
Ref: c-api/arg c PyArg_ParseTuple11533240
Ref: 39311533240
Ref: c-api/arg c PyArg_VaParse11533534
Ref: 3e9011533534
Ref: c-api/arg c PyArg_ParseTupleAndKeywords11533763
Ref: 6c111533763
Ref: c-api/arg c PyArg_VaParseTupleAndKeywords11534364
Ref: e9e11534364
Ref: c-api/arg c PyArg_ValidateKeywordArguments11534662
Ref: 3e9111534662
Ref: c-api/arg c PyArg_Parse11534965
Ref: 10f011534965
Ref: c-api/arg c PyArg_UnpackTuple11535569
Ref: f0811535569
Node: Building values11537500
Ref: c-api/arg building-values11537618
Ref: 3e9211537618
Ref: c-api/arg c Py_BuildValue11537667
Ref: 3f011537667
Ref: c-api/arg c Py_VaBuildValue11545219
Ref: 3e9311545219
Node: String conversion and formatting11545473
Ref: c-api/conversion doc11545619
Ref: 3e9411545619
Ref: c-api/conversion string-conversion11545619
Ref: 3e9511545619
Ref: c-api/conversion string-conversion-and-formatting11545619
Ref: 3e9611545619
Ref: c-api/conversion c PyOS_snprintf11545760
Ref: f0b11545760
Ref: c-api/conversion c PyOS_vsnprintf11546021
Ref: f0c11546021
Ref: c-api/conversion c PyOS_string_to_double11547732
Ref: ced11547732
Ref: c-api/conversion c PyOS_double_to_string11549452
Ref: 3e9711549452
Ref: c-api/conversion c PyOS_stricmp11551044
Ref: 3e9811551044
Ref: c-api/conversion c PyOS_strnicmp11551252
Ref: 3e9911551252
Node: Reflection11551490
Ref: c-api/reflection doc11551635
Ref: 3e9a11551635
Ref: c-api/reflection id111551635
Ref: 3e9b11551635
Ref: c-api/reflection reflection11551635
Ref: 3e9c11551635
Ref: c-api/reflection c PyEval_GetBuiltins11551670
Ref: 3e9d11551670
Ref: c-api/reflection c PyEval_GetLocals11551918
Ref: 3e9e11551918
Ref: c-api/reflection c PyEval_GetGlobals11552146
Ref: 3e9f11552146
Ref: c-api/reflection c PyEval_GetFrame11552376
Ref: 3ea011552376
Ref: c-api/reflection c PyFrame_GetBack11552629
Ref: 24a11552629
Ref: c-api/reflection c PyFrame_GetCode11552871
Ref: 24911552871
Ref: c-api/reflection c PyFrame_GetLineNumber11553108
Ref: 24b11553108
Ref: c-api/reflection c PyEval_GetFuncName11553278
Ref: 3ea111553278
Ref: c-api/reflection c PyEval_GetFuncDesc11553458
Ref: 3ea211553458
Node: Codec registry and support functions11553836
Ref: c-api/codec doc11553940
Ref: 3ea311553940
Ref: c-api/codec codec-registry11553940
Ref: 6e511553940
Ref: c-api/codec codec-registry-and-support-functions11553940
Ref: 3ea411553940
Ref: c-api/codec c PyCodec_Register11554027
Ref: 3ea511554027
Ref: c-api/codec c PyCodec_KnownEncoding11554304
Ref: 3ea611554304
Ref: c-api/codec c PyCodec_Encode11554514
Ref: 3ea711554514
Ref: c-api/codec c PyCodec_Decode11554995
Ref: 3ea811554995
Node: Codec lookup API11555560
Ref: c-api/codec codec-lookup-api11555706
Ref: 3ea911555706
Ref: c-api/codec c PyCodec_Encoder11556024
Ref: 3eaa11556024
Ref: c-api/codec c PyCodec_Decoder11556182
Ref: 3eab11556182
Ref: c-api/codec c PyCodec_IncrementalEncoder11556339
Ref: 3eac11556339
Ref: c-api/codec c PyCodec_IncrementalDecoder11556560
Ref: 3ead11556560
Ref: c-api/codec c PyCodec_StreamReader11556781
Ref: 3eae11556781
Ref: c-api/codec c PyCodec_StreamWriter11557017
Ref: 3eaf11557017
Node: Registry API for Unicode encoding error handlers11557253
Ref: c-api/codec registry-api-for-unicode-encoding-error-handlers11557399
Ref: 3eb011557399
Ref: c-api/codec c PyCodec_RegisterError11557514
Ref: 3eb111557514
Ref: c-api/codec c PyCodec_LookupError11558606
Ref: 3eb211558606
Ref: c-api/codec c PyCodec_StrictErrors11558915
Ref: 3eb311558915
Ref: c-api/codec c PyCodec_IgnoreErrors11559042
Ref: 3eb411559042
Ref: c-api/codec c PyCodec_ReplaceErrors11559201
Ref: 3eb511559201
Ref: c-api/codec c PyCodec_XMLCharRefReplaceErrors11559371
Ref: 3eb611559371
Ref: c-api/codec c PyCodec_BackslashReplaceErrors11559562
Ref: 3eb711559562
Ref: c-api/codec c PyCodec_NameReplaceErrors11559769
Ref: 89611559769
Node: Abstract Objects Layer11559967
Ref: c-api/abstract doc11560107
Ref: 3eb811560107
Ref: c-api/abstract abstract11560107
Ref: 3d7e11560107
Ref: c-api/abstract abstract-objects-layer11560107
Ref: 3eb911560107
Node: Object Protocol11560836
Ref: c-api/object doc11560932
Ref: 3eba11560932
Ref: c-api/object object11560932
Ref: 3ebb11560932
Ref: c-api/object object-protocol11560932
Ref: 3ebc11560932
Ref: c-api/object c Py_NotImplemented11560977
Ref: 3ebd11560977
Ref: c-api/object c Py_RETURN_NOTIMPLEMENTED11561153
Ref: 3ebe11561153
Ref: c-api/object c PyObject_Print11561364
Ref: 118111561364
Ref: c-api/object c PyObject_HasAttr11561739
Ref: 3ebf11561739
Ref: c-api/object c PyObject_HasAttrString11562238
Ref: 3ec111562238
Ref: c-api/object c PyObject_GetAttr11562800
Ref: 3ec011562800
Ref: c-api/object c PyObject_GetAttrString11563133
Ref: 3d3411563133
Ref: c-api/object c PyObject_GenericGetAttr11563474
Ref: 3ec211563474
Ref: c-api/object c PyObject_SetAttr11564097
Ref: 3ec311564097
Ref: c-api/object c PyObject_SetAttrString11564593
Ref: 3ec511564593
Ref: c-api/object c PyObject_GenericSetAttr11565103
Ref: 3ec711565103
Ref: c-api/object c PyObject_DelAttr11565760
Ref: 3ec411565760
Ref: c-api/object c PyObject_DelAttrString11566002
Ref: 3ec611566002
Ref: c-api/object c PyObject_GenericGetDict11566262
Ref: 3ec811566262
Ref: c-api/object c PyObject_GenericSetDict11566538
Ref: 3ec911566538
Ref: c-api/object c PyObject_RichCompare11566813
Ref: 3d7c11566813
Ref: c-api/object c PyObject_RichCompareBool11567442
Ref: 109c11567442
Ref: c-api/object c PyObject_Repr11568215
Ref: a4911568215
Ref: c-api/object c PyObject_ASCII11568716
Ref: 3eca11568716
Ref: c-api/object c PyObject_Str11569200
Ref: a4a11569200
Ref: c-api/object c PyObject_Bytes11569750
Ref: 3ecb11569750
Ref: c-api/object c PyObject_IsSubclass11570181
Ref: 88d11570181
Ref: c-api/object c PyObject_IsInstance11571157
Ref: 88c11571157
Ref: c-api/object c PyObject_Hash11572128
Ref: 3ecc11572128
Ref: c-api/object c PyObject_HashNotImplemented11572469
Ref: df711572469
Ref: c-api/object c PyObject_IsTrue11572816
Ref: 3ecd11572816
Ref: c-api/object c PyObject_Not11573058
Ref: 3ece11573058
Ref: c-api/object c PyObject_Type11573292
Ref: 3ecf11573292
Ref: c-api/object c PyObject_TypeCheck11573930
Ref: 3d8511573930
Ref: c-api/object c PyObject_Size11574128
Ref: 3ed011574128
Ref: c-api/object c PyObject_Length11574183
Ref: 3ed111574183
Ref: c-api/object c PyObject_LengthHint11574495
Ref: a0d11574495
Ref: c-api/object c PyObject_GetItem11574942
Ref: 3dc711574942
Ref: c-api/object c PyObject_SetItem11575207
Ref: 3dc511575207
Ref: c-api/object c PyObject_DelItem11575554
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Ref: c-api/object c PyObject_Dir11575788
Ref: 3ed311575788
Ref: c-api/object c PyObject_GetIter11576325
Ref: 3ed411576325
Ref: Object Protocol-Footnote-111576733
Ref: Object Protocol-Footnote-211576782
Node: Call Protocol11576831
Ref: c-api/call doc11576951
Ref: 3ed511576951
Ref: c-api/call call11576951
Ref: 3e4311576951
Ref: c-api/call call-protocol11576951
Ref: 3ed611576951
Node: The tp_call Protocol11577176
Ref: c-api/call the-tp-call-protocol11577278
Ref: 3ed711577278
Node: The Vectorcall Protocol11578015
Ref: c-api/call the-vectorcall-protocol11578144
Ref: 3ed911578144
Ref: c-api/call vectorcall11578144
Ref: 2b811578144
Ref: c-api/call c vectorcallfunc11579534
Ref: 3edd11579534
Ref: c-api/call c PY_VECTORCALL_ARGUMENTS_OFFSET11580483
Ref: 3edf11580483
Ref: The Vectorcall Protocol-Footnote-111582095
Node: Recursion Control<2>11582144
Ref: c-api/call recursion-control11582255
Ref: 3ee211582255
Node: Vectorcall Support API11582667
Ref: c-api/call vectorcall-support-api11582778
Ref: 3ee311582778
Ref: c-api/call c PyVectorcall_NARGS11582841
Ref: 3ede11582841
Ref: c-api/call c PyVectorcall_Function11583279
Ref: 3ee411583279
Ref: c-api/call c PyVectorcall_Call11583868
Ref: 3eda11583868
Node: Object Calling API11584471
Ref: c-api/call capi-call11584596
Ref: 3ed811584596
Ref: c-api/call object-calling-api11584596
Ref: 3ee511584596
Ref: c-api/call c PyObject_Call11589224
Ref: 23c11589224
Ref: c-api/call c PyObject_CallNoArgs11589857
Ref: 25011589857
Ref: c-api/call c PyObject_CallOneArg11590221
Ref: 25611590221
Ref: c-api/call c PyObject_CallObject11590628
Ref: 3d2911590628
Ref: c-api/call c PyObject_CallFunction11591092
Ref: 3f111591092
Ref: c-api/call c PyObject_CallMethod11591899
Ref: 3ee611591899
Ref: c-api/call c PyObject_CallFunctionObjArgs11592770
Ref: 3ee711592770
Ref: c-api/call c PyObject_CallMethodObjArgs11593297
Ref: 111411593297
Ref: c-api/call c PyObject_CallMethodNoArgs11593834
Ref: 3ee811593834
Ref: c-api/call c PyObject_CallMethodOneArg11594275
Ref: 3ee911594275
Ref: c-api/call c PyObject_Vectorcall11594753
Ref: 3ee111594753
Ref: c-api/call c PyObject_VectorcallDict11595322
Ref: 3eea11595322
Ref: c-api/call c PyObject_VectorcallMethod11596074
Ref: 3ee011596074
Node: Call Support API11597168
Ref: c-api/call call-support-api11597261
Ref: 3eec11597261
Ref: c-api/call c PyCallable_Check11597312
Ref: 3eed11597312
Node: Number Protocol11597513
Ref: c-api/number doc11597635
Ref: 3eee11597635
Ref: c-api/number number11597635
Ref: 3eef11597635
Ref: c-api/number number-protocol11597635
Ref: 3ef011597635
Ref: c-api/number c PyNumber_Check11597680
Ref: 39411597680
Ref: c-api/number c PyNumber_Add11597930
Ref: 3ef111597930
Ref: c-api/number c PyNumber_Subtract11598180
Ref: 3ef211598180
Ref: c-api/number c PyNumber_Multiply11598441
Ref: 3ef311598441
Ref: c-api/number c PyNumber_MatrixMultiply11598701
Ref: 89c11598701
Ref: c-api/number c PyNumber_FloorDivide11599016
Ref: 3ef411599016
Ref: c-api/number c PyNumber_TrueDivide11599281
Ref: 3ef511599281
Ref: c-api/number c PyNumber_Remainder11599772
Ref: 3ef611599772
Ref: c-api/number c PyNumber_Divmod11600042
Ref: 3ef711600042
Ref: c-api/number c PyNumber_Power11600316
Ref: 3ef811600316
Ref: c-api/number c PyNumber_Negative11600779
Ref: 3ef911600779
Ref: c-api/number c PyNumber_Positive11601010
Ref: 3efa11601010
Ref: c-api/number c PyNumber_Absolute11601220
Ref: 3efb11601220
Ref: c-api/number c PyNumber_Invert11601450
Ref: 3efc11601450
Ref: c-api/number c PyNumber_Lshift11601687
Ref: 3efd11601687
Ref: c-api/number c PyNumber_Rshift11601958
Ref: 3efe11601958
Ref: c-api/number c PyNumber_And11602230
Ref: 3eff11602230
Ref: c-api/number c PyNumber_Xor11602495
Ref: 3f0011602495
Ref: c-api/number c PyNumber_Or11602768
Ref: 3f0111602768
Ref: c-api/number c PyNumber_InPlaceAdd11603031
Ref: 3f0211603031
Ref: c-api/number c PyNumber_InPlaceSubtract11603360
Ref: 3f0311603360
Ref: c-api/number c PyNumber_InPlaceMultiply11603700
Ref: 3f0411603700
Ref: c-api/number c PyNumber_InPlaceMatrixMultiply11604039
Ref: 89d11604039
Ref: c-api/number c PyNumber_InPlaceFloorDivide11604423
Ref: 3f0511604423
Ref: c-api/number c PyNumber_InPlaceTrueDivide11604774
Ref: 3f0611604774
Ref: c-api/number c PyNumber_InPlaceRemainder11605334
Ref: 3f0711605334
Ref: c-api/number c PyNumber_InPlacePower11605673
Ref: 3f0811605673
Ref: c-api/number c PyNumber_InPlaceLshift11606268
Ref: 3f0911606268
Ref: c-api/number c PyNumber_InPlaceRshift11606618
Ref: 3f0a11606618
Ref: c-api/number c PyNumber_InPlaceAnd11606969
Ref: 3f0b11606969
Ref: c-api/number c PyNumber_InPlaceXor11607313
Ref: 3f0c11607313
Ref: c-api/number c PyNumber_InPlaceOr11607665
Ref: 3f0d11607665
Ref: c-api/number c PyNumber_Long11608007
Ref: 39511608007
Ref: c-api/number c PyNumber_Float11608262
Ref: 39611608262
Ref: c-api/number c PyNumber_Index11608517
Ref: 3f0e11608517
Ref: c-api/number c PyNumber_ToBase11608745
Ref: 107711608745
Ref: c-api/number c PyNumber_AsSsize_t11609206
Ref: 3f0f11609206
Ref: c-api/number c PyIndex_Check11609935
Ref: 26e11609935
Node: Sequence Protocol11610163
Ref: c-api/sequence doc11610288
Ref: 3f1011610288
Ref: c-api/sequence sequence11610288
Ref: 3f1111610288
Ref: c-api/sequence sequence-protocol11610288
Ref: 3f1211610288
Ref: c-api/sequence c PySequence_Check11610337
Ref: 3f1311610337
Ref: c-api/sequence c PySequence_Size11610747
Ref: 118211610747
Ref: c-api/sequence c PySequence_Length11610804
Ref: 3f1411610804
Ref: c-api/sequence c PySequence_Concat11611017
Ref: 3f1511611017
Ref: c-api/sequence c PySequence_Repeat11611283
Ref: 3f1611611283
Ref: c-api/sequence c PySequence_InPlaceConcat11611575
Ref: 3f1711611575
Ref: c-api/sequence c PySequence_InPlaceRepeat11611921
Ref: 3f1811611921
Ref: c-api/sequence c PySequence_GetItem11612282
Ref: 118311612282
Ref: c-api/sequence c PySequence_GetSlice11612523
Ref: 3f1911612523
Ref: c-api/sequence c PySequence_SetItem11612825
Ref: 118411612825
Ref: c-api/sequence c PySequence_DelItem11613324
Ref: 118511613324
Ref: c-api/sequence c PySequence_SetSlice11613536
Ref: 3f1a11613536
Ref: c-api/sequence c PySequence_DelSlice11613814
Ref: 3f1b11613814
Ref: c-api/sequence c PySequence_Count11614082
Ref: 3f1c11614082
Ref: c-api/sequence c PySequence_Contains11614406
Ref: 3f1d11614406
Ref: c-api/sequence c PySequence_Index11614701
Ref: 3f1e11614701
Ref: c-api/sequence c PySequence_List11614956
Ref: 3f1f11614956
Ref: c-api/sequence c PySequence_Tuple11615271
Ref: 3f2011615271
Ref: c-api/sequence c PySequence_Fast11615679
Ref: 3f2111615679
Ref: c-api/sequence c PySequence_Fast_GET_SIZE11616363
Ref: 3f2311616363
Ref: c-api/sequence c PySequence_Fast_GET_ITEM11616759
Ref: 3f2411616759
Ref: c-api/sequence c PySequence_Fast_ITEMS11617053
Ref: 3f2511617053
Ref: c-api/sequence c PySequence_ITEM11617457
Ref: 3f2611617457
Node: Mapping Protocol11617806
Ref: c-api/mapping doc11617933
Ref: 3f2711617933
Ref: c-api/mapping mapping11617933
Ref: 3f2811617933
Ref: c-api/mapping mapping-protocol11617933
Ref: 3f2911617933
Ref: c-api/mapping c PyMapping_Check11618090
Ref: 3f2a11618090
Ref: c-api/mapping c PyMapping_Size11618469
Ref: 118611618469
Ref: c-api/mapping c PyMapping_Length11618525
Ref: 3f2b11618525
Ref: c-api/mapping c PyMapping_GetItemString11618732
Ref: 3f2c11618732
Ref: c-api/mapping c PyMapping_SetItemString11619063
Ref: 3f2d11619063
Ref: c-api/mapping c PyMapping_DelItem11619426
Ref: 3f2e11619426
Ref: c-api/mapping c PyMapping_DelItemString11619714
Ref: 3f2f11619714
Ref: c-api/mapping c PyMapping_HasKey11619967
Ref: 3f3011619967
Ref: c-api/mapping c PyMapping_HasKeyString11620410
Ref: 3f3111620410
Ref: c-api/mapping c PyMapping_Keys11620922
Ref: 53011620922
Ref: c-api/mapping c PyMapping_Values11621193
Ref: 53111621193
Ref: c-api/mapping c PyMapping_Items11621468
Ref: 53211621468
Node: Iterator Protocol11621802
Ref: c-api/iter doc11621927
Ref: 3f3211621927
Ref: c-api/iter iterator11621927
Ref: 3f3311621927
Ref: c-api/iter iterator-protocol11621927
Ref: 3f3411621927
Ref: c-api/iter c PyIter_Check11622042
Ref: 114911622042
Ref: c-api/iter c PyIter_Next11622195
Ref: 3f3511622195
Node: Buffer Protocol11623161
Ref: c-api/buffer doc11623289
Ref: 3f3611623289
Ref: c-api/buffer buffer-protocol11623289
Ref: 3f3711623289
Ref: c-api/buffer bufferobjects11623289
Ref: 171c11623289
Node: Buffer structure11625811
Ref: c-api/buffer buffer-structure11625908
Ref: 3f3911625908
Ref: c-api/buffer id111625908
Ref: 3f3a11625908
Ref: c-api/buffer c Py_buffer11626983
Ref: bee11626983
Ref: c-api/buffer c Py_buffer buf11627006
Ref: 3f3c11627006
Ref: c-api/buffer c Py_buffer obj11627467
Ref: 3f3e11627467
Ref: c-api/buffer c Py_buffer len11628048
Ref: 3f4111628048
Ref: c-api/buffer c Py_buffer readonly11628648
Ref: 3f4411628648
Ref: c-api/buffer c Py_buffer itemsize11628818
Ref: 3f4511628818
Ref: c-api/buffer c Py_buffer format11629735
Ref: 3f4611629735
Ref: c-api/buffer c Py_buffer ndim11630062
Ref: 3f4911630062
Ref: c-api/buffer c Py_buffer shape11630660
Ref: 3f4811630660
Ref: c-api/buffer c Py_buffer strides11631207
Ref: 3f3d11631207
Ref: c-api/buffer c Py_buffer suboffsets11631727
Ref: 3f4a11631727
Ref: c-api/buffer c Py_buffer internal11632614
Ref: 3f4c11632614
Node: Buffer request types11632989
Ref: c-api/buffer buffer-request-types11633109
Ref: 3f4d11633109
Ref: c-api/buffer id211633109
Ref: 3f4e11633109
Node: request-independent fields11633717
Ref: c-api/buffer request-independent-fields11633824
Ref: 3f4f11633824
Node: readonly format11634092
Ref: c-api/buffer readonly-format11634232
Ref: 3f5011634232
Ref: c-api/buffer c PyBUF_WRITABLE11634283
Ref: 3f4311634283
Ref: c-api/buffer c PyBUF_FORMAT11634616
Ref: 3f4711634616
Node: shape strides suboffsets11635197
Ref: c-api/buffer shape-strides-suboffsets11635330
Ref: 3f5111635330
Ref: c-api/buffer c PyBUF_INDIRECT11635867
Ref: 3f5211635867
Ref: c-api/buffer c PyBUF_STRIDES11636058
Ref: 3f5311636058
Ref: c-api/buffer c PyBUF_ND11636240
Ref: 3f5411636240
Ref: c-api/buffer c PyBUF_SIMPLE11636431
Ref: 3f4211636431
Node: contiguity requests11636533
Ref: c-api/buffer contiguity-requests11636668
Ref: 3f5511636668
Ref: c-api/buffer c PyBUF_C_CONTIGUOUS11637277
Ref: 3f5611637277
Ref: c-api/buffer c PyBUF_F_CONTIGUOUS11637530
Ref: 3f5711637530
Ref: c-api/buffer c PyBUF_ANY_CONTIGUOUS11637785
Ref: 3f5811637785
Node: compound requests11638180
Ref: c-api/buffer compound-requests11638282
Ref: 3f5911638282
Ref: c-api/buffer c PyBUF_FULL11639157
Ref: 3f5b11639157
Ref: c-api/buffer c PyBUF_FULL_RO11639487
Ref: 3f5c11639487
Ref: c-api/buffer c PyBUF_RECORDS11639814
Ref: 3f5d11639814
Ref: c-api/buffer c PyBUF_RECORDS_RO11640144
Ref: 3f5e11640144
Ref: c-api/buffer c PyBUF_STRIDED11640468
Ref: 3f5f11640468
Ref: c-api/buffer c PyBUF_STRIDED_RO11640799
Ref: 3f6011640799
Ref: c-api/buffer c PyBUF_CONTIG11641123
Ref: 3f6111641123
Ref: c-api/buffer c PyBUF_CONTIG_RO11641454
Ref: 3f6211641454
Node: Complex arrays11641647
Ref: c-api/buffer complex-arrays11641775
Ref: 3f4b11641775
Node: NumPy-style shape and strides11641981
Ref: c-api/buffer numpy-style-shape-and-strides11642108
Ref: 3f6311642108
Node: PIL-style shape strides and suboffsets11643988
Ref: c-api/buffer pil-style-shape-strides-and-suboffsets11644115
Ref: 3f6411644115
Node: Buffer-related functions11645341
Ref: c-api/buffer buffer-related-functions11645440
Ref: 3f6511645440
Ref: c-api/buffer c PyObject_CheckBuffer11645509
Ref: 26c11645509
Ref: c-api/buffer c PyObject_GetBuffer11645794
Ref: deb11645794
Ref: c-api/buffer c PyBuffer_Release11646742
Ref: e1911646742
Ref: c-api/buffer c PyBuffer_SizeFromFormat11647123
Ref: 10c411647123
Ref: c-api/buffer c PyBuffer_IsContiguous11647343
Ref: 3f5a11647343
Ref: c-api/buffer c PyBuffer_GetPointer11647682
Ref: 3f6611647682
Ref: c-api/buffer c PyBuffer_FromContiguous11647921
Ref: 3f6711647921
Ref: c-api/buffer c PyBuffer_ToContiguous11648229
Ref: 3f6811648229
Ref: c-api/buffer c PyBuffer_FillContiguousStrides11648639
Ref: 3f6911648639
Ref: c-api/buffer c PyBuffer_FillInfo11649027
Ref: 3f4011649027
Node: Old Buffer Protocol11650004
Ref: c-api/objbuffer doc11650106
Ref: 3f6a11650106
Ref: c-api/objbuffer old-buffer-protocol11650106
Ref: 3f6b11650106
Ref: c-api/objbuffer c PyObject_AsCharBuffer11650868
Ref: 3f6c11650868
Ref: c-api/objbuffer c PyObject_AsReadBuffer11651342
Ref: 3f6d11651342
Ref: c-api/objbuffer c PyObject_CheckReadBuffer11651803
Ref: 3f6e11651803
Ref: c-api/objbuffer c PyObject_AsWriteBuffer11652248
Ref: 3f6f11652248
Node: Concrete Objects Layer11652680
Ref: c-api/concrete doc11652847
Ref: 3f7011652847
Ref: c-api/concrete concrete11652847
Ref: 3f7111652847
Ref: c-api/concrete concrete-objects-layer11652847
Ref: 3f7211652847
Node: Fundamental Objects11653832
Ref: c-api/concrete fundamental11653934
Ref: 3f7411653934
Ref: c-api/concrete fundamental-objects11653934
Ref: 3f7511653934
Node: Type Objects<2>11654131
Ref: c-api/type doc11654226
Ref: 3f7611654226
Ref: c-api/type type-objects11654226
Ref: 3f7711654226
Ref: c-api/type typeobjects11654226
Ref: 3f7811654226
Ref: c-api/type c PyTypeObject11654269
Ref: 3f511654269
Ref: c-api/type c PyType_Type11654365
Ref: 3f7911654365
Ref: c-api/type c PyType_Check11654523
Ref: 109411654523
Ref: c-api/type c PyType_CheckExact11654769
Ref: 109511654769
Ref: c-api/type c PyType_ClearCache11654998
Ref: 3f7a11654998
Ref: c-api/type c PyType_GetFlags11655121
Ref: 101211655121
Ref: c-api/type c PyType_Modified11655615
Ref: 3f7b11655615
Ref: c-api/type c PyType_HasFeature11655872
Ref: 101011655872
Ref: c-api/type c PyType_IS_GC11656067
Ref: 3f7c11656067
Ref: c-api/type c PyType_IsSubtype11656259
Ref: 3f7d11656259
Ref: c-api/type c PyType_GenericAlloc11656619
Ref: 39911656619
Ref: c-api/type c PyType_GenericNew11656963
Ref: 3d5411656963
Ref: c-api/type c PyType_Ready11657255
Ref: 3d5911657255
Ref: c-api/type c PyType_GetSlot11658109
Ref: a0911658109
Ref: c-api/type c PyType_GetModule11658642
Ref: 24611658642
Ref: c-api/type c PyType_GetModuleState11659414
Ref: 24711659414
Node: Creating Heap-Allocated Types11659986
Ref: c-api/type creating-heap-allocated-types11660067
Ref: 3f7e11660067
Ref: c-api/type c PyType_FromModuleAndSpec11660224
Ref: 24511660224
Ref: c-api/type c PyType_FromSpecWithBases11661296
Ref: 102d11661296
Ref: c-api/type c PyType_FromSpec11661528
Ref: 23a11661528
Ref: c-api/type c PyType_Spec11661691
Ref: 3f8111661691
Ref: c-api/type c PyType_Spec PyType_Spec name11661762
Ref: 3f8211661762
Ref: c-api/type c PyType_Spec PyType_Spec basicsize11661896
Ref: 3f8311661896
Ref: c-api/type c PyType_Spec PyType_Spec itemsize11661942
Ref: 3f8411661942
Ref: c-api/type c PyType_Spec PyType_Spec flags11662141
Ref: 3f8511662141
Ref: c-api/type c PyType_Spec PyType_Spec slots11662387
Ref: 3f8611662387
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Ref: c-api/float c PyFloat_AS_DOUBLE11681017
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Ref: c-api/float c PyFloat_GetMin11681593
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Ref: c-api/complex doc11681825
Ref: 3fc111681825
Ref: c-api/complex complex-number-objects11681825
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Ref: c-api/complex complexobjects11681825
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Ref: c-api/complex c PyComplex_RealAsDouble11685761
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Ref: c-api/complex c PyComplex_ImagAsDouble11685879
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Ref: c-api/bytes doc11687275
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Ref: c-api/bytearray c PyByteArray_GET_SIZE11700528
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Ref: c-api/unicode unicode-objects-and-codecs11700782
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Ref: c-api/unicode unicodeobjects11700782
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Ref: Unicode Objects-Footnote-111702717
Ref: Unicode Objects-Footnote-211702766
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Ref: c-api/unicode unicode-type11702916
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Ref: c-api/unicode c PyUnicode_GET_LENGTH11705262
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Ref: c-api/unicode c PyUnicode_2BYTE_DATA11705569
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Ref: c-api/unicode c PyUnicode_4BYTE_DATA11705629
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Ref: c-api/unicode c PyUnicode_WCHAR_KIND11706094
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Ref: c-api/unicode c PyUnicode_1BYTE_KIND11706128
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Ref: c-api/unicode c PyUnicode_2BYTE_KIND11706162
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Ref: c-api/unicode c PyUnicode_4BYTE_KIND11706196
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Ref: c-api/unicode c PyUnicode_KIND11706437
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Ref: c-api/unicode c PyUnicode_DATA11706770
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Ref: c-api/unicode c PyUnicode_WRITE11706993
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Ref: c-api/unicode c PyUnicode_READ_CHAR11707840
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Ref: c-api/unicode c Py_UNICODE_ISSPACE11711197
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Ref: c-api/unicode c Py_UNICODE_ISUPPER11711482
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Ref: c-api/unicode c Py_UNICODE_ISTITLE11711625
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Ref: c-api/unicode c Py_UNICODE_ISDIGIT11712050
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Ref: c-api/unicode c Py_UNICODE_ISNUMERIC11712183
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Ref: c-api/unicode c Py_UNICODE_ISALPHA11712320
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Ref: c-api/unicode c Py_UNICODE_ISALNUM11712464
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Ref: c-api/unicode c Py_UNICODE_ISPRINTABLE11712610
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Ref: c-api/unicode c Py_UNICODE_TOLOWER11713278
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Ref: c-api/unicode c Py_UNICODE_TOUPPER11713474
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Ref: c-api/unicode c Py_UNICODE_TODECIMAL11713866
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Ref: c-api/unicode c Py_UNICODE_TODIGIT11714084
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Ref: c-api/unicode c Py_UNICODE_TONUMERIC11714296
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Ref: c-api/unicode c Py_UNICODE_IS_SURROGATE11714546
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Ref: c-api/unicode c Py_UNICODE_IS_HIGH_SURROGATE11714656
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Ref: c-api/unicode c Py_UNICODE_IS_LOW_SURROGATE11714776
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Ref: c-api/unicode c Py_UNICODE_JOIN_SURROGATES11714894
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Ref: 401211715281
Ref: c-api/unicode c PyUnicode_New11715465
Ref: ba411715465
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Ref: ba111725687
Ref: c-api/unicode c PyUnicode_Fill11726164
Ref: bce11726164
Ref: c-api/unicode c PyUnicode_WriteChar11726643
Ref: ba711726643
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Ref: c-api/unicode c PyUnicode_AsUCS411727855
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Ref: c-api/unicode c PyUnicode_AsUCS4Copy11728286
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Ref: Creating and accessing Unicode strings-Footnote-111728666
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Ref: Creating and accessing Unicode strings-Footnote-411729125
Ref: Creating and accessing Unicode strings-Footnote-511729278
Ref: Creating and accessing Unicode strings-Footnote-611729431
Ref: Creating and accessing Unicode strings-Footnote-711729584
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Ref: c-api/unicode deprecated-py-unicode-apis11730808
Ref: 401611730808
Ref: c-api/unicode c PyUnicode_FromUnicode11731186
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Ref: c-api/unicode c PyUnicode_AsUnicode11732232
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Ref: c-api/unicode c PyUnicode_TransformDecimalToASCII11733129
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Ref: Deprecated Py_UNICODE APIs-Footnote-111735881
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Ref: c-api/unicode c PyUnicode_DecodeLocale11737374
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Ref: File System Encoding-Footnote-211743119
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Ref: c-api/unicode wchar-t-support11743264
Ref: 401c11743264
Ref: c-api/unicode c PyUnicode_FromWideChar11743370
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Ref: c-api/unicode c PyUnicode_AsWideCharString11744541
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Ref: c-api/unicode built-in-codecs11745752
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Ref: c-api/unicode builtincodecs11745752
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Ref: c-api/unicode generic-codecs11747268
Ref: 401e11747268
Ref: c-api/unicode c PyUnicode_Decode11747352
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Ref: c-api/unicode utf-8-codecs11749235
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Ref: c-api/unicode c PyUnicode_EncodeUTF811751610
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Ref: c-api/unicode utf-32-codecs11752340
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Ref: c-api/unicode c PyUnicode_DecodeUTF3211752421
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Ref: c-api/unicode c PyUnicode_DecodeUTF32Stateful11753571
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Ref: c-api/unicode c PyUnicode_AsUTF32String11754193
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Ref: c-api/unicode c PyUnicode_EncodeUTF3211754528
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Ref: c-api/unicode utf-7-codecs11759250
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Ref: c-api/unicode c PyUnicode_EncodeUTF711760128
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Ref: c-api/unicode c PyUnicode_DecodeUnicodeEscape11761209
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Ref: c-api/unicode c PyUnicode_AsUnicodeEscapeString11761527
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Ref: c-api/unicode c PyUnicode_EncodeUnicodeEscape11761847
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Ref: c-api/unicode raw-unicode-escape-codecs11762498
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Ref: c-api/unicode c PyUnicode_DecodeRawUnicodeEscape11762621
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Ref: c-api/unicode c PyUnicode_AsRawUnicodeEscapeString11762946
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Ref: c-api/unicode c PyUnicode_EncodeRawUnicodeEscape11763273
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Node: Latin-1 Codecs11763858
Ref: c-api/unicode latin-1-codecs11763979
Ref: 403211763979
Ref: c-api/unicode c PyUnicode_DecodeLatin111764176
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Ref: c-api/unicode c PyUnicode_AsLatin1String11764480
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Ref: c-api/unicode c PyUnicode_EncodeLatin111764781
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Node: ASCII Codecs11765357
Ref: c-api/unicode ascii-codecs11765473
Ref: 403411765473
Ref: c-api/unicode c PyUnicode_DecodeASCII11765621
Ref: 403511765621
Ref: c-api/unicode c PyUnicode_AsASCIIString11765922
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Ref: c-api/unicode c PyUnicode_EncodeASCII11766215
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Node: Character Map Codecs11766787
Ref: c-api/unicode character-map-codecs11766912
Ref: 403611766912
Ref: c-api/unicode c PyUnicode_DecodeCharmap11767391
Ref: 403711767391
Ref: c-api/unicode c PyUnicode_AsCharmapString11768215
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Ref: c-api/unicode c PyUnicode_EncodeCharmap11768875
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Ref: c-api/unicode c PyUnicode_Translate11769573
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Ref: c-api/unicode c PyUnicode_TranslateCharmap11770412
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Node: MBCS codecs for Windows11771060
Ref: c-api/unicode mbcs-codecs-for-windows11771188
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Ref: c-api/unicode c PyUnicode_DecodeMBCS11771548
Ref: 403b11771548
Ref: c-api/unicode c PyUnicode_DecodeMBCSStateful11771847
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Ref: c-api/unicode c PyUnicode_AsMBCSString11772312
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Ref: c-api/unicode c PyUnicode_EncodeCodePage11772603
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Ref: c-api/unicode c PyUnicode_EncodeMBCS11773001
Ref: bdf11773001
Node: Methods & Slots11773613
Ref: c-api/unicode methods-slots11773712
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Node: Methods and Slot Functions11773763
Ref: c-api/unicode methods-and-slot-functions11773876
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Ref: c-api/unicode unicodemethodsandslots11773876
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Ref: c-api/unicode c PyUnicode_Concat11774199
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Ref: c-api/unicode c PyUnicode_Split11774377
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Ref: c-api/unicode c PyUnicode_Splitlines11774842
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Ref: c-api/unicode c PyUnicode_Join11775192
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Ref: c-api/unicode c PyUnicode_Tailmatch11775419
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Ref: c-api/unicode c PyUnicode_Find11775820
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Ref: c-api/unicode c PyUnicode_FindChar11776368
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Ref: c-api/unicode c PyUnicode_Count11777047
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Ref: c-api/unicode c PyUnicode_Replace11777305
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Ref: c-api/unicode c PyUnicode_Compare11777657
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Ref: c-api/unicode c PyUnicode_CompareWithASCIIString11777979
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Ref: c-api/unicode c PyUnicode_RichCompare11778435
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Ref: c-api/unicode c PyUnicode_Format11778965
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Ref: c-api/unicode c PyUnicode_Contains11779191
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Ref: c-api/unicode c PyUnicode_InternInPlace11779496
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Ref: c-api/unicode c PyUnicode_InternFromString11780271
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Ref: c-api/tuple tuple-objects11780787
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Ref: c-api/tuple tupleobjects11780787
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Ref: c-api/tuple c PyTuple_Type11780943
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Ref: c-api/tuple c PyTuple_GetSlice11782830
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Ref: c-api/tuple c _PyTuple_Resize11784158
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Ref: c-api/tuple c PyStructSequence_NewType11785500
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Ref: c-api/tuple c PyStructSequence_InitType11785813
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Ref: c-api/list listobjects11790460
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Ref: c-api/list c PyList_Type11790612
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Ref: c-api/list c PyList_Check11790811
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Ref: c-api/concrete container-objects11795710
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Ref: c-api/concrete mapobjects11795710
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Ref: c-api/dict c PyDict_Check11796273
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Ref: c-api/dict c PyDictProxy_New11796770
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Ref: c-api/dict c PyDict_Clear11797096
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Ref: Multi-phase initialization-Footnote-211844920
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Ref: c-api/module c PyState_RemoveModule11852500
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Ref: c-api/descriptor id111854821
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Ref: c-api/slice c Py_Ellipsis11861016
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Ref: c-api/memoryview memoryview-objects11861276
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Ref: c-api/memoryview c PyMemoryView_FromBuffer11862292
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Ref: c-api/memoryview c PyMemoryView_GET_BASE11863597
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Ref: c-api/weakref weakrefobjects11864088
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Ref: c-api/weakref c PyWeakref_GetObject11866374
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Ref: c-api/weakref c PyWeakref_GET_OBJECT11866880
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Ref: c-api/capsule c PyCapsule11867386
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Ref: c-api/capsule c PyCapsule_Destructor11867830
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Ref: c-api/capsule c PyCapsule_CheckExact11868090
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Ref: c-api/capsule c PyCapsule_GetPointer11869157
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Ref: c-api/capsule c PyCapsule_IsValid11871527
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Ref: c-api/capsule c PyCapsule_SetContext11872307
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Ref: c-api/capsule c PyCapsule_SetDestructor11872542
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Ref: c-api/capsule c PyCapsule_SetName11872796
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Ref: c-api/capsule c PyCapsule_SetPointer11873179
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Ref: c-api/gen c PyGen_NewWithQualName11874653
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Ref: c-api/coro c PyCoro_CheckExact11875534
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Ref: c-api/contextvars c PyContext_Enter11878741
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Ref: c-api/contextvars c PyContextVar_Reset11880485
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Ref: Context Variables Objects-Footnote-111880821
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Ref: c-api/datetime c PyDateTime_FromTimestamp11889103
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Ref: c-api/typehints c Py_GenericAlias11889909
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Ref: Global configuration variables-Footnote-111899603
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Ref: Low-level API-Footnote-111942952
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Ref: c-api/init c Py_tss_t11961690
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Ref: c-api/init c Py_tss_NEEDS_INIT11962130
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Ref: Thread Specific Storage TSS API-Footnote-111962418
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Ref: 41cb11962572
Ref: c-api/init c PyThread_tss_alloc11962853
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Ref: c-api/init c PyThread_tss_free11963073
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Ref: c-api/init c PyThread_tss_is_created11963906
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Ref: c-api/init c PyThread_tss_delete11964512
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Node: Sequence Object Structures12162138
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Node: Slot Type typedefs12170897
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Node: Supporting Cyclic Garbage Collection12179898
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Node: Distributing Python Modules12189704
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Node: Open source licensing and collaboration12193398
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Node: Installing the tools12194566
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Node: Reading the Python Packaging User Guide12195744
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Node: How do I…?12196653
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Node: … choose a name for my project?12196964
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Node: … create and distribute binary extensions?12197674
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Node: Installing Python Modules12198304
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Node: Basic usage12201985
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Node: How do I …?12203838
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Node: … install pip in versions of Python prior to Python 3 4?12204357
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Node: … install packages just for the current user?12205040
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Node: … install scientific Python packages?12205514
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Node: … work with multiple versions of Python installed in parallel?12206330
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Node: Common installation issues12207464
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Node: Installing into the system Python on Linux12207749
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Node: Pip not installed12208447
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Node: Installing binary extensions12208991
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Node: Python HOWTOs12210093
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Node: Porting Python 2 Code to Python 312211096
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Node: The Short Explanation12212305
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Node: Details12214220
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Node: Drop support for Python 2 6 and older12215803
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Node: Make sure you specify the proper version support in your setup py file12217375
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Node: Have good test coverage12218206
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Node: Learn the differences between Python 2 & 312219131
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Node: Update your code12220030
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Node: Division12222712
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Node: Text versus binary data12223861
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Node: Use feature detection instead of version detection12230566
Ref: howto/pyporting use-feature-detection-instead-of-version-detection12230701
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Node: Prevent compatibility regressions12232448
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Node: Check which dependencies block your transition12234095
Ref: howto/pyporting check-which-dependencies-block-your-transition12234294
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Ref: Check which dependencies block your transition-Footnote-112235156
Node: Update your setup py file to denote Python 3 compatibility12235204
Ref: howto/pyporting update-your-setup-py-file-to-denote-python-3-compatibility12235415
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Node: Use continuous integration to stay compatible12235929
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Ref: Use continuous integration to stay compatible-Footnote-112237450
Node: Consider using optional static type checking12237487
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Ref: Consider using optional static type checking-Footnote-212238440
Node: Porting Extension Modules to Python 312238481
Ref: howto/cporting doc12238649
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Ref: Porting Extension Modules to Python 3-Footnote-212239482
Ref: Porting Extension Modules to Python 3-Footnote-312239539
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Ref: For More Information-Footnote-212266191
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Ref: howto/functional introduction12317531
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Ref: howto/functional references12368275
Ref: 435212368275
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Ref: 436112385070
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Ref: howto/logging handlers12394307
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Ref: howto/logging logging logging Formatter __init__12396942
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Ref: Running a logging socket listener in production-Footnote-112447697
Ref: Running a logging socket listener in production-Footnote-212447729
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Ref: 221812448025
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Ref: 438512457254
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Ref: 438612467929
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Ref: howto/logging-cookbook deploying-web-applications-using-gunicorn-and-uwsgi12469124
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Ref: Deploying Web applications using Gunicorn and uWSGI-Footnote-112469784
Ref: Deploying Web applications using Gunicorn and uWSGI-Footnote-212469814
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Ref: Inserting a BOM into messages sent to a SysLogHandler-Footnote-112501915
Ref: Inserting a BOM into messages sent to a SysLogHandler-Footnote-212501964
Ref: Inserting a BOM into messages sent to a SysLogHandler-Footnote-312502023
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Ref: 43c912622544
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Ref: howto/sockets creating-a-socket12627672
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Ref: howto/sockets ipc12630985
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Ref: howto/sockets using-a-socket12631554
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Ref: howto/sockets binary-data12637755
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Ref: howto/sockets non-blocking-sockets12641481
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Ref: howto/sorting doc12645421
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Ref: howto/sorting sorting-basics12646140
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Ref: howto/sorting key-functions12647063
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Ref: howto/sorting ascending-and-descending12650113
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Ref: Sort Stability and Complex Sorts-Footnote-112652452
Ref: Sort Stability and Complex Sorts-Footnote-212652518
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Ref: 43dd12652742
Ref: The Old Way Using Decorate-Sort-Undecorate-Footnote-112654431
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Ref: howto/sorting the-old-way-using-the-cmp-parameter12654649
Ref: 43de12654649
Node: Odd and Ends12657125
Ref: howto/sorting odd-and-ends12657232
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Ref: howto/unicode doc12659102
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Ref: howto/unicode id112659102
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Ref: d0412659102
Node: Introduction to Unicode12659504
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Node: Definitions12659746
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Node: References<3>12666752
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Node: Python’s Unicode Support12668166
Ref: howto/unicode python-s-unicode-support12668315
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Node: The String Type12668684
Ref: howto/unicode the-string-type12668790
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Node: Converting to Bytes12671902
Ref: howto/unicode converting-to-bytes12672055
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Node: Unicode Literals in Python Source Code12673901
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Ref: Unicode Literals in Python Source Code-Footnote-112676164
Node: Unicode Properties12676213
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Node: Comparing Strings12678204
Ref: howto/unicode comparing-strings12678347
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Node: Unicode Regular Expressions12681194
Ref: howto/unicode unicode-regular-expressions12681332
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Node: References<4>12682473
Ref: howto/unicode id212682585
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Ref: References<4>-Footnote-112683373
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Ref: References<4>-Footnote-312683520
Node: Reading and Writing Unicode Data12683589
Ref: howto/unicode reading-and-writing-unicode-data12683735
Ref: 43ee12683735
Node: Unicode filenames12687446
Ref: howto/unicode unicode-filenames12687580
Ref: 43ef12687580
Node: Tips for Writing Unicode-aware Programs12690018
Ref: howto/unicode tips-for-writing-unicode-aware-programs12690174
Ref: 43f012690174
Node: Converting Between File Encodings12691539
Ref: howto/unicode converting-between-file-encodings12691685
Ref: 43f112691685
Node: Files in an Unknown Encoding12692456
Ref: howto/unicode files-in-an-unknown-encoding12692602
Ref: 43f212692602
Node: References<5>12693505
Ref: howto/unicode id312693635
Ref: 43f312693635
Ref: References<5>-Footnote-112694245
Ref: References<5>-Footnote-212694318
Ref: References<5>-Footnote-312694423
Node: Acknowledgements<10>12694491
Ref: howto/unicode acknowledgements12694602
Ref: 43f412694602
Node: HOWTO Fetch Internet Resources Using The urllib Package12695128
Ref: howto/urllib2 doc12695281
Ref: 43f512695281
Ref: howto/urllib2 howto-fetch-internet-resources-using-the-urllib-package12695281
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Ref: howto/urllib2 urllib-howto12695281
Ref: 2deb12695281
Ref: HOWTO Fetch Internet Resources Using The urllib Package-Footnote-112695828
Ref: HOWTO Fetch Internet Resources Using The urllib Package-Footnote-212695883
Node: Introduction<16>12695959
Ref: howto/urllib2 introduction12696089
Ref: 43f712696089
Ref: Introduction<16>-Footnote-112697685
Ref: Introduction<16>-Footnote-212697758
Node: Fetching URLs12697807
Ref: howto/urllib2 fetching-urls12697968
Ref: 43f812697968
Node: Data12700216
Ref: howto/urllib2 data12700286
Ref: 43f912700286
Ref: Data-Footnote-112702939
Node: Headers12703008
Ref: howto/urllib2 headers12703078
Ref: 43fa12703078
Ref: Headers-Footnote-112704592
Ref: Headers-Footnote-212704624
Ref: Headers-Footnote-312704838
Ref: Headers-Footnote-412704962
Node: Handling Exceptions<2>12705084
Ref: howto/urllib2 handling-exceptions12705244
Ref: 43fc12705244
Node: URLError12705729
Ref: howto/urllib2 urlerror12705814
Ref: 43fd12705814
Node: HTTPError12706368
Ref: howto/urllib2 httperror12706476
Ref: 43fe12706476
Ref: HTTPError-Footnote-112707358
Node: Error Codes12707407
Ref: howto/urllib2 error-codes12707464
Ref: 43ff12707464
Ref: Error Codes-Footnote-112712217
Node: Wrapping it Up12712266
Ref: howto/urllib2 wrapping-it-up12712357
Ref: 440012712357
Node: Number 112712578
Ref: howto/urllib2 number-112712654
Ref: 440112712654
Node: Number 212713276
Ref: howto/urllib2 number-212713352
Ref: 440212713352
Node: info and geturl12713886
Ref: howto/urllib2 info-and-geturl12714053
Ref: 43fb12714053
Ref: info and geturl-Footnote-112714939
Node: Openers and Handlers12714976
Ref: howto/urllib2 openers-and-handlers12715141
Ref: 440312715141
Node: Basic Authentication12716791
Ref: howto/urllib2 id512716948
Ref: 440412716948
Ref: Basic Authentication-Footnote-112720363
Node: Proxies12720436
Ref: howto/urllib2 proxies12720591
Ref: 440512720591
Ref: Proxies-Footnote-112721615
Ref: Proxies-Footnote-212721922
Ref: Proxies-Footnote-312721995
Node: Sockets and Layers12722122
Ref: howto/urllib2 sockets-and-layers12722266
Ref: 440612722266
Node: Footnotes12723287
Ref: howto/urllib2 footnotes12723415
Ref: 440712723415
Node: Argparse Tutorial12723505
Ref: howto/argparse doc12723684
Ref: 440812723684
Ref: howto/argparse argparse-tutorial12723684
Ref: 440912723684
Ref: howto/argparse id112723764
Ref: 218512723764
Node: Concepts12724445
Ref: howto/argparse concepts12724526
Ref: 440a12724526
Node: The basics12726616
Ref: howto/argparse the-basics12726738
Ref: 440b12726738
Node: Introducing Positional arguments12727914
Ref: howto/argparse introducing-positional-arguments12728058
Ref: 440c12728058
Node: Introducing Optional arguments12731350
Ref: howto/argparse introducing-optional-arguments12731527
Ref: 440d12731527
Node: Short options12734536
Ref: howto/argparse short-options12734616
Ref: 440e12734616
Node: Combining Positional and Optional arguments12735422
Ref: howto/argparse combining-positional-and-optional-arguments12735597
Ref: 440f12735597
Node: Getting a little more advanced12743846
Ref: howto/argparse getting-a-little-more-advanced12744001
Ref: 441012744001
Node: Conflicting options12746027
Ref: howto/argparse conflicting-options12746113
Ref: 441112746113
Node: Conclusion12749273
Ref: howto/argparse conclusion12749376
Ref: 441212749376
Node: An introduction to the ipaddress module12749641
Ref: howto/ipaddress doc12749787
Ref: 441312749787
Ref: howto/ipaddress an-introduction-to-the-ipaddress-module12749787
Ref: 441412749787
Ref: howto/ipaddress ipaddress-howto12749787
Ref: 304312749787
Node: Creating Address/Network/Interface objects12750530
Ref: howto/ipaddress creating-address-network-interface-objects12750701
Ref: 441512750701
Node: A Note on IP Versions12751128
Ref: howto/ipaddress a-note-on-ip-versions12751254
Ref: 441612751254
Node: IP Host Addresses12752037
Ref: howto/ipaddress ip-host-addresses12752189
Ref: 441712752189
Node: Defining Networks12753376
Ref: howto/ipaddress defining-networks12753522
Ref: 441812753522
Node: Host Interfaces12755880
Ref: howto/ipaddress host-interfaces12756000
Ref: 441912756000
Node: Inspecting Address/Network/Interface Objects12757005
Ref: howto/ipaddress inspecting-address-network-interface-objects12757215
Ref: 441a12757215
Node: Networks as lists of Addresses12759565
Ref: howto/ipaddress networks-as-lists-of-addresses12759747
Ref: 441b12759747
Node: Comparisons<4>12760546
Ref: howto/ipaddress comparisons12760721
Ref: 441c12760721
Node: Using IP Addresses with other modules12761080
Ref: howto/ipaddress using-ip-addresses-with-other-modules12761273
Ref: 441d12761273
Node: Getting more detail when instance creation fails12761704
Ref: howto/ipaddress getting-more-detail-when-instance-creation-fails12761874
Ref: 441e12761874
Node: Argument Clinic How-To12763932
Ref: howto/clinic doc12764108
Ref: 441f12764108
Ref: howto/clinic argument-clinic-how-to12764108
Ref: 442012764108
Node: The Goals Of Argument Clinic12765145
Ref: howto/clinic the-goals-of-argument-clinic12765265
Ref: 442112765265
Node: Basic Concepts And Usage12767631
Ref: howto/clinic basic-concepts-and-usage12767790
Ref: 442212767790
Node: Converting Your First Function12770225
Ref: howto/clinic converting-your-first-function12770371
Ref: 442312770371
Node: Advanced Topics12786518
Ref: howto/clinic advanced-topics12786631
Ref: 442512786631
Node: Symbolic default values12787611
Ref: howto/clinic symbolic-default-values12787762
Ref: 442612787762
Node: Renaming the C functions and variables generated by Argument Clinic12788392
Ref: howto/clinic renaming-the-c-functions-and-variables-generated-by-argument-clinic12788596
Ref: 442712788596
Node: Converting functions using PyArg_UnpackTuple12790259
Ref: howto/clinic converting-functions-using-pyarg-unpacktuple12790455
Ref: 442812790455
Node: Optional Groups12791000
Ref: howto/clinic optional-groups12791201
Ref: 442912791201
Node: Using real Argument Clinic converters instead of “legacy converters”12795250
Ref: howto/clinic using-real-argument-clinic-converters-instead-of-legacy-converters12795416
Ref: 442a12795416
Ref: Using real Argument Clinic converters instead of “legacy converters”-Footnote-112804354
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Ref: howto/clinic py-buffer12804573
Ref: 442b12804573
Node: Advanced converters12804889
Ref: howto/clinic advanced-converters12805011
Ref: 442c12805011
Node: Parameter default values12806716
Ref: howto/clinic default-values12806851
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Ref: howto/clinic parameter-default-values12806851
Ref: 442d12806851
Node: The NULL default value12807380
Ref: howto/clinic the-null-default-value12807535
Ref: 442e12807535
Node: Expressions specified as default values12808009
Ref: howto/clinic expressions-specified-as-default-values12808164
Ref: 442f12808164
Node: Using a return converter12810559
Ref: howto/clinic using-a-return-converter12810718
Ref: 443012810718
Node: Cloning existing functions12813363
Ref: howto/clinic cloning-existing-functions12813502
Ref: 443112813502
Node: Calling Python code12814826
Ref: howto/clinic calling-python-code12814969
Ref: 443212814969
Node: Using a “self converter”12815888
Ref: howto/clinic using-a-self-converter12816031
Ref: 443312816031
Node: Writing a custom converter12817777
Ref: howto/clinic writing-a-custom-converter12817934
Ref: 443412817934
Node: Writing a custom return converter12821638
Ref: howto/clinic writing-a-custom-return-converter12821789
Ref: 443512821789
Node: METH_O and METH_NOARGS12822368
Ref: howto/clinic meth-o-and-meth-noargs12822521
Ref: 443612822521
Node: tp_new and tp_init functions12823092
Ref: howto/clinic tp-new-and-tp-init-functions12823254
Ref: 443712823254
Node: Changing and redirecting Clinic’s output12824199
Ref: howto/clinic changing-and-redirecting-clinic-s-output12824355
Ref: 443812824355
Node: The #ifdef trick12835635
Ref: howto/clinic the-ifdef-trick12835800
Ref: 443912835800
Node: Using Argument Clinic in Python files12838582
Ref: howto/clinic using-argument-clinic-in-python-files12838696
Ref: 443a12838696
Node: Instrumenting CPython with DTrace and SystemTap12839392
Ref: howto/instrumentation doc12839520
Ref: 443b12839520
Ref: howto/instrumentation instrumentation12839520
Ref: 60612839520
Ref: howto/instrumentation instrumenting-cpython-with-dtrace-and-systemtap12839520
Ref: 443c12839520
Node: Enabling the static markers12840718
Ref: howto/instrumentation enabling-the-static-markers12840858
Ref: 443d12840858
Node: Static DTrace probes12845005
Ref: howto/instrumentation static-dtrace-probes12845178
Ref: 443e12845178
Node: Static SystemTap markers12847619
Ref: howto/instrumentation static-systemtap-markers12847789
Ref: 443f12847789
Node: Available static markers12849834
Ref: howto/instrumentation available-static-markers12850001
Ref: 444012850001
Node: SystemTap Tapsets12852546
Ref: howto/instrumentation systemtap-tapsets12852701
Ref: 444112852701
Node: Examples<37>12854321
Ref: howto/instrumentation examples12854443
Ref: 444212854443
Node: Python Frequently Asked Questions12855766
Ref: faq/index doc12855878
Ref: 444312855878
Ref: faq/index faq-index12855878
Ref: 144c12855878
Ref: faq/index python-frequently-asked-questions12855878
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Node: General Python FAQ12856202
Ref: faq/general doc12856314
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Ref: faq/general general-python-faq12856314
Ref: 444612856314
Node: General Information12856426
Ref: faq/general general-information12856533
Ref: 444712856533
Node: What is Python?12857522
Ref: faq/general what-is-python12857641
Ref: 444812857641
Ref: What is Python?-Footnote-112858591
Node: What is the Python Software Foundation?12858643
Ref: faq/general what-is-the-python-software-foundation12858825
Ref: 444912858825
Ref: What is the Python Software Foundation?-Footnote-112859429
Node: Are there copyright restrictions on the use of Python?12859475
Ref: faq/general are-there-copyright-restrictions-on-the-use-of-python12859684
Ref: 444a12859684
Ref: Are there copyright restrictions on the use of Python?-Footnote-112860556
Ref: Are there copyright restrictions on the use of Python?-Footnote-212860600
Node: Why was Python created in the first place?12860647
Ref: faq/general why-was-python-created-in-the-first-place12860841
Ref: 444b12860841
Node: What is Python good for?12863173
Ref: faq/general what-is-python-good-for12863363
Ref: 444c12863363
Ref: What is Python good for?-Footnote-112864233
Node: How does the Python version numbering scheme work?12864258
Ref: faq/general how-does-the-python-version-numbering-scheme-work12864450
Ref: 444d12864450
Ref: How does the Python version numbering scheme work?-Footnote-112866325
Node: How do I obtain a copy of the Python source?12866374
Ref: faq/general how-do-i-obtain-a-copy-of-the-python-source12866579
Ref: 444e12866579
Ref: How do I obtain a copy of the Python source?-Footnote-112867363
Node: How do I get documentation on Python?12867406
Ref: faq/general how-do-i-get-documentation-on-python12867619
Ref: 444f12867619
Ref: How do I get documentation on Python?-Footnote-112868182
Node: I’ve never programmed before Is there a Python tutorial?12868213
Ref: faq/general i-ve-never-programmed-before-is-there-a-python-tutorial12868437
Ref: 445012868437
Ref: I’ve never programmed before Is there a Python tutorial?-Footnote-112868850
Node: Is there a newsgroup or mailing list devoted to Python?12868902
Ref: faq/general is-there-a-newsgroup-or-mailing-list-devoted-to-python12869132
Ref: 445112869132
Ref: Is there a newsgroup or mailing list devoted to Python?-Footnote-112870011
Ref: Is there a newsgroup or mailing list devoted to Python?-Footnote-212870072
Node: How do I get a beta test version of Python?12870142
Ref: faq/general how-do-i-get-a-beta-test-version-of-python12870365
Ref: 445212870365
Ref: How do I get a beta test version of Python?-Footnote-112870904
Node: How do I submit bug reports and patches for Python?12870941
Ref: faq/general how-do-i-submit-bug-reports-and-patches-for-python12871176
Ref: 445312871176
Ref: How do I submit bug reports and patches for Python?-Footnote-112871887
Ref: How do I submit bug reports and patches for Python?-Footnote-212871944
Node: Are there any published articles about Python that I can reference?12871981
Ref: faq/general are-there-any-published-articles-about-python-that-i-can-reference12872203
Ref: 445412872203
Node: Are there any books on Python?12872716
Ref: faq/general are-there-any-books-on-python12872932
Ref: 445512872932
Node: Where in the world is www python org located?12873309
Ref: faq/general where-in-the-world-is-www-python-org-located12873482
Ref: 445612873482
Ref: Where in the world is www python org located?-Footnote-112873768
Node: Why is it called Python?12873796
Ref: faq/general why-is-it-called-python12873994
Ref: 445712873994
Ref: Why is it called Python?-Footnote-112874400
Node: Do I have to like “Monty Python’s Flying Circus”?12874451
Ref: faq/general do-i-have-to-like-monty-python-s-flying-circus12874595
Ref: 445812874595
Node: Python in the real world12874745
Ref: faq/general python-in-the-real-world12874852
Ref: 445912874852
Node: How stable is Python?12875232
Ref: faq/general how-stable-is-python12875356
Ref: 445a12875356
Ref: How stable is Python?-Footnote-112876377
Ref: How stable is Python?-Footnote-212876426
Ref: How stable is Python?-Footnote-312876468
Node: How many people are using Python?12876518
Ref: faq/general how-many-people-are-using-python12876701
Ref: 445b12876701
Node: Have any significant projects been done in Python?12877207
Ref: faq/general have-any-significant-projects-been-done-in-python12877429
Ref: 445c12877429
Ref: Have any significant projects been done in Python?-Footnote-112878143
Ref: Have any significant projects been done in Python?-Footnote-212878195
Ref: Have any significant projects been done in Python?-Footnote-312878223
Ref: Have any significant projects been done in Python?-Footnote-412878251
Node: What new developments are expected for Python in the future?12878282
Ref: faq/general what-new-developments-are-expected-for-python-in-the-future12878530
Ref: 445d12878530
Ref: What new developments are expected for Python in the future?-Footnote-112879119
Node: Is it reasonable to propose incompatible changes to Python?12879180
Ref: faq/general is-it-reasonable-to-propose-incompatible-changes-to-python12879430
Ref: 445e12879430
Ref: Is it reasonable to propose incompatible changes to Python?-Footnote-112880234
Node: Is Python a good language for beginning programmers?12880283
Ref: faq/general is-python-a-good-language-for-beginning-programmers12880464
Ref: 445f12880464
Ref: Is Python a good language for beginning programmers?-Footnote-112884323
Ref: Is Python a good language for beginning programmers?-Footnote-212884374
Node: Programming FAQ12884436
Ref: faq/programming doc12884579
Ref: 446012884579
Ref: faq/programming programming-faq12884579
Ref: 446112884579
Node: General Questions12884814
Ref: faq/programming general-questions12884905
Ref: 446212884905
Node: Is there a source code level debugger with breakpoints single-stepping etc ?12885325
Ref: faq/programming is-there-a-source-code-level-debugger-with-breakpoints-single-stepping-etc12885525
Ref: 446312885525
Ref: Is there a source code level debugger with breakpoints single-stepping etc ?-Footnote-112886965
Ref: Is there a source code level debugger with breakpoints single-stepping etc ?-Footnote-212887009
Ref: Is there a source code level debugger with breakpoints single-stepping etc ?-Footnote-312887062
Ref: Is there a source code level debugger with breakpoints single-stepping etc ?-Footnote-412887107
Ref: Is there a source code level debugger with breakpoints single-stepping etc ?-Footnote-512887156
Ref: Is there a source code level debugger with breakpoints single-stepping etc ?-Footnote-612887195
Ref: Is there a source code level debugger with breakpoints single-stepping etc ?-Footnote-712887225
Ref: Is there a source code level debugger with breakpoints single-stepping etc ?-Footnote-812887282
Node: Are there tools to help find bugs or perform static analysis?12887325
Ref: faq/programming are-there-tools-to-help-find-bugs-or-perform-static-analysis12887593
Ref: 446412887593
Ref: Are there tools to help find bugs or perform static analysis?-Footnote-112887967
Ref: Are there tools to help find bugs or perform static analysis?-Footnote-212887999
Ref: Are there tools to help find bugs or perform static analysis?-Footnote-312888041
Ref: Are there tools to help find bugs or perform static analysis?-Footnote-412888071
Ref: Are there tools to help find bugs or perform static analysis?-Footnote-512888103
Node: How can I create a stand-alone binary from a Python script?12888144
Ref: faq/programming faq-create-standalone-binary12888400
Ref: 446512888400
Ref: faq/programming how-can-i-create-a-stand-alone-binary-from-a-python-script12888400
Ref: 446612888400
Ref: How can I create a stand-alone binary from a Python script?-Footnote-112890114
Ref: How can I create a stand-alone binary from a Python script?-Footnote-212890142
Ref: How can I create a stand-alone binary from a Python script?-Footnote-312890178
Ref: How can I create a stand-alone binary from a Python script?-Footnote-412890231
Ref: How can I create a stand-alone binary from a Python script?-Footnote-512890283
Ref: How can I create a stand-alone binary from a Python script?-Footnote-612890332
Node: Are there coding standards or a style guide for Python programs?12890363
Ref: faq/programming are-there-coding-standards-or-a-style-guide-for-python-programs12890549
Ref: 446712890549
Ref: Are there coding standards or a style guide for Python programs?-Footnote-112890823
Node: Core Language12890872
Ref: faq/programming core-language12890991
Ref: 446812890991
Node: Why am I getting an UnboundLocalError when the variable has a value?12892361
Ref: faq/programming why-am-i-getting-an-unboundlocalerror-when-the-variable-has-a-value12892548
Ref: 446912892548
Node: What are the rules for local and global variables in Python?12894407
Ref: faq/programming what-are-the-rules-for-local-and-global-variables-in-python12894685
Ref: 446a12894685
Node: Why do lambdas defined in a loop with different values all return the same result?12895586
Ref: faq/programming why-do-lambdas-defined-in-a-loop-with-different-values-all-return-the-same-result12895843
Ref: 446b12895843
Node: How do I share global variables across modules?12897752
Ref: faq/programming how-do-i-share-global-variables-across-modules12898012
Ref: 446c12898012
Node: What are the “best practices” for using import in a module?12898815
Ref: faq/programming what-are-the-best-practices-for-using-import-in-a-module12899039
Ref: 446d12899039
Node: Why are default values shared between objects?12901795
Ref: faq/programming why-are-default-values-shared-between-objects12902047
Ref: 446e12902047
Node: How can I pass optional or keyword parameters from one function to another?12904435
Ref: faq/programming how-can-i-pass-optional-or-keyword-parameters-from-one-function-to-another12904680
Ref: 446f12904680
Node: What is the difference between arguments and parameters?12905267
Ref: faq/programming faq-argument-vs-parameter12905521
Ref: 447012905521
Ref: faq/programming what-is-the-difference-between-arguments-and-parameters12905521
Ref: 447112905521
Node: Why did changing list ‘y’ also change list ‘x’?12906211
Ref: faq/programming why-did-changing-list-y-also-change-list-x12906458
Ref: 447212906458
Node: How do I write a function with output parameters call by reference ?12909861
Ref: faq/programming how-do-i-write-a-function-with-output-parameters-call-by-reference12910102
Ref: 447312910102
Node: How do you make a higher order function in Python?12912507
Ref: faq/programming how-do-you-make-a-higher-order-function-in-python12912727
Ref: 447412912727
Node: How do I copy an object in Python?12914301
Ref: faq/programming how-do-i-copy-an-object-in-python12914507
Ref: 447512914507
Node: How can I find the methods or attributes of an object?12914914
Ref: faq/programming how-can-i-find-the-methods-or-attributes-of-an-object12915117
Ref: 447612915117
Node: How can my code discover the name of an object?12915431
Ref: faq/programming how-can-my-code-discover-the-name-of-an-object12915651
Ref: 447712915651
Node: What’s up with the comma operator’s precedence?12917271
Ref: faq/programming what-s-up-with-the-comma-operator-s-precedence12917495
Ref: 447812917495
Node: Is there an equivalent of C’s “? ” ternary operator?12918053
Ref: faq/programming is-there-an-equivalent-of-c-s-ternary-operator12918286
Ref: 447912918286
Node: Is it possible to write obfuscated one-liners in Python?12918881
Ref: faq/programming is-it-possible-to-write-obfuscated-one-liners-in-python12919126
Ref: 447a12919126
Node: What does the slash / in the parameter list of a function mean?12920605
Ref: faq/programming faq-positional-only-arguments12920783
Ref: 172912920783
Ref: faq/programming what-does-the-slash-in-the-parameter-list-of-a-function-mean12920783
Ref: 447b12920783
Node: Numbers and strings12921883
Ref: faq/programming numbers-and-strings12921999
Ref: 447c12921999
Node: How do I specify hexadecimal and octal integers?12922734
Ref: faq/programming how-do-i-specify-hexadecimal-and-octal-integers12922876
Ref: 447d12922876
Node: Why does -22 // 10 return -3?12923525
Ref: faq/programming why-does-22-10-return-312923734
Ref: 447e12923734
Node: How do I get int literal attribute instead of SyntaxError?12924495
Ref: faq/programming how-do-i-get-int-literal-attribute-instead-of-syntaxerror12924694
Ref: 447f12924694
Node: How do I convert a string to a number?12925269
Ref: faq/programming how-do-i-convert-a-string-to-a-number12925477
Ref: 448012925477
Node: How do I convert a number to a string?12926801
Ref: faq/programming how-do-i-convert-a-number-to-a-string12926985
Ref: 448112926985
Node: How do I modify a string in place?12927536
Ref: faq/programming how-do-i-modify-a-string-in-place12927729
Ref: 448212927729
Node: How do I use strings to call functions/methods?12928585
Ref: faq/programming how-do-i-use-strings-to-call-functions-methods12928825
Ref: 448312928825
Node: Is there an equivalent to Perl’s chomp for removing trailing newlines from strings?12930153
Ref: faq/programming is-there-an-equivalent-to-perl-s-chomp-for-removing-trailing-newlines-from-strings12930397
Ref: 448412930397
Node: Is there a scanf or sscanf equivalent?12931156
Ref: faq/programming is-there-a-scanf-or-sscanf-equivalent12931427
Ref: 448512931427
Node: What does ‘UnicodeDecodeError’ or ‘UnicodeEncodeError’ error mean?12932078
Ref: faq/programming what-does-unicodedecodeerror-or-unicodeencodeerror-error-mean12932255
Ref: 448612932255
Node: Performance<4>12932453
Ref: faq/programming performance12932578
Ref: 448712932578
Node: My program is too slow How do I speed it up?12932795
Ref: faq/programming my-program-is-too-slow-how-do-i-speed-it-up12932967
Ref: 448812932967
Ref: My program is too slow How do I speed it up?-Footnote-112935847
Ref: My program is too slow How do I speed it up?-Footnote-212935873
Node: What is the most efficient way to concatenate many strings together?12935938
Ref: faq/programming efficient-string-concatenation12936110
Ref: 448912936110
Ref: faq/programming what-is-the-most-efficient-way-to-concatenate-many-strings-together12936110
Ref: 448a12936110
Node: Sequences Tuples/Lists12937080
Ref: faq/programming sequences-tuples-lists12937193
Ref: 448b12937193
Node: How do I convert between tuples and lists?12937937
Ref: faq/programming how-do-i-convert-between-tuples-and-lists12938073
Ref: 448c12938073
Node: What’s a negative index?12938920
Ref: faq/programming what-s-a-negative-index12939115
Ref: 448d12939115
Node: How do I iterate over a sequence in reverse order?12939695
Ref: faq/programming how-do-i-iterate-over-a-sequence-in-reverse-order12939889
Ref: 448e12939889
Node: How do you remove duplicates from a list?12940238
Ref: faq/programming how-do-you-remove-duplicates-from-a-list12940450
Ref: 448f12940450
Node: How do you remove multiple items from a list12941277
Ref: faq/programming how-do-you-remove-multiple-items-from-a-list12941474
Ref: 449012941474
Node: How do you make an array in Python?12942022
Ref: faq/programming how-do-you-make-an-array-in-python12942218
Ref: 449112942218
Node: How do I create a multidimensional list?12943205
Ref: faq/programming faq-multidimensional-list12943406
Ref: 176512943406
Ref: faq/programming how-do-i-create-a-multidimensional-list12943406
Ref: 449212943406
Ref: How do I create a multidimensional list?-Footnote-112944628
Node: How do I apply a method to a sequence of objects?12944658
Ref: faq/programming how-do-i-apply-a-method-to-a-sequence-of-objects12944903
Ref: 449312944903
Node: Why does a_tuple[i] += [‘item’] raise an exception when the addition works?12945097
Ref: faq/programming faq-augmented-assignment-tuple-error12945379
Ref: 15ba12945379
Ref: faq/programming why-does-a-tuple-i-item-raise-an-exception-when-the-addition-works12945379
Ref: 449412945379
Node: I want to do a complicated sort can you do a Schwartzian Transform in Python?12948603
Ref: faq/programming i-want-to-do-a-complicated-sort-can-you-do-a-schwartzian-transform-in-python12948888
Ref: 449512948888
Node: How can I sort one list by values from another list?12949373
Ref: faq/programming how-can-i-sort-one-list-by-values-from-another-list12949570
Ref: 449612949570
Node: Objects12950165
Ref: faq/programming objects12950274
Ref: 449712950274
Node: What is a class?12951420
Ref: faq/programming what-is-a-class12951506
Ref: 449812951506
Node: What is a method?12952232
Ref: faq/programming what-is-a-method12952340
Ref: 449912952340
Node: What is self?12952649
Ref: faq/programming what-is-self12952824
Ref: 449a12952824
Node: How do I check if an object is an instance of a given class or of a subclass of it?12953266
Ref: faq/programming how-do-i-check-if-an-object-is-an-instance-of-a-given-class-or-of-a-subclass-of-it12953443
Ref: 449c12953443
Node: What is delegation?12955740
Ref: faq/programming what-is-delegation12955990
Ref: 449d12955990
Node: How do I call a method defined in a base class from a derived class that overrides it?12957840
Ref: faq/programming how-do-i-call-a-method-defined-in-a-base-class-from-a-derived-class-that-overrides-it12958077
Ref: 449e12958077
Node: How can I organize my code to make it easier to change the base class?12958762
Ref: faq/programming how-can-i-organize-my-code-to-make-it-easier-to-change-the-base-class12959039
Ref: 449f12959039
Node: How do I create static class data and static class methods?12959589
Ref: faq/programming how-do-i-create-static-class-data-and-static-class-methods12959833
Ref: 44a012959833
Node: How can I overload constructors or methods in Python?12961402
Ref: faq/programming how-can-i-overload-constructors-or-methods-in-python12961641
Ref: 44a112961641
Node: I try to use __spam and I get an error about _SomeClassName__spam12962548
Ref: faq/programming i-try-to-use-spam-and-i-get-an-error-about-someclassname-spam12962798
Ref: 44a212962798
Node: My class defines __del__ but it is not called when I delete the object12963599
Ref: faq/programming my-class-defines-del-but-it-is-not-called-when-i-delete-the-object12963850
Ref: 44a312963850
Node: How do I get a list of all instances of a given class?12965824
Ref: faq/programming how-do-i-get-a-list-of-all-instances-of-a-given-class12966060
Ref: 44a412966060
Node: Why does the result of id appear to be not unique?12966401
Ref: faq/programming why-does-the-result-of-id-appear-to-be-not-unique12966622
Ref: 44a512966622
Node: When can I rely on identity tests with the is operator?12967514
Ref: faq/programming when-can-i-rely-on-identity-tests-with-the-is-operator12967753
Ref: 44a612967753
Ref: When can I rely on identity tests with the is operator?-Footnote-112970961
Node: How can a subclass control what data is stored in an immutable instance?12971010
Ref: faq/programming how-can-a-subclass-control-what-data-is-stored-in-an-immutable-instance12971190
Ref: 44a712971190
Node: Modules<3>12972666
Ref: faq/programming modules12972744
Ref: 44a812972744
Node: How do I create a pyc file?12973284
Ref: faq/programming how-do-i-create-a-pyc-file12973405
Ref: 44a912973405
Ref: How do I create a pyc file?-Footnote-112975986
Node: How do I find the current module name?12976035
Ref: faq/programming how-do-i-find-the-current-module-name12976220
Ref: 44aa12976220
Node: How can I have modules that mutually import each other?12976778
Ref: faq/programming how-can-i-have-modules-that-mutually-import-each-other12977000
Ref: 44ab12977000
Node: __import__ ‘x y z’ returns <module ‘x’>; how do I get z?12978886
Ref: faq/programming import-x-y-z-returns-module-x-how-do-i-get-z12979166
Ref: 44ac12979166
Node: When I edit an imported module and reimport it the changes don’t show up Why does this happen?12979456
Ref: faq/programming when-i-edit-an-imported-module-and-reimport-it-the-changes-don-t-show-up-why-does-this-happen12979672
Ref: 44ad12979672
Node: Design and History FAQ12981119
Ref: faq/design doc12981269
Ref: 44ae12981269
Ref: faq/design design-and-history-faq12981269
Ref: 44af12981269
Node: Why does Python use indentation for grouping of statements?12983368
Ref: faq/design why-does-python-use-indentation-for-grouping-of-statements12983562
Ref: 44b012983562
Node: Why am I getting strange results with simple arithmetic operations?12985282
Ref: faq/design why-am-i-getting-strange-results-with-simple-arithmetic-operations12985535
Ref: 44b112985535
Node: Why are floating-point calculations so inaccurate?12985710
Ref: faq/design why-are-floating-point-calculations-so-inaccurate12985937
Ref: 44b212985937
Node: Why are Python strings immutable?12987476
Ref: faq/design why-are-python-strings-immutable12987707
Ref: 44b312987707
Node: Why must ‘self’ be used explicitly in method definitions and calls?12988310
Ref: faq/design why-must-self-be-used-explicitly-in-method-definitions-and-calls12988540
Ref: 44b412988540
Ref: faq/design why-self12988540
Ref: 449b12988540
Node: Why can’t I use an assignment in an expression?12991030
Ref: faq/design id112991331
Ref: 44b512991331
Ref: faq/design why-can-t-i-use-an-assignment-in-an-expression12991331
Ref: 13ac12991331
Ref: Why can’t I use an assignment in an expression?-Footnote-112991703
Node: Why does Python use methods for some functionality e g list index but functions for other e g len list ?12991752
Ref: faq/design why-does-python-use-methods-for-some-functionality-e-g-list-index-but-functions-for-other-e-g-len-list12992044
Ref: 44b612992044
Node: Why is join a string method instead of a list or tuple method?12993383
Ref: faq/design why-is-join-a-string-method-instead-of-a-list-or-tuple-method12993650
Ref: 44b712993650
Node: How fast are exceptions?12995461
Ref: faq/design how-fast-are-exceptions12995679
Ref: 44b812995679
Node: Why isn’t there a switch or case statement in Python?12996492
Ref: faq/design why-isn-t-there-a-switch-or-case-statement-in-python12996754
Ref: 44b912996754
Ref: Why isn’t there a switch or case statement in Python?-Footnote-112998127
Node: Can’t you emulate threads in the interpreter instead of relying on an OS-specific thread implementation?12998176
Ref: faq/design can-t-you-emulate-threads-in-the-interpreter-instead-of-relying-on-an-os-specific-thread-implementation12998464
Ref: 44ba12998464
Ref: Can’t you emulate threads in the interpreter instead of relying on an OS-specific thread implementation?-Footnote-112999111
Node: Why can’t lambda expressions contain statements?12999167
Ref: faq/design why-can-t-lambda-expressions-contain-statements12999464
Ref: 44bb12999464
Node: Can Python be compiled to machine code C or some other language?13000329
Ref: faq/design can-python-be-compiled-to-machine-code-c-or-some-other-language13000550
Ref: 44bc13000550
Ref: Can Python be compiled to machine code C or some other language?-Footnote-113000985
Ref: Can Python be compiled to machine code C or some other language?-Footnote-213001012
Ref: Can Python be compiled to machine code C or some other language?-Footnote-313001043
Node: How does Python manage memory?13001078
Ref: faq/design how-does-python-manage-memory13001320
Ref: 44bd13001320
Ref: How does Python manage memory?-Footnote-113002989
Ref: How does Python manage memory?-Footnote-213003019
Node: Why doesn’t CPython use a more traditional garbage collection scheme?13003047
Ref: faq/design why-doesn-t-cpython-use-a-more-traditional-garbage-collection-scheme13003273
Ref: 44be13003273
Node: Why isn’t all memory freed when CPython exits?13004189
Ref: faq/design why-isn-t-all-memory-freed-when-cpython-exits13004434
Ref: 44bf13004434
Node: Why are there separate tuple and list data types?13005129
Ref: faq/design why-are-there-separate-tuple-and-list-data-types13005340
Ref: 44c013005340
Node: How are lists implemented in CPython?13006574
Ref: faq/design how-are-lists-implemented-in-cpython13006781
Ref: 44c113006781
Node: How are dictionaries implemented in CPython?13007522
Ref: faq/design how-are-dictionaries-implemented-in-cpython13007718
Ref: 44c213007718
Node: Why must dictionary keys be immutable?13008669
Ref: faq/design why-must-dictionary-keys-be-immutable13008875
Ref: 44c313008875
Node: Why doesn’t list sort return the sorted list?13013078
Ref: faq/design why-doesn-t-list-sort-return-the-sorted-list13013299
Ref: 44c413013299
Node: How do you specify and enforce an interface spec in Python?13014143
Ref: faq/design how-do-you-specify-and-enforce-an-interface-spec-in-python13014347
Ref: 44c513014347
Node: Why is there no goto?13016664
Ref: faq/design why-is-there-no-goto13016876
Ref: 44c613016876
Node: Why can’t raw strings r-strings end with a backslash?13017954
Ref: faq/design why-can-t-raw-strings-r-strings-end-with-a-backslash13018182
Ref: 44c713018182
Node: Why doesn’t Python have a “with” statement for attribute assignments?13019283
Ref: faq/design why-doesn-t-python-have-a-with-statement-for-attribute-assignments13019540
Ref: 44c813019540
Node: Why don’t generators support the with statement?13021742
Ref: faq/design why-don-t-generators-support-the-with-statement13022006
Ref: 44c913022006
Node: Why are colons required for the if/while/def/class statements?13022411
Ref: faq/design why-are-colons-required-for-the-if-while-def-class-statements13022660
Ref: 44ca13022660
Node: Why does Python allow commas at the end of lists and tuples?13023405
Ref: faq/design why-does-python-allow-commas-at-the-end-of-lists-and-tuples13023595
Ref: 44cb13023595
Node: Library and Extension FAQ13024696
Ref: faq/library doc13024854
Ref: 44cc13024854
Ref: faq/library library-and-extension-faq13024854
Ref: 44cd13024854
Node: General Library Questions13025103
Ref: faq/library general-library-questions13025211
Ref: 44ce13025211
Node: How do I find a module or application to perform task X?13025723
Ref: faq/library how-do-i-find-a-module-or-application-to-perform-task-x13025906
Ref: 44cf13025906
Ref: How do I find a module or application to perform task X?-Footnote-113026494
Ref: How do I find a module or application to perform task X?-Footnote-213026519
Node: Where is the math py socket py regex py etc source file?13026550
Ref: faq/library where-is-the-math-py-socket-py-regex-py-etc-source-file13026791
Ref: 44d013026791
Node: How do I make a Python script executable on Unix?13027575
Ref: faq/library how-do-i-make-a-python-script-executable-on-unix13027805
Ref: 44d113027805
Node: Is there a curses/termcap package for Python?13029282
Ref: faq/library is-there-a-curses-termcap-package-for-python13029505
Ref: 44d213029505
Ref: Is there a curses/termcap package for Python?-Footnote-113030344
Ref: Is there a curses/termcap package for Python?-Footnote-213030403
Node: Is there an equivalent to C’s onexit in Python?13030452
Ref: faq/library is-there-an-equivalent-to-c-s-onexit-in-python13030662
Ref: 44d313030662
Node: Why don’t my signal handlers work?13030882
Ref: faq/library why-don-t-my-signal-handlers-work13031038
Ref: 44d413031038
Node: Common tasks13031363
Ref: faq/library common-tasks13031487
Ref: 44d513031487
Node: How do I test a Python program or component?13031685
Ref: faq/library how-do-i-test-a-python-program-or-component13031834
Ref: 44d613031834
Node: How do I create documentation from doc strings?13033785
Ref: faq/library how-do-i-create-documentation-from-doc-strings13033984
Ref: 44d713033984
Ref: How do I create documentation from doc strings?-Footnote-113034360
Ref: How do I create documentation from doc strings?-Footnote-213034399
Node: How do I get a single keypress at a time?13034429
Ref: faq/library how-do-i-get-a-single-keypress-at-a-time13034575
Ref: 44d813034575
Node: Threads13034821
Ref: faq/library threads13034939
Ref: 44d913034939
Node: How do I program using threads?13035267
Ref: faq/library how-do-i-program-using-threads13035386
Ref: 44da13035386
Node: None of my threads seem to run why?13035698
Ref: faq/library none-of-my-threads-seem-to-run-why13035883
Ref: 44db13035883
Node: How do I parcel out work among a bunch of worker threads?13037432
Ref: faq/library how-do-i-parcel-out-work-among-a-bunch-of-worker-threads13037638
Ref: 44dc13037638
Node: What kinds of global value mutation are thread-safe?13040234
Ref: faq/library what-kinds-of-global-value-mutation-are-thread-safe13040455
Ref: 44dd13040455
Node: Can’t we get rid of the Global Interpreter Lock?13041961
Ref: faq/library can-t-we-get-rid-of-the-global-interpreter-lock13042116
Ref: 44de13042116
Ref: Can’t we get rid of the Global Interpreter Lock?-Footnote-113044807
Node: Input and Output<2>13044867
Ref: faq/library input-and-output13045001
Ref: 44df13045001
Node: How do I delete a file? And other file questions…13045636
Ref: faq/library how-do-i-delete-a-file-and-other-file-questions13045773
Ref: 44e013045773
Node: How do I copy a file?13047023
Ref: faq/library how-do-i-copy-a-file13047204
Ref: 44e113047204
Node: How do I read or write binary data?13047415
Ref: faq/library how-do-i-read-or-write-binary-data13047613
Ref: 44e213047613
Node: I can’t seem to use os read on a pipe created with os popen ; why?13048810
Ref: faq/library i-can-t-seem-to-use-os-read-on-a-pipe-created-with-os-popen-why13049025
Ref: 44e313049025
Node: How do I access the serial RS232 port?13049546
Ref: faq/library how-do-i-access-the-serial-rs232-port13049788
Ref: 44e413049788
Node: Why doesn’t closing sys stdout stdin stderr really close it?13050106
Ref: faq/library why-doesn-t-closing-sys-stdout-stdin-stderr-really-close-it13050271
Ref: 44e513050271
Node: Network/Internet Programming13051498
Ref: faq/library network-internet-programming13051634
Ref: 44e613051634
Node: What WWW tools are there for Python?13052091
Ref: faq/library what-www-tools-are-there-for-python13052250
Ref: 44e713052250
Node: How can I mimic CGI form submission METHOD=POST ?13052834
Ref: faq/library how-can-i-mimic-cgi-form-submission-method-post13053056
Ref: 44e813053056
Node: What module should I use to help with generating HTML?13054172
Ref: faq/library what-module-should-i-use-to-help-with-generating-html13054398
Ref: 44e913054398
Ref: What module should I use to help with generating HTML?-Footnote-113054643
Node: How do I send mail from a Python script?13054695
Ref: faq/library how-do-i-send-mail-from-a-python-script13054930
Ref: 44ea13054930
Node: How do I avoid blocking in the connect method of a socket?13056271
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Ref: 44eb13056443
Ref: How do I avoid blocking in the connect method of a socket?-Footnote-113057784
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Ref: 44ec13057965
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Ref: Are there any interfaces to database packages in Python?-Footnote-113058793
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Ref: 44ee13059011
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Ref: 44ef13059516
Node: How do I generate random numbers in Python?13059639
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Ref: 44f013059743
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Ref: faq/extending doc13060853
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Ref: faq/extending extending-embedding-faq13060853
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Ref: faq/extending can-i-create-my-own-functions-in-c13062482
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Ref: faq/extending id113063038
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Node: Writing C is hard; are there any alternatives?13063425
Ref: faq/extending c-wrapper-software13063639
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Ref: Writing C is hard; are there any alternatives?-Footnote-613064623
Ref: Writing C is hard; are there any alternatives?-Footnote-713064679
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Ref: faq/extending how-can-i-execute-arbitrary-python-statements-from-c13064952
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Node: How can I evaluate an arbitrary Python expression from C?13065498
Ref: faq/extending how-can-i-evaluate-an-arbitrary-python-expression-from-c13065733
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Node: How do I extract C values from a Python object?13066049
Ref: faq/extending how-do-i-extract-c-values-from-a-python-object13066296
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Node: How do I use Py_BuildValue to create a tuple of arbitrary length?13067535
Ref: faq/extending how-do-i-use-py-buildvalue-to-create-a-tuple-of-arbitrary-length13067767
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Ref: faq/extending how-do-i-call-an-object-s-method-from-c13068244
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Node: How do I interface to C++ objects from Python?13072030
Ref: faq/extending how-do-i-interface-to-c-objects-from-python13072266
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Ref: faq/extending i-added-a-module-using-the-setup-file-and-the-make-fails-why13073052
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Node: How do I debug an extension?13073402
Ref: faq/extending how-do-i-debug-an-extension13073654
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Node: I want to compile a Python module on my Linux system but some files are missing Why?13074205
Ref: faq/extending i-want-to-compile-a-python-module-on-my-linux-system-but-some-files-are-missing-why13074457
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Node: How do I tell “incomplete input” from “invalid input”?13074941
Ref: faq/extending how-do-i-tell-incomplete-input-from-invalid-input13075233
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Node: How do I find undefined g++ symbols __builtin_new or __pure_virtual?13081345
Ref: faq/extending how-do-i-find-undefined-g-symbols-builtin-new-or-pure-virtual13081663
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Node: Python on Windows FAQ13082851
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Node: How do I make Python scripts executable?13087268
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Node: Why does Python sometimes take so long to start?13088038
Ref: faq/windows why-does-python-sometimes-take-so-long-to-start13088251
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Node: How do I make an executable from a Python script?13089130
Ref: faq/windows how-do-i-make-an-executable-from-a-python-script13089337
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Node: Is a * pyd file the same as a DLL?13089588
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Node: How can I embed Python into a Windows application?13090794
Ref: faq/windows how-can-i-embed-python-into-a-windows-application13091018
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Node: How do I keep editors from inserting tabs into my Python source?13095556
Ref: faq/windows how-do-i-keep-editors-from-inserting-tabs-into-my-python-source13095793
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Ref: How do I keep editors from inserting tabs into my Python source?-Footnote-113096670
Node: How do I check for a keypress without blocking?13096719
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Node: Graphic User Interface FAQ13097246
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Node: What GUI toolkits exist for Python?13097780
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Ref: faq/gui how-do-i-freeze-tkinter-applications13099412
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Node: Can I have Tk events handled while waiting for I/O?13100359
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Ref: faq/gui i-can-t-get-key-bindings-to-work-in-tkinter-why13101208
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Node: “Why is Python Installed on my Computer?” FAQ13101760
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Node: Can I delete Python?13104087
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Node: Glossary13104968
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Node: About these documents13161905
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Node: expat13215468
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Node: libffi13216996
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Node: zlib<3>13218467
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Node: libmpdec13221779
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Node: W3C C14N test suite13223487
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Node: Distributing Python Modules Legacy version13225518
Ref: distutils/index doc13225677
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Ref: Distributing Python Modules Legacy version-Footnote-113227161
Node: An Introduction to Distutils13227227
Ref: distutils/introduction doc13227367
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Ref: distutils/introduction an-introduction-to-distutils13227367
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Ref: distutils/introduction distutils-intro13227367
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Node: Concepts & Terminology13228122
Ref: distutils/introduction concepts-terminology13228237
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Node: A Simple Example<2>13229441
Ref: distutils/introduction a-simple-example13229591
Ref: 457013229591
Ref: distutils/introduction distutils-simple-example13229591
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Node: General Python terminology13233442
Ref: distutils/introduction general-python-terminology13233600
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Ref: distutils/introduction python-terms13233600
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Node: Distutils-specific terminology13235595
Ref: distutils/introduction distutils-specific-terminology13235725
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Ref: distutils/introduction distutils-term13235725
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Node: Writing the Setup Script13236882
Ref: distutils/setupscript doc13237067
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Ref: distutils/setupscript setup-script13237067
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Ref: distutils/setupscript writing-the-setup-script13237067
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Node: Listing whole packages13240462
Ref: distutils/setupscript listing-packages13240580
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Ref: distutils/setupscript listing-whole-packages13240580
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Node: Listing individual modules13243040
Ref: distutils/setupscript listing-individual-modules13243195
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Node: Describing extension modules13244004
Ref: distutils/setupscript describing-extension-modules13244185
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Ref: distutils/setupscript describing-extensions13244185
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Node: Extension names and packages13245924
Ref: distutils/setupscript extension-names-and-packages13246048
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Node: Extension source files13247147
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Node: Preprocessor options13248696
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Node: Library options13251854
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Node: Other options13252963
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Node: Relationships between Distributions and Packages13254220
Ref: distutils/setupscript relationships-between-distributions-and-packages13254393
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Node: Installing Scripts13257771
Ref: distutils/setupscript distutils-installing-scripts13257939
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Ref: distutils/setupscript installing-scripts13257939
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Node: Installing Package Data13259046
Ref: distutils/setupscript distutils-installing-package-data13259193
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Node: Installing Additional Files13260900
Ref: distutils/setupscript distutils-additional-files13261049
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Node: Additional meta-data13262938
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Node: Debugging the setup script13270452
Ref: distutils/setupscript debug-setup-script13270568
Ref: 458e13270568
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Node: Writing the Setup Configuration File13271643
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Ref: distutils/configfile writing-the-setup-configuration-file13271830
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Ref: distutils/configfile distutils-build-ext-inplace13275039
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Ref: Writing the Setup Configuration File-Footnote-113277498
Node: Creating a Source Distribution13277612
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Ref: distutils/sourcedist source-dist13277803
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Ref: Creating a Source Distribution-Footnote-113280898
Ref: Creating a Source Distribution-Footnote-213280948
Node: Specifying the files to distribute13280973
Ref: distutils/sourcedist manifest13281107
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Ref: distutils/sourcedist specifying-the-files-to-distribute13281107
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Node: Manifest-related options13287082
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Node: Creating Built Distributions13288319
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Node: Creating RPM packages13296154
Ref: distutils/builtdist creating-rpm-packages13296276
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Node: Creating Windows Installers13303866
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Node: Cross-compiling on Windows13306312
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Node: The Postinstallation script13308163
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Ref: distutils/builtdist create_shortcut13310438
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Node: Vista User Access Control UAC13311155
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Node: Distutils Examples13311791
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Node: Pure Python distribution by module13312892
Ref: distutils/examples pure-mod13313025
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Node: Pure Python distribution by package13314809
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Node: Single extension module13318743
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Node: Checking a package13320007
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Node: Reading the metadata13321830
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Ref: distutils/extending extending-distutils13323722
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Node: Integrating new commands13325005
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Node: Adding new distribution types13328023
Ref: distutils/extending adding-new-distribution-types13328141
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Node: Command Reference13328595
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Node: Installing modules the install command family13329257
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Node: install_data13329739
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Node: install_scripts13329980
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Node: Creating a source distribution the sdist command13330222
Ref: distutils/commandref creating-a-source-distribution-the-sdist-command13330378
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Node: API Reference13333150
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Node: distutils core — Core Distutils functionality13339291
Ref: distutils/apiref distutils-core-core-distutils-functionality13339441
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Ref: distutils core — Core Distutils functionality-Footnote-113357319
Ref: distutils core — Core Distutils functionality-Footnote-213357356
Node: distutils ccompiler — CCompiler base class13357405
Ref: distutils/apiref distutils-ccompiler-ccompiler-base-class13357607
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Ref: distutils/apiref module-distutils ccompiler13357607
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Ref: distutils/apiref distutils ccompiler CCompiler shared_object_filename13379924
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Ref: distutils/apiref distutils ccompiler CCompiler execute13380119
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Ref: distutils/apiref distutils ccompiler CCompiler spawn13380403
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Ref: distutils/apiref distutils ccompiler CCompiler warn13380974
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Ref: distutils/apiref distutils ccompiler CCompiler debug_print13381063
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Node: distutils unixccompiler — Unix C Compiler13381252
Ref: distutils/apiref distutils-unixccompiler-unix-c-compiler13381452
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Ref: distutils/apiref module-distutils unixccompiler13381452
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Node: distutils msvccompiler — Microsoft Compiler13382219
Ref: distutils/apiref distutils-msvccompiler-microsoft-compiler13382418
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Ref: distutils/apiref module-distutils msvccompiler13382418
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Node: distutils bcppcompiler — Borland Compiler13383406
Ref: distutils/apiref distutils-bcppcompiler-borland-compiler13383606
Ref: 460013383606
Ref: distutils/apiref module-distutils bcppcompiler13383606
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Ref: distutils/apiref distutils-cygwincompiler-cygwin-compiler13384041
Ref: 460113384041
Ref: distutils/apiref module-distutils cygwinccompiler13384041
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Node: distutils archive_util — Archiving utilities13384423
Ref: distutils/apiref distutils-archive-util-archiving-utilities13384623
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Ref: distutils/apiref module-distutils archive_util13384623
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Ref: distutils/apiref distutils archive_util make_zipfile13386534
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Node: distutils dep_util — Dependency checking13387048
Ref: distutils/apiref distutils-dep-util-dependency-checking13387252
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Ref: distutils/apiref distutils dep_util newer_pairwise13387881
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Ref: distutils/apiref distutils dep_util newer_group13388203
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Node: distutils dir_util — Directory tree operations13389104
Ref: distutils/apiref distutils-dir-util-directory-tree-operations13389308
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Ref: distutils/apiref distutils dir_util remove_tree13392163
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Ref: distutils dir_util — Directory tree operations-Footnote-113392477
Node: distutils file_util — Single file operations13392523
Ref: distutils/apiref distutils-file-util-single-file-operations13392741
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Node: distutils util — Miscellaneous other utility functions13394956
Ref: distutils/apiref distutils-util-miscellaneous-other-utility-functions13395167
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Ref: distutils/apiref module-distutils util13395167
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Ref: distutils/apiref distutils util get_platform13395405
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Ref: distutils/apiref distutils util change_root13398506
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Ref: distutils/apiref distutils util subst_vars13399250
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Ref: distutils/apiref distutils util split_quoted13400066
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Ref: distutils/apiref distutils util rfc822_escape13403542
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Ref: distutils util — Miscellaneous other utility functions-Footnote-113403835
Ref: distutils util — Miscellaneous other utility functions-Footnote-213403884
Ref: distutils util — Miscellaneous other utility functions-Footnote-313403933
Ref: distutils util — Miscellaneous other utility functions-Footnote-413403982
Node: distutils dist — The Distribution class13404030
Ref: distutils/apiref distutils-dist-the-distribution-class13404238
Ref: 461a13404238
Ref: distutils/apiref module-distutils dist13404238
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Node: distutils extension — The Extension class13404480
Ref: distutils/apiref distutils-extension-the-extension-class13404672
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Ref: distutils/apiref module-distutils extension13404672
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Node: distutils debug — Distutils debug mode13404891
Ref: distutils/apiref distutils-debug-distutils-debug-mode13405083
Ref: 461c13405083
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Node: distutils errors — Distutils exceptions13405226
Ref: distutils/apiref distutils-errors-distutils-exceptions13405443
Ref: 461d13405443
Ref: distutils/apiref module-distutils errors13405443
Ref: 5913405443
Node: distutils fancy_getopt — Wrapper around the standard getopt module13405943
Ref: distutils/apiref distutils-fancy-getopt-wrapper-around-the-standard-getopt-module13406161
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Ref: 462313408800
Ref: distutils/apiref distutils fancy_getopt FancyGetopt generate_help13409044
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Node: distutils filelist — The FileList class13409324
Ref: distutils/apiref distutils-filelist-the-filelist-class13409547
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Node: distutils log — Simple PEP 282-style logging13409768
Ref: distutils/apiref distutils-log-simple-pep-282-style-logging13409962
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Ref: distutils/apiref module-distutils log13409962
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Node: distutils spawn — Spawn a sub-process13410083
Ref: distutils/apiref distutils-spawn-spawn-a-sub-process13410292
Ref: 462713410292
Ref: distutils/apiref module-distutils spawn13410292
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Node: distutils sysconfig — System configuration information13410631
Ref: distutils/apiref distutils-sysconfig-system-configuration-information13410836
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Ref: distutils/apiref module-distutils sysconfig13410836
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Ref: distutils/apiref distutils sysconfig PREFIX13411679
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Ref: distutils/apiref distutils sysconfig get_python_inc13413234
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Ref: distutils/apiref distutils sysconfig customize_compiler13414570
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Node: distutils text_file — The TextFile class13415563
Ref: distutils/apiref distutils-text-file-the-textfile-class13415773
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Node: distutils version — Version number classes13422943
Ref: distutils/apiref distutils-version-version-number-classes13423157
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Node: distutils cmd — Abstract base class for Distutils commands13423270
Ref: distutils/apiref distutils-cmd-abstract-base-class-for-distutils-commands13423474
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Node: Creating a new Distutils command13424764
Ref: distutils/apiref creating-a-new-distutils-command13424975
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Ref: distutils/apiref distutils cmd Command initialize_options13425844
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Ref: distutils/apiref distutils cmd Command run13426788
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Ref: distutils/apiref distutils cmd Command sub_commands13427214
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Node: distutils command — Individual Distutils commands13428205
Ref: distutils/apiref distutils-command-individual-distutils-commands13428408
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Ref: distutils/apiref module-distutils command13428408
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Node: distutils command bdist — Build a binary installer13428535
Ref: distutils/apiref distutils-command-bdist-build-a-binary-installer13428776
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Ref: distutils/apiref module-distutils command bdist13428776
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Node: distutils command bdist_packager — Abstract base class for packagers13428905
Ref: distutils/apiref distutils-command-bdist-packager-abstract-base-class-for-packagers13429156
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Ref: distutils/apiref module-distutils command bdist_packager13429156
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Node: distutils command bdist_dumb — Build a “dumb” installer13429321
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Node: distutils command bdist_msi — Build a Microsoft Installer binary package13429737
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Ref: distutils command bdist_msi — Build a Microsoft Installer binary package-Footnote-113430683
Node: distutils command bdist_rpm — Build a binary distribution as a Redhat RPM and SRPM13430753
Ref: distutils/apiref distutils-command-bdist-rpm-build-a-binary-distribution-as-a-redhat-rpm-and-srpm13431040
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Node: distutils command bdist_wininst — Build a Windows installer13431233
Ref: distutils/apiref distutils-command-bdist-wininst-build-a-windows-installer13431501
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Node: distutils command sdist — Build a source distribution13431721
Ref: distutils/apiref distutils-command-sdist-build-a-source-distribution13431961
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Node: distutils command build — Build all files of a package13432096
Ref: distutils/apiref distutils-command-build-build-all-files-of-a-package13432342
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Ref: distutils/apiref module-distutils command build13432342
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Node: distutils command build_clib — Build any C libraries in a package13432479
Ref: distutils/apiref distutils-command-build-clib-build-any-c-libraries-in-a-package13432735
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Node: distutils command build_ext — Build any extensions in a package13432894
Ref: distutils/apiref distutils-command-build-ext-build-any-extensions-in-a-package13433161
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Node: distutils command build_py — Build the py/ pyc files of a package13433316
Ref: distutils/apiref distutils-command-build-py-build-the-py-pyc-files-of-a-package13433582
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Ref: distutils/apiref distutils command build_py build_py_2to313433791
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Node: distutils command build_scripts — Build the scripts of a package13434408
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Ref: distutils/apiref module-distutils command build_scripts13434663
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Node: distutils command clean — Clean a package build area13434820
Ref: distutils/apiref distutils-command-clean-clean-a-package-build-area13435066
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Node: distutils command config — Perform package configuration13435510
Ref: distutils/apiref distutils-command-config-perform-package-configuration13435737
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Ref: distutils/apiref module-distutils command config13435737
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Node: distutils command install — Install a package13435878
Ref: distutils/apiref distutils-command-install-install-a-package13436119
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Ref: distutils/apiref module-distutils command install13436119
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Node: distutils command install_data — Install data files from a package13436238
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Node: distutils command install_headers — Install C/C++ header files from a package13436661
Ref: distutils/apiref distutils-command-install-headers-install-c-c-header-files-from-a-package13436946
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Node: distutils command install_lib — Install library files from a package13437129
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Node: distutils command install_scripts — Install script files from a package13437584
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Node: distutils command register — Register a module with the Python Package Index13438044
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Ref: distutils/apiref module-distutils command register13438323
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Ref: distutils command register — Register a module with the Python Package Index-Footnote-113438670
Node: distutils command check — Check the meta-data of a package13438719
Ref: distutils/apiref distutils-command-check-check-the-meta-data-of-a-package13438916
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Node: Installing Python Modules Legacy version13439258
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Node: Introduction<17>13440679
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Node: Distutils based source distributions13441771
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Node: Standard Build and Install13443147
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Node: Platform variations13443705
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Node: Splitting the job up13444731
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Node: How building works13446173
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Node: How installation works13448043
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Node: Alternate Installation13452947
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Node: Alternate installation the user scheme13454797
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Node: Alternate installation the home scheme13457337
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Node: Alternate installation Unix the prefix scheme13459336
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Node: Alternate installation Windows the prefix scheme13463579
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Node: Custom Installation13465007
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Node: Modifying Python’s Search Path13472161
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Node: Distutils Configuration Files13475971
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Node: Location and names of config files13476860
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Node: Syntax of config files13480916
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Node: Building Extensions Tips and Tricks13482973
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Node: Tweaking compiler/linker flags13483729
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Node: Using non-Microsoft compilers on Windows13486949
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Node: Borland/CodeGear C++13487259
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Node: GNU C / Cygwin / MinGW13489553
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Node: Older Versions of Python and MinGW13490870
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Node: Python Module Index13492683
Node: Index13515813

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